JP2003043761A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device in which the reproducibility and the image quality of a halftone part are hardly influenced with respect to the change of developing contrast Vcont in addition to realizing further stabilization of the image quality of a solid image part. SOLUTION: In this image forming device, a developing means 8 has a developer carrier 6 for carrying developer and performs development by applying a developing electric field having at least a DC component Vdc to the developer carrier 6 and imparting the developing contrast Vcont being a potential difference between the image part potential of an electrostatic latent image formed on an image carrier 1 and the DC component Vdc. The developing contrast Vcont is set to a region where the inclination (ΔDt/ΔVcont) of the transmission density Dt of the developer except transfer material P at the solid image part on the transfer material P to the change of the developing contrast Vcont is within 0.001 (V<-1> ).

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 for forming an image on a transfer material by an electrophotographic method or an electrostatic recording method, such as a copying machine, a printer or a facsimile machine.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus using an electrophotographic photoconductor or an electrostatic recording system, an electrostatic latent image corresponding to an image information signal is formed on an image carrier which is an electrophotographic photoconductor or a dielectric. Then, a developing device supplies a developer in accordance with the electrostatic latent image to form an image by the developer, that is, a so-called toner image on the image carrier. Next, this toner image is transferred onto a transfer material, for example, a sheet such as a recording paper or an OHP sheet, and then fixed to obtain an output image.

FIG. 8 shows a schematic structure of an example of a conventional electrophotographic image forming apparatus. The image forming apparatus has an electrophotographic photosensitive member (photosensitive member) 1 of, for example, a drum type as an image bearing member. As the photoconductor 1 rotates in the direction of the arrow in the figure, the surface of the photoconductor 1 is uniformly charged by the primary charging device 2 as a charging means. Next, the surface of the uniformly charged photoreceptor 1 is
An exposure unit 3 such as a laser scanner scans and exposes in accordance with image information to form an electrostatic latent image on the photoconductor 1.
In response to the electrostatic latent image, the developing device 8 as a developing unit supplies the developer to the photoconductor 1 and forms an image (toner image) on the photoconductor 1 by the developer.

The developing device 8 includes a container 8a for containing a developer.
And a developer carrier 6 for carrying and transporting the developer to the photoconductor 1.
Is equipped with. In addition, the doctor blade 7 is a regulating member for regulating the amount of the developer carried on the developer carrying member 6.
Is provided in contact with or close to the developer carrying member 6.
Then, a developing electric field is applied to the developer carrying member 6 from the developing bias applying means 5, and a predetermined developer carrying member potential Vdevelop is given to the developer carrying member 6 to perform development. A developing electric field is applied from the developing bias applying means 5 at the time of developing.

Thereafter, the toner image on the photosensitive member 1 is transferred onto the transfer material P conveyed in synchronization with the formation of the toner image.
The image is transferred by the action of a transfer device (transfer charging device) 9 serving as a transfer unit. Further, the transfer material P is separated by a separating device (separation charging device) 10
Is separated from the photoconductor 1 by the action of, and then conveyed to a fixing device (not shown).

The unfixed toner image transferred to the transfer material P is fixed by heat and pressure by the fixing device,
Is discharged to the outside of the image forming apparatus. The developer remaining on the photoconductor 1 after the transfer of the toner image is removed by the cleaner 11, and the photoconductor 1 is repeatedly used for image formation.

Further, in the image forming apparatus having such a structure,
A photoreceptor surface potential detection unit 4 that detects the surface potential of the photoreceptor 1 may be provided. Photoconductor surface potential detection means 4
The detection output of the image forming condition calculation means 1 as the control means.
2 is supplied. Then, the image forming condition calculation means 12
Depending on the detection result of the photoreceptor surface potential detecting means 12,
Amount of charge by the primary charging device 2, developing bias applying means 5
Developing field applied to the developer carrying member 6 by the exposure means 3
The image forming conditions are controlled by controlling the image exposure conditions and the like.

Conventionally, in this type of image forming apparatus, in many cases, in order to stably output a high quality image, the DC component bias Vdc applied to the developer carrying member 6 and the photosensitive member 1 are used.
The development contrast potential Vcont, which is the potential difference from the potential Vimage of the image portion of the electrostatic latent image formed above, is set as follows. That is, as shown in FIG. 9, variations in the development contrast Vcont due to deterioration of the photoconductor, uneven charging and exposure, or reading error of the photoconductor surface potential detection means, control error of the developing electric field, and the like expected in the image forming apparatus. Within the range, the development contrast Vco is set so that the variation of the reflection density Dr of the solid image portion of the output image (on the transfer material P) does not become too large.
The set development contrast VcontT is set in the saturation region Sr of the reflection density Dr with respect to nt.

[0009]

However, according to this method, the amount of change in the reflection density Dr of the solid image portion due to the variation of the development contrast Vcont can be reduced, but the amount of developer applied changes, so that the reflection of the halftone portion is changed. Concentration Dr
There was a problem in that the change in may become large.

Further, in the case of a digital image forming apparatus for forming a binary image, halftones are reproduced by hitting a certain number of dots per unit area, so that the reflection density Dr of the solid image portion is only stable. The stability of dot reproduction is poor, and as a result,
There is a problem that the change in the reflection density Dr in the halftone becomes large.

Further, conventionally, in an image forming apparatus in which the developer is rapidly deteriorated and outputs at a high speed, a high-quality image can be obtained in a short time by selectively developing only a good quality developer which is not deteriorated. However, there is a problem in that the deteriorated developer may be accumulated in the developing device due to the endurance, and the image quality and the density may be lowered.

Therefore, an object of the present invention is to further stabilize the image quality of a solid image portion and to add the development contrast Vcont.
It is an object of the present invention to provide an image forming apparatus in which the reproducibility of the halftone portion and the image quality are unlikely to be affected by changes in

Another object of the present invention is to achieve the above object,
It is an object of the present invention to provide a developing device in which the deterioration of a developer and the reproducibility of a halftone portion due to durability and the deterioration of image quality are small.

[0014]

As a result of intensive studies in view of the above problems, the present inventor has found that, as shown in FIG. 1, a saturated region St of the transmission density Dt of the solid image on the transfer material with respect to the development contrast Vcont is present. Setting value of development contrast V
It has been found that the above problem can be solved by setting contT. Further, as shown in FIG. 2, it has been found that the above problem can be solved by setting a development contrast setting value VcontT in a saturation region Sα of the development efficiency α on the image carrier with respect to the development contrast Vcont.

That is, the above object is achieved by the image forming apparatus according to the present invention. In summary, the first aspect of the present invention is an image forming apparatus for developing an electrostatic latent image formed on an image bearing member with a developer by a developing means and transferring the obtained developed image to a transfer material. The developing means has a developer carrying member that conveys a developer, and applies a developing electric field having at least a direct current component Vdc to the developer carrying member to form an electrostatic latent image formed on the image carrying member. Image portion potential and the DC component V
The development contrast Vcont, which is a potential difference from dc, is applied to develop, and the development contrast Vcont
Is the slope (ΔDt / ΔVcont) of the transmission density Dt of the developer excluding the transfer material in the solid image portion on the transfer material with respect to the change in the development contrast Vcont.
The image forming apparatus is characterized in that the area is set within 1 (V ^-1 ).

According to the second aspect of the present invention, the electrostatic latent image formed on the image bearing member is developed by a developing means using a developer, and the obtained developed image is transferred to a transfer material. In the apparatus, the developing means has a developer carrier that moves at a peripheral speed ratio (η) with the opposing image carrier to convey the developer, and at least the DC component Vd is applied to the developer carrier.
By applying a developing electric field having a value c, a developing contrast Vcont, which is a potential difference between the image portion potential of the electrostatic latent image formed on the image carrier and the DC component Vdc, is applied to develop, The amount of developer applied per unit area on the agent carrier is Md, and the amount of developer applied on the solid image portion formed on the image carrier is Mp.
Is defined by the following equation, α≡Mp / Md × η, the development contrast Vcont is
The slope (Δα / ΔVcont) of the developing efficiency α with respect to the change of the developing contrast Vcont is 0.003.
There is provided an image forming apparatus characterized by setting the area within (V ^-1 ).

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION An image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Embodiment 1 In this embodiment, the present invention is applied to an electrophotographic image forming apparatus having the basic structure described with reference to FIG.
Therefore, elements having the same configurations and functions as those described above are designated by the same reference numerals, and redundant description will be omitted.

In this embodiment, the image forming apparatus has a drum type electrophotographic photosensitive member (photosensitive member), that is, a photosensitive drum 1 as an image bearing member. Further, in the present embodiment, the developing device 8 as the developing means is rotatable as a developer carrying member so as to be closely opposed to each other along the longitudinal direction of the photosensitive drum 1 (direction substantially orthogonal to the transport direction of the transfer material P). It has a roller-shaped developer bearing member, that is, the developing roller 6, which is rotatably supported by. And
The developing roller 6 rotating in the direction of the arrow conveys the developer to the vicinity of the surface of the photosensitive drum 1 rotating in the direction of the arrow, and friction due to the potential difference between the potential of the developing roller 6 and the surface potential of the photosensitive drum 1. The charged developer is supplied to the image portion of the electrostatic latent image formed on the photosensitive drum 1.

The developed image (toner image) is transferred onto a transfer material by a transfer charging device 9 which is a transfer device, separated by a separation charging device 10 which is a separating device, and then developed by a fixing device (not shown). The agent is fixed on the transfer material and output as an image. The developer that has not been transferred is removed from the photosensitive drum 1 by the cleaner 11.

In this embodiment, the electrostatic latent image formed on the photosensitive drum 1 is developed by reversal development with a developer that is triboelectrically charged with the same polarity as the charging polarity of the photosensitive drum 1.

That is, the photosensitive drum 1 is an OPC photosensitive drum having a negatively chargeable OPC photosensitive layer on the surface of a metal drum, and is rotationally driven at a peripheral speed of 280 mm / s. Then, the primary charging device 2 uniformly charges the negative polarity, and the developer is supplied to the image portion where the negative charge is attenuated by the exposure, and is visualized as a toner image.

The developing device 8 of this embodiment has a developing roller 6 which has a fixed magnet roll inside and is rotatably supported by a non-magnetic sleeve as a magnetism generating means. The developer is carried on the surface of the developer by the magnetic field generated by and is conveyed to the photosensitive drum 1. Further, in this embodiment, as the developer, a negatively chargeable magnetic one-component developer (toner) mainly composed of a resin and a magnetic material was used.

Next, the set value of the output potential of each part in this embodiment will be described.

Image forming condition calculating means 12 as a control means
Means that while the surface potential of the photosensitive drum 1 is measured by the photosensitive member surface potential detecting means 4, the charging potential (latent image non-exposed portion → image white background portion potential) Vblank of the photosensitive drum 1 is set potential V.
The charge amount of the photosensitive drum 1 by the primary charging device 2 is adjusted so as to be −500V which is blankT.

Similarly, in the image forming condition calculating means 12, the potential of the image portion of the electrostatic latent image formed on the photosensitive drum 1 (latent image exposure portion → image black background portion potential) Vimage is the set potential Vi.
The exposure amount of the exposure unit 3 is adjusted so as to be ± 0 V which is the magT.

Further, in the image forming condition calculating means 12, the development contrast Vcont is the set value VcontT 40.
The DC component bias Vdc applied to the developing roller 6 is adjusted to -400V (= 0-400) so that it becomes 0V.

As the photosensitive member surface potential detecting means 4,
A potential sensor known to those skilled in the art can be arbitrarily selected and used. As is well known to those skilled in the art, the image forming condition calculation means 12 is, for example, a control circuit including a microprocessor having a control unit, a calculation unit, and a storage unit, and is set in advance. According to the program, the image forming conditions can be controlled by a table or an arithmetic expression in which the output of the photoconductor surface potential detecting means 4, the output of the developing bias applying means 5 and the like and the control amounts of the above respective parts are related.

Next, the setting of the set value VcontT of the development contrast in this embodiment will be described.

In the image forming apparatus, at least the DC component bias Vd is applied to the developing roller 6 which rotates at the peripheral speed ratio η of the photosensitive member.
c is applied, and the electrostatic latent image is developed by the development contrast Vcont (V) which is a potential difference between the DC component bias Vdc and the potential Vimage of the image portion of the electrostatic latent image formed on the photosensitive drum 1. Incidentally, as in the embodiment described later, also in this embodiment, an alternating electric field due to the DC component bias dc and the AC component can be applied to the developing roller 6.

In this embodiment, as shown in FIG. 1, the transmission density Dt of the developer excluding the transfer material P in the solid image portion formed on the transfer material P with respect to the development contrast Vcont (hereinafter simply referred to as " A set value VcontT of the development contrast is set in a saturation region St of a solid image portion transmission density Dt on the transfer material). For more details,
The transfer material P against the change of the development contrast Vcont
The slope of the transmission density Dt of the solid image area (ΔDt / ΔVc
ont) (V ⁻¹ ) is set to 0.001 or less, the set value VcontT of the development contrast is set.

Conventionally, the slope of the reflection density Dr (ΔDr / ΔV
cont) (V ⁻¹ ) is within 0.001 Vc
This slope ΔDt / ΔVcon for setting ontT
Since t (V ⁻¹ ) is not taken into consideration and (gradient of reflection density) <(gradient of transmission density), ΔDt /
ΔVcont (V ⁻¹ )> 0.001.

The "solid image" is an image of maximum density, and can be obtained by controlling the development contrast Vcont so that an image of maximum density can be obtained on the photoconductor.

Further, in this embodiment, the amount of the developer applied per unit area on the developing roller 6 is Md (mg / cm 2).
² ), Mp (mg / cm ² ) is the applied amount of the developer per unit area of the solid image portion developed on the photosensitive drum 1, and the development efficiency α is expressed by the following equation: α≡Mp / Md × η 2, the set value VcontT of the development contrast is set in the saturation region Sα of the development efficiency α with respect to the development contrast Vcont. More specifically, the set value VcontT of the development contrast is set in a region where the slope (Δα / ΔVcont) (V ⁻¹ ) of the development efficiency α with respect to the change of the development contrast Vcont is within 0.003 (V ⁻¹ ).

Conventionally, the slope of the reflection density Dr (ΔDr / ΔV
cont) (V^-1) Is within 0.001
This slope Δα / ΔVcont for setting ontT
(V ^-1) Is not taken into consideration, and (Development efficiency
Slope) ∝ (slope of transmission density), ΔDt / ΔVcon
t (V^-1) = 0.001, Δα / ΔVcont (V
^-1) = 0.003, Δα / ΔVcont (V
^-1)> 0.003.

In this embodiment, in order to determine the set value VcontT of the development contrast, the above-mentioned inclination Δα / Δ
Vcont (V ^-1 ) and slope ΔDt / ΔVcont (V
⁻¹ ), both of the indexes are taken into consideration, but according to the study by the present inventor, the present invention can sufficiently work if the set value VcontT of the development contrast is determined by one of the indexes. confirmed.

Here, in the present specification, the transmission density Dt
Is a value measured by Macbeth TD904J.

In the present specification, the amount of developer Md per unit area on the developing roller (developer carrier) 6 and the unit area of the solid image portion on the photosensitive drum (image carrier) 1 per unit area. The amount of applied developer Mp is a value measured by the following method. The developing roller 6 and the photosensitive drum 1
Since the method of measuring the amount of applied developer Md and Mp is the same, the amount of applied developer Md of the developing roller 6 will be described as an example.

The mass of the developer is defined as the amount Md (applied amount) of the developer per unit area on the developing roller 6 (unit: mg / cm ² ). Then, by using a suction Faraday gauge, the tribo (charge) of the developer on the developing roller 6 can be measured, and at the same time, the area can be obtained, and the obtained mass can be calculated.

That is, the amount of applied developer is measured by using a suction type Faraday gauge, a suction device (vacuum cleaner), a precision balance, etc., as schematically shown in FIG. First, the cylindrical filter paper 101 is weighed. The cylindrical filter paper is attached to the Faraday gauge 100. A suction device 10 for connecting the developer on the developing roller 6 to the Faraday gauge 100.
Aspirate by 2. Then, the cylindrical filter paper 101 is taken out from the Faraday gauge 100 and weighed. Further, the developer on the developing roller 6 after being sucked by the mending tape is sampled. Peel the mending tape and measure the suction area. Then, the amount of applied developer is obtained from the following equation. Amount of applied developer Md (mg / cm ² ) = amount of developer in filter paper / suction area

In this embodiment, the developer carried on the surface of the developing roller 6 is a regulating member (doctor blade).
7, the amount of developer Md per unit area on the surface layer of the developing roller 6 is 1.0 mg / cm ² , and the developing roller 6 has a peripheral speed ratio η to the photosensitive member of 1.5. To be rotated. Further, in this embodiment, the amount Mp of applied developer per unit area in the solid image portion developed on the photosensitive drum 1 is the development contrast Vcont.
Is 1.1 mg / cm ² when is 400 V.

Therefore, according to the above definition of the development efficiency α,
When the output potentials of the above respective parts are as set values, the development efficiency α is set to α = (1.1 mg / cm ² ) / (1.0 mg / cm ² × 1.5) = 0.73. .

Similarly, when the output potentials of the respective portions are as set, the transmission density Dt of the developer excluding the transfer material P in the solid image portion on the transfer material P is set to 1.5. .

Then, at the developing contrast setting values VcontT and 400 V in this embodiment, the slope (ΔD) of the transmission density Dt with respect to the developing contrast Vcont.
t / ΔVcont) is 0.001 (V ⁻¹ ), and the slope of the development efficiency with respect to the development contrast Vcont (Δα / ΔV
cont) is 0.002 (V ^-1 ).

By the way, although the output potentials of the respective parts are adjusted to the above-mentioned set values as described above, in practice, charging and exposure unevenness, reading errors of the photoconductor surface potential detecting means 4, and other parts. Due to a variation due to a control error and the like, the actual development contrast VcontM is 380V, which is 20V from the set value VcontT of 400V, not the set center value.

In the image forming apparatus of this embodiment, the charging and the photosensitive characteristics of the photosensitive drum 1 changed due to the durability.
Photoconductor surface potential detecting means 4 and image forming condition calculating means 12
By the development contrast adjusting means configured with
Development contrast Vcont is 380V even if durability is advanced
That is, it was within a deviation of 20V from the set value of 400V.

Thus, the actual development contrast Vc
ontM is the set development contrast Vcont
Although it is lower than T by 20V, in this embodiment, the saturation area St of the transmission density Dt of the solid image portion on the transfer material P and the set value VcontT of the development contrast are set in the saturation area Sα of the development efficiency α. Therefore, the development contrast Vco
The change amount of the transmission density Dt of the solid image portion on the transfer material P due to the variation of nt is 0.02 (= 0.001 (V ⁻¹ ) ×
20 (V)), the amount of change in the development efficiency α is 0.04 (= 0.
002 (V ⁻¹ ) × 20 (V)), which hardly changes. As a result, the actual transmission density Dt of the solid image portion on the transfer material P was 1.48, and the developing efficiency α was 0.726.

As a result, the amount of developer applied is stabilized, the image quality of the solid image portion is further stabilized, and the area of one dot formed digitally is also stabilized, and the line width is also stabilized.

Further, according to this embodiment, the reproducibility of the halftone portion and the image quality can be stabilized against the change in the development contrast Vcont. Next, this point will be described in more detail with reference to FIG.

As is well known to those skilled in the art, in a binary digital image, halftone is reproduced by the number of dots per unit area. Here, as described above, conventionally, in order to stably output an image, the development contrast Vco is added to the saturated region Sr of the reflection density Dr of the solid image portion of the output image (on the transfer material).
ntT was set. In this region Sr, the slope (ΔDt / ΔVcont) of the transmission density Dt of the solid image on the transfer material P with respect to the development contrast Vcont is 0.0.
03 (V ⁻¹ ), the slope of the development efficiency α with respect to the development contrast Vcont (Δα / ΔVcont) is 0.00
It was found that it was about 5 (V ^-1 ) (Fig. 3
(A)).

According to such a conventional method, the change amount of the reflection density Dr of the solid image portion due to the variation of the development contrast Vcont can be reduced (FIG. 3A), but the change amount of the developer changes 1 The size of the dot changes,
As a result, the area occupied by the developer per unit area was changed, and the reflection density Dr in the halftone portion was changed (FIG. 3).
(B)).

On the other hand, in this embodiment, the development contrast Vcont is set in the saturation region St of the transmission density Dt of the solid image portion on the transfer material P or the saturation region Sα of the development efficiency α.
Set T. As a result, as described above, the amount of applied developer is stable regardless of variations and durability of each portion of the image forming apparatus, and therefore not only the solid image portion but also the halftone portion can be stably reproduced (FIG. 3). (B)).

Further, the transmission density Dt of the solid image portion, which is proportional to the amount of the applied developer, and the reflection density Dr of the same image portion, which is proportional to the appearance of a human, have a relationship as shown in FIG. That is, when the transmission density Dt becomes high to some extent, the reflection density Dr
There is a relation that the increase amount of is saturated.

Therefore, the transmission density Dt is set in the saturation region of the reflection density Dr in consideration of the variation in the transmission density Dt, so that the transmission density Dt, that is, the amount of the applied developer changes in the solid image portion. The reflection density Dr hardly changes.

In consideration of appearance quality, the transfer material P
Ideally, the transmission density Dt of the solid image area above is set to 1.2 or more. Generally, if the transmission density Dt is less than 1.2, the image in the solid black portion becomes white, and the texture becomes poor, which is not preferable. More preferably, this transmission density Dt is set to 1.4 or more.

Further, the transmission density Dt of the solid image portion on the transfer material P and the developer consumption amount have a substantially linear relationship as shown in FIG. For example, the peripheral speed of the photosensitive drum 1 is 280 mm /
In the image forming apparatus having a high peripheral speed of the photosensitive drum 1 of 250 mm / s or more, like the image forming apparatus of the present embodiment, it is particularly effective from the viewpoint of running cost to keep the developer consumption low. Required. For example, in order to suppress the amount of developer consumption to 500 mg in the entire solid image portion with the formed image size of A4, the transmission density Dt of the solid image portion on the transfer material P must be 1.6 or less. As described above, the transmission density of the developer excluding the transfer material P in the solid image portion formed on the transfer material P is preferably 1.
2 to 1.6.

In the image forming apparatus of this embodiment, the transmission density of the solid image portion on the transfer material P is 1.48, the consumption of the developer is suppressed to a small level, and the reflection density and the quality of the solid image portion are reduced. Obtainable.

Incidentally, the developing efficiency α is such that the developer is the developing roller 6
Therefore, it is set to 0.7 or more in order to prevent deterioration.

As described above, according to this embodiment, the development contrast Vcont is set to the saturation region St of the transmission density of the solid image portion on the transfer material P with respect to the development contrast Vcont, or the saturation region Sα of the development efficiency α with respect to the development contrast Vcont. By setting, the development contrast Vc
Variations in the amount of developer applied due to variations and changes in ont are reduced, and further stabilization of the image quality of solid image portions, reproducibility of halftone portions, and stabilization of image quality can be achieved.

Further, in this embodiment, the development contrast V due to the durability is controlled by the development contrast control means including the photoconductor surface potential detecting means 4 and the image forming condition calculating means 12.
By adopting a configuration that prevents the change of cont, the image quality of the solid image portion, the reproducibility of the halftone portion, and the image quality are stabilized for a long period of time.

Embodiment 2 Next, another embodiment of the present invention will be described. The image forming apparatus of the present embodiment has basically the same configuration as the image forming apparatus of the first embodiment. Therefore, the same configuration as the above embodiment,
The elements having functions are denoted by the same reference numerals, and detailed description thereof will be omitted.

In the present embodiment, as shown in FIG. 6, the potential (developer carrier potential) Vdevelop applied to the developing roller 6 in the developing device 8 is the DC component bias Vdc and the AC component Vac as the developing electric field. It is formed by an alternating electric field which is a superposed electric field. In the present embodiment, the DC component bias Vdc of the developing electric field is -400V, and the AC component is a rectangular wave with Vpp of 1000V. Of course, the present invention does not limit the AC component to a rectangular wave.

In this embodiment, the setting value VcontT of the development contrast is set in the same manner as in the first embodiment, and
More specifically, the electric field strength, which will be described later in detail, is controlled to increase the developing efficiency, and particularly in a high-speed image forming apparatus in which the peripheral speed of the photosensitive drum 1 is 250 mm / s or more, the reproducibility of the halftone portion due to deterioration and durability of the developer. Also, the configuration is such that deterioration of image quality can be prevented.

In this embodiment, the developing roller 6 conveys the developer to the vicinity of the photosensitive drum 1 as it rotates, and the potential Vd formed by the alternating electric field applied to the developing roller 6 is reached.
The electrostatic latent image is developed by evelop. In this embodiment, a case where the distance G between the developing roller 6 and the surface of the photosensitive drum 1 shown in FIG. 8 is 180 μm will be described.

The maximum electric field strength F between the photosensitive drum 1 and the developing roller 6 is (1) the potential Vdevel of the developing roller 6.
Op developing potential, that is, the developing-side peak potential (Vac_peak_developing side) of the AC component Vac, the DC component bias Vdc of the developing roller 6 potential Vdevelop, and the image portion of the electrostatic latent image formed on the photosensitive drum 1. ΔVmax (the image portion potential Vimage of the electrostatic latent image and the potential Vdevelop given to the developing roller 6 by the alternating electric field) which is the sum of the development contrast Vcont which is the potential difference from the potential (image portion bright portion potential) Vimage. Maximum potential difference), and (2) the distance G between the developing roller 6 and the surface of the photosensitive drum 1, which is calculated by the following formula: F = ΔVmax / G = (Vcont + Vac_peak_developing side) / G.

In the configuration of this embodiment, F = (400 + 500) / 180 = 5.0 (V / μm) Is.

When the maximum electric field strength F is strong, the developing roller 6
Since the force applied to the upper developer toward the photosensitive drum 6 is increased, the development efficiency is increased.

However, if the maximum electric field strength F is too strong, leakage will occur, which may cause deterioration of the photoconductor or destruction of the photoconductor. The maximum electric field strength F is 5.5 (V / μ when considering that it is used in low-pressure areas.
m) is the leak limit. Further, the maximum electric field strength F is 4.0 (V / μm) in order to cause the developer to fly over the developing roller 6 by applying the electric field strength and reach the photosensitive drum 1.
That is all. Therefore, the maximum electric field strength F is 4.0 ≦ F
≦ 5.5.

In the structure of this embodiment, since the electric field strength is 5.0 (V / μm) as described above, no leak occurs even in a region where the atmospheric pressure is low, and the actual developing efficiency is 0.80, which is very high. You can get a high condition.

As shown in FIG. 7, conventionally, in an image forming apparatus for forming an image at high speed, only a high-quality developer which is not deteriorated is selectively developed, so that the development deteriorated in the developing apparatus due to durability. The agent may accumulate, resulting in deterioration of image quality and reduction of concentration.

On the other hand, in this embodiment, the electric field strength between the photosensitive drum 1 and the developing roller 6 is set to the leak limit to maintain high developing efficiency, so that the speed of the photosensitive drum 1 is 280 mm / Even at a high speed of s, the developer is developed before it is deteriorated, and the state of the developer in the developing device 8 is stabilized. As a result, as shown in FIG. 7, the transmission density Dt of the solid image portion was stable even when the durability was advanced. As a result, the line width, the solid image portion, and the reflection density of the halftone portion formed by the halftone dots were also stable.

As described above, according to the present embodiment, as in the first embodiment, the development contrast Vcont is set to the saturation region St of the transmission density of the solid image portion on the transfer material P with respect to the development contrast Vcont, or the development contrast Vcont. By setting the saturation region Sα of the efficiency α, the variation in the amount of developer applied due to the variation or change in the development contrast Vcont is reduced, the image quality of the solid image portion is further stabilized, the reproducibility of the halftone portion and the image quality are reduced. The stabilization of can be achieved.

Further, in the present embodiment, the development contrast Vc due to durability is controlled by the development contrast control means including the photoconductor surface potential detection means 4 and the image forming condition calculation means 12.
In addition, the photosensitive drum 1 is configured to prevent the change of ont.
By setting the electric field strength between the developing roller 6 and the developing roller 6 to the leak limit to increase the developing efficiency, the speed of the photosensitive member is 250 mm.
Even with a high-speed image forming apparatus of / s or more, the deterioration of the developer is reduced, the image quality of the solid image portion, the reproducibility of the halftone portion, and the change in the image quality are suppressed over a long period of time, and the image is close to the initial state. Can continue to form.

Although the present invention has been described with reference to the specific embodiments, the present invention is applied to the dimensions, materials and shapes of the constituent parts described in each of the above embodiments. The scope of the present invention is not limited to the above-mentioned embodiments, and should be appropriately changed according to the configuration of the device and various conditions.

[0075]

As described above, according to the present invention,
The image forming apparatus uses the set development contrast VcontT.
Is the slope (ΔDt / ΔVcont) of the transmission density Dt of the developer excluding the transfer material in the solid image portion on the transfer material with respect to the change of the development contrast Vcont is 0.001 /
Saturation area within V or development contrast Vcont
Of the development efficiency α with respect to the change of (Δα / ΔVcon
Since t) is set to a saturation region within 0.003 / V, in addition to further stabilizing the image quality of the solid image portion,
It is possible to make it difficult for the reproducibility of the halftone portion and the image quality to be affected by changes in the development contrast Vcont.
Further, according to the present invention, if the maximum electric field strength between the image bearing member and the developer bearing member is set to the leak limit, the deterioration of the developer and the reproducibility of the halftone portion due to the durability and the deterioration of the image quality are further reduced. Can be reduced.

[Brief description of drawings]

FIG. 1 is a graph for explaining a correlation between a development contrast Vcont and a transmission density Dt.

FIG. 2 is a graph for explaining the correlation between development contrast Vcont and development efficiency α.

FIG. 3 is a graph for explaining a correlation between a development contrast Vcont, (a) a transmission density Dt and a reflection density Dr of a solid image portion, and (b) a reflection density Dr of a halftone portion. .

FIG. 4 is a transmission density Dt and a reflection density D in a solid image portion.
It is a graph figure for demonstrating the correlation with r.

FIG. 5 is a graph for explaining a correlation between a transmission density Dt and a developer consumption amount in a solid image portion.

FIG. 6 is a diagram for explaining a latent image potential on a photosensitive drum and a developing roller potential.

FIG. 7 is a graph for explaining the transition of the transmission density Dt of a solid image portion due to durability.

FIG. 8 is a schematic configuration diagram of a main part of an image forming apparatus to which the present invention can be applied.

FIG. 9 is a graph for explaining the correlation between development contrast and reflection density Dr.

FIG. 10 is a schematic diagram for explaining a method for measuring the amount of applied developer.

[Explanation of symbols]

1 Photosensitive drum (electrophotographic photosensitive member, image bearing member) 2 Primary charging device 3 exposure means 4 Photoconductor surface potential detection means 5 Development bias applying means 6 developer carrier 7 Doctor blade (restriction member) 8 developing device 9 Transfer device 10 Separation device 11 cleaner 12 Image forming condition calculation means P transfer material

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H027 DA02 DA04 DA09 DD07 DE07                       EA05 EB03 EC06 EC11                 2H073 AA02 AA05 BA02 BA13 BA23                       BA24 CA02                 2H077 AD06 AD13 AD37 DA03 DA24                       DA43 DA47 DA64 DA80 DB08                       EA13 GA03 GA17

Claims (10)

[Claims] 1. An image forming apparatus for developing an electrostatic latent image formed on an image bearing member by a developing means using a developer, and transferring the obtained developed image to a transfer material, wherein the developing means is a developing means. A developing agent carrier for carrying a developer, and a developing electric field having at least a direct current component Vdc is applied to the developing agent carrier, and the image portion potential of the electrostatic latent image formed on the image carrier and Development is performed by applying a development contrast Vcont, which is a potential difference from the DC component Vdc, and the development contrast Vcont is the transmission density of the developer excluding the transfer material in the solid image area on the transfer material with respect to the change in the development contrast Vcont. Slope of Dt (Δ
An image forming apparatus characterized in that it is set in a region where Dt / ΔVcont) is within 0.001 (V ⁻¹ ). 2. An image forming apparatus for developing an electrostatic latent image formed on an image bearing member by a developing means with a developer and transferring the obtained developed image to a transfer material, wherein the developing means are opposed to each other. The image carrier and the peripheral speed ratio (η)
Of the electrostatic latent image formed on the image carrier by applying a developing electric field having at least a direct current component Vdc to the developer carrier, which has a developer carrier for moving and carrying the developer. Development is performed by applying a development contrast Vcont, which is a potential difference between the image portion potential and the DC component Vdc, and the amount of the developer applied per unit area on the developer carrying member is Md. When the amount of developer applied on the formed solid image portion is Mp and the developing efficiency α is defined by the following equation, α≡Mp / Md × η, the developing contrast Vcont is
The slope (Δα / ΔVcont) of the developing efficiency α with respect to the change of the developing contrast Vcont is 0.003.
An image forming apparatus, wherein the image forming apparatus is set to an area within (V ^-1 ). 3. The developing contrast Vcont
Is the slope (ΔDt / ΔVcont) of the transmission density Dt of the developer excluding the transfer material in the solid image portion on the transfer material with respect to the change in the development contrast Vcont.
The image forming apparatus according to claim 2, wherein the area is set to be within 1 (V ^-1 ). 4. The developer carrying member moves at a peripheral speed ratio (η) with the opposing image carrying member to carry the developer,
The amount of developer applied per unit area on the developer bearing member is Md, the amount of developer applied on the solid image portion formed on the image bearing member is Mp, and the developing efficiency α is The image forming apparatus according to claim 1, wherein the developing efficiency α is 0.7 or more when defined by ≡Mp / Md × η. 5. The image forming apparatus according to claim 2, wherein the developing efficiency α is 0.7 or more. 6. The electrostatic latent image formed on the image carrier is developed by the developing means by applying an alternating electric field having a direct current component Vdc and an alternating current component Vac to the developer carrier. From the maximum potential difference ΔVmax between the image portion potential Vimage and the potential Vdevelop given to the developer carrier by the alternating electric field, and the distance G between the developer carrier and the surface of the photoconductor, F = ΔVmax / The maximum electric field strength F (V / μm) between the image bearing member and the developer bearing member calculated by G satisfies the following relationship: 4.0 ≦ F ≦ 5.5. The image forming apparatus according to claim 1. 7. The transmission density Dt of the developer excluding the transfer material in the solid image portion formed on the transfer material is 1.2 to 1.
6. The image forming apparatus according to claim 1, wherein the image forming apparatus is 6. 8. Further, (a) a potential detecting means for detecting a surface potential of the image carrier, and (b) control is performed so as to keep the developing contrast Vcont constant in accordance with a detection result by the potential detecting means. The image forming apparatus according to claim 1, further comprising image forming condition calculation means. 9. The image carrier is an electrophotographic photoreceptor,
The image forming apparatus further includes a charging unit that charges the electrophotographic photosensitive member and an exposing unit that exposes the charged electrophotographic photosensitive member to form an electrostatic latent image, and the image forming condition calculating unit is Controlling the amount of charge on the surface of the electrophotographic photosensitive member, the amount of exposure on the surface of the electrophotographic photosensitive member, the DC component Vdc of the developing electric field applied to the developer carrier, or any combination or all of these. The image forming apparatus according to claim 8, wherein 10. The moving speed of the surface of the image carrier is 250.
The image forming apparatus according to any one of claims 1 to 9, wherein the image forming apparatus has a diameter of mm / s or more.