JPH10250166A - Ink-jet printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely and stably attract and hold various printing media to a drum and enable stable high-quality printing. SOLUTION: The ink-jet printer is provided with a charging roller 21 which can press a printing medium to an outer circumferential face 11 (12) of a rotating drum 10 while a voltage is impressed or in a grounded state, and a drum- charging member 31 which is arranged at the upper side in a rotation direction of the drum (Y direction) than the charging roller 21 and can charge the outer circumferential face 11 (12) of the drum with charges of an opposite polarity to that of the printing medium.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of adsorbing and holding a print medium on the outer peripheral surface of a drum rotatable at a constant peripheral speed by using a charge attraction force, and spraying ink on the print medium rotating with the drum. The present invention relates to an inkjet printer formed so as to be capable of printing.

[0002]

2. Description of the Related Art A nozzle head for each color is reciprocated over the entire length in a row direction, and printing is performed during each forward movement to print one line. After printing one line, a printing medium [plain paper, plastic film (OHP) is printed. Film)] Compared to a so-called serial type ink jet printer in which M is fed one line in the column direction and repeats these steps, printing speed can be greatly increased and continuous printing operation can be performed over many sheets. The present applicant has proposed an ink jet printer capable of achieving a significant reduction in size as compared with (for example, Japanese Patent Application No. 8-296959).

In FIG. 7, a drum 10 is rotatable at a constant peripheral speed and can hold a print medium M on an outer peripheral surface 11 thereof. That is, the print medium M is held on the outer peripheral surface 11 of the drum 10 by using the holding force of the medium holding means, and is rotated and transported by using the rotation of the drum 10.

A nozzle head (print head) 200 for each color is arranged in the rotation (Y) direction of the drum 10. Therefore, an integrated nozzle head 200 for each color or an integrated nozzle head 200 for each color in which a plurality of nozzle head elements are arranged in the row direction over the entire length in the row direction (perpendicular to the paper surface), for example, by the pitch between inkjet nozzles. Ink is sprayed from the inkjet nozzles 207 for each color onto the rotating print medium M while being reciprocated, thereby printing in the row direction, and printing in the column direction using the rotation of the drum 10 during the forward movement of the pitch between the inkjet nozzles. Can be. That is, since the line-direction printing and the column-direction printing can proceed simultaneously, the printing speed can be greatly increased.

Further, since the nozzle heads 200 for each color and the ink tanks (ink cassettes) 213 for the respective colors are arranged at separate positions, the nozzle heads 200 for the respective colors are provided.
In addition to the fact that the printing speed can be reduced and the reciprocating speed in the row direction can be greatly increased, the printing speed can be further increased, and the capacity of the ink tank (ink cassette) 213 for each color can be greatly increased. This allows continuous printing operation.

In order to realize these, one side (right side in FIG. 7) of the drum 10 is provided with a feeding means 60 and a medium feeding means 9.
0, and on the other side (left side in FIG. 7), the medium peeling means 140, the medium discharge / conveyance means 160, and the direction switching means 190
Are provided.

The feeding means 60 can selectively feed the printing medium M one by one from one of the cassette feeding means 71 and the manual feeding means 61. The medium supply means 90 feeds the fed print medium M to the drum 1 at a predetermined timing.
Feed to the 0 side. The medium peeling means 140 peels the print medium M from the drum 10 after printing, and
Numeral 0 discharges and conveys the separated print medium M to the left in FIG. The direction switching unit 190 selectively switches between the discharge tray 192 and the upper discharge tray 193.

Thus, the feeding, supply, holding, rotational transfer, printing, peeling, and discharging and conveying of the printing medium M can be continuously performed, so that multicolor printing of, for example, 20 sheets or more of A4 size in one minute can be performed. it can.

Here, in order to obtain the holding force of the printing medium M, it is conceivable to construct the printing medium M by using any one or an arbitrary combination of a charge attracting force, a negative pressure attracting force, and a mechanical clamping force. In particular, for miniaturization, adoption of a charging means utilizing a charge attracting force is effective.

[0010]

Therefore, the charging roller 21 is pressed against the printing medium M from the side opposite to the drum outer peripheral surface 11 and the drum outer peripheral surface 11 (12) is located upstream of the charging roller 21 in the drum rotation direction. The applicant of the present invention has proposed an ink jet printer in which an opposite polarity charging member (31) for charging is provided, and the print medium M and the drum outer peripheral surface 11 are formed so as to be capable of charging charges having different polarities from each other (Japanese Patent Application No. 9-575).
No. 41). As a result, the print medium M could be reliably and stably held on the drum outer peripheral surface 11.

However, there are cases where the print medium M cannot be stably held on the drum outer peripheral surface 11 depending on the type of the print medium M, such as the thickness and paper quality. Investigation of the cause reveals that when a constant voltage is applied to the charging roller 21, depending on the type of the printing medium M, the charge from the charging roller 21 penetrates the printing medium M and is charged by the opposite polarity charging member (31). It has been found that the charge on the drum outer peripheral surface 11 disappears and the charge adsorbing force is reduced. More specifically, the charge easily penetrates in the order of the plastic film (the OHP film), the surface-coated special paper, and the plain paper, and therefore, in the case of plain paper in particular, unstable retention is likely to occur.
If such a situation occurs, stable high-quality printing is hindered.

SUMMARY OF THE INVENTION An object of the present invention is to provide an ink jet printer capable of stably performing high quality printing while reliably and stably holding various printing media on a drum.

[0013]

According to a first aspect of the present invention, there is provided a drum rotatable at a constant peripheral speed, and a charging device capable of pressing a printing medium against an outer peripheral surface of the rotating drum while a voltage is applied or grounded. A roller, a print head capable of spraying ink onto the print medium held by the charge adsorption on the drum, and a print head, and a print head disposed upstream of the charging roller in the drum rotation direction and having a polarity opposite to that of the charge charged on the print medium. And a drum charging member capable of charging the outer peripheral surface of the drum with a charge.

In the case of this invention, for example, when plain paper (A4 size paper or the like) is selected as a print medium, a voltage (for example, voltage (eg, DC + 5 kV) is applied. As a result, charges (positive charges) are charged on the outer peripheral surface of the drum.

When plain paper is supplied to the outer peripheral surface of the drum, the charging roller is grounded when contact with the plain paper is started.

As a result, the plain paper comes into contact with the grounded charging roller, and the plain paper is inductively charged with a charge having a polarity opposite to that of the charge on the outer peripheral surface of the drum.

As a result, a charge attracting force acts between the plain paper and the outer peripheral surface of the drum, and the plain paper is securely held on the outer peripheral surface of the drum.

For example, when the printing medium is a plastic film (an OHP film), a charge (positive charge) is charged on the outer peripheral surface of the drum in the same manner as described above, and the outer peripheral surface of the drum is charged on the plastic film by a charging roller. The charge (negative charge) having the opposite polarity to the charge charged to the surface is contact-charged.

As a result, a charge attracting force acts between the plastic film and the outer peripheral surface of the drum, and the plastic film is securely held on the outer peripheral surface of the drum.

Therefore, high quality printing can be performed by reliably holding various printing media on the outer peripheral surface of the drum.

According to a second aspect of the present invention, there is provided a conductive member disposed downstream of the charging roller in the direction of rotation of the drum and capable of contacting a printing medium on the outer peripheral surface of the drum in a state where a voltage is applied or grounded. And a contact / separation means capable of contacting / separating the conductive member from / to the outer peripheral surface of the drum.

According to this invention, when the printing medium is plain paper, the outer peripheral surface of the drum is charged with a charge (for example, positive charge), and the plain paper supplied to the outer peripheral surface of the drum is charged with a grounded charging roller. And a conductive member. As a result, the charge of the opposite polarity to the charge charged on the drum outer peripheral surface is more effectively induced-charged on the plain paper. As a result, the charge attraction force acts more stably between the plain paper and the drum outer peripheral surface, and the plain paper is more reliably held on the drum outer peripheral surface.

When the printing medium is OHP, the drum outer peripheral surface and the plastic film are charged with charges having different polarities in the same manner as in the first aspect of the present invention, so that the OHP is charged.
Film can be securely held on the outer peripheral surface of the drum.

Further, according to a third aspect of the present invention, the charging roller has an electric resistance value of 1 × 10 ⁴ to 1 × 10 ⁶ Ω · cm, and the charging roller is charged from the outer peripheral surface of the drum after charging of the printing medium is completed. 1 × 10 ¹²
An ink jet printer having an electric insulating layer of about 1 × 10 ²⁰ Ω · cm formed and capable of switching a voltage applied to the drum charging member.

In this invention, the charging roller has a low resistance (1
× 10 ⁴ to 1 × 10 ⁶ Ω · cm) and a high resistance (1 × 10 ¹² to 1 × 10 ²⁰ Ω · c) on the outer peripheral surface of the drum.
m), the electrical insulation layer is formed, and the voltage applied to the drum charging member is switchable, so that the printing medium can be more efficiently charged and more suitable for the type of printing medium. The outer peripheral surface of the drum can be charged by the charging voltage. Further, by separating the charging roller from the outer peripheral surface of the drum after charging is completed, the charging roller is prevented from contacting the print medium with ink sprayed from the print head.

Therefore, high quality printing can be performed by holding various printing media more securely on the outer peripheral surface of the drum.

Further, the invention according to a fourth aspect is an ink jet printer wherein the voltage applied to the charging roller is switchable.

In the case of this invention, charges of different polarities can be charged on the outer peripheral surface of the drum and the print medium according to the type of the print medium without excess or shortage. Therefore,
Various print media can be more reliably held on the outer peripheral surface of the drum to perform high quality printing.

Further, the invention of claim 5 is characterized in that the voltage applied to the conductive member is switchable.

In the case of such an invention, electric charges of different polarities can be charged to the outer peripheral surface of the drum and the print medium according to the type of the print medium without any excess or shortage. Therefore,
Various print media can be more reliably held on the outer peripheral surface of the drum to perform high quality printing.

[0031]

Embodiments of the present invention will be described below with reference to the drawings. This inkjet printer is shown in FIG.
As shown in FIG. 6, a drum charging member (31), a charging roller 21, and a conductive member (41) are provided around a drum 10.
The components are arranged in this order from the upstream side to the downstream side in the drum rotation direction (Y direction).

A description will be given of a case where the overall configuration is constructed in the same manner as that of the previously proposed ink jet printer (FIG. 7). However, the description of the same parts as those in FIG. 7 will be simplified or omitted.

In FIG. 1, the drum 10 is, for example, 20 drums.
It is rotatable around the shaft 15 at 120 rpm at which multicolor printing of PPM can be achieved. The shaft 15 of the drum 10 is connected to the ground by a ground wire 19 (grounded).

On the outer peripheral surface 11 of the drum 10, an electric insulating layer 12 having an electric resistance value (volume resistivity) of 1 × 10 ¹² to 1 × 10 ²⁰ Ω · cm is formed. This is to ensure a surface potential after charging (for example, 800 V or more). In this embodiment, the thickness 2 is closely adhered to the drum outer peripheral surface 11.
It is formed from a 5 μm polyester film sheet. The reason why the thickness of the polyester film sheet was set to 25 μm was that the printing medium M could be reliably held by the drum 11 when the thickness was 25 μm as a result of experiments on the holding condition of the printing medium M with various thicknesses. Because he did. The electric insulating layer 12 may be formed by a Teflon resin coating method.

Around the drum 10, a drum charging member (31), a medium supply means 90, a charging roller 21 forming the medium holding means 20, a conductive member (41), a charge removing means 26, a medium peeling means 140 and The nozzle units (print heads) 200 for the respective colors are arranged in this order from the upstream side to the downstream side in the rotation (Y) direction.

The charging roller 21 can be selectively switched between a solid line state (pressure contact) and a two-dot chain line state (separation) shown in FIG. It is formed so that it can be directly charged (negatively charged).

The charging roller 21 has an electric resistance value (volume resistivity) of 1 × 10 ⁴ -1 to improve charging efficiency.
It is made of a conductive rubber of × 10 ⁶ Ω · cm. The conductive rubber is selected from urethane rubber, silicon rubber, and the like. In this embodiment, urethane rubber is employed. The power supply device 2 is connected to the charging roller 21 via a selection switching circuit 23.
2, a negative voltage is applied. The power supply device 22 is formed so that the applied voltage can be switched.

The selection changeover circuit 23 includes a changeover switch 23S
And the electric paths (23L1, 23L2, etc.), and are formed so that the charging roller 23 and the power supply device 22 can be connected / disconnected and the charging roller 21 can be grounded by electric circuit switching by the changeover switch 23S.

As shown in FIG. 2, the contact / separation means 29 includes a link lever 29L rotatable about a pin member 29P and a spring for pulling one side (upper side) 29LF of the link lever 29L to the left in the figure. 29SP and an eccentric cam 29C for pushing the other side (lower side) 29LB downward in the figure against the pulling force of the spring 29SP. The charging roller (21) is connected to a link lever 29L via a support shaft 29S.
It is rotatably mounted on.

Therefore, the other side 29
When the LB is not pushed down, the spring 29
The charging roller (21) is generated by the urging force (tensile force) of the SP.
From the drum outer peripheral surface 11 (12) to the print medium M. In addition, they come into contact with a certain pressing force. If the other end 29LB is pushed down by the eccentric cam 29C, the charging roller (21) can be separated from the drum outer peripheral surface 11 (12).

The contact / separation means 29 is moved forward and backward by a drive control unit 250 described later. At least the advance is performed at a timing at which the leading end of the print medium M can be charged immediately after the charging roller 21 contacts the drum outer peripheral surface 11 (12).

The drum charging member (31) includes a charging roller 2
1, a charge (positive charge) having a polarity opposite to that of the charge (negative charge) charged on the print medium M is disposed on the drum outer peripheral surface 11 (electric insulating layer 12). It is a means for charging.

In this embodiment, the drum charging member is formed of a corona discharger 31 disposed upstream of the charging roller 21 in the drum rotation direction. A positive voltage is applied to the corona discharger 31 from a power supply device 32. The power supply device 32 is formed so that the applied voltage can be switched.

The conductive member (41) is disposed downstream of the charging roller 21 in the drum rotation direction (Y direction), and the drum outer peripheral surface 11 (1
2) It is formed so as to be able to contact the upper print medium M. The conductive member (41) is brought into contact with and separated from the drum outer peripheral surface 11 (12) by using the conductive member contact / separation means 45.

In this embodiment, the conductive member is formed of a conductive brush 41 disposed downstream of the charging roller 21 in the drum rotation direction. This conductive brush 4
1 includes the power supply device 22 and the selection switching circuit 23 described above.
A voltage is applied (or grounded) by using.
That is, the conductive brush 41 is connected to the connection circuit (the electric circuit 42).
L, the changeover switch 42S, etc.) and the selection changeover circuit 23 so that the power supply device 22 can be connected / disconnected and grounded.

The contacting / separating means for the conductive member includes a conductive member (4
It is formed from a solenoid 45 connected to 1).
When the solenoid 45 is excited, the conductive member (41) is separated from the drum outer peripheral surface 11, and is brought into contact with the drum outer peripheral surface 11 by demagnetizing.

The charging condition setting means (250) includes a drum charging member (31), a charging roller 21, and a conductive member (41).
This is a means for setting the charging conditions (including grounding) for the print medium M according to the type of the print medium M. In this embodiment, the charging condition setting means is formed by a drive control section 250 for controlling the drive of the entire inkjet printer shown in FIG. The drive control unit 250 includes a CPU, a ROM, a RAM, a keyboard, and the like, and includes a main motor 10M that rotationally drives the drum 10 and the like, power supply devices (22, 32), changeover switches (23S, 42S), and a medium supply unit 90. , Nozzle unit 200 for each color, various sensors (10S, 97,
98) are connected.

More specifically, the charging condition setting means includes a setting unit (for example, RAM) capable of setting and storing the charging condition selected according to the type of the printing medium M (for example, plastic film (OHP film), plain paper). Etc.) and print medium M
The charging member (31), the charging roller 21, and the conductive member (41) are charged (or grounded) under an input unit (e.g., a keyboard) for inputting the type of the printing medium and charging conditions according to the input printing medium M. Power supply units (22, 3
2), a control unit (CPU, RO, etc.) capable of controlling driving of the changeover switches (23S, 42S) and the contact / separation means (29, 45).
M etc.).

The charging conditions in this embodiment are as follows. When the printing medium M is plain paper, the voltage applied to the drum charging member (31) is DC + 4.5 (or +5) kV, the charging roller 21 and the conductive member ( 41) is a ground. When the print medium M is a plastic film (an OHP film), the voltage applied to the drum charging member (31) is DC +5 kV, and the voltage applied to the charging roller 21 alone (or the charging roller 21 and the conductive member (41)). The voltage to be applied is DC-800V.

The charge removing means 26 is formed of a corona discharger to which an AC potential can be applied, and before the mechanical peeling by the medium peeling means 140, the electric charge between the outer peripheral surface 11 (12) and the printing medium M is absorbed. Force can be dissipated.

The medium supply means 90 includes a pair of supply rollers 9.
In addition to the medium supply function to the drum 10
It has a function of adjusting the attitude of the print medium M and a function of standby for supply.

That is, the leading end of the printing medium M fed from below in FIG.
3 and is elastically deformed in the guide 94 on the upstream side. Therefore, the leading end of the print medium M is placed on the drum (shaft 1).
5) It can be supplied without skew because it is aligned in the axial direction.
Whether or not the posture adjustment process has been started can be confirmed by the medium sensor 97.

When the posture adjustment is completed, both rollers 9
Reference numerals 1 and 92 move the print medium M to the drum 10 side along the downstream guide 96 until the leading end of the print medium M is detected by the medium sensor 98. As a result, the leading end side of the print medium M is engaged by the rollers 91 and 92, and a supply standby state to the drum 10 side is established.

The print medium M can be supplied to the drum 10 (11) at a predetermined timing. After the leading end of the supplied print medium M is held on the outer peripheral surface 11,
On the other hand, the roller 91 is moved rightward as shown by a two-dot chain line in FIG. 1 by the engagement / separation means 95 shown in FIG. Therefore, the rear end side of the print medium M becomes free, and does not become a load of the rotation transfer by the drum 10. The engagement / separation means 95 is formed in the same manner as the contact / separation means 29.

Next, the operation of this embodiment will be described. When the device power supply (power) is turned on (ON), the drive control unit 250 drives the main motor 10M that can drive the drum 10 and the like. Next, the drive control unit 250
When the drum rotation position sensor 10S detects that the rotation position (angle) of the drum 10 has reached a preset rotation position, the medium supply unit 90 is driven to print the print medium M that has been in the supply standby state. It is supplied to the drum 10 shown in FIG. 1 at a moving speed equivalent to the drum peripheral speed.

Prior to this (or simultaneously), the drive control unit 250 controls the drum charging member under the charging conditions corresponding to the type of the print medium M (for example, a plastic film (OHP film)) input from the input unit. (31), the power supply units (22, 32), the changeover switches (23S, 42S), and the contact / separation means (29, 45) so that the charging roller 21 and the conductive member (41) are charged (or grounded). Drive control.

As a result, DC + 5 kV is applied to the drum charging member (31), and as shown in FIG.
The charging roller 21 is brought into contact with the drum outer peripheral surface 11 (12), and DC-800 V is applied to the charging roller 21. Alternatively, as shown in FIG. 5, the charging roller 21 and the conductive member (41) are brought into contact with the drum outer peripheral surface 11 (12), and the charging roller 21 and the conductive member (41) are in contact with each other.
C-800V is applied.

Therefore, the supplied printing medium M
From the point in time when the tip of the [plastic film (OHP film)] enters between the charging roller 21 and the electrical insulating layer 12 that rotate following the rotation of the drum 10, the printing medium M
Is charged with a negative charge. In other words, more charge is applied to the leading end of the print medium M, and the auxiliary charge attracting force allows the print medium M to be more reliably and stably adsorbed and held on the outer peripheral surface 11 (12) of the drum 10.

When the holding of the leading end is established, in this embodiment, when it is confirmed from the output signal of the drum rotation position detector 10S, the drive control unit 250 moves the one roller 91 of the medium supply means 90 to the two points in FIG. Move to dashed line state. Therefore, the rear end side of the print medium M is in a free state from both rollers 91 and 92, so that the rotation transfer load of the drum 10 is not generated.

Thus, the printing medium M (plastic film (OHP film)) is charged while being pressed against the electric insulating layer 12 of the drum 10 by the charging roller 21 having a low electric resistance. As a result, the print medium M is brought into close contact with the drum outer peripheral surface 11 (the electrical insulating layer 12), and the drum 1
With the rotation of 0, it is rotationally transferred in the Y direction.

As described above, the outer peripheral surface 11 (1
2), a charge (positive charge) having a polarity opposite to the charge (negative charge) charged on the print medium M is charged.
[Plastic film (OHP film)] can be securely and stably held on the drum 10.

When plain paper (A4 size paper or the like) is selected as a print medium, a voltage is applied to the drum charging member (31) before the plain paper is supplied to the drum outer peripheral surface 11 (12). (DC +4.5 kV or +5 kV) is applied. As a result, charges (positive charges) are charged on the drum outer peripheral surface 11 (12).

When plain paper is supplied to the drum outer peripheral surface 11 (12), as shown in FIG.
And the conductive member (41) is connected to the drum outer peripheral surface 11 (12).
Contact. Then, the charging roller 21 and the conductive member (41) are grounded from the time when the contact with the plain paper is started.

As a result, the plain paper comes into contact with the grounded charging roller 21 and the conductive member (41), and the plain paper has a polarity opposite to that of the charge charged on the drum outer peripheral surface 11 (12). Is inductively charged.

As a result, the plain paper and the drum outer peripheral surface 11 (1
The charge adsorbing force acts between (2) and (2), and the plain paper is securely held on the drum outer peripheral surface 11 (12).

When the drum rotation position sensor 10S detects (confirms) that the rear end of the print medium M has passed through the charging roller 21 during one rotation of the drum 10, the charging roller 21 is brought into contact with the contact / separation means 29. 1 and is separated from the electric insulating layer 12 side. Also,
The conductive member (41) is also retracted and separated from the electric insulating layer 12 side. Therefore, the printing medium M is the drum outer peripheral surface 1
1 (12), and is rotationally transferred in the Y direction.

While the drum 4 (2 to 5) is rotating, ink is jetted from the print head (nozzle unit for each color) 200, and printing is performed on the print medium M which is rotating and transporting.

When the multi-color printing on the print medium M is completed by the rotation of the drum 4, the drive control unit 250 sets
By operating 0, the leading end side of the printed print medium M is mechanically peeled off. The separated printing medium M is delivered to the medium discharge / conveying means (160) by a medium removing means (peeling claw) 140 which also serves as a delivering means.

Thus, according to this embodiment, the charging roller 21 capable of pressing the printing medium M against the outer peripheral surface 11 (12) of the rotating drum 10 with the voltage applied or grounded.
A print head (200) capable of spraying ink on the print medium M held by the drum 10 to adsorb and print thereon, and a print medium disposed upstream of the charging roller 21 in the drum rotation direction (Y direction). Since the drum charging member (31) capable of charging the drum outer peripheral surface 11 (12) with the charge of the opposite polarity to the charge charged to the M is provided, the various print media M are reliably held on the drum 10 while being held at a high level. Quality printing can be performed stably.

A conductive member (41) which is disposed downstream of the charging roller 21 in the direction of rotation of the drum and is capable of contacting the printing medium M on the drum outer peripheral surface 11 (21) in a state where a voltage is applied or grounded. And a contacting / separating means for contacting / separating the conductive member (41) to / from the drum outer peripheral surface 11 (12). Can be performed stably.

The charging roller 21 is 1 × 10 ⁴ to 1
A print medium M having an electric resistance of × 10 ⁶ Ω · cm
Spaced capable consist outer peripheral surface of the drum 11 (12) after charging completion to, the outer peripheral surface of the drum 11 1 × 10 ¹² ~1 × 1
Since the electrical insulating layer 12 of 0 ²⁰ Ω · cm is formed and the voltage applied to the drum charging member (31) can be switched, the printing medium M can be more efficiently charged and the printing medium M can be more efficiently charged. The drum outer peripheral surface 11 (12) can be charged with a more suitable charging voltage according to the type of M. Further, after the charging is completed, the charging roller 21 and the conductive member (41) are separated from the drum outer peripheral surface 11 (12), so that the charging roller 21 and the like are sprayed on the print medium M from the print head (200). Contact is prevented. Accordingly, high quality printing can be performed by holding various printing media M more securely on the drum outer peripheral surface 11 (12).

Further, since the voltage applied to the charging roller 21 is configured to be switchable, electric charges of opposite polarity are more or less supplied to the drum outer peripheral surface 11 (12) and the print medium M according to the type of the print medium M. Without any charge. Accordingly, high quality printing can be performed by holding various printing media M on the drum outer peripheral surface 11 (12) more securely.

Since the voltage applied to the conductive member (41) is switchable, charges of opposite polarity are applied to the drum outer peripheral surface 11 (12) and the print medium M according to the type of the print medium M. It can be charged even more and more. Accordingly, high quality printing can be performed by holding various printing media M on the drum outer peripheral surface 11 (12) more securely.

As the charging conditions in the above embodiment, the printing medium M is made of plain paper and plastic film (OH
However, the present invention is not limited to this. For example, the voltage applied to the drum charging member (31) may be DC +
The voltage applied to the charging roller 21 alone (or 4.5 (or +5) kV [or the charging roller 21 and the conductive member (31)]) may be DC-200V.

[0075]

According to the first aspect of the present invention, the charging roller capable of pressing the outer peripheral surface of the drum while the printing medium is rotating with the voltage applied or grounded, and the printing medium which is held by the charge adsorption on the drum. A print head that can print by spraying ink, and a drum charging member that is disposed upstream of the charging roller in the direction of rotation of the drum and is capable of charging the outer peripheral surface of the drum with a charge having a polarity opposite to the charge charged on the print medium. Is provided, high quality printing can be stably performed while various printing media are securely held on the drum.

According to the second aspect of the present invention, the conductive member is disposed downstream of the charging roller in the direction of rotation of the drum and is capable of contacting the printing medium on the outer peripheral surface of the drum in a state where a voltage is applied or grounded. And a contacting / separating means capable of contacting / separating the conductive member from / to the outer peripheral surface of the drum, so that high-quality printing can be stably performed while various printing media are further held on the drum.

According to the third aspect of the present invention, the charging roller has an electric resistance value of 1 × 10 ⁴ to 1 × 10 ⁶ Ω · cm, and after the charging of the print medium is completed, the charging roller has an electric resistance of 1 × 10 ⁴ Ω · cm. It is configured to be separable, and 1 × 10 ¹² to 1 ×
Since an electric insulating layer of 10 ²⁰ Ω · cm is formed and the voltage applied to the drum charging member is switchable, the same effect as that of the invention of claim 1 can be obtained, and printing can be performed more smoothly. In addition to this, the charging efficiency can be further improved.

Further, according to the invention of claim 4, since the voltage applied to the charging roller is configured to be switchable,
In accordance with the type of the print medium, the outer peripheral surface of the drum and the print medium can be charged with electric charges of opposite polarities even more and more. Accordingly, high quality printing can be performed by holding various printing media more securely on the outer peripheral surface of the drum.

Further, according to the fifth aspect of the present invention, since the voltage applied to the conductive member is configured to be switchable, electric charges of opposite polarity are applied to the outer peripheral surface of the drum and the print medium according to the type of the print medium. Can be charged without excess or shortage. Accordingly, high quality printing can be performed by holding various printing media more securely on the outer peripheral surface of the drum.

[Brief description of the drawings]

FIG. 1 is a diagram for describing an embodiment of the present invention.

FIG. 2 is a view for explaining contact / separation means for a charging roller.

FIG. 3 is a diagram for explaining a drive control unit.

FIG. 4 is a view for explaining charging conditions when a plastic film (an OHP film) is held on the outer peripheral surface of a drum.

FIG. 5 is a view for explaining another charging condition when a plastic film (OHP film) is held on the outer peripheral surface of the drum.

FIG. 6 is a view for explaining a charging condition when plain paper is held on the outer peripheral surface of the drum.

FIG. 7 is a diagram for explaining a previously proposed inkjet printer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Drum 11 Outer peripheral surface 12 Electric insulating layer 21 Charging roller 22 Power supply device 29 Contacting / separating means 31 Corona discharger (drum charging member) 32 Power supply device 41 Conductive brush (conductive member) 45 Solenoid (conductive member separating / separating means) ) 200 Nozzle unit for each color (print head)

Claims (5)

[Claims] 1. A drum rotatable at a constant peripheral speed, a charging roller capable of pressing a print medium against an outer peripheral surface of a rotating drum while a voltage is applied or grounded, and a print held by electric charge on the drum A print head that can print by spraying ink on the medium, and a drum charger that is arranged upstream of the charging roller in the drum rotation direction and that can charge the charge on the outer peripheral surface of the drum with a charge of the opposite polarity to the charge charged on the print medium An ink jet printer comprising: a member; 2. A conductive member disposed downstream of the charging roller in the direction of rotation of the drum and capable of contacting a printing medium on the outer peripheral surface of the drum in a state where voltage is applied or grounded. 2. The ink jet printer according to claim 1, further comprising: a contact / separation unit capable of contacting / separating the drum outer peripheral surface. 3. The method according to claim 1, wherein the charging roller is 1 × 10 ⁴ to 1 × 1.
0 has an electrical resistance of ⁶ Omega · cm, and spaced capable constructed from the outer peripheral surface of the drum after charging completion of the print medium,
2. An electric insulating layer of 1 * 10 < ¹² > to 1 * 10 < ²⁰ > [Omega] .cm is formed on the outer peripheral surface of the drum, and a voltage applied to the drum charging member is switchable. The inkjet printer according to claim 2. 4. The apparatus according to claim 1, wherein a voltage applied to said charging roller is switchable.
The inkjet printer according to any one of the above. 5. The apparatus according to claim 2, wherein a voltage applied to said conductive member is switchable.
The inkjet printer according to any one of the above.