US2340485A - Process of producing stencils - Google Patents

Description

Feb. 1, 1944. Y E. o. NORRls PROCESS OF PRODUCING STENCILS 2 Sheets-Sheet l Filed June 5, 1941 INVENTOR libwww 0. MHP/.

ATTORNEY Feb. 1, 1944. E o, NORRIS 2,340,485

PROCESS 0F PRODUCING STENGILS Filed June 5. 1941 2 Sheets-Sheet 2 50 lNvEN-roR fon/A RD /VoHH/s ATTORNEY UNITED STATT-:s PATENT o1-Fica PROCESS F PRUDUCING STENGILS Edward 0. Norris, Westport, Conn., assignor to Edward 0. Norris, Ine., New

poration of New York Application June 5, 1941, Serial No. 396,681

11 claims.Y (ci. 2 04-.11)

This application is a continuation-impart of myco-pending application Ser. No. 376,769, led January 31, 1941, now Patent No. 2,282,203, May 5, 1942.

The invention relates to as are used for making ink and paint impressions of designs, depositing adhesive in the form of a a design, and in general making impressions of a large variety of materials. More particularly, it relates to processes of producing stencils of the general character just described, so constructed that fine lines of the design to be impressed or printed are clearly defined and unbroken, and the edges of larger areas are clearly demarked and free from the ragged or saw-tooth appearance which often characterizes work done with the ordinary screen stencil.

The objects will be presently more clearly brought out as the stencil itself and the mode4 of constructing it are explained in connection with the drawings.

AReferring to the drawings, Y

Fig. 1 is an isometric view showing a portion of stencil base which consists preferably of electroformed foraminous sheet. On` the sheet is indicated an area in thel form of an annulus which may be taken for purposes of illustration as the design that is to be printed or impressed;

Fig. 2 is an isometric view showing the foraminous sheet oi!i Fig. 1 covered with two successive layers of material in association with aprinting plate; l

Fig. 3 is an isometric view showing the design blocked out;

Figs. 4 and 5 show successive steps in theprocess; Fig. 6 shows a completedstencil;

Figs. 7-12 show a modication of the process. It is to be realized that the drawings are on a vastly larger scale than would be employed in practice. vUsually the yhase screen would have in the order of from 25 to 100 meshes to the linear inch, and as much as possible .of the area would be open, the limit of open area obviously being ilxed by the strength of the material, the nature of the use to which the stencil is to be put, etc. In most cases the design would be of a more elaborate nature than what I show in the drawings. However, the principle involved in my invention is the same regardless of the elaborateness of the design, and so I have selected a very simple one by which to explain the process-an the linal product. l

screen stencils such i 'design for flock-printing, applying dyes to form known as lands.

York, N. Y., a cor- Fig. 1 shows a portion of an electroformed screen consisting of the wires I9 intersected normally by the wires il. Preferably, as stated above, the open areas I2 are as large as possible consistent with suitable structural strength. Such a screen and a method of producing it by electroforming on a matrix are illustrated and described in my United States Patent No. 2,166,366 issued July 18, 1939, and therefore it is not necessary at present to go into details as to how the screen itself is produced.

In using the term wires to describe the component parts of the screen structure, I am aware that the wordA is used in a sense somewhat be yond the usual. However, it is afact that a true wire structure, such as woven wire screen, would serve my purposes, although, as I have found, not as satisfactorily as does the electroformed screen. In screen of the electroformed type, what I have termed wires are frequently In general, such screen structures may be termed mesh fabric, which includes, in the ordinary accepted meaning of the term, not only woven fabric but also that which is punched. etched or electroformed as well.

To make the process clear, I have shown on Fig. 1 in dotted lines an annular'area which will correspond with the open area of the completed stencil, the remaining areas of the stencil of course being blockedout, as will be presently described, by imperforate sheet superimposed thereon. 1

In order to make clear the description, it should be explained that it involves selective etchingi. e., the employment of etching agents that corrosively react on one material to the exclusion of another, and to avoid complicated language it will be assumed that the material of the base screen is of nickel. 0n the nickel screen which will eventually serve as a backing for the layers of imperforate material to be laid thereon, is deposited a layery I3 of copper, the copper completely covering the base screen itself to a substantial thickness. copper is ap#- plied preferably by electroplating, the bottom (with reference to the orientation of the screen as shown in the drawing) being suitably maskedV by covering with waxed paper or according to other methods well-known in the electroplatlng and electroforming arts. As an incident to the electroplating step (unless the holes are iirst filled `with electrically non-conductive material) the copper not only overlies the base screen but it also extends into the holes. As will be apparent however, as the description goes on, it is merely necessary that the copper overlie the screen.

The next step consists in applying to the copper layer the light-sensitive layer 20 of photoengravers glue, cr light-sensitized shellac. The Well-known coatings known as Coldtop and Gluetop also serve the purpose very well. The

particular type of coatingis not, however, im-.

portant, provided that when developed it is passive to electrolytic depositiongand is not deleteriously aiected by the electrolyte which 'will be employed in a subseq'uent step, as will be later explained.

The next step (see Figs. 2 and 3) is to photoprint the design on the coating of light-sensitive material, which is accomplished by means of the coat is then developed by washing in water if the Gluetop is used, consequently exposing the copper as shown. in Fig. 3, where previously covered by the opaque area. If shellac be used, the developing could be carried out with an alcoholic preparation sold under the tradename of "Chemco Glascote Developer. The isteps of blocking out the-design on the copper are wellknown and need no detailed or further description. It might be added, however, that the developed coat 24 that blocks out the design should preferably be further hardened by baking.

A step that may be carried out at this stage, although it could as well be carried out at any time after the copper layer I3 has been deposited, consists in applying to the bottom of the screen a very thin layer 30 of nickel which covers `the screen itself as well as the copper and forms webs, bridging the apertures in the screen. It should be noted that the term .very thin is used relatively in comparison with the mesh number of the screen, its thickness, and the thickness of the 'copper layer-for example, in the caseof a 1D0-mesh screen (100 screen units to the linear inch), and with the screen itself .005 thick and the copper the same, the thickness of the layer could properly be in the order of .00005". The same proportions would serve as the screen units per linear inch were increased or decreased from the assumed number. The important thing is that its strength shall be suflicient to withstand the handling to which the structure will besubjected in the course of applying a heavy layer of nickel presently to be referred to; on the other hand, it should preferably be no thicker than is suflicient to serve this purpose since, a's will further appear, it should be possible to etch it quickly through without removing any substantial amount of material from the rest of the structure. The thin layer 30 reached. These results can be accomplished with a suflicient degree of accuracyV by properly adjusting the thickness of the copper layer with respect to the width of the band of glue and with respect to the width and height of the screen wires. In other words. if the band of glue be excessively narrow, the etchant will reach the screen wires before -the copper has been undercut o'r suiciently undercut beneath the glue band, and, as will become obvious, after the full process -has been explained, it would then not be possible to etch the ink-feeding passages from one face of the stencil to theother. A suitable etchantfor the combination of materials that have been specifiedA by way of example, is chromic acid inasmuch as, although it readily etches the copper, it does not affect the band of hardened glue nor the material of the screen nor the layer 30 of nickel. There is then applied by electroplating a heavy deposit 3l of nickel. 'I'his deposit covers the wires of the screen, the areas of the layer'30 that are exposedbetween the meshes of the screen with or without a residual layer of copper dependent upon the stage at which the copper etching step has been arrested, and also what is left of the copper layer I3 beneath the band of glue; and its upward growth is limited. by the overhang o'f the latter. The thickness of this heavy depositV is such as to give it the necessary strength to withstand the printing pressures to which the stencil will be subjected in actual use without collapsing and blocking the ink passages which will subsequently be opened up. This point lwill become clear as the description proceeds.

The heavy deposit of nickel having been applied, the band 24 of the developed glue is removed by thek application, for example, of caustic having'been-applied, the structure Yof Fig. 3 isv potash, and then what is left o`f the copper layer I3 or most of it is etched Vo ut by chromic acid which has no effect or substantial effect on the nickel deposit 3|. This operation opens up passages through to the thin layer 3U of nickel. After removing the thin nickel layer 30, which may be doneby brushing, the result is shown in Fig. 6, where, as it will be observed, the fine line of the design is not blocked against the passage of ink by any of the wires of the screen. The layer 30 may also -be removed by anodic treatmentin a dilute sulphuric acid bath, which operation is promptly arrested when passages have been completely opened up from the design areas around the wires of the screen lto its rear face. The object of making the nickel layer 30 as thin as possible is now obvious. Its only purpose is to serve as a base in the apertures of the screen on which t'o deposit th'e heavy nickel layer 3l. Therefore, it need be no thicker nor stronger than is necessary to serve this purpose and to withstand the handling that is necessary in applying the heavy nickel layer 3|. The thinner it is, the more easily may it be brushed orf to open up the passages referred to; also, the thinner it is in comparison with the thickness of the heavy nickel layer 3I, the sooner the anodic treatment may be arrested and the less will be the amount of material removed from the heavy layer.

In applying the several layers of metal, electropl'ating acts satisfactorily. Where etching is referred to, electrolytic deplating is included wherever the process is applicable.

lThe advantages of the stencil can now be brought out more clearly than before. By referring back to Fig. 1, it will be seen that, when the design includes fine lines such as the annular ordinary process of simply blocking out the stencil tovform the design leaves these fine lines in many cases overlying and blocked by portions of the lands. This may be illustrated by reference to Fig. l, where, for example, a portion of the design traverses for a short distance the landA Ita as indicated. It also crosses various other lands and is blocked out by the land Il, Consequently, when a stencil of the simple forni just referred to is used for printing fine lineiigures. especially where the lines are about the width ofr a screen unit or less, the-lines, when printed, appear broken for the reason that the ink is not delivered atthose portions where the design is blocked out by the screen lands. By the term screen unit is meant the linear dimension of a wire and an adjacent aperture combined.A My

stencil, however, is distinguished from the stand,

ard construction which I have described in that in the former' the fine line discharge orifice for the inkis ofpen at all points to the source of supply on the opposite or rear side of the stencil, and thus the ink or the like comes through freely, passing around the Wires of the screen.

and thence through the discharge orifice in uniform volume and in an unbroken stream. As

an extension of the foregoing, the stencil also j has definite advantages even where an area covering many apertures of screen isopen, in that the edges of the printed design do not present a ragged or saw-tooth appearance as they would and do where access 0f ink to them is partially.

obstructed by the screen lands.

In explaining the invention I have up to this point preferred. for the -sake of clarity, to name a specific combination of materials in describingl how it may be carried out. However, it will be seen that the underlying principles do not necessarily involve the use of the specific materials that I have named; for example, if the base screen and the layer were of copper instead of nickel, the 1ayer i3 could be of zinc instead ofcopper. In such case. obviously thechoice of etching agents would need to be adapted to bring about the selective actions that are necessary in the case just supposed; for' instance, the etchant for the zinc could be dilute sulphuric acid since dilute sulphuric acid does not react on copper although it actively reacts on zinc. The etchant for the zinc should also be of such a character that the developed light-sensitive coating area 24 is passive to it; likewise, the light-sensitive coa-ting 24 should be passive to the action of the Figs. 7-12 show a modification of the process of the previous figures.

Referring to Fig. 7 there is shown, in dotted lines, a cathode matrix of the type hereinbefore referred to and which may comprise a metal plate I0 one face of which is provided with a multitude of pits filled flush with the surface with electrically non-conductive material Il. such as Bakelite. the surface therefore comprising a multitude of 'electrically non-conductive areas delimited by crossed lanes of conductive areas, these lanes corresponding in 'pattern to the pattern of the screen to be produced. Priorto the electroforming step the screen is covered with a stripping layer-e. g., wax, which is ap- Dlied in such a thin coat that, while it does not prevent electrodeposition, it does render the entire surface of the matrix non-adherent thereto. The matrix being thus prepared, there is electroformedV on it a screen of nickel indicated by the numeral 42, and thereupon and before the e1ectroformed screen is stripped, its interstices or apertures are filled with a plastic substance I3.

such as wax. -Any surplus wax of which, of course, there will always be some is then rubbed off until the crowns 43a of the screen wires are exposed and free from it. The entire surface is then smeared with finely divided graphite (fiocculent graphite being a desirable form) which renders the surfaces of the plastic fillings electrically conductive and capable of taking an elecvtroplated deposit. The surface is then brushed to remove any graphite that lies on the crowns of the screen wires in order that they also may be capable of receiving an adherent; electroplated deposit. There is then electroplated on the surface thus prepared a heavy layer 44 of copper.

The structure thus formed is then stripped from the matrix and the wax and graphite washed out with acetone or other solvent accompanied by brushing .and scrubbing. The stripped structure with the wax removed is thenused as a cathode in a nickel electroplating bath (the surface of the copper having been properly masked by the application of a resist in accordance with well-known methods), the result of 'which is that the wires of the screen and the areas of the copper layer exposed by the removal of the wax are covered with a layer of nickel Il `which forms webs closing the apertures in the screen. This layer of nickel for reasons that will portions would serve as the screen units Aper linear inch are increased or decreased from the assumed numbers. 4 The next step `(see Fig. 9) is to'apply a lightsensitive layer of photo-engravers glue or lightsensitive shellac to the surface of the copper and,`

after the design 45 has been photoprinted there on and developed in accordance with Well-known methods, the structure of Fig. 9 is subjected to the action of an etchant which does not affect the glue or the nickel but does'etch the copper. A suitable etchant is diluted chromic acid inasmuchv as it answers the requirements just referred to. In brief, the photoprinting process may be similar to that described with respect to the first described process. If photo-engravers glue is used, it should be hardened by baking in the usual way.

The result of the copper etching process is shown in Fig. 10 where thepdesign in glue is supported by a ridge 46 of copper. This ridge con- The glue (if glue be used) is then removed by the application of caustic potash and the copper ridges 46 etched out with chromic acid, resulting in the structure `of Fig. 11. After removing the resist that has been employed in the previous step. the entire structure is treated anodically in a dilute sulphuric acid bath which results in etching the thin nickel layer, which procedure is arrested when passages 50 from the design area 5l around the wires of the screen and to its rear face have been opened up. As in the case of the nickel layer 30 of the first process described, the

. purpose in making the nickel layer 41 as thin as possible as compared with the heavy layer 49 is so that the passages referred to may be opened up before any substantial amount of material has been removed from the heavy nickel layer. As in the case of the nickel layer 30 rst described herein, the only function that the thin nickel layer 41 performs is that of a base upon which the heavy layer 49 of nickel may be electroplated, and therefore the layer 41 need be no thicker nor stronger than is necessary to serve this purpose and to withstand whatever handling is necessary before the heavy layer has been deposited.

As in the process rst described (Figs. 1-6), other combinations of metals and light-sensitive material may be adopted, provided they lend themselves to the principles of selective etching that have -been hereinbefore stated.

I have described above certain methods of practicing the invention, including a preferred f method, but I Wish it to be understood that these methods are illustrative. and not limitative of the invention and that still other methods can be practiced, including varying the order in which the several steps shall be carried out, and 'such 'variations still fall Within the spirit'and scope of my invention as set' forth in the claims.

I claim:

1.'The process of producing a stencil, which comprises closing the apertures in a nickel screen k with thin Webs of nickel, electroplating on the,

surface of the webs and the screen lands an unbroken heavy layer of copper, applying to the layer of copper a design in baked photographers glue, etching the copper until it is undercut beneath the marginal areas of the design, electroplating a thick layer of nickel on the areas exposed by the etching step thereby adding a continuous metal layer to the surfaces-delimited by the design areas, removing the glue, etching away the copper left unprotected by the removal of the glue, and then etching the entire structure until ink-feeding passages have been opened from the design areas of the heavy layer of nickel through the thin layer of nickel to the rear face of the screen.

2. The process of producing mesh fabric sten-I cil, which comprisessuperimposing on one face of a sheet of nickel screen a solid layer of copper, blocking out a design on said layer of copper by the application of a coating of material passive to electrolytic deposition, .applying to the opposite face ofthe screen a solid thin layer of nickel, etching the copper layer until the portions not covered by the blocking-out coating are slightly undercut beneath the blocking-out coating, electroplating a solid layer of nickel on the surface exposed by the etching operation thereby adding a continuous metal layer to the surfaces delimited by the design areas, removing the blockingout coating, etching the portions of the copper layer remaining after the before-mentioned applying to the opposite face of the screen a solid l thin layer of metal passive to saifA etchant, etching the superimposed layer until it has-been slightly undercut beneath the blocking-out coating, electroplating a solid layer of metal likewise passive to said etchant on the surface exposed by the'rst-mentioned etching operation thereby adding a continuous metal layer to the surfaces delimited by the design areas, removing the blockingout coating, etching the portions of the superimposed layer remaining after the said etching operation until they havebeen removed, and then removing the layer` on the said opposite face of the screen.v

A 4. The process of'producing mesh fabric stencil, which comprises superimposing on one face of a sheet of nickel screen a solid layer of another metal active to an etchant to which the screen is passive, blocking out a design on said superimposed layer by the application of a coating of material passive to electrolytic deposition, applying to the opposite face of the screen a solid thin layer of nickel, etching the superimposed layer until it has been slightly undercut beneath the blocking-out coating, the thickness of said superimposed layer being so adjusted that when the undercutting is-completed the great part of the material of said layer not protected by the coat willbe removed, electroplating a solid vlayer of metal likewise passive to said etchant on the surface exposed by the first-mentioned etching operation thereby adding a continuous metal layer to the surfaces delimited by the design areas, removing the blocking-out coating, etching the portions'of the superimposed layer remain-ing after the said etching operation until they have been removed, and then removing the layer on the said opposite face of the screen.

5. The process of producing mesh fabric stencil, ,which comprises superimposing on one face of a sheet of nickel screen a solid layer of another metal active to an etchant to which the screen is passive, blocking out a design on said superimposed layer by the application of a coating of material passive to electrolytic'deposition. applying to the opposite face of the screen a solid thin layer of metal passive to said etchant, etching the superimposed layer until the portions not covered by the blocking-out coating are at least nearly all removed, electroplating a solid layer of nickel on the surface exposed by the firstmentioned etching operation thereby adding a continuousl metal layer to the surfaces delimited by the design areas, removing the blockingout coating, etching the portions of the superimposed layer remaining after the said'etching operation until they have been removed, .and the layer on the said'opposite face screen is passive, blocking' out a design on said superimposed layer by the application of a coating of material passive to electrolytic deposition,

applying to the opposite face of the screen,` a solid thin layer of metal passive to said etchant, etching the superimposed layer until it has been slightly undercut beneath the blocking-out coating, the thickness of the said superimposed layer ybeing so adjusted that when the undercutting is '1. 'Ihe process of producing mesh fabric stencil, which comprises superimposing on one face of a sheet of metal screen a solid layer of another metal than that of the screen, blocking out a design on said layer bythe application of a coat of material passive to electrolytic deposition, applying to the opposite face of the screen a thin second solid layer of metal, etching the iirstmentioned layer until the portions not covered by the blocking-out' coat are substantially all re moved, electroplating on the surface exposed by said etching a third 'layer of metal thereby adding a continuous metal layer to the surfaces de- 9. The process of producing vmesh fabric stenc il, which comprises superimposing on one face of a sheet of metal screen a solid layer of metal different from that of the screen, the metal of the superimposed layer being active to an etchant to which the screen is passive, blocking out a design on the superimposed layer by coating with material likewise passive to said etchant and also to electrolytic deposition, applying to the other face of the screen a solid layer of metal also passive to said etchant, etching awa-y su-bstantially al1 of the superimposed layer over those areas not covered by said coating until the said layer has lbeen undercut beneath the said coating, electroplating a layer of metal over the areas exposed by the etching operation thereby adding a continuous metal layer to the surfaces delimited by the design areas, removing the coating and by means of said etchantfetching the material of the superimposed'layer remaining after the first etching operation and underlying the design area from which the coating has Ibeen removed, and removing the layer that has been applied to the said other face of the screen. r

10. The process of producing a stencil, which comprises closing the apertures in metal screen with thin webs of metal, applying to the surface `of the webs and the screen lands an unbroken heavy layer of metal active to an etchant to which the screen and the webs are passive, blocking out a design on the said heavy layer with limited by the design areas, etching awayiheM-material alscipas'sive to the said etchant, etching portions of the first layer remaining after' the first etching operation until the said portions are entirely removed, and then removing the second layer, Vthe metals of the several layers, the etchant, and the blocking-out material being so chosen that the etchant has a selective action on the metal of the second layer to the exclusion of the metal of, the screen of the second layer and the blocking-out material, and the blocking-out material is passive tothe action of an electrolyte from which the metals of the second layer and the third layer` are deposited.

l 8. The process of producing mesh fabric stencil, which comprises superimposingL on one face of a sheet of metal screen a solid layer of metal different from that of the screen, one of the metals being active to an etchant to which. the

v otheris passive, blockingout a design on the superimposed layer by coating with material like- Awise passive to said etchant and also to electrolytic deposition, applying to the other face of the screen a solid layer of metal also passive to said said.` heavy layer with said etchant leavin-g the design in relief, applying to the areas exposed by said etching operation a heavy layer of metal passive to said etohant'thereby adding a continuous metal layer to the surfaces delimited by the design areas, removing'theblocking-out material, etching away by means of said etchant 40 those portions of the first-mentioned heavy layer etching said heavy layer leaving the design inrelief, applying to the areas exposed by the said etching operation a heavy layer of metal, thereby adding a continuous metal layer to the surfaces etchant, etching away the superimposed hiverl denmited by the design areasremcvingtne blockrial of the superimposed layer remaining after the ilrst etching operation -and underlying the design 'area from which the coating has been removed, and removing the layer that has been ap- 55 plied to the said other face of the screen.

ing layer, etching away those portions of the first-mentioned heavy layer remaining after the first-mentioned etching operation, and then removing the said webs until connecting passages are opened leading from the design areas to the rear face of the screen, the etching agent employed in each etching operation being active only to the metal of the first-mentioned heavy layer.

EDWARD O. NO RRIS.l

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