JP2002055516A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a printer capable of restraining the occurrence of surface staining by decreasing low electrified toner and reversely electrified toner on a developing roller and realizing low potential development that the absolute value of the uniform electrification potential of a photoreceptor is restrained to be <=400 V at which abnormal discharge or the like hardly occurs. SOLUTION: The printer is equipped with a developing device 4 provided with the developing roller 402 carrying toner 10 on its surface and feeding it to a developing area A1 opposed to the photoreceptor 1, a magnetic brush roller 403 carrying and feeding developer 12 including the toner and magnetic particles 11 to a toner supply area A2 opposed to the rover 402 and supplying the toner in the developer 12 to the developing roller, and a power source 409 applying developing bias voltage to the developing roller. The printer is provided with a power source 410 applying toner supply bias voltage to the roller 403 so as to make the value of developing potential at which toner adhesive amount on the photoreceptor 1 starts to be saturated <=100 V in developing gamma characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile, and more particularly, to a toner carrier that carries toner on its surface and conveys the toner to a development area facing a latent image carrier. A toner supply member that carries a two-component developer containing toner and magnetic particles, conveys the toner to a toner supply area facing the toner carrier, and supplies the toner in the two-component developer to the toner carrier. The present invention relates to an image forming apparatus provided with a developing device having:

[0002]

2. Description of the Related Art Conventionally, as a developing device used in this type of image forming apparatus, a two-component developing device for developing an electrostatic latent image on a latent image carrier using a two-component developer containing toner and magnetic particles is used. A one-component developing device that develops an electrostatic latent image on a latent image carrier using toner as a one-component developer is known. Of these developing devices, the latter one-component developing device is:
There is an advantage that the configuration is simple and the size can be reduced. In addition, since magnetic particles are not used, a phenomenon in which the magnetic brush of the two-component developer hits the latent image carrier and is not faithful to the electrostatic latent image and a little uneven development occurs, a so-called magnetic brush mark Does not occur. Further, as compared with a two-component developing apparatus, the developer layer is thinner, and the phenomenon called the edge effect is less. Therefore, the one-component developing device is excellent in reproducibility of a high-definition image. Above all, those using a non-magnetic one-component developer are excellent in colorization and are suitable as a developing device for obtaining a high-definition color image.

However, in a normal one-component developing apparatus, the charging of the toner on the toner carrier is controlled by frictional charging by a contact member such as a blade or a toner supply roller which comes into contact with the toner carrier. There is a problem that it is difficult to respond to high speed control and high durability.
Further, there is a possibility that the toner on the toner carrier is stressed due to the pressurization of the contact member to cause toner filming, or that an external additive enters the toner, thereby deteriorating the image quality. Further, the friction between the toner carrier and the above-mentioned contact member may cause both of them to be worn and the development characteristics to change over time. In order to solve these problems, it is preferable that the toner charged to a predetermined polarity is supplied and carried on the toner carrying member without using the frictional charging by the contact member such as the conventional blade and the toner supplying roller.

A magnetic brush made of a two-component developer is formed on the surface of a developing device which can supply and carry toner charged to a predetermined polarity on a toner carrier without using frictional charging by the contact member. A developing device using a toner supply member and supplying only the toner from a magnetic brush on the toner supply member to the toner carrier has been proposed (for example, JP-A-56-40862, JP-A-59-5959).
172662). In these developing devices,
A two-component developer is carried on a toner supply member (magnetic roller, magnetic brush forming body) to form a magnetic brush. The toner in the magnetic brush is charged to a predetermined polarity by friction with the magnetic particles. Then, only the toner charged to a predetermined polarity from the magnetic brush on the toner supply member is moved and carried on the toner carrier (developing roller, toner layer holder).

[0005]

However, a developing device in which only toner is supplied onto a toner carrier from a magnetic brush formed on a toner supply member as described in Japanese Patent Application Laid-Open No. Sho 56-40862. In some cases, depending on the toner supply conditions when the toner is supplied from the toner supply member to the toner carrier, a predetermined developing ability may not be obtained or background stain may occur. In order to secure the predetermined developing ability, the uniform charging potential of the latent image carrier is set to 500 V or more in absolute value, and the potential difference between the potential of the latent image on the latent image carrier and the developing bias voltage is set. It is conceivable to increase a certain development potential. However, when the uniform charging potential of the latent image carrier is set to a higher value, abnormal discharge or leakage occurs between the latent image carrier and other members, and the image quality is remarkably deteriorated, for example, the image is disturbed. There was a fear. Further, the potential difference between the potential of the background portion on the latent image carrier and the developing bias voltage is inevitably increased, so that a so-called reverse bias background stain is easily generated. Therefore, it is preferable to perform low-potential development in which the uniform charging potential of the latent image carrier is suppressed to 400 V or less, at which discharge or leakage hardly occurs.

SUMMARY OF THE INVENTION The present invention has been made in view of the above background, and an object of the present invention is to reduce the amount of low-charged toner and oppositely-charged toner on a toner carrier, thereby suppressing the occurrence of background contamination. Another object of the present invention is to provide an image forming apparatus capable of low-potential development in which the absolute value of the uniform charging potential of the latent image carrier is suppressed to 400 V or less where abnormal discharge or the like is unlikely to occur.

[0007]

According to a first aspect of the present invention, there is provided a latent image carrier, wherein a surface of the latent image carrier is uniformly charged, and the surface of the latent image carrier is uniformly charged based on image information. Latent image forming means for forming a latent image by irradiating the surface with light, a developing device for developing the latent image on the latent image carrier into a toner image, and a toner on the latent image carrier A transfer device for transferring an image to a transfer material, wherein the developing device includes a toner carrier that carries toner on a surface thereof and conveys the toner to a development area opposed to the latent image carrier; and a toner and magnetic particles. A toner supply member that carries the component developer and conveys the toner in the two-component developer to the toner supply region facing the toner carrier, and a developing bias voltage applied to the toner carrier. An image forming apparatus having a developing bias power supply for applying A toner supply bias power supply for applying a toner supply bias voltage to the supply member, wherein a developing potential value at which the amount of toner adhering to the latent image carrier at which the latent image carrier starts to saturate in developing gamma characteristics is 100 V or less. It is a feature. Here, the conditions for defining the value of the predetermined development potential include the absolute value of the average charge amount of the toner on the toner carrier, the amount of the colorant added to the toner, and the shape of the toner.

According to the first aspect of the present invention, the toner is sufficiently charged by frictional charging between the toner and the magnetic particles on the toner supply member. Then, the toner having a predetermined charge amount out of the toner in the two-component developer on the toner supply member is formed by the toner supply electric field formed between the toner supply member to which the toner supply bias voltage is applied and the toner carrier. It is selectively moved to the toner carrier side. Due to the movement of the toner by the toner supply electric field, the toner having a small variation in the charge amount can be carried on the toner carrier, and the amount of the low-charge toner and the reverse-charge toner can be reduced. Further, by setting the developing potential at which the toner adhesion amount on the latent image carrier begins to be saturated in the developing gamma characteristic to 100 V or less, the absolute value of the uniform charging potential of the latent image carrier causes abnormal discharge or leakage. 400 V or less, which is difficult to perform.

According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the surface moving direction of the latent image carrier and the surface moving direction of the toner carrier in the developing area are the same. A surface moving speed ratio of the toner carrier to the image carrier is 1.2 to 3.5, and a toner supply potential, which is a potential difference between the toner carrier and the toner supply member, is 50 to 200 V; The toner concentration on the toner supply member is 5 to 10 wt%, and the absolute value of the average toner charge amount on the toner supply member is 10 to 30 μm.
C / g] and the absolute value of the average toner charge amount on the toner carrier under the condition that the toner adhesion amount on the toner carrier is 0.3 to 1.0 [mg / cm ² ]. 10-16
[ΜC / g].

In the image forming apparatus, the absolute value of the average charge amount of the toner on the toner carrier is set to 16 [μC / g] or less under the above-mentioned predetermined condition, so that the slope in the development gamma curve is reduced. The developing potential is set to 100 V or less, at which the toner adhesion amount starts to be saturated. Further, the absolute value of the average charge amount of the toner on the toner carrier is set to 10 [μC
/ G] or more, it is possible to suppress a remarkable decrease in the developing ability and to prevent background contamination due to insufficient charging of the toner.

According to a third aspect of the present invention, in the image forming apparatus of the first aspect, the surface moving direction of the latent image carrier and the surface moving direction of the toner carrier in the developing area are the same. A surface moving speed ratio of the toner carrier to the image carrier is 1.2 to 3.5, and a toner supply potential, which is a potential difference between the toner carrier and the toner supply member, is 50 to 200 V; The toner concentration on the toner supply member is 5 to 10 wt%, and the absolute value of the average toner charge amount on the toner supply member is 10 to 30 μm.
C / g], the toner adhesion amount on the toner carrier is 0.3 to 1.0 [mg / cm ² ], and the absolute value of the average toner charge amount on the toner carrier is 10 to 20 [ΜC /
g], the amount of the colorant added to the toner is 5
[Wt%] or more.

According to the third aspect of the present invention, under the above conditions,
When the amount of the colorant added to the toner is 5 wt% or more, the absolute value of the average charge amount of the toner on the toner carrier is 20 μC / g, which is larger than 16 μC / g. Also, the inclination in the image density gamma curve can be increased, and the developing potential at which the image density starts to be saturated can be set to 100 V or less.

According to a fourth aspect of the present invention, in the image forming apparatus of the first aspect, the surface movement direction of the latent image carrier and the surface movement direction of the toner carrier in the developing area are the same. A surface moving speed ratio of the toner carrier to the image carrier is 1.2 to 3.5, and a toner supply potential, which is a potential difference between the toner carrier and the toner supply member, is 50 to 200 V; The toner concentration on the toner supply member is 5 to 10 wt%, and the absolute value of the average toner charge amount on the toner supply member is 10 to 30 μm.
C / g], the toner adhesion amount on the toner carrier is 0.3 to 1.0 [mg / cm ² ], and the absolute value of the average toner charge amount on the toner carrier is 10 to 20 [ΜC /
g], wherein the toner subjected to the spheroidization treatment is used.

According to the fourth aspect of the present invention, the non-electrostatic adhesive force between the toners is suppressed by using the spheroidized toner having a sphericity of 90% or more under the above-mentioned predetermined condition. As a result, the fluidity of the toner increases. As a result, the developing potential at which toner adhesion starts in the developing gamma curve is reduced, and the absolute value of the average toner charge amount on the toner carrier is 20 [μC / g], which is larger than 16 [μC / g].
g], the developing potential at which the toner adhesion amount on the developing gamma curve starts to saturate can be set to 100 V or less.

According to a fifth aspect of the present invention, in the image forming apparatus of the second, third or fourth aspect, a ratio of a surface moving speed of the toner carrier to the latent image carrier is set to 1.5 or less. Things.

In the developing device according to the fifth aspect, by setting the ratio of the surface moving speed of the toner carrier to the latent image carrier to 1.5 or less, a phenomenon called "toner shift" may occur at the rear end of the solid portion. Avoid it.

According to a sixth aspect of the present invention, there is provided a latent image carrier, and a latent image forming a latent image by uniformly charging the surface of the latent image carrier and irradiating the surface with light based on image information. Forming means, a developing device for developing the latent image on the latent image carrier to form a toner image, and a transfer device for transferring the toner image on the latent image carrier to a transfer material, wherein the developing device A toner carrier that carries toner on its surface and conveys it to a development area facing the latent image carrier, and a toner supply area that carries a two-component developer containing toner and magnetic particles and faces the toner carrier And a developing bias power supply for applying a developing bias voltage to the toner carrier, and a toner supply member for supplying the toner in the two-component developer to the toner carrier. Toner that applies toner supply bias voltage to the member Supplying bias power provided when the maximum static friction coefficient of the surface of the latent image bearing member and mu PC, and the maximum static friction coefficient of the surface of the toner carrying member and MyuDr,
μPC> μDr.

In the developing device of the present invention, the toner is sufficiently charged by frictional charging between the toner and the magnetic particles on the toner supply member. An electric field formed between the toner supply member to which the toner supply bias voltage is applied and the toner carrier selectively causes the toner having a predetermined charge amount among the toners in the two-component developer on the toner supply member. To the toner carrier side. Due to the movement of the toner by the toner supply electric field, the toner having a small variation in the charge amount can be carried on the toner carrier, and the amount of the low-charge toner and the reverse-charge toner can be reduced. Further, since the maximum static friction coefficient μPC of the surface of the latent image carrier is larger than the maximum static friction coefficient μDr of the surface of the toner carrier, the non-electrostatic adhesive force on the surface of the toner carrier decreases, The toner easily moves on the surface of the carrier. As a result, the developing capability of the toner carrier is increased, and the developing potential at which toner adhesion starts in the development gamma curve is reduced, so that the uniform charging potential (absolute value) of the latent image carrier is unlikely to be abnormally discharged or leaked. It can be 400 V or less.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to an electrophotographic laser printer (hereinafter, referred to as a "printer") as an image forming apparatus and a developing device used in the printer will be described. First, the overall schematic configuration of the printer according to the present embodiment will be described with reference to FIG. This printer irradiates a photosensitive member 1 around a drum-shaped photosensitive member 1 as a latent image carrier with a charging device 2 for uniformly charging the surface of the photosensitive member 1 and a laser beam modulated based on image information. Exposure device 3, developing device 4 for forming a toner image by attaching charged toner on developing roller 402 to the electrostatic latent image formed on photoconductor 1, photoconductor 1
A transfer device 5 for transferring the toner image formed on the transfer paper 20 as a transfer material, a cleaning device 6 for removing the toner remaining on the photoconductor 1 after the transfer, and the like are arranged in this order. A latent image forming means for forming an electrostatic latent image on the photoreceptor 1 includes the charging device 2 and the exposure device 3. Also, a paper feeder (not shown) that feeds and transports transfer paper from a paper feed tray (not shown) and a fixing device (not shown) that fixes the toner image transferred by the transfer device 5 to the transfer paper 20 are provided. I have.

A part of the plurality of devices constituting the printer may be configured as an integral structure (unit) so as to be detachable from the printer main body. For example, as shown in FIG. 3, the photosensitive member 1, the charging device 2, the developing device 4, and the cleaning device 6 can be detachably attached to the printer main body.
You may comprise as an image forming process unit which is an integral structure.

In the printer having the above configuration, the surface of the photosensitive member 1 rotating in the direction of arrow a is uniformly charged by the charging device 2, and then a laser beam modulated based on image information is scanned in the axial direction of the photosensitive member. Irradiated. As a result, an electrostatic latent image is formed on the photoconductor 1. The electrostatic latent image formed on the photoreceptor 1 is developed in the developing area A1 by attaching toner charged by the developing device 4 to become a toner image. On the other hand, the transfer paper 20 is fed and conveyed by a paper feeder (not shown), and is sent and conveyed by a registration roller 7 to a transfer unit where the photoconductor 1 and the transfer device 5 face each other at predetermined timing. Then, by the transfer device 5,
The toner image formed on the photoconductor 1 is transferred to the transfer paper 20 by applying a charge having a polarity opposite to that of the toner image on the photoconductor 1 to the transfer paper 20. Next, the transfer paper 20 is separated from the photoconductor 1 and sent to a fixing device (not shown), and the transfer paper 20 on which the toner image is fixed by the fixing device is output.
The surface of the photoconductor 1 after the transfer of the toner image by the transfer device 5 is cleaned by the cleaning device 6 and
The toner remaining on the top is removed.

Next, each member constituting this embodiment will be described in detail. The photoreceptor 1 has a photosensitive layer formed by applying an inorganic or organic photoreceptor having photosensitivity to a base tube made of aluminum or the like, and has a relatively small thickness such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN). ), It is also possible to use a belt photoreceptor having a photosensitive layer formed on nickel or the like. In the present embodiment, the photosensitive member 1 that is uniformly charged to a negative polarity is used. However, a photosensitive member that is uniformly charged to a positive polarity is used as necessary in consideration of the relationship with the charging polarity of the toner. Is also good. Further, the diameter of the photoconductor 1 of the present embodiment is 50 mm, and the linear velocity is 200 mm /
It is rotationally driven in seconds.

An electrostatic latent image is formed on the photosensitive member 1 as follows. In the printer of the present embodiment, the light writing conditions in the exposure device 3 are set so that the beam spot diameter is smaller and the writing energy is increased compared to the conventional optical writing system. here,
The optical writing condition will be described using a parameter called differential sensitivity S of the photoconductor 1. The differential sensitivity S is a relation between the surface potential V (E) of the photoconductor 1 and the exposure amount E obtained when the photoconductor 1 is uniformly exposed to a light beam having the same wavelength as the light beam irradiated by the exposure device 3. Is defined by Specifically, when the photosensitive member 1 is exposed at a certain exposure amount E, and the photosensitive member surface potential when the exposure amount E is increased by a small value ΔE from the exposure amount is set to V (E + ΔE), the differential sensitivity S is as follows. It is defined by the following equation.

[0024]

S = | V (E + ΔE) −V (E) | / ΔE

In general, the differential sensitivity S decreases as the exposure E increases. The “value that sufficiently reduces the differential sensitivity” means a value of the exposure amount that can use a region of the attenuation characteristic of the photoconductor 1 sufficient to obtain the required stability. In this case, the “determined stability” refers to a uniform dot in a binary process for expressing the gradation of the image by the density per unit area of the toner-attached pixel to which the toner is applied among the pixels constituting the image. That is, it is possible to form a plurality of dot images having a diameter and a predetermined development density, and it does not significantly change over time. However, the development density may be insufficient due to an increase in the post-exposure potential due to the deterioration with time of the photoconductor 1. Therefore, the value of the exposure amount for setting the post-exposure potential so as not to lower the image quality is “a value that sufficiently reduces the differential sensitivity”.
For example, the differential sensitivity S of the photosensitive layer is 1 / its maximum value.
3 or less. From the viewpoint of development conditions, in order to form a plurality of dot images having a uniform dot diameter and a predetermined development density in the above-described binary process, the electrostatic latent image on the photoconductor 1 may be subjected to saturation development. preferable.

FIG. 4 shows the structure of the photosensitive layer 1t of the photosensitive member 1 in this embodiment. The photosensitive layer 1t is composed of a charge generation layer 1a and a charge transport layer 1b, and has a total thickness TP of 13 μm. Then, the photosensitive layer 1t
Is set so as to satisfy the relationship of the following equation.

[0027]

## EQU2 ## 2TP <Db <8TP

Here, the exposure diameter Db of the light beam is
1 is (x, y), the surface coordinates of
Energy distribution of light beam P (x, y, t) [W /
m²] Is defined as the integral of exposure time
Exposure distribution E (x, y) [J / m ²1] from the peak value of
/ E²Is defined as the minimum diameter at

E (x, y) = （P (x, y, t) dt

FIG. 5 is an explanatory diagram of the exposure amount distribution on the photoreceptor 1. In the present embodiment, in order to form an electrostatic latent image for one pixel on the photoconductor 1, when the exposure is performed by about 20 μm in the sub-scanning direction, the exposure diameter of the light beam in the exposure amount distribution becomes as shown in FIG. Approx. 38μ in both main scanning direction and sub scanning direction
m. That is, approximately 38 μm in both the main and sub scanning directions.
2 shows a Gaussian distribution of m. Therefore, the exposure diameter Db of the light beam defined as the minimum value diameter at 1 / e ² from the peak value of the exposure amount distribution is 38 μm.

FIG. 6 is a graph showing experimental results obtained by measuring the attenuation characteristics of the surface potential of the photosensitive member 1 with respect to the exposure amount.
The symbol “◆” in FIG. 6 is the actual measurement data, and the symbols “■”,
“Δ” and a broken line connecting them are plotted to explain the differential sensitivity. The slope of each broken line is the differential sensitivity. The exposure apparatus 3 in this embodiment is adjusted so that the wavelength of the light beam is 670 nm and the exposure power is 0.23 mW on the surface of the photoconductor 1. Thus, the exposure amount at the peak value of the exposure amount distribution, that is, the maximum exposure amount within the exposure diameter Db is a value that sufficiently reduces the differential sensitivity of the photosensitive layer 1t.

The decay characteristic of the surface potential of the photosensitive member 1 shown in FIG.
Then, the maximum differential sensitivity is 28 [V · m ²/ MJ],
The exposure amount E corresponding to the differential sensitivity S of 1/3 or less is differentiated.
This is a value that sufficiently reduces the sensitivity. State for reference
In the attenuation characteristic of the photoreceptor 1 shown in FIG.
Exposure value E of the peak value (peak exposure amount) is 20 [mJ / m²]
And the differential sensitivity S corresponding to this is 5 [V · m²/ M
J]. Therefore, it is about 1/5 of the maximum differential sensitivity.
You.

In the present embodiment, the developing roller 4
02 has a volume resistivity of 10 ³ Ω · cm, which is lower than that of a conventional one-component developing apparatus. Therefore, when looking at the γ curve (development amount with respect to the development potential) in the development characteristics, the slope of the rising portion is large as shown by the curve C1 in FIG. A curve C2 in FIG. 7 is a γ curve in the conventional one-component developing device shown as a comparative example. The use of the developing roller 402 having a developing characteristic showing a steep rising as shown by a curve C1 in FIG.
It is relatively easy to develop the entire amount of toner on the developing roller 402 in a solid image while keeping the amount of toner carried on the developing roller 402 constant. However, in order to form small-diameter dots, if the differential sensitivity is not sufficiently reduced under the conventional photoconductor and various writing conditions, the development amount is likely to change. As a result, a change in the dot diameter is observed. In the present embodiment, the latent image forming condition is sufficiently set at the latent image dot diameter defined by 1 / e ² , and the differential sensitivity is reduced. And a dot image having a development density can be formed.

FIG. 1 is a schematic structural view of the developing device 4.
Inside the casing 401 of the developing device 4, a developing roller 402 as a toner carrier, a magnetic brush roller 403 as a toner supply member,
Transport members 404 and 405 are provided. The two-component developer (hereinafter, referred to as “developer”) 12 containing the toner 10 and the magnetic particles 11 in the casing 401 is stirred by the stirring / conveying members 404 and 405, and a part thereof is placed on the magnetic brush roller 403. It is carried on. Magnetic brush roller 403
After the thickness of the developer 12 is regulated by the regulating blade 406 as a developer regulating member, the developer 12 comes into contact with the developing roller 402 in the toner supply area A2. This toner supply area A2
To the toner 1 from the developer 12 on the magnetic brush roller 403
0 is separated and supplied to the developing roller 402.

In the developing device of this embodiment, since the rigid drum-shaped photosensitive member 1 based on an aluminum tube is used, the developing roller 402 is preferably made of a rubber material and has a hardness of 10 mm.
The range of up to 70 ° (JIS-A) is good. The diameter of the developing roller 402 is preferably 10 to 30 mm.
In the present embodiment, one having a diameter of 16 mm was used. Further, the surface of the developing roller 402 was appropriately roughened to have a roughness Rz (ten-point average roughness) of 1 to 4 μm. The range of the surface roughness Rz is 13 to 80% with respect to the volume average particle diameter of the toner 10, and is a range in which the toner 10 is conveyed without being buried in the surface of the developing roller 402. Here, the developing roller 4
Silicone that can be used as the rubber material of No. 02,
Butadiene, NBR, hydrin, EPDM and the like can be mentioned. Further, when a so-called belt photoconductor is used, the hardness of the developing roller 402 does not need to be reduced, and a metal roller or the like can be used. It is preferable that the surface of the developing roller 402 is appropriately coated with a coating material in order to stabilize the quality over time. Further, the function of the developing roller 402 in the present embodiment is only to carry the toner, and as in a conventional one-component developing device, a charge is applied to the toner 10 by frictional charging between the toner 10 and the developing roller 402. Is unnecessary, the developing roller 402 only needs to satisfy the electrical resistance, surface properties, hardness and dimensional accuracy, and the range of material selection can be greatly expanded.

The surface coating material of the developing roller 402 may have the opposite polarity to the toner 10 or may have the same polarity if it does not have a function of frictionally charging the toner to a desired polarity. Silicon,
Examples of the material include a resin such as acrylic and polyurethane, and a material containing rubber. In addition, as the latter surface coating material, a material containing fluorine can be exemplified. A so-called Teflon (registered trademark) -based material containing fluorine has a low surface energy and excellent releasability, so that toner filming over time is extremely unlikely to occur. In addition, as general resin materials that can be used for the surface coating material, polytetrafluoroethylene (PTFE),
Tetrafluoroethylene perfluoroalkyl vinyl ether (PFA), tetrafluoroethylene hexafluoropropylene polymer (FEP), polychlorotrifluoroethylene (PCTFE), tetrafluoroethylene ethylene copolymer (ETFE), chlorotrifluoroethylene -Ethylene copolymer (ECTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), etc. can be mentioned. In order to obtain conductivity, a conductive material such as carbon black is often included in the composition. More uniformly developing roller 402
In some cases, other resins may be mixed so that the resin can be coated. Regarding the electric resistance, the volume resistivity of the bulk including the coat layer is set, and the resistance of the base layer is adjusted so that it can be set to 10 ³ to 10 ⁸ Ω · cm. The volume resistivity of the base layer used in the present embodiment is 10 ³ to 10 ^5.
Ω · cm, the volume resistivity of the surface layer may be set slightly higher.

The volume resistivity of the surface of the developing roller 402 is measured by the method shown in FIGS. 8A and 8B. First, the developing roller 402 to be measured is set on a grounded conductive base plate 300, and F ends are respectively attached to both ends of a core metal (rotating shaft) 402a of the developing roller 402.
= 4.9 N (500 gf) load, and F =
Apply a load of 9.8 N (1 kgf). As a result, as shown in FIG.
To form A DC power supply 302 is connected to a core metal 402 a of the developing roller 402 via an ammeter 301. Then, a DC voltage V (= 1 V) is applied, and the current value I [A] at that time is read. The measured values of the applied voltage value V [V] and the current value I [A] and various dimensions L1 [cm], L2
Using the measured values of [cm] and W [cm], the volume resistivity ρv of the elastic layer 402b of the developing roller 402 is expressed by the following equation.
Ask for.

[0037]

Ρv = (V / I) · (L1 × W) / L2

The thickness of the coating layer of the developing roller 402 is preferably in the range of 5 to 50 .mu.m. When the hardness difference between the hardness of the coating layer exceeding 50 .mu.m and the hardness of the base layer is large, cracks are generated when stress is generated. Is more likely to occur.
On the other hand, if the thickness is less than 5 μm, if the surface wear proceeds, the base layer is exposed, and the toner tends to adhere.

The toner 10 constituting the developer 12 is as follows:
A charge control agent (CCA) and a colorant are mixed with a resin such as polyester, polyol, and styrene acryl, and fluidity is enhanced by adding external additives such as silica and titanium oxide around the resin. I have. The particle size of the additive is usually 0.1.
It is in the range of 1 to 1.5 μm. Examples of the coloring agent include carbon black, phthalocyanine blue, quinacridone, and carmine. In some cases, a toner in which the above-mentioned type of additive is externally added to a base toner in which wax or the like is dispersed and mixed can be used. The volume average particle diameter of the toner 10 is preferably in the range of 3 to 12 μm. The volume average particle diameter of the toner 7 used in the present embodiment is 7 μm, and it can sufficiently cope with a high-resolution image of 1200 dpi or more. Further, in the present embodiment, the toner 10 having a negative charging polarity is used, but a toner having a positive charging polarity may be used according to the charging polarity of the photoconductor 1 or the like.

The magnetic particles 11 have a core of metal or resin and contain a magnetic material such as ferrite, and the surface layer is coated with a silicon resin or the like. The diameter of the magnetic particles 11 is preferably in the range of 20 to 50 μm. The resistance of the magnetic particles 11 is 10 ⁴ to 10 as a dynamic resistance DR.
A range of ⁸ Ω is preferred. Here, the measurement of the dynamic resistance DR of the magnetic particles 11 was performed as follows using the measuring device shown in FIG. First, above the grounded pedestal 200, a fixed magnet is built in a predetermined position and has a diameter of 20 mm.
The rotatable sleeve 201 is set. The surface of the sleeve 201 has a width W = 65 mm and a length L = 0.
Opposing electrode (doctor) 20 having an opposing area of 5-1 mm
2 are opposed to each other with a gap g = 0.9 mm. Next, the sleeve 201 is rotated at a rotational speed of 600 rpm (linear speed of 628 [m
m / sec]). Then, a predetermined amount (14 g) of the magnetic particles to be measured is carried on the rotating sleeve 201, and the magnetic particles are stirred for 10 minutes by the rotation of the sleeve 201. Next, the sleeve 20
In a state where no voltage is applied to the current meter 1, a current Ioff [A] flowing between the sleeve 201 and the counter electrode 202 is measured by an ammeter 20.
Measure at 3. Next, the DC power supply 204
The applied voltage EV of the withstand voltage upper limit level (400 V for high-resistance silicon-coated carriers to several V for iron powder carriers) is set to 1.
Is applied for 5 minutes. In this embodiment, 200 V is applied. Then, a current Ion [A] flowing between the sleeve 201 and the counter electrode 202 with the voltage E applied is measured by the ammeter 203. From these measurement results, the dynamic resistance DR [Ω] is calculated using the following equation.

[0041]

## EQU5 ## DR = E / (Ion-Ioff)

The magnetic brush roller 403 comprises a non-magnetic rotatable sleeve 408 containing a magnet member 407 having a plurality of magnetic poles. The magnet member 407 is fixedly arranged so that a magnetic force acts when the developer 12 passes a predetermined location on the sleeve 408.
The sleeve 408 used in this embodiment has a diameter of φ18 m.
m, and the surface roughness Rz (ten-point average roughness) is 10 to 20.
It is sandblasted so as to fall within the range of μm.

The magnet member 407 built in the magnetic brush roller 403 has N pole (N1), S
Pole (S1), N pole (N2), S pole (S2), S pole (S
3) The five magnetic poles are provided. The arrangement of the magnetic poles of the magnet member 407 is not limited to the configuration shown in FIG. 1, but may be set to another arrangement according to the arrangement of the regulating blade 406 around the magnetic brush roller 403. In the example of the developing device shown in FIG. 1, the magnet member 407 is fixedly arranged and the sleeve 408 is driven to rotate.
8 may be fixedly arranged so that the roller-shaped magnet member inside thereof is rotated.

The developer 13 composed of the toner 10 and the magnetic particles 11 is carried on the sleeve 408 in a brush shape by the magnetic force of the magnet member 407. Then, the toner 10 in the magnetic brush on the magnetic brush roller 403 obtains a prescribed charge amount by being mixed with the magnetic particles 11. The charge amount of the toner on the magnetic brush roller 403 is −1
The range of 0 to -30 [μC / g] is preferable.

The developing roller 402 is opposed to the magnetic brush on the magnetic brush roller 4 in the toner supply area A2 adjacent to the magnetic pole N2 in the magnetic brush roller 403, and the photosensitive member 1 is in the developing area A1. It is arranged so that it may face. In the present embodiment, the distance between the regulating blade 406 and the magnetic brush roller 403 at the closest portion is set to 500 μm, and the magnetic pole N1 of the magnet member 407 facing the regulating blade 406 is positioned at the position facing the regulating blade 406. Than magnetic brush roller 4
03 is inclined several degrees to the upstream side in the rotation direction. Thereby, the circulation flow of the developer 12 in the casing 401 can be easily formed.

The regulating blade 406 contacts the magnetic brush so as to regulate the amount of the developer 12 formed on the magnetic brush roller 4 at a portion facing the magnetic brush roller 403, and a predetermined amount of the developer is The toner is transported to the supply area, and frictional charging between the toner 10 in the developer 12 and the magnetic particles 11 is promoted.

Further, the developing roller 402 and the magnetic brush roller 403 are respectively driven to rotate in the directions indicated by arrows b and c in FIG. 1 by a rotary driving device (not shown), and the surfaces of both rollers are opposite to each other in the toner supply area A2. It is designed to move. In the present embodiment, the developing roller 402 is driven at a linear velocity of 2 [mm / s] of the photosensitive
It is driven to rotate at a speed of 40 to 700 [mm / s] (a linear velocity ratio with respect to the photosensitive member is 1.2 to 3.5). The gap between the developing roller 402 and the sleeve of the magnetic brush roller 403 in the toner supply area A2 was set to 0.5 mm.

A power supply 409 for applying a developing bias voltage Vb for forming a developing electric field in the developing area A1 is connected to the shaft of the developing roller 402. A power supply 410 for applying a toner supply bias voltage Vsup for forming a toner supply electric field in the toner supply area A2 is connected to the sleeve 408 of the magnetic brush roller 403.

In the developing device 4 having the above-described structure, the developer 12 accommodated in the casing 401 is a mixture of the toner 10 and the magnetic particles 11,
04, 405 and the sleeve 40 of the magnetic brush roller 403
8 and the magnetic force of the magnet member 407 stirs,
At this time, a charge is applied to the toner 10 by frictional charging with the magnetic particles 11.

On the other hand, the developer 12 carried on the magnetic brush roller 403 is regulated by the regulating blade 406, and a certain amount of the developer 12 is transferred to the developing roller 402 by an electric field or the like formed by the toner supply bias. The rest is returned into the casing 401.

In the toner supply area A2, the toner in the magnetic brush is separated and transferred to the developing roller 402, and the thin layer toner 10 is carried. And the developing roller 4
02 on the roller 4
By the rotation of No. 02, it is transported to the development area A1. And
The developing electric field formed by the developing bias selectively adheres to the electrostatic latent image on the photoconductor 1, and the electrostatic latent image is developed.

Next, a description will be given of a plurality of experimental results obtained by measuring the relationship between the image quality and the particle size and charge amount distribution of the toner on the developing roller 402 in the developing device of this embodiment. E-SPART is used for measuring the particle size and charge amount distribution of the toner.
ANALYZER (analyzer manufactured by Hosokawa Micron Corporation, hereinafter referred to as “E-SPART analyzer”) was used. This E-SPART analyzer employs a method using a dual beam frequency shift type laser Doppler velocimeter and an elastic wave that perturbs the movement of particles in an electrostatic field, and applies air to the toner on the developing roller 402. The data on the particle size and the charge amount of each toner can be obtained by spraying and blowing and capturing the movement in the electric field. In this confirmation experiment, 3000 toners were sampled and the difference in distribution was observed.

Here, if the charge in each toner is uniformly present throughout the toner, the toner charge amount is proportional to the cube of the toner particle size, but is actually proportional to the toner particle size itself. As described above, since the toner charge amount and the toner particle size are in a proportional relationship, in this confirmation experiment, the value obtained by dividing the toner charge amount q by the particle size d, that is, the influence of the toner particle size was eliminated (q / For the value of d), the number distribution of the toner was measured.

FIG. 10 shows a measurement result of the toner charge amount distribution on the developing roller 402 measured by the E-SPART analyzer. The symbol “◆” in FIG. 10 indicates measurement data in the developing device of the present embodiment. The symbol "□"
9 is measurement data measured as a comparative example in a conventional one-component developing device not using a magnetic brush roller as a toner supply member. As can be seen from FIG. 10, the toner 10 carried on the developing roller 402 of the developing device of the present embodiment is
Is sharper than when a conventional one-component developing apparatus is used.

The index relating to the sharpness of the charge amount distribution profile is generally represented by a half width, and it is considered that the smaller the value, the sharper the image. Generally, when the charge amount distribution profile of the toner is sharp, many toners having the same charge amount q / d exist, and uniform development can be achieved because the toners have the same developing ability. Conversely, when the charge amount distribution profile of the toner is broad, the range of the charge amount of the toner is widened and the range of the developing capability is also widened, so that the development amount is fluctuated.

Looking at the experimental results in FIG. 10 in detail, the distribution range of the toner charge amount q / d in the conventional one-component developing device is different from that in the developing device of the present embodiment in that both curves intersect. In the range of q / d outside of P1 and P2,
The number is large. 10, that is, q /
In the range where the absolute value of d is large, the amount of charge is large and the force for developing is large, but the development electric field attenuates due to the progress of development, so that much of the amount carried on the developing roller cannot be developed. As a result, a part remains on the developing roller. On the right side of FIG. 10, that is, in a range where the absolute value of q / d is small, the amount of development may increase because the shape depends on the charge amount of the photoconductor. Also, the presence of low-charge or reverse-charge toner tends to cause background contamination on the background.

Further, as in the developing device of this embodiment, the number ratio of the portion where the toner charge amount q / d is widened is 50% or less in frequency (number) of both adjacent channels with respect to the number of peak value channels. Is optimal. As described above, in the developing device of the present embodiment, since the toner charge amount q / d distribution is sharp, development is performed uniformly, and a high-quality image can be formed. By the way, a channel having a peak of the toner charge amount q / d is adjacent to the channel having the peak (the interval is 1 [fC /
10μm]) and the ratio of frequency (number)
When the small channels are averaged), the ratio is 78% in the conventional one-component developing device and 35% in the developing device of the present embodiment.

Further, in the printer having the developing device having the above configuration, the charged potential of the photosensitive member 1 before the exposure is set to -30.
The development is performed at -250 V below 0 V, the potential after exposure is -80 V, and the developing bias voltage is -230 V. Normally, when the surface potential of the photoconductor 1 exceeds -400 V, discharge is performed according to Paschen's discharge law. When the toner flows from the surface of the photoconductor 1 to the developing roller 402, an abnormal image such as development is not performed is generated. Image quality degradation due to abnormal discharge from
Since it is not necessary to apply an excessive voltage to the charging device 2,
It is possible to avoid adverse effects due to abnormal discharge. When used in such a condition range, how to reduce the development potential required for predetermined development becomes an issue.

Therefore, in this embodiment, the developing roller 40
The average charge amount q / m of the toner carried on
[ΜC / g] or less. FIG. 11 shows experimental results obtained by measuring the development gamma characteristic, which is the relationship between the development potential and the toner adhesion amount, using the average toner charge amount q / m as a parameter. Symbols “◆”, “■”, and “▲” in the figure indicate data when the toner average charge amount q / m is 24, 19, and 16 [μC / g] in absolute value, respectively. In this experiment, the surface moving speed ratio (linear speed ratio) of the developing roller 402 to the photoconductor 1 was 1.2 to 3.5,
A toner supply potential Vsup, which is a potential difference between the developing roller 402 and the magnetic brush roller 403, is 50 to 20.
0 V, the toner concentration on the magnetic brush roller 403 is 5-1
0 [wt%], the average toner charge amount on the magnetic brush roller 403 is -10 to -30 [μC / g], and the toner adhesion amount on the developing roller 402 is 0.3 to 1.0 [mg / cm].
² ].

As shown in FIG. 11, the developing roller 402
The average toner charge in the upper thin toner layer is 1 in absolute value.
6 [μC / g] (q / m = 24, 19 [μ
C / g]), the developing potential at which the toner adhesion amount starts to be saturated becomes as high as 250 to 500 V, and low-potential development by the charging potential of the photoconductor of −300 V cannot be achieved. This is because the amount of charge per unit mass of the toner increases in opposition to the photoconductor 1 having a sufficient developing ability,
This is because a large amount of development potential is required to reach a saturated development amount in order to reduce the amount of toner to be developed. On the other hand, when the average toner charge amount of the thin toner layer on the developing roller 402 is 16 [μC / g] in absolute value, the developing potential at which the toner adhesion amount starts to saturate is about 100 V and the sufficiently saturated developing amount is Have been obtained. When the absolute value | q / m | of the average toner charge amount is smaller than 10 [μC / g], the developing ability is significantly reduced and the background stain is significantly generated. Therefore, the average toner charge amount q / m in the thin toner layer on the developing roller 402
[ΜC / g] is preferably in the range of 10 <| q / m | ≦ 16.

As described above, according to the present embodiment, the profile of the toner charge amount q / d distribution on the developing roller 402 becomes sharper than when a magnetic brush roller as a conventional toner supply member is not provided. In addition, since low-charge toner and reverse-charge toner can be reduced, it is possible to reliably prevent background contamination.

Further, according to the present embodiment, the toner average charge amount q /
By specifying m, while preventing the occurrence of soiling,
Since the developing ability can be increased so that the developing potential at which the toner adhesion amount in the developing gamma curve starts to be saturated is 100 V or less, the absolute value of the charging potential of the photoconductor 1 is suppressed to 400 V or less where abnormal discharge or the like hardly occurs. Low-potential development.

Further, according to the present embodiment, only the charged toner can be supplied from the magnetic brush (two-component developer) on the magnetic brush roller 403 to the developing roller 402 and carried. Therefore, there is no need to frictionally charge the toner on the developing roller 402 with a contact member such as a thinning blade, and the temporal change in the developing characteristics due to toner filming on the developing roller 402 and abrasion of the developing roller and the contact member. Problems such as are eliminated. Further, the developing roller 4
Since a stable charge amount distribution can be obtained with little variation in the charge amount of the toner carried on the toner 02, stable saturation development can be achieved particularly when an image is formed by a binary process. Therefore, it is possible to stably form an image without roughness due to background smear or insufficient image density (missing dots).

In the above embodiment, the developing roller 40
2, the toner average charge amount q / m is specified.
It is supplied from the brush roller 403 to the developing roller 402 and
The amount of the colorant to be added to the toner may be specified. Figure
Reference numeral 12 denotes the amount of the colorant added to the toner as a parameter,
Image density, which is the relationship between development potential and image density ID
It is the experimental result which measured the degree gamma characteristic. Symbols in the figure
"◆" and "■" are the amount of toner colorant added
Shows data when the values are 3 [wt%] and 5 [wt%].
ing. In this experiment, the developing roller for the photosensitive member 1 was used.
402, the surface moving speed ratio (linear speed ratio) is 1.2 to 3.5;
The voltage between the developing roller 402 and the magnetic brush roller 403
The toner supply potential Vsup, which is a potential difference, is 50 to 20.
0 V, the toner concentration on the magnetic brush roller 403 is 5-1
0 [wt%], average toner on magnetic brush roller 403
The charge amount is −10 to −30 [μC / g], and the developing roller 40
2 is 0.3 to 1.0 [mg / c]
m ²And the average charge amount of the toner on the developing roller 402
Performed under conditions where the absolute value is 10 to 20 [μC / g]
I have.

As shown in FIG. 12, when the amount of the colorant added to the toner is 5 [wt%], the slope of the rising portion where the image density is increased becomes large, and becomes saturated with a smaller developing potential. I have. That is, when the addition amount of the colorant of the toner is 5 [wt%], the image density is saturated at a developing potential of about 200 V, whereas when the addition amount of the colorant of the toner is 5 [wt%], the development is performed. The potential reaches the saturation region at about 100V.

In the above embodiment, the shape of the toner particles supplied from the magnetic brush roller 403 to the developing roller 402 and carried may be defined. FIG. 8 is an experimental result obtained by measuring a development gamma characteristic, which is a relationship between a development potential and a toner adhesion amount, using the shape of the toner as a parameter. The symbols “◆” and “■” in the figure represent the case where the spherical toner A having the sphericity of 96% was used and the case where the irregular shaped toner B having the sphericity of 88% was used, respectively. Shows the data. Here, the “sphericity” is (perimeter of a circle having the same area as the projected area of the particle) /
(Perimeter of particle projection image) × 100 [%],
Also called "circularity." The projected image of the particles is measured using a microscope. This sphericity decreases as the toner becomes pulverized toner, with the true sphere as 100%. Examples of the method of the spheroidizing treatment include a polymerization method and a method of heating the pulverized toner to melt the surface and restore the surface.

The toner A contains silica 0.5
[Wt%] and titanium oxide 0.7 [wt%] were added, and the comparative toner B was added with silica 0.2 [wt%] and titanium oxide 0.3 [wt%]. One of the main functions of these additives is to reduce the cohesive force between the toners to prevent the toner from forming an agglomerated mass, and to make the toner as loose as possible to obtain uniform development and transfer characteristics. At this time, considering the ratio of the toner A that adheres to the periphery of the base toner in terms of the coverage, the toner A is almost spherical, so the irregular toner B
The surface area is smaller than that of. As a result, the coverage of the toner A with the additive is increased, the fluidity is improved, and the developing ability is improved.

In the experiment shown in FIG.
The contact pressure of the second photoconductor 1 with respect to the photoconductor 1 is 59 [N / m] (6 [g
f / mm]), the linear velocity ratio of the developing roller 3 to the photoconductor 1 was set to 1.2, and the amount of toner coloring agent added was set to 3 wt% or more. Other experimental conditions were set the same as in the case of FIG.

From the experimental results shown in FIG. 13, it can be seen that, when the spherical toner A is used as compared with the pulverized toner B, the development potential at the start of development at which toner adhesion starts is reduced in the negative direction. Although the difference in development potential from the development start point to the point where the toner adhesion amount starts to be saturated is the same, in the case of spherical toner A, the development start point decreases in the negative direction. Therefore, the charging potential of the photoconductor 1 is set to 4 in absolute value.
It can be reduced to 00V or less.

In the above embodiment, instead of defining the toner supply conditions, a magnitude relationship between the maximum friction coefficient of the photosensitive member surface and the friction coefficient of the developing roller surface may be defined. In an image forming apparatus using a conventional one-component developing device, in order to reduce background contamination, the maximum static friction coefficient μDr of the developing roller is compared with the maximum static friction coefficient μPC of the photoconductor.
Was set higher. That is, μPC <μDr. On the other hand, in the apparatus of the present embodiment including the magnetic brush roller 403 as a toner supply member,
In order to reduce the variation in the amount of toner charge on the developing roller 402 and to prevent background contamination,
C> μDr.

FIG. 14 shows ΔID indicating the development potential and the degree of background contamination between the case where μPC> μDr is satisfied using the developing device of this embodiment and the case where a conventional one-component developing device is used. It is an experimental result comparing the relationship with. Here, ΔID as an index indicating the degree of background contamination in FIG. 14 is measured as follows. First, the toner adhering to the background of the photoreceptor 1 is transferred to a transparent adhesive tape, and the light reflection characteristics of the adhesive tape are measured. Then, from the measured values of the incident light intensity Iin and the reflected light intensity Ir, the optical density ID (measurement target) is obtained by using the following equation (6). Similarly, the optical density ID (reference) for the adhesive tape of the reference sample is obtained.
ΔID is obtained by using the calculation formula shown by. Also, this ΔI
The target value of D is 0.02 or less.

[0072]

ID = log ₁₀ (Ir / Iin)

[Mathematical formula-see original document] [Delta] ID = ID (measurement target) -ID (reference)

The maximum static friction coefficient μ of the photosensitive member and the developing roller was measured by using the measuring system shown in FIG. First, paper (manufactured by Ricoh Co., Ltd., TYP
E6200, A4 size, T eyes) 297mm x 30m
m, and a thread 101 is attached to both ends to form a measurement piece 100. The characteristics of the measurement sheet 100 are as shown in Table 1 below.

[0074]

[Table 1]

Next, the support member 10 on the table 102
3 on the photoreceptor 1, for example.
00 so that the back surface is in contact with it, and a weight 1 of 0.98 N (= 100 g weight)
Then, the other thread 101 is connected to a digital force gauge (digital push-pull gauge) 105. Then, the measuring sheet 100 is pulled by the weight 104, and the value of the gauge 105 when the measuring sheet 100 starts to move is read. Assuming that the value at this time is F [N], the maximum static friction coefficient μ is obtained by the following equation.

Μ = {ln (F / 0.98)} / (π / 2)

The maximum static friction coefficient μ of the photoreceptor 1 in the untreated state where no lubricant or the like is applied to the surface by the above method.
The measured value of PC is 0.45 to 0.6, and tends to increase with time. On the other hand, when the maximum static friction coefficient μDr of the developing roller 402 is measured, the value is 0.15
０．４0.4.

When the maximum static friction coefficient .mu. Has a magnitude relationship, the method of pressing the photosensitive member 1 and the developing roller 402 through the toner layer is preferably a method of abutting with a spring. It is. In particular, when contact is made with a plurality of springs, contact unevenness can be reduced. A coil spring, a leaf spring, or the like can be used as the contact spring. Also,
Assuming that the hardness of the developing roller 402 is 30 ° (JIS-A), the contact linear pressure of the developing roller 3 against the photosensitive member 1 is 9.8.
The range is preferably from 128 to 128 [N / m] (1 to 16 [gf / mm]).

From the results of the experiment shown in FIG. 14, when the conventional one-component developing device is used, toner adhesion particularly at a portion where the developing potential becomes negative (a portion corresponding to the background portion of the photosensitive member in the reversal developing method). You can see that the amount is large. This is due to the large proportion of the low-charged toner or the oppositely-charged toner. On the other hand, when the developing device of the present embodiment is used, as shown in FIG. 10 described above, the distribution of the number of charges is sharper than that of the conventional device. The toner adhesion amount at the potential becomes extremely small, and the occurrence of background contamination can be more reliably prevented.

As described above, the occurrence of background contamination can be reliably prevented. Therefore, even if the maximum static friction coefficient of the photosensitive member 1 and the developing roller 402 is set so as to satisfy the relation of μPC> μDr, the background contamination can be prevented. This does not occur, and the toner can easily move from the developing roller 402 to the surface of the photoreceptor to perform development. Photoconductor 1 and developing roller 402
Because the maximum static friction coefficient μDr of the developing roller 402 is relatively lower than the maximum static friction coefficient μPC of the photoconductor 1, the toner moves on the developing roller 402. And the development is facilitated by the developing electric field between the two.

In the above embodiment, the linear speed ratio of the developing roller 402 to the photosensitive member 1 is preferably set to 1.5 or less. Increasing the linear speed ratio improves the uniformity of the halftone portion of the image, but if it exceeds 1.5, the so-called "toner shift" occurs at the rear end of the solid portion, causing a significant decrease in the image. Bring.

In the above embodiment, the case where the toner image formed on the photoreceptor is directly transferred to the transfer paper has been described. However, in the present invention, the toner image on the photoreceptor is temporarily transferred to the intermediate transfer member. Thereafter, the present invention can be applied to an image forming apparatus for transferring a toner image on the intermediate transfer body to transfer paper and a developing apparatus used for the image forming apparatus. For example, a toner image for each color is sequentially formed on one photoconductor, and each color toner image on the photoconductor is superimposed and transferred on an intermediate transfer belt as an intermediate transfer body by a primary transfer device. The present invention can also be applied to a color image forming apparatus that collectively transfers the upper superposed toner image to transfer paper by a secondary transfer device and a developing device used in the device. Further, for example, a plurality of image forming units including photoconductors are arranged and arranged along a linear movement path portion of an intermediate transfer belt as an intermediate transfer body, and toner images of different colors are formed on the photoconductor of each image forming unit. To form
A tandem-type color image in which toner images on the respective photoconductors are superimposed and transferred on the intermediate transfer belt by a primary transfer device, and the superimposed toner images on the intermediate transfer belt are collectively transferred to transfer paper by a secondary transfer device. The present invention can also be applied to a forming device and a developing device used in the forming device.

In the above embodiment, the case of the printer and the developing device used therefor has been described. However, the present invention can be applied to other image forming devices such as a copying machine and a facsimile and the developing device used therefor.

[0083]

According to the first to sixth aspects of the present invention, low-charge toner and reverse-charge toner on the toner carrier can be reduced to suppress the occurrence of background fouling. This has the effect that low-potential development is possible in which the absolute value of the charge potential is suppressed to 400 V or less, at which abnormal discharge or the like is unlikely to occur.

In particular, according to the second aspect of the present invention, by defining the absolute value of the average toner charge amount on the toner carrier, the amount of toner adhesion on the development gamma curve can be saturated while preventing the occurrence of background contamination. Development potential is 10
The developing capacity is increased to be 0 V or less, and the absolute value of the charging potential of the latent image carrier is set to 400 V at which abnormal discharge is unlikely to occur.
There is an effect that the following can be suppressed.

In particular, according to the third aspect of the present invention, the absolute value of the average charge amount of the toner on the toner carrier is increased by setting the amount of the colorant added to the toner, which is advantageous in preventing background contamination. Even at 20 [μC / g], the developing potential at which the image density starts to be saturated is set to 100 V or less, and the absolute value of the charging potential of the latent image carrier is hardly abnormal discharge.
There is an effect that the voltage can be suppressed to 00 V or less.

In particular, according to the fourth aspect of the present invention, by using the toner subjected to the spheroidizing treatment, the absolute value of the average charge amount of the toner on the toner carrier is increased to 20 [advantageous in preventing background smear]. μC / g], the developing potential at which the toner adhesion amount starts to be saturated is set to 100 V or less, and the absolute value of the charging potential of the latent image carrier can be suppressed to 400 V or less at which abnormal discharge or the like is unlikely to occur. There is.

In particular, according to the invention of claim 5, there is an effect that "toner shift" at the rear end of the solid portion can be prevented.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a developing device used in a printer according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of the printer.

FIG. 3 is a partial perspective view of a process unit that can be used in the printer.

FIG. 4 is a sectional view of a photosensitive layer of the photosensitive member.

FIG. 5 is an explanatory diagram of an exposure amount distribution on a photoconductor.

FIG. 6 is a graph showing a relationship between an exposure amount and a surface potential of a photoconductor.

FIG. 7 is an explanatory diagram of a development gamma characteristic (a development amount with respect to a development potential).

FIGS. 8A and 8B are explanatory diagrams of a volume resistivity measuring system of a surface portion of a developing roller.

FIG. 9 is an explanatory diagram of a system for measuring dynamic resistance of magnetic particles of a developer.

FIG. 10 is a graph showing a measurement result of a toner charge amount distribution on a developing roller.

FIG. 11 is a graph showing a relationship between a development potential and a toner adhesion amount (development amount) with respect to a plurality of toner average charge amounts.

FIG. 12 is a graph showing a relationship between a development potential and an image density ID with respect to a colorant addition amount of a plurality of toners.

FIG. 13 is a graph showing a relationship between a development potential and a toner adhesion amount (development amount) for a plurality of types of toner particles.

FIG. 14 is a graph showing a relationship between a development potential and a background stain ΔID.

FIG. 15 is an explanatory diagram of a measurement system for a maximum static friction coefficient μ of a photoconductor surface.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photoconductor 2 charging device 3 exposure device 4 developing device 5 transfer device 6 cleaning device 10 toner 11 magnetic particles 12 two-component developer 20 transfer paper 50 image forming process unit 401 casing 402 developing roller (toner carrier) 403 magnetic brush roller (Toner supply member) 404, 405 Stirring / conveying member 406 Regulator blade 407 Magnet member 408 Sleeve 409 Power supply (for developing bias) 410 Power supply (for toner supplying bias) A1 Development area A2 Toner supply area

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court ゛ (Reference) G03G 15/08 507 G03G 15/08 507E (72) Inventor Takashi Hojima 1-3-3 Nakamagome, Ota-ku, Tokyo No. 6 F-term in Ricoh Co., Ltd. (reference) 2H005 AA21 AB09 EA01 EA07 EA10 FA01 2H068 AA01 2H073 AA03 BA13 BA23 BA25 CA03 2H077 AC04 AC12 AD06 AD35 AE04 BA03 DB08 EA03

Claims (6)

[Claims] A latent image bearing member; a latent image forming means for uniformly charging a surface of the latent image bearing member and irradiating the surface with light based on image information to form a latent image; A developing device that develops the latent image on the latent image carrier into a toner image, and a transfer device that transfers the toner image on the latent image carrier to a transfer material, wherein the developing device applies toner to the surface. A toner carrier that is carried and transported to a development area facing the latent image carrier; and a two-component developer containing toner and magnetic particles is carried and transported to a toner supply area facing the toner carrier. In an image forming apparatus having a toner supply member for supplying toner in a two-component developer to the toner carrier and a developing bias power supply for applying a developing bias voltage to the toner carrier, a toner supply bias is applied to the toner supply member. Toner supply bias voltage for applying voltage The provided image forming apparatus characterized by values of the developing potential and the amount of toner deposited on the latent image bearing member starts to saturate was configured to be less than 100V in the developing gamma characteristic. 2. The image forming apparatus according to claim 1, wherein a surface moving direction of the latent image carrier in the developing area is the same as a surface moving direction of the toner carrier. A surface moving speed ratio of the toner carrier is 1.2 to 3.5; a toner supply potential, which is a potential difference between the toner carrier and the toner supply member, is 50 to 200 V; Toner concentration of 5 to 10 [wt%]
The absolute value of the average toner charge amount on the toner supply member is 10
-30 [μC / g], and the toner adhesion amount on the toner carrier is 0.3-1.0 [m
g / cm ² ], the absolute value of the average toner charge amount on the toner carrier is 10 to
An image forming apparatus characterized by being set in a range of 16 [μC / g]. 3. The image forming apparatus according to claim 1, wherein a surface moving direction of the latent image carrier in the developing area is the same as a surface moving direction of the toner carrier. A surface moving speed ratio of the toner carrier is 1.2 to 3.5; a toner supply potential which is a potential difference between the toner carrier and the toner supply member is 50 to 200 V; Toner concentration of 5 to 10 [wt%]
The absolute value of the average toner charge amount on the toner supply member is 10
-30 [μC / g], and the toner adhesion amount on the toner carrier is 0.3-1.0 [m
g / cm ² ], and the absolute value of the average toner charge amount on the toner carrier is 10 to
An image forming apparatus, wherein the amount of the colorant added to the toner is 5 wt% or more under a condition of 20 μC / g. 4. The image forming apparatus according to claim 1, wherein a surface moving direction of the latent image carrier in the developing area is the same as a surface moving direction of the toner carrier. A surface moving speed ratio of the toner carrier is 1.2 to 3.5; a toner supply potential, which is a potential difference between the toner carrier and the toner supply member, is 50 to 200 V; Toner concentration of 5 to 10 [wt%]
The absolute value of the average toner charge amount on the toner supply member is 10
-30 [μC / g], and the toner adhesion amount on the toner carrier is 0.3-1.0 [m
g / cm ² ], and the absolute value of the average toner charge amount on the toner carrier is 10 to
An image forming apparatus characterized in that a spheroidized toner is used under a condition of 20 [μC / g]. 5. The image forming apparatus according to claim 2, wherein the ratio of the surface moving speed of the toner carrier to the latent image carrier is 1.5 or less. 6. A latent image carrier, and a latent image forming means for forming a latent image by uniformly charging the surface of the latent image carrier and irradiating the surface with light based on image information; A developing device that develops the latent image on the latent image carrier into a toner image, and a transfer device that transfers the toner image on the latent image carrier to a transfer material, wherein the developing device applies toner to the surface. A toner carrier that carries and conveys to a development area facing the latent image carrier, and carries a two-component developer containing toner and magnetic particles and conveys the toner to a toner supply area facing the toner carrier; In an image forming apparatus having a toner supply member for supplying toner in a two-component developer to the toner carrier and a developing bias power supply for applying a developing bias voltage to the toner carrier, a toner supply bias is applied to the toner supply member. Toner supply bias voltage for applying voltage The provided, and μPC the maximum static friction coefficient of the surface of the latent image bearing member,
An image forming apparatus, wherein μPC> μDr is satisfied, where μDr is the maximum static friction coefficient of the surface of the toner carrier.