JPH0922191A - Developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the adhesion of carrier and carrier scattering, to obtain complete image quality and to apply the device to a superposing developing method. SOLUTION: Plural lines of developing magnetic poles 5(5a to 5d) obtained by alternately arranging different polarities are arrayed in a magnetic member 3 corresponding to an effective developing area Y opposed to a latent image carrier 4, and at least one or more carrying magnetic poles 6 (6a to 6d) obtained by alternately arranging the different polarites continuously from the developing magnetic poles 5a and 5d near to a boundary in the area Y are arrayed in an area adjacent to the area Y, then a distance A between the adjacent magnetic poles of the respective magnetic poles 5 and 6 in the area Y and the area adjacent to the area Y is set nearly the same, and a pair of developing magnetic poles 5b and 5c near the closest part of a developer carrier 1 to the latent image carrier 4 is arranged to put the closest part in between, and further the peak value B of the magnetic flux density in the radial direction on the surace of the developer carrier 1 of the respective magnetic poles 5 and 6 is set nearly the same.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device used in an image forming apparatus such as an electrophotographic copying machine or a printer for forming a monochromatic or multicolor image, and more particularly, to a developing device on a developer carrying member. A thin layer of a magnetic brush composed of a component developer is formed, and the thin layer of the magnetic brush is carried and conveyed so as not to contact the latent image carrier, and a developing bias composed of an AC voltage superimposed with a DC voltage is applied. The present invention relates to an improvement in a developing device that applies an electric charge to a developer carrier to develop an electrostatic latent image on the latent image carrier.

[0002]

2. Description of the Related Art In a conventional image forming apparatus such as a copying machine, an electrostatic latent image formed on a latent image carrier is developed by a developing device, and the developed image (visual image) is transferred onto recording paper. It is configured to copy an image or the like. At that time, as a developing device for developing the electrostatic latent image formed on the latent image carrier, a two-component developer composed of toner and a magnetic carrier is brought into contact with the surface of the latent image carrier so that the electrostatic latent image is formed. There are many proposals that employ a so-called contact-type two-component magnetic brush developing device that visualizes. Although this developing device has a problem that the toner density in the developer needs to be controlled and a stirring mechanism for the developer is required, resulting in an increase in size of the device, in view of image quality characteristics and maintainability, It is the mainstream.

However, in the above-mentioned contact type two-component magnetic brush developing device, since the magnetic brush mechanically rubs the surface of the latent image carrier, image defects such as so-called brush marks and sweeping due to the magnetic brush are likely to occur. . In particular, the contact type two-component after the second developing step in the so-called overdeveloping method, in which a plurality of color images are formed on the latent image carrier and the color images are collectively transferred to a recording paper to obtain a color image When a magnetic brush developing device is used, there is a drawback that the toner image is likely to be disturbed due to brushing or sweeping due to the magnetic brush on the preceding toner image. In addition, the first-stage toner image is scraped off from the latent image carrier in the second and subsequent second-stage development steps and mixed in the second-stage developer, resulting in a decrease in the concentration of the first-stage image and a significant decrease in the life of the second-stage developer. There is also the drawback of doing so. Therefore, in order to avoid these technical problems, a large number of so-called non-contact type two-component magnetic brush developing devices have been proposed which develop without developing the developer on the surface of the latent image carrier.

A conventional non-contact type two-component magnetic brush developing device of this type is disclosed in, for example, JP-A-56-144452, a thin layer of a two-component developer comprising toner and a magnetic carrier on a developing roll (developing magnetic field). Brush) to bring the surface of the latent image carrier and the developing magnetic brush into non-contact with each other,
It is disclosed that a developer layer is developed by giving a disturbing effect by a magnetic, electrical or mechanical element. Further, in JP-A-60-176069, magnetic poles are arranged so as to avoid a position where the developing roll and the latent image carrier are closest to each other.
It is disclosed that a developing layer is developed under an oscillating electric field while applying a horizontal magnetic field component in the developing roll circumferential direction.

However, JP-A-56-144452
In the developing device disclosed in the publication, in order to give the developer layer a disturbing effect by the above-mentioned elements, the entire developer layer is magnetic,
It will vibrate electrically or mechanically. Therefore, when the disturbance effect is increased in order to obtain a sufficient image density, the vibration of the developer layer increases, and the developer layer comes into contact with the surface of the latent image carrier. When the contact occurs, there is a technical problem that so-called carrier adhesion occurs in which carrier particles in the two-component developer adhere to the surface of the latent image carrier.

When the carrier adheres, the carrier transferred onto the latent image carrier comes into contact with the recording paper in the transfer area together with the toner image, so that the toner image is chipped or missing. Further, since the carrier flows out little by little from the developing device, the life of the developer is shortened. Further, when used after the second development in the overlap development method, there is a technical problem that the front toner image is disturbed or scraped due to the contact of the developer layer with the surface of the latent image carrier. Can be seen.

On the other hand, in the developing device disclosed in JP-A-60-176069, the magnetic brush is strongly restrained on the developing roll by the action of the horizontal magnetic field. For this reason, the toner is developed only from the upper layer portion of the magnetic brush, and there is a technical problem that it is difficult to obtain a sufficient image density. Further, in order to obtain a sufficient image density, it is necessary to increase the oscillating electric field density, so that the action of the oscillating electric field causes the developer layer to vibrate and the developer layer to come into contact with the surface of the latent image carrier. Will end up. When contact occurs, there is a technical problem that carrier adhesion occurs as described above.

Further, in the case of being used after the second development in the overlap development method, the contact of the developer layer with the surface of the latent image carrier causes the disturbance and scraping of the former toner image. Challenges are seen. When the amplitude of the oscillating voltage is increased in order to obtain a sufficient image density, the electric field acting in the direction of causing the pre-stage toner image on the latent image carrier to fly back to the developing roll side becomes strong, so that the pre-stage toner There are also technical problems such as electrical distortion and scraping of images.

Therefore, in order to avoid the above-mentioned technical problems, various techniques regarding the arrangement and configuration of magnetic poles inside the developing roll have been proposed. For example, JP-A-63-210
In the developing device disclosed in Japanese Patent No. 874, the magnetic pole pitch of the portion where the developing roll faces the latent image carrier is increased as the developing roll moves away from the closest contact point with the latent image carrier, and the height of the magnetic brush is increased. It is configured as follows.

Further, in the developing device disclosed in JP-A-1-172882, a substantially central portion of the developing magnetic pole is arranged at the closest portion between the developing roll and the latent image carrier, and 6 mm before and after the developing magnetic pole. A developing magnetic pole and a complementary magnetic pole having a different polarity are provided within the developing roller and the closest distance d between the developing roller and the latent image carrier is 0.3 to 0.
The distance S is between 7 mm, and the distance S between the ears of the developer on the developing magnetic pole and the latent image carrier is between (0.1 to 0.6) × d (mm).

Further, JP-A-63-278082,
The developing device disclosed in JP-A-63-278083 is provided on the opposite side of the developer bearing member from the electrostatic latent image bearing member so as to face the developing unit that supplies toner particles to the electrostatic latent image bearing member. The
Further, it is configured to have a magnetic field generating means having a plurality of magnetic poles that are close to each other.

[0012]

However, in the developing device disclosed in Japanese Patent Laid-Open No. 63-210874, the magnetic brush on the magnetic pole at the developing roll position away from the closest contact point with the latent image carrier is Since the chain structure of the developer becomes long and the gap between the chains becomes wide and rough, it is difficult to form a uniform thin layer of developer, resulting in poor image uniformity and poor edge reproduction of line images. Has technical challenges. Further, since the chain structure of the developer on the magnetic pole becomes long and the centrifugal force acting on the carrier becomes strong, the chain structure of the developer becomes longer when the developing roll is rotated than when it is stationary, and the latent image carrier of the developer layer is formed. There is also a technical problem that carrier scattering occurs as well as contact with the surface. When the carrier is scattered, the image quality is deteriorated as in the case where the carrier is adhered, and the life of the developer is shortened. Further, the carrier is contaminated.

On the other hand, in the developing device disclosed in Japanese Unexamined Patent Publication No. 1-172882, since the developing roller and the latent image bearing member are provided with a developing pole and a substantially central portion of the developing magnetic pole, the developing roller is located in the developing area. Only one magnetic pole is arranged in the area where the electrostatic latent image is developed by the above developer. In such a configuration, in the approximately central portion of the developing magnetic pole, since the chain structure of the magnetic brush has a wide interval as described above, poor image uniformity and poor edge reproduction of the line image due to the effect of the chain structure. Has a technical problem that occurs.

Further, when the developer layer thickness above the magnetic pole is set within the above-specified range, the amount of the developer per unit area on the developing roll becomes small. Therefore, in order to obtain a sufficient image density, the oscillating electric field is required. It is necessary to increase strength. Therefore, when the apparatus is used in the overdeveloping method, it is difficult to achieve both color mixture on the pre-stage toner image on the latent image carrier and image density. Further, in order to obtain a sufficient image density, it is necessary to increase the strength of the oscillating electric field, so that there is a problem that the action of the oscillating electric field causes the disturbance, scraping, and carrier adhesion of the pre-stage toner image as described above. is there.

Further, JP-A-63-278082,
In the developing device disclosed in JP-A-63-278083,
A plurality of magnetic poles that are close to each other are arranged inside the effective developing area (area that effectively contributes to the development). The state of the magnetic field formed on the plurality of magnetic pole groups depends on the magnetic pole outside the effective developing area. Therefore, it is difficult to form a uniform developer layer.

FIG. 7 is a schematic diagram showing the state of magnetic force lines in the effective developing area. In FIG. 7, 110 is a photosensitive drum as a latent image carrier, 111 is a developing roll consisting of a rotatable non-magnetic cylindrical sleeve 112 and a magnet roll 113 fixedly installed in the sleeve 112, S1, N.
2, S2, N3 are a plurality of magnetic poles inside the effective developing area, N1, S3
Are magnetic poles arranged on both outer sides of the effective development area and having a magnetic flux density in a direction perpendicular to the surface of the sleeve 111 larger than the magnetic poles inside the effective development area.

Further, in FIG. 7, arrows indicate the general directions and directions of the magnetic force lines, and due to the influence of the magnetic force lines formed between the magnetic poles N1 and S3, between the magnetic poles S1 and N2 and between the magnetic poles S2 and N3. Between the photosensitive drum 110 and the sleeve 11
In the gap of 2, the reversal of the direction of the magnetic field component in the horizontal direction (hereinafter referred to as the horizontal magnetic field) occurs on the surface of the sleeve 110. Therefore, the developer layer on the sleeve 112 is arranged along the magnetic field lines between the adjacent magnetic poles near the surface of the sleeve 112, and the magnetic field lines formed between the magnetic poles N1 and S3 apart from the surface of the sleeve 112. Therefore, it is difficult to form a uniform developer layer between the magnetic poles S1 to N3. Also, the sleeve 112
Since the magnetic field formed by the magnetic poles is attenuated as the distance from the surface of the magnetic pole is decreased, the magnetic binding force acting on the tips of the magnetic brushes arranged along the magnetic lines of force formed between the magnetic poles N1 and S3 becomes weak, and carrier adhesion Also, there is a technical problem that carrier scattering occurs.

Further, the developing roll 11 is arranged so that the developer layer is not arranged along the magnetic lines of force formed between the magnetic poles N1 and S3.
When the amount of developer per unit area on 1 is small, it is necessary to increase the oscillating electric field strength in order to obtain a sufficient image density. Therefore, when the apparatus is used in the overdeveloping method, it is difficult to achieve both the color mixture on the pre-stage toner image on the photoconductor drum 110 and the image density. Further, in order to obtain a sufficient image density, it is necessary to increase the strength of the oscillating electric field, so that the action of the oscillating electric field causes the disturbance, scraping, and carrier adhesion of the pre-stage toner image as described above. .

Further, another technical problem arises even when the reversal of the direction of the horizontal magnetic field does not occur in the gap between the photoconductor drum 110 and the sleeve 112 between the magnetic poles N1 and S3. That is, the states of the magnetic brushes on the magnetic poles S1 and N3 inside the effective developing area are affected by the magnetic poles N1 and S3 whose magnetic flux density in the direction perpendicular to the surface of the sleeve 112 is larger than the magnetic pole inside the effective developing area. More specifically, due to the magnitude relationship of the magnetic flux density in the vertical direction of the magnetic poles, the peak value of the magnetic flux density in the horizontal direction is greater between S1 and N1 than between S1 and N2, and between N3 and S3. Is N3 ~
It is larger than between S2. Therefore, the position where the magnetic flux density in the horizontal direction becomes 0 on the magnetic poles S1 and N3 does not coincide with the position where the magnetic flux density in the vertical direction has a peak, and exists in the inner side of the effective developing area from the peak position. To do. At this time, since the carrier chains of the magnetic brush are arranged vertically at the position where the magnetic flux density in the horizontal direction is 0, the magnetic brush carrier chains are arranged vertically. Does not match the position. Therefore, at the position where the magnetic brush stands perpendicular to the surface of the sleeve 112 on the magnetic poles S1 and N3, the magnetic restraining force acting on the tip of the magnetic brush becomes weak, and carrier adhesion and carrier scattering occur. Will lead to.

Therefore, the present invention has been made in view of such a background, and an object thereof is to prevent occurrence of carrier adhesion and carrier scattering, obtain sufficient image quality, and perform overdevelopment. It is to provide a developing device applicable to the method.

[0021]

That is, the present invention provides:
As shown in FIG. 1, a rotatable non-magnetic sleeve 2 has a developer carrier 1 on which a magnet member 3 is fixedly installed, and the developer carrier 1 is arranged to face a latent image carrier 4. A two-component developer composed of a non-magnetic toner and a magnetic carrier is carried on the developer carrier 1 in a non-contact state with the latent image carrier 4, and between the latent image carrier 4 and the developer carrier 1. In an effective developing area Y facing the latent image carrier 4 in a developing device for developing an electrostatic latent image Z on the latent image carrier 4 by applying an alternating electric field EAC on which a DC component is superposed. A plurality of rows of developing magnetic poles 5 (for example, 5a to 5d) in which different polarities are alternately arranged are arranged on the corresponding magnet member 3, and a boundary in the effective developing area Y is provided in an area adjacent to the effective developing area Y. Different polarities are arranged alternately from the developing magnetic poles 5a and 5d. At least one conveying pole 6
(For example, 6a to 6d) are arranged, and the magnetic pole intervals A of the developing magnetic poles 5 in the effective developing area Y and at least one or more carrier magnetic poles 6 in the area adjacent to the effective developing area Y are adjacent to each other.
Are set to be substantially the same, and a pair of developing magnetic poles 5b, 5 near the closest position between the developer carrying member 1 and the latent image carrying member 4 are provided.
c is arranged so as to sandwich the closest portion, and further, the developer carrying member 1 of each of the developing magnetic poles 5 and the one or more carrying magnetic poles 6.
The peak value B of the magnetic flux density in the radial direction on the surface is set to be substantially the same.

In such technical means, the effective developing area Y means an area where the toner acts on the latent image carrier 4 to effectively develop the latent image on the latent image carrier 4, For example, in the case of a two-component alternating electric field developing system type, the toner is produced by applying the same alternating electric field as that applied during development in a state where the developer carrier 1 and the latent image carrier 4 are stopped. Means a region that flies to the latent image carrier 4.

The magnet member 3 is not particularly limited to a roll shape, and the method of forming the magnetic poles 5 and 6 provided on the magnet member 3 is a sheet magnetized in advance around the core material. -Shaped magnet may be fixed, or it may be directly magnetized to the magnetic roll core material,
Alternatively, the design may be changed as appropriate by providing a separate magnetic pole member on the core material.

Further, the target magnetic pole of the present invention may be the developing magnetic pole 5 in the effective developing area Y and the one carrying magnetic pole 6 separated from the effective developing area Y adjacent to the effective developing area Y, but the effective developing area Y From the viewpoint of generating a more uniform magnetic force distribution among the respective developing magnetic poles 5 in the inside, the positional relationship between the plurality of upstream and downstream magnetic poles deviating from the effective developing region Y and the magnetic force value are also as much as possible. It is preferable to set the same as the developing magnetic pole 5.

The developing magnetic poles 5 (5a to 5d) and the carrier magnetic poles 6 (6a to 6) in the area adjacent to the effective developing area Y are also provided.
The peak value B of b) is preferably 200 Gauss or more from the viewpoint of ensuring a sufficient magnetic binding force for carriers.

[0026]

According to the technical means as described above, the adjacent magnetic pole intervals A of each developing magnetic pole 5 in the effective developing area Y and at least one or more carrying magnetic poles 6 in the area adjacent to the effective developing area Y are Since the peak values B of the magnetic flux densities in the radial direction on the surface of the developer carrying member 1 of the developing magnetic poles 5 and the one or more carrying magnetic poles 6 are set to be substantially the same, it is effective. The state of the magnetic field formed on the plurality of developing magnetic poles 5 in the developing area Y is not affected by the carrier magnetic pole 6 outside the effective developing area Y, and a uniform thin layer of developer is formed in the effective developing area Y. Then, the developer layer is held in a non-contact state with the surface of the latent image carrier 4.

Further, since a plurality of developing magnetic poles 5 having different polarities are alternately arranged inside the developer carrying member 1 in the effective developing area Y, rolling of the developer layer in the effective developing area Y, That is, the upper and lower layers of the developer layer are interchanged several times. Therefore, the developer in which the toner has been consumed and the developer in which the toner has not been consumed are replaced with each other, and higher development efficiency can be obtained as compared with the case where the developer layer does not roll. Further, for this reason, it is possible to set the AC electric field to a low level, the vibration of the carrier due to the electric field is suppressed, and the occurrence of carrier adhesion is prevented.

Further, since the developer layer is held in a non-contact state with the surface of the latent image carrier 4 and a high developing efficiency can be obtained under a low AC electric field, even when applied to the overdeveloping method, Sufficient image density can be obtained without causing color mixture on the former toner image and disturbance or scraping of the former toner image.

Furthermore, the developer carrier 1 and the latent image carrier 4
Since the pair of developing magnetic poles 5b and 5c near the closest portion of the developer layer are arranged so as to sandwich the closest portion, the portion where the layer thickness of the developer layer is the highest, that is, the peak portion of the magnetic flux density in the vertical direction. Is arranged so as to avoid the portion where the developer carrying member 1 is closest to the latent image carrying member 4. Therefore, a larger amount of the developer is held in a non-contact state with the latent image carrier 4, and high developing performance can be obtained under a low AC electric field.
Vibration of carriers due to the electric field is suppressed to a small level, and carrier adhesion is prevented.

In the present invention, the developing magnetic pole 5 (5
a-5d) and the carrier magnetic poles 6 (6a-6d), the peak value B of the magnetic flux density in the radial direction on the surface of the developer carrying member 1 is 20.
If it is set to 0 Gauss or more, a sufficient magnetic binding force acts on the carrier, and carrier scattering is prevented.

[0031]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below in detail based on the embodiments shown in the accompanying drawings. FIG. 2 shows an embodiment of a color image recording apparatus to which the developing device according to the present invention is applied. In the figure, reference numeral 11 denotes a photosensitive drum as a latent image carrier, and the photosensitive drum 11 has a cylindrical photosensitive member 11a made of a conductive material and a thin photosensitive layer 11b formed on the surface thereof. is there. As the photoconductor layer 11b, for example, a negatively charged organic photoconductor is used. The outer diameter of the photosensitive drum 11 is set to 160 mm, for example, and the surface moving linear velocity, that is, the process speed is set to 160 mm / s, for example.

In addition, around the photosensitive drum 11,
Along the rotation direction, a charging device 12 made of, for example, a scorotron, an exposure device 13 made of, for example, a laser writing device, and first to fourth developing devices 14 for yellow, magenta, cyan, and black (specifically, 14a to 14
b) and a pre-transfer charger 1 made of, for example, a corotron for making the charging characteristics of the toner image on the photosensitive drum 11 uniform before transfer.
5, a transfer charger 16 that transfers the toner image on the photosensitive drum 11 to the recording paper 20, and is composed of, for example, a corotron,
A peeling charger 17 for peeling the transferred recording paper 20 from the photosensitive drum 11, for example, a corotron, a cleaner 18 for removing residual toner on the photosensitive drum 11, and a residual charge on the photosensitive drum 11. The electrophotographic recording devices including the optical static eliminator 19 are sequentially arranged.

In this embodiment, the exposure device 13 is used.
Is to expose the area corresponding to the image area.
The developing device 14 uses a two-component developer composed of non-magnetic toner and magnetic carrier, and applies a developing bias to the sleeve of the developing roll to form an electrostatic latent image on the photosensitive drum 11. It is a non-contact reversal development. Further, the cleaner 18 is configured so that the whole or a part of the apparatus can be retracted, and is in a non-contact state with the photoconductor drum 11 during the formation of the toner image. The toner image is not disturbed. Further, the cleaning and photo-erasing of the photoconductor drum 11 are performed in a cycle after the transfer is completed, and after the transfer of the image just before is completed, the cleaner 18 causes the photoconductor drum 1
1, and the optical static eliminator 19 is turned on. After that, the cleaner 18 retreats so that the toner image formed in the next image recording step does not come into contact with the photosensitive drum 11 before reaching the cleaner 18. Similarly, the optical static eliminator 19 finishes lighting.

In such an image recording apparatus, the photosensitive drum 11 is rotationally driven in the direction of the arrow by a driving means (not shown). As the first image forming cycle,
The surface of the photoconductor drum 11 is uniformly charged by the charger 12 to a predetermined voltage. Then, the surface of the photoconductor drum 11 is exposed by the exposure device 13 in accordance with the yellow image to form an electrostatic latent image. Next, the yellow image is developed by the yellow toner of the first developing device 14a.

Next, as the second image forming cycle,
The surface of the photoconductor drum 11 is recharged by the charger 12, and the surface portion of the photoconductor drum 11 whose potential has dropped due to the exposure of the exposure device 13 in the previous yellow image forming step is restored to the original potential again. It is charged up close. Then, the surface of the photoconductor drum 11 is exposed by the exposure device 13 in accordance with a magenta image to form an electrostatic latent image. Then, the magenta image is developed by the magenta toner of the second developing device 14b.

Thereafter, similarly, as the third image forming cycle, recharging by the charging device 12, formation of an electrostatic latent image of cyan by exposure of the exposing device 13, development of cyan toner by the third developing device 14c, and fourth time. As an image forming cycle, the steps of recharging by the charger 12, formation of a black electrostatic latent image by exposure of the exposing device 13, and development of black toner by the fourth developing device 14d are sequentially performed. Then, at the time when the developing process by the fourth developing device 14d is completed, there are yellow, magenta, cyan, and black toner images corresponding to the exposure on the photosensitive drum 11.

Next, each toner image formed on the photoconductor drum 11 is charged by the pre-transfer charger 15 as necessary, and the charging characteristics are made uniform. Then, the transfer charger 1
The toner images are collectively transferred onto the recording paper 20 by the charging of No. 6, and then the recording paper 20 is peeled from the surface of the photoconductor drum 11 by the charging of the peeling charger 17.
Thereafter, the recording paper 20 is conveyed to a fixing device (not shown), the toner image is fixed on the recording paper 20, and the image recording is completed. The surface of the photoconductor drum 11 on which the toner image transfer and the recording paper 20 peeling process have been completed is cleaned by the cleaner 18 to remove residual toner, and then exposed to light by the static eliminator 19 to remove residual charges. Prepare for the next image recording step.

Next, the developing device 14 (14a to 14d) used in this embodiment will be described with reference to FIG. still,
In this embodiment, the developing devices 14a to 14d have the same configuration. In the figure, the developing device 14 has a developing roll 30 in which a magnet roll 32 is fixedly installed in a non-magnetic cylindrical sleeve 31 rotatable in the arrow direction.
Further, the outer diameter of the non-magnetic cylindrical sleeve 31 is set to 18 mm, and a plurality of magnetic poles having different polarities are arranged in the effective developing area Y and in an area adjacent to the effective developing area Y along the rotation direction of the sleeve 31. 41 to 48 are arranged alternately. In this embodiment, the magnetic poles 43 to 46 are
Is a developing magnetic pole located in the effective developing area Y, and
The magnetic poles 41 and 42 are carrier magnetic poles located in the upstream adjacent area of the effective developing area Y, and the magnetic poles 47 and 48 are also provided.
Is a carrying magnetic pole located in the area adjacent to the downstream side of the effective developing area Y. Then, in this embodiment, the magnetic poles 41 to
The peak value of the magnetic flux density in the direction (radial direction) perpendicular to the surface of the 48 non-magnetic cylindrical sleeve 31 is 300 gauss, and the gap between the magnetic flux density peak positions in the radial direction between adjacent magnetic poles is the non-magnetic cylindrical sleeve. It is set to 3 mm on the circumference of 31. Reference numeral 49 is a layer thickness regulating magnetic pole that is provided substantially opposite to a layer thickness regulating member 53 to be described later to smoothly regulate the layer thickness of the developer, and reference numerals 50 and 51 are the same for removing the developer. A pair of repulsive magnetic poles having polarities.

The magnet roll 32 is used for the photosensitive drum 1.
1 and the magnetic poles 44 and 45 are fixed so as to face each other. In this embodiment, the gap between the photosensitive drum 11 and the non-magnetic cylindrical sleeve 31 is 500 μm.
A portion facing the photosensitive drum 11, that is, the magnetic pole 4
The developer layer thickness in the approximately middle portion between 4 and 45 is set to 200 μm, respectively, and the developer layer is held in a non-contact state with the photosensitive drum 11.

Further, the non-magnetic cylindrical sleeve 31 has
A predetermined developing bias is applied by the developing bias power source 52. This developing bias is an AC voltage on which a DC voltage is superimposed.

Further, reference numeral 53 is a layer thickness regulating member for regulating the layer thickness of the developer conveyed in a state of being adhered to the non-magnetic cylindrical sleeve 31, and the layer thickness regulating member 53 regulates the layer thickness. The developer is a non-magnetic cylindrical sleeve 31
It is configured to be conveyed to the effective developing area Y facing the photosensitive drum 11 with the rotation of.

Next, the developer used in the developing device according to this embodiment will be described. As the developer, a two-component developer including toner and magnetic carrier is used. The toner is negatively charged and the carrier is positively charged. As the toner, a negatively chargeable polyester-based toner having a weight average particle diameter of 7 μm was used. As the carrier, a so-called magnetic powder dispersion type resin carrier in which magnetic powder was dispersed in a binder resin was used. This is a positively chargeable one obtained by melt-kneading a styrene-acrylic copolymer, magnetite and nigrosine and then finely pulverizing them. As the carrier used in the non-contact development method as in the present embodiment, it is preferable that the magnetization per unit volume is small and the density is low.
By reducing the magnetization per unit volume, the magnetic repulsive force between the chains of the magnetic brush is weakened, and a high density and thin developer layer is formed on the developing roll 30. Therefore, it is possible to reproduce an image with good uniformity.
Further, since the chain length of the magnetic brush is short and the carrier is low in density, the centrifugal force acting on the carrier is weakened and carrier adhesion and carrier scattering are suppressed. Specifically, the carrier has a density of 4.0 g.
/ Cm ³ or less, and the magnetization per volume in a magnetic field of 1 kilo Oersted is 40 emu / cm ³ or more and 150 or more.
It is preferably emu / cm ³ or less. At this time, the particle size of the carrier is 20 μm in weight average particle size.
It is preferably 70 μm or more. When the thickness is 20 μm or less, the magnetic binding force acting on the carrier becomes weak, so that carrier adhesion and scattering easily occur. Also, 70 μm
In the above case, since the density of the developer layer becomes low, defective image uniformity tends to occur. The carrier used in this embodiment has a weight average particle diameter of 40 μm and a density of 2.5 g /
The magnetization per volume in a magnetic field of cm ³ , 1 kilo Oersted is 100 emu / cm ³ .

[Experimental Example 1] The present inventors conducted an experiment to confirm the developing performance for a single color by using the color image recording apparatus shown in FIG. In this embodiment, only the second developing device 14b is used, and the other developing devices 14a, 14c, and 14d are removed and the experiment is performed. The image forming process of Experimental Example 1 will be described below with reference to FIG. By the charger 12, the photoconductor drum 11
Was uniformly charged to −450 V (FIG. 4 (a)).
Then, exposure with a laser beam is performed by the exposure device 13 to form an electrostatic latent image with an exposure portion potential of −200V (FIG. 4).
(B)). Then, the electrostatic latent image is transferred to the second developing device 14b.
To develop with magenta toner (FIG. 4 (c)). Further, before the transfer, the pre-transfer charger 15 uniformly negatively charges the carrier attached to the photosensitive drum 11 together with the toner so that the carrier is transferred onto the recording paper 20. After that, the magenta toner image on the photosensitive drum 11 is collectively transferred onto the recording paper 20, and the toner image is fixed on the recording paper 20 by a fixing device (not shown).

In such an image forming process, a predetermined developing bias is applied to the non-magnetic cylindrical sleeve 31 by the developing bias power source 52. This developing bias is an AC voltage on which a DC voltage is superimposed. The DC component of the developing bias voltage is -40 to prevent the occurrence of background fog.
It was set to 0V. The AC component of the developing bias voltage is a rectangular wave with a frequency of 6 kHz, and the peak value voltage is 1.5 kV.
Set to. The surface moving linear velocity of the non-magnetic cylindrical sleeve 31 was set to 320 mm / s.

Further, the mixing ratio of the toner in the developer and the carrier was adjusted so that the mixing ratio of the toner in the developer was 12% by weight. The toner charge amount is approximately -15 μC /
It was adjusted to be g. First, an experiment was conducted to investigate the length of the effective developing area Y. Here, the effective developing area is a condition in which a developing bias voltage is applied so that an electric field equivalent to the electric field applied during development acts while the photosensitive drum 11 and the non-magnetic cylindrical sleeve 31 are stopped. The region where the toner on the magnetic cylindrical sleeve 31 flies onto the photosensitive drum 11 is shown. As a result, the length of the effective developing area Y was about 10 mm on the circumference of the non-magnetic cylindrical sleeve 31. Therefore, since the magnetic pole interval in the effective developing area is 3 mm, the magnetic pole 4 in FIG.
Four magnetic poles from 3 to the magnetic pole 46 will be arranged.

On the surface of the non-magnetic cylindrical sleeve 31 of the magnetic pole (hereinafter referred to as the adjacent external magnetic pole (corresponding to the magnetic poles 42 and 47 in FIG. 3)) adjacent to the effective development area Y outside the effective development area Y. The peak value of the magnetic flux density in the vertical direction (hereinafter referred to as the magnetic flux density peak value) and the gap between the adjacent inner magnetic poles of the effective developing region Y on the circumference of the non-magnetic cylindrical sleeve 31 (hereinafter referred to as the magnetic pole gap). And change
The relationships between carrier adhesion, image density, and line image edge defects were investigated. Further, the magnetic flux density peak value and the magnetic pole interval of the adjacent external magnetic poles are the same on the upstream side (the magnetic pole 42) and the downstream side (the magnetic pole 47) in the rotational direction of the non-magnetic cylindrical sleeve 31 with respect to the effective developing region Y. Table 1 shows the five types of magnetic pole arrangement patterns used. The arrangement of magnetic poles other than the internal magnetic poles of the effective developing area and the adjacent external magnetic poles in FIG. 3 is appropriately changed according to each pattern.

[0047]

[Table 1]

In evaluating the results, the carrier adhesion was evaluated at a so-called alternating line portion in which the line image and the background portion are lined up at a constant period as shown in FIG. The alternating line has a cycle of 2 cycle / mm and the ratio of the image part to the background part is 1:
It is one. Image analysis device (Product name: LUZEX-500
0) was used to measure the area percentage of toner particles on the background. If the area ratio of the carrier particles is 1.0% or less, there is no problem in practical use. Therefore, 1.0% or less is ◯, and when it exceeds 1.0%, it is x. The image density was measured for a solid image with a reflection densitometer (trade name: X-RITE310). If the image density is 1.8 or more, both the solid image and the line image are sufficient. Therefore, 1.8 or more was evaluated as ◯ and less than 1.8 was evaluated as x. Further, the edge defect of the line image was visually evaluated, and the state in which no jaggedness was visually confirmed was ◯, the level in which there was a small amount of jaggedness was not practically problematic, and the unusable level was x. Table 2 as a result
I got In the overall evaluation, those with no x in all the above three items were marked with o, and those with at least one were marked with x.

[0049]

[Table 2]

When the magnetic flux density peak value of the adjacent outer magnetic pole is high, as described above, the state of the developer layer on the inner magnetic pole of the effective developing area Y becomes non-uniform due to the influence of the adjacent outer magnetic pole, and Contact with the surface of the photoconductor drum 11 occurs, carrier adhesion and line image edge defects occur. Further, when the magnetic flux density peak value of the adjacent outer magnetic pole is low, the magnetic binding force acting on the carrier between the adjacent outer magnetic pole and the adjacent inner magnetic pole of the effective developing region Y becomes weak, so that the developer layer of the developer layer Contact with the surface of the photoconductor drum 11 easily occurs, and carrier adhesion occurs. Furthermore,
The magnetic flux density peak value of the adjacent external magnetic pole is the same as that of the effective development area Y internal magnetic pole, but even when the magnetic pole spacing is wide,
Since the magnetic restraining force acting on the carrier is weakened similarly to the above, contact of the developer layer with the surface of the photosensitive drum 11 is likely to occur, and carrier adhesion occurs.

According to Tables 1 and 2, the magnetic pole spacing between the adjacent external magnetic poles and the internal magnetic poles of the effective developing area Y is made equal to the magnetic pole spacing between the magnetic poles inside the effective developing area Y, and the magnetic flux density peak value of the adjacent external magnetic poles. Is the same as the magnetic flux density peak value of the inner magnetic pole of the effective developing area, a uniform developer layer can be formed, and since a sufficient magnetic binding force acts on the carrier, carrier adhesion and line image It can be seen that sufficient image density can be obtained without the edge defect exceeding the allowable level.

Experimental Example 2 Further, the present inventors conducted an experiment for actually recording a color image using the color image recording apparatus shown in FIG. In Experimental Example 2, the first developing device 14a and the second developing device 14b
Was used to form a two-color image of yellow and magenta. At this time, as in Experimental Example 1, another developing device 14c,
14d is removed. In this experimental example, the experiment was conducted by changing the toner type in the second developing device 14b.

The image forming process of Experimental Example 2 will be described below with reference to FIG. By the charger 12, the photosensitive drum 1
The surface of No. 1 was uniformly charged to −450 V (FIG. 6).
(A)). Then, exposure with a laser beam was performed by the exposure device 13 to form an electrostatic latent image with an exposed portion potential of -200V (FIG. 6B). Then, this electrostatic latent image was developed with yellow toner by the first developing device 14a (FIG. 6C).
Then, charging was performed by the charger 12. The electric potential after charging is −450 V for both the first image area and the first non-image area (FIG. 6 (d)). Subsequently, the exposure device 13 performs exposure with a laser beam to form an electrostatic latent image having an exposure portion potential of −200 V (FIG. 6 (e)), and then develops with magenta toner by the second developing device 14b. (FIG.6 (f)). Further, before the transfer, in order that the carrier attached to the photosensitive drum 11 is transferred onto the recording paper 20 together with the toner, the pre-transfer charger 15 uniformly negatively charges the carrier. .
After that, the yellow and magenta toner images on the photoconductor drum 11 are collectively transferred onto the recording paper 20, and the toner images are fixed on the recording paper 20 by a fixing device (not shown).

In such an image forming process, the magnetized pattern of the magnet roll 32 in the first developing device 14a and the second developing device 14b was the pattern type of Experimental Example 1 (see Table 1). In the first developing device 14a,
As for the mixing ratio of the toner in the developer and the carrier, the mixing ratio of the toner in the developer is 12% by superposition, and the charge amount of the toner is about −15.
It was adjusted to be μC / g. On the other hand, the second developing device 1
In 4b, the toner charge amount was changed by changing the toner type. The same carrier as used in Experimental Example 1 was used, and the mixing ratio of the toner and the carrier was 12% by weight. Toner charge amount is -3 μC / g, -15 μC / g
Three types, g and -25 μC / g, were used. The other developing conditions are the same as in Experimental Example 1.

The evaluation items are the three items of Experimental Example 1, and the five items of the density reduction of the first image and the color mixture of the second toner in the first image. The decrease in the density of the first image is caused by the second developing device 14b.
The evaluation was made by the difference between the first image density during the formation of a single color image in the state where the second developing device 14b is removed and the first image density during the formation of a two color image when the second developing device 14b is operated. Here, the first image density is the reflection densitometer (trade name: X-
RITE310), and if there is no decrease in concentration, ○,
The case where there was a decrease in the density was marked with x. The color mixture of the second toner in the first image was visually evaluated using a limit sample. Grade (hereinafter referred to as G) 1 is a state in which no color mixture is visually confirmed. There was a slight amount of color mixing, but there was no problem in practical use, the level was G2, and the unusable level was G3. G1 and G2 were marked with ◯, and G3 was marked with x. Table 3 was obtained as a result.

[0056]

[Table 3]

From Table 3, the magnetic pole spacing between the adjacent external magnetic poles and the internal magnetic poles of the effective developing area Y is made equal to the magnetic pole spacing between the magnetic poles inside the effective developing area Y, and the magnetic flux density peak value of the adjacent external magnetic poles is effective. By making it equal to the magnetic flux density peak value of the magnetic poles inside the developing area, a uniform developer layer can be formed, and since a sufficient magnetic binding force acts on the carrier, it may be different from the case where the toner charge amount is low. In both cases, it is understood that sufficient image density can be obtained without carrier adhesion and line image edge defects exceeding the allowable level.

Further, since the developer layer is held in a non-contact state with the surface of the photosensitive drum 11 and the first toner image on the surface of the photosensitive drum 11, the first image is mechanically scraped. There is no. Further, since a plurality of magnetic poles having mutually different polarities are alternately arranged inside the effective developing area Y, as described above, rolling of the developer layer occurs in the effective developing area, and high developing is performed with a low AC electric field. Since the efficiency is obtained, a sufficient image density can be obtained without disturbing or scraping the first toner image due to the action of the AC electric field and causing the color mixture of the second toner in the first image.

Therefore, even when the toner charge amount is affected by the environment or changes with time, a sufficient image density is obtained without causing a decrease in the first image density, color mixing of the second toner in the first image, and carrier adhesion. Can be reproduced.

Comparative Example Further, in the image recording apparatus having the same structure as in Experimental Example 1 or Experimental Example 2, the developing roll structure of the developing device used is set to a position facing the closest position between the developing roll and the photosensitive drum. With respect to the structure similar to that of Experimental Example 1, the magnetic poles are arranged, the alternating electric field of the developing bias is changed, and the carrier adhesion, the image density, and the presence or absence of the line image edge defect are evaluated. In addition to the above-mentioned three items, the same configuration as in Experimental Example 2 was evaluated for density reduction of the first image and presence / absence of color mixture of the second toner in the first image. As a result, a sufficient image density cannot be obtained unless the alternating electric field of the developing bias is set higher than that in the embodiment, and since the alternating electric field becomes large, the carrier adhesion amount (carrier area) becomes larger than that in the embodiment. It is understood that the rate will increase. Here, as specific data, for example, in order to obtain the same layer thickness as the inter-electrode facing portion of the present embodiment at the highest level, the amount of developer conveyed (the amount of developer per unit area on the developing roll is ) Needs to be reduced to about 2/3, and in order to obtain a sufficient concentration in this state, the AC component should be, for example, 2 kVp-
It was confirmed that it must be set to p.

In the above embodiment, a so-called magnetic powder dispersion type resin carrier in which magnetic powder is dispersed in a binder resin is used as the magnetic carrier in the two-component developer, but spherical spherical ferrite particles are coated with resin. Arbitrary ones such as those subjected to can be used. Further, in the above-described embodiment, the rectangular wave is used as the waveform of the AC component of the developing bias voltage, but when a sine wave or a triangular wave, a waveform asymmetrical to the average voltage, or any other waveform is used. Also has the same effect. Furthermore, in the above-described embodiment, the image area exposure and the reversal development are repeatedly performed, but the image forming process is not limited to this, and can be applied in any process. Furthermore, in the above-described embodiment, the color image recording apparatus using the monochromatic image recording apparatus and the overlapping developing method has been described, but the image recording apparatus is not limited to this, and the electrophotographic recording method is used. It is applicable to any image recording device. Further, in the above-described embodiment, the photoconductor is used as the latent image carrier, but a dielectric is used as the latent image carrier, and a discharge recording head used in an electrostatic printer or JP-A-59-190854. The electrostatic latent image may be formed by the ion flow recording head disclosed in the publication.

[0062]

As described above, a plurality of rows of developing magnetic poles having different polarities are alternately arranged on the magnet member corresponding to the effective developing area, and the magnetic pole corresponding to the effective developing area is arranged in the area adjacent to the effective developing area. At least one transport magnetic pole having different polarities alternately arranged from the developing magnetic pole near the boundary in the effective developing area is arranged, and the intervals between the magnetic poles in the effective developing area and the area adjacent thereto are substantially the same. And the peak value of the magnetic flux density in the vertical direction (radial direction) on the surface of the developer carrier of each magnetic pole is set to be substantially the same, so that the magnetic flux is formed on a plurality of developing magnetic poles in the effective developing area. The state of the magnetic field is not affected by the carrier magnetic pole outside the effective developing area, and a thin layer of high density and uniform developer can be formed in the effective developing area, and the latent image carrier surface of the developer layer is formed. Non-contact with State it is possible to satisfactorily hold.

Further, since a sufficient magnetic restraining force acts on the carrier, carrier adhesion and carrier scattering can be effectively prevented, and sufficient image quality can be obtained.

Further, a pair of developing magnetic poles in the vicinity of the closest portion of the latent image carrier and the developer bearing member are arranged so as to sandwich the closest portion, so that the developing pole of the developing magnetic pole with respect to the closest portion is arranged. The peak value of the magnetic flux density in the vertical direction does not act directly, and the layer thickness of the developer can be suppressed more than that at other portions in the closest portion by that amount. Therefore, it becomes possible to hold a larger amount of the developer in a non-contact state with the latent image carrier, and accordingly, a high developing efficiency can be obtained under a low AC electric field. Therefore, in the non-contact developing method, it is possible to obtain high developing efficiency while suppressing the carrier vibration due to the electric field to be small, and even when applied to the overdeveloping method, the color mixture on the pre-stage toner image and the pre-stage toner are performed. It is possible to reliably obtain a color image with sufficient image density without causing image distortion or scraping.

Further, in the present invention, if the peak value of the magnetic flux density in the radial direction of each magnetic pole in the effective developing area and the area adjacent to the effective developing area is set to 200 Gauss or more, a sufficient magnetic binding force can be applied to the carrier. This makes it possible to prevent carrier scattering more effectively.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration of a developing device according to the present invention.

FIG. 2 is an explanatory diagram showing an embodiment of a color image forming apparatus using a developing device to which the invention is applied.

FIG. 3 is an explanatory diagram showing a specific configuration of the developing device according to the embodiment.

4 (a) to 4 (c) are potential explanatory diagrams each showing an image forming process in Experimental Example 1. FIG.

FIG. 5 is an explanatory diagram of an alternating line portion.

6 (a) to 6 (f) are potential explanatory diagrams showing image forming steps in Experimental Example 2, respectively.

FIG. 7 is an explanatory diagram illustrating a state of magnetic force lines in a conventional effective development area.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Developer carrying body, 2 ... Non-magnetic sleeve, 3 ... Magnet member, 4 ... Latent image carrying body, 5 (5a-5d) ... Developing magnetic pole, 6
(6a to 6d) ... Transport magnetic pole, Y ... Effective development area, Z ... Electrostatic latent image, A ... Magnetic pole spacing, B ... Radial magnetic flux density peak value

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] November 16, 1995

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Fig. 4

[Correction method] Change

[Correction contents]

FIG. 4 is a potential theory showing an image forming process in Experimental Example 1 .
FIG.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] Fig. 6

[Correction method] Change

[Correction contents]

6 is a potential theory showing an image forming process in Experimental Example 2. FIG.
FIG.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinji Sasahara 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd.Ebina Business Office (72) Inventor Heiwa Koren 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd. Ebina Business In-house

Claims (2)

[Claims] 1. A rotatable nonmagnetic sleeve (2) has a developer carrier (1) on which a magnet member (3) is fixedly installed, and the developer carrier (1) is used as a latent image carrier. A latent image carrier (4) is provided so as to face the developer carrier (1) and a two-component developer comprising a non-magnetic toner and a magnetic carrier is disposed on the developer carrier (1).
The latent image bearing member (4) and the developer bearing member (1) are supported in a non-contact state with each other, and an alternating electric field (EAC) in which a DC component is superposed is applied between the latent image bearing member (4) and the developer bearing member (1). ) In the developing device adapted to develop the electrostatic latent image (Z) above, the magnet member (3) corresponding to the effective developing area (Y) facing the latent image carrier (4) has different polarities. A plurality of rows of developing magnetic poles (5: 5a to 5d) alternately arranged are arranged, and in the area adjacent to the effective developing area (Y), the developing magnetic poles (5a, 5a, 5d)
From the above, at least one carrier magnetic pole (6: 6a to 6d) in which different polarities are alternately arranged is arranged, and each developing magnetic pole (5) and effective developing area (Y) in the effective developing area (Y) are arranged. ), At least one or more carrier magnetic poles (6) adjacent to each other have substantially equal magnetic pole intervals (A), and the developer carrier (1) and the latent image carrier (4) are A pair of developing magnetic poles (5b, 5c) near the closest portion of the developing magnetic pole (5b, 5c) sandwiching the closest portion of the developing magnetic pole (5b, 5c), and further, each of the developing magnetic poles (5) and one or more carrying magnetic poles (6) carry a developer. A developing device, wherein the peak value (B) of the magnetic flux density in the radial direction on the surface of the body (1) is set to be substantially the same. 2. The developing device according to claim 1, wherein the peak value (B) is 200 gauss or more.