JP2000194195A - Developing device and image forming device provided therewith - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact developing device constituted so that a uniform black solid image can be obtained without causing the irregularity of screw pitch at the black solid part of the image even when magnetic carrier magnetized a little is adopted in order to prolong the service life of developer or an image forming device equipped with this developing device. SOLUTION: A stirring and carrying screw 24 is constituted so that an angle formed by a straight line leading to the center of a developing sleeve 21 from the surface position thereof being near to the screw 24 and a straight line leading to the center of the sleeve 21 from the surface position thereof where the intensity of a magnetic field in the normal direction of the surface of the sleeve 21 by a magnetic pole S3 becomes the maximum is >=30 deg.. Thus, the purpose is accomplished.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for developing an electrostatic latent image formed on a latent image carrier corresponding to an image to be recorded with a developer and recording the image on a recording medium such as paper. Things.

[0002]

2. Description of the Related Art Conventionally, various types of developing devices have been proposed and put to practical use in developing devices provided in electrophotographic image forming apparatuses. Such developing devices are roughly classified into a developing device using a one-component developing method and a developing device using a two-component developing method.

Most of the developing devices of the one-component developing system are of the non-contact type, but a typical developing method is a one-component jumping developing method using a magnetic toner.

The one-component jumping developing method can provide high-quality image with a simple structure, but has a drawback that a color image cannot be obtained because the toner contains a magnetic substance.

In the one-component developing method using a non-magnetic toner, a color image can be obtained, but it is difficult to apply the toner on a developing sleeve as a developer carrier, and an elastic blade as a regulating member is used. At present, it is coated, and it lacks stability and durability.

On the other hand, in a developing device using a two-component developing method, a toner is transported to a developing area by a magnetic carrier to perform development. Usually, a developer is brought into contact with a photosensitive drum as a latent image carrier. To perform the development process.

Here, the developing step will be described with reference to FIG.

In FIG. 3, reference numeral 30 denotes a developing sleeve as a developer carrying member; 35, a magnet roller as magnetic field generating means fixedly arranged in the developing sleeve 30; 31, 32, a conveying screw as stirring and conveying means; A regulating blade 34, which is a regulating member disposed to form a thin layer on the surface of the developing sleeve 30, is a developer container.

Here, a description will be given of a developing step of visualizing the electrostatic latent image formed on the photosensitive drum by a two-component magnetic brush method using the developing device of FIG. 3 and a developer circulation system.

First, the amount of the developer pumped onto the developing sleeve 30 by the magnetic pole N3 with the rotation of the developing sleeve 30 regulates the amount of the developer carried on the developing sleeve 30 in the process of being transported from the magnetic pole S2 to the magnetic pole N1. Blade 3
3 and a thin layer is formed on the developing sleeve 30. Here, when the developer formed in a thin layer is conveyed to the magnetic pole S1, which is the main developing pole, ears are formed by the magnetic force. The electrostatic latent image is developed by the spike-shaped developer, and thereafter, the developer on the developing sleeve 30 is repelled by the repulsive magnetic field generated by the magnetic pole N3 and the magnetic pole N2.
It is returned into the developer container 34.

As described above, in the developing device based on the two-component developing method, by arranging the magnetic poles having the same polarity side by side, the developer after the development is once peeled off from the developing sleeve so that the image history is not left. It is common.

The developing sleeve 30 has a power supply (not shown).
, A DC bias and an AC bias are applied. Generally, in the two-component developing method, when an AC bias is applied, the developing efficiency is increased, and the image becomes high quality.

As a latent image forming method, an electrophotographic photosensitive member as a latent image carrier is scanned and exposed by a laser beam modulated in accordance with an image signal to be recorded, and a dot distribution shape, that is, a latent image on dots is converted into an image. Methods of forming correspondingly distributed electrostatic latent images are known. Among them, the so-called pulse width modulation (PWM) method, which modulates the width of a driving pulse current of a laser (that is, the duration time) according to the density of an image to be recorded, can obtain a high recording density (that is, a high resolution). And high gradation can be obtained.

Incidentally, in recent years, in response to the downsizing of the apparatus, development of downsizing of the developing apparatus by the two-component developing method as described above has been promoted.
Not only the developer container but also the developing sleeve and the stirring and conveying screw need to be miniaturized.

One of the major problems in reducing the size of such a developing device is that the design latitude of each component is reduced.

[0016] In addition to the miniaturization of such devices, development of higher image quality and longer life has been promoted. Among them, in order to achieve a longer life of the developing device by the two-component developing method, it is necessary to adopt a configuration in which the developer is not compressed and to prevent toner deterioration and carrier deterioration (carrier spent). Becomes

The place where the developer is compressed in the developer container is a portion where the layer thickness of the developer on the developing sleeve is regulated. Usually, in such a configuration of the developing device, the developer is regulated by the regulating blade. A developer layer thickness regulating magnetic pole for carrying the developer on the developing sleeve is located near the regulating blade and upstream of the regulating blade in the rotation direction of the developing sleeve. As a result, the developer attracted onto the developing sleeve by the developer layer thickness regulating magnetic pole is compressed between the developing sleeve and the developer container.

Therefore, in order to weaken the compression of the developer between the developing sleeve and the developer container, the magnetic pole for regulating the thickness of the developer layer attracts the developer onto the developing sleeve (acts in a direction perpendicular to the developing sleeve). Force) It is effective to weaken Fr. For this purpose, the magnetization of the carrier in the developer should be reduced (the direction of decreasing the magnetization of the carrier is the toner image developed on the photoconductor in the developing unit). This is a direction in which the image quality is improved in that the force of rubbing is weak), and the magnetic field lines from the developer layer thickness regulating magnetic poles are hard to wrap around to the adjacent magnetic poles, and are projected in the radial direction of the developing sleeve as much as possible. Is to build.

As one of the latter methods, a developing method has been proposed in which a repelling magnetic field is formed by a repelling pole in a developing sleeve and the repelling pole is used as a magnetic pole for regulating the thickness of a developer layer (Japanese Patent Application No. 9-316478). .

As described above, when the magnetic poles having the same polarity are adjacent to each other to form a repulsive magnetic field, the lines of magnetic force of each magnetic pole come out perpendicular to the surface of the developing sleeve. In this case, since the rate of change of the magnetic flux density in the direction perpendicular to the surface of the developing sleeve is small, as a result, the force for attracting the developer to the developing sleeve decreases, and the degree of compression of the developer decreases.

[0021]

However, in the construction of such a conventional developing device using the two-component developing method, that is, in the construction in which one magnetic pole of the repulsive magnetic pole is used as the developer layer thickness regulating magnetic pole, The magnetic field strength in the vertical direction of the developing sleeve surface due to the thickness-regulated magnetic pole peaks (maximum)
If the surface position of the developing sleeve is close to the position of the conveying screw, there is a possibility that density unevenness in the form of a screw pitch will occur at the rear end of the recording medium on which the solid black image is formed.

There are two patterns in which the density unevenness occurs.

One is that if the developer pool formed by the developer layer thickness regulating magnetic pole and the transport screw overlap, the transport screw will bend when it rotates, so that toner is consumed after development. This is a pattern in which the toner density unevenness of the developer occurs in the form of a screw pitch when mixed with the developer remaining in the developer layer pressure regulating magnetic pole after the removed developer is peeled off.

The other is that, when the transport screw is close to the developer pool formed by the developer layer thickness regulating magnetic pole, pressure unevenness of the developer pool at the developer pool is caused by the rotation of the transport screw. This is a pattern in which the developer bulk density unevenness occurs, and the unevenness in the amount of the developer coated on the developing sleeve shape becomes a screw pitch-like density unevenness.

This phenomenon tends to occur particularly when the size of the developing device holder is reduced. The reason for this is that as the size of the developing device is reduced, the transport screw itself becomes smaller and the strength is reduced, and the volume of the developer reservoir formed by the developer layer thickness regulating magnetic pole also becomes smaller, and the pressure increases. This is because it is easier to pick up unevenness.

The above-mentioned phenomenon is likely to occur when the magnitude of the magnetization of the magnetic carrier is reduced. This is because the developer needs to be compressed to some extent evenly over the entire length of the image area, whereas when the magnetization of the magnetic carrier is small, the developer is attracted magnetically to the developing sleeve. This is because if the transport screw exists near the developer layer thickness regulating magnetic pole, mechanical pressure unevenness is likely to occur over the image area.

As a result, the developer using the low-magnetization carrier also helps to reduce the transportability on the developing sleeve, and the amount of the developer carried on the developing sleeve tends to be uneven.

Therefore, according to the present invention, even when a magnetic carrier having a small size and a small magnetization is used in order to extend the life of the developer, the screw pitch unevenness does not occur in the black solid portion of the image and the uniformity can be obtained. It is an object of the present invention to provide a developing device capable of obtaining a solid black image or an image forming apparatus including the developing device.

[0029]

According to the present application, the above object is achieved by applying a developer containing a magnetic carrier and a non-magnetic toner to a latent image carrier that carries a latent image.
A developing device that renders the latent image a visible image, comprising: a developer container for storing a developer; a rotatable developer carrier for supporting the developer in the developer container; A magnetic field generating means having a plurality of circumferentially arranged magnetic poles fixedly disposed inside the developer carrier so as to provide a developer carrying force;
Rotatable stirring and conveying means for stirring the developer near the developer carrier in the developer container and conveying the developer toward the developer carrier,
In a developing device having a regulating member for regulating the amount of developer on a developer carrier, a magnetic field generating means includes a first magnetic pole disposed near a regulating member inside the developer container, and a first magnetic pole. A first magnetic pole and a second magnetic pole having the same polarity as the first magnetic pole. And the angle between the straight line from the developer carrier surface position where the intensity of the magnetic field in the normal direction of the developer carrier surface by the first magnetic pole becomes the maximum to the center of the developer carrier, It is also achieved by the first invention that is at least 30 °.

According to the present application, the above object is also achieved by the second invention in the first invention, wherein the developer carrier is a nonmagnetic cylinder having a diameter of 20 mm or less.

Further, according to the present application, the above object is achieved according to the first or second aspect, wherein the developer carrying member is disposed so as to face the latent image carrying member. The present invention is also achieved by the third invention in which the surface and the latent image carrier move in opposite directions at their facing portions.

According to the present application, the above object is achieved in any one of the first to third aspects of the present invention in that the magnetic carrier has a magnetization of 30 emu in a magnetic field of 1000 gauss.
/ Cm ³ or more and 200 emu / cm ³ or less.

Further, according to the present application, the above object is to provide an image forming apparatus for recording an image formed by a series of image forming processes on a recording medium, comprising the developing device of the first invention. This is also achieved by the fifth invention.

According to the present application, the above object is also achieved by the sixth invention in the fifth invention, wherein the developer carrier is a nonmagnetic cylinder having a diameter of 20 mm or less.

Further, according to the present application, the above object is achieved according to the fifth or sixth invention, wherein the developer carrier is disposed so as to face the latent image carrier. The present invention is also achieved by the seventh invention in which the surface and the latent image carrier move in opposite directions at opposite portions.

According to the present application, the above object is achieved in any one of the fifth to seventh inventions, wherein the magnetic carrier has a magnetization of 30 emu in a magnetic field of 1000 gauss.
/ Cm ³ or more and 200 emu / cm ³ or less.

That is, according to the first aspect of the present invention, the first magnetic pole carries the developer on the surface of the developer carrier without being affected by the rotation of the stirring and conveying means near the first magnetic pole. After that, the developer amount of the developer is regulated by regulating means.

Further, in the second invention according to the present application, the developer in which the first magnetic pole is a non-magnetic cylinder having a diameter of 20 mm without being affected by rotation of the stirring and conveying means near the first magnetic pole. After the developer is carried on the surface of the carrier, the amount of the developer is regulated by regulating means.

Further, in the third invention according to the present application, the developer carrier rotates in the opposite direction to the latent image carrier, and the first magnetic pole rotates near the first magnetic pole by the rotation of the stirring and conveying means. After the developer is carried on the surface of the developer carrying member without being affected by the developer, the amount of the developer in the developer is regulated by the regulating means.

Further, in the fourth invention according to the present application, the first magnetic pole is not affected by the rotation of the stirring and conveying means in the vicinity of the first magnetic pole, and the magnetization is optimized. After the developer containing is carried on the surface of the developer carrying member, the amount of the developer is regulated by regulating means.

Further, according to the first invention of the present application, the first magnetic pole carries the developer on the surface of the developer carrier without being affected by the rotation of the stirring and conveying means near the first magnetic pole. After that, the developer amount of the developer is regulated by regulating means.

Further, in the second invention according to the present application, the developer in which the first magnetic pole is a non-magnetic cylinder having a diameter of 20 mm in the vicinity of the first magnetic pole without being affected by rotation of the stirring and conveying means. After the developer is carried on the surface of the carrier, the amount of the developer is regulated by regulating means.

Further, in the third invention according to the present application, the developer carrier rotates in the opposite direction to the latent image carrier, and the first magnetic pole rotates near the first magnetic pole by the rotation of the stirring and conveying means. After the developer is carried on the surface of the developer carrying member without being affected by the developer, the amount of the developer in the developer is regulated by the regulating means.

Further, in the fourth invention according to the present application, the first magnetic pole is not affected by the rotation of the stirring and conveying means in the vicinity of the first magnetic pole, and the magnetization of the magnetic carrier is optimized. After the developer containing is carried on the surface of the developer carrying member, the amount of the developer is regulated by regulating means.

[0045]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

(First Embodiment) First, a first embodiment of the present invention will be described.

FIG. 1 is a schematic sectional view showing a schematic configuration of an electrophotographic color printer (hereinafter, referred to as a printer) as an example of an image forming apparatus according to the present embodiment.

In this printer, as shown in FIG. 1, an electrophotographic photosensitive drum 3 (hereinafter referred to as a photosensitive drum 3) as a latent image carrier rotating in the direction of an arrow is provided. An image forming means including a charger 4, a developing device 1, a transfer discharger 10, a cleaning means 12, and a laser beam scanner LS disposed above the photosensitive drum 3 is provided.

The developing device 1 includes developing units 1M, 1C, 1Y,
1BK, and each developing device 1M, 1C, 1Y, 1BK
A developer containing toner particles and carrier particles (two-component developer) is supplied to the surface of the photosensitive drum 3. The developing devices 1M, 1C, 1Y, and 1BK use a developer containing a magenta toner, a cyan toner, a yellow toner, and a black toner, respectively.

The original to be copied is read by an original reading device (not shown). This reading device has a photoelectric conversion element, such as a CCD, for converting a document image into an electric signal, and outputs image signals respectively corresponding to magenta image information, cyan image information, yellow image information, and black-and-white image information of the document. It is supposed to. The semiconductor laser incorporated in the scanner LS is controlled in accordance with these image signals and emits a laser beam L.
An output signal corresponding to image information from an electronic computer or the like can be printed out.

Next, the sequence of the entire color printer will be briefly described by taking a full color mode as an example.

In this printer, first, the surface of the photosensitive drum 3 is uniformly charged by the charger 4.

Next, scanning exposure is performed by the laser beam L modulated by the magenta image signal, and the photosensitive drum 3
An electrostatic latent image having a dot distribution is formed thereon, and the electrostatic latent image is reversely developed by a magenta developing device 1M provided at a predetermined developing position in advance.

After being taken out of the cassette C, the transfer material such as the paper fed through the paper feed guide 5a, the paper feed roller 6, and the paper feed guide 5b is held by the gripper 7 of the transfer drum 9. It is electrostatically wound around the transfer drum 9 by the contact roller 8 and its opposite pole.

The transfer drum 9 rotates in the direction of the arrow shown in FIG.
The magenta visual image developed in M is transferred to a transfer material by a transfer charger 10 in a transfer section. Transfer drum 9
Continues the rotation as it is to prepare for the transfer of the image of the next color (cyan in this example shown in FIG. 1).

On the other hand, the photosensitive drum 3 is neutralized by the charger 11, cleaned by the cleaning means 12, charged again by the charger 4, and similarly to the above by the laser beam L modulated by the next cyan image signal. To form an electrostatic latent image. During this time, the developing device 1 rotates, and the cyan developing device 1C is fixed at a predetermined developing position, performs reversal development of the dot distribution electrostatic latent image corresponding to cyan, and forms a cyan visible image.

Subsequently, the above-described steps are performed for the yellow image signal and the black image signal, respectively, and when the transfer of the four-color image (toner image) is completed, the transfer material is transferred to each of the chargers 13. 14, the gripper 7 is released, and the separation claw 15 transfers the transfer drum 9.
, And sent to a fixing device (a heat-pressure roller fixing device) 17 by a transport belt 16. The fixing device 17 fixes the visible images of four colors overlapping on the transfer material by heating and pressing.

Thus, a series of full-color print sequences is completed, and a desired full-color print image is formed.

The configuration of the image forming apparatus according to the present embodiment is merely an example. For example, the charger 3 is not limited to a corona charger, but may be a charging roller, and the transfer charger 7 may be a transfer roller. Various methods can be applied, and an image is basically formed by the steps of charging, exposure, development, transfer, and fixing as described above.

Next, the developing device according to the present embodiment will be described with reference to FIG. 2, using the developing device 1M as an example. The configuration of the developing devices 1C, 1Y, and 1BK is the same as the configuration of the developing device 1M because only the developer used is different.
The description is omitted.

FIG. 2 is a configuration diagram showing the developing device 1M according to the embodiment of the present invention.

The developing device 1M includes a developer container 27 as shown in FIG.

The inside of the developer container 27 is divided into a developing chamber (first chamber) R1 and a stirring chamber (second chamber) R2 by a partition wall 29, and the toner is stored above the stirring chamber R2 via the partition wall 29. A chamber R3 is formed, and a supply toner (non-magnetic toner) 28 is stored in the toner storage chamber R3. In addition, a supply port 26 is provided in the partition wall 29, and an amount of supply toner 28 corresponding to the toner consumed through the supply port 26 is dropped and supplied into the stirring chamber R2.

On the other hand, the developer 19 is stored in the developing chamber R1 and the stirring chamber R2. The developer 19 is obtained by externally adding 1% by weight of titanium oxide having an average particle diameter of 20 nm to a non-magnetic toner (hereinafter, referred to as toner) having an average particle diameter of 8 μm manufactured by a pulverization method, and magnetizing at 1000 Gauss. Is 270 emu / cm ³ average particle size 3
This is a two-component developer containing 5 μm magnetic particles and magnetic carriers. The mixing ratio between the toner of the developer and the magnetic carrier was such that the toner was about 7% by weight.

An opening is formed in a portion of the developer container 27 on the photosensitive drum 3 side, and the developing sleeve 2 serving as a developer carrier is formed.
1 so that the developing sleeve 2 projects out of the opening.
1 is rotatably incorporated near the opening of the developer container 27. In the present embodiment, the developing sleeve 2
The diameter of 1 is 16 mm. The developing sleeve 21 is made of a non-magnetic material such as SUS305AC, and has a magnet
Are fixedly arranged.

The magnet 23 includes a magnetic pole N1 which is a developing magnetic pole disposed near a developing area which is an opposing portion of the photosensitive drum 3 and the developing sleeve 21, and a magnetic pole which is a first magnetic pole which is a magnetic pole for regulating a developer layer thickness. S3 and magnetic poles N2, S2, and S1 for transporting the developer 19 while supporting the developer 19 on the developing sleeve 21.
And

The magnet 23 has a magnetic pole N1 which is a developing magnetic pole.
Are arranged in the developing sleeve 21 so as to face the photosensitive drum 3.

The magnetic pole N1 forms a magnetic field near the developing section between the developing sleeve 21 and the photosensitive drum 3, and the magnetic field forms a magnetic brush. In the developing section, as the developing sleeve 21 rotates, FIG.
The developer carried in the direction of the arrow shown in FIG.
And the electrostatic latent image on the photosensitive drum 3 is developed. At this time, the developing sleeve 21 and the photosensitive drum 3 move in opposite directions (counter direction) at a position (developing portion) close to the developing sleeve 21 and the photosensitive drum 3. The developer that has been developed at the magnetic pole N1 is peeled off from the developing sleeve 21 by the repulsive magnetic field formed by the magnetic poles S1 and S3, and falls into the developing chamber R1.

Note that an oscillating bias voltage in which a DC voltage is superimposed on an AC voltage is applied to the developing sleeve 21 by a power supply 20. The dark portion potential (non-exposed portion potential) and light portion potential (exposed portion potential) of the latent image on the photosensitive drum 3 are located between the maximum value and the minimum value of the vibration bias potential. As a result, an alternating electric field whose direction changes alternately is formed in the developing section. The toner and the magnetic carrier violently vibrate in the alternating electric field, and the toner shakes off the electrostatic restraint on the developing sleeve 21 and the magnetic carrier, so that the amount of toner corresponding to the latent image potential adheres to the photosensitive drum 3.

In this embodiment, the photosensitive drum 3
The upper dark portion potential is -550 V, the bright portion potential is -100 V, and a DC bias is applied to the developing sleeve 21 as -3.
00V DC voltage is applied, and V
pp = 2.0 kV, Frq. = 6 kHz AC voltage is applied.

Below the developing sleeve 21, a regulating blade 18 (hereinafter, referred to as a blade 18) as a regulating member is arranged at a predetermined distance from the developing sleeve 21. In the present embodiment, the distance between the developing sleeve 21 and the blade 18 is 400 μm.

The blade 18 is fixed to the developer container 27. The blade 18 is made of a magnetic material such as iron, and magnetically regulates the layer thickness of the developer 19 on the developing sleeve 21.

In the developing chamber R1, a transport screw 24 serving as a stirring transport means is accommodated. Transport screw 24
Has a diameter of 14 mm.

The transport screw 24 is rotated in the direction shown by the arrow in the figure, and the developer 19 in the developing chamber R 1 is transported in the longitudinal direction of the developing sleeve 21 by the rotation of the transport screw 24. ing.

In this embodiment, the transport screw 24
Is disposed below the developing sleeve 21 in the direction of gravity. The reason for this will be described later, since the uppermost surface of the developer surface of the developer accommodated in the transport screw 24 is set between the magnetic pole S3 which is a developer layer thickness regulating magnetic pole and the magnetic pole S1 which is a stripping magnetic pole. It is.

The transport screw 25 is accommodated in the storage room R2. The transport screw 25 has a diameter of 14 mm, similar to the transport screw 24.

The conveying screw 25 conveys the toner along the longitudinal direction of the developing sleeve 21 by the rotation thereof,
The toner is allowed to freely fall from the supply port 26 into the stirring chamber R2.

Here, the toner used in the present embodiment will be described.

The toner according to this embodiment has a triboelectric charge of about 2.0 × 10 ⁻² C / kg.

The volume average particle size of the toner is 4 to 15 μm.
m can be suitably used. Here, as the volume average particle diameter of the toner, for example, the one measured by the following measurement method is used.

In the above measuring method, a Coulter counter TA-II type (manufactured by Coulter Inc.) was used as the measuring device.
And an interface (manufactured by Nikkaki) for outputting a number average distribution and a volume average distribution and a CX-i personal computer (manufactured by Canon) are connected, and a 1% NaCl aqueous solution is adjusted using primary-grade sodium chloride as an electrolytic solution.

The measuring method is as follows.
In 150 ml, 0.1 to 5 ml of a surfactant (preferably alkylbenzene sulfonate) is added as a dispersant, and 0.5 to 50 mg of a measurement sample is further added.

The electrolytic solution in which the sample was suspended was subjected to a dispersion treatment for about 1 to 3 minutes using an ultrasonic disperser, and the particle size distribution of particles having a particle size of 2 to 40 μm was measured using the Coulter Counter TA-II with a 100 μm aperture as an aperture. Is measured to determine the volume distribution. From these determined volume distributions, the volume average particle size of the sample is obtained.

In addition to the above-mentioned toner, by coating the (toner) surface with an external additive, there are two hardware effects.

One is that the fluidity is improved, and the replenishment toner is easily mixed and stirred with the two-component developer in the developer container 27, and the other is that the external additive is interposed on the toner surface. Thereby, the releasability of the toner (developed on the photosensitive drum 3) from the photosensitive drum 3 is increased, and the transfer efficiency is improved.

The external additive used in the present invention preferably has a particle size of 1/10 or less of the weight average particle size of the toner particles from the viewpoint of durability when added to the toner. The particle diameter of the external additive means an average particle diameter thereof obtained by observing the surface of the toner particles with an electron microscope.

Examples of the external additives include metal oxides (aluminum oxide, titanium oxide, strontium titanate, cerium oxide, magnesium oxide, chromium oxide, tin oxide, zinc oxide, etc.), nitrides (silicon nitride, etc.), Metal salts of carbides (such as silicon carbide) (such as calcium sulfate, barium sulfate, and calcium carbonate), metal salts of fatty acids (such as zinc stearate and calcium stearate), carbon black, and silica are used.

The external additive is used in an amount of 0.01 to 10 parts by weight based on 100 parts by weight of the toner particles.
0.05 to 5 parts by weight are used. These external additives may be used alone or in combination. Those subjected to a hydrophobic treatment are more preferable.

In this embodiment, the average particle size is 20 nm
Of which 1% by weight of titanium oxide is externally added.

Next, as the carrier constituting the developer used in the present invention together with the above-mentioned toner, conventionally known carriers can be used. For example, magnetite is dispersed as a magnetic material in resin, and carbon black is dispersed for conductivity and resistance adjustment.Resistance adjustment is performed by oxidizing and reducing the surface of magnetite alone such as ferrite. May be used, or may be coated with a magnetite simple substance resin such as ferrite and subjected to resistance adjustment.
In the present invention, the method for producing these magnetic carriers is not particularly limited.

In this embodiment, the magnetic carrier has a weight average particle diameter of 20 to 100 μm, preferably 2 to 100 μm.
Those having a size of 0 to 70 μm are used.

Next, the magnetic pole S3, which is a developer layer thickness regulating magnetic pole of the developing device used in the present embodiment, the magnetic pole S1, which is a stripping magnetic pole that forms a repulsive magnetic field, and the screw 24 near the developing sleeve 21, The positional relationship including its operation will be described in detail.

In the present embodiment, of the magnetic pole S3 and the magnetic pole S1 forming the repulsive magnetic field, the magnetic pole S3 is used as the developer layer thickness regulating magnetic pole.

In this embodiment, the peak position of the magnetic field strength of the magnetic pole S3 in the direction perpendicular to the surface of the developing sleeve 21 and the tip of the (restriction) blade 18 are 5 ° (the center position of the developing sleeve is Standards).

Since the magnetic pole S3 forms a repulsive magnetic field with the magnetic pole S1, the magnetic field lines of the magnetic pole S3 are
Diverges perpendicular to one surface. As a result, the rate of change of the magnetic field (magnetic field line density) in the direction perpendicular to the surface of the developing sleeve 21 is reduced, which means that the force for attracting the developer to the developing sleeve 21 is reduced. With such a configuration, the force with which the developer is compressed at the magnetic pole S3 which is the developer layer thickness regulating magnetic pole is weakened, and the deterioration of the developer such as toner deterioration and spent carrier is suppressed, and the life of the developer is reduced. Will be extended.

Conventionally, when a developing device (including a developing sleeve, a stirring and conveying screw, and a developing container) is miniaturized and one of the magnetic poles constituting the repulsive magnetic pole is used as the developer layer thickness regulating magnetic pole, the developer layer thickness regulating is restricted. If the stirring and conveying screw exists near the magnetic pole, there is a possibility that a screw pitch-like density unevenness may occur.

One of the patterns of the density unevenness is that when the stirring / conveying screw is close to the developer reservoir formed by the developer regulating magnetic pole, the stirring / conveying screw rotates and accumulates in the developer reservoir. This is a screw pitch-like density unevenness caused by unevenness in the pressure of the developer, unevenness in the developer bulk density, and unevenness in the amount of the developer coated on the developing sleeve. Another pattern of density unevenness is that the transport and agitation screw itself is also reduced in size, the strength is weakened, and when the developer reservoir formed by the developer layer thickness regulating magnetic pole and the agitation and transport screw overlap, the agitation and transport When the screw rotates, the toner is deflected when the toner is consumed. After the developer is peeled off and mixed with the developer accumulated in the developer regulating portion after the developer is stripped, the toner concentration unevenness of the developer causes a screw pitch. It occurs in the shape.

In the present embodiment, the magnetic field strength (Gauss) in the direction perpendicular to the surface of the developing sleeve 21 due to the magnetic pole S3, which is the developer layer thickness regulating magnetic pole, starts from the surface position of the developing sleeve 21 where the peak (maximum value) is reached. The angle between the straight line to the center of the developing sleeve 21 and the straight line from the surface position of the developing sleeve 21 closest to the stirring and conveying screw 24 to the center of the developing sleeve 21 is 42 °.

As a result of some investigations, it was found that the angle was 30 °.
It was found that if a configuration apart from the above could be adopted, screw pitch-like unevenness would not occur in the solid black portion of the image formed on the recording medium.

Further, in the present embodiment, as shown in FIG. 3, the photosensitive drum 3 and the developing sleeve 21 are counter-rotated in the developing section, but the invention is not limited to this. However, as shown in FIG. 3, by regulating the thickness of the developer layer on the developing sleeve at the lower part in the direction of gravity of the developing device, it is easier to form a configuration having a small developer compression degree as in the present embodiment (adsorption to the developing sleeve). This is because the undeveloped developer exists in the lower part in the direction of gravity in the developer container.) Therefore, when the transfer section is located below the photosensitive drum, it is preferable to rotate the developing sleeve and the photosensitive drum in the counter direction because the configuration of the developing device becomes easier.

Therefore, according to the present embodiment, the magnetic pole S3
However, after the developer is carried on the surface of the developing sleeve 21 without being affected by the rotation of the stirring / conveying screw 24 near the magnetic pole S3, the amount of the developer is regulated by the regulating blade 18. Therefore, it is not affected by the bending or the like of the stirring and conveying screw 24 during rotation due to the downsizing of the apparatus.
A uniform black solid image can be obtained without causing screw pitch unevenness in the black solid portion of the image.

(Comparative Example) As a comparative example of the embodiment of the present invention, a case where an image is formed on an image forming apparatus having the same configuration as that of the first embodiment except that the following positional relationship is changed will be described.

In this comparative example, the developing sleeve 21 whose magnetic field intensity (Gauss) in the direction perpendicular to the developing sleeve surface due to the magnetic pole S3, which is the developer layer thickness regulating magnetic pole, peaks.
The angle between the straight line from the surface position to the center of the developing sleeve and the straight line from the surface position of the developing sleeve closest to the stirring and conveying screw 24 to the center of the developing sleeve is 28 °.
It has become. As a result of outputting a black solid image of A3 size with the configuration of this comparative example, screw pitch-shaped image density unevenness occurred in the middle of the image.

(Second Embodiment) Next, a second embodiment of the present invention will be described. In addition, about the structure similar to the structure of 1st embodiment, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

In the present embodiment, as the magnetic carrier in the two-component developer, one having a magnetization of 150 emu / cm ³ in a magnetic field of 1000 gauss is used. still,
All other conditions are the same as in the first embodiment.

In the present embodiment, for example, the magnetic field S3, which is a magnetic pole for regulating the thickness of the developer layer, has a magnetic field strength (Gauss) in a direction perpendicular to the surface of the developing sleeve 21 at a peak (maximum value). Developing sleeve 21 from sleeve surface position
The angle between the straight line to the center of the developing sleeve 21 and the straight line from the closest position of the developing sleeve 21 to the stirring and conveying screw 24 to the center of the developing sleeve 21 is 42 °.

When a carrier having a small magnetization is used, if a stirring and conveying screw exists near the developer layer thickness regulating magnetic pole, a screw pitch-like density unevenness is likely to occur. That is, while the developer needs to be compressed to a certain extent uniformly over the entire length of the image area in the developer layer thickness regulating section, the force of magnetically attracting the developer to the developing sleeve is not sufficient. This is because mechanical pressure unevenness is likely to occur in the longitudinal direction of the image area. As a result, unevenness occurs in the amount of the developer coated on the developing sleeve, and screw pitch-shaped unevenness is likely to occur. On the other hand, when a carrier having a small magnetization is used, the compressibility of the developer at the magnetic pole for regulating the thickness of the developer layer is further reduced, and the life of the developer is further extended.

As a result of some investigations, a magnetic carrier in a two-component developer having a magnetization of 30 emu / cm ³ or more and 200 eum ³ or less in a magnetic field of 1000 gauss was used. A straight line from the developing sleeve surface position where the strength of the magnetic field in the direction perpendicular to the developing sleeve peaks to the center of the developing sleeve, and a straight line from the developing sleeve position closest to the stirring and conveying screw to the center of the developing sleeve. If the angle is set to 30 ° or more, the life of the developer can be extended, and a uniform black and white image can be formed.

Therefore, according to the present embodiment, the magnetic pole S3
After the developer containing the magnetic carrier whose magnetization has been optimized is supported on the surface of the developing sleeve 21 without being affected by the rotation of the stirring and conveying screw 24 in the vicinity of the magnetic pole S3, the developer is developed. Since the amount of the developer is regulated by the regulating blade 18, it is not affected by the bending or the like of the stirring and conveying screw 24 during rotation due to the downsizing of the apparatus. Even when a magnetic carrier having a small size is employed, a uniform black solid image can be obtained without causing screw pitch unevenness in a black solid portion of the image.

[0110]

As described above, according to the first aspect of the present invention, the first magnetic pole is not affected by the rotation of the stirring / conveying means near the first magnetic pole, and the developer is loaded on the first magnetic pole. After the developer is carried on the body surface, the amount of the developer is regulated by the regulating means. Even when using a small magnetic carrier with a small magnetization to extend the life of the developer,
A uniform black solid image can be obtained without causing screw pitch unevenness in the black solid portion of the image.

Further, according to the second invention of the present application,
The first magnetic pole, without being affected by the rotation of the stirring and conveying means in the vicinity of the first magnetic pole, after the developer is carried on the surface of the developer carrier which is a non-magnetic cylinder having a diameter of 20 mm, and then the developer of the developer Since the amount is regulated by the regulating means, it is not affected by the deflection of the stirring and conveying means during rotation due to the downsizing of the apparatus. Even when a carrier is employed, a uniform black solid image can be obtained without causing screw pitch unevenness in a black solid portion of the image.

Further, according to the third aspect of the present invention, the developer carrier rotates in the opposite direction to the latent image carrier, and the first magnetic pole is rotated by the stirring and conveying means near the first magnetic pole. After the developer is carried on the surface of the developer carrier without being affected, the amount of developer in the developer is regulated by the regulating means. Unaffected by flexure during rotation, it is small, even when employing a magnetic carrier with a small magnetization to extend the life of the developer, without causing screw pitch unevenness in the black solid portion of the image. A uniform black solid image can be obtained.

Further, according to the fourth invention of the present application,
The first magnetic pole, without being affected by the rotation of the stirring and conveying means in the vicinity of the first magnetic pole, after carrying the developer containing the magnetic carrier whose magnetization has been optimized on the surface of the developer carrying member, Since the developer amount of the developer is regulated by the regulation means, the size of the apparatus is not affected by the deflection of the stirring and conveying means during rotation due to the downsizing of the apparatus, so that the size is small and the life of the developer is extended. Even when a magnetic carrier having a small magnetization is used, a uniform black solid image can be obtained without causing screw pitch unevenness in a black solid portion of the image.

Further, according to the first aspect of the present invention, the first magnetic pole allows the developer to be carried on the surface of the developer carrier without being affected by the rotation of the stirring and conveying means near the first magnetic pole. After that, since the developer amount of the developer is regulated by the regulating means, the developer is not affected by the bending of the stirring and conveying means due to the rotation of the stirring and conveying means due to the downsizing of the apparatus. Even if a magnetic carrier having a small magnetization is used to increase the length, a uniform black solid image can be obtained without causing screw pitch unevenness in the black solid portion of the image.

Further, according to the second invention of the present application,
The first magnetic pole, without being affected by the rotation of the stirring and conveying means in the vicinity of the first magnetic pole, after the developer is carried on the surface of the developer carrier which is a non-magnetic cylinder having a diameter of 20 mm, and then the developer of the developer Since the amount is regulated by the regulating means, it is not affected by the deflection of the stirring and conveying means during rotation due to the downsizing of the apparatus. Even when a carrier is employed, a uniform black solid image can be obtained without causing screw pitch unevenness in a black solid portion of the image.

Further, according to the third invention of the present application, the developer carrier rotates in the opposite direction to the latent image carrier, and the first magnetic pole is rotated by the stirring and conveying means near the first magnetic pole. After the developer is carried on the surface of the developer carrier without being affected, the amount of developer in the developer is regulated by the regulating means. Unaffected by flexure during rotation, it is small, even when employing a magnetic carrier with a small magnetization to extend the life of the developer, without causing screw pitch unevenness in the black solid portion of the image. A uniform black solid image can be obtained.

According to the fourth invention of the present application,
The first magnetic pole, without being affected by the rotation of the stirring and conveying means in the vicinity of the first magnetic pole, after carrying the developer containing the magnetic carrier whose magnetization has been optimized on the surface of the developer carrying member, Since the developer amount of the developer is regulated by the regulation means, the size of the apparatus is not affected by the deflection of the stirring and conveying means during rotation due to the downsizing of the apparatus, so that the size is small and the life of the developer is extended. Even when a magnetic carrier having a small magnetization is used, a uniform black solid image can be obtained without causing screw pitch unevenness in a black solid portion of the image.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a schematic configuration of a full-color printer as an example of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a schematic sectional view showing a schematic configuration of a developing device provided in the image forming apparatus of FIG.

FIG. 3 is a schematic sectional view showing a schematic configuration of a conventional developing device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 developing device 3 photosensitive drum (latent image carrier) 18 regulating blade (regulator) 21 developing sleeve (developer carrier) 23 magnet (magnetic field generating unit) 24 stirring and conveying screw (stirring and conveying unit) 27 developer container (development) Agent container) N1, N2, N3, S1, S2 Magnetic pole

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masanori Shida 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Ichiro Ozawa 3-2-2 Shimomaruko, Ota-ku, Tokyo Canon F term in reference (reference) 2H005 EA02 FA01 2H031 AB02 AC01 AC09 AC11 AC14 AC19 AC20 AC33 AC34 AD03 BA09 2H077 AB02 AC02 AD02 AD06 AD13 AD18 AD36 BA07 BA08 EA01

Claims (8)

[Claims] 1. A developing device for forming a latent image into a visible image by applying a developer containing a magnetic carrier and a non-magnetic toner to a latent image carrier for carrying a latent image. A developer container accommodating the developer, a rotatable developer carrier for carrying the developer in the developer container, and a developer carrier inside the developer carrier so as to provide a developer carrying force on the developer carrier. Magnetic field generating means having a plurality of magnetic poles circumferentially fixed and arranged, rotatable stirring and conveying means for stirring the developer in the vicinity of the developer carrier in the developer container and conveying the developer toward the developer carrier, and developing And a regulating member for regulating the amount of developer on the developer carrier, wherein the magnetic field generating means comprises:
A first magnetic pole disposed in the vicinity of the regulating member on the inner side of the developer container, and a second magnetic pole having the same polarity as the first magnetic pole adjacent to a portion of the first magnetic pole on the inner side of the developer container; The unit has a maximum value of the intensity of the magnetic field in the direction normal to the surface of the developer carrier by the first magnetic pole from the straight line from the surface of the developer carrier close to the agitating and conveying unit to the center of the developer carrier. A developing device, wherein an angle between a straight line from the surface position of the developer carrier to the center of the developer carrier is 30 ° or more. 2. The developing device according to claim 1, wherein the developer carrier is a non-magnetic cylinder having a diameter of 20 mm or less. 3. The developer carrier is disposed opposite to the latent image carrier, and the developer carrier and the latent image carrier move in opposite directions at the facing portion. The developing device according to claim 1, wherein the developing device comprises: 4. The magnetic carrier has a magnetization in a magnetic field of 1000 gauss of ³⁰ emu / cm ³ or more and 200 emu.
The developing device according to any one of claims 1 to 3, wherein the density is not more than / cm ³ . 5. An image forming apparatus for recording an image formed by a series of image forming processes on a recording medium, comprising the developing device according to claim 1. 6. The image forming apparatus according to claim 5, wherein the developer carrier is a non-magnetic cylinder having a diameter of 20 mm or less. 7. The developer carrying member is disposed so as to face the latent image carrying member, and the developer carrying member and the latent image carrying member move in opposite directions at the facing portion. The image forming apparatus according to claim 5 or 6, wherein 8. The magnetic carrier has a magnetization in a magnetic field of 1000 Gauss of ³⁰ emu / cm ³ or more and 200 emu.
/ Imaging apparatus according to any one of cm ³ claim 5 or claim 7, it less.