JP2021130238A - Image forming device and thickened state determination method - Google Patents

Abstract

To provide an image forming device and a thickened state determination method which enable determination of thickened state of ink droplets in transferring an image onto a recording medium.SOLUTION: An image forming device 1 comprises: an image forming unit that forms an image on a transfer body 20 by ejecting ink from an inkjet head 10; a thickening unit 25 that thickens ink ejected onto the transfer body, before an image is transferred onto a recording medium P; a detection unit 27 that detects a ratio of amount of remaining ink remaining on the transfer body without being transferred onto the recording medium to amount of ink ejected from the inkjet head; and a determination unit that determines a thickened state of thickened ink, on the basis of the detected ratio.SELECTED DRAWING: Figure 1

Description

The present invention relates to an image forming apparatus and a method for determining a thickening state.

In recent years, as an apparatus for forming (recording) a high-definition image on various recording media such as paper and cloth, an image forming apparatus by an inkjet method in which ink droplets are ejected from an inkjet head to form an image on the recording medium. (Hereinafter referred to as "inkjet image forming apparatus") is widely used.

In the inkjet image forming apparatus, an intermediate transfer method is proposed in which ink droplets ejected from an inkjet head are formed as an image on an intermediate transfer body such as an intermediate transfer belt, and the formed image is transferred to a recording medium by a transfer nip. (See, for example, Patent Document 1). By this intermediate transfer method, the amount of ink droplets can be suppressed in advance, and the ink droplets can be crushed by the transfer pressure of the transfer nip and expanded to a desired size (diameter). In other words, an image with high image coverage can be formed with a small amount of ink droplets.

In the intermediate transfer type inkjet image forming apparatus, in order to ensure the transferability of the image to the recording medium, an ink (including a polymerizable monomer) that is cured (thickened) by active energy rays (for example, ultraviolet rays) is used and activated. Examples thereof include a configuration using an intermediate transfer material having energy ray transmittance. In this configuration, the image (ink droplet) sandwiched and pressed (nip) in the transfer nip is irradiated with active energy rays from the outer peripheral surface side or the inner peripheral surface side of the intermediate transfer body to irradiate the ink droplet. Adjust the viscosity. As a result, it is possible to improve the transferability by ensuring the viscosity so that the ink droplets are not crushed while maintaining the wettability of the ink droplets in contact with the recording medium.

Japanese Unexamined Patent Publication No. 2012-19342

By the way, in the inkjet image forming apparatus, the thickening state (thickness matching) of the ink droplets when the image is transferred to the recording medium by the transfer nip according to the usage history of the intermediate transfer body and the difference in the type of the recording medium. ) May change. For example, if the thickening state of the ink droplets is an excessive thickening state, that is, if the thickening degree of the ink droplets is too high, transfer failure of the image to the recording medium occurs. Further, even if the thickening state of the ink droplets is insufficient thickening, that is, the thickening degree of the ink droplets is too low, poor image transfer to the recording medium occurs. Therefore, for example, in order to feed back to the operation of the inkjet image forming apparatus so as not to cause image transfer failure on the recording medium, it is desirable to determine the thickening state of the ink droplets when the image is transferred to the recording medium. ..

An object of the present invention is to provide an image forming apparatus and a thickening state determination method capable of determining the thickening state of ink droplets when an image is transferred to a recording medium.

The image forming apparatus according to the present invention is
An image forming unit that forms an image on the transfer body by ejecting ink from the inkjet head,
Before the image is transferred to the recording medium, a thickening portion that increases the viscosity of the ink ejected onto the transfer body, and a thickening portion.
A detection unit that detects the ratio of the amount of residual ink remaining on the transfer body without being transferred to the recording medium with respect to the amount of ink ejected from the inkjet head.
Based on the detected ratio, a determination unit that determines the thickening state of the ink after the viscosity has been increased, and a determination unit.
To be equipped.

The thickening state determination method according to the present invention is
An image is formed on the transfer body by ejecting ink from the inkjet head,
Before the image is transferred to the recording medium, the viscosity of the ink ejected onto the transfer body is increased.
The ratio of the amount of residual ink remaining on the transfer body without being transferred to the recording medium to the amount of ink ejected from the inkjet head is detected.
Based on the detected ratio, the thickening state of the ink after the viscosity is increased is determined.

According to the present invention, it is possible to determine the thickening state of ink droplets when an image is transferred to a recording medium.

It is a figure which shows schematic the whole structure of the inkjet image forming apparatus. It is a block diagram which shows the main functional structure of an inkjet image forming apparatus. It is a figure explaining the difference of the thickening state of an ink droplet. It is a flowchart explaining the thickening state determination operation example of an inkjet image forming apparatus. It is a figure which shows typically the modification of the whole structure of the inkjet image forming apparatus. It is a figure which shows typically the modification of the whole structure of the inkjet image forming apparatus.

Hereinafter, the inkjet image forming apparatus according to the present embodiment will be described in detail with reference to the drawings. FIG. 1 is a diagram schematically showing the overall configuration of the inkjet image forming apparatus 1. Further, FIG. 2 is a block diagram showing a main functional configuration of the inkjet image forming apparatus 1.

As shown in FIGS. 1 and 2, the inkjet image forming apparatus 1 includes a head unit 10 on which the inkjet head 102 is mounted, a transfer belt 20, a driven roller 21 and 22 for rotatably tensioning the transfer belt 20, and a drive. It includes a transfer roller 23 as a roller, a transfer drum 24 that conveys the recording medium P, and a control unit 40 that controls the entire apparatus.

The head unit 10 functions as the "image forming unit" of the present invention. Further, the transfer belt 20 functions as the "transfer body" of the present invention. Further, the control unit 40 functions as a "detection unit", a "determination unit" and a "control unit" of the present invention.

Further, the inkjet image forming apparatus 1 has a first irradiation unit 25 that adjusts the viscosity of the ink droplets ejected on the transfer belt 20, a second irradiation unit 26 that cures the ink transferred to the recording medium P, and a transfer. A detection unit 27 that detects the amount of residual ink remaining on the belt 20, a cleaning unit 28 that comes into contact with the transfer belt 20 to clean the residual ink, and a transfer drive unit 51 that drives the transfer roller 23 and the transfer drum 24. (See FIG. 2). The first irradiation unit 25 functions as the "thickening unit" of the present invention.

Although not shown, the inkjet image forming apparatus 1 has a feeding unit that loads the recording medium P and feeds it to the transport drum 24, and discharges the recording medium P on which the image is transferred to the downstream side in the transport direction of the transport drum 24. It is provided with a discharge unit, a display unit for displaying the status of the device, and the like. Since these have known configurations, illustration and description thereof will be omitted.

Further, as the recording medium P, in addition to paper such as plain paper and coated paper, various media such as cloth or sheet-like resin capable of transferring ink droplets landed on the surface of the transfer belt 20 are used. be able to.

The transfer belt 20 is bridged between the driven rollers 21 and 22 arranged above and the transfer roller 23 (drive roller) arranged below, and the transfer motor (not shown) of the transfer drive unit 51. By transmitting the driving force to the transfer roller 23, it rotates (moves) in the clockwise direction in FIG.

In the present embodiment, a heating source (for example, a heater) is provided in the driven roller 22. The temperature of the heating source is controlled by the control unit 40. The driven roller 22 is heated by the heating source, and as a result, the temperature of the transfer belt 20 is heated to reach the target temperature. The target temperature is a temperature set so that the dot diameter of the ink droplets ejected on the transfer belt 20 becomes a predetermined diameter.

In the present embodiment, the transfer belt 20 has an active energy ray-transmitting property, and has an elastic layer of silicon rubber, a reflective layer on which aluminum (Al) is vapor-deposited, and polypropylene on a polyimide (PI) base material. An endless belt in which the surface layer of (PP) and the surface layer of (PP) are laminated is used.

Further, as the transfer roller 23, for example, a rubber roller having a diameter of 100 mm and a rubber thickness of 10 mm on the surface layer is used. As the base material, a resin material such as polyimide (PI) may be used, or a stainless steel material may be used.

In the inkjet image forming apparatus 1, the transfer belt 20 rotates in the clockwise direction by driving the transfer motor based on the control signal of the control unit 40 and rotating the transfer roller 23 in the clockwise direction in FIG. Driven. In the present embodiment, the rotation speed of the transfer roller 23 is controlled so that the transfer belt 20 rotates at a speed (printing speed) of 600 mm / sec under the control of the control unit 40.

The transport drum 24 is around a rotation axis extending in a direction perpendicular to the drawing of FIG. 1 (hereinafter, referred to as “orthogonal direction”) while holding the recording medium P on a cylindrical outer peripheral curved surface (conveyor surface). By rotating with, the recording medium P is conveyed in the conveying direction along the conveying surface.

Specifically, the transfer drum 24 includes a transfer drum motor (not shown), and the transfer drum motor is driven by the control of the control unit 40 to rotate in the counterclockwise direction in FIG. In the present embodiment, a large-sized (for example, triple cylinder for a printing machine) metal drum is used as the transport drum 24.

The transfer belt 20, transfer roller 23, and transfer drum 24 described above have a width of 800 mm, that is, an axial length.

The transfer roller 23 is arranged so as to face the upper part of the transfer drum 24, and pressurizes the transfer drum 24 via the transfer belt 20. Further, the transfer drum 24 is pressed against the transfer roller 23 with the transfer belt 20 sandwiched therein, so that a transfer nip NP for transferring an image from the transfer belt 20 to the recording medium P is formed. In the present embodiment, the value of the transfer load or pressure contact force (hereinafter referred to as “transfer pressure”) in the transfer nip NP is set to 300 N.

The head unit 10 ejects ink droplets onto the transfer belt 20 from a nozzle opening provided on the ink ejection surface facing the transfer belt 20 to form an image on the transfer belt 20. The transfer drum 24 conveys the recording medium P so that the image formed on the transfer belt 20 is transferred to a predetermined position on the recording medium P by the transfer nip NP.

In the inkjet image forming apparatus 1 according to the present embodiment, the transfer belt 20 has four head units 10 corresponding to four colors of inks of yellow (Y), magenta (M), cyan (C), and black (K). They are arranged so as to be arranged at predetermined intervals in the order of Y, M, C, and K colors from the upstream side in the rotation direction (movement direction).

Each head unit 10 includes an inkjet head 102 (see FIG. 2). The inkjet head 102 is provided with a plurality of recording elements each having a pressure chamber for storing ink, a piezoelectric element provided on the wall surface of the pressure chamber, and a nozzle. When a drive signal that deforms the piezoelectric element is input to this recording element, the pressure chamber is deformed due to the deformation of the piezoelectric element, the pressure in the pressure chamber changes, and ink droplets are ejected from a nozzle communicating with the pressure chamber. do.

The arrangement range of the nozzles included in the inkjet head 102 in the orthogonal direction covers the width of the recording medium P conveyed by the transfer drum 24 in the orthogonal direction of the region where the image is formed. The head unit 10 is used with its position fixed with respect to the rotation axis of the transport drum 24 when forming an image. That is, the inkjet image forming apparatus 1 is a single-pass type inkjet image forming apparatus.

In the present embodiment, as the ink ejected from the inkjet head 102 to the transfer belt 20, an ink having ultraviolet curability that is cured by being irradiated with ultraviolet rays is used. More specifically, an ink whose viscosity changes according to the amount of active energy rays supplied to the transfer belt 20 (the amount of ultraviolet rays (UV) emitted from the first irradiation unit 25) is used. An ink having a property that the viscosity increases as the amount of light of the active energy rays emitted from the first irradiation unit 25 increases is used. That is, the image forming portion of the inkjet image forming apparatus 1 adopts a UV curable inkjet method.

The first irradiation unit 25 is arranged on the outer peripheral surface side of the transfer belt 20, and under the control of the control unit 40, irradiates the ink droplets ejected on the transfer belt 20 with active energy rays to obtain the ink liquid. Increases the viscosity of the drop (semi-cures). The first irradiation unit 25 functions as the "thickening unit" of the present invention.

In FIG. 1, the arrow extending from the first irradiation unit 25 indicates an active energy ray emitted from the surface side of the transfer belt 20 with respect to the ink droplets ejected on the transfer belt 20. In the present embodiment, the first irradiation unit 25 includes a UV light source that outputs UV light having a wavelength of 395 nm, and the default value of the irradiation intensity in a normal print job is set to ^{1 W / cm 2.}

The second irradiation unit 26 is arranged so as to irradiate the recording medium P transported downstream of the transfer nip NP with active energy rays, and the image transferred by the transfer nip NP under the control of the control unit 40. This cures (ink droplets). In the present embodiment, the second irradiation unit 26 includes a UV light source that outputs UV light having a wavelength of 395 nm, and the default value of the irradiation intensity in a normal print job is set to ^{10 W / cm 2.}

The detection unit 27 is provided on the surface side of the transfer belt 20 and between the transfer roller 23 and the driven roller 21 in the moving direction of the transfer belt 20. The detection unit 27 detects the thickness of the ink (residual ink) remaining on the transfer belt 20 without being transferred to the recording medium P. In the present embodiment, the detection unit 27 is a light-reflecting photosensor, which irradiates the surface of the transfer belt 20 with irradiation light to detect the reflected light from the surface, and remains after the detection result. Detects the thickness of ink. Then, the control unit 40 detects the amount of the residual ink based on the thickness of the residual ink detected by the detection unit 27. For example, the control unit 40 detects the amount of residual ink by referring to the correlation information indicating the correlation between the thickness of the residual ink and the amount of residual ink.

The cleaning unit 28 includes a brush roller that is arranged to face the surface of the transfer belt 20 between the driven roller 21 and the detection unit 27 in the moving direction of the transfer belt 20 and cleans the surface of the transfer belt 20. The cleaning unit 28 may be provided with a sponge roller instead of the brush roller.

The brush roller of the cleaning unit 28 is configured to be in contact with and separated from the transfer belt 20 and is rotatable, and is in contact with (contacts) with the transfer belt 20 and rotates under the control of the control unit 40. As a result, the surface of the transfer belt 20 is cleaned to remove residual ink and paper dust adhering to the surface.

Next, other main functional configurations in the inkjet image forming apparatus 1 will be described mainly with reference to FIG. The inkjet image forming apparatus 1 includes a head drive unit 101 and an inkjet head 102 included in the head unit 10, a control unit 40, a transport drive unit 51, and an input / output interface 52.

The head drive unit 101 outputs a drive signal for deforming the piezoelectric element according to the image data to the recording element of the inkjet head 102 at an appropriate timing based on the control of the control unit 40, so that the inkjet head 102 An amount of ink droplets corresponding to the pixel value of the image data is ejected from the nozzle.

The control unit 40 includes a CPU 41 (Central Processing Unit), a RAM 42 (Random Access Memory), a ROM 43 (Read Only Memory), and a storage unit 44.

The CPU 41 reads out various control programs and setting data stored in the ROM 43, stores them in the RAM 42, executes the programs, and performs various arithmetic processes. In addition, the CPU 41 controls the overall operation of the inkjet image forming apparatus 1 in an integrated manner.

The RAM 42 provides the CPU 41 with a working memory space and stores temporary data. The RAM 42 may include a non-volatile memory.

The ROM 43 stores various control programs, setting data, and the like executed by the CPU 41. Instead of the ROM 43, a rewritable non-volatile memory such as an EEPROM (Electrically Erasable Programmable Read Only Memory) or a flash memory may be used.

A print job (specifically, an image formation instruction including various user setting information such as the number of prints) input from the external device 2 via the input / output interface 52 and an image related to the print job are stored in the storage unit 44. Data is stored. As the storage unit 44, for example, an HDD (Hard Disk Drive) may be used, or a DRAM (Dynamic Random Access Memory) or the like may be used in combination.

The transfer drive unit 51 supplies a drive signal to the transfer drum motor of the transfer drum 24 based on the control signal supplied from the control unit 40 to rotate the transfer drum 24 at a predetermined speed and timing. Further, the transport drive unit 51 supplies a drive signal to the motor of the transfer roller 23 based on the control signal supplied from the control unit 40, and rotates the transfer belt 20 at a predetermined speed and timing.

The input / output interface 52 mediates the transmission and reception of data between the external device 2 and the control unit 40. The input / output interface 52 is composed of, for example, any of various serial interfaces, various parallel interfaces, or a combination thereof.

The external device 2 is, for example, a personal computer, and supplies print jobs, image data, and the like to the control unit 40 via the input / output interface 52.

By the way, in the inkjet image forming apparatus 1, the thickening state of the ink droplets when the image is transferred to the recording medium P by the transfer nip NP according to the usage history of the transfer belt 20 and the difference in the type of the recording medium P (the thickening state of the ink droplets ( (Thickness increase) may change. For example, if the thickening state of the ink droplets is an excessive thickening state, that is, if the thickening degree of the ink droplets is too high, poor image transfer to the recording medium P will occur. Further, even if the thickening state of the ink droplets is insufficient thickening, that is, even if the thickening degree of the ink droplets is too low, poor image transfer to the recording medium P will occur. Therefore, for example, in order to feed back to the operation of the inkjet image forming apparatus 1 so as not to cause an image transfer defect to the recording medium P, it is determined to determine the thickening state of the ink droplets when the image is transferred to the recording medium P. Is desirable.

Therefore, in the present embodiment, the control unit 40 of the inkjet image forming apparatus 1 determines the amount of residual ink remaining on the transfer belt 20 without being transferred to the recording medium P with respect to the amount of ink ejected from the inkjet head 102. The ratio is detected, and the thickened state of the ink after the viscosity is increased is determined based on the detected ratio.

FIG. 3 is a diagram for explaining the difference in the thickening state of the ink droplets. FIG. 3A shows a state in which a transfer residue is generated by a normal image forming process on the recording medium P (that is, a state in which no transfer defect has occurred). As shown in FIG. 3A, the thickening of the ink droplets ejected on the transfer belt 20 is appropriate, and after the recording medium P passes through the transfer nip NP, a large amount of ink 32 is transferred to the recording medium P. On the other hand, a small amount of ink 30 (residual ink) remains on the transfer belt 20 without being transferred to the recording medium P.

FIG. 3B shows a state in which image transfer failure with respect to the recording medium P has occurred. As shown in FIG. 3B, since the thickening of the ink droplets ejected on the transfer belt 20 is too high, there is almost no ink transferred to the recording medium P after the recording medium P passes through the transfer nip NP. Most of the ink 30 is not transferred to the recording medium P and remains on the transfer belt 20. This is because the thickening state of the ink droplets before transfer is an excessive thickening state (excessive curing state), and the adhesive force of the ink 30 to the recording medium P is impaired.

FIG. 3C shows a state in which image transfer failure with respect to the recording medium P has occurred. As shown in FIG. 3C, since the thickening of the ink droplets ejected on the transfer belt 20 is too low, the amount of ink 32 transferred to the recording medium P after the recording medium P passes through the transfer nip NP. The amount of ink 30 remaining on the transfer belt 20 without being transferred to the recording medium P is about the same. This is because the thickened state of the ink droplets before transfer is an insufficient thickening state (insufficient curing state), and the ink droplets ejected on the transfer belt 20 are broken inside the ink droplets during transfer. Because.

An example of the thickening state determination operation (corresponding to the “thickening state determination method” of the present invention) of the inkjet image forming apparatus 1 will be described with reference to the flowchart of FIG. The process shown in FIG. 4 is executed every time the image data related to the print job is supplied to the control unit 40 and an amount of ink droplets corresponding to the pixel value of the image data is ejected from the nozzle of the inkjet head 102. NS.

First, the control unit 40 detects the ratio of the amount of residual ink remaining on the transfer belt 20 without being transferred to the recording medium P to the amount of ink ejected from the inkjet head 102 (step S100). Here, the control unit 40 estimates the thickness of the ink ejected from the inkjet head 102 based on the input image, and detects the amount of ink according to the estimated thickness of the ink. For example, the control unit 40 detects the amount of ink by referring to the correlation information indicating the correlation between the thickness of the ink and the amount of the ink. Further, the control unit 40 detects the amount of residual ink based on the thickness of the residual ink detected by the detection unit 27.

Next, the control unit 40 determines whether or not the ratio detected in step S100 is less than the first threshold value (for example, 20%) (step S120). As a result of the determination, when the detected ratio is less than the first threshold value (step S120, YES), the control unit 40 determines that the thickening state of the ink droplet before transfer is a normal state (appropriate thickening state). Determine (step S140). When the process of step S140 is completed, the inkjet image forming apparatus 1 ends the process in FIG.

On the other hand, when the detected ratio is not less than the first threshold value (step S120, NO), the control unit 40 determines whether or not the detected ratio in step S100 is equal to or more than the second threshold value (for example, 70%). Determine (step S160). As a result of the determination, when the detected ratio is equal to or higher than the second threshold value (step S160, YES), the control unit 40 determines that the thickening state of the ink droplet before transfer is an excessive thickening state (step). S180). When the process of step S180 is completed, the inkjet image forming apparatus 1 ends the process in FIG.

On the other hand, when the detected ratio is not equal to or higher than the second threshold value, that is, is equal to or higher than the first threshold value and lower than the second threshold value (step S160, NO), the control unit 40 is in a thickened state of the ink droplet before transfer. Is determined to be in an insufficient thickening state (step S200). When the process of step S200 is completed, the inkjet image forming apparatus 1 ends the process in FIG.

As described in detail above, in the present embodiment, the inkjet image forming apparatus 1 (image forming apparatus) is a head unit that forms an image on the transfer belt 20 (transfer body) by ejecting ink from the inkjet head 102. From the 10 (image forming unit), the first irradiation unit 25 (thickening unit) that increases the viscosity of the ink ejected on the transfer belt 20 before the image is transferred to the recording medium P, and the inkjet head 102. A control unit 40 (detection unit) that detects the ratio of the amount of residual ink remaining on the transfer belt 20 without being transferred to the recording medium P to the amount of ejected ink, and a viscosity based on the detected ratio. A control unit 40 (determination unit) for determining the thickening state of the ink after the increase in ink is provided.

According to the present embodiment configured as described above, the number of ink droplets increased when an image is transferred to the recording medium P by the transfer nip NP according to the usage history of the transfer belt 20 and the difference in the type of the recording medium P. Even when the viscous state changes, the thickening state of the ink droplets can be determined and fed back to the operation of the inkjet image forming apparatus 1 so that, for example, image transfer failure to the recording medium P does not occur.

In the above embodiment, the control unit 40 has described an example of detecting the amount of ink ejected from the inkjet head 102 based on the input image, but the present invention is not limited to this. For example, the control unit 40 may detect the amount of ink ejected from the inkjet head 102 based on the image formed on the transfer belt 20. In this case, the control unit 40 estimates and estimates the thickness of the ink ejected from the inkjet head 102 based on the reading result of the image reading unit (not shown) that reads the image formed on the transfer belt 20. The amount of ink is detected according to the thickness of the ink.

Further, in the above embodiment, an example in which the control unit 40 detects the amount of residual ink based on the thickness of the residual ink detected by the detection unit 27, which is a light reflection type photo sensor, has been described. The present invention is not limited to this. For example, the control unit 40 may detect the amount of residual ink based on the image density of the residual ink detected by the detection unit 27, which is a light transmissive photo sensor. For example, the control unit 40 detects the amount of residual ink by referring to the correlation information indicating the correlation between the image density of the residual ink and the amount of residual ink.

FIG. 5 is a diagram schematically showing a modified example of the overall configuration of the inkjet image forming apparatus 1. In the configuration shown in FIG. 5, the transfer belt 20 has active energy ray transmission (light transmission). The first irradiation unit 25 is arranged on the inner peripheral surface side of the transfer belt 20 and irradiates the ink droplets ejected on the transfer belt 20 with active energy rays to increase the viscosity of the ink droplets ( Semi-cured). In FIG. 5, the arrow extending from the first irradiation unit 25 indicates an active energy ray irradiated from the back surface side of the transfer belt 20 with respect to the ink droplets ejected on the transfer belt 20.

The detection unit 27 includes an irradiation unit 27A that irradiates the surface of the transfer belt 20 with irradiation light, and an irradiation light detection unit 27B that detects the irradiation light transmitted through the transfer belt 20, and the detection result of the irradiation light detection unit 27B. (Specifically, the image density of the residual ink is detected according to the amount of irradiation light). Then, the control unit 40 detects the amount of residual ink based on the image density detected by the detection unit 27.

The control unit 40 may detect the amount of residual ink based on the image density of the residual ink and the dot diameter of the residual ink. When detecting the amount of residual ink based on the image density detected by the detection unit 27, which is a light transmissive photo sensor, there is no problem if the residual ink constitutes a so-called solid portion, but a so-called halftone portion is configured. In the residual ink, the ink dots are crushed and the hiding rate tends to increase, and the image density of the residual ink tends to increase more than it actually is. In this case, the image density of the residual ink and the amount of the residual ink may not correlate with each other. Therefore, the control unit 40 acquires the measured value of the dot diameter of the residual ink (for example, measured by the image reading unit), and considers whether or not the dot diameter of the residual ink is enlarged as compared with the dot diameter of the ink before transfer. However, it is desirable to detect the amount of residual ink.

Further, in the above embodiment, as shown in FIG. 6, the detection unit 27 is provided on the surface side of the transfer drum 24 and between the transfer nip NP and the second irradiation unit 26 in the moving direction of the transfer drum 24. May be done. In this case, the detection unit 27 detects the amount of residual ink based on the image density of the image transferred to the recording medium P. Specifically, the detection unit 27 is a light-reflecting photo sensor, which irradiates the surface of the image transferred to the recording medium P with irradiation light to detect the reflected light from the surface, and uses the detection result as a result. Accordingly, the image density of the image transferred to the recording medium P is detected. Then, the control unit 40 detects the amount of residual ink based on the image density detected by the detection unit 27. For example, when the image density detected by the detection unit 27 is high (that is, when the transfer rate is high), the control unit 40 detects that the amount of residual ink is small, while the image density detected by the detection unit 27. When is small (that is, when the transfer rate is low), it is detected that the amount of residual ink is large.

Further, in the above embodiment, when the control unit 40 determines that the thickening state of the ink droplet is an insufficient thickening state or an excessive thickening state, the head unit 10 forms an image on the transfer belt 20. The processing to be performed may be stopped. With this configuration, it is possible to prevent the occurrence of image transfer failure with respect to the recording medium P due to the thickening state of the ink droplets being an insufficient thickening state or an excessive thickening state.

Further, in the above embodiment, the control unit 40 may change the contact conditions of the cleaning unit 28 based on the determined thickening state of the ink droplets. This is because if the thickening state of the ink droplets fluctuates, the downstream process of transfer may be significantly affected. For example, the control unit 40 may separate the cleaning unit 28 from the transfer belt 20 when it is determined that the thickening state of the ink droplets is insufficient. With this configuration, it is possible to prevent the residual ink in the uncured state from adhering (contaminated) to the cleaning portion 28 in contact with the transfer belt 20 and reattaching the residual ink adhering to the cleaning portion 28 to the transfer belt 20.

Further, when the control unit 40 determines that the thickening state of the ink droplets is insufficiently thickening, the cleaning unit 28 is separated from the transfer belt 20 and the viscosity of the ink droplets is increased by the first irradiation unit 25. May be brought into contact with the cleaning portion 28 on the transfer belt 20 after the ink is increased again. With this configuration, the thickened state of the ink droplets can be reliably cleaned by the cleaning unit 28 (normal state), and then the ink droplets can be appropriately cleaned.

Further, when the control unit 40 determines that the thickening state of the ink droplets is in the excessive thickening state, the cleaning power of the cleaning unit 28 is increased as compared with the case where it is not determined that the thickening state is the excessive thickening state. The cleaning conditions of the cleaning unit 28 may be changed so as to do so. This is because, under normal cleaning conditions, the cleaning unit 28 may not be able to completely clean the residual ink on the transfer belt 20. The control unit 40 determines the thickened state of the ink before the residual ink is cleaned by the cleaning unit 28. Therefore, in the detection unit 27, before the residual ink on the transfer belt 20 is cleaned by the cleaning unit 28, the control unit 40 acquires the detection result of the detection unit 27 and determines the thickened state of the ink. Placed in possible positions.

For example, the control unit 40 changes the cleaning conditions by increasing the pressing load of the cleaning unit 28 (brush roller), the amount of biting into the transfer belt 20, the rotation speed, and the like (that is, increasing the cleaning strength). In this case, the control unit 40 increases the rotation speed of the brush roller when the rotation direction of the brush roller with respect to the movement direction of the transfer belt 20 is the counter direction. When the rotation direction of the brush roller with respect to the movement direction of the transfer belt 20 is the with direction, the control unit 40 reduces the rotation speed of the brush roller or changes the rotation direction of the brush roller to the counter direction.

Further, in the above embodiment, when the control unit 40 determines that the thickening state of the ink droplet is the insufficient thickening state, the first irradiation unit 25 is not determined to be the insufficient thickening state. As compared with the case, the viscosity of the ink droplet may be further increased by increasing the intensity of the active energy ray and the irradiation time. Further, in the first irradiation unit 25, when it is determined that the thickening state of the ink droplet is the excessive thickening state, the intensity of the active energy ray is higher than that when it is not determined to be the excessive thickening state. The increase in the viscosity of the ink droplets may be suppressed by reducing the irradiation time and the ink droplets. When the thickening state of the ink droplets is fed back to the thickening condition for increasing the ink droplets, an abnormality (insufficient thickening state or excessive thickening state) actually occurs on the image formed on the transfer belt 20. It is desirable to change the thickening condition before doing so. Therefore, a threshold value that triggers to change the thickening condition may be set separately from the threshold values (first and second threshold values) for detecting an abnormality (insufficient thickening state or excessive thickening state).

Further, in the above embodiment, an example in which the first irradiation unit 25 functions as the “thickening unit” of the present invention has been described, but the present invention is not limited to this. For example, when water-based ink is used as the ink ejected from the inkjet head 102 to the transfer belt 20, a heating portion that heats the ink droplets ejected on the transfer belt 20 to increase the viscosity of the ink droplets is provided. It may function as the "thickening portion" of the present invention.

Further, in the above embodiment, the detection unit 27 uses the residual ink that remains on the transfer belt 20 without being transferred to the recording medium P among the images (inks) formed on the transfer belt 20 based on the input image. Although an example of detecting the thickness of the ink has been described, the present invention is not limited to this. For example, the detection unit 27 does not transfer to the recording medium P based on the image (ink) formed on the transfer belt 20 based on the patch image prepared to detect the amount of residual ink, and the transfer belt 27 does not transfer to the recording medium P. The thickness of the residual ink remaining on the 20 may be detected.

Further, in the above embodiment, the example in which the active energy ray irradiated by the first irradiation unit 25 is ultraviolet rays has been described, but the present invention is not limited to this. For example, the active energy ray may be an electron beam. In this case, it is preferable to use an ink whose viscosity changes according to the electron beam.

Further, in the above-described embodiments, all of them are merely examples of embodiment of the present invention, and the technical scope of the present invention should not be construed in a limited manner by these. That is, the present invention can be implemented in various forms without departing from its gist or its main features.

1 Inkjet image forming device 2 External device 10 Head unit 20 Transfer belt 21 and 22 Driven roller 23 Transfer roller 24 Conveying drum 25 1st irradiation unit 26 2nd irradiation unit 27 Detection unit 28 Cleaning unit 40 Control unit 41 CPU
42 RAM
43 ROM
44 Storage unit 51 Transport drive unit 52 Input / output interface 101 Head drive unit 102 Inkjet head NP Transfer nip P Recording medium

Claims (18)

An image forming unit that forms an image on the transfer body by ejecting ink from the inkjet head,
Before the image is transferred to the recording medium, a thickening portion that increases the viscosity of the ink ejected onto the transfer body, and a thickening portion.
A detection unit that detects the ratio of the amount of residual ink remaining on the transfer body without being transferred to the recording medium with respect to the amount of ink ejected from the inkjet head.
Based on the detected ratio, a determination unit that determines the thickening state of the ink after the viscosity has been increased, and a determination unit.
An image forming apparatus comprising. When the ratio is less than the first threshold value, the determination unit determines that the thickening state of the ink is a normal state, and when the ratio is equal to or more than the first threshold value and less than the second threshold value. It is determined that the thickening state of the ink is an insufficient thickening state, and when the ratio is equal to or higher than the second threshold value, the thickening state of the ink is determined to be an excessive thickening state.
The image forming apparatus according to claim 1. When it is determined that the thickening state of the ink is an insufficient thickening state or an excessive thickening state, the image forming unit stops the process of forming an image on the transfer body.
The image forming apparatus according to claim 2. A cleaning unit that comes into contact with the transfer body and cleans the residual ink is provided.
The image forming apparatus according to claim 2 or 3. A control unit for changing the contact conditions of the cleaning unit based on the determined thickening state of the ink is provided.
The image forming apparatus according to claim 4. When the control unit determines that the thickening state of the ink is insufficiently thickening, the control unit separates the cleaning unit from the transfer body.
The image forming apparatus according to claim 5. When the control unit determines that the thickening state of the ink is insufficiently thickening, the cleaning unit is separated from the transfer body, and the thickening part again increases the viscosity of the ink. After that, the cleaning portion is brought into contact with the transfer body.
The image forming apparatus according to claim 5. When the control unit determines that the thickening state of the ink is an excessive thickening state, the cleaning force of the cleaning unit is increased as compared with the case where the thickening state of the ink is not determined to be an excessive thickening state. , Change the cleaning conditions of the cleaning part,
The image forming apparatus according to claim 5. The determination unit determines the thickened state of the ink before the residual ink is cleaned by the cleaning unit.
The image forming apparatus according to any one of claims 4 to 8. When it is determined that the thickening state of the ink is in the insufficient thickening state, the thickening portion further increases the viscosity of the ink as compared with the case where it is not determined that the thickening state is insufficient.
The image forming apparatus according to any one of claims 2 to 9. When the thickening portion of the ink is determined to be in an excessive thickening state, the thickening portion suppresses an increase in the viscosity of the ink as compared with a case where it is not determined to be in an excessive thickening state. ,
The image forming apparatus according to any one of claims 2 to 9. The detection unit detects the amount of ink ejected from the inkjet head based on the input image.
The image forming apparatus according to any one of claims 1 to 11. The detection unit detects the amount of ink ejected from the inkjet head based on the image formed on the transfer body.
The image forming apparatus according to any one of claims 1 to 11. The detection unit detects the amount of the residual ink based on the thickness of the residual ink.
The image forming apparatus according to any one of claims 1 to 13. The detection unit detects the amount of the residual ink based on the image density of the residual ink.
The image forming apparatus according to any one of claims 1 to 13. The detection unit detects the amount of the residual ink based on the image density of the residual ink and the dot diameter of the residual ink.
The image forming apparatus according to any one of claims 1 to 13. The detection unit detects the amount of the residual ink based on the image density of the image transferred to the recording medium.
The image forming apparatus according to any one of claims 1 to 13. An image is formed on the transfer body by ejecting ink from the inkjet head,
Before the image is transferred to the recording medium, the viscosity of the ink ejected onto the transfer body is increased.
The ratio of the amount of residual ink remaining on the transfer body without being transferred to the recording medium to the amount of ink ejected from the inkjet head is detected.
Based on the detected ratio, the thickening state of the ink after the viscosity is increased is determined.
Thickening state determination method.

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