JP2001083779A - Electrostatic charging device, and image forming device adopting same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrostatic charging device making an always stable charge state obtainable by preventing soil owing to toner on a discharging electrode or the like, without adopting such a complicated structure letting a new charging unit successively to face to an image carrier, and the image forming device adopting the same. SOLUTION: In this electrostatic charging device 2, provided with a dielectric body layer 13, a dielectric electrode 12 laminated on one hand of the dielectric body layer, the discharging electrode 14 laminated on the other hand of the dielectric body layer, and moreover the discharging area generating the along surface discharge, being formed in the vicinity of the discharging electrode by applying the AC voltage between the dielectric electrode and the discharging electrode, this charging device is constituted so as to apply AC voltage on the discharging electrode in the specified timing. Preferably, the charging device is let to set, Vp-(p) of the AC voltage applying to the discharging electrode at the specified timing, being 0.6 kV to 2 kV, and the frequency of the above AC voltage, 1 kHz to 3 kHz.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device used in an image forming apparatus such as a copying machine or a printer using an electrophotographic system, and an image forming apparatus using the same.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine or a printer using this type of electrophotographic system, a roller charger or a corona charger is generally used as a charging device. The roller charger is configured such that a semiconductive roller is brought into direct contact with the photoreceptor and AC or DC is applied to the roller.
By applying a voltage and causing a discharge in a minute gap between the photoconductor and the roller, the photoconductor is charged.

[0003] However, the roller charger has a problem that the surface of the roller is stained by paper dust or toner and charging failure occurs because the roller is in direct contact with the photosensitive member. Further, the roller charger has a problem that it is necessary to accurately control the pressure between the roller and the photoreceptor in order to prevent uneven wear of the roller, which requires labor such as adjustment work. I have.

On the other hand, a corona charger typified by a scorotron performs charging in a non-contact state with a photoreceptor, and therefore has a feature that it is less likely to be soiled and is easier to install than a roller charger. However, this in the case of the corona charger, discharge wire silicone oil used as a toner release agent in the fixing unit is the SiO ₂ oxidized is contaminated, charging has a problem of uneven.

In order to solve such problems, for example, Japanese Patent Application Laid-Open Nos. Hei 5-333664 and Hei 8-24064 are disclosed.
The technology disclosed in, for example, Japanese Patent Application Publication No. 968 has already been proposed.

[0006] The charging device according to the above-mentioned Japanese Patent Application Laid-Open No. 5-333664 is provided with an electrode on a substrate made of glass or the like, further provided with a resistive film thereon, and by applying a voltage to the electrode, a voltage is applied to the surface of the resistive film. This is to generate planar corona discharge, generate ions, and charge the photoreceptor.

Further, the discharge device according to the above-mentioned Japanese Patent Application Laid-Open No. 8-240968 discloses a dielectric device, an induction electrode laminated on one surface of the dielectric layer, and a dielectric layer laminated on the other surface of the dielectric layer. By applying a voltage for generating charged particles in the vicinity of the discharge electrode between the induction electrode and the discharge electrode, and applying a voltage for controlling the charged particles to the discharge electrode. It is a device for charging a photoconductor.

[0008]

However, the prior art described above has the following problems. That is, in the charging device according to Japanese Patent Application Laid-Open No. 5-333664, the discharging surface is set at 0.
It is necessary to face each other at a minute interval of 3 mm to 1.0 mm. For this reason, this charging device basically has a problem that, although non-contact, paper dust or toner adheres to the discharge surface and charging becomes unstable. In addition, in the charging device according to this proposal, when the discharge surface becomes dirty, the lowermost one of the plurality of chargers arranged in a stacked state is removed, so that new chargers face the photoconductor one after another. As described above, although the configuration is devised, it is necessary to hold a plurality of chargers in a stacked state, and there is a problem in terms of size and cost.

Further, in the discharge device according to Japanese Patent Laid-Open Publication No. Hei 8-240968, an oscillating electric field acts on the attached toner by applying an alternating voltage for generating charged particles near the discharge electrode. Compared with the charging device disclosed in Japanese Unexamined Patent Publication No. Hei 5-333664, it has a feature that the toner is less contaminated.

However, Japanese Patent Application Laid-Open No. 8-24096 discloses
Even in the case of the discharge device according to Japanese Patent Publication No. 8 (1999) -1991, in a long-term print test, the floating toner is adsorbed by an extremely strong electric field formed at the edge of the opening of the discharge electrode located on the discharge surface, and the opening of the discharge electrode is opened. The problem is that the floating toner accumulates on the edges of the electrodes and the discharge becomes partially unstable.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide a complicated structure in which new chargers are successively opposed to an image carrier. SUMMARY OF THE INVENTION It is an object of the present invention to provide a charging device and an image forming apparatus using the charging device, which can prevent a discharge electrode or the like from being stained by toner without taking any measures and can always obtain a stable charging state.

[0012]

In order to solve the above-mentioned problems, the invention described in claim 1 provides a dielectric layer, an induction electrode laminated on one surface of the dielectric layer, and the dielectric layer. A discharge electrode stacked on the other surface of the body layer, and a discharge region formed near the discharge electrode and generating a creeping discharge by applying an alternating voltage between the induction electrode and the discharge electrode. By applying an alternating voltage between the induction electrode and the discharge electrode, to generate charged particles along with the creeping discharge in the discharge region, by applying a voltage to control the charged particles to the discharge electrode, A charging device for charging a member to be charged, wherein an alternating voltage is applied to the discharge electrode at a predetermined timing.

As the member to be charged, for example, a photosensitive drum which is an electrostatic latent image carrier is used. However, the present invention is not limited to this, and a dielectric drum or the like may be used. It may be a recording medium such as recording paper on which a toner image is transferred from a photosensitive drum or the like, which is an electrostatic latent image carrier.

At this time, when the charging device is used to uniformly charge the surface of an electrostatic latent image carrier such as a photosensitive drum, the charging device charges the photosensitive drum and the like. This constitutes a so-called primary charger. Further, when the charging device is used to transfer a toner image formed on an electrostatic latent image carrier such as a photosensitive drum onto a recording medium, the charging device applies the recording medium from the back surface. It constitutes a so-called transfer charger which is charged.

Further, according to the invention described in claim 2, the alternating voltage Vp applied to the discharge electrode at a predetermined timing.
−p is 0.6 kV to 2 kV, and the frequency of the alternating voltage is 1
2. The frequency is set to a frequency of 3 kHz to 3 kHz.
It is a charging device of the above.

Further, according to the present invention, a dielectric layer, an induction electrode laminated on one surface of the dielectric layer, and a discharge electrode laminated on the other surface of the dielectric layer When,
A discharge region formed in the vicinity of the discharge electrode to generate a creeping discharge by applying an alternating voltage between the induction electrode and the discharge electrode; and forming an alternating voltage between the induction electrode and the discharge electrode. Applying a voltage to control the charged particles by applying a voltage to control the charged particles to the discharge electrode, thereby generating a charged particle along the surface discharge in the discharge region. An image forming apparatus that forms an image on a recording medium by charging an image forming member by applying an alternating voltage to a non-image forming area to a discharge electrode of the charging device. is there.

Still further, the invention described in claim 4 is as follows.
The alternating voltage Vp-p applied to the discharge electrode is 0.6 k
V to 2 kV, and the frequency of the alternating voltage is 1 kHz to 3 kHz.
The image forming apparatus according to claim 3, wherein z is set to z.

Further, the invention according to claim 5 is characterized in that a toner having a sphericity of 100 to 120 is used as a toner for forming an image on the recording medium. An image forming apparatus according to any one of the preceding claims.

According to a sixth aspect of the present invention, the toner for forming an image on the recording medium has an average particle diameter of 3 to 3.
The image forming apparatus according to claim 3, wherein the thickness of the image forming apparatus is 10 μm.

Further, in the invention described in claim 7, the toner for forming an image on the recording medium has a glass transition point (Tg) of 60 ° C. or more. An image forming apparatus according to any one of the above.

[0021]

According to the charging device of the present invention having the above-described structure and an image forming apparatus using the same, an alternating voltage is applied to the discharge electrode of the charging device during non-image formation, and the toner adhered to the discharge surface of the discharge electrode is formed. By vibrating, the adhesion of the toner is weakened and the toner is returned to the charging member, thereby preventing the toner from adhering to the discharge surface and preventing image trapping due to uneven charging.

So far, the present inventors have investigated the toner attached to the grid of the scorotron and the toner attached to the surface of the roll charger. However, positive and negative charged toners are mixed, and It was difficult to remove the adhered toner.

However, when the surface corona discharge element to which the alternating voltage is applied is used as a charger, the present inventors have conducted intensive studies on toner adhering to the discharge surface of the charger, and as a result, the toner adhering to the discharge surface has been found. Has the same polarity as the charging polarity of the charger. Although the mechanism is not clear, it is supposed that when an alternating voltage is applied to the creeping corona discharge element, the charging polarity of the charger is increased even if toners of both positive and negative polarities are mixed due to the high ion density near the discharge surface. It is thought that the cause is that the toner is charged.

Based on this fact, according to the present invention, when a creeping corona discharge element to which an alternating voltage is applied is used as a charging device, the toner adhered to the discharging surface by the alternating electric field is removed from the member to be charged and the discharging surface of the charging device. The purpose is to reduce the adhesive force of the toner by vibrating between them, and to remove the toner from the discharge surface by an electric field. With this alternating voltage, if Vp-p is too low, the toner cannot be vibrated and the attached toner cannot be removed. On the other hand, if Vp-p is too high, the moving speed of the toner increases, so that the toner strongly collides with the discharge surface of the charging device, so that the adhesive force of the toner increases, and as a result, the toner cannot be removed. Thus, according to the experiments of the present inventors, Vp-p is 0.6 kV or more,
It is desirable to use at a value of kV or less, preferably 0.8 kV or more and 1.8 kV or less.

If the frequency of the alternating electric field is too low, the vibration of the toner becomes insufficient, and the toner removing property is reduced. If it is too high, the toner cannot respond to the frequency, and the removability is reduced. For this reason, according to the experiments of the present inventors, the frequency is used at a value of 1.0 kHz or more and 3 kHz or less, preferably 1.5 kHz or more.
It is desirable to use a value of 5 kHz or less.

[0026]

Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1 FIG. 2 shows an image forming apparatus to which a charging device according to Embodiment 1 of the present invention is applied.

In FIG. 2, reference numeral 1 denotes a photosensitive drum as an electrostatic latent image carrier.
Is driven to rotate at a predetermined speed in the direction of the arrow by a driving means (not shown). The surface of the photosensitive drum 1 is uniformly charged to a predetermined polarity and a predetermined potential by a primary charger 2 as a charging device according to the first embodiment of the present invention, and then subjected to image exposure 3. Then, an electrostatic latent image corresponding to the image information is formed. The electrostatic latent image formed on the photosensitive drum 1 is visualized by the developing device 4 to become a toner image. The toner image formed on the photosensitive drum 1 is transferred onto a recording sheet 6 by a transfer charger 5 as a charging device according to Embodiment 1 of the present invention, and then the toner image is transferred. The recording paper 6 thus separated is separated from the surface of the photosensitive drum 1 and the fixing device 7
Transported to The toner image is fixed on the recording paper 6 onto which the toner image has been transferred by heat and pressure by the fixing device 7, and the toner image is discharged out of the apparatus, thereby completing the image forming process.

After the toner image transfer step is completed, the residual charge on the surface of the photosensitive drum 1 is erased by the charge removing lamp 8 to prepare for the next image forming step.

The image forming apparatus according to this embodiment is a so-called cleaner-less image forming apparatus that does not use a cleaning device for removing untransferred toner remaining on the photosensitive drum 1.

Therefore, in this image forming apparatus, the toner in the developer used in the developing device 4 uses a toner having a high degree of sphericity to a certain extent as the toner in the developer.
The configuration is such that the adhesion of the toner to the surface is weakened, and the transfer rate of the toner image formed on the photosensitive drum 1 to the recording paper 6 is approximately 100%.

Further, by using the toner having a high degree of sphericity to some extent as described above, it is possible to suppress the toner from adhering to the charging device 2.

Next, the toner will be described. As the type of the toner, kneading, pulverizing, kneading and pulverizing the raw materials of the toner, or a kneaded and pulverized toner, or a polymerized toner obtained by suspension polymerization or emulsion polymerization using a reactive monomer having a vinyl group, or For example, a dissolved suspension toner in which the binder resin and the colorant are dissolved in an organic solvent, the resultant is dispersed in water, and granulation is performed can be used. From the viewpoint of toner removability, the spherical shape of these toners can be expected to be excellent in removability because of low adhesion and excellent removability. A processed spherical toner is desirable.

Here, as an index of toner spheroidization,
Specified by the degree of sphericity. An image of the toner shape taken with an FE-SEM (Electron Scanning Microscope) is sampled at random, and the image is analyzed by an image analyzer (Luzex: manufactured by Nicolet) and derived from the following formula. The numerical value obtained was used as the degree of sphericity. S = {π × (MXLNG) ² } / {4 × (ARE
A))｝ × 100 MXLNG: Absolute maximum length AREA: Projected area of toner

As the degree of sphericity of the toner approaches 100, it approaches a true sphere, and it can be said that the toner is in a state of almost a true sphere at 100 to 110. Such a spherical toner has a small contact area with the discharge surface of the charging device, and therefore has a small adhesive force and a stable removal performance as compared with a normal amorphous toner having a sphericity of about 130. Can be obtained.

The particle size of the toner particles has a large effect on the image quality. The larger the particle size, the coarser the image. Although there is no practical problem with toner having an average particle diameter of about 20 μm, it is desirable that the toner has an average particle diameter of 10 μm or less from the viewpoint of fine line resolution. However, as the toner diameter decreases, the physical adhesive force acting between the toner and the discharge surface of the charging device becomes dominant, and the removability of the toner decreases. Further, when the toner diameter is small, aggregation of the toner is apt to occur, which causes a problem in handling. From such a point, the toner used in the present invention preferably has an average particle diameter of 3 μm.
m or more and 10 μm or less are used.

Further, the following are used as the main binder resin for the toner. For example, polystyrene,
Styrene-propylene copolymer, styrene-butadiene copolymer, styrene-vinyl chloride copolymer, styrene-vinyl acetate copolymer, styrene-acrylate copolymer, styrene-methacrylate copolymer, polyester resin And a polyurethane resin and the like. If necessary, a single resin or a mixture of a plurality of binder resins is used.

In addition, a wax component such as an olefin homo- or copolymer such as ethylene and propylene and a carnauba wax may be added from the viewpoint of enhancing the releasability from the roll and preventing toner offset during heat roll fixing. At this time, the amount of the wax component added is preferably 0.5 wt% or more and 10 wt% or less based on the toner.
If the amount is less than this, the effect of the wax component will not be obtained. On the other hand, if the addition amount is larger than this, the toner is likely to be deformed by heat, and the chargeability of the developer is changed, so that a stable image density cannot be obtained.

Further, from the viewpoint of increasing the mechanical strength of the toner and increasing the cohesive strength of the toner during heat roll fixing to prevent toner offset, a weight average molecular weight of 10% is used.
It may contain a high molecular weight polymer of 000 or more or a crosslinked polymer. The content of the high molecular weight polymer or the crosslinked polymer is desirably 60 wt% or less based on the toner. If the content is higher than this, the toner does not melt and fix well during fixing, and a problem of poor fixing occurs.

Although the glass transition temperature Tg of the toner at this time is too low, it tends to adhere to the discharge surface and cannot be removed. It is considered that, in addition to the temperature of the discharge surface of the surface discharge device reaching about 50 ° C. during continuous printing, the heat generated when the toner collides with the discharge surface due to the vibration caused by the alternating electric field influences. Therefore, in the present invention, Tg
Is 60 ° C. or higher.

The present invention is not limited to the developing method, and any developing method such as magnetic one-component development, two-component development, non-magnetic one-component development, and two-component development may be used. As for the colorant of the toner, carbon black, nigrosine, graphite, magnetite, and philite are used as the black type.

The chromatic colors include (yellow or orange pigments) CI Pigment Orange 31, CI Pigment Orange 43, CI Pigment Yellow 21, CI Pigment Yellow 14, CI Pigment Yellow 17, CI Pigment Orange 93,
CI Pigment Yellow 94, CI Pigment Yellow 138, CI Pigment Yellow 174 (magenta or red pigment) CI Pigment Red 5, CI Pigment Red 48: 1, CI Pigment Red 53: 1, CI Pigment Red 57: 1, C.I.
I. Pigment Red 122, CI Pigment Red 12
3, CI Pigment Red 139, CI Pigment Red 144, CI Pigment Red 149, CI Pigment Red 166, CI Pigment Red 177, CI Pigment Red 178, CI Pigment Red 222 (Sian or green pigment) CI Pigment Green 7, CI Pigment Blue 15: 1, CI Pigment Blue 15: 2, CI Pigment Blue 15: 3,
A known coloring agent such as CI Pigment Blue 60 is used.

The content of the toner colorant is preferably 0.5% by weight or more and 20% by weight or less based on the toner. If the amount is less than 0.5% by weight, the color developability is insufficient and a clear image cannot be obtained. If the content is more than 20% by weight, unevenness in image quality occurs due to poor dispersion of the colorant in the toner.

Further, a magnetic fine powder may be contained in order to impart magnetism to the toner. In the case of two-component development, examples of the carrier include iron, ferrite, and a magnetic particle carrier made of metal particles such as magnetite, and a polymer carrier obtained by mixing a magnetic powder with a polymer. Is also good. Since the polymer carrier generally has lower magnetization than the magnetic particle carrier, a soft and high-density magnetic brush can be formed, and a high-quality image can be obtained. In addition, there is an advantage that the possibility of damaging the surface of the electrostatic latent image carrier when adhered to the electrostatic latent image carrier is reduced. Further, since the specific gravity of the carrier is small, the mass of the carrier is also small, so that there is an advantage that when the developer is mixed in the developing device, the developer with a small stress on the toner and a long life can be provided. on the other hand,
The magnetic particle carrier has a large carrier mass due to the large specific gravity of the carrier, and the stress on the toner increases when the developer is mixed in the developing device. On the other hand, the charge of the developer is rapidly raised. There are advantages. Therefore, the carrier may be properly used depending on the performance required for the developer.

Regarding the particle size of the carrier, the smaller the particle size, the denser the magnetic brush. Average particle size of 60
When the thickness is less than μm, the effect starts to appear. However, when the carrier has a small particle diameter such that the average particle diameter is less than 35 μm, the magnetic binding force of the carrier is weakened, and the carrier adheres to the latent image carrier. From these facts, the carrier particle diameter is such that the average particle diameter is 35 μm or more,
A carrier of 0 μm or less is desirable.

The charge amount of the toner when the developer is obtained by mixing the toner and the carrier. If the charge amount is too high, the adhesion of the toner to the carrier becomes too high, and the toner is not developed this time. And a phenomenon such as not being transferred occurs. If the charge amount is too low, the adhesion of the toner to the carrier becomes too weak, and a toner cloud due to free toner is generated, which causes fogging in printing. If the charge amount of the toner in the developer is specified from the viewpoint of the developing property and the transfer property of the toner, the absolute value is 5 to 50 μm.
C / g, preferably in the range of 10 to 40 μC / g.

The charging device according to the present embodiment comprises a dielectric layer, an induction electrode laminated on one surface of the dielectric layer, and a discharge electrode laminated on the other surface of the dielectric layer. And a discharge region formed in the vicinity of the discharge electrode and generating a creeping discharge by applying an AC voltage between the induction electrode and the discharge electrode, wherein an alternating current is applied between the induction electrode and the discharge electrode. By applying a voltage, a charged particle is generated along with the surface creeping discharge in the discharge region, and a voltage for controlling the charged particle is applied to a discharge electrode, thereby charging a member to be charged. An AC voltage is applied to the electrodes at a predetermined timing.

The charging device according to the first embodiment is used as the primary charger 2 and the transfer charger 5.

This charging device 10 is, as shown in FIG.
It is formed in an elongated flat plate shape and includes an insulating substrate 11 made of ceramic or the like. This insulating substrate 11
On the top, as shown in FIG. 1 and FIG.
It is formed linearly in the center in the width direction along the longitudinal direction. On the insulating substrate 11 on which the induction electrode 12 is formed, a dielectric layer 13 is formed in a state of being uniformly laminated, and on this dielectric layer 13, the discharge electrode 1 is formed.
4 are formed linearly along the longitudinal direction. As shown in FIG. 1, the discharge electrode 14 is provided with a discharge region 15 formed of a space at the center in the width direction. Further, as shown in FIG. 4, the discharge electrode 14 has a comb-teeth shape in which the side close to the induction electrode 12 is divided.
The tip of the comb tooth is arranged so as to partially overlap the induction electrode 12.

The charging device 10 having the above-described configuration includes an induction electrode 12, a dielectric layer 13, and a discharge electrode 1 on a ceramic substrate 11.
4 can be easily formed using thick film printing technology. As the electrode material, a printing metal paste such as gold, tungsten, or nickel is used, and as the dielectric layer material, a printing insulating paste such as alumina or glass is used. As an example of the size of the component, the thickness of the induction electrode 12 is about 1 to 40 μm. If the thickness is too small, the wiring resistance is large and a power loss is generated. If the thickness is too large, a printing step after the next layer after the printing of the induction electrode 12 is caused, and uniformity of the layer thickness cannot be obtained. . Width d
Is about 60 to 500 μm, and is preferably set to 100 to 200 μm from the viewpoint of productivity and discharge efficiency. The thickness of the dielectric layer 13 is about 10 to 50 μm. If it is too thin, pinholes are likely to be generated at the time of manufacture, causing a decrease in dielectric strength, and if it is too thick, the voltage required for starting discharge becomes high. Therefore, it is preferably set to 20 to 30 μm. The width w of the divided portion forming the discharge region 15 of the comb-shaped convex discharge electrode 14 is about 60 to 500 μm, and is preferably 100 to 20 μm in view of manufacturing uniformity in the printing process.
It is set to 0 μm. The pitch L of the comb-toothed electrodes of the discharge electrode 14 is set to 0.1. It is about 1 to 5 mm, and preferably 0.3 to 1 mm from the viewpoint of charging uniformity. Further, the width of the child-like portion sandwiching the insulating layer between the discharge electrode 14 and the induction electrode 12 is set to 10 to 100 μm.

As shown in FIG. 1, between the induction electrode 12 and the discharge electrode 14 of the charging device 10,
6 applies an AC voltage, and further applies a bias voltage to the discharge electrode 14 by a DC power supply 17. The AC voltage applied by the AC power supply 16 is several kHz to several MH.
z, preferably 100 Hz to 2 M from the generation rate of charged particles
And a high-frequency high voltage of 1 to 3 kVp-p at a frequency of 1 Hz. When an AC voltage is applied to these electrodes with the dielectric layer 13 interposed therebetween, as shown in FIG. Discharge region 1 forming a pair of discharge electrodes 14 divided in a tooth shape
A creeping discharge 20 along 5 occurs, and positive and negative charged particles are generated in the vicinity thereof. When a negative voltage is applied as a bias voltage, only negatively charged particles can be extracted.

In the charging device 10, the distance between the discharge electrode 14 and the surface of the photosensitive member is set to 0.4 to 0.6 mm. When the surface potential of the photosensitive member 1, which is the member to be charged, becomes substantially equal to the bias voltage, the charging is performed. The particles are no longer withdrawn, and charging ends. When the recording speed is 300 mm / s, the bias voltage 17 is −900 V using the OPC photoconductor for negative charging.
, The surface of the photoreceptor could be charged to -830 V, and a good image sample having relatively no unevenness could be obtained.

In this embodiment, as shown in FIG. 1, in a non-image area during a printing operation or a non-printing operation, an AC voltage is applied to a discharge electrode 14 of the charging device 10 by an AC power supply 18 to switch the same. 19 to be selectively applied. The non-image area at the time of the printing operation or the non-printing operation is, for example, an area where a sheet is interposed when printing a plurality of sheets, or even when printing one sheet, the photosensitive drum 1 is rotating. However, any area may be used as long as it is a non-image forming area that does not affect the image area, such as an area before and after printing.

Experimental Example 1 Next, the present inventors prototyped an image forming apparatus using a charging device as shown in FIG. 1 and FIG. An experiment was conducted to confirm the contamination of the discharge electrode 14 of the device 10.

At this time, the following two-component developer was used as the developer. (Carrier) Styrene-acrylic copolymer (number average molecular weight: 23,000, weight average molecular weight: 98,000, T
g = 78 ° C.) 30 wt%, carbon black (basic carpon black: ph = 8.5) 3 wt%, granular magnetite (maximum magnetization 80 emu / g, particle size 0.5 μm) 6
7 wt% was kneaded, crushed and classified to prepare a carrier having an average particle size of 45 μm. The relative of the carrier was 2.2. The average particle size is a value measured by Microtrac (manufactured by Nikkiso Co., Ltd.). The charging polarity is positive. The electrical resistance is
It was 10 ¹² Ωcm. (Toner) Polyester (number average molecular weight: 4,300,
Weight average molecular weight: 9,800, Tg = 56 ° C) 90 wt
%, And 10 wt% of carbon black were kneaded and pulverized, and then classified to prepare colored particles having an average particle size of 7 μm and a sphericity of 125. The average particle size is a value measured by a Coulter counter (manufactured by Coulter Inc.). The Tg of the toner at this time is 5
9 ° C.

Next, a hydrophobicity of 60 having an average particle diameter of 20 nm,
Silica fine particles having a volume resistivity of 10 ¹² Ωcm were externally added to the above-mentioned colored particles to obtain a toner. The coverage of the silica fine particles with respect to the colored particles is 80%.

The coverage was determined as follows. The coverage is f (%), the average particle size of the colored particles is dt (m), the average particle size of the fine particles is da (m), the specific gravity of the colored particles is βt,
When the specific gravity of the fine particles is βa and the weight of the fine particles is Wa (kg), f (%) = {3 × dt × ρt × Wa} / {2π × da
× ρa × Wt｝ × 100 The specific gravity of the colored particles was 1.1, and the specific gravity of the silica particles was 2.2.

(Developer) A sample developer was prepared by mixing the toner and the carrier. At this time, the toner concentration in the developer (TC: Toner Concentrati)
on) was 10%. TC was determined as follows. TC (wt%) = (toner weight) / ｛(toner weight) +
(Carrier weight) x 100

3 g of the developer thus adjusted is applied to the bottom area 3
cm ^2, placed in a glass bottle cylindrical height of 3.5 cm, where the amplitude 30 cm, mixes 3 minutes at a rate of 30 reciprocating in one minute was measured charge amount of the toner at that time in a blow-off method, the toner The charge amount is 110 to -20μ
C / g range. These developers were loaded into the developing device 3 and used for development.

Further, to the primary charging device 2 as the charging device 10, an AC voltage 18 in which a bias voltage 17 is superimposed with 1900 V in a portion corresponding to an image portion and 1900 V in a portion corresponding to a non-image portion is applied. Then, a continuous print test of 100 kPV was performed. Note that no voltage is applied to the induction electrode 12 in a portion corresponding to the non-image portion. Further, the alternating voltage is set to 0.1 V by Vp in increments of 0.2 kV.
2 kV to 3 kV, frequency is 0.5 kHz steps,
The frequency was changed from 5 kHz to 10 kHz.

FIG. 6 is a table showing the results of the above experiment.
As a result, as apparent from FIG. 6, the alternating voltage is Vp
When printing is performed under the condition that 1p is 0.6 kV or more and 2 kV or less and the frequency is 1 kHz or more and 3 kHz or less, although streak-like density unevenness occurs slightly, it is a level that does not cause a problem in practical use. A small amount of the toner adhered to the discharge surface of the charging device 2 later. On the other hand, under the other conditions, streaky density unevenness was observed, and toner adhered to the discharge surface of the charger after printing, confirming that the position corresponded to the streaky density unevenness position. Was done.

As a comparative example, using the above apparatus,
When continuous printing was performed with the bias voltage kept at 1900 V, the print test was stopped because density unevenness became noticeable at around 50 kPV. When the discharge surface of the charging device 2 at this time was observed, toner adhesion was observed in some places, and it was confirmed that the toner adhesion portion corresponded to the position where the uneven density of the streaks occurred.

Experimental Example 2 The colored particles obtained by kneading and pulverizing and classifying the above Experimental Example 1 were
By hot air treatment, average particle size 7μm, sphericity 1
Colored particles of 00, 110, and 120 were subjected to an external additive treatment under the same conditions as in Experimental Example 1 to obtain a toner. The same test as in Experimental Example 1 was performed, and similar results were obtained. However, 100kPV
(1 kPV = 1000 prints), no line-like unevenness occurred at all, and there was no toner contamination on the discharge surface of the charging device 2.

Experimental Example 3 In the above Experimental Example 2, the polyester resin as the toner binder was changed to one having a number average molecular weight of 4,800, a weight average molecular weight of 11,000, and Tg = 59 ° C. The classified colored particles are subjected to high-temperature hot-air treatment to obtain an average particle size of 7 μm and a degree of sphericity of 100, 110, 12
0 colored particles. The Tg of the toner at this time is 60
° C. An external additive treatment was performed under the same conditions as in Experimental Example 1, and a toner was subjected to the same test as in Experimental Example 1 to obtain similar results. However, it was confirmed that no line-like unevenness occurred at 100 kPV (lkPV = 1000 prints), and no toner contamination on the discharge surface of the charging device 2 occurred.

[0065]

As described above, according to the present invention, it is possible to prevent the discharge electrodes and the like from being contaminated by the toner without always having a complicated structure in which new chargers are successively opposed to the image carrier, and to maintain a stable state. It is possible to provide a charging device capable of obtaining a charged state and an image forming apparatus using the charging device.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of a charging device according to the present invention.

FIG. 2 is a configuration diagram showing an image forming apparatus to which the charging device according to the present invention is applied.

FIG. 3 is a plan view showing Embodiment 1 of the charging device according to the present invention.

FIG. 4 is an enlarged view of a main part of FIG.

FIG. 5 is an explanatory diagram showing a discharging state of the charging device.

FIG. 6 is a table showing experimental results.

[Explanation of symbols]

1: photosensitive drum (charged member, electrostatic latent image carrier), 2
(10): charging device, 11: insulating substrate, 12: induction electrode, 13: dielectric layer, 14: discharge electrode, 18: AC power supply.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Kazuhiro Hayashi 2274 Hongo, Ebina-shi, Kanagawa Fuji Xerox Co., Ltd. (72) Inventor Seiji Miyauchi 2274 Hongo, Ebina-shi, Kanagawa Fuji Xerox Co., Ltd. F-term (Reference) 2H003 BB11 CC01 EE03 EE08 EE12 EE16

Claims (7)

[Claims] 1. A dielectric layer, an induction electrode laminated on one surface of the dielectric layer, a discharge electrode laminated on the other surface of the dielectric layer, and a discharge electrode formed near the discharge electrode. A discharge region that generates a creeping discharge by applying an alternating voltage between the induction electrode and the discharge electrode, and applying an alternating voltage between the induction electrode and the discharge electrode to form the discharge region. In the charging device for charging the member to be charged by applying a voltage for controlling the charged particles to the discharge electrode by generating charged particles along with the creeping discharge, an alternating voltage is applied to the discharge electrode at a predetermined timing. A charging device. 2. The method according to claim 1, wherein Vp-p of the alternating voltage applied to the discharge electrode at a predetermined timing is set to 0.6 kV to 2 kV, and the frequency of the alternating voltage is set to 1 kHz to 3 kHz. Charging device. 3. A dielectric layer, an induction electrode laminated on one surface of the dielectric layer, a discharge electrode laminated on the other surface of the dielectric layer, and a discharge electrode formed near the discharge electrode. A discharge region that generates a creeping discharge by applying an alternating voltage between the induction electrode and the discharge electrode; and applying an alternating voltage between the induction electrode and the discharge electrode to form the discharge region. Generating charged particles along with the surface creeping discharge, and applying a voltage for controlling the charged particles to the discharge electrode, thereby using a charging device for charging the image forming member, and charging the image forming member by the charging device. An image forming apparatus for forming an image on a recording medium, wherein an alternating voltage is applied to a discharge electrode of the charging device to a non-image forming area. 4. An alternating voltage Vp applied to the discharge electrode.
−p is 0.6 kV to 2 kV, and the frequency of the alternating voltage is 1
4. The frequency is set in a range of kHz to 3 kHz.
The image forming apparatus as described in the above. 5. The image forming apparatus according to claim 3, wherein a toner having a sphericity of 100 to 120 is used as a toner for forming an image on the recording medium. 6. The image forming apparatus according to claim 3, wherein an average particle diameter of a toner for forming an image on the recording medium is 3 to 10 μm. 7. The image forming apparatus according to claim 3, wherein a glass transition point (Tg) of a toner for forming an image on the recording medium is 60 ° C. or higher.