JPH11180020A - Printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate occurrence of a mark in connection with a decrease in a quality of a printed matter due to a gripper mark or the like by effectively releasing a printing sheet from a nip forming member of an impression cylinder or the like without attaching a wave pattern due to an air blowing to a print image and without generating a curling. SOLUTION: A plurality of pattern formed electrodes 9 are provided at an interval in a circumferential direction on a surface of an impression cylinder 6 as a nip forming member. When a voltage is applied to the electrodes 9, a printing sheet is attracted to the surface of the cylinder 6 by an electrostatic force. Only the electrodes 9 approached to a guide plate 10 are sequentially interrupted at a voltage supply at a delivery side of the cylinder 6. Thus, the electrostatic force is removed or weakened only at the delivery side to easily release a leading end of the sheet.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a printing device such as a stencil printing device.

[0002]

2. Description of the Related Art In a stencil printing machine, for example, ink is supplied to an inner peripheral surface of a plate cylinder from an ink supply means provided inside a porous plate cylinder, and a nip forming member such as a press roller or an impression cylinder is connected to the plate cylinder. The printing cylinder generates printing pressure by cooperating with the printing cylinder to transfer ink that has oozed from the perforated portion of the master wound around the outer surface of the plate cylinder through the opening portion of the plate cylinder to printing paper, and performs printing. The printing paper is separated from the outer peripheral surface and discharged. The separation of the printing paper on the discharge side is generally performed by a peeling claw provided near the discharge side of the plate cylinder.
There is no ink image at the leading edge of the printing paper, that is, there is a blank area where there is no close contact with the plate cylinder due to the adhesive force of the ink. The nail is made to enter, and the rest is continuously peeled off from the plate cylinder.

However, if there is a so-called solid image portion having a high pixel density at the center of the leading edge of the printing paper, the peeling claw does not smoothly enter, and the printing paper rotates while the printing paper adheres to the plate cylinder by the adhesive force of the ink. That is, a so-called curling occurs, and a discharge error is likely to occur. To deal with this problem,
Japanese Patent Application Publication No. 15509 proposes a paper discharge device that blows air from the distal end of a peeling claw to surely peel off the leading end of a printing sheet. Further, when an impression cylinder is used as the nip forming member, the leading end of the printing paper fed from the sheet feeding unit is sandwiched by the claw claws arranged on the outer peripheral surface of the impression cylinder and wound around the impression cylinder. After printing, air is blown from a peeling claw provided in the vicinity of the paper discharge side of the impression cylinder to peel off.

[0004]

By the way, the ink transferred to the printing paper peeled off from the plate cylinder is not yet sufficiently dried. However, in the conventional separation technique using the peeling claw, the ink is peeled off in such a state. Since air is locally blown from the nails, there are problems such as ripples on the image, resulting in deterioration in the quality of the printed matter, and peeling nail marks (rubbing marks, etc.) remaining on the printed matter. In addition, since the air is blown locally only at the center in the width direction of the printing paper, the leading end of the printing paper has no certainty, and the printing paper may still wind up.

[0005] On the other hand, in the case of using the fly claw, curling does not occur at the leading end of the image where the separation is performed while being sandwiched by the fly claw, but in the portion where the separation is performed with the fly claw opened. Some curling will occur. This difference in the peeling state (strictly, the difference in the peeling angle) changes the image density of the solid portion, which leads to the deterioration of the quality of the printed matter. In addition, in the case of the squeeze nail method, there is a regulation that a predetermined margin is required at the leading end of the printing paper as a squeeze nail margin, and there is also a problem that squeeze nail marks remain on the printed matter to deteriorate the quality of the printed matter.

[0006]

Means for Solving the Problems If the printing paper is brought into close contact with the nip forming member with a force larger than the adhesive force of the ink without mechanical clamping, and if this adhesive force can be freely manipulated, air blowing is required. Thus, uniform peeling can be reliably performed over the entire area of the printing paper, and the above-described problems such as ripples and crepe nail marks can be eliminated. This is the purpose of the present invention. Specifically, the invention according to claim 1 includes a rotatable plate cylinder, and a rotatable nip forming member that generates printing pressure in cooperation with the plate cylinder to transfer ink to printing paper. A printing apparatus comprising: a printing paper suction means for attracting a printing paper to the nip forming member with electrostatic force; and an electrostatic force attenuating means for removing or weakening the electrostatic force on the paper discharge side of the nip forming member. Has been adopted.

According to a second aspect of the present invention, in the configuration of the first aspect, the printing paper suction means includes an electrode provided on the nip forming member, and means for applying a voltage to the electrode. It has a configuration.

According to a third aspect of the present invention, in the configuration of the first aspect, the printing paper suction means includes a pressing member comprising an electrode for pressing the printing paper to the nip forming member, and a voltage applied to the pressing member. Means for performing
The configuration is adopted.

According to a fourth aspect of the present invention, in the configuration of the second aspect, the electrode is patterned and provided on the surface of the nip forming member.

According to a fifth aspect of the present invention, in the constitution of the fourth aspect, a conductive material is vapor-deposited on one surface, and an insulating film having an electrode pattern formed on the vapor-deposited surface is wound around the surface of the nip forming member. The configuration is adopted.

According to a sixth aspect of the present invention, in the configuration of the second aspect, the electrode is made of conductive rubber in which a conductive material is dispersed in an insulating rubber material, and is integrally formed with an insulating sheet. The configuration is adopted.

According to a seventh aspect of the present invention, in the configuration of the second aspect, electrodes extending in the axial direction of the nip forming member are provided on the surface of the nip forming member at intervals in the circumferential direction of the nip forming member. A plurality of means for applying the voltage are configured to sequentially contact each electrode as the nip forming member rotates.

According to an eighth aspect of the present invention, in the configuration according to the seventh aspect, the electrostatic force attenuating means contacts a discharge-side electrode remote from the voltage applying means to invert the polarity of the electrode. And a voltage applying means.

According to a ninth aspect of the present invention, in the configuration of the eighth aspect, the means for applying the voltage and the electrostatic force attenuating means share one power supply.

According to a tenth aspect of the present invention, in the configuration of the seventh aspect, an electrode detecting means for detecting the electrode,
Means for determining the arrival time of an electrode to which a voltage is to be applied based on the detection information of the electrode detection means, and applying the voltage so that the voltage is applied to the electrode only when the electrode to which the voltage is to be applied arrives Is provided.

According to an eleventh aspect of the present invention, in the configuration of the tenth aspect, the control means controls the means for applying the voltage so that the polarity of the applied voltage is inverted each time an electrode arrives. Has been adopted.

According to a twelfth aspect of the present invention, in the configuration of the tenth or eleventh aspect, the electrostatic force attenuating means is configured to apply a polarity reversal voltage application contacting an electrode on the paper discharge side remote from the voltage application means. Means, wherein the control means comprises:
The polarity inversion voltage applying means is controlled so as to apply a voltage having a polarity opposite to the polarity of the voltage applied by the voltage applying means.

According to the thirteenth aspect, in the second aspect,
In the configuration described in 4, 6, 7, 8, 9, 10, 11 or 12, the configuration is adopted in which the upper surface of the electrode is covered with a protective layer.

According to a fourteenth aspect of the present invention, in the configuration of the third aspect, the pressing member is a roller having a small diameter, and the pressing member has a structural strength by a backup roller having a larger diameter and rotating at the same linear speed. Is protected.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. As shown in FIG. 1, the stencil printing apparatus according to the present embodiment generally includes a paper feeding unit 1, a printing unit 2, and a paper discharging unit 3. The paper supply unit 1 includes a paper supply tray (not shown), a paper supply roller, a separation roller, a guide plate 4, a pair of registration rollers 5a,
5b, a pressing member 7 which can be freely moved toward and away from an impression cylinder 6 which will be described later.
It is mainly composed of Printing paper is fed from a paper feeding tray (not shown) to the registration roller pairs 5a and 5b by paper feeding rollers and separation rollers (not shown), and the printing paper fed at a predetermined timing by the registration roller pairs 5a and 5b is pressed. It is pressed against the impression cylinder 6 by the member 7.

The printing unit 2 includes a rotatable cylindrical plate cylinder 8 having an ink supply unit 14 therein, and a pressurizing portion (nip portion) of a printing paper pressed between the plate cylinder 8 and the plate cylinder 8. ) To form an impression cylinder 6 as a nip forming member. Printing pressure is generated by the pressure contact of the impression cylinder 6 (cooperation with the plate cylinder 8), and ink from the plate cylinder 8 can be transferred to printing paper. The plate cylinder 8 includes a support shaft 11 which also serves as an ink supply pipe.
, And has a clamper 12 on its outer peripheral surface for holding a plate-making master (not shown). The clamper 12 is provided on the outer peripheral surface of the plate cylinder 8 by a shaft 13 so as to be openable and closable, and is opened and closed by opening and closing means (not shown). Further, a mesh-shaped opening (not shown) is formed on the outer peripheral surface of the plate cylinder 8, and the ink supplied by the ink supply means 14 oozes out of the opening and passes through the opening of the master (not shown). And transfer to printing paper.

The ink supply means 14 includes an ink roller 15
And a doctor roller 16. The ink roller 15 is rotatably supported by a side plate (not shown) in the plate cylinder 8 via a support shaft 17 such that the outer peripheral surface of the ink roller 15 keeps a slight gap from the inner peripheral surface of the plate cylinder 8. When the driving force is transmitted from a printing drum driving means for driving the printing drum 8 by a driving force transmission means (not shown) such as a gear or a belt, the printing drum 8 is driven to rotate in the same direction in synchronization with the printing drum 8. Doctor roller 16
Is rotatably supported by a side plate (not shown) in the plate cylinder 8 so that a slight gap is formed between the outer peripheral surface and the outer peripheral surface of the ink roller 15. As a result, the ink roller 15 is driven to rotate in the opposite direction.

When ink is supplied between the ink roller 15 and the doctor roller 16 through an ink pipe 18 attached to the support shaft 11, a wedge-shaped ink reservoir 19 is formed. This ink is applied to the doctor roller 16
The ink is supplied onto the outer peripheral surface of the ink roller 15 while the layer thickness is regulated to be constant.

The paper discharge section 3 mainly comprises a guide plate 10 disposed on the paper discharge side of the impression cylinder 6 and a transport belt 20 for discharging print paper to a paper discharge tray (not shown). . The guide plate 10 guides the printing paper to the transport belt 20, and has a function of injecting air from the leading end. The transport belt 20 mainly includes a driving roller 20a, a driven roller 20b, an endless belt 20c, and a suction fan 20d. The printing paper is conveyed in the direction of the arrow while being attracted onto the endless belt 20c by the suction force of the suction fan 20d, and is discharged to a discharge tray (not shown).

As shown in FIG. 2 and FIG. 3 (development), a comb-shaped electrode 9 called an interdigital type is axially opposed to the surface of the impression cylinder 6 as a nip forming member. It is arranged so as to engage with each other (claim 4). A plurality of combination blocks of the electrodes 9 are arranged at intervals in the circumferential direction of the impression cylinder 6. Note that FIG.
Are hatched for easy understanding of the shape of the electrode 9. The electrode 9 is composed of a wide power supply portion 9a corresponding to the main body of the comb and each electrode strip 9b corresponding to a tooth. As shown in FIG. It is bent and pasted. In the vicinity of both ends of the impression cylinder 6, an electrode plate 32 connected to an AC power source 30 and an electrode plate 32
And a conductive brush 34 (or a sliding electrode plate made of phosphor bronze) fixedly connected to the power supply portion 9a.
Is brought into contact with the electrode plate 32 as the impression cylinder 6 rotates, and a voltage is applied to each electrode 9 independently. Means for applying a voltage by the AC power supply 30 and the ground and an electrode plate 32 connected to the AC power supply 30, a conductive brush 34, and the like are configured,
Printing paper suction means for electrostatically attracting the printing paper to the impression cylinder 6 is constituted by the means for applying this voltage and the electrode 9 (claims 1 and 2). Further, the electrode plate 32 serves as an electrostatic force attenuating means for removing or weakening the electrostatic force on the discharge side of the impression cylinder 6. FIG. 4 schematically shows a voltage application configuration. In the figure, the thickness of the electrode 9 is exaggerated. The electrode plate 32 is set to have a length from the sheet feeding portion to the vicinity of the guide plate 10 on the sheet discharge side, whereby the voltage is sequentially applied from the block of the electrode 9 approaching the guide plate 10 as the impression cylinder 6 rotates. Supply has been cut off.

As shown in FIG. 3, each electrode strip 9b
Is 2 mm, and the distance between the centers of the electrode strips 9 b is 8 m.
m, the gap (insulation interval) between the electrode strips 9b in the engaged state is set to 2 mm. The electrode 9 is
A copper thin film of 50 μm or less is stuck on a cylindrical insulator 35 described later, and is patterned by etching. Each corner of the electrode 9 is etched so that the roundness R is not smaller than 0.3 mm in order to prevent discharge from the edge. By fixing the cylindrical insulator on which the electrode 9 is formed to the surface of the impression cylinder 6, the electrode 9 is formed on the surface of the impression cylinder 6. The electrode 9 may be formed directly on the surface insulating layer of the impression cylinder 6. More specifically, as shown in FIG. 5, the upper surface of the electrode 9 is covered with an insulating layer 27 as a protective layer in order to prevent the electrode 9 from being worn or dropped due to contact with printing paper or the like. (Claim 13). The insulating layer 27 in this embodiment is formed of a polyethylene terephthalate (PET) film that is higher than the upper surface of the electrode 9 by 10 μm to 20 μm.
In FIG. 5, reference numeral 35 denotes a cylindrical insulator as a base insulating layer, and its thickness t ₁ is about 1 mm. Insulating layer 27
Other examples include chlorosulfonated polyethylene (C
SM), polyethylene, rigid polyvinyl chloride (RPV)
C), soft polyvinyl chloride (PVC), polytetrafluoroethylene (PTFE), ethylene tetrafluoride hexafluoropropylene copolymer (FEP), polypropylene, polyester, polycarbonate, insulating paint and the like are preferable.

Next, the printing operation of the stencil printing apparatus based on the above configuration will be described. In FIG. 1, a paper feed roller (not shown) rotates, and the uppermost sheet of printing paper stacked on a paper feed tray (not shown) is fed toward the pair of registration rollers 5a and 5b by the paper feed roller and the separation roller. . The printing paper is further fed between the impression cylinder 6 and the pressing member 7 at a predetermined timing synchronized with the plate cylinder 8 by the pair of registration rollers 5a and 5b. At this time, the pressing member 7 which was not in contact with the impression cylinder 6 contacts the impression cylinder 6 immediately before the printing paper is sent between the impression cylinder 6 and the pressing member 7, and is conveyed after the contact. The printing paper is pressed against the impression cylinder 6. Then, an AC voltage is applied to the electrode 9 provided on the surface of the impression cylinder 6. When the voltage is applied, as shown in FIG. 5, an uneven electric field is formed in the vicinity of the electrode 9, and the printing paper 36 is attracted to the surface of the impression cylinder 6 by electrostatic force.

The application conditions at this time may be set to optimal values obtained by experiments and the like. FIG. 6 shows the relationship between the AC frequency at each applied voltage and the attraction force obtained by the experiment. The experimental conditions are as follows. Environment: room temperature Experimental electrode: Pattern pitch formed in a flat plate shape (distance between centers of electrode strips 9b in meshed state) 4
mm interdigital electrodes facing each other Measured value: A4 size, which is a general copy paper, is sucked on the electrode, and the tensile force when pulled horizontally with a force gauge is measured as the suction force

The required electrostatic force, in other words, an electrostatic force that is greater than the adhesive force of the ink and does not cause curling, is about 0.5 kgf or more from experience.
Therefore, under the experimental conditions of this time, the range below the broken line shown in FIG. 6 can be regarded as insufficient adsorption force, and the range beyond the broken line, that is, the applied voltage is about 2 kv or more, and the responsiveness and the plate thickness are changed as AC frequency. 1 considering the rotational speed of the torso 8
It can be said that the range of about to 100 Hz is preferable. The thickness t of the cylindrical insulator 35 depends on the voltage and the material to be used, but if an alternating current having an amplitude of about 2 kv, a general insulating material of 1 mm is sufficient. The safety thickness of the cylindrical insulator 35 can be designed by various handbooks or experiments. For example, although silicon rubber has an excessive thickness, a thickness of 1 mm sufficiently maintains insulation.

The printing paper 36 adsorbed on the surface of the impression cylinder 6 by electrostatic force is pressed by the nip between the impression cylinder 6 and the plate cylinder 8,
The print image is transferred to the upper surface (front surface). As shown in FIG. 7, each electrode 9 on the surface of the impression cylinder 6 is cut off the voltage at a position close to the guide plate 10 after passing through the nip portion for each block, and the adsorption action by the electrostatic force disappears. Or weakened. The leading end of the printing paper 36 released from the electrostatic force is
The air is easily separated from the impression cylinder 6 by air ejected from the guide plate 10 toward the lower surface thereof at a predetermined timing, and is sent to the transport belt 20 via the guide plate 10. Since the air jet by the guide plate 10 is performed toward the lower surface where there is no print image, there is no ripple in the print image unlike the related art. Also, as is clear from FIG.
The printing paper 36 is released from the electrostatic force by the guide plate 10.
, And the paper portion immediately after the nip portion is attracted to the impression cylinder 6, so that no curling occurs even in an image having many solid portions. Further, since the printing paper 36 is not mechanically held, there is no possibility of the conventional claw marks or the like remaining on the printing paper 36 after the discharge.

The printing paper 36 peeled off from the impression cylinder 6 by the guide plate 10 and coming on the conveyor belt 20 is conveyed in the direction of the arrow in FIG. 1 while being sucked onto the endless belt 20c by the suction force of the suction fan 20d. Thereafter, the sheet is discharged to a discharge tray (not shown).

FIG. 8 shows another example of electrode formation on the surface of the impression cylinder. 1 m wide by etching on the evaporation surface of the aluminum evaporation mylar film 40 having a thickness of about 12 μm.
The m electrode strips 9d are formed in an interdigital pattern at an insulation interval of 1 mm, and are adhered to the surface of the impression cylinder 6 with the evaporation surface facing down (claim 5). At both ends of the insulating surface layer portion 38 of the impression cylinder 6, a power supply portion 9c is disposed in a state of being bent at a substantially right angle so as to exist over the end surface and the outer peripheral surface. When pasted, the electrode strip 9d is electrically connected to the power supply 9c. In this embodiment, since the mylar film itself functions as the insulating layer 27 in the above embodiment, there is an advantage in manufacturing that a protective layer can be simultaneously formed. Note that the configuration for applying the voltage is the same as that in the above-described embodiment, and will not be described. Further, in the above-described embodiment, an AC power supply is used as a voltage supply source. However, even if a DC power supply is used, a similar attraction force by electrostatic force can be obtained.

FIGS. 9 to 11 show another embodiment. As shown in FIG. 9, a plurality of stripe-shaped electrodes 44 extending in the axial direction are provided on the surface of the impression cylinder 42 at insulating intervals in the circumferential direction. On the paper discharge side of the impression cylinder 42, a grounded neutralizing brush 45 as an electrostatic force attenuating means is provided. When the neutralizing brush 45 comes into contact with the end surface of the electrode 44, the charge of the electrode 44 is removed. Power is removed or weakened. Impression cylinder 42
As shown in FIG. 10, a grounded conductor layer 46, an intermediate insulating layer 47 made of silicon rubber, and an electrode sheet 48
It is composed of The electrode sheet 48 is formed by dispersing a conductive material such as carbon in an insulating rubber material such as silicon rubber to form a conductive rubber material, and using this as an electrode, and integrally forming the same with the insulating sheet using a mold. (Claim 6). The width of the electrode 44 is 3 mm, and the insulation interval between the electrodes 44 is 2 mm. The thickness t ₃ of the thickness t ₂ and the intermediate insulating layer 47 of electrode sheet 48 are both 3 mm. Due to the flow of the rubber material and the molding, the thickness t _{4 of the} electrode 44 is set to 0.
5 mm or more. The impression cylinder 42 is finally completed by fitting a molded cylindrical electrode sheet 48 on the intermediate insulating layer 47 and fixing it by means such as adhesion. In this embodiment, no protective layer is provided on the electrode 44, but the electrode 4
The safety can be ensured by adjusting the resistance of the conductive rubber 4 (conductive rubber). Needless to say, a protective layer may be provided by painting, heat shrinking tube, attaching a film, or the like. In this case, troubles such as falling off of the electrode 44 can be reduced. If the distance between the electrode 44 and the conductor layer 46 is determined in consideration of the dielectric strength of the material to be used or experimentally confirmed, it is determined that
Safety and performance can be ensured.

Roller electrode 50 extending in the axial direction of impression cylinder 42
And a means for applying a voltage by the AC power supply 30 and the like, and a printing paper suction means by this and the electrodes 44. The outer diameter of the roller electrode 50 in this embodiment is 2 mm. With the rotation of the impression cylinder 42, the roller electrode 5
Electric charges are accumulated in each of the electrodes 44 in contact with 0. As a result, an uneven electric field is formed on the surface of the impression cylinder 42, and an attraction force is generated by electrostatic force (claim 7). On the paper discharge side, the exposed end face of the electrode 44 contacts the neutralizing brush 45,
The charge is neutralized. As a result, the attraction force is weakened, and the adhesive force is easily separated from the impression cylinder 42 by the guide plate 10 as in the first embodiment. FIG. 11 shows the positional relationship between the electrode 44, the guide plate 4, and the like. Here, the paper holding member 7
Is a high resistance member, the guide plate 4 is an insulator, and the guide plate 10 is a grounded semi-conductor. The electrode 44 may be formed of a copper thin film as in the first embodiment.

FIGS. 12 and 13 show a modified example of how to remove or weaken the electrostatic force on the paper discharge side. The structure of the impression cylinder 52 in this embodiment is substantially the same as that shown in FIGS. 9 to 11, but as shown in FIG. 13, a portion excluding both ends is further covered with a surface insulating layer 54. Are different. The uncoated end portion of the electrode 44 serves as a power supply unit. Further, in this embodiment, the static elimination brush 45 is not used.

As shown in FIG. 12, a charging electrode 56 connected to the AC power supply 30 is provided so as to be able to come into contact with the electrode 44 in an area before the paper feeding place, and the same AC power supply 30 is provided on the discharge side. Is provided so as to be able to contact the electrode 44. Means for applying a voltage is constituted by the AC power supply 30 and the charging electrode 56 and the like connected thereto, and the means for applying the voltage and the electrode 44 constitute a printing paper suction means. The AC power supply 30
And a voltage applying means comprising the static elimination electrode 58 connected thereto serves as an electrostatic force attenuating means. (Claims 8 and 9). The contact with the charging electrode 56 causes the electrode 44 to be regularly in a positive / negative or charged / uncharged state, thereby generating an attraction force by electrostatic force. The printing paper is transferred to the impression cylinder 5 until the area where the suction force is applied by the pressing member 7 shown in the first embodiment.
2 and the printing paper is attracted to the electrode 44 by electrostatic force when it enters the area. After the printing is completed, a bias having a polarity opposite to that of the charging is applied to the discharge side by the discharging electrode 58, and a charge having the same polarity as the charge generated by polarization or injection is applied to the surface of the printing paper. That is, polarity inversion (removal of electrostatic force) is performed. The corresponding portion of the printing paper is separated from the surface of the impression cylinder 52 by the repulsive electrostatic force. The means for applying voltage and the power supply for the electrostatic force attenuating means may be separate. However, if the number of electrodes 44 between both means is an even number, the above-described separation function can be realized by one AC power supply 30 and the configuration is simplified. This is advantageous in terms of cost and cost.

It is desirable that the absolute value of the voltage supplied to the charge eliminating electrode 58 be equal to or less than the value to the charged electrode 56 at the maximum. This is because, when a large voltage is supplied, the polarity of the charge on the printing paper side is also inverted, and the suction force is restored. For this reason,
It is preferable that the voltage supplied to the charging electrode 56 be divided by a resistor or the like to supply the voltage to the discharging electrode 58. There is a time lag between the change in the polarity of the electrode and the change in the polarity on the printing paper side. Even after the polarity of the electrode is reversed, the charge of the polarity before the reversal is accumulated on the printing paper side for a while. The effect of promoting the separation by the polarity reversal utilizes this phenomenon.

It is possible to generate an attraction force by alternately applying a predetermined potential and a zero potential to the electrode 44 by the charging electrode 56, but in this case, a charge of the opposite polarity is given by the charge removing electrode 58. This is not because the printing paper is charged up to one polarity and a weak but steady suction force is generated as an offset, so this is not an optimal method.

The electrostatic attraction effect occurs when the printing paper enters a range where the electric force lines from the electrodes 44 reach, and this range is almost the same distance as the interval between the electrodes 44. If the surface insulating layer 54 has a thickness of 50% or more of the electrode pitch, the attraction force is remarkably impaired. Therefore, the thinner the protective layer, the better.

Next, another embodiment will be described with reference to FIG. The configuration is almost the same as that shown in FIGS. The difference is that the static elimination electrode 58 is connected to the AC power supply 31 separate from the AC power supply 30, and the AC power supply 30 and the AC power supply 31 are controlled by the control unit 55. Further, in this embodiment, an electrode detecting means 57 for detecting each electrode 44 is provided, and the electrode detecting means 57 outputs the detection information to the control means 55.

The electrode detecting means 57 in this embodiment has a structure for detecting the electrode 44 by utilizing the optical density difference between the electrode 44 and the non-electrode portion. If the electrode 44 is made of a ferromagnetic material, it may be magnetized to detect the difference in magnetic permeability. Further, an optical encoder, a magnetic encoder, or the like may be used. When the electrode detecting means 57 detects the electrode 44 at a certain position, the control means 55 determines, based on the detected information, the electrodes 44 to which a voltage should be applied to some of the electrodes 44.
The arrival time of. This determination is made, for example, by the control unit 5
The calculation is performed based on the electrode interval and the peripheral speed of the impression cylinder 52 which are input in advance to the counter 5. When the electrode 44 to which the voltage is to be applied arrives, the control means 55 operates the means for applying the voltage, and applies the voltage to the electrode 44. This control means 5
By continuously determining the arrival time according to 5, the voltage is applied to all the electrodes 44. The control means 55 inverts the polarity of the voltage from the AC power supply 30 for each electrode 44. In the method of applying a voltage to the electrode 44 detected by the electrode detecting means 57, the rotation speed of the impression cylinder 52 must be slow.
In the method of judging the arrival time, the time from detection to application can be ensured, so that even when the impression cylinder 52 is rotating at high speed, it is possible to reliably apply only to the electrode 44.

In the embodiments shown in FIGS. 9 to 13, since the application of the voltage is continuously performed, the material around the electrodes is charged up, and an electric field different from the one intended at the beginning of the design is formed. There is a concern that the suction power is insufficient. In the present embodiment, since the voltage is applied only when the electrode 44 arrives,
The above concerns can be resolved. The control means 55
Is an electrode 44 that is separated from the charging electrode 56 by a predetermined distance toward the paper discharge side.
Is determined based on the electrode detection information, the AC power supply 31 is operated, and a voltage of the opposite polarity is applied by the charge removing electrode 58. The charging paper 56
A charge having a polarity opposite to the polarity of the applied voltage is induced, and does not disappear immediately even when the voltage of the electrode 44 becomes zero. Therefore, when a voltage of the opposite polarity is applied to the electrode 44, a repulsive force is generated between charges of the same polarity, and the attracting force instantaneously becomes the repulsive force. Therefore, the printing paper that has been strongly absorbed is more likely to be separated. AC power supply 3
1 and the static elimination electrode 58, but may be the static elimination brush 45 shown in FIG. Further, the charging electrode 56
When alternately applying voltages of opposite polarities, the number of electrodes 44 between the charging electrode 56 and the discharging electrode 58 may be an even number, and one AC power supply may be shared.

The position of the electrode 44 and the position of the electrode 44 are determined by the position of the electrode detecting means 57 and the distance between the electrodes, the marker of the specific electrode 44 or the code (electrode identification code) of each electrode 44. I understand. Based on this information, if some trouble (breakage or deterioration) occurs in some of the electrodes 44 and a load is applied to the power supply by applying a voltage, the voltage application to the electrodes 44 is stopped. It is also possible to perform such control. Electrode 4
Since the position of 4 is known, if there is a failure, the number and distribution of the failure can be known. At least, the same information can be obtained by determining the suction electrode 44 serving as a reference, counting the number of obstacles in one round of the impression cylinder 52, and measuring the number of counts and the frequency of count-up. These pieces of information are used as a guide when replacing parts. Whether or not the electrode 44 has a failure can be identified by monitoring the amount of current flowing from the power supply. If it is sufficient to detect only the defective electrode 44, in the self-diagnosis routine after turning on the apparatus, the current is measured while rotating the impression cylinder 52, and the electrode 44 in which the abnormal current flows is determined to be defective. Then, a method can be adopted in which marking is performed on the electrode 44 by magnetic or optical means, and this is detected during operation.

In consideration of the adhesion of paper powder and the occurrence of noise due to charge leakage, it is desirable to remove the charge remaining on the electrode 44 at the end of printing. It is sufficient to rotate the impression cylinder 52 one or more rounds while the AC power supply 30 is grounded. However, in order to complete this operation in a short time, it is necessary to detect that the rotation has completed one round. From such a viewpoint, the electrode position detection by the electrode detection means 57 is useful.

FIGS. 15 and 16 show other embodiments. In each of the above embodiments, the electrodes are provided on the impression cylinder, whereas the pressing members are electrodes. The stencil printing apparatus according to the present embodiment mainly includes a paper feeding unit 21, a printing unit 22, and a paper discharging unit 23. The overall configuration is substantially the same as that of the first embodiment. The same reference numerals are used. A description of the configuration and function of the same part is omitted, and only different parts will be described below.

An AC power source 30 as a means for applying a voltage is connected to the pressing member 24 composed of an electrode which can be freely moved toward and away from the impression cylinder 25 as a nip forming member. These form a printing paper suction means (claim 3). Paper holding member 2
It is preferable to use a medium resistance material (electrical resistivity of 10 ⁶ to 10 ¹⁰ Ω · cm) as a material property of a portion in contact with the printing paper of No. 4. The outer surface of the impression cylinder 25 is formed of a conductive member or a conductive member whose surface layer is covered with a medium resistance layer. Note that no electrode is formed on the impression cylinder 25. On the discharge side of the impression cylinder 25, a grounded static elimination needle 26 as an electrostatic force attenuating means is provided so as not to contact the printing paper.

Next, the printing operation of the stencil printing machine according to the present embodiment will be described. In FIG. 15, a paper feed roller (not shown) rotates, and the uppermost sheet of printing paper stacked on a paper feed tray (not shown) is sent to the pair of registration rollers 5a and 5b by the paper feed roller and the separation roller. Further, the printing paper is fed between the impression cylinder 25 and the pressing member 24 at a predetermined timing synchronized with the rotation of the plate cylinder 8 by the pair of registration rollers 5a and 5b. At this time, the pressing member 24 that has been in a position that is not in contact with the impression cylinder 25 contacts the impression cylinder 25 immediately before the printing paper is sent between the impression cylinder 25 and the sheet pressing member 24, and is conveyed after the contact. The incoming printing paper is pressed against the impression cylinder 25.

Then, an AC voltage is applied to the pressing member 24, and electric charges are injected into the printing paper 36 as shown in FIG. As a result, an electrostatic attraction force is generated between the charged printing paper 36 and the induced charge on the surface of the impression cylinder 25 opposed thereto, and the printing paper 36 is attracted to the surface of the impression cylinder 25. The printing paper 36 adsorbed on the surface of the impression cylinder 25 is
The print image is transferred to the surface (upper surface) of the plate cylinder 8 by pressing the nip between the plate 5 and the plate cylinder 8. After passing the nip position,
The printing paper 36 is placed near the guide plate 10 at the position where the static elimination needle 2 is positioned.
6 removes the charge. This static elimination removes or weakens the electrostatic force between the impression cylinder 25 and the printing paper 36.

The leading end of the printing paper 36 released from the electrostatic force is easily separated from the impression cylinder 25 by air jetted from the guide plate 10 toward the lower surface at a predetermined timing, and passes through the guide plate 10. To the transport belt 20. Since the air jet by the guide plate 10 is performed toward the lower surface where there is no print image, there is no ripple in the print image unlike the related art. Further, the printing paper 36 is released from the electrostatic force only in the portion adjacent to the guide plate 10, and the paper portion immediately after the nip portion is attracted to the impression cylinder 25. Does not occur. Further, since the printing paper 36 is not mechanically held, there is no possibility of the conventional claw marks or the like remaining on the printing paper 36 after the discharge.

The printing paper 36 peeled off from the impression cylinder 25 by the guide plate 10 and coming on the conveyor belt 20 is conveyed in the direction of the arrow in FIG. 15 while being sucked onto the endless belt 20c by the suction force of the suction fan 20d. Thereafter, the sheet is discharged to a discharge tray (not shown).

The diameter of the holding member 24 as an electrode is safe considering that the size of the electrode pitch in the above-described embodiment is about the same as the electrode pitch. However, when the diameter is reduced in this manner, a problem in mechanical strength appears. Therefore, as shown in FIG. 17, a configuration may be adopted in which a backup roller 60 having a diameter larger than that of the pressing member 24 is provided to protect the pressing member 24 (claim 14). The diameter of the backup roller 60 is about 10 mm, and the backup roller 60 is rotated at the same linear velocity as the pressing member 24. Also, the backup roller 60
Is made conductive and has the same potential as the holding member 24. As shown in FIG. 18, the holding member 24 and the backup roller 60 are rotatably held by the same frame 62, and the backup roller 60 is driven by attaching a gear 66 to a rotation shaft 64 of the backup roller 60. I have.

In each of the above embodiments, voltage supply is used. Therefore, if the power supply is short-circuited due to any accident, there is a risk that a large current flows in the worst case. In order to avoid this, a limiting resistor may be provided in series with the power supply, or a current detection / limiting circuit may be provided. If an AC power supply with a current detection circuit is used in the constant current amplitude mode with the upper limit of the voltage amplitude set, the occurrence of accidents can be avoided. Can be kept small.

[0053]

As described above, according to the present invention,
The printing paper is attracted to the nip forming member by electrostatic force, and the electrostatic force is removed or weakened on the paper discharge side to be peeled off, so that the printed image does not have ripples and the electrostatic force is removed or weakened. Can be partially ensured, so that no curling occurs even in an image having many solid portions. Further, since the printing paper is not mechanically pinched, the conventional printing paper after discharge does not have a squeeze mark or the like. Therefore, it contributes to an improvement in the efficiency of the printing operation and an improvement in the quality of the printed matter (the above is a basic effect).

In particular, according to the fifth aspect of the present invention, since the insulating film on which the electrode pattern is formed is wound around the surface of the nip forming member to form the electrode, in addition to the above-described basic effects, protection is simultaneously achieved. Since a layer can be formed, manufacturing efficiency can be improved.

In particular, according to the ninth aspect of the invention, since the power supply of the means for applying a voltage and the power supply of the electrostatic force attenuating means for inverting the polarity are made the same, the structure is simplified in addition to the above basic effects. Can be achieved.

In particular, according to the tenth to twelfth aspects of the present invention, since the arrival time of the electrode is determined and the voltage is applied only to the electrode, the area around the electrode is charged up and the electric field changes. It is possible to prevent a decrease in the attraction force.

In particular, according to the thirteenth aspect of the present invention, since the upper surface of the electrode is covered with the protective layer, in addition to the above-described basic effects, the electrode can be prevented from being worn or dropped, and can be used for a long time. As a result, a stable adsorption and peeling action can be obtained.

In particular, according to the fourteenth aspect of the present invention, since the diameter of the pressing member as the electrode is protected by the backup roller, a stable voltage can be obtained while suppressing discharge and the like in addition to the above basic effects. Supply can be made.

[Brief description of the drawings]

FIG. 1 is an overall schematic front view of a stencil printing apparatus according to an embodiment of the present invention.

FIG. 2 is a perspective view of a main part of the impression cylinder in the embodiment shown in FIG.

FIG. 3 is a development view of an electrode in the embodiment shown in FIG.

FIG. 4 is a schematic side view showing a voltage supply configuration in the embodiment shown in FIG.

FIG. 5 is a sectional view showing an electric field on the surface of the impression cylinder in the embodiment shown in FIG.

FIG. 6 is a graph showing a relationship between an attractive force and a frequency in the embodiment shown in FIG.

FIG. 7 is a front view of an essential part showing a peeled state on the paper discharge side in the embodiment shown in FIG. 1;

FIG. 8 is a perspective view of a main part showing another example of electrode formation on the surface of the impression cylinder.

FIG. 9 is a perspective view of an impression cylinder showing another embodiment.

10 is a front view of the impression cylinder in the embodiment shown in FIG.

FIG. 11 is a front view showing a positional relationship between an electrode, a paper guide plate, and the like in the embodiment shown in FIG. 9;

FIG. 12 is a front view of an impression cylinder showing another embodiment.

13 is a perspective view of an end portion of the impression cylinder in the embodiment shown in FIG.

FIG. 14 is a block diagram illustrating a main part of a stencil printing apparatus according to another embodiment.

FIG. 15 is an overall schematic front view of a stencil printing apparatus according to another embodiment.

FIG. 16 is an enlarged front view of a main part showing a suction state of printing paper in the embodiment shown in FIG.

FIG. 17 is a schematic front view of an example in which the pressing member in the embodiment shown in FIG. 15 is protected by a backup roller.

FIG. 18 is a perspective view of a main part of a backup roller configuration in the embodiment shown in FIG.

[Explanation of symbols]

 6, 25, 42, 52 Impression cylinder as nip forming member 8 Plate cylinder 9, 44 Electrode 24 Pressing member as electrode 26 Static elimination needle 30 as electrostatic force attenuation means 30 AC power supply as means for applying voltage 45 Static power attenuation Static elimination brush 54 as means 54 Surface insulating layer as protective layer 55 Control means 57 Electrode detection means 60 Backup roller

Claims (14)

[Claims] 1. A printing apparatus comprising: a rotatable plate cylinder; and a rotatable nip forming member for transferring ink to printing paper by generating printing pressure in cooperation with the plate cylinder. A printing apparatus, comprising: printing paper suction means for attracting printing paper to a member by electrostatic force; and electrostatic force attenuating means for removing or weakening the electrostatic force on the discharge side of the nip forming member. 2. A printing apparatus according to claim 1, wherein said printing paper suction means comprises an electrode provided on said nip forming member, and means for applying a voltage to said electrode. . 3. The printing paper according to claim 1, wherein said printing paper suction means comprises a pressing member comprising an electrode for pressing the printing paper against said nip forming member, and means for applying a voltage to said pressing member. Printing paper characterized by the following. 4. The printing apparatus according to claim 2, wherein the electrodes are formed in a pattern and provided on the surface of the nip forming member. 5. The printing apparatus according to claim 4, wherein a conductive material is vapor-deposited on one surface, and an insulating film having an electrode pattern formed on the vapor-deposited surface is wound around the surface of the nip forming member. Printing device. 6. A printing apparatus according to claim 2, wherein said electrodes are made of conductive rubber in which a conductive material is dispersed in an insulating rubber material, and are integrally formed with an insulating sheet. apparatus. 7. The printing apparatus according to claim 2, wherein a plurality of electrodes extending in an axial direction of the nip forming member are provided on a surface of the nip forming member at intervals in a circumferential direction of the nip forming member. A printing apparatus, wherein the means for applying a voltage sequentially contacts each electrode as the nip forming member rotates. 8. A printing apparatus according to claim 7, wherein said electrostatic force attenuating means comprises a voltage applying means for inverting the polarity of said electrode by contacting an electrode on the paper discharge side remote from said voltage applying means. A printing device, comprising: 9. The printing apparatus according to claim 8, wherein the means for applying the voltage and the means for attenuating electrostatic force share one power supply. 10. A printing apparatus according to claim 7, wherein an electrode detection means for detecting said electrode, and an arrival time of an electrode to which a voltage is to be applied are determined based on detection information of said electrode detection means, and said voltage is determined. A printing apparatus, comprising: control means for controlling a means for applying the voltage so that a voltage is applied to the electrode only when the electrode to be applied arrives. 11. A printing apparatus according to claim 10, wherein said control means controls said means for applying said voltage so that the polarity of the applied voltage is inverted each time an electrode arrives. 12. A printing apparatus according to claim 10, wherein said electrostatic force attenuating means comprises a polarity inversion voltage applying means contacting an electrode on a paper discharge side remote from said voltage applying means. A printing apparatus, wherein the control means controls the polarity inversion voltage applying means so as to apply a voltage having a polarity opposite to the polarity of the voltage applied by the voltage applying means. 13. The method of claim 2, 4, 6, 7, 8, 9, 10,
13. The printing device according to claim 11, wherein an upper surface of the electrode is covered with a protective layer. 14. A printing apparatus according to claim 3, wherein said holding member is a roller having a small diameter, and said holding member is protected in its structural strength by a backup roller having a larger diameter and rotating at the same linear speed. A printing device characterized by the above-mentioned.