JP4573962B2 - Image forming apparatus, open-cell foam roller, and process cartridge - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile, which forms an image by an electrophotographic method or an electrostatic recording method.Furthermore, open-cell foam foam roller and process cartridge incorporated thereinAbout.
[0002]
[Prior art]
FIG. 6 is a schematic configuration diagram illustrating an example of a conventional electrophotographic image forming apparatus.
This image forming apparatus is an image forming apparatus using a contact charging method and a contact developing method and having no cleaning unit.
[0003]
The image forming apparatus includes a photosensitive drum 1 as an image carrier, and includes a charging device 2, an exposure device 3, a developing device 4, and a transfer roller 5 around the photosensitive drum 1, and is formed between the photosensitive drum 1 and the transfer roller 5. A fixing device 6 is installed on the downstream side of the transfer nip N where the transfer material P is conveyed.
[0004]
In this conventional example, the photosensitive drum 1 has a photosensitive layer (not shown) obtained by coating a photoconductor on an aluminum drum base (not shown). The photosensitive drum 1 is rotationally driven in the direction of arrow a (clockwise) at a predetermined peripheral speed by driving of a drive motor (not shown), and is negatively charged uniformly by the charging roller 7 that contacts in the rotation process. .
[0005]
The charging device 2 includes a charging roller 7 having elasticity as a rotatable contact charging member that comes into contact with the photosensitive drum 1, a rotatable metal roller 8 that comes into contact with the charging roller 7, a charging roller 7, and a metal roller. 8 is provided with a charging bias power source 9 for applying a charging bias voltage. The charging roller 7 uniformly charges the photosensitive drum 1 to a predetermined negative potential by a charging bias applied from a charging bias power source 9. The charging roller 7 is driven to rotate as the photosensitive drum 1 is driven to rotate. The metal roller 8 rotates following the rotation of the charging roller 7.
[0006]
The exposure device 3 scans and exposes the surface of the charged photosensitive drum 1 by outputting a laser beam modulated in accordance with the time-series electric digital pixel signal of the input image information from a laser output unit (not shown). As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 1.
[0007]
The developing device 4 is a contact one-component developing device that performs development with a non-magnetic toner t as a one-component developer. The developing device 4 is disposed opposite to the photosensitive drum 1 at the opening of the developing container 10 and is in contact with the photosensitive drum 1. A developing roller 11 is provided as a developer carrying member that is rotatable in an arrow direction (counterclockwise direction) for supplying toner t to the portion (developing portion).
[0008]
Around the developing roller 11, the toner t comes into contact with the developing roller 11 and supplies the toner t to the developing roller 11, and also comes into contact with the rotatable peeling supply roller 12 and the developing roller 11 that peel off the toner t from the surface of the developing roller 11. A regulating blade 13 that applies a desired charge amount to the toner t attached to the surface of the developing roller 11 and regulates the layer thickness of the toner t on the surface of the developing roller 11, and a developing bias power source 14 that applies a developing bias to the developing roller 11 are provided. I have.
[0009]
The transfer roller 5 as a contact transfer means forms a transfer nip N by contacting the surface of the photosensitive drum 1 with a predetermined pressing force, and the transfer nip N by a transfer bias applied from a transfer bias power source (not shown). The toner image on the surface of the photosensitive drum 1 is transferred to a transfer material P such as paper.
[0010]
The fixing device 6 has a rotatable fixing roller 6a and a pressure roller 6b, and heats the toner image transferred onto the surface of the transfer material P at the fixing nip between the fixing roller 6a and the pressure roller 6b. Press to fix heat.
[0011]
Next, an image forming operation by the image forming apparatus will be described.
[0012]
When image information is input from a host computer (not shown), the photosensitive drum 1 is driven to rotate at a predetermined peripheral speed in the direction of arrow a (clockwise) by a drive motor (not shown). The surface of the charging roller 2 to which a charging bias (for example, -1300V) is applied is uniformly charged to a predetermined potential (for example, -700V). Then, by applying scanning exposure L by laser light from the exposure device 3 onto the charged photosensitive drum 1, the potential on the photosensitive drum 1 is lowered and the input image is reduced. An electrostatic latent image corresponding to the signal is formed.
[0013]
Then, the electrostatic latent image formed on the photosensitive drum 1 is photosensitized by the developing roller 11 of the developing device 4 to which a developing bias having the same polarity as the charging polarity (negative polarity) of the photosensitive drum 1 is applied in the developing unit. The toner t charged with the same polarity as the charged polarity (negative polarity) of the drum 1 is attached, and the toner image is reversely developed (visualized). At this time, in this embodiment, a developing bias of −350 V is applied to the developing roller 11 from the developing bias power source 14.
[0014]
When the toner image on the photosensitive drum 1 reaches the transfer nip N between the photosensitive drum 1 and the transfer roller 5, the transfer material P such as paper in a cassette (not shown) is fed to the paper feed roller (not shown) in accordance with this timing. The sheet is conveyed to the transfer nip portion N by the like.
Then, due to the electrostatic force generated between the photosensitive drum 1 and the transfer roller 5 on the transfer material P conveyed to the transfer nip portion N by the transfer roller 5 to which a transfer bias having a reverse polarity (positive polarity) to the toner is applied. The toner image on the photosensitive drum 1 is transferred.
[0015]
Then, the transfer material P onto which the toner image has been transferred is conveyed to the fixing device 6, and the toner image is heated and pressed against the transfer material P at the fixing nip between the fixing roller 6a and the pressure roller 6b, and then externally fixed. The image forming operation is terminated.
[0016]
Further, the transfer residual toner remaining on the photosensitive drum 1 after the transfer (a reversal toner charged to a positive polarity opposite to the normal polarity) is in contact with the charging roller 7 as the photosensitive drum 1 rotates. To. Then, due to the potential relationship between the surface of the photosensitive drum 1 and the charging roller 7 (metal roller 8), the transfer residual toner adheres to the charging roller 7, and further adheres to the metal roller 8 contacting the charging roller 7 and is collected.
[0017]
A voltage is applied from the same power source (charging bias power supply 9) to the metal core 8 of the charging roller 7 and the metal roller 8, but the charging roller 7 is provided with an elastic layer and a resistance layer on the outer periphery of the metal core. The surface potential of the roller 7 is slightly lower than the voltage applied to the cored bar. As a result, transfer residual toner attached to the surface of the charging roller 7 can be collected on the metal roller 8 due to a slight potential difference generated between the surfaces of the metal roller 8 and the charging roller 7.
[0018]
[Problems to be solved by the invention]
By the way, in the above-described conventional image forming apparatus, there is some toner that has not been transferred onto the photosensitive drum 1 after transfer (reversed toner charged to positive polarity), that is, so-called transfer residual toner.
[0019]
As described above, the untransferred toner adheres to the charging roller 7 due to the potential relationship between the surface of the photosensitive drum 1 and the charging roller 7. Thereafter, the transfer residual toner adhering to the charging roller 7 adheres to and accumulates on the metal roller 8 that is in contact therewith, but there is little transfer residual toner at the initial use or when the toner is not deteriorated. It seems that there is no particular problem because there is enough time for the transfer residual toner accumulated in the metal roller 8 to be saturated.
[0020]
However, when the toner deteriorates due to long-time use or use under high temperature conditions and the transfer residual toner increases, the transfer residual toner immediately accumulates and saturates on the surface of the metal roller 8, and the saturation component The above transfer residual toner adheres to the charging roller 7. As a result, a charging failure occurs and a desired latent image cannot be formed, and an image failure occurs.
[0021]
Further, when the transfer residual toner exceeding the saturation amount cannot be held on the charging roller 7 as well, the transfer residual toner adheres to the photosensitive drum 1, resulting in poor exposure and the generation of a desired electrostatic latent image. It becomes impossible to form.
[0022]
Further, when the same image pattern is formed in a large amount, the transfer residual toner is saturated and accumulated at positions corresponding to the image portions of the charging roller 7 and the metal roller 8 to cause charging failure and image failure. Even when the image is not saturated, there is a difference in the saturation accumulation time between the image portion and the non-image portion, so that a charging failure or an image failure due to saturation accumulation of the transfer residual toner partially occurs later.
[0023]
In addition, if a large amount of untransferred toner adheres to the charging roller 7 and is rotated in contact with the photosensitive drum 1, the toner is softened by friction and heat generation at the contact portion, and the toner is pressed by the contact pressure. They are crushed and fused to the charging roller 7 and the photosensitive drum 1. As a result, an electrostatic latent image formation failure due to light shielding on the photosensitive drum 1 may occur, or the resistance of the charging roller 7 may fluctuate, resulting in a charging failure.
[0024]
  Accordingly, the present invention provides an image forming apparatus capable of collecting the transfer residual toner adhering to the charging roller and preventing the occurrence of image defects and charging defects.Furthermore, open-cell foam foam roller and process cartridge incorporated thereinThe purpose is to provide.
[0025]
[Means for Solving the Problems]
  To achieve the above object, the present invention has a rotatable image carrier that carries a toner image, and a flexibility that abuts the image carrier and charges the image carrier by applying a charging bias voltage. In an image forming apparatus comprising a rotatable contact charging member, the contact charging member is elastically compressed and placed in contact with the contact charging member.The toner adhering to the contact charging member is taken inside.Comprising a rotatable open-cell foam roller, the open-cell foam roller comprises:To move the toner inward from the surface,Bubble diameterTheSurface more than insideMade smallerIt is characterized by that.
[0026]
  Further, the present invention is used in an image forming apparatus that forms an image using toner, and elastically compresses and contacts the mating member, and the toner adhering to the mating member is removed.Import insideA freely open foam foam roller,To move the toner inward from the surface,Bubble diameterTheSurface more than insideMade smallerIt is characterized by that.
[0027]
  Further, the present invention is configured to be detachable from an image forming apparatus that forms an image using toner, and elastically compresses and contacts the mating member, and the toner adhering to the mating member is removed.Import insideA process cartridge comprising a rotatable open-cell foam roller, wherein the open-cell foam roller comprises:To move the toner inward from the surface,Bubble diameterTheSurface more than insideMade smallerIt is characterized by that.
[0036]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described based on the illustrated embodiments.
[0037]
<Embodiment 1>
FIG. 1 is a schematic configuration diagram showing an image forming apparatus according to Embodiment 1 of the present invention.
The same members as those in the image forming apparatus of the conventional example shown in FIG.
[0038]
The image forming apparatus includes a photosensitive drum 1 as an image carrier, and includes a charging device 2, an exposure device 3, a developing device 4, and a transfer roller 5 around the photosensitive drum 1, and is formed between the photosensitive drum 1 and the transfer roller 5. A fixing device 6 is installed on the downstream side of the transfer nip N where the transfer material P is conveyed.
[0039]
  The charging device 2 in this embodiment includes a rotatable charging roller 7 that contacts the photosensitive drum 1, a charging bias power source 9 that applies a charging bias to the charging roller 7, and a charging roller 7.Compress elasticallyContact roller 7(Parts)Rotating open-cell foam that takes in transfer residual toner adhering to the surfacerollerThe sponge roller 20 is provided. The uppermost vertex of the sponge roller 20 is located below the rotation center of the charging roller 7 and downstream of the charging roller 7 in the rotation direction with respect to the charging nip where the charging roller 7 contacts the photosensitive drum 1. Is driven to rotate. Details of the sponge roller 20 will be described later.
[0040]
As shown in FIG. 2, the photosensitive drum 1 and the charging device 2 (the charging roller 7 and the sponge roller 20 excluding the charging bias power source 9) are integrated into a unit as a process cartridge 21, and can be attached to and detached from the image forming apparatus. It is possible to easily replace the photosensitive drum 1 when the photosensitive drum 1 reaches the end of its life by forming a predetermined number of images. Details of the charging roller 7 of the charging device 2, the developing roller 11 and the regulating blade 13 of the developing device 4, and the toner t to be used will be described later.
[0041]
Also in the present embodiment, an image forming operation is performed in the same manner as in the conventional image forming apparatus described above. In this embodiment, description of the image forming operation is omitted.
[0042]
Next, the sponge roller 20 of the charging device 2 will be described.
[0043]
As shown in FIGS. 3 (a) and 3 (b), the sponge roller 20 includes a metal cored bar 22 as a support shaft, a conductive material-dispersed urethane rubber in which the wall surface of the bubble portion communicates with the peripheral surface thereof, It is composed of a roller-like foam layer 23 made of silicon rubber, EPDM rubber, acrylic rubber or the like.
[0044]
  Sponge roller20Can be produced as follows, for example. First, an unvulcanized / unfoamed urethane rubber layer in which a compounding agent of a conductive material such as a foaming agent or carbon black is uniformly dispersed is formed on a metal cored bar 22. These are set in a cylindrical mold molding cabinet (not shown) and heated to vulcanize and foam the unvulcanized / unfoamed rubber layer, and the conductivity within the molding cabinet conforms to the mold. Molded as a sponge.
[0045]
At this time, the gas generated by the foaming is discharged from the side surface of the mold through the continuous bubbles formed by the foaming. At this stage, the bubbles of the open-cell sponge formed on the through hole in the peripheral surface of the cored bar 22 have a skin layer, and the bubbles are in a closed state.
And the sponge roller 20 of the desired outer diameter provided with the foam layer 23 on the surrounding surface of the metal core 22 is obtained by polishing the surface of the open-cell sponge and breaking the skin layer.
[0046]
In addition to the above manufacturing method, it is also possible to polish the surface of the open-cell sponge after heat-treating the unvulcanized / non-foamed urethane rubber layer in a free state without being placed in the molding cabinet.
[0047]
Further, as shown in FIGS. 4A and 4B, in the case of a sponge roller having a plurality of (two layers in the figure) foam layers 23a and 23b on the peripheral surface of the core metal 22, the single-layer configuration described above is used. The foam layer 23 can be formed by repeating the manufacturing process.
[0048]
Examples of the material for forming the foam layer 23 (23a, 23b) of the sponge roller 20 in the present invention include urethane rubber, silicon rubber, EPDM rubber, acrylic rubber, nitrile rubber, hydrin rubber, and fluorine rubber. I do not. Examples of the blowing agent generally include inorganic blowing agents such as sodium hydrogen carbonate, sodium carbonate, and ammonium carbonate, and organic blowing agents such as nitroso compounds, azo compounds, and sulfonyl hydrazide compounds, but are not particularly specified.
[0049]
Conductive agents can be broadly classified into electronic conductive agents and ionic conductive agents. Examples of electronic conductive agents include carbon black and metal oxides. Examples of ionic conductive agents include quaternary ammonium salts and aliphatic alcohol sulfate salts. Are not specified.
[0050]
  Further, the elastic body is not particularly limited to a single layer structure, and may be a plurality of two or more layers as shown in FIGS. 4A and 4B if necessary.AlsoThe layer structure is such that the bubble diameter decreases from the core 22 toward the roller surface.To do. ThisThe transfer residual toner peeled off in the vicinity of the contact portion with the charging roller 7 can be moved more smoothly to the central portion of the roller.
[0051]
As the characteristic values of the sponge roller 20 in the present embodiment, the following are preferable.
[0052]
The resistance value of the foam layer 23 of the sponge roller 20 is 10^FiveThe rubber hardness is 15 ° or less in terms of Asker C hardness, more preferably 50 ° or less in terms of Asker CSC2 hardness. This is because if the resistance is too high, the toner adhering to the charging roller 7 may be charged up due to rubbing caused by contact with the charging roller 7 and mechanically peeled off.
[0053]
Further, the average cell diameter of the above-mentioned open-cell sponge depends on the particle diameter and shape of the toner, but is preferably 10 times or more the average particle diameter of the powder in order to sufficiently take the toner into the bubbles. In addition, the amount of penetration into the charging roller 7 is necessarily less than the thickness of the foam layer 23, and although it depends on the thickness of the foam layer 23, it is more preferably less than half the thickness.
[0054]
The contact pressure (linear pressure) of the sponge roller 20 with the charging roller 7 is preferably 0.049 to 0.98 N / cm. When the contact pressure with the charging roller 7 is 0.049 N / cm or less, a peeling failure occurs at the contact portion with the charging roller 7, and charging is performed when the toner that has not been removed remains on the surface of the charging roller 7. It may cause defects. Conversely, if the contact pressure with the charging roller 7 is 0.98 N / cm or more, the rotational torque increases or the rubbing force increases, so that the toner taken into the sponge roller 20 is softened by rubbing. As a result, there is a risk of fusing to the surface of the charging roller 7.
[0055]
Incidentally, the contact pressure (linear pressure) was measured by the following method. Prepare a SUS thin plate with a length of 100 mm × width 15 mm × thickness 30 μm as a drawing plate, and a SUS thin plate with a length of 180 mm × width 30 mm × thickness 30 μm folded as a sandwich plate so that the length is halved, A drawing plate is inserted between the folded sandwich plates. In this state, the sandwiching plate is inserted between the charging roller 7 and the sponge roller 20. Then, only the spring attached to the extraction plate is pulled, the extraction plate is extracted at a constant speed, and the value indicated by the spring at that time is read. The contact pressure (linear pressure) between the charging roller 7 and the sponge roller 20 can be measured by dividing the value of the spring alone by 1.5 cm which is the width of the drawing plate.
[0056]
As a measure of the degree of openness of the foam layer 23, 1000 cm of the foam layer 23^ThreeThe air flow rate per minute is 500 to 5000 ml / (min · 1000 cm^ThreeMore preferably 1000 to 4000 ml (min · 1000 cm)^Three).
500ml / (min · 1000cm^ThreeIn the case of the following, not only the hardness increases and the contact pressure with the charging roller 7 increases, but also the amount of toner that can be contained is small, so that it must be frequently replaced. Also, 5000ml / (min · 1000cm^ThreeThis is because, if it is above, the bubbles are too connected to maintain the desired average cell diameter, and the collected toner cannot be held in the bubbles.
[0057]
In this embodiment, a sponge having a single foam layer 23 made of open-cell urethane sponge rubber having a layer thickness of 4 mm, in which carbon black is dispersed and blended as a conductive material on a metal core bar 22 having a diameter of 4 mm. A roller 20 was used. The amount of toner t that can be sucked into the foam layer 23 by the sponge roller 20 is about 30 g.
[0058]
Moreover, the conditions of the sponge roller 20 of this Embodiment were set as follows.
Resistance value is 10^FiveAbout Ω, rubber hardness is about 15 ° in Asker CSC2 hardness, the average cell diameter in the surface layer of the foam layer 23 is 200 μm, and the contact pressure (linear pressure) with the charging roller 7 is 0.196 N / cm The air flow rate representing the openness of the foam layer 23 is 1800 (min · 1000 cm^Three).
[0059]
The charging roller 7 of the present embodiment has an elastic layer, a conductive layer, and a resistance layer from below on a conductive substrate such as metal.
[0060]
The hardness of the elastic layer is preferably 30 ° or less in terms of rubber hardness based on JIS AGS-706 from the viewpoint of adhesion to the photosensitive drum 1 due to flexibility and vibration absorption. The layer thickness of the elastic layer is preferably 2 mm or more.
[0061]
The conductive layer has a volume resistivity of 10⁷Ω · cm or less is preferable, and a metal vapor deposition film, a conductive particle-dispersed resin, a conductive resin, or the like can be used. The thickness of the conductive layer is preferably 2 mm or less from the viewpoint of flexibility of the charging roller 7.
[0062]
The resistive layer has a volume resistivity of 10⁷-10¹²It is configured to be higher than the conductive layer at about Ω · cm, and a semiconductive resin, a conductive particle-dispersed insulating layer, or the like can be used. The thickness of the resistance layer is preferably 500 μm or less from the viewpoint of chargeability.
[0063]
In this embodiment, the charging roller 7 having a 3 mm-thick elastic layer, 10 μm-thick conductive layer, and 100 μm-thick resistance layer on a 6-mm diameter conductive core bar such as stainless steel is used. Further, the charging roller 7 does not need to have a three-layer structure as in this embodiment, and may be a single layer or three or more layers. The layer constituting material is not particularly limited, but the transfer residual toner can be easily peeled off when the surface of the charging roller 7 has a high releasability.
[0064]
In this embodiment, the charging bias applied from the charging bias power source 9 to the charging roller 7 is −1300 V, the non-image portion potential on the photosensitive drum 1 is −700 V, and the image portion potential is −150 V. In the present embodiment, a DC voltage is applied from the charging bias power source 9 to the charging roller 7. However, a charging bias in which a DC voltage and an AC voltage are superimposed may be applied.
[0065]
As described above, the image forming apparatus according to the present embodiment includes the charging device 2 including the charging roller 7 with which the sponge roller 20 is in contact, and the transfer remaining on the photosensitive drum 1 after the transfer. The remaining toner (reversed toner charged to positive polarity) reaches the vicinity of the contact portion (charging nip) between the photosensitive drum 1 and the charging roller 7 by the rotation of the photosensitive drum 1, and the surface potential of the photosensitive drum 1 and the charging bias. It adheres to the surface of the charging roller 7 by the electric field formed from
[0066]
Transfer residual toner (reversal toner) adhering to the charging roller 7 is peeled off from the charging roller 7 by rubbing against the irregularities on the surface of the foam layer 23 at the contact portion between the charging roller 7 and the sponge roller 20. Since the foam layer 23 has a low hardness, the contact pressure can be lowered even if a sufficient contact width is secured for stripping. Further, when the sponge roller 20 passes through the contact portion with the charging roller 7, the shape of the sponge roller 20 is restored by the elastic force. At that time, the toner existing on the surface of the sponge roller 20 and in the foam layer 23 is attracted to the inside thereof. It will be done.
[0067]
In this embodiment, since the top of the sponge roller 20 is disposed below the rotation center of the charging roller 7, the transfer that has entered the foam layer 23 in the vicinity of the contact portion with the charging roller 7 is performed. The residual toner (reversal toner) moves to the inside of the foam layer 23 by gravity, and the transfer residual toner that has been peeled off is not reapplied on the charging roller 7.
[0068]
The developing roller 11 of the developing device 4 of the present embodiment is formed to have an outer diameter of 16 mm by molding an elastic body on a conductive metal core having a diameter of 8 mm such as stainless steel. The elastic body has a two-layer structure of silicone rubber in the lower layer and a polyamide resin of about 10 μm in the surface layer, hardness of about 35 ° (Asker C), and volume resistance of 10⁷It is about Ωcm.
[0069]
The dynamic friction coefficient of the surface of the developing roller 11 is 0.02 to 0.8, preferably 0.02 to 0.4. The dynamic friction coefficient of the present embodiment is about 0.1. This is because, when the dynamic friction coefficient is high, various problems such as excessive charging of toner and defective peeling occur.
[0070]
The dynamic friction coefficient is a dynamic friction coefficient with respect to the stainless steel thin plate on the surface of the developing roller 11 measured by the following method. The reason for measuring the dynamic friction coefficient of the surface of the developing roller 11 with respect to the stainless steel thin plate is that the photosensitive drum 1 also has a photosensitive layer having a thickness of about several tens of μm on a substrate such as aluminum. This is because a stainless steel sheet is used as the blade 13 in the present embodiment, and it is determined that it is more appropriate to compare the dynamic friction coefficient of the surface of the developing roller 11 with respect to the stainless steel sheet near the current situation.
[0071]
Further, the elastic body of the developing roller 11 does not need to have a two-layer structure as in this embodiment, and may be a single layer or two or more layers. Further, the material is not particularly limited, and a generally used rubber material or resin may be used. The volume resistance is 10^TenΩcm or less is preferable. Volume resistance is 10^TenThis is because excessive charge-up of the toner can be prevented when it is Ωcm or less.
[0072]
The surface roughness of the developing roller 11 has a correlation with the particle diameter of the toner to be used. When the toner particle diameter is about 7 μm, the ten-point average roughness Rz is preferably 3 to 15 μm.
If it is 3 μm or less, sufficient toner conveying force cannot be obtained, and if it is 15 μm or more, the unevenness on the developing roller 11 affects the image quality when the electrostatic latent image on the photosensitive drum 1 is visualized as a toner image. Because there is. When the toner particle size becomes smaller, it is preferable to make the ten-point average roughness Rz slightly smaller.
[0073]
The regulating blade 13 of the developing device 4 of the present embodiment is obtained by bending a position of about 2 mm from the tip of a stainless steel thin plate (thickness: about 0.1 mm) in the direction opposite to the developing roller 11, and the bending. The part comes into contact with the developing roller 11 in a state of slightly biting. The contact pressure (linear pressure) at this time is preferably 0.098 to 0.45 N / cm.
[0074]
If the density is 0.098 N / cm or less, the toner cannot be properly charged, resulting in “fogging”, resulting in a decrease in image quality, or a decrease in the life of the sponge roller 20 due to an increase in toner that is not transferred. is there. When it is 0.45 N / cm or more, the toner deterioration is promoted by being melted in the case of a low melting point toner due to pressure, frictional heat, etc., or the external additive mixed in the toner is easily peeled off from the toner surface. End up.
[0075]
In the regulation blade 13 of the present embodiment, a stainless steel thin plate is used in edge contact with the developing roller 11, but a metal thin plate may be brought into surface contact with the developing roller 11.
[0076]
As described above, the image forming apparatus according to the present embodiment includes the developing device 4 including the developing roller 11 and the regulating blade 13 described above, and remains on the developing roller 11 without being consumed by the developing unit. The toner is returned to the developing container 10 together with the developing roller 11 by the rotation of the developing roller 11. The toner on the developing roller 11 is peeled off by the rubbing of the developing roller 11 and the peeling supply roller 12 at the contact portion between the developing roller 11 and the peeling supply roller 12 and collected in the developing container 10. At the same time, new toner t is supplied from the inside of the developing container 10 onto the developing roller 11 by the rotation of the stripping supply roller 12 and conveyed again to the contact portion between the regulating blade 13 and the developing roller 11.
[0077]
In this embodiment, the developing bias voltage applied from the developing bias power supply 14 to the developing roller 11 is −350V. In the present embodiment, a DC voltage is applied from the developing bias power supply 14 to the developing roller 11, but a developing bias in which a DC voltage and an AC voltage are superimposed may be applied.
[0078]
The shape of the toner t used in the present embodiment is preferably spherical and / or spindle-shaped. This is because it is more efficient for the sponge roller 20 to be taken into the bubbles and to allow many bubbles to pass therethrough, and as a result, the stripping can be performed stably and constantly without clogging.
[0079]
As an index of the sphericity of the toner t, it is preferable that the value of the shape factor SF-1 is 100 to 160 and the value of the shape factor SF-2 is 100 to 140. The values of SF-1 and SF-2 indicating these shape factors are obtained by randomly sampling 100 toner images enlarged by a magnification of 500 times using a Hitachi FE-SEM (S-800). Were introduced into an image analysis apparatus (Luxex 3) manufactured by Nicole via an interface and analyzed, and defined from the values obtained from the following equation.
[0080]
SF-1 = {(MXLNG)²/ AREA} × (π / 4) × 100
SF-2 = {(PERI)²/ AREA} × (1 / 4π) × 100
Where AREA: toner projected area, MXLNG: absolute maximum length of toner, and PERI: peripheral length of toner.
[0081]
The shape factor SF-1 of the toner t indicates the degree of roundness of the toner particles, and gradually becomes indefinite from a spherical shape. SF-2 indicates the degree of unevenness of the toner particles, and the unevenness of the toner surface becomes remarkable. When SF-1 exceeds 160, since the shape of the toner t becomes indefinite, the toner t is difficult to move in the foam layer 23 of the sponge roller 20, and the toner t may not be sucked to the inside. .
[0082]
As for the particle size of the toner t, the coefficient of variation (A) in the number distribution represented by the following formula is preferably 35% or less.
[0083]
Coefficient of variation (A) = (S / D1) × 100
Here, S represents the standard deviation value in the number distribution of toner particles, and D1 is the number average particle diameter (μm) of the toner particles.
[0084]
As the coefficient of variation in the number distribution of toner increases, the width of the particle size distribution becomes wider. When the coefficient of variation (A) in the number distribution is 35% or more, toner with a very large particle size is clogged on the sponge surface, This is because the toner t may not be sucked into the foam layer 23 of the sponge roller 20.
[0085]
Further, as a characteristic of the toner t used in the present embodiment, in addition to the condition that the coefficient of variation (A) in the number distribution is 35% or less, the weight average particle diameter is 10 μm or less, preferably 4 μm to 8 μm. Preferably there is. In the case of toner particles having a weight average particle size of less than 4 μm, a large amount of toner particles remain on the photosensitive drum 1 due to a decrease in transfer efficiency, and when the weight average particle size of the toner particles exceeds 10 μm, the surface of the photosensitive drum 1 And adhesion to the regulating blade 13 or the like is likely to occur. Further, when the coefficient of variation in the number distribution of toner particles exceeds 35%, the tendency is further increased.
[0086]
In this embodiment, toner t having an SF-1 value of 130 and an SF-2 value of 120, a weight average particle diameter of about 7 μm, and a coefficient of variation in the number distribution of 20% was used.
[0087]
As described above, in the image forming apparatus according to the present embodiment described above, the transfer residual toner attached to the charging roller 7 can be recovered well by the sponge roller 20 even in a cleanerless configuration without a cleaning unit or a waste toner container. Therefore, it is possible to prevent the toner on the surface of the charging roller 7 from being contaminated with toner over a long period of time, and to perform good image formation, and to reduce the size and simplification of the image forming apparatus.
[0088]
The amount of toner (transfer residual toner) that can be collected in the foam layer 23 of the sponge roller 20 is about 30 g, and the transfer residual toner amount per 1000 sheets of a 5% printing rate image is about 5 to 5. Since it is about 7 g, even if a paper jam in the middle of printing or an image output with a high printing rate is taken into consideration, for example, if the process cartridge 21 is replaced every time about 3000 sheets of 5% printed images are output, the sponge roller 20 Thus, the toner attracted to the toner is discharged again, and the charging roller 7 and the photosensitive drum 1 are prevented from being stained with the toner, so that good image formation can always be performed.
[0089]
Further, by replacing the process cartridge 21 in accordance with the number of usable sponge rollers 20, the useful life of the photosensitive drum 1 can be set to be shortened accordingly, so that the photosensitive drum 1 can be manufactured at low cost. Furthermore, by changing the layer thickness of the sponge roller 20, it is possible to adjust the collection amount of the transfer residual toner, and the product life of the process cartridge 21 can be set to a desired period.
[0090]
<Embodiment 2>
FIG. 5 is a schematic configuration diagram showing an image forming apparatus according to Embodiment 2 of the present invention.
The same members as those in the image forming apparatus according to the first embodiment illustrated in FIGS. 1 to 4 are denoted by the same reference numerals, and redundant description is omitted.
[0091]
In the present embodiment, a bias voltage is applied from the recovery bias power supply 24 to the sponge roller 20 of the charging device 2. Separately from the process cartridge 21, the sponge roller 20 is a replaceable single unit. Other configurations are the same as those of the first embodiment, and the description thereof is omitted in this embodiment.
[0092]
The surface of the charging roller 7 due to the contact of the sponge roller 20 is applied to the sponge roller 20 from the recovery bias power source 24 by applying a potential on the negative polarity side of the charging bias potential applied to the charging roller 7 from the charging bias power source 9. In addition to the physical peeling and collection of the toner (transfer residual toner) adhering to the toner, the reverse roller toner (transfer residual toner) can be urged to the sponge roller 20 by the electric field effect. It can be cleaned more efficiently.
[0093]
Further, by applying a negative bias voltage from the recovery bias power supply 24 to the sponge roller 20, the foam layer 23 is caused by the potential difference due to the voltage drop of the sponge in the radial direction from the surface of the sponge roller 20 to the inner cored bar 22. The positive polarity reversal toner (transfer residual toner) collected inside can be moved to the inside of the foam layer 23 more reliably. Further, since there is a collecting effect due to the electric field action, even if the contact pressure of the sponge roller 20 against the charging roller 7 is reduced, sufficient peeling and collecting can be performed.
[0094]
The characteristics of the sponge roller 20 suitable for the present embodiment are substantially the same as those of the first embodiment, but the resistance value is 10 higher than that of the first embodiment.⁸Ω or more, preferably 10^TenΩ or more. This is to prevent conduction at the contact portion between the charging roller 7 and the sponge roller 20.
[0095]
Further, the potential difference between the surface of the charging roller 7 and the surface of the sponge roller 20 is less than the discharge threshold value, and is preferably | 200 | V or less. This is because if the discharge threshold value is exceeded, discharge occurs and pinholes may be formed in the charging roller 7 and the sponge roller 20 or the photosensitive drum 1 may not be charged normally.
[0096]
In the present embodiment, -1400 V is applied from the recovery bias power source 24 to the sponge roller 20, −1300 V is applied from the charging bias power source 9 to the charging roller 7, and −350 V is applied from the developing bias power source 14 to the developing roller 11. The non-image part potential was -700 V, and the image part potential was -150 V.
[0097]
In the image forming apparatus of the present embodiment configured as described above, the amount of toner that can be collected by the sponge roller 20 is about 30 to 35 g, which is slightly larger than that in the first embodiment.
This is because in the present embodiment, the toner charged positively by the electric field effect between the charging roller 7 and the sponge roller 20 can be reliably held in the foam layer 23.
[0098]
In this embodiment, the transfer residual toner amount per 1000 sheets of the 5% printing rate image is about 5 to 7 g, and the transfer residual toner amount per 1000 sheets of the 5% printing rate image is about Since it is about 5 to 7 g, the sponge roller 20 that is unitized every time about 4000 prints of 5% print images are taken into account even when considering paper jamming during printing or outputting an image with a high printing rate. By replacing the toner, the toner sucked by the sponge roller 20 is discharged again, and the charging roller 7 and the photosensitive drum 1 are prevented from being stained with the toner, so that good image formation can always be performed.
[0099]
Further, by making the sponge roller 20 a separate unit from the photosensitive drum 1 and the charging roller 7, the user only needs to replace the sponge roller 20 that is regularly unitized, reducing the maintenance cost burden on the user. can do.
[0100]
Further, even if the sponge roller 20 is brought into contact with the charging roller 7 under a lower contact pressure condition (for example, about 0.14 N / cm) than in the case of the first embodiment, it is the same as in the first embodiment due to the collection effect by the electric field action. Or more stripping and recovery can be performed.
[0101]
As described above, also in this embodiment, the transfer residual toner adhering to the charging roller 7 can be satisfactorily collected by the sponge roller 20, so that the toner on the surface of the charging roller 7 is prevented from being contaminated by the toner over a long period of time. The image forming apparatus can be formed and the image forming apparatus can be reduced in size and simplified.
[0102]
Moreover, in each embodiment mentioned above, although the foam layer which comprises the sponge roller 20 was made into roller shape, it is not limited to this, For example, block shape may be sufficient.
[0103]
Further, in each of the above-described embodiments, the process cartridge 21 including the sponge roller 20 and the unitized sponge roller 20 are replaced every predetermined number of prints. Other methods may be used.
[0104]
Further, in each of the above-described embodiments, the developing device 4 is an example of a negative polarity reversal contact development system, but other than this, a regular development system, a positive polarity reversal development system, or a non-contact development system development device But you can.
[0105]
【The invention's effect】
  As described above, according to the present invention, the contact charging member(Parts)Open cell foam that can rotate freelyrollerThe remaining developer remaining on the contact charging memberrollerTherefore, the contact charging member is prevented from being soiled by the developer, charging failure is prevented over a long period, and a good image can be obtained.Further, the toner peeled off in the vicinity of the contact portion with the contact charging member (counter member) can be moved more smoothly to the center of the roller.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus according to a first embodiment of the present invention.
FIG. 2 is a schematic diagram showing a process cartridge of the image forming apparatus according to the first embodiment of the invention.
3A is a longitudinal sectional view showing a sponge roller of the charging device of the image forming apparatus according to the first embodiment of the present invention, and FIG. 3B is a charging of the image forming apparatus according to the first embodiment of the present invention. The cross-sectional view which shows the sponge roller of an apparatus.
4A is a longitudinal sectional view showing a modification of the sponge roller of the charging device of the image forming apparatus according to the first embodiment of the present invention, and FIG. 4B is an image forming process according to the first embodiment of the present invention. The cross-sectional view which shows the modification of the sponge roller of the charging device of an apparatus.
FIG. 5 is a schematic configuration diagram showing an image forming apparatus according to a second embodiment of the present invention.
FIG. 6 is a schematic configuration diagram showing an image forming apparatus in a conventional example.
[Explanation of symbols]
  1 Photosensitive drum (image carrier)
  2 Charging device
  3 Exposure equipment
  4 Development device
  5 Transfer roller
  6 Fixing device
  6a Fixing roller
  6b Pressure roller
  7 Charging roller (contact charging member, Mating member)
  9 Charging bias power supply
  11 Development roller
  14 Development bias power supply
  20 Sponge roller (open cell foamroller)
  21 Process cartridge
  22 Core
  23, 23a, 23b Foam layer
  24 Recovery bias power supply

Claims (3)

A rotatable image carrier carrying a toner image;
An image forming apparatus including a flexible contact charging member having flexibility and charging the image carrier by applying a charging bias voltage in contact with the image carrier.
Comprising a rotatable open-cell foam roller that is elastically compressed and abutted on the contact charging member, and that takes in toner adhering to the contact charging member ;
The open-cell foam roller has a smaller bubble diameter on the surface than on the inner surface so that the toner moves inward from the surface.
An image forming apparatus. A rotatable open-cell foam roller that is used in an image forming apparatus that forms an image using toner and that elastically compresses and contacts a mating member and takes in toner adhering to the mating member. ,
As you move the toner from the surface to the inside, and a cell diameter smaller towards the surface than inside,
An open cell foam roller characterized by that. A rotatable open-cell foam roller configured to be detachable from an image forming apparatus that forms an image using toner, elastically compressing and abutting against a mating member, and taking in toner adhering to the mating member A process cartridge comprising:
The open-cell foam roller has a smaller bubble diameter on the surface than on the inner surface so that the toner moves inward from the surface.
A process cartridge characterized by that.

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