JP3050941B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic apparatus, an electrostatic printer, etc., which forms an electrostatic latent image on an image carrier such as a photoreceptor and develops the electrostatic latent image. The present invention relates to an image forming apparatus provided with a transfer device for transferring an image to a transfer material such as paper.

[0002]

2. Description of the Related Art In electrophotographic apparatuses and electrostatic printers,
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 the developer image is transferred by a transfer unit. Is recorded by transferring it to paper.

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

Further, since an electrostatic latent image and a developer that cannot be completely transferred remain on the photoreceptor after transfer, the residual developer is removed by a cleaning device, and then the electrostatic latent image is removed. Removed by static eliminator. Thereafter, the same basic operation is repeatedly performed.

In recent years, along with the demand for downsizing of the apparatus, the harmfulness of ozone generated by corona discharge has been raised as a problem, and ozone removing means or roller transfer with less ozone generation has been proposed. Means are needed.

[0006]

However, there are several reasons why the roller transfer method has not been widely used in spite of the above advantages.

In the roller transfer, it is required that a material to be transferred such as paper is pressed against an image surface of a developer such as a photoreceptor with an appropriate pressure. When the pressure is insufficient, uneven transfer is caused. Since the developer (toner) sticks to cause transfer omission, etc., high mechanical accuracy (straightness: about ± 50 microns) and appropriate softness (JIS hardness of about 1)
(0 to 40 degrees), but it has been difficult to achieve both of these with the conductive rubber used conventionally.

In particular, when a sheet having a thickness of 100 microns is used, an excessive pressure is generated and a transfer failure occurs.
Complex control such as separation is required.

Further, the electric resistance of the transfer roller for applying an electrostatic force to the toner image must be maintained at a value which can prevent the destruction of the recording material due to discharge in any environment. Limits the choice of mechanical properties of

Under such circumstances, there is a need for an image forming apparatus which solves the above-mentioned problems and sufficiently satisfies the required characteristics.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus which can easily maintain an appropriate pressing force on a material to be transferred without extremely high mechanical accuracy with a very simple structure. It is assumed that.

[0012]

According to the present invention, there is provided an electrostatic latent image forming means for forming an electrostatic latent image on an image carrier, and a static image formed by the electrostatic latent image forming means. Developing means for supplying a developer to the electro-latent image to form a developer image; and elasticity for pressing a transfer-receiving material against the image carrier by contacting a leading end thereof at a predetermined angle with respect to the image carrier. And 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 of 20 ms or more. Voltage applying means for applying the developer image to transfer the developer image onto the transfer material.

[0013]

By pressing the material to be transferred onto the image carrier by means of the conductive plate member having elasticity, it is possible to obtain a pressing force on the image carrier with a large mechanical allowance that enables appropriate transfer. I made it possible.

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 of 20 ms or more to the conductive plate member, At the time of starting or stopping the image forming operation, the developer adhering to the conductive plate-like member is prevented from being discharged to and adhered to the image carrier.

[0015]

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

FIG. 2 shows a recording apparatus, and its main body H
A photosensitive drum 1 as an image carrier is rotatably provided in a substantially central portion of FIG.

The photosensitive drum 1 is an organic photosensitive member (OP)
C) It is made of a photoconductive material.

An image exposing device (electrostatic latent image forming means) 3 comprising a charging charger 2 and an LED (light emitting diode) array around the photosensitive drum 1 in order along the rotation direction thereof. , A developing device (developing means) 4, a transfer device 5, and a cleaning device 6 are provided.

The charging charger 2 is located above the photosensitive drum 1, and the surface of the photosensitive drum 1 is -5.
The negative charge is made substantially uniformly at 00 to -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 a charged area according to image information to be recorded. 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 containing a one-component developer (toner) T having a triboelectric charging property. And a developing roller 8 for developing the developer supplied from the intermediate roller 9 by rubbing it against the photosensitive drum 1.

The developing roller 8 is 10 ² to 10 ⁸ Ωcm.
Surface layer 1 made of conductive elastic resin having electric resistance
An elastic layer 11 made of foamable urethane, silicone rubber, EPDM, or the like is disposed inside the elastic layer 11 to form an elastic roller 8 as a whole.

An elastic blade 12 made of phosphor bronze, urethane or silicone resin for forming a thin layer is pressed against the developing roller 8 while frictionally charging the developer T. The passing developer T is the photosensitive drum 1
One or two developer layers are formed with negative triboelectric charge of the same polarity as the above.

The surface layer 10 of the developing roller 8 needs to be selected in consideration of the triboelectric charging of the developer and in consideration of appropriate elasticity and friction.

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

The transfer device 5 is provided substantially below the photosensitive drum 1 via a sheet transport path 14 so as to face the peripheral surface of the photosensitive drum 1.

The transfer device 5 is configured as shown in FIGS. That is, reference numeral 15a in the figure denotes a support member 15a made of a conductive metal or the like.
a is rotatably supported by a support shaft 15d. A transfer brush 15b as a conductive plate-like member having elasticity is attached to the rotation end side of the support member 15a. The transfer brush 15b has, for example, a brush shape in which conductive fibers made by mixing conductive carbon with a rayon are bundled in a plate shape at an appropriate density. With the rotation, the photosensitive drum 1 slides at least over the effective image width.

The transfer brush 15b of the transfer device 5 has 8
A voltage of 00 to 2000 volts is applied, and a voltage of 400 to 800
The toner image is transferred to the paper 16 from the photosensitive drum 1 by electrostatically attracting the toner image on the photosensitive drum 1 by being charged by a bolt.

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

Hereinafter, experimental results regarding transfer characteristics performed by experimentally producing various transfer brushes 15b using various conductive fibers will be described, and preferable characteristics and shapes will be described.

First, five kinds of electrical resistances of fibers were produced as effective resistances per fiber in the range of 10 ⁴ to 10 ¹⁰ ohms (Ω) / millimeter (mm).

Ten kinds of fibers were produced in the thickness range of 0.5 to 30 deniers.

The flocking density is 1 thread / mm to 2000 pieces / mm.
And a brush fiber having a length (effective length not including the supporting portion) of 2 to 30 mm is appropriately manufactured as a trial, and the transfer is performed while changing the pressing condition (mainly the amount of deflection = support angle) on the photosensitive drum 1. The characteristics were investigated.

As a result, as a suitable condition for the above parameters, if the fiber length is 3 mm or less, it is difficult to obtain uniform contact with the entire paper, and it is difficult to adjust the transfer properties.

When the fiber length is in the range of 3 to 20 mm, a fiber having a moderate thickness of about 1 to 8 denier is mechanically good, and the electric resistance per fiber is 10 ⁵ to 10 ⁵ . 1
0 ⁹ O - showed excellent transfer properties in torr (mm) Range - beam (Omega) / Mirime.

For a fiber length of 20 to 30 mm, 5 to 1
A material of about 5 denier showed a good result.

Although the study was omitted, it is clear from the above results that the fiber can function even if the length is longer than this if the length of the fiber is appropriately selected.

However, if the size is larger than this, the size of the apparatus is increased, and practical value is lost.

The flocking density (fiber / unit length) has to be selected experimentally to determine the strength of pressing the paper against the photoreceptor drow 1 together with the thickness and length.

However, among these, the flocking density has another important factor.

That is, if the density is reduced to a certain value or less in order to adjust the pressing force, an image missing portion called a transfer omission gradually occurs in the transferred image in the image traveling direction.

This is because the paper is charged due to the occurrence of local discharge from the leading end of the fiber to the paper at the time of transfer due to the applied voltage, but if the distance between the leading ends of the fibers is too large, the paper is not charged. It is understood that an image of this portion is missing without being transferred because a portion is generated.

The conditions for the occurrence of the transfer loss vary depending on the type of paper used for the transfer and the environmental humidity. However, in the case of a normally used paper, at a relative humidity of about 30 to 70%, the brush-like brush 15b is not used. It has been found that when the distance between the tips of the fibers is about 1 to 2 mm or less, it hardly occurs.

From the above, the order of determining the above factors is as follows: first, the density of flocking is determined (preferably, the number of fibers is increased so as to be 1 mm or less), and then the thickness and length suitable for this are determined. You have to decide.

The required fiber density varies depending on the paper to be used. When a transparent film or the like having a high electric resistance is used, the thinnest fiber is required, and about 10 or more fibers are required per 1 mm. About three or more sheets of paper to be used can withstand use.

However, when the number of fibers is as small as possible, unevenness in density due to changes in the fibers occurs with the passage of time, which tends to cause poor transfer, and the elastic force for mechanically pressing the paper becomes weak. In addition, it is preferable to use as many fibers as thin as possible because problems such as the necessity of an elastic plate that backs up from behind the fibers are liable to occur.

When the optimum conditions are extracted from the above examination results, the density of the fibers of the brush-like transfer brush 15b is 3 /
mm (most preferably 100 to 800 fibers / mm), and the fiber thickness is 1 to 15 denier.
With a thickness of about 3 to 30 mm with a thickness with a moderate degree of flexibility (this is selected in relation to the length),
The electrical resistance per wire is 10 ⁵ to 10 ⁹ ohms (Ω)
The transfer brush 15 which exhibits appropriate transfer characteristics by adjusting the conductivity so that the transfer brush 15 / mm (mm).
b can be made.

This transfer device 5 (four denier fibers, length 17 mm, number of fibers 700 / mm) is the most preferable softness (J) for a transfer roller using a conventional conductive rubber.
A roller having a temperature of (I30 degrees) was experimentally manufactured and the transfer performance was compared.

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

FIG. 4 shows the result.

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

Each of the rollers and the transfer brushes is also actually conducting an image transfer experiment, and the results show that the above-mentioned transfer omission occurs at a load of about 80 g (g) / cm or more.

Further, even if the load is too small, the relative humidity becomes 80%.
About 20 g /
cm or less, transfer omission due to insufficient mechanical adhesion and insufficient charging was observed.

Therefore, when these are superimposed on FIG. 4, the mechanical digging amount at which a proper transfer can be performed by the conventional rubber roller is at most 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 10 times or more that of the conventional brush, and contributes to the simplification of component accuracy and position setting. It was found that the problem of setting accuracy, which was a major obstacle, could be solved.

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

As described above, the reason why the tip of the transfer brush 15b is inclined in the downstream direction with respect to the tangent line to the photoreceptor 1 is not only for adjusting the pressing force but also for entering the transfer area. The plate-like transfer brush 15b used in the present invention is used to more smoothly guide the incoming paper.
Is convenient for tilting the photosensitive drum 1 as shown in FIG.

It is not preferable that the tip of the transfer brush 15b is lifted from the photoconductor 1 at the time of setting, and it is necessary that the tip of the transfer brush 15b be supported so that the tip contacts or the antinode near the tip contacts. This is because in this state, it is possible to minimize the unevenness in charging and to achieve a state in which the sheet easily passes (does not become a mechanical obstacle).

As described above, in the transfer by the transfer brush 15b using the elastic fiber as in the embodiment of the present invention, the pressing force of the transfer paper is extremely easily reduced to 80 g / m, which is optimal for the transfer.
cm or less and with great mechanical tolerances.

Such a contact-type transfer means exhibits stable transfer characteristics even under humid conditions, and thus has the effect of reducing the amount of residual transfer developer to reduce the cleaning load, as well as reducing the amount of paper in the transfer paper. Since it also has a powder removing effect, it reduces the load on the cleaning device and contributes to improving reliability.

On the other hand, below the photosensitive drum 1,
A paper supply unit 18 that supplies the paper 16 to the transport path 14 is provided.

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

Above the storage unit 18, a paper feed roller 19 for supplying the paper 16 from the paper supply unit 18 to the transport path 14 by rotation is provided.

Further, at the end of the transport path 14, the paper 16
Is provided with a fixing device 20 for fixing the transferred toner image. A gate 31 is provided on the discharge side of the fixing device 20, and the sheet P is selectively discharged to the first or second discharge portion 32, 33 by the rotation of the gate 31. The developed toner image is conveyed to the next transfer area facing the transfer device 5 as described above.

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

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.

Here, the transfer brush 15b is connected to the transfer brush 15b by the DC power supply 21 via the conductive support 15a.
A voltage of 2000 volts is applied.

The transfer brush 15b is contaminated by toner and the like during use. To prevent this, the transfer brush 15b reciprocates around the rotation shaft 15d of the support 15a as shown by the arrow R in FIG. It is controlled so as to move away from the photosensitive drum 1 in an area where there is no recording paper.

As a result, the transfer brush 15b can be made very clean, and there is no problem in printing about 10,000 to 20,000 sheets.

However, even in this case, cleaning is necessary for long-term use.

In the present embodiment, the conductive transfer brush 1
When the voltage applied to the transfer brush 15b by the DC power supply 21 applied to the transfer brush 5b is not transferred, another power supply 22 that generates a voltage having the same polarity (negative in this case) as the developer toner is used. By applying this voltage, toner can be attached to the photosensitive drum 1 side, thereby preventing contamination.

Another method of cleaning the transfer brush 15b is to remove some toner by simply turning off the voltage applied to the transfer brush 15b at the non-transfer portion of the photosensitive drum 1 to zero. In the non-transfer area, the belt-shaped area where the charge of the photosensitive drum 1 is zero is transferred to the transfer brush 1
There is also a cleaning effect by passing through 5b, and it is preferable to implement any of these cleaning means during continuous use.

By this cleaning, the transfer brush 15b becomes 10
A good transfer function could be maintained over 10,000 or more prints.

Also, the results of tests conducted by changing the relative humidity of the environment in the range of 30 to 80% are clearly higher than the method using corona transfer under an environment of about 70% or more. The transfer efficiency (the ratio of the transferred toner to the toner amount on the photoreceptor before transfer) was exhibited, and it was also confirmed that the toner was excellent.

When the bias voltage applied to the transfer brush 15b was examined in more detail, the next inexplicable development was found.

That is, the toner adhered to the transfer brush 15b is removed immediately after the DC power supply 21 is turned on at the time of printing of the electrophotographic apparatus described above or when the DC power supply is turned off at the end of the operation of the apparatus. The toner is discharged onto the surface of the photosensitive drum 1 at a stroke, and the toner adheres in a belt shape.

This is a preferable phenomenon if the cleaning can be performed by the cleaning device 6 later, but sometimes the amount of adhesion is large and the cleaning is insufficient, which may affect the next image.

As a result of investigating this cause, the transfer brush 15
As shown in FIG. 5, when the bias voltage applied to b is 90% rise time ton at the time of switch-on or fall time at the time of off-time, and the time toff is about 20 milliseconds (msec.) or less, remarkable. It was found to happen.

Judging from this, the transfer brush 15
It is considered that the toner of the same polarity is repelled and emitted by the induction of the back electromotive force caused by the electric resistance and the capacitance of b.

In any case, 20 msec or more is preferable, and 50 to 150 msec. Is added by adding a circuit including a capacitor and a resistor for dulling the output of the bias DC power supply. This phenomenon is completely eliminated by using a DC power supply that gradually outputs a voltage over a certain period.

The transfer device 5 has a transfer brush 1
An accommodation portion 23 for the falling toner is provided so that the toner may fall from 5b or the like.

In the case where thin paper is used, if the paper is charged by the transfer brush 15b or the like before the paper comes into contact with the photosensitive drum 1, a part of the toner may be removed before the paper is brought into close contact with the photosensitive drum 1. It may fly (transfer) and cause image defects such as double images.

As a countermeasure, as shown in FIG. 6, an insulating elastic plate 15e having a thickness of about 0.1 to 0.3 mm is provided on the support plate 15a on the transfer paper entry surface side of the transfer brush 15b.
If the sheet is fitted together with b, the above-mentioned problem can be prevented because the sheet is not charged until immediately before the sheet comes into close contact.

As described above, the elastic conductive transfer brush 1
In the transfer by the transfer device 5 using the transfer device 5b, the cost is not increased, ozone is hardly generated, and the transfer device can be easily cleaned. Since the transfer is continued and the paper 16 is in direct contact with the paper 16 at the time of the transfer, the paper dust adhering to the paper 16 can be efficiently absorbed and removed.
The attachments remaining on the cleaning device 5 are greatly reduced.
It has been confirmed that the burden on the user can be reduced.

Further, since the transfer device 5 has a large mechanical tolerance when mechanically pressing the paper 16, transfer omission (no partial transfer) is effectively prevented. In the case of the transfer method, when the thickness of the paper becomes thick, the pressing force exceeds the allowable range, so that there is a restriction that a complicated countermeasure mechanism is required. It is worth noting that the effect is small, and a clear image is transferred regardless of the paper thickness.

In addition, as a material of the conductive fiber,
As long as it has appropriate flexibility, mechanical strength, dispersibility with carbon, and the like, for example, those using an acrylic resin or a nylon resin can be used.

As shown in FIG. 7, the transfer brush 15
An elastic backup 25 made of a polyester film or the like may be provided on the lower surface side of b, and a mechanical load may be applied by this elastic backup 25 to press the leading end of the transfer brush 15 b against the photosensitive drum 1.

In the above-described embodiment, a brush is used as an example. However, the present invention is not limited to this, and as shown in FIG. When using a brush, the same procedure is used to determine the plate thickness, length (effective length in the direction of contact bending), support angle (adjustment of bite amount, pressing force), etc. in the same procedure as for the brush. Function can be exhibited.

The transfer member 15c is made of, for example, urethane rubber (resin) or silicon rubber (resin) having elasticity and a conductive carbon, and has a thickness of about 0.5 to 2 mm. The member is made of a material having appropriate elasticity and conductivity and also excellent in abrasion resistance.

Like the transfer brush 15b, the conductive plate-like member 15c is used with its free end in contact with the photosensitive drum 1 in the vicinity of the leading end or the leading end abdominal surface with an appropriate load.

[0090]

As described above, according to the present invention,
Since the transfer is performed using the conductive plate member having elasticity, the image can be transferred without increasing the cost and generating almost no ozone.

Also, the mechanical tolerance when mechanically pressing the material to be transferred is large, and transfer omission is effectively prevented. In particular, in the case of the conventional roller transfer method, the thickness of the material to be transferred is large. When the thickness is large, the pressing force exceeds the allowable range, so there were restrictions such as the need for a complex countermeasure mechanism, but in the transfer according to the present invention, since the allowable range of the bite amount is large,
The effect is small, and a clear image can be transferred regardless of the thickness of the material to be transferred.

Further, since 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 of 20 ms or more is applied to the conductive plate member, At the start or stop of the image forming operation, the developer adhering to the conductive plate-shaped member is not released and adhered to the image carrier, so that there is no adverse effect on the next image formation.

[Brief description of the 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 illustrating 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 of FIG. 1;

FIG. 4 is a graph showing the relationship between the amount of bite of the transfer brush of FIG.

FIG. 5 is a bluff diagram showing a relationship between a 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 the transfer device.

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

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photoreceptor drum (image carrier), 3 ... Image exposure apparatus (electrostatic latent image forming means), 4 ... Developer (developing means), 15a ... Transfer brush (conductive plate member), 15c ... Transfer member (Conductive plate member), 21... Voltage applying means.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-57-29064 (JP, A) JP-A-3-1311884 (JP, A) Jpn. Field (Int.Cl. ⁷ , DB name) G03G 15/16

Claims (1)

(57) [Claims] A developing means for supplying a developer to the latent image formed on the image carrier to form a developer image; and A conductive plate member having elasticity for pressing the transfer material against the image carrier; and a 90% rising time at the start of the image forming operation or a 90% rising time at the start of the image forming operation on the conductive plate member. An image forming apparatus comprising: a voltage application unit configured to apply a bias voltage having a fall time of 20 milliseconds or more to transfer the developer image to a transfer material.