JPH1048911A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device by which the adhesion of foreign matter to a charge-providing member can be prevented and uniform electrification can be stably carried out with a simple constitution, and also a stable image quality can be obtained for a long period of time without exerting any influence on the other process or the like. SOLUTION: An image forming device is provided with a toner-image carrier 1 for carrying a toner image on its surface, a charge-providing member 2 for providing a prescribed charge to the toner-image carrier 1, a toner-image forming means for forming a toner image according to image information on the toner-image carrier 1 to which a charge has been provided by the charge- providing member 2, and a transferring means for transferring the toner image on the toner-image carrier 1 to a recording medium. Further, the charge- providing member 2 is made to have a surface energy relatively lower than the surface energy of the toner-image carrier 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as an electrophotographic copying machine or a printer.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as an electrophotographic copying machine or a printer, the surface of a toner image carrier such as a photoreceptor drum is charged and then image-exposed to form a surface of the toner image carrier. An electrostatic latent image is formed, the electrostatic latent image is visualized by developing the electrostatic latent image with a developer to form a developed image on the toner image carrier, and the developed image is recorded on a recording medium such as paper. The image is formed on the recording medium by transferring and fixing to the recording medium. Such an image forming apparatus includes a charger for charging the toner image carrier by uniformly applying a charge to the toner image carrier carrying the toner image, and removing the charge accumulated on the toner image carrier. Therefore, a static eliminator or the like that uniformly applies a charge to the toner image carrier is used. As the charger, two types of charging systems, a non-contact charging system using corona discharge or the like, and a contact charging system using a charging roll using discharge in a minute gap are used.

In a charger using corona discharge, a high voltage is applied to a wire stretched opposite to the surface of a toner image carrier to which a charge is to be applied, so that a corona is applied between the toner image carrier and the wire. A discharge is generated, and a predetermined charge is applied to the toner image carrier. Although this type of charger is excellent in charging uniformity, it generates a large amount of discharge products such as ozone and NOx, so that a processing device is required, which tends to increase the size and cost of the image forming apparatus. There are drawbacks. In addition, the electrode wires may become dirty with dust, toner, discharge products, fuser oil and the like in the air, resulting in non-uniform charging, which may cause image defects.

For this reason, recently, instead of the corona discharge method, the use of a contact charging method in which a charge applying member is brought into direct contact with a toner image carrier to perform charging has been studied. In this contact charging system, a roll-shaped or brush-shaped charge applying member having semi-conductivity is arranged so as to be in contact with the surface of the toner image carrier, and a voltage is applied to the charge applying member to apply a voltage to the toner image carrier at the contact portion. Electric charges are applied to the toner image carrier by generating a discharge in the upper minute gap. In this method, corona discharge is not used, so that the amount of generated ozone is extremely small, and since the charge applying member is in contact with the toner image carrier, the method is suitable for reducing the size and weight of the apparatus.

However, an apparatus using a roll-shaped charge applying member has a drawback that the structure tends to be complicated because a roll supporting mechanism and the like are required. Further, it is necessary to form a stable micro void by improving the adhesion between the charge applying member and the toner image carrier by forming the charge applying member with an elastic material such as rubber in order to perform uniform charging, Therefore, a large amount of process oil or the like must be added to the rubber, and there is a problem that the process oil easily transfers to the toner image carrier and adversely affects the image quality. Although a method of finishing the outer shape of the roll with high accuracy has been proposed to improve the adhesion to the toner image carrier, it is very difficult to finish the elastic body with high accuracy, and the cost is reduced due to a decrease in yield. It is easy to invite up.

Further, in an apparatus using a brush-like charge applying member, it is relatively easy to make the charge applying member uniformly contact the toner image carrier, but it takes time and effort to manufacture the brush, and the brush is swept. There is a problem that the eyes tend to appear on the image as uneven charging. Further, as an improved type of the contact charging system, Japanese Patent Application Laid-Open Nos.
Japanese Patent Application Laid-Open No. Hei 4-249279 discloses a charger which employs a blade-shaped charge applying member and also serves as a cleaning blade. A conventional charger is disclosed. However, it is difficult for the above-mentioned charger, which serves both as a blade-shaped charge applying member and a cleaning blade, to maintain both cleaning accuracy and to maintain a minute gap required for discharging, and to perform uniform and good charging. It is difficult. In a charger using a blade-shaped charge applying member, since the charge applying member is stationary with respect to the toner image carrier, contamination such as toner and external additives remaining on the toner image carrier after transfer is caused. There is a problem that these stains easily cause image quality defects and abnormal discharge.

[0007] In the case of a contact charger using a film-like charge applying member, a stable contact state can be easily obtained with a simple configuration and the member cost is inexpensive as compared with a charger using another charge applying member. However, as in the case of the blade-shaped charge applying member, there is a problem that dirt due to foreign matter such as toner easily adheres to the contact nip, and the charging potential tends to be nonuniform.

[0008] As described above, since the contact charger brings the charge applying member into contact with the toner image carrier, dirt such as toner, discharge products, dust in the air, and paper dust easily adheres to the charge applying member. If such dirt adheres, abnormal discharge or unstable discharge occurs, and there is a problem that image quality defects such as fog are easily caused. The non-uniform charging due to the adhesion of dirt becomes particularly remarkable when a DC voltage is applied, and an image quality defect due to the non-uniform charging may be a fatal problem particularly for an image forming apparatus for high image quality.

Therefore, as a solution to the above-mentioned problem of dirt, Japanese Patent Application Laid-Open Nos. 5-53413 and 5-2.
No. 65307 discloses a method of providing cleaning means for removing dirt on the surface of the charge applying member,
Also, JP-A-4-303861, JP-A-6-34
No. 2236 discloses a method of including a lubricant on the surface of the charge applying member. These methods have the effect of reducing the amount of toner attached to the charge applying member,
Non-uniform charging due to adhesion of dirt can be suppressed to some extent.

[0010]

However, these methods have the following problems. That is, JP-A-5-53413 and JP-A-5-265307 described above.
In the method disclosed in Japanese Patent Application Laid-Open No. H11-207, not only is it difficult to maintain the effect of preventing contamination from adhering for a long period of time, but also foreign matters such as toner due to friction between the cleaning means and the charge applying member. It may adhere to the surface of the charge imparting member and cause a new cause of non-uniform charging due to abnormal discharge or the like. In addition, the method of incorporating a lubricant into the surface of the charge applying member disclosed in JP-A-4-303861 and JP-A-6-342236 is difficult to maintain the effect of preventing the adhesion of dirt for a long period of time. The agent may adhere to the toner image carrier, causing new image defects such as white spots.

By the way, from the viewpoint of preventing the generation of waste toner, transfer residual without providing cleaning means on the toner image carrier is disclosed in JP-A-59-133573 and JP-A-59-157661. When a contact charger is used in a cleaner-less type image forming apparatus that collects toner in a developing unit at the same time as developing, the toner that enters the charging unit is compared with an image forming apparatus in which a cleaning unit is provided on a toner image carrier. And it is extremely difficult to prevent non-uniform charging due to dirt.

Further, JP-A-2-1870, JP-A-2-81053, JP-A-2-118671, JP-A-2-118672, JP-A-2-157.
In the method disclosed in, for example, Japanese Patent Application Publication No. 766, which discloses a method of achieving cleanerlessness by lowering the adhesive force between a toner and a toner image carrier by using peelable fine particles or the like to increase transfer efficiency, There is a drawback that foreign matters are more difficult to remove because they adhere to the charge applying member together with the toner.

The present invention has been made in view of the above circumstances, and has a simple structure which prevents foreign matters from adhering to a charge providing member, stably performs uniform charging, and does not affect other processes. It is an object of the present invention to provide an image forming apparatus capable of obtaining stable image quality for a long time.

[0014]

According to a first aspect of the present invention, there is provided a toner image carrier having a toner image on a surface thereof, and a predetermined charge applied to the toner image carrier. A charge applying member, a toner image forming means for forming a toner image corresponding to image information on a toner image carrier to which a charge is applied by the charge applying member, and a toner image formed by the toner image forming means. An image forming apparatus provided with a transfer unit for transferring the toner image onto a predetermined recording medium, wherein the charge applying member has a surface energy relatively lower than a surface energy of the toner image carrier. I do.

Here, the charge applying member is provided with surface energy maintaining means for maintaining the surface energy of the charge applying member at a surface energy relatively lower than the surface energy of the toner image carrier. More preferably, as the surface energy maintaining means, a powder having a particle diameter relatively smaller than the particle diameter of the toner used in the toner image forming means and having water repellency is provided on the surface of the charge applying member. It is also preferred that the composition is formed by coating.

The second object of the present invention to achieve the above object is as follows.
The image forming apparatus includes a toner image carrier that carries a toner image on a surface thereof, a charge applying member that applies a predetermined charge to the toner image carrier, and a toner image carrier that is provided with an electric charge by the charge applying member. An image forming apparatus comprising: a toner image forming unit that forms a toner image corresponding to image information thereon; and a transfer unit that transfers a toner image formed by the toner image forming unit to a predetermined recording medium. The application member has a surface property in which the contact angle of water on the surface of the charge application member is relatively larger than the contact angle of water on the surface of the toner image carrier.

Here, the charge applying member has contact angle maintaining means for maintaining the contact angle of water on the surface of the charge applying member at a contact angle relatively larger than the contact angle of water on the surface of the toner image carrier. It is preferable to have
The contact angle maintaining means is obtained by applying a water-repellent powder having a particle diameter relatively smaller than that of the toner used in the toner image forming means to the surface of the charge applying member. It is also preferred.

Further, in the first image forming apparatus or the second image forming apparatus of the present invention,
It is also preferable that the toner image carrier is a contact-type member that is in contact with the toner image carrier and applies a predetermined voltage to the toner image carrier. It is also preferable to provide a surface layer made of a polymer material. Further, the toner image carrier is formed by the toner image forming means while carrying the toner remaining on the toner image carrier after the toner image on the toner image carrier is transferred to the recording medium. It is also a preferable embodiment that the process proceeds to the step of carrying the next toner image.

[0019]

Embodiments of the present invention will be described below. FIG. 1 is a schematic diagram of a charger used in the first embodiment of the image forming apparatus of the present invention. FIG. 1A is a cross-sectional view of a charge acceptor 1 and a charge applying member 2 of a charger 10 for applying a charge to the charge acceptor 1, and FIG. The figure is shown. FIG. 1 (a)
As shown in FIG. 1B, the charger 10 comprises a cylindrical electrode support member 3 which is spaced apart on a charge receptor 1 movable in the direction of arrow A, and an electrode support member 3. A semi-conductive film-shaped charge applying member 2 having a circumference longer than the circumference of the encircling electrode support member 3 and rotating in the direction of arrow B while being in contact with the electrode support member 3 and the charge receptor 1; And a DC power supply 4 for applying a DC voltage for charging. The charge acceptor 1 simulates a toner image carrier in an image forming apparatus, and the toner image carrier, which is usually in the form of a rotating drum, is formed in a flat plate shape for testing the charger 10. Things.
The charge receptor 1 has a two-layer structure in which a photoconductive layer 1a is laminated on a conductor substrate 1b, and the conductor substrate 1b is electrically grounded.

Since the peripheral length of the film-shaped charge applying member 2 is longer than the circumference of the electrode support member 3 as described above, when no voltage is applied, the charge applying member 2 as shown in FIG. It is in contact with the charge receptor 1 under its own weight of 2. When a DC voltage is applied to the electrode support member 3 from the DC power supply 4 while moving the charge acceptor 1 in the direction of arrow A, a voltage is generated between the charge providing member 2 in contact with the electrode support member 3 and the charge acceptor 1. The charge applying member 2 is attracted to the charge acceptor 1 by the electrostatic force and pressed against the charge acceptor 1, and is bent in the direction of arrow A as the charge acceptor 1 moves. In this state, discharge occurs in the minute gap 5 near the contact portion between the charge providing member 2 and the charge receptor 1, and the surface of the charge receptor 1 is charged.

The charge applying member 2 has a thickness of about 30 to 2
A semiconductive film member having a flexibility of 00 μm is used. This film-shaped member may be configured as a single-layer structure composed of only the substrate, or may be configured as a two-layer structure composed of the substrate and the surface layer. As a substrate,
Any substance that has semiconductivity can be used. For example, polyester, polyamide,
Polyethylene, polycarbonate, polyolefin, polyurethane, polyvinylidene fluoride, polyimide, PE
N, PEK, PES, PPS, PFA, PVdF, ET
It is possible to use resin such as FE or CTFE or synthetic rubber such as silicon rubber, ethylene propylene rubber, butyl rubber, acrylic rubber, urethane rubber, nitrile rubber mixed with conductive powder such as carbon black or metal powder. it can. Further, a polar rubber such as epichlorohydrin rubber, chloroprene rubber, EPDM rubber, or a semiconductive inorganic material such as amorphous silicon formed by depositing a thin film or a thick film on an insulating substrate may be used. However, since the polar rubber has a high adhesive force, it is necessary to coat the surface after forming the charge imparting member with a low-adhesive material or the like. In the case where the charge providing member is formed by depositing a thin film or a thick film of an inorganic material on an insulating substrate, the charge providing member 2 may be disposed in non-contact with the charge receptor 1 because of its high hardness. desirable.

It is necessary to adjust the amount of the conductive powder such as carbon black and metal powder to be mixed into the polymer material so that the charge providing member 2 has a preferable volume resistivity as a charging electrode. is there. That is, when the volume resistivity is 10 ² Ω · cm or less, spark discharge easily occurs,
If the volume resistivity is 10 ¹¹ Ω · cm or more, it is easy to cause dot-shaped charging failure, so that it is 10 ³ Ω · cm to ^{10 10} Ω · cm.
It is desirable to adjust the volume resistivity within the range described above. In addition,
When the volume resistivity is in the range of 10 ³ Ω · cm to 10 ⁶ Ω · cm, the applied voltage can be set low, and the charger can be operated at a process speed of 150
When used in a high-speed image forming apparatus of mm / sec or more, it is preferable because potential fluctuation can be suppressed to be small.

The surface layer of the charge applying member 2 includes polyester, polyamide, polyethylene, polycarbonate, polyolefin, polyurethane, polyvinylidene fluoride, polyimide, PEN, PEK, PES, PPS,
Resin such as PFA, PVdF, ETFE, CTFE, or synthetic rubber such as silicon rubber, ethylene propylene rubber, butyl rubber, acrylic rubber, urethane rubber, nitrile rubber mixed with conductive powder such as carbon black or metal powder, A polymer material formed by dispersing a highly water-repellent fine powder such as fluorine powder can be used.

The mixing amount of the water-repellent fine powder is adjusted based on the relative relationship with the surface properties of the charge receptor 1. That is, in the first image forming apparatus of the present invention, the charge applying member 2 is configured to have a surface energy relatively lower than the surface energy of the charge acceptor 1, and the second image forming apparatus of the present invention , The charge applying member 2 is configured to have a surface property having a contact angle relatively larger than the contact angle of water on the surface of the charge receptor 1.

The electrode supporting member 3 has a function of supplying power to the charge applying member 2. Therefore, a conductive material, for example, a metal such as aluminum or stainless steel, or a volume resistivity For example, a conductive polymer material formed so as to be equal to or less than the volume resistivity of the charging electrode 2 is used. As shown in FIG. 1B, the electrode support member 3 has a length L ′ slightly longer than the length L of the charge applying member 2 in the longitudinal direction C.

The electrode support member 3 is fixed to the main body of the charger 10 and does not rotate. Although the DC power supply 4 is used for the charger 10, the voltage applied to the charge applying member 2 is not limited to DC, and a voltage obtained by superimposing an AC voltage on a DC voltage may be applied. Good.
When a DC voltage on which an AC voltage is superimposed is used, the surface energy of the charge receiver 1 and the charge applying member 2 increases due to the sputtering by the AC component, which may cause a cleaning failure or increase the wear of the toner image carrier. Further, there is a disadvantage that the charger 10 vibrates according to the frequency of the alternating current and a specific charging noise is generated. Further, a charger using an AC superimposed DC voltage has a problem that charging efficiency is low. Therefore, it is preferable to use a DC voltage.

As an image forming apparatus in which such a charger 10 is incorporated, a black and white or color copying machine or a printer provided with a photosensitive member cleaning device can be cited. Further, the present invention can be suitably used in a cleanerless image forming apparatus not provided with a cleaning device or an image forming apparatus provided with a dummy cleaning device. An embodiment relating to a cleanerless image forming apparatus will be described later.

Next, the surface properties of the charge applying member 2 in the charger 10 will be described. First, several types of tube films having different contact angles (surface energy) of water on the surface of the charge applying member 2 are prepared. As a base material of the tube film, a conductive nylon tube having a diameter of 12.5 mm in which carbon black is dispersed in nylon is used. The following six types of resins were selected as polymer materials for forming the surface layer of the film tube. Table 1 shows the surface energy of the six types of resins and the measurement results of the contact angles of water on the resin surfaces.

[0029]

[Table 1]

Table 1 shows that polytetrafluoroethylene,
The surface energy γs and water contact angle θw of the six kinds of resins of polypropylene, polyethylene, polyvinylidene fluoride, polyethylene terephthalate, and nylon 66 and the photoreceptor surface material as the charge acceptor 1 are listed in the order of the surface energy γs. ing. From Table 1, the surface energy of the three types of resins, polytetrafluoroethylene, polypropylene, and polyethylene, is smaller than the surface energy of the photoreceptor surface material, and the contact angle of water is smaller than the contact angle of water of the photoreceptor surface material. large. In addition, the surface energy of the three kinds of resins, polyvinylidene fluoride, polyethylene terephthalate, and nylon 66, is larger than the surface energy of the photoconductor surface material, and the contact angle of water is smaller than the water contact angle of the photoconductor surface material. . Next, a coating material for forming a surface layer is prepared by mixing and dispersing 100 parts of resin and 5 parts of conductive carbon with 100 parts of an appropriate mixed solvent for each of the above six types of resins. Next, using a bell-type electrostatic coating machine (manufactured by Landsberg Industry Co., Ltd.), the above-mentioned coating material for forming a surface layer was electrostatically coated on a conductive nylon tube so that the film thickness after drying was 10 μm. Form surface layer on nylon tube,
Various types of charge applying members are manufactured. Table 2 shows the results of measuring the contact angles of water for the six types of charge imparting members A, B, C, D, E, and F thus produced.

[0031]

[Table 2]

As shown in Table 2, the addition of a small amount of conductive carbon slightly changed the contact angle θw of water as compared with the original resin (see Table 1). The magnitude relation for the contact angle of water has not changed. Table 2
The charging test is performed by the method described below using the six types of charge applying members shown in FIG. FIG. 2 is a schematic diagram showing an outline of the charging test apparatus.

The charging test apparatus shown in FIG. 2 includes a surface potential sensor 11 disposed around the drum-shaped charge receptor 1 rotating in the direction of arrow A for detecting the surface potential of the charge receptor 1, A charge removing lamp 13 for removing charge on the surface of the receptor 1 is provided, and a surface potential meter 12 is connected to the surface potential sensor 11. The charger 10 shown in FIG. 1 is arranged on the charge receptor 1 on the upstream side of the surface potential sensor 11, and the conductive charge applying member 2 is arranged in contact with the surface of the charge receptor 1. I have. A DC power supply 14 is connected to the charger 10, and a DC charging voltage is applied to the charge applying member 2. This DC power supply 14 can arbitrarily change the output voltage, and measures the surface potential of the charge receptor 1 that changes according to the increase or decrease of the applied voltage.
2.

FIG. 3 shows an example of the charging test apparatus shown in FIG.
6 is a graph showing the results of a charging test using six types of charge applying members shown in Table 2. As shown in FIG. 3, when the applied voltage to the charge applying member is changed from 0 V to 2,000 V, the surface potential of the charge acceptor 1 starts to increase when the applied voltage reaches about −550 V, Applied voltage -200
At 0 V, a surface potential of about -1,450 V is reached. In all of the six types of charge imparting members shown in Table 2, no abnormal discharge occurred and good results were obtained.

Next, a description will be given of the result of an image quality maintenance characteristic test by an actual image forming apparatus. FIG. 4 is a schematic diagram of an image forming apparatus configured using the charge applying members shown in Table 2. The image forming apparatus shown in FIG. 4 includes a photosensitive drum 20 (toner image carrier according to the present invention) that rotates in the direction of arrow A, and a charger 10 that uniformly charges the surface of the photosensitive drum 20 (see FIG. 1). ), An exposure device 21 for forming an electrostatic latent image by irradiating the surface of the photosensitive drum 20 with laser light corresponding to image information, and developing the electrostatic latent image to form a toner image on the photosensitive drum 20. A developing device 22 for forming, a transfer device 25 for transferring the toner image on the photosensitive drum 20 to the recording paper 24, and a cleaning device 27 for removing the toner remaining on the photosensitive drum 20 after the transfer is performed; A charge removing lamp 28 for removing the charge on the photosensitive drum 20, a recording paper cassette 23 for storing the recording paper 24, a paper guide 29 for guiding the recording paper 24, and a fixing device 26 for fixing the toner image. It has been. Of these, the charger 10 corresponds to the charge applying member according to the present invention, the exposure device 21 and the developing device 22 correspond to the toner image forming means according to the present invention, and the transfer device 25 corresponds to the transfer device according to the present invention. It corresponds to a means.

In such an image forming apparatus, after the photosensitive drum 20 is charged to a predetermined surface potential by the charger 10, a laser beam corresponding to image information is irradiated by the exposure device 21, An electrostatic latent image is formed on the image. This electrostatic latent image is developed with toner by the developing device 22 to form a visible toner image on the photoconductor 20. On the other hand, the recording paper 24 in the recording paper cassette 23 is transported along the paper guide 29 to the nip portion between the photosensitive drum 20 and the transfer device 25, and the transfer device 25
0 is transferred onto the recording paper 24. The toner image transferred onto the recording paper 24 is fixed on the recording paper 24 by the fixing device 26, and a print image is obtained. On the other hand, the untransferred toner remaining on the photoconductor drum 20 after the transfer is completed is cleaned by the cleaning device 27, and after the surface of the photoconductor drum 20 is discharged by the discharging lamp 28, the charged toner is again charged by the charger 10. The process proceeds to the next image forming process. The DC voltage applied to the charger 10 is about -900 V, whereby the surface potential of the photosensitive drum 20 is charged to about -350 V.

Print images are formed using such an image forming apparatus, and the results of a reliability test of the charger 10 are shown in FIGS. Reliability test is 10,000
This is performed by printing a sheet and confirming the image quality maintenance characteristics from the print sample. Evaluation of image quality,
This is done by comparing the sample with a fog limit sample, which gives good image quality with no fog at fog grade 0,
Grade 5 is an image quality in which fog is very remarkable. In addition,
Black on the entire surface is assumed to be fog grade 10. The generally acceptable fog grade is 0 or 1.

FIG. 5 is a diagram showing a print sample according to the first embodiment. FIG. 5A shows a print sample in an initial state of a print test. FIG. 5B shows three types of charges A, B, and C among the six types of charge applying members shown in Table 2. 10,0 using an application member
FIG. 5C shows one of the six types of charge applying members shown in Table 2 using D, E, and F3 types of charge applying members.
A print sample after printing 000 sheets is shown.

In the case of the charge applying members A, B, and C having a water contact angle exceeding the water contact angle (90 degrees) of the photoreceptor surface material, as shown in FIG. After printing, a good image having almost the same image quality as the print sample in the initial state shown in FIG. 5A was obtained. However, in the case of the charge applying members D, E, and F having a water contact angle equal to or smaller than the water contact angle (90 degrees) of the photoreceptor surface material, as shown in FIG. Streaks frequently occurred and the image quality was extremely deteriorated.

FIG. 6 is a graph showing the relationship between the contact angle of water on the surface of the charge applying member and the fog grade for each print sample in the first embodiment. FIG. 6 shows the contact angles of water on the surfaces of the six types of charge applying members A, B, C, D, E, and F, and the fog grade of a print sample performed using each of the charge applying members. Is plotted.

As shown in FIG. 6, the fogging grade of the charge applying members A, B, and C in which the contact angle of water on the surface of the charge applying member exceeds the contact angle of water (90 degrees) of the surface material of the photoreceptor is from about 0 to 0. In contrast to about 0.5, the fogging grades of the charge imparting members D, E, and F whose contact angles of water are equal to or less than the contact angle of water (90 degrees) of the surface material of the photoreceptor are about 5. Was.

FIG. 7 is a graph showing the relationship between the surface energy of the charge applying member and the fog grade for each print sample in the first embodiment. As shown in FIG. 7, the charge applying members A, B, and C having a surface energy equal to or less than the surface energy of the photoconductor surface material (39.5 dyn / cm).
The fogging grade of C was about 0 to 0.5, whereas the fogging grade of charge imparting members D, E and F whose surface energy was higher than the surface energy (39.5 dyn / cm) of the photosensitive member surface material. Showed about 5.

Charge imparting members A, which can obtain good image quality,
As a result of observing the charge applying members after printing 10,000 sheets for B and C, almost no deposits were observed, whereas the charge applying members D, E and F having poor image quality after printing 10,000 sheets were observed. As a result of observing the charge applying member, the surface of the charge applying member was almost covered with the deposit. The image quality was degraded by this large amount of deposits.

From the above results, it can be seen that the charge applying member has a surface energy relatively lower than that of the photoreceptor, that is, the toner image carrier, or that the charge applying member has The contact angle of water on the member surface is a photoreceptor, that is, having a surface property that is a contact angle relatively larger than the contact angle of water on the surface of the toner image carrier, thereby preventing foreign matter from adhering to the charge applying member. Thus, an image forming apparatus capable of obtaining stable image quality for a long period of time by stably performing uniform charging can be obtained.

In the case of the charge applying members A, B, and C, a print test is performed under the same conditions as those of the charge applying members D, E, and F. Therefore, the toner, the discharge product,
Soil such as dust and paper dust naturally adheres to the charge applying member. In the case of the charge applying members D, E, and F, these stains are only attached to and accumulated on the charge applying member. In the case of the members A, B, and C, even if the dirt adheres to the charge applying member, the dirt is immediately moved toward the photoconductor, so that the dirt is not accumulated on the charge applying member. In addition, since the dirt moved to the photoreceptor is removed by a cleaner, collected by a developing device, or transferred to a recording sheet, any problem caused by dirt on the charge applying member can be avoided. can do. That is, in the present embodiment, dirt is attached to the photoreceptor having means for removing the attached dirt, without attaching the dirt to the charge applying member having no means for removing the attached dirt.

In the first embodiment, a film-like member is used as the charge-providing member. However, the charge-providing member in the present invention is not limited to a film-like member, but may be a rubber roll, a brush, or an insulating roll. Rolls on which semiconductive electrodes are deposited, metal rolls, blades, etc.
The member may have any shape as long as it can contact or approach the photoconductor. However, in the case of a member other than a film-shaped member, in addition to the electrostatic attraction force, a pressing force for pressing the charge applying member against the photosensitive member is applied between the charge applying member and the photoreceptor, and foreign matter is present on the surface of the charge applying member. Since rubbing is inevitable, a charge-applying member that makes light contact, such as a film-like member, is preferred. In addition, since the effect of removing foreign matter on the surface of the photoconductor increases as the pressing force on the photoconductor decreases, it is preferable to use a film tube (see FIG. 1) that comes into light contact with the photoconductor.

Next, a second embodiment of the image forming apparatus of the present invention will be described. First, the surface properties of the charge applying member 2 in the second embodiment will be described. As in the first embodiment, a conductive nylon tube having a diameter of 12.5 mm is used as the base material of the tube film.
Next, 100 parts of acryl / melamine / epoxy resin to which 5 parts of conductive carbon and Teflon powder of the following addition amount are added are mixed with 100 parts of an appropriate mixed solvent to prepare a paint for forming a surface layer. . The amount of Teflon powder to be added is set in six steps from 0 to 100 parts in increments of 20 parts. Next, similarly to the first embodiment, a surface layer forming paint is electrostatically applied to the conductive nylon tube so that the film thickness after drying is 10 μm, thereby forming a surface layer on the charge applying member 2. The charge applying member 2 having the shape shown in FIG. 1 is manufactured.

Table 3 shows the measurement results of the contact angles of water of the six types of charge imparting members G, H, I, J, K, and L thus produced.

[0049]

[Table 3]

As shown in Table 3, the contact angle θw of water increases as the amount of Teflon powder as a water-repellent resin increases. The charging device shown in FIG. 1 was constructed using the above-described six types of charge applying members, and a charging test was performed by the charging test device shown in FIG. 2, whereby good charging characteristics were obtained as in FIG.

Next, using the image forming apparatus shown in FIG. 4, the above six kinds of charge applying members G, H, I, J, K, L
8 and 9 show the results of a charging performance reliability test performed on each of them. The method of the reliability test is the same as in the first embodiment. FIG. 8 is a diagram illustrating a print sample according to the second embodiment.

FIG. 8A shows a print sample in an initial state of a print test. FIG. 8B shows three of G, H, and I of the six types of charge applying members shown in Table 3. FIG. 8C shows a print sample after printing 10,000 sheets using the various types of charge applying members. Among the six types of charge applying members shown in Table 3, J, K, and
A print sample after printing 10,000 sheets using the three types of charge applying members L is shown.

As shown in Table 3 and FIG. 8, in the case of the charge applying members G, H, and I having a water contact angle exceeding the water contact angle (90 degrees) of the photosensitive member surface material, FIG. As shown in FIG. 8B, after printing 10,000 sheets, a good image having almost the same image quality as the print sample in the initial state shown in FIG. 8A was obtained. However, in the case of the charge applying members J, K, and L having a water contact angle equal to or less than the water contact angle (90 degrees) of the photoreceptor surface material, as shown in FIG. Streaks frequently occurred and the image quality was extremely deteriorated.

FIG. 9 is a graph showing the relationship between the contact angle of water on the surface of the charge applying member and the fog grade for each print sample in the second embodiment. FIG. 9 shows the six types of charge applying members G, H, I, and
A graph is shown in which the contact angles of water on the J, K, and L surfaces and the fog grade of a print sample by each of the charge applying members are plotted.

As shown in FIG. 9, the fog grade of the charge applying members G, H, and I in which the contact angle of water on the surface of the charge applying member exceeds the contact angle of water (90 degrees) on the surface material of the photoreceptor is from about 0 to 0. While the contact angle of water on the surface of the charge applying member is about 0.5,
F) The fogging grades of the following charge imparting members J, K, and L showed about 5.

As described above, when the charge applying members G, H, and I having good image quality were observed on the charge applying members after printing 10,000 sheets, almost no deposits were recognized. Charge imparting members J, K,
As a result of observing the charge applying member after printing 10,000 sheets for L, the charge applying member surface was almost completely covered with the attached matter. The image quality was degraded by this large amount of deposits.

From the above results, it can be seen that the charge applying member has a surface energy relatively lower than that of the photoreceptor, that is, the toner image carrier, or that the charge applying member has The contact angle of water on the member surface is a photoreceptor, that is, having a surface property that is a contact angle relatively larger than the contact angle of water on the surface of the toner image carrier, thereby preventing foreign matter from adhering to the charge applying member. An image forming apparatus capable of obtaining stable image quality for a long period of time can be obtained by preventing the charge and stably performing uniform charging.

In the second embodiment, as in the first embodiment, a film-like member is used as the charge applying member. However, the charge applying member in the present invention is not limited to a film-like member. It may be a member having any shape such as a roll shape, a blade shape, and the like. However, in the case of a charge applying member other than a film-shaped member, since a pressing force for pressing the charge applying member against the photoreceptor is applied between the charge applying member and the photoreceptor in addition to the electrostatic attraction force, the foreign matter adheres to the surface of the charge applying member. A member such as a film-like member that comes into light contact with the photoreceptor is preferable because it is easily rubbed.

As described above, in the case of a charge applying member other than a film-like member, foreign matter is easily rubbed into the surface of the charge applying member.
By adjusting the hardness of the binder of the water-repellent paint for forming the surface layer, the abrasion easiness of the charge applying member can be adjusted. That is, by lowering the hardness of the binder of the water-repellent paint and making the amount of wear of the charge applying member relatively large with respect to the amount of wear of the member in contact with the charge applying member, the water repellency of the surface of the charge applying member during the charging process is reduced. By gradually abrading the coating material, a new surface can always be produced, foreign matter can be prevented from rubbing into the surface of the charge applying member, and the contact angle (surface energy) of water in the initial state can always be maintained. Conversely, by increasing the hardness of the binder of the water-repellent paint, it is possible to prevent foreign substances from rubbing or burying on the surface of the charge applying member.

Next, a third embodiment of the image forming apparatus of the present invention will be described. In the third embodiment, a charge applying member in which fine powder of polyvinylidene fluoride is applied to the surface of a nylon-based film tube, a charge applying member in which fine powder of polyvinylidene fluoride is applied to the surface of a PVdF film tube, and acrylic A fine powder of polyvinylidene fluoride is mixed in a resin, and the surface of a film tube formed by centrifugal molding is sanded to prepare a total of three types of charge applying members. The shape of the film tube is as shown in the charger 10 shown in FIG. For these three types of charge applying members, the same charging test as in the first embodiment was performed using the charging test apparatus shown in FIG. 2 and the image forming apparatus shown in FIG. As a result of the charging test, the contact angle of water on the surface of the charge imparting member 2 was 105 degrees when a fine powder of polyvinylidene fluoride was applied to a nylon-based film tube, and the contact angle of water on the surface of the PVdF film tube was 105 degrees. The degree was 115 degrees when the powder was applied, and 118 degrees for a film tube prepared by mixing polyvinylidene fluoride in an acrylic resin. When an image forming test was performed using these three types of charge applying members, good results similar to those in the first embodiment were obtained for all three types of charge apply members. Therefore, as long as the contact angle of water on the surface of the charge providing member is equal to or greater than the contact angle of water on the surface of the photoreceptor, it can be understood that any method of producing the surface of the charge providing member may be used.
Incidentally, the contact angle in the case of only dispersing carbon in the nylon-based film was 85 degrees, and the contact angle in the case of merely dispersing carbon in the PVdF film was 91 degrees. As described above, by applying the fluorine-based fine powder to the surface, the contact angle can be increased, and a good image can be formed.

Next, a fourth embodiment of the image forming apparatus of the present invention will be described. In the fourth embodiment, the first
As in the third to third embodiments, instead of using a charge applying member formed by dispersing a highly water-repellent fine powder in a polymer material adjusted to a preferable volume resistivity as a charging electrode,
A charge applying member is formed using a polymer material adjusted to a preferable volume resistivity as a charging electrode, and a contact angle of water on the surface of the charge applying member by applying a dried water-repellent powder to the surface of the charge applying member. Increase. Examples of the water-repellent powder include polymer materials such as polyvinylidene fluoride and polymethacrylate, zinc stearate, barium stearate, lead stearate, nickel stearate, cobalt stearate, copper stearate, zinc oleate, and magnesium oleate. , Zinc palmitate,
Cobalt palmitate, lead caprylate, lead caproate,
Metal salts of fatty acids such as lead linolenate can be used. The particle size of the water-repellent powder needs to be relatively smaller than the particle size of the toner used for forming a toner image. More specifically, if the thickness exceeds 10 μm, the water-repellent powder is buried in the charge applying member.
μm or less, and more preferably 1 μm or less in consideration of the adhesive force between the charge imparting member and the water-repellent powder.

As a method of applying the water-repellent powder to the surface of the charge applying member, a method of applying the water-repellent powder to the charger in advance when the charger is incorporated into the image forming apparatus, or a method of placing the charger near or in contact with the charger. There is also a method of providing fine powder application means. FIG. 10 shows a specific example of the fine powder applying means. FIG. 10 is a schematic diagram of a charger including a toner image carrier and a charge applying member used in a fourth embodiment of the image forming apparatus of the present invention.

FIG. 10 (a) shows a charge receiving member 1, a charge providing member 2 of a charger 40 for providing a charge to the charge receiving member 1,
And a cross-sectional view of the water-repellent powder coating device 41 is shown,
FIG. 1B shows a side view thereof. FIG.
As shown in FIG. 10A and FIG.
As in the case of the charger 10 shown in FIG. 1, a cylindrical electrode support member 3 spaced apart from the charge receptor 1 and a circumference longer than the circumference of the electrode support member 3 surrounding the electrode support member 3. A semiconductive film-shaped charge applying member 2 rotating in the direction of arrow B while being in contact with the electrode support member 3 and the charge acceptor 1, and a DC power supply 4 for applying a charging DC voltage to the electrode support member 3. In addition, a water-repellent powder coating device 41 is provided so as to be close to or in contact with the charge applying member 2. The water-repellent powder coating device 41 is constituted by a roll 42 having a relatively coarse nonwoven fabric formed in a cylindrical shape around a shaft 43 and a shaft 43,
A non-woven fabric roll 42 contains water-repellent fine powder. By installing the charger 40 thus configured in the image forming apparatus shown in FIG. 4 and performing a print test, it is possible to obtain a good image having a uniform charging potential and no image defects. In addition, almost no foreign matter adhered to the surface of the charge applying member 2 was observed.
It can be seen that 1 is effective in preventing the surface of the charge applying member 2 from being stained. In this test, the water-repellent powder coating device 4
1 is brought into contact with the charge applying member 2, and the water repellent powder contained in the nonwoven fabric is applied to the charge applying member 2 by friction caused by the rotation of the charge applying member 2. However, the method for applying the water-repellent powder is not limited to this method. For example, the roll 42 is rotated by transmitting the rotation of the photoconductor to the shaft 43, or the rotation of the photoconductor is performed in the axial direction using a crank. Alternatively, a method may be adopted in which the water-repellent powder is dropped onto the charge applying member 2 by vibrating the roll 42.

The member for applying the water-repellent powder to the surface of the charge-imparting member may be any member as long as it can adhere the fine particles of the water-repellent powder to the surface of the charge-imparting member. The surface of the charge applying member is rubbed using a rotating member such as a roll made of fiber, felt, rubber, nonwoven fabric, foam, brush, web, blade, paddle, gel, resin, metal, or a reciprocating brush-like member. You may make it. Further, by imparting conductivity to these members, the water-repellent powder may be electrically attached to the surface of the charge applying member, or the above two methods may be combined. However, in the case where the member to which the water-repellent powder is applied is in contact with the surface of the charge applying member, the pressure at the contact portion is desirably small, and a sponge, felt, nonwoven fabric, brush, or the like is preferable.

Next, a fifth embodiment of the image forming apparatus of the present invention will be described. FIG. 11 is a schematic diagram of an image forming apparatus according to the fifth embodiment of the present invention. The image forming apparatus shown in FIG. 11 is similar to the image forming apparatus shown in FIG. 4, but the image forming apparatus shown in FIG. 11 uses the toner remaining on the photosensitive drum 20 after the transfer has been performed. This is a cleanerless image forming apparatus that does not have a cleaning device for removing (see FIG. 4) and does not discharge waste toner. In this image forming apparatus, the photosensitive drum 20 carries the next toner image formed by the toner image forming means while carrying the toner remaining on the photosensitive drum 20 after the toner image is transferred onto the recording paper. It is configured to transition to. The image forming apparatus includes a transfer belt 51 circulating in the direction of arrow B, a drive roll 52 for driving the transfer belt 51, rolls 53 and 54 for suspending the transfer belt 51 together with the drive roll 52, and a transfer belt static eliminator 55. And so on. Other charger 1
0, a toner image forming means including a photosensitive drum 20, an exposure device 21, and a developing device 22, a transfer device 25, and a discharging lamp 28
The operations are the same as those of the image forming apparatus shown in FIG.

FIG. 4 shows a process in this image forming apparatus until the toner image formed on the photosensitive drum 20 is transferred onto the recording paper at the nip N between the photosensitive drum 20 and the transfer unit 25. This is the same as the image forming apparatus. The difference from the image forming apparatus shown in FIG. 4 is that recording paper supplied along a transport path P from a recording paper cassette (not shown) is placed on the transfer belt 51 and transported. In the nip portion N between the photoconductor drum 20 and the transfer unit 25, the toner image on the photoconductor drum 20 is transferred onto the recording paper by the photoconductor drum 20 and the transfer unit 25 in a state where the photoconductor drum 20 and the recording paper are overlapped. Is done. The toner image transferred onto the recording paper is fixed by a fixing device (not shown), and a print image is formed on the recording paper. After the transfer, the photosensitive drum 20 rotates in the direction of arrow A, and the untransferred toner remaining on the photosensitive drum 20 passes below the charge removing lamp 28,
The surface of the photosensitive drum 20 is neutralized. Then, the photosensitive drum 20 shifts to the next image forming step which starts charging by the charger 10 again.

By forming a print image using the image forming apparatus shown in FIG. 11 and performing an image quality test, it is possible to obtain a good image having a uniform charging potential and no image quality defects such as poor charging. When the amount of charge of the residual toner on the photosensitive drum 20 after passing through the portion of the charger 10 is measured, it is -5.4 [mu] C / g, which is slightly shifted to the minus side. On the other hand, in a conventional image forming apparatus using a storotron charger, the photosensitive drum 2
When the amount of charge of the residual toner on 0 was measured, it was almost 0 μC /
g. This is because, in a charger using corona discharge such as a scorotron, the discharge area is wide, so the energy of the electrons emitted from the electrodes becomes smaller as it approaches the vicinity of the photoconductor drum, and foreign substances such as toner on the photoconductor drum are removed. Only the photosensitive drum is charged while avoiding it, and the discharge state is controlled by an average potential difference. However, in the charger using the minute gap as in the present embodiment, since the discharge region is narrow, the energy of the electrons emitted from the electrode is hardly attenuated, and the surface of the photosensitive drum is charged. As a result, the discharge state is controlled, so that a foreign substance or the like can be sufficiently charged. By utilizing this phenomenon, even if the residual toner or the like that has passed through the charger 10 enters the developing area by the developing unit 22, the residual toner is not collected in the developing unit because the polarity of the residual toner is negative, and is not directly transferred to the transfer area. Finally, the image can be transferred onto the recording paper by the transfer device 25. This phenomenon can be used regardless of the developing method of the developing device 22 (for example,
Contact development with a magnetic brush). Therefore, if the amount of the residual toner does not disturb the image exposure by the exposure device 21, the deterioration of the image quality due to the penetration of the residual toner into the developing device 22 can be prevented, and the stable image can be always formed. it can. From the above, the image forming apparatus of the present invention can be effectively used in a cleanerless electrophotographic system.

[0068]

As described above, according to the image forming apparatus of the present invention, the surface energy of the charge applying member is set to be relatively lower than the surface energy of the toner image carrier. Alternatively, by setting the contact angle of water on the surface of the charge applying member to a contact angle relatively larger than the contact angle of water on the surface of the toner image carrier, the toner,
Dirt such as discharge products, dust in the air, and paper dust can be prevented from adhering or sticking to the surface of the charge imparting member, and poor charging due to the dirt can be prevented and a good image can be obtained. . Further, since a complicated mechanism is not required, the size and weight of the image forming apparatus can be reduced. Further, the present invention can be effectively used in a cleanerless electrophotographic system having no cleaning device for removing untransferred toner on the photosensitive member.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a charger used in first to fourth embodiments of the image forming apparatus of the present invention.

FIG. 2 is a schematic diagram showing an outline of a charging test apparatus.

FIG. 3 shows the results shown in Table 2 using the charging test apparatus shown in FIG.
9 is a graph showing the results of a charging test using various types of charge applying members.

FIG. 4 is a schematic diagram of an image forming apparatus configured using the charge applying members shown in Table 2.

FIG. 5 is a diagram illustrating a print sample according to the first embodiment.

FIG. 6 is a graph showing the relationship between the contact angle of water on the surface of the charge imparting member and the fog grade for each print sample in the first embodiment.

FIG. 7 is a graph showing the relationship between the surface energy of the charge imparting member and the fog grade for each print sample in the first embodiment.

FIG. 8 is a diagram illustrating a print sample according to the second embodiment.

FIG. 9 is a graph showing the relationship between the contact angle of water on the surface of the charge applying member and the fog grade for each print sample in the second embodiment.

FIG. 10 is a schematic diagram of a charger including a toner image carrier and a charge applying member used in a fourth embodiment of the image forming apparatus of the present invention.

FIG. 11 is a schematic diagram of an image forming apparatus according to a fifth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Charge receptor, toner image carrier 1a Photoconductive layer 1b Conductive substrate 2 Charge application member 3 Electrode support member 4 DC power supply 5 Micro gap 10 Charger 11 Surface potential sensor 12 Surface voltmeter 13 Static elimination lamp 14 DC power supply 20 Photoconductor Drum 21 Exposure device 22 Developing device 23 Recording paper cassette 24 Recording paper 25 Transfer device 26 Fixing device 27 Cleaning device 28 Static elimination lamp 29 Paper guide 40 Charger 41 Water repellent powder coating device 42 Roll 43 Shaft 51 Transfer belt 52 Drive belt 53, 54 Roll 55 Transfer belt static eliminator

Claims (9)

[Claims] 1. A toner image carrier that carries a toner image on a surface, a charge applying member that applies a predetermined charge to the toner image carrier, and a toner image carrier on which a charge is applied by the charge applying member. An image forming apparatus comprising: a toner image forming unit that forms a toner image corresponding to image information; and a transfer unit that transfers a toner image formed by the toner image forming unit to a predetermined recording medium. An image forming apparatus, wherein the member has a surface energy relatively lower than a surface energy of the toner image carrier. 2. The image forming apparatus according to claim 1, wherein the charge applying member includes a surface energy maintaining unit that maintains a surface energy of the charge applying member at a surface energy relatively lower than a surface energy of the toner image carrier. The image forming apparatus according to claim 1. 3. As the surface energy maintaining means, a powder having a particle diameter relatively smaller than the particle diameter of the toner used in the toner image forming means and having water repellency is applied to the surface of the charge applying member. The image forming apparatus according to claim 2, wherein the image forming apparatus comprises: 4. A toner image carrier for carrying a toner image on a surface thereof, a charge applying member for applying a predetermined charge to the toner image carrier, and a toner image carrier on which a charge is applied by the charge applying member. An image forming apparatus comprising: a toner image forming unit that forms a toner image corresponding to image information; and a transfer unit that transfers a toner image formed by the toner image forming unit to a predetermined recording medium. An image forming apparatus, wherein the member has a surface property in which the contact angle of water on the surface of the charge applying member is relatively larger than the contact angle of water on the surface of the toner image carrier. 5. A contact angle maintaining means for maintaining a contact angle of water on the surface of the charge applying member to a contact angle relatively larger than a contact angle of water on the surface of the toner image carrier. The image forming apparatus according to claim 4, wherein: 6. A powder having a particle size relatively smaller than a particle size of a toner used in the toner image forming unit and having water repellency is applied to the surface of the charge applying member as the contact angle maintaining unit. 6. The image forming apparatus according to claim 5, wherein the image forming apparatus comprises: 7. The charge-applying member according to claim 1, wherein the charge-applying member is a contact-type member that contacts the toner image carrier and applies a predetermined voltage to the toner image carrier. Image forming apparatus. 8. The image forming apparatus according to claim 1, wherein the charge applying member has a surface layer made of a polymer material in which water-repellent fine powder is dispersed on the surface. . 9. The toner image carrier according to claim 1, wherein the toner image carrier is configured to carry toner remaining on the toner image carrier after the toner image on the toner image carrier is transferred to the recording medium. 5. The image forming apparatus according to claim 1, wherein the process shifts to a step of carrying the next formed toner image.