JP2000141736A - Image-forming apparatus of powder developer jet type - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image-forming apparatus of a powder developer jet type which can restrict a quantity of a developer adhering to an inner face of a through hole to a minimum and obtain images of a desired density. SOLUTION: A pulse 44 for urging a developer 18 held by a developer carrier 12 to a back electrode 20 is impressed from an image control part 38 to an individual electrode 36. In consequence, the developer 18 held by the developer carrier 12 flies through a through hole 34 of a diaphragm 26 and adheres to a recording medium 28 present between the diaphragm 26 and the back electrode 20. For restricting the adhesion and clogging of the developer 18 to the through hole 34 to a minimum, the pulse 44 has an incline part 50 increasing a signal value in accordance with a time at a leading edge part before the signal value reaches a peak.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a powder developer jet type image forming apparatus in which a powder developer carried on a developer carrier is caused to fly by an electric force and adhere to a recording medium.

[0002]

2. Description of the Related Art As a powder developer injection type image forming apparatus,
Some are disclosed in U.S. Pat. No. 5,477,250. The image forming apparatus includes a developer carrying roller for carrying a charged powder developer, a back electrode facing the developer carrying roller at a predetermined interval, and a back electrode for supplying the developer on the developer carrying roller. A power source for creating an electric field that is energized toward A partition is arranged between the developer carrying roller and the back electrode, and a space through which a recording medium can pass is formed between the partition and the back electrode. The partition has a plurality of through holes formed in a portion located in a region where the developer carrying roller and the back electrode face each other. Also, the partition wall,
Individual electrodes are provided around each through hole, and each individual electrode is connected to a driving device.

According to this image forming apparatus, an image signal corresponding to an image to be created is applied to an individual electrode. At this time, the image signal has a polarity that electrically urges the developer held on the developer carrying roller toward the back electrode. Therefore, the urging force generated by the application of the image signal and the urging force of the electric field formed between the developer carrying roller and the back electrode cooperate with each other to face the individual electrode to which the image signal is applied. A group of the developer is separated from the developer carrying roller, reaches a recording medium between the partition wall and the back electrode through the corresponding through hole, and a dot of the developer is formed on the recording medium. Then, a target image is created on the recording medium by the collection of dots.

[0004]

However, in such an image forming apparatus in which the powder developer flies through the through hole, the developer adheres to the inner surface of the through hole, and the amount of the developer gradually increases. Then, there is an essential problem that the diameter of the dot formed on the recording medium becomes small. Further, in the worst case, a situation occurs in which the through holes are blocked with the developer, and the dots in the corresponding portions are not created. In particular, when an image signal of a complete rectangular pulse is applied to the individual electrode, a large amount of developer enters the through hole at a time, and as a result, there is a high risk that the through hole is clogged.

Accordingly, an object of the present invention is to provide an image forming apparatus capable of obtaining an image having a desired density while minimizing the amount of a developer adhering to the inner surface of a through hole.

[0006]

In order to achieve this object, an image forming apparatus according to the present invention is provided. The image forming apparatus comprises: a developer carrier for supporting a charged powder developer; It has a back electrode facing at an interval, and a bias power supply for urging the developer carried on the developer carrier toward the back electrode. Between the developer carrier and the back electrode,
A partition wall made of an insulating material, which has at least one through hole in a region where the developer carrying member and the back electrode face each other and forms a space through which a recording medium can pass, is arranged between the developer carrier and the back electrode. An individual electrode is arranged near the through hole. Further, an image control unit is provided, and a pulse signal for urging the developer carried on the developer carrier toward the back electrode can be applied to the individual electrodes from the image control unit. Based on the pulse signal, the developer held by the developer carrier is caused to fly through the through hole of the partition and adhere to the recording medium between the partition and the back electrode. In order to minimize the adhesion of the developer to the through-hole, the pulse signal has an inclined portion at which the signal value increases with time at the leading edge until the signal value reaches a peak value.

[0007]

According to this image forming apparatus, the pulse signal has, at its leading edge, an inclined portion whose signal value increases with time. While the inclined portion is applied to the individual electrode, the electric field formed between the individual electrode and the developer carrier gradually increases. Therefore, the amount of the developer flying from the developer carrier immediately after the application of the pulse signal is small, and the amount gradually increases. Therefore, a large amount of developer does not rush into the through hole at one time, and clogging of the through hole and adhesion of the developer to the through hole are reduced. Therefore, even if the developer adheres to the through-hole, the amount of the developer can be minimized, and it is possible to obtain an image of a desired density with dots of a target size or a size almost close to the target size. it can.

[0008]

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows an image forming section 10 in a powder developer injection type image forming apparatus according to the present invention.
The schematic configuration of is shown. The image forming section 10 has a developer carrying roller (developer carrying member) 12 made of a conductive material. The developer carrying roller 12 is rotatably supported in a direction indicated by an arrow 14. Further, the developer carrying roller 12
Is connected to a first bias power supply 16 so that a predetermined voltage (in this embodiment, a negative bias voltage V _B1 ) can be applied. A powder developer 18 is carried on the outer periphery of the developer carrying roller 12, and the developer 18 is charged to a predetermined polarity (a negative electrode in the present embodiment).

Below the developer carrying roller 12, a back electrode roller (back electrode) 20 is provided in parallel with the developer carrying roller 12 at a predetermined interval from the developer carrying roller 12. The back electrode roller 20 is rotatably supported in a direction indicated by an arrow 22. Also, the back electrode roller 2
0 is connected to the second bias power supply 24 so that a predetermined voltage (positive bias voltage V _{B2 in} this embodiment) can be applied. The values of the bias voltages V _B1 and V _B2 are
The negatively charged developer 18 carried on the developer carrying roller 12 is attracted toward the rear electrode roller 20 by an electric field formed between the developer carrying roller 12 and the back electrode roller 20 due to a potential difference between the developer carrying roller 12 and the back electrode roller 20. However, the adjustment is performed so that the developer 18 is not separated from the developer carrying roller 12 by only the suction force.

The developer carrying roller 12 and the back electrode roller 2
A partition 26 is arranged between the two. The distance L ₁ between the developer carrying roller 12 and the partition 26 is equal to the developer carrying roller 1.
In order to prevent the developer 18 held in 2 from being scraped off by the contact with the partition 26, a small gap is provided between the two or the contact pressure between the two is set to a minimum. On the other hand, the distance L ₂ between the back electrode roller 20 and the partition 26
The space 30 is formed such that the recording medium 28 (for example, paper or resin film) can pass between them and, as described later, the developer 18 attached to the recording medium 28 does not contact the partition 26. To be set.

The partition 26 is formed of a thin plate made of a non-conductive material. As shown in FIGS. 1 and 2, a part of the partition wall 26, that is, the developer carrying roller 12 and the back electrode roller 2
A plurality of holes 34 penetrating the partition wall 26 are provided at predetermined intervals on a line parallel to the central axis of the developer carrying roller 12 in a portion included in a region (printing region 32) where 0 faces. Is formed. Inside or on the surface of the partition 26,
A ring-shaped individual electrode 36 is provided so as to surround each hole 34. The individual electrode 36 is a controller (image control unit) 3
8 from the controller 38 to each individual electrode 3
6, a printing signal, that is, a pulse 44 can be applied.

The controller 38, as shown in FIG.
The image forming apparatus includes an image signal output unit 40 that outputs a signal corresponding to an image created by the image forming apparatus, and a pulse generator 42 that generates a pulse 44 at a constant cycle. Image signal output unit 40
And the output section of the pulse generator 42 are connected to the corresponding individual electrodes 36 via an AND circuit 46 and an amplifier 48, and when signals are output from the image signal output section 40 and the pulse generator 42, respectively. , Pulse 44 is amplified by an amplifier 48, and the amplified pulse 44 is
6 is applied.

When the recording medium 28 is conveyed to the printing area 32 during the image producing operation of the image producing section 10 having such a configuration, the controller 3 is synchronized with the recording medium 28.
From 8, a pulse 44 is applied to the individual electrode 36. The pulse 44 applied at this time has a positive polarity.

As a result, the negative developer 18 held by the developer carrying roller portion is applied between the individual electrode 36 and the developer carrying roller portion facing the individual electrode 36 toward the back electrode roller 20. A new exciting electric field is formed. This newly formed electric field is combined with the electric field already formed between the developer carrying roller 12 and the back electrode roller 20 by the first and second bias power supplies 16 and 24,
A group of developer 1 carried on a developer carrying roller portion
8 is separated from the developer carrying roller 12 and is caused to fly.

The group of the developer that has flown passes through the corresponding hole 34 and adheres to the portion of the recording medium facing the hole 34 to form a dot. Then, a target image is created from a set of a large number of dots thus formed. The developer adhering to the recording medium 28 is carried to a fixing step (not shown) together with the recording medium 28, where it is heated and melted and fixed to the recording medium 28.

Next, a pulse 44 applied to the individual electrode 36
Will be described. As shown in FIG. 4A, the pulse 44 has, at its leading edge, an inclined portion 50 whose signal value, that is, voltage, increases with time. Specifically, the voltage value of the pulse 44 begins to rise from a time point t ₀ (voltage (reference voltage at time t _0):
V _REF ), and then reaches a maximum value (peak voltage): V _PEAK at time t ₁ . Peak voltage V _PEAK is maintained for a predetermined time, then the reference voltage V at the time of the voltage value at time t _2
It drops to _REF .

Since the pulse 44 has such a waveform, when the pulse 44 is applied to the individual electrode 36,
The force for attracting the developer 18 carried on the developer carrying roller 12 to the back electrode roller 20 at the position facing the individual electrode 36 gradually increases. As a result, the developer carrying roller 1
The developer 18 held in the corresponding portion 2 gradually separates from the developer carrying roller 12 and enters the corresponding hole 34, and further passes through the hole 34 to reach the recording medium 28.

Therefore, when a rectangular pulse having no inclined portion is applied to the leading edge portion, a large amount of the developer may fly at one time to close the hole, but the pulse 44 having the inclined portion 50 at the leading edge portion may be generated. When the voltage is applied, the hole 34 is not clogged with the developer 18 and the subsequent flying of the developer is not inhibited.

The waveform of the pulse 44 is not limited to the waveform shown in FIG. 4A, but may be any waveform having a slope at the leading edge (for example, as shown in FIGS. 4B to 4D). Waveform).

[0020] FIG. 4 (b) shows a modification of the pulse 44 in FIG. 4 (a), at time t ₁ after the time t ₁ ', V the voltage value from the peak voltage V _{PEAK I} (<V _PEAK ).

FIG. 4C shows another embodiment of the pulse.
In this pulse waveform, the voltage value rises from V _REF to V _I (> V _REF ) at a stretch at time t ₀ . afterwards,
The voltage value gradually increases and reaches a maximum value (peak voltage): V _PEAK at time t ₁ . Peak voltage V _PEAK is maintained for a predetermined time, it drops once at time t ₂ to the reference voltage V _REF.

[0022] FIG. 4 (d), shows a modification of the pulse in FIG. 4 (c), at time t ₁ after the time t ₁ ', V the voltage value from the peak voltage V _{PEAK I} (<V _PEAK ).

Under the following conditions, a pulse of the waveform shown in FIG. 4D is continuously applied to the individual electrodes to print one sheet of A4 size solid, and the clogged hole after printing (opening ratio: printing) The area of the hole after / the area of the hole before printing) was visually confirmed with an electron microscope. Further, the density of the solid image printed on the recording medium was measured. (A) pulse conditions · V _I: +300 volts · V _P: +550 volts · t ₁ -t _0: 0,10,20,30,40,50μse
c · t ₁ ′ −t ₁ : 20 μsec ・ t ₂ −t ₁ ′: 30 μsec (B) Partition wall material: Polyimide resin ・ Individual electrode material: Copper ・ Pore size: 100 μm ・ L ₁ : 20 μm, 50 μm ・ L ₂ : 200 μm (C) Bias voltage ・ Bias voltage V _B1 : -100 volts ・ Bias voltage V _B2 : +800 volts (D) Developer (toner) ・ Average particle size: 8 μm ・ Charge amount: -10 μC / g

FIG. 5 shows the results of the experiment. As is clear from this figure, when a complete rectangular pulse without a slope was applied, the aperture ratio was reduced to about 40%, but when a pulse with a slope was applied, the time of the slope (t ₁ − The aperture ratio increases with an increase in t ₀ ), and the ramp time is increased to 40 and 50 μsec.
In the case of setting to c, the aperture ratio showed a high value of about 80%.

As shown in FIG. 6, the aperture ratio and the density of a solid image printed on a recording medium tend to increase as the aperture ratio increases. Therefore, according to the image forming apparatus of the present invention, even if the developer adheres to the holes, the amount of the developer can be minimized, and the size of the target size, or the size almost An image having a desired density is obtained by the dots.

Similarly, a pulse having the waveform shown in FIG. 4B was applied to the individual electrodes, and the relationship between the tilt time, the aperture ratio, and the concentration was examined. The experimental conditions were the same as those described above. As a result, as shown in FIG. 7, the aperture ratio tended to increase as the inclination time became longer, similarly to the above-described experimental results.

The above description relates to one embodiment of the present invention, and the present invention can be variously modified. For example,
As shown in FIGS. 8 and 9A, the partition wall 26 is provided with a second electrode 52 on the back electrode side of the individual electrode 36, and the second electrode 52 is synchronized with the pulse 44 applied to the individual electrode 36. Another pulse may be applied to the electrode. In this case, the second electrode 52
The shape, voltage and waveform applied to the pulse can be changed according to the purpose. For example, for the purpose of converging the developer, a voltage having the same polarity as the developer 18 is applied to the second electrode. Also, changing the flight direction of the developer 18,
That is, in the case of deflection, as shown in FIG. 9B, the second electrode 52 is divided into a plurality of small electrodes 54, and the voltage applied to each small electrode is made different.

The polarities and magnitudes of the bias voltages V _B1 and V _B2 applied to the developer carrying roller 12 and the back electrode roller 20 and the polarity of the developer do not adversely affect the flying of the developer described above. Can be changed within a range.

Further, the developer carrier and the back electrode are not limited to rollers, but may be belts or rigid plates.
In short, the developer carrier may be any member that can carry the developer, and the back electrode cooperates with the developer carrier to attract the developer held on the developer carrier toward the back electrode. Anything that can be done is acceptable.

Further, a plurality of rows of holes formed in the partition wall 26 may be provided, and the arrangement may be in a staggered state.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically illustrating an image forming unit of an image forming apparatus according to the present invention.

FIG. 2 is a plan view showing an arrangement of holes formed in a partition.

FIG. 3 is a circuit diagram of a controller that applies a pulse to an individual electrode.

FIG. 4 is a waveform diagram of a pulse.

FIG. 5 is a graph showing the relationship between the slope time of the pulse (FIG. 4 (d)) in the slope portion and the aperture ratio of the hole obtained by an experiment.

FIG. 6 is a graph showing the relationship between the aperture ratio and the image density.

FIG. 7 is a graph showing the relationship between the slope time of a different pulse (FIG. 4 (b)) and the aperture ratio of a hole by an experiment.

FIG. 8 is a cross-sectional view schematically illustrating an image forming unit according to another embodiment.

FIG. 9 is a plan view of a second electrode.

[Explanation of symbols]

10: image forming unit, 12: developer carrying roller (developer carrying body), 16: first bias power supply, 18: developer, 2
0: back electrode roller (back electrode), 24: second bias power supply, 26: partition, 28: recording medium, 34: hole, 3
6: individual electrode, 38: controller, 44: pulse 4
4.

Claims (1)

[Claims] 1. A developer carrying member for carrying a charged powder developer, a back electrode facing the developer carrying member at a predetermined distance, and a developer carried on the developer carrying member. A bias power source for urging toward the back electrode, disposed between the developer carrier and the back electrode, and having at least one through hole in a region facing the developer carrier and the back electrode; A partition wall made of an insulating material, which forms a space through which a recording medium can pass, an individual electrode disposed near the through-hole, and a developer carried on the developer carrier facing the back electrode. An image control unit that applies a pulse signal to be applied to the individual electrode, based on the pulse signal, causes the developer held on the developer carrier to fly through the through hole of the partition, and When attached to the recording medium between the back electrode In addition, the pulse signal has an inclined portion at which the signal value increases with time at the leading edge until the signal value reaches the peak value.