JPH08146668A - Development device - Google Patents

Abstract

(57) [Summary] [Object] To provide a developing device capable of suppressing carrier adhesion and toner scattering, having a sufficiently high density, free of roughness, and capable of stably obtaining a clear and high-quality image. The developing device does not rotate a two-component developer having a non-magnetic toner having a volume average particle diameter of 10 μm or less and a magnetic carrier having a weight average particle diameter of 80 μm or less inside a magnet roller 23 having a plurality of magnetic poles. Developing sleeve 21 disposed in
The latent image on the drum 3 is developed under the application of an oscillating electric field by forming a magnetic brush of the developer by carrying the developer to a developing area facing the photosensitive drum 3. The magnetic strength of the magnetic carrier in the developing area is 30 at a magnetic field strength of 1000 gauss.
˜150 emu / cm ³ , the peak position of the magnetic force F _{r in} the normal direction on the sleeve 21 is within 10 ° from the closest position between the sleeve 21 and the drum 3 to the downstream side in the moving direction of the drum 3, and in the developing area. The carrier volume ratio Mc is 5 to 30%, and the toner supply coefficient K is 4 or more.

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 for developing and visualizing an electrostatic latent image formed on an image bearing member by an electrophotographic method or an electrostatic recording method, and more particularly to a dry developer. The present invention relates to a developing device that develops by using.

[0002]

2. Description of the Related Art A magnetic brush developing method is widely used as a developing method in an image forming apparatus such as an electrophotographic copying apparatus, an electrostatic recording apparatus and a magnetic recording apparatus. As the magnetic brush developing method, there are a one-component developing method using a one-component developer made of a magnetic toner and a two-component developing method using a two-component developer made of a non-magnetic toner and a magnetic carrier.

The one-component developing system has a simple structure, but it is difficult to obtain an image of a desired color because the toner contains a magnetic material. On the other hand, the two-component developing method uses a non-magnetic toner and is therefore suitable for forming a color image.

A magnetic brush rubbing development method is known as one of the two-component development methods. In this developing method, a non-magnetic cylinder (developing sleeve) rotatably attached to the developing container.
A magnet roller having a plurality of magnetic poles fixed in the developing sleeve, and a regulating blade for regulating the layer thickness of the developer on the developing sleeve. The developing sleeve is rotated to face the developer to the photosensitive drum. Then, the magnetic brush is formed on the developer by the developing pole disposed at the developing position of the magnet roller, and the magnetic brush is rubbed against the photosensitive drum to perform the development. At this time, for the purpose of improving the image quality, it is known that an oscillating electric field is applied to the developing sleeve to prevent the image from slipping and improving the reproducibility of the halftone image.

[0005]

In this type of magnetic brush developing method, a developer contributing to the development can be sufficiently supplied to the developing area, so that a high image density can be obtained, but at the developing position. Since the ears of the magnetic brush are sparse, the image may be rough and poor, especially in highlight and halftone density regions.

Further, in recent years, the demand for high-quality images has been increasing, and great demands have been made for various original images, particularly full-color images. Therefore, while maintaining a sufficiently high image density in solid black areas, the reproducibility of highlight areas is improved,
It is necessary to obtain a fine image even in the halftone portion.

From this, for example, the toner and the magnetic carrier of the two-component developer are reduced in particle size. However, although the image quality is improved, carrier adhesion occurs on the photosensitive drum, and in the worst case, the image loss occurs. It happened.

[0008] As a method for suppressing carrier adhesion when the particle size of such a magnetic carrier is reduced, US Pat.
No. 070,812 (Corresponding Japanese application: JP-A-3-426
No. 2), it is known that the peak position of the magnetic force Fr in the normal line direction on the developing sleeve is arranged near the re-proximity position between the developing sleeve and the photosensitive drum.

Further, a method of making the brush of the magnetic brush denser by reducing the saturation magnetization of the magnetic carrier has been attempted, but in the conventional two-component developing device, carrier adhesion occurs and the image density becomes low. There was an occasion.

It is an object of the present invention to provide a developing device capable of suppressing carrier adhesion and toner scattering, and having a sufficiently high density and no rattling and capable of stably obtaining a clear and high-quality image. is there.

[0011]

The above object can be achieved by the developing device according to the present invention. In summary, the present invention relates to a non-magnetic toner having a volume average particle diameter of 10 μm or less and a weight average particle diameter of 8 μm.
A two-component developer having a magnetic carrier of 0 μm or less,
A magnetic field generating means having a plurality of magnetic poles is supported on a developer supporting means which is non-rotatably arranged inside, and is conveyed to a developing area facing the image carrier, and a magnetic brush of the developer is formed in the developing area. Then, in the developing device for developing the latent image on the image carrier under the formation of the oscillating electric field in the developing region, the strength of magnetization of the magnetic carrier per unit volume is 100.
It is ³⁰ to 150 emu / cm ³ at 0 gauss, and the peak position of the magnetic force F _r in the normal direction on the developer supporting means is measured from the closest position between the developer supporting means and the image bearing body to the image carrier. Within 10 ° downstream of the moving direction,
The volume ratio Mc of the magnetic carrier in the developing area is 5 to 30%.
Where the volume ratio Mc is expressed by the formula (B): Mc [%] = (M / h) × (1 / ρc) × {C / (T + C)} × 100 (B) where M : Amount of developer in a non-brushing state per unit area on the developer supporting means [g / cm ² ] h: height of developing area space [cm] ρc: true density of magnetic carrier [g / cm ³ ] C / (T + C): weight ratio of the magnetic carrier in the developer on the developer supporting means, and the toner supply coefficient K is 4 or more, where the toner supply coefficient K is expressed by the formula (C): K = M × (1 / ρt) × {T / (T + C)} × (1 / Dt) × (Vs1 / Vdr) × 15000 (C) where M: non-ear per unit area on the developer supporting means Amount of developer in standing state [g / cm ³ ] ρt: true density of toner [g / cm ³ ] Dt: particle size of toner [μm] T / (T + C ): Weight ratio of toner in the developer on the developer support means Vs1: Peripheral speed of developer support means [mm / sec] Vdr: Peripheral speed of image carrier [mm / sec] Vs1 / Vdr: Developer support means And a peripheral speed ratio of the image bearing member.

In another aspect of the present invention, the intensity of magnetization per unit volume of the magnetic carrier is ³⁰ to 150 emu / cm ³ at a magnetic field intensity of 1000 gauss, and the developer supporting means and the image carrier are separated from each other. The maximum value of the magnetic force index X, which is the relative value of the magnetic force in the normal direction on the developer supporting means, is 60 or more within the range of 10 ° downstream from the closest position to the moving direction of the image carrier. Where the magnetic force index X is expressed by the formula (A): X = {B ² (r) −B ² (r + Δr)} × (a / Δr) (A) where B ² (r) = B ² _r (r) + B ² _t (r) B ² (r + Δr) = B ² _r (r + Δr) + B ² _t (r +
Δr) a: Proportional constant. When Δr is 0.5 mm, a / Δr = 2
× 10 ^-4 _Br (r): Magnetic flux density in the normal direction at the position r on the developer supporting means [Gauss] B _r (r + Δr): Magnetic flux in the normal direction at the position of 0.5 mm on the developer supporting means Density [Gauss] B _t (r): Magnetic flux density in tangential direction at position r on developer support means [Gauss] B _t (r + Δr): Magnetic flux density in tangential direction at position 0.5 mm on developer support means [Gauss] and the volume ratio Mc of the magnetic carrier in the developing region represented by the formula (B) is 5 to 30%, and the volume ratio Mc is represented by the formula (C).
The toner supply coefficient K represented by is 4 or more.

In still another embodiment of the present invention, the strength of magnetization of the magnetic carrier per unit volume is 100.
It is ³⁰ to 150 emu / cm ³ at 0 gauss, and the peak position of the magnetic force F _r in the normal direction on the developer supporting means is measured from the closest position between the developer supporting means and the image bearing body to the image carrier. Within 10 ° downstream of the moving direction,
Further, from the closest position to the moving direction of the image carrier ±
In less 10 °, B _r of the developer magnetic flux density in the normal direction on the support means B _r and the tangential direction of the magnetic flux density B _t
A region having a / B _t ratio of 3 or more is present with a width of 12 ° or more.

In still another embodiment of the present invention, the strength of magnetization of the magnetic carrier per unit volume is 100.
It is ³⁰ to 150 emu / cm ³ at 0 gauss, and is within 10 ° on the downstream side with respect to the moving direction of the image bearing member from the closest position between the developer bearing member and the image bearing member. The maximum value of the magnetic force index X, which is the relative value of the magnetic force in the normal direction at 60, is 60 or more, and the magnetic force index X is represented by the formula (A). Within ± 10 ° with respect to the moving direction of the toner, the region where the B _r / B _t ratio of the magnetic flux density B _r in the normal direction and the magnetic flux density B _{t in} the tangential direction on the developer supporting means is 3 or more is 12 °. It is characterized in that it exists in the above width.

In either case, preferably, the resistance value of the magnetic carrier is 10 ⁷ to 10 ¹⁵ Ω · cm, the volume average particle diameter dt [μm] of the nonmagnetic toner and the weight average particle diameter dc [μm] of the magnetic carrier are large. , Dt <dc <50 μm.

[0016]

【Example】

Embodiment 1 FIG. 1 is a sectional view showing an embodiment of the developing device of the present invention. The image forming apparatus provided with the main developing device has a photosensitive drum 3 as an image bearing member, and a charging means, an image exposing means, and the above-mentioned not shown as well-known electrophotographic process means around the photosensitive drum 3. The developing device is arranged,
Further, a transfer unit, a cleaning mechanism, a charge eliminating unit, etc. are arranged. The exposing means PWM-modulates an image density signal using a laser beam to expose the photosensitive drum 3 with the image.

In the developing device of this embodiment, a non-magnetic cylinder made of aluminum, stainless steel or the like is used as a developer supporting means in the opening of a developing container 20 containing a two-component developer containing a non-magnetic toner and a soft ferromagnetic carrier. The developing sleeve 21 has a body, and the developing sleeve 21 rotates counterclockwise as indicated by an arrow to support and convey the developer in the container 20,
The sheet is conveyed to the developing area facing the photosensitive drum 3. In the opening of the developing container 20 where the developing sleeve 21 is installed, a regulating blade 25 is arranged above the developing sleeve 21 with a small gap between the developing sleeve 21 and the developing sleeve 21. The layer thickness is regulated.

The developer conveyed to the developing area by the developing sleeve 21 is supplied to the photosensitive drum 3 moving in the direction of the arrow, whereby the latent image formed on the photosensitive drum 3 is developed and visualized as a toner image. It At the time of development, an oscillating bias voltage in which a DC voltage is superimposed on an AC voltage is applied as a developing bias to the developing sleeve 21 by the power source 22, and an oscillating electric field is formed in the developing area between the developing sleeve 21 and the photosensitive drum 3. . A rectangular wave, a sine wave, or the like is used as the waveform of the vibration bias voltage.

A roller-shaped magnet (magnet roller) 23 is non-rotatably installed in the developing sleeve 21, and this magnet roller 23 has three N-pole magnetic poles N ₁ , N ₂ ,
It has N ₃ and two south poles S ₁ , S ₂ . S
₁ pole is the development pole, N ₂ pole and N ₃ pole are stripping off the developer.
The S ₂ pole is a magnetic pole having a pumping / conveying action, and the S ₂ pole is a magnetic pole having a function of regulating the developer layer in cooperation with the regulating blade 25. The N ₁ pole is a carrying magnetic pole having a developer carrying function. Of the above magnetic poles, the N ₂ pole and the N ₃ pole have the same polarity and form a repulsive magnetic field between them, which contributes to the temporary separation of the developer having passed through the developing area from the developing sleeve 21.

The developer once separated from the developing sleeve 21 is agitated and mixed with the developer in the container 20 by the screw 24. The agitated developer is adsorbed on the developing sleeve 21 by the magnetic force of the N ₃ pole, and conveyed to the developing area via the S ₂ pole and the N ₁ pole. The terms upstream and downstream shall be used in relation to the direction of development.

In this example, a two-component developer containing a negatively chargeable non-magnetic toner was used. The developer in the invention will be described. The developer preferably used in the present invention is a two-component developer including a non-magnetic toner and magnetic particles (carrier).

In the present invention, the toner contains colored resin particles (including a binder resin, a colorant and, if necessary, other additives) themselves, and external additives such as colloidal silica fine powder added thereto. Includes colored particles. In this embodiment, a toner having a volume average particle diameter of 8 μm is used which is a negatively chargeable polyester resin. The true density of the toner was about 1.1 g / m ³ .

The magnetic carrier used was a ferrite particle coated with an extremely thin resin and having a weight average particle diameter of 45 μm. The magnetic field strength of this magnetic carrier is 1000
Magnetization strength per unit volume in Gauss (σ
₁₀₀₀ (emu / cm ³⁾⁾ is 66emu / cm ^3, the permeability is about 5.
0, the true density was about 5.2 g / cm ³ .

According to experiments conducted by the present inventor, it has been found that it is effective to set σ ₁₀₀₀ of the magnetic carrier to 150 emu / cm ³ or less in order to obtain a dense image free of rattling. . This is the σ of the magnetic carrier
_It is considered that by setting ₁₀₀₀ to 150 emu / cm ³ or less, the density of the magnetic brush on the developing sleeve can be increased, and for this reason, a dense image without shakiness was obtained. On the other hand, if σ ₁₀₀₀ of the magnetic carrier is less than ³⁰ emu / cm ³ , the developer transportability on the developing sleeve becomes poor, the image quality of the developed image is deteriorated, and the developer easily scatters. The lower limit of ₁₀₀₀ is 30 emu / cm ³ or more.

Next, the carrier attachment will be described.

Carrier adhesion is a phenomenon in which the carrier adheres to the photosensitive drum 3. When the carrier adheres to the photosensitive drum, an air gap is created between the transfer material and the photosensitive drum 3 during transfer, which weakens the electric field in this portion,
The transfer of the toner in the vicinity of the carrier becomes insufficient, which may cause image loss. When this carrier is transferred onto a transfer material, not only the transferred carrier is not fixed on the transfer material, but also toner in the vicinity thereof is not fixed, which may cause fixing failure. When the unfixed image is scraped off, an image defect occurs and the transfer material is contaminated. In addition, the unfixed carrier may move during fixing, causing defects in other images. On the other hand, if the carrier attached to the photosensitive drum remains on the transfer material without being transferred, the photosensitive drum may be damaged when the carrier is removed by the cleaner, which may cause a defect in the image. there were.

In the two-component developer, the toner and the carrier are charged with opposite polarities. That is, when the toner is positively charged, the carrier is negatively charged, and when the toner is negatively charged, the carrier is positively charged. Therefore, when the toner adheres to the image area on the photosensitive drum due to development, the carrier easily adheres to the non-image area. This carrier adhesion is affected by the contrast potential (Vback) between the non-image portion of the photosensitive drum 3 and the developing sleeve 21. If this Vback is small, so-called "fogging" in which toner adheres to the non-image portion is apt to occur, and conversely Vba
When ck is large, carrier adhesion is likely to occur in the non-image area. When applying only the DC electric field as the developing electric field,
Although only the Vback potential is applied between the non-image area and the developing sleeve, when the vibration bias voltage is applied as in the present embodiment, the maximum is “½ × amplitude voltage (peak-to-peak voltage) + Vback”. Since the electric potential is applied, carrier adhesion is likely to occur. Although the method using the above-mentioned vibration bias voltage has the effect of improving the image quality, there is a problem that carrier adhesion easily occurs.

When a carrier having a small magnetic field strength of 1000 gauss is used to improve the image quality as in this embodiment, the force for restraining the carrier on the developing sleeve becomes weak. Therefore, there is a problem that carrier adhesion is likely to occur.

In order to prevent the carrier adhesion, it is necessary to increase the magnetic force (magnetic attraction) that attracts the carrier onto the developing sleeve in the developing area.

FIG. 2 is a diagram for explaining the magnetic force on the developing sleeve 21, where F is the magnetic force on the surface of the developing sleeve 21, and F _r is the vertical direction (generally the normal line) of the surface of the developing sleeve 21. Direction) (a vertical direction component of F (normal direction component)), and F _t is a horizontal direction (generally tangential direction) of the developing sleeve 21 surface (horizontal direction component of F (tangential direction component)). )) Is shown.

Here, the magnetic force F _r is F _r ∝ {B ² (r) -B ² (r + Δr)} / Δr, where B ² (r) = B ² _r (r) + B ² _t (r) B ² (r + Δr) = B ² _r (r + Δr) + B ² _t (r +
Δr) B (r): magnetic flux density at position r on the developing sleeve (magnetic flux density at position r on the surface of the developing sleeve in the normal direction) [Gauss] B _r (r): normal line at position r on the developing sleeve Direction magnetic flux density (magnetic flux density in the direction normal to the surface of the developing sleeve, which is the magnetic flux density at position r on the direction normal to the surface)
[Gauss] B _t (r): Magnetic flux density in the tangential direction at the position r on the developing sleeve (magnetic flux density in the tangential direction on the surface of the developing sleeve, which is the magnetic flux density at the position r on the surface normal direction)
It becomes [Gauss].

Therefore, {B ² (r) -B ² (r
+ Δr)} / be determined the value of [Delta] r, it is possible to know the relative magnitude of the magnetic force F _r, the distribution form of F _r, it is possible to know the peak position of the F _r. Moreover, if Δr is fixed,
F _r ∝ {B ² (r) −B ² (r + Δr)}.

The magnetic force index X is expressed as a relative value of the magnetic force F _{r in} the formula (A): X = {B ² (r) −B ² (r + Δr)} × (a / Δr) (A) where If a is defined as a proportionality constant, then F _r ∝X, so X = {B ² (r) −
It suffices to obtain B ² (r + Δr)} × (a / Δr).

In practice, r is the radius of the developing sleeve 21, and Δr = 0.5 mm is fixed, and the magnetic flux density B in the normal direction is
_r (r), B _r (r + Δr), tangential magnetic flux density B _t
(R) and B _t (r + Δr) are measured using a Gauss meter manufactured by Bell Co. as described later. Then, using the measured value, the magnetic force index X = {B ² (r) −B ² (r + Δr)} ×
(A / Δr) was calculated, and the relative value of the magnetic force F _r was calculated from this. The proportional constant a of the equation (A) is set to a / Δr = 2 × 10 ⁻⁴ for Δr of 0.5 mm (that is, a = 0.5).
× 2 × 10 ^-4 = 1 × 10 ^-4 ).

R is the radius of the developing sleeve 21, and Δr is 0.
Since it is set to 5 mm, B _r (r) is equal to the developing sleeve 21.
Normal direction of the magnetic flux density on the surface, B _{r (r} + Δr) is the normal direction of the magnetic flux density in the position of 0.5mm from the developing sleeve 21 surface, B _t (r) is the tangential direction of the magnetic flux of the developing sleeve 21 surface The density, B _r (r + Δr), is determined by the developing sleeve 21.
The magnetic flux density in the tangential direction is 0.5 mm from the surface.

FIG. 3 is a diagram for explaining the distribution form of the magnetic flux density B _r of the developing magnetic pole S ₁ of the magnet roller 23 and the distribution form of the magnetic force F _r . The horizontal direction in the figure indicates the developing sleeve 2.
The position of 1 in the circumferential direction is shown by the angle with respect to the center of rotation, and the vertical direction shows the magnetic force index X (relative value of the magnetic force F _r ) and the magnetic flux density B _r on the developing sleeve.

In this example, the magnetic force F _{r is applied} to one developing magnetic pole.
Of the peak there are two, the position of the developing magnetic pole and P _0, the magnetic force F P ₁ the larger peak of the downstream relates two peaks of which the developing sleeve moving direction of _r, the peak towards the upstream small and P _2. theta _1, theta ₂ is at an angle between the position of the peak P _1, P ₂ position P ₀ and the magnetic force F _r of the developing magnetic pole, the peak P _1, P ₂ is the development magnetic pole position P of the magnetic force F _r
When it is on the upstream side of _0, it is −, and when it is on the downstream side, it is +. In FIG. 3, K ₀ indicates the closest position to the photosensitive drum on the developing sleeve. K _-10 and K ₊₁₀ are angles 10 from the closest position K ₀ to the upstream side and the downstream side, respectively.
Indicates the position of °.

In the case shown in FIGS. 3A and 3B, the developing magnetic pole position P ₀ is the closest position K ₀ to the photosensitive drum.
The positions of the peaks P ₁ and P ₂ of the magnetic force F _r are θ _{1 with} respect to the closest position K ₀ , respectively.
, Θ ₂ . The cases shown in FIGS. 3A and 3C indicate that the developing magnetic pole position P ₀ is at a position of + θ on the downstream side with respect to the closest position K ₀ , and the peak of the magnetic force F _r . The positions of P ₁ and P ₂ are θ ₁ + θ and θ ₂ + θ, respectively, with respect to the closest position K ₀ . Thus, the magnetic force F
The positions of the peaks P ₁ and P ₂ of _r can be indicated by the angles θ ₁ and θ ₂ .

When the present inventors confirmed by experiments,
In order to suppress the carrier adhesion, the magnetic force index X (relative value of the magnetic force F _r ) in the range between the position K ₀ closest to the photosensitive drum on the developing sleeve and the position 10 ° downstream thereof. It has been found that increasing the maximum value is effective. That is, by arranging the peak position of the magnetic force F _r in this range, carrier adhesion can be effectively suppressed.

Next, the method of measuring the magnetic flux density according to the present invention will be described with reference to FIGS. Gauss meter model 640 manufactured by Bell was used for the measurement.

FIG. 4 is an explanatory diagram showing a method of measuring the magnetic flux density B _{r in} the direction normal to the developing sleeve 21. As shown in FIG. 4, the above model has a rod-shaped axial probe 42 connected to a Gauss meter 41. The developing sleeve 21 is horizontally fixed, and an internal magnet roller 23 is rotatably attached. A horizontal probe 42 is placed at a right angle to the developing sleeve 21 with a slight gap, and the developing sleeve 21 and the probe 42 are fixed so that their centers are located on substantially the same horizontal plane. Measure the magnetic flux density. The magnet roller 23 is a cylindrical body that is substantially concentric with the developing sleeve 21, and the spacing between the developing sleeve 21 and the magnet roller 23 may be considered to be equal everywhere. Therefore, while rotating the magnet roller 23, the magnetic flux density B _r in the normal direction at the surface position of the developing sleeve 21 and at a position 0.5 mm from the surface is measured, so that it is measured at all positions in the circumferential direction of the developing sleeve 21. You can replace it with the one you did.

FIG. 5 is an explanatory diagram showing a method of measuring the magnetic flux density B _{t in} the tangential direction on the developing sleeve 21. The probe 4 in a vertical posture with a slight distance from the developing sleeve 21.
2 are arranged in parallel and fixed so that the developing sleeve 21 and the center of the measurement portion of the probe 42 are located on substantially the same horizontal plane, and the magnetic flux density is measured in that state. Similarly to the above, by rotating the magnet roller 23, the developing sleeve 21
The magnetic flux density B _t in the tangential direction at the surface position and at a position 0.5 mm from the surface position can be measured in the entire circumferential direction of the developing sleeve 21.

As in the present invention, when the magnetic carrier had a σ ₁₀₀₀ of 30 to 150 emu / cm ³ , the image density tended to be slightly lower than when the σ ₁₀₀₀ was larger than this. This is because when the magnetic carrier has a large σ ₁₀₀₀ and the density of the brushes of the magnetic brush of the developer is rough, the toner on the developing sleeve can easily move toward the photosensitive drum in the developing process, so that the developing efficiency is high. When σ ₁₀₀₀ of the magnetic carrier is as small as about ³⁰ to 150 emu / cm ³ as in the example, the density of the ears of the magnetic brush of the developer becomes dense,
It is considered that this is because the movement of the toner is somewhat limited and the developing efficiency is slightly lower than that in the case where the density of the ears is coarse.

Therefore, the magnetic carrier preferably used in the present invention can obtain a dense image without any roughness, but the following measures are required to obtain a sufficient image density.

In this embodiment, first, the volume ratio Mc of the magnetic carrier in the developing region, that is, the volume ratio of the magnetic carrier in the developing space is set to 5 to 30%. The volume ratio Mc follows the following formula (B).

Mc (%) = (M / h) × (1 / ρc) × {C / (T + C)} × 100 (B) However, M: Non-peaking state per unit area on the sleeve Amount of developer [g / cm ³ ] h: height of developing area space [cm] ρc: true density of magnetic carrier [g / cm ³ ] C / (T + C): weight of magnetic carrier in developer on sleeve Proportion

When the volume ratio Mc is less than 5%, the image density tends to be low, and uneven streaks are likely to occur in the high density portion. On the other hand, if it is more than 30%, the developer tends to stay in the developing area, and image unevenness is likely to occur.

The volume ratio Mc of the carrier is set to a predetermined value by correlatively setting the gap between the developing sleeve and the developer layer thickness regulating blade, the gap between the developing sleeve and the photosensitive drum, and the toner concentration of the developer. Can be set.

Further, the toner supply coefficient K, that is, the area ratio of the toner supplied to the developing area is set to 4 or more. The toner supply coefficient K is more preferably 5 or more, and particularly preferably 6 or more. The toner supply coefficient K follows the following formula (C).

K = M × (1 / ρt) × {T / (T + C)} × (1 / Dt) × (Vs1 / Vdr) × 15000 (C) where M: per unit area on the sleeve Amount of developer in non-brushing state [g / cm ³ ] ρt: true density of toner [g / cm ³ ] Dt: particle size of toner [μm] T / (T + C): of toner in developer on sleeve Weight ratio Vs1: peripheral speed of sleeve [mm / sec] Vdr: peripheral speed of photosensitive drum [mm / sec] Vs1 / Vdr: peripheral speed ratio of sleeve and drum

Here, the toner supply coefficient K is an index showing the cross-sectional area of the toner supplied per unit area of the latent image, and the coefficient K = 1 is a solid latent image due to all the toner on the developing sleeve. It is an ideal critical value for further filling. Actually, the cross-sectional area of the toner is substantially circular, and even if the developing efficiency is assumed to be 100%, the solid latent image cannot be filled with the supply coefficient K = 1. Although it depends on the hiding power of the toner, a toner amount of about 3 layers is preferable in order to obtain a sufficient image density. The development efficiency is 10
Not 0%.

From these facts, in order to obtain a sufficient image density, the toner supply coefficient K of about 3 is insufficient, and 4
It is preferable to make the above.

The developer used in this embodiment will be described.

Preparation of Toner Polyester resin obtained by condensing propoxylated bisphenol and fumaric acid (weight average molecular weight 150, number average molecular weight 3300) 100 parts by weight Magenta colorant (rhodamine pigment) 3 parts by weight Negative charge control agent (dialkyl substitution Salicylic acid metal complex) 4 parts by weight

The above materials were melt-kneaded, cooled and pulverized, and the obtained pulverized product was classified by a fixed wall type classifier to prepare a negatively chargeable magenta toner having a volume average particle size of 8 μm.
100 parts by weight of this magenta toner was mixed with 0.4 parts by weight of negative triboelectrically-charged hydrophobic colloidal silica to obtain a magenta toner externally added to silica.

Preparation of Developer Next, ferrite magnetic particles 9 having a weight average particle diameter of 45 μm and coated with a styrene-acrylic acid ester copolymer are used.
A two-component magenta developer was prepared by mixing 5 parts by weight and 5 parts by weight of the above magenta toner having silica added thereto.

Similarly, silica externally added cyan toner, yellow toner and black toner were prepared, and two-component cyan developer, two-component yellow developer and two-component black developer were prepared. The following colorants were used for these toners.

Colorant Cyan Toner: Phthalocyanine Pigment Yellow Toner: Pigment Yellow Pigment Black Toner: Pigment Yellow Pigment, Pigment Red Pigment and Pigment Black Pigment Mixture

The volume of the two-component developer for each of these colors is 100
After being placed in a milliliter polyethylene container and vigorously stirred about 30 times by hand, the triboelectric charge amount of the toner was measured. The toner showed a charge amount of about −30 μC / g for each color.

Next, a numerical example will be described. In this embodiment, the dark portion potential (background portion potential) of the photosensitive drum 3 is-
The light potential (visible portion potential) was set to 650V and -200V. The vibration bias voltage applied to the developing sleeve 21 by the power source 22 has a frequency of 2 kHz and a peak-to-peak voltage Vpp of 2
This is a DC voltage of −550V superposed on an AC voltage of kV. The peripheral speed of the photosensitive drum 3 is 160 mm / sec, and the outer diameter is 8
0 mm, the peripheral speed of the developing sleeve 21 was 280 mm / sec, and the outer diameter was 32 mm. Therefore, the peripheral speed ratio of the sleeve and the drum (developing sleeve peripheral speed / photosensitive drum peripheral speed) is 1.75. The closest distance between the photosensitive drum 3 and the developing sleeve 21 was 0.5 mm. Developing sleeve 21 and regulating blade 2
The interval of 5 was 0.8 mm.

At this time, the amount of the developer of each color of the two-component developer per unit area on the developing sleeve (non-brushing state) is about 40 mg / cm ² , and the volume ratio Mc of the carrier in the developing area is about. 15%, and the toner supply coefficient K was about 6.0.

As the magnet roller 23 fixed in the developing sleeve 21, the following two rollers A and B were used.

Magnet roller A: magnetic flux density of developing magnetic pole; 1280 gauss, peak position of magnetic force F _r ; θ ₁ = + 6 °, θ ₂ = −4 ° Magnet roller B: magnetic flux density of developing magnetic pole; 1270 gauss, magnetic force F Peak position of _r ; θ ₁ = + 2 °

Using these magnet rollers, the magnetic pole position of the developing roller and the peak position of the magnetic force index F _r were variously changed and used for development, and the resulting image was examined for roughness, image density and carrier adhesion. The results are shown in Table 1. In Table 1,
The symbol □ is very good, ◎ is quite good, ○ is good, △
Slightly bad, x shows bad.

[0065]

[Table 1]

As shown in Table 1, Experimental Example No. 1 in which image evaluation could not be performed because carrier adhesion occurred. 2-5 except for any of the experimental example Nos. However, in the highlight and halftone density regions, there was no image roughness, and a dense and good image was obtained. This is the σ _{1000 of} the magnetic carrier.
It is considered that when the density is 150 emu / cm ³ or less, the density of the magnetic brush on the developing sleeve can be increased, and for this reason, a dense image free of roughness can be obtained.

The image density was sufficiently good. Although details will be shown in an experimental example described later, the volume ratio Mc is
Is 5 to 30% and the toner supply coefficient K is 4 or more, a high image density can be obtained.

There is a relation between the peak position of the magnetic force F _r and the carrier adhesion, and the peak position of the magnetic force F _r is in the range between the closest position K ₀ between the developing sleeve and the photosensitive drum and 10 ° downstream thereof. In the case of 1), the carrier adhesion was scarcely generated, and a good result was obtained. However, when it exceeded this range, the carrier adhesion occurred.

A comprehensive evaluation of prevention of roughness, improvement of image density and prevention of carrier adhesion shows that the magnetic carrier has a σ ₁₀₀₀ of 30 to 150 emu / cm ³ and the peak position of the magnetic force F _r is the closest position K ₀ and its downstream position. In the range between the side 10 °,
The volume ratio Mc of the magnetic carrier in the developing area is 5 to 30%.
When the toner supply coefficient K is 4 or more, the reproducibility of the low-density area (highlight area) and the intermediate-density area (halftone area) is good, and the image is free from shakiness and uneven density. The density was sufficiently high, no carrier was attached, and clear and high-quality images were stably obtained for a long period of time.

As explained above, σ of the magnetic carrier is
By setting ₁₀₀₀ to 30 to 150 emu / cm ³ and adjusting the peak position of the magnetic carrier volume ratio Mc, the toner supply coefficient K and the magnetic force F _r , carrier adhesion is suppressed and the image density is sufficiently high and high. It has become possible to obtain high quality images.

The present inventor has further confirmed by experiments that, in order to suppress carrier adhesion, the magnetic force index X in the range between the closest position K ₀ to the photosensitive drum on the developing sleeve and 10 ° downstream thereof. It is effective to increase the maximum value of the (relative value of the magnetic force F _r ), and by setting the maximum value of the magnetic force index X in this range to 60 or more, preferably 80 or more, more preferably 100 or more, The carrier adhesion could be suppressed within the preferable range.

Embodiment 2 This embodiment is characterized in that the magnet roller 23 in the developing sleeve 21 in Embodiment 1 is changed. The other structure of this embodiment is the same as that of the first embodiment.

In this embodiment, the following three magnet rollers C to E were used as the magnet roller 23. The magnet rollers C and D are used in this embodiment, and the magnet roller E is used in a comparative example.

Magnet roller C: magnetic flux density of developing magnetic pole; 1540 gauss Maximum value and position of magnetic force index X; X = 104, θ ₁ = + 6 ° Magnet roller D: magnetic flux density of developing magnetic pole; 1200 gauss Magnetic force index X Value and position; X = 63, θ ₁ = + 9 ° Magnet roller E: magnetic flux density of developing magnetic pole; 800 gauss Maximum value and position of magnetic force index X; X = 27, θ ₁ = −3 °

Using these magnet rollers, the magnetic force index X (relative value of the magnetic force F _r ) in the range between the developing magnetic pole position, the closest position of the developing sleeve and the photosensitive drum, and 10 ° downstream thereof is used. The maximum value was variously changed and used for development, and the resulting image was examined for roughness, image density and carrier adhesion. The results are shown in Tables 2 and 3. In Tables 2 and 3, the meanings of the symbols are the same as in Table 1, □ is very good, ⊚ is quite good, ◯ is good, Δ is a little bad, and × is a bad.

In Tables 2 and 3, Experimental Example No. 3 (3
-1 to 3-4), No. 4 (4-1 to 4-3) and N
o. For 5 (5-1 to 5-3), a developer having a magnetic carrier σ ₁₀₀₀ of 66 emu / cm ³ was used. Experimental example No. 6
In (6-1 to 6-3), σ _{1000 of} the magnetic carrier is 232.
emu / cm ³ was used. Experimental example No. No. 6 is the other condition. Same as 5.

[0077]

[Table 2]

[0078]

[Table 3]

As shown in Tables 2 and 3, Experimental Example No. 1 in which σ _{1000 of} the magnetic carrier was 66 emu / cm ³ . No. 3 having a large magnetic force index X among Nos. 3 to 5. In Nos. 3 and 4, there was no carrier adhesion, which was good, but the magnetic force index X was extremely small N
o. In No. 5, carrier adhesion occurred. Therefore, No. 5
I couldn't evaluate the image. Experimental example No. 3 and 4
In, in the highlight and halftone regions, there was no image roughness, and a dense and good image was obtained. this is,
By setting σ ₁₀₀₀ of the magnetic carrier to 150 emu / cm ³ or less, it is possible to increase the magnetic brush density on the developing sleeve, and it is considered that a dense image free of roughness is obtained.

The closest position K between the developing sleeve and the photosensitive drum
There is a relationship between the maximum value of the magnetic force index X in the range between ₀ and 10 ° on the downstream side and the carrier adhesion. If the maximum value of the magnetic force index X in this range is 60 or more,
The carrier adhesion was suppressed and good, and when it was 80 or more, the carrier adhesion was further suppressed, and when it was 100 or more, the effect of suppressing the carrier adhesion was particularly large, but when it was less than 60, the carrier adhesion was caused and it was poor.

Experimental Example No. No. 6, as described above, uses a developer having a magnetic carrier σ ₁₀₀₀ of 232 emu / cm ³ , but although carrier adhesion did not occur, the reproducibility of the highlight and halftone regions was poor, and the image was rugged. There was a poor image.

The image density was sufficiently high and good. Also in this embodiment, the volume ratio M is the same as in the first embodiment.
By setting c to 5 to 30% and the toner supply coefficient K to 4 or more, a high image density was obtained.

Thus, σ ₁₀₀₀ of the magnetic carrier is 15
When the density is 0 emu / cm ³ or less, the density of the magnetic brush on the developing sleeve can be increased, and thus a dense image without shakiness can be obtained, but since the density of the magnetic brush is increased, the toner on the developing sleeve is increased. Tends to move toward the photosensitive drum. On the other hand, the volume ratio Mc of the magnetic carrier and the toner supply coefficient K may be set appropriately, and the image density can be improved.

A comprehensive evaluation of prevention of roughness, improvement of image density, and prevention of carrier adhesion shows that the magnetic carrier has a σ ₁₀₀₀ of 30 to 150 emu / cm ³ , and the closest position K ₀ between the developing sleeve and the photosensitive drum and its downstream side. The maximum value of the magnetic force index X in the range between 10 ° is 60 or more, more preferably 80 or more, most preferably 100 or more, and the volume ratio Mc of the magnetic carrier in the developing region is 5 to 30%, When the toner supply coefficient K is 4 or more, the reproducibility of the low-density area (highlight area) and the intermediate-density area (halftone area) is good, the image is free of roughness, the density is uniform, and the image density is low. Sufficiently high quality, no carrier adhesion, and clear and high-quality images were stably obtained for a long period of time.

As explained above, σ of the magnetic carrier is
By setting ₁₀₀₀ to 30 to 150 emu / cm ³ and appropriately adjusting the volume ratio Mc of the magnetic carrier, the toner supply coefficient K, and the magnetic force index X, carrier adhesion is suppressed, and the image density is sufficiently high and a high quality image is obtained. It became possible to obtain.

Example 3 This example is the same as the experimental example No. 2 of Example 2. The other conditions are the same, except that the carrier of developer is different from that of 3-3.

Recording density (distribution density of dot-shaped latent image)
A latent image was formed by changing the main scanning direction (beam scanning direction) and the sub-scanning direction (photoreceptor moving direction) to 200 dpi and 400 dpi, and a latent image was formed using a developer in which σ ₁₀₀₀ of the magnetic carrier was variously changed. Table 4 shows the results of the resulting image roughness.

In Table 4, the meanings of the symbols in the column for the evaluation of rubbish are as follows. A: Very smooth image quality without "sharpness" B: Very smooth image quality without "sharpness" C: Smooth image quality without noticeable smoothness,
D: Image quality where "Gasatsuki" stands out, E: Image quality where "Gasatsuki" stands out significantly.

[0089]

[Table 4]

As shown in Table 4, σ _{1000 of} the magnetic carrier
When the value was 150 emu / cm ³ or less, a dense image without graze was obtained. This is σ ₁₀₀₀ of the magnetic carrier is 15
By setting it to 0 emu / cm ³ or less, it is considered that the density of the magnetic brush on the developing sleeve can be increased, so that a dense image without shakiness was obtained. on the other hand,
When the sigma ₁₀₀₀ of the magnetic carrier is less than 30 emu / cm ^3, becomes poor transportability of the developer on the developing sleeve, deteriorated image quality of the developed image, since the scattering of the developer is likely to occur, sigma ₁₀₀₀ is It is preferably ³⁰ emu / cm ³ or more.

Example 4 This example is the same as Example No. 2 of Example 2. 3-3, the particle diameters of the toner and the carrier of the developer, the mixing ratio of the toner and the carrier, and the peripheral speed ratio of the developing sleeve to the photosensitive drum were changed. At this time, the gap between the developing sleeve 21 and the regulating blade 25 was appropriately adjusted so that the amount of the developer on the developing sleeve 21 was about 40 mg / cm ² per unit area. The other conditions of this example are Experimental Example No. Same as 3-3.

The toner and carrier particle diameters are changed variously, and the volume ratio Mc of the magnetic carrier in the developing area and the toner supply coefficient K are changed variously, and the image is developed. The results of carrier attachment are shown in Table 5. In Table 5, the symbols are the same as before, □ is very good, ◎ is quite good, ○ is good,
Δ indicates a little defect, and × indicates a defect.

[0093]

[Table 5]

As shown in Table 5, according to this example, carrier adhesion did not occur, and there was no image roughness in the highlight and halftone density regions, and a dense and good image was obtained. The maximum value of the magnetic force index X is 1
04 is large, carrier adhesion is suppressed, and σ _{1000 of} the magnetic carrier is as small as 66 emu / cm ³ , so it is possible to increase the density of the magnetic brush on the developing sleeve and obtain a dense image with no roughness. It seems that it was done.

When the volume ratio Mc is 5 to 30% and the toner supply coefficient K is 4 or more, the image density is high and good results are obtained. When it is 5 or more, a higher image density is obtained, and 6 or more. For example, the image density is particularly high, but when it is less than 4, the image density is low and the result is poor.

Comprehensive evaluation of prevention of roughness, improvement of image density and prevention of carrier adhesion shows that the magnetic carrier has a σ ₁₀₀₀ of 30 to 150 emu / cm ³ , and the closest position K ₀ between the developing sleeve and the photosensitive drum and its downstream side. The maximum value of the magnetic force index X in the range between 10 ° is 60 or more, more preferably 80 or more, most preferably 100 or more, and the volume ratio Mc of the magnetic carrier in the developing region is 5 to 30%, When the toner supply coefficient K is 4 or more, more preferably 5 or more, even more preferably 6 or more, the reproducibility of the low density region (highlight region) and the intermediate density region (halftone region) is good, and the image A clear, high-quality image was obtained stably for a long period of time without any roughness, no uneven density, a sufficiently high image density, no carrier adhesion.

As explained above, σ of the magnetic carrier is
By setting ₁₀₀₀ to 30 to 150 emu / cm ³ and appropriately adjusting the magnetic force index X, the volume ratio Mc of the magnetic carrier and the toner supply coefficient K, carrier adhesion is suppressed and the image density is sufficiently high and a high quality image is obtained. It became possible to obtain.

Example 5 In this example, the magnetic carrier had a σ ₁₀₀₀ of 30 to 150 em.
The following measures are required to prevent a decrease in image density due to the use of u / cm ³ and obtain a sufficient image density.

It has been confirmed by experiments by the inventor of the present invention that even if such a magnetic carrier is used, in order to obtain a sufficient image density, within ± 10 ° from the closest position between the developing sleeve and the photosensitive drum. In the developing sleeve, the width of the region where the B _r / B _t ratio of the magnetic flux density B _r in the normal direction and the magnetic flux density B _{t in} the tangential direction is 3 or more is 12 ° or more, preferably 14 ° or more, more preferably It has been found that it is effective to set the angle above 16 °.

This is because by setting the B _r / B _t ratio to 3 or more, the magnetic brush on the developing sleeve can be made to stand sufficiently, so that the toner on the developing sleeve is made of the magnetic carrier on the developing sleeve in the developing step. Without being hindered by
Since it can be easily moved in the direction of the photosensitive drum, it seems that the developing efficiency is improved and the image density is improved.

Especially when a small-diameter developing sleeve having an outer diameter of 20 mm or less is used, the developing area becomes relatively narrow, which is disadvantageous to the image density, but in such a case, a particularly large effect is obtained. Have.

Numerical examples in this embodiment will be described.
In this embodiment, the dark potential (background potential) of the photosensitive drum 3 is -650 V, and the light potential (visible potential) is -200.
It was set to V. The vibration bias voltage applied to the developing sleeve 21 by the power supply 22 has a frequency of 2 kHz and a peak-to-peak voltage Vp.
p is a DC voltage of −550V superposed on an AC voltage of 2 kV. The peripheral speed of the photosensitive drum 3 is 160 mm / sec, the outer diameter is 80 mm, and the peripheral speed of the developing sleeve 21 is 280 mm / sec.
Second, the outer diameter was 32 mm. Therefore, the peripheral speed ratio between the sleeve and the drum (developing sleeve peripheral speed / photosensitive drum peripheral speed) is 1.7.
It becomes 5. The closest distance between the photosensitive drum 3 and the developing sleeve 21 was 0.5 mm. The distance between the developing sleeve 21 and the regulation blade 25 was 0.8 mm.

At this time, the amount of developer of the two-component developer of each color per unit area on the developing sleeve (non-brushing state) is about 40 mg / cm ² , and the volume ratio Mc of the carrier in the developing area is about. 15%, and the toner supply coefficient K was about 6.0.

As the magnet roller 23 fixed in the developing sleeve 21, the following three rollers F, G and H were used.

Magnet roller F: magnetic flux density of developing magnetic pole; 1260 gauss Peak position of magnetic force F _r ; θ ₁ = + 8 °, θ ₂ = −12 ° Magnet roller G: magnetic flux density of developing magnetic pole; 1270 gauss Magnetic force F Peak position of _r ; θ ₁ = + 3 ° Magnet roller H: magnetic flux density of developing magnetic pole; 1270 gauss Peak position of magnetic force F _r ; θ ₁ = + 6 °, θ ₂ = −2 °

By using these magnet rollers, the developing magnetic pole position and the peak position of the magnetic force index F _r are variously changed, and the normal line on the developing sleeve is within ± 10 ° from the re-proximity position between the developing sleeve and the photosensitive drum. The magnetic flux density B _r in the directional direction and the magnetic flux density B _{t in} the tangential direction are developed while changing the width of the region where the B _r / B _t ratio is 3 or more. Examined. The results are shown in Table 6-
9 shows. In Tables 6 to 9, the symbol □ is very good,
⊚ is very good, ○ is good, Δ is slightly bad, and × is bad.

In Tables 6 to 9, Experimental Example No. 12 (1
2-1 to 12-11) have a magnetic carrier σ ₁₀₀₀ of 23.
Experimental Example No. ³ except that a developer of 2 emu / cm ³ was used. 1
The conditions are the same as 0 (10-1 to 10-11). Experimental example No. 9 (9-1 to 9-11), No. 10 (10-
1-10-11) and No. 11 (11-1 to 11-1
In 1), a developer having a magnetic carrier σ ₁₀₀₀ of 66 emu / cm ³ was used.

[0108]

[Table 6]

[0109]

[Table 7]

[0110]

[Table 8]

[0111]

[Table 9]

As shown in Tables 6 to 9, the magnetic carrier has σ ₁₀₀₀ of 66 emu / cm ³ in Experimental Example No. Out of 9-10
Experimental example No. in which images could not be evaluated because carrier adhesion occurred. 9-1 to 9-3 and No. 10-9 to 1
Except for 0-11, the image was not rough in the highlight and halftone density regions, and a dense and good image was obtained. This is σ ₁₀₀₀ of magnetic carrier 150emu / cm ³
By the following, it is possible to increase the magnetic brush density on the developing sleeve, and it is considered that a dense image with no roughness is obtained.

Further, B _r / B _t ≧ 3 width within ± 10 ° from the closest position between the developing sleeve and the photosensitive drum (of the magnetic flux density B _r in the normal direction and the magnetic flux density B _{t in} the tangential direction on the developing sleeve. (Width of region where B _r / B _t ratio is 3 or more)
There is a relationship between the image density and the image density. If the width B _r / B _t ≧ 3 is 12 ° or more, the image density is high and the image density is 14 °.
If it is at least above, the image density will be further improved, and if it is at least 16 °, the image density will be remarkably improved. However, B _r / B _t
When the ≧ 3 width is less than 12 °, the image density is low and somewhat poor, and when it is less than 10 °, the image density is poor and low.

Considering this reason, the fact that the width B _r / B _t ≧ 3 is large means that the region in which the developer is sufficiently spiked is wide, and the spike is sufficiently raised in the developing step. In this area, the toner on the developing sleeve can be easily moved toward the photosensitive drum without being obstructed by the ears of the magnetic carrier, so the developing efficiency is high and sufficient toner can be attached to the high image density area. It is considered possible.

In the present invention, σ ₁₀₀₀ of the magnetic carrier is set to 15
0 emu / cm ³ and in the following, thereby increasing the density of the magnetic brush on the developing sleeve, is obtained a dense images without roughness, by increasing the density of the magnetic brush, the toner on the developing sleeve is a photosensitive It tends to be difficult to move in the drum direction. Therefore, increasing the width of B _r / B _t ≧ 3 is particularly effective when such a magnetic carrier is used, and is effective in improving the image density.

Further, there is a relation between the peak position of the magnetic force F _r and the carrier adhesion. The peak position of the magnetic force F _r is the closest position K ₀ between the developing sleeve and the photosensitive drum and 10 ° downstream thereof.
Within the range between and, good results were obtained with almost no carrier adhesion, but beyond this range, carrier adhesion occurred.

Experimental Example No. As described above, No. 12 uses a developer having a magnetic carrier σ ₁₀₀₀ of 232 emu / cm ³ , but although carrier adhesion did not occur, the reproducibility of highlight and halftone areas was poor, and the image was rugged. There was a poor image.

Comprehensive evaluation of prevention of roughness, improvement of image density and prevention of carrier adhesion shows that the magnetic carrier has a σ ₁₀₀₀ of 30 to 150 emu / cm ³ and within ± 10 ° from the closest position between the developing sleeve and the photosensitive drum. B _r / B _t ≧ 3
The width is 12 ° or more (more preferably 14 ° or more, more preferably 16 ° or more), and the peak position of the magnetic force F _r is in the range between the closest position K ₀ and 10 ° downstream thereof. In addition, the reproducibility of the low density area (highlight area) and the intermediate density area (halftone area) is good, there is no image roughness, there is no density unevenness, the image density is sufficiently high, there is no carrier adhesion, and it is clear. A high quality image was stably obtained over a long period of time.

As explained above, σ of the magnetic carrier
₁₀₀₀ was a 30~150emu / cm ^3, by a proper peak position of B _r / B _t ≧ 3 width and the magnetic force F _r, suppresses carrier adhesion, the image density is sufficiently high, a high quality image It became possible to obtain.

The present inventor has further confirmed by experiments that, in order to suppress carrier adhesion, the magnetic force index X in the range between the closest position K ₀ to the photosensitive drum on the developing sleeve and 10 ° downstream thereof. It is effective to increase the maximum value of the (relative value of the magnetic force F _r ), and by setting the maximum value of the magnetic force index X in this range to 60 or more, preferably 80 or more, more preferably 100 or more, The carrier adhesion could be suppressed within the preferable range.

Sixth Embodiment This embodiment is characterized in that the magnet roller 23 in the developing sleeve 21 in the fifth embodiment is replaced. Other configurations of this embodiment are similar to those of the fifth embodiment. In this example, the following five magnet rollers I to M were used as the magnet roller 23. The magnet rollers I to L are used in this embodiment, and the magnet roller H is used in the comparative example.

Magnet roller I: magnetic flux density of developing magnetic pole; 1560 gauss Maximum value and position of magnetic force index X; X = 102, θ ₁ = + 6 ° Magnet roller J: magnetic flux density of developing magnetic pole; 1200 gauss Magnetic force index X Maximum value and position; X = 74, θ ₁ = + 12 ° Magnet roller K: magnetic flux density of developing magnetic pole; 1180 gauss Maximum value and position of magnetic force index X; X = 62, θ ₁ = + 9 ° Magnet roller L: Magnetic flux density of developing magnetic pole; 1520 gauss Maximum value and position of magnetic force index X; X = 143, θ ₁ = + 6 ° Magnet roller M: Magnetic flux density of developing magnetic pole; 750 gauss Maximum value and position of magnetic force index X; X = 24, θ ₁ = −3 °

Using these magnet rollers, the magnetic force index X (relative value of the magnetic force F _r ) in the range between the developing magnetic pole position, the closest position of the developing sleeve and the photosensitive drum, and 10 ° downstream thereof is used. The maximum value is changed variously, and B _r / B _t ≧ 3 width within ± 10 ° from the closest position between the developing sleeve and the photosensitive drum (the magnetic flux density B _r in the normal direction on the developing sleeve and the magnetic flux in the tangential direction). B _r / B of density B _t
The width of a region having a _t ratio of 3 or more) was changed to perform development, and the resulting image was examined for roughness, image density and carrier adhesion. The results are shown in Tables 10-15. Tables 10-15
In the same way, □ is very good for the meaning of the symbol, ◎
Is fairly good, ◯ is good, Δ is slightly bad, and x is bad.

In Tables 10 to 15, Experimental Example No. 18
(18-1 to 18-11) is Experimental Example N except that a developer having a magnetic carrier σ ₁₀₀₀ of 232 emu / cm ³ was used.
o. 17 (17-1 to 17-5) and the conditions are the same.
Experimental example No. 13 (13-1 to 13-11), No. 1
4 (14-1 to 14-11), No. 15 (15-1 ~
15-11), No. 16 (16-1 to 16-11) and No. For No. 17 (17-1 to 17-5), a developer having a magnetic carrier σ ₁₀₀₀ of 66 emu / cm ³ was used.

[0125]

[Table 10]

[0126]

[Table 11]

[0127]

[Table 12]

[0128]

[Table 13]

[0129]

[Table 14]

[0130]

[Table 15]

As shown in Tables 10 to 15, the magnetic carrier has a σ ₁₀₀₀ of 66 emu / cm ³ in Experimental Example No. Nos. 13 to 17 having a large magnetic force index X. In Nos. 13 to 16, the carrier adhesion was good with almost no adhesion, but the magnetic index X was extremely small. In No. 17, carrier adhesion occurred.
Therefore, No. In No. 17, the image could not be evaluated. Experimental example No. In Nos. 13 to 16, a dense and good image was obtained without any image roughness in the highlight and halftone regions. This is σ ₁₀₀₀ of magnetic carrier 150em
It is considered that the magnetic brush density on the developing sleeve can be increased by setting it to be u / cm ³ or less, and therefore, a dense image with no roughness can be obtained.

There is a relationship between the maximum value of the magnetic force index X in the range between the closest position of the developing sleeve and the photosensitive drum and 10 ° downstream thereof and the carrier adhesion, and the magnetic force within this range is present. When the maximum value of the index X is 60 or more, carrier adhesion is suppressed and is good, when it is 80 or more, carrier adhesion is further suppressed, and when it is 100 or more, the effect of suppressing carrier adhesion is particularly large. If it is less than the above range, carrier adhesion is caused and it is not good.

Experimental Example No. No. 18, as described above, uses a developer having a magnetic carrier σ ₁₀₀₀ of 232 emu / cm ³ , but although carrier adhesion did not occur, the reproducibility of the highlight and halftone areas was poor, and the image was rugged. There was a poor image.

Further, there is a relation between the B _r / B _t ≧ 3 width and the image density within ± 10 ° from the closest position between the developing sleeve and the photosensitive drum, and B _r / B _t ≧ 3 width is 12 or less. If it is at least °, the image density is high and good, if it is at least 14 °, the image density is further improved, and if it is at least 16 °, the image density is remarkably improved. However, when the width B _r / B _t ≧ 3 was less than 12 °, the image density was low and the image quality was a little poor, and when it was less than 10 °, the image density was poor and the image density was low.

As described above, this is B _r / B _t ≧ 3
The large width means that the area where the developer is fully spiked is large, and the toner on the developing sleeve interferes with the spikes of the magnetic carrier in the portion where the spikes are sufficiently spiked in the developing process. It is considered that the toner can be easily moved in the direction of the photosensitive drum without being subjected to the above operation, and thus the development efficiency is high and sufficient toner can be attached to the high image density region.

In the present invention, σ ₁₀₀₀ of the magnetic carrier is set to 15
By setting the density to 0 emu / cm ³ or less, the density of the magnetic brush on the developing sleeve can be increased, and a dense image without graze can be obtained, while by increasing the density of the magnetic brush,
Although the toner on the developing sleeve tends to be difficult to move toward the photosensitive drum, increasing the width B _r / B _t ≧ 3 is particularly effective when such a magnetic carrier is used, and the image density Effective for improvement.

Comprehensive evaluation of prevention of roughness, improvement of image density and prevention of carrier adhesion shows that the magnetic carrier has a σ ₁₀₀₀ of 30 to 150 emu / cm ³ , and the closest position between the developing sleeve and the photosensitive drum and 10 ° downstream thereof. The maximum value of the magnetic force index X in the range between and is 60 or more (more preferably 80
And more preferably 100 or more), and B within ± 10 ° from the closest position between the developing sleeve and the photosensitive drum.
_{When r} / B _t ≧ 3 width is 12 ° or more (more preferably 14 ° or more, more preferably 16 ° or more), the low density region (highlight region) and the intermediate density region (halftone region) are The reproducibility was good, the image was free from shakiness, the density was not uneven, the image density was sufficiently high, there was no carrier adhesion, and clear and high-quality images were stably obtained for a long period of time.

As explained above, σ of the magnetic carrier is
₁₀₀₀ was a 30~150emu / cm ^3, by the proper B _r / B _t ≧ 3 width and the magnetic force index X, suppresses carrier adhesion, the image density is sufficiently high, to obtain a high quality image Became possible.

The embodiments of the present invention have been described above. The developers that are preferably used in the invention are described below.

In the present invention, an insulating non-magnetic toner can be used as the toner of the developer. The non-magnetic toner has a volume average particle diameter of 3 μm in that a developed image with high resolution can be obtained. More than 10 μm, especially 4
Those having a size of not less than μm and not more than 8 μm are preferable. The magnetic carrier has a weight average particle size of 10 μm or more and 80 μm or more from the viewpoint that it can be triboelectrically charged by being mixed well with such toner.
The following are particularly preferable 20 μm or more and 50 μm
The following are used:

Further, in terms of the particle diameters of the non-magnetic toner and the magnetic carrier, the weight average particle diameter of the magnetic carrier is larger than the volume average particle diameter of the non-magnetic toner from the viewpoint that the toner can be sufficiently tribocharged. It is preferable. However, if the weight average particle diameter of the magnetic carrier is relatively large, the proportion of the toner in the developer decreases. For this reason, the amount of toner contributing to development may decrease, and the density of the developed image may decrease, or the toner may be triboelectrically charged, and the density of the developed image may decrease.

The volume average particle diameter d of the non-magnetic toner is adjusted so that the toner and the magnetic carrier are mixed well and the toner is favorably triboelectrically charged to obtain a high-resolution developed image.
t (μm) and weight average particle diameter dc (μm) of the magnetic carrier
Preferably has a relationship of dt <dc <50 μm.

Electric resistance value (volume resistivity) of magnetic carrier
Is preferably 10 ⁷ to 10 ¹⁵ Ω · cm, more preferably 10 ⁹ to 10 ¹³ Ω · cm. When the resistance value of the magnetic carrier is less than 10 ⁹ Ω · cm, when the photosensitive drum is scratched, an electric leak is apt to occur between the developing sleeve and the photosensitive drum, and when it is less than 10 ⁷ Ω · cm Even if it does not exist, a leak is likely to occur. On the other hand, if the resistance value of the magnetic carrier exceeds 10 ¹³ Ω · cm, the density of the central portion of the solid image may become low, and if it exceeds 10 ¹⁵ Ω · cm, the image may have a feeling of blurring. .

In the present invention, the measuring methods used for measuring various physical properties of the developer are shown below.

The volume average particle diameter of the non-magnetic toner is 1
Coulter counter TA with 00 μm aperture
-II. That is, a Coulter Counter TA-II (manufactured by Coulter, Inc.) is used as a measuring device, an interface (manufactured by Nikkaki) and a CX-i personal computer (manufactured by Canon) for outputting a number average distribution and a volume average distribution are connected, and electrolysis is performed. As a liquid, a 1% NaCl aqueous solution was prepared using first-grade reagent sodium chloride.

The measuring method is as follows. Above Na
A surfactant, preferably 0.1 to 5 ml of alkylbenzene sulfonate is added as a dispersant to 100 to 150 ml of an electrolytic solution containing a Cl aqueous solution, and a measurement sample of 0.5 to
Add 50 mg. Then, the electrolytic solution in which the sample is suspended is subjected to a dispersion treatment for about 1 to 3 minutes with an ultrasonic disperser, and the particle size distribution of particles of 2 to 40 μm is measured by the Coulter Counter TA-II using an aperture of 100 μm. To obtain the volume average distribution. The volume average particle size is obtained from the volume average distribution thus obtained.

The weight average particle diameter of the magnetic carrier was measured as follows. First, the particle size distribution of the carrier is measured by the following procedure.

(1) About 100 g of a sample is weighed to the order of 0.1 g. (2) The standard sieve of 100 mesh to 400 mesh is used as the sieve, and 100, 145, 200, 2 from the top.
50, 350, 400 are stacked in order of decreasing size, a saucer is placed on the bottom, the sample is placed on the top sieve, and the lid is closed. However, the size of the frame of the sieve should be such that the inner diameter above the sieve surface is 200 mm and the depth from the upper surface to the sieve surface is 45 mm. (3) The above-mentioned stacked sieves are horizontally swung at a rate of 28 per minute by a vibrator.
Shake for 5 minutes at 5 ± 6 times and 150 ± 10 times per minute for 15 minutes. (4) After shaking, add 0.1% of iron powder in each sieve and pan.
Weigh to the digit g. (5) Calculate the weight percentage to the second decimal place, and round to the first decimal place according to JIS-Z8401. However, the total weight of the carrier particles in each part should not be less than 99% of the weight of the sample initially weighed.

The weight average particle diameter is determined according to the following formula from the above measured particle size distribution.

Average particle size (μm) = {(remaining amount of 100 mesh sieve) × 140 + (remaining amount of 145 mesh sieve) × 12
2+ (remaining amount of 200 mesh sieve) × 90 + (remaining amount of 250 mesh sieve) × 68 + (remaining amount of 350 mesh sieve) ×
52+ (remaining amount of 400 mesh sieve) × 38 + total sieve passing amount × 17} × 1/100

The amount of carrier below 500 mesh is 5
The amount of the sample containing 0 g is placed on a 500-mesh standard sieve, suctioned, and calculated from the weight reduction.

The resistance value of the magnetic carrier was measured by using a sandwich type measuring cell having a measuring electrode area of 4 cm ² and an inter-electrode distance of 0.4 cm, and applying magnetic carrier particles to one of the electrodes under a pressure of 1 kg. A voltage was applied between the two electrodes sandwiched between them, and the value was obtained from the current value flowing in the measurement circuit at that time.

The saturation magnetic susceptibility and magnetic permeability of the magnetic carrier were measured by a vibrating sample magnetometer (VSM-P- manufactured by Toei Industry Co., Ltd.).
1). The magnetization of the magnetic carrier particles placed in a magnetic field of maximum 10,000 oersted was measured, and the saturation magnetic susceptibility and magnetic permeability were determined based on the hysteresis curve drawn on the recording paper at that time.

[0154]

As described above, according to the developing device of the present invention, carrier adhesion can be suppressed, and the density is sufficiently high, and clear and high-quality images can be stably obtained.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a developing device of the present invention.

FIG. 2 Magnetic force F _r on a developing sleeve by a magnet roller
FIG. 6 is a diagram for explaining F _t and F _t .

FIG. 3 is an explanatory diagram showing a distribution form of a magnetic flux density B _{r and} a distribution form of a magnetic force F _r of a developing magnetic pole of a magnet roller.

FIG. 4 Surface position of developing sleeve and 0.5 m from there
It is explanatory drawing which shows the measuring method of the magnetic flux density B _r of the normal direction in the m position.

FIG. 5: Surface position of developing sleeve and 0.5 m from there
It is an explanatory view showing a method of measuring the tangential direction of the magnetic flux density B _t at m positions.

[Explanation of symbols] 3 photosensitive drum 21 developing sleeve 22 vibration bias power supply 23 magnet roller 25 regulating blade S ₁ developing magnetic pole P ₀ developing magnetic pole position P ₁ , P ₂ peak position of magnetic force F _r θ re-adjacent position and developing magnetic pole Angle with position θ ₁ , θ ₂ Angle between developing magnetic pole position and peak position of magnetic force F _r X Magnetic force index

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location G03G 15/08 L 15/09 ZA

Claims (12)

[Claims] 1. A two-component developer having a non-magnetic toner having a volume average particle diameter of 10 μm or less and a magnetic carrier having a weight average particle diameter of 80 μm or less is non-rotatably disposed inside a magnetic field generating means having a plurality of magnetic poles. The image is carried while being supported on the provided developer supporting means and conveyed to a developing area facing the image carrier, and a magnetic brush of the developer is formed in the developing area, and an oscillating electric field is formed in the developing area. In a developing device for developing a latent image on a body, the strength of magnetization of the magnetic carrier per unit volume is 30 to 150 when the magnetic field strength is 1000 gauss.
emu / cm ³ , and the peak position of the magnetic force F _r in the normal direction on the developer supporting means is determined from the closest position between the developer supporting means and the image carrier with respect to the moving direction of the image carrier. The volume ratio Mc of the magnetic carrier in the developing region is 5 to 30%, and the volume ratio Mc is
Is the formula (B): Mc [%] = (M / h) × (1 / ρc) × {C / (T + C)} × 100 (B) where, M: unit area on the developer carrier Amount of non-brushing developer per unit [g / cm ² ] h: Height of developing area space [c
m] ρc: true density of magnetic carrier [g / cm ³ ] C / (T + C): weight ratio of magnetic carrier in developer on sleeve, and toner supply coefficient K is 4 or more, where: The toner supply coefficient K is expressed by the formula (C): K = M × (1 / ρt) × {T / (T + C)} × (1 / Dt) × (Vs1 / Vdr) × 15000 (C) where M : Developer amount in a non-brushing state per unit area on the developer supporting means [g / cm ³ ] ρt: true density of toner [g / cm ³ ] Dt: toner particle size [μm] T / (T + C ): Weight ratio of toner in the developer on the developer support means Vs1: Peripheral speed of developer support means [mm / sec] Vdr: Peripheral speed of image carrier [mm / sec] Vs1 / Vdr: Developer support means And a peripheral speed ratio of the image carrier. Wherein the resistance value of the magnetic carrier is 10 ⁷ to 10 ¹⁵
The developing device according to claim 1, which has an Ω · cm. 3. The volume average particle diameter dt [μ of the non-magnetic toner
m] and the weight average particle diameter dc [μm] of the magnetic carrier have a relationship of dt <dc <50 μm. 4. A two-component developer having a non-magnetic toner having a volume average particle diameter of 10 μm or less and a magnetic carrier having a weight average particle diameter of 80 μm or less is non-rotatably disposed inside a magnetic field generating means having a plurality of magnetic poles. The image is carried while being supported on the provided developer supporting means and conveyed to a developing area facing the image carrier, and a magnetic brush of the developer is formed in the developing area, and an oscillating electric field is formed in the developing area. In a developing device for developing a latent image on a body, the strength of magnetization of the magnetic carrier per unit volume is 30 to 150 when the magnetic field strength is 1000 gauss.
emu / cm ^3, which is within the range of 10 ° from the closest position between the developer supporting means and the image bearing member to the moving direction of the image bearing member within 10 ° of the normal direction on the developer supporting means. The maximum value of the magnetic force index X, which is the relative value of the magnetic force, is 60 or more, and the magnetic force index X is expressed by the formula (A): X = {B ² (r) −B ² (r + Δr)} × ( a / Δr) (A) where B ² (r) = B ² _r (r) + B ² _t (r) B ² (r + Δr) = B ² _r (r + Δr) + B ² _t (r +
Δr) a: Proportional constant. When Δr is 0.5 mm, a / Δr = 2
× 10 ^-4 _Br (r): Magnetic flux density in the normal direction at the position r on the developer supporting means [Gauss] B _r (r + Δr): Magnetic flux in the normal direction at the position of 0.5 mm on the developer supporting means Density [Gauss] B _t (r): Magnetic flux density in tangential direction at position r on developer support means [Gauss] B _t (r + Δr): Magnetic flux density in tangential direction at position 0.5 mm on developer support means [Gauss] and the volume ratio Mc of the magnetic carrier in the developing region represented by the formula (B) of claim 1 is 5 to 30%, and the toner supply coefficient K represented by the formula (C). Is 4 or more. 5. The resistance of the magnetic carrier ¹⁰⁷ to ¹⁵
The developing device according to claim 4, which has an Ω · cm. 6. The volume average particle diameter dt [μ of the non-magnetic toner
m] and the weight average particle diameter dc [μm] of the magnetic carrier have a relationship of dt <dc <50 μm. 7. A two-component developer comprising a non-magnetic toner having a volume average particle diameter of 10 μm or less and a magnetic carrier having a weight average particle diameter of 80 μm or less is non-rotatably disposed inside a magnetic field generating means having a plurality of magnetic poles. The image is carried while being supported on the provided developer supporting means and conveyed to a developing area facing the image carrier, and a magnetic brush of the developer is formed in the developing area, and an oscillating electric field is formed in the developing area. In a developing device for developing a latent image on a body, the strength of magnetization of the magnetic carrier per unit volume is 30 to 150 when the magnetic field strength is 1000 gauss.
emu / cm ³ , and the peak position of the magnetic force F _r in the normal direction on the developer supporting means is determined from the closest position between the developer supporting means and the image carrier with respect to the moving direction of the image carrier. The magnetic flux density B _r in the normal direction and the magnetic flux density in the tangential direction on the developer supporting means are within 10 ° on the downstream side and within ± 10 ° with respect to the moving direction of the image carrier from the closest position. B _r / B _t ratio of B _t is three or more regions 12
A developing device characterized by being present at a width of at least °. 8. The resistance value of the magnetic carrier is 10 ⁷ to 10 ¹⁵
The developing device according to claim 7, which has an Ω · cm. 9. The volume average particle diameter dt [μ of the non-magnetic toner]
m] and the weight average particle diameter dc [μm] of the magnetic carrier have a relationship of dt <dc <50 μm. 10. A two-component developer having a non-magnetic toner having a volume average particle diameter of 10 μm or less and a magnetic carrier having a weight average particle diameter of 80 μm or less is non-rotatably disposed inside a magnetic field generating means having a plurality of magnetic poles. The image is carried while being supported on the provided developer supporting means and conveyed to a developing area facing the image carrier, and a magnetic brush of the developer is formed in the developing area, and an oscillating electric field is formed in the developing area. In a developing device for developing a latent image on a body, the strength of magnetization of the magnetic carrier per unit volume is 30 to 150 when the magnetic field strength is 1000 gauss.
emu / cm ^3, which is within the range of 10 ° from the closest position between the developer supporting means and the image bearing member to the moving direction of the image bearing member within 10 ° of the normal direction on the developer supporting means. The maximum value of the magnetic force index X, which is the relative value of the magnetic force, is 60 or more, and the magnetic force index X is expressed by the formula (A): X = {B ² (r) −B ² (r + Δr)} × ( a / Δr) (A) where B ² (r) = B ² _r (r) + B ² _t (r) B ² (r + Δr) = B ² _r (r + Δr) + B ² _t (r +
Δr) a: Proportional constant. When Δr is 0.5 mm, a / Δr = 2
× 10 ^-4 _Br (r): Magnetic flux density in the normal direction at the position r on the developer supporting means [Gauss] B _r (r + Δr): Magnetic flux in the normal direction at the position of 0.5 mm on the developer supporting means Density [Gauss] B _t (r): Magnetic flux density in tangential direction at position r on developer support means [Gauss] B _t (r + Δr): Magnetic flux density in tangential direction at position 0.5 mm on developer support means [Gauss], and within ± 10 ° from the closest position to the moving direction of the image carrier, the magnetic flux density B _r in the normal direction and the magnetic flux density B in the tangential direction on the developer supporting means. developing apparatus B _r / B _t ratio _t is 3 or more regions are characterized by the presence in the 12 ° or wider. 11. A magnetic carrier having a resistance value of 10 ⁷ to 10 10.
The developing device according to claim 10, wherein the developing device has a resistance of ¹⁵ Ω · cm. 12. A volume average particle diameter dt [μ of non-magnetic toner]
m] and the weight average particle diameter dc [μm] of the magnetic carrier have a relationship of dt <dc <50 μm.