JP2003107928A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of realizing stable transfer even when an image receiving means is deformed in a feeding path. SOLUTION: This image forming device is equipped with a transfer means forming a transfer area while abutting on an image carrier means and having flexibility, the image receiving means which is fed to the transfer area and to which a developer image on the image carrier means is transferred, a 1st feeding means for feeding the image receiving means, a 2nd image receiving means feeding means being a 2nd feeding means for feeding the image receiving means and arranged at a position where the length of the feeding path for the image receiving means from the 1st image receiving means feeding means to the 2nd image receiving means feeding means is shorter than the length of the image receiving means, and a current supply means for supplying a constant current to the transfer means having the flexibility.

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 applied to a copying machine, a facsimile, a printer, etc., and particularly, an image is formed by transferring a developer image formed on an image carrier to an image receiving means. The present invention relates to an image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, there has been an increasing demand for higher image quality, smaller device size, and lower cost for image forming devices using electrophotography.

As a factor that determines the image quality, there is a toner particle size in the electrophotographic system, and in order to form a highly delicate image, there is an increasing tendency to reduce the particle size. With the trend toward smaller particle sizes, the development of polymerized toner is increasing from the viewpoint of easily producing a toner having a small particle size and a narrow particle size distribution.

In recent years, the number of printers and copying machines capable of outputting color images has increased. There is a demand from the market for image output that suppresses image gloss, and in response to this, so-called oilless fixing, in which the mechanism for applying fixing oil to the fixing device is removed, is being developed. However, if the fixing oil is not applied to the fixing device, the toner adheres to the fixing device and the fixability deteriorates.
There is a problem in that the transparency of an image in which a plurality of colors are layered is reduced and it becomes difficult to form an image on an OHP sheet.
In order to solve such a problem, a method is used in which a large amount of wax is dispersed in the toner to improve the releasability and the transparency of the toner at the time of fixing.

On the other hand, there is a transfer device as another factor of the image quality. A corona discharger is a conventionally used transfer device. In the transfer area where the image bearing means such as the photoconductor and the image receiving means such as plain paper or OHP sheet come into contact with each other, corona ions are supplied to the back surface of the image receiving means to form an electric field formed between the image receiving means and the image bearing means. Is a method of electrostatically attracting and transferring the toner on the image carrying means to the image receiving means. However, corona ions are also supplied to the back surface of the image receiving means in the areas before and after the image carrying means plunges into the transfer area, and an electric field is formed in the gap between the image carrying means and the image receiving means. When a strong electric field is formed in the gap before entering the transfer area, the toner on the image carrying means flies toward the image receiving means, and so-called "front fly" toner scattering occurs. Further, when a strong electric field is formed in the gap after passing through the transfer area, the toner once transferred onto the image receiving unit scatters to the surroundings, so-called "backward flying", toner scattering occurs. When the corona discharger is used as a transfer device as described above,
The charge required for transfer is supplied to the back surface of the image receiving means in addition to the transfer area, so that there is a problem that toner scattering occurs.

On the other hand, Japanese Patent Laid-Open Nos. 51-12142 and 51-59636 propose a roller-shaped transfer member, that is, a transfer roller. In the case of the transfer roller, since the transfer can be performed while directly contacting the image carrier, the electric charge is supplied only to the contact area between the image carrier and the transfer member, that is, the transfer area, as compared with the conventional corona discharger. Accordingly, there is an advantage that the above-mentioned toner scattering does not easily occur. However, when a transfer roller is used, it is necessary to bring it into contact with the image carrier with a linear pressure of at least 2.5 kgf / m in order to secure a predetermined transfer area. If the linear pressure is too high, there is a problem in that the center of the thin line formed on the image bearing means is agglomerated and the transfer cannot be performed by electrostatic force, that is, a so-called hollow defect occurs. In particular, when a toner having an average volume particle size of 7 μm or less is used, or when a toner contains a large amount of wax, the cohesive force between the toner particles is increased and the hollow phenomenon becomes remarkable. Therefore, high image quality by reducing the particle size of the toner and output of a color image by the toner containing wax,
There is a problem in that the use of the transfer roller is in the opposite direction. Further, in the case of a transfer roller, a cored bar is provided with an elastic layer for use. With such a structure, when the core bar becomes thin, the warp of the core bar becomes large, which causes uneven pressure contact force in the longitudinal direction of the transfer roller, and in order to realize low pressure contact force, the elastic layer is at least 1.5 mm. From the point that it is necessary to provide the above, it was difficult to downsize the transfer roller. In addition, when using a sponge as the elastic layer, a long-term manufacturing process is required, in which the raw material is molded around the core metal, then foamed, and then left to stand until the electrical resistance stabilizes, which leads to cost reduction. It had a problem that it was difficult.

To solve these problems, Japanese Patent Laid-Open No.
No. 0-229079 and JP-A No. 60-216361, a transfer member having a brush shape, that is, a method using a transfer brush, and a film-shaped transfer member described in JP-A-8-76611. A method using a member, that is, a transfer film has been proposed. When these transfer members are used, it is possible to secure a sufficient transfer area with a low pressure contact force as compared with the transfer roller, so that there is an advantage that the hollow phenomenon does not easily occur. Moreover, since a brush or a film can be attached to a plate-shaped metal member for use, it is suitable for downsizing and cost reduction.

[0008]

However, since the transfer brush and the transfer film come into contact with the image carrying means with a low pressure contact force, they do not have a carrying force for carrying the image receiving means. Therefore, it is necessary to use a registration roller, a fixing device, or the like as a means for conveying the image receiving means. Therefore, it has the following problems.

That is, with the recent miniaturization of the image forming apparatus, the conveyance path of the image receiving means from the registration roller to the fixing device through the transfer area tends to be shortened.
Therefore, the image receiving unit is in the following state during the image forming process.

(1) A state of being sandwiched and conveyed only by the registration rollers (2) A state of being sandwiched and conveyed by both the registration rollers and the fixing device (3) A state of being sandwiched and conveyed only by the fixing device As a result of diligent study by the present inventor among the above-mentioned three types of states, particularly in the state of (2), it is found that the toner scattering state greatly changes at the front end, the center, and the rear end of the image receiving unit. did. It was also found that this tendency becomes more remarkable as the image receiving means having a smaller basis weight. The reason for this is shown below.

That is, the peripheral speeds of the registration roller and the fixing device are different from each other. In particular, since the fixing device uses a roller in which silicon rubber is wrapped around a core metal, it is easily deformed by thermal expansion. Further, since the rubber of low hardness is used, it is difficult to polish the surface, so that it is extremely difficult to improve the dimensional accuracy in the circumferential direction. Therefore, if the rotation speed of the fixing roller is constant, the peripheral speed of the fixing roller changes. Therefore, the image receiving unit in the state (2) takes various postures according to the fluctuation of the peripheral speed of the fixing roller. Especially when the peripheral speed of the fixing device is slower than that of the registration roller, the image receiving means is bent in the conveying path due to the speed difference between the two. Therefore, the transfer means such as a transfer brush or a transfer film which is in contact with the low-pressure contact force is deformed according to the deflection of the image receiving means, and as a result, the contact area between the image carrying means and the transfer means via the image receiving means, that is, the transfer The area changes. This allows
The electric resistance R from the transfer means to the image carrying means via the image receiving means fluctuates, and the charge amount Q supplied to the back surface of the image receiving means also fluctuates. Therefore, the electric field strength E = Q / ε formed between the surface of the image receiving means and the image carrying means changes at the head, center, and rear end of the image receiving means. As a result, it is considered that the state of toner scattering changes significantly.

In order to solve the above phenomenon, it is necessary to change the voltage applied to the transfer means, that is, the transfer voltage according to the attitude of the image receiving means. However, the flexural rigidity of the image receiving means greatly differs depending on the humidity inside the image forming apparatus and the material of the image receiving means, and it is extremely difficult to predict what posture the image receiving means will take in the transport path. Therefore, it is difficult to change the transfer voltage according to the attitude of the image receiving unit in the transport path. Another solution is to match the peripheral speeds of the registration roller and the fixing device. However, it is extremely difficult to precisely process the peripheral surface dimension of the fixing roller wound with low hardness rubber and to maintain a constant dimensional accuracy regardless of the ambient temperature change. Since it is difficult to suppress the fluctuation of the peripheral surface size of the fixing device, it is extremely difficult to match the peripheral speeds of the registration roller and the fixing device even if the rotational speeds of the both are matched.

In view of the above problems, the present invention has a problem that the transfer unevenness or the toner scattering unevenness is caused in the plane of the image receiving means even when a transfer member having a high flexibility such as a transfer brush or a transfer film is used. No image formation is uniform.

[0014]

An image forming apparatus according to the present invention is fixed to an image carrying means for carrying and carrying a developer image and a position facing the image carrying means, and abutting on the image carrying means to transfer the image. A flexible transfer unit that forms an area, an image receiving unit that is conveyed to the transfer region and to which the developer image on the image carrying unit is transferred, and an image receiving unit that is located upstream of the transfer region when viewed from the transfer region. First image receiving means transporting means for transporting the image receiving means, and second image receiving means transporting means for transporting the image receiving means, which is arranged on the downstream side in the image receiving means transporting direction as viewed from the transfer area, A second image receiving means transporting means arranged at a position such that the transporting path length of the image receiving means from the first image receiving means transporting means to the second image receiving means transporting means is shorter than the length of the image receiving means; For transfer means with flexibility A current supply means for supplying a current,
Is to have.

The operation of the present invention will be described with reference to FIG.

FIG. 1 is a sectional view showing the state of the image receiving means in the image forming apparatus for explaining the operation of the present invention, and FIG. 2 is a sectional view in the vicinity of the transfer area. 1 and 2,
Reference numeral 1 is a photoconductor corresponding to an image carrier. Reference numeral 2 is a registration roller corresponding to the first image receiving means conveying means. Reference numeral 3 denotes a transfer unit, which is configured by attaching a film or a brush-shaped flexible member 3b on the support member 3a. 4 is a fixing device corresponding to the second image receiving means conveying means, and 5 is an image receiving means. Further, in FIG. 2, D indicates the width of the transfer area where the transfer means, the image receiving means, and the photoconductor are in contact with each other.

As shown in FIG. 1, when the image receiving means is sandwiched and conveyed by both the registration roller and the fixing device, there is a difference in peripheral speed between the registration roller and the fixing device.
The slack of the image receiving means as shown by the middle arrow A occurs. This slack increases as the time during which the image receiving means is held between the two conveying means increases. As a result, the attitude of the image receiving means changes in the direction of arrow A in FIG. Since the transfer means is in contact with the photoconductor with a low pressure contact force, when the attitude of the image receiving means changes, the transfer means is pressed by the image receiving means and deforms, and as a result, the transfer area width D changes.

Based on the above configuration, the charge Q accumulated on the back surface of the image receiving means will be obtained below. When the constant voltage V is supplied to the transfer means, the time for the image receiving means to pass through the transfer area D is t,
If the current flowing through the transfer means during this period is i, then Q = i · t = V · t / R = V · D · w · t / h · ρ (1) In the formula (1), w is an image receiving means and a transfer means. The width in the lengthwise direction of contact with and, h is the thickness of the image receiving means, and ρ is the volume resistance of the image receiving means. Note that the equation (1) does not consider the resistance component of the toner layer.

When the transport speed of the image receiving means is v, t = D
Since / v holds, the equation (1) becomes Q = V · D ² · w / v · h · ρ (2), and the charge Q is proportional to the square of D.

On the other hand, in the case of applying the constant current according to the present invention, the charge Q is Q = i · t = i · D / v (3), which is proportional to D.

As can be seen by comparing equations (2) and (3), the charge Q accumulated on the back surface of the image receiving means is affected by D. In particular, when a constant voltage is applied, since it is proportional to the square of D, it is easily affected by changes in D. On the other hand, in the case of applying a constant current, since it is proportional to D, the influence of Q on the change of D is smaller than that of applying a constant voltage. As a result, even if the image receiving unit is loosened due to the difference in peripheral speed between the registration roller and the fixing device and the transfer area width D is changed, the influence is suppressed by applying the constant current.

Further, when the transfer means is fixed, rubbing against the image receiving means makes it easy for the contents of the image receiving means such as paper powder and filler to adhere to the surface of the transfer means. When the image receiving means is passed through the paper for a long period of time, these image receiving means-containing substances adhere to the surface of the transfer means. When the fixed image receiving means-containing material acts as an impedance component, in the case of constant voltage application, the voltage between the image receiving means and the image carrying means is reduced by the amount divided by the impedance component of the image receiving means-containing material, As a result, there is a problem that transfer failure occurs. On the other hand, in the present invention, since a constant current is supplied, it is possible to supply a constant charge to the back surface of the image receiving means without affecting the impedance component of the fixed image receiving means-containing material, and thus printing for a long period of time. Even then, stable transfer is possible.

Further, the image forming apparatus of the present invention is fixed to an image carrying means for carrying and carrying a developer image and a position opposed to the image carrying means, and abuts on the image carrying means to form a transfer area. A transfer unit having flexibility, an image receiving unit that is conveyed to the transfer region and to which the developer image on the image carrying unit is transferred, and an image receiving unit that is arranged on the upstream side in the image receiving unit conveyance direction when viewed from the transfer region. A first image receiving means transporting means for transporting the image receiving means and a second image receiving means transporting means for transporting the image receiving means, the second image receiving means transporting means being disposed on the downstream side in the image receiving means transporting direction as viewed from the transfer area. The conveying path length of the image receiving means from the conveying means to the second image receiving means conveying means is
A second image receiving means transporting means arranged at a position shorter than the length of the image receiving means, and the width W of the transfer means having flexibility in the image receiving means transporting direction is W When the contact width between the transfer means and the image carrying means is D, then W> D.

As a result, even if the image receiving means is deformed in the conveying path, the contact area between the image carrying means and the image receiving means or the contact area between the image receiving means and the transfer means is changed only by changing the position of the transfer area. Does not change significantly. Therefore, the amount of charge accumulated on the back surface of the image receiving unit can be constantly stabilized, and as a result, the transfer efficiency and the toner scattering state can be kept uniform over the entire surface of the image receiving unit.

Further, a constant current supply means for supplying a constant current to the transfer means may be provided.

Further, the image forming apparatus of the present invention is fixed to an image carrying means for carrying and carrying a developer image and a position opposed to the image carrying means, and is in contact with the image carrying means to form a transfer area. A transfer unit having flexibility, an image receiving unit that is conveyed to the transfer region and to which the developer image on the image carrying unit is transferred, and an image receiving unit that is arranged on the upstream side in the image receiving unit conveyance direction when viewed from the transfer region. A first image receiving means transporting means for transporting the image receiving means and a second image receiving means transporting means for transporting the image receiving means, the second image receiving means transporting means being disposed on the downstream side in the image receiving means transporting direction as viewed from the transfer area. The conveying path length of the image receiving means from the conveying means to the second image receiving means conveying means is
A second image receiving means conveying means arranged at a position shorter than the length of the image receiving means, wherein the rigidity of the flexible transfer means is lower than the rigidity of the image receiving means. It is what

That is, the plain paper being passed is not only deformed in the direction of the conveying path, but also in the direction orthogonal to the conveying direction of the image receiving means (longitudinal direction of the image carrying means). In particular, plain paper having a small basis weight has a low bending rigidity, and therefore has a large amount of deformation. Further, since the circumferential dimensions of the first and second conveying means are not highly accurate, when the conveying means rotates at a constant rotation speed, a peripheral speed difference is likely to occur in the longitudinal direction of the conveying means. As a result, the image receiving means is easily deformed in the orthogonal direction from the center to the rear end. When the image receiving unit is slightly deformed in the direction orthogonal to the transport path, the transfer unit having flexibility with bending rigidity smaller than that of the image receiving unit is deformed along with the deformation of the image receiving unit. As a result, since the transfer means having flexibility is in close contact with the back surface of the image receiving means, sufficient electric charge for transfer is supplied.
As a result, even if there is a minute gap formed between the image carrying means and the image receiving means due to the deformation of the image receiving means in the conveying path, the uniform transfer is performed on the entire surface of the image receiving means.

The flexural rigidity described above is the same as that defined in material mechanics. That is, when the plate is bending rigidity (per unit area) N = E × I = E × h 3/12,
(However, E: Young's modulus, I: second moment of area, h:
Thickness).

In addition to the above-mentioned invention, a constant current supply means for supplying a constant current to the transfer means may be provided.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration and operation of the image forming apparatus of the present invention will be described below with reference to FIG.

FIG. 3 is a sectional view showing the construction of the image forming apparatus of the present invention.

In FIG. 3, reference numeral 1 denotes a photosensitive drum corresponding to an image bearing means, in which a photosensitive layer is provided on a metal drum. An OPC layer, an a-SiH layer, a selenium layer, or the like is used as the photoreceptor layer. Further, a conductive undercoat layer may be provided between the aluminum tube and the CGL so that scratches or stains on the tube do not affect the charging characteristics of the photoconductor. The diameter of the photosensitive drum is
It is preferably 24 mm or less, and more preferably 16 mm. If the value exceeds the above value, the variation in the electrostatic attraction energy of the image receiving means on the photosensitive drum due to the image pattern,
The separation of the image receiving means from the photosensitive drum is affected, and the separation position of the image receiving means greatly differs depending on the image pattern. As a result, when the transfer means is in contact with the photoconductor drum at a low pressure, variations in the separation position of the image receiving means lead to variations in the transfer area, and the toner scattering state also changes. Further, by using the small-diameter photosensitive drum as described above, it is possible to reduce the voids that are apt to cause “front jump” and “rear jump”. As a result, high-quality transfer with less toner scattering is possible.

Reference numeral 6 is a charging member for charging the surface of the photosensitive drum 1. Although a roller-shaped charging member, a so-called charging roller, is shown in FIG. 3, a scorotron, a brush-shaped charging member, a magnetic brush charging member, a film-shaped charging member, or the like may be used instead. A predetermined DC voltage or a voltage obtained by superimposing an AC voltage on a DC voltage is applied to the charging member.

Reference numeral 7 denotes an exposure source that irradiates the charged surface of the photosensitive drum 1 with light to form an electrostatic latent image. Laser light, LED light, CRT light, EL light, or the like may be used as the exposure source as long as the photosensitive drum emits light having a high absorption spectrum.

Reference numeral 8 denotes a developing device for developing the electrostatic latent image on the photosensitive drum 1, which is a toner hopper 8 for storing toner.
a, a developing roller 8b that carries a toner layer and supplies toner to the electrostatic latent image on the photosensitive drum 1 to develop it, and at the same time as removing the toner layer on the developing roller 8b after development, the developing roller 8b In addition, a supply roller 8c for supplying toner from the toner hopper 8a and a regulating member 8d for forming a layer of the toner supplied by the supply roller 8c on the developing roller 8b. The developer may be a one-component toner or a two-component developer, and may be a non-magnetic toner or a magnetic toner. The toner may be produced by a suspension polymerization method, an emulsion polymerization method or a mechanical pulverization method. However, it is preferable that the surface of the toner before the external addition treatment, that is, the toner base is smooth and the shape of the toner base is spherical. If the surface of the toner base is not smooth, the external additive adheres unevenly to the base of the toner.
It is considered that the charge distribution in the toner particles also becomes non-uniform. If the toner base is not spherical, the contact area with the photosensitive drum is considered to change depending on the shape of the toner particles. If the variation in the charge distribution in the toner particles and the contact state with the photosensitive drum are large, the amount of toner that remains on the photosensitive drum without being transferred to the image receiving unit side even with a predetermined transfer voltage increases. Coulter counter (Nikkaki Co., Ltd.)
Volume median diameter of toner measured by
(M), specific area measuring device FlowSorbII2300
The specific surface area measured by (manufactured by Shimadzu Corporation) is S (m
2 / g) and the specific gravity of the toner is ρ (g / m3),
It is preferable that the sphericity C shown by the following formula is 0.78 to 0.98.

C = 6 / DρS In addition, the developing device also has a structure in which a magnet roller is included in the developing roller or a structure in which a spiral stirring member for stirring and conveying the two-component developer is provided in accordance with the developer. May be.

Reference numeral 3 is a transfer device, and a constant current power supply 3 is provided on the transfer means to which the metal base material 3a and the conductive flexible member 3b are attached.
This is a configuration in which c is connected. The flexible member 3b is arranged so as to contact the photosensitive drum 1 at a predetermined angle with respect to the photosensitive drum. As the flexible member 3b, a film-shaped member made of polycarbonate, polyethylene terephthalate, PTFE, polyimide, polyolefin or the like, or a brush-shaped member made of conductive fiber such as nylon or rayon is used.

The flexible member 3b preferably contacts the photosensitive drum 1 with a predetermined width from the tip. Flexible member 3
If there is a region at the tip of b that is not in contact with the photoconductor drum 1, an electrostatic field is formed between the photoconductor drum 1 and the flexible member 3b behind the transfer region. Due to this electrostatic field, the toner image once transferred to the image receiving means is easily scattered around the toner, which is called "backward flight". Also,
Since the chances of the image receiving means and the flexible member in the transport path contacting each other increase, if the attitude of the image receiving means in the transport path changes,
The flexible member is pushed by the image receiving means and deforms, and the contact state between the flexible member and the photosensitive drum also tends to change. Therefore, in order to minimize the fluctuation of the transfer area with respect to the fluctuation of the attitude of the image receiving means, it is preferable to arrange the photosensitive film such that the leading end of the conductive film is in contact with the photosensitive drum.

Further, the bending rigidity of the flexible member is preferably smaller than that of the image receiving means. As described above, the image receiving unit takes various bending postures in the transport direction. If the flexural rigidity of the flexible member is larger than the flexural rigidity of the image receiving means, it becomes difficult for the flexible member to come into close contact with the deformed image receiving means, and a gap may occur between the two. If there is a gap between the two, not only is it impossible to supply sufficient charges to the back surface of the image receiving unit, but also dielectric breakdown occurs in the gap, and as a result discharge marks are formed on the flexible member, which deteriorates the flexible member. There is a risk that Further, the image receiving means may take a wavy posture in a direction (longitudinal direction of the photosensitive drum) orthogonal to the transport direction. If there is waviness in the orthogonal direction, not only the problem due to the decrease in the adhesion between the image receiving means and the flexible member as described above occurs, but also the impedance component from the flexible member to the photosensitive drum varies in the orthogonal direction. , Transfer unevenness is likely to occur in the orthogonal direction. In particular, when a constant current is applied to the transfer unit, if the adhesion between the image receiving unit and the flexible member is poor, the amount of charge supplied to the back surface of the image receiving unit also varies, and the region where the charge supply amount is excessive and the region where it is insufficient. And are formed at the same time. As a result, a region where toner scattering is likely to occur and a region where transfer efficiency is reduced are formed, and the uniformity of image density is further reduced.

Reference numeral 9 is a toner collecting means for collecting the residual toner on the photosensitive drum 1. In FIG. 3, the toner collecting means has a roller shape, but a brush shape or a blade shape may be used. Further, a so-called cleanerless system may be used in which the developing device 3 collects residual toner at the same time as development without using the toner collecting means 9.

Reference numeral 2 is a registration roller which conveys the image receiving means at a predetermined speed. As the registration roller, a metal roller provided with a resin layer is used.

Reference numeral 5 is an image receiving means such as plain paper, postcard paper, or OHP sheet. Further, 10 is a registration roller 2
It is an upstream side guiding means for guiding the conveying direction of the image receiving means 5 from to the photosensitive drum 1. It is preferable that the image receiving means 5 is first conveyed to the photoconductor drum 1 and then conveyed so as to enter the transfer area where the flexible member 3b and the photoconductor drum 1 are brought into contact with each other. When the image receiving means 5 is conveyed so as to come into contact with the flexible member 3b and then to enter the transfer area, the image receiving means 5 is conveyed.
Not only is the flexible member 3b deformed by the impact of the tip of the flexible member, but also the flexible member vibrates and the transfer area becomes unstable. In particular, when the contact area between the image receiving unit and the flexible member increases, the flexible member vibrates in the image receiving unit conveyance direction due to frictional resistance with the image receiving unit, and the transfer area becomes further unstable.
Also, if there is a slight waviness of the image receiving means in the longitudinal direction of the photosensitive drum, the flexible member will be deformed along it,
The adhesion between the image receiving means and the photoconductor drum is reduced.
As a result, the impedance component from the flexible member to the photosensitive drum varies in the longitudinal direction of the photosensitive drum, causing uneven transfer. On the other hand, by bringing the image receiving unit into contact with the photosensitive drum 1 first, the problem of the flexible member caused by the collision of the image receiving unit is avoided. Further, the image receiving means is electrostatically attracted to the surface of the photosensitive drum by the electric charges on the surface of the photosensitive drum in a slightly wavy state and becomes smooth. Therefore, the adhesion between the photoconductor drum and the image receiving unit is improved, and the occurrence of transfer unevenness due to the variation of the impedance component is suppressed. Therefore, it is preferable that the upstream guide unit 10 is arranged so as to guide the image receiving unit 5 so that the image receiving unit 5 first comes into contact with the photosensitive drum 1 before the image receiving unit 5 enters the transfer area.

A fixing device 4 fixes the toner image transferred on the image receiving means 5. Further, reference numeral 11 is a downstream side guiding means for guiding the conveying direction of the image receiving means from the transfer area to the fixing device 4.

In a high-humidity environment, the image receiving means 5 has a low resistance, and a current leaks from the flexible member 3b to the guiding means 10 and 11 via the image receiving means 5. For this reason, sufficient charges are not supplied to the back surface of the image receiving unit 5, and transfer failure occurs. In order to solve this problem, the guide means 1
It is preferable that 0 and 11 are composed of insulating members or that a voltage having the same polarity as the current polarity of the constant current power source 3c is applied. Further, a self-bias element such as a resistance element or a Zener diode element may be connected between the guide means 10 and 11 and the ground.

Next, the operation of the image forming apparatus of the present invention will be described with reference to FIG.

First, the image forming apparatus receives an image signal transmitted from the outside such as a computer and starts the image forming operation. First, the fixing device is heated, and after reaching a predetermined temperature, the rotation driving of the fixing device is started. At the same time, the photosensitive drum, the charging device, and the developing device are also started. At this time, a predetermined voltage is applied to the charging device and the developing device so that the toner does not adhere to the photosensitive drum from the developing device.
Further, the image receiving means stored in a paper feeding cassette (not shown in FIG. 3) feeds up to the registration rollers and maintains a state of being sandwiched between the registration rollers.

Next, a predetermined voltage is applied to the charging device,
The photosensitive drum is charged to a predetermined surface potential. When the charged surface of the photosensitive drum is conveyed to a position facing the exposure source, the surface of the photosensitive drum is irradiated with light according to the received image signal. As a result, the charging potential of the surface of the photosensitive drum in the area irradiated with the light is lowered. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum. When the electrostatic latent image on the surface of the photoconductor drum is conveyed to a position facing the developing device, the toner on the developing roller to which a predetermined voltage is applied is exposed in accordance with the potential difference between the electrostatic latent image and the developing roller. Move to the body drum. As a result, toner adheres to the surface of the photoconductor drum according to the electrostatic latent image, and a toner image is formed on the photoconductor drum. The toner image formed on the surface of the photosensitive drum is conveyed to a contact area between the flexible member 3b and the photosensitive drum, that is, a transfer area. A predetermined current is supplied to the flexible member by the constant current power supply 3c.

On the other hand, the rotational driving of the registration roller is started, and in synchronism with the transfer of the toner image to the transfer area, the transfer of the image receiving means sandwiched between the registration rollers is started. The conveying speed of the image receiving unit at this time is the peripheral speed v1 of the registration roller. The image receiving means 5 conveyed along the upstream guide means 10 first comes into contact with the photosensitive drum 1 and then enters the transfer area. While passing through the transfer area, a current flows from the constant current power source 3c to the back surface of the image receiving means through the flexible member, and charges are accumulated. An electric field E is formed between the image receiving means and the photoconductor drum by the accumulated charges.
As a result, the electric charge q of the toner and the Coulomb force F = qE by the electric field E act to transfer the toner on the photosensitive drum to the image receiving unit side. The toner that is not charged to the regular polarity or the toner that has an excessive mechanical adhesive force is not attracted to the image receiving unit side by the Coulomb force F and remains on the surface of the photosensitive drum. This residual toner is removed from the surface of the photosensitive drum by the toner collecting means.

The image receiving means that has passed through the transfer area is conveyed to the fixing device along the downstream guide means 11. At this time, the image receiving means is in a state of being sandwiched between the registration roller and the fixing device. If the peripheral speed of the fixing device is v2, the peripheral speed difference | v1-V2 | between the registration roller and the fixing device
The image receiving means is conveyed while being deformed in the conveying path from the registration roller to the fixing device. The flexible member also comes into contact with the back surface of the image receiving unit while deforming in accordance with the deformation of the image receiving unit. At this time, the transfer area also changes due to the deformation of the image receiving unit, but since the constant current is supplied by the constant current power source, the fluctuation of the transfer electric field is smaller than that when the constant voltage power source is used.

While passing through the fixing device, the toner image on the image receiving means is heated and fixed. Further, when the conveyance of the image receiving unit progresses, the rear end of the image receiving unit is separated from the registration roller and is conveyed by the driving force of only the fixing device. The conveying speed of the image receiving unit at this time is the peripheral speed v2 of the fixing device. When the rear end of the image receiving means passes through the transfer area and then passes through the fixing device, the image receiving means is discharged outside the image forming apparatus, and the output of the fixed print image is completed.

Specific embodiments according to the present invention will be described below.

(First Embodiment) A first embodiment will be described with reference to FIGS.

In this embodiment, as the photosensitive drum 1, an aluminum tube having a thickness of about 0.8 mm and a diameter of 16 mm is used.
A drum in which a phthalocyanine-based CGL layer and a hydrazone-based CTL were sequentially coated to form a negatively-charged OPC layer having a layer thickness of about 20 μm was used. Also, the charging roller has a diameter of 8 mm.
A roller provided with epichlorohydrin-based conductive rubber on the core metal was used. The charging roller has a DC voltage of -1.2k.
V was applied to set the surface potential of the photoconductor to about -600V.
As an exposure source, a beam diameter of about 60 μm and a wavelength of 780 n
m laser light was used. Further, as the constitution of the developing device, a conductive silicon rubber roller having a diameter of 12 mm was used as the developing roller 8b, and a conductive silicon sponge roller having a diameter of 12 mm was used as the supply roller. Silicon rubber attached to the tip of a phosphor bronze plate is used as the regulating member 8d.
It was pressed against b and used. Further, the developing roller 8b and the regulating member 8d were set to the same potential, and a voltage of -300V was applied to both. A voltage of -400V was applied to the supply roller 8c.
Further, the toner has an average median particle diameter of about 7 μm produced by a suspension polymerization method, a coefficient of variation of particle size distribution of about 25%, and a sphericity of 0.
90 insulating non-magnetic toners were used. The charge amount of the toner was adjusted to be about −20 μC / g.

As the transfer device, the registration roller 2 is used.
The metal base material 3a was arranged at an angle of about 75 ° with respect to the tangent line connecting the photosensitive drum 1 and the photosensitive drum 1. An aluminum plate having a thickness of 1 mm was used as the metal member. A polyolefin-based conductive film "Sumilite FS-4654 (manufactured by Sumitomo Bakelite Co., Ltd.)" was used for the flexible member 3b. In FIG. 4, the metal substrate 3a
The perspective view of the transfer means comprised by the conductive film is shown. The characteristic of the conductive film 3b is that the surface resistance is 600Ω.
/ □, volume resistance of 3 Ω · cm, and film thickness of 50 μm were used. The free end length of the conductive film 3b is 4 to 5
mm and about 2 to 3 mm from the tip of the conductive film 3b
The transfer means was arranged so that the photosensitive drum 1 and the conductive film 3b were in contact with each other within the width of. A high-voltage power supply TREK610C (manufactured by Trek) was used as the constant current power supply 3c, and the supply current value was set to 6 μA. The voltage monitor terminal of the high-voltage power supply was connected to an oscilloscope, and the output transfer voltage was measured.

Two types of image patterns were printed: a halftone image in which dots having a diameter of about 80 μm are uniformly dispersed at a hiding ratio of about 10% on the surface of the image receiving means, and a solid black image having a hiding ratio of 100%. Further, as the image receiving means used, a basis weight of about 50 g / m ² , 90 g / m ² , 160 g / m ²
I used plain paper. Further, the process speed of the image forming apparatus is set to 60 mm / s.

Under the above conditions, the transfer efficiency at the front end and the central portion of the plain paper in the transport direction and the toner scattering around the dots were evaluated. The evaluation method was as follows. First, while the solid black image was being transferred onto plain paper, the image forming apparatus was forcibly stopped and the transfer residual toner on the photosensitive drum was collected with a transparent adhesive tape. The halftone image was transferred to plain paper and then passed through a fixing device. The transfer residual toner and the halftone image on the plain paper, which were sampled as described above, were magnified and photographed with a 256-gradation picture using a microscope photographic device. An image analysis device (dot analyzer DA-5000, Oji Scientific Instruments Co., Ltd.)
After the binarization was performed at a predetermined threshold value by using a product, the ratio of the transfer residual toner (transfer residual toner coverage) and the number of toners around the dots were measured.

Table 1 shows the evaluation results of transfer efficiency and toner scattering at the front, center and rear edges of plain paper.
In Table 1, "○" in the column of transfer efficiency is 1% coverage.
Less than, “Δ” indicates 1% or more and less than 2%, and “x” indicates 2% or more. Further, in the column of toner scattering, “◯” indicates that the number of scattered toner particles around one dot is less than 20, “Δ” indicates 20 or more and less than 30, and “x” indicates 30 or more.

[0058]

[Table 1]

Further, (Table 2) shows transfer voltages measured by an oscilloscope at the front end, the center, and the rear end of plain paper.

[0060]

[Table 2]

As can be seen from Table 1, the basis weight is 50 g /
It was possible to obtain an image with good transfer efficiency and little toner scattering except for the center of plain paper of m ² . In the center of the plain paper having a basis weight of 50 g / m ² , the transfer efficiency was slightly inferior, but the toner scattering was small and a uniform halftone image was obtained on the entire surface of the plain paper.

Further, as can be seen from (Table 2), the smaller the basis weight, the greater the difference in transfer voltage between the front and rear edges and the central portion of plain paper. The cause is considered as follows.

That is, when the front end and the rear end of the plain paper are in the transfer area, the plain paper is nipped by either one of the registration rollers or the fixing device. At this time, the plain paper obtains a driving force from the sandwiched conveying means and is conveyed at a speed equivalent to the peripheral speed of the conveying means. Therefore, if the peripheral speed of the registration roller and the fixing device is constant, the transport speed of plain paper is also constant. On the other hand, when the center of the plain paper is in the transfer area, the plain paper is sandwiched between the roller and the fixing device by the conveying means. At this time, the plain paper receives a driving force from both of the sandwiched conveying means. If there is a difference in peripheral speed between the registration roller and the fixing device, the plain paper takes either an excessively stretched or loosened position in the conveyance path. In the case of the present embodiment, when the image forming apparatus is forcibly stopped while the plain paper is sandwiched between the registration roller and the fixing device, the plain paper is not subjected to excessive tension. It is probable that the plain paper was slower than the registration roller and the plain paper was in a loose state in the conveying path. Considering from the above results, when a plain paper having a small basis weight is nipped by both the registration roller and the fixing device,
Due to the difference in peripheral speed between the two, it greatly bends in the conveyance path. The bent plain paper pushes the flexible member 3b, which comes into contact with the photosensitive drum 1 with a low pressure, in a direction away from the photosensitive drum. As a result, the contact area between the conductive film and the plain paper or between the plain paper and the photosensitive drum is reduced. As a result, it is considered that the impedance component from the conductive film to the photoconductor drum increased, and as a result, the transfer voltage value also increased. The reason why the transfer efficiency was slightly reduced in the center of plain paper with a basis weight of 50 g / m ² was that the contact area of the plain paper became smaller, so that sufficient charge was not accumulated on the back surface of the plain paper, resulting in a weak transfer electric field. it is conceivable that.

The reason why the plain paper having a basis weight of 160 g / m ² showed a constant transfer voltage from the leading edge to the trailing edge is considered as follows. That is, because the rigidity of plain paper is large, even if there is a difference in peripheral speed between the registration roller and the fixing device, the plain paper does not deform in the transport path, and the plain paper is not deformed by either the registration roller or the fixing device. It is thought that it slipped. Further, the reason why the transfer voltage of the plain paper having a basis weight of 160 g / m ² is lower than that of other plain paper is considered to be because the contact area with the conductive film increases as the plain paper becomes thicker.

(Second Embodiment) Next, a second embodiment will be described with reference to FIGS.

In this embodiment, a conductive brush is used as the flexible member 3b instead of the conductive film used in the first embodiment. In FIG. 5, the conductive brush 3 is provided on the metal base 3a.
The perspective view of the transfer means which attached b is shown. The conductive brush has a thickness of 600D / with carbon dispersed in nylon fiber.
Using 100F conductive yarn, fiber density 86 bundles / inc
h, a pile length of 4 mm was used. The base cloth of the conductive brush was bonded with a conductive adhesive. FIG. 6 is a sectional view showing a schematic correlation position between the photosensitive drum 1 and the transfer means. The mounting angle with respect to the photoconductor drum 1 was the same as in the first embodiment. Also, instead of the photosensitive drum 1, a diameter of 16 mm
As a result of measuring the current flowing by applying a voltage of 250 V to the transfer means, the electric resistance of the transfer means was about 0.25 MΩ. Other components are the same as those in the first embodiment.

The same evaluation as that of the first embodiment was carried out by the image forming apparatus having the above-mentioned configuration.
Images other than the center of plain paper having a basis weight of 50 g / m ² could be obtained with good transfer efficiency and little toner scattering. Basis weight 5
At the center of the plain paper of 0 g / m ² , the transfer efficiency was slightly inferior, but the toner scattering was small and a uniform halftone image was obtained on the entire plain paper. From this result, it is considered that the conductive brush used in the present embodiment behaves similarly to the conductive film of the first embodiment.

(Third Embodiment) Next, a third embodiment will be described with reference to FIGS.

In this embodiment, as the flexible member 3b, a flat conductive brush is used instead of the conductive film used in the first embodiment. FIG. 7 shows a perspective view of the transfer means in which the flat conductive brush 3b is attached to the metal base 3a on the metal base 3a. The conductive brush was made of a conductive thread having a thickness of 600D / 100F in which carbon was dispersed in nylon fiber, and had a fiber density of 100 kF / inch ² , a pile length of 4 mm, and a width W of 6 mm. The base cloth of the conductive brush was bonded with a conductive adhesive. FIG. 8 is a sectional view showing the correlation position between the photosensitive drum 1 and the transfer means. The mounting angle with respect to the photoconductor drum 1 was such that the direction in which the image receiving means entered the transfer area was parallel to the metal base material 3a. The straight line connecting the midpoint of the width W and the center of rotation of the photosensitive drum 1 is made to coincide with the normal line of the surface of the photosensitive drum. Further, the transfer means was attached so that the contact width between the photosensitive drum 1 and the transfer brush was about 3 mm. Also, instead of the photoconductor drum 1, an aluminum tube having a diameter of 16 mm was attached, a voltage of 250 V was applied to the transfer means, and the flowing current was measured. As a result, the electric resistance of the transfer means was about 0.2 MΩ.
Met. Other components are the same as those in the first embodiment.

With the image forming apparatus having the above-mentioned structure, the same evaluation as in the first embodiment was carried out. Table 3 shows the evaluation results of the transfer efficiency and the toner scattering at the front end, center, and rear end of plain paper. In Table 3, "○" in the column of transfer efficiency is less than 1% of coverage, "△" is 1% or more and less than 2%,
“X” indicates 2% or more. Further, in the column of toner scattering, “◯” indicates that the number of scattered toner particles around one dot is less than 20, “Δ” indicates 20 or more and less than 30, and “x” indicates 30 or more.

[0071]

[Table 3]

Further, (Table 4) shows transfer voltages measured by an oscilloscope at the front end, the center, and the rear end of plain paper.

[0073]

[Table 4]

As can be seen from (Table 3), good transfer efficiency and an image with less toner scattering were obtained under all conditions.

Observation of the cross section of the conveying path from the photosensitive drum to the fixing device revealed that when the plain paper reaches the fixing device, the plain paper having a basis weight of 90 g / m ² or less is largely bent. In addition, when a plain paper having a basis weight of 90 g / m ² was sandwiched between the photoconductor drum and the transfer device and pulled toward the fixing device via a tension gauge, about 10 times about 1/100 of the transfer roller was obtained. A torque of ~ 20g was measured. Therefore, it is considered that the plain paper is deformed in the present embodiment as well as near the transfer area. However, as can be seen from (Table 4), the phenomenon that the transfer voltage changes depending on the position of the plain paper as seen in the first embodiment was not seen. This is because the position of the transfer area changes even if the plain paper is deformed in the conveying path, but the contact area between the photosensitive drum 1 and the plain paper and the contact area between the plain paper and the conductive brush are large. Since it did not change, the impedance component from the conductive brush to the photosensitive drum is considered to be stable. As a result, the amount of electric charge accumulated on the back surface of the plain paper was always stable, and it is considered that the transfer efficiency and the toner scattering state were kept uniform over the entire plain paper.

When plain paper having a basis weight of 160 g / m ² was used, the transfer voltage was lower than that of other plain paper.
It is considered that this is because the plain paper bites into the conductive brush due to the increase in the thickness of the plain paper, and as a result, the contact area between the plain paper and the conductive brush increases, so that the impedance component becomes low.

(Fourth Embodiment) Next, a fourth embodiment will be described.

In this embodiment, the width W of the flat type conductive brush used in the third embodiment is 6 mm to 3 mm.
Changed to. Further, the conductive brush was arranged so that the contact width between the photosensitive drum 1 and the conductive brush was W = 3 mm. All other components are the same as those in the third embodiment.

With the above-described structure of the image forming apparatus, the same evaluation as in Embodiment 1 was performed. As a result, Embodiments 1 and 2
The result is similar to. The reason why even if the flat conductive brush similar to that of the third embodiment is used in the present embodiment, it does not become “◯” under all the conditions as in the third embodiment will be considered below.

That is, in the third embodiment, the width W of the conductive brush is longer than the contact width of the photosensitive drum and the plain paper, or the contact width of the plain paper and the conductive brush. However, it is probable that the contact width did not change significantly even if the contact position moved. However, in the present embodiment, the contact width and the width W of the conductive brush are
Therefore, it is considered that not only the contact position moved along with the deformation of the plain paper but also the contact width changed. As a result, as in the first and second embodiments, the basis weight is 50 g.
It is considered that in the case of plain paper of / m ^2, the amount of electric charge supplied from the transfer means was insufficient at the center of the plain paper, and transfer failure occurred.

Comparative Example 1 With the structure of the transfer means shown in the first embodiment, a constant voltage was applied instead of the constant current application.
A high voltage power supply TREK610C (manufactured by Trek) was used as the constant voltage power supply 3c. As the applied voltage, three kinds of voltages of 750V, 1000V and 1500V measured in the first embodiment were applied.

With the image forming apparatus having the above-mentioned structure, the same evaluation as in the first embodiment was performed. (Table 5), (Table 6), and (Table 7) show evaluation results of transfer efficiency and toner scattering at transfer voltages of 750V, 1000V, and 1500V. (Table 3)
Medium, "○" in the column of transfer efficiency is less than 1% coverage,
“Δ” indicates 1% or more and less than 2%, and “x” indicates 2% or more.
Further, in the toner scattering column, “◯” indicates that the number of scattered toner particles around one dot is less than 20, and “Δ” indicates 20 or more and 3 or more.
Less than 0, "x" indicates 30 or more.

[0083]

[Table 5]

[0084]

[Table 6]

[0085]

[Table 7]

As can be seen from (Table 5) to (Table 7), when the constant voltage was applied, the transfer efficiency and the toner scattering greatly changed depending on the position of the plain paper. The amount of change depended on the basis weight of plain paper.

The cause is considered as follows. That is, plain paper having a basis weight of 50 g / m ² and 100 g / m ² has a low rigidity and is easily deformed in the transport path. Therefore, the contact area between the conductive film and the plain paper changes. In the case of a constant voltage, the amount of charge accumulated on the back surface of plain paper with respect to the contact area is larger than that when a constant current is applied.Therefore, the amount of charge accumulated on the back surface of the plain paper changes significantly at the front, center, and rear edges. Conceivable. For example, at an applied voltage of 750V, the transfer efficiency differs depending on the position of plain paper. It is considered that the sufficient electric charge was not supplied in the region where the transfer efficiency was low, so that the strength of the transfer electric field formed between the plain paper and the photoconductor drum was lowered, and the toner could not be sufficiently electrostatically attracted. . Further, in the case of 1500 V, the transfer efficiency is lowered depending on the position of the plain paper, and the toner scattering is remarkable. It is considered that excessive charges were accumulated in the region where the transfer efficiency was lowered and the toner scattering was remarkable. That is, when excessive charges are accumulated, a strong electric field is formed between the photoconductor drum and the plain paper when they are separated. As a result, a discharge phenomenon occurs between the two, and as a result, the charge polarity of the toner is reversed, so-called retransfer occurs, and it is considered that the transfer efficiency is reduced. As for the toner scattering, it is considered that the excessively supplied electric charge formed a sneak electric field around the dots, so that the toner transferred to the plain paper was scattered around the dots.

(Comparative Example 2) The surface of the flexible member 3b shown in the first embodiment on the side opposite to the surface in contact with the photosensitive drum 1,
A PET film having a thickness of 150 μm is attached with a double-sided tape to enhance bending rigidity, and the same as in the first embodiment,
A solid black image and a halftone image were printed on three types of plain paper. Other components are the same as those in the first embodiment.

As a result, with plain paper having a basis weight of 160 g / m ² , a toner image having a uniform image density was obtained on the entire plain paper. On the other hand, with 90 g / m ² and 50 g / m ² plain paper, a “white spot” phenomenon, in which the toner image was not transferred at all and was not seen in some cases, was observed, which was not seen in the first embodiment. In particular,
From the center of the plain paper where the front end of the plain paper reached the fixing device to the rear end, the "white spot" phenomenon was noticeable. The cause is considered as follows.

That is, the plain paper being passed is not only deformed in the direction of the transport path, but also in the direction orthogonal to the plain paper transport path (the longitudinal direction of the photosensitive drum 1). In particular, plain paper having a small basis weight has a low bending rigidity, and therefore has a large amount of deformation. Further, since the circumferential size of the fixing roller used in the fixing device is not highly accurate, when the fixing roller rotates at a constant rotational speed, a peripheral speed difference easily occurs in the longitudinal direction of the fixing roller. As a result, it is considered that the plain paper is easily deformed in the orthogonal direction from the center to the rear end. When the plain paper is slightly deformed in the direction orthogonal to the transport path, the flexible member having the small bending rigidity as shown in the embodiment is deformed along with the deformation of the plain paper. As a result, even if there is a minute gap between the photoconductor drum and the plain paper, the flexible member is in close contact with the plain paper, so that sufficient electric charge for transfer is supplied. On the other hand, in this comparative example, since the bending rigidity of the flexible member is larger than that of plain paper and the pressure contact force with the photosensitive drum 1 is also low, the flexible member does not deform along with the deformation of the plain paper, and conversely It is pushed away from the drum. As a result, sufficient charges for transfer are not supplied to the back surface of plain paper, causing "white spots".
It is considered that a phenomenon has occurred.

In the present embodiment, a single color image forming apparatus has been described, but the present invention may be applied to a color image forming apparatus that prints a plurality of colors. FIG. 10 is a schematic sectional view of a color image forming apparatus to which the present invention is applied. In FIG. 10, 21Y, 21M, 21C, and 21K are photoconductor drums on which toner images of yellow, magenta, cyan, and black are formed, respectively, and are arranged along the conveyance direction of the image receiving means 5. Around the respective photosensitive drums, a charging device 26, a developing device 28, a toner removing device 2
9 are provided. Further, reference numeral 23 denotes a transfer device that comes into contact with each photoconductor drum at a low pressure, and is composed of the conductive film or the conductive brush described in the first to third embodiments. A constant current power supply is connected to each transfer device, and a predetermined current is supplied to the transfer device. The other reference numerals are the same as those in FIG.

In the color image forming apparatus as shown in FIG. 10, when the image receiving means transporting path from the registration roller 2 to the fixing device 5 is shorter than the length of the image receiving means, a constant current is supplied to the transfer device. The effects as shown in the first to third forms are obtained.

In FIG. 10, the transfer device arranged on the most downstream side in the image receiving means conveyance direction is a flexible member such as a conductive film or a conductive brush as in the case of other transfer devices, but a rubber roller, a sponge roller or the like is used. You may use the transfer roller of this. Then, instead of the fixing device, the image receiving unit may be conveyed by the transfer roller and the photoconductor drum facing the transfer roller. Since the rubber roller used in the fixing device has a low rubber hardness and a large rubber thickness, it is difficult to increase the dimensional accuracy in the circumferential direction. Further, since the rubber expands due to heat, the circumferential dimension is likely to change. On the other hand, the transfer roller can easily improve the accuracy in the circumferential direction as compared with the fixing roller, and since it is separated from the fixing device, the dimensional change due to thermal expansion is small. Therefore, the peripheral speed is more stable than that of the fixing roller, and banding due to the change in the conveying speed of the image receiving unit is less likely to occur. Further, since the image receiving means conveying path from the registration roller is shortened, it becomes possible to convey even the image receiving means having a small size.

The image receiving means used in the present invention is not limited to the above, and for example, the conveying means may be arranged on the downstream side of the fixing device.

[0095]

As described above, according to the present invention, the peripheral speeds of the registration rollers, the fixing device, and other conveying means are different,
Even if the image receiving unit is deformed in the conveying path, the amount of electric charge supplied to the back surface of the image receiving unit does not largely vary, and stable transfer is performed. As a result, an inexpensive and high-quality image is formed.

[Brief description of drawings]

FIG. 1 is a sectional view showing a state of an image receiving unit in an image forming apparatus of the present invention.

FIG. 2 is a sectional view in the vicinity of a transfer area of the present invention.

FIG. 3 is a sectional view showing the configuration of an image forming apparatus according to the present invention.

FIG. 4 is a perspective view of a transfer unit according to the first embodiment of the present invention.

FIG. 5 is a perspective view of a transfer unit according to a second embodiment of the present invention.

FIG. 6 is a cross-sectional view showing a schematic relative position between a photosensitive drum and a transfer unit according to a second embodiment of the present invention.

FIG. 7 is a perspective view of a transfer unit according to a third embodiment of the present invention.

FIG. 8 is a cross-sectional view showing a schematic relative position between a photosensitive drum and a transfer unit according to a third embodiment of the present invention.

FIG. 9 is an explanatory view explaining the operation of the present invention in the third embodiment of the present invention.

FIG. 10 is a schematic configuration sectional view of a color image forming apparatus to which the present invention is applied.

[Explanation of symbols]

1 photoconductor drum 2 Registration roller 3 Transfer means 4 fixing device 5 Image receiving means 6 charging device 7 Exposure means 8 developing device 9 Toner removal means 10 Upstream guide means 11 Downstream guide means

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yoshitaka Kitaoka             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F term (reference) 2H072 AB07 BA03 BB01 CA01 CB07                       CB08 JA02                 2H200 FA16 JA02 JA27 JA28 JA29                       JB16 JB32 MC20 NA02 PA14                 3F101 LA02 LA07 LB03

Claims (4)

[Claims] 1. An image carrier that carries and conveys a developer image, and a transfer unit that is fixed at a position facing the image carrier and has a flexibility that abuts on the image carrier and forms a transfer area. An image receiving unit that is transported to the transfer region and to which the developer image on the image carrying unit is transferred; and a first image receiving unit that is disposed upstream of the image receiving unit in the transport direction as viewed from the transfer region and that transports the image receiving unit. A second image receiving means transporting means which is disposed on the downstream side in the image receiving means transporting direction as viewed from the transfer area and which transports the image receiving means, and a second image receiving means from the first image receiving means transporting means A constant current is supplied to the second image receiving means conveying means arranged at a position where the conveying path length of the image receiving means to the means conveying means is shorter than the length of the image receiving means, and the transfer means having flexibility. Current supply means for An image forming apparatus characterized by. 2. An image carrying means for carrying and carrying a developer image, and a transfer means which is fixed at a position facing the image carrying means and has a flexibility to contact the image carrying means to form a transfer area. An image receiving unit that is transported to the transfer region and to which the developer image on the image carrying unit is transferred; and a first image receiving unit that is disposed upstream of the image receiving unit in the transport direction as viewed from the transfer region and that transports the image receiving unit. A second image receiving means transporting means which is disposed on the downstream side in the image receiving means transporting direction as viewed from the transfer area and which transports the image receiving means, and a second image receiving means from the first image receiving means transporting means A second image receiving means conveying means arranged at a position such that the conveying path length of the image receiving means to the means conveying means is shorter than the length of the image receiving means, and flexibility in the image receiving means conveying direction is provided. The width of the transfer means having , When the contact width between the transfer means and the image bearing means having a flexible and D, W> image forming apparatus which is a D. 3. An image carrier that carries and conveys a developer image, and a transfer unit that is fixed at a position facing the image carrier and has a flexibility that contacts the image carrier and forms a transfer area. An image receiving unit that is transported to the transfer region and to which the developer image on the image carrying unit is transferred; and a first image receiving unit that is disposed upstream of the image receiving unit in the transport direction as viewed from the transfer region and that transports the image receiving unit. A second image receiving means transporting means which is disposed on the downstream side in the image receiving means transporting direction as viewed from the transfer area and which transports the image receiving means, and a second image receiving means from the first image receiving means transporting means And a second image receiving means conveying means arranged at a position such that the conveying path length of the image receiving means to the means conveying means is shorter than the length of the image receiving means. The rigidity is the rigidity of the image receiving means. Ri low that the image forming apparatus according to claim. 4. The image forming apparatus according to claim 2, further comprising a constant current supply unit that supplies a constant current to the transfer unit.