US 3632376 A
Heat-stencil assembly for producing an imaged stencil sheet corresponding to an imaged original sheet by means of infrared radiation. The stencil sheet comprises an ink-impervious layer over an ink-permeable substrate, and said layer is removable to the receptive layer on a copy sheet in the heated areas.
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Description (OCR text may contain errors)
United States Patent References Cited UNITED STATES PATENTS Novotny Elliott Newman Roshkind Barbour Frasher et a1... Newman Primary ExaminerMurray Katz Attorney.lohnson & Kline ABSTRACT: Heat-stencil assembly for producing an imaged stencil sheet corresponding to an imaged original sheet by means of infrared radiation. The stencil sheet comprises an ink-impervious layer over an ink-permeable substrate, and said layer is removable to the receptive layer on a copy sheet in the heated areas.
HEAT-STENCIL ASSEMBLY The present invention relates to the production of imaged stencil sheets corresponding to imaged original sheets, and represents an improvement over the prior art procedures for effecting this result. Such prior art procedures rely upon the melting of ink-impervious coatings, layers of fibers present on or in a stencil sheet whereby the heated areas of the stencil sheet are rendered pervious to liquid ink and the stencil can be employed to produce numerous copies in the stencil duplicating field. Copies are formed from the imaged stencil by applying liquid ink to the rear of the stencil whereby the ink passes through the stencil only at the open imaged areas to stain a copy sheet in corresponding areas. The quality of the images formed on the copy sheet is dependent upon the quality of the image openings on the stencil sheet.
I have discovered that the quality of the images formed in a stencil sheet according to prior known procedures is limited because of the fact that the ink-impervious material in the heated areas is not removed completely but rather is dispersed into the support or dispersed laterally. Thus the outlines of the image openings are not sharp and/or the openings contain inkimpervious deposits, on or in the stencil support, which may block the passage of ink so as to produce voids or low-intensity portions in the images formed on the copy sheet.
It is the principle object of the present invention to provide stencil sheets which can be imaged thermographically in such a manner that the ink-impervious material in the heated areas is removed from the ink-pervious stencil support so that the image openings offer substantially no resistance to the passage of ink to each copy sheet and so that the image openings have sharp, clear borders and correspond closely to the quality of the original images.
This and other objects and advantages of this invention will be clear to those skilled in the art in the light of the present disclosure, including the drawings, in which:
FIG. 1 is a diagrammatic cross section, to an enlarged scale, of a stencil-forming sheet, a receptive sheet and an imaged original sheet superposed under exposure to an infrared radiation source but separated for purposes of illustration.
FIG. 2 is a diagrammatic cross section, to an enlarged scale, of the stencil sheet and receptive sheet imaged according to FIG. I.
The objects and advantages of the present invention are accomplished by providing a novel stencil'forming assembly which is substantially completely permeable to infrared radiation and which comprises an ink-impermeable stencil-forming sheet and a receptor sheet which removes portions from said stencil-forming sheet in predetermined areas under the effect of heat to render the latter sheet ink-permeable in such areas thereby producing a stencil sheet.
As shown in FIG. 1 of the drawings, the assembly comprising the stencil-forming sheet 1 and the receptor sheet are superposed over an original sheet carrying infrared radia tion-absorbing images 22, and exposed to an infrared radiation-emission lamp 30. The radiation is selectively absorbed by the images and an imagewise heat pattern is conducted to the transferable barrier layer 3 on the stencil-forming sheet and to the receptive surface on the receptor sheet to cause softening of the barrier layer and bonding with the receptive surface which preferably carries a heat-tackifiable layer which becomes softened as illustrated by layer 12 in FIGS. 1 and 2.
When the sheets are removed from the radiation and are separated, the bonded portions of the barrier layer are stripped over to the receptive layer on the imaged receptor sheet 10a as images 13 leaving imagewise ink-permeable openings 4 in the barrier layer to produce the stencil sheet la.
The stencil-forming sheets I comprise an ink-permeable support 2 and an ink-impermeable, continuous barrier layer 3 which covers said support and which softens but does not melt to flowable condition during the thermographic exposure. The present receptor sheets 10 comprise a sheet 11 having a receptive surface which preferably is a heat-softenable receptive layer 12 which becomes adhesive or tacky but does not melt to flowable condition during the thermographic exposure. The
receptive surface faces the barrier layer of the stencil-forming sheet and has an affinity for said barrier layer, when the latter is in heat-softened condition, and bonds therewith as a result of the thermographic exposure and strips the bonded portions from the support of the stencil-forming sheet when the sheets are separated after such exposure.
There are several essential features of the assemblies of the present invention which are critical and which make it possible to produce sharper and more accurate stencils corresponding to an imaged original sheet than heretofore possible. Firstly, the assembly must be permeable or transmissive or infrared radiation to such an extent that no bonding will occur between the barrier layer and the receptor surface under exposure to infrared radiation except in areas where infrared radiation-absorbing images are positioned against the assembly. Secondly, the degree of heat generated by such images upon brief exposure to infrared radiation must be suffrcient to soften the barrier layer on the stencil-forming sheet but insufficient to reduce it to flowable condition, so that the barrier layer is prevented from flowing into and integrating with the ink-permeable support in the heated areas. Thirdly, the receptive surface of the receptor sheet must be capable of bonding to the heat-softened portions of the barrier layer and of stripping such portions from their support when the assembly is removed from exposure and the sheets are separated.
The novel stencil-forming sheets 1, as shown in FIG. 1, comprise an ink-permeable heat-resistance support 2 such as a thin sheet of woven or nonwoven fibers or filaments, a fine mesh screen or similar ink-permeable support conventional in the stencil sheet field. The preferred support is the so-called Japanese stencil paper or tengujo paper which is a coarse tis sue paper which has high ink-permeability.
The barrier layer 3 present on the stencil support 2 comprises a layer of synthetic thermoplastic resin composition which softens but does not melt to flowable condition or liquefy at the particular thermographic temperature employed, which generally ranges between about 200 and 500 F. The barrier layer is applied to the support in such a way that its does not penetrate the support to any substantial extent but rather is retained at the surface of the support as a nonintegrated layer. This is accomplished by treating the support with a material which prevents the barrier layer from penetrating into the support to any substantial extent, such as by first applying a very thin resinous layer to the surface of the sup port and then applying the heavier barrier layer or by first impregnating the support with a weak acidic latex coagulant such as acetic acid or formic acid and then applying the barrier layer as a latex which coagulates at the surface of the support.
The barrier layer consists of a suitably plasticized synthetic thermoplastic resin such as a vinyl chloride or vinylidene chloride polymer or copolymer with other monomers such as vinyl acetate, and also includes solid particulate matter which reduces the cohesive properties of the resin binder and renders the barrier layer more brittle whereby it can be disrupted more cleanly than a layer consisting of the resin alone. According to one embodiment, the barrier layer 3 contains a colored pigment or dyestuff whereby the transfer of colored portions of the barrier layer 13 to the receptor sheet provides a duplicate copy 10a of the original sheet being used, as shown in FIG. 2. In all cases the materials present in the barrier layer must not absorb or reflect substantial amounts of infrared radiation. Suitable solid particulate materials include silica, milori blue pigment clay, and heat-meltable solid aromatic acids such as salicylic acid, benzoic acid, o-toluic acid, acetyl salicylic acid, and the like. Materials of the latter type provide excellent results, and I refer to the disclosure of copending application Ser. No. 692,164, filed Dec. 2, 1967, now abandoned, and incorporate by reference that portion of the disclosure relating to resinous heat-transferable layers containing such heat-meltable solids. The heat-transferable layers of the earlier application are perfectly suitable for use as the barrier layer of the present invention.
The receptor sheets suitable for use herein vary depending upon the nature of the barrier layer present on the stencilforming sheet. if the barrier layer is one which becomes tacky or adhesive when softened, then the receptor sheet may be a plastic film or paper sheet. if the barrier layer contains sufficient solid additive such as clay or silica that it is not very tacky or adhesive when softened, then the receptor sheet should carry a thin receptive layer 12 of heat-tackifiable composition, preferably of synthetic thermoplastic resin, which will adhere to the barrier layer in the heated areas and pull it from its support on separation of the sheets, as illustrated by FIGS. 1 and 2 of the drawings.
The following example is given by way of illustration of one type of stencil-forming assembly and its use, and should not be considered to be limitative.
A stencil-forming sheet is produced in the following manner. An ink-permeable web of Japanese stencil paper (tengujo) having a thickness of about 5 mils is printed on its undersurface with a very thin base layer of the following dilute solution using a printing roller:
ingredients Parts by Weight Pliolite S730 Butadiene-styrene 7 .8
Methyl ethyl ketone 74.4
iOQLO The solvent is evaporated rapidly to leave a thin continuous base layer of the resin deposited at the paper surface in a weight of about one-fourth pound per ream (equaling 500 sheets which are 25 inches X38 inches in dimensions).
Next the dried web is printed over the thin base layer with a thin layer of the following barrier layer composition:
ingredients Parts by Weight Pliolite S732 Butadiene-styrene 6.3 Toluene 14.4 Salicylic acid 14.3 Methyl ethyl ketone 60.0 Methyl isohutyl ketmre 5.0 100.0
Ingredients Parts by Weight Styrene-butadiene (48% aqueous emulsion) 50.0 Clay (70% solids) 20.0 \Vater 30.0 [00.0
The web is dried by evaporation of the water to leave a nontacky receptive layer having a weight of about l.5 pounds per ream at the paper surface. The web is cut into sheet lengths.
For purposes of convenience, the stencil-forming sheets and receptive sheets are releasably attached to each other along one edge, the barrier layer of the former being adjacent the receptive layer of the latter. The units are suitable for use in the reflex thermographic imaging process because of their infrared radiation-transmitting properties. Thus the assembly is positioned over an imaged original sheet, such as a typed letter, and the sheets are exposed to infrared radiation in the order shown in FIG. 1, such as by passing them through a Thermo-Fax machine. The heat generated in the image areas heats the barrier layer 3 and the receptive layer 12, causing them to soften and tackify and adhere to each other in such areas. When the sheets exit the exposure machine and are separated, the portions 13 of the barrier layer adhered to the receptive layer release from the stencil support 2 and strip over to the receptor sheet and carry with them the corresponding portions of the base layer. This leaves ink-permeable openings 4 in the barrier layer so that liquid ink can pass freely through the stencil sheet in the imaged areas to produce copies corresponding to the original sheet in the conventional stencil duplicating process.
if desired, the barrier layer may contain a colorant such as a small amount of a blue dye or other material that does not absorb infrared radiation so that the imaged receptor sheet is also a legible copy of the original subject matter.
The receptor sheet may also be a plastic film which is either heat-softenable or is coated with a clear resinuous receptive layer so that the imaged film is suitable for use as a projection transparency of the original subject matter, as taught in aforementioned copending application, Ser. No. 692,164.
The resinous binder materials used may be selected from those synthetic thermoplastic materials which provide coatings which soften but do not melt at the thermographic temperature which will be within the range of from about 200 F. to about 500 F. Most vinyl resins are suitable, including the acrylic resins and polystyrene. Cellulose resins such as ethyl cellulose and cellulose acetate are also suitable. Synthetic rubbers such as butadiene polymers and copolymers with styrene and acrylonitrile provide excellent results. In many cases conventional plasticizers should be added to reduce the softening temperature of the particular resin and/or to render the resin coating more adhesive and transferable in the heated state. Primary and secondary plasticizers may be used, as will be clear to those skilled in the resin art.
The barrier layer may advantageously be applied as an aqueous dispersion or emulsion. After application, the water is evaporated and the resin particles are fused sufficiently to form the ink-impermeable barrier layer on the surface of the support. Acrylic emulsions and rubber latices are preferred for this purpose.
1. An infrared radiation-transmissive stencil-forming assembly comprising a stencil sheet and a receptor sheet, said stencil sheet comprising an ink-permeable support containing a material which prevents a barrier layer from into said support to any substantial extent and having substantially completely on the surface thereof a continuous, ink-impermeable barrier layer which is softenable without melting to flowable condition at a temperature within the range of from about 200 to 500 F. said layer comprising a vinyl resin and solid particulate matter selected from the group consisting of silica, milori blue pigment, clay and solid aromatic acid which reduces the cohesive properties of the vinyl resin and renders the barrier layer brittle, and said receptor sheet comprising a support carrying a continuous thin receptive layer of synthetic thermoplastic resin which is heat tackifiable at the softening temperature of said barrier layer, said barrier layer being substantially completely removable from its support to said receptive layer when heat-softened in contact therewith.
2. A stencil-forming assembly according to claim 1. in which said particulate matter comprises salicylic acid.
3. A stench-forming assembly according to claim 1 in which the said material contained on the support of the stencil sheet comprises a latex coagulant and the barrier layer is a latex which is coagulated thereby and thus prevented from penetrating into the support.
4. A stencil-forming assembly according to claim I in which the said material contained on the support of the stencil sheet comprises a very thin surface layer of vinyl resin to which the thicker barrier layer is applied and which prevents the barrier layer from penetrating into the support and which is removable to the receptive layer with the barrier layer.
5. A stencil-forming assembly according to claim 1 in which said barrier layer comprises a heat-fused dispersion of vinyl resin particles.
UNITED STATES PATENT OFFICE CERTIFICATE @F CURECTEQN 3,632,376 Dated January L 197-2 Patent No Inventor(s) 51 8 A Newman It is certified that error appears in the above-identifiedpatent* and that said Letters Patent are hereby corrected asv shown below:
F Column 1, line 6, before "fibers", "of" should read or 3" Column 2, line 1 0, before "does", "its" should read it line 69, the filing date should read c. 20, 1967 not "Dec. 2,1967".
Column L line go, before "into" the word penetrating has been omitted.
Signed and sealed this 30th day of May1972.
EDWARD M.FLETCHEB,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents