JP3450764B2 - 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 an electrophotographic image forming apparatus or an electrostatic recording image forming apparatus such as a copying machine or a printer, and more particularly to an image forming apparatus characterized by its developing device.

[0002]

2. Description of the Related Art In an electrophotographic type and electrostatic recording type image forming apparatus, a developing sleeve (developer carrying body) carrying a developer of a developing device is made to correspond to an image carrying body carrying an electrostatic latent image. Development is generally performed, and a developing bias is applied to the developing sleeve in order to form a developing electric field between the image carrier and the developing sleeve.

As this developing bias, as shown in FIG. 6, a component in which an AC component is superimposed on a DC component has been used, and the rectangular wave of the AC component shown in FIG. 6 has a frequency of 2 kHz (1 / 2 cycles = 250 μs) and a peak-to-peak voltage (Vpp) of about 2 kV were used, and a good developed image was obtained.

[0004]

However, the developing bias as shown in FIG. 6 has the drawback that the highlight portion of the image is “gritty” and the toner particle size of the developer is small. In this case, there is a drawback that a sufficient image density cannot be obtained.

In order to improve this drawback, the applicant of the present invention has proposed to use a developing bias in which an AC component is intermittently superposed on a DC component as shown in FIG.

A developing bias (referred to as a blank pulse bias or a BP bias in this specification) as shown in FIG. 7 is composed of a pulse portion and a rest portion (blank portion), and the frequency of the pulse portion is generally 4 kHz. (1/2
Vpp of the pulse portion is set to about 2 kV for a period of 125 seconds or more), but the developability is better than that of the developing bias (referred to as a rectangular bias in this specification) as shown in FIG. the is no Satsuki, Ru Ah can evenly reproduce latent image dots.

However, Vpp of the pulse portion exceeds 2 kV,
Further, in order to set the frequency to 4 kHz or more, when a conductive foreign substance is mixed in the developing portion, abnormal discharge occurs in that portion, a ring-shaped spot is formed on the image, and the image quality is remarkably deteriorated. There was a problem.

Therefore, when the BP bias is used,
Although it is required to suppress Vpp to be smaller than that of the conventional rectangular bias, in that case, there arises a problem that sufficient density cannot be obtained.

An object of the present invention is to perform good development with an appropriate developing bias to prevent the highlight portion from rubbing, to obtain a sufficient image density, and to prevent image defects due to abnormal discharge. Is to provide.

[0010]

The above object can be achieved by an image forming apparatus according to the present invention. In summary, the first aspect of the present invention provides an image carrier and a developer including a toner and a carrier.
A developer carrier that is carried and conveyed to a portion facing the image carrier.
The body and the electrostatic latent image formed on the image carrier
At this time, DC voltage and AC voltage were superposed on the developer carrier.
Image forming having application means for applying a developing bias
In the device, return the toner back to the developer carrier
Flying that causes the peak voltage and toner to fly to the image carrier
DC voltage only after applying peak voltage multiple times in this order
So that the step of applying continuously is repeated.
And the flying peak voltage and the developing bias.
The potential difference from the effective center voltage of the
Make it larger than the potential difference from the effective center voltage of the developing bias.
An image forming apparatus characterized by that.

According to one embodiment of the first invention, said
Flight peak voltage application time and return peak voltage application
Make the times almost equal. An embodiment of the first aspect of the present invention
Then, the potential between the flying peak voltage and the effective center voltage
The difference is Vg [V], the return peak voltage and the effective central voltage
If the potential difference from the pressure is Vb [V], then 1 <Vg / Vb ≦
Satisfies 1.5.

According to the second aspect of the present invention, the image carrier and the toner
And an image bearing member carrying a developer containing a carrier
On the image carrier, and
When the formed electrostatic latent image is developed,
Apply a developing bias that superimposes DC voltage and AC voltage
In the image forming apparatus including the applying unit, the toner is
The peak voltage to be returned to the developer carrier and the toner are
The peak voltage to fly to the image carrier is applied multiple times in this order.
Periodically repeats the vibrating part and the rest part that cuts off the AC voltage
Configure the developing bias so that the
Before the peak voltage to fly and the developing bias is in effect
The potential difference from the core voltage is compared with the other peak voltage of the vibrating section.
Make it larger than the potential difference from the effective center voltage of the developing bias.
An image forming apparatus is provided. Second
According to an embodiment of the present invention, in the vibrating section,
The flight is made to have the same potential difference from the effective center voltage.
The peak voltage and the peak voltage to be pulled back were alternately applied.
Then, mark the peak voltage to fly just before reaching the rest section.
Add In the embodiment of the second invention, the flight
Peak voltage application time and peak voltage to be pulled back
Application time is made almost equal.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will now be described in more detail with reference to the drawings.

Embodiment 1 FIG. 1 is a schematic block diagram showing an embodiment of the image forming apparatus of the present invention.

In FIG. 1, a photosensitive drum 1 as an electrostatic latent image carrier rotates in the direction of arrow R in the figure, and its surface is uniformly charged by a primary charger 2. After that, the photosensitive drum 1 is exposed to a laser beam L corresponding to an image, and an electrostatic latent image is formed on the surface. In the electrostatic latent image, the exposure width of the laser light L is controlled by a signal whose pulse width is modulated according to digital image data, and a laser spot having an exposure width corresponding to the image data is projected on the photosensitive drum 1. Form.

The formed electrostatic latent image has a developing unit 4Y containing therein a two-component developer composed of toner and carrier.
It is developed by applying a developing bias by 4M, 4C or 4K and is visualized as a toner image. In this embodiment,
Toner is negatively charged. The obtained toner image is conveyed by the paper conveying device and transferred onto the paper carried on the transfer drum 5a by the transfer charger 5b.

This series of steps is performed for four colors of yellow (Y), magenta (M), cyan (C), and black (K), and then the paper on which the toner images of the four colors are superposed and transferred is fixed to the fixing device 9. The toner image is sent, fixed, and output as an image.

In the transfer step, transfer residual toner remaining on the photosensitive drum 1 is cleaned by a cleaning device 6 having a cleaning blade pressed against the photosensitive drum 1. After that, the photosensitive drum 1 is destaticized by the pre-exposure device 11 and is used again for image formation.

In the present invention, the developing device 4 (4Y-4
A characteristic is that a BP bias is applied to the developing sleeve (developer carrying member) of K) as a developing bias from a developing power source (not shown) which is a bias applying unit, and the BP bias is devised. The developing bias used in this embodiment is shown in FIG. This developing bias voltage is a BP bias (blank pulse bias) including a rest portion (blank portion) and a vibrating portion. The vibrating section is formed of four pulses, and the time Tb = Tg of each pulse is 62.5 μs (microseconds), and the four pulses are 250 μsec.

Regarding the pulse peak voltage of the vibrating portion, the peak voltage (time Tg) of the pulse for causing the toner to fly to the photosensitive drum 1 is 900 V due to the potential difference from the rest portion, and the peak of the pulse for returning the toner to the developing sleeve. Voltage (time T
b) shows a potential difference with the rest portion of 800 V, and the rest portion has a potential of −400 V. The effective center voltage of the BP bias is about -417V, and the potential difference Vg between the effective center voltage value of the main bias and the pulse peak voltage of the toner in the vibrating portion in the flying direction of the photosensitive drum is 883V. The potential difference Vb from the pulse peak voltage in the sleeve return direction is 817V, and Vg is designed to be larger than Vb.

In the conventionally proposed BP bias as shown in FIG. 7, the peak voltage of each pulse of the vibrating section is such that the toner is ejected from the potential of the rest section toward the photosensitive drum 1.
The peak voltage in the direction of returning the toner to the developing sleeve is almost the same, and for example, the peak-to-peak voltage Vpp is 2.0.
With a bias of kV, they are -1 kV and +1 kV, respectively. In such a conventional bias, the effective center voltage is approximately -400V when the rest potential is -400V.
And Vg and Vb are almost the same.

Here, the bias Vpp in FIG. 2 is set to 1.7 k.
V, Vpp of the bias in FIG. 7 is 2 kV, and V when the image is output under the same conditions using the biases in FIGS.
The -D (development contrast vs. image density) curve is shown in FIG.

As shown in FIG. 3, the BP bias of the present invention (FIG. 2) provides a higher concentration than the conventional BP bias (FIG. 7). That is, according to the bias of the present invention, the concentration which could not be obtained until now by increasing the Vpp of the BP bias to 2 kV can be sufficiently obtained even when the Vpp is lowered to 1.7 kV.

In this embodiment, the Vpp of the BP bias can be suppressed to 1.7 kV in this way, and as a result, even if a conductive foreign substance is mixed in the developing portion, it is a problem which has been a problem in the past. No image defects due to discharge occur,
A high-density image can be stably obtained. Further, according to the bias of the present invention, the effect of reducing the roughness in the highlight portion, which is a characteristic of the BP bias, is obtained in the same manner as the conventional bias.

With the BP bias, the toner subjected to the vibration bias in the developing section is the developing sleeve and the photosensitive drum 1.
By repeating the vibration between the two, the toner is adhered to the latent image faithfully to the latent image, so that the dot reproducibility in the low contrast portion is good, but the BP bias of the present invention is effective even at the same latent image potential. , The difference between the peak voltage in the direction in which the toner flies to the photosensitive drum and the latent image potential (flying contrast) and the difference between the peak voltage in the direction to return the toner to the developing sleeve and the latent image potential (return contrast) are Since it is larger than the conventional BP bias, the amount of toner is larger than that of the conventional BP bias, and the toner vibrates in a biased manner toward the photosensitive drum side.
Therefore, it is considered that the concentration can be further increased and Vpp can be set low.

When the developer deteriorates due to long-term use,
Toner having a charge amount suitable for development is reduced in the developer and a sufficient density cannot be obtained with the conventional BP bias, but the BP bias of the present invention can obtain a sufficient density even with such a developer. .

Further, in the non-image portion, the BP bias of the present invention has a potential in the direction of returning the toner to the developing sleeve more than the effective bias center in the BP bias of the present invention. Fogging is unlikely to occur.

According to the experiments conducted by the present inventors, the above Vg
Ratio Vg of (potential difference between the effective center voltage value and the pulse peak voltage of the toner in the flying direction of the photosensitive drum) and Vb (potential difference between the effective center voltage value and the pulse peak voltage of the toner in the developing sleeve returning direction) As shown in Table 1, as / Vb increases, the development density increases, but if it is too high, the low density portion (highlight image) becomes less rough.

[0029]

[Table 1] This is because the toner is too biased toward the photosensitive drum side and does not vibrate much, and the toner attached to the latent image does not rearrange sufficiently and remains attached to the latent image, so the image is faithfully reproduced on the latent image. It seems that it is not possible.

According to Table 1, Vg / Vb is 1 <Vg /
Vb ≦ 1.5 is preferable, and in this embodiment, Vg / Vb =
833/817 = about 1.08.

In this embodiment, the BP bias as shown in FIG. 2 was applied to the developing sleeve as the developing bias, but the present invention is not limited to this, and various BP biases can be used. In this case, even if the electric field in the direction of causing the toner to fly to the photosensitive drum is larger than the electric field in the direction of returning the toner to the developing sleeve, the application time Tb of the electric field in the returning direction causes the toner to fly in the vibrating portion of the BP bias. If the applied time Tg of the electric field in the direction is longer than the applied time Tg, the amount of toner that vibrates biased toward the photosensitive drum side decreases, and the effect of the present invention decreases. Therefore, it is preferable that Tg and Tb are almost the same.

The BP bias, developing device and developer suitable for the present invention will be described.

In this embodiment, a two-component developer comprising a non-magnetic toner and a magnetic carrier (magnetic particles) is used as the developer. The mixing ratio is the weight ratio, and the non-magnetic toner is about 5
It was set to be%. The non-magnetic toner has a volume average particle diameter of about 8 μm. The magnetic carrier consists of resin-coated ferrite particles (maximum magnetization 60 emu / g), the weight average particle size is 50 μm, and the resistance value is 10 μm.
Indicates a value of ⁸ Ωcm or more. The magnetic permeability of the magnetic carrier is about 5.0. The toner triboelectric charge is about -2.0x
It is 10 ^-2 C / kg.

In the present invention, the triboelectric charge amount of the toner is
It measured using the measuring apparatus shown in FIG.

First, the toner for which the triboelectric charge amount is to be measured is combined with a carrier to form a two-component developer, and the amount of 50 to 50 is obtained.
Put in a polyethylene bottle of 100 ml capacity, about 10
Shake by hand for ~ 40 seconds, then add about 0.5 ~ of this developer.
1.5g, 500 mesh bottom conductive screen 14
3 into a metal measuring container 142,
A metal lid 144 is put on the cover. Measuring container 14 in this state
2 Weigh the whole and set this as W1 (kg).

Next, the measurement container 142 is installed in the suction device 141 (at least the portion of the suction device 141 that is in contact with the measurement container 142 is an insulator), suction is performed from the suction port 147, and the air volume control valve 146 is adjusted to create a vacuum. Total pressure of 145 is 250m
mAq. In this state, suction is performed sufficiently, preferably for 2 minutes, to remove the toner by suction. Measuring container 1 at this time
The potential indicated by the electrometer 149 connected to 42 is read, and this is defined as V1 (V). The weight of the entire measurement container 142 after suction is measured and designated as W2 (kg). Measuring container 14
If the capacity of the capacitor 148 connected in parallel with the electrometer 149 is C1 (μF), the toner triboelectric charge amount can be calculated by the following formula: toner triboelectric charge amount (μC / kg) = C1 × V1 × 10
It is calculated as ^-3 / (W1-W2).

The developing device 4 (4Y to 4K) is provided with an opening at a portion of the developing container containing the two-component developer in the vicinity of the photosensitive drum 1, and a developing sleeve as a developer carrying member is provided from this opening. It projects to the outside. The developing sleeve is rotatably incorporated in the developing container, and is arranged so that the distance from the photosensitive drum 1 is 500 μm. The outer diameter of the developing sleeve is 25 mm, and the peripheral speed thereof is 280 mm / sec.

In this embodiment, Vb: potential difference [V] between the effective center value of the developing bias and the peak voltage in the direction of returning the toner in the vibrating portion to the developer carrier, Tb: development on the developer carrier Maximum time [sec] for pulling back toner to the developer bearing member of alternating bias voltage, Vcont: image contrast potential [V] (potential difference between effective center value of developing bias and latent image potential when maximum image density is output) ), Q: average triboelectric charge amount [C / kg] of toner, d: | Vb-Vcont | · Tb ² as a developing bias when the distance [m] between the image carrier and the developer carrier is set. ^{/ 2 <d 2 / | Q} | alternating voltage as satisfying an alternating electric field is formed intermittently in is applied.

According to the experiments conducted by the present inventors, A = | Vpp-
^{Vcont | · Tb 2/2,} B = d 2 / | Q | as these relations only if the A <B, to maintain a high concentration in solid, reproducibility further highlight was good .

To explain this, let the charge amount of the toner be q,
The mass X is m, the acceleration is a, the potential difference between the photosensitive drum and the developing sleeve is ΔV, and the gap between the photosensitive drum and the developing sleeve is d. To be The peeling voltage that is pulled back to the developing sleeve is applied to the toner for Tb seconds as the maximum time during the application of the oscillating electric field. The distance X that the toner can move during this period is obtained by the following equation (1): X = | Q | · | Vb−Vcont | · Tb ² / 2d (1)

Here, by setting the condition that the toner developed on the photosensitive drum is not returned to the developing sleeve at the moving distance X when the stripping voltage is applied for the maximum time, the toner on the photosensitive drum is set. Repeated vibration biased to. The condition at this time is that X is smaller than the gap d between the photosensitive drum and the developing sleeve.

[0042] is represented by the formula, X = | Vb-Vcont | · Tb 2/2 <d 2 / | Q | ··· (2) and developed in such conditions, stripping voltage is maximum time The reciprocating motion between S and D cannot be sufficiently performed even by the electric field. Moreover, as in the present invention, the vibrating portion causes
Since the electric field is set to be larger than the electric field in the direction of returning the toner to the developing sleeve, a large amount of toner vibrates while being biased toward the photosensitive drum side. After that, at the resting portion, the toner vibrating with being biased toward the photosensitive drum side stops the vibration and adheres to the latent image on the photosensitive drum. Further, since the toner is concentrated on the latent image portion and the dots are faithfully reproduced on the photosensitive drum by intermittently repeating the vibration, only a non-uniform image can be obtained by the conventional rectangular bias. A uniform image can be output even with such a shallow latent image.

[0043] As described above, according to the present invention, the BP bias applied as a developing bias to the developer carrying member of the developing device, | Vb-Vcont | · Tb 2/2 <d 2 / | Q | conditions By satisfying the above condition, it is possible to obtain an image having no roughness in the low density portion and a sufficient density in the high density portion by the development without increasing Vpp of the developing bias.

Embodiment 2 In Embodiment 1, the BP bias shown in FIG. 2 was used as the developing bias, but as described above, the bias effective in the present invention is not limited to this.

FIG. 5 shows the BP bias used as the developing bias in this embodiment. The pulse peak voltage of the vibrating portion of the BP bias of the present embodiment is such that the peak voltage (time Tb) of the pulse for returning the toner to the developing sleeve is 800 V due to the potential difference with the rest portion, and the toner is caused to fly to the photosensitive drum 1. The peak voltage (time Tg) of the first pulse is 800 V due to the potential difference from the rest portion, but the peak voltage (time Tg) of the pulse in the direction of causing the toner to fly to the photosensitive drum immediately before changing from the vibrating portion to the rest portion. ) Has a potential difference of 9 from the rest part.
It is designed to be 00V.

When the potential of the rest portion is -400V, the effective center voltage value of this bias is about -408V. This effective center voltage value and that of the vibrating portion immediately before changing from the vibrating portion to the rest portion. The potential difference Vg2 between the toner and the pulse peak voltage in the flying direction of the photosensitive drum is 892V, but the potential difference Vg1 between the first toner peak pulse voltage in the vibrating part of the toner in the flying direction of the photosensitive drum and the toner developing sleeve return. The potential difference Vb from the pulse peak voltage in the direction is Vg
1 = Vb is 808V.

In order to obtain a sufficient density by development, it is necessary to bias a large amount of toner to the photosensitive drum side immediately before the resting portion and vibrate. As in this embodiment, the toner is moved in the returning direction before the resting portion. Sufficient concentration can be obtained by increasing the electric field in the flight direction immediately before the rest portion rather than the electric field.

Further, increasing the potential by one pulse in this way is more effective than increasing the potential of both pulses in the first embodiment when conductive foreign matter is mixed in the developing portion. The rate of abnormal discharge in the part is reduced, and it becomes difficult to generate an abnormal image that deteriorates the image quality.

Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications can be made within the technical idea of the present invention.

[0050]

As described above , according to the present invention,
The image carrier and the developer containing toner and carrier are carried.
Image carrier and the developer carrier that conveys the image to the opposite side of the image carrier.
When developing an electrostatic latent image formed on a carrier, carry a developer
Apply a developing bias that superimposes DC voltage and AC voltage on the body
The image forming apparatus having the application means for: (1) Return peak voltage for returning the toner to the developer carrying member
And the flying peak voltage that causes the toner to fly to the image carrier
Apply multiple times in sequence and then apply only DC voltage
Configure the development bias so that the process is repeated, and
The potential difference between the peak voltage and the effective center voltage of the developing bias.
The voltage between the write-back peak voltage and the effective center voltage of the developing bias.
It is configured to be larger than the position difference, or (2) the peak voltage and the torque for pulling the toner back to the developer carrying member.
The peak voltage that causes the toner to fly to the image carrier in this order.
The vibrating part that is applied once and the resting part that cuts off the AC voltage are periodically
Immediately before reaching the resting part by configuring the developing bias to repeat
Voltage that causes the toner to fly and the effective center voltage of the developing bias
The potential difference between the other peak voltage of the vibration part and the development bias
It is configured to be larger than the potential difference from the effective center voltage.
Therefore, the development bias should be a blank pulse bias.
Abnormal electrical discharge while suppressing roughness in highlight areas.
In order to prevent the occurrence of image defects due to
Even if the peak-to-peak voltage (Vpp) is reduced,
The toner is urged toward the image carrier by the peak voltage.
In this state, toner is attached to the electrostatic latent image at the resting part.
It is possible to prevent the image density from decreasing . That is, according to the present invention
With this , even under the condition of high frequency and low peak-to-peak voltage, an image with high uniformity and an image with sufficient density can be obtained.
It became possible to stably obtain high-quality images without image defects due to abnormal discharge.

[Brief description of drawings]

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

FIG. 2 is a waveform diagram showing a BP bias used in the example of FIG.

FIG. 3 is a diagram showing a V-D curve when images are output under the same conditions using the biases of FIGS. 2 and 7.

FIG. 4 is a perspective view showing a measuring device used to measure the triboelectric charge amount of toner in a two-component developer according to the present invention.

FIG. 5 is a waveform diagram showing a BP bias used in another embodiment of the present invention.

FIG. 6 is a waveform diagram showing a rectangular bias.

FIG. 7 is a waveform diagram showing a conventional BP bias.

[Explanation of symbols]

1 photosensitive drum 2 Primary charger 4 developing device 5 Transfer device 9 Fixing device

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP 2000-66494 (JP, A) JP 8-6366 (JP, A) JP 4-44054 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G03G 13/06-13/095 G03G 15/06-15/095

Claims (6)

(57) [Claims] 1. An image carrier, including a toner and a carrier.
The current carrying developer is conveyed to a portion facing the image carrier.
An image carrier and an electrostatic latent image formed on the image carrier.
When developing, a DC voltage and an AC voltage are applied to the developer carrier.
An applying unit that applies a superimposed developing bias.
In the image forming apparatus, a return peak voltage for returning the toner to the developer carrying member and
The flying peak voltage that causes the toner to fly to the image carrier is
After applying multiple times in order, apply only DC voltage continuously.
The developing bias is configured so that the steps described above are repeated,
The flying peak voltage and the effective center voltage of the developing bias
The potential difference between the return peak voltage and the developing bias.
It is characterized by making it larger than the potential difference from the effective center voltage.
Image forming apparatus. 2. The application time of the flying peak voltage and the return
It is characterized by making the application time of the peak voltage almost equal.
The image forming apparatus according to claim 1. 3. The flying peak voltage and the effective center voltage
The potential difference between Vg [V], the return peak voltage and the actual
3. The image formation according to claim 1 , wherein 1 <Vg / Vb ≦ 1.5 is satisfied , where Vb [V] is a potential difference from the effective center voltage.
apparatus. 4. An image carrier, including a toner and a carrier
The current carrying developer is conveyed to a portion facing the image carrier.
An image carrier and an electrostatic latent image formed on the image carrier.
When developing, a DC voltage and an AC voltage are applied to the developer carrier.
An applying unit that applies a superimposed developing bias.
In the image forming apparatus, the peak voltage and toner which pull the toner back to the developer carrier are
The peak voltage that causes the beam to fly to the image carrier in this order.
The vibrating part that is applied several times and the resting part that cuts off the AC voltage are periodically
The developing bias so as to repeat
Voltage and the developing bias to fly immediately before reaching
Potential difference from the effective center voltage of
Than the potential difference between the pressure and the effective center voltage of the developing bias
An image forming apparatus having a large size. 5. The effective center voltage in the vibrating section.
And the peak voltage to be flown before the same potential difference with
After alternately applying the peak voltage for pulling back,
It is special to apply the peak voltage to fly just before reaching
The image forming apparatus according to claim 4, which is a characteristic. 6. An application time of the flying peak voltage and
The application time of the peak voltage to be pulled back should be almost equal.
The image forming apparatus according to claim 4, wherein: