JPH04462A - Electrophotographic image forming device - Google Patents

Abstract

PURPOSE:To obtain an electrophotographic image forming device which corrects the fluctuation of a surface potential with high accuracy and forms a stable image by controlling an electrostatic charging voltage based on the correction value of the specified electrostatic charging voltage which is stored by a control means in the case of forming the image. CONSTITUTION:The surface of a photosensitive body 34A is electrostatically charged by a corona charger 35 immediately after the device starts, and two or more surface potentials at the point of time when a specified time elapses are detected by a surface potential sensor 32. A host CPU 22 calculates the dark attenuation characteristic curve of the surface based on the obtained plural surface potential data and calculates the surface potential at the time of developing from the curve. Then, it compares the obtained surface potential at the time of developing with the target surface potential at the time of developing, decides the correction value of the electrostatic charging voltage and stores it in a memory 15. Thus, the CPU 22 controls the electrostatic charging voltage based on the correction value of the electrostatic charging voltage stored in the memory 15 at the time of forming the image. Therefore, the fluctuation of the surface potential caused by the dark attenuation characteristic of the photosensitive body is corrected with high accuracy and the stable image is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrophotographic image forming apparatus that forms an electrostatic latent image on the surface of a photoreceptor and forms a toner image using this electrostatic latent image.

[Prior art]

Conventionally, electrophotographic image forming apparatuses have been applied to many copying machines, printers, etc. due to their simplicity, high speed, and low cost. In particular, wet-type electrophotographic image forming apparatuses have higher resolution than dry-type electrophotographic image forming apparatuses, and are therefore known to be suitable for electrophotographic image forming apparatuses that require high image quality.

In addition, when applying the above-mentioned wet electrophotographic image forming apparatus to fields that require extremely high image quality, such as commercial printing proofs, it is necessary to produce uniform and stable static images over a large area of at least A3 size or larger. It is necessary to form an electrolatent image and a toner image.

[Problem to be solved by the invention]

However, in the photoreceptors used in the above-mentioned electrophotographic image forming apparatuses, development The surface potential of the photoreceptor changes slightly at the time. For this reason, it has been extremely difficult to obtain stable images. In addition, fluctuations in the surface potential of the photoreceptor due to the dark decay characteristics of the photoreceptor can be corrected by conventional methods such as correction of charging voltage variations among electrophotographic image forming apparatuses, and environmental fluctuations (temperature fluctuations and humidity fluctuations). ), there is a problem in that it cannot be sufficiently improved by correcting the charging voltage or the like.

The present invention has been made in consideration of the above facts, and an object of the present invention is to obtain an electrophotographic image forming apparatus that can highly accurately correct fluctuations in surface potential due to the dark decay characteristics of a photoreceptor and can form stable images. be.

[Means to solve the problem]

The electrophotographic image forming apparatus according to the present invention forms an electrostatic latent image on the surface of a photoreceptor and forms a toner image using the electrostatic latent image, and a charging means for charging; a surface potential detection means disposed at a position facing the surface of the photoreceptor for detecting the surface potential of the photoreceptor; At least two or more surface potentials at the same position on the surface of the photoconductor are extracted, a dark decay characteristic curve of the photoconductor surface is calculated, and a surface potential during development is calculated from the calculated dark decay characteristic curve. a calculation means for determining a charging voltage correction value by comparing the surface potential at the time of development and a target surface potential at the time of development; a storage means for storing the charging voltage correction value determined by the calculation means; The present invention is characterized in that a charging voltage control means is provided for controlling the charging voltage during image formation based on the correction value of the charging voltage stored in the storage means.

[Effect]

According to the above means, at a predetermined timing by the charging means,
For example, the surface of the photoreceptor is charged immediately after the apparatus is started up, and the surface potential of the charged photoreceptor is detected by a surface potential detection means at least two predetermined times after charging. Next, a dark decay characteristic curve of the surface of the photoreceptor is calculated from the plurality of detected surface potential data, and a surface potential during development is calculated from the calculated dark decay characteristic curve,
The calculated surface potential during development is compared with the target surface potential during development to determine a charging voltage correction value, and this charging voltage correction value is stored in the storage means. Accordingly, during image formation, the charging voltage control means controls the charging voltage based on the charging voltage correction value stored in the storage means.

Therefore, variations in surface potential due to the dark decay characteristics of the photoreceptor can be corrected with high precision, and stable images can be formed.

Note that by arranging a plurality of surface potential detection means, the time required to extract at least two or more surface potentials at the same position on the surface of the photoreceptor can be shortened.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a layout diagram of each processing section constituting a wet-type electrophotographic image forming apparatus as an electrophotographic image forming apparatus according to an embodiment of the present invention.

Exposure section 10 forming part of a wet electrophotographic image forming apparatus
is connected to a semiconductor laser 12, a control unit 14 for controlling the output state of the semiconductor laser 12, a condenser lens 16.26, a scanning lens 28, a reflection mirror 24.30, and a buffer 19, and receives the incident laser beam. It records image information supplied from a multi-AOM (acousto-optic modulator) 18 that divides the ultrasound into a plurality of parts according to the frequency of the ultrasound, a polygon mirror 20, and a host computer 22 that serves as calculation means and charging voltage control means. photosensitive drum 3
A memory 15 as a storage means that stores a correction value of the charging voltage for correcting the dark decay characteristic of the photoreceptor 34A on the outer peripheral surface of No. 4.
It is made up of.

As the semiconductor laser 12, for example, Al-Ga-A
s laser can be used. A laser beam emitted from the semiconductor laser 12 is irradiated onto the multi-AOM 18 via a condensing lens 16. Further, ultrasonic waves of different frequencies generated according to the image information stored in the memory 15 are supplied to the multi-AOM 18. This causes the laser beam to be diffracted in different directions depending on the frequency of the ultrasound.

This laser beam is condensed by a condensing lens 26, and is further incident on a polygon mirror 20 rotating at high speed via a reflection mirror 24. The laser beam reflected by the polygon mirror 20 is sent to the scanning lens 28 and the reflection mirror 3.
0 to the image forming area on the surface of the photosensitive drum 34. In this embodiment, since a multi-AOM is used, a plurality of (eg, eight) laser beams are scanned simultaneously.

The photosensitive drum 34 is connected to a drive means (not shown), and is rotated clockwise in FIG. 1 (in the direction of the arrow in FIG. 1) by this drive means. Further, the rotation angle of the photosensitive drum 34 (the rotational position of the photosensitive drum 34 from the home position) is detected by a well-known photosensitive drum rotational position detection device, and is manually input to the host computer 22 at any time.

A photoreceptor 34A is provided on the outer peripheral surface of the photoreceptor drum 34 made of aluminum. As the photoreceptor 34, a well-known organic photoconductor or inorganic photoconductor can be used.

It is also possible to use a dielectric material charged with a charging needle.

Organic photoconductors include a variety of well-known organic photoconductors. Specifically, “Research Disclosure J
(Research Disclosure) Magazine: 10
938 (May 1973 issue, page 61 et seq., an article entitled "Electrophotographic Elements, Materials and Processes").

For example, poly-N-vinylcarbazole 1,4,7-IJ nitrofluorene-
9-one (U.S. Patent No. 3,48
4.237), poly-N-vinylcarbazole sensitized with pyrylium salt dye (Japanese Patent Publication No. 48-25658
No.), an electrophotographic photoreceptor whose main component is an organic pigment (Japanese Patent Application Laid-open No. 49-37543), an electrophotographic photoreceptor whose main component is a eutectic complex consisting of a dye and a resin (Japanese Patent Application Laid-Open No. 47-10735)
No.), an electrophotographic photoreceptor in which copper phthalocyanine is dispersed in a resin (Japanese Patent Publication No. 1667/1983), and the like. Others, Journal of the Society of Electrophotography, Vol. 25, No. 3 (1986), 62-
There are substances listed on page 76.

In addition, as the inorganic photoconductor used in the present invention, [Electro Photography J (rElectro-p
photography J RoM, 5chaffer
(Author, Focal Press (London))
(1975), pages 260 to 374, etc., various inorganic compounds are representative. Specific examples include zinc oxide, zinc sulfide, cadmium sulfide, selenium, selenium-tellurium alloy, selenium-arsenic alloy, selenium-tellurium-arsenic alloy, and the like.

In addition, amorphous silicon can also be used. This amorphous silicon has fast dark decay but can be used repeatedly, so it is suitable for this embodiment.

A corona charger 35 serving as a charging means is disposed upstream in the rotational direction of the photoreceptor at a position where the laser beam is incident on the photoreceptor 34A. This corona charger 35 is equipped with a corona wire and a grid wire, and the corona charger 35 is connected to an AC
and connected to a DCIE source. Further, the corona charger 35 is connected to the host computer 22, and the discharge voltage is controlled by the host computer 22 based on the correction value of the charging voltage stored in the memory 15.

As a result, the photosensitive drum 34 before electrostatic latent image formation is rotated clockwise in FIG. 1 after the surface of the photosensitive member 34A is uniformly charged positively or negatively by the corona charger 35.

Further, as will be described later, by connecting the corona charger 35 to a DC power source and applying a charge having the same polarity as the toner through DC corona discharge, the charge on the toner can be strengthened (precharge).

Further, as will be described later, by connecting the corona charger 35 to an AC power source and performing AC corona discharge, the photoreceptor 34A
The charges on the photoreceptor are neutralized, and the residual potential on the photoreceptor can be removed (static charge removal).

A surface potential sensor 32 serving as surface potential detection means is disposed downstream of the corona charger 35 (on the rotational direction side of the g-optical drum 34). The surface potential of the photoreceptor 34A can be detected. Further, the surface potential sensor 32 is connected to the host computer 22, and the host computer 22 determines from the surface potential detected by the surface potential sensor 32 at 0 rotation, after 1 rotation, and after 2 rotation of the same measurement point of the photoreceptor 34A. The latter three different surface potentials are extracted, the dark decay characteristic curve of the photoreceptor 34A is calculated, and the surface potential during development is calculated from the calculated dark decay characteristic curve. Determine the charging voltage correction value by comparing it with the target surface potential during development,
The information is stored in the memory 15.

The part of the photoconductor 34A where the laser beam is incident becomes conductive and the charge on the surface disappears, causing the photoconductor 34A to become conductive.
An electrostatic latent image is formed on the surface of 4A.

As shown in FIG. 1, an exposure lamp 11 is located downstream of the surface potential sensor 32 (on the rotational direction side of the photosensitive drum 34).
is located. The light from this exposure lamp 11 is applied to the photoreceptor 3.
By irradiating the photoreceptor 34A with the photoreceptor 34A, the charges on the photoreceptor 34A can be neutralized (photostatic charge removal). This optical charge removal has the same function as the charge removal by the corona charger 35, and can perform pre-exposure to improve the transfer efficiency of the toner attached to the photoreceptor 34A, as will be described later.

As shown in FIG.
A pre-wet device 50 is provided downstream of the position where the light is incident (on the rotational direction side of the photosensitive drum 34 with respect to the incident position). This pre-wetting device 50 is adapted to apply a carrier liquid, which is a dispersion medium for liquid developer, for the purpose of preventing toner from adhering to non-image areas and improving transferability of toner images onto a transfer material.

A developer unit 36 is arranged downstream of the pre-wet device 50 (on the rotational direction side of the photosensitive drum 34).

The developer unit 36 includes a box with an open top, and a liquid developer 38 is housed in the box. This liquid developer 38 has four types of toner particle colors: black, yellow magenta, and cyan. This liquid developer 38 can be a known developer, for example,
424, Special Publication No. 50-40017, Special Publication No. 49-986
34, JP 58-129438, JP 61-180
248, Fundamentals and Applications of Electrophotography Technology (Electrophotography Technology Edition,
Examples include the developer disclosed in Corona Co., Ltd. (1988).

These liquid developers generally include a carrier liquid, a colorant that forms toner particles, a coating agent made of a polymeric resin that provides fixation properties for the colorant, and a coating agent that promotes the dispersion of toner particles and works to stabilize the dispersion. It consists of a dispersant to control the polarity and charge amount of the toner particles, and a charge control agent to control the polarity and charge amount of the toner particles.

As the coating agent, various known resins can be used, but in particular, Japanese Patent Application Laid-Open No. 61-180248 and Japanese Patent Application No. 63-4
1272, copolymers of ethylene and (meth)acrylic acid, copolymers of ethylene and vinyl acetate, copolymers of ethylene and ethyl acrylate, and ethylene and (meth)acrylic acid esters disclosed in Japanese Patent Application No. 63-41273. Ethylene-based copolymers such as a copolymer of , a terpolymer of ethylene/(meth)acrylic acid/(meth)acrylic acid ester are preferred. The amount of toner particles in the developer is not particularly limited, but is 0.1 to 200 g/l per 1β of the developer.

(i.e. 1g of toner particles/5~100OO of carrier liquid)
Becomes CC. ) Various known charge control agents can be used, and their weight concentration is 0.01 to 10 g per 1β of the developer.
, preferably 0.01 to 1 g.

Further, various known dispersants can be used, and the weight concentration thereof is 0.0 to 50 g, preferably 0.1 to 10 g, per developer 11.

A plurality of developing rollers 40 are arranged in the developer unit 36 and extend in the axial direction of the photosensitive drum 34 and correspond to the image forming area of the photosensitive member 34A. This developing roller 4
A part of the outer circumferential surface of 0 is immersed in liquid developer 38.

These developing rollers 40 are rotated by a drive mechanism (not shown).

Further, the developing roller 40 is moved by a mechanism (not shown) from a position where the developing roller 40 is away from the image forming area to a position where it contacts the image forming area (see FIG. 1), and the liquid developer 38 is moved through the developing roller 40. It is designed so that it can be applied to the image forming area. Further, the developing roller 40 is moved from the contact state to a state away from the image forming area (movement in the direction of arrow B in FIG. 1) by a mechanism not shown. By changing the type of developer unit 36 through this movement, four types of coloring can be achieved.

A squeeze device 41 having an air jet section 41A extending in the axial direction of the photosensitive drum 34 and facing the image forming area is disposed on the side of the developer unit 36 in the rotational direction of the photosensitive drum 34. The excess liquid developer 38 supplied to the tank is removed and discharged to a waste liquid tank.

A squeeze device 4 extending in the axial direction of the photosensitive drum 34 is provided on the downstream side of the squeeze device 41 in the rotational direction of the photosensitive drum 34.
3 is placed. The squeeze device 43 has an air jet section 4.
3A is formed, and a liquid developer discharge path 43B, ! is formed across the air jetting portion 43A. A liquid outlet passage 43C is formed.

These air jetting portions 43A1, liquid developer discharge path 43B,
! The liquid output path 43C extends in the axial direction of the photosensitive drum 34 and faces the image forming area. The liquid developer discharge path 43B and the liquid developer discharge path 43C are connected to a waste liquid tank (not shown), and the air jetted from the air jetting portion 43A onto the excess liquid developer and rinse liquid attached to the photoreceptor 34A. is sprayed, and the liquid developer and rinse liquid are discharged to the waste liquid tank through the liquid developer discharge passage 43B and the rinse liquid discharge passage 43C, respectively.

A rinse liquid unit 42 is arranged downstream of the squeeze device 43 in the rotational direction of the photosensitive drum 34 . The rinsing liquid unit 42 includes a box with an open top. A rinsing liquid 44 is contained in this box. As the rinsing liquid 44, a non-polar non-aqueous solvent having an electrical resistance of 1×10 9 Ω·0 m or more and a dielectric constant of 3 or less can be used.

Examples of the non-aqueous solvent include solvents such as linear or branched aliphatic hydrocarbons, aliphatic hydrocarbons, aromatic hydrocarbons, and halogenated hydrocarbons, but there are concerns regarding volatility, safety, odor, etc. In terms of octane, isooctane, decane,
Isopar E1 Isopar G1 Isopar H1 Isopar L (Isopar rIso
per J is the product name of Exxon), Tsurpets 100
, Shell Silua 1 (manufactured by Shell), etc. are suitable.

A plurality of rinse rollers 46 are arranged in the rinse liquid unit 42 so as to face the image forming area and extend in the axial direction of the photosensitive drum 34 . A portion of the outer peripheral surface of this rinse roller 46 is immersed in the rinse liquid 44. The rinse roller 46 is connected to the rinse roller 4 by a mechanism (not shown).
6 is moved from a position away from the image forming area to a position in contact with the image forming area shown in FIG.
can be applied to the image forming area via a rinse roller 46.

Further, the rinse roller 46 is moved by a mechanism (not shown) from the contact state to a state away from the image forming area (the first
(movement in the direction of arrow C in the figure).

Further, the rinse roller 46 is brought into contact with the image forming area during development processing and is moved away from the image forming area by a mechanism not shown.

A squeeze device 62 is disposed downstream of the rinsing liquid unit 42 (on the rotational direction side of the photosensitive drum 34) and has an air jetting section 62A that extends in the axial direction of the photosensitive drum 34 and faces the image forming area. The rinsing liquid supplied to the image forming area is removed from the image forming area by the air ejected from the air ejecting portion 62A and is guided to a waste liquid tank (not shown).

An exhaust duct 66 that constitutes a part of the drying processing section 64 is arranged downstream of the squeeze device 62 (on the rotational direction side of the photosensitive drum 34). The exhaust duct 66 has an arc-shaped opening 66B having a radius of curvature equal to the distance between the photoreceptor 34A and the photoreceptor 34A on the side facing the photoreceptor 34A.

Further, on the downstream side of the exhaust duct 66 in the drum rotation direction, there is an intake chamber 6 that constitutes the drying processing section 64 together with the exhaust duct 66.
8 is placed.

The side of this intake chamber 68 opposite to the photosensitive drum 34 is connected to a blower (not shown), and the side of the photosensitive drum 34 is connected to an exhaust duct 66.
It faces the air inlet opening 66A on the downstream side. Air sent from the air inlet opening 66A (arrow W in FIG. 1) passes through the opening 66B and is blown onto the photoreceptor 34A, thereby drying the wet photoreceptor 34A.

The air sent to the photoreceptor 34 is discharged to the outside of the apparatus via the air discharge port 66C.

A transfer unit 70 is arranged downstream of the intake chamber 68 (on the rotational direction side of the photosensitive drum 34). The transfer section 70 is moved by a drive mechanism (not shown) in the direction toward and away from the outer periphery of the photoreceptor 34A (in the direction of the arrow in FIG. 1).

A pair of transfer rollers 72 extending in the axial direction of the photosensitive drum 34 are provided in the transfer section 70 in close proximity to the photosensitive member 34A. A transfer guide 74 extending in a direction away from the photosensitive drum 34 is arranged above the transfer rollers 72 . The transfer guide 74 includes a tray 7 for storing transfer materials.
The transfer material set on the tray 75 is guided by a transfer guide 74, reaches a position where it is held between the transfer roller 72 and the photoreceptor 34A, and is transferred.

A cleaning section 76 is arranged downstream of the transfer roller 72 (on the rotational direction side of the photosensitive drum 34), and on the downstream side of the cleaning section 76 (on the rotational direction side of the photosensitive drum 34).
A cleaning brush 77 is arranged. The cleaning section 76 is equipped with a take-up roller 78 and a web roller 79. A cleaning web 82 made of nonwoven fabric or the like is wound around the take-up roller 78 and the web roller 79.

Further, the cleaning section 76 is provided with a cleaning roller 84 having a plurality of through holes 84A formed therein so as to extend in the axial direction of the photosensitive drum 34.

This cleaning roller 84 has the above-mentioned isopar G.
Contains a carrier liquid such as This cleaning roller 84 is wound around the middle part of the cleaning web 82. The cleaning roller 84 faces the image forming area via the cleaning web 82. The cleaning unit 76 is moved by a drive mechanism (not shown) in a direction in which it comes into contact with the outer peripheral surface of the photoreceptor 34A and in a direction in which it separates (in the direction of arrow G in FIG. 1).

In the cleaning process, the cleaning roller 84 is driven by the mechanism described above to a position close to the photoreceptor 34A, and the cleaning web 82 comes into contact with the photoreceptor 34A. The cleaning web 82 is also wound clockwise by the take-up roller 78. The cleaning roller 84 is rotated clockwise following the winding operation, and with this rotation, the carrier liquid flows out from the through hole 84A, and the portion of the cleaning web 82 penetrated by the carrier liquid is attached to the photoreceptor 34A. By sliding along the surface, residual toner etc. after transfer are removed.

A cleaning brush 77 is arranged downstream of the cleaning section 76 (on the rotational direction side of the photosensitive drum 34). The cleaning brush 77 is constructed by planting a large amount of animal hair on the cylindrical surface of a cylindrical body, extends in the axial direction of the photosensitive drum 34, and is brushed against the outer circumferential surface of the photosensitive member 3'4A by a drive mechanism (not shown). It is moved in the contact direction and the separation direction (direction of arrow H in FIG. 1). In a cleaning step to be described later, a cleaning brush 77 is slid along the surface of the photoreceptor 34A to remove foreign matter attached to the photoreceptor 34A without disturbing the toner image formed on the photoreceptor 34A.

The operation of this embodiment will be explained below.

In this embodiment, by providing a non-image area on the photoreceptor drum 34 as shown in FIG. Potential measurement is being carried out.

First, a blank image is formed, and then yellow, magenta, and cyan images are formed on top of the black image. Further, in this embodiment, a developer containing negatively charged toner particles is used.

First, a case will be described in which a blank image is formed on the photoreceptor 34A. Image information of the image to be copied is supplied from the host computer 22.

By turning on a start switch (not shown) or by receiving a start signal from outside, the photosensitive drum 34 is rotated clockwise in FIG. The top of the photoreceptor 34A is positively charged (Charging in FIG. 5(A)). In this case, the discharge voltage of the corona charger 35 is controlled by the host computer 22, which will be described later, based on a charging voltage correction value (Dl) stored in the memory 15. Therefore, a decrease in the surface potential of the photoreceptor 34A during development can be corrected with high accuracy. Therefore, a stable image can be formed in the development process described later.

The surface potential at the measurement point of the photoreceptor 34A is detected by the surface potential sensor 32, and the surface potential (EO) at the measurement point immediately after charging shown in FIG. 2 is read into the host computer 22.

When the image forming portion of the photoreceptor 34A, whose surface is uniformly and positively charged, is positioned at the exposure position, the laser beam emitted from the semiconductor laser 12 is modulated according to image information, thereby exposing the photoreceptor 34A to an image. (Figure 5 (A) exposure).

When the surface of the photoreceptor 34A is imagewise exposed, the portion irradiated with the laser beam becomes conductive, and the positive charges on the surface move to form an electrostatic latent image corresponding to image information.

Note that the non-image area for surface potential measurement is not exposed to light and remains charged.

The photoreceptor 34A, on which the electrostatic latent image is formed, is further
The photoreceptor 3 is rotated clockwise in the figure, and the pre-wet device 50
The carrier liquid is uniformly applied to the surface of 4A.

The pre-wet portion of the photoreceptor 34A further rotates clockwise in FIG. 1 and reaches a position corresponding to the developer unit 36. In this case, a developer unit 36 containing a liquid developer containing black toner particles is arranged in advance. This developer unit 36 applies a liquid developer containing black toner particles to the area where the electrostatic latent image is formed via a developing roller 40 (FIG. 5(A) development).
.

As a result, negatively charged toner particles in the developer adhere to the image area where the electrostatic latent image is formed, and the electrostatic latent image is visualized, resulting in a toner image corresponding to the image area or non-image area. is formed (FIG. 6(A)).

The portion of the photoreceptor 34A on which the toner image is formed further rotates clockwise in FIG. 1 and reaches a position corresponding to the squeeze device 41. The area where the toner image is formed is squeezed by being blown with air ejected from the air ejection section 41A, thereby guiding the excess liquid developer 38 to a tank (not shown) (FIG. 5(A) Squeeze 1).

The portion of the photoreceptor 34 on which the toner image is formed further rotates clockwise in FIG. 1 and reaches a position corresponding to the rinse liquid unit 42 filled with the rinse liquid 44. Photoreceptor 34
A rinsing liquid 44 is supplied to the surface of the photoconductor 34A via a rinsing roller 46, and the developer containing unnecessary toner particles adhering to areas of the photoreceptor 34A other than the image area to which the toner should adhere is washed away (see Fig. 5). (A) Rinse).

The excess rinsing liquid 44 supplied to the photoconductor 34A is flowed downstream along the outer peripheral surface of the photoconductor 34A, but is removed from the surface of the photoconductor 34A by air jetted from the air jet section 43A of the squeeze device 42. and the discharge path 43C
is discharged to a waste liquid tank (not shown) via the
A) Squeeze 2).

The photoreceptor 34A further rotates clockwise in FIG. 1 and faces the opening 66A of the exhaust duct 66.

From this opening 66A, dry air supplied from a blower (not shown) is blown onto the surface of the photoreceptor 34A. This dry air dries the moist surface of the photoreceptor 34A (FIG. 5(A) drying).

From this state, the photoreceptor 34A is further rotated clockwise in FIG. 1, and the photoreceptor 34A shifts to the second rotation. In this second cycle, only the drying process is performed (Fig. 5 (B)
dry).

Note that the developing roller 40 is moved at the timing when the non-image forming area formed on the photoreceptor 34A in the first rotation passes through each of the developing, rinsing, transfer, and cleaning processes.
, rinse roller 46, transfer section 70, cleaning section 76
and cleaning brush 77, respectively, as indicated by arrow B in FIG.
C5DSG.

It moves in the H direction and is separated from the photosensitive drum 34.

By the drying performed in the second round, the rinsing liquid and carrier liquid existing between the toner particles forming the electrostatic latent image are evaporated, and the interaction (binding force) between the toner particles is increased.

In the second rotation, at the timing when the non-image area forming area comes under the surface potential sensor 32, the surface potential (El) of the measurement point after the photosensitive drum 34 has made one rotation as in the first rotation is determined.
is read into the host computer 22.

As the photoreceptor 34A rotates around the third rotation, the portion of the photoreceptor 34A facing the corona charger 35 sequentially becomes the corona charger 3.
Static electricity is removed by AC corona discharge by No. 5 (No. 5
Figure (C) Static elimination).

Further, the light emitted from the exposure lamp 11 is supplied to this charge-eliminated portion, and the charge remaining on the photoreceptor 34A after the charge removal is removed (FIG. 5(C) optical charge removal). Thereafter, the drying process is continued until the third rotation is completed.

In the third rotation, the surface potential (E2) at the measurement point after two rotations is read into the host computer 22 at the timing when the non-image forming area comes under the surface potential sensor 32.

The host computer 22 determines the surface potential (EOl) at the three points.
El, E2), the dark decay characteristic curve F of the photoreceptor 34A shown in FIG. 2 is calculated.

Furthermore, according to this dark decay characteristic curve F, the development time (T
1) Calculate the subsequent surface potential (VO), find the ratio (ΔV=V1/VO) between the calculated surface potential (VD> and the target surface potential (Vl) during development, and calculate the charging voltage ( DO) correction value (D1=ΔV·DO) is calculated and stored in the memory 15.

Next, the process moves to the second color (yellow) image formation process (
4th lap). In this second color application process, first, the cleaning brush 77 is moved onto the photoreceptor 3 by a drive mechanism (not shown).
The foreign matter attached to the photoreceptor 34A is removed by sliding along the surface of the photoreceptor 4A (FIG. 5(D) puff). As the photoreceptor 34A rotates, the portion of the photoreceptor 34A from which the foreign matter has been removed is sequentially charged (charging in FIG. 5(D)) and exposed to light (exposure in FIG. 5(D)) in the same manner as described above. , an electrostatic latent image is formed on the photoreceptor 34A.

The charging for the second color is performed based on the charging voltage correction value (Dl) stored in the memory 15 based on the data measured for the first color.

The area on the photoreceptor 34A where the electrostatic latent image is formed is pre-wet (pre-wet in FIG. 5(D)) before the development process in the same way as described above, to prevent toner particles from adhering to the non-image area. After that, the development is performed, and a toner image of yellow toner particles is formed on the photoreceptor 34A, superimposed on the toner image formed of the blank toner particles (FIG. 5(D) Development, Figure 6 (B)). At this time, the developer unit 36 is moved so that the unit containing the developer containing yellow toner comes into contact with the surface of the photoreceptor 34A. Thereafter, the same squeeze 1 (Fig. 5 (D) squeeze 1), rinsing (Fig. 5 (D) rinse), squeeze 2 (Fig. 5 (D) squeeze), and drying treatment (Fig. 5 (D) squeeze) as described above are carried out. (D) Drying) is performed.

Next, in the same way as in the process of applying toner particles of the first color, the photoreceptor 3
Drying is performed during the period of rotation around the fifth circumference of 4A (Drying in Figure 5 (E)), and further, in the sixth rotation, static electricity is removed (Charge removal in Figure 5 (F)) and light exposure (Figure 5 (F)). light exposure) and drying.

In the same way as applying the second color liquid developer, apply the third color (
A liquid developer containing toner particles of magenta is applied. As a result, a toner image of magenta toner particles is formed on the photoreceptor 34A, superimposed on the toner image formed of the yellow toner particles. As a result, three toner layers of black, yellow, and magenta toner particles are formed on the photoreceptor 34A (FIG. 6(C)).

When applying the fourth color (cyan), that is, the last color, use a puff (removal of foreign matter with a cleaning brush) in the same way as when applying the second and third colors (see Figure 5). (G) Puff), charging (Figure 5 (G) Charging), exposure (Figure 5)
After performing pre-wetting (Fig. 5 (G) Pre-wet) and preventing toner particles from adhering to non-image areas, development (Fig. 5 (G) Development) is performed. A toner image of cyan toner particles is formed on the photoreceptor 34A, superimposed on the toner image formed of the magenta toner particles.

As a result, toner layers of four colors, black, yellow, magenta, and cyan, are formed on the photoreceptor 34A. After that, the same squeeze 1 as above (Figure 5 (G) squeeze 1)
, rinsing (Fig. 5 (G) Rinse), squeeze 2 (Fig. 5 (G) Squeeze 2), and drying (Fig. 5 (G) Drying). The above operations are performed while the photosensitive drum 34A rotates once. The drying process is performed during the period in which the photoreceptor 34A is further rotated once in the clockwise direction in FIG. 1 (Drying in FIG. 5(H)). This second and final color rotation is only for drying.

The photoreceptor 34A is further rotated and moves to the third rotation. In this third rotation, first the corona charger 35
An electric charge having the same polarity as that of the toner is applied to the photoreceptor 34A by DC corona discharge caused by the DC corona discharge, resulting in precharging (Fig. 5 (I)).
precharge) is performed.

The portion of the photoreceptor 34A that is not precharged is further
It rotates clockwise in the figure and reaches a position corresponding to the exposure lamp 11. The light emitted from the exposure lamp 11 is applied to the photoreceptor 34A.
and pre-exposure is performed.

The pre-exposed portion of the photoreceptor 34A further rotates clockwise in FIG. 1 and reaches a position corresponding to the pre-wet device 50. As described above, the droplet-shaped carrier liquid is ejected from the pre-wetting device 50 and applied to the pre-exposed area, thereby performing pre-wetting before transfer.

On the other hand, the transfer material guided by the guide 74 to a position where it is sandwiched between the photoconductor 34A and the roller 72 is sandwiched by the portion of the photoconductor 34A where the toner particle layers of the four colors are formed, and the transfer material is A transferred image is formed by the toner layer (FIG. 6(D)). As a result, an original image is formed on the surface of the transfer material.

Further, the photosensitive drum 34A is rotated clockwise in FIG. 1 to proceed to a cleaning process. In this cleaning step, web cleaning and further drying processing are performed to bring the photoreceptor to the initial state before exposure as shown in FIG. 5(A).

Although negatively charged toner particles are used in the above example, positively charged toner particles may also be used. In this case, the photoreceptor 34A is negatively charged.

Further, in the above embodiment, the charging voltage correction value is calculated by the above method at the time of startup of the wet electrophotographic image forming apparatus, or every predetermined period of time after startup, and is stored in the memory 15. However, instead of this, During main rotation for drying the photoreceptor 34 after development,
A correction value for the charging voltage may be calculated using the above method and stored in the memory 15.

In this case, as shown in FIGS. 3 and 4, the photoreceptor 3
The surface potential measurement point 4A (P) is the non-image area 34B (the shaded area in FIGS. 3 and 4) of the photoreceptor 34A.

Further, in the above embodiment, one surface potential sensor 32 is arranged on the downstream side in the rotational direction of the photosensitive drum 34 of the corona charger 35, but instead of this, one surface potential sensor 32 is arranged on a different side opposite to the photosensitive drum 34A. A plurality of surface potential measurement points (
P), the surface potentials at the surface potential measurement points (P) may be read into the host computer 22, respectively.

In addition to the shape shown in FIG. 4, the non-image forming area has the following shapes:
The shape is shown in FIG. 3, and the developing roller 40 and rinse roller 4
6. The same effect can be obtained even if the transfer section 70, the cleaning section 76, and the cleaning brush 77 are configured not to be in pressure contact with each other.

〔Effect of the invention〕

Since the present invention has the above-mentioned configuration, it is possible to accurately correct variations in the surface potential due to the dark decay characteristics of the photoreceptor, and it is possible to obtain an excellent effect that a stable image can be formed.

[Brief explanation of drawings]

FIG. 1 is a layout diagram of each processing section constituting a wet electrophotographic image forming apparatus according to an embodiment of the present invention, and FIG. 2 is a diagram of a photoreceptor of a wet electrophotographic image forming apparatus according to an embodiment of the present invention Graphs showing dark decay characteristics, Figures 3 and 4E! 5(A) to 5(A) are perspective views showing the range of the non-image forming area provided in the area for measuring the surface potential of the photoreceptor of a wet type electrophotographic image forming apparatus according to an embodiment of the present invention; FIG. 5 (J) is an explanatory diagram explaining the operation of the wet electrophotographic image forming apparatus, and FIG.
A) to FIG. 6(D) are cross-sectional views showing the process of forming four-layer images on a photoreceptor. 15...Memory, 22...Host computer, 32...Surface potential sensor, 34...Photosensitive drum, 34A...Photoconductor, 35...Corona charger.

Claims (1)

[Claims] (1) An electrophotographic image forming apparatus that forms an electrostatic latent image on the surface of a photoreceptor and forms a toner image using the electrostatic latent image, the apparatus comprising: a charging means that charges the surface of the photoreceptor at a predetermined timing; a surface potential detection means disposed at a position facing the body surface to detect the surface potential of the photoreceptor; and at least one surface potential at the same position on the photoreceptor surface based on the surface potential of the photoreceptor surface detected by the surface potential detection means. Two or more surface potentials are extracted, a dark decay characteristic curve of the surface of the photoreceptor is calculated, a surface potential during development is calculated from the calculated dark decay characteristic curve, and the calculated surface potential during development and a target are calculated. a calculation means for determining a correction value for the charging voltage by comparing the surface potential during development; a storage means for storing the correction value for the charging voltage determined by the calculation means; and a storage means for storing the correction value for the charging voltage determined by the calculation means; An electrophotographic image forming apparatus comprising: a charging voltage control means for controlling a charging voltage during image formation based on a correction value.