JP7428474B2 - Ink detection device and inkjet recording device - Google Patents

Description

The present invention relates to an ink detection device, an ink detection method, and an inkjet recording device.

An inkjet recording apparatus forms an image on a recording medium by ejecting ink onto a recording medium from a plurality of nozzles arranged in an inkjet head. In this inkjet recording apparatus, the nozzles may become clogged or the ejection mechanism may malfunction (defective ink ejection).

Such nozzle clogging and ejection mechanism failure cause blurred and uneven images, resulting in a reduction in image quality. In order to detect ink ejection failure, an inkjet recording device is capable of distinguishing between a recording medium and colored ink (CMYK ink) based on a reading density difference between the recording medium and colored ink (CMYK ink), for example. Equipped with an image reading sensor (inline sensor).

For example, in Patent Document 1, colored ink is ejected onto a blank sheet of paper, and a test pattern of white ink is ejected onto the colored ink, thereby creating a state in which the white ink is overlaid on the colored ink. A technique for detecting ejection failure has been disclosed.

Japanese Patent Application Publication No. 2010-125605

However, with the image reading sensor described above, for example, when white ink is applied on white paper, it is difficult to produce a difference in reading density between the white paper and the white ink, making it difficult to distinguish between the white paper and the white ink. There was a problem.

Furthermore, in the technology described in Patent Document 1, in order to detect a discharge failure of white ink, it is necessary to apply colored ink as a base onto a blank sheet of paper, so there is a problem that the amount of colored ink consumed increases. be.

An object of the present invention is to provide an ink detection device, an ink detection method, and an inkjet recording device that can accurately distinguish between a recording medium and ink without increasing ink consumption.

In order to achieve the above object, the ink detection device according to the present invention includes:
an irradiation unit that irradiates red light as irradiation light to the recording medium to which the ink is attached;
a light receiving unit that receives red light among the light transmitted through the recording medium based on the irradiation light;
a detection unit that detects the adhesion state of the ink to the recording medium based on the intensity of the received red light;
Equipped with
The intensity of the light received by the light receiving section is the intensity of each light received by the light receiving section when the irradiation light is applied to each of a plurality of locations provided along the transport direction of the recording medium. is the average value of

The inkjet recording device according to the present invention includes:
The ink detection apparatus includes the ink detection device and an ejection section that ejects the ink onto the recording medium.

According to the present invention, it is possible to accurately discriminate between a recording medium and ink without increasing ink consumption.

1 is a diagram showing a schematic configuration of an inkjet recording apparatus according to an embodiment of the present invention. 1 is a block diagram showing the main functional configuration of an inkjet recording apparatus according to an embodiment of the present invention. FIG. 3 is a diagram showing the spectral reflectance of a recording medium and the spectral reflectance of white ink. 3 is a flowchart illustrating an example of ink detection processing.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of an inkjet recording apparatus 1 in this embodiment. The inkjet recording apparatus 1 includes a paper feed section 10, an image recording section 20, a paper discharge section 30, and a control section 40 (see FIG. 2).

In the inkjet recording apparatus 1, under the control of the control section 40, the recording medium P stored in the paper feed section 10 is conveyed to the image recording section 20, and the image recording section 20 records an image on the recording medium P. The recorded recording medium P is conveyed to the paper discharge section 30. As the recording medium P, in addition to paper such as plain paper or coated paper, various media capable of fixing ink that has landed on the surface, such as cloth or sheet-like resin, can be used.

The paper feed unit 10 includes a paper feed tray 11 that stores the recording medium P, and a medium supply unit 12 that transports and supplies the recording medium P from the paper feed tray 11 to the image recording unit 20. The medium supply unit 12 includes a ring-shaped belt whose inner side is supported by two rollers, and rotates the rollers with the recording medium P placed on this belt to feed the recording medium P from the paper feed tray 11. It is transported to the image recording section 20.

The image recording section 20 includes a transport drum 21 , a delivery unit 22 , a heating section 23 , a head unit 24 , a fixing section 25 , and a delivery section 26 .

The conveyance drum 21 holds the recording medium P on its cylindrical outer curved surface (conveyance surface) and rotates around a rotating shaft extending in a direction perpendicular to the drawing in 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. The transport drum 21 includes a claw portion (not shown) and a suction portion (not shown) for holding the recording medium P on its transport surface. The recording medium P is held on the conveyance surface by having its ends pressed by the claws and drawn toward the conveyance surface by the suction section. The transport drum 21 has a transport drum motor (not shown) for rotating the transport drum 21, and rotates by an angle proportional to the amount of rotation of the transport drum motor.

The delivery unit 22 delivers the recording medium P transported by the medium supply section 12 of the paper feed section 10 to the transport drum 21 . The delivery unit 22 is provided at a position between the medium supply section 12 of the paper supply section 10 and the conveyance drum 21, and picks up one end of the recording medium P conveyed from the medium supply section 12 by holding it with a swing arm section 221. , and delivered to the transport drum 21 via the delivery drum 222.

The heating unit 23 is provided between the arrangement position of the delivery drum 222 and the arrangement position of the head unit 24, and is configured to heat the transport drum 21 so that the recording medium P transported by the transport drum 21 has a temperature within a predetermined temperature range. The conveying surface of the recording medium P and the recording medium P are heated. The heating unit 23 includes, for example, an infrared heater, and generates heat by supplying electricity to the infrared heater based on a control signal supplied from the control unit 40 (see FIG. 2).

The head unit 24 injects the recording medium P from nozzle openings provided on the ink ejection surface facing the conveyance surface of the conveyance drum 21 at appropriate timing according to the rotation of the conveyance drum 21 holding the recording medium P. Record an image by ejecting ink. The head unit 24 is arranged such that the ink ejection surface and the conveyance surface are separated by a predetermined distance.

In the inkjet recording apparatus 1 according to the present embodiment, five head units 24 respectively correspond to five colors of ink: white (W), yellow (Y), magenta (M), cyan (C), and black (K). The colors are arranged in the order of W, Y, M, C, and K from the upstream side in the conveyance direction of the recording medium P at predetermined intervals.

Each head unit 24 includes a recording head 242 (see FIG. 2, which corresponds to the "ejection section" of the present invention). The recording head 242 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 causes the piezoelectric element to perform a deforming operation is input, the pressure chamber is deformed by the deformation of the piezoelectric element, the pressure within the pressure chamber changes, and ink is ejected from a nozzle communicating with the pressure chamber.

The arrangement range of the nozzles included in the recording head 242 in the orthogonal direction covers the width in the orthogonal direction of the area on which an image is recorded on the recording medium P conveyed by the conveyance drum 21. The head unit 24 is used with its position fixed relative to the rotation axis of the transport drum 21 when recording an image. That is, the inkjet recording apparatus 1 is a single-pass type inkjet recording apparatus.

The ink ejected from the recording head 242 has the property of changing its phase to a gel-like or sol-like state depending on the temperature and hardening when irradiated with energy rays such as ultraviolet rays. Further, in this embodiment, an ink that is gel-like at room temperature and becomes sol-like when heated is used. The head unit 24 includes an ink heating section (not shown) that heats ink stored within the head unit 24. The ink heating section operates under the control of the control section 40 and heats the ink to a temperature at which it becomes a sol. The head unit 24 ejects ink that is heated and becomes a sol. When this sol-like ink is ejected onto the recording medium P, the ink droplets land on the recording medium P and are naturally cooled, so that the ink quickly becomes a gel and solidifies on the recording medium P.

The fixing section 25 has a light emitting section arranged across the width of the transport drum 21 in the orthogonal direction. The fixing unit 25 applies a predetermined energy to the ink ejected onto the recording medium P by irradiating the recording medium P placed on the conveyance drum 21 with energy rays such as ultraviolet rays from a light emitting unit. , thereby curing and fixing the ink. The light emitting section of the fixing section 25 is arranged to face the transport surface of the transport drum 21 between the position of the recording head 242 and the position of the delivery drum 261 (delivery section 26) in the transport direction.

The delivery unit 26 includes a belt loop 262 having a ring-shaped belt whose inner side is supported by two rollers, and a cylindrical delivery drum 261 that delivers the recording medium P from the transport drum 21 to the belt loop 262. The recording medium P transferred from the conveyance drum 21 onto the belt loop 262 by the transfer drum 261 is conveyed by the belt loop 262 and sent to the paper discharge section 30 .

The paper discharge section 30 has a plate-shaped paper discharge tray 31 on which the recording medium P sent out from the image recording section 20 by the delivery section 26 is placed.

FIG. 2 is a block diagram showing the main functional configuration of the inkjet recording apparatus 1. As shown in FIG. The inkjet recording apparatus 1 includes a heating section 23, a recording head drive section 241 and a recording head 242 included in a head unit 24, a fixing section 25, a detection unit 27A, a control section 40, a conveyance drive section 51, and an input/output section. An interface 52 is provided.

The recording head driving section 241 drives the recording head 242 by supplying a driving signal to the recording element of the recording head 242 to deform the piezoelectric element in accordance with image data at an appropriate timing based on the control of the control section 40. The amount of ink 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 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 recording 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 in place 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 a print job (image recording command) input from the external device 2 via the input/output interface 52 and image data related to the print job. 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 21 based on the control signal supplied from the control section 40, and rotates the conveyance drum 21 at a predetermined speed and timing. Further, the conveyance drive section 51 supplies drive signals to motors for operating the medium supply section 12, the transfer unit 22, and the delivery section 26 based on the control signal supplied from the control section 40, and transfers the recording medium P. Supply to the transport drum 21 and discharge from the transport drum 21 are performed.

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 an image recording command (print job), image data, etc. to the control unit 40 via an input/output interface 52.

According to the above configuration, the recording medium P stored in the paper feed section 10 is conveyed to the image recording section 20, where an image is recorded with ink ejected from the nozzles, and the recording medium P is transferred to the delivery section 26. The paper is sent out to the paper discharge section 30. However, ink may not be ejected to a predetermined area on the recording medium P due to nozzle clogging or a malfunction of the ejection mechanism. Since nozzle clogging or the like causes deterioration of image quality, it is necessary to perform a test (nozzle missing test) to determine whether or not ink is reliably ejected from the nozzle.

Next, the nozzle missing inspection will be explained. Here, a case will be described in which the recording medium P is a blank paper and white ink is ejected onto the blank paper. The white ink contains, for example, a component (eg, titanium oxide) that absorbs light with wavelengths in the visible light region. Note that the area where dots are recorded when the white ink ejected from the nozzle lands on the white paper is referred to as the "landing area".

The nozzle missing test is performed by an ink detection device. The ink detection device in this embodiment includes a detection unit 27A and a control section 40. The detection unit 27A includes an irradiating section 27 and a light receiving section 28.

The irradiating section 27 and the light receiving section 28 are arranged to face the conveying surface of the conveying drum 21 between the position of the fixing section 25 and the position of the delivery drum 261 (delivery section 26) in the conveying direction.

The irradiation section 27 operates under the control of the control section 40 and irradiates the landing section with irradiation light.

The irradiation section 27 irradiates the landing section with irradiation light. A known light source is used for the irradiation section 27. Specifically, the irradiation section 27 uses a red LED (light emitting diode). Note that a standard light source (light source A), a white LED, or the like may be used as the light source.

The light receiving section 28 is arranged so as to be able to receive light transmitted through the landing section based on the irradiated light.

The light receiving section 28 includes a light sensor 281 that receives light with a wavelength in the visible light range. For example, an in-line sensor is used as the optical sensor 281. The inline sensor is composed of an image line sensor such as a CCD or CMOS.

The light receiving section 28 operates the optical sensor 281 under the control of the control section 40 . Thereby, the optical sensor 281 detects the intensity of light that has passed through the landing section based on the irradiation light in accordance with the timing at which the irradiation section 27 irradiates the landing section with the irradiation light.

Note that when the irradiation section 27 irradiates the landing section with irradiation light of a predetermined wavelength and the optical sensor 281 detects the light of the predetermined wavelength, the intensity of the irradiation light of the irradiated predetermined wavelength and the detected predetermined wavelength The ratio of wavelength to light intensity is called "spectral reflectance."

Due to poor ejection of white ink, the white ink may not land on the white paper, or the ejected white ink may not land on a predetermined landing area. The spectral reflectance when the white ink lands on the landing portion is the spectral reflectance of the white ink, which is the ratio of the intensity of the irradiation light irradiated to the white ink and the intensity of the received light. On the other hand, the spectral reflectance when the white ink does not land on the landing area is the spectral reflectance of the white paper, which is the ratio of the intensity of the irradiated light irradiated to the white paper (the background of the white paper) and the intensity of the received light. It is. The spectral reflectance of white ink and the spectral reflectance of white paper are different. Therefore, based on the spectral reflectance, it is possible to determine whether or not there is a defective ejection of white ink.

Next, the spectral reflectance of white paper and the spectral reflectance of white ink will be explained with reference to FIG. 3. FIG. 3 is a diagram showing the spectral reflectance of white paper and the spectral reflectance of white ink. In the following description, Maricoat and Invercoat (registered trademark) manufactured by Hokuetsu Kishu Paper Co., Ltd. are cited as examples of white paper. The horizontal axis of FIG. 3 shows the wavelength [nm] of the light received by the light receiving section 28, and the vertical axis of FIG. 3 shows the spectral reflectance [%]. In FIG. 3, the spectral reflectance of Malicoat is shown by a solid line, the spectral reflectance of Invercoat is shown by a chain line, and the spectral reflectance of white ink is shown by a chain double-dot line. Further, in FIG. 3, the difference between the spectral reflectance of Malicoat and the white ink is shown by a broken line, and the difference between the spectral reflectance of Invercoat and the spectral reflectance of white ink is shown by a dotted line.

First, the difference between the spectral reflectance of Malicoat and the spectral reflectance of white ink (spectral reflectance difference) shown by the broken line in FIG. 3 will be explained. When the wavelength of the irradiation light is 640 [nm], the spectral reflectance difference is 19%. Further, when the wavelength of the irradiation light is 660 [nm], the spectral reflectance difference is 20%. Further, when the wavelength of the irradiation light is 680 [nm], the spectral reflectance difference is 21%. Further, when the wavelength of the irradiation light is 700 [nm], the spectral reflectance difference is 22%. On the other hand, when the wavelength range of the irradiation light is 450 [nm] or more and 640 [nm] or less, the spectral reflectance difference is 18% or less. This shows that the spectral reflectance difference is relatively large when the wavelength range of the irradiated light is 640 [nm] or more and 700 [nm] or less.

Next, the difference between the spectral reflectance of the invar coat and the spectral reflectance of the white ink (spectral reflectance difference) shown by the dotted line in FIG. 3 will be explained. When the wavelength of the irradiation light is 640 [nm], the spectral reflectance difference is 10%. Further, when the wavelength of the irradiation light is 660 [nm], the spectral reflectance difference is 11%%. Further, when the wavelength of the irradiation light is 680 [nm], the spectral reflectance difference is 12%. Furthermore, when the wavelength of the irradiation light is 700 [nm], the spectral reflectance difference is 12%. On the other hand, when the wavelength range of the irradiation light is 450 [nm] or more and 640 [nm] or less, the spectral reflectance difference is 9% or less. This shows that the spectral reflectance difference is relatively large when the wavelength range of the irradiated light is 640 [nm] or more and 700 [nm] or less.

What can be said in common from the above is that when the wavelength range of irradiation light is 640 [nm] or more and 700 [nm] or less, the spectral reflectance of white paper (Maricoat, Invercoat) and the spectral reflectance of white ink are different. It can be seen that the difference is relatively large. In other words, it can be seen that white ink absorbs light with longer wavelengths in the visible light region (for example, red light) than light with shorter wavelengths. Here, the above-mentioned 700 [nm] means an example of the longest wavelength in the wavelength region of red light. Further, the above-mentioned 640 [nm] means an example of the lower limit value of the wavelength range of red light that is allowable in terms of detection accuracy of nozzle discharge failure. Therefore, the lower limit value of the wavelength range of red light becomes shorter as the detection accuracy of nozzle discharge failure increases.

In this embodiment, the irradiation unit 27 emits red light as irradiation light, and the optical sensor 281 receives the red light. The control unit 40 calculates the spectral reflectance based on the intensity of the received red light, and determines whether the spectral reflectance is the spectral reflectance of white ink or the spectral reflectance of white paper (the background of the white paper). It has a function as a detection unit that determines whether the nozzle is defective or not and detects discharge failure of the nozzle. In the following description, the red light emitted by the irradiation unit 27 will be referred to as "first red light." Further, the red light received by the light receiving section 28 is referred to as "second red light".

The irradiation section 27 in this embodiment irradiates the landing section with the first red light as irradiation light. The wavelength of the first red light is within a wavelength range of 640 [nm] or more and 700 [nm] or less, where the difference between the spectral reflectance of the white paper and the spectral reflectance of the white ink is relatively large.

The light receiving section 28 in this embodiment includes a bandpass filter 282 (corresponding to the "second transmission member" of the present invention). The bandpass filter 282 is arranged between the conveying surface of the conveying drum 21 and the optical sensor 281. The bandpass filter 282 transmits only the second red light among the light that has passed through the landing section based on the irradiation light, and blocks light other than the second red light. The wavelength range λ _w2r of the second red light transmitted by the bandpass filter 282 is 640 [nm] or more and 700 [nm] or less, where the difference between the spectral reflectance of white paper and the spectral reflectance of white ink is relatively large. This is the wavelength region.

The optical sensor 281 detects the intensity of the second red light under the control of the control unit 40. The control unit 40 (detection unit) detects the discharge state of the white ink (adhesion state of the ink to the white paper) based on the intensity of the detected second red light.

Specifically, the control unit 40 calculates the spectral reflectance of a predetermined wavelength from the intensity of the first red light irradiated from the irradiation unit 27 to the landing area and the intensity of the second red light detected by the optical sensor 281. calculate. If the spectral reflectance of the predetermined wavelength is close to the spectral reflectance of blank paper, the control unit 40 determines that the spectral reflectance of the predetermined wavelength is the spectral reflectance of blank paper, and that the ejection of white ink is defective. Further, if the spectral reflectance difference at the predetermined wavelength is close to the spectral reflectance of the white ink, the control unit 40 determines that there is no white ink ejection defect by using the spectral reflectance at the predetermined wavelength as the spectral reflectance of the white ink. In other words, white paper and white ink are discriminated based on the reading contrast difference between white paper and white ink based on spectral reflectance.

More specifically, when the recording medium P is Maricoat, the control unit 40 controls the intensity of the light with a wavelength of 700 [nm] irradiated onto the landing part and the wavelength of 700 [nm] detected by the optical sensor 281. The spectral reflectance is calculated from the light intensity. If the spectral reflectance is closer to the spectral reflectance of Malicoat than that of white ink, the control unit 40 determines that the spectral reflectance is that of white paper (see FIG. 3) and that the white ink is defective in ejection. Further, if the spectral reflectance is closer to the spectral reflectance of white ink than that of Maricoat, the control unit 40 determines that it is the spectral reflectance of white ink (see FIG. 3) and that there is no defective ejection of white ink.

In addition, when the recording medium P is invar coated, the control unit 40 controls the intensity of the light with a wavelength of 700 [nm] irradiated to the landing part and the light with a wavelength of 700 [nm] detected by the optical sensor 281. Spectral reflectance is calculated from the intensity. If the spectral reflectance is closer to the spectral reflectance of the invar coat than that of the white ink, the control unit 40 determines that the spectral reflectance is the spectral reflectance of white paper (see FIG. 3) and that the white ink is defective in ejection. Further, if the light reflectance is closer to the spectral reflectance of the white ink than that of the invar coat, the control unit 40 determines that the spectral reflectance is the spectral reflectance of the white ink (see FIG. 3), and determines that there is no defective ejection of the white ink. .

Next, ink detection processing will be explained with reference to FIG. 4. FIG. 4 is a flowchart illustrating an example of ink detection processing. Here, it is assumed that the irradiation section 27 irradiates the landing section with the first red light as irradiation light. Furthermore, the bandpass filter 282 blocks the light that passes through the landing section based on the irradiation light, except for the second red light, and the optical sensor 281 receives the second red light. shall be. This flow starts when a print job is executed.

First, in step S100, the control section 40 (detection section) obtains the intensity of light that has passed through the landing section based on the irradiation light. The control unit 40 calculates the spectral reflectance of a predetermined wavelength based on the intensity of the acquired light.

Next, in step S110, the control unit 40 determines whether the spectral reflectance of the predetermined wavelength is close to the spectral reflectance of white ink or the spectral reflectance of white paper. If the spectral reflectance of the predetermined wavelength is close to the spectral reflectance of white ink (step S110: YES), the process transitions to step S120. If the spectral reflectance of the predetermined wavelength is not the spectral reflectance of white ink but is close to the spectral reflectance of white paper (step S110: NO), the process transitions to step S130.

In step S120, the control unit 40 determines that there is no white ink ejection failure. Thereafter, the process shown in FIG. 4 ends.

In step S130, the control unit 40 determines that there is a white ink ejection failure. Thereafter, the process shown in FIG. 4 ends.

According to the ink detection device in the above embodiment, the irradiation unit 27 irradiates the white paper with the first red light as irradiation light onto the white paper onto which white ink has been ejected from the recording head 242, and the irradiation unit 27 irradiates the white paper with the first red light as the irradiation light. It includes a light receiving section 28 that receives the second red light among the lights, and a control section 40 that detects the ejection state of white ink from the recording head 242 based on the intensity of the received second red light. As a result, there is no need to apply colored ink as a base, so it is possible to detect white paper and white ink with high accuracy without increasing the amount of colored ink consumed. As a result, it becomes possible to determine whether the white ink is defective in ejection.

Further, according to the ink detection device in the above embodiment, a general light source such as a red LED is used as the irradiation section 27, and a special light source such as an ultraviolet LED is not used, thereby reducing manufacturing costs. becomes possible.

In addition, the wavelength range λ _w1r of the first red light is 640 nm, which is a wavelength range in which a larger spectral reflectance difference can be obtained in order to increase the reading contrast difference between white paper and white ink due to spectral reflectance. ] or more and 700 [nm] or less. This makes it possible to detect blank paper and white ink with even higher accuracy.

Furthermore, in the light receiving section 28, the sensitivity to the wavelength of the second red light is higher than the sensitivity to the wavelength of the light that has passed through the landing section except for the second red light. This also makes it possible to detect blank paper and white ink with higher accuracy.

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

For example, in the above embodiment, the wavelength range λ _w2r of the second red light is the same wavelength range as the first red light, but the present invention is not limited to this, and the wavelength range λ _w2r of the second red light is The wavelength range may be different from that of the first red light. For example, the wavelength range λ _w1r of the first red light is 640 [nm] or more and 700 [nm] or less, whereas the wavelength range λ _w2r of the second red light is 680 [nm] or more and 700 [nm] or less. The following may be sufficient. As shown in FIG. 3, as the wavelength of the second red light becomes longer, the difference in spectral reflectance between Malicoat and Invarcoat increases, so it is possible to detect white paper and white ink with higher accuracy. It becomes possible.

Further, when the light irradiated from the irradiation unit 27 is white light including the first red light, for example, the light irradiated from the irradiation unit 27 (white light A bandpass filter (corresponding to the "first transmitting member" of the present invention) that transmits only the first red light among the light) may be disposed.

Further, for example, in the above embodiment, the detection of the ink ejection state is performed based on the intensity of the light that has passed through one landing part based on the irradiation light, but the present invention is not limited to this. Alternatively, the determination may be performed based on the average value of the intensity of light that has passed through the landing portion. Note that the plurality of landing portions may be provided, for example, along the conveyance direction of the recording medium P. By averaging the intensity of the light, it is possible to increase the signal-to-noise ratio, thereby increasing the detection accuracy of the ink ejection state.

Further, for example, in the embodiment described above, the ejection state is detected for white ink, but the present invention is not limited to this, and the present invention is not limited to this. Any ink that causes a rate difference may be used. For example, transparent ink may be used.

Further, for example, in the above embodiment, the upper limit of the wavelength of the first red light is 700 [nm], but even if the wavelength of the first red light is 750 [nm], blank paper and white ink can be detected. Therefore, the upper limit of the wavelength of the first red light may be set to 750 [nm].

Further, in the above embodiment, the inkjet recording apparatus 1 to which the ink detection device according to the present invention is applied has been described, but the present invention can also be applied to image forming apparatuses other than the inkjet recording apparatus 1. .

Next, examples of the present invention will be described.

In the examples, the white ink described below was used. In the example, the above-mentioned inkjet device 1 was used to eject white ink onto a blank sheet of paper, irradiate the landing area with irradiation light, and determine whether or not the ejection of the white ink was defective.

<Example of white ink> (mass%)
White dispersion 25.0
Photopolymerizable compound 1 5.0
Photopolymerizable compound 2 32.9
Photopolymerizable compound 3 35.0
Photoinitiator 2 1.5
Surfactant 1 0.1
Polymerization inhibitor 1 0.2
Gelling agent 1 0.1
Gelling agent 2 0.2

<White dispersion>
71 parts by mass of tripropylene glycol diacrylate and 9 parts by mass of Ajisper PB824 (Ajinomoto Fine Techno Co., Ltd.) as a dispersant were placed in a stainless steel beaker, and stirred for 1 hour while heating on a hot plate at 65°C. The dispersant was dissolved.

Next, the obtained dispersant solution was cooled to room temperature, and then 20 parts by mass of Pigment Black 7 (#52; Mitsubishi Chemical Corporation) was added as a black pigment to prepare a mixed solution.

Next, the mixed solution was put into a glass bottle with 200 g of zirconia beads having a diameter of 0.5 mm, the bottle was tightly stoppered, and the bottle was dispersed in a paint shaker for 5 hours. The zirconia beads were removed from the dispersion to prepare a black (K) pigment dispersion.

(Preparation of white dispersion)
In preparing the above black dispersion, titanium oxide (TCR-52; Sakai Chemical Industry Co., Ltd.) was used as a white pigment instead of the black pigment, and the amount added was changed to 60 parts by mass. (W) A pigment dispersion liquid was prepared.

<Photopolymerizable compound>
Compound 1: N-vinylcaprolactam (manufactured by BASF)
Compound 2: Tripropane glycol diacrylate (manufactured by Shin-Nakamura Chemical Industry Co., Ltd.)
Compound 3: 3PO modified trimethylolpropane triacrylate

<others>
Photoinitiator 2: IRGACURE 819 (manufactured by BASF)
Surfactant 1: BYK UV3500 (manufactured by BYK Chemie Japan)
Polymerization inhibitor 1: Irgatab UV10 (manufactured by BASF)
Gelling agent G1: WEP2 (manufactured by NOF Corporation)
Gelling agent G2: EMALEX EG-di-S (manufactured by Nippon Emulsion Co., Ltd.)

(white ink)
One feature of the white ink according to the present invention is that titanium oxide is used as the white pigment, and it is preferable that 50% by mass or more of the titanium oxide is rutile titanium dioxide. The titanium oxide used in the present invention can be further surface-treated with alumina, silica, zinc, zirconia, organic substances, and the like.

The average particle size of the titanium oxide particles according to the present invention is preferably within the range of 50 to 500 nm, more preferably within the range of 100 to 300 nm. By adjusting the average particle size of the titanium oxide particles to the range specified above, the effects of the present invention are significantly exhibited, and the effects of the invention are significantly improved, such as suppressing nozzle clogging in the inkjet head and improving the storage stability of the white ink composition for inkjet. In particular, it is preferable because it can sufficiently exhibit the suppression of sedimentation) and the ability to hide the print substrate.

Titanium oxide particles applicable to the present invention are also available as commercial products, such as CR-50, CR-57, CR-58, CR-67, CR-Super- manufactured by Ishihara Sangyo Co., Ltd. 70, CR-80, CR-90, CR-90-2, CR-93, CR-95, CR-EL, R-550, R-580, R-630, R-670, R-680, R- 780, R-820, R-830, R-850, R-930, R-980, PF-736, PF-737, PF-742, SR-41, R-5N, R- manufactured by Sakai Chemical Industry Co., Ltd. 7E, R-11P, R-21, R-25, R-32, R-42, R-44, R-45M, R-62N, R-310, R-650, TCR-52, GTR-100, Examples include D-918 and FTR-700.

The amount of titanium oxide added in the white ink of the present invention is preferably in the range of 5.0 to 35% by mass, more preferably in the range of 10 to 20% by mass, based on the total mass of the ink. By adjusting the amount of titanium oxide added in the white ink according to the present invention within the range specified above, it is possible to achieve both the storage stability of the white ink (especially suppression of sedimentation) and the shielding property for the print substrate. be able to.

The white ink according to the present invention may also contain a known white pigment other than the titanium oxide according to the present invention, if necessary. Other white pigments applicable to the present invention include, for example, inorganic white pigments, organic white pigments, and white hollow polymer particles.

Inorganic white pigments include alkaline earth metal sulfates such as barium sulfate, alkaline earth metal carbonates such as calcium carbonate, silicas such as finely divided silicic acid and synthetic silicates, calcium silicate, alumina, and alumina. Examples include hydrates, zinc oxide, talc, clay, etc.

1 Inkjet recording device 2 External device 10 Paper feeding section 11 Paper feeding tray 12 Medium supply section 20 Image recording section 21 Conveyance drum 22 Delivery unit 23 Heating section 24 Head unit 25 Fixing section 26 Delivery section 27A Detection unit 27 Irradiation section 28 Light receiving section 30 Paper discharge section 40 Control section 242 Recording head 281 Optical sensor 282 Band pass filter

Claims (9)

an irradiation unit that irradiates red light as irradiation light to the recording medium to which the ink is attached;
a light receiving unit that receives red light among the light transmitted through the recording medium based on the irradiation light;
a detection unit that detects the adhesion state of the ink to the recording medium based on the intensity of the received red light;
Equipped with
The intensity of the light received by the light receiving section is the intensity of each light received by the light receiving section when the irradiation light is applied to each of a plurality of locations provided along the transport direction of the recording medium. is the average value of
Ink detection device. an irradiation unit that irradiates red light as irradiation light to the recording medium to which the ink is attached;
a light receiving unit that receives red light among the light transmitted through the recording medium based on the irradiation light;
a detection unit that detects the adhesion state of the ink to the recording medium based on the intensity of the received red light;
Equipped with
the ink is white ink;
Ink detection device. The wavelength of the red light as the irradiation light is 640 nm or more and 700 nm or less,
The ink detection device according to claim 1 or 2 . The irradiation unit includes a first transmission member that transmits only the red light as the irradiation light among the light irradiated from the irradiation unit.
The ink detection device according to any one of claims 1 to 3 . In the light receiving section, the sensitivity to the wavelength of the red light is higher than the sensitivity to the wavelength of the light transmitted through the recording medium excluding the red light.
The ink detection device according to any one of claims 1 to 4 . The light receiving section includes a second transmitting member that transmits only the red light among the light that has passed through the recording medium.
The ink detection device according to claim 5 . The wavelength range of the red light received by the light receiving unit is the same wavelength range as the red light as the irradiation light,
The ink detection device according to any one of claims 1 to 6 . The wavelength range of the red light received by the light receiving unit is a different wavelength range from the red light as the irradiation light,
The ink detection device according to any one of claims 1 to 6 . An inkjet recording apparatus comprising: the ink detection device according to claim 1 ; and an ejection section that ejects the ink onto the recording medium.

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