Title:
HEAT-SENSITIVE STENCIL SHEET
United States Patent 3715267
Abstract:
A heat-sensitive stencil sheet comprising a porous supporting sheet and a thermoplastic resin film which is bonded to one surface of the supporting sheet with an adhesive containing at least one metal salt of a higher fatty acid having from 10 to 22 carbon atoms.
US Patent References:
Method of manufacturing stencils
Hoover - January 1955 - 2699113
Method for copying indicia by particle transfer
Vander Weel - September 1960 - 2954311
Copy-sheet and method
Reitter - June 1963 - 3094620
Dry processed photothermographic printing plate and process
Rauner et al. - August 1963 - 3100702
Heat-sensitive copying-paper
Owen - October 1963 - 3108896
Method of manufacturing stencils
Hoover - January 1955 - 2699113
Method for copying indicia by particle transfer
Vander Weel - September 1960 - 2954311
Copy-sheet and method
Reitter - June 1963 - 3094620
Dry processed photothermographic printing plate and process
Rauner et al. - August 1963 - 3100702
Heat-sensitive copying-paper
Owen - October 1963 - 3108896
Inventors:
Kubo, Keishi (Yokohama, JA)
Sakai, Kiyoshi (Tokyo, JA)
Sato, Takashi (Urawa, JA)
Sakai, Kiyoshi (Tokyo, JA)
Sato, Takashi (Urawa, JA)
Application Number:
05/075725
Publication Date:
02/06/1973
Filing Date:
09/25/1970
View Patent Images:
Export Citation:
Assignee:
Ricoh Co., Ltd. (Tokyo, JA)
Primary Class:
Other Classes:
430/308, 430/964, 101/128.210
International Classes:
B41N1/24; B41N1/24; B32B27/10; B32B27/30
Field of Search:
117/3.1,3.2,3.4,3.5,3.6,35.5,35.6,36.1-36.4,36.7-36.9,134,167,87,90 101/128.1,128.2 346/135 161/249,250,265,165,410,413,254 156/336,234,240
US Patent References:
| 3120611 | Method and apparatus for the negative reproduction of masters on a copy bearer utilizing a heat absorbing layer | February 1964 | Lind | |
| 3125458 | March 1964 | Dalton | ||
| 3223838 | Method for the preparation of relief images by the use of a heat-sensitive sheet | December 1965 | Hoshino et al. | |
| 3241997 | Heat-sensitive copying material | March 1966 | Schutzner | |
| 3260612 | Thermographic recording process and heat-sensitive elements therefor | July 1966 | Dulmage et al. | |
| 3280732 | Stencil construction | October 1966 | Mooney et al. |
Primary Examiner:
Burnett, Robert F.
Assistant Examiner:
Gil, Joseph C.
Claims:
What we claim is
1. A heat-sensitive stencil sheet of the class in which perforations corresponding to a graphic original are thermally produced by selective melting of the film in a thermoplastic resin film on a porous support comprising a porous supporting sheet and a thermoplastic resin film from 5 to 10 microns thick, said film being bonded to a surface of said supporting sheet with an adhesive containing therein at least one salt selected from the group consisting of metal salts of higher fatty acids having 10 to 22 carbon atoms which melt without chemical change at substantially the same temperature at which said perforations are produced in a thermoplastic film.
2. A stencil sheet according to claim 1, wherein the metal salts have a melting point in the range of from about 70° to 150° C.
3. A stencil sheet according to claim 1, wherein the amount of said adhesive to be applied is in the range of from about 0.5 to 2.5 grams per square meter, and the amount of metal salt contained in the adhesive is such that it is applied in the range of from about 0.2 to 2.0 grams per square meter.
4. A stencil sheet according to claim 1, wherein the metals constituting said metal salts are selected from those metals in Groups I, II, Iv, VII and VIII of the Periodic Table.
5. A stencil sheet according to claim 1, wherein said adhesive is a vinyl resin or an acrylic resin.
6. A stencil sheet according to claim 5, wherein said acrylic resin is a polyacrylic acid, polymethacrylate, polyethylacrylate, polypropylacrylate, polybutylacrylate, butylacrylate-vinylacetate copolymer or a acrylonitrile-methacrylic acid copolymer, and said vinyl resin is a polyvinyl acetate, vinyl acetate-ethylene copolymer, vinyl acetate-maleic acid copolymer, vinyl acetate-methyl acrylate copolymer, vinyl acetate-acrylic acid copolymer, vinyl acetate-butyl methacrylate copolymer or a vinyl acetate-crotonic acid copolymer.
1. A heat-sensitive stencil sheet of the class in which perforations corresponding to a graphic original are thermally produced by selective melting of the film in a thermoplastic resin film on a porous support comprising a porous supporting sheet and a thermoplastic resin film from 5 to 10 microns thick, said film being bonded to a surface of said supporting sheet with an adhesive containing therein at least one salt selected from the group consisting of metal salts of higher fatty acids having 10 to 22 carbon atoms which melt without chemical change at substantially the same temperature at which said perforations are produced in a thermoplastic film.
2. A stencil sheet according to claim 1, wherein the metal salts have a melting point in the range of from about 70° to 150° C.
3. A stencil sheet according to claim 1, wherein the amount of said adhesive to be applied is in the range of from about 0.5 to 2.5 grams per square meter, and the amount of metal salt contained in the adhesive is such that it is applied in the range of from about 0.2 to 2.0 grams per square meter.
4. A stencil sheet according to claim 1, wherein the metals constituting said metal salts are selected from those metals in Groups I, II, Iv, VII and VIII of the Periodic Table.
5. A stencil sheet according to claim 1, wherein said adhesive is a vinyl resin or an acrylic resin.
6. A stencil sheet according to claim 5, wherein said acrylic resin is a polyacrylic acid, polymethacrylate, polyethylacrylate, polypropylacrylate, polybutylacrylate, butylacrylate-vinylacetate copolymer or a acrylonitrile-methacrylic acid copolymer, and said vinyl resin is a polyvinyl acetate, vinyl acetate-ethylene copolymer, vinyl acetate-maleic acid copolymer, vinyl acetate-methyl acrylate copolymer, vinyl acetate-acrylic acid copolymer, vinyl acetate-butyl methacrylate copolymer or a vinyl acetate-crotonic acid copolymer.
Description:
BACKGROUND OF INVENTION
This invention relates to heat-sensitive stencil sheets comprising a porous thin support, usually paper, bonded to a thermoplastic resin film with an adhesive which contains at least one metal salt of a higher fatty acid.
Stencil sheets are normally prepared by bonding a thermoplastic resin film to a porous supporting sheet. Typical thermoplastic resins which are so employed include polystyrene, polypropylene, polyethylene and vinylidene chloride-vinyl chloride copolymers. The thickness of the resin film is normally from about 5-10 microns. The weight of the porous supporting sheet is usually from about 8-10 g per square meter. It normally is prepared from a natural fiber obtained from mitsumata, paper mulberry, manila hemp, and the like; or synthetic fibers such as rayon, vinylon, tetron, acrylic resin, or the like.
The stencil sheets are used to prepare stencils and these in turn are utilized for the preparation of copies of an original. The usual practice is that the original having the desired image is superposed upon the film-bonded surface of the stencil sheet and the original is exposed to electromagnetic waves including infrared rays. The heat which is thereby produced effects perforations of the film in areas congruent to the image areas of the original. Because the support is porous the resulting stencil may be used to transfer ink to a copy and to thereby reproduce the original.
The intensity of the electromagnetic waves, i.e. the amount of exposure of the stencil sheet to such waves, will, of course, influence the clarity of the perforated image on the stencil. If the exposure is insufficient the perforated image will be defective and there will result an indistinct image when the stencil is used for printing. If the exposure is excessive a similar result will be observed. Since the thermoplastic resin film on the porous support of the stencil sheet is extremely thin it is difficult to judge by observation with the naked eye whether the perforated image on the stencil is one which will be capable of producing clear printed images. It is normally necessary to make such a determination by a trial and error method in which a number of stencil sheets are prepared and actually utilized in printing. The prints obtained are then compared to determine which of the several stencils is suitable. This is expensive and time-consuming.
THE INVENTION
Stencil sheets have now been discovered from which stencils, the suitability of which for printing can be readily determined by visual observation with the naked eye, can be prepared. The stencil sheets of this invention comprise porous supporting sheets and a thermoplastic resin film bonded to a surface thereof with an adhesive which contains at least one heat-sensitive metal salt of a higher fatty acid having from 10-22 carbon atoms.
The adhesives utilized in the practice of this invention are those which have been conventionally utilized in the preparation of the stencil sheets of the prior art. They include especially those mainly comprising vinyl resins, for instance, polyvinyl acetate, vinyl acetate-ethylene copolymer, vinyl acetate-maleic acid copolymer, vinyl acetate-methyl acrylate copolymer, vinyl acetate-acrylic acid copolymer, vinyl acetate-butyl methacrylate copolymer and vinyl acetate-crotonic acid copolymer; or those mainly comprising acrylic resin, for instance, polyacrylic acid, polymethylacrylate, polyethylacrylate, polypropylacrylate, polybutylacrylate, butylacrylate-vinylacetate copolymers and acrylonitrile-methacrylic acid copolymers. Specific examples of commercially available adhesives suitable for the present invention include, for example, an adhesive manufactured by NIPPON GOSEI K.K. (i.e. NIPPON SYNTHETIC CHEMICAL INDUSTRY CO., LTD.) and sold under the tradename `GOHSENYL M-50 Y-5`, which comprises a vinyl acetate homopolymer having the polymerization degree of about 1100 in methanol solution, an adhesive manufactured by NISSETSU KOGYO K.K. (i.e. NISSETSU INDUSTRY CO., LTD.) and sold under the tradename `SUPER DAIN FB-85`, which comprises acrylic resin dissolved in alcohol. Particularly preferred thermoplastic films are those containing a vinylidene chloride-vinyl chloride copolymer as the principal component.
A variety of heat-fusible metal salts of fatty acids may be employed in the preparation of the stencil sheets of the present invention. Since the resin employed as the adhesive is generally utilized in the liquid state as a solution in alcohol, or other liquid, it is desirable that the heat-fusible compound be soluble in the liquid. However, even if the heat-fusible compound is insoluble it may still be usefully employed by first pulverizing it to a fine powdery state and thereafter mixing it with the adhesive.
More specifically, the heat-fusible compounds to be employed for the preparation of the stencil sheet in accordance with the present invention include metal salts of higher saturated and unsaturated fatty acids having 10 - 22 carbon atoms. They include, for example, stearic acid, palmitic acid, lauric acid, myristic acid oleic acid, erucic acid and behenic acid. The metal component of the salt may be selected from those of Group II of the Periodic Table, such as calcium, zinc, cadmium, magnesium, etc., those in Group IV of the Table, such as lead, those of Group VII of the Table, such as manganese, those of Group VIII of the Table, such as iron, cobalt, nickel, etc., and those metals of Group 1 of the Table, such as copper. These heat-fusible compounds normally have a melting point in the range of from about 70°. to 150°C.
The amount of the heat-fusible compound to be admixed with the adhesive is selected so that the quantity of heat-fusible compound in the stencil sheet is in the range from about 0.2 - 2.0 g per square meter. This quantity of heat-fusible compound or compounds is conveniently obtained in the stencil sheet by mixing with an adhesive and thereafter utilizing the adhesive in the range from about 0.5 - 2.5 g per square meter in the stencil sheet.
While a moderate degree of variation from the above defined limits may be tolerated it has been found that there is a lowering of the perforation efficiency when an excessive quantity of adhesive and heat-fusible compound is employed and that there is a definite deterioration of the clarity of the perforated image when the amount of these materials is insufficient. In either case, it becomes progressively more difficult and finally impossible to judge by observation of a stencil with the unaided eyes the correctness of the amount of exposure of the stencil sheet to electromagnetic waves. Additionally, where the amount of adhesive employed is insufficient the preservability of the stencil sheet is adversely affected.
It is desirable that the heat-fusible compound melt at a temperature less than 170°C. since this is normally the highest temperature at which perforation of the thermoplastic film may be effected by exposure to infrared rays.
Ideally the metal salt should be uniformly distributed in the adhesive and should melt as close as possible to the same temperature at which perforation of the thermoplastic film takes place to thereby form a transparent visible image reproducing the original in the adhesive layer at the same time at which the film becomes perforated in accordance with the image of the original.
The process of preparing a stencil utilizing the stencil sheets of this invention is similar to the standard procedure for preparing ordinary stencils. Thus the original is superposed on the stencil sheet and exposed to electromagnetic energy with the result that the film becomes visible. The reason for the visibility is that the heat-fusible compound in the adhesive melts, becomes transparent and concentrates on the edges of the perforated image. Additionally, a small part of the melt adheres to the fibers of the porous substrate. There is, therefore, produced a readily observable transparent image distinguishable from the background color of the stencil sheet which is normally milky white or red. The observation of the perforated image is similar to the observation of the negative of a black and white photograph. The image is distinctly transparent and in striking contrast to the opaque background of the stencil.
The stencil sheets of the invention are readily prepared by standard processes. For example, the selected amount of heat-fusible compound or compounds is dispersed or dissolved in a solution containing the selected quantity of adhesive. The resultant composition is coated either on a surface of the porous substrate or on a surface of a thermoplastic film and the substrate and film are bonded to each other and dried. Coating of the adhesive may be effected by roll-coating, spray-coating, and the like.
While it may be possible to utilize metal salts of fatty acids containing less than 10 carbon atoms or more than 22 carbon atoms, it is most practical to operate in the above defined range. The fatty acid salts having less than 10 carbon atoms have an extremely offensive odor as is well known. Metal salts of fatty acids having more than 22 carbon atoms, while they are available, are often difficult and expensive to obtain.
The principal advantage of the stencil sheet of this invention is that it is possible to determine by visual observation with the naked eye the exact amount of electromagnetic radiation appropriate to produce the best possible stencil. In other words, the actual clarity of the image on the stencil can be observed so that it is readily possible to make a judgment as to whether the exposure to infrared rays is of an appropriate quantity to produce a stencil suitable for the preparation of duplicate copies of original images. The stencils of the invention, therefore, overcome a very serious defect of stencils which have been previously known.
The following non-limiting examples are given by way of illustration only:
EXAMPLE 1
By adding 20gr of zinc stearate to 1,500 ml of a 6 percent methanol solution of vinyl acetate homopolymer and dispersing it by mixing well for 3 hours with a ball mill, a liquid adhesive containing the heat fusible compound was prepared. Subsequently, by applying this adhesive, a thermoplastic film 7 μ thick comprising transparent vinylidene chloride-vinyl chloride copolymer as its principal component was bonded onto a porous thin paper with manila hemp fibers as its principal component and weighting 9 gr per square meter, to prepare a stencil sheet. The amount of adhesive applied for bonding was 1.7 gr per square meter based on the dried solid content of the adhesive, while the content of the heat fusible compound within the layer of said adhesive was 0.8 gr per square meter.
An original carrying a printed image was superposed on the film-bonded surface of the stencil sheet, and infrared rays were applied, employing THERMOFAX (a manufacture of 3-M Co., Ltd.), for about 4 seconds by way of the surface of the porous thin paper, to effect perforation. As a result, there was formed a transparent perforated image which was clear against a white background. It was possible to determine easily an appropriate amount of infrared-ray exposure by observation and comparison with the original image. The obtained stencil, when employed for printing with a commercialized rotary press machine, proved capable of producing a multiplicity of clear-cut prints which faithfully reproduced the original image.
For the purpose of comparison, 4 different stencils were prepared employing 4 identical stencil sheets obtained by affixing the foregoing film and porous thin paper without using said heat fusible compound, superposing an original carrying printed images onto the respective sheets, and exposing them to infrared rays by means of the foregoing THERMOFAX for differingperiods of time, (i.e. for about 3 minutes, 4 minutes, 5 minutes and 6 minutes respectively. It was found that the perforated images formed on each stencil were almost illegible and it was impossible to judge which was properly exposed. And, when said stencils were respectively employed for printing with a commercialized rotary press machine, the stencil prepared through about 4 minutes' exposure was capable of faithfully reproducing points of the original images, but all the remaining stencils produced only indistinct prints.
EXAMPLE 2
By adding 18 gr of cadmium stearate to 1,500 ml of a 6 percent methanol solution of vinyl acetate homopolymer, the same as that in Example 1, and dispersing it by mixing well for 3 hours on a ball mill, a liquid adhesive containing a heat fusible compound was prepared. Subsequently, by applying thus prepared adhesive, a thermoplastic film of 7 μ thick containing transparent and red-colored (spectrotransparency for the thickness of 450 = 45 percent) vinylidene chloride vinyl chloride copolymer as the principal component, was bonded onto a porous thin paper.
The resultant stencil sheet, when subjected to infrared-ray exposure through the same operation as in Example 1, produced a stencil carrying a red-colored and transparent perforated image, which was clear against an opaque and reddish-white ground.
EXAMPLE 3
By adding 35 gr of lead palmitate of 1,500 ml of a 8 percent methanol solution of vinyl acetate homopolymer, the same as in Example 1, and dispersing it by mixing well for 5 hours on a ball mill, a liquid adhesive containing a heat fusible compound was prepared. Subsequently, by applying thus prepared adhesive, a thermoplastic film containing red-colored and transparent vinylidene chloride-vinyl chloride copolymer, the same as that employed in Example 2, as its principal component, was bonded onto a porous thin paper.
The resultant stencil sheet, when subjected to infrared-ray exposure through the same operation as in Example 1, produced a stencil carrying a red-colored and transparent perforated image, which was clear against an opaque and reddish-white ground.
EXAMPLE 4
By adding 12 gr of magnesium stearate and 10 gr of lead palmitate to 1500 ml of a 7 percent methanol solution of vinyl acetate homopolymer, the same as that in Example 1, and dispersing them by mixing well for 5 hours on a ball mill, a liquid adhesive containing a mixture of heat fusible compounds was prepared. Subsequently, by applying thus prepared adhesive, a thermoplastic film containing red-colored and transparent vinylidene chloride-vinyl chloride copolymer, the same as that employed in Example 2, as the principal component, was bonded onto a porous thin paper.
The resultant stencil sheet, when subjected to infrared-ray exposure through the same operation as in Example 1, produced a stencil carrying a red-colored and transparent perforated image, which was clear against an opaque and reddish-white ground.
EXAMPLE 5
By using various heat fusible compounds identified in the following Table, stencil sheets were prepared according to the procedure described in Example 1.
Heat Fusible Compounds
No. Fatty Acid Metal ____________________________________________________________ ______________ 1 Lauric Acid Co 2 " Zn 3 " Pb 4 " Mg 5 " Cu 6 Palmitic Acid Zn 7 " Co 8 " Cd 9 Behenic Acid Ca 10 " Mn 11 " Ni 12 Oleic Acid Pb 13 " Co 14 Erucic Acid Pb 15 " Zn ____________________________________________________________ ______________
This invention relates to heat-sensitive stencil sheets comprising a porous thin support, usually paper, bonded to a thermoplastic resin film with an adhesive which contains at least one metal salt of a higher fatty acid.
Stencil sheets are normally prepared by bonding a thermoplastic resin film to a porous supporting sheet. Typical thermoplastic resins which are so employed include polystyrene, polypropylene, polyethylene and vinylidene chloride-vinyl chloride copolymers. The thickness of the resin film is normally from about 5-10 microns. The weight of the porous supporting sheet is usually from about 8-10 g per square meter. It normally is prepared from a natural fiber obtained from mitsumata, paper mulberry, manila hemp, and the like; or synthetic fibers such as rayon, vinylon, tetron, acrylic resin, or the like.
The stencil sheets are used to prepare stencils and these in turn are utilized for the preparation of copies of an original. The usual practice is that the original having the desired image is superposed upon the film-bonded surface of the stencil sheet and the original is exposed to electromagnetic waves including infrared rays. The heat which is thereby produced effects perforations of the film in areas congruent to the image areas of the original. Because the support is porous the resulting stencil may be used to transfer ink to a copy and to thereby reproduce the original.
The intensity of the electromagnetic waves, i.e. the amount of exposure of the stencil sheet to such waves, will, of course, influence the clarity of the perforated image on the stencil. If the exposure is insufficient the perforated image will be defective and there will result an indistinct image when the stencil is used for printing. If the exposure is excessive a similar result will be observed. Since the thermoplastic resin film on the porous support of the stencil sheet is extremely thin it is difficult to judge by observation with the naked eye whether the perforated image on the stencil is one which will be capable of producing clear printed images. It is normally necessary to make such a determination by a trial and error method in which a number of stencil sheets are prepared and actually utilized in printing. The prints obtained are then compared to determine which of the several stencils is suitable. This is expensive and time-consuming.
THE INVENTION
Stencil sheets have now been discovered from which stencils, the suitability of which for printing can be readily determined by visual observation with the naked eye, can be prepared. The stencil sheets of this invention comprise porous supporting sheets and a thermoplastic resin film bonded to a surface thereof with an adhesive which contains at least one heat-sensitive metal salt of a higher fatty acid having from 10-22 carbon atoms.
The adhesives utilized in the practice of this invention are those which have been conventionally utilized in the preparation of the stencil sheets of the prior art. They include especially those mainly comprising vinyl resins, for instance, polyvinyl acetate, vinyl acetate-ethylene copolymer, vinyl acetate-maleic acid copolymer, vinyl acetate-methyl acrylate copolymer, vinyl acetate-acrylic acid copolymer, vinyl acetate-butyl methacrylate copolymer and vinyl acetate-crotonic acid copolymer; or those mainly comprising acrylic resin, for instance, polyacrylic acid, polymethylacrylate, polyethylacrylate, polypropylacrylate, polybutylacrylate, butylacrylate-vinylacetate copolymers and acrylonitrile-methacrylic acid copolymers. Specific examples of commercially available adhesives suitable for the present invention include, for example, an adhesive manufactured by NIPPON GOSEI K.K. (i.e. NIPPON SYNTHETIC CHEMICAL INDUSTRY CO., LTD.) and sold under the tradename `GOHSENYL M-50 Y-5`, which comprises a vinyl acetate homopolymer having the polymerization degree of about 1100 in methanol solution, an adhesive manufactured by NISSETSU KOGYO K.K. (i.e. NISSETSU INDUSTRY CO., LTD.) and sold under the tradename `SUPER DAIN FB-85`, which comprises acrylic resin dissolved in alcohol. Particularly preferred thermoplastic films are those containing a vinylidene chloride-vinyl chloride copolymer as the principal component.
A variety of heat-fusible metal salts of fatty acids may be employed in the preparation of the stencil sheets of the present invention. Since the resin employed as the adhesive is generally utilized in the liquid state as a solution in alcohol, or other liquid, it is desirable that the heat-fusible compound be soluble in the liquid. However, even if the heat-fusible compound is insoluble it may still be usefully employed by first pulverizing it to a fine powdery state and thereafter mixing it with the adhesive.
More specifically, the heat-fusible compounds to be employed for the preparation of the stencil sheet in accordance with the present invention include metal salts of higher saturated and unsaturated fatty acids having 10 - 22 carbon atoms. They include, for example, stearic acid, palmitic acid, lauric acid, myristic acid oleic acid, erucic acid and behenic acid. The metal component of the salt may be selected from those of Group II of the Periodic Table, such as calcium, zinc, cadmium, magnesium, etc., those in Group IV of the Table, such as lead, those of Group VII of the Table, such as manganese, those of Group VIII of the Table, such as iron, cobalt, nickel, etc., and those metals of Group 1 of the Table, such as copper. These heat-fusible compounds normally have a melting point in the range of from about 70°. to 150°C.
The amount of the heat-fusible compound to be admixed with the adhesive is selected so that the quantity of heat-fusible compound in the stencil sheet is in the range from about 0.2 - 2.0 g per square meter. This quantity of heat-fusible compound or compounds is conveniently obtained in the stencil sheet by mixing with an adhesive and thereafter utilizing the adhesive in the range from about 0.5 - 2.5 g per square meter in the stencil sheet.
While a moderate degree of variation from the above defined limits may be tolerated it has been found that there is a lowering of the perforation efficiency when an excessive quantity of adhesive and heat-fusible compound is employed and that there is a definite deterioration of the clarity of the perforated image when the amount of these materials is insufficient. In either case, it becomes progressively more difficult and finally impossible to judge by observation of a stencil with the unaided eyes the correctness of the amount of exposure of the stencil sheet to electromagnetic waves. Additionally, where the amount of adhesive employed is insufficient the preservability of the stencil sheet is adversely affected.
It is desirable that the heat-fusible compound melt at a temperature less than 170°C. since this is normally the highest temperature at which perforation of the thermoplastic film may be effected by exposure to infrared rays.
Ideally the metal salt should be uniformly distributed in the adhesive and should melt as close as possible to the same temperature at which perforation of the thermoplastic film takes place to thereby form a transparent visible image reproducing the original in the adhesive layer at the same time at which the film becomes perforated in accordance with the image of the original.
The process of preparing a stencil utilizing the stencil sheets of this invention is similar to the standard procedure for preparing ordinary stencils. Thus the original is superposed on the stencil sheet and exposed to electromagnetic energy with the result that the film becomes visible. The reason for the visibility is that the heat-fusible compound in the adhesive melts, becomes transparent and concentrates on the edges of the perforated image. Additionally, a small part of the melt adheres to the fibers of the porous substrate. There is, therefore, produced a readily observable transparent image distinguishable from the background color of the stencil sheet which is normally milky white or red. The observation of the perforated image is similar to the observation of the negative of a black and white photograph. The image is distinctly transparent and in striking contrast to the opaque background of the stencil.
The stencil sheets of the invention are readily prepared by standard processes. For example, the selected amount of heat-fusible compound or compounds is dispersed or dissolved in a solution containing the selected quantity of adhesive. The resultant composition is coated either on a surface of the porous substrate or on a surface of a thermoplastic film and the substrate and film are bonded to each other and dried. Coating of the adhesive may be effected by roll-coating, spray-coating, and the like.
While it may be possible to utilize metal salts of fatty acids containing less than 10 carbon atoms or more than 22 carbon atoms, it is most practical to operate in the above defined range. The fatty acid salts having less than 10 carbon atoms have an extremely offensive odor as is well known. Metal salts of fatty acids having more than 22 carbon atoms, while they are available, are often difficult and expensive to obtain.
The principal advantage of the stencil sheet of this invention is that it is possible to determine by visual observation with the naked eye the exact amount of electromagnetic radiation appropriate to produce the best possible stencil. In other words, the actual clarity of the image on the stencil can be observed so that it is readily possible to make a judgment as to whether the exposure to infrared rays is of an appropriate quantity to produce a stencil suitable for the preparation of duplicate copies of original images. The stencils of the invention, therefore, overcome a very serious defect of stencils which have been previously known.
The following non-limiting examples are given by way of illustration only:
EXAMPLE 1
By adding 20gr of zinc stearate to 1,500 ml of a 6 percent methanol solution of vinyl acetate homopolymer and dispersing it by mixing well for 3 hours with a ball mill, a liquid adhesive containing the heat fusible compound was prepared. Subsequently, by applying this adhesive, a thermoplastic film 7 μ thick comprising transparent vinylidene chloride-vinyl chloride copolymer as its principal component was bonded onto a porous thin paper with manila hemp fibers as its principal component and weighting 9 gr per square meter, to prepare a stencil sheet. The amount of adhesive applied for bonding was 1.7 gr per square meter based on the dried solid content of the adhesive, while the content of the heat fusible compound within the layer of said adhesive was 0.8 gr per square meter.
An original carrying a printed image was superposed on the film-bonded surface of the stencil sheet, and infrared rays were applied, employing THERMOFAX (a manufacture of 3-M Co., Ltd.), for about 4 seconds by way of the surface of the porous thin paper, to effect perforation. As a result, there was formed a transparent perforated image which was clear against a white background. It was possible to determine easily an appropriate amount of infrared-ray exposure by observation and comparison with the original image. The obtained stencil, when employed for printing with a commercialized rotary press machine, proved capable of producing a multiplicity of clear-cut prints which faithfully reproduced the original image.
For the purpose of comparison, 4 different stencils were prepared employing 4 identical stencil sheets obtained by affixing the foregoing film and porous thin paper without using said heat fusible compound, superposing an original carrying printed images onto the respective sheets, and exposing them to infrared rays by means of the foregoing THERMOFAX for differingperiods of time, (i.e. for about 3 minutes, 4 minutes, 5 minutes and 6 minutes respectively. It was found that the perforated images formed on each stencil were almost illegible and it was impossible to judge which was properly exposed. And, when said stencils were respectively employed for printing with a commercialized rotary press machine, the stencil prepared through about 4 minutes' exposure was capable of faithfully reproducing points of the original images, but all the remaining stencils produced only indistinct prints.
EXAMPLE 2
By adding 18 gr of cadmium stearate to 1,500 ml of a 6 percent methanol solution of vinyl acetate homopolymer, the same as that in Example 1, and dispersing it by mixing well for 3 hours on a ball mill, a liquid adhesive containing a heat fusible compound was prepared. Subsequently, by applying thus prepared adhesive, a thermoplastic film of 7 μ thick containing transparent and red-colored (spectrotransparency for the thickness of 450 = 45 percent) vinylidene chloride vinyl chloride copolymer as the principal component, was bonded onto a porous thin paper.
The resultant stencil sheet, when subjected to infrared-ray exposure through the same operation as in Example 1, produced a stencil carrying a red-colored and transparent perforated image, which was clear against an opaque and reddish-white ground.
EXAMPLE 3
By adding 35 gr of lead palmitate of 1,500 ml of a 8 percent methanol solution of vinyl acetate homopolymer, the same as in Example 1, and dispersing it by mixing well for 5 hours on a ball mill, a liquid adhesive containing a heat fusible compound was prepared. Subsequently, by applying thus prepared adhesive, a thermoplastic film containing red-colored and transparent vinylidene chloride-vinyl chloride copolymer, the same as that employed in Example 2, as its principal component, was bonded onto a porous thin paper.
The resultant stencil sheet, when subjected to infrared-ray exposure through the same operation as in Example 1, produced a stencil carrying a red-colored and transparent perforated image, which was clear against an opaque and reddish-white ground.
EXAMPLE 4
By adding 12 gr of magnesium stearate and 10 gr of lead palmitate to 1500 ml of a 7 percent methanol solution of vinyl acetate homopolymer, the same as that in Example 1, and dispersing them by mixing well for 5 hours on a ball mill, a liquid adhesive containing a mixture of heat fusible compounds was prepared. Subsequently, by applying thus prepared adhesive, a thermoplastic film containing red-colored and transparent vinylidene chloride-vinyl chloride copolymer, the same as that employed in Example 2, as the principal component, was bonded onto a porous thin paper.
The resultant stencil sheet, when subjected to infrared-ray exposure through the same operation as in Example 1, produced a stencil carrying a red-colored and transparent perforated image, which was clear against an opaque and reddish-white ground.
EXAMPLE 5
By using various heat fusible compounds identified in the following Table, stencil sheets were prepared according to the procedure described in Example 1.
Heat Fusible Compounds
No. Fatty Acid Metal ____________________________________________________________ ______________ 1 Lauric Acid Co 2 " Zn 3 " Pb 4 " Mg 5 " Cu 6 Palmitic Acid Zn 7 " Co 8 " Cd 9 Behenic Acid Ca 10 " Mn 11 " Ni 12 Oleic Acid Pb 13 " Co 14 Erucic Acid Pb 15 " Zn ____________________________________________________________ ______________