JPH1165313A - Transfer device and image forming device provided with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain stable transfer performance at all times, without increasing the cost, even if the conditions of a recording paper such as a kind and size are different and further, excellent separation performance from a transfer belt, of the recording sheet after a transfer is performed, as well. SOLUTION: All supporting rollers 21 and 22 for the transfer belt 20 are in nongrounded states and a charge supplying means consists of a constant- current power source 23 connected to at least one of the supporting rollers 21 and 22. Further, the outside diameter of the supporting roller 21 disposed in a position for separating the recording sheet P after the transfer is performed from the transfer belt 20 is set to obtain a dimension capable of permitting the recording sheet to self-separate from the transfer belt and it to smoothly extend.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transfer device in an image forming apparatus such as a copying machine or a printer having an image bearing member on which a toner image is formed, and more particularly to a transfer device for supplying an electric charge to an endless belt. The present invention relates to a so-called belt-type transfer device for transferring a toner image on a carrier to a recording sheet conveyed by a belt, and an image forming apparatus having the transfer device.

[0002]

2. Description of the Related Art As this type of transfer device, for example, a transfer device of the type shown in FIG. 3 is known. In this transfer device, a transfer belt c composed of an endless belt stretched over a plurality of support rollers a and b is brought into contact with or close to an image carrier d such as a photosensitive drum on which a toner image is formed. Are formed so as to rotate and synchronize with the image carrier d, and a predetermined charge (transfer bias) is applied to the transfer belt c from a transfer power source f. It is configured to be supplied via a roller g.

In this transfer apparatus, the recording sheet h
Is transported to the transfer portion e while being held on the transfer belt c,
The toner image formed on the image carrier d by electrophotography or the like is electrostatically transferred to the recording sheet h side at the transfer portion e. Note that the recording sheet h after the completion of the transfer is separated from the transfer belt c and sent to a fixing device i disposed downstream thereof.

In such a belt-type transfer apparatus, the recording sheet h is generally not easily separated from the transfer belt c after the transfer because the recording sheet h is held by the electrostatic attraction force on the transfer belt c. There is a problem that. The type (thickness and material) of the recording sheet h to be used
If the size of the transfer belt is different, the electrical resistance at the transfer portion e changes, and the condition of the electric charge supplied to the transfer belt c also changes, resulting in a problem that the transfer performance becomes unstable.

In order to solve the former problem, it is known that the support rollers a and b are grounded to reduce the electrostatic attraction force of the transfer belt c to the recording sheet h as shown in FIG. Have been. In order to solve the latter problem, it has been proposed to use a constant current power supply as the transfer power supply f, for example (Japanese Patent Application Laid-Open No. Sho 57-57).
-27286).

However, especially in the case of a transfer device in which the support rollers a and b are grounded, the electric charge supplied from the transfer power source f flows from the transfer belt c through the support rollers a and b so as to be grounded. Current paths j and k are formed (see FIG. 3). For this reason, when a recording sheet h having a high electric resistance value is used in such a situation,
Since the resistance value at the transfer position e where the recording sheet h is present is increased, the amount of the electric charge supplied from the transfer power source f that flows through the current paths j and k and is grounded is increased. At the transfer position e, the current (transfer current) flowing toward the image carrier d decreases, and as a result, there is a problem that it is not possible to sufficiently supply charges necessary for transfer to the transfer belt c.

Further, in the transfer apparatus in which the support rollers a and b are grounded, even if the constant current power supply is used as the transfer power supply f as described above (FIG. 3), the recording sheet h If the condition of the electric resistance value changes due to the difference in the type and size, the current flowing from the constant current power supply f through the current paths j and k also increases, and the supply of the original charge to the transfer belt c becomes insufficient. Since a case may occur, there is a problem that stable transfer performance to a recording sheet h of a different type or size cannot be obtained.

[0008] Under such circumstances, Japanese Patent Laid-Open Publication No.
In No. 4 publication, without being affected by environmental changes,
A transfer device that has both good transfer performance and performance of separating a recording sheet from a transfer belt has been proposed. This is shown in FIG.
As shown in FIG. 3, the amount of current flowing into at least one of the plurality of support rollers (a, b, m) (support roller a in the illustrated case) is detected, and a transfer power source f is determined in accordance with the amount of current.
Is provided to control the amount of current flowing to the image carrier d side to an appropriate value irrespective of changes in the environment. In the drawing, reference numeral q indicates a transfer electrode.

However, the proposed transfer apparatus has an advantage that stable transfer performance can be ensured for recording sheets h of different types and sizes, but requires a control circuit as the control means n, and thus costs are reduced. Be up. In addition, since the charge supplied from the transfer power source f flows through the grounded support roll and is lost, the transfer site e must always supply more charge than originally required. Requires a large output capacity, which also increases the cost. Further, when the electric resistance value of the transfer belt c in the rotational movement direction is low or the resistance unevenness of the belt c is large, there is a problem that the controllability of the control unit n is reduced.

Japanese Patent Application Laid-Open No. 57-100456 discloses a belt-type transfer apparatus in which two support rollers a and b of a transfer belt c are used without being grounded. As shown in FIG. 5, an endless belt having an insulating layer having special physical properties is used as a transfer belt c, and the transfer belt c is charged by a charging device r ₁ to perform transfer. The charge applied to the transfer belt c by r _{1 is} removed by a charging device r ₂ for peeling, so that even if a human body comes into contact with the transfer belt c, there is no discomfort and the transfer belt c The recording sheet h is easily peeled off. However, in the case of this transfer device, the transfer belt c is charged by the charging device r ₁ , and therefore, when the charge moves on the transfer belt c, the transferred toner image is disturbed. I do. For this reason, the surface resistance of the transfer belt c must be kept high. In this case, if the transfer operation is repeated many times, a problem that charges are accumulated on the surface of the transfer belt c tends to occur. There is a drawback that a static eliminator or the like for removing charges is further required.

[0011]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a recording medium which can always be manufactured without increasing the cost even if the conditions such as the type and size of the recording sheet are different or the electric resistance characteristic of the transfer belt is changed due to environmental changes. An object of the present invention is to provide a belt-forming transfer device capable of obtaining stable transfer performance, and to provide an image forming device having the transfer device.

Another object of the present invention is to provide a transfer device for forming a belt excellent in the performance of separating a recording sheet from a transfer belt after transfer, and an image forming apparatus having the transfer device.

[0013]

To achieve the above object,
The invention according to claim 1 is an endless belt that runs on an image carrier on which a toner image is formed, in a state of being stretched over a plurality of support rollers, in contact with or in proximity to form a transfer portion, A charge supply unit that supplies electric charges to the endless belt, a transfer device that transports a recording sheet to a transfer portion by the endless belt and transfers the toner image on the image carrier to the recording sheet side, All of the support rollers of the endless belt are grounded, and the charge supply means is constituted by a constant current power supply connected to at least one of the support rollers.

According to this means, since all the supporting rollers of the endless belt are in a non-grounded state, a current path such that the electric charge supplied from the constant current power supply as the electric charge supplying means is grounded through the supporting roller. Without being formed, the charge from the charge supply means can be supplied to the endless belt at the transfer position without loss. Further, since the charge supply means is a constant current power supply, the endless belt always has a constant charge (current) even if the type or size of the recording sheet is different or the electric resistance characteristic of the transfer belt is changed due to environmental changes. ) Can be supplied. Furthermore, no control circuit is required. By setting the resistance of the endless belt to an appropriate range by this means, the above-described disadvantages that occur in the transfer belt used in the conventional non-grounded state can be avoided. To the recording sheet. Specifically, regarding the resistance of the endless belt, its volume resistance value is 10 ⁸ to 10 ^10.5 Ω · cm, and its surface resistance is 10 ⁵ to 10 ⁵ .
It is preferable to set so as to fall within the range of 10 ^10.5 Ω. By setting the resistance of the endless belt in this manner, the recording sheet after the transfer is separated from the endless belt by the stiffness of the sheet itself in the curved portion of the endless transfer belt stretched on the support roller. A separating action occurs.

[0015] In the transfer apparatus having this configuration, the outer diameter of the support roller, which is disposed at a position where the recording sheet after the transfer from the endless belt is separated from the endless belt, is determined by the recording sheet itself. It is preferable to set the size in a range in which the endless belt is separated from the endless belt and the endless belt is stretched smoothly.

With this configuration, the recording sheet after transfer can be satisfactorily separated from the endless belt by its own power due to the curvature of the outer peripheral surface of the support roller whose outer diameter is specified. In addition, since the endless belt is maintained in a smooth stretched state by the support rollers, the recording sheet is conveyed to the transfer position in a smooth state, so that transfer unevenness does not occur.

Further, the invention according to claim 3 is an image forming apparatus having the transfer device of each configuration as described above.

According to this means, even if the type or size of the recording sheet changes, good transfer by the transfer device is stably performed, so that the obtained image also has a stable image quality.

[0019]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows an embodiment of an image forming apparatus to which the present invention is applied. In FIG. 1, reference numeral 1 denotes a photosensitive drum as an image carrier, which rotates in the direction of arrow a. Around the photosensitive drum 1, a charger 11 for uniformly charging the surface (photosensitive layer) of the drum, an optical image corresponding to image information is exposed on the charged photosensitive drum 1, and an electrostatic latent image is formed. An image exposure apparatus 12 for forming
A developing device 13 that supplies a developer (toner) to the surface of the photosensitive drum 1 to develop an electrostatic latent image into a toner image; a belt-type transfer device 2 that transfers the toner image to the recording sheet P;
A cleaning device 14 for removing toner and the like remaining on the photosensitive drum 1 after the transfer is provided.

Reference numeral 15 denotes a paper feed tray for stacking and storing the recording sheets P, 15a denotes a feed roller for feeding the recording sheets P one by one from the paper feed tray 15, and 16 denotes a recording roller fed from the paper feed tray 15. The sheet P is transferred between the photosensitive drum 1 and the transfer device 2 (corresponding to a transfer position described later).
A registration roller 17 sends the toner image onto the recording sheet P at a predetermined timing. The dashed line in FIG.
1 shows a transfer route of the first embodiment.

The transfer device 2 includes a transfer belt 20 composed of an endless belt, support rollers 21 and 22 for supporting the transfer belt 20 so as to run in synchronization with the photosensitive drum 1 in a stretched state, and a transfer belt. The main parts thereof are constituted by a constant current power supply 23 for supplying an electric charge (transfer bias) necessary for transfer to the transfer belt 20 so as to have a constant current, and a cleaning blade 24 for removing toner and the like adhering to the transfer belt 20. . The transfer belt 20 includes two support rollers 2
The transfer portion (nip) N is formed by abutting or approaching the photosensitive drum 1 in a state where the transfer portion (nip) N is stretched. Of the two support rollers, the roller 22 is a driving roll. Further, the constant current power supply 23 is connected to the side of the two support rollers 21 and 22 that is disposed on the upstream side in the belt movement direction from the transfer portion N in the belt movement direction.

In the image forming apparatus having such a configuration, an image is formed as follows.

First, after the photosensitive layer of the rotating photosensitive drum 1 is uniformly charged by the charger 11, an optical image or image modulated by converging the reflected light from the original on the charged surface by the image exposure device 12. An optical image composed of a laser beam is irradiated to form an electrostatic latent image. Subsequently, the developing device 13
Supplies the toner and adheres to the electrostatic latent image to form a toner image T. Predetermined recording sheets P are fed one by one from the paper feed tray 15 in synchronization with the timing of forming the toner image T, and sent out toward the transfer position N by the registration rollers 16. At the same time as the supply of the recording sheet P, a predetermined transfer bias is applied to the transfer belt 20 from the constant current power supply 23 via the support roller 21.

As a result, the recording sheet P is sent to the transfer position N while being electrostatically attracted to the transfer belt 20, and the toner image T is electrostatically transferred from the photosensitive drum 1 at the transfer position N. . The recording sheet P to which the toner image T has been transferred is transferred to a transfer belt 2 supported by a support roller 22.
After being separated from the belt and separated at the portion, the toner image T is sent to the fixing device 17 and subjected to a fixing process of the toner image T.
Finally, it is discharged outside the device. Thus, an image is formed.

After the transfer, the photosensitive drum 1 is cleaned by the cleaning device 14. The transfer belt 20 in the transfer device 2 is also cleaned by the cleaning blade 24 after the recording sheet P is separated. By performing the cleaning of the transfer belt 20, it is possible to prevent the toner remaining on the transfer belt 20 from staining the rear surface of the recording sheet that is attracted to the transfer belt at the next transfer.

Next, the following test was performed using this image forming apparatus.

That is, a predetermined current is applied from the constant current power supply 23, and the A4 plain paper, the tracing paper and the OHP sheet as the recording sheet P are passed through the transfer position N in a state where they are attracted to the transfer belt 2, respectively. At this time, the current flowing into the photosensitive drum 1 (corresponding to the transfer current) was measured by an ammeter, and the transferability of the toner image and the separation property of the recording sheet were examined. Further, under these conditions, the image quality of the image formed on each recording sheet when the same density toner image was transferred was examined.

In this test, an organic photosensitive member having an outer diameter of 84 mm was used as the photosensitive drum 1, and the process speed was set to 250 mm / s. Transfer belt 2
0 is a tubular belt base material having a thickness of 0.5 mm and a width of 300 to 330 mm prepared by adding carbon black to chloroprene rubber to a volume resistivity of 10 ^8.9 Ω · cm, and exposing the base material to light. A low friction layer (surface resistance: ^109.4 Ω) made of a fluorine film and having a thickness of about 5 μm was formed on the surface in contact with the drum 1 by a spray coating method. The outer diameter of the support roller 21 is 16
The aluminum roller having an outer diameter of 12 mm was used as the supporting roller 22. The transfer belt 20 is supported by the support rollers 21 and 22.
The belt 20 is stretched and supported only by the elasticity of the belt 20 itself. Elongation rate of belt at this time [｛(belt circumference in stretched state-belt circumference before stretching)
/ The belt circumference in the stretched state｝ × 100] was about 2%. From the constant current power supply 23, +20 μA and +40 μA
A two kinds of currents were applied.

For comparison, a similar test was performed using a conventional transfer device as shown in FIG. In this comparative example, both the support rollers k and j are grounded,
Further, the current application from the constant current power supply 23 is performed when the outer diameter is 10 mm.
Was performed under the same conditions as in the above Example except that the process was performed through the aluminum electrode roller g. Therefore, the transfer belt c and the support rollers k and j are the same as the transfer belt 20 of the present embodiment.
And the supporting rollers 21 and 22 were used.

Table 1 shows the measurement results of the transfer current in this test. In the table, plain paper indicates A4 size plain paper (vertically fed), trepe indicates tracing paper, and OHP indicates OHP sheet.

[0032]

[Table 1]

From the results in this table, in the case of this example, the transfer current of the same numerical value was obtained for the current (20 μA, 40 μA) applied from the constant current power supply 23, and in the case of the comparative example, It was confirmed that a transfer current of a numerical value reduced in each case with respect to the applied current was obtained. Moreover, in the case of the comparative example, the amount of decrease in the transfer current varies depending on the type of the recording sheet, and is particularly halved for the OHP sheet.
It is assumed that the decrease in the transfer current with respect to the applied current in this comparative example corresponds to the amount of current grounded through the support roller as a result of the support roller being grounded.

In the case of this embodiment, any of the recording sheets was conveyed while being stably and smoothly adsorbed to the transfer belt 20, and good transfer was performed. In addition, after the transfer, the recording sheet does not wind around the photosensitive drum 1 and continues to be conveyed while being attracted to the transfer belt 20. (Position 2), the toner was smoothly separated from the belt surface by itself without being attracted to the belt side.
Further, when the images obtained on the respective recording sheets were observed, they were all obtained as images having a constant density, and no defect in image quality was observed.

On the other hand, in the case of the comparative example, particularly the transferability is deteriorated as compared with the case of the present example, and even when the images obtained on the respective recording sheets are observed, a decrease in the density is recognized. Was done. A relatively high-density image was formed on both sides of each recording sheet using a transfer belt having twice or more resistance unevenness in the belt surface as the transfer belt c of the transfer device of this comparative example. In the double-sided image, remarkable density unevenness was recognized corresponding to the change (decrease) of the transfer current. By the way, when the same transfer belt having the uneven resistance was applied to the present example, a good quality image without uneven density was obtained.

Subsequently, a similar test was performed under the same conditions as in the above-described embodiment except that the outer diameter of the downstream support roll 22 in the transfer device of the present embodiment was changed to 14 mm. As good as in the case,
Regarding the separability of the recording sheet, only the tracing paper did not separate on the downstream side of the transfer belt 20, but remained wound around the belt.

A similar test was carried out under the same conditions as in the present embodiment except that the outer diameter of the downstream support roll 22 in the transfer apparatus of the present embodiment was changed to 9 mm. It was confirmed that the transfer belt 20 was warped due to the stretching of the transfer belt 20. When the transfer was performed in this state, the recording sheet was not sufficiently attracted to the transfer belt 20,
Moreover, after the transfer, the photosensitive drum 1 was wound around the surface.

Further, as shown in FIG. 2, except that the constant current power supply 23 in the transfer apparatus of the present embodiment is connected to the support roller 21 in addition to the constant current power supply 23, the same conditions as in the above embodiment are used. As a result of the test, it was confirmed that the same result (effect) as that of the above-described example was obtained.

In the present invention, the material and thickness of the transfer belt 20 are not particularly limited as long as the transfer belt 20 satisfies the mechanical strength required for the belt.
For example, for the material, in addition to the material of the transfer belt used in the above test, a rubber material such as EPDM rubber, NBR rubber, silicon rubber, urethane rubber, or a synthetic resin film made of nylon, Teflon, or the like is used. be able to. However, a rubber material is preferable from the viewpoint of simplifying the configuration of the drive system without slipping when the belt is driven.
As described above, the transfer belt 20 has a volume resistivity of 10 ⁸ to 10 ^10.5 Ω · cm and a surface resistance of 10 ⁵
It is preferably set in a range of to 10 ^10.5 Omega, if this volume resistivity and surface resistivity exceeds the upper limit of the above range is supposed to transfer belt is excessively charged, It is not preferable because it is necessary to provide a static elimination means for eliminating the static electricity.

It is desirable that the transfer belt 20 has a low friction surface layer from the viewpoint of preventing the transfer belt 20 from being stained by toner adhesion on the belt surface during long-term use. This low friction surface layer not only prevents toner from adhering, but also bends when passing through the support roll and prevents the cleaning blade 2 from being bent.
4 is made of a material that is unlikely to cause peeling or cracking due to the rubbing by No. 4. Specifically, in addition to the fluorine of the low friction surface layer in the above-described test, it can be formed of silicon, nylon, high-density polyethylene, or the like. The thickness of the low friction surface layer is not particularly limited as long as it does not impair the original function of the transfer belt. The method of forming the low-friction surface layer is not particularly limited, and is arbitrary. For example, in addition to the above-described spray coating method, an electrostatic coating method, a dip coating method, a roll coating method, and a two-layer forming method. A film method or the like can be applied.

Further, in the present invention, the plurality of support rolls is not limited to the two in the above embodiment, but may be more. In addition, the outer diameter of the support roller, which is provided at a position where the recording sheet after transfer from the transfer belt is separated from the transfer belt, of the plurality of support rolls is such that the recording sheet does not need a peeling unit such as a peeling nail, and the transfer belt is driven by itself. And the transfer belt must have a size within a range in which the transfer belt can be stretched smoothly without wrinkles or slack. For example, the outer diameter of the support roller 22 in the present embodiment is slightly different depending on the elongation rate when the transfer belt 20 is stretched, but may be set in the range of 10 to 13 mm.

[0042]

As described above, according to the transfer apparatus of the present invention, all the support rollers of the endless belt are set to the non-ground state, and the charge supply means is connected to at least one of the support rollers. Since it is configured with a constant current power supply, stable transfer performance can always be obtained even if the conditions such as the type and size of the recording sheet are different or the electrical resistance characteristics of the transfer belt are changed due to environmental changes. Also,
Since a control circuit unlike the related art is not required to obtain such good transfer performance, unnecessary cost increase does not occur. Further, when the resistance of the endless belt is set in an appropriate range, there is no need to provide a static eliminator for eliminating the static electricity of the belt, so that unnecessary cost increase can be prevented.

The outer diameter of a support roller disposed at a position where the recording sheet after transfer from the endless belt is separated is
When the recording sheet is separated from the endless belt by itself and is set to a dimension within which the endless belt is stretched smoothly, good separation performance of the recording sheet from the transfer belt after transfer is obtained. In addition, transfer unevenness does not occur when the recording sheet is conveyed on the belt in a smooth state. Thus, there is no need to provide a recording sheet peeling unit, and this can also prevent unnecessary cost increase.

Further, according to the image forming apparatus of the present invention, since the image forming apparatus has the transfer device capable of obtaining the above-described effects, the image quality is deteriorated due to the difference in the type and size of the recording sheet and the difference in the environmental conditions. No good images can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a configuration of an image forming apparatus and a transfer device according to an embodiment of the present invention.

FIG. 2 is a schematic diagram illustrating a configuration of a transfer device according to another embodiment of the present invention.

FIG. 3 is a schematic diagram illustrating an example of a conventional transfer device.

FIG. 4 is a schematic diagram illustrating another example of a conventional transfer device.

FIG. 5 is a schematic diagram illustrating another example of a conventional transfer device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum (image carrier), 2 ... Transfer device, 20 ... Transfer belt (endless belt), 21, 22 ... Support roller,
23: constant current power supply (charge supply means), T: toner image, N
... Transfer site, P ... Recording sheet.

Claims (3)

[Claims] An endless belt that runs so as to form a transfer portion in contact with or close to an image carrier on which a toner image is formed while being stretched over a plurality of support rollers; A charge supply means for supplying a charge to a belt, wherein the endless belt conveys a recording sheet to a transfer portion and transfers a toner image on the image carrier to the recording sheet side, wherein the endless belt A transfer device, wherein all the support rollers of the belt are in a non-ground state, and the charge supply means is constituted by a constant current power supply connected to at least one of the support rollers. 2. The recording sheet according to claim 1, wherein the outer diameter of the supporting roller disposed at a position where the recording sheet after transfer from the endless belt is separated from the endless belt is separated from the endless belt by itself. 2. The transfer device according to claim 1, wherein the size of the endless belt is set within a range in which the endless belt is stretched smoothly. 3. An image forming apparatus comprising the transfer device according to claim 1.