JP2000081749A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable satisfactory electrification and image formation by restricting excessive supply of electrification acceleration particles to the electrifying member of a contact electrifier, thereby steadily supplying it. SOLUTION: The contact electrifier has the electrifying roller 2 holding electrification acceleration particles (m) constituted of conductive particles, contacts a photoreceptive drum 1 via the electrification acceleration particles, and injects charges into the photoreceptive drum 1 by means of an applied electrification bias, thereby electrifying it. The developing unit 3 stores magnetic toner 31, in which the electrification acceleration particles (m) are mixed, attaches the electrification acceleration particles (m) to the photoreceptive drum 1 from a developing sleeve 32 in a developing part opposite the photoreceptive drum 1, and carries and supplies the electrification acceleration particles (m) to the electrifying roller 2 by means of the photoreceptive drum 1, thereby holding it there. In order to accelerate the supply of the electrification acceleration particles (m) to the electrifying roller 2, an amount of the charges after the restriction of toner 31 on the developing sleeve 32 by an elastic blade 34 is kept at 4-12 μC/g.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as an electrophotographic system or an electrostatic recording system, an image carrier such as an electrophotographic photosensitive member or an electrostatic recording dielectric is uniformly charged to a required polarity and potential (opposite). Corona chargers have been used to charge to polarity (ie, also include static elimination).

[0003] A corona charger is a non-contact type charging device, which is provided with a discharge electrode such as a discharge wire and a shield electrode surrounding the discharge electrode, and has a discharge opening portion in non-contact with an image carrier as a member to be charged. The surface of the image bearing member is charged by exposing the surface of the image bearing member to a discharge current (corona shower) generated by applying a high voltage to the discharge electrode and the shield electrode.

In recent years, as a charging device for a member to be charged such as an image carrier, there are many advantages such as low ozone and low power as compared with a corona charger, so that many contact-type charging devices have been proposed and put into practical use. Have been.

In a contact charging device, a charging member such as a roller, a fur brush, a magnetic brush or a blade is brought into contact with a member to be charged such as an image carrier, and a predetermined charging bias is applied to the charging member. , The surface of the member to be charged
It is charged to a potential.

In contact charging, there are two types of charging mechanisms, (1) discharge charging mechanism and (2) injection charging mechanism, and each characteristic appears depending on which one is dominant.

(1) Discharge Charging Mechanism The surface of the member to be charged is charged by a discharge phenomenon occurring between the charging member and the member to be contacted with the member. Since the discharge charging mechanism has a fixed discharge threshold between the contact charging member and the member to be charged, it is necessary to apply a voltage higher than the charging potential to the charging member. Although the amount of generation is much smaller than that of the corona charger, the generation of discharge products such as ozone is unavoidable in principle, so that the harmful effects of the discharge products are unavoidable.

(2) Injection Charging Mechanism By injecting charges from a medium resistance charging member into a member to be contacted with the charging member, basically without using a discharge phenomenon,
It is a direct charging mechanism that charges an object to be charged, and is also called a direct charging mechanism. In this method, charging is performed by injecting charges to the surface of the member to be charged, so that the member to be charged can be charged to a potential corresponding to the applied voltage even when the voltage applied to the contact charging member is equal to or lower than the discharge threshold. it can. Since this injection charging mechanism does not involve generation of a discharge product, no adverse effect is caused by the discharge product.

However, because of direct charging, the contact property of the charging member with the member to be charged greatly affects the charging property. Therefore, it is necessary to form the contact charging member more densely and to have a large speed difference from the member to be charged so as to contact the member to be charged with high frequency.

Conventionally, a charging roller, a fur brush, a magnetic brush or the like has been used as a contact charging member. Among them, the charging roller is made of a conductive or medium-resistance rubber material or foam, and these are laminated to have desired characteristics. The charging roller is
The charged member has elasticity in order to obtain a constant contact state with the photosensitive member, and therefore has a large frictional resistance. In many cases, the photosensitive member is driven or driven with a slight speed difference. Therefore, even if the photosensitive member is directly charged, it is inevitable that insufficient contact, roller-shaped charging unevenness, and charging unevenness due to the adhesion of the photosensitive member occur. Dominant.

FIG. 7 is a graph showing the charging efficiency in contact charging. The horizontal axis represents the bias applied to the charging member, and the vertical axis represents the charging potential of the photosensitive member obtained at that time.

The charging characteristic of the charging roller when a DC voltage is applied is as shown by a straight line A in FIG.
Charging has started after the discharge threshold value of V has passed. Therefore, when charging to -500 V, a DC voltage of -1000 V is applied, or an AC voltage of 1200 V between peaks is applied so as to always have a potential difference equal to or greater than the discharge threshold in addition to the DC voltage of -500 V. Then, a method of converging the photosensitive member potential to the charged potential is generally used.

More specifically, when a charging roller is brought into contact with an OPC photosensitive member having a thickness of 25 μm to be charged, a voltage of about 640 V or more is applied to the charging roller.
The surface potential of the photoconductor starts to rise, and thereafter, the surface potential of the photoconductor increases linearly with a slope of 1 with respect to the applied voltage. Assuming that the threshold voltage is a charging start voltage Vth, in order to obtain the surface potential Vd of the photoconductor required for electrophotography,
The charging roller is required to apply a DC voltage of Vd + Vth which is more than necessary.

The method of charging the photosensitive member by applying only the DC voltage to the charging member in this manner is called a DC charging method. However, in the DC charging method, the resistance of the charging member fluctuates depending on environmental fluctuations, and the charging start voltage Vth fluctuates when the film thickness changes due to abrasion of the photoconductor. Was difficult.

Therefore, in order to further uniform the charger, a DC voltage corresponding to a desired surface potential Vd is reduced to 2 × V, as disclosed in Japanese Patent Application Laid-Open No. 63-149669.
A voltage that superimposes an AC component having a peak-to-peak voltage of at least th is applied to the charging member to directly charge the image carrier.
A C charging method is used. This utilizes the leveling of the potential by the AC voltage. The potential of the image carrier converges to Vd, which is the center of the peak of the AC voltage, and is not affected by disturbances such as the environment.

However, even in such contact charging, the essential charging mechanism uses a discharge phenomenon from the charging member to the photosensitive member. Therefore, as described above, the voltage required for charging is limited to the photosensitive member. Requires a voltage higher than the surface potential Vd + discharge threshold voltage, and thus a small amount of ozone is generated. In addition, the generation of vibration noise (AC charging noise) between the charging member and the photoconductor due to the electric field of the AC voltage, the deterioration of the photoconductor surface due to the discharge, and the like become remarkable, and this has been a new problem.

In the fur brush charging, a fur brush provided with a conductive fiber brush as a contact charging member is used, the conductive fiber brush is brought into contact with a photosensitive member as a member to be charged, and a predetermined charging bias is applied. The surface of the photoreceptor is charged to a predetermined potential and polarity. The fur brush charging is also dominated by the discharge charging mechanism (1).

As the fur brush charger, a fixed type and a roll type are in practical use. The fixed type is made by folding a medium-resistance fiber into a base cloth, bonding this into a pile, and bonding it to the electrode.
It is created by winding a pile into a cored bar.

A fiber density of about 100 fibers / mm ² can be obtained relatively easily, but in order to perform sufficiently uniform charging by direct charging, the fiber density of this level is insufficient in terms of contact. However, in order to perform sufficiently uniform charging by direct charging, it is necessary to provide a speed difference to the photoreceptor by a mechanical mechanism, which is not practical.

The charging characteristics of the fur brush are shown in FIG.
Therefore, in the case of the fur brush, both the fixed type and the roll type apply a high charging bias and perform charging using a discharge charging mechanism.

The magnetic brush used for charging is a charging member formed by brushing conductive magnetic particles by magnetically constraining them with a magnet roller or the like. A bias is applied to charge the surface of the photoconductor to a predetermined polarity and potential. This magnetic brush charging is dominated by the injection charging mechanism of (2). Uniform direct charging becomes possible by using conductive magnetic particles having a particle size of 5 to 50 μm and providing a sufficient speed difference between the magnetic brush and the photosensitive member.

With respect to the charging characteristics of the magnetic brush, as shown by a straight line C in FIG. 7, it is possible to obtain a charging potential substantially proportional to the applied bias. However, there are also problems such as a complicated device configuration and magnetic particles falling off and adhering to the photoreceptor.

Japanese Patent Application Laid-Open No. Hei 6-3921 proposes a method of injecting charges into a charge holding member such as conductive particles in a trapping order or a charge injection layer on the surface of a photoreceptor and injecting and charging the surface of the photoreceptor. ing. Since the discharge phenomenon is not used, the voltage required for charging is only the desired potential of the photoconductor surface, and no ozone is generated. Furthermore, since no AC voltage is applied, there is no generation of charging noise, and this is an excellent ozone-less and low-power charging system as compared with the roller charging system.

In the transfer type image forming apparatus,
Transfer residual toner remaining on the photoreceptor after the transfer is removed from the surface of the photoreceptor by a cleaner, and is discarded as waste toner. It is desirable that the waste toner does not come out from the viewpoint of environmental protection.

Accordingly, there has emerged a cleaner-less image forming apparatus of the simultaneous cleaning with development type, in which the cleaner is eliminated and the transfer residual toner is collected at the time of development by a developing device. In this simultaneous cleaning with development, the transfer residual toner on the photoconductor is recovered by a fog removal bias (a potential difference between a direct voltage applied to the developing device and the surface potential of the photoconductor, a fog removal potential difference Vback) at the time of development after the next step. Things.

According to this method, since the transfer residual toner can be collected in the developing device and reused in the next process and thereafter, waste toner can be eliminated, and troublesome maintenance can be reduced. Further, since the cleaner can be eliminated, the advantage in terms of space is great, and the image forming apparatus can be significantly reduced in size.

In the cleaner-less method, as described above, the transfer residual toner is not removed from the surface of the photoreceptor by a dedicated cleaner, but the photoreceptor is passed through a charging means to reach a developing device to use a developing process. Therefore, when a contact charging device is used as a charging unit, in a state where an insulating toner is interposed in a contact portion between the photosensitive member and the charging member,
The challenge is how to charge the photoreceptor.

In the above-described charging with a charging roller or a fur brush, a method is often used in which a transfer residual toner on a photoreceptor is diffused and non-patterned, and a large bias is applied to charge by discharging. In magnetic brush charging, conductive magnetic particles, which are powders, are used as the contact charging member, so there is an advantage that the magnetic brush can flexibly contact and charge the photoconductor, but the device configuration is complicated,
The harmful effects of the drop of the conductive magnetic particles constituting the magnetic brush are great.

In the contact charging device, a mechanism for applying powder to the contact surface of the charging member with the member to be charged is disclosed in Japanese Patent Publication No. 7-994 in order to prevent charging unevenness and perform stable and uniform charging.
No. 42, the charging member is driven to rotate by the member to be charged, and the generation of discharge products such as ozone is significantly reduced as compared with a corona charger such as a scorotron. As in the case of the roller charging described above, the device still mainly has a discharge charging mechanism. In particular, in order to obtain more stable charging uniformity, a DC voltage + AC voltage is applied, so that more discharge products are generated. Therefore, when the contact charging device is used for a long time,
When a cleaner-less image forming apparatus is used for a long time, adverse effects such as image deletion due to discharge products are likely to occur.

[0030]

When an injection charging mechanism is used, conductive particles are applied or mixed into a charging member as charging promoting particles in order to improve contact and promote charging. According to this, it is possible to obtain close contact, it is difficult to cause poor charging due to insufficient contact, and it is possible to obtain good chargeability.

However, in some cases, the charge accelerating particles on the charging member are reduced in the charging portion, and the charging property is reduced. For this reason, it is necessary to newly supply the charge-promoting particles, and a system in which the supply of the charge-promoting particles is performed from the inside of the developing device is advantageous for downsizing because the developing device can be used and no special supply means is required. .

However, in the supply of the charge-promoting particles from the developing device, when the charge-promoting particles are excessively supplied to the charging member, image formation may be hindered. Further, even when the charge-supplying particles are not stably supplied, the chargeability is reduced.

An object of the present invention is to provide an image forming apparatus which can stably supply charge-promoting particles to a charging member of a contact charging device while suppressing excessive supply thereof, and perform good charging and image formation. It is to provide a device.

[0034]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention relates to a method in which a charging member carrying charge-promoting particles made of conductive particles is brought into contact with a rotating image carrier via the charge-promoting particles, and the image bearing member is charged by a charging bias applied to the charging member. A contact charging means for charging the image carrier, and a developing device in which an electrostatic latent image obtained by imagewise exposing the charged image carrier is carried on a developer carrier and transported to a developing section opposed to the image carrier. An image forming apparatus including: a developing unit that stores the developer; the developing unit includes a charge accelerating particle mixed with the developer, and the charge accelerating particle is loaded with the developer in the developing unit. The toner adheres to the image carrier from the body, is conveyed to the charging member via the image carrier, and supplies the charge-promoting particles to the charging member, and the developer on the developer carrier The charge amount after regulation by the elastic regulation member is 4 to 12 μC /
g is maintained.

According to the present invention, preferably, the charge-promoting particles have a particle size of 1/2 or less of the developer, a specific resistance of 10 ¹² Ωcm or less, and more preferably a specific resistance of 10 ¹⁰ Ωcm or less. Ωcm or less. According to the present invention, the developer carrier is provided by providing a resin layer in which conductive particles are dispersed on the surface of the developer carrier, or by providing a surface layer in which conductive particles are dispersed on the surface of the elasticity regulating member. The amount of charge of the developer on the body after regulation by the elastic regulation member is 4
１２12 μC / g can be maintained.

[0036]

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

Embodiment 1 In the present invention, a charge accelerating particle is mixed into a developer, and the charge accelerating particle is charged from a developing device to a charging member which contacts the photoreceptor via the charge accelerating particle to charge the photoreceptor. At this time, the charge amount Q / M of the toner on the developing sleeve, which is a developer carrying member of the developing device, is set to 4 μC / g or more.
By maintaining the charge rate at not more than μC / g, the stable supply of the charge-promoting particles is made possible.

FIG. 1 is a schematic diagram showing an embodiment of the image forming apparatus of the present invention.

In FIG. 1, reference numeral 1 denotes a drum-shaped electrophotographic photosensitive member as an image carrier, that is, a photosensitive drum. In this embodiment, a reversal developing method is used for development, and the photosensitive drum 1 has a negative charging property. I have. Specifically, the diameter is 30m
m OPC photoreceptors were used. The photosensitive drum 1 is driven to rotate in the direction of the arrow at a peripheral speed of 94 mm / sec.

The surface of the photosensitive drum 1 is in contact with a charging roller 2 made of a conductive elastic roller as a charging member of a contact charging device. The charging roller 2 has a contact surface with the photosensitive drum 1 and has a peripheral speed of 100 around the photosensitive drum 1 in the opposite direction.
% At the peripheral speed.

In the present embodiment, the charging roller 2 is used with a surface on which the charge accelerating particles m from the developing device 3 are carried.
The surface of the photosensitive drum 1 contacts the surface of the photosensitive drum 1 via the charge promoting particles and is charged. A charging bias for charging the surface of the photosensitive drum 1 to approximately -700 V is applied to the charging roller 2 from a charging bias power source S1.

The surface of the photosensitive drum 1 charged by the charging roller 2 is scanned and exposed with a laser beam L from a laser scanner (not shown) including a laser diode and a polygon mirror. This laser beam L
Is subjected to intensity modulation corresponding to the time-series electric digital pixel signal of the target image information, so that an electrostatic latent image corresponding to the image information is formed on the surface of the photosensitive drum 1.

The electrostatic latent image formed on the photosensitive drum 1 is
The image is reverse-developed by the developing device 3 using the negatively charged magnetic toner 31, and is visualized as a toner image.

The developing device 3 is constituted by a magnetic one-component non-contact developing device, in which a magnetic toner 31 is accommodated, a non-magnetic developing sleeve 32 is provided in an opening facing the photosensitive drum 1, and a predetermined gap is provided between the developing device 3 and the photosensitive drum 1. Open and rotatably arranged. A magnet roller 33 is non-rotatably disposed within the developing sleeve 32, and an elastic blade 34 is disposed in contact with an approximately top surface of the developing sleeve 32.

The surface of the developing sleeve 32 is coated with a thermosetting phenol resin in order to enhance the charging property to the toner 31. The developing sleeve 32 has an outer diameter of 16
mm, the gap with the photosensitive drum 1 is set to 500 mm, and the photosensitive drum 1 is rotated at a constant speed.

The elastic blade 34 is made of a silicone rubber elastic body in order to regulate the amount of the toner 31 and charge the toner 31, and has a hardness of 45 ° (JIS A) and a thickness of 1 in order to have appropriate elasticity. 0.4 mm and a free length of 10 mm. The contact pressure of the elastic blade 34 with the lower pick 32 was set to about 30 g / cm.

The magnetic toner 31 accommodated in the developing device 3
Is sucked up on the surface of the rotating developing sleeve 32 by the magnetic force of the magnet roller 33, and the elastic blade 34
And is frictionally charged by being rubbed by the elastic blade 34, and is formed on the developing sleeve 32 as a thin toner layer. The toner 31 formed in a thin layer is conveyed to the developing section facing the photosensitive drum 1 with the rotation of the developing sleeve 32, and is transferred from the developing power source S2 to the developing sleeve 32.
The flying bias is applied to the electrostatic latent image on the surface of the photosensitive drum 1 by the developing bias applied thereto, and the latent image is jumped and developed. The developing bias is an oscillating voltage obtained by superimposing a DC voltage of -350 V on an AC voltage having a frequency of 1.6 kHz and a peak-to-peak voltage of 1.7 kV.

In this embodiment, the magnetic toner 31 has an average particle diameter of 6 μm.
Are mixed. The mixing amount of the charge accelerating particles is
2 parts by weight with respect to 0 parts by weight. However, the mixing amount of the charge promoting particles is not limited to this.

On the other hand, a transfer material P as a recording material is supplied to a photosensitive drum 1 from a paper feed unit (not shown), and a contact portion (transfer portion) between the photosensitive drum 1 and a transfer roller 4 contacting the photosensitive drum 1 at a predetermined pressure. ) Is introduced at a predetermined timing. The transfer material P introduced into the transfer unit is conveyed while being sandwiched between the photosensitive drum 1 and the transfer roller 4, and the toner image on the photosensitive drum 1 is applied to the surface of the transfer material P by the transfer bias applied to the transfer roller 4. The image is transferred by the electrostatic force and the pressing force of the photosensitive drum 1 and the transfer roller 4.

The transfer roller 4 is an elastic roller having a medium resistance. In this embodiment, the resistance value is set to 5 × 10 ⁸ Ω. A DC voltage of +3000 V was applied to the transfer roller 4 from the transfer power source S3. Note that a non-contact type corona charger or the like can be used instead of the transfer roller 4.

The transfer material P on which the toner image has been transferred is separated from the surface of the photosensitive drum 1 and is introduced into a fixing device 5 such as a heat fixing system, where the toner image is fixed on the transfer material P,
The print image is discharged out of the apparatus.

In this embodiment, the image forming apparatus is of a process cartridge type, and the three process devices of the photosensitive drum 1, the charging roller 2 and the developing device 3
And is installed in the main body of the image forming apparatus in a detachable manner, but is not limited to this.

The charging roller 2 is formed by forming a medium resistance layer 22 of rubber or foam on a core metal 21. For example, the medium resistance layer 22 is formed in a roller shape on the core metal 21 by using a material having a formulation in which conductive particles such as carbon black, a sulfide agent, a foaming agent, and the like are mixed in a resin such as urethane.
Thereafter, the surface of the roller is polished as necessary to finish it to a desired length and diameter.

The resistance of the charging roller 2 used in this embodiment is
5 × 10 ⁶ measured in an environment with a temperature of 25 ° C. and a humidity of 60%
Ω. The resistance was measured by replacing the photosensitive drum 1 with an aluminum drum, and thereafter, pressing the aluminum drum and the charging roller 2 under pressure at a predetermined pressure, between the aluminum drum and the metal core 21 of the charging roller 2.
The resistance of the charging roller 2 was determined by applying 0 V and measuring the value of the current flowing at that time.

The average cell diameter on the surface of the medium resistance layer 22 of the charging roller 2 was 20 μm for each roller having any resistance value. The average cell diameter was measured by observation with an optical microscope.

In the magnetic toner 31 used in this embodiment, a binder resin containing a styrene-acrylic copolymer as a main component, 60% by weight of magnetite, and 1% by weight of a metal complex salt of a monoazo dye as a negative charge control agent. % is contained in the manufactured insulating toner of about 10 ¹³ [Omega] cm volume resistivity, the silica fine particles made hydrophobic as fluidizing agent is obtained by externally added in an amount of 0.8 wt%.

The volume resistivity of the toner 31 was measured by a tablet method. About 0.5 g of the toner of the measurement sample is placed in a cylinder having a bottom area of 2.26 cm ² , and 15 kg of pressure is applied to the electrodes sandwiching the toner layer from above and below, and 100 kg is applied between the electrodes.
A voltage of V was applied to measure the resistance value of the toner layer, and then normalized per toner unit volume to calculate the volume resistivity.

The charge amount (tribo) of the toner 31 on the developing sleeve 32 was measured using a measuring device shown in FIG. The measuring device has an insulating cylinder 72 in which a filter 75 is installed, and a diameter of 5 m at one end of the cylinder 72.
m, and a suction pipe 74 is attached to the other end of the cylinder 72.
Is connected to a suction pump such as a vacuum cleaner. A measurement probe (not shown) connected to the electricity meter 73 by a cord 76 is attached to the filter 75. As the electricity meter 73, a 616 electrometer manufactured by Keithley Co. was used.

When the suction pipe 71 is pressed against the surface of the developing sleeve 32 and sucked by the suction pump to suck the toner on the developing sleeve, the toner is sucked into the cylinder 72 and captured by the filter 75. The weight M (g) of the toner captured by the filter 75 is obtained as a weight difference by measuring the weight of the cylinder 72 before and after suction. On the other hand, the quantity of electricity Q (μC) of the toner that has been captured by passing through the inside of the cylinder 72 is measured by the electricity meter 73 via the measurement probe. From the toner weight M and the quantity of electricity Q, the charge amount of the toner is Q / M (μC / g).
Is obtained as

The electric quantity Q of the toner is positive for the positive toner and negative for the negative toner. In this embodiment, since the negative toner is used, the value of Q / M is negative.
Since the magnitude of the absolute value is important, the description will be omitted with reference numerals omitted.

When the toner on the developing sleeve is absorbed, the particles of the charge-promoting particles mixed in the toner are also absorbed, so that the sum of the two charges is measured. Since the charge is not so large and the amount is small, the charge amount of the charge accelerating particles can be neglected.

In the present embodiment, as the charge accelerating particles m,
Conductive zinc oxide particles having a specific resistance of 10 ⁷ Ωcm and an average particle size of 10 μm were used.

The specific resistance of the charge accelerating particles m was measured by the tablet method, similarly to the specific resistance of the toner. That is, a cylinder having a bottom area of 2.26 cm ² is filled with about 0.5 g of a measurement sample of the charge-promoting particles, and the particle-filled layer is sandwiched between the electrodes from above and below, and a pressure of 15 kg is applied thereto. A voltage of 100 V was applied, and the resistance value of the filling layer was determined from the current value flowing at that time, and then normalized to determine the specific resistance of the charge promoting particles.

The particle size of the charge accelerating particles m is measured by observing the charge accelerating particles with an optical microscope or an electron microscope.
The extraction was performed by extracting 100 or more particles, calculating the volume particle size distribution of the particles having the maximum horizontal chord length of the particles, and determining the 50% average particle size as the particle size. When the charge promoting particles formed an aggregate, the average particle size of the aggregate was defined as the particle size of the charge promoting particles.

As the charge accelerating particles m, colorless or powerful particles are appropriate so as not to hinder the latent image exposure.
If the particle size of the charge accelerating particles m is about の of the particle size of the toner, image exposure may be interrupted. Therefore, the particle size needs to be smaller than this. If it is too low, the toner may be charged, so the lower limit of the particle size of the charge-promoting particles is about 0.01 μm.

The specific resistance of the charge accelerating particles m
To satisfactorily perform charging to, but preferably 10 ¹² [Omega] cm or less, the particle size of the charging performance enhancement particles is too small, the charging accelerating particles adhered to the toner surface, to lower the charging ability of the toner, ¹⁰⁵ Ωcm or more is required.

As the charge-promoting particles m, conductive inorganic particles such as conductive metal oxide powder, a mixture of these and organic materials, or various kinds of conductive particles obtained by subjecting these particles to surface treatment are used. It is possible.

In this embodiment, as described above, the contact charging device uses the charging roller 2 by carrying the charging promoting particles m from the developing device 3 on the surface of the charging roller 2 of the charging member. The charge promoting particles m are supplied from the developing device 3.

The charge-promoting particles m mixed with the magnetic toner 31 in the developing device 3 are rubbed with the negatively-charged toner 31 during development and are frictionally charged to the opposite positive polarity.
The toner is carried on the developing sleeve 32 while being mixed with the toner, and is conveyed to the developing unit facing the photosensitive drum 1. The charge promoting particles m in the toner fly on the surface of the photosensitive drum 1 together with the toner due to the potential difference between the developing sleeve 32 and the photosensitive drum 1 and adhere to the surface of the photosensitive drum.

The charge accelerating particles m adhered to the photosensitive drum 1 have a charge of the opposite polarity to the toner 31, and therefore remain untransferred in the transfer portion, and only the toner is transferred to the transfer material P. With the rotation of the photosensitive drum 1, the charge accelerating particles m remaining on the photosensitive drum 1 are transported to a contact portion between the charging roller 2 and the photosensitive drum 1, supplied to the charging roller 2, and supplied to the charging roller 2. Coated on the surface.

In the present embodiment, the charge amount Q / M of the toner coated on the developing sleeve 32 is changed by changing the amount and type of the negative charge control agent externally added to the toner 31, thereby changing the charge. The change in the coating amount of the promoting particles m was measured.

In order to measure the accurate supply amount of the charge-promoting particles m from the developing device 3, a cleaning blade is provided immediately after the charging roller 2 only when the number of the charge-promoting particles is measured. The particles were prevented from leaking to the developing section.

The measurement of the number of charge accelerating particles was carried out as follows. The image forming apparatus during image formation was stopped, and the surface of the photosensitive drum 1 after passing through the developing section was photographed with a video microscope (OVM1000N manufactured by OLYMPUSU) and a digital still recorder (SR-3100 manufactured by DELTAS). At the time of shooting, 200 on the video microscope
A double objective lens was attached.

In order to separate the number of individual particles from the obtained digital image, binarization processing was performed with a certain threshold after changing the constant dispersion emphasis processing, and the obtained binarization was performed. The number of particles was counted. Further, as an image pattern for measuring the supply amount of the charge accelerating particles, a repetitive pattern of a horizontal black line having a width of 1 dot and a white background having a width of 3 dots was used. In addition, a character pattern having an image ratio of 4% was repeatedly formed on the image except at the time of measuring the charge accelerating particles.

FIG. 2 shows a change in the supply amount of the charge promoting particles when the charge amount Q / M of the toner is changed. For convenience, cases A to I are classified according to the magnitude of the charge amount Q / M of the toner.

As shown in FIG. 2, the Q / M of the toner is 4 to
In cases C, G, and I in the range of 12 μC / g, the supply amount of the charge-promoting particles at 100, 500, and 1000 prints does not change so much. On the other hand, in the cases E and H where the Q / M of the toner exceeds 12 μC / g, the charge accelerating particles are excessively supplied when the number of printed sheets is 100, and thereafter, the supplied amount is reduced. Q / M is 4
In cases A, B, D, and F where the value is μC / g or less, printing 1
When the sheet is not printed, the charge accelerating particles are not supplied so much.
At the time of 0 sheets, it was oversupplied.

As described above, in the present embodiment, the charge promoting particles m are mixed with the toner 31 in the developing device 3 and the charge promoting particles are supplied to the charging roller 2 via the photosensitive drum 1. Since the charge amount Q / M was in the range of 4 to 12 μC / g, the supply amount of the charge promoting particles from the developing device 3 to the charging roller 2 could be stabilized even when the number of prints was increased.

Table 1 shows the evaluation of the charging property of the photosensitive drum 1 by the contact charging device for supplying the charging accelerating particles from the developing device 3 to the charging roller 2. Fig. 1
An image was formed using the image forming apparatus of No. 1, and evaluation was made based on the degree of prevention of ghosting of the image at the time of 100 sheets, 500 sheets, and 1000 sheets. In Table 1, the sign is ×:
A ghost is seen on a white background after solid black, and ○: no ghost is seen on a white background after solid black.

Here, in the present embodiment, the ghost refers to the photosensitive drum 1
In the first cycle, the portion exposed to the image becomes insufficiently charged in the second cycle, and the image pattern of the first cycle is more strongly developed, and the image pattern appears in the finally obtained image. A phenomenon.

[0080]

[Table 1]

As shown in Table 1, the cases A, B, and B in which the supply amount of the charge promoting particles to the photosensitive drum 1 is insufficient.
In D and F, a ghost occurs when the number of formed images is 100. In cases C, G, and I, in which the supply amount of the charge-promoting particles was stably obtained over 100, 500, and 1000 sheets, a good image without ghosts could be obtained.

As described above, in this embodiment, the charge promoting particles are supplied from the developing device 3 to the charging roller 2 by setting the charge amount Q / M of the toner in the range of 4 to 12 μC / g. By using the contact charging device using the charging roller 2, the photosensitive drum 1 can be satisfactorily charged to obtain a ghost-free high-quality image.

Embodiment 2 In this embodiment, as shown in FIG. 3, a photosensitive drum 1A having an improved surface charge injection property is used instead of the photosensitive drum 1 in the embodiment 1, so that a contact charging device is used. The charging enabled higher uniform charging of the photosensitive drum 1A for a long period of time.

In this embodiment, as shown in FIG. 4, an undercoat layer 12, a positive charge injection preventing layer 13, a charge generation layer 14, and a charge transport layer 15 are formed on a photosensitive drum 1A on an aluminum drum base 11, as shown in FIG. Are applied in order from the bottom to a photosensitive drum provided with a general organic photosensitive layer, and a charge injection layer 16 is further applied. The charge injection layer 16 enhances the charge mobility of the photosensitive layer. And improved charge injection properties.

The charge injection layer 16 is made of a photocurable acrylic resin as a binder, SnO ₂ ultrafine particles 16 a having a conductive particle diameter of 30 nm as conductive filler, tetrafluoroethylene resin (trade name: Teflon), etc. Are mixed and dispersed, and coated on the charge transport layer 15 and then formed into a film by a photo-curing method.

According to the photosensitive drum 1, the SnO2 ultra-fine particles 16a are dispersed in the surface charge injection layer 16, so that the charge mobility of the surface layer is improved and the contact with the charging roller 2 is improved. Therefore, the chargeability by charge injection from the charging roller 2 is improved. Therefore, good charging can be performed, and a higher quality image can be obtained.

In this embodiment, when an image was formed by the image forming apparatus shown in FIG. 3, the photosensitive drum 1A had a good charge injection property on the surface layer. By performing such charging, a high-quality image without ghost could be obtained.

In the above description, the charge injection layer 16 in which conductive fine particles are dispersed is provided on the photosensitive layer on the surface to improve the charge injection property on the surface of the photosensitive drum 1A. However, it is not limited to this.

Embodiment 3 This embodiment is characterized in that the surface of a developing sleeve 32 of a developing device 3 is coated with a resin layer 32a in which a conductive material is dispersed, as shown in FIG.

As a result, the resistance of the surface of the developing sleeve 32 is reduced, the excessive charging of the magnetic toner 31 by the developing sleeve 32 is suppressed, and the charging amount of the toner 31 is stabilized for a long time. Thus, the supply of the charge accelerating particles m to the charging roller 2 via 1 was more stabilized.

In this embodiment, as an example, the resin layer 32a
A thermosetting phenol resin was used, and carbon particles were dispersed therein as a conductive material. However, it is not limited to this.

According to this embodiment, the surface of the developing sleeve 32 is coated with the resin layer 32a in which carbon particles are dispersed. Therefore, even when the toner 31 is excessively charged (charged up), the carbon particles remain in the toner. Since it acts as a charge leak site, excessive charging of the toner can be prevented. For this reason, the charge amount of the toner can be stably controlled within the range of 4 to 12 μC / g, which is suitable for supplying the charge accelerating particles m. And high quality images can be obtained by good charging.

In the above description, in order to prevent the toner 31 from being excessively charged, the surface of the developing roller 32 is coated with a resin layer 32a in which a conductive material is dispersed to reduce the resistance of the surface of the developing roller 32. The surface of No. 34 may be made to have a low resistance by a similar method, and the same effect is obtained.

[0094]

As described above, according to the present invention,
The charge-promoting particles are carried on the charging roller of the contact charging device, and when the charging roller is brought into contact with the image carrier through the charge-promoting particles to be charged, the charge-promoting particles are mixed with the developer in the developing device. Then, the charge accelerating particles are supplied from the developing device to the charging roller through the image bearing member.
１２12 μC / g, so that excessive supply of the charge-promoting particles to the charging roller is suppressed, so that an appropriate amount of the charge-promoting particles is stably carried on the charging roller, and the charge of the image carrier is reduced. Can be offered. Therefore, the ozone-less direct charging can be realized at a low applied voltage by supplying the charging accelerating particles by the automatic replenishment method without using a special supplying means of the charging accelerating particles, and a high-quality image without ghost can be stable for a long time. Can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment of an image forming apparatus of the present invention.

FIG. 2 shows the relationship between the number of particles of the charge accelerating particles on the charging roller of the contact charging device of the image forming apparatus of FIG. 1 and the charge amount of the toner on the developing sleeve of the developing device for several image forming sheets. FIG.

FIG. 3 is a schematic configuration diagram showing another embodiment of the image forming apparatus of the present invention.

FIG. 4 is a cross-sectional view illustrating a layer configuration of a photosensitive layer of a photosensitive drum used in the image forming apparatus of FIG.

FIG. 5 is a schematic configuration diagram showing still another embodiment of the image forming apparatus of the present invention.

FIG. 6 is a schematic view showing an apparatus for measuring the charge amount of the toner used in the present invention.

FIG. 7 is a graph showing charging efficiency in various types of contact charging.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photosensitive drum 1A photosensitive drum 2 charging roller 3 developing device 22 medium resistance layer 31 magnetic toner 32 developing sleeve 32a resin layer m charge promoting particles

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasunori Kono 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Ryo Inoue 3-30-2 Shimomaruko, Ota-ku, Tokyo Kia Non-corporation F-term (reference) 2H003 AA01 AA18 BB11 CC05 DD03 EE11 2H027 EA01 EA06 EC15 ED03 ED09 EF10 HB15 JA02 ZA07 2H077 AA37 AD06 AD13 AD36 AE03 CA08 DB02 DB08 DB12 DB14 EA16 FA25 GA02 GA17

Claims (5)

[Claims] An image carrier is charged by a charging bias applied to the charging member by contacting a charging member carrying charge-promoting particles made of conductive particles with a rotating image carrier via the charge-promoting particles. Developing the electrostatic latent image obtained by imagewise exposing the charged image carrier to a developing unit which is carried on a developer carrier and conveyed to a developing unit opposed to the image carrier. An image forming apparatus comprising: a developing unit containing the developer; wherein the developing unit mixes the charge-promoting particles with the developer, and transfers the charge-promoting particles from the developer carrier to the developing unit. Attached to the carrier, conveyed to the charging member via the image carrier, to supply the charging promoting particles to the charging member, and the elasticity regulating member of the developer on the developer carrier Charge after regulation by 4-1
An image forming apparatus, wherein the image forming apparatus is maintained at 2 μC / g. 2. The image forming apparatus according to claim 1, wherein the particle size of the charge-promoting particles is not more than の of that of the developer, and the specific resistance is not more than 10 ¹² Ωcm. 3. The charge-promoting particles have a specific resistance of 10 ¹⁰ Ωc.
The image forming apparatus according to claim 2, wherein m is equal to or less than m. 4. By providing a resin layer in which conductive particles are dispersed on the surface of the developer carrier, the amount of charge of the developer on the developer carrier after regulation by an elastic regulation member is 4 to 4.
The image forming apparatus according to claim 1, wherein the image forming apparatus is maintained at 12 μC / g. 5. The method according to claim 5, wherein a surface layer in which conductive particles are dispersed is provided on the surface of the elastic regulating member, so that the amount of charge of the developer on the developer carrier after regulation by the elastic regulating member is 4 to 4.
The image forming apparatus according to claim 1, wherein the image forming apparatus is maintained at 12 μC / g.