JP7388234B2 - Image forming apparatus and thickening state determination method - Google Patents

Description

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

In recent years, inkjet-based image forming devices that form images on recording media by ejecting ink droplets from an inkjet head have become popular as devices that form (record) high-definition images on various recording media such as paper and fabric. (hereinafter referred to as "inkjet image forming apparatus") are widely used.

In inkjet image forming devices, an intermediate transfer method has been 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 using a transfer nip. (For example, see Patent Document 1). With this intermediate transfer method, the amount of ink droplets can be suppressed in advance, and the ink droplets can be crushed and expanded to a desired size (diameter) by the transfer pressure of the transfer nip. In other words, an image with high image coverage can be formed with a small amount of ink droplets.

In an intermediate transfer type inkjet image forming apparatus, ink (containing a polymerizable monomer) that is cured (thickened) by active energy rays (e.g., ultraviolet rays) is used to ensure the transferability of the image to the recording medium. An example is a configuration using an intermediate transfer body that is transparent to energy rays. In this configuration, active energy rays are irradiated from the outer circumferential surface side or the inner circumferential surface side of the intermediate transfer member to the image (ink droplets) that is held and pressed (nipped) in the transfer nip, and the ink droplets are Adjust viscosity. This makes it possible to maintain the wettability of the ink droplets that come into contact with the recording medium while ensuring a viscosity that does not crush the ink droplets, thereby improving transferability.

JP2012-91342A

Incidentally, in the above-mentioned inkjet image forming apparatus, the viscosity state (degree of viscosity increase) of the ink droplets when transferring an image to the recording medium in the transfer nip depends on the usage history of the intermediate transfer member and the type of recording medium. ) may change. For example, if the viscosity of the ink droplets is excessively thickened, that is, if the degree of viscosity of the ink droplets is too high, defective image transfer to the recording medium will occur. Further, even if the viscosity of the ink droplets is insufficiently thickened, that is, the degree of viscosity increase of the ink droplets is too low, defective transfer of the image to the recording medium will occur. Therefore, it is desirable to determine the thickening state of ink droplets when transferring an image to a recording medium, in order to provide feedback to the operation of the inkjet image forming apparatus, for example, to prevent defective image transfer to the recording medium. .

SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus and a method for determining a thickened state of ink droplets that can determine the thickened state of ink droplets when an image is transferred to a recording medium.

The image forming apparatus according to the present invention includes:
an image forming unit that forms an image on the transfer body by ejecting ink from an inkjet head;
a viscosity increasing part that increases the viscosity of the ink ejected onto the transfer body before the image is transferred to the recording medium;
a detection unit that detects a 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;
a determination unit that determines a thickened state of the ink after the viscosity has been increased based on the detected ratio;
Equipped with.

The thickening state determination method according to the present invention includes:
An image is formed on a transfer body by ejecting ink from an inkjet head,
Before the image is transferred to the recording medium, increasing the viscosity of the ink ejected onto the transfer body,
detecting 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;
Based on the detected ratio, a thickened 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 transferring an image to a recording medium.

1 is a diagram schematically showing the overall configuration of an inkjet image forming apparatus. 1 is a block diagram showing the main functional configuration of an inkjet image forming apparatus. FIG. 3 is a diagram illustrating differences in the thickened state of ink droplets. 3 is a flowchart illustrating an example of the thickening state determination operation of the inkjet image forming apparatus. FIG. 3 is a diagram schematically showing a modification of the overall configuration of an inkjet image forming apparatus. FIG. 3 is a diagram schematically showing a modification of the overall configuration of an inkjet image forming apparatus.

Hereinafter, an 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 an inkjet image forming apparatus 1. As shown in FIG. Further, FIG. 2 is a block diagram showing the main functional configuration of the inkjet image forming apparatus 1. As shown in FIG.

As shown in FIGS. 1 and 2, the inkjet image forming apparatus 1 includes a head unit 10 equipped with an inkjet head 102, a transfer belt 20, driven rollers 21 and 22 that rotatably tension the transfer belt 20, and a drive roller. It includes a transfer roller 23 as a roller, a conveyance drum 24 that conveys the recording medium P, and a control section 40 that controls the entire apparatus.

Note that the head unit 10 functions as an "image forming section" of the present invention. Further, the transfer belt 20 functions as a "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.

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

Although not shown, the inkjet image forming apparatus 1 includes a feeding unit that loads recording media P and feeds them to the transport drum 24, and discharges the recording medium P on which the image has been transferred to the downstream side of the transport drum 24 in the transport direction. The device is equipped with a discharge section for displaying the device, a display section for displaying the status of the device, and the like. Since these are well-known configurations, illustration and description will be omitted.

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

The transfer belt 20 spans over driven rollers 21 and 22 disposed above and a transfer roller 23 (drive roller) disposed below, and is driven by a transfer motor (not shown) of a conveyance drive section 51. As the driving force is transmitted to the transfer roller 23, the transfer roller 23 rotates (moves) in the clockwise direction in FIG.

In this embodiment, a heat source (for example, a heater) is provided within the driven roller 22. The temperature of the heating source is controlled by the controller 40. The driven roller 22 is heated by the heat source, and as a result, the temperature of the transfer belt 20 is heated to the target temperature. The target temperature is a temperature set so that the dot diameter of ink droplets discharged onto the transfer belt 20 becomes a predetermined diameter.

In this embodiment, the transfer belt 20 is transparent to active energy rays, and is made of polyimide (PI), an elastic layer of silicone rubber, a reflective layer on which aluminum (Al) is vapor-deposited, and a polypropylene base material. An endless belt is used in which a surface layer of (PP) is laminated.

Further, as the transfer roller 23, for example, a rubber roller having a diameter of 100 mm and a rubber surface layer having a thickness of 10 mm is used. Note that for 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 is rotated clockwise by driving the transfer motor described above based on a control signal from the control unit 40 and rotating the transfer roller 23 clockwise in FIG. Driven. In this embodiment, under the control of the control unit 40, the rotational speed of the transfer roller 23 is controlled such that the transfer belt 20 rotates at a speed of 600 mm/sec (printing speed).

The conveyance drum 24 holds the recording medium P on its cylindrical outer peripheral curved surface (conveyance surface) and rotates around a rotating shaft extending in a direction perpendicular to the drawing of FIG. 1 (hereinafter referred to as the "orthogonal direction"). By rotating, the recording medium P is conveyed in the conveyance direction along the conveyance surface.

Specifically, the conveyance drum 24 includes a conveyance drum motor (not shown), and is rotated in the counterclockwise direction in FIG. 1 by driving the conveyance drum motor under the control of the control unit 40 . In this embodiment, a large metal drum (for example, a triple cylinder for a printing press) is used as the conveyance drum 24.

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

The transfer roller 23 is arranged to face the top of the conveyance drum 24 and presses the conveyance drum 24 via the transfer belt 20 . Furthermore, the conveying drum 24 is pressed against the transfer roller 23 with the transfer belt 20 in between, thereby forming a transfer nip NP for transferring the image from the transfer belt 20 to the recording medium P. In this embodiment, the value of the transfer load or pressing force (hereinafter referred to as "transfer pressure") in the transfer nip NP is set to 300N.

The head unit 10 forms an image on the transfer belt 20 by ejecting ink droplets onto the transfer belt 20 from nozzle openings provided on an ink ejection surface facing the transfer belt 20 . The conveyance 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 at the transfer nip NP.

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

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 of the pressure chamber, and a nozzle. In this recording element, when a drive signal that deforms the piezoelectric element is input, the pressure chamber deforms due to the deformation of the piezoelectric element, the pressure inside the pressure chamber changes, and ink droplets are ejected from the 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 in the orthogonal direction of the area on which an image is formed of the recording medium P transported by the transport drum 24. The head unit 10 is used with its position fixed relative to the rotation axis of the transport drum 24 during image formation. That is, the inkjet image forming apparatus 1 is a single-pass type inkjet image forming apparatus.

In this embodiment, as the ink ejected from the inkjet head 102 onto the transfer belt 20, an ink having ultraviolet curing properties that is cured by being irradiated with ultraviolet light is used. More specifically, an ink whose viscosity changes depending on the amount of active energy rays supplied to the transfer belt 20 (the amount of ultraviolet rays (UV) emitted from the first irradiation section 25) is used. The ink used has a property that the greater the amount of active energy rays irradiated from the first irradiation unit 25, the higher the viscosity. That is, the image forming section of this inkjet image forming apparatus 1 employs a UV curing inkjet system.

The first irradiation unit 25 is disposed on the outer circumferential surface side of the transfer belt 20, and under the control of the control unit 40, irradiates the ink droplets ejected onto the transfer belt 20 with active energy rays to remove the ink liquid. Increase the viscosity of the drop (semi-harden). Note that the first irradiation section 25 functions as a "thickening section" of the present invention.

In FIG. 1, an arrow extending from the first irradiation unit 25 indicates an active energy ray irradiated from the surface side of the transfer belt 20 to the ink droplets ejected onto the transfer belt 20. In the present embodiment, the first irradiation unit 25 includes a UV light source that outputs UV light with 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 to irradiate active energy rays to the recording medium P conveyed downstream of the transfer nip NP, and is arranged to irradiate the recording medium P conveyed downstream of the transfer nip NP with the image transferred by the transfer nip NP under the control of the control unit 40. (ink droplets) are fully cured. In the present embodiment, the second irradiation unit 26 includes a UV light source that outputs UV light with 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 front 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 ink that is not transferred to the recording medium P and remains on the transfer belt 20 (residual ink). In this embodiment, the detection unit 27 is a light reflection type photosensor, which irradiates the surface of the transfer belt 20 with irradiation light, detects the reflected light from the surface, and detects the residual amount depending on the detection result. Detects ink thickness. Then, the control unit 40 detects the amount of 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 correlation information indicating a correlation between the thickness of the residual ink and the amount of the residual ink.

The cleaning section 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 section 27 in the moving direction of the transfer belt 20 and cleans the surface of the transfer belt 20. Note that the cleaning section 28 may include a sponge roller instead of the brush roller.

The brush roller of the cleaning section 28 is configured to be able to come into contact with and separate from the transfer belt 20 and to rotate, and is rotated while coming into contact with the transfer belt 20 under the control of the control section 40. As a result, the surface of the transfer belt 20 is cleaned to remove residual ink and paper powder adhering to the surface.

Next, other main functional configurations of the inkjet image forming apparatus 1 will be described mainly with reference to FIG. 2. The inkjet image forming apparatus 1 includes a head drive section 101 and an inkjet head 102 included in the head unit 10 , a control section 40 , a transport drive section 51 , and an input/output interface 52 .

The head drive unit 101 controls the inkjet head 102 by outputting a drive signal to the recording element of the inkjet head 102 at an appropriate timing to cause the piezoelectric element to perform a deforming operation according to the image data based on the control of the control unit 40. Ink droplets are ejected from the nozzle in an amount corresponding to the pixel value of image data.

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 various control programs and setting data stored in the ROM 43, stores them in the RAM 42, and executes the programs to perform various calculation processes. Further, the CPU 41 centrally controls the overall operation of the inkjet image forming apparatus 1 .

The RAM 42 provides a working memory space for the CPU 41 and stores temporary data. Note that the RAM 42 may include nonvolatile memory.

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

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

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

The input/output interface 52 mediates data transmission and reception between the external device 2 and the control unit 40. The input/output interface 52 is configured of, for example, one 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, etc. to the control unit 40 via the input/output interface 52.

Incidentally, in the inkjet image forming apparatus 1, the thickening state ( (degree of viscosity increase) may change. For example, if the viscosity of the ink droplets is excessively thickened, that is, if the degree of viscosity of the ink droplets is too high, defective image transfer to the recording medium P will occur. Further, even if the viscosity of the ink droplets is insufficiently thickened, that is, the degree of viscosity increase of the ink droplets is too low, a defective image transfer to the recording medium P will occur. Therefore, for example, in order to provide feedback to the operation of the inkjet image forming apparatus 1 so as to prevent defective image transfer to the recording medium P, it is necessary to determine the thickened state of ink droplets when transferring an image to the recording medium P. is desirable.

Therefore, in the present embodiment, the control unit 40 of the inkjet image forming apparatus 1 controls 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 illustrating the difference in the thickening state of ink droplets. FIG. 3A shows a state in which transfer residue occurs during normal image forming processing on the recording medium P (that is, a state in which no transfer failure occurs). As shown in FIG. 3A, the degree of thickening of the ink droplets discharged onto 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 a defective image transfer to the recording medium P has occurred. As shown in FIG. 3B, the degree of thickening of the ink droplets discharged onto the transfer belt 20 is so high that almost no ink is transferred to the recording medium P after the recording medium P passes through the transfer nip NP. , most of the ink 30 remains on the transfer belt 20 without being transferred to the recording medium P. This is because the viscosity of the ink droplets before transfer is excessively thickened (excessively hardened), and the adhesion of the ink 30 to the recording medium P is impaired.

FIG. 3C shows a state in which a defective image transfer to the recording medium P has occurred. As shown in FIG. 3C, since the degree of thickening of the ink droplets discharged onto 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 approximately the same. This is because the viscosity of the ink droplets before transfer is insufficiently thickened (insufficiently cured), and the ink droplets ejected onto the transfer belt 20 break internally during transfer. It is from.

An example of the thickening state determining operation of the inkjet image forming apparatus 1 (corresponding to the "thickening state determining method" of the present invention) will be described with reference to the flowchart of FIG. 4. Note that the process shown in FIG. 4 is executed every time image data related to a print job is supplied to the control unit 40 and ink droplets of an amount corresponding to the pixel value of the image data are ejected from the nozzles of the inkjet head 102. Ru.

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 correlation information indicating a correlation between the thickness of the ink and the amount of 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 the ratio detected in step S100 is less than a first threshold (for example, 20%) (step S120). As a result of the determination, if the detected ratio is less than the first threshold (step S120, YES), the control unit 40 determines that the thickened state of the ink droplets before transfer is a normal state (appropriate thickened state). Determination is made (step S140). Upon completion of the process in step S140, the inkjet image forming apparatus 1 ends the process in FIG. 4.

On the other hand, if the detected proportion is not less than the first threshold (step S120, NO), the control unit 40 determines whether the detected proportion in step S100 is greater than or equal to the second threshold (for example, 70%). Determination is made (step S160). As a result of the determination, if the detected ratio is equal to or greater than the second threshold (step S160, YES), the control unit 40 determines that the thickened state of the ink droplets before transfer is an excessively thickened state (step S160, YES). S180). Upon completion of the process in step S180, the inkjet image forming apparatus 1 ends the process in FIG. 4.

On the other hand, if the detected ratio is not greater than or equal to the second threshold, that is, greater than or equal to the first threshold and less than the second threshold (step S160, NO), the control unit 40 determines the viscosity state of the ink droplets before transfer. It is determined that the viscosity is insufficiently thickened (step S200). Upon completion of the process in step S200, the inkjet image forming apparatus 1 ends the process in FIG. 4.

As described in detail above, in this embodiment, the inkjet image forming apparatus 1 (image forming apparatus) includes a head unit that forms an image on the transfer belt 20 (transfer body) by ejecting ink from the inkjet head 102. 10 (image forming section), a first irradiation section 25 (viscosity increasing section) that increases the viscosity of the ink ejected onto the transfer belt 20 before the image is transferred to the recording medium P, and an inkjet head 102. A control unit 40 (detection unit) 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 the control unit 40 (detection unit) detects the viscosity based on the detected ratio. The control unit 40 (determination unit) determines the thickened state of the ink after the increase in viscosity.

According to this embodiment configured in this way, the number of ink droplets increases when transferring an image to the recording medium P in the transfer nip NP, depending on the usage history of the transfer belt 20 and the type of recording medium P. Even when the viscosity state changes, the viscosity 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, defective image transfer to the recording medium P does not occur.

Note that in the above embodiment, an example has been described in which the control unit 40 detects the amount of ink ejected from the inkjet head 102 based on an 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 the thickness of the ink ejected from the inkjet head 102 based on the reading result of an image reading unit (not shown) that reads the image formed on the transfer belt 20, and estimates the thickness of the ink ejected from the inkjet head 102. The amount of ink is detected according to the thickness of the ink.

Further, in the above embodiment, an example was described 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 photosensor. 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 transmission type photosensor. For example, the control unit 40 detects the amount of residual ink by referring to correlation information indicating the correlation between the image density of the residual ink and the amount of the residual ink.

FIG. 5 is a diagram schematically showing a modification of the overall configuration of the inkjet image forming apparatus 1. As shown in FIG. In the configuration shown in FIG. 5, the transfer belt 20 has active energy ray transparency (light transparency). The first irradiation unit 25 is disposed on the inner peripheral surface side of the transfer belt 20, and irradiates the ink droplets ejected onto the transfer belt 20 with active energy rays to increase the viscosity of the ink droplets ( semi-cure). In FIG. 5, an arrow extending from the first irradiation unit 25 indicates an active energy ray that is irradiated from the back side of the transfer belt 20 to the ink droplets ejected onto 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 that has passed through the transfer belt 20, and detects the detection result of the irradiation light detection unit 27B. (Specifically, the image density of the residual ink is detected depending on the amount of irradiated light). Then, the control unit 40 detects the amount of residual ink based on the image density detected by the detection unit 27.

Note that 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 photosensor, there is no problem if the residual ink constitutes a so-called solid area, but there is no problem if the residual ink constitutes a so-called halftone area. With residual ink, the ink dots are crushed and the hiding rate increases, and the image density of the residual ink tends to be higher than it actually is. In this case, there is a possibility that the image density of the residual ink and the amount of the residual ink are not correlated. Therefore, the control unit 40 acquires a measured value of the dot diameter of the residual ink (for example, measured by an image reading unit), and considers whether or not the dot diameter of the residual ink has expanded compared to 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 section 27 is provided on the front side of the conveyance drum 24 and between the transfer nip NP and the second irradiation section 26 in the moving direction of the conveyance drum 24. It's okay to be beaten. 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 reflection type photosensor, irradiates the surface of the image transferred to the recording medium P with irradiation light, detects the reflected light from the surface, and uses the detection 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, and the control unit 40 detects that the amount of residual ink is small. 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 embodiment described above, the head unit 10 forms an image on the transfer belt 20 when the controller 40 determines that the thickening state of the ink droplets is insufficiently thickened or excessively thickened. You may also stop the process. With this configuration, it is possible to prevent a defective transfer of an image to the recording medium P from occurring due to the ink droplet being thickened insufficiently or excessively thickened.

Further, in the embodiment described above, 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 changes, there is a possibility that downstream processes of transfer will be greatly affected. For example, the control unit 40 may separate the cleaning unit 28 from above the transfer belt 20 when it is determined that the viscosity of the ink droplets is insufficiently thickened. With this configuration, it is possible to prevent uncured residual ink from adhering to the cleaning section 28 that contacts the transfer belt 20 (contamination) and from re-adhering the residual ink that has adhered to the cleaning section 28 to the transfer belt 20 .

Further, when it is determined that the viscosity increase state of the ink droplets is insufficient, the control unit 40 separates the cleaning unit 28 from above the transfer belt 20 and causes the first irradiation unit 25 to increase the viscosity of the ink droplets. After the transfer belt 20 is increased again, the cleaning section 28 may be brought into contact with the transfer belt 20. With this configuration, the thickened state of the ink droplets can be brought into a state (normal state) that can be reliably cleaned by the cleaning section 28, and then the ink droplets can be appropriately cleaned.

In addition, when it is determined that the viscosity of the ink droplets is excessively thickened, the control section 40 increases the cleaning force of the cleaning section 28 compared to when it is not determined that the viscosity is excessively thickened. The cleaning conditions of the cleaning section 28 may be changed so that the cleaning conditions are changed. This is because under normal cleaning conditions, the cleaning section 28 may not be able to completely clean the remaining ink on the transfer belt 20. Note that the control unit 40 determines the thickened state of the ink before the residual ink is cleaned by the cleaning unit 28. Therefore, the detection section 27 allows the control section 40 to acquire the detection result of the detection section 27 and determine the thickened state of the ink before the residual ink on the transfer belt 20 is cleaned by the cleaning section 28. be placed in a possible position.

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 rotational speed, etc. (that is, increasing the cleaning intensity). 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 moving direction of the transfer belt 20 is a counter direction. When the rotation direction of the brush roller with respect to the moving direction of the transfer belt 20 is in 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 a counter direction.

Further, in the embodiment described above, when the control unit 40 determines that the thickening state of the ink droplet is insufficiently thickened, the first irradiating unit 25 does not determine that the thickening state of the ink droplet is insufficiently thickened. The viscosity of the ink droplets may be further increased by increasing the intensity or irradiation time of the active energy rays compared to the case in which the viscosity of the ink droplets is increased. The first irradiation unit 25 also controls the intensity of the active energy ray when it is determined that the ink droplet is in an excessively thickened state, compared to when it is not determined that the ink droplet is in an excessively thickened state. The increase in the viscosity of the ink droplets may be suppressed by decreasing the irradiation time or the irradiation time. Note that when feeding back the thickening state of ink droplets to the thickening condition for increasing the number of 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 conditions before the thickening process. Therefore, in addition to the thresholds (first and second thresholds) for detecting an abnormality (insufficient viscosity thickening state or excessive viscosity thickening state), a threshold value that becomes a trigger for changing the viscosity increasing conditions may be set.

Further, in the embodiment described above, an example has been described in which the first irradiation section 25 functions as the "thickening section" of the present invention, 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 onto the transfer belt 20, a heating section that heats the ink droplets ejected onto the transfer belt 20 to increase the viscosity of the ink droplets is provided. It may function as a "thickening part" of the present invention.

In the embodiment described above, the detection unit 27 detects residual ink remaining on the transfer belt 20 without being transferred to the recording medium P, out of the image (ink) formed on the transfer belt 20 based on the input image. Although an example of detecting the thickness of the film has been described, the present invention is not limited thereto. For example, the detection unit 27 determines whether an image (ink) formed on the transfer belt 20 based on a patch image prepared for detecting the amount of residual ink remains on the transfer belt 20 without being transferred to the recording medium P. The thickness of the residual ink remaining on 20 may also be detected.

Further, in the above embodiment, an example has been described in which the active energy rays irradiated by the first irradiation section 25 are ultraviolet rays, 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 ink whose viscosity changes depending on the electron beam.

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

1 Inkjet image forming apparatus 2 External device 10 Head unit 20 Transfer belt 21, 22 Driven roller 23 Transfer roller 24 Conveyance drum 25 First irradiation section 26 Second irradiation section 27 Detection section 28 Cleaning section 40 Control section 41 CPU
42 RAM
43 ROM
44 Storage unit 51 Conveyance 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 an inkjet head;
a viscosity increasing part that increases the viscosity of the ink ejected onto the transfer body before the image is transferred to the recording medium;
a detection unit that detects a 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;
a determination unit that determines a thickened state of the ink after the viscosity has been increased based on the detected ratio;
An image forming apparatus comprising: The determination unit determines that the thickened state of the ink is normal when the ratio is less than a first threshold, and when the ratio is equal to or more than the first threshold and less than a second threshold. , determining that the viscosity increase state of the ink is an insufficient viscosity increase state, and determining that the viscosity increase state of the ink is an excessive viscosity increase state when the ratio is equal to or higher than the second threshold;
The image forming apparatus according to claim 1. The image forming unit stops the process of forming an image on the transfer body when it is determined that the viscosity of the ink is insufficiently thickened or excessively thickened.
The image forming apparatus according to claim 2. a cleaning unit that comes into contact with the transfer body to clean the residual ink;
The image forming apparatus according to claim 2 or 3. comprising a control unit that changes a contact condition of the cleaning unit based on the determined thickening state of the ink;
The image forming apparatus according to claim 4. The control unit separates the cleaning unit from above the transfer body when it is determined that the viscosity increase state of the ink is insufficiently thickened.
The image forming apparatus according to claim 5. When it is determined that the viscosity increase state of the ink is insufficient, the control unit moves the cleaning unit away from the transfer body, and causes the viscosity increase unit to increase the viscosity of the ink again. and then bringing the cleaning section into contact with the transfer body.
The image forming apparatus according to claim 5. The control unit is configured to increase the cleaning force of the cleaning unit when it is determined that the ink is in an excessively thickened state, compared to when it is not determined that the ink is in an excessively thickened state. , changing the cleaning conditions of the cleaning section;
The image forming apparatus according to claim 5. The determination unit determines a 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. The viscosity increasing unit increases the viscosity of the ink when it is determined that the viscosity increase state of the ink is insufficiently thickened, compared to when it is not determined that the viscosity increase state is insufficiently thickened.
The image forming apparatus according to any one of claims 2 to 9. The thickening unit suppresses an increase in the viscosity of the ink when the thickening state of the ink is determined to be an excessive thickening state, compared to a case where the thickening state of the ink is not determined to be 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 a transfer body by ejecting ink from an inkjet head,
Before the image is transferred to the recording medium, increasing the viscosity of the ink ejected onto the transfer body,
detecting 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;
determining a thickened state of the ink after the viscosity has been increased based on the detected ratio;
Method for determining thickening state.

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