JP6751340B2 - Developing device and image forming device - Google Patents

Description

The present invention relates to a developing device provided with a charging member that charges the surface of a latent image carrying member, and an image forming apparatus using the developing device.

Electrophotographic image forming apparatuses are widely used. This is because a clear image can be obtained in a short time as compared with an image forming apparatus of another system such as an inkjet system.

The electrophotographic image forming apparatus includes a developing device that attaches toner to the latent image, and the developing device includes a charging member that charges the surface of the latent image carrying member.

In the image forming step, after the toner attached to the latent image is transferred to the medium, the toner is fixed on the medium, so that the image is formed on the surface of the medium.

Various proposals have already been made regarding the configuration of the image forming apparatus. Specifically, when a charging member (charging roller) is used, a voltage is applied to the conductive blade in order to suppress the occurrence of ghost (image unevenness due to the history of previous images remaining) ( For example, see Patent Document 1.).

JP, 2010-224460, A

Specific studies have been made to improve the image quality when a charging member is used, but there is room for improvement because the measures are not yet sufficient.

The present invention has been made in view of such problems, and an object thereof is to provide a developing device and an image forming apparatus capable of obtaining a high-quality image.

The developing device according to one embodiment of the present invention includes a latent image carrying member whose surface is charged and a latent image is formed on the surface, and a charging device which extends in a predetermined direction and charges the surface of the latent image carrying member. Member and a developing member for adhering toner to the latent image formed on the surface of the latent image bearing member, and the load length rate tp of the surface of the charging member is expressed by the following equations (1) and (2), respectively. It satisfies the condition represented by.

Load length ratio tp (40%)=13% or more and 25% or less (1)
Load length ratio tp (60%)=35% or more and 60% or less (2)

An image forming apparatus according to an exemplary embodiment of the present invention includes a developing unit, a developing unit that attaches toner to a latent image, a transfer unit that transfers the toner attached to the latent image to a medium, and a toner transferred to the medium. And a fixing unit for fixing the same to the medium, and the developing device has the same configuration as that of the developing device according to the embodiment of the present invention described above.

Here, the "load length ratio tp (40%)" is the load length ratio tp when the cutting level C (%) is 40%, and the "load length ratio tp (60%)". Is the load length ratio tp when the cutting level C is 60%. However, the reference length L (mm) for calculating the load length ratio tp is the length in the direction intersecting the extending direction of the charging member.

According to the developing device or the image forming apparatus of one embodiment of the present invention, the load length ratio tp on the surface of the charging member satisfies the conditions shown in the equations (1) and (2), respectively. A high quality image can be obtained.

FIG. 1 is a plan view showing the configuration of a developing device according to an embodiment of the present invention. FIG. 3 is a cross-sectional view showing the configuration of a charging roller. FIG. 1 is a plan view illustrating a configuration of an image forming apparatus according to a first exemplary embodiment of the present invention. FIG. 3 is a block diagram showing a configuration of an image forming apparatus. FIG. 3 is a plan view showing a positional relationship of main components of the image forming apparatus. FIG. 6 is a diagram illustrating an operation timing of the image forming apparatus during image formation (no voltage application to the cleaning blade). It is a block diagram showing the structure of the image forming apparatus of the second embodiment of the present invention. FIG. 7 is a diagram illustrating an operation timing of the image forming apparatus (when a voltage is applied to the cleaning blade) during image formation. FIG. 9 is a diagram illustrating an operation timing of the image forming apparatus (when a voltage is applied to the cleaning blade) during cleaning of the charging roller. It is a figure showing the correlation of the cutting level C (%) regarding the surface of the charging roller, and the load length ratio tp. It is a top view for explaining an image for image quality evaluation. FIG. 6 is a plan view for explaining a situation of occurrence of an afterimage. It is a figure showing the correlation of the voltage applied to a cleaning blade, and image density.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. The order of description is as follows.

1. Developing device 1-1. Overall configuration 1-2. Configuration of charging roller 1-3. Physical Properties of Charging Roller 1-4. Operation 1-5. Action and effect 2. Image forming apparatus (first embodiment)
2-1. Overall configuration 2-2. Block configuration 2-3. Toner Configuration 2-4. Operation 2-5. Action and effect 3. Image forming apparatus (second embodiment)
3-1. Configuration 3-2. Operation 3-3. Actions and effects 4. Modification

<1. Development device>
A developing device according to an embodiment of the present invention will be described.

<1-1. Overall configuration>
First, the configuration of the developing device according to the embodiment of the present invention will be described.

The developing device described here is used, for example, in an electrophotographic image forming apparatus. This developing device mainly performs a developing process of attaching toner to a latent image (electrostatic latent image).

FIG. 1 shows a planar configuration of a developing device 100 which is a developing device according to an embodiment of the present invention. However, FIG. 1 shows, for example, a state in which the toner cartridge 200 and the light source 300 are attached to the developing device 100.

For example, as shown in FIG. 1, the developing device 100 includes a photosensitive drum 102, a charging roller 103, a cleaning roller 104, a developing roller 105, a supply roller 106, and a developing blade inside a housing 101. 107, a cleaning blade 108, and a static elimination optical substrate 109.

(Case)
The housing 101 is a container that mainly houses the photosensitive drum 102, the charging roller 103, and the like. The housing 101 includes, for example, one kind or two or more kinds of a metal material and a polymer material.

(Photosensitive drum)
The photoconductor drum 102 is the “latent image carrying member” of one embodiment of the present invention. The surface of the photosensitive drum is charged and an electrostatic latent image is formed on the surface of the photosensitive drum 102. The photosensitive drum 102 extends, for example, in the Y-axis direction and is rotatable about the Y-axis. A part of the photosensitive drum 102 is exposed from the opening 110 provided in the housing 101.

The photoconductor drum 102 also includes, for example, a cylindrical conductive support and a photoconductive layer that covers the outer peripheral surface of the conductive support. The conductive support contains, for example, one kind or two or more kinds of metal materials such as aluminum. The photoconductive layer is, for example, a laminated body including a charge generation layer, a charge transport layer, and the like.

(Charging roller)
The charging roller 103 is the “charging member” of the embodiment of the present invention, and mainly charges the surface of the photosensitive drum 102. The charging roller 103 extends in a predetermined direction (Y-axis direction) and is rotatable about the Y-axis. The charging roller 103 is pressed against the photosensitive drum 102 in order to charge the surface of the photosensitive drum 102.

Among a series of constituent elements that appear later, the constituent element that includes the word “roller” in its name extends in the Y-axis direction and rotates about the Y-axis, as with the charging roller 103. It is possible.

The detailed configuration of the charging roller 103 will be described later (see FIG. 2).

(Cleaning roller)
The cleaning roller 104 mainly removes foreign matter attached to the surface of the charging roller 103. The foreign matter is, for example, toner remaining on the surface of the photosensitive drum 102 without being used for image formation due to defective transfer or the like. The foreign matter is, for example, fine particles contained in the toner, and more specifically, it is an external additive or the like described later. The definition of the foreign matter described here is the same in the following.

The cleaning roller 104 includes, for example, a cylindrical core metal and a foam elastic layer that covers the outer peripheral surface of the core metal. The core metal includes, for example, one kind or two or more kinds of metal materials such as aluminum. The foam elastic layer contains, for example, one kind or two or more kinds of polymer materials such as urethane. The cleaning roller 104 is pressed against the charging roller 103 in order to remove foreign matter attached to the surface of the charging roller 103.

(Developing roller)
The developing roller 105 is the “developing member” of one embodiment of the present invention, and mainly retains the toner supplied from the supply roller 106 and also forms an electrostatic latent image on the surface of the photosensitive drum 102. Attach toner.

The developing roller 105 includes, for example, a cylindrical cored bar and a semiconductive layer that covers the outer peripheral surface of the cored bar. The core metal includes, for example, one kind or two or more kinds of metal materials such as aluminum. The semi-conductive layer contains, for example, any one kind or two or more kinds of polymer materials such as urethane rubber.

(Supply roller)
The supply roller 106 mainly holds the toner supplied from the toner cartridge 200, and also supplies the toner to the surface of the developing roller 105. The supply roller 106 is, for example, a so-called sponge roller that includes a cylindrical core metal and a semiconductive foamed silicone sponge layer that covers the outer peripheral surface of the core metal. The supply roller 106 is in sliding contact with the developing roller 105 in order to supply toner to the surface of the developing roller 105.

(Development blade)
The developing blade 107 mainly regulates the thickness of the toner supplied to the surface of the developing roller 105. The developing blade 107 is disposed, for example, at a position separated from the developing roller 105 by a predetermined distance, and the toner thickness is controlled based on the distance (interval) between the developing roller 105 and the developing blade 107. To be done. Further, the developing blade 107 includes, for example, one kind or two or more kinds of metal materials such as stainless steel. The developing blade 107 is in pressure contact with the developing roller 105 in order to regulate the thickness of the toner supplied to the surface of the developing roller 105.

(Cleaning blade)
The cleaning blade 108 is a plate-shaped elastic member that mainly scrapes off foreign matter attached to the surface of the photosensitive drum 102. The cleaning blade 108 extends, for example, in a direction substantially parallel to the extending direction of the photosensitive drum 102, and is pressed against the photosensitive drum 102.

In addition, the cleaning blade 108 includes, for example, one kind or two or more kinds of polymer materials such as polyurethane, silicone resin, fluororesin, and fluororubber. Of these, polyurethane is preferred. This is because excellent mechanical strength and elastic pressure contact can be obtained.

The cleaning blade 108 may include, for example, one kind or two or more kinds of conductive agents and the like in addition to the above-mentioned polymer material. The type of the conductive agent is not particularly limited, and examples thereof include an electronic conductive agent and an ionic conductive agent, and the electronic conductive agent is, for example, graphite, carbon black, a metal oxide, and a metal material. Carbon black is, for example, acetylene black, Ketjen black and furnace black. The metal oxide is, for example, iron oxide, titanium oxide, zinc oxide, tin oxide, calcium titanate, or the like. The metallic material is powder such as nickel and copper. The type of the ionic conductive agent is not particularly limited, and examples thereof include a structure charge specific anion and a surfactant, and the structure charge specific anion includes, for example, a quaternary ammonium salt, borate, and perchlorine. Examples include lithium acid and potassium perchlorate.

A voltage may or may not be applied to the cleaning blade 108 during the development process, for example. Along with this, the cleaning blade 108 may or may not have conductivity, for example. The cleaning blade 108 having conductivity contains, for example, any one kind or two kinds or more of the above-mentioned polymer materials and one kind or two kinds or more among the above-mentioned conductive agents. There is. The non-conductive cleaning blade 108 contains, for example, one kind or two or more kinds of the above-mentioned polymer materials.

Above all, it is preferable that the cleaning blade 108 has conductivity and that a voltage is applied to the cleaning blade 108 during the development processing. Specifically, for example, when the toner has a predetermined charging polarity, it is preferable that a voltage (DC voltage) having the same polarity as the charging polarity of the toner is applied to the cleaning blade 108. This is because the foreign matter attached to the surface of the photoconductor drum 102 is electrostatically adsorbed to the surface of the cleaning blade 108, so that the foreign matter is easily scraped off by the cleaning blade 108. The conductive cleaning blade 108, to which a voltage having the same polarity as the charging polarity of the toner is applied, is the “scraping member” of one embodiment of the present invention.

More specifically, for example, as will be described later, since the toner is a negatively charged toner, when the toner has a negative charging polarity, a negative DC voltage is applied to the cleaning blade 108. It is preferable. Even if fine particles such as an external additive drop off from the toner, if the fine particles have a positive charging polarity, the fine particles are likely to be electrostatically adsorbed on the surface of the cleaning blade 108, and thus the cleaning blade This is because the particles 108 are easily scratched off. That is, even if the fine particles pass through the gap between the photoconductor drum 102 and the cleaning blade 108, the fine particles are easily captured by the cleaning blade 108 by using the electrostatic force. As a result, even if the foreign matter attached to the surface of the photoconductor drum 102 has a minute particle diameter, the foreign matter is sufficiently scraped off by the cleaning blade 108.

When a negative DC voltage is applied to the cleaning blade 108, the value of the negative DC voltage is not particularly limited, but is preferably as large as possible. This is because foreign matter is more likely to be adsorbed on the surface of the cleaning blade 108, so that the cleaning blade 108 is more likely to scrape foreign matter. However, “a large value of the negative DC voltage” described here means that the negative value is large. That is, as an example, it means that −200V is preferable to −100V, and −300V is preferable to −200V.

The tendency of the fine particles (external additive) to fall off from the toner becomes more remarkable as the content of the external additive is increased in order to improve the fluidity of the toner. Further, the tendency of the cleaning blade 108 to scratch off the external additive becomes more remarkable as the particle size of the external additive becomes smaller.

Here, when the cleaning blade 108 becomes hard to scrape off foreign matter such as an external additive, the foreign matter not only unintentionally stays on the surface of the photoconductor drum 102, but also the foreign matter unintentionally moves to the charging roller 103. It may adhere to the surface and the surface of the developing roller 105. When foreign matter adheres to the surface of the charging roller 103 and the surface of the developing roller 105, defective formation of an electrostatic latent image, defective charging of the surface of the photosensitive drum 102, and defective adhesion of toner to the electrostatic latent image are likely to occur. .. Therefore, when an image is formed on the surface of the medium using the image forming apparatus equipped with the developing device 100, an afterimage is likely to occur unintentionally in a region other than the image forming region. The “afterimage” is an unnecessary image formed in a region other than the original image formation region, and is an image similar to the original image.

On the other hand, as described above, when a DC voltage having the same polarity as the charging polarity of the toner is applied to the cleaning blade 108, the cleaning blade 108 not only physically scrapes the foreign matter but also the cleaning blade 108. 108 electrostatically scrapes the foreign matter. As a result, foreign matter having a polarity different from the charging polarity of the toner can be easily scraped off sufficiently by the cleaning blade 108 by using the electrostatic force. That is, when the toner has a negative charging polarity, the external additive having a positive charging polarity is easily collected by the cleaning blade 108. Therefore, foreign matter is less likely to adhere to the surface of the charging roller 103 and the surface of the developing roller 105, so that an afterimage is less likely to occur even when an image is formed on the surface of the medium using the image forming apparatus equipped with the developing device 100. Become.

The cleaning blade 108 may include, for example, a blade portion that is a plate-shaped elastic member and a holding portion that holds the blade portion. The material of the blade portion is, for example, the same as the material of the cleaning blade 108 described above. That is, the electrically conductive blade portion contains, for example, a conductive material together with a polymer material. The non-conductive blade portion contains, for example, a polymer material. The holding portion includes, for example, one type or two or more types of a steel plate having rigidity.

(Static elimination light board)
The charge removal light substrate 109 mainly erases the electrostatic latent image formed on the surface of the photoconductor drum 102. The static elimination light substrate 109 includes, for example, a light emitting diode (LED) chip that generates light for erasing.

(Toner cartridge)
The toner cartridge 200 mainly contains toner. The toner cartridge 200 is attachable to and detachable from the developing device 100, and can supply toner to the developing device 100 (supply roller 106) as needed. The types (colors) and configurations of toner will be described later.

(light source)
The light source 300 is an exposure device that mainly forms an electrostatic latent image on the surface of the photoconductor drum 102 by exposing the surface of the photoconductor drum 102 through an opening 111 provided in the housing 101. The light source 300 is, for example, an LED head or the like. The LED head includes, for example, an LED element and a lens array, and the LED element and the lens array and the like form light (irradiation light) output from the LED element on the surface of the photosensitive drum 102. Are arranged as follows.

Here, for example, since the toner cartridge 200 and the light source 300 are not constituent elements of the developing device 100, the toner cartridge 200 and the light source 300 are externally attached to the developing device 100. However, the developing device 100 may include the toner cartridge 200 as a constituent element or the light source 300 as a constituent element.

<1-2. Structure of charging roller>
Next, the configuration of the charging roller 103 will be described.

FIG. 2 shows a sectional configuration of the charging roller 103 shown in FIG. However, FIG. 2 shows a cross section of the charging roller 103 along the XZ plane.

For example, as shown in FIG. 2, the charging roller 103 includes a conductive core metal 103A, an elastic layer 103B that covers the outer peripheral surface of the core metal 103A, and a surface layer that covers the outer peripheral surface of the elastic layer 103B. 103C and.

The core metal 103A is, for example, a cylindrical metal shaft and contains any one kind or two or more kinds of metal materials such as aluminum.

The elastic layer 130B is, for example, any of polymer materials (rubber) such as epichlorohydrin rubber, ethylene propylene rubber (EPM, EPDM), nitrile rubber (NBR), chloroprene rubber (CR), urethane rubber and silicone rubber. Or one or more types are included. Among them, epichlorohydrin rubber having semiconductivity is preferable.

The type of epichlorohydrin rubber is not particularly limited, but examples thereof include epichlorohydrin homopolymer (CO), copolymer of epichlorohydrin and ethylene oxide (ECO), epichlorohydrin and allyl glycidyl ether. Copolymer (GCO), epichlorohydrin and propylene oxide, epichlorohydrin and liquid oxide and allyl glycidyl ether (GECO), and epichlorohydrin and propylene oxide And a copolymer of allyl glycidyl ether. Of these, epichlorohydrin rubber containing ethylene oxide as a polymerization component is preferable, and more specifically, ECO and GECO are preferable.

The elastic layer 103B may include, for example, one kind or two or more kinds of a conductive agent and the like together with the above-mentioned polymer material. The type of conductive agent is not particularly limited, but is, for example, carbon black or the like. This carbon black is, for example, acetylene black or Ketjen black.

The rubber hardness of the elastic layer 103B is not particularly limited. Specifically, the Asker C hardness of the elastic layer 103B is, for example, 60 degrees to 80 degrees.

The surface layer 103C contains, for example, a polymer material and a plurality of particles dispersed in the polymer material. Since the surface of the charging roller 103 (surface layer 103C) is roughened so as to have irregularities, the surface state (surface roughness) of the charging roller 103 is easily controlled to be appropriate as described later. Is.

The type of polymer material is not particularly limited, and examples thereof include ethylene propylene rubber, urethane rubber, butadiene rubber, styrene butadiene rubber, acrylic rubber, nitrile rubber, polyurethane elastomer, polyester and nylon.

The type of the plurality of particles is not particularly limited, but is, for example, any one type or two or more types of polymer particles and inorganic particles. The polymer particles include any one kind or two or more kinds of polymer materials such as nylon resin, acrylic resin, urethane resin, fluororesin, polyamide resin and phenol resin. The inorganic particles include, for example, any one kind or two or more kinds of inorganic materials such as silica, alumina and calcium carbonate.

The thickness of the surface layer 103C is not particularly limited, but is, for example, 3 μm to 30 μm. The average particle diameter of the plurality of particles (for example, median diameter D50) is not particularly limited, but is, for example, 5 μm to 30 μm. The reason that the average particle diameter of the plurality of particles is within the above range is that the surface state (surface roughness) of the charging roller 103 is easily controlled appropriately by using the plurality of particles. The shape of the plurality of particles is not particularly limited, but is preferably a substantially spherical shape, and more preferably a true sphere.

The surface of the surface layer 103C may be subjected to any one kind or two or more kinds of a series of treatments such as a surface treatment, a coating treatment, and an ultraviolet irradiation treatment. This is because the surface contamination of the photosensitive drum 102 is prevented and the electric resistance of the elastic layer 103B is adjusted.

The type of material used in the series of treatments described above is not particularly limited, and examples thereof include isocyanate compounds, acrylic resins, urethane resins, alkyd resins, amide resins, phenol resins, fluororesins, silicone resins and modified products thereof. Any one of them or two or more of them.

When the surface of the surface layer 103C is subjected to the ultraviolet irradiation treatment, for example, the surface layer 103C may be oxidized by the ultraviolet rays to form an oxide film on the surface of the surface layer 103C. This is because the surface of the surface layer 103 is protected by this oxide film.

The surface layer 103C includes, for example, a conductive material, a filler, a stabilizer, an ultraviolet absorber, an antistatic agent, a reinforcing agent, a lubricant, a release agent, and a flame retardant together with the above-described polymer material and a plurality of particles. Any one of them or two or more of them may be included. The type of conductive agent included in the surface layer 103C is, for example, the same as the type of conductive agent included in the elastic layer 103B.

<1-3. Physical properties of charging roller>
Next, the physical properties of the charging roller 103 will be described.

When foreign matter adheres to the surface of the photoconductor drum 102 and then the foreign matter adheres to the surface of the charging roller 103, the charging state of the charging roller 103 changes at the place where the foreign matter adheres. As a result, when the surface of the photosensitive drum 102 is charged by the charging roller 103, the charged state of the surface of the photosensitive drum 102 may become uneven. When the charged state of the surface of the photoconductor drum 102 becomes non-uniform, the adhered state of the toner to the electrostatic latent image becomes non-uniform. Therefore, when an image is formed using the image forming apparatus equipped with the developing device 100, A phenomenon that images are sparse, so-called image roughness occurs.

In particular, among foreign matters, an external additive having a fine particle diameter is stored in the gap between the photoconductor drum 102 and the cleaning blade 108 so as to easily pass through it, and if the external additive is attached to the surface of the charging roller 103. , The roughness of the image is likely to occur.

In order to prevent the roughness of the image from occurring, it is necessary to prevent foreign matter from adhering to the surface of the charging roller 103. Therefore, the surface state (surface roughness) of the charging roller 103 is optimized as described below.

Specifically, the load length ratio tp (%) on the surface of the charging roller 103 simultaneously satisfies the two conditions represented by the following equations (1) and (2).

Load length ratio tp (40%)=13% to 25% (1)
Load length ratio tp (60%)=35% to 60% (2)

Here, the “load length ratio tp” used to define the surface state (surface roughness) of the charging roller 103 corresponds to the reference length L from the surface roughness curve of the charging roller 103. This is a value in which the ratio of the sum Dz of the cut lengths to the reference length L after the portion to be cut (reference roughness curve) is extracted is expressed as a percentage. That is, the load length ratio tp is represented by the load length ratio tp=(sum of cutting lengths Dz/reference length L)×100.

The sum Dz of cutting lengths is the sum of a plurality of cutting lengths D1 to Dn obtained when the reference roughness curve is cut based on the cutting level C (%) parallel to the crest line, and Dz=D1+D2+D3+. ..+Dn-1+Dn.

The cutting level C is a value representing the ratio of the cutting distance Dc to the maximum distance Dmax in percentage, and is expressed by C=(Dc/Dmax)×100. The maximum distance Dmax is the distance from the peak of the reference roughness curve (the peak of the highest peak) to the bottom of the valley (bottom point of the lowest valley). The cutting distance Dc is the distance from the above-mentioned mountain peak.

As described above, the "load length ratio tp (40%)" is the load length ratio tp when the cutting level C (%) is 40%, and the "load length ratio tp (60%)". )” is the load length ratio tp when the cutting level C is 60%.

However, since the reference length L (mm) for calculating the load length ratio tp is the length in the direction intersecting the extending direction (Y-axis direction) of the charging roller 103, the load length ratio tp. Is a value measured in a direction intersecting the extending direction (Y-axis direction) of the charging roller 103. That is, for example, as shown in FIG. 2, when the charging roller 103 has a cylindrical shape extending in the Y-axis direction, the load length ratio tp is the outer peripheral direction R of the charging roller 103. Is the value measured at.

Regarding the load length ratio tp on the surface of the charging roller 103, the two conditions shown in the equations (1) and (2) are satisfied at the same time. This is because the surface state (surface roughness) of the charging roller 103 is optimized from the viewpoint of suppressing the adhesion of foreign matter. This makes it difficult for the image to be rough.

Further, when defining the surface state (surface roughness) of the charging roller 103 based on the load length ratio tp, attention is paid to the two cutting levels C=40% and 60% because the ten-point average roughness is This is because, as compared with the case where the surface state of the charging roller 103 is defined based on Rz, it becomes easier to strictly grasp the correlation between the surface state of the charging roller 103 and the occurrence state of image roughness. As a result, it is possible to find an effective condition for the surface state of the charging roller 103 that can substantially and effectively suppress the roughness of the image.

More specifically, as the parameter for defining the surface state of the charging roller 103, the above-mentioned ten-point average roughness Rz can be considered in addition to the load length ratio tp. However, the ten-point average roughness Rz is calculated mainly by considering the maximum height of the peaks and the maximum depth of the valleys of the roughness curve. Therefore, when the surface condition of the charging roller 103 is optimized by using the ten-point average roughness Rz, if the ten-point average roughness Rz is replaced with the load length ratio tp, the load length ratio in the vicinity of the summit is calculated. tp (10%) and the load length ratio tp (90%) around the valley bottom will be used.

In this case, if extremely high peaks and extremely low valleys are present in the roughness curve due to fine scratches and damages generated on the surface of the charging roller 103, the extreme Since the ten-point average roughness Rz is calculated by adding a high peak portion and an extremely low valley portion, the error included in the ten-point average roughness Rz becomes large. As a result, when the surface state of the charging roller 103 is defined by using the ten-point average roughness Rz, the surface state of the charging roller 103 defined by the ten-point average roughness Rz and the occurrence state of the image roughness are determined. Large errors are likely to be included. Therefore, when the ten-point average roughness Rz is used to define the surface state of the charging roller 103, an appropriate range of the ten-point average roughness Rz that can substantially and effectively suppress the roughness of the image is found. Is difficult.

On the other hand, the surface condition of the charging roller 103 is defined by using the load length ratio tp at the two cutting levels C=40% and 60%, that is, the load length ratios tp (40%) and tp (60%). In this case, the proper range of the load length ratio tp is found without being greatly affected by the maximum height of the peaks and the maximum depth of the valleys of the roughness curve. Specifically, even if extremely high peaks and extremely low valleys are present in the roughness curve due to minute scratches and damages generated on the surface of the charging roller 103, the extreme The load length ratio tp is calculated with little consideration of extremely high peaks and extremely low valleys. Accordingly, when the surface condition of the charging roller 103 is defined using the load length ratios tp (40%) and tp (60%), it is defined by the load length ratios tp (40%) and tp (60%). A large error is unlikely to be included between the surface state of the charging roller 103 and the occurrence state of image roughness. Therefore, if the load length ratios tp (40%) and tp (60%) are used to define the surface state of the charging roller 103, the load length that can substantially and effectively suppress the roughness of the image. It is possible to find an appropriate range of the ratios tp (40%) and tp (60%). Therefore, as described above, by defining an appropriate range of the load length ratios tp (40%) and tp (60%) in relation to the occurrence state of image roughness, the image roughness can be substantially and effectively achieved. Can be suppressed.

The load length ratios tp (40%) and tp (60%) are measured by the following procedure, for example. First, using a surface roughness measuring device, the load length ratios tp (40%) and tp (60%) are measured at arbitrary places on the surface of the charging roller 103. In this case, for example, a surface shape/roughness measuring device Surfcoder SEF3500 manufactured by Kosaka Laboratory is used as the surface roughness measuring device. Further, as the measurement conditions, reference length L=10 mm, stylus radius=2 μm, stylus pressure=0.7 mN, stylus feed speed=0.5 mm/sec, and cutoff value=0.8 mm. Subsequently, the load length ratios tp (40%) and tp (60%) are similarly measured at two different locations other than the above-described measurement locations. Thereby, the three load length ratios tp (40%) are measured, and the three load length ratios tp (60%) are measured. Finally, the average value of the three load length ratios tp (40%) is calculated, and the average value of the three load length ratios tp (60%) is calculated.

As long as the load length ratio tp satisfies the above two conditions, other physical properties that affect the surface state of the charging roller 103 are not particularly limited. Above all, the ten-point average roughness Rz of the surface of the charging roller 103 is preferably 13 μm to 17 μm, and the average interval Sm of the irregularities on the surface of the charging roller 103 is 0.14 mm to 0.20 mm. Is preferred. This is because the surface condition of the charging roller 103 is optimized. As a result, foreign matter is less likely to adhere to the surface of the charging roller 103, so that the image is less likely to be roughened.

The procedure for measuring the ten-point average roughness Rz is, for example, the above-described load length except that the ten-point average roughness Rz is measured in place of the load length rate tp using a surface roughness measuring device. It is similar to the procedure for measuring the rate tp. That is, the ten-point average roughness Rz described above is an average value of three ten-point average roughness Rz.

The procedure for measuring the average interval Sm is the same as the procedure for measuring the load length ratio tp described above, except that the average interval Sm is measured using a surface roughness measuring device instead of the load length ratio tp. It is the same. That is, the average interval Sm described above is an average value of the three average intervals Sm.

The load length rate tp, the ten-point average roughness Rz, and the average interval Sm described herein are measured in accordance with JIS B0601-1994, for example.

<1-4. Operation>
Next, the operation of the developing device 100 will be described.

When the developing device 100 performs a developing process, first, when the photosensitive drum 102 rotates, a DC voltage is applied to the surface of the photosensitive drum 102 while the charging roller 103 rotates. As a result, the surface of the photoconductor drum 102 is uniformly charged. In this case, since the cleaning roller 104 rotates in accordance with the rotation of the charging roller 103, the foreign matter attached to the surface of the charging roller 103 is removed.

Then, the light source 300 irradiates the surface of the photosensitive drum 102 with light based on the image data supplied to the developing device 100 from the outside. As a result, the surface potential of the surface of the photoconductor drum 102 is attenuated (light is attenuated) at the light irradiation portion, so that an electrostatic latent image is formed on the surface of the photoconductor drum 102.

On the other hand, the toner contained in the toner cartridge 200 is discharged toward the developing device 100 (supply roller 106).

Then, after a voltage is applied to the supply roller 106, the supply roller 106 rotates. As a result, the toner is supplied to the surface of the supply roller 106.

Subsequently, after a voltage is applied to the developing roller 105, the developing roller 105 rotates while being pressed against the supply roller 106. As a result, the toner supplied to the surface of the supply roller 106 is attracted to the surface of the developing roller 105, and the toner is conveyed by utilizing the rotation of the developing roller 105. In this case, part of the toner adsorbed on the surface of the developing roller 105 is removed by the developing blade 107, so that the thickness of the toner adsorbed on the surface of the developing roller 105 is made uniform.

Finally, after the photosensitive drum 102 is rotated while being pressed against the developing roller 105, the toner adsorbed on the surface of the developing roller 105 is transferred to the surface of the photosensitive drum 102. As a result, the toner adheres to the surface (electrostatic latent image) of the photoconductor drum 102 using the Coulomb force, and the developing process is completed.

<1-5. Action and effect>
In this developing device 100, the surface state (surface roughness) of the charging roller 103 is defined by the load length ratio tp, and the load length ratios tp (40%) and tp (60%) are 2 as described above. The two conditions are met at the same time. In this case, as described above, as compared with the case where the surface state of the charging roller 103 is defined by the ten-point average roughness Rz, in view of suppressing foreign matter from adhering to the surface of the charging roller 103, The surface condition of the charging roller 103 is substantially optimized. As a result, foreign matter is less likely to adhere to the surface of the charging roller 103, so that when an image is formed using the image forming apparatus in which the developing device 100 is mounted, the image is less likely to be roughened. Therefore, a high quality image can be obtained.

Particularly, regarding the surface of the charging roller 103, if the ten-point average roughness Rz is 13 μm to 17 μm and the average interval Sm of the irregularities is 0.14 mm to 0.20 mm, the surface state of the charging roller 103 is more appropriate. Therefore, a higher effect can be obtained.

Further, if the cleaning blade 108 has conductivity and a DC voltage having the same polarity as the charging polarity of the toner is applied to the cleaning blade 108, foreign matter attached to the surface of the photoconductor drum 102 will be removed. 108 is easily electrostatically adsorbed. Therefore, the cleaning blade 108 can more easily scrape the foreign matter, and a higher effect can be obtained. In this case, the toner is negatively charged toner, and if a negative DC voltage is applied to the cleaning blade 108, a positively charged external additive or the like having a minute particle size is electrostatically applied to the cleaning blade 108. Since it is more likely to be adsorbed on, it is possible to obtain a higher effect.

<2. Image forming apparatus (first embodiment)>
Next, an image forming apparatus of the first embodiment of the present invention using the above-mentioned developing device will be described.

The image forming apparatus described here is, for example, an apparatus that forms an image on the surface of a medium M (see FIG. 3) described later using toner, and is a so-called electrophotographic full-color printer. The material of the medium M is not particularly limited, but is, for example, any one kind or two or more kinds of paper and film.

This image forming apparatus includes a developing unit 30 corresponding to the developing device 100 described above. In the following description, the constituent elements of the developing device 100 will be referred to when describing the configuration of the developing unit 30.

<2-1. Overall configuration>
First, the configuration of the image forming apparatus will be described.

FIG. 3 shows a planar configuration of the image forming apparatus. In this image forming apparatus, the medium M is transported along the transport paths R1 to R5. In FIG. 3, each of the transport paths R1 to R5 is indicated by a broken line.

For example, as shown in FIG. 3, the image forming apparatus includes a tray 10, a delivery roller 20, a developing unit 30, a transfer unit 40, a fixing unit 50, and conveyance rollers 61 to 61 inside a housing 1. 68 and conveyance path switching guides 69 and 70.

[Case]
The housing 1 includes, for example, one kind or two or more kinds of a metal material and a polymer material. The casing 1 is provided with a stacker unit 2 for ejecting the medium M on which the image is formed, and the medium M on which the image is formed is ejected from the ejection port 1H provided in the casing 1. It

[Tray and delivery roller]
The tray 10 is detachably attached to the housing 1 and accommodates the medium M, for example. The delivery roller 20 extends, for example, in the Y-axis direction and is rotatable about the Y-axis. Among a series of constituent elements described below, a constituent element including the word “roller” in its name extends in the Y-axis direction and rotates about the Y-axis, similarly to the delivery roller 20. It is possible.

The tray 10 stores, for example, a plurality of media M in a stacked state. The plurality of media M stored in the tray 10 are taken out from the tray 10 one by one by the delivery roller 20, for example.

The number of trays 10 and the number of delivery rollers 20 are not particularly limited, and may be only one or two or more. In FIG. 3, for example, the number of trays 10 is one and the number of feed rollers 20 is one.

[Development part]
The developing unit 30 has the same configuration as that of the developing device 100 described above, and performs a developing process using toner.

The photoconductor drum 102 is rotatable, for example, via a drum motor 87 (see FIG. 4) described later, and the series of rollers such as the charging roller 103 includes, for example, a roller motor 85 (see FIG. 4) described later. It can be rotated through. The developing unit 30 can be moved up and down, for example, via a moving motor 89 described later. More specifically, the developing unit 30 moves, for example, between a position where the photosensitive drum 102 contacts an intermediate transfer belt 41 described later and a position where the photosensitive drum 102 is separated from the intermediate transfer belt 41. It is possible.

In this image forming apparatus, for example, no voltage is applied to the cleaning blade 108 during image formation (during development processing). Accordingly, the cleaning blade 108 may or may not have electrical conductivity, for example.

The number of developing units 30 is not particularly limited, and may be, for example, only one or two or more. Here, the image forming apparatus includes, for example, four developing units 30 (30K, 30C, 30M, 30Y).

Each of the developing units 30K, 30C, 30M, and 30Y is, for example, detachably attached to the housing 1 and arranged along the movement path of the intermediate transfer belt 41. Here, the developing units 30K, 30C, 30M, and 30Y are arranged in this order from the upstream side to the downstream side in the moving direction (arrow F5) of the intermediate transfer belt 41, for example.

The developing units 30K, 30C, 30M, and 30Y have the same configuration except that, for example, the types (colors) of the toners stored in the toner cartridges are different. For example, black toner is stored in the toner cartridge of the developing unit 30K. For example, cyan toner is stored in the toner cartridge of the developing unit 30C. For example, magenta toner is stored in the toner cartridge of the developing unit 30M. For example, yellow toner is stored in the toner cartridge of the developing unit 30Y.

[Transfer part]
The transfer unit 40 performs a transfer process using the toner developed by the developing unit 30. Specifically, the transfer unit 40 mainly transfers the toner attached to the electrostatic latent image by the developing unit 30 onto the medium M.

The transfer section 40 includes, for example, an intermediate transfer belt 41, a driving roller 42, a driven roller (idle roller) 43, a backup roller 44, a primary transfer roller 45, a secondary transfer roller 46, and a cleaning blade 47. Includes and.

The intermediate transfer belt 41 is a medium (intermediate transfer medium) to which the toner is temporarily transferred before the toner is transferred to the medium M, and is, for example, an endless elastic belt. The intermediate transfer belt 41 includes, for example, one kind or two or more kinds of polymer materials such as polyimide. The intermediate transfer belt 41 is movable in accordance with the rotation of the drive roller 42 in a state of being stretched by the drive roller 42, the driven roller 43, and the backup roller 44.

The drive roller 42 is rotatable, for example, via a belt motor 91 described later. Each of the driven roller 43 and the backup roller 44 can be rotated according to the rotation of the drive roller 42, for example.

The primary transfer roller 45 transfers (primarily transfers) the toner attached to the electrostatic latent image to the intermediate transfer belt 41. The primary transfer roller 45 is pressed against the developing section 30 (photosensitive drum) via the intermediate transfer belt 41. The primary transfer roller 45 can rotate according to the movement of the intermediate transfer belt 41.

The number of primary transfer rollers 45 is not particularly limited, and may be, for example, only one or two or more. Here, the transfer unit 40 includes, for example, four primary transfer rollers 45 (45K, 45C, 45M, 45Y) corresponding to the above-described four developing units 30 (30K, 30C, 30M, 30Y). Contains. The transfer section 40 also includes one secondary transfer roller 46 corresponding to one backup roller 44.

The secondary transfer roller 46 transfers the toner transferred to the intermediate transfer belt 41 to the medium M (secondary transfer). The secondary transfer roller 46 is in pressure contact with the backup roller 44, and includes, for example, a metal core material and an elastic layer such as a foamed rubber layer that covers the outer peripheral surface of the core material. The secondary transfer roller 46 can rotate according to the movement of the intermediate transfer belt 41.

The cleaning blade 47 is pressed against the intermediate transfer belt 41 and scrapes off foreign matter such as unnecessary toner remaining on the surface of the intermediate transfer belt 41.

[Fixer]
The fixing unit 50 performs the fixing process using the toner transferred to the medium M by the transfer unit 40. Specifically, the fixing unit 50 fixes the toner on the medium M mainly by heating and pressing the toner transferred onto the medium M by the transfer unit 40.

The fixing unit 50 includes, for example, a heating roller 51 and a pressure roller 52.

The heating roller 51 heats the toner. The heating roller 51 includes, for example, a hollow cylindrical metal core and a resin coat that covers the surface of the metal core. The metal core includes, for example, one kind or two or more kinds of metal materials such as aluminum. The resin coat contains, for example, one or more kinds of polymer materials such as a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether (PFA) and polytetrafluoroethylene (PTFE). I'm out.

The heating roller 51 is rotatable, for example, via a fixing motor 95 described later. Inside the heating roller 51 (metal core), for example, a heater 93 (see FIG. 4) described later is installed, and the heater is, for example, a halogen lamp or the like. In the vicinity of the heating roller 51, for example, a thermistor 94 (see FIG. 4) described later is arranged so as to be separated from the heating roller 51. This thermistor measures, for example, the surface temperature of the heating roller 51.

The pressure roller 52 is pressed against the heating roller 51 and presses the toner. The pressure roller 52 is, for example, a metal rod or the like, and is rotatable according to the rotation of the heating roller 51. The metal rod contains, for example, one kind or two or more kinds of metal materials such as aluminum.

[Conveyor roller]
Each of the transport rollers 61 to 68 includes a pair of rollers arranged to face each other via the transport paths R1 to R5 of the medium M, and transports the medium M taken out by the delivery roller 20.

When an image is formed on only one surface of the medium M, the medium M is transported by the transport rollers 61 to 64 along the transport paths R1 and R2, for example. When images are formed on both sides of the medium M, the medium M is transported by the transport rollers 61 to 68 along the transport paths R1 to R5, for example.

[Conveyor path switching guide]
The transport path switching guides 69 and 70 are in accordance with conditions such as a format of an image formed on the medium M (whether an image is formed on only one side of the medium M or an image is formed on both sides of the medium M). Then, the transport direction of the medium M is switched.

<2-2. Block structure>
Next, the block configuration of the image forming apparatus will be described.

FIG. 4 shows a block configuration of the image forming apparatus. However, FIG. 4 also shows some of the components of the image forming apparatus described above.

For example, as shown in FIG. 4, the image forming apparatus includes a control unit 71, an interface (I/F) control unit 72, a reception memory 73, an editing memory 74, a panel unit 75, and an operation unit 76. , Various sensors 77, light source control unit 78, charging voltage control unit 79, developing voltage control unit 80, supply voltage control unit 81, transfer voltage control unit 82, charge removal light control unit 83, roller drive control. A section 84, a drum drive control section 86, a movement control section 88, a belt drive control section 90, and a fixing control section 92 are provided.

The control unit 71 mainly controls the operation of the entire image forming apparatus. The control unit 71 includes, for example, a control circuit, a memory, an input/output port, a timer and the like. The control circuit includes, for example, a central processing unit (CPU) and the like. The memory includes, for example, any one type or two or more types of storage elements such as a read only memory (ROM) and a random access memory (RAM).

The I/F control unit 72 mainly receives information such as data transmitted from an external device to the image forming apparatus. This external device is, for example, a personal computer that can be used by the user of the image forming apparatus, and the information transmitted from the external device to the image forming apparatus is, for example, image data.

The reception memory 73 mainly stores information such as data received by the image forming apparatus. The editing memory 74 mainly stores data obtained by editing the image data stored in the receiving memory 73.

The panel unit 75 includes, for example, a display panel that displays information necessary for the user to operate the image forming apparatus. The type of the display panel is not particularly limited, but is, for example, a liquid crystal panel. The operation unit 76 includes, for example, a button operated by a user when operating the image forming apparatus.

The various sensors 77 include, for example, one or more of a temperature sensor, a humidity sensor, an image density sensor, a medium position detection sensor, a toner remaining amount detection sensor, and a human sensor.

The light source controller 78 mainly controls the exposure operation of the light source 300. The charging voltage controller 79 mainly controls the voltage applied to the charging roller 103. The developing voltage controller 80 mainly controls the voltage applied to the developing roller 105. The supply voltage controller 81 mainly controls the voltage applied to the supply roller 106. The transfer voltage controller 82 mainly controls the voltage applied to each of the primary transfer roller 45 and the secondary transfer roller 46. The static elimination light control unit 83 mainly controls the operating state (lighting and extinction) of the static elimination light substrate 109. These series of voltages can be set, for example, according to an instruction from the control unit 71, and can be arbitrarily changed according to an instruction from the control unit 71.

Although the illustration is simplified in FIG. 4, the image forming apparatus includes, for example, four light source control units 78 corresponding to the four developing units 30 (30K, 30C, 30M, 30Y). .. Specifically, for example, a light source control unit 78 that controls the light source 300 installed in the developing unit 30K, a light source control unit 78 that controls the light source 300 installed in the developing unit 30C, and a light source controlling unit 78 installed in the developing unit 30M. The light source control unit 78 controls the light source 300 and the light source control unit 78 controls the light source 300 mounted on the developing unit 30Y.

The description about the light source controller 78 is the same for each of the charging voltage controller 79, the developing voltage controller 80, the supply voltage controller 81, the transfer voltage controller 82, and the charge removal light controller 83, for example. .. That is, the image forming apparatus includes, for example, four charging voltage control units 79, four developing voltage control units 80, four supply voltage control units 81, corresponding to the four developing units 30. It includes four transfer voltage control units 82 and four charge removal light control units 83.

The roller drive control unit 84 mainly controls the rotation operation of a series of rollers such as the charging roller 103, the developing roller 105, and the supply roller 106 via the roller motor 85. The drum drive control unit 86 mainly controls the rotation operation of the photosensitive drum 102 via the drum motor 87. The movement control unit 88 mainly controls the movement operation of the developing unit 30 via the movement motor 89. The belt drive controller 90 mainly controls the movement operation of the intermediate transfer belt 41 via the belt motor 91. The fixing controller 92 mainly controls the temperature of the heater 93 based on the temperature measured by the thermistor 94, and also controls the rotating operation of the heating roller 51 via the fixing motor 95.

What has been described above regarding the light source control unit 78 is the same for each of the roller drive control unit 84, the drum drive control unit 86, and the movement control unit 88, for example. That is, the image forming apparatus includes, for example, four roller drive control units 84, four drum drive control units 86, and four movement control units 88 corresponding to the four developing units 30. I'm out.

<2-3. Toner composition>
Each of the yellow toner, the magenta toner, the cyan toner, and the black toner is, for example, a one-component developing type negatively charged toner, that is, the series of toners described here has, for example, a negatively charged polarity. ..

The one-component developing method is a method in which an appropriate amount of charge is applied to the toner itself without using a carrier (magnetic particles) for giving an electric charge to the toner. On the other hand, the two-component development method is a method in which the carrier and the toner are mixed and the friction between the carrier and the toner is utilized to impart an appropriate charge amount to the toner.

The toner manufacturing method is not particularly limited. Specifically, the toner manufacturing method may be, for example, a pulverizing method, a polymerization method, or a method other than them. Of course, two or more of the above manufacturing methods may be used together. The polymerization method is, for example, a dissolution suspension method.

The yellow toner contains, for example, a yellow colorant, a binder, an external additive, a release agent and a charge control agent. The yellow colorant contains, for example, one kind or two or more kinds of a yellow pigment and a yellow dye. The yellow pigment is, for example, Pigment Yellow 74 or the like. The yellow dye is, for example, C.I. I. Pigment Yellow 74 and Cadmium Yellow.

The magenta toner has the same configuration as the yellow toner, except that the magenta toner contains a magenta colorant instead of the yellow colorant. The magenta colorant contains, for example, one kind or two or more kinds of a magenta pigment and a magenta dye. The magenta pigment is, for example, quinacridone. The magenta dye is, for example, C.I. I. Pigment Red 238 and the like.

The cyan toner has the same configuration as the yellow toner, except that it contains a cyan colorant instead of the yellow colorant, for example. The cyan colorant contains, for example, one kind or two or more kinds of a cyan pigment and a cyan dye. The cyan pigment is, for example, phthalocyanine blue (CI Pigment Blue 15:3). The cyan dye is, for example, Pigment Blue 15:3.

The black toner has the same configuration as that of the yellow toner except that it contains a black colorant instead of the yellow colorant, for example. The black colorant contains, for example, one kind or two or more kinds of a black pigment and a black dye. The black pigment is, for example, carbon. The black dye is, for example, carbon black, and the carbon black is, for example, furnace black and channel black.

The binder mainly binds a colorant or the like. The binder contains one kind or two or more kinds of polymer materials such as polyester resin, styrene-acrylic resin, epoxy resin and styrene-butadiene resin.

Among them, the binder preferably contains a polyester resin. This is because the polyester-based resin has a high affinity for the medium M such as paper, and thus the toner containing the polyester-based resin as the binder is easily fixed to the medium M. Further, since the polyester resin has high physical strength even when the molecular weight is relatively small, the toner containing the polyester resin as the binder has excellent durability.

The crystalline state of the polyester resin is not particularly limited. Therefore, the polyester resin may be crystalline polyester, amorphous polyester, or both. Of these, crystalline polyester is preferable. This is because the toner is more easily fixed on the medium and the durability of the toner is further improved.

This polyester resin is, for example, a reaction product (condensation polymer) of one or more alcohols and one or more carboxylic acids.

The type of alcohol is not particularly limited, but among them, alcohols having a valence of 2 or more and derivatives thereof are preferable. This dihydric or higher alcohol is, for example, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, cyclohexanedimethanol, xylene glycol, dipropylene glycol, polypropylene glycol, bisphenol A. Hydrogenated bisphenol A, bisphenol A ethylene oxide, bisphenol A propylene oxide, sorbitol and glycerin.

The type of carboxylic acid is not particularly limited, but among them, divalent or higher carboxylic acids and derivatives thereof are preferable. This divalent or higher carboxylic acid includes, for example, maleic acid, fumaric acid, phthalic acid, isophthalic acid, terephthalic acid, succinic acid, adipic acid, trimellitic acid, pyromellitic acid, cyclopentanedicarboxylic acid, succinic anhydride, and anhydrous. Examples include trimellitic acid, maleic anhydride and dodecenyl succinic anhydride.

The external additive mainly improves the fluidity of the toner by suppressing aggregation of the toner and the like. The external additive contains, for example, one kind or two or more kinds of an inorganic material and an organic material. The inorganic material is, for example, hydrophobic silica. The organic material is, for example, melamine resin.

The release agent mainly improves the fixing property and offset resistance of the toner. The release agent is, for example, any one or two of waxes such as aliphatic hydrocarbon wax, oxide of aliphatic hydrocarbon wax, fatty acid ester wax, and deoxidation of fatty acid ester wax. Includes more than one type. In addition, the release agent may be, for example, a block copolymer of the series of waxes described above.

The aliphatic hydrocarbon wax is, for example, low molecular weight polyethylene, low molecular weight polypropylene, copolymer of olefin, microcrystalline wax, paraffin wax, Fischer-Tropsch wax and the like. The oxide of the aliphatic hydrocarbon wax is, for example, oxidized polyethylene wax. The fatty acid ester wax is, for example, carnauba wax and montanic acid ester wax. The deoxidized fatty acid ester wax is a wax obtained by partially or completely deoxidizing the fatty acid ester wax, for example, deoxidized carnauba wax.

The charge control agent mainly controls the triboelectric charging property of the toner. The charge control agent used for the negatively charged toner contains, for example, any one kind or two or more kinds of an azo complex, a salicylic acid complex, a calixarene complex and the like.

<2-4. Operation>
Next, the operation of the image forming apparatus will be described.

FIG. 5 shows a positional relationship of main constituent elements of the image forming apparatus. The main components are, for example, the photosensitive drum 102, the charging roller 103, the developing roller 105, the cleaning blade 108, and the primary transfer roller 45.

FIG. 6 shows the operation timing of the image forming apparatus during image formation. However, FIG. 6 shows a case where no voltage is applied to the cleaning blade 108.

As shown in FIG. 5, the charging roller 103, the developing roller 105, the cleaning blade 108, and the primary transfer roller 45 are in contact with the photosensitive drum 102 at different positions. Specifically, the charging roller 103 is in contact with the photosensitive drum 102 at the contact point 103T. The developing roller 105 is in contact with the photosensitive drum 102 at a contact point 105T. The cleaning blade 108 is in contact with the photosensitive drum 102 at the contact 108T. The primary transfer roller 45 is in contact with the photosensitive drum 102 at a contact 45T. The photoconductor drum 102 rotates in the direction of arrow W during image formation.

The lines L1 to L4 shown in FIG. 5 are all virtual lines. Specifically, the line L1 is a straight line passing through the center 102P of the photosensitive drum 102 and the contact 103T of the charging roller 103. The line L2 is a straight line passing through the center 102P of the photosensitive drum 102 and the contact point 105T of the developing roller 105. The line L3 is a straight line passing through the center 102P of the photosensitive drum 102 and the contact point 45T of the primary transfer roller 45. The line L4 is a straight line passing through the center 102P of the photosensitive drum 102 and the contact point 108T of the cleaning blade 108.

Here, as shown in FIG. 5, the time required for the surface of the photoconductor drum 102 to move from the contact point 103T to the contact point 105T is T1, and for the surface of the photoconductor drum 102 to move from the contact point 105T to the contact point 45T. The time required is T2, the time required for the surface of the photosensitive drum 102 to move from the contact 45T to the contact 108T is T3, and the time required for the surface of the photosensitive drum 102 to move from the contact 108T to 103T is T4. For example, the relationship of T2>T1>T3>T4 is established between the times T1 and T4.

When forming an image on the surface of the medium M, the image forming apparatus performs the developing process, the primary transfer process, the secondary transfer process, and the fixing process in this order, as described below, as well as necessary. A cleaning process is performed accordingly.

(Development processing)
First, the medium M stored in the tray 10 is taken out by the feed roller 20. The medium M taken out by the delivery roller 20 is conveyed by the conveying rollers 61 and 62 along the conveying path R1 in the direction of arrow F1.

Subsequently, the developing unit 30K performs the same developing process as that of the image forming apparatus 100 described above. As a result, an electrostatic latent image is formed on the surface of the photoconductor drum 102, and black toner is attached to the electrostatic latent image.

In this case, when the image forming operation (developing process) is started, each of the photoconductor drum 102, the charging roller 103, the developing roller 105, and the charge eliminating optical substrate 109 is operated.

Specifically, the roller drive control unit 84 drives the roller motor 85 to rotate a series of rollers such as the charging roller 103 via the roller motor 85. The drum drive control unit 86 drives the drum motor 87 to rotate the photosensitive drum 102 via the drum motor 87. The charging voltage control unit 79 applies a negative voltage (for example, −1000 V) to the charging roller 103 to charge the surface of the photosensitive drum 102 via the charging roller 130. The developing voltage controller 80 applies a positive voltage (for example, +100 V) to the developing roller 105. The charge removal light control unit 83 lights the charge removal light substrate 109.

The developing voltage controller 80 applies a positive voltage to the developing roller 105 until the time T1 has elapsed from the start of the image forming operation, and then applies a negative voltage (for example, -200V) to the developing roller 105. .. The reason why the positive voltage is applied to the developing roller 105 at the start of the image forming operation is to prevent the toner from unintentionally migrating from the surface of the developing roller 105 to the surface of the photosensitive drum 102. ..

The surface potential of the photosensitive drum 102 decreases as time passes. Therefore, the supply voltage control unit 81 does not apply the voltage to the supply roller 106 until the time T1 elapses from the start of the image forming operation, and a negative voltage (for example, a negative voltage to the supply roller 106 after the time T1 elapses). , -300 V) is applied. The voltage is not applied to the supply roller 106 until the time T1 elapses in order to prevent the toner from unintentionally migrating from the surface of the supply roller 106 to the surface of the developing roller 105. On the other hand, the reason why the negative voltage is applied to the supply roller 106 after the lapse of the time T1 is to transfer the toner from the surface of the supply roller 106 to the surface of the developing roller 105.

(Primary transfer process)
Then, in the transfer unit 40, when the drive roller 42 rotates, each of the driven roller 43 and the backup roller 44 rotates according to the rotation of the drive roller 42. As a result, the intermediate transfer belt 41 moves in the direction of arrow F5.

In the primary transfer process, the transfer voltage control unit 82 does not apply the voltage to the primary transfer roller 45 until the time (T2+T1) elapses from the start of the image forming operation, and the time (T2+T1) elapses. Then, a positive voltage (for example, +2000 V) is applied to the primary transfer roller 45. As a result, the primary transfer roller 45K is pressed against the photosensitive drum 102 via the intermediate transfer belt 41, so that the black adhered to the surface (electrostatic latent image) of the photosensitive drum 102 in the above-described developing process. The toner is transferred to the surface of the intermediate transfer belt 41.

After this, the intermediate transfer belt 41 to which the black toner has been transferred continues to move in the direction of arrow F5. As a result, in the developing units 30C, 30M, 30Y and the primary transfer rollers 45C, 45M, 45Y, the developing process and the primary transfer process are performed in the same procedure as the developing unit 30K and the primary transfer roller 45K. Therefore, the cyan toner, the magenta toner, and the yellow toner are transferred onto the surface of the intermediate transfer belt 41.

Specifically, cyan toner is transferred onto the surface of the intermediate transfer belt 41 by the developing unit 30C and the primary transfer roller 45C. Then, the magenta toner is transferred onto the surface of the intermediate transfer belt 41 by the developing unit 30M and the primary transfer roller 45M. Then, the yellow toner is transferred onto the surface of the intermediate transfer belt 41 by the developing unit 30Y and the primary transfer roller 45Y.

Of course, whether or not the developing process and the primary transfer process are actually performed by the developing units 30K, 30C, 30M and 30Y and the primary transfer rollers 45K, 45C, 45M and 45Y is the color necessary for forming an image ( Color combination).

(Secondary transfer process)
Subsequently, the medium M transported along the transport path R1 passes between the backup roller 44 and the secondary transfer roller 46.

In the secondary transfer process, a voltage is applied to the secondary transfer roller 46. Since the secondary transfer roller 46 is pressed against the backup roller 44 via the medium M, the toner transferred to the intermediate transfer belt 41 in the above-mentioned primary transfer process is transferred to the medium M. The "toner" described here is a general term for the above-mentioned black toner, cyan toner, magenta toner, and yellow toner, and the meaning of the "toner" is the same hereinafter.

(Fixing process)
Then, after the toner is transferred to the medium M in the secondary transfer process, the medium M is further conveyed in the direction of the arrow F1 along the conveyance route R1, and is thus input to the fixing unit 50.

In the fixing process, the surface temperature of the heating roller 51 is controlled to be a predetermined temperature. When the pressure roller 52 rotates while being pressed against the heating roller 51, the medium M is conveyed so as to pass between the heating roller 51 and the pressure roller 52.

As a result, the toner transferred to the surface of the medium M is heated, so that the toner is melted. Moreover, since the molten toner is pressed against the medium M, the toner adheres firmly to the medium M.

Therefore, the toner is fixed on a specific region of the surface of the medium M based on the image data supplied from the outside to the image forming apparatus, so that an image is formed on the surface of the medium M.

The medium M on which the image is formed is conveyed in the direction of arrow F2 by the conveying rollers 63 and 64 along the conveying path R2. As a result, the medium M is discharged to the stacker unit 2 from the discharge port 1H.

When the image forming operation is completed, the drum drive control unit 86 stops the rotation of the photosensitive drum 102 by stopping the drum motor 87, and the static elimination light control unit 83 turns off the static elimination light substrate 109. Each of the charging voltage controller 79, the developing voltage controller 80, the supply voltage controller 81, and the transfer voltage controller 82 stops the application of voltage. This completes the image forming operation.

The procedure of transporting the medium M is changed according to the mode of the image formed on the surface of the medium M.

For example, when images are formed on both sides of the medium M, the medium M that has passed through the fixing unit 50 is transported in the directions of arrows F3 and F4 by the transport rollers 65 to 68 along the transport paths R3 to R5. After that, it is again conveyed in the direction of arrow F1 by the conveyance rollers 61 and 62 along the conveyance route R1. In this case, the transport direction of the medium M is controlled by the transport path switching guides 69 and 70. As a result, the developing process, the primary transfer process, the secondary transfer process, and the fixing process are performed on the back surface of the medium M (the surface on which an image is not yet formed).

(Cleaning process of photoconductor drum)
In each of the developing units 30K, 30C, 30M, and 30Y, unnecessary toner may remain on the surface of the photoconductor drum 102. The unnecessary toner is, for example, a part of the toner used in the primary transfer processing, and is the toner or the like remaining on the surface of the photosensitive drum 102 without being transferred to the intermediate transfer belt 41.

Therefore, since the photosensitive drum 102 rotates while being pressed against the cleaning blade 108, the toner remaining on the surface of the photosensitive drum 102 is scraped off by the cleaning blade 108. Therefore, since unnecessary toner is removed from the surface of the photoconductor drum 102, the surface of the photoconductor drum 102 is cleaned.

(Intermediate transfer belt cleaning process)
In the transfer section 40, a part of the toner transferred to the surface of the intermediate transfer belt 41 in the primary transfer processing is not transferred to the surface of the medium M in the secondary transfer processing and remains on the surface of the intermediate transfer belt 41. There is a case.

Therefore, when the intermediate transfer belt 41 moves in the direction of arrow F5, the toner remaining on the surface of the intermediate transfer belt 41 is scraped off by the cleaning blade 47. Therefore, since unnecessary toner is removed from the surface of the intermediate transfer belt 41, the surface of the intermediate transfer belt 41 is cleaned.

<2-5. Action and effect>
This image forming apparatus includes a developing unit 30 (30K, 30C, 30M, 30Y) having the same configuration as the developing device 100 described above. In this case, for the same reason as described with respect to the developing device 100, it becomes difficult for foreign matter to adhere to the surface of the charging roller 103, and thus the image is less likely to be roughened. Therefore, a high quality image can be obtained.

Other operations and effects of the image forming apparatus of the first embodiment are similar to those of the developing device 100.

<3. Image forming apparatus (second embodiment)>
Next, an image forming apparatus of the second embodiment of the present invention using the above-mentioned developing device will be described.

<3-1. Composition>
The image forming apparatus of the second embodiment has the same configuration as the image forming apparatus of the first embodiment except that the configuration of the developing unit 30 and the block configuration of the image forming apparatus are different.

The developing unit 30 described here has the same configuration as the developing unit 30 of the first embodiment, except that the cleaning blade 108 has conductivity. The configuration of the cleaning blade 108 is the same as the configuration of the cleaning blade 108 of the first embodiment except that it has conductivity, for example.

FIG. 7 shows a block configuration of the image forming apparatus, and corresponds to FIG. The image forming apparatus described here has the same block configuration as the image forming apparatus of the first embodiment except that the cleaning voltage control unit 96 is provided.

The cleaning voltage controller 96 mainly controls the voltage applied to the cleaning blade 108. This voltage can be set, for example, according to an instruction from the control unit 71, and can be arbitrarily changed according to an instruction from the control unit 71. Although the illustration is simplified in FIG. 7, the image forming apparatus includes, for example, four cleaning voltage control units 96 corresponding to the four developing units 30 (30K, 30C, 30M, 30Y). There is.

Specifically, the cleaning voltage controller 96 applies a DC voltage having the same polarity as the charging polarity of the toner to the cleaning blade 108 at the time of forming an image and cleaning the charging roller 103 described later. That is, the cleaning voltage controller 96 applies a negative DC voltage to the cleaning blade 108 when the toner is negatively charged toner, for example.

<3-2. Operation>
In the image forming apparatus of the second embodiment, the cleaning voltage controller 96 applies a voltage to the cleaning blade 108 at the time of forming an image, and the cleaning process of the charging roller 103 is performed after the image is formed. It operates similarly to the image forming apparatus of the first embodiment.

FIG. 8 shows the operation timing of the image forming apparatus when an image is formed, and corresponds to FIG. However, FIG. 8 shows a case where a voltage is applied to the cleaning blade 108.

FIG. 9 shows the operation timing of the image forming apparatus when cleaning the charging roller 103, and corresponds to FIG.

(Image forming operation)
The operation of the image forming apparatus during the image forming operation is the operation of the image forming apparatus of the first embodiment except that the cleaning voltage controller 96 applies a voltage having the same polarity as the charging polarity of the toner to the cleaning blade 108. (FIG. 6).

Specifically, in the image forming apparatus, at the time of image formation (developing process, primary transfer process, secondary transfer process, and fixing process), for example, as shown in FIG. A voltage having the same polarity as the charging polarity of the toner is applied to the blade 108.

The cleaning voltage controller 96 applies a positive voltage (for example, +100 V) to the cleaning blade 108 after the start of the image forming operation until the time T3 elapses, and then applies a negative voltage (for example, +100 V) to the cleaning blade 108. -300V) is applied. The positive voltage is applied to the cleaning blade 108 until the time T3 elapses in order to prevent the amount of foreign matter adsorbed on the surface of the cleaning blade 108 from increasing excessively. This is because the foreign matter adsorbed on the surface of the is intentionally discharged electrostatically toward the photoconductor drum 102. On the other hand, the reason why the negative voltage is applied to the cleaning blade 108 after the lapse of the time T3 is that the foreign matter adhered to the surface of the photosensitive drum 102 is electrostatically adsorbed to the surface of the cleaning blade 108. is there.

As a result, as described above, foreign matter such as an external additive having a minute particle size is easily scraped off sufficiently by the cleaning blade 108, and thus an afterimage is less likely to occur in the image.

(Charging roller cleaning operation)
Further, in the image forming apparatus, after the image forming operation is completed, the cleaning process of the charging roller 103 is performed as necessary. The time T5 described below is, for example, the time required for the charging roller 103 to rotate twice.

Specifically, for example, as shown in FIG. 9, after the cleaning operation of the charging roller 103 is started, the drum drive control unit 86 continues to rotate the photosensitive drum 102 via the drum motor 87. The charging voltage control unit 79 subsequently applies a negative voltage (for example, −1000V) to the charging roller 103. The developing voltage controller 80 subsequently applies a negative voltage (for example, -200V) to the developing roller 105. The supply voltage control unit 81 subsequently applies a negative voltage (for example, −300 V) to the supply roller 106. The cleaning voltage controller 96 subsequently applies a negative voltage (for example, −300 V) to the cleaning blade 108.

On the other hand, after the cleaning operation of the charging roller 103 is started, the transfer voltage control unit 82 stops the application of the voltage to the primary transfer roller 45, and the charge removal light control unit 83 turns off the charge removal light substrate 109. ..

The cleaning voltage controller 96 applies a positive voltage (for example, +100 V) to the cleaning blade 108 when time T3 has elapsed from the start of the cleaning operation of the charging roller 103, and then again when time T5 elapses. Is applied with a negative voltage (for example, -300 V). The positive voltage is applied to the cleaning blade 108 because the foreign matter adsorbed on the surface of the cleaning blade 108 is intentionally discharged toward the photosensitive drum 102.

The charging voltage control unit 79 stops the application of the voltage to the charging roller 103 when a time (T3+T4) has elapsed from the start of the cleaning operation of the charging roller 103, and thereafter, when the time T5 elapses, the charging roller 103 becomes negative again. A voltage (for example, -1000V) is applied. The application of the voltage to the charging roller 103 is stopped because the photosensitive drum 102 rotates while the surface potential is maintained at a state where the surface potential is slightly lower than -500V, so that the foreign matter attached to the surface of the charging roller 103 is stopped. Is intentionally emitted toward the surface of the photoconductor drum 102. In this case, even if foreign matter is discharged from the surface of the cleaning blade 108 toward the surface of the photoconductor drum 102, the foreign matter is not attached to the surface of the charging roller 103.

The developing voltage control unit 80 applies a positive voltage (for example, +100 V) to the developing roller 105 when a time (T3+T4+T1) has elapsed from the start of the cleaning operation of the charging roller 103, and then performs a developing operation again when a time T5 elapses. A negative voltage (for example, -200V) is applied to the roller 105. The positive voltage is applied to the developing roller 105 to prevent the toner attached to the surface of the developing roller 105 from unintentionally transferring to the surface of the photoconductor drum 102.

The supply voltage control unit 81 stops the voltage to the supply roller 106 when the time (T3+T4+T1) has elapsed from the start of the cleaning operation of the charging roller 103, and then again supplies the negative voltage ( For example, -300V) is applied.

As a result, foreign matter is discharged from the surface of the charging roller 103 toward the photoconductor drum 102, so that the surface of the charging roller 103 is cleaned. Moreover, the foreign matter emitted from the surface of the charging roller 103 is not collected by the developing roller 105, and therefore is not attached to the surface of the developing roller 105.

It should be noted that a part of the foreign matter discharged from the surface of the charging roller 103 is, for example, attached to the intermediate transfer belt 41, and thus is conveyed by the intermediate transfer belt 41. The foreign matter attached to the intermediate transfer belt 41 is scraped off by, for example, the cleaning blade 47.

On the other hand, the rest of the foreign matter discharged from the surface of the charging roller 103 reaches the cleaning blade 108 because it moves in accordance with the rotation of the photosensitive drum 102, for example. The size of the remaining foreign matter becomes large due to aggregation in the process of reaching the cleaning blade 108, so the remaining foreign matter is sufficiently scraped off by the cleaning blade 108.

When the cleaning operation of the charging roller 103 is completed, the drum drive control unit 86 stops the rotation of the photosensitive drum 102 by stopping the roller motor 85. Further, each of the charging voltage control unit 79, the developing voltage control unit 80, the supply voltage control unit 81, and the cleaning voltage control unit 96 stops applying the voltage. As a result, the cleaning operation of the charging roller 103 is completed.

<3-3. Action and effect>
In this image forming apparatus, while a DC voltage having the same polarity as the charging polarity of toner is applied to the cleaning blade 108, development processing is performed by the developing unit 30 having the same configuration as that of the developing device 100 described above. In this case, for the same reason as described with respect to the developing device 100, it becomes difficult for foreign matter to adhere to the surface of the charging roller 103, and thus the image is less likely to be roughened. Moreover, since the foreign matter attached to the surface of the photosensitive drum 102 is easily electrostatically attracted to the cleaning blade 108, an afterimage due to the foreign matter attached to the charging roller 103 is less likely to occur in the image. Therefore, a higher quality image can be obtained.

Other actions and effects of the image forming apparatus of the second embodiment are similar to those of the developing device 100.

<4. Modification>
The configurations and operations of the developing device and the image forming apparatus described above can be appropriately changed. Specifically, the series of voltage values described regarding the operation of the image forming apparatus are merely examples, and can be arbitrarily changed.

Embodiments of the present invention will be described in detail. The order of description is as follows.

1. Evaluation of image roughness 2. Evaluation of afterimages in images

<1. Evaluation of image roughness>
By the following procedure, an image was formed using an image forming apparatus equipped with a charging roller, and the image quality (roughness) of the image was examined.

(Experimental Examples 1 to 6)
First, an image forming apparatus was prepared. As an image forming apparatus, a color printer MC863 manufactured by Oki Data Co., Ltd. was used.

In this case, a charging roller having an elastic layer (epichlorohydrin rubber) and a surface layer (nylon and nylon particles) formed on the outer peripheral surface of a core metal (aluminum) was used. Further, the surface state (surface roughness) of the charging roller was changed by changing the average particle diameter (median diameter D50) and the content of the plurality of particles (nylon particles) contained in the surface layer. The parameters that define the surface roughness of the charging roller are the load length ratio tp (%), the ten-point average roughness Rz (%), and the average interval Sm (mm). The load length rate tp, the ten-point average roughness Rz, and the average interval Sm are measured as described above. When changing the load length ratio tp, the cutting level C (%) was changed in 9 steps so that the load length ratio tp was in steps of 10% within the range of 10% to 90%.

The measurement results of the load length ratio tp, the ten-point average roughness Rz, and the average interval Sm are as shown in Table 1. Further, the correlation between the cutting level C (%) and the load length rate tp (%) on the surface of the charging roller is as shown in FIG.

To explain before confirmation, in FIG. 10, the load length rate tp when the cutting level C is 40% is the load length rate tp (40%), and the cutting level C is 60%. The load length ratio tp in this case is the load length ratio tp (60%).

Subsequently, an image forming apparatus was used to continuously form a continuous print image on the surface of the medium, and then an image for image quality evaluation was formed on the surface of the medium. In this case, a conductive cleaning blade was used, but no voltage was applied to the cleaning blade when forming an image for image quality evaluation. The cleaning blade contains polyurethane.

As a medium, a color printer paper Excellent White A4 manufactured by Oki Data Co., Ltd. was used. As the toner, a one-component type negatively charged toner (yellow toner, magenta toner, cyan toner and black toner) was used.

When continuously forming continuously printed images, a process for continuously forming continuously printed images on the surface of 3,000 sheets of medium per day in an environment of normal temperature and normal humidity (temperature = 20°C, relative humidity = 50%). By performing the process for 10 days, the continuous print image forming process was repeated until the total number of used sheets of the medium reached 30,000. In this case, the moving direction of the medium=longitudinal direction, the moving speed of the medium=corresponding to 40 ppm, the image pattern of the continuous printed image=blank paper, and the number of continuously printed images formed per job=3. The reason why the image pattern of the continuous print image is blank is that by increasing the area of the unexposed region on the surface of the medium as much as possible, the positively charged external additive that has fallen off from the toner can be used as a condition for forming the continuous print image. This is because the conditions that easily adhere to the surface of the photoconductor drum are set.

In the case of forming an image for image quality evaluation, after the continuous formation of the continuous print image was completed, the image shown in FIG. 11 was formed on the surface of the medium. The other conditions at the time of forming the image for image quality evaluation were the same as the conditions at the time of the formation process of the continuous print image.

In the image for image quality evaluation, as shown in FIG. 11, a bold character 401 is arranged on the front side in the traveling direction of the medium M (longitudinal direction of the medium M), and is black behind the bold character 401. Halftone pattern 402 is arranged. The bold character 401 is an image composed of six characters ABCABC, and the six characters are arranged in the lateral direction of the medium M. The halftone pattern 402 is a rectangular pattern extending in the lateral direction of the medium M, and is formed over the entire image formable region in the lateral direction of the medium M. The formation range of the halftone pattern 402 is a range corresponding to 30% of the entire image formable area on the surface of the medium M. That is, the area ratio of the dots forming the halftone pattern 402 is 30%.

Finally, the halftone pattern 402 was visually confirmed to evaluate the occurrence of image roughness, and the results shown in Table 1 were obtained.

In this case, the size of the plurality of dots in the halftone pattern 402 does not vary, and a part of the plurality of dots is not missing, so that the case where the image is not rough is determined as “A”. did. On the other hand, in the halftone pattern 402, when the sizes of a plurality of dots are varied and a part of the plurality of dots is missing, the image is rough, so that it is determined as “C”.

Based on the correlation between the load length ratio tp and the image quality (roughness) shown in Table 1, the influence of the load length ratios tp (40%) and tp (60%) on the image quality was examined. As a result, the two conditions that the load length ratio tp (40%) is 13% to 25% and the load length ratio tp (60%) is 35% to 60% are satisfied at the same time (experiment In Examples 1 to 3), image roughness did not occur. On the other hand, when the load length ratios tp (40%) and tp (60%) do not satisfy the above two conditions at the same time (Experimental Examples 4 to 6), image roughness occurs.

In particular, when the load length ratios tp (40%) and tp (60%) satisfy the above two conditions, the ten-point average roughness Rz is 13 μm to 17 μm, and the average interval Sm is 0. When it was 0.14 mm to 0.20 mm, the roughness of the image was sufficiently suppressed.

<2. Evaluation of afterimages in images>
Next, an image for image quality evaluation was formed by the same procedure using the image forming apparatus in which the charging rollers of Experimental Examples 1 to 6 described above were mounted, and then the image quality (afterimage) of the image was examined.

(Experimental examples 7 to 12)
When forming an image for image quality evaluation using the image forming apparatus, the same as in Experimental Examples 1 to 6 except that a negative DC voltage (=-300 V) was applied to the cleaning blade during image formation. Went through the steps.

FIG. 12 illustrates an image when the afterimage is generated in order to describe the afterimage generation state, and corresponds to FIG. 11.

If foreign matter such as an external additive adheres to the surface of the charging roller, the charged state of the surface of the photosensitive drum becomes non-uniform. Therefore, as shown in FIG. The afterimage 403 of the bold character 401 is likely to occur near the open position (inside the halftone pattern 402). In this case, in particular, while the afterimage 403 is generated, a halftone is caused due to foreign matters such as external additives being attached not only to the surface of the charging roller but also to the surface of the photosensitive drum and the surface of the developing roller. Since the image density of the pattern 402 is lowered, the afterimage 403 thereof is likely to become visible. The distance D shown in FIG. 11 is a distance corresponding to one round of the outer circumference of the photosensitive drum.

When the occurrence state of the afterimage 403 was evaluated by visually confirming the image for image quality evaluation (halftone 402), the results shown in Table 2 were obtained. For comparison, when the voltage was not applied to the cleaning blade (Experimental Examples 1 to 6), the occurrence state of the afterimage 403 was similarly evaluated, and the results shown in Table 1 were obtained.

When examining the occurrence state of the residual 403, the image density (internal density) at the internal position 403X of the afterimage 403 is measured inside the halftone pattern 402, and the image density (external density) at the external position 403Y of the afterimage 403 is measured. ) Was measured, and the difference between the internal concentration and the external concentration (concentration difference=internal concentration−external concentration) was calculated. As the image density measuring device, a densitometer X-Rite 528 manufactured by X-Rite was used.

As a result, since the density difference was 0.007 or less, the case where the afterimage 403 was hardly visually recognized was determined to be “A”. On the other hand, when the density difference is larger than 0.007, the afterimage 403 is generated and the case where the afterimage 403 can be visually recognized is determined as “C”.

As shown in Tables 1 and 2, when the voltage was applied to the cleaning blade (Experimental Examples 7 to 12), the same result as when the voltage of the cleaning blade was not applied (Experimental Examples 1 to 6) was obtained. was gotten. That is, when the load length ratios tp (40%) and tp (60%) satisfy the above two conditions (Experimental Examples 7 to 9), when the two conditions are not simultaneously satisfied (Experimental Example 10). ~ 12), the roughness of the image did not occur.

Moreover, when a voltage was applied to the cleaning blade (Experimental Examples 7 to 9), almost no residual image 403 was generated as compared with the case where no voltage was applied to the cleaning blade (Experimental Examples 1 to 3).

Before the confirmation, the correlation between the voltage applied to the cleaning blade and the image density was examined, and the results shown in FIG. 13 were obtained. In FIG. 13, the horizontal axis represents voltage (V) and the vertical axis represents image density (internal density and external density).

As is apparent from FIG. 13, the internal concentration was almost constant without depending on the voltage, but the external concentration gradually increased as the voltage increased. The reason why the external concentration gradually increases as the voltage increases is that the amount of positively charged external additive electrostatically adsorbed to the cleaning blade increases as the voltage applied to the cleaning blade increases. it is conceivable that.

In this case, when the voltage was −300 V or more, the density difference was 0.07 or less, so that the afterimage 403 was hardly visible.

From these facts, if the load length ratios tp (40%) and tp (60%) of the surface of the charging roller simultaneously satisfy the two conditions shown in the equations (1) and (2), respectively, The occurrence of image roughness was suppressed. Therefore, a high quality image could be obtained.

The present invention has been described above with reference to the embodiment, but the present invention is not limited to the mode described in the above embodiment, and various modifications can be made.

Specifically, for example, the image forming method of the image forming apparatus according to the embodiment of the present invention is not limited to the intermediate transfer method using the intermediate transfer belt, and other image forming methods may be used. The other image forming method is, for example, an image forming method that does not use an intermediate transfer belt. In the image forming method that does not use the intermediate transfer belt, the toner attached to the latent image is not indirectly transferred to the medium via the intermediate transfer belt, but the toner attached to the latent image is directly transferred to the medium. Be transcribed.

Further, for example, the image forming apparatus according to the embodiment of the present invention is not limited to the printer, and may be a copying machine, a facsimile, a multi-function peripheral, or the like.

30... Developing unit, 40... Transfer unit, 50... Fixing unit, 100... Developing device, 102... Photosensitive drum, 103... Charging roller, 105... Developing roller, 108... Cleaning blade.

Claims (5)

A surface is charged, and a latent image carrying member on which a latent image is formed,
A charging member that extends in a predetermined direction and charges the surface of the latent image bearing member,
A developing member for adhering toner to the latent image formed on the surface of the latent image carrying member,
The load length ratio tp on the surface of the charging member satisfies the conditions represented by the following equations (1) and (2),
Development device.
Load length ratio tp (40%)=13% or more and 25% or less (1)
Load length ratio tp (60%)=35% or more and 60% or less (2) The ten-point average roughness Rz of the surface of the charging member is 13 μm or more and 17 μm or less,
The surface of the charging member has irregularities, and the average spacing Sm of the irregularities on the surface of the charging member is 0.14 mm or more and 0.20 mm or less.
The developing device according to claim 1. The toner has a predetermined charging polarity,
Furthermore, a conductive scraping member is provided which scrapes off foreign matter attached to the surface of the latent image carrying member and which is applied with a DC voltage having the same polarity as the charging polarity of the toner.
The developing device according to claim 1. The toner has a negative charging polarity,
A negative DC voltage is applied to the scraping member,
The developing device according to claim 3. A developing unit that includes a developing device and that attaches toner to the latent image;
A transfer unit for transferring the toner attached to the latent image onto a medium,
A fixing unit configured to fix the toner transferred onto the medium onto the medium,
The developing device is
A surface is charged, and a latent image carrying member on which the latent image is formed,
A charging member that extends in a predetermined direction and charges the surface of the latent image bearing member,
A developing member for adhering the toner to the latent image formed on the surface of the latent image carrying member,
The load length ratio tp on the surface of the charging member satisfies the conditions represented by the following equations (1) and (2),
Image forming apparatus.
Load length ratio tp (40%)=13% or more and 25% or less (1)
Load length ratio tp (60%)=35% or more and 60% or less (2)

Images