JP2010015145A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device can obtain stable developability without reducing leakage proofness, in the image forming device of touch-down development system. <P>SOLUTION: A toner carrier contains an aluminum base material 30, a surface of the aluminum base material 30 is anodized and sealed, and is coated by a silicone modified urethane resin layer 33 containing a conductive agent, and a volume resistivity of the toner carrier including an anodized film 31 and the silicone modified urethane resin layer 33 is regulated within a range of 1.0×10<SP>12</SP>Ωcm or more to 1.5×10<SP>14</SP>Ωcm or less. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine using an electrophotographic system. In particular, a two-component developer that charges non-magnetic toner using a magnetic carrier is used, only the charged toner is held on the toner carrier, and the toner on the toner carrier is allowed to fly to the electrostatic latent image. The present invention relates to an image forming apparatus that uses the touch-down development method to develop the latent image.

  Conventionally, toner is transported from a magnetic roller carrying a two-component developer via a magnetic brush formed on the surface thereof, a toner thin layer is formed on the developing roller, and the toner is ejected from the toner thin layer. A developing method for developing an electrostatic latent image on a photoreceptor is known, and is called a touch-down developing method.

  In the touch-down development method using two rollers, a magnetic roller and a developing roller, a two-component developer is used between the magnetic roller and the developing roller (hereinafter sometimes referred to as between the MSs), and on the developing roller. A toner layer is formed. Usually, each roller is made of aluminum or stainless steel (SUS), and a voltage is applied to both to generate an electric field. In the case where the applied voltage is an alternating voltage that vibrates at a constant period, the superposition of the alternating waveforms of both forms an actual voltage difference. When the voltage difference having this AC component exceeds a certain amplitude, there is a problem that voltage leakage occurs between the MSs.

In order to solve this problem, a method has been proposed in which the surface of a developing roller or magnetic roller is anodized in an acid aqueous solution to form a leak-resistant layer (resistance layer) on each roller (for example, , See Patent Document 1). This method is a so-called alumite treatment, and it has been clarified that leakage resistance between MSs is improved by performing this alumite treatment. That is, the alumite film formed by the alumite treatment has a high volume resistivity (10 ⁷ to 10 ¹⁵ Ωcm), can suppress the leakage of the voltage applied when the toner moves from the magnetic roller to the developing roller, and has a potential. The saturation time is short.

  However, in the touch-down development method, there is a problem in developability with respect to a dot latent image that draws a halftone image or the like when toner is moved by development on the photosensitive drum. That is, as the dot interval becomes narrower, the developability becomes unstable, and toner development is performed in a state where the dot diameter varies, and as a result, image unevenness is caused. In the present specification, poor developability means that the printed dot diameter varies, thereby causing image unevenness, and that developability is stable or high developability is printed. This means that there is little variation in dot diameter and there is almost no image unevenness.

  In addition, as the process speed increases, the time required to pass through the development area is shortened, and it is necessary to narrow the gap between the development roller and the photosensitive drum or increase the development bias in order to improve toner flying performance. is there. However, a developing roller that has been subjected to alumite treatment that does not have a good releasability with the toner needs to increase the developing bias in order to improve the releasability, which may cause leakage.

  On the other hand, as a developing roller in a non-magnetic one-component developing system, an alumite film is formed on the outer periphery of an aluminum alloy sleeve, and a resin layer made of a siloxane-modified polyurethane resin containing a conductive agent such as carbon black is formed thereon. Is known (see, for example, Patent Document 2). This developing roller improves the interlaminar adhesion strength between the sleeve and the resin layer due to the anchoring effect of the holes present in the anodized film, and also provides the anodized film on the surface of the aluminum alloy sleeve, thereby improving the leak resistance of the developing roller. It is going to improve.

  Japanese Patent Application Laid-Open No. H10-228561 describes that the developer carrying member is subjected to an alumite treatment, followed by an electrolytic treatment, and further a sealing treatment to make the chargeability of the toner uniform. Patent Document 4 discloses that a developer carrier is subjected to an alumite treatment and further subjected to a sealing treatment with nickel acetate.

United States Patent No. 7043181 JP 2008-76618 A JP-A-2-73381 JP 2003-35992 A

  According to the study by the present inventors, when the alumite film is coated with a resin layer containing a conductive agent such as carbon black as described above, the conductive agent such as carbon black enters the pores on the surface of the alumite film. It has been clarified that the volume resistance is partially reduced and the leakage resistance may be reduced.

  Further, according to the study by the present inventors, since the alumite film does not have high releasability with respect to the toner, there is a problem that developability deteriorates if the development time is not sufficient. That is, when the photosensitive member peripheral speed (the developing roller peripheral speed is about 1.5 times that of the photosensitive member) increases, the developability tends to decrease. In order to ensure developability, it is necessary to increase the applied bias, and in this case, voltage leakage tends to occur.

  Further, according to the study by the present inventors, even when the alumite film is coated with a resin layer, the developability may not always be sufficiently stable. The graph shown in FIG. 5 to be described later shows the result of measuring the transition of the surface potential on the developing roller with respect to the driving time by providing a potential difference between the MSs. In the case of a developing roller whose surface is an alumite film (control in FIG. 5), the surface potential saturation time is about 1 second, whereas, for example, 17 wt. In the case of a developing roller in which a silicone-modified urethane resin layer containing 1% is formed by a single coating operation (see Comparative Example 4 and Table 2 described later), it takes 15 seconds for the surface potential to be saturated.

  Further, with respect to the saturation potential, in the case of the developing roller in which the silicone-modified urethane resin layer is formed on the anodized film, the surface is higher by about 35V than the developing roller having the anodized film. As described above, it has been found by the examination of the present inventors that the development property at the start cannot always be sufficiently stabilized simply by forming the silicone-modified urethane resin layer containing carbon black on the alumite film. .

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus that solves the above-described problems and can obtain stable developability without reducing leak resistance.

As a result of intensive studies to solve the above problems, the inventors of the present invention have performed alumite treatment and sealing treatment on the surface of the aluminum substrate of the toner carrier, and a silicone modified urethane resin layer containing a conductive agent. In the case where the volume resistivity of the toner carrier including the alumite film and the silicone-modified urethane resin layer is adjusted to a range of 1.0 × 10 ¹² Ωcm to 1.5 × 10 ¹⁴ Ωcm. Thus, the inventors have found that stable developability can be obtained without reducing leakage resistance, and the present invention has been completed.

That is, the present invention provides the following image forming apparatus.
(1) A two-component developer containing at least a carrier and toner is held on a two-component developer carrier, and the toner is transferred from the two-component developer carrier to form a thin layer of toner on the toner carrier. In the image forming apparatus having a developing device that develops the electrostatic latent image by causing the toner on the toner carrier to fly onto the electrostatic latent image carrier, the toner carrier includes an aluminum base, and the aluminum base The surface of the material is anodized and sealed, and further covered with a silicone-modified urethane resin layer containing a conductive agent, and the volume resistivity of the toner carrier including the anodized film and the silicone-modified urethane resin layer Is 1.0 × 10 ¹² Ωcm or more and 1.5 × 10 ¹⁴ Ωcm or less.
(2) The toner carrier is applied so that an electric field in a direction in which the toner moves from the toner carrier to the electrostatic latent image carrier is 6 × 10 ⁶ V / m or more. The image forming apparatus according to (1).
(3) The image forming apparatus as described in (1) or (2) above, wherein the duty ratio of the AC bias applied to the toner carrier is 40% or more and 90% or less.
(4) The silicone-modified urethane resin layer is formed by dividing the coating process into at least a first layer and a second layer, and the first layer is a silicone-modified urethane containing a conductive agent on the alumite film surface. After the resin coating liquid is dried, it is formed by coating and drying so that the layer thickness is 0.2 to 0.5 μm. The second layer is a silicone-modified urethane containing a conductive agent on the first layer. The resin coating solution is formed by applying and drying so that the sum of the thicknesses of the first layer and the second layer after drying is 0.7 to 1.0 μm. The image forming apparatus according to any one of (1) to (3).

In the present invention, an alumite film is formed on the surface of the aluminum substrate of the toner carrier (developing roller) by anodizing (anodizing). The alumite film can suppress the leakage of the voltages applied during a high volume resistivity (10 ⁷ ~10 ¹⁵ Ωcm), from the magnetic roller movement of the toner to the developing roller.

  However, there are minute holes on the surface of the developing roller that has been anodized. The pores have a size of about 0.1 μm, and when used in a state with pores, a conductive agent such as carbon black contained when forming a resin layer on the pores enters the pores and forms a surface layer. There is a risk of reducing the resistance. Therefore, in the present invention, the use of a sealed alumite film prevents the conductive agent from entering the pores.

Further, when a silicone-modified urethane resin layer containing a conductive agent such as carbon black is formed on the anodized anodized film, the layer thickness of the silicone-modified urethane resin coating solution containing the conductive agent is 0. It is applied and dried so as to be 2 to 0.5 μm, and further, the silicone-modified urethane resin coating liquid containing a conductive agent is further dried so that the total layer thickness becomes 0.7 to 1.0 μm. By coating and drying, a silicone-modified urethane resin layer having a volume resistivity of 1.0 × 10 ¹² Ωcm or more and 1.5 × 10 ¹⁴ Ωcm or less can be stably formed. Before the toner on the roller reaches the saturation layer thickness, the surface potential on the developing roller including the toner layer can be saturated, and stable developability can be obtained.

That is, according to the invention described in item (1), the volume resistivity of the toner carrier including the alumite film and the silicone-modified urethane resin layer is 1.0 × 10 ¹² Ωcm or more and 1.5 × 10 ¹⁴ Ωcm. By adjusting to the following, it is possible to maintain the stable development because the rise time to the saturated charge amount on the surface of the developing roller when the toner thin layer is formed can be kept stable without charge accumulation thereafter. can do.

Wherein (2) According to the invention described in claim, applying a toner carrying member, so that the electric field in a direction from said the toner carrying member to the electrostatic latent image bearing member toner moves becomes more ⁶ × 10 6 V / m By doing so, developability can be further enhanced.
According to the invention described in (3) above, the developability can be further improved by setting the duty ratio of the AC bias applied to the toner carrier to 40% or more and 90% or less.

According to the invention described in (4) above, the formation of the silicone-modified urethane resin layer containing the conductive agent is performed by dividing the coating process into at least the first layer and the second layer, so that carbon black or the like can be used in the drying process. The alumite film and the silicone-modified urethane resin layer having a volume resistivity in the range of 1.0 × 10 ¹² Ωcm or more and 1.5 × 10 ¹⁴ Ωcm or less that can suppress the precipitation of the conductive agent and decrease in dispersion. The layer containing can be formed stably.

1 is an explanatory diagram showing a schematic configuration of an image forming apparatus of a touchdown development system according to an embodiment of the present invention. It is a schematic block diagram which shows a part of developing means of FIG. FIG. 2 is a partial cross-sectional view illustrating a surface portion of the developing roller in FIG. 1. It is a graph which shows the relationship between the volume resistance / layer thickness of a silicone modified urethane resin layer and the charge amount of the developing roller surface in Examples 1-3 and Comparative Examples 1-3. 14 is a graph showing a change in surface potential on the developing roller with respect to driving time in Comparative Example 4. 10 is a graph showing a change in surface potential on the developing roller with respect to driving time in Example 4. 10 is a graph showing a change in toner amount on the developing roller with respect to driving time in Example 4 and Comparative Example 4. 6 is a graph showing the relationship between the photoreceptor peripheral speed and the image density in Example 4. 10 is a graph showing the relationship between the image density and the electric field applied to the developing roller in Example 4 in the direction in which the toner moves from the developing roller to the photoreceptor.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is an explanatory diagram showing a schematic configuration of an image forming apparatus of a touch-down development system according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram showing a part of the developing means of FIG. FIG. 3 is a partial cross-sectional view showing a surface portion of the developing roller of FIG.

(Image forming device)
As shown in FIG. 2, the image forming apparatus according to the present embodiment uses a two-component developer composed of a magnetic carrier 4 and a toner 5 and uses a two-component carried on a magnetic roller 1 (two-component developer carrying member). A toner thin layer 9 is formed on the developing roller 2 (toner carrier) by a developer, and the toner 5 is ejected from the toner thin layer 9 to form a static image formed on the photosensitive member 3 (electrostatic latent image carrier). This is an image forming apparatus using a so-called touch-down method for developing an electrostatic latent image. As shown in FIG. 1, the image forming apparatus includes the photoreceptor 3, and around the photoreceptor 3, a charging unit 8, an exposing unit 16, a developing unit 18, a primary transfer unit 22, and a secondary transfer unit 25. The fixing unit 26, the cleaning unit 24, and the like are disposed.

  Image formation by the image forming apparatus is performed as follows. That is, the surface of the photosensitive member 3 is uniformly charged by the charging unit 8, and the charged surface is exposed by the exposure unit 16 to form an electrostatic latent image. The toner 5 is attached to the obtained electrostatic latent image from the developing means 18 and the electrostatic latent image is developed as a toner image. This toner image is transferred from the photoreceptor 3 onto an intermediate transfer member (intermediate transfer belt) 20 by a primary transfer roller 22 as a primary transfer unit. After the toner images of a plurality of colors are transferred onto the intermediate transfer body 20 in an overlapping manner, the secondary transfer roller 25 as a secondary transfer unit transfers the toner image to the transfer target conveyed from the paper feed cassette 27 to the secondary transfer position. Transfer the toner image. The transferred body is conveyed to a fixing roller 26 as a fixing unit, where the toner image is fixed on the transferred body and then discharged onto, for example, a discharge tray (not shown). Undeveloped toner remaining on the surface of the photoreceptor 3 after the transfer is removed by the cleaning means 24.

  As the photoconductor 3, for example, an inorganic photoconductor such as selenium or amorphous silicon, or an organic photoconductor in which a single-layer or multi-layer photoconductor containing a charge generator, a charge transport agent, a binder resin, etc. is formed on a conductive substrate. A body (OPC) etc. are mentioned. Examples of the charging unit 8 include a scorotron system, a charging roller, and a charging brush. Examples of the exposure means 16 include an LED or a semiconductor laser. Moreover, as the cleaning means 24, for example, a doctor blade type or the like can be used, and known ones can be used.

  The developing means 18 has a plurality of magnetic members fixed therein, a sleeve-like magnetic roller 1 (two-component developer carrier) rotating around the outer periphery of the magnetic member, and the magnetic roller 1 inside. A magnetic member having a different polarity from the magnetic member is fixed, and a sleeve-like developing roller 2 (toner carrier) that rotates on the outer peripheral portion of the magnetic member, and different magnetic poles of the magnetic roller 1 and the developing roller 2 are provided. A magnetic field is formed by this magnetic force, and a restriction blade 7 for keeping the height of the magnetic brush 6 formed on the magnetic roller 1 constant by this magnetic field is constituted. Further, a bias power source 12 including an alternating current (AC) bias power source 12a and a direct current (DC: Vdc2) bias power source 12b applied to the developing roller 2 is provided, and an alternating current (AC) bias power source 11a and a direct current applied to the magnetic roller 1 are provided. The bias power supply 11 including the (DC: Vdc1) bias power supply 11b is configured to be superimposed on the bias power supply 12 of the developing roller 2.

  On the other hand, the image forming apparatus according to the present embodiment includes a housing 46. The housing 46 includes a developing roller 2 disposed opposite to the photosensitive member 3, a magnetic roller 1 disposed opposite to the developing roller 2, a stirring screw 44 disposed below the magnetic roller 1, and the stirring An agitating screw 40 disposed opposite to the screw 44 via a partition plate 42 is accommodated. The housing 46 stores a toner container (not shown) in which the toner 5 is stored. The toner 5 supplied from the toner container to the two-component developer storage unit 45 that stores the two-component developer is stored in the housing 46. The carrier 4 is agitated with the agitating screws 40 and 44 to be charged. That is, the housing 46 communicates with both ends of the partition plate 42, and supplies the two-component developer supplied from the stirring screw 40 to the stirring screw 44 through the one end side to the magnetic roller 1. The two-component developer is circulated from the other end side opposite to the one end to the stirring screw 40 side.

(Development method)
As shown in FIG. 2, a magnetic brush 6 comprising a carrier 4 (magnetic particles) magnetically constrained by a fixed magnet contained in a magnetic roller 1 and a toner 5 charged and held on the surface thereof. Is rotated on the surface of the magnetic roller 1 and conveyed to the developing roller 2. The surface of the magnetic roller 1 can be conveyed more smoothly by using a blasted or grooved surface.

  A developing bias voltage 12 in which an alternating voltage (AC) 12a is superimposed on a direct current voltage (DC: Vdc2) 12b is applied to the developing roller 2, and an alternating voltage (AC) is applied to the direct current voltage (DC: Vdc1) 11b. ) A value obtained by superimposing the developing bias voltage 11 superimposed on the developing bias voltage 11 on the developing bias voltage 12 is applied. The magnetic brush 6 is formed on the magnetic roller 1. The magnetic brush 6 is regulated by a regulating blade 7 and conveyed by a potential difference (conveying bias) between the magnetic roller 1 and the developing roller 2. The toner 5 moves to the developing roller 2 through the magnetic brush 6 to form a thin toner layer 9. Then, by applying a developing bias between the photosensitive member 3 and the developing roller 2, the toner 5 is ejected from the toner thin layer 9 on the developing roller 2 to develop the electrostatic latent image on the photosensitive member 3.

  After the development, the developing roller 2 having the residual toner layer is closest to the magnetic roller 1 having the magnetic brush 6 at the facing position, and the mechanical force by the magnetic brush 6 and the magnetic roller 1 at the facing position. The toner thin layer 9 on the developing roller 2 is scraped off and collected by a bias applied between the developing roller 2 and the developing roller 2. At the same time, the toner 5 is supplied from the developer layer on the magnetic roller 1 to the developing roller 2 side in accordance with the transport bias applied between the magnetic roller 1 and the developing roller 2 to form a new thin toner layer 9. Is done.

  The thin toner layer 9 on the developing roller 2 may be recovered by the magnetic brush 6 by changing the DC bias (Vdc2) 11b while applying the AC bias 12a at the end of development. When the toner 5 is peeled off from the developing roller 2 every time the development is completed, the toner 5 is always refreshed. However, it takes time to form the stable toner thin layer 9 again, and it becomes difficult to achieve a sufficient printing speed. In order to maintain a good printing speed, it is only necessary to adjust the time for peeling and forming the toner thin layer 9 on the developing roller 2 in a certain period by adjusting the sheet interval. In order to supply sufficient toner to the latent image on the photoconductive drum 3 without increasing the paper interval, the peripheral speed of the developing roller 2 is set to 1.5 times or more with respect to the photoconductive drum 3 for a short time. The toner can be taken in and out. Further, when the magnetic roller 1 is set to a speed exceeding 1 and 2 times that of the developing roller 2, the replacement of the toner thin layer 9 is promoted. At this time, it is preferable that the rotating direction of the magnetic roller 1 is opposite to the developing roller 2.

  The electrostatic latent image on the photoreceptor 3 can be formed by using the exposure unit 16 where the surface of the photoreceptor 3 is charged to +250 to 800 V by the charging unit 8. When an OPC photoconductor is used, +70 to 220 V is obtained in all exposures, and an amorphous silicon photoconductor provides a post-exposure potential of 10 to 50 V. For the exposure, either a semiconductor laser or an LED can be used.

  At the time of development, for example, when a regular positively charged toner is used as the toner, +300 to 500 V is applied to the magnetic roller 1 and +100 V is applied to the developing roller 2 as a developing bias condition. The potential difference for forming the thin layer is appropriately 200 to 400 V, and may be adjusted according to the balance with the charge amount of the toner 5.

  The AC conditions are as follows: For the magnetic roller 1, Vpp (peak AC bias) = 0.1 to 2.0 kV having the same frequency, the same period, and the opposite phase, and the frequency = 2-5 kHz, and the duty ratio = For the developing roller 2, 60 to 80% is preferably Vpp = 1.0 to 2.0 kV, frequency = 2 to 5 kHz, and duty ratio = 30 to 90% (preferably 40 to 90%). If the duty ratio of the magnetic roller 1 is less than 60%, the toner layer may not be sufficiently formed. On the other hand, if it exceeds 80%, the toner layer thickness becomes too thick and toner scattering and image fogging may occur. If the duty ratio of the developing roller 2 is less than 30%, the flying time of the toner to the photoreceptor 3 becomes too short, and the image density defect and the dot reproducibility may be insufficient. On the other hand, if it exceeds 90%, a leak may occur between the developing roller 2 and the photoreceptor 3. In consideration of developer deterioration and environmental fluctuations, the duty ratio is more preferably 40 to 90%. When Vpp is increased, the thin layer is formed more instantaneously, but on the other hand, the leak resistance is weakened and causes noise.

  As the toner 5, either a positively charged toner or a negatively charged toner can be used, but a positively charged toner is preferable because of the relationship with the silicone-modified urethane resin used for the resin layer of the developing roller 2. The volume average particle diameter of the toner 5 is preferably 4.0 to 7.5 μm. If the thickness is less than 4.0 μm, the influence of non-electrostatic adhesion increases, and developability and recoverability deteriorate. If the thickness is greater than 7.5 μm, it is difficult to obtain a high-quality image such as smooth image quality. The charge amount of the toner 5 is preferably about 6 to 30 μC / g. If the charge amount is lower than this, the toner 5 will fly from the magnetic brush 6 and stain the periphery, and if it is higher than this, the thin layer formation will be weakened.

  The toner volume average particle diameter can be measured using Multisizer III (manufactured by Beckman Coulter, Inc.) with an aperture diameter of 100 μm (measurement range: 2.0 to 60 μm). The toner charge amount can be measured with a QM meter (manufactured by TREK, MODEL 210HS).

  A known carrier 4 can be used, but a carrier whose surface is coated with a resin using a ferrite core is preferably used. The coating resin may be a known one such as silicone, fluorine epoxy, fluorine silicone, polyamide, and polyamideimide. Also, use of a carrier particle size (weight average particle size) of 25 to 50 μm increases the holding force by magnetic force, the density of the magnetic brush 6 becomes moderate, and the formation of the toner thin layer 9 becomes smooth. preferable. Further, the saturation magnetization of the carrier 4 is preferably 35 to 90 emu / g for good carrier jumping and formation of a uniform thin layer. The saturation magnetization of the carrier 4 can be measured with a magnetic field of 79.6 kA / m (1 kOe) using “VSM-P7” manufactured by TOEI.

  The gap between the magnetic roller 1 and the developing roller 2 is 200 to 600 μm, preferably 300 to 400 μm. The gap is the most effective factor for instantly forming a thin layer. If the width is wide, the efficiency is lowered, and problems such as development ghosts occur. On the other hand, if it is narrow, the magnetic brush 6 that passes through the blade gap cannot pass through the gap and the toner thin layer 9 is disturbed.

(Development roller)
The developing roller 2 is a sleeve-like roller that rotates around the outer periphery of a fixed magnetic member. As shown in FIG. 3, the developing roller 2 includes a sleeve-like aluminum base material 30, and the surface thereof is anodized to form an alumite film 31 as a leak-proof layer. The plurality of holes present on the surface of the alumite film 31 are sealed. Therefore, a plurality of sealed holes 32 exist on the surface of the alumite film 31. In the developing roller 2, a silicone-modified urethane resin layer 33 containing a conductive agent is formed on an alumite film 31 that has been further sealed.

Here, in this embodiment, the volume resistivity of the developing roller 2 including the alumite film 31 and the silicone-modified urethane resin layer 33 is 1.0 × 10 ¹² Ωcm or more and 1.5 × 10 ¹⁴ Ωcm or less. Thereby, the maintenance of stable developability is achieved. That is, the toner thin layer 9 is formed on the silicone-modified urethane resin layer 33. When the volume resistivity of the developing roller 2 including the alumite film 31 and the silicone-modified urethane resin layer 33 is adjusted to the specific range, When the toner thin layer 9 is formed, the rise time to the saturation charge amount on the surface of the developing roller 2 is fast, and a stable state can be maintained without charge accumulation thereafter, so that stable developability can be maintained.

On the other hand, if the volume resistivity value of the developing roller 2 including the alumite film 31 and the silicone-modified urethane resin layer 33 is larger than 1.5 × 10 ¹⁴ Ωcm, the rise time until saturation charging is delayed, and stable developability is obtained. I can't get it. Further, if the volume resistivity value is less than 1.0 × 10 ¹² Ωcm, electric field leakage may occur.

  The volume resistivity (Ωcm) of the developing roller 2 including the alumite film 31 and the silicone-modified urethane resin layer 33 is 100 V applied between the surface of the developing roller 2 and the sleeve-shaped aluminum substrate 30, and ULTRA HIGH RESISTANCE METER (ADVANTEST). ). In this embodiment, the length of the resin layer 33 in the longitudinal direction of the developing roller 2 is set to 300 mm, and the volume resistivity is measured and calculated by applying 300 mm in the longitudinal direction and 2 mm in the rotational direction.

  In the present embodiment, the silicone-modified urethane resin layer 33 has a two-layer structure. That is, the silicone-modified urethane resin layer 33 is coated with a silicone-modified urethane resin coating solution containing the first conductive agent 35 on the surface of the alumite film 31 and dried to obtain a first layer having a thickness of 0.2 to 0.5 μm. A silicone-modified urethane resin layer 34 is formed, and a silicone-modified urethane resin coating solution containing a second conductive agent 37 is further applied thereon and dried to a total layer thickness of 0.7 to 1.0 μm. A second silicone-modified urethane resin layer 36 is formed.

Thus, by forming the silicone-modified urethane resin layer containing a conductive agent such as carbon black separately in the first layer and the second layer, the conductive agent settles down in the drying step and the dispersion decreases. it can be suppressed to a volume resistivity of it is possible to stably form a silicone-modified urethane resin layer 33 in the following range 1.0 × 10 ⁷ Ωcm or more and 1.5 × 10 ¹⁴ Ωcm, alumite film 31 And the volume resistivity value of the developing roller 2 including the silicone-modified urethane resin layer 33 can be in the range of 1.0 × 10 ¹² Ωcm or more and 1.5 × 10 ¹⁴ Ωcm or less. The first conductive agent 35 and the second conductive agent 37 may be the same or different in kind and primary particle diameter, but usually the same kind and the same primary particle diameter can be used. .

  As described above, the developing roller 2 in which the silicone-modified urethane resin layer 33 containing a conductive agent such as carbon black is formed on the alumite film 31 subjected to the sealing treatment by two coating operations has a surface with an alumite film. The developing roller has a surface potential saturation time substantially equal to that of the developing roller, and the saturation potential is equivalent to that of the developing roller having an alumite film on the surface.

  More specifically, examples of the aluminum material used for the aluminum substrate 30 of the developing roller 2 include pure aluminum, Al-Mn, Al-Mg, Al-Mg-Si, Al-Cu, An aluminum alloy such as an Al—Zn—Mg system can be given. A sleeve-like aluminum substrate 30 is anodized to form an alumite film 31 on the surface. The anodizing treatment is performed as an electrolytic bath in an aqueous solution of an acid such as sulfuric acid, chromic acid, phosphoric acid, or oxalic acid. Since the surface layer of the alumite film 31 formed by such anodizing treatment has a plurality of pores as described above, the sealing treatment is performed. The sealing treatment can be performed in a bath containing nickel acetate or the like, but is not limited thereto. The thickness of the anodized anodized film 31 thus obtained is preferably in the range of 5 to 25 μm, more preferably 10 to 20 μm.

A silicone-modified urethane resin layer 33 containing a conductive agent is formed on the alumite film 31 that has been sealed. The content and composition of the conductive agent is such that the volume resistivity of the developing roller 2 including the alumite film 31 and the silicone-modified urethane resin layer 33 is 1.0 × 10 ¹² Ωcm or more and 1.5 × 10 ¹⁴ Ωcm or less, preferably It is selected to be in the range of 2.0 × 10 ¹² or more and 1.0 × 10 ¹⁴ Ωcm or less, more preferably 4.0 × 10 ¹² or more and 8.0 × 10 ¹³ Ωcm or less.
The thickness of the silicone-modified urethane resin layer 33 is preferably in the range of 0.7 to 1.0 μm. If the thickness of the silicone-modified urethane resin layer 33 is less than 0.7 μm, leakage is likely to occur. If the thickness exceeds 1.0 μm, the time for the charge to escape from the silicone-modified urethane resin layer is delayed, so that charges accumulate. It becomes easy to do. Depending on the state of dispersion of the conductive agent in the silicone-modified urethane resin layer 33, a leak may occur partially or charges may be accumulated. That is, if the dispersion of the conductive agent is not uniform in the layer thickness direction, the volume resistance of the resin layer 33 is influenced by the ratio between the layer thickness of the conductive agent rich and the layer thickness with a small amount of the conductive agent. Leakage and charge accumulation occur. By setting the volume resistivity of the developing roller 2 including the alumite film 31 and the silicone-modified urethane resin layer 33 to a range of 1.0 × 10 ¹² Ωcm or more and 1.5 × 10 ¹⁴ Ωcm or less, the dispersibility of the conductive agent is increased. Can be managed. Therefore, even if the thickness is adopted as the thickness of the silicone-modified urethane resin layer 33, it is possible to uniformly disperse the conductive agent in the resin layer 33 to suppress leakage and charge accumulation. .

  Examples of the conductive agent contained in the silicone-modified urethane resin layer include carbon black (acetylene black, ketjen black, aniline black, etc.), potassium titanate, titanium oxide, and the like, and carbon black is particularly preferable. As carbon black, the average particle diameter of primary particles is preferably 20 to 60 nm from the viewpoint of conductivity, dispersibility, and the like. The average particle size of the carbon black is, for example, randomly sampled 100 carbon blacks magnified 30000 times using a field emission scanning electron microscope (FE-SEM) (JSM-7401F) manufactured by JEOL Co., Ltd. The image information can be calculated by image analysis particle size distribution measurement software (Mac-View) manufactured by Mountec.

  In the silicone-modified urethane resin layer 33, the thickness of the first silicone-modified urethane resin layer 34 is preferably in the range of 0.2 to 0.5 μm, and the first silicone-modified urethane resin layer 34 and the second silicone-modified urethane resin layer 36 are The combined layer thickness is preferably in the range of 0.7 to 1.0 μm. If the thickness of the first silicone-modified urethane resin layer 34 is less than the above range, coating unevenness may occur. If the thickness exceeds the above range, the conductive agent may settle, resulting in poor dispersion. If the total thickness of the first silicone-modified urethane resin layer 34 and the second silicone-modified urethane resin layer 36 is less than the above range, leakage may occur, and if it exceeds the range, charge accumulation may occur. Regarding the solid content concentration and the conductive agent concentration in the first silicone-modified urethane resin layer coating solution and the second silicone-modified urethane resin layer coating solution, from the viewpoint of coating properties and conductive agent dispersibility, the solid content concentration Is preferably 5 to 30% by weight, and the conductive agent concentration is preferably 10 to 20% by weight. The said electrically conductive agent density | concentration means the electrically conductive agent density | concentration in solid content, and is prescribed | regulated similarly below.

  Examples of the silicone-modified urethane resin include those described in JP-A Nos. 2001-026648 and 2002-20607. Specific examples include (A) a hydrocarbon compound in which at least one aliphatic unsaturated bond and at least one active hydrogen coexist in the same molecule in the side chain and / or main chain of the molecular chain, and Polyurethane resin having an aliphatic unsaturated group obtained by reacting an aliphatic unsaturated group-containing polysiloxane, an organic polyisocyanate, a polyol and / or a polyamine, and, if necessary, a chain extender A resin composition comprising 100 parts by weight, (B) 0.1 to 100 parts by weight of an organohydrogenpolysiloxane having two or more hydrosilyl groups in one molecule, and (C) a catalytic amount of a hydrosilylation catalyst. What is obtained by making it react is mentioned.

  When forming the silicone-modified urethane resin layer containing the conductive agent by dividing the coating process into the first layer and the second layer, the silicone-modified urethane resin in the first silicone-modified urethane resin layer 34 and the second silicone-modified urethane resin The silicone-modified urethane resin in the layer 36 may be the same or different.

  Examples of commercially available silicone-modified urethane resins that can be used in the present invention include X-93-1343, X-93-1549, X-93-1248K, and X-93-1249C manufactured by Shin-Etsu Chemical Co., Ltd. Is mentioned.

In the present embodiment, a potential difference is applied to between the developing roller 2 and the photosensitive member 3 so that the direction of the electric field is ⁶ × 10 6 V / m or more toner 5 from the developing roller 2 to the photosensitive member 3 moves It is preferable. Thereby, even when the peripheral speed of the photosensitive member 3 exceeds 300 mm / sec, the developability of the toner 5 on the photosensitive member 3 can be satisfied.

The electric field in the direction in which the toner 5 moves from the developing roller 2 to the photoreceptor 3 is preferably set to 11 × 10 ⁶ V / m or less. If the electric field exceeds 11 × 10 ⁶ V / m, there is a risk of leakage between the developing roller 2 and the photoreceptor 3.

  In the present embodiment, it is preferable that the duty ratio of the AC bias (Vpp) applied to the developing roller 2 is 40% or more and 90% or less. Thereby, the occurrence of leakage between the developing roller 2 and the photoreceptor 3 is suppressed, and the developability can be further improved.

  EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated further more concretely, this invention is not limited by these examples.

The image forming apparatus of the present invention shown in FIGS. 1 to 3 was manufactured according to the following specifications. The dimensions and peripheral speeds of the sleeves of the photosensitive drum 3, the developing roller 2, and the magnetic roller 1 are as follows. Amorphous silicon was used for the photosensitive drum 3, and an aluminum substrate was used for the sleeve of each magnetic roller, and alumite treatment and sealing treatment were performed. See below for the development roller.
Photosensitive drum: outer diameter 30 mm, peripheral speed 350 mm / sec
Developing roller: outer diameter 20 mm, peripheral speed 420 mm / sec
Magnetic roller: outer diameter 25mm, peripheral speed 630mm / sec
Gap width between magnetic roller and developing roller: 250 μm
Gap width between the developing roller and the photosensitive drum: 180 μm

As the two-component developer, the following toner particles and carrier were used. The toner particles are positively charged.
Toner particle size (volume average particle size): 6.5 μm
Carrier particle size (weight average particle size): 35 μm
Toner / carrier mixing weight ratio (T / C): 6.0%

The electric field conditions during operation of the image forming apparatus are as follows.
Photoconductor drum surface potential: + 300V
Developing roller: Vdc2 = 100 V, Vpp = 1.2 kV, frequency f = 4.5 kHz, duty ratio = 50%
Magnetic roller: Vdc1 = 300V, Vpp = 1.4kV, frequency f = 4.5kHz, duty ratio = 70%

  A developing roller having the structure shown in FIG. 3 was produced. The aluminum tube was anodized in a sulfuric acid electrolytic bath to form an alumite film having a thickness of 15 μm on the surface, and then electrolyzed in an acetic acid aqueous solution for sealing treatment. A silicone-modified urethane resin coating solution containing carbon black was applied onto the alumite film subjected to the sealing treatment and dried at 150 ° C. for 40 minutes to form a carbon black-containing silicone-modified urethane resin layer.

  X-93-1343 manufactured by Shin-Etsu Chemical Co., Ltd. was used as the silicone-modified urethane resin coating solution. As carbon black, MA-100 manufactured by Mitsubishi Chemical Corporation (average particle diameter of primary particles: 22 nm) was used. The average particle size of carbon black was measured by the above-described measuring method.

[Examples 1-3 and Comparative Examples 1-3]
The carbon black (CB) content and the resin layer thickness in the silicone-modified urethane resin layer are changed as shown in Table 1 to form a carbon black-containing silicone-modified urethane resin layer with different volume resistance and resin layer thickness values. A developing roller was prepared. The volume resistivity (Ωcm) was measured by the aforementioned measuring method.

In Examples 1 and 2 and Comparative Example 1, a 0.5 μm first layer was formed, and a second layer was further formed to make the resin layer thickness 1.0 μm.
In Example 3, a 0.2 [mu] m first layer was formed, and a second layer was further formed so that the resin layer thickness was 0.7 [mu] m.
In Comparative Examples 2 and 3, the resin layer thickness was formed to be 1.0 μm by one application.

  Using the image forming apparatus incorporating the developing roller thus prepared, the charge amount when the toner thin layer was formed by driving for 60 seconds was measured, and the volume resistivity of the developing roller and the surface of the developing roller were measured. The relationship with the charge amount was determined. The charge amount was measured using a surface potential meter MODEL344-F-JK (manufactured by TREK Co., Ltd.) (measurement gap was 1 to 5 mm). The results are shown in Table 1 and FIG.

As is clear from the results shown in Table 1 and FIG. 4, the toner thin layer can be formed by adjusting the volume resistivity of the developing roller including the alumite film and the silicone-modified urethane resin layer to 1.5 × 10 ¹⁴ Ωcm or less. The rising time to the saturated charge amount on the developing roller surface at that time is fast, and a stable state can be maintained without being charged thereafter. If the volume resistivity exceeds 1.5 × 10 ¹⁴ Ωcm, charges are likely to be accumulated, the rise time until saturation charging is delayed, and stable developability cannot be obtained. If the volume resistivity is less than 1.0 × 10 ¹² Ωcm, leakage may occur.

[Example 4 and Comparative Examples 4 to 7]
The following developing roller was produced.
Example 4
A silicone-modified urethane resin coating solution containing carbon black is applied on the above-mentioned anodized anodized film, dried at 150 ° C. for 40 minutes, and has a thickness containing 17% by weight of carbon black (acetylene black). A 0.4 μm silicone-modified urethane resin layer is formed, and further a silicone-modified urethane resin coating solution containing carbon black is applied thereon and dried at 150 ° C. for 40 minutes to contain 17% by weight of carbon black. A developing roll was prepared by forming a silicone-modified urethane resin layer having a thickness of 0.8 μm. The same carbon black and silicone-modified urethane resin coating solution as described above was used. When the volume resistivity of the resin layer was measured in the same manner as described above, it was 1.0 × 10 ⁸ Ωcm. In the following, the developing roller of Example 4 may be indicated as “sealing-treated alumite / silicone-modified urethane (two layers)”.

(Comparative Example 4)
A developing roller was produced in the same manner as in Example 4 except that the silicone-modified urethane layer was formed as a single layer in Example 4. The volume resistivity of this developing roller was measured in the same manner as described above.

(Comparative Example 5)
A developing roller was produced in the same manner as in Example 4 except that the silicone-modified urethane layer was formed as a single layer in Example 4 and the resin layer thickness was 1.2 μm.

(Comparative Example 6)
In Example 4, a developing roller was produced in the same manner as in Example 4 except that a resin layer was provided on the alumite film not subjected to sealing treatment.

(Comparative Example 7)
A developing roller was produced in the same manner as in Example 4 except that the silicone-modified urethane layer was formed as a single layer in Comparative Example 6 and the resin layer thickness was 1.2 μm. A developing roll was formed by merely forming the above-mentioned anodized film and not performing any treatment thereon. The volume resistivity of this developing roll was measured in the same manner as described above.

(Leak margin value)
With respect to the image forming apparatus in which the developing rollers of Example 4 and Comparative Examples 4 to 7 were incorporated, a leakage margin value between the developing roller and the magnetic roller (hereinafter referred to as an MS leakage margin value) was measured. Here, the leak margin value refers to the minimum applied voltage at which electric field leakage occurs. In order to convey the developer to the magnetic roller and generate an electric field between the developing roller and the magnetic roller, an AC voltage was applied to the magnetic roller, and the developing roller was grounded so that the voltage was always zero volts. The AC bias conditions applied to the magnetic roller were as follows.

Frequency: 4.5kHz
Duty ratio: 60%
Vdc = 0V
Vmax: 500-1400V
Vmin: -500 to -1400V
Vpp = | Vmax | + | Vmin | = 2.8 kV

  As for the leak margin value between MSs, when Vmax is fixed and Vmin is changed (in this case, the leak margin value is displayed as “+ upper side”), and when Vmin is fixed and Vmax is changed (in this case) The leakage margin value is displayed as “−lower”. The obtained leak margin values are shown in Table 2 together with the volume resistivity of the developing roller.

As is clear from Table 2, the volume resistivity of the developing roller including the alumite film and the silicone-modified urethane resin layer is in the range of 1.0 × 10 ¹² Ωcm or more and 1.5 × 10 ¹⁴ Ωcm or less, and the sealing treatment It can be seen that the silicone-modified urethane-coated alumite has a higher volume resistivity and a higher leak margin value than those in which the non-sealed treated alumite is coated with the silicone-modified urethane, thereby suppressing leakage. It can also be seen that the silicone-modified urethane-coated one layer and two layers have a lower volume resistivity even when the two layers have the same layer thickness and suppress leakage. On the other hand, in the case where the carbon black-containing silicone-modified urethane resin layer is formed on the alumite film that has not been sealed, the carbon black enters the pores of the alumite film, resulting in a significant decrease in volume resistivity and leakage margin. The value is also low.

(Change in surface potential and toner amount with respect to driving time)
Example 4 [sealed anodized / silicone modified urethane (2 layers), volume resistivity = 1.0 × 10 ¹³ Ωcm] developing roller and comparative example 4 (sealed anodized / silicone modified urethane (1 layer)) The developing roller is grounded, the developing roller is grounded, Vdc = 200 V, Vpp = 2.0 kV, frequency = 4.5 kHz, Duty = 70% is applied to the magnetic roller, and the developing roller with respect to the driving time is applied. The change of the upper surface potential was examined. The surface potential was measured by the above measuring method. As a control, a developing roller whose surface is an alumite film was used. The results are shown in the graphs of FIGS.

Further, a developing roller of Example 4 [sealed anodized / silicone modified urethane (2 layers), volume resistivity = 1.0 × 10 ¹³ Ωcm] and Comparative Example 4 (sealed anodized / silicone modified urethane (1 layer) With respect to the image forming apparatus incorporating the developing roller of ()), the change in the toner amount on the developing roller with respect to the driving time was examined. The toner amount (mg / cm ² ) on the developing roller is calculated by sucking the toner amount per unit area of the toner layer formed on the developing roller after each driving time with a QM meter (TREK, MODEL 210HS). did. As a control, a developing roller whose surface is an alumite film was used. The results are shown in the graph of FIG.

  As apparent from FIGS. 5 and 6, a developing roller (sealing) in which a silicone-modified urethane resin layer containing carbon black was formed on the alumite film subjected to the sealing treatment of Example 4 by two coating operations. In the case of pore-treated alumite / silicone-modified urethane (two layers)), a development in which a silicone-modified urethane resin layer containing carbon black is formed on the alumite film subjected to the sealing treatment of Comparative Example 4 by a single coating operation. Compared to the roller (sealed anodized / silicone modified urethane (one layer)), the surface potential saturation time has been shortened from about 15 seconds to about 1 second (the developing roller (control) whose surface is an anodized film) The saturation potential is also reduced by about 35 V (the surface is equivalent to a developing roller having an alumite film).

  Further, as apparent from FIG. 7, a developing roller (sealing treatment) in which a silicone-modified urethane resin layer containing carbon black was formed on the alumite film subjected to the sealing treatment of Example 4 by two coating operations. In the case of anodized / silicone-modified urethane (two layers), the amount of toner is stable from the beginning of driving as in the case of a developing roller (control) having an anodized coating, but the sealing treatment of Comparative Example 4 was performed. In a developing roller (sealing-treated alumite / silicone-modified urethane (one layer)) in which a silicone-modified urethane resin layer containing carbon black is formed on the alumite film by a single coating operation, as the circumference of the developing roller is repeated, The toner amount decreases and changes from the first round to about 1/3.

  That is, the phenomenon that the charge is accumulated in the silicone-modified urethane resin layer, the electric field strength between the developing roller and the magnetic roller is reduced, and the toner amount of the toner thin layer is reduced is suppressed in the fourth embodiment of the present invention. I understand that.

  Further, from the above results, a developing roller (sealing-treated alumite / sealed / uncoated) was formed by applying a silicone-modified urethane resin layer containing carbon black on the alumite film subjected to the sealing treatment of Example 4 twice. For silicone-modified urethane (two layers), a developing roller (sealing) in which a silicone-modified urethane resin layer containing carbon black is formed on the alumite film subjected to the sealing treatment of Comparative Example 4 by a single coating operation. Compared with the treated alumite / silicone-modified urethane (one layer), the developing roller surface potential is more stable, indicating that the developability at the initial stage of driving is more stable.

  This experimental result is obtained when the toner thin layer is formed. If the printing or the like is further continued, the amount of toner decreases when the surface is a developing roller (control) having an alumite film. The toner amount is maintained at the developing roller.

(Relationship between photoreceptor peripheral speed and developability)
Regarding the image forming apparatus incorporating the developing roller of Example 4 [sealed alumite / silicone-modified urethane (two layers), volume resistivity = 1.0 × 10 ¹³ Ωcm], the relationship between the peripheral speed of the photoreceptor and the developability I investigated. The developability was evaluated by the image density. The image density was measured using a spectrophotometer SpectroEye manufactured by Gretag Macbeth. As a control, a developing roller whose surface is an alumite film was used. The results are shown in Table 3 and the graph of FIG.

  As is apparent from Table 3 and FIG. 8, in the developing roller (control) having an alumite film on the surface, when the peripheral speed of the photoreceptor exceeded 340 mm / sec, the image density decreased, but the anodized film on which sealing treatment was performed. In the developing roller of Example 4 (sealing-treated alumite / silicone-modified urethane (two layers)) in which a silicone-modified urethane resin layer containing carbon black was formed by two coating operations, the peripheral speed of the photoreceptor was It can be seen that the image density does not decrease even if it exceeds 340 mm / sec.

(Relationship between electric field applied to developing roller and direction of toner moving from developing roller to photoreceptor) and developability
Example 4 [Developing Roll Applied to Developing Roller for Image Forming Apparatus Incorporating Developing Roll of Sealed Anodized / Silicone Modified Urethane (2 Layers, Volume Resistivity = 1.0 × 10 ¹³ Ωcm]] The relationship between the electric field in the direction in which the toner moves from the toner to the photoreceptor and the developability was examined. The developability was evaluated by the image density. In the image forming apparatus, a waveform of an applied bias is formed by a WAVE FACTORY WF-1946A (manufactured by NF), and is applied after being amplified 1000 times by an AC / DC AMPLIFIER NVA4321 (manufactured by NF). did. The electric field was changed by varying this waveform. The results are shown in Table 4 and FIG. In the evaluation, the image density of 1.400 or more was evaluated as “◎”, and 1.300 to 1.399 was evaluated as “◯”.

As apparent from Table 4 and FIG. 9, a developing roller (sealing) in which a silicone-modified urethane resin layer containing carbon black was formed on the alumite film subjected to the sealing treatment of Example 4 by two coating operations. In the case of hole-treated alumite / silicone-modified urethane (two layers), the electric field is applied to the developing roller so that the electric field in the direction in which the toner moves from the developing roller to the photoreceptor is 6 × 10 ⁶ V / m or more. Higher image density can be obtained.

(Relationship between duty ratio of AC bias applied to developing roller and developability)
Example 4 [Sealing Anodized / silicone-modified urethane (2 layers), volume resistivity = 1.00 × 10 ¹³ Ωcm] of the developing roller and Comparative Example 4 [Sealing Anodized / silicone-modified urethane (one layer), The relationship between the duty ratio of the AC bias applied to the developing roller and the developability of the image forming apparatus incorporating the developing roller having a volume resistivity = 5.0 × 10 ¹⁴ Ωcm) was examined. With the toner layer thickness on the developing roller kept constant, the developability from the developing roller was evaluated by the image density. As shown in FIG. 2, in a configuration in which the DC power and AC power applied to the magnetic roller are superimposed on the DC power and AC power of the developing roller, the DC voltage and AC voltage applied to the magnetic roller are fixed and applied to the developing roller. The duty ratio of the AC voltage to be changed was changed. The toner image was applied to the magnetic roller for 1 minute and then applied to the developing roller to form a toner image (solid), and the image density was measured. The results are shown in Tables 5 and 6. The evaluation was performed based on the same criteria as the evaluation in Table 4.

  As is clear from Tables 5 and 6, a developing roller (sealing) in which a silicone-modified urethane resin layer containing carbon black was formed on the alumite film subjected to the sealing treatment of Example 4 by two coating operations. In the hole-treated alumite / silicone-modified urethane (two layers)), the image density becomes higher by setting the duty ratio of the applied AC bias to be in the range of 40 to 90%. However, in the developing roller of Comparative Example 4, The image density is not so high.

1 Two-component developer carrier (magnetic roller)
2 Developing roller (toner carrier)
3 Electrostatic latent image carrier (photoreceptor)
4 Carrier 5 Toner 6 Magnetic Brush 7 Regulating Blade 8 Charging Means 9 Toner Thin Layer 11a AC Power Supply 11b DC Power Supply 12a AC Power Supply 12b DC Power Supply 16 Exposure Means 22 Exposure Means 22 Primary Transfer Means 24 Cleaning Means 25 Secondary Transfer Means 26 Fixing Means 30 Aluminum Base Material 31 Anodized coating 32 Sealed hole 33 Silicone-modified urethane resin layer 34 First silicone-modified urethane resin layer 35 First conductive agent 36 Second silicone-modified urethane resin layer 37 Second conductive agent

Claims (4)

A two-component developer containing at least a carrier and a toner is held on a two-component developer carrier, and the toner is transferred from the two-component developer carrier to form a thin toner layer on the toner carrier. In an image forming apparatus having a developing device for developing an electrostatic latent image by causing toner on the toner carrier to fly to the electrostatic latent image carrier,
The toner carrier includes an aluminum base, the surface of the aluminum base is anodized and sealed, and is further coated with a silicone-modified urethane resin layer containing a conductive agent. The anodized film and the silicone An image forming apparatus, wherein the toner carrier including a modified urethane resin layer has a volume resistivity of 1.0 × 10 ¹² Ωcm or more and 1.5 × 10 ¹⁴ Ωcm or less. The toner carrier is applied so that an electric field in a direction in which the toner moves from the toner carrier to the electrostatic latent image carrier is 6 × 10 ⁶ V / m or more. The image forming apparatus according to 1.   3. The image forming apparatus according to claim 1, wherein a duty ratio of an AC bias applied to the toner carrier is 40% or more and 90% or less.   The silicone-modified urethane resin layer is formed by dividing the coating process into at least a first layer and a second layer, and the first layer is coated with a silicone-modified urethane resin containing a conductive agent on the alumite film surface. After the liquid is dried, it is formed by coating and drying so that the layer thickness is 0.2 to 0.5 μm. The second layer is coated with a silicone-modified urethane resin containing a conductive agent on the first layer. 2. The liquid is formed by coating and drying so that the sum of thicknesses of the first layer and the second layer after drying is 0.7 to 1.0 μm. 4. The image forming apparatus according to any one of items 1 to 3.

Images