JP5322967B2 - Developing device and image forming apparatus - Google Patents

Description

  The present invention relates to a developing device and an image forming apparatus including the developing device.

  As a developing device used in an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile, and a composite machine of these, there are various developing systems, for example, a so-called touch-down developing system. This developing device is preferably used because it can form a high-quality image. The developing device of the touchdown developing system is a developing device using a two-component developer containing toner and a carrier as a developer, and a magnetic roller (developer carrier) that carries and conveys the two-component developer; And a developing roller (toner carrier) that is disposed opposite to the image carrier and the magnetic roller and carries and conveys the toner in the two-component developer. That is, the two-component developer is carried on the surface of the magnetic roller and conveyed, and the conveyed two-component developer is brought into contact with or close to the developing roller, whereby the toner in the two-component developer is transferred to the developing roller. A developing device that moves onto the surface, carries the transferred toner on a developing roller, conveys the toner to the vicinity of the image carrier, and flies the conveyed toner toward the surface of the image carrier to develop the toner. . An image forming apparatus provided with such a developing device transfers the toner image formed by the developing device to a recording medium such as paper, and then fixes the toner image on the recording medium, whereby the image is recorded on the recording medium. Form on top.

  In the developing device, the developing roller and the photosensitive drum are separated from each other. When the toner conveyed by the developing roller is caused to fly to the photosensitive drum, the photosensitive drum (D) and the developing sleeve (S) of the developing roller are used. ) Between (DS) and an electric field is formed between the DSs.

  Further, as the developing roller, for example, a roller having a surface portion made of a resin layer is used. And the conductive material is added to the said resin layer as a resistance regulator, and resistance values, such as a surface resistivity, of the said resin layer are adjusted. In addition, carbon black is usually used as the conductive material because of cost and the like. Since carbon black is a conductive material with high conductivity and high performance for reducing the resistivity of the resin layer, the resin layer should be stably adjusted to a relatively high resistance value, that is, a moderate resistance value. It was difficult. Therefore, a developing roller or the like is used in which carbon black is used as the conductive material and the resistance value of the resin layer is adjusted to have a relatively low resistance value.

  On the other hand, the developing device is required to shorten the developing time in order to increase the image forming speed. In order to satisfy this requirement, for example, it is conceivable to increase the voltage applied between the DSs to form an electric field having a strong electric field strength between the DSs. However, when a strong electric field strength is formed, a so-called leak phenomenon tends to occur, in which a leak current flows between the developing roller and the photosensitive drum that are separated from each other. In order to suppress the occurrence of this leakage phenomenon, in the case of a developing roller having a resin layer as described above, it is conceivable to increase the resistance value of the resin layer by reducing the amount of carbon black added to the resin layer. .

  However, when the amount of carbon black added is reduced to increase the resistance value of the resin layer, there is a problem that the image density is lowered. This is considered to be because when a voltage is applied between the DSs, charges are easily accumulated on the surface of the developing roller, and the amount of toner conveyed by the developing roller is reduced by the charges accumulated on the surface. .

  Therefore, it has been difficult to obtain an image having a good image density while adjusting the amount of carbon black added to suppress the occurrence of a leak phenomenon. In addition, since the dielectric breakdown voltage of the amorphous silicon photoconductor is about 1.6 kV and the dielectric breakdown voltage of the organic photoconductor is about 6.0 kV, when an amorphous silicon photoconductor is used as the image carrier, Amorphous silicon photoconductors are more susceptible to leakage than organic photoconductors. Therefore, when an amorphous silicon photoconductor is used as the image carrier, it is particularly difficult to achieve a good image density while suppressing the occurrence of a leak phenomenon.

  Moreover, as another developing system developing device provided with a developing roller having a surface portion formed of a resin layer, for example, a developing device described in Patent Document 1 below can be cited. Patent Document 1 includes a developing roller having a base and a resin layer containing a binder resin for a coating layer and a positively chargeable material formed on the base, and the binder resin and coloring are used as a developer. A two-component developing device is described that uses a developer containing toner and toner particles having a predetermined circularity and conductive fine particles.

JP 2003-162145 A

  As described above, in the touch-down type developing device, the leakage phenomenon is caused by adjusting the resistance value of the resin layer constituting the surface portion of the developing roller that conveys the toner in the two-component developer with carbon black. It was difficult to obtain an image having a good image density while suppressing.

  In Patent Document 1, the resin layer coated on the surface of the developing roller contains a positively charged substance and a conductive substance. This conductive substance is a toner and a toner that is conveyed by the developing roller. It is added to prevent overcharging of a two-component developer containing a carrier. The developing roller for conveying the two-component developer is different from the one for conveying only the toner contained in the two-component developer, and the performance required for the resin layer coated on the surface is different. That is, it has not been aimed at achieving a good image density while adjusting the type and amount of the conductive substance to suppress the occurrence of the leak phenomenon. Therefore, a developing roller in which a conductive material is added to a resin layer coated on the surface of the developing roller to prevent overcharging of the two-component developer together with a positively charged material is used as a touch-down developing device. Even if applied as it is, it was not possible to achieve a good image density while suppressing the occurrence of a leak phenomenon. Patent Document 1 exemplifies titanium oxide as a conductive substance together with a carbon-based material such as carbon black. However, since what is actually considered in the examples is a carbon-based material, in Patent Document 1, titanium oxide is added to a resin layer of a developing roller used in a touch-down developing device. It can be seen that it has not been recognized at all that the leakage phenomenon can be suppressed and the image density can be improved.

  The present invention has been made in view of such circumstances, and provides a touch-down developing device that can achieve a good image density while suppressing the occurrence of a leak phenomenon. For the purpose. It is another object of the present invention to provide an image forming apparatus including the developing device.

  As a result of detailed studies, the present inventors have found that when a conductive material generally contained in the resin layer constituting the surface portion of the developing roller, for example, carbon black is used, the occurrence of a leak phenomenon is suppressed. The reason why it is difficult to achieve a good image density by reducing the amount of the conductive material added is that when a voltage is applied between the DSs, charges are easily accumulated on the surface of the developing roller. . Then, it was considered that the amount of toner conveyed by the developing roller is reduced by the charge accumulated on the surface. Furthermore, it was considered that the reason why charges are likely to be accumulated is that the distance between each conductive material is increased because the amount of conductive material added is reduced. From these facts, it is considered that a conductive material generally contained in the resin layer constituting the surface portion of the developing roller, for example, particles having a higher resistance value than that of carbon black may be used and the addition amount thereof should be increased.

  However, when only a large number of particles having a high resistance value are added and used, when image formation is performed over a long period of time, the image density may be lowered and a good image density may not be achieved. This is considered to be because when the voltage is applied between the DSs, the potential on the surface of the developing roller rises gradually.

  Therefore, as a result of intensive studies on the types of conductive materials, the present inventors have arrived at the present invention as follows.

  A developing device according to an aspect of the present invention is a developing device that visualizes an electrostatic latent image formed on a surface of an image carrier as a toner image, and includes a two-component developer including toner and a carrier on the surface. A magnetic roller that is carried on the carrier and conveys the carried two-component developer, and is disposed opposite to the image carrier and the magnetic roller, and is in contact with the two-component developer carried by the magnetic roller, or And a developing roller that carries the toner in the two-component developer on the surface and conveys the carried toner to the vicinity of the image carrier, and at least the surface portion of the developing roller is titanium oxide. A roller comprising a resin layer containing particles and a resin is used.

  According to the above configuration, it is possible to provide a touch-down developing device that can achieve a good image density while suppressing the occurrence of a leak phenomenon.

  This is considered to be due to the following.

  First, the titanium oxide particles not only have a higher resistance value than a conductive material generally contained in the resin layer constituting the surface portion of the developing roller, for example, carbon black, but also have a high relative dielectric constant of 30 or more. is there.

  Since the titanium oxide particles are particles having a relatively high resistance value as described above, the titanium oxide particles are contained in the resin layer in a relatively large amount, thereby shortening the distance between the titanium oxide particles as the conductive material. In addition, accumulation of electric charges in the resin layer of the developing roller can be suppressed. Furthermore, since the titanium oxide particles are particles having a relatively high resistance value, the resistance value of the resin layer of the developing roller can be kept high even when the titanium oxide particles are filled relatively high, and a leakage phenomenon is caused. It is thought that generation | occurrence | production can be suppressed. Therefore, it is considered that the occurrence of a leak phenomenon can be suppressed while suppressing a decrease in image density due to charge accumulation.

  Furthermore, since the titanium oxide particles have a high relative dielectric constant, it is considered that the capacitance of the resin layer can be sufficiently increased. For this reason, it is possible to accumulate charges at a low voltage, and it is considered that the potential increase of the developing roller can be suppressed to a low level.

  Since the potential increase of the developing roller can be suppressed low, it is considered that the potential increase with time is also suppressed. Therefore, it is considered that even when image formation is performed over a long period of time, a decrease in image density is suppressed.

  Therefore, it is considered that a good image density can be achieved while suppressing the occurrence of the leak phenomenon.

In the developing device, the surface resistivity of the developing roller is preferably less than 1 × 10 ¹² Ω / □. According to such a configuration, it is possible to achieve a better image density while suppressing the occurrence of the leak phenomenon. In particular, it is possible to further suppress a decrease in image density when an image is formed over a long period of time. This means that, as described above, the resin layer of the developing roller has a high resistance value and a high relative dielectric constant so that the surface resistivity of the developing roller is less than 1 × 10 ¹² Ω / □. It is considered that the inclusion of titanium oxide particles can further increase the capacitance of the resin layer.

  In the developing device, the content of the titanium oxide particles is preferably 70 to 300 parts by mass with respect to 100 parts by mass of the resin. According to such a configuration, it is possible to achieve a better image density while suppressing the occurrence of the leak phenomenon. This is considered to be because it is a suitable content that can suppress the dropping of the titanium oxide particles and that can sufficiently exhibit the effects of suppressing the occurrence of the leak phenomenon and achieving a good image density. .

  Moreover, in the said developing device, it is preferable that the average primary particle diameter of the said titanium oxide particle is 10-50 nm. According to such a configuration, it is possible to achieve a better image density while suppressing the occurrence of the leak phenomenon. This is considered because the titanium oxide particles are relatively uniformly dispersed in the resin when the titanium oxide particles are relatively filled in the resin. Therefore, it is considered that even if the titanium oxide particles are filled relatively high, the resistance value of the resin layer of the developing roller can be maintained high, and the occurrence of a leak phenomenon can be suppressed.

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

  According to the above configuration, it is possible to provide an image forming apparatus capable of forming a high-quality image that can maintain a good image density even after image formation over a long period of time while suppressing occurrence of a leak phenomenon. be able to.

  In the image forming apparatus, the image carrier is preferably an amorphous silicon photoconductor.

  Amorphous silicon photoreceptors are generally known to be less susceptible to surface wear and higher durability than organic photoreceptors, but are susceptible to leakage. Provided is an image forming apparatus capable of suppressing a leak phenomenon and forming a high-quality image even when such an amorphous silicon photoreceptor is used in combination with the developing device. can do. That is, the obtained image forming apparatus can suppress the occurrence of a leak phenomenon while improving the durability of the image carrier.

  According to the present invention, it is possible to provide a touch-down developing device that can achieve a good image density while suppressing the occurrence of a leak phenomenon. In addition, an image forming apparatus including the developing device is provided.

1 is a schematic diagram illustrating a configuration of an image forming apparatus (copier) to which a developing device according to an embodiment of the present invention is applied. FIG. 2 is a schematic diagram showing the periphery of an image forming unit of the copying machine shown in FIG. 1. FIG. 10 is a schematic diagram illustrating a configuration of another image forming apparatus to which the developing device according to the embodiment of the invention is applied. 1 is a schematic cross-sectional view illustrating a developing device according to an embodiment of the present invention. It is the schematic which shows the structure of a developing roller.

  Hereinafter, although the embodiment concerning the present invention is described, the present invention is not limited to these.

  A copying machine 60 shown in FIG. 1 will be described as an example of an image forming apparatus to which a developing device according to an embodiment of the present invention is applied. FIG. 1 is a schematic diagram showing the configuration of an image forming apparatus (copier) to which a developing device according to an embodiment of the present invention is applied. The copier 60 includes a paper feeding unit 200 disposed at a lower portion of the copier body, an image forming unit 300 disposed above the paper feeding unit 200, and on the discharge side from the image forming unit 300. A so-called cylinder including a fixing unit 400 disposed, an image reading unit 500 disposed on an upper portion of the copier body, and a paper discharge unit 600 disposed between the copier body and the image reading unit 500. This is an internal discharge type copier. The copying machine main body is provided with a paper transport unit 100 that connects the paper feeding unit 200, the image forming unit 300, the fixing unit 400, and the paper discharge unit 600.

  The image forming unit 300 forms a predetermined toner image on a sheet by an electrophotographic method. The photosensitive drum 301 is rotatably supported on the photosensitive drum 301 and the photosensitive drum 301 is rotated in the rotation direction A. Along with this, a charging unit 302, an exposure unit 303, a developing unit (developing device) 20, a transfer unit 305, and a cleaner 306 are provided. The developing unit 20 develops the electrostatic latent image with toner and forms a toner image on the surface of the photosensitive drum 301.

  The fixing unit 400 is disposed on the downstream side of the image forming unit 300 in the sheet conveying direction, and the sheet on which the toner image is transferred in the image forming unit 300 is transferred to a pair of rollers (a heating roller 401 and a pressure roller 402). And the toner image is fixed on the paper.

  The image reading unit 500 irradiates a document placed on a contact glass (not shown) with light from an exposure lamp, and guides the reflected light to a photoelectric conversion unit through a reflecting mirror, thereby image information on the document. Is to read.

  The paper feed unit 200 includes a plurality of paper feed cassettes 201, 202, and 221. Of these, the paper feed cassette 221 is a bypass tray that replenishes paper from the side of the copier, and can be closed by the lid 222.

  A paper transport path 110 is connected to each of the paper feed cassettes 201, 202, and 221. The paper transport path 110 is directed to the image forming unit 300, and further to the paper discharge unit 600 through the fixing unit 400. These paper transport paths 110 constitute the paper transport unit 100. In addition, the sheet for which copying has been completed is discharged from the discharge roller pair 605 of the paper discharge unit 600 onto the discharge tray 610.

  FIG. 2 is a schematic diagram showing the periphery of the image forming unit 300 of the copying machine 60. The image forming unit 300 forms a predetermined toner image on the recording paper 115 by an electrophotographic process. The image forming unit 300 is sequentially arranged around the photosensitive drum 301 having photosensitivity along the rotation direction A of the photosensitive drum 301. A charging unit 302, an exposure unit 303, a developing unit 20, a transfer unit 305, a charge eliminating unit 307, and a cleaning unit 306. It should be noted that the charge removal unit 307 and the cleaning unit 306 may be reversed.

  The charging unit 302 applies a predetermined potential to the surface of the photosensitive drum 301 by generating corona discharge. The exposure unit 303 forms an electrostatic latent image by selectively attenuating the surface potential of the photosensitive drum 301 by irradiating light corresponding to a desired image. The developing unit 20 develops an electrostatic latent image formed on the surface of the photosensitive drum 301 with toner to form a toner image, and is a so-called touch-down developing device described later. The transfer unit 305 transfers the toner image formed on the photosensitive drum 301 onto the recording paper 115. The neutralizing unit 307 neutralizes the residual surface charge of the photosensitive drum 301 with lamp light. The cleaning unit 306 includes a fur brush 316 and a rubber blade 326, and removes toner remaining on the surface of the photosensitive drum 301, additives, and the like. The cleaning unit 306 in the illustrated example has both the fur brush 316 and the rubber blade 326, but there may be a cleaning unit 306 having only one.

  The recording paper 115 onto which the toner image has been transferred by the image forming unit 300 is heated and pressed by the fixing unit 400 (heating roller 401 and pressure roller 402) to fix the toner image, and then the discharge roller ( The sheet is discharged onto a sheet discharge tray (not shown).

  The image forming apparatus according to the present embodiment is not particularly limited as long as it includes a developing device described later.

  Specifically, the copying machine has been described as an example of the image forming apparatus. However, the image forming apparatus is not limited to this, and any image forming apparatus using an electrophotographic method may be a facsimile machine, a printer, or the like. There may be.

  Further, the image bearing member has been described by taking a photosensitive drum as a drum-shaped photosensitive member as an example. However, the image bearing member is not limited to this, and the belt-shaped photosensitive member, the sheet-shaped photosensitive member, etc. Is also applicable.

  Furthermore, the image forming apparatus is an apparatus that directly transfers a toner image onto a sheet, but is not limited to such an image forming apparatus. For example, as shown in FIG. 3, a multi-color toner image is temporarily transferred to an intermediate transfer belt, and the multi-color toner image transferred to the intermediate transfer belt is transferred to a sheet, so-called tandem color image. It may be a forming device.

  FIG. 3 is a schematic diagram showing the configuration of another image forming apparatus to which the developing device according to the embodiment of the present invention is applied.

  As shown in FIG. 3, the image forming apparatus 1 has a box-shaped device main body 1a. In the apparatus main body 1a, a toner image based on image data and the like is transferred to the paper P while feeding the paper P fed from the paper feeding unit 2 and the paper P fed from the paper feeding unit 2. An image forming unit 3 and a fixing unit 4 for performing a fixing process for fixing the unfixed toner image transferred onto the paper P by the image forming unit 3 to the paper P are provided. Further, on the upper surface of the apparatus main body 1a, a paper discharge unit 5 for discharging the paper P subjected to the fixing process by the fixing unit 4 is provided.

  The paper feed unit 2 includes a paper feed cassette 121, a pickup roller 122, paper feed rollers 123, 124 and 125, and a registration roller pair 126. The paper feed cassette 121 is provided so as to be detachable from the apparatus main body 1a, and stores the paper P of each size. The pickup roller 122 is provided at the upper left position of the paper feed cassette 121 shown in FIG. 1 and takes out the paper P stored in the paper feed cassette 121 one by one. The paper feed rollers 123, 124, and 125 send the paper P taken out by the pickup roller 122 to the paper transport path. The registration roller pair 126 temporarily waits for the paper P sent to the paper transport path by the paper feed rollers 123, 124, and 125, and then at a predetermined timing, the secondary roller between the secondary transfer roller 32 and the backup roller 35. Supply to transfer nip.

  The paper feeding unit 2 further includes a manual feed tray (not shown) and a pickup roller 127 that are attached to the left side surface of the device main body 1a shown in FIG. The pickup roller 127 takes out the paper P placed on the manual feed tray. The paper P taken out by the pickup roller 127 is sent out to the paper conveyance path by the paper feed rollers 123 and 125, and the secondary between the secondary transfer roller 32 and the backup roller 35 at a predetermined timing by the registration roller pair 126. Supplied to the transfer nip.

  The image forming unit 3 includes an image forming unit 7, an intermediate transfer belt 31 on which a toner image based on image data transmitted from a computer or the like to the surface (contact surface) of the image forming unit 7 is primarily transferred, A secondary transfer roller 32 is provided for secondary transfer of the toner image on the intermediate transfer belt 31 onto the paper P fed from the paper feed cassette 21.

  The image forming unit 7 includes a black unit 7K, a yellow unit 7Y, a cyan unit 7C, and a magenta unit 7M, which are sequentially arranged from the upstream side (right side in FIG. 3) to the downstream side. I have. In each of the units 7K, 7Y, 7C, and 7M, a photosensitive drum 301 as an image carrier is disposed at the center position so as to be rotatable in the direction of an arrow (clockwise). Around each photosensitive drum 301, a charger 39, an exposure device 38, a developing device (developing unit) 20, a cleaning device (not shown), a static eliminator, and the like are sequentially arranged from the upstream side in the rotation direction of the photosensitive drum 301. Each is arranged.

  The charger 39 uniformly charges the peripheral surface of the photosensitive drum 37 rotated in the direction of the arrow. Examples of the charger 39 include a non-contact discharge type corotron type and scorotron type charger, a contact type charging roller, a charging brush, and the like. The exposure device 38 is a so-called laser scanning unit, which irradiates the circumferential surface of the photosensitive drum 301 uniformly charged by the charger 39 with laser light based on image data input from an image reading device or the like, thereby An electrostatic latent image based on the image data is formed on the drum 301. The developing unit 20 develops an electrostatic latent image formed on the surface of the photosensitive drum 301 with toner to form a toner image, and is a so-called touch-down developing device described later. The toner image is primarily transferred to the intermediate transfer belt 31. The cleaning device cleans the toner remaining on the peripheral surface of the photosensitive drum 37 after the primary transfer of the toner image to the intermediate transfer belt 31 is completed. The static eliminator neutralizes the peripheral surface of the photosensitive drum 37 after the primary transfer is completed. The peripheral surface of the photosensitive drum 37 cleaned by the cleaning device and the charge eliminator goes to the charger for a new charging process, and a new primary transfer is performed.

  The intermediate transfer belt 31 is an endless belt-like rotating body, and includes a driving roller 33, a driven roller 34, a backup roller 35, and a surface (contact surface) side in contact with the peripheral surface of each photosensitive drum 301. It is spanned across a plurality of rollers such as the primary transfer roller 36. Further, the intermediate transfer belt 31 is configured to rotate endlessly by the driving roller 33 in a state where the intermediate transfer belt 31 is pressed against the photosensitive drum 301 by a primary transfer roller 36 disposed to face each photosensitive drum 301. The driving roller 33 is rotationally driven by a driving source such as a stepping motor, and gives a driving force for rotating the intermediate transfer belt 31 endlessly. The driven roller 34, the backup roller 35, and the primary transfer roller 36 are rotatably provided, and are driven to rotate with the endless rotation of the intermediate transfer belt 31 by the driving roller 33. These rollers 34, 35, 36 are driven to rotate via the intermediate transfer belt 31 in accordance with the main rotation of the drive roller 33 and support the intermediate transfer belt 31.

  The primary transfer roller 36 applies a primary transfer bias (a polarity opposite to the toner charging polarity) to the intermediate transfer belt 31. By doing so, the toner image formed on each photoconductive drum 37 is moved in the direction of the arrow (counterclockwise) by the drive roller 33 between each photoconductive drum 37 and the primary transfer roller 36. The images are sequentially transferred (primary transfer) to the rotating intermediate transfer belt 31 in an overcoated state.

  The secondary transfer roller 32 applies a secondary transfer bias having a polarity opposite to that of the toner image to the paper P. By doing so, the toner image primarily transferred onto the intermediate transfer belt 31 is transferred onto the paper P at the secondary transfer nip between the secondary transfer roller 32 and the backup roller 35, and thereby onto the paper P. A color transfer image (unfixed toner image) is transferred.

  The fixing unit 4 performs a fixing process on the transfer image transferred to the paper P at the secondary transfer nip, and is disposed opposite to the heating roller 41 heated by the energization heating element and the heating roller 41. And a pressure roller 42 whose surface is pressed against the peripheral surface of the heating roller 41.

  The transferred image transferred to the paper P by the secondary transfer roller 32 at the secondary transfer nip is subjected to a fixing process by heating when the paper P passes between the heating roller 41 and the pressure roller 42. Fixed to P. The paper P subjected to the fixing process is discharged to the paper discharge unit 5. Further, in the image forming apparatus 1 according to the present embodiment, the conveyance roller pair 6 is disposed between the fixing unit 4 and the paper discharge unit 5 at an appropriate position.

  The paper discharge unit 5 is formed by recessing the top of the apparatus main body 1a of the image forming apparatus 1, and a paper discharge tray 51 for receiving the discharged paper P is formed at the bottom of the concave portion. Yes.

  Hereinafter, the developing unit (developing apparatus) 20 according to the embodiment of the present invention used in the image forming apparatus will be described. The developing device according to the embodiment of the present invention is a so-called touch-down developing device as shown in FIG. That is, a developing device that visualizes an electrostatic latent image formed on the surface of an image carrier as a toner image, and carries a two-component developer containing toner and a carrier on the surface. A magnetic roller for conveying a component developer; and the two-component developer disposed opposite to the image carrier and the magnetic roller, in contact with or close to the two-component developer conveyed by the magnetic roller And a developing roller that carries the toner on the surface and conveys the carried toner to the vicinity of the image carrier. As the developing roller, a roller having at least a surface portion formed of a resin layer containing titanium oxide particles and a resin is used.

  FIG. 4 is a schematic cross-sectional view showing the developing device 20 and is shown together with the photosensitive drum 301.

  The developing device 20 is a touch-down developing type developing device, and includes a developing roller 61, a magnetic roller 62, stirring rollers 63 and 64, a blade 65, and the like.

  The agitation rollers 63 and 64 have spiral blades and agitate the two-component developer while conveying the two-component developer in opposite directions to charge the toner of the two-component developer. Further, the stirring roller 63 supplies a two-component developer containing charged toner and a carrier to the magnetic roller 62.

  The magnetic roller 62 conveys the two-component developer by adsorbing the two-component developer with a magnet fixedly disposed therein. At this time, the two-component developer becomes a magnetic brush by a magnet inside the magnetic roller 62, and the thickness of the magnetic brush is regulated when the magnetic brush passes between the blade 65 and the magnetic roller 62. The Then, the toner in the two-component developer conveyed to the vicinity of the developing roller 61 is transferred to the developing roller 61 by the voltage applied between the developing roller 61 and the magnetic roller 62.

  The developing roller 61 carries the toner transferred from the magnetic roller 62 while carrying it on the surface. Then, the toner conveyed to the vicinity of the photosensitive drum 301 shifts to the photosensitive drum 301 when the potential difference between the photosensitive drum 301 and the developing roller 61 satisfies a predetermined condition.

  With the above operation, the developing device 20 performs development based on the electrostatic latent image formed on the photosensitive drum 301.

  Next, the developing roller 61 provided in the touch-down developing type developing device 20 will be described. FIG. 5 is a schematic diagram showing a configuration of the developing roller 61 provided in the touch-down developing type developing device 20. 5A is a cross-sectional view of an example of the developing roller 61, FIG. 5B is a perspective view of the developing roller 61 shown in FIG. 5A, and FIG. 5C is a developing roller. FIG. 5D is a perspective view of the developing roller 61 shown in FIG. 5C.

  First, the developing roller 61 shown in FIG.

  As shown in FIGS. 5A and 5B, the developing roller 61 includes a cylindrical rotating sleeve 13 and a fixed shaft 15 included in the rotating sleeve 13. The rotating sleeve 13 is configured to rotate around the fixed position.

  As shown in FIGS. 5A and 5B, the rotating sleeve 13 has a resin layer 18 coated on a base material 19. The base material 19 is a cylindrical member made of, for example, aluminum or stainless steel. The fixed shaft 15 is connected to a shaft 22 supported by the developing unit 20 by a plurality of ribs 28.

  The resin layer 18 is not particularly limited as long as it contains titanium oxide particles and a resin. Specific examples of the resin include polyamide resins such as polyamide resins, urethane resins, silicone-modified urethane resins, and polyamide urethane resins.

  Further, the titanium oxide particles are not particularly limited, but those having an average primary particle diameter of 10 to 50 nm are preferable. If the titanium oxide particles are too small, reaggregation occurs and dispersion tends to be difficult. Moreover, when the titanium oxide particles are too large, it is difficult to hold them in the resin, and there is a tendency that they are detached from the resin. Further, the film surface becomes rough, and the toner or the like tends to adhere to the surface of the resin layer 18.

  In addition, the average primary particle diameter of titanium oxide can be understood from a standard value of a product, a measurement using a general particle size meter, or the like. Specifically, for example, it can be measured using a vibration viscometer manufactured by CBC Corporation.

Further, the surface resistivity of the developing roller 61, that is, the surface resistivity of the resin layer 18 is preferably less than 1 × 10 ¹² Ω / □, and is 1 × 10 ⁷ to 1 × 10 ¹¹ Ω / □. Is more preferable. If the surface resistivity of the developing roller 61 is too small, a leak tends to occur between the photosensitive drum (D) and the developing sleeve (S) of the developing roller (between DS). In addition, if the surface resistivity of the developing roller 61 is too large, the image density tends to decrease.

  The surface resistivity of the developing roller 61 was measured by a method based on JIS K 6911, for example. More specifically, it can be measured using, for example, Hiresta UP MCP-HT450 type manufactured by Mitsubishi Chemical Analytech Co., Ltd.

  Moreover, it does not specifically limit as content of a titanium oxide particle. Specifically, for example, the content is preferably such that the surface resistivity of the developing roller falls within the above range, and more preferably 70 to 300 parts by mass with respect to 100 parts by mass of the resin. When the content of the titanium oxide particles is too small, electric charges are accumulated in the roller, and there is a tendency that the density is rapidly lowered during continuous paper feeding. Moreover, when there is too much content of a titanium oxide particle, the binding property of a titanium oxide and resin will become weak, and there exists a tendency for the film | membrane scraping of the resin layer 18 to generate | occur | produce in lifetime evaluation.

  The thickness of the resin layer 18 is preferably 2 to 15 μm.

  Next, the developing roller 61 shown in FIG.

  As shown in FIGS. 5C and 5D, the developing roller 61 includes a roller main body 24 and a resin layer 23 coated on the surface of the roller main body 24. The roller body 24 is rotatably supported with respect to the shaft 25 by flanges (with bearings) fitted to both ends of the roller body 24. The flange on one end side is provided with a gear and receives a driving force from the outside. The roller body 24 is, for example, a so-called Mitsuya tube made of aluminum or stainless steel. The resin layer 23 can be the same as the resin layer 18.

  Further, the manufacturing method of the developing roller 61 is not particularly limited. Specifically, in the case of the developing roller 61 shown in FIG. 5A, for example, a resin composition containing the resin and titanium oxide particles is applied onto the substrate 19 and heated. By doing so, the resin layer 18 is formed on the substrate 19, and the developing roller 61 is manufactured. In the case of the developing roller 61 shown in FIG. 5C, for example, a resin composition containing the resin and titanium oxide particles is applied onto the roller body 24 and heated. By doing so, the resin layer 23 is formed on the roller body 24, and the developing roller 61 is manufactured. And the said resin composition should just contain the said resin and a titanium oxide particle, for example, in order to apply | coat uniformly on the base material 19, a solvent is added and the state in which the titanium oxide particle was disperse | distributed. It may be a resin solution. In that case, it is preferable to adjust so that it may become 70-200 mass% of solid content concentration. Examples of the solvent include cyclohexane and methyl ethyl ketone. Moreover, as heating temperature, it is preferable that it is 100-150 degreeC, for example, and it is preferable that it is 10 to 50 minutes as heating time, for example.

  By using the developing roller 61 as a developing roller of a touch-down developing device, a developing device capable of achieving a good image density while suppressing occurrence of a leak phenomenon is obtained.

  Hereinafter, the present invention will be described more specifically with reference to examples. In addition, this invention is not limited at all by the Example.

  In the image forming apparatus according to the example and the comparative example, the developing roller of the developing device of the copying machine (TASKalfa 400ci manufactured by Kyocera Mita Corporation) is replaced with the following developing roller. The developing roller to be replaced is a developing roller having a resin layer on the surface as described later.

[Example 1]
First, a method for manufacturing a developing roller according to Example 1 is described below.

  As the developing roller, a developing roller having a resin layer on the surface as shown in FIGS. 5A and 5B was produced.

Specifically, first, 100 parts by mass of a polyamide urethane resin (manufactured by Shin-Etsu Chemical Co., Ltd.) and 200 parts by mass of titanium oxide particles having an average primary particle size of 20 nm are adjusted to a methyl content of 20% by mass. Mixed. An aluminum sleeve having a diameter of 300 mm was applied to the surface of the roller by a spray method so that the resin layer obtained by mixing had a layer thickness of 2 μm finally obtained. Thereafter, it was heated and dried at 80 ° C. for 0.5 hours. By doing so, the developing roller according to Example 1 was obtained. The obtained developing roller had a surface portion composed of a resin layer and a surface resistivity of 3 × 10 ¹¹ Ω / □. The surface resistivity of the developing roller was measured using Hiresta UP MCP-HT450 type manufactured by Mitsubishi Chemical Analytech Co., Ltd. The average primary particle diameter of the titanium oxide particles is based on the standard value of the product.

  Other configurations of the image forming apparatus, detailed development conditions, and the like are as follows.

  As the photosensitive drum, an amorphous silicon photosensitive member (a-Si photosensitive member) having a diameter of 30 mm was used and rotated at a peripheral speed (drum linear speed) of 270 mm / second, and the surface potential was set to 230V.

  As the developing roller, the developing roller was used and rotated at a peripheral speed of 400 mm / second.

  As the magnetic roller, a knurled magnetic roller having a diameter of 20 mm was used and rotated at a peripheral speed of 600 mm / second.

  The gap (DS gap) between the photosensitive drum and the developing roller was 100 μm, and the gap (MS gap) between the developing roller and the magnetic roller was 300 μm.

  The developing roller has a peak-to-peak value Vpp (slv) of 1800 V, a bias voltage Vdc (slv) of 50 V, a duty ratio Vduty (slv) of 45%, and a frequency f (slv) of 4.7 kHz. A superimposed voltage in which an AC component is superimposed on a DC component was applied.

  The magnetic roller has a peak-to-peak value Vpp (mag) of 2300 V, a bias voltage Vdc (mag) of 350 V, a duty ratio Vduty (mag) of 70%, and a frequency f (mag) of 4.7 kHz. A superimposed voltage in which an AC component is superimposed on a DC component was applied.

  As the toner and developer, the toner and developer used in the above-described copying machine (TASKalfa 400ci manufactured by Kyocera Mita Corporation) were used.

[Evaluation]
(Leak generation)
Under the above development conditions, image formation was performed in a room temperature and normal humidity environment at a temperature of 20 to 23 ° C. and a relative humidity of 50 to 65% RH. If no occurrence of leak was confirmed, it was evaluated as “◯”, and if occurrence of leak was confirmed, it was evaluated as “x”.

(Image density)
Similar to the evaluation of the occurrence of leakage, image formation was performed under the above-described development conditions in a room temperature and normal humidity environment at a temperature of 20 to 23 ° C. and a relative humidity of 50 to 65% RH, and evaluated according to the following criteria.

  Specifically, first, the developer was set in the developer container of the image forming apparatus, and the image forming apparatus was turned on and stabilized. Then, the sample image containing a 100% solid part was output in the normal temperature normal humidity environment. This image was used as the initial image. Thereafter, 100 sample images were printed in a room temperature and humidity environment. The image obtained when printing on the 100th sheet was taken as an image after printing 100 sheets.

  The image density (reflection density ID) of the 100% solid portion of the initial image and the 100-sheet printed image was measured using a reflection densitometer (Spectrophotometer SpectroEyeLT manufactured by Gretag Macbeth). Respectively, an image density ID (initial) and an image density ID (after 100 sheets) were set.

  If the measured image density IDs are both 1.35 or more, it is evaluated as “◯”, if it is 1.25 or more and less than 1.35, it is evaluated as “Δ”, and if it is less than 1.25, “ “×”.

(Abrasiveness)
First, the resin composition used for forming the resin layer constituting the surface portion of the developing roller was applied onto a disk-shaped aluminum plate using a bar coder method. Thereafter, it was heated and dried at 80 ° C. for 0.5 hours. By doing so, what formed the resin layer of the same composition as the resin layer which comprises the surface part of the said developing roller on the said aluminum plate was obtained. The resin layer formed on this aluminum plate was evaluated for polishing properties by a method based on JIS-K-7204 using a Taber abrasion tester (abrasion loss measuring device manufactured by Toyo Seiki Seisakusho Co., Ltd.). . Specifically, CS-10 is used as a grindstone for the Taber abrasion tester, the grindstone is brought into contact with the resin layer, and a load of 40 g per grindstone is applied, and the grindstone is rotated at 60 rpm. It was rotated with. After the grindstone was rotated 1000 times, the difference in height between the area where the grindstone was in contact with the area where the grindstone was not in contact was measured as the amount of scraping. And when the amount of abrasion was 0.1 μm or less, it was evaluated as “◯”, and when it exceeded 0.1 μm, it was evaluated as “x”.

  Here, the scraping amount is the scraping amount of the resin layer having the same composition as the resin layer constituting the surface portion of the developing roller. Therefore, the smaller the scraping amount, the harder the resin layer of the developing roller is worn. be able to.

  The results are shown in Table 2.

[Example 2]
Example 1 is the same as Example 1 except that titanium oxide particles having an average primary particle diameter of 100 nm were used instead of titanium oxide particles having an average primary particle diameter of 20 nm. The developing roller obtained in Example 2 had a surface portion composed of a resin layer and a surface resistivity of 3 × 10 ¹¹ Ω / □. And evaluation similar to Example 1 was performed.

[Example 3]
It is the same as that of Example 1 except using 275 mass parts instead of using 200 mass parts of titanium oxide particles with an average primary particle diameter of 20 nm. The developing roller obtained in Example 3 had a surface portion composed of a resin layer and a surface resistivity of 1 × 10 ¹¹ Ω / □. And evaluation similar to Example 1 was performed.

[Example 4]
It is the same as that of Example 1 except using 100 mass parts instead of using 200 mass parts of titanium oxide particles with an average primary particle diameter of 20 nm. The developing roller obtained in Example 4 had a surface portion composed of a resin layer and a surface resistivity of 1 × 10 ¹² Ω / □. And evaluation similar to Example 1 was performed.

[Example 5]
Example 1 is the same as Example 1 except that 350 parts by mass of titanium oxide particles having an average primary particle diameter of 20 nm is used instead of 200 parts by mass. The developing roller obtained in Example 5 had a surface portion composed of a resin layer and a surface resistivity of 5 × 10 ¹⁰ Ω / □. And evaluation similar to Example 1 was performed.

[Example 6]
Example 1 is the same as Example 1 except that titanium oxide particles having an average primary particle diameter of 250 nm were used instead of titanium oxide particles having an average primary particle diameter of 20 nm. The developing roller obtained in Example 6 had a surface portion made of a resin layer and a surface resistivity of 3 × 10 ¹¹ Ω / □. And evaluation similar to Example 1 was performed.

[Comparative Example 1]
Example 1 is the same as Example 1 except that 20 parts by mass of carbon black having an average primary particle diameter of 48 nm was used instead of 200 parts by mass of titanium oxide particles having an average primary particle diameter of 20 nm. The developing roller obtained in Comparative Example 1 had a surface portion made of a resin layer and a surface resistivity of 5 × 10 ⁴ Ω / □. And evaluation similar to Example 1 was performed.

  Each of the above conditions is shown in Table 1, and the evaluation of each example and comparative example is shown in Table 2.

表２からわかるように、現像ローラとして、少なくとも表面部が酸化チタン粒子と樹脂とを含有する樹脂層で構成されるローラを用いた場合（実施例１〜６）は、リークの発生を抑制できた。これに対して、酸化チタン粒子の代わりにカーボンブラックを用いた場合（比較例１）は、リークの発生を抑制できなかった。

As can be seen from Table 2, when a roller composed of a resin layer having at least a surface portion containing titanium oxide particles and a resin is used as the developing roller (Examples 1 to 6), the occurrence of leakage can be suppressed. It was. On the other hand, when carbon black was used instead of titanium oxide particles (Comparative Example 1), the occurrence of leakage could not be suppressed.

Furthermore, if the surface resistivity of the developing roller is ^{10 12 Ω} / □ under 1 × (Examples 1-3, Example 5, and Example 6), the surface resistivity of the developing roller is 1 × ^{10 12 Ω} / □ Compared with the above case (Example 4), a high image density could be maintained even after printing 100 sheets. From this, it was found that the surface resistivity of the developing roller is preferably less than 1 × 10 ¹² Ω / □.

  Moreover, when content of a titanium oxide particle is 70-300 mass parts with respect to 100 mass parts of resin (Examples 1-4 and Example 6), content of a titanium oxide particle is 300 mass parts. More than the case (Example 5), the evaluation of abrasiveness was more preferable. From this, it was found that the content of the titanium oxide particles is preferably 70 to 300 parts by mass with respect to 100 parts by mass of the resin.

13 Rotating Sleeve 15 Fixed Shaft 18, 23 Resin Layer 19 Base Material 20 Developing Device (Developing Unit)
22, 25 Shaft 24 Roller body 28 Rib 60 Copying machine 61 Developing roller 62 Magnetic roller 63 Stirring roller 65 Blade

Claims (4)

A developing device that visualizes an electrostatic latent image formed on the surface of an image carrier as a toner image,
A magnetic roller carrying a two-component developer containing toner and a carrier on the surface and conveying the carried two-component developer;
The toner in the two-component developer is carried on the surface in contact with or close to the two-component developer conveyed by the magnetic roller, which is disposed opposite to the image carrier and the magnetic roller. A developing roller that conveys the carried toner to the vicinity of the image carrier,
As the developing roller, at least the surface portion is a roller composed of a resin layer containing titanium oxide particles and a resin ,
The developing roller has a surface resistivity of less than 1 × 10 ¹² Ω / □,
The content of the titanium oxide particles is 70 to 300 parts by mass with respect to 100 parts by mass of the resin,
The developing device, wherein the titanium oxide particles have an average primary particle diameter of 10 to 50 nm . The developing device according to claim 1, wherein the resin is a polyamide urethane resin. An image forming apparatus comprising the developing device according to claim 1 and an image carrier. The image forming apparatus according to claim 3 , wherein the image carrier is an amorphous silicon photoconductor.

Images