JP6461546B2 - Electron emission device - Google Patents

Description

  The present invention relates to an electron emission device that emits electrons from an electrode surface by applying a voltage.

  2. Description of the Related Art Conventionally, an electrophotographic image forming apparatus includes a charging device that charges the surface of a photosensitive member that is a charged body. Although a corona charger is well known as a charging device, there is a possibility that ozone and various oxides may be generated to deteriorate the photosensitive member and the surrounding resin structure, etc. because it has a structure with discharge. On the other hand, in recent years, electron-emitting devices that do not generate oxides such as ozone, such as MIM (Metal-Insulator-Metal) type, MIS (Metal-Insulator-Semiconductor) type, or BSD (Ballistic electron Surface-emitting Device) type. Are known. This type of electron-emitting device accelerates electrons by utilizing the quantum size effect inside the device and a strong electric field, and emits electrons from the planar device surface (surface electrode). Since these electron-emitting devices emit electrons accelerated by an electron acceleration layer inside the device, a strong electric field is not required outside the device.

  Patent Documents 1 and 2 include a lower electrode and an upper surface electrode arranged opposite to each other, and an electron acceleration layer interposed therebetween, and a drive voltage is applied between the lower electrode and the surface electrode. An electron-emitting device is described. The electron acceleration layer is a layer in which an insulator material and conductive fine particles are aggregated, and has semiconductivity. When a driving voltage is applied to the semiconductive electron acceleration layer, a current flows in the electron acceleration layer, and a part thereof is emitted as ballistic electrons by a strong electric field formed by the applied voltage.

JP 2009-146891 A Japanese Patent No. 5238795

  This time, the inventor said that in the research and development of the types of electron-emitting devices described in Patent Documents 1 and 2, a large inrush current is caused to flow transiently during a certain period immediately after the start of driving, thereby increasing the amount of electron emission. It came to discover that it shows a peculiar phenomenon. The reason is that, immediately after the start of driving, the temperature rise due to Joule heat is low and the electrical resistance is low. Also, electrons are trapped (electron trap) in the electron acceleration layer made of an insulator, and the insulator is charged up. This may be due to the time required. Since it has also been experimentally confirmed that the total amount of electron emission is related to the lifetime of the device, a transient increase in the amount of electron emission immediately after the start of driving rapidly consumes the device lifetime. Become. For this reason, in order to realize a long lifetime of the device, it is necessary to suppress the transient increase in the amount of electron emission.

The present invention has been made in view of the above, and an object of the present invention is to provide an electron emission device capable of suppressing the inrush current at the start of driving and extending the life.

The present invention relates to an electron-emitting device having a first electrode, a second electrode, and an intermediate layer laminated between the first electrode and the second electrode, and between the first electrode and the second electrode. In the electron emission device that emits electrons from the second electrode by applying a drive voltage signal to the first electrode, the electron emission device further comprises drive means for gradually increasing the drive voltage signal at the start of driving of the electron-emitting device. Is a pulse train signal, and the drive means increases the peak value of the pulse train signal stepwise at the start of the drive.

  According to the present invention, the rise of the current (in-element current) flowing through the intermediate layer at the start of driving is suppressed by increasing the peak value of the pulse train signal, which is the driving voltage signal, in a stepwise manner at the start of driving, that is, in the initial period. This prevents the inrush current from occurring. As a result, the current in the element flowing through the intermediate layer from the start of driving is stably maintained at a low level, and unnecessary electron emission is suppressed.

  The pulse train signal has a predetermined duty ratio. According to this configuration, electron emission is stably performed by using a pulse train signal having a predetermined duty ratio as a drive voltage signal.

  In addition, a timing unit that counts the power supply stop period, a storage unit that stores a plurality of types of rising characteristics of the drive voltage signal corresponding to the length of the power supply stop period, and a rise corresponding to the timing result of the timing unit Selecting means for selecting a drive voltage signal having characteristics. According to this configuration, since the amount of electrons trapped in the intermediate layer is affected by the length of the power stop period, a change is seen in the inrush current characteristic at the start of the next drive. By setting and applying a plurality of drive voltage signals corresponding to the above, the element current flowing through the intermediate layer is stably maintained at a low level.

  In addition, the electron-emitting device is disposed so as to face a photoconductor as a member to be charged. According to this configuration, the electron emission device can be applied to the charging device of the image forming apparatus.

According to the present invention, inrush current at the start of driving can be suppressed.

It is a schematic block diagram which shows the relationship between the electron emission apparatus which concerns on 1st Embodiment, and a photoreceptor. It is a block diagram which shows an example of the power supply part of the electron emission apparatus of FIG. It is a block diagram which shows an example of the control part of the electron emission apparatus of FIG. (A) is a time chart showing the characteristics of the drive voltage signal Ve and the relationship between the output period and the rest period, and (b) is a time chart showing the in-element current Id flowing through the fine particle layer. (A) is a time chart which shows the state of the peak value of the pulse train signal which is a drive voltage signal, (b) is a time chart explaining print timing, (c) is a figure explaining the duty ratio of each pulse.

(First embodiment)
An electron-emitting device 1 shown in FIG. 1 includes an electron-emitting device 10 that emits electrons and a drive unit 20. The drive unit 20 includes a control unit 30 that performs control for driving the electron-emitting device 10, and a power supply unit 40 that is operated by a control signal from the control unit 30. The power supply unit 40 includes a drive signal circuit unit 41 that generates a drive voltage signal described later, and a bias circuit unit 42 that generates a bias voltage described later by a PWM (Pulse Width Modulation) method.

  In the present embodiment, the electron-emitting device 10 is used as a charging device that is disposed to face the surface of the photosensitive member 100 that is a member to be charged, which constitutes a part of an image forming apparatus for an electrophotographic process. The electron-emitting device 10 supplies negative surface oxygen ions generated by emitting electrons to the surface of the photoreceptor 100 as described later. The electron-emitting device 10 functions as an ion supply source that supplies ions for uniformly charging the surface of the photoreceptor 100.

  The drive signal circuit unit 41 outputs a drive voltage signal for driving the electron-emitting device 10, while the bias circuit unit 42 applies a negative DC bias voltage to the entire electron-emitting device 10 via the drive signal circuit unit 41. Float with. That is, the drive voltage signal is superimposed on the negative DC bias voltage. Details of the drive signal circuit unit 41 and the bias circuit unit 42 will be described later.

  The photoreceptor 100 functions as an image carrier in an electrophotographic process. The photoreceptor 100 has a cylindrical shape having an axis in the depth direction of the drawing, and rotates around the axis. Although illustration of the electrophotographic process is omitted, as is well known, a cleaning device and a static eliminator (not shown) are disposed on the upstream side in the rotation direction of the photoreceptor 100, and the electron-emitting device 10 is disposed on the downstream side. Established. Further, on the downstream side of the electron-emitting device 10, a laser scanning unit that irradiates a laser beam light-modulated with an image signal to form an electrostatic latent image of the image, and further, an electrostatic latent image is made visible by attaching toner. A developing section is provided. The exposed toner image is transferred onto a recording sheet conveyed from the conveying unit, and is fixed by the fixing unit to be printed. Further, since other configurations of the image forming apparatus are also known, description thereof will be omitted.

  The control unit 30 is preferably composed of a microcomputer having a CPU (Central Processing Unit). The control unit 30 outputs a control signal to the drive signal circuit unit 41 via the D / A port (output terminal of the D / A converter). Further, the control unit 30 outputs a bias generation signal to the bias circuit unit 42.

  The electron-emitting device 10 includes a lower electrode 11 that also serves as a substrate, an upper electrode 12 made of a conductive thin film, and a fine particle layer 13 that functions as an electron acceleration layer therebetween. The electron-emitting device 10 has a length corresponding to the axial length of the photoreceptor 100 and a predetermined width in the circumferential direction of the photoreceptor 100 so as to function as a charging device. In addition, it is preferable that a substrate member made of an insulating material such as a resin is separately laid on the lower layer of the lower electrode 11 for attachment to the electrophotographic process side.

  The fine particle layer 13 is composed of a conductive nano-sized conductive fine particle having a strong antioxidant effect, a nano-sized insulating substance (insulating fine particle) larger than the conductive fine particle, and a binder resin for fixing them. including. For example, when silica fine particles formed of silicon dioxide are used as the insulating fine particles, it can function as an electron trap. The same function can be obtained even when the fine particle layer 13 is constituted by a silicone resin made of siloxane and the above-described nano-sized conductive fine particles.

  The upper electrode 12 becomes an electron emission surface. The upper electrode 12 only needs to be a material having a function as an electrode and a function of oxidizing in the atmosphere. For example, a metal film made of gold or palladium is preferable. A contact point connected to the output signal line from the power supply unit 40 is formed at an appropriate position of the lower electrode 11 and an end portion of the upper electrode 12.

  The configuration of the power supply unit 40 will be described with reference to FIG. The drive signal circuit unit 41 includes an input circuit 411 to which a pulsed control signal having a predetermined duty ratio output from the D / A port (see FIG. 1) is input, an insulating circuit 412, and the electron-emitting device 10. A buffer circuit 413 and an inverting amplifier circuit 414 are provided as output units that output drive voltage signals to be driven. The input circuit 411 functions as a protection circuit, and includes a circuit that functions as a voltage limit and a current limit for an input signal.

  The insulating circuit 412 electrically insulates the input circuit 411 and the circuit on the buffer circuit 413 side, and transmits a control signal input to the input circuit 411 to the buffer circuit 413. As is well known, the insulating circuit 412 insulates the primary side and the secondary side through transformer coupling or optical coupling means (photo interrupter or the like). The insulation circuit 412 is designed to have insulation between the primary side and the secondary side and sufficient signal frequency band characteristics, and does not require an amplification function. The withstand voltage is a voltage (for example, about 800V) that can withstand a negative bias voltage (for example, −600V) from the bias circuit 42 side, and the frequency band performs duty control for a pulse train of 5 kHz, for example. In some cases, about 50 kHz is sufficient.

  The buffer circuit 413 is a known equal-magnification amplifier provided with an operational amplifier, and shapes the output signal of the insulating circuit 412 into a pulse train waveform. The inverting amplifier circuit 414 is a known inverting amplifier including an operational amplifier, an input resistor connected to at least an inverting input terminal, and a feedback resistor. The operational amplifier of the inverting amplifier circuit 414 is connected to, for example, a power supply of −24V and + 5V, and further has a configuration for adjusting an offset voltage between ± 5V input to the non-inverting input terminal, so that the wave height of 0 to −20V can be obtained. A level driving voltage signal (pulse train signal) is output.

  The bias circuit unit 42 includes a DC high-voltage generation circuit including a PWM circuit and an insulation circuit such as a transformer coupling. More specifically, the bias circuit unit 42 generates, for example, a 20 kHz and corresponding duty pulse signal (PWM signal) from the 0 and 1 signals from the control unit 30, and an input stage from the PWM circuit. A switching element such as a transistor is provided, and a known rectifying / smoothing circuit that rectifies and smoothes the voltage induced on the secondary side by connecting the output to the primary side of the step-up transformer. The frequency of the PWM signal is, for example, 20 kHz, and a DC bias voltage is output in the range of, for example, −500 V to −800 V by adjusting the duty ratio. By applying the bias voltage output from the bias circuit unit 42 to the drive signal circuit unit 41, the electron-emitting device 10 is floated with the bias voltage. By floating the electron-emitting device 10 with a negative bias voltage, an electric field with the electron-emitting device 10 having a negative potential with respect to infinity can be generated, and the emitted electrons that have jumped to the surface of the upper electrode 12 can fly outward. It is said.

  When a drive voltage signal is applied between the lower electrode 11 and the upper electrode 12 of the electron emitter 10 so that the upper electrode 12 has a positive potential, electrons supplied from the lower electrode 11 pass through the fine particle layer 13. Then, when moving to the upper electrode 12, some energy is given to the electrons, and the electrons are emitted from the upper electrode 12 to the outer space. Electron emission generates negative oxygen ions, which are supplied to the photoreceptor 100.

  As for the physical phenomenon leading to electron emission, there are many unclear points at the present time, and there is no estimation, but the Joule heat caused by the current flowing through the fine particle layer 13 and the local strong electric field region formed in the fine particle layer 13 Is expected to be involved. Generally, thermionic emission, photoelectron emission, field electron emission, secondary electron emission, and the like are known as physical mechanisms by which electrons are emitted from the inside of the solid to the outside. Thermal electron emission emits electrons into the vacuum by applying energy (work function) corresponding to the energy barrier between the Fermi level (level filled with electrons at zero K) and the vacuum level by heat. It is a phenomenon to make. In the field electron emission (cold field electron emission), the electric field strength formed between the metal surface and the vacuum is set to about 1 × 10 9 V / m, and the energy barrier is made very thin. Is a phenomenon in which is released into a vacuum. This phenomenon in which thermionic emission and field electron emission are mixed is called thermal field emission, and is considered to be the most appropriate mechanism as the electron emission mechanism of the electron-emitting device. That is, it is thought that electron emission is caused by a combination of a decrease in the apparent work function due to Joule heat, a decrease in the energy barrier due to a strong electric field, and a tunnel phenomenon.

  In FIG. 3, the control unit 30 includes an operation unit 31 that can be operated from the outside, and a storage unit 32. The operation unit 31 includes a mouse, a keyboard, or a touch panel, and performs an input operation from the outside, for example, power on / off, a print instruction, and the like. The storage unit 32 includes a ROM unit that stores a control program and necessary data, and a RAM unit that temporarily stores data being processed. The control signal storage unit 321 is a table that sequentially stores peak value data of a pulse train signal, which is a control signal output from the D / A port, for a predetermined time from the time when the electron emission device 1 is activated.

  The control unit 30 functions as a control signal output processing unit 301 and a bias voltage output processing unit 302 when the control program is activated. When the printing operation is instructed and the electron emission device 1 starts driving, that is, when the printing operation from the first sheet is started, the control signal output processing unit 301 receives the peak value data from the control signal storage unit 321 in a predetermined manner. The process of reading in order by time width (cycle) is performed. The bias voltage output processing unit 302 performs a process of outputting a signal for generating a bias voltage during the printing operation period.

  Reading of the peak value data from the control signal storage unit 321 is performed by sequentially reading with a time width corresponding to a predetermined duty ratio (for example, 50%) at a period corresponding to, for example, 5 KHz, and the D / A port Is output as a pulse train signal. The ON time of each pulse can be controlled by counting a reference clock having a frequency higher than 5 KHz by a value corresponding to the duty ratio.

  FIG. 4 shows the characteristics of the drive voltage signal Ve, the relationship between the output period and the rest period, and the relation between the element current Id flowing through the fine particle layer 13, and FIG. 5 shows the wave of the pulse train signal that is the drive voltage signal. 6 is a time chart showing the relationship between high value adjustment and print timing.

  First, as shown in FIG. 4, the drive voltage signal Ve rises from the drive start time t11, enters the pause period T1 at a time t12 when a predetermined output time elapses, and then continues when the period T1 elapses (time t21). Is output. Thereafter, the output period and the pause period are repeated. Thus, the electron emission efficiency is stabilized by providing the output period and the pause period T1. This is because, by providing the fine particle layer 13 functioning as an electron acceleration layer with a time during which the electric field for accelerating electrons is not applied (resting period T1), the electrons trapped in the electron acceleration layer can be removed, that is, lost. It depends on what is considered.

  Further, as indicated by the wavy line in FIG. 4B, the in-element current Id flowing through the fine particle layer 13 has an inrush current id ′ as indicated by a broken line during the drive start period when the level of the drive voltage signal is fixed. Flow to increase the amount of electron emission. Therefore, as shown in FIG. 4A, the in-element current Id flowing through the fine particle layer 13 is controlled to the stable current id by adjusting the level of the drive voltage signal to gradually increase during the drive start period. ing. By controlling the stable current id from the drive start period, the unnecessary electron emission amount Ie can be suppressed, and uniform charging on the photoconductor 100 is also possible. The rising characteristic of the level of the drive voltage signal can be set in advance from experience or experiment.

  FIG. 5 is a more specific time chart showing the drive voltage signal as a pulse train signal. The pulse train signals P1, P2, P3... Show how their peak values e1, e2, e3. Yes. As shown in FIG. 5B, the period T0 indicates a print period for one sheet. In the present embodiment, one pause is performed after a print period for three sheets (3 × T0), that is, an output period. The period is set so that the period T1 is interposed. Note that T0 = T1 may be satisfied. Further, as shown in FIG. 5C, the pulse signal Pi has a period τ0 and the ON period τ1 is ½ of the period τ0, that is, the duty ratio is 50%.

  When the number of print instructions is four or more, a pulse train signal is output as shown in FIGS. 5A and 5B. On the other hand, when the number of print instructions is one, for example, the first T0 is output. The operation ends with the pulse train signal of the period. Further, since the number of pulse train signals output in the transition period after the start of driving becomes enormous, the same peak value may be applied for several cycles in order to reduce the amount of data. Furthermore, after the transition period of the drive start has passed, the peak value of a fixed pulse train signal set in advance may be used on the assumption that the operation has shifted to a steady operation.

(Second Embodiment)
In the first embodiment, the pulse duty ratio has been described as 50%, but this value may be other values. In the second embodiment, pulse train signals having a plurality of types of duty ratios may be used. That is, a timer 33 is provided for measuring the elapsed time from power-off immediately before the image forming apparatus to power-on. The control signal storage unit 321 stores a selectable pulse train signal data table having a plurality of types of rising characteristics corresponding to the time from the previous power-off to the power-on. The data of the pulse train signal having a plurality of types of rising characteristics is not limited to each element, for example, those having different peak values and their changing gradients, those having different duty ratios (for example, 25%, 50%, 75%, etc.) A combination of different combinations can be used. This is because the ion supply amount obtained from the electron emitter 10 can be controlled also by the duty ratio.

(Third embodiment)
In this embodiment, a pulse train signal whose peak value gradually increases is used. However, as the third embodiment, the current of the upper electrode 12 is measured and compared with a threshold value obtained in advance from an experiment according to the measured current value. Thus, at least one of the peak value and the duty ratio may be adjusted so that the measurement current matches the threshold value. In this case, it is possible to cope with this by storing in advance in the control signal storage unit 321 pulse train signal data experimentally obtained corresponding to the difference from the threshold.

  Further, in the above-described embodiment, the peak value data of each pulse is stored in the drive signal storage unit 321, read out for a predetermined period corresponding to the duty ratio, and output as a pulse train signal from the D / A port. However, instead of this, theoretically, a CR time constant circuit may be used, and a circuit for pulse shaping the output waveform may be provided. In this case, the drive voltage data of each pulse is integration time data.

  In the above-described embodiment, the electron emission device 1 is described as being applied to a charging device that charges the surface of a photoreceptor of an electrophotographic image forming apparatus. However, the electron emission device 1 is combined with an electron beam curing device and a light emitter. It is also possible to apply to an image display device or an ion wind generator using an ion wind generated by emitted electrons.

  In addition, the description of the above-described embodiment is an example in all respects, and should be considered not restrictive. The scope of the present invention is shown not by the above embodiments but by the claims. Furthermore, the scope of the present invention is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.

DESCRIPTION OF SYMBOLS 1 Electron emission apparatus 10 Electron emission element 20 Drive part (drive means)
30 Control part (part of driving means)
31 Control signal output processor (part of drive means, selection means)
321 Control signal storage unit (storage means)
33 Timekeeping (Timekeeping means)
40 Power supply circuit (part of drive means)
41 Drive signal circuit section (part of drive means)
42 Bias circuit (part of drive means)
100 photoconductor

Claims (3)

A driving voltage signal between the first electrode and the second electrode for an electron-emitting device having a first electrode, a second electrode, and an intermediate layer stacked between the first electrode and the second electrode. In the electron emission device for emitting electrons from the second electrode by applying
A driving means, a timing means, a storage means, and a selection means,
The drive means outputs the drive voltage signal ,
The drive voltage signal is a pulse train signal;
The driving means gradually increases the peak value of the pulse train signal at the start of driving of the electron-emitting device, and provides a pause period during which the generation of the pulse train signal is interrupted for a predetermined time in the middle of the increase, It will continue to rise after the rest period ,
The time measuring means is for measuring a power stop period,
The storage means stores a plurality of types of rising characteristics of the drive voltage signal corresponding to the length of the power supply stop period,
The electron emission apparatus according to claim 1, wherein the selection means selects a drive voltage signal having a rising characteristic corresponding to a time measurement result of the time measurement means .   2. The electron emission device according to claim 1, wherein the pulse train signal has a predetermined duty ratio. The electron-emitting device according to claim 1 , wherein the electron-emitting device is disposed to face a photosensitive member that is a charged body .

Images