JPH0493863A - Electrostatic charging device and image forming device - Google Patents

Abstract

PURPOSE:To miniaturize an image forming device which uses an electrostatic charging device, to accomplish low power consumption and to reduce cost by intermittently impressing voltage having either polarity on an electrostatic charging member. CONSTITUTION:The peripheral surface of a rotary photosensitive body 1 is electrostatically charged by contact to have specified polarity and potential by an electrostatic charging roller 2 functioning as the electrostatic charging member on which the voltage is impressed. The surface of the photosensitive body 1 which is uniformly electrostatically charged by the roller 2 is exposed to the light of aimed image information by an exposing means 10, so that an electrostatic latent image corresponding to the aimed image information is formed on the peripheral surface. By impressing the intermittent voltage of either polarity on the roller 2 which abuts on the photosensitive body 1 by the use of a per source 3, the surface of the photosensitive body 1 is electrostatically charged to have the specified polarity and potential without using a transformer for generating low frequency AC high voltage. Thus, the electrostatic charging device is miniaturized, the low power consumption is accomplished, and the cost is reduced.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a contact-type charging device that performs charging (including static elimination) by bringing a charging member to which a voltage is applied into contact with the surface of a charged object;
and an image forming apparatus using the charging device.

(Prior art) For example, in image forming devices such as electrophotographic devices (copying machines, optical printers, etc.) and electrostatic recording devices, the surface of an image carrier as a charged object such as a photoreceptor or dielectric is subjected to charging processing. Conventionally, corona discharge devices have been widely used as means for this purpose.

A corona discharge device is effective as a means for uniformly charging the surface of an object to be charged, such as an image carrier, to a predetermined potential. but,
It requires a high-voltage power supply and has problems such as the generation of undesirable ozone due to corona discharge.

In contrast to such corona discharge devices, the contact-type charging device, which charges the surface of the charged object by bringing the charging member to which a voltage is applied as described above into contact with the surface of the charged object, can reduce the voltage of the power source and remove ozone. For example, in an image forming apparatus, instead of a corona discharge device, it can be used as a charging treatment device for image carriers such as photoreceptors and dielectrics, and other charged objects. It has attracted attention as a technology, and research into its practical application is underway.

For example, the present applicant first proposed (Patent Application No. 62-51492
No. 62-230334, etc.), in a contact charging device, an oscillating electric field (alternating By forming an electric field (an electric field) between the charging member and the charged object, and by using a charging member with a high resistance layer on the surface layer, it is possible to improve the charging uniformity of the charged object and the surface of the charged object such as a photoreceptor. It is possible to prevent leaks due to holes, scratches, etc.

FIG. 6 is a cross-sectional view of a schematic configuration of an example of a contact charging device. 1 is an object to be charged. In this example, a rotating drum type electrophotographic photoreceptor is used. The photoreceptor 1 has a structure in which the basic layers are a conductive base layer 1b made of aluminum or the like and a photoconductive layer 1a formed on the outer surface of the conductive base layer 1b.

2 is a charging member. This example is a roller type (hereinafter referred to as a charging roller). The charging roller 2 consists of a central metal core 20 as an electrode, a conductive elastic layer 2b formed concentrically around the outer periphery of the central metal core 20 into a roller shape by molding, etc., and a resistive layer 2a further formed on the outer periphery.

The charging roller 2 is arranged parallel to the drum-shaped photoreceptor 1 with both ends of the core metal 20 rotatably supported by bearing members (not shown), and is pressed against the surface of the photoreceptor 1 by a pressing means (not shown). It is pressed with a pressing force and rotates as the photoreceptor 1 rotates.

Reference numeral 30 denotes a bias application power source to the charging roller 2.

This power source 30 and the core metal 2c of the charging roller 2 are electrically connected, and a predetermined bias is applied to the charging roller 2 by the power source 30.

When the photoreceptor 1, which is an object to be charged, is rotationally driven, the outer circumferential surface of the photoreceptor is set to a predetermined polarity by a charging roller 2, which is a charging member that is pressed against the photoreceptor 1 and to which a bias voltage is applied. It is charged to a potential.

FIG. 7 shows details of the power source 30 for applying bias voltage to the charging roller 2. As shown in FIG. The power source 30 is a DC (
DC) high voltage generation circuit 31 and AC (alternating current) generation circuit 32
It consists of two parts.

The DC high voltage generation circuit 31 inputs the output of the DC generation circuit 33 of 10 Hz or higher to a step-up transformer 34, and rectifies the output with a rectifier circuit 35 consisting of a diode and a capacitor to obtain a DC voltage.

On the other hand, the AC high voltage generation circuit 32 inputs the output of the AC generation circuit 36 at a frequency of 1 Hz or less to a step-up transformer 37, and obtains an AC high voltage with a peak-to-peak voltage of 2 V at the same frequency as the input voltage.

FIG. 8 shows the output voltage waveform of the second power supply 30. By applying the above-mentioned voltage to the charging roller 2 from the electric current W30, the surface of the photoreceptor is charged to a potential of approximately (maximum value of output voltage+minimum value of output voltage)/2.

(Problems to be Solved by the Invention) By the way, in the above-mentioned contact-type charging device, if the AC frequency applied to the charging member is too high, the object to be charged may be a photoreceptor of an image forming apparatus, for example. If so, so-called toner fusion, in which toner adheres to the surface of the photoreceptor, may occur, so it is usually set to a low frequency range of 1 Hz or less.

On the other hand, if a step-up transformer has the same gain, the lower the frequency it is used for, the less efficient it becomes, and the larger and more expensive it becomes. This is particularly noticeable at frequencies below IKHz.

Therefore, in conventional contact-type charging devices and image forming apparatuses using such charging devices, the A of the power supply that applies voltage to the charging member is
Since the transformer for generating C high voltage is large, has low efficiency, and is expensive, it has been a problem in reducing the space of the device, preventing temperature rise inside the machine, reducing power consumption, and reducing costs.

Although the present invention is also a contact-type charging device, it is an object of the present invention to provide a device that solves the above-mentioned problems with power supply devices.

(Means for Solving the Problems) The present invention provides a charging device that charges the surface of a charged object by bringing a charging member applied with a voltage into contact with the charged object, in which a unipolar voltage is applied intermittently to the charging member. This is a charging device characterized in that it applies an electric current to an electric current.

Further, the present invention is an image forming apparatus using the charging device having the above-mentioned configuration as a means for charging a rotating image bearing member as a charged member.

(Function) That is, by bringing the charging member to which a positive or negative unipolar voltage is intermittently applied to the charging member into contact with the surface of the charged object, the charging member can be used as a power supply device for applying voltage to the charging member as described above. The surface of the charged object can be charged to the desired polarity and potential without using a problematic transformer for generating low frequency AC high voltage.

Therefore, it is possible to downsize the charging device or an image forming apparatus using the charging device, reduce power consumption, and reduce costs.

(Example) <Example 1> (1) Example of image forming apparatus FIG. 1 shows a schematic configuration of an example of an image forming apparatus using a charging device according to the present invention.

Similar to the one shown in FIG. 6, the circumferential surface of the rotating photoreceptor 1 as an object to be charged is contact-charged to a predetermined polarity and potential by a charging roller 2 as a charging member to which a voltage is applied.

The surface of the photoreceptor 1, which has been uniformly charged by the charging roller 2, is then exposed to target image information by the exposure means 10 (laser beam scanning exposure, slit exposure of the original image, etc.), so that the target image is formed on its peripheral surface. An electrostatic latent image is formed corresponding to the image information.

The latent image is then sequentially visualized as a toner image by the developing means 11.

This toner image is then conveyed from the transfer means 12 to a transfer section between the photoreceptor 1 and the transfer means 12 at an appropriate timing in synchronization with the rotation of the photoreceptor 1 from a paper feed means (not shown). The images are sequentially transferred onto the surface of the transfer material 14. The transfer means 12 in this example is a transfer roller, and the transfer material 1
By charging the photoconductor 1 with the opposite polarity to the toner from the back of 4,
The toner image on the front side is transferred to the front side of the transfer material 14.

The transfer material 14 to which the toner image has been transferred is separated from the surface of the photoreceptor, conveyed to an image fixing means (not shown), subjected to image fixation, and output as an image formed product. Alternatively, if an image is to be formed on the back side as well, the sheet is conveyed to a re-conveying means to the transfer section.

After the image has been transferred, the surface of the photoreceptor 1 is cleaned by a cleaning means 13 to remove adhered contaminants such as residual toner, and is used repeatedly for image formation.

(2) Power supply 3 FIG. 2 shows details of the power supply 3 for applying bias voltage to the charging roller 2. This electric power W3 consists of a low frequency generating circuit 3a and a DC high voltage generating circuit 3b.

The DC high voltage generation circuit 3b supplies the output of the AC generation circuit 3c of 10 KHz or higher to a step-up transformer 3d, and rectifies the output with a rectification circuit 3e consisting of a diode and a capacitor to obtain a DC voltage.

This DC high voltage generation circuit 3b is periodically turned on and off (
ONloFF) to obtain a positive or negative unipolar intermittent voltage of about 2 KV between peaks.

FIG. 3 shows an example of the output waveform of this power supply 3. In this example, the time constant at voltage fall is larger than that at voltage rise;
Reduce the pulse width of the low frequency type by 50% to obtain sufficient decay time.
Less than.

By applying a unipolar intermittent voltage to the charging roller 2 in contact with the photoreceptor 1 using such a power source 3, the photoreceptor 1 can be charged without using a conventional transformer for generating low frequency AC high voltage. The surface of the image forming apparatus can be charged to a predetermined polarity and potential, making it possible to reduce the size, power consumption, and cost of a charging device or an image forming device.

(3) Experimental example In the image forming apparatus shown in FIG.
2), the frequency of the low frequency oscillation circuit 3a is set to 15
The experiment was conducted with the frequency of the AC generating circuit 3c set to 0H2 and 25 KHz.

The process speed (rotational peripheral speed) of photoreceptor 1 is 25 m.
m/sec.

As shown in Table 1, the peak-to-peak voltage of the high voltage output is 1.6V.
In the above manner, the surface of the photoreceptor could be uniformly charged to a voltage that is half of the voltage E.

Table 1 Note that the charging member is not limited to the roller type in the above example, but may be a plate type, block type, or pad type, or any other suitable shape or form such as a rod shape, belt shape, sheet shape, etc.

The roller type charging member 2 may be driven in accordance with the object to be charged 1 which is driven in plane movement as in the above example, or may be non-rotating, or may be driven in the direction of movement of the object to be charged 1 in a plane. It may also be configured to actively rotate at a predetermined circumferential speed in the forward or reverse direction.

<Embodiment 2> Normally, in a transfer type image forming apparatus or the like, after image formation is completed, the photoreceptor is neutralized to prevent memory damage and the like.

In an image forming apparatus using a conventional contact-type charging device, this charge removal process is performed at (maximum peak value + minimum value of peak)/2
This has been done by applying a bias superimposed with an AC voltage with the value of OV to the charging member.

However, in the charging device of the first embodiment according to the present invention, the minimum value of the bias applied to the charging roller 2 by the power source 3 is OV, and it is not possible to generate an AC voltage with the average value of the voltage being Ov.

Therefore, in the image forming apparatus of this embodiment (FIG. 1), in order to eliminate static electricity from the photoreceptor 1 after image formation is completed, the exposure device 10 uniformly exposes the surface of the photoreceptor 1 to remove the static electricity.

FIG. 4 shows the static elimination exposure sequence.

That is, after image formation is completed, the photoreceptor is uniformly exposed over one revolution or more (three revolutions in this example). The charging bias for the charging roller 2 is such that the photoreceptor is placed in the charging device from the time when static elimination exposure is started.
The process is stopped between time T, which is earlier than when the exposure position is moved, and time T2, when the exposed portion for static elimination arrives at the charging device.

Example 3 In Example 1, as shown in Table 1, in order to obtain a dark potential of 700 V or less on the photoreceptor 1, the peak-to-peak voltage must be lowered, resulting in non-uniform charging.

To avoid this problem, it is sufficient to irradiate the non-image area with a smaller amount of light than when writing an image. FIG. 5 shows the change over time in the surface potential of the image area and non-image area of the photoreceptor.

First, charging is performed in a high peak-to-peak voltage range where uniform charging can be obtained. Next, the image area is irradiated with a normal amount of image writing light, and the non-image area is irradiated with a smaller amount of light than when writing an image.

In this way, a low uniform dark potential of 700V or less can be obtained.

Note that the weak light irradiation may be performed using the same or different exposure apparatus for normal image writing. Further, the exposure timing of the weak light may be before, after, or simultaneously with the image writing exposure.

(Effects of the Invention) As described above, according to the present invention, the power source for applying a voltage to the charging member of a contact type charging device is simplified, downsized, and reduced in cost, so that the charging device or the charging device can be The image forming apparatus used can be made smaller, consume less power, and be less costly.

Reference numeral 1 denotes a rotating photoreceptor as an object to be charged, 2 a charging roller as a charging member, and 3 and 30 a voltage applying power source.

Claims (4)

[Claims] (1) A charging device that charges the surface of a charged object by bringing a charging member to which a voltage has been applied into contact with the charged object, the charging device being characterized in that a unipolar voltage is intermittently applied to the charging member. (2) In an image forming apparatus in which image formation is performed by applying an image forming process including a step of charging the surface of the image carrier to a rotating image carrier as a charged body, and the image carrier is repeatedly subjected to image formation. , the charging process means is a charging device that charges the surface of the image carrier by bringing a charging member that intermittently applies a unipolar voltage into contact with the image carrier, and the charging process means charges the surface of the image carrier at least once after image formation is completed; An image forming apparatus characterized in that static electricity is removed from the surface of the image carrier by performing exposure processing on the surface of the image carrier by post-rotating the surface. (3) having an exposure device having a first light amount for image writing and a second light amount lower than the first light amount, and irradiating the non-image portion of the image carrier with light using the second light amount; 3. The image forming apparatus according to claim 2, wherein the image forming apparatus performs the following steps. (4) The voltage applying power source to the charging member includes at least the following:
Claim 1, 2, or 3, characterized in that it consists of an alternating current generating circuit, a switch circuit that turns on and off the alternating current generating circuit at a cycle longer than the alternating current cycle, a booster circuit, and a rectifier circuit. Charging device or image forming device.