Stencil printing apparatus

Abstract: A printing apparatus is provided, which comprises an ink-permeable cylindrical printing drum (5) which is rotated about the axis of rotation thereof with heat-sensitive stencil sheet (13) wound around the circumferential surface thereof; a liquid ejecting means (25) which ejects a photothermal conversion material contained in a liquid (26) to heat-sensitive stencil sheet in accordance with image information, so that the photothermal conversion material is transferred to the stencil sheet as a reproduction of the image; a light radiating means (30) which radiates a visible or infrared ray (31) to the stencil sheet to which the photothermal conversion material has been transferred, so that the stencil sheet is perforated by heat emitted by the photothermal conversion material; and a pressing means (6) which presses at least either said printing drum or printing sheet that is being moved synchronously with rotation of the printing drum, to bring them into close contact with each other, so that stencil printing ink that is fed in the printing drum is transferred to the printing sheet through the stencil sheet perforated, in which said liquid ejecting means is further capable of ejecting a photothermal conversion material and/or a colorant contained in a liquid directly to printing sheet in accordance with the image information, so that the image can be reproduced directly on the printing sheet. Printing can be effected in two modes of stencil printing and printing directly from the liquid ejecting means. Upon perforation, stencil sheet is not required to contact any substance such as an original or a thermal printer head.

Description: The present invention relates to a printing apparatus which can efficiently obtain a small to large number of copies of print in two different printing modes. The so-called "digital printing machine" has already become popular as a printing machine which is high in printing speed and low in running cost. In the digital printing machine, heat-sensitive stencil sheet composed of a thermoplastic film is molten and perforated by such a heating means as a thermal head which emits heat in a form of dots in accordance with image information into which an image including letters, figures and photographs has been transformed as electric signals, and then the stencil sheet is wound around a printing drum containing stencil printing ink therein to transfer the printing ink through perforations of the stencil sheet onto printing paper. However, when stencil sheet is perforated in the digital printing machine, there often occur deficient perforations, failure of conveying and wrinkling of the stencil sheet due to unevenness of pressure exerted to press the stencil sheet to the thermal head. Furthermore, while the conventional digital printing machine is useful to obtain a large number of copies of print, it is high in cost for obtaining a small number of copies. Under the circumstances, it would be suggested that the printing machine is equipped with heat-sensitive recording paper or thermal transfer recording paper for obtaining a small number of copies of print. However, it would have to make the printing machine larger in size, and would make operation of the printing machine complicated since both printing paper and recording paper must be ready for printing in the printing machine. A printing machine has been suggested, in which one kind of regular paper can be printed by an electrophotographic process when a small number of copies are obtained, and by a stencil printing process when a large number of copies are needed. However, the printing system as a whole has to be expensive and much larger in size. Furthermore, when color printing is effected by the digital printing machine, it requires plural printing drums each containing each stencil printing ink of different color. The plural drums may be interchanged with one another in the printing machine when printing is effected in different colors on different regions of paper. However, operation of the interchange is troublesome, thereby lowering working efficiency. It is an object of the present invention to provide a printing apparatus which overcomes the above mentioned problems, can efficiently obtain a small to large number of copies of print at a low running cost even in color, and can be small in size. According to the above object, the present invention provides a printing apparatus which comprises an ink-permeable cylindrical printing drum which is rotated about the axis of rotation thereof with heat-sensitive stencil sheet wound around the circumferential surface thereof; a liquid ejecting means which ejects a photothermal conversion material contained in a liquid to heat-sensitive stencil sheet in accordance with image information, so that the photothermal conversion material is transferred to the stencil sheet as a reproduction of the image; a light radiating means which radiates a visible or infrared ray to the stencil sheet to which the photothermal conversion material has been transferred, so that the stencil sheet is perforated by heat emitted by the photothermal conversion material; and a pressing means which presses at least either said printing drum or printing sheet that is being moved synchronously with rotation of the printing drum, to bring them into close contact with each other, so that stencil printing ink that is fed in the printing drum is transferred to the printing sheet through the stencil sheet perforated, in which said liquid ejecting means is further capable of ejecting a photothermal conversion material and/or a colorant contained in a liquid directly to printing sheet in accordance with image information, so that the image can be reproduced directly on the printing sheet. The first feature of the present printing apparatus, which is different in stencil sheet perforation systems from the conventional rotary stencil printing apparatus, is that it employs a method for perforating heat-sensitive stencil sheet, which comprises a first step of transferring a photothermal conversion material to heat-sensitive stencil sheet by ejecting a liquid which contains the photothermal conversion material, from a liquid ejecting means to the heat-sensitive stencil sheet, and the second step of perforating the heat-sensitive stencil sheet specifically at sites to which the photothermal conversion material has been transferred, by subjecting the stencil sheet to a visible or infrared ray. The liquid ejecting means may be a device which comprises an ejecting head of nozzles, slits, porous materials, porous films or the like providing 10 - 2000 openings per inch (i.e., 10 to 2000 dpi) and connected to piezoelectric elements, heating elements, liquid-conveying pumps or the like so as to eject the liquid containing the photothermal conversion material intermittently or continuously, that is, in a form of dots or lines, in accordance with the electric signals for letters or images. The first step of the perforating method can be practiced, for example, by controlling a liquid ejecting means to eject the liquid from an ejecting head onto heat-sensitive stencil sheet while the liquid ejecting head is located a little bit apart from the heat-sensitive stencil sheet and moved parallel to the stencil sheet in accordance with image data that have previously been transformed into electric signals, and then evaporating the liquid that has been transferred to the heat-sensitive stencil sheet, so that the image is reproduced on the surface of the heat-sensitive stencil sheet as solid adherends mainly composed of the photothermal conversion material. In the second step of the perforating method, when a visible or infrared ray is radiated to the heat-sensitive stencil sheet to which a photothermal conversion material has been transferred, the photothermal conversion material absorbs light to emit heat. As a result, the thermoplastic film of the heat-sensitive stencil sheet is molten and perforated to obtain a master for stencil printing directly from the stencil sheet itself. The visible or infrared ray can readily be radiated using xenon lamps, flash lamps, halogen lamps, infrared heaters or the like. In this way, the perforating method does not require stencil sheet to contact any substance such as an original or thermal head to make a master, but requires only stencil sheet to be exposed to a visible or infrared ray. Thus, no wrinkling of stencil sheet occurs upon making a master. In the present invention, the first step and the second step mentioned above may be each conducted before the heat-sensitive stencil sheet is wound around the printing drum or after the heat-sensitive stencil sheet has been wound around the printing drum. The second feature of the present invention is that the printing apparatus is a printing apparatus which can effect printing in two modes, i.e., stencil printing and jet printing, by enabling the liquid ejecting means to further eject a photothermal conversion material and/or a colorant contained in a liquid directly to printing sheet such as printing paper and plastic sheet in accordance with image information, so that the image can be reproduced directly on the printing sheet. In the present printing apparatus, the liquid ejecting means may comprise a single ejecting head which can turn to heat-sensitive stencil sheet and printing sheet selectively to eject the photothermal conversion material to both of them, or may comprise a plurality of ejecting heads one of which ejects the photothermal conversion material to heat-sensitive stencil sheet and another of which ejects the photothermal conversion material and/or a colorant to a printing sheet. Furthermore, in order to make multicolor printing possible, the liquid ejecting means may have a plurality of ejecting heads each of which ejects each colorant of different color to a printing sheet, or may have a single ejecting head which can eject a plurality of colorants of different colors to a printing sheet. In the present printing apparatus, a large number of copies can be printed with stencil printing by ejecting a photothermal conversion material from a liquid ejecting means to heat-sensitive stencil sheet and perforate the stencil sheet by use of a light radiating means, and a small number of copies may be readily printed by ejecting a photothermal conversion material and/or a colorant from the liquid ejecting means directly to printing sheet. Thus, printing of both a small number and a large number of copies can efficiently effected by controlling the liquid ejecting means in the printing apparatus while only one kind of printing sheet is necessary with heat-sensitive stencil sheet in the printing apparatus. It is also possible to allow the liquid ejecting means to eject a photothermal conversion material and/or a colorant to a sheet that has been printed by stencil printing so as to effect overlay printing or multicolor printing. Furthermore, printing in black, which is frequently demanded, may be effected by stencil printing and printing in blue, red and yellow, which is not frequently demanded, may be effected by printing directly from the liquid ejecting means so as to increase efficiency of color printing. The photothermal conversion material used in the present invention is a material which can transform light energy into heat energy, and is preferably materials efficient in photothermal conversion, such as carbon black, lampblack, silicon carbide, carbon nitride, metal powders, metal oxides, inorganic pigments, organic pigments, and organic dyes. Among them, particularly preferred are those having a high light-absorbency within a specific range of wavelength, such as phthalocyanine colorings, cyanine colorings, squalirium colorings, and polymethine colorings. The colorant used in the present invention may be the same as the photothermal conversion material if the color of the former is the same as that of the latter. Examples of the colorant are organic or inorganic pigments such as furnace carbon black, lampblack, phthalocyanine blue, Victoria blue, Brilliant Carmine 6B, Permanent Red F5R, Rhodamine B Lake, Benzidine Yellow, Hansa Yellow, Naphthol Yellow, titanium oxide and calcium carbonate, and dyes such as of azo, anthraquinone, quinacridone, xanthene and acridine. The liquid in which the above photothermal conversion material or the above colorant is contained, may be solvents such as of aliphatic hydrocarbons, aromatic hydrocarbons, alcohols, ketones, esters, ethers, aldehydes, carboxylic acids, amines, low molecular weight heterocyclic compounds, oxides, and water. More specific examples thereof are hexane, heptane, octane, benzene, toluene, xylene, methyl alcohol, ethyl alcohol, isopropyl alcohol, n-propyl alcohol, butyl alcohol, ethylene glycol, diethylene glycol, propylene glycol, glycerin, acetone, methyl ethyl ketone, ethyl acetate, propyl acetate, ethyl ether, tetrahydrofuran, 1,4-dioxane, formic acid, acetic acid, propionic acid, formaldehyde, acetaldehyde, methylamine, ethylene diamine, dimethylformamide, pyridine, and ethylene oxide. These liquids may be used alone or in combination, and are preferably those which evaporate quickly after having been transferred from the liquid ejecting means to the heat-sensitive stencil sheet. To the liquid, may be added dyes, pigments, fillers, binders, hardening agents, preservatives, wetting agents, surfactants, pH-adjusting agents, or the like, as required. Thus, a composition for perforating heat-sensitive stencil sheet and a colorant composition can be prepared by appropriately dispersing or mixing the above photothermal conversion material and/or the above colorant in or with the above liquid in a form readily ejectable from the liquid ejecting means. The heat-sensitive stencil sheet used in the present invention may be stencil sheet to at least one side of which the photothermal conversion material can be transferred and which can be molten and perforated by heat emitted by the photothermal conversion material. The stencil sheet may be made of a thermoplastic film only, or may be a thermoplastic film laminated to a porous substrate. The thermoplastic film includes a film made from polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyurethane, polycarbonate, polyvinyl acetate, acrylic resins, silicone resins, and other resinous compounds. These resinous compounds may be used alone, in combination, or as a copolymer. Suitable thickness of the thermoplastic film is 0.5 - 50 µm, preferably 1 - 20 µm. If the film is less than 0.5 µm in thickness, it is inferior in workability and strength. If the film is greater in thickness than 50 µm, it is not economical to be perforated requiring a great amount of heat energy. The above porous substrate may be a thin paper, a nonwoven fabric, a gauze or the like, which is made from natural fibers such as Manila hemp, pulp, Edgeworthia, paper mulberry and Japanese paper, synthetic fibers such as of polyester, nylon, vinylon and acetate, metallic fibers, or glass fibers, alone or in combination. Basis weight of these porous substrates is preferably 1 - 20 g/m 2 , more preferably 5 - 15 g/m 2 . If it is less than 1 g/m 2 , stencil sheet is weak in strength. If it is more than 20 g/m 2 , stencil sheet is often inferior in ink permeability upon printing. Thickness of the porous substrate is preferably 5 - 100 µm, more preferably 10 - 50 µm. If the thickness is lower than 5 µm, stencil sheet is weak in strength. If it is greater than 100 µm, stencil sheet is often inferior in ink permeability upon printing. The heat-sensitive stencil sheet used in the present invention preferably has a liquid absorbing layer laminated to the stencil sheet on a side to which the liquid is ejected, in order to prevent the liquid from blurring on the stencil sheet or to accelerate drying of the liquid on the stencil sheet. In this case, perforations faithful to the original image are obtained when stencil sheet is exposed to light, and thus sharp image can be printed. The liquid absorbing layer is preferably formed on the outermost surface of the stencil sheet as a resinous layer which is molten and perforated similarly to the thermoplastic film when the stencil sheet is exposed to light to obtain a master. The liquid absorbing layer can be made of any material so long as it can prevent the liquid from blurring in the planar direction and fix the photothermal conversion material on stencil sheet. Preferably, the liquid absorbing layer is made of a material high in affinity with the above liquid used. For example, if the liquid is aqueous, the liquid absorbing layer can be made of polymer compounds such as polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, polyvinyl pyrrolidone, ethylene-vinyl alcohol copolymers, polyethylene oxide, polyvinyl ether, polyvinyl acetal, and polyacrylamide. These resinous compounds may be used alone, in combination or as a copolymer. If the liquid is an organic solvent, the liquid absorbing layer can be made of polymer compounds such as polyethylene, polypropylene, polyisobutylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, polyvinyl fluoride, polyvinyl acetate, acrylic resins, polyamide, polyimide, polyester, polycarbonate, and polyurethane. These resinous compounds may be used alone, in combination, or as a copolymer. Further, organic or inorganic particulates may be added to the liquid absorbing layer. Such particulates include organic particulates such as of polyurethane, polyester, polyethylene, polystyrene, polysiloxane, phenol resin, acrylic resin, and benzoguanamine resin, and inorganic particulates such as of talc, clay, calcium carbonate, titanium oxide, aluminum oxide, and kaolin. The liquid absorbing layer can be obtained by applying a liquid containing the above polymer compound and if necessary the above particulate, to stencil sheet by use of a coating means such as a gravure coater and a wire bar coater, and then drying it. The heat-sensitive stencil sheet used in the present invention preferably has a light reflecting layer which reflects the visible or infrared ray, in order to prevent light energy from being converted to heat at portions of stencil sheet to which no photothermal conversion material is transferred. In this case, only image portions where the photothermal conversion material is transferred are perforated, while non-image portions are not perforated. Thus, perforated heat-sensitive stencil sheet can be obtained without so-called "pin-holes". The light reflecting layer can be formed as a metal film by vacuum deposition of a metal on the above thermoplastic film, or can be formed by applying a liquid containing a metal powder and a polymer compound of the above thermoplastic film onto the thermoplastic film of the stencil sheet by use of a coating means such as a gravure coater and a wire bar coater, and then drying it. The metal is preferably one that is high in light reflectivity such as gold, aluminum and tin. When the light reflecting layer is a metal film vacuum-deposited on stencil sheet, the thermoplastic film of the stencil sheet is molten upon exposure to light, causing the metal film to lose its supporting structure and to be detached therefrom at portions where the photothermal conversion material has been transferred, so that perforations are made in the stencil sheet. When the light reflecting layer is made from the mixture of metal powders and polymer compounds, the thermoplastic film of the stencil sheet and the light reflecting layer are simultaneously molten upon exposure to light, at portions where the photothermal conversion material has been transferred, so that perforations are made in the stencil sheet. When the light reflecting layer and the liquid absorbing layer are both laminated to the present stencil sheet, the liquid absorbing layer may be laminated onto the light reflecting layer, or the light reflecting layer may be laminated onto one side of the thermoplastic film of the stencil sheet while the liquid absorbing layer is laminated onto the other side of the thermoplastic film. Upon printing, the perforated heat-sensitive stencil sheet is wound around the circumferential surface of an ink-permeable cylindrical printing drum that is rotated about the axis of rotation thereof, as in the conventional rotary stencil printing apparatus. Then, printing is effected by allowing printing ink that has been fed in the inner wall of the printing drum to pass through the perforated portions of the stencil sheet and transfer to printing sheet with an aid of a pressing means which presses at least one of the rotated printing drum and the printing sheet which is being moved synchronously with the rotation of the printing drum so as to bring the printing sheet into close contact with the printing drum by way of the stencil sheet wound therearound. The pressing means may be, for example, a press roller which is located outside and opposite to the printing drum and can press the exterior circumferential wall of the drum, or may be a squeeze roller or blade which is located inside and tangentially to a flexible circumferential wall of the printing drum and can extend the wall of the drum outwardly to press it onto another cylindrical drum located outside and opposite to the printing drum. Printing ink that is fed to the inside of the printing drum may be those conventionally used in stencil printing, such as oil ink, aqueous ink, water-in-oil (W/O) emulsion ink, oil-in-water (O/W) emulsion ink, and heat-meltable ink. Hereinafter, the present invention will be explained in more detail by way of a presently-preferred embodiment with reference to the accompanying drawings in which: Figure 1A is a sectional side view which diagrammatically shows a state in which a liquid containing a photothermal conversion material is ejected from a liquid ejecting means to a liquid absorbing layer of heat-sensitive stencil sheet, Figure 1B is a sectional side view which diagrammatically shows a state in which a photothermal conversion material is transferred onto heat-sensitive stencil sheet, Figure 1C is a sectional side view which diagrammatically shows a state in which light is radiated to heat-sensitive stencil sheet onto which a photothermal conversion material has been transferred, Figure 1D is a sectional side view which diagrammatically shows a state in which heat-sensitive stencil sheet is perforated after exposed to light, and Figure 2 is a side view which diagrammatically shows an inner structure of an embodiment of the present printing apparatus. It should be construed that the following embodiment is presented for only illustrative purpose, and the present invention is not limited to the embodiment. Now, referring to Figure 1, a mechanism of perforating stencil sheet in the present printing apparatus will be explained. Figure 1A shows heat-sensitive stencil sheet 13 which has a four-layer structure consisting of a liquid absorbing layer 21, a thermoplastic film 22, a light reflecting layer 23 and a porous substrate 24. A liquid 26 containing a photothermal conversion material is ejected from an ejecting head 25 of a liquid ejecting means to the liquid absorbing layer 21 of the stencil sheet 13 in a form of letter images so that the photothermal conversion material 28 is transferred onto the stencil sheet 13 as shown in Figure 1B. Then, a visible or infrared ray 31 is radiated with a light radiating means 30 having a light reflector 29 to the stencil sheet in the region of letter image which is constituted by the photothermal conversion material 28 transferred and fixed, as shown in Figure 1C. While the radiated ray 31 is reflected by the light reflecting layer 23 on portions other than the letter image portion, it causes only the portion to which the photothermal conversion material 28 has been fixed to emit heat. Thus, the liquid absorbing layer 21 and the thermoplastic film 22 are molten, and the light reflecting layer 23 is detached or molten to form a perforation 32 in the stencil sheet specifically at the site where the photothermal conversion material is fixed, as shown in Figure 1D. Next, referring to an embodiment shown in Figure 2, the present printing apparatus will be explained. Figure 2 diagrammatically shows the inside structure of an embodiment of the present printing apparatus. The printing apparatus has a casing C in which a cylindrical printing drum 5 is disposed. The printing drum 5 has in its inside a squeeze roller 51 which contacts the inner annular surface of the drum, and a doctor roller 52 which supplies the squeeze roller 51 with printing ink. A press roller 6, which can be raised and lowered to be attached to or detached from the circumferential surface of the printing drum 5, is disposed just below the printing drum 5 and opposite to the squeeze roller 51. Upon stencil printing, the printing drum 5 is rotated counterclockwise as seen in Figure 2. A paper feeding tray 8 is disposed in the side wall of the casing C on the left side as seen in Figure 2. Above the paper feeding tray 8, is disposed a paper feeding belt 11 which feeds printing paper 14 piece by piece from the paper feeding tray 8 toward the printing drum 5. Adjacent to the paper feeding belt 11, are disposed paper feeding rollers 12a consisting of a pair of upper and lower rollers by which printing paper 14 that has been fed by the paper feeding belt 11 is further fed between the printing drum 5 and the press roller 6 in accord with timing of rotation of the drum 5 upon printing. Also, paper discharging rollers 12b consisting of a pair of upper and lower rollers are disposed adjacent to the printing drum 5 on the right side as seen in Figure 2. By the discharging rollers 12b, paper 15 that has been printed between the printing drum 5 and the press roller 6 and is leaving them is conveyed to a paper discharging tray 9 disposed in the right side of the casing C as seen in Figure 2. As shown in Figure 2, a cover S is disposed above the casing C . On the back side of the cover S , an image sensor 1 is mounted. An original feeding roller 19 is disposed opposite to the image sensor 1 on the upper surface of the casing C , so that an original can be fed between the original feeding roller 19 and the image sensor 1 from the outside of the cover S to scan an image on the original and transform it into image information of electric signals. In the casing C , a roll of heat-sensitive stencil sheet 13 is placed below the original feeding roller 19 and supported on a suitable means for holding the roll rotatably about the axis thereof. To convey the stencil sheet therefrom toward the printing drum 5, stencil sheet feeding rollers 10 consisting of a pair of upper and lower rollers are disposed in the casing C . And, a stencil disposal box 7 into which used stencil sheet is discarded are disposed adjacent to the printing drum 5 on the side opposite to the feeding rollers 10. In order to achieve ejection of a photothermal conversion material to the stencil sheet according to the present invention, the liquid ejecting means may have, for example, an ejecting head 2a disposed adjacent to the way A on which stencil sheet 13 is fed to the printing drum 5 while the ejecting head 2a is directed to the stencil sheet 13 in the printing apparatus as shown in Figure 2. Alternatively, the liquid ejecting means may have an ejecting means 2b disposed adjacent to the printing drum 5 while the ejecting head 2b is directed to the drum 5 as shown in Figure 2. In order to perforate the stencil sheet in the printing apparatus shown in Figure 2, a light radiating means can be disposed, for example, adjacent to the way A on which stencil sheet 13 is fed to the printing drum 5, while being directed to the stencil sheet 13 as denoted by "4a" in Figure 2. Alternatively, a light radiating means which is directed to the printing drum 5 as denoted by "4b" in Figure 2 may be disposed adjacent to the printing drum 5. In addition, in order to print an image on printing paper 14 directly from the liquid ejecting means according to the present invention, a liquid ejecting means may have, for example, an ejecting head 3a disposed adjacent to the way B on which printing paper 14 is conveyed from the printing drum 5 downwardly to the discharging tray 15 while the ejecting head 3a is directed to printing paper as shown in Figure 2. Alternatively, the liquid ejecting means may have an ejecting head 3b disposed adjacent to the way B on which printing paper 14 is conveyed from the feeding belt 11 to the printing drum 5 while the ejecting head 3b is directed to printing paper 14 as shown in Figure 2. In the printing apparatus shown in Figure 2, the liquid ejecting means may have both or either of ejecting heads 2a and 2b for perforating heat-sensitive stencil sheet, and may have both or either of ejecting heads 3a and 3b for effecting printing on printing paper directly therefrom. Alternatively, the liquid ejecting means may have a single ejecting head 2b which can turn to both the printing drum and the printing paper so that only the single head is sufficient to perforate heat-sensitive stencil sheet and effect printing on printing paper directly therefrom. The printing apparatus shown in Figure 2 can reproduce an image on stencil sheet and printing paper by placing an original below the cover S to have the image sensor 1 scan an image on the original that is being conveyed by the original feeding roller 19 so as to transform the image into image information of electric signals, and then controlling movement of ejecting heads relative to the stencil or printing paper as well as liquid ejection therefrom on the basis of the image information. Alternatively, an image may be reproduced by controlling the operation of ejecting heads directly by a personal computer (not shown) on the basis of image information which has previously been stored in the personal computer. When a small number of copies are printed, the liquid ejecting means may be controlled so that the ejecting head denoted by 3a or 3b in the drawings ejects a liquid containing a colorant and/or a photothermal conversion material to reproduce an image directly on printing paper 14 that is being conveyed from the paper feeding tray 8 by the paper feeding belt 11 and the paper feeding rollers 12a and 12b while the printing drum 5 and the press roller 6 are detached from each other. Printing paper thus printed is stacked on the paper discharging tray 9 as printed paper 15. When color printing is effected on printing paper 14, the liquid ejecting means may have a plurality of ejecting heads each of which is controlled to eject each different color of ink on printing paper 14. For example, if each different color of a colorant is ejected from each of the ejecting head 3a and 3b, printing in two colors are effected. When a large number of copies are printed, the liquid ejecting means is controlled so that the ejecting head denoted as 2a in the drawings ejects a liquid containing a photothermal conversion material to reproduce an image on stencil sheet 13 that is being conveyed by the feeding rollers 10 toward the printing drum 5. Then, the stencil sheet 13 is exposed to a visible or infrared ray emitted from the light radiating means 4a to perforate the stencil sheet 13, and then is wound around the printing drum 5. Alternatively, the stencil sheet 13 may be first wound around the printing drum 5 and then exposed to a visible or infrared ray emitted from a light radiating means 4b to make perforations. Since the present invention can perforate stencil sheet in contact with no substance, stencil sheet 13 may be perforated by first winding it around the printing drum 5, controlling the liquid ejecting means to eject a liquid containing a photothermal conversion material from the ejecting head 2b to reproduce an image on the stencil sheet 13 that has been wound around the printing drum 5, and then radiating a visible or infrared ray from the light radiating means 4b to the wound stencil sheet 13. Upon printing, the printing drum 5 which has been wound with the perforated stencil sheet 13 around the circumferential surface thereof, is rotated about the axis counterclockwise as seen in Figure 2, and is simultaneously fed with stencil printing ink on its inner surface by the doctor roller 52 by way of the squeeze roller 51. Printing paper 14, which is being conveyed by the paper feeding belt 11 and the paper feeding roller 12a synchronously with the rotation of the printing drum 5, is brought into close contact with the printing drum 5 by the press roller 6 so that stencil printing ink is transferred through perforations of the stencil sheet 13 to the printing paper 14 to effect printing. Then, printing paper 14 thus printed is further conveyed by the paper discharging roller 12b to the paper discharging tray 9 and stacked thereon as printed paper 15. In order to obtain a piece of paper which is printed with both stencil printing and direct printing by ejection of a colorant containing liquid, printing paper 14 is pressed by the press roller 6 to the printing drum to effect stencil printing and also printed directly by the ejecting head 3a or 3b. In this case, the liquid ejecting means may have a single ejecting head which can move to the position of the ejecting head 2a depicted in Figure 2 upon stencil printing and move to the position of the ejecting head 3a depicted in Figure 2 upon printing directly from the liquid ejecting means, or may have a rotatable single ejecting head which can turn to the printing drum 5 like the ejecting head 2b depicted in Figure 2 upon stencil-printing and turn to printing paper 14 like the ejecting head 3b depicted in Figure 2 upon printing directly from the liquid ejecting means. However, when multicolor printing is effected, it is advantageous that the liquid ejecting means has a plurality of ejecting heads. The order of printing in these two modes may be, for example, such that printing paper 14 is first printed in one of the two modes and stacked on the paper discharging tray 9 as printed paper 15, and then the printed paper 15 is again returned to the paper feeding tray 8 to print in the other mode, or that the direct printing is effected from the ejecting head 3a and/or the ejecting head 3b before and/or after printing paper 14 is stencil-printed by the printing drum 5. In the latter case, both the stencil printing and the direct printing can be effected during one step in which printing paper 14 is conveyed from the paper feeding tray 8 to the paper discharging tray 9. The present invention does not require stencil sheet to contact any substance such as an original and a thermal head, but requires it simply to be exposed to an visible or infrared ray, and thus prevents stencil sheet from wrinkling, when stencil sheet is perforated. According to the present invention, stencil printing can be effected only when a large number of copies are printed, and the direct printing on printing sheets may be effected when a small number of copies are printed. As in the conventional rotary printing apparatus, the only sheets that must be installed in the present printing apparatus are printing sheet and heat-sensitive stencil sheet. Thus, the present printing apparatus can be small in size and can efficiently effect printing at low running cost. According to the present invention, a combination of the two modes of direct printing and stencil printing makes possible overlaying printing and multicolor printing, and also makes it easier to print in full color.

Claims: A printing apparatus which comprises an ink-permeable cylindrical printing drum which is rotated about the axis of rotation thereof with heat-sensitive stencil sheet wound around the circumferential surface thereof, a liquid ejecting means which ejects a photothermal conversion material contained in a liquid to a heat-sensitive stencil sheet in accordance with image information, so that said photothermal conversion material is transferred to said stencil sheet as a reproduction of said image, a light radiating means which radiates a visible or infrared ray to said stencil sheet to which said photothermal conversion material has been transferred, so that said stencil sheet is perforated by heat emitted by said photothermal conversion material, and a pressing means which presses at least either said printing drum or printing sheet that is being moved synchronously with rotation of said printing drum, to bring them into close contact with each other, so that stencil printing ink that is fed in said printing drum is transferred to said printing sheet through said perforated stencil sheet, in which said liquid ejecting means is further capable of ejecting a photothermal conversion material and/or a colorant contained in a liquid directly to printing sheet in accordance with image information, so that said image can be reproduced directly on said printing sheet. A printing apparatus defined in claim 1, in which said liquid ejecting means comprises a single ejecting head which can be directed to both said stencil sheet and said printing sheet to eject said photothermal conversion material to them selectively. A printing apparatus defined in claim 1, in which said liquid ejecting means comprises a plurality of ejecting heads which can eject colorants to said printing sheet so that color printing can be effected by ejecting each different color of colorant from each ejecting head. A printing apparatus defined in claim 1, in which said heat-sensitive stencil sheet comprises a thermoplastic film and a liquid absorbing layer laminated to said thermoplastic film, said photothermal conversion material being ejected to said liquid absorbing layer, and said heat-sensitive sheet being perforated by perforation of said thermoplastic film with said light radiating means. A printing apparatus defined in claim 4, in which said liquid absorbing layer is made of a resinous compound, and said heat-sensitive stencil sheet is perforated by perforation of said liquid absorbing layer and said thermoplastic film with said light radiating means. A printing apparatus defined in claim 4, in which said liquid absorbing layer is laminated to one side of said thermoplastic film, and a light reflecting layer which reflects said visible or infrared ray is laminated to the other side of said thermoplastic film. A printing apparatus defined in claim 4, in which said liquid absorbing layer is laminated to said thermoplastic film by way of a light reflecting layer which reflects said visible or infrared ray. A printing apparatus defined in any one of claims 4 to 7, in which said heat-sensitive stencil sheet comprises a porous substrate which is laminated thereto on a side remote from said liquid absorbing layer.

Inventors: KATSUYAMA JUNNOSUKE, WATANABE HIDEO, KATSUYAMA, JUNNOSUKE, WATANABE, HIDEO, Katsuyama, Junnosuke, c/o Riso Kagaku Corp., WATANABE, HIDEO, C/O RISO KAGAKU CORP.
Applicants: RISO KAGAKU CORP, RISO KAGAKU CORPORATION
Application year: 1996
Main classification: B41C1
IPC codes: B41L13, B41M1, B41J2, B41C1