Title:
THREE-LAYER STENCIL ASSEMBLY HAVING PLASTIC OVERLAY SHEET
United States Patent 3595166
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.
US Patent References:
/1092768.html
Fuerth - April 1914 - 1092768
Stencil film
Heath - June 1940 - 2203280
Coated backing sheet and stencil-sheet assembly embodying same
Frasher et al. - November 1961 - 3009416
Stencil paper and coating composition
Shelffo - November 1962 - 3062675
Duplicating stencils
Blake et al. - April 1968 - 3376810
/1092768.html
Fuerth - April 1914 - 1092768
Stencil film
Heath - June 1940 - 2203280
Coated backing sheet and stencil-sheet assembly embodying same
Frasher et al. - November 1961 - 3009416
Stencil paper and coating composition
Shelffo - November 1962 - 3062675
Duplicating stencils
Blake et al. - April 1968 - 3376810
Application Number:
04/800972
Publication Date:
07/27/1971
Filing Date:
02/20/1969
View Patent Images:
Export Citation:
Assignee:
Bell & Howell Company (Chicago, IL)
Primary Class:
Other Classes:
428/311.310, 428/514, 430/200, 428/486, 428/511
International Classes:
B41N1/24; B41N1/24
Field of Search:
161/113,254,218,241,247,251,256,149,156,166,235 117/35.5,35.6,36.1,38,36.7,36.8,36.9,135,155 101/128.2,127,128,128.1,128.3,128.4 156/90
Primary Examiner:
Goolkasian, John T.
Assistant Examiner:
Hoag W. E.
Claims:
What I claim is
1. A mimeograph stencil assembly having a sandwichlike construction comprising:
2. A mimeograph stencil assembly as in claim 1, wherein:
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:
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:
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.
1. A mimeograph stencil assembly having a sandwichlike construction comprising:
2. A mimeograph stencil assembly as in claim 1, wherein:
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:
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:
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.
Description:
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 of a thermocopier and by means of a conventional typewriter.
DESCRIPTION OF THE 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 of emulsion 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. 1 a typical prior art typing stencil which consists 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, numerals, 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 of a 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 "chop-outs."
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 apertures just as if it 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. 1 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 aperture 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 improved 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
FIGS. 1 and 2 illustrate prior art stencils capable of being prepared by means of a typewriter only.
FIG. 3 shows a prior art thermostencil known as the "Weber stencil."
FIG. 4 illustrates a second prior art thermostencil known as the "Riso stencil."
FIG. 5 is a diagrammatic view illustrating a preferred embodiment of the 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 11 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 16. Attached to this sandwich along the line 20 is the overlay sheet 17 consisting of a 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. 1 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 of the invention as set forth in the appended claims.
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 of a thermocopier and by means of a conventional typewriter.
DESCRIPTION OF THE 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 of emulsion 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. 1 a typical prior art typing stencil which consists 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, numerals, 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 of a 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 "chop-outs."
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 apertures just as if it 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. 1 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 aperture 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 improved 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
FIGS. 1 and 2 illustrate prior art stencils capable of being prepared by means of a typewriter only.
FIG. 3 shows a prior art thermostencil known as the "Weber stencil."
FIG. 4 illustrates a second prior art thermostencil known as the "Riso stencil."
FIG. 5 is a diagrammatic view illustrating a preferred embodiment of the 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 11 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 16. Attached to this sandwich along the line 20 is the overlay sheet 17 consisting of a 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. 1 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 of the invention as set forth in the appended claims.