JP2000250293A - Developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the density of an image formed from being changed in the case that the interval of an image carrier and a developer carrier opposed through a necessary interval fluctuates in the case of executing development by applying AC voltage to the carriers. SOLUTION: Developer 2 is led to a developing area opposed to the image carrier 1 through the necessary interval (d) by the developer carrier 11, and the development is executed by applying the AC voltage to the developer carrier 11. In this case, the AC voltage which consists of rectangular waves and at which the acting time of voltage acting a direction in which the developer is fed to the image carrier is set to be less than 50% of an average voltage value is applied to the developer carrier through a resistor 15, or the developer carrier to which the AC voltage is applied is provided with a resistance layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device used for developing an electrostatic latent image formed on an image carrier in an image forming apparatus such as a copying machine or a printer. A developer carrier to be held and an image carrier on which an electrostatic latent image is formed are provided so as to face each other with a required interval, and an AC voltage is applied to the developer carrier, and the developer carrier is In a developing device in which an AC electric field is applied between the image carrier and the developing device, the developer held on the developer carrier is supplied to an electrostatic latent image formed on the image carrier to perform development.
Even when the distance between the developer carrier and the image carrier fluctuates, the density of the formed image does not fluctuate greatly, and a good image having a stable image density can be obtained. The feature of the present invention resides in the following point.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine or a printer, various developing devices have been used to develop an electrostatic latent image formed on an image carrier.

In such a developing device, a developer carrier is provided so as to be in contact with the image carrier, and the developer is guided by the developer carrier to a development area in contact with the image carrier to perform development. A developing device of a contact developing system, which is to be carried out, and a developer carrier are provided so as to face the image carrier at a predetermined interval, and the developer is used by the developer carrier to a developing area facing the image carrier. Then, an AC voltage is applied to the developer carrier to cause an AC electric field to act between the developer carrier and the image carrier, thereby supplying the developer to the electrostatic latent image formed on the image carrier. There is known a non-contact developing type developing apparatus which performs development by using a developing method.

Here, in the case of the above-described contact developing type developing device, since the developing is performed by bringing the developer into contact with the image bearing member,
Although excellent in the reproducibility of the electrostatic latent image formed on the image carrier, the developer also adheres to non-image portions where the electrostatic latent image is not formed, and fogging occurs in the formed image, There has been a problem that the surface of the image carrier is worn by the developer carrier.

On the other hand, in the case of a non-contact developing type developing device in which a developer carrying member is provided so as to be opposed to an image carrying member at a predetermined interval, the above-described problems in the contact developing type developing device are reduced. .

However, in the case of such a non-contact developing type developing apparatus, for example, the molding accuracy and the mounting accuracy of the image carrier and the developer carrier are poor, so that the image carrier and the developer carrier cannot be connected to each other. The distance may fluctuate, and when the distance between the developer carrier and the image carrier becomes smaller, the AC electric field acting between the developer carrier and the image carrier becomes stronger, and the density of the formed image becomes lower. On the other hand, when the distance between the developer carrier and the image carrier increases, the AC electric field acting between the developer carrier and the image carrier weakens, and the density of the formed image decreases. However, there is a problem that density unevenness or the like occurs in an image formed by the above method, and a good image having a stable image density cannot be obtained.

[0007]

According to the present invention, a developer is held on a developer carrier, and the developer is guided to a developing area opposed to the image carrier at a predetermined interval. To solve the above-described problem in a developing device in which an AC voltage is applied to the developing device to perform the development by supplying the developer from the developer carrier to the electrostatic latent image formed on the image carrier. It is an issue.

That is, according to the present invention, in the above-described developing device, when the distance between the developer carrier and the image carrier fluctuates, it is possible to suppress a change in the density of an image to be formed. It is another object of the present invention to stably obtain a good image having a low density unevenness and a constant image density.

[0009]

According to a first aspect of the present invention, in order to solve the above-described problems, a developer is held on a developer carrying member, and the developer is supplied to the developing device. To a developing area facing the image carrier with a required interval, and applying an AC voltage to the developer carrier to supply a developer to an electrostatic latent image formed on the image carrier, An AC voltage having a rectangular wave, the AC voltage having a duration of less than 50% of a voltage acting in a direction in which the developer is sent to the image carrier is smaller than an average voltage value of the AC voltage via a resistor; Is applied.

In a second developing device according to a third aspect of the present invention, in order to solve the above-mentioned problem, a developer is held on a developer carrier, and the developer is transferred to an image carrier. And lead to the opposite development area via the required interval,
In a developing device for applying an AC voltage to the developer carrier to supply a developer to an electrostatic latent image formed on the image carrier, a resistance layer is provided on the developer carrier, and an AC A voltage, the AC voltage of which voltage is less than 50% of the voltage acting in the direction of sending the developer to the image carrier than the average voltage value, is applied to the developer carrier provided with the resistance layer. It was made to apply.

Here, as in the first and second developing devices of the present invention, when an AC voltage is applied via a resistor to a developer carrier provided at a required distance from the image carrier, When the case where the resistive layer is provided on the developer carrier is represented by an equivalent circuit, as shown in FIG. 1, the power source S is composed of an image carrier and a developer carrier opposed to the resistor R with a required interval therebetween. And a capacitor element C connected in series.

In such a circuit, when an AC voltage composed of a rectangular wave is applied from the power source S, the potential on the surface of the developer carrier rises with a time constant.

Here, when the distance d between the image carrier and the developer carrier decreases, the capacitance of the capacitor element C increases and the time constant increases, while the image carrier and the developer carrier become separated. When the distance d facing increases, the capacitance of the capacitor element C decreases, and the time constant decreases.

In the first and second developing devices described above, as shown by the broken lines in FIGS. 2A and 2B, the AC voltage is a rectangular wave AC voltage which is higher than the average voltage value VL. The image carrier and the developer carrier are opposed to each other when an AC voltage is applied to the developer carrier in which the operation time of the voltage on the developing side acting in the direction of sending the developer to the image carrier is less than 50%. When the interval d is small, the time constant becomes large as described above, and the rise of the potential on the surface of the developer carrier is greatly delayed, and the waveform of the AC voltage actually acting on the surface of the developer carrier is shown in FIG. A) is as shown by the solid line.
Here, when the rise of the potential on the surface of the developer carrier is greatly delayed as described above, the effect is shorter than the voltage on the recovery side acting in the direction of returning the developer to the developer carrier. Therefore, the voltage becomes large at the voltage on the developing side where the voltage change is large. For this reason, the average voltage value VL 'of the AC voltage actually acting on the surface of the developer carrier moves toward the collecting side with respect to the average voltage value VL of the AC voltage output from the power supply S, thereby suppressing the development. As a result, even when the distance d between the image carrier and the developer carrier is reduced and the AC electric field acting between the image carrier and the developer carrier is increased, the image carrier is formed. An increase in the density of the image is prevented.

On the other hand, when the distance d between the image carrier and the developer carrier increases, the time constant decreases as described above, and the rise of the potential on the surface of the developer carrier is delayed. And the waveform of the AC voltage actually acting on the surface of the developer carrier hardly changes from the AC voltage output from the power source S as shown by the solid line in FIG. , The decrease in the image density is reduced.

Therefore, in the first and second developing devices of the present invention, even when the distance d between the image carrier and the developer carrier fluctuates, the image density of the formed image varies. And a good image having a constant image density can be stably obtained. In the first and second developing devices according to the present invention, when the distance d between the image carrier and the developer carrier is reduced as described above, the density of the formed image is reduced to the predetermined density. While suppressing the further increase, the image density is reduced when the interval d between the image carrier and the developer carrier is large, and the density difference between the two is reduced. When obtaining an image having a high density, the peak-to-peak value of the AC voltage applied to the developer carrying member should be increased or the DC voltage should be set higher in a direction in which development is promoted as compared with the normal developing conditions. Etc. are required.

Here, in the first and second developing devices of the present invention, the AC voltage as described above is applied to the developer carrier via a resistor, or the developer carrier having a resistance layer is provided. When the resistance or the resistance value of the resistance layer is low, the influence of the time constant as described above is weakened, and the change in the image density of the formed image cannot be sufficiently suppressed. On the other hand, if the resistance value is too high, the AC electric field acting between the developer carrier and the image carrier is weakened, and an image having a sufficient image density cannot be obtained. Is 10 ³ to 10 ^7.
It is preferable to be in the range of Ω.

In the case where the AC voltage is applied to the developer carrying member via a resistor as in the first developing device according to the first aspect of the present invention, a variable resistor is used as the resistor. When a predetermined pattern is developed by the developing device and its density is detected, the resistance value of the variable resistor is adjusted based on the detection result, and the distance d between the image carrier and the developer carrier fluctuates. It is preferable to more appropriately control the change in the image density at.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a developing device according to an embodiment of the present invention will be specifically described with reference to the accompanying drawings.

(Embodiment 1) In a developing device according to this embodiment, as shown in FIG. 3, a developer carrier 11 in the form of a roller is opposed to the image carrier 1 with a required distance d therebetween. The toner 2 contained in the apparatus main body 10 is supplied to the developer carrier 11 by the supply member 12.

Then, the developer carrier 11 to which the toner 2 is supplied is rotated so that the toner 2 is transported by the developer carrier 11 and a regulating member 13 is provided on the surface of the developer carrier 11. To regulate the amount of the toner 2 conveyed by the regulating member 13 and frictionally charge the toner 2. The charged toner 2 faces the image carrier 1 via a required distance d. To the developing area. Here, as the developer carrier 11, for example, a metal roller whose surface has been blasted to have a ten-point average roughness Rz of about 7 μm is used. However, a plate material of stainless steel or phosphor bronze having a thickness of 0.08 mm to 0.2 mm is used.

In the developing device of this embodiment, a resistor 15 having a resistance value in a range of 10 ³ Ω to 10 ⁷ Ω is provided between the developer carrier 11 and the power source 14. 14 is an AC voltage composed of a rectangular wave, the AC voltage having an operation time of less than 50% of the voltage acting in the direction of sending the toner 2 to the image carrier 1 being less than the average voltage value is superimposed on the DC voltage. The developing bias voltage is output, and the developing bias voltage is applied to the developer carrier 11 via the resistor 15, whereby the toner 2 held by the developer carrier 11 is applied to the image carrier 1. The image is supplied to the formed electrostatic latent image for development.

After the development in this way,
The toner 2 after the development is guided to the apparatus main body 10 by the developer carrier 11, and the toner 2 is removed from the developer carrier 11 by the removing member 16 and returned into the apparatus main body 10.

Here, as in the developing device according to the present embodiment, the above-described developing bias voltage is applied to the developer carrier 11 via the resistor 15 to perform development.
In the case where the developing bias voltage as described above is directly applied to the developer carrying member 11 without passing through the resistor 15 to perform the development, the voltage value of the DC voltage applied from the power source 14 is changed to perform the developing. By changing the average voltage of the bias voltage, development characteristics were examined when the distance d between the image carrier 1 and the developer carrier 11 was large and small, and the results are shown in FIG. In FIG. 4, the development characteristics in the case where the development bias voltage is applied to the developer carrier 11 via the resistor 15 as in the development device of the embodiment to perform the development are indicated by solid lines, The development characteristics in the case where the development was performed by applying the development bias voltage directly to the developer carrier 11 without passing through the resistor 15 are indicated by broken lines.

As a result, when the developing is performed by applying the above-described developing bias voltage to the developer carrier 11 through the resistor 15 as in the developing device in this embodiment, the developing is performed without the resistor 15. The image carrier 1 and the developer carrier 11 are compared with the case where the development is performed by applying the voltage directly to the developer carrier 11.
The difference in image density between the case where the distance d is large and the case where the distance d is small is small, and the change in the image density when the distance d between the image carrier 1 and the developer carrier 11 fluctuates is suppressed. A good image having a stable image density with less occurrence is obtained.

In the developing device according to this embodiment, a resistor 15 having a resistance value in the range of 10 ³ to 10 ⁷ Ω is connected between the developer carrier 11 and a power supply 14 for supplying a developing bias voltage. However, as in the developing device shown in FIG. 5, the developer carrier 11 and the power
4, a variable resistor 15a capable of changing the resistance value is provided, and a sensor 16 for detecting the toner density of the toner image formed on the developer carrier 11 is provided in proximity to the developer carrier 11, Based on the toner density measured by the sensor 16, the controller 17 can change the resistance value of the variable resistor 15a.

(Embodiment 2) In the developing device of this embodiment, as shown in FIG. 6, a developing device is provided without providing a resistor 15 between a developer carrier 11 and a power supply 14 for supplying a developing bias voltage. On the surface of the agent carrier 11, a resistance layer 11a in the range of 10 ³ to 10 ⁷ Ω is provided.

The power supply 14 supplies the developer carrier 11 provided with the resistance layer 11a with an AC voltage composed of a rectangular wave, and the toner 2 has a higher voltage than the average voltage.
Of the voltage acting in the direction in which the
The developing is performed by applying a developing bias voltage in which the AC voltage that is less than 0% is superimposed on the DC voltage, and the other conditions are the same as those in the first embodiment.

Here, in the developing device of this embodiment, a conductive roller such as a metal roller is used as the developer carrier 11, and an EPD is provided on the surface of the developer carrier 11.
A resistance layer 11a made of a rubber material such as M, silicone rubber, urethane rubber or the like, or a resin material such as polystyrene, polyolefin, polyurethane, polyester, polyvinyl chloride, polybutadiene, or polyamide is provided.

Then, like the developing device in this embodiment, the developer carrier 11 provided with the resistance layer 11a is provided.
The AC voltage from the power supply 14 is an AC voltage composed of a square wave, and the AC voltage in which the operation time of the voltage acting in the direction of sending the toner 2 to the image carrier 1 is less than 50% of the average voltage value is converted to the DC voltage. When the developing is performed by applying the superposed developing bias voltage, similarly to the developing device of the first embodiment, the image density when the distance d between the image carrier 1 and the developer carrier 11 fluctuates. Is suppressed, and a good image having a stable image density with less occurrence of density unevenness can be obtained.

[0031]

Next, a developing device according to a specific embodiment of the present invention will be compared with a developing device according to a comparative example. In the developing device according to the embodiment of the present invention, an image carrier, a developer carrier, It is clarified that the change in image density is suppressed even when the interval of fluctuates, and a good image with less density unevenness can be obtained.

Here, in the developing device of the first embodiment,
In the developing device of the first embodiment shown in FIG. 3, the resistance between the developer carrier 11 and the power source 14 is 50
In the developing device of the second embodiment shown in FIG. 6, a resistance of 500 kΩ is provided on the surface of the developer carrier 11 in the developing device of the second embodiment shown in FIG. The one having the layer 11a formed thereon was used. On the other hand, in the developing device of the comparative example, the developer carrier 11 without the resistance layer 11a was used, and the resistor 15 was not provided between the developer carrier 11 and the power supply 14.

In each of the developing devices of Examples 1 and 2 and the comparative example, the peak-to-peak value Vpp is 1.3 kV and the frequency is 2.6 k together with the DC voltage from the power supply 14.
Hz, which is an AC voltage consisting of a rectangular wave of which frequency is 30% shorter than the average voltage value of the voltage acting in the direction of sending the toner 2 to the image carrier 1. The average value of the developing bias voltage is changed by changing the voltage value of the DC voltage to be applied from the above. When the distance d between the image carrier 1 and the developer carrier 11 is 0.12 mm and 0.17 mm And the development characteristics of
FIG. 7 shows the result when the developing device of Example 1 was used, FIG. 8 shows the result of the developing device using Example 2, and FIG. 9 shows the result of the developing device using Comparative Example. Was. In FIGS. 7 to 9, the results when the distance d between the image carrier 1 and the developer carrier 11 is 0.12 mm are indicated by ○ and broken lines, and The interval d is 0.17 mm
The result in the case of is shown by a solid line and ●.

As a result, in the vicinity of the image density 1.5 where a sufficient density image can be obtained, the distance d between the image carrier 1 and the developer carrier 11 is 0.12 mm and 0.17 mm.
Comparing the image densities of the two cases, the difference between the image densities in the developing device of the comparative example was larger than that in the developing device of the comparative example. There is almost no difference between the image carrier 1 and the developer carrier 1 under the conditions of actual development.
Even if the distance d from 1 fluctuates, density unevenness hardly occurs in the formed image, and a good image having a constant image density can be stably obtained.

[0035]

As described in detail above, in the developing device of the present invention, when an AC voltage is applied to a developer carrier provided at a required distance from the image carrier to perform development, the AC voltage is applied. As the voltage, an AC voltage composed of a rectangular wave and having an operation time of less than 50% of a voltage acting in a direction in which the developer is sent to the image bearing member is smaller than an average voltage value of the AC voltage is used. Is applied to the developer carrier via a resistor, or a resistance layer is provided on the developer carrier to which this AC voltage is applied, so that the potential on the surface of the developer carrier rises with a time constant. Due to the influence of the time constant, even when the distance between the image carrier and the developer carrier fluctuates, the change in image density of the formed image is suppressed.

As a result, in the developing device of the present invention, even when the distance between the image carrier and the developer carrier fluctuates, the occurrence of density unevenness is small, and a good image having a constant image density is stable. And got it.

[Brief description of the drawings]

FIG. 1 is a diagram showing an equivalent circuit of a circuit composed of a developing device and an image carrier according to the present invention.

FIG. 2 is a cross-sectional view of the developing device according to the present invention, in which the waveform of the AC voltage applied to the developer carrier and the waveform of the AC voltage actually acting on the surface of the developer carrier are different between the image carrier and the developer carrier; FIG. 4 is a diagram showing a state where the distance changes according to the facing distance.

FIG. 3 is a schematic explanatory view of a developing device according to Embodiment 1 of the present invention in which a resistor is provided between a power supply and a developer carrier.

FIG. 4 shows the relationship between the image carrier and the developing device of the first embodiment in which a resistance is provided between the power supply and the developer carrier, and the developing device in which a resistance is not provided between the power source and the developer carrier. FIG. 8 is a diagram comparing changes in developing characteristics when the distance between the developer carrier and the developer carrier is large and small.

FIG. 5 is a schematic explanatory view showing a modification of the developing device of the first embodiment in which a variable resistor is provided between a power supply and a developer carrier.

FIG. 6 is a schematic explanatory diagram of a developing device according to a second embodiment of the present invention in which a resistance layer is provided on a developer carrying member.

FIG. 7 is a diagram illustrating a change in development characteristics when the distance between the image carrier and the developer carrier is large and small in the developing device according to the first embodiment of the present invention.

FIG. 8 is a diagram illustrating changes in development characteristics when the distance between the image carrier and the developer carrier is large and small in the developing device according to the second embodiment of the present invention.

FIG. 9 is a diagram illustrating a change in development characteristics when the distance between the image carrier and the developer carrier is large and small in the developing device of the comparative example.

DESCRIPTION OF SYMBOLS 1 Image carrier 2 Toner (developer) 11 Developer carrier 11a Resistive layer 14 Power supply 15 Resistance 15a Variable resistance d Distance between image carrier and developer carrier

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Tateki Oka 2-3-13 Azuchicho, Chuo-ku, Osaka-shi Osaka International Building Minolta Co., Ltd. F-term (reference) 2H027 DA10 DE07 EA05 EC06 ED09 ZA07 2H073 AA02 BA04 BA06 BA13 BA41 BA45

Claims (4)

[Claims] 1. A developer is held on a developer carrier, and the developer is guided to a developing area opposed to the image carrier at a predetermined interval, and an AC voltage is applied to the developer carrier to cause image development. In a developing device for supplying a developer to an electrostatic latent image formed on a carrier, an AC voltage composed of a rectangular wave, which is a voltage acting in a direction in which the developer is sent to the image carrier, is smaller than an average voltage value. A developing device characterized in that an AC voltage having an operation time of less than 50% is applied to a developer carrying member via a resistor. 2. The developing device according to claim 1, wherein
A developing device wherein the resistance value of the resistor is in the range of 10 ³ to 10 ⁷ Ω. 3. A developer is held on a developer carrier, and the developer is guided to a developing area facing the image carrier at a predetermined interval, and an AC voltage is applied to the developer carrier to cause image development. In a developing device for supplying a developer to an electrostatic latent image formed on a carrier, a resistive layer is provided on the developer carrier, and an alternating voltage of a rectangular wave is used. A developing device, characterized in that an AC voltage having a voltage acting time of less than 50% in a direction in which the voltage is applied to the image carrier is applied to the developer carrier provided with the resistance layer. 4. The developing device according to claim 3, wherein
A developing device, wherein the resistance value of the resistance layer is in the range of 10 ³ to 10 ⁷ Ω.