JP6170874B2 - Developing device, developing method, and image forming apparatus - Google Patents

Description

  The present invention relates to a developing device, a developing method, and an image forming apparatus.

  As a developing device used in an image forming apparatus using an electrophotographic system, such as a copying machine, a printer, a facsimile machine, and a multifunction machine of these, there are various developing systems. As such a developing device, for example, a toner carried on the surface is conveyed to the vicinity of the image carrier on which an electrostatic latent image is formed, and the conveyed toner is caused to fly toward the surface of the image carrier. Examples thereof include a developing device provided with a carrier.

  As a toner carrier provided in such a developing device, for example, a developing roller in which a resin layer is coated on a base material may be used for the purpose of reducing toner adhesion. As such a developing roller, the developing roller of patent document 1 is mentioned, for example.

  In Patent Document 1, in a magnetic developing roller in which a magnet roller is disposed in a sleeve, the sleeve is formed by molding a conductive resin composition containing a synthetic resin such as polyamide and a conductive agent. A magnetic developing roller formed by integrally forming a flange portion at one end is described.

JP 2001-1544489 A

  According to Patent Document 1, it can be produced by a simple process, has good processing accuracy, can easily express desired surface properties, and has a very high practical value. It is disclosed.

  However, according to the study by the present inventors, when a developing roller having a resin layer coated on a substrate as described in Patent Document 1 is used as the toner carrier, the toner is overcharged (charge-up). ). Specifically, the developing device including such a developing roller is preferentially supplied from an easily flying toner to the image carrier and used for development, and the toner that is difficult to fly is attached to the toner carrier. Tend to be. Such a state is likely to occur particularly when printing an image with a low printing rate in a low-humidity environment such as low temperature and low humidity (LL). When printing is performed in this state, friction between the toner carrier and the toner or the like may occur. The toner in the vicinity of the toner carrier is overcharged. When the toner is overcharged, a decrease in image density, fogging, and the like occur, making it difficult to form a high-quality image.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a developing device and a developing method capable of forming a high-quality image. It is another object of the present invention to provide an image forming apparatus including the developing device.

  As a result of studying the above phenomenon, the present inventors have found that the higher the resistance of the toner, the more likely it is that the image quality is deteriorated due to overcharging of the toner. It has been found that the charge decay constant α is small, for example, often less than 0.01.

  In addition, the present inventors have found that there is a case where a high-quality image cannot be obtained only by using a toner having a large charge attenuation constant α in order to suppress overcharging of the toner. This is presumably because when the charge decay constant of the toner is too large, the toner is hardly charged, and thus toner scattering occurs.

  Further, according to the study by the present inventors, since the toner is charged by friction with the toner carrier, the ease of increasing the toner charge amount is not only the toner charge decay constant but also the toner carrier. It was found that the surface potential of the body is also affected by changes.

  As a result of various studies as described above, the present inventors have found that the above object can be achieved by the present invention as described below.

A developing device according to an aspect of the present invention includes a toner carrier that is disposed to face an image carrier on which an electrostatic latent image is formed, and that supplies toner carried on the surface to the image carrier. The toner has a charge decay constant α of 0.01 to 0.05, the toner carrier comprises a base material and a resin layer formed on the base material, and has a surface of 0.001 coulomb / After the charge of m ² is applied, the average change amount of the maximum value of the surface potential from 2 seconds to 3 seconds is 3 to 5V.

  According to such a configuration, it is possible to provide a developing device capable of forming a high-quality image. This is considered to be due to the following.

  First, if the toner used has a charge decay constant α within the above range, the toner is difficult to be charged, but it is considered that the toner has sufficient resistance to the extent that toner scattering can be sufficiently suppressed.

  Further, it is considered that if the toner carrier has a change amount of the surface potential within the above range, the toner can be prevented from being charged excessively.

  For these reasons, when the toner and the toner carrier described above are used in combination, it is possible to sufficiently suppress the occurrence of toner scattering and sufficiently suppress the deterioration in image quality that may be caused by toner overcharging. Conceivable. Therefore, it is considered that a high-quality image can be formed with the developing device configured as described above.

  In the developing device, the toner includes an anionic core particle and a cationic shell layer covering the core particle, and the toner has a charge decay constant α of 0.02 to 0. .05 is preferred.

  According to such a configuration, a higher quality image can be formed. With such a toner, it is considered that the occurrence of toner scattering can be sufficiently suppressed, and the deterioration of the image quality that may be caused by toner overcharging can be further suppressed.

  In the developing device, the base material preferably includes an aluminum base material and an oxide layer formed on the aluminum base material.

  According to such a configuration, it is possible to provide a developing device in which the adhesion of the resin layer to the base material is increased, the peeling of the resin layer can be suppressed, and a high-quality image can be formed over a long period of time. it can.

  In the developing device, it is preferable that the resin layer includes a polyamide resin and a conductive material dispersed in the polyamide resin, and the conductive material is at least one of titanium oxide and carbon black.

  According to such a configuration, it is possible to provide a developing device that can form a higher quality image.

  Further, the developing device includes a developer carrier that supplies toner contained in the two-component developer to the toner carrier from a two-component developer including toner and carrier carried on the surface, The toner carried on the surface of the toner carrying member is preferably a toner supplied from the developer carrying member.

  According to such a configuration, since it is so-called touch-down development, a higher quality image can be formed.

The developing method according to another aspect of the present invention includes a step of transporting toner carried on a surface of a toner carrier to an image carrier on which an electrostatic latent image is formed, and the toner carrying member carrying the toner. And a step of causing the formed toner to fly to the surface of the image carrier to visualize an electrostatic latent image formed in advance on the surface of the image carrier as a toner image. A toner having α of 0.01 to 0.05 is used, and the toner carrier is provided with a base material and a resin layer formed on the base material, and has a surface of 0.001 coulomb / m ² . A toner carrier having an average amount of change in the maximum value of the surface potential from 2 seconds to 3 seconds after applying the charge is 3 to 5 V.

  According to such a configuration, it is possible to provide a developing method capable of forming a high-quality image.

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

  According to such a configuration, a high-quality image can be formed.

  According to the present invention, it is possible to provide a developing device and a developing method capable of forming a high-quality image. An image forming apparatus including the developing device is provided.

FIG. 1 is a schematic diagram illustrating an overall configuration of an image forming apparatus including a developing device according to an embodiment of the present invention. FIG. 2 is a schematic sectional view showing the developing device according to the embodiment of the present invention. FIG. 3 is a perspective view showing an example of a developing roller provided in the developing device according to the embodiment of the present invention. 4 is a cross-sectional view of the developing roller shown in FIG. FIG. 5 is a perspective view showing another example of the developing roller provided in the developing device according to the embodiment of the present invention. 6 is a cross-sectional view of the developing roller shown in FIG. FIG. 7 is a schematic diagram showing the configuration of the electrostatic diffusivity measuring apparatus. FIG. 8 is a diagram for explaining a situation at the time of measurement in the electrostatic diffusivity measuring apparatus shown in FIG.

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

  Here, as an image forming apparatus including the developing device according to the embodiment of the present invention, a tandem image forming apparatus will be described as an example. However, any image forming apparatus using an electrophotographic method may be used. It is not limited to the image forming apparatus. The type of image forming apparatus will be described by taking a color printer as an example. However, for example, it may be a copying machine, a facsimile machine, a multifunction machine, or the like, and is not limited to a color printer.

  An image forming apparatus 10 including a developing device according to an embodiment of the present invention performs image forming processing based on image information transmitted from an external device such as a computer, and is a so-called tandem image forming apparatus (color A printer 10 will be described as an example. FIG. 1 is a schematic diagram illustrating an overall configuration of an image forming apparatus including a developing device according to an embodiment of the present invention.

  As shown in FIG. 1, the image forming apparatus 10 includes a paper feeding unit 12 that feeds paper P and is fed from the paper feeding unit 12. An image forming unit 13 that forms a toner image based on image information on the paper P, and a fixing unit 14 that performs a fixing process for fixing an unfixed toner image formed on the paper P by the image forming unit 13 to the paper P. Is provided. Further, on the upper part of the apparatus main body 11, a paper discharge unit 15 for discharging the paper P subjected to the fixing process by the fixing unit 14 is formed.

  At an appropriate position on the upper surface of the apparatus main body 11, an operation panel (not shown) for inputting an output condition for the paper P or the like is provided. The operation panel is provided with a power key and various keys for inputting output conditions.

  In the apparatus main body 11, the paper P is transported from the paper feed unit 12 to the paper discharge unit 15, and the paper P being transported passes through the transfer unit and the fixing unit 14 of the image forming unit 13. A conveyance path 111 is formed. In the paper transport path 111, a transport roller pair 112 for transporting the paper P is provided at an appropriate place.

  The paper feed unit 12 includes a paper feed tray 121, a pickup roller 122, and a paper feed roller pair 123. The paper feed tray 121 is detachably mounted at the entrance of the paper transport path 111, in FIG. 1, at a position below the image forming unit 13 in the apparatus main body 11, and a paper bundle in which a plurality of paper sheets P are stacked. Store. The pickup roller 122 is provided at an upper position on the upstream side of the paper feed tray 121 in the conveyance direction of the paper P, specifically, at an upper left position shown in FIG. The top sheet P is taken out one by one. The paper feed roller pair 123 sends the paper P taken out by the pickup roller 122 to the paper transport path 111. Through these operations, the paper feeding unit 12 feeds the paper P toward the image forming unit 13.

  The paper feeding unit 12 further includes a manual feed tray 124, a pickup roller 125, and a paper feed roller pair 126 that are attached to the right side surface of the apparatus main body 11 shown in FIG. The manual feed tray 124 is for supplying the paper P toward the image forming unit 13 by manual feed operation. The manual feed tray 124 can be stored on the side surface of the apparatus main body 11, and when the paper P is manually fed, as shown in FIG. 1, the manual feed tray 124 is pulled out from the side surface of the apparatus main body 11 to be manually fed. The pickup roller 125 takes out the paper P placed on the manual feed tray 124. The paper P taken out by the pickup roller 125 is sent out to the paper transport path 111 by the paper feed roller pair 126. Through these operations, the paper feeding unit 12 feeds the paper P toward the image forming unit 13.

  The image forming unit 13 forms an image such as a color image on the paper P fed from the paper feeding unit 12 by predetermined image processing. The image forming unit 13 includes a plurality of image forming units 131, an intermediate transfer belt (intermediate transfer member) 132, a primary transfer roller 133, and a secondary transfer roller 134.

  In the present embodiment, the image forming unit 131 is magenta (M) that is sequentially disposed from the upstream side to the downstream side in the rotation direction of the intermediate transfer belt 132 (from the right side to the left side in FIG. 1). Magenta unit 131M using a color developer, cyan unit 131C using a cyan (C) developer, yellow unit 131Y using a yellow (Y) developer, and black (K) developer A black unit 131K using the above is provided. Each unit 131 includes a photosensitive drum 135 as an image carrier, and forms a toner image corresponding to each color on the photosensitive drum 135 based on image information, and performs primary transfer onto the intermediate transfer belt 132.

  In the image forming unit 131, a photosensitive drum 135 as an image carrier is arranged at the center position so as to be rotatable in the direction of an arrow (indicated by an arrow A in FIG. 2). In addition, when the position (primary transfer) transferred by the primary transfer roller 133 is set to the most upstream side in the rotation direction of the photosensitive drum 135 around the photosensitive drum 135, the position moves from there to the downstream side. In this order, a cleaning device 24, a charging device 21, an exposure device 22, and a developing device 23 are arranged.

  The photosensitive drum (image carrier) 135 forms a toner image corresponding to each color based on image information on the peripheral surface thereof by a charging process, an exposure process, a development process, and a charge removal process, which will be described later. Is for. The photoconductor drum 135 is not particularly limited as long as it is a photoconductor drum that can be provided in the image forming apparatus, and examples thereof include an organic photoconductor (OPC) drum and an amorphous silicon (a-Si) photoconductor drum. It is done.

  The charging device 21 charges the peripheral surface of the photosensitive drum 135 rotated in the direction of the arrow. The charging device 21 is not particularly limited as long as it is a charging device that can be provided in the image forming apparatus. Specifically, for example, a charging device including a charging roller and applying a predetermined charging bias to the charging roller to charge the peripheral surface of the photosensitive drum, or a non-contact discharge corotron type And a scorotron type charging device.

  The exposure device 22 irradiates the peripheral surface of the photosensitive drum 135 whose peripheral surface is charged by the charging device 21 with laser light or LED light based on image information, and converts the image information onto the peripheral surface of the photosensitive drum 135. For forming an electrostatic latent image based thereon. The exposure device 22 is not particularly limited as long as it is an exposure device provided in the image forming apparatus. Specifically, an LED head unit, a laser scanning unit (LSU), etc. are mentioned, for example.

  The developing device 23 is for developing the electrostatic latent image formed on the peripheral surface of the photosensitive drum 135 into a toner image. The configuration of the developing device 23 will be described later.

  The cleaning device 24 transfers (primary transfer) the toner image on the circumferential surface of the photosensitive drum 135 to the intermediate transfer belt 132 by the primary transfer roller 133, and then remains on the circumferential surface of the photosensitive drum 135. This is for removing the toner. The peripheral surface of the photosensitive drum 135 from which the toner remaining after the primary transfer is removed by the cleaning device 24 is directed to a charging position by the charging device 21 for a new image forming process. The waste toner removed by the cleaning device 24 is collected and stored in a toner collection bottle (not shown) through a predetermined path.

  Further, before the toner is removed by the cleaning device 24, the peripheral surface of the photosensitive drum 135 may be neutralized by a neutralizing device (not shown). By doing so, the toner remaining on the peripheral surface of the photosensitive drum 135 after the primary transfer is suitably removed by the cleaning device 24.

  The intermediate transfer belt 132 is for transferring (primary transfer) a toner image based on image information to the peripheral surface (contact surface) of the plurality of image forming units 131. That is, in this embodiment, the intermediate transfer belt 132 is a transfer target that is sandwiched between the photosensitive drum 135 and the primary transfer roller 133 and has a peripheral surface to which a toner image is transferred from the photosensitive drum 135. .

  Further, the intermediate transfer belt 132 is an endless belt-like rotating body, and the driving roller 136, the belt support roller 137, and the tension roller 139 so that the circumferential surface side thereof is in contact with the circumferential surface of each photoconductor 135. It is stretched over. Further, the intermediate transfer belt 132 is pressed against each photoconductor drum 135 by each primary transfer roller 133 disposed at a position facing each photoconductor drum 135 via the intermediate transfer belt 132, and the driving roller 136. It is comprised so that it may rotate endlessly by rotational drive. The driving roller 136 is rotationally driven by a driving source such as a stepping motor, and gives a driving force for rotating the intermediate transfer belt 132 endlessly. The belt support roller 137 and the tension roller 139 are driven rollers that are rotatably provided and rotate following the endless rotation of the intermediate transfer belt 132 by the driving roller 136. These driven rollers 137 and 139 are driven to rotate via the intermediate transfer belt 132 according to the main rotation of the driving roller 136 and support the intermediate transfer belt 132. Further, the tension roller 139 applies tension (tension) to the intermediate transfer belt so that the intermediate transfer belt 132 does not loosen. The tension roller 139 is biased by a biasing member such as a spring body, for example, so that the intermediate transfer belt 132 is moved from the back surface (inner peripheral side) to the front surface (outer peripheral side). The tension is generated by applying a pressing force to the belt 132.

  The primary transfer roller 133 is for primary transfer of the toner image formed on the photosensitive drum 135 to the intermediate transfer belt 132. That is, in this embodiment, the primary transfer roller 133 holds the intermediate transfer belt 132 between the photosensitive drum 135 and the toner image on the circumferential surface of the photosensitive drum 135 to the intermediate transfer belt 132 for primary transfer. It is a transfer part to be made

  Further, the primary transfer roller 133 is disposed at a position facing each photosensitive drum 135 with the intermediate transfer belt 132 interposed therebetween. The primary transfer roller 133 is provided for each photosensitive drum 135. In addition, the primary transfer roller 133 rotates depending on the endless rotation of the intermediate transfer belt 132 while being in contact with the intermediate transfer belt 132. At that time, by applying a primary transfer bias having a polarity opposite to the charging polarity of the toner to each primary transfer roller 133, a toner image formed on each photoconductor drum 135 becomes a photoconductor drum 135. And the corresponding primary transfer rollers 133 are primarily transferred to the intermediate transfer belt 132. As a result, the toner images formed on the respective photosensitive drums 135 are sequentially primary-transferred sequentially in an overcoated state on the intermediate transfer belt 132 that rotates in the direction of an arrow (clockwise in FIG. 1).

  The secondary transfer roller 134 is for transferring (secondary transfer) the toner image on the intermediate transfer belt 132 onto the paper P fed from the paper feeding unit 12. That is, in the present embodiment, the secondary transfer roller 134 contacts the peripheral surface of the intermediate transfer belt 132 to form a nip portion, and the intermediate transfer belt 132 is formed on a sheet P that is a recording medium passing through the nip portion. 2 is a secondary transfer portion for secondary transfer of the toner image on the peripheral surface of the toner.

  The secondary transfer roller 134 is disposed at a position facing the drive roller 136 with the intermediate transfer belt 132 interposed therebetween. Further, the secondary transfer roller 134 is rotated in accordance with the endless rotation of the intermediate transfer belt 132 while being in contact with the intermediate transfer belt 132. At that time, the toner on the circumferential surface of the intermediate transfer belt 132 is secondarily transferred between the secondary transfer roller 134 and the driving roller 136 onto the paper P fed from the paper feeding unit 12. As a result, the toner image based on the image information is transferred onto the paper P in an unfixed state.

  The image forming unit 13 further includes a belt cleaning device 138 at a position downstream of the secondary transfer position in the rotational direction of the intermediate transfer belt 132 and upstream of the primary transfer position in the rotational direction. The belt cleaning device 138 is for cleaning the intermediate transfer belt 132 by removing the toner remaining on the peripheral surface of the intermediate transfer belt 132 after the secondary transfer. The peripheral surface of the intermediate transfer belt 132 cleaned by the belt cleaning device 138 goes to the primary transfer position for a new primary transfer process. The waste toner removed by the belt cleaning device 138 is collected and stored in a toner collection bottle (not shown) through a predetermined path.

  The fixing unit 14 performs a fixing process on the toner image on the paper P that has been secondarily transferred by the secondary transfer roller 134. The fixing unit 14 is stretched between a heating roller 141 including an energization heating element serving as a heating source therein, a fixing roller 142 disposed opposite to the heating roller 141, and the fixing roller 142 and the heating roller 141. A fixing belt 143 and a pressure roller 144 disposed to face the fixing roller 142 with the fixing belt 143 interposed therebetween are provided.

  The paper P supplied to the fixing unit 14 is heated and pressed by passing through a fixing nip formed between the fixing belt 143 and the pressure roller 144. As a result, the toner image secondarily transferred to the paper P by the secondary transfer roller 134 is fixed to the paper P. The sheet P that has been subjected to the fixing process is discharged toward the sheet discharge tray 151 of the sheet discharge unit 15 provided at the top of the apparatus main body 11 through the sheet conveyance path 111 extending from the upper part of the fixing unit 14. Paper.

  The paper discharge unit 15 is formed by recessing the top of the apparatus main body 11, and a paper discharge tray 151 for receiving the discharged paper P is formed at the bottom of the concave portion.

  Next, the developing device according to the embodiment of the present invention will be described.

  A developing device according to an embodiment of the present invention includes a toner carrier that is disposed to face an image carrier on which an electrostatic latent image is formed and supplies toner carried on the surface to the image carrier. Device. The developing device according to the embodiment of the present invention only needs to include such a toner carrier, and may be a one-component developing device using a one-component developer that does not include a carrier, or a toner and a carrier. Although a two-component developer is used, a toner carrying member may be a so-called touch-down developing type developing device that carries toner. Here, a developing apparatus of a touch-down developing method will be described as an example. Such a developing device will be described with reference to FIG. FIG. 2 is a schematic sectional view showing the developing device according to the embodiment of the present invention. FIG. 2 also shows the photosensitive drum as well as the developing device.

  Further, the touch-down developing type developing device, specifically, the toner contained in the two-component developer from the toner carrier and the two-component developer carried on the surface including the toner and the carrier. And a developer carrier to be supplied to the toner carrier. Since such a developing device is a so-called touch-down developing type developing device, more suitable image formation can be realized.

  As described above, the developing device 23 is for developing the electrostatic latent image formed on the peripheral surface of the photosensitive drum 135 into a toner image. As shown in FIG. 2, the developing device 23 includes a developing roller (toner carrier) 231, a magnetic roller (developer carrier) 232, and a stirring and conveying member 237 that are built in the developing container 236. ing. The developing roller 231 is connected to a developing bias applying unit (first bias applying unit) 241, and the magnetic roller 232 is connected to a toner supply bias applying unit (second bias applying unit) 242.

  The developing container 236 is a developing tank that constitutes the outline of the developing device 23 and contains a two-component developer including a carrier and toner. The developing container 236 has an opening 236 a that exposes the developing roller 231 toward the photosensitive drum 135. The developing container 236 is formed with a first transport path 236c and a second transport path 236d that are partitioned by a partition portion 236b. Further, the developing container 236 rotatably holds the developing roller 231, the magnetic roller 232, and the stirring and conveying member 237.

  The developing roller 231 faces each of the photosensitive drum 135 and the magnetic roller 232 and is spaced apart with their opposed peripheral surfaces close to each other. That is, the developing roller 231 and the photosensitive drum 135 are spaced apart from each other with their peripheral surfaces close to each other, thereby forming a developing region D for supplying toner to the photosensitive drum 135. Further, the developing roller 231 and the magnetic roller 232 are also arranged apart from each other with their peripheral surfaces close to each other.

  The magnetic roller 232 is conveyed to the vicinity of the developing roller 231 by carrying a two-component developer containing toner on its peripheral surface by a magnetic pole member M fixedly arranged inside and rotating in that state. By doing so, the magnetic roller 232 supplies the toner of the two-component developer to the developing roller 231.

  The developing roller 231 carries the toner supplied from the magnetic roller 232 on the peripheral surface thereof, and rotates the toner roller 231 in the state to convey the toner to the vicinity of the photosensitive drum 135. By doing so, the electrostatic latent image previously formed on the peripheral surface of the photosensitive drum 135 is visualized (developed) as a toner image.

  The stirring and conveying member 237 includes a first stirring and conveying member (stirring mixer) 234 and a second stirring and conveying member (paddle mixer) 233. The first stirring and conveying member 234 is provided in the first conveying path 236c, and the second stirring and conveying member 233 is provided in the second conveying path 236d.

  The paddle mixer 233 and the agitation mixer 234 have spiral blades and agitate while conveying the two-component developer in opposite directions to charge the toner contained in the two-component developer. Further, the paddle mixer 233 supplies a two-component developer containing charged toner to the magnetic roller 232.

  The ear cutting blade 235 is arranged so that one end thereof is opposed to the peripheral surface of the magnetic roller 232, and regulates the thickness of the two-component developer carried on the magnetic roller 232.

  The magnetic roller 232 includes a roller shaft 232a, a magnetic pole member M, and a nonmagnetic sleeve 232b made of a nonmagnetic material. As described above, the magnetic roller 232 carries the developer supplied by the paddle mixer 233 of the stirring and conveying member 237, and supplies toner from the carried developer to the developing roller 231. The magnetic pole member M is a member in which a plurality of magnets having different magnetic poles on the outer peripheral portion formed in a sector shape are alternately arranged and fixed to the roller shaft 232a by adhesion or the like. The roller shaft 232a is supported by the developing container 236 in a non-rotatable manner within the nonmagnetic sleeve 232b with a predetermined gap between the magnetic pole member M and the nonmagnetic sleeve 232b. The nonmagnetic sleeve 232b is rotated in the arrow direction (the same direction as the developing roller 231 and the clockwise direction in FIG. 2) by a driving mechanism including a motor and gears (not shown).

  The developing roller 231 includes a fixed shaft 231a, a developing sleeve 231b, and the like. The fixed shaft 231a is supported by the developing container 236 so as not to rotate. The developing sleeve 231b is rotated in the direction of the arrow (in the clockwise direction in FIG. 2) by a driving mechanism including a motor and gears (not shown).

  The toner supply bias application unit (second bias application unit) 242 applies a toner supply bias (second bias) to the roller shaft 232 a of the magnetic roller 232. By applying the toner supply bias, the magnetic roller 232 carries the toner of the two-component developer carried on the surface thereof and transported to the vicinity of the developing roller 231 to the developing roller 231.

  The development bias application unit (first bias application unit) 241 applies a development bias (first bias) to the fixed shaft 231a of the development roller 231. By applying a developing bias, the developing roller 231 carries the toner carried on the surface thereof and transported to the vicinity of the photosensitive drum 135 to the photosensitive drum 135.

  The developing bias applying unit 241 and the toner supply bias applying unit 242 include an AC power source that applies an AC voltage. In other words, the development bias applied by the development bias application unit 241 and the toner supply bias applied by the toner supply bias application unit 242 include an AC component. Further, the development bias applying unit 241 and the toner supply bias applying unit 242 may further include a DC power source for applying a DC voltage, as shown in FIG. That is, the development bias applied by the development bias application unit 241 and the toner supply bias applied by the toner supply bias application unit 242 may be a superimposed voltage in which an AC component is superimposed on a DC component.

As described above, the developing device according to the present embodiment supplies the toner of the two-component developer conveyed by the magnetic roller 232 that is the developer carrying member to the developing roller 231 that is the toner carrying member, and is supplied thereto. The toner is carried on the developing roller 231. The carried toner is applied to the developing roller 231 to fly to the photosensitive drum 135 as an image carrier. In order to make this flight suitable, the present inventors have found that a specific toner and a toner carrier described later are used in combination. Specifically, the developing device according to the embodiment of the present invention uses toner having a charge decay constant α of 0.01 to 0.05 as the toner. In addition, the developing device includes, as the toner carrier, a base material and a resin layer formed on the base material, and after applying a charge of 0.001 coulomb / m ^{2 to} the surface, 2 seconds later And a toner carrier having an average change amount of the maximum surface potential of 3 to 5 V after 3 seconds.

  By using a combination of the toner and the toner carrier as described above, it is possible to sufficiently suppress the occurrence of toner scattering while sufficiently reducing the image quality such as a decrease in image density that may be caused by toner overcharging. Can be suppressed. From this, the developing device according to the present embodiment can form a high-quality image.

  Next, the developing roller (toner carrier) provided in the developing device according to the embodiment of the present invention will be described.

This toner carrier satisfies the above-described configuration, that is, the average amount of change in the maximum value of the surface potential from 2 seconds to 3 seconds after applying a charge of 0.001 coulomb / m ² to the surface. Is within the above-mentioned change amount range, and examples thereof include the following developing rollers. The average change amount of the maximum value of the surface potential from 2 seconds to 3 seconds after applying a charge of 0.001 coulomb / m ² to the surface can be measured by the method described later.

  First, the developing roller shown in FIGS. 3 and 4 will be described.

  FIG. 3 is a perspective view showing an example of a developing roller provided in the developing device according to the embodiment of the present invention. FIG. 3 shows the developing roller with a part thereof cut. 4 is a cross-sectional view of the developing roller shown in FIG.

  As shown in FIGS. 3 and 4, the developing roller 231 includes a cylindrical rotating sleeve 32 and a fixed shaft 33 included in the rotating sleeve 32, and the position of the fixed shaft 33 is fixed. The rotating sleeve 32 rotates around the periphery.

  As shown in FIGS. 3 and 4, the rotating sleeve 32 has a resin layer 36 coated on a base material 35. Examples of the substrate 35 include a cylindrical member made of aluminum, stainless steel, or the like. Examples of the fixed shaft 33 include a shaft 37 that is pivotally supported by the developing device and that is connected by a plurality of ribs 38.

  The resin layer 36 is not particularly limited as long as the average change amount of the maximum value of the surface potential is within the above range. The resin layer 36 includes, for example, a polyamide resin and a conductive material dispersed in the polyamide resin, and the conductive material is preferably at least one of titanium oxide and carbon black.

  The polyamide resin is not particularly limited as long as it is a polyamide resin capable of realizing the resin layer as described above. Specifically, the polyamide resin is preferably a polyamide resin soluble in alcohol such as methanol. With such a polyamide resin, when the resin layer is formed by a so-called dipping method in which the base material is immersed in a liquid containing the polyamide resin and the conductive material, alcohol is used as a solvent for the liquid. By using, the said polyamide resin melt | dissolves suitably and it becomes the liquid in which the polyamide resin melt | dissolved uniformly as said liquid. A suitable resin layer can be formed by using such a liquid and forming a resin layer by a dipping method.

  The polyamide resin preferably has a number average molecular weight of 1000 to 50000.

  As the polyamide resin, more specifically, Amilan CM8000 manufactured by Toray Industries, Inc. can be preferably used.

  The conductive material is preferably at least one of titanium oxide and carbon black. The conductive material may contain carbon black, but preferably contains at least titanium oxide, and more preferably consists of titanium oxide. This titanium oxide is, for example, another conductive material. Compared with carbon black or the like, it has higher resistance and higher dielectric constant. From this, it is considered that by using titanium oxide as a conductive material, the obtained toner carrier can suitably remove charges accumulated on the surface thereof. That is, since titanium oxide is included as the conductive material, the ease of change of the surface potential is considered to be a toner carrier that stably satisfies the amount of change as described above. For this reason, the conductive material contained in the resin layer is preferably made of titanium oxide.

  Moreover, although a conductive material is not specifically limited, The thing whose average primary particle diameter is 10-50 nm is preferable. When the conductive material is too small, re-aggregation occurs and dispersion in the resin layer tends to be difficult. On the other hand, if the conductive material is too large, it is difficult to hold it in the resin layer, and the conductive material tends to be easily detached.

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

  Moreover, although content of an electrically conductive material is not specifically limited, For example, it is preferable that it is 50-125 mass parts with respect to 100 mass parts of said polyamide resins. If the content of the conductive material is too small, electric charges are likely to be accumulated in the developing roller, and there is a tendency that a rapid density drop is likely to occur during continuous paper feeding. Moreover, when there is too much content of an electrically conductive material, there exists a tendency for the binding property of an electrically conductive material and resin to weaken or to become easy to peel a resin layer from a base material.

  The thickness of the resin layer is preferably 2 to 15 μm, more preferably 2 to 11 μm, and further preferably 2 to 9 μm.

  The base material is preferably an aluminum base material, and the surface of the aluminum base material is more preferably subjected to an oxidation treatment such as alumite treatment. That is, the base material preferably includes an aluminum base material and an oxide layer formed on the aluminum base material. By providing such an oxide layer, the substrate has improved adhesion to the resin layer.

  Moreover, although the thickness of the said oxide layer is not specifically limited, For example, it is preferable that it is 5-15 micrometers.

  Next, the developing roller shown in FIGS. 5 and 6 will be described.

  FIG. 5 is a perspective view showing another example of the developing roller provided in the developing device according to the embodiment of the present invention. FIG. 6 is a cross-sectional view of the developing roller shown in FIG.

  As shown in FIGS. 5 and 6, the developing roller 231 includes a roller body 52 and a resin layer 53 coated on the surface of the roller body 52. Examples of the roller main body 52 include a roller 55 that is connected to a shaft 55 that is pivotally supported by the developing device by a plurality of ribs 58. The resin layer 53 can be the same as the resin layer 36. The roller body 52 corresponds to the base material 35, and the laminate 51 including the roller body 52 and the resin layer 53 corresponds to the rotating sleeve 32.

The average amount of change in the maximum value of the surface potential from 2 seconds to 3 seconds after applying a charge of 0.001 coulomb / m ² to the surface can be measured, for example, by the following method. it can.

First, a charge is given to the confirmation sample by performing corona discharge on the confirmation sample. Thereafter, the surface potential of the confirmation sample given the charge is measured. From the measured surface potential and the capacitance of the confirmation sample, the charge given to the confirmation sample is calculated based on Coulomb's law (charge Q = capacitance C × voltage V). A condition is found where the calculated charge is 0.001 coulomb / m ² , that is, a condition where the applied charge is 0.001 coulomb / m ² .

  Specifically, for example, the following method is used.

As a confirmation sample, a polyethylene terephthalate (PET) film with an aluminum-deposited film (Metal Me (TS (# 50) thickness 50 μm) manufactured by Toray Industries, Inc.) is used. As in the measurement, the sample is left for 12 hours in an environment with a temperature of 32.5 ° C. and a relative humidity of 80%. , Corona discharge for 0.5 seconds, and then measure the surface potential.When the confirmation sample is placed in the electrostatic diffusivity measuring device, the PET side of the confirmation sample is the upper surface and the aluminum surface is the lower surface ( The sample for confirmation is placed so that it contacts the sample stage, and the aluminum surface of the sample for confirmation is grounded. 001 find coulomb / ^{m 2} and composed such conditions.

  The corona discharge and the measurement of the surface potential can be performed using an electrostatic diffusivity measuring apparatus as shown in FIGS. FIG. 7 is a schematic diagram showing the configuration of the electrostatic diffusivity measuring apparatus, and FIG. 8 is a diagram for explaining the situation at the time of measurement in the electrostatic diffusivity measuring apparatus shown in FIG.

  The electrostatic diffusivity measuring device 70 includes a sample stage 72 on which the measurement target 71 is placed, a measurement unit 73 that performs corona discharge on the measurement target 71 and measures the surface potential of the measurement target 71, and a measurement unit 73. And a control unit 74 for controlling. The measurement unit 73 includes a discharge unit 75 that performs corona discharge on the measurement target 71, a potential measurement unit 76 that measures the surface potential of the measurement target 71, the discharge unit 75, and the potential measurement unit 76. A relative position with respect to the sample stage 72 is provided with a moving part 77. This measuring unit 73 is contained in a constant temperature and humidity chamber 78. The electrostatic diffusivity measuring device 70 performs measurement as follows under the control of the control unit 74. First, the discharge unit 75 performs corona discharge on the measurement object 71. Thereafter, the moving unit 77 moves the sample stage 72 so that the measuring object 71 is directly below the potential measuring unit 76. Thereafter, the potential measuring unit 76 measures the surface potential of the measurement object 71. That is, as shown in FIG. 8, ions 81 are supplied to the measurement object 71 by corona discharge. Thereafter, the surface potential of the measurement object 71 supplied with the ions 81 is measured. In this way, the electrostatic diffusivity measuring apparatus charges the measurement object by supplying ions, and measures the change in the surface potential of the charged measurement object.

  Specific examples of the electrostatic diffusivity measuring device include NS-D100 type manufactured by Nano Seeds Co., Ltd. Moreover, said measuring method is a method based on JISC61340-2-1.

And the change of the surface potential of the developing roller provided in the developing device according to the present embodiment is measured using the electrostatic diffusivity measuring device. Specifically, for the developing roller after standing for 12 hours in an environment of a temperature of 32.5 ° C. and a relative humidity of 80%, the charge found as described above is 0.001 coulomb / m ² . Corona discharge is performed under such conditions, and the amount of change in the maximum value of the surface potential is measured from 2 seconds to 3 seconds after the corona discharge. And if the variation | change_quantity is measured in multiple times and the average value is a developing roller with which the developing device which concerns on this embodiment is equipped, it will be 3-5V. That is, the average value of the developing roller provided in the developing device according to the present embodiment is 3 to 5V. Within such a range, the developing roller can sufficiently suppress the toner from being charged excessively, and a suitable charged state of the toner can be realized.

  Moreover, the manufacturing method of the developing roller 231 is not particularly limited as long as the developing roller described above can be manufactured. First, in the case of the developing roller shown in FIGS. 3 and 4, for example, the surface layer is first oxidized by subjecting an aluminum cylindrical base material generally used as a rotating sleeve of the developing roller to an alumite treatment. An alumite layer as a layer is formed. Although the diameter of this cylindrical base material is not specifically limited, For example, it is preferable that it is 12-20 micrometers. And the rotating sleeve in which this alumite layer was formed is heat-processed. By performing this heat treatment, cracks are formed in advance in the alumite layer in order to prevent new cracks from being formed in the alumite layer in the drying step described later when forming the resin layer. Although it will not specifically limit if this heat processing can form such a crack, For example, it is preferable to perform for a time longer than a drying process. Specifically, this heat treatment is preferably performed at 100 to 140 ° C. for 5 to 15 minutes. Next, the polyamide resin and the titanium oxide are mixed using an alcohol such as methanol as a dispersion medium. In that case, it is preferable that the mixing ratio of the polyamide resin and the titanium oxide is a ratio capable of realizing the content of the conductive material. The amount of alcohol used is not particularly limited as long as it is an amount capable of dissolving the polyamide resin. For example, it is preferably 200 to 900 parts by mass with respect to 100 parts by mass of the polyamide resin. The rotating sleeve subjected to the heat treatment is immersed in the liquid containing the polyamide resin and the titanium oxide thus obtained, and then the rotating sleeve is taken out of the liquid and dried. By such an immersion method, a resin layer can be formed on the surface of the rotating sleeve. This drying is not particularly limited as long as a resin layer can be formed on the surface of the rotating sleeve, but is preferably performed at 110 to 150 ° C. for 5 to 20 minutes, for example.

  Next, the toner used in the developing device according to the present embodiment will be described.

  The toner is not particularly limited as long as its charge decay constant α is 0.01 to 0.05. Further, the charge attenuation constant α of the toner may be 0.01 to 0.05, and preferably 0.02 to 0.05. If the toner is within such a range, it becomes a toner having a resistance that prevents the toner from being overcharged while suppressing the occurrence of toner scattering, and a suitable image can be formed.

  The charge decay constant α of the toner is a charge decay rate that can be measured using the electrostatic diffusivity measuring apparatus. Specifically, for example, it can be measured as follows.

  First, as a measurement cell, a metal measurement cell in which a recess having an inner diameter of 10 mm and a depth of 1 mm is formed is used. Toner is put into this measurement cell and pushed in from above with a slide glass. Then, the overflowing toner is scraped off from the measurement cell by reciprocating the surface of the measurement cell with the slide glass that has been pushed in. At this time, the degree of pressing with the slide glass is adjusted so that the amount of toner filling the recesses is 0.04 g or more and 0.06 g or less.

  Next, the measurement cell filled with toner is left in an environment of 32.5 ° C. and 80% relative humidity for 12 hours, and then placed in the electrostatic diffusivity measurement device in a grounded state, and corona discharge is performed. I do. Then, after 0.7 seconds have elapsed from the end of corona discharge, the surface potential of the toner is continuously measured. Based on the measurement result, a charge decay constant (charge decay rate) α is calculated from the following equation.

V = V ₀ exp (−α√t)
In the above formula, V represents the surface potential (V), V ₀ represents the initial surface potential (V), α represents the charge decay constant (charge decay rate), and t represents the decay time (seconds). Indicates.

  The toner is not particularly limited as long as the charge decay constant α is within the above range. Examples of the toner include toner in which anionic core particles (toner core material) are coated with a cationic shell layer (toner shell).

  The toner core material is not particularly limited as long as the charge attenuation constant α of the finally obtained toner can be within the above range. Specifically, the toner core material is preferably anionic. Examples of the toner core material include classified products produced by a general pulverization method. Whether or not the toner core material exhibits anionicity can be detected by friction charging with a standard carrier provided by the Imaging Society of Japan. For the anionic property of the toner core material under an aqueous medium, measurement at a zeta potential is effective. Specifically, if the toner core material exhibits negative chargeability of −10 μC / g or more by frictional charging with the standardized carrier, it is considered to be anionic. Further, when the zeta potential of the toner core material under an aqueous medium is −10 mV or more, the toner core material is considered to be anionic.

  The toner shell is not particularly limited as long as the charge attenuation constant α of the finally obtained toner can be within the above range. Specifically, the toner shell is preferably cationic. Examples of the toner shell include a thermosetting resin. This toner shell manufacturing method, that is, forming the toner core into a shell was performed by coating the surface of the toner core with a resin constituting the toner shell, for example, a thermosetting resin. The coating method is not particularly limited, but a method capable of realizing a desired average particle size and particle size distribution is preferable. Examples of the coating method include a method in which a film is formed on a solid toner core so that the resin raw material can be produced only by supplying the reaction raw material from the aqueous medium side. More specifically, as the coating method, an in situ polymerization method, a submerged curing coating method, a coacervation method, and the like are preferable, and an in situ polymerization method is more preferable from the viewpoint of reactivity and the like. In this in situ polymerization method, the raw material of the toner shell exists only in the aqueous medium, and this raw material reacts on the toner core to form a resin, thereby forming a film.

  The resin constituting the toner shell is not particularly limited as long as the toner shell is formed. As this resin, for reasons such as toner aggregation can be sufficiently suppressed and film formability is excellent, urea resins such as melamine resins and urea resorcin resins, urethane resins, amide resins, olefin resins, Examples include gelatin and gum arabic resin. Of these, urea resins such as melamine resins and urea resorcin resins are preferred because of their low water absorption and excellent storage stability. That is, since urea resins such as melamine resins and urea resorcin resins have low water absorption, the thin film coated toner is prevented from binding when the thin film coated toner is dried, and the average particle size of the toner is reduced. In addition, the change in particle size distribution can be suppressed, and the rot during storage can be sufficiently suppressed.

  As a method for producing the toner shell, specifically, methylol melamine or methylolated urea, which is a precursor (methylolated product) produced by an addition reaction between melamine and formaldehyde or an addition reaction between urea and formaldehyde, is used. By using it, it is possible to form a film on the surface of the toner core. Moreover, it is preferable to perform these film formation in the solvent which can melt | dissolve this methylolation thing, Specifically, it is preferable to use water, methanol, or ethanol as this solvent. When the shell layer (toner shell) is formed in a solvent such as water, methanol, or ethanol, the toner core is highly dispersed in the solvent in order to uniformly coat the methylolated product on the surface of the toner core. It is preferable. Further, in order to highly disperse the toner core in the solvent, a dispersant may be contained in the solvent.

  The dispersing agent is not particularly limited as long as the object of the present invention is not impaired. Examples of the dispersant include sodium polyacrylate, polyparavinylphenol, partially saponified polyvinyl acetate, isoprene sulfonic acid, polyether, isobutylene / maleic anhydride copolymer, sodium polyaspartate, starch, gum arabic, Examples include polyvinyl pyrrolidone and sodium lignin sulfonate. These dispersants may be used alone or in combination of two or more.

  The amount of the dispersant used is not particularly limited as long as the object of the present invention is not impaired. The amount of the dispersant used is preferably, for example, 75 parts by mass or less with respect to 100 parts by mass of the toner core.

  Further, the temperature at which the toner shell is produced is not particularly limited. The temperature for forming the toner shell (shell layer), for example, the temperature for forming the core shell using methylol melamine or methylol urea in a solvent in which the toner core is highly dispersed is, for example, 40 ° C. or higher. It is preferably 80 ° C. or lower, and more preferably 55 ° C. or higher and 70 ° C. or lower. By forming the shell layer on the surface of the toner core at a temperature in such a range, the formation of the shell layer covering the surface of the toner core proceeds well, and a dispersion of shelled toner can be obtained. Thereafter, a shelled toner is obtained through a washing step and a drying step as necessary.

  In addition, the toner according to the exemplary embodiment can be obtained by adjusting the resistance by adjusting the thickness of the shell layer toner, silica, titanium oxide, or the like, which is an external additive added to the outside of the shell layer. It can be obtained by adjusting the damping constant.

  Such a toner may have the following characteristics, for example.

  The glass transition point Tg of the toner is preferably lower than the curing start temperature of the shell layer, for example, 55 ° C. For example, when the shell layer is a melamine resin, the curing temperature is generally about 55 ° C. or higher and 100 ° C. or lower. Even if the toner core material has a glass transition point Tg of not more than the minimum curing temperature, for example, 55 ° C., it is important that aggregation is suppressed during the shelling reaction. If the Tg of the toner core material is higher than 55 ° C., sufficient fixing strength tends not to be obtained in a high-speed fixing system. The Tg of the toner core is preferably 20 ° C. or higher and 55 ° C. or lower, and preferably 30 ° C. or higher and 50 ° C. or lower.

  Moreover, it is preferable that a shell layer (capsule) has a some destruction location. Specifically, by making the core of the toner before the capsule indefinite, and adding additional particles such as wax, pigment, silica particles to the surface, the encapsulation progresses and the toner is rounded by the surface tension. It has a structure in which there are multiple breakage points of the capsule film when the thermal pressure is applied due to the thickness of the film and minute protrusions, and it instantly adheres to the fixing medium such as paper. ing. On the other hand, when shelling (encapsulation) is performed by thermosetting reaction, a strong film quality is formed by polycondensation reaction, and at the same time, reaction with an anionic toner core surface results in 20 nm or less. Even a thin film is difficult to be destroyed instantaneously by thermal pressure.

  The following methods etc. are mentioned as a confirmation method of a breaking point. For example, when a polyester-based binder is used, it can be measured by a standing test in an alkaline activator having a pH of about 10 as a method for specifying a plurality of destruction sites. Depending on the material and composition of the toner core, it can be observed that a large number of through-holes are opened by an immersion test of an alkaline solution, and the structure that forms a plurality of broken portions of the film can be confirmed.

  Moreover, it is preferable that the thickness of a capsule is 20 nm or less, and it is more preferable that they are 1 nm or more and 10 nm or less. For example, when a melamine resin is used, such a range is preferable, but when a modifier is added to the melamine resin film to make it flexible, the thickness remains in this range. Instead, it is preferable that the thickness is converted when the resin is used alone. If the capsule is too thick, sufficient fixability tends to be difficult to obtain.

  Further, the melting temperature (Tm (T1 / 2)) of the shelled toner (capsule toner) is preferably 100 ° C. or less, and preferably 95 ° C. or less. This Tm is the temperature at the time of half outflow in the viscosity measurement of the toner of the flow tester. When this temperature is within the above range, sufficient fixability can be obtained even during high-speed printing.

  Further, the SP value of the binder resin of the toner is preferably 10 or more. This SP value is the wettability to an aqueous medium which is important when an anionic dispersant is not used. In order to improve the wettability of the toner, it is important to give the toner core agent an anionic property, for example, by introducing a hydrophilic functional group into the binder resin. The SP value (solubility index) of water is 23. As a result of the experiment, if the SP value is too low, the wettability with an aqueous medium is poor, and there is a tendency that the cationic capsule monomer or prepolymer cannot be uniformly attracted to the toner surface. On the other hand, when the SP value is 10 or more, the affinity is greatly improved because it approaches the SP value of water.

  Further, the total organic carbon TOC of the toner is preferably 15 mg / L or less. Once the amount of total organic carbon (TOC) in the wastewater is reduced, it is an important issue when circulating the wastewater. In the case of a toner obtained by carrying out polymerization by directly attaching a cationic monomer and prepolymer to the surface of an anionic toner without using a dispersant or an activator, the amount of organic substances contained in the filtration and cleaning liquid is small. If the organic matter is small, a special wastewater treatment apparatus is not required, and the wastewater can be circulated and used. Specifically, the TOC is preferably 15 mg / L or less, and more preferably 10 mg / L or less.

  As described above, the toner as described above is used as a toner in a developing device such as a dutch down developing type developing device that is carried on a toner carrying member, and the toner carrying member as described above. By using the developing roller, a developing device capable of forming a high-quality image can be obtained. Therefore, an image forming apparatus provided with such a developing device can form a high-quality image.

  The present invention will be described more specifically with reference to the following examples. However, the scope of the present invention is not limited to these examples.

  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 Document Solutions Co., Ltd.) 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. Further, this image forming apparatus uses toner as described later as toner used in the developing device.

[Production of toner]
(Production of toner core (core particles))
First, bisphenol A (manufactured by Mitsui Chemicals), potassium hydroxide (manufactured by Showa Chemical Co., Ltd.) and ethylene oxide are placed in an autoclave having a stirring function and a temperature control function, and conditions of 140 ° C. and 0.3 MPa The mixture was stirred for 2 hours. After the stirring, an adsorbent (KYOWARD 600, 2MgO.6SiO ₂ .XH ₂ O manufactured by Kyowa Chemical Industry Co., Ltd.) was introduced into the autoclave and aged at 90 ° C. for 30 minutes. Thereafter, the contents in the autoclave were filtered. The obtained filtrate was an ethylene oxide adduct of bisphenol A. The obtained bisphenol A ethylene oxide adduct was reacted with terephthalic acid (high-purity terephthalic acid manufactured by Mitsui Chemicals, Inc.), which is an acid having a polyfunctional group, to produce a polyester resin. The produced polyester resin had a hydroxyl value (OHV) of 10 mgKOH / g, an acid value (AV) of 20 mgKOH / g, a melting temperature Tm of 100 ° C., and a glass transition temperature Tg of 49 ° C.

  Next, 5 parts by mass of phthalocyanine pigment 15: 3 type and 5 parts by mass of ester wax (Nissan Electol WEP-3 manufactured by NOF Corporation) are added to 100 parts by mass of this polyester resin, and mixed with a Henschel mixer. Then, the mixture was kneaded with a PCM-30 type kneader. The chips obtained by this kneading were pulverized to about 6 μm by a turbo mill. Thereafter, the particles were classified with an elbow jet to obtain particles having an average particle diameter of 6 μm. These particles were used as a toner core.

  This toner core had a Tg of 42 ° C. and a Tm of 90 ° C. The toner core was -15 mV as measured by zeta potential at pH 4. From this, it was found that this toner core is made of an anion.

(Shell layer coating)
300 mL of ion-exchanged water was placed in a 1 liter three-necked flask in a 30 ° C. water bath, and the ion-exchanged water was adjusted to pH 4 with hydrochloric acid. 2 ml of hexamethylol melamine initial polymer (Milben 607, Showa Polymer Co., Ltd.), which is a precursor produced by the addition reaction of melamine and formaldehyde so that a shell layer with a thickness of 6 nm is formed in this solution. Was added and dissolved. 300 parts by mass of the toner core was added to an aqueous solution in which milben 607 was dissolved in such an amount that a shell layer having a thickness of 6 nm was formed, and stirred sufficiently. Further, while adding 300 ml of ion-exchanged water and stirring, the temperature was raised at a rate of 0.5 ° C./min and held at 70 ° C. for 2 hours. Thereafter, the solution was neutralized to pH 7, filtered, washed and dried. By doing so, a capsule toner coated with a shell layer was obtained. The conductivity after filtration was 4 μS / cm.

  The charge decay constant of the obtained toner was measured by the above method and found to be 0.018. Hereinafter, this toner is referred to as toner C.

  Various toners (toners A, B, D to G) were prepared in the same manner except that the amount of milben added was changed. The results (toner charge decay constant) are shown in Table 1. The amount of milben added (ml) and the thickness of the shell layer (nm) are shown in Table 1. The thickness of the shell layer is a thickness calculated from the amount of milben added.

[Manufacture of developing roller]
Next, the manufacturing method of a developing roller is shown below.

  As the developing roller, a developing roller having a resin layer on the surface as shown in FIGS. 3 and 4 was produced.

  Specifically, first, an alumite layer having a thickness of 10 μm was formed on the surface layer by subjecting an aluminum sleeve having a diameter of 16 mm to an alumite treatment. And the sleeve in which this alumite layer was formed was heat-processed at 120 degreeC for 10 minute (s), and the crack was generated in the alumite layer.

Next, 100 parts by mass of polyamide resin (Amilan CM8000 manufactured by Toray Industries, Inc.) and 25 parts by mass of titanium oxide (ET300W manufactured by Ishihara Sangyo Co., Ltd., primary particle size 15 nm) subjected to 4% by mass siloxane treatment, The mixture was added to 800 parts by mass of methyl ethyl ketone and mixed for 48 hours by a ball mill using zirconia beads having a diameter of 1 mm. The sleeve thus heat-treated was immersed in the liquid thus obtained, and then the sleeve was taken out of the liquid and dried at 130 ° C. for 10 minutes. The developing roller according to Example 1 was obtained by such an immersion method. The surface of the obtained developing roller was composed of a resin layer, and the thickness of the resin layer was 10 μm. The surface resistivity of the developing roller was 1 × 10 ⁸ Ω / □.

And the above-mentioned test method was performed about the change of the surface potential of this developing roller. As a result, the average change amount (potential change amount) of the maximum value of the surface potential from 2 seconds to 3 seconds after applying a charge of 0.001 coulomb / m ² to the surface was 5.5V. . Hereinafter, this developing roller is referred to as a developing roller a.

  Further, various developing rollers were produced in the same manner except that the addition amount of titanium oxide was changed. The results (potential change amount of each developing roller) are shown in Table 2 together with the type of resin used and the added amount of titanium oxide.

  Moreover, as resin used when manufacturing a developing roller, using the urethane resin (Desmophene by Sumika Bayer Urethane Co., Ltd.), except having manufactured the developing roller, it is the developing roller f similarly to the developing roller a. Manufactured. The results (potential change amount of each developing roller) are shown in Table 2 together with the type of resin used and the added amount of titanium oxide.

  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) was used, rotated at a peripheral speed (drum linear speed) of 150 mm / second, and the surface potential was set to 270 V on the white background portion and 20 V on the image portion. . The printing speed was 30 sheets / minute.

  As the developing roller, each of the developing rollers described above was used, and adjacent peripheral surfaces were rotated in the same direction (with rotation) with respect to the rotation of the photosensitive drum, and the peripheral speed ratio was 1.5.

  As the magnetic roller, a magnetic roller having a fixed magnet inside and having an outer cylinder portion which is a rotatable aluminum base material and whose surface is anodized is used. Further, the magnetic rollers have their peripheral surfaces rotating in the opposite direction (counter rotation) with respect to the rotation of the developing roller, and the peripheral speed ratio is 1.1.

  The distance between the photosensitive drum and the developing roller (DS distance) was 120 μm, and the distance between the developing roller and the magnetic roller (MS distance) was 300 μm.

  The developing roller has a peak-to-peak value Vpp (slv) of 1500 V, a bias voltage Vdc (slv) of 50 V, a duty ratio Vduty (slv) of 45%, and a frequency f (slv) of 3.7 kHz. A superimposed voltage in which an AC component is superimposed on a DC component was applied.

  The magnetic roller includes a bias voltage Vdc (mag) such that the potential difference of the DC component between the developing roller and the magnetic roller is 200 to 400 V (variable), and the duty ratio of the AC component between the developing roller and the magnetic roller. Is a duty ratio Vduty (mag) such that the frequency becomes 70%, a frequency f (mag) such that the frequency of the AC component between the developing roller and the magnetic roller is 3.7 kHz, and between the developing roller and the magnetic roller. A superimposed voltage in which the alternating current component is superimposed on the direct current component and satisfying Vpp (slv) such that the peak-to-peak value of the alternating current component is 2300 V is applied.

  As the toner, the above toners were used, and as the carrier, the carrier used in the above-mentioned copying machine (TASKalfa 400ci manufactured by Kyocera Document Solutions Co., Ltd.) was used.

[Evaluation]
Using the developing roller and toner shown in Table 3 below, image formation was performed in a normal temperature and humidity environment at a temperature of 20 to 23 ° C. and a relative humidity of 50 to 65% RH.

(Image density)
Specifically, first, the image forming apparatus was turned on and stabilized. Thereafter, an image was printed, and the reflection density of this image was measured using a reflection densitometer (RD-918 manufactured by Gretag Macbeth). This reflection density was defined as an image density ID.

  If the image density is 1.4 or more, it is evaluated as “◯”, if it is 1.2 or more and less than 1.4, it is evaluated as “Δ”, and if it is less than 1.2, “ “×”.

(Toner scattering)
The printed image was visually confirmed after printing 3000 sheets of the image. If toner scattering could not be confirmed on the image, it was evaluated as “◯”, and if it was confirmed, it was evaluated as “x”.

(Comprehensive evaluation)
If the evaluation of the image density and toner scattering were both “◯”, it was evaluated as “◯”, and if any evaluation was “x”, it was evaluated as “x”. Further, when the evaluation of toner scattering was “◯” and the evaluation of image density was “Δ”, the evaluation was “Δ”.

  The results of the evaluation are shown in Table 3.

  As can be seen from Table 3, when a toner having a charge decay constant of 0.01 to 0.05 is used, and a developing roller having a potential change amount of 3 to 5 V is used as a toner carrier, it is compared with the case where it is not Thus, a sufficiently high image density could be realized while suppressing the occurrence of toner scattering.

  Further, when a toner having a charge decay constant of 0.02 or more was used as the toner, the image density was higher. From this, it was found that the charge decay constant of the toner is preferably 0.02 to 0.05.

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 11 Apparatus main body 12 Paper supply part 13 Image forming part 14 Fixing part 15 Paper discharge part 21 Charging apparatus 22 Exposure apparatus 23 Developing apparatus 24 Cleaning apparatus 32 Rotating sleeve 33 Fixed shaft 35 Base material 36 Resin layer 37 Shaft 38 Rib 51 Laminated body 52 Roller body 53 Resin layer 55 Shaft 58 Rib 135 Photosensitive drum 232 Magnetic roller 241 Development bias applying unit 242 Toner supply bias applying unit

Claims (7)

A toner carrier that is disposed opposite to an image carrier on which an electrostatic latent image is formed and that supplies toner carried on the surface thereof to the image carrier;
The toner has a charge decay constant α of 0.01 to 0.05,
The toner carrier includes a base material and a resin layer formed on the base material, and has an electric charge of 0.001 coulomb / m ^{2 on} the surface in an environment of a temperature of 32.5 ° C. and a relative humidity of 80%. A developing device characterized in that the average change amount of the maximum value of the surface potential from 2 seconds to 3 seconds after the application is 3 to 5 V. The toner includes an anionic core particle and a cationic shell layer that covers the core particle;
The developing device according to claim 1, wherein a charge decay constant α of the toner is 0.02 to 0.05.   The developing device according to claim 1, wherein the substrate includes an aluminum-based substrate and an oxide layer formed on the aluminum-based substrate. The resin layer includes a polyamide resin and a conductive material dispersed in the polyamide resin,
The developing device according to claim 1, wherein the conductive material is at least one of titanium oxide and carbon black. A developer carrier for supplying toner contained in the two-component developer to the toner carrier from a two-component developer containing toner and carrier carried on the surface;
The developing device according to claim 1, wherein the toner carried on the surface of the toner carrying member is toner supplied from the developer carrying member. Conveying the toner carried on the surface of the toner carrying body to an image carrying body on which an electrostatic latent image is formed;
A step of causing the toner conveyed by the toner carrier to fly to the surface of the image carrier and developing an electrostatic latent image previously formed on the surface of the image carrier as a toner image;
As the toner, a toner having a charge decay constant α of 0.01 to 0.05 is used.
The toner carrier includes a base material and a resin layer formed on the base material , and the surface has a charge of 0.001 coulomb / m ^{2 on} the surface in an environment of a temperature of 32.5 ° C. and a relative humidity of 80%. A developing method comprising using a toner carrier having an average change amount of a maximum surface potential of 3 to 5 V from 2 seconds to 3 seconds after application.   An image forming apparatus comprising the developing device according to claim 1 and the image carrier.

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