US3595166A - Three-layer stencil assembly having plastic overlay sheet - Google Patents

Abstract

There is disclosed an improvement in the mimeograph stencil art comprising the manufacture of an overlay sheet for either a conventional typewriter stencil or in particular a stencil which can be prepared by means of heat transfer with a thermocopier and with this overlay sheet is capable of either thermal production or conventional typewritten production, comprising a sheet of tissue which has been coated on one side, only, with a film of elastomeric plastic, such as polyvinyl chloride or polypropylene.

Description

limited States Patent Inventor Herbert P. Sherman Chicago, Ill.

Appl. No. 800,972

Filed Feb. 20, 1969 Patented July 27, 1971 Assignee Bell 8: Howell Company Chicago, 111.

THREE-LAYER STENCIL ASSEMBLY HAVING PLASTIC OVERLAY SHEET 10 Claims, 6 Drawing Figs.

U.S.Cl 101/1282, 1l7/35.5,117/135,117/155,161/149,161/156, l6l/160, 161/235, 161/249, 161/251, 161/256 lnt.Cl B4111 1/24 FieldoiSearch 161/113, 254, 218, 241, 247, 251, 256,149,156,166, 235; 117/355, 35.6, 36.1, 38, 36.7, 36.8, 36.9,135, 155;]01/1282, l27,128,128.1,128.3, 128.4;

[Mm Aria [56] References Cited UNITED STATES PATENTS 1.092,768 4/1914 Fuerth..... 101/1282 2,203,280 6/1940 Heath 101/1282 3,009,416 11/1961 Frasher etal. 101/1282 3,062,675 11/1962 Shelffo 117/355 3,376,810 4/1968 Blake etal. 117/35.5

FORElGN PATENTS 446,018 1/1948 Canada 101/1282 Primary Examiner-John T. Goolkasian Assistant Examiner-W. E. Hoag Attorney-Jack H. Hall Jam 4 6667 THREE-LAYER STENCIL ASSEMBLY HAVING PLASTIC OVERLAY SHEET FIELD OF THE INVENTION The present invention relates generally to improvements in the mimeograph stencil art and more particularly to a new and improved stencil assembly wherein the stencil is capable of being prepared by means ofa thermocopier and by means ofa conventional typewriter.

DESCRIPTION OFTHE PRIOR ART One of the most critical problems concerning designers of mimeograph stencils has been the problem of designing a stencil which can be prepared by means of a thermocopier or by conventional typing. This problem is overcome by the present invention. To completely understand the instant invention it is necessary to outline the prior art stencils that are available and to describe their differences.

Broadly, there are four types of mimeograph stencils: One is prepared by the use of a typewriter or a blunt pointed instrument referred to as a stylus. A second can be prepared by means of a photographic system, whereby a sheet ofcmulsion coated tissue is exposed photographically and the blacks on the emulsion are eliminated chemically leaving exposed apertures. A third type is prepared by the use of an electronic scanning device which burns tiny apertures into a plastic sheet. The fourth and newest type, referred to as a thermal stencil, is prepared with a thermocopier. Referring now to the conventional typing stencils, there is shown in FIG. I a typical prior art typing stencil whichvconsists of two sheets, a first backing sheet which is made of a heavy although flexible paper much like that from which postcards are made, and second sheet which is the stencil layer and is made by coating or impregnating a sheet of fine fibered tissue paper with a film of highly plasticized material, such as nitrocellulose on both sides or it can even be coated instead with wax. Fig. 2 shows a modification of the conventional typing stencil wherein a clear plastic overlay is placed on top of the stencil layer sheet. Openings which would represent alphabetical letters, nu merals, or drawn lines are made in this waxlike coating by striking this coating or if an overlay is present, by striking this overlay with the type face ofa typewriter key. In either case, no part of the waxlike coating is actually removed. It is merely pushed" to the outer edges of the holes or aperture made by the typewriter or the stylus. With the advent of electric typewriters however, the conventional stencil has suffered from what is commonly referred to as chop-outs. This means that the center of the 0," a, e," etc. can be actually cut out and thereby destroy the perfection of the stencil. There are actually two reasons for this: first, because the force of the strike by the typewriter not only pushes aside the waxlike coating, but also cuts the fibers of the tissue; and second, because most plasticizers used for coating the stencil sheet have a pH rating on the acid side and, after a time and exposure to oxygen, the tissue fibers become brittle and thus break very easily. While the conventional clear plastic overlay shown in FIG. 2 primarily accomplishes the function of preventing "chop-outs" it does not overcome the problem existing in pushing" the wax material to the side of the letters thereby causing a broader aperture. Therefore, the current clear plastic overlaid stencils prepared by typewriter do not yield an image as clear and sharp as desired without chopouts."

The other type of stencil to which this invention relates is the thermal stencil. Shown in FIG. 3 is the most popular type of thermal stencil known in the trade as the Weber stencil." This stencil comprises a conventional backing sheet of flexible oil resistant paper. Attached to this backing sheet is a plasticized plastic coated tissue stencil sheet. Attached to this layer is a tissue layer which in thermal stencil making acts as a receptor sheet. The original sheet which is to be copied is placed face up between the backing sheet and the plasticized plastic coated tissue stencil sheet. The entire sandwich combination is placed into a thermocopier and through heat transfer the latent image appears on the stencil sheet represented by aperturesjust as ifit had been accomplished by typewriting. This because the overlay of plain tissue, acting as a receptor, absorbs the plasticized plastic coating which has been melted away, so to speak, at the point of contact between the coating and the latent image. This Weber stencil can also be used as a typewriter stencil. The typing is done either on the tissue or directly on the coated sheet layer but the force of the keys in either case can make holes in the middle stencil layer representative of the letters. However, a great deal of chop-outs as well as pushing" as described above in the conventional typing stencils is present and the suitability of this stencil for typewritten preparation is limited. A second type of thermostencil known to the prior art is shown in FIG. 4. This stencil is known as the Riso stencil. The stencil is a two-layer stencil consisting of a conventional backing sheet attached to a second sheet which is a tissue having a laminated plastic coating of unknown composition on the under side thereof and forms the stencil sheet. The operation of this stencil is similar to that of the Weber stencil" described above. This stencil cannot be prepared by a typewriter however. A third type of thermal stencil is available and operates in a similar manner to the above two stencils. This stencil, known as the American stencil," is constructed similarly to the Weber stencil; however the stencil sheet utilizes a different type of coating. This stencil is also incapable of being prepared with a typewriter and can only be used in conjunction with a thermocopying device. Needless to say, the typewriter stencil shown in FIGS. 1 and 2 cannot be used with a heat transfer process.

SUMMARY OF INVENTION The general purpose of this invention is to provide a stencil which embraces all the advantages of similarly employed stencils and possesses none of the aforedescribed disadvantages. To attain this, the present invention contemplates a unique arrangement whereby a sheet of tissue, coated on one side only with a film of elastomeric plastic, such as polyvinyl chloride, or polypropylene, is used as an overlay on either a conventional typing stencil as shown in FIG. I or instead of the overlay sheet or receptor on what is known as the Weber stencil as shown in FIG. 3. This plastic coated tissue sheet which is used as an overlay on these two stencils provides a unique single stencil which is capable of being prepared with a typewriter or with a thermocopier and providing a clear aperturc which does not contain cutouts and does not employ pushing" of the coated stencil material to form this aperture but rather absorbs it.

It is therefore an object of the present invention to provide a stencil which is capable of being prepared by a typewriter or by a thermocopier.

Another object is to provide a typewriter stencil which does not have cutouts" and whose apertures are not formed by pushing the coated stencil material aside.

A further object of the invention is to provide a stencil which is inexpensive to manufacture and which provides im proved results.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 5 is a diagrammatic view illustrating a preferredembodiment ofthe invention when utilized with a thermostencil.

FIG. 6 is a diagrammatic view illustrating a second embodiment of the invention when utilized with a conventional typewriter stencil.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings wherein like reference characters designate like or corresponding parts throughout the several views, there is shown in FIG. 5, which illustrates a preferred embodiment, a stencil assembly ll capable of being prepared by either thermocopying or by conventional typewriting. The stencil assembly is a three-layer stencil having a backing layer 13. a stencil layer 14, and a coated overlay layer 17 and in some respects is similar to the stencil shown in FIG. 3 and described as the prior art. Backing sheet 13 is conventional and is made from a sheet of heavy flexible paper. Fastened to backing sheet 13 along a line 20 is the stencil layer 14 consisting of a tissue layer 15 coated with a plastic substance l6. Attached to this sandwich along the line is the overlay sheet 17 consisting ofa tissue 18 coated with a film of elastomeric plastic 19 on its uppermost side. While any elastomeric plastic such as polyvinyl chloride or polypropylene may be used, polyvinyl chloride is presently preferred. Layer 17 gives the stencil the capability of both being a thermostencil and a conventional typewriter stencil. This layer acts as both a cushion sheet and an absorbing receptor layer. When a typewriter is utilized for preparing the stencil, this layer prevents chop-outs due to the plastic surface 19 and prevents pushing" of the stencil plastic coating material due to tissue layer 18 actually absorbing the plastic material from stencil layer 14 thereby providing a clean aperture.

A further result of providing the cushioning sheet with the plastic film 19 is evident when this same stencil assembly is used as a thermostencil; a more uniform coating 16 and consequently, a cleaner and sharper aperture in stencil sheet 14 is achieved. One reason for this occurrence is the fact that a great concentration of heat is transferred to the stencil sheet at the points of contact between the characters on the original and the coated stencil layer when the plastic film is present than with the, previously referred to, prior art stencils.

Now referring to FIG. 6, which constitutes an alternative embodiment, there is shown a typewriter stencil assembly 21 wherein an elastomeric plastic coated overlay 17 is placed on a conventional typing stencil such as that shown in FIG. 1. The stencil assembly comprises a backing layer 13 connected to a stencil sheet 23 which is comprised of either a wax or cellulose coating 25 placed upon a tissue layer 24, the stencil sheet and backing sheet being fastened together along a line 20 in a conventional manner. Also attached along line 20 is the coated overlay 17 which, as described above in connection with FIG. 5, is made up of a tissue layer 18 and an elastomeric plastic coating 19 laminated thereto. As described with reference to the prior art, the conventional typing stencils shown in FIG. I suffer from the defect of having chop-outs" and from a pushing" effect of the wax stencil coating when struck by a typewriter key. By utilizing the overlay layer 17 these effects are eliminated. The elastomeric plastic coating 19 acts as a cushioning layer for the typewriter keys thereby preventing chop-outs while tissue layer 18 of the laminated structure absorbs the wax or cellulose coating from stencil sheet 23 thereby preventing "pushing" of the stencil coating material. This results in a clean aperture. This absorbent feature is completely lacking in any of the prior art stencils.

While the results obtained from utilizing this elastomeric plastic laminated overlay appear deceptively simple, it is to be emphasized that the use of this overlay layer now provides a stencil assembly which is capable of both preparation by conventional typing means or by means of a thermocopier. It further provides an absorbent tissue layer to remove any excess material from the stencil layer and gives a cushioning effect which prevents chop-outs." When the stencil sheet is prepared with a thermocopier this elastomeric plastic coated overlay provides a higher melting temperature than previous overlays thereby absorbing more material from the stencil sheet. Even utilizing this layer with a conventional typing stencil as shown in FIG. 6 an improved result is obtained by providing a cushioning layer as an absorbing layer thereby preventing chop-outs and pushing effects which have previously not been accomplished. It should be understood, of course, that the foregoing disclosure relates to only preferred embodiments of the invention and that numerous modifications or alterations may be made therein without departing from the spirit and the scope ofthe invention as set forth in the appended claims.

What I claim is:

l. A mimeograph stencil assembly having a sandwiehlike construction comprising:

a first sheet;

a second sheet positioned on said first sheet wherein said second sheet comprises a stencil layer; and

a third sheet comprising a tissue layer having an elastomeric plastic film coated on one side thereof and wherein the uncoated side of said tissue layer is placed adjacent to and facing said stencil layer.

2. A mimeograph stencil assembly as in claim 1, wherein:

said stencil layer comprises a tissue layer coated with a plasticized plastic coating having a melting point lower than said elastomeric plastic coating; and wherein said third sheet is adapted to absorb the coating of said stencil layer thereby forming apertures in said stencil layer upon the application of heat or pressure thereto.

3. The mimeograph stencil assembly of claim 2 wherein said third layer is adapted to provide a cushioning effect thereby protecting said stencil layer from excessive pressure being applied thereto.

4. A mimeograph stencil assembly as in claim 1, wherein:

said second sheet comprises a tissue layer coated with plasticized material; and wherein said third sheet is adapted to absorb the coating of said stencil layer thereby forming apertures in said stencil layer upon the application of pressure thereto and wherein said third sheet further is adapted to provide a cushioning ef fect thereby protecting said stencil layer from excessive pressure being applied thereto.

5. The mimeograph stencil assembly of claim 4 wherein said plasticized coating material said stencil layer is nitrocellulose. 6. A mimeograph stencil assembly as in claim 1, wherein:

said stencil layer comprises a tissue layer coated with a waxlike material; and wherein said third sheet is adapted to absorb the coating of said stencil layer thereby forming apertures in said stencil layer upon the application of pressure thereto and wherein said third sheet further is adapted to provide a cushioning ef fect thereby protecting said stencil layer from excessive pressure being applied thereto.

7. The mimeograph stencil assembly of claim 6 wherein said elastomeric plastic film is polyvinyl chloride.

8. The mimeograph stencil assembly of claim 6 wherein said elastomeric plastic film is polypropylene.

9. The mimeograph stencil assembly of claim 1 wherein said elastomeric plastic film is polyvinyl chloride.

10. The mimeograph stencil assembly of claim 1 wherein said elastomeric plastic film is polypropylene.

Claims (10)

1. A mimeograph stencil assembly having a sandwichlike construction comprising: a first sheet; a second sheet positioned on said first sheet wherein said second sheet comprises a stencil layer; and a third sheet comprising a tissue layer having an elastomeric plastic film coated on one side thereof and wherein the uncoated side of said tissue layer is placed adjacent to and facing said stencil layer.

2. A mimeograph stencil assembly as in claim 1, wherein: said stencil layer comprises a tissue layer coated with a plasticized plastic coating having a melting point lower than said elastomeric plastic coating; and wherein said third sheet is adapted to absorb the coating of said stencil layer thereby forming apertures in said stencil layer upon the application of heat or pressure thereto.

3. The mimeograph stencil assembly of claim 2 wherein said third layer is adapted to provide a cushioning effect thereby protecting said stencil layer from excessive pressure being applied thereto.

4. A mimeograph stencil assembly as in claim 1, wherein: said second sheet comprises a tissue layer coated with plasticized material; and wherein said third sheet is adapted to absorb the coating of said stencil layer thereby forming apertures in said stencil layer upon the application of pressure thereto and wherein said third sheet further is adapted to provide a cushioning effect thereby protecting said stencil layer from excessive pressure being applied therEto.

5. The mimeograph stencil assembly of claim 4 wherein said plasticized coating material said stencil layer is nitrocellulose.

6. A mimeograph stencil assembly as in claim 1, wherein: said stencil layer comprises a tissue layer coated with a waxlike material; and wherein said third sheet is adapted to absorb the coating of said stencil layer thereby forming apertures in said stencil layer upon the application of pressure thereto and wherein said third sheet further is adapted to provide a cushioning effect thereby protecting said stencil layer from excessive pressure being applied thereto.

7. The mimeograph stencil assembly of claim 6 wherein said elastomeric plastic film is polyvinyl chloride.

8. The mimeograph stencil assembly of claim 6 wherein said elastomeric plastic film is polypropylene.

9. The mimeograph stencil assembly of claim 1 wherein said elastomeric plastic film is polyvinyl chloride.

10. The mimeograph stencil assembly of claim 1 wherein said elastomeric plastic film is polypropylene.

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