JP2001282004A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of reducing an image defect and obtaining a high-quality image. SOLUTION: A toner image formed on an image carrier drum 11 on the surface of which the toner image in accordance with an image signal is formed is primarily transferred by an intermediate transfer body belt 16, and the toner image on the belt 16 is secondarily transferred and fixed on paper 23, whereby an image consisting of the fixed toner image is formed on the paper 23, in the color image forming device 100. The belt 16 has a surface layer where an optical exciting hydrophilic phenomenon that adhesive force to toner is enhanced by the irradiation of ultraviolet rays on its surface is generated, and the device 100 is equipped with an ultraviolet ray irradiation device 101 for irradiating the surface of the belt 16 with the ultraviolet rays at the upstream part of a primary transfer position P1 in the moving direction of the belt 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a facsimile, a printer, and a printing machine. More specifically, the present invention transfers a toner image formed on an image carrier to an intermediate transfer body, The present invention relates to an image forming apparatus that forms an image composed of a fixed toner image on a recording medium by transferring and fixing the toner image transferred to an intermediate transfer member onto a recording medium.

[0002]

2. Description of the Related Art Among image forming apparatuses using electrophotography, particularly in a color image forming apparatus, there is a need to stably convey a recording medium such as a transfer sheet and a necessity to repeat transfer of a plurality of sheets. A transfer drum method or a transfer belt method in which a recording medium is conveyed while being electrostatically or mechanically held on a recording medium conveying member, or a method in which a plurality of colors are once transferred onto an intermediate transfer body and then collectively transferred to the recording medium An intermediate transfer method or the like is used.

In particular, in the case of the intermediate transfer system, there is no need to hold the recording medium on the recording medium conveying member as in the transfer drum system, so that the holding mechanism is unnecessary. In addition, most color image forming apparatuses employ an intermediate transfer method instead of a transfer drum method because they have the advantage that a toner image can be easily transferred to thick paper or the like which is difficult to hold by winding. Has begun.

[0004]

However, since a toner image formed on an image carrier is temporarily superimposed on an intermediate transfer member and transferred, and the superimposed toner image is transferred onto a sheet, an intermediate image is formed. The transfer body itself is required to have conflicting functions. That is, in a series of image forming processes, the adhesive force between the toner and the surface of the intermediate transfer member is required to have mutually contradictory properties such as being high at one time and low at another time.

In the research and development so far, the transfer of a toner image has a great influence not only on the force due to the electrostatic force due to the transfer electric field, but also due to the force due to the non-electrostatic adhesion between the toner and the transfer destination medium and the transfer source medium. I know it will give.
In the case of the primary transfer in which the image is transferred from the image carrier to the intermediate transfer member, the “transfer destination medium” and the “transfer source medium” described above are used.
Corresponds to an “intermediate transfer member” and an “image carrier”. That is, if the non-electrostatic adhesion of the surface of the image carrier is larger than that of the intermediate transfer member, transfer may not be performed even if a driving force due to electrostatic force is applied. This occurs particularly when the toner particle layer present between the image carrier and the intermediate transfer member during transfer is subjected to excessive pressure by a transfer roller or the like,
At the center of the transferred line image, there is an image defect such as a hole (hollow phenomenon, that is, a hollow character). Here, the mechanism of the hollow character will be described with reference to FIG.

FIG. 12 is a diagram showing a mechanism for generating a hollow character.

FIG. 12A shows an image carrier 108 and toner particles 103 located on the surface of the image carrier 108.
And a toner image representing a line image composed of the following, and an intermediate transfer member 109 located above the toner image.

FIG. 12B shows a state in which the intermediate transfer body 109 and the image carrier 108 are close to each other at the transfer nip, and pressure is applied to the toner image in the direction indicated by arrow A. At this time, since the toner particles 103 can move in the direction indicated by the arrow B at the end of the toner image, deformation of the toner particles 103 hardly occurs in this region. On the other hand, since other toner particles 103 are present around the toner particles 103 in the central part of the toner image, these toner particles 1
It is difficult to move away from 03. In this case, it is impossible to escape from the pressure action from the transfer roller (not shown), and the toner particles 103 are significantly deformed. In FIG. 12B, black spots are shown on the toner particles 103 where the deformation of the toner particles 103 is increased so that the degree of deformation of the toner particles 103 can be easily understood visually.

Further, as shown in FIG. 12C, the image carrier 108 is located at the center of the transfer nip (in the circle shown by the broken line).
The distance between the toner and the intermediate transfer member 109 is further shortened, and the amount of deformation of the toner particles 103 is increased as a whole. However, the relationship that the toner particles 103 at the center of the toner image have a larger deformation amount than the toner particles 103 at the end of the toner image is maintained. At this time, as the toner particles 103 are deformed, the contact areas between the toner particles 103 and the image carrier 108 and between the toner particles 103 and the intermediate transfer member 109 are increased. That is, the adhesion between the toner particles 103 and the image carrier 108 and between the toner particles 103 and the intermediate transfer member 109 are greatly increased. The adhesive force here is an intermolecular force such as van der Waals force. As a result, in the central portion of the toner image, the adhesive force between the image carrier 108 and the intermediate transfer member 109 and the toner particles 103 increases.

[0010] The transfer process further proceeds, and FIG.
When the toner image starts to pass through the transfer nip, a force acts in the direction indicated by arrow C to release the pressure on the toner image as shown in FIG. At this time, when the deformation amount of the toner particles 103 is a small deformation amount which is an elastic region, the deformation disappears with the release of the pressure, and at the same time, the increased adhesive force returns to the magnitude before the pressure application. However, since the amount of deformation of the toner particles 103 at the central portion of the toner image is large enough to reach the plastic deformation region, the amount of deformation is maintained to some extent even when the pressure is released. This is called elastic hysteresis (elastic hysteresis). As a result, the state where the adhesive force is increased is maintained.

The non-electrostatic adhesion of the surface of the image carrier 108 is larger than that of the intermediate transfer member 109, and the increased adhesion is about one or two digits larger than the electrostatic force. Further, a detailed description will be given with reference to FIG.

FIG. 13 is a diagram showing the magnitude relationship between the adhesion force of a compressed toner image and the electrostatic transfer force.

FIG. 13 shows the state after passing through the transfer nip ((FIG. 12
The relationship between the position of the toner particles 103 and the force acting on the toner particles 103 in the state (d) is shown. Here, the direction of the force moving to the intermediate transfer member 109 is the forward direction. As shown in FIG. 13, the adhesive force (= cohesive force) between the toner particles 103 and the toner particles 1
03 and the image carrier 108,
From the toner to the intermediate transfer member 109, that is, the electrostatic force, the toner particles 103 and the intermediate transfer member 1
09 is much larger than the resultant force of the adhesive force with C.09. as a result,
At the edge of the toner image, the toner particles 103 can move due to the electrostatic force and the adhesive force between the toner particles 103 and the intermediate transfer member 109. However, the toner particles 103 at the central portion of the toner image are moved due to the increased adhesive force with the image carrying medium 108. Transfer becomes impossible.
Finally, it is observed as a phenomenon called a hollow character.

FIG. 14 is a diagram showing an example of an image in which a hollow character has occurred.

FIG. 14A shows, for comparison, a normal image (character 'A') in which no hollow character has occurred. On the other hand, FIG. 14B shows a hollow state in which a hollow character is generated and toner particles are not attached to a part of the character 'A'.

Here, if the adhesive force of the image carrier 108 is made smaller than the adhesive force of the intermediate transfer member 109, a hollow character can be prevented. However, in the system using the intermediate transfer member 109, not only the primary transfer but also the intermediate transfer member 1
It is also necessary to carry out secondary transfer from 09 to paper. In order to prevent the hollow character from being generated even in the primary and secondary transfer portions, the magnitude relationship of the adhesive force must be determined by the image carrier <
It is necessary to set as intermediate transfer member <paper.

However, at present, a material satisfying this condition has not been sufficiently developed, and as an improvement measure, the cohesiveness of the toner particles 103 is reduced so that the coagulation does not occur, or a transfer belt or a transfer roll is used. Examples include reducing the pressure value on the toner image or increasing the strength of the electrostatic force. However, it is difficult to control the pressure stably, and even if the transfer electric field is applied up to the limit discharge voltage according to Paschen's rule, compared to before applying the pressure,
It is difficult to stably apply an electrostatic force that exceeds the adhesive force that has increased by one or two digits. For these reasons, no satisfactory remedy exists. for that reason,
Since the invention of electrophotography, hollow characters have been a long-standing problem, but have not yet reached a fundamental solution.

The present invention has been made in view of the above circumstances, and has as its object to provide an image forming apparatus capable of obtaining high-quality images with reduced image defects.

[0019]

In order to achieve the above object, an image forming apparatus according to the present invention comprises: an image carrier having a surface on which a toner image is formed in accordance with an image signal; An intermediate transfer member for receiving a transfer of the toner image formed on the image carrier at a primary transfer position close to or in contact with the intermediate transfer member and conveying the toner image to a predetermined secondary transfer position; An image forming apparatus for forming an image composed of a fixed toner image on a recording medium by transferring and fixing the toner image on the intermediate transfer body conveyed to the transfer position to a predetermined recording medium, Has a surface layer that causes a photo-excited hydrophilization phenomenon in which the surface of the intermediate transfer member is irradiated with excitation light to increase the adhesive force to the toner. The upstream portion of the shooting position, characterized by comprising a light irradiation device for irradiating excitation light to the intermediate transfer member surface.

Here, the surface layer of the intermediate transfer member may contain at least one of titanium oxide (TiO ₂ ), zinc oxide (ZnO), and strontium titanate (SrTiO ₃ ). preferable.

It is also preferable that the light irradiation device irradiates the surface of the intermediate transfer member with excitation light containing light having a wavelength that causes the photoexcited hydrophilization phenomenon on the surface of the intermediate transfer member.

Further, it is preferable that the light irradiation device irradiates an excitation light to a region corresponding to a toner adhesion pattern in a toner image based on an image signal on which a toner image is formed. It is.

[0023]

Embodiments of the present invention will be described below.

FIG. 1 is a schematic configuration diagram of a first embodiment of the image forming apparatus of the present invention.

The color image forming apparatus 1 shown in FIG. 1 is provided with an image reading section 2 for reading an image on a document 4.
The image reading unit 2 includes a platen glass 3, a light source 5, scanning mirrors 6, 7_1 and 7_2, an imaging lens 8, a color CCD sensor 9, and the like. The reflected light image from the document 4 illuminated by the light source 5 is scanned by the CCD sensor 9 via the scanning mirrors 6, 7 _ 1, 7 _ 2 and the imaging lens 8 into RG images
The image signal is read as a B image signal. In addition, the color image forming apparatus 1 also includes an image signal processing unit 10,
The read RGB image signal is transmitted to the image signal processing unit 1.
0 indicates yellow (Y), magenta (M), cyan (C),
The image signal is converted to a black (K) image signal, and is temporarily stored in a memory provided inside the image signal processing unit 10 as necessary.

The color image forming apparatus 1 includes an image forming unit 30 and an intermediate transfer unit 31.

The image forming unit 30 includes an image carrier drum 11 on which a toner image corresponding to an image signal is formed on the surface by rotating in the direction of arrow A, a charger 12, a laser beam scanner 13, and a developing device. Vessels 14a, 14b, 14c, 14d
And a cleaning device 32.

After the image carrier drum 11 is uniformly charged to a predetermined negative potential by the charger 12, an electrostatic latent image is formed by the laser beam scanning unit 13. The laser beam scanning unit 13 outputs yellow (Y), magenta (M), cyan (C), and yellow (Y) sequentially output from the image signal processing unit 10.
By scanning the image carrier drum 11 with a laser beam corresponding to image data of each color of black (K), image exposure is performed, and an electrostatic latent image of each color is formed on the image carrier drum 11.

The electrostatic latent image formed on the image carrier drum 11 is developed by developing units 14a, 14b, 14c and 14d, whereby yellow (Y), magenta (M), cyan (C), black A toner image of each color (K) is formed. The toner of each color is negatively charged and adheres to the area of the image carrier drum 11 irradiated with the laser beam. Each time the image carrier drum 11 makes one rotation, a toner image for one color is formed, and four rotations form a toner image for four colors. The untransferred toner remaining on the surface of the image carrier drum 11 is removed by the cleaning device 32, and is prepared for the next image forming cycle.

The intermediate transfer unit 31 includes a primary transfer roll 15, a drive roll 17, and an idler roll 18.
, A secondary transfer backup roll 19, a tension roll 20, and an intermediate transfer belt 16 that is stretched by the rollers 17, 18, 19, and 20 and moves in the direction of arrow B (the intermediate transfer member according to the present invention). Equivalent). The intermediate transfer belt 16 has a surface layer that causes a photo-excitation hydrophilization phenomenon in which the surface of the intermediate transfer belt 16 is irradiated with excitation light to increase the adhesion to toner.
The intermediate transfer member according to the present invention does not need to be in the form of a belt, but may be in the form of a drum.

Further, the color image forming apparatus 1 includes an ultraviolet irradiating device 101 for irradiating the upstream portion of the primary transfer position P1 with respect to the moving direction of the intermediate transfer belt 16 with excitation light on the surface of the intermediate transfer belt 16. (Corresponding to the light irradiation device according to the present invention). Further, the color image forming apparatus 1 includes a paper feed cassette 21 for storing the paper 23,
A feed roll 22 for feeding a sheet 23, a registration roll 28 for conveying the sheet 23 to a secondary transfer position P2, a secondary transfer roll 24 for performing a secondary transfer, and the fixing device 2.
6 are provided. Further, a tray 27 for receiving a sheet 23 on which an image formed of a fixed toner image is formed is also provided.

In the present embodiment, in order to reduce hollow characters, which are image defects, and obtain a high-quality image, the adhesiveness of the surface of the intermediate transfer belt 16 is switched by using a material that exhibits a photoexcitation hydrophilization phenomenon. The structure which makes it do is adopted. This enhances the adhesion of the intermediate transfer belt 16 so that the toner image can easily move from the image carrier drum 11 to the intermediate transfer belt 16 during the primary transfer, and conversely, the secondary transfer belt during the secondary transfer. It is possible to lower the adhesion of the intermediate transfer belt 16 so that the intermediate transfer belt 16 can easily move from the sheet 16 to the sheet 23. The details will be described below.

FIG. 2 is a diagram showing a cross-sectional structure of the intermediate transfer belt shown in FIG.

The intermediate transfer belt 16 includes a base layer 16a,
A protective layer 16b formed on the base layer 16a and a photoexcited reactant-containing layer 16c formed on the protective layer 16b;
It is composed of Photoexcitation reactant-containing layer 16c
Contains titanium oxide (TiO ₂ ). If the photoexcited reactant-containing layer 16c is formed directly on the base layer 16a of the intermediate transfer belt 16, the base layer 16a is gradually decomposed by a photocatalytic reaction every time light is irradiated. Therefore, FIG.
As shown in the figure, the photoexcited reactant-containing layer 16c and the base layer 16
This problem is solved by providing the protective layer 16b between the layers a. In addition, the protective layer 16b includes a base layer 16a,
It also functions as an adhesive layer for each of the photoexcited reactant-containing layers 16c. The photoexcited reactant-containing layer 16c of the intermediate transfer belt 16 is made of titanium oxide (TiO ₂ ).
It is not limited to those containing the above substances, such as zinc oxide (ZnO) and strontium titanate (SrTiO ₃ ).
May be contained.

Next, the principle of superhydrophilization of the photoexcited hydrophilizing substance will be described with reference to FIGS.

FIG. 3 is a view showing a photo-excited hydrophilization phenomenon which increases the adhesion of the surface of the intermediate transfer member, and FIG. 4 is a view showing a state where water is dropped on a flat plate in a hydrophobic state and a hydrophilic state. is there.

The surface layer of the intermediate transfer belt 16 shown in FIG. 3 contains titanium oxide (TiO ₂ ) as a photoexciting substance. The titanium oxide in a state where light is not irradiated is shown in FIG.
As shown in (a), oxygen is crosslinked between titanium and titanium, and is stabilized. This is called crosslinking oxygen. In this state, the surface of the intermediate transfer belt 16 shows hydrophobicity. For example, even if water is dropped on the surface of the flat plate (here, the intermediate transfer belt 16) as shown in FIG. Would. When this surface is irradiated with ultraviolet rays, part of the crosslinked oxygen is eliminated and oxygen vacancies are generated (see FIG. 3B). Moisture in the air is dissociated and adsorbed to these oxygen vacancies, resulting in chemisorbed water.
(Surface hydroxyl group) 111 is formed and becomes hydrophilic (FIG. 3).
(C)). Further, as shown in FIG. 3D, the moisture in the air is adsorbed on the chemically adsorbed water 111 and the physically adsorbed water 112 is generated by hydrogen bonding, whereby the hydrophilicity is enhanced.

In the present embodiment, the surface of the intermediate transfer belt 16 contains titanium oxide, which is a photo-excited hydrophilizing substance, and the ultraviolet rays are located upstream of the primary transfer position P1 in the rotation direction of the intermediate transfer belt 16. The irradiation device 101 irradiates the intermediate transfer belt 16 with ultraviolet rays. Thereby, the above-mentioned photoexcitation hydrophilization process is developed. A description will be given with reference to FIG. 5 in addition to FIGS.

FIG. 5 is a view showing a state in which a liquid bridge is formed between the toner particles and the intermediate transfer belt by the physically adsorbed water generated on the surface of the intermediate transfer belt.

As a result of developing the above-mentioned photoexcitation hydrophilization process, as shown in FIG. 5, at the transfer nip position, the image is transferred from the image carrier drum 11 by physical adsorption water generated on the surface of the intermediate transfer belt 16. Liquid bridge 110 is formed between toner particles 103 and an intermediate transfer belt 16 constituting an image to be formed. As a result, the adhesion of the intermediate transfer belt 16 is greatly increased, and the image of the image carrier drum 11 is transferred to the intermediate transfer belt 16 by the resultant force of the greatly increased adhesion and the electrostatic force due to the transfer electric field. . Incidentally, the adhesion in the hydrophobic state (FIG. 3 (a)) and the photo-excited hydrophilized state (FIG. 3 (d)) before irradiation with ultraviolet light is generally referred to as the "contact angle with water" as an index.
At 80 ° (FIG. 4A) and 0 °, respectively.
(FIG. 4 (b)), which can produce a large change in adhesive force.

Next, at the secondary transfer position, the intermediate transfer belt 1
When transferring the toner image from 6 to the surface of the paper 23,
Contrary to the case of the primary transfer position, it is necessary to greatly reduce the adhesive force between the toner particles 103 and the intermediate transfer belt 16 so that the toner image moves easily. This is performed using the following properties.

When the irradiation of the ultraviolet rays is stopped, the photoexcited and hydrophilized titanium oxide is replaced with oxygen in the surface hydroxyl groups, and returns to the hydrophobic state shown in FIG.

FIG. 6 is a view showing a state in which the liquid bridge has returned to the hydrophobic state and the liquid bridge formed between the toner particles and the intermediate transfer belt has disappeared.

As shown in FIG. 6, when the irradiation of the ultraviolet rays is stopped, the toner particles 103 become hydrophobic, and it becomes impossible to form a liquid bridge between the toner particles 103 and the surface of the intermediate transfer belt 16. And intermediate transfer belt 1
Adhesive force with No. 6 decreases.

FIG. 7 is a perspective view of various ultraviolet irradiation devices.

FIG. 7A is a perspective view of the ultraviolet irradiation device 101 shown in FIG. 7A, the moving direction of the intermediate transfer belt 16 is a vertical direction (hereinafter, referred to as a lateral direction) so that at least the image forming area of the intermediate transfer belt 16 can be irradiated with the ultraviolet light 101a. ).
The irradiation intensity of the ultraviolet light 101a is 20 mW / cm ² .

FIG. 7B shows an ultraviolet irradiation device 201 having a configuration in which a plurality of ultraviolet irradiation units 101_1, 101_2, and 101_3 are arranged in a staggered manner. Further, FIG. 7 (c) shows an ultraviolet irradiation unit 101_1.
1 is an ultraviolet irradiation device 3 built in the driving device 113
01 is shown. The driving unit 113 scans the ultraviolet irradiation unit 101_11 in the process direction.

FIG. 8 is a perspective view of an ultraviolet irradiation device including a plurality of small-diameter mouth ultraviolet irradiation units.

As shown in FIG. 8, the ultraviolet irradiation device 114 may be constructed by assembling a plurality of small-diameter mouth type ultraviolet irradiation units 114a. Further, although not shown, a beam scanning unit using a polygon mirror, which is also used in the charging process of the image carrier drum 11, may be used.

As described above, as shown in FIGS. 7 and 8, various ultraviolet irradiation devices can be used. The light irradiating device according to the present invention is not limited to such an ultraviolet irradiating device, and the excitation light including light having a wavelength that causes a photo-excitation hydrophilization phenomenon on the surface of the intermediate transfer member is converted to the intermediate transfer member. What is necessary is just to irradiate the surface of.

FIG. 9 is a view showing a state where the first and second color toners are transferred to the surface of the intermediate transfer member belt.
FIG. 7 is a diagram showing a change in a contact angle of water on the surface of the intermediate transfer belt in each process.

First, at a position upstream of the primary transfer position P1, the surface of the intermediate transfer belt 16 is irradiated with ultraviolet rays by the ultraviolet irradiation device 101 as shown in FIG. In this state, the first color toner image 103K formed on the image carrier drum 11 is transferred to the intermediate transfer belt 16 at the primary transfer nip (FIG. 9).
(B)-(d)). Next, the toner image 103Y of the second color formed on the image carrier drum 11 is transferred to the intermediate transfer belt 16 in the photo-excited and hydrophilic state at the primary transfer nip similarly to the first color (FIGS. 9E to 9E). g)). Then, as shown in FIG. 10, the contact angle of the surface of the intermediate transfer belt 16 with respect to water is restored to around 80 ° before being transferred onto the sheet 23 at the secondary transfer position, and the hydrophobic state before irradiation with ultraviolet rays is restored. (FIG. 9 (h)). At that time, the first color toner 10
The toner 103Y of the third color and the toner 103Y of the second color are attached by electrostatic force or cohesive force between toners. However, the adhesive force between the lowermost toner in contact with the surface of the intermediate transfer belt 16 loses the liquid bridge because the surface of the intermediate transfer belt 16 is in a hydrophobic state. As a result, the adhesive force at the interface is reduced, and the interface is easily moved to the surface of the sheet 23 at the secondary transfer position P2. Here, only the case of two colors has been described, but even in the case of four colors, the number of color superimposition processes is increased but the basic principle is not changed at all.

Returning to FIG. 1, the description will be continued. After the four color toner images are transferred onto the intermediate transfer belt 16, the intermediate transfer belt 16 further moves to synchronize with the four color toner images reaching the secondary transfer position P <b> 2. The paper 23 stored in the paper feed cassette 21 is fed by the feed roll 22 and is conveyed to the secondary transfer position P2 by the registration roll 28.

At the secondary transfer position P2, a secondary transfer roll 24 is provided so as to face the secondary transfer backup roll 19, and a positive charge is supplied to the sheet 23 by the secondary transfer roll 24. The toner image on the intermediate transfer belt 16 is electrostatically transferred onto the sheet 23 by the action of the charge on the sheet 23. The sheet 23 to which the toner image has been transferred is subjected to a fixing process by heat and pressure in a fixing unit 26,
It is carried out onto the tray 27, and a series of color image forming cycles is completed.

The intermediate transfer belt 16 which has completed the transfer at the secondary transfer position P2 is cleaned by a cleaning device 33 to remove the residue on the surface of the intermediate transfer belt 16, and the ultraviolet rays again upstream of the primary transfer position P1. Irradiation device 1
01, and the process proceeds to the next image forming cycle.

Next, a second embodiment of the image forming apparatus of the present invention will be described.

FIG. 11 is a schematic diagram showing a state in which the surface of the intermediate transfer belt is irradiated with ultraviolet rays according to an image in the second embodiment of the image forming apparatus of the present invention.

The configuration of the image forming apparatus according to the second embodiment is substantially the same as the configuration of the image forming apparatus 1 according to the first embodiment shown in FIG.
Is the driving method. In the first embodiment, the ultraviolet irradiation device 101 uniformly irradiates the intermediate transfer body belt 16 with ultraviolet light in the lateral direction, whereas in the second embodiment, the ultraviolet irradiation device 101 Is irradiated on the region corresponding to the toner adhesion pattern in the toner image based on the image signal which is the basis of the above. That is, FIG.
As shown in FIG. 7, the intermediate transfer belt 16 is irradiated with ultraviolet rays in accordance with the toner image formed on the image carrier drum 11.
As a result, the ultraviolet irradiation section 115 and the non-irradiation section 116 exist on the intermediate transfer belt 16 immediately before the transfer nip. This produces the effects described below.

First, in the case of a configuration in which a driving device (see FIG. 7 (c)) is used to scan the ultraviolet irradiation device in the process direction in order to selectively irradiate ultraviolet light instead of uniformly irradiating it. Can reduce the time required for irradiation. Thereby, productivity can be improved. Second, the image carrier drum 11 and the intermediate transfer belt 16 are easily separated from each other after passing through the transfer nip portion. As a result, stable driving of the image carrier drum 11 and the intermediate transfer belt 16 can be performed. Since the wettability of the intermediate transfer belt 16 is greatly improved by photoexcitation hydrophilization using the ultraviolet irradiation device 101, the image carrier drum 11 and the intermediate transfer belt 16 are in direct contact with each other at the non-image portion 116. Sometimes. In this case, since they mutually strongly adhere to each other, it may be difficult to separate them from each other after passing through the transfer nip. Therefore, when the second embodiment is used, the non-image portion 116 is not irradiated with ultraviolet rays, so that the above-described problem can be significantly reduced.

[0060]

As described above, according to the present invention,
Image defects are reduced, and a high-quality image can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a first embodiment of an image forming apparatus of the present invention.

FIG. 2 is a diagram showing a cross-sectional structure of the intermediate transfer member belt shown in FIG.

FIG. 3 is a diagram showing a photo-excitation hydrophilization phenomenon that increases the adhesion of the surface of an intermediate transfer member.

FIG. 4 is a diagram illustrating a state where water is dropped on a flat plate in a hydrophobic state and a hydrophilic state.

FIG. 5 is a diagram illustrating a state in which a liquid bridge is formed between toner particles and the intermediate transfer belt by physical adsorption water generated on the surface of the intermediate transfer belt.

FIG. 6 is a diagram showing a state in which the liquid bridge formed between the toner particles and the intermediate transfer member belt has disappeared after returning to the hydrophobic state.

FIG. 7 is a perspective view of various ultraviolet irradiation devices.

FIG. 8 is a perspective view of an ultraviolet irradiation device including a plurality of small-diameter opening type ultraviolet irradiation devices.

FIG. 9 is a diagram illustrating a state in which first-color and second-color toners are transferred to the surface of the intermediate transfer belt.

FIG. 10 is a diagram illustrating a change in a contact angle of water on the surface of the intermediate transfer belt in each process.

FIG. 11 is a schematic diagram illustrating a state in which the surface of an intermediate transfer belt is irradiated with ultraviolet rays according to an image in a second embodiment of the image forming apparatus of the present invention.

FIG. 12 is a diagram showing how a hollow character is generated.

FIG. 13 is a diagram illustrating a magnitude relationship between an adhesive force of a compressed toner image and an electrostatic transfer force.

FIG. 14 is a diagram illustrating an example of an image in which a hollow character has occurred.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Color image forming apparatus 2 Image reading part 3 Platen glass 4 Document 5 Light source 6, 7_1, 7_2 Scanning mirror 8 Imaging lens 9 CCD sensor for color 10 Image signal processing part 11 Image carrier drum 12 Charger 13 Laser beam scanning Units 14a, 14b, 14c, 14d Developing device 15 Primary transfer roll 16 Intermediate transfer belt 16a Base layer 16b Protective layer 16c Photoexcitation reactant-containing layer 17 Drive roll 18 Idler roll 19 Secondary transfer backup roll 20 Tension roll 21 Paper cassette REFERENCE SIGNS LIST 22 feed roll 23 paper 24 secondary transfer roll 26 fixing device 27 tray 28 registration roll 30 image forming unit 31 intermediate transfer body unit 32, 33 cleaning device 101, 114, 201, 301 ultraviolet irradiation device 101_, 10 _2,101_3,101_11 ultraviolet irradiation unit 101a UV 103 toner particles 103K, 103Y toner image 110 liquid bridge portion 111 chemically adsorbed water 112 physically adsorbed water 113 drives 114a small diameter hole ultraviolet irradiation unit 115 ultraviolet irradiation execution unit 116 non-irradiated portion

Claims (4)

[Claims] An image carrier on which a toner image corresponding to an image signal is formed on a surface thereof; and a toner image formed on the image carrier at a primary transfer position that moves in a predetermined direction and approaches or comes into contact with the image carrier. An intermediate transfer member that receives the transferred toner image and conveys the toner image to a predetermined secondary transfer position.
An image forming apparatus that forms an image composed of a fixed toner image on the recording medium by transferring and fixing the toner image on the intermediate transfer body conveyed to the secondary transfer position to a predetermined recording medium, The intermediate transfer member has a surface layer that causes a photo-excitation hydrophilization phenomenon in which the surface of the intermediate transfer member is irradiated with excitation light to increase the adhesive force to the toner, and the image forming apparatus is configured to perform the primary transfer with respect to the moving direction of the intermediate transfer member. An image forming apparatus, comprising: a light irradiation device for irradiating excitation light to the surface of the intermediate transfer member at a portion upstream of the transfer position. 2. The method according to claim 2, wherein the surface layer of the intermediate transfer member is made of titanium oxide.
_2. The image forming apparatus according to claim 1, wherein the image forming apparatus contains at least one substance selected from the group consisting of (TiO ₂ ), zinc oxide (ZnO), and strontium titanate (SrTiO ₃ ). 3. The light irradiation device irradiates the surface of the intermediate transfer member with excitation light containing light having a wavelength that causes the photoexcited hydrophilization phenomenon on the surface of the intermediate transfer member. The image forming apparatus according to claim 1. 4. The light irradiation device according to claim 1, wherein the light irradiation device irradiates an excitation light to a region corresponding to a toner adhesion pattern in the toner image based on an image signal on which a toner image is formed. The image forming apparatus according to claim 1.