JP2000258965A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent peeling-discharging at a transfer part and a separation part which occurs when recording material is dried under a low humidity environment. SOLUTION: In the case of detecting by an environment detecting means 53 that the peeling-discharging is easily generated under the present low humidity environment, a recording material carrying speed is controlled to be half a conventional speed (100 mm/sec), that is, 50 mm/sec. Then, an air gap capacitor is inserted in accordance with the peeling of the recording material, then, even in the case a potential difference is generated because of the storage of charges on both polarities, the number of discharging times per unit time is substantially reduced and the peeling-discharging is suppressed, because the recording material carrying speed is controlled to be low.

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 a copying machine, a facsimile, and a printer for forming an image on a recording material by using an electrophotographic method to obtain a hard copy.

[0002]

2. Description of the Related Art Conventionally, a plurality of image forming sections are provided, each of which forms a toner image of a different color, and the toner images are sequentially superimposed on the same recording material and transferred to form a color image. Various image forming apparatuses have been proposed.

Under these circumstances, an electrophotographic color image forming apparatus using an endless recording material carrier is used for high-speed recording.

For example, in a color image forming apparatus of the type described above, first, second, third, and fourth image forming sections are arranged in parallel in the apparatus, and toner images of different colors are latent images, developed, It is formed through a transfer process.

Each image forming section has a dedicated image carrier (hereinafter referred to as "photosensitive drum"), and a toner image of each color is formed on each photosensitive drum by each image forming means. A recording material carrier (hereinafter, referred to as a “transfer belt”) is installed adjacent to each photosensitive drum, and a toner image of each color formed on the photosensitive drum is carried on the transfer belt while being carried on the transfer belt. Is transferred at the transfer section. Further, the recording material to which the toner images of each color have been transferred is discharged outside the apparatus as a recording image after the toner image is fixed by heating and pressing in a fixing unit.

[0006]

However, when the color image forming apparatus is used in a low-humidity environment, a peeling discharge occurs at the peeling portion between the photosensitive drum of the transfer portion and the recording material, and the toner image is disturbed or transfer failure occurs. Or wake up. Further, after the transfer, when the recording material separates from the transfer belt, peeling discharge occurs at the separation portion, and the toner image may be disturbed.

Here, the mechanism of the peeling discharge will be described.

As shown in FIG. 3A, for example, between a charged photosensitive drum and capacitors Cp and Cd of a recording material,
As shown in FIG. 3B, when the capacitor Ca of the air layer is inserted, the charge density Q ₀ is stored on the surface, and a potential difference Va is generated. The distance between the electrodes of the capacitor Ca in the air layer after separation increases with time. The potential difference Va of the air layer when the air layer thickness becomes d is as follows: Va = Q ₀ d / ε ₀ (1) When the potential difference Va exceeds the discharge starting voltage, a peeling discharge occurs. Here, ε ₀ is the vacuum permittivity.

Since the discharge starting voltage depends on the Paschen's law and depends only on the distance between the electrodes under this condition, the relation between the potential difference Va and the air layer thickness d obtained by the above equation (1) satisfies the Paschen's law. When this occurs, peeling discharge occurs. The graph of FIG. 4 shows the discharge starting voltage according to the Paschen's rule when the potential difference Va and the air layer thickness d are relative to the change in the air layer thickness in the above equation.

In FIG. 4, when the recording material is peeled to the air gap, which is the intersection of Paschen's rule and equation (1),
Peeling discharge occurs between the front surface of the transfer belt and the back surface of the recording material.

The above equation (1) changes the slope of the increase depending on the magnitude of the charge density Q ₀ stored before separation. For example, when a current of 10 μA flows into the above-described system when the process speed, that is, the conveyance speed of the recording material is 100 mm / sec, and the transfer belt width is 300 mm, the charge density Q ₀ is: Q ₀ = 3.3 × 10 ^{− 4} [C / m ² ] of electric charge will be stored. The discharge start gap at this time is about 10 μm. However, the charge density Q ₀ is Q ₁ ,
When Q ₂ , Q ₃ , and Q ₄ decrease, the slope decreases as indicated by the dotted line in the figure, and the intersection with the Paschen's law curve also moves.

When the charge density Q ₀ stored in the air gap at the intersection point a is reduced to Q ₁ by peeling discharge, the state of the system transits from the straight line of Q _{0 to} the straight line of Q _1. The material is discharged at the next intersection point b due to the peeling of the material. Repeating such transition, when reduced to the charge density Q _4, separation discharge in the air gap will not occur.

Further, it has been clarified by experiments of the present inventors that these phenomena occur remarkably when the recording material is dry in a low humidity environment or the like.

Accordingly, an object of the present invention is to provide an image forming apparatus capable of preventing peeling discharge at a transfer section and a separation section which occurs when a recording material is dried in a low humidity environment, and preventing occurrence of image disorder. To provide.

[0015]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
In an image forming apparatus having an image bearing member for carrying a toner image and charge applying means for supplying a charge having a polarity opposite to the charge polarity of the toner to the toner image and transferring the charge to a recording material, the temperature and humidity in the apparatus are detected. An image forming apparatus having an environment detecting unit, wherein a conveying speed of a recording material is changed according to a detection signal of the environment detecting unit.

According to another aspect of the present invention, there is provided an image carrier for carrying a toner image, and charge applying means for supplying a charge having a polarity opposite to the charge polarity of the toner to the toner image and transferring the charge to a recording material. An image forming apparatus having a detecting means for detecting a current flowing when a predetermined voltage is applied to the recording material, or a voltage when a predetermined current is applied to the recording material, according to a detection signal of the detecting means. The image forming apparatus is characterized in that the conveying speed of the recording material is changed by changing the conveying speed.

According to another aspect of the present invention, there is provided an image carrier for carrying a toner image, and a charge applying means for supplying a charge having a polarity opposite to the charge polarity of the toner to the toner image and transferring the charge to a recording material. And a fixing unit for fixing an image on the recording material, in the image forming apparatus having a fixing unit for fixing the image on the back surface of the recording material than the conveying speed of the recording material when forming the image on the surface of the recording material. An image forming apparatus characterized in that the transport speed is reduced.

[0018] In the above invention, it is preferable that the image forming apparatus includes a recording material carrier for conveying the recording material, and a transfer unit for transferring the toner image on the image carrier to the recording material carrier. In addition, a recording material carrier for conveying the recording material is provided, and the conveying speed of the recording material is a speed of the recording material carried on the recording material carrier.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

Embodiment 1 First, a first embodiment of the present invention will be described with reference to FIG. 1 and FIG.

In the color image forming apparatus of this embodiment, as shown in FIG. 1, first, second, third, and fourth image forming units Pa, Pb, Pc, and Pd are provided in parallel in the apparatus. The toner images of different colors are formed through the processes of latent image, development, and transfer.

Each of the image forming units Pa to Pd includes a dedicated image carrier, in this embodiment, an electrophotographic photosensitive drum (hereinafter, simply referred to as a "photosensitive drum") 3a, 3b, 3c, 3d. A toner image of each color is formed on 3a to 3d. A recording material carrier (hereinafter, referred to as a “transfer belt”) 130 is installed adjacent to each of the photosensitive drums 3a to 3d, and a toner image of each color formed on the photosensitive drums 3a to 3d is transferred onto the transfer belt 130. Is transferred onto the recording material P which is carried and conveyed on the recording medium P. Further, the recording material P on which the toner images of the respective colors have been transferred is heated and pressed to fix the toner images by a fixing device (fixing unit) 9 and then discharged out of the device as a recorded image.

More specifically, the photosensitive drums 3a to 3a
Exposure lamps 111a and 111 are provided around 3d, respectively.
b, 111c, 111d, drum chargers 2a, 2b, 2
c, 2d, potential sensors 113a, 113b, 113c,
113d, developing units 1a, 1b, 1c, 1d, transfer chargers 24a, 24b, 24c, 24 as charge applying means
d, and cleaners 4a, 4b, 4c, and 4d are provided, and a light source device and a polygon mirror 117 (not shown) are further provided above the device.

The laser light emitted from the light source device is scanned by rotating the polygon mirror 117, the light beam of the scanning light is deflected by the reflection mirror, and is condensed on the generatrix of the photosensitive drums 3a to 3d by the fθ lens. By performing the exposure, a latent image corresponding to the image signal is formed on the photosensitive drums 3a to 3d.

The developing units 1a to 1d are filled with a predetermined amount of cyan, magenta, yellow and black toners, respectively, as a developer by a supply device (not shown). The developing devices 1a to 1d are respectively provided with the photosensitive drums 3a to 3d.
The latent image on d is developed and visualized as a cyan toner image, a magenta toner image, a yellow toner image, and a black toner image.

The recording material P is accommodated in a recording material cassette 10, is supplied onto a transfer belt 130 through a plurality of conveyance rollers 11 and registration rollers 12, and faces the photosensitive drums 3 a to 3 d by conveyance by the transfer belt 130. It is sequentially sent to the transfer unit.

The transfer belt 130 is made of a dielectric resin sheet such as a polyethylene terephthalate resin (PET resin), a polyvinylidene fluoride resin sheet, or a polyurethane resin sheet. Shaped or seamless (seamless) belts are used.

The transfer belt 130 is driven by the driving roller 13.
When it is confirmed that the recording material P is at a predetermined position, the recording material P is sent out from the registration roller 12 to the transfer belt 130, and the recording material P is transferred to the first image forming unit Pa. Transported to the department. At the same time, the image writing signal is turned on, and an image is formed on the photosensitive drum 3a of the first image forming unit Pa at a certain timing based on the signal.

The transfer charger 24a applies an electric field or electric charge having a polarity opposite to the charge polarity of the toner at the lower transfer portion of the photosensitive drum 3a, so that the first color toner formed on the photosensitive drum 3a is formed. The image is transferred onto the recording material P. Further, by this transfer, the recording material P is transferred to the transfer belt 13.
On the other hand, the sheet P is firmly held by the electrostatic attraction force and is conveyed to the second image forming portion Pb and thereafter.

Image formation and transfer in the second to fourth image forming units Pb to Pd are performed in the same manner as in the first image forming unit Pa.

Next, the recording material P on which the four color toner images have been transferred is neutralized by the separation charger 32 at the separation section downstream of the transfer belt 130 in the transport direction, and the electrostatic attraction force is attenuated. Disengage from the end of 130.

Recording material P detached from transfer belt 130
Is transferred to the fixing device 9 by the transport unit 62 through the separation guide 64.
Transported to The separation guide 64 functions to stabilize the leading edge behavior of the recording material P.

The photosensitive drums 3a to 3d after the transfer are completed.
The transfer residual toner is cleaned and removed by each of the cleaners 4a to 4d, and is prepared for the formation of the next latent image.

The toner and other foreign matters remaining on the transfer belt 130 are wiped off by bringing a cleaning web (nonwoven fabric) 19 into contact with the surface of the transfer belt 130. The cleaning web 19 is a feeding roller 18.
While being fed out from the roller and being wound on the winding roller 17, the pressing roller 22 and the backup roller 21 of the pressing roller 22 contact the transfer belt 130.

The fixing device 9 includes a fixing roller 51 and a pressure roller 52, heat-resistant cleaning members 54 and 55 for cleaning both rollers 51 and 52, and both rollers 51 and 52.
52, heaters 56 and 57 installed in the fixing roller 51, an application roller 50 for applying a release agent oil such as dimethyl silicone oil to the fixing roller 51, and an oil reservoir 53 thereof.
And a thermistor 58 that detects the temperature of the surface of the pressure roller 52 and controls the fixing temperature.

The recording material P to which the four color toner images have been transferred is
In the fixing device 9, the color mixture of the toner image and the fixation to the recording material P are performed, a full-color copy image is formed, and the image is discharged to the paper discharge tray 63.

In the case of double-sided copying, the switching guide 7
The recording material P on which the single-sided copying operation has been performed is guided to the transport vertical path 71, and then reversed by the reversing roller 73 via the reversing path 72, and stored in the intermediate tray 65. Next, after the required number of sheets have been stacked, the sheet is conveyed to the registration roller 12 by the sheet feeding roller 11, the same two-sided copy is performed through the same process as that of the one-sided copy, and the sheet is discharged to the sheet discharge tray 63.

Next, the features of the present invention will be described. In this embodiment, the peeling discharge in the transfer unit and the separation unit is prevented by reducing the process speed of the color image forming apparatus, that is, the conveying speed of the recording material.

Also in this embodiment, as described in the above-mentioned conventional example, a capacitor having an air gap is inserted with the peeling of the recording material, charges are stored in both electrodes, and a potential difference is generated. However, since the process speed is low, the number of discharges per unit time is reduced. For this reason, it is less likely that the toner image is disturbed or the toner charging polarity is inverted.

For example, the conventional process speed (100 m
m / sec) of 50 mm / sec, and when a current of 5 μA flows into the above-described system when the transfer belt width is 300 mm, the charge density Q ₀ becomes Q ₀ = 3. Charges of 3 × 10 ⁻⁴ [C / m ² ] will be stored. That is, the description of FIG. 4 is the same as that of the conventional example.

However, in this embodiment, since the process speed is half that of the conventional example, the frequency of the discharge is one time of the conventional example.
/ 2, and the number of discharges per unit time is also 1/2.
It has become.

In the same manner as in the separation of the photosensitive drum and the recording material in the transfer section, the separation speed between the transfer belt and the recording material is similarly reduced by reducing the process speed in the separation section of the transfer belt and the recording material. Can be eased.

As described above, in the present embodiment, the above-described image defects could be reduced by reducing the process speed of image formation in a low humidity environment where peeling discharge easily occurs.

The process speed can be reduced by automatically switching when the environment detecting means in the main body detects a low humidity environment, or by allowing the operator or serviceman to manually select from the operation unit. .

Embodiment 2 Next, a second embodiment of the present invention will be described with reference to FIG. The image forming apparatus of the present embodiment has a configuration substantially similar to that of the image forming apparatus of FIG. 4, but as shown in FIG. 3, an environment detecting means 53 for detecting temperature and humidity inside the apparatus main body.
And an impedance detecting means 51 for detecting the impedance of the recording material P.

In this embodiment, the process speed is reduced only when it is determined that the detection result of the recording material P by the impedance detecting means 51 is higher than a predetermined value.

The electrical resistivity of the recording material varies greatly from 10 ⁸ to 10 ¹³ [Ωcm] according to the amount of moisture in the atmosphere. The above image defect occurs only when the electric resistivity of the recording material is high. Here, the high electric resistivity means, for example, 10
^It indicates the case where it is higher than ¹² [Ωcm].

The impedance detecting means 51 is disposed between a sheet feeding section or a sheet feeding section and a transfer section of the recording material, and detects the electric resistance of the recording material.

To explain further with reference to FIG. 2, when the conveying roller pair 50 located upstream of the registration roller 12 sandwiches the recording material P, the impedance detecting means 51 applies a predetermined voltage. Is read, the resistance value is calculated therefrom, and a signal is sent to the CPU 52. Also,
A predetermined current may be applied from the impedance detecting means 51 to the transport roller pair 50, and a voltage value generated at that time may be detected to calculate a resistance value.

For example, assume that the applied voltage is 30 V and the application time is 0.5 seconds. It is assumed that the output current value at this time is 100 μA in a high humidity environment and 0.01 μA in a low humidity environment. When 0.01 μA in a low humidity environment is too small to detect, the applied voltage is changed to 300 V and 3000 V. In this way, the electrical resistance can be detected as 0.3 MΩ in a high humidity environment and 3000 MΩ in a low humidity environment.

Then, only when the CPU 52 determines that the value of the recording material P is high, it issues a command to the drive unit 54 to reduce the process speed.

It is to be noted that a recording material thickness detecting means for detecting the thickness of the recording material is provided to detect the thickness of the recording material. You may. That is, the thickness of the recording material is L, the resistance as an output signal of the impedance detecting means is R, the resistivity is ρ, and the nip width of the conveying roller pair (electrode) 50 of the impedance detecting means and the thrust width of the recording material are determined. Assuming that the cross-sectional area of the product is S, R = ρ · L / S. From this equation, the resistivity ρ can be obtained.

For example, the thickness L of the recording material is 100 μm,
Assuming that the recording material has a thrust width of 297 mm and a nip width of 1 mm, the resistivity ρ is 10 ⁸ Ω · m in a high humidity environment and 10 ¹² Ω · m in a low humidity environment.

As described above, only when the CPU 52 determines that the resistivity of the recording material P is high,
To reduce the process speed.

As described above, when it is determined that the electric resistance or the electric resistivity of the recording material is high at the time of image formation, image defects can be reduced by reducing the process speed.

The mode may be set when the environment detecting means 53 detects a low humidity environment and determines that the resistance value of the recording material is high.

Embodiment 3 Next, a third embodiment of the present invention will be described with reference to FIGS.

In this embodiment, the surface of the recording material (or
The image formation on the "first surface" is performed at a normal process speed, and the image formation on the back surface of the recording material (or the "second surface") is performed at a low process speed.

That is, even when the recording material is not dried and has a low resistance value during the transfer of the first surface of the recording material, the recording material is once passed through the fixing device 9 and heated during the transfer of the second surface. The recording material has dried and the resistance has increased. Therefore, the image defect is more likely to occur on the second surface.

Therefore, the above-mentioned image defect can be reduced by reducing the process speed only when forming the image on the second side.

The mode may be set when the environment detecting means 53 detects a low humidity environment and determines that the resistance value of the recording material is high.

The mode in which the process speed is slow as described in the first to third embodiments may be automatically entered when the image forming apparatus main body detects an environment, or may be entered only when an image defect occurs. May be selectable. The mode may be selected by a user or a serviceman.

Further, if the process speed is reduced, the throughput of image formation is reduced. For example, it is set so that the process speed is automatically switched as described above only when the user selects the "high image quality mode". May be. On the other hand, when the user selects the “normal mode” that emphasizes the throughput of image formation, the process speed may not be automatically switched as described above.

The image bearing member as the member to be charged is not limited to the electrophotographic photosensitive member, but may be a dielectric in electrostatic recording.

As a means for developing an electrostatic latent image on an image carrier, generally, a non-magnetic toner is coated with a blade or the like, and a magnetic toner is coated by a magnetic force and transported. One-component non-contact developing method for developing in a non-contact state with a toner, a one-component contact developing method for developing in a contact state to an image carrier, and a mixture of toner particles and a magnetic carrier are used as a developer. And a two-component non-contact development method in which the two-component developer is brought into a non-contact state and developed by bringing the two-component developer into a non-contact state. Is done. In the present invention, the developing method may be any of the above methods. However, the two-component contact development method is preferred from the viewpoint of high image quality and high stability.

[0066]

As is apparent from the above description, according to the present invention, there is provided an environment detecting means for detecting the temperature and humidity in the apparatus, and the conveying speed of the recording material is controlled in accordance with the detection signal of the environment detecting means. By changing, or has a detection means for detecting a current flowing when a predetermined voltage is applied to the recording material, or a voltage when a predetermined current is applied to the recording material, the detection signal of the detection means The conveyance speed of the recording material when forming an image on the back surface of the recording material is changed by changing the conveyance speed of the recording material accordingly, or by lowering the conveyance speed of the recording material when forming an image on the front surface of the recording material. That is, by reducing the transport speed of the recording material in a low-humidity environment where the recording material is dry, it is possible to prevent the occurrence of peeling discharge at the transfer unit and the separation unit, and to reduce image disturbance. .

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an image forming apparatus according to a first embodiment and a third embodiment of the present invention.

FIG. 2 is a configuration diagram of an image forming apparatus according to a second embodiment of the present invention.

FIG. 3 is a schematic diagram illustrating a state (a) of each capacitor of the photosensitive drum and the recording material and a state (b) when a capacitor of an air layer is inserted between the capacitors, for explaining the peeling discharge. is there.

FIG. 4 is a graph showing a potential difference with respect to a change in air layer thickness and a discharge starting voltage according to Paschen's law.

[Explanation of symbols]

3a, b, 3c, 3d Photosensitive drum (image carrier) 9 Fixing unit 24a, 24b, 24c, 24d Transfer charger (charge applying unit) 51 Detecting unit 53 Environment detecting unit 130 Transfer belt (recording material carrier)

Claims (5)

[Claims] 1. An image forming apparatus comprising: an image carrier that carries a toner image; and a charge applying unit that supplies a charge having a polarity opposite to the charge polarity of the toner to the toner image and transfers the charge to a recording material. An image forming apparatus comprising: an environment detecting unit that detects temperature and humidity; and changing a conveyance speed of a recording material according to a detection signal of the environment detecting unit. 2. An image forming apparatus comprising: an image carrier that carries a toner image; and a charge applying unit that supplies the toner image with a charge having a polarity opposite to the charge polarity of the toner and transfers the charge to a recording material. Detecting means for detecting a current flowing when a predetermined voltage is applied to the recording material or a voltage when a predetermined current flows to the recording material, and changing a conveying speed of the recording material according to a detection signal of the detecting means. An image forming apparatus. 3. An image bearing member for carrying a toner image, charge applying means for supplying a charge having a polarity opposite to the charge polarity of the toner to the toner image and transferring the charge to a recording material, and fixing the image on the recording material. In the image forming apparatus having the fixing unit, the conveying speed of the recording material when forming an image on the back surface of the recording material is made slower than the conveying speed of the recording material when forming an image on the front surface of the recording material. Image forming device. 4. The image forming apparatus according to claim 1, further comprising a recording material carrier for conveying the recording material, and a transfer unit for transferring a toner image on the image carrier to the recording material carrier. . 5. A recording material carrier for conveying a recording material,
4. The image forming apparatus according to claim 1, wherein the transport speed of the recording material is a speed of the recording material carried on the recording material carrier. 5.