JPH0695242B2 - Image forming method - Google Patents

Description

The present invention relates to an image forming method in a laser color printer, a color image copying machine or the like, and more particularly to an image forming method for superposing a plurality of toner images on an image forming body. .

[Prior art]

Conventionally, light emitted from a color image original is decomposed by a color filter, and the decomposed light is applied to a charged image forming body surface to form an electrostatic image, and the electrostatic image is associated with a yellow filter corresponding to a color filter. A toner image is obtained by developing with toner particles of any color of magenta, cyan, or black, and the toner image is transferred to a recording paper, and the color of the toner image is changed to perform electrostatic image formation and development to form the toner image. A copying machine is known in which a toner image is superposed on a recording sheet by transferring the same onto a recording sheet and repeating the transfer. In this copying machine, since the transfer is performed on the recording paper each time the development of each color is completed, a mechanism for rotating or reciprocating the recording paper is required, so that the machine becomes large and the time required for image formation becomes long, There is a problem that it is difficult to align the transfer position on the recording paper.

Therefore, as a solution to the above-mentioned problems of the copying machine, an electrophotographic recording apparatus in which toner images are superposed on an image forming body and finally transferred to a recording sheet is disclosed in, for example, Japanese Patent Application Laid-Open Publication No.
No. 56-144452. In this recording device, in order to prevent the toner image previously formed on the image forming body from being disturbed in the subsequent development, the toner particles are ejected from the developer transport carrier under the oscillating electric field in the second and subsequent developments to form an image. The non-contact development method of adhering to the formed body is used.
However, in the case of the image forming method of superposing the toner images on the image forming body, even if the developing control of the toner particles is performed by the oscillating electric field under the non-contact condition of the development as described above, the The toner particles adhering to the image forming body may be transferred back to the subsequent developer transport carrier by the action of the oscillating electric field, causing color mixing in the developer or disturbing the toner image previously formed. However, there is a problem in that a color image is not clearly reproduced for that reason. This is because the phase of the alternating component of the oscillating electric field causes an electric force in the direction in which toner particles between the image forming body and the developer conveying carrier are transferred from the developer conveying carrier to the image forming body and an electric force in the opposite direction. It is due to the latter effect, because force and force come into action. Then, if the DC component of the oscillating electric field is adjusted to prevent the reverse transfer of the toner particles, fogging will occur. Therefore, only the adjustment of the oscillating electric field will not cause the reverse transfer or the fogging of the toner particles. Very difficult to do.

[Object of the Invention]

The present invention has been made in order to solve the above-mentioned problems in image formation in which toner images are superimposed on each other on an image forming body, and flight control of toner particles that prevents reverse transfer without causing fog vibrates. It is easily carried out by the electric field, and therefore, the toner image formed earlier is not disturbed and the mixing of toner particles of different colors occurs in the developing device after that,
Provided is an image forming method capable of stably and clearly reproducing a color image.

[Structure of Invention]

The present invention forms an electrostatic image on an image forming body and causes toner particles to fly from a developer layer having a layer thickness that does not contact the image forming body on a developer transport carrier under an oscillating electric field in a developing area, thereby forming an electrostatic image. In an image forming method in which a toner image is superposed on an image forming body to form a color image by repeating the image forming step of adhering the toner to the image forming body a plurality of times, the amplitude of the oscillating electric field becomes smaller as in the subsequent image forming step. The image forming method is characterized in that the frequency is increased and the amount of toner particles conveyed by the developer conveying carrier to the developing area per unit time is increased as in the subsequent image forming step. ,
This feature facilitates flight control that prevents reverse transfer without causing fogging of toner particles due to an oscillating electric field, thus making it possible to achieve the above object.

〔Example〕

 Hereinafter, the present invention will be described with reference to the drawings.

FIG. 1 is a schematic block diagram showing an example of a recording apparatus for carrying out the method of the present invention, and FIG. 2 is a partial sectional view showing a configuration example of a developing device.

In the recording apparatus shown in FIG. 1, a drum-shaped image forming body 1 having a photosensitive layer on its surface rotates in the direction of the arrow, and its surface has a charger 2.
(In the illustrated example, a scorotron is used), the charged surface is exposed to image exposure 3A for one of the colors, and an electrostatic image is formed. Two
The developing device 4A having the structure shown in the figure develops a toner image of a color corresponding to the image exposure 3A, and the surface on which the toner image is formed has the same structure as that of the developing device 4A. After passing through the positions of the developing devices 4B, 4C, 4D containing the particles and the positions of the transfer device 5 and the separator 6, the charge is removed by the charge remover 7, and the charge removed surface is not affected by the cleaning device 8 again. It is uniformly charged by the charging device 2, and the charged surface is irradiated with image exposure 3B for another color to form an electrostatic image again, and this electrostatic image is developed by the developing device 4B this time. After that, the image forming process is repeated in the same manner, and when development is finally performed by the developing device 4D, a color image formed by superimposing toner images of different colors is formed on the surface of the image forming body 1, and the color image is formed. Recording paper that is sent in contact with the surface of the image forming body 1 in synchronism The surface of the image forming body 1 is separated by the separator 6 from the recording paper transferred by the transfer device 5 to the color paper, and the color image is fixed by a fixing device (not shown), and the color image is transferred. The surface of the body 1 is destaticized by the destaticizer 7, and the residual toner particles are removed by the cleaning device 8 to complete the entire process of recording one color image.

In the above steps, the static elimination by the static eliminator 7 can be omitted except for the final static elimination. Then, when the development before and after the elimination of the charge removal is the reversal development in which the toner particles are attached to the portion where the image exposure is incident, when the image exposure does not overlap the dot exposure at the same position,
The charging by the charger 2 can be omitted except for the first charging.

According to the present invention, in the recording process as described above, when the developing devices 4A to 4D configured as shown in FIG. The oscillating electric field generated in the developing area has a smaller amplitude and a larger frequency in the later developing, and the amount of toner particles brought to the developing area per unit time is larger in the later developing. I am trying to become.

Under the same oscillating electric field, by increasing the amount of toner particles conveyed to the developing area, it becomes possible to fly more toner particles to the image forming body 1. By doing so, the reverse transfer of the toner particles previously attached to the image forming body 1 to the developer carrying carrier due to the action of the oscillating electric field is reduced, and the ratio of color mixture to the developer is also reduced. However, when more toner particles fly in the later development, more toner particles adhere to the image forming body 1 in the later development, which impairs the color balance. On the other hand, when the toner particles are made to fly under an oscillating electric field for development, if a small amplitude or a large frequency is used, it becomes difficult for the toner particles to fly and the image density is lowered, but the toner image is less disturbed. And has a characteristic that color mixing is reduced.

That is, according to the present invention, the oscillating electric field generated in the developing area is set to have a smaller amplitude or a larger frequency as it is developed in a later time. By increasing the amount of the toner particles in the subsequent development, it becomes easier for the toner particles to fly and transfer from the developer transport carrier 41 to the image forming body 1 in the subsequent development, and the toner particles can be generated without causing reverse transition due to the oscillating electric field. Is facilitated, and the toner images of different colors that are not disturbed on the image forming body 1 are superposed in a well-balanced and stable manner.

This point will be further described with reference to FIG.
In 4D, the developer carrier 41 is made of a non-magnetic material such as aluminum or stainless steel, and has a plurality of N, S inside.
A magnet body 42 having a magnetic pole on the surface is provided, and in the illustrated example, the developer transport carrier 41 rotates counterclockwise,
The magnet body 42 rotates clockwise, the magnetic force of the magnet body 42 causes the developer in the developer reservoir 43 to be adsorbed on the surface of the developer carrier 41,
It moves in the same direction as the rotation of the developer transport carrier 41 by the rotation of both of them and forms the developer layer whose layer thickness is regulated by the layer thickness regulating blade 44, and to the developing zone. The toner particle supply amount is controlled by controlling the layer thickness of the developer layer by the layer thickness regulating blade 44, and moving the developer layer by adjusting the rotational speed of one or both of the developer transport carrier 41 and the magnet body 42. This can be carried out by controlling the speed and changing the ratio of the toner particles in the developer when the developer is a mixture of toner particles and carrier particles. this house,
The method of changing the layer thickness of the developer layer is performed by using the developer layer and the image forming member 1.
There is a problem in that the influence of changing the supply amount of toner particles becomes complicated in relation to the surface gap of the above or the surface gap between the developer transport carrier 41 and the image forming body 1. Therefore, it is preferable to use one or both of a method of changing the moving speed of the developer layer and a method of changing the mixing ratio of the toner particles by using a two-component developer.

In order to prevent unnecessary toner particles from adhering to the image forming body 1 and the toner particles already forming a toner image from being reversely transferred to the developing device, the developer is not used in the developing device. It is desirable to stop the rotation of the carrier 41 and the magnet body 42 so that the developer layer is not carried.

Further, by using a two-component developer for the developing devices 4A to 4D, it becomes easy to control the toner particles to be frictionally charged by stirring the developer in the developer reservoir 43 by the stirring means 45, and to use the magnetic material as the toner particles. It is preferable in that the vividness of the color of the toner particles can be obtained, since it is not necessary to add it to the toner, or even if it is contained for preventing fogging, a small amount thereof is required. The triboelectrification of the toner particles is 5 to 50 μm in average charge amount in order for the toner particles to be sufficiently controlled by the oscillating electric field.
It is preferably charged to C / g, but it is easily obtained by using a two-component developer.

The power source 9 applies to the developer carrier 41 of each of the developing devices 4A to 4D an AC voltage having a smaller amplitude or a larger frequency or a bias voltage also containing a DC component, as the developing device that develops at a later time. The toner particles which generate an oscillating electric field between the base member and the image forming body 1 whose ground is connected to the developing unit, which is developed later as described above, are supplied to the developing region by the developer carrier 41. By virtue of this large oscillating electric field, it is possible to stably carry out the development each time without disturbing the previously formed toner image or impairing the color balance by the oscillating electric field. Also in this case, the developing device that does not contribute to the development is prevented so that unnecessary toner particles do not adhere to the image forming body 1 and the toner particles that have already formed a toner image do not reversely transfer to the developing device. It is desirable not to apply the AC component of the bias voltage.

The gap between the image forming body 1 and the developer carrying carrier 41 which provides the developing area is in the range of several tens to 2000 μm within a range in which the developer layer formed on the developer carrying carrier 41 is not brought into contact with the surface of the image forming body 1. The thickness of the developer layer regulated by the layer thickness regulating blade 44 is preferably smaller than that. If the gap in the developing area is too narrow, the thickness of the developer layer becomes too thin and a uniform layer thickness cannot be obtained. Therefore, the toner particles cannot be stably supplied to the developing area. Not only that, discharge easily occurs between the developer transport carrier 41 and the image forming body 1 to easily damage the developer and scatter toner particles. On the other hand, if the gap in the developing area is too wide, the above-mentioned flight control by the oscillating electric field will not be performed.

In order to prevent discharge between the developer transport carrier 41 and the image forming body 1 and facilitate control of toner particle flight by an oscillating electric field, when the developer is a two-component developer, the magnetic carrier particles also have a resistivity. Is preferably 10 ⁸ Ωcm or more and is insulative. As such carrier particles, carrier particles composed of carrier particles in which a resin coating is formed on the surface of magnetic particles or resin particles in which magnetic particles are dispersed and used are used. The resistivity of the insulating particles was measured by placing the particles in a container having a cross-sectional area of 0.5 cm ² and tapping them, and then applying a load of 1 Kg / cm ² on the packed particles, between the load and the bottom electrode. This is a value obtained by reading the current value when a voltage that generates an electric field of 1000 V / cm is applied to the. It is also preferable to provide an insulating or semi-insulating surface layer such as a resin coating or an oxide coating on the surface of the developer transport carrier 41.

If the above conditions are adopted for the developing devices 4A to 4D, the power source 9
As a result, it becomes easy to apply the above-mentioned bias voltage in which the appropriate AC voltage and DC voltage are superimposed to the developer transport carrier 41, and the supply amount of the toner particles to the developing region is gradually increased. In addition, each time development is carried out without reverse transfer of toner particles or color balance being impaired, but in order to achieve superposition of toner images with good resolution and sharpness, the average particle size of toner particles Diameter is 20μ
m or less, particularly 1 to 10 μm, and in the case of a two-component developer, the average particle size of the carrier particles is 5 to 50 μm.
It is preferably m. If the average particle size of the toner particles becomes too small, the charge amount due to the friction of one toner particle becomes small, and the Van der Waals force becomes relatively large, which easily causes aggregation, and makes it difficult for separation and flight. On the other hand, if the average particle size becomes too large, the charge amount for superposition decreases and flight control becomes difficult.
The resolution will be reduced. Further, when the average particle size of the carrier particles is too small, the force of being attracted by the magnetic force of the magnet body 42 becomes weak, while the electric Coulomb force and the Van der Waals force become strong, which causes the carrier to be strong. The particles easily migrate to the surface of the image forming pair 1 together with the toner particles. On the contrary, when the average particle diameter becomes too large, the developer layer formed on the developer transport carrier 41 becomes coarse and the developer layer. It becomes difficult to form a thin and uniform
The adhesion state of the toner particles in the developer layer is not uniform, and breakdown of the voltage applied to the developer transport carrier 41 and discharge are likely to occur, which makes it difficult to control the transfer and flight of the toner particles.

In the developing area, the developer layer on the developer carrying carrier 41 on which the electrostatic image of the image forming body 1 has been developed as described above is scraped off from the surface of the developer carrying carrier 41 by the cleaning blade 46. It is reduced to the developer pool 43. Then, toner particles corresponding to the amount consumed in the development are replenished from the toner hopper 47 by the toner replenishing roller 48 to the developer reservoir 43.

The present invention is carried out as described above, and concrete examples of the present invention will be shown below.

Example 1 A recording apparatus as shown in FIGS. 1 and 2 was used. The image forming body 1 has a Se photosensitive layer on the surface and has a diameter of 12
It rotates in the direction of the arrow at 0 mm and a surface speed of 220 mm / sec, and is uniformly charged to 600 V by the charger 2.

The image exposures 3A to 3D are dot exposures in which He-Ne laser light is modulated.

In each of the developing devices 4A to 4D, the diameter of the developer transport carrier 41 is
The gap with the image forming body 1 is set to 0.5 mm, that is, 500 μm at 30 mm, and the magnetic flux density on the surface of the developer carrying carrier 41 by the magnet body 42 having 8 poles of N and S magnetic poles is the maximum.
It is 800G.

A two-component developer is used in each of the developing units 4A to 4D, and insulating carrier particles having an average particle size of 20 μm obtained by coating the ferrite particles with styrene / acrylic resin are used, and silica is also appropriately added. . The toner particles consist of particles having a mean particle size of 12 μm obtained by fractionating a colorant and a charge control agent in a polyester resin, yellow toner particles in the developing unit 4A, magenta toner particles in the developing unit 4B,
Cyan toner particles were used for the developing unit 4C, and black toner particles were used for the developing unit 4D. The proportion of toner particles in the developer was set to 20% by weight. The average charge amount of the toner particles in the developer pool 43 of this developer was 20 μC / g in all cases.

In the developing devices 4A to 4D, the developer transport carrier 41 is 180 mm / sec in the developing device 4A and 200 mm / se in the developing device 4B, respectively, during development.
c, the developing device 4C rotates counterclockwise at a surface speed of 220 mm / sec, the developing device 4D rotates at 250 mm / sec, the magnet body 42 rotates equally at 600 rpm to the right, and is proportional to the speed on the surface of the developer carrier 41. And a developer layer that moves in the same direction is formed to have a thickness of 0.3 mm by the layer thickness regulating blade 44, and the developer transport carrier 41 has a DC voltage of 500 V by the power source 9 and is shown in Table 1. A bias voltage formed by superimposing an AC voltage is applied at each development to perform each development. In other words, the conditions for the development bias are: when the same AC voltage is applied in each development (No. 1), when the amplitude of the AC voltage is made smaller in the later development (No. 2), A comparative study was carried out assuming that the frequency of the AC voltage was increased as in the development (No. 3).

In each image forming process, a negative latent image is formed by image exposure 3A to 3D, and so-called reversal development in which toner particles are attached to the incident portion of image exposure 3A to 3D by developing devices 4A to 4D. It depends.

When a color image was recorded under the above conditions, No. 1 ~
In each case of 3, the toner images of the respective colors were not disturbed or mixed, and stable and clear color images could be reproduced.
The condition was inferior in terms of color balance. On the other hand, under the conditions of Nos. 2 and 3, the color balance of the obtained color image was good, and the disorder and color mixture of the toner image were small and the sharpness was further excellent.

Example 2 The same conditions as in Example 1 were applied except for the following conditions.

The left rotation speed of the developer transport carrier 41 at the time of each development of the developing devices 4A to 4D is set to 220 mm / sec surface speed, and the ratio of the toner particles in the two-component developer is 15 wt in the developing device 4A.
%, 18 Wt% for developing unit 4B, 20 Wt% for developing unit 4C,
In 4D, the amount of toner particles supplied to the developing area was set to be 24 wt% so that the supply amount was gradually increased.

The color image was reproduced and recorded under the above conditions. In any of Nos. 1 to 3 in Table 1, the same recorded image as in Example 1 was obtained. That is, in each of Nos. 1 to 3, there was little disorder and color mixture of the toner images of each color, and stable and clear color images could be reproduced, but the conditions of No. 1 were inferior in terms of color balance. did. On the other hand, under the conditions of Nos. 2 and 3, the color balance of the obtained color image was good, and the disorder and color mixture of the toner image were small and the sharpness was further excellent.

Example 3 The same conditions as in Example 1 were applied except for the following conditions.

The left rotation speed of the developer transport carrier 41 and the right rotation speed of the magnet body 42 at the time of each development of the developing devices 4A to 4D are set as shown in Table 2, and the ratio of the toner particles in the developer is 15 wt%.
And

As a result, the same results as in Example 1 were obtained. That is, in each of Nos. 1 to 3, there was little disorder and color mixture of the toner images of each color, and stable and clear color images could be reproduced, but the conditions of No. 1 were inferior in terms of color balance. did. On the other hand, under the conditions of Nos. 2 and 3, the color balance of the obtained color image was good, and the disorder and color mixture of the toner image were small and the sharpness was further excellent.

Although all of the above Examples 1 to 3 are based on the reversal development, the invention is not limited to this, and it is also possible to form an image by the regular development. A one-component developer composed of magnetic toner particles can also be used as the developer. Further, the present invention can be applied to an image forming body having a transparent insulating layer on a photoconductor layer to form an electrostatic latent image, or the present invention can be applied to an electrostatic recording type recording apparatus. Can be applied. Transfer of the toner images superposed on the image forming body to the recording paper by the method of the present invention is not limited to the electrostatic transfer method, but may be an adhesive transfer method or the like.

〔The invention's effect〕

According to the present invention, in each development for superposing the toner images on the image forming body, the oscillating electric field generated in the development area has a smaller amplitude in the subsequent development,
Since the frequency is increased and the amount of toner particles introduced into the developing area per unit time is increased as it is in the subsequent development, the transfer control of the toner particles by the oscillating electric field in each development is thereby performed. Easy to
In addition, the toner image is not disturbed or reversely transferred, so that a color image having stable and excellent sharpness can be reproduced.

[Brief description of drawings]

FIG. 1 is a schematic block diagram showing an example of a recording apparatus for carrying out the method of the present invention, and FIG. 2 is a partial sectional view showing a configuration example of a developing device. 1 ... Image forming body, 2 ... Charging device, 3A-3D ... Image exposure, 4A-4D ... Developing device, 5 ... Transfer device, 6 ... Separator, 7 ... Static eliminator, 8 ... Cleaning device, 9 ... Power supply, 41 ... Developer carrier, 42 ... Magnet body, 43 ... Development image pool, 44 ... Layer thickness regulating blade, 45 ... Stirring means, 46 ... Cleaning blade, 47 ...... Toner hopper, 48 ...... Toner supply roller.

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Claims (3)

[Claims] Claim: What is claimed is: 1. An electrostatic image is formed on an image forming body, and toner particles are ejected from a developer layer having a layer thickness which does not come into contact with the image forming body on a developer transport carrier under an oscillating electric field in a developing area to electrostatically discharge toner particles. In an image forming method in which an image forming step of adhering to an image is repeated a plurality of times to form a color image by superimposing toner images on an image forming body, the oscillating electric field has a smaller amplitude in a later image forming step. The image forming method is characterized in that the frequency is increased and the amount of toner particles conveyed by the developer conveying carrier to the developing zone per unit time is increased as in the subsequent image forming step. 2. The image forming method according to claim 1, wherein a developer is used in which the proportion of toner particles mixed with carrier particles is gradually increased toward the subsequent image forming step. 3. The image forming method according to claim 1, wherein the moving speed of the developer layer on the developer transporting carrier is sequentially increased in the subsequent image forming step.