JPH0822167A - Electrostatically charged member, electrostatically charging device, image forming device and process cartridge - Google Patents

Abstract

PURPOSE:To prevent electric charge from laterally flowing in a surface direction in the vicinity of the surface of an electrostatically charged member and to realize uniform electrostatic charge processing by dispersing and containing insulating additive whose resistance is higher than binding resin in the surface layer of the electrostatically charged member. CONSTITUTION:By the electrostatically charging device, an electrostatically charged roller 2 is made to abut on a photoreceptive drum 1 or arranged closely to the drum 1. Then, the drum 1 is electrostatically charged by applying a voltage on the roller 2. The roller 2 is provided with an electrical conductive elastic layer 2b for imparting elasticity and electrical conductivity to a core bar 2a on which the DC voltage or the voltage obtained by superimposing the DC voltage on the AC voltage is applied, a resistance control layer 2d for controlling the resistance of the electrostatically charged member as necessary and the surface layer 2c. Then, the relation of the volume resistivity of electrical conductive agent, the insulating additive and the binding resin constituting the layer 2c is as follow, the electrically conductive agent < the binding resin < the insulating additive. Besides, it is preferable that the volume resistivity of the electrically conductive agent is <=10<6>OMEGAcm and the volume resistivity of the insulating additive is >=10<13>OMEGAcm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging member, a charging device,
The present invention relates to an image forming apparatus and a process cartridge.

More specifically, a. A charging member of a charging device that brings the charging member into contact with or close to the member to be charged and applies a voltage to the charging member to charge the member to be charged (including static elimination process). B. A charging device that brings the charging member into contact with or close to the member to be charged and applies a voltage to the charging member to charge the member to be charged c. Image forming apparatus for performing image formation by an image forming process including a step of charging an image bearing member (charged member) with a charging device d. The present invention relates to a process cartridge that includes at least an image carrier and a charging device for the image carrier and that is attached to and detached from an image forming apparatus.

[0003]

2. Description of the Related Art Conventionally, for example, an electrophotographic apparatus (copier,
An image forming apparatus such as a printer) or an electrostatic recording device includes a step of charging an image bearing member such as a photoconductor or a dielectric, and other members to be charged (such as a transfer material).

The corona charging method is generally used as the charging treatment method. However, the corona charging method often produces undesired ozone and the like and requires an additional means or mechanism for coping with it. There is a problem that the device tends to be large and costly.

Therefore, recently, a contact charging method has been studied as a new charging method replacing the corona charging method, and has been partially put into practical use.

According to the contact charging method, a charging member to which a voltage is applied is brought into contact with a member to be charged with a predetermined pressing force to charge the member to be charged. Since ozone generation is greatly reduced as compared with the corona charging method, the corona charging method has an advantage that an additional means or mechanism essential to the corona charging method is unnecessary.

There are a method of charging by applying only a DC voltage to the charging member (DC applying method) and a method of applying an oscillating voltage to charge (AC applying method). The AC application method often uses a superimposed voltage of a DC voltage and an AC (alternating) voltage having a peak-to-peak voltage that is about twice the charging start voltage of the member to be charged (Japanese Patent Laid-Open No. 63-149669).

The charging member is not necessarily in contact with the surface of the body to be charged, and even the dischargeable area determined by the gap voltage and the correction Paschen curve is surely guaranteed between the charging member and the surface of the body to be charged. For example, non-contact (proximity) does not matter, and in this case as well, it is within the category of contact charging.

[0009]

However, the contact charging method or the same apparatus has the following problems.

That is, as the constitution of the charging member, it is often the case that at least two layers of a lower layer and an upper layer (hereinafter referred to as a surface layer) are provided on a conductive substrate. In the case of a two-layer structure, the lower layer often has conductivity and elasticity, and an oil, a plasticizer, or the like is added to have appropriate elasticity. The surface layer has an appropriate surface resistance to prevent leakage due to pinholes on the surface of the body to be charged (hereinafter specifically referred to as the photoreceptor of an electrophotographic device) and to allow oil contained in the lower layer to bleed to the surface. It is provided for the purpose of preventing bleeding.

An electrophotographic charging member having a two-layer structure as described above, in which a resin or rubber having an appropriate resistance in the surface layer is used alone without a conductive agent added (simple matrix state) When used as a charging member for the primary charging of the device,
There is a problem that streak-shaped image defects occur on an image, particularly in a halftone image area. It is considered that this phenomenon is caused by the lateral flow of electric charges in the vicinity of the surface of the charging member during discharge toward the surface direction, resulting in streak-like charging defects on the image, but the clear mechanism is not known.

This phenomenon is likely to occur in the DC application method in which only the DC voltage is applied to the charging member, and is unlikely to occur in the AC application method in which the oscillating electric field such as the AC voltage is superimposed on the DC voltage and is applied. . This is A for DC application
It is considered that there is no "leveling effect" of the charging potential due to an oscillating electric field such as an AC voltage in the C application method.

If a charging member having a surface layer in which a conductive agent is contained in resin and rubber is used, streak-shaped image defects in the halftone image area can be reduced, but in that case, the conductive agent is appropriately added. It is necessary to add a certain amount and disperse it uniformly. If the conductive agent is evenly distributed, the conductive agent will be present on the surface of the charging member at an appropriate interval, so when a voltage is applied to the charging member, a current flows through the charging member through the conductive agent and the charging Therefore, it is considered that the flow of electric charges in the lateral direction of the surface is prevented due to the above. But,
It is difficult to uniformly disperse the conductive agent. In the system in which the conductive agent is dispersed, it is easy to reflect the dispersed state of the conductive agent, and if the conductive agent is agglomerated due to poor dispersion, the charging becomes non-uniform and the occurrence of streak-shaped image defects cannot be suppressed. There is a problem that black spots and the like are generated on the image when the degree of aggregation increases. Further, there is a risk that a leak may occur at a portion where the conductive agent is aggregated.

As another method for solving the streak-shaped charging failure, a charging member having a surface layer in which an insulating additive such as an insulating pigment is contained in resin and rubber is used as a primary charging member for an electrophotographic apparatus. When used, a streak-like image defect in the halftone image area as described above is not seen, and a good image can be obtained. However, when a plurality of images are continuously printed using such a charging member, there arises a problem that the image density gradually decreases. This tends to cause a problem when the DC voltage is applied to the charging member only by the DC voltage. This phenomenon is considered to be caused by the charge up of the charging member, and especially the charge up near the surface.

Therefore, the present invention solves the above-mentioned problems with the charging member in the contact charging method, that is, the case where the voltage applied to the charging member is the DC voltage only and the DC voltage is the AC voltage. In both cases of the superimposed AC application method, good uniform charging characteristics can be ensured, output image quality and the like can be secured in the image forming apparatus, charging member is difficult to charge up, and continuous plural images are output. The charging member has features such that the image density is hardly reduced, the charging member has high withstand voltage, and the risk of leakage is very small, and the charging device using the charging member, and the charging device. An object of the present invention is to provide an image forming apparatus and a process cartridge using the same.

[0016]

The present invention is directed to a charging member characterized by the following constitution, and a charging device using the charging member.
An image forming apparatus / process cartridge.

(1) A charging member of a charging device which brings a charging member into contact with or close to a member to be charged and applies a voltage to the member to charge the member to be charged, and the charging member is at least a conductive agent. And a surface layer composed of an insulating additive and a binder resin, and the relationship between the conductive agent, the insulating additive and the volume specific resistivity of the binder resin forming the surface layer is as follows: conductive agent <binder resin < A charging member characterized by being an insulating additive.

(2) The volume resistivity of the conductive agent is 10
The charging member according to (1), which is ⁶ Ωcm or less.

(3) The charging member according to (1), wherein the insulating additive has a volume resistivity of 10 ¹³ Ωcm or more.

(4) The charging member according to (1), wherein the insulating additive is spherical particles and has an average particle diameter of 50 μm or less.

(5) The member to be charged is an image carrier of an image forming apparatus, and the charging member is a member for primary charging of the image carrier, (1) to (4) The charging member according to 1.

(6) The charging member according to any one of (1) to (5), wherein the applied voltage is a DC voltage or an oscillating voltage.

(7) It is characterized in that the oscillating voltage is a superimposed voltage of an alternating voltage having a peak-to-peak voltage that is at least twice the charging start voltage of the member to be charged when the DC voltage and the DC voltage are applied ( The charging member according to 6).

(8) The charging member according to any one of (1) to (7), which is a roller type.

(9) A charging device for bringing a charging member into contact with or close to a member to be charged and applying a voltage to the charging member to charge the member to be charged, wherein the charging member is at least electrically conductive and electrically insulating. There is a surface layer consisting of an additive and a binder resin, and the relationship between the conductive agent, the insulating additive and the volume specific resistivity of the binder resin forming the surface layer is as follows: conductive agent <binder resin <insulating additive An image forming apparatus characterized by being an object.

(10) In an image forming apparatus for forming an image by an image forming process including a step of charging an image carrier with a charging device, the charging device brings a charging member into contact with the image carrier, and the charging member is charged. Is a device for electrifying the image carrier by applying a voltage to the charging member, wherein the charging member has at least a surface layer composed of a conductive agent, an insulating additive and a binder resin, and a conductive agent forming the surface layer, An image forming apparatus characterized in that the relationship between the volume resistivity of the insulating additive and the binder resin is: conductive agent <binder resin <insulating additive.

(11) In a process cartridge including at least an image carrier and a charging device for the image carrier, which is attached to and detached from the main body of the image forming apparatus, the charging device applies a charging member to the image carrier. A device for charging an image bearing member by bringing it into contact with each other and applying a voltage to the charging member, wherein the charging member has at least a surface layer composed of a conductive agent, an insulating additive and a binder resin. The process cartridge characterized in that the relationship between the volume resistivity of the conductive agent, the insulating additive and the binder resin constituting the above is: conductive agent <binder resin <insulating additive.

[0028]

[Operation] By dispersing and containing an insulating additive having a higher resistance than the binder resin in the surface layer of the charging member, it is possible to prevent the lateral flow of charges near the surface of the charging member, which is considered to be the cause of streak-like charging failure. It is possible to prevent this, uniform charging processing becomes possible, and a good image can be obtained in the image forming apparatus.

.. The charging member contains an insulating additive in its surface layer, but at the same time contains an appropriate amount of a conductive agent, so that the charging member will not be charged up even if a voltage is applied for a long time. In that case, no decrease in image density is observed even when a plurality of images are continuously output.

[0030] Since the surface layer contains an insulating additive, it is possible to prevent leakage even if the conductive agent aggregates.

The surface layer of the charging member of the present invention is provided by coating the conductive elastic layer by dip coating or spray coating.

A) Conductive agent The conductive agent used in the present invention includes conductive particles such as carbon black and metal oxides. The volume resistivity is preferably 10 ⁶ Ωcm or less.

There is no limitation on the manufacturing method of the carbon black, and carbon black manufactured by the furnace method, the channel method and the thermal method can be used.

The main performance items of the carbon black used in the present invention are DBP oil absorption and specific surface area. The DBP oil absorption amount is preferably in the range of 50 to 250 (m1 / 100g). The specific surface area (nitrogen adsorption specific surface area; BET method) is preferably in the range of 45 to 300 (m ² / g).

Examples of the metal oxide-based conductive agent include a single body obtained by solid solution of tin oxide and antimony and a solid solution of zinc oxide and aluminum, and a composite conductor in which the surface of titanium oxide is coated with tin oxide doped with antimony. Can be used.

The above conductive agents may be used alone or in combination of two or more.

B) Insulating Additive In addition, examples of the insulating additive used in the present invention include resin powder and elastic fine particles. Since it is desired that the surface of the charging member is smooth, the insulating additive used in the present invention is spherical particles, and the average particle diameter is preferably 50 μm or less. The volume resistivity is preferably 10 ¹³ Ωcm or more.

In the present invention, the surface layer is often provided by coating or the like, and when a coating liquid for coating is prepared, the insulating additive used in the present invention is a resin powder or the like having a small specific gravity. A stable dispersed state can be maintained in the coating liquid, and sedimentation is less likely to occur. Further, the resin powder or the like enters between the conductive agent particles having a large specific gravity and acts as a spacer for preventing the conductive agent from settling, thereby stabilizing the dispersion of the conductive agent.

Further, the difference in solubility coefficient between the solvent used for preparing the coating solution and the insulating additive is 1.0 or more, more preferably 1 because the insulating additive is present as particles in the surface layer. Choose to be greater than or equal to .5.

Examples of the resin powder include fluororesin powder, silicone resin powder, polyamide resin powder, methacrylic acid ester resin powder and phenol resin.

Examples of the elastic fine particles include silicone rubber fine powder, polyacrylic ester fine powder, urethane fine powder and the like.

The above insulating additives may be used alone or in combination of two or more.

C) Binder Resin The binder resin for the surface layer used in the present invention is preferably a resin or rubber having a volume resistivity of 10 ⁶ to 10 ¹⁴ Ωcm.

As the binder resin, for example, polyamide resin,
Examples thereof include polyurethane resin, fluororesin, hydrin rubber, urethane rubber, chloroprene rubber, and acrylonitrile rubber.

In the combination of the insulating additive and the binder resin of the present invention, it is preferable that there is a difference of two digits or more in the volume resistivity of both. A difference of two digits or more is more effective in preventing streaky charge defects.

For the voltage application to the charging member of the present invention, either a DC application method using only a DC voltage or an AC application method applying a superimposed voltage of a DC voltage and an AC voltage can be used.

[0047]

【Example】

<Embodiment 1> (1) Example of image forming apparatus FIG. 1 is a schematic configuration diagram of an example of an electrophotographic apparatus (copying machine) in which a contact charging device using a charging member according to the present invention is used as a primary charging unit of an image carrier. Is.

Reference numeral 1 denotes a rotary drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as a member to be charged, which is rotationally driven in a clockwise direction indicated by an arrow at a predetermined peripheral speed (process speed). Reference numeral 1a is a conductive drum base such as aluminum of the photosensitive drum 1, and 1b is a photosensitive layer formed on the outer peripheral surface of the drum base 1a.

Reference numeral 2 denotes a contact charging member, which is a roller body (hereinafter referred to as a charging roller) arranged in pressure contact with a predetermined pressing force in parallel with the drum generatrix direction of the surface of the photosensitive drum 1 in this example. It rotates following the rotation of the drum 1.

As shown in the layer structure model diagram of FIG. 2, the charging roller 2 of the present example provides a core metal 2a for applying a DC voltage or a superimposed voltage of a DC voltage and an AC voltage, and imparts elasticity and conductivity. The conductive elastic layer 2b and the resistance control layer 2d for controlling the resistance of the charging member are formed on the conductive elastic layer 2b, and if the conductive elastic layer 2b or the resistance control layer 2d is provided, the surface layer 2c is provided on the outer side thereof. . The conductive elastic layer 2b, the resistance control layer 2d, and the surface layer 2c of the charging roller 2 of this example will be described later.

Reference numeral 3 denotes a voltage application power source for the charging roller 2. By applying a predetermined voltage to the core metal 2a of the charging roller 2 from this power source, the surface of the rotating photosensitive drum 1 is contact charged by a predetermined potential. Is charged.

The voltage applied to the charging roller 2 may be a DC voltage only (DC application method) or a DC voltage may be superposed with an oscillating electric field such as an AC voltage (AC application method). The AC application method is more advantageous in terms of uniform charging. However, a charging noise is generated.

An exposing means (not shown) for forming an electrostatic latent image by exposing 4 according to the image information of the original document around the surface of the photosensitive drum 1 which has been uniformly primary-charged to a predetermined potential by the charging roller 2. A developing device 5 for forming a toner image by adhering toner to the electrostatic latent image, a transfer charger 7 for transferring the toner image on the photosensitive drum 1 to the transfer material P supplied from the paper feed cassette 6, and a transfer charger after transfer. A cleaning device 9 for removing the residual toner on the photosensitive drum 1 is provided with a pre-exposure means (not shown) for giving the entire surface exposure 10 to the photosensitive drum to remove the charges on the drum 1 in preparation for the next primary charging. Transfer charger 7
A fixing device 8 for fixing the toner image transferred onto the transfer material P to the transfer material P is disposed on the downstream side of the.

Reference numeral 11 denotes a process cartridge which is attachable to and detachable from the main body of the image forming apparatus. In this embodiment, the photosensitive drum 1, the charging roller 2, the developing device 5, and the cleaning device 9 are provided.
4 process equipments are included. Reference numerals 12 and 12 denote holding members for the process cartridge 11 mounted in the apparatus.

(2) Charging roller 2. Conductive Elastic Layer 2b In the charging roller 2, the conductive elastic layer 2b has an appropriate conductivity in order to secure power supply to the photosensitive drum 1 as a member to be charged and good uniform adhesion of the charging roller 2 to the photosensitive drum 1. And has elasticity.

Further, in order to ensure uniform adhesion between the charging roller 2 and the photosensitive drum 1, the conductive elastic layer 2b is polished so as to have a shape in which the longitudinal central portion is thickest and becomes thinner toward both ends, that is, a so-called crown shape. Often formed.

Since the charging roller 2 that is generally used is in contact with the photosensitive drum 1 by applying a predetermined pressing force to both ends of the core metal 2a, the pressing force at the central portion is small and the pressing force at both ends is large. Therefore, if the straightness of the charging roller 2 is sufficient, there is no problem. However, if it is not sufficient, density unevenness may occur in the image corresponding to the central portion and both end portions. The crown shape is formed to prevent this.

The conductivity of the conductive elastic layer 2b is adjusted by adding a conductive substance such as carbon black to an elastic material such as rubber. Elasticity is adjusted by adding process oils, plasticizers and the like. Specific elastic materials for the conductive elastic layer 2b include, for example, natural rubber, EPDM, SBR, silicone rubber, urethane rubber, synthetic rubber such as IR, BR, NBR, CR, polyamide resin, polyurethane resin, silicone resin, and the like. The resin of is also mentioned.

[0059] Resistance Control Layer 2d The resistance control layer 2d is often provided to control the resistance of the charging member 2. Specific materials for the resistance control layer 2d include polyamide resin, polyurethane resin, fluororesin,
Examples thereof include resins such as silicone resin, epichlorohydrin, urethane rubber, chloroprene, and acrylonitrile rubber.

A conductive material such as carbon black, tin oxide or titanium oxide is often dispersed also in the resistance control layer 2d.

.. Surface layer 2c The surface layer 2c is composed of a conductive agent, an insulating additive, and a binder resin as described in the section of action. Since the posting of the specific material has been described above, it is omitted here.

The charging member provided with the surface layer 2c as in the present invention can be uniformly charged even when the voltage applied to the charging member is only the DC voltage, and the occurrence of streak-shaped charging defects is observed. You can get a good image.

The charging member provided with the surface layer 2c as in the present invention has a small charge-up due to long-term energization, and the image density is not reduced even when a plurality of continuous images are output. However, when the surface layer 2c is composed of an insulating additive and a binder resin, a good image can be obtained, but there is a problem in that the image density is lowered when a plurality of continuous images are output due to easy charge-up. As I mentioned before,
In the present invention, it is considered that the charge-up of the charging member can be prevented because the conductive agent is also added.

On the other hand, even if the surface layer 2c is made of a conductive agent, an insulating additive, and a binder resin, if the volume resistivity of the binder resin is high, the surface layer 2c is electrically conductive to adjust the resistance of the charging member. Since it is necessary to add a large amount of the agent, the dispersibility of the conductive agent is lowered, and there is a high risk of non-uniform charging due to poor dispersion, resulting in black spots on the image.

Further, the charging roller 2 as a charging member which comes into contact with the photosensitive drum 1 as the member to be charged may be a non-driven rotation type or may be rotationally driven. Further, the charging member 2 is not limited to the roller type, and may have an appropriate shape such as a blade type or a block type as shown in FIGS. 3A and 3B. The roller-type charging member described above is obtained by using a charging member in which the volume resistivity of the conductive agent, the insulating additive, and the binder resin forming the layer 2c is: conductive agent <binder resin <insulating additive. The same effect as can be obtained.

(3) Specific Structure of Charging Roller 2 The volume resistivity of the present invention is measured according to JIS K 6911. 100 kg / c of powder substance
The measurement was performed after press molding at a pressure of m ² .

The nitrogen adsorption specific surface area of carbon black in the present invention is measured by the BET method utilizing nitrogen adsorption.

DBP of carbon black in the present invention
The oil absorption was determined by using an absorption meter, and the DB per 100 g was calculated from 70% of the maximum torque when DBP (dibutyl phthalate) was added to carbon black.
It is a value showing the P oil absorption amount.

The solubility coefficient in the present invention will be described. Each liquid has its own cohesive energy; CED (Co
hesive energy densities). CED is expressed by the following equation (1).

CED = (ΔH-RT) / V (1) ΔH; heat of vaporization (cal / mol) R; gas constant (1.928 cal / mol) T; absolute temperature (k) V; molar volume (cc / mol) In other words, CED is the internal energy and shows a value close to the intermolecular force.

If the cohesive energy; CED is solved, the solubility coefficient; SP (Solubility Parameter) can be obtained by the following equation (2).

SP = σ = (CED) ^1/2 (2) Now, the cohesive energy of a solid; CED is very difficult because it must obtain the heat of sublimation. Therefore, in the case of a solid, there is no choice but to directly obtain σ. That is, a method of immersing in several solvents whose solubility coefficient: SP is known and observing which solvent swells. It can be determined by, for example, a method of adding a non-solvent to the solvent and then gradually adding the non-solvent to measure the point at which turbidity starts (dull point).

A charging roller 2 as a charging member according to the present invention was prepared according to the following procedure.

.. Conductive elastic layer 2b SBR 100 superposed portion carbon black 30 superposed portion zinc oxide 5 superposed portion fatty acid 2 superposed portion 1 with a closed mixer having the above materials adjusted to 60 ° C.
After kneading for 0 minutes, 20 parts of naphthene-based oil is added to SBR100, and the mixture is kneaded for 20 minutes in a closed mixer cooled to 20 ° C to adjust the raw material compound.

Further, 0.5 parts of sulfur as a vulcanizing agent, 1 part of thiazole type and 1 part of thiuram type as a vulcanization accelerator were added to the SBR100 part of the raw material rubber, and the mixture was cooled to 20 ° C. Kneading is performed for 10 minutes by the two-roll machine.

Using this compound, the conductive elastic layer 2b was vulcanized by press molding around the φ9 stainless steel cored bar 2a so as to have an outer diameter φ16.

.. Surface layer 2c Methylolated nylon (binder resin) 100 superposed portion Silicone resin powder (insulating additive) 30 superposed portion 25 composite metal oxide-based conductive agent 25 superposed portion dispersed and dissolved in a mixed solvent of methanol / toluene to surface Create a layer coating liquid.

This coating liquid was applied on the above-mentioned conductive elastic layer 2b by a dipping method to form a surface layer 2c having a thickness of 30 μm to form a roller-shaped contact charging member 2 (charging roller).

However, the volume resistivity of the methylolated nylon used for the surface layer 2c was 10 ¹⁰ Ωcm, the volume resistivity of the silicone resin powder was 10 ¹⁶ Ωcm, and the volume resistivity of the composite metal oxide-based conductive agent was 10. It was ¹ Ωcm.

The silicone resin powder had an average primary particle size of 5 μm and a solubility coefficient of 7.3.

The solvents used for preparing the coating solution were methanol and toluene, and their respective solubility coefficients were 14.6 and 8.8.

(4) Evaluation The resistance value of the charging roller 2 thus obtained was measured at a temperature of 23.5 ° C.
Under a humidity of 50% (environment 1), an aluminum foil is tightly wound around the outer periphery of the charging roller 2 and a DC voltage (250v) is applied between the support and the aluminum foil to obtain a resistance meter "HIOKI 31".
19 DEGITAL MΩ HI TESTER (Hioki Electric Co., Ltd.) ”. Table 2 shows the results.

This charging roller 2 is used as the charging roller 2 at the position of the primary charging device of the copying machine "NP6030 (Canon Inc.)" as shown in FIG. 1, and the core metal 2a of the charging roller 2 is- A direct current voltage of 1500 V was applied to charge the photosensitive drum 1, and a durability test was performed on a plurality of 50,000 sheets of images.

The images were evaluated by visually observing the images obtained at the initial stage and after running for 50,000 sheets. The results are shown in Table 1. In the table, ◯ indicates that the obtained image is good, Δ indicates that the image can be used, and x indicates that it cannot be used.

In addition, the potential on the surface of the photosensitive drum 1 at the initial stage of the image output durability test of 50,000 sheets and after the endurance of 50,000 sheets is measured by an electrometer "MODEL344 (TREK,
INC. ) ”. Table 2 shows the results. Although the surface potential of the photosensitive drum is decreased by several tens of volts, it is at a level where there is no problem in practical use.

The above-mentioned image output and potential measurement were carried out at a temperature of 23.5 ° C. and a humidity of 50% (environment 1) and at a temperature of 23.5 ° C. and a humidity of 5% (environment 2).

The charging roller 2 was measured with a withstand voltage measuring device shown in FIG.
When applied up to a temperature of 23.5 ° C. and a humidity of 50% (environment 1), it was found that no leakage occurred even at a DC voltage of −2000 V, and that it had a high withstand voltage. The results are also shown in Table 2.

To measure the withstand voltage, the charging roller 2 is rotated in contact with the metal drum 41, and the high voltage source 47 and the core metal of the charging roller 2 are connected. The charging roller 2 has 50
A weight of 0 g is added to the metal drum 41. 48
Is a low-pass filter, 49 is a digital multimeter,
50 is a recorder.

Example 2 The surface layer 2c in Example 1
A conductive resin and a binder resin used therein were polyurethane resin (binder resin) 100 superposed parts, and mixed metal oxide conductive agent 35 superposed parts were dispersed and dissolved in a methyl ethyl ketone (MEK) solvent. Evaluation was carried out in the same manner as.
The results are shown in Tables 1 and 2.

However, the volume resistivity of the polyurethane resin used in the surface layer 2c was 10 ¹³ Ωcm, and the volume resistivity of the conductive agent was 10 ¹ Ωcm.

The solubility coefficient of methyl ethyl ketone used for preparing the coating solution is 9.3.

Example 3 Surface layer 2c in Example 1
The conductive agent and the binder resin used therein were the same as in Example 1 except that the fluororesin (binder resin) 100 superposed parts and the conductive titanium oxide 30 superposed parts were dispersed and dissolved in a dimethylformamide (DMF) solvent. Was evaluated. The results are shown in Tables 1 and 2.

However, the fluororesin used in the surface layer 2c had a volume resistivity of 10 ¹⁴ Ωcm, and the conductive titanium oxide had a volume resistivity of 10 ⁰ Ωcm.

The solubility coefficient of dimethylformamide used for preparing the coating solution is 12.1.

Example 4 Surface layer 2c in Example 1
The evaluation was performed in the same manner as in Example 1 except that the insulating additive used was 30 parts of fluororesin powder. The results are shown in Tables 1 and 2.

However, the volume resistivity of the fluororesin powder used in the surface layer 2c was 10 ¹⁵ Ωcm, the average primary particle size was 0.3 μm, and the solubility coefficient was 6.2.

Example 5 The surface layer 2c in Example 1
Evaluation was performed in the same manner as in Example 1 except that the insulating additive used was a silicone resin powder having an average primary particle size of 10 μm. The results are shown in Tables 1 and 2.

However, the volume resistivity of the silicone resin powder used in the surface layer 2c is 10 ¹⁶ Ωcm, and the solubility coefficient is 7.3.

Example 6 Surface layer 2c in Example 3
The evaluation was performed in the same manner as in Example 3 except that the insulating additive used was polymethylmethacrylate resin powder 30 superposed portions. The results are shown in Tables 1 and 2.

However, the volume resistivity of polymethylmethacrylate resin powder was 10 ¹⁶ Ωcm, and the average primary particle size was 6 μm.
m, the solubility coefficient was 9.4.

Example 7 Surface layer 2c in Example 2
Evaluation was performed in the same manner as in Example 2 except that the insulating additive used was 30 parts of silicone rubber fine powder. The results are shown in Tables 1 and 2.

However, the silicone rubber fine powder has a volume resistivity of 10 ¹⁶ Ωcm, an average primary particle diameter of 5 μm, and a solubility coefficient of 7.3.

Example 8 A resistance control layer 2d was formed on the conductive elastic layer 2b formed in Example 1 as follows. As the material of the resistance control layer 2d, polyurethane resin 100 superposed portion and conductive titanium oxide 75 superposed portion are dispersed and dissolved in a solvent of methyl ethyl ketone to prepare a resistance control layer coating material. This coating material is applied on the conductive elastic layer 2b by a dipping method to form a resistance control layer 2 having a thickness of 100 μm.
d was formed.

A surface layer 2c similar to that of Example 1 was formed on the resistance control layer 2d to prepare a charging roller 2 as shown in FIG. Using the charging roller 2 obtained, the same evaluation as in Example 1 was performed. The results are shown in Tables 1 and 2.

Example 9 Evaluations were made in the same manner as in Example 1 except that the surface of the conductive elastic layer 2b formed in Example 1 was subjected to polishing treatment to form a crown shape. The results are shown in Tables 1 and 2.

As is apparent from Tables 1 and 2, good results were obtained in the charging members (charging rollers) according to the present invention in Examples 1 to 9 or in the image forming apparatus using the charging members. .

Comparative Example 1 Surface layer 2c in Example 1
The evaluation was performed in the same manner as in Example 1 except that the conductive agent was not included. The results are shown in Tables 1 and 2.

As shown in Table 2, the potential on the surface of the photosensitive member is lowered by about 150v after the continuous image formation of 50,000 sheets, and the image density is lowered. It was found that such a structure of the charging roller lacks durability.

Comparative Example 2 Surface layer 2c in Example 1
The evaluation was performed in the same manner as in Example 1 except that the insulating additive was not included therein. The results are shown in Tables 1 and 2.

When an image was printed at a temperature of 23.5 ° C. and a humidity of 5% (environment 2), a very slight streak-like charging failure occurred in the halftone region of the obtained image. It is considered that since the conductive agent was not uniformly dispersed, it was not possible to suppress the occurrence of streak-shaped charging defects. If a uniform dispersed state is obtained, streak-shaped image defects are at a level that poses no practical problem.

Further, when the withstand voltage was measured in the same method and under the same environment as in Example 1, it was found that there was a leak at -1700 V and the withstand voltage was slightly problematic.

Comparative Example 3 Surface layer 2c in Example 1
Evaluation was performed in the same manner as in Example 1 except that the binder resin and the conductive agent used therein were a silicone resin (binder resin) 100 superposed portion and a conductive titanium oxide 100 superposed portion.
The results are shown in Tables 1 and 2.

In the halftone image area of the obtained image, slight black spots and extremely slight stripe-shaped charging defects were found.

When the withstand voltage was measured in the same method and under the same environment as in Example 1, it was found that there was a leak at -1300 V and there was a problem with the withstand voltage.

However, the volume resistivity of the silicone resin used as the binder resin was 10 ¹⁶ Ωcm. Therefore, as described above, it was necessary to contain a large amount of the conductive agent in the 100 superposed portions for the purpose of adjusting the resistance of the charging roller. Since the conductive agent was contained in a large amount, the degree of dispersion of the conductive agent was lowered and black spots were generated on the image.

Comparative Example 4 Surface layer 2c in Example 2
Evaluation was carried out in the same manner as in Example 2 except that the insulating additive used was a polymethyl methacrylate resin powder 30 superposed portion.
The results are shown in Tables 1 and 2.

However, the volume resistivity of polymethylmethacrylate used for the surface layer 2c is 10 ¹⁶ Ωcm, the average primary particle size is 6 μm, and the solubility coefficient is 9.4.

The polymethylmethacrylate resin powder used in Comparative Example 4 has a danger of being dissolved because the solubility coefficient of the methyl ethyl ketone solvent (solubility coefficient 9.3) used for preparing the coating solution is very close.

The presence of polymethylmethacrylate in the form of particles on the surface layer 2c of the charging roller 2 obtained in Comparative Example 4 was observed with an electron microscope to confirm the polymethylmethacrylate in the form of particles. I couldn't.

It is considered that the streak-like charging failure occurred because the polymethylmethacrylate powder was dissolved and did not exist in the form of particles, and the composition was out of the scope of the present invention.

[0121]

[Table 1]

[0122]

[Table 2]

[0123]

As described above, according to the present invention, in the charging member for contacting and charging the member to be charged, the surface layer of the charging member has a conductive agent, an insulating additive and a binder. The conductive resin, the insulating additive, and the binder resin are applied to the charging member by the relationship of conductive agent <binder resin <insulating additive, which is formed of a binder resin. Good uniform charging characteristics and output image quality and the like can be secured for the image forming apparatus both when the voltage is only the DC voltage and when the AC voltage is superimposed on the DC voltage.

Since the charging member is less likely to be charged up, the image density of the image forming apparatus hardly decreases even when a plurality of images are continuously output.

Further, since the charging member has a high withstand voltage, the risk of leakage is extremely small, and it can be effectively used as a contact charging type charging member.

Further, the performance of the contact charging type charging device, the image forming apparatus using the charging device, and the process cartridge is improved.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus.

FIG. 2 Model diagram of layer structure of charging roller

3A and 3B are schematic diagrams of (charging blade, charging block) of another example of the charging member.

FIG. 4 is an explanatory diagram of measurement of withstand voltage of a charging member.

[Explanation of symbols]

1 Charged Object (Photosensitive Drum) 2 Charging Member (Charging Roller, Charging Blade, Charging Block) 2a Core Bar 2b Conductive Elastic Layer 2c Surface Layer 3 Power Supply 4 Exposure Light 5 Developing Device 6 Paper Feed Cassette 7 Transfer Charger 8 Fixing Device 9 Cleaning device 10 Pre-exposure light 11 Process cartridge P Transfer material

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

Claims (11)

[Claims] 1. A charging member of a charging device, wherein a charging member is brought into contact with or close to a member to be charged and a voltage is applied to the charging member to charge the member to be charged, and the charging member is at least a conductive agent. There is a surface layer composed of an insulating additive and a binder resin, and the relationship between the conductive agent, the insulating additive, and the volume specific resistivity of the binder resin forming the surface layer is as follows: conductive agent <binder resin <insulation A charging member characterized by being a functional additive. 2. The volume resistivity of the conductive agent is 10 ⁶ Ω.
The charging member according to claim 1, wherein the charging member has a size of not more than cm. 3. The volume resistivity of the insulating additive is 1
The charging member according to claim 1, wherein the charging member has a resistance of 0 ¹³ Ωcm or more. 4. The insulating additive is spherical particles and has an average particle diameter of 50 μm or less.
The charging member according to 1. 5. The charging member is an image bearing member of an image forming apparatus, and the charging member is a member for primary charging of the image bearing member. Charging member. 6. The charging member according to claim 1, wherein the applied voltage is a DC voltage or an oscillating voltage. 7. The oscillating voltage is a superimposed voltage of an alternating voltage having a peak-to-peak voltage that is at least twice the charging start voltage of the member to be charged when the DC voltage and the DC voltage are applied. 6. The charging member according to item 6. 8. The charging member according to claim 1, which is a roller type. 9. A charging device for charging a charging member by bringing a charging member into contact with or close to the charging member and applying a voltage to the charging member, wherein the charging member is at least a conductive agent and an insulating additive. Of a conductive agent, an insulative additive and a binder resin which form the surface layer, and the volume resistivity of the binder resin is as follows: conductive agent <binder resin <insulating additive And an image forming apparatus. 10. An image forming apparatus for performing image formation by an image forming process including a step of charging an image carrier with a charging device, wherein the charging device brings a charging member into contact with the image carrier and This is a device for charging the image bearing member by applying a voltage, wherein the charging member has at least a surface layer composed of a conductive agent, an insulating additive and a binder resin. An image forming apparatus characterized in that the relationship between the volume resistivity of the conductive additive and the binder resin is: conductive agent <binder resin <insulating additive. 11. A process cartridge including at least an image carrier and a charging device for the image carrier, which is attached to and detached from an image forming apparatus main body, wherein the charging device brings a charging member into contact with the image carrier. A device for charging an image bearing member by applying a voltage to the charging member, wherein the charging member has a surface layer comprising at least a conductive agent, an insulating additive and a binder resin, and constitutes the surface layer. A process cartridge characterized in that the relationship between the volume resistivity of the conductive agent, the insulating additive and the binder resin is: conductive agent <binder resin <insulating additive.