EP0805048A1

EP0805048A1 - Stencil printing device

Info

Publication number: EP0805048A1
Application number: EP97302813A
Authority: EP
Inventors: Hideo Riso Kagaku Corp. R&D Center Watanabe; Junnosuke Riso Kagaku Corp. R&D Ctr. Katsuyama
Original assignee: Riso Kagaku Corp
Current assignee: Riso Kagaku Corp
Priority date: 1996-05-01
Filing date: 1997-04-24
Publication date: 1997-11-05
Also published as: JPH09295452A

Abstract

A stencil printing device prevents offsetting of ink (7), seeping-through of ink, and side-escaping or end-escaping of ink by the improvement in ink-drying performance through use, during stencil printing, of a solid ink which changes phase between solid and liquid at a certain temperature. The stencil printing device includes an ink-permeable plate cylinder (1;2) which is adapted to rotate and around which a stencil sheet (3) that has undergone plate-making is wound; and ink feed means which is provided inside the plate cylinder and which is used for feeding ink onto the inner surface of the plate cylinder. The ink feed means is adapted to transfer ink onto a printing medium (9) from the plate cylinder through perforations formed in the stencil sheet for stencil-printing. The ink feed means includes a squeegee device (6;17) which is arranged so as to slidably contact the inner surface of the plate cylinder and a heating device (4;15;16) for heating a solid ink fed into the plate cylinder in order to obtain a liquid ink.

Description

The present invention relates to a stencil printing device, and more particularly to a stencil printing device capable of preventing offsetting of ink, seeping-through of ink, and the like by the improvement in ink-drying performance through use of a solid ink which changes phases between solid and liquid.
Stencil printing is widely used due to a plate being easy to prepare. However, stencil printing has the following problems: ink takes time to dry after stencil printing; when printed paper is directly held in one's hand, ink is transferred onto the hand; when printed sheets of paper are piled in continuous printing, ink is offset onto the back of a neighboring sheet; and these phenomena are particularly noticeable with postcard paper, into which ink penetrates relatively poorly. These problems stem from the fact that a conventional stencil printing ink dries merely through penetration of oil-phase components and evaporation of aqueous-phase components. Accordingly, ink drying performance significantly deteriorates in the case of printing on paper into which ink penetrates relatively poorly.
There have been proposed measures to cope with these problems, including a method in which a thermosetting component is incorporated into the oily phase and/or the aqueous phase (Japanese Patent Application Laid-Open (kokai) Nos. 6-128516 and 6-172691) and a method in which solid particles are added to an emulsion ink (Japanese Patent Application Laid-Open (kokai) No. 6-116525). However, satisfactory results have not been obtained from these measures.
Also, viscosity of a conventional emulsion ink varies in accordance with ambient temperature. For example, at high temperatures, ink softens with the resultant occurrence of seeping-through of ink, side- or end-escaping of ink (escape of ink from an edge portion of printed paper), or the like.
The present inventors have proposed a solid ink which can prevent offsetting of ink, seeping-through of ink, and side- or end-escaping of ink during printing through improvement of ink drying performance. The ink changes its solid phase to a liquid phase at a temperature of 30 to 150 °C (Japanese Patent Application Nos. 7-40600, 7-42068, and 7-49999).
An aim of the present invention is to provide a stencil printing device capable of preventing offsetting of ink, seeping-through of ink, and side- or end-escaping of ink during printing by improvement in ink-drying performance through use of a solid ink which changes phase at a predetermined temperature.
To achieve the above aim, the present invention provides a stencil printing device including an ink-permeable plate cylinder which is adapted to rotate and around which a stencil sheet that has undergone plate-making is wound; and ink feed means which is provided inside the plate cylinder and which is used for feeding ink onto the inner surface of the plate cylinder, the ink feed means being adapted to transfer ink onto a printing medium from the plate cylinder through perforations formed in the stencil sheet for stencil-printing, wherein the ink feed means comprises a squeegee device, arranged so as to slidably contact the inner surface of the plate cylinder and a heating device for heating a solid ink fed into the plate cylinder in order to obtain a liquid ink.
Preferably, the heating device preferentially heats the squeegee device.
Preferably, the heating device is provided in the squeegee device.
Preferably, the solid ink changes to have a liquid phase at a temperature of 30 to 150 °C .
The stencil printing device of the present invention uses a solid ink which reversibly changes phase at a predetermined temperature. Since the solid ink is changed to a liquid ink having a predetermined viscosity by the heating device during stencil printing, the liquid ink transfers onto a printing medium through perforations formed in the stencil sheet. The liquid ink transferred onto the printing medium instantaneously changes to have a solid phase while the printing medium is being conveyed, so that the ink can be fixed onto the printing medium within a short period of time. Accordingly, even when a printed material is touched by one's hand immediately after being delivered from the stencil printing device of the present invention, the hand is not smeared with the ink. Also, offsetting of the ink does not occur in continuous printing. In addition, since the ink used in the present invention does not penetrate into a printing medium, seeping-through of the ink does not occur. Furthermore, according to the present invention, the liquid ink transferred onto a printing medium instantaneously changes to a solid phase, and thus printing is possible on not only ordinary printing paper and postcard paper with poor ink permeability, but also plastic film, metal, and the like.
A solid ink used in the stencil printing device of the present invention changes phase from solid to liquid at a temperature of 30 to 150°C, preferably 40 to 120°C . If a phase change temperature is 30°C or lower, ink will be fluidized when an ambient temperature or an interior temperature of the stencil printing device becomes 30 °C , possibly causing smearing of the stencil printing device or side- or end-escaping of ink. By contrast, if a phase change temperature is not lower than 150 °C, the size of a heating device for changing the phase of ink will increase, resulting in potential loss of thermal energy. Moreover, since in such a case it takes a longer time for ink to reach a phase change temperature, there is an accompanying increase in waiting time until printing becomes ready.
The above-described solid ink contains a reversibly phase-changing component, such as waxes, fatty acid amides, esters of fatty acid, or resins, having a melting point or a softening point of 30 to 150°C, preferably 40 to 120°C . Examples of such a component include carnauba wax, microcrystalline wax, polyethylene wax, montan wax, paraffin wax, candelilla wax, shellac wax, wax oxide, ester wax, beeswax, Japan wax, spermaceti, stearic acid amide, lauryl acid amide, behenic acid amide, caproic acid amide, palmitic acid amide, low molecular weight polyethylene, polystyrene, alpha-methylstyrene polymers, polyvinyl toluene, indene resins, polyamide, polypropylene, acrylic resins, alkyd resins, polyvinyl acetate, ethylene-vinyl acetate copolymers, and vinyl chloride-vinyl acetate copolymers.
In addition to the above-described reversibly phase-changing component, a coloring agent is contained in the solid ink. Examples of such a coloring agent include organic and inorganic pigments, such as furnace carbon black, lamp black, Cyanine Blue, Lake Red, Cyanine Green, titanium oxide, and calcium carbonate, as well as azo-type, anthraquinone-type, and quinacridone-type dyes. Also, as needed, an anionic, cationic, or nonionic dispersant may be added. Examples of such a dispersant include sorbitan fatty acid esters, fatty acid monoglycerides, and quaternary ammonium salts.
The solid ink may assume the form of an oil ink or a W/O type emulsion ink. An oil ink is prepared by dissolvingly mixing a reversibly phase-changing component, a coloring agent, a dispersant, etc. An emulsion ink is prepared by dissolvingly mixing a reversibly phase-changing component, a coloring agent, and a dispersant, followed by emulsification established by adding an aqueous component to the resultant mixture while stirring. A coloring agent may be contained in an aqueous-phase component.
When stencil printing is conducted using the solid ink of the present invention, the solid ink is preferably heated such that during printing, its viscosity falls within a range of 10 to 1,000,000 cps, more preferably a range of 100 to 100,000 cps. When the ink viscosity is not higher than 10 cps during printing, side- or end-escaping of the ink is likely to occur and the ink is likely to quickly penetrate into printed paper with resultant seeping-through.
When the ink viscosity is not lower than 1,000,000 cps, it becomes difficult for the ink to pass through perforations formed in a stencil sheet, resulting in a lowered printing density and uneven printing.
In the stencil printing device of the present invention, when a liquid ink is passed through perforations formed in a stencil sheet and transferred onto printing paper, the stencil sheet and the printing paper are pressed against each other at a pressure of 0.01 to 10 kg/cm², preferably 0. 05 to 5 kg/cm², and stencil printing is carried out within 0.001 to 10 seconds, preferably 0.005 to 5 seconds. When the printing pressure is relatively low and the printing time is relatively short, it becomes difficult for the liquid ink to pass through perforations formed in the stencil sheet, resulting in a relatively small amount of ink being transferred onto the printing paper. Therefore, a lower printing density and uneven printing may result. On the contrary, when the printing pressure is relatively high and the printing time is relatively long, a relatively large amount of ink passes through the stencil sheet, resulting in a relatively large amount of ink being transferred onto the printing paper. Therefore, bleeding or blurred printing may result, and seeping-through and offsetting are likely to occur. Accordingly, in the stencil printing device of the present invention, the printing time is increased when the printing pressure is relatively low, and the printing time is decreased when the printing pressure is relatively high, to thereby yield high quality printing.
The stencil printing device of the present invention is used for processing any of pressure-sensitive stencil sheets, heat-sensitive stencil sheets, or soluble stencil sheets. A pressure-sensitive stencil sheet is prepared by directly cutting desired letters or images in a blank stencil sheet through use of a stencil pen, a dot-matrix printer, or the like. A heat-sensitive stencil sheet is prepared by flash-exposing a stencil sheet superposed on a heat-absorbent original or by melting desired letters or images in a stencil sheet through use of a thermal head. A soluble stencil sheet is prepared by transferring a solvent from a solvent discharge device onto a stencil sheet in the form of desired letters or an image to thereby dissolve corresponding holes in the stencil sheet.
Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:

FIG. 1 shows a sectional view of a stencil printing device according to an embodiment of the present invention;
FIG. 2 shows a sectional view of a stencil printing device according to another embodiment of the present invention;
FIG. 3 shows a sectional view of a stencil printing device according to yet another embodiment of the present invention; and
FIG. 4 shows a sectional view of a stencil printing device according to a still another embodiment of the present invention.

A stencil printing device of the present invention will now be described with reference to the drawings. However, the present invention is not to be limited thereto.
FIG. 1 shows a sectional view of the structure of a stencil printing device according to an embodiment of the present invention.
In FIG. 1, the stencil printing device comprises a printing drum 1, a halogen lamp 4 and a reflector 11 provided within the printing drum 1, a metallic roller 6, and a rotating press roller 8. The printing drum 1 has an ink-permeable wall and is adapted to rotate. A porous membrance 2 and a stencil sheet 3, in that order, are wound around the printing drum 1. The metallic roller 6 is arranged within the printing drum 1 so as to slidably contact the inner surface of the printing drum 1. The press roller 8 presses the stencil sheet 3 through printing paper 9 and feeds forward the printing paper 9.
The printing drum 1 may be a metallic drum having ink-permeable holes and used in an ordinary stencil printing machine. The porous membrance 2, usually made of metallic fiber, synthetic fiber, metallic porous material, polymeric porous material, or the like, is wound around the printing drum 1, and further, the stencil sheet 3 is wound around the porous membrance 2.
The halogen lamp 4 and the reflector 11 shown in FIG. 1 form an example heating device for heating a solid ink fed into the printing drum 1 at a predetermined temperature. In the present invention, the heating device is not particularly limited so long as it can heat a squeegee device, which will be described later, provided within the printing drum 1 and a solid ink which undergoes a phase change. Preferably, the heating device preferentially heats the squeegee device with the aim of efficiently heating a solid ink and speeding up printing. For example, the heating device may be located in the vicinity of or in contact with the squeegee device, or the heating device may also serve as a squeegee device.
Potential heating devices other than the halogen lamp include nichrome wire heaters, sheet-like heating elements, ceramic heaters, conductive carbon heaters, electromagnetic induction heaters, infrared heaters, xenon lamps, and microwave heaters.
The metallic roller 6 shown in FIG. 1 is an example of a squeegee device arranged so as to slidably contact the inner surface of the printing drum 1. The metallic roller 6 is rotated synchronously with the printing drum 1 and in the same direction. The squeegee device has the function of transferring a liquid ink, i.e. a solid ink which has undergone a phase change due to exposure to heat from a heating device, onto the printing paper 9 through the stencil sheet 3. Accordingly, the squeegee device in the present invention must be sufficiently heated during stencil printing. Such a squeegee device usually comprises a rigid or elastic heat-resistant member such as a metallic roller, a plastic blade, a plastic belt, or the like.
In the above-described structure, a solid ink fed into the printing drum 1 is heated together with the metallic roller 6 by light beams 5 emitted from the halogen lamp 4, and thus becomes a liquid ink. The metallic roller 6 causes the resultant liquid ink 7 to be fed to the porous membrance 2 and the stencil sheet 3 through the printing drum 1. The printing paper 9 is fed forward while being pressed against the stencil sheet 3 by the press roller 8. The liquid ink 7 which has passed through the stencil sheet 3 is transferred onto the printing paper 9. The thus-transferred liquid ink 7 instantaneously changes to a solid ink 10 while the printing paper 9 is being fed forward.
FIG. 2 shows a sectional view of the structure of a stencil printing device according to another embodiment of the present invention.
The structure of FIG. 2 is different from that of FIG. 1 in that a halogen lamp 4 serving as a heating device is located within a metallic pipe 6a serving as a squeegee device to thereby heat the inner surface of the metallic pipe 6a by light beams 5 emitted from a halogen lamp 4. This structure has an advantage that the metallic pipe 6a is efficiently heated to change a solid ink fed into the printing drum 1 to a liquid ink 7.
FIG. 3 shows a sectional view of the structure of a stencil printing device according to yet another embodiment of the present invention.
The structure of FIG. 3 is different from that of FIG. 1 in the following respects: a squeegee device comprises two belt-driving rollers 14, a metallic roller 6, and a belt 12 looped around these rollers for travelling; a ceramic heater 11 is provided in contact with the belt 12; and a plastic sheet 13, not the printing paper 9, is used as a printing medium.
FIG. 4 shows the sectional structure of a stencil printing device according to still another embodiment of the present invention.
The structure of FIG. 4 is different from that of FIG. 3 in the following respects: a blade 17 made of an elastic plate or the like and serving as a squeegee device is stationarily located at a predetermined position such that its tip end abuts the inner surface of a printing drum 1; and a sheet-like heater 16 is attached onto the surface of the blade 17.

EXAMPLES

The present invention will now be described by way of example.

Example 1:

Through use of the stencil printing device of FIG. 1, stencil printing was conducted as described below.
Polyester fabrics of 200-mesh and 300-mesh serving as the porous membrance 2 were wound in layers around the printing drum 1 having a diameter of 10 cm and holes of 1 mm diameter. An unillustrated pressing mechanism and the metallic roller 6 having a diameter of 3 cm were mounted within the printing drum 1 such that the metallic roller 6 slidably contacted the inner surface of the printing drum 1.
The 500 W halogen lamp 4 was mounted such that the metallic roller 6 was preferentially irradiated by the light beams 5.
Next, the heat-sensitive stencil sheet 3, in which letters and images have been cut, was wound around the layered porous membrance 2 of the printing drum 1. Then, within the printing drum 1 was placed a solid ink, comprising 5 parts by weight of carbon black, 70 parts by weight of paraffin wax, and 25 parts by weight of ethylene-vinyl acetate copolymer. When the metallic roller 6 was heated to a temperature of 80°C by the halogen lamp 4, the solid ink changed to the liquid ink 7.
Then, the plate cylinder 1 was driven to rotate, and the printing paper 9 was passed between the rotating printing drum 1 and the press roller 8 while being pressed against the printing drum 1 by the press roller 8. The liquid ink 7 passed through perforations formed in the stencil sheet 3 and was transferred onto the printing paper 9. The liquid ink 7 transferred onto the printing paper 9 instantaneously changed to the solid ink 10 on the printing paper 9, thereby printing clear letters and images on the printing paper 9.
The printed paper was rubbed by hand immediately after printing, but the hand was not smeared with ink. Also, in the above-described state, 100 sheets of the printing paper 9 were continuously printed, but the piled printed sheets were free from offsetting.

Example 2:

Through use of the stencil printing device of FIG. 2, stencil printing was conducted as described below.
The porous membrance 2 similar to those of Example 1 were wound in layers around the printing drum 1, which was similar to that of Example 1. An unillustrated pressing mechanism and the metallic pipe 6a having a diameter of 4 cm were mounted within the printing drum 1 such that the metallic pipe 6a slidably contacted the inner surface of the printing drum 1. The 500 W halogen lamp 4 was mounted at the central portion of the interior of the metallic pipe 6a such that the inner surface of the metallic pipe 6a was preferentially irradiated by the light beams 5.
Next, in a manner similar to that of Example 1, the heat-sensitive stencil sheet 3 was wound around the layered porous members 2 of the printing drum 1, and stencil printing was carried out using a solid ink. As a result, clear offsetting-free printings were obtained.

Example 3:

Through use of the stencil printing device of FIG. 3, stencil printing was conducted as described below.
As the porous membrance 2, sponge having holes of a mean diameter of 30 µm and a thickness of 1 mm was wound around the printing drum 1 in a manner similar to that of Example 1. Next, a squeegee device, comprising an unillustrated pressing mechanism, the belt 12 made of polyimide film, the ceramic heater 15, the belt-driving roller 14, and the metallic roller 6, was mounted within the printing drum 1 such that the squeegee device slidably contacted the inner surface of the printing drum 1.
Next, in a manner similar to that of Example 1, the heat-sensitive stencil sheet 3 was wound around the printing drum 1 covered with the sponge, and then the metallic roller 6 was heated to a temperature of 75°C by the ceramic heater 15 to thereby change a solid ink to the liquid ink 7 by application of heat. By use of the liquid ink 7, stencil printing was conducted on the plastic sheet 13 in a manner similar to that of Example 1. The printed plastic sheet was rubbed by hand, but the hand was not smeared with ink. Also, in this state, 100 plastic sheets 13 were continuously printed, but the piled printed sheets were free from offsetting.

Example 4:

Through use of the stencil printing device of FIG. 4, stencil printing was conducted as described below.
The porous membrance 2 similar to that of Example 3 was wound around the printing drum 1 in a manner similar to that of Example 3. Next, a squeegee device, comprising an unillustrated pressing mechanism, the sheet-like heater 16, and the blade 17 made of polyurethane, was mounted within the printing drum 1 such that the tip end portion of the blade 17 slidably contacted the inner surface of the printing drum 1. Next, in a manner similar to that of Example 1, the heat-sensitive stencil sheet 3 was wound around the printing drum 1 covered with the porous membrance 2, and then the blade 17 was heated to a temperature of 75 °C by the sheet-like heater 16 to thereby change a solid ink to a liquid ink by application of heat. Stencil printing was conducted on the plastic sheets 13 in a manner similar to that of Example 3. As a result, clear offsetting-free printings were obtained.
As described above, when the stencil printing device of the present invention is used, a solid ink that changes its phase to have a liquid phase at a temperature between 30 and 150 °C can be effectively heated to transform into a liquid ink. As a result, there can be obtained excellent prints that are free from offsetting or seeping-through. Moreover, since the prints do not smear hands even when they are touched immediately after being printed, high performance printing can be attained. In addition, due to the fact that ink immediately changes from liquid to solid on printing paper, not only ordinary printing paper or post card paper with poor ink permeability but also plastic film and metal can be used for being printed.

Claims

A stencil printing device comprising
an ink-permeable plate cylinder which is adapted to rotate and around which a stencil sheet that has undergone plate-making is wound; and

ink feed means which is provided inside the plate cylinder and which is used for feeding ink onto the inner surface of the plate cylinder,

the ink feed means being adapted to transfer ink onto a printing medium from the plate cylinder through perforations formed in the stencil sheet for stencil-printing, wherein

the ink feed means comprises a squeegee device, arranged so as to slidably contact the inner surface of the plate cylinder and a heating device for heating a solid ink fed into the plate cylinder in order to obtain a liquid ink.
The stencil printing device according to Claim 1, wherein the heating device preferentially heats the squeegee device.
The stencil printing device according to Claim 1, wherein the heating device is provided in the squeegee device.
The stencil printing device according to Claim 1, wherein the solid ink changes to a liquid phase at a temperature of 30 to 150°C .