JPH10333446A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of a failure in transferring and a defect in an image, for obtaining an excellent image, even if a recording medium whose resistance is made low is used by applying a positive or negative bias voltage to a conductive member. SOLUTION: When an image is formed on the recording medium (p), in a high humidity and high temperature environment (room temperature is 30 deg.C and relative humidity is 80%), the recording medium (p) short-circuits a driving roller 13 as the conductive member grounded to face a separating electrifier 32 and a transferring part, so that toner images developed on photoreceptor drums 3a-3d are not excellently transferred to the recording medium (p) or a conspicuous failure in transferring such as the retransfer of the toner images after being transferred to the recording medium (p) once, to a downstream drum occurs. In such a case, a positive voltage bias of several kilo volts is applied to the driving roller 13, to make the potential of the recording medium (p) high, so that the inflow of a negative electric charge into the transferring part is prevented. Consequently, the negative charge never flows into the transferring part, to prevent the conspicuous failure in transferring and the defect in the image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a facsimile, and a printer for obtaining a hard copy by forming an image on a recording material by using an electrophotographic method.

[0002]

2. Description of the Related Art Conventionally, a plurality of image forming units are provided, and each image forming unit 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.

In such a situation, a multicolor electrophotographic color copying machine using an endless recording material carrier is used for high-speed recording.

FIG. 1 shows an example of a color electrophotographic image forming apparatus.
It will be described based on. First, second, third, and fourth image forming units Pa, Pb, Pc, and Pd are arranged in the apparatus, and toner images of different colors are formed through processes of a latent image, development, and transfer. Is done.

The first to fourth image forming units Pa to Pd are dedicated image carriers, in this example, the electrophotographic photosensitive drum 3
a, 3b, 3c, 3d, and each of the photosensitive drums 3a-3
A toner image of each color is formed on d.

A recording material carrier (hereinafter, referred to as a transfer belt) 130 is provided adjacent to each of the photosensitive drums 3a to 3d.
The toner images of each color formed on the photosensitive drums 3a to 3d are transferred onto a recording material p carried and conveyed on the transfer belt 130. Further, the recording material p on which the toner images of the respective colors are transferred is fixed to the toner image by heating and pressurizing in the fixing unit 9, and then is discharged as a recording image to a discharge tray 63 outside the apparatus.

Exposure lamps 111a, 111b, 111c, and 111 are provided on the outer circumference of the photosensitive drums 3a to 3d, respectively.
d, drum chargers 2a, 2b, 2c, 2d, potential sensors 113a, 113b, 113c, 113d, developing device 1
a, 1b, 1c, 1d, transfer chargers 24a, 24b, 2
4c, 24d and cleaners 4a, 4b, 4c, 4d
Are provided, and a light source device and a polygon mirror 117 (not shown) are further provided above the device.

The polygon mirror 117 rotates and scans the laser beam emitted from the light source device to scan, deflects the light beam of the scanning beam by the reflection mirror, and condenses it 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 devices 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 units 1a to 1d develop the latent images on the photosensitive drums 3a to 3d, respectively, and visualize the latent images as cyan, magenta, yellow, and black toner images.

The recording material p is accommodated in a recording material cassette 10 and is supplied onto a transfer belt 130 through a plurality of conveyance rollers 11 and registration rollers 12 to face the photosensitive drums 3a to 3d 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 sheet (PET resin), a polyvinylidene fluoride resin sheet, or a polyurethane resin sheet. Either endless or seamless (seamless) belts are used.

Now, the driving roller 13 and the supporting roller 1
When the transfer belt 130 is rotated by 4 and 15 and is confirmed to be 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
Is conveyed toward the transfer section of the first image forming section Pa. 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 at the lower transfer portion of the photosensitive drum 3a, so that the first color toner image formed on the photosensitive drum 3a is transferred onto the recording material p. You. Due to this transfer, the recording material p is firmly held on the transfer belt 130 by electrostatic attraction, and is conveyed to the second image forming portion Pb and thereafter.

In the transfer chargers 24a to 24d, non-contact chargers such as corona discharge, or blades, rollers,
A contact charger using a transfer charging member such as a brush is used. Non-contact chargers generate ozone,
Since it is charged via air, it is vulnerable to changes in the temperature and humidity environment of the atmosphere, and there is a problem that an image cannot be stably formed. on the other hand,
With a contact charger, ozone-less, resistant to temperature and humidity environmental fluctuations,
There are advantages such as high image quality.

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 separated from the end of the transfer belt 130 by removing the charge by the separation charger 32 and attenuating the electrostatic attraction force in the downstream portion of the transfer belt 130 in the transport direction. . Normal drive roller 130
Are grounded for stable separation. In addition, since the separation charger 32 charges the recording material p in a state where the toner image is not fixed, a non-contact charger is used.

The recording material p detached from the transfer belt 130
Is fixed by the fixing unit 9 by the transport unit 62 via the relay member 64.
Transported to

The fixing device 9 includes a fixing roller 51, a pressure roller 52, heat-resistant cleaning members 54 and 55 for cleaning each of them, roller heaters 56 and 57 installed in the rollers 51 and 52, and a fixing roller. An application roller 50 for applying a release agent oil such as dimethyl silicone oil to a pressure roller 51;
And a thermistor 58 for controlling the fixing temperature by detecting the temperature of the surface 2.

The recording material p to which the four color toner images have been transferred is
By the fixing, 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 copy image is discharged to the discharge tray 63.

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 the apparatus is prepared for the next process of forming a latent image. The toner and other foreign matters remaining on the transfer belt 130 are wiped off by bringing the cleaning web (nonwoven fabric) 19 into contact with the surface of the transfer belt 130. The cleaning web 19 includes an unwinding roller 17, a winding roller 18, and a tension roller 2.
2, and the backup roller 2 of the tension roller 22
1 controls the contact with the transfer belt 130.

The transfer belt used in the image forming apparatus having the above configuration is a dielectric sheet such as a PET sheet, a polyvinylidene fluoride sheet, or a polyurethane sheet as described above, and has a volume resistance of 10 ¹³ to 10 ^18.
Ωcm is common.

It is also known that an image is stabilized when the current contributing to the transfer of the transfer charging means is fixed at an appropriate current. Therefore, it is common to perform constant current control so that a constant current can be obtained even when the volume resistance value changes depending on the type (thickness, material, etc.) of the recording material, moisture absorption conditions, and the like. The transfer voltage is several kV to tens of kV.

In an image forming apparatus that performs multiple transfer, a higher voltage is required at each transfer stage than at the time of the previous transfer, and particularly at the time of the last transfer, the voltage is at a much higher transfer than at the time of the first transfer.

[0023]

However, with this configuration, when an image is formed on a recording material p whose resistance has been reduced by, for example, being left in a high-humidity environment, the above-mentioned grounded counter electrode of the separation charger 32 is used. The recording material p is moved between the transfer roller and the driving roller (separating section) 13 as a conductive member.
Is short-circuited, the toner image developed on the photosensitive drum 3 is not satisfactorily transferred to the recording material p (hereinafter referred to as phenomenon 1), or the toner image once transferred to the recording material p is a downstream image. A remarkable transfer failure (image failure) such as a phenomenon (hereinafter referred to as phenomenon 2) of retransfer to the drum of the forming unit occurs. Generally, the volume resistance of a recording material is about 10 ⁷ to 10 ¹¹ [Ωc depending on the type and moisture absorption conditions.
m].

This phenomenon will be described with reference to FIG. When the recording material p short-circuits the photosensitive drum 3d of the fourth image forming portion Pd and the driving roller 13 during image formation, a portion of the transfer belt 130 that is in contact with the recording material p and the driving roller 13 at the same time (hatched portion in FIG. 2) E)), a part of the charge pair charged in the drive roller 1, and the positive charge on the back side is grounded.
At 3, the negative charges on the surface flow through the recording material p to the transfer charging section, and as a result, are neutralized. At this time, a transfer current (in the directions indicated by arrows A and B in FIG. 2) to flow from the transfer charger to the photosensitive drum 3d, which is the opposite electrode, is supplied to the transfer belt E through the recording paper having lower resistance (see FIG. 2 arrow A,
D) A sufficient transfer current cannot be obtained, and phenomenon 1 occurs.

Further, when the resistance of the recording material decreases, the transfer belt E not only removes all the transfer current but also tries to supply a positive charge from the photosensitive drum side, and the current flows in the A and D directions. , C, and D directions. This current direction C is
The direction of the transfer current during normal image formation is opposite to the direction B, and the phenomenon of the phenomenon 2 occurs when the current in the reverse direction C flows.

Here, the member short-circuited by the recording material p is not limited to the drive roller 13 and the transfer portion, but may be a transfer portion, an attraction / charging portion, a recording material carrier support portion, or a fixing portion.
Alternatively, it may be a guide section, a resist section, or a static elimination needle. In this case, only phenomenon 1 occurs.

The members short-circuited by the recording material p are not limited to those described above, and may include the drive roller 13 or the static elimination needle.
It may be an adsorption charging section, a guide section, or a resist section. In this case, only phenomenon 2 occurs.

Further, the driving roller 13 may be a recording material supporting member that does not transmit driving.

Accordingly, an object of the present invention is to provide an image forming apparatus capable of preventing a transfer failure and an image defect from occurring and obtaining a good image even when a low-resistance recording material is used. is there.

[0030]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
An image carrier on which a visible image is formed, a recording material carrier for carrying and transporting a recording material, and a transfer charging unit facing the image carrier via the recording material carrier; An image forming apparatus in which a recording material contacts a plurality of conductive members or contacts through a dielectric layer, wherein a positive or negative bias voltage is applied to the conductive members.

The conductive member or the dielectric layer is provided on the image carrier, the recording material carrier supporting portion for supporting the recording material carrier, or the transfer charging section, or the recording material on the recording material carrier. It is preferable to be a suction charging unit for electrostatically adsorbing, a fixing unit for fixing an image on the recording material, a guide unit for the recording material, a resist unit for the recording material, or a static elimination needle.

It is preferable that a detecting means for detecting temperature and humidity is provided, and the applied bias voltage is controlled according to the detected temperature and humidity information. According to another aspect, it is preferable to control the applied bias voltage according to the type of the recording material. The image forming method is preferably a multiple transfer method.

[0033]

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. In the following description of the embodiment, it is assumed that the present invention is embodied in the full-color image forming apparatus shown in FIG. Therefore, description of the overall configuration and functions of the full-color image forming apparatus will be omitted, and only the features of the present invention will be described.

Embodiment 1 Embodiment 1 of the image forming apparatus according to the present invention will be described.

As the dielectric sheet material for the transfer belt 130, PET, polyacetal, polyamide, polyvinyl alcohol, polyether ketone, polystyrene,
Polybutylene terephthalate, polymethylpentene, polypropylene, polyethylene, polyphenylene sulfide, polyurethane, silicone resin, polyamide imide,
Polycarbonate, polyphenylene oxide, polyether sulfone, polysulfone, aromatic polyester,
Engineered plastic film-shaped sheets such as polyetherimide and aromatic poimide are generally used. In this example, a polyimide resin was used in terms of mechanical properties, electrical properties, flame retardancy, and the like. Volume resistance is 1
A seamless type having a thickness of 0 ¹⁶ Ωcm and a thickness of 10 μm was used.

The process speed is 100 mm / s.

Transfer chargers 24a, 24b, 24c, 24
d is a rectangular plate-shaped conductive rubber extending in a direction perpendicular to the recording material conveyance direction (hereinafter, referred to as a thrust direction). The plate-shaped conductive rubber is pressed so as to be in contact with the photosensitive drums 3a, 3b, 3c, 3d via the transfer belt 130. By the transfer chargers 24a to 24d, the recording material p conveyed to the transfer section is charged from the rear surface side with the opposite polarity (positive in this example) to the toner, so that the toner images on the photosensitive drums 3a to 3d surface side are formed. Is electrostatically transferred to the surface of the recording material p. In this embodiment, the constant current control is performed, and the transfer current is set to 10 μA.

The separation charger 32 is located at the uppermost downstream of the transfer belt 130, that is, the driving roller 1 of the transfer belt 130.
3 and is provided with a discharge wire. The discharge wire is stretched in the thrust direction, and a tension is maintained by providing a spring at one end of the discharge wire. Power is supplied to the discharge wire from a main body side connector via a power supply terminal (not shown), a power supply pin, and a spring. Further, the drive roller 13 is connected to the main body ground and also functions as a counter electrode of the discharge wire. In this embodiment, the distance between the transfer charger 24d and the separation charger 32 is 5
0 mm, and an AC voltage of 10 kVpp was applied to the separation charging section.

The recording material p completely conditioned in a high-humidity environment (80% / RH) has a very low volume resistivity of 10 ¹⁰ [Ωcm] or less, although there are differences depending on the material and the like. Therefore, in the configuration of the present embodiment, when an image is formed on the recording material p in a high-humidity and high-temperature environment (room temperature 30 ° C., relative humidity 80%), the recording material p is grounded in opposition to the separation charger 32. Drive roller 1 as the above-described conductive member
3 and the transfer portion are short-circuited, and the toner image developed on the photosensitive drum 3 is not transferred well to the recording material p, or the toner image once transferred to the recording material p is re-transferred to the downstream drum in reverse. Remarkable transfer failure occurs. This is because a portion of the transfer belt 130 that is in contact with the recording material p and the drive roller 13 at the same time is neutralized, and a negative charge is supplied to the transfer portion.

Therefore, in this embodiment, the potential of the driving roller 13 itself is increased by applying a positive voltage bias of several kV to the driving roller 13 so that negative charges do not flow into the transfer portion. As a result, the negative charge did not flow into the transfer portion, and the remarkable transfer failure and image defect as described above could be prevented.

Embodiment 2 Next, Embodiment 2 according to the present invention will be described. In the present embodiment, the positive voltage bias applied to the drive roller 13 is made variable according to the atmospheric humidity of the atmosphere.

A recording material p conditioned in a low humidity environment;
With the recording material p conditioned in a high-humidity environment, the volume resistance changes by at most about four digits. For this reason, it is considered that the amount of inflow of negative charges also greatly changes depending on the environment. For this reason, in the present embodiment, the applied voltage is reduced in a low humidity environment and is increased in a high humidity environment to control the amount of negative charges flowing into the transfer section.

As described above, in a low humidity environment, the recording material p
Has a high volume resistance value of 10 ¹² [Ωcm] or more, so that the amount of negative charges flowing into the transfer portion decreases. Therefore, it is preferable that the positive voltage applied to the driving roller 13 is also reduced.

On the other hand, in a high-humidity environment, the volume resistivity of the recording material p is as low as 10 ¹⁰ [Ωcm] or less, so that the amount of the negative charges flowing into the transfer portion increases. Therefore, the driving roller 1
It is better to increase the positive voltage applied to 3 as well.

Environment A Absolute moisture content 20 g / kg or more: 7 kV Environment B Absolute moisture content 1.5 g / kg or more and less than 20 g / kg: 4 kV Environment C Absolute moisture content less than 1.5 g / kg: 1 kV Environments A, B, and C Thus, the volume resistance value of the recording material p is roughly
It changed to 10 ¹⁰ , 10 ¹¹ , and 10 ¹⁵ [Ωcm].

By adopting such a configuration, an image forming apparatus in which the transfer failure does not occur regardless of the environment can be obtained.

The atmospheric humidity may be automatically detected by providing a humidity detecting sensor in the image forming apparatus main body, and the impedance may be controlled. You may enter it.

Third Embodiment Next, a third embodiment according to the present invention will be described. In this embodiment, the positive voltage bias applied to the driving roller 13 is changed according to the type of the recording material.

The basis weight of the normal recording material used in an image forming apparatus, there approximately wide and up to ^{50g / m 2 ~200g / m 2} , thereby since the different greater resistance of each of the recording material p, during image formation Does not depend on the characteristics of the recording material p.

In the case of the recording material p having a large weight, the resistance between the front and the back becomes large because the recording material is thick, and the resistance between the transfer charging section and the driving roller 13 becomes small. Such a recording material p
When an image is formed on the transfer portion, the amount of the negative charges flowing into the transfer portion increases, and the transfer failure is likely to occur. on the other hand,
The opposite is true for a recording material p with a small weighing because the recording material thickness is thin. Therefore, when an image is formed on a thick recording material such as thick paper, the positive voltage applied to the drive roller 13 is increased to reduce the amount of the negative charges flowing into the transfer section, and the image forming apparatus does not cause the transfer failure. Can be obtained.

The type of the recording material can be detected automatically by using a mechanical or optical sensor, or specified by an operator through an operation unit or the like.

As the transfer charger, a corona charger, a conductive elastic roller, a brush or the like may be used as the transfer charging member, and the same effect as described above was obtained. Further, not only the transfer belt but also a transfer drum configuration may be used.

The conductive member is not limited to the driving roller, but may be an image carrier, a recording material carrier support, a transfer charging unit, an adsorption charging unit, a fixing unit, a recording material guide, or a recording material. May be a resist part or a static elimination needle.

Even if the recording material is not in contact with the conductive member, if it is sufficiently close, the air layer is regarded as a dielectric.

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

The image carrier may be an intermediate transfer member in an intermediate transfer system.

As the developing means 1a to 1d of the electrostatic latent images on the image carriers 3a to 3d, generally, a non-magnetic toner is coated on a sleeve by a blade or the like, and a magnetic toner is coated by a magnetic force. One-component non-contact developing method in which the toner is transported and developed in a non-contact state with the image carrier, a one-component contact developing method in which the image carrier is developed in a contact state with the image carrier, and a magnetic carrier for the toner particles A two-component contact development method in which a mixture of the two is used as a developer and conveyed by magnetic force to develop the image carrier in a contact state; and a two-component non-contact method in which the two-component developer is developed in a non-contact state. It is roughly classified into four types, namely, a developing method. In the present invention, the developing means may be any of them. The two-component contact development method is often used in terms of high image quality and high stability.

[0058]

As is apparent from the above description, according to the present invention, even if a low-resistance recording material is used by applying a positive or negative bias voltage to the conductive member, transfer failure is caused. Further, generation of image defects can be prevented, and a good image can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus according to first to third embodiments.

FIG. 2 is an explanatory diagram illustrating a flow of negative charges flowing into a transfer unit.

[Explanation of symbols]

3a, 3b, 3c, 3d Photosensitive drum (image carrier) 5 Adsorption charger 9 Thermal fixing device 12 Registration roller 13 Drive roller 14, 15 Support roller 24a, 24b, 24c, 24d Transfer charger 32 Separation charger 130 Transfer belt (Recording material carrier)

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kiichi Yoichi 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc.

Claims (5)

[Claims] 1. An image carrier on which a visible image is formed, a recording material carrier for carrying and conveying a recording material, and a transfer charging section facing the image carrier via the recording material carrier. An image forming apparatus, wherein a recording material contacts a plurality of conductive members or contacts via a dielectric layer during image formation, wherein a positive or negative bias voltage is applied to the conductive members. Forming equipment. 2. The image bearing member according to claim 1, wherein the conductive member or the dielectric layer is opposed to the image bearing member via the image bearing member, a recording material bearing member supporting the recording material bearing member, or a recording material bearing member. Transfer charging section, or an adsorption charging section for electrostatically adhering a recording material to the recording material carrier, or a fixing section for fixing an image on the recording material, or a recording material guide section, or a recording material resist section, or The image forming apparatus according to claim 1, wherein the image forming apparatus is a static elimination needle. 3. The image forming apparatus according to claim 1, further comprising detecting means for detecting temperature and humidity, and controlling the applied voltage according to the detected temperature and humidity information. 4. The image forming apparatus according to claim 1, wherein the applied voltage is controlled according to the type of the recording material. 5. The image forming apparatus according to claim 1, wherein the image forming apparatus employs a multiple transfer method.