JPH1173008A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device in which even in the case where a resin-coat carrier in which the resistance of the coat layer itself has been reduced is used, the uniformity of dots is excellent so that the image noise is not produced. SOLUTION: Resin-coat carriers in which carbon is dispersed into magnetic particles are used, and a developer is conveyed in the state that it is not in contact with a photoreceptor. Further, a vibrating electric field is formed in the developing region, and denoting by t1 , t2 , LT, and Lc respectively the time of the phase for moving a toner to an electrostatic latent image part, the period of a vibrating electric field, the weight average grain size of the toner, and the weight average grain size of the magnetic carrier, the respective conditions of the developing device are set to satisfy the following expressions. 1.0×10<-4> <t1 <2> /LT<1.0×10<-3> [sec<2> /m] and t2 <2> /LC<0.005 (sec<2> /m).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, and the like.

[0002]

2. Description of the Related Art Two-component development is known as a development method which is particularly excellent in high-speed responsiveness in electrophotographic and other image forming methods using powder toner. In recent years, it has been used as a mainstream technology in product fields such as copiers and laser printers.

In two-component development, the developer is transported to the surface of a non-magnetic sleeve, which is a developer carrier, in which a magnet is provided, and the developer is held in a brush shape (magnetic brush) to be transferred to the image carrier. The toner is selectively brought into contact with or close to the latent image surface by an electric field between the image carrier on which the electrostatic latent image is formed and the sleeve to which an electric bias is applied, thereby performing development.

However, in a market (apparatus) that requires higher quality, there is a problem that toner is irregularly attached to an electrostatic latent image and image noise is likely to appear. For example, printers and digital copiers require uniform formation of dots formed at intervals of several tens of μm in order to smoothly reproduce halftones. However, when the dot image is enlarged and observed with a microscope or the like, it is observed that the shape and area of the dots vary greatly and that toner adheres irregularly between the dots. When these degrees are large, the image is conspicuous in roughness and poor in uniformity.

In order to solve such a problem in image quality, JP-A-6-19213 and JP-A-7-7269 have been proposed.
9 and JP-A-7-114223 have proposed a method of applying a developing bias having a vibration component (hereinafter, referred to as an AC bias).

However, in the conventional developing methods described in the above publications, the image quality may not be improved depending on the application condition of the developing bias, but rather may be degraded. This point has been confirmed in experiments performed by the inventor of the present application. This is expected to be because the movement of the toner and the carrier is affected by various factors.

[0007]

Problems to be Solved by the Invention
The third publication describes the range of the toner particle size and the carrier particle size, and the condition of the frequency of the vibration bias, and it is said that the frequency is preferably a high frequency of 6000 Hz or more. Further, in order to maintain the development efficiency, the volume resistivity of the carrier is set to 101.
It is said that it is preferable to set the resistance to 0 Ωcm or less.

However, according to an additional test conducted by the inventor of the present application, a phenomenon in which the rear end of a solid image is blurred in this frequency domain (hereinafter, referred to as a “semi-image”).
(Referred to as "rear edge blurring"). Further, the result was obtained that the effect of applying the AC bias was lost when the frequency was increased without limit. The use of a low-resistance carrier slightly improves the image quality, but does not provide satisfactory image quality.

[0009] Several types of carriers have been known in the past, but those having magnetic particles coated with a resin in order to obtain durability are widely used (for example, Japanese Patent Application Laid-Open No. 6-19213). ). Also, Japanese Patent Application Laid-Open No. 7-7
Japanese Patent No. 2699 describes a method of developing in a non-contact state while applying an AC bias (vibration bias) using a magnetic resin-coated carrier.

However, according to the additional test conducted by the inventor of the present invention, there was a problem in image quality such as insufficient uniformity of the dot area and occurrence of phenomena such as blurring of the edges. This is presumably because the carrier has a high resistance, and when the toner separates from the surface of the carrier, an electric charge of the opposite polarity to the toner remains, causing noise for the movement of other toner.

There are several methods for lowering the resistance of a magnetic resin-coated carrier. Among them, those which reduce the resistance by making the coat layer thinner have a problem in extending the life of the developer. As another method, it is conceivable to lower the resistance of the coat layer itself. Specifically, a material in which ferrite or magnetite is used as a core material and carbon is dispersed in a coating layer of a silicone resin or the like is practical because it is inexpensive and has stable characteristics.

However, when the present inventor performed development by applying an AC bias to the above-described ferrite or magnetite as a core material and using a carrier in which carbon was dispersed in a coat layer such as a silicone resin, the toner of the image was developed. A phenomenon (hereinafter, referred to as white spots) in which the adhered portion comes off white and small was observed.

Further experiments have shown that the reduction of the peak voltage of the AC bias reduces the amount of white spots,
It has been clarified that it occurs only in the toner-attached portion (the portion where the potential difference from the peak value of the AC bias is large) and that white spots do not occur when a type of carrier that does not disperse carbon is used. From these facts, it is inferred that the white spot generation phenomenon is caused by discharge from carbon near the carrier surface to the image carrier.

The present invention solves the above-mentioned problems in the prior art and is suitable for high durability (the resistance of the coating layer itself is reduced).
It is an object to provide an image forming apparatus which is excellent in dot uniformity and does not generate image noise even when a resin-coated carrier is used.

Another object of the present invention is to provide an image forming apparatus capable of obtaining an image free from white spots even when a developing bias having a vibration component is applied.

[0016]

The above object is achieved by the present invention.
A developer comprising a toner and a carrier,
And the developer is brought into contact with the image carrier without contact with the image carrier.
Moves the toner to the area between the carrier and the developer carrier
An image forming apparatus that performs development by forming an oscillating electric field
And the phase time for moving the toner to the image carrier is t
₁, The weight average particle size of the toner is L_T1.0 ×
10^-4<T₁ ²/ L_T<1.0 × 10 ^-3[Sec²/ M
 So that the above holds.₁, L_TTo set
More resolved.

Further, in order to solve the above-mentioned problems, the present invention provides a method for supporting a developer comprising a toner and a carrier on a developer carrier, and contacting the developer without contacting the image carrier. In an image forming apparatus that performs development by forming an oscillating electric field for moving toner in a region between the toner carrier and the developer carrier, the period of the oscillating electric field is t ₂ , and the weight average particle size of the carrier is Lc. , _t ^{2 2} /Lc<0.005[sec
² / m] is proposed to set the above t ₂ , Lc.

In order to solve the above-mentioned problems, the present invention
Is to transfer the developer consisting of toner and carrier to the developer carrier
Carrying the developer without contacting the image carrier with the image carrier.
The toner is moved to an area between the carrier and the developer carrier.
In an image forming apparatus that forms an oscillating electric field
The phase time for moving the toner to the image carrier
t ₁, The period of the oscillating electric field is t₂， Weight average particle of toner
Diameter L_T, When the weight average particle size of the carrier is Lc,
1.0 × 10^-4<T₁ ²/ L_T<1.0 × 10
^{− 3}[Sec²/ M] and t₂ ²/Lc<0.005 [sec
²/ M] so that t is satisfied.₁, T₂, L_T, Lc
Propose to set.

In order to solve the above-mentioned problems, the present invention provides a method for supporting a developer comprising a toner and a carrier on a developer carrier and contacting the developer without contacting the image carrier. In an image forming apparatus that performs development by forming an oscillating electric field that moves toner to a region between the image carrier and the developer carrier, the closest distance between the image carrier and the developer carried on the developer carrier Is d [m], the absolute value of the potential difference between the surface potential of the image carrier and the maximum potential of the developer carrier is 5.0.
It is proposed to be less than × 10 ⁸ d [V].

In order to solve the above-mentioned problems, the present invention
Is to transfer the developer consisting of toner and carrier to the developer carrier
Carrying the developer without contacting the image carrier with the image carrier.
The toner is moved to an area between the carrier and the developer carrier.
In an image forming apparatus that forms an oscillating electric field
The phase time for moving the toner to the image carrier
t ₁, The weight average particle size of the toner is L_T, Image carrier and developer
The closest distance to the developer carried on the carrier is d [m]
1.0 × 10^-4<T₁ ²/ L_T<1.0
× 10^-3[Sec²/ M] and the surface potential of the image carrier
The absolute value of the potential difference from the maximum potential of the developer carrier is 5.0 ×
10⁸d [V] or less so that t₁, L_T, D
Suggest to set.

Further, in order to solve the above-mentioned problems, the present invention provides a developer carrying a developer comprising a toner and a carrier, and contacting the developer without contacting the image carrier. And an image forming apparatus for developing an image by forming an oscillating electric field for moving toner in a region between the toner carrier and the developer carrying member, wherein the period of the oscillating electric field is t ₂ , the weight average particle size of the carrier is Lc, When the closest distance between the developer and the developer carried on the developer carrying member is d [m], t ₂ ² / Lc
<0.005 [sec ² / m ² ], and the absolute value of the potential difference between the surface potential of the image carrier and the maximum potential of the developer carrier is 5.0.
× 10 ⁸ d [V] or less so that t ₂ , Lc, d
Propose to set.

In order to solve the above-mentioned problems, the present invention
Is to transfer the developer consisting of toner and carrier to the developer carrier
Carrying the developer without contacting the image carrier with the image carrier.
The toner is moved to an area between the carrier and the developer carrier.
In an image forming apparatus that forms an oscillating electric field
The phase time for moving the toner to the image carrier
t ₁, The period of the oscillating electric field is t₂， Weight average particle of toner
Diameter L_T, The weight average particle size of the carrier is Lc,
The closest distance to the developer carried on the developer carrier is d
When [m], 1.0 × 10^-4<T₁ ²/ L_T<
1.0 × 10^-3[Sec²/ M] and t₂ ²/ Lc <
0.005 [sec²/ M] and the surface potential of the image carrier
The absolute value of the potential difference from the maximum potential of the developer carrier is 5.0 ×
10⁸d [V] or less so that t₁, T₂,
L_T, Lc, d.

In order to solve the above problems, the present invention proposes that the carrier contains conductive fine particles. In order to solve the above-mentioned problems, the present invention proposes that the conductive fine particles are carbon.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing a specific embodiment, the description starts with the background of the present invention and the operation of the present invention.

The inventor of the present application has made intensive studies based on various problems in the conventional image forming apparatus, and as a result,
When the image carrier and the developer on the developer carrier are developed in a non-contact state in the area where the toner can move between the image carrier and the developer carrier, the white spots are generated even when an AC bias is applied. It was found that the occurrence of dots was suppressed. Further, it has been found that the image quality is improved under the limited condition of the AC bias.

In an experiment conducted by the inventor of the present invention, a rectangular wave bias having a constant cycle was applied to the developer carrier, and the time required for the toner to move in the direction of the image carrier (the toner having the rectangular wave bias was applied to the image carrier) When the image was formed while changing the dot area, the pulse width was in a specific range (the period was constant. (Meaning the range), the data was obtained in which the variation was small and the dot uniformity was improved. The data is shown in the graph of FIG. In this graph, the horizontal axis indicates the pulse width of the rectangular wave bias, and the vertical axis indicates the variation in the dot area (standard deviation divided by the average value). As can be seen from this figure, the variation of the dot area is small within a predetermined pulse width range (here, a predetermined duty ratio range).

The variation in dot area was evaluated by measuring a plurality of dot areas with an image analyzer and dividing the standard deviation by the average area to obtain an evaluation value. When the value is 0.15 or less, the dot uniformity is good, and when the value is 0.1 or less, more excellent dot uniformity is exhibited, as a result of the study by the present inventors.

On the other hand, when a simple model is set and predicted, when charged particles are placed in an oscillating electric field, the particles start to reciprocate, and the amplitude of the movement is inversely proportional to the square of the frequency of the oscillating electric field and the particle size. It turned out to be. That is, the frequency of the oscillating electric field f, E ₀ the amplitude of the electric _field, when the particle size of the toner was L _T, the amplitude A of the reciprocating motion of the toner is expressed by the following equation. Here, k is a constant. ^{_{A = k · E 0 / (}} f 2 · L T)

Based on these results, the inventors of the present application hypothesized that the time required for the toner to move at a high speed toward the image carrier, the particle size of the toner, and the image quality were related, and conducted a confirmation experiment. Was.

In the confirmation experiment, an image was formed by changing the toner particle size and the duty ratio of the rectangular wave bias, and the evaluation was performed. As a result, the time during which the toner receives a force directed to the image carrier (the width of a pulse that applies a force that directs the toner to the image carrier)
It has been clarified that setting a value obtained by dividing the square of by the toner particle size in a specific range dramatically improves dot reproducibility. The experimental data is shown in the graph of FIG. In this graph, the horizontal axis indicates the pulse width of the rectangular wave bias, and the vertical axis indicates the toner particle diameter. The items were marked with ● (black circles). As is clear from this graph, the conditions with good dot uniformity are distributed in a region between two parabolas.

The carrier used in this confirmation experiment was:
It is a magnetic carrier in which a magnetite core is coated with a silicone resin, and its volume resistivity is controlled to about 10 ¹⁰ Ωcm by dispersing carbon in a coat layer.

From the above results, the inventor of the present application has set the time (pulse width) of the phase for moving the toner to the image portion of the electrostatic latent image on the image carrier in the oscillating electric field (AC bias) to be t.
_1, when the weight average particle size of the toner and ^{_{L T, 1.0 × 10 -4 <}} t 1 2 / L T <1.0 × 10 -3 [sec 2 / m] ····· · and It was concluded that forming the electric field so as to improve the image quality.

Further, the inventor of the present application also examined the movement of the carrier. According to previous research, it was predicted that, when the carrier performed intense motion, the carrier would separate from the magnetic brush on the developer carrier (developing sleeve) and adhere to the image carrier, resulting in deterioration of image quality. .

Therefore, if the carrier is regarded as a charged particle similarly to the toner, the movement of the carrier is 2 times the frequency of the oscillating electric field.
It can be assumed that it is inversely proportional to the power and the carrier particle size. Based on the assumption, the image was formed by changing the carrier particle size and the oscillating electric field frequency, and the quality was evaluated. The value obtained by dividing the square of the period of the oscillating electric field by the carrier particle size was applied to the image plane in a specific range. It was clarified that carrier adhesion was eliminated and the image quality was improved. That is, the period of _{t 2} of an oscillating electric field, when the weight average particle diameter of the magnetic carrier and Lc, the electric field so that ^{_{t 2 2 /Lc<0.005[sec 2 / m]}} ······ Forming results in improved image quality.

Therefore, by setting the above-mentioned equations and conditions so as to satisfy the above equations, it is possible to realize a state where the toner is easy to move and the carrier hardly moves.
As a result, not only the reproducibility of halftones was improved, but also phenomena called image noise such as background smearing and blurring of the rear end could be extremely reduced.

As described above, by using the carrier in which carbon is dispersed in the coating layer in a non-contact state in the developing region, local discharge (discharge from the carbon near the carrier surface to the image carrier) is prevented. This can prevent the occurrence of white spots, which have been a problem, and increase the magnitude of the oscillating electric field in the development area, thereby making toner movement more vigorous. Is attached to the toner. Furthermore, since the carrier resistance is low, the charge on the carrier surface is likely to be uniform, and the electrostatic attraction acting on the toner once separated from the carrier is unlikely to be large, so that images such as edge blurring may occur. The effect that noise is no longer generated is also recognized.

Now, a specific embodiment of the present invention will be described. FIG. 1 shows a configuration near a developing unit in an example of an image forming apparatus according to the present invention. The developing device 1 shown in FIG. 1 includes a developing sleeve (developer carrier), a stirring member 4, a doctor blade 5, and the like. The developing sleeve 2 is made of a non-magnetic conductive member, and the surface thereof is provided with appropriate unevenness by sandblasting or the like.
The developing sleeve 2 rotates counterclockwise in the figure as shown by the arrow,
A plurality of fixed magnets 3 are arranged inside. A developing bias (AC bias) to be described later is applied to the developing sleeve 2 from a bias power supply 6. The developer reservoir of the developing device is provided with two stirring members 4 for moving the developer in directions opposite to each other. Further, a doctor blade 5 for regulating the transport amount of the developer to the developing area is provided near the upper portion of the developing sleeve 2.

The developer stirred and conveyed by the two stirring members 4 is pumped to the developing sleeve 2 by the action of the internal magnet 3 when reaching the vicinity of the developing sleeve 2. Then, convection of the developer occurs on the upstream side of the doctor blade 5 (the upstream side in the rotation direction of the sleeve 2 = on the right side of the blade 5 in the drawing), and the toner and the carrier are mixed to sufficiently and uniformly charge the toner.

Due to the gap between the doctor blade 5 and the developing sleeve 2, the amount of the developer conveyed to the developing area becomes constant. In the developing area, a magnetic brush (formed of a toner and a carrier in a brush shape) formed by the action of the internal magnet 3 approaches (non-contacts) the photosensitive drum (image carrier) 10, and The toner moves due to an electric field formed between the voltage and the electrostatic latent image on the photosensitive drum 10.

FIG. 2 shows a state in which a developing sleeve is
2 shows the waveform of the developing bias (AC bias) applied to
It is a waveform diagram. The horizontal axis of the waveform diagram is time, and the vertical axis is the toner sensitivity.
The light receiving the force toward the optical drum 10
The pressure value. In this figure, the toner is the photosensitive drum 1
The voltage value when receiving the maximum force toward zero is V₁, Tona
When the maximum force is applied to the developing sleeve 2
Pressure value to V₀And V ₁Time (V₁Pulse width)
To t₁ And the cycle of the vibration bias is t₂And In addition,
The integrated average Va of the pressure value is -5 like a normal DC bias.
It is set to about 00V to -700V. Where Va =
V₀+ (V₁-V₀) ・ T₁/ T₂And

As a first example of the present embodiment, the carrier has a volume resistivity of about 10 ¹⁰ by coating a magnetite core having a weight average particle diameter of 50 μm with a silicone resin and dispersing carbon in the coating layer. The one controlled to Ωcm was used. The toner has a weight average particle size of 7.5.
μm was used. Then, the toner concentration of 5 wt.
% (Mass ratio of toner to developer). Further, an electrostatic latent image having a background potential of -700 V and an image potential of -100 V was formed on the photosensitive drum 10.

When the thickness of the developer layer on the developing sleeve 2 in this embodiment was measured, it was at most about 500 μm. The development gap is set to 600 μm. Therefore, the distance (the closest distance) d between the photosensitive drum 10 and the developer held on the developing sleeve is 100 μm.

As the developing bias in this case, the integral average Va is set to -600 V, the vibration component is set to a frequency of 5 kHz, the peak-to-peak voltage is set to 1.5 kV, and the duty ratio is changed so as to satisfy the above equations and the equations. As a result, an image having excellent dot uniformity could be obtained when the duty ratio (t ₁ / t ₂ ) of the vibration bias was in the range of 15% to 40%.

When the duty ratio is within the above-mentioned appropriate range (15 to 40)
%), For example, 10%, the amount of development was reduced, sufficient image density was not obtained, and the variation in dot area was increased. If the duty ratio exceeds the appropriate range, for example, 45%, the toner is excessively developed, and the toner adheres to the background near the edge of the image.
As the dots become larger, the density value of the halftone becomes higher, causing a problem that the balance of the tone reproducibility is lost and the uniformity of the dot area is reduced. Conversely, the duty ratio is 20-3
At 0%, excellent dot uniformity was exhibited. The variation in dot area was evaluated by measuring a plurality of dot areas with an image analyzer and dividing the standard deviation by the average area. As described earlier with reference to FIG. 3, the results of the study by the present inventors have revealed that when the value is 0.15 or less, the dot uniformity is good, and when the value is 0.1 or less, more excellent dot uniformity is exhibited. Was.

[0045] The _t ¹ 2 / _{L T} in the above suitability conditions 1.2 ×
From 10 ⁻⁴ [sec ² / m] to 8.5 × 10 ⁻⁴ [sec ² / m]
Range, _also, ^t 2 2 / Lc is 8 × ^{10 -4} [sec ²
/ M]. The maximum value of the absolute value of the electric field generated between the tip of the developer on the developing sleeve 2 and the photoconductor 10 is 1.4 to 1.
It becomes 8 × 10 ⁷ V / m.

When the duty ratio is 15%, the minimum potential of the photosensitive drum 10 (the surface potential of the image portion) is -100.
V, the maximum potential of the developing sleeve 2 (the potential at which the absolute value becomes the largest) is −1875 V, so the maximum value of the electric field between the tip of the developer on the developing sleeve 2 and the photosensitive drum 10 is about −1.8 × 10 ⁷ [V / m]. Similarly, when the duty ratio is 40%, the maximum value of the electric field between the tip of the developer on the developing sleeve 2 and the photosensitive drum 10 is about -1.4.
× 10 ⁷ [V / m]. Also, the duty ratio is 15%
In this case, when the peak-to-peak voltage is 2 kV, the maximum value of the electric field between the front end of the developer on the developing sleeve 2 and the photosensitive drum 10 is about -2.2 × 10 ⁷ [V / m]. No white spots occurred under any of these conditions.

At this time, when the position of the doctor blade 5 was adjusted and the tip of the magnetic brush was brought closer to the photosensitive drum 10, no abnormality was observed up to a gap of 5 μm.
At 4 μm, white spots increased sharply.

As a second example of the present embodiment, when the same developer as that used in the first example is used and the duty ratio of the developing bias is fixed to 20%, the frequency of the developing bias is 2.5 kHz. An image with excellent dot uniformity could be obtained in the range of ７7 kHz.

When the developing bias frequency falls below the above-mentioned appropriate range, for example, at 2.3 kHz, the toner is excessively developed, and the toner adheres to the background near the edge of the image, and the dots become large, so that the halftone tone is increased. There is a problem that the density value becomes higher, the balance of gradation reproducibility is lost, and the dot area uniformity is also reduced. Further, when the developing bias frequency was higher than the above range, for example, set to 7.4 kHz, the developing amount was reduced, sufficient image density was not obtained, and the variation in dot area was increased.

Under the above suitability conditions, t₁ ²/ L_TIs 1.1
× 10^-4[Sec²/ M] to 8.5 × 10^-4[Sec²
/ M] and t₂ ²/ Lc is 4.1 × 10^-4
[Sec ²/ M] to 3.2 × 10^-3[Sec²/ M] range
Becomes Further, the tip of the developer on the developing sleeve 2 and the photosensitive member
The maximum value of the absolute value of the electric field generated during 10 is 1.7 × 10
⁷V / m.

Further, as a third example of this embodiment,
The same developer as in the above embodiments was used, and the duty ratio was 10
%, The developing bias frequency is 2 kHz to 3 kHz.
A good image could be obtained in the range of 5 kHz. When the frequency was 2 kHz or less, the carrier adhesion to the image was significantly increased.

When the developing bias frequency was higher than the appropriate range, for example, set to 3.7 kHz, the developing amount was reduced, sufficient image density was not obtained, and the variation in dot area was increased. Conversely, the developing bias frequency is 3.2 kHz
From 3.5 to 3.5 kHz, the effect of preventing carrier adhesion was particularly high.

Under the above suitability conditions, t₁ ²/ L_TIs 1.1
× 10^-4[Sec²/ M] to 3.3 × 10^-4[Sec²
/ M] and t₂ ²/ Lc is 1.6 × 10^-3
[Sec ²/ M] to 5.0 × 10^-3[Sec²/ M] range
Becomes Further, the tip of the developer on the developing sleeve 2 and the photosensitive member
The maximum value of the absolute value of the electric field generated during 10 is 1.85 × 1
0⁷V / m.

Further, as a fourth example of this embodiment,
When a toner having a particle size of 5 μm is used (the carrier particle size is the same as in each of the above-described embodiments), if the frequency is fixed to 5 kHz, an image with good dot uniformity can be obtained in a duty ratio range of 15 to 30%. Was completed.

When the duty ratio was lower than the above-mentioned appropriate range, for example, set at 11%, the development amount was reduced, sufficient image density was not obtained, and the variation in dot area was increased. If the duty ratio exceeds the appropriate range, for example, is set to 36%, the toner is excessively developed, and the toner adheres to the background near the edge of the image, or the dot becomes large, and the density value of the halftone is reduced. However, there is a problem that the balance of gradation reproducibility is lost and the uniformity of the dot area is reduced.

Under the above suitability conditions, t₁ ²/ L_TIs 1.8
× 10^-4[Sec²/ M] to 7.2 × 10^-4[Sec²
/ M] and t₂ ²/ Lc is 8.0 × 10^-4
[Sec ²/ M]. The developer on the developing sleeve 2
The maximum value of the absolute value of the electric field generated between the tip and the photoconductor 10 is
1.6 × 10⁷1.8 × 10 from V / m⁷V / m range
Becomes

Further, as a fifth example of this embodiment,
Using the same developer as in the fourth embodiment, the duty ratio is set to 2
When fixed to 0%, the frequency of the developing bias is 3 to 8.5.
An image with good dot uniformity could be obtained in the kHz range.

When the developing bias frequency is lower than the above-mentioned proper range, for example, 2.8 kHz, the toner is excessively developed, and the toner adheres to the background near the edge of the image, or the dot becomes large, and the halftone is changed. There is a problem that the density value becomes higher, the balance of gradation reproducibility is lost, and the dot area uniformity is also reduced. When the frequency is further reduced to 2 kHz, carrier adhesion occurs. Further, the developing bias frequency exceeds the above range, for example, 9
When the frequency was set to kHz, the amount of development was reduced, sufficient image density was not obtained, and the variation in dot area was increased. Conversely, when the developing bias frequency was 4 to 6 kHz, excellent dot uniformity was exhibited.

Under the above suitability conditions, t₁ ²/ L_TIs 1.1
× 10^-4[Sec²/ M] to 8.9 × 10^-4[Sec²
/ M] and t₂ ²/ Lc is 2.8 × 10^-4
[Sec ²/ M] to 2.2 × 10^-3[Sec²/ M] range
Becomes Further, the tip of the developer on the developing sleeve 2 and the photosensitive member
The maximum value of the absolute value of the electric field generated during 10 is 1.7 × 10
⁷V / m.

Further, as a sixth example of this embodiment,
The development was performed under the same conditions as in the first embodiment by changing the minimum gap between the developer layer on the developing sleeve 2 and the photoconductor 10 by adjusting the distance between the doctor blade 5 and the developing sleeve 2. Minimum gap (closest distance:
When d) was 5 μm, white spots were not generated, but it was clarified that the white spots were generated when the minimum gap was made smaller.

When the minimum gap is 5 μm, the maximum value of the absolute value of the electric field generated between the tip of the developer on the developing sleeve 2 and the photosensitive member 10 is 3.6 × 10 ⁸ V / m. However,
Under this condition, a strong electric field is locally generated, and in rare cases, white spots may be generated. By increasing the gap between the developer layer and the photoconductor, the maximum value of the electric field is set to 5.0.
By setting to 10 ⁷ V / m, white spots can be completely prevented.

As described above, the closest distance between the photosensitive drum 10 and the developer held on the developing sleeve 2 is represented by d.
[M], the absolute value of the potential difference between the surface potential of the photoconductor 10 and the maximum potential of the developing sleeve 2 is 5.0 × 10 ⁸
It has been found that if it is configured to be d [V] or less, the occurrence of white spots can be prevented.

Further, as a seventh example of the present embodiment,
When a toner having a particle diameter of 9 μm is used in place of the toner of the first embodiment (other conditions are the same as in the first embodiment), if the developing bias frequency is fixed at 5 kHz, the duty ratio becomes 15%.
An image with good dot uniformity could be obtained in the range of up to 45%.

When the duty ratio was below the appropriate range, for example, set at 14%, the development amount was reduced, sufficient image density was not obtained, and the variation in dot area was increased. If the duty ratio exceeds the appropriate range, for example, is set to 48%, the toner is excessively developed, the toner adheres to the background near the edge of the image, or the dot becomes large, and the density value of the halftone is reduced. However, there is a problem that the balance of gradation reproducibility is lost and the uniformity of the dot area is reduced.

Under the above suitability conditions, t₁ ²/ L_TIs 1.0
× 10^-4[Sec²/ M] to 9.0 × 10^-4[Sec²
/ M] and t₂ ²/ Lc is 8.0 × 10^-4
[Sec ²/ M]. The developer tip on the developing sleeve 2
The maximum value of the absolute value of the electric field generated between the photoconductors 10 is 1.3.
× 10⁷1.8 × 10 from V / m⁷V / m range
You.

Further, as an eighth example of the present embodiment,
When a carrier having a particle diameter of 40 μm is used in place of the carrier of the first embodiment, if the duty ratio is fixed at 15% and the peak-to-peak voltage is fixed at 2 kV, the developing bias frequency is 2.3 to 3.0.
An image with good dot uniformity could be obtained in the range of 5 kHz (other conditions were the same as in the first embodiment). At this time, the thickness of the developer layer was 400 μm,
The closest distance between 0 and the developer: d is 200 μm.

When the developing bias frequency falls below the above-mentioned appropriate range, for example, at 2.2 kHz, carrier adhesion to an image is significantly increased. Further, if the developing bias frequency exceeds the above range, for example, is set to 5.5 kHz,
The development amount was reduced, and a sufficient image density was not obtained, and the variation in the dot area was increased.

Under the above suitability conditions, t₁ ²/ L_TIs 1.2
× 10^-4[Sec²/ M] to 5.7 × 10^-4[Sec²
/ M] and t₂ ²/ Lc is 1.0 × 10^-3
[Sec ²/ M] to 4.7 × 10^-3[Sec²/ M] range
Becomes Further, the tip of the developer on the developing sleeve 2 and the photosensitive member
The maximum value of the absolute value of the electric field generated during 10 is 1.1 × 10
⁷V / m.

Further, as a ninth example of the present embodiment,
When a carrier having a particle diameter of 70 μm is used in place of the carrier of the first embodiment, when the duty ratio is fixed at 15% and the peak-to-peak voltage is fixed at 1 kV, the developing bias frequency is 1.7 to
An image with good dot uniformity was obtained in the range of 3.5 kHz (other conditions were the same as in the first embodiment). In addition,
At this time, the thickness of the developer layer is 550 μm, and the closest distance d between the photosensitive drum 10 and the developer is 50 μm.

When the developing bias frequency falls below the above-mentioned appropriate range, for example, 1.6 kHz, carrier adhesion to an image is significantly increased. Further, if the developing bias frequency exceeds the above range, for example, is set to 5.5 kHz,
The development amount was reduced, and a sufficient image density was not obtained, and the variation in the dot area was increased.

Under the above suitability conditions, t₁ ²/ L_TIs 1.1
× 10^-4[Sec²/ M] to 4.6 × 10^-4[Sec²
/ M] and t₂ ²/ Lc is 1.2 × 10^-3
[Sec ²/ M] to 4.9 x 10^-3[Sec²/ M] range
Becomes Further, the tip of the developer on the developing sleeve 2 and the photosensitive member
The maximum value of the absolute value of the electric field generated during 10 is 2.8 × 10
⁷V / m.

FIG. 5 shows "t" in each embodiment.₁ ²/
L_T"Indicates an appropriate range. As shown in FIG.₁ ²
/ L_TIs 1.0 to 10 × 10^-4[Sec²/ M]
1.0 × 10^-4~ 1.0 × 10^-3[Sec²/ M]
The range is the appropriate range for dot uniformity, and
Examples show values within this range. Also, "t₁ ²/
L _TIs 2.0 to 5.0 × 10^-4[Sec²/ M] range
Shows that even better dot uniformity can be obtained.
I'm crazy.

FIG. 6 shows “t ₂ ² / L” in each embodiment.
c "indicates an appropriate range. As shown in this figure, _"t ^{2 2} /
Lc ”is 50 × 10 ⁻⁴ [sec ² / m], that is, 5.0 ×
10 - ³ in the appropriate range of ^{[sec 2 /} m] or less in the range for carrier adhesion, the above embodiment shows a number within the range. “T ₂ ² / Lc” is 20 × 10
⁻⁴ [sec ² / m], that is, 2.0 × 10 ⁻³ [sec ² / m]
m] or less, it is clear that it is more effective in preventing carrier adhesion.

FIG. 7 shows the “development sleeve” in each embodiment.
Absolute value of the electric field generated between the top of the developer and the photoconductor "
Shows the suitability range of In the present invention, this suitability range is 5.0 ×
10 ⁸d [V / m] or less, that is, 50 × 10⁷d [V
/ M] or less, and above this value white spots
Occur. In the figure, the conditions under which white spots occur at the “x” mark
, The good conditions are marked with a circle and the white spots are further marked with a mark
The conditions effective for prevention are shown. The value of each of the above embodiments is
It is shown by a mark “◎” in FIG.
Multiple conditions are shown).

Although the present invention has been described in detail with reference to the embodiment shown in FIG. 1 and each example thereof, the present invention is not limited to the above-described embodiment and each example, but falls within the scope of the present invention. Various changes are possible. For example, the image forming apparatus shown in FIG. 1 uses a negative-positive method (as described in the first embodiment, the potential on the photoconductor is attenuated at a background potential of the photoconductor drum -700 V and an image portion potential of -100 V). The present invention can be applied to a positive-positive type (regular development) apparatus.

[0076]

As described above, according to the image forming apparatus of the present invention, the developer is conveyed without being in contact with the image carrier, an oscillating electric field is formed in the developing area, and the oscillating electric field is formed according to the toner particle size. To set the time for moving the toner in the developer to the image carrier, so that an oscillating electric field under optimal conditions can be formed in the developer, and the toner can efficiently adhere to the electrostatic latent image. it can. As a result, an image with excellent dot uniformity (excellent halftone uniform reproducibility) and little noise can be formed.

According to the second aspect of the invention, since the carrier is prevented from adhering to the image carrier, a high quality image can be formed. According to the configuration of the third aspect, it is possible to form a high quality image having excellent dot uniformity and no carrier adhesion.

According to the structure of the fourth aspect, local discharge in the low-resistance carrier can be prevented, dot uniformity can be excellent, and generation of white spots can be prevented, so that a high-quality image can be formed.

According to the structure of the fifth aspect, it is possible to form a high-quality image having excellent dot uniformity and preventing occurrence of white spots. According to the configuration of the sixth aspect, it is possible to form a high-quality image in which carrier adhesion is prevented, dot uniformity is excellent, and generation of white spots is prevented.

According to the structure of the seventh aspect, it is possible to form a high-quality image in which carrier adhesion is prevented, dot uniformity is excellent, and generation of white spots is prevented. According to the configuration of claim 8, even if the carrier contains conductive fine particles, a local discharge does not occur, the dot uniformity is excellent, and a high-quality image in which white spots are prevented is formed. Can be.

According to the ninth aspect of the present invention, even when carbon is dispersed in the carrier coat layer, a local discharge does not occur, the dot uniformity is excellent, and the high quality of preventing white spots is prevented. An image can be formed.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing the vicinity of a developing unit in an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a waveform diagram showing a waveform of a developing bias applied to a developing sleeve of the developing device shown in FIG.

FIG. 3 is a graph showing a relationship between a pulse width of a rectangular wave developing bias and a variation in dot area.

FIG. 4 is a graph showing the distribution of dot reproducibility when the toner particle size and the duty ratio of the rectangular wave bias are changed.

FIG. 5 is a graph showing an appropriate range in a relationship between a transfer time for moving a toner to an image carrier and a toner weight average particle diameter in each example of the embodiment.

FIG. 6 is a graph showing an appropriate range in a relationship between a cycle of a developing bias and a weight average particle diameter of a carrier in each example of the present embodiment.

FIG. 7 is a graph showing an appropriate range of an absolute value of an electric field generated between a tip of a developer on a developing sleeve and a photosensitive member in each example of the embodiment.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 developing device 2 developing sleeve (developer carrier) 3 internal magnet 4 stirring member 5 doctor blade 6 bias power supply 10 photoconductor drum (image carrier)

──────────────────────────────────────────────────続 き Continued on front page (51) Int.Cl. ⁶ Identification code FI G03G 15/09 G03G 9/10 361

Claims (9)

[Claims] 1. A developer comprising a toner and a carrier is carried on a developer carrier, and the developer is brought into contact with the image carrier in an area between the image carrier and the developer carrier. an image forming apparatus for forming to develop the oscillating electric field for moving the toner, t ₁ a phase time for moving the toner to the image bearing _member, when the weight average particle size of the toner and L _T, 1.0 × ^{_{10 -4 <t 1 2 / L}} T <1.0 × 10
^-3 [sec ² / m] Image forming apparatus, wherein a set of the _t 1, _{L T} to stand. 2. A developer comprising a toner and a carrier is carried on a developer carrier, and the developer is provided in a region between the image carrier and the developer carrier without contacting the image carrier. an image forming apparatus for forming to develop the oscillating electric field for moving the toner, _{t 2} period of the oscillating electric field, when the weight average particle diameter of the carrier and Lc, _t ^{2 2} /Lc<0.005[sec ² / m], wherein t ₂ and Lc are set. 3. Developing a developer comprising a toner and a carrier
The developer is carried on the image carrier and the developer is not in contact with the image carrier.
To a region between the image carrier and the developer carrier.
Image type that develops by generating an oscillating electric field that moves the toner
In the image forming apparatus, a phase time for moving the toner to the image carrier is t₁,Previous
The period of the oscillating electric field is t ₂, Weight average particle size of toner
L_TWhen the weight average particle size of the carrier is Lc,
0x10^-4<T₁ ²/ L_T<1.0 × 10^-3[Sec
²/ M] and t₂ ²/Lc<0.005 [sec²/ M]
Is established so that₁, T₂, L_T, Lc
An image forming apparatus comprising: 4. A developer comprising a toner and a carrier is carried on a developer carrier, and the developer is provided in a region between the image carrier and the developer carrier without contacting the image carrier. In an image forming apparatus that performs development by forming an oscillating electric field that moves toner, the image carrier is provided when the closest distance between the image carrier and the developer carried on the developer carrier is d [m]. The absolute value of the potential difference between the surface potential of the developer and the maximum potential of the developer carrying member is 5.0 × 1
0 image forming apparatus characterized by 8 is ^{d [V]} or less. 5. A developer comprising a toner and a carrier is carried on a developer carrier, and the developer is brought into contact with the image carrier in a region between the image carrier and the developer carrier without being in contact with the image carrier. an image forming apparatus for forming to develop the oscillating electric field for moving the toner, t ₁ a phase time for moving the toner to the image bearing _member, a weight average particle size of the toner L _T, the image bearing member and the developer carrying when the closest distance between the developer carried on the body and ^{d [m], 1.0 × 10} -4 <t 1 2 / L T <1.0 × 10
^{-3 [sec 2 /} m] and the absolute value of the potential difference between the maximum potential of the surface potential and the developer carrying member of the image bearing member is 5.0 × 10 ⁸ d
Wherein t ₁ [V] as to become _less, L T, the image forming apparatus characterized by setting the _d. 6. A developer carrying a toner and a carrier on a developer carrier, and contacting the developer in a region between the image carrier and the developer carrier without contacting the image carrier. In an image forming apparatus for performing development by forming an oscillating electric field for moving toner, the period of the oscillating electric field is t ₂ , the weight average particle diameter of the carrier is Lc, and the development carried on the image carrier and the developer carrier. when the closest distance between the agent and ^{_{d [m], t 2 2}} / Lc <
0.005 [sec ² / m ² ] and the absolute value of the potential difference between the surface potential of the image carrier and the maximum potential of the developer carrier is 5.0 × 1
An image forming apparatus, wherein t ₂ , Lc, and d are set so as to be equal to or less than 0 ⁸ d [V]. 7. Developing a developer comprising a toner and a carrier
The developer is carried on the image carrier and the developer is not in contact with the image carrier.
To a region between the image carrier and the developer carrier.
Image type that develops by generating an oscillating electric field that moves the toner
In the image forming apparatus, a phase time for moving the toner to the image carrier is t₁,Previous
The period of the oscillating electric field is t ₂, Weight average particle size of toner
L_TLc, weight average particle size of carrier, image carrier and development
The closest distance to the developer carried on the developer carrier is d
When [m], 1.0 × 10^-4<T₁ ²/ L_T<
1.0 × 10^-3[Sec²/ M] and t₂ ²/ Lc <
0.005 [sec²/ M] and the surface potential of the image carrier and the current
The absolute value of the potential difference from the maximum potential of the image agent carrier is 5.0 × 1
0⁸d [V] or less so that t₁, T₂, L_T,
An image forming apparatus characterized by setting Lc and d. 8. The image forming apparatus according to claim 1, wherein the carrier contains conductive fine particles. 9. The image forming apparatus according to claim 8, wherein said conductive fine particles are carbon.