JP2009282074A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device for stably and uniformly coating the surface of a developer carrier with toner for a long period of time even when one-component magnetic toner is used and achieving high image quality, and to provide an image forming apparatus. <P>SOLUTION: The developing device has a regulating member 3j for regulating the layer thickness of a toner carried by a first toner carrier 3a and uses the first toner carrier to regulate the layer thickness of a toner carried by a second toner carrier 3b. In the developing device, if a quantity of toner remaining on each toner carrier after toner is sucked from a predetermined suction area S (cm<SP>2</SP>) of the toner carrier with a predetermined sucking force W (W) for a predetermined time T (sec) is represented by My (mg), an equilibrium time required for toner to stabilize in quantity after the suction is represented by Ts (sec), and the adhering force Af of toner relative to the toner carrier is represented by (My×W/S)×(Ts/T), the adhering force Af of toner relative to the first toner carrier is smaller than that relative to the second toner carrier. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a developing device that develops an electrostatic latent image formed on an image carrier such as a photoconductor to form a developer image, and an image forming apparatus including the developing device.

  2. Description of the Related Art In recent years, image forming apparatuses such as copying machines and printers need to rotate a developer carrier of a developing device at a high speed in response to a high-speed response that is a need from a user. For this reason, the time for visualizing the electrostatic latent image on the photosensitive member with the developer on the developer carrying member is shortened, and there is a problem that development failure occurs.

  In addition, the demand for high durability and high reliability is increasing as the speed increases. However, it is well known that the conventional electrophotographic technology affects the image quality depending on the use conditions of the user, for example, the use environment, the type of transfer paper, the number of used sheets per day, the image ratio of the document, and the like. Furthermore, in recent years, work efficiency has been improved, and the operation time of the image forming apparatus has been regarded as a problem. Particularly, in a high-speed (100 ppm or more) image forming apparatus, high productivity and high durability that do not stop even after 10 hours or more are continued. Sex is also required.

  Furthermore, in order to increase the work efficiency of users and services, improvement in maintainability is required in the market.

  In the prior art, a technique using a plurality of developer carriers has been proposed in order to realize high speed and high image quality.

  In Patent Document 1 (Japanese Patent Application Laid-Open No. 2004-163906), the Sm of the upstream developer carrier having a plurality of developer carriers is greater than the Sm of the developer carrier downstream. The surface is roughened so as to increase. As a result, high image quality and high speed are achieved, the amount of adhesion is suppressed, and the concentration is stabilized by durability.

  In Patent Document 2 (Japanese Patent Application Laid-Open No. 2005-99394), in a development system having a plurality of developer carriers, the surface of the developer carrier is coated with a phenol resin, and a quaternary ammonium salt is applied only to the downstream developer carrier. Put in. Furthermore, in order to increase speed, improve image quality, and improve durability, the durability life is made common with spherical carbon particles.

JP 2004-163906 A JP 2005-99394 A

  However, the conventional example has the following problems.

  a) With the Sm rule alone, deterioration (toner adhesion, charge amount) of the upstream and downstream developer carrier cannot be maintained for a long time. Large Sm, that is, small-diameter substances (external additives, fine powder toner) tend to get stuck in the gap between the peaks, and in particular, in a developing device using a plurality of developer carriers, the developer carrier adheres to the upstream developer carrier. There are issues that arise.

  b) In the resin coating, there is a problem that the image quality is deteriorated due to durability and wear, the toner amount is decreased, the charging ability is decreased.

  c) When a resin coat is used on the downstream side, there is a problem in that the charging ability is reduced as compared with the upstream side and the image quality is deteriorated.

  Therefore, the present invention provides a development that can stably and uniformly coat a developer (toner) over a long period of time and achieve high image quality even when a magnetic one-component toner (one-component developer) is used. An object is to provide an image forming apparatus and an image forming apparatus.

In order to solve the above problems, a typical configuration of a developing device and an image forming apparatus according to the present invention is provided close to each other so as to develop an electrostatic image formed on an image carrier. First and second toner carriers carried and conveyed, and a regulating member that regulates the layer thickness of the toner carried on the first toner carrier, and the second toner carrier In the developing device that regulates the layer thickness of the carried toner by the first toner carrier, a predetermined suction area S (of the toner carrier for a predetermined time T (sec) with a predetermined suction force W (W). The amount of toner remaining on the toner carrier after the toner is sucked from cm ² ) is My (mg), and the equilibrium time until the toner amount is stabilized after the suction is Ts (sec). Wear force Af (My x W / S) × (Ts / T), the toner adhesion force Af to the first toner carrier is smaller than the toner adhesion force Af to the second toner carrier.

  According to the present invention, even when a magnetic one-component toner (one-component developer) is used, the developer (toner) can be stably and uniformly coated on the developer carrier for a long period of time, and high image quality can be achieved.

[First embodiment]
A first embodiment of a developing device and an image forming apparatus according to the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of an image forming apparatus including a developing device 3 according to the present embodiment.

(Image forming device)
As shown in FIG. 1, an image forming apparatus includes a primary charger 2, a developing device 3, and a pre-transfer charger (post-charge) around a photosensitive drum (positively charged a-Si photosensitive member) 1 as an image carrier. 4), a transfer charger (transfer means) 5, a separation charger 6, a cleaning device 7, and a fixing device 8. In addition, a transfer portion is formed between the photosensitive drum 1 and the transfer charger 5. The fixing device 8 is disposed on the downstream side in the transfer material conveyance direction from the transfer unit.

  The photosensitive drum 1 has a diameter of 84 mm and rotates clockwise (in the direction of the arrow) at a predetermined peripheral speed (450 mm / sec). The photosensitive drum 1 is charged to, for example, +500 V by the primary charger 2. The charged photosensitive drum 1 is given an image exposure L at 1200 dpi by an exposure device (not shown), and an electrostatic latent image (electrostatic image) corresponding to input image information is formed.

  The two developer carriers (first toner carrier, second toner carrier) 3a and 3b of the developing device 3 have a developing bias (AC component superimposed on the DC component) having the same polarity as the charged polarity of the photosensitive drum 1. Applied bias). The developer carriers 3a and 3b apply developer (magnetic toner (magnetic one-component toner)) t charged to the opposite polarity to the charged polarity of the photosensitive drum 1 on the surface of the photosensitive drum 1 (development site of the electrostatic latent image). The toner image is adhered and developed by a jumping development method to be visualized as a toner image.

  The surface of the photosensitive drum 1 on which the toner image is formed is pre-charged by a pre-transfer charger (post-charger) 4. The toner image on the surface of the photosensitive drum 1 reaches the transfer portion between the photosensitive drum 1 and the transfer charger 5. In accordance with this timing, a transfer material P such as paper in a paper feed cassette (not shown) is conveyed to the transfer unit. The toner image is transferred to the transfer material P by the transfer charger 5 to which a transfer voltage having a polarity opposite to that of the toner is applied. The transfer material P onto which the toner image has been transferred is separated from the photosensitive drum 1 by the separation charger 6 and conveyed to the fixing device 8. At the fixing nip portion between the fixing roller 8a and the pressure roller 8b of the fixing device 8, the toner image is heated and pressed against the transfer material P and thermally fixed, and then the transfer material P is discharged to the outside.

  The transfer residual toner (residual developer) remaining on the surface of the photosensitive drum 1 after the toner image transfer is removed and collected by a cleaning device (cleaning means) 7.

(Developing device 3)
Next, the developing device 3 will be described in detail. By applying a high pressure to the developer carrier 3a coated with the developer, the developer on the surface of the developer carrier 3a flies to the photoreceptor 1 and the electrostatic latent image can be visualized. . In the case of regular development, the developer can be visualized with a developer having the same polarity as the charged potential. Conversely, in the case of reversal development, the developer can be visualized with a developer having the opposite polarity to the charged potential.

  In the developing device 3, developer carriers 3a and 3b as developer carriers that are rotatable in the direction of the arrow (counterclockwise) close to the opening of the developing container 3c so as to face the photosensitive drum 1 are photosensitive. They are arranged along the rotation direction of the drum 1. The developer carrier 3 a is located upstream of the developing portion facing the photosensitive drum 1 in the rotation direction of the photosensitive drum 1 and is in close proximity to the photosensitive drum 1. The developer carrier 3b is located downstream of the developer carrier 3a in the rotation direction of the photosensitive drum 1, and is in close proximity to the photosensitive drum 1 and the developer carrier 3a.

  An upstream magnet roll 3h is provided inside the developer carrier 3a. A downstream magnet roll 3i is provided inside the developer carrier 3b. In the developing container 3c, the developer moves from the second stirring unit (toner stirring member) 3e to the first stirring unit (toner stirring member) 3d and is supplied to the developer carriers 3a and 3b.

  In the developer carrier 3a, the coat thickness of the toner t is regulated by a layer thickness regulating blade (regulating member) 3j. In the developer carrier 3b, the coat thickness of the toner t is regulated by the developer carrier 3a disposed in the vicinity.

  Charge is applied to the developer image visualized by the developing device 3 by using a pre-transfer charger 4 (post-charging). It functions to weaken the electrostatic attraction between the developer and the photoconductor generated when transferring with the pre-transfer charger 4. For this reason, it becomes easy to separate the transfer material P from the photosensitive drum 1 in the next transfer step.

  In the developing container 3c, there are two toner stirring members 3d and 3e and a toner amount detection sensor (not shown) for detecting the toner amount in the developing container 3c. The toner agitating members 3d and 3e agitate the toner t in the developing container 3c and convey it to the developer carrying members 3a and 3b. The toner (magnetic one-component toner) t is a negative toner, the weight average particle diameter is 5.0 to 10.0 μm, and the resin is composed of at least one of styrene acrylic resin or polyester resin, and the magnetic substance is 50 to 100. Part by weight. Moreover, 0.2 to 2.0% (weight%) SiO2 is contained as an external additive.

  The surfaces 3f and 3g of the developer carriers 3a and 3b were blasted with FGB # 600 on SUS305 having a diameter of 20 mm, which is a nonmagnetic member, so that the surface roughness Rz was 3 μm. For the measurement of the surface roughness Rz, a contact-type surface roughness meter (Surfcoder SE-3300, Kosaka Laboratory) was used. The measurement conditions are a cut-off value of 0.8 mm, a measurement length of 2.5 mm, a feed speed of 0.1 mm / sec, and a magnification of 5000 times. The downstream developer carrier is thicker than the upstream developer carrier.

  The developer carriers 3a and 3b rotate at a speed of 50 to 150% with respect to the rotation speed (process speed) of the photosensitive drum 1, and a gap between the developer carriers 3a and 3b and the photosensitive drum 1 at the development position. (Gap) is 100 to 400 μm. The toner is carried on the developer carrier 3a by the magnetic force of the upstream magnet roll 3h. The toner is carried on the downstream developer carrier 3b by the magnetic force of the upstream magnet roll 3h. A gap (gap) between the developer carrier 3a and the developer carrier 3b on a straight line connecting the rotation centers of the upstream developer carrier 3a and the downstream developer carrier 3b is 100 to 400 μm.

  A developer bias in which a DC bias of +300 V and an AC bias are superimposed is applied to the developer carrying members 3a and 3b from a developing bias power source (bias applying means) (not shown), whereby toner (magnetic one-component toner) is transferred to the photosensitive drum. The electrostatic latent image is developed in a non-contact manner by flying to one side. The AC bias is a rectangular wave having a peak-to-peak voltage (Vpp) of 900 to 2000 V and a frequency of 1.0 to 4.0 kHz as shown in FIG. In this embodiment, a rectangular wave may be used, but it is necessary to optimize the waveform shape according to the type of toner, the photosensitive drum, the latent image method, and the like. The development contrast at this time was 200V in the flight direction, and the fog removal contrast was 150V.

  In this way, the AC bias is applied to the upstream and downstream developer carriers 3a and 3b so as to be superimposed on the DC bias. As a result, excess toner that has not contributed to the development by the upstream developer carrier 3a can be collected by the downstream developer carrier 3b and returned to the developing container 3c again, thereby reducing toner consumption. it can.

  For example, when an image of a 6% image ratio is output as an image, a conventional developing device using a magnetic one-component toner consumes 50 to 60 mg / sheet, but in the developing device 3 of the present embodiment, toner is consumed. Consumption was about 40 mg / sheet.

(Developer adherence to sleeve)
The developing device 3 of the present embodiment is configured to reduce the adhesive force of the developer to the sleeve as compared with the conventional technology.

  FIG. 3 shows the relationship between the reflection density and the toner adhesion amount on the upstream / downstream developer carrier surface (upstream / downstream sleeve surface) with respect to the number of sheets passed in the prior art. The experimental conditions were a temperature of 26 degrees, a humidity of 45%, an image ratio of 5%, and continuous durability of 1000k sheets (1 million sheets).

  As the number of sheets passed increases, the reflection density decreases. For example, the reflection density (spectral colorimetric densitometer X-Rite 500 measurement value) has decreased by only 0.05 at the time of 150k, but falls below 1.30 at the time of 200k. Furthermore, when the paper was continued, there was a problem that it decreased to about 1.2 at 1000k.

  In this case, regarding the decrease in concentration, attention was paid to the deposits on the upstream and downstream sleeve surfaces, and the deposit amount was simultaneously observed. The upstream and downstream sleeve surfaces are sucked at a constant pressure, the remaining deposits are peeled off with tape, and the substance remaining on the tape is measured with a transmission densitometer.

  An adhesion amount of 0.05 has already been detected at the initial 100 k. Further, at 200k when the concentration is further lowered, it is remarkably increased to 0.15. Thereafter, it can be seen that the amount of adhesion increases in proportion.

The tape stripping measurement in this case will be described. In this case, the surface of the developing sleeve was sucked with a suction force of 500 W, and the toner was sucked with a suction device in a region of 10 cm ² for about 20 seconds. The suction machine has a filter and measures the toner in the filter. Further, the toner adhering to the surface of the developing sleeve is peeled off with a tape (scotch mending tape substrate acetate film, adhesive material: acrylic adhesive). Then, the amount of adhered toner is converted using a transmission densitometer (Macbeth TDS904).

  FIG. 5 shows the relationship between the sleeve adhesion amount and the transmission density. The adhering substance on the sleeve surface is the result of performing mass analysis of the adhering substance on the sleeve surface using an electron beam microscope and an elemental analyzer. When the amount of adhesion due to the permeation concentration increases, the mass of the adhering substance on the sleeve surface increases in substantially the same relationship. The relationship is almost proportional, and it is possible to indirectly measure the amount of adhesion on the sleeve surface by the transmission density.

  FIG. 4 shows the relationship between the sleeve adhesion amount and the reflection density. When the reflection density standard is 1.4, the sleeve adhesion amount standard is about 0.1. In the present embodiment, the ease of attaching the sleeve is compared based on the standard value.

  From the above experimental results, it can be said that the density lowers when reaching a certain amount where the sleeve adheres, that is, if the adhering amount is reduced, the density decline can be suppressed.

  It can be said that the toner adhering to the developing sleeve even when sucked is a toner having a strong adhering force that cannot be peeled off with a constant force. The adhering toner adheres electrostatically, mechanically and viscously to the sleeve. That is, it means “cannot be peeled off with a constant suction force” = “attached toner has a constant adhesion force (electrostatic, viscous force, etc.)”.

  However, the amount of adhesion has an effect on the suction force, which is the power of suction, the suction time, and the suction area. For example, the stronger the suction power, the longer the suction time, and the smaller the suction area, the more strongly the toner that adheres electrostatically may be sucked and the difference may not be judged. There are also cases where the amount of adhesion varies depending on the initial toner amount on the sleeve.

  FIG. 6 shows the remaining amount of toner when the suction force is changed to 400, 600, and 800 W with respect to time. Since the amount of adhesion varies depending on the suction time, suction force, and suction area, it is difficult to make a constant evaluation.

Therefore, the adhesion force, not the adhesion amount, is defined below. The adhesion force (Af: mg · W / cm ² ) is a force with which the developer (M: mg) adheres to the surface of the developer carrying member. Expressed as a constant amount of developer (My: mg) when sucked on the surface of the developer carrying member (W: Watt), a certain time (T seconds), and a certain area (S: cm ² ). The

M = Mx + My (Formula 1)
Af = My * (W) / S * Ts / T (Formula 2)
Developer amount on the surface of the developer carrying member (M: mg), amount of developer sucked by suction (Mx: mg), remaining amount of developer on the surface of the developer carrying member (My: mg), suction force (W: Watt), suction time (T: sec), suction area (S: cm ² ), adhesive force (Af: mg · W / cm ² ), equilibrium time (Ts: sec) during which the developer amount is stabilized by suction.

FIG. 21 shows the adhesion amount and the adhesion force (Af), which are transmission densities when the suction power is changed from 400 W and 800 W, and the time is changed from 0 sec to 60 sec. The equilibration time is a previously measured value, and the suction area is fixed at 10 cm ² .

  As shown in FIG. 21, the transmission density My increases as the suction time T increases. The greater the suction force W, the greater the force to peel off the substance adhering to the sleeve surface. Further, when sucked for a certain period of time, the transmission density is stable. This means that the adhesion force of the substance electrostatically adhering to the sleeve surface is greater than or equal to the suction force. This state is called an equilibrium state, and the time to reach the equilibrium state is the equilibrium time Ts. In the case of 400 w, the equilibrium state is reached in about 50 seconds.

In the above experiment, there is a drawback that the adhesion force cannot be accurately determined because the permeation density changes when not in an equilibrium state. FIG. 21 shows the adhesive force. It is possible to calculate almost the same value as the transmission density. When the suction force is 800 W, it is 20 mg · W / cm ² . Even when the suction time is short, it can be calculated with some expectation. Moreover, in the case of 400W, it is 5 mg * W / cm < ² >.

  FIG. 7 shows the relationship between the adhesion force and the transmission density (adhesion force vs. adhesion amount). Thus, when it measures with the same suction | attraction force, if it is within a fixed time, it can calculate as the same adhesion force. Thus, by calculating the adhesion force, it becomes possible to indirectly and accurately measure the electrostatic and viscous forces of the toner adhering.

  Next, the adhered substance will be described. The adhering substances are mainly divided into fine powders and external additives having a high charge amount, and substances that are sensitive to temperature, such as toner and WAX.

  The former is likely to occur when the charging capability is high, such as in a low humidity environment or when the image ratio is low. In particular, strong negative materials such as fine powder and silica are likely to adhere to the sleeve surface due to the mirroring force, which is a factor in reducing the concentration.

  Adhesive force can be roughly classified into the following three types. (1) Electrostatic force attached by the mirroring force of the toner and the sleeve. (2) A mechanical force that attracts and adheres to the sleeve surface where the toner is uneven. (3) Viscous force attached by surface tension such as WAX on viscous toner surface or water droplets on sleeve surface. The adhesion force in this case can represent the above three forces with one index.

  FIG. 8 shows Q / M, which is the charge amount of the upstream sleeve, and the upstream sleeve adhesion force. When the absolute water content is 1 g / Kg DryAir, the image ratio is 50% for the two modes of 1% (acceleration) and 5% (standard). The result of having performed the sheet passing test is shown. As the Q / M on the sleeve increases, the amount of adhesion on the upstream sleeve also increases. In particular, when the image ratio is 1%, the increasing tendency is remarkable as compared with 5%. When the on-sleeve Q / M is changed from 5 to 15, the adhesive force increases three times, and when the image ratio is 5%, the adhesion force increases five times. That is, when Q / M is increased, sleeve adhesion increases.

  The Q / M on the sleeve is one of the most important parameters in image formation. In general, the higher the Q / M, the more accurately the latent image on the photosensitive drum can be reproduced with a small amount of toner and without edge enhancement, so that scattering, tailing, etc. are improved, and consumption can be reduced. To achieve this, it is important to eliminate the adhesion of high Q / M materials.

  FIG. 9 shows detailed data on the sleeve adhesion force with respect to the image ratio when the absolute water content is 1, 10, 20 g / Kg DryAir (absolute water content (g) / DryAir (Kg)). As shown in FIG. 9, it can be seen that the smaller the absolute water content, the higher the charge amount and the worse the sleeve adhesion. Further, by reducing the image ratio, the charge-up becomes intense and the sleeve adhesion is also deteriorated. Specifically, when the image ratio is changed from 15% to 1%, it is 5 times (when the absolute water content is 1 g / Kg DryAir), and when the water content is changed from 20 g to 1 g, it is 2.5 times (the image ratio is 1). %)) Has increased.

  Adhesion is easily affected by regulatory forces. The upstream developer carrier 3a of the present case has roughness. As shown in FIG. 1, the developer carrier 3a is in contact with the regulating blade 3j, and the upstream developer carrier 3a is easily rubbed mechanically. That is, the toner is likely to adhere.

  Regarding the relationship between the upstream sleeve carrying member 3a (upstream sleeve) and the SB gap (μ), which is the gap between the regulating blade 3j, and the upstream sleeve adhesion force, the absolute moisture amount is changed to 1, 10, 20 g / KgDryAir. The data is shown in FIG.

  As shown in FIG. 10, the smaller the SB gap, the worse the sleeve adhesion. Also, the greater the absolute moisture content, the greater the sleeve adhesion. On the other hand, the absolute water content is almost the same at 1 g and 10 g. This is because when the amount of water is small, Q / M increases and high Q / M adhesion occurs. In this experiment, the in-machine temperature was set to 47 degrees in order to see the effects of heat and pressure in an accelerated manner. The number of sheets to be passed is 50 k, the image ratio is 5%, and Vslv is 500 mm / s. As for the adhesion force, the same adhesion occurs between the upstream developer carrying member and the downstream developer carrying member (hereinafter referred to as the SS portion).

FIG. 11 shows the degree of compression of the SS part, that is, the adhesion force to the SS gap (μm). As the SS gap increases, the sleeve adhesion decreases. It can also be seen that the upstream sleeve has a greater adhesion than the downstream sleeve. For example, the SS gap is stable when exceeding 400 μm, the upstream sleeve adhesion is about 0.7 mg · W / cm ² , and the downstream sleeve adhesion is 0.25 mg · W / cm ² .

  In this way, adhesion occurs at the SS portion as well as at SB. That is, in the upstream / downstream sleeve, it can be said that the upstream sleeve in contact with SB and SS is more likely to adhere than the downstream sleeve.

(Developer carrier to which toner adheres)
The developer carrier (sleeve) to which the toner adheres will be described. The sleeve has a function of feeding and charging the toner. Therefore, it is important to have certain irregularities (roughness).

  Various materials are used to form roughness. A sandpaper method of rubbing the surface of a developer carrying member with sandpaper, a bead blasting method using spherical particles, a sandblasting method using irregular particles, or a mixing method thereof, and a chemical etching method using chemical treatment, etc. have been proposed. It has been implemented.

  There are AL, SUS, and the like as the material of the developer carrier, and the developer carrier itself may be directly polished and roughened. In addition, there is also a treatment in which glass beads or the like are applied to the surface of the developer carrying member while applying pressure from a constant abrasive outlet and rotating the developer carrying member. There are various kinds of materials such as materials with a high degree of circularity of the shape of the abrasive grains such as alundum type, molundum type, white molundum type, and those having a sharp shape. Moreover, each abrasive grain has a particle size, and it is used according to a use to 0.1micro-10micro.

  However, even if the above coating properties, charge amount, and developability are satisfied, various drawbacks occur depending on environmental fluctuations and durability conditions. Due to long-term use, there is a problem that the toner or components in the toner are easily caught by the rough valleys of the roughened surface and easily adhered.

  The toner adhering to the valleys is fused by frictional heat applied to the developer over a long period of use, and as a result, the surface of the developer carrying member is contaminated with the toner. In particular, there is a drawback that the amount of adhesion increases as there are a plurality of contact portions. That is, the shape of the sleeve surface is an important parameter along with the toner charge amount, image ratio, SB gap, SS gap, and the like.

(Heat, pressure)
Heat and pressure also have an effect on the sleeve adhesion, and when a certain amount of heat and pressure are applied to the toner, the sleeve adhesion increases. The toner has the property of melting at a certain temperature. Naturally, the toner is fused even when the ambient temperature rises at a place other than the fixing unit. Further, the WAX contained in the toner oozes out from the inside of the toner, adheres to the sleeve surface, becomes a nucleus, and deteriorates the sleeve adhesion level. On the other hand, there is also sleeve adhesion due to pressure dependence with temperature. In the case of jumping development, a certain pressure is applied mechanically or magnetically because the toner and the toner and the sleeve are frictionally charged. For this reason, when the pressure is too high, the toner may be rubbed against the sleeve and sticking to the sleeve may occur.

  FIG. 12 shows data obtained by changing the absolute moisture amount from 1 to 20 g with respect to the sleeve adhesion amount with respect to the sleeve rotation speed (Vslv) that affects the heat generation. As the speed increases, the sleeve adhesion also deteriorates. It can also be seen that the higher the absolute water content, the more the tendency is. This is because the amount of heat generated increases due to high-speed rotation, the frictional force between the toner and the sleeve increases, the toner deteriorates, and adheres to the sleeve. The rotational speed of the sleeve directly affects the productivity of the image forming apparatus. It is no exaggeration to say that the number of output sheets per minute is determined by the rotational speed. Therefore, it is important to find a condition in which sleeve adhesion does not occur at any high speed. It can also be seen that the upstream sleeve has an increased amount of adhesion than the downstream sleeve.

  As described above, the adhesion of the sleeve depends on the toner charge amount (Q / M), the roughness of the developing sleeve, the material, the regulation of the SB portion and the SS portion, the image duty, the durable number, the temperature / pressure factor, the rotational speed factor, etc. There are various.

(Method to improve sleeve adhesion)
Next, a method for improving the adhesion of the sleeve will be described. There are various methods for improving sleeve adhesion. For example, there are a method of mechanically removing substances adhered to the surface of the developer carrying member, a method of discharging a deposit by applying a bias, a method of constructing the developer carrying member itself with a soft resin and wearing the surface with durability. is there.

  However, the life of the developer carrier itself is reduced, it cannot be completely peeled off by bias, the roughness changes when the developer carrier surface is scraped, and the toner amount, charge amount, etc. change after the initial and endurance. There are problems such as image defects.

  FIG. 22 shows experimental results comparing the example (1) and the conventional example. In this experiment, SB gap 200μ, SS gap 400μ, upstream / downstream developer carrier rotation speed 500mm / sec, environment 23 degrees 70%, image duty 5%, sleeve adhesion force and image quality are measured by continuous paper feeding. . The sleeve adhesive force is measured within 1 minute to 5 minutes after continuous paper feeding in order to stabilize the measurement value.

  As shown in FIG. 22, in Example (1), the upstream / downstream sleeve adhesion, dust scattering of image quality toner, and durability that is durable density stability were verified. Main parameters used were toner-related parameters such as particle size, external additive silica amount, toner fine powder amount, developer carrier (sleeve) surface roughness Rz, and the like.

  The amount of external additive silica in the toner mainly controls the charge amount of the toner. The greater the amount, the higher the negative impartability and the greater the sleeve adhesion. In Example (1) -1, the amount of silica was reduced to half (1%) of 2% (weight ratio) of the conventional example, so that the upstream sleeve adhesion was reduced from the conventional 0.2 to 0.18 by 10%. Reduced.

  The amount of fine powder of toner is the amount of small particle toner contained in the toner. When the amount of fine powder is small, the amount of substance adhering to the irregularities on the sleeve surface is reduced, so that the sleeve adhesion is reduced. In Example (1) -2, the amount of fine powder is reduced from 20% to 10% (vs. the total amount of toner) compared to the conventional example, so that the sleeve adhesion is reduced from 0.18 to 0.17.

  The larger the particle size (μm), the more difficult it is to adhere to the irregularities on the upstream and downstream sleeve surfaces. In Example (1) -3 as compared with the conventional example, the sleeve adhesion force is reduced from 0.17 to 0.16 by increasing the particle size from 8 to 10.

  However, the above-described particle size, silica amount, and fine powder amount affect the image quality and durability stability. In fact, by reducing the amount of silica, scattering indicating the dust of the toner of the image (index: calculated by the distance and area from a certain line. The larger the value, the worse the dust is). Worse. In addition, by increasing the particle size, the area of Chile increases and the scattering index deteriorates from 22 to 25. Further, the durability indicating the stability of the concentration and the fog has conventionally been ensured by 500 k sheets, but is reduced to 400 k by reducing the amount of silica.

  In this case, in order to improve image quality and productivity, as a countermeasure, attention is paid to the surface shape of the developer carrier, and a method for preventing durability and adhesion of the developer carrier is proposed. First, the developer carrier surface roughness is shown in FIG. 16 (a), FIG. 17 and FIG. 18 with names and symbols, and FIG. 16 (b) shows the three-dimensional shape (see JISb0601-1982, 1994, ISO468-1982 Surfacousness). . Rz is an average roughness of 10 points on the surface and represents an average value of 5 high points and 5 low points in a certain width.

  When the surface roughness (Rz) of the developing sleeve is large, the fine powder that causes the sleeve to adhere becomes difficult to adhere, so that the sleeve adhesion can be reduced. In the embodiment (1) -4 of FIG. 22, the Rz of the upstream sleeve, particularly with poor sleeve adhesion, is increased from the conventional 6 μm to 8 μm. As a result, the sleeve adhesive force is dramatically improved to 0.15 compared to the conventional 0.2, and the scattering is 21 as in the conventional case, and the durability is improved from the sleeve adhesive force to 500 k sheets to 650 k sheets, about 1 It can be seen that it has improved up to 3 times.

Further, an example in which the surface roughness Rz is increased to 10 is shown in Example (1) -5. The adhesion of the upstream sleeve is reduced to 0.14, and the durability with a reflection density of 1.4 or more is improved to 675k. However, the height and thickness (referred to as coating properties) of the spikes that are magnetically formed between the toners on the developer carrying member are non-uniform, and image unevenness is aggravated. This is because the roughness Rz is high, the carrying amount mg / cm ² on the sleeve is very large, and the toner amount exceeds the magnetic regulation force.

  From the above, the roughness Rz of the upstream sleeve is preferably 6-8. In order to increase the Rz of the upstream sleeve, the surface roughness Rz was set to 10 μm by blasting with FGB # 400 on SUS305. When the blast count is reduced, the particle size of the blasting particle is increased, the irregularities on the surface of the upstream sleeve can be increased, and Rz can be increased.

  When the adhesion force of the downstream sleeve is lowered in the same manner as that of the upstream sleeve, for example, when Rz is increased, the sleeve adhesion is reduced similarly to the upstream. However, the toner amount increases, the charge amount decreases, and the image quality, particularly dot reproducibility, scattering, and the like deteriorate. In other words, the image quality, durability, and coatability can be satisfied in a well-balanced manner by controlling the adhesion of the downstream sleeve while maintaining a certain degree. Preferably, the 10-point average roughness of the upstream developer carrying member is 6.0 or more and 8.0 or less, and the 10-point average roughness of the downstream developer carrying member is 3.0 or more and 6.0 or less.

As described above, the amount of toner remaining on the toner carrier after the toner is sucked from the predetermined suction area S (cm ² ) of the toner carrier over a predetermined time T (sec) with a predetermined suction force W (W). My (mg), when Ts (sec) is the equilibration time until the toner amount is stabilized after suction, and (My × W / S) × (Ts / T) is the adhesion force Af of the toner to the toner carrier, The adhesion force Af of the toner to the developer carrier 3a is made smaller than the adhesion force Af of the toner to the developer carrier 3b. As a result, the image quality is stable and the durability of the density can be improved.

[Second Embodiment]
Next, a second embodiment of the developing device and the image forming apparatus according to the present invention will be described with reference to the drawings. About the part which overlaps with said 1st embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  In the first embodiment, this is dealt with by increasing the Rz of the upstream sleeve from the downstream and reducing the adhesive force, but it cannot be said that there is sufficient durability (concentration reduction).

  If there are large irregularities on the surface of the developer-carrying member, toner adheres, which is a phenomenon in which toner adheres particularly around the convex portion, that is, in the concave portion, becomes a nucleus, and new toner adheres and grows. As a result, first, the amount of toner in the development area decreases, so that the image density decreases. Conventionally, in order to perform good development, a developing bias on which a DC voltage and / or an AC voltage is superimposed is applied to the developer carrier during development. However, when toner fusing occurs on the surface of the developer carrier, a high resistance layer is formed on the surface of the developer carrier, and a desired electric field is generated in the development region between the developer carrier and the image carrier during development. Does not form. As a result, a sufficient developing effect due to the developing bias cannot be obtained, the image density is lowered, and an image defect such as white spots occurs. The toner fusion described above is different from the adhesion of high Q / M toner such as fine powder. It is necessary not to provide more protrusions than necessary.

  Therefore, in the present embodiment, attention is paid to K (shape factor) as a countermeasure. First, the developer carrier surface roughness is shown in FIG. 16 (a), FIG. 17 and FIG. 18 with names and symbols, and FIG. 16 (b) shows the three-dimensional shape (see JISb0601-1982, 1994, ISO468-1982 Surfacousness). . Sm represents the average distance between the peaks, and Δa represents Tan of the slope angle θa of the peaks. Rmax indicates the height of the high point and the low point.

  In the present embodiment, in addition to the above roughness, a method for preventing developer carrier adhesion by paying attention to a shape factor K (K = Rv / Rmax) composed of a valley height Rp, a valley depth Rv, and a mountain valley height Rmax. Has proposed.

  Rp means the height from the average line of roughness to the top of the mountain, and Rv is the height from the average line of roughness to the bottom of the valley with respect to the average value that bisects the surface roughness area of the developer carrier. Say it. That is, Rp + Rv = Rmax.

  As described above, the developer carrying member adheres mainly in the concave and convex portions of the developer carrying member. Fine particles adhere to the recesses to form nuclei, and other substances adhere to and grow around them, causing developer carrier contamination. That is, if the concave portion is eliminated, it does not adhere. Since the concave portion is located in the valley portion of the roughness, the developer carrier contamination can be solved by flattening it ideally to minimize the roughness of the valley.

  The K value can be controlled by changing the blast condition. For example, the K value can be reduced by increasing the pressure, increasing the blast time, and increasing the distance between the developer carrying member and the blast tip.

  FIG. 13 shows an ideal roughness shape. In FIG. 13A, the roughness of the valley is flattened, and the entire roughness is maintained at a constant level, thereby reducing the developer carrier adhesion while maintaining the toner amount. In FIG. 13B, the valley has a certain roughness, and the overall roughness is the same. An example of each three-dimensional shape is shown in FIGS. 13 (c) and 13 (d).

  FIG. 14 shows the calculation result of the shape factor K. The shape factor K is determined by Rv and Rmax. When the number of concave portions is reduced, that is, when the height of the valley is reduced, this can be dealt with by reducing Rmax or reducing the shape factor. The basic conditions for shape creation in this experiment are sleeve material aluminum, FGB # 600, blast pressure 2 kgf, rotational speed 10 rpm, blasting time 10 sec, blasting distance 150 mm, and blasting diameter Φ10. In order to increase Rmax, the blast pressure can be increased, and in order to decrease RV, the FGB count can be increased, or the blast time can be increased. There are innumerable combinations, and it is desirable to optimize them according to the material of the sleeve and the physical properties of the toner.

19, the upstream sleeve adhesion to the shape factor, which is the data when changing the Q / M on the sleeve from 4μc / cm ² until 20μc / cm ^2. In this case, since the upstream adhesive force has a higher degree of contribution to the image density durability than the downstream, only upstream data is used.

  The experimental conditions are sleeve material aluminum, FGB # 600, blast pressure 2 kgf, rotation speed 10 rpm, blasting time 10 sec, blasting distance 150 mm, blast aperture Φ10, negative toner, image ratio 1%, moisture content 1 g, acceleration, 50k time point data. . The Q / M size can be dealt with by changing the external additive formulation of the toner.

  As shown in FIG. 19, it can be seen that when the shape factor exceeds 0.45, the sleeve adhesion increases. In other words, the shape of the base that does not adhere to the bumps needs to have a peak-to-valley ratio of 55:45. This is also related to the toner particle size and Q / M. In this embodiment, about 5 μm to 7 μm of toner and a negative external additive of 50 nm to 100 nm are employed. That is, if the diameter is further reduced, the shape factor needs to be lowered. As the particle size increases, the image quality, particularly the splattering and the reproducibility of characters, deteriorates. Generally, since toner of 7 μm or less is used, 0.45 or less is sufficient.

  Next, the lower limit shape factor will be described. The shape factor can be given a certain value on the desktop.

  FIG. 15 shows a diagram used for the calculation. When it does not adhere to the ground, that is, when the roughness of the ground is almost zero, the lower limit shape factor is obtained. First, when Rmax was measured with a toner particle size of 5 μm to 7 μm and a stable toner amount, it was 10.419 μm, and the base length Sm2 was approximately 60 μm. In this embodiment, since the shape of the abrasive grain to be blasted is substantially circular, the circumscribed circle angle θa is 60 degrees. From these conditions, assuming that the area higher than the average value is S1 and the area of the lower valley portion is S2, the value satisfying S1 = S2 is the lower limit shape factor.

Solving the following simultaneous equations,
S1 = (Sm1 + Sm2) × y / 2
S2 = (x / 3 ^0.5 ) × 2 × x / 2
X + y = Rmax
Sm1 = Sm2-y / 3 ^0.5
The area is about 48 μm ² and the shape factor is 0.1247.

  The experimental results of this embodiment are shown in FIG. The conditions of this experiment were: SB gap 200 μ, SS gap 400 μ, upstream / downstream developer carrier rotation speed 500 mm / sec, silica amount 2%, particle size 8 μm, fine powder amount 20%, environment 23 ° 70%, image duty 5%, The sleeve adhesion and image quality are measured by continuous paper feeding.

  As shown in FIG. 23, in Example (2) -1, compared with Example (1) -4, the shape factor of the upstream three was smaller than that of the downstream and decreased to 0.45. As a result, the upstream sleeve adhesion force can be reduced to 0.10, and the density durability with a reflection density of 1.4 or more is improved from 650 k sheets to 700 k sheets. Further, in Example (2) -2, when the shape factor is lowered to 0.25, the upstream sleeve adhesive force is lowered to 0.08, and the durable number of the reflection density of 1.4 or more is improved to 750k.

  In Example (2) -3 in which the particle size of the toner is reduced (8 μ to 5.5 μ), the adhesion force is increased although it is the same shape factor. This is because fine powder increased. Furthermore, in Example (2) -4, when the shape factor is lowered to 0.2, the micro coatability is deteriorated. Coatability is the uniformity of the height and thickness of the spikes that are magnetically formed between the toners. The coating property is mainly determined by the magnetic regulation force and the toner amount. Macro coatability is affected by the large toner amounts Rz and Rmax. On the other hand, the shape factor affects the micro coatability and the formation of spikes between peaks of Rz. The above-described shape factor is theoretically limited to about 0.12, but if it becomes too flat, micro-ears (50 μ intervals) cannot be formed, affecting high-resolution dot reproducibility and the like. . In this case, since the particle size of the toner is 5 to 7 μm, in the experiment, the shape factor of 0.20 or more and 0.45 or less was a region where the coating property is stabilized.

  In Example (2) -5, when both the upstream and downstream sleeves have a shape factor of 0.25, the downstream sleeve adhesion force is reduced to 0.05. However, the micro coatability deteriorated in the downstream sleeve. The cause is the same as the upstream sleeve. The reason why the downstream side is bad despite the same toner and the same shape factor is that the magnetic regulating force of the downstream sleeve is larger than that of the upstream side. Upstream is regulated by the magnetic flux density of the magnet and the magnetism of the regulating blade. On the other hand, since the downstream sleeve is regulated by the magnetic flux density of the downstream magnet and the upstream density, the magnetic binding force is larger than that of the upstream sleeve. Accordingly, the micro coatability cannot be satisfied unless the toner amount is a certain amount.

  Thus, by reducing the shape factor of the downstream developer carrier compared to the upstream developer carrier, the adhesion of the upstream developer carrier is lowered, the image quality is stabilized, and the durability stability is improved. I was able to improve. Preferably, the shape factor of the upstream developer carrier is 0.20 or more and 0.45 or less, and the shape factor of the downstream developer carrier is 0.3 or more and 0.55 or less.

  Note that the development conditions in this case are merely examples, and it is desirable to optimize them according to the specifications and conditions of the image forming apparatus.

[Third embodiment]
Next, a third embodiment of the developing device and the image forming apparatus according to the present invention will be described with reference to the drawings. About the part which overlaps with said 1st embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  In the second embodiment, the sleeve adhesion force is reduced and the density stability can be achieved. However, the image quality is almost the same as the conventional example. For example, the scattering is almost the same as 21 in the embodiment (2) -1 compared to the conventional 21. Therefore, in the present embodiment, a method for improving the image quality, particularly the scattering, while reducing the sleeve adhesion force is proposed.

  Spattering during development causes toner to fly according to the electric field formed between the latent image and the development, and inappropriate toner, for example, toner with a low negative charge amount, is latent at the edges of line latent images and dot latent images. It is a phenomenon of flying to a place where there is no image. In addition, when transferring the toner image on the surface of the photosensitive drum, the toner may be scattered from the latent image forming portion even when a charge is applied to the toner image. That is, by increasing the tribo which is the charge amount of the toner itself, it is possible to improve the scattering by increasing the attractive force with the drum.

  However, as described above, when the amount of silica as an external additive is increased or the particle size is reduced in order to increase the tribo, sleeve adhesion occurs, and the concentration decreases due to durability.

  Therefore, in this embodiment, the charge amount of the toner is controlled not by the toner but by the developer carrying member. As described above, the upstream developer carrying member mainly has high sleeve adhesion. Therefore, attention was paid to the downstream developer carrier.

  In the case of the embodiment (1) shown in FIG. 22, the sleeve developer adhesion force of the downstream developer carrier is approximately half that of the upstream developer carrier, slightly less than 0.1. In addition, the durability of concentration does not decrease even when the adhesion force of the downstream sleeve increases.

  Therefore, the charge amount was increased by lowering the roughness Rz of the downstream developer carrier, and the influence of the image quality was verified. The experimental results are shown in FIG. The conditions of this experiment are: SB gap 200 μ, SS gap 400 μ, upstream / downstream developer carrier rotation speed 500 mm / sec, upstream developer carrier / photosensitive drum distance 200 μm, downstream developer carrier / photosensitive drum Distance 300μm, development bias Vpp1.5kv, f2.7kHz, silica amount 2%, particle size 8μm, fine powder amount 20%, environment 23 degrees 70%, image duty 5%, sleeve adhesive force and image quality measured continuously. is doing.

As shown in FIG. 24, in Example (3) -1, the Rz of the downstream developer carrier (sleeve) is reduced from 6 μ to 5 μ compared to Example (2) -1. As a result, the sleeve adhesion has increased from 0.1 mg · W · cm ² to 0.15 mg · W · cm ² , but the splatter has improved from 21 to 19, and the durability stability has changed to 700k sheets. Not done. This occurs because the functions of the upstream and downstream developer carriers are different.

  In this embodiment (3), the upstream developer carrier mainly develops a solid latent image, and the downstream developer carrier is small dots (about 21 μ × 21 μ in the case of 3 dots, 5 dots, and 1 dot resolution of 1200 dpi), It achieves functional separation for developing line latent images. As a result, even if the downstream developer carrier is somewhat attached to the sleeve, it does not affect the durability stability such as the concentration. On the other hand, scattering and dot reproducibility are improved by increasing the charge amount of the downstream developer carrier. Specifically, the charge amount (μc / mg) of the toner carried on the developer carrier 3a is made smaller than the charge amount (μc / mg) of the toner carried on the developer carrier 3b. Thereby, scattering and dot reproducibility are improved.

  In Example (3) -1, Rz was changed from 6 μ to 5 μ as compared with Example (2) -1. As a result, the applied amount of toner is reduced, and the charge amount is increased from 9 μc / mg to 12 μc / mg. As a result, the scattering is improved from the conventional 21 to 19, and the durability with a reflection density of 1.4 or more has almost the same life as 700k sheets.

  In Example (3) -3, the roughness Rz of the downstream sleeve is lowered to 3 μm. As a result, the amount of toner loaded is reduced, the charge amount is increased to 14, and the scattering is improved to 17. Concentration durability is also maintained at 700k. However, the coatability becomes non-uniform on the developer carrying member, and the image unevenness is worsened. This is because the roughness Rz is low and the toner amount is smaller than the magnetic regulation force. Thus, the roughness Rz of the downstream sleeve is preferably 4 μm to 6 μm.

The charge amount (Q: μc / mg) in Example (3) is a charge amount per unit mass held by the developer (M: mg), and the surface of the developer carrying member has a constant suction force (W: Watt), constant time (T seconds), and constant area (S: cm ² ) Q / M when sucked.

M = Mx + My (Formula 3)
Q = Mx / S (Formula 4)
The amount of developer (M) on the surface of the developer carrying member, the amount of developer sucked by suction (Mx: mg), the remaining amount of developer (My: mg), the suction force (W: Watt), the suction time (T: sec), suction area (S: cm ² ), suction charge (Q: μc)

  As described above, by optimizing the surface roughness (Rz and shape factor) of the developing sleeve, the sleeve can reduce the adhesive force and increase the charge amount, thereby improving image quality and durability stability.

  According to the present embodiment, by defining the roughness such as the shape factor and the maximum height, it is possible to suppress adhesion of a small-diameter substance in the gap between the peaks. The average crest spacing can stabilize the toner amount and sufficiently stabilize the coat even at high speed. It is possible to stably and uniformly coat a developer (toner) thin layer on the surface of the developer carrying member, and to cope with environmental fluctuations, durability fluctuations, and the like for a long time, and to reduce adhesion of the developer carrying member, in particular.

  The development conditions in this case are merely examples, and it is desirable to optimize them according to the specifications and conditions of the image forming apparatus.

  FIG. 20 is a diagram describing the effect when the parameters described above are changed.

1 is a configuration diagram of an image forming apparatus including a developing device according to a first embodiment. It is a figure which shows development bias. It is a figure which shows the sleeve adhesion amount and density | concentration transition of a prior art example. FIG. 6 is a relationship diagram between sleeve adhesion force and reflection density. FIG. 6 is a relationship diagram between a sleeve adhesion amount (transmission density) and an adhesion amount. It is a related figure of the amount of sleeve adhesion to suction time. FIG. 6 is a relationship diagram of adhesion force (transmission density) with respect to sleeve adhesion force. FIG. 5 is a relationship diagram of sleeve adhesion force with respect to charge amount. FIG. 6 is a relationship diagram of sleeve adhesion force with respect to image ratio. It is a related figure of the sleeve adhesive force with respect to SB gap. It is a related figure of the sleeve adhesive force with respect to SS gap. FIG. 6 is a relationship diagram of sleeve adhesion force with respect to rotation speed. It is a figure which shows the surface roughness of the developing agent carrier which concerns on 2nd embodiment. It is a figure which shows the relationship between the height of the valley which concerns on 2nd embodiment, and a shape factor. It is a figure which shows the surface roughness of the developing agent carrier which concerns on 2nd embodiment. It is a figure which shows the surface roughness of a developing agent carrier. It is a figure which shows the surface roughness of a developing agent carrier. It is a figure which shows the surface roughness of a developing agent carrier. It is a figure which shows the relationship between the shape factor and sleeve adhesive force in 2nd embodiment. It is a figure which shows the relationship between a parameter and an effect. Relationship between transmission density and adhesion It is a figure which shows the experimental result of Example (1). It is a figure which shows the experimental result of Example (2). It is a figure which shows the experimental result of Example (3).

Explanation of symbols

L ... Image exposure P ... Transfer material t ... Toner 1 ... Photosensitive drum (image carrier)
2 ... Primary charger 3 ... Developing device 3a ... Developer carrier (first toner carrier)
3b ... developer carrier (second toner carrier)
3c ... developing container 3d ... first stirring unit 3e ... second stirring unit 3f ... surface 3g ... surface 3h ... upstream magnet roll 3i ... downstream magnet roll 3j ... layer thickness regulating blade (regulating member)
4 ... Post charger 5 ... Transfer charger 6 ... Separation charger 7 ... Cleaning device 8 ... Fixing device

Claims (5)

First and second toner carriers, which are provided close to each other to develop an electrostatic image formed on the image carrier and magnetically carry and convey magnetic toner, and the first toner carrier A developing member that regulates the layer thickness of the toner carried on the second toner carrier by the first toner carrier; and a regulating member that regulates the layer thickness of the carried toner.
The amount of toner remaining on the toner carrier after the toner is sucked from the predetermined suction area S (cm ² ) of the toner carrier over a predetermined time T (sec) with a predetermined suction force W (W) is expressed as My (mg ) When the equilibrium time until the toner amount is stabilized after suction is Ts (sec), and the adhesion force Af of the toner to the toner carrier is (My × W / S) × (Ts / T),
The developing device according to claim 1, wherein an adhesion force Af of the toner to the first toner carrier is smaller than an adhesion force Af of the toner to the second toner carrier.
When the height of the peak is Rp, the height of the valley is Rv, and the height of the valley is Rmax with respect to the average value that bisects the surface roughness area of the toner carrier,
The shape factor K of the first toner carrier is 0.20 to 0.45, the shape factor K of the second toner carrier is 0.3 to 0.55, and the first toner carrier is 2. The developing device according to claim 1, wherein a shape factor K (K = Rv / Rmax) of the toner carrier is smaller than a shape factor K of the second toner carrier.
The charge amount (μc / mg) of the toner carried on the first toner carrier is smaller than the charge amount (μc / mg) of the toner carried on the second toner carrier. The developing device according to claim 1 or 2.
The surface roughness Rz of the first toner carrier is 6.0 or more and 8.0 or less, the surface roughness Rz of the second toner carrier is 3.0 or more and 6.0 or less, and the first toner carrier 4. The developing device according to claim 1, wherein the surface roughness Rz of the second toner carrier is smaller than the surface roughness Rz of the first toner carrier. 5.
  5. The apparatus according to claim 1, further comprising bias applying means for applying a developing bias in which a DC voltage and an AC voltage are superimposed on the first toner carrier and the second toner carrier. The developing device described.