US2282203A - Stencil - Google Patents

Description

May 5, 1942. Q, NQERlS ZSZZSZS STENCIL Filed Jan. 3l, 1941 3 Sheets-Sheet 2 XNVENTOR 1 50W/150 0 /Vome/s f "S P l ATTORNEY May 5, 1942. O, NORM 2,282,203

STENCIL Filed Jan. 3l, 1941 3 Sheets--Sheel 3 Patented May 5, 11942 UNITED STATES PATENT OFFICE (Cl. 10i-127) 5 Claims.

defined and unbroken, and the edges of larger areas are clearly demarked and free from the ragged or ,saw-toothed appearance which often characterizes work done with the ordinary screen stencil.

The objects Will be presently more clearly brought out a's the stencil itself and the mode of constructing it are explained in connection with the drawings.

Referring to the drawings,

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 the 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 of a portion of the screen of Fig. 1 showing the screen of Fig. 1 covered with three layers of materials partly broken away;

Figs. 3, 4, and 5 show successive steps in the production of the nal stencil;

Fig. 6 illustrates a further step whereby the design is opened up through the stencil to permit free passage of the printing agent;

Fig. 7 shows the completed stencil;

Figs. 8, 9, 10, and 11 show a modied process of producing the stencil of Fig. 7.

Figs. 12, 13, 14, and 15 illustrate successive steps in a third method cf effecting the objects of the invention.

It is to be realized that the drawings are on a vastly' larger scale than would be employed in practice. Usually the base 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 fixed 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 and the iinal product.

' the usual.

Referring specically to the drawings,

Fig. l shows a portion of an electroformed screen consisting of the wires l0 intersected normally by the wires II. Preferably, as stated above, the open areas l2 are as large as possible consistent with suitable structural strength. Such a screen and a method of producing it are illustrated and described in my United States Patent No. 2,166,366, issued July 18, 1939, and therefore it is not necessary 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 word is used in a sense somewhat beyond However, it is a fact that a true wire structure, such as woven wire screen, would serve my purposes, although, as I have found, not assatsfactorily as does the electroformed screen.

In screen of the electroformed type, what I have termed wires arefrequently known as lands 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 blocked out. as will. be presently described, by imperforate sheet superimposed thereon.

In order to carry through the description it should be explained that it involves selective etching-i. e., the employment of etching agents that corrosively react on one material to the eX- clusion of another, and to avoid complicated language it will be assumed that the material of the base screen is of nickel. On the nickel screen which will eventually serve as a backing for the layers of imperforate material to be laid thereon, is deposited a layer I3 of copper, the copper completely covering the `,base screen `itself to a substantial thickness which..however, is not critical. This copper is applied preferably by electroforming, the bottom (with referencevto the orientation vof the screen as shown in the drawings) being suitably masked according to methods wellknown in the electroplating and electroforming arts. An incident to the electroforming step (unless the holes are rst filled with electrically non-conductive material). the copper not only overlies the base screen but it also extends into the holes. As will be vapparent however, as the description goes on, it is merely necessary that ing I5 of glue or shellac rendered light-sensitive by the presence of ammonium bichromate.. The well-known coatings known as Coldtop and Gluetop serve the purpose very well. The particular type of coating is not however important as long as it is resistant tothe etching agent f The result is that in printing, the' design ao-v which is employed to etch the nickel, as will be v explained.

The next step (see Fig. 3) is to photoprint the design on the coating of emulsion, whichis done `by the plate I B exhibiting a positive of the design indicated by shading in Fig. 3. In other words, the shaded portion is opaque to light and the remaining portion is transparent. The printing' being completed, the result is that the area of the Alight-sensitive coat `protected by the shaded area of the plate I6 from the light source is unaffected, while the remaining area is hardened and insoluble to water. The light-sensitive coat is then developed by washing in water if the glue top be used, consequently exposing .the nickel I4, as indicated at I1 (see Fig. 4),

Where previously covered by the design area. 1f shellac be used, it would be washed out with an alcoholic preparation sold under the trade name of` Chemco Glascote Developer. The steps of producing the design on the sensitized coat and the steps of developing and exposing the nickel to correspond with it are well-known and need no detailed or further description,

does not affect the developed-coating I5, and

therefore the area of its corrosive action is accurately delimited -by the edges of the latter. The nickel'layer is preferably very thin-say, in the order of .003" and, since the etching process is arrested when the nickel has been completely etched through to the copper layer I3, orperhaps when it has progressed very slightly into the copper, and since there is no opportunity for any perceptible undercutting of the nickel during the brief period of action, the edges of the nickel that delimit the design are smooth and well defined. 4 The result of the foregoing etching step is shown in Fig. 5, where the nickel has been etched completely through andthe area IBfof the copper surface below it is exposed.

The next step is toycontinue the etching with an agent that will act corrosively on the copper of the layer I3 but will not affect the material of the layer` I4 or the material of the base screen. A suitableetching agent for this purpose is chromic acid which actively etches copper but which, since it has no eiect or appreciable effect on nickel, will not attack either the layer I4 or the base screen itself. 'I'his etching step is carf previously described.

ried to the point where the copper of the layer I3 is etched until it is free and clear of the lands of the base screen; so that ink or other substance to be forced through the stencil to print the desired design will freely travel through the conducting passages between the screen and the copper and emerge in uniform volume and in e solid continuous mass on to the surface being pri-nted. 'I'he general conformation of the ink passage is shown in Fig. 6, the spacing between the copper and the screen lands being indicated by the numeral I9.

pears in a complete unbroken line, the ink or other substance passing through the stencil unobstructed by the lands of the screen. Prior to actually employing the stencil for printing purposes, the developed coating I5 is removed. by the application of a suitable agent such, for example, as caustic potash. The completed stencil is shown in Fig. 7, its printing face-i. e., the

face that contacts with the work being upperv most as shown in the drawings.

The advantages of the stencil can now be brought out more clearly than before. By referring back to Fig.. l, it will vbe seen that, when the/l designv includes fine lines such as the annular figure which I am using as anr illustration, the ordinary process of simply blocking out the stencil to form the'design leaves these fine lines in many cases overlying and blocked by portions of the lands.` This is brought out in Fig. l, where, vfor example, a portion of the annulardesign traverses for a short distance the land |08 as indicated. It also crosses various other lands and is blocked'out by the land IIa. Consequently, when a stencil of this simple form is used for printing neline figures, especially where the lines are about the width of the screen land 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 screen lands. My stencil, however, is distinguished from the standard construction which I have described in that in the former the ne line discharge orifice for the ink is open at all points to the sourcev of supply on the opposite or rear side of the stencil, and thus the ink or the like .comes through freely, passing around the lands of the screen and thence through the discharge orifice in uniform volume vand in an unbroken mass. As an extension of the foregoing, the stencil also has denite advantages even where Aan area covering many meshes of screen is open,

in that the edges of the printed design do not present a ragged or saw-tooth lappearance as they would and do where they are partially cut intoby the screen lands. v

Figs. 8-11, both inclusive, show of the process. In this case, asv in the previous case, the base screen may be assumed to be of nickel with the copper deposit I3 completely lilling the holesand covering the screen itself. From then on the process varies from the process v Instead of applyingV to the copper a 'coat of nickel, then a sensitized coat, and printing with apositive of the design, the light-sensitized layer 20 is laid directly on the copper I3. Printing is then'done by a plate 2I which is a negative of the design, the shaded areas 22 being opaque and the unshaded area 23 in the form of the desired design being transparent." The result after printing and developing is shown in Fig. y9 in which the copper surface of the layer I3 is exposed and there is sua modification Y in the nickcl plate 25.

perimposed thereon in theform of a hardened sensitized coat the area 24, 24. The structure of Fig. 9 is then subjected to an electro-forming operation, whereby the layer 25 of nickel is adherently laid on the copper. The hardened coat 24 is then removed by the application of a. suitable agent such as caustic potash, leaving the area 26 of the copper surface exposed in the form of the design. The structure of Fig. is then subjected to an etching process, the etching agent being of a character that does not aiiect the nickel of the layer 25 or the material of the screen itself. As in the process of Figs. 1 7, this agent may be Chromic acid and the etching is carried through to the bottom of the plate, creating a lrce passage for ink or the like from the rear face to and out ol the annular orifices In other words, the ultimate result is the stencil of Fig. 11 in all essential respects similar in construction and mode of operation to the stencil of Fig. 7.

In explaining the invention I have up to this point preferred, for the sake of clarity, to name a combination of specific materials in describing a way in which it may be carried out. However, it will be seen that the underlying principles do not necessarily involve the use of thev specific materials that I have named. For example, if the base screen were of copper instead of nickel, the layer I3 could be of Zinc instead of copper and the layer I4 of copper in place of nickel. In such case, however, the selection of etching agents would need to be adapted to bring about the selective actions that arenecessary. In the case just supposed, for example. the photographic printing might be through a positive transparency of the design as shown in Fig. 3. The first etching agent could be ferric chloride as before, for the reason that, while it attacks the copper, it does not affect the developed coating I5. This first etching would remove or dissolve the copper and perhaps, to a very slight depth, the zinc. The next etching must, however, be of such a nature as to etch the zinc but not affect the copper, for the reason that the base screen, which is of copper, must be preserved and also the edges of the copper layer must remain intact. A suitable etching agent for this purpose is sulphuric acid diluted with water, which actively attacks zinc but does not affect copper.

If other combinations of metals than nickel or zinc and copper or other types of sensitized coating are used, it is necessary to select etching agents that will act selectively in accordance with the foregoing principles. As to the combination of nickel and copper, I have selected them as preferable because they are adaptable for stencil purposes, are readily etched selectively, are comparatively inexpensive, and lend themselves readily to electroforming process. A further example might be given, such as the combination of a nickel base screen, a layer of copper superimposed thereon, and a second layer or facing of chrome. In this case the chrome would be etched or could be etched down to the copper by hydrochloric acid. The second etching step through the copper to expose the base screen can then be accomplished by means of a second agent consisting of a mixture of sulphuric and chromic acids and watere. g.,

Sulphuric acid lbs 2 Chromic acid lb-- 1 Water -gals-- 10 This mixture will not attack nickel except possibly very slowly, and the etching of the copper by it would, in practice, be arrested by the operator before the nickel of the base screen became appreciably affected.

A third method of accomplishing the 'objects of the invention is illustrated by Figs. l2-15. This method may be best understood by reference to Fig. 9. Up to Fig. 9 it is similar to the second method illustrated in Figs. 8-11. Starting therefore with Fig.9, a very thin layer 3 0 of nickel is electrolytically deposited on the rear face of the structure, the purpose of which will presently appear. Following this step the copper I3 is etched away by, for example, chromic acid, but, inasmuch as it is partially protected by the band of solidiiied glue 24, the portions of the copper beneath the band are left as shown in Fig. 13,. the etching step of course being arrested before those portions are entirely removed. By this step the wires of the base screenA and also the thin layer 30 of nickel are exposed and are capable of receiving a heavy adherent deposit 3I of nickel, as shown in Fig. 14. After the heavy deposit of nickel has been applied, theband 24 of developed glue is removed by the application, for example, of caustic potash, andA then the exposed copper is etched out by chromic acid which does not affect the nickel deposit 3l. After removing the thin nickel layer 30 to open the ink passages, which may be done by brushing4 (since its thickness is only in the order of say .000O5), ,thev result is shown in Fig. 15, where the fine line of the design is not blocked against the passage of ink by any of the wires of the screen. The sameprinciples of selectivity should be followed in choosingmetals, etching agents, and other materials in carrying out the third method which I describe as inthe case of the first and second methods.

In applying the successive layers of metal in my several methods, electroforming acts most satisfactorily. Where etching is referredl to, electrolytic depleting is included wherever the process is applicable.

I have described above certain embodiments of my invention, but I wish it to be understood that these are illustrative and vnot limitative and that I reserve the right to make various changes in form, construction, and arrangement of partsthatstill fall within the spirit and scope of my invention as set forth in the claims.

I claim:

1. A screen stencil comprising metal mesh fabric having an area of open mesh forming a design, said area being delimited by areas of solid sheet metal covering the fabric and lling the meshes where covered, said design comprising a band atleast as narrow as the wires of the fabric, vand passages leading from the bands around the wires and opening at the opposite face of the stencil. Y

2. A screen stencil comprising metal mesh fabric provided with areas of imperforate sheet metal superimposed thereon, said areas being separated by open mesh areas conforming to the design to be printed, said open mesh areas comprising bands narrower than the wires of the fabric, the said narrow areas communicating with the rear face of the fabric by means of passages leading to and opening at said rear face and around said portions of the wires as are directly beneath [the said narrow areas'.v

3. A screen stencil, comprising a metallic base screen with areas blocked out on one face by a layer of imperforate metal superimposed thereon, leaving exposed areas of the base screen denning the design to be printed, some of the ex'posed areas being of a width not substantially exceeding that of the base screen wires underlying them, liquid communication through the stenci1.frorn last-mentioned areas Abeing established by passages leading from them through meshes of the'base screen adjacent said underlying Wires. 1 4. A screen stencil, comprising metal meshlO fabric and having a printing face of open mesh `areas conforming to the design to be printed and delimited by closed mesh areas of imperforate metal, some of the design areas being of a width not substantially exceeding that of the wires of the fabric underlying them, the stencil being provided with liquid feeding passages 'areas of the -fabric conforming to the design to be printed, some of the design areas being of a width not substantiailyrexceeding the width of the'wires of the fabric, the stencil being provided with liquid feeding passages leading from the last-mentioned design areas, thence around the wires underlying said areas and emerging at the opposite face of the stencil through the meshes f yadjacent said underlying wires.

EDWARD o. NoRRIs. l

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