JP3248047B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus which develops an electrostatic latent image formed on an image carrier corresponding to an image to be recorded with a developer and records the image on paper or the like.

[0002]

2. Description of the Related Art With the spread of digital color copying machines, demands for higher speed and higher image quality have been increasing, and image forming apparatuses as shown in FIG. 2 have been devised. In this image forming apparatus, an image forming unit (image forming unit) is provided for each developer of four colors, and in each image forming unit, a visible image of each color is formed on a photosensitive drum as an image carrier by an image forming process described later. This is an electrophotographic digital color image forming apparatus which forms, sequentially transfers these visible images to a transfer material supplied from the outside, and fixes them collectively to obtain a color image. The greatest advantage of this method is that high speed can be achieved.

[0003] The first, second, third and fourth four image forming portions P _M in the color image forming apparatus apparatus body, P _C,
PY and _PK are provided, and a paper feed unit 7 is provided at one end, that is, on the right side in FIG. 2, and a fixing unit 8 is provided on the opposite side, that is, on the left side in FIG. Further, below the path from the paper supply unit 7 to the fixing device 8 in the printer body,
An endless transfer material conveying means for conveying the transfer material, in this conventional example, a conveyance belt 10 is stretched between a plurality of rollers in a known manner.

[0004] The conveyor belt 10 is driven in the direction indicated by an arrow, it carries a transfer material fed through the feeding unit, the image forming portions P _M described above, P _C, P _Y, and P _K Sequentially.

Each of the image forming units P _M , P _C , P _Y, and P _K has substantially the same structure, and is a photosensitive drum 1 M, which is an image carrier that is driven to rotate in the direction of the arrow as shown in the drawing. 1C, 1
And primary chargers 2M, 2C, 2Y and 2 that uniformly charge the photosensitive drum around each photosensitive drum.
K: Image exposure device 3 for forming an electrostatic latent image on a photosensitive drum
M, 3C, 3Y, and 3K; developing units 4M, 4C, 4Y, and 4K that develop the electrostatic latent image formed on the photosensitive drum;
Corona charger 6 for transferring the developed visible image to a transfer material
M, 6C, 6Y and 6K; drum cleaners 5M, 5C, 5Y and 5 for removing toner remaining on the photosensitive drum
K, are sequentially arranged in the drum rotation direction.

The developing unit 4M contains magenta toner, the developing unit 4C contains cyan toner, the developing unit 4Y contains yellow toner, and the developing unit 4K contains black toner. I have. The image exposure devices 3M, 3C, 3
In this example, Y and 3K are LED heads in which LED light emitting elements are arranged in the generatrix direction of the drum. The LED heads are decomposed into a large number of pixels by an image pickup element such as a color CCD, read, and converted into digital signals. The drum surface is exposed between the primary chargers 2M, 2C, 2Y and 2K and the developing devices 4M, 4C, 4Y and 4K in response to the input of digital pixel signals for the respective color images. Thus, an electrostatic latent image of a corresponding color is formed. A pixel signal corresponding to the magenta component image of the color image is supplied to the image exposure device 3M, a pixel signal corresponding to the cyan component image of the color image is supplied to the image exposure device 3C, and the yellow component image of the color image is supplied to the image exposure device 3Y. The pixel signal corresponding to
Pixel signals corresponding to the black component image of the color image are input to the image exposure device 3K. Between the first image forming portion P _M and the sheet feeding portion, a pair of adsorption charger for adsorbing the transfer material is opposed disposed across the conveyor belt 10. On the other hand, between the fourth image forming portion _PK and the fixing device 8, a charge removing device is provided, and a power source (not shown) is provided to separate the transfer material adsorbed on the transport belt 10.
More AC voltage is applied.

In the above-described color printer, the transfer material fed from the paper feed cassette 7 onto the transport belt 10 is electrostatically attracted and transported as the transport belt 10 moves in the direction of the arrow shown in the figure. In conjunction to the conveyance of the transfer material, the toner image on the photosensitive drum 1M in the first image forming portion P _M magenta, the photosensitive drum 1C of the second image forming portion P _C the cyan toner image is, the third photosensitive drum 1 of the image forming portion P _Y
The yellow toner image in Y is the photosensitive drum 1K for the fourth image forming portion P _K is shared black toner image, respectively,
It is developed according to the electrostatic latent image.

Here, the developing step will be described. Generally, the developing method is a method in which non-magnetic toner is coated on a sleeve with a blade or the like, and magnetic toner is coated with a magnetic force, conveyed, and developed in a non-contact state with respect to a photosensitive drum (one-component non-contact development). ), A method in which the toner coated as described above is developed in contact with the photosensitive drum (one-component contact development), and a method in which a mixture of toner particles and a magnetic carrier is used as a developer. There are four main types: a method in which the developer is transported by force and developed in contact with the photosensitive drum (two-component contact development), and a method in which the two-component developer is developed in a non-contact state (two-component non-contact development). Separated. The two-component contact developing method is often used from the viewpoints of high image quality and high stability.

FIG. 3 is a schematic view of a developing device 4 for two-component magnetic brush development in the conventional example. In the drawing, 16 is a developing sleeve, 17 is a magnet roller fixedly arranged in the developing sleeve, 18 and 19 are agitating screws, 20 is a regulating blade arranged to form a thin layer of developer on the surface of the developing sleeve, 21 Denotes a developing container. Here, a developing step of visualizing the electrostatic latent image by a two-component magnetic brush method using the above-described developing apparatus and a developer circulation system will be described.

First, the rotation of the developing sleeve 16 causes N ₃
In the process of being transported from the S ₂ pole to the N ₁ pole, the developer pumped by the poles is regulated by the regulating blade 20 arranged perpendicularly to the developing sleeve 16, and a thin layer is formed on the developing sleeve 16. You. Here a thin layer formed developer, brush is formed by the conveyed to the developing main pole S ₁ pole magnetic force. The electrostatic latent image is developed by the spike-shaped developer, and thereafter the developer on the developing sleeve 16 is returned into the developing container 21 by the repulsive magnetic field of the N ₃ pole and the N ₂ pole.

A DC bias and an AC bias are applied to the developing sleeve 16 from a power supply (not shown). In general, in the two-component developing method, when an AC bias is applied, the developing efficiency increases, and the image becomes high-quality.

[0012] The toner image developed in this way, on the photosensitive drum, the photosensitive drum 1M~1K of the first to fourth image forming portions P _M to P _K transfer material by the movement of the conveyor belt 10
Of the image forming units while sequentially passing through the lower part of the image forming unit and conveyed toward the fixing unit.
The color image is sequentially superimposed and transferred onto the transfer material by K to synthesize a color image. After the transfer material having passed through the fourth image forming portion P _K, the AC voltage is discharged by charge removing charger is applied, it is separated from the conveyor belt 10. The transfer material separated from the transport belt 10 is discharged to the tray 9 from the transfer material discharge port after the image transferred by the fixing device 8 is fixed.

On the other hand, transfer residual toner adheres to the surface of the photosensitive drum after the transfer of the toner image, and when this enters the next transfer step, it appears as an image stain at the next image formation. Is discharged from above the drum by the drum cleaner 5 and sent to a waste toner box provided therewith. In this conventional example, a method is used in which an elastic blade is brought into contact with a photosensitive drum to scrape off toner.

However, the appearance of waste toner is not very desirable in view of the environment and the complexity of maintenance. On the other hand, there is an increasing demand for downsizing OA equipment such as copiers in terms of space saving.

As a method for solving these problems at once, there is a simultaneous development cleaning. FIG. 4 shows an example using this method. This is a method in which in a reversal development process in which toner is developed in an exposed portion, transfer residual toner in a non-image portion is collected in a developing container by a fogging potential in a developing process of the next image formation. The collected toner is mixed with the carrier again and used for image formation, so that no waste toner is discharged. At the same time, the need for a drum cleaner is eliminated, thus enabling downsizing. In particular, in an image forming apparatus having a plurality of image forming units having the same configuration as in the conventional example, it is apparent that the size reduction is particularly effective.

This process will be briefly described with reference to FIG. This figure shows (1) after transfer, (2) after charging,
(3) Schematic representation of the potential on the drum after development and (4) the arrangement of toner on the drum after development. V _D is the potential on the drum, the V _C and V _b is the potential difference to the developing sleeve potential of the non-image portion of each image portion. Since the transfer residual toner is affected by corona discharge at the time of transfer, so-called inverted toner whose polarity is inverted is also included [(1): After transfer]. However, the reversal toner is normalized at the same time as the photosensitive drum is charged [(2): After charging]. A new latent image is formed [(3): after exposure], and the toner adhering to the non-image area is collected in the developing container by the fog removal potential _Vb [(4): after development]. However, when the transfer residual toner is large, there is a possibility that charging unevenness may occur at the time of charging, or the latent image may be disturbed by being shielded from light. For this reason, it is essential to use a spherical toner having a high transfer efficiency and a high recovery efficiency at the time of development for simultaneous cleaning with development. This is because the non-spherical toner has a chance to come into contact with the carrier only at the protrusions, and since the protrusions are locally charged at a high density, the electrostatic adhesion acts strongly when contacting the drum. On the other hand, the spherical toner has an opportunity to come into contact with the carrier without unevenness and is uniformly charged, so that the electrostatic adhesion at the time of contact with the drum is weaker than the non-spherical toner. In addition, the fact that the spherical toner has a higher rolling property than the non-spherical toner also contributes to the higher recovery efficiency.

[0017]

When a cleanerless system is used in an image forming apparatus in which a plurality of image forming units are arranged along a transport belt, a problem of color mixing due to retransfer occurs. This is due to the repulsion that occurs during the transfer of the second and subsequent colors due to the adhesion between the toner and the drum of the different color toner already transferred on the transfer material and the transfer material because the polarity is reversed by the transfer charger. This occurs because the force causes the toner to adhere to the drum from the transfer and be collected in a developing device of a different color. This color mixture progresses every time an image is formed, and it is difficult to reproduce an accurate color tone.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide an image forming apparatus capable of preventing color mixing due to retransfer and maintaining an image without a change in color tone.

[0019]

According to the present invention, a latent image is formed on an image carrier uniformly charged, and the latent image is formed by a developer containing a spherical toner and a carrier carried on a developer carrier. Developing means for developing the latent image to form a toner image, the developing means having a toner selected from the group consisting of yellow toner, cyan toner, magenta toner and black toner, developing means also serves as the simultaneous development cleaning <br/> grayed means for recovering at the same time developing a residual toner remaining on the image carrier after it has been transferred to a transfer material the toner image, the developing-cleaning unit An image forming unit is formed, a plurality of the image forming units are arranged in line along a conveyor belt, and the transfer material is conveyed by the conveyor belt and passes through the plurality of image forming units to form a color. br />-Image The image forming apparatus of a cleaner-less method to form, the ratio of the area spherical toner particles are covered with external additive to be externally added to the spherical toner particles of the spherical toner is 50% or less than 15% spherical shaped toner Has a shape factor SF-1 of 100 to 140, and SF-2 of 100 to
120 relates to a cleaner-less type image forming apparatus, wherein the range is 120.

The present invention also relates to an image forming apparatus in which an endless intermediate transfer member is used instead of the transport belt in the image forming apparatus, and the image forming units are arranged along the intermediate transfer member.

A detailed description of the device of the present invention will be given in the following examples.

[0022]

【Example】

(Embodiment 1) The basic configuration of a color image forming apparatus according to Embodiment 1 of the present invention is the same as that of the conventional example shown in FIG.
The image forming process used is the same as that of the conventional simultaneous cleaning in development, and a description thereof will be omitted here.

As a result of studying a method of reducing retransfer to solve the above-described problem of color mixing, retransfer was performed by determining the ratio of the area of the toner surface covered by the external additive added to the toner to the surface area of the toner particles, That is, it turned out that it largely depends on the coverage. The effect of external additives is usually
Although there are improvements in the fluidity of the developer, the improvement in the charge imparting property, the stability of the charge amount with respect to environmental fluctuations, and the improvement in the transferability by reducing the adhesion to the drum, etc. It was found to be very effective in preventing transfer.

In the present invention, the shape factor SF of the toner
Those having -1 of 100 to 140 and SF-2 of 100 to 120 are suitably used, and more preferably those of SF-1 of 100 to 130 and SF-2 of 100 to 115. SF-1, which indicates the shape factor used in the present invention,
SF-2 is FE-SEM (S-80) manufactured by Hitachi, Ltd.
0), sample 100 toners at random,
The image information is introduced into an image analysis device (Luzex3) manufactured by Nicole via an interface, analyzed, and a value calculated by the following equation is used as the shape coefficient S in the present invention.
F-1 and SF-2 were defined.

[0025]

(Equation 1) (AREA: toner projection area, MXLNG: absolute maximum length, PERI: circumference)

The shape factor SF-1 of the toner indicates a degree of spherical shape. If the shape factor SF-1 is larger than 140, the shape gradually changes from spherical to irregular. SF-2 indicates the degree of unevenness. If it is larger than 120, the unevenness of the surface area of the toner becomes remarkable.

The effect of the shape of the toner is to reduce the influence of the photosensitive member charging member on the toner surface as much as possible and to suppress the generation of reactive low molecular weight components in the toner. That is, a spherical shape having the smallest possible toner surface area is preferable.

The effect of the present invention can be enhanced by using a toner in which part or all of the toner is formed by a polymerization method. In particular, in the case of a toner in which such a portion of the toner surface is formed by a polymerization method, a necessary portion is formed as a pre-toner (monomer composition) particle in a dispersion medium by a polymerization reaction. Can be obtained. If SF-1 exceeds 140 or SF-2 exceeds 120, fog may increase or durability may be slightly inferior.

Further, the toner used in the image forming apparatus of the present invention can be manufactured more easily by using a toner having a core / shell structure of the toner and a shell portion formed by polymerization. . In this sense, a toner having a core / shell structure is preferably used in the present invention. It goes without saying that the action of the core / shell structure can provide blocking resistance without impairing the excellent fixing property of the toner.

In the first embodiment of Example 1, a spherical toner (SF-1 is 108, S
F-2 is 108), and the average particle diameter is 20 n as an external additive.
Table 1 shows the results of evaluating the coverage and the re-transfer amount at the optimum transfer current value when using m (silica) (SiO ₂ ). As the photoreceptor, a photoreceptor having a surface layer in which Teflon particles are dispersed in the outermost layer and having excellent releasability is used.

For a toner having a substantially spherical shape as used in the present invention, the coverage can be expressed by the following equation.

[0032]

(Equation 2)

[0033] Here, the coverage of the external additive of R is the toner surface (%), A is an outer hydrogenation ratio _{(wt%), r t,} d t The average toner radius ([mu] m) and a specific gravity (g / cm ), R _a , d _a
Are the average radius (μm) and specific gravity (g / c) of the external additive, respectively.
m). However, if r _a external additive to form agglomerates
Is the average radius of the agglomerates.

From Table 1, it was found that when the coverage of the external additive on the toner surface was 15% or more, retransfer did not occur.

As a second embodiment of Example 1, the results of evaluating the coverage and the re-transfer amount at the optimum transfer current value when using titanium oxide (TiO ₂ ) having an average particle size of 50 nm as an external additive are shown. It is shown in Table 2. Also in the second embodiment, when the coverage of the external additive was 15% or more, no retransfer occurred.

From the above, it can be seen that when a spherical polymerized toner by the suspension polymerization method is used, the amount of retransfer most depends not on the material or particle size of the external additive but on the coverage of the toner surface. Considering the durability of the developer, it is advantageous to increase the external additive amount to maintain the external additive effect and obtain a stable retransfer rate. And other adverse effects also occur. In addition to the above, when the coverage exceeds 50% in the examination in the present invention,
The developability tends to decrease in the low-density portion, and therefore, the coverage is preferably 50% or less. This phenomenon occurs because a large amount of the external additive adheres to the carrier due to excessive external addition, and the external additive adheres and accumulates on the surface of the photoreceptor during development, and the releasability is extremely increased.

In the image forming process of this embodiment, since the blade cleaning is omitted, the extraneous matter on the surface of the photoreceptor is not removed, and it is necessary to avoid excessive external addition which causes the extraneous matter. Therefore, the coverage of the external additive on the toner surface is preferably 15% or more, and more preferably 15% or more and 50% or less.

In this example, the external additives were used alone, but the present invention is not limited to this. A plurality of external additives may be used in combination. In this case, the coverage is, of course, the sum of the coverage of each external additive. . Also, more <br/> favored arbitrary even towards those treated hydrophobic surface external additives is from stability against environmental changes. The configuration of the apparatus in this embodiment is an example, and the same effect can be obtained even if the transfer charger is a roller charger instead of a corona charger.

As described above, in the image forming apparatus using the simultaneous cleaning process for development and having a plurality of image forming units arranged along the conveyor belt, the coverage of the toner surface with the external additive should be 15% or more. As a result, retransfer was prevented, and an output image having an accurate color tone without deterioration in color reproducibility even after long-term use could be obtained.

[0040]

[Table 1]

[0041]

[Table 2]

Embodiment 2 FIG. 1 is a schematic side view of a color image forming apparatus according to Embodiment 2. In the first embodiment, the transfer material is electrostatically fixed on the transfer material transport belt 10 and sequentially passed through the image forming unit, so that the color image is formed by directly superimposing the single color toner on the transfer material. On the other hand, in the present embodiment, an intermediate transfer belt 11 which is an image holding member is used instead of the transfer material transport belt 10 of the first embodiment. Except for the intermediate transfer member, the configuration of the apparatus is the same as that of the first embodiment, and a description thereof will be omitted. However, a roller charger (6 'in the figure) is used as the transfer charger.

The image forming process in this embodiment will be briefly described. The toner images formed in the respective image forming units are sequentially transferred to an intermediate transfer belt 11, which is an image holding member, to form a color image, which is collectively transferred onto a transferred transfer material.
Since a small amount of untransferred toner remains on the intermediate transfer body 11 after the transfer, the toner is collected by the cleaner 12.
Since the outline of the other image processes is the same as that of the first embodiment, the description is omitted here.

As a feature of the image forming process using the intermediate transfer member as in this embodiment, in addition to being capable of supporting various paper types as a transfer material, an intermediate transfer member belt set to an appropriate resistance value is used. By doing so, unlike a transfer to a transfer material such as paper, transfer to a uniform material without resistance unevenness or the like is performed, so that high transfer efficiency and prevention of retransfer can be realized. Therefore, the color mixture is further reduced than in the first embodiment.

Here, as the intermediate transfer belt,
For example, materials such as polyurethane resin, polyester resin, polystyrene resin, polyolefin resin, polybutadiene resin, polyamide resin, polyvinyl chloride resin, polyethylene resin, fluorine resin, etc. What mixed and dispersed particles and metal powder is used. In this example, a material in which carbon particles were dispersed in a polyurethane resin was used.

As described above, by using the intermediate transfer member in addition to setting the coverage of the toner surface with the external additive to 15 to 50%, retransfer is more reliably prevented, and the color change due to color mixing is prevented. The output image without the defect was continuously obtained.

[0047]

According to the present invention, there is provided an image forming apparatus in which a plurality of image forming units which also serve as a cleaning means for collecting residual toner particles remaining on the latent image carrier are arranged in a row along the transfer-receiving body. When the ratio of the area covered by the external additive externally added to the toner particles to the surface area of the toner particles is 15% or more, color mixing due to retransfer can be prevented, and an image without color change can be maintained. It became so.

[Brief description of the drawings]

FIG. 1 is a schematic side view of a color image forming apparatus according to a second embodiment of the present invention.

FIG. 2 is a schematic side view of a known color image forming apparatus.

FIG. 3 is a schematic side view illustrating a known developing operation.

FIG. 4 is a schematic side view of a known or the first embodiment of the color image forming apparatus adopting the simultaneous development cleaning method.

FIG. 5 is a schematic diagram of a post-transfer aspect showing the behavior of the toner and the surface potential of the image carrier in the simultaneous cleaning process of development.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum (image carrier) 2 Primary charger 3 Image exposure device 4 Developer 5 Drum cleaner 6 Corona charger 6 'Roller charger 7 Paper feeder 8 Fixer 9 Tray 10 Conveyor belt 11 Intermediate transfer belt 12 Cleaner P Image forming unit (image forming unit)

Continuation of the front page (72) Inventor Masahiro Ito 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) References JP-A-61-160777 (JP, A) JP-A-4-355461 ( JP, A) JP-A-63-149662 (JP, A) JP-A-4-88368 (JP, A) JP-A-3-110580 (JP, A) JP-A-61-279864 (JP, A) JP-A-1-185654 (JP, A) JP-A-4-204664 (JP, A) JP-A-5-333591 (JP, A) JP-A-5-281784 (JP, A) (58) Fields studied (Int .Cl. ⁷ , DB name) G03G 9/08 G03G 15/08

Claims (3)

(57) [Claims] 1. A latent image is formed on an uniformly charged image carrier, and the latent image is developed with a developer containing a spherical toner and a carrier carried on a developer carrier to form a toner image. Developing means, wherein the developing means is a yellow toner, a cyan toner,
And a developing unit that collects the remaining toner remaining on the image carrier after transferring the toner image to a transfer material, simultaneously with development. Present
The simultaneous image cleaning unit also functions as an image simultaneous cleaning unit. The image simultaneous cleaning unit forms an image forming unit. The image forming units are arranged in plural rows along a conveyor belt. the image forming apparatus of a cleaner-less method for forming a color image by passing the image forming unit, the ratio of the area spherical toner particles are covered with external additive to be externally added to the spherical toner particles of the spherical toner is 15 %. The cleaner-less type image forming apparatus, wherein the spherical toner has a shape factor SF-1 of 100 to 140 and an SF-2 of 100 to 120. 2. The cleaner-less type image forming apparatus according to claim 1, wherein said image forming units are arranged along an endless intermediate transfer member. 3. The cleaner-less type image forming apparatus according to claim 1, wherein said spherical toner particles are produced by a polymerization method.