JP2009294673A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the occurrence of transfer dust and transfer void being problems when a toner image is electrostatically transferred from an intermediate transcript to a transfer material. <P>SOLUTION: In the transferring method where a toner image transferred from an image carrier to an intermediate transfer belt 51 is electrostatically transferred to transfer paper P using a transfer roller 56, the surface layer of the face stuck with toner in the intermediate transfer belt 51 is provided with an elastic layer, the space between the transfer roller 56 and the intermediate transfer belt 51 is provided with a means 56d applying pressure, transfer bias current between the intermediate transfer belt 51 and the transfer roller 56 is 0.05 to 0.2 μA/cm, and pressure of 1 to 10 N/cm is applied to the space between the transfer roller 56 and the backup roller 55 of the intermediate transfer belt 51. In this way, a transfer magnetic field can be applied without depending on toner height, thus the charging amount of the transfer paper is suppressed, discharge upon separation can be reduced, and diffused transfer can be reduced. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming method and an image forming apparatus such as a copying machine, a printer, a plotter, and a facsimile using the image forming method. The present invention relates to a transfer method characterized by the transfer of a toner image from a toner to an intermediate transfer member and the transfer of a toner image from an intermediate transfer member to a transfer material, and an image forming method and an image forming apparatus using the transfer method.

In recent years, high image quality is also required in electrophotographic color image forming methods, which have been improved by reducing the diameter of toner and improving development. However, when observing each image forming process, it is clear that the latent image, development, intermediate transfer, transfer paper transfer, and fixing are deteriorated in each process. In particular, there is a large deterioration in the transfer process. As a phenomenon, generation of dust due to pre-transfer at the time of transfer and discharge at the time of peeling after transfer is a big problem.
Many proposals have been made for these issues. For example, in Patent Document 1, a pressing roller that presses the intermediate transfer belt from the inner peripheral surface side to the photosensitive drum is provided at least in a contact region of the intermediate transfer belt with the photosensitive drum in the lateral direction of the belt. It has been proposed to improve the adhesion of the intermediate transfer belt, increase the toner cohesion at the contact nip, and prevent partial transfer defects and transfer dust caused by insufficient adhesion between the photosensitive drum and the intermediate transfer belt. Yes.

  Further, in Patent Document 2, in a color image forming method, a pressing pressure of 15 g / cm or more of contact pressure is used as a transfer process in order to solve transfer dust and worm-like transfer failure in transfer from a photosensitive member to an intermediate transfer member. In addition, the linear speed ratio between the intermediate transfer belt and the photosensitive member is set to 0.85 to 1.10, the surface / volume resistance, etc. are defined as the intermediate transfer belt characteristics, and the cohesion degree, bulk density, and grain are further defined as the toner characteristics. It has been proposed to define the diameter and optimize the adhesion force between the toner, the transfer gap, the charge holding force of the intermediate transfer belt, and the like.

In recent years, image quality has been further improved, and polymerized toner has been used as the toner. As toner characteristics, characteristics such as further reduction in diameter, spheroidization, uniform shape, uniform charge amount and the like are easily obtained, leading to an improvement in image quality.
In the above conventional example, when polymerized toner is used, there is a lot of transfer dust, and it looks smooth, but it is an image with poor sharpness and lack of sharpness, and difficulty in reading fine characters. Yes.
In particular, as a characteristic of a color image, toners having different heights in the Z-axis direction (direction perpendicular to the belt surface) of one to three colors are attached on the intermediate transfer belt. For this reason, depending on the toner layer thickness, a portion where the toner is in close contact with the transfer paper and a portion where there is a gap appear. As a result, the electric field around the toner in the portion where the void is present is smaller than that in the portion where the toner is large (the dielectric constant of the void is 1, whereas the dielectric constant of the toner layer is about 3; The electric field of the air gap with respect to the layer corresponds to 1/3). As a result, it is necessary to increase the electric field required for transfer, and the transfer paper charge amount due to the transfer bias increases. In addition, a discharge phenomenon is likely to occur during separation, resulting in an increase in transfer dust.

  The present invention has been made in view of the above-described problems. The object of the present invention is to use an intermediate transfer member having a surface elastic layer, apply transfer pressure during transfer from the intermediate transfer member to a transfer material, To provide a transfer method capable of reducing a gap and applying a minimum transfer bias in order to maintain a transfer electric field sufficient for transfer and preventing transfer dust due to discharge during transfer separation, and To provide an image forming method capable of obtaining a sharp image with little transfer dust in a process of electrostatic transfer from an intermediate transfer member to a transfer material using a transfer method, and further to form the image. An image forming apparatus capable of providing an optimum toner characteristic used in a method and obtaining an image having a small amount of transfer dust, a sharp image, and a small amount of white transfer by using the image forming method. It is to provide.

To achieve the above object, the invention according to claim 1 is directed to a transfer method in which a toner image transferred from an image carrier to an intermediate transfer member is electrostatically transferred to a transfer material using a transfer unit. The transfer member has an elastic layer on the surface of the surface to which the toner is adhered, has a means for applying pressure between the transfer means and the intermediate transfer body, and a transfer bias current between the intermediate transfer body and the transfer means is It is 0.05 to 0.2 μA / cm.
According to a second aspect of the present invention, in the transfer method according to the first aspect, the intermediate transfer member is an intermediate transfer belt supported by a plurality of rollers, and the transfer means is a transfer roller or a transfer supported by the rollers. It is a belt, and a pressure of 1 to 10 N / cm is applied between the transfer means and the backup roller of the intermediate transfer belt.
Furthermore, the invention according to claim 3 is the transfer method according to claim 1 or 2, wherein the intermediate transfer member has one or more elastic layers on the support, and the outermost surface layer has a thickness of 0.1 to 0.00. The elastic layer has a thickness of 2 mm and a hardness of 15 to 40 degrees.
Furthermore, the invention according to claim 4 is the transfer method according to claim 1, 2 or 3, wherein the elastic layer of the intermediate transfer member is subjected to surface treatment, and the friction coefficient of the surface layer of the intermediate transfer member is set to 0. .7 or less.

The invention according to claim 5 includes one or more steps of forming a latent image on an image carrier, developing the latent image with toner to form a toner image, and transferring the toner image to an intermediate transfer member. The toner image of one or more colors is transferred onto the intermediate transfer member, and the toner image transferred to the intermediate transfer member is electrostatically transferred to a transfer material using a transfer unit. In an image forming method for fixing an image transferred on a material to form an image, the transfer method according to any one of claims 1 to 4 is used.
The invention according to claim 6 is characterized in that, in the image forming method according to claim 5, a toner having a cohesion degree of 15 to 40% is used as a toner used for development.
Further, the invention according to claim 7 is the image forming method according to claim 5, wherein a toner having a hardness of 7 to 12 degrees is used as a toner for development.

  According to an eighth aspect of the present invention, there is provided a latent image forming unit for forming a latent image on an image carrier, a developing unit for developing the latent image with toner to form a toner image, and the toner image on an intermediate transfer member. An image provided with an intermediate transfer means for transferring, a transfer means for electrostatically transferring the toner image transferred to the intermediate transfer body onto a transfer material, and a fixing means for fixing the toner image transferred onto the transfer material In the forming apparatus, the image forming method according to any one of claims 5 to 7 is used.

Hereinafter, the present invention will be described in more detail.
The toner image transferred from the image carrier (eg, photoconductor) to the intermediate transfer member (eg, intermediate transfer belt) is electrostatically transferred onto a transfer material (eg, transfer paper) using a transfer means (transfer roller or transfer belt). In the transfer method for transferring, electrostatic transfer from the intermediate transfer belt to the transfer paper moves depending on the electric field around the toner and the charge amount of the toner. However, if the transfer electric field is sufficiently applied, the charge amount of the transfer paper increases, causing a discharge phenomenon during transfer separation, resulting in toner transfer dust. In particular, in the case of a color image formed by superimposing a plurality of toners, if there is a difference in the height of the toner layer on the intermediate transfer belt in the Z-axis direction (direction perpendicular to the belt surface), naturally, the transfer efficiency depends on the condition. Therefore, a transfer bias suitable for the worse one is applied. As a result, the transfer paper is charged too much, causing discharge during transfer separation, resulting in transfer dust.
Therefore, in the transfer method of the present invention, an elastic layer is provided on the surface layer of the intermediate transfer belt on which the toner adheres, and a means for applying pressure between the transfer means (transfer roller or transfer belt) and the intermediate transfer belt is provided. The transfer bias current between the belt and the transfer unit is 0.05 to 0.2 μA / cm (Claim 1), and further, 1 to 10 N is provided between the transfer unit and the backup roller of the intermediate transfer belt. Since the transfer electric field can be applied without depending on the toner height, the charge amount of the transfer paper can be suppressed to a small level, and the pressure during separation can be reduced. Discharge can be reduced, and transfer dust can be reduced. Therefore, a sharp image with little transfer dust can be obtained in the process of electrostatic transfer from the intermediate transfer belt to the transfer paper.

Next, when forming a color image, the color image transferred to the intermediate transfer belt has a height in the Z-axis direction (direction perpendicular to the belt surface) and is 10 μm and 30 μm for one color toner layer and three color toner layers. There is a difference. As a matter of course, the transfer efficiency is determined by applying a transfer bias according to the worse condition. As a result, the transfer paper is charged too much, causing discharge during transfer separation, resulting in transfer dust. In particular, multi-layer toner dust is conspicuous.
Therefore, in the present invention, the intermediate transfer belt has one or more elastic layers on the support, and has an elastic layer having a thickness of 0.1 to 0.2 mm and a hardness of 15 to 40 degrees on the outermost surface layer. Since it is configured (Claim 3), by applying a pressure between the intermediate transfer belt and the transfer paper, the toner bites into the surface soft elastic layer, and the toner and the transfer paper have good adhesion. As a result, the charge amount of the transfer paper can be suppressed to a small level, discharge during separation can be reduced, and transfer dust can be reduced. Therefore, a sharp image with little transfer dust can be obtained in the process of electrostatic transfer from the intermediate transfer belt to the transfer paper. If the elastic layer of the intermediate transfer belt is too thick, the toner layer will be displaced. Therefore, in the present invention, the outermost surface layer has a thickness of 0.1 to 0.2 mm so as to be the optimum thickness. .

Next, in the electrostatic transfer method in which a strong pressure is applied between the intermediate transfer belt and the transfer paper of the present invention, the toner tends to adhere to each other or the toner and the intermediate transfer belt. That is, when a pressure is applied to the toner, it deforms plastically and increases the contact surface, and the external additive is buried in the toner and easily adheres with a viscous force. Further, the toner between the intermediate transfer belt and the transfer paper may adhere and may adhere to either the transfer paper or the intermediate transfer belt at the time of peeling. When it adheres to the intermediate transfer belt, transfer white spots are caused.
Since the characteristic that the toner hardly adheres to the surface of the intermediate transfer belt is the friction coefficient, in the present invention, the surface treatment is performed on the elastic layer of the intermediate transfer belt so that the friction coefficient of the surface layer of the intermediate transfer belt is 0.7 or less. (Claim 4), even when toners adhere to each other, they can adhere to the transfer paper side and prevent white spots. Therefore, by processing the friction coefficient of the surface of the intermediate transfer belt to 0.7 or less, it is possible to obtain an image with less transfer dust and less transfer white spots.

Next, in the electrostatic transfer method in which a strong pressure is applied between the intermediate transfer belt and the transfer paper, the toner easily adheres to the intermediate transfer belt and the transfer paper due to viscosity. When the toner cohesion becomes small, it becomes dry and becomes strong against pressure. On the other hand, when the toner cohesion becomes large, the “stickiness” becomes strong. It easily adheres to paper and intermediate transfer belts. Therefore, an optimum toner aggregation degree is required for electrostatic transfer.
Therefore, in the image forming method and apparatus of the present invention, the transfer method according to any one of claims 1 to 4 is used, and further, toner having an aggregation degree of 15 to 40% is used as a toner used for development. (Claims 5, 6, and 8) By optimizing the toner aggregation degree to 15 to 40%, it is possible to obtain an image with less transfer dust and less transfer white spot.

Next, in the electrostatic transfer method in which a strong pressure is applied between the intermediate transfer belt and the transfer paper, the toner easily adheres to the intermediate transfer belt and the transfer paper due to viscosity. The higher the toner hardness, the more difficult it is to adhere, and the stronger the pressure, the harder it is to fix. On the other hand, when the toner hardness is small, “stickiness” becomes strong, and when pressure is applied to the toner, it tends to adhere to toners, transfer paper, and transfer belt due to viscosity. Therefore, an optimum hardness is required for electrostatic transfer.
Therefore, in the image forming method and apparatus of the present invention, the transfer method according to any one of claims 1 to 4 is used, and toner having a hardness of 7 to 12 degrees is used as a toner used for development. In addition, by optimizing the hardness of the toner to 7 to 12 degrees, it is possible to obtain an image with less transfer dust and less transfer white spot.

  In the transfer method of the present invention, an elastic layer is provided on the surface of the intermediate transfer member (for example, intermediate transfer belt) on which toner is adhered, and means for applying pressure between the transfer means (transfer roller or transfer belt) and the intermediate transfer belt And a transfer bias current between the intermediate transfer belt and the transfer means is 0.05 to 0.2 μA / cm (Claim 1), and further, a backup roller for the transfer means and the intermediate transfer belt Since a pressure of 1 to 10 N / cm is applied between them (Claim 2), a transfer electric field can be applied without depending on the toner height, so that the charge amount of the transfer paper is kept small. Therefore, discharge during separation can be reduced, and transfer dust can be reduced. Therefore, a sharp image with little transfer dust can be obtained in the process of electrostatic transfer from the intermediate transfer belt to the transfer paper.

  In the transfer method of the present invention, the intermediate transfer belt has one or more elastic layers on the support, has a thickness of 0.1 to 0.2 mm on the outermost surface layer, and a hardness of 15 to 40 degrees. Since the elastic layer is provided (Claim 3), by applying pressure between the intermediate transfer belt and the transfer paper, the toner bites into the surface soft elastic layer, and the toner and the transfer paper are improved in adhesion. As a result, the charge amount of the transfer paper can be suppressed to a small level, discharge during separation can be reduced, and transfer dust can be reduced. Therefore, a sharp image with little transfer dust can be obtained in the process of electrostatic transfer from the intermediate transfer belt to the transfer paper. If the elastic layer of the intermediate transfer belt is too thick, the toner layer will be displaced. Therefore, in the present invention, the outermost surface layer has a thickness of 0.1 to 0.2 mm so as to be the optimum thickness. .

  Furthermore, in the transfer method of the present invention, the surface treatment is performed on the elastic layer of the intermediate transfer belt so that the friction coefficient of the surface layer of the intermediate transfer belt is 0.7 or less (claim 4). Even when toners adhere to each other, they can adhere to the transfer paper side to prevent white spots. Therefore, by processing the friction coefficient of the surface of the intermediate transfer belt to 0.7 or less, it is possible to obtain an image with less transfer dust and less transfer white spots.

In the image forming method and apparatus of the present invention, the transfer method according to any one of claims 1 to 4 is used, and toner having an aggregation degree of 15 to 40% is used as a toner used for development. In addition, by optimizing the toner aggregation degree to 15 to 40%, it is possible to obtain an image with less transfer dust and less transfer white spot.
In the image forming method and apparatus of the present invention, the transfer method according to any one of claims 1 to 4 is used, and toner having a hardness of 7 to 12 degrees is used as a toner used for development. (Claims 5, 7, and 8) By optimizing the hardness of the toner to 7 to 12 degrees, it is possible to obtain an image with less transfer dust and less transfer white spot.

1 is a schematic configuration diagram of an image forming apparatus showing an embodiment of the present invention. FIG. 4 is an explanatory diagram of a mechanism for generating transfer dust when a toner image is transferred from an intermediate transfer belt to transfer paper. FIG. 6 is a schematic configuration diagram of a main part illustrating a configuration example of a second transfer unit that transfers a toner image from an intermediate transfer belt to transfer paper. FIG. 5 is a diagram illustrating a transfer paper transfer model in a case where a conventional intermediate transfer belt including only a support is used when a toner image is transferred from an intermediate transfer belt to transfer paper. FIG. 4 is a diagram showing a transfer paper transfer model when the toner image is transferred from the intermediate transfer belt to the transfer paper when the intermediate transfer belt of the present invention is used. It is a figure which shows the evaluation rank sample of transcription | transfer dust. It is a figure which shows the evaluation rank sample of a transfer white-out.

Hereinafter, the configuration, operation and action of the present invention will be described in detail with reference to the drawings.
In a color image forming apparatus using an intermediate transfer member (for example, an intermediate transfer belt), transfer dust is generated as a problem in the second transfer step in which a toner image is transferred from the intermediate transfer belt to a transfer material (for example, transfer paper). There's a problem. This transfer dust will be considered with reference to FIG.
In FIG. 2, reference numeral 51 denotes an intermediate transfer belt, 56 denotes a transfer roller, and P denotes transfer paper. In the second transfer step of transferring the toner image from the intermediate transfer belt 51 to the transfer paper P, before and after the transfer region [B]. In the areas [A] and [C] where the transfer paper P and the intermediate transfer belt 51 are not in contact, transfer dust is generated due to the influence of the electric field. The main cause is discharge phenomenon when close to each other.

Here, the force F for transferring the toner from the intermediate transfer belt 51 to the transfer paper P is:
F = qE (1)
q: Charge amount of toner E: Electric field around toner between transfer paper and intermediate transfer belt, and electric field E around toner is
E = (Vp−Vbelt) / (dp / εp + dt / εt + dblt / εbelt + g) (2)
Vp−Vbelt: Potential difference between transfer belt and transfer paper dp / εp: Dielectric thickness of transfer paper dt / εt: Dielectric thickness of toner layer dblt / εbelt: Dielectric thickness of belt layer g: Air gap (air gap)
It is.

In order to reduce the discharge in the [A] area and the [C] area, it is necessary to reduce the potential difference between the intermediate transfer belt and the transfer paper (transfer roller).
As the improvement measures, there are the following methods.
1) When the air gap between the intermediate transfer belt and the transfer paper is reduced while keeping the electric field around the toner between the transfer paper and the intermediate transfer belt constant, the potential difference between the intermediate transfer belt and the transfer paper is obtained from the above equation (2). Can be reduced. As an actual means, there is provided means for applying pressure between the transfer roller as the transfer means and the intermediate transfer belt, and pressure is applied between the transfer roller having a relatively hard rubber-like surface layer and the back roller of the intermediate transfer belt. In addition, this can be achieved by increasing the close contact between the transfer paper and the intermediate transfer belt and reducing the average average gap.
2) In the case of a color image, it is necessary to transfer toner layers having different heights of one-color toner and three-color superimposed toner. Therefore, in order to correct the adhesion failure between the transfer paper and the toner, the intermediate transfer belt has a two-layer structure, and a soft rubber layer is thinly formed on the surface. Further, the aforementioned pressure is applied to bring the transfer paper into contact with the toner. As a result, the gap around the toner can be reduced, and the potential difference between the transfer paper and the intermediate transfer belt can be reduced. As a result, the toner, the transfer paper, and the intermediate transfer belt are in close contact with each other, and the transfer efficiency does not change. In addition to the dust in the toner in the transfer area [B] in FIG. Can be reduced and transfer dust is reduced.
3) Further, in the present invention, the white spot in the transfer by pressure application transfer observed in the conventional transfer is improved. Phenomenon that transfer toner is agglomerated due to pressure and dust due to discharge at the time of separation is reduced as a cause of whitening of transfer, but it is not transferred to transfer paper due to toner adhesion to the photoreceptor or intermediate transfer belt due to aggregation It is. Therefore, as a countermeasure, a hard toner that hardly aggregates toner is used, and a toner that does not stick to the intermediate transfer belt even when a pressure is applied during transfer is used. Further, it is assumed that the charge amount of the transfer paper is reduced to prevent discharge during separation.
By the above means, the electric field around the toner has a sufficient value, and the charge amount of the transfer paper can be reduced.
This makes it possible to obtain a condition in which the potential difference between the intermediate transfer belt and the transfer paper is small at the time of peeling after transfer and the occurrence of discharge hardly occurs, and an image with little transfer dust, sharpness and little transfer whiteout can be obtained.

Hereinafter, specific embodiments of the present invention will be described.
FIG. 1 is a schematic configuration diagram of an image forming apparatus showing an embodiment of the present invention, and shows an outline of a color image forming apparatus using a known electrophotographic system and using an intermediate transfer belt.
This image forming apparatus includes a drum-shaped photoconductor 1 as an image carrier, and the photoconductor 1 rotates in the direction of an arrow in the figure. Around the photosensitive member 1, a charging unit 2, an exposure unit (latent image forming unit) 3, a developing unit 4, an intermediate transfer unit 5, and a cleaning unit 6 are used to perform an image forming process along the rotation direction. Is arranged. A transfer means 56 for transfer paper is disposed below the intermediate transfer means 5, and a transport belt 57 and a fixing means 7 are disposed downstream of the transfer paper transfer means 56 in the transfer paper transport direction. . Further, a paper feed bank 101 for storing transfer paper is disposed at the lower part of the main body of the image forming apparatus, and a paper feed roller 102 and a transport roller 103 are provided on a transport path from the paper feed bank 101 to the transfer paper transfer means 56. A registration roller 104 is provided. When the image forming apparatus is a copying machine or the like, a known document reading device (color scanner) 31 is provided at the top of the main body.

In FIG. 1, as the charging unit 2, for example, various chargers such as a charging charger, a charging roller, and a charging brush are used to uniformly charge the surface of the photoreceptor 1.
As the exposure means (latent image forming means) 3, for example, an optical scanning type exposure apparatus 32 provided with a laser light source, an optical deflector (rotating plane mirror, rotating polygon mirror, pyramid mirror, etc.), a scanning imaging optical system, and the like is used. Then, a laser beam 34 modulated in accordance with the image data is emitted from the exposure device 32 and exposed to the surface of the photoreceptor 1 through the folding mirror 33 to form an electrostatic latent image. In addition, as the exposure means, an optical writing device using a light emitting diode (LED) array and an imaging element array can be used.
As the developing means 4, for example, a rotary developing device (revolver type developing device) is used. In the rotary developing device 4, a yellow developing device 41 using yellow toner, a magenta developing device 42 using magenta toner, Four color developing units, a cyan developing unit 43 using cyan toner and a black developing unit 44 using black toner, are housed around a rotation axis O, and these developing units are rotated about the rotation axis O, These color developing devices are moved to a position facing the photoconductor 1, and the electrostatic latent image on the photoconductor 1 is developed with toner of each color. Further, as each developing device, for example, a two-component developing type developing device is used, but a one-component developing type developing device can also be used.
The intermediate transfer unit 5 is, for example, an intermediate transfer belt device that uses an intermediate transfer belt 51 as an intermediate transfer member, and the intermediate transfer belt 51 is supported by a plurality of rollers 52 to 55. Among the plurality of rollers, 52 is an intermediate transfer roller that supports the intermediate transfer belt 51 at the intermediate transfer portion, and a transfer bias is applied to electrostatically transfer the toner image on the photoreceptor 1 to the intermediate transfer belt 51 ( First transfer). Reference numeral 55 denotes a backup roller that supports the intermediate transfer belt 51 at a transfer portion to transfer paper. An intermediate transfer drum can also be used as the intermediate transfer member.
The cleaning unit 6 is a cleaning device that includes a cleaning blade 61, a cleaning brush 62, toner collection units 63 and 64, and collects transfer residual toner on the photoreceptor 1.
The transfer paper transfer means 56 is, for example, a transfer roller. When transferring from the intermediate transfer belt 51 to the transfer paper (second transfer), the transfer paper is transferred to the intermediate transfer belt 51 side by a contact / separation mechanism (not shown) and a transfer bias is applied. When applied, the toner image on the intermediate transfer belt 51 is transferred to the transfer paper. As the transfer paper transfer means, a transfer belt supported by a roller can be used.
The fixing unit 7 is a fixing device including a fixing roller 71 having a heat source (electric heater, halogen lamp, etc.) and a pressure roller 72 therein, and fixes the toner image transferred from the intermediate transfer belt 51 to the transfer paper. To do.

Since the image forming apparatus having the configuration shown in FIG. 1 is a one-drum intermediate transfer type color image forming apparatus, for example, images of each color of yellow, magenta, cyan, and black are sequentially formed on the photosensitive member 1. Are transferred to the intermediate transfer belt 51 in the order of formation, and a four-color superimposed image is formed on the intermediate transfer belt.
More specifically, when the image forming operation is started, the photosensitive member 1 is first uniformly charged by the charger 2, and then a laser beam 34 corresponding to yellow image data is emitted from the exposure device 32 of the exposure means 3 to the photosensitive member. The top is exposed to form a yellow electrostatic latent image. The formed latent image is developed with the yellow toner of the yellow developing device 41 to be visualized, and then electrostatically transferred onto the intermediate transfer belt 51. Further, the transfer residual toner remaining on the surface of the photoreceptor after the transfer is removed by the cleaning device 6. Next, the same processes from charging to intermediate transfer and cleaning as described above are repeated in order of magenta, cyan, and black, and four color toners are superimposed and transferred onto the intermediate transfer belt 51. Next, although not shown, the transfer paper transfer roller 56 separated from the intermediate transfer belt 51 comes into contact with the intermediate transfer belt 51 by the contact / separation mechanism, and the transfer paper is fed from the paper supply bank 101 in synchronization therewith. The registration roller 104 feeds the nip portion between the intermediate transfer belt 51 and the transfer paper transfer roller 56, and the toner images on the intermediate transfer belt 51 are simultaneously transferred onto the transfer paper sandwiched between the nip portions. Then, the transfer paper separated from the intermediate transfer belt 51 is conveyed to the fixing device 7 by the conveying belt 57, and the toner image is fixed on the transfer paper by the heated fixing roller 71 and the pressure roller 72 of the fixing device 7, and after fixing. The transfer sheet is discharged to a discharge tray or the like outside the apparatus.

Next, a characteristic transfer configuration of the present invention used in the image forming apparatus having the above configuration and operation will be described with reference to FIG. FIG. 3 shows only the configuration of the second transfer unit that transfers the toner image on the intermediate transfer belt 51 to the transfer paper P.
As shown in FIG. 3, the transfer roller 56 includes a solid elastic layer 56a made of EPDM, silicone, NBR, urethane or the like on a core metal 56b made of stainless steel (SUS), iron (Fe) or the like and having a diameter of 20 to 30 mm. The elastic layer 56a has a thickness of 0.1 to 1.0 mm, a hardness of 60 to 80 degrees (when loaded with Asker C / 1 kg), and a volume resistance of 1 × 10 ⁸ to 1 × 10 ¹¹ Ωcm. The surface resistance is optimally equal to or greater than the volume resistance.
The contact / separation mechanism (not shown) that contacts and separates the transfer roller 56 from the intermediate transfer belt 51 is provided with a pressurizing unit. As the pressurizing unit, bearings 56 c are provided at both ends of the shaft of the transfer roller 56. The bearings 56c at both ends are pressed in the direction of the intermediate transfer belt 51 by springs (springs, etc.) 56d. When the transfer roller 56 is brought into contact with the intermediate transfer belt 51 by a contact / separation mechanism (not shown). The transfer roller 56 is pressed against the intermediate transfer belt 51 (backup roller 55). The measurement of the pressing force is presented by a value obtained by dividing the total pressing force of the springs 56d provided at both ends of the shaft of the transfer roller 56 by the length of the transfer roller, and the unit is indicated by N / cm.

Next, the configuration and operation of the intermediate transfer belt 51 used in the image forming apparatus of the present invention will be described.
The layer structure of the intermediate transfer belt 51 is a structure in which two elastic layers having different hardnesses are provided on a support, and the surface layer side is a soft elastic layer having a thickness of 0.1 to 0.2 mm and a hardness of 15 to 40 degrees. The internal elastic layer (intermediate elastic layer) is composed of an elastic layer having a thickness of 0.1 to 0.3 mm and a hardness of 60 to 80 degrees. Further, in order to prevent toner adhesion, the surface of the elastic layer on the surface layer side is coated with a fluorine resin (for example, Teflon (registered trademark)) so that the surface friction coefficient is 0.7 or less, and the volume resistance is The surface resistivity was 4 × 10 ¹² Ω at 2 × 10 ¹² Ωcm. The operation of the intermediate transfer belt 51 will be described with reference to FIGS.

  FIG. 4 is a diagram showing a transfer paper transfer model when an intermediate transfer belt made of only a conventional support is used. The toner transferred on the intermediate transfer belt is random from one to three layers. When the transfer paper is brought into contact with the transfer roller with the transfer roller in this state, the contact and distance between the toner sheet of one color and the multi-layer toner layer are different from each other and the uniform electric field E cannot be obtained. Therefore, the current flowing to the transfer paper increases. As a result, the multilayer toner layer collapses or is easily discharged during separation, and transfer dust is generated.

  Next, FIG. 5 is a diagram showing a transfer paper transfer model when the intermediate transfer belt of the present invention is used. The intermediate transfer belt according to the present invention has a soft elastic layer on the surface layer, and when transferring to the transfer paper, a pressure is applied between the intermediate transfer belt 51 and the transfer paper transfer roller 56 by a spring 56d as shown in FIG. As a result, the toner layer bites into the surface layer of the intermediate transfer belt 51, and further pressure is applied, so that the transfer paper P, the transfer roller 56, and the intermediate transfer belt 51 are in close contact with each other, and a minimum transfer current is sufficient. An image with little transfer dust is obtained during both transfer and transfer separation.

Here, the measurement of the resistance value and the friction coefficient of the intermediate transfer belt will be described.
For the surface resistance and volume resistance of the intermediate transfer belt, measured values at an applied voltage of 500 V and a measurement time of 10 seconds were used, using a Hirester manufactured by Mitsubishi Oil Chemical.
The friction coefficient was measured using a Friction Abrasion Analyzer DF, PM-SS manufactured by Kyowa Interface Chemical Co., Ltd., with a stainless ball indenter weight of 100 g.

Next, characteristics of the toner used for development in the image forming method (apparatus) of the present invention will be described.
The toner used for development in the image forming method (apparatus) of the present invention preferably has a smaller cohesive force. However, if the toner cohesion is too small, the fluidity of the toner is too good and transfer dust is likely to occur. If the toner cohesion is large, the toner tends to adhere to each other and adhere to the intermediate transfer belt 51. Transfer white spots are likely to occur.
Here, the cohesion force of the toner can be expressed as an aggregation degree (%). Therefore, it can be said that the larger the cohesion value, the stronger the cohesion of the toner.

As a method for measuring the degree of aggregation of the toner, “Powder Tester PT-N type (manufactured by Hosokawa Micron Corporation)” is used as a measuring device, and the operation method basically follows the instruction manual of “Powder Tester PT-N type”. The following points have changed.
1. Use sieve: 75 μm, 45 μm, 22 μm.
2. Vibration time: 30 seconds.

The degree of aggregation of the toner used for development in the image forming method (apparatus) of the present invention is 15 to 40%, more preferably 15 to 35%. When the degree of aggregation of the toner is 15% or less, the fluidity of the toner is too good and dust is likely to be generated during transfer. On the other hand, when the degree of aggregation is 40% or more, the cohesive force of the toner is increased and the transferability is deteriorated. In addition, transfer white spots occur.
Furthermore, the hardness of the toner used for development in the image forming method (apparatus) of the present invention is related to the adhesion between the toners and the fixing characteristics. In the case of the pressure transfer system as in the present invention, it is preferable that the hardness is high, but the optimum value is used because the fixing characteristics are adversely affected.

  As a method for measuring the toner hardness, a “micro compression tester MCTM-500 (manufactured by Shimadzu Corporation)” is used as a measuring device. As a measuring method, first, the molten toner is rolled and cooled to form a flat plate. The surface is then polished and smoothed using # 1200 sandpaper. Then, a load is added at 1.0 gf, measurement is performed 5 times, and the average value is defined as hardness.

  The toner used for development in the image forming method (apparatus) of the present invention has a hardness of 7 to 12, more preferably 8 to 11. When the hardness of the toner is 7 or less, when the toner particles come into contact with each other, plastic deformation occurs, so that the contact area between the toners increases, the cohesive force of the toner increases, and it becomes difficult to make the toner layer uniform. When the toner has a hardness of 12 or more, there is no problem in the transfer process, but the fixability may deteriorate in the fixing process.

Next, the prescription of toner used for development in the image forming method (apparatus) of the present invention will be described.
As the binder resin used in the toner used in the present invention, all conventionally known resins can be used. For example, styrene, poly-α-still styrene, styrene-chlorostyrene copolymer, styrene-propylene copolymer, styrene-butadiene copolymer, styrene-vinyl chloride copolymer, styrene-vinyl acetate copolymer, styrene -Styrene such as maleic acid copolymer, styrene-acrylic acid ester copolymer, styrene-methacrylic acid ester copolymer, styrene-α-chloroacrylic acid methyl copolymer, styrene-acrylonitrile-acrylic acid ester copolymer Resin (monopolymer or copolymer containing styrene or styrene-substituted product), polyester resin, epoxy resin, vinyl chloride resin, rosin-modified maleic acid resin, phenol resin, polyethylene resin, polypropylene resin, petroleum resin, polyurethane resin, Ketone resin, ethylene-ethylene Examples thereof include a acrylate copolymer, a xylene resin, and a polyvinyl butyrate resin.

In the toner used in the present invention, all known release agents can be used, and in particular, de-free fatty acid type carnauba wax, montan wax and oxidized rice wax can be used alone or in combination.
As the external additive, inorganic fine particles can be preferably used. Specific examples of the inorganic fine particles include, for example, silica, alumina, titanium oxide, barium titanate, magnesium titanate, calcium titanate, strontium titanate, zinc oxide, tin oxide, silica sand, clay, mica, wollastonite, Examples thereof include diatomaceous earth, chromium oxide, cerium oxide, pengala, antimony trioxide, magnesium oxide, zirconium oxide, parium sulfate, barium carbonate, calcium carbonate, silicon carbide, and silicon nitride.

The toner used in the present invention may contain a charge control agent as necessary. Any known charge control agent can be used. For example, nigrosine dyes, triphenylmethane dyes, chromium-containing metal complex dyes, molybdate chelate pigments, rhodamine dyes, alkoxy amines, quaternary ammonium salts (fluorine) Modified quaternary ammonium salts), alkylamides, 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.
In addition, as the colorant used in the toner used in the present invention, all of the pigments and dyes conventionally used as toner colorants are applied. Specifically, carbon black, lamp black, iron black, ultramarine blue, nigrosine dye, aniline blue, calco oil blue, oil black, azo oil black and the like are not particularly limited.

As a method for producing the toner used in the present invention, a conventionally known method may be used. A binder resin, a magnetic material, a release agent, a colorant, and in some cases, a charge control agent and the like are mixed using a mixer or the like, and heated. After kneading using a kneader such as a roll or an extruder, the mixture is cooled and solidified, pulverized by pulverization with a jet mill, turbojet, kryptron, etc., and then classified.
In addition, in order to add inorganic non-powder, fatty acid metal salt, and the like to the toner, a mixer such as a super mixer or a Henschel mixer is used.

Hereinafter, the present invention will be described with reference to specific examples.
<Evaluation method of transfer rate, fixability, transfer dust, transfer white spot>
The evaluation machine used a modified Ricoh color copying machine (IMAGIO Color 5100). The unit configuration of the image forming unit is the same as the schematic configuration of the color image forming apparatus shown in FIG. As the developing means, a rotary developing device 4 having four-color two-component developing type developing devices 41 to 44 is used. As the intermediate transferring means 5, an intermediate transfer belt 51 is used, and a transfer bias is applied to the intermediate transfer roller 52. Is applied to the intermediate transfer belt 51 to perform electrostatic transfer (first transfer). After the above-described yellow-black latent image formation, development, and intermediate transfer steps are completed, the transfer paper transfer roller 56 is brought into contact with the intermediate transfer belt 51 by a contact / separation mechanism (not shown) and the pressurizing unit described above. Then, a transfer bias is applied to the transfer roller 56 to perform electrostatic transfer (second transfer) from the intermediate transfer belt 51 to the transfer sheet. The transfer paper onto which the four-color superimposed image has been transferred is conveyed to the fixing device 7 by the conveying belt 57. In the fixing device 7, the surface pressure is 9.3 N / cm ² at the nip portion between the fixing roller 71 and the pressure roller 72. Fixing is performed at a pressure and temperature of 165 to 185 ° C.
Using the image forming apparatus configured as described above, a test chart centered on gray scale, sharpness chart, character chart, and color patch formed from dots having a pixel density of 600 dpi (dots / inch) is printed and sampled. I got an image.

<Evaluation of transfer rate>
The developed chart on the photosensitive member 1 is transferred onto the transfer paper via the intermediate transfer belt 51, and the machine is stopped when the transfer paper is on the transport belt 57. Paying attention to the black solid portion of the chart, the transfer residual toner amount of the black solid portion on the photosensitive member 1 is peeled off with an adhesive tape, and the residual toner amount on the photosensitive member is obtained. On the other hand, the toner transferred onto the transfer paper is cut off from the solid black portion and blown off the toner with compressed air. Find the amount of toner transferred from the weight before and after blowing,
(Transfer toner amount / (transfer toner + remaining toner amount)) × 100 (%)
To obtain the transfer rate (%). The allowable transfer rate is 70% or more in a general environment. A transfer rate of 80% or more was judged as “◯”, 70 to 79% was judged as “Δ”, and 69% or less was judged as “X”. The allowable level is “Δ” or more.

<Evaluation of fixability>
Next, the fixability is evaluated by the smear method. A cloth adhered to a weight of 8.8 N / 15φ at a halftone portion of ID: 0.6 to 0.8 was placed on a transfer paper, and evaluation was performed based on the density on the cloth when rubbed 5 times. A level of 0.3 or lower where there is no problem is indicated by “◯”, an allowable level of 0.5 or lower is indicated by “Δ”, and a level of 0.51 or higher is indicated by “x”.

<Evaluation of transfer dust and transfer white spots>
Since no general evaluation method has been established for transfer dust and transfer blank, samples and rank samples were subjected to visual sensory evaluation. A rank sample of transfer dust is shown in FIG. 6, and a rank sample of transfer white spot is shown in FIG. Among the three types of images, rank 3 “Δ” is an acceptable level, “OK” is higher than that, and “NG” is lower than rank 3 “Δ”.

[Example 1]
Next, as a more specific example, an image forming apparatus (Ricoh, Imagio Color 5100) having the same configuration as that shown in FIG. 1 is used as a test machine, and a transfer unit (intermediate transfer belt, second transfer unit) of the test machine is used. ) Was modified and used. Further, the intermediate transfer belt was processed so that the contact between the photosensitive member 1 and the intermediate transfer belt 51 and between the intermediate transfer belt 51 and the transfer roller 56 was stabilized.

Here, a method for manufacturing the intermediate transfer belt will be described.
Polyvinylidene fluoride (KF-850; Kureha Chemical Industry): 100 parts by weight Carbon black (Printex 40; Degussa): 5 parts by weight Molybdenum disulfide: 20 parts by weight Melting and kneading 20 parts by weight was extruded to 0. A seamless belt of 2 to 0.3 mm was prepared and used as a support for the intermediate transfer belt. A silicone elastic layer having a hardness of 15 to 40 degrees (when loaded with Asker C / 1 kg) and a thickness of 0.1 to 0.2 mm was provided on the surface of the support. Further, the surface was coated with a fluorine-based resin (for example, Teflon (registered trademark)) (coated and dried by heating to form a resin layer of 20 μm). The resistance is 2 × 10 ¹² Ωcm in volume resistance and 4 × 10 ¹² Ω in surface resistance. The surface friction coefficient was 0.22.

Using the intermediate transfer belt 51 configured as described above, after the first transfer from the photoreceptor 1 to the intermediate transfer belt 51, the second transfer for transferring the toner on the intermediate transfer belt 51 onto the transfer paper was performed. The means for pressing the transfer roller 56 against the intermediate transfer belt 51 is the pressing by the spring 56d of the transfer roller 56 shown in FIG. 3, and the transfer pressure is 0.5, 1.0, 5.0, 8.0 [ N / cm] and four levels of current flowing by controlling the transfer bias voltage applied between the transfer roller 56 and the intermediate transfer belt 51 are 0.03, 0.05, 0.2, and 0.3 μA / cm. Then, the above-described test chart was transferred and printed by the image forming apparatus. Evaluation was confirmed by transfer dust (see FIG. 6) and transfer whitening (see FIG. 7). The evaluation results are shown in Table 1 below.
Note that the current value is a transfer current of 0.3 to 0.4 μA / cm and the pressure is about 1 N / cm. As the toner, a toner having a toner formulation 5 described later was used.

From the results of Table 1, using the above intermediate transfer belt, the pressure ranges from 1.0 to 5.0 N / cm, the transfer current ranges from 0.05 to 0.20 μA / cm, transfer rate, transfer dust, and transfer white. It was in a good range with omission. When the transfer current is increased, a leakage phenomenon of the transfer paper occurs, toner reverse charges are injected, and the transfer rate tends to decrease. On the other hand, if the transfer current is too small, the force attracted to the transfer paper (F in equation (1) above) becomes too small to transfer. With respect to the transfer pressure, if the pressure is as low as 0.05 N / cm, the adhesion between the transfer paper and the intermediate transfer belt is weak, the transfer rate is lowered, and transfer dust tends to occur. On the other hand, if the pressure is increased to 10.0 N / cm, the pressure is too strong, and if the toner layer is large during transfer, it tends to adhere to the intermediate transfer belt and collapse easily, and as a result, good data cannot be obtained. It was.
Further, the surface characteristics of the used intermediate transfer belt are too soft when the Asker C hardness is less than 15 degrees, and the toner remains on the intermediate transfer belt. On the other hand, if the hardness exceeds 40 degrees, the toner is so hard that the toner bites in the Z-axis direction and the air gap is not reduced.
Further, when the thickness of the soft elastic layer on the intermediate transfer belt is less than 0.1 mm, the coating unevenness is large and sufficient toner biting cannot be obtained. On the other hand, if the thickness exceeds 0.2 mm, the toner easily adheres to the intermediate transfer belt and collapses as in the case where the pressure is large, and as a result, good data cannot be obtained.

[Example 2]
In the same manner as in Example 1, when the surface of the elastic layer of the intermediate transfer belt is coated with a fluororesin, it is spray-coated with the following three levels of prescription, heat-dried, and three kinds of intermediates A transfer belt was created.

<Coating treatment prescription 1>
Fluorine-based resin (Lumiflon 601C; Asahi Glass): 100 parts by weight Curing agent for Lumiflon: 20 parts by weight Boron nitride: 20 parts by weight <Coating treatment prescription 2>
Formulation 1 material: 140 parts by weight Fluorine fine powder (1 μm): 5 parts by weight <Coating treatment formulation 3>
・ Prescription 1 material: 140 parts by weight ・ Fluorine fine powder (1 μm): 10 parts by weight

The above formulation was mixed with 200 parts of methyl isobutyl ketone and 100 parts of xylene, milled with a ball mill for about 60 hours, and spray coated.
The friction coefficient of the intermediate transfer belt subjected to the prescription 1 coating is 0.22, the friction coefficient of the intermediate transfer belt subjected to the prescription 2 coating is 0.68, and the friction of the intermediate transfer belt subjected to the prescription 3 coating. The coefficient was 0.96.

Using these three types of intermediate transfer belts, an image sample was obtained by the same apparatus configuration and method as in Example 1.
The surface layer of the intermediate transfer belt support was provided with a silicone elastic layer having a hardness of 15 to 40 degrees (Asker C / 1 kg load) and a thickness of 0.1 to 0.2 mm. And the coating layer of said fluororesin was provided on it. The transfer pressure was 3.2 N / cm, and the transfer current was 0.15 μA / cm.
Table 2 below shows the results of evaluation of transfer dust (see the evaluation rank in FIG. 6) and transfer white spot (see the evaluation rank in FIG. 7).

  From the above results, it is a good condition that the friction coefficient of the surface layer of the intermediate transfer belt is 0.7 or less. If the friction coefficient is small, transfer pressure is applied to the toner, transfer paper, and intermediate transfer belt, and even if toners adhere to each other, they do not adhere to the intermediate transfer belt, and the transferred toner moves onto the transfer paper. On the other hand, the friction coefficient is too high, the adhesive force between the toner and the intermediate transfer belt is increased, and the toner and the intermediate transfer belt are likely to adhere due to the transfer separation. It remains attached to the belt, resulting in white spots on the transfer, resulting in an abnormal image.

[Example 3]
Next, examples of toner characteristics and transfer characteristics prepared by changing the formulation of the toner used for development will be described.
<Toner Formula 1>
Polyester resin (weight average molecular weight: 310000, Tg: 65 ° C.): 44 parts by weight Styrene-n-butyl acrylate copolymer (weight average molecular weight: 85000, Tg: 68 ° C.): 40 parts by weight Carnauba wax: 5 parts by weight-Carbon black (# 44: Mitsubishi Chemical): 10 parts by weight-Charge control agent (Spiron Black TR-H: Hodogaya Chemical): 1 part by weight

After kneading at 130 ° C. using a biaxial extruder with the above formulation, pulverizing and classifying with a mechanical pulverizer to a weight average particle size of 8.5 μm, silica (R-972 Nippon Aerosil) using a Henschel mixer ) 0.5% by weight was mixed to obtain a toner. This toner had a hardness of 8, a cohesion degree of 30%, and a volume resistivity of 8.5 × 10 ⁸ Ωcm.

<Toner Formula 2>
Polyester resin (weight average molecular weight: 185,000, Tg: 67 ° C.): 71 parts by weight Carnauba wax (average particle size: 300 μm): 3 parts by weight Iron trioxide (EPT-1000: Toda Kogyo): 15 parts by weight Parts ・ Carbon black (# 44: Mitsubishi Chemical): 10 parts by weight ・ Charge control agent (Spiron Black TR-H: Hodogaya Chemical): 1 part by weight

After kneading at 160 ° C. using a biaxial extruder with the above formulation, pulverizing and classifying with a mechanical pulverizer to a weight average particle size of 5.5 μm, using a Henschel mixer, silica (R-972 Nippon Aerosil) 1 0.0 wt% was mixed to obtain a toner. This toner had a hardness of 11, a cohesion degree of 8.0%, and a volume resistivity of 5.5 × 10 ⁸ Ωcm.

<Toner Formula 3>
Styrene / n-butyl methacrylate / 2-ethylhexyl acrylate copolymer (composition ratio: 75/10/15 weight average molecular weight: 210000 Tg: 57 ° C.): 55 parts by weight polyester resin (weight average molecular weight: 160000 Tg: 64 ° C): 23 parts by weight Polyethylene wax (molecular weight 900): 10 parts by weight Carbon black (# 44: Mitsubishi Chemical): 10 parts by weight Charge control agent (Spiron Black TR-H: Hodogaya Chemical): 2 parts by weight

After kneading at 90 ° C. using a biaxial extruder with the above formulation, pulverizing and classifying with an airflow pulverizer to obtain a weight average particle diameter of 7.5 μm, silica (R-972 Japan) using a Henschel mixer Aerosil) 0.2% by weight was mixed to obtain a toner. This toner had a hardness of 6, a cohesion degree of 55.0%, and a volume resistivity of 8.8 × 10 ⁸ Ωcm.

<Toner Formula 4>
Polyester resin (weight average molecular weight: 274000, Tg: 68 ° C.): 79 parts by weight Polyethylene wax (molecular weight 900): 3 parts by weight Carbon black (# 44: Mitsubishi Chemical): 15 parts by weight Charge control agent (Spi Ron Black TR-H: Hodogaya Chemical): 3 parts by weight

After kneading at 150 ° C. using a biaxial extruder with the above formulation, pulverizing and classifying with an airflow pulverizer to a weight average particle size of 9.5 μm, using a Henschel mixer, silica (R-972 Japan) Aerosil) 1.0% by weight was mixed to obtain a toner. This toner had a hardness of 14, a cohesion degree of 8.5%, and a volume resistivity of 4.2 × 10 ⁸ Ωcm.

<Toner Formula 5>
Polyester resin (weight average molecular weight: 310000, Tg: 65 ° C.): 49 parts by weight Styrene-n-butyl acrylate copolymer (weight average molecular weight: 85000, Tg: 68 ° C.): 35 parts by weight Carnauba wax: 4 parts by weight, carbon black (# 44: Mitsubishi Chemical): 10 parts by weight, charge control agent (spiron black TR-H: Hodogaya Chemical): 2 parts by weight

After kneading at 130 ° C. using a biaxial extruder with the above formulation, pulverizing and classifying with a mechanical pulverizer to a weight average particle size of 8.5 μm, silica (R-972 Japan) using a Henschel mixer Aerosil) 0.5% by weight was mixed to obtain a toner. This toner had a hardness of 10, a cohesion degree of 20%, and a volume resistivity of 9.5 × 10 ⁸ Ωcm.

<Toner Formula 6>
Polyester resin (weight average molecular weight: 185,000, Tg: 67 ° C.): 73 parts by weight Carnauba wax (average particle size: 300 μm): 5 parts by weight Iron trioxide (EPT-1000: Toda Kogyo): 10 parts by weight Parts ・ Carbon black (# 44: Mitsubishi Chemical): 10 parts by weight ・ Charge control agent (Spiron Black TR-H: Hodogaya Chemical): 2 parts by weight

After kneading at 160 ° C. using a biaxial extruder with the above formulation, pulverizing and classifying with a mechanical pulverizer to a weight average particle size of 6.5 μm, using a Henschel mixer, silica (R-972 Japan) (Aerosil) 0.75 wt% was mixed to obtain a toner. This toner had a hardness of 11, a cohesion degree of 31%, and a volume resistivity of 9.8 × 10 ⁸ Ωcm.

<Toner Formula 7>
Polyester resin (weight average molecular weight: 310000, Tg: 65 ° C.): 56 parts by weight Styrene-n-butyl acrylate copolymer (weight average molecular weight: 85000, Tg: 68 ° C.): 35 parts by weight Carnauba wax: 3 parts by weight Carbon black (# 44: Mitsubishi Chemical): 5 parts by weight Charge control agent (Spiron Black TR-H: Hodogaya Chemical): 1 part by weight

After kneading at 80 ° C. using a biaxial extruder with the above formulation, pulverizing and classifying with a mechanical pulverizer to obtain a weight average particle size of 8.5 μm, and then using a Henschel mixer, silica (R-972) Nippon Aerosil) 0.5% by weight was mixed to obtain a toner. This toner had a hardness of 10, a cohesion degree of 15%, and a volume resistivity of 3.5 × 10 ⁹ Ωcm.

<Toner Formula 8>
Polyester resin (weight average molecular weight: 310000, Tg: 65 ° C.): 56 parts by weight Styrene-n-butyl acrylate copolymer (weight average molecular weight: 85000, Tg: 68 ° C.): 35 parts by weight Carnauba wax: 3 parts by weight Carbon black (# 44: Mitsubishi Chemical): 5 parts by weight Charge control agent (Spiron Black TR-H: Hodogaya Chemical): 1 part by weight

After kneading at 80 ° C. using a biaxial extruder with the above formulation, pulverizing and classifying with a mechanical pulverizer to obtain a weight average particle size of 8.5 μm, and then using a Henschel mixer, silica (R-972) Nippon Aerosil) 1.0% by weight and 0.20 parts by weight of zinc stearate fine powder were mixed to obtain a toner. This toner had a hardness of 10, a cohesion degree of 35.0%, and a volume resistivity of 1.8 × 10 ⁹ Ωcm.

The transfer characteristics were evaluated under the same conditions as in Example 2 using the toners prepared in the above formulations 1-8. As the intermediate transfer belt, an intermediate transfer belt having a surface friction coefficient of 0.68 was used.
As evaluation items, transfer dust (see the rank sample in FIG. 6) and transfer white spot (see the rank sample in FIG. 7) were evaluated, and favorable conditions were selected for both items. The evaluation results are shown in Table 3 below.

From the above evaluation data, the toner having a toner hardness of 8 to 11 and a cohesion degree of 15 to 35% shows a well-balanced toner characteristic in the transferred image.
From this result, the degree of aggregation of the toner is 15 to 40%, more preferably 15 to 35%. When the toner aggregation degree is 15% or less, the fluidity of the toner is too good and dust is likely to be generated during transfer. On the other hand, when the toner aggregation degree is 40% or more, the cohesive force of the toner is increased and the transferability is deteriorated. In addition, transfer white spots occur.

  The toner hardness is 7 to 12, more preferably 8 to 11. When the toner hardness is 7 or less, when the toner particles are in contact with each other, plastic deformation occurs, so that the contact area between the toners increases, the cohesive force of the toner increases, and the toner layer and the intermediate transfer belt easily adhere to each other. Transfer white spots are easy to occur. When the toner hardness is 12 or more, there is no problem in the transfer process, but the fixability may deteriorate in the fixing process.

1 Photoconductor (image carrier)
2 Charger (charging means)
3 Exposure means (latent image forming means)
4 Rotating type developing device (developing means)
5 Intermediate transfer belt device (intermediate transfer means)
6 Cleaning device (cleaning means)
7 Fixing device (fixing means)
32 Exposure device 33 Folding mirror 34 Laser light 41 Yellow developing device 42 Magenta developing device 43 Cyan developing device 44 Black developing device 51 Intermediate transfer belt (intermediate transfer member)
52 Intermediate transfer roller 55 Backup roller 56 Transfer paper transfer roller (transfer paper transfer means)
57 Conveying belt 61 Cleaning blade 62 Cleaning brush 71 Fixing roller 72 Pressure roller 101 Paper feeding bank 102 Paper feeding roller 103 Conveying roller 104 Registration roller

JP 2000-22188 A JP 2001-209255 A

Claims (8)

In a transfer method for electrostatically transferring a toner image transferred from an image carrier to an intermediate transfer member onto a transfer material using a transfer unit,
A transfer bias between the intermediate transfer body and the transfer means, having an elastic layer on the surface of the surface of the intermediate transfer body on which the toner is adhered, and a means for applying pressure between the transfer means and the intermediate transfer body; A transfer method wherein the current is 0.05 to 0.2 μA / cm. The transfer method according to claim 1,
The intermediate transfer member is an intermediate transfer belt supported by a plurality of rollers, and the transfer unit is a transfer roller or a transfer belt supported by a roller. A transfer method characterized by applying a pressure of 10 N / cm. The transfer method according to claim 1 or 2,
The intermediate transfer member has one or more elastic layers on the support, and has an elastic layer having a thickness of 0.1 to 0.2 mm and a hardness of 15 to 40 degrees on the outermost surface layer. Characteristic transfer method. The transfer method according to claim 1, 2, or 3,
A transfer method comprising: performing a surface treatment on the elastic layer of the intermediate transfer member, and processing the friction coefficient of the surface layer of the intermediate transfer member to 0.7 or less. The latent image is formed on the image carrier, the latent image is developed with toner to form a toner image, and the toner image is transferred to the intermediate transfer member one or more times. After the toner image of one or more colors is transferred to the toner image, the toner image transferred to the intermediate transfer member is electrostatically transferred to a transfer material using a transfer means, and the toner image transferred onto the transfer material In an image forming method for fixing an image to form an image,
An image forming method using the transfer method according to claim 1. The image forming method according to claim 5.
An image forming method, wherein a toner having a cohesion degree of 15 to 40% is used as a toner used for development. The image forming method according to claim 5.
An image forming method, wherein a toner having a hardness of 7 to 12 degrees is used as a toner used for development. A latent image forming means for forming a latent image on the image bearing member; a developing means for developing the latent image with toner to form a toner image; an intermediate transfer means for transferring the toner image to an intermediate transfer member; In an image forming apparatus including a transfer unit that electrostatically transfers a toner image transferred to an intermediate transfer member to a transfer material, and a fixing unit that fixes the toner image transferred onto the transfer material.
An image forming apparatus using the image forming method according to claim 5.

Images