JPH117200A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of always forming an excellent image stably by preventing or reducing the memory generation on an image carrier due to overshooting at the time of the start of a power source of a transfer bias. SOLUTION: This device is constituted by equipping a primary electrifying unit (electrifying means) 11, an image exposure (image information write-in means) 12, a developing device (developing means) 13, a transferring roller (transferring means) 16 transferring a toner image formed by this developing device 13 on a transfer material 18 and a discharge needle (separating means) 19 for accelerating the separation of the transfer material 18 from a photoreceptor 10 after transferring. In this case, the device composed so as to apply a contact transfer system for the transferring roller 16, to equip a transfer bias power source (transfer bias feeding means) 21 feeding a transfer bias on the transferring roller 16 and a separating bias power source separating bias feeding means) 22 feeding a separate bias on the discharge needle 19 so that the separating bias power source 22 starts the separate bias feeding synchronizing with the transfer bias feeding start time of the transfer bias power source 21 or prior to that.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus such as an electrostatic copying machine and an electrostatic printer using an electrostatic transfer process.

[0002]

2. Description of the Related Art An image forming apparatus for transferring a transferable toner image formed on the surface of an image carrier to a transfer material such as paper has been widely used.

FIG. 5 is a schematic sectional view showing a typical example of a main part of such an image forming apparatus. In this image forming apparatus, an image carrier (hereinafter, referred to as a photoconductor) rotating in the direction of arrow X is shown. 10) The surface of 10 is uniformly charged by a primary charger 11 and when the charged surface is irradiated with an image exposure 12 such as an image-modulated laser beam, the potential of the portion is attenuated and the electrostatic latent An image is formed.

When the electrostatic latent image reaches a developing site where the photoconductor 10 and the developing device 13 are opposed to each other, toner is supplied to the electrostatic latent image to form a toner image. And
The rotation of the photoconductor 10 causes the toner image to be
When the transfer material and the contact transfer charger 16 arrive at a transfer site opposed to each other, the transfer material 18 conveyed in time therewith.
Is supplied so as to be in close contact with the photoconductor 10 at the transfer portion, and at the same time, the toner image on the photoconductor 10 is transferred to the transfer material 18 by the action of the transfer electric field formed by the contact transfer charger 16.

Thereafter, the transfer material 18 is separated from the photoreceptor 10 by an electric action of the separating means 19 and is conveyed to a fixing portion (not shown) where the toner image is fixed. The residual toner on the surface of the photoconductor 10 is removed by the cleaner 17 and the photoconductor 10 is prepared for the next image forming process.

In recent years, a contact transfer charger represented by a transfer roller has become widespread as a transfer charger, and this kind of contact transfer charger has a power supply compared to a non-contact transfer charger such as a corona charger. Advantages are that the capacity can be reduced, and the amount of discharge products represented by ozone is small.
Incidentally, a separating charger, a static elimination needle, or the like is used as the separating means.

The image forming system includes a regular developing system in which a charged photosensitive member surface is exposed corresponding to a background portion of image information (background exposure system) and a portion other than the background is developed. Conversely, there is a reversal development system in which exposure is performed corresponding to the image information section (image exposure system), and a portion to be exposed is developed.

Further, as a separating means (including a means for assisting the separation), there are a separating charger by corona discharge, a static elimination needle having a tip end shaped like a sawtooth, and the like. , Or a bias having a polarity opposite to that of a transfer bias having a higher removal effect is applied. Normally, the separation bias is applied at the same time as the transfer material is always grounded or reaches the transfer portion. When the rear end of the transfer material has passed through the transfer portion, the application of the separation bias is stopped.

[0009]

However, when the contact transfer system is generally employed, the following problems are likely to occur.

That is, when the transfer bias is applied to the contact transfer charger, an output larger than the control value is generally output momentarily at the rise of the power supply (hereinafter, referred to as overshoot). The overshoot is more likely to occur in the case of constant current control because of the circuit configuration and the like.

Generally, the transfer bias is applied to the contact transfer charger before or before the transfer material reaches the transfer site.
Therefore, for example, when the power supply rises, an electrostatic memory is generated on the photosensitive member due to overshoot, and a charging failure is generated by the memory. As a result, a density difference due to a potential difference is generated in that portion.

In particular, in a method of forming a toner image on the surface of a photoreceptor having the same polarity as the toner as represented by the reversal developing method, the transfer polarity at the time of transfer is opposite to that of the surface of the photoreceptor charged by the charging means. Polarity, a memory that is particularly intense as compared with the normal development system is generated, and in some cases, the memory may not be permanently erased, so that image formation cannot be performed.

The memory is a contact transfer charger (hereinafter referred to as a contact transfer charger).
This is more remarkable as the volume resistance of the transfer roller is smaller. Therefore, the volume resistance of the transfer roller can be improved to some extent by increasing the volume resistance of the transfer roller. , Fundamental improvements could not be made,
Good image formation cannot always be performed.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to prevent or reduce the occurrence of memory on the image carrier due to overshoot at the time of power supply rise of the transfer bias, thereby always providing a high quality image. An object of the present invention is to provide an image forming apparatus that can stably form.

[0015]

In order to achieve the above object, according to the present invention, there is provided a charging means for uniformly charging an image carrier, and an image for writing image information on the charged image carrier. Information writing means, developing means for visualizing an electrostatic latent image formed by the image information writing means, transfer means for transferring a toner image formed by the developing means to a transfer material, and In an image forming apparatus having a separation unit for promoting separation of the transfer material from an image carrier, a transfer bias supply unit that employs a contact transfer system for the transfer unit and supplies a transfer bias to the transfer unit, A separation bias supply unit for supplying a separation bias to the unit, wherein the separation bias supply unit is synchronized with or before the transfer bias supply start time of the transfer bias supply unit. Characterized in that so as to start the separation bias supply.

According to a second aspect of the present invention, in the first aspect of the present invention, the separation bias supply unit supplies the separation bias A corresponding to a transfer bias supply start time.
And the separation bias B supplied after the separation bias A corresponding to the transfer bias supply start time can be output.

According to a third aspect of the present invention, in the second aspect, the separation bias A and the separation bias B
And at least one of the two is switchable in accordance with the resistance value of the contact transfer member of the transfer unit.

According to a fourth aspect of the present invention, there is provided a charging device for uniformly charging an image carrier, an image information writing device for writing image information on the charged image carrier, and a recording medium formed by the image information writing device. Developing means for converting an electrostatic latent image into a visible image, a transferring means for transferring a toner image formed by the developing means to a transfer material, and a device for promoting separation of the transfer material from the image carrier after transfer. In the image forming apparatus having the separation unit, a contact transfer method is adopted as the transfer unit, and a transfer bias supply unit that supplies a transfer bias to the transfer unit and a separation bias supply unit that supplies a separation bias to the separation unit are provided. A variable resistor is interposed between the separation unit and the separation bias unit; and the separation bias supply unit supplies a transfer bias of the transfer bias supply unit. The separation bias supply is started in synchronization with or before the start time, and the resistance value of the variable resistor is made smaller than that after the transfer bias supply start time in accordance with the transfer bias supply start time. Features.

According to a fifth aspect of the present invention, there is provided a charging means for uniformly charging an image carrier, an image information writing means for writing image information on the charged image carrier, and a recording medium comprising the image information writing means. Developing means for converting an electrostatic latent image into a visible image, a transferring means for transferring a toner image formed by the developing means to a transfer material, and a device for promoting separation of the transfer material from the image carrier after transfer. In the image forming apparatus having the separation unit, the transfer unit employs a contact transfer system, a transfer bias supply unit that supplies a transfer bias to the transfer unit is provided, and the separation unit is connected via a variable resistor or a conduction switch. And the resistance value of the variable resistor is set to be smaller than that after the transfer bias supply start time in accordance with the transfer bias supply start time of the transfer bias supply means. And or conducting the conducting switch in response to the transfer bias supply start time, characterized in that so as to release the conduction at a predetermined time.

According to a sixth aspect of the present invention, in the first to fourth or fifth aspects of the present invention, the start of the transfer bias supply by the transfer bias supply means is synchronized with or before the transfer portion arrival time of the transfer material. It is characterized by doing.

According to a seventh aspect of the present invention, in the first to fourth or fifth aspects of the present invention, the transfer bias supply means is controlled at a constant current at least at the start of the transfer bias supply.

According to an eighth aspect of the present invention, in the first to fourth or fifth aspects, a visualized image is formed by reversal development.

According to a ninth aspect of the present invention, in the first to fourth or fifth aspects of the present invention, the separation bias has a polarity opposite to that of the transfer bias.

According to a tenth aspect of the present invention, in the first to fourth or fifth aspects of the present invention, the shape of a portion of the separating means facing the image carrier is pointed.

[0025]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

<Embodiment 1> FIG. 1 is a schematic sectional view of a main part of an image forming apparatus according to Embodiment 1 of the present invention. In this figure, the same elements as those shown in FIG. In the following, description thereof will be omitted.

In the image forming apparatus according to the present embodiment, the polarity of the toner of the toner image on the photosensitive member 10 is set to minus, the polarity of the transfer bias is set to plus, and the reversal developing method is used as the developing method. .

In FIG. 1, reference numeral 21 denotes a transfer bias power supply for applying a bias to the transfer roller 16, and reference numeral 22 denotes a separation bias power supply for applying a bias to the static elimination needle 19 as separation means.

In this embodiment, the constant current control output to the transfer roller 16 by the transfer bias power supply 21 is started about 0.5 second before the transfer material 18 reaches the transfer portion, and the constant current control of the transfer roller 16 is started. About 0.5 seconds before the start of the output, the constant bias control output to the static elimination needle 19 by the separation bias power supply 22 is performed. In the image forming apparatus according to the present embodiment, the paper passing speed of the transfer material 18 is 105 mm.
/ Sec, constant current control outputs 9 μA, and overshoot outputs 20 μmA. Further, the static elimination needle 19 is located in the vicinity of not contacting the transfer roller 16, and is output under the control of a predetermined constant voltage control value.

Thus, by adopting the above configuration, a desired amount of transfer current flows to the charge eliminating needle 19 at the time of overshoot, and a good image is formed without causing a memory in the photoconductor 10. I was able to.

In this embodiment, the actual transfer bias is also controlled by the constant current control. However, for example, a voltage applied to the transfer roller 16 at the time of 9 μA constant current control output during non-sheet passing is detected, and the detected voltage is detected. The constant voltage value at the time of paper passing may be determined based on the value, and constant voltage output control (hereinafter, referred to as ATVC control) may be performed.

Second Embodiment Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 2 is a timing chart showing the transfer of the transfer material and the application timing of the transfer bias and the separation bias in the image forming apparatus according to the present embodiment.

Since the configuration of the image forming apparatus according to the present embodiment is the same as that of the first embodiment, each component will be described below using the same reference numerals as those shown in FIG.

In this embodiment, the transfer bias power supply 21
The output value for supplying the bias from the separation bias power supply 22 to the static elimination needle 19 is set to a value different from that at the time of image formation in response to the overshoot generated when the bias supply to the transfer roller 16 is started (specifically, large). Do).

In the present embodiment, the paper passing speed of the transfer material 18 is 105 mm / sec, and the constant current control value is 9 μm.
A, The constant voltage control was ATVC control. The polarity of the toner of the toner image on the photoconductor 10 is assumed to be negative, the polarity of the transfer bias is assumed to be positive, and the reversal development method is used.

FIG. 2 shows a timing chart at a transfer portion in the image forming apparatus according to the present embodiment. FIG. 2 shows the timing at which the transfer material passes from the top to the transfer site, the timing at which the transfer bias is supplied, and the timing at which the separation bias is supplied.

In this embodiment, assuming that the arrival time of the transfer material 18 at the transfer portion is 0 second, the output is started with the output of the separation bias A about 1 second before the output. The transfer bias is applied five seconds before, and the transfer material 18 reaches the transfer part at 0 seconds. And 0.5
After 2 seconds, switching is performed so as to output an output value of separation bias B. In this embodiment, the separation bias A is set to -3 kV, and the separation bias B is set to -2 kV.

In general, when the separation bias is increased to a polarity opposite to that of the transfer bias (for example, from −2 kV to −3 kV), the transfer bias easily flows to the charge removing needle 19,
It becomes difficult to secure a substantial transfer charge on the transfer material. If the size is reduced, it is difficult to prevent the occurrence of the drum memory and to improve the separability.

However, by adopting the configuration of the present embodiment, it is possible to prevent both the occurrence of drum memory due to overshoot at the time of applying a transfer bias and to ensure high separation and to secure transfer charges at the time of transfer. Good image formation can be performed.

In the present embodiment, the output is performed at the timing shown in FIG. 2, but it is needless to say that the present invention is not limited to this timing and output value.

<Third Embodiment> Next, a third embodiment of the present invention will be described.

In the present embodiment, at least one of the separation bias A and the separation bias B of the second embodiment can be switched according to the resistance value of the contact transfer member.

The configuration of the image forming apparatus according to the present embodiment is the same as that of the image forming apparatus according to the second embodiment.
The transfer material passing speed was 105 mm / sec, the constant current control value was 9 μA, and the constant voltage control was ATVC control.

Generally, when the resistance value of the contact transfer member is low as described above, drum memory due to overshoot is likely to occur. Therefore, by switching the bias value of the separation bias A in accordance with the resistance value of the contact transfer member, it is possible to prevent both the occurrence of the drum memory and to secure the transfer charge at the leading end portion of the transfer material. Similarly, by switching the bias value of the separation bias B according to the resistance value of the contact transfer member even during the transfer of the transfer material, it is possible to secure the transfer charge and prevent a problem due to excessive transfer charge.

<Fourth Embodiment> Next, a fourth embodiment of the present invention will be described with reference to FIG. FIG. 4 is a schematic sectional view of a main part of the image forming apparatus according to the present embodiment. In FIG. 4, the same elements as those shown in FIG. Is omitted.

In the present embodiment, a variable resistor 23 is arranged in series between the static elimination needle 19 and the separation bias power supply 22,
The resistance value of the variable resistor 23 is reduced in response to the overshoot generated when the supply of bias to the transfer roller 16 is started, and is increased during image formation. In particular, two types of output values are provided as separation bias. No need.
Specifically, a resistance value C corresponding to the separation bias A and a resistance value D corresponding to the separation bias B shown in FIG. 2 are switched. The resistance value C is 1 MΩ, and the resistance value D is 50M.
Ω, and the separation bias output value was fixed at −3 kV.
Note that the resistance values C and D are not limited to the values shown here.

Thus, by adopting the configuration as in the present embodiment, it is possible to obtain substantially the same effect as switching the separation bias.

Although the resistance value is changed by the variable resistor 23 in the present embodiment, the same effect can be obtained by providing a fixed resistor circuit and switching the resistance value of the circuit by means such as a conductive switch. Can be

<Fifth Embodiment> Next, a fifth embodiment of the present invention will be described with reference to FIG. FIG. 4 is a schematic sectional view of a main part of an image forming apparatus according to Embodiment 5 of the present invention. In this figure, the same elements as those shown in FIG. The description of is omitted.

In the present embodiment, the static elimination needle 19 is grounded,
A variable resistor 23 is arranged in series between the static elimination needle 19 and the ground, and the resistance 23 of the variable resistor 23 corresponds to the overshoot generated when the bias supply to the transfer roller 16 is started.
Is reduced, and is increased during image formation.
This is particularly effective when a power supply is not used as the separation bias.

In this embodiment, the resistance value E corresponding to the resistance value C (500 kΩ in this embodiment) and the resistance value F corresponding to the resistance value D (this By setting it to 5 MΩ in the embodiment, the amount of the transfer bias flowing to the static elimination needle 19 can be appropriately controlled with respect to the ground, and even if a relatively simple configuration of grounding the static elimination needle 19 is employed, Good image formation can be performed while preventing generation of a drum memory.

The values of the resistance values E and F are not limited to the values shown in this embodiment.

[0053]

As is apparent from the above description, according to the present invention, a desired amount of transfer current flows to the separating means at the time of overshoot, and therefore, the image carrier is caused by the overshoot at the time of the rise of the transfer bias power supply. The effect of preventing or reducing the occurrence of memory and stably forming a high-quality image at all times is obtained.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a main part of an image forming apparatus according to Embodiment 1 of the present invention.

FIG. 2 is a timing chart showing transfer material conveyance and application timings of a transfer bias and a separation bias in the image forming apparatuses according to Embodiments 2 and 3 of the present invention.

FIG. 3 is a schematic sectional view of a main part of an image forming apparatus according to Embodiment 4 of the present invention.

FIG. 4 is a schematic sectional view of a main part of an image forming apparatus according to Embodiment 5 of the present invention.

FIG. 5 is a schematic sectional view of a main part of a conventional image forming apparatus.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 photoconductor (image carrier) 11 primary charger (charging unit) 12 image exposure (image information writing unit) 13 developing unit (developing unit) 16 transfer roller (transfer unit) 18 transfer material 19 discharging needle (separating unit) 21 Transfer bias power supply (transfer bias supply means) 22 Separation bias power supply (separation bias supply means) 23 Variable resistor

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takeo Yamamoto 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc.

Claims (10)

[Claims] A charging means for uniformly charging the image carrier; an image information writing means for writing image information on the charged image carrier; and an electrostatic latent image formed by the image information writing means. An image having a developing unit for forming a visible image, a transferring unit for transferring a toner image formed by the developing unit to a transfer material, and a separating unit for promoting separation of the transfer material from the image carrier after transfer In the forming apparatus, a transfer bias supply unit that supplies a transfer bias to the transfer unit and a separation bias supply unit that supplies a separation bias to the separation unit are provided. Wherein the separation bias supply is started in synchronization with or before the transfer bias supply start time of the transfer bias supply means. Apparatus. 2. The separation bias supply means according to claim 1, wherein said separation bias supply means supplies a separation bias A corresponding to a transfer bias supply start time.
2. The image forming apparatus according to claim 1, wherein a separation bias B supplied after the separation bias A corresponding to a transfer bias supply start time can be output. 3. The image forming apparatus according to claim 2, wherein at least one of the separation bias A and the separation bias B is switchable according to a resistance value of a contact transfer member of the transfer unit. . 4. A charging device for uniformly charging an image carrier, an image information writing device for writing image information on the charged image carrier, and an electrostatic latent image formed by the image information writing device. An image having a developing unit for forming a visible image, a transferring unit for transferring a toner image formed by the developing unit to a transfer material, and a separating unit for promoting separation of the transfer material from the image carrier after transfer In the forming apparatus, the transfer unit employs a contact transfer method, and a transfer bias supply unit that supplies a transfer bias to the transfer unit and a separation bias supply unit that supplies a separation bias to the separation unit are provided. A variable resistor is interposed between the separation bias unit and the separation bias supply unit, and the separation bias supply unit is synchronized with a transfer bias supply start time of the transfer bias supply unit. Image forming apparatus characterized by initiates separation bias supplied earlier, is smaller than the resistance value after the transfer bias supply start time of the variable resistor in response to the transfer bias supply start time. 5. A charging device for uniformly charging an image carrier, an image information writing device for writing image information on the charged image carrier, and an electrostatic latent image formed by the image information writing device. An image having a developing unit for forming a visible image, a transferring unit for transferring a toner image formed by the developing unit to a transfer material, and a separating unit for promoting separation of the transfer material from the image carrier after transfer In the forming apparatus, a contact transfer method is used for the transfer unit, a transfer bias supply unit that supplies a transfer bias to the transfer unit is provided, and the separation unit is grounded via a variable resistor or a conduction switch. The resistance value of the variable resistor is set to be smaller than that after the transfer bias supply start time corresponding to the transfer bias supply start time of the bias supply means, or Conducting the conducting switch in response to the supply start time image forming apparatus is characterized in that so as to release the conduction at a predetermined time. 6. The image forming apparatus according to claim 1, wherein the start of supply of the transfer bias by the transfer bias supply unit is synchronized with or earlier than the arrival time of the transfer material on the transfer portion. apparatus. 7. The image forming apparatus according to claim 1, wherein the transfer bias supply unit is controlled at a constant current at least at the start of transfer bias supply. 8. The image forming apparatus according to claim 1, wherein a visualized image is formed by reversal development. 9. The image forming apparatus according to claim 1, wherein the separation bias has a polarity opposite to that of the transfer bias. 10. A shape of a portion of said separating means facing said image bearing member is a pointed shape.
An image forming apparatus according to any one of claims 4 to 5.