JP2002296911A - Electrophotographic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To output a high quality image at high speed using electrophotographic technique. SOLUTION: When the surface potential of the photosensitive layer varied by having toner particles within the liquid developer 4-2 stuck to the photosensitive layer surface is ΔV in an electrophotographic device for developing an electrostatic latent image formed on the surface of a photosensitive layer 1-2 with liquid developer 4-2, amorphous silicon, for example, is used as the photosensitive layer so that ΔV is within the range of 10 to 100 V.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrophotographic apparatus, and more particularly to an electrophotographic apparatus using a liquid developer.

[0002]

2. Description of the Related Art Conventionally, electrophotographic apparatuses used in copying machines and the like are mainly dry electrophotographic apparatuses using a dry developer, but in recent years, higher quality image formation has been performed on electrophotographic apparatuses. It has become required.

[0003] Since a dry developer generally requires the use of relatively large toner particles of about 10 µm or more,
It is difficult to form images with high precision.

In a wet electrophotographic apparatus, since a liquid developer in which toner particles are dispersed in a carrier liquid is used, extremely fine toner particles of a submicron level can be used. For this reason, wet electrophotographic apparatuses have come to be expected as electrophotographic apparatuses suitable for high-precision image formation.

However, like the wet electrophotographic apparatus commercially available by the present inventors, a photosensitive drum using an organic material for a photosensitive layer is used as a latent image holder, and a developing electrode and a rotating photosensitive drum are used. When liquid developer was supplied to the gap and development was performed, a higher-precision image could be obtained than when a dry-type developer was used. However, when a higher-precision image was obtained, development was performed. The amount of toner particles became excessive, and so-called image collapse occurred.

In order to reduce the amount of toner particles to be developed,
The gap between the developing electrode and the photosensitive drum was narrowed to about 10 μm to reduce the absolute amount of the liquid developer used for development.
Since it is extremely difficult to uniformly control the gap between the rotating photosensitive drum and the developing electrode at 10 μm, uniform developing characteristics cannot be obtained, and the concentration of toner particles in the liquid developer is reduced to 0.1 μm. An attempt was made to suppress excessive development by diluting it to about 2 wt%, but it was difficult to stably supply a liquid developer having a low toner particle concentration, and as a result, a density distribution different from the image information in the obtained image was obtained. Has been completed.

As described above, various methods of theoretically controlling the amount of toner to be developed are conceivable. However, it is difficult to realize the method due to mechanical control and various other restrictions, and a more accurate image is obtained. In order to do this, further ingenuity was required.

[0008]

As described above, a wet electrophotographic apparatus can form a high-precision image because fine toner particles can be used. However, further improvement is required to further increase the image precision. there were.

An object of the present invention is to provide an electrophotographic apparatus capable of forming an image with higher precision.

[0010]

According to the present invention, there is provided an electrophotographic apparatus comprising: a latent image carrier having a photosensitive layer on which an electrostatic latent image is formed; And a developing electrode that selectively supplies toner particles in the liquid developer interposed between the gaps to the surface of the electrostatic latent image according to the electrostatic latent image. The thickness of the liquid developer sandwiched between the latent image holding member and the developing electrode is dt (m), and the position coordinates dt × in the thickness direction of the liquid developer when the surface of the developing electrode is the origin. k / M (M is an integer of 10 or more,
k is 0, 1, 2, 3,... M), and is determined from the charge mobility of the toner particles contained in the liquid developer and the time during which the liquid developer is subjected to the development. The total amount of charge of the toner particles per unit volume is Pk
(C / m ³ ), the charge mobility of the impurity having a counter ion contained in the liquid developer at the position coordinates dt × k / M and the time during which the liquid developer is subjected to the development. The total amount of charge of the impurity per unit volume is Nk (C / m ³ ), and the potential of a portion of the electrostatic latent image to which the toner particles are selectively adhered is V0.
(V), the developing potential is Vb (V), the dielectric constant of the photosensitive layer is εp (C / V · m), and the thickness of the photosensitive layer is dp.
(M) An electrophotographic apparatus characterized by satisfying the following expression (1) when the dielectric constant of the carrier liquid is εt (C / V · m).

(Equation 2) Further, the electrophotographic apparatus of the present invention has a photosensitive layer on which an electrostatic latent image is formed, and a latent image holder for moving the photosensitive layer;
An electrophotographic apparatus comprising: a developing electrode that is arranged with a gap to the latent image holding body, is supplied with a predetermined developing potential, and develops the electrostatic latent image with a liquid developer sandwiched in the gap. The photosensitive layer is made of amorphous silicon, and the absolute value ΔV of the potential change of the potential of the photosensitive layer after development with respect to the potential of the photosensitive layer before development is 10%.
It is not less than V and not more than 100 V.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The electrophotography of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic view showing a wet electrophotographic apparatus having a four-color image forming apparatus as an example of the electrophotographic apparatus of the present invention, and FIG. 2 is an enlarged view of one of the four colors. The figure is shown.

The latent image carrier 1 is formed by forming a photosensitive layer 1-2 made of an inorganic photosensitive material such as amorphous silicon on the surface of a conductive substrate 1-1 such as aluminum.
For example, the conductive substrate 1-1 shown in FIG. 1 has a drum shape, and the photosensitive layer 1-2 is moved by rotating the drum-shaped conductive substrate 1-1 (rightward in FIG. 1) (see FIG. 1). 2 (right direction). The surface potential is set to 0 by grounding the conductive substrate 1-1.

The moving speed of the photosensitive layer 1-2 is, for example, 50 m
The speed is set to about / m or more and about 220 m / sec or less. When the moving speed of the photosensitive layer becomes slow, the image forming speed becomes slow.

The thickness of the photosensitive layer is usually 20 μm or more and 70 μm or more.
m or less is used. Photosensitive layer thickness is 20μ
If it is smaller than m, it is difficult to sufficiently charge the photosensitive layer surface, and if it is larger than 70 μm, dark decay causes
Since the loss of the charged electric charge becomes large, it becomes difficult to form a stable electrostatic latent image having a different charge ratio on the surface of the photoconductor.

Around the latent image holding member 1, first to fourth image forming apparatuses A to D, a transfer device 5, and a cleaning device 8 are sequentially arranged from the upstream side in the rotation direction of the latent image holding member.

As shown in FIG. 2, the image forming apparatus includes a charging device 2, an exposing device 3, and a developing device 4.

As the charging device 2, a known charging device such as a scotron charger or a scorotron charger can be used, and the surface of the latent image holding member 1 is charged to a potential V1, for example, 5 by the charging device 2.
It is uniformly charged between 00 V and 1000 V.

The exposure device 3 includes a laser optical system device and an LE
D or the like can be used. By selectively irradiating the surface of the latent image holding member 1 with light from the exposure device 3 in accordance with image information, the light-irradiated portion is selectively exposed to a potential V0, for example, 2
Attenuate from 0 V to 200 V (| V1 |> | V
0 |). As a result, on the surface of the latent image holding member 1, an electrostatic latent image composed of a portion at the potential V1 and a portion at the potential V0 is formed.

The developing device 4 is disposed at a predetermined distance from the latent image holding member 1, and has a developing potential Vb (| V0 | <|
Vb | <| V1 |), for example, a developing electrode 4-1 to which a potential of 400 V or more and 650 V or less is supplied.

A liquid developer 4-2 is supplied to a gap between the developing electrode 4-1 and the latent image holding member 1, and a developing electrode 4-1 is provided between the developing electrode 4-1 and the latent image holding member 1. The liquid developer 4-2 is held by the surface tension between the image developer 1 and the latent image holder 1. That is, as shown in FIG. 2, a layer of the liquid developer 4-2 having a predetermined width E is formed in the gap between the developing electrode 4-1 and the latent image holding member 1. The liquid developer 4-2 is obtained by dispersing about 1% by weight of toner particles in a carrier liquid. If toner particles charged to the same polarity as the charge of the latent image holding member are used, the liquid developer Ions having a polarity opposite to that of the toner particles (counter ion) are imparted to the impurities.

On the other hand, during the time when the electrostatic latent image passes through the area having the width E, the electrostatic latent image is subjected to development, and the toner particles in the liquid developer 4-2 are electrophoresed according to the surface potential of the latent image holding member 1. And
As a result, a toner image is formed (hereinafter, a region where a liquid developer layer having a width E is formed is referred to as a development region). Specifically, at the portion where the surface potential of the latent image holding member 1 is V0, the toner particles electrophores toward the latent image holding member 1, and at the portion where the surface potential of the latent image holding member 1 is V1, the toner particles are not charged with the latent image. Body 1
Move away from. That is, the portion of the potential V0 is a portion where the toner particles of the electrostatic latent image are selectively attached. The time during which the electrostatic latent image is subjected to development can be determined from the measured value of the surface speed of the latent image holding member and the width E of the development area.

The method of supplying the liquid developer 4-2 to the development area is not particularly limited. For example, the developing device shown in FIG.
A roller-shaped developing electrode (hereinafter referred to as a developing roller) 4-1 is used, and the developing roller 4-1 is arranged so as to be in contact with the liquid developer 4-2 stored in the developing device 4-3. By rotating the developing roller 4-1, the liquid developer 4-2 stored in the developing device 4-3 is transported to the developing area.
Supply. Alternatively, the liquid developer may be supplied to the surface of the developing roller using a supply nozzle or the like, or a supply nozzle may be used between the plate-like development electrode and the latent image holding member using a plate-like development electrode. May directly supply the liquid developer.

The gap between the developing electrode and the photosensitive layer is usually 50
The thickness is set to be not less than μm and not more than 200 μm. It is difficult to stably make the gap between the moving photosensitive layer and the developing electrode smaller than 50 μm. If the gap is made larger than 200 μm, the electric field formed in this gap becomes small, so the electrostatic force acting on the toner particles Is reduced, and an image having a sufficient image density may not be obtained.

The carrier liquid used in the liquid developer is an insulating, non-polar material, and if a material having low harmfulness is selected, a material having a degree of 2ε0 or more and 4ε0 or less (00 is a dielectric constant of vacuum) is used. Become.

The image forming apparatuses A to D may have the same other conditions except that toner particles of different colors are used. In addition, the charging potential, the exposure amount, The development potential and the like may be adjusted to different conditions according to, for example, the charging characteristics of the toner particles before use.

The toner images developed on the surface of the latent image carrier 1 by the image forming apparatuses A to D are transferred to a recording medium such as a sheet by a transfer device as shown in FIG.
A transfer device 5 shown in FIG. 1 has an elastic layer on the surface, and an intermediate transfer roller 6 arranged by pressing the elastic layer against the latent image holding member 1, and a pressurizing member pressed against the intermediate transfer roller 6. And a roller 7. The toner image formed on the surface of the latent image holding member 1 is temporarily transferred to an intermediate transfer roller using the adhesive force of the toner particles. The toner image transferred to the intermediate transfer roller is transferred to the sheet 9 supplied between the intermediate transfer roller 6 and the pressure roller 7 by using the adhesive force of the toner particles.

The transfer from the latent image holding member 1 to the intermediate transfer roller 6 or the transfer from the intermediate transfer roller 6 to the paper may be performed by using electrostatic force in addition to the adhesive force of the toner. In this case, an electric field in a predetermined direction may be formed between the latent image holding member 1 and the intermediate transfer roller 6 or between the intermediate transfer roller 6 and the pressure roller 7. The transfer using electrostatic force includes, for example, a method in which a toner image is electrophoresed in a carrier liquid.

Further, the image may be directly transferred from the surface of the latent image holding member to the sheet without using the intermediate transfer roller.

After transferring the toner image from the latent image holding member 1,
Since a part of the toner particles forming the toner image may remain on the surface of the latent image holding member 1, the cleaning device 8 is disposed as necessary to remove the residual toner on the surface of the latent image holding member 1. You may.

The present inventors have studied an apparatus design for obtaining a high-quality image with sufficient image density and no image collapse when forming an image using such an electrophotographic apparatus. Was. In particular, focusing on material properties and process conditions in the development process, the dielectric constant of the photoconductor,
Process parameters such as the thickness of the photoconductor, the dielectric constant of the developer, the charge amount of the toner particles, and other parameters due to the physical properties of the material, the distance between the developing electrode and the electrostatic latent image holder, and the developing potential were changed. In such a case, the conditions for obtaining a high-quality image were intensively studied.

The potential of the exposed portion of the electrostatic latent image before development is V0 as described above, but when the development is completed, the potential of the exposed portion due to the presence of charged toner particles at the exposed portion is reduced. The potential rises.

If the potential ΔV is large, it indicates that a large amount of toner particles have adhered to the latent image holding member. If the potential ΔV is small, it indicates that a small amount of toner particles have adhered. In the description of the embodiment of the present invention, a case is described in which the photosensitive member is positively charged and the toner also uses the positively charged toner. At this time, ΔV is a positive value. On the other hand, when the photosensitive member is negatively charged and negatively charged toner is used, ΔV also takes a negative value, so it is necessary to consider ΔV as the absolute value of the potential change.

The inventors of the present invention have made intensive studies and have found that ΔV which enables formation of an image with sufficient image density without image fogging.
By examining the appropriate value of ΔV and defining various parameters, it becomes possible to provide an electrophotographic apparatus satisfying the appropriate value of ΔV.

The method of calculating ΔV will be described below.

First, the relationship between the electric field E and the potential V at the coordinate x is shown by the Maxwell equation shown in the equation (2), and by integrating this, the potential difference between two points x = A and x = B is obtained. V (a) -V (B) is represented as in equation (3).

(Equation 3) Here, the gap between the developing electrode and the photosensitive layer is dt (μm), the potential of the photosensitive layer surface (exposed portion) before development is V 0, the potential rise due to development is ΔV, and the photosensitive layer after development is If the potential difference between the surface potential Vp (Vp = V0 + .DELTA.V) and the developing electrode surface potential (Vb) is shown according to equation (3), it is expressed as equation (4). Further, when equation (4) is solved for .DELTA.V, equation (4) is obtained. It is shown as 5).

(Equation 4) Hereinafter, Equation (5) will be described with various parameters with reference to the drawings.

FIG. 3 is a drawing for explaining the positional relationship between the latent image holding member (exposed portion), the liquid developer and the developing electrode in the vicinity of the developing area, and their physical property values.

As described above, the latent image holding member has a structure in which a photosensitive layer is formed on the surface of a conductive substrate, and a liquid developing member is provided between the developing electrode and the latent image holding member (photosensitive layer). The agent is pinched.

The potential of the grounded conductive substrate is 0, the potential of the exposed portion of the surface of the latent image holding member is attenuated to V0 (V), and the developing electrode is supplied with the potential Vb (V).

The layer thickness of the liquid developer (the distance between the latent image holding member and the developing electrode) is dt (m), and the thickness of the photosensitive layer is dp.
(M). Therefore, when the x-axis is taken in the direction from the developing electrode to the latent image holding member, the distance x from the developing electrode to the photosensitive layer is represented by dt, and the distance x from the conductive substrate to dt + dp.

The dielectric constant of the photosensitive layer is εp (C / V · m), and the dielectric constant of the carrier liquid is εt (C / V · m).
Since the toner particle component in the liquid developer is about 1 wt%, the dielectric constant of the liquid developer can be approximated as εt.

Further, the total charge amount of the toner particles per unit area of the surface of the latent image holding member is represented by σp (C / mm ² ), and the charge amount of the impurities is represented by σn (C / mm ² ).

Further, the electric field inside the photosensitive layer is set to Ep (V /
m), and the electric field on the surface of the photosensitive layer is EM (V / m).

Under these conditions, when the continuous coordinates x are converted into discrete coordinates Δx = dt / M when the distance dt between the developing electrode and the latent image holding member is equally divided by M, the following equation (5) is obtained. When the third term on the right side is transformed into discrete coordinates Δx = dt / M, the following equation (6) is obtained.
Thus, Equation (5) is transformed into Equation (7). Note that M is an integer equal to or greater than 10, and by setting M to a large value, a more accurate ΔV can be obtained.

(Equation 5) Next, Ek and EM will be examined.

When each parameter is as shown above, from the boundary conditions relating to the electric field, the dielectric constant, and the charge density per unit area at a distance x = dt from the developing electrode, the equation (8) is obtained.
Is given, and equation (9) is obtained by solving equation (8) for Ep.

(Equation 6) Further, assuming that the electric field in the liquid developer at a distance x from the developing electrode is Et (V / m), x = 0 to x = dt + d
From the relationship between the line integral of the electric field up to t and the potential difference, Equation (1)
0) is given.

(Equation 7) The continuous coordinate x is defined as the distance dt between the developing electrode and the latent image
When the discrete coordinates Δx = dt / M at the time of equal division are replaced, and the integral of the expression (10) by the continuous coordinates is replaced by the sum by the discrete coordinates, the expression (11) is obtained. Further, E of the equation (11)
By substituting equation (9) into p, equation (12) is obtained.

(Equation 8) Here, in the equation (14) obtained by discretizing the Poisson equation shown in the equation (13), if b = Δx / εt is set, the equation (1) is obtained.
4) is represented by equation (15).

(Equation 9) When E0 is obtained from Expression (15), E0 is expressed by Expression (16) or Expression (17).

(Equation 10) Also, from equation (15), E1 + E2 +.
8) or Equation (19).

[Equation 11] By substituting equation (17) and equation (19) into equation (12), equation (20) is obtained, and Δx = dt / M
And substituting for the transformation, equation (21) is obtained. When equation (21) is further solved for EM, EM is represented by equation (22).

.Sigma.p is represented by .sigma.p = .epsilon.p.V0 / dp + PM..DELTA.x. Since .DELTA.x is .DELTA.x = dt / M, when these are substituted into equation (22), equation (22) becomes equation (23). Indicated by

(Equation 12) Note that Pk (C / m ³ ) and Nk (C / m ³ ) are a continuous equation relating to the charge of the toner particles (24) and a continuous equation relating to the charge of the impurities in the carrier liquid (25).
Can be obtained by performing a numerical analysis by replacing the simultaneous equations of the Poisson equation (26) with the discrete coordinates Δx.

(Equation 13) That is, when Pk and Nk are represented by discrete coordinates, the time t during which the toner particles and the impurities in the carrier liquid are subjected to development.
And k with variables as equations (27) and (28). The charge mobility of the toner particles in the carrier liquid is represented by μp (m ² / V · sec), and the charge mobility of the impurity ions is represented by μn (m ² / V · sec).

[Equation 14] That is, EM and Ek at ΔV represented by equation (7) could be represented by each parameter by equations (23) and (14).

The present inventors have designed the apparatus by changing each parameter and examined the relationship between the potential increase ΔV and the image accuracy. When ΔV is 10 V or more and 100 V or less, a high-accuracy image can be obtained. It was confirmed.

That is, if .DELTA.V is smaller than 10 V, a sufficient image density cannot be obtained, and if .DELTA.V is larger than 100 V, toner particles adhere to a wider area than the exposed portion, causing so-called image collapse.

Further, since the various parameters described above have a correlation with each other, the adjustment of ΔV by the various parameters is restricted. In the experiments of the present inventors, an organic material (usually, , Dielectric constant 2ε0-4
When ε0 is used, ΔV cannot be kept within the range of 10 V or more and 100 V or less, and ΔV becomes 10 V or more and 100 V or less for the first time when amorphous silicon which is a material having a dielectric constant of 10 ε0 or more and 14 ε0 or less is used. It was possible to stay within the range. [Examples] Examples of the present invention will be specifically described below.

Example 1 In this example, a liquid developer in which toner particles obtained by adding a cyan pigment to an acrylic resin were dispersed in a carrier liquid composed of Isopar L (manufactured by Exxon Chemical) as a hydrocarbon solvent was used. Was used.

Here, the average particle size of the toner particles is 0.8 μm.
m, the charge amount was 100 μC / g, the density of the carrier liquid was 0.772 g / cm ³ , and the toner particle concentration in the liquid developer was 2 wt%. From these values, the previous value of Pk for performing development Motomari and 1.54C / m ^3, also from the charge neutrality condition, Nk also becomes 1.54C / m ^3.

The dielectric constant of the carrier liquid is 2.03ε0
(C / V · m), the charge mobility of toner particles in the developer is 4 × 10 ⁻¹⁰ m ² / V · sec, and the charge mobility of impurities is 2 × 10 ⁻¹⁰ m ² / V · sec. And a photosensitive layer having a dielectric constant of 12ε0 (C / V · m) and a film thickness of 30 μm.
m latent image holding member using an amorphous silicon material was used.

First, the surface of the photosensitive layer is charged by using a scorotron charger so that the surface potential of the photosensitive layer becomes 750 V. Then, the surface of the photosensitive layer is subjected to selective exposure.
The voltage was lowered to 00 V to form an electrostatic latent image. The shape of the exposed portion was a linear shape having a width of 600 μm, and three exposed portions of this linear shape were formed at intervals of 180 μm.

Therefore, the potential supplied to the developing electrode is set to 600
V, the liquid developer was supplied with the distance between the photosensitive layer and the developing electrode set to 150 μm, and the developing time was 50 msec determined from the measured values of the developing area and the moving speed of the photosensitive layer.
Liquid development was performed under the following conditions.

Under this condition, ΔV shown in the above equation (7) is 71.1V.

Under the developing conditions, an image formed on the surface of the photosensitive layer was observed, and the amount of toner particles on the surface of the photosensitive layer was measured. As a result, it was found that 0.92 g / m ² of toner particles had adhered. Image density could be obtained. FIG. 4 shows an enlarged view of the image at this time. As shown in FIG. 4, an image faithful to the electrostatic latent image was formed, and no deterioration in image quality due to image collapse was observed.

Example 2 The same procedure as in Example 1 was carried out except that ΔV was adjusted within the range of 10 V to 100 V by changing the thickness of the photosensitive layer, the distance between the developing electrode and the photosensitive layer, and the developing potential. To form an image, and the obtained image was evaluated.

When ΔV was in the range of 10 V or more and 100 V or less, three lines in the image could be confirmed as independent lines.

FIG. 5 shows the relationship between ΔV and image density.
When ΔV was 10 V or more, a sufficient image density was obtained.

Comparative Example 1 The developing bias voltage was set to 200 V, and ΔV was set to 8.4 V.
The image formation was performed under the same conditions as in Example 1 except that the above conditions were adopted.

When the image was evaluated in the same manner as in Example 1, the amount of toner particles per unit area of the photosensitive layer surface was 0.22 g / m ² as shown in FIG.
Was significantly lower than the image density when it was between 10 V and 100 V.

Comparative Example 2 The developing bias voltage was set to 1200 V, and ΔV was set to 13
An image was formed under the same conditions as in Example 1 except that the voltage was changed to 7.2 V.

When the image was evaluated in the same manner as in Example 1, the development amount per unit area was 1.24 g / m 2.
² , which indicates that a sufficient image density was obtained.

However, when the obtained image was observed, an image in which three lines were overlapped due to image collapse was found. FIG. 6 shows an enlarged view of the image obtained in Comparative Example 2.

Comparative Example 3 An image was formed in the same manner as in Example 1 except that an organic material having a layer thickness of 25 μm and a dielectric constant of 3.3ε0 was used as the photosensitive layer. ΔV at this time is 177.3V.

When image evaluation was performed in the same manner as in Example 1, a sufficient image density could be obtained. However, as in Comparative Example 2, an image in which three line drawings overlap due to image collapse was obtained. Was.

[0067]

As described above, according to the present invention, it is possible to form an image with higher precision.

[Brief description of the drawings]

FIG. 1 is a drawing showing an example of an electrophotographic apparatus of the present invention.

FIG. 2 is an enlarged view illustrating an example of an image forming apparatus.

FIG. 3 is a diagram for explaining a configuration near a development area of the image forming apparatus, a positional relationship thereof, and the like.

FIG. 4 is an enlarged view of an image obtained in Example 1.

FIG. 5 is a diagram showing a relationship between ΔV and image density.

FIG. 6 is an enlarged view of an image obtained in Comparative Example 2.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Latent image holder 1-1 ... Conductive drum 1-2 ... Photosensitive layer 2 ... Charger 3 ... Exposure device 4 ... Developing device 4-1 ... Developing electrode 4-2 ... Liquid developer 4-3 ... Developing device 5 Transfer device 8 Cleaner 9 Paper

Claims (1)

[Claims] A latent image holding member having a photosensitive layer on which an electrostatic latent image is formed; a latent image holding member disposed with a gap between the latent image holding member and a predetermined developing potential; And a developing electrode for selectively adhering toner particles in the liquid developer to the surface of the electrostatic latent image according to the electrostatic latent image, wherein the developing device sandwiches the latent image holding member and the developing electrode. Where dt (m) is the film thickness of the liquid developer to be obtained, and position coordinates dt × in the film thickness direction of the liquid developer when the origin is the developing electrode surface.
k / M (M is an integer of 10 or more, k is 0, 1, 2, 3,...
In M), the charge mobility of the toner particles per unit volume determined from the charge mobility of the toner particles contained in the liquid developer and the time during which the liquid developer is subjected to the development. The total amount is Pk (C / m ³ ), the charge mobility of an impurity having a counter ion contained in the liquid developer at the position coordinates dt × k / M, and the liquid developer is subjected to the development. Nk (C / m ³ ), the total amount of charge of the impurity per unit volume obtained from time, V0 (V), the potential of the portion of the electrostatic latent image to which the toner particles are selectively adhered, The developing potential is Vb (V), the dielectric constant of the photosensitive layer is εp (C / V · m), the thickness of the photosensitive layer is dp (m), and the dielectric constant of the carrier liquid is εt (C / V · m). ), Where the following formula (1) is satisfied. Child-photographic apparatus. (Equation 1)