US2332592A - Process of producing screen stencils - Google Patents

Description

Patented ocr. 2c, 1943 PROCESS F PRODUCING SCREEN STENCILS Edward 0. Norris, Westport,

Edward 0. Norris, Inc., poration of New York Application June 5, 1941, Serial No. 396,682 4 4 Claims. (Cl. 204-11) Thel invention relates to screen stencils such as are used for making ink and paint impressions of designs, depositing adhesive in the form of a design for flock-printing, applying dyes to form a design and, in general, making impressions of a large variety of materials.

More particularly, it relates to a process of producing stencils of the general character just described so constructed that iine lines of the design to be impressed or imprinted are clearly defined and unbroken, and the edges of larger areas are clearly demarked and free from the jagged or saw-tooth appearance which often characterizes work done with the ordinary screen stencil. In referring to fine lines dotsf are included.

In my'eo-pending United States applications' Ser. No. 376,769, led Janury 31, 19441; Ser. No. 393,731, filed May 16, 1941; and application for Y "Process of producing stencils filed as of even date with the filing of this application, I describe stencils that will serve the above-.described purposes, and processes of producing them. However, these processes involve themse of at least two diiferent metals or other materials, one of which may be selectively etched to the exclusion of the other.

The invention of this application is a process of producing results similar to those accomplished in the above recited applications by the use of a single metal throughout, or by a combination of metals selected without regard to their. respective etching characteristics.

' also the process of "etching l Conn., assigner to New York, N.l Y., a corbase screen would have in the order of from 25 to 100 meshes to the linear inch, and as much as possible of the total area would be open, the limit of open area obviously being lixed 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 have shown in the drawing. However, the principle involved, insofar as the design is concerned is the same regardless of how elaborate it may be, and so I have selected a very simple one by which to explain .the process and the product.

At times the term Wires will be used to describe the component parts of the base screen structure, although I am aware that the word so used is used in a sense somewhat beyond its ordinary meaning. In screen of the electroformed type, what I have termed wires are frequently known as lands, which in this application will be deemed to.be equivalent terms; will be frequently referred to and, whenever applicable, is to be deemed to include electrolytic deplating-i. e., anodic treatment in an electrolytic bath.

Referring in detail to the drawing,

In Fig. l there is shown diagrammatically in dotted lines a matrix of a type suitable for electroforming thereon a .base screen which will,

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

Referring to the drawing:

Fig. 1 is an isometric vview showing in dotted lines a conventional matrix for the electroforming of screen with the screen itself formed thereon and the apertures filled with readily removable material;

Fig. 2 is an isometric view of the electroformed screen after it has been stripped from the matrix, and includes a superimposed layer of material deposited thereon;

Fig. 3 is an isometric view illustrating the rst step in producing the intended design; l

Figs. 4 and 5 illustrate successive steps in producing the design;

Fig. 6 is an isometric view showing the .completed stencil. l

It is to be realized that the drawing is on a vastly larger scale than would be useful in practice. Usually, in industrial applications the when the process is completed, form the open areas of the stencil and support the stencil blocking out material covering the remaining areas. Such a matrix is illustrated and described in my United States Patent No. 2,166,366, issued July 18, 1939, and, as it is further a, known product, it will be described only briefly.

It may consist of a metallic plate l0 the surface of which is provided with a multitude of minute pits preferably in rows and columns and lled with electrically non-conductive material Il, such as Bakelite or similar substance. surfaces of the fillings may be flush with the'surface of the metallic plate. Thus, the deposit surface comprises crossed lanes of exposed metal of the plate which isolate' the non-conductive areas, 'the lanes corresponding in design to the screen to be electroformed and the non-conductive areas corresponding in design to the apertures in the screen. However, the electroforming step is usually continued until the deposit has encroached considerably upon the insulated areas, and therefore the screen wires are wider than the lands of the matrix and the apertures of the screen are smaller than the non-conductive areas. In electroforming on such a matrix,

the deposit-receiving surface is first, in accordance with known practice, covered with a strippingfilm" which-may consist of a very thin application of beeswax. rThe thin coating, while not preventing electrolytic deposit on the lanes, prevents such deposit from adhering thereto, and therefore any deposit thereon may be readily stripped therefrom.

The base screen, "cated by the numeral I2, is then electroformed on the matrix in the usual way. For specic description of a process, reference may had to my United States Patent No. above referred to.

Preferably while the base screen is still on the matrix, the apertures are filled with some material-e. g., wax I3 that may be readily removed therefrom in a subsequent step. A suitable substance is beeswax since it is readily dissolved by several solvents--forl example, acetone-and may be readily removed in the dissolved condition by brushing, scrubbing, spraying, agitating in the solvent, and other mechanical aids, with further washing with the solvent. In the operation of filling the apertures some of the filling material will, as might be expected` cover the lands of the screen, and therefore, the surface is carefully rubbed until the crowns I3b of the screen wires are exposed and clean. Thereupon the surface of the structure thus formed is dusted with fine graphite I3a (flocculent graphite being suitable) or fine bronze powder, or some fine powder that by washing with water, whereupon the areas that were obstructed by the opaque area of the transparency are washed away leaving themetal bare except where it is covered by the design I5. It is best that the coating be baked in order to harden f it and thus render it resistant to disintegration by the electrolytes which will subsequently be emthe wires of which are indibe again A is electrically conductive. The powder is then I pressed into the wax by rolling, rubbing or patting which renders the4 exposed surface of the wax electrically conductive, and therefore the entire surface is active to electrolyticdepo'sition.

While, as will be explained later, the process is not limited to the use of any particular metal, it will first be described in connection with a specifled metal and then it will be pointed out how it may be carried out with a number of other metals and combinations of metals. It may therefore for present purposes be assumed that the screen is of copper and that copper will be used throughout. There is next deposited on the iilled screen of Fig. l a thin layer I4 of copper.

' This deposit may be made before or after the filled screen is stripped from the matrix, although preferably it is made before. Regardless, however, of the stage at which it is applied, the result is shown in Fig. 2, where it will be seen that the apertures of the screen are closed by webs of thin sheet copper which is bonded metallically to the crowns of the. screen wires although only mildly adherent to the graphite surface of the wax.

The wax and adherent graphite are then cleaned out by dissolving in,- for example, acetone, accompanied if necessary with scrubbing, brushing, or like mechanical operations. The coating I5 is then applied by anbrdinary photographic process. The design shown is selected because of its suitability for illustrating the objects of the invention. It is shown as an arc of a circle so that the relationship between it and the wires of the screen will, regardless of the angle at which they cross eachother, be brought out, as will later ployed in the course of carrying out the process.

The design having been applied, the structure is then treated cathodically in a copper electrolyte bath in accordance with standard practice and the surface of the copper layer Il is electroplated with a second copper layer I6, the operation of plating with the layer I6 being continued until the thickness of the deposit is increased over that of the coating. As an incident to this, the coating creeps over the marginal areas of the coating as shown at I1. It may be remarked at this point that the creeping is not.- an object in itself butlis a necessary sequence of increasing the thickness of the layer I6 over that of the coat.

yIn the last-mentioned electroplating operation the bottom--i. e., the base screen side, of the structure is properly masked with a resist 'which is removed after all electroplating operations have been completed. The entire procedure would be somewhat facilitated if the wax I3 were allowed to remain in the vapertures of the base screen until all electroplating has been completed. In other words, the wax itself is a good resistant to the copper electrolyte and, if it were allowed to remain as stated, the applicationof resist to the bottom of the structure would be easy, and the number of applications 'of resist and the number of times removed would be reduced.

It may also be noted that there is a practical limit to the thickness to which an adherent coating of photo-engravers glue can be laid on a surface. If too thick,v it does not adhere and, of course, the definition of the marginal edges of the design is impaired. This is remarked because one of the objects that it is sought to accomplish is to build a stencil thick enough and therefore strong enough to withstand the printing pressures without collapsing and closing up the ink-feeding passages which are developed as a last step in the process. This will become clear as the explanation continues.

To still further increase the thickness and strength of the stencil, the intaglio design I8 created by the fact that the layer I6 is thicker than the coat I5 is filled with a readily removable plastic, such as asphaltum I8 which -is then rubbed off until its surface is flush with the surface of the layer I6. This structure is, in turn, cathodically treated in a copper electrolytic bath and the layer 20 plated on the layer I6. If it is desired to still further increase the thickness of4 the stencil, an operation similar to that involved in plating on the layer 20 can be carried out and the same repeated until the design opening has been reduced to such an extent that ink cannot 'be fed through it from the base screen side of the stencil, as will be shortly explained.

When a suflicient number of successive layers of copper have been added, the asphaltum is washed out with gasoline or naphtha, Aaccompanied by brushing or scrubbing, or other mechanical aid. 'I'he hardened photo-engravers .structure anodically in a dilute sulphuric acid bath until the thin layer Il is broken through will consume so little time that the quantity of material removed from the remainder of the j structure will be negligible. Even this negligible quantity may be still further reduced by masking the surface of the layer with a resist before starting the deplating operation.

I'he advantages of the stencil itself can now be brought out more clearly than before. By referring back to Fig. 3, it will be seen that, when'the design includes fine lines such as the ing wm be of the dimensions of that desired in the printed design.

Thus far, in accordance with what has been previously remarked, only specific materials have been mentioned. It will be clear, however, that many other metals than copper that could be employed-e. g., nickel could be employed throughout, the deplating operation in that case being carried out in a dilute sulphuric acid electrolytic bath to which both the hardened photoengravers glue and the asphaltum are resistant. In the case of silver, the deplating could be carried out in a sodium cyanide bath. Still other metals would be depleted in their respective apannular figure which I am using as an illustration, the ordinary process of simply blocking-out the screen to form the design leaves these fine lines in many cases overlying and blocked by portions of the screen Wires. This is brought out in Fig. 3, Where, for example, a portion of the annular design traverses for a short distance the Wire 22 as indicated. It also crosses various other Wires that Wholly or partially block it and it is blocked by the wire 23. Consequently, when a stencil of the simple formjust referred to is used for printing fine line figures, especially where the lines are about the width of a screen unit or less, the lines when printed appear broken, for the reason that the ink is not delivered at those portions where the design is blocked out by the wires. By the term screen unit I mean the total Width of a screen wire and an adjacent aperture. On the other hand, in the stencil herein described, the ineline discharge orifice for the ink is everywhere open to the source of supply on the opposite or rear side, and thus the ink or the like comes through freely, passing around the wires of the screen and thence through the discharge orice in uniform volume and in an unbroken mass. The stencil also has definite advantages even where an area covering many screen units is open, in that the edges of the printed design do not present a jagged or saw-tooth appearance as they do when, as in screen stencils made in the conventional Way,

, they are partially cut into bythe screen Wires.

Further with regard to the thickness of the rst layer of copper I4, it Will be obvious that it need be no thicker than is necessary to serve as a base for the photo-printing operation and kthe electroplating of the layer I6, and those standards should preferably be a measure of its maximum thickness. O n the other hand, each successive layer superimposed on the thin layer should preferably be as thick as photographic and electroplating limitations permit and there is no difficulty in electroplating them to a thickness considerably greater than the preferred standard that has been set for the thin layer. In any event the combined thickness of the superimposed layers can easily be made much greater than the thickness of the thin layer.

It will be noted that each successive layer of copperencroaches on the design opening, thus step by step reducing its width. Therefore, in the case of a design Where definite dimensions are required, the dimensions of the design coating should be adjusted so 'that the ultimate openpropriate electrolytes. Inplace of wax for the fillings of the base screen, asphaltum might be used, although it is not as resistant to most electrolytes asis wax.

It will be apparent that, while permissible, it is not necessary that the metal of the base screen be the same as that of the thin layer or of the superimposed layers, nor need the layers themselves be of the same metal; e. g., as a variation of the specic illustration which I have described, nickel might be substituted for copper in the base screen, and the superimposed layers might be of any metals that lend themselves to the process I of electroplating. These metals may be selected Without regard to their selective etching characteristics, and obviously this circumstance creates a'wide range of choice in the metals to be used, which is a great advantage in that they can b e selected for their properties of durability. strength, electroplating characteristics, activity to etching, resistance to corrosion, and for other properties that make them desirable for any reason.

Deplating has been described as a method of opening up the ink-feeding passages through the thin layer I4. It is, however, preferred only because it is more controllable than ordinary etching and is more even in its action. However, etching non-electrolytically by simple chemical action serves the same purpose measurably well.

The particular kind of light-sensitized lm to be employed in applying the design to the thin layer Itis not important, provided that (if, for' example, copper be used) -it resists the action of copper electrolyte or if other metals be used resistant to the particular electrolyte by which they are deposited; e. g., the well-known coatings `known as Coldtop and Gluetop also serve the purpose in the cases of most electrolytes.

I have described above certain methods of practicing the invenlon, including a preferred 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 consists in electroforming a base screen, superimposing thereon by electroplatinga thin sheet of metal, applying to the thin layer a coating in the form of a design, electroplating a thick layer of metal on the uncovered areas of the thin sheet and continuing the operation until the thickness of the layer exceeds that of the coating, lling as the first-mentioned layer, removing the coatt' ing and the readily removable material, deplating the thin layer and arresting the deplating step as soon as passages are opened up leading from the design areas through to the exposed face of the base screen.'the coating and the readily removable material both being passive to electroplating and not being deleteriously affected by the electrolyte used in the deplating operation, each electroplating step after the deposit o'f the said thin sheetof metal being arrestedbefore the design areas have been closed.

2. The process of producing a stencil,4 which consists in electroforming a metal base screen, superimposing thereon vby electroplating a thin sheet of metal, blocking out a. design on said thin sheet by the application thereto'oi a coating of a readily removable material passive to electro-A plating, electroplating a layer offmetal onsaid thin sheet, arresting the electroplating operation when the thickness ofgthe said layer exceeds that of the coating but while the design areas Aare still exposed, removing the coating, then deplating the structure thus formed and arresting the deplating step as soon as the thin sheet isbroken through and liquid-feedingpassages are established leading from the design areas to the rear face of the screen. l

3. The process of producing a stencil, which consists in electroforming a metal base screen, superimposing thereon by electroplating a thin sheet of metal; blockingout a design onsaid thin sheet by the application thereto o! a coating of a .readily removable material passive to electroplating, electroplating a layer o! metal on said thin sheet, arresting the electroplating operation when the thickness of the saidlayer exceeds that v of the coating but while the design areas are-stili exposed, removing the coating, then deplating the structure thus formed and arresting the deplating step as soon as the thin sheet is broken through andliquid-feeding passages are established leading from the design areas to the rear face of the screen, the screen and all metal added thereto*- in the 'process being homogeneous.

4. The process of producing a stencil, which consists in electrotorming a metal base screen, superimposing thereon by electroplating successive layers of metal, the layer adherent to the screen being thin in comparison with the combined thicknesses of subsequent layers.' said Vsubsequent layers being' provided with an intaglio design, the bottom of which is the thin layer, then depleting the structure thus formed and arresting' the depleting step as 4soon as the thin sheet is broken through and liquid-feeding passages 'are' established leading from the design areas to the rear face of the screen, the screen and all metal added thereto in the process being homogeneous.

EDWARD o. Noaars.

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