JP2000293012A - Electrostatic charging member, electrostatic charging device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten a polishing time, to reduce a cost and to obviate the degradation in productivity by making the surface roughness at the end in the longitudinal direction of an electrostatic charging member larger than the surface roughness in the central part. SOLUTION: The surface roughness at the end in the longitudinal direction of the electrostatic charging member is made larger than the surface roughness in the central part. The electrostatic charging member 2 is provided with an elastic body 2b on an arbor 2a. A coating liquid for a dip coating method, roll coating method, etc., is used in the process for producing a resistance control layer 2c and a surface layer 2d. The coating liquid prepared by dissolving a resin, such as polyamide, into a solvent and dispersing a conducting agent, such as conductive carbon black, is used as the coating liquid. For example, a urethane coating material dispersed with the conductive carbon is formed by a paint shaker and elastic layer 2b is dip coated with the urethane coating material and is subjected to the evaporation of the solvent component in a hot oven, following which the elastic layer is provided with the surface layer 2d. Only the central part corresponding to the image region of the electrostatic charging member composed of the two layers in the manner described above is subjected to a polishing treatment and the end corresponding to the non-image region is not subjected to the polishing treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging member mainly used in an electrophotographic image forming apparatus, a charging device having the charging member, and an image forming apparatus having the charging device.

[0002]

2. Description of the Related Art An electrophotographic image forming apparatus such as an electrophotographic copying machine, an electrophotographic printer, and an electrostatic recording apparatus is provided with a primary charging means for uniformly charging an image carrier, and a developer on the image carrier with a printing material. It includes a unit for uniformly charging the object to be charged, such as a transfer unit that draws upward.

[0003] As a charging method used at that time, a contact charging method which generates much less ozone than the conventional corona charging method has been devised, and has been put into practical use in a configuration such as a roller shape, a brush shape, or a blade shape. .

[0004] The contact charging method is broadly classified into a method of charging an image carrier using a discharge phenomenon and a method of charging an image carrier using an injection phenomenon.

The main component of the discharge generated between the charging member and the image carrier is a discharge generated in a minute gap formed on both sides of the contact portion between the charging member and the image carrier. In the case of a rough surface, a discharge component generated in a minute gap formed in a contact portion with the image carrier cannot be ignored.

The method of charging using the injection phenomenon is a method of charging by injecting charges into the image carrier with a current flowing in a contact portion between the charging member and the image carrier.

FIG. 1 is a sectional view of an example of a contact-type charging member. The charging member 2 controls the core metal 2a, the elastic layer 2b for giving elasticity to the charging member, the seepage preventing layer for preventing the plasticizer or the like from bleeding out from the elastic layer 2b, the electrode layer or the electrical characteristics of the charging member 2. It is common to use a plurality of functionally separated layers such as a resistance control layer 2c and a surface layer 2d provided in order to prevent scratches and contamination on an image carrier such as a photoconductor.

FIG. 2 shows a schematic configuration diagram of an image forming apparatus (copier) using a contact charging method. The charging member 2 is in contact with the image carrier 1 with a predetermined contact force by pressing means (not shown). The image carrier 1 includes a conductive support 1a and a photosensitive layer 1b. An oscillating voltage such as a DC voltage or a superimposed voltage of a DC voltage and an AC voltage is applied to the metal core 2 a from the power supply 3, and the photosensitive layer 1 b with which the charging member 2 contacts is charged.
Here, the charging member 2 and the image carrier 1 rotate in the directions of the arrows, respectively, but the charging member 2 generally follows the image carrier 1 by frictional force. Charged photosensitive layer 1b
Forms a latent image in an exposure step 4, and a photosensitive layer 1b in a development step 5.
A developer is attached on the top to form a visible image. The visible image is transferred onto the printing material 7 in the transfer process 6 and becomes an image on the printing material 7 in a fixing process (not shown). The photosensitive layer 1b that has undergone the transfer step 6 is charged again by the charging member 2 through a cleaning step 8 of physical cleaning and, if necessary, a pre-exposure step (not shown) of electrical initialization.

As described above, in the contact charging method, since the charging member 2 contacts the image carrier 1 to perform charging, the surface property of the charging member 2 directly affects the charging uniformity of the image carrier 1. .

That is, when there are partial irregularities due to manufacturing defects or scratches on the surface of the charging member 2, abnormal discharge or abnormal charge injection occurs starting from the irregularities,
The charging uniformity of the image carrier 1 is impaired, and image defects such as black spots and white spots on the image occur.

Further, even if foreign matter adheres to the surface of the charging member 2, an image defect similarly occurs. Examples of the foreign matter include an untransferred developer that cannot be completely removed in the cleaning process 8 and a paper powder that is a residue of the printing material 7.

As measures to prevent foreign substances from adhering to the surface of the charging member 2, it is effective to use a highly releasable material on the surface of the charging member 2 and to reduce the surface roughness of the charging member 2. It is known that there is.

However, if the surface roughness of the charging member 2 is too small when a highly releasable material is used, the coefficient of friction between the charging member 2 and the image carrier 1 becomes small, and the member becomes slippery. There is a problem that the charging member 2 does not follow the image carrier 1.

In this case, a driving device for rotating the charging member 2 by itself is newly provided. The surface roughness of the charging member 2 is appropriately adjusted depending on the amount, size, and shape of the adhered foreign matter so that the foreign matter does not excessively adhere to the surface and is large enough not to slip on the image carrier 1. JP-A-5-257362
As disclosed in Japanese Patent Application Laid-Open No. H11-163, measures have been taken such as newly providing a member having a large friction coefficient in a non-image area to secure a followable frictional force.

[0015]

However, the charging member 2 using the above-mentioned highly releasable material or reducing the surface roughness has the following problems.

First, there is an increase in the polishing time required to reduce the surface roughness as compared with the prior art. Prolonging the polishing time causes a decrease in productivity and an increase in cost due to an increase in man-hours.

Second, when a driving device for the charging member 2 is newly provided, the cost is increased due to an increase in the size of the device and an increase in the number of parts.

Third, there is a reduction in productivity in the case where the adjustment of the surface roughness allows both the reduction of the adhesion amount and the securing of the frictional force. This is because the allowable range of the surface roughness that can satisfy the contradictory characteristics is narrow, so that precise polishing or strict sorting is required, and the yield rate is reduced.

Fourth, when a member having a large coefficient of friction is newly provided at the end, the cost is increased and the reliability is low. The initial frictional force can be obtained simply by providing a member having a large friction coefficient. However, if image formation is continuously performed, the developer and the like also accumulate on the surface of the end portion of the charging member. May change to a smaller value, and the charging member may not follow the image carrier.

An object of the present invention is to provide a charging member, a charging device, and an image forming apparatus which do not reduce productivity or increase costs even in the above-described image forming apparatus.

[0021]

SUMMARY OF THE INVENTION The present invention provides a charging member for charging an image carrier while applying a voltage to the image carrier while contacting the image carrier. , A charging member characterized by being larger than the surface roughness of the central portion, more preferably a roller-shaped charging member.

It is important that the "central portion" includes at least the image area, and the "end portion" refers to all portions except the "central portion". In addition, the "end"
Is preferably present on both sides of the “central portion”, but since the function may be performed on one side, the “end portion” does not necessarily have to be provided on both sides. It may be coincident with one end of the charging member. Of course, both ends of the “central portion” cannot coincide with both ends of the charging member.

In the present invention, the object to be charged may be charged by applying a voltage to the charging member, and more preferably by applying a voltage having only a DC voltage having no vibration component. A charging device characterized by the following. Still more preferably, the charging device is characterized in that the charging member is driven by the image carrier by frictional force.

Also, the present invention provides at least the charging device, an exposure device for forming an electrostatic latent image on an image carrier, and a developer, more preferably, a developer formed on the electrostatic latent image by a polymerization method. An image forming apparatus, comprising: a developing device for attaching a developer chemically synthesized by the method described above to form a visualized image; and a transfer device for transferring the visualized image to a printing medium. Still more preferably, the image forming apparatus described above does not have a container for collecting and storing the developer remaining on the image carrier without being transferred.

According to the present invention, there is provided the image forming apparatus as described above, wherein the ten-point average roughness at the center in the longitudinal direction of the charging member is smaller than the volume average particle diameter of the developer. In the above image forming apparatus, the ten-point average roughness of the end portion in the longitudinal direction of the charging member is larger than the volume average particle diameter of the developer.

According to the present invention, first, the time required for the surface roughness changing step such as polishing or blasting can be reduced, and the cost can be reduced. When the surface roughness of the charging member before the surface roughness changing step is larger than the desired surface roughness, polishing is performed to reduce the surface roughness, but in the present invention, only a necessary portion may be subjected to polishing. Therefore, the time can be reduced and the life of the abrasive can be extended as compared with the conventional case where the entire surface is polished.
When the surface roughness of the charging member before the surface roughness changing step is smaller than the desired surface roughness, blasting or the like is performed to increase the surface roughness. Therefore, the time can be reduced and the amount of the roughening material to be sprayed can be reduced as compared with the conventional case where the entire surface is blasted.

When the surface roughness is reduced in order to prevent the developer from adhering to the central portion of the surface of the charging member, the surface roughness is the ten-point average roughness (Rz) of JIS-B0601.
Is preferably smaller than the volume average particle diameter of the developer to be attached. This is to prevent the developer from being buried in microscopic unevenness existing on the surface of the charging member. When the developer is buried, even if the image carrier is repeatedly contacted, only the force in the direction perpendicular to the surface of the charging member acts on the buried developer, so that the developer adheres more firmly to the surface of the charging member. Would. However, if the ten-point average roughness of the surface of the charging member is smaller than the volume average particle size of the developer, even if the developer is attached, the attached developer is in a state of protruding from the irregularities, A force parallel to the surface of the charging member, that is, a shearing force acts upon repeated contact with the image carrier. Since this shearing force acts in a direction to move the attached developer laterally, the developer drops off, and it becomes possible to prevent the developer from being deposited.

The surface roughness in the case where the surface roughness of the surface end is increased in order to secure a frictional force that allows the charging member to follow the image carrier is determined by the ten-point average roughness (R) of JIS-B0601.
z) is preferably larger than the volume average particle size of the developer used. As described above, when the ten-point average roughness of the charging member is smaller than the volume average particle size of the developer, when the developer adheres to the edge, the attached developer comes out of the irregularities. State. Therefore, since the developer that has come out of the face instead of the convex portion of the charging member surface comes into contact with the image carrier repeatedly, the frictional force between the charging member and the image carrier changes, and the frictional force decreases. In such a case, it becomes impossible to follow. However, if the ten-point average roughness of the charging member is larger than the volume average particle diameter of the developer, even if the developer adheres to the edge, the adhered developer is buried in the irregularities. Therefore,
The protrusions on the surface of the charging member can be repeatedly brought into contact with the image carrier, so that the frictional force that can be driven does not change.

Here, as a method for measuring the surface roughness of the charging member, the ten-point average roughness (Rz) of JIS-B0601 is preferable. The maximum height (Ry) is not suitable for displaying the entire surface of the charging member because the influence of surface defects such as flaws is easily picked up. Further, the arithmetic average roughness (Ra) is not preferable as an index of the present invention because it is difficult to distinguish between a case where there are many small irregularities and a case where large irregularities are scattered.

Recently, image forming apparatuses have been improved in image quality.
A reduction in size and cost are required, and methods of reducing the diameter of the developer, eliminating the cleaning step 8, and using only the DC power supply as the power supply 3 and omitting the AC power supply are being studied. To improve image quality, it is becoming necessary to stabilize the shape in addition to reducing the diameter of the developer. Conventionally, a pulverization method has been generally used as a method for producing a developer, but a developer formed by a pulverization method has an uneven shape. On the other hand, the developer chemically synthesized by the polymerization method is
Since the shape is stable in a spherical shape, a developer using a polymerization method has been studied.

If the cleaning step 8 is omitted, the untransferred developer and paper dust present on the image carrier 1 after the transfer step 6 are not removed and come into contact with the charging member 2. The amount of deposits increases.

When the diameter of the developer is reduced, the untransferred developer easily passes through the cleaning step 8, so that the charging member 2
Deposits on the top increase.

When the developer becomes spherical, the untransferred developer that has passed through the cleaning step 8 plays a role of a roller on the contact surface between the charging member 2 and the image carrier 1 and becomes slippery. It is difficult to follow the image carrier 1.

If the AC power supply is omitted and only the DC power supply is used, the effect of leveling the potential by the AC component is lost.
The uniformity of charging on the image carrier 1 is substantially controlled only by the uniformity of resistance and the uniformity of the surface of the charging member 2, and the allowable amount of adhesion of foreign substances is smaller than that during the AC superposition.

As described above, in an image forming apparatus capable of achieving high image quality, miniaturization, and cost reduction, the amount of foreign substances adhering to the charging member 2 increases, the allowable adhering amount is small, and Thus, the charging member 2 and the image carrier 1 have a more slippery relationship.

According to the structure of the present invention, the amount of foreign matter adhering to the surface of the charging member can be reduced without impairing the frictional force with the image carrier, so that any of the above cases can be solved at low cost. is there.

[0037]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The inventor has described the high image quality described above,
Even in image forming apparatuses corresponding to miniaturization and cost reduction,
A detailed study of the charging member, the charging device and the image forming apparatus, which does not increase the cost by minimizing the surface roughness and newly installing the charging member driving device, found that the surface roughness of the end portion in the longitudinal direction of the charging member was centered It has been found that the problem can be solved by increasing the surface roughness of the part.

Among the charging members 2 applicable to the present invention, as the elastic body 2b provided on the core metal 2a, a conductive elastic body in which conductive carbon is dispersed in silicone rubber or the like can be used. The conductive elastic body includes rubbers and thermoplastic elastomers such as isoprene rubber, styrene rubber, butadiene rubber, nitrile rubber, chloroprene rubber, butyl rubber, acrylic rubber, urethane rubber, fluorine rubber, ethylene propylene rubber and epichlorohydrin rubber, and graphite. Alternatively, a conductive material such as a metal fine powder and a metal oxide may be added in an appropriate amount.

The elastic body 2b can be formed by using an injection molding machine and vulcanizing simultaneously with molding in a straight or crown-shaped mold. As other methods, a foaming agent is added to form a sponge formed by foaming simultaneously with vulcanization in a vulcanizing can, or a thermoplastic elastomer is extruded into a tube and pressed into a cored bar 2a to form a sponge. It may be formed into a straight or crown shape by polishing.

As a method for producing the above-mentioned bleeding prevention layer, electrode layer or resistance control layer 2c, and surface layer 2d, a method using a coating solution such as a dip coating method and a roll coating method is generally used.

As the coating liquid, a liquid in which a resin such as polyamide is dissolved in a solvent and a liquid in which a conductive agent such as conductive carbon black is dispersed can be used. In addition to polyamide, polyester, polyurethane, fluorine, silicone, acrylic, polyolefin,
Resins such as phenol and blends thereof can be used, but fluorine, silicone, and a part of polyamide are preferable because of high releasability. As the conductive agent,
In addition to conductive carbon, metal oxides such as tin oxide and titanium oxide, metal powders, and ionic conductive agents such as lithium perchlorate can be used.

Recently, a method has also been devised in which a seamless tube is coated to provide the seepage prevention layer, the electrode layer or the resistance control layer 2c, and the surface layer 2d. The seamless tube is roughly classified into a heat-shrinkable tube and a non-heat-shrinkable tube depending on a coating method, and any of the present invention can be applied.

When a heat-shrinkable tube is used, a heat-shrinkable tube is prepared with an inner diameter larger than the maximum diameter of the object to be coated, the object to be coated is inserted inside the tube, heat is applied, and the tube is shrunk. Integrate with the object to be coated.

When a non-heat-shrinkable tube is used, thermoplastic elastomer tubes such as thermoplastic styrene elastomers, thermoplastic urethane elastomers, thermoplastic olefin elastomers, thermoplastic amide elastomers and thermoplastic polyester elastomers, and polymer alloys thereof. Is used as a base resin, and additives such as a conductive agent are added depending on the purpose of use. The compound thus obtained is extruded by extrusion into a tube having an inner diameter smaller than the minimum outer diameter of the object to be coated to obtain a non-heat-shrinkable tube. When coating the tube on the object to be coated, pressurized air or the like is blown into the inside of the tube, and the tube is coated while expanding the tube to an inner diameter larger than the maximum outer diameter of the object to be coated. When an object is inserted and the widening means such as air pressure is shut off, the tube tends to return to the initial inner diameter due to its elasticity, and the tube and the object to be covered come into close contact with each other and are integrated.

Although the method of forming the charging roller has been described above, the charging member of the present invention is formed by injecting a charging blade or a thermoplastic resin formed by curing liquid urethane or the like in a mold using a casting machine. It can also be applied to fixed chargers created by molding machines. The charging member created by these methods,
If necessary, it is polished to a desired surface roughness before use.

[0046]

The present invention will be described with reference to the following examples. In the embodiment, the description is made using the contact-type charging roller, but the present invention is not limited to this embodiment.

Example 1 (Preparation of Elastic Body) A vulcanizing agent and a foaming agent were blended with EPDM rubber in which conductive carbon was dispersed by a Banbury mixer with two rolls, and formed into a tube by extrusion. did.
When this tube-shaped molded product was foamed in a vulcanizing can,
A sponge tube having a length of 240 mm, an inner diameter of 5 mm, and an outer diameter of 15 mm was obtained.

A core having a length of 240 mm and an outer diameter of 6 mm to which an adhesive was applied was inserted into the inside of the sponge tube.
An elastic layer was formed by bonding the core metal and the elastic body in a heat oven.

The sponge elastic layer was adjusted to a length of 220 mm so that both ends of the cored bar were left by 10 mm by the cut-off. The entire surface of the elastic layer with the metal core was polished uniformly and finished in a straight shape with an outer diameter of 11.35 mm. The skin layer was removed to expose the foam cells, and the surface roughness of the elastic layer was about 50 μm in terms of a ten-point average roughness.

(Preparation of Surface Layer) A urethane paint in which conductive carbon was dispersed was prepared using a paint shaker.
The elastic layer was dip-coated with the urethane paint, and the solvent component was volatilized in a hot oven to provide a surface layer having a thickness of 80 μm.

(Adjustment of Surface Roughness) A charging member having a two-layer structure was prepared as described above, and its surface roughness was measured. The roughness was uniform and the ten-point average roughness was 12 μm. Was.
Polishing was performed only on the central portion corresponding to the image area of the charging member, and polishing was not performed on the edge corresponding to the non-image area. When the surface roughness was measured, the tenth-point average roughness of the non-polished end was 12 μm, which was unchanged, but the polished central part was ten-point average roughness of 9 μm.
m. In addition, the polishing time was 20 seconds per one.

(Setting of Condition of Charging Apparatus) A contact-type charging apparatus in which the contact-type charging member is brought into contact with a photoreceptor, and an oscillating voltage obtained by superimposing an AC voltage and a DC voltage is applied to a core bar to charge the photoreceptor I got A configuration was adopted in which the charging member was driven by the photosensitive member without providing a driving device.

(Setting of Conditions of Image Forming Apparatus) This contact type charging apparatus is incorporated in an image forming apparatus including a cleaning step, and an image is formed at a resolution of 600 dpi using a developer having a volume average particle diameter of 9 μm prepared by a pulverizing method. An evaluation was performed. The image evaluation was performed on the 500th sheet, the 8,000th sheet, and the 10,000th sheet in the initial and A4 sizes.

(Result of Image Evaluation) The image was good over the entire length of the charged area. Further, when the image evaluation was continued,
From the time when 8,000 sheets of four sizes passed, slight image defects due to charging failure occurred in a low temperature (15 ° C.) and low humidity (10% RH) environment. When the charging member was observed, the developer was deposited only on a part of the charging member. Although there is no problem in practical use,
Compared with the result of Comparative Example 2 described later, it shows that the ten-point average roughness of the central part of the charging member in comparison with the volume average particle diameter of the developer is the upper limit.

Comparative Example 1 (Preparation of Elastic Body) Same as in Example 1.

(Formation of Surface Layer) Same as Example 1.

(Adjustment of Surface Roughness) The entire surface of the charging member is polished, the surface roughness of the charging member is uniform at 9 μm in terms of a ten-point average roughness, and the polishing time is 25 times per line. Same as Example 1 except that it was seconds.

(Setting of Charge Device Conditions) Same as in the first embodiment.

(Setting of Conditions of Image Forming Apparatus) Same as in the first embodiment.

(Image Evaluation Result) The image evaluation result was the same as that of the first embodiment. However, in the comparative example 1, the polishing time was longer than that of the first embodiment by 5 seconds, so that the cost was increased.

Comparative Example 2 (Preparation of Elastic Body) Same as in Example 1.

(Formation of Surface Layer) Same as in Example 1.

(Adjustment of Surface Roughness) Example 1 was repeated except that the entire surface of the charging member was not polished, and the surface roughness of the charging member was still 12 μm in terms of the ten-point average roughness. the same.

(Setting of Charging Device Conditions) Same as in the first embodiment.

(Setting of Conditions of Image Forming Apparatus) Same as in the first embodiment.

(Results of Image Evaluation) The image was good over the entire length of the charged area. Further, when the image evaluation was continued,
Halftone image defects occurred in a low-temperature (15 ° C.) and low-humidity (10% RH) environment from the time when five hundred sheets of four sizes had passed. When the charging member was observed, the developer was deposited in the concave portions on the surface of the charging member. This is because charging failure has occurred in the developer accumulation portion. This is a level that cannot be put to practical use.

[Embodiment 2] (Preparation of elastic body) Same as Embodiment 1.

(Formation of Surface Layer) The same as in Example 1 except that the urethane paint was changed to a highly releasable fluorine paint.

(Adjustment of Surface Roughness) Same as in Example 1.

(Setting of Charging Device Conditions) Same as in the first embodiment.

(Setting of Conditions of Image Forming Apparatus) Same as in the first embodiment.

(Results of Image Evaluation) The image was good over the entire charged area. Further, when the image evaluation was continued,
Even after printing 10,000 sheets of four sizes, no deterioration was observed in the image, and the image was very good. Therefore, in addition to 600 dpi, 12
When the image was evaluated at a resolution of 00 dpi, it was difficult to reproduce the halftone from the beginning. This is a level that is not problematic for normal image quality, but cannot be provided for high image quality.

Example 3 (Preparation of Elastic Body) Same as Example 1.

(Formation of Surface Layer) Same as Example 2.

(Adjustment of Surface Roughness) Same as in Example 1.

(Setting of Charging Device Conditions) Same as in the first embodiment.

(Setting of Conditions of Image Forming Apparatus) Same as Example 1 except that a developer having a volume average particle diameter of 6 μm prepared by a pulverization method was used.

(Evaluation Result of Image) The evaluation result at a resolution of 600 dpi was the same as that of the embodiment 2, and was at a practical level.
Therefore, when the image evaluation was performed even at a resolution of 1200 dpi, the initial image was good over the entire charged area.
Further, when the image evaluation was continued, a halftone dot image defect occurred in a low-temperature (15 ° C.) low-humidity (10% RH) environment when about 500 sheets of A4 size had passed. When the charging member was observed, the developer was deposited in the concave portions on the surface of the charging member. This is because charging failure has occurred in the developer accumulation portion. This is a practical level for normal image quality, but not for high image quality.

Embodiment 4 (Preparation of Elastic Body) Same as in Embodiment 1.

(Preparation of Surface Layer) Except that the lifting speed during the dip coating was increased to make the thickness of the surface layer 100 μm,
Same as Example 2.

(Adjustment of Surface Roughness) The surface roughness before the polishing treatment is uniform with a ten-point average roughness of 9 μm, and only the central portion corresponding to the image area of the charging member is subjected to the polishing treatment. The edge corresponding to the image area was not polished, and its surface roughness was measured. The edge not polished had a ten-point average roughness of 9 μm, which was unchanged, but the center of the polished center was unchanged. The same as Example 1 except that the part had a six-point average roughness of 6 μm.

(Setting of Charge Device Conditions) Same as in the first embodiment.

(Setting of Conditions for Image Forming Apparatus) Same as in the third embodiment.

(Evaluation result of image) The evaluation result at the resolution of 600 dpi was the same as that of the embodiment 2 and was at a practical level.
Therefore, when the image evaluation was performed even at a resolution of 1200 dpi, the initial image was good over the entire charged area.
Further, when the image evaluation was continued, slight image defects due to defective charging occurred in a low-temperature (15 ° C.) low-humidity (10% RH) environment around 8,000 sheets of A4 size. When the charging member was observed, the developer was deposited only on a part of the charging member. Although there is no problem in practical use, for high image quality, the upper limit is the ten-point average roughness of the central part of the charging member as compared to the volume average particle diameter of the developer.

Example 5 (Preparation of Elastic Body) Same as in Example 1.

(Formation of Surface Layer) Same as Example 1.

(Adjustment of Surface Roughness) Same as in Example 1.

(Setting of Conditions of Charging Device) The same as Example 1 except that only a DC voltage was applied to the cored bar.

(Setting of Conditions of Image Forming Apparatus) Same as in the first embodiment.

(Result of Image Evaluation) The image was good over the entire length of the charged area. Further, when the image evaluation was continued,
From the time when 8,000 sheets of four sizes passed, slight image defects due to charging failure occurred in a low temperature (15 ° C.) and low humidity (10% RH) environment. When the charging member was observed, the developer was deposited only on a part of the charging member. Although there is no problem in practical use,
It shows that the upper limit is the ten-point average roughness of the central part of the charging member as compared to the volume average particle diameter of the developer.

[Embodiment 6] (Preparation of elastic body) Same as Embodiment 1.

(Formation of Surface Layer) Same as Example 4.

(Adjustment of Surface Roughness) Same as in Example 4.

(Setting of Charging Device Conditions) Same as in the fifth embodiment.

(Setting of Conditions of Image Forming Apparatus) Same as Example 1 except that a developer having a volume average particle diameter of 6 μm prepared by a pulverization method was used.

(Result of Image Evaluation) The image was good over the entire charged area. Further, when the image evaluation was continued,
Even after printing 10,000 sheets of four sizes, no deterioration was observed in the image, and the image was very good.

Example 7 (Preparation of Elastic Body) Same as in Example 1.

(Formation of Surface Layer) Same as in Example 4.

(Adjustment of Surface Roughness) Same as in Example 4.

(Setting of Charging Device Conditions) Same as in the fifth embodiment.

(Setting of Conditions of Image Forming Apparatus) The same as the sixth embodiment except that the image forming apparatus has no cleaning step.

(Result of Image Evaluation) The image was good over the entire length of the charged area. Further, when the image evaluation was continued,
From the time when 8,000 sheets of four sizes passed, slight image defects due to charging failure occurred in a low temperature (15 ° C.) and low humidity (10% RH) environment. When the charging member was observed, the developer was deposited only on a part of the charging member. When the charging member was observed, the developer was deposited only on a part of the charging member. Although there is no problem in practical use, the upper limit is the ten-point average roughness of the central portion of the charging member in comparison with the volume average particle diameter of the developer.

[Embodiment 8] (Preparation of elastic body) Same as in Embodiment 1.

(Formation of Surface Layer) Same as in Example 4.

(Adjustment of Surface Roughness) Same as Example 4.

(Setting of Charging Device Conditions) Same as in the fifth embodiment.

(Setting of Conditions for Image Forming Apparatus) The same as Example 7 except that the developer used was a developer having a volume average particle diameter of 6 μm prepared by a polymerization method.

(Result of Image Evaluation) The image was good over the entire charged area. Further, when the image evaluation was continued,
Even after printing 10,000 sheets of four sizes, no deterioration was observed in the image, and the image was very good.

Comparative Example 3 (Preparation of Elastic Body) A silicone rubber compound was obtained by mixing a vulcanizing agent with two rolls into silicone rubber in which conductive carbon was dispersed using a Banbury mixer. A core metal having a length of 240 mm and an outer diameter of 6 mm to which an adhesive has been applied is injection-molded into a mold previously set at the center, and a rubber length of 220 mm and a rubber outer diameter of 11.3 are provided.
An elastic body of a 5 mm solid rubber roller was prepared. The surface roughness of the elastic layer was 1.2 μm as a ten-point average roughness.

(Preparation of Surface Layer) A high release fluorine coating material in which conductive carbon was dispersed was prepared using a paint shaker. The elastic layer was dip-coated with the fluorine paint, and the solvent component was volatilized in a hot oven to provide a surface layer having a thickness of 10 μm.

(Adjustment of Surface Roughness) A charging member having a two-layer structure was prepared as described above, and its surface roughness was measured. The roughness was uniform and the ten-point average roughness was 3 μm. Was. Polishing was not performed on the entire surface of the charging member, and the surface roughness of the charging member was kept at a uniform 10-point average roughness of 3 μm.

(Setting of Charge Device Conditions) Same as in the fifth embodiment.

(Setting of Conditions of Image Forming Apparatus) Same as in the eighth embodiment.

(Results of Image Evaluation) From the beginning, abnormal noise was generated from the charging device, and image disturbance frequently occurred. When the charging device in operation was observed, it was easily confirmed that the charging member was not driven when the photosensitive member was started, a slip sound was generated, and the charging member was not driven. The image was disturbed because the charging member was unevenly charged when the charging member rubbed against the photoreceptor, and a large torque was applied to the rotation of the photoreceptor, and the rotation of the photoreceptor became non-uniform. It is.

Example 9 (Preparation of Elastic Body) Same as Comparative Example 3.

(Formation of Surface Layer) Same as Comparative Example 3.

(Adjustment of Surface Roughness) The central portion corresponding to the image area of the charging member is masked, and the blast processing is performed with the end corresponding to the non-image area exposed, and the surface roughness is measured. As a result, the center part subjected to masking had a ten-point average roughness of 3 μm, which was unchanged, but the end part subjected to blasting had a ten-point average roughness of 6 μm.
The same as Comparative Example 3 except that

(Setting of Charging Device Conditions) Same as in the fifth embodiment.

(Setting of Conditions of Image Forming Apparatus) Same as in the eighth embodiment.

(Result of Image Evaluation) The image was good over the entire charged area. Further, when the image evaluation was continued,
Even after printing 10,000 sheets of four sizes, no deterioration was observed in the image, and the image was very good. Although there is no problem on the image, an abnormal noise may be generated from the charging device at the start of image formation. When an image was output while observing the charging device, a phenomenon that the charging member did not follow when the photoreceptor was started and a slip sound was generated, and the charging member followed following a breathing, was rarely observed. Since the delay was about one breath, there was no problem in the image because the photosensitive member was being rotated in front. It shows that the ten-point average roughness of the end portion of the charging member in comparison with the volume average particle size of the developer is the lower limit.

[0121]

As described above, in the charging member for charging the image carrier while applying voltage to the image carrier while contacting the image carrier, the surface roughness of the end portion in the longitudinal direction of the charging member is reduced to the center. Larger than the surface roughness of the portion, more preferably, the ten-point average roughness of the central portion in the longitudinal direction of the charging member is smaller than the volume average particle size of the developer, or the end portion in the longitudinal direction of the charging member. Since the ten-point average roughness is larger than the volume average particle size of the developer, not only can it be possible to achieve cost reduction by shortening the polishing time, but also a small-diameter developer and a spherical developer for high image quality, Even in image forming apparatuses that have eliminated the cleaning process and AC power supply for the purpose of miniaturization and cost reduction,
It is possible to solve problems such as poor charging due to the accumulation of the developer, a failure in which the charging member does not follow the image carrier, resulting in a defective image, or an increase in cost due to a new charging member driving device provided for preventing slip.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a charging member of the present invention.

FIG. 2 is a schematic configuration diagram illustrating an example of an image forming apparatus using a charging member according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image carrier 1a Conductive support 1b Photosensitive layer 2 Charging member 2a Core 2b Elastic layer 2c Resistance control layer 2d Surface layer 3 Power supply 4 Exposure step 5 Development step 6 Transfer step 7 Printed matter 8 Cleaning step

 ────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Hiroyuki Nagata 3-30-2 Shimomaruko, Ota-ku, Tokyo F-term in Canon Inc. (reference) 2H003 AA12 BB07 BB11 CC05 2H005 AB06 3J103 AA02 AA15 AA23 AA32 AA37 AA51 AA72 FA07 FA15 FA18 FA19 FA30 GA02 GA57 GA58 GA66 HA04 HA20 HA53 HA54 5G067 AA27 AA65 DA01 DA18

Claims (10)

[Claims] 1. A charging member for charging an image carrier while contacting the image carrier by applying a voltage, wherein a surface roughness of an end portion in a longitudinal direction of the charging member is larger than a surface roughness of a central portion thereof. A charging member characterized by being large. 2. The charging member according to claim 1, wherein the charging member has a roller shape. 3. A charging device, wherein a voltage is applied to the charging member according to claim 1 to charge the image carrier. 4. The charging device according to claim 3, wherein the charging member is driven by the image carrier by a frictional force. 5. The charging device according to claim 3, wherein the applied voltage is only a DC voltage having no vibration component. 6. A charging device according to claim 3, an exposure device for forming an electrostatic latent image on an image carrier, and a developer attached to the electrostatic latent image. An image forming apparatus comprising: a developing device for developing a visible image; and a transfer device for transferring the developed image to a print substrate. 7. The image forming apparatus according to claim 6, wherein there is no container for collecting and storing the developer remaining on the image carrier without being transferred. 8. The image forming apparatus according to claim 6, wherein the developer is a developer chemically synthesized by a polymerization method. 9. The developer according to claim 6, wherein the ten-point average roughness at the center in the longitudinal direction of the charging member is smaller than the volume average particle diameter of the developer.
The image forming apparatus according to claim 1. 10. The developer according to claim 6, wherein the ten-point average roughness of the end portion in the longitudinal direction of the charging member is larger than the volume average particle diameter of the developer.
The image forming apparatus according to claim 1.