JPH07225519A - Image forming device - Google Patents

Abstract

(57) [Abstract] [Purpose] Good transfer of a toner image is performed without providing a peripheral speed difference between a photosensitive drum and a transfer roller. [Structure] Registration nip portion N ₂ of registration roller pair 30
The recording material P is supplied to the transfer nip portion N ₁ between the photosensitive drum 1 and the transfer roller 6 via the upper transfer guide 31a and the lower transfer guide 31b by the toner image on the photosensitive drum 1 on the recording material P. Transcribe. The angle between the vertical surface S ₀ and the transfer surface S ₁ is the transfer angle θ ₀₁ , the angle between the vertical surface S ₀ and the introduction surface S ₂ is the introduction angle θ ₀₂ , and the transfer nip surface S ₃ and the registration nip surface S ₄ are The angle formed by the resist angle θ ₃₄ , the lower transfer guide 31b
Let r be the shortest distance between the tip of the sheet and the surface of the photosensitive drum 1, and f be the contact pressure of the transfer roller 6. Set each value to 0 ° ≤ θ ₀₁
≤15 °, 30 ° ≤ θ ₀₂ ≤ 42 °, 5 ° ≤ θ ₃₄ ≤ 40
°, 0.5 mm ≤ r ≤ 3.5 mm, 0.3 g / cm ≤ f
Good transfer is achieved by setting ≦ 10 g / cm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine or a laser beam printer, and more specifically, a contact transfer member for transferring a toner image formed on an image carrier onto a recording material surface. The present invention relates to an image forming apparatus including.

[0002]

2. Description of the Related Art Conventionally, for example, in an electrophotographic image forming apparatus or an electrostatic recording type image forming apparatus, a visible image (toner image) formed on an image carrier such as a photoconductor or a dielectric is printed on paper. A transfer device (corona charger) that uses corona discharge is widely used as a transfer unit that transfers to a recording material such as.

Such a corona transfer device transfers a toner image on an image carrier to a recording material by applying a predetermined electric charge to the recording material in a non-contact state without contacting the recording material. It is effective as a means. However, a considerably high voltage must be applied in order to generate corona discharge, which requires a high-voltage power supply, and has problems such as ozone generation during corona discharge.

Therefore, in recent years, an image forming apparatus using a contact charging type transfer means capable of charging by applying a relatively low voltage has been developed. This contact charging type transfer means generally comprises a charging member such as a conductive roller and a conductive brush that come into contact with the back surface of the recording material, and by applying a relatively low transfer bias voltage to the charging member,
The toner image on the image carrier is transferred to a recording material.
Since such a contact charging type transfer means is required to apply a low voltage, it has advantages such as a small power source, a light weight, a low cost, and a small amount of ozone generation.

In FIG. 3, a primary charging device for uniformly charging the image carrier and a transfer device for transferring a visible image (toner image) on the image carrier to a recording material are respectively contact charging type. An example of an electrophotographic image forming apparatus using the charging device and the transfer device of FIG.

This image forming apparatus has a photosensitive drum (image carrier) 1 which is driven to rotate in the direction of arrow R1. Around the photosensitive drum 1, a primary charging device 2 that charges the surface of the photosensitive drum 1 uniformly along the rotation direction thereof, and an exposure unit 3 that forms an electrostatic latent image on the photosensitive drum 1 according to image information. A developing device 5 for forming a toner image by adhering toner to the electrostatic latent image, a roller type contact charging type transfer device 6 for transferring the toner image on the photosensitive drum 1 to the recording material P, a toner image A cleaner 7 for removing residual toner on the photosensitive drum 1 after transfer, a static eliminator (lamp) 9 for initializing the surface of the photosensitive drum 1, an upper and lower registration rollers (registration roller pair) 30 for conveying the recording material P, recording An upper transfer guide 31a and a lower transfer guide 31 that guide the material P to the transfer site.
A transfer guide 31 and the like, which are composed of b and the like, are provided.

The above-mentioned photosensitive drum 1 is a drum-type electrophotography having a conductive substrate 1b made of aluminum, iron or the like and a photoconductive layer 1a made of, for example, an organic photoconductor covering the outer peripheral surface thereof as a basic structure. It is a photoconductor, and is rotationally driven around its supporting shaft 1c in the direction of arrow R1 in the figure at a predetermined peripheral speed (process speed). The conductive substrate 1b
Is grounded.

Further, the contact charging type primary charging device 2 has a conductor roller 2c such as a metal roller as a core, a conductive layer 2b formed on the outer peripheral surface thereof, and a resistance layer 2a formed on the outer peripheral surface thereof. ₂ , a charging roller composed of 2a ₁ . Both ends of the charging roller 2 are rotatably supported by bearings (not shown) and arranged in parallel with the photosensitive drum 1. A predetermined pressing force is applied to the photosensitive drum 1 by pressing means such as a spring (not shown). Pressed with. As a result, the outermost resistance layer 2a ₁ is transferred to the photosensitive drum 1.
When the photosensitive drum 1 is rotated in the arrow R1 direction, the entire charging roller 2 is driven to rotate in the arrow R2 direction. Further, the conductive roller 2 of the charging roller 2
An electric contact 10a is in contact with c, and a predetermined DC bias voltage is applied from the power source 10 via the electric contact 10a. The charging roller 2 is configured to uniformly contact and charge the surface of the photosensitive drum 1 to a predetermined polarity and a predetermined potential by applying this voltage and driven to rotate in the direction of the arrow R2.

The transfer device 6 is a transfer roller composed of a conductive roller 6a such as a metal roller which is a core metal, and a cylindrical conductive layer 6b formed on the outer peripheral surface thereof. The transfer roller 6 is rotatably supported by bearing members (not shown) at both ends of the conductor roller 6a, is arranged in parallel with the photosensitive drum 1, and is fixed to the photosensitive drum 1 by pressing means such as a spring (not shown). It is pressed with a predetermined contact pressure. As a result, the transfer roller 6 forms the transfer nip portion N ₁ for sandwiching and conveying the recording material P between the photosensitive layer 1 and the outer conductive layer 6b in pressure contact with the photosensitive drum 1. When the recording material P is fed to the transfer nip portion N ₁ , the conductive layer 6b comes into contact with the back surface of the recording material P and is driven to rotate in the direction of arrow R6 as the recording material P is conveyed in the direction of arrow K1. Further, a power source 11 is connected to the conductor roller 6a of the transfer roller 6, and the transfer roller 6 is
A predetermined bias voltage is applied by this power supply 11,
The toner image on the photosensitive drum 1 is transferred to the surface of the recording material P by directly applying an electric charge having a polarity opposite to that of the toner to the back surface of the recording material P. The contact charging type charging roller 2 and the transfer roller 6 are the conductive roller 2
Gears may be attached to c and 6a so that they are forcibly driven by drive means such as a motor.

Next, the image forming process of the image forming apparatus having the above structure will be briefly described. The surface of the photosensitive drum 1 is uniformly charged by a contact charging type charging roller 2, and then exposed by scanning light according to image information from an exposing unit 3 such as a laser scanner or slit exposing unit to obtain an electrostatic latent image. An image is formed. This electrostatic latent image is stored in the developing container 5b of the developing device 5 and is developed by the toner (developer) carried in layers on the surface of the developing sleeve 5a to become a toner image. The toner image on the photosensitive drum 1 is transferred by the action of the transfer roller 6 to the surface of the recording material P supplied to the transfer nip portion N ₁ between the photosensitive drum 1 and the transfer roller 6 by a sheet feeding mechanism (not shown). To be done. afterwards,
The recording material P is separated from the photosensitive drum 1 and sent to an image fixing unit (not shown) to fix the transfer image, a desired print image is formed, and the recording material P is discharged to the outside of the image forming apparatus main body. On the other hand, the photosensitive drum 1 continues to rotate as it is, the adhering substances such as the residual toner adhering to the surface thereof are removed by the cleaner 7, and the charge is removed by the charge eliminator 9 to be initialized, which is used for the next image forming process. To be done.

[0011]

However, according to the above conventional technique, the recording material P after the toner image transfer is
In some cases, there was a portion referred to as a hollow portion where toner was hardly transferred. Such a phenomenon tends to occur when the recording material P has a large thickness d such as a postcard, and when the recording material P has a high rigidity (stiffness) such as an OHP film. This is because the contact pressure of the transfer roller 6 with respect to the photosensitive drum 1 at the transfer nip portion N ₁ is the recording material P.
Since the contact pressure is set to a predetermined value in the state where the recording material P is not pinched, the thick recording material P and the recording material P having high rigidity are
When the toner passes through the transfer nip portion N ₁ , the toner is strongly pressed between the photosensitive drum 1 and the transfer roller 6, and the toner that should originally be attracted to the recording material P side by the action of the electric field of the transfer roller 6 is the photosensitive drum 1 and the recording material P. Mechanically compacted between the surface,
It is generated because it is not transferred onto the recording material P and remains on the photosensitive drum 1. In addition, when the contact pressure of the transfer roller 6 is reduced to prevent the hollow portion and the introduction angle is set so as to reduce the pressure on the photosensitive drum 1 with the recording material P having high rigidity, this time, at the time of transfer, Toner may scatter.

Therefore, conventionally, a peripheral speed difference is provided between the moving speed of the surface of the photosensitive drum 1 and the moving speed of the surface of the transfer roller 6, and the toner image is scraped off from the surface of the photosensitive drum 1 by shearing force. It was taken and transferred to the surface of the recording material P by rubbing it, thereby preventing the hollow portion. However, in the case where the peripheral speed difference is provided between the photosensitive drum 1 and the transfer roller 6 as described above, the toner image transferred onto the recording material P is recorded on the recording material P when the peripheral speed of the photosensitive drum 1 is faster. The transfer roller 6 is contracted in the conveying direction (arrow K1 direction), and on the contrary, when the transfer roller 6 is faster, the transfer roller 6 is expanded. In either case, the image quality is deteriorated. Further, the surface of the photosensitive drum 1 is rubbed against the surface of the recording material P when the recording material P is present in the transfer nip portion N ₁ due to the difference in peripheral speed, and on the surface of the transfer roller 6 when there is no recording material P. The surface of the photosensitive drum 1 is damaged by the foreign matter or the like if the foreign matter or the like intrudes between the photosensitive drum 1 and the recording material P or between the photosensitive drum 1 and the transfer roller 6, for example. The problem occurs.

Therefore, according to the present invention, the peripheral speed difference is not provided between the image carrier and the transfer device (the photosensitive drum 1 and the transfer roller 6 in the above description). SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus capable of preventing a hollow portion without causing damage to the image forming apparatus.

[0014]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and a transfer device is brought into contact with the surface of a cylindrical image carrier from a substantially lower side with a predetermined contact pressure. A linear transfer nip portion is formed along the generatrix direction of the image carrier, and a transfer charge is applied to the back side of the recording material nipped and conveyed in the transfer nip portion via the transfer device. As a result, in the image forming apparatus that transfers the toner image on the image carrier to the surface side of the recording material, if the contact pressure per unit length of the transfer device at the transfer nip portion is f, the contact pressure is Pressure f is 0.3g / cm
A vertical plane that satisfies ≦ f ≦ 10 g / cm and that passes through the central axis of the image carrier S ₀ , and a plane that passes through the central axis of the image carrier and the width center of the transfer nip portion is the transfer surface S ₁ , when the transfer surface S ₁ with respect to the vertical plane S ₀ is a transfer angle theta ₀₁ the angle in the upstream side of the recording material, the transfer angle theta ₀₁ is a 0 ° ≦ θ ₀₁ ≦ 15 ° It is characterized in that each value is set so as to satisfy.

An upper transfer guide and a lower transfer guide for guiding the recording material to the transfer nip portion are provided on the upstream side of the transfer nip portion, and between the tip of the lower transfer guide and the surface of the image carrier. If the shortest distance is r, then the shortest distance r is 0.
Meet 5 mm ≦ r ≦ 3.5 mm, also, the image bearing member central axis and the lower transfer guide tips and introduction surface S ₂ of the plane passing through the said introduction surface S ₂ with respect to the vertical plane S ₀ When the angle formed is the introduction angle θ ₀₂ , the introduction angle θ ₀₂ is 30 ° ≦
Each value can be set so as to satisfy θ ₀₂ ≦ 42 °.

A registration roller pair is provided on the upstream side of the lower transfer guide to contact each other to form a resist nip portion, and a plane passing through the transfer nip portion and in contact with the image carrier is a transfer nip surface S ₃ , the resist. A plane that passes through the nip portion and contacts the pair of registration rollers is a registration nip surface S.
₄ , the transfer nip surface S ₃ and the registration nip surface S ₄
An angle bets forms when the resist angle theta _34, the resist angle theta ₃₄ is able to set its value to satisfy _{5 ° ≦ θ 34 ≦ 40 °} .

Assuming that an angle formed by the transfer surface S ₁ and the introduction surface S ₂ is a relative angle θ ₁₂ , the relative angle θ ₁₂ is 20 ° ≦.
The value may be set so as to satisfy θ ₁₂ ≦ 40 °.

The transfer member may be a transfer roller having a roller-shaped conductive elastic body that comes into contact with the surface of the image carrier.

The Asker C hardness of the transfer roller is 15
It is preferable that the angle is not less than ° and not more than 35 °.

The lower transfer guide may have a notch at the leading end corresponding to the paper passing width of the postcard.

[0021]

According to the above construction, by setting the contact pressure f, the transfer angle θ ₀₁ , the introduction angle θ ₀₂ , the registration angle θ ₃₄ , the relative angle θ _12, etc. within the above-mentioned ranges, the thickness and rigidity of the recording material can be improved. Also, even when the environment such as temperature and humidity changes, it is possible to prevent hollowing and scattering.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. <Embodiment 1> FIG. 1 schematically shows the vicinity of an image carrier of an image forming apparatus according to the present invention. This is an electrophotographic image forming apparatus, and as will be described later, a charging device for charging the image carrier and a transfer device for transferring the toner image on the image carrier to a recording material are provided. , All use the contact charging type.

First, the structure and operation of the entire image forming apparatus will be briefly described with reference to FIG. This image forming apparatus includes, as an image carrier, a photosensitive drum 1 rotatably supported by an image forming apparatus body (not shown) (hereinafter simply referred to as "apparatus body"). The photosensitive drum 1 is a cylindrical electrophotographic photosensitive member having a conductive base 1b made of aluminum or the like and a photoconductive layer 1a formed on the outer periphery thereof as a basic configuration. It has a support shaft 1c at its center, and is driven to rotate in the direction of arrow R1 about this support shaft 1c by a drive means (not shown).

Above the photosensitive drum 1, a primary charging device 2 is provided.
Are arranged. The primary charging device 2 is in contact with the surface of the photosensitive drum 1 and uniformly charges the surface to a predetermined polarity and potential, and is configured as a roller as a whole (hereinafter referred to as "charging roller 2"). ) The charging roller 2 is
Both ends of the core metal 2c are composed of a conductive roller (core metal) 2c arranged in the center, a conductive layer 2b formed on the outer periphery thereof, and resistance layers 2a ₂ and 2a ₁ formed on the outer periphery thereof. Is rotatably supported by a bearing member (not shown) and is arranged parallel to the photosensitive drum 1. The bearing members at these end portions are urged toward the photosensitive drum 1 by pressing means (not shown),
The resistance layer 2a _{1 on the} surface of the charging roller 2 is pressed against the surface of the photosensitive drum 1 with a predetermined contact pressure. Charging roller 2
Is the arrow R as the photosensitive drum 1 rotates in the direction of the arrow R1.
It rotates in two directions. The core metal 2c of the charging roller 2 includes
The electric contactor 10a connected to the power supply 10 is contacted. A bias voltage is applied to the charging roller 2 by the power source 10, and thereby the surface of the photosensitive drum 1 is uniformly and uniformly contact-charged.

An exposure means 3 is arranged downstream of the charging roller 2 in the rotation direction of the photosensitive drum 1. The exposure unit 3 performs, for example, slit exposure of an original image and forms an electrostatic latent image according to image information on the surface of the photosensitive drum 1 by this exposure.

The developing device 5 arranged on the downstream side of the exposing means 3 is provided with a developing container 5b for containing toner and a developing sleeve 5a for attaching the toner to the electrostatic latent image. . The toner in the developing container 5b is applied to the surface of the developing sleeve 5a with a predetermined thickness, and is carried by the rotation of the developing sleeve 5a in the direction of arrow R5. At the developing position facing the surface of the photosensitive drum 1, the toner is removed from the developing sleeve 5a. Transferred onto the photosensitive drum 1, the photosensitive drum 1
It is attached to the electrostatic latent image above. Toner is attached to the electrostatic latent image to form a visible image (toner image). The toner is charged to have a predetermined polarity.

Below the photosensitive drum 1 on the downstream side of the developing device 5, a roller-shaped transfer device 6 (hereinafter referred to as "transfer roller 6") is arranged. The transfer roller 6 has a power source 11
And a conductive layer 6b formed in a cylindrical shape on the outer peripheral surface thereof. The transfer roller 6 is arranged in parallel with the photosensitive drum 1, and both ends of the cored bar 6a are rotatably supported in the direction of arrow R6 by bearing members (not shown). This bearing member is biased toward the photosensitive drum 1 by a pressing member such as a spring, whereby the conductive layer 6b of the transfer roller 6 is pressed against the surface of the photosensitive drum 1 with a predetermined contact pressure,
A transfer nip portion N is provided between the photosensitive drum 1 and the transfer roller 6.
₁ is formed. The recording material P conveyed by the upper and lower registration rollers 30 is guided to the transfer nip portion N ₁ by the transfer guide 31 and is supplied in synchronization with the rotation of the photosensitive drum 1. The recording material P is nipped and conveyed at the transfer nip portion N _1. At this time, the front surface side is in contact with the photosensitive drum 1 and the rear surface side is in contact with the transfer roller 6. At the time of this passage, a bias voltage having a polarity opposite to the polarity of the toner is applied to the back surface of the recording material P by the power source 11, whereby the toner image on the photosensitive drum 1 is transferred to the surface of the recording material P.

The recording material P, to which the toner image has been transferred, is separated from the photosensitive drum 1 and conveyed to an image fixing means (not shown), where the toner image is fixed and then a final copy of the apparatus main body. It is discharged to the outside, or in the case of multiplex copying or double-sided copying, it is sent again to the image forming section including the photosensitive drum 1 via the re-conveying means.

After the image transfer, the photosensitive drum 1 is subjected to the next image forming process after the cleaner 7 removes the adhered substances such as residual toner and the charge is removed by the charge eliminator 9. Hereinafter, the present invention will be described in more detail.

In the above-mentioned structure, the resistance value of the conductive layer (conductive elastic body) 6b of the transfer roller 6 is 10 ⁷ to 10.
A single-foamed or open-foamed EPDM, SBR, BR or the like processed into a roller diameter of 20 mm and a length of 300 mm was used so as to have a resistance of about 10 ¹⁰ Ω · cm. Regarding the hardness of the transfer roller 6, the Asker C hardness is 15 ° to
35 ° is preferable, and in this embodiment, 24 ° is used.

Further, the transfer roller 6 is attached to the surface of the photosensitive drum 1.
To form a transfer nip portion N _1, and the contact pressure f per unit length in the transfer nip portion N ₁ is f = 3
g / cm (0.3g / cm ≦ f ≦ 10g / cm is preferable)
Set to.

Next, in FIG. 1, some surfaces and angles formed by these surfaces are determined.

First, regarding the surface, the vertical plane passing through the central axis of the photosensitive drum 1 is the vertical plane S ₀ , and the center of the width of the central axis of the photosensitive drum 1 and the transfer nip portion N ₁ (center in the rotational direction of the transfer roller 6). The plane passing through and is the transfer surface S ₁ , the photosensitive drum 1
The central axis and the lower transfer guide 31b guide surface S ₂ of the plane passing through the tip of the transfer nip N ₁ as the photosensitive drum 1 (or transfer roller 6) of the plane tangent to the transfer nip plane S ₃ of the resist roller pair 30 A plane which passes through the resist nip portion N ₂ formed in the contact portion and contacts the resist roller pair 30 is defined as a resist nip surface S ₄ . Each of the above surfaces will be simply referred to as surfaces S _{0 to} S _{4 in} the following description.

Next, regarding the angle, the surface S ₀ and the surface S _0
The angle formed by ₁ is the transfer angle θ ₀₁ , the angle formed by the surfaces S ₀ and S ₂ is the introduction angle θ ₀₂ , the angle formed by the surfaces S ₁ and S ₂ is the relative angle S ₁₂ , and the surface S ₃ is the surface. The angle formed with S ₄ is determined as the resist angle ₃₄ .

Furthermore, the shortest distance between the lower transfer guide 31b and the surface of the photosensitive drum 1 is determined as r. In the present embodiment, the above angles and the shortest distance r are set as follows. Transfer angle θ ₀₁ = 10 ° (0 ° ≦ θ ₀₁ ≦ 15 ° is preferable) Introduction angle θ ₀₂ = 36 ° (30 ° ≦ θ ₀₂ ≦ 42 ° is preferable) Registration angle θ ₃₄ = 13.5 ° (5 ° ≦ θ ₃₄ ≦ 40 ° is preferred) Shortest distance r = 1.5 mm (0.5 mm ≦ r ≦ 3.5 mm
Note that the relative angle θ ₁₂ is not an absolute _{value based} on the surface S ₀ , and when the position of the surface S ₁ is _first determined, the relative angle θ ₁₂ of the surface S ₂ is preferable with respect to the surface S ₁ . The position is decided. The value is determined as a relative angle θ ₁₂ = 26 ° (20 ° ≦ θ ₁₂ ≦ 40 ° is preferable).

When the image forming apparatus is constructed based on each of the above-mentioned values and an image is formed, there is no void even if the peripheral speed difference is not provided between the photosensitive drum 1 and the transfer roller 6. A good image could be obtained. Further, since there is no difference in peripheral speed between the photosensitive drum 1 and the transfer roller 6, the photosensitive drum 1 which has begun to be damaged by about 60,000 sheets in the past can be used up to about 100,000 sheets without damage. (Comparative Example) As a comparative example, the transfer angle θ ₀₁ , the introduction angle θ ₀₂ , the registration angle θ ₃₄ , the shortest distance r, the contact pressure f, and the hardness of the transfer roller 6 of the above-described Example 1 are “suitable”, respectively.
A case where the value deviates from the value shown as will be described.

First, when the transfer angle θ ₀₁ exceeds 15 °, a hollow image occurs on the recording material P having high rigidity such as OHP. On the contrary, when it is less than 0 ° (when the transfer surface S ₁ is on the downstream side of the vertical surface S ₀ ), the toner is scattered on the surface of the recording material P in a low humidity environment with a humidity of 15% or less, so-called scattering. An image has occurred.

Next, when the introduction angle θ ₀₂ exceeds 42 °, a hollow image is formed on a postcard or the like, and when it is less than 30 °, a scattered image occurs in a low humidity environment.

Next, when the resist angle θ ₃₄ exceeds 40 °, a hollow image is formed on a postcard or the like, and when it is less than 5 °, a scattered image occurs in a low humidity environment.

Next, when the shortest distance r exceeds 3.5 mm, the scattered image in a low humidity environment is less than 0.5 mm, and when the shortest distance r is less than 0.5 mm, a hollow image and a transfer guide stain (such as toner) on a postcard. ) Occurred.

Next, the transfer roller 6 for the photosensitive drum 1
When the contact pressure f per unit length of exceeds 10 g / cm, a hollow image is generated on a postcard, etc.
If it is less than / cm, a phenomenon of poor transfer or poor transport of thick paper (for example, the recording material P slips) occurs.

Finally, when the hardness (Asker C) of the transfer roller 6 exceeds 35 °, a hollow image occurs on a postcard or the like. On the other hand, when the angle was less than 15 °, the recording material P having a large curl amount and high rigidity produced an image having a poor transfer in a low humidity environment. <Embodiment 2> In Embodiment 1, when an image is formed on the recording material P having high rigidity such as OHP at a density higher than the proper density, about 1 out of 100 sheets may cause a slight hollow. It was Therefore, as the developing device 5, the developing sleeve 5a has a toner charge amount of 16.0 μC / unit mass /
When a toner having a toner composition of g and a toner mass per unit area of 0.9 mg / cm ² was used, it was possible to obtain an image having no void. <Embodiment 3> A double-sided copy of a postcard was made using the image forming apparatus having the configuration of the first or second embodiment. When the second side was copied, the image density was high and the postcard was 15 mm.
If you have curled more than once, about 1 in 100,
Occasionally, there was a slight dropout in the image.

Therefore, as shown in the top view of FIG. 2, at the tip of the lower transfer guide 31b, a depth slightly wider than the paper passing area of a postcard (100 mm for a normal postcard, 142 mm for a reciprocating postcard). When the image formation was performed by providing the cutout portion 31c of about 10 mm, it was possible to obtain a good image with no void.

[0044]

As described above, according to the present invention,
Recording is performed by maintaining the contact pressure f per unit length of the transfer device, the transfer angle θ ₀₁ , the shortest distance r, the introduction angle θ ₀₂ , the registration angle θ ₃₄ , the relative angle θ _12, etc. within the above-mentioned ranges. Even if the thickness of the material or the environment changes, it is possible to form a good image by preventing the hollow image and the scattering of the image without providing the peripheral speed difference between the image carrier and the transfer device. Further, since there is no difference in peripheral speed, it is possible to extend the life of the image bearing member and maintain good image quality for a long time.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view illustrating the configuration of an image forming apparatus according to a first exemplary embodiment.

FIG. 2 is a top view showing the configuration of a lower transfer guide of the third embodiment.

FIG. 3 is a vertical cross-sectional view showing the configuration of a conventional image forming apparatus.

[Explanation of symbols]

1 image carrier (photosensitive drum) 2 primary charging device 3 exposure means 5 developing device 6 transfer device (transfer roller) 7 cleaner 9 static eliminator 10 power supply 30 registration roller 31 transfer guide 31a upper transfer guide 31b lower transfer guide P recording material r Shortest distance (distance between lower transfer guide and photosensitive drum surface) N ₁ transfer nip N ₂ registration nip S ₀ vertical surface S ₁ transfer surface S ₂ introduction surface S ₃ transfer nip surface S ₄ registration nip surface θ ₀₁ transfer angle θ ₀₂ Introduction angle θ ₁₂ Relative angle θ ₃₄ Registration angle

Claims (7)

[Claims] 1. A linear transfer nip portion is formed along a generatrix direction of the image carrier by bringing a transfer device into contact with a surface of a cylindrical image carrier from a substantially lower side with a predetermined contact pressure. The transfer of the toner image on the image bearing member to the front surface side of the recording material by applying a transfer charge to the back surface side of the recording material nipped and conveyed in the transfer nip portion via the transfer device. In the image forming apparatus, when the contact pressure per unit length of the transfer device at the transfer nip portion is f, the corresponding contact pressure f satisfies 0.3 g / cm ≦ f ≦ 10 g / cm 2, and A vertical plane passing through the central axis of the image carrier is S ₀ , a plane passing through the central axis of the image carrier and the width center of the transfer nip portion is a transfer surface S ₁ , and the transfer is performed with respect to the vertical plane S ₀ . the angle at which the surface S ₁ is formed in the upstream side of the recording medium When shooting angle theta _01, the transfer angle theta ₀₁ is, to satisfy _{0 ° ≦ θ 01 ≦ 15 °} , and setting the respective values, the image forming apparatus characterized by. 2. An upper transfer guide and a lower transfer guide that guide the recording material to the transfer nip portion are provided on the upstream side of the transfer nip portion, and the tip of the lower transfer guide and the surface of the image carrier are provided. When the shortest distance between them is r, the shortest distance r satisfies 0.5 mm ≦ r ≦ 3.5 mm, and a plane passing through the central axis of the image carrier and the tip of the lower transfer guide is introduced surface. S ₂ and the angle formed by the introduction surface S ₂ with respect to the vertical surface S ₀ are the introduction angles θ ₀₂ , the respective values are set so that the introduction angle θ ₀₂ satisfies 30 ° ≦ θ ₀₂ ≦ 42 °. The image forming apparatus according to claim 1, wherein: 3. A registration roller pair is provided on the upstream side of the lower transfer guide to contact each other to form a registration nip portion, and a plane which passes through the transfer nip portion and is in contact with the image carrier is a transfer nip surface S ₃ . A plane that passes through the registration nip portion and contacts the pair of registration rollers is a registration nip surface S.
₄ , the transfer nip surface S ₃ and the registration nip surface S ₄
The registration angle θ ₃₄ is defined as an angle formed by and, and the registration angle θ ₃₄ is set such that the value satisfies 5 ° ≦ θ ₃₄ ≦ 40 °. Image forming device. 4. When a relative angle θ ₁₂ is an angle formed by the transfer surface S ₁ and the introduction surface S ₂ , the relative angle θ ₁₂ is set so that the relative angle θ ₁₂ satisfies 20 ° ≦ θ ₁₂ ≦ 40 °. The image forming apparatus according to claim 1, wherein the image forming apparatus is set. 5. The image according to any one of claims 1 to 4, wherein the transfer member is a transfer roller having a roller-shaped conductive elastic body that comes into contact with the surface of the image carrier. Forming equipment. 6. The Asker C hardness of the transfer roller is 1
The image forming apparatus according to claim 5, wherein the angle is 5 ° or more and 35 ° or less. 7. The image forming apparatus according to claim 1, wherein the lower transfer guide has a notch portion at a leading end portion, the notch portion having a sheet passing width of a postcard.