Stencil printing machine, stencil sheet therefor, and a method of stencil printing

Abstract: A stencil printing machine comprising a perforating section (9) for perforating a stencil sheet (S) produced by bonding a resin film (S1) to a substrate (S2) with an adhesive; a printing drum (11) on the outer peripheral surface of which the stencil sheet (S) perforated at the perforating section is wrapped with the resin film (S1) inside, and, after removal of a substrate (S2) from the stencil sheet (S) thus wrapped, printing is done by pressing ink supplied to an inner peripheral surface, out from the perforated portion of the resin film (S1) remaining on the outer peripheral surface; an impressing member (13) for pressing a printing paper (P) against the printing drum (11) during printing; a separating means (21) for separating and discharging the substrate (S2) from the stencil sheet wrapped around the printing drum (11), prior to starting printing; and a resin film removing section for removing the resin film (S1) of the stencil sheet (S) from the printing drum (11) after completion of printing.

Description: The present invention relates to a stencil printing machine. There has been known a stencil sheet as is produced by bonding a resin film and a multi-porous substrate of a multi-porous sheet with an adhesive. This stencil sheet is prepared by perforating the film section by the use of a heat source such as a thermal head, and then wrapping it around a printing drum with the multi-porous substrate inside. Then, printing is done by passing ink through the stencil sheet to a printing paper. In this type of printing using the above-described stencil printing machine, however, the multi-porous substrate itself has low perviousness to the ink, resulting in non-uniform ink transfer to a printing paper, that is, in an non-uniformly printed image. This is because the multi-porous substrate produced of a multi-porous sheet has uneven density and thickness. To make the ink non-uniformly transferred to the paper look as if uniform, it is necessary to spread the ink from the portion where the ink has passed into the printing area of the paper, to the portion where no ink has been transferred. Thus spreading the ink, however, will result in the presence of an excessive amount of ink within the printed area on the printing paper where the ink passes through, and accordingly in ink offset and strike-through. As a means for improving the non-uniform ink condition on the paper, there is used only a resin-film stencil for printing, that is, without using the multi-porous sheet substrate. In this case, the stencil sheet cannot be conveyed in the machine, being wrinkled in stencil preparation or when wrapped around the printing drum, and accordingly printed matters faithful to an original mater copy are unobtainable. Such a technology has been disclosed in Japanese Patent Laid-Open No. Hei 5-220919. The stencil sheet produced by bonding a conventional resin film and a porous substrate such as a porous sheet with an adhesive is generally of the order of 30 to 50 µm in thickness. Therefore, for discharging the stencil sheet of this thickness by means of the stencil discharge section provided within the stencil printing machine, as large a space as this thickness is needed. In this case, however, a limit quantity of discharged stencils is around 20 to 100, albeit it depends on the discharge system and capacity, and the discharge section is not capable of accommodating a large quantity of spent stencils. Furthermore, the substrate such as the multi-porous sheet of the stencil sheet to be discharged to the stencil discharge section contains much of the ink; that is, the ink is used wastefully. By the way, the prior art technique for printing by the use of only a perforated resin-film stencil has been disclosed in Japanese Patents Laid-Open No. Hei 5-309932 and No. Hei 5-318900. According to the technique of Japanese Patent Laid-Open No. Hei 5-309932, an apparatus according to the preamble of claim 1, a resin film and a substrate that have been separated are stripped off either at the stencil discharge apparatus and received in a common receiving box. Therefore, the quantity of stencil papers discharged makes no difference from that of the stencil sheet made by bonding the prior art resin film and a multi-porous substrate of a multi-porous sheet with an adhesive. According to the technique disclosed in Japanese Patent Laid-Open No. Hei 5-318900, the separated porous substrate is held inside the machine and accordingly the provision of a capacity large enough to hold the porous substrate within the machine is required. For printing by the use of a prior art stencil sheet made by bonding a resin film and a multi-porous substrate such as a multi-porous sheet with an adhesive, the stencil sheet is wrapped around the printing drum. At this time, if a perforated resin film which is on the outer side of the stencil sheet is impressed, the ink passes through the perforated portion of the resin film, smearing the pressed member. Therefore, the stencil sheet, when wrapped around the printing drum, cannot be impressed, and accordingly it is necessary to wrap the stencil sheet around the printing drum by using an impressing member with the printing paper inserted between the printing drum and the impressing member. Furthermore, for fully impregnating a stencil sheet with the ink from a multi-porous substrate such as a multi-porous sheet through to a perforated resin film, a considerable pressure and/or impression time are required, resulting in excessive ink transfer to the printing paper used in wrapping the stencil sheet around the printing drum. When printing is continuously performed immediately after the wrapping of the stencil sheet around the printing drum, the printing paper used in wrapping the stencil sheet is discharged onto a discharge tray, on which succeeding papers are stacked continuously. Since much ink remains on the paper used in wrapping, the ink will transfer to the back side of the paper discharged thereon. The paper used in wrapping is a printed matter not faithful to the original master copy because of presence of such a defect as excessive strike-through. That is, the printing paper is used wastefully. Furthermore, when the stencil sheet is wrapped around the printing drum with a decreased pressure and/or impression time required for wrapping around the printing drum, the first one to three printing sheets are not fully impregnated with the ink, resulting in a failure in producing a printed matter faithful to an original master copy. Embodiments of the present invention to provide a stencil printing machine which is capable of smoothly conveying the stencil sheet, obtaining quality images, and remarkably increasing the discharged stencil sheet receiving capacity in a specific volume and a stencil sheet useful for use in such a stencil printing machine. The stencil printing machine according to the present invention is as claimed in claim 1. In a stencil printing machine according to the present invention, the separating means in the stencil printing machine also has a function to separate an inked paper from the printing drum. In a stencil printing machine according to a further embodiment of the present invention, the substrate of the stencil sheet used in the stencil printing machine of the first aspect has a cut made along a direction intersecting with the direction of rotation of the printing drum and a plurality of holes formed at a specific spacing along the direction of rotation of the printing drum. The separating means stated above may be a rotatable roller provided with a plurality of engaging members which engage with the holes of the substrate; the engaging member of the roller is engaged with the holes of the substrate of the stencil sheet wrapped around the outer peripheral surface of the printing drum, thereby rotating the roller to cur off the substrate at the cut from the resin film. A stencil sheet is produced by separably bonding the resin film with an adhesive to an ink-receptive sheet as a substrate, said ink-receptive sheet being capable of being printed with said ink. In a stencil sheet the adhesive stated above in the stencil sheet is a thermoplastic resin adhesive which is dissolved or swollen with a component in the printing ink. The stencil sheet is wrapped around the printing drum with the perforated resin film inside and with the ink-receptive sheet outside. When wrapping the stencil sheet, a pressure is applied by the impressing member from the ink-receptive side, and thereafter the ink-receptive sheet of the stencil sheet is separated by the substrate separating part. To this ink-receptive sheet thus separated, the ink is transferred through the perforated portion of the resin film to print an image, thus making a test printing. It is, therefore, unnecessary to use a printing paper P for the purpose of test printing at the time of wrapping the stencil sheet on the printing drum. That is, an printed image has been formed on the ink-receptive sheet discharged out of the stencil printing machine, from which the fidelity of the perforated stencil sheet to the original master copy can be ascertained. After the separation of the ink-receptive sheet, only the perforated resin film remains on the printing drum and is used for actual printing. Therefore, since there is used no multi-porous substrate that formerly gave an adverse effect to printing, it is possible to obtain a printed matter which is faithful to the original copy. After completion of printing, the stencil discharge section for removing the resin film from the printing section is required to receive only a very thin resin film, and consequently the discharge stencil sheet receiving capacity in a specific volume can be remarkably improved. Embodiments of all aspects of the present invention will now be described, by way of example only, with reference to the accompanying drawings. The above and other objects, aspects and advantages will become apparent to those skilled in the art by the preferred embodiment consistent with the principle of the invention, which will be discussed and illustrated in connection with these accompanying drawings of which: Fig. 1 is a schematic view of a stencil printing machine according to the present invention; Fig. 2 is a view showing a fragmentary sectional view of the stencil printing machine of Fig.1; Fig. 3 is a view showing a stencil sheet according to the present invention; Fig. 4 is a fragmental view of the stencil printing machine of Fig. 1; Fig. 5 is an enlarged view of Fig. 4; and Fig. 6 is a comparison table for comparing the effect of an embodiment of the present invention with that of a prior art example. The stencil printing machine is provided with an original image reading section 5 including an image scanner 3, for reading an image of an original master copy to be printed; and a stencil perforating section 9 a stencil perforating device 7 for duplicating an image by perforating a stencil sheet S in accordance with an original image data read by the original image reading section 5. The stencil perforating device 7 adopts a perforating system using a thermal head or other means to perforate the stencil sheet S. Each hole of the perforated stencil sheet is preferably separated from each other but said holes need not necessarily be made apart completely. The stencil sheet is required to have a good printing resistance to withstand a tearing force during printing and can be smoothly conveyed to a stencil discharge section 27 described later. It should be noticed that the stencil sheet S perforated to a normal image by a stencil perforating section 9 is sufficient. Also it should be noted that, in the embodiment, the stencil sheet S rolled as illustrated is fed out successively and cut to a specific length after being perforated by the perforating device, but the stencil sheet S may be fed in a form of sheets which will be used one by one by each stencil preparation. The stencil sheet S, after preparation, must be stably conveyed as far as a printing section 10. Since a perforated resin film S2 is integral with the ink-receptive sheet which is a substrate of the stencil sheet, the stencil sheet will never be wrinkled at the time of stencil perforation and wrapping around a printing drum 11. The resin film S2 thus perforated by the stencil perforating section 9 is mounted, integrally with the ink-receptive sheet S1, around the outer peripheral surface of the printing drum 11 in the printing section 10. At this time, the stencil sheet S is wrapped with the resin film S2 on the printing drum 11 side. This wrapping is done by rotating the printing drum 11 in the direction of the arrow in the drawing with the leading edge of the stencil sheet S securely clamped with a clamper 11a. The stencil sheet S, when wrapped, is simultaneously pressed against the printing drum 11 side by means of an impressing member 13, thus completing the installation of the stencil sheet on the printing drum 11. Thereafter the ink-receptive sheet S1 is separated from the resin film by the substrate separating section, being discharged out of the machine. For this substrate separating section, an existing separating pawl 21 is usable as the printing paper separating section as shown in Fig. 2. In the present embodiment, the ink-receptive sheet S1 is discharged out of the machine by this separating pawl, not by a special support separating section. The printing drum 11 after the separation of the ink-receptive sheet S1 carries only the resin film S2 and is ready for printing on the printing paper P immediately by the use of the impressing member 13. At this time, no multi-porous substrate which will give an adverse effect to printing is in use, and the resin film S2 alone is present on the printing drum 11. It is, therefore, possible to obtain a printed matter faithful to the original master copy. The printing paper P is fed out from the paper feed table 15. After being fed out one by one by means of the paper feed roller 17, the paper is fed in at a specific timing by the paper feed timing roller 19 between the printing drum 11 and the impressing member 13. With the rotation of the printing drum 11, printing is done on the printing paper P, correspondingly to the image perforated on the stencil sheet S, with the pressure of the impressing member 13. The printing paper P is separated from the printing drum 11 by means of a separating pawl 21 as a printing paper separating section, and conveyed by a belt conveyor system of a delivery apparatus 23, being discharged out to a paper receiving tray 25. In the case of a roll-type stencil sheet S, the ink-receptive sheet S1 should be designed to be easily separable; for example, there should be provided a separating portion in other than a perforable area, so that the ink-receptive sheet S1 can easily be separated thereat. Furthermore, after the completion of printing, the resin film S2 of the stencil sheet S wrapped around the printing drum 11 is stripped from the printing drum 11 by means of the stencil discharge section 27 having the discharge pawl, discharge roller, etc. for discharging the stencil sheet S, being discharged into a stencil discharge box. Since the ink-receptive sheet S1 is used as a substrate, a molten component resulting from the perforation of the resin film S2 at the perforating section 9 permeates to the interior of the ink-receptive sheet S1. Therefore, the stencil sheet S having a low adhesive power increases in the adhesive power at the perforated portion more than at the unperforated portion. However, in the portion increased in the adhesive power by perforation, the ink is permeated into the interior of the ink-receptive sheet S1 by the pressure of the impressing member 13, dissolving and/or swelling the molten component resulting from perforation, and therefore the adhesive power in the perforated portion decreases to facilitate the separation of the perforated resin film S2 from the ink-receptive sheet S1. Forming a separating section 35 in a fixed position from the edge of the ink-receptive sheet S1 of the stencil sheet S is effective. This separating section 35 facilitates the separation of the ink-receptive sheet S1 from the resin film S2. As a method for providing this separating section 35, perforations are formed. The length of the perforations nearly agrees with the width of the clamper 11a as shown in Fig. 2. Also, the separating section 35 may have been fully cut. Furthermore, in the case the ink-receptive sheet S1 may be a sheet similarly designed for easy separation. The condition of a printed image on the paper evaluated by using an image analyzer on a whole solid-printed portion is shown in the table of Fig. 6. As an example of comparison is used a conventional stencil sheet S produced by attaching the resin film to the multi-porous sheet. Figures of high values used in the table indicate printed matters faithful to the original master copy; that is, figures of low values indicate printed matters of low fidelity to the original master copy. In Fig. 1, a stencil discharge section 27 is disposed on the opposite side of the stencil perforating section 9; on the printing drum 11 only the perforated resin film S2 is present, and therefore only the extremely thin resin film S2 is received in the stencil discharge section. Also shown in Fig. 6 is the quantity of discharged stencil papers received in the stencil discharge section 27, the holding capacity of which is 2.0 litres and is evaluated by a compression-type stencil discharge apparatus. As an example of comparison is used a conventional stencil sheet S produced by attaching a resin film to a multi-porous sheet. Figures of high values used in the table indicate a large discharge stencil holding capacity, while figures of low values indicate a small discharge stencil holding capacity. By the way, in the present invention is used the ink-receptive sheet S1 as a substrate of the stencil sheet S. If an ink-unreceptive sheet is used, the ink on the sheet that has been discharged out of the stencil printing machine will not permeate into the sheet but will remain on the sheet surface. If the operator holds the discharged ink-unreceptive sheet by hand, his hands will be smeared with the ink. The ink-receptive sheet is not limited and may be any type of sheet pervious to the printing ink such as a quality printing paper or a synthetic resin sheet, cloth, and unwoven cloth which has been so processed as to be ink-receptive. Furthermore, a colored ink-receptive sheet can be discriminated from the printing paper P when discharged out of the machine, and also is usable as a tape sorter in order to sort the types of printing papers that have been stacked. For the resin film S2 of the stencil sheet S of the present invention, a thermoplastic resin film perforated by a heat source like a thermal head, for example, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polyester, polystyrene, polyurethane, polycarbonate, acrylic resin, silicone resin, etc., of which particularly the poly-vinylidene chloride and polyester are desirable for use. It is also possible to use a resin film which is perforable by dissolving by an ink jet system other than the heat source such as the thermal head. For the adhesive for bonding the resin film S2 of the stencil sheet S of the present invention to the substrate S1 for supporting the resin film S2, a thermoplastic adhesive is preferably used. For example, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polyester, polystyrene, polyurethane, polycarbonate, acrylic resin, and silicone resin are usable. Of these, a material which is dissolved and/or swollen by a component of the printing ink used in the stencil printing machine must be selected. When the ink-receptive sheet is separated by using an adhesive material, which is not dissolved and/or swollen with the component of the ink, for bonding the resin film to the ink-receptive sheet, the adhesive power required for bonding the resin film of the stencil sheet S of the present invention to the substrate supporting the resin film must be so weak as to allow easy separation of the resin film from the substrate supporting the resin film. Next, Fig. 3 shows another example of the stencil sheet of the present invention. The stencil sheet S, as illustrated, is a continuous body having a plurality of perforations 30 at a specific spacing at both ends. And the ink-receptive sheet S1 is provided with perforations 31 at a specific spacing. The printable area of the resin film S1 is to be a range L not extending to the perforations 30. The stencil sheet S is received in a rolled state in the stencil perforating section 9, and is sent out to the printing drum 11 side while being perforated similarly to the above-described embodiment. The stencil sheet S is discharged by the stencil printing machine partly shown in Fig. 4. In the lower part of the printing drum 11 is provided a feed roller 32 near the separating pawl 21. This feed roller 32 has engaging pawls 32a which engage with the perforations 30 as shown in the enlarged view of Fig. 5. The engaging pawls 32a are arranged at the same spacing as the pitch of the perforations 30. Therefore, The stencil sheet S after perforation is secured at the leading edge with the clamper 11a, being wrapped as far as the position shown in the drawing around the printing drum 11 with the rotation of the printing drum 11. Then, with the rotating drum 11 rotating, the feed roller 32 is turned in the direction of the arrow in the drawing, thereby separating the ink-receptive sheet S1 at the perforations 31 from the printing drum 11 and the resin film S2. Thus the stencil sheet S can easily be sent out and discharged. According to the stencil printing machine of the present invention, the perforated resin film, being integral with the ink-receptive sheet which is a substrate, can be conveyed with stability without wrinkling at the time of perforation and wrapping around the printing drum. The ink-receptive sheet which is a substrate of the stencil sheet is separated from the resin film by means of the substrate separating section and discharged out of the stencil printing machine. Therefore, in the stencil discharge section for holding the resin film of the stencil sheet removed after printing from the printing section, only the resin film is discharged, thereby enabling to remarkably increase the capacity for holding discharged stencil papers in a specific volume. Furthermore, as only the perforated resin film is wrapped around the printing drum and printed, printed matters faithful to the original copy are obtainable. Furthermore, according to the stencil printing machine, since the constitution of an existing printing paper separating section is usable for separation and discharge of the printing paper, the substrate can be discharged out of the machine, thus enabling the simplification of the machine itself. Furthermore, according to the stencil sheet of the present invention, the ink-receptive sheet which is a substrate is used and discharged out of the stencil printing machine, and therefore the fidelity of the perforated stencil sheet to the original copy can be ascertained. Consequently, no printing paper will be wasted by test printing. Furthermore, according to the stencil sheet, since the ink-receptive sheet is used as the substrate, a component dissolved at the time of perforation of the resin film permeates into the interior of the ink-receptive sheet: however, because the component thus permeating is dissolved and/or swollen with a component in the ink, the perforated film can easily be separated from the ink-receptive sheet, thus enabling the provision of a highly reliable printing machine.

Claims: A stencil printing machine, comprising: a perforating section (9) arranged to perforate a stencil sheet (S) produced by bonding a resin film (S2) to a substrate (S1) with an adhesive; a printing drum (11) having an outer and inner peripheral surface, the machine being arranged to wrap said stencil sheet (S) perforated at said perforating section (9)on said printing drum (11) with said resin film (S2) inside, to remove the substrate (S1) from said stencil sheet (S) thus wrapped, and to press ink supplied to the inner peripheral surface, and out from the perforated portion of said resin film (S2) remaining on said outer peripheral surface, thereby effecting printing; an impressing member (13) for pressing a printing paper (P) against said printing drum (11) during printing; a separating means (21) arranged to separate and discharge said substrate (S1) from said stencil sheet (S) wrapped around said printing drum (11), prior to starting printing; a resin film removing section (27) arranged to remove said resin film (S2) of said stencil sheet (S) from said printing drum (11) after completion of printing; characterised in that: the machine is arranged such that only the resin film (S2) is received in the resin film removing section (27) for storage. A stencil printing machine according to claim 1, wherein said separating means (21) has also a function for separating a printed paper (P) from said printing drum (11). A stencil printing machine according to claim 1 or 2, including said stencil sheet and wherein said substrate (S1) of said stencil sheet (S) has a cut (35) formed along a direction intersecting with the direction of rotation of said printing drum (11), and a plurality of holes (30) formed at a specific spacing along the direction of rotation of said printing drum (11); said separating means is a rotatable roller having a plurality of engaging members which engage with holes (30) of said substrate (S1); and said substrate (S1) is torn off at a cut (35), and separated from said resin film (S2) by engaging said engaging member of said roller with said holes (30) of said substrate (S1) of said stencil sheet (S) wrapped around said outer peripheral surface of said printing drum (11) to rotate said roller.

Inventors: SADANAO OKUDA, SADANAO, OKUDA, Sadanao, Okuda, c/o Riso Kagaku Corporation
Applicants: RISO KAGAKU CORP, RISO KAGAKU CORPORATION
Application year: 1995
Main classification: B41L13
IPC codes: B41C1, B41L13, B41N1