JP6933008B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus.

In the image forming apparatus, by providing a guide for guiding the recording medium to the nip portion near the inlet of the nip portion in the transfer portion, the gap between the recording medium and the transfer rotating body near the inlet of the nip portion is reduced, which is caused by electric discharge. A technique for suppressing image defects is disclosed in, for example, Japanese Patent Application Laid-Open No. 11-73031 (Patent Document 1).

Japanese Unexamined Patent Publication No. 11-73031

However, it is still required to suppress image defects caused by electric discharge in the nip portion. An object of the present invention is to provide an image forming apparatus capable of suppressing image defects caused by electric discharge.

The present inventors have confirmed that when a pressurized rotating body including a foamed elastic layer is used in an image forming apparatus, image defects in which a part of the toner image is not transferred are likely to occur. Local discharge is likely to occur in the foamed elastic layer having many voids. Due to the local discharge in the foamed elastic layer, the discharge in the recording medium is induced, so that image defects are likely to occur.

When the amount of water in the recording medium is low (in a low humidity environment, when printing the second surface during double-sided printing, etc.), the present inventors are particularly likely to generate an electric discharge in the recording medium, resulting in image defects. I found that it is easy.

Therefore, the present inventors have further studied to ensure good image quality even in a low humidity environment and when printing the second side of double-sided printing, and have completed the present invention.

This image forming apparatus includes a transfer rotating body, a pressurized rotating body, and a pressing member. The transfer rotating body transfers the toner image to the recording medium. The pressurized rotating body faces the transfer rotating body and forms a nip portion with the transfer rotating body. The pressurized rotating body includes a foamed elastic layer forming an outer peripheral surface. The pressing member is arranged on the upstream side in the rotation direction of the pressurized rotating body with respect to the nip portion, and by pressing the foamed elastic layer, a part of the foamed elastic layer is compressed toward the rotation center of the pressurized rotating body. Transform .

According to the above-mentioned image forming apparatus, the electric discharge in the foamed elastic layer is suppressed, and the occurrence of white-out image defects due to the occurrence of this electric discharge can be suppressed.

In the above image forming apparatus, the pressing member has a shape extending in the axial direction of the pressurized rotating body. The length of the pressing member in the thickness direction of the pressing member orthogonal to the axial direction and the length direction perpendicular to the axial direction is substantially constant over the axial direction.

According to the above-mentioned image forming apparatus, since the foamed elastic layer can be uniformly pressed, the foamed elastic layer can be uniformly deformed in the axial direction.

In the above image forming apparatus, the pressing member includes a tip portion that presses the foamed elastic layer and a support portion that supports the tip portion. The thickness of the tip portion in the thickness direction is smaller than the thickness of the support portion in the thickness direction.

According to the above-mentioned image forming apparatus, the foamed elastic layer can be reliably pressed in a narrow space near the entrance of the nip portion.

In the above image forming apparatus, the thickness of the tip portion in the thickness direction is larger as the portion closer to the center in the axial direction of the tip portion. As a result, it is possible to prevent the entire tip portion from being deformed in an arc shape.

In the above image forming apparatus, the closer to the center of the tip in the axial direction, the shorter the length of the tip in the length direction orthogonal to the thickness direction and the axial direction. As a result, the foamed elastic layer can be pressed uniformly.

In the above image forming apparatus, the portion closer to the center in the axial direction of the tip portion is arranged at a position closer to the foamed elastic layer in the thickness direction. As a result, the foamed elastic layer can be pressed uniformly.

In the above image forming apparatus, the outer diameter of the pressurized rotating body is larger as the portion closer to the center in the axial direction of the pressurized rotating body. As a result, the foamed elastic layer can be pressed uniformly.

The image forming apparatus described above further includes a control unit that controls the operation of the pressing member. As a result, creep deformation can be suppressed and image quality can be ensured.

In the above image forming apparatus, when forming an image on both sides of the recording medium, the control unit is more than the amount of pressing of the pressing member against the foam elastic layer when the transfer rotating body transfers the toner image to the first surface of the recording medium. , The amount of pressure when the transfer rotating body transfers the toner image to the second surface of the recording medium is increased. As a result, the occurrence of white-out image defects can be effectively suppressed.

In the above image forming apparatus, when forming an image on both sides of the recording medium, the control unit causes the pressing member to press the foamed elastic layer only when the transfer rotating body transfers the toner image to the second surface of the recording medium. As a result, it is possible to suppress a decrease in the life of the secondary transfer roller.

The above-mentioned image forming apparatus further includes a temperature / humidity detecting means for detecting the temperature / humidity inside the image forming apparatus. The control unit makes the pressing amount when the temperature / humidity detecting means detects the low humidity state larger than the pressing amount of the pressing member against the foam elastic layer when the temperature / humidity detecting means detects the high humidity state. As a result, the occurrence of white-out image defects can be effectively suppressed.

In the above image forming apparatus, the control unit causes the pressing member to press the foamed elastic layer only when the temperature / humidity detecting means detects a low humidity state. As a result, creep deformation can be suppressed and image quality can be ensured.

The image forming apparatus further includes a recording medium detecting means for detecting the type of recording medium in which an image is formed. The control unit adjusts the amount of pressing of the pressing member against the foam elastic layer according to the detection result by the recording medium detecting means. As a result, the occurrence of white-out image defects can be effectively suppressed.

In the above image forming apparatus, the control unit causes the pressing member to press the foamed elastic layer only when the recording medium detecting means detects the uncoated paper. As a result, creep deformation can be suppressed and image quality can be ensured.

In the above image forming apparatus, the control unit separates the pressing member from the foamed elastic layer in a state where no image is formed on the recording medium. As a result, creep deformation can be suppressed and image quality can be ensured.

In the above image forming apparatus, the control unit separates the pressing member from the foamed elastic layer at the end of image forming. As a result, creep deformation can be suppressed and image quality can be ensured.

According to this image forming apparatus, it is possible to realize an image forming apparatus capable of further suppressing image defects caused by electric discharge.

It is the schematic of the image forming apparatus. It is an enlarged view of the secondary transfer part according to Embodiment 1. FIG. It is the schematic of the pressing member when viewed from the direction III in FIG. It is sectional drawing which follows the IV-IV line shown in FIG. It is the figure which showed the nip part by the simple structure. It is a table which showed the occurrence state of the white-out image defect for each push-in amount and each applied voltage. It is the schematic which shows the nip part of the conventional secondary transfer part. It is a figure which shows the outline of the control waveform of the pushing amount and the applied voltage in the evaluation test in the configuration shown in FIG. It is a table which showed the timing of each voltage application of FIG. 8 and the occurrence state of the white-out image defect with respect to each applied voltage. It is the schematic of the pressing member according to Embodiment 2 when viewed from the direction III in FIG. It is sectional drawing which follows the XI-XI line shown in FIG. It is sectional drawing which follows the XII-XII line shown in FIG. It is the schematic of the pressing member according to Embodiment 3 when viewed from the direction III in FIG. It is sectional drawing which follows the XIV-XIV line shown in FIG. It is sectional drawing which follows the XV-XV line shown in FIG. It is the schematic of the pressing member according to Embodiment 4 when viewed from the direction III in FIG. It is sectional drawing which follows the XVII-XVII line shown in FIG. FIG. 6 is a cross-sectional view taken along the line XVIII-XVIII shown in FIG. It is a schematic diagram which shows the secondary transfer roller according to Embodiment 5 when viewed from the XIX direction in FIG. It is a table which shows the evaluation result of the occurrence of the white-out image defect in Examples 1-5, Comparative Example 1, and Comparative Example 2. It is a table which shows the evaluation result of the band-shaped density unevenness and the deterioration state of the secondary transfer roller in Example 6, Example 7, Comparative Example 3, and Comparative Example 4.

Hereinafter, the image forming apparatus according to each embodiment will be described with reference to the drawings. In the embodiments shown below, the same or substantially the same configuration will be designated by the same reference numerals, and duplicate description will not be repeated. Each configuration of the embodiments described below may be selectively combined as appropriate.

<Image forming device 1>
(Embodiment 1)
Examples of the image forming method include a direct transfer method and an intermediate transfer method. In the direct transfer method, the image is formed by going through a step of directly transferring the toner image formed on the photoconductor to the recording medium and a step of heating and fixing the toner image transferred on the recording medium.

In the intermediate transfer method, a step of transferring the toner image formed on the photoconductor to the intermediate transfer belt (primary transfer) and a step of transferring the toner image transferred on the intermediate transfer belt to a recording medium (secondary transfer). The image is formed by passing through the steps of heating and fixing the toner image transferred onto the recording medium.

In the first embodiment, the image forming apparatus 1 that employs the intermediate transfer method will be described. FIG. 1 is a schematic view of the image forming apparatus 1.

The image forming apparatus 1 includes a latent image forming apparatus 21, an image information input unit 30, and an image information processing unit 31. Image information is input to the image information input unit 30 by signals from, for example, an image reading device (not shown) included in the image forming device 1, a personal computer, or the like.

The image information processing unit 31 processes the image information obtained from the image information input unit 30, and transmits the processed image information to the latent image forming device 21.

The image forming apparatus 1 further includes an image forming unit 10 (10Y, 10M, 10C, 10K). The image forming unit 10 (10Y, 10M, 10C, 10K) forms each color toner image of Y (yellow), M (magenta), C (cyan), and K (black), respectively.

Each of the image forming units 10Y, 10M, 10C, and 10K includes a photoconductor 11 that carries a toner image, a charging device 12 that charges the surface of the photoconductor 11, and a developing device 13.

Each photoconductor 11 is exposed by the latent image forming apparatus 21 based on the image information transmitted by the image information processing unit 31. An electrostatic latent image corresponding to the image information is formed on the surface of each photoconductor 11.

Each developing device 13 supplies toner of each color to the electrostatic latent image formed on the surface of each photoconductor 11. Each developing device 13 forms a toner image of each color on the surface of each photoconductor 11.

The image forming apparatus 1 further includes a driving roller 22a, a rotating roller 22b, an intermediate transfer belt 22, and a primary transfer roller 23. The intermediate transfer belt 22 is stretched by a drive roller 22a and a rotary roller 22b. The drive roller 22a is driven and rotated by a motor or the like (not shown). The intermediate transfer belt 22 and the rotary roller 22b rotate in a driven manner as the drive roller 22a rotates.

The toner images of each color formed on the surface of each photoconductor 11 are transferred onto the intermediate transfer belt 22 by the primary transfer rollers 23 arranged to face each photoconductor 11. The toner images of each color are superimposed on the intermediate transfer belt 22.

Each image forming unit 10Y, 10M, 10C, 10K further includes a cleaning device 14 and an erasing device 15. The cleaning device 14 removes the residual toner on the photoconductor 11 after the toner image formed on the surface of the photoconductor 11 is transferred to the intermediate transfer belt 22. After the cleaning device 14 removes the residual toner, the erasing device 15 removes static electricity from the surface of each photoconductor 11.

The toner image transferred to the intermediate transfer belt 22 by each primary transfer roller 23 is conveyed to the secondary transfer unit 38. In the secondary transfer unit 38, the secondary transfer roller 24 is arranged so as to face the drive roller 22a. The secondary transfer roller 24 forms a drive roller 22a and a nip portion N via an intermediate transfer belt 22. Details of the secondary transfer unit 38 will be described later.

At the same time that the toner image transferred on the intermediate transfer belt 22 is conveyed to the secondary transfer unit 38, the recording medium S housed inside the image forming apparatus 1 is conveyed to the secondary transfer unit 38. The recording medium S is conveyed from the paper feed roller 25 to the secondary transfer unit 38 via the timing roller 26.

The timing roller 26 conveys the recording medium S to the secondary transfer unit 38 so that the toner image transferred on the intermediate transfer belt 22 rushes into the nip portion N and at the same time the recording medium S rushes into the nip portion N.

In the secondary transfer unit 38, the secondary transfer roller 24 presses against the drive roller 22a and pressurizes the recording medium S, so that the toner image transferred on the intermediate transfer belt 22 is transferred onto the recording medium S. NS.

The image forming apparatus 1 further includes a cleaner 27. The cleaner 27 removes the toner remaining on the intermediate transfer belt 22 without being transferred to the recording medium S in the secondary transfer unit 38.

After the toner image is transferred to the recording medium S in the secondary transfer unit 38, the recording medium S is conveyed to the fixing device 28. The fixing device 28 pressurizes and heats the recording medium S on which the toner image is transferred to fix the toner image on the recording medium S. In the case of single-sided printing, the recording medium S is ejected to the outside of the image forming apparatus 1 via the paper ejection roller 29 after the toner image is fixed by the fixing apparatus 28.

In the case of double-sided printing, the recording medium S in which the toner image is fixed on one side (first side) of the recording medium S is conveyed from the paper ejection roller 29 through the reverse paper passing path c along the direction of arrow B. NS. The recording medium S is again conveyed to the secondary transfer unit 38 via the timing roller 26. In the secondary transfer unit 38, the toner image transferred on the intermediate transfer belt 22 is transferred to the other surface (second surface) of the recording medium S.

After the toner image is transferred to the second surface of the recording medium S, the recording medium S is conveyed to the fixing device 28. The fixing device 28 fixes the toner image on the second surface of the recording medium S. After the toner image is fixed on the second surface of the recording medium S, the recording medium S is discharged to the outside of the image forming apparatus 1 via the paper ejection roller 29.

(Secondary transfer unit 38)
FIG. 2 is an enlarged view of the secondary transfer unit 38 according to the first embodiment. In the secondary transfer unit 38, the pressure rotating body is arranged so as to face the transfer rotating body that transfers the toner image to the recording medium S. In the first embodiment, the transfer rotating body is a drive roller 22a and an intermediate transfer belt 22. The pressurized rotating body is a secondary transfer roller 24.

The secondary transfer roller 24 includes a conductive core metal 24b and a foamed elastic layer 24a that covers the core metal 24b and constitutes the outer peripheral surface of the secondary transfer roller 24.

The core metal 24b is made of, for example, stainless steel. The outer diameter of the core metal 24b is, for example, 8 mm. The foamed elastic layer 24a is formed by foaming a rubber material (for example, polyurethane, EPDM (ethylene propylene rubber), silicone, etc.) in which a conductive filler such as carbon is dispersed or a material containing an ionic conductive material. Is formed.

The volume resistivity of the foamed elastic layer 24a is adjusted to be ^{, for example, about 1 × 10 5} to 1 × 10 ^{9 Ω · cm.} The radial thickness of the foamed elastic layer 24a is, for example, 5 mm. The surface hardness of the foamed elastic layer 24a is, for example, about 20 to 70 ° (Asker-C). A large number of voids are formed on the surface of the foamed elastic layer 24a. The size of the void (cell diameter) is, for example, 150 μm.

The core metal 24b is connected to the secondary transfer voltage source 24c. The drive roller 22a is grounded. A predetermined electric field is formed in the nip portion N by the secondary transfer roller 24, the drive roller 22a, and the secondary transfer voltage source 24c.

A guide 34 is arranged in the secondary transfer unit 38. The guide 34 is arranged on the upstream side of the secondary transfer roller 24 in the rotational direction DR5 with respect to the nip portion N.

The recording medium S conveyed by the timing roller 26 is guided by the guide 34 and plunges into the nip portion N along the surface of the intermediate transfer belt 22.

By plunging the recording medium S into the nip portion N along the surface of the intermediate transfer belt 22, the gap between the recording medium S and the intermediate transfer belt 22 can be reduced in the vicinity of the inlet of the nip portion N. As a result, image defects caused by electric discharge near the inlet of the nip portion N (point A in FIG. 2) can be suppressed.

In the secondary transfer unit 38, a pressing member 33 that presses the foamed elastic layer 24a and a moving means 39 are arranged. The pressing member 33 is located on the upstream side of the secondary transfer roller 24 in the rotational direction DR5 with respect to the nip portion N, and is arranged near the inlet of the nip portion N. The pressing member 33 is arranged at a position that does not interfere with the transportation of the recording medium S. The pressing member 33 can be moved away from the foamed elastic layer 24a or closer to the foamed elastic layer 24a by the moving means 39.

The pressing member 33 includes a tip portion 33a and a support portion 33b. The tip portion 33a has a leaf spring shape. A metal plate such as stainless steel can be used as the tip portion 33a. The support portion 33b supports the tip portion 33a. The moving means 39 is connected to the support portion 33b and moves the support portion 33b.

The moving means 39 moves the support portion 33b so as to approach the foamed elastic layer 24a, so that the tip portion 33a moves so as to approach the foamed elastic layer 24a, and the tip portion 33a presses the foamed elastic layer 24a. The tip portion 33a deforms the surface of the foamed elastic layer 24a so as to approach the inside of the secondary transfer roller 24 in the radial direction. By deforming the foamed elastic layer 24a, the voids in the foamed elastic layer 24a are crushed and the size of the voids becomes smaller. The deformed portion (region X in FIG. 2) of the foamed elastic layer 24a plunges into the nip portion N in the deformed state.

FIG. 3 is a schematic view of the pressing member 33 when viewed from the direction III in FIG. FIG. 4 is a cross-sectional view taken along the line IV-IV shown in FIG. The pressing member 33 has a shape extending in the axial direction DR1 of the secondary transfer roller 24. The pressing member 33 has a predetermined thickness in the thickness direction DR2 of the pressing member 33 orthogonal to the axial direction DR1.

The thickness of the pressing member 33 near the center (region E in FIG. 3) in the axial direction DR1 and the thickness of the pressing member 33 near the end T are substantially equal. The length of the pressing member 33 in the length direction DR3 orthogonal to the axial direction DR1 and the thickness direction DR2 is substantially constant over the axial direction DR1.

As a result, the foamed elastic layer 24a can be uniformly pressed, so that the foamed elastic layer 24a can be uniformly deformed over the axial DR1.

Further, the thickness of the tip portion 33a in the thickness direction DR2 is smaller than the thickness of the support portion 33b in the thickness direction DR2. As a result, the foamed elastic layer 24a can be reliably pressed in the narrow space near the inlet of the nip portion N.

<Occurrence of white image defects>
As shown in FIG. 2, the guide 34 suppresses the gap between the recording medium S and the intermediate transfer belt 22 near the inlet of the nip portion N, while the gap between the recording medium S and the secondary transfer roller 24 becomes large. , A discharge is generated between the recording medium S and the secondary transfer roller 24.

When the secondary transfer roller 24 including the foamed elastic layer 24a constituting the outer peripheral surface is used, the present inventors are particularly likely to generate an electric discharge, and the electric charge amount of the toner fluctuates (or is caused by this electric discharge). It was found that white spot-like image defects (a state in which a part of the toner image is not formed on the recording medium and the background is exposed. Hereinafter, white spot image defects) are likely to occur. bottom. The state in which a part of the toner image is not formed on the recording medium and the base is exposed occurs because a part of the toner image transferred to the intermediate transfer belt 22 is not transferred to the recording medium.

(Test to confirm factors related to white image defects)
The present inventors investigated the factors related to the white image defect. FIG. 5 is a diagram showing the nip portion N in a simple configuration. In order to perform a confirmation test for white-out image defects, the vertical direction on the paper surface in FIG. 5 is set to the stacking direction DR4, and the positive electrode (core metal), foam elastic layer, recording medium, toner image, intermediate transfer belt, are arranged in this order from the top. Each of the negative electrodes (driving rollers) was configured in the shape of a parallel flat plate.

Further, the push-in amount can be controlled by pressing from the positive electrode side (white arrow in FIG. 5), and the situation where the secondary transfer roller 24 pressurizes the drive roller 22a is reproduced.

(Evaluation conditions)
The volume resistivity of the foamed elastic layer was about 1 × 10 ⁸ Ω · cm. The thickness of the foamed elastic layer in the stacking direction DR4 was 5 mm, and the surface hardness of the foamed elastic layer was 31 °. The average diameter of the voids (cells) in the foamed elastic layer was set to 150 μm. The volume resistivity of the intermediate transfer belt was about 1 × 10 ⁷ Ω · cm, the thickness of the intermediate transfer belt in the stacking direction DR4 was 80 [mu] m. The amount of toner was 8 g / m ² . For the evaluation of white-out image defects, plain paper manufactured by Konica Minolta, trade name J-paper was used.

(Evaluation method)
Various voltages were applied to each pushing amount from the positive electrode side, and it was investigated whether or not a white-out image defect had occurred. The voltage application time was 8 ms. A solid image was transferred to a recording medium by applying a voltage, and the occurrence of white-out image defects in the transferred solid image was visually confirmed. The case where the white image defect did not occur was evaluated as "good", the case where the white image defect occurred slightly was evaluated as "possible", and the case where the white image defect occurred was evaluated as "impossible".

(Evaluation results)
FIG. 6 is a table showing the occurrence status of white image defects for each pressing amount and each applied voltage. When the applied voltage is increased, discharge is likely to occur and white-out image defects are likely to occur. Therefore, the evaluation result tends to be “impossible” in the range where the applied voltage is large.

However, by increasing the pushing amount, the voids in the foamed elastic layer are crushed, and the generation of electric discharge in the foamed elastic layer can be suppressed. As a result, white-out image defects due to the generation of electric discharge in the foamed elastic layer are less likely to occur. From FIG. 6, it can be seen that when the pressing amount is 0.2 mm or more, the effect of suppressing the occurrence of white-out image defects is exhibited.

FIG. 7 is a schematic view showing a nip portion of a conventional secondary transfer portion. At point B2 in FIG. 7, the amount of deformation of the foamed elastic layer (corresponding to the amount of pushing in the evaluation test in the configuration shown in FIG. 5) is large. At point A2, the amount of deformation of the foamed elastic layer is almost zero. Therefore, a white image defect is unlikely to occur in the vicinity of the B2 point, and a white image defect is likely to occur in the vicinity of the A2 point (nip portion entrance).

The indentation amount in the configuration shown in FIG. 5 is controlled so as to correspond to the deformation amounts at points A2, B2, and C2 in the nip portion of FIG. 7, and an evaluation test for white-out image defects is performed in the same manner as in FIG. rice field.

FIG. 8 is a diagram showing an outline of a control waveform of a pushing amount and an applied voltage in an evaluation test in the configuration shown in FIG. The pushing amount was controlled by setting the timing corresponding to the points A2 and C2 shown in FIG. 7 to zero and setting the timing corresponding to the point B2 shown in FIG. 7 to the pushing amount 0.4 mm. At each voltage application timing (timing A2, timing B2, timing C2), the voltage was applied at intervals of 8 ms. Other evaluation conditions and evaluation methods are the same as those at the time of evaluation in FIG.

FIG. 9 is a table showing the timing of application of each voltage of FIG. 8 and the occurrence status of white image defects with respect to each applied voltage. From FIG. 9, compared with the application timing A2 (corresponding to the voltage application at the point A2 in FIG. 7) where the pushing amount is small, the application timing B2 (corresponding to the voltage application at the point B2 in FIG. 7) where the pushing amount is large is outlined. It can be seen that the occurrence of image defects is suppressed.

At the application timing C2 (corresponding to the voltage application at the C2 point in FIG. 7), the pushing amount is zero on the control waveform, but at the time of the application timing B2, the foamed elastic layer is pressed and deformed. Since the deformed state has not recovered at the time of application timing C2, the occurrence of white-out image defects is suppressed as compared with the time of application timing A2.

From the above, it was confirmed that the occurrence of white-out image defects can be suppressed by pressing and deforming the foamed elastic layer. As shown in FIG. 2, the image forming apparatus 1 of the present embodiment includes a pressing member 33 that presses the foamed elastic layer 24a near the entrance of the nip portion N (point A in FIG. 2).

The pressing member 33 presses and deforms the foamed elastic layer 24a before the foamed elastic layer 24a enters the nip portion N, and gives the foamed elastic layer 24a a pressing deformation history (region X in FIG. 2). By giving the foamed elastic layer 24a a press deformation history, the voids formed on the surface of the foamed elastic layer 24a are crushed.

Since the foamed elastic layer 24a is made of a rubber material, the pressing deformation history given near the inlet of the nip N is not instantly recovered, and the foamed elastic layer 24a rushes into the nip portion N with the pressing deformation history left.

Since it rushes into the nip portion N while leaving the pressing deformation history (while the voids in the foamed elastic layer 24a are crushed), the discharge in the foamed elastic layer 24a is suppressed. As a result, it is possible to suppress the occurrence of white-out image defects caused by the occurrence of electric discharge in the foamed elastic layer 24a.

(Control unit 35)
The frequency of occurrence of white-out image defects varies depending on the environment around the image forming apparatus 1 and the situation of the image forming apparatus 1. For example, in a low humidity environment, when the amount of water in the recording medium is small and the recording medium is dry, the resistance value of the recording medium becomes large and the distribution voltage to the recording medium becomes large. It is necessary to increase the applied voltage.

As a result of increasing the applied voltage, electric discharge is likely to occur between the foamed elastic layer and the recording medium, and white-out image defects are likely to occur due to this electric discharge. Further, even when an image is formed on both sides of the recording medium S, when the image is formed on the first surface, the image is passed through the fixing device 28, so that the recording medium S is heated and the amount of water in the recording medium S is reduced. Therefore, when an image is formed on the second surface of the recording medium S, whiteout image defects are likely to occur.

As shown in FIGS. 1 and 2, the image forming apparatus 1 further includes a control unit 35 that controls the operation of the pressing member 33. The control unit 35 controls the moving means 39 to move the pressing member 33. The control unit 35 controls the amount of movement of the moving means 39. The control unit 35 controls the moving means 39 to press the foam elastic layer 24a against the pressing member 33. The control unit 35 controls the amount of pressure of the pressing member 33 against the foamed elastic layer 24a. The control unit 35 separates the pressing member 33 from the foamed elastic layer 24a.

If the state in which the pressing member 33 is pressed against the foamed elastic layer 24a continues, the amount of deformation of the foamed elastic layer 24a gradually increases (creep deformation), and it becomes difficult to return to the original shape of the foamed elastic layer 24a. When creep deformation occurs, band-shaped density unevenness occurs when the toner image is transferred to the recording medium S, and the image quality deteriorates.

By making the pressing member 33 separable from the foamed elastic layer 24a, creep deformation can be suppressed and image quality can be ensured.

When forming an image on both sides of the recording medium S, the control unit 35 determines that the pressing amount of the pressing member 33 against the foamed elastic layer 24a when the intermediate transfer belt 22 transfers the toner image to the first surface of the recording medium S is larger than the amount of pressing. The amount of pressure applied when the intermediate transfer belt 22 transfers the toner image to the second surface of the recording medium S is increased.

By increasing the amount of pressure of the pressing member 33 against the foamed elastic layer 24a when transferring the toner image to the second surface of the recording medium S where white image defects are likely to occur, the occurrence of white image defects is effective. Can be suppressed.

Further, by reducing the pressing amount of the first surface, which is less likely to cause white-out image defects as compared with the second surface, it is possible to suppress the wear of the foamed elastic layer 24a. As a result, it is possible to effectively suppress the occurrence of white-out image defects and suppress the decrease in the life of the secondary transfer roller 24.

When an image is formed on both sides of the recording medium S, the amount of pressure of the pressing member 33 on the foamed elastic layer 24a when transferring the toner image to the first surface of the recording medium S may be set to zero. That is, the pressing member 33 may press the foamed elastic layer 24a only when the intermediate transfer belt 22 transfers the toner image to the second surface of the recording medium S.

By forming the foam elastic layer 24a to be pressed only when the toner image is transferred to the second surface of the recording medium S, the occurrence of white-out image defects is suppressed while suppressing creep deformation and ensuring image quality. Further, it is possible to further suppress the decrease in the life of the secondary transfer roller 24.

As shown in FIG. 1, the image forming apparatus 1 further includes a temperature / humidity detecting means 36. The temperature / humidity detecting means 36 detects the temperature / humidity inside the image forming apparatus 1. The temperature / humidity detecting means 36 detects the temperature / humidity of the secondary transfer unit 38.

In the control unit 35, the temperature / humidity detecting means 36 is in a low humidity state (for example, the humidity is lower than the pressing amount of the pressing member 33 against the foam elastic layer 24a when the temperature / humidity detecting means 36 detects a high humidity state (for example, humidity 85%). For example, when humidity (15%) is detected, the amount of pressing is increased.

In a low humidity state where white-out image defects are likely to occur, the occurrence of white-out image defects can be effectively suppressed by increasing the amount of pressure of the pressing member 33 against the foamed elastic layer 24a.

Further, since the amount of pressing of the pressing member 33 against the foamed elastic layer 24a in a high humidity state where white-out image defects are unlikely to occur can be reduced, wear of the foamed elastic layer 24a can be suppressed. As a result, it is possible to effectively suppress the occurrence of white-out image defects and suppress the decrease in the life of the secondary transfer roller 24.

The amount of pressure of the pressing member 33 on the foamed elastic layer 24a when the temperature / humidity detecting means 36 detects a high humidity state may be set to zero. That is, the pressing member 33 may press the foamed elastic layer 24a only when the temperature / humidity detecting means 36 detects a low humidity state. As a result, it is possible to suppress the occurrence of white-out image defects while suppressing creep deformation and ensuring image quality, and further, it is possible to further suppress a decrease in the life of the secondary transfer roller 24.

As shown in FIG. 1, the image forming apparatus 1 further includes a recording medium detecting means 37. The recording medium detecting means 37 detects the type of the recorded recording medium S to be conveyed. The recording medium detecting means 37 detects coated paper such as coated paper and non-coated paper such as plain paper. The recording medium detecting means 37 detects the thickness of the thick recording medium.

The control unit 35 adjusts the amount of pressing of the pressing member 33 against the foamed elastic layer 24a according to the detection result of the type of recording medium S by the recording medium detecting means 37. In the case of the recording medium S in which white-out image defects are likely to occur, the occurrence of white-out image defects can be effectively suppressed by increasing the pressing amount.

Further, since the amount of pressing of the pressing member 33 against the foamed elastic layer 24a in the case of the recording medium S in which whiteout image defects are unlikely to occur can be reduced, wear of the foamed elastic layer 24a can be suppressed. As a result, it is possible to effectively suppress the occurrence of white-out image defects and suppress the decrease in the life of the secondary transfer roller 24.

The amount of pressure of the pressing member 33 on the foamed elastic layer 24a when the recording medium detecting means 37 detects something other than uncoated paper may be set to zero. That is, the pressing member 33 may press the foamed elastic layer 24a only when the recording medium detecting means 37 detects the uncoated paper.

Non-coated paper is more likely to generate an electric discharge in the paper than coated paper. By configuring the foam elastic layer 24a to be pressed only when the recording medium detecting means 37 detects uncoated paper, creep deformation is suppressed, image quality is ensured, and the occurrence of white-out image defects is suppressed. Further, it is possible to further suppress the decrease in the life of the secondary transfer roller 24.

The control unit 35 separates the pressing member 33 from the foamed elastic layer 24a in a state where no image is formed on the recording medium S. By configuring the pressing member 33 to be separated from the foamed elastic layer 24a in a state where the recording medium S does not pass through the secondary transfer unit 38, creep deformation is further suppressed and image quality is ensured, while white-out image defects are formed. Can be suppressed, and further, a decrease in the life of the secondary transfer roller 24 can be further suppressed.

The control unit 35 separates the pressing member 33 from the foamed elastic layer 24a at the end of image formation. As a result, it is possible to suppress a decrease in the life of the secondary transfer roller 24 while suppressing creep deformation and ensuring image quality.

(Embodiment 2)
FIG. 10 is a schematic view of the pressing member 33 according to the second embodiment when viewed from the direction III in FIG. FIG. 11 is a cross-sectional view taken along the line XI-XI shown in FIG. FIG. 12 is a cross-sectional view taken along the line XII-XII shown in FIG.

Unlike the first embodiment, the portion of the tip portion 33a closer to the center in the axial direction DR1 (region F in the middle of FIG. 10) has a larger thickness of the tip portion 33a in the thickness direction DR2.

In the pressing member 33 according to the second embodiment, the portion of the tip portion 33a closer to the center in the axial direction DR1 and the thickness of the tip portion 33a in the thickness direction DR2 are increased, so that the portion closer to the center of the tip portion 33a has flexural rigidity. Becomes larger.

When moving the support portion 33b, a force is applied to the vicinity of the ends T1 (region Y) on both sides of the support portion 33b. By increasing the flexural rigidity in the vicinity of the region F, when the tip portion 33a is pressed against the foamed elastic layer 24a, it is possible to suppress the entire tip portion 33a from being deformed in an arc shape, and the foamed elastic layer 24a is made uniform. Can be pressed against. As a result, it is possible to suppress non-uniform discharge in the foamed elastic layer 24a, and it is possible to suppress the occurrence of white-out image defects caused by the occurrence of discharge in the foamed elastic layer 24a.

(Embodiment 3)
FIG. 13 is a schematic view of the pressing member 33 according to the third embodiment when viewed from the direction III in FIG. FIG. 14 is a cross-sectional view taken along the line XIV-XIV shown in FIG. FIG. 15 is a cross-sectional view taken along the line XV-XV shown in FIG.

Unlike the first embodiment, the closer to the center of the tip 33a in the axial direction DR1 (region G in FIG. 13), the shorter the length of the tip 33a in the length direction DR3.

In the pressing member 33 according to the third embodiment, the portion closer to the center of the tip portion 33a in the axial direction DR1 and the length of the tip portion 33a in the length direction DR3 are shortened, so that the portion closer to the region G is the tip portion 33a. The magnitude of the moment acting on is reduced.

In the pressing member 33 according to the third embodiment, the foam elastic layer 24a can be uniformly pressed as in the pressing member 33 according to the second embodiment, and the occurrence of white-out image defects can be suppressed. can get.

(Embodiment 4)
FIG. 16 is a schematic view of the pressing member 33 according to the fourth embodiment when viewed from the direction III in FIG. FIG. 17 is a cross-sectional view taken along the line XVII-XVII shown in FIG. FIG. 18 is a cross-sectional view taken along the line XVIII-XVIII shown in FIG. Unlike the first embodiment, the portion of the tip portion 33a closer to the center in the axial direction DR1 (region H in the middle of FIG. 16) is arranged at a position closer to the foamed elastic layer 24a in the thickness direction DR2.

When a force is applied to the vicinity of the end portions T1 (region Z) on both sides of the support portion 33b to press the support portion 33b, the tip portion 33a near the end portions T1 on both sides becomes a portion near the center (region H in FIG. 16). It is more likely to bend in the thickness direction DR2 than the tip 33a.

In the pressing member 33 according to the fourth embodiment, the portion where the tip portion 33a is closer to the center in the axial direction DR1 (region H in the middle of FIG. 16) is arranged at a position closer to the foamed elastic layer 24a in the thickness direction DR2. The layer 24a can be pressed uniformly. As a result, non-uniform discharge in the foamed elastic layer 24a can be suppressed, and the occurrence of white-out image defects due to the occurrence of this discharge can be suppressed.

(Embodiment 5)
FIG. 19 is a schematic view showing a secondary transfer roller 24 according to the fifth embodiment when viewed from the XIX direction in FIG. The secondary transfer roller 24 according to the fifth embodiment has a larger outer diameter (so-called crown shape) as the portion closer to the center in the axial DR1 of the secondary transfer roller 24.

When a force is applied to the vicinity of the ends T1 (region W) on both sides of the support portion 33b shown in FIG. 3 to press the support portion 33b, the entire tip portion 33a is deformed into an arc shape. By adopting the crown-shaped secondary transfer roller 24 for the secondary transfer portion 38, the tip portion 33a is deformed along the outer diameter of the secondary transfer roller 24.

As a result, the foamed elastic layer 24a can be uniformly pressed. Therefore, it is possible to suppress non-uniform discharge in the foamed elastic layer 24a, and it is possible to suppress the occurrence of white-out image defects caused by the occurrence of this discharge.

(Confirmation of white image defect suppression effect)
Hereinafter, examples will be described. An image forming apparatus in which the shapes of the pressing member 33 and the secondary transfer roller according to each embodiment were modified by modifying Konica Minolta's bizhub C358 was prepared as Examples 1 to 5, Comparative Example 1, and Comparative Example 2.

In each of the image forming apparatus of Examples 1 to 5, Comparative Example 1, and Comparative Example 2, a solid image was printed on both sides, and the generated white-out image defect was visually evaluated. The case where no white image defect occurred was evaluated as "good", the case where a slight white image defect occurred was evaluated as "possible", and the case where a white image defect occurred was evaluated as "impossible".

FIG. 20 is a table showing the evaluation results of the occurrence of white image defects in Examples 1 to 5, Comparative Example 1, and Comparative Example 2.

The image forming apparatus 1 of Examples 1 to 4 employs a straight-shaped secondary transfer roller 24 extending straight in the axial direction DR1 as the secondary transfer roller 24, and employs the pressing members 33 of the first to fourth embodiments, respectively. doing. The image forming apparatus of the fifth embodiment employs, as the secondary transfer roller 24, a crown-shaped secondary transfer roller 24 in which the outer diameter at the central portion in the axial direction DR1 is 1 mm larger than the outer diameter at the end portion. The pressing member 33 according to 1 is adopted.

In Comparative Example 1 and Comparative Example 2, the pressing means was not provided, and the shape of the secondary transfer roller was a straight shape and a crown shape, respectively.

In Examples 1 to 5 in which the pressing member 33 was provided, the evaluation result was "OK" or higher. It can be seen that the occurrence of white-out image defects can be suppressed by providing the pressing member 33.

Comparing Example 1 and Example 5, it can be seen that the evaluation result on the second surface during double-sided printing is better in Example 5 than in Example 1. From this result, it can be seen that the occurrence of white-out image defects can be further suppressed by changing the shape of the secondary transfer roller 24 to a crown shape.

In Comparative Example 1 and Comparative Example 2 in which the pressing member 33 is not provided, the evaluation of the occurrence of whiteout image defects on the second surface during double-sided printing is "impossible". From this result, it can be seen that when printing the second surface of the recording medium, the occurrence of white-out image defects cannot be suppressed by a conventional image forming apparatus without a pressing member.

(Confirmation of band-shaped density unevenness and shortened life of secondary transfer roller)
A halftone image is printed using an image forming apparatus having a configuration according to the first embodiment, and the band-shaped density unevenness on the image due to the creep deformation of the secondary transfer roller and the foamed elastic layer are pressed by the pressing member. The deterioration state of the secondary transfer roller was visually evaluated. The evaluation test was performed after the image forming apparatus was stopped for one week.

Regarding the evaluation of the band-shaped density unevenness, the case where the density unevenness did not occur was evaluated as "possible", and the case where the density unevenness occurred was evaluated as "impossible". Regarding the deteriorated state of the secondary transfer roller 24, a state in which there was no noticeable deterioration was set as "possible", and a state in which deterioration was observed on the surface of the secondary transfer roller 24 was set as "impossible".

The deteriorated state of the secondary transfer roller was visually evaluated after printing 10,000 pages of A4 horizontal size. The breakdown of 10,000 page printing is 3000 pages in HH environment (temperature 30 ° C, humidity 85%), 4000 pages in NN environment (temperature 23 ° C, humidity 60%), and LL environment (temperature 10 ° C, humidity 15%). It was 3000 pages, and 1000 pages were printed on both sides in each environment.

FIG. 21 is a table showing the evaluation results of the band-shaped density unevenness and the deterioration state of the secondary transfer roller in Example 6, Example 7, Comparative Example 3 and Comparative Example 4.

In the sixth embodiment, when the image is not formed (when the image is not formed), the pressing member 33 is separated from the foamed elastic layer 24a. The pressing member 33 presses the foamed elastic layer 24a only when an image is formed on the second surface of the recording medium S.

In the seventh embodiment, when the image is not formed, the pressing member 33 is separated from the foamed elastic layer 24a. At the time of image formation, the pressing member 33 presses the foamed elastic layer 24a only when the humidity is low (humidity 15%).

In Comparative Example 3, the pressing member always presses the foamed elastic layer even when the image is not formed or when the image is formed.

In Comparative Example 4, when the image is not formed, the pressing member is separated from the foamed elastic layer. The pressing member always presses the foamed elastic layer at the time of image formation.

From the results of FIG. 21, by controlling the pressure contact separation of the pressing member 33 according to the situation of the image forming apparatus 1 and the surrounding environment, the creep deformation of the secondary transfer roller 24 can be suppressed, and the band-shaped density unevenness can be prevented. It can be seen that it can be suppressed. Further, since the deterioration of the secondary transfer roller 24 can be suppressed, the life of the image forming apparatus 1 can be extended.

Similar results were obtained when the evaluation was performed using the image forming apparatus 1 of the second to fifth embodiments.

Although the image forming apparatus 1 adopting the intermediate transfer method has been described in the first to fifth embodiments, it can also be applied to an image forming apparatus adopting the direct transfer method. In the direct transfer method, the transfer rotating body is a photoconductor.

The pressing member 33 may be separated from the foamed elastic layer 24a by releasing the pressing of the secondary transfer roller 24 on the drive roller 22a and separating the secondary transfer roller 24 and the drive roller 22a. good.

When the support portion 33b is moved by the moving means 39, it may be moved in parallel along the thickness direction DR2 and the length direction DR3, or may be moved by rotational movement.

The embodiments and examples disclosed this time should be considered to be exemplary and not restrictive in all respects. The scope of the present invention is shown by the scope of claims rather than the above description, and it is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

1 image forming apparatus, 24 secondary transfer roller, 24a foam elastic layer, 33 pressing member, 33a tip, 33b holding part, 34 guide, 35 control unit, 36 temperature / humidity detecting means, 37 recording medium detecting means, 38 secondary Transfer section, 39 means of transportation, DR1 axial direction, DR2 thickness direction, DR3 length direction, DR4 stacking direction, DR5 rotation direction.

Claims (16)

A transfer rotating body that transfers a toner image to a recording medium,
A pressurized rotating body facing the transfer rotating body and forming a nip portion with the transfer rotating body,
A pressing member arranged on the upstream side in the rotation direction of the pressurized rotating body with respect to the nip portion is provided.
The pressurized rotating body includes a foamed elastic layer constituting an outer peripheral surface, and includes a foamed elastic layer.
The pressing member is an image forming apparatus that presses the foamed elastic layer to compress and deform a part of the foamed elastic layer toward the center of rotation of the pressurized rotating body. The pressing member has a shape extending in the axial direction of the pressurized rotating body.
The first aspect of claim 1, wherein the thickness direction of the pressing member orthogonal to the axial direction and the length of the pressing member in the length direction orthogonal to the axial direction are substantially constant over the axial direction. Image forming device. The pressing member includes a tip portion that presses the foamed elastic layer and a support portion that supports the tip portion.
The image forming apparatus according to claim 2, wherein the thickness of the tip portion in the thickness direction is smaller than the thickness of the support portion in the thickness direction. The image forming apparatus according to claim 3, wherein the portion of the tip portion closer to the center in the axial direction has a larger thickness of the tip portion in the thickness direction. The image forming apparatus according to claim 3 or 4, wherein the portion of the tip portion closer to the center in the axial direction has a shorter length of the tip portion in the length direction. The method according to any one of claims 3 to 5, wherein the tip portion is arranged at a position closer to the foam elastic layer in the thickness direction as the portion of the tip portion closer to the center in the axial direction. Image forming device. The image forming apparatus according to any one of claims 1 to 6, wherein the pressurized rotating body has a larger outer diameter toward a portion closer to the center in the axial direction of the pressurized rotating body. The image forming apparatus according to any one of claims 1 to 7, further comprising a control unit that controls the operation of the pressing member. When forming an image on both sides of the recording medium, the control unit transfers the transfer more than the amount of the pressing member pressing against the foam elastic layer when the transfer rotating body transfers the toner image to the first surface of the recording medium. The image forming apparatus according to claim 8, wherein the pressing amount when the rotating body transfers the toner image to the second surface of the recording medium is increased. 9. When forming an image on both sides of a recording medium, the control unit presses the foamed elastic layer against the pressing member only when the transfer rotating body transfers a toner image to the second surface of the recording medium. The image forming apparatus according to. Further provided with a temperature / humidity detecting means for detecting the temperature / humidity inside the image forming apparatus,
The control unit presses the pressing member when the temperature / humidity detecting means detects a low humidity state, rather than the amount of pressing of the pressing member against the foamed elastic layer when the temperature / humidity detecting means detects a high humidity state. The image forming apparatus according to any one of claims 8 to 10, wherein the amount is increased. The image forming apparatus according to claim 11, wherein the control unit presses the foamed elastic layer against the pressing member only when the temperature / humidity detecting means detects a low humidity state. Further equipped with a recording medium detecting means for detecting the type of recording medium in which an image is formed,
The image forming according to any one of claims 8 to 12, wherein the control unit adjusts the amount of pressing of the pressing member against the foamed elastic layer according to the detection result by the recording medium detecting means. Device. The image forming apparatus according to claim 13, wherein the control unit presses the foamed elastic layer against the pressing member only when the recording medium detecting means detects uncoated paper. The image forming apparatus according to any one of claims 8 to 14, wherein the control unit separates the pressing member from the foamed elastic layer in a state where no image is formed on the recording medium. The image forming apparatus according to claim 15, wherein the control unit separates the pressing member from the foamed elastic layer at the end of image formation.

Images