JP3023192B2 - 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, and the like, and an image obtained by developing an electrostatic latent image formed on an image carrier such as a photoreceptor is transferred onto paper or the like. The present invention relates to an image forming apparatus for transferring an image to a material.

[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 transfer device, electrostatic means such as a corona transfer method, a roller transfer method, and the like, and mechanical means, such as an adhesive transfer method, are known.

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.

[0004] 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. It has been demanded.

[0005]

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 to press a transfer material such as paper against a developer image surface on a photoreceptor with an appropriate pressure. If the pressure is insufficient, transfer unevenness is caused. High mechanical precision (straightness: about ± 50 microns) because (toner) sticks and causes transfer omissions
And moderate softness corresponding to this (JIS hardness of about 10
40 °), but it was difficult to achieve both of them with the conductive rubber used conventionally.

Particularly, when a sheet having a thickness of 100 microns is used, an excessive pressure is generated to cause transfer failure.
Complex control such as separation is required.

Further, the electric resistance of the transfer roller for applying an electrostatic force to the toner image needs to maintain a value which can prevent the destruction of the recording material due to electric discharge in any environment. Restricts the selection range of characteristics. Against this background, there has been a demand for an excellent transfer device 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 a transfer apparatus which can easily maintain an appropriate pressing force on a material to be transferred without an extremely high mechanical accuracy with a very simple structure. Is what you do.

[0010]

According to the present invention, there is provided a latent image forming means for forming an electrostatic latent image on an image carrier.
And developing the electrostatic latent image formed by the latent image forming means.
Of supplying a developer to form a developer image on the image carrier
Means for supplying a transfer material toward the image carrier
A step and a plurality of conductive fibers, wherein the conductive fibers are
The image carrier is disposed so as to be in contact with the image carrier.
And transferring the transfer material supplied from the supply unit to the image carrier.
And formed by the developing means.
Transfer means for transferring the transferred developer image onto the transfer material
Voltage applying means for applying a transfer voltage to the transfer means
And at a contact portion between the conductive fiber and the image carrier.
The angle of the transfer unit with respect to the tangent line of the image carrier is 0 to 60.
° and supporting means for supporting the transfer means.
Have.

[0011]

The transfer member is pressed against the image carrier by the conductive plate member having elasticity, so that the pressing force against the image carrier enabling proper transfer can be obtained with a large mechanical tolerance. Ozone generation can be reduced.

[0012]

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 a photosensitive drum 1 as an image carrier is rotatably provided in a substantially central portion of a main body H in an arrow A direction. The photoconductor drum 1 is formed of an organic photoconductor (OPC) -based photoconductive material.

Around the photosensitive drum 1, the charging charger 2, an image exposure device (electrostatic latent image forming means) 3 comprising an LED (light emitting diode) array, and 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 so that 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. Further, the developing device 4 has a hopper 7 containing a one-component developer (toner) having a triboelectric property and having an average particle diameter of 5 to 15 μm.
Inside, a rotating intermediate roller 9 for supplying the developer T to the developing roller 8, and a developing roller 8 for developing the developer supplied from the intermediate roller 9 by rubbing against the photosensitive drum 1
Are provided.

The developing roller 8 has a capacity of 10 ² -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, and the developer passing therethrough is pressed. 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 frictional charging of the developer and 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 and facing the peripheral surface of the photosensitive drum 1 via a paper conveyance path 14.

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 kneading conductive carbon into rayon are bundled in a plate shape at an appropriate density, and the transfer brush 15b rotates as the photosensitive drum 1 rotates. , At least over 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 2000 volts is applied, and a voltage of 400 to 800
The toner image on the photosensitive drum 1 is electrostatically attracted and charged from the photosensitive drum 1 to the paper 16 by being charged by the bolt. What is important in the transfer device 5 is the characteristics of the transfer brush 15b made of conductive fibers. In the following, experimental results on transfer characteristics performed by experimentally producing various transfer brushes 15b using various conductive fibers will be shown, and preferable characteristics and shapes will be described. First, the electrical resistance of the fiber is 10 ⁴ as the effective resistance per fiber. Five prototypes in the range of -10 to 10 ¹⁰ ohms (Ω) / mm (mm). Fiber thickness is 0.5-30
Prototype of 10 kinds in denier range.

The flocking density is 1 / mm to 2,000 / 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, 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 make adjustments that satisfy transferability.

When the fiber length is in the range of 3 to 20 mm,
Having a moderate flexibility of about 1 to 8 denier in thickness
Is mechanically good and the electrical resistance per wire is 10^Five ~ 1
0⁹ Good in ohm (Ω) / mm (mm) range
Transfer characteristics were shown. In the case of fiber length 20-30mm
A product of about 5 to 15 denier showed a good result. Consideration
Although omitted, the fiber length can be selected as appropriate for longer lengths.
It is clear from the above results that it works. Only
However, a larger size would lead to an increase in the size of the device.
And practical value is lost. Flocking density (fiber / unit length
Is), and the paper, along with the thickness and length,
You have to choose experimentally to determine the strength of pressing on lau 1
No. However, among these, the flocking density is further
Has important factors.

That is, as the pressing force is reduced to a certain density 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 fibers of the brush-like brush 15b are removed. It has been found that when the distance between the tips is approximately 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 the flocking is determined (preferably, the number of fibers is increased so as to be 1 mm or less), and then the appropriate thickness and length 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, density unevenness occurs due to a change in the fibers with time, which tends to cause transfer failure, and the elastic force for mechanically pressing the paper becomes weak. It is preferable to use as many thinner fibers as possible, since problems such as the necessity of an elastic plate that backs up from behind the fibers are required. Extracting the optimal conditions from the above study results,

The density of the bristles of the fibers of the brush-like transfer brush 15b is at least 3 fibers / mm (most preferably 100 to 800 fibers / mm).
mm), and the thickness of the fiber is 1 to 1
The thickness is about 3 to 30 mm with a thickness having a moderate flexibility of about 5 denier (this is selected in relation to the length), and the electric resistance per piece is 10 ^5. -10 ⁹ By adjusting the conductivity so as to be in ohms (Ω) / mm (mm), a transfer brush 15b exhibiting appropriate transfer characteristics can be produced.

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.
(I30 degrees), and transfer performance was compared.

The comparison was made by comparing the allowable width of the amount 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.
Is the amount of bite (pressing distance) by pressing the rubber roller and brush against the spring tsubo and the indicated value of tsubo (value divided by the contact length)
This shows the relationship.

Each of the rollers and the transfer brush is also actually subjected to an image transfer experiment, and the result shows 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 shape transfer brush 15b has a mechanical tolerance of about 1.2 ± 0.7 mm, which is 10 times or more that of the conventional technology, and contributes to the simplicity of component accuracy and position setting. It has been found that the problem of the setting accuracy can be solved.

In order to maintain this degree 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 toward the downstream with respect to the tangent line to the photoreceptor 1 is not only to adjust the pressing force but also to enter 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 rises 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 can be 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 developer remaining after transfer to reduce the cleaning load. 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 feed 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, the paper 1
A paper feed roller 19 that supplies the sheet 6 to the conveyance path 14 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 rotation of the gate 31 allows the sheet P to be selectively discharged to the first or second discharge portion 32, 33 after development. Is transported to the next transfer area facing the transfer device 5 as described above. On the other hand, the paper 16 is sent from the paper supply unit 18 to the transfer area in synchronization with the rotation of the photosensitive drum 1 by the rotation of the paper supply 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 1
A voltage of 800 to 2000 volts is applied to 5b by the DC power supply 21 via the conductive support 15a.

The transfer brush 15b is contaminated by toner or the like during use, and is reciprocated about the rotation shaft 15d of the support 15a as shown by an arrow R in FIG. In an area where there is no recording paper, the area is controlled to be separated from the photosensitive drum 1. As a result, the transfer brush 15b can be made extremely clean, and there was no problem in printing about 10,000 to 20,000 sheets. However, even in this case, cleaning is necessary for longer-term use.

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

As another method for cleaning the transfer brush 15b, a small amount of toner is removed by simply turning off the voltage applied to the transfer brush 15b in the non-transfer portion of the photosensitive drum 1 to zero. In the transfer area, the belt-shaped area where the charge of the photosensitive drum 1 is zero is transferred to the transfer brush
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 was able to maintain a good transfer function over 100,000 or more prints.

Also, the results of tests conducted by changing the relative humidity of the environment in the range of 30 to 80% show that, under an environment of about 70% or more, the transfer efficiency (transfer efficiency) is clearly higher than the corona transfer method. (The ratio of the transferred toner to the amount of toner on the photosensitive member before transfer) was exhibited, and it was also confirmed that the toner was excellent. By the way, 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 adhering 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 and when the apparatus is turned off at the time of the differential termination operation of the apparatus. The toner is discharged onto the photosensitive drum 1 at a stroke, and the toner adheres in a belt shape.

This is a preferable phenomenon if it can be cleaned by the cleaning device 6 later, but sometimes the amount of adhesion is so large that the cleaning is insufficient and the next image may be affected.

As a result of investigating this cause, the transfer brush 15
As shown in FIG. 5, when the bias voltage applied to the switch b is 90% rise time ton when the switch is turned on or fall time when the switch is turned off, and the time toff is about 20 milliseconds (msec.) or less, the phenomenon occurs significantly. I understood that.

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, by adding a circuit including a capacitor and a resistor for dulling the output of the bias DC power supply, 20 msec or more is preferable.
１５０150 msec. This phenomenon can be completely eliminated by using a DC power supply that gradually outputs a voltage over a certain period, so that it can be adopted if necessary. In addition, the transfer device 5 is provided with an accommodating portion 23 for the dropped toner so that the toner may fall from the transfer brush 15b or the like.

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 photosensitive drum 1, a part of the toner flies before it comes into close contact with the photosensitive drum 1. (Transfer) and image defects such as double images may occur.

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. However, when the thickness of the paper is large, the pressing force exceeds the allowable range, so that there is a restriction that a complicated countermeasure mechanism is required. However, in the transfer according to the present invention, the allowable range of the biting amount is large. Therefore, it is worth noting that the influence 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 or nylon resin can be used.

Further, as shown in FIG.
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 embodiment, a brush is used as an example. However, the present invention is not limited to this. As shown in FIG. 8, a conductive plate-like transfer member 15c having elasticity other than a brush is used. 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, for example, a member having a thickness of about 0.5 to 2 mm formed by mixing conductive rubber with urethane rubber (resin) or silicon rubber (resin) having elasticity. A material having a suitable elasticity and conductivity and excellent abrasion resistance is used.

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.

[0058]

As described above, according to the present invention,
Since the developer image is transferred 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 transfer material is large, and transfer omission is effectively prevented. In particular, in the case of the conventional roller transfer method, the thickness of the transfer material is reduced. When the thickness is large, the pressing force exceeds the allowable range, and there are restrictions such as a need for a complicated countermeasure mechanism. However, in the transfer according to the present invention, the allowable range of the bite amount is large,
The effect is that the influence is small and a clear image can be transferred regardless of the thickness of the material to be transferred.

[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 biting 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]

1. Photosensitive drum (image carrier), 15a Transfer brush (conductive plate member), 15c Transfer member (conductive plate member).

──────────────────────────────────────────────────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] (1)Latent image formation for forming an electrostatic latent image on an image carrier
Means, A developer is applied to the electrostatic latent image formed by the latent image forming unit.
Developing means for supplying and forming a developer image on the image carrier
When, Supply means for supplying a transfer material toward the image carrier, A plurality of conductive fibers, wherein the conductive fibers support the image;
The image carrier is disposed opposite the image carrier so as to contact the body,
The transfer material supplied from the supply means is directed to the image carrier.
Along with the current formed by the developing means.
A plate-shaped transfer unit for transferring an image agent image onto the transfer material, Voltage applying means for applying a transfer voltage to the transfer means, Image bearing at a contact portion between the conductive fiber and the image carrier
The angle of the transfer means is 0 to 60 ° with respect to the tangent of the holding body.
And support means for supporting the transfer means.
An image forming apparatus characterized in that: