JPH04303873A - Image forming device - Google Patents

Abstract

PURPOSE:To offer an image forming device whose configuration is extremly simple, where littel ozone is evolved, which easily maintains proper pressing force to a material to be transferred without mechanical high demand accuray. CONSTITUTION:The tip end part of an electrical conductive plate-like member 15a is brought into contact with an image carrier carrying a developer image by giving a prescribed angle. By pressing the material to be transaferred to the image carrier by the plate-like member 15a, the developer image is transferred on the matrial to be transferred. Besides, a bias voltage whose 90% of the rising time at the time of starting an image forming cation or whose 90% of the falling time at the time of stopping the image forming action is >=20 millisecond is impressed on the plate-like member 15a.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is used in electrophotographic devices, electrostatic printers, etc. to form an electrostatic latent image on an image bearing member such as a photoreceptor, and to develop an image obtained by developing this electrostatic latent image. The present invention relates to an image forming apparatus equipped with a transfer device that transfers images onto a transfer material such as paper.

0002

[Prior Art] In electrophotographic devices, electrostatic printers, etc.
After forming an electrostatic latent image on a photoreceptor (image carrier), a developer is electrostatically attached to the electrostatic latent image to form a developer image, and then this developer image is transferred by a transfer means. , recorded by transferring it to paper.

As the above-mentioned transfer device, electrostatic means such as a corona transfer method and a roller transfer method, and mechanical means such as an adhesive transfer method are known.

Furthermore, since the electrostatic latent image and the developer that has not been transferred remain on the photoreceptor after the transfer, this residual developer is removed by a cleaning device, and then the electrostatic latent image is removed. It is removed using a static eliminator. Thereafter, the same basic operations are repeated.

[0005]In recent years, along with the demand for miniaturization of devices, the harmfulness of ozone generated by corona discharge has become a problem. A means is required.

[0006]

[Problems to be Solved by the Invention] However, despite the roller transfer method having the above advantages, there are several reasons why it has not become generally popular.

[0007] In roller transfer, it is necessary to press the transfer material such as paper against the developer image surface on the photoreceptor with a moderate amount of pressure. Insufficient pressure may cause uneven transfer, while too much pressure may cause uneven transfer. To prevent the developer (toner) from sticking and causing transfer failure, high mechanical precision (straightness approximately ±50 microns) and appropriate softness (JIS hardness approximately 10) are required.
-40 degrees), but it was difficult to achieve both with conventionally used conductive rubbers.

In particular, when paper with a thickness of 100 microns is used, excessive pressure is generated, resulting in poor transfer.
Complex control is required to separate them.

Furthermore, the electrical resistance of the transfer roller for applying electrostatic force to the toner image must be maintained at a value that can prevent the recording material from being destroyed by discharge under any environmental conditions. This limits the range of mechanical properties that can be selected.

Against this background, there is a need for an excellent image forming apparatus that can solve the above-mentioned problems and fully satisfy the required characteristics.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an image forming apparatus that has an extremely simple configuration, generates little ozone, and can easily maintain an appropriate pressing force on a transfer material without requiring high mechanical accuracy. That is.

0012

[Means for Solving the Problems] In order to solve the above problems, the present invention provides an electrostatic latent image forming means for forming an electrostatic latent image on an image bearing member, and an electrostatic latent image forming means for forming an electrostatic latent image on an image carrier. A developing means for supplying a developer to the electrolatent image to form a developer image; and an elastic member for pressing a transferred material against the image carrier by bringing a tip thereof into contact with the image carrier at a predetermined angle. A bias voltage having a 90% rise time at the start of the image forming operation or a 90% fall time at the stop of the image forming operation is 20 milliseconds or more is applied to the conductive plate-like member. and a voltage applying means for applying a voltage to transfer the developer image to a transfer material.

[0013]

[Operation] By pressing the transferred material against the image carrier using an elastic conductive plate member, it is possible to obtain a pressing force against the image carrier with a large mechanical tolerance to enable appropriate transfer. I made it possible.

[0014] Furthermore, by applying a bias voltage having a 90% rise time at the start of the image forming operation or a 90% fall time at the stop of the image forming operation to the conductive plate-like member of 20 milliseconds or more, When the image forming operation is started or stopped, the developer attached to the conductive plate member is discharged onto the image carrier to prevent it from being attached.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained below with reference to an embodiment shown in FIGS. 1 to 5.

FIG. 2 shows a recording device, and its main body H
A photoreceptor drum 1 serving as an image carrier is provided approximately at the center of the photosensitive drum 1 so as to be rotatable in the direction of arrow A.

The photoreceptor drum 1 is an organic photoreceptor (OPC).
) type photoconductive material.

Further, around the photoreceptor drum 1, an image exposure device (electrostatic latent image forming means) 3 consisting of a charger 2 and an LED (light emitting diode) array is arranged sequentially along the rotation direction of the photoreceptor drum 1. , a developing device (developing means) 4, a transfer device 5, and a cleaning device 6 are provided.

The charger 2 is located above the photoreceptor drum 1, and charges the surface of the photoreceptor drum 1 by -5.
It is designed to be negatively charged approximately uniformly between 00 and -800 volts.

The image exposure device 3 irradiates the surface of the photosensitive drum 1 with LED light to form an electrostatic latent image on the charged area according to image information to be recorded. Further, in the developing device 4, a rotating intermediate roller for supplying the developer T to the developing roller 8 is provided in a hopper 7 that stores a one-component developer (toner) T having frictional charging properties. A developing roller 8 is provided which rubs the developer supplied from the intermediate roller 9 on the photosensitive drum 1 to develop the image.

The developing roller 8 has a resistance of 102 to 108 Ω.
It has a conductive surface layer 10 made of a conductive elastic resin having an electrical resistance of cm, and an elastic layer 11 made of foamable urethane, silicone rubber, EPDM, etc. is disposed inside it.
The roller 8 as a whole is elastic.

An elastic blade 12 made of phosphor bronze, urethane, silicone resin, etc. is pressed against the developing roller 8 and is used to frictionally charge the developer T and form a thin layer. The developer T passing through the photosensitive drum 1
One to two developer layers are formed by being negatively triboelectrically charged with the same polarity as the developer.

The surface layer 10 of the developing roller 8 needs to be selected in consideration of the frictional electrification of the developer and appropriate elasticity and frictional properties.

Further, a bias power supply 13 serving as a voltage applying means is connected to the developing roller 8, and is electrically connected to the surface layer 10. Thereby, a predetermined development bias (-140 to -400V) is applied during development.

The transfer device 5 is provided substantially below the photoreceptor drum 1, facing the circumferential surface of the photoreceptor drum 1 via the paper conveyance path 14.

The transfer device 5 is constructed as shown in FIGS. 1 and 3. That is, in the figure, 15a is a support member 15a made of conductive metal or the like;
a is rotatably supported by a support shaft 15d. A transfer brush 15b, which is an elastic conductive plate member, is attached to the rotating end side of the support member 15a. The transfer brush 15b has a brush shape in which conductive fibers made by mixing conductive carbon with rayon are bundled into a plate shape at an appropriate density, and is a brush-like brush made of conductive fibers made by mixing conductive carbon with rayon and bundled into a plate shape at an appropriate density. As the photosensitive drum 1 rotates, it comes into sliding contact over at least the effective image width of the photosensitive drum 1.

The transfer brush 15b of the transfer device 5 has 8
A voltage of 00 to 2,000 volts is applied, and a voltage of 400 to 800 volts is applied to the back side of the paper 16 that has been conveyed.
The bolt is charged, electrostatically attracts the toner image on the photosensitive drum 1, and transfers it from the photosensitive drum 1 to the paper 16.

What is important in the transfer device 5 is the characteristics of the transfer brush 15b made of conductive fibers.

[0029] Below, experimental results regarding the transfer characteristics of various transfer brushes 15b made using various conductive fibers will be shown, and preferred characteristics and shapes will be explained.

First, five types of fibers were trial-produced with an effective resistance of 104 to 1010 ohms (Ω)/millimeter (mm) per fiber.

[0031] Ten types of prototypes were produced with fiber thickness ranging from 0.5 to 30 denier.

[0032] The flocking density is 1/mm to 2000/mm.
We fabricated 10 types of brush fibers with appropriate lengths (effective length not including the supporting part) of 2 to 30 mm.
The transfer characteristics were investigated by changing the pressing conditions (mainly the amount of deflection = support angle).

As a result, when the above-mentioned parameters are suitable, if the fiber length is 3 mm or less, it is difficult to obtain uniform contact over the entire sheet, and it is difficult to make adjustments to satisfy the transferability.

When the fiber length is in the range of 3 to 20 mm, fibers with a thickness of about 1 to 8 deniers and having appropriate flexibility are mechanically good, and the electrical resistance per fiber is 105 to 8 denier.
Good transfer characteristics were exhibited in the 109 ohm (Ω)/millimeter (mm) range.

[0035] In addition, when the fiber length is 20 to 30 mm, 5 to 1
Good results were obtained with approximately 5 denier.

Although the examination was omitted, it is clear from the above results that even fibers with longer lengths can function if the fiber length is appropriately selected.

However, if the size is larger than this, the device will become larger and its practical value will be lost.

The flocking density (fiber/unit length), along with the thickness and length, must be selected experimentally to determine the strength with which the paper is pressed against the photoreceptor drawer 1.

However, among these, the flocking density has other important factors.

[0040] If the density is reduced below a certain level in order to adjust the pressing force, image missing portions called transfer omissions will gradually appear in the transferred image in the direction of image progress.

[0041] This is because a local discharge occurs due to the voltage applied from the fiber tips to the paper during transfer, and the paper becomes electrically charged. However, if the distance between the fiber tips is too far apart, the paper is not electrically charged. It is understood that the image of this portion is not transferred and is therefore missing.

The conditions under which this transfer omission occurs vary depending on the type of paper used for transfer and the environmental humidity, but when the paper is normally used and the relative humidity is about 30 to 70%, the brush-like brush 15b is It has been found that when the distance between the tips of the fibers is approximately 1 to 2 mm or less, this phenomenon is difficult to occur.

From this, the order of determining the above factors is to first determine the flocking density (preferably by planting a large number of fibers so that the density is 1 mm or less), and then to determine the appropriate thickness and length. should be determined.

[0044] This required fiber density varies depending on the paper used, and the thinnest one is required when using a transparent film with high electrical resistance, and approximately 10 or more fibers are required per 1 mm, but usually Regarding the paper used, about three or more sheets can withstand use.

However, when the number of fibers is as small as possible, density unevenness occurs over time due to changes in the fibers, which tends to cause transfer defects, and the elastic force that mechanically presses the paper becomes weak. However, it is preferable to use as many thin fibers as possible because this tends to cause problems such as the need for an auxiliary elastic plate to back up the fibers from behind.

[0046] Extracting the optimum conditions from the above study results, the fiber growth density of the brush-like transfer brush 15b is set to 3 fibers/
mm or more (most preferably 100 to 800 fibers/mm), and the fiber thickness is 1 to 15 denier.
The length is about 3 to 30 mm, with a thickness that has appropriate flexibility (this is selected in relation to the length),
By adjusting the conductivity so that the electrical resistance per brush is 105 to 109 ohms (Ω)/millimeter (mm), it is possible to create a transfer brush 15b that exhibits appropriate transfer characteristics. .

This transfer device 5 (fibers are 4 denier, length 17 mm, number of fibers 700/mm) has the most preferable softness (J
A roller having an I of 30 degrees) was prototyped and the transfer performance was compared.

The comparison was made by comparing the permissible range of the amount of biting of the transfer brush and the transfer rubber roller into the photosensitive drum 1 (the amount of deflection of the transfer brush was measured by changing the support angle), that is, the required mechanical accuracy.

FIG. 4 shows the results.

FIG. 4 shows the relationship between the amount of biting (pressing distance) and the indicated value of tsubo (value divided by the contact length) when a rubber roller and brush are pressed against the spring tsubo.

[0051] Actual image transfer experiments have been carried out using each roller and transfer brush, and the results show that the above-mentioned transfer failure occurs under a load of approximately 80 grams (g)/cm or more.

[0052] Even if the load is too small, the relative humidity will be 80%.
Approximately 20g/in high humidity conditions of over 20%
Transfer omission due to insufficient mechanical adhesion and insufficient charging was observed at a thickness of less than cm.

Therefore, when these are superimposed on FIG. 4, it can be seen that in the conventional transfer using a rubber roller, the amount of mechanical intrusion that allows proper transfer is at most in the range of about 0.1±0.05 mm. The brush-like transfer brush 15b has a mechanical tolerance of about 1.2±0.7 mm, which is more than 10 times the conventional width, contributing to component accuracy and ease of position setting, and making it practical for rubber rollers. It was found that the problem of setting accuracy, which was a major obstacle above, could be resolved.

In order to maintain this level of mechanical precision, the support angle θ of the support member 15a of the transfer brush 15b with respect to the tangent between the photosensitive drum 1 and the transfer brush 15b as shown in FIG.
By fixing the angle to about 60 degrees, preferably about 5 to 30 degrees, the amount of bite (distortion amount), that is, the pressing force can be adjusted.

As described above, the reason why the tip of the transfer brush 15b is inclined downstream with respect to the tangent to the photoreceptor 1 is not only to adjust the pressing force, but also to prevent the tip from intruding into the transfer area. The plate-shaped transfer brush 15b used in the present invention is used to guide the coming paper more smoothly.
It is convenient to tilt the photosensitive drum 1 as shown in the figure to also serve as a guide.

Note that it is not preferable for the tip of the transfer brush 15b to be lifted from the photoreceptor l when it is set, and it is necessary to support it so that the tip is in contact with it or the belly near the tip is in contact with it. This is possible because in this state, there is the least uneven charging and the paper can easily pass through (not become a mechanical obstacle).

As described above, in the transfer using the transfer brush 15b using elastic fibers as in the embodiment of the present invention, it is very easy to adjust the pressing force of the transfer paper to 80 g/p which is optimum for transfer.
It has the great advantage that it can be maintained at less than cm and with a large mechanical tolerance.

[0058] Such a contact type transfer means exhibits stable transfer characteristics even under high humidity conditions, so it has the effect of reducing the amount of developer remaining after transfer and reducing the cleaning load, and also reduces the amount of paper in the transfer paper. Since it also has the effect of removing powder, it reduces the burden on cleaning equipment and contributes to improved reliability.

On the other hand, in the lower part of the photosensitive drum 1,
A paper feed unit 18 is provided that supplies paper 16 to the transport path 14.

The paper feed unit 18 stores a paper 16 as a transfer material onto which an image is to be transferred.

A paper feed roller 19 is provided above the storage unit 18 to feed the paper 16 from the paper feed unit 18 to the transport path 14 by rotation.

Further, at the end of the conveyance path 14, the paper 16
A fixing device 20 is provided for fixing the transferred toner image. A gate 31 is provided on the ejection side of the fixing device 20, and by rotating this gate 31, the paper P is selectively ejected to the first or second ejection section 32, 33. The developed toner image is conveyed to the transfer area facing the next transfer device 5, as described above.

On the other hand, the paper 16 is fed to the transfer area from the paper feed unit 18 by the rotation of the paper feed roller 19 in synchronization with the rotation of the photosensitive drum 1.

The back side of the paper 16 is charged to a positive polarity by the transfer brush 15b.

Therefore, the toner image on the surface of the photosensitive drum 1 is electrostatically attracted to the paper 16 and transferred.

[0066] Here, the transfer brush 15b is supplied with a voltage of 800 to
A voltage of 2000 volts is applied.

Since the transfer brush 15b is contaminated with toner and the like during use, in order to prevent this as much as possible, the transfer brush 15b is moved back and forth around the rotating shaft 15d of the support 15a as shown by arrow R in FIG. It is controlled to move away from the photosensitive drum 1 in areas where there is no recording paper.

[0068] As a result, stains on the transfer brush 15b can be extremely reduced, and there was no problem when printing about 10,000 to 20,000 sheets.

However, even with this method, cleaning is required for long-term use.

In this example, for this reason, the conductive transfer brush 1
When the transfer brush 15b is not transferred, the voltage applied to the transfer brush 15b by the DC power supply 21 applied to the DC power supply 5b is changed to -100 to -300 volts by another power supply 22 that generates a voltage of the same polarity as the developer toner (negative in this case). By applying this voltage, toner can be attached to the photoreceptor drum 1 side, thereby preventing staining.

As another method for cleaning the transfer brush 15b, some toner can be removed by simply turning off the voltage applied to the transfer brush 15b to zero in the non-transfer area of the photosensitive drum 1; Transfer brush 1 transfers a band-shaped area in which the charge of photoreceptor drum 1 is reduced to zero in the non-transfer area.
5b also has a cleaning effect, and it is preferable to implement one of these cleaning means during continuous use.

By this cleaning, the transfer brush 15b is
Good transfer function was maintained over more than 10,000 prints.

[0073] Also, in the results of tests in which the relative humidity of the environment was varied in the range of 30 to 80%, in an environment of approximately 70% or more, the relative humidity was clearly higher than that of the corona transfer method. It was also confirmed that the transfer efficiency (ratio of transferred toner to the amount of toner on the photoreceptor before transfer) was exhibited and was excellent.

By the way, a more detailed study of the bias voltage applied to the transfer brush 15b revealed the following mysterious development.

That is, the toner adhering to the transfer brush 15b is removed immediately after the DC power supply 21 is turned on during printing using the electrophotographic apparatus described in detail above, and when it is turned off at the end of the operation of the apparatus. The toner is ejected all at once onto the surface of the photoreceptor drum, and the toner adheres in a band-like manner.

This would be a preferable phenomenon if it could be cleaned by the cleaning device 6 afterwards, but sometimes the amount of adhesion is large and cleaning is insufficient, which may affect the next image.

As a result of investigating the cause of this, the transfer brush 15
As shown in Fig. 5, when the bias voltage applied to b becomes less than 20 milliseconds (msec.), the 90% rise time ton at switch-on or the fall time toff at switch-off becomes less than approximately 20 milliseconds (msec.). I found out that it occurs.

Judging from this, the transfer brush 15
It is believed that toner of the same polarity is repelled and ejected due to the induction of a back electromotive force caused by the electrical resistance and capacitance of b.

In any case, by adding a circuit consisting of a capacitor and a resistor to slow down the output of the bias DC power supply, the output time is preferably 20 msec or more, and 50 to 150 msec. This phenomenon can be completely eliminated by using a DC power source that outputs voltage gradually over time.

Note that the transfer device 5 also includes a transfer brush 1.
In case the toner falls from the toner 5b, a falling toner storage section 23 is provided.

Furthermore, when thin paper is used, if the paper is charged by the transfer brush 15b or the like before it comes into contact with the photoreceptor drum 1, some of the toner may be removed before it comes into close contact with the photoreceptor drum 1. This may cause image defects such as double images due to flying (transfer).

As a countermeasure for this, as shown in FIG. 6, an insulating elastic plate 15e with a thickness of about 0.1 to 0.3 mm is attached to the support plate 15a of the transfer brush 15b on the side where the transfer paper enters.
If they are fitted together with b, the above-mentioned problem can be prevented because the paper is not charged until just before it comes into close contact.

As described above, the elastic conductive transfer brush 1
5b, the transfer by the transfer device 5 does not increase the price, generates almost no ozone, and the transfer device is easy to clean, so it is highly efficient and can be used in a wide range of environments for a long time. In addition to sustaining the transfer, since the paper 16 is in direct contact with the paper 16 during the transfer, paper dust adhering to the paper 16 can be efficiently adsorbed and removed.
The amount of appendages remaining in the cleaning device 5 is greatly reduced.
It has been confirmed that this reduces the burden on

Furthermore, since the transfer device 5 has a large mechanical tolerance when mechanically pressing the paper 16, transfer omissions (partial non-transfer) can be effectively prevented, especially when using a conventional roller. When using the transfer method, when the thickness of the paper becomes thick, the pressing force exceeds the allowable range, which requires a complicated countermeasure mechanism.However, the transfer method according to the present invention has limitations such as the need for a complicated countermeasure mechanism. It is also worth mentioning that because the transfer rate is large, there is little effect, and a clear image is transferred regardless of paper thickness.

[0085] Other materials for the conductive fibers include:
Those using acrylic or nylon resins can be similarly used as long as they have appropriate flexibility, mechanical strength, and dispersibility with carbon.

Furthermore, as shown in FIG. 7, the transfer brush 15
An elastic backup 25 such as a polyester film may be provided on the lower surface side of the transfer brush 15b, and a mechanical load may be applied by the elastic backup 25 to press the tip of the transfer brush 15b against the photoreceptor drum 1.

In the above embodiment, a brush was used as an example, but the invention is not limited to this, and as shown in FIG. 8, an elastic conductive plate-like transfer member 15c other than the brush When using a brush, the same procedure can be used to determine the plate thickness, length (effective length in the contact deflection direction), support angle (adjustment of biting amount, pressing force), etc. as in the case of a brush. can perform the functions of

The transfer member 15c has a thickness of 0 and is made of a mixture of elastic urethane rubber (resin) or silicone rubber (resin) and conductive carbon.
．． The member is approximately 5 to 2 mm thick, and is made of a material that has appropriate elasticity and conductivity, and is also excellent in abrasion resistance.

Similar to the transfer brush 15b, this conductive plate-like member 15c is used by abutting its free end against the photoreceptor drum 1 near the tip or the belly surface of the tip with an appropriate load.

[0090]

[Effects of the Invention] As explained above, according to the present invention,
Since the image is transferred using an elastic conductive plate-like member, the price does not increase and the image can be transferred with almost no ozone generation.

In addition, the mechanical tolerance when mechanically pressing the transferred material is large, and transfer omissions are effectively prevented. In particular, when using the conventional roller transfer method, the thickness of the transferred material is When the biting becomes thick, the pressing force exceeds the permissible range, which necessitates a complicated countermeasure mechanism.However, with the transfer according to the present invention, the permissible range of the biting amount is large, so there is less influence, and the transferred Clear images can be transferred regardless of the thickness of the material.

Furthermore, since a bias voltage is applied to the conductive plate-like member such that the 90% rise time at the start of the image forming operation or the 90% fall time at the stop of the image forming operation is 20 milliseconds or more, The developer attached to the conductive plate-like member is not discharged and attached to the image carrier when the image forming operation is started or stopped, and there is no adverse effect on the next image formation.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing a transfer device according to an embodiment of the present invention.

FIG. 2 is a configuration diagram showing an image forming apparatus including the transfer device of FIG. 1;

FIG. 3 is a perspective view showing a transfer brush of the transfer device in FIG. 1;

FIG. 4 is a graph showing the relationship between the amount of bite of the transfer brush in FIG. 3 into the photosensitive drum and the generated load in comparison with that of the rubber roller.

FIG. 5 is a bluff diagram showing the relationship between the bias voltage applied to the transfer brush of FIG. 3 and time.

FIG. 6 is a configuration diagram showing a first other example of the transfer device.

FIG. 7 is a configuration diagram showing a second other example of a transfer device.

FIG. 8 is a configuration diagram showing a third other example of the transfer device.

[Explanation of symbols]

1... Photosensitive drum (image carrier), 3... Image exposure device (electrostatic latent image forming means), 4... Developing device (developing means), 15a... Transfer brush (conductive plate-like member), 15c... Transfer member (Conductive plate-like member), 21... Voltage application means.

Claims (1)

[Claims] 1. A developing means for forming a developer image by supplying a developer to a latent image formed on an image carrier; A conductive plate-like member having elasticity that presses the transfer material against the image carrier, and a conductive plate-like member having an elasticity of 90% at the start of the image forming operation.
Startup time or 90% when image forming operation stops
An image forming apparatus comprising: voltage applying means for applying a bias voltage having a fall time of 20 milliseconds or more to transfer the developer image to a transfer material.