JP2022021038A - Printer and printing method - Google Patents

Abstract

To enable printing with an excellent printing quality even wet-on-wet coating of aqueous inks by controlling a dry state.SOLUTION: A control part 12 operates a dry condition of a pre-dry part 21 based on a detection result of a detection part 23, and controls a dry state of a color ink after drying by the pre-dry part 21 and before a white ink is discharged. With this, a dry state of the color ink is controlled before printing by the white ink so as to bring a state of the color ink to a state for facilitating fixation of the white ink. As a result of this, even wet-on-wet coating of aqueous inks of the color ink and the white ink can be printed with an excellent printing quality.SELECTED DRAWING: Figure 2

Description

The present invention relates to a printing apparatus and a printing method for printing on a printing medium with a water-based ink, and more particularly to a technique for drying the ink.

Conventionally, as a first device of this type, there is one provided with an ink applying device, a liquid absorbing device, a fixing belt, an image pickup device, and a device control unit (see, for example, Patent Document 1). The ink applying device ejects ink to a printing medium to perform printing. The liquid absorber reduces the liquid component from the ink ejected to the print medium. The fixing belt is pressed against a printing medium containing ink having a reduced liquid component to perform heat and pressure fixing. The photographing device photographs the surface of the fixing belt and detects the presence or absence of adhesion of the liquid component. The device control unit changes the operating conditions of the liquid absorbing device according to the presence or absence of adhesion of the liquid component on the fixing belt, and sets the operating conditions so that the liquid does not adhere.

Further, as a second device of this type, there is one provided with a treatment liquid application unit, an image forming unit, a drying processing unit, and an irradiation unit (see, for example, Patent Document 2). The treatment liquid application unit applies a treatment liquid that causes an agglutination reaction with the ink to the print medium. The image forming unit attaches ink to the print medium via the image forming drum. The drying treatment unit heats the printing medium so that the surface temperature becomes 35 to 55 ° C. to dry the moisture. In the irradiation unit, the ink is cured and fixed by irradiating the print medium with ultraviolet rays. A paper moisture meter is provided inside the irradiation unit. Of the water content measured by the paper moisture meter, drying is performed so that the difference in water content between the non-image area and the ink-applied area is a predetermined value (2 to 4 g / m ² ).

Further, as a third device of this type, there is one provided with a drying device, a detection device, and a control device (see, for example, Patent Document 3). The drying device dries the printed medium on which the ink is ejected. The detection device detects the moisture content of the print medium immediately after being dried by the drying device. Based on the measurement result of the moisture content by the detection device, the control device controls the drying conditions of the temperature and the air volume so that the drying state of the print medium by the drying device becomes constant.

Japanese Unexamined Patent Publication No. 2019-14246 Japanese Unexamined Patent Publication No. 2013-180453 Japanese Unexamined Patent Publication No. 2000-79678

However, in the case of the conventional example having such a configuration, there are the following problems.
That is, a printing apparatus that ejects a first water-based ink onto a printing medium to print an image, then performs pre-drying, superimposes the first water-based ink on the first water-based ink, ejects a second water-based ink, and then performs main drying. be. In such a printing apparatus for recoating water-based ink, an appropriate drying process may not be possible by the conventional method such as the first to third apparatus. Therefore, when the water-based ink is overcoated, there is a problem that printing may not be possible with good print quality.

That is, the first to third devices detect the dry state of the print medium after the drying process after the printing process, and operate the drying conditions according to the detected state. However, in the case of printing in which the second water-based ink is ejected on top of the first water-based ink, the dry state is detected and the drying conditions are operated as in the first to third devices after the main drying. However, it may not be possible to perform proper drying to obtain good print quality.

The present invention has been made in view of such circumstances, and provides a printing apparatus and a printing method capable of printing with good print quality even if a water-based ink is overcoated by controlling a dry state. The purpose is to do.

As a result of diligent research to solve the above problems, the present inventor has obtained the following findings.
It has been found that when pre-drying is performed after printing the first water-based ink, the following problems occur depending on the dry state of the first water-based ink. That is, (1) insufficient drying causes color mixing between the first water-based ink and the second water-based ink. Further, when the first water-based ink is a single color, an ink flow occurs in which the ink flows from a desired position and shifts. (2) In overdrying, ink flow occurs in the first water-based ink and the second water-based ink.

By the way, when the print medium is hydrophobic, a process of forming a primer layer on the print medium is performed prior to ejecting the first water-based ink. In the first water-based ink, the components of the primer layer are dissolved, and the fixing power is obtained by binding and aggregating with the pigment contained in the first water-based ink. In order to improve the coating state of the second water-based ink, when the first water-based ink dries, the component of the primer layer must be appropriately dissolved in the water content of the first water-based ink. is necessary.

However, when the first water-based ink of (1) is insufficiently dried, the component of the primer layer is diluted with the first water-based ink. If the second water-based ink is ejected in this state, sufficient fixing force cannot be obtained for the second water-based ink. Therefore, the above-mentioned color mixing and printing defects of ink flow occur.

On the other hand, when the first water-based ink of (2) is overdried, the first water-based ink has almost no water content. If there is no water in the film of the first water-based ink, the components of the primer layer cannot be dissolved. Although water is supplied from the second water-based ink, in order to exert the fixing power, after the second water-based ink is ejected, the water dissolves in the film of the first water-based ink and becomes the first water-based ink. It is necessary to elute the components of the primer layer. However, in the overdried state, the water does not immediately dissolve in the water-based ink, and it takes time to elute the components of the primer layer. As a result, the time required for charging to the main drying is shorter than the time required for elution of the components of the primer layer. Therefore, as a result, before the second water-based ink is fixed, the hot air of the main drying causes an ink flow in the first water-based ink and the second water-based ink. Even when the primer layer is not formed, the same problem as described above may occur when the water-based ink is repeatedly applied. The present invention based on such findings is configured as follows.

That is, the invention according to claim 1 comprises a transport unit that conveys a print medium, a first printing unit that ejects a first water-based ink to the print medium conveyed by the transport unit, and the first printing unit. A drying unit that dries the first water-based ink ejected to the printing medium in the printing unit, and a second printing unit that ejects a second water-based ink to the printing medium dried by the drying unit. Detection of detecting the dried state of the first water-based ink ejected to the printing medium by the first printing unit after drying by the drying unit and before printing by the second printing unit. Based on the detection result of the unit and the detection unit, the drying conditions of the drying unit are manipulated to perform the first method after drying by the drying unit and before the second water-based ink is ejected. It is characterized by including a control unit for controlling a dry state of the water-based ink.

[Action / Effect] According to the first aspect of the present invention, the control unit operates the drying conditions of the drying unit based on the detection result of the detecting unit, and after drying by the drying unit, the second unit. The dry state of the first water-based ink before the water-based ink is ejected is controlled. Therefore, since the dry state of the first water-based ink is controlled before printing with the second water-based ink, the state of the first water-based ink can be changed to a state in which the second water-based ink is easily fixed. As a result, it is possible to print with good print quality even if the water-based ink is overcoated.

Further, in the present invention, it is preferable that the control unit operates at least one of the temperature and the drying time of the drying unit (claim 2).

By operating at least one of the temperature and the drying time in the drying portion, the drying state of the first water-based ink can be controlled. Therefore, the dry state of the first water-based ink can be easily controlled to a desired state so that the second water-based ink can be easily fixed.

Further, in the present invention, it is preferable that the drying unit includes a gas discharging unit that discharges the dried gas to the printing medium (claim 3).

The first water-based ink can be dried by ejecting the dried gas from the gas ejection unit onto the printing medium.

Further, in the present invention, it is preferable that the control unit operates at least one of the temperature, air volume, and discharge time of the gas discharged from the gas discharge unit (claim 4).

The dry state of the first water-based ink can be controlled by manipulating at least one of the temperature, air volume, and ejection time of the gas ejected from the gas ejection unit. Therefore, the dry state of the first water-based ink can be easily controlled to a desired state so that the second water-based ink can be easily fixed.

Further, in the present invention, it is preferable that the control unit sets the temperature of the gas discharged from the gas discharge unit in the range of 40 ° C. or higher and 80 ° C. or lower (claim 5).

By setting the temperature of the gas in the range of 40 ° C. or higher and 80 ° C. or lower, it is possible to prevent the print medium from being altered by heat even if the print medium is sensitive to high temperatures. Therefore, even after the first water-based ink is dried by the drying portion, printing with the second water-based ink can be performed with high quality.

Further, in the present invention, it is preferable that the detection unit measures the water content of the first water-based ink ejected to the print medium (claim 6).

The detection unit measures the water content of the first water-based ink, so that the dry state of the first water-based ink can be determined. Therefore, the dry state of the first water-based ink can be detected with high accuracy.

Further, in the present invention, the control unit has a water content of 0% or more detected by the detection unit with respect to the water content of the first water-based ink ejected from the first printing unit to the print medium. It is preferable to operate the drying portion so that the content is 99.2% or less (claim 7).

The first water-based ink contains a pigment, a resin, an organic solvent, and water. When the solvent has a high boiling point, the first water-based ink is in a wet state even if the water content is 0%. Therefore, by operating the drying portion so that the water content is 0% or more and 99.2%, the dry state of the first water-based ink can be changed to a state in which the second water-based ink is easily fixed.

Further, in the present invention, it is preferable that the detection unit measures the thickness of the first water-based ink ejected to the print medium (claim 8).

The detection unit does not directly detect the water content of the first water-based ink, but can determine the water content of the first water-based ink by measuring the thickness. Therefore, the dry state of the first water-based ink can be easily detected as compared with the case where the water content is directly measured.

Further, in the present invention, it is preferable that the detection unit measures the amount of the component contained in the first water-based ink ejected to the print medium (claim 9).

The first water-based ink contains a pigment, a resin, an organic solvent, and water. The water content of the first water-based ink can be determined by measuring all the components together instead of measuring any of the components. Therefore, the dry state of the first water-based ink can be easily detected as compared with the case where only the water content is directly measured.

Further, in the present invention, before the first printing unit ejects the first water-based ink to the printing medium, the first water-based ink and the primer through which the second water-based ink can permeate are printed. It is preferable to further include a coating portion for coating on the medium (claim 10).

Some print media are made of a material in which the first water-based ink and the second water-based ink are difficult to fix. In the case of such a print medium, the primer is applied to the print medium by the coating unit before ejecting the first water-based ink. As a result, the first water-based ink and the second water-based ink can be stably fixed on the print medium.

Further, in the present invention, the first water-based ink contains a pigment, a resin, an organic solvent, and water, and the organic solvent is 5% by mass or more and 40% by mass with respect to the first water-based ink. % Or less, and the amount of the water is preferably 40% by mass or more and 80% by mass or less with respect to the first water-based ink (claim 11).

By using the first water-based ink having such a content, it is possible to easily control the drying state of the first water-based ink by manipulating the drying conditions of the drying portion.

That is, the invention according to claim 12 includes a transport step of transporting a print medium, a first printing step of ejecting a first water-based ink to the print medium conveyed in the transport step, and a first printing step. In the first printing step, a drying step of drying the first water-based ink ejected to the printing medium in a drying section and a second water-based ink to the printing medium dried in the drying step are applied. A dry state of the first water-based ink ejected to the printing medium in the first printing step after the second printing step of ejecting and after the drying step and before the second printing step. The drying step comprises a detection step for detecting the above, and the drying step operates the drying conditions of the drying portion based on the detection result of the detection step, and after the drying step and after the second printing step. It is characterized in that the dry state of the first water-based ink is controlled in front of the above.

[Action / Effect] According to the invention according to claim 12, in the drying step, the drying conditions of the drying portion are manipulated based on the detection result of the detection step, and after the drying step, and in the second printing. The dry state of the first water-based ink before the process is controlled. Therefore, since the dry state of the first water-based ink is controlled before printing with the second water-based ink, the state of the first water-based ink can be changed to a state in which the second water-based ink is easily fixed. As a result, it is possible to print with good print quality even if the water-based ink is overcoated.

According to the printing apparatus according to the present invention, the control unit operates the drying conditions of the drying unit based on the detection result of the detection unit, and after the drying by the drying unit, the second water-based ink is ejected. The dry state of the first water-based ink is controlled before the printing. Therefore, since the dry state of the first water-based ink is controlled before printing with the second water-based ink, the state of the first water-based ink can be changed to a state in which the second water-based ink is easily fixed. As a result, it is possible to print with good print quality even if the water-based ink is overcoated.

It is a schematic block diagram which shows the whole of the inkjet printing apparatus which concerns on Example. It is a front view which shows the detailed structure of a printing part. Examples of white ink application states for different pre-drying states are shown, where (a) indicates insufficient drying, (b) indicates moderate drying, and (c) indicates overdrying. It is a graph which shows an example of the relationship between the waiting time after printing of a color ink, and the water content of a color ink. Of the graphs of FIG. 4, it is an enlarged graph of a region having a short waiting time. It is a table which shows the relationship between the pre-drying time and the print quality.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram showing the entire inkjet printing apparatus according to the embodiment.

The inkjet printing device 1 corresponding to the "printing device" in the present invention includes a paper feeding unit 3, a coating unit 5, a printing unit 7, a main drying unit 9, a paper ejection unit 11, and a control unit 12. ing. The left-right direction in FIG. 1 is defined as the transport direction X. Further, the left direction of the transport direction X is the downstream side, and the right direction is the upstream side. The width direction Y is defined as the front direction of the paper surface in FIG. 1. The vertical direction in FIG. 1 is defined as the height direction Z. The paper feeding unit 3, the coating unit 5, the printing unit 7, the main drying unit 9, and the paper ejection unit 11 are arranged in this order toward the downstream side in the transport direction X.

The paper feed unit 3 supplies the flexible packaging film WF to be printed to the coating unit 5. The paper feed unit 3 rotatably holds the rolled flexible packaging film WF around the horizontal axis. The paper feed unit 3 unwinds the flexible packaging film WF with the printing surface facing upward with respect to the coating unit 5. The material of the flexible packaging film WF is, for example, a hydrophobic base material, and has low absorbency of water-based ink. Examples of the flexible packaging film WF include plastic films such as polypropylene-based resin, vinyl chloride-based resin, and polyimide resin.

The flexible packaging film WF described above corresponds to the "printing medium" in the present invention.

The coating unit 5 applies a primer for forming a primer layer to the flexible packaging film WF. The primer layer is also referred to as a pretreatment layer, an ink penetrating layer or an ink receiving layer. The primer is a coating liquid, and is also called an undercoating liquid or a base adjusting liquid. Specifically, the coating unit 5 includes a pan 13, a gravure roller 15, and a transport unit 17. Pan 13 stores the primer. The lower portion of the gravure roller 15 is partially immersed in the primer stored in the pan 13, and the upper portion of the gravure roller 15 supplies the primer to the printed surface of the flexible packaging film WF by rotating. The transport unit 17 unwinds the flexible packaging film WF from the paper feed unit 3 and conveys the flexible packaging film WF to the gravure roller 15. In the region where the primer is supplied by the gravure roller 15, the transport direction of the flexible packaging film WF and the rotation direction of the peripheral surface of the gravure roller 15 are opposite to each other. The primer is applied to the flexible packaging film WF by the so-called reverse kiss method. The transport unit 17 transports the flexible packaging film WF from the coating unit 5 to the printing unit 7 with the printing surface of the flexible packaging film WF coated with the primer facing upward.

Examples of the primer include those containing a resin, a polyvalent metal salt, alcohols, a surface tension modifier, and pure water. Examples of the resin include shellac, examples of the polyvalent metal salt include, for example, calcium lactate, examples of alcohols include, for example, ethanol, and examples of the surface tension adjusting agent include SY glycer. Illustrated.

The printing unit 7 includes a color printing unit 19, a pre-drying unit 21, a detection unit 23, a white printing unit 25, an upper drying unit 27, and a transport unit 29. The color printing unit 19 prints a color image on the printed surface of the flexible packaging film WF coated with the primer layer, for example, by ejecting multicolor ink. The pre-drying unit 21 pre-drys the printed surface of the color-printed flexible packaging film WF. The detection unit 23 detects the dry state of color printing on the printed surface of the flexible packaging film WF. The white printing unit 25 discharges white ink onto the printed surface on which the color printing of the flexible packaging film WF is performed, and prints a white image. The upper drying unit 27 dries the printed surface of the flexible packaging film WF on which the white image is printed. The transport unit 29 transports the flexible packaging film WF from the color printing unit 19 described above to the upper drying unit 27. The details of the printing unit 7 will be described later.

The main drying unit 9 dries both the printed surface and the opposite surface of the flexible packaging film WF printed by the printing unit 7. Specifically, the main drying unit 9 includes a first drying unit 31, a second drying unit 33, a third drying unit 35, a first transport unit 37, and a second transport unit 39. , A third transport unit 41 is provided. The first drying section 31 dries the printed surface of the flexible packaging film WF transported to the downstream side in the transport direction X by the first transport section 37. The second drying section 33 dries both sides of the flexible packaging film WF transported to the upstream side in the transport direction X by the second transport section 39. The third drying section 35 dries both sides of the flexible packaging film WF transported to the downstream side in the transport direction X by the third transport section 41. The first drying unit 31, the second drying unit 33, and the third drying unit 35 discharge a gas heated to a predetermined temperature to the flexible packaging film WF. As a result, the image printed on the printed surface of the flexible packaging film WF is dried. The main drying unit 9 discharges, for example, a gas at 80 to 90 ° C. at a wind speed of 27 to 30 m / s.

The paper ejection unit 11 winds up the flexible packaging film WF dried by the main drying unit 9 around the horizontal axis.

The control unit 12 comprehensively controls the coating unit 5, the printing unit 7, and the main drying unit 9. The control unit 12 is composed of a CPU, a memory, a communication unit, and the like. The control unit 12 is connected to a host computer (not shown). The image printed on the flexible packaging film WF is given to the control unit 12 by the host computer as print data.

Incidentally, the total length of the transport path in the transport direction X in the inkjet printing apparatus 1 is about 50 m. Further, the transport time of the flexible packaging film WF in the transport path is within about 1 minute. In the inkjet printing apparatus 1 according to the present embodiment, the back surface of the flexible packaging film WF is used as the printing surface, and printing is performed by so-called back printing. In the printed matter printed on the back side, the back side, which is the printed side, is attached to the member, and the image is visually recognized from the front side of the transparent flexible packaging film WF.

Here, the details of the above-mentioned printing unit 7 will be described with reference to FIG. 2. Note that FIG. 2 is a front view showing a detailed configuration of the printing unit.

The printing unit 7 is a transfer unit 29 provided with a plurality of transfer rollers 291 including a drive roller, so that the flexible packaging film WF is applied from the coating unit 5 from the upstream side in the transfer direction X, which is downward in the height direction Z. take in. The captured flexible packaging film WF is turned upward in the height direction Z at the most downstream side of the printing unit 7, and turned upward toward the upstream side in the transport direction X. Then, the flexible packaging film WF is once turned downward in the height direction Z and is conveyed to the downstream side in the conveying direction X so as to draw an arc protruding upward. A color printing unit 19 is arranged on the transport path in which an arc is drawn. The transport unit 29 transports the flexible packaging film WF at a transport speed of, for example, 50 to 75 m / min. This transport speed is preferably set in consideration of the substantial pre-drying processing time in the pre-drying unit 21. For example, the transport speed is set so that the time from loading into the pre-drying section 21 to loading and unloading is within 30 seconds, preferably within 5 seconds.

The color printing unit 19 includes a plurality of (for example, six) ejection heads 191. Each ejection head 191 ejects water-based ink by, for example, an inkjet method. Each ejection head 191 ejects, for example, color inks of different colors. The color ink in this example means an ink other than white. For example, examples of the color ink include cyan (C), magenta (M), yellow (Y), and black (K). The color printing unit 19 prints a color image on the printed surface of the flexible packaging film WF by ejecting color ink from each ejection head 191 onto the printed surface of the flexible packaging film WF.

The above color ink contains a pigment, a resin, an organic solvent, and water. The ratio of each component is preferably as follows, for example. The pigment is 3 to 15% by mass with respect to the color ink. The organic solvent is 5 to 40% by mass with respect to the color ink. The water content is in the range of 40 to 80% by mass with respect to the color ink. By using the color ink having such a content, it is possible to easily control the drying state of the color ink by manipulating the drying conditions of the pre-drying unit 21.

Examples of the pigment of the color ink include carbon black, red iron sesquioxide, yellow iron sesquioxide, iron tetraoxide (black iron oxide), and lake pigment. Other pigments include, for example, CI Pigment Red 5, 7, 12, 57: 1, 122, 146, 202, 282, CI Pigment Blue 1, 2, 15: 3, 15: 4, 16, 17, 60. , 17, 60, CI Pigment Yellow 12, 13, 14, 17, 74, 83, 93, 128, 139, 151, 154, 155, 180, 185, 213. The pigment is not limited to the above-mentioned pigment.

The resin of the color ink includes cellac resin, aminoalkyl methacrylate copolymer E, methacrylic acid copolymer L, methacrylic acid copolymer LD, dried methacrylic acid copolymer LD, methacrylic acid copolymer S, ammonioalkyl methacrylate copolymer, ethyl acrylate / methyl methacrylate. Examples thereof include copolymers, ethyl celluloses and vinyl acetate resins. The resin is not limited to the above-mentioned resin.

Examples of the organic solvent for the color ink include propylene glycol, glycerin, ethanol, butanol, isobutanol, propanol, isopropanol, pentyl alcohol, ethyl lactate, ethyl acetate, triethyl citrate, and acetone. The organic solvent is not limited to the above-mentioned ones.

The color printing unit 19 described above corresponds to the "first printing unit" in the present invention, and the color ink corresponds to the "first ink" in the present invention. Further, printing by the color printing unit 19 corresponds to the "first printing step" in the present invention.

The color-printed flexible packaging film WF is turned downward in the height direction Z and then transported to the upstream side in the transport direction X. A pre-drying section 21 is arranged in this region. The pre-drying unit 21 includes a plurality of (for example, nine) gas discharge units 211. The gas discharge unit 211 discharges the dried gas onto the printed surface of the flexible packaging film WF. The gas is regulated to a predetermined temperature. The pre-drying unit 21 can adjust the temperature, air volume, and discharge time of the gas discharged from the gas discharge unit 211. The adjustable gas temperature range in the pre-drying section 21 is, for example, 40-80 ° C. This is preferably set to a temperature range in which the print quality can be maintained when the flexible packaging film WF prints an image on the printing surface. Therefore, if the print quality can be maintained even at a high temperature, the temperature of the gas may be adjusted in the range of 40 to 90 ° C. Further, the air volume of the gas that can be adjusted in the pre-drying unit 21 is, for example, 15 to 30 m / s in terms of wind speed.

The above-mentioned pre-drying section 21 corresponds to the "drying section" in the present invention. Further, the drying process by the pre-drying unit 21 corresponds to the "drying step" in the present invention.

After passing through the pre-drying section 21, the flexible packaging film WF is turned upward in the height direction Z on the upstream side in the transport direction X. Above it, the flexible packaging film WF is oriented downstream in the transport direction X. The white printing unit 25 is arranged in the area where the orientation is changed. The white printing unit 25 includes one ejection head 251. The ejection head 251 is, for example, an inkjet nozzle. The ejection head 251 ejects white ink and prints the white image on the printing surface on which the color image of the flexible packaging film WF is printed.

The white ink described above contains a pigment, a resin, an organic solvent, and water. The ratio of each component is not particularly limited. Examples of the pigment of the white ink include titanium oxide. Examples of the resin for white ink include cellac resin, aminoalkyl methacrylate copolymer E, methacrylic acid copolymer L, methacrylic acid copolymer LD, dried methacrylic acid copolymer LD, methacrylic acid copolymer S, ammonioalkyl methacrylate copolymer, and ethyl methacrylic acid acrylate. Examples thereof include methyl acid copolymers, ethyl celluloses and vinyl acetate resins. Examples of the organic solvent for white ink include propylene glycol, glycerin, ethanol, butanol, isobutanol, propanol, isopropanol, pentyl alcohol, ethyl lactate, ethyl acetate, triethyl citrate, and acetone. The components of the white ink are not limited to those described above.

The white printing unit 25 described above corresponds to the "second printing unit" in the present invention, and the white ink corresponds to the "second ink" in the present invention. Further, printing by the white printing unit 25 corresponds to the "second printing step" in the present invention.

A detection unit 23 for detecting the dry state of the printed surface printed by the color printing unit 19 is arranged between the pre-drying unit 21 and the white printing unit 25. The detection unit 23 can use various measuring instruments as long as it can detect the dry state of the printed surface. The detection unit 23 in this embodiment is composed of, for example, a moisture meter that measures the moisture content of the color ink on the printing surface. In addition to the moisture meter, a solvent component monitor for measuring the amount of solvent among the components of the color ink on the printing surface, a film thickness meter for measuring the thickness of the color ink on the printing surface, and the like can be used. The solvent component monitor measures the solvent component contained in the color ink on the printing surface, and the amount of the solvent component can determine the dry state as well as the amount of water. In the film thickness meter, the amount of water and the amount of the solvent component are displaced according to the dry state, and the thickness of the ink droplet is displaced. Therefore, the dry state can be determined by measuring the film thickness on the printed surface. The detection unit 23 is preferably an infrared multi-component meter capable of measuring various physical quantities described above in a non-contact manner using infrared rays.

The detection of the dry state by the detection unit 23 described above corresponds to the "detection step" in the present invention.

The upper drying portion 27 is arranged in the region where the direction is changed to the downstream side of the transport direction X and the posture is horizontal. The upper drying unit 27 includes a plurality of nozzles 271. Each nozzle 271 injects air from above toward the printed surface of the conveyed flexible packaging film WF. The air is, for example, room temperature. The upper drying unit 27 dries the white image printed by the white printing unit 25.

The control unit 12 operates the drying conditions by the pre-drying unit 21 in the printing unit 7. Specifically, after the drying process in the pre-drying unit 21, the white printing unit 25 controls the drying state of the color ink before printing the white image with the white ink. Specifically, the control unit 12 operates at least one of the parameters of the temperature of the pre-drying unit 21 and the substantial drying time being dried by the pre-drying unit 21. The parameter temperature is controlled by the control unit 12 operating the temperature control unit (not shown) of the pre-drying unit 21. The drying time is controlled by the control unit 12 by operating the transfer speed in the transfer system such as the transfer units 17, 29, the first transfer unit 37, the second transfer unit 39, and the third transfer unit 41.

In this embodiment, the pre-drying unit 21 is provided with a gas discharge unit 211, and the drying process is performed with the dried gas. Therefore, the control unit 12 may adjust at least one of the temperature, air volume, and discharge time of the gas discharged from the gas discharge unit 211 to control the dry state of the color ink.

In order to control the drying state of the color ink, for example, after the drying process by the pre-drying unit 21 and before printing the white image by the white printing unit 25, the water content of the color ink becomes 0% or more and 99.2%. It is preferable to operate the pre-drying unit 21 as described above. As a result, the control unit 12 can set the dry state of the color ink to a state in which the white ink is easily fixed.

Here, reference is made to FIG. Note that FIG. 3 shows an example of a white ink application state for each different pre-drying state, where (a) shows insufficient drying, (b) shows moderate drying, and (c) shows over-drying.

FIG. 3A shows the printing result of a white image when the dry state of the color ink in the pre-drying portion 21 is insufficiently dried. If the pre-drying portion 21 is insufficiently dried, the components of the primer layer are diluted in the color ink. If the white ink is ejected in this state, sufficient fixing force cannot be obtained for the white ink. Therefore, as shown in FIG. 3A, color mixing and printing defects in ink flow occur.

FIG. 3B shows the printing result of the white image when the dry state of the color ink in the pre-drying portion 21 is appropriate. When the drying in the pre-drying portion 21 is appropriate, the component of the primer layer is appropriately contained in the color ink. Since the white ink is ejected in that state, the white ink can also obtain the fixing power. As a result, as shown in FIG. 3B, a printed matter having good print quality without color mixing or ink flow can be obtained.

FIG. 3C shows the printing result when the dry state of the color ink in the pre-drying portion 21 is too dry. When the color ink is overdried, the color ink has almost no water content. If there is no water in the color ink film, the components of the primer layer cannot dissolve. Although water is supplied from the white ink to the color ink, in order to exert the fixing power, it is necessary for the water to dissolve in the film of the color ink after the color ink is ejected and to elute the components of the primer layer into the color ink. be. However, in the overdried state, the water does not immediately dissolve in the water-based ink, and it takes time to elute the components of the primer layer. As a result, the time required for charging the components of the primer layer into the upper drying section 27 and the main drying section 9 is shorter than the time required for elution of the components of the primer layer. Therefore, as a result, before the white ink is fixed, ink flow occurs in the color ink and the white ink due to the hot air of the upper drying and the main drying. As a result, printing defects in the ink flow occur as shown in FIG. 3 (c).

As a result of conducting various experiments, the present inventor has determined the parameters of the operation target of the pre-drying unit 21 described above. An example of the experiment that was the basis for this is described.

Printing was performed with color ink on the flexible packaging film WF on which the primer layer was formed. The print is 240% halftone dots. After that, a drying process was performed, and after a waiting time, the water content was measured by the detection unit 23. At that time, the water content was measured while changing the waiting time in various ways. The results are shown in FIGS. 4 and 5. Note that FIG. 4 is a graph showing an example of the relationship between the waiting time after printing the color ink and the water content of the color ink. Further, FIG. 5 is an enlarged graph of a region of the graph of FIG. 4 in which the waiting time is short.

From this result, it can be seen that the water content decreases as the waiting time increases. The absorbance on the vertical axis is a physical quantity that increases as the amount of water is increased because light is absorbed. Specifically, when the waiting time is 5 seconds, the absorbance is 0.1542, which is 99.2% in terms of water content. When the waiting time is 7 seconds, the absorbance is 0.153, which is 98.5% in terms of water content. When the waiting time is 17 seconds, the absorbance is 0.147, which is 94.7% in terms of water content. From this result, it can be seen that it is preferable that the upper limit of the water content of the pre-dried portion 21 is 99.2% and the lower limit is 0%. The color ink contains a pigment, a resin, an organic solvent, and water. When the solvent has a high boiling point, the color ink is not completely dried and is in a wet state even if the water content is 0%. Therefore, by operating the pre-drying unit 21 so that the water content is 0% or more and 99.2%, the dry state of the color ink can be changed to a state in which the white ink is easily fixed as shown in FIG. 3 (b). ..

Next, the results of another experiment will be described with reference to FIG. Note that FIG. 6 is a table showing the relationship between the pre-drying time and the print quality.

In this experiment, the temperature of the gas in the pre-drying section 21 is set to about 50 ° C, and the wind speed is set to about 5 m / s. From this result and the result of FIG. 5, the drying time by the pre-drying unit 21 is set to 30 seconds or less at the maximum, preferably 5 seconds or less, so that the white ink can be easily fixed as shown in FIG. 3 (b). .. Therefore, the drying time may be changed instead of the water content of the operation target in the above embodiment. From this result, it is preferable that the upper limit of the water content of the pre-drying portion 21 is 99.2% and the lower limit is 0%. The color ink contains a pigment, a resin, an organic solvent, and water. When the solvent has a high boiling point, the color ink is not completely dried and is in a wet state even if the water content is 0%. Therefore, by operating the pre-drying unit 21 so that the water content is 0% or more and 99.2%, the dry state of the color ink can be changed to a state in which the white ink is easily fixed as shown in FIG. 3 (b). ..

According to this embodiment, the control unit 12 operates the drying conditions of the pre-drying unit 21 based on the detection result of the detection unit 23, and after drying by the pre-drying unit 21, white ink is ejected. Controls the dry state of the color ink in front. Therefore, since the dry state of the color ink is controlled before printing with the white ink, the state of the color ink can be set to a state in which the white ink is easily fixed. As a result, it is possible to print with good print quality even if the water-based ink of the color ink and the white ink is overcoated.

The present invention is not limited to the above embodiment, and can be modified as follows.

(1) In the above-described embodiment, a case where a primer layer is formed on a flexible packaging farm WF and printing is performed has been described as an example. However, the present invention is also applicable when the primer layer is not formed.

(2) In the above-described embodiment, the configuration in which the pre-drying unit 21 is provided with the gas discharge unit 211 is taken as an example. However, in the present invention, the pre-drying unit 21 may be configured as a heater type or an optical type.

(3) In the above-described embodiment, the printing medium is a flexible packaging film WF, but the present invention can also be applied to a single-wafer type flexible packaging film and other types of printing media.

(4) In the above-described embodiment, the first water-based ink has been described as a color ink, but the present invention is not limited to such a configuration. For example, the first water-based ink may be a monochromatic ink.

(5) In the above-described embodiment, the pre-drying unit 21 is configured in the printing unit 7 so that after the color ink is ejected, the printing unit 7 is dried in a posture in which the printed surface faces downward. However, the present invention is not limited to such a configuration. For example, the pre-drying unit 21 may perform drying while keeping the printing surface on which the color ink is ejected facing upward.

As described above, the present invention is suitable for a printing apparatus and a printing method for printing on a printing medium with water-based ink.

1 ... Inkjet printing device 3 ... Feeding unit 5 ... Coating unit 7 ... Printing unit 9 ... Main drying unit 11 ... Paper ejection unit 12 ... Control unit 13 ... Pan 15 ... Gravure roller 19 ... Color printing unit 191 ... Discharge head 21 ... Pre-drying unit 211 ... Gas discharge unit 23 ... Detection unit 25 ... White printing unit 251 ... Discharge head 27 ... Upper drying unit 271 ... Nozzle 29 ... Transport unit WF ... Flexible packaging film

Claims (12)

A transport unit that transports print media and
A first printing unit that ejects a first water-based ink to the printing medium conveyed by the transport unit, and a first printing unit.
A drying unit for drying the first water-based ink ejected to the printing medium in the first printing unit, and a drying unit.
A second printing unit that ejects a second water-based ink to the printing medium dried in the drying unit, and a second printing unit.
A detection unit that detects the dried state of the first water-based ink ejected to the printing medium by the first printing unit after drying by the drying unit and before printing by the second printing unit. When,
Based on the detection result of the detection unit, the drying conditions of the drying unit are operated to obtain the first water-based ink after drying by the drying unit and before the second water-based ink is ejected. A control unit that controls the dry state,
A printing device characterized by being equipped with. In the printing apparatus according to claim 1,
The control unit is a printing apparatus characterized in that at least one of the temperature and the drying time of the drying unit is operated. In the printing apparatus according to claim 2,
The drying unit is a printing apparatus including a gas discharging unit that discharges a dried gas to the printing medium. In the printing apparatus according to claim 3,
The control unit is a printing apparatus characterized by operating at least one of the temperature, air volume, and discharge time of the gas discharged from the gas discharge unit. In the printing apparatus according to claim 3 or 4.
The control unit is a printing apparatus characterized in that the temperature of the gas discharged from the gas discharge unit is set in the range of 40 ° C. or higher and 80 ° C. or lower. In the printing apparatus according to any one of claims 1 to 5.
The detection unit is a printing apparatus characterized by measuring the water content of the first water-based ink ejected to the print medium. In the printing apparatus according to claim 6,
In the control unit, the water content detected by the detection unit is 0% or more and 99.2% or less with respect to the water content of the first water-based ink ejected from the first printing unit to the print medium. A printing apparatus characterized in that the drying portion is operated so as to be. In the printing apparatus according to any one of claims 1 to 7.
The detection unit is a printing apparatus characterized by measuring the thickness of a first water-based ink ejected onto the print medium. In the printing apparatus according to any one of claims 1 to 8.
The detection unit is a printing apparatus characterized by measuring the amount of components contained in the first water-based ink ejected to the print medium. In the printing apparatus according to any one of claims 1 to 9.
Before the first printing unit ejects the first water-based ink to the printing medium, a coating unit that applies a primer capable of penetrating the first water-based ink and the second water-based ink to the printing medium. A printing device characterized by being further equipped with. In the printing apparatus according to any one of claims 1 to 10.
The first water-based ink contains a pigment, a resin, an organic solvent, and water.
The organic solvent is 5% by mass or more and 40% by mass or less with respect to the first water-based ink.
A printing apparatus characterized in that the amount of water is 40% by mass or more and 80% by mass or less with respect to the first water-based ink. The transport process for transporting the print medium and
A first printing step of ejecting a first water-based ink to the print medium conveyed in the transfer step, and a first printing step.
A drying step of drying the first water-based ink ejected to the printing medium in the drying portion in the first printing step.
A second printing step of ejecting a second water-based ink to the printing medium dried in the drying step, and a second printing step.
After the drying step and before the second printing step, a detection step of detecting the dry state of the first water-based ink ejected to the printing medium in the first printing step, and a detection step.
Equipped with
In the drying step, based on the detection result of the detection step, the drying conditions of the drying portion are manipulated to control the drying conditions of the first water-based ink after the drying step and before the second printing step. A printing method characterized by controlling a dry state.

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