JPH09127804A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To always excellently transfer a toner image without forming a fault image even by an image forming device of a reversal developing system whose transfer means is a contact type electrification system, and constituted so as to abut on an image carrier with a light pressure and rotate following the image carrier. SOLUTION: The toner image is formed by reversely developing an electrostatic latent image formed on the surface of the image carrier 1. The transfer means 6 is a rotating body brought into contact with the carrier 1 with an abutting pressure being <=3.0g/mm in a state where a recording material P is interposed in the carrier 1 and rotates following the carrier 1. Besides, the material P is interposed and carried at a transfer nip part N being the abutting part of the carrier 1 and the transfer rotating body at a speed corresponding to the rotating speed of the carrier 1. Then, the toner image forming on the carrier 1 side is transferred on the material P side by imparting electric charge for transfer to the back surface of the material P by the transfer rotating body. Besides, this device is provided with a recording material carrying means interposing and carrying the material P and feeding it to the transfer nip part N. Then, the carrying speed of the recording material by the recording material carrying means is set to be 0.01-3% higher than the rotating speed of the carrier 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic process / electrostatic recording on the surface of an image bearing member (first recording medium) such as an electrophotographic photosensitive member / electrostatic recording dielectric which is rotationally driven at a predetermined speed. A transfer method in which a toner image corresponding to target image information is formed by an appropriate image forming process means such as a process, and the toner image is transferred to a recording material (second recording medium) by the transfer means to execute image formation. Image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, in a transfer type image forming apparatus as described above, as a means for transferring a toner image from an image carrier side to a recording material side, a corona transfer device (corona charger) utilizing corona discharge is used. Widely used.

This is because at the transfer portion, the back surface of the recording material fed to the image carrier is subjected to a corona charging process by a corona charger in the opposite polarity to the toner of the toner image on the side of the image carrier to carry the toner image. The electrostatic transfer is performed from the body side to the recording material side, and it is effective as a means for transferring the toner image from the image bearing body side to the recording material side in a non-contact method without bringing the transfer means into contact with the recording material.

However, in order to generate corona discharge, a considerably high voltage must be applied to the corona charger, which necessitates a high voltage power source, and has a problem that ozone is generated during corona discharge. ing.

In recent years, an image forming apparatus has been developed which uses a contact charging type transfer means which only needs to apply a relatively low voltage.

This contact charging type transfer means is generally provided with a charging member such as a conductive roller or a conductive brush that comes into contact with the back surface of the recording material, and a relatively low transfer bias voltage is applied to this charging member. The toner image is electrostatically transferred from the image carrier side to the recording material side by subjecting the back surface of the recording material to contact charging with a polarity opposite to that of the toner of the toner image on the image carrier side. Since such a contact charging type transfer means only needs to apply a low voltage, it has advantages that the power source can be made small, lightweight and low cost, and that the amount of ozone generated is small.
It has received a lot of attention.

FIG. 5 shows a schematic view of an example of the contact charging type transfer means. An image carrier 1 is, for example, a rotary drum type electrophotographic photosensitive member. The figure shows only part of it. The photoconductor 1 is rotationally driven in a clockwise direction indicated by an arrow at a predetermined peripheral speed, and a toner image corresponding to desired image information is formed on the peripheral surface thereof by an image forming process means (not shown).

Reference numeral 6 denotes a transfer roller (conductive roller) as a contact charging type transfer means. The shaft portions on both ends are rotatably supported by bearing members and arranged in parallel with the photoconductor 1. The transfer nip portion N is formed by contacting the photoconductor 1 with a predetermined contact pressure by a pressing means such as a spring. The photoconductor 1 rotates in the forward direction with respect to the rotation of the photoconductor 1. A power source 11 applies a predetermined transfer bias voltage to the transfer roller 6.

Reference numeral 12 is a pair of registration rollers as a recording material pinching and conveying means for feeding the recording material (transfer material) P to the transfer nip portion N.

The recording material P is nipped and conveyed by the registration roller pair 12 to the transfer nip portion N at a predetermined control timing and fed. The fed recording material P has a transfer nip portion N.
And is conveyed while being nipped and conveyed through the transfer nip portion N.

A predetermined transfer bias voltage is applied from the power source 11 to the transfer roller 6 while the recording material P is nipped and conveyed in the transfer nip portion N, and the rear surface of the recording material P is brought into contact with the rear surface of the recording material P in the transfer nip portion N. By the transfer roller 6 to which the above voltage is applied, a charge having a polarity opposite to that of the toner of the toner image on the photoconductor 1 side is directly applied (contact charging), and from the photoconductor 1 side to the surface side of the recording material P. The toner images are sequentially electrostatically transferred.

Further, in recent years, an image forming apparatus such as a copying machine or a laser beam printer which employs an image exposure method for exposing an image on an image bearing member and a reversal development method for forming a toner image on an image exposing portion. Is used a lot.

The image forming apparatus of the reversal development type develops the electrostatic latent image formed on the surface of the image bearing member with a toner (negative toner) having the same polarity as the polarity of the latent image (charging processing polarity of the image bearing member). The latent image is visualized by adhering toner to the potential attenuation portion, which is the exposed bright portion of the latent image.

For example, if the photosensitive member 1 as an image bearing member is -7
Primary charge to about 00V, and the charged surface is image-exposed by an image exposure means such as a laser scanner to attenuate the surface potential of the photosensitive member in the exposed bright portion to about -400 to -100V to form an electrostatic latent image, The negative toner is electrostatically attached to the potential attenuating portion, which is the exposed bright portion of the latent image, by the difference from the surface potential due to the developing bias value applied to the developing sleeve of the developing means.

In the regular development, a toner (positive toner) having a polarity opposite to that of the latent image is used to electrostatically adhere the toner to a high potential portion which is an exposed dark portion of the latent image to make the latent image visible. It is to be visualized.

[0016]

In the case of an image forming apparatus of the reversal developing system, the toner adheres on the photosensitive member of the same polarity as an image carrier as compared with the case of the regular developing system. Phenomenon in which the attraction force is small and is easily affected by environmental changes and electrostatic / mechanical effects, and for example, the toner image on the photoconductor jumps to the surface of the recording material (just before the target) before reaching the transfer area. Is likely to occur. As a countermeasure, there is a method of increasing the electric field of the transfer portion (transfer bias UP).

However, in the case of the image forming apparatus of the reversal developing system, the polarity of the transfer bias is opposite (+) to the charging polarity (eg, −) of the photoconductor, so that if the transfer bias is increased, the normal developing system is set. Compared with this, it is difficult to increase the transfer bias so much because a memory is likely to occur in the photoconductor.

Therefore, the toner holding force of the recording material in the transfer area cannot be increased, and the toner is easily affected electrostatically and mechanically.

Further, in the contact charging type transfer means, the contact pressure of the transfer roller to the photosensitive member as the image bearing member is set to a light pressure so that the photosensitive member is rotated by the rotation of the photosensitive member so that the recording material is transferred from the photosensitive member. It is possible to prevent the characters in the transfer toner image from being dropped and the image from being distorted. On the other hand, since the transfer roller is brought into contact with the photosensitive member with light pressure and driven to rotate, the recording material gripping force at the transfer nip portion is small and the recording material nip conveying force at the transfer nip portion is small.

Therefore, when there is a difference between the peripheral speed of the photosensitive member and the recording material conveying speed of the recording material sandwiching and conveying means for feeding the recording material to the transfer nip portion, the influence of the recording material in the transfer area is caused by the influence. Vibration and uneven transport speed cannot be suppressed, and an image defect may occur.

Therefore, the present invention does not cause an image defect even in an image forming apparatus of a reversal development type and a transfer means of a contact charging type which is brought into contact with an image carrier at a light pressure and driven to rotate. The purpose is to always perform good toner image transfer.

[0022]

SUMMARY OF THE INVENTION The present invention is an image forming apparatus having the following configuration.

(1) A toner image corresponding to desired image information is formed on the surface of an image bearing member which is rotationally driven at a predetermined speed by an image forming process means, and the toner image is transferred onto a recording material by a transfer means to form an image. In a transfer-type image forming apparatus that executes formation, a toner image is formed by reversal development of an electrostatic latent image formed on the surface of an image carrier, and a transfer unit is 3.0 g / mm
The recording material is a rotating body that is driven by the rotation of the image carrier and brought into contact with the following contact pressure. The toner image on the image carrier side is transferred to the recording material side by being nipped and conveyed at a speed corresponding to the rotation speed of the recording material, and a transfer charge is applied to the back surface of the recording material by the transfer rotating body. A recording material conveying means for nipping and conveying and feeding the recording material to the transfer nip portion is provided, and the recording material conveying speed by the recording material conveying means is 0.01 to 3% higher than the rotation speed of the image carrier. Image forming apparatus.

(2) The image forming apparatus according to (1), wherein the contact pressure of the transfer rotary member to the image carrier is set to 0.8 g / mm or less with the recording material interposed.

(3) The recording material conveying speed by the recording material conveying means is set to be 0.1 to 2% higher than the rotational speed of the image carrier, according to (1) or (2). Image forming apparatus.

(4) A means for detecting the thickness of the recording material to be fed is provided, and the recording material conveying speed of the recording material conveying means is variably controlled according to the recording material thickness detection information of the detecting means. The image forming apparatus as described in any one of (1) to (3) above.

(5) Recording is performed according to the recording material length information of the means for detecting the length of the fed recording material in the conveying direction or the recording material length information of the recording material designated by the used recording material size designating means. The image forming apparatus described in any one of (1) to (4), wherein the recording material conveying speed is variably controlled by the material conveying means.

<Operation> a) Recording is performed by setting the recording material conveying speed for the transfer nip portion by the recording material conveying means to be 0.01 to 3% larger than the rotation speed (image forming speed) of the image carrier. In the process of feeding and conveying one recording material from the material conveying means to the transfer nip portion, a bending loop of the recording material occurs in the recording material portion that straddles the recording material conveying means and the transfer nip portion.

Even if the loop causes a difference between the rotation speed of the image carrier and the recording material conveying speed of the recording material conveying means, the loop is vibrated by the action of intermittent back tension of the recording material in the transfer area. It also serves as a buffer section (buffer section) that suppresses irregularities in transport speed and absorbs electrostatic and mechanical influences.

Therefore, in order to prevent the characters of the transferred toner image from the image carrier to the recording material to be omitted or the images to be distorted, the transfer rotary member of the contact charging type transfer means is brought into a slight pressure contact with the image carrier and driven. In the case of rotating the recording material, even if the recording material gripping force at the transfer nip portion is small and the recording material holding and conveying force at the transfer nip portion is small, the recording material varies in the recording material conveying speed of the recording material conveying means. Without being affected, the transfer nip is stably conveyed electrostatically and mechanically at a speed corresponding to the rotation speed of the image carrier, and a toner image is always excellent without causing image defects such as image misalignment. Transfer can be performed.

B) When the recording material conveying speed by the recording material conveying means is less than 0.01 with respect to the rotational speed of the image carrier, the amount of the recording material loop formed is small and the function as the buffer portion is insufficient. If it is larger than 3%, the recording material loop is excessively formed, and the recording material loop comes into contact with other objects to slide and become dirty, or the recording material loop at the transfer nip portion is damaged. In the present invention, the content is specified to be 0.01 to 3% because it may adversely affect the transportation state. It is preferable to set 0.1 to 2%.

C) The contact pressure of the transfer rotary member to the image carrier is
In order to prevent the characters in the transferred toner image from the image carrier to the recording material and the image distortion, the light pressure is set to 3.0 g / mm or less, preferably 0.8 g / mm or less with the recording material interposed. Good to do. The contact pressure may be substantially zero.

The thickness of a recording material usually used in an image forming apparatus such as a printer is about 40 to 300 μm (for example, thin paper 60 μm to postcard 220 μm). The contact pressure is set to be 3.0 g / mm or less even when a thick paper having a recording material thickness range of about 300 μm is fed. Therefore, the contact pressure of the transfer rotator with respect to the image carrier without the recording material is set lower than the above. For example, 2.7 g / mm or less, preferably 0.
It is set to 7 g / mm or less. The contact pressure may be substantially zero. In short, the contact pressure of the transfer rotator to the image carrier is a thick paper that is normally used when the recording material is fed to the transfer nip and the recording material is interposed between the image carrier and the transfer rotator. Even if the recording material is No. 3, the contact pressure state of 3.0 g / mm or less may be maintained. The contact pressure with the recording material interposed may be substantially zero.

D) A means for detecting the thickness of the recording material to be fed is provided, and the recording material conveying speed of the recording material conveying means is changed according to the recording material thickness detection information (thick paper or thin paper) of the detecting means. By adopting a configuration in which the recording material is variably controlled, in addition to the effect of a) above, a transfer material image when the recording material is thick paper by forming a recording material loop of an appropriate amount corresponding to the thickness of the recording material. Shrinkage can also be prevented.

E) Recording material length information of means for detecting the length of the fed recording material in the conveying direction or recording material length information of the recording material designated by the used recording material size designating means (small size, large size) By adopting a configuration in which the recording material conveying speed of the recording material conveying means is variably controlled according to the size),
In addition to the effect of the above, a proper amount of recording material loop is formed corresponding to the length of the recording material in the conveyance direction, and the loop portion is excessively formed in the large-sized recording material, and the loop portion comes into contact with other parts. It is possible to prevent the occurrence of stains and the like due to this.

[0036]

BEST MODE FOR CARRYING OUT THE INVENTION

<Embodiment 1> (FIG. 1) (1) Example of image forming apparatus FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus. The image forming apparatus of this example is a laser beam printer using a transfer type electrophotographic process.

Reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as an image bearing member. The photosensitive drum 1 of the present embodiment has a grounded conductive base layer 1b made of aluminum, iron or the like and a photoconductive layer 1a formed on the outer peripheral surface thereof, which is, for example, an organic photoconductive layer, as a basic component, and has a central support shaft. 1c is rotated in the clockwise direction of arrow R1 by a driving unit (not shown) at a predetermined peripheral speed (image forming speed, process speed).

Reference numeral 2 is a primary charging means for uniformly and uniformly charging the surface of the photosensitive drum 1 to a predetermined polarity and potential. The charging means of this example is a contact charging means using the charging roller 2.

The charging roller 2 includes a conductive roller (core metal) 2c at the center, and a conductive layer 2b formed on the outer periphery of the conductive roller 2c.
Further, the resistance layers 2a ₁ and 2a ₂ sequentially formed on the outer periphery thereof
Is a multi-layer roller composed of a core metal 2c, and both ends of the core metal 2c are rotatably supported by a bearing member and are arranged in parallel with the photosensitive drum 1.

The bearing members at both ends of the cored bar 2c are urged to move toward the photosensitive drum 1 by pressing means such as springs, whereby the charging roller 2 is provided on the surface of the photosensitive drum 1 in a predetermined manner. The photosensitive drum 1 is pressed under the contact pressure of, and is driven to rotate in the direction of the arrow R2 as the photosensitive drum 1 rotates. A predetermined charging bias voltage is applied to the charging roller 2 from a charging bias applying power source 10 via an electric contactor 10a and a cored bar 2c in contact with the electric contactor 10a.
The peripheral surface of the rotary photosensitive drum 1 is subjected to a primary charging process by a contact charging method uniformly and uniformly to a predetermined surface potential.

Next, a laser beam whose intensity is modulated corresponding to the time-series electric digital pixel signal of the target image information by the laser beam scanner 3 as the image exposure means is applied to the surface of the rotary photosensitive drum 1 subjected to the primary charging. By performing the scanning exposure L, the surface potential of the exposed bright portion on the surface of the photosensitive drum 1 is attenuated, and an electrostatic latent image corresponding to the target image information is formed on the surface of the photosensitive drum 1. Then, the formed electrostatic latent image is developed as a toner image by the developing device 5. This example is a jumping developing type reversal developing device using a one-component magnetic toner (negative toner) as a developer. The toner in the developing container 5b is rotatably driven in the direction of arrow R5, and is applied to the surface of the developing sleeve 5a to which a predetermined developing bias voltage is applied from the developing bias applying power source 5c so as to have a predetermined thickness. And developing sleeve 5
The developing sleeve 5a at the developing portion, which is the portion facing a.
From the side, the toner adheres to the exposed bright portion of the electrostatic latent image on the surface of the photosensitive drum 1, and the reversal development of the electrostatic latent image is performed.

On the other hand, the recording material P is fed from a paper feeding portion (not shown), and the recording material P is predetermined by the registration roller pair 12 as a recording material conveying means for the transfer portion in synchronization with the rotation of the photosensitive drum 1. At the control timing of, the sheet is fed in the direction of arrow K1 to the transfer nip portion N which is the contact portion between the photosensitive drum 1 and the transfer roller 6 as the transfer means. The above-mentioned predetermined control timing is such that the front end portion of the recording material P has just reached the transfer nip portion N when the front end portion of the toner image area formed on the surface of the rotary photosensitive drum 1 has reached the transfer nip portion N. It is the timing to become.

The transfer roller 6 is a conductor roller (core bar) 6a.
And a conductive layer 6b formed on the outer peripheral surface thereof, and both ends of the cored bar 2c are rotatably supported by bearings on bearings and arranged in parallel with the photosensitive drum 1.

The bearing members at both ends of the cored bar 2c are urged to move toward the photosensitive drum 1 by pressing means 26 such as springs, whereby the transfer charging roller 2 is moved to the surface of the photosensitive drum 1. With a light contact pressure, and as the photosensitive drum 1 rotates, the arrow R
It rotates in the direction of 6. The recording material P fed to the transfer nip portion N by the pair of registration rollers 12 is nipped and conveyed in the transfer nip portion N by the rotating photosensitive drum 1 and the transfer roller 6 driven to rotate. After the leading edge of the recording material P reaches the transfer nip portion N, until the trailing edge of the recording material P finishes passing through the pressure contact nip portion N ₁₂ of the registration roller pair 12, the pressure contact nip portion of the registration roller pair 12 is reached. It is conveyed across N ₁₂ and the transfer nip portion N.

While the recording material P is nipped and conveyed to the transfer roller 6 through the transfer nip portion N, the toner image on the surface of the photosensitive drum 1 is transferred from the transfer bias applying power source 11 through the core metal 2c. A bias voltage having a polarity opposite to that of the toner is applied, the back surface of the recording material P contacts the back surface, and the above-mentioned transfer bias voltage is applied to the driven rotation transfer roller 6.
Is subjected to contact charging with a polarity opposite to the polarity of the toner of the toner image, so that the toner image on the surface of the rotary photosensitive drum 1 is transferred to the transfer nip portion N of the recording material P which is nipped and conveyed. Electrostatic transfer is sequentially performed on the front side.

Generally, the transfer bias voltage is applied to the transfer roller 6 at the same time as the front end of the recording material P fed from the registration roller pair 12 reaches the transfer nip portion N or immediately before (at about 0 to 1 cm). It is controlled to start at the same time as when the transfer nip portion N at the trailing end portion of the recording material P has finished or immediately after it has passed (about 0 to 1 cm).

In addition, the transfer roller 6 may be partially or entirely operated from the start of image formation to the start of transfer, from the end of transfer to the start of next transfer, and from the end of transfer to the end of image formation. In general, the transfer roller 6 is cleaned by applying a predetermined bias (cleaning bias) having a polarity opposite to that of the transfer bias to fly the toner attached to the transfer roller 6 onto the photosensitive drum 1.

The recording material P which has received the transfer of the toner image through the transfer nip portion N is separated from the surface of the photosensitive drum 1 and conveyed to an image fixing means (not shown), where it undergoes fixing processing of the toner image, The final image-formed product (print, copy) is discharged outside the apparatus main body. Alternatively, in the case of the multiple copy mode or the double-sided copy mode, the sheet is fed to the transfer nip portion N again without being turned upside down or turned upside down via the re-conveying means.

After the transfer of the toner image to the recording material P, the cleaner 7 removes the adhering substances such as residual toner by the cleaner 7, and the static eliminator 9 removes the electric charges to initialize the photosensitive drum 1. After that, the next image forming process is performed. Be used for.

(2) Registration Roller Pair 12 and Transfer Roller 6 The registration roller pair 12 of this example as a recording material sandwiching and conveying means for the transfer nip portion N comprises a hard rubber roller 12a and a metal roller 12b, and a spring (not shown) or the like. strong grip of the recording material is applied pressure contact with each other by pressure means, mainly hard Gomurara 12a is rotated in the arrow R12 direction, are incorporated in addition the recording material P is nip-conveyed in the press nip N ₁₂ It The hard rubber roller 12a is rotationally driven for a predetermined period by transmitting the rotational force of the drive source 14 via the clutch 13 which is intermittently controlled at a predetermined timing.

In this example, the transfer roller 6 rotated by the rotation of the photosensitive drum 1 is a conductive layer 6b, and its resistance value is 1
A roller diameter of 16 m is used for EPDM, SBR, BR, etc. having single-cell or continuous-cell properties so as to be about 0 ⁷ to 10 ¹⁰ Ω · cm.
m, and a length of about 300 mm was used.

In this example, the contact pressure of the transfer roller 6 with respect to the photosensitive drum 1 is set to 0.33 g / mm when the recording material P is not present in the transfer nip portion N.
In this contact pressure setting, in this example, the transfer nip portion N is
Even when a thick recording material such as 300 μm is used among the recording materials of various paper thicknesses that are normally used, the contact pressure of the transfer roller 6 against the photosensitive drum 1 in the presence of the recording material is 3.0 g / A light pressure state of mm or less is maintained.

The image forming speed (process speed) of the apparatus, that is, the rotational peripheral speed of the photosensitive drum 1 is 100 in this example.
mm / s.

Thus, in this example, the conveyance speed of the recording material P to the transfer nip portion N was varied to adjust the rotation speed of the registration roller pair 12 as the recording material conveying means to the transfer nip portion N. As a result, the recording material conveying speed of the registration roller pair 12 is 0.01 with respect to the rotation speed of the photosensitive drum 1, that is, the image forming speed.
By increasing by 3% or less, image defects such as deviation of the toner image transferred from the surface of the photosensitive drum 1 to the recording material P at the transfer nip portion N can be prevented and reduced, and in particular, the registration roller can resist the image forming speed. The recording material conveyance speed of pair 12 is 0.1 to 2
The best setting was to increase it.

In this example, the recording material conveying speed of the pair of registration rollers 12 during one recording material conveyance is constant, but the transfer nip portion N and the pressure contact nip portion N ₁₂ of the registration roller pair 12 are not separated from each other. The recording material conveyance speed during one recording material conveyance of the registration roller pair 12 may be variable in consideration of the increase amount of the recording material loop formed therebetween.

The contact pressure of the transfer roller 6 as the contact charging type transfer means with respect to the photosensitive drum 1 as the image carrier is the spring constant of the spring for biasing both end shafts of the transfer roller 6 toward the photosensitive drum 1 side. It can be variably adjusted by changing the length. Then, the contact pressure on the photosensitive drum 1 on both ends of the transfer roller 6 is measured by using a strain sensor or a load cell, and the linear pressure g / mm is calculated from the total pressure of the measured values. The contact pressure can be adjusted and set so as to be a predetermined set value.

<Embodiment 2> (FIGS. 2 and 3) In this embodiment, the image forming apparatus according to the first embodiment is used as a recording material conveying means in accordance with the thickness of the recording material fed to the apparatus. The recording material conveying speed of the registration roller 12 is controlled.

In this example, the DC power source 21 is connected to the metal roller 12b of the registration roller pair 12, and the hard rubber roller 1 is connected.
The current measuring device 22 is connected to 2a, and the registration roller pair 1
2 also has a function as a means for detecting the thickness of the recording material P that has been fed and used in the apparatus.

[0059] That is, in a state in which the recording material P is incorporated in addition to the press nip N ₁₂ of the pair of registration rollers 12, it flows through the recording material P when applying a voltage in the power source 21 between the roller pairs 12a · 12b By detecting the current amount with the current measuring device 22, the thickness of the fed recording material P can be detected from the current amount. Then, the recording material conveying speed of the registration roller pair 12 is controlled based on the detected recording material thickness information.

In general, when the recording material P is thick, the transfer charge can be evenly placed on the paper surface, and the scattering of images tends to be small. Also, the recording material is less likely to vibrate near the transfer nip portion N.

On the other hand, on the other hand, the rigidity is strong (the waist is strong).
Therefore, a recording material loop is not easily formed between the nip portion N-N ₁₂ , and the elastic force is strong. Therefore, the registration roller pair 12
If the recording material conveying speed is too higher than the image forming speed, the toner image transferred from the surface of the photosensitive drum 1 to the recording material P contracts at the transfer nip portion N, or the trailing end of the recording material P has the registration roller pair 12 formed. After passing through the nip portion N ₁₂ , de-shock may occur, resulting in image misalignment or a defective image.

Therefore, in this example, in the image forming apparatus according to the first embodiment, the recording material conveying speed of the registration roller 12 is controlled according to the thickness of the recording material fed to the apparatus as described above. Further, the contraction and deshocking of the transfer toner image, which is likely to occur when the fed recording material P is thick, are prevented and reduced.

FIG. 3 shows a ratio A of the thickness d of the recording material P and the recording material conveying speed of the registration roller pair 12 to the image forming speed.
It is a graph which shows the relationship with (%).

These data are stored in advance in the control circuit, and the ratio A of the recording material conveying speed of the registration roller pair 12 to the image forming speed is determined according to the thickness d of the recording material P detected by the measuring device 22. By changing the recording material P, even when a thick material such as thick paper is used as the recording material P, it is possible to prevent and reduce image shrinkage and image defects due to shock-free, and widely correspond to the thickness of the recording material. it can.

The thickness of the recording material P can be detected also by measuring the light transmittance.

The other structure of the image forming apparatus is the same as that of the first embodiment (FIG. 1), and therefore the repetitive description will be omitted.

<Third Embodiment> (FIG. 4) In this embodiment, in the image forming apparatus of the first embodiment, the recording material is fed in accordance with the length of the recording material P fed in the apparatus in the feeding direction. The recording material conveying speed of the registration roller 12 as a means is controlled.

Generally, when the recording material conveying speed by the registration roller pair 12 as the recording material conveying means is higher than the image forming speed, a bending loop of the recording material P is formed between the nip portion N-N ₁₂ , and Since the loop amount increases as the conveyance progresses, the longer the feeding recording material P in the conveyance direction, the larger the loop amount. When the loop amount increases, the recording material becomes dirty due to the contact of the loop portion with another portion, and the elastic force in the traveling direction of the recording material becomes large. As a result, the recording material exceeds the gripping force at the transfer nip portion N. Image slippage is likely to occur due to slipping.

Therefore, in this example, in the image forming apparatus according to the first embodiment, the recording material is conveyed by the registration roller 12 in accordance with the length in the conveying direction of the recording material P that is used for feeding the recording material to the apparatus as described above. By controlling the speed so as to have an optimum loop amount according to the length of the fed recording material, stains on the recording material and image deviation are prevented and reduced.

FIG. 4 is a graph showing the relationship between the length l of the recording material P in the conveying direction and the ratio A of the recording material conveying speed of the registration roller pair 12 to the image forming speed.

These data are stored in the control circuit in advance, and the detection information of the feeding recording material length measuring device (not shown) using a sheet sensor or the like, and the recording material P specified by the user by specifying the recording material size to be used. By changing the ratio A of the recording material conveying speed of the registration roller pair 12 to the image forming speed according to the selection designation information of the length l, it is possible to form a loop amount suitable for various sizes as the recording material P. This makes it possible to prevent or reduce stains on the recording material and image misalignment, and perform better image formation.

In this example, the ratio A is changed only for the length l of the recording material, but the ratio A is changed based on both the recording material thickness d and l, d of the second embodiment. Good.

Further, in consideration of the increase amount of the loop formation of the recording material between the nip portion N-N ₁₂ , the loop increase amount detecting means such as a photoelectric sensor is provided so as to prevent excessive loop formation. Alternatively, the recording material conveying speed of the registration roller pair 12 during one recording material conveyance may be variably controlled by predicting the formation loop amount from the size information of the fed recording material P by the control circuit. For example, after a predetermined amount of recording material loop is formed between the nip portion N-N ₁₂ , the recording material conveying speed of the registration roller pair 12 is changed to substantially the same speed as the image forming speed. An excessive loop amount is absorbed. Rotation of the registration roller pair 12 is stopped until
Alternatively, the speed may be controlled to be slower than the image forming speed, and when an excessive amount of loop is absorbed, the registration roller pair 12 may be re-rotated or returned to the original predetermined recording material conveying speed state. it can.

<Other Embodiments> 1) In the image forming apparatus of the embodiment, the contact charging roller 2 as the primary charging means may be forcibly driven by a driving means such as a motor. Other types of contact charging members such as blade type and rod type may be used. A corona charger, which is a non-contact charging type, may be used as the primary charging means.

2) The image exposure means may be other appropriate exposure means / mechanism such as slit exposure means for the original image.

3) The electrophotographic photosensitive member as the image bearing member is not limited to the drum type, but may be a rotating member of other forms such as a rotating belt type. It can also be of the injection charging type. Not limited to the electrophotographic photosensitive member, it may be an electrostatic recording dielectric or the like.

4) The transfer roller 6 as the contact charging type transfer means is a single-layer transfer roller having the conductor roller 6a and the conductive layer 6b in the embodiment, but may be a multi-layer transfer roller. The rotating body is not limited to the roller type and may be another rotating body such as a belt type.

5) The recording material conveying means 12 for feeding the recording material to the transfer nip portion N may be a pair of normal rollers having no registration roller function, or a recording material pinching and conveying mechanism composed of upper and lower rotating belts. .

[0079]

As described above, according to the present invention, even in the image forming apparatus of the reversal developing type, the transfer means is of the contact charging type and is brought into contact with the image carrier by light pressure and driven to rotate. It is possible to always execute good toner image transfer without causing image defects.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus according to the present invention.

FIG. 2 is a schematic configuration diagram of a main part of an image forming apparatus according to a second exemplary embodiment.

FIG. 3 is a diagram showing a relationship between a thickness of a recording material and a ratio of a recording material conveying speed of a registration roller pair to an image forming speed.

FIG. 4 is a diagram showing a relationship between a recording material conveyance direction length and a ratio of a recording material conveyance speed of a registration roller pair to an image forming speed in the image forming apparatus of the third embodiment.

FIG. 5 is a schematic configuration diagram of an example of a contact charging type transfer unit.

[Explanation of symbols]

1 ... Image bearing member (electrophotographic photosensitive drum), 2 ... Charging roller, 3 ... Laser scanner, 5 ... Developing device, 6 ...
・ Transfer roller, 7 ・ ・ Cleaner, 9 ・ ・ Electrification eliminator, 10
..11..Bias voltage applying power source, 26..Pressing means such as spring, P..Recording material (transfer material)

Claims (5)

[Claims] 1. A toner image corresponding to target image information is formed by an image forming process means on the surface of an image carrier which is rotationally driven at a predetermined speed, and the toner image is transferred to a recording material by a transfer means to form an image. In the image forming apparatus of the transfer system for executing the toner image formation, the toner image is formed by reversal development of the electrostatic latent image formed on the surface of the image carrier, and the transfer means is 3.0 in the presence of the recording material on the image carrier.
The recording material is a rotating body that is rotated by the rotation of the image carrier and is brought into contact with a contact pressure of g / mm or less. The toner image on the image carrier side is transferred to the recording material side by being nipped and conveyed at a speed corresponding to the rotation speed of the image carrier, and the transfer charge is applied to the back surface of the recording material by the transfer rotating body. A recording material conveying means for nipping and conveying the recording material and feeding it to the transfer nip portion, and the recording material conveying speed by the recording material conveying means is 0.01 to 3% higher than the rotation speed of the image carrier. An image forming apparatus characterized by. 2. The image forming apparatus according to claim 1, wherein the contact pressure of the transfer rotator on the image carrier is set to 0.8 g / mm or less in the presence of the recording material. 3. The image forming apparatus according to claim 1, wherein the recording material conveying speed by the recording material conveying means is set to be 0.1 to 2% higher than the rotational speed of the image carrier. . 4. A recording material conveying speed is variably controlled according to recording material thickness detection information of the detecting means, which has means for detecting the thickness of the recording material to be fed. The image forming apparatus according to any one of claims 1 to 3, characterized in that. 5. The recording material according to the recording material length information of the means for detecting the length of the fed recording material in the conveying direction or the recording material length information of the recording material designated by the used recording material size designating means. The image forming apparatus according to any one of claims 1 to 4, wherein the recording material conveying speed by the conveying means is variably controlled.