JPH08339113A - Electrifying device - Google Patents

Abstract

PURPOSE: To prevent electrification fault due to intrusion of foreign matter, to prevent dielectric breakdown due to low resistance of an electrifying member and to prevent leaking of charges to the material to be electrified, by specifying the particles which constitute a particle layer. CONSTITUTION: The particle layer consists of a mixture of first particles having a volume resistivity between 6.0×10<3> Ωcm and <1.0×10<5> Ωcm and second particles having >=6.3×10<5> Ωcm volume resistivity, and the proportion of the first particles is <=40wt.% of the particle layer. By mixing particles of plural kinds having different resistances, both of electrification property and a preventing effect for leaking through pin holes are made compatible with each other a preferable level, which is different from a device in which particles of electrifying member consist of one kind of material having a specified resistivity. By using magnetic particles having different resistance distributions for electrification, the macroscopic resistance is determined by the magnetic particles having higher resistance because magnetic particles having low resistance and magnetic particles having medium resistance are both present, and thereby, concentration of electrifying currents to a pin hole on the photoreceptor can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device having a charging member capable of contacting an object to be charged such as a photoconductor or a dielectric. The charging device is preferably applied to an image forming device such as a copying machine or a printer, or a process cartridge detachably attached to the device.

[0002]

2. Description of the Related Art Conventionally, Japanese Patent Laid-Open No. 6-3921 discloses that a charge injection layer is provided on the surface of a photoreceptor, and a contact charging member is brought into contact with the charge injection layer to inject and charge the photoreceptor.

Further, the use of a particle layer such as a magnetic brush as the contact charging member is disclosed in JP-A-61-57958.

Further, as the charge injection layer on the photosensitive member, a material in which conductive fine particles are dispersed in an insulating and translucent binder is preferably used. By contacting this charge injection layer with a charged magnetic brush to which a voltage is applied, the conductive particles exist as if they were infinite floating electrodes on the conductive base of the photoconductor, and these floating electrodes form these. It can be expected that the capacitor will be charged.

However, the injection charging method using a magnetic brush as the charging member has the following drawbacks.

(1) Poor charging due to mixing of impurities into the magnetic brush In the injection charging method using the magnetic brush as the charging member, the individual magnetic particles forming the magnetic brush contact each other to form a conductive path. It is necessary to charge and charge the surface of the photoconductor by the electric charge that flows through this conductive path.However, if dust or the like is mixed in the magnetic brush, toner that adheres to the surface of the photoconductor due to image formation, etc. However, when the magnetic brush reaches the magnetic brush without being cleaned, the conductive path is blocked by these insulating impurities, which makes charging difficult.

Actually, even in an image forming apparatus that was initially charged well, toner and the like that could not be completely cleaned at the previous image formation are mixed into the magnetic brush as the durable paper feed is performed, so that the charging property is improved. Deteriorates. Specifically, there has been a problem that the surface potential of the photosensitive member once lowered by the exposure cannot be recharged, and in the reversal development type apparatus, fog is caused due to charging failure.

(2) Pinhole leak due to low-resistance particles only In order to efficiently inject charged charges into the photoreceptor, it is preferable that the contact charging member has a low resistance value, for example, 1 × 10 ⁵
When a charging member having a volume resistance value of less than Ωcm is used for charging, when a defect such as a pinhole occurs on the photoconductor, the charging current concentrates on the defect and is applied to the charging member. There are problems that the applied voltage drops and a linear charging failure image occurs, or the charging member and the photoconductor are destroyed.

(3) Particle Adhesion of Low-Resistance Particles When low-resistance particles are used, in addition to the above-mentioned leakage in the drum pinhole, there is particle adhesion caused by low resistance. This phenomenon occurs because the electric resistance is easily induced in the particles at the tip of the magnetic brush due to the low resistance of the magnetic particles, and the adhesion force to the drum acts.

Japanese Unexamined Patent Publication (Kokai) No. 6-274005 discloses a magnetic brush having high resistance particles of 5 × 10 ⁴ Ωcm or more and 5 × 1.
Although it is disclosed that it is composed of a mixture with conductive particles of 0 ³ Ωcm or less, the above-mentioned problems could not be sufficiently solved.

[0011]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a charging device which prevents a charging failure due to the inclusion of foreign matter.

Another object of the present invention is to provide a charging device capable of preventing the dielectric breakdown of the charged body and the leakage to the charged body due to the low resistance of the charging member.

Another object of the present invention is to provide a charging device which prevents particles of a charging member from adhering to a member to be charged.

[0014]

The present invention comprises a body to be charged and a charging member for charging the body to be charged. The charging member is capable of applying a voltage and has a particle layer in contact with the body to be charged. In the charging device, the volume resistivity of the particle layer is 6.0 ×.
First particles having a volume resistivity of 6.3 × 10 ⁵ Ωcm or more and first particles having a resistivity of 10 ³ Ωcm or more and less than 1.0 × 10 ⁵ Ωcm.
Particles are mixed, and the first particles account for 40% by weight or less of the particle layer.

[0015]

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

(First Embodiment) FIG. 1 is a schematic side view of an image forming apparatus to which the charging device of the present invention is applied. Figure 1
The image forming apparatus of this embodiment is a laser beam printer using an electrophotographic process.

Reference numeral 1 is a rotary photosensitive drum type electrophotographic photosensitive member as an image bearing member. Hereinafter referred to as a photosensitive drum. This embodiment is an OPC photosensitive member having a diameter of 30 mm and is rotationally driven in the clockwise direction indicated by arrow D at a process speed (peripheral speed) of 100 mm / sec.

Reference numeral 2 is a conductive magnetic brush as a contact charging member that is in contact with the photosensitive drum 1. The charging magnetic particles 23 are attached to the rotatable non-magnetic charging sleeve 21 by the magnetic force of the magnet 22. There is. This magnetic brush 2
A −700V DC charging bias is applied from the charging bias applying power source S1 to the charge injection charging, so that the outer peripheral surface of the photoconductor 1 is uniformly charged to about −700V.

The charged surface of the photosensitive member 1 is intensity-modulated corresponding to the time-series electric digital pixel signal of the target image information output from a laser beam scanner (not shown) including a laser diode, a polygon mirror and the like. Scanning exposure L is performed by the laser beam, and an electrostatic latent image corresponding to desired image information is formed on the peripheral surface of the photoconductor 1. The electrostatic latent image is developed as a toner image by the reversal developing device 3 using the negatively charged magnetic one-component insulating toner. 3a has a diameter of 16 mm including a magnet
This non-magnetic developing sleeve is coated with the negative toner described above, and the distance from the surface of the photoconductor 1 is set to 30.
While being fixed at 0 μm, the photosensitive drum 1 is rotated at a constant speed, and a developing bias voltage is applied to the sleeve 3a from the developing bias power source S2. As the voltage, a DC voltage of -500 V and a rectangular AC voltage having a frequency of 1800 Hz and a peak-to-peak voltage of 1600 V are superimposed, and jumping development is performed between the sleeve 3 a and the photoconductor 1.

On the other hand, a transfer material P as a recording material is supplied from a paper feeding unit (not shown), and a transfer of medium resistance as a contact transfer means abutting against the photosensitive drum 1 with a predetermined pressing force is performed. It is introduced into the pressure contact nip portion (transfer portion) T with the roller 4 at a predetermined timing. A predetermined transfer bias voltage is applied to the transfer roller 4 from the transfer bias applying power source S3.

In this embodiment, the roller resistance value is 5 × 10 ⁸ Ω.
Then, a DC voltage of +2000 V was applied to transfer.

The transfer material P introduced into the transfer portion T is nipped and conveyed by the transfer portion T, and the toner images formed and carried on the surface of the photosensitive drum 1 on the surface side thereof are sequentially subjected to electrostatic force and pressing force. Will be transcribed.

The transfer material P having the toner image transferred thereto is separated from the surface of the photosensitive drum 1 and is fixed by a fixing device 5 such as a heat fixing system.
Then, the toner image is fixed and is discharged to the outside of the apparatus as an image formed product (print, copy).

The surface of the photosensitive drum after the transfer of the toner image to the transfer material P is cleaned by the cleaning device 6 to remove adhered contaminants such as residual toner, and is repeatedly used for image formation.

The image forming apparatus of the present embodiment includes the photosensitive drum 1
A cartridge type device in which the four process devices of the contact charging member 2, the developing device 3, and the cleaning device 6 are included in the cartridge 20 and can be attached to and detached from the main body of the image forming apparatus at once, but is not limited to this. Not a thing.

Next, the photosensitive member used in this embodiment will be described.

The photoreceptor is a negatively charged OPC photoreceptor, and five functional layers are provided on an aluminum drum having a diameter of 30 mm.

The first layer is an undercoat layer, the second layer is a positive charge injection preventing layer, the third layer is a charge generating layer, and the fourth layer is a charge transporting layer in this order from the aluminum base layer side. Although the function-separated OPC photosensitive material is used, the layers up to this point do not essentially limit the constitution of the present invention.
It is also possible to use a single-layer type photoconductor such as OPC, ZnO, selenium, or amorphous silicon.

The fifth layer is a charge injection layer and is made of a photo-curable acrylic resin in which SnO ₂ ultrafine particles are dispersed.
Specifically, SnO ₂ particles having an average particle diameter of about 0.03 μm, which is doped with antimony and has a low resistance, are dispersed at a weight ratio of 5: 2 with respect to the resin.

In actuality, the volume resistance value of the charge injection layer changes depending on the dispersion amount of SnO ₂ , which is electrically conductive, and the resistance value of the charge injection layer is 1 × 1 in order to satisfy the condition that image deletion does not occur.
0 ⁸ Ωcm or more than it is desirable.

The resistance value of the charge injection layer is obtained by coating the charge injection layer on an insulating sheet and measuring the surface resistance with a high resistance meter 4329A manufactured by Hewlett-Packard (HP) at an applied voltage of 100V. Is.

The coating liquid thus prepared was applied to a thickness of about 3 μm by a suitable dipping coating method to form a charge injection layer.

In this embodiment, the volume resistance value of the charge injection layer is 1
A film having a density of × 10 ¹² Ωcm was used.

The volume resistivity of the charge injection layer is from 1 × 10 ⁸ to
It is preferably 1 × 10 ¹⁵ Ωcm.

Next, the contact charging member will be described.

The conductive magnetic brush is a non-magnetic conductive sleeve 2
1. The magnet roll 22 contained therein and the magnetic conductive particles 23 on the sleeve are fixed. The magnet roll 22 is fixed, and the sleeve surface is opposite to the peripheral speed direction of the photosensitive drum at the position where the sleeve 21 and the photosensitive member 1 are close to each other. Is rotated to move to. The magnetic flux density on the sleeve surface at the closest position between the photoconductor and the charging sleeve is 950 gauss, and the spikes of the magnetic brush are the magnetic blade 2 facing the sleeve.
It is regulated by 4 and forms a spike of about 1 mm. In the longitudinal direction of the charging member (the direction orthogonal to the paper surface of FIG. 1), the magnetic brush has a magnetic magnetic particle adhesion width of 200 mm, and the magnetic brush has an amount of magnetic magnetic particles of about 10 g.
1 and the photosensitive drum 1 nip gap is 500μm
Is.

Now, the peripheral speed ratio between the sleeve and the photosensitive member will be described. The peripheral speed ratio is defined by the following formula. Peripheral speed ratio% = (magnetic brush peripheral speed-drum peripheral speed) / drum peripheral speed x 100 It is preferable that the peripheral speed ratio is large in terms of improving the injection property, but from the viewpoint of the cost and safety of the device. It is preferable that it is as small as possible while ensuring the injection property. Actually, when the magnetic brush comes into contact with the moving direction of the photoconductor at a slow speed in the forward direction (the same direction when the sleeve and the photoconductor are close to each other), the magnetic particles of the magnetic brush tend to adhere to the drum ± 100%. Although the above is preferable, -100% is the state in which the brush is stopped, and therefore the stopped shape on the surface of the photoconductor of the brush may be charged as it is and may appear in the image. Therefore, in this embodiment, the peripheral speed ratio of the surface of the sleeve to the photosensitive member is such that the sleeve is driven and rotated at a position close to the sleeve and the photosensitive member in a direction opposite to the moving direction of the photosensitive member at a speed of 150% of the speed of the photosensitive member. .

In the present embodiment, the relationship between the voltage (V) applied to the charging member and the charging potential (V) of the photoconductor is directly proportional, and it is preferable that the inclination is 1.

Next, the magnetic particles used in this example will be described.

In this embodiment, as the magnetic particles, two kinds of low resistance A and medium resistance B having different electric resistance values were mixed and used.

A: Average particle size 25 μm, volume resistance value 8 × 1
0 ⁴ Ωcm magnetite particles (saturation magnetization 59.6A
m ² / kg) B: Ferrite particles having an average particle size of 25 μm and a volume resistance value of 6 × 10 ⁷ Ωcm (saturation magnetization 58.0 A · m ² / kg) Here, a method for measuring the average particle size and resistance value of the particles is described. explain.

The particle size of the particles is randomly extracted by an optical microscope or a scanning electron microscope, and 100 or more particles are randomly extracted. The volume particle size distribution is calculated with the maximum chord length in the horizontal direction, and the average particle size at 50% of the total volume is calculated. The average particle size is used. Further, using a laser diffraction particle size distribution measuring device HEROS (manufactured by JEOL Ltd.), the range of 0.05 μm to 200 μm is measured by 32 divisions, and the average particle size of 50% of the volume distribution may be used as the average particle size. .

The resistance value of the particles, 6.6 kg / cm ² to 2g filled with magnetic particles in a cylindrical vessel of the low area of 227 mm ²
It was defined as a value obtained by applying pressure and applying a voltage of 100 V from the top and bottom, calculating from the current flowing through this, and normalizing.

The saturation magnetization of the particles is measured by using an oscillating magnetic field type magnetic characteristic automatic recording apparatus BHV-30 manufactured by Riken Denshi Co., Ltd. The magnetic characteristic value of the carrier powder is an external magnetic field of ± 1 kilo-oersted, and the strength of magnetization when the magnetic field is 1 kilo-oersted is obtained from the hysteresis curve at that time.

The above-mentioned magnetic brush was constructed by changing the mixing ratio of particles (ratio of the weight of A particles to the total weight), and as a comparative example, image comparison was performed using A and B particles alone. . The image output was performed by the image forming apparatus described above. Further, the charging potential was measured in order to investigate the charging performance of the particles, and the charging potential of the photosensitive member after passing through the charging section once for the potential applied to the sleeve was used as the potential convergence rate and used as an index of the charging property. If the potential convergence rate is 95% or more, there is no practical problem.

The results are shown in Table 1. If the leak is NG, black line-shaped charging failure has occurred, and the leak is almost OK.
The term "is a usable level, although it causes a charging failure to the extent that it bleeds around the pinhole.

[0047]

[Table 1]

From these results, the B particles alone cannot sufficiently converge the potential. On the other hand, it can be seen that the drum pinhole leak occurs in the A particles alone.
Both of the above can be satisfied by mixing A and B particles. However, as the mixing ratio of the low-resistance A particles increases, a conductive path is formed only by the low-resistance A particles among the particles, causing a drum pinhole leak. In mixing the A and B particles, the A particles are preferably 40 wt% or less in order to prevent leakage.
Further, in order to improve the charging property, it is desirable that the A particles are 5 wt% or more.

Then, the mixing ratio is fixed at 10 wt% and B
The particles were left as they were and the particles A were changed to those having different resistances, and image formation and potential measurement were carried out.

The results are shown in Table 2.

[0051]

[Table 2]

From this result, if the resistance of the low resistance particles is too low, the particles tend to adhere to the photosensitive member, resulting in a defective image. This phenomenon is because the resistance of the particles is low, so that electric charges are easily induced in the particles in contact with the drum at the tip of the magnetic brush, and the electric charges cause the electric charges to adhere to the particles. When the particles adhere to the drum, the adhered particles block the exposure at the image exposure position of the photoconductor, resulting in an image defect, and when the particles enter the developing device, a development leak or a development fog is caused. Further, when the image is transferred from the drum to the transfer material, the image is not fixed on the transfer material and becomes a rough image. Furthermore, when the particles are reduced, the magnetic brush cannot contact the drum uniformly, and the defective contact portion results in a defective charging image. Here, one of the A4 size transfer materials is used as an adhesion index.
The case where a charging failure occurred after printing 000 sheets was designated as NG. Specifically, when the resistance value was 3.5 × 10 ³ Ωcm, there was a large amount of adhesion, and charging failure occurred after printing 800 sheets.

When the resistance of the low-resistance particles becomes high, the potential convergence deteriorates, and when the resistance is 1.0 × 10 ⁵ Ωcm, it becomes 90.
%, Which is the potential converging property that causes charging failure. The charging failure referred to here is not a partial charging failure caused by insufficient contact between the drum and the charging member, but a uniform charging failure in which the previously exposed portion cannot be sufficiently charged.

Therefore, the resistance of the low-resistance particles is 6.0 × 10 ³ Ωcm or more and 1.0 × 1 from the viewpoint of particle adhesion and chargeability.
The optimum value is less than 0 ⁵ Ωcm.

Next, image formation was carried out while changing the resistance and mixing ratio of the low resistance particles while leaving the B particles as they were. The results are shown in the graph of FIG.

As shown in FIG. 2, the volume resistivity of the low resistance particles is 6.0 × 10 ³ Ωcm or more and 1.0 from the viewpoints of adhesion of the particles to the photoreceptor, chargeability of the photoreceptor, and leakage to the photoreceptor. × 10 ⁵
It is less than Ωcm, and the ratio of the low resistance particles to the entire particles is preferably 40% by weight or less. Further, assuming that the volume resistivity of the low resistance particles is x (Ωcm) and the ratio of the low resistance particles to all particles is Y (% by weight), Y ≦ 15 + 2.5 log
_It is desirable to set it to ₁₀ x.

Next, low resistance particles were added to 9.5 × 10 ⁴ Ωc.
The mixing ratio was fixed to 30% and the resistance of the medium resistance particles was changed to measure the potential. Table 3 shows the results.

[0058]

[Table 3]

From this result, when the resistance of the medium resistance particles is low, the drum pinhole leak is caused.
On the other hand, it was found that when the resistance of the medium resistance particles is high, the charging property is not significantly deteriorated even if the resistance is increased to some extent. It is considered that this is because the mixed low resistance particles secure the conductive path. 1 for conventional medium resistance particles alone
Since a charge of × 10 ⁸ Ωcm or more was insufficient, the range of usable medium resistance particles was expanded by mixing the particles.

Therefore, the resistance of the medium resistance particles is 6.3 × 10.
^{It is 5} Ωcm or more, preferably 1.0 × 10 ⁶ Ωcm or more. The resistance of the medium resistance particles is preferably less than 1.0 × 10 ¹⁰ Ωcm.

Here, the effects based on this embodiment will be described.

The pinhole leak performance is specifically shown in FIG.
As shown. When the charging member r having a low volume resistance value is used, the pinholes formed on the photoconductor are shown in FIG.
As described above, the charging current flows intensively through the surface of the charging member. Therefore, not only the potential of the pinhole part but also A
The potential at the point also drops to about 0 V, which is the basic potential of the photoconductor, and causes a charging failure at the point A. This is because the resistance of the magnetic particles existing between the pinhole and the point A is as shown in FIG.
This is because there is only a value of 2r in (b). In order to prevent this, it is necessary to set the resistance value of the charging member to 1 × 10 ⁵ Ωcm or more. On the other hand, in the direct charge injection charging, the charge is directly injected from the surface of the magnetic particles to the charge injection layer on the surface of the photoconductor, so that the injection property is improved by using the charging member having a low resistance value. It is considered that this is because the lower the resistance value of the magnetic particles, the smaller the injection time constant, and the lower the contact resistance value at the interface between the magnetic particles and the photoconductor.

Therefore, it is difficult to satisfy both the anti-pinhole leak performance and the charge injection property when the magnetic particles having a single resistance distribution are charged as in the conventional case.

However, when charging is performed with magnetic particles having different resistance distributions as in the present embodiment, a macro resistance value of a resistance value becomes a macro resistance value due to a mixture of low resistance magnetic particles and medium resistance magnetic particles. Since it is determined by the high magnetic particles, the charging current does not flow intensively into the pinholes on the photoconductor.

Specifically, as shown in FIG. 3A, the resistance value of the magnetic particles between the pinhole portion and the point A is R + r to R.
This is because the resistance becomes a medium resistance that does not lower the potential at point A.

Further, since the injection time constant is small in the portion where the magnetic particles having a low resistance value are in contact with the photosensitive member,
Since the electric resistance at the interface is small, electric charges are injected onto the photoconductor, and good charging can be realized.

On the other hand, for particles having low resistance, particle adhesion to the drum had occurred.
When it was 10 ³ Ωcm or more, particle adhesion did not occur.

In the present embodiment, magnetic particles having two kinds of resistance values were mixed, but this does not limit the concept of the present invention, and mixing particles having three or more kinds of resistance values, Similar effects can be obtained by using magnetic particles having a broad resistance distribution.

In this embodiment, as particles having different resistance values,
The same ferrite particles with different surface treatments and magnetite were used, but in addition to these, resin and magnetic powder such as magnetite were mixed and molded into particles,
Alternatively, a mixture of conductive carbon or the like for adjusting the resistance value, a sintered ferrite, or a material in which the resistance value is adjusted by reducing these, or a resin in which these magnetic particles are plated or the resistance is adjusted. The same effect was obtained by mixing and using, for example, those whose surface had been coated to have an appropriate resistance value, and the like.

As described above, unlike the case where the particles of the charging member are composed of the specific resistance of one kind of material, the structure of the present embodiment mixes a plurality of kinds of particles having different resistances to cause pinhole leakage. It has become possible to achieve both prevention and chargeability at a good level. Furthermore, by setting the resistance of the low resistance particles to 6.0 × 10 ³ Ωcm or more,
Particle adhesion can also be prevented.

Further, since the charging member of this embodiment and the charge injection layer (having a resistance value of 1 × 10 ⁸ to 1 × 10 ¹⁵ Ωcm) of the photoconductor are used, they are sufficiently uniform even in a short charging time in the electrophotographic apparatus. It was possible to obtain a good chargeability because charging was possible, there was no image deletion, and no particle adhesion.

Further, the type of the photoconductor is not limited to the OPC, and even in the case of a silicon drum in which the resistance value of the surface silicon carbide is 5 × 10 ¹³ Ωcm,
By using the charging member of this example, good charge injection could be performed. Specifically, the drum surface could be charged to 480 V with respect to the voltage applied to the sleeve of 500 V.

Further, by directly performing the charge injection charging as described above, it becomes possible to completely eliminate the generation of ozone and the deterioration of the surface of the photosensitive member which have been conventionally caused by the discharge, and the effect is durable. It can be maintained regardless of the paper.

(Second Embodiment) In this embodiment, the magnetic particles forming the charging magnetic brush are particles having different resistances mixed, and the particles having a lower resistance have an average particle diameter than the particles having a higher resistance. Is small.

When electric charges are moved by using a discharge like the conventional contact charging, the electric charges are moved and charged even if a dischargeable gap is formed between the magnetic particles and the photoconductor. .

However, in the direct charge injection charging, the charge on the photosensitive member is caused by movement of the charge in the conductive path between the magnetic particles,
Further, the magnetic particles and the charge injection layer on the surface of the photoreceptor are in direct contact to inject charges. Therefore, when insulative dust such as toner is mixed in the magnetic particles during durable paper feeding, or when the magnetic particles are deteriorated due to toner fusion on the surface of the magnetic particles and the resistance value of the portion increases, the conductive path is If it is cut off, microscopically charged areas will remain on the photoconductor.

In such a situation, the poorly charged region becomes a black spot in the electrophotographic process of the reversal development system, and the macro has a blackened portion where the potential is attenuated by image exposure or the like during the previous image formation. So-called charging positive ghost occurs.

In order to suppress this, it is effective to reduce the average particle diameter in order to increase the chances of contact between the magnetic particles and the magnetic particles and the photoconductor. Therefore, there is a problem in that magnetic particles adhere to the photoconductor because the magnetic restraining force is reduced.

In this embodiment, in order to solve the problem of charging failure due to the mixing of insulating dust and the adhesion of magnetic particles at the same time, particles having different resistances are mixed and particles having a lower resistance have a lower resistance. It is characterized by having a smaller average particle size than high particles.

In this example, the medium resistance B used in Example 1 was used.
Particles and C particles were used as low resistance particles.

B: Average particle diameter 25 μm, volume resistance value 6.4
× 10 ⁷ Ωcm ferrite particles C: average particle size 10 μm, volume resistance value 8.9 × 10 ⁴ Ωc
Magnetite particles of m These particles were mixed at B: C = 9: 1 (the ratio of C particles to all particles was 10 wt%) to form a magnetic brush.

Here, the method for measuring the resistance value of the particle diameter (average particle diameter) of the particles was the method described in Example 1.

As described above, when particles having different average particle diameters are used, an insulating material such as toner or paper powder is mixed in the magnetic particles of the durable paper to cause conduction between the magnetic particles and between the magnetic particles and the drum. Even if the power is cut off, the small-diameter magnetic particles form an electrically conductive path between the large-diameter magnetic particles as shown in FIG. 4, and the conduction is maintained, so that the charging failure can be prevented. Became.

Also, the presence of small-diameter magnetic particles between the magnetic particles and the photosensitive drum serves to increase the contact nip between the magnetic particles and the photosensitive member, so that the charging property can be further improved. become.

Furthermore, by mixing the large-diameter particles and the small-diameter magnetic particles, the small-diameter magnetic particles are magnetically and physically bound to the large-diameter magnetic particles, and the magnetic particles are less likely to adhere to each other. Become.

At this time, as shown in the first embodiment, even if the volume resistance value of one of the particles is low, the resistance value of the entire magnetic particle is determined by the particle having a high volume resistance value, and the resistance value of the pair of particles of the photoconductor is increased. Since the hole property can be maintained, it is preferable that the resistance value of the magnetic particles on the small particle size side forming the conductive path is smaller than that on the large particle size side.

Actually, the above grain structure was the same as that described in Example 1 except that the magnetic particles were the same (process speed was 100 mm / sec), and the paper was subjected to a durable paper feed. Good chargeability was obtained even when the image was formed on 10000 sheets of the material.

Observation of the magnetic particles after passing 10,000 sheets with an electron microscope reveals that the toner is mixed, but the conductive magnetic particles of small particle size, which is the feature of the constitution of this embodiment, are present between the large magnetic particles. It was confirmed that it entered and maintained the conductive path. In addition, the small magnetic particles improve the fluidity of the entire magnetic particles, and the magnetic particles themselves play a role of reducing the shearing force between the magnetic particles. Almost no fusion occurred.

Comparative Example 1 Charging member consisting of a single ferrite magnetic particle having an average particle size of 15 μm and a volume resistance value of 6.9 × 10 ⁷ Ωcm Initially uniform charging was performed and a good image was obtained, but 4000 sheets were passed. After carrying out the charging failure occurs,
It became a charging ghost in reversal development.

Comparative Example 2 Ferrite magnetic particles having an average particle diameter of 15 μm and a volume resistance value of 6.9 × 10 ⁷ Ωcm were added to ferrite magnetic particles having an average particle diameter of 10 μm and a volume resistance value of 6.9 × 10 ⁷ Ωcm by a weight ratio of 1.
Mixing at a ratio of 0: 1 (9.1 wt%) A charging ghost occurs when 5000 sheets are passed.

Comparative Example 3 An electrification failure occurred due to a decrease in the number of particles when 1000 charging members of a single ferrite magnetic particle having an average particle size of 10 μm and a volume resistance value of 6.9 × 10 ⁷ Ωcm were passed.

To evaluate the charging ghost, a solid white image (entire black image) is output after a solid black image (entire black image), and fogging after one round of the solid black post-photoreceptor drum due to incomplete charging is performed. Macbeth dark watch (Macbeth RD-1
255) and used as an index of charging performance. In Comparative Examples 1 and 2, it was confirmed that the fog increased as the durable paper passed.

When the surfaces of the magnetic particles of Comparative Examples 1 and 2 were observed with an electron microscope, it was confirmed that fine powder of toner was mixed in the magnetic particles in both cases. It was found that the particles, etc. fused to each other and hindered the movement of charges in the magnetic particles.

Here, since it has been found that there is a preferable relationship between the resistance and the average particle diameter of the magnetic particles having low resistance, this will be described.

First, in Table 4, ferrite particles having a resistance value of 6.7 × 10 ⁹ Ωcm of the magnetic particles on the medium resistance side (average particle size 5
(0 μm) magnetic particles having different volume resistance and average particle diameter are mixed at a ratio of 10 wt% of low resistance particles, and the result of confirming an image is shown.

[0096]

[Table 4] From this result, the resistance value of the low resistance magnetic particles to be mixed is 1
When the average particle size was less than 10 ⁵ Ωcm and the average particle size was 30 μm or less, it was possible to obtain a slightly good charging property without a charging ghost when 5000 sheets were continuously fed.

Furthermore, if the resistance value of the low-resistance magnetic particles to be mixed is less than 5 × 10 ⁴ Ωcm and the average particle size is 15 μm or less, there is no charging ghost in 10,000 continuous sheets, which is good. A chargeability was obtained.

Next, Table 5 shows the results for ferrite particles having a resistance value of 6.9 × 10 ⁷ Ωcm of the magnetic particles on the medium resistance side.

[0099]

[Table 5]

From these results, it is seen that when the resistance value of the magnetic particles to be mixed is less than 1 × 10 ⁵ Ωcm and the average particle size is 30 μm or less, good charging property without charging ghost can be obtained in 10000 continuous sheets. was gotten. Furthermore, the resistance value of the mixed magnetic particles is less than 5 × 10 ⁴ Ωcm and the average particle size is 1
When the thickness is 5 μm or less, a very good charging property without a charging ghost was obtained when 100,000 sheets were continuously fed.

As described above, by mixing medium-resistance large-diameter magnetic particles and low-resistance small-diameter magnetic particles and using them as a charging member, magnetic particle contamination and electrification failure due to durable paper feeding, which has been a problem in the past, are affected. Can now be solved. Here, the low-resistance small-diameter magnetic particles have a resistance value of 6.0 × 10 ³ Ωcm or more and 1.0 × 10 ⁵ due to adhesion and charging property.
It is desirable that the average particle size is less than Ωcm and the average particle size is 30 μm or less from the viewpoint of charging uniformity. In addition, the medium-resistance large-diameter magnetic particles have a resistance value of 6.3 × 10 ⁵ Ωcm to prevent pinhole leakage.
The above is desirable. Further, the medium-resistance large-diameter magnetic particles preferably have a resistance value of less than 1 × 10 ¹⁰ Ωcm, and the average particle size is preferably 15 μm or more and 100 μm or less in view of particle adhesion and charging uniformity.

In the present embodiment, two types of magnetic particles having different average particle sizes on the large particle size side and the small particle size side are mixed for convenience, but three or more kinds of particles are mixed. It is also possible to prevent magnetic particles from adhering and to secure chargeability by using a powder having a broad particle size distribution having both the large particle size range and the small particle size range described in this example. It is possible to obtain an effect.

(Third Embodiment) In this embodiment, the surface energy of the charge injection layer located on the surface of the photoconductor is lowered, and the magnetic particles of small particle size are generated by the intermolecular force between the photoconductor and the photoconductor. Lubricant particles were dispersed in order to suppress the detachment of the magnetic particles. In this example, PTFE particles having an average particle diameter of 0.3 μm (Teflon, trade name, manufactured by DuPont) were dispersed in a binder weight ratio of 30%.

Usually, when Teflon particles or the like are dispersed in the charge transport layer in order to impart lubricity to the photoreceptor, the charge transport layer has a large film thickness of about 20 μm, which may scatter the image exposure, and hence a large amount. However, unlike the case of the charge transport layer, the charge injection layer is formed as a thin film having a thickness of 2 to 3 μm. It is possible.

In this embodiment, since Teflon particles are dispersed as lubricant particles in the charge injection layer, the surface energy of the charge injection layer is lowered and the releasability of the particles is improved. As compared with the case where the particles were not dispersed, the small-diameter magnetic particles were significantly less attached to the surface of the photoconductor.

Specifically, a magnetic brush in which ferrite particles of 15 μm and magnetite particles were mixed as magnetic particles at a ratio of 20: 1 was combined with a drum in which lubricant particles were not dispersed, and after 1000 sheets of paper were passed, particles were transferred. When the ratio of 1 μm magnetite is 1000: 1,
However, the fog caused by the deterioration of the charging property was also increased. However, the same mixed magnetic particles are combined with the above-mentioned drum in which Teflon is dispersed to combine the images to obtain 1000 images.
After passing a single sheet, the charging property was good, and there was almost no change in the particle ratio.

In this example, Teflon particles were dispersed as the lubricant particles, but similar effects could be obtained by dispersing polyolefin particles and silicone particles.

[0108]

As described above, according to the present invention,
It is possible to improve the charging property of the charged body while preventing the current from concentrating on the pinhole of the charged body.

Further, it is possible to prevent the particles of the charging member from adhering to the member to be charged.

[Brief description of drawings]

FIG. 1 is a schematic side view of an image forming apparatus.

FIG. 2 is a graph showing the relationship between the volume resistivity of low resistance particles and the mixing ratio.

FIG. 3 is an explanatory diagram showing a leak phenomenon to a pinhole portion.

FIG. 4 is an explanatory diagram when toner is mixed in a charging member of magnetic particles having different average particle diameters.

[Explanation of symbols]

 1 Photosensitive Drum 2 Charging Member 21 Blade for Regulating Thickness of Magnetic Particle Layer 22 Magnet Roll 23 Conductive Magnetic Particles

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Seiji Mashita 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (15)

[Claims] 1. A charging device comprising: a member to be charged; and a charging member for charging the member to be charged, the charging member being capable of applying a voltage, and comprising a particle layer in contact with the member to be charged. The particle layer includes first particles having a volume resistivity of 6.0 × 10 ³ Ωcm or more and less than 1.0 × 10 ⁵ Ωcm, and second particles having a volume resistivity of 6.3 × 10 ⁵ Ωcm or more. And are mixed, and the first particles account for 40% by weight or less of the particle layer. 2. The average particle size of the first particles is the second particle size.
The charging device according to claim 1, wherein the charging device is smaller than the average particle size of the particles. 3. The charging device according to claim 1, wherein the average particle diameter of the first particles is less than 30 μm. 4. The volume resistivity of the second particles is 1.0.
The charging device according to claim 1, wherein the charging device has a resistance of less than × 10 ¹⁰ Ωcm. 5. The charging device according to claim 1, wherein the charging member is movable, and the peripheral speed of the charging member is different from the peripheral speed of the body to be charged. 6. The charging device according to claim 1, wherein the first particles are magnetite, and the second particles are ferrite. 7. The charged body is provided with a charge injection layer having a volume resistivity of 1.0 × 10 ⁸ Ωcm to 1.0 × 10 ¹⁵ Ωcm on the surface thereof. Charging device. 8. The charging device according to claim 1, wherein the first particles account for 5% by weight or more of the particle layer. 9. The volume resistivity of the first particles is x (Ωc
m), the ratio of the first particles to the particle layer is y
9. The charging device according to claim 1, wherein y ≦ 15 + 2.5 log ₁₀ x is satisfied when (% by weight). 10. The charged body comprises a photosensitive layer inside the charge injection layer, and the charge injection layer has conductive fine particles dispersed in a light transmissive and insulating binder. Item 7. The charging device. 11. The charging device according to claim 10, wherein a lubricant powder is dispersed in the charge injection layer. 12. The charging device according to claim 11, wherein the lubricant powder is one of a fluororesin, a polyolefin resin, and a silicone resin. 13. The charging device according to claim 1, wherein the first and second particles are magnetic particles. 14. The charging device according to claim 1, wherein the member to be charged is an electrophotographic photosensitive member. 15. The charging device according to claim 1, wherein the charging device is provided in a process cartridge that is attachable to and detachable from the image forming apparatus.