JP2005301150A - Image forming method and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming method capable of preventing the occurrence of a void phenomenon in images on a first surface and second surface of a transfer material undergoing a fixing process. <P>SOLUTION: The image forming method has a step of transferring a toner image carried on an image carrier to a transfer material by using a transfer bias and a step of fixing the transferred image carried on the transfer material and is capable of executing the step of fixing the image transferred to the first surface of the transfer material, and then transferring the toner image from the image carrier onto the second surface of the transfer material, wherein the line speed ratio of the image carrier and the transfer material is changed according to environmental humidity during the image transfer to the second surface. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming method and an image forming apparatus, and more particularly to a method for preventing color misregistration when forming a multicolor image.

In an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a printing machine, a toner image obtained by developing an electrostatic latent image formed on a photosensitive member as a latent image carrier is one of recording media. A transfer process for transferring to the sheet is executed.
In the transfer process, the toner image may be directly transferred from the photosensitive member to the sheet as in the case of a monochrome image, and an image for each color is formed as in the case of a full color image. The image for each color is directly transferred to the sheet passing through the position of the photoconductor and directly transferred onto the sheet, and the image for each color formed by each photoconductor is sequentially transferred to the intermediate transfer body once. In some cases, after the (primary transfer), the image superimposed and transferred onto the intermediate transfer member is transferred to the sheet at once (secondary transfer).

  As an intermediate transfer member used for primary transfer and secondary transfer, there are a drum and a belt. However, in recent years, when a belt is used, instead of batch transfer to a sheet fed from a paper feeding device. A structure similar to the direct transfer method described above has been proposed in which a sheet is attracted to a belt and a toner image formed in each image forming unit is transferred to the sheet in the process of moving the sheet as the belt moves. (For example, Patent Documents 1 and 2).

  The configuration disclosed in each of the above publications adsorbs an image (toner image) formed by each image forming unit arranged along the extending direction of a belt used as a transfer body on one side of the sheet. There is a system referred to as a 4-drum tandem system that sequentially transfers onto a sheet or belt (for example, Patent Document 3).

  A recording medium such as a sheet on which images of a plurality of colors are superimposed and transferred is subjected to a fixing process by heating and pressure of the image carried on the surface, and the toner in the image melts and penetrates into the medium. It is fixed.

By the way, when a multicolor image such as a full-color image is obtained by superimposing and transferring a plurality of color images, color misregistration may occur if the transfer positions of the color images are not aligned. On the other hand, apart from the generation of a defective image due to color misregistration, a phenomenon that causes a defective image is a void phenomenon in which a part of the image is lost without being transferred normally.
Conventionally, as a technique for preventing the hollow-out phenomenon, the surface energy of the toner image carrier is made equal to or less than the surface energy of the transfer material, while the transfer material conveyance speed is arbitrarily set during the transfer process. (For example, Patent Document 4), a means for adjusting the moving speed of the transfer means and the latent image carrier corresponding to environmental conditions such as temperature is provided, and the linear velocity difference of each means is made constant regardless of changes in the environmental conditions. Configuration (for example, Patent Document 5), transfer conditions for the transfer material in each transfer process when the first and second transfer processes are performed on the transfer material once passed through the fixing process. There is a configuration to be changed (for example, Patent Document 6).

JP-A-5-270686 ("0016" column, FIG. 1) JP-A-8-152790 ("0030" column, FIG. 1) JP 9-319179 A (paragraphs “0007” and “0026” columns) JP-A-9-106194 (paragraph "0015" column) JP-A-10-161441 (paragraph "0005" column) JP-A-11-24339 (paragraph "0026" column)

However, the configuration disclosed in the above-mentioned patent document for preventing the void phenomenon has the following problems.
In the configuration disclosed in Patent Document 4, if the linear speeds of the latent image carrier and the transfer material are set to different values, the transfer material transport state may become unstable, and toner of two or more colors may be used. When superimposing, color misregistration may easily occur.
In the configuration disclosed in Patent Document 5, the type of transfer material, the state of the toner, and the transfer characteristics constantly change. Therefore, when trying to follow this change, the transfer speed becomes unstable during the transition period. There is a possibility that color misregistration may occur due to this.
In the configuration disclosed in Patent Document 6, the transfer efficiency of the second transfer than the first transfer is taken into consideration with respect to the transfer material after the fixing process is performed, taking into account the change in resistivity of the transfer material after fixing. In order to increase the shearing force, the shearing force acting on the toner is increased so that the transfer material is transferred onto the first surface and the second surface of the transfer material in a state where the transfer material is continuously conveyed. When performing, it is necessary to change the moving speed at which each surface reaches the transfer position. However, since changing the moving speed for each surface complicates the control and becomes extremely difficult because it is almost impossible, the fixing of the first surface and the first surface of the continuously conveyed transfer material is difficult. It is almost impossible to prevent the hollowing out of the second surface that moves later.

  In view of the problems in the conventional image forming method, an object of the present invention is an image forming method and an image forming apparatus capable of preventing the occurrence of image dropout on the first surface and the second surface of a transfer material that has undergone a fixing process. It is to provide.

  The invention described in claim 1 includes a step of transferring a toner image carried on an image carrier to a transfer material using a transfer bias, and a step of fixing the transfer image carried on the transfer material. And an image forming method capable of performing a step of transferring a toner image from the image carrier onto the second surface of the transfer material after fixing the image transferred onto the first surface of the transfer material. It is characterized in that the linear velocity ratio between the image carrier and the transfer material is changed according to the environmental humidity during image transfer to the second surface.

  According to a second aspect of the present invention, there is provided a step of transferring a toner image carried on an image carrier to a transfer material via one or more intermediate transfer members, and a transfer carried on the transfer material. An image fixing step, and after the image transferred on the first surface of the transfer material is fixed, the step of transferring the toner image from the image carrier onto the second surface of the transfer material can be executed. In the image forming method, the linear velocity ratio between the image carrier located at the final stage of the image carrier and the transfer material is changed according to the environmental humidity when the image is transferred to the second surface. .

  According to a third aspect of the present invention, in the image forming method according to the first or second aspect, when the humidity is low, the linear velocity ratio at the time of transfer to the second surface is set larger than that in the case of high humidity. It is a feature.

  According to a fourth aspect of the present invention, in the image forming method according to one of the first to third aspects, the linear velocity of the transfer material is set to the linear velocity of the image carrier or the image carrier positioned at the final stage. It is characterized by being set late.

  According to a fifth aspect of the present invention, in the image forming method according to any one of the first to fourth aspects, the transfer bias for the second surface is set higher than the transfer bias for the first surface. Yes.

  The invention described in claim 6 is characterized in that the image forming method according to one of claims 1 to 5 is used in an image forming apparatus.

  According to a seventh aspect of the invention, in the image forming apparatus according to the sixth aspect, the toner image carried on the image carrier is developed by a plurality of developing means.

  According to an eighth aspect of the present invention, in the image forming apparatus according to the sixth or seventh aspect, the toner image is formed using a tandem structure in which image forming portions capable of forming latent images for a plurality of colors are arranged side by side. It is characterized by that.

  According to a ninth aspect of the present invention, in the image forming apparatus according to one of the sixth to eighth aspects, the average circularity of the toner used is 0.90 to 0.99.

  According to a tenth aspect of the present invention, in the image forming apparatus according to one of the sixth to ninth aspects, the toner shape count SF-1 used is 120 to 180.

  According to an eleventh aspect of the present invention, in the image forming apparatus according to any one of the sixth to tenth aspects, the volume average particle diameter (Dv (μm)) and the number average particle diameter (Dn (μm)) of the toner to be used. ), Dv / Dn is 1.05-1.30.

  According to the first and second aspects of the present invention, the linear velocity ratio on the second surface can be made different according to the change in humidity that affects the change in resistivity of the transfer material. The transfer failure due to the increased resistance can be avoided, and the same amount of toner adhesion as that of the first surface can be ensured by the increase of the shearing force acting on the toner, so that the transfer rate of the same level as that of the first surface. Can be secured. In particular, when the humidity is low, the transfer rate after fixing differs greatly between the first surface and the second surface, so the linear velocity ratio on the first surface is reduced and the linear velocity ratio on the second surface is reduced. By increasing the size, the transfer rate between the first surface and the second surface can be balanced. In addition, when the linear velocity ratio is increased, there is a concern about the occurrence of color misregistration due to deterioration of conveyance raw material such as conveyance deviation of the transfer material, but in order to prevent color misregistration on the first surface, the linear velocity ratio is decreased, On the second surface, by increasing the linear speed ratio to improve the transfer rate, it is possible to prevent the occurrence of defective images such as the density of the transferred image between the first and second surfaces.

  In addition, even when the first surface and the second surface are continuously conveyed, the linear velocity ratio to the first surface and the linear velocity ratio to the second surface are simply made different by adjusting the speed of the transfer means for these surfaces. Thus, it is possible to balance the image transfer rates on the first and second surfaces.

  According to the third aspect of the present invention, it is possible to prevent the transfer rate from being different when the humidity is low.

  According to the fourth aspect of the present invention, since the linear velocity of the transfer material is made slower than the image carrier, the periodicity is obtained when the linear velocity of the transfer material is made faster than the linear velocity of the image carrier. It is possible to balance the transfer rate between the first and second surfaces in a state in which the speed fluctuation is suppressed and the conveyance life is not deteriorated.

  According to the fifth aspect of the present invention, the transfer rate of the toner image onto the second surface is increased by increasing the transfer bias with respect to the second surface while increasing the linear velocity ratio between the image carrier and the transfer material. Can be balanced with that. In particular, it is possible to balance the transfer rate without causing abnormal discharge or the like at the transfer portion by combining the linear speed ratio with the control of only the transfer bias.

  According to the sixth to eighth aspects of the invention, even when a plurality of image forming units are provided, the first and second surfaces can be controlled by controlling the linear velocity ratio between the first surface and the second surface according to the environmental humidity. It is possible to eliminate the difference in transfer rate between the two.

  According to the ninth aspect of the invention, since the average circularity of the toner is set to 0.90 to 0.99, high-definition image formation becomes possible. In other words, if the average circularity exceeds 0.99, in an image forming system employing blade cleaning or the like, a cleaning failure occurs in the latent image carrier or the transfer body, and the image becomes dirty. In particular, in the case of an image with a low image area ratio, there is little transfer residual toner and there is no problem of poor cleaning. However, in the case of an image with a high area image ratio such as a color photographic image, an untransferred image remains due to poor conveyance of the recording medium. In such a case, it becomes easy to cause a cleaning failure.

  According to the tenth aspect of the present invention, since the toner shape count SF-1 is set to 120 to 180, the cause is an extreme increase in fluidity of the toner and a weakening of the attractive force (mirror power). The occurrence of poor cleaning can be suppressed, and an image free from background stains caused by contamination of the latent image carrier due to poor cleaning can be obtained.

According to the invention of the eleventh aspect, the following effects can be obtained by setting the ratio of the volume average particle diameter to the number average particle diameter of the toner within a narrow range of 1.05 to 1.30.
First, since a phenomenon such as a selection range on the particle diameter side of the toner (toner particles having a toner particle diameter corresponding to an image pattern is selectively developed) hardly occurs, a stable image can be formed at all times. This makes it possible to obtain a high-resolution and high-definition image.
Secondly, there are cases where a large amount of detailed toner particles that are difficult to be transferred when using a toner recycling system are recycled in a large quantity. However, it is difficult to receive the above effect by narrowing the particle size distribution of the toner originally. And a stable image can be formed at all times.
Third, in a two-component developer, even if a long-term balance of the toner is performed, there is little fluctuation in the toner particle diameter in the developer, and good and stable developability can be obtained even when a long-term stirring is performed. It is done.
Fourth, even in the case of a one-component developer, the toner particle size fluctuation is small, there is no filming due to the thinning of the toner, there is no fusion to the cleaning blade, and it is stable even after long-term stirring. Developability and images can be obtained.

  The best mode for carrying out the present invention will be described below with reference to the illustrated embodiments.

FIG. 1 is a diagram showing one of image forming apparatuses used for executing an image forming method according to an embodiment of the present invention. The image forming apparatus shown in FIG. 1 displays a full-color image by the above-described quadruple tandem method. A formable copier or printer is used.
In addition to this, there is a facsimile apparatus capable of performing the same image forming process as the above-described copying machine and printer based on a received image signal. Note that the image forming apparatus includes not only the above-described color image but also an apparatus that targets a single color image.

  The image forming apparatus 20 shown in FIG. 1 forms a color image directly from a latent image carrier onto a transfer material by superimposing and transferring the color separation image onto a transfer material such as paper adsorbed on a transfer belt used as a transfer body. Is used.

In FIG. 1, an image forming apparatus 20 includes the following apparatuses.
Image forming devices 21M, 21C, 21Y, and 21BK that form images of respective colors according to the original image, transfer devices 22 that are arranged to face the image forming devices 21M, 21C, 21Y, and 21BK, and the respective image forming devices A first paper feed cassette 24A, a first paper feed cassette 24A provided in a paper feed device 24, a manual feed tray 23 serving as a sheet supply means for feeding a transfer material to a transfer region where the devices 21M, 21C, 21Y, 21BK and the transfer device 22 face each other. Two sheet feeding cassettes 24B, registration rollers 30 for supplying transfer materials conveyed from the manual feed tray 23 and the sheet feeding cassettes 24 and 24 in accordance with the image forming timings of the image forming apparatuses 21M, 21C, 21Y, and 21BK; A fixing device 1 that fixes a sheet-like medium after transfer in a transfer region.

  Although not described in detail, the fixing device 1 is configured to employ a belt fixing system in which a heated belt is disposed on the side facing the image. For this reason, the fixing device 1 is equipped with a heat source for heating the belt and a fixing roller and a pressure roller that constitute a nip portion that is a fixing region while nipping and conveying the sheet facing the belt, and the belt is fixed. It is configured to pass between the roller and the heat source and pass through the nip portion.

  The transfer device 22 corresponds to a belt device using a belt (hereinafter referred to as a transfer belt) 22A that is wound around a plurality of rollers as a transfer body, and the details will be described in FIG. Transfer bias means 22M, 22C, 22Y, and 22BK for applying a transfer bias are disposed at positions facing the photosensitive drum in the image forming apparatus, respectively, and the moving direction of the transfer belt 22A (the direction indicated by arrow A in FIG. 1). ), A suction bias means 31 for applying a suction bias for attracting the transfer material to the transfer belt 22A prior to the transfer of the first color can contact the transfer belt 22A on the side to which the first color is transferred. Is arranged.

The image forming apparatus 20 has a larger heat capacity than plain paper, which is generally used for copying, 90K paper such as OHP sheets, cards, postcards, thick paper having a basis weight of about 100 g / m ₂ or more, and envelopes. Any so-called special sheet can be used as a transfer material.

FIG. 2 is a schematic diagram schematically showing the configuration of the transfer device 22, in which the transfer belt 22 </ b> A is composed of a high-resistance endless single-layer belt having a volume resistivity of 10 ⁹ to 10 ¹¹ Ωcm. The material is PDVDF (polyvinylidene fluoride).
The transfer belt 22A is wound around support rollers 32 to 37 so as to be able to pass through transfer positions that are in contact with and face the photosensitive drums 25M, 25Y, 25C, and 25K located in the respective image forming units.

Among the supporting rollers, at a position facing the entrance roller 37 on the upstream side in the moving direction of the transfer material on the stretched surface side of the transfer belt 22 </ b> A facing each photoconductor, a predetermined voltage from the power supply 38 is applied. The roller transfer belt 22 </ b> A as the bias unit 31 is disposed on the outer peripheral surface.
Of the supporting rollers, a roller denoted by reference numeral 33 is a driving roller that frictionally drives the transfer belt 22A, and is connected to a driving source (not shown) and can rotate in the direction of the arrow shown.

  Transfer bias applying members 39Y, 39M, 39C, and 39K are provided at positions on the inner side of the belt that face each photoconductor across the transfer belt 22A so as to contact the slope of the transfer belt 22A. These bias applying members are bias rollers having a sponge or the like on the outer periphery, and a transfer bias is applied to the roller core from each transfer bias power source 40Y, 40M, 40C, 40K. Due to the action of the applied transfer bias, a transfer charge is applied to the transfer belt 22A, and a transfer electric field having a predetermined strength is formed between the transfer belt 22A and the surface of the photosensitive drum at each transfer position. Further, a backup roller 41 is provided in order to appropriately maintain the contact between the transfer material and the photoconductor in the area where the transfer is performed and to obtain the best transfer nip.

  The transfer bias applying members 39Y, 39M, and 39C and the backup roller 41 disposed in the vicinity thereof are integrally held by the swing bracket 42 so as to be rotatable, and can be rotated about the rotation shaft 42A. This rotation is clockwise when the cam 43 is rotated in the direction of the arrow.

The entrance roller 37 and the attracting bias means 31 composed of the roller are supported by the entrance roller bracket 44 and can be rotated clockwise from the state of FIG. 2 with the roller shaft 36A as the center of rotation.
A hole 42 </ b> B provided in the swing bracket 42 is engaged with a pin 44 </ b> A fixed to the entrance roller bracket 44, and rotates in conjunction with the rotation of the swing bracket 42. By the clockwise rotation of the brackets 42 and 44, the bias applying members 39Y, 39M, and 39C and the backup roller 41 disposed in the vicinity thereof are separated from the photoconductors 25Y, 25M, and 25C, and are attracted to the entrance roller 37. The biasing means 31 also moves downward. It is possible to avoid contact between the photoconductors 25Y, 25M, and 25C and the transfer belt 22A during black-only image formation.

  On the other hand, the transfer bias member 39K and the backup roller 41 adjacent to the transfer bias member 39K located on the downstream side of the transfer belt 22A in the transfer belt 22A in the transfer belt 22A form an exit bracket 45 that can rotate about the rotation shaft of the exit roller 32 as a fulcrum. When the transfer device 22 is attached to and detached from the main body of the image forming apparatus, it can be rotated clockwise by operating a handle (not shown). The transfer bias member 39K and the backup bias member 39K can be rotated from the photosensitive member 25K for black image formation. The roller 41 can be separated.

  In FIG. 1, a cleaning device 46 having a brush roller and a cleaning blade capable of contacting the transfer belt 22A is provided outside the transfer belt 22A mounted on the drive roller 33. Foreign matter such as adhering toner can be removed.

  A roller 34 is provided downstream of the drive roller 33 in the moving direction of the transfer belt 22A in a direction to push the outer peripheral surface of the transfer belt 22A, and a winding angle of the transfer belt 22A around the drive roller 33 is secured. The roller 35 positioned in the loop of the transfer belt 22A further downstream than the roller 34 functions as a tension roller that applies a pressing force by a pressing member (spring) 47 to the transfer belt 22A and applies tension.

  In the image forming apparatus 20 shown in FIG. 1, since the transfer device 22 extends obliquely, the space occupied by the transfer device 22 in the horizontal direction can be reduced.

In the image forming apparatus 20 having the above configuration, image formation is performed based on the following steps and conditions. In the following description, an image forming apparatus in which image formation is performed using magenta toner denoted by reference numeral 21M on behalf of each image forming apparatus will be described, but the same applies to other image forming apparatuses. Preface.
At the time of image formation, the photosensitive drum 25M is rotationally driven by a main motor (not shown), and is neutralized by an AC bias (DC component is zero) applied to the charging device 27M, and its surface potential is a predetermined potential (for example, approximately −50V). Is set to the reference potential.
Next, the photosensitive drum 25M is uniformly charged to a potential substantially equal to the DC component by applying a DC bias superimposed with an AC bias to the charging device 27M.

  When the photosensitive drum 25M is uniformly charged, a writing process is executed. An image to be written is written for forming an electrostatic latent image using a writing device 29 in accordance with digital image information from a controller unit (not shown). That is, in the writing device 29, laser light from a laser light source that emits light based on a laser diode light emission signal binarized for each color corresponding to digital image information is converted into a cylinder lens (not shown), a polygon motor 29A, A photosensitive drum carrying an image for each color via an fθ lens (not shown), first to third mirrors, and a WTL lens. In this case, the photosensitive drum 25M is irradiated and irradiated for convenience. The surface potential on the surface of the photosensitive drum of the portion thus made becomes a predetermined potential (for example, approximately −50 V), and an electrostatic latent image corresponding to the image information is formed.

  The electrostatic latent image formed on the photosensitive drum 25M is subjected to visible image processing by using a toner having a color complementary to the color separation color by the developing device 26M. In the developing process, an AC bias is applied to the developing sleeve. Is applied, the toner is developed only in the image portion where the potential is lowered by the irradiation of the writing light, and a toner image is formed.

The toner images of the respective colors that have been subjected to the visible image processing in the development process become the ridges that are transferred to the transfer material that is fed out with the registration timing set by the registration roller 30, but before the transfer material reaches the transfer belt 22A. The sheet is biased to the transfer belt 22A by applying a suction bias by a sheet suction bias means 31 composed of a roller.
The transfer material electrostatically attracted to the transfer belt 22A and conveyed and moved together with the transfer belt 22A is transferred bias members 39Y, 39M, and 39C provided in the transfer device 22 at positions facing the photosensitive drums in the respective image forming devices. The toner image is electrostatically transferred from the photosensitive drum by applying a bias having a polarity opposite to that of the toner by 39K.

  The transfer material that has undergone the transfer process of each color is subjected to curvature separation using the curvature of the exit roller 32, and is conveyed toward the fixing device 1 (see FIG. 1), and passes through a fixing nip constituted by a fixing belt and a pressure roller. By passing, the toner image is fixed on the transfer paper. Thereafter, in the case of single-sided printing, the first paper discharge direction B toward the in-body paper discharge tray 20A (see FIG. 1) or external paper discharge. The paper is discharged by being switched by the discharge switching claw 48 in any one of the second paper discharge directions C toward the tray.

  When the first paper discharge direction B is selected, the transfer material is stacked in a face-down state with the image surface facing downward. When the second paper discharge direction C is selected, the transfer material is installed on the outer casing, although not shown. The sheet is conveyed toward a post-processing device (such as a sorter or a binding device) or a recirculation path for image formation on both sides through a switchback.

  In this embodiment for the image forming apparatus 20 having the above-described configuration, the linear velocity ratio at the time of transferring the toner image onto the first surface and the second surface of the transfer material is made different according to the environmental humidity. ing. In other words, the transfer material once the toner image is fixed has a high resistance due to a decrease in the moisture content unlike that before transfer. For this reason, when a transfer bias is applied under a condition where the current value is constant, the potential of the transfer material is increased, so that the transfer of toner due to charge concentration cannot be performed smoothly and a part of the toner is lost or discharged. Toner scattering may occur.

  In this embodiment, the transfer rate between the first surface and the second surface is lower when the resistance on the second surface is changed by the fixing with respect to the first surface of the transfer material and the humidity is lower. In order to prevent the change, the linear velocity ratio on the second surface is increased, and the transfer rate is increased by effectively utilizing the action of the shearing force on the toner.

Now, as shown in FIG. 3, the linear velocity ratio when the linear velocity of the image carrier such as the photosensitive member or the intermediate transfer member is V1, and the linear velocity of the transfer material is V2, is the transfer linear velocity ratio. Define with an expression.
Transfer linear speed ratio (%) = (V1-V2) / V2 × 100
As the transfer linear velocity ratio increases, shearing force is more likely to act on the toner, and the transfer rate increases.

FIG. 4 is a diagram showing the relationship between the linear speed ratio and the transfer rate with reference to an arbitrarily set transfer bias. In FIG. 4, it is preferable to increase the transfer linear speed ratio on both the first surface and the second surface. The transfer rate is good. The reason for this will be described with reference to FIG.
FIG. 5 is a diagram showing the relationship between the transfer bias and the transfer rate with respect to the first and second surfaces. In FIG. 5, the transfer rate is lower at the transfer bias of the first surface than the second surface. Is saturated. On the other hand, in a low humidity environment, abnormal discharge occurs before the transfer rate is saturated on the second surface, so a bias lower than the discharge start bias is set. In FIG. 5, the alternate long and short dash line indicates the transfer bias setting value that provides the result shown in FIG.

  When the transfer bias indicated by the alternate long and short dash line in FIG. 5 is used as a reference, the result is that the transfer rate of the first surface is almost saturated, but the second surface is in an unsaturated state. If the transfer linear velocity ratio is set in this state, the transfer rate on the first surface does not change so much, but the transfer rate on the second surface is significantly increased. From this, it can be seen that when the transfer bias is set to an arbitrary value, the second surface is more dependent on the transfer linear velocity ratio than the first surface, as is apparent in FIG. For this reason, when transferring to the second surface, the transfer rate to the third surface can be balanced with the transfer rate of the first surface by making the transfer linear velocity ratio different from that of the first surface.

  On the other hand, FIG. 6 is a diagram showing the relationship between the linear velocity ratio and the number of occurrences of color misregistration (in this case, the color misregistration is assumed to be a deviation of 100 μm or more). Then, the probability of occurrence of color misregistration increases due to the deterioration of the transferability of the transfer material. When the transfer linear velocity ratio is set to 1.0% or more, the number of color misregistrations increases abruptly. Therefore, it is desirable to set the transfer linear velocity ratio to 1.0% or less. For this reason, in this embodiment, the transfer linear velocity ratio for the second surface is set between 0.5 and 1.0% in consideration of transferability of the transfer material and taking into account the increase in transfer rate. It is like that.

  By the way, the transfer material after fixing passes through the fixing device 1 in the image forming apparatus 20 shown in FIG. 1 and then is reversed and fed again to the transfer position. In other words, the transfer material is conveyed. In the case where the transfer of the color image from each image forming device is sequentially transferred in the process, the final transfer target for the transfer material is the photoconductor, so the transfer speed of the transfer material relative to the linear speed of the photoconductor The linear speed ratio is set with the relationship of slowing down.

On the other hand, unlike the case of the image forming apparatus shown in FIG. 1, the toner image from the photoconductor provided in each image forming apparatus is primarily transferred to an intermediate transfer body provided in a single stage or a plurality of stages. In the case where the toner image superimposed by the primary transfer is collectively transferred to the transfer material at the secondary transfer position as the final transfer position, the intermediate transfer member and the transfer material positioned at the final stage among the intermediate transfer members In order to set the linear speed ratio between the two, the transfer speed of the transfer material is lowered.
If the transfer speed of the transfer material is set to a speed higher than that of the photosensitive member or the intermediate transfer body, the transfer material may undergo periodic speed fluctuations, which may cause color misregistration. This is caused by uneven conveyance caused by a mechanical error in the transfer driving system of the transfer material. From this, the occurrence cycle of the uneven conveyance is delayed with respect to the transfer material moving distance. Thus, it is advantageous to reduce the speed of the transfer material.

  On the other hand, when a single transfer material is the target, it is preferable that the transfer material slows down the wow speed as described above. For example, the transfer onto the first surface on the same conveyor belt. When the transfer material that receives the transfer onto the second surface of the transfer material that has been fixed on the first surface is transferred continuously to the transfer material that receives the transfer material, the moving speed of the transfer belt is set to the first surface and the second surface. Therefore, it is difficult to perform speed switching during the movement. Therefore, in this embodiment, as shown in FIG. 7, the transfer material S1 that receives the transfer onto the first surface on the same conveying belt and the transfer material S2 that receives the transfer onto the second surface after fixing the first surface. Are continuously conveyed, the linear velocity of the photosensitive member located in the image forming unit is changed in order to change the transfer linear velocity ratio of the second surface to the first surface when the humidity is low. Is switched to the linear velocity for the second surface.

  This method is the same not only when the above-mentioned transfer target member to the transfer material is a photosensitive member but also when an intermediate transfer member is used as shown in FIG.

  On the other hand, as a method for increasing the transfer rate on the second surface with respect to the first surface when the humidity is low, a method for increasing the transfer bias for the second surface than for the first surface in order to increase the adhesion of the toner. It is also possible to use.

The toner used in this example has an average circularity of 0.90 to 0.99, a shape count SF-1 of 120 to 180, and a volume average particle diameter (Dv (μm)). Those having a ratio of 1.05 to 1.30 with the number average particle diameter (Dn (μm)) are used. By setting the toner characteristics as described above, the following effects can be obtained.
When the average circularity of the toner is less than the lower limit value, it means an irregularly shaped toner that is too far from the spherical shape. In the case where a blade is used as a cleaning member, the occurrence of cleaning on the photosensitive member or transfer member becomes significant, and the image may be contaminated.

  The shape count SF-1 means the roundness of the shape of the toner, and when the value is 100, it becomes a true sphere. For this reason, it is possible to obtain a point contact between toners or a contact partner such as a photoconductor by bringing them close to a spherical shape, thereby increasing the fluidity of the toner and weakening the adhesion to the contact partner. It is easy to be affected by the transfer electric field, thereby increasing the transfer efficiency. On the other hand, if it is close to a perfect sphere, the recovery efficiency during cleaning deteriorates due to a decrease in the adhesive force with the contact partner, and it passes between rubbing bodies such as a cleaning blade. In view of such a point that the cleaning efficiency is deteriorated and the cleaning efficiency is deteriorated, it is possible to prevent the transfer efficiency from being lowered and the cleaning property from being deteriorated by setting the value within the above range.

  The particle size ratio is as described as the effect of the invention according to claim 11 in the effect of the invention.

1 is a schematic diagram illustrating an example of an image forming apparatus to which an image forming method according to an embodiment of the present invention is applied. FIG. 2 is a schematic diagram for explaining a configuration of a transfer device used in the image forming apparatus shown in FIG. 1. It is a figure for demonstrating the relationship of a linear speed ratio. It is a figure for demonstrating the relationship between the transfer linear velocity ratio and transfer rate under arbitrary transfer bias. It is a figure for demonstrating the relationship between the transfer bias and transfer rate which make object the 1st surface and the 2nd surface. It is a figure for demonstrating the relationship between a transcription | transfer linear velocity ratio and the number of color shift generation | occurrence | production. It is a schematic diagram which shows an example of the structure by which a 1st surface and a 2nd surface are conveyed continuously. FIG. 4 is a schematic diagram illustrating a positional relationship between an intermediate transfer member and a transfer material.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fixing device 20 Image forming device 21 Image forming device 22 Transfer device 25 Photosensitive drum 26 Developing device 26A Developing roller 27 Charging device 29 Writing device

Claims (11)

A step of transferring a toner image carried on the image carrier to the transfer material by using a transfer bias, and a step of fixing the transfer image carried on the transfer material. In an image forming method capable of executing a step of transferring a toner image from the image carrier to the second surface of the transfer material after fixing the image transferred on the one surface,
An image forming method, wherein a linear velocity ratio between the image carrier and a transfer material is changed in accordance with environmental humidity during image transfer onto the second surface. A step of transferring a toner image carried on the image carrier to a transfer material via one or a plurality of intermediate transfer members, and a step of fixing the transfer image carried on the transfer material. In the image forming method capable of performing the step of transferring the toner image from the image carrier to the second surface of the transfer material after fixing the image transferred to the first surface of the transfer material,
An image forming method comprising changing a linear velocity ratio between an image carrier located at the final stage of the image carrier and a transfer material during image transfer to the second surface in accordance with environmental humidity. The image forming method according to claim 1 or 2,
An image forming method, wherein when the humidity is low, a linear speed ratio at the time of transfer to the second surface is set larger than that at a high humidity. The image forming method according to any one of claims 1 to 3,
An image forming method, wherein a linear velocity of a transfer material is set slower than a linear velocity of an image carrier or an image carrier positioned at a final stage. The image forming method according to claim 1, wherein:
An image forming method, wherein a transfer bias for the second surface is set higher than a transfer bias for the first surface.   An image forming apparatus using the image forming method according to claim 1. The image forming apparatus according to claim 6.
An image forming apparatus, wherein a toner image carried on an image carrier is developed by a plurality of developing means. The image forming apparatus according to claim 6 or 7,
The toner image is formed using a tandem structure in which image forming portions capable of forming latent images for a plurality of colors are juxtaposed. The image forming apparatus according to claim 6, wherein:
An image forming apparatus having an average circularity of a toner used of 0.90 to 0.99. The image forming apparatus according to claim 6, wherein:
An image forming apparatus having a toner shape count SF-1 of 120 to 180. The image forming apparatus according to claim 6, wherein:
An image forming apparatus wherein Dv / Dn is 1.05 to 1.30 when the volume average particle diameter (Dv (μm)) and the number average particle diameter (Dn (μm)) of the toner to be used are set. .

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