JP3335065B2 - 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 image forming apparatus used for a laser printer, a copying machine, a laser facsimile and the like.

[0002]

2. Description of the Related Art Conventionally, a toner is attached to an electrostatic latent image formed on a photosensitive drum and developed, and this toner image is
2. Description of the Related Art There is an image forming apparatus that transfers an image onto a transfer sheet wound around a transfer drum.

Such an image forming apparatus is, for example, shown in FIG.
As shown in FIG. 5, a corona charger 102 for adsorbing a transfer sheet P inside a cylinder 101 having a dielectric layer 101a,
A corona charger 104 for transferring the toner image formed on the surface of the photosensitive drum 103 to the transfer sheet P is separately provided, and the attraction and transfer of the transfer sheet P are separately performed by each charger 102. It is supposed to do.

Further, as shown in FIG. 14, a cylinder 2 having a two-layer structure of an outer semiconductive layer 201a and an inner substrate 201b is provided.
01 and a gripping mechanism 202 for holding the transferred transfer sheet P along the cylinder 201. In this image forming apparatus, after the conveyed transfer sheet P is gripped by the gripping mechanism 202 at its end and is made to follow the surface of the cylinder 201, a voltage is applied to the outer semiconductive layer 201 a of the cylinder 201. Alternatively, the surface of the cylinder 201 is charged by discharging by a charger provided inside the cylinder 201, and the photosensitive drum 1 is charged.
The toner image No. 03 is transferred to the transfer sheet P.

However, in the image forming apparatus shown in FIG. 13, since the cylinder 101 as the transfer roller has a single-layer structure of only the dielectric layer 101a, the above-described corona chargers 102 and 104 are disposed inside thereof. There is a need to. For this reason, the size of the cylinder 101 is limited, and there is a problem that the size of the apparatus cannot be reduced.

In the image forming apparatus shown in FIG. 14, the cylinder 201 for transferring a toner image onto the transfer sheet P is charged by forming the cylinder 201 as a transfer roller into a two-layer structure. The number of chargers is small. However, the provision of the grip mechanism 202 complicates the configuration of the entire image forming apparatus, thereby increasing the number of components of the entire apparatus and increasing the cost of manufacturing the apparatus. I have.

Therefore, as an image forming apparatus for solving the above-mentioned problems, for example, Japanese Patent Application Laid-Open No. 2-74975 discloses a transfer drum having a conductive rubber and a dielectric film laminated on a grounded metal roll. In some cases, a corona charger driven by a unipolar power supply is provided near a sheet peeling position.

In the above-described image forming apparatus, electric charges are induced in the dielectric film by the corona charger, and the transfer sheet is attracted to the transfer drum. Further, when the transfer sheet is attracted, electric charge is further induced, and transfer is performed.

Therefore, according to the above-described image forming apparatus, the surface of the transfer drum is charged by one charger, and the transfer sheet is attracted and transferred, so that only one charger is required. The size of the drum can be reduced. Further, a mechanism such as the above-described grip mechanism 202 for holding the transfer sheet is not required, and the transfer sheet can be sucked with a simple structure.

[0010]

However, in the image forming apparatus disclosed in the above publication, the surface of the transfer drum is charged by air discharge from a corona charger. Therefore, in the case of color printing, that is, in the case where the transfer process is performed a plurality of times, the charge is supplied by the corona charger each time one transfer is completed. Therefore, a charging unit including a unipolar power supply for controlling the driving of the corona charger is required, and the number of components of the apparatus increases. As a result, there is a problem that the cost for manufacturing the device increases.

Further, if the surface of the transfer drum is flawed, the electric field region becomes small by charging by aerial discharge, the electric field balance is disturbed at the above-mentioned flaws, and poor transfer such as white spots occurs at that part, resulting in poor image quality. Causes a decrease in

Further, since the surface of the transfer roller is charged by air discharge, the voltage required for charging becomes large, and the driving energy of the image forming apparatus increases. Furthermore, since air discharge is easily affected by the environment such as the humidity of the air, the surface potential of the transfer roller tends to vary,
There is a problem that poor transfer sheet sticking and print bleeding are likely to occur.

Further, the transfer efficiency differs depending on the type of the transfer sheet even when the same voltage is applied. That is, for example, when the transfer sheet is a synthetic resin sheet for OHP, the transfer efficiency is good even when the applied voltage is high, but when the applied voltage is too high, the transfer efficiency tends to deteriorate. Furthermore, since the transfer efficiency changes depending on the humidity, it is necessary to control the applied voltage according to the humidity in order to perform the transfer efficiently.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and has as its object to maintain the surface potential of a transfer device such as a transfer roller uniformly and stably with a simple configuration.
Thus, an image forming apparatus capable of eliminating defective suction of the transfer sheet to the transfer device and defective transfer of the toner image to the transfer sheet, improving the image formed on the transfer sheet, and efficiently performing the transfer can be provided. To provide.

[0015]

Means for Solving the Problems An image forming apparatus comprising an image carrier on which a toner image is formed on the surface (e.g., photosensitive drum), abut against the transfer sheet to the image carrier by, transfer means for transferring the toner image formed on said image bearing member (e.g., transfer drum) in the image forming apparatus having the above-mentioned transfer means, the nip width between the image carrier 2mm~ 7 mm, from the contact surface side of the transfer sheet, for example, a dielectric layer having a thickness of 100 μm to 300 μm made of polyvinylidene fluoride, for example, a semiconductive layer having a thickness of 2 mm to 5 mm made of urethane foam, and aluminum, for example. Conductive layers are sequentially stacked, and the volume resistivity of the semiconductive layer is 10 ⁶ Ω · cm.
10 25 range and hardness of ¹⁰ Omega · cm is Asker C
And the volume resistivity of the dielectric layer is 1
Be in the range of ^{0 9 Ω · cm~10 13 Ω ·} cm, the voltage applying means for applying a predetermined voltage to the conductive layer (e.g., a DC power source) and, upstream from the transfer position of the dielectric layer surface on the surface side, the transfer sheet by contacting through the transfer sheet which has an electrode member which is grounded is adsorbed on the surface of the dielectric layer (e.g., a conductive roller), the above voltage application means, and the transfer means 1,0
It is characterized in that a voltage in the range of 00 V to 2,500 V is applied.

According to a second aspect of the present invention, there is provided an image forming apparatus.
In addition to the above configuration, the transfer sheet is paper. According to a third aspect of the present invention, in addition to the structure of the first or second aspect , the image forming apparatus further comprises a transfer means for transferring the image data to the image forming apparatus.
It is characterized in that a voltage in the range of 00 V to 2,000 V is applied.

According to the first and second aspects of the present invention, the voltage applying means applies a predetermined voltage to the conductive layer, and the electrode member is provided on the surface of the dielectric layer on the upstream side from the transfer position via the transfer sheet. Contact, the charge of the same polarity as the polarity of the voltage applied to the conductor layer is accumulated in the semi-conductor layer,
Further, charges having the same polarity are also induced on the surface of the dielectric layer and the transfer sheet pressed against the surface of the dielectric layer. That is, a charge having a polarity opposite to the polarity of the voltage applied to the conductor layer is induced on the back surface of the transfer sheet in contact with the dielectric layer. With this, simply applying a voltage to the conductor layer,
The transfer sheet can be electrostatically attracted to the surface of the dielectric layer, that is, the surface of the transfer means, and has a predetermined difference between the electric potential of the transfer sheet surface and the electric potential of the toner image on the image carrier surface. Is provided, the toner image can be transferred to the transfer sheet.

Thus, the transfer sheet is not attracted and transferred by charge injection by air discharge as in the prior art, but is carried out by attracting and transferring the transfer sheet by inducing electric charges. Easy to control. In addition, it is possible to eliminate voltage variations due to external pressure.

Therefore, the voltage applied to the transfer means can be kept constant without being affected by the environment such as humidity and temperature, so that the transfer efficiency can be improved and the image quality can be improved.

Further, the above-mentioned voltage applying means may be arranged so that the volume resistivity of the semiconductive layer is in the range of 10 ⁶ Ω · cm to ^{10 10} Ω · cm, the hardness of Asker C is in the range of 25 to 50 , and
The volume resistivity of the dielectric layer is 10 ⁹ Ω · cm to 10 ¹³ Ω · c
m and the transfer means is 1,000 V to 2.5
By applying a voltage in the range of 00 V, transfer efficiency can be improved, especially when the transfer sheet is paper.
When the transfer sheet is paper, the transfer efficiency depends on the applied voltage. However, for example, when the transfer sheet is a synthetic resin sheet for OHP, the transfer efficiency hardly depends on the applied voltage regardless of the volume resistivity of the semiconductive layer or the dielectric layer.

Therefore, the volume resistivity of the semiconductive layer is 10 ⁶
Asker with hardness in the range of Ω · cm to 10 ¹⁰ Ω · cm
In the range of 25 to 50 in C, and and the volume resistivity of the dielectric layer is in the range of ^{10 9 Ω · cm~10 13 Ω ·} cm,
By applying a voltage in the range of 1,000 V to 2,500 V to the transfer unit, transfer can be performed efficiently whether the transfer sheet is paper or a synthetic resin sheet for OHP. That is, when the transfer sheet is a synthetic resin sheet for OHP, the applied voltage can be determined so as to be advantageous for paper adsorption. Further, when the transfer sheet is paper, the transfer efficiency can be improved. Further, the transfer efficiency can be further improved by applying a voltage within the range of 1,500 V to 2,000 V to the transfer means.

[0022]

[0023]

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS.

FIG. 2 shows an image forming apparatus according to this embodiment.
As shown in FIG. 1, a paper feed unit 1 for stocking and supplying a transfer sheet P (see FIG. 1) as a recording sheet on which an image is formed with toner, a transfer unit 2 for transferring a toner image to the transfer sheet P, and a toner image Developing unit 3 to be formed and transfer sheet P
Fixing unit 4 for fusing and fixing the toner image transferred to
It is composed of

In the sheet feeding section 1, the transfer section 2 is provided detachably at the lowermost stage of the main body and stocks the transfer sheet P.
And a manual feed unit 6 which is provided on the front side of the main body and manually feeds the transfer sheets P one by one from the front side. A pick-up roller 7 that feeds out the sheets, a PF roller 8 that conveys the transfer sheet P sent out by the pick-up roller 7, a manual feed roller 9 that conveys the transfer sheet P from the manual feed unit 6, the PF roller 8, and the manual feed roller 9 A pre-curl roller 10 for curling the transfer sheet P conveyed by the printer is provided.

The feed cassette 5 is provided with a feed member 5a urged upward by a spring or the like, and the transfer sheets P are stacked on the feed member 5a. Thereby, the transfer sheet P in the sheet cassette 5 is
The uppermost portion is in contact with the pickup roller 7 and the PF is rotated one by one by rotating the pickup roller 7 in the direction of the arrow.
The sheet is sent to the roller 8 and is conveyed to the pre-curl roller 10.

On the other hand, the transfer sheet P supplied from the manual supply unit 6 is also
Transported to zero.

The pre-curl roller 10 curls the transfer sheet P conveyed as described above. This is because the transfer sheet P is attracted to the surface of the cylindrical transfer drum 11 provided in the transfer section 2. This is to make it easy to be performed.

The transfer section 2 is provided with a transfer drum 11 as the above-described transfer means. Around the transfer drum 11, a conductive roller 12 made of a conductive member as a grounded electrode member is provided. A guide member 13 for guiding the transfer sheet P so as not to fall off the transfer drum 11;
A peeling claw 14 for forcibly peeling off the transfer sheet P attracted to the transfer drum 11 is provided. The transfer drum 11 is configured to adsorb the transfer sheet P on the surface by static electricity. Therefore, around the transfer drum 11, there is further provided a charge removing device 11 a as a charge removing unit for removing charges charged on the surface of the transfer drum 11, and a cleaning device as a cleaning unit for removing toner and the like attached to the surface of the transfer drum 11. 11b is provided. The peeling claw 14 is provided on the surface of the transfer drum 11 so as to be able to freely contact and separate. The details of the structure of the transfer drum 11 will be described later.

The developing unit 3 includes the transfer drum 11
A photosensitive drum 15 is provided as an image carrier that is in pressure contact with the photosensitive drum. The photosensitive drum 15 is formed of a grounded conductive aluminum tube 15a, and has an OPC on its surface.
The film 15b (FIGS. 8 and 9) is applied.

Further, around the photosensitive drum 15,
Developing devices 16, 17, 18, and 19 containing yellow, magenta, cyan, and black toners are radially arranged, and a charger 2 that charges the surface of the photosensitive drum 15.
A cleaning blade 21 for scraping and removing the residual toner on the surface of the photosensitive drum 15 is provided, and a toner image is formed on the photosensitive drum 15 for each toner. That is, according to the photosensitive drum 15, charging, exposure, development, and transfer are repeated for each color.
Therefore, in the case of the color transfer, the toner image of one color is transferred to the transfer sheet P every time the transfer drum 11 makes one rotation with respect to the transfer sheet P electrostatically attracted to the transfer drum 11, and the transfer sheet P is rotated up to four times. One color image is obtained.

The photosensitive drum 15 and the transfer drum 11 are pressed against each other so that a pressure of 8 kg is applied at the transfer portion from the viewpoint of transfer efficiency and image quality.

Further, the fixing unit 4 fuses the toner image at a predetermined temperature and pressure to fix it to the transfer sheet P. After the toner image is transferred, the toner image is peeled off from the transfer drum 11 by the peeling claw 14. A fixing guide 22 for guiding the transfer sheet P to the fixing roller 23 is provided.

A discharge roller 24 is provided on the downstream side of the transfer of the transfer sheet P from the fixing unit 4, and discharges the transfer sheet P after fixing from the apparatus main body onto a discharge tray 25.

Here, the structure of the transfer drum 11 will be described. As shown in FIG. 1, the transfer drum 11 uses a cylindrical conductive layer 26 made of aluminum as a base material, and has a semiconductive layer 27 made of elastic urethane foam on the upper surface of the conductive layer 26. Is provided.

Further, on the upper surface of the semiconductive layer 27,
A dielectric layer 28 made of polyvinylidene fluoride is provided.

A power supply unit 32 as a voltage applying means is connected to the conductor layer 26.
, A stable voltage is maintained over the entire circumference.

The above layers 26, 27 and 28 are not bonded by an adhesive or the like. For example, as shown in FIG. 3, the semiconductive layer 27 and the dielectric layer 28 are formed in a sheet shape. Bosses 30a provided on the sheet holding plate 30 are fitted into a plurality of through holes 29 penetrating each layer provided at both ends, and the bosses 30a are provided on the upper surface of the conductor layer 26. The semiconductive layer 27 and the dielectric layer 28 are fixed to the conductive layer 26 by being fitted into the openings 26a.

In the fixing method described above, the semiconductive layer 27 and the dielectric layer 28 are tensioned on the inner side of the conductive layer 26 by the sheet presser plate 30. It is designed to prevent loosening.

Further, since each of the above layers is merely fixed by the sheet holding plate 30, each layer can be easily replaced.

In addition to the above fixing method, for example, as shown in FIG.
There is a method of fixing a sheet including the semiconductive layer 27 and the dielectric layer 28 to the conductive layer 26 by the sheet pressing member 31 provided with 1b. In this fixing method, the fitting holes 2 provided at both ends of the opening 26a of the conductor layer 26 are provided.
6b, the bosses 31a of the sheet pressing member 31 described above.
And the fixing member 31b of the sheet pressing member 31 is inserted into the opening 26a to fix the sheet composed of the semiconductive layer 27 and the dielectric layer 28 to the conductive layer 26. .

Even if each layer is fixed by such a method, each layer can be easily replaced as described above.

[0044]

[0045]

[0046]

[0047]

Further, the conductive roller 12 is used for the transfer drum 1.
The transfer sheet P is passed between the first roller 1 and the conductive roller 12, and at the same time, is pressed against the transfer drum 11 via the transfer sheet P. Then, a voltage is applied to the transfer drum 11 and charging of the transfer sheet P is started.

The charging of the transfer sheet P is continued until the transfer sheet P makes one rotation of the transfer drum 11. After the charging of the transfer sheet P is completed, the conductive roller 12
Are separated from the transfer drum 11.

The operation of separating and moving the conductive roller 12 to and from the transfer drum 11 is performed by connecting a solenoid 12b (FIG. 1) as an electrode member driving means to both ends of the rotation center of the conductive roller 12.
0) is arranged so as to be performed mechanically.

Here, the operation of attracting and transferring the transfer sheet P by the transfer drum 11 will be described below with reference to FIGS. It is assumed that a positive voltage is applied to the conductor layer 26 of the transfer drum 11 from the power supply unit 32.

First, the suction process of the transfer sheet P will be described. As shown in FIG. 5, the transfer sheet P conveyed to the transfer drum 11 is pressed against the surface of the dielectric layer 28 by the conductive roller 12, and the charges accumulated in the semiconductive layer 27 move to the dielectric layer 28. Then,-charges are induced on the surface of the dielectric layer 28. As a result, positive charges are induced inside the transfer sheet P, that is, on the contact surface side with the dielectric layer 28. Thus, the transfer sheet P is electrostatically attracted to the transfer drum 11. Note that this adsorption force does not vary as long as the applied voltage is stable, and the transfer sheet P
Can be adsorbed to the transfer drum 11.

As described above, since the contact charging is performed instead of the air discharge, the conductive layer 26 is charged.
It is sufficient to apply a low voltage, and from the results of various experiments, the applied voltage is preferably +3 kV or less, and more preferably,
With +2 kV, charging can be performed favorably.

Further, the transfer sheet P attracted to the transfer drum 11 is charged in a state where the outside is negatively charged.
With the rotation in the direction of the arrow, the transfer point X of the toner image
Transported to

Next, the transfer process of the transfer sheet P will be described. As shown in FIG. 6, the photosensitive drum 15 has
Charged toner is adsorbed. Therefore, the transfer sheet P whose surface is negatively charged is transferred to the transfer point X
Is transferred to the surface of the transfer sheet P by the potential difference between the positive charge applied to the conductive layer 26 and the negative charge of the toner, and the toner is transferred. That is, the photosensitive drum 15
Due to the electric field formed by the above-mentioned negatively charged toner and the positively applied voltage on the transfer drum 11, the negatively charged toner is attracted to the negatively charged transfer paper P, attracted and transferred.

The transfer drum 11 and the photosensitive drum 1
5 is pressed against the transfer point X so as to have a predetermined nip width. Therefore, the transfer efficiency, that is, the image quality is affected by the nip width.

Table 1 shows the relationship between the nip width and the image quality.

[0058]

[Table 1]

From the results shown in Table 1, the nip width was 2 m
It can be seen that the image quality can be improved by setting the nip width in the range of m to 7 mm, and it is desirable to set the nip width in the range of 3 mm to 6 mm.

The semiconductive layer 27 has a volume resistivity of 10 ⁸ Ω · cm, a layer thickness of 2 mm to 5 mm, and a hardness of Asker C of 25 to 50. this is,
In the present embodiment, the transfer drum 11 and the photosensitive drum 15
Are set because they are pressed at a pressure of 8 kg.

That is, if the material of the semiconductive layer 27 is changed, the pressing force between the transfer drum 11 and the photosensitive drum 15 is changed, and the semiconductive layer 27 is changed according to the material so that a desired image quality is obtained. The thickness, hardness, and the like of No. 27 are changed.

Therefore, in the present embodiment, the semi-conductor layer 27 having the above-mentioned layer thickness and hardness has an appropriate nip width range.

The above-mentioned Asker C is a standard of the Japan Rubber Association, and a needle for hardness measurement having a spherical tip is pressed against the surface of a sample by the force of a spring, and the drag of the sample and the spring force are measured. When the force is balanced, the hardness is represented by the depth at which the needle is pushing the sample (push depth). According to the standard of Asker C, when the hardness of a sample is set to 0 degree so that the depth of pushing of the needle when the load of 55 g is applied to the spring is equal to the maximum displacement of the needle, and the load of 855 g is applied to the spring. The hardness of the sample is set to 100 degrees so that the indentation depth of the needle becomes zero.

The volume resistivity of the semiconductive layer 27 is 0Ω.
Cm, a voltage drop occurs before the transfer sheet P reaches the transfer point X due to the conductive roller 12 disposed at the suction start point of the transfer sheet P. In order to prevent this voltage drop, the semiconductive layer 27 has a predetermined volume resistivity, and the semiconductive layer 27 acts as a capacitor to prevent a voltage drop.

Here, Table 2 shows the relationship between the volume resistivity and the image quality when the applied voltage is 1,000 V and the volume resistivity of the dielectric layer 28 is 10 ¹³ Ω · cm.

[0066]

[Table 2]

From the results shown in Table 2, the volume resistivity of the semiconductive layer 27 is in the range of 10 ⁶ Ω · cm to ^{10 10} Ω · cm. You can see that it can be done. Further, the volume resistivity is 10 ⁹
It is understood that a range of Ω · cm to 10 ¹⁰ Ω · cm is more preferable.

Therefore, as described above in this embodiment, if the volume resistivity of the semiconductive layer 27 is set to 10 ⁸ Ω · cm, it is possible to perform good transfer and obtain good image quality. it can. The relationship between the volume resistivity and the image quality is as follows:
It is not limited to the above conditions, and the applied voltage is 1
Similar results are obtained within a range of 000 V to 2,500 V.

The dielectric layer 28 generally has a high dielectric constant,
In addition, it is a necessary condition to have a charge retaining ability. Therefore, the dielectric layer 28 is made of vinylidene fluoride as described above, and its dielectric constant is set in the range of 8 to 12.

Therefore, the charge amount c of the dielectric layer 28 is calculated from the equation of c = ε · s / l (c: charge amount, ε: dielectric constant, s: area, l: thickness).

From this, if the dielectric constant ε is small, the electric charge c is small from the above equation, and the transfer efficiency is improved. Further, since the charge amount is small, the attraction force is also small.
If the thickness is small, the charge amount c increases from the above equation, and the transfer efficiency deteriorates. Further, since the charge amount c is large, the attraction force is increased.

From the above, it is necessary to appropriately set the dielectric constant ε and the layer thickness. Therefore, the dielectric layer 28
Has a dielectric constant in the range of 8 to 12 and a layer thickness of 100 μm to 30 μm.
When the thickness is in the range of 0 μm, the attraction force and transfer efficiency of the transfer sheet P become appropriate.

Further, as shown in FIG. 7, the width of the dielectric layer 28 of the transfer drum 11 is larger than the width of the photosensitive tube (aluminum tube 15a) forming the photosensitive drum 15.
Also, the width of the photosensitive drum is larger than the effective transfer width,
Further, the effective transfer width is determined by the effective image width (OPC film 15).
b application width).

The width of each layer of the transfer drum 11 is set as shown in FIG.
As shown in the figure, when the semiconductor layer 26 is formed so as to satisfy the relationship of the conductive layer 26> the semiconductive layer 27> the dielectric layer 28, the semiconductive layer 2
7 is a grounded aluminum tube 1 of the photosensitive drum 15
5a.

That is, the power supply unit 32 controls the conductor layer 26.
When a positive voltage is applied to the dielectric layer 2 of the conductive layer 26,
On the 8 side, a negative charge is induced. At this time, if the grounded aluminum tube 15a of the photosensitive drum 15 and the semiconductive layer 27 come into contact with each other, all the electric charges charged in the semiconductive layer 27 transfer to the aluminum tube 15a. For this reason, the transfer drum 11 cannot adsorb the negatively charged toner adsorbed on the OPC film 15b, and a transfer failure occurs.

Therefore, in each layer of the transfer drum 11, as shown in FIG. 9, the width of the conductor layer 26 and the width of the dielectric layer 28 are made the same, and the width of the semi-conductor layer 27 is made larger than the respective widths. By reducing the size, it is possible to prevent contact between the semiconductive layer 27 and the grounded aluminum tube 15a, thereby preventing charge leakage.

As a result, the transfer drum 11 can adsorb the negatively charged toner adsorbed on the OPC film 15b, and can eliminate transfer defects.

The diameter of the transfer drum 11 is such that one transfer sheet P can be wound without overlapping, that is, the maximum width of the transfer sheet P that can be used in the present image forming apparatus.
Alternatively, it is formed in a size corresponding to the length.

As a result, the transfer sheet P can be stably wound around the transfer drum 11, and as a result, the transfer efficiency can be improved and the image quality can be improved.

Here, the image forming process in the image forming apparatus having the above configuration will be described below with reference to FIGS. 2, 5 and 6.

First, as shown in FIG. 2, in the case of automatic sheet feeding, the transfer sheets P are sequentially transferred one by one by a pickup roller 7 from the top to the sheet feeding cassette 5 provided at the lowermost stage of the main body. 8 and the PF roller 8
The transfer sheet P that has passed through is curled by the pre-curl roller 10 along the shape of the transfer drum 11.

On the other hand, in the case of manual paper feeding, the transfer sheets P are sent out one by one from a manual feed unit 6 provided on the front of the main body, and are conveyed to the pre-curl roller 10 by the manual feed roller 9. Then, the transfer sheet P is placed on the pre-curl roller 1.
At 0, the sheet is curled along the shape of the transfer drum 11.

Next, as shown in FIG. 5, the transfer sheet P curled by the pre-curl roller 10 is conveyed between the transfer drum 11 and the conductive roller 12, and is transferred to the semiconductive layer 27 of the transfer drum 11. Is induced on the surface of the transfer sheet P via the surface of the semiconductive layer 27 and the inner surface of the transfer sheet P. As a result, the transfer sheet P is electrostatically attracted to the surface of the transfer drum 11.

Thereafter, the transfer sheet P attracted to the transfer drum 11 is conveyed to a transfer point X which is a pressure contact portion between the transfer drum 11 and the photosensitive drum 15 as shown in FIG. Transfer sheet P due to the potential difference between the charge of the toner formed on
The above-mentioned toner image is transferred to the image.

At this time, the photosensitive drum 15 is charged, exposed, developed, and transferred for each color. Therefore, the transfer sheet P rotates on the transfer drum 11 while being attracted to the transfer drum 11, and one color transfer is performed every one rotation, so that one full-color image is obtained with a maximum of four rotations. I have. However, when a monochrome image or a monocolor image is obtained, the rotation of the transfer drum 11 may be one time.

Further, when all the toner images are transferred onto the transfer sheet P, the transfer sheet P is forcibly moved from the surface of the transfer drum 11 by the separation claws 14 provided on the circumference of the transfer drum 11 so as to be detachable from and separated from each other. And is guided to the fixing guide 22.

Thereafter, the toner image on the transfer sheet P is guided to the fixing roller 23 by the fixing guide 22, and is fused and fixed on the transfer sheet P by the temperature and pressure of the fixing roller 23.

Then, the fixed transfer sheet P is discharged onto a discharge tray 25 by discharge rollers 24.

As described above, the transfer drum 11 is formed of the conductive layer 26 made of aluminum, the semiconductive layer 27 made of urethane foam, and the dielectric layer 28 made of polyvinylidene fluoride from the inside. Thus, by applying a voltage to the conductor layer 26, charges are induced sequentially from the conductor layer 26, and the charges are accumulated in the semi-conductor layer 27. When the transfer sheet P is transported between the transfer drum 11 and the conductive roller 12, the transfer sheet P
Then, the electric charge accumulated in the semiconductive layer 27 moves, and the transfer sheet P is electrostatically attracted to the transfer drum 11.

Accordingly, the transfer sheet P is not attracted and transferred by charge injection by air discharge as in the prior art, but the transfer sheet P is attracted and transferred by induction of electric charge. Is easy to control. In addition, it is possible to eliminate voltage variations due to external pressure.

As a result, the voltage applied to the transfer drum 11 can be kept constant without being affected by the environment such as humidity and temperature, so that the transfer efficiency can be improved.
Image quality can be improved.

In addition, the surface of the transfer drum 11 can be charged more stably than in the conventional case where the surface of the transfer drum 11 is charged by inducing electric charges on the surface of the transfer drum 11 by electric discharge. Transfer can be performed stably.

Further, only by applying a voltage to the conductive layer 26, electric charges are induced in the order of the semiconductive layer 27 and the dielectric layer 28 to charge the surface of the transfer drum 11, so that the conventional method can be used. Since a lower voltage is required as compared with the case where the surface of the transfer drum 11 is charged by air discharge, voltage control is simplified and driving energy is reduced.

Further, since only one voltage application point is required, it is not necessary to apply a voltage to each charger as in the prior art. This simplifies the apparatus and reduces the manufacturing cost. It can be.

Also, since the transfer drum 11 is charged by contact charging, the electric field region does not change even if the surface of the transfer drum 11 is flawed. There is no. As a result, transfer failure such as white spots does not occur at that portion, so that transfer efficiency can be improved.

Further, since it is hard to be affected by the environment such as the temperature and humidity of the air as in the case of air discharge, the surface potential of the transfer drum 11 does not vary, and it is possible to eliminate poor adsorption of the transfer sheet P and print run-out. it can. This can also improve the transfer efficiency and improve the image quality.

By changing the applied voltage depending on the type of the transfer sheet P, the transfer efficiency can be further improved. This is because even if the same voltage is applied, the transfer sheet P
This is because the transfer efficiency of the transfer sheet P differs depending on the type of the transfer sheet P, for example, whether the transfer sheet P is paper or a synthetic resin sheet for OHP.

Here, the volume resistivity of the semiconductive layer 27 is 1
0 in the range of ^{6 Ω · cm~10 10 Ω · cm} , and the volume resistivity of the dielectric layer 28 is ^{10 9 Ω · cm~10 13 Ω ·} cm
Table 3 shows the measurement results of the relationship between the applied voltage and the transfer efficiency when paper was used as the transfer sheet P and when a synthetic resin sheet for OHP was used.
Shown in The paper used was 65 g paper. 65 g paper refers to paper having a g number of 65 g per 1 m ² .

[0099]

[Table 3]

From the results shown in Table 3, the transfer sheet P
In the case of the synthetic resin sheet for HP, it is understood that the transfer efficiency hardly depends on the applied voltage regardless of the volume resistivity of the semiconductive layer 27 and the volume resistivity of the dielectric layer 28.

However, when the transfer sheet P is paper, the transfer efficiency is good when the applied voltage is in the range of 1,500 V to 2,000 V.
It has been found that when the voltage is less than 0 V or exceeds 2,500 V, the transfer efficiency may be poor.

Therefore, when the transfer sheet P is made of 65 g paper and the volume resistivity of the semiconductive layer 27 is 10 ⁶ Ω · cm or less.
The transfer efficiency was set to be within the range of 10 ¹⁰ Ω · cm and the volume resistivity of the dielectric layer 28 within the range of 10 ⁹ Ω · cm to 10 ¹³ Ω · cm. %, The optimum applied voltage is determined as shown in Table 4. Note that the transfer efficiency of 85% or more means that the toner remains on the photosensitive drum 15 and that 8%
The case where 5% was transferred is shown.

[0103]

[Table 4]

From the results shown in Table 4, it can be seen that when the transfer sheet P is paper, the transfer can be performed efficiently by setting the applied voltage within the range of 1,000 V to 2,500 V. Further, the applied voltage is set to 1,500 V to 2,000.
It can be seen that setting within the range of V is more preferable.

Also, the number of grams per 1 m ^{3 of} paper is 65 g to
When the same experiment was performed with various changes within the range of 128 g, the same result as in Table 4 was obtained.

As described above, even if the same voltage is applied to the conductor layer 26, the transfer efficiency changes depending on the type of the transfer sheet P. Therefore, by changing the applied voltage according to the type of the transfer sheet P, the applied voltage is always changed. Transfer can be performed efficiently. At this time, the volume resistivity of the semiconductive layer 27 is 10 ⁶ Ω · cm.
In the range of ~10 ¹⁰ Ω · cm, and, if the volume resistivity of the dielectric layer 28 is in the range of ^{10 9 Ω · cm~10 13 Ω ·} cm, 1,000V~2,500V the transfer drum 11
In particular, the transfer sheet P
When is paper, the transfer efficiency can be improved.

The volume resistivity of the semiconductive layer 27 is 10
^When the volume resistivity of the dielectric layer 28 is within the range of ⁶ Ω · cm to ^{10 10} Ω · cm and the volume resistivity of the dielectric layer 28 is within the range of 10 ⁹ Ω · cm to 10 ¹³ Ω · cm, the transfer sheet P is paper. Even OHP
Even if it is a synthetic resin sheet for
By applying a voltage in the range of 000 V to 2,500 V, transfer can be performed efficiently. That is, when the volume resistivity of the semiconductive layer 27 and the volume resistivity of the dielectric layer 28 are within the above ranges, 1,000 V
By applying a voltage in the range of ２，2,500 V, transfer can be performed efficiently without switching the voltage depending on the type of transfer sheet.

Further, even if the applied voltage is the same, the transfer efficiency changes depending on the humidity at the time of transfer. That is, since the volume resistivity of the semiconductive layer 27, the dielectric layer 28, and the transfer sheet P changes depending on the humidity, a difference in transfer efficiency occurs even when the same voltage is applied to the conductive layer 26. For this reason, it is necessary to apply an optimal voltage to the conductor layer 26 according to the humidity.

Therefore, in order to detect the humidity at the time of transfer,
As shown in FIG. 2, a humidity sensor (humidity measuring device) 33 as a humidity detecting means is provided near the transfer drum 11,
Before the suction operation of the transfer sheet P, the humidity is read by the humidity sensor 33 and the applied voltage is determined.
2, the optimal voltage according to the humidity can be applied to the conductor layer 26.

At this time, in order to perform efficient transfer,
The higher the humidity, the lower the applied voltage needs to be set. On the other hand, if the applied voltage is set too low when the humidity is high, the adsorbing force of the paper is weakened and the transfer cannot be performed satisfactorily. In consideration of the above, the volume resistivity of the semiconductive layer 27 is in the range of 10 ⁶ Ω · cm to ^{10 10} Ω · cm, and the volume resistivity of the dielectric layer 28 is 10 ⁹ Ω · cm to 10 ⁹ Ω · cm. ¹³ Ω
Determining the optimal applied voltage for humidity when it is within the range of cm gives the results shown in Table 5.

[0111]

[Table 5]

As shown in Table 5, when the humidity is within the range of 0% to 40%, the applied voltage is 1,000 V to 2,000 V.
It is preferable to set it within the range of 00 V,
% To 60%, the applied voltage is
It is preferable to set within the range of 0V to 2,500V. When the humidity is in the range of 61% to 80%, the applied voltage is preferably set in the range of 1,500 V to 2,500 V, and when the humidity is in the range of 81% to 100%. Means that the applied voltage is from 1500 V to 2,000
It is preferable to set it within the range of 0V. If the applied voltage is within the above range, transfer can be performed efficiently,
In particular, the transfer can be performed most efficiently by setting the applied voltage to an intermediate value within the above range.

Here, the control of the application of the voltage to the transfer drum 11 when the humidity sensor 33 is used will be described.
This will be described below with reference to the flowchart shown in FIG. However, the following control of each member is performed by the control device 37 shown in FIG.

First, the power switch of the main body (not shown) is turned on.
When the determination is N, preparations for paper suction operation and transfer operation such as cleaning and static elimination are performed (S1).
After the preparation is completed, the transfer drum 11 stops. Then
The humidity near the transfer drum 11 is measured by the humidity sensor 33 (S2), and the applied voltage is determined according to the humidity measured by the humidity sensor 33 (S3). At this time, when the humidity measured by the humidity sensor 33 is in the range of 0% to 40%, the applied voltage is set in the range of 1,000 V to 2,000 V, and the humidity is set in the range of 41% to 60%. , The applied voltage is set in the range of 1,000 V to 2,500 V. When the humidity is in the range of 61% to 80%, the applied voltage is set in the range of 1,500 V to 2,500 V, and when the humidity is in the range of 81% to 100%, the applied voltage is set. The voltage is set within the range of 1,500 V to 2,000 V. After that, the transfer drum 11 is rotated,
A series of paper suction and transfer operations are performed (S4).

As described above, the humidity sensor 33
The humidity is read before the transfer sheet P is attracted to the transfer drum 11, and the power supply unit 32 applies an optimum voltage according to the humidity to the conductive layer 26, so that an optimum transfer efficiency is obtained even under any humidity. be able to. In particular, when the transfer sheet P is paper, it is easily affected by humidity, and the transfer efficiency is affected by the applied voltage.
The transfer efficiency can be further improved by applying a voltage corresponding to the detection result of (1) to the conductor layer 26 by the power supply unit 32.

In this embodiment, cylindrical aluminum is used as the conductor layer 26, but another conductor may be used. Further, although the semiconductive layer 27 is formed of urethane foam, an elastic body such as silicon may be used as another semiconductive body. Further, although the dielectric layer 28 is formed of polyvinylidene fluoride, a resin such as polyethylene terephthalate may be used as another dielectric.

In place of the transfer drum 11, as shown in FIG. 12, the innermost layer is made up of a conductor layer 26 and a semi-conductor layer, and the dielectric constant and the resistance value corresponding to the semi-conductor layer 27 of the transfer drum 11 are used. Transfer drum 36 in which a semi-conductive film 34 composed of a dielectric film 35 and a dielectric film 35 composed of a dielectric constant and a resistance value corresponding to the dielectric layer 28 are sequentially laminated.
May be used. Also in this case, a voltage is applied to the conductor layer 26 by the power supply unit 32.

[0118]

According to the first aspect of the present invention, there is provided an image forming apparatus comprising:
As described above, the image bearing member on which a toner image is formed on the surface, a transfer sheet by abutting on said image bearing member,
In the image forming apparatus having a transfer unit for transferring the toner image formed on said image bearing member, said transfer means, nip width between the image carrier is 2Mm～7mm, contact surface of the transfer sheet From the side, the layer thickness is 100 μm to 300 μm
A dielectric layer, a semiconductive layer having a layer thickness of 2 mm to 5 mm, and a conductive layer are sequentially laminated, and the volume resistivity of the semiconductive layer is
Is in the range of 10 ⁶ Ω · cm to ^{10 10} Ω · cm and the hardness is
Asker C in the range of 25 to 50 and the dielectric layer
Volume resistivity of 10 ⁹ Ω · cm to 10 ¹³ Ω · cm
In the inner upper, a voltage applying means for applying a predetermined voltage to the conductive layer, on the upstream side of the surface from the transfer position of the dielectric layer surface, by contacting through the transfer sheet
The serial transfer sheet which has an electrode member which is grounded is adsorbed on the surface of the dielectric layer, the above voltage application means, the upper
In this configuration, a voltage in the range of 1,000 V to 2,500 V is applied to the transfer unit.

An image forming apparatus according to a second aspect of the present invention has a configuration in which the transfer sheet is paper in addition to the configuration of the first aspect. An image forming apparatus according to a third aspect of the invention is configured to apply a voltage in the range of 1,500 V to 2,000 V to the transfer unit in addition to the configuration of the first or second aspect.

Therefore, according to the structure of the first aspect, the voltage applying means applies a predetermined voltage to the conductive layer, and the electrode member applies the transfer sheet to the surface of the dielectric layer on the upstream side from the transfer position. Contact, the electric charge having the same polarity as the polarity of the voltage applied to the conductor layer is accumulated in the semi-conductor layer, and further, on the surface of the dielectric layer and the transfer sheet pressed against the surface of the dielectric layer. Also, charges of the same polarity are induced. That is, a charge having a polarity opposite to the polarity of the voltage applied to the conductor layer is induced on the back surface of the transfer sheet in contact with the dielectric layer. Thus, the transfer sheet can be electrostatically attracted to the surface of the dielectric layer, that is, the surface of the transfer means, by simply applying a voltage to the conductor layer, and the potential due to the charge on the transfer sheet surface and the image carrier surface The toner image can be transferred to the transfer sheet by providing a predetermined difference between the potential of the toner image and the potential of the toner image.

Thus, the transfer sheet is not attracted and transferred by charge injection by air discharge as in the prior art, but the transfer sheet is attracted and transferred by the induction of electric charge. Easy to control. In addition, it is possible to eliminate voltage variations due to external pressure.

Therefore, the voltage applied to the transfer means can be kept constant without being affected by the environment such as humidity and temperature, so that the transfer efficiency can be improved and the image quality can be improved.

Further, the above-mentioned voltage applying means may be arranged so that the volume resistivity of the semiconductive layer is in the range of 10 ⁶ Ω · cm to ^{10 10} Ω · cm, the hardness of Asker C is in the range of 25 to 50 , and
The volume resistivity of the dielectric layer is 10 ⁹ Ω · cm to 10 ¹³ Ω · c
m and the transfer means is 1,000 V to 2.5
By applying a voltage in the range of 00V, especially when the transfer sheet is paper, the transfer efficiency can be improved. When the transfer sheet is paper, the transfer efficiency depends on the applied voltage. However, for example, when the transfer sheet is a synthetic resin sheet for OHP, the transfer efficiency hardly depends on the applied voltage regardless of the volume resistivity of the semiconductive layer or the dielectric layer.

Accordingly, the volume resistivity of the semiconductive layer is 10 ⁶
Asker with hardness in the range of Ω · cm to 10 ¹⁰ Ω · cm
In the range of 25 to 50 in C, and and the volume resistivity of the dielectric layer is in the range of ^{10 9 Ω · cm~10 13 Ω ·} cm,
By applying a voltage in the range of 1,000 V to 2,500 V to the transfer means, transfer can be performed efficiently whether the transfer sheet is paper or a synthetic resin sheet for OHP. That is, when the transfer sheet is a synthetic resin sheet for OHP, the applied voltage can be determined so as to be advantageous for paper adsorption. Further, when the transfer sheet is paper, the effect that the transfer efficiency can be improved is also exhibited. Further, by applying a voltage in the range of 1,500 V to 2,000 V to the transfer means, there is an effect that the transfer efficiency can be further improved.

[0125]

[0126]

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram near a transfer drum provided in an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of an image forming apparatus including the transfer drum shown in FIG.

FIG. 3 shows a conductive layer constituting the transfer drum shown in FIG.
FIG. 3 is an explanatory diagram showing a connection state with a semiconductive layer and a dielectric layer.

FIG. 4 shows a conductor layer constituting the transfer drum shown in FIG.
FIG. 5 is another explanatory diagram showing a connection state with a semiconductive layer and a dielectric layer.

FIG. 5 is an explanatory view showing a charged state of the transfer drum shown in FIG. 1, and is an explanatory view showing an initial state in which a transfer sheet is conveyed to the transfer drum.

FIG. 6 is an explanatory view showing a charged state of the transfer drum shown in FIG. 1, and is an explanatory view showing a state in which a transfer sheet is conveyed to a transfer position of the transfer drum.

FIG. 7 is an explanatory diagram showing a comparison between a charging width of the transfer drum shown in FIG. 1 and an effective image width.

FIG. 8 is an explanatory diagram showing charge transfer between the transfer drum and the photosensitive drum shown in FIG. 1, and showing charge transfer when the width of each layer of the transfer drum satisfies dielectric layer <semiconductor layer <conductor layer. It is.

FIG. 9 is an explanatory diagram showing charge transfer between the transfer drum and the photosensitive drum shown in FIG. 1, and showing charge transfer when the width of each layer of the transfer drum satisfies a condition of semiconductor layer <dielectric layer = conductor layer. It is.

FIG. 10 is a block diagram of a control device provided in the image forming apparatus having the above configuration.

FIG. 11 is a flowchart showing control of voltage application to the transfer drum shown in FIG. 1 when a humidity sensor is used.

FIG. 12 is a schematic configuration diagram of the vicinity of another transfer drum provided in the image forming apparatus according to the present invention.

FIG. 13 is a schematic configuration diagram of a conventional image forming apparatus.

FIG. 14 is a schematic configuration diagram of another conventional image forming apparatus.

[Explanation of symbols]

 REFERENCE SIGNS LIST 11 transfer drum (transfer means) 12 conductive roller (electrode member) 15 photoconductor drum (image carrier) 26 conductive layer 27 semiconductive layer 28 dielectric layer 32 power supply section (voltage applying means) 33 humidity sensor (humidity) Detecting means) 36 Transfer drum (Transfer means) P Transfer sheet X Transfer point (Transfer position)

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-47-13289 (JP, A) JP-A-4-256978 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15/16 G03G 15/01

Claims (3)

(57) [Claims] An image bearing member having a surface on which a toner image is formed;
By abutting the transfer sheet to the image bearing member, an image forming apparatus having a transfer unit for transferring the toner image formed on the <br/> image bearing member, said transfer means, the image carrier Nip width between body and 2mm ~
7 mm, and a layer thickness of 10 mm from the contact surface side of the transfer sheet.
0 μm to 300 μm dielectric layer, layer thickness 2 mm to 5 mm
Semi conductor layer and a conductive layer are laminated in this order, the semiconductor of
Volume resistivity of the conductor layer is 10 ⁶ Ω · cm to ^{10 10} Ω · cm
Within the range and hardness is in the range of 25-50 in Asker C,
And the volume resistivity of the dielectric layer is 10 ⁹ Ω · cm to 1
Be in the range of 0 ¹³ Ω · cm, and a voltage applying means for applying a predetermined voltage to the conductive layer, on the upstream side of the surface from the transfer position of the dielectric layer surface, the <br/> transfer sheet the transfer sheet which has an electrode member which is grounded adsorbed onto the dielectric layer surface by contacting through said voltage applying means, 1,000V～ to the transfer means
An image forming apparatus, wherein a voltage within a range of 2,500 V is applied. 2. The image forming apparatus according to claim 1, wherein said transfer sheet is paper. 3. The method according to claim 1, wherein the transfer means has a voltage of 1,500 V to 2,000 V.
The image forming apparatus according to claim 1, wherein a voltage within the range is applied.