JPH0713432A - Developing method and device - Google Patents

Abstract

PURPOSE:To eliminate the uneven density of an image by making a magnetic brush high in density and patterned in form. CONSTITUTION:A recessed part having width (a) and a projecting part having width (b) are repetitively formed on the surface of a cylindrical developing sleeve 32 as shown by (a) so that a cyclic pattern is entirely formed. As for the thickness of the developing sleeve 32, the sleeve 32 becomes thick in the recessed part and thin in the projecting part. A magnet roller is fixed and arranged inside the sleeve 32, and the magnetic brush MB for developing an electrostatic latent image on a photoreceptor drum is formed on the surface of the sleeve 32. The magnetic brush is made high-density by using developer having low magnetization magnetic carrier, and further the magnetic brush MB is made a pattern as shown by (b) owing to the cyclic change of the thickness of the sleeve 32. It is conceivable to make a material a pattern.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device suitable for being mounted on a digital type electrophotographic copying machine, a laser beam printer or the like, and more specifically, a dot latent image formed on an image bearing member The present invention relates to a developing device that develops with a magnetic brush using a two-component developer composed of particles and toner.

[0002]

2. Description of the Related Art Recently, digitalization of copying machines, printers and the like has been advanced with the full colorization and systemization of image forming apparatuses. For example, laser beam printers, etc., which scan a laser beam and form a latent image on a photosensitive member to record a desired image by turning the laser beam on and off, have become widely known. Its typical use is letters,
This is a binary recording of figures and the like. In this respect, since printing of characters and figures does not require halftone, the printer structure can be simplified.

By the way, there is known a printer capable of forming a halftone even with such a binary recording system. As such a printer, one using a dither method, a density pattern, or the like is well known. However, as is well known, a printer adopting the dither method or the density pattern method cannot obtain high resolution.

Therefore, in recent years, a method of forming a halftone pixel in each pixel without reducing the high recording density has been proposed. This is for forming a halftone by modulating the pulse width (PWM) of a laser beam with an image signal. According to this method, an image with high resolution and high gradation can be formed.

Here, a conventional example of the electrophotographic copying machine as shown in FIG. 3 will be briefly described.

First, the document D is set on the document table 17 with the side to be copied facing down. Then, copying is started by pressing the copy button. Unit 19 that integrates a document irradiation lamp, a short focus lens array, a CCD sensor, etc.
Then, by scanning while scanning the document D, the light reflected from the document surface of the illumination scanning light is imaged by the short focus lens array and is incident on the CCD sensor. The CCD sensor is composed of a light receiving section, a transfer section and an output section. C
The optical signal is converted into an electric signal in the CD light receiving section, and is sequentially transferred to the output section in synchronization with the clock pulse in the transfer section.
The output section converts the charge signal into a voltage signal, amplifies it, lowers its impedance, and outputs it. The analog signal thus obtained is subjected to known image processing to be converted into a digital signal and sent to the printer section. In the printer section,
Upon receiving the above image signal, an electrostatic latent image is formed as follows. The photosensitive drum 1 is rotationally driven around a central support shaft at a predetermined peripheral speed, and in the course of its rotation, a uniform charging process of positive polarity or negative polarity is performed by the charger 2 and the uniformly charged surface is exposed. Means 3, that is, ON corresponding to the image signal,
An electrostatic latent image corresponding to the original image is sequentially formed on the surface of the photosensitive drum 1 by scanning the light of the solid laser element that emits OFF light by the rotating polygon mirror that rotates at a high speed.

FIG. 6 shows a schematic structure of a laser scanning section (exposure means) 3 for scanning a laser beam in the above apparatus. When scanning the laser beam by the laser scanning unit 3, first, the solid-state laser element 3b is blinked at a predetermined timing by the light emission signal generator 3a based on the input image signal. Then, the laser light emitted from the solid-state laser element 3b is converted into a substantially parallel light flux by the collimator lens system 3c, and further scanned in the arrow C ₀ direction by the rotating polygon mirror 3d rotating in the arrow R3 direction and f
The photosensitive drum 1 by the θ lens groups 3e ₁ , 3e ₂ , and 3e _3.
A spot-like image is formed on the surface to be scanned (front surface) 1a.

An exposure distribution for one scanning of an image is formed on the surface to be scanned 1a of the photosensitive drum 1 by such scanning of the laser beam, and the surface to be scanned 1a is positioned perpendicular to the scanning direction for each scanning. Scanned surface 1a by scrolling a fixed amount
An exposure distribution corresponding to the image signal is obtained above.

FIG. 4 shows a vertical cross section of the developing device 5. In the drawing, 22 is a developing sleeve, 23 is a magnet roller fixedly arranged inside the developing sleeve, 26 and 27 are stirring screws, 25 is a regulating blade arranged to form a thin layer of developer on the developing sleeve surface, and 20 is Developer container, 20a
Is an opening of the developing container 20.

The developing process for developing the electrostatic latent image by the two-component magnetic brush method using the developing device 5 and the developer circulation system will be described below. First,
The developer drawn up by the magnetic pole N ₂ with the rotation of the developing sleeve 22 is regulated by the regulating blade 25 arranged perpendicularly to the developing sleeve 22 in the process of being conveyed with the magnetic poles S ₂ and N _1, and is developed. A thin layer is formed on the sleeve 22. When the thin-layered developer is conveyed to the main developing electrode S ₁ , a magnetic brush (peaking) is formed by the magnetic force. The developer on the developing sleeve 22 in which the electrostatic latent image on the photosensitive drum 1 has been developed by the magnetic brush formed in the shape of the spikes is then collected in the developing container 20 by the repulsive magnetic field of the magnetic poles N ₃ and N _2. .

The toner image thus formed on the photosensitive drum 1 is electrostatically transferred onto the transfer material by the transfer charger 6 as shown in FIG. After that, the transfer material is electrostatically separated by the separation charging device 7 and conveyed to the fixing device 15, where it is thermally fixed and an image is output.

On the other hand, the surface of the photosensitive drum 1 after the transfer of the toner image is repeatedly used for image formation after the cleaner 9 removes adhered contaminants such as transfer residual toner.

[0013]

However, in the above-mentioned conventional technique, when a halftone image having a reflection density of 0.3 or less is output, nonuniform unevenness occurs, which is very difficult to see. It is had. The reflection density of 0.3 or less is a density which is not often seen in a text original or the like, but is very high in a photographic image and the like, and a photographic image cannot be output in an electrophotographic apparatus like a conventional example. It was very difficult.

When the cause of the uneven unevenness was examined, the following was found. When forming a latent image of a highlight portion with a normal dot latent image, when viewed microscopically, the latent image on the photosensitive drum 1 is not a broad latent image like an analog latent image but a locally sharp latent image. ing. Therefore, when developing such a latent image with a two-component developer, the contact state of the magnetic brush greatly contributes to the development efficiency, so that non-periodic due to dot loss or the like corresponding to the unevenness of the ears of the magnetic brush. The unevenness is likely to occur.

Therefore, an object of the present invention is to provide a developing device in which unevenness of an image is eliminated by forming a periodic magnetic brush on the developing sleeve.

[0016]

The present invention has been made in view of the above circumstances, and accommodates a two-component developer composed of magnetic particles and non-magnetic toner, and an opening facing the image carrier. And a magnetic field generating member having a plurality of magnetic poles fixed inside the developer carrier, and the magnetic field generating member. In the developing device, in which the developer in the developing container is carried and conveyed on the surface of the developer carrier, and a magnetic brush is formed to develop the dot latent image on the image carrier, the developer carrier is , At least one of material, thickness, and shape has a periodic pattern for patterning the formation of the magnetic brush in the longitudinal direction and the rotating direction.

In this case, a member having a magnetic permeability different from that of the developer carrying member can be periodically attached to the surface of the developer carrying member in the longitudinal direction and the rotating direction.

Further, one period of the change pattern of the magnetic brush is set to 1.5 mm or less, or the strength of magnetization in the developing region of the magnetic particles is 120 (emu / cm).
³ ) or less, or the density of the magnetic brush may be 1 or more per 30 pixels of the dot latent image.

[0019]

[Function] Generally, when developing a dot latent image, it is sharper than an analog latent image, but it becomes a local latent image, so unevenness (drops of dots) corresponding to the ears of the magnetic brush occurs more. Easier to do. Therefore, when developing the dot latent image, it is desired that the state of the brush of the magnetic brush is denser.

According to the above-mentioned constitution of the present invention, the magnetic brush density is increased by using the magnetic particles of low magnetization, and further, the developer carrying member (eg developing sleeve).
Of at least one of the material, thickness, and shape of the magnetic field generating member having a periodic pattern in the longitudinal direction and the rotational direction of the magnetic field generating member fixed inside the developer carrier (for example, The magnetic force generated by the magnet roller) can be changed by providing a periodic pattern on the surface of the developer carrier, so that the magnetic brush of the developer on the developer carrier is highly dense and periodic. It is formed with various patterns. Therefore, the above-described non-periodic unevenness hardly occurs, and a good halftone image can be obtained in the entire density region.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. <Embodiment 1> In the present embodiment, formation of the magnetic brush MB with the developer is carried out by the developing sleeve (developer carrying member) 32
Is formed in a periodic pattern in the longitudinal direction and the rotation direction, the unevenness is formed on the outer circumference of the aluminum developing sleeve 32 as shown in FIG. 2A and the thickness thereof is as shown in FIG. As described above, the patterns were changed in the longitudinal direction and the rotation direction with a periodic pattern.

Here, in FIG. 2A, a = 20
0 μm, b = 100 μm, c = 800 μm, d = 100
It was set to 0 μm.

By providing a concavo-convex shape on the outer circumference of the developing sleeve 32 with such a pattern and changing the wall thickness, the magnetic force generated by the magnet roller 33 fixedly arranged inside the developing sleeve 32 is applied to the developing sleeve. Three
The thinner part of the two surfaces is relatively stronger than the thicker part. Therefore, when the developing sleeve 32 is coated with the developer, the magnetic brush MB is formed corresponding to the magnetic force, so that the magnetic brush MB is also patterned as shown in FIG.

As described above, when developing the dot latent image,
The density of the magnetic brush MB by the developer needs to be higher. As a method of changing the density of the magnetic brush MB on the developing sleeve 32, there is a method of changing the magnetic characteristics of the magnetic carrier (magnetic particles). FIG. 7 shows the strength of magnetization in the developing region of ferrite from 40 to 1.
The result of measuring the density of the magnetic brush MB on the conventional developing sleeve 32 using the carrier changed to 90 (emu / cm ³ ) is shown. The magnetic brush MB becomes denser as the strength of magnetization weakens. Next, the size of one pixel of the dot latent image was changed, and the image quality was evaluated using the magnetic carriers of these samples and the above-described patterned developing sleeve 32. As a result, in the case of a dot latent image, it was found that if the density of the magnetic brush MB is not high as the size of one pixel becomes small, the roughness will occur even if the above-described patterned developing sleeve 32 is used. Then, when the roughness was evaluated with respect to the number of magnetic brushes MB per 100 pixels, the results as shown in FIG. From this result, the magnetic brush M of the two-component developer on the developing sleeve 32 facing the photosensitive drum 1
It was found that by setting the density of B to be 1 or more per 30 pixels of the dot latent image, it is possible to eliminate the roughness and form an image with excellent highlight reproducibility and uniformity. Further, in order to make one line or more per 30 pixels, it is desirable to set the magnetization intensity in the developing region to 120 (emu / cm ³ ) or less, depending on the size of one pixel.

In this embodiment, as the magnetic carrier,
Coercive force Hc = 0 [Oe], saturation magnetization σs = 120 emu
/ Cm ³ , a ferrite carrier having an average particle diameter of 45 μm was used, and as the non-magnetic toner, a negatively chargeable polyester resin toner having an average particle diameter of 8 μm in which hydrophobic colloidal silica was externally added to colored resin particles was used. By using a mixture of the magnetic carrier and the non-magnetic toner as described above in a weight ratio of 6: 1 as a developer, a high-density magnetic brush MB can be formed.

A developing device using the developer and the developing sleeve 32 described above will be described. FIG. 5 shows a developing device used in the present invention. Here, 32 is the above-mentioned developing sleeve, 33 is a magnet roller having a magnet pattern as shown in FIG. 5, 31 is a developing roller constituted by combining the developing sleeve 32 and the magnet roller 33, 3
Reference numerals 6 and 37 are screws used for stirring and conveying the developer, 39 are stripping blades used for peeling the developer from the developing sleeve 32, and 38 is used for supplying the developer to the developing sleeve 32. Transport member,
Reference numeral 35 is a regulating blade arranged to form a thin layer of developer on the surface of the developing sleeve 32, and 30 is a developing container.

Using the developing device of the present invention as described above,
An embodiment of the electrophotographic copying machine as shown in FIG. 3 will be briefly described. First, the document D is set on the document table 17 with the side to be copied facing down. Then, copying is started by pressing the copy button. The document irradiation lamp, the short-focus lens array, and the CCD sensor serve as a unit 19 to scan the document D while irradiating the document D, and the light reflected from the document surface of the illumination scanning light is imaged by the short-focus lens array. Is incident on the CCD sensor. The CCD sensor is composed of a light receiving section, a transfer section and an output section. An optical signal is converted into an electric signal in the CCD light receiving part, and is sequentially transferred to the output part in synchronization with the clock pulse in the transfer part, and the charge signal is converted into a voltage signal in the output part, amplified, made into a low impedance and outputted. The analog signal thus obtained is subjected to known image processing to be converted into a digital signal and sent to the printer section. The printer unit receives the above image signal and forms an electrostatic latent image as follows.
The photosensitive drum 1 is rotationally driven at a predetermined peripheral speed around a central supporting shaft, and in the course of its rotation, a uniform charging process of positive polarity or negative polarity is performed by the charging device 2, and an image is formed on the uniform charging surface. The rotating polygon mirror 3 that rotates the light of the solid-state laser element 3b (see FIG. 6) that emits ON and OFF in response to a signal at high speed.
By scanning with d, the surface of the photosensitive drum 1 is
An electrostatic latent image corresponding to the original image is sequentially formed.

The developing process for developing this electrostatic latent image by the developing device shown in FIG. 5 and the circulation system of the developer will be described below. First, the developer drawn up by the magnetic pole N ₂ as the conveying member 38 rotates is regulated by the regulating blade 35 arranged perpendicularly to the developing sleeve 32 in the process of being conveyed to the magnetic poles S ₂ and N _1. Is
A thin layer is formed on the developing sleeve 32. When the thin-layered developer is conveyed to the main developing electrode S ₁ , a magnetic brush (peaking) is formed by the magnetic force. Since this magnetic brush is formed by a magnetic force, the wall thickness of the developing sleeve 32 is changed in the longitudinal direction and the rotating direction of the developing sleeve 32 in a periodic pattern as shown in FIG. By doing so, the magnetic brush MB made of the developer is formed in a pattern as shown in FIG. 1B from the relationship of the relative strength of the magnetic force (in addition to the relationship of the relative strength of the magnetic force, the regulation blade 35 is used. When the developer is regulated, the effect that the concave portion has a wider regulation gap than the convex portion is added. In this way, the electrostatic latent image is developed by the magnetic brush MB of the developer which is periodically patterned, and thereafter, the developer accumulated on the developing sleeve 32 by the repulsive magnetic field of the magnetic poles N ₃ and N ₂ is It is collected in the developing container 30 by the stripping blade 39.

The toner image formed on the photosensitive drum 1 in this way is, as shown in FIG.
1. The transfer charger 6 electrostatically transfers the image onto the transfer material supplied to the photosensitive drum 1 via the transport roller 12. After that, the transfer material is electrostatically separated by the separation charging device 7, is transported to the fixing device 15 via the transport member 13, is thermally fixed, and is discharged onto the paper discharge tray 16.

On the other hand, the surface of the photosensitive drum 1 after the transfer of the toner image is subjected to removal of adhering contaminants such as transfer residual toner by the cleaner 9, and is further precharged by the static eliminator 10 before the next image forming process. Be served.

As described above, an image obtained by developing the dot latent image on the photosensitive drum 1 by increasing the density of the magnetic brush MB by the developer and further periodically patterning the image is the entire density region. A good image was obtained over which non-periodic unevenness hardly occurred. <Embodiment 2> In Embodiment 1, in order to form the magnetic brush MB with the developer in the longitudinal direction and the rotation direction of the developing sleeve 32 in a periodic pattern as shown in FIG. 1B, Although the developing sleeve 32 (aluminum) is provided with irregularities on its outer side to change the wall thickness by providing a periodic pattern, in this embodiment, as shown in FIG.
By embedding iron in the developing sleeve 32 made of aluminum as shown in (b), the magnetic lines of force in the portion where the iron is embedded are concentrated and the magnetic force becomes relatively stronger than in other portions. The magnetic brush MB is formed with a periodic pattern in the longitudinal direction and the rotating direction of the developing sleeve 32.

Here, in FIG. 2B, a = 200.
μm, b = 100 μm, c = 600 μm, d = 1000
μm.

Further, in this embodiment, an image is output by the same image forming process using the developer using the same magnetic carrier as in the first embodiment.

As described above, the image obtained by developing the dot latent image on the photosensitive drum by periodically patterning the magnetic brush MB with the developer, as in the first embodiment, A good image was obtained over which non-periodic unevenness hardly occurred. <Embodiment 3> In Embodiments 1 and 2, the pattern on the surface of the developing sleeve 32 is a =
Although 200 μm and b = 100 μm are set, in the present embodiment, a and b are changed as shown in FIG. 9 and other configurations are the same as those in the first embodiment (c = 800 μm, d = 1000).
.mu.m), the magnetic force was changed in a pattern by changing the pattern on the surface of the developing sleeve 32. Further, in this example, the developer using the same magnetic carrier as in Example 1 was used, and an image was output by the same image forming process.

When the pattern on the surface of the developing sleeve 32 is roughened, the manufacturing is easy and the manufacturing cost can be reduced. Further, when the formation state of the magnetic brush MB on the developing sleeve 32 is observed, the magnetic brush MB formed per unit area from the magnetic characteristics of the magnetic carrier.
The number of ears of each pattern is substantially the same as in Examples 1 and 2, and when the period (a + b) of the magnetic force change pattern is 1.5 mm or less, the number of ears of each pattern on the developing sleeve 32 is equal to or smaller than that of each pattern. The formation condition was almost constant. When the period (a + b) was 1.5 mm or more, the number of ears for each pattern was almost the same, but the formation state of ears became random.

When an image is output in the developing device using these sleeves and the cycle (a + b) of the magnetic force change pattern is 1.5 mm or less as shown in FIG. Similarly to the above, a good image was obtained in which non-periodic unevenness hardly occurred over the entire density region.

[0037]

As described above, according to the present invention,
Using a two-component developer consisting of magnetic particles and non-magnetic toner,
A magnetic brush made of a developer is formed on a developer carrier (developing sleeve) in which a magnetic field generating member (magnet roller) is fixed, and the latent image on the image carrier (photosensitive drum) is visualized by this magnetic brush. In developing devices that are becoming
The aperiodic unevenness that has occurred corresponding to the pattern of the magnetic brush of the developer is caused by using the low-magnetization magnetic carrier for the developer, and the material, thickness, and shape of the developer carrier are periodically changed. By changing the pattern with a pattern, the magnetic force generated by the magnetic field generating member can be periodically changed on the surface of the developer carrying member, and the magnetic brush by the developer can be formed with a high-density periodic pattern. Therefore, non-periodic unevenness can be greatly reduced in the entire density region.

[Brief description of drawings]

FIG. 1A is an enlarged view of a developing sleeve surface pattern. FIG. 6B is an enlarged view of a magnetic brush formation pattern on the developing electrode.

FIG. 2A is an enlarged vertical cross-sectional view near the surface of the developing sleeve used in Examples 1 and 3. FIG. (B)
6A is an enlarged vertical sectional view of the vicinity of the surface of the developing sleeve used in Example 2. FIG.

FIG. 3 is a schematic diagram showing an example of the configuration of a digital electrophotographic copying apparatus.

FIG. 4 is a vertical cross-sectional view schematically showing the configuration of a conventional developing device.

FIG. 5 is a vertical cross-sectional view schematically showing the configuration of the developing device used in the examples of the present invention.

FIG. 6 is a schematic explanatory diagram of a laser scanning unit.

FIG. 7 is a table showing a relationship between carrier magnetization intensity and magnetic brush density.

FIG. 8 is a table showing the relationship between the number of magnetic brushes per 100 pixels and image unevenness when the developing sleeve of the present invention is used.

FIG. 9 is a table showing the relationship between the developing sleeve surface pattern period and image unevenness when the developing sleeve of the present invention is used.

[Explanation of symbols]

1 image carrier (photosensitive drum) 30 developing container 30a opening 32 developer carrier (developing sleeve) 32a member having different magnetic permeability (iron) 33 magnetic field generating member (magnet roller) MB magnetic brush N ₁ , N ₂ , N ₃ , S ₂ magnetic pole S ₁ developing main pole

Continued Front Page (72) Inventor Masaru Hibino 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (5)

[Claims] 1. A developer container containing a two-component developer comprising magnetic particles and a non-magnetic toner and having an opening facing the image carrier, and a developer carrying member rotatably disposed in the opening. A body and a magnetic field generating member having a plurality of magnetic poles fixed inside the developer carrier, and carrying and transporting the developer in the developing container to the surface of the developer carrier by the magnetic field generating member, In a developing device formed by forming a magnetic brush to develop a latent dot image on the image carrier, the developer carrier has at least one of material, thickness and shape in a longitudinal direction and a rotation direction. A developing device having a periodic pattern for patterning the formation of the magnetic brush. 2. The developing device according to claim 1, wherein a member having a magnetic permeability different from that of the developer carrying member is periodically attached to the surface of the developer carrying member in the longitudinal direction and the rotating direction. . 3. The one cycle of at least one of the material, thickness, and shape of the developer carrying member is set to 1.5 mm or less. Developing device. 4. The developing device according to claim 1, wherein the strength of the magnetization of the magnetic particles under the developing region is 120 (emu / cm ³ ) or less. 5. The developing device according to claim 1, wherein the density of the magnetic brush is one or more per 30 pixels of the dot latent image.