JP3187209B2 - 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 a copying machine, an LB
The present invention relates to an electrophotographic or electrostatic recording type image forming apparatus such as P, facsimile or the like.

[0002]

2. Description of the Related Art Conventionally, a color image forming apparatus which includes a plurality of image forming units, forms toner images of different colors in each image forming unit, and sequentially superimposes and transfers the toner onto the same recording material. Various image forming apparatuses have been proposed. Among these color image forming apparatuses, an electrophotographic method of forming a multicolor image by applying a transfer bias from the back side of the transfer sheet by a charging unit while adsorbing and transporting the recording material onto the transfer sheet is well known.

An example of such an electrophotographic color image forming apparatus will be described with reference to FIG. The apparatus body includes first, second, third, and fourth image forming units Pa, P
b, Pc, and Pd are provided side by side, and each image forming section has an electrophotographic photosensitive drum 1a, 1
b, 1c and 1d are provided.

On the outer periphery of the photosensitive drums 1a, 1b, 1c and 1d, latent image forming units 2a, 2b, 2c and 2d, and a developing unit 3
a, 3b, 3c, 3d, and cleaning units 5a, 5
b, 5c and 5d are provided respectively. Further, a transfer sheet 8 as a transporting means for transporting the recording material 6 to each transfer position is disposed below each of the image forming units Pa, Pb, Pc, and Pd, and inside each of the photosensitive drums 1a, 1b, and 1d.
Transfer portions 4a, 4b, 4c, and 4d are arranged to face c and 1d.

In this configuration, first, a latent image of a cyan component color is formed on the photosensitive drum 1a of the first image forming unit Pa by the latent image forming unit 2a based on image information read from an image reader (not shown). The latent image is a developing unit 3a
Is made visible with a developer having cyan toner, and the cyan toner image is transferred to the recording material cassette 6 in the transfer section 4a.
The image is transferred by applying an appropriate transfer voltage to the recording material 6 fed from 0 through the registration roller 13.

On the other hand, while the cyan toner image is being transferred to the recording material 6 in the transfer section 4a, a magenta component color latent image is formed on the photosensitive drum 1b in the second image forming section Pb, and subsequently developed. The magenta toner image converted to a visible image by the unit 3b is transferred onto the recording material 6 at a predetermined position when the recording material 6 after the transfer in the first image forming unit Pa is carried into the transfer unit 4b. .

[0007] Similarly, the third and fourth image forming units P
At c and Pd, yellow and black images are formed, and yellow and black toner images are further transferred onto the same recording material 6 in a superimposed manner.

After the above-described image forming process is completed, the image on the recording material 6 is fixed on the recording material 6 by the fixing unit 7, and a multicolor image is completed. On the other hand, each of the photosensitive drums 1 whose transfer has been completed
a, 1b, 1c and 1d are cleaning units 5a, 5b and 5
In steps c and 5d, the residual toner is removed to prepare for the subsequent latent image formation.

Here, the transfer sheet 8 may be a polyethylene terephthalate resin film sheet (PET sheet),
It is a film made of a dielectric resin such as a polyvinylidene fluoride resin film sheet or a carbon-dispersed polycarbonate resin film sheet, and its both ends are overlapped and joined to each other to form an endless shape or have no seams ( (Seamless) belt shape is used.

In the above image forming process, the transfer of the toner image to the recording material 6 at the transfer section is performed as follows.
That is, as shown in FIG. 7, the toner forming the toner image on the photosensitive drum 1 has a negative charge and is attracted to the positively charged photosensitive drum 1. Here, in order to transfer the toner image onto the recording material 6, the charging unit 4 is charged from the back side of the transfer sheet 8 to a positive potential higher than the potential of the photosensitive drum 1. Is attracted to the charging means 4 side, and is transferred onto the recording material 6 between the photosensitive drum 1 and the charging means 4. However, in practice, not all of the toner is transferred, and there is a process in which residual toner remains on the photosensitive drum 1 and is removed by the cleaning unit.

As the transfer charging system, there are known a non-contact charging type by corona discharge using a non-contact wire or the like, and a contact charging type in which a charging means is brought into contact with the transfer sheet to discharge.

The non-contact charging type has an advantage that the charging means is hardly affected by stains on the transfer sheet because the charging means is not in contact with the transfer sheet.
Since the corona discharge is performed in the air, there is a disadvantage that the discharge stability is poor due to the influence of environmental changes such as ambient temperature and humidity.
₃ ) Since it generates nitrogen oxides (NOx), it is not desirable from the viewpoint of environmental conservation.

On the other hand, in the contact charging type, the charging means is constantly in contact with the transfer sheet during transfer, so that the ambient temperature,
It is excellent in stability against environmental changes such as humidity, and has the advantage that generation of ozone, nitrogen oxides, etc. is extremely small because there is no corona discharge.

However, in the contact charging type, since the charging means is always in contact with the back side of the transfer sheet, it deteriorates due to long-time use, foreign matter 9 adheres as shown in FIG.
For some reason, such as a mistake in mounting the charging unit and the transfer sheet, the resistance value between the charging unit and the transfer sheet may be larger than in a normal state. In such a case, the charging unit is charged to a potential higher than a normal state, and when a certain potential is exceeded, a spark discharge may be generated toward the photosensitive drum.

At this time, if the material of the transfer sheet is, for example, carbon-dispersed polycarbonate, the path through which the spark discharge has passed in the transfer sheet is melted by the heat due to the discharge, and then the temperature drops sharply as shown in FIG. Hole 10
Can be. At the same time, carbon is deposited on the inner wall of the hole 10,
The inner wall portion of the hole 10 becomes conductive. As a result, the electric resistance becomes lower than that of the other parts, and this state is maintained thereafter.

[0016]

In order to extend the durable life of such a charging means, there is also a system having means for separating the charging means from the transfer sheet. In this method, when the transfer is not performed, the charging unit is separated from the transfer sheet, and only when the transfer is performed, the charging unit is brought into contact with the transfer sheet. . However, even in the case of this method, when the transfer is performed, the charging unit and the transfer sheet may not be normally contacted for some reason. Spark discharge.

As a result, as described above, the electric resistance of the path through which the spark discharge has passed in the transfer sheet is much smaller than that of other normal portions.

In a normal discharge, as shown in FIG. 9, since the dielectric constant of the transfer sheet 8 is uniform, the discharge to the photosensitive drum 1 is also performed uniformly. As a result, the transfer to the recording material 6 is also performed. Normally done.

However, when the resistance value becomes smaller than that of the surroundings due to the spark discharge as described above, FIG.
As shown in (1), during the transfer, the discharge to the photosensitive drum 1 is not uniform, and the discharge is concentrated at once from the hole 10 which is the spark discharge path.

As a result, a sufficient potential difference between the photosensitive drum and the charging means does not occur, so that no suction force is generated toward the charging means in the spark discharge path, and the toner image on the photosensitive drum is normally applied to the recording material 6. Will not be transferred.

In this state, the transferred image on the recording material has a circular portion having a diameter of about 100 to 800 μm, which is a ground color portion of the recording material on which the toner is not transferred, and has a problem of deteriorating the image quality.

Further, it is known that the above-described spark discharge has an adverse effect on the photosensitive layer of the photosensitive drum, and there is a problem of shortening the life of the photosensitive drum.

Accordingly, it is an object of the present invention to provide an image forming apparatus provided with a transfer device in which spark discharge does not occur during transfer.

[0024]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
A latent image carrier on which a latent image is formed, transport means for transporting a recording material facing the latent image carrier, and a recording material and the transport means interposed between the latent image carrier and the latent image carrier; An image forming apparatus having a charging unit arranged to be in contact with the conveying unit, wherein a ground wire is connected to the charging unit via an electric resistor, and a resistance value of the electric resistor is:
The image forming apparatus is characterized in that the resistance is set to be larger than the resistance value between the charging unit and the latent image carrier.

[0025]

According to another aspect of the present invention, a latent image carrier on which a latent image is formed, transport means for transporting a recording material facing the latent image carrier, and the latent image carrier And a charging unit disposed so as to be in contact with the conveyance unit with the recording material and the conveyance unit interposed therebetween, wherein a ground wire is connected to the charging unit via an electric resistor. The resistance value of the electrical resistor is set to be larger than a normal resistance value between the charging unit and the latent image carrier and smaller than an abnormal resistance value. An image forming apparatus is provided.

Preferably, the charging means is configured to be able to arbitrarily select a contact / non-contact state with the transport means.

Preferably, the image forming apparatus has means for detecting a current flowing through the electric resistor.

[0029]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of an image forming apparatus according to the present invention. In the embodiments described below, the present invention is described as being embodied in the electrophotographic color image forming apparatus shown in FIG. Therefore, a detailed description of the overall configuration and functions of the color image forming apparatus will be omitted, and features of the present invention will be described.

In FIG. 1, which schematically shows a transfer section, a transfer sheet 8 as a means for conveying a recording material is movably arranged so as to face the photosensitive drum 1 as a latent image carrier. The transfer sheet 8 is made of a carbon-dispersed polycarbonate resin, and a sheet 6 as a recording material is carried on the surface thereof. The transfer brush 4 serving as a charging unit is disposed in contact with the back surface of the transfer sheet 8. A ground wire 90 for grounding is electrically connected to the transfer brush 4 via a resistor 20 having a resistance value R. It should be noted that foreign matter 15 of an electrically negligible degree may adhere to the surface of the transfer sheet 8, and in FIG.
2 shows a state in which the transfer sheet 8 is in contact with the transfer sheet 8 via the.

As shown in FIG. 1, an electrostatic latent image (+ a) formed of a positive charge is carried on the photosensitive drum 1, and a negative charge is applied thereto by developing means (not shown). The toner T is absorbed and a toner image is formed.

In order to transfer the toner image onto the sheet 6, the toner T is uniformly discharged from the back side of the transfer sheet 8 onto the photosensitive drum 1 with a positive potential greater than the potential on the surface of the photosensitive drum 1 to expose the toner T to the photosensitive drum 1. The toner image is attracted to the sheet 6 by overcoming the suction force to the drum 1, and the toner image is transferred onto the sheet 6.

The discharge inside the transfer sheet 8 made of carbon-dispersed polycarbonate resin is, for example, as shown in FIG. That is, a positive charge q is applied from the back side (the lower side in the figure) of the transfer sheet 8 by the transfer brush.
Is given, the positive charge q moves in the direction of the dotted arrow in the drawing via the carbon atoms 12 in the transfer sheet 8,
Discharge is performed on the front side (upper side in the figure) of the transfer sheet 8.

The transfer brush 4 is normally in contact with the transfer sheet 8 at its leading end. At this time, the electric resistance value r between the transfer brush 4 and the photosensitive drum 1 sandwiching the transfer sheet 8 and the paper 6 and the ground The resistance value R of the resistor 20 connected to the line 90 satisfies the relationship of r <R, and electricity does not flow to the resistor 20 side but discharges normally to the photosensitive drum 1 side.

However, as shown in FIG. 3, the foreign matter 3 that cannot be electrically ignored between the transfer sheet 8 and the transfer brush 4
When 0 is sandwiched, the electric resistance value r ′ between the transfer brush 4 and the photosensitive drum 1 and the negligible foreign matter 1
The relationship between the electric resistance value r between the transfer brush 4 and the photosensitive drum 1 when there is no 5 is r <r ′. If the current continues to flow through the transfer brush 4 even when the foreign matter 30 that cannot be ignored is sandwiched in this way, positive charges accumulate in the transfer brush 4 and the potential on the back side of the transfer sheet 8 gradually increases. When this state continues, the transfer brush 4
If the ground wire is not connected to the transfer sheet 8
Spark discharge occurs in a part of the surface.

On the other hand, in the case of this embodiment, the transfer sheet 8
Even if the high potential state on the back side continues, the ground wire 90 is connected to the transfer brush 4 via the resistor 20, and the resistance value R is set so as to satisfy r <R and r ′> R. This allows electricity to flow through resistor 20 to ground before spark discharge occurs.

Further, as shown in FIG. 4, one end is connected to the transfer brush 4, and the other end is provided with a tension spring 12 fixed to the apparatus main body. Even in the case where both the contact state with the sheet 8 and the non-contact state indicated by the broken line can be taken, the transfer brush 4 is grounded via the resistor 20 having the predetermined resistance value R in the same manner as described above. The wires 90 are preferably connected.

When the transfer brush 4 is configured to be selectable between contact and non-contact as described above, for example, when the transfer brush 4 must be at a position indicated by a solid line, a broken line due to a defect of a movable portion of the transfer brush 4 is used. In the position shown by
A state in which the transfer brush 4 does not contact the transfer sheet 8 may occur. At this time, the space between the transfer brush 4 and the transfer sheet 8 is filled with air as a dielectric, and the photosensitive drum 1 and the transfer brush 4
The resistance value r between them increases, and the possibility of spark discharge increases. However, since the electricity on the back side of the transfer sheet 8 can be passed to the ground via the resistor R as described above, spark discharge can be prevented.

The resistance value r between the transfer brush 4 and the photosensitive drum 1 increases when the foreign matter 30 is interposed between the transfer brush 4 and the photosensitive drum 1, as described above. In addition, even if the contact area is reduced due to settling, the contact area increases. Even in such an abnormal state, it is possible to prevent spark discharge to the photosensitive drum by adopting the configuration shown in this embodiment.

Accordingly, it is possible to stabilize the quality of the transferred image, improve the image quality, and extend the life of the transfer sheet and the photosensitive drum.

Next, another embodiment of the image forming apparatus according to the present invention will be described with reference to FIG. 5, which schematically shows a transfer device.

This embodiment has substantially the same configuration as the above embodiment shown in FIG. 1, and an ammeter 14 as a current detecting means is connected to a ground wire 90 connecting the transfer brush 4 and the resistor 20.
The feature is that it is interposed. The ammeter 14 can detect the value of the current flowing to the ground via the resistor 20 when the transfer brush 4 is in an abnormal state. In addition, the ammeter 14
Since it is assumed that a large current suddenly flows, it is desirable that the capacitor has a sufficiently large electric capacity.

When an abnormal current flows through the ammeter 14, it is possible to recognize that some abnormality has occurred in the transfer device of the image forming apparatus, and it is also possible to determine to some extent the type of abnormal state based on the current value. .

For example, when the current value is slightly increasing from the normal value, the transfer sheet 8 or the transfer brush 4
Can be inferred to be dirty, and the user of the main body apparatus can be instructed to take appropriate measures such as cleaning the transfer sheet 8 and the transfer brush 4. When the current value increases sharply, it is assumed that the electrical contact between the transfer sheet 8 and the transfer brush 4 is suddenly cut off. At this time, by temporarily stopping the transfer high-voltage power supply and the image forming sequence and displaying an error, it is possible to prevent damage to portions other than the transfer portion even in the worst case, fire, and the like.

Instead of the ammeter, a simple means such as a switch which operates only when a predetermined current value is exceeded and cuts off the current may be used as the current detecting means. In this case, the high-voltage power supply is shut off in conjunction with the operation of the switch,
By configuring such that the operation of the apparatus main body is stopped, the worst situation such as the above-described fire can be prevented.

In the description of the above embodiment, the present invention has been described as being embodied in an electrophotographic color image forming apparatus as shown in FIG. The present invention can be applied to all image forming apparatuses that perform transfer charging by contacting the image forming apparatus.

[0047]

As is apparent from the above description, the present invention relates to a latent image carrier on which a latent image is formed, and a conveying means for conveying a recording material opposite the latent image carrier. An image forming apparatus comprising: a charging member disposed so as to be in contact with a conveying device with a recording material and a conveying device interposed between the recording material and the latent image carrier; B. A ground wire is connected to the charging means via an electric resistor, and the resistance value of the electric resistor is set to be larger than the resistance value between the charging means and the latent image carrier; A ground wire is connected to the charging means via an electric resistor, and the resistance value of the electric resistor is larger than the normal resistance value between the charging means and the latent image carrier, and the resistance value in the abnormal state. Since the configuration is set to be smaller than the value, even if the possibility of spark discharge occurs, it is possible to prevent spark discharge beforehand by being able to flow electricity to the ground via an electrical resistor Can be. As a result, the quality of the transferred image can be stabilized, the image quality can be improved, and the life of the transfer sheet and the latent image carrier can be extended.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an embodiment of a transfer unit of an image forming apparatus according to the present invention.

FIG. 2 is an explanatory diagram showing a discharge state in the transfer sheet of FIG.

FIG. 3 is an explanatory view showing a state in which a foreign substance is interposed between a transfer brush and a transfer sheet in the transfer section of FIG. 1;

FIG. 4 is an explanatory diagram showing a state in which the transfer brush of FIG. 1 is configured to be able to select contact or non-contact with a transfer sheet.

FIG. 5 is an explanatory view showing another embodiment of the transfer section of the image forming apparatus according to the present invention.

FIG. 6 is an overall configuration diagram illustrating an example of an electrophotographic color image forming apparatus.

FIG. 7 is an explanatory diagram illustrating a transfer unit of a conventional image forming apparatus.

FIG. 8 is an explanatory diagram showing a state in which a spark discharge path has occurred in the transfer unit of FIG. 7;

FIG. 9 is an explanatory diagram showing a normal discharge state.

FIG. 10 is an explanatory diagram showing a spark discharge state.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photosensitive drum (latent image carrier) 4 transfer brush (charging means) 6 paper (recording paper) 8 transfer sheet (transporting means) 10 holes 15 electrically negligible foreign substances 20 electrical resistor 30 foreign substances that cannot be electrically negligible T toner (developer)

Claims (4)

(57) [Claims] 1. A latent image carrier on which a latent image is formed, a transport unit for transporting a recording material facing the latent image carrier,
An image forming apparatus comprising: a charging member disposed so as to be in contact with the conveyance unit with the recording material and the conveyance unit sandwiched between the latent image carrier and the latent image carrier; An image forming apparatus, wherein a resistance value of the electric resistor is set to be larger than a resistance value between the charging unit and the latent image carrier. 2. A latent image carrier on which a latent image is formed, a conveying unit for conveying a recording material facing the latent image carrier,
An image forming apparatus comprising: a charging member disposed so as to be in contact with the conveyance unit with the recording material and the conveyance unit sandwiched between the latent image carrier and the latent image carrier; A ground wire is connected, and a resistance value of the electric resistor is larger than a normal resistance value between the charging unit and the latent image carrier,
In addition, the image forming apparatus is set to be smaller than the resistance value at the time of abnormality. 3. The image forming apparatus according to claim 1, wherein the charging unit is configured to be able to arbitrarily select a contact state or a non-contact state with the transport unit. 4. An image forming apparatus according to claim 1, further comprising means for detecting a current flowing through said electric resistor.