GB2033300A

GB2033300A - Stencil duplicator

Info

Publication number: GB2033300A
Application number: GB7934663A
Authority: GB
Original assignee: Riso Kagaku Corp
Current assignee: Riso Kagaku Corp
Priority date: 1978-10-18
Filing date: 1979-10-05
Publication date: 1980-05-21
Also published as: FR2439091A1; GB2033300B; JPS5555889A; FR2439091B1; DE2941863A1; DE2941863C2

Abstract

A single drum type stencil duplicator includes a porous cylindrical drum 1 rotatable and adapted to support a stencil sheet therearound, an ink supply roller 7 rotatable with cart of its outer peripheral surface kept in contact with part of the inner peripheral surface of the drum, and a means which supplies ink onto the outer peripheral surface of the roller in the form of a layer whose thickness is exactly controlled to a value which provides the desired thickness of the ink image to be formed on a copy sheet by contact with the stencil sheet wrapped around the drum. Roller 8 meters the ink film, and ink is supplied to body of ink 11 from pipe 10 under control of microswitch 15 actuated by lever 13 resting on the body of ink. <IMAGE>

Description

SPECIFICATION Stencil duplicator BACKGROUND OF THE INVENTION The present invention relates to a stencil duplicator, and, more particularly, to a single drum type stencil duplicator.

A single drum type stencil duplicator is known which has a porous cylindrical drum which is supported so as to rotate around its central axis and is adapted to support a stencil sheet wrapped around it and is supplied with ink onto its inner peripheral surface and produces duplicates out of the stencil as it is brought into rotary contact with sheets such as paper by the adhesion to the material of ink which has passed through the perforations of it and the stencil.Conventionally, a single drum type stencil duplicator of the abovementioned structure includes a backup roller which is supported so as to rotate around its central axis arranged in parallel to that of the drum with part of its outer peripheral surface being kept in contact with the part of the inner peripheral surface of the drum opposite to the part of the outer peripheral surface of the drum which contacts the copy sheet. In this case, ink is supplied so as to form a wedge-shaped deposit in the wedge-shaped space formed between the inner peripheral surface of the drum and the outer peripheral surface of the back-up roller where they are moving into contact with each other.Part of the porous cylindrical drum and of the perforated stencil sheet passing under the wedge-shaped deposit of ink are charged with ink by the squeezing action applied by the backup roller, the ink thus charged being transferred across the perforations in the drum and the stencil sheet so as to be finally attached onto the surface of the copy sheet which comes into contact with the outer surface of the cylindrical drum.

However, by this conventional single drum type stencil duplicator it is very difficult to obtain duplicates, particularly a large number of duplicates, having highly uniform and constant quality, because of poor controllability of the amount of ink actually supplied through the perforations of the cylindrical drum and the stencil sheet. Further, when a deposit of a substantial amount of ink is held at a standstill for a long time on the lamination of the porous wall of the cylindrical drum and the perforated stencil sheet when the duplicator is at rest, ink oozes through the porous cylindrical drum and through the perforated stencil by its own weight and causes serious ink blotting. Further, as water and oil vaporize from the ink deposit, solid substances remain and form hard dregs, which obstruct quick and smooth restarting of the duplication.This trouble also occurs with regard to the entire inner peripheral surface of the drum where a relatively thick ink layer is formed.

SUMMARY OF THE INVENTION It is therefore the object of the present invention to provide an improved single drum type stencil duplicator in which the porous cylindrical drum is constantly supplied with a necessary and sufficient amount of ink, but no more, at a necessary rate, only when the duplicator is performing duplication.

According to the present invention, the abovementioned object is accomplished by a stencil duplicator comprising a porous cylindrical drum which is supported so as to rotate around its central axis and is adapted to support a stencil sheet around it, an ink supply roller which is supported so as to rotate around its central axis arranged in parallel to the central axis of said drum with part of its outer peripheral surface being kept in contact with part of the inner peripheral surface of said drum, a means for supplying continuously an ink layer of a predetermined thickness onto the outer peripheral surface of said roller only when said roller rotates, and a means for exerting pressing force against the part of the outer peripheral surface of said drum which is opposite to the part of the inner peripheral surface of said drum at which said ink supply roller contacts said drum.

As a result of various experimental researches, we have found that, when ink is supplied onto the outer peripheral surface of the ink supply roller in such a manner that the thickness of the ink layer formed on the outer peripheral surface of the ink supply roller is properly controlled, the ink of the ink layer filling the perforations of the porous wall of the drum and the perforated stencil sheet is shifted definitely for a predetermined distance through the porous wall of the drum and the perforated stencil sheet when the ink supply roller, which carries the ink layer of a controlled thickness on its outer peripheral surface and which also serves as a backup roller, is pressed against part of the inner peripheral surface of the drum, whereby ink layers each having a predetermined thickness are transferred orh the surface of a copy sheet which is brought into contact with part of the outer peripheral surface of the stencil sheet mounted around the cylindrical drum, according to the pattern of perforation formed in the stencil sheet, thereby providing a duplicated copy which has high uniformity over its entire surface with regard to the thickness of the ink supplied thereon, regardless of the destiny of perforations on the stencil sheet, or, in other words, regardless of the kind of characters, figures, patterns, etc. of the duplicate to be made.

Further, as long as the thickness of the ink layer supplied onto the outer peripheral surface of the ink supply roller is controlled to such a necessary and sufficient amount for producing the desired thickness of duplication, no accumulation of ink is formed in the wedge-shaped space formed between the inner peripheral surface of the cylindrical drum and the outer peripheral surface of the ink supplying roller at the region where they approach to each other towards mutual contact.

Therefore, a large number of prints having the same quality are obtained, and even when the duplicator is kept at rest for a long time no oozing out of standiny ink from the perforated cylindrical drum occurs, and no substantial dregs are formed.

According to a particular feature of the present invention, a squeeze roller may be provided in close proximity to the ink supply roller so as to control the thickness of the ink layer supplied onto the outer peripheral surface of the ink supply roller.

BRIEF DESCRIPTION OF THE DRAWING The present invention will become more fully understood from the detailed description of a preferred embodiment given hereinbelow, and the accompanying drawing, which are given by way of illustration only, and thus are not limitative of the present invention. In the drawing, the sole figure is a diagrammatical illustration of an embodiment of the stencil duplicator according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, 1 generally designates a porous cylindrical drum, which, in this embodiment, has a laminated structure including a cylinder 2 made of a perforated sheet of metal such as stainless steel, a layer 3 of a foamed synthetic resin having continuous perforations provided around the cylinder 2, and a meshed layer 4 of a polyester synthetic resin provided around the layer 3. The cylindrical drum 1 is supported so as to rotate around its central axis C1 in the anticlockwise direction as viewed in the figure by an electric motor not shown in the figure.The cylindrical drum 1 also has a stencil sheet mounting device 6 at a part of its outer peripheral portion, to which is mounted the mounting margin of a perforated stencil sheet 5 which is mounted around the drum 1 and is held there by the adhesion of ink so as to rotate together as a unitary body with the drum 1.

At the inside of the cylindrical drum 1 is provided an ink supply roller 7, which has a diameter a little smaller than a half of that of the drum 1, and which is supported to rotate around its central axis C2 arranged in parallel to the axis C1 with part of its outer peripheral surface being kept in contact with part of the inner peripheral surface of the drum 1, and so as to be driven around its central axis C2 in the anticlockwise direction as viewed in the figure when the drum 1 is driven in the same direction, due to frictional engagement at their contacting parts.

In close proximity to an upper part of the ink supply roller 7 is provided a squeeze roller 8, which is supported so as to rotate around its central axis C3 arranged substantially in parallel to the axes C1 and C2, so as to define a clearance 9 through which ink is fed out as a layer of a predetermined thickness carried on the outer peripheral surface of the ink supply roller 7.

However, a non-rotatable squeeze element such as, for example, a rod element having a crosssectional form similar to the roller 8, may be provided instead of the squeeze roller 8, or the roller 8 may be arranged not to rotate.

An ink supply pipe 10 is provided so as to open towards the wedge-shaped space formed between the outer peripheral surfaces of the ink supply roller and the squeeze roller 8 at the region where those two surfaces approach towards each other when the ink supply roller 7 is driven in the anticlockwise direction as viewed in the figure and when the squeeze roller 8 is driven in the clockwise direction as viewed in the figure due to the traction force exerted by way of an ink layer formed between these two rollers, as explained hereinunder. The ink supplied from the ink supply pipe 10 forms an ink deposit 11 in the abovementioned wedge-shaped space.The ink supply pipe 10 is supplied with ink from an ink feed pump not shown in the figure, and supplies ink to the wedge-shaped space under such automatic control that when the size of the ink deposit 11 becomes smaller than a predetermined value, the pipe supplies ink towards the wedgeshaped space, and when the size of the ink deposit 11 becomes larger than a predermined value, the pipe 10 stops supplying ink, so that the size of the ink deposit is maintained within a predetermined range depending upon the hysteresis effect of the control system. The size of the ink deposit 11 is detected by a rod 13, which is pivotally supported by a pivot shaft 14, with one end of it being located so as to touch the ink deposit 11 when the size of the ink deposit is larger than a predetermined value.The other end of the rod 13 supports a weight 1 3a and is adapted to operate a microswitch 1 5 in accordance with pivoting action of the rod 13.

In more detail, when the drum 11 is driven around its central axis C1 in the anticlockwise direction as viewed and shown by an arrow in the figure, by an electric motor not shown in the figure, the ink supply roller 7 is rotated around its central axis C2 in the anticlockwise direction as viewed and shown by an arrow in the figure. In accordance with this, in the ink deposit 11, whose weight is principally supported by the ink supply roller 7, is generated a circulation of ink in the clockwise direction as viewed and shown by arrows in the figure. This circulation or churning is particularly effective for ensuring that a uniform supply of ink is provided along the axial direction of the ink supply roller 7. In fact, in this machine, supply of ink by the ink supply pipe 10 need only be made at one place along the axial length of the roller 7, because the circulation and churning quickly and effectively cause ink supplied at that place to be evenly distributed along the axis of the roller 7, so that the ink deposit 11 is substantially of uniform cross-section. Therefore, when the one end of the rod 13 touches the ink deposit 11 during operation of the duplicator, the end of the rod is driven downward in the figure, so that the rod 13, which was turned clockwise due to the weight 1 3a so as to turn the switch 1 5 on while the end of the rod 13 was not in touch with the ink deposit 11, is now pivoted around its pivot shaft 14 so as to turn the switch 1 5 off.The switch 1 5 controls a motor (not shown) for the abovementioned ink feed pump. Therefore, when the ink deposit 11 has grown so large as to contact the end of the rod 1 3, the ink supply pump is stopped. By contrast, when the size of the ink deposit has reduced so far that it comes out of contact with the end of the rod 13, the rod is pivoted clockwise in the figure around its pivot shaft 14 by the weight 1 3a, so as to turn the switch 1 5 on. In this case, since an inevitable mechanical delay exists between the instant of turning the switch 1 5 on or off and that of actually starting or stopping the supply of ink to the wedge-shaped space, a proper hysteresis is incorporated in the control of the size of the ink deposit 11.

In proximity to the outer peripheral surface of the ink supply roller 7, properly remote from the wedge-shaped space in which the ink deposit 11 is formed, toward the trailing side of it as viewed in the rotating direction of the roller 7, is provided a barrier 12, which serves to prevent the ink of the ink deposit 11 from reaching the inside surface of the drum 1 as a blob when the drum 1 is rotated in the reverse direction at the time of removing the stencil sheet from the drum. It is important that the barrier 12 should be located so as to leave a predetermined clearance between itself and the outer peripheral surface of the roller.

Further, in order to prevent the ink of the ink deposit 11 from flowing down along the outer peripheral surface of the roller 7 in the direction opposite to the rotating direction of the roller 7 is due to the weight of the ink when the duplicator is at rest, it is desirable that the wedge-shaped space in which the ink deposit 11 is formed should be located on the advancing side of the perpendicular plane which includes the central axis C2 of the roller 7, when the duplicator is positioned in its normal attitude (such as placed on a horizontal plane), i.e. that the ink deposit should be on the side of the squeeze roller 8 of the perpendicular plane. Therefore, it is desirable that the squeeze roller 8 is positioned slightly on the advancing side of the above defined perpendicular plane, as viewed in the rotating direction of the ink supply roller 7.

At the outside of the cylindrical drum 1 is provided a press roller 16, which is supported by a shaft 19 so as to rotate around its central axis C4 arranged in parallel to axes C1, C2, and C3, with part of its outer peripheral surface being pressed against the part of the outer peripheral surface of the drum 1 which is opposite to the part of the inner peripheral surface of the drum at which the ink supply roller 7 contacts the drum 1.The shaft 9 is supported by a pair of levers 18 (only one of these is shown in the figure) which in turn are supported by a pivot shaft 17, which is supported by the housing structure of the duplicator (not shown in the figure) The press roller 1 6 is resiliently pressed against the drum 1 by a pair of springs 20 (only one of these is shown in the figure), which exert spring force on the levers 18 so as to bias the shaft 19 upwards in the figure.

The shaft 19 also supports a cam follower 21, which engages with a cam 22 which is fixed to a side portion of the cylindrical drum 1 so as to corotate with the drum around the axis C1. By this arrangement, when the stencil mounting device 6 passes in front of the press roller 1 6, the press roller is shifted downward in the figure so as not to interfere with the stencil mounting device 6.

Copy sheets 23 on which a duplicated image is to be printed are stacked on a supply platform 24, and are taken one by one off the top of the stack by a feed roller 25 and fed to a sheet clamping and feeding device comprising a timing roller 26 and a guide roller 27, which feed each sheet to the printing path formed between the perforated stencil sheet 5 mounted around the drum 1 and the press roller 16, in relation to the rotation of the drum 1. Each printing sheet is supplied with a duplicated ink image on its surface while it passes along the printing path, and the printed sheets are finally collected on a collect Dlatform 28.

In operation, as the ink supply roller 7 rotates, ink of the ink deposit 11 rotates in the clockwise direction around axes which are parallel with the axis C2, and part of the ink is formed into an ink layer 29 supported on the outer peripheral surface of the ink supply roller 7. The thickness of the ink layer 29 is determined by the magnitude of the clearance 9 formed between the ink supply roller 7 and the squeeze roller 8.When the part of the outer peripheral surface of the ink supply roller 7 which carries the ink layer 29 is pressed against the part of the inner peripheral surface of the drum 1 , at places where the stencil sheet is perforated, shifting of ink through the perforated wall of the cylindrical drum and the perforated stencil sheet occurs, due to semi-hydraulic pressure generated by the compression of the ink layer 29 effected between the drum 1 and the roller 7. In this connection, the ink which is best for use in the duplicator of the present invention is an emulsion ink in which fine water particles are suspended in a continuous layer of oil, and which has higher viscosity than conventional ink for stencil duplication. It is desirable that the viscosity of ink should be so high that the "One-minute value" by a spread meter is less than 32. At places where the stencil sheet is not perforated, the ink of the ink layer 29 remains between the inner peripheral surface of the drum 1 and the outer peripheral surface of the roller 7, and this ink substantially all adheres onto the outer peripheral surface of the roller 7 when this outer peripheral surface, which has a smaller radius of curvature than the inner peripheral surface of the drum 1, separates from this less curved inner peripheral surface, due to the difference of surface tensions.

The magnitude of the clearance 9 formed between the ink supply roller 7 and the squeeze roller 8 must be adjusted in accordance with the kind of ink used, the kind of copy sheet used, atmospheric temperature, etc.. Generally, the magnitude of this clearance should be 0.01 -0.1 mm.

As mentioned before, although a squeeze roller 8 is empioyed in the shown embodiment, a rod, a blade or other non-rotatable squeeze element may be used instead of the squeeze roller. Further, the ink supply pipe 10 may be incorporated in such a non-rotatable squeeze element.

Although the invention has been shown and described with reference to a preferred embodiment thereof, it should be understood that various changes and omissions of the form and the detail of any particular embodiment may be made by a man skilled in the art, without departing from the scope of the invention.

Claims

1. A stencil duplicator comprising a porous cylindrical drum which is supported so as to rotate around its central axis apd is adapted to support a stencil sheet around it, an ink supply roller which is supported so as to rotate around its central axis arranged in parallel to the central axis of said drum with part of its outer peripheral surface being kept in contact with part of the inner peripheral surface of said drum, a means for supplying continuously an ink layer of a predetermined thickness onto the outer peripheral surface of said roller only when said roller rotates, and a means for exerting pressing force against the part of the outer peripheral surface of said drum which is opposite to the part of the inner peripheral surface of said drum at which said ink supply roller contacts said drum.

2. The stencil duplicator of claim 1, wherein said ink layer supplying means includes a squeeze element provided in close proximity to said ink supply roller so as to define a wedge-shaped space and a thin clearance between it and said ink supply roller.

3. The stencil duplicator of claim 2, wherein said squeeze element is a roller.

4. The stencil duplicator of claim 2 or claim 3, wherein the magnitude of said clearance is 0.01--0.1 mm.

5. The stencil duplicator of claim 2 or claim 3, said ink layer supplying means further including a pipe which supplies ink to a portion of said wedgeshaped space.

6. A stencil duplicator substantially as herein described with reference to and as shown in the accompanying drawings.