JP2000267458A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a potential difference between a part where toner is transferred at secondary transfer and a non-image part where the toner is not transferred, and to prevent a transfer electric field from extending to the non-image part. SOLUTION: The device is provided with an image carrier PR having a surface on which a toner image is formed, and an intermediate transfer body B containing photoconductive material whose resistance value is reduced when the material is irradiated with light, and functioning as a high-resistance dielectric body when the body is not irradiated with light. Besides, the device is provided with a primary transfer device T1 for primarily transferring the toner image on the image carrier PR on to the intermediate transfer body B, a light irradiating/destaticizing device JK for destaticizing the intermediate transfer body B passing through a destaticizing area by the irradiation of light, a secondary transfer device T2 for secondarily transferring the primarily transferred toner image to a recording sheet S in a secondary transfer area Q4, a fixing device F for fixing the secondarily transferred image on the recording sheet passing through a fixing area Q5, and an intermediate transfer body potential adjusting device K for adjusting the potential on the intermediate transfer body B in a potential adjusting area Q6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a facsimile, a printer, and the like, and more particularly, to a method in which a toner image formed on an image carrier is primarily transferred to an intermediate transfer member. The present invention also relates to an image forming apparatus configured to secondarily transfer the primary transfer toner on the intermediate transfer member to a recording sheet.

[0002]

2. Description of the Related Art As an image forming method (transfer method) in a color image forming apparatus such as an electrophotographic copying machine, a toner image (developed image) formed on an image carrier such as a photoreceptor drum is temporarily transferred to a place other than transfer paper. A method is known in which a primary transfer is performed on an intermediate transfer member, and then a secondary transfer is performed again on a transfer sheet to obtain a copy image. It is known that by using this method, it is possible to suppress the occurrence of multiple transfer defects and misregistration of color registration due to many factors such as the holding state of the transfer sheet, the thickness and strain of the transfer sheet, and the surface properties of the transfer sheet. I have. For example, the following prior art (J01) is known as an image forming apparatus using the intermediate transfer member.

(J01) Technology shown in FIG. 8 FIG. 8 is an explanatory view of a conventional image forming apparatus using an intermediate transfer member. In FIG. 8, the image forming apparatus U includes an automatic document feeder U1 and an image forming apparatus main body (copier) U2 having a platen glass PG for supporting the same.
The automatic document feeder U1 moves a document feed tray TG1 on which a plurality of documents Gi to be copied are placed one upon another and a copy position (document reading position) on the platen glass PG from the document feed tray TG1. And a document discharge tray TG2 from which the document Gi conveyed and conveyed is discharged. The image forming apparatus main body U2 has a UI (user interface) for a user to input an operation command signal such as copy start, an exposure optical system A, and the like. A document conveyed to the platen glass PG by the automatic document feeder U2 or a document manually placed on the platen glass PG (not shown)
Is reflected by the CCD through the exposure optical system A.
(Solid-state imaging device) converts the signals into R (red), G (green), and B (blue) electric signals. The IPS (image processing system) converts the RGB electric signals into K (black), Y
(Yellow), M (magenta), and C (cyan) image data, which are temporarily stored and output to the laser drive circuit DL at a predetermined timing.

The surface of the image carrier (photosensitive drum) PR which rotates in the direction of the arrow Ya is uniformly charged by the charger CR in the charging area Q0, and the latent image forming position Q1, the developing area Q2 and the primary It sequentially passes through the transfer area Q3. An ROS (latent image writing device) driven by the laser drive circuit DL exposes and scans the latent image forming position Q1 with the laser beam L to form an electrostatic latent image on the surface of the image carrier PR. When forming a full-color image, K (black), Y
An electrostatic latent image corresponding to four color images (yellow), M (magenta), and C (cyan) is sequentially formed. In the case of a monochrome image, only an electrostatic latent image corresponding to a K (black) image is formed. Is done.

[0005] The surface of the image carrier PR on which the electrostatic latent image is formed is rotated and sequentially passes through the development area Q2 and the primary transfer area Q3. The rotary developing device G rotates K in the developing area Q2 sequentially with the rotation of the rotation shaft GA.
It has four color developing units GK, GY, GM and GC of (black), Y (yellow), M (magenta) and C (cyan).
Each of the developing units GK, GY, GM, and GC has a developing roll GR for transporting a developer to the developing area Q2.
The electrostatic latent image on the image carrier PR passing through the development area Q2 is developed into a toner image Tn. As a developer, for example, a two-component developer having a toner and a carrier is used, and as a yellow, magenta, cyan, and black toner, a negatively chargeable toner is used.

Below the image carrier PR, a slide frame F1 (2) is provided by a pair of left and right slide rails SR, SR.
(Indicated by a dashed line) is slidably supported back and forth (in a direction perpendicular to the paper surface). A belt frame F2 of the belt module BM is supported on the slide frame F1 so as to be rotatable up and down around a hinge axis F2a. The belt module BM includes a plurality of belt support rolls (Rd, Rt, Rw, Rf, T2a) that rotatably support the intermediate transfer belt (belt-shaped intermediate transfer body) B, and a primary transfer roll T1. , The belt frame F2 supporting them
And The plurality of belt support rolls (Rd,
Rt, Rw, Rf, T2a) are a belt drive roll Rd, a tension roll Rt, a walking roll Rw, an idler roll (free roll) Rf, and a backup roll T2.
Contains a.

The primary transfer unit T1 is supplied with a transfer voltage having a polarity opposite to the charge polarity of the toner by a power supply circuit E controlled by a controller C, and transfers the toner image Tn on the surface of the image carrier PR to a primary transfer area. 1 in the intermediate transfer belt B in Q3
Next transfer. In the case of a full-color image, the toner images Tn of each color sequentially formed on the surface of the image carrier PR are sequentially superimposed on the surface of the intermediate transfer belt B in the primary transfer area Q3.
The next transfer is performed, and a full-color multiple toner image is finally formed on the intermediate transfer belt B. When a monochromatic monocolor image is formed, only one developing unit is used, and the monochromatic toner image is primarily transferred onto the intermediate transfer belt B. After the primary transfer, the surface of the image carrier PR is cleaned of residual toner by the image carrier cleaner CLp, and is discharged by the image carrier discharger JR.

[0008] Below the backup roll T2a,
A secondary transfer slide frame Fs slidable back and forth (in a direction perpendicular to the paper surface) by a pair of left and right slide rails SR, SR is detachably supported on the image forming apparatus main body. The secondary transfer lifting frame Ft of the secondary transfer unit Ut supported by the secondary transfer slide frame Fs so as to be rotatable up and down around a hinge axis Fta can be moved up and down between a raised use position and a lowered retreat position. It is. The secondary transfer unit Ut includes a secondary transfer roll T2b.
, A secondary transfer roll cleaner CL3, a roll support lever Lr, a post-transfer sheet guide SG2, a sheet transport belt BH, and the secondary transfer lifting frame Ft supporting these.

The roll support lever Lr is a lever that supports the secondary transfer roll T2b. When the secondary transfer unit Ut is moved to the use position, the roll support lever Lr is rotated around a hinge axis La by a motor (not shown), and the secondary transfer roll T2b is rotated.
Is moved between a secondary transfer position in contact with the intermediate transfer belt B and a standby position separated from the intermediate transfer belt B. A secondary transfer area Q4 is formed by the contact area between the secondary transfer roll T2b and the intermediate transfer belt B, and the secondary transfer roll T2b, the backup roll T2a, and a metal electrode roll T2c that comes into contact with the backup roll T2a. Constitutes a secondary transfer device T2.

The recording sheets S stored in the paper feed tray TR1 are taken out by a pickup roll Rp at a predetermined timing, separated one by one by a separating roll Rs, and conveyed to a registration roll Rr. The recording sheet S conveyed to the registration roll Rr is transferred to the pre-transfer sheet guide SG in synchronization with the movement of the primary-transferred multi-toner image or single-color toner image to the secondary transfer area Q4.
It is transported from 1 to the secondary transfer area Q4. When the recording sheet S passes through the secondary transfer area Q4, the power supply circuit E controlled by the controller C is provided to the electrode roll T2c of the secondary transfer device T2.
, A secondary transfer voltage having the same polarity as the charged polarity of the toner is applied. The secondary transfer unit T2 collectively secondary-transfers the color toner image primarily transferred onto the intermediate transfer belt B onto the recording sheet S in the secondary transfer area. The residual toner is removed from the intermediate transfer belt B after the secondary transfer by the belt cleaner CLb. The toner adhered to the surface of the secondary transfer roll T2b is collected by the secondary transfer roll cleaner CL3.

Incidentally, the secondary transfer roll T2b and the belt cleaner CLb are arranged so as to be able to freely contact (separate and contact) with the intermediate transfer belt B, and when a color image is formed, the final color is formed. Unless the unfixed toner image is primarily transferred to the intermediate transfer belt B, the toner image is separated from the intermediate transfer belt B. The recording sheet S on which the toner image is secondarily transferred is conveyed to a fixing area Q5 by a post-transfer sheet guide SG2 and a sheet conveying belt BH, and includes a heating roll Fh and a pressure roll Fp when passing through the fixing area Q5. The fixing is performed by a fixing device F having a pair of fixing rolls. The recording sheet S on which the toner image has been fixed is discharged to the recording sheet discharge tray TR2. The code Rp,
The sheet conveying device SH is constituted by the elements indicated by Rs, Rr, SG1, SG2, and BH.

[0012]

[Problems to be Solved by the Invention]
Problem 1) In the image forming apparatus using the intermediate transfer member of the prior art (J01), a filler such as carbon or a metal compound is dispersed as a conductive agent in a polymer material so far in the intermediate transfer member. (See Japanese Patent Application Laid-Open No. 8-320622). However, it is known that there is a close relationship between the resistance of the intermediate transfer body formed in this way and the image quality of the toner image. (See JP-A-08-248779).
If the resistance value of the intermediate transfer member is too low, the transfer electric field is likely to be applied to the area without the toner layer by the action of the transfer electric field and the transfer current by the primary transfer roll, so that the transfer area is widened, and the toner is scattered by the action. It is thought that it is transcribed.

When the resistance value of the intermediate transfer member is high, or when the intermediate transfer member is made of a dielectric material, the charge retention of the intermediate transfer member in the toner image area increases, and an electric field required for transfer is appropriately applied to the toner. can do. On the other hand, since the charge transfer on the surface and inside of the intermediate transfer member in the adjacent non-image portion is reduced, the toner transfer to this region in primary and secondary transfer hardly occurs. As a result, when the resistance value of the intermediate transfer member is high, or when the intermediate transfer member is made of a dielectric material or the like, a toner-formed image of good image quality with less toner scattering is obtained. However, in this case, the electric charge is accumulated in the intermediate transfer member after the toner transfer, so that the electric charge is adversely affected at the time of the next image formation. Further, even if the average resistance value of the intermediate transfer member is within a favorable resistance value range, the following problems can be raised. That is, when a filler such as carbon or a metal compound is dispersed in a polymer resin, the variation in resistance in the intermediate transfer body due to the dispersion state of the filler is about 1%.
That is, the resistance of the intermediate transfer member may be reduced with time due to dielectric breakdown of a minute polymer resin portion between the fillers and rearrangement of the fillers due to energization. As described above, the resistance of the intermediate transfer member partially or entirely deviates from the favorable resistance value range, and there is a problem that the image quality is significantly reduced.

Therefore, we have proposed a photoconductive intermediate transfer member in Japanese Patent Application No. Hei 10-123999 (Japanese Patent Application Laid-Open No. Hei. 9-1992). This is different from a conventional medium-resistance intermediate transfer member in which conductive powder such as carbon black is dispersed, and has a high resistance as a dielectric during the first and second transfer. For this reason, a good image can be obtained without an electric field spreading at the time of the first and second transfer.
After the first and second transfer, electric charges are accumulated on the intermediate transfer body by the transfer electric field, respectively. However, by irradiating the intermediate transfer body with light after the second transfer, non-contact and generation of ozone or the like can be achieved. Without charge.

FIG. 9 shows an image bearing member (photosensitive member) using a high-resistance photoconductive intermediate transfer member as disclosed in Japanese Patent Application No. 10-123999 (Japanese Patent Application Laid-Open No. Hei.
9A is a diagram illustrating a toner image and a potential around the toner image when a toner image is transferred to an intermediate transfer member from FIG. 9A is a diagram illustrating a potential on an image carrier, FIG. 9B is a diagram illustrating a potential on an intermediate transfer member,
FIG. 9B 'is a diagram showing the potential on the surface of the intermediate transfer member after the fourth primary transfer, and FIG. 9C is a diagram showing the secondary transfer electric field. FIG.
9A, in FIG. 9B, as a transfer characteristic of the photoconductive intermediate transfer member having a high resistance at the time of transfer, the potential distribution of the photoconductor at the time of primary transfer including the toner image to be transferred is also primary transfer. Sometimes it is transferred to an intermediate transfer member. For this reason, the potential of the peripheral non-image portion is higher than that of the image portion including the toner image transferred on the intermediate transfer member, and the toner image is restrained and does not scatter around.

(First Problem) In FIG. 9B ', when the primary transfer is performed for the first to fourth times, the transferred toner image becomes large on the negative side. In FIG. 9C, when the potential difference between the surface potential of the secondary transfer roll (secondary transfer voltage) and the non-image portion of the intermediate transfer body is larger than the potential difference between the surface potential of the secondary transfer roll and the image portion, the secondary transfer is performed. The electric field spreads to the non-image area,
The transfer electric field in the image area is low. That is, as a first problem in the photoconductive intermediate transfer member, particularly at the time of secondary transfer when the resistance value of the sheet is low under high temperature and high humidity, the transfer electric field spreads to the non-image portion where the potential difference is large, and the toner also scatters. Therefore, blurring of the image occurs, and it is difficult to obtain a good image.

(Second Problem) As a second problem, the final toner transfer efficiency of an intermediate transfer member containing a photoconductive substance is almost the same as that of a conventional medium-resistance intermediate transfer member. It has been demanded to realize higher transfer efficiency from the viewpoints of image structure and color reproducibility and running cost. (Third Problem) The third problem is that since the intermediate transfer member has a high resistance as a dielectric during the primary transfer, the toner image is transferred onto the intermediate transfer member a plurality of times, such as when forming a color image. When the image is transferred to the second color,
It was necessary to increase the next transfer voltage. For this reason, a high voltage is applied particularly at the time of the primary transfer of the final color toner, and a power supply having a larger capacity is required, which is a factor of increasing the cost.

The present invention has been made in view of the above circumstances (and the results of examination), and has an object to describe the following contents (O01) and (O02) in an image forming apparatus using an intermediate transfer member containing a photoconductive substance. (O01) Image part at the time of secondary transfer (part where toner is transferred)
And non-image area (part where toner is not transferred, background area of image)
To prevent the transfer electric field from spreading to the non-image area by reducing the potential difference between the transfer electric field and the non-image area. (O02) The toner images of different colors are superimposed on the intermediate transfer member, and
In the next transfer, the primary transfer can be favorably performed by a low-voltage primary transfer power supply.

[0019]

Next, the present invention devised to solve the above-mentioned problems will be described. Elements of the present invention are used to facilitate correspondence with elements of the embodiments described later. , The reference numerals of the elements of the embodiment are enclosed in parentheses. The reason why the present invention is described in correspondence with the reference numerals of the embodiments described below is to facilitate understanding of the present invention, and not to limit the scope of the present invention to the embodiments.

(First Invention) In order to solve the first and second problems, the image forming apparatus of the first invention has the following requirements (A01) to (A08). (A0
1) Rotating and moving sequentially through the charging area (Q0), the latent image forming position (Q1), the developing area (Q2), and the primary transfer area (Q3), and being charged when passing through the charging area (Q0). An image carrier (PR) having a surface on which an electrostatic latent image is formed when passing a latent image forming position (Q1) and a toner image is formed when passing a developing area (Q2); (A02) the primary transfer area ( Q3), potential adjustment area (Q6), secondary transfer area (Q
4) and an intermediate transfer member (B) that rotates and passes sequentially through the static elimination region (Q7), which contains a photoconductive substance whose resistance value decreases when irradiated with light and is not irradiated with light The intermediate transfer member (B), which is a high-resistance dielectric in the state,
(A03) The recording sheet (S) stored in the paper feed tray (TR1) is transferred to the secondary transfer area (Q4) and the fixing area (Q5).
And a sheet conveying device (S
H), (A04) a primary transfer device (T1) for primarily transferring a toner image on the image carrier (PR) onto the intermediate transfer member (B) in the primary transfer area (Q3), (A05) A secondary transfer device (T2) for secondary-transferring the primary transfer toner image on the intermediate transfer member (B) to the recording sheet (S) in the secondary transfer region (Q4), (A06) the charge removal region (Q7) And (A07) a secondary transfer toner image on the recording sheet (S) passing through the fixing area (Q5). A fixing device (F) for fixing, (A08) an intermediate transfer member potential adjuster (K) for adjusting the potential on the intermediate transfer member (B) in the potential adjustment region (Q6).

(Operation of the First Invention)
In the image forming apparatus according to the present invention, the image carrier (PR) that rotates while sequentially passing through the charging area (Q0), the latent image forming position (Q1), the developing area (Q2), and the primary transfer area (Q3).
Is charged when passing through the charging area (Q0), an electrostatic latent image is formed when passing through the latent image forming position (Q1), and a toner image is formed when passing through the developing area (Q2). The intermediate transfer member (B), which contains a photoconductive substance whose resistance value decreases when irradiated with light and is a high-resistance dielectric when not irradiated with light, includes the primary transfer region (Q3) , And sequentially rotates through the potential adjustment area (Q6), the secondary transfer area (Q4), and the charge removal area (Q7). The sheet conveying device (SH) sequentially conveys the recording sheet (S) stored in the sheet feeding tray (TR1) to the secondary transfer area (Q4), the fixing area (Q5), and the sheet discharge section.

The primary transfer device (T1) primarily transfers the toner image on the image carrier (PR) onto the intermediate transfer member (B) in the primary transfer area (Q3). Light irradiation static eliminator (JK)
Is the intermediate transfer member (B) passing through the charge elimination area (Q7)
Is discharged by light irradiation. The secondary transfer unit (T2) is provided on the intermediate transfer member (B) in the secondary transfer area (Q4).
The next transfer toner image is secondarily transferred to the recording sheet (S). The fixing device (F) fixes the secondary transfer toner image on the recording sheet (S) passing through the fixing area (Q5). In the potential adjustment area (Q6), the intermediate transfer member potential adjuster (K) adjusts the potential on the intermediate transfer member (B).

Unlike the medium-resistance intermediate transfer member in which a conductive filler such as carbon black is dispersed, which has been conventionally proposed, the photoconductive intermediate transfer member (B) serves as a dielectric material during the first and second transfer. High resistance value is maintained. For this reason, as shown in FIG. 5A and FIG. 5B, after the primary transfer, the surface of the photoconductive intermediate transfer member has the potential distribution held by the photoconductor at the time of image formation. In the case of reversal development, the periphery of the toner image formed on the intermediate transfer member (B) has a higher potential, so that the transferred toner image can be obtained without scattering to the periphery and a good primary transfer image can be obtained.

However, especially when the resistance value of the sheet is low under high temperature and high humidity, the secondary transfer electric field spreads to the non-image area (see FIG. 9C), and the toner is transferred along the spread of the electric field. Therefore, it is difficult to obtain a good image. Therefore, by irradiating light to the photoconductive intermediate transfer member after the primary transfer and before the secondary transfer, the difference between the surface potential of the non-image portion of the photoconductive intermediate transfer member and the surface potential of the toner image portion is reduced (FIG. 5C). Reference) The spread of the transfer electric field at the time of the secondary transfer can be suppressed, and the toner image can be transferred onto a final transfer material such as paper without scattering. However, in this case, if light irradiation is performed so that the potential of the non-image portion is lower than the potential of the image portion, the toner layer is scattered due to repulsion between toners charged to the same polarity or an electric field from the non-image portion, The image scatters around.

As still another method, a corona discharge phenomenon can be used. In this case, a method is used in which AC and DC voltages are superimposed and applied to the corotron, and the surface of the intermediate transfer member is leveled near the DC voltage value applied to the corotron.
For example, when the photosensitive member and the intermediate transfer belt are negatively charged and are subjected to reversal development, the DC voltage applied to the corotron is set to an intermediate potential between the image portion and the non-image portion on the intermediate transfer belt.
FIG. 6 is an explanatory diagram of a mechanism of potential adjustment when a corotron is used as an intermediate transfer member potential adjuster. FIG. 6A shows a DC voltage applied to the corotron applied to an intermediate potential between an image portion and a non-image portion on the intermediate transfer belt. FIG. 6B is a diagram illustrating a state in which the potentials of the image portion and the non-image portion change when set to. FIG. 6B is a diagram illustrating a state in which the potentials of the image portion and the non-image portion change when the corotron performs corona discharge, and FIG. FIG. 7 is a diagram illustrating a potential state of an image portion and a non-image portion after changes in the voltage.
In FIG. 6, by setting the DC voltage applied to the corotron to an intermediate potential between the image portion and the non-image portion on the intermediate transfer belt, a negative component current flows in the image portion having a lower potential than the DC voltage value VDC of the corotron. DC voltage value V applied
It is charged to near DC. Also, the DC voltage V of the corotron
A positive component current flows through the non-image portion having a higher potential than DC, and the current can be reduced to near the applied DC voltage value VDC.
In this case, the corona discharge by the corotron shown in FIG.
The state of B becomes the state of FIG. 6C.

As a result, the difference in the potential level between the image area and the non-image area becomes small. Therefore, even when the secondary transfer is performed on a sheet having a reduced resistance value under high temperature and high humidity, the electric field spreads, that is, the transfer toner Can be suppressed.
Further, at this time, since a charge is further added to the toner layer in the image portion, the transfer electric field is further increased, and the transfer efficiency can be improved. Further, the transfer of the fog toner can be suppressed because the charge of the fog toner in the non-image portion is reduced or the polarity is reversed.

(Second Invention) To solve the third problem, the image forming apparatus of the second invention has the following requirements (B01) to (B01).
(B01) characterized by having (B09), (B01) rotating and passing sequentially through a charging area (Q0), a latent image forming position (Q1), a developing area (Q2), and a primary transfer area (Q3). And an image carrier having a surface on which a latent image is formed when passing through the charging area (Q0), an electrostatic latent image is formed when passing through the latent image forming position (Q1), and a toner image is formed when passing through the developing area (Q2). (PR), (B02) the primary transfer region (Q
3) an intermediate transfer member (B) that rotates sequentially through the potential adjustment region (Q6), the secondary transfer region (Q4) and the charge removal region (Q7), and has a resistance value when irradiated with light. The intermediate transfer members (B) and (B0), which contain a photoconductive substance that decreases and are high-resistance dielectrics when no light is irradiated.
3) A sheet transport device (S) for sequentially transporting the recording sheet (S) stored in the paper feed tray (TR1) to the secondary transfer area (Q4), the fixing area (Q5), and the sheet discharge section.
H), (B04) a primary transfer device (T1) for primarily transferring a toner image on an image carrier (PR) onto an intermediate transfer member (B) in the primary transfer area (Q3); A light irradiator (JK) for irradiating the intermediate transfer member (B) passing through the charge elimination region (Q7) by light irradiation; and (B06) a primary light on the intermediate transfer member (B) in the secondary transfer region (Q4). A secondary transfer unit (T2) for secondary transfer of the transfer toner image to the recording sheet (S); (B07) a secondary transfer toner image on the recording sheet (S) passing through the fixing area (Q5); Fixing device (F) for fixing, (B08) Intermediate transfer member potential adjustment for adjusting the potential on intermediate transfer member (B) in potential adjustment region (Q6) set on the movement path of intermediate transfer member (B) (K), (B09) a potential adjuster control means for executing the potential adjustment each time the primary transfer is performed ( C7 ').

(Operation of the Second Invention)
In the image forming apparatus according to the present invention, the image carrier (PR) that rotates while sequentially passing through the charging area (Q0), the latent image forming position (Q1), the developing area (Q2), and the primary transfer area (Q3).
Is charged when passing through the charging area (Q0), an electrostatic latent image is formed when passing through the latent image forming position (Q1), and a toner image is formed when passing through the developing area (Q2). The intermediate transfer member (B), which contains a photoconductive substance whose resistance value decreases when irradiated with light and is a high-resistance dielectric when not irradiated with light, includes the primary transfer region (Q3), Potential adjustment area (Q6), secondary transfer area (Q4) and static elimination area (Q
7) sequentially pass through and rotate. Sheet transport device (S
H) shows the recording sheet (S) accommodated in the paper feed tray (TR1) with the secondary transfer area (Q4) and the fixing area (Q5).
And sequentially transported to a sheet discharge section.

The primary transfer unit (T1) primarily transfers the toner image on the image carrier (PR) onto the intermediate transfer body (B) in the primary transfer area (Q3). Light irradiation static eliminator (JK)
Is the intermediate transfer member (B) passing through the charge elimination area (Q7)
Is discharged by light irradiation. In the secondary transfer area (Q4), the secondary transfer unit (T2)
The next transfer toner image is secondarily transferred to the recording sheet (S). The fixing device (F) fixes the secondary transfer toner image on the recording sheet (S) passing through the fixing area (Q5).

In the potential adjustment area (Q6) set on the movement path of the intermediate transfer member (B), the intermediate transfer member potential adjuster (K) adjusts the potential on the intermediate transfer member (B).
The potential adjuster control means (C7 ') executes the potential adjustment each time the primary transfer is performed. The potential adjustment can be performed by light irradiation or corona discharge.

That is, by irradiating the intermediate transfer member (B) with light after the primary transfer, the potential distribution of the photosensitive member at the time of forming the image transferred to the intermediate transfer member (B) can be adjusted. At this time, the potential level is equal to or higher than the sum of the potential of the surface of the intermediate transfer member in the image portion and the potential of the toner image formed thereon. In this case, as in the case of the secondary transfer, if the potential of the non-image portion is lowered, the toner image scatters around. By lowering the potential level of the intermediate transfer member during the primary transfer, it is possible to prevent a large increase in the primary transfer voltage even when transferring the second and subsequent color toner images. Similarly, when the potential of the surface of the intermediate transfer member including the toner layer is adjusted by a discharge phenomenon caused by a corotron or the like, the potential of the entire intermediate transfer member (B) can be lowered, and the primary transfer voltage can be prevented from greatly increasing. . The potentials of the image portion and the non-image portion on the intermediate transfer member (B) change depending on the settings of the primary and secondary transfer, and the potential adjusted by a corotron or the like may be set as needed. .

[0032]

(Embodiment 1) Embodiment 1 of the image forming apparatus of the present invention is characterized in that the first or second invention has the following requirement (AB01): (AB01) The intermediate transfer member potential adjuster (K) including a light irradiator that irradiates the intermediate transfer member (B) with light.

(Operation of Embodiment 1) In Embodiment 1 of the image forming apparatus of the present invention having the above-described configuration, the intermediate transfer member potential adjuster (K) emits light to the intermediate transfer member (B). It is composed of a light irradiator for irradiation. The potential of the intermediate transfer member (B) containing a photoconductive substance can be adjusted by light irradiation.

(Embodiment 2) Embodiment 2 of the image forming apparatus of the present invention is characterized in that the first or second invention has the following requirement (AB02). (AB02) Corona discharge The intermediate transfer member potential adjuster (K) constituted by an electric device.

(Operation of Embodiment 2) In Embodiment 2 of the image forming apparatus of the present invention having the above-described configuration, the intermediate transfer member potential adjuster (K) is constituted by a corona discharger. The potential of the intermediate transfer member (B) can be adjusted by a corona discharger.

EXAMPLES Next, specific examples (examples) of the embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following examples.

(Embodiment 1) FIG. 1 is an overall explanatory view of an image forming apparatus according to Embodiment 1 of the present invention. Example 1 shown in FIG.
In the description of the image forming apparatus U, the same constituent elements as those of the conventional image forming apparatus shown in FIG. 8 are denoted by the same reference numerals as those used in FIG. Is omitted. The first embodiment of the image forming apparatus of the present invention shown in FIG. 1 is configured substantially the same as the conventional image forming apparatus shown in FIG. 8, but differs in the following points.

In the potential adjusting region Q6 set on the upstream side of the intermediate transfer belt B in the conveying direction of the secondary transfer region Q4 of the image forming apparatus shown in FIG. 1, an intermediate portion constituted by a red LED (light irradiator) is provided. A transfer member potential adjuster K is provided. An earth roll (earthed roll) Re is disposed at a position facing the intermediate transfer member potential adjuster K with the intermediate transfer belt B interposed therebetween. The potential of the intermediate transfer belt B is adjusted by light irradiation by the intermediate transfer member potential adjuster K. Light irradiation constituted by a red LED (light irradiator) is applied to the intermediate transfer body static elimination area Q7 set on the secondary transfer area Q4 of the image forming apparatus shown in FIG. The static eliminator JK is arranged. A grounded idler roll Re is disposed at a position facing the light irradiation neutralizer JK with the intermediate transfer belt B interposed therebetween. In the intermediate transfer body static elimination area Q7, the intermediate transfer belt B is neutralized by light irradiation by the light irradiator JK. The voltage applied to the intermediate transfer member potential adjuster K and the light irradiation static eliminator JK is supplied from a power supply circuit E (see FIG. 1, wiring is not shown).

(Secondary transfer unit T2) Secondary transfer disposed so as to be able to be separated (separated and approachable) between the backup roll T2a and a separated position distant from the backup roll T2a and a close position pressed. A secondary transfer unit T2 is constituted by the roll T2b and the metal electrode roll T2c which is in contact with the backup roll T2a. The backup roll T2a is formed by winding a semiconductive elastic body around a conductive metal roll, and its surface resistivity is adjusted to, for example, 1 × 10 ⁷ Ω / □ or more. Also,
The grounded secondary transfer roll T2b is formed by wrapping the surface of a metal roll with a carbon dispersed urethane foam and covering the outside with a semiconductive thin film, for example, its volume resistivity is adjusted to 10 ⁹ Ωcm. .

(Intermediate Transfer Belt B) FIG. 2 is a view showing the structure of the intermediate transfer belt used in the first embodiment of the image forming apparatus of the present invention. Intermediate transfer belt (belt-shaped intermediate transfer body) used in Embodiment 1 of the image forming apparatus
B is configured as follows. In FIG. 2, the intermediate transfer belt B has a four-layer structure in which a belt base material B1, a blocking layer B2a, a charge generation layer B2b, and a charge transport layer B2c are sequentially laminated from the back surface to the front surface. The photoconductive layer B2 is composed of the charge generation layer B2b and the charge transport layer B2c. (Belt base material B1) It is made of a polyimide resin to which 15% by weight of carbon black is added, and has a thickness of 75 μm. Volume resistivity is 10 ^9.5 Ωcm, surface resistance is 10
It is set to ¹² Ω / □.

(Blocking Layer B2a) The blocking layer (B2a) can be formed, for example, as follows. Acetylacetone zirconium butoxide (Orgatics ZC540, manufactured by Matsumoto Kosho Co., Ltd.) 20 parts by weight γ-aminopropyltriethoxysilane 2 parts by weight Polyvinyl butyral resin (ESREC BM-S, manufactured by Sekisui Chemical Co., Ltd.) 1.5 parts by weight n-butyl Alcohol 70 parts by weight After applying a solution comprising the above components to the surface of the base material (B1),
It is dried to form, for example, 0.9 μm. The blocking layer (B2a) has a function of permitting the movement of the electron which is the carrier of the-(minus) polarity, but preventing the movement of the hole which is the carrier of the + (plus) polarity.

(Charge Generating Layer B2b) PVK (Poly vinyl carbazole, phthalocyanine pigment-based charge generating agent added)
Polyvinylcarbazole) formed with a film thickness of 0.2
This is a 5 μm layer. When irradiated with light, it generates + (plus) and-(minus) charges.

(Charge Transporting Layer (Hole Transporting Layer) B2c) It is composed of a polycarbonate resin to which a triphenylamine-based charge transporting agent is added, and has a thickness of 25 μm. It has a function of permitting the movement of holes that are carriers of + (plus) polarity but preventing the movement of electrons that are carriers of-(minus) polarity. That is, the charge transport layer B2c of the first embodiment is a hole transport layer.

FIG. 3 is a block diagram of the control unit according to the first embodiment. A UI (user interface) is connected to the controller C. The UI has a copy start key (job start key) UIa, a full color mode selection key UIb, a numeric keypad UIc, a display UId, and the like. A detection signal of the next sensor is input to the controller C. SNB: Belt Position Sensor The belt position sensor SNB (see FIGS. 1 and 3) detects a mark (mark) attached to the intermediate transfer belt B, and outputs a detection signal to the controller C. SN1: sheet size sensor The sheet size sensor SN1 is a sensor for detecting the presence / absence of a sheet (sheet) passage and the sheet size (sheet size), and outputs a detection signal to the controller C.
The controller C receives detection signals from a sheet discharge sensor (not shown), a fixing device temperature sensor, and other sensors.

The controller C to which signals from the UI (user interface) and the various sensors SNB, SN1,... Are input includes an IPS operation timing control signal, a laser drive signal output device DL operation timing control signal, A belt drive circuit D for driving a belt drive motor M for rotating the intermediate transfer belt B, and a power supply circuit E
The operation control signals for the primary transfer power supply circuit E1, the secondary transfer power supply circuit E2, the power supply E3 for adjusting the potential of the intermediate transfer member, and the power supply circuit E4 for the neutralizer are output. A power supply E for adjusting the potential of the intermediate transfer member according to a control signal output from the controller C
Reference numeral 3 drives the intermediate transfer member potential adjuster K, and the power supply circuit E4 for the static eliminator drives the light irradiation static eliminator JK.

The controller C, which executes processing according to the various input signals, performs I / O (input / output interface) for inputting / outputting an external signal and adjusting the input / output signal level, and performs necessary processing. ROM (Read Only Memory) storing programs and data for execution, RAM for temporarily storing necessary data
(Random access memory), and a computer having a CPU (central processing unit) for performing input / output control and arithmetic processing according to a program stored in the ROM, and the like. Various functions can be realized by executing the program. That is, the controller C has the following functions.

C1: Belt position detecting means The belt position detecting means C1 is provided with the belt position sensor SNB.
Detects the rotational position of the intermediate transfer belt B by measuring the elapsed time from the time when the belt mark MK is detected. C2: Sheet Size Detecting Unit The sheet size detecting unit C2 detects the sheet size in the sheet (paper) conveying direction based on the passage times of the leading and trailing edges of the sheet (paper) detected by the sheet size sensor SN1.

C3: Write Timing Notification Signal Output Means The write timing notification signal output means C3 outputs a write timing notification signal based on the belt mark detection signal of the belt position sensor SNB to the IPS and laser drive signal output device. Output to DL. That is, the toner image transfer start position on the intermediate transfer belt B reaches the primary transfer area Q3 a predetermined time after the detection of the belt mark by the belt position sensor SNB. It is necessary to cause the front end of the toner image formed on the PR to reach the primary transfer position Q3. For that purpose, it is necessary to start writing the image to the latent image forming position Q1 by the ROS at a predetermined timing. For this reason, the write timing notification signal output means C3 outputs the write timing notification signal. The IPS and the laser drive signal output device DL output a laser drive signal to the ROS at a predetermined timing after the write timing notification signal is output.

C4: Belt control means The belt control means C4 outputs a control signal of a belt drive circuit D of a belt drive motor M for driving the intermediate transfer belt B to rotate. C5: Primary transfer unit control means The primary transfer unit control means C5 is a primary transfer unit T1 when the image forming area of the intermediate transfer belt B passes through the primary transfer area Q3.
Is applied with a constant primary transfer current or voltage. C6: Secondary Transfer Unit Control Unit The secondary transfer unit control unit C6 is fixed to the secondary transfer unit T2 to perform secondary transfer when the image forming area of the intermediate transfer belt B passes through the secondary transfer area Q3. A secondary transfer current or voltage is applied.

C7: Potential adjuster control means The potential adjuster control means C7 adjusts the potential of the surface of the intermediate transfer belt B passing through the potential adjustment area Q6 on the upstream side of the secondary transfer area Q4 of the intermediate transfer belt B. It outputs a lighting control signal for the body potential adjuster (red LED) K.

C8: Static eliminator lighting control means The static eliminator lighting control means C8 illuminates the light irradiation static eliminator JK when the portion of the intermediate transfer belt B on which the secondary transfer has been performed passes through the static elimination area Q7. And outputs a static eliminator lighting control signal to the static eliminator power supply circuit E4 (see FIG. 3).

A light source control circuit (C + E4) is constituted by the controller C having the neutralizer lighting control means C7 and the neutralizer power supply circuit E4. A controller C having the static eliminator lighting control means C7, a static eliminator power supply circuit E4, and a light irradiation static eliminator JK are used to control a resistivity (C +
E4 + JK).

(Operation Timing of Potential Adjuster K and Light Irradiator JK) FIG. 4 shows the primary transfer device T1, the intermediate transfer member potential adjuster K, the secondary transfer device T2, and the light irradiator neutralizer of the first embodiment. It is a time chart of JK. In FIG. 4, the intermediate transfer member potential adjuster K of the image forming apparatus of the first embodiment is shown.
Adjusts the potential of the photoconductive intermediate transfer member by light irradiation after the end of a plurality of primary transfers (after the end of the primary transfer of the final transfer toner image in the four color toner images) and before the secondary transfer. Is controlled as follows. Further, the light irradiation static eliminator JK is controlled so as to perform charge elimination of the intermediate transfer belt B by light irradiation after the completion of the secondary transfer.

(Operation of the First Embodiment) Next, using the image forming apparatus of the first embodiment, high temperature and high humidity (28 ° C., 85
%), The operation when the image forming operation is performed will be described. (Paper) The paper was stored under high temperature and high humidity (28 ° C., 85%) for 12 hours, and the resistance was sufficiently lowered. At this time, the volume resistivity of the paper is set to Kethly 487 Picoammeter and 80
When measured with a 09 Resistiolity test fixture, it was 4.58 × 10 ⁸ Ω · cm.

(Primary transfer voltage) Table 1 shows the values of Examples 1 and 2
9 is a table showing DC voltage applied to the primary transfer roll required when no exposure is performed after the next transfer, and DC voltage applied to the primary transfer roll required when an exposure is performed in Examples 3 and 4 described below.

[Table 1] As shown in Table 1, in order to allow the primary transfer current to flow at 6 μA, the positive voltage applied to the primary transfer roll T1 in Example 1 (the voltage in the case of no exposure) is exposed after the primary transfer ( A higher voltage is required than in the case of Examples 3 and 4 described later).

Table 2 shows the primary transfer voltage and the surface potential of the intermediate transfer member in Examples 1 and 2 without exposure after primary transfer (without adjustment of the potential adjuster K), and Example 3 described later. 3 is a table showing a primary transfer voltage and a surface potential of an intermediate transfer member required when the exposure is performed.

[Table 2]

When a positive voltage of a constant current control of 6 μA is applied to the primary transfer roll T 1 and the applied voltage is sequentially changed from the first color to the fourth color, the DC applied voltage of the primary transfer roll is as shown in Table 1. And the potential of the non-image area on the surface of the intermediate transfer member is as follows (see Table 2). After the first color transfer: -125 V, after the second color transfer: -300 V, after the third color transfer: -450 V, and at the fourth color transfer: -625 V.

After the exposure (after the potential adjustment) when the potential of the surface of the intermediate transfer member is adjusted by the intermediate transfer member potential adjuster K composed of a red LED after the primary transfer of the fourth color and before the secondary transfer. The non-image portion potential was -400V. FIG. 5 shows a toner image when a toner image is transferred from the image carrier (photoconductor) PR to the intermediate transfer member B using the high-resistance photoconductive intermediate transfer member (intermediate transfer belt) B of the first embodiment. 5A is a diagram showing the potential on the image carrier PR, and FIG. 5B is a diagram showing the potential on the intermediate transfer member B.
FIG. 5B ′ shows that the potential on the surface of the intermediate transfer member decreases by exposure after the fourth primary transfer, and FIG. 5B ′ shows that the potential (−potential) increases each time the next transfer is repeated.
FIG. 5C is a diagram showing a state in which the difference between the image potential on the surface of the intermediate transfer member B and the non-image potential has been reduced, and the spread of the secondary transfer electric field to the non-image portion has disappeared. In the state of FIG. 5C, since the secondary transfer electric field does not spread to the non-image portion compared to FIG. 9C, scattering of toner and the like are reduced. (Secondary Transfer Voltage) In the first embodiment, in the state of FIG.
Transfer was performed by applying a constant voltage of 1000 V to the secondary transfer roll T2b.

(Image Pattern) Two types of image patterns of the print sample are prepared, and the first sheet is composed of a single color of yellow, magenta, cyan, and black, a secondary color, a tertiary color of a 2 cm square solid, and a single color of black toner. The set consists of kanji of different sizes.
Two types of samples were output alternately as a line / inch halftone image. The surface potential of the intermediate transfer member immediately after the second transfer of the first print is from −70 V to −100 V
Surface potential unevenness depending on the degree of image pattern,
After light irradiation by the light irradiation static eliminator JK, the surface potential of the intermediate transfer member becomes almost uniform between -10 V and -30 V, and there is no density unevenness or scattering in the next print sample, a 400 line / inch halftone image. A uniform image was obtained. Although two types of print samples were alternately output for a total of 20,000 sheets, a good image without density unevenness, scattering, and fatness was obtained.

Embodiment 2 An image forming apparatus according to Embodiment 2 of the present invention differs from the image forming apparatus of Embodiment 1 in the following points, but is similar to Embodiment 1 in other points. It is configured. The first embodiment uses the intermediate transfer member potential adjuster K constituted by a light irradiator, whereas the second embodiment employs an intermediate transfer member potential adjuster K constituted by a scotron. . The operation timing of the intermediate transfer member potential adjuster K and the light irradiator JK of the image forming apparatus of the second embodiment is the same as that of the first embodiment. That is, the timing chart is the same as that of FIG. That is, the intermediate transfer member potential adjuster K operates after the completion of the primary transfer for a plurality of times (4
The control is performed so that the potential of the photoconductive intermediate transfer member is adjusted by light irradiation before the secondary transfer (after the primary transfer of the final transfer toner image in the color toner image). Further, the light irradiation static eliminator JK is controlled to perform static elimination only after the end of the secondary transfer.

(Operation of Embodiment 2) Next, the image forming apparatus of Embodiment 2 was used under high temperature and high humidity conditions (28 ° C., 85 ° C.).
%), The operation when the image forming operation is performed will be described. (Paper) The same paper as in the first embodiment was used. (Primary transfer voltage) A positive voltage of 6 μA constant current control was applied to the primary transfer roll T1, so that the applied voltage could be sequentially changed from the first color to the fourth color. The potential of the non-image portion on the surface of the intermediate transfer member at this time was as follows. After the first color transfer: -125 V, after the second color transfer: -300 V, after the third color transfer: -450 V, and at the fourth color transfer: -625 V.

After the primary transfer of the fourth color and before the secondary transfer, the potential of the surface of the intermediate transfer member is adjusted by the intermediate transfer member potential adjuster K constituted by a scorotron. The image portion potential was -400V. (Secondary transfer voltage) A constant voltage of 1000 V was applied to the secondary transfer roll T2b to perform transfer.

(Image Pattern) Two types of image patterns of the print sample are prepared. The first sheet is a single color of yellow, magenta, cyan, black, a secondary color, a tertiary color of a 2 cm square solid and a black toner single color. The set consists of kanji of different sizes.
Two types of samples were output alternately as a line / inch halftone image. The surface potential of the intermediate transfer member immediately after the second transfer of the first print is from −70 V to −100 V
Surface potential unevenness depending on the degree of image pattern,
After the potential adjustment by the light irradiation static eliminator JK, the surface potential of the intermediate transfer body becomes almost uniform between -10V and -30V,
The next print sample, 400 line / inch
In the halftone image, a uniform image without density unevenness and scattering was obtained. Two types of print samples were alternately output for a total of 20,000 sheets, but density unevenness, scattering,
A good image without thickening of the image was obtained.

Embodiment 3 Embodiment 3 of the image forming apparatus of the present invention is different from the image forming apparatus of Embodiment 1 in the following points, but is similar to Embodiment 1 in other points. It is configured. In the image forming apparatus of the third embodiment, the operation timing of the intermediate transfer member potential adjuster K is different from that of the first embodiment. FIG. 7 shows a primary transfer device T1, an intermediate transfer member potential adjuster K, a secondary transfer device T2, and a light irradiator JK of the third embodiment.
It is a time chart. The intermediate transfer member potential adjuster K of the first embodiment emits light after the end of a plurality of primary transfers (after the end of the primary transfer of the final transfer toner image in the four color toner images) and before the secondary transfer. , The potential of the photoconductive intermediate transfer member is controlled so that the potential of the intermediate transfer member K of the third embodiment changes every time the primary transfer ends, as shown in FIG. , The potential of the photoconductive intermediate transfer member is adjusted by light irradiation. The intermediate transfer member potential adjuster K
Is performed by the potential controller control means C7 'of the controller C of the third embodiment.

(Operation of Embodiment 3) Next, the image forming apparatus of Embodiment 3 is used under high temperature and high humidity conditions (28 ° C., 85 ° C.).
%), The operation when the image forming operation is performed will be described. (Paper) The same paper as in the first embodiment was used. (Primary transfer voltage) A positive voltage of 6 μA constant current control was applied to the primary transfer roll T1, so that the applied voltage could be sequentially changed from the first color to the fourth color. At this time, the intermediate transfer member potential adjuster K (red LE
Light irradiation according to D) was performed to adjust the surface potential of the intermediate transfer member as needed. The potential of the non-image portion on the surface of the intermediate transfer member at this time was as follows. After the first color transfer: -90V, After the second color transfer: -185V, After the third color transfer: -260V, At the time of the fourth color transfer: -350V.

Table 1 shows the DC voltage applied to the primary transfer roll in the case of exposure after the primary transfer in Example 3 and the DC voltage applied to the primary transfer roll required for the absence of exposure for comparison. Have been. . As shown in Table 1, the positive voltage applied to the primary transfer roll T1 is lower than that in the case where no exposure is performed after the primary transfer.

Table 2 shows that the primary transfer voltage and the surface potential of the intermediate transfer member when the exposure after the primary transfer of Example 3 was performed (when the potential adjuster K was adjusted), and the exposure for comparison. The graph shows the required primary transfer voltage and the surface potential of the intermediate transfer member in the case of no transfer.

(Secondary Transfer Voltage) A constant voltage of 1000 V was applied to the secondary transfer roll T2b to perform transfer.

(Image Pattern) Two types of image patterns of the print sample are prepared. The first sheet is a single color of yellow, magenta, cyan, black, a secondary color, a tertiary color of a 2 cm square solid and a black toner single color. The set consists of kanji of different sizes.
Two types of samples were output alternately as a line / inch halftone image. Immediately after the second transfer of the first print, the surface potential of the intermediate transfer body was uneven from −60 V to −80 V according to the image pattern. However, after the light irradiation by the light irradiation static eliminator JK, the intermediate transfer was performed. The surface potential of the body became almost uniform between -10 V and -30 V, and a uniform image without density unevenness and scattering was obtained in the next print sample, a 400-line / inch halftone image. Although two types of print samples were alternately output for a total of 20,000 sheets, a good image without density unevenness, scattering, and fatness was obtained.

(Embodiment 4) An image forming apparatus according to Embodiment 4 of the present invention is different from the image forming apparatus of Embodiment 1 in the following points, but is similar to Embodiment 1 in other points. It is configured. In the first embodiment, the intermediate transfer member potential adjuster K constituted by a light irradiator is used, whereas in the fourth embodiment, the intermediate transfer member potential adjuster K constituted by a scotron is used. I have. In the image forming apparatus of the fourth embodiment, the operation timing of the intermediate transfer member potential adjuster K is different from that of the first embodiment. That is, the first embodiment
The intermediate transfer member potential adjuster K has a photoconductive property due to light irradiation after the end of a plurality of primary transfers (after the end of the primary transfer of the final transfer toner image in the four color toner images) and before the secondary transfer. In contrast to the control for adjusting the potential of the intermediate transfer member, the intermediate transfer member potential adjuster K of the fourth embodiment has a corona discharge of the scorotron (DC and AC voltage superimposed each time the primary transfer is completed). Is controlled so as to adjust the potential of the photoconductive intermediate transfer member. Therefore, the time chart of the fourth embodiment is the same as the time chart of the third embodiment (see FIG. 7).

(Operation of Embodiment 4) Next, the image forming apparatus of Embodiment 4 was used under high temperature and high humidity conditions (28 ° C., 85 ° C.).
%), The operation when the image forming operation is performed will be described. (Paper) The same paper as in the first embodiment was used. (Primary transfer voltage) A positive voltage of 6 μA constant current control was applied to the primary transfer roll T1, so that the applied voltage could be sequentially changed from the first color to the fourth color. At this time, after each primary transfer of the toner of each color, corona discharge was performed by an intermediate transfer member potential adjuster (scorotron) K to adjust the surface potential of the intermediate transfer member. The DC voltage applied to the intermediate transfer member potential regulator (scorotron) K at this time was as follows. After the first color transfer: -90V, After the second color transfer: -175V, After the third color transfer: -240V, At the time of the fourth color transfer: -330V.

In this case, the potential of the non-image portion on the surface of the intermediate transfer member after the potential adjustment by the intermediate transfer member potential adjuster (scorotron) K was as follows. After the first color transfer: -100 V, after the second color transfer: -195 V, after the third color transfer: -270 V, and at the fourth color transfer: -360 V.

(Secondary Transfer Voltage) A constant voltage of 1000 V was applied to the secondary transfer roll T2b to perform transfer.

(Image Pattern) Two types of image patterns of the print sample are prepared. The first sheet is a single color of yellow, magenta, cyan, and black, a secondary color, a tertiary color of a 2 cm square solid, and a single color of black toner. The set consists of kanji of different sizes.
Two types of samples were output alternately as a line / inch halftone image. Immediately after the second transfer of the first print, the surface potential of the intermediate transfer body was uneven from −60 V to −80 V according to the image pattern. However, after the light irradiation by the light irradiation static eliminator JK, the intermediate transfer was performed. The surface potential of the body became almost uniform between -10 V and -30 V, and a uniform image without density unevenness and scattering was obtained in the next print sample, a 400-line / inch halftone image. Although two types of print samples were alternately output for a total of 20,000 sheets, a good image without density unevenness, scattering, and fatness was obtained.

(Comparative Example) The operation of the image forming apparatus without the intermediate transfer member potential adjuster K will be described as a comparative example. (Operation of Comparative Example) Next, an operation when an image forming operation is performed under high temperature and high humidity (28 ° C., 85%) using the image forming apparatus of the comparative example will be described. (Paper) The same paper as in the first embodiment was used. (Primary transfer voltage) A positive voltage of 6 μA constant current control was applied to the primary transfer roll T1, so that the applied voltage could be sequentially changed from the first color to the fourth color. At this time, the surface potential of the intermediate transfer member after the primary transfer of the toner of each color was as follows. After the first color transfer: -125 V, after the second color transfer: -300 V, after the third color transfer: -450 V, and at the fourth color transfer: -625 V.

(Secondary Transfer Voltage) A constant voltage of 1000 V was applied to the secondary transfer roll T2b to perform transfer.

(Image Pattern) Two types of image patterns of the print sample are prepared, and the first sheet is a single color of yellow, magenta, cyan, black, a secondary color, a tertiary color of a 2 cm square solid and a black toner single color. The set consists of kanji of different sizes.
Two types of samples were output alternately as a line / inch halftone image. The surface potential of the intermediate transfer member immediately after the second transfer of the first print is from -80 V to -110 V
Surface potential unevenness depending on the degree of image pattern,
After the light irradiation by the light irradiation static eliminator JK, the surface potential of the intermediate transfer member becomes almost uniform between -10 V and -30 V, and in a halftone image of 400 line / inch, which is the next print sample, under high temperature and high humidity. This resulted in an image in which density unevenness and scattering were considered to be caused by the decrease in paper resistance and the bias of the transfer electric field.

(Modifications) Although the embodiments of the present invention have been described in detail, the present invention is not limited to the above-described embodiments, but falls within the scope of the present invention described in the appended claims. Thus, various changes can be made. Modified embodiments of the present invention will be exemplified below. (H01) The intermediate transfer member used in the present invention can be used in a tandem type image forming apparatus provided with a plurality of image carriers. (H02) The secondary transfer device T2 includes a backup roll T2a,
A secondary transfer roll T2b and the backup roll T
It is possible to configure by a contact roll abutting on 2a. (H03) In the above embodiment, an example is shown in which an intermediate transfer member having a four-layer structure in which an underlayer, a charge generation layer, and a charge transport layer are formed in this order on the lowermost layer surface in which carbon black is dispersed is used. Even when the transfer body is a single layer having photoconductivity or a two-layer structure in which a photoconductive layer is formed on the surface of an underlayer in which carbon black or the like is dispersed, good image quality can be stably obtained by the same action. it can. (H04) Although the potential adjustment of the intermediate transfer member by light irradiation in the above embodiment is performed from the surface side of the intermediate transfer member, when the photoconductive intermediate transfer member is a single layer, or even in the case of multiple layers, the lowermost layer is transparent. In this case, light irradiation can be performed from the back surface.

[0079]

The above-described image forming apparatus of the present invention has the following effects. (E01) Image part at the time of secondary transfer (part where toner is transferred)
And non-image area (part where toner is not transferred, background area of image)
, It is possible to prevent the transfer electric field from spreading to the non-image area. Therefore, even when the sheet resistance value decreases under high temperature and high humidity conditions, a good image can be transferred without scattering the toner image. (E02) In the primary transfer, even in the photoconductive intermediate transfer member having a high resistance as a dielectric, the primary transfer can be continuously performed a plurality of times without greatly increasing the applied primary transfer voltage. Therefore, when primary transfer is performed by superposing toner images of different colors on the intermediate transfer member, the primary transfer can be favorably performed by a low-voltage primary transfer power supply.

[Brief description of the drawings]

FIG. 1 is an overall explanatory diagram of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration of an intermediate transfer belt used in Embodiment 1 of the image forming apparatus of the present invention.

FIG. 3 is a block diagram of a control unit according to the first embodiment.

FIG. 4 is a time chart of a primary transfer device T1, an intermediate transfer member potential adjuster K, a secondary transfer device T2, and a light irradiator JK of the first embodiment.

FIG. 5 is a diagram illustrating the transfer of a toner image from an image carrier (photoreceptor) PR to an intermediate transfer member B using a high-resistance photoconductive intermediate transfer member (intermediate transfer belt) B according to the first exemplary embodiment. FIG. 5A is a diagram showing the potential on the image carrier PR, and FIG. 5B is a diagram showing the potential on the intermediate transfer member B. The potential is shown each time the primary transfer is repeated. FIG. 5B ′ shows that the potential of the surface of the intermediate transfer member decreases by exposure after the fourth primary transfer, and FIG. 5C shows that the surface of the intermediate transfer member B decreases. FIG. 7 is a diagram illustrating a state in which the difference between the image potential and the non-image potential has been reduced, so that the secondary transfer electric field has not spread to the non-image portion.

FIG. 6 is an explanatory diagram of a potential adjustment mechanism when a corotron is used as an intermediate transfer member potential adjuster;
FIG. 6A is an explanatory diagram of a state where the potentials of the image portion and the non-image portion change when the DC voltage applied to the corotron is set to an intermediate potential between the image portion and the non-image portion on the intermediate transfer belt;
FIG. 6B is a diagram illustrating a state where the potentials of the image portion and the non-image portion change when the corotron performs corona discharge, and FIG. 6C is a diagram illustrating a potential state of the image portion and the non-image portion after the potential changes.

FIG. 7 is a time chart of a primary transfer device T1, an intermediate transfer member potential adjuster K, a secondary transfer device T2, and a light irradiator JK of a third embodiment.

FIG. 8 is an explanatory diagram of a conventional image forming apparatus using an intermediate transfer member.

FIG. 9 is a diagram showing a configuration in which a high-resistance photoconductive intermediate transfer member as disclosed in Japanese Patent Application No. Hei 10-123999 (Japanese Patent Application Laid-Open No. HEI 10-1992) is used to transfer an intermediate transfer member from an image bearing member (photoreceptor). FIG. 9A is a diagram showing a toner image when a toner image is transferred to the image carrier, and FIG. 9A is a diagram showing a potential on the image carrier;
9B 'is a diagram showing the potential on the intermediate transfer member, FIG. 9B' is a diagram showing the potential on the surface of the intermediate transfer member after the fourth primary transfer, and FIG. 9C is a diagram showing the secondary transfer electric field.

[Explanation of symbols]

B: Intermediate transfer member, C7 ': Potential adjuster control means, F: Fixing device, JK: Light irradiation static eliminator, K: Intermediate transfer member potential adjuster, Q0: Charged area, Q1: Latent image forming position, Q2 ... Developing area, Q3: primary transfer area, Q4: secondary transfer area, Q5: fixing area, Q6: potential adjusting area, Q7: static elimination area, PR: image carrier, S: recording sheet, SH: sheet transport device , T
1. Primary transfer unit, T2 Secondary transfer unit, TR1 Paper feed tray.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Satoshi Shigezaki 1600 Takematsu, Minamiashigara-shi, Kanagawa Prefecture F-term in Fuji Xerox Co., Ltd. 2H030 AD02 AD05 AD17 BB02 BB24 BB42 BB44 BB55 2H032 AA05 AA15 BA01 BA09 BA15 BA21 BA26 CA02 CA13 2H072 AA36 AB18 AB19 AB20 BA03 BA12 CA01 CA02 CA05

Claims (2)

[Claims] 1. An image forming apparatus having the following requirements (A01) to (A08): (A01) passing sequentially through a charging area, a latent image forming position, a developing area, and a primary transfer area. (A02) an image carrier having a surface on which the toner is charged while passing through the charging area, an electrostatic latent image is formed when passing through the latent image forming position, and a toner image is formed when passing through the developing area. An intermediate transfer member that rotates and sequentially passes through a secondary transfer region, a potential adjustment region, a secondary transfer region, and a charge removal region, and contains a photoconductive substance whose resistance value decreases when irradiated with light; (A03) Sheet transport for sequentially transporting the recording sheet stored in the (A03) paper feed tray to the secondary transfer area, the fixing area, and the sheet discharge unit when the intermediate transfer body is a dielectric material having a high resistance when not irradiated. Apparatus, (A04) the primary transfer area (A) a primary transfer device that primarily transfers a toner image on an image carrier onto an intermediate transfer member in an area.
05) a secondary transfer device for secondary-transferring the primary transfer toner image on the intermediate transfer member onto the recording sheet in the secondary transfer region; (A06) discharging the intermediate transfer member passing through the discharge region by light irradiation (A07) a fixing device for fixing a secondary transfer toner image on a recording sheet passing through the fixing area, and (A08) an intermediate transfer for adjusting a potential on an intermediate transfer body in the potential adjusting area. Body potential regulator. 2. An image forming apparatus having the following requirements (B01) to (B09): (B01) the image forming apparatus sequentially passes through a charging area, a latent image forming position, a developing area, and a primary transfer area. (B02) an image carrier having a surface on which the toner is charged while passing through the charging area, an electrostatic latent image is formed when passing through the latent image forming position, and a toner image is formed when passing through the developing area. An intermediate transfer member that rotates and sequentially passes through a secondary transfer region, a potential adjustment region, a secondary transfer region, and a charge removal region, and contains a photoconductive substance whose resistance value decreases when irradiated with light; (B03) Sheet transport for sequentially transporting the recording sheet stored in the sheet feeding tray to the secondary transfer area, the fixing area, and the sheet discharge unit, which is a dielectric material having a high resistance when not irradiated. Device, (B04) the primary transfer area (B) a primary transfer device that primarily transfers the toner image on the image carrier to the intermediate transfer member in the area
05) a light irradiation static eliminator for erasing the intermediate transfer body passing through the charge elimination area by light irradiation; and (B06) secondary transferring the primary transfer toner image on the intermediate transfer body to the recording sheet in the secondary transfer area. (B07) a fixing device for fixing a secondary transfer toner image on a recording sheet passing through the fixing area, and (B08) a potential adjusting area set on a moving path of the intermediate transfer body. An intermediate transfer member potential adjuster for adjusting the potential on the intermediate transfer member; (B09) a potential adjuster control means for performing the potential adjustment each time the primary transfer is performed.