JP2006259122A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily and effectively suppress failures, such as transfer dust, dot image reproduction failure, toner scattering, and reverse transfer of a previous process transfer toner to an image carrier, by preventing the transfer of the toner in slight gaps on upstream and downstream of a transfer nip at the time of transfer without depending on a surface potential distribution (toner sensible image pattern) of an image carrier in developing. <P>SOLUTION: The image forming apparatus equipped with a photoreceptor, a developing roller for carrying and conveying a developer, and a means for transferring the toner image formed on the photoreceptor by an electric field to a transfer material, in which the development is performed under the conditions of satisfying the relation ä¾Q2¾-¾Q1¾}/¾Q1¾ ≥-0.3, when Q1 denotes the average charge quantity of the toner in the developer carried on the developing roller just before passing through the counter area between the developing roller and the photoreceptor in a state where a potential difference between the surface of the developing roller and the surface of the photoreceptor is almost 0 V and Q2 denotes the average charge quantity of the surface toner image of the transfer material right after the electric field transfer to the surface for the next transfer material from the photoreceptor. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention is used for black and white, mono-color or full-color electrophotographic copying machines, facsimiles, printers, etc., and transfers toner on a latent image carrier formed by an electrophotographic system or electrostatic recording system to recording paper or the like. The present invention relates to an image forming apparatus that obtains an image by transferring a material by applying a transfer electric field. More specifically, an image forming apparatus of a direct transfer method in which a toner image formed on a latent image carrier is directly transferred to a recording medium, and an intermediate transfer method in which the toner image is primarily transferred to an intermediate transfer member and then secondarily transferred to the recording medium. Furthermore, a direct transfer system that obtains a color image by superimposing and transferring a plurality of toner images formed on a latent image carrier onto a recording medium a plurality of times, and superimposing a plurality of times on an intermediate transfer member. The present invention relates to an intermediate transfer type color image forming apparatus that obtains a color image by batch transfer to a recording medium after intermediate transfer.

JP 2004-062140 A JP-A-10-010886 Japanese Patent Laid-Open No. 05-100534 JP 2003-084504 A JP 2003-241518 A JP 2002-357939 A

  In an image forming apparatus using an electrophotographic method or the like, an electrostatic latent image is formed on a latent image carrier (or image carrier) such as a photoconductor by performing exposure according to a document image or image information. The electrostatic latent image is developed with the toner of the developing means to be visualized, and then the toner image is transferred onto a transfer material such as recording paper and fixed to form an image. As a developing method in this case, currently, a two-component developing method using a two-component developer composed of a toner and a magnetic carrier as a developer, or a one-component developing method using a one-component developer that does not use a carrier. However, when higher image quality and higher speed are required, a two-component development system is preferably used. In the two-component development system, the two-component developer forms a spike called a developing magnetic brush on the developer carrying member, and this developing magnetic brush is in contact with the developing carrier in the developing process. Contact development and so-called non-contact development in which development is performed without contact are known. Usually, when high image quality and high density are required, the former contact development is often used.

  In the conventional image forming process, there are mechanisms and methods such as controlling the transfer current based on the development current and data obtained in advance according to the environment, and limiting the order of charge amounts of the process color toners before and after. It is complicated. On the other hand, there is a high possibility that the reliability of the control will be lost due to changes in the developer over time or due to environmental changes.

  It is also known that a phenomenon called toner dust (hereinafter referred to as transfer dust) may occur when a toner image is transferred from an image carrier to a transfer material such as an intermediate transfer member or a recording medium by applying a transfer electric field. Yes. Transfer dust means that when a toner image is transferred from an image carrier to a transfer material, the toner image (visible image) formed on the image carrier is not transferred to a position where it should originally be transferred, but around it. This is a phenomenon in which the image is blurred and transferred, resulting in blurring of the image, and particularly the sharpness of the image at the thin line portion is impaired. This phenomenon is conspicuous when superimposing images, and when superimposing three or four colors, the phenomenon of transfer dust is more likely to occur, and there is a problem that the image itself has poor graininess and becomes a rough image.

  In forming a color image with two or more colors of toner, Patent Document 1 develops a latent image on an image carrier in order to prevent the occurrence of a transfer dust phenomenon and to improve the graininess (roughness) of the image. In the image forming apparatus, the developing device includes a developing device that includes two or more two-component developing type developing devices having different developer colors as the developing device. A doctor blade that regulates the transport amount and layer thickness of the two-component developer carried and transported by the agent carrier, and the toner charge amount Q in each developing device of the developing device is Q1 < A configuration in which Q2 <Q3 <Q4 is high is proposed.

  In order to prevent generation of transfer dust when a toner image on a photoconductor is transferred onto an intermediate transfer belt without causing an abnormal image due to transfer failure or the like, Patent Document 2 discloses an intermediate transfer belt and a photoconductor. It has been proposed to provide a scorotron charger that applies a charge of the same polarity as the toner charge polarity toward the transfer surface of the intermediate transfer belt, upstream of the transfer nip portion between the toner and the intermediate transfer belt. Yes.

  In Patent Document 3, a developing current measuring circuit is connected between the developing sleeve and the developing bias power source in order to perform good transfer under an accurate transfer condition without being influenced by environmental changes in temperature and humidity. A transfer control circuit is connected between the development current measuring circuit and the transfer power source, and data representing the relationship between the development current and the appropriate transfer current with respect to changes in temperature and humidity is stored in the transfer control circuit. It has been proposed to select an optimum transfer current based on the development current detected by the measurement circuit and to set the transfer power source to be controlled.

  In Patent Document 4, in order to suppress a change in the charged charge amount of the toner carried on the developer carrying member, to suppress an afterimage phenomenon, and to form an image having a uniform density, Patent Document 4 describes a development roller and a photosensitive drum. When the potential difference from the surface is 0 V, the average charged charge amount of the toner immediately after passing through the facing region between the developing roller and the photosensitive drum is Q1, the developing bias is applied to the developing roller, and the surface potential of the photosensitive drum is not | Q2 | − | Q1 | / | Q1 | ≦ ± 0.45, where Q2 is the average charge amount of the toner immediately after passing through the facing region between the developing roller and the photosensitive drum when the potential is the image portion. It has been proposed to perform development under conditions that satisfy this relationship.

  Furthermore, in order to reduce the narrowing of the horizontal line, the trailing edge blank, the missing of the isolated dot image, and the rough feeling of the halftone image, and to reduce the scavenging effect and the edge effect, Patent Document 5 discloses a small diameter. Disclosed is a developer carrier having a small diameter (φ16 mm or less) that conveys a magnetic brush to a latent image carrier (φ30 or less), and setting a plurality of predetermined parameters, and toner for the image carrier In order to prevent image deterioration due to reverse transfer of toner, in Patent Document 6, discharge is generated between the surface of the photoconductor that does not participate in image formation immediately before the primary transfer and the toner on the intermediate transfer belt. It is disclosed that the potential difference between the surface potential of the photoreceptor and the surface potential of the intermediate transfer belt due to the primary transfer electric field is controlled so as not to occur.

  In the present invention, against the background of the above-described conventional technology, toner transfer in a fine gap at the upstream and downstream of the transfer nip during transfer is performed with respect to the surface potential distribution (toner visible image) of the image carrier (photoreceptor) during development. The problem is to easily and effectively suppress defects such as transfer dust, poor dot image reproduction, toner scattering, and reverse transfer of toner transferred from the previous process to the image carrier. It is.

According to the present invention, there is provided a developer carrier (developing roller) that carries and conveys an image carrier (photoconductor) and a developer (one-component developer or a two-component developer composed of toner and a magnetic carrier) according to the present invention. A developing sleeve incorporating a fixed or rotating magnet in the case of using a two-component developer), and means for electric field transfer of a toner image formed on the image carrier to a transfer material; When the potential difference between the surface of the developer carrier and the surface of the image carrier is almost 0 V, it is carried on the developer carrier just before passing through the opposing area between the developer carrier and the image carrier. The average charge amount of the toner in the developer is Q1, and the transfer material immediately after electric field transfer from the image carrier to the surface of the next transfer material (final transfer material such as paper in the direct transfer system, intermediate transfer body in the indirect transfer system) The average charge amount of the surface toner image is Q2 If it is,
{│Q2│-│Q1│} /│Q1│≧-0.3
This problem can be solved by developing under the condition satisfying the above relationship. The aim of the present invention is to reduce the difference (reduction amount) between the average charge amount of the toner in the developer and the average charge amount of the toner at the time of development or transfer, which is a subsequent step. In some cases, the toner charge is increased in some way, such as corona charger charge in the middle of transfer, and in that case, the “average charge amount of the toner image” on the primary transfer body (intermediate transfer body) and the secondary transfer body The “average charge amount of the toner image” in the (final transfer material) may be a problem at the same time.

  Here, | Q1 | and | Q2 | represent absolute values of the toner charge amount. When the toner volume average particle diameter is about 5 to 12 μm, −15 to −50 μC / g is preferable when Q1 is negative. And Q2 is preferably −10.5 to −60 μC / g. The amount of charge applied to the toner before reaching the development process is set to an appropriate level, and the problem of an increase in the ratio of low-charged toner that is transferred by the gap electric field before and after the transfer nip can be prevented. The transfer phenomenon that is the main cause of transfer dust from the toner to the transfer material can be prevented. If | Q1 | is less than 15 μC / g, the ratio of the toner charged to the polarity opposite to the normal polarity (+ polarity in the above example) in the toner related to the development becomes excessive, and the toner is scattered from the developing unit. There are problems such as contaminating the inside of the machine and increasing the amount of background stains on the image carrier in the development process. If | Q1 | exceeds 50 μC / g, it becomes difficult to develop a sufficient amount of toner on the high-density image portion of the image carrier in the development step.

  If | Q2 | is less than 10.5 μC / g, the toner on the image carrier involved in the transfer has a very low ratio of normal polarity charged toner (weakly charged toner), and there is a gap between the image carrier and the transfer material. Even if there is a gap and a weak transfer electric field is applied, there is a large proportion of the toner that the weakly charged toner is likely to move away from the image carrier and transfer to the transfer material. The degree of “transfer dust” that scatters is severe. When | Q2 | exceeds 60 μC / g, the transfer electric field strength is high (in the example of the present invention, the transfer bias voltage applied to the transfer material is 1.5 kV at most, but a transfer voltage of, for example, 2.0 kV is high. When a bias is applied), it is difficult to obtain an image with a sufficient transfer rate of 90% or more in the high density portion image on the transfer material after transfer. Furthermore, when the high voltage is used as a transfer bias, discharge easily occurs in the gap before and after the transfer nip, and the discharge adheres to a low density portion image or a low area ratio image (dots, lines, etc.) on the image carrier. Toner (the average charge amount is lower than the toner of the solid image with high density) has a higher rate of polarity reversal, making it difficult to transfer (transfer failure), and the image once transferred to the transfer material is re-imaged. The reverse transfer phenomenon that is transferred to the carrier tends to occur.

According to the present invention, there is provided an image forming apparatus comprising: an image carrier; a developer carrier; and a means for transferring an electric field of a toner image formed on the image carrier to a transfer material. When the potential difference between the surface of the agent carrier and the surface of the image carrier is 0 V, the average charge amount of the toner in the developer immediately before passing through the opposing region between the developer carrier and the image carrier is Q1, When the average charge amount of the surface toner image of the image carrier immediately before electric field transfer from the image carrier to the surface of the next transfer material is Q3,
{│Q3│-│Q1│} /│Q1│≧-0.3
This problem can be solved by developing under the condition satisfying the above relationship. This is to maintain the toner charge level immediately before transfer at a predetermined level charge by adding some charge charge such as a corona charger that suppresses the attenuation of the toner charge amount and does not disturb the image on the image carrier.

Here, | Q1 | and | Q3 | represent the absolute value of the toner charge amount. When the toner volume average particle diameter is about 5 to 12 μm, −15 to −50 μC / g is preferable when Q1 is negative. Q3 is preferably −10.5 to −60 μC / g. Regarding the toner with sufficient charge amount before reaching the development step, the problem of increasing the ratio of low-charged toner that is transferred by a weak transfer electric field in the middle step of reaching the transfer step is increased by increasing the volume resistivity of the toner ( In the present invention, 3 g of toner was applied with a weight of 6 tons / 5 cm ² to be molded into a toner pellet having a thickness of about 2 mm, and a resistance of 10 ¹² Ω was measured after 1 minute when a voltage of 1 kV was applied in the thickness direction. (Cm or more) By suppressing the attenuation of the toner holding charge or increasing the toner charge amount by negative corona charging before transfer, the weakly charged toner ratio is prevented from becoming excessive during transfer. The front-rear gap can prevent the transfer phenomenon that is the main cause of transfer dust from the image carrier to the transfer material.

  | Q1 | is as described above. When | Q3 | is less than 10.5 μC / g, the toner on the image carrier involved in transfer has a very low ratio of normal polarity charged toner (weakly charged toner), and between the image carrier and the transfer material. Even if there is a gap and a weak transfer electric field acts, the ratio of the toner with which the weakly charged toner is likely to move away from the image carrier and transfer to the transfer material is large, and the toner is scattered around the image on the transfer material after transfer. The degree of “transfer dust” becomes severe. When | Q3 | exceeds 60 μC / g, the transfer electric field strength is high (in the example of the present invention, the transfer bias voltage applied to the transfer material is 1.5 kV at most, but for example, a high voltage of 2.0 kV is sufficient. It is necessary to apply a transfer bias), and it is difficult to obtain an image with a sufficient transfer rate of 90% or more in the high density portion image on the transfer material after transfer. Further, since the high voltage is used as a transfer bias, discharge easily occurs in the gap before and after the transfer nip, and the discharge adheres to a low density portion image or a low area ratio image (dots, lines, etc.) on the image carrier. The toner (which has a lower average charge than the toner of the high density solid image) has a higher polarity reversal rate, making it difficult to transfer (transfer failure), and the image once transferred to the transfer material is again transferred to the photoreceptor. The reverse transfer phenomenon that causes transfer is likely to occur.

According to the present invention, there is provided an image forming apparatus comprising: an image carrier; a developer carrier; and a means for transferring an electric field of a toner image formed on the image carrier to a transfer material. When the potential difference between the surface of the agent carrier and the surface of the image carrier is 0 V, the average charge amount of the toner in the developer immediately before passing through the opposing region between the developer carrier and the image carrier is Q1, When a developing bias is applied to the developer carrying member and the potential on the surface of the image carrying member is the image portion potential, the image portion on the surface of the image carrying member immediately after passing through the opposing region between the developer carrying member and the image carrying member. When the average charge amount of the developed toner is Q4,
{│Q4│-│Q1│} /│Q1│≧-0.3
This problem can be solved by developing under the condition satisfying the above relationship. This is characterized in that a change in the toner charge amount in the developing process is suppressed.

Here, | Q1 | and | Q4 | represent absolute values of the toner charge amount. When the toner volume average particle diameter is about 5 to 12 μm, −15 to −50 μC / g is preferable when Q1 is negative. Q4 is preferably −10.5 to −60 μC / g. Regarding the toner that has been given enough charge before reaching the development process, there is a problem that the ratio of low-charged toner that is transferred by a weak transfer electric field increases during the development / transfer process. The toner is positioned on the normal polarity side in the triboelectric charge series, or the upper limit of the volume resistivity of the toner is suppressed (in the example of the present invention, a thickness of about 2 mm by applying a weight of 6 tons / 5 cm ² to 3 g toner) When a voltage of 1 kV is applied in the thickness direction, the measured resistance is 10 ¹⁵ Ω · cm or less after 1 minute. The toner is vibrated by superimposing an alternating electric field on the development electric field of the toner to increase the amount of frictional charge with the carrier, thereby transferring without auxiliary means such as a preliminary corona charging process before the transfer before the transfer process. The weakly charged toner ratio can prevent the excessive, the transition phenomenon is a major cause of transfer dust to the transfer material from the photosensitive member at the transfer nip before and after the gap can be prevented. The injected charge is easy to discharge, so the lower limit of the volume resistivity of the toner is desirably 10 ¹² Ω · cm or more as described above.

  | Q1 | is as described above. When | Q4 | is less than 10.5 μC / g, the toner on the image carrier involved in the transfer has a very low ratio of normal polarity charged toner (weakly charged toner), and there is a gap between the image carrier and the transfer material. Even if there is a gap and a weak transfer electric field acts, the ratio of the toner with which the weakly charged toner is likely to move away from the image carrier and transfer to the transfer material is large, and the toner is scattered around the image on the transfer material after transfer. The degree of “transfer dust” becomes severe. When | Q3 | exceeds 60 μC / g, the transfer electric field strength is high (in the example of the present invention, the transfer bias voltage applied to the transfer material is 1.5 kV at most, but for example, a high voltage of 2.0 kV is sufficient. It is necessary to apply a transfer bias), and it is difficult to obtain an image with a sufficient transfer rate of 90% or more in the high density portion image on the transfer material after transfer. Furthermore, since the high voltage is used as a transfer bias, discharge easily occurs in the gap before and after the transfer nip, and the discharge adheres to the low density portion image and the low area ratio image (dots, lines, etc.) on the photoconductor. Toner (average charge is lower than that of high-density solid image toner) increases the rate of polarity reversal, making it difficult to transfer (transfer failure), and the image once transferred to the transfer material is transferred to the photoreceptor again The reverse transfer phenomenon that occurs is likely to occur.

  It is preferable to provide means for applying a charge having the same polarity as the normal polarity of the toner to the toner image on the surface of the image carrier between the development process and the transfer process. By increasing the toner charge amount by charging the toner with the same polarity as the normal polarity of the toner (for example, negative polarity when the normal charge polarity of the toner is negative) By preventing the weakly charged toner ratio from becoming excessive during transfer, it is possible to prevent a transfer phenomenon mainly caused by transfer dust from the image carrier to the transfer material in the gap before and after the transfer nip.

  Under the condition of a DC developing electric field satisfying 0 <| VD | − | VB | <| VD−VL | <400 V, where VD is the background potential before development on the surface of the image bearing member, VL is the image portion potential, and VB is the developing bias voltage. If developed, the potential difference between the developer carrier and the image carrier is small, and it is possible to prevent a discharge phenomenon that reduces the normal polarity charge of the toner in the development area, and to charge the toner image on the surface of the image carrier before transfer. Without applying, it is possible to prevent a transfer phenomenon that generates transfer dust between the image carrier and the transfer material in the gap before and after the transfer nip.

In the case of one-component development, the resistance between the developer carrier core and the surface layer is 10 ⁸ Ω or less (measurement conditions are a voltage application electrode, one developer carrier core, the other is a metal plate, or conductive tape. The electrode and the developer carrying member are in contact with each other in an area corresponding to the developing nip, and the applied voltage is preferably suppressed to 200 to 400 V). In the two-component development, it is preferable to keep the development gap at 0.2 to 1 mm and the carrier resistance to 10 ¹⁴ Ω · cm (100 times tapping filling. Measurement electrode gap 2 mm; applied voltage 1 kV) or less.

If the relative dielectric constant of the toner is 2.5 to 4 and the volume specific resistance is 10 ¹⁰ to 10 ¹⁵ Ω · cm, the toner to which the triboelectric charge is mainly applied in the developing device has a volume specific resistance of 10 ¹⁵ Ω. When the thickness is less than or equal to cm, the effect of increasing the charged charge due to electrostatic induction or charge injection phenomenon is likely to work in the developing electric field, and the charge given by the charged charge increasing effect is the discharge time constant of the toner charge (resistance and relative dielectric constant) Is easy to hold up to the transfer process, works effectively in the transfer process, is less likely to change the amount of charged charge due to electrostatic induction or charge injection due to the non-image part facing the image carrier, and before and after the transfer nip It is possible to prevent a transition phenomenon that generates transfer dust between the image carrier and the transfer material in the gap. More preferably, the relative dielectric constant of the toner is 2.5 to 3, and the volume resistivity is 10 ¹⁰ to 10 ¹² Ω · cm.

  If an alternating voltage having a mode in which a level higher and lower than the surface potential of the image portion of the image carrier is repeated for at least one cycle in the developing region is used as the developing bias, the toner which is mainly given triboelectric charge in the developing device is used. On the other hand, toner vibration easily occurs in the developing electric field, and the effect of increasing the triboelectric charge tends to work even in the developing electric field, and the charge applied by the effect of increasing the charged charge is the discharge time constant of the toner charge (the product of resistance and relative dielectric constant). When the (proportional) is large, it is easy to hold up to the transfer process, so it works effectively even in the transfer process, and electrostatic charge induced by the non-image part facing the image carrier and change in the charge amount due to charge injection hardly occur. It is possible to prevent a transfer phenomenon that generates transfer dust between the image carrier and the transfer material. The frequency at the time of development of the alternating voltage is preferably 1 KHz to 10 KHz, and the difference between the maximum value and the minimum value of the voltage is preferably 500 V to 100 V.

  Even without a dedicated cleaning means for cleaning and collecting the toner, the charge amount of the toner can be maintained in an appropriate range (10.5 to 60 μC / g in absolute value in the example of the present invention) in the transfer process, and transfer is performed with high efficiency transfer. The residual toner is very small, and the residual image and toner filming on the surface of the image carrier can be prevented.

  According to the first aspect of the present invention, it is possible to prevent a problem that the ratio of the low-charged toner that is transferred by a weak transfer electric field is increased with respect to the toner that has been sufficiently charged before reaching the developing process, and the gap before and after the transfer nip. Therefore, it is possible to prevent a transfer phenomenon that generates transfer dust between the image carrier and the transfer material.

  According to the second aspect of the present invention, with respect to the toner that has been sufficiently charged before reaching the developing step, the ratio of the low-charged toner that is transferred by a weak transfer electric field in the middle of the transfer step is increased. And a transfer phenomenon that generates transfer dust between the image carrier and the transfer material in the gap before and after the transfer nip.

  According to the third aspect of the present invention, it is possible to prevent an increase in the ratio of the low-charged toner that is transferred by a weak transfer electric field in the developing process, with respect to the toner that has been sufficiently charged before reaching the developing process. A transfer phenomenon that generates transfer dust between the image carrier and the transfer material in the gap before and after the transfer nip can be prevented without performing a charge imparting process on the toner image on the surface of the image carrier before.

According to the fourth aspect of the present invention, even if the ratio of the low-charged toner that is transferred by a weak transfer electric field in the development process is increased with respect to the toner that has been sufficiently charged before reaching the development process, before the transfer. By applying a charge imparting process to the toner image on the surface of the image carrier, the ratio of low-charged toner in the toner image can be reduced, and the transfer phenomenon that generates transfer dust between the image carrier and the transfer material in the gap before and after the transfer nip can be prevented. . The problem of an increase in the ratio of low-charged toner that is transferred by the transfer electric field is due to corona charging, etc., with a charge of the same polarity as the normal polarity of the toner on the image carrier surface (negative polarity when the normal charge polarity of the toner is negative) The toner charge amount is increased so that the ratio of the weakly charged toner is not excessive at the time of transfer, and the transfer phenomenon, which is the main cause of transfer dust from the image carrier to the transfer material, is prevented in the gap before and after the transfer nip. Comprises at most AC component of about 5kV maximum-minimum potential difference V _P-P in 0.5～10KHz, using a corona charger charges the direct current component is biased to the normal polarity of the toner, increasing the toner charge without excess or deficiency May be.

  According to the fifth aspect of the present invention, since the difference between the developer carrier and the image carrier is small, it is possible to prevent a discharge phenomenon that reduces the normal polarity charge of the toner in the development region, and the image carrier before transfer. A transfer phenomenon that generates transfer dust between the image carrier and the transfer material in the gap before and after the transfer nip can be prevented without applying a charge imparting process to the toner image on the surface. Examples of suitable conditions include combination conditions in which the absolute value of VD is 600 V or less, the absolute value of VL is 50 to 300 V, and the absolute value of the difference between VD and VL is less than 400 V.

According to the sixth aspect of the present invention, when the toner mainly imparted with triboelectric charge in the developing device is 10 ¹⁵ Ω · cm or less, the effect of increasing the charged charge by electrostatic induction or charge injection phenomenon in the developing electric field. And the charge imparted by the effect of increasing the charged charge has a large discharge time constant (proportional to the product of resistance and relative dielectric constant) of the toner charge, so that it is easy to hold up to the transfer process, so it is also effective in the transfer process. Therefore, the electrostatic induction due to the non-image portion facing the image carrier and the change in the amount of charged charge due to the charge injection hardly occur, and the transfer phenomenon that generates transfer dust between the image carrier and the transfer material in the gap before and after the transfer nip can be prevented. More preferably, the relative dielectric constant of the toner is 2.5 to 3, and the volume resistivity is 10 ¹⁰ to 10 ¹² Ω · cm. Further, the absolute value of the average toner charge amount is preferably 20 to 40 μC / g, and the toner volume average particle size is preferably 4 to 10 μm.

  According to the seventh aspect of the present invention, the toner which is mainly given the triboelectric charge in the developing device is likely to vibrate in the developing electric field, and the triboelectric charge increasing effect is apt to work in the developing electric field. The charge imparted by the effect of increasing the charged charge has a large discharge time constant (proportional to the product of resistance and relative dielectric constant) of the toner charge, so that it can be easily held up to the transfer process, and thus works effectively in the transfer process. Changes in the amount of charged charge due to electrostatic induction due to the image portion facing or charge injection are unlikely to occur, and a transition phenomenon that generates transfer dust between the image carrier and the transfer material in the gap before and after the transfer nip can be prevented. The frequency at the time of development of the alternating voltage is preferably 1 KHz to 10 KHz, and the difference between the maximum value and the minimum value of the voltage is preferably 500 V to 100 V.

  According to the eighth aspect of the present invention, since there is very little transfer residual toner with high-efficiency transfer, it is possible to prevent the residual image and toner filming on the surface of the image carrier. At least one of the developing means (preferably using black toner) is provided with a cleaning function to collect the transfer residual toner on the image carrier, so that the toner filming and afterimage of the image carrier without the dedicated cleaning means are provided. Preventing image generation is suitable for space saving and cost reduction. In the present invention, the toner charge charge amount distribution is suitable for transfer and the transfer rate can be maintained high, so that the residual image due to the transfer residual toner can be prevented even in a mode in which the amount of transfer residual toner is small and development also serves as cleaning.

The details of the present invention will be described below based on the example shown in the drawings.
FIG. 1 shows a schematic configuration of a color laser printer (hereinafter referred to as a printer) which is an image forming apparatus to which the present invention is applied. In FIG. 1, around a drum-shaped photoreceptor 1 as an image carrier rotating in the direction of an arrow, there are a photoreceptor cleaning unit 2, a charger 4 as a charging means for uniformly charging the photoreceptor, and image information. Correspondingly, an exposure unit 5 as exposure means for irradiating the photosensitive member 1 with light, developing means 6, 7, 8, 9 for developing an electrostatic latent image on the photosensitive member, an intermediate transfer belt 10 and the like are arranged. The toner image forming means for forming a toner image on the photoreceptor is constituted by the charger 4, the exposure unit 5, the developing means 6, 7, 8, 9 and the like.

  The developing means includes four developing units, a yellow developing unit 6, a magenta developing unit 7, a cyan developing unit 8, and a black developing unit 9. When forming a full-color image, a toner image (visible image) is formed in the order of the yellow developing device 6, the magenta developing device 7, the cyan developing device 8, and the black developing device 9, and the toner images of the respective colors are sequentially superimposed on the intermediate transfer belt 10. A full color image is formed by the transfer. The surface of the photoreceptor 1 after the toner image is transferred to the intermediate transfer belt 10 is cleaned by the blade 3 of the photoreceptor cleaning unit 2.

The intermediate transfer belt 10 is stretched by a drive roller 13, a primary transfer bias roller 11, and driven rollers 12a and 12b, and is driven by a drive motor (not shown). The pressure contact force of the primary transfer bias roller 11 is adjusted by a pressure contact spring 30. The intermediate transfer belt 10 has an electrical resistance by dispersing a conductive material such as carbon black in PVDF (vinylidene fluoride), ETFE (ethylene-tetrafluoroethylene copolymer), PI (polyimide), PC (polycarbonate), or the like. Can be used by combining two or more types of mixed / synthetic materials with adjusted volume, and when the volume resistivity is in the range of 10 ⁷ to 10 ¹⁵ Ωcm, the toner image on the photoreceptor is transferred to the surface of the intermediate transfer belt (primary transfer). It is difficult to cause defects that cause transfer dust when

  The example shown in FIG. 2 is an example in which the photoreceptor 1 ′ employs an endless belt and development uses a one-component development system. The resistance characteristics, material, and configuration of the intermediate transfer belt 10 are the same as in the example of FIG.

Here, the contact pressure between the photoreceptor 1 and the intermediate transfer belt 10 caused by the pressure contact by the primary transfer bias roller 11 is preferably 5 × 10 ⁻⁴ Mpa or more and 5 × 10 ⁻² Mpa or less. Within this range, transferability deterioration due to insufficient pressure contact force and toner aggregation due to overpressure contact can be prevented, transfer efficiency can be improved, and occurrence of void images can be prevented.

  The surface of the intermediate transfer belt has elasticity, and preferably the surface micro hardness is adjusted to a range of 30 to 70 degrees as measured by a micro rubber hardness meter (for example, MD-1 manufactured by Kobunshi Keiki Co., Ltd.) It is possible to prevent the transfer pressure from concentrating on the toner image portion at the transfer nip of the transfer, to prevent a non-electrostatic adhesive force increase between the toner image and the image carrier during the primary transfer, and to prevent the primary transfer from being lost. . Furthermore, regardless of the surface properties of the transfer material and the transfer paper as the recording medium, it is possible to perform transfer without occurrence of white spots, voids, character collapse, color misregistration, etc., and high quality full color images can be printed. .

  In addition, the intermediate transfer belt is provided with an elastic layer having compressibility in the thickness direction, and preferably the surface micro hardness is 30 degrees as measured by a micro rubber hardness meter (for example, MD-1 manufactured by Kobunshi Keiki Co., Ltd.). Even within the range of 70 degrees, it is possible to prevent the transfer pressure from being concentrated on the toner image portion at the transfer nip of the primary transfer, and to prevent a non-electrostatic adhesion increase between the toner image and the image carrier during the primary transfer. In addition, it is possible to improve the degree of prevention of the transfer failure in the primary transfer.

In addition, a small amount (about 0.1 to 1.0 part) of silicone oil SH200 (manufactured by Toray Dow Corning Silicone) is present in the protective layer on the surface of the photoreceptor, or a lubricant such as zinc stearate is added to the surface of the photoreceptor. When the static friction coefficient μ ₁ measured by the Euler-belt method of the intermediate transfer belt is relatively larger than the static friction coefficient μ ₂ or more of the photosensitive member (μ ₁ ≧ μ ₂ ). The increase in non-electrostatic adhesion between the toner image and the image carrier during transfer can be suppressed, and the prevention margin for primary transfer loss can be improved.

By using a toner with an average circularity of 0.90 to 0.99, which is close to a spherical toner such as a polymerized toner, and suppressing the increase in non-electrostatic adhesion between the toner image and the photoreceptor, the primary transfer electric field strength can be suppressed, It is possible to improve the degree of prevention of primary transfer transfer leakage. In the base toner, a toner containing a release agent such as wax is used so that it is not necessary to apply oil at the fixing portion, and the toner image is made in a state where there is a slight release agent on the toner surface. If the increase in non-electrostatic adhesion force between the photosensitive member and the photosensitive member is suppressed, the primary transfer electric field strength can be suppressed, and the degree of prevention of transfer failure during primary transfer can be improved. When hydrophobic inorganic fine particles are externally added to the base toner, and more preferably silica (SiO ₂ ) is externally added to improve the fluidity of the toner and suppress the increase in non-electrostatic adhesion between the toner image and the photoreceptor. In addition, the primary transfer electric field strength can be suppressed, and the prevention margin for the transfer failure in the primary transfer can be improved. Silica is more preferably hydrophobized on the surface with a silane coupling agent, silicone oil or the like.

  Further, the surface of the intermediate transfer belt 10 may be coated with a release layer as necessary. Materials used for this coating include ETFE, PTFE (polytetrafluoroethylene), PVDF, PEA (perfluoroalkoxy fluororesin), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), PVF (fluorinated). A fluororesin such as vinyl) can be used, but is not limited thereto.

Next, the case where the static friction coefficient is measured by the Euler method will be described. First, a piece of paper (TYPE 6200, A4T: manufactured by Ricoh Co., Ltd.) is cut into 297 mm × 30 mm, and yarns are attached to both ends to create a measurement piece. The properties of the paper piece are: Weighing: 71.7 g / m 2, Thickness: 89 μm, Density: 0.81 g / cm ³ , Smoothness: Table: 40 s, Back: 37 s, Volume resistance: 1.2E + 11 Ω · cm, Friction coefficient: Table / Back; (Body with rubber) Tan θ, length: 0.64, width: 0.65. A piece of measurement paper is placed on the photosensitive drum 1 supported at one end of the table by using a support member, and a weight of 0.98 N (100 g weight) is tied to one thread, and a digital push-pull gauge is tied to the other thread. . In this state, the measurement paper piece is pulled through the thread by the digital push-pull gauge, and the value of the digital push-pull gauge when the measurement paper piece starts to move is read. If the value at this time is F (N), the coefficient of static friction μ is
μ = (2 / π) × [ln (F / 0.98)]
Is required.

  Examples of the method for manufacturing the intermediate transfer belt 10 include a casting method and a centrifugal molding method. When reducing the surface roughness Rz, it is possible to adjust the value of the surface roughness Rz of the belt by reducing the surface roughness Rz on the mold side corresponding to the surface of the belt. Note that the belt surface may be polished and adjusted as necessary.

  The belt cleaning unit 19 that can contact and separate from the intermediate transfer belt 10 includes a cleaning blade 18 and a contact / separation mechanism 26 that contacts and separates the cleaning blade 18 from the intermediate transfer belt 10, and the first color yellow image. During the primary transfer of the second, third, and fourth colors after the primary transfer, the contact / separation mechanism 26 separates the surface from the surface of the intermediate transfer belt 10. The contact / separation mechanism 26 is in contact with a biasing means (not shown) that biases the cleaning unit 19 so that the cleaning blade 18 is in contact with the surface of the photosensitive member 1 and a bottom surface of the cleaning unit 19 that swings. Thus, an eccentric cam that is rotationally driven by a control unit 200 described later is used.

  Further, a belt position detection mark 23 is provided at an end portion in the width direction of the outer peripheral surface of the intermediate transfer belt 10. By starting the image forming process for each color at the timing when the mark 23 is detected by the mark sensor 24. Thus, accurate color superposition of each color image becomes possible. This technique is effective in preventing color misregistration because there is no stretching distortion or change in the rotation direction of the intermediate transfer belt.

The secondary transfer unit 15 includes a secondary transfer bias roller 14 and a contact / separation mechanism 16 that contacts and separates the secondary transfer bias roller 14 from the intermediate transfer belt 10. The contact / separation mechanism 16 includes a spring member as a biasing unit that biases the secondary transfer unit 15 so that the secondary transfer bias roller 14 is separated from the intermediate transfer belt 10, and a bottom surface on which the secondary transfer unit 15 swings. It is comprised using the eccentric cam rotated by the control part 200 mentioned later in the state contact | abutted to the part. The secondary transfer bias roller 14 is configured by coating a metal core such as SUS with an elastic body such as urethane adjusted to a resistance value of 10 ⁶ to 10 ¹⁰ Ω with a conductive material. The resistance value of the secondary transfer bias roller 14 is measured by installing the secondary transfer bias roller 14 on a conductive metal plate and applying a load of 4.9 N on one side (total of 9.8 N on both sides) to both ends of the core metal. In the state which applied, it computed from the electric current value which flows when a voltage of 1000V is applied between a metal core and a metal plate.

  The secondary transfer bias roller 14 is given a driving force by a driving gear (not shown), and its peripheral speed is adjusted to be substantially the same as the peripheral speed of the intermediate transfer belt 10. The secondary transfer bias roller 14 is usually separated from the surface of the intermediate transfer belt 10, but the timing when the four-color superimposed images formed on the surface of the intermediate transfer belt 10 are collectively transferred to the transfer paper 22. Then, it is pressed by the contact / separation mechanism 16 and a secondary transfer bias is applied to the secondary transfer bias roller 14 by a high-voltage power source 100 as a secondary transfer bias applying means, whereby the intermediate transfer belt 10 is transferred to the transfer paper 22. Transcription.

  In the printer having the above-described configuration, the transfer paper 22 is fed by the paper feed roller 25 and the registration roller 21 at the timing when the leading end of the four-color superimposed image on the intermediate transfer belt 10 reaches the secondary transfer position. . The four-color superimposed image transferred to the transfer paper 22 is fixed by the fixing unit 17 and then discharged.

  The toner used in the printer preferably has a volume average particle size in the range of 4 to 10 μm. By reducing the particle size of the toner within the above range, toner scattering can be prevented and high-resolution image formation can be achieved. Deterioration of toner and toner aggregation can be prevented, and the occurrence of a void image can be effectively prevented.

  As the binder resin used for the toner, all those conventionally used as a binder resin for toner can be applied. Specifically, polyol resins, styrene acrylic copolymers, styrene such as polystyrene, polychlorostyrene, polyvinyltoluene, and the like, homopolymers of styrene / p-chlorostyrene copolymers, and styrene / propylene copolymers. Polymer, styrene / vinyl toluene copolymer, styrene / vinyl naphthalene copolymer, styrene / methyl acrylate copolymer, styrene / ethyl acrylate copolymer, styrene / butyl acrylate copolymer, styrene / acrylic acid Octyl copolymer, styrene / methyl methacrylate copolymer, styrene / ethyl methacrylate copolymer, styrene / butyl methacrylate copolymer, styrene / α-chloromethyl methacrylate copolymer, styrene / acrylonitrile copolymer , Styrene / vinyl ethyl ether copolymer Styrene / vinyl methyl ketone copolymer, styrene / butadiene copolymer, styrene / isoprene copolymer, styrene / acrylonitrile / indene copolymer, styrene / maleic acid copolymer, styrene / maleic acid ester copolymer Styrene-based copolymers such as polymethyl methacrylate, polybutyl methacrylate, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, polyester, polyvinyl butyl butyral, polyacrylic acid resin, rosin, modified rosin, terpene resin, Phenol resin, aliphatic or alicyclic hydrocarbon resin, aromatic petroleum resin, chlorinated paraffin, paraffin wax and the like can be used, and these are used alone or in admixture of two or more.

  As the colorant used in the toner, all dyes and pigments that have been conventionally used as toner colorants can be applied. Specifically, carbon black, nigrosine dye, iron black, naphthol yellow S, Hansa yellow (10G, 5G, G), cadmium yellow, yellow iron oxide, ocher, yellow lead, titanium yellow, oil yellow, Hansa yellow, (GR, A, RN, R), Pigment Yellow L, Benzidine Yellow (G, GR), Permanent Yellow (NCG), Vulcan Fast Yellow (5G, R), Tartrazine Lake, Quinoline Yellow Lake, Anslagen Yellow BGL, Isoindolinone yellow, Bengala, red lead, lead red, cadmium red, cadmium mercury red, antimony red, permanent red 4R, para red, fire red, parachlor ortho nitroaniline red, risor fast scarlet G, brilliant Fast Scarlet, Brilliant Carmine BS, Permanent Red (E2R, F4R, FRL, FRLL, F4RH), Fast Scarlet VD, Belkan Fast Rubin B, Brilliant Scarlet G, Resol Rubin GX, Permanent Red F5R, Brilliant Carmine 6B, Pigment Scarlet 3B Bordeaux 5B, Toluidine Marine, Permanent Bordeaux F2K, Helio Bordeaux BL, Bordeaux 10B, Bon Marine Light, Bon Marine Medium, Eosin Lake, Rhodamine Lake B, Rhodamine Lake Y, Alizarin Lake, Thioindigolet B, Thioindigo Maroon, Oil Red, quinacridone red, pyrazolone red, chrome vermilion, benzidine orange, perinone orange, orange Le Orange, Cobalt Blue, Cerulean Blue, Alkaline Blue Lake, Peacock Blue Lake, Victoria Blue Lake, Metal-Free Phthalocyanine Blue, Phthalocyanine Blue, Fast Sky Blue, Indanthrene Blue (RS, BC), Indigo, Ultraviolet, Bituminous, Anthraquinone Blue, Fast Violet B, Methyl Violet Lake, Cobalt Purple, Manganese Purple, Dioxazine Violet, Anthraquinone Violet, Chrome Green, Zinc Green, Chrome Oxide, Pyridian Emerald Green, Pigment Green B, Naphthol Green B, Green Gold, Acid Green Lake, Malachite Green Lake, Phthalocyanine Green, Anthraquinone Green, Titanium Oxide, Zinc Hana, Litobon and it It is possible to use a mixture of these. In addition, generally the usage-amount of the said coloring agent is 0.1-50 weight part with respect to 100 weight part of binder resin.

  In this example, four colors of toner are used, but toner of three colors, two colors, single color, or five colors or more may be used. The type of color used may be any color, but it is preferable to select a color that can reproduce a full color. In particular, as described above, it is preferable that the toner colors are black, yellow, cyan, and magenta because the number of developments can be reduced and a relatively wide color tone range can be covered.

  The toner may contain a charge control agent as necessary. Any known charge control agent can be used. Specifically, nigrosine dyes, triphenylmethane dyes, chromium-containing metal complex dyes, molybdate chelate pigments, rhodamine dyes, alkoxy amines, quaternary ammonium salts (including fluorine-modified quaternary ammonium salts), alkyls Amides, phosphorus simple substances or compounds, tungsten simple substances or compounds, fluorine-based activators, salicylic acid metal salts, metal salts of salicylic acid derivatives, and the like can be used.

  The amount of the charge control agent used is determined by the type of binder resin, the presence or absence of additives used as necessary, the toner production method including the dispersion method, etc. However, it is preferably used in the range of 0.1 to 10 parts by weight with respect to 100 parts by weight of the binder resin. More preferably, the range of 2 to 5 parts by weight is good. Here, when the amount is less than 0.1 parts by weight, the toner is insufficiently charged and is not practical. On the other hand, when the amount exceeds 10 parts by weight, the chargeability of the toner is too high, and the electrostatic attraction force with the carrier, the developing sleeve or the like increases, and the image density is lowered due to spent or filming. If necessary, a plurality of charge control agents may be used in combination.

  In the printer of this example, development may be performed by a so-called one-component development method in which an electrostatic latent image is visualized by using toner alone as a developer, or a two-component developer obtained by mixing toner and a carrier is used. Then, development may be performed by a two-component development method for visualizing the electrostatic latent image. When the two-component development method is used, the same carrier as conventional ones such as iron powder, ferrite, and glass beads can be used. These carriers may be those coated with a resin, and as this resin, polyfluorinated carbon, polyvinyl chloride, polyvinylidene chloride, phenol resin, polyvinyl acetal, silicone resin and the like can be used. In any case, the mixing ratio of the toner and the carrier is generally about 0.5 to 6.0 parts by weight with respect to 100 parts by weight of the carrier.

  The toner may be mixed with an additive as necessary. Examples of the additives include fluidity imparting agents composed of inorganic fine particles such as hydrophobic silica, hydrophobic titanium oxide, and hydrophobic aluminum oxide, anti-caking agents, lubricants such as ethylene tetrafluoride resin and zinc stearate, carbon black, Conductivity imparting agents such as tin oxide, abrasives such as cerium oxide and silicon carbide, fixing aids such as low molecular weight polyolefins, and the like can be used. These may be used alone or in combination of two or more. The addition amount of these additives is desirably 0.1 to 5 parts by weight with respect to 100 parts by weight of the toner.

  In producing the toner, after mixing the constituent materials as described above in a mixer such as a Henschel mixer, the mixture is heated and kneaded in a kneader such as a continuous kneader or a roll kneader, and the kneaded product is cooled and solidified. A method of obtaining a desired average particle size by pulverization and classification is preferred. As other production methods, there are a spray drying method, a polymerization method, a microcapsule method and the like. The toner thus obtained can be sufficiently mixed with a desired additive with a mixer such as a Henschel mixer, if necessary, to produce a toner.

  The toner of this example uses a polyester resin as a binder resin and a zinc salicylate derivative as a charge control agent as a material common to each color. This zinc salicylate derivative is contained in a ratio of 4 parts by weight to 100 parts by weight of the polyester resin. In addition, each color toner contains a colorant, and for 100 parts by weight of the polyester resin, 5 parts by weight of carbon black is used for black toner, and disazo yellow pigment (CI PIGMENTYELLOW17 for yellow toner). ) Is 5 parts by weight, cyan toner contains 4 parts by weight of copper phthalocyanine blue pigment (CI PIGMENTBLUE 15), and magenta toner contains quinacdrine magenta pigment (CI PIMGENTRED 184) at a ratio of 4 parts by weight. Yes.

  Hereinafter, image evaluation in which image formation was performed in Examples and Comparative Examples of the present invention will be described. The image evaluation was made by comparing the transfer rate and the transferred dust image. Table 1 shows the main contents of the comparative evaluation results.

  In both Examples 1 and 2, the transfer rate is higher than that of the conventional example, and transfer dust is very small. FIGS. 3 to 5 show changes in the charge amount distribution of the examples compared in Table 1, and show values measured by an E-SPART analyzer manufactured by Hosokawa Micron. 3 corresponds to the first embodiment, FIG. 4 corresponds to the second embodiment, and FIG. 5 corresponds to the conventional example.

  By the way, when the intermediate transfer belt having an elastic layer is formed of a single elastic layer, it is preferable that an elongation preventing layer is provided because elongation occurs when the belt is driven, causing color misregistration and the like. The elongation preventing layer may be laminated on the intermediate transfer belt, or may be configured such that the elongation preventing layer and the elastic layer are the same in a form of being mixed with an elastic material in a single elastic layer. Further, a surface coating layer having a higher hardness but a thinner surface may be provided to prevent the surface from changing with time.

  The elongation preventing layer may be constituted by a core body layer using a resin such as PI (polyimide), PC (polycarbonate), PET (polyethylene terephthalate), or fibers. As fibers used for the core layer, natural fibers such as cotton, silk and hemp, recycled fibers such as chitin fibers and alginic acid fibers, semi-synthetic fibers such as acetate fibers, polyester fibers, nylon fibers, acrylic fibers, polyolefin fibers, Synthetic fibers such as polyurethane fibers, polyacetal fibers and aramid fibers, inorganic fibers such as carbon fibers and glass fibers, and the like can be used. In this example, an aramid fiber having a thickness of 100 μm was used in the form of a woven fabric. Materials used for the elastic layer include styrene-butadiene rubber, high styrene rubber, butadiene rubber, isoprene rubber, ethylene-propylene copolymer, nitrile butadiene rubber, chloroprene rubber, butyl rubber, silicone rubber, fluorine rubber, nitrile rubber, urethane. Examples thereof include rubber, acrylic rubber, epichlorohydrin rubber and norbornene rubber. In this example, a nitrile butadiene rubber having a hardness of 60 degrees (JIS-A) was used. The thickness of the elastic layer was 500 μm. As the material used for the surface coat layer, styrene-butadiene rubber, high styrene rubber, butadiene rubber, isoprene rubber, ethylene-propylene copolymer, nitrile butadiene rubber, chloroprene rubber, butyl rubber, silicone rubber, fluorine rubber, nitrile rubber, Examples thereof include urethane rubber, acrylic rubber, epichlorohydrin rubber, norbornene rubber, and thermoplastic elastomer. In this example, polyurethane coated with a fluororesin was used. The coating thickness was several μm to several tens of μm (preferably 1 to 10 μm).

  In addition, said embodiment was described in order to make an understanding of this invention easy, Comprising: This invention is not limited. For example, in the present embodiment, the photosensitive drum is used as the image carrier. However, the present invention is not limited to this and can be applied to all image carriers such as a photosensitive belt. In the embodiment of FIG. 1, the photosensitive drum is in a single form, but it can also be applied to a so-called quadruple tandem full-color image forming system form using dedicated photosensitive drums for black, yellow, cyan, and magenta colors. It is. In this embodiment, the transfer roller is used as the primary transfer unit. However, a contact transfer system such as a transfer brush, a transfer blade, and a transfer plate is used as well as a rotary contact transfer system such as a rotary transfer brush. The present invention can be applied to any image forming apparatus.

1 is a schematic configuration diagram of an image forming apparatus according to the present invention. It is a schematic block diagram of another image forming apparatus which concerns on this invention. It is a graph which shows the result in Example 1 in transition of charge amount distribution at the time of image evaluation. It is a graph which shows the result in Example 2 in transition of the charge amount distribution at the time of image evaluation. It is a graph which shows the result in a prior art example in transition of charge amount distribution at the time of image evaluation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Cleaning unit 4 Charger 5 Exposure unit 6, 7, 8, 9 Developing means 10 Intermediate transfer belt 11 Primary transfer bias roller 12 Driven roller 13 Drive roller 14 Secondary transfer bias roller 15 Secondary transfer unit 16 Contact / separation Mechanism 17 Fixing means 18 Cleaning blade 19 Belt cleaning unit 21 Registration roller 22 Transfer paper 23 Belt position detection mark 24 Mark sensor 25 Paper feed roller 26 Contact / separation mechanism 30 Pressure contact spring

Claims (8)

In an image forming apparatus comprising an image carrier, a developer carrier, and means for transferring an electric field of a toner image formed on the image carrier to a transfer material,
When the potential difference between the surface of the developer carrier and the surface of the image carrier is 0 V, the average charge amount of the toner in the developer immediately before passing through the opposing region between the developer carrier and the image carrier Q1, when the average charge amount of the transfer material surface toner image immediately after the electric field transfer from the image carrier to the surface of the next transfer material is Q2,
{│Q2│-│Q1│} /│Q1│≧-0.3
The image forming apparatus is developed under a condition that satisfies the above relationship. In an image forming apparatus comprising an image carrier, a developer carrier, and means for transferring an electric field of a toner image formed on the image carrier to a transfer material,
When the potential difference between the surface of the developer carrier and the surface of the image carrier is 0 V, the average charge amount of the toner in the developer immediately before passing through the opposing region between the developer carrier and the image carrier Q1, when the average charge amount of the image carrier surface toner image immediately before the electric field transfer from the image carrier to the surface of the next transfer material is Q3,
{│Q3│-│Q1│} /│Q1│≧-0.3
The image forming apparatus is developed under a condition that satisfies the above relationship. In an image forming apparatus comprising an image carrier, a developer carrier, and means for transferring an electric field of a toner image formed on the image carrier to a transfer material,
When the potential difference between the surface of the developer carrier and the surface of the image carrier is 0 V, the average charge amount of the toner in the developer immediately before passing through the opposing region between the developer carrier and the image carrier Q1, when a developing bias is applied to the developer carrying member and the potential on the surface of the image carrying member is the image portion potential, the surface of the image carrying member immediately after passing through the opposing region between the developer carrying member and the image carrying member. When the average charge amount of the toner developed on the image portion is Q4,
{│Q4│-│Q1│} /│Q1│≧-0.3
The image forming apparatus is developed under a condition that satisfies the above relationship.   2. The image forming apparatus according to claim 1, wherein means for applying a charge having the same polarity as the normal polarity of the toner is provided to the toner image on the surface of the image carrier between the development step and the transfer step.   Under the condition of a DC developing electric field satisfying 0 <| VD | − | VB | <| VD−VL | <400 V, where VD is the background potential before development on the surface of the image bearing member, VL is the image portion potential, and VB is the developing bias voltage. The image forming apparatus according to claim 1, wherein development is performed. The image forming apparatus according to claim 1, wherein the toner has a relative dielectric constant of 2.5 to 4 and a volume resistivity of 10 ¹⁰ to 10 ¹⁵ Ω · cm.   7. The image forming apparatus according to claim 6, wherein an alternating voltage having a mode in which a level higher and lower than the image portion surface potential of the image carrier is repeated at least one period in the developing region is used as the developing bias.   The image forming apparatus according to claim 1, wherein a dedicated cleaning unit that cleans and collects toner is not provided.

Images