JP2006330613A - Image forming apparatus and process cartridge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To maintain cleaning performance of a cleaning member to remove foreign matters deposited on an electrifying member. <P>SOLUTION: Experiments on a cleaning roll to be in contact with the electrifying roll to clean the electrifying roll are carried out by using various members having different cell densities and by changing contact pressures. The results reveal the conditions free from problems of cleaning are within a range of 40 to 80 cells/25 mm cell density and within a range of 0.05 to 0.6 N/cm contact pressure. That is, cleaning performance of the cleaning roll can be maintained when an image forming operation is carried out under the above conditions. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and a process cartridge using an electrophotographic system such as a copying machine, a printer, a facsimile machine, and a multifunction machine of these.

In general, in an image forming apparatus such as an electrophotographic copying machine or a printer, for example, for the purpose of writing an electrostatic latent image on an image carrier such as a photosensitive drum, the image carrier is charged in advance. A charging device is used. As this type of charging device, a contact charging method is known in which a charging member such as a charging roll member is disposed in contact with an image carrier and a predetermined charging bias is applied to the charging member.
In addition, a removal member such as a blade for removing the residual toner on the photosensitive drum after the toner image on the photosensitive drum is transferred is disposed around the photosensitive drum. Then, after the residual toner is removed by the removing member, charging is performed by the charging member.

Here, in the contact charging method, since the discharge surface of the charging member is in direct contact with the photosensitive member, foreign matters such as toner slipping from the removing member and external additives added to the toner are likely to adhere to the charging member. When such a foreign substance adheres to the charging member, the surface resistance changes, and an image defect due to a charging failure occurs.
For this reason, an apparatus has been proposed in which foreign substances adhering to the surface of the charging member are removed by a cleaning member. And as this cleaning member, the structure using the rotatable roll-shaped cleaning member which formed the outer peripheral part which contacts a roll-shaped charging member with the porous sponge layer is proposed (for example, refer patent document 1). .

JP-A-8-62948 (page 3, FIG. 1)

  However, when the cleaning member is used for a long period of time, foreign substances gradually accumulate on the outer peripheral surface of the cleaning member, clogging occurs, and the cleaning performance deteriorates. As a result, there is a problem in that the foreign matter that cannot be completely removed is streaked on the surface of the charging member, resulting in a charging failure. Further, there is a problem that the foreign matter clogged in the cleaning member is strongly rubbed against the charging member, thereby changing the surface resistance and causing an image defect due to a charging failure.

  Recently, various external additives are mixed in a developer containing toner. Since these external additives have a remarkably small particle size as compared with the toner, they easily pass through the cleaner provided on the photoreceptor. Therefore, many external additives adhere to the cleaning member via the charging member.

  The present invention has been made to solve the above technical problems, and an object of the present invention is to maintain the cleaning performance of a cleaning member that removes foreign matters adhering to the charging member.

For this purpose, an image forming apparatus to which the present invention is applied includes an image carrier that rotates by receiving a driving force, a charging member that is driven to rotate in contact with the image carrier, and charges the image carrier. A cleaning member that is rotated in contact with the charging member and is driven to rotate, and the contact pressure at which the cleaning member contacts the charging member is within a range of 0.05 to 0.6 N / cm. It is a feature.
The cleaning member may be a porous elastic body that has a reaction force of 0.2 to 2.2 N received by the member that is pushed into the cleaning member by 0.5 mm. A more preferable range in the reaction force range defined here is 0.5 to 1.7 N.
The cleaning member may have a porous elastic layer having a number of cells of 100/25 mm or less. A more preferable range in the range of the number of cells specified here is 40 to 80 cells / 25 mm.

From another point of view, an image forming apparatus to which the present invention is applied rotates by receiving a driving force, an image bearing member that carries a toner image, a driving source that applies a driving force to the image bearing member, an image A rotatable cleaning member having a charging member which is rotated in contact with the carrier to be charged and charges the image carrier, and a porous elastic body which cleans toner adhering to the charging member by biting into the charging member. The ratio of the amount of biting to the thickness of the porous elastic body of the cleaning member is in the range of 0.1 to 0.6. The more preferable range in the range of the ratio prescribed | regulated here is 0.2-0.5.
The toner constituting the toner image carried on the image carrier may be a polymerized toner. Further, the toner constituting the toner image carried on the image carrier can be characterized by having silica (SiO ₂ ) as an external additive.

Further, from another viewpoint, the image forming apparatus to which the present invention is applied includes an image carrier that rotates by receiving a driving force and an axial core, and is rotated in contact with the image carrier, A charging member that charges the image bearing member, and a rotatable cleaning member that is pressed by the charging member and cleans the charging member. The torque for driven rotation of the charging member is 0 per 1 cm of the length of the charging member. .00882 N · m or less.
A more preferable range of the torque for drivenly rotating the charging member is 0.00024 N · m or less per 1 cm of the length of the charging member.

It is also conceivable to apply the present invention to a process cartridge that is detachably attached to the image forming apparatus main body. That is, it includes an image carrier on which a toner image is carried, and a charging member that is configured to be rotatable and is charged in contact with the image carrier. And a rotatable cleaning member that is pressed against the charging member to clean the charging member, and the contact pressure at which the cleaning member contacts the charging member is in a range of 0.05 to 0.6 N / cm. It is what.
Further, as this cleaning member, a rotatable cleaning member that has a porous elastic body that bites into the charging member and cleans the charging member on the surface is used, and the amount of biting relative to the thickness of the porous elastic body of the cleaning member is The ratio is in the range of 0.1 to 0.6.
Further, as this cleaning member, a cleaning member that is configured to be rotatable and cleans in contact with the charging member is used, and the torque for driven rotation of the charging member is 0.00882 N per 1 cm of the axial length of the charging member. -It is characterized by being m or less.
Here, the above-described configuration can further include a cleaning blade for cleaning by removing residual toner adhering to the surface by contacting the surface of the image carrier. Further, a transfer belt for transferring the toner image carried on the image carrier to the recording material can be further included.

  According to the present invention, it is possible to maintain the cleaning performance of the cleaning member that removes the foreign matter attached to the charging member.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
FIG. 1 is a diagram showing the overall configuration of an image forming apparatus to which this embodiment is applied, and shows a digital color printer using a rotary (rotary) developing device. The image forming apparatus shown in FIG. 1 includes a photosensitive drum (image carrier) 11 that forms an electrostatic latent image on a main body 1 and carries a toner image, and a charger that charges the photosensitive drum 11 by charging it. 12. Further, the image forming apparatus exposes the charged photosensitive drum 11 to the main body 1 using, for example, a ROS (Raster Output Scanner) based on an image signal from an image processing apparatus (IPS: Image Processing System) (not shown). And an developing device 14 that develops the electrostatic latent image formed on the photosensitive drum 11 by the exposing device 13 to form a toner image.

  The developing device 14 is a rotary developing device, and forms toner images of four colors of yellow (Y), magenta (M), cyan (C), and black (K). The four developing devices 50 are provided, and a developing roll (developer carrying member) 51 for developing the photosensitive drum 11 is provided on the periphery of the developing device 14. The developing device 14 rotates by 90 degrees about the developing device center 14 a so that the developing roll 51 provided in the desired developing device 50 faces the photosensitive drum 11. More specifically, for one print output, the Y, M, C, and K developing devices 50 are opposed to the photosensitive drum 11 in this order to enable full color output. Further, each developing device 50 is configured to be pressed on the normal line by a coil spring 55 disposed at the developing device center 14a so that the tracking roll 52 for positioning can be surely brought into contact with the photosensitive drum 11. Yes. The photosensitive drum 11 rotates in the direction of the arrow (clockwise) in the figure, and the developing device 14 counterclockwise so that the movement in the tangential direction is the same as the rotation of the photosensitive drum 11 (clockwise). Rotate in the direction.

  Further, on the downstream side of the developing device 14 on the photosensitive drum 11, an intermediate transfer belt (intermediate transfer member) 15 that temporarily holds a toner image developed by the developing device 50 and formed on the photosensitive drum 11; The image forming apparatus includes a secondary transfer roll 16 that transfers a toner image formed on the intermediate transfer belt 15 to the sheet, and a fixing device 17 that fixes the toner image formed on the sheet by heating and pressing. . Further, around the photosensitive drum 11, a cleaning blade 18 that scrapes residual toner remaining on the photosensitive drum 11 after the primary transfer to the intermediate transfer belt 15, and toner scraped off by the cleaning blade 18 are removed. And a toner recovery bottle 19 for storing the toner. The intermediate transfer belt 15 rotates four times when forming one print image. The secondary transfer roll 16 is separated from the intermediate transfer belt 15 during the first three rotations, that is, when holding the Y, M, and C toner images, and the last K toner image is superimposed. In this case, it is configured to contact the intermediate transfer belt 15.

  The intermediate transfer belt 15 contacts or abuts in a wrap shape so as to be wound around the photosensitive drum 11 by a predetermined range, thereby enabling so-called wrap transfer. For example, chloroprene having excellent oil resistance and weather resistance, EPDM having excellent weather resistance, and the like are used for the intermediate transfer belt 15 having a thickness of about 0.5 mm and a circumferential length of 443 mm. In the present embodiment, the intermediate transfer belt 15 itself is not provided with a drive source, but is configured to follow the rotation of the photosensitive drum 11 using contact by wrapping, and the rotation direction of the contact portion is the same. Thus, it is rotating counterclockwise.

  Inside the intermediate transfer belt 15, a wrap-in roll 21 that specifies the wrap position of the intermediate transfer belt 15 on the upstream side of the rotation of the photosensitive drum 11 and a toner image formed on the photosensitive drum 11 are intermediate. A primary transfer roll 22 to be transferred onto the transfer belt 15 and a wrap-out roll 23 for specifying the wrap position of the intermediate transfer belt 15 on the downstream side of the wrap position are provided. A predetermined electric field is applied to the primary transfer roll 22 to assist primary transfer. The wrap-in roll 21 and the wrap-out roll 23 are placed in a GND or floating state.

  A backup roll 24 that assists secondary transfer by the secondary transfer roll 16 is provided inside the intermediate transfer belt 15. In the secondary transfer portion where the secondary transfer is performed by the secondary transfer roll 16 and the backup roll 24, a predetermined potential difference is required between the backup roll 24 and the secondary transfer roll 16. When the secondary transfer roll 16 is connected to a high voltage, the other backup roll 24 that faces is connected to the GND.

An intermediate transfer body cleaner 30 that removes toner on the intermediate transfer belt 15 after the secondary transfer is provided downstream of the secondary transfer portion on the intermediate transfer belt 15. The intermediate transfer body cleaner 30 includes a scraper 25 for scraping off toner remaining after the secondary transfer, a brush roll 26 for further scraping off toner remaining after cleaning by the scraper 25, and the scraper 25 and the brush roll. And a second toner recovery bottle 29 for recovering the toner scraped off by the toner. Inside the intermediate transfer belt 15, a cleaning backup roll 27 that assists the cleaning work by the scraper 25 and a cleaning backup roll 28 that assists the cleaning work by the brush roll 26 are provided.
Note that the scraper 25 and the brush roll 26 are separated from the intermediate transfer belt 15 at the beginning of image formation so as not to scrape off the toner image being superimposed, and they are integrated at a predetermined timing. It is configured to contact the intermediate transfer belt 15.

  The image forming apparatus to which the exemplary embodiment is applied is formed on the intermediate transfer belt 15 provided adjacent to the control unit 40 that controls the movement of each member of the image forming apparatus and the intermediate transfer belt 15. And a reflective photosensor 41 for detecting a toner patch. The photo sensor 41 can detect the position of the intermediate transfer belt 15 in the rotational direction by reading a patch formed in the longitudinal direction of the intermediate transfer belt 15.

  Next, an image forming process using the image forming apparatus shown in FIG. 1 will be described. The image forming apparatus receives an output request from an externally connected PC (Personal Computer), an image reading apparatus, or the like, and starts an image forming process based on an instruction from the control unit 40. In the case of full-color print output, the developing device 14 first rotates so that the yellow developing device 50 faces the photosensitive drum 11. First, when a yellow toner image is formed, the photosensitive drum 11 that rotates in the clockwise direction is charged by the charger 12 and then turned yellow at the exposure unit by, for example, laser light from the exposure device 13. Exposure based on corresponding image information is performed, and an electrostatic latent image is formed. Thereafter, after development is performed by the developing roller 51, a yellow toner image is transferred to the intermediate transfer belt 15 in a lap-shaped contact range or lap range. At this time, the secondary transfer roll 16, the scraper 25, and the brush roll 26 are retracted (separated) from the intermediate transfer belt 15, and the toner image on the intermediate transfer belt 15 is not scraped off by these.

  After the primary transfer, the surface of the photosensitive drum 11 is scraped off by the cleaning blade 18 and moves to the charger 12 for the next toner image formation. Further, the developing device 14 rotates in time for the development timing, and the magenta developing device 50 faces the photosensitive drum 11. A magenta toner image is sequentially formed and superimposed on the intermediate transfer belt 15 from the latent image exposed by the exposure device 13 based on the magenta image information. Similarly, cyan and black toner images are sequentially superimposed on the intermediate transfer belt 15 to complete the primary transfer.

  The secondary transfer roll 16 completes the primary transfer of the cyan toner image by the exposure device 13, and the toner image superimposed up to cyan is transferred to the secondary transfer portion (where the secondary transfer is performed by the secondary transfer roll 16). The intermediate transfer belt 15 is advanced (extruded) before the exposure for forming a black electrostatic latent image is started in the inter image after passing through. Then, the secondary transfer roll 16 is in contact (contact) with the intermediate transfer belt 15 to prepare for the secondary transfer. Further, the scraper 25 and the brush roll 26 are advanced with respect to the intermediate transfer belt 15 when the black portion is exposed and the cleaner portion (where the scraper 25 and the brush roll 26 are cleaned) is an inter-image. To do.

  On the other hand, the feed roll 32 is driven from the paper feed cassette 31 at a predetermined timing based on the control by the control unit 40, and the sheets are sequentially taken out and are fed one by one by the retard roll 33, to the registration roll 34. To reach. The registration roll 34 functions in accordance with the secondary transfer timing in the secondary transfer portion and feeds the paper to the secondary transfer portion at a predetermined timing.

  The sheet on which the toner image is transferred in the secondary transfer unit is conveyed to the fixing device 17. In the fixing device 17, the toner image on the paper is heated by the heat roll 35 and is pressed against the paper by the pressure roll 36 to be fixed. After that, it is output to the outside of the apparatus through the discharge roll 37 and is stored in the discharge tray 38 provided on the upper part of the main body 1. As described above, the image forming process for outputting one color print is completed.

FIG. 2 is a diagram for explaining the relationship among the photosensitive drum 11, the developing device 14, and the intermediate transfer belt 15.
The photosensitive drum 11 shown in FIG. 2 is a tubular member having a diameter of about 47 mm, and a photosensitive layer whose resistance value is reduced by light irradiation is formed on the surface of the aluminum pipe, and is made of aluminum provided at both ends of the aluminum pipe. The driving force of a motor (not shown) is received from the shaft 11a at the center via a flange (not shown).
Each of the developing devices 50 (Y, M, C, K) constituting the developing device 14 shown in FIG. 2 makes the distance between the developing roll 51 carrying the developer and the developing roll 51 and the photosensitive drum 11 constant. A tracking roll 52 for maintaining, and a supply auger 53 and an admix auger 54 for stirring the developer supplied to the developing roll 51 are provided. The developing roll 51 is made of, for example, a tubular member having a diameter of 16 mm, and a carrier contained in the developer is adsorbed by a magnetic force by a magnet roll (not shown) disposed inside, and developed on the surface of the developing roll 51. A magnetic brush of the agent is formed, and the toner adsorbed on the carrier is conveyed to the developing area of the photosensitive drum 11. The magnetic brush formed in this way is developed with the tip touching the surface of the photosensitive drum 11, so that the distance between the photosensitive drum 11 and the developing roll 51 is kept constant by the tracking roll 52. That is, the tracking roll 52 is formed to have a slightly larger radius (about 0.3 mm) than the developing roll 51 and to be coaxial with the developing roll 51 at both ends of the developing roll 51. As the tracking roll 52, a synthetic resin such as polyacetal is used.

  The intermediate transfer belt 15 shown in FIG. 2 is in contact with the lap range shown in FIG. 2 by the wrap-in roll 21 and the wrap-out roll 23 so as to cover the photosensitive drum 11. The lap range (wrap-shaped contact range) is an arc range formed at an angle of about 90 degrees at the peripheral edge of the photosensitive drum 11. The intermediate transfer belt 15 is an elastic belt and presses the photosensitive drum 11 with a relatively strong load. In the present embodiment, no driving force is applied to the intermediate transfer belt 15 itself, and the intermediate transfer belt 15 is driven by the drive of the photosensitive drum 11 rotating in the clockwise direction in FIG. .

FIG. 3 is a configuration diagram showing the configuration of the charger 12.
As shown in FIG. 3, the charger 12 includes a charging roll member (BCR) 60 that is always in contact with the surface of the photosensitive drum 11 to be charged, and a cleaning roll member 70 that is always in contact with the charging roll member 60. And has. The charger 12 does not include a drive source for driving the charging roll member 60 and the cleaning roll member 70. That is, as the photosensitive drum 11 rotates, the charging roll member 60 is driven (rotated), and as the charging roll member 60 rotates, the cleaning roll member 70 is driven (rotated).

In the charging roll member 60, a charging roll 62, which is an elastic layer made of a rubber material or a resin material, is formed on an axial core 61 (see FIG. 7) made of a metal shaft or pipe. Then, in order to ensure adhesion and charging characteristics, and to impart durability and stain resistance, a coating film such as an intermediate layer and a surface layer is formed by applying a coating material on the surface of the elastic layer. Here, AC is superimposed on the DC bias and applied to the shaft core 61 of the charging roll member 60, thereby charging the photosensitive drum 11. Note that only a DC bias may be applied to the shaft core 61.
An elastic body layer made of a rubber material or a resin material is formed on the charging roll 62. Then, in order to ensure adhesion and charging characteristics, and to impart durability and stain resistance, a coating film such as an intermediate layer and a surface layer is formed by applying a coating material on the surface of the elastic layer.
Here, as the material of the elastic body layer, polyester resin, acrylic resin, melamine resin, epoxy resin, urethane resin, silicone resin, urea resin, polyamide resin and other synthetic resins, ethylene-propylene rubber, epichlorohydrin rubber, silicone rubber, Synthetic rubber such as fluororubber, or the above-mentioned synthetic resin or synthetic rubber foam is used. Further, in order to impart conductivity to the elastic layer, one kind of conductive filler such as carbon black, zinc oxide, tin oxide, tin oxide-coated barium sulfate and / or an ionic compound such as a quaternary ammonium salt is used. Or 2 or more types are mixed, and also 1 type, or 2 or more types of organic fillers, such as inorganic fillers, such as a talc, an alumina, and a silica, and the fine powder of a fluororesin or silicon rubber, are mixed as needed. The coating film used for forming the coating film contains a synthetic resin such as a polyester resin, an acrylic resin, a melamine resin, an epoxy resin, a urethane resin, a silicon resin, a urea resin, a polyamide resin, and the coating film. In order to impart conductivity, conductive fillers such as carbon black, zinc oxide, tin oxide, and tin oxide-coated barium sulfate and / or ionic compounds such as quaternary ammonium salts that exhibit ionic conductivity, as well as the elastic layer 1 type or 2 or more types are mixed, and if necessary, 1 type or 2 or more types of inorganic fillers such as talc, alumina and silica, and organic fillers such as fine powder of fluororesin and silicon resin are mixed. The Further, a surfactant, a charge control agent and the like are added as necessary.

The cleaning roll member 70 is provided with a cleaning roll 72 on an axis 71 (see FIG. 7). The shaft core 71 is placed in a so-called “floating state”. Note that the same voltage as that of the shaft core 61 of the charging roll member 60 may be applied to the shaft core 71.
The cleaning roll 72 is made of a roll-like sponge formed with a predetermined cell density. As the cleaning roll 72, for example, ether-based urethane foam, polyethylene foam, polyolefin foam, melamine foam, micropolymer, or the like can be used. Other insulating materials can be used as the cleaning roll 72. The production method will be briefly described. In the case of polyurethane foam, it is produced using polyol, isocyanate, water, catalyst (amine catalyst, metal catalyst, etc.) and foam stabilizer (surfactant). Additives such as pigments are used. When these raw materials are mixed and stirred, a chemical reaction occurs, and a urethane resin foam is completed.
Here, toner and external additives that could not be cleaned on the photosensitive drum 11 by the cleaning blade 18 adhere to the charging roll 62 at the nip with the photosensitive drum 11. The cleaning roll 72 of the cleaning roll member 70 is always in contact with the charging roll 62 of the charging roll member 60 and is driven to follow, thereby preventing the toner and external additives from adhering to the charging roll 62.

Next, an evaluation experiment of the cleaning performance of the charging roll 62 by the cleaning roll 72 will be described.
4A is a graph showing the relationship between the amount of biting of the cleaning roll 72 and the contact pressure (linear pressure), where the vertical axis is the contact pressure (N / cm) and the horizontal axis is the bite. Amount (mm). FIG. 4B is an enlarged view of the side where the contact pressure is low. That is, with respect to FIG. 4B, the scale is changed so that the plot points do not overlap.
Evaluation of the cleaning performance (dirt condition) of the charging roll 62 by the cleaning roll 72 was performed using a porous elastic member shown in Table 1.

As shown in Table 1, in this evaluation experiment, the following is used as a sample of the cleaning roll 72. The material of samples 1 to 6 is an ether-based urethane foam, and the material of sample 7 is polyethylene. The member name of sample 1 is EP70, the member name of sample 2 is RR26, the member name of sample 3 is RR80, and the member name of sample 4 is RMM. The member name of sample 5 is SP80, the member name of sample 6 is PORON, and the member name of sample 7 is MAPS.
These samples 1 to 7 are not the same in cell density (also referred to as the number of cells in this specification), and differ depending on the samples. That is, the cell density of sample 1 is 65 cells / 25 mm, the cell density of sample 2 is 40 cells / 25 mm, the cell density of sample 3 is 40 cells / 25 mm, and the cell density of sample 4 is 50 cells / 25 mm. 25 mm. The cell density of sample 5 is 80 cells / 25 mm, the cell density of sample 6 is 125 cells / 25 mm, and the cell density of sample 7 is 500 cells / 25 mm. In addition, the cell density here means the number of foam holes per 25 mm.

About each of such samples 1-7, changing the amount of biting, the degree (dirt condition) of the cleaning roll 72 of the charging roll 62 was investigated and evaluated. Specifically, the biting amounts are 0.15 mm, 0.25 mm, 0.5 mm, 0.75 mm, 1.0 mm, and 1.25 mm. And the contact pressure (linear pressure) corresponding to these biting amounts was measured. Further, the experiment was conducted by pressing the shaft cores 71 at both ends of the cleaning roll member 70 in the direction of the charging roll member 60 to cause the cleaning roll 72 to bite into the charging roll 62. That is, the charged charging roll member 60 that was attached to the actual machine and was not cleaned by the cleaning roll 72 was prepared, and the performance was evaluated by examining the cleaning property (the degree of contamination of the charging roll 62) by changing the amount of biting.
Each evaluation result of these biting amounts is shown by the difference in the display format of the plot in FIG. That is, when the cleaning property is good (in the case of OK), the plot is shown only by the outer frame (hollow or hollow), and when the cleaning property is not good (in the case of NG), the plot is filled (solid). Is shown.
As shown in FIGS. 4A and 4B, Sample 6 and Sample 7 did not satisfy the cleaning performance even when the contact pressure (the amount of biting) was changed. Further, as shown in FIG. 4B, when the biting amount was 0.15 mm, the cleaning performance was not satisfied for samples 1 to 5 as well. When the amount of biting was 0.25 mm, only Sample 5 did not satisfy the cleaning performance. In addition, when the biting amount is 0.25 mm, the central part is floating and the load is applied to both ends, so in reality, there is no problem with the contamination of the charging roll 62 at both ends. The contamination of the charging roll 62 was a problem.

Here, paying attention to the cell density of Samples 1 to 7, Sample 6 with a cell density of 125 cells / 25 mm and Sample 7 with a cell density of 500 cells / 25 mm did not improve the cleaning properties even when the contact pressure was changed. On the other hand, in samples 1 to 5 having a cell density of 40 to 80 cells / 25 mm, the cleaning performance deteriorates when the contact pressure is too low, but good results are obtained when the contact pressure is at a certain level. Could get.
That is, if a member having a cell density of 125 cells / 25 mm or more is used, the cleaning property is deteriorated. Furthermore, if a member having a cell density of 100 cells / 25 mm or less is used, it can be said that there is no problem in cleaning properties. And the cleaning property is sufficiently secured by using a member having a cell density of 40 to 80 cells / 25 mm.

FIG. 5 is a graph showing the relationship between the deflection rate of the cleaning roll 72 and image defects (cleanability), where the vertical axis is the image defect grade and the horizontal axis is the deflection rate (%). This deflection rate can also be called a biting rate. The deflection rate here is T ₀ (see FIG. 7), and the amount of biting into the charging roll 62 by the cleaning roll 72 is t (see FIG. 7). Then, the percentage of the value (t / T ₀ ) obtained by dividing the biting amount t by the thickness T ₀ is the deflection rate. Further, the image defect grade here is such that the image defect becomes larger as the numerical value becomes larger. If the numerical value of the image defect grade is 3 or less, there is no problem with the image, and an image defect that is not allowed when the value exceeds 3 is determined.
FIG. 5 shows a sample 1 (cell density: 65/25 mm) and sample 2 (cell density: 40/25 mm) shown in Table 1. As this sample 1, Lot. B, Lot. C and Lot. Three types of D are illustrated. This Lot. B to D are illustrated by taking into account that the cell density is 65 cells / 25 mm, but the hardness varies depending on the lot.

As shown in FIG. 5, although the numerical values of the image defect grades in Samples 1 and 2 are slightly different, it can be said that the difference is small. And in any sample, when the deflection rate is too large or too small, the numerical value of the image defect grade becomes high. Moreover, in any sample, if the deflection rate is in the range of 10 to 60% (ratio is 0.1 to 0.6), the numerical value of the image defect grade is 3 or less, and no image defect is generated. Judgment can be made. In other words, 0.1 ≦ t / T ₀ ≦ 0.6 when expressed using the biting amount t and the thickness T ₀ .
In other words, if the deflection rate is smaller than 10% (ratio is 0.1), the load on the charging roll 62 of the cleaning roll 72 is too small, and the followability to the charging roll 62 is reduced. For this reason, if the deflection rate is less than 10%, the rubbing is performed rather than the discharge of the adhered matter, and the life of the charging roll 62 is drastically reduced. On the other hand, when the deflection rate exceeds 60% (the ratio is 0.6), the load on the charging roll 62 of the cleaning roll 72 increases rapidly. For this reason, the followability of the charging roll 62 to the photosensitive drum 11 is deteriorated, and the surface of the charging roll 62 is excessively worn. Thus, the deflection rate is preferably in the range of 10 to 60%.

In consideration of the variation of the porous elastic body and the like, if the deflection rate is in the range of 20 to 50% (ratio is 0.2 to 0.5), it is more preferable in terms of suppressing image defects. That is, more preferably, 0.2 ≦ t / T ₀ ≦ 0.5. In consideration of the deflection of the shaft (axial core 71) when a load is applied, in order to remove the matter adhering to the charging roll 62 by contacting the charging roll 62 at the center in the length direction, It is necessary to secure a biting amount of 0.2 mm or more.

Here, the thickness T ₀ of the porous elastic body is required to be at least 1 mm. That is, if the thickness T ₀ of the porous elastic body is less than 1 mm, it is affected by the adhesive at the time of attachment, so the thickness T ₀ of the porous elastic body needs to be 1 mm or more. Thus, the reason why the thickness T ₀ of the porous elastic body is 1 mm or more is as follows.
If the thickness T ₀ of the porous elastic body is 1 mm, the biting amount t is 0.4 mm when the deflection rate is 40%. If the outer diameter tolerance on the processing accuracy of the sponge as the porous elastic body is ± 0.2 mm, when this tolerance is taken into consideration, it becomes 0.4 mm ± 0.2 mm, that is, 0.2 to 0.6 mm. When the thickness T ₀ is 1 mm, the deflection rate is 20 to 60%. Since this deflection rate is substantially the same as the range that does not cause image defects, the thickness T ₀ of the porous elastic body is required to be 1 mm or more.

FIG. 6 is a graph showing the relationship between the roll hardness of the cleaning roll 72 and image defects (cleanability), where the vertical axis is the image defect level and the horizontal axis is the roll hardness (N). The roll hardness here refers to a load applied when a circular pressing member having a diameter of 50 mm is pushed into the cleaning roll 72 by 0.5 mm. Further, the image defect level here is the same as in the case of FIG. 5 described above, and if the numerical value exceeds 3, it is assumed that the image defect is not allowed.
Here, the evaluation experiment shown in FIG. 6 was performed under the following conditions. That is, the charging roll 62 (see FIG. 7) contaminated with the external additive in advance is rotated by being brought into contact with the cleaning roll 72 (see FIG. 7), and then charged in the image forming apparatus (see FIG. 7). The image defect was confirmed by attaching. FIG. 6 is a graph showing the image defect level at that time. Such an evaluation experiment was performed by changing the material and roll hardness of the cleaning roll 72. 6 is a corresponding line between the confirmed image defect level and roll hardness.
FIG. 6 shows samples 1 to 7 shown in Table 1. Further, as sample 1, Lot. A, Lot. B, Lot. C and Lot. 4 types of D are illustrated. Lot. B, Lot. C and Lot. About D, the same thing as the case of FIG. 5 is used.

As shown in FIG. 6, the roll hardness varies greatly depending on the sample, but if the roll hardness is in the range of 0.2 to 2.2 N, it is considered that there is no problem in terms of image defects. In other words, the cleaning performance can be satisfied from the line of correspondence between the confirmed image defect level and the roll hardness (upward slanted line in FIG. 6) when the roll hardness is 0.2 N or more. That is, 0.2N can be adopted as the lower limit value in terms of image defects. Further, as the upper limit value, a value of 2.2N can be adopted from the viewpoint of damage to the charging roll (BCR) 62.
Moreover, as shown in FIG. 6, the range whose roll hardness is 0.5-1.7N is employable as a more preferable range. This range confirms the correspondence with the image defect by an evaluation experiment. If a material having a roll hardness within this range is used, the cleaning performance can be satisfied more reliably.

Here, even within the range of the roll hardness described above, when the cell density was 100/25 mm or more, the numerical value of the image defect grade was high. That is, in the case of Sample 6 with a cell density of 125/25 mm and Sample 7 with 500/25 mm, the image defect grade exceeds 3 even if the roll hardness is in the range of 0.2 to 2.2 N. ing. Actually, when a test was performed using a member having a cell density of 100 cells / 25 mm or more, the same result was obtained. To explain this, even if a member having a cell density of 100/25 mm is brought into contact with a charging roll 62 previously contaminated with an external additive and driven to rotate, it appears as an image defect and actually outputs an image over 12,000 sheets. When it was repeated, an image defect appeared, and the result corresponded to the evaluation method described above.
In addition, although the image output was actually repeated over 12,000 sheets using the member in which the biting amount was 0.75 mm and the contact pressure was in the range of 0.05 N / cm, no image defect was observed. However, when the image output is repeated over a long period of time with respect to a member having a biting amount of 0.75 mm and a contact pressure of 0.6 N / cm or more, the surface of the charging roll 62 itself is heavily worn, and the lower surface is Appearance and image defects on the print were observed.

FIG. 7 is a conceptual diagram for explaining a method for measuring the rotational torque of the charging roll member 60.
As shown in FIG. 7, the charging roll member 60 and the cleaning roll member 70 are held so as to have a prescribed biting amount. The charging roll member 60 and the cleaning roll member 70 are held via ball bearings so as to reduce the rotational load. The driving force of the charging roll member 60 at which the surface speed of the charging roll member 60 becomes 150 mm / second is measured, and the measurement result is used as the rotational torque of the charging roll member 60.
With such a configuration, the rotational torque of the charging roll member 60 is measured by a measuring device, and the image quality of the print sample and the damage evaluation result of the charging roll member 60 at the rotational torque are shown in Table 2. That is, the results shown in Table 2 are obtained by performing an acceleration test of damage to the charging roll 62 so that the cleaning roll 72 is brought into contact with the charging roll 62 to which the toner is adhered, and the cleaning roll 72 is not fixed to the charging roll 62. .

The acceleration test here is a test performed using a set of the photosensitive drum 11, the charging roll member 60, the cleaning roll member 70, the intermediate transfer belt 15, and the cleaning blade 18 shown in FIG. Specifically, the acceleration test is equivalent to 800 sheets by repeating the operation of rotating the photosensitive drum 11 for 12 seconds and stopping for 1 second (one color) with a small amount of toner applied on the photosensitive drum 11. And continued. Such an acceleration test is carried out with a voltage applied to the charging roll.
The charging roll member 60 has a voltage of 1.2 kHz and 1.6 kVpp, and a DC bias of −620V. At this time, the charging roll 62 has a diameter of 12 mm and 4 rotations / second. The length of the charging roll 62 is 20 cm.
The results measured by the measurement method as shown in FIG. Table 2 summarizes the results of measurement in a laboratory environment, a high temperature and high humidity environment, and a low temperature and low humidity environment.

As shown in Table 2, as the rotational torque of the charging roll member 60 increases, the damage received by the charging roll 62 increases. When the rotational torque decreases, the damage received by the charging roll 62 decreases. In addition, there is no problem in terms of image quality regardless of whether the rotational torque of the charging roll member 60 is large or small.
That is, when the rotational torque of the charging roll member 60 is 17.64 mN · m (0.1764 N · m) or less, no problem occurs in terms of image quality and damage to the charging roll 62. Since the length of the charging roll 62, which is the length with which the cleaning roll 72 contacts the charging roll 62, is 20 cm, the rotational torque per 1 cm when there is no problem is 0.882 mN · m (0.00882 N · m). It is as follows.
Further, if the rotational torque of the charging roll member 60 is 0.48 mN · m (0.0048 N · m) or less, it is particularly preferable in that the damage to the charging roll 62 is further reduced. The rotational torque per cm in this preferred case is 0.024 mN · m (0.00024 N · m) or less.
In addition, when the material of the sponge roll as the cleaning roll 72 is selected, the charging roll 62 is damaged by causing the amount of biting with the charging roll 62 to be the amount of biting specified from the rotational torque. Therefore, good cleaning can be performed.

  Next, the developer D used in the digital color printer will be described in detail with reference to FIG. As shown in FIG. 8A, the developer D includes a magnetic carrier C and a toner T colored yellow, magenta, cyan, or black. Further, the developer D contains an external additive S as shown in FIG.

In the developer D, as the carrier C, ferrite beads having an average particle diameter of about 35 μm are used.
As the external additive S, inorganic fine particles such as silica (SiO ₂ ), titania (TiO ₂ ), and ceria (CeO ₂ ) having an average particle diameter of 5 to 200 nm are used.
Further, the toner T has a polarity that is negatively charged, and a binder resin such as polyester or styrene acrylic is added with a colorant, wax by suspension polymerization, emulsion aggregation and coalescence, dissolution suspension, or the like. Is a fine particle formed by internally adding. The particle diameter was measured by a Coulter counter (manufactured by Coulter Co.), and the volume average particle diameter was about 6.4 μm. The toner shape (degree of sphere) is represented by a shape factor, and an enlarged photograph of the toner obtained with an optical microscope (Microphoto FXA: manufactured by Nikon Corporation) is subjected to image analysis with an image analyzer Luzex3 (manufactured by Nireco Corporation), and the following formula Calculated with

  This expression is expressed as a ratio between the projected area of the toner T and the area of a circle circumscribing the toner T, and is 100 in the case of a true sphere, and the number increases as the shape moves away from the sphere. If the shape factor is small, the amount of residual toner that remains without being transferred during transfer is reduced. Therefore, the shape factor of the toner T is desirably about 100 to 140. In this embodiment, the toner T The shape factor was 134. The volume average particle diameter of the toner T is preferably in the range of 3 to 10 μm from the viewpoint of forming a good image.

  Here, Table 3 shows a configuration example of the magenta developer D used in the present embodiment. In the cyan developer D, the red pigment is a blue pigment, in the yellow developer D, the red pigment is a yellow pigment, and in the black developer D, the red pigment is polyethylene.

  Table 4 shows a configuration example of the magenta toner T used in the present embodiment. As in the case of the developer D described above, in the cyan toner T, the red pigment is a blue pigment, and in the yellow toner T, the red pigment is a yellow pigment. Further, Table 5 shows a configuration example of the black toner T.

Further, as for the external additive S, 1.48% by weight of silica is added to the toner T. In addition to silica, 0.8% by weight of titania and ceria are added.
Here, the average particle diameter of the silica used as the external additive S is 100 nm, its shape factor is 140 or less, and has a substantially spherical shape.

Next, the behavior of the developer D (carrier C, toner T, and external additive S) in the image forming process described above will be described.
In the developing device 50 shown in FIG. 1, the developer D of each color is agitated and conveyed by a supply auger 53 and an admix auger 54, and the carrier T and the toner T are rubbed to charge the toner T to a negative polarity. . The developer D agitated and conveyed in this manner is transferred to the developing roll 51 and conveyed, and forms a magnetic brush at a portion facing the photosensitive drum 11 to develop the electrostatic latent image on the photosensitive drum 11. To do. At this time, a part of the toner T and the external additive S adhering to the toner T are transferred onto the photosensitive drum 11, but the remaining toner T, carrier C and external additive S remain on the developing roll 51.

  Next, the toner T and the external additive S transferred and attached to the photosensitive drum 11 are conveyed to a lap range in contact with the intermediate transfer belt 15 as the photosensitive drum 11 rotates, and the toner T on the photosensitive drum 11 is transferred. Most of the toner image is primarily transferred to the intermediate transfer belt 15. At this time, a part of the external additive S adhering to the toner T is also transferred to the intermediate transfer belt 15 side. On the other hand, the toner T and the external additive S that have not been primarily transferred remain on the surface of the photosensitive drum 11 after the primary transfer. Here, in the present embodiment, the external additive S functions as a transfer auxiliary agent for enhancing the releasability of the toner T, and the external additive S tends to remain on the photosensitive drum 11 after the primary transfer. ing.

  Then, the toner T and the external additive S remaining on the intermediate transfer belt 15 after the primary transfer reach the portion facing the cleaning blade 18 as the photosensitive drum 11 rotates. At this time, the toner T adhering to the photosensitive drum 11 and the external additive S adhering to the toner T are scraped off by the cleaning blade 18. On the other hand, for example, the external additive S directly adhered to the photosensitive drum 11 passes through the cleaning blade 18 due to its small particle size, and the portion facing the charging roll 62 (charging nip) as the photosensitive drum 11 further rotates. Part). At this time, the titania and ceria contained in the external additive S are mostly kept attached to the toner T, and most of them are scraped off together with the toner T by the cleaning blade 18. On the other hand, most of the silica contained in the external additive S does not adhere to the toner T, and most of the silica passes through the cleaning blade 18. According to the inventor's investigation, 90% or more of the external additive S that passes through the cleaning blade 18 and is transferred and adhered to the charging roll 62 is silica.

The external additive S conveyed to the charging nip portion is transferred and adhered from the photosensitive drum 11 to the charging roll 62. The external additive S adhering to the charging roll 62 is conveyed to a portion facing the cleaning roll 72 (cleaning nip portion) as the charging roll 62 rotates. Then, the external additive S as the foreign matter conveyed to the cleaning nip portion is transferred and adhered from the charging roll 62 to the cleaning roll 72.
In this way, the external additive S does not accumulate on the cleaning roll 72 and clogging occurs, and the cleaning performance of the cleaning roll 72 can be maintained over a long period of time. Therefore, the surface of the charging roll 62 is kept clean, and the charging performance of the charging roll 62 can be maintained over a long period of time.

Next, maintainability of the image forming apparatus shown in FIG. 1 will be described with reference to FIG.
FIG. 9 is a diagram for describing maintenance work of the image forming apparatus according to the present embodiment.
In the image forming apparatus shown in FIG. 9, it is possible to open and close the open / close cover 102 that is a part of the casing of the main body 1 around the rotation fulcrum 101 of the main body 1. The opening / closing cover 102 includes a discharge tray 38, and the photo sensor 41 provided on the back side of the discharge tray 38 is simultaneously opened and closed. The rotation fulcrum 101 is provided at the same height as the developing device 14 that is vertically below the intermediate transfer belt 15. More precisely, as shown in FIG. 9, it is provided at the same height as the developing device center 14 a, and the opening / closing cover 102 can be opened around the rotation fulcrum 101. By forming the opening portion of the apparatus by the opening / closing cover 102 in this way, it is possible to easily insert / remove members above the developing device 14 such as the intermediate transfer belt 15 and the intermediate transfer body cleaner 30.

  When a user or a service worker performs maintenance work, first, for example, a part of the opening / closing cover 102 on the upper surface of the main body 1 is grasped, and the opening / closing cover in the main body 1 in the direction (i) shown in FIG. 102 is rotated around the rotation fulcrum 101. By rotation of the opening / closing cover 102, the inside of the apparatus, that is, the upper portion of the image forming portion such as the intermediate transfer belt 15 and the intermediate transfer body cleaner 30 is opened. In the arrangement of each member in the image forming apparatus of the present embodiment, the developing device 14, the intermediate transfer belt 15, the intermediate transfer body cleaner 30, and the like are laid out in the vertical direction. Also, intermediate transfer means such as the intermediate transfer belt 15 and the intermediate transfer body cleaner 30 are provided in the vicinity of the casing in the main body 1. In particular, the intermediate transfer belt 15 and the discharge tray 38 that forms the casing are substantially parallel. It is arranged to be. Therefore, by rotating the opening / closing cover 102 including the discharge tray 38, the upper part of the intermediate transfer unit above the developing device 14 is opened.

  Next, as shown in (ii) of FIG. 9, the process cartridge 103 which is a replacement part is taken out. In the present embodiment, the process cartridge 103 corresponds to the photosensitive drum 11 and the charger 12 including the charging roll member 60 and the cleaning roll member 70 that are charged by contacting the photosensitive drum 11. Further, it is conceivable that the process cartridge 103 includes the intermediate transfer belt 15 and various rolls (21 to 24, 27, 28) inside the intermediate transfer belt 15. Furthermore, the process cartridge 103 can include a cleaning blade 18 that cleans the photosensitive drum 11 or a toner recovery bottle 19 that includes the cleaning blade 18. These replacement parts are preferably formed into a cartridge and integrally formed. When the cartridge is formed, for example, a mode in which a predetermined frame (frame) is provided on the front side and the rear side of the apparatus and each replacement part is attached to the frame is conceivable. Since each replacement part is attached to the frame, the process cartridge 103 can be easily inserted and removed.

  The process cartridge 103 as these replacement parts is opened upward by opening the opening / closing cover 102, can be pulled up integrally in the direction of the arrow (ii) shown in FIG. 9, and can be detached from the main body 1. That is, by opening the opening / closing cover 102, the process cartridge 103 can be smoothly taken out without interfering with other mechanical parts of the main body 1. In the present embodiment, an intermediate transfer belt 15 that is a replacement part is disposed vertically above the developing device 14 that is not a replacement part. Further, a vertical paper path is adopted as the paper conveyance path, and the fixing device 17 is arranged on the upper right side shown in FIG. Therefore, it is preferable that the direction of taking out the process cartridge 103 is the arrow direction (ii) shown in FIG.

  After the process cartridge 103 is taken out in the direction of the arrow (ii) shown in FIG. 9, only the toner recovery bottle 19 can be detached from the process cartridge 103 as shown in (iii). As a result, only the toner collection bottle 19 is removed from the process cartridge 103 when, for example, the toner collection bottle 19 is full of waste toner in a state where the photosensitive drum 11 or the intermediate transfer belt 15 has not reached the end of its life. It is also possible to exchange them.

1 is a diagram illustrating an overall configuration of an image forming apparatus to which the exemplary embodiment is applied. FIG. 4 is a diagram for explaining a relationship among a photosensitive drum, a developing device, and an intermediate transfer belt. It is a block diagram which shows the structure of a charging device. It is a graph which shows the relationship between the amount of biting of a cleaning roll, and contact pressure (linear pressure), a vertical axis is contact pressure (N / cm), and a horizontal axis is the amount of biting (mm). It is a graph which shows the relationship between the deflection rate of a cleaning roll, and an image defect, and a vertical axis | shaft is an image defect grade and a horizontal axis is a deflection rate (%). It is a graph which shows the relationship between the roll hardness of a cleaning roll, and an image defect, A vertical axis | shaft is an image defect level and a horizontal axis is roll hardness (N). It is a conceptual diagram for demonstrating the method to measure the rotational torque of a charging roll member. (A) is a figure which shows the carrier and toner which comprise a developing agent, (b) is a figure which shows a toner and an external additive. FIG. 4 is a diagram for describing maintenance work of the image forming apparatus according to the present embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Photosensitive drum, 12 ... Charger, 15 ... Intermediate transfer belt, 18 ... Cleaning blade, 60 ... Charging roll member, 62 ... Charging roll, 70 ... Cleaning roll member, 72 ... Cleaning roll, 103 ... Process cartridge

Claims (17)

An image carrier that rotates by receiving a driving force;
A charging member that is driven to rotate in contact with the image carrier and charges the image carrier;
A cleaning member that contacts and rotates with the charging member to clean the charging member;
And an abutting pressure at which the cleaning member abuts on the charging member is in a range of 0.05 to 0.6 N / cm.   The image forming apparatus according to claim 1, wherein the cleaning member is a porous elastic body in which a reaction force received by a member pushed into the cleaning member by 0.5 mm is 0.2 to 2.2 N. .   2. The image forming apparatus according to claim 1, wherein the cleaning member is a porous elastic body in which a reaction force received by a member pushed into the cleaning member by 0.5 mm is 0.5 to 1.7 N. .   The image forming apparatus according to claim 1, wherein the cleaning member has a porous elastic layer having a number of cells of 100 (cells / 25 mm) or less.   The image forming apparatus according to claim 1, wherein the cleaning member includes a porous elastic layer having 40 to 80 cells / 25 mm. An image carrier that rotates by receiving a driving force and carries a toner image;
A driving source for applying a driving force to the image carrier;
A charging member that is driven to rotate in contact with the image carrier and charges the image carrier;
A rotatable cleaning member having a porous elastic body on the surface for cleaning toner adhering to the charging member by biting into the charging member;
And the ratio of the biting amount of the cleaning member to the thickness of the porous elastic body is in the range of 0.1 to 0.6.   The image forming apparatus according to claim 6, wherein a ratio of a biting amount of the cleaning member to a thickness of the porous elastic body is in a range of 0.2 to 0.5.   The image forming apparatus according to claim 6, wherein the toner constituting the toner image carried on the image carrier is a polymerized toner. The image forming apparatus according to claim 6, wherein the toner constituting the toner image carried on the image carrier has silica (SiO ₂ ) as an external additive. An image carrier that rotates by receiving a driving force;
A charging member that includes an axial core, is rotated in contact with the image carrier, and charges the image carrier;
A rotatable cleaning member that is pressed against the charging member to clean the charging member;
The image forming apparatus is characterized in that a torque for driven rotation of the charging member is 0.00882 N · m or less per 1 cm length of the charging member.   The image forming apparatus according to claim 10, wherein a torque for driven rotation of the charging member is 0.00024 N · m or less per 1 cm of the length of the charging member. A process cartridge that is detachably attached to the image forming apparatus main body,
An image carrier on which a toner image is carried;
A charging member configured to be rotatable and charged in contact with the image carrier;
A rotatable cleaning member that is pressed against the charging member to clean the charging member;
And a contact pressure at which the cleaning member contacts the charging member is in a range of 0.05 to 0.6 N / cm.   13. The process cartridge according to claim 12, further comprising a cleaning blade that removes residual toner adhering to the surface of the image carrier and cleans the toner by contacting the surface of the image carrier.   13. The process cartridge according to claim 12, further comprising a transfer belt for transferring the toner image carried on the image carrier to a recording material. A cleaning blade for cleaning by removing residual toner adhering to the surface by contacting the surface of the image carrier;
A transfer belt for transferring the toner image carried on the image carrier to a recording material;
The process cartridge according to claim 12, further comprising: A process cartridge that is detachably attached to the image forming apparatus main body,
An image carrier on which a toner image is carried;
A charging member configured to be rotatable and charged in contact with the image carrier;
A rotatable cleaning member that has a porous elastic body on the surface that bites into the charging member and cleans the charging member;
And a ratio of the amount of biting to the thickness of the porous elastic body of the cleaning member is in the range of 0.1 to 0.6. A process cartridge that is detachably attached to the image forming apparatus main body,
An image carrier on which a toner image is carried;
A charging member configured to be rotatable and charged in contact with the image carrier;
A cleaning member configured to rotate and abutted against the charging member for cleaning;
And a torque for driven rotation of the charging member is 0.00882 N · m or less per 1 cm of the axial length of the charging member.

Images