JP3232228B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copier, a printer, and a recorded image display device which form a visible image by developing an electrostatic latent image formed on an image carrier by an electrophotographic system or an electrostatic recording system. And an image forming apparatus such as a facsimile.

[0002]

2. Description of the Related Art Conventionally, a dry developer as a developer is carried on the surface of a developer carrier, and the developer is transported and supplied to the vicinity of the surface of an image carrier carrying an electrostatic latent image. A developing method for developing an electrostatic latent image to produce a visible image while applying an alternating (alternating) electric field between the image carrier and the developer carrier is well known.

As an example of this developing method, for example, Japanese Unexamined Patent Publication Nos.
As disclosed in JP-A-65082 and the like, a magnetic brush is formed on the surface of a developing sleeve as a developer carrying member having a magnet disposed therein, using a developer having a two-component composition (carrier particles and toner particles). The magnetic brush is rubbed or brought close to the photosensitive drum as an image bearing member which is opposed to the photosensitive drum while keeping a small developing interval, and continuously between the developing sleeve and the photosensitive drum (between SD). A so-called magnetic brush development method is known, in which an alternating electric field is applied to repeatedly develop toner particles by repeatedly transferring toner particles from the developing sleeve to the photosensitive drum and in the opposite direction.

Further, for example, JP-A-56-14268, JP-A-58-68051, and JP-A-56-1
44452, JP-A-59-181362,
As disclosed in JP-A-60-176069, a non-contact alternating electric field development method using a two-component developer for simple color development or multiple development is also known.

[0005] These developing methods are used in, for example, laser beam printers, and adoption of an electrophotographic system makes it possible to provide a particularly high-speed and low-noise printer among printer apparatuses.

A typical use of this printer is for binary recording of images such as characters and figures, and the structure of the printer is simple in the initial stage of development because it does not require halftones. However, since then, there has been a growing demand for a laser beam printer of the binary recording type to be able to express halftones.
A density pattern method and the like have been proposed.

However, as is well known, it is difficult to obtain a high resolution with a printer employing a dither method and a density pattern method.

In recent years, there has been proposed a method of forming a halftone image while obtaining high resolution without lowering the recording density.

In this method, a halftone pixel is formed by modulating the width of a pulse signal for driving a laser by an image signal, that is, the light emission time length per pixel of the laser is reduced by the image density. Accordingly, the irradiation length of the photosensitive drum per pixel of the laser beam for scanning the photosensitive drum is controlled in accordance with the image density.

More specifically, the pulse width of the pulse signal is shortened for a low-density image portion, thereby shortening the irradiation time of the photosensitive drum. To lengthen the photosensitive drum irradiation time length. According to such a pulse width modulation (PWM) method, an image with high resolution and high gradation can be formed. Therefore, this method is indispensable especially for a color image forming apparatus requiring high resolution and high gradation. It has become something.

[0011]

However, when an image is output by a conventional laser beam printer in accordance with the above-described method, there is a case where roughness occurs in a highlight region having a reflection density of 0.3 or less.

[0012] This roughness is, in a character manuscript or the like,
It did not occur very much, and occurred frequently in low density areas such as photographic images.

[0013] Then, when the cause of the occurrence of roughness was examined, the following was found.

Normally, when a latent image of a highlight portion is formed by a dot latent image, when viewed microscopically, the latent image on the photosensitive drum is not a broad latent image like an analog latent image, but a local latent image. It is a latent image. Furthermore, lower concentrations of attempts to reproduce the latent image from the effects of thickness of the photosensitive drum accent, maximum contrast V ₀ becomes gradually smaller as shown in FIG. For example, if an image having a reflection density of about 0.2 is to be reproduced, V ₀ of the latent image at that time is 15
It will be about 0-250V. Also, when the development of the reflection, to take his head, the surface potential of the non-image portion, because they are 100~200V set higher than the DC component of the developing bias, the developing bias when V ₀ is 150~250V The potential difference V _cont with the DC component is about 0 to 100 V. The reason that V _cont is 0 to 100 V is a very unstable contrast whether the toner adheres to the photosensitive drum side or the developing sleeve side. Therefore, when the latent image is developed with the two-component developer, the contact state of the magnetic brush greatly contributes to the development efficiency, and roughness is likely to occur due to dropout of dots corresponding to unevenness of the ears of the magnetic brush. It is.

Further, conventionally, the two-component developing system using this type of alternating electric field has a wide fogging latitude and hardly causes a trace of developer, so that the rotating direction of the photosensitive drum and the rotating direction of the developing sleeve are disadvantageous. In order to reduce the relative speed in the direction, a rotation direction in which the rotation direction of the developing sleeve is the same at a portion facing the drum has been used.

However, when this developing method is used, a plurality of developing units 24y, 24c, 24m,
When 24 Bk is fixedly arranged around the photosensitive drum 1 and a configuration for forming a full-color image with the laser beam scanner 3 is employed, the following phenomenon occurs.

That is, in order to arrange the plurality of developing units 24y, 24c, 24m, and 24Bk around the photosensitive drum 1, the developing sleeves 11y, 11c, 11m, and 11Bk are required.
The diameter of the photosensitive drum 1 is not at least four times larger than the diameter of the developing sleeve 11y, 11c, 11c.
If the diameter of the photosensitive drum 1 is four times or more larger than the diameters of m and 11Bk, uneven development may occur due to the step at the boundary of the latent image on the photosensitive drum 1. .

This phenomenon will be described in detail with reference to FIGS. 8 and 9. As shown in FIG. 8, when a black solid portion comes after a highlight image, the boundary between the highlight image and the black solid portion becomes high. In some cases, a phenomenon in which a light image is whitened occurs.

This may occur when the diameter of the photosensitive drum is at least four times the diameter of the developing sleeve, as the ratio of the diameter of the developing sleeve to the diameter of the photosensitive drum. Was. Conversely, when the diameter of the photosensitive drum was four times or less, such a phenomenon did not occur. This can be explained as follows.

FIG. 9 shows the shape of the equipotential surface and the lines of electric force when the highlight portion is on the photosensitive drum, followed by the solid portion, and the boundary between the highlight portion and the solid portion faces the developing sleeve. FIG. From this figure, it can be seen that the line of force at the boundary is largely drawn toward the solid portion.
Here, it is considered that the diameter of the developing sleeve is largely related to the developing area, and the diameter of the photosensitive drum is largely related to the distortion of the line of force at the boundary. In other words, if the diameter of the developing sleeve becomes relatively smaller than the diameter of the photosensitive drum, the developing area becomes relatively smaller with respect to the boundary of the distorted latent image, and the direction of the lines of electric force is completely within the developing area. In some cases, it was left facing the solid area. Therefore, in the conventional sleeve rotation in the forward direction, the toner in the supplied developer cannot be supplied to the rear end of the highlight portion, and is developed along the line of electric force toward the solid portion. Therefore, it is conceivable that a white spot may occur at the rear end of the highlight. This largely depends on the ratio between the diameter of the photosensitive drum and the diameter of the developing sleeve. As a result of the experiment, this may occur when the diameter of the photosensitive drum becomes four times or more the diameter of the developing sleeve as described above. Was.

It has been confirmed that the countermeasure for the supply direction of the developer can completely eliminate the problem. In other words, by reversing the direction of supply, the rear end of the highlight is not obstructed by the line of electric force,
Supply, and the problem of white spots can be solved.

In the case of the highlight tip after black solid, the black solid portion is filled with toner, and the electric charge generated by the toner raises the potential of the black solid portion. As a result, the tip of the highlight image did not fall out white.

As described above, by performing the counter development, even when the diameter of the photosensitive drum becomes four times or more the diameter of the developing sleeve, there is no problem that the image becomes white at the boundary between the highlight portion and the solid black portion. It turned out to be.

In addition, it was confirmed that the counter development was effective for eliminating the above-mentioned roughness. The reason for this is that the magnetic brush ears look completely distorted if counter-rotated as compared to the developing sleeve forward rotation when viewed from the photosensitive drum side. It is considered that the unevenness was eliminated.

However, when the developing method of the counter-rotation is used, the relative speed between the developing sleeve and the photosensitive drum becomes too large, and as a result, the force of rubbing by the spikes of the developer becomes too strong. The ground fogging cannot be completely removed, and the rubbing by the spikes is too strong, so that the developability is improved and the dropout of dots and the like disappears, but the rubbing marks by the spikes appear on the image separately. Sometimes the image quality did not improve as expected.

Accordingly, an object of the present invention is to provide an image forming apparatus which can eliminate roughness of an image, prevent white spots and prevent background fog, and can obtain an image of good quality. To provide.

[0027]

According to a first aspect of the present invention, there is provided an image bearing member , a developer container containing a developer having toner and a carrier, and an image bearing member.
An electrostatic image by carrying a developer in the developer container to be developed by the developing unit ears of the developer have a a developer carrying member for feeding transportable <br/> in contact with the image bearing member The diameter of the image carrier is
The average diameter of the carrier is larger than 4 times the diameter of the carrier.
In the image forming apparatus is 0μm or less, in the developing unit
Definitive movement direction of said image bearing member and said developer carrying member each other
A reverse direction have, during development, toner from the image bearing member
The developer bearing member toward the direction of the voltage V ₁ and the toner is above
Direction of the voltage V directed from serial developer carrier to the image carrier
₂ and after a predetermined number of times alternately applying, is set to apply the voltage V ₁ and the voltage V ₃ is the average of the electrocoating <br/> voltage V _2,
The times for applying the voltages V ₁ , V ₂ , and V ₃ are T ₁ ,
T ₂ , T ₃ , when a gap between the image carrier and the developer carrier is d,

[0028]

(Equation 2)

This is achieved by satisfying the following.

According to the second invention of the present application,
According to the first object of the present invention, in the first aspect, when developing, the toner
In but the image carrier collecting <br/> voltage V ₁ and the toner in the direction toward the developer carrying member from said image bearing member from the developer carrying member
Headed after repeated application several times direction of the voltage V ₂ alternately, voltage V ₃ is the average of the voltage V ₁ and the voltage V ₂
Is set to be applied.

Further, according to the third invention of the present application, the above object is achieved in the first invention by the following steps.
Direction from the image carrier to the developer carrier
The image carrier voltage V ₁ and the toner from the developer carrying member
After applying once the voltage V ₂ direction towards the body alternately,
Is accomplished by being set to apply the voltage V ₁ and the voltage V ₃ is the average of the voltage V _2.

According to the fourth aspect of the present invention,
The above object is the invention according to any one of the first to third inventions, wherein the developer container and the developer carrier are
A plurality of the developer carriers are provided around the image carrier.
This is achieved by forming toner images of different colors from each other on the image carrier by means of a body .

Furthermore, according to the fifth aspect of the present application, the object is any one of the first invention to the fourth invention, the exposure means for performing laser exposure to the image bearing member Luminous flux emission per pixel of laser
This is achieved by controlling the time length according to the image density signal .

That is, according to the first aspect of the present invention, since the diameter of the image carrier is larger than four times the diameter of the developer carrier, a plurality of developing devices are arranged around the image carrier. However, when the diameter of the developer carrying member is small, the developing area becomes small, and when the diameter of the image carrying member is large, the electric field lines may be distorted. However, since the moving direction of the developer carrier is opposite to the moving direction of the image carrier at the position facing the image carrier, the developer is supplied without being hindered by the lines of electric force, and Does not cause the phenomenon. At the same time, the unevenness of the ears of the magnetic brush formed on the developer carrying member is eliminated, thereby preventing image roughness. However, by setting the moving direction of the developer carrier in this way, the relative speed between the image carrier and the developer carrier becomes too large, and the force of rubbing by the ears of the developer becomes strong.
Since the carrier has a particle size of 40 μm or less, no rubbing marks due to ears are generated. Further, when the force of rubbing by the ears increases, the ground fogging tends to occur. However, the developing bias voltage is defined as a voltage V ₁ in the direction in which the toner moves from the image carrier to the developer carrier, and an application time T _1. , the toner is applied an alternating voltage and the applied time T ₂ the voltage V ₂ of the force toward the image bearing member from the developer carrying member, then the application time of the voltage V ₃ is the average of the voltages V ₁ and the voltage V ₂ Having set to apply as T _3, the image portion near developed on the image bearing member toner forces pulled back from the image carrier by the voltages V ₁ acts, but the voltage V ₂ and the voltage V _The force to move the image carrier again due to ( ₃₎ acts on the image carrier, which eventually causes the biased vibration of the toner to move toward the image carrier, so that the image area is uniformly developed, and the voltage V is applied to the toner near the non-image area.
₁ causes a force to be pulled back from the image carrier, and the voltage V ₂ causes a force to transfer to the image carrier again. However, the voltage V ₃ causes a force to be pulled back to the developer carrier again. Since a biased vibration that is pulled back to the body side occurs, no fogging occurs in the non-image portion. In particular, the application time T ₁ of the voltage V ₁ is

[0035]

(Equation 3)

[0036] By setting like, without returning to the developer bearing member toner having high triboelectric charge is by the voltage V _1, further application time T ₃ of the voltage V _3,

[0037]

(Equation 4)

By setting as described above, the toner having a low triboelectricity flies to the image portion on the image carrier by the above-mentioned voltages V ₂ and V ₃ , and sufficient developing property is obtained. Furthermore, since applying the voltage V ₃ after applying an alternating voltage of the V ₁ and V _2, also subjected to vibration toner adhering to the high carrier tribo, participate in development. As described above, according to the first invention of the present application, a high-quality image with no fog, no roughness, no rubbing trace, and no fog is obtained.

According to the second aspect of the present invention,
Since the high frequency vibration is applied a plurality of times, the toner adhering to the carrier is sufficiently separated from the carrier, the toner flies sufficiently, and the developing ability is improved.

Further, according to the third aspect of the present invention, since a higher frequency is applied, the developing ability is further improved.

According to the fourth aspect of the present invention,
The developer container and the developer carrier are the same as the image carrier.
A plurality of peripheral parts are provided, and the image is
In the apparatus for forming toner images of different colors on the carrier , as described above, a high-quality multicolor image with no white spots, no roughness, no rubbing traces and no fogging can be obtained.

[0042] Further, according to the fifth aspect of the present application, have the exposure means for performing laser exposure to the image bearing member
The light emission time length per pixel of the laser is
Even if a solid image and a highlight image coexist, a high-quality image with no white spots, rough images, rubbing marks, and uniform fog at the boundary of the image can be obtained by a device that controls according to the degree signal. obtain.

[0043]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 shows a schematic diagram of an electrophotographic copying apparatus which is an embodiment of the image forming apparatus of the present invention.

In the present embodiment, the latent image forming means A, the developing device B, the transfer means C, and the like are provided around the photosensitive drum 1 rotatably supported in the direction of the arrow as an image carrier in the same manner as in the prior art.
Cleaning means D and the like are arranged. Since these configurations are means known to those skilled in the art, detailed description is omitted,
Here, the developing device B in the image forming apparatus of the present invention will be described.

In the present embodiment, the outer diameter of the photosensitive drum 1 is 160 mm. In order to visualize the electrostatic latent image formed on the photosensitive drum 1 by the latent image forming means A, A developing device B is arranged to face the photosensitive drum 1.

The developing device B has a developer container 16 as shown in FIG.
It is partitioned into a developing chamber (first chamber) R ₁ and stirring chamber (second chamber) R ₂ by the the toner storage chamber R _3, a toner (non-magnetic toner) 18 is accommodated replenishment. Note that the toner storage chamber R _3, supply opening 20 is provided, the supply port 20
Replenishing toner 1 in an amount corresponding to the toner consumed through
8 is dropped replenished into the stirring chamber R _2.

On the other hand, the developer 19 is accommodated in the developing chambers R ₁ and R ₂ .

The developer 19 is a two-component developer composed of non-magnetic toner and magnetic particles (carrier). The mixing ratio was such that the nonmagnetic toner was about 5% by weight. In the present embodiment, the non-magnetic toner has a volume average particle size of about 8 μm, and the magnetic particles are resin-coated ferrite particles (maximum magnetization of 60 emu / g), and the weight average of the ferrite particles is 60 emu / g. The particle size was 35 μm, and its resistance value was 10 ⁸ Ωcm or more. Also,
The magnetic permeability of the magnetic particles was about 5.0. As a result of various investigations, when the particle diameter of the carrier is selected to be 40 μm or less as in the present invention, the rotation of the developing sleeve 11 as the developer carrier is set in the counter direction at the portion facing the photosensitive drum 1. However, it was possible to eliminate rubbing marks.

An opening is provided in a portion of the developer container 16 close to the photosensitive drum 1, and an opening is provided from the opening.
The developing sleeve 11 projects outside. The developing sleeve 11 is rotatably incorporated in the developer container 16. In the present embodiment, the outer diameter of the developing sleeve 11 is
The peripheral speed was 280 mm / sec. The developing sleeve 11 is arranged so that the distance between the developing sleeve 11 and the photosensitive drum 1 is 500 μm. The developing sleeve 11 is made of a non-magnetic agent, and has a magnet 12 fixed therein as a magnetic field generating means.

The magnet 12 has a developing magnetic pole S ₁ , a magnetic pole N ₃ located downstream thereof, and magnetic poles N ₂ , S ₂ and N ₁ for transporting the developer 19. The magnet 12 is disposed in the developing sleeve 11 such that the developing magnetic pole S ₁ faces the photosensitive drum 1. Developing magnetic pole S ₁ forms a magnetic field in the vicinity of the developing portion between the developing sleeve 11 and the photosensitive drum 1, the magnetic brush is formed by the magnetic field.

Further, below the developing sleeve 11, a blade 15 is fixedly arranged on the developer container 16 at a predetermined distance from the developing sleeve 11, and the distance between the developing sleeve 11 and the blade 15 is 800 μm. ing.
The blade 15 is made of a non-magnetic agent such as aluminum SUS 316, and regulates the layer thickness of the developer 19 on the developing sleeve 11.

[0052] In addition, the developing chamber R ₁ transport screw 1
3 are accommodated. Conveying screw 13 is rotated in the direction indicated by an arrow in the figure, the developer 19 in the developing chamber R ₁ by the driving rotation of the conveying screw 13 is developing sleeve 1
1 is conveyed in the longitudinal direction.

[0053] Then, the developing chamber R _2, the conveying screw 14 is housed. Conveying screw 14 is conveyed along the toner in the longitudinal direction of the developing sleeve 11 by the rotation, the toner falls freely to the stirring chamber R in ₂ from the supply port 20.

In the above-described developing device, the developing sleeve 11 carries the developer at a position near the magnetic pole N ₂ , and the developer 19 is transported toward the developing unit with the rotation of the developing sleeve 11. Is conveyed in the counter direction to the photosensitive drum. When the developer 19 reaches the vicinity of the developing unit, the magnetic particles of the developer 19 rises from the developing sleeve 11 while succession by the magnetic force of the magnetic pole S _1, a magnetic brush of the developer 19 is formed.

The tip of the magnetic brush rubs the surface of the photosensitive drum 1. However, since the average particle diameter of the carrier is 40 μm or less, no rubbing marks are generated. Furthermore, according to the present invention,
By applying the developing bias voltage shown in FIG. 2 between the developing sleeve 11 and the photosensitive drum 1, an image having a smooth highlight portion and no fog can be obtained.

Next, the characteristics of the applied developing bias according to the present invention will be described with reference to FIG. First, according to the present invention,
When the pull-back voltage V ₁ is applied as the bias voltage for the time T ₁ , both the toner in the image area and the toner in the non-image area on the photosensitive drum 1 receive a force in the direction toward the developing sleeve 11 uniformly. Then, the toner in the developing region and applying a developing voltage V ₂ T ₂ hours receives a force toward to the non-image portion in the image portion. In addition, DC considering fog removal of non-image parts
Voltage corresponding to bias V ₃ = (１ ／) · (V ₁ +
When V ₂ ) is applied for T _3, a force in the direction toward the developing sleeve 11 is applied to the toner in the non-image portion, and the image portion (the portion corresponding to the highlight portion shown in FIG. 6 used in the description of the conventional example). ) Is given a force in a direction toward the photosensitive drum 1.

If this process is repeated several tens of times or more during development, the toner vibrates unevenly in the vicinity of the image portion as described above. In the non-image area, the toner vibrates near the sleeve, so that a smooth image without fogging can be obtained.

Here, in order to obtain a uniform image with little fog, the potential difference of the developing bias and the distance d between the SD and d are required.
(M) and the relationship between the voltage application times T ₁ , T ₂ , and T ₃ are important, and the relationship will be described below.

First, the above relationship will be described while explaining the movement of the toner. FIG. 3 is a diagram showing a state of the developer in the developing unit. In practice, the carrier forms a spike as shown in the figure between the carrier and the photosensitive drum 1 during development, and more than half of the space is in a state where the toner can freely reciprocate. Is explained in a form ignoring. In addition, many experiments were consistent with the results of the present invention, and it was found that there was no problem even if the existence of carriers was ignored as described above. Further, regarding the rubbing marks, the particle size of the carrier was set to 40 μm as described above.
m or less, it can be lost.
As long as the fog is completely removed by the bias, a uniform image can be stably obtained.

In FIG. 3, q is the amount of charge, m is the mass, a is the acceleration, ΔV is the potential difference between the photosensitive drum 1 and the developing sleeve 11, and d is the gap between the photosensitive drum 1 and the developing sleeve 11. .

According to the present invention, the developed toner on the photosensitive drum 1 is removed by the time T ₁ during which the pull-back voltage V ₁ is applied.
By setting a condition that the toner is not returned to the developing sleeve 11 during this period, the toner repeats the bias vibration on the photosensitive drum 1.

Here, a condition for not returning to the developing sleeve 11 will be described in consideration of the potential of the image portion of the photosensitive drum 1.
As described above, the potential of the latent image when reproducing an image having a density of about 0.2 depends on the DC component of the developing sleeve 11 (the voltage in the direction of causing the image to fly to the image portion or pulling back to the non-image portion). They are almost equal.

Therefore, in the present invention, a so-called pull-back voltage V ₁ is applied to the developer in the direction from the photosensitive drum 1 to the developing sleeve 11, and the developer is directed from the developing sleeve 11 to the photosensitive drum 1. A voltage of a so-called intermediate value (DC component) of the flying voltage V ₂ that gives a force in the direction, that is,
1/2 (V ₂ + V ₁ ) is defined as the potential of the highlight image area of the photosensitive drum 1, and the toner is transferred to the developing sleeve 1 under the condition that the pull-back voltage V ₁ of the developing sleeve 11 is applied.
All you have to do is give a time that will not bring you back to 1. This is represented by the following equation.

[0064]

(Equation 5)

Here, the larger | Q | is, the more affected by the electric field, the easier it is to reciprocate. In the present invention, a selection is made such that even a toner having a large Q is not returned to the developing sleeve 11. Therefore,
The maximum value of Q that takes into account the transfer even in a normal tribo distribution is
Because it is 5.0 × 10 ^-2 C / kg, as a condition of T _1, the following expression is established.

[0066]

(Equation 6)

Further, in the present invention, after a voltage for pulling back the developer and a voltage for causing the developer to fly are applied a plurality of times, the voltage in the direction in which the developer is caused to fly and the direction in which the developer is pulled back (the voltage of the DC component described above) is applied to the non-image portion. ) is applied to T ₃ hours, the T ₃
The length of time is also characterized.

Under the above-described conditions, a condition is set that, when the toner having a high tribo is developed into a latent image having substantially the same potential as that of the developing sleeve 11, the toner is not returned to the developing sleeve 11 again by the pull-back electric field. When the toner is applied between the developing sleeve 11 and the photosensitive drum 1 by the developing voltage V ₂ and the blank voltage V ₃ , the developing sleeve 11
Conditions for flying from above to the highlight image area were determined. If the toner having a low triborate flies, selectivity is reduced to the highlight portion, and sufficient developability can be obtained. The condition for that is expressed by the following equation.

[0069]

(Equation 7)

Here, transfer to toner with low tribo is considered.
The minimum value considered is 15 × 10^-12 Put it in C / kg
Then

[0071]

(Equation 8)

[0072] By applying above show T ₃ hours or more, less image highlight reproduction of uniform fog can be obtained.

Further, as described above, the present invention is characterized in that only the DC bias is applied for T ₃ time after the pull-back electric field and the flying electric field of the toner are applied a plurality of times. During this time, the toner having a high triboelectricity and adhering to the carrier is also likely to be vibrated by the electric field and become involved in the development. This will be described in detail below.

First, the higher the frequency of (T ₁ + T ₂ ), the more the frequency of vibration of the developer increases, so that the uniformity of the highlight portion increases. As a result of the experiment, the SD distance 5
When the potential difference between V _{2 and} V ₁ is ₂ kV at 00 μm,
If the time of (T ₁ + T ₂ ) is set to 2.5 × 10 ⁻⁴ seconds or less,
A very uniform image was obtained.

However, as (T ₁ + T ₂ ) becomes shorter, the image quality becomes better, but a phenomenon occurs in which the density is hardly obtained. This is considered as follows.

As shown in FIG. 2, the toner having a high tribo adhered to the carrier is not sufficiently separated from the carrier by applying the high-frequency vibration only once, so that the toner flying as described above is sufficiently performed. As a result, the developing ability is reduced. Therefore, as shown in FIG. 4, the bias voltages V ₁ to provide a force toward the developing sleeve 11 to the toner, a bias voltage V ₂ a plurality of times to provide a force toward the photosensitive drum 1 into a toner (FIG. 4 Then twice)
It is more preferable to apply the toner, and the toner having a high tribo is also separated from the carrier and used for development.

As a result, a uniform high-density image can be stably obtained.

Next, an embodiment based on the present invention will be described.

Example 1 An image was formed under the following conditions as developing conditions. The developing device B was configured as shown in FIG. 1, and developed by the above-described operation.

Developing sleeve outer diameter 25 mm Photoconductor drum outer diameter 160 mm Developing sleeve peripheral speed 280 mm / sec Photoconductor drum peripheral speed 160 mm / sec SD distance 500 μm Average toner particle diameter 6 μm Average carrier particle diameter 35 μm As developing bias The bias method shown in FIG. 2 was used. The toner used was a positive toner. That is, in FIG. 2, T ₁ , T ₂ , and T ₃ are T ₁ = 6.25 × 10 under the condition of V _D = 600 V V _L = 50 V V ₁ = −550 V V ₂ = 1450 V V ₃ = 450 V. ⁻⁵ sec T ₂ = 6.25 × 10 ⁻⁵ sec T ₃ = 3.75 × 10 ⁻⁴ sec That is,

[0081]

(Equation 9)

When the development was carried out under the conditions described above, the reproduction of highlights was good, and a uniform image free from white spots, fogging and rubbing marks was obtained.

Example 2 In this example, the same developing conditions as in Example 1 were used except for the bias voltage and the charging polarity of the toner. The tribo of the toner is minus and the bias method shown in FIG. 2 is used, and the value of the bias voltage is as follows: V _D = −600 V V _L = −50 V V ₁ = −50 V V ₂ = −1450 V V ₃ = −550 V T ₁ , T ₂ , and T ₃ are: T ₁ = 5.0 × 10 ⁻⁵ sec T ₂ = 5.0 × 10 ⁻⁵ sec T ₃ = 4.0 × 10 ⁻⁴ sec

[0084]

(Equation 10)

The development was carried out under the conditions of Example 1.
Highlight reproducibility equal to or higher than that of, and an image with little fog was obtained.

(Embodiment 3) In this embodiment, similarly to the above-described embodiment 2, under the condition that V _D = −600 V V _L = −50 V V ₁ = −50 V V ₂ = −1450 V V ₃ = −550 V The development was performed using the bias method shown in FIG. The conditions for T ₁ , T ₂ , and T ₃ are as follows: T ₁ = 4.16 × 10 ⁻⁵ sec T ₂ = 4.16 × 10 ⁻⁵ sec T ₃ = 4.99 × 10 ⁻⁴ sec

[0087]

[Equation 11]

As a result, the image quality, density and highlight reproducibility were higher than those of Example 2, and an image with less fog was obtained.

(Embodiment 4) In this embodiment,
As in Example 2, V_D= -600V V_L= -50V V₁= -50V V_Two= -1450V V_Three= -550 V, using the bias method shown in FIG.
Was. T₁, T_Two, T_ThreeThe condition of T₁= 3.57 × 10^-Five sec T_Two= 3.57 × 10^-Fivesec T_Three= 4.99 × 10^-Foursec In other words,

[0090]

(Equation 12)

As a result, an image having the same image quality, density and highlight reproducibility as in Example 3 was obtained, and an image with little fog was obtained.

(Comparative Example 1) As in Example 2, the bias system shown in FIG. 2 was used under the following conditions: V _D = −600 V V _L = −50 V V ₁ = −50 V V ₂ = −1450 V V ₃ = −550 V Was used for development. The conditions for T ₁ , T ₂ , and T ₃ are as follows: T ₁ = 6.25 × 10 ⁻⁵ sec T ₂ = 6.25 × 10 ⁻⁵ sec T ₃ = 1.25 × 10 ⁻⁴ sec

[0093]

(Equation 13)

When an image was displayed under the conditions described above, the uniformity of the highlighted portion was not sufficient, the fog did not completely disappear, and only an unstable image was obtained.

(Comparative Example 2) Under the same conditions as in Example 1, when only the carrier diameter was 50 μm and the average particle diameter was 50 μm, rubbing traces of the ears of the developer occurred, and the highlight image was unsatisfactory. Only uniform and rugged images were obtained.

Although the present embodiment has been described based on the image forming apparatus shown in FIG. 1, a color printer having a laser beam scanner as an exposure means like the apparatus shown in FIG. 7 used in the description of the conventional example. By applying the present invention to an image forming apparatus, a high-quality color image can be obtained.

In the above description of the present embodiment,
As the average particle diameter of the toner and the carrier, a volume average value by a Coulter counter method was used.

Further, regarding the triboelectric charge amount of the toner,
It measured using the apparatus shown in FIG. As shown in FIG. 10, a 500 mesh screen 1
There is provided a metal measuring container 142 having a 43. At the time of measurement, it is necessary to measure the triboelectric charge amount.
The component developer is placed in a polyethylene bottle having a capacity of 50 to 100 ml and shaken by hand for about 10 to 40 seconds. Then, about 0.5 to 1.5 g of the developer is placed in the measuring container 142, and a metal lid is placed. 144. Then, the weight of the entire measurement container 142 at this time is weighed to be W ₁ (kg). Next, in the suction device 141 (at least the portion in contact with the measurement container 142 is at least an insulator), suction is performed from the suction port 147 and the air volume control valve 146 is adjusted to increase the pressure of the vacuum gauge 145 to 250 (mm).
Aq). In this state, suction is performed sufficiently (preferably for 2 minutes) to remove the resin by suction. Electrometer 14 at this time
The potential of No. 9 is V (V). Here, reference numeral 148 denotes a capacitor having a capacity of C (F). The weight of the entire measuring container 142 after suction is measured and is referred to as W ₂ (kg). From the above measured values, the triboelectric charge amount (C / k
g) is calculated as in the following equation.

Amount of triboelectric charge of resin (C / kg) = C × V ×
10 ^-3 / (W ₁ -W ₂ )

[0100]

As described above, the first embodiment according to the present application is described.
According to the invention, the upper during development, toner from the image bearing member
Serial developer direction of the voltage V ₂ to the voltage V ₁ and the toner in the direction towards the bearing member toward said image bearing member from the <br/> developer carrier
After a predetermined number of times alternately applied to the door, the voltage V ₁ and the collector
Is set to apply a voltage V ₃ is the average of the pressure V _2,
The times for applying the voltages V ₁ , V ₂ , and V ₃ are T ₁ ,
T ₂ , T ₃ , the gap between the image carrier and the developer carrier
If d

[0101]

[Equation 14]

By satisfying the relationship of (1), white spots occurring at the rear end of the highlight image
Image carrier and developer carrying in the developing section to prevent image
Despite having made the body movement directions opposite to each other
Therefore, it is possible to prevent the occurrence of ground fogging.
That is, the occurrence of a white spot phenomenon at the rear end of the highlight image
An image with good image quality can be obtained by preventing both raw and fogging .

According to the second aspect of the present invention,
Since the high frequency vibration is applied a plurality of times, the toner adhering to the carrier is sufficiently separated from the carrier, the toner flies sufficiently, and the developing ability is improved.

Further, according to the third aspect of the present invention, since a higher frequency is applied, the developing ability is further improved.

Further, according to the fourth invention of the present application,
The developer container and the developer carrier are the same as the image carrier.
A plurality of peripheral parts are provided, and the image is
In the apparatus for forming toner images of different colors on the carrier , as described above, a high-quality multicolor image with no white spots, no roughness, no rubbing traces and no fogging can be obtained.

[0106] Further, according to the fifth aspect of the present application, have the exposure means for performing laser exposure to the image bearing member
The light emission time length per pixel of the laser is
Even if a solid image and a halftone image are mixed, a high-quality image with no white spots, no image roughness, no rubbing marks, and no fogging marks at the boundary of the image can be obtained. obtain.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating an example of a waveform of a developing bias voltage according to an embodiment of the present invention.

FIG. 3 is a diagram illustrating a state of a developing unit and a developer in one embodiment of the present invention.

FIG. 4 is a diagram showing another example of the waveform of the developing bias voltage according to the embodiment of the present invention.

FIG. 5 is a diagram illustrating another example of the waveform of the developing bias voltage according to the embodiment of the present invention.

FIG. 6 is a surface potential diagram showing latent images of a solid portion and a halftone portion.

FIG. 7 is a diagram illustrating a schematic configuration of a conventional image forming apparatus.

FIG. 8 is a diagram for explaining a blank portion in a conventional image forming apparatus.

FIG. 9 is a diagram illustrating shapes of equipotential surfaces and lines of electric force in a portion facing a developer carrier when a highlight portion and a solid portion are present on the image carrier.

FIG. 10 is a diagram illustrating an apparatus for measuring a triboelectric charge amount of a developer.

[Explanation of symbols]

 Reference Signs List 1 photoconductor drum (image carrier) 16 developer container 11 developing sleeve (developer carrier) 19 developer

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-7-311497 (JP, A) JP-A-63-309981 (JP, A) JP-A-63-298375 (JP, A) 233464 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15/08-15/095 G03G 9/08

Claims (5)

(57) [Claims] And 1. A image bearing member, a developer container containing a <br/> developer including toner and carrier, an electrostatic image on the image bearing member
It carries a developer in the developer container to be developed by the developing unit
Ears of the developer possess a developer carrying member for conveying in contact with the image bearing member, the diameter of the image carrier diameter of the developer carrying member
And the average particle size of the carrier is 40 μm or less.
In the image forming apparatus is the lower, the moving direction of the image carrier and the developer carrier in the developing unit is a reverse direction to each other, the direction in which during development, toner toward the developer carrying member from said image bearing member voltage V ₁ and the toner from the developer carrying member of the
Predetermined times alternately and the voltage V ₂ in a direction toward said image bearing member
After several applied, the set to apply a voltage V ₁ and the voltage V ₃ is the average of the voltage V _2, respectively T ₁ a time for applying the voltages V _1, V _2, V _3,
T ₂ , T ₃ , where d is the gap between the image carrier and the developer carrier, An image forming apparatus characterized by satisfying the following. 2. During development, toner is transferred from the image carrier to the toner.
Voltage direction toward the developer carrying member V ₁ and toner said present
The voltage V _{2 in the} direction from the image material carrier to the image carrier is
After repeatedly applied a plurality of times alternately, the voltage V ₁ and the upper
The image forming apparatus according to claim 1, characterized in that it is configured to apply a voltage V ₃ serial is the average of the voltage V _2. 3. During development, toner is transferred from the image carrier to the toner.
Voltage direction toward the developer carrying member V ₁ and toner said present
The voltage V _{2 in the} direction from the image material carrier to the image carrier is
After applying once alternately, the voltage V ₁ and the voltage V ₂
That is configured to apply a voltage V ₃ Ru average der
The image forming apparatus according to claim 1, wherein. 4. The developer container and the developer carrier
A plurality of the developer carriers are provided around the image carrier.
The image forming apparatus according to any one of claims 1 to 3, characterized in that to form a different color toner images on the image carrier by the body. 5. An exposure means for performing laser exposure on said image bearing member, wherein a light flux emission time per pixel of the laser is provided.
The image forming apparatus according to any one of claims 1 to 4, characterized in that controlled according to the length to the image density signal.