JP2007127889A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a transfer dust when transferring a toner image from an image carrier to a transfer body with a simpler structure in an image forming apparatus for forming a toner image of a plurality of colors on the transfer body, and to obtain a good image. An image forming apparatus that can be obtained is provided.
A toner image is transferred to an intermediate transfer belt 5 as a transfer member by applying pressure and a transfer electric field to each color toner image in a primary transfer nip for each of the four colors, thereby forming a four-color full-color toner image. In the image forming apparatus, four color toner images are transferred onto the respective photosensitive drum drums 2Y, 2M, 2C, and 2K as latent image carriers before passing through the primary transfer nip and intermediate transfer after passing through the secondary transfer nip. On the belt 5, the load F applied to the secondary transfer nip is adjusted so that the non-electrostatic adhesion force between the toners forming the toner image increases by 3 [nN] or more.
[Selection] Figure 1

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, or a fax machine, and more specifically, images on a plurality of image carriers are transferred to a transfer body, and a plurality of color toner images are transferred onto the transfer body. The present invention relates to an image forming apparatus to be formed.

Conventionally, as such an image forming apparatus, an image forming apparatus using an intermediate transfer belt as an intermediate transfer member is known. In an electrophotographic image forming apparatus using an intermediate transfer belt, a toner image formed on a latent image carrier as an image carrier is transferred to a toner at a primary transfer nip formed by the latent image carrier and the intermediate transfer belt. The image is transferred onto the intermediate transfer belt by applying a pressure and a transfer electric field. Then, secondary transfer is performed on a recording medium such as paper, and a final image is obtained after a fixing process by pressure and heating.
When obtaining a color image, a color image is formed by sequentially superimposing a plurality of color toner images formed on one or a plurality of electrostatic latent image carriers on an intermediate transfer belt, and then onto a recording medium. The final image is obtained through secondary transfer and fixing processes. In order to obtain a high-quality image, the toner image formed on the latent image carrier is accurately superimposed on the latent image on the latent image carrier and accurately transferred onto the intermediate transfer belt. However, it is necessary to finish the fixing process while maintaining this state.

As described above, the toner on the electrostatic latent image carrier moves onto the intermediate transfer belt by the transfer electric field and pressure near the primary transfer nip formed by the electrostatic latent image carrier and the intermediate transfer belt. Then, the electrostatic force received by the toner transferred onto the intermediate transfer belt due to the transfer bias of the primary transfer nip decreases rapidly after passing through the primary transfer nip. For this reason, the force to hold the toner to the intermediate transfer belt side is weakened, and the toner is scattered by the electrostatic repulsive force between the toners.
The dust image generated after passing through the primary transfer nip becomes prominent particularly when a plurality of color toner images are superimposed on the intermediate transfer belt and the amount of toner forming the image is increased. In order to obtain a good final image, it is necessary to suppress the dust image generated after passing through the primary transfer nip.

In order to suppress such dust before and after passing through the primary transfer nip, there is a method of controlling the electric field of the primary transfer nip.
As a method for controlling the electric field of the primary transfer nip, Patent Document 1 discloses a peeling discharge that occurs at a location where the intermediate transfer belt and the image carrier are separated from each other by applying a potential having the same polarity as the toner to the intermediate transfer belt downstream of the primary transfer nip. This prevents the toner from charging up. Further, in Patent Document 2, two electrodes are provided on the downstream side of the primary transfer nip, and transfer dust is suppressed by applying a potential having a polarity opposite to that of the toner to the back surface of the intermediate transfer belt.

Japanese Patent Application Laid-Open No. 2005-77861 JP 2000-89583 A

  However, the method of controlling the electric field of the primary transfer nip needs to be controlled by adding an electrode for controlling the electric field, and the structure becomes complicated and the manufacturing cost increases.

  The present invention has been made in view of the above problems, and an object of the present invention is an image forming apparatus that forms a toner image of a plurality of colors on a transfer member, and the toner image is carried by a simpler structure. It is an object of the present invention to provide an image forming apparatus capable of reducing transfer dust when transferring from a body to a transfer body and obtaining a good image.

In order to achieve the above object, the invention of claim 1 comprises a plurality of image carriers and a plurality of image forming means for forming toner images of different colors on each image carrier, and each image carrier. Forming a plurality of color toner images on the transfer body by applying pressure and a transfer electric field to each color toner image at each transfer nip opposite to the transfer body. The plurality of transfer nips passed through the transfer nip more than the non-electrostatic adhesion force between the toners constituting the toner image carried on the image carrier portion before passing through the transfer nip. The load applied to the transfer nip is adjusted so that the non-electrostatic adhesion force between toners of the toner constituting the toner image carried on the transfer member later becomes 3 [nN] or more. It is characterized by this.
The invention according to claim 2 is the image forming apparatus according to claim 1, wherein the non-electrostatic adhesive force between the toners of each color is 20 [nN] after passing through any of the transfer nips. The load applied to the transfer nip is adjusted so as to be as follows.
The invention according to claim 3 is the image forming apparatus according to claim 1 or 2, wherein the toner transferred in the transfer nip on the downstream side in the surface movement direction of the transfer body is closer to the distance between the toner after passing through the transfer nip. The load applied to each of the transfer nips is adjusted so that the non-electrostatic adhesion force is increased.
According to a fourth aspect of the present invention, in the image forming apparatus according to the first, second, or third aspect, the linear velocity of the at least one image carrier among the plurality of image carriers and the linear velocity of the transfer member are speeds. It is characterized by providing a difference.
According to a fifth aspect of the present invention, in the image forming apparatus according to the first, second, third, or fourth aspect, at least one of the plurality of image forming units uses the toner having a roundness of less than 1.3. Between the friction coefficient μ ₀ of the surface of the image carrier on which the toner image is formed by the image forming means and the friction coefficient μ _t of the surface of the transfer body. The image carrier is configured such that a relationship of ≧ μ _t > μ ₀ is established.
According to a sixth aspect of the present invention, in the image forming apparatus according to the first, second, third, fourth, or fifth aspect, at least one of the plurality of image forming units includes the toner having a roundness of 1.3 or more. Between the friction coefficient μ ₀ of the surface of the image carrier on which the toner image is formed by the image forming means and the friction coefficient μ _t of the surface of the transfer body, _{The image} carrier is configured so that a relationship of _t −μ ₀ > 0.2 is established.
According to a seventh aspect of the present invention, in the image forming apparatus according to the first, second, third, fourth, or sixth aspect, the transfer member is an intermediate transfer member.
The invention according to claim 8 is the image forming apparatus according to claim 1, 2, 3, 4, 5, 6 or 7, wherein the transfer member is a recording medium.
The invention of claim 9 is the image forming apparatus of claims 1, 2, 3, 4, 5, 6, 7 or 8, wherein Sn is the area of the transfer nip and F is the load applied to the transfer nip. when applied by _{P C = I × F / Sn} (I is 1 or more arbitrary real number), we obtain the pressure P _C of I times the transfer nip pressure P, and compression pressure corresponding to the pressure P _C in the toner Calculated by the Rumpf equation: Ft = St × D ² × ε / (1−ε), where St is the breaking stress of the toner measured later, St is the toner particle size, and ε is the toner layer porosity. Ft is used as the non-electrostatic adhesion force between the toners.
According to a tenth aspect of the present invention, in the image forming apparatus according to the ninth aspect, the I is I = 100 / v where the image area ratio is v.
According to an eleventh aspect of the present invention, in the image forming apparatus according to the tenth aspect, the image area ratio v = 5 [%].

  In the image forming apparatus according to any one of the first to eleventh aspects, the non-electrostatic adhesion force between toners is greater than 3 [nN] after passing through the transfer nip than before passing through the transfer nip. As described above, the load applied to the transfer nip is adjusted. By adjusting the load applied to the transfer nip in this way, the adhesion force between the toners exceeds the electrostatic repulsion force between the toners that causes transfer dust, and the transfer dust can be reduced by experiments described later. Became. In addition, since the load on the transfer nip is adjusted to reduce transfer dust, the structure can be made simpler than a structure in which an electrode is added and controlled for electric field control.

  According to the first to eleventh aspects of the present invention, there is an excellent effect that a transfer image when transferring a toner image from an image carrier to a transfer body can be reduced with a simple structure, and a good image can be obtained.

[Embodiment 1]
A first embodiment in which the present invention is applied to a color image forming apparatus will be described below.
FIG. 1 is a schematic configuration diagram of an entire apparatus of a printer 100 as a color image forming apparatus according to the first embodiment. In FIG. 1, a printer 100 includes four image forming units 20Y, 20M, 20C, and 20K that use toners of four different colors (yellow: Y, magenta: M, cyan: C, and black: K) as intermediate transfer members. 3 is a tandem type image forming apparatus arranged in parallel along the moving direction of the intermediate transfer belt 5.
Each of the image forming units 20Y, 20M, 20C, and 20K includes photoconductor drums 2Y, 2M, 2C, and 2K, and charging devices 3K, 3C, 3M, and 3Y that charge the surface of each photoconductor drum by corona discharge. Yes. Further, based on the image information, LED array heads 8Y, 8M, 8C as exposure devices that form latent images on the surfaces of the photosensitive drums 2Y, 2M, 2C, and 2K by exposing the charged surfaces to each other. 8K is provided. Further, each of the developing devices 1Y, 1M, 1C, and 1K as image forming means for converting the latent images on the photosensitive drums 2Y, 2M, 2C, and 2K into toner images, and the photosensitive drums 2Y, 2M, 2C, and 2K. Photoconductor cleaning devices 10Y, 10M, 10C, and 10K for cleaning the surface are provided. Further, a lubricant application device including lubricant supply rollers 11Y, 11M, 11C, and 11K for supplying a lubricant to the surface of the photoconductor is provided downstream of the photoconductor cleaning devices 10Y, 10M, 10C, and 10K. .

  The photosensitive drums 2Y, 2M, 2C, and 2K of the four sets of image forming units are rotationally driven by a photosensitive drum driving device (not shown). Alternatively, the black photosensitive drum 2K and the color photosensitive drums 2Y, 2M, and 2C may be independently driven to rotate. Thus, for example, only the black photosensitive drum 2K is rotationally driven when forming a monochrome image, and the four photosensitive drums 2Y, 2M, 2C, and 2K are simultaneously rotationally driven when forming a color image. it can. Here, when forming a monochrome image, the intermediate transfer unit having the intermediate transfer belt 5 is partially swung so as to be separated from the color photosensitive drums 2Y, 2M, and 2C.

  The intermediate transfer belt 5 is formed of, for example, an endless belt material having medium resistance, and is wound around a plurality of support rollers such as a secondary transfer roller 7 and support rollers 51 and 52. By rotating one of the support rollers, the intermediate transfer belt 5 can be moved endlessly in the direction of the arrow in the figure.

  Further, at the primary transfer position where the toner image is transferred from the photosensitive drums 2Y, 2M, 2C, and 2K to the intermediate transfer belt 5, the photosensitive drums 2Y, 2M, 2C, and 2K are interposed with the intermediate transfer belt 5 interposed therebetween. Primary transfer rollers 4Y, 4M, 4C, and 4K are provided so as to oppose each other. The intermediate transfer belt 5 as a transfer body is pressed against the photosensitive drums 2Y, 2M, 2C, and 2K by being pressed by the primary transfer rollers 4Y, 4M, 4C, and 4K, and the respective photosensitive drums 2Y, 2Y, A primary transfer nip is formed at a portion facing 2M, 2C, and 2K.

  When forming a color image with the printer 100 having the above-described configuration, the toner images of the respective colors formed on the photosensitive drums 2Y, 2M, 2C, and 2K are intermediated by the action of pressure and a transfer electric field at each primary transfer nip. The images are sequentially superimposed and transferred onto the transfer belt 5. As a result, a full color toner image composed of four color toner images is formed on the intermediate transfer belt 5. The full-color toner image superimposed on the intermediate transfer belt 5 is transferred onto a transfer paper P as a recording medium at a secondary transfer nip formed between the secondary transfer device 6 and the secondary transfer roller 7, Fixing is performed by the fixing device 9.

Next, the characteristic part of Embodiment 1 is demonstrated. However, the types of components used in the following embodiments do not limit the scope of the present invention.
In particular, in the embodiment, an image for evaluation is formed using an existing image forming apparatus. The essence of the present invention is the change in the interaction between toners after passing through the primary transfer nip and the definition of the absolute value. The method of applying the load to the part may be arbitrary.

[Example 1]
Next, a method for measuring the non-electrostatic adhesion between toner and toner used in Example 1 will be described.
The production method of the toner used in this example is shown below.
Use 90 [parts by weight] of styrene monomer as resin, 55 [parts by weight] of n-butyl methacrylate, and 3.5 [parts by weight] zinc salicylate as a charge control agent (Bontron E84, manufactured by Orient Chemical Co., Ltd.). . As the colorant, 7.5 [parts by weight] of carbon black (carbon black # 44, manufactured by Mitsubishi Chemical Corporation) is used as the black toner. Yellow toner is C.I. I. Pigment Yellow 180 5 [parts by weight] (PV Fast Yellow HG (Clariant)) is used. Magenta-toner is C.I. I. 4 [parts by weight] (Hostaperm Pink E (Clariant)) of Pigment Red 122 is used. The cyan toner is C.I. I. CI Pigment Blue 15: 3 is used at 2.5 [parts by weight] (Lionol Blue FG-7351 (Toyo Ink)).
After blending each of the above materials, polymerization is performed using a polymerization initiator (2,2-azobisisobutyronitrile), and the polymerization is stopped at a particle size of 6.7 [μm]. After washing with water, it is dried to obtain black, yellow, magenta, and polymerized toner particles.

The toner particles were observed with an electron microscope, and the roundness was determined. As a result, the toner of each color was 1.2. Each of these color toners was mixed with 100 [parts by weight] of silica fine powder R972 (manufactured by Nippon Aerosil Co., Ltd.) at a ratio of 0.5 [parts by weight] to prepare a negatively chargeable developing toner.
The roundness is
Roundness = (perimeter of toner) ² / (4π × projection area)
The value obtained more is used.

The carrier used in Example 1 can be manufactured as follows.
After mixing 300 parts by weight of silicone resin SR2411 (Toray Dow Corning) and 1200 parts by weight of toluene to prepare a coating solution, the coating solution and ferrite carrier 5 [kg] having an average particle size of 35 [μm] are prepared. ] Is mixed to coat the carrier. Further, the coated carrier is heated at 250 [° C.] for 120 [minutes] to age the coating film.

The developer to be fed into the image output machine for evaluation was prepared and prepared so that the toner density was 5% and the total weight of the toner and the coated carrier was 1000 g.
The non-electrostatic adhesion force between the toner and Ft, powder layer compression and tensile strength automatic measuring system, the rupture stress was measured by applying a predetermined compression pressure P _C using UGG robot (manufactured by Hosokawa Micron) St, toner When the particle diameter is D and the toner layer porosity is ε,
Rumpf's formula: Ft = St × D ² × ε / (1-ε)
Can be used to calculate.

Then, using the cyan toner used in Example 1, the powder layer compression and tensile strength automatic measuring system, with UGG robot, by changing the value of the compression pressure P _C, breaking stress for the values of a plurality of compression pressure P _C St was measured. Then, it was determined with non-electrostatic adhesion force Ft between the toner using the rupture stress St, compression pressure P _C to the toner between the non-electrostatic adhesion force Ft and the toner layer is determined as circles in FIG. 2 It was. Similar experimental results were obtained for black, magenta, and yellow (no significant difference was observed for each color).

As shown in FIG. 2, since the plotting of the values of the inter-toner non-electrostatic adhesion force Ft when changing the value of the compression pressure P _C is a linear, compression pressure does not measure the rupture stress St P _C Also, the non-electrostatic adhesion force Ft between toners can be obtained from this regression line. The toner between non-electrostatic adhesion force Ft when uncompressed is when the compression pressure is not applied, the compression pressure P _C from the regression line labeled in FIG. 1 is determined as the value of the vertical axis when the zero. Moreover, seeking non-electrostatic adhesion force Ft between the toner to no compression pressure P _C of the measurement data from the regression line, the compression pressure P _C is considered the difference between the non-electrostatic adhesion force Ft between the toner in the case of zero Also good. In this embodiment, the measurement data is linearly regressed to obtain the non-electrostatic adhesion force between the toners at the time of non-compression, but the interpolation of the measurement data is not limited to the regression line, and any function may be used.
In addition, when the non-compressed non-electrostatic adhesion force Ft of each color used in Example 1 in the above-described method was determined, yellow, cyan, and magenta were 4.9 [nN], and black was 4.7 [nN. It became.

  The primary transfer nip area Sn is a pressure distribution measuring system I-SCAN (Nitta) in a state where a predetermined load F is applied to a primary transfer member (primary transfer rollers 4Y, 4M, 4C, 4K using foamed rubber in this embodiment). (Made by Co., Ltd.). Note that the load F applied to the primary transfer nip includes its own weight in addition to the load applied from the primary transfer member pressing means.

  Next, IPSio CX400 was used as an image output machine for evaluation. When the primary transfer nip width N with respect to the load F in this image output machine for evaluation was measured, the values shown in Table 1 were obtained.

From Table 1, the primary transfer nip width N [mm] with respect to the load F [N] can be obtained, and the contact length in the axial direction of the primary transfer roller (240 [mm] in the image output machine for evaluation described above) is obtained. By applying, the primary transfer nip area S [mm ² ] is obtained. Then, by dividing the load F [N] by the primary transfer nip area S [mm ² ], the primary transfer nip pressure P [N / mm ² ] in a load application state can be obtained.
Further, the compression pressure P _C [N] can be obtained by applying an arbitrary value I to the primary transfer nip pressure P. Here, for an arbitrary value I, it can be considered that, in the nip portion, only the portion where the toner image is present is in contact and the non-image portion is in a floating state, and the pressure is concentrated on the toner image. Therefore, the pressure applied to the toner generally depends on the area ratio of the toner. If the inside of the nip is filled with toner, the pressure applied to the toner can be obtained with I = 1.
Therefore, in Example 1, when the image area ratio is v, a value obtained by I = 100 / v is adopted. In the standard image evaluation, the area ratio is 5 [%]. Therefore, in Example 1, v = 5, I = 20, and compression pressure P _C [N] = primary transfer nip pressure P × 20. investigated.
In general, the value of I is preferably a value corresponding to the image area ratio v used in the image forming apparatus. Usually, since the image area ratio v = 1 to 10 [%], I = 100 to 10 is preferable. Is 20.

Then, determined for each color toner from the regression line showing the toner between non-electrostatic adhesion force during the primary transfer nip pressure P compression pressure P _C applied was 20 times in FIG. 2, inter-toner non-electrostatic adhesion force of the respective color toners When the load F [N] at which Ft is 8 [nN] was obtained, it was found that the load F should be set to 8 [N] in each primary transfer nip.
Here, since the non-electrostatic adhesion force Ft between toners when uncompressed is 4.9 [nN] for yellow, cyan, and magenta, and 4.7 [nN] for black, the load F is 8 [N]. By setting the non-electrostatic adhesion force Ft between toners to 8 [nN], the amount of increase in the non-electrostatic adhesion force Ft between toners can be 3 [nN] or more.

[Experiment 1]
Next, Experiment 1 in which the generation state of transfer dust is compared between Example 1 and Comparative Example 1 will be described.
As Comparative Example 1, image evaluation was also performed when the load F applied to the primary transfer nip portion was 2 [N] for each color in the above-described evaluation image output machine. In this case, the increase in non-electrostatic adhesion between toners was about 1.5 [nN] for each color toner.
The image forming conditions in the image output machine for evaluation are adjusted so that the same toner transfer efficiency is obtained with the primary transfer nip load of Example 1 and Comparative Example 1, and the toner amount on the intermediate transfer belt becomes equal. It is like that. Further, in the image output machine for evaluation, the intermediate transfer belt conveyance speed and the rotation speed (linear speed) of each electrostatic latent image carrier are made equal. Further, the coefficient of friction between the photosensitive drum 2 as the latent image carrier and the intermediate transfer belt 5 measured by using the Euler belt method was 0.20 and 0.35, respectively.

As images for evaluation, yellow, magenta, cyan, black, red (yellow + magenta), green (yellow + cyan), blue (magenta + cyan), and three-color black (yellow + magenta + cyan) were employed. For each color, an image having an image area ratio of about 5 [%] for each ten lines of 4 dots (600 [dpi]) in width in the intermediate transfer belt conveyance direction (length is the maximum in the width of the intermediate transfer belt). The final image of 100 final images after the completion of fixing was ranked in five stages by matching the appearance of dust in the images with the sample images of each rank.
Rank 5 is "Situation without dust", Rank 4 is "Situation where there is no dust but can hardly be visually confirmed, and there is no problem with image quality", Rank 3 is "Slightly dust is confirmed visually""Situation where image quality is considered to be somewhat problematic", Rank 2 is "Situation where there is a lot of dust that is visually confirmed and there is a problem with image quality", and Rank 1 is "Situation where image is not established" Visually evaluated. Then, the average of the ranks of 100 final images was used as the evaluation value.
The results of Experiment 1 are shown in Table 2.

As shown in Table 2, in Example 1, in any evaluation image, the rank was 4.5 or more, and a good image with almost no transfer dust could be obtained. On the other hand, in Comparative Example 1, a good image almost the same as that of Example 1 was obtained for the single color line, but the amount of generation of dust was abruptly around rank 3 for the lines overlaid with the toners of a plurality of colors. As a result, the image quality was not high enough.
As described above, in Example 1 in which the increase amount of the non-electrostatic adhesive force between the toners is 3 [nN] or more, even when the color image is composed of the toner images of a plurality of colors, the transfer dust is reduced and a good image is obtained. I was able to get it. On the other hand, in Comparative Example 1 in which the increase in non-electrostatic adhesion between toners was about 1.5 [nN], a large amount of transfer dust was generated in a color image composed of a plurality of color toner images. As a result, by adjusting the load F so that the increase amount of the non-electrostatic adhesion force between the toners is 3 [nN] or more, the electrostatic repulsion between the toners causing the transfer dust to cause the transfer dust. It has become clear that the transfer dust can be reduced.

Next, adjustment of the load F will be described.
First, using a powder layer compression / tensile strength automatic measurement system, Ag Robot (manufactured by Hosokawa Micron), measure the compression pressure applied to the toner used and the non-electrostatic adhesion force between the toners at different points by changing the compression pressure. Then, a regression line as shown in FIG. 2 is obtained. The interpolation of measurement data is not limited to a regression line, and an arbitrary function may be used. Here, the non-electrostatic adhesion force between the toners when the regression line is extrapolated to the point of 0 load is defined as Ft0 when the load is not applied to the toner.
Next, the load F applied to the primary transfer nip is adjusted by adjusting a spring attached to the primary transfer roller. Then, the average pressure P and the nip width in the nip when the load F is applied using I-SCAN are measured. The nip area Sn is obtained by multiplying the measured nip width by the axial contact length of the primary transfer member, and the value of the load F is obtained by F = P × Sn.
Then, by using the regression line obtained earlier, the non-electrostatic adhesion force between the toners when a compression pressure that is I times the pressure P at the time of the load F can be obtained. By adjusting the spring of the primary transfer roller so that this value is Ft and Ft−Ft0 ≧ 3 [nN], the load F suitable for image formation can be obtained.

[Example 2]
Next, a method for measuring the non-electrostatic adhesive force between the toner and the toner used in Example 2 will be described.
The production method of the toner used in this example is shown below.
100 [parts by weight] of the polyester resin as the resin, 2 [parts by weight] of zinc salicylate as the charge control agent (Bontron E84, manufactured by Orient Chemical Co., Ltd.), and the black toner is 7.5 [carbon black] as the colorant. Parts by weight] (carbon black # 44, manufactured by Mitsubishi Chemical Corporation). Yellow toner is C.I. I. Pigment Yellow 180 5 [parts by weight] (PV Fast Yellow HG (Clariant)) is used. Magenta-toner is C.I. I. 4 [parts by weight] (Hostaperm Pink E (Clariant)) of Pigment Red 122 is used. The cyan toner is C.I. I. 2 [parts by weight] of Pigment Blue 15: 3 (Lionol Blue FG-7351 (Toyo Ink)) is used.
After preparing the agents of the above-mentioned prescription amounts, preliminary kneading was performed with a mixer, and then melt kneading was performed with a three-roll mill. Next, the kneaded product was cooled, roughly pulverized to about 0.5 to 3 [mm], and then pulverized with an IDS2 type jet pulverizer. Then, classification was performed to obtain a toner having an average particle size of 7.75 [μm], a number [%] of 5 [μm] or less of 12.85, and a volume [%] of 16 [μm] or more of 0.07.
The roundness of the obtained toner was 1.5 for each color toner.
The toner obtained as described above is an irregular (pulverized) toner compared to the spherical toner of Example 1.

The carrier used in Example 2 can be prepared as follows.
2-hydroxyethyl metalate / methyl methacrylate / styrene copolymer and vinylidene fluoride / tetrafluoroethylene copolymer in a 75/25 weight ratio resin with an average particle size of 35 [μm] A coated carrier obtained by coating 0.75 [wt%] (based on the core material) on the core material is used.

As the developer, the developer is prepared by measuring so that the toner density is 5 [%] and the total amount of the toner and the carrier is 1000 [g].
In Example 2, the non-electrostatic adhesion force Ft between toners was measured in the same manner as in Example 1.
Then, using the cyan toner used in Example 1, the powder layer compression and tensile strength automatic measuring system, with UGG robot, by changing the value of the compression pressure P _C, breaking stress for the values of a plurality of compression pressure P _C St was measured. Then, it was determined with non-electrostatic adhesion force Ft between the toner using the rupture stress St, compression pressure P _C to the toner between the non-electrostatic adhesion force Ft and the toner layer is determined as circles in FIG. 3 It was. Similar experimental results were obtained for black, magenta, and yellow (no significant difference was observed for each color).
Further, when the non-electrostatic adhesion force Ft between the uncompressed colors of each color used in Example 2 was determined in the same manner as in Example 1, yellow and cyan were 11.3 [nN], and magenta was It became 10.9 [nN] and black became 10.7 [nN].

  Next, IPSio CX400 was used as an evaluation image output machine in the same manner as in Example 1, and the load to the primary transfer nip was set in the same manner. Further, in the image output machine for evaluation, the intermediate transfer belt conveyance speed and the rotation speed (linear speed) of each electrostatic latent image carrier are made equal. Further, the coefficient of friction between the photosensitive drum 2 and the intermediate transfer belt 5 measured using the Euler belt method was 0.20 and 0.35, respectively, as in Example 1.

[Experiment 2]
Next, Experiment 2 in which the state of occurrence of transfer dust is compared between Example 2 and Comparative Example 2 will be described.
In Example 2, the load F was set to 3 [N] in each primary transfer nip. At this time, the non-electrostatic adhesion between the toners of the respective color toners was about 18 [nN].
On the other hand, as Comparative Example 2, image evaluation was also performed in the case where the load F applied to the primary transfer nip with the image output machine for evaluation was 8 [N] for each color. In this case, the non-electrostatic adhesion between toners is about 22 [nN] for each color toner.
The image forming conditions in the image output machine for evaluation were adjusted so that the same toner transfer efficiency was obtained with the primary transfer nip load in each of Example 2 and Comparative Example 2, and the amount of toner on the intermediate transfer belt was It is designed to be equivalent.
Note that the same pattern as in Experiment 1 was used as the evaluation image.
The results of Experiment 2 are shown in Table 3.

  As shown in Table 3, both Example 2 and Comparative Example 2 were able to obtain an image with almost no transfer dust, but Comparative Example 2 produced a hollow image and was low as a comprehensive image. It became quality. On the other hand, in Example 2, it was possible to obtain a high quality image without occurrence of a hollow image.

[Example 3]
Example 3 in which the load F applied to a plurality of primary transfer nips in the printer 100 of Embodiment 1 is changed so as to increase toward the downstream side in the surface movement direction of the intermediate transfer belt 5 will be described.
In the third embodiment, the load applied to the primary transfer nip is different for the printer 100 shown in FIG. 1 that forms an image on the intermediate transfer belt 5 in the order of yellow, magenta, cyan, and black from the most upstream portion. Specifically, the yellow primary transfer nip load is 8 [N], the magenta primary transfer nip load is 8.5 [N], the cyan primary transfer nip load is 8.9 [N], and The black primary transfer nip load is 9.0 [N]. In this configuration, the non-electrostatic adhesive force between the toners increases every time it passes through the nip.
Table 4 shows the results of the evaluation of transfer dust as in Example 1.

  As shown in Table 4, in an image in which toners of two or more colors are overlapped, an image having a higher quality than that in Example 1 can be obtained.

[Example 4]
In Comparative Example 2 used in Experiment 2, the conveyance speed of the intermediate transfer belt 5 is set to 1 [from the rotation speeds (linear speeds) of the photosensitive drums 2Y, 2M, 2C, and 2K, which are latent image carriers set in common to the respective colors. %] Was fastened as Example 4 and evaluated in the same manner as in Experiment 2.
Table 5 shows the results of evaluating the presence or absence of a hollow image as in Experiment 2.

As shown in Table 4, in Example 4, it was possible to suppress the void image generated when the electrostatic adhesion force between the toners became 20 [nN] or more. In addition, since the method for calculating the non-electrostatic adhesion force between toners described in the first embodiment is an average value of a large number of non-electrostatic adhesion forces between toners, a toner having a large roundness with a large variation in shape (amorphous toner) ), There is a possibility that some non-electrostatic adhesion between toners may greatly exceed the value obtained by calculation. In such a case, as in the fourth embodiment, it is an effective measure to make the linear speed of the intermediate transfer belt 5 faster than the linear speed of the photosensitive drum 2.
In this embodiment, in order to prevent overlapping dust, as a result, the amount of toner attached to the image increases. Then, the stress applied to the toner in the nip is large, and a case where a hollow image is generated can be considered. Therefore, by making the linear speed of the intermediate transfer belt 5 faster than the linear speed of the photosensitive drum 2, it is possible to prevent overlapping dust and omission at the same time.

[Example 5]
A case where a device for supplying a lubricant to the intermediate transfer belt 5 with the same configuration as that of the first embodiment is added and the friction coefficient of the intermediate transfer belt 5 is set to 0.25 is referred to as a fifth embodiment. In the configuration of Example 1 and the configuration of this example, after 10,000 images for evaluation were output, the cleaning status of the intermediate transfer belt 5 was confirmed.
The output images in both Example 1 and Example 5 were good without transfer dust and void images. On the other hand, on the intermediate transfer belt 5 after printing, there was some dirt such as a filming phenomenon in the case of Example 1, but it was confirmed that the dirt was greatly reduced when the configuration of Example 5 was adopted. It was.
When spherical toner is used as in the first embodiment, it is difficult for voids to occur, so there is no need to increase the static friction coefficient of the intermediate transfer belt. It becomes easy.

[Example 6]
In Comparative Example 2, the photosensitive drums 2Y and 2M have a friction coefficient of 0.45 for the intermediate transfer belt 5 and the friction coefficients of the photosensitive drums 2Y, 2M, 2C, and 2K that are the latent image carriers are 0.20. Example 6 was prepared by adjusting the amount of lubricant supplied to 2C and 2K, and the same evaluation as in Experiment 2 was performed. As a result of the evaluation, the transfer dust was the same as that of Comparative Example 2, and a good image having no hollow image could be obtained.

In the first embodiment, the load applied to the primary transfer nip is controlled so that the non-electrostatic adhesion force between the toners has a certain level in order to suppress dust generated after passing through the primary transfer nip. The load only determines the primary transfer nip pressure P, and the pressure received by the actual toner depending on the image area can take various values with the primary transfer nip pressure as a lower limit. In practice, it is desirable to set the load so that the non-electrostatic adhesion force between the toners increases by a certain value or more when the toner receives a compression pressure based on the image area ratio of the output image. However, the transferred dust image is often a problem in an image having a relatively low image area ratio, particularly an image containing many characters.
According to the study by the present inventors, toner generated in the primary transfer nip when the image area ratio is 5%, that is, when the force received by the toner in the primary transfer nip is 20 times the primary transfer nip pressure P. It was found that the non-electrostatic adhesion force between the toner and the non-electrostatic adhesion force between the toners after passing through the primary transfer nip are preferable parameters for evaluating the transfer dust. Accordingly, the particularly important to define the non-electrostatic adhesion force and the amount of change between the toner at the compression pressure P _C of a 20-fold primary transfer nip pressure P.

As described above, according to the first embodiment, pressure and a transfer electric field are applied to the toner images of the respective colors at the primary transfer nips of the four colors, so that the toner images are transferred to the intermediate transfer belt 5 that is a transfer body, and four full colors are obtained. In an image forming apparatus for forming a toner image, each of the four color toner images before passing through the primary transfer nip on each of the photosensitive drum drums 2Y, 2M, 2C, and 2K as the latent image carrier and passing through the secondary transfer nip. The load F applied to the secondary transfer nip is adjusted so that the non-electrostatic adhesion force between the toners forming the toner image increases by 3 [nN] or more on the intermediate transfer belt 5 later. Thereby, the adhesion force between the toners exceeds the electrostatic repulsion force between the toners that causes transfer dust, and transfer dust can be reduced. In addition, since the load on the transfer nip is adjusted to reduce transfer dust, the structure can be made simpler than a structure in which an electrode is added and controlled for electric field control. Therefore, the transfer dust when transferring the toner image from the image carrier to the transfer body can be reduced with a simple structure, and a good image can be obtained.
Further, by setting I = 20 for the compression pressure P _C that can be expressed as P _C = P × I with respect to the transfer nip pressure P, generation of transfer dust occurs in an image where transfer dust is particularly likely to be noticeable. Thus, it is possible to obtain a good image.
Further, by setting the non-electrostatic adhesive force between toners to 20 [nN] or less, a part of the toner on the photosensitive drum 2 cannot be transferred onto the intermediate transfer belt 5, and the inside of the image is lost. It is possible to reduce missing images.
Further, the load is increased toward the primary transfer nip on the downstream side in the surface movement direction of the intermediate transfer belt 5 and applied to each primary transfer nip so that the non-electrostatic adhesion between the toners becomes larger as the toner transferred at the downstream portion. By adjusting the load F, when the second and subsequent color toners are transferred to the intermediate transfer belt 5, the toner adhesion force between the toners on the intermediate transfer belt 5 becomes larger, and the second and subsequent color toners are transferred to the first color toner. It is possible to efficiently suppress transfer dust generated more significantly when superimposed on the toner. As a result, a good image free from transfer dust can be obtained.
Also, by providing a speed difference between the rotational speed (linear speed) of at least one photoconductor drum 2 and the surface moving speed of the intermediate transfer belt 5, it is possible to obtain a good image free from transfer dust and a hollow image. it can.
Further, when the roundness of the toner used for image formation is less than 1.3, the friction coefficient of the photosensitive drum 2 with respect to the friction coefficient μ _opc of at least one photosensitive drum 2 and the friction coefficient μ _b of the intermediate transfer belt 5 is determined. The coefficient is adjusted to 0.20 and the friction coefficient of the intermediate transfer belt 5 is adjusted to 0.25 so that the relationship of 0.25 ≧ μ _b > μ _opc is satisfied. Thereby, in addition to suppressing transfer dust and void images, the toner remaining on the photosensitive drum 2 can be cleaned well, so that it is possible to obtain a good image free from transfer dust, voids and background smudges. .
Further, when the roundness of the toner used for image formation is 1.3 or more, the friction coefficient μ _opc of at least one photosensitive drum 2 and the friction coefficient μ _b of the intermediate transfer belt 5 are the same as those of the intermediate transfer belt 5. The friction coefficient is adjusted to 0.45, and the friction coefficient of the photosensitive drum 2 is adjusted to 0.20 so as to satisfy the relationship of μ _b −μ _opc > 0.2. As a result, the toner removal effect of the intermediate transfer belt 5 occurs due to the difference in friction coefficient between the intermediate transfer belt 5 and the photosensitive drum 2, and in addition to the transfer dust, it is possible to suppress the occurrence of a void image. Therefore, it is possible to obtain a good image with no voids.

[Embodiment 2]
In the first embodiment, the transfer material on which the toner image is transferred from the photosensitive drum 2 as the image carrier is the intermediate transfer belt 5. Next, Embodiment 2 in which the transfer material transferred from the photosensitive drum 2 is a transfer sheet P that is a recording medium will be described.
FIG. 4 is a schematic configuration diagram of the entire apparatus of the printer 100 as the color image forming apparatus according to the second embodiment. In FIG. 2, the printer 100 includes four sets of image forming units 20Y, 20M, 20C, and 20K that use toners of four different colors (yellow: Y, magenta: M, cyan: C, black: K) as transfer materials. The image forming apparatuses are arranged side by side along the transfer path of the transfer paper P. That is, as the transfer paper P is conveyed by the recording material conveyance belt 50, the images are sequentially superimposed on each other by passing through the primary transfer nips between the photosensitive drums 1 and the primary transfer rollers 4. A color image is formed.
It differs from FIG. 1 only in the presence / absence of an intermediate transfer belt, and the other points are the same, so that the description thereof is omitted.
As shown in FIG. 4, the printer 100 according to the second embodiment does not include an intermediate transfer member unlike the first embodiment, and thus can be a simpler printer, and can save space and cost. I can do it.

1 is a schematic configuration diagram of a printer according to Embodiment 1. FIG. 3 is an explanatory diagram illustrating a relationship between a non-electrostatic adhesion force between toner and a compression pressure according to the first exemplary embodiment. FIG. 6 is an explanatory diagram illustrating a relationship between a non-electrostatic adhesion force between toner and a compression pressure in Example 2. FIG. 3 is a schematic configuration diagram of a printer according to a second embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Developing device 2 Photoconductor drum 3 Charging device 4 Primary transfer roller 5 Intermediate transfer belt 6 Secondary transfer device 7 Secondary transfer roller 8 LED array head 9 Fixing device 10 Photoconductor cleaning device 11 Lubricant supply roller 20 Image forming unit 50 Recorder transport belt 100 Printer

Claims (11)

A plurality of image carriers;
A plurality of image forming means for forming toner images of different colors on each image carrier;
By applying pressure and a transfer electric field to each color toner image at each transfer nip facing each image carrier, the toner image is transferred to the transfer body to form a plurality of color toner images on the transfer body. In the image forming apparatus,
For all of the plurality of transfer nips, the non-electrostatic adhesion force between the toners of the toner constituting the toner image carried on the image carrier part before passing through the transfer nip,
The non-electrostatic adhesion force between the toners of the toner constituting the toner image carried on the transfer body portion after passing through the transfer nip,
An image forming apparatus, wherein a load applied to the transfer nip is adjusted so as to be larger than 3 [nN]. The image forming apparatus according to claim 1.
After passing through any of the transfer nips, the load applied to the transfer nip is adjusted so that the non-electrostatic adhesion force between the toners of each color is 20 [nN] or less. An image forming apparatus. The image forming apparatus according to claim 1 or 2,
The load applied to each of the transfer nips is such that the toner transferred at the transfer nip on the downstream side of the surface of the transfer body in the transfer nip increases the non-electrostatic adhesion between the toners after passing through the transfer nip. An image forming apparatus that is adjusted. The image forming apparatus according to claim 1, 2 or 3.
An image forming apparatus, wherein a speed difference is provided between a linear velocity of at least one of the plurality of image carriers and a linear velocity of the transfer member. The image forming apparatus according to claim 1, 2, 3, or 4.
At least one of the plurality of image forming units uses the toner having a roundness of less than 1.3,
Between the friction coefficient μ ₀ of the surface of the image carrier on which the toner image is formed on the surface by the image forming unit and the friction coefficient μ _t of the surface of the transfer body,
0.25 ≧ μ _t > μ ₀
An image forming apparatus characterized in that the image carrier is configured so that The image forming apparatus according to claim 1, 2, 3, 4, or 5.
At least one of the plurality of image forming units uses the toner having a roundness of 1.3 or more,
Between the friction coefficient μ ₀ of the surface of the image carrier on which the toner image is formed on the surface by the image forming unit and the friction coefficient μ _t of the surface of the transfer body,
μ _t −μ ₀ > 0.2
An image forming apparatus characterized in that the image carrier is configured so that The image forming apparatus according to claim 1, 2, 3, 4, 5 or 6.
An image forming apparatus, wherein the transfer member is an intermediate transfer member. The image forming apparatus according to claim 1, 2, 3, 4, 5, 6 or 7.
An image forming apparatus, wherein the transfer member is a recording medium. The image forming apparatus according to claim 1, 2, 3, 4, 5, 6, 7 or 8.
Assuming that the area of the transfer nip is Sn and the load applied to the transfer nip is F, P _C = I × F / Sn (I is an arbitrary real number equal to or greater than 1). seeking P _C, the breaking stress of the toner measured after applying a compression pressure corresponding to the pressure P _C to the toner as St, the toner particle size is D, the toner layer porosity epsilon,
Rumpf's formula: Ft = St × D ² × ε / (1-ε)
An image forming apparatus using the Ft calculated by the above formula as the non-electrostatic adhesion force between the toners. The image forming apparatus according to claim 9.
The image forming apparatus according to claim 1, wherein I is I = 100 / v where the image area ratio is v. The image forming apparatus according to claim 10.
An image forming apparatus having the image area ratio v = 5 [%].

Images