JPH04371978A - Method and device for forming picture image - Google Patents

Abstract

PURPOSE:To provide a device for picture image forming which makes use of the both advantages of a normal size toner and a small size toner. CONSTITUTION:In a first developing device 7, the following is used; a toner having 11mum average particle size and -20muc/g average Q/M (weight average), while in the second developing device 8, a toner having 6mum average particle size and -30muc/g average Q/M is used. An electrostatic latent image on the image carrier is faced at first to the first developing device 7 to develop a rather large area with high picture density, and then fine lines and dots remaining are developed in the second developing device 8.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to an image forming method and apparatus for use in printers, copiers, facsimile machines, etc. that form recorded images by electrophotography, and particularly relates to technology for obtaining high quality toner images. It is.

0002

2. Description of the Related Art Conventionally, in this type of image forming apparatus, when developing a latent image on an image bearing member such as a photoreceptor, a particle size of 10
Toner of about μm size is most commonly used. A developing method using toner having a smaller particle size has already been proposed (for example, Japanese Patent Laid-Open No. 153862/1983).

0003

[Problems to be Solved by the Invention] Since the surface area per unit weight of small particle size toner increases, the amount of charge per unit weight (hereinafter referred to as Q/M) generally tends to increase due to frictional charging with a carrier. be. When developing with such small particle size toner, it is necessary to increase the electric field that moves the toner to the latent image surface in the developing section (for example, by reducing the development gap or increasing the charging potential). , changing the configuration of the photoreceptor and carrier), but in addition to improving resolution, it also makes it possible to reproduce small dot patterns, which improves gradation reproduction using area gradation methods. On the other hand, the particle size is 10 μm.
Since the relatively large toner described above has a small charge per unit weight (hereinafter referred to as Q/M), it is easy to obtain appropriate development conditions, but on the other hand, there is a problem in that background smear is likely to occur. In order to prevent this, it is necessary to set the developing bias with a margin. For this reason, gradation reproducibility has to be sacrificed.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to propose an image forming method and apparatus that take advantage of the advantages of both normal particle size toner and small particle size toner.

[0005]

Means for Solving the Problems In order to achieve the above object, an image forming method according to claim 1 is an image forming method in which development is carried out by attaching toner to a latent image formed on an image bearing member. A first toner is attached to the latent image formed on the image carrier to perform development, and then a second toner having an average particle size different from that of the first toner is attached to perform development. It is something to do. The image forming method according to claim 2 is an image forming method in which development is performed by attaching toner to a latent image formed on an image bearing member, and in which a first toner is applied to a first latent image formed on the image bearing member. After the toner is attached and developed, a second latent image is formed, and a second toner having an average particle size different from that of the first toner is attached to the second latent image, and development is performed. It is something. The image forming method according to claim 3 is the image forming method according to claim 2.
In the image forming method, the second latent image is formed at a recording density different from that of the first latent image. The image forming apparatus according to claim 4 includes an image bearing member, a latent image forming means for forming a latent image on the image bearing member, a first developing means capable of developing the latent image with a first toner, and an average particle toner. a second developing means capable of developing a latent image with a second toner having a diameter different from that of the first toner; a mode in which the latent image is developed only with the first developing means; and a mode in which the latent image is developed only with the second developing means. a mode selection means for selectively executing one of a mode in which a latent image is developed by the first and second developing means and a mode in which the same latent image is developed by the first and second developing means; The present invention is characterized in that a speed switching means is provided for switching the moving speed of the surface of the image carrier according to the selected mode.

[0006]

[Operation] The invention as claimed in claim 1 subjects the latent image on the image carrier to a plurality of developing steps having mutually different average particle diameters, thereby:
A toner with a relatively large particle size has little density change and develops a wide latent image area, and a toner with a relatively small particle size works to develop a part of the latent image that changes finely. The invention according to claim 2 forms a latent image on the image carrier each time the development is performed using toners having different average particle diameters,
It functions to form an image by superimposing toner images on the image carrier. According to the third aspect of the present invention, each latent image is formed at a different recording density when forming a latent image on the image carrier for each development using toners having different average particle diameters. The invention of claim 4 is:
It is possible to select a developing means to be used for development from among a plurality of developing means using toners with different average particle diameters, and the development characteristics depending on the particle size of the toner used in the selected developing means, for example, the toner particle size When it becomes smaller, the moving speed of the image carrier is switched in response to, for example, a slowing of the developing speed.

[0007]

【Example】

[Embodiment 1] FIG. 1 is a schematic diagram of an image forming apparatus according to an embodiment of the present invention. First, the overall outline will be explained. In this apparatus, recorded images are formed using an electrophotographic method. The image carrier 1 has a photoconductive layer provided on an electrically grounded conductive substrate. In this embodiment, the image carrier 1 is a drum-shaped organic photoreceptor (OP
C) is used. Further, as an image exposure means, an image carrier is irradiated with light (hereinafter referred to as LD light) from a semiconductor laser (hereinafter referred to as LD) 5 using an optical system 4 comprising a rotating polygon mirror 2, a lens 3, etc. I am using it. L.D.
An image signal for driving 5 is transmitted from outside. First of all,
The surface of the image carrier 1 is uniformly -8 by the charger 6.
The image carrier is charged to approximately 00V, and then the charge on the portion of the image carrier that is irradiated with the LD light is erased by the optical system 4, and an electrostatic latent image is formed. Here, the lowest potential portion irradiated with the LD light is about -100V. Next, the formed electrostatic latent image is developed by a first developer 7 and a second developer 8 to form a toner image, as will be described later. The toner images formed by the two developing devices 7 and 8 are transferred onto a transfer material by a transfer charger 9. The transfer material on which the toner image has been transferred is separated from the image carrier 1 by a separation charger 10, and then transferred to a fixing device 11.
After the toner image is fixed on the transfer material, it is discharged outside the machine. On the other hand, the surface of the image carrier after the toner image transfer is cleaned by a cleaning device 12.

Next, the first developing device 7 and the second developing device 8 will be described in detail. The two developing units 7 and 8 each have conductive and non-magnetic sleeves 71 and 81 containing rotating magnetic rollers, developer layer thickness regulating members 72 and 82, and developer stirring members 73 and 83. A developer consisting of a mixture of a non-magnetic toner mainly made of resin and containing a colorant and a magnetic carrier is stored therein. This developing sleeve 71,
81 is driven to rotate in the forward direction of the moving direction of the image carrier 1 as shown by an arrow, and a bias is applied to form a developing electric field. With the above-described configuration, each of the developing devices 7 and 8 forms a magnetic brush by binding the developer near the sleeves 71 and 81 onto the sleeves 71 and 81 by the magnetic force of the magnetic roller.
The amount of developer conveyed is controlled by the sleeve developer layer thickness regulating members 72 and 82 to supply a predetermined amount of developer to the surface of the image carrier 1, and toner, which is a charged particle, is moved as the sleeve developer layer thickness regulating members 72 and 81 rotate. Reversal development is performed by attaching the electrostatic latent image on the image bearing member to the portion where the charge has been erased.

In this example, the carrier is a particle made of a magnetic material such as ferrite and coated with a resin, or a particle containing magnetic powder in the resin, and the weight average particle diameter is is 20~100μ
It is preferable to use m. In the first developing device 7, the toner has an average particle size of 11 μm and an average Q/M of -20.
μc/g (both averages are weight averages), and in the second developing device 8, the average particle size is 6 μm and the average Q/M is -30 μm.
c/g is used. The bias applied to the sleeve is suitably in the range of -300 to -700v for the first developing device 7 and -500 to -800v for the second developing device 8. Further, the distance between the image carrier 1 and the sleeves 71, 81 is preferably 200 to 1000 μm depending on the particle size of the carrier.

In the above configuration, the electrostatic latent image on the image carrier 1 first faces the first developing device 7, and the toner from the first developing device 7 adheres to the portion of the image carrier 1 from which the electric charge has been erased. do. In the development by the first developing device 7, a portion having a relatively large area and high image density is obtained. The surface potential of the image carrier 1 increases by an amount corresponding to the amount of charge held by the attached toner. However, normally the potential does not reach saturation, and 2
It only increases by about 00 to 300v. Furthermore, because the toner is first developed with a large particle size, fine dots and lines remain undeveloped. However, if you do not set the development conditions so that the development is moderate, you will end up with crushed dots or lines. Then, the toner image by the first developing device 7 is directly opposed to the second developing device 8 as the surface of the image carrier moves, and the toner from the second developing device 8 remains even after the development by the first developing device 7. Develop the electrostatic latent image. Development using the small particle diameter toner from the second developer 8 is not so much about increasing the amount of toner adhesion as it is about reproducing minute parts such as edges, dots, and lines of the image that were not developed by the first developer 7. The main focus is on As a result, the resulting image has improved resolution and gradation reproducibility.

[0011] As a developing method using a two-component developer as in this embodiment, the developer on the sleeve is brought into contact with the image carrier 1, and the toner is moved on the electrostatic latent image surface while being charged with electricity. There are two methods: applying force in close proximity to move the toner from the carrier to the image carrier 1 (contact development), and keeping the two in non-contact and applying electric force relatively remotely to transfer only the toner to the electrostatic latent image surface. A method (non-contact development) is known. In particular, in the latter case, since the toner image once formed is not damaged by the magnetic brush, a high-quality image can be obtained. In order to realize this method, it is necessary to make the magnetic brush as short as possible and to sandwich the development gap, and for this purpose it is important to make the carrier small. Furthermore, it is preferable to apply a voltage containing a vibration component as a developing bias. Also, in the former method, it is necessary to make the magnetic brush as flexible as possible and to reduce its mechanical effect on the toner image attached to one surface of the image carrier, and for this purpose, the particle size of the carrier is made small. This is effective. When a non-contact developing method is employed in the second developing device 8, problems such as disturbing the toner image formed by the first developing device 7 or mixing toner into the second developing device 8 can be prevented.

[Embodiment 2] In the image forming apparatus of Embodiment 1, the toner in the first developing device 7 has a toner particle size of 1
Using a red toner with a Q/M of -20 μc/g at 1 μm,
The toner in the second developing device 8 has a particle size of 7 μm and a Q/M of -
Development was carried out using 30 μc/g blue toner and other conditions similar to those of Example 1. As a result, red toner with large particle size mainly adhered to areas with relatively little change in density, and only blue toner with small particle size adhered to edges, halftone dots, lines, etc. [Example 3] In the image forming apparatus of Example 1, the developer in the first developing device 7 and the second developing device 8 was replaced. In this case, the procedure is to first form the fine parts of the image and then obtain the density. The effects of the invention were sufficiently confirmed in this example as well. [Example 4] In the image forming apparatus of Example 1, after the electrostatic latent image formed by image exposure is developed by the first developer 7, the second developer 8, transfer charger 9, separation charger 10, The image carrier 1 is rotated with the cleaning device 12 etc. inactive, and when the toner image formed by the first developing device 7 faces the charger 6, the charger 6 is turned again.
The surface of the image carrier 1 on which the toner image is formed is uniformly charged and subjected to image exposure, and the electrostatic latent image thus formed is developed by the second developer 8 (the first developer 7 is The final toner image thus formed was transferred to a transfer material, separated and fixed, and the surface of the image carrier was cleaned. Here, the two developing devices 7 and 8 contain the same developer as in the first embodiment. The above-mentioned image exposure has different electrostatic latent image patterns between the first time to form an electrostatic latent image developed by the first developing device 7 and the second time to form an electrostatic latent image developed by the second developing device 8. Write. 1
In the second image exposure, a pattern with a relatively low spatial frequency (
(with a gentle density gradient, such as a wide area area) is written, and the electrostatic latent image thus formed is developed with toner of large particle size from the developing device 7. In the second image exposure,
Patterns with relatively high spatial frequencies (edges, thin lines, etc.)
is written, and the electrostatic latent image thus formed is developed with toner of small particle size from the second developing device 8. As a result, toner images are synthesized on the image carrier 1, and an image with high contrast, good halftone reproducibility, and resolution can be obtained.

[Embodiment 5] In the image forming apparatus of Embodiment 1, the electrostatic latent image formed by image exposure is transferred to the second developing device 8.
After developing (first developing device 7 is inactive), transfer charger 9, separation charger 10, cleaning device 1
When the image bearing member 1 is rotated with the second developing device 8 inactive and the toner image formed by the second developing device 8 faces the charging charger 6, the image bearing member on which the toner image is formed by the charging charger 6 again. 1 surface is uniformly charged and subjected to image exposure, the electrostatic latent image thus formed is developed by the first developer 7 (the second developer 8 is inactive), and the final image formed thereby is Transfer the toner image to a transfer material and separate it.
In addition to fixing, the surface of the image carrier was cleaned. Here, the two developing devices 7 and 8 contain the same developer as in the first embodiment. The above-mentioned image exposure has different electrostatic latent image patterns between the first time to form an electrostatic latent image developed by the second developing device 8 and the second time to form an electrostatic latent image developed by the first developing device 7. Write. In the first image exposure, a pattern with a relatively high spatial frequency (edges, thin lines, etc.) is written, and the electrostatic latent image formed thereby is developed with toner of small particle size from the second developer 8. In the second image exposure, a pattern with a relatively low spatial frequency (a pattern with a gentle density gradient such as a wide area) is written, and the electrostatic latent image formed thereby is transferred to a toner with a large particle size from the developer 7. Develop it with As a result, as in Example 4, toner particles having different particle sizes constituted different portions, and a toner image with good image quality was obtained.

[Embodiment 6] FIG. 2 is a schematic configuration diagram of an image forming apparatus according to this embodiment. In this device,
Two chargers, two optical systems, and two developing devices are provided (first charger 6, second charger 6a, first optical system 4, second optical system 4a, first developing device 7, second developing device). Developing device 8). The two developing units 7 and 8 have the same configuration as in Example 1, and the first developing unit 7 has an average particle size of 11.
A toner with an average Q/M of −20 μc/g in μm (both averages are weight averages) is used, and the second developer 8 has an average particle size of 6
A toner with an average Q/M of −30 μc/g in μm is used. The two optical systems 4 and 4a use LDs like the optical system in the first embodiment, and in this example they share the rotating polygon mirror 3.

First, the surface of the image carrier 1 is uniformly charged to about -800V by the first charger 6, and then,
The first optical system 4 erases the charge on the portion of the image carrier 1 that is irradiated with the LD light, and an electrostatic latent image is formed. Here, the lowest potential portion irradiated with the LD light is about -100V. Next, the formed electrostatic latent image is developed by toner, which is a charged particle, in the first developing device 7. The toner adheres to the portion of the image carrier 1 from which the charge has been erased. The image carrier 1 on which the toner image has been formed in this manner is uniformly charged again by the second charger 6a. Further, an electrostatic latent image is formed by the second optical system 4a, and this electrostatic latent image is developed by the second developing device 8. As a result, a toner image in which the two types of toner are combined is formed on the image carrier 1. This toner image is transferred onto a transfer material by a transfer charger 9. Then, the transfer material with the toner image transferred is
After being separated from the image carrier 1 by a separation charger 10, the toner image is passed through a fixing device 11 to be fixed on a transfer material, and then discharged outside the apparatus. On the other hand, the surface of the image carrier after the toner image transfer is cleaned by a cleaning device 12.

In the device of this embodiment, two optical systems 4 are used.
, 4a can be configured to input image data from different signal sources. FIG. 3 is a block diagram showing an example of the electrical equipment section in that case. This example uses an image reading device such as a scanner and a computer that processes character/line information as different signal sources. When image information is input from the scanner, the signal processing circuit 30
Then, signal processing is performed accordingly, and the image data is stored in the buffer 31. Data is sent to the first LD drive circuit 32 that drives the first LD 33 according to a control signal from the control section 38 . As a result, the first LD 33
irradiate. Further, when a signal consisting of characters, lines, etc. formed by a computer is input, the signal processing circuit 34 performs signal processing accordingly and the image data is stored in the buffer 35, and the second LD 37 The data is sent to a second LD drive circuit 36 that drives the second LD 37, thereby causing the second LD 37 to irradiate the image carrier 1. Each optical system 4, 4a is attached to the same image carrier 1.
Image exposure is performed by irradiating D light, but when forming an image by combining the two, it is necessary to take the irradiation position into consideration and shift the timing of LD drive. The control section 38 performs this control. In this way, image information requiring higher resolution can be written in the second optical system 4a and developed in the second developer 8 with good detail reproducibility.

[Embodiment 7] FIG. 4 is a schematic diagram of an image forming apparatus according to this embodiment. The schematic structure of the apparatus of this embodiment is the same as that of the apparatus of embodiment 6 shown in FIG. 2 except for the difference in the structure of the optical system. The apparatus of this embodiment also includes two optical systems 4, 4b as in the sixth embodiment, but the two optical systems 4, 4b used in this embodiment have different recording densities with respect to the image carrier, and the first optical System 4 is 300d
pi, the second optical system 4b exposes the image carrier 1 at 600 dpi. In this example, the rotating polygon mirror is not shared, and the diameter of the irradiation beam and the main scanning direction and sub-scanning direction are approximately 1/2 that of the first optical system 4 in the second optical system 4b. If a rotating polygon mirror is used for every other surface on the low density side, the rotating polygon mirror can be shared by two optical systems as in the eighth embodiment. When an image is formed under the same conditions as in Example 6, the electrostatic latent image formed at high recording density by the second optical system 4b is developed with small particle diameter toner from the second developing device 8, resulting in high resolution. Even image information can be faithfully reproduced.

[Embodiment 8] In this embodiment, the apparatus of Embodiment 1 shown in FIG. 1 is used, and the following three modes are provided in the developing process by sequence control. The rotation speed (i.e. recording speed) is changing. Mode ■: Uses only small particle size toner
Rotation speed 100mm/sec mode ■; Uses only large particle size toner
Rotation speed 150mm/sec mode ■
; Use both toners
In the mode (2) at a rotational speed of 200 mm/sec, an image with high resolution can be obtained by developing the formed electrostatic latent image with small particle diameter toner of the second developing device 8 over time. This toner is Q/M
is large and requires strong electrostatic force to develop.
By lowering the development speed, more toner can be supplied to the development area. As a result, developability and image quality are improved. In mode (2), development is performed by the first developing device 7. The stored toner has a small Q/M, can be developed relatively easily, and is suitable for high-speed development. Therefore, this mode is executed when giving priority to recording speed. Mode ■ uses two developing devices for development, so
Furthermore, high-speed development becomes possible. This mode is also executed when giving priority to recording speed. Further, it is preferable to set conditions for each process such as charging, exposure, transfer, cleaning, and fixing according to the speed of each mode and the toner used.

[0019]

According to the invention as claimed in claim 1, a toner with a relatively large particle size can develop a wide latent image area with little change in density, and a toner with a relatively small particle size can develop fine changes in the latent image. This has the advantage of being able to form a toner image that takes advantage of the strengths of each toner and has high contrast, excellent gradation reproducibility, and high resolution. Furthermore, according to the inventions of claims 2 and 3, a latent image is formed on the image carrier for each development using toners having different average particle sizes, thereby forming a latent image that matches the particle size of the toner. Therefore, in addition to the effect of the invention of claim 1, there is an effect that a toner image of even better image quality can be formed. According to the invention of claim 4, since the developing means to be used for development can be selected from among the plurality of developing means using toners having different average particle diameters, development can be performed using toner having an optimum particle diameter depending on the image to be recorded. In addition, since the moving speed of the image carrier is changed according to the development characteristics of the toner particle size used in the selected developing means, the advantages of the toner can be fully utilized and excellent performance can be achieved. This has the excellent effect of providing an image forming apparatus that can form toner images of image quality.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of an image forming apparatus according to another embodiment of the present invention.

FIG. 3 is a block diagram showing an example of an electrical component in the example of the image forming apparatus shown in FIG. 2;

FIG. 4 is a schematic configuration diagram of an image forming apparatus according to still another embodiment of the present invention.

[Explanation of symbols]

1 Photoreceptor drum
, 4 (first) optical system 4a, 4b second optical system
, 6 (first) electrification charger 6a second electrification charger
, 7 First developing device 8 Second developing device
, 9 Transfer charger 10 Separate charger
, 11 Fixing device 12 Cleaning device

Claims (4)

[Claims] Claim 1: An image forming method in which development is performed by attaching toner to a latent image formed on an image carrier, in which development is performed by attaching a first toner to the latent image formed on the image carrier. After that, a second toner having an average particle size different from that of the first toner is attached to perform development. 2. An image forming method in which development is performed by attaching toner to a latent image formed on an image carrier, in which development is performed by attaching a first toner to a first latent image formed on the image carrier. After that, a second latent image is formed, and a second toner having an average particle size different from that of the first toner is attached to the second latent image for development. 3. The image forming method according to claim 2, wherein the second latent image is formed at a recording density different from that of the first latent image. 4. An image bearing member, a latent image forming means for forming a latent image on the image bearing member, a first developing means capable of developing the latent image with a first toner, and an average particle diameter of the first toner. A second developing means capable of developing a latent image with a second toner different from the first toner, a mode in which the latent image is developed only with the first developing means, and a mode in which the latent image is developed only with the second developing means. mode selection means for selectively executing one of a developing mode and a mode in which the same latent image is developed by the first and second developing means;
An image forming apparatus comprising: speed switching means for switching the moving speed of the image carrier surface according to the mode selected by the mode selection means.