JP2001272858A - Developing device, image forming apparatus and image forming processing unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing device, a printer and an image forming processing unit where a contact member for triboelectric toner on a developing roller need not be provided and by which a high-quality toner image having no density irregularity on a low-contrast image continuous to an image partially having a solid image can be formed. SOLUTION: This developing device is equipped with a developing roller 402 carrying the toner and a magnetic brush roller 403 carrying two-component developer 12, feeding it to a toner supply area A2 and supplying only the toner 10 from the developer 12 to the roller 402. Then, a toner supply condition by the roller 403 is set so that the toner of maximum carrying amount per unit area on the surface of the roller 402 is supplied to be carried on the surface of the roller 402 when the surface of the roller 402 where the toner is not carried passes through a toner supply area A2 once.

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, a facsimile, etc., and a developing device and an image forming process unit used in the apparatus. A two-component developer containing toner and magnetic particles, which is transported to a developing area opposed to the latent image carrier, and is transported to a toner supply area opposed to the toner carrier; The present invention relates to a developing device having a toner supply member for supplying only toner from a developer to a toner carrier, an image forming apparatus including the developing device, and an image forming process unit.

[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. There has been proposed a developing device that uses a toner supply member and supplies only the toner from a magnetic brush on the toner supply member to a toner carrier to carry the toner (for example, JP-A-56-40862, JP-A-59-198462). 172662). In these developing devices, a magnetic brush is formed by carrying a two-component developer on a toner supply member (magnetic roller, magnetic brush forming body). 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, as described in Japanese Patent Application Laid-Open No. Sho 56-40862 or the like, a developing method in which only toner is supplied onto a toner carrier from a magnetic brush formed on a toner supplying member. When a solid image and a low-contrast image are continuously developed using the apparatus, density unevenness sometimes occurs in the low-contrast image that should have a uniform density. Specifically, as shown in FIG. 16, the latent image on the surface of the latent image carrier to be developed by the developing device is formed by arranging the solid image 300a and the white image 300b in the width direction (the direction orthogonal to the surface moving direction). The above-described density unevenness occurs in the case where the preceding image portion 300 and the subsequent image portion 301 of low contrast formed over the entire width following the preceding image portion are formed. In FIG. 16, since the toner in the portion corresponding to the solid image on the toner carrier is used in a large amount by the development of the solid image 300a of the preceding image portion 300, the low-contrast subsequent image portion 30
1 of 3 which is developed following the solid image 300a
01a causes an image density shortage, and a density difference occurs with another portion 301b. As a result, density unevenness occurs in the low-contrast subsequent image portion 301 which should have a uniform image density. In the example of FIG. 16, the density unevenness on the low-contrast image when a solid image is formed in a part of the latent image carrier in the width direction is shown. This may occur if a part of the preceding image part has a solid image, regardless of the solid image forming position in the part.

The inventors of the present invention have examined the cause of density unevenness in the low-contrast image by experiments and the like. It was found that the lack of toner supply from the supply member and a partial shortage of the amount of toner carried was the cause of the density unevenness in the low contrast image.

The present invention has been made in view of the above background, and has as its object to eliminate the need to provide a contact member for frictionally charging toner on a toner carrier and to partially print a solid image. Developing device capable of forming a high-quality toner image without density unevenness in the low-contrast image even when developing a low-contrast image having a uniform image density following the image having the image forming apparatus. An apparatus and an image forming process unit are provided.

[0008]

According to a first aspect of the present invention, there is provided a toner carrying a toner on a surface movable endlessly and conveying the toner to a developing area facing a latent image carrier. Toner that carries a two-component developer containing a carrier and toner and magnetic particles and conveys the toner to a toner supply area facing the toner carrier, and supplies only the toner from the two-component developer to the toner carrier The toner carrying member has a maximum amount of toner per unit area on the surface of the toner carrying member when the surface of the toner carrying member that does not carry toner passes through the toner supply region once. The toner supply conditions of the toner supply member are set so that the toner is supplied to and carried on the surface of the toner carrier.

Here, the "maximum carrying amount" per unit area on the surface of the toner carrier is defined as a value obtained by rotating a toner carrier having no toner carried on the surface.
This is the maximum value when the toner carrying characteristic shows such that the amount of toner carried per unit area on the surface of the toner carrying member at the certain finite number of rotations has the maximum value. For example, as shown by a curve C1 in FIG. 17, when the toner carrier has a saturation characteristic such that the toner carrying amount per unit area of the surface of the toner carrier is saturated when the toner carrier rotates by a certain number of rotations. Is the saturated carrying amount (the amount indicated by “Asat” in the figure) is the above “maximum carrying amount”. Further, as shown by a curve C2 in FIG. 17, when the toner carrier rotates by a certain number of rotations, the amount of toner carried per unit area on the surface of the toner carrier reaches a peak, and in the subsequent rotation, the toner carrying amount is increased. If the properties show a slight decrease in volume,
The supported amount at the peak (the amount indicated by “Apeak” in the figure) is the “maximum supported amount”.

According to the first aspect of the invention, the two-component developer carried by the toner supply member is transported to the toner supply area facing the toner carrier. In this toner supply area,
Only the toner is supplied from the developer of the toner supply member to the toner carrier and carried. The supply of the toner is performed such that when the surface of the toner carrier that does not carry the toner passes through the toner supply area once, the maximum amount of toner per unit area on the surface of the toner carrier is transferred to the toner carrier. It is performed so that it is supplied and carried on the surface. Therefore, even if there is a portion of the surface of the toner carrier that consumes a large amount of toner in the development of a partial solid image, a sufficient amount of toner is supplied to the portion where the large amount of toner is consumed. It can be carried. Therefore, even when a low-contrast image having a uniform image density is developed subsequent to an image having a partial solid image, density unevenness does not occur in the low-contrast image.

According to a second aspect of the present invention, there is provided a toner carrier carrying toner on an endlessly movable surface and transporting the toner to a development area facing the latent image carrier, and carrying a two-component developer containing toner and magnetic particles. And a toner supply member that conveys the toner to the toner carrier from the two-component developer and conveys the toner of the toner carrier to the toner carrier. When the unsupported surface passes through the toner supply area once, the toner supply amount is adjusted so that the amount of toner carried per unit area on the surface of the toner carrier falls within a range of -30 to + 30% of a target amount. It is characterized in that toner supply conditions by members are set.

In the developing device according to the present invention, when the toner-carrying surface of the toner carrying member passes through the toner supply area once, the toner carrying amount per unit area on the toner carrying surface is equal to the target amount. The toner is supplied to the toner carrier so as to fall within a range of -30 to + 30%. By this toner supply, even if there is a portion of the surface of the toner carrier that consumes a large amount of toner in the development of a partial solid image, a sufficient amount of toner is supplied to the portion where the large amount of toner is consumed. It can be supplied and supported. Therefore, even when a low-contrast image is developed after the solid image, the afterimage ratio in the low-contrast image can be suppressed to 2% or less.

Here, the "afterimage ratio R" is obtained by forming a low-contrast image consisting of a 2-by-2 dot pattern immediately after a solid image and a white image, and determining the image density of a portion of the low-contrast image immediately after the solid image by ID. _A is defined by the following equation, where _A is the image density of the part immediately after the white image and ID _B is the image density.

[0014]

[Number 1] _{R = {(ID A -ID B} ) / (ID A + I
D _B )｝ × 100 [%]

According to a third aspect of the present invention, there is provided a toner carrier carrying toner on an endlessly movable surface and transporting the toner to a development area facing the latent image carrier, and carrying a two-component developer containing toner and magnetic particles. And a toner supply member that conveys the toner to the toner carrier from the two-component developer and conveys the toner of the toner carrier to the toner carrier. When the unsupported surface passes once through the toner supply area, the amount of toner carried per unit area on the surface of the toner carrier is set to 0.
The toner supply condition by the toner supply member is set so as to be 35 to 0.7 [mg / cm ² ].

According to the third aspect of the present invention, when the surface of the toner carrier that does not carry toner passes through the toner supply area once, the amount of toner carried per unit area on the surface of the toner carrier is 0.1. 35 to 0.7 [mg / c
m ² ] is supplied to the toner carrier. By this toner supply, even if there is a portion of the surface of the toner carrier that consumes a large amount of toner in the development of a partial solid image, a sufficient amount of toner is supplied to the portion where the large amount of toner is consumed. It can be supplied and supported.

According to a fourth aspect of the present invention, the latent image carrier is formed so as to express the gradation of the image by the density per unit area of the toner-adhered pixels for adhering toner among the pixels constituting the image. 4. The developing device according to claim 1, wherein the toner-adhered pixel of the latent image is developed, and a maximum amount of toner per unit area of the toner carrier is attracted to the latent image on the latent image carrier. The toner amount is smaller than the maximum amount of toner per unit area that can be adhered.

In the developing device, the maximum amount of toner per unit area of the toner carrier is larger than the maximum amount of toner per unit area that can be attracted and adhered to the latent image on the latent image carrier. Since it is small, it is possible to reliably perform saturated development on the latent image. In addition, the toner carrying amount on the toner carrying member does not become insufficient even after the solid image is developed as described above.

According to a fifth aspect of the present invention, the latent image carrier is formed so as to express the gradation of the image by the density per unit area of the toner-adhered pixels to which the toner is adhered among the pixels constituting the image. 4. The developing device according to claim 1, wherein the toner-adhered pixel of the latent image is developed when the toner-adhered pixel of the latent image formed on the latent image carrier passes through the developing area. The developing conditions are set such that all of the toner on the toner carrier opposite to the toner-attached pixel is used for developing the toner-attached pixel.

In the developing device according to the present invention, when the toner-adhered pixel of the latent image formed on the latent image carrier passes through the development area, the toner on the toner carrier opposes the toner-adhered pixel. By using all of the toner in the portion where the toner adheres to the development of the toner-attached pixel, it is possible to reliably perform the saturation development for the latent image. In addition, the toner carrying amount on the toner carrying member does not become insufficient even after the solid image is developed as described above.

According to a sixth aspect of the present invention, there is provided a developing device, comprising: a toner carrier carrying toner on an endlessly movable surface and transporting the toner to a developing area facing the latent image carrier; and a two-component developer containing toner and magnetic particles. And a toner supply member for carrying the toner to a toner supply area opposed to the toner carrier and supplying only the toner from the two-component developer to the toner carrier. The amount of toner carried per unit area on the surface when the surface not carrying the toner has passed once through the toner supply area is the maximum per unit area that can be attracted to and adhered to the latent image of the latent image carrier. The toner supply condition by the toner supply member is set so as to be larger than the toner adhesion amount.

In the developing device according to the present invention, when the surface of the toner carrier that does not carry toner passes through the toner supply area once, the amount of toner carried per unit area on the surface is determined by the amount of the latent image carrier. To be larger than the maximum amount of toner adhered per unit area that can be attracted and adhered to the latent image,
The toner is supplied to the toner carrier. Due to this toner supply, even if there is a portion of the surface of the toner carrier that consumes a large amount of toner in the development of a partial solid image, the maximum toner adhesion amount with respect to the latent image on the latent image carrier Of toner can be attached.

According to a seventh aspect of the present invention, there is provided a toner carrier which carries a toner on an endlessly movable surface and conveys the toner to a development area opposed to a latent image carrier, and carries a two-component developer containing toner and magnetic particles. A toner supply member that conveys the toner to the toner carrier by conveying the toner to the toner carrier, and supplies only the toner from the two-component developer to the toner carrier. A rotatable sleeve having a built-in member is used, and the surface movement direction of the toner carrier and the surface movement direction of the sleeve in the toner supply area are reversed, and the dynamic resistance of the magnetic particles of the two-component developer is 10 ⁸ Ω or less, and a potential difference between a developing bias applied to the toner carrier and a toner supply bias applied to the toner supply member is 70 V or more. Under the condition that the linear velocity ratio of the sleeve to the carrier is 2 times or more, the coverage of the magnetic particles by the toner on the magnetic brush composed of the two-component developer formed on the toner supply member is 36% or more. It is characterized by having been set.

Here, the "dynamic resistance" of the magnetic particles is measured using a measurement system shown in FIG. 9 described later. Further, the “coverage ratio” is defined as the toner concentration of the two-component developer (weight ratio of the toner to the magnetic particles) TC [w
t%], the toner particle radius r [μm], the magnetic particle radius R [μm], the true specific gravity ρr of the toner, and the true specific gravity ρc of the magnetic particles. However, it is assumed that the toner covering the magnetic particles is one layer.

[0025]

(Equation 2)

In the developing device of the present invention, the toner carrier and the toner supply member are set by setting the coverage of the magnetic particles with the toner to be 36% or more under the conditions such as the dynamic resistance of the magnetic particles. The probability of contact with the above toner is increased. Accordingly, the toner supply capability of the toner supply member is enhanced, and even if a large amount of toner on the toner carrier is consumed in developing a solid image, the amount of toner carried on the toner carrier can be quickly recovered. .

[0027] According to the present invention, a toner carrier carrying toner on an endlessly movable surface and transporting the toner to a developing area opposed to the latent image carrier, and a two-component developer containing toner and magnetic particles are carried. A toner supply member that conveys the toner to the toner carrier by conveying the toner to the toner carrier, and supplies only the toner from the two-component developer to the toner carrier. A rotatable sleeve having a built-in member is used, and the surface movement direction of the toner carrier and the surface movement direction of the sleeve in the toner supply area are reversed, and when the toner concentration of the two-component developer is 5 wt% or more, The dynamic resistance of the magnetic particles of the two-component developer is 10 ⁸ Ω or less, and the developing bias applied to the toner carrier and the toner supply applied to the toner supply member are controlled. The linear velocity ratio of the sleeve to the toner carrier is set to 2.5 times or more under the condition that the potential difference from the supply bias is 70 V or more.

In the developing device according to the present invention, the linear velocity ratio of the sleeve of the toner supply member to the toner carrier is set to 2.5 times or more under the conditions such as the toner concentration of the two-component developer. Thus, the probability of contact between the toner carrier and the toner on the toner supply member is increased.
Accordingly, the toner supply capability of the toner supply member is enhanced, and even if a large amount of toner on the toner carrier is consumed in developing a solid image, the amount of toner carried on the toner carrier can be quickly recovered. .

According to a ninth aspect of the present invention, there is provided a toner carrier which carries toner on an endlessly movable surface and conveys the toner to a developing area opposed to a latent image carrier, and carries a two-component developer containing toner and magnetic particles. A toner supply member that conveys the toner to the toner carrier by conveying the toner to the toner carrier, and supplies only the toner from the two-component developer to the toner carrier. A rotatable sleeve having a built-in member is used, and the surface movement direction of the toner carrier and the surface movement direction of the sleeve in the toner supply area are reversed, and when the toner concentration of the two-component developer is 5 wt% or more, A potential difference between a developing bias applied to the toner carrier and a toner supply bias applied to the toner supply member is 70 V or more; Those linear speed ratio of leave under conditions at least twice, characterized in that the dynamic resistance of the magnetic particles of the two-component developer carried on the toner supply member was set below 10 ³ Omega is there.

In the developing device according to the ninth aspect, the dynamic resistance of the magnetic particles in the two-component developer is set to 10 ³ Ω or less under the conditions such as the toner concentration of the two-component developer. The dielectric constant is increased, and the supply electric field for moving the toner toward the toner carrier in the toner supply region is increased. Accordingly, the toner supply capability of the toner supply member is increased, and even if a large amount of toner on the toner carrier is consumed in developing a solid image, the amount of toner carried on the toner carrier can be quickly recovered. .

[0031] The invention of claim 10 is the invention of claim 7, 8 or 9
The absolute value of the potential difference between the developing bias and the toner supply bias is set to 150 V or less.

According to a tenth aspect of the present invention, the absolute value of the potential difference between the developing bias and the toner supply bias is set to 1
The voltage is set to 50 V or less so that excessive toner is not carried on the toner carrier during the undeveloped state. In this way, by suppressing the excessive amount of toner carried on the toner carrier and keeping it at or below an appropriate amount, even if a large amount of toner is consumed in the development of the solid image, the amount of toner carried on the toner carrier can be reduced. You can recover quickly.

According to an eleventh aspect of the present invention, a latent image carrier, a latent image forming means for forming a latent image on the latent image carrier, and a latent image on the latent image carrier are developed into a toner image. An image forming apparatus comprising: a developing device; and a transfer unit configured to transfer the toner image on the latent image carrier to a transfer material, wherein the developing device is used as a developing device. It is characterized in that 6, 7, 8, 9 or 10 developing devices are used.

According to a twelfth aspect of the invention, a latent image carrier, a latent image forming means for forming a latent image on the latent image carrier, and a latent image on the latent image carrier are developed into a toner image. A developing device, an intermediate transfer member to which the toner image on the latent image carrier is transferred, a primary transfer device for transferring the toner image on the latent image carrier to the intermediate transfer member, And a secondary transfer device for transferring the toner image to a transfer material, wherein the developing device is used as a developing device.
It is characterized by using the developing device of 8, 9 or 10.

According to a thirteenth aspect of the present invention, there is provided a latent image carrier, a charging device for uniformly charging the surface of the latent image carrier, and a developing device for developing a latent image on the latent image carrier into a toner image. And an image forming process unit configured to be detachable from the image forming apparatus as an integrated structure, wherein the developing device is used as the developing device. 9 or 1
0 developing device is used.

In the image forming apparatus according to the present invention, the latent image on the latent image carrier can be developed by using the toner carried on the toner carrier in an appropriate amount. Therefore, even when a low-contrast image is developed immediately after an image partially including a solid image, a high-quality image having no density difference can be stably obtained.

[0037]

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 constituted as an integral structure (unit) so as to be detachable from the printer main body. For example, as shown in FIG. 2, the photoconductor 1, the charging device 2, the developing device 4, and the cleaning device 6 can be detachably attached to the printer main body.
The image forming process unit 50 may be configured as an integrated structure.

In the printer having the above structure, 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 a 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, the structure of the photosensitive member 1 and the formation of a latent image on the photosensitive member in the present 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.
It is also possible to use a belt photoreceptor having a photosensitive layer formed on T), polyethylene naphthalate (PEN), nickel or the like. In the present embodiment, the photoconductor 1 that is uniformly charged to a negative polarity is used, but a photoconductor that is uniformly charged to a positive polarity may be used as necessary. The diameter of the photoconductor 1 of the present embodiment is 50 mm, and the linear velocity is 200 mm / s.
The motor is driven to rotate at ec.

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 reduced and the writing energy is increased as compared with the conventional optical writing system.

Here, the above-described optical writing condition will be described using a parameter called differential sensitivity S of the photosensitive member 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.

[0043]

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. 3 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.

[0046]

## EQU4 ## 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 a value obtained by integrating the 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. 4 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. 5 is a graph showing experimental results obtained by measuring the decay characteristics of the surface potential of the photosensitive member 1 with respect to the exposure amount.
The symbol “◆” in FIG. 5 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.

Attenuation characteristics 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 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, 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. 6 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 rise 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.

Next, the configuration of the developing device 4 will be described in detail. As shown in FIG. 7, the casing 4 of the developing device 4
Inside the photoreceptor 01, a developing roller 402 as a toner carrier, a magnetic brush roller 403 as a toner supply member, and stirring / transport members 404 and 405 are arranged from the photoconductor 1 side. 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. After the thickness of the developer 12 on the magnetic brush roller 403 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. In the toner supply area A2, the magnetic brush roller 403
Only the toner 10 is separated from the upper developer 12 and supplied to the developing roller 402.

In the developing device of the present embodiment, since the photosensitive drum 1 is a rigid drum based on an aluminum tube, 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 where 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 selection range of the material is greatly increased.

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.
= 4.9N (= 500gf), and the total 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.

[0056]

Ρv = (V / I) · (L1 × W) / L2

Further, the thickness of the coating layer of the developing roller 402 is preferably in the range of 5 to 50 μm, and when a difference between the hardness of the coating layer exceeding 50 μm and the hardness of the base layer is large, cracks may occur 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 contain a magnetic material such as ferrite with a metal or resin as a core, 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 preferably 10 ³ Ω or less as a dynamic resistance DR. Here, the measurement of the dynamic resistance DR of the magnetic particles 11 was performed as follows using the measurement system shown in FIG. First, above the grounded pedestal 200,
A rotatable sleeve 201 having a diameter of 20 mm and containing a fixed magnet at a predetermined position is set. This sleeve 201
Has a width W = 65 mm and a length L = 0.5-1 m
An opposing electrode (doctor) 202 having an opposing area of m is opposed with a gap g = 0.9 mm. Next, sleeve 2
01 at a rotational speed of 600 rpm (linear speed 628 mm / se).
Rotation drive is started in c). 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, a current Ioff [A] flowing between the sleeve 201 and the counter electrode 202 is measured by an ammeter 203 without applying a voltage to the sleeve 201. Next, the DC power supply 204 applies an upper voltage limit level (400 V for a high-resistance silicon-coated carrier) to the sleeve 201.
Therefore, an applied voltage E [V] of several V for an iron powder carrier 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.

[0060]

## EQU7 ## 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. 7, but may be set to another arrangement according to the arrangement of the regulating blade 406 around the magnetic brush roller 403. For example, FIG.
As shown in the figure, N pole (N1), S in the rotation direction of the magnetic brush roller 403 from the location regulated by the regulation blade 406.
Four magnetic poles of a pole (S1), a north pole (N2), and a south pole (S2) may be arranged. In the example of the developing device shown in FIG. 7, the magnet member 407 is fixedly arranged and the sleeve 408 is driven to rotate. However, the sleeve 408 is fixedly arranged and the roller-shaped magnet member inside the sleeve 408 is rotated. You may.

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 -40 [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 comes in contact with 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. 8 by a rotation driving device (not shown). In the toner supply area A2, the surfaces of both rollers are opposite to each other. It is designed to move. In the present embodiment, the developing roller 402 is moved at a linear speed of 300 mm for a linear speed of 200 mm / s of the photoconductor 1.
It is rotationally driven at mm / s. Further, the toner supply area A
2, the gap between the developing roller 402 and the sleeve of the magnetic brush roller 403 was set to 0.6 mm.

A developing bias Vb for forming a developing electric field in the developing area A1 is provided on the shaft of the developing roller 402.
Is connected to the power supply 409 for applying the. A power supply 410 for applying a toner supply bias 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.

Next, the operation of the developing device 4 having the above configuration will be described. The developer 12 contained in the casing 401 is
The toner and the magnetic particles 11 are mixed, and the stirring and conveying members 404 and 405 and the magnetic brush roller 403 are mixed.
The toner is stirred by the rotational force of the sleeve 408 and the magnetic force of the magnet member 407.
Charge is applied by frictional charging with

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 plurality of experimental results obtained by measuring the relationship between the toner supply condition to the developing roller 402 in the developing device of the present embodiment and the density difference in a low-contrast image due to a residual image of a solid image will be described in more detail. This will be described as an example. In the evaluation of the afterimage of the solid image, an original image having an image 300 partially having a solid image 300a as shown in FIG. 11 and a low contrast image 301 behind the image 300 was used.

Embodiment 1 In this embodiment, a toner 10 having a volume average particle diameter of 7 μm is used, and a volume average particle diameter of 50 μm is used.
The magnetic particles 11 of silicon coating having a dynamic resistance DR of 10 ⁸ Ω were used. The toner concentration TC in the developer 12 was 5% by weight. Calculating the toner coverage at this time (see the above-described equation (2)) yields 36.7%
Met. In this calculation, the true specific gravity ρ _{T of the} toner was set to 1.15, and the true specific gravity ρ _C of the magnetic particles was set to 5.2. The linear velocity ratio αSu of the magnetic brush roller 403 to the developing roller 402 in the toner supply area A2 is 2, and the toner supply potential ΔVsup is 350V.
Met. The toner supply potential ΔVsup is calculated by the following equation using the developing bias Vb and the toner supply bias Vsup.

ΔVsup = Vb−Vsup

The image forming conditions are as follows: charging potential VD = −450
V, post-exposure potential VL = −60 V, developing bias Vb = −
310 V, and the developing potential (VL-Vb) is 2
It is set to 50V. Above toner supply potential Δ
Vsup is 1.6 times the developing potential.

When the latent image formation and development of the original image were performed under the above conditions, a stable thin toner layer with little change even when the image was not developed could be formed on the developing roller 402.
A uniform image without negative afterimage was obtained in the low contrast image immediately after the solid image.

Here, as a comparative example, when the toner supply potential ΔVsup was set to 400 V, the aforementioned FIG.
As shown in FIG. 6, a negative afterimage (ghost) in which the development density of the portion 301a located on the rear side of the solid image 300a is reduced occurs, and the other portion 30 of the low contrast image is formed.
1b. When the residual image ratio (refer to the above-described definition expression 1) calculated for the two portions 301a and 301b of the low-contrast image was larger than -2% on the minus side.

As can be seen from the above-described formula for defining the toner coverage Tn, the toner coverage Tn is different from the toner density TC.
To change. For example, when the toner concentration TC is 5 wt%,
For 5 wt% and 6 wt%, the toner coverage Tn is 3.67%, 40.6% and 44.5%, respectively. When the images were compared under these three conditions, 5 wt%
That is, when the coverage was 36% or more, it was confirmed that a uniform image without the negative afterimage was obtained. On the other hand, when the toner concentration TC was less than 5 wt%, the density of the low-contrast image immediately after toner consumption due to the development of the solid image was low.

The toner coverage Tn also changes depending on the particle size of the toner. Here, when the volume average particle diameter of the toner is 7 μm, 6 μm, and 5 μm, the lower limit toner concentration TCmin at which the coverage Tn of the magnetic particles by the toner becomes 40% is calculated as shown in FIG. In the case of the toner having a diameter of 7 μm according to the present embodiment, the above TCmin is 5.5 wt.
% For the toner having a diameter of 6 μm,
For a toner having a diameter of 5 μm, the lower limit is 3.8 wt%. By reducing the toner particle size in this manner, the coverage T
It is possible to lower the toner TC while maintaining n, and it is possible to suppress adverse effects such as toner scattering.
When the coverage of each toner falls below the above-mentioned 36%, a negative afterimage occurs due to a decrease in the developing ability immediately after the solid consumption, and the image quality is degraded.

[Embodiment 2] In this embodiment, the toner supply potential ΔVsup is set to 150 V or less, and the linear speed ratio of the sleeve of the magnetic brush roller 403 to the developing roller 402 is set to 2.5 or more. In the developing device of the present embodiment, the developing roller 402 is disposed in a non-contact manner on the sleeve of the magnetic brush roller 403, and there is no contact of the member with the developing roller 402. Then, between the developing roller 402 and the magnetic brush roller 403,
An electric field is formed by a potential difference (toner supply potential) due to a bias voltage applied to both rollers. If the toner supply potential ΔVsup is not set to 150 V or less, when the developing roller 402 is operated in an undeveloped state, the developing roller 40
2, the toner adhesion amount increases. In this case, the ability to supply the toner to the developing roller 3 after the solid consumption is inevitably reduced. To compensate for this, it is effective to increase the linear velocity ratio of the sleeve of the magnetic brush roller 403 to the developing roller 402. .

In this embodiment, a toner 10 having a volume average particle diameter of 7 μm is used, and silicon-coated magnetic particles 11 having a volume average particle diameter of 50 μm and a dynamic resistance DR of 10 ⁸ Ω.
Was used. The toner concentration TC in the developer 12 is 5 wt.
%Met. Then, under the same conditions, when the generation state of the negative afterimage when only the linear velocity ratio αSu was changed was compared with the residual image ratio, as shown in FIG. 13, the linear velocity ratio αSu was obtained.
When> 2.5, the afterimage ratio was within the range of ± 2%, which was a level without any problem.

[Embodiment 3] As described in the embodiment 2, when the condition for stabilizing the amount of adhesion of the magnetic brush roller 403 to the developing roller 3 at the time of non-development is set, the solid consumption is inevitable. The ability to supply toner to the developing roller 3 later decreases. In this embodiment, to compensate for the toner supply in that case, the dynamic resistance DR of the magnetic particles in the developer 12 on the magnetic brush roller 403 is 10Ω which is 10 ³ Ω or less. The method of measuring the dynamic resistance DR is as described above, but the applied voltage is set at a level of several volts. In the present embodiment, the toner 10 having a volume average particle diameter of 7 μm is used, and the magnetic particles 1 having a volume average particle diameter of 50 μm are used.
1 was used. The toner concentration TC in the developer 12 is 5 w
t%. The linear velocity ratio of the sleeve of the magnetic brush roller 403 to the developing roller 402 was set to 2.

FIG. 14 shows the magnetic particles 1 under the conditions of this example.
Developing roller 40 due to difference in dynamic resistance DR
2 shows the result of measuring the time change of the amount of toner attached to No. 2. As can be seen from this result, the dynamic resistance D
Compared with the case where magnetic particles having a resistance R of 10 ⁸ Ω were used, the magnetic particles having a dynamic resistance DR of 10 Ω as in the present embodiment had a faster rise of the toner adhesion amount, and the toner supply property was stable. ing.

[Embodiments 4 to 6] In this embodiment, the linear velocity ratio of the sleeve of the magnetic brush roller 403 to the developing roller 402, the toner supply potential ΔVsup, and the coverage Tn of the magnetic particles by the toner are different. so,
The relationship between the rotation speed of the developing roller 402 and the amount of adhered toner was measured. Table 1 shows the conditions in Examples 4 to 6 and Comparative Examples 1 and 2.

Table 2 and FIG. 15 show the results obtained by measuring the relationship between the number of rotations of the developing roller 402 and the amount of adhered toner under the above conditions. The target value of the toner adhesion amount in Table 2 is 0.
55 mg / cm ² . From these results, the following conditions can be given as conditions for preventing a density difference due to an afterimage from occurring in the low contrast image immediately after the solid image. (1) Magnetic brush roller 40 for developing roller 402
The linear velocity ratio of the sleeve No. 3 is set to × 2.5 or more. (2) Make the toner supply potential 70 V or more. (3) The coverage Tn of the magnetic particles with the toner is set to 36% or more.

Further, based on the above results, the developing roller 40
It can be seen that the toner supply condition may be set so that the toner adhesion amount (toner carrying amount) in the first rotation of No. 2 falls within the range of −30 to + 30% of the target amount. Further, the toner supply condition may be set such that the toner adhesion amount (toner carrying amount) at the first rotation of the developing roller 402 is 0.35 to 0.7 [mg / cm ² ]. Further, based on the toner adhesion amount (toner carrying amount) in the first rotation of the developing roller 402, the toner is adjusted so that the increasing ratio of the toner adhesion amount on the developing roller after the second rotation becomes + 70% or less. It is preferable to set supply conditions.

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.

Further, in the above-described 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.

[0087]

According to the first to thirteenth aspects of the present invention, it is not necessary to provide a contact member for frictionally charging the toner on the toner carrier. Also, there is no problem such as a change over time in the development characteristics due to wear of the contact member. In addition, even when developing a low-contrast image having a uniform image density subsequent to an image having a solid image partially, a high-quality toner image without density unevenness in the low-contrast image can be formed. is there.

In particular, according to the inventions of claims 4 and 5, 2
When a low-contrast image is formed subsequent to a solid image in the value process, it is possible to prevent density unevenness caused by the solid image and to adjust the diameter and image density of each toner-attached pixel (dot) constituting the low-contrast image. There is an effect that it can be made uniform.

In particular, according to the tenth aspect of the present invention, even when an undeveloped state continues, excessive toner carrying on the toner carrier is suppressed, and occurrence of density unevenness in the low contrast image is prevented. There is an effect that can be.

[Brief description of the drawings]

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

FIG. 2 is a partial perspective view of a process unit that can be used in the printer.

FIG. 3 is a sectional view of a photosensitive layer of the photosensitive member.

FIG. 4 is an explanatory diagram of an exposure amount distribution on a photoconductor.

FIG. 5 is a graph showing a relationship between an exposure amount and a surface potential of a photoconductor.

FIG. 6 is a graph of a γ curve (development amount with respect to development potential) in development characteristics.

FIG. 7 is a schematic configuration diagram of a developing device used in the printer.

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 schematic configuration diagram of a developing device according to a modification.

FIG. 11 is an explanatory diagram of an original image used for evaluation of an afterimage.

FIG. 12 is a graph showing the relationship between the toner particle size and the toner concentration for setting the magnetic particle coverage to 40%.

FIG. 13 is a graph showing a relationship between a linear velocity ratio of a sleeve of a magnetic brush roller to a developing roller and an afterimage ratio.

FIG. 14 is a graph showing a change over time of a toner adhesion amount on a developing roller, which changes with the rotation of the developing roller.

FIG. 15 is a graph showing the relationship between the number of rotations of the developing roller and the amount of toner attached to the developing roller.

FIG. 16 is an explanatory diagram of a negative afterimage generated in a low contrast image immediately after a solid image.

FIG. 17 is a graph showing the relationship between the number of rotations of the toner carrier and the amount of toner carried on the toner carrier.

[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 code FI Theme coat ゛ (Reference) G03G 15/06 101 G03G 15/09 Z 15/09 15/08 507E 507X (72) Inventor Takashi Hojima Tokyo 1-3-6 Nakamagome, Ota-ku Ricoh F-term (reference) 2H005 EA01 EA07 EA10 FA02 2H031 AC03 AC30 AC33 AD03 BA05 BA09 BB05 CA01 CA13 EA03 2H073 AA01 BA01 BA13 BA21 BA25 BA41 BA45 CA03 2H077 AC04 AD05 AD06 AD35 AE06 BA02 BA03 BA09 DB08 EA01

Claims (13)

[Claims] A toner carrying member for carrying a toner on a surface capable of endless movement, and transporting the toner to a developing area facing the latent image carrying member;
A toner supply member that carries a two-component developer containing toner and magnetic particles and conveys the toner to a toner supply area facing the toner carrier, and supplies only toner from the two-component developer to the toner carrier. A developing device provided with the toner carrying member, wherein when the surface of the toner carrying member that does not carry toner passes through the toner supply area once, the toner carrying amount of the maximum carrying amount per unit area on the surface of the toner carrying body is A developing device wherein toner supply conditions by the toner supply member are set so as to be supplied and carried on a body surface. 2. A toner carrier which carries a toner on an endlessly movable surface and conveys the toner to a developing area facing the latent image carrier;
A toner supply member that carries a two-component developer containing toner and magnetic particles and conveys the toner to a toner supply area facing the toner carrier, and supplies only toner from the two-component developer to the toner carrier. In the developing device, when the surface of the toner carrier that does not carry toner passes through the toner supply area once, the amount of toner carried per unit area on the surface of the toner carrier is a target amount of −3.
A developing device wherein toner supply conditions by the toner supply member are set so as to fall within a range of 0 to + 30%. 3. A toner carrier carrying toner on an endlessly movable surface and transporting the toner to a development area facing the latent image carrier;
A toner supply member that carries a two-component developer containing toner and magnetic particles and conveys the toner to a toner supply area facing the toner carrier, and supplies only toner from the two-component developer to the toner carrier. In the developing device, when the surface of the toner carrier that does not carry toner passes through the toner supply area once, the amount of toner carried per unit area on the surface of the toner carrier is 0.35 to 0.35.
A developing device wherein toner supply conditions by the toner supply member are set so as to be 0.7 [mg / cm ² ]. 4. A toner of a latent image formed on a latent image carrier so as to express a gradation of the image by a density per unit area of a toner-attached pixel to which a toner among pixels constituting an image is attached. 4. The developing device according to claim 1, wherein the developing unit develops the attached pixel, wherein a maximum amount of toner per unit area of the toner carrier is attracted to and adhered to the latent image on the latent image carrier. A developing device characterized in that it is smaller than the maximum amount of toner adhered per unit area. 5. The toner of a latent image formed on a latent image carrier so as to express the gradation of the image by the density per unit area of a toner-attached pixel to which the toner adheres among the pixels constituting the image. 4. The developing device according to claim 1, wherein the developing unit develops the attached pixels, wherein the toner-attached pixels of the latent image formed on the latent image carrier pass through the development area. Wherein the developing conditions are set such that all of the toner of the portion facing the toner-attached pixel is used for developing the toner-attached pixel. 6. A toner carrier which carries a toner on an endlessly movable surface and conveys the toner to a developing area facing the latent image carrier.
A toner supply member that carries a two-component developer containing toner and magnetic particles and conveys the toner to a toner supply area facing the toner carrier, and supplies only toner from the two-component developer to the toner carrier. In the developing device, the toner carrying amount per unit area on the surface of the toner carrier when the surface of the toner carrier that does not carry toner passes through the toner supply area once is a latent image of the latent image carrier. Wherein the toner supply condition by the toner supply member is set so as to be larger than the maximum amount of toner per unit area that can be sucked and adhered to the developing device. 7. A toner carrier that carries toner on a surface that can move endlessly and conveys the toner to a development area facing the latent image carrier;
A toner supply member that carries a two-component developer containing toner and magnetic particles and conveys the toner to a toner supply area facing the toner carrier, and supplies only toner from the two-component developer to the toner carrier. In the developing device, a rotatable sleeve containing a magnet member is used as the toner supply member, and the surface movement direction of the toner carrier and the surface movement direction of the sleeve in the toner supply region are reversed. The dynamic resistance of the magnetic particles of the two-component developer is 10
⁸ Ω or less, the potential difference between the developing bias applied to the toner carrier and the toner supply bias applied to the toner supply member is 70 V or more, and the linear velocity ratio of the sleeve to the toner carrier is twice or more. A developing device, wherein the coverage of the magnetic particles with the toner in the magnetic brush made of the two-component developer formed on the toner supply member is set to 36% or more under the following condition. 8. A toner carrier which carries toner on a surface capable of endless movement and conveys the toner to a developing area facing the latent image carrier;
A toner supply member that carries a two-component developer containing toner and magnetic particles and conveys the toner to a toner supply area facing the toner carrier, and supplies only toner from the two-component developer to the toner carrier. In the developing device, a rotatable sleeve containing a magnet member is used as the toner supply member, and the surface movement direction of the toner carrier and the surface movement direction of the sleeve in the toner supply region are reversed. The toner concentration of the two-component developer is 5 wt% or more;
The dynamic resistance of the magnetic particles of the two-component developer is 10 ⁸
Ω or less, and under the condition that the potential difference between the developing bias applied to the toner carrying member and the toner supplying bias applied to the toner supplying member is 70 V or more, the linear velocity ratio of the sleeve to the toner carrying member is defined as: 2.5
A developing device characterized in that it is set to at least twice. 9. A toner carrier that carries toner on a surface capable of endless movement and conveys the toner to a development area facing the latent image carrier;
A toner supply member that carries a two-component developer containing toner and magnetic particles and conveys the toner to a toner supply area facing the toner carrier, and supplies only toner from the two-component developer to the toner carrier. In the developing device, a rotatable sleeve containing a magnet member is used as the toner supply member, and the surface movement direction of the toner carrier and the surface movement direction of the sleeve in the toner supply region are reversed. The toner concentration of the two-component developer is 5 wt% or more;
The potential difference between the developing bias applied to the toner carrier and the toner supply bias applied to the toner supply member is 7
Under the condition that the linear velocity ratio of the sleeve to the toner carrier is 2 times or more, the dynamic resistance of the magnetic particles in the two-component developer carried on the toner supply member is 10 ³ Ω. A developing device having the following settings. 10. The developing device according to claim 7, wherein an absolute value of a potential difference between said developing bias and said toner supply bias is set to 150 V or less. 11. A latent image carrier, a latent image forming means for forming a latent image on the latent image carrier, a developing device for developing the latent image on the latent image carrier into a toner image, And a transfer unit for transferring the toner image on the latent image carrier to a transfer material, wherein the developing device is used as the developing device.
An image forming apparatus using the developing device of 7, 8, 9 or 10. 12. A latent image carrier, a latent image forming means for forming a latent image on the latent image carrier, a developing device for developing the latent image on the latent image carrier into a toner image, An intermediate transfer member on which the toner image on the latent image carrier is transferred, a primary transfer device for transferring the toner image on the latent image carrier to the intermediate transfer member, and a transfer of the toner image on the intermediate transfer member An image forming apparatus comprising: a secondary transfer device configured to transfer to a material;
An image forming apparatus using the developing device of 7, 8, 9 or 10. 13. A latent image carrier, a charging device for uniformly charging the surface of the latent image carrier, and a developing device for developing a latent image on the latent image carrier to form a toner image. An image forming process unit configured as an integrated structure that is detachably attached to a forming apparatus, wherein the developing apparatus is used as a developing apparatus.
An image forming process unit using the developing device of 7, 8, 9 or 10.