JP2019060938A - Image forming device, image forming method and developing device - Google Patents

Abstract

To provide an image forming device with which it is possible to obtain good mat followability even when a toner having excellent durability is used.SOLUTION: Provided is an image forming device, where when it is assumed that Δv represents the ratio of peripheral velocity of an image carrier to a developer carrier, C represents electrostatic capacitance between the image carrier and the developer carrier in a state where a developer carried by the developer carrier is caught in a nip part in which the developer is supplied to the image carrier when ΔV represents a development contrast, and Q/S represents a charge amount per unit area of the developer carried by the image carrier, the expression |Q/S×Δv|>|C×ΔV| holds true, and the remaining amount of the developer on the developer carrier after the developer is developed from the developer carrier to the image carrier is 50% or more of the developer amount carried by the developer carrier.SELECTED DRAWING: Figure 5

Description

  The present invention relates to an image forming apparatus that forms an image on a recording material using an electrophotographic method.

  Conventionally, in an electrophotographic image forming apparatus, an image carrier such as an electrophotographic photosensitive member is charged and then exposed according to image information to form an electrostatic latent image, and the electrostatic latent image is formed according to the electrostatic latent image. The developer is supplied to the image carrier by the developing means to form a developer image. Next, the developer image is transferred to a recording material such as a recording sheet, an OHP sheet, a cloth or the like by a transfer unit, and then the developer image is fixed on the recording material by a fixing unit to obtain a recorded image.

  Nonmagnetic single component contact development is known as the above developing means. Unlike a so-called jumping development system in which a contact development system developing device forms a gap between an image carrier and a developer carrier and forms an alternating electric field therebetween to fly toner for development, the image carrier and The developer carrier is brought into contact to perform development. Therefore, it is excellent in that scattering of the developer generated at the time of the developing process is small, and since the developer image can be faithfully formed on the electrostatic latent image on the image carrier, it has been put into practical use in recent years.

  In non-magnetic one-component contact development, after the toner layer thickness on the developer carrier is regulated to a fixed amount by the developer regulation member, the developer is conveyed to the development region near the contact portion with the electrostatic latent image carrier , Visualize the electrostatic latent image as a toner image.

  The toner in the developing device is subject to rubbing between the toners at the agitating portion and rubbing with the developer regulating member on the developer carrier, and also rubbing with the image carrier during development. Receive By repeating such rubbing, the toner in the developing device becomes different from the toner in the new state.

  Specifically, an external additive such as silica externally added to the toner surface is embedded in the toner particles themselves. Therefore, the toner is required to gradually change the performance such as fluidity and chargeability required as a developer. This phenomenon, that is, the change in physical properties of the toner, becomes more pronounced when the image forming operation is repeated many times.

  In order to cope with the embedding of such external additives, a large amount of external additives is coated on the toner base in advance to make it easy to disperse the stress on the external additives, and the external additives are embedded in the toner base. Can be considered.

  Further, Patent Document 1 discloses a toner having a surface layer containing an organosilicon polymer as a toner excellent in development durability. In the case of such a toner, since the toner particles are covered with the surface layer, the external force can be dispersed, and the development durability can be achieved without changing the surface property.

Unexamined-Japanese-Patent No. 2016-27399

  However, when the coverage of the external additive such as silica is high, if the toner surface is covered with the surface layer, it tends to be difficult to transfer the charge to the toner.

  As a result, in the developing device, a large amount of toner with a low charge amount is present, and the toner is also supplied to the developer carrier. However, the toner having a low charge amount is weak in electrostatic adhesion and hardly adheres to the developer carrier.

  As a result, when consumption is promoted by developing the toner on the developer carrier onto the image carrier, for example, when high density output such as a solid image is performed, a desired amount of toner on the developer carrier is obtained. It may be insufficient for In this case, a so-called solid follow-up defect tends to occur, in which the density decreases toward the rear end of the image.

  In order to achieve the above object, an image forming apparatus according to the present invention develops an image bearing member, a charging unit, and an electrostatic image formed on the image bearing member in contact with the image bearing member with a developer. The support, the application means for applying a developing bias to the development support, and the surface of the image support charged by the charging means are irradiated with light to form a bright area potential and a dark area potential. A latent image forming unit for forming an electrostatic image on an image carrier, the image carrier and the development carrier rotate at a peripheral speed ratio Δv, and the application unit A development bias is applied such that the potential difference between the potential of the surface of the image carrier at the movement destination portion and the development bias is the development contrast ΔV, and the developer carried by the development carrier is supplied to the image carrier In which the developer is caught in the nip where the When the capacitance between the image carrier and the development carrier in C is C, and the charge amount per unit area of the developer carried on the development carrier is Q / S, | Q / S × The relationship of Δv |> C × ΔV | holds, and the amount of the developer remaining on the development carrier after developing the developer from the development carrier to the image carrier is the value before the development. An image forming apparatus characterized in that it is 50% or more of the amount of developer carried on a development carrier.

  According to the present invention, good solid followability can be maintained even when a developer with a high coverage is used.

Schematic cross-sectional view of an image forming apparatus according to the present embodiment Block diagram of image forming apparatus according to the present embodiment Schematic cross-sectional view of a process cartridge according to the present embodiment Schematic diagram of the toner according to the present embodiment Relationship between developable amount, toner supply amount and circumferential speed according to the present embodiment Relationship between the amount of toner on the photosensitive drum and the density on the paper according to the present embodiment Relationship between development contrast and toner amount on photosensitive drum according to the present embodiment

  Hereinafter, with reference to the drawings, a mode for carrying out the present invention will be exemplarily described in detail based on examples. However, the dimensions, materials, shapes, relative positions, etc. of the components described in this embodiment are appropriately changed according to the configuration of the apparatus to which the present invention is applied and various conditions, so there is no particular description. As long as the scope of the invention is not limited to them, the scope of the invention is not limited thereto.

<Overall Schematic Configuration of Image Forming Apparatus>
First, the overall configuration of the electrophotographic image forming apparatus (image forming apparatus) according to the present invention will be described. FIG. 1 is a schematic cross-sectional view of an image forming apparatus 100 of the present embodiment. The image forming apparatus 100 of the present embodiment is a full-color laser printer adopting an in-line method and an intermediate transfer method. The image forming apparatus 100 can form a full color image on a recording material (for example, a recording sheet, a plastic sheet, a cloth or the like) according to image information. Image information is input to the image forming apparatus main body 100A from an image reading apparatus connected to the image forming apparatus main body 100A or a host device such as a personal computer communicably connected to the image forming apparatus main body 100A.

  The image forming apparatus 100 includes, as a plurality of image forming units, first, second, and third for forming an image of each color of yellow (Y), magenta (M), cyan (C), and black (K). , And fourth image forming units SY, SM, SC, and SK. In the present embodiment, the first to fourth image forming units SY, SM, SC, and SK are arranged in a line in a direction intersecting the vertical direction.

  In the present embodiment, the configurations and operations of the first to fourth image forming units SY, SM, SC, and SK are substantially the same except that the colors of the images to be formed are different. Therefore, hereinafter, in the case where distinction is not particularly required, subscripts Y, M, C, and K given to reference numerals to indicate that they are elements provided for any color are omitted, and collectively explain.

  In the present embodiment, the image forming apparatus 100 has four drum-shaped electrophotographic photosensitive members, ie, the photosensitive drums 1 arranged in parallel in the direction intersecting the vertical direction as a plurality of image carriers. The photosensitive drum 1 is rotationally driven by a drive unit (drive source) in the direction of the arrow A (clockwise direction). A charging roller 2 as charging means for uniformly charging the surface of the photosensitive drum 1 around the photosensitive drum 1, a laser is irradiated based on image information, and an electrostatic image (electrostatic A scanner unit (exposure device) 3 is disposed as an exposure unit that forms a latent image. Further, a developing unit (developing device) 4 as developing means for developing an electrostatic image as a toner image around the photosensitive drum 1, and toner remaining on the surface of the photosensitive drum 1 after transfer (transfer residual toner) A cleaning member 6 is disposed as a cleaning means for removing the In the drawing, the cleaning member 6 corresponds to a cleaning blade. Further, opposite to the four photosensitive drums 1, an intermediate transfer belt 5 as an intermediate transfer member for transferring the toner image on the photosensitive drum 1 onto the recording material 12 is disposed.

  In the present embodiment, the developing unit 4 uses a toner of a nonmagnetic one-component developer as a developer. Further, in this embodiment, the developing unit 4 performs reverse development by bringing a developing roller (described later) as a developer bearing member into contact with the photosensitive drum 1. That is, in the present embodiment, the developing unit 4 is a portion where the toner charged to the same polarity (in the present embodiment, the negative polarity) as the charging polarity of the photosensitive drum 1 is attenuated by the exposure on the photosensitive drum 1 ( The electrostatic image is developed by being attached to the image portion (exposure portion).

  In this embodiment, the photosensitive drum 1, and the charging roller 2, the developing unit 4 and the cleaning member 6 as process means acting on the photosensitive drum 1 are integrated, that is, integrally formed into a cartridge, A process cartridge 7 is formed. The process cartridge 7 is attachable to and detachable from the image forming apparatus 100 via mounting means such as a mounting guide and a positioning member provided on the image forming apparatus main body 100A. In the present embodiment, the process cartridges 7 for the respective colors all have the same shape, and yellow (Y), magenta (M), cyan (C), black (in the process cartridges 7 for the respective colors). The toner of each color of K) is stored.

  The intermediate transfer belt 5 formed of an endless belt as an intermediate transfer member abuts on all the photosensitive drums 1 and circulates (rotates) in a direction indicated by an arrow B (counterclockwise). The intermediate transfer belt 5 is stretched around a driving roller 51, a secondary transfer opposing roller 52, and a driven roller 53 as a plurality of supporting members.

  On the inner circumferential surface side of the intermediate transfer belt 5, four primary transfer rollers 8 as primary transfer means are arranged in parallel so as to face the respective photosensitive drums 1. The primary transfer roller 8 presses the intermediate transfer belt 5 toward the photosensitive drum 1 to form a primary transfer portion N1 in which the intermediate transfer belt 5 and the photosensitive drum 1 are in contact with each other. Then, from the primary transfer bias power source (high voltage power source) as primary transfer bias application means, a bias having a polarity opposite to the regular charging polarity of the toner is applied to the primary transfer roller 8. Thus, the toner image on the photosensitive drum 1 is transferred (primary transfer) onto the intermediate transfer belt 5.

  In addition, a secondary transfer roller 9 as a secondary transfer unit is disposed at a position facing the secondary transfer opposing roller 52 on the outer peripheral surface side of the intermediate transfer belt 5. The secondary transfer roller 9 is in pressure contact with the secondary transfer opposing roller 52 via the intermediate transfer belt 5 to form a secondary transfer portion N2 in which the intermediate transfer belt 5 and the secondary transfer roller 9 abut. Then, from the secondary transfer bias power source (high voltage power source) as secondary transfer bias application means, a bias having a polarity opposite to the regular charging polarity of the toner is applied to the secondary transfer roller 9. By this, the toner image on the intermediate transfer belt 5 is transferred (secondary transfer) to the recording material 12.

  More specifically, at the time of image formation, first, the surface of the photosensitive drum 1 is uniformly charged by the charging roller 2. Next, the charged surface of the photosensitive drum 1 is scan-exposed by a laser beam corresponding to the image information emitted from the scanner unit 3, and an electrostatic image according to the image information is formed on the photosensitive drum 1. Next, the electrostatic image formed on the photosensitive drum 1 is developed as a toner image by the developing unit 4. The toner image formed on the photosensitive drum 1 is transferred (primary transfer) onto the intermediate transfer belt 5 by the action of the primary transfer roller 8.

  For example, when forming a full color image, the above-described process is sequentially performed in the first to fourth image forming units SY, SM, SC, and SK, and toner images of respective colors are then superimposed on the intermediate transfer belt 5. Primary transfer.

  Thereafter, the recording material 12 is conveyed to the secondary transfer portion N2 in synchronization with the movement of the intermediate transfer belt 5. The four-color toner images on the intermediate transfer belt 5 are secondarily transferred collectively onto the recording material 12 by the action of the secondary transfer roller 9 in contact with the intermediate transfer belt 5 via the recording material 12.

  The recording material 12 to which the toner image has been transferred is conveyed to a fixing device 10 as a fixing unit. By applying heat and pressure to the recording material 12 in the fixing device 10, the toner image is fixed to the recording material 12.

  Further, the primary transfer residual toner remaining on the photosensitive drum 1 after the primary transfer process is removed and collected by the cleaning member 6. Further, secondary transfer residual toner remaining on the intermediate transfer belt 5 after the secondary transfer process is cleaned by the intermediate transfer belt cleaning device 11.

  The image forming apparatus 100 can also form single-color or multi-color images using only one desired image forming area or using only some (not all) image forming areas. It is supposed to be.

<Block Diagram of Image Forming Apparatus>
FIG. 2 shows a block diagram of the image forming apparatus 100 of this embodiment. A control unit 200 controls various peripheral devices. For example, the configuration of a central processing unit, a memory, an input / output I / F, etc., which are similar to known microcomputers for built-in devices is provided.

  The motors 201 to 203 are connected so as to be able to transmit the driving force to the corresponding driving mechanisms 204 to 206, respectively, and supply the rotational driving force to the members connected to the driving mechanisms. The blocks 220 to 225 correspond to the toner supply roller of each color, the developing roller, and the photosensitive drum described above.

  Reference numeral 210 corresponds to the exposure apparatus 3 described above, which is a scanner unit as an exposure unit / latent image formation unit for forming an electrostatic image (electrostatic latent image), or an LED array. The high-voltage power supply circuit 211 applies various high-voltage loads such as the charging bias, the primary transfer bias, and the secondary transfer bias described above to the connected members, thereby charging bias means, primary transfer bias application means, and It functions as a next transfer bias means.

<Schematic Configuration of Process Cartridge>
Next, the overall configuration of the process cartridge 7 mounted in the image forming apparatus 100 of the present embodiment will be described. In this embodiment, the configuration and operation of the process cartridge 7 for each color are substantially the same except for the type (color) of the toner contained.

  FIG. 3 is a schematic cross-sectional view (main cross-sectional view) of the process cartridge 7 of the present embodiment as viewed along the longitudinal direction (rotational axis direction) of the photosensitive drum 1. The attitude of the process cartridge 7 shown in FIG. 3 is an attitude in a state where the process cartridge 7 is mounted on the main body of the image forming apparatus, and when describing the positional relation and direction of each member of the process cartridge, the positional relation and direction in this attitude And so on.

  The process cartridge 7 is configured by integrating a photosensitive unit 13 including a photosensitive drum 1 and the like and a developing unit 4 including a developing roller 17 and the like.

  The photosensitive unit 13 has a cleaning frame 14 as a frame for supporting various elements in the photosensitive unit 13. The photosensitive drum 1 is rotatably attached to the cleaning frame 14 via a bearing (not shown). The photosensitive drum 1 is rotationally driven in the direction of an arrow A (clockwise) according to an image forming operation by transmitting the driving force of a driving motor as a driving means (driving source) to the photosensitive unit 13. . In the present embodiment, the photosensitive drum 1 which is the center of the image forming process is an organic photosensitive drum in which an undercoating layer which is a functional film, a carrier generation layer, and a carrier transfer layer are sequentially coated on the outer peripheral surface of an aluminum cylinder. 1 is used.

  Further, in the photosensitive unit 13, the cleaning member 6 and the charging roller 2 are disposed in contact with the circumferential surface of the photosensitive drum 1. The transfer residual toner removed from the surface of the photosensitive drum 1 by the cleaning member 6 falls into the cleaning frame 14 and is accommodated.

  The charging roller 2, which is a charging unit, is driven to rotate by pressing a roller portion of conductive rubber against the photosensitive drum 1.

  Here, a predetermined DC voltage is applied to the photosensitive drum 1 as a charging step to the core metal of the charging roller 2, whereby the surface potential of the photosensitive drum 1 is uniformly darkened (Vd). Is formed. The spot pattern of the laser beam emitted corresponding to the image data by the laser beam from the scanner unit 3 described above exposes the photosensitive drum 1, and the exposed portion has the charge on the surface by the carrier from the carrier generation layer. It disappears and the potential drops. As a result, an electrostatic latent image having a predetermined bright area potential (V1) at the exposed area and a predetermined dark area potential (Vd) at the unexposed area is formed on the photosensitive drum 1. In this embodiment, Vd = -500V and Vl = -100V.

<Description of developing unit>
On the other hand, the developing unit 4 has a developing roller 17 as a developer carrier for carrying the toner 40 and a developing chamber in which a toner supply roller 20 as a supply member for supplying the toner to the developing roller 17 is disposed. doing. Further, the developing unit 4 is provided with a toner storage chamber 18 having a toner storage portion (developer storage portion) 18 a for storing toner, in the direction of gravity below the toner supply roller 20.

  In the toner storage chamber 18, a stirring and conveying member 22 is provided. The stirring and conveying member 22 is also for stirring the toner stored in the toner storage chamber 18 and transporting the toner toward the upper portion of the toner supply roller 20 in the direction of the arrow G in the drawing. In the present embodiment, the stirring and conveying member is driven to rotate at 60 rpm.

  The developing roller 17 and the photosensitive drum 1 rotate so that the respective surfaces thereof move in the same direction (in the present embodiment, from the bottom to the top) in the facing portion.

  Then, due to the potential difference with the developing bias at the developing nip portion where the toner negatively charged due to frictional charging comes into contact with the photosensitive drum 1 by a predetermined DC bias (developing bias) applied to the developing roller 17 It transfers only to the potential portion to visualize the electrostatic latent image. The potential difference between the developing bias and the light portion potential portion at this time is called developing contrast. The setting of the development contrast and the development bias will be described later. The toner supply roller 20 and the developing roller 17 rotate in the direction in which the respective surfaces move from the upper end to the lower end of the nip portion N. That is, the toner supply roller 20 rotates in the direction of arrow E (clockwise direction), and the developing roller 17 rotates in the direction of arrow D (counterclockwise direction). The toner supply roller 20 is an elastic sponge roller in which a foam layer is formed on the outer periphery of a conductive cored bar. The toner supply roller 20 and the developing roller 17 are in contact with each other with a predetermined penetration amount ΔE.

  The toner supply roller 20 and the developing roller 17 are rotated in the same direction at the nip portion N with a peripheral speed difference, and the toner supply roller 20 supplies toner to the developing roller 17 by this operation. . At this time, the amount of toner supplied to the developing roller can be adjusted by adjusting the potential difference between the toner supply roller and the developing roller.

  In the present embodiment, both the developing roller 17 and the toner supply roller 20 have an outer diameter of 15 mm. Further, the amount of toner supply roller 20 entering the developing roller 17, that is, the amount of depression ΔE with which the toner supply roller 20 is made concave by the developing roller 17 is set to 1.0 mm. Further, the toner supply roller and the developing roller are disposed so that the height (position) of the center is the same.

<Details of Toner>
The toner of the present invention desirably has a toner surface coverage of 80% or more by the external additive or surface layer. When the surface coverage is 80% or more, when external stress is applied to the toner, more external additives are subjected to external force and the stress is dispersed. This makes it difficult for the external additive to be embedded in the toner matrix. On the other hand, when the surface coverage is less than 80%, the stress applied to the external additive is difficult to disperse because the amount of external additive that receives stress is small, and the toner is embedded in the toner base after many times of image forming operation. Is more likely to occur. This is considered to be a major cause of deterioration in fog during repeated image formation. The phenomenon in which the toner adheres to the non-image area which should be white spots by development of the developer and the density becomes high is generally referred to as fogging.

  In addition, when the inventors conducted experiments by changing the surface layer several times under the same conditions of coverage, it was found that the organosilicon polymer toner having the surface layer containing the organosilicon polymer is preferable I understand. Since the surface of the toner particles is covered with the surface layer having a wide area, the external force can be dispersed over the wide area, and the embedding in the toner base can be further suppressed.

  A schematic view of the toner used in this embodiment is shown in FIG. In this embodiment, an inorganic particle external additive toner 45 obtained by externally adding silica 45b (organic silica polymer) as an external additive to a mother particle 45a, and an organosilicon having a surface layer 46b containing an organosilicon polymer in a mother particle 46a. A polymer toner 46 is used. The details and the production method of the mother particles 45a are as described in JP-A-2016-38591, and the mother particles 46a are as described in JP-A-2016-27399.

For the toners a to b, the toner 45 manufactured according to the description of JP-A-2016-38591 is used, and the silica (SiO ₂ ) coverage is set to 80, 95%. The adhesion rate of silica was changed by using an Henschel mixer (manufactured by Nippon Coke Industry Co., Ltd.) and changing the amount of external addition and the peripheral speed and time which are external addition conditions. Table 1 below shows the external addition conditions of the toners a and b and the adhesion rate of the silica particles. In addition, the detail about the circumferential speed which is external addition conditions and time is as description of Unexamined-Japanese-Patent No. 2016-38591.

  As the toner c, the toner 46 manufactured according to the description of Example 1 of JP-A-2016-27399 was used. The toner c is covered with a surface layer containing an organosilicon polymer as shown in FIG. 4 (b).

  In the present example, the coverage of the organosilicon polymer is set to 95%, and is set by adjusting the polymerization conditions of the particles. Table 2 shows the polymerization conditions and the coverage. About polymerization conditions, it follows the description of Example 1 of Unexamined-Japanese-Patent No. 2016-27399.

  In addition, although the measurement of the coverage of toner ac is applicable to various well-known measurement methods, in this example, the measurement was carried out according to the description of paragraph 29 to paragraph 30 of JP 2013-152460 A .

  According to these experiments, the inventor found that when the surface coverage of the toner is high, it is possible to suppress the burying of the external additive and the surface layer due to the paper passage durability, but on the other hand, the charge transfer of the toner becomes difficult. If the charge transfer is difficult, the transfer of charge due to rubbing between the toners decreases, and it becomes difficult to obtain the charge from the toner supply roller 20 and the developing blade 21, so the charge amount of the toner is considered to be suppressed low. . However, it was found that the toner having a low charge amount had a tendency to weaken the electrostatic adhesion and to be hard to adhere to the developer carrier.

  As a result, when consumption is promoted by developing the toner on the developing roller 17 when high density output such as a solid image is performed, the toner on the developing roller 17 is insufficient for a desired amount There is. In this case, as described in Table 4, a so-called solid follow-up failure occurs in which the density decreases toward the rear end of the image.

  In the toners a to c used in this embodiment, the toner amount per unit area on the developing roller 17 (hereinafter referred to as M / S) and the charge amount of toner per unit area (hereinafter referred to as Q / S) The setting of the developing blade 21 was adjusted so as to maximize the charge amount. The results are shown in Table 3.

  In this state, when a solid image is developed which develops all the toner on the developing roller 17, the following M / S and Q / S on the developing roller 17 immediately after outputting the solid image are determined as shown in Table 4. It became so. When a solid image is printed, it can be understood that the toner on the developing roller 17 is insufficient.

<Description of development efficiency>
First, the development efficiency is defined as follows: Development efficiency = (A−B) / A × 100 (%). A and B are as follows.
A = Developer amount per unit area of the developing roller surface in the developing blade 21 (developer amount regulating member) upstream of the developing roller and photosensitive drum nip B = developing roller downstream of the developing roller and photosensitive drum The amount of developer per unit area of the developing roller surface upstream of the toner supply roller nip The inventors set the developing efficiency to less than 100% while trying to find a method to suppress the solid following property by trial and error in the experiment. By doing this, I learned that there is a tendency to improve the solid tracking failure. This is because the toner remains on the developing roller 17 after development, and the charge amount of the remaining toner works to attract the toner supplied to the developing roller 17, and the toner supply following property to the developing roller 17 is improved. Conceivable.

  In order to further confirm this effect, the toner a was used to confirm the relationship between the development efficiency and the degree of density unevenness caused by poor solid followability. Table 5 shows the results. The inventors set the development contrast so that the density is 1.45 when the development efficiency is 100%, and the circumferential speed ratio between the photosensitive drum 1 and the developing roller 17 (hereinafter simply referred to as "circumferential speed ratio" The development efficiency was adjusted by changing. With regard to density unevenness, five sheets of solid black images were printed continuously on an A4 size sheet, and the presence or absence of density unevenness at that time was confirmed. More specifically, the density of the entire solid black image formed at the four corners of A4 paper is measured with a densitometer, and density unevenness is determined by the difference between the maximum density and the minimum density. If the density unevenness in a page is 0.1 or less in all five sheets, "○", if the density unevenness is 0.15 or less in all five sheets, "Δ", even if one sheet is uneven in density 0.15 If it exceeds, it was considered as "x". The circumferential speed ratio is one index that expresses the difference in rotational speed between the photosensitive drum 1 and the developing roller 17. For example, similar circumferential speeds may be calculated using the circumferential speed difference as an index instead of the circumferential speed ratio. It goes without saying that you can.

  From the above results, the inventors found that as the development efficiency is lowered, the density unevenness caused by the solid following property failure is improved. The inventors obtained from experimental results that good results can be obtained particularly when the development efficiency is 50% or less. This is considered to be because, when the developing roller 17 carries twice or more of the toner amount to be developed, the desired coat amount on the developing roller 17 can be achieved even if the newly supplied toner is small. Therefore, in the present embodiment, the peripheral speed ratio is set so that the development efficiency is 50% or less.

  Next, a method of leaving development residual toner will be described with reference to FIG. FIG. 5 shows the relationship between the developable amount of toner, the amount of toner supplied from the developing roller 17 and the peripheral speed.

  The developable amount of the toner developed by the development contrast in the bright part is (i) the electrostatic capacity (C) between the photosensitive drum 1 and the development roller 17 in the development part carrying the toner and (ii) the development contrast (ΔV) It is decided by the product of That is, C × ΔV represents the total amount of charged electric charge of toner per unit area that can be developed from the developing roller 17 to the photosensitive drum 1 at the developing nip portion (straight line 1 in FIG. 5). Here, the developing nip portion is a portion where the toner carried by the photosensitive drum 1 is supplied to the developing roller 17, and the photosensitive drum 1 and the developing roller 17 are formed facing each other. Further, the total amount of charge of the toner supplied to the photosensitive drum 1 is determined according to the charge amount (Q / S) per unit area on the developing roller 17 and the peripheral speed ratio (Δv) to the photosensitive drum 1. It is represented by the product of Q / S × Δv (straight line 2 in FIG. 5).

  Therefore, when Q / S × Δv ≦ C × ΔV, the total charge amount of the toner supplied from the developing roller 17 is smaller than the charge amount that the photosensitive drum 1 can receive, so the toner on the developing roller 17 is photosensitive. The condition is that all development is performed on the drum 1. At this time, the toner charge amount Q / S × Δv on the drum is obtained.

Conversely, when Q / S × Δv> C × ΔV, the total charge amount of the toner supplied from the developing roller 17 is larger than the charge amount that the photosensitive drum 1 can receive. Therefore, after the toner on the developing roller 17 is developed on the photosensitive drum 1, a part of the toner remains on the developing roller 17 (on the developing carrier). When the above inequality holds, the toner charge amount on the drum is C × ΔV. There are various ways of obtaining the capacitance C, but in the present embodiment, the following was done to obtain the effective C. The fact that Q / S × Δv = C × ΔV holds is that q / s (or M / S) on the drum does not increase by increasing the circumferential speed ratio Δv while fixing to a certain development contrast . Therefore, the capacitance C can be obtained by using Δv and ΔV at that time and Q / S in Table 2. When the development contrast of the toner a according to this embodiment is 140 V, the circumferential speed ratio Δv is 110%, and q / s (the amount of charge per unit area) on the drum does not increase. Therefore, when the capacity C was obtained, it was C = 9.5 × 10 ⁻⁷ .

<Development contrast, setting of circumferential speed ratio Δv>
The following describes the setting of the peripheral speed ratio Δv using the toner a. The other toners are set in the same manner.

(5) Setting of development contrast From the above conditions, when the setting of development efficiency less than 100% (Q / S × Δv> C × ΔV), the toner amount on the photosensitive drum 1 is determined by the charge amount C × ΔV which the photosensitive drum can receive. Since the image forming density is determined by the amount of toner on the photosensitive drum 1, the development contrast ΔV is determined by the desired density.

FIG. 6 shows the toner amount [kg / m ² ] from the developing roller 17 to the photosensitive drum 1 and the image forming density characteristic. In order to obtain a density of 1.45 (Macbeth RD-918) generally required for office documents, it is understood that a toner amount of about 0.0038 [kg / m ² ] is required on the photosensitive drum 1.

  FIG. 7 shows the relationship between the development contrast of the toner a and the toner amount of the photosensitive drum 1.

As the development contrast is increased, the amount of toner on the photosensitive drum 1 is increased. Further, it can be seen from FIG. 7 that the increase in the supply amount is slowed down from around a certain development contrast depending on the peripheral speed ratio. This indicates that the developing efficiency is 100% and all the toner on the developing roller 17 set in Table 3 has been developed. As described in FIG. 6, it is now assumed that the toner amount 0.0038 [kg / m ² ] for obtaining the density 1.45 required in the office document. It can be understood from FIG. 7 that in order to set the M / S on the drum to 0.0038 [kg / m ² ], it is necessary to set the development contrast 140 V. Therefore, in order to obtain development contrast 140V, development bias was set to -240V.

(2) Setting of the peripheral speed ratio As described above, in the relationship of Q / S × Δv> C × ΔV, development residual can be left if Δv> 110% is set. In this embodiment, the developing efficiency is 50% or less (50% or more of the toner amount (developer amount) carried on the developing roller before the development at the developing nip). The relationship between the peripheral speed ratio and the development efficiency was determined by experiments. The relationship between the peripheral speed ratio of the toner a and the development efficiency and the remaining amount of development is as shown in Table 6 below. From the results of Table 6, in the toner a, the circumferential speed ratio was set to 210% or more.

<Content of experiment>
In this example, using toners a to c, the development efficiency was adjusted by swinging some of the peripheral speed ratios, and the degree of the solid density unevenness caused by the followability defect was confirmed.

  When the peripheral speed ratio is too high, the development residue on the developing roller 17 increases, the number of times of toner rubbing between the developing roller 17 and the photosensitive drum 1 increases, and toner deterioration may occur. In the present embodiment, therefore, the degree of fogging caused by toner deterioration was confirmed.

  In the present example and the comparative example, five sheets of solid black images were printed continuously using A4 size paper, and the presence or absence of solid density or density unevenness at that time was confirmed. In addition, solid density is measured by measuring the four corners of A4 paper with a densitometer, and if the density unevenness within a page is 0.1 or less, the visibility is low, so "O", and the others are "O". × ".

  Also, to check the influence on development durability, after intermittently passing 15000 sheets at a 4% printing rate (for example, stop the image forming apparatus after printing 2 sheets, then print 2 sheets again and repeat this printing operation And the presence or absence of fogging due to toner deterioration. For measurement of fog, use a reflection densitometer DENSITOMETER (TC-6DS / A30) and subtract the density of the reflection of the original paper (white part of the paper before image formation) from the density of the white part of the paper after image formation Expressed in%. If the fogging value is within 1.0%, “” ”is within 3%,“ 〇 ”, and the others are“ × ”. The measurement was performed in an environment of 23 ° C. and 50% RH.

Comparative Example 1
As Comparative Example 1, the same experiment as that of this example was conducted using the toners of toners a to c and at a peripheral speed ratio at which the development efficiency is higher than 50%.

Comparative Example 2
As Comparative Example 2, the same experiment as in this example was conducted using toner d having a lower coverage than the toner in the example.

As the toner d, the toner 45 manufactured according to the description of JP-A-2016-38591 is used, and the silica (SiO ₂ ) coverage is set to 70%. The adhesion rate of silica was changed by using an Henschel mixer (manufactured by Nippon Coke Industry Co., Ltd.) and changing the amount of external addition and the peripheral speed and time which are external addition conditions. Table 7 below shows the external addition conditions of toner d and the adhesion rate of silica particles. In addition, the detail about the circumferential speed which is external addition conditions and time is as description of Unexamined-Japanese-Patent No. 2016-38591.

  In the toner d used in the comparative example, M / S on the developing roller 17 and Q / S per unit area were set. It is shown in Table 8 below.

<Confirmation of effect>
The results are shown in Table 9. As shown in Table 9, in the configuration of the example, the density unevenness level in the page was also a good result while maintaining each density. Further, in any toner of the embodiment, the fogging value is also good between the circumferential speed ratio of 220% to 280%, and deterioration due to sheet passing can be suppressed. In particular, the toner d covered with the surface layer containing the organosilicon polymer has a fog value of less than 1.0% up to a peripheral velocity ratio of 250%, and can be extremely suppressed from being deteriorated.

  On the other hand, in Comparative Example 1 (the peripheral speed ratio in which the development efficiency is higher than 50%) which is a conventional example, the follow-up defect can not be suppressed, and density unevenness occurs. Specifically, when the development efficiency is 55%, the amount of developer carried on the development roller is equal to that after the second and third images are formed, as compared to the case where the development efficiency is less than 50%. It will decrease. When the development efficiency exceeds 50%, the amount of developer not transferred to the photosensitive drum on the development roller is smaller than that in the case of less than 50% development efficiency, which is considered to cause solid density unevenness.

  Further, in Comparative Example 2 in which toner d having a low coverage was used, the uneven density was good even when the development efficiency slightly exceeded 50%. However, when the circumferential speed ratio is 180% or more, the fogging value exceeds 3%, the toner is deteriorated, and it is not possible to achieve both density unevenness and durability. This is because the developer remaining amount on the developing roller is increased by lowering the developing efficiency, the number of times the toner remaining on the developing roller is rubbed against the developing blade 21 is increased, and the developer coverage may be low. The reason is considered to be that the toner has deteriorated.

  Generally, when using a developer with a high coverage rate, the problem of fogging is eliminated, but the charge amount is low and the adhesion of the developer to the developer carrier is weak, so that the toner supply amount is insufficient. As a result, the problem of poor follow-up in solidity occurs. However, in the configuration of the present embodiment, when a large amount of developer in a cartridge such as a solid image is used in a short period, the adhesion of the developer to the developing roller 17 is high using the developer with a high coverage. Even when it is weak, it has become possible to obtain concentration stability. This is because, as shown in the graph of FIG. 5, by making the peripheral speed ratio high, the amount of charge that can be supplied by the developing roller becomes excessive, leaving a large amount of residual developer on the developing roller, and insufficient developer supply. It is because it resolved. More specifically, in the process where new toner adheres to the developing roller 17, if there is developing residual toner to which charge has been applied, the new toner is attracted to the electric charge of the residual developing toner, and development is performed from the toner supply roller 20. Adhesion to the roller 17 proceeds. It is considered that this makes it difficult to cause uneven density. Further, in the present embodiment, since the toner having the coverage of 80% or more is used, the stress related to the toner surface layer can be easily dispersed, the change in durability of the toner can be suppressed, and the degree of fogging can be made favorable. That is, in the present embodiment, by using a toner having a coverage of 80% or more, the development efficiency is reduced by increasing the peripheral speed ratio and contained within 50% (the remaining amount of toner is increased). Both concentration stability can be achieved. The setting conditions used in the description of the present embodiment are also an example and not limited thereto.

  In the first embodiment, the developing method of the developer has been described by way of an example of the reversal developing method in which the developer is moved to the surface portion of the photosensitive drum having the bright portion potential (Vl). However, the present invention is not limited to this. The present invention is also applicable to a developing method in which the potential of the photosensitive drum surface (the surface of the image carrier) at the movement destination portion of the developer is the dark area potential, that is, the normal developing method. In the case of reversal development, the principle is the same as in the case of normal development, but in the case of normal development, the difference between the development bias and the dark area potential (development contrast) is | Q / S × Δv |> | C × ΔV It applies to ΔV in the relation of |. The other configuration is the same as that of the first embodiment, and thus the detailed description is omitted.

  As can be seen from the experimental results in Table 9, the peripheral speed ratio (ratio) at which the fogging deterioration is observed differs depending on the degree of coverage. In Table 9, Toner a (80% coated area), Toner b (90% coated area), Toner c (95% coated area), the circumferential speed ratio at which the deterioration of the fog is seen as the coverage increases is different. There is. That is, the photosensitive drum 1 and the developing roller 17 may be rotated at a circumferential speed ratio Δv corresponding to the coverage. More specifically, various control units (motors) may be controlled by the control unit 200 of the image forming apparatus 100 at a peripheral speed ratio Δv corresponding to the coverage. For the developer coverage, for example, information on the developer coverage is stored in a non-volatile memory tag provided in the process cartridge for each color, and the controller 200 reads the information, and the controller 200 reads the information. The peripheral speed ratio Δv is set in accordance with the calculated coverage. More specifically, the control unit 200 sets a higher peripheral speed ratio as the coverage rate is higher, and drives each member. The other configuration is the same as that of the first embodiment, and thus the detailed description is omitted.

Reference Signs List 1 photosensitive drum 2 charging roller 4 developing unit 5 intermediate transfer belt 6 cleaning member 7 process cartridge 8 primary transfer roller 9 secondary transfer roller 10 fixing device 11 intermediate transfer belt cleaning device 12 recording material 13 photosensitive unit 14 cleaning frame 17 Developing roller 18 toner storage chamber 20 toner supply roller 21 developing blade 22 stirring conveyance member 40 toner 45 inorganic particle external added toner 46 organosilicon polymer toner 51 drive roller 52 secondary transfer opposite roller 53 driven roller

Claims (9)

An image forming apparatus,
An image carrier,
Charging means,
A development carrier which develops the electrostatic image formed on the image carrier in contact with the image carrier with a developer;
Application means for applying a development bias to the development carrier;
The latent image forming unit is configured to form an electrostatic image on the image carrier by irradiating light to the surface of the image carrier charged by the charging unit to form a light portion potential and a dark portion potential.
The image carrier and the development carrier rotate with a peripheral speed ratio Δv,
The application means applies a development bias so that the potential difference between the potential of the surface of the image carrier and the development bias at the movement destination portion of the developer becomes a development contrast ΔV.
The electrostatic capacity between the image carrier and the development carrier in a state where the developer is nipped by the nip portion where the developer carried by the development carrier is supplied to the image carrier is When the charge amount per unit area of the developer carried on the development carrier is Q / S,
The relationship of | Q / S × Δv |> | C × ΔV | holds.
The remaining amount of the developer on the development carrier after developing the developer from the development carrier to the image carrier is 50% or more of the amount of developer carried on the development carrier before development. An image forming apparatus characterized by   The image forming apparatus according to claim 1, wherein a coverage of the developer is 80% or more.   The image forming apparatus according to claim 2, wherein the developer having a coverage of 80% or more has a coverage of 80% or more with an external additive.   3. The image forming apparatus according to claim 2, wherein the developer having a coverage of 80% or more is a developer having toner particles having a surface layer containing an organic silica polymer.   The electric potential of the image carrier surface of the movement destination portion of the developer is a light portion electric potential to which the light is irradiated or a dark portion electric potential to which the light is irradiated. An image forming apparatus according to claim 1. With the development room,
A storage chamber disposed below the developing chamber to store the developer;
A transport member for transporting the developer contained in the storage chamber to the developing chamber;
The image forming apparatus according to any one of claims 1 to 5, wherein the transport member transports the developer from the storage chamber to the developing chamber.   The image forming apparatus according to any one of claims 1 to 5, wherein a peripheral speed ratio of the developer carrier to a peripheral speed of the image carrier is set by a coverage of the developer. An image carrier, a charging unit, a developer carrier for developing an electrostatic image formed on the image carrier in contact with the image carrier with a developer, and an application for applying a development bias to the developer carrier Means,
The latent image forming unit is configured to form an electrostatic image on the image carrier by irradiating light onto the surface of the image carrier charged by the charging unit to form a light portion potential and a dark portion potential. An image forming method in a forming apparatus,
The image carrier and the development carrier rotate with a peripheral speed ratio Δv,
The application means applies a development bias so that the potential difference between the potential of the surface of the image carrier and the development bias at the movement destination portion of the developer becomes a development contrast ΔV.
The electrostatic capacity between the image carrier and the development carrier in a state where the developer is nipped by the nip portion where the developer carried by the development carrier is supplied to the image carrier is When the charge amount per unit area of the developer carried on the development carrier is Q / S,
The relationship of | Q / S × Δv |> | C × ΔV | holds, and the residual amount of the developer on the development carrier after developing the developer from the development carrier to the image carrier is And 50% or more of the amount of developer carried on the development carrier prior to development. Light is irradiated to the surface of the image carrier charged by the image carrier, charging means, application means for applying a developing bias to the development carrier, and an electrostatic image is formed on the image carrier. And a latent image forming unit to be formed on the image forming apparatus.
And a development carrier for developing the electrostatic image formed on the image carrier in contact with the image carrier with a developer.
The image carrier and the development carrier rotate with a peripheral speed ratio Δv,
The application means applies a development bias so that the potential difference between the potential of the surface of the image carrier and the development bias at the movement destination portion of the developer becomes a development contrast ΔV.
The electrostatic capacity between the image carrier and the development carrier in a state where the developer is nipped by the nip portion where the developer carried by the development carrier is supplied to the image carrier is When the charge amount per unit area of the developer carried on the development carrier is Q / S,
The relationship of | Q / S × Δv |> | C × ΔV | holds, and the residual amount of the developer on the development carrier after developing the developer from the development carrier to the image carrier is And 50% or more of the amount of developer carried on the development carrier before development.

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