JP2012037663A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that reduces toner contamination of a transcription guide member due to a potential difference between the transcription guide member and an image carrier.SOLUTION: An image forming apparatus of the present invention acquires a latent image potential of an image carrier and applies voltage to a transcription guide member based on the acquired latent image potential.

Description

  The present invention relates to an image forming apparatus for forming a developer (hereinafter referred to as toner) image on a recording material via an image carrier such as a copying machine, a printer, a facsimile machine, etc., which improves toner contamination on a transfer guide member.

  In an electrophotographic apparatus typified by a copying machine, an image carrier is uniformly charged, an electrostatic latent image is formed on the image carrier by image exposure, and then the electrostatic latent image is recorded from a developing device. The toner, which is a material, is charged by a regulating member or the like and supplied to form a toner image on the surface of the image bearing member. The toner image is transferred from the surface of the image bearing member onto a recording material such as paper, and the transferred toner image is fixed by heat, pressure or the like, thereby forming an image.

  By the way, in order to transfer the toner image carried on the image carrier to the recording material, it is necessary to insert the recording material between the image carrier and the transfer device at an appropriate timing or an insertion angle. For this reason, the image forming apparatus is provided with a transfer guide member that defines the path of the recording material upstream of the image carrier in the recording material conveyance direction.

  In recent years, devices using electrophotography, such as copying machines and laser printers, have been increasing in speed due to market demands. When these devices are operated at high speed, the amount of heat per unit time that is mainly discharged from the fixing device increases. Therefore, if the air volume of the cooling device is not increased, the temperature inside the apparatus will increase significantly. However, when the air volume of the cooling device is increased, a strong air flow is generated in the equipment.

  As is widely known, electrophotography is a technique for forming an image by controlling fine powder toner by using the force of an electric field or a magnetic field. Therefore, it is easily affected by the air flow in the image forming apparatus. If there is a strong air flow in the device due to the above-mentioned speeding up, the toner that has lost control by the electric field or magnetic field will scatter into the machine. In particular, when the scattered toner adheres to the transfer path of the recording material, which is a transfer guide member, the scattered toner moves to the recording material when the recording material passes through the transfer guide member, which causes recording material contamination.

  On the other hand, an image forming apparatus that reduces toner contamination on the transfer guide member by applying a predetermined voltage having the same polarity as the toner to the transfer guide member has been proposed (Patent Document 1).

JP 2000-181322 A

  The present invention is a further improvement of the prior art, the purpose of which is not based on the image to be printed, and an image that makes it difficult to cause a potential difference between the transfer guide member and the image carrier, and to prevent the transfer guide member from becoming dirty. It is to provide a forming apparatus.

  In order to achieve the above object, a typical configuration of an image forming apparatus according to the present invention includes an image carrier, latent image forming means for forming an electrostatic latent image on the image carrier, and the electrostatic latent image. Developing means for developing an image with toner to form a toner image on the image carrier, transfer means for transferring the toner image on the image carrier onto a recording material, and transporting the recording material to the transfer means In the image forming apparatus, comprising: a transfer guide member that is provided upstream in the direction and guides a recording material between the transfer unit and the image carrier; and a voltage application unit that applies a voltage to the transfer guide member. A latent image potential acquisition unit configured to acquire a latent image potential of the carrier; and a voltage control unit configured to apply a voltage to the transfer guide member based on the latent image potential acquired by the latent image potential acquisition unit.

  According to the present invention, a potential difference is hardly generated between the transfer guide member and the image carrier without depending on the image to be printed, and contamination of the transfer guide member can be prevented.

1 is an overall configuration diagram of an image forming apparatus according to an embodiment of the present invention. FIG. 6 is a diagram illustrating scattering of negative toner from an image carrier to a pre-transfer guide member according to the first and second embodiments of the present invention. FIG. 6 is a diagram illustrating scattering of positive toner from an image carrier to a pre-transfer guide member. FIG. 6 is a diagram illustrating the presence of positive toner. FIG. 4 is a diagram illustrating that toner is not scattered from an image carrier to a pre-transfer guide member. It is a figure explaining the voltage application to the guide member before transfer which concerns on the 3rd Embodiment of this invention. It is a figure explaining the voltage application in the comparative example with respect to the 3rd Embodiment of this invention. It is a figure which shows the relationship between a printing rate and a photoreceptor average surface potential. FIG. 5 is an explanatory diagram for determining a voltage applied to a transfer guide member when a latent image potential is acquired in a unit region in the entire region of a latent image formed on a recording material or in a direction in which the latent image is crossed. A voltage applied to the transfer guide member when a latent image potential is acquired in one of the entire region and the other in the unit region among the transport direction of the latent image formed on the recording material and the direction crossing the latent image is determined. It is explanatory drawing of this.

<< First Embodiment >>
(Image forming device)
Hereinafter, a laser beam printer for forming a monochrome image of a process cartridge attaching / detaching method using an electrophotographic process as an image forming apparatus according to the present embodiment will be described with reference to FIG. Reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member as an image carrier, which is an organic photosensitive member in which a photosensitive layer made of an organic photoconductive layer (OPC) is formed on the outer periphery of a grounded cylindrical aluminum substrate. The OPC photosensitive member 1 is rotationally driven in a clockwise direction indicated by an arrow at a predetermined process speed (circumferential speed), for example, 200 mm / sec. Reference numeral 2 denotes a charging roller as a contact charging member brought into contact with the OPC photoreceptor 1, and is driven to rotate as the photoreceptor 1 is driven to rotate. In the rotation process, the photosensitive member 1 is uniformly charged to a predetermined polarity (negative polarity in the present embodiment) by a charging roller 2 to which an oscillating voltage (VAC + VDC) is applied. Then, scanning exposure by the laser 5 modulated corresponding to the time-series electric digital image signal as image information output from the laser scanner is received through the mirror 4 on the charging processing surface. As a result, the potential of the exposed portion of the surface of the photoreceptor 1 is lowered from the dark potential to the bright potential, and an electrostatic latent image corresponding to the image exposure pattern is formed on the drum surface by the potential contrast between the dark potential portion and the light potential portion. It is formed on an image carrier. In this embodiment, the charging roller 2 and the laser 5 function as a latent image forming unit that forms an electrostatic latent image on the image carrier.

  The electrostatic latent image is reversely developed on the image carrier by applying a predetermined developing application voltage from a high voltage power source to the developing sleeve 6 of the developing device 3 and supplying negatively charged toner from the developing sleeve 6. To form a toner image. In the reverse development, toner charged to the same polarity as the charged polarity on the surface of the photoreceptor 1 is used, and the toner is attached to the light potential portion of the electrostatic latent image on the surface of the photoreceptor 1 by utilizing the potential difference. The latent image is developed as a toner image.

  On the other hand, the recording material P is fed from a paper feeding unit (not shown) to a contact nip (transfer unit) between the photoconductor 1 and the transfer roller 8 in synchronization with the toner image on the surface of the photoconductor 1. The toner image on the surface of the photosensitive member 1 is transferred onto the recording material. A predetermined transfer application voltage is applied to the transfer roller 8 from a high voltage power source, and the toner image is transferred by the transfer application voltage. A transfer guide member 7 is provided upstream of the transfer roller 8 in the conveyance direction of the recording material, and guides the recording material between the transfer roller 8 and the photosensitive member 1 that is an image carrier. The recording material P that has passed through the transfer portion is separated from the surface of the photoreceptor 1 and introduced into the fixing device 30, undergoes a toner image fixing process, and is output as an image formed product (print).

  The process cartridge 16 is detachable from the printer main body 29. In the printer of this embodiment, the process cartridge 16 includes four process devices including the photosensitive member 1, the charging roller 2 as a contact charging member, the developing device 3, and the cleaning device 9. It is. The process cartridge 16 may include the photosensitive member 1 and at least one of the charging member 2, the developing device 3, and the cleaning device 9.

  The process cartridge 16 has a slit window hole portion through which laser light is incident and an opening / closing shutter portion (not shown) for the lower surface exposed portion of the photosensitive member 1 and is closed when the process cartridge 16 is taken out from the printer main body. Time is kept open. When mounted on the printer main body, the photoconductor 1 and the developing sleeve 6 of the developing device 3 can be driven by a driving mechanism on the printer main body side by mechanically and electrically coupling with the printer main body. In addition, a predetermined voltage can be applied to the charging roller 2 and the developing sleeve 6 from the power source on the printer body side.

  The developing sleeve 6 is a rotatable developer carrier and rotates in the direction of the arrow and has a diameter of 14 mm. The developing sleeve 6 is made of an aluminum pipe having a thickness of 1 mm, and its surface is roughened by an irregular blasting process. A magnet is fixed in the developing sleeve 6. The developing device 3 shown in the present embodiment further includes a developer container 12 and a sheet metal 14. The toner stored in the developer storage container 12 is composed of a magnetic one-component negative toner, and the toner seal member 11 is removed during use to communicate with the developing sleeve 6 side. This toner is frictionally charged by the developing sleeve 6 and the regulating blade 10 and is carried on the developing sleeve 6. Then, the developing sleeve 6 is transported to the developing area facing the photosensitive member 1 by the rotation of the developing sleeve 6.

  The transfer guide member 7 that guides the recording material P to the transfer portion is made of a conductive material, and specifically, a sheet metal or the like is used. A voltage can be applied to the transfer guide member 7 from a power source, and the transfer guide member 7 and the inside of the apparatus are insulated.

  In FIG. 1, reference numeral 40 denotes a latent image potential acquisition unit that acquires a latent image potential of the photosensitive member 1 that is an image carrier, and reference numeral 50 denotes a voltage application unit that applies a voltage to the transfer guide member 7. Reference numeral 60 denotes voltage control means for applying a voltage to the transfer guide member 7 so as to become a potential approaching the representative potential of the photosensitive member 1 determined based on the latent image potential acquired by the latent image potential acquisition means 40.

(Acquisition of latent image potential of photoconductor)
The acquisition of the latent image potential in the present invention refers to obtaining the average surface potential in the entire area or unit area (partial area) of the latent image of the photoreceptor 1 formed on the recording material as information indirectly or directly. That is.

  As a method for acquiring the latent image potential of the photosensitive member 1, the latent image potential of the photosensitive member 1 can be directly obtained with a surface potentiometer. In the present embodiment, however, the latent image potential is indirectly obtained based on the printing rate. It was adopted. The printing rate is a parameter determined from the dot ratio, and there is a correlation as shown in FIG. 8 between the printing rate and the latent image potential which is the average surface potential. Therefore, the relationship between the printing rate and the latent image potential is measured in advance, this correlation is recorded and stored in the electrophotographic apparatus main body, and the latent image potential is acquired based on the printing rate.

The surface of the photoconductor 1 is charged to about −600 V by a charging roller. The value of the charged photoconductor 1 is changed to about −100 V by laser exposure. The latent image potential when the entire unit area of 3 cm × 3 cm is not laser-exposed is −600V. However, when the entire unit area is laser-exposed, the latent image potential is −100V. Since an actual image has shading, the shading is expressed as a ratio of a place where laser exposure is performed and a place where laser exposure is not performed. The ratio of the exposed area is the printing rate. If the printing rate is known, the latent image potential can be acquired.

  When the latent image potential is acquired from the printing rate for the entire image region (A-1 in FIG. 9), the acquired latent image potential is one. On the other hand, when the latent image potential is acquired from the printing rate for the partial area, a plurality of latent image potentials are acquired. In the present embodiment, a 3 cm side square area (9 square cm area) is defined as one unit area (A-2 in FIG. 9) as a partial area, and the printing rate of one unit area is determined from the dot ratio per unit area. A latent image potential was obtained for each unit area.

(Determination of applied voltage to transfer guide member)
When the latent image potential is acquired from the printing rate for the entire image area, the acquired latent image potential is one (B-1 in FIG. 9), and applied to the transfer guide member based on this latent image potential. Determine the voltage to be used. On the other hand, when the latent image potential is acquired from the printing rate for the partial area of the image area, there are a plurality of latent image potentials to be acquired, and a representative potential is determined from the plurality of acquired latent image potentials. The voltage applied to the transfer guide member is determined.

  In this embodiment, a square with a side of 3 cm (area is 9 cm 2) is set as one unit area as a partial area, and the latent image potential is obtained by scanning the recording material without gaps for each unit area. Then, the latent image potential of one unit region having the highest printing rate was determined as a representative potential (B-2 in FIG. 9), and the voltage to be applied to the transfer guide member was determined based on this representative potential.

  The reason why the voltage corresponding to the highest part is applied is that the amount of scattered toner increases as the printing rate increases, so in the case of darkness, the voltage based on the latent image potential corresponding to the darker one is applied. This is because the effect is high.

(Timing of voltage control to the transfer guide member)
It is preferable that the voltage applied to the transfer guide member is controlled to change to a preferable value when the latent image formed on the photoconductor 1 comes close to the transfer guide, preferably closest to the transfer guide. . In this embodiment, since an image having no shading as described below is targeted, when a latent image corresponding to the leading end in the recording material loading direction comes close to the transfer guide, it is preferably closest to the transfer guide. When this is done, the voltage to the transfer guide member is controlled.

(Application of the present invention to an image having no shading)
When toner accumulates on the transfer guide member 7, the recording material conveyance path is soiled to cause contamination on the recording material passing through the conveyance path. In the present embodiment, this contamination is improved.

  In this embodiment, a negatively charged toner is used, and the dark potential of the photoreceptor 1 in a state where the laser exposure is not performed is −500 V, and the bright potential in a state where the laser exposure is performed is −100 V. Table 1 shows the observation of the stain on the transfer guide member 7 and the stain on the recording material by changing the voltage applied to the transfer guide member 7 from −1000 V to 0 V.

  In Table 1, the applied voltage of the transfer guide member 7 was changed for two types of −150 V and −450 V as the average latent image potential of the photosensitive member 1 on the premise that an image having no shading is formed over the entire surface. The former corresponds to the case where there are many areas exposed in a plurality of areas constituting one pixel and, as a result, the amount of toner is large, and the latter is a few areas exposed in a plurality of areas constituting one pixel, As a result, it corresponds to the case where the toner amount is small. Here, the average latent image potential of the photosensitive member 1 was changed by changing the scanning exposure pattern, that is, changing the printing rate.

  Here, when the average latent image potential of the OPC photosensitive member is −150 V, the representative potential of the image carrier determined based on the latent image potential acquired by the latent image potential acquisition unit is −150 V. That is, as described above, the latent image potential corresponding to the unit region with the highest printing rate among the latent image potentials acquired for each unit region is −150V.

  When the average latent image potential of the OPC photosensitive member is −150 V, the voltage applied to the transfer guide member 7 is rank A in the range of −100 V to −250 V including −150 V, which is the same as the average latent image potential of the OPC photosensitive member. It was. Further, when a voltage of −300 V or higher was applied to the transfer guide member 7, it was ranked B. Rank C was obtained when the transfer guide member 7 was set to 0 V (ground).

  When the representative potential is −150 V, a voltage is applied to the transfer guide member 7 so that the potential approaches the representative potential. The applied voltage is −175 V, which is an average value of rank A (25 V lower than the representative potential −150 V). In the range of ± 40%, more preferably ± 30%.

  Next, the same verification was performed by setting the average latent image potential of the OPC photosensitive member to −450V. Here, when the average latent image potential of the OPC photosensitive member is −450 V, the representative potential of the image carrier determined based on the latent image potential acquired by the latent image potential acquisition unit is −450 V. That is, as described above, the latent image potential corresponding to the unit region with the highest printing rate among the latent image potentials acquired for each unit region is −450V.

  When the applied voltage of the transfer guide member was -350 V to -600 V including -450 V as the average latent image potential of the OPC photosensitive member, the rank A was obtained. The rank was B when -700 V or more was applied to the transfer guide member 7. At this time, Rank 0 was obtained when 0 V to −100 V was applied to the transfer guide member 7.

  When the representative potential is −450 V, a voltage is applied to the transfer guide member 7 so that the potential approaches the representative potential. The applied voltage is an average value of rank A of −475 V (25 V lower than the representative potential −450 V). In the range of ± 40%, more preferably ± 30%.

  From the above experimental results, it can be seen that there is a causal relationship between how the transfer guide member 7 is soiled and the voltage applied to the transfer guide member 7. The conceptual diagram is shown in FIG. 2, FIG. 3, and FIG. A black circle represents a negatively charged toner, and a white circle represents a positively charged toner. Assuming that the potential of the transfer guide member 7 is higher (for example, −300 V) than the average latent image potential of the photosensitive member 1 (for example, −350 V), the transfer guide member 7 is increased by increasing the voltage of the transfer guide member to the negative side. The toner adhering to the toner is reduced and the transfer guide member 7 is improved in dirt (FIG. 2). However, if the average latent image potential of the OPC photosensitive member is set to the minus side, the transfer guide member is contaminated again (FIG. 3). This is because triboelectrically charged toner has a certain charge distribution, and even if the average of the distribution is negative, there is a portion related to the positive polarity as the base portion of the charge distribution. This is because they are attracted (FIG. 4). However, since the proportion of positively charged toner is small, it is better when the negative potential increases than when the positive potential increases.

<< Second Embodiment >>
(Application of the present invention to images with shading)
In the first embodiment, the average latent image potential of the OPC photoconductor is uniform, but a normal and practical image usually has a mixture of a dark portion and a thin portion. In the present embodiment, on the premise of a dark and light image, the stain on the transfer guide member 7 is compared as in the first embodiment, and the result is shown in Table 2.

  Here, when the average latent image potential of the OPC photosensitive member is −350 V, the image carrier is determined based on the latent image potential (A-2, B-2 in FIG. 9) acquired by the latent image potential acquisition unit. The representative potential is -350V. That is, as described above, the latent image potential corresponding to the unit region having the highest printing rate among the latent image potentials acquired for each unit region is −350V.

  When the average latent image potential of the OPC photosensitive member is −350 V, the voltage applied to the transfer guide member 7 is rank A in the range from −250 V to −500 V including −350 V, which is the same as the average latent image potential of the OPC photosensitive member. It was. In addition, when a voltage of −600 V or higher or −200 V or lower was applied to the transfer guide member 7, it was ranked B. Rank C was obtained when the transfer guide member was at 0 V (ground).

  When the representative potential is −350 V, a voltage is applied to the transfer guide member 7 so that the potential approaches the representative potential. The applied voltage is −375 V, which is an average value of rank A (25 V lower than the representative potential −350 V). In the range of ± 40%, more preferably ± 30%.

  In this embodiment, when a voltage near the latent image potential of the OPC photosensitive member 1 corresponding to a dark image portion, that is, a unit area having the highest printing rate, is applied to the transfer guide member, scattering contamination on the transfer guide member is reduced. . This is because a darker image has a larger amount of toner held on the OPC photoconductor and has a greater influence on the amount of toner scattering. In this verification, a good result is obtained when the potential difference between the transfer guide member and the OPC photosensitive member is within 100V.

  In this way, by reducing the potential difference between the transfer guide member 7 and the photosensitive member 1 as much as possible, the electric force received by the toner carried on the image carrier from the pre-transfer guide can be minimized. . As a result, it is possible to provide an image forming apparatus that can reduce the pre-transfer guide contamination of scattered toner at low cost regardless of the image pattern.

<< Third Embodiment >>
In the first and second embodiments, the voltage applied to the transfer guide member 7 when the latent image formed on the recording material passes near the transfer guide member 7 is constant. In the present embodiment, the voltage applied to the transfer guide member 7 is variable when a latent image formed on the recording material passes near the transfer guide member 7. Unlike the first and second embodiments, other points are the same. In the present embodiment, the latent image potential is acquired for each unit area that is a partial area divided in the recording material conveyance direction and the direction intersecting the recording material conveyance direction. In the present embodiment, the representative potentials that differ in the circumferential direction of the photosensitive member 1 that is the image carrier are the highest in the printing ratio among the latent image potentials corresponding to the plurality of unit regions in the direction intersecting the transport direction. The latent image potential corresponding to the unit area is used. That is, a voltage that changes every 3 cm in the transport direction is applied to the transfer guide member 7 (A-3 and B-3 in FIG. 9).

In FIG. 6, P is a dark image, Q is a light image, R is a light image, and the potential applied to the transfer guide member 7 is shown on the lower side of the figure corresponding to each image. In FIG. 6, it is −350 V for the image P, −500 V for the image Q, and −350 V for the image R. That is, when there is a difference in shading in a plurality of unit areas in the direction intersecting the transport direction as in the image R,
The latent image potential corresponding to the darker unit region is set as the representative potential. Then, a voltage is applied to the transfer guide member 7 so that the potential applied to the transfer guide member 7 becomes a potential that approaches the representative potential.

  Here, the comparative example with respect to this embodiment is shown in FIG. Regardless of the images P, Q, and R, the representative potential is uniformly set to −350V. In this case, for the image P and the image R, the potential applied to the transfer guide member 7 can be set to a potential approaching the representative potential of the image carrier determined based on the acquired latent image potential. However, for the image Q, a potential difference Δ is generated, and the potential applied to the transfer guide member 7 cannot be a potential that approaches the representative potential of the image carrier determined based on the acquired latent image potential. .

  The timing of voltage control to the transfer guide member in the present embodiment is the same as in the first and second embodiments. That is, control is performed so that the voltage to the transfer guide member changes to a preferable value when the latent image formed on the photoreceptor 1 comes close to the transfer guide, preferably when it is closest to the transfer guide. Is preferred. In this embodiment, since the applied voltage is variable during the sheet passing operation of the transfer guide member, the voltage control cycle is every time the photosensitive member 1 moves 3 cm in the length of one unit region in the circumferential direction. .

<< Fourth Embodiment >>
In the present embodiment, the latent image potential is acquired for each unit region that is a whole region that is not divided in the conveyance direction of the recording material and is a partial region (length 3 cm) divided in the direction intersecting the conveyance direction (see FIG. 10 A-4). Then, among the latent image potentials corresponding to the plurality of unit regions in the direction intersecting the transport direction, the latent image potential corresponding to the unit region with the highest printing rate is set as the representative potential. As a result, a voltage is applied to the transfer guide member 7 so that the potential applied to the transfer guide member 7 becomes a potential approaching this representative potential (B-4 in FIG. 10).

<< Fifth Embodiment >>
In the present embodiment, a latent image potential is acquired for each unit area that is a partial area (3 cm in length) divided in the conveyance direction of the recording material and is a partial area that is an entire area that is not divided in a direction intersecting the conveyance direction. (A-5 in FIG. 10). Of the latent image potentials corresponding to the plurality of unit regions in the transport direction, the latent image potential corresponding to the unit region with the highest printing rate is set as the representative potential, and the potential applied to the transfer guide member 7 approaches this representative potential. A voltage is applied to the transfer guide member 7 so as to be a potential (B-5 in FIG. 10).

<< Sixth Embodiment >>
This embodiment is the same as the third embodiment in that the voltage applied to the transfer guide member 7 is variable when the latent image formed on the recording material passes near the transfer guide member 7. is there. In the present embodiment, a latent image potential is acquired for each unit area that is a partial area (3 cm in length) divided in the conveyance direction of the recording material and is a partial area that is an entire area that is not divided in a direction intersecting the conveyance direction. (A-6 in FIG. 10). Then, a voltage that changes every 3 cm in the transport direction is applied to the transfer guide member 7 so that the potential applied to the transfer guide member 7 becomes a potential that approaches each acquired latent image potential (B- in FIG. 10). 6).

  The timing of voltage control to the transfer guide member in the present embodiment is the same as in the third embodiment. That is, control is performed so that the voltage to the transfer guide member changes to a preferable value when the latent image formed on the photoreceptor 1 comes close to the transfer guide, preferably when it is closest to the transfer guide. Is preferred. In this embodiment, since the applied voltage is variable during the sheet passing operation of the transfer guide member, the voltage control cycle is every time the photosensitive member 1 moves 3 cm in the length of one unit region in the circumferential direction. .

(Modification)
Although the above description has been made on the assumption that the image bearing member is a photosensitive drum, the present invention is not limited to this, and an electrostatic latent image may be formed using magnetism, for example.

1 .... OPC photoreceptor (organic photoreceptor), 2. Charge roller (charging member), 3. Development device, 4. Mirror, 5. Laser, 6. Development sleeve, 7. Transfer guide member 8 .. Transfer roller, 9 .. Cleaning device, 10 .. Elastic blade, 11 .. Toner seal member, 12 .. Toner container, 14 .. Sheet metal, 16 .. Process cartridge, 29.

Claims (12)

An image carrier;
Latent image forming means for forming an electrostatic latent image on the image carrier;
Developing means for developing the electrostatic latent image with toner to form a toner image on the image carrier;
Transfer means for transferring a toner image on the image carrier onto a recording material;
A transfer guide member that is provided upstream of the transfer unit in the conveyance direction of the recording material and guides the recording material between the transfer unit and the image carrier;
Voltage applying means for applying a voltage to the transfer guide member;
In an image forming apparatus having
Latent image potential acquisition means for acquiring a latent image potential of the image carrier;
An image forming apparatus comprising voltage control means for applying a voltage to the transfer guide member based on the latent image potential acquired by the latent image potential acquisition means.   2. The image formation according to claim 1, wherein a voltage applied to the transfer guide member is variable when a latent image formed on the recording material passes in the vicinity of the transfer guide member. apparatus.   One latent image potential acquired by the latent image potential acquisition unit is acquired corresponding to the entire area of the recording material, and a voltage is applied to the transfer guide member based on the acquired latent image potential. The image forming apparatus according to claim 1, wherein:   The latent image potential acquired by the latent image potential acquisition unit is acquired corresponding to each unit area of the recording material, and the representative potential of the image carrier is determined based on the acquired latent image potential, and the representative potential 3. The image forming apparatus according to claim 1, wherein a voltage is applied to the voltage application unit based on the image quality.   The representative potential of the image carrier is determined as a latent image potential corresponding to a unit area having the highest printing rate among the latent image potentials of the image carrier acquired corresponding to each unit area of the recording material. The image forming apparatus according to claim 4.   The image forming apparatus according to claim 5, wherein the unit area is a partial area divided in a conveyance direction of the recording material and a direction crossing the conveyance direction.   The image forming apparatus according to claim 5, wherein the unit area is a partial area that is divided in the conveyance direction of the recording material, and is an entire area that is not divided in a direction that intersects the conveyance direction.   The image forming apparatus according to claim 5, wherein the unit area is an entire area that is not divided in the conveyance direction of the recording material, and is a partial area that is divided in a direction that intersects the conveyance direction.   A latent image potential is acquired for each unit area which is a partial area divided in the recording material conveyance direction and a direction intersecting the recording material conveyance direction, and the representative potential of the image carrier in the recording material conveyance direction is the recording material. Among the latent image potentials of the image carrier acquired corresponding to each unit region in a direction crossing the transport direction of the image, respectively, and determined as the latent image potential corresponding to the unit region with the highest printing rate, and the representative potential The image forming apparatus according to claim 1, wherein a voltage is applied to the transfer guide member on the basis of the image.   One latent image potential is obtained for each unit area, which is a partial area divided in the recording material conveyance direction and is not divided in a direction intersecting the conveyance direction, and the recording material in the conveyance direction of the recording material The image forming apparatus according to claim 1, wherein a voltage is applied to the transfer guide member based on the acquired latent image potential.   The latent image potential acquisition means measures in advance a correlation between a printing rate and a latent image potential which is an average surface potential, and acquires the latent image potential from the printing rate based on the correlation. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 1, wherein the latent image potential acquisition unit is a surface electrometer that acquires a latent image potential of the image carrier.