JP3267848B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a laser printer,
The present invention relates to an electrophotographic image forming apparatus using a reversal developing method such as a digital copying machine and a plain paper facsimile, and more particularly, to a paper adsorption for electrostatically adhering paper or transfer paper such as OHP to a transfer drum surface. The present invention relates to a transfer drum type image forming apparatus having a mechanism.

[0002]

2. Description of the Related Art Conventionally, a toner is attached to an electrostatic latent image formed on the surface of a photosensitive drum as an image carrier, developed, and the toner image is transferred to a transfer paper wound around a transfer drum. There is an image forming apparatus. For example, in the image forming apparatus shown in FIG. 13, the corona charger 1 for adsorbing the transfer paper P inside the transfer drum 101 having the dielectric layer 101a.
02 and a corona charger 104 for transferring the toner image formed on the surface of the photosensitive drum 103 to the transfer paper P are separately provided. Then, the attraction and transfer of the transfer paper P are separately performed by the respective chargers 102 and 104.

In the image forming apparatus shown in FIG. 14, a transfer drum 201 having a two-layer structure including an outer semiconductive layer 201a and an inner base material 201b, and the transferred transfer paper P are transferred along the transfer drum 201. Grip mechanism 2 for holding together
02. Then, the end of the conveyed transfer paper P is gripped by the grip mechanism 202 and the transfer drum 2
01, the transfer drum 201 is charged by applying a voltage from a power supply 203 connected to the semiconductive layer 201a which is the outer layer of the transfer drum 201, and the photosensitive drum 103 is charged.
Is transferred to the transfer paper P.

However, in the image forming apparatus shown in FIG. 13, the transfer drum 101 has a single-layer structure of only the dielectric layer 101a, and unlike the apparatus in which a voltage is applied to directly charge the transfer drum itself, The configuration is such that corona chargers 102 and 104 are disposed inside to charge the transfer drum 101. For this reason, the size of the transfer drum 101 is limited, and there is a problem that the transfer drum and the image forming apparatus itself cannot be downsized. on the other hand,
In the image forming apparatus shown in FIG. 14, the transfer drum 201 has a two-layer structure, and a voltage is applied by a power supply 203 to charge the transfer drum 201 and transfer the toner image to the transfer paper P. Requires less. However, since the grip mechanism 202 is provided, the configuration of the entire image forming apparatus is complicated, and the number of components as a whole is increased. As a result, there is a problem that the cost for manufacturing the image forming apparatus increases.

To solve the above-mentioned problem, Japanese Patent Laid-Open Publication No. 2-74975 discloses, for example, FIG.
As shown in FIG. 5, a transfer drum 304 in which a conductive rubber 302 and a dielectric film 303 are laminated on a grounded metal roll 301 is provided. An image forming apparatus provided with a corona charger 306 driven by a power supply 305 has been proposed.

In this image forming apparatus, the corona charger 30
6, the dielectric film 303 is set at -1600V to -20.
It is charged to a negative potential of 00V. And the transfer paper P
Is sent by the paper feed roller 307 and the pressure roller 308
When pressed against the transfer drum 304 by the
Is electrostatically attracted to the transfer drum 304 and an electric charge is induced. At this time, the surface potential of the transfer paper P is -1000
V, this potential value is a potential sufficient to transfer the toner image to the transfer paper P, and the transfer is performed when the transfer paper P comes into contact with the photosensitive drum 309 on which the toner image is formed. Then, the toner image transferred onto the transfer paper P is fixed by the fixing device 310 provided downstream of the transfer drum 304 in the transport direction.

In the case of color development, since development and transfer must be repeated, the positive charge of the photosensitive drum 309 neutralizes and lowers the potential on the surface of the transfer paper P. Therefore, when the transfer paper P reaches the position of the corona charger 306, a negative charge is supplied.

On the other hand, on the photosensitive drum 309, an output beam of the semiconductor laser 310 for selectively forming an electrostatic latent image based on image data is applied to a polygon mirror 311, f-θ.
The photosensitive drum 30 via the lens 312 and the mirror 313
An electrostatic latent image is formed on the surface of the photosensitive drum 309 which is irradiated on the surface of the photosensitive drum 9 and charged positively by the charger 314. Then, toner is attached to the electrostatic latent image by the developing device 315, and a toner image is formed on the surface of the photosensitive drum 309 and is visualized. In the figure, reference numeral 316 denotes a cleaner for removing the residual toner attached to the photosensitive drum 309, and 317 denotes an eraser for neutralizing and removing the charge of the photosensitive drum 309 and setting it to an initial state.

According to this, one corona charger 306 provided outside the transfer drum 304 transfers the transfer drum 3
The surface of the photoconductor drum 309 can be transferred by charging the surface of the photoconductor 04 and electrostatically attracting the transfer paper P. Therefore, only one charger is required, and the transfer drum 304
Since no charging device is provided inside, the transfer drum can be downsized. Moreover, the transfer paper P can be electrostatically attracted to the transfer drum 304 with a simple structure without requiring a grip mechanism or the like for holding the transfer paper P.

However, when a color image is formed, that is, when the transfer step is performed a plurality of times, it is necessary to replenish the transfer paper P with the corona charger 306 each time one transfer is completed. Therefore, a unipolar power supply 305 for controlling the driving of the corona charger 306 is provided.
Thus, a charging unit composed of the above is required, and the number of components increases. As a result, there is a problem that the cost for manufacturing the image forming apparatus increases.

As described above, when the transfer drum is charged by air discharge from the charger, the output voltage required for charging becomes large, and the driving energy of the image forming apparatus increases. Further, it is affected by the environment such as the atmospheric pressure at the time of charging and the temperature and humidity of air. That is, when the temperature is high and the humidity is high, the surface potential of the transfer drum tends to fluctuate easily, and poor transfer paper adsorption and printing disorder are likely to occur. Also, if the surface of the transfer drum has flaws, the electric field region becomes smaller, and the electric field balance is disturbed at the flaws.
Transfer failure such as white spots may occur at the time of image formation at that portion, which may cause deterioration in image quality.

In view of this, as an image forming apparatus which eliminates the adverse effects of charging due to air discharge, for example, Japanese Patent Laid-Open Publication No. Hei 6-3972 discloses an endless dielectric belt 400 as shown in FIG. There has been proposed an image forming apparatus in which a transfer means for transferring the transfer paper P is provided by being stretched by 402, an auxiliary roller 403 is further provided inside the dielectric belt 400, and the dielectric belt 400 is directly charged by a bias power supply 404.

In this image forming apparatus, the roller 401 and the auxiliary roller 403 are connected to a bias power source 404,
The roller 402 is grounded. In addition, the conductive substrate 40
The photosensitive layer 40 on the surface of the photosensitive drum 405 with the ground 5a
5b, a toner image is formed. Then, a roller 401 and a roller 401 are applied to the endless dielectric belt 400 from the bias power supply 404.
The surface of the dielectric belt 400 is charged by being supplied with electric charges via 403.

At this time, the output current Io of the bias power supply 404 and the current Ia flowing to the ground through the roller 402
And a current Ip flowing through the photosensitive drum 405 is detected. Then, since the output current Io of the bias power supply 404 is divided into the current Ia and the current Ip, a comparison operation is performed by the control unit, and the output of the bias power supply 404 is controlled with a constant current so that the current Ip becomes a predetermined value. The amount of charge applied to the dielectric belt 400 is varied. In the figure, 406
Is a cleaning blade for removing dust such as paper dust.

In such a configuration, the dielectric belt 4
The transfer paper P conveyed to 00 is electrostatically attracted to the dielectric belt 400 and conveyed, and abuts on the photosensitive drum 405 to perform transfer. Then, when the transfer paper P is further fed and comes to the position of the roller 402 serving as the ground electrode, the electrostatic attraction force with the dielectric belt 400 almost disappears, and the rigidity and waist of the transfer paper P itself cause the transfer paper P to move from the dielectric belt 400. Separated.

According to this, the charging method is performed directly instead of air discharge, and the photosensitive drum 405 is adjusted in accordance with the state of the transfer paper P which fluctuates due to environmental conditions such as temperature and humidity.
Alternatively, since the charge amount of the dielectric belt 400 is controlled, there is no influence on the environment.

[0017]

By the way, the water content of the transfer paper changes due to changes in the environment such as temperature and humidity when the image forming apparatus is used, and when the water content increases, the resistance value of the transfer paper decreases. When the resistance value decreases, the charge applied to the transfer paper surface moves inside, and the surface of the transfer paper is no longer charged. Therefore, the stability of adsorption of the transfer paper to the transfer drum is poor, and the case where the transfer paper is not adsorbed may occur, resulting in poor image quality formed on the transfer paper.

Further, if the charge amount is increased due to the adsorption of the transfer paper, the toner image on the surface of the photosensitive drum is transferred to the transfer paper, causing image deterioration. Therefore, in order to obtain a high-quality image, it is not preferable to increase the charge amount of the transfer paper.

The image forming apparatus disclosed in Japanese Patent Application Laid-Open No. Hei 6-3972 performs constant current control between the dielectric belt 400 and the photosensitive drum 405 via the attracted transfer paper so that the image forming apparatus is not affected by the environment. The purpose is to make the potential constant, and no consideration is given to stabilizing the electrostatic attraction of the transfer paper to the dielectric belt 400. For this reason, a change in the state of the transfer paper due to a change in the environment causes a transfer paper to be sucked poorly, and the transfer paper is separated from the dielectric belt 400 or displaced during conveyance.

Conventionally, as described above, there has been no solution to the problem of changes in the environment such as temperature and humidity with respect to the transfer paper, that is, the effect of the moisture content of the transfer paper on adsorption. In view of the above, an object of the present invention is to provide an image forming apparatus capable of stably adsorbing transfer paper independent of the environment such as temperature and humidity and forming a good image.

[0021]

Means for Solving the Problems According to the present invention, there is provided an image bearing member on which a toner image is formed on a surface, and a transfer paper formed on the image bearing member by sucking a transfer paper and bringing the transfer paper into contact with the image bearing member. In the image forming apparatus having a transfer means for transferring the transferred toner image to the transfer paper, the water content of the transfer paper is reduced in order to stably adsorb the transfer paper regardless of the temperature and humidity environmental conditions and the state of the transfer paper. This is provided with means for reducing the water content. As a means for reducing the water content, a heating mechanism for heating the transfer paper being conveyed is provided.

Accordingly, even if the water content of the transfer paper changes due to the environment such as temperature and humidity, the transfer paper is heated before the transfer paper is adsorbed and the water content of the transfer paper is reduced. As a result, the transfer of electric charges in the transfer paper is hindered, the surface of the transfer paper is easily charged, and stable transfer paper adsorption is obtained.

As a more specific means for solving the problem, the transfer means is provided with a transfer drum which is charged by an applied voltage and adsorbs the transfer paper, and provides a curvature to the transfer paper upstream of the transfer drum in the transport direction. Precurl roller is provided,
A heater is provided on the pre-curl roller as a means for reducing the water content.

According to this, the transfer drum is directly charged by the application of the voltage without being affected by the environment. Then, the transfer paper is heated by the heater of the pre-curl roller, the water content is reduced before reaching the transfer drum, and the transfer paper can be stably adsorbed even when the environment such as temperature and humidity changes.

Further, the set temperature rising time of the heating mechanism is set shorter than the set temperature rising time of the fixing roller for fixing the toner image transferred onto the transfer paper. According to this, image formation can be started without waiting for the fixing roller having the higher set temperature to reach the set temperature, and the machine printable time can be shortened. Here, the rise time refers to the time from when the heating mechanism or the heater of the fixing roller is turned on to when the set temperature is reached.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 2, an image forming apparatus according to the present embodiment includes a paper supply unit 1 for stocking and supplying transfer paper P as recording paper on which an image is formed by toner, and a toner image. The image forming apparatus includes a transfer unit 2 that transfers the toner image to the transfer paper P, a developing unit 3 that forms the toner image, and a fixing unit 4 that fuses and fixes the toner image transferred to the transfer paper P.

The paper feed unit 1 is detachably disposed at the lowermost stage of the main body, and is provided with a paper feed cassette 5 for stocking the transfer paper P and supplying it to the transfer unit 2; And a manual supply port 6 for manually supplying P one by one. In addition, in order to supply the transfer paper P to the transfer unit 2, a pickup roller 7 that feeds the top transfer paper P of the paper feed cassette 5 one by one, and a PF that conveys the transfer paper P sent by the pickup roller 7. A roller 8, a manual feed roller 9 that conveys the transfer paper P supplied from the manual feed port 6, and a pre-curl roller 10 that curls the conveyed transfer paper P to provide a curvature.

The paper feed cassette 5 is provided with a delivery member 5a urged upward by a spring or the like, and the transfer paper P is stacked on the delivery member 5a.

The transfer section 2 is provided with a transfer drum 11 for adsorbing the transfer paper P and making contact with the image carrier of the developing section 3, and a ground roller 12 as a grounded electrode member is provided around the transfer drum 11. A guide member 13 for guiding the paper P so as not to fall from the transfer drum 11, a peeling claw 14 for forcibly peeling the transfer paper P adsorbed on the transfer drum 11, and the like are provided, and these constitute a transfer unit. . In addition, the peeling claw 14 is provided on the surface of the transfer drum 11 so as to be able to freely contact and separate.

Further, environmental conditions such as temperature and humidity and transfer paper P
In order to stably adsorb the transfer paper P to the transfer drum 11 irrespective of the state, a water content reducing means for reducing the water content of the transfer paper P is provided.

The water content reducing means is constituted by providing a pre-curl roller 10 with a heating mechanism. As shown in FIGS. 1 and 3, the pre-curl roller 10 is disposed upstream of the transfer drum 11 in the transport direction, and has a pair of cylindrical upper rollers 10.
a and the lower roller 10b. Both rollers 10a, 10b
The transfer paper P is curled by the arc-shaped nip generated by the pressure contact of the transfer paper P so that the transfer paper P is easily attracted along the surface of the transfer drum 11. The upper roller 10a is a heat roller having a heater lamp 10c therein as a heating mechanism. When the transfer paper P is conveyed to the pre-curl roller 10, the transfer roller P is heated by the upper roller 10a to evaporate the water content. To reduce the water content.

The upper roller 10a is formed of a rigid body and is driven to rotate by a motor. The lower roller 10b is formed of a low hardness elastic body, and is urged toward the upper roller 10a by a spring. The material of the upper roller 10a is preferably a metal, particularly preferably aluminum.
This is because if the material of the upper roller 10a is a resin roller such as a soft urethane, the curl amount of a thick paper or the like becomes small. In addition, the cost can be reduced by using aluminum.

The developing section 3 is provided with a photosensitive drum 15 which is an image carrier pressed against the transfer drum 11. Further, around the photosensitive drum 15, yellow,
Developing units 16, 17, 18, and 19 containing magenta, cyan, and black toners are arranged radially. Further, a charger 2 for charging the surface of the photosensitive drum 15
0, a cleaning blade 21 for scraping and removing residual toner on the surface of the photosensitive drum 15 is provided.

As shown in FIG. 1, the photosensitive drum 15 has an OPC film 15b applied to the surface of a grounded conductive aluminum tube 15a. The photosensitive drum 1 formed by laser exposure based on the image data
A toner image is formed for each toner on the electrostatic latent image on the five surfaces. That is, in the case of a color image, charging, exposure, development, and transfer are repeated for each color.

The photosensitive drum 15 and the transfer drum 11
"8" means 8 at the transfer site X in consideration of transfer efficiency and image quality.
They are pressed so as to apply a pressure of Kg.

The fixing section 4 includes a pair of fixing rollers 22 for fusing the toner image by heating and pressure to fix the toner image on the transfer paper P.
And the peeling claw 14 from the transfer drum 11 after the transfer of the toner image.
And a fixing guide 23 for guiding the transfer paper P peeled off by the fixing roller 22 to the fixing roller 22. A discharge roller 24 is provided downstream of the fixing roller 22.
The transfer paper P after fixing is discharged onto a discharge tray 25.

Here, the structure of the transfer drum 11 will be described in detail. The transfer drum 11, as shown in FIG.
The conductive layer 26, the semiconductive layer 27, and the dielectric layer 28 are sequentially laminated. The conductor layer 26 is made of cylindrical aluminum, and is connected to a power supply unit 32 for applying a voltage. A positive charge is applied to the conductor layer 26 from the power supply unit 32, and the entire circumference of the conductor layer 26 is , A stable voltage is maintained. The semiconductive layer 27 is made of elastic urethane foam, and the dielectric layer 28
Consists of polyvinylidene fluoride. The conductor layer 26
May be replaced with aluminum and another conductor may be used.
In addition, another semiconductor that is an elastic body such as silicon may be used for the semiconductor layer 27. Further, another dielectric such as polyethylene terephthalate resin may be used for the dielectric layer 28.

The diameter of the transfer drum 11 is
The transfer sheet P is formed in a size that allows one sheet to be wound without overlapping, that is, a size corresponding to the maximum width or length of the transfer sheet P that can be used in the image forming apparatus of the present embodiment. As a result, the transfer paper 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.

The layers 26, 27, and 28 are not bonded by an adhesive or the like, but as shown in FIG. 4, the semiconductive layer 27 and the dielectric layer 28 formed in a sheet shape.
A boss 30a, which is a cylindrical projection provided on the sheet holding plate 30, is fitted into a plurality of through holes 29 penetrating both layers 27, 28 provided at both ends of the sheet. Then, the boss 30a is connected to the opening 26a provided in the conductor layer 26.
To fix the semiconductive layer 27 and the dielectric layer 28 to the conductive layer 26.

According to this fixing method, since the semiconductive layer 27 and the dielectric layer 28 are tensioned on the inner side of the conductive layer 26 by the sheet pressing plate 30, the floating of each of the layers 27 and 28 can be prevented. It can prevent loosening. In addition, since each of the layers 27 and 28 is only fixed by the sheet holding plate 30, even when replacement is necessary, it can be easily replaced simply by removing the sheet holding plate 30.

As another fixing method, as shown in FIG. 5, for example, a sheet pressing member 31 having bosses 31a at both ends of each layer 27 and 28 and a fixing member 31b at the center.
There is a method of fixing a sheet composed of the semiconductive layer 27 and the dielectric layer 28 to the conductive layer 26.

In this fixing method, the bosses 31a of the sheet holding member 31 are fitted into fitting holes 26b provided at both ends of the opening 26a of the conductor layer 26, and the sheet holding member 31 is fixed to the opening 26a. Part 31b is inserted, and the sheet composed of the semiconductive layer 27 and the dielectric layer 28 is
Fix to 6.

Even if the layers 26, 27 and 28 are fixed by this method, the layers 27 and 28 can be easily replaced by attaching and detaching the fixing portion 31b of the sheet pressing member 31.

Incidentally, the photosensitive drum 15 and the transfer drum 11 are pressed against each other so as to have a predetermined nip width at the transfer portion X. 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. According to this, the image quality can be improved by setting the nip width in the range of 2 mm to 7 mm, and further, the nip width is set to 3 mm to 6 mm. It is understood that it is desirable to set the range.

[0045]

[Table 1]

The semiconductive layer 27 of the transfer drum 11
Has a volume resistance of 10 ⁸ Ω · cm and a layer thickness of 2 mm to 5 m
m, hardness is in the range of 25 to 50 by Asker C. This is set in the present embodiment because the transfer drum 11 and the photosensitive drum 15 are pressed against each other at a pressure of 8 kg.

That is, when the material of the semiconductive layer 27 changes, the pressure contact force between the transfer drum 11 and the photosensitive drum 15 changes, and a half of the material according to the material of the semiconductive layer 27 is changed so as to obtain a desired image quality. The thickness, hardness and the like of the conductor layer 27 are changed. Therefore, in the present embodiment, the nip width is in a proper range.

Incidentally, Asker C is a standard of the Japan Rubber Association. The shape of the needle is spherical, and the spring load is 55 g at 0 degree and 855 g at 100 degree.

The semi-conductor layer 27 has a volume resistance of 0 Ω.
Cm, a voltage drop occurs before the transfer paper P reaches the transfer site X due to the ground roller 12 disposed at the suction start point of the transfer paper P. In order to prevent this voltage drop, the semiconductor layer 27 has a predetermined volume resistance value, and the semiconductor layer 27 functions as a capacitor to prevent the voltage drop.

As shown in Table 2, the relationship between the volume resistance value of the semiconductive layer 27 and the image quality is shown in Table 2. The volume resistance value of the semiconductive layer 27 is in the range of 10 ⁵ Ω · cm to 10 ⁸ Ω · cm. It can be seen that there is no retransfer or transfer failure and transfer can be performed efficiently. It is also found that the volume resistivity is more preferably in the range of 10 ⁶ Ω · cm to 10 ⁷ Ω · cm.

[0051]

[Table 2]

Therefore, when the volume resistivity of the semiconductive layer 27 is 10 ⁸ Ω · cm as in the present embodiment, the transfer can be performed well, and a good image quality can be obtained.

The dielectric layer 28 generally has a high dielectric constant,
In addition, since it is a necessary condition to have a charge retaining ability, the material is made of vinylidene fluoride and has a dielectric constant ε of 8 to
Twelve ranges are set.

Further, C = ε · S / l (C: charge amount, ε:
The charge amount C of the dielectric layer 28 is calculated from the equation of dielectric constant, S: area, l: layer thickness). According to this equation, when the dielectric constant ε is small, the charge amount C becomes small. Therefore, it is understood that the transfer efficiency is improved and the attraction force is reduced. Furthermore, the layer thickness l
Is smaller, the charge amount C becomes larger. Therefore, the transfer efficiency is deteriorated, and the attraction force is increased.

Therefore, in the present embodiment, it is necessary to appropriately set the dielectric constant ε and the layer thickness l, and the dielectric layer 28 has a dielectric constant in the range of 8 to 12 and a layer thickness l of 100 μm to 300 μm.
In the range of m, the attraction force and transfer efficiency of the transfer paper P become appropriate.

Further, as shown in FIG. 6, 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.
The width of the photosensitive drum is larger than the effective transfer width, and the effective transfer width is larger than the effective image width (application width of the OPC film 15b).

Each of the layers 26, 27,
As shown in FIG. 7, when the width is formed such that the width of the conductive layer 26> the width of the semiconductive layer 27> the width of the dielectric layer 28, the semiconductive layer 27 is formed. Is the photosensitive drum 1
There is a risk of contact with the grounded aluminum pipe 15a. That is, when a positive voltage is applied to the conductive layer 26 by the power supply unit 32, a positive charge is induced in the conductive layer 26, and the positive charge moves to the surface of the semiconductive layer 27.

At this time, if the grounded aluminum tube 15a of the photosensitive drum 15 comes into contact with the semiconductive layer 27, all the electric charges charged in the semiconductive layer 27 transfer to the aluminum tube 15a, Positive charges cannot be induced on the surface of the body layer 28. Therefore, the transfer drum 11 cannot adsorb the negatively charged toner adsorbed on the OPC film 15b of the photoreceptor drum 11, and a transfer failure occurs.

Therefore, in order to prevent this, as shown in FIG. 8, the width of the conductor layer 26 and the width of the dielectric layer 28 are made the same,
By making the width of the semiconductive layer 27 smaller than the width of both layers 26 and 28, contact between the semiconductive layer 27 and the grounded aluminum tube 15a is prevented, and leakage of electric charge is prevented. . Thereby, the transfer drum 11 becomes the OPC film 15b.
The negatively charged toner adsorbed on the surface can be reliably adsorbed, and transfer failure can be eliminated.

In the above configuration, an electrostatic latent image based on image data is formed on the photosensitive drum 15, toner is adhered to the photosensitive drum 15 by the developing unit 3, and the electrostatic latent image is developed and visualized.

On the other hand, the uppermost transfer paper P in the paper feed cassette 5
Are fed to the PF roller 8 one by one by the rotation of the pickup roller 7 in the direction of the arrow, and are conveyed to the pre-curl roller 10. When the transfer paper P such as an envelope is supplied from the manual feed port 6, the transfer paper P is conveyed to the pre-curl roller 10 by the manual feed roller 9.

The transfer paper P is transferred to the pre-curl roller 1
A water content reduction step of reducing the water content by heating while curling in accordance with the shape of the transfer drum 11 is performed.

In the water content reducing step, first, when the power switch is turned on, the heater lamp 10c of the upper roller 10a is turned on.
And the pre-curl roller 10 is prepared and heated.
At this time, the set temperature (180 ° C.) of the fixing roller 22 is higher than the set temperature (90 ° C.) of the pre-curl roller 10, and the set temperature reaching time (120 sec) is long. However, there is a method of increasing the amount of power supplied to the fixing roller 22 to shorten the time required to reach the set temperature, but has a disadvantage in that the amount of power consumption increases.

The fixing roller 22 is located downstream of the pre-curl roller 10 in the transport direction, and there is a time lag between the transfer paper P reaching the position of the pre-curl roller 10 and the fixing roller 22. In consideration of the above, the set temperature arrival time (60 sec) is set. Thus, the set temperature rising time of the pre-curl roller 10 is shorter than the set temperature rising time of the fixing roller 22, as shown in FIG. Here, the pre-curl roller 1
If the rise time of 0 is equal to or longer than the rise time of the fixing roller 22, the machine printable time is delayed, which results in an increase in the wait time. Therefore, the amount of power supplied to the fixing roller 22 can be reduced because heating is not required.

As for the temperature control of the pre-curl roller 10, as shown in FIG. 10, the controller 34 detects the temperature from the data obtained by the roller surface temperature detection sensor 33 provided near the upper roller 10a of the pre-curl roller 10. I do. Then, the value is transmitted to the heater lamp control unit 35. The heater lamp control unit 35 determines the ON / OFF time of one cycle of the power pulse supplied to the heater lamp 10c inside the upper roller 10a based on the detected value. Table 3 shows the ratio
As shown in FIG.
The temperature is controlled so that the time ratio is 1: 3 and the set temperature is maintained.

[0066]

[Table 3]

At this time, the set temperature of the pre-curl roller 10 is desirably a temperature sufficient to evaporate the moisture contained in the transfer paper P. As shown in Table 4, the surface temperature of the pre-curl roller 10 is set at 60 ° C. It is easy to be adsorbed at ℃, the effect of reducing the water content can be confirmed. Therefore, it is preferable to set the temperature of the pre-curl roller 10 to 90 ° C. or higher.

[0068]

[Table 4]

Then, the upper roller 1 on which the transfer paper P is heated
By passing between the lower roller 10a and the lower roller 10b while being pressed, the transfer paper P is curled while the wrinkles are extended, and moisture contained in the transfer paper P is evaporated.

The change in the water content is caused by a change in the moisture absorption state of the transfer paper P from the air due to the environment such as the ambient temperature and humidity of the transfer paper P. Then, heating by the heater lamp 10c is performed to reduce the water content of the transfer paper P and increase the resistance value of the transfer paper P. When the resistance value of the transfer paper P is low, when the transfer paper P is attracted to the transfer drum 11, the electric charge induced on the surface of the transfer paper P by the ground roller 12 passes through the transfer paper P and moves to the surface of the transfer drum 11, Transfer paper P is transferred to transfer drum 11
And the transfer paper P is peeled off. Therefore, by increasing the resistance value, the transfer paper P is easily attracted to the transfer drum 11.

For example, in an NN environment (air temperature 25 ° C., humidity 50
%), The water content of the paper is about 5-6%, regardless of the weight of the paper
In an HH environment (air temperature 35 ° C., humidity 80%), the water content is more than doubled and becomes 10 to 15%.
Table 5 shows the resistance value of the transfer paper P in each environment and the resistance value of the transfer paper P that has been subjected to the water content reduction step. Thereby, when the temperature and humidity are high (HH
It can be seen that the resistance value of the transfer paper P is increased by passing through the pre-curl roller 10 although the resistance value is low in the environment.

[0072]

[Table 5]

Next, the transfer paper P curled by the pre-curl roller 10 and having a reduced water content is conveyed between the transfer drum 11 and the ground roller 12 as shown in FIG. It is pressed against the surface of the layer 28. The electric charge accumulated in the semiconductive layer 27 moves to the dielectric layer 28, and a positive electric charge is induced on the surface of the dielectric layer 28, so that the electric charge accumulates inside the transfer paper P, that is, on the contact surface side with the dielectric layer 28. A negative charge is induced, and the transfer paper P is electrostatically attracted to the transfer drum 11. Note that the suction force does not vary as long as the applied voltage is stable. Further, since the transfer paper P has a reduced water content and a high resistance value, the transfer paper P can be stably suctioned to the transfer drum 11. .

As described above, since the charging is performed by contact, not by air discharge, the conductor layer 26 is charged.
It is sufficient to apply a voltage of +3 kV or less from the results of various experiments, and more preferably +2 kV.
With kV, charging can be performed satisfactorily.

The transfer paper P adsorbed on the transfer drum 11 is charged in a state where the outside is positively charged.
Is transported to the transfer site X of the toner image with the rotation in the direction of the arrow. Then, as shown in FIG.
The toner image is transferred to the transfer paper P by the potential difference between the negative charge of the toner attached to the surface of the transfer paper 5 and the positive charge of the transfer paper P.

At this time, on the photosensitive drum 15, charging, exposure, development, and transfer are performed for each color. Accordingly, the transfer paper P rotates together with the transfer drum 11 while being attracted to the transfer drum 11, and one color transfer is performed every rotation, so that one full-color image is obtained with a maximum of four rotations. However, when a black-and-white image or a mono-color image is obtained, the rotation of the transfer drum 11 may be one time.

When all the toner images have been transferred onto the transfer paper P, the transfer paper P is forcibly moved from the surface of the transfer drum 11 by the separation claw 14 provided on the circumference of the transfer drum 11 so as to be able to be separated. And guided to the fixing guide 23.

Thereafter, the toner image on the transfer paper P is guided to the fixing roller 22 by the fixing guide 23, and is fused and fixed on the transfer paper P by the temperature and pressure of the fixing roller 22. Then, the fixed transfer paper P is transferred to the discharge roller 24.
Is discharged onto the discharge tray 25.

As described above, since the transfer paper P is not attracted and transferred by charge injection by air discharge, but the transfer paper P is attracted and transferred by the induction of electric charge, the voltage can be kept low. Also easy to do. In addition, it is possible to eliminate variations in voltage due to atmospheric pressure. As a result, the voltage applied to the transfer drum 11 is not affected by the environment such as temperature and humidity, and the voltage can be kept constant, so that the transfer efficiency can be improved and the image quality can be improved. Further, since the surface of the transfer drum 11 can be stably charged as compared with the case where charge is induced on the surface of the transfer drum 11 by electric discharge, adsorption and transfer of the transfer paper P can be performed stably. it can.

Further, since only one voltage application point is required, it is not necessary to apply a voltage to each of a plurality of chargers.
The apparatus can be simplified, and the manufacturing cost can be reduced.

Further, 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. Absent. This allows
Since transfer defects such as white spots do not occur in that portion, 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, the surface potential of the transfer drum 11 does not vary, and the printing disturbance and the like can be eliminated. This can also improve the transfer efficiency and improve the image quality.

Further, in the present invention, since the transfer paper P is heated by the pre-curl roller 10 and the water content of the transfer paper P is reduced, the resistance value of the transfer paper P is increased and the transfer paper P is easily charged. Therefore, even if the environmental conditions such as temperature and humidity and the state of the transfer paper P change, the transfer paper P is stably adsorbed to the transfer drum 11, thereby enabling stable transfer.
Good image formation is possible.

Further, a heater lamp 1 for heating the transfer paper P to a pre-curl roller 10 for giving a curvature to the transfer paper P
Because 0c is provided, without taking up space,
It also leads to downsizing of the device. Further, since the transfer paper P passes while being pressed by the pre-curl roller 10 heated from both sides, the occurrence of wrinkling of the paper can be reduced.

Further, since the rise time of the set temperature of the pre-curl roller 10 is shorter than the rise time of the fixing roller 22, the machine printable time can be shortened and the wait time can be shortened. In addition, since the rising time of the set temperature of the fixing roller 22 may be delayed, it is not necessary to apply high power to quickly reach the set temperature, and the fixing roller 22 or the pre-curl roller 10 can be controlled with low power.

The present invention is not limited to the above-described embodiment, and it goes without saying that many modifications and changes can be made to the above-described embodiment within the scope of the present invention.

For example, when a transfer belt is used in place of the transfer drum in the transfer means, a heater is built in a transport roller for transporting the transfer paper to the transfer belt. Further, as the water content reducing means, a means for blowing hot air to the transfer paper using a fan and a heater may be used.

[0088]

As is apparent from the above description, according to the present invention, since the water content reducing means for reducing the water content of the transfer paper is provided, the environmental conditions of temperature and humidity and the state of the transfer paper change. However, the water content of the transfer paper is reduced, the resistance value can be increased, and the transfer paper can be stably adsorbed. Therefore, stable transfer is possible without being affected by the environment, and a good image can be formed. Furthermore, since the water content of the transfer paper can be reduced before the transfer paper is adsorbed, stable and stable adsorption can be performed.

Further, since the transfer drum for adsorbing the transfer paper is directly charged by the applied voltage, the charging of the transfer drum is not affected by the environment, and a heater is provided on the pre-curl roller as a water content reducing means. In addition, adsorption of the transfer paper which does not depend on the environment can be achieved. Moreover, it is not necessary to take a special space for providing the heating mechanism, and space can be saved.

Further, since the set temperature rise time of the pre-curl roller is shorter than the rise time of the fixing roller, the machine printable time can be shortened and the wait time can be shortened. Further, since the set temperature rise time of the fixing roller may be delayed, it is not necessary to apply high power to the fixing roller to quickly reach the set temperature, and the fixing roller or the pre-curl roller can be controlled with low power, thereby saving energy. Becomes

[Brief description of the drawings]

FIG. 1 is a configuration diagram near a transfer drum of an image forming apparatus according to an embodiment.

FIG. 2 is a configuration diagram of an image forming apparatus of the present embodiment.

FIG. 3 shows a pre-curl roller.

FIG. 4 is a diagram showing attachment of each layer of the transfer drum.

FIG. 5 is a diagram showing another mounting of each layer of the transfer drum.

FIG. 6 is a diagram illustrating a dimensional comparison between a charging width of a transfer drum and an effective image width.

FIG. 7 is a diagram showing the relationship between the width of each layer of the transfer drum when the transfer of electric charge between the transfer drum and the photosensitive drum is defective;

FIG. 8 is a diagram showing the relationship between the width of each layer of the transfer drum when the transfer of electric charge between the transfer drum and the photosensitive drum is good;

FIG. 9 is a diagram showing a temperature rise curve of a pre-curl roller and a fixing roller.

FIG. 10 is a temperature control block diagram of a pre-curl roller.

FIG. 11 is a diagram illustrating an initial charging state when a transfer sheet is conveyed to a transfer drum;

FIG. 12 is a diagram illustrating a charged state when a transfer sheet is transported to a transfer position on a transfer drum.

FIG. 13 is a configuration diagram near a transfer drum of a conventional image forming apparatus.

FIG. 14 is a configuration diagram near a transfer drum of a conventional image forming apparatus.

FIG. 15 illustrates a configuration of a conventional image forming apparatus.

FIG. 16 is a diagram illustrating a configuration of a conventional image forming apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Precurl roller 10c Heater lamp 11 Transfer drum 15 Photoconductor drum 22 Fixing roller

Claims (4)

(57) [Claims] An image carrier having a toner image formed on a surface thereof, and a toner image formed on the image carrier is transferred to the transfer paper by adsorbing a transfer paper and bringing the transfer paper into contact with the image carrier. Transfer means and the toner image transferred to the transfer paper.
In an image forming apparatus having a fixing unit to be attached, in order to stably adsorb the transfer sheet regardless of environmental conditions such as temperature and humidity and the state of the transfer sheet, the transfer sheet during transfer is transferred before transfer.
Moisture content reducing means for reducing the water content of the transfer sheet is heated at a temperature set to transfer paper is provided on the hydrated water reduction means
The time required to reach the set temperature is determined by the transfer paper
Set based on the time it takes to reach the fuser from the position
An image forming apparatus characterized by that. 2. An image bearing member having a surface on which a toner image is formed.
And a curl that conveys the transfer paper to give it a curvature.
A recurling roller and the transfer paper that has been curled
By being brought into contact with the image carrier, it is formed on the image carrier.
Transfer means for transferring the transferred toner image to the transfer paper, and transfer
A fixing unit for fixing the toner image transferred to the paper.
In the image forming apparatus, environmental conditions such as temperature and humidity and the
Stable adsorption of the transfer paper regardless of the state of the paper
Before the transfer, the transfer paper being transported is heated at the set temperature.
A heater for heating is provided on the pre-curl roller, and
The time required for the pre-curl roller to reach the set temperature
The time it takes to reach the fixing unit from the position of the curl roller
An image forming apparatus characterized in that the image forming apparatus is set based on the setting. 3. The pre-curl roller is a rigidly driven roller.
Body roller, and an elastic roller pressed against the roller.
Comprising a heater inside the rigid roller.
The image forming apparatus according to claim 2, wherein: 4. When the set temperature is 60 ° C. or more, setting of the fixing unit is performed.
2. A temperature lower than the temperature.
Or the image forming apparatus according to 2.