JP2006163098A - Developing roller, developing device, process cartridge and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing roller capable of reliably suppressing occurrence of defects on an output image, such as pitch unevenness and density unevenness and toner sticking on a sleeve surface, and capable of stably scooping up a developer over time, and to provide a developing device, a process cartridge and an image forming apparatus. <P>SOLUTION: The sleeve 23a2 of the developing roller 23a is formed so that its peripheral surface becomes an irregularly uneven surface. The peripheral surface of the sleeve 23a2 is provided with a surface roughness Rz in roughness profile within a range of 5-20 μm and the number of depressed portions of ≥1 μm depth is set to a range of 1-5 per 0.2 mm measured length. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an electrophotographic method such as a copying machine, a printer, a facsimile machine, or a multifunction machine thereof, a developing roller installed therein, a developing device and a process cartridge provided with the developing roller. In particular, the present invention relates to a developing roller, a developing device, a process cartridge, and an image forming apparatus using a two-component developer composed of a toner and a carrier.

Conventionally, in an image forming apparatus such as a copying machine or a printer, a developing device containing a two-component developer composed of a non-magnetic toner and a magnetic carrier (including a case where an external additive or the like is added) is often used. (For example, refer to Patent Document 1).
In such a two-component developing type developing apparatus, a developing roller having a magnet and a sleeve is opposed to an image carrier (photosensitive drum), and a developer is carried on the developing roller to form an image on the image carrier. The latent image formed in step 1 is developed.

  As described above, the developing roller having an important function in the image forming process is generally formed with an uneven surface on the surface of the sleeve in order to improve the transportability and pumping performance with respect to the developer. Specifically, the sleeve surface of the developing roller is roughened by sandblasting or the like to form a relatively irregular and fine irregular surface on the sleeve surface, and a plurality of circumferential directions on the sleeve surface by drawing or the like. A technique is known in which a groove is provided to form a regular uneven surface on the sleeve surface.

On the other hand, in Patent Document 1 and the like, a polygon is formed on a sleeve surface provided with a conductive resin film, a metal treatment layer, or the like for the purpose of preventing toner from sticking to the roughened sleeve surface (uneven surface). A technique for forming a plurality of ridge line protrusions and forming fine irregularities therearound is disclosed.
Further, in Patent Document 2, etc., for the purpose of preventing the wax component in the polymerized toner from adhering to the blasted sleeve surface, the surface roughness Rz of the sleeve surface is set to 4 to 20 μm, and the average interval of the irregularities A technique for setting Sm to 30 to 80 μm is disclosed.

JP-A-8-160736 JP 2000-10336 A

  The conventional developing roller has problems such as problems in the output image such as pitch unevenness and density unevenness, and cannot sufficiently prevent the toner from adhering to the sleeve surface, or the developer cannot be pumped stably over time. It was.

The shape of the sleeve surface of the developing roller (the outer peripheral surface of the sleeve) greatly contributes to the image quality of the output image, developer transportability / pumping property, toner adhesion to the sleeve surface, and the like.
When a plurality of grooves are provided on the surface of the sleeve of the developing roller by drawing or the like, the ability to draw the developer onto the sleeve is unlikely to deteriorate over time. On the other hand, when the pitch between the grooves is relatively large, groove pitch unevenness (pitch unevenness) may occur on the output image. Further, unevenness that coincides with the rotation period of the developing roller may occur due to the deviation of the groove pitch.
In summary, the developing roller subjected to the groove processing has a small margin with respect to pitch unevenness although the variation with time of the pumping amount is small.

On the other hand, when the surface of the sleeve of the developing roller is roughened by sandblasting or the like, there is a problem that the pumping property is deteriorated with time although the pitch unevenness is not generated and the initial image quality is excellent.
This is because the surface of the sleeve that has been roughened is worn over time due to friction with the developer, and the developer slides on the sleeve surface in which the level difference of the unevenness is reduced. In addition, over time, the toner is fused to the surface of the carrier, the charging ability is reduced, and the friction coefficient is reduced, so that the pumping performance is reduced.
Further, since the unevenness is finer in the rough surface processing than in the groove processing, it is easy for the toner to adhere to the concave portion over time. As a result, even when the initial image quality is good, the image quality often deteriorates over time.
In summary, although the development roller subjected to the rough surface processing does not cause pitch unevenness, the pumping amount varies with time and the margin for toner fixation is small.

  On the other hand, the technique disclosed in Patent Document 1 is to form a plurality of polygonal ridge line protrusions on the surface of a multilayer sleeve provided with a conductive resin film, a metal treatment layer, etc., and to form fine irregularities around it. And the manufacturing process was complicated. Further, the uneven surface of the sleeve surface formed through such a complicated process is extremely fine, and a sufficient effect of suppressing toner sticking to the recess over time cannot be expected.

  Further, in the technique of Patent Document 2 or the like, in order to form a relatively smooth uneven surface on the sleeve surface, the surface roughness Rz of the sleeve surface is 4 to 20 μm, and the average interval Sm of the unevenness is 30 to 80 μm. However, since it is not possible to obtain a smooth concavo-convex surface necessary for suppressing toner fixation simply by defining the surface roughness Rz and the average interval Sm, it is sufficient to suppress toner adhesion to the recesses over time. The effect cannot be expected.

  The present invention has been made to solve the above-described problems, and can reliably prevent problems on the output image such as pitch unevenness and density unevenness and toner sticking to the sleeve surface. It is an object of the present invention to provide a developing roller, a developing device, a process cartridge, and an image forming apparatus that can stably draw up.

The inventor of the present application has made researches to solve the above-described problems, and as a result, has come to know the following matters.
That is, in order to suppress the occurrence of pitch unevenness, it is necessary to form irregular irregular surfaces on the outer peripheral surface of the sleeve by roughening. By forming irregular irregular surfaces smoothly, toner adhesion to the sleeve surface is suppressed. Furthermore, by forming irregular irregular surfaces smoothly, wear on the sleeve surface itself is reduced, and damage to the developer conveyed on the sleeve surface (surface wear) is also reduced. The developer can be pumped up stably.
This irregular and smooth optimal irregular surface shape defines the surface roughness Rz (ten-point average roughness) and the number per unit length of recesses having a depth of 1 μm or more in the roughness profile. By doing so, it can be realized.

  The present invention is based on the above-described matters. That is, the developing roller according to the first aspect of the present invention develops a latent image formed on the image carrier facing the image carrier. A developing roller that has a plurality of fixed magnetic poles, and a sleeve that includes the magnet and carries a developer composed of toner and a carrier and relatively rotates around the magnet. The sleeve is formed such that an outer peripheral surface thereof is an irregular uneven surface, and the outer peripheral surface has a surface roughness Rz in a roughness profile in a range of 5 to 20 μm and a depth of 1 μm. The number of the concave portions is formed so as to be in the range of 1 to 5 per measurement length of 0.2 mm.

  The developing roller according to a second aspect of the present invention is the developing roller according to the first aspect, wherein the concave portion having a depth of 1 μm or more on the outer peripheral surface is conical or polygonal and has an apex angle. Is formed to be 90 degrees or more.

The developing roller according to a third aspect of the present invention is the developing roller according to the first or second aspect, wherein the outer peripheral surface has a pitch between adjacent ones of the recesses having a depth of 1 μm or more. Assuming that the average value of the pitch is P ₀ and the average particle diameter of the carrier is D,
P ₀ /3<D<P/0.7
It is formed so that the following relationship is established.

  According to a fourth aspect of the present invention, there is provided the developing roller according to any one of the first to third aspects, wherein the gap with the image carrier is in the range of 0.1 to 0.4 mm. Is to be installed.

  A developing roller according to a fifth aspect of the present invention is the developing roller according to any one of the first to fourth aspects, wherein the sleeve is formed of a nonmagnetic material.

  A developing roller according to a sixth aspect of the present invention is the developing roller according to any one of the first to fifth aspects, wherein the carrier is formed so that an average particle diameter is in a range of 20 to 50 μm. It is a thing.

  A developing roller according to a seventh aspect of the present invention is the developing roller according to any one of the first to sixth aspects, wherein the carrier is a resin-coated film formed on a magnetic core material. The resin coat film is obtained by adding a charge adjusting agent to a resin component obtained by crosslinking a thermoplastic resin and a melamine resin.

  The developing roller according to an eighth aspect of the present invention is the toner composition according to any one of the first to seventh aspects, wherein the toner comprises at least a prepolymer, a colorant, and a release agent. The toner composition is dispersed together with resin fine particles in an aqueous medium, and the toner composition is subjected to a polyaddition reaction.

  A developing device according to a ninth aspect of the present invention includes the developing roller according to any one of the first to eighth aspects, and accommodates the developer.

  A process cartridge according to a tenth aspect of the present invention is a process cartridge that is detachably installed on a main body of an image forming apparatus, and the developing device according to the ninth aspect and the image carrier It is an integrated body.

  An image forming apparatus according to an eleventh aspect of the present invention includes the developing device according to the ninth aspect and the image carrier.

  In the present application, the “process cartridge” refers to a charging unit that charges the image carrier, a developing device (developing unit) that develops a latent image formed on the image carrier, and a cleaning on the image carrier. It is defined as a unit in which at least one of the cleaning units and the image carrier are integrated and configured to be detachable from the image forming apparatus main body.

  Since the present invention optimizes the shape of the uneven surface formed on the outer peripheral surface of the sleeve in the developing roller, problems on the output image such as pitch unevenness and density unevenness and toner sticking to the sleeve surface are surely suppressed. Thus, it is possible to provide a developing roller, a developing device, a process cartridge, and an image forming apparatus in which the developer can be pumped up stably over time.

Embodiment.
Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

First, the configuration and operation of the entire image forming apparatus will be described with reference to FIG.
In FIG. 1, 1 is an apparatus main body of a color copying machine as an image forming apparatus, 2 is a writing section (exposure section) that emits laser light based on input image information, and 20Y, 20M, 20C, and 20BK are colors (yellow, magenta). , Cyan, and black), 21 is a photosensitive drum as an image carrier accommodated in each of the process cartridges 20Y, 20M, 20C, and 20BK, 22 is a charging unit that charges the photosensitive drum 21, Reference numerals 23Y, 23M, 23C, and 23BK denote developing devices (developing units) that develop the electrostatic latent image formed on the photosensitive drum 21, and 24 denotes a toner image formed on the photosensitive drum 21 to the intermediate transfer belt 27. A transfer bias roller 25 for transferring represents a cleaning unit for collecting untransferred toner on the photosensitive drum 21.

  In addition, 27 is an intermediate transfer belt on which toner images of a plurality of colors are transferred in an overlapping manner, 28 is a second transfer bias roller for transferring the toner image formed on the intermediate transfer belt 27 to the recording medium P, and 29 is an intermediate transfer belt. 27 is an intermediate transfer belt cleaning unit that collects untransferred toner, 30 is a conveyance belt that conveys a recording medium P on which a four-color toner image is transferred, and 32Y, 32M, 32C, and 32BK are developing devices 23Y and 23M. , 23C and 23BK, a toner replenishing unit for replenishing each color toner, 51 a document conveying unit for conveying the document D to the document reading unit 55, 55 for a document reading unit (scanner) for reading image information of the document D, and 61 for transferring A paper feed unit 66 for storing a recording medium P such as paper, and a fixing unit 66 for fixing an unfixed image on the recording medium P are shown.

Here, each of the process cartridges 20Y, 20M, 20C, and 20BK is obtained by integrating the photosensitive drum 21, the charging unit 22, and the cleaning unit 25, respectively. The process cartridges 20Y, 20M, 20C, and 20BK are exchanged with respect to the apparatus main body 1 in a predetermined exchange cycle. Similarly, the developing devices 23Y, 23M, 23C, and 23BK are also replaced with a predetermined replacement cycle with respect to the apparatus main body 1 based on the lifetime of the developer accommodated in the devices.
Image formation of each color (yellow, magenta, cyan, black) is performed on the photosensitive drum 21 in each of the process cartridges 20Y, 20M, 20C, and 20BK.

Hereinafter, an operation during normal color image formation in the image forming apparatus will be described.
First, the document D is transported from the document table in the direction of the arrow in the drawing by the transport roller of the document transport unit 51 and placed on the contact glass 53 of the document reading unit 55. Then, the document reading unit 55 optically reads the image information of the document D placed on the contact glass 53.

  Specifically, the document reading unit 55 scans the image of the document D on the contact glass 53 while irradiating light emitted from the illumination lamp. Then, the light reflected by the document D is imaged on the color sensor via the mirror group and the lens. The color image information of the document D is read for each RGB (red, green, blue) color separation light by the color sensor, and then converted into an electrical image signal. Further, an image processing unit (not shown) performs color conversion processing, color correction processing, spatial frequency correction processing, and the like on the basis of RGB color separation image signals, so that yellow, magenta, cyan, and black are processed. Get color image information.

  Then, the image information of each color of yellow, magenta, cyan, and black is transmitted to the writing unit 2. Then, laser light (exposure light) based on the image information of each color is emitted from the writing unit 2 toward the photosensitive drums 21 of the corresponding process cartridges 20Y, 20M, 20C, and 20BK.

On the other hand, the four photosensitive drums 21 rotate in the clockwise direction in FIG. First, the surface of the photosensitive drum 21 is uniformly charged at a position facing the charging unit 22 (a charging process). Thus, a charged potential is formed on the photosensitive drum 21. Thereafter, the surface of the charged photosensitive drum 21 reaches the irradiation position of each laser beam.
In the writing unit 2, laser light corresponding to the image signal is emitted from the light source corresponding to each color. The laser light is incident on the polygon mirror 3 and reflected, and then passes through the lenses 4 and 5. The laser light after passing through the lenses 4 and 5 passes through different optical paths for each of the yellow, magenta, cyan, and black color components (this is an exposure process).

  The laser beam corresponding to the yellow component is reflected by the mirrors 6 to 8 and then irradiated onto the surface of the photosensitive drum 21 of the first process cartridge 20Y from the left side of the drawing. At this time, the yellow component laser light is scanned in the rotation axis direction (main scanning direction) of the photosensitive drum 21 by the polygon mirror 3 that rotates at high speed. Thus, an electrostatic latent image corresponding to the yellow component is formed on the photosensitive drum 21 charged by the charging unit 22.

  Similarly, the laser beam corresponding to the magenta component is reflected by the mirrors 9 to 11 and then irradiated to the surface of the photosensitive drum 21 of the second process cartridge 20M from the left side of the paper, thereby causing an electrostatic latent image corresponding to the magenta component. An image is formed. The cyan component laser light is reflected by the mirrors 12 to 14 and then irradiated to the surface of the photosensitive drum 12 of the third process cartridge 20C from the left side of the drawing to form a cyan component electrostatic latent image. The black component laser light is reflected by the mirror 15 and then irradiated on the surface of the photosensitive drum 21 of the fourth process cartridge 20BK from the left side of the paper, thereby forming an electrostatic latent image of black component.

Thereafter, the surface of the photosensitive drum 21 on which the electrostatic latent images of the respective colors are formed reaches positions facing the developing devices 23Y, 23M, 23C, and 23BK, respectively. Then, the respective color toners are supplied from the developing devices 23Y, 23M, 23C, and 23BK onto the photosensitive drum 21, and the latent image on the photosensitive drum 21 is developed (this is a developing step).
Thereafter, the surface of the photosensitive drum 21 after the development process reaches the position facing the intermediate transfer belt 27 after passing the position facing the photosensor 41 (see FIG. 2). Here, the transfer bias roller 24 is installed at each facing position so as to contact the inner peripheral surface of the intermediate transfer belt 27. Then, at the position of the transfer bias roller 24, the images of the respective colors formed on the photosensitive drum 21 are sequentially superimposed and transferred onto the intermediate transfer belt 27 (first transfer step).

Then, the surface of the photosensitive drum 21 after the first transfer process reaches a position facing the cleaning unit 25. The untransferred toner remaining on the photosensitive drum 21 is collected by the cleaning unit 25 (this is a cleaning process).
Thereafter, the surface of the photosensitive drum 21 passes through a static elimination unit (not shown), and a series of image forming processes on the photosensitive drum 21 is completed.

On the other hand, the surface of the intermediate transfer belt 27 on which the images of the respective colors on the photosensitive drum 21 are transferred in an overlapping manner travels in the direction of the arrow in the drawing and reaches the position of the second transfer bias roller 28. Then, the full-color image on the intermediate transfer belt 27 is secondarily transferred onto the recording medium P at the position of the second transfer bias roller 28 (second transfer step).
Thereafter, the surface of the intermediate transfer belt 27 reaches the position of the intermediate transfer belt cleaning unit 29. Then, the untransferred toner on the intermediate transfer belt 27 is collected by the intermediate transfer belt cleaning unit 29, and a series of transfer processes on the intermediate transfer belt 27 is completed.

Here, the recording medium P at the position of the second transfer bias roller 28 is transported from the paper feeding unit 61 via the transport guide 63, the registration roller 64, and the like.
Specifically, the transfer paper P fed by the paper feed roller 62 from the paper feed unit 61 that stores the recording medium P passes through the conveyance guide 63 and is guided to the registration roller 64. The recording medium P that has reached the registration roller 64 is conveyed toward the position of the second transfer bias roller 28 in synchronization with the toner image on the intermediate transfer belt 27.

Thereafter, the recording medium P on which the full-color image is transferred is guided to the fixing unit 66 by the conveyance belt 30. In the fixing unit 66, the color image is fixed on the recording medium P at the nip between the heating roller 67 and the pressure roller 68.
Then, the recording medium P after the fixing process is discharged as an output image by the paper discharge roller 69 to the outside of the apparatus main body 1, and a series of image forming processes is completed.

Next, the image forming unit of the image forming apparatus will be described in detail with reference to FIGS. FIG. 2 is a cross-sectional view showing the image forming unit, and FIG. 3 is a cross-sectional view in the longitudinal direction (vertical direction in FIG. 2) showing the developing device.
The four image forming units installed in the apparatus main body 1 have substantially the same structure except that the color of the toner T used in the image forming process is different. (Y, M, C, BK) is omitted for illustration.

  As shown in FIG. 2, the process cartridge 20 mainly contains a photosensitive drum 21 as an image carrier, a charging unit 22, and a cleaning unit 25 integrally in a case 26. The cleaning unit 25 is provided with a cleaning blade 25 a and a cleaning roller 25 b that are in contact with the photosensitive drum 21.

  The developing device 23 mainly includes a developing roller 23a that faces the photosensitive drum 21, a first transport screw 23b that faces the developing roller 23a, and a second transport screw that faces the first transport screw 23b via a partition member 23e. 23c and a doctor blade 23d facing the developing roller 23a. Referring to FIG. 3, the developing roller 23a includes a magnet 23a1 fixed inside and having a plurality of magnetic poles, a sleeve 23a2 rotating around the magnet 23a1, a flange for supporting them, and the like. In the developing device 23, a two-component developer G composed of carrier C and toner T is accommodated. The sleeve 23a2 and the developer G will be described in detail later.

The above-described image forming process will be described in more detail with a focus on the developing process.
The developing roller 23a rotates in the direction of the arrow in FIG. As shown in FIG. 3, the developer G in the developing device 23 is generated by the rotation of the first conveying screw 23 b and the second conveying screw 23 c arranged so as to interpose the partition member 23 e therebetween in the arrow direction. It circulates in the longitudinal direction while being agitated and mixed with the toner T replenished from the replenishing section 32 through the toner replenishing port 23f (circulation in the direction of the broken arrow in FIG. 3).

  The toner T that is frictionally charged and adsorbed on the carrier C is carried on the developing roller 23a (on the outer peripheral surface of the sleeve 23a2) together with the carrier C. The developer G carried on the developing roller 23a then reaches the position of the doctor blade 23d. The developer G on the developing roller 23a is adjusted to an appropriate amount at the position of the doctor blade 23d, and then reaches a position facing the photosensitive drum 21 (developing area).

Thereafter, in the development area, the toner T in the developer G adheres to the electrostatic latent image formed on the surface of the photosensitive drum 21. Specifically, the toner T is latently exposed by the electric field formed by the potential difference (development potential) between the latent image potential (exposure potential) of the image area irradiated with the laser light L and the development bias applied to the development roller 23a. Adhere to the image.
In the present embodiment, in order to achieve high image quality, the gap (development gap) between the developing roller 23a (sleeve 23a2) and the photosensitive drum 21 is in the range of 0.1 to 0.4 mm. Is set to

  Thereafter, most of the toner T adhering to the photosensitive drum 21 in the developing process is transferred onto the intermediate transfer belt 27. The untransferred toner T remaining on the photosensitive drum 21 is collected in the cleaning unit 25 by the cleaning blade 25a and the cleaning roller 25b.

  Here, a toner replenishing unit 32 provided in the apparatus main body 1 includes a toner bottle 33 configured to be replaceable, a toner hopper unit 34 that holds and rotates the toner bottle 33 and replenishes the developing device with fresh toner T. , Is composed of. The toner bottle 33 contains toner T (any one of yellow, magenta, cyan, and black). In addition, a spiral protrusion is formed on the inner peripheral surface of the toner bottle 33.

  The toner T in the toner bottle 33 is appropriately replenished into the apparatus from the toner replenishing port 23f as the toner T in the apparatus is consumed. The toner T in the apparatus is consumed by a reflection type photo sensor 41 facing the photosensitive drum 21 and a magnetic sensor 40 (toner density detecting means) installed below the second conveying screw 23c of the developing device 23. Detected indirectly or directly. Further, the toner replenishing port 23f is provided at one end in the longitudinal direction of the second transport screw 23c (the left-right direction in FIG. 3) and above the second transport screw 23c.

Hereinafter, the sleeve 23a2 of the developing roller 23a, which is characteristic in the present embodiment, will be described in detail.
The sleeve 23a2 of the developing roller 23a is a cylindrical body made of a non-magnetic material, and has a magnet 23a1 that forms a magnetic field on the outer peripheral surface thereof so as to cause the rise of the developer. The sleeve 23a2 is formed so that the shake is within a predetermined range in order to suppress the occurrence of uneven density in the rotation period on the output image.

The sleeve 23a2 is formed so that the outer peripheral surface thereof is an irregular uneven surface. This outer peripheral surface (irregular uneven surface) is a relatively smooth uneven surface, and when the roughness profile is performed, the surface roughness Rz (ten-point average roughness) is in the range of 5 to 20 μm. Thus, the number of recesses having a depth of 1 μm or more is formed in a range of 1 to 5 (within 5) per measurement length of 0.2 mm.
In this way, by forming a smooth uneven surface defined in a predetermined shape on the surface of the sleeve 23a2 by the surface roughness Rz and the number of recesses having a depth of 1 μm or more per unit length, occurrence of pitch unevenness can be achieved. The toner can be prevented from sticking to the surface of the sleeve, and the developer can be stably pumped over time.

FIG. 4A and FIG. 4B are diagrams showing roughness profiles on the outer peripheral surface of the sleeve 23a2 (this embodiment) defined as described above. FIG. 4C is a view showing a roughness profile on the outer peripheral surface of the conventional sleeve 23a2. Comparing FIGS. 4A and 4B and FIG. 4C, the outer peripheral surface of the sleeve 23a2 according to the present embodiment has a gradual change (unevenness) on the whole irregularly. I understand that. In this case, the minute roughness is a measurement error level.
When the developing roller 23a having such a surface of the sleeve 23a2 is mounted on the developing device 23, the state of friction with the developer for obtaining the developer conveying force is necessary and sufficient, and the fine roughness Therefore, the problem that the toner and the components in the toner adhere to the sleeve surface is prevented, and good image quality can be maintained from the initial stage to the passage of time.

When such a roughness profile is embodied as a characteristic value, it is difficult to express only the existing standard defined by JIS or the like. In the present embodiment, in addition to the existing surface roughness Rz, the number of recesses having a depth of 1 μm or more per unit length is used to embody the desired uneven surface shape.
Referring to FIG. 5, in JIS and the like, the average interval Sm of unevenness is used as a characteristic value representing the peak pitch, but Sm represents the interval of the peaks with respect to the average line N of the roughness profile. As described above, it is difficult to realize an irregular roughness curve shape.

  Here, the number of recesses per unit length (per measurement length of 0.2 mm) represents how many recesses are present in the length, and is effective for the effect of the present embodiment. Considering the size of the contribution, extremely minute recesses are not counted, but only recesses of 1 μm or more are counted.

Specifically, description will be made with reference to FIGS.
6A to 6C are schematic views showing a state in which the carrier C is carried on the outer peripheral surface of the sleeve 23a2 in which the concave portion 43 is formed. FIG. 6 (A) shows a case where the number of recesses 43 having a depth of 1 μm or more is an appropriate amount, and FIG. 6 (B) shows a case where the number of recesses 43 having a depth of 1 μm or more is large. FIG. 6C shows the case where the number of recesses 43 having a depth of 1 μm or more is small.

Referring to FIG. 6B, when the number of the concave portions 43 having a depth of 1 μm or more is large (in the case of a fine concave and convex shape), the cross-sectional area of one convex portion is small. The tip of the convex portion is worn due to friction with the surface. In such a case, the developer transportability in the developing roller 23a is lowered, and the carrier surface (coat layer) is worn to deteriorate the carrier.
On the other hand, referring to FIG. 6C, when the number of the recesses 43 having a depth of 1 μm or more is small (in the case of a rough uneven shape), the friction between the sleeve surface and the developer is reduced. In addition, slippage occurs between the sleeve surface and the developer. Even in such a case, the carrier surface (coat layer) is worn and the carrier deteriorates.

  Therefore, the condition for obtaining necessary and sufficient friction between the carrier and the sleeve surface is that the recess 43 is formed to some extent uniformly on the sleeve surface, and the pitch (P) between the recesses 43 is the friction with the carrier. Is formed to a certain size so that it is easy to obtain (the state of FIG. 6A).

As a result of repeated studies by the inventors of the present application, the following two conditions can be derived as further optimum conditions for the recesses formed in the sleeve 23a2 under the above-described conditions.
First, the recess having a depth of 1 μm or more is formed in a substantially conical shape or a substantially polygonal pyramid shape so that the apex angle (α in FIG. 6A) is 90 degrees or more. It is preferred that As a result, when the carrier C is at the position of the recess 43, the gap between the carrier C and the recess 43 is reduced, and the toner (or toner component) is less likely to adhere to the outer peripheral surface.

Secondly, in the recess having a depth of 1 μm or more, the pitch between adjacent ones is P, the average value of the pitch P is P ₀ , and the average particle size (weight average particle size) of the carrier C is D. When
P ₀ /3<D<P/0.7
It is preferable that the relationship is established.
The minimum pitch between the recesses is a condition for the line contact between the carrier and the sleeve surface, and is preferably 0.7 times or more (P> 0.7D) of the average particle diameter D of the carrier. Further, in order to ensure the conveyance force for the developer on the sleeve surface, it is preferable that the average pitch P ₀ is not too large and is not more than three times the average particle diameter of the carrier (P ₀ <3D).

Note that the pitch P between the recesses and the average value P ₀ thereof can be obtained by using a roughness profile converted for pitch conversion as shown in FIG. Specifically, from the profile acquired by the roughness meter, the vertex of the concave portion and the vertex of the convex portion are connected by a straight line, the pitch of the adjacent concave portions is read, and the pitch P between the concave portions and the average value P ₀ are calculated.
The average particle size of the carrier can be measured using, for example, “Coulter Counter TA-II” (manufactured by Coulter) or “Coulter Multisizer II” (manufactured by Coulter).

  As a processing method for forming the sleeve surface having such a roughness profile, a blasting method in which a medium collides with the sleeve surface can be used. At that time, it is preferable to use a cut wire having a relatively large shape (a metal wire cut into a short shape) as a medium.

  As described above, in the present embodiment, since the shape of the uneven surface formed on the outer peripheral surface of the sleeve 23a2 in the developing roller 23a is optimized, there are problems in the output image such as pitch unevenness and density unevenness and the sleeve. The toner sticking to the surface is reliably prevented, and the developer can be stably pumped on the sleeve over time.

  In the present embodiment, as described above, the development gap (the gap between the photosensitive drum 21 and the development roller 23a) is set to be in the range of 0.1 to 0.4 mm. . Furthermore, the carrier C is formed so that the average particle diameter is in the range of 20 to 50 μm. As a result, high image quality of the output image is achieved.

When the development gap is smaller than 0.1 mm, the electric field formed in the development area becomes too strong, causing a problem that the carrier adheres on the photosensitive drum 21. On the other hand, when the development gap is larger than 0.4 mm, the electric field formed in the development area is reduced, so that the development efficiency is lowered and the edge effect of the electric field is increased at the edge of the image area. Becomes uneven.
Further, when the average particle diameter of the carrier C is smaller than 20 μm, the magnitude of magnetization of one carrier becomes small, so that the magnetic binding force received from the developing roller 23a is weakened, and carrier adhesion occurs. On the other hand, when the average particle diameter of the carrier C is larger than 50 μm, the electric field between the carrier and the latent image on the photosensitive drum 21 becomes sparse, and a uniform image cannot be obtained. End up.

In the present embodiment, referring to FIG. 8, a carrier C in which a magnetic core material 46 (which is a magnetic body such as ferrite) is coated with a resin coat film 47 is used. The resin coat film 47 is a resin component obtained by crosslinking a thermoplastic resin such as acrylic and a melamine resin, and contains alumina (large particles) as the charge adjusting agent 48 (large particles).
Since the resin coat film 47 formed in this manner has elasticity and strong adhesive force, it absorbs an impact on the carrier and suppresses the carrier film scraping, and holds the alumina 48 with a strong force. Further, the large-alumina alumina 48 prevents a direct impact on the resin coat film 47 and cleans the spent object.
By using the carrier configured as described above, the carrier film shaving and spent can be reduced, the life of the developer can be extended, and the pumping property of the developer can be stabilized.

In this embodiment, as the toner T, at least a toner composition composed of a prepolymer, a colorant, and a release agent is dispersed together with resin fine particles in an aqueous medium, and the toner composition is subjected to a polyaddition reaction. Is used. By using the toner T configured as described above, high image quality of the output image is achieved.
When an image is formed by an image forming apparatus equipped with a conventional developing roller having a sleeve surface using the toner T, the initial image quality is excellent, but the extract from the toner and the additive over time on the carrier. In other words, the amount of pumping up by accumulating on the sleeve greatly decreases and the image quality deteriorates. On the other hand, when the developing roller 23a having the sleeve surface of the present embodiment is used, a decrease in the pumping amount with time can be reduced, and good image quality can be maintained over a long period of time.

Hereinafter, an experiment for confirming the effect of the present embodiment will be described with reference to FIGS. 9 and 10.
9 and 10 are table diagrams showing the conditions and results of the effect confirmation experiment.

In the effect confirmation experiment in FIG. 9, three developing rollers 23a (Example 1, Comparative Example 1 and Comparative Example 2) having different surface properties on the sleeve surface (the outer peripheral surface of the sleeve 23a2) are prepared, and a running test is performed respectively. It was done.
Referring to FIG. 9, the three developing rollers 23a have different surface roughness Rz (ten-point average roughness), the number of recesses having a depth of 1 μm or more, and the pitches (P, P ₀ ) between the recesses. All the three developing rollers 23a have a sleeve diameter of 18 mm. Carrier C has an average particle diameter of 35 μm.

In the running test, the degree of decrease in the pumping amount on the developing roller 23a after 60,000 sheets were passed (image formation) was evaluated.
In FIG. 9, “◯” indicates the result that the reduction rate of the pumping amount is 5% or less, “△” indicates the result that the reduction rate of the pumping amount is 5 to 10%, and “×” indicates the pumping amount. The result that the rate of decrease is 10% or more is shown.

As shown in Comparative Example 1, when the pitch P (minimum pitch) between the recesses is 70% or less (D> P / 0.7) of the average particle diameter D of the carrier, the carrier is in point contact with the recesses. It can be seen that the pumping amount greatly decreases with time. Further, as shown in Comparative Example 2, when the average pitch P ₀ between the recesses is three times or more the average particle diameter D of the carrier (P _0/3 > D), the conveyance force with respect to the carrier is insufficient, It can be seen that the pumping amount decreases with time.
As shown in the first embodiment, when the relationship of P ₀ /3<D<P/0.7 is established, it is possible to reduce the decrease in the pumping amount with time.

On the other hand, in the effect confirmation experiment in FIG. 10, two types of developing rollers 23a (Examples 2 to 4 and Comparative Examples 3 to 4) having different surface properties on the sleeve surface were prepared, and the average particle diameter D ( The running test was conducted by changing the level of the carrier diameter) and the development gap.
In the developing rollers 23a of Examples 2 to 4, the number of recesses having a depth of 1 μm or more is 1 to 4. In the developing rollers 23a of Comparative Examples 3 to 4, the number of recesses having a depth of 1 μm or more is 4 to 9. The average particle diameter D of the carrier is two levels of 35 μm and 55 μm. The development gap has two levels of 0.3 mm and 0.5 mm.

In the running test, the image quality of the output image before and after 100,000 sheets were passed (image formation) was evaluated (sensory evaluation).
In FIG. 10, “は” indicates a state where the image quality is very good, “◯” indicates a state where the image quality is good, “Δ” indicates a state where the image quality is degraded, and “×” Indicates a state in which the image quality is greatly deteriorated.

  From the experimental results shown in FIG. 10, the sleeve surface of the developing roller is a smooth and irregular surface, and when the carrier diameter D and the development gap are optimized, it is very good from the beginning to the time. It can be seen that the image quality can be maintained.

  In the present embodiment, the process cartridges 20Y, 20M, 20C, and 20BK are configured by integrating the photosensitive drum 21, the charging unit 22, and the cleaning unit 25, respectively. Further, each developing device 23Y, 23M, 23C, 23BK is configured as a single unit. On the other hand, the developing devices 23Y, 23M, 23C, and 23BK can be integrated with the process cartridges 20Y, 20M, 20C, and 20BK. In other words, the process cartridge 20 can be configured by the photosensitive drum 21, the charging unit 22, the developing device 23, and the cleaning unit 25. Also in this case, the same effect as in the present embodiment can be obtained. Furthermore, the maintainability of the image forming unit is improved.

  It should be noted that the present invention is not limited to the present embodiment, and it is obvious that the present embodiment can be modified as appropriate within the scope of the technical idea of the present invention, other than suggested in the present embodiment. is there. In addition, the number, position, shape, and the like of the constituent members are not limited to the present embodiment, and the number, position, shape, and the like suitable for implementing the present invention can be achieved.

1 is an overall configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a cross-sectional view illustrating an image forming unit in the image forming apparatus of FIG. 1. It is sectional drawing which looked at the developing device to the longitudinal direction. It is a figure which shows the roughness profile in an uneven surface. It is a figure which shows the average space | interval Sm in an uneven surface. It is a schematic diagram which shows the state with which the carrier was carry | supported by the outer peripheral surface of the sleeve in a developing roller. It is a figure which shows the roughness profile converted in order to obtain | require the pitch between recessed parts. It is sectional drawing which shows the structure of a carrier. It is a table | surface figure which shows the conditions and result of the experiment for confirming the effect in embodiment. It is a table | surface figure which shows the conditions and result of another experiment for confirming the effect in embodiment.

Explanation of symbols

1 image forming apparatus body (apparatus body),
20, 20Y, 20M, 20C, 20BK Process cartridge,
21 photosensitive drum (image carrier), 22 charging unit,
23, 23Y, 23M, 23C, 23BK Developing device (developing unit),
23a Development roller (developer carrier),
23a1 magnet, 23a2 sleeve,
23b 1st conveyance screw, 23c 2nd conveyance screw,
23e partition member, 23f toner supply port, 25 cleaning section,
32, 32Y, 32M, 32C, 32BK toner supply unit,
43 concave portion, 46 core material, 47 resin coat film, 48 alumina,
G Two-component developer (developer), T toner, C carrier.

Claims (11)

A developing roller for developing a latent image formed on the image carrier facing the image carrier,
A magnet having a plurality of fixed magnetic poles;
A sleeve that is provided inside the magnet and carries a developer composed of toner and a carrier and relatively rotates around the magnet;
The sleeve is formed such that its outer peripheral surface is an irregular uneven surface,
The outer peripheral surface has a surface roughness Rz in the roughness profile in the range of 5 to 20 μm, and the number of recesses having a depth of 1 μm or more is in the range of 1 to 5 per measurement length of 0.2 mm. A developing roller formed as described above. 2. The developing roller according to claim 1, wherein the concave portion having a depth of 1 μm or more on the outer peripheral surface is formed in a conical shape or a polygonal pyramid shape and has an apex angle of 90 degrees or more. . The outer peripheral surface, when the pitch between adjacent ones of the recesses having a depth of 1 μm or more is P, the average value of the pitch is P ₀ , and the average particle diameter of the carrier is D,
P ₀ /3<D<P/0.7
The developing roller according to claim 1, wherein the developing roller is formed so as to satisfy the following relationship. The developing roller according to claim 1, wherein the developing roller is installed such that a gap with the image carrier is in a range of 0.1 to 0.4 mm. The developing roller according to claim 1, wherein the sleeve is made of a nonmagnetic material. The developing roller according to claim 1, wherein the carrier is formed so that an average particle diameter is in a range of 20 to 50 μm. The carrier is obtained by forming a resin coat film on a magnetic core material,
7. The developing roller according to claim 1, wherein the resin coat film is a resin component obtained by crosslinking a thermoplastic resin and a melamine resin, and a charge adjusting agent is contained therein. 8. . The toner is formed by dispersing a toner composition including at least a prepolymer, a colorant, and a release agent together with resin fine particles in an aqueous medium, and subjecting the toner composition to a polyaddition reaction. The developing roller according to claim 1. A developing device comprising the developing roller according to claim 1, wherein the developer is accommodated. A process cartridge that is detachably installed on the main body of the image forming apparatus,
10. A process cartridge, wherein the developing device according to claim 9 and the image carrier are integrated. An image forming apparatus comprising the developing device according to claim 9 and the image carrier.

Images