JP4565543B2 - Image forming apparatus - Google Patents

Description

The present invention, a copier, a printer, a facsimile, or those related to the image forming apparatus using an electrophotographic system, such as those of the MFP.

  2. Description of the Related Art Conventionally, in an image forming apparatus using an electrophotographic system such as a copying machine or a printer, a toner image formed on an image carrier such as a photosensitive drum or an intermediate transfer belt is transferred to a transfer paper regardless of the use environment of the apparatus. The development of a transfer device for transferring a material onto a material to be transferred without any problem has been actively conducted.

  Specifically, Japanese Patent Laid-Open No. 2004-228561 is based on the detection result of a temperature / humidity sensor that detects humidity in the image forming apparatus for the purpose of preventing the transfer efficiency from being lowered when the usage environment is high humidity. A technique for adjusting the size of a nip (transfer nip) between an image carrier and a transfer belt is disclosed.

  Japanese Patent Application Laid-Open No. 2004-228867 discloses image formation for the purpose of preventing the transfer material that contacts the image carrier during the transfer process from becoming difficult to separate from the image carrier when the usage environment is high humidity. A technique for adjusting the position of a nip (transfer nip portion) of a transfer roller with respect to an image carrier based on a detection result of a temperature / humidity sensor that detects humidity in the apparatus is disclosed.

Japanese Patent Laid-Open No. 11-338279 JP 2001-5311 A

  In the above-described conventional image forming apparatus, there is a case where the transfer material in contact with the image carrier is not separated from the image carrier during the transfer process.

Details are as follows.
Generally, when the material to be transferred absorbs moisture in a high humidity environment and the moisture content in the material to be transferred becomes high, the waist of the material to be transferred becomes weak. The material to be transferred that has become weak in this way is difficult to separate from the image carrier while remaining in contact with the image carrier during the transfer process.

  The material to be transferred that has been set in the paper feed unit of the image forming apparatus for a long time is familiar with the use environment (humidity) of the image forming apparatus. Therefore, as in Patent Document 1 and Patent Document 2, the humidity in the image forming apparatus is detected, and the contact condition such as the nip width and the nip position with respect to the image carrier is adjusted based on the detection result. Thus, it is possible to maintain good separation of the transfer material during the transfer process.

  However, the transfer material immediately after being set in the paper feeding unit of the image forming apparatus from a different environment from the environment in which the image forming apparatus is used requires a certain amount of time until it adapts to the environment in which the image forming apparatus is used. Therefore, when image formation is performed immediately after a transfer material that has been stored for a long time in a high humidity environment is set in an image forming apparatus in a low humidity environment, the humidity detection result in the image forming apparatus is Therefore, even if the contact condition of the transfer material with respect to the image carrier is adjusted, it is not possible to ensure good separation of the transfer material. In such a case, the material to be transferred may come into close contact with the image carrier and not be separated, resulting in a paper jam.

  In addition, when image formation is performed immediately after a transfer material that has been stored for a long time in a low humidity environment is set in an image forming apparatus in a high humidity environment, the humidity detection result in the image forming apparatus Even if the contact condition of the transfer material with respect to the image carrier is adjusted based on the above, the transfer material cannot be separated at an appropriate timing. In such a case, the separability with respect to the transfer material becomes too high, and the transfer efficiency may be lowered.

  As described above, the state where the actual moisture absorption state of the transfer material is not correlated with the use environment of the image forming apparatus is used even when the transfer material is set in the image forming apparatus for a long time. This may occur when an image is formed immediately after the environment changes rapidly. For example, when a transfer material is set in an image forming apparatus in a high humidity environment for a long period of time, and an image is formed immediately after the use environment is rapidly changed from a high humidity environment to a low humidity environment. Even in such a case, even if the contact condition of the transfer material to the image carrier is adjusted based on the humidity detection result in the image forming apparatus, it is possible to ensure good separation and transfer properties of the transfer material. become unable.

The present invention has been made to solve the above-described problems, and provides a highly reliable image forming apparatus in which a transfer material is reliably separated during a transfer process regardless of the moisture absorption state of the transfer material. It is to provide.

According to a first aspect of the present invention, an image forming apparatus includes: a transfer device that transfers a toner image formed on an image carrier to a transfer material ; and the image carrier that is in contact with the image carrier. A roller-shaped charging unit that charges the upper surface to form a ground potential, and the moisture content of the transfer material is from a paper supply unit that stores the transfer material to a position of contact with the image carrier. The leading end of the transfer material that is detected toward the contact position with the image carrier when the moisture content of the transfer material is greater than a predetermined value. Only this reduces the background potential when contacting only the image carrier.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect of the present invention, in the path of the transfer material from the paper feeding unit to the contact position with the image carrier, A moisture content detecting means for detecting the moisture content of the transfer material is provided.

The image forming apparatus according to a third aspect of the present invention is the image forming apparatus according to the second aspect , wherein the moisture content detecting means is configured such that the moisture receiving material is timed toward the contact position with the image carrier. It is installed at the position of the registration roller that controls and conveys.

An image forming apparatus according to a fourth aspect of the present invention is the image forming apparatus according to the second or third aspect , wherein the moisture content detecting means applies a voltage across both surfaces of the transfer material. The moisture content is detected from the resistance value.

According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the detection result by the moisture content detecting means is based on at least one of the size and thickness of the transfer material. Is corrected.

According to a sixth aspect of the present invention, there is provided the image forming apparatus according to the second or third aspect , wherein the moisture content detecting means is a voltage between two positions on one side of the transfer material. The moisture content is detected from the resistance value when the is applied.

The image forming apparatus according to a seventh aspect of the present invention is the image forming apparatus according to the second or third aspect , wherein the moisture content detecting means is configured to apply the microwave when the transfer material is irradiated with microwaves. The moisture content is detected from the size of the microwave transmitted through the transfer material.

An image forming apparatus according to an eighth aspect of the present invention is the image forming apparatus according to the second or third aspect , wherein the moisture content detecting means applies a voltage between two positions on the transfer material. The moisture content is detected from the magnitude of the electrostatic capacity.

In the present invention, the moisture content of the transfer material is detected, and the contact condition of the transfer material with respect to the image carrier is varied according to the detection result, so the transfer material can be transferred regardless of the moisture absorption state of the transfer material. It is possible to provide a highly reliable image forming apparatus in which a transfer material is reliably separated during the process.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

Embodiment 1 FIG.
A first embodiment of the present invention will be described in detail with reference to FIGS.
First, the configuration and operation of the entire image forming apparatus will be described with reference to FIG.
In FIG. 1, 1 is an apparatus main body of a laser printer as an image forming apparatus, 3 is an exposure unit that irradiates a photosensitive drum 18 with exposure light L based on image information, and 4 is an image forming unit installed in the apparatus main body 1. A process cartridge as a unit, 7 a transfer device for transferring a toner image formed on a photosensitive drum 18 as an image carrier to a transfer material P, and 9 a fixing for fixing an unfixed image on the transfer material P , 10 is a paper discharge tray on which an output image is placed, 12 is a paper feed unit in which a transfer material P such as transfer paper is stored, 13 is a registration roller for transporting the transfer material P to the transfer device 7, 15 Indicates a manual sheet feeder.

With reference to FIG. 1, an operation during normal image formation in the image forming apparatus will be described.
First, exposure light L such as laser light based on image information is emitted from the exposure unit 3 (writing unit) toward the photosensitive drum 18 of the process cartridge 4. A photoconductive drum 18 as an image carrier rotates in the clockwise direction in the drawing, and corresponds to image information on the photoconductive drum 18 through a predetermined image forming process (charging process, exposure process, development process). A toner image is formed.
Thereafter, the toner image formed on the photosensitive drum 18 is transferred onto the transfer material P conveyed by the registration roller 13 at the position of the transfer device 7.

On the other hand, the transfer material P conveyed to the transfer device 7 operates as follows.
First, the uppermost sheet of the transfer material P stored in the paper feeding unit 12 is transported toward the position of the transport path K. Thereafter, the transfer material P passes through the conveyance path K and reaches the position of the registration roller 13. Then, the transfer material P that has reached the position of the registration roller 13 is conveyed toward the transfer device 7 at the same timing in order to align with the toner image formed on the photosensitive drum 18.

After the transfer process, the transfer material P passes through the position of the transfer device 7 and then reaches the fixing unit 9 through the conveyance path. The transfer material P that has reached the fixing unit 9 is fed between the fixing roller and the pressure roller, and the toner image is fixed by the heat received from the fixing roller and the pressure received from both rollers. Thereafter, the transfer material P on which the toner image is fixed is discharged from the image forming apparatus main body 1 as an output image and placed on the paper discharge tray 10.
Thus, a series of image forming processes is completed.

Next, with reference to FIGS. 2 and 3, the configuration and operation around the transfer device 7 (image forming unit) installed in the image forming apparatus main body 1 will be described in detail.
FIG. 2 is a cross-sectional view showing an image forming unit around the transfer device 7. FIG. 3 is a block diagram illustrating the control unit 30 of the image forming apparatus main body 1.

As shown in FIG. 2, the transfer device 7 mainly includes a transfer belt 71, a driving roller 72, a driven roller 73, a transfer bias roller 74, cleaning mechanisms 76 to 79, nip width variable mechanisms 80 to 82, and the like.
The transfer belt 71 is an endless belt made of a material having a predetermined electrical resistance, such as urethane rubber, chloroprene rubber, polycarbonate, polyvinylidene fluoride, and the like. The transfer belt 71 is stretched and supported by a driving roller 72 and a driven roller 73. Then, when the drive roller 72 is driven to rotate counterclockwise in FIG. 2 by a drive motor (not shown), the transfer belt 71 rotates in the arrow direction in FIG.

  The transfer belt 71 is in contact with the photosensitive drum 18 to form a nip (nip width N). This nip width N (nip size) can be varied by nip width varying mechanisms 80 to 82 as variable means.

  The nip width varying mechanisms 80 to 82 mainly include a cam 80, a lever 81, an engaging portion 82, and the like. The cam 80 is rotated by a predetermined angle by the stepping motor 41. One end of the lever 81 is in contact with the peripheral surface of the cam 80, and the other end is in contact with the engaging portion 82. The engaging portion 82 is provided integrally with a case (not shown) that holds the transfer belt 71, the driving roller 72, and the driven roller 73.

With such a configuration, when the cam 80 is rotated by a predetermined angle, the lever 81 rotates in the direction of the arrow in FIG. 2 and pushes the engaging portion 82 upward. As a result, the transfer belt 71 is also pushed upward, and the nip width N is increased. On the other hand, when the cam 80 is rotated and the lever 81 is rotated in the clockwise direction in FIG. 2, the engaging portion 82 and the transfer belt 71 are lowered and the nip width N is reduced.
The nip width varying mechanisms 80 to 82 vary the nip width N as a contact condition according to the moisture content of the transfer material P involved in the transfer process. This will be described in detail later.
The nip width varying mechanisms 80 to 82 further rotate the cam 80 to completely remove the transfer belt 71 from the photoconductive drum 18 so that the transfer material P jammed at the position of the transfer belt 71 can be removed. be able to.

  The transfer bias roller 74 is installed so as to contact the inner peripheral surface of the transfer belt 71. The transfer bias roller 74 is connected to a power supply unit 45 that supplies a transfer bias. With such a configuration, a transfer bias is applied from the transfer bias roller 74 to the transfer belt 71, and the toner image formed on the photosensitive drum 18 is transferred to the transfer material P on the transfer belt 71. .

  The cleaning mechanisms 76 to 79 include a cleaning blade 76, a cleaning bias roller 77, a bias roller cleaning blade 78, a toner recovery coil 79, and the like. The cleaning mechanisms 76 to 79 are for removing adhered substances such as toner adhered on the transfer belt 71 and transporting the adhered substances to a waste bottle.

  Specifically, the toner or the like adhering to the transfer belt 71 is removed by the cleaning blade 76 that contacts the transfer belt 71 and the cleaning bias roller 77 that contacts the transfer belt 71 and is applied with a predetermined voltage. The toner collected by the cleaning blade 76 and the cleaning bias roller 77 is conveyed from the transfer device 7 toward a waste bottle (not shown) by a toner collection coil 79 installed in the collection space. The toner collected by the cleaning bias roller 77 is scraped off into the collection space by the bias roller cleaning blade 78.

  On the other hand, the registration roller 13 described with reference to FIG. Referring to FIG. 2, the registration roller 13 includes an upper roller 13b and a lower roller 13a. Then, the transfer material P conveyed from the paper supply unit 12 is sandwiched between the upper roller 13b and the lower roller 13a, which are stopped from rotating, and is stopped for a predetermined time while being bent by a predetermined amount. Then, the upper roller 13b and the lower roller 13a are started to rotate so that the toner image formed on the photosensitive drum 18 is transferred to a desired position on the transfer material P, and the rotation of the upper roller 13b and the lower roller 13a is started. P is conveyed toward the contact position N.

Here, a moisture detection sensor 40 (moisture meter) as a moisture content detecting means is installed at the position of the registration roller 13.
The moisture detection sensor 40 applies a predetermined voltage between the upper roller 13b and the lower roller 13a sandwiching the transfer material P (when a predetermined voltage is applied to both surfaces of the transfer material P). The resistance value of the transfer material P is detected. Data on the resistance value of the transfer material P detected by the moisture detection sensor 40 is transmitted to the control unit 30, and the control unit 30 determines the moisture content (moisture content) of the transfer material P. When the resistance value of the transfer material P is small, it is determined that the moisture content of the transfer material P is large.

  Specifically, when it is determined that the resistance value of the transfer material P detected by the moisture content detection sensor 40 is smaller than a predetermined value and the moisture content of the transfer material P is larger than the predetermined value, Adjustment control is performed so that the nip width N at the contact position between the transfer belt 71 and the photosensitive drum 18 is reduced by the nip width variable mechanisms 80 to 82 described above.

In the first embodiment, when the moisture content (moisture content) obtained by the control unit 30 is less than 10%, the nip width variable mechanisms 80 to 82 as variable means so that the nip width N is 8 mm. To control. The nip width of 8 mm is an optimal condition for the transfer material P having relatively little moisture absorption to be separated satisfactorily while ensuring a sufficient transfer rate.
On the other hand, when the moisture content (moisture content) obtained by the control unit 30 is 10% or more, the nip width variable mechanisms 80 to 82 as variable means are controlled so that the nip width N is 6 mm. . The nip width of 6 mm is an optimal condition for the material P to be transferred, which absorbs a lot of moisture, to be separated well without being wound around the photosensitive drum 18 during the transfer process.

  As described above, in the first embodiment, the moisture content of the transfer material P is directly detected, and the nip width N as the contact condition is adjusted based on the detection result. Even when there is no correlation between the use environment and the moisture absorption state of the transfer material P, it is possible to always maintain good separation.

  Note that the moisture content of the transfer material P may be detected at any position on the conveyance path K from the paper feed unit 12 or the manual paper feed unit 15 to the transfer device 7. However, since the position of the registration roller 13 is a position immediately before the transfer process is performed and the position where the transfer material P is stopped for a certain time, in order to perform moisture content detection and nip width adjustment. Is preferred. That is, it is possible to secure sufficient time for highly accurate moisture detection and nip width adjustment.

  Here, when it is determined that the moisture content of the transfer material P is larger than the predetermined value based on the detection result detected by the moisture detection sensor 40, the above-described nip width variable mechanisms 80 to 82 It is preferable to perform adjustment control so that the nip width N is reduced only at the front end portion of the transferred material P to be transferred (a region where an image of about 0 to 15 mm is not formed from the front end). Specifically, when the moisture content (moisture content) obtained by the control unit 30 is 10% or more, the nip width N when the tip of the transfer material P is fed into the nip is 6 mm, The variable nip width mechanisms 80 to 82 are controlled in a stepwise manner so that the nip width N immediately after the tip portion is delivered from the nip is 8 mm.

  As a result, the transfer material P having a high moisture content is favorably separated without its front end being wound around the photosensitive drum 18, so that the entire transfer material P is well separated by its inertial force. It will be. Furthermore, since the transfer process is performed with a sufficient nip width N (8 mm) in the image area other than the front end portion of the transfer material P, it is possible to secure a high transfer rate and maintain good image quality. it can.

  Here, the moisture content calculated by the control unit 30 based on the resistance value detected by the moisture detection sensor 40 is corrected by the size (mainly the width in the transport direction) and the thickness of the transfer material P. It is preferable. As a result, the resistance value variation detected by applying a voltage to both surfaces of the material to be transferred P takes into account the variation due to the size and thickness of the material to be transferred P. The amount can be obtained with high accuracy.

  In the first embodiment, when it is determined that the moisture content of the transfer material P is larger than a predetermined value, the nip width N is adjusted and controlled. The predetermined value of the moisture content, which is a threshold value when adjusting the nip width N, can be changed depending on the type of the transfer material P. In other words, the material to be transferred P absorbs moisture, and the waist becomes weak and the separability decreases, but the strength of the original waist varies depending on the type of the material to be transferred P. Therefore, when the transfer material P is set in the paper feeding unit 12, information related to the type of the transfer material P (mainly information related to the waist) is input to the information unit 30, and based on the information. The predetermined value of moisture content for control is changed. Note that information input regarding the type of transfer material P can be achieved, for example, by embedding a minimal wireless IC chip in the transfer material P and collecting information on the IC chip.

On the other hand, referring to FIG. 2, a process cartridge 4 is installed around the transfer device 7.
In the process cartridge 4, a photosensitive drum 18, a charging unit 19, a developing unit 20, and a cleaning unit 21 are mainly integrated. The process cartridge 4 is configured to be detachable from the image forming apparatus main body 1.

The photosensitive drum 18 is formed by forming a charge generation layer, a charge transport layer, and the like on a base tube made of aluminum. Then, the process cartridge 4 is installed in the apparatus main body 1, and a nip is formed between the photosensitive drum 18 and the transfer belt 71 of the transfer device 7.
The charging unit 19 is formed by forming a roller unit made of a conductive material in which conductive powder is dispersed in a resin on a shaft formed of stainless steel.
The cleaning unit 21 is provided with a blade 21 a that is made of a rubber material and that contacts the photosensitive drum 18 and cleans untransferred toner.

  The developing unit 20 mainly includes a developing roller 20a facing the photosensitive drum 18, a replenishing roller 20b in sliding contact with the developing roller 20a, and an agitating member that agitates and conveys toner T (one-component developer) in the developing unit 20. 20c, a doctor blade 20d in contact with the developing roller 20a, and a toner storage portion 20f that supplies the toner T stored by the toner supply roller 20e.

Referring to FIG. 3, the control unit 30 includes a CPU 31, a ROM 32, a RAM 33, an input circuit 34, a motor driver 35, a power supply driver 36, an I / O 37, and the like.
The detection information of the moisture content detection sensor 40 described above is transmitted to the CPU 31 via the input circuit 34 of the control unit 30. The CPU 31 to which the detection information has been transmitted obtains the moisture content of the transfer material P based on a program held in the ROM 32 or RAM 33 and determines whether or not the nip width N has been changed. As a result, when changing the nip width N, an operation signal is transmitted to the stepping motor 41 via the motor driver 35. As a result, the cam 80 is rotated for a predetermined time (predetermined angle), and the nip width N is changed.

The control unit 30 is configured to be able to control on / off and the magnitude of the transfer bias supplied from the power supply unit 45 to the transfer bias roller 74 via the power supply driver 36.
Information relating to the size of the transfer material P input from the operation panel 42 (operation unit) is also transmitted to the control unit 30.

Hereinafter, the image forming process performed on the photosensitive drum 18 will be described in detail with reference to FIG.
The photosensitive drum 18 is rotationally driven in a clockwise direction in FIG. 2 by a drive motor (not shown). The surface of the photosensitive drum 18 is charged to a desired charging potential at a position where the photosensitive drum 18 faces the charging unit 19 (charging process). This charged potential is a background potential (the potential of the non-image portion) on the photosensitive drum 18.

Thereafter, the surface of the charged photosensitive drum 18 reaches the irradiation position of the exposure light L. Then, a desired electrostatic latent image corresponding to the image information is formed on the photosensitive drum 18 while being exposed in the scanning direction of the exposure light L (the direction perpendicular to the paper surface).
Thereafter, the surface of the photosensitive drum 18 on which the latent image is formed reaches a position facing the developing unit 20. The developing unit 20 develops the latent image on the photosensitive drum 18 to form a desired toner image.

Here, the developing roller 20a rotates in the direction of the arrow in FIG. The toner T in the developing unit 20 is stirred and conveyed by the stirring member 20c and reaches the position of the replenishing roller 20b. The toner T that has reached the position of the replenishing roller 20b is conveyed to a contact portion with the developing roller 20a, and is frictionally charged there. The toner T that is frictionally charged and carried on the developing roller 20a is thinned at the position of the doctor blade 20d, and then reaches a position facing the photosensitive drum 18. Then, the toner T on the developing roller 20a adheres to the latent image on the photosensitive drum 18.
The toner T stored in the toner storage unit 20f is appropriately supplied into the developing unit 20 by the rotation of the toner supply roller 20e as the toner T in the developing unit 20 is consumed.

  Thereafter, the surface of the photosensitive drum 18 on which the toner image is formed reaches a position facing the transfer belt 71 of the transfer device 7 (a position having a nip width N). Then, the toner image on the photosensitive drum 18 is transferred onto the transfer material P conveyed from the registration rollers 13a and 13b so that the center position of the nip width N coincides with the image leading edge position of the transfer material P. The At this time, as described above, the nip width N is optimized based on the moisture content of the transfer material P detected at the positions of the registration rollers 13a and 13b.

A small amount of untransferred toner that has not been transferred to the transfer material P remains on the photosensitive drum 18 after the transfer process. The surface of the photosensitive drum 18 to which the untransferred toner is attached reaches the position of the blade 21a. Then, the untransferred toner on the photosensitive drum 18 is removed from the drum surface by the blade 21a that is in contact with the photosensitive drum 18. Untransferred toner removed from the surface of the photosensitive drum 18 is collected in a collection space of the cleaning unit 21. Thereafter, the surface of the photosensitive drum 18 reaches the irradiation position of the static elimination light emitted from the static elimination unit (not shown). Then, the surface potential on the photosensitive drum 18 is initialized while receiving the static elimination light.
Thus, a series of image forming processes performed on the photosensitive drum 18 is completed.

On the other hand, the transfer material P on which the toner image is transferred at the position of the nip width N is satisfactorily separated from the photosensitive drum 18 by the contact condition with the optimized nip width N described above. The material P to be transferred after being separated from the photosensitive drum 18 is conveyed as the transfer belt 71 moves in the circumferential direction, and is separated from the transfer belt 71 at the position of the drive roller 72. The transfer material P separated from the transfer belt 71 is conveyed to the fixing unit 9 described with reference to FIG.
Further, the surface of the transfer belt 71 after the transfer material P is separated is cleaned at the positions of the cleaning blade 76 and the cleaning bias roller 77, and a series of transfer processes is completed.

  As described above, in the first embodiment, the moisture content of the transfer material P is detected, and the nip width N (contact condition) of the transfer material P with respect to the photosensitive drum 18 is set according to the detection result. It is variable. Accordingly, the transfer material P can be reliably separated during the transfer process regardless of the moisture absorption state of the transfer material P.

  In the first embodiment, the moisture content of the transfer material P is detected, and the nip width N of the transfer material P with respect to the photosensitive drum 18 is varied according to the detection result. On the other hand, the moisture content of the transfer material P can be detected, and the transfer bias supplied to the transfer bias roller 74 can be varied according to the detection result. Specifically, when it is determined that the moisture content of the transfer material P is larger than a predetermined value, the transfer bias magnitude (absolute value) is changed to be small. That is, when the moisture content of the transfer material P is large, the adhesion of the transfer material P to the photosensitive drum 18 is weakened, and the separability of the transfer material P is improved. Also in this case, it is preferable to weaken the transfer bias only when the leading end portion of the transfer material P is in the nip N. Even in such a case, since the contact condition of the transfer material P with respect to the photosensitive drum 18 is changed according to the moisture absorption state of the transfer material P, a good separation property is always ensured.

  It is also possible to detect the moisture content of the transfer material P and vary the background potential on the photosensitive drum 18 in accordance with the detection result. Specifically, when it is determined that the moisture content of the transfer material P is larger than a predetermined value, the charging unit 19 is adjusted and controlled so that the background potential (absolute value) is reduced. That is, when the moisture content of the transfer material P is large, the adhesion of the transfer material P to the photosensitive drum 18 is weakened, and the separability of the transfer material P is improved. Also in this case, it is preferable to weaken the background potential only when the leading end portion of the transfer material P is in the nip N. Even in such a case, since the contact condition of the transfer material P with respect to the photosensitive drum 18 is changed according to the moisture absorption state of the transfer material P, a good separation property is always ensured.

In the digital image forming apparatus as in the first embodiment, the background potential is varied by adjusting the charging unit 19. In the analog image forming apparatus, the background potential is adjusted by adjusting the exposure unit. Will be variable.
Further, instead of adjusting the charging unit 19 to change the background potential, a light irradiation unit that irradiates light such as LED light on the photosensitive drum 18 can be provided at a position facing the photosensitive drum 18. . Also in this case, since the background potential on the photosensitive drum 18 can be changed before the transfer process, the contact condition of the transfer material P is changed according to the moisture absorption state of the transfer material P, and the good separation property is obtained. Can be secured.

  In the first embodiment, when the moisture content of the transfer material P is 10% or more, the nip width N is changed from 8 mm to 6 mm. On the other hand, the moisture content is divided into three or more stages (for example, three stages of 10%, 15% and 20%), and the nip width N is changed stepwise (for example, 6 mm). 4mm and 2mm, which is a three-stage change).

Embodiment 2. FIG.
The second embodiment of the present invention will be described in detail with reference to FIG.
FIG. 4 is a schematic diagram showing the moisture detection sensor according to the second embodiment, and is a top view of the upper roller 13b of the registration roller 13 installed in the image forming apparatus as viewed from above. The moisture content detection sensor 40 according to the second embodiment applies a voltage between both surfaces of the transfer material P because the resistance value is detected by applying a voltage to two positions on one surface of the transfer material P. Thus, it is different from that of the first embodiment in which the resistance value is detected.

  As shown in FIG. 4, the upper roller 13b of the registration roller includes two conveying rollers 13b1 and 13b2 on the core shaft. The transfer material P sandwiched between the transport rollers 13b1 and 13b2 of the upper roller 13b and the lower roller (not shown) is transported toward the transfer device 7 as in the first embodiment. (This is the movement in the direction of the arrow in FIG. 4)

  In the second embodiment, the two conveying rollers 13b1 and 13b2 of the upper roller 13b are formed of a conductive material such as a metal material, and a predetermined voltage is applied between them by the moisture detection sensor 40. The That is, a predetermined voltage is applied between the two conveying rollers 13b1 and 13b2 that are in contact with the transfer material P. The moisture-containing detection sensor 40 detects the resistance value at that time and transmits the information to the control unit 30. In the control unit 30, as in the first embodiment, the moisture content of the transfer material P is obtained based on the detection result of the moisture detection sensor 40. When the resistance value of the transfer material P is small, it is determined that the moisture content of the transfer material P is large.

  Specifically, when it is determined that the resistance value of the transfer material P detected by the moisture content detection sensor 40 is smaller than a predetermined value and the moisture content of the transfer material P is larger than the predetermined value, As in the first embodiment, the nip width variable mechanisms 80 to 82 adjust and control the nip width N to be small.

As described above, in the second embodiment, the moisture content of the transfer material P is directly detected, and the nip width N as the contact condition is adjusted based on the detection result. Even when there is no correlation between the usage environment and the moisture absorption state of the transfer material P, it is possible to prevent the occurrence of poor separation.
In the second embodiment, since the resistance value between the fixed distances on one side of the transfer material P (the surface onto which the toner image is transferred) is detected, the detection result is the transfer material. The detection process is simplified by being less influenced by the size and thickness of P.

Embodiment 3 FIG.
A third embodiment of the present invention will be described in detail with reference to FIG.
FIG. 5 is a cross-sectional view showing the periphery of the transfer apparatus according to the third embodiment, and corresponds to FIG. 2 of the first embodiment. The transfer device 7 of the third embodiment is different from that of the first embodiment using the transfer belt 71 in that a transfer roller 85 is used.

  As shown in FIG. 5, in the third embodiment, a transfer roller 85 is installed as the transfer device 7. The transfer roller 85 is a roller member made of a conductive material using urethane rubber, chloroprene rubber or the like as a raw material. The transfer roller 85 is driven to rotate counterclockwise in FIG. 5 by a drive motor (not shown).

The transfer roller 85 is in contact with the photosensitive drum 18 to form a nip (nip width N). The nip width N can be varied by a raising motor 46 as a variable means. The ascending motor 46 is configured to be able to move the position of the transfer roller 85 in the direction of the double arrow in FIG.
The ascending motor 46 varies the nip width N according to the moisture content of the transfer material P detected by the moisture detection sensor 40.

The transfer roller 85 is supplied with a transfer bias from the power supply unit 45. The magnitude of the transfer bias supplied to the transfer roller 85 can be varied.
Then, the power supply unit 45 varies the transfer bias supplied to the transfer roller 85 according to the moisture content of the transfer material P detected by the moisture detection sensor 40.

The image forming apparatus configured as described above operates as follows.
First, a desired toner image is formed on the photosensitive drum 18 through a charging process, an exposure process, and a development process, as in the first embodiment.
On the other hand, the transfer material P fed from the paper feeder is detected by the moisture detection sensor 40 at the positions of the registration rollers 13a and 13b, as in the first embodiment. Based on the detection result, the moisture content of the transfer material P is determined by the control unit 30.

  As a result, when it is determined that the resistance value of the transfer material P detected by the moisture detection sensor 40 is smaller than the predetermined value and the moisture content of the transfer material P is larger than the predetermined value, the ascending motor Adjustment control is performed by 46 so that the nip width N is reduced. Further, the power supply unit 45 performs adjustment control so that the transfer bias supplied to the transfer roller 85 is reduced.

Thereafter, the transfer material P is conveyed from the registration rollers 13 a and 13 b toward the contact position between the transfer roller 85 and the photosensitive drum 18. At the contact position, the toner image on the photosensitive drum 18 is transferred onto the transfer material P, and the transfer material P is separated from the photosensitive drum 18. At this time, even if the moisture content of the material to be transferred P is large, the contact condition of the material to be transferred P in the transfer process is optimized, so that good separability can be ensured.
Thereafter, the transfer material P after the transfer process is discharged out of the apparatus main body 1 through the fixing process, as in the first embodiment.

  As described above, in the third embodiment, the moisture content of the transfer material P is detected, and the nip width N and the transfer bias are varied according to the detection result. Accordingly, the transfer material P can be reliably separated during the transfer process regardless of the moisture absorption state of the transfer material P.

Embodiment 4 FIG.
A fourth embodiment of the present invention will be described in detail with reference to FIG.
FIG. 6 is a cross-sectional view showing the periphery of the transfer device according to the fourth embodiment, and corresponds to FIG. 2 of the first embodiment. The transfer device 7 of the fourth embodiment is different from that of the first embodiment using the transfer belt 71 in that a transfer charger 86 that performs corona discharge and a separation charger 87 are used.

  As shown in FIG. 6, in the fourth embodiment, a transfer charger 86 and a separation charger 87 are installed as the transfer device 7. The transfer charger 86 and the separation charger 87 are each composed of a wire made of tungsten or the like for performing corona discharge toward the photosensitive drum 18 and a metal plate provided around the wire.

Here, a DC transfer bias having a polarity different from the polarity of the toner is supplied from the power supply unit 45 to the wire of the transfer charger 86. As a result, the toner image on the photosensitive drum 18 is transferred onto the transfer material P. On the other hand, a DC and AC separation bias is superimposed and supplied from the power supply unit 45 to the wire of the separation charger 87. As a result, the adhesion of the transfer material P to the photosensitive drum 18 is reduced, and the transfer material P is separated from the photosensitive drum 18.
The magnitudes of the transfer bias supplied to the transfer charger 86 and the separation bias supplied to the separation charger 87 can be varied.
The power supply unit 45 varies the transfer bias and the separation bias in accordance with the moisture content of the transfer material P detected by the moisture detection sensor 40.

Further, the transfer charger 86 is provided with an opening adjusting plate 89 as a variable means for changing the size of the opening D by the metal plate surrounding the wire. Specifically, the opening adjustment plate 89 is configured to be slidable in the left-right direction in FIG.
Then, the drive unit 47 varies the size of the opening D by the opening adjustment plate 89 according to the moisture content of the transfer material P detected by the moisture detection sensor 40.

The transfer charger 86 is provided with a guide member 88 as a variable means for guiding the transfer material P to a contact position with the photosensitive drum 18. Specifically, the guide member 88 is configured to be slidable in the vertical direction in FIG.
The drive unit 47 varies the adhesion of the transfer material P to the photosensitive drum 18 by the guide member 88 according to the moisture content of the transfer material P detected by the moisture detection sensor 40.

The image forming apparatus configured as described above operates as follows.
First, a desired toner image is formed on the photosensitive drum 18 through a charging process, an exposure process, and a development process, as in the first embodiment.
On the other hand, the transfer material P fed from the paper feeder is detected by the moisture detection sensor 40 at the positions of the registration rollers 13a and 13b, as in the first embodiment. Based on the detection result, the moisture content of the transfer material P is determined by the control unit 30.

  As a result, when it is determined that the resistance value of the transfer material P detected by the moisture detection sensor 40 is smaller than a predetermined value and the moisture content of the transfer material P is larger than the predetermined value, the drive unit 47, the opening adjusting plate 89 is moved so that the opening D becomes narrow, and the separation property of the transfer material P is improved. Further, the guide member 88 is moved so as to be retracted from the photosensitive drum 18 by the driving unit 47, so that the separability of the transfer material P is improved. Further, the power supply unit 45 performs adjustment control so that the transfer bias is reduced and the separation bias is increased, so that the separation property of the transfer material P is improved.

Thereafter, the transfer material P is conveyed from the registration rollers 13 a and 13 b toward the position where the transfer charger 86 and the photosensitive drum 18 face each other. Then, the toner image on the photosensitive drum 18 is transferred onto the transfer material P at the facing position. Further, the transfer material P is separated from the photosensitive drum 18 at a position where the separation charger 87 and the photosensitive drum 18 face each other. At this time, even if the moisture content of the material to be transferred P is large, the contact condition of the material to be transferred P in the transfer process is optimized, so that good separability can be ensured.
Thereafter, the transfer material P after the transfer process is discharged out of the apparatus main body 1 through the fixing process, as in the first embodiment.

  As described above, also in the fourth embodiment, the moisture content of the transfer material P is detected, and the contact condition of the transfer material P with respect to the photosensitive drum 18 is varied according to the detection result. Accordingly, the transfer material P can be reliably separated during the transfer process regardless of the moisture absorption state of the transfer material P.

In each of the above embodiments, the moisture content detecting means 30 and 40 using the electrical resistance method for detecting the moisture content from the resistance value of the transfer material P are used. Instead, the moisture content of the microwave transmission method is used. It is also possible to use a quantity detection means or a capacitance type moisture content detection means.
Specifically, in the case of a microwave moisture content detecting means, the microwave is irradiated to one side of the transfer material P and the magnitude of the microwave transmitted from the other side is detected. When the moisture content of the transfer material P is large, the microwave loses energy and attenuates, so that the size of the microwave becomes small. Therefore, when the magnitude of the microwave that passes through the transfer material P becomes smaller than a predetermined value, the contact condition of the transfer material P such as the nip width N is controlled.
In the case of the electrostatic capacity type moisture content detection means, a voltage is applied between two positions (two points on one side or two points on both sides) on the transfer material P. Applied to detect the magnitude of the capacitance. When the moisture content of the transfer material P is large, the dielectric constant increases and the capacitance increases. Therefore, when the capacitance of the transfer material P becomes larger than a predetermined value, the contact condition of the transfer material P such as the nip width N is controlled.
Even in these cases, the same effects as those of the above embodiments can be obtained.

  In each of the above embodiments, the photosensitive drum 18 is used as the image carrier facing the transfer device 7, but the application of the present invention is not limited to this. Specifically, the present invention can also be applied to an image forming apparatus using an intermediate transfer belt, a photosensitive belt, or the like as an image carrier facing the transfer device 7. Here, the intermediate transfer belt is an image carrier frequently used in a color image forming apparatus, and a plurality of color toner images are superimposed and carried as one color toner image, and the color toner is transferred onto the transfer material P. It is for transferring an image. The photosensitive belt is an endless belt-shaped image carrier having a photosensitive layer in the same manner as the photosensitive drum.

  Furthermore, the present invention is not limited to the above-described embodiments, and within the scope of the technical idea of the present invention, the embodiments can be modified as appropriate in addition to those suggested in the above-described embodiments. it is obvious. Further, the number, position, shape, and the like of the constituent members are not limited to the above-described embodiments, and the number, position, shape, and the like that are suitable for implementing the present invention can be used.

1 is an overall configuration diagram illustrating an image forming apparatus according to Embodiment 1 of the present invention. FIG. 2 is a cross-sectional view showing the periphery of a transfer device in the image forming apparatus of FIG. 1. FIG. 2 is a block diagram illustrating a control unit in the image forming apparatus of FIG. 1. It is the schematic which shows the moisture containing detection sensor in Embodiment 2 of this invention. It is sectional drawing which shows the circumference | surroundings of the transfer apparatus in Embodiment 3 of this invention. It is sectional drawing which shows the circumference | surroundings of the transfer apparatus in Embodiment 4 of this invention.

Explanation of symbols

1 image forming apparatus main body (apparatus main body), 3 exposure unit,
4 Process cartridge,
7 transfer device, 9 fixing unit, 12 paper feeding unit, 13 registration roller,
18 Photosensitive drum (image carrier), 19 charging unit, 20 developing unit,
21 cleaning unit, 30 control unit,
40 moisture content detection sensor (moisture content detection means), 41 stepping motor,
45 power supply, 46 ascending motor, 47 drive,
71 transfer belt, 72 driving roller, 73 driven roller,
74 transfer bias roller, 80 cam, 81 lever,
82 engaging portion, 85 transfer roller,
86 Transfer charger, 87 Separation charger, 88 Guide member,
89 Opening adjustment plate, P transfer material, N nip width, D opening.

Claims (8)

A transfer device for transferring a toner image formed on the image carrier to a transfer material;
A roller-shaped charging unit that contacts the image carrier and charges the image carrier to form a ground potential;
With
The moisture content of the material to be transferred is detected in a path from the paper feed unit that houses the material to be transferred to the contact position with the image carrier,
The charging unit is configured when the moisture content of the material to be transferred is greater than a predetermined value, only the tip portion of the transfer material that is conveyed toward the contact position between the image bearing member to said image bearing member An image forming apparatus characterized by reducing a ground potential when contacting. 2. The moisture content detecting means for detecting the moisture content of the material to be transferred is provided in a path of the material to be transferred from the paper feeding unit to a contact position with the image carrier. The image forming apparatus described in 1. 3. The moisture content detecting means is installed at a position of a registration roller that transports the transfer material while controlling the timing toward a contact position with the image carrier. Image forming apparatus. The image forming apparatus according to claim 2, wherein the moisture content detecting unit detects the moisture content from a resistance value when a voltage is applied between both surfaces of the transfer material. The image forming apparatus according to claim 4, wherein a detection result by the moisture content detection unit is corrected based on at least one of a size and a thickness of the transfer material. 4. The image according to claim 2, wherein the moisture content detection unit detects the moisture content from a resistance value when a voltage is applied between two positions on one side of the transfer material. 5. Forming equipment. The moisture content detection means detects moisture content from the magnitude of the microwave that has passed through the transfer material when the transfer material is irradiated with microwaves. The image forming apparatus described. The moisture content detection means detects moisture content from the magnitude of the electrostatic capacitance when a voltage is applied between two positions on the transfer material. Image forming apparatus.

Images