Printing device

Abstract

To provide a printing device that can increase the number of colors other than a process color and express low-density gradations.SOLUTION: A printing device is provided with: an ink supply part 29 that supplies ink of a reference color and density-adjustment ink for adjusting densities of the ink of a reference color; a mixed color ink tank 43 that mixes the ink of a reference color and the density-adjustment ink supplied by the ink supply part 29 with each other to generate ink of mixed colors; and an inkjet head 31 that discharges the ink of mixed colors generated by the mixed color ink tank 43 to a substrate 15 to perform printing thereon.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a printing device that performs printing by ejecting ink onto a substrate. [Background technology]

[0002] Traditionally, gradation expressions using powder coating or spray painting have been used for applications that are observed at close range, such as furniture, clock faces, and nails.

[0003] However, the above-mentioned powder coating and spray painting methods rely on craftsmanship, resulting in large variations in results and low productivity. Furthermore, there are problems with quality control and the process from design consideration to commercialization, which requires time, cost, and effort.

[0004] As a result, there are discussions about digitizing powder coating and spray painting, and one of these efforts is using inkjet technology. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2012-86489 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, when using inkjet technology instead, it is extremely difficult to express gradations in a single color other than process colors.Gradations expressed by painting are expressed using pre-mixed single-color inks, so it is possible to express uniform gradations from low to high gradations.

[0007] On the other hand, with inkjet technology, high-gradation areas (areas with high printing rate) where dots are not visible to the naked eye are comparable to painted images, but in areas with low printing rate, the process color dots are visible to the naked eye, resulting in a significant loss of hue.

[0008] In other words, while inkjet technology, which can control minute ink droplets, is attracting attention as a way to replace the craftsmanship of painting, the issues mentioned above are one of the reasons that are preventing digitalization.

[0009] Furthermore, Patent Document 1 proposes an inkjet printing device that generates an ink of a target color other than the process color by circulating and mixing two process color inks in an ink circulation path, and then performs an ink ejection operation of the generated target color ink using an inkjet head to print a monochrome image in the target color.

[0010] However, in the inkjet printing device of Patent Document 1, the ink density cannot be adjusted unless the process color ink itself is changed, so the number of target colors is small, making it difficult and time-consuming to reproduce the target colors.

[0011] Furthermore, with the inkjet printing device of Patent Document 1, because it is not possible to adjust the ink density as described above, there is a limit to the printing of areas with low coverage, making it difficult to express light density gradations.

[0012] SUMMARY OF THE PRESENT DISCLOSURE In view of the above circumstances, an object of the present invention is to provide a printing device that can increase the number of colors other than process colors and can also express low density gradations. [Means for solving the problem]

[0013] The printing device of the present invention comprises a base color supply unit that supplies base color ink, a concentration adjustment liquid supply unit that supplies concentration adjustment liquid to adjust the concentration of the base color ink, a mixing unit that mixes the base color ink supplied by the base color supply unit with the concentration adjustment liquid supplied by the concentration adjustment liquid supply unit to generate a mixed color ink, and a head unit that ejects the mixed color ink generated by the mixing unit onto a substrate to perform printing. Effect of the Invention

[0014] According to the printing device of the present invention, a mixed color ink is produced by mixing a basic color ink with a concentration adjustment liquid, and the mixed color ink is then ejected onto a substrate to perform printing. This makes it possible to increase the number of colors other than the basic colors (process colors) and to express light density gradations. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is an external perspective view showing a schematic configuration of an inkjet printing apparatus using an embodiment of a printing apparatus according to the present invention; [Diagram 2] FIG. 1 shows a schematic configuration of a shuttle unit. [Diagram 3] FIG. 1 is a diagram showing the specific configuration of an ink supply unit, a cleaning unit, and a circulation unit. [Figure 4] FIG. 2 is a block diagram showing the configuration of a control system of the inkjet printing apparatus shown in FIG. [Diagram 5] FIG. 13 is a diagram showing an example of a mixture ratio table. [Figure 6] FIG. 1 is a diagram showing an example of a waveform of a driving voltage of an inkjet head; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] An inkjet printing apparatus using one embodiment of the printing apparatus of the present invention will be described in detail below with reference to the drawings. The inkjet printing apparatus of this embodiment is characterized by printing using mixed color inks, but first, the configuration of the inkjet printing apparatus as a whole will be described. FIG. 1 is a schematic configuration diagram of an inkjet printing apparatus 1 of this embodiment. Note that the up, down, left, right, front, back, and rear directions indicated by arrows in FIG. 1 are the up, down, left, right, front, and rear directions of the inkjet printing apparatus 1.

[0017] As shown in FIG. 1, the inkjet printing apparatus 1 of this embodiment includes a shuttle base unit 2, a flat bed unit 3, and a shuttle unit 4.

[0018] The shuttle base unit 2 supports the shuttle unit 4 and moves the shuttle unit 4 in the front-rear direction (sub-scanning direction). Specifically, the shuttle base unit 2 includes a stand portion 11 and a sub-scanning drive motor 12 (see FIG. 4).

[0019] The base unit 11 is formed in a rectangular frame shape and supports the shuttle unit 4. Sub-scanning drive guides 13A and 13B extending in the front-rear direction are formed on the left and right frames of the base unit 11, respectively. The sub-scanning drive guides 13A and 13B guide the shuttle unit 4 to move in the front-rear direction. The sub-scanning drive motor 12 moves the shuttle unit 4 in the front-rear direction.

[0020] The flatbed unit 3 supports the substrate 15 to be printed. The flatbed unit 3 is disposed in a rectangular parallelepiped recess formed inside the stand portion 11 of the shuttle base unit 2. The flatbed unit 3 has a medium placement surface 3a, which is a horizontal surface on which the substrate 15 is placed. The flatbed unit 3 has a lifting mechanism formed of a hydraulic drive mechanism or the like (not shown), which is configured to adjust the height of the medium placement surface 3a.

[0021] In addition, the flatbed unit 3 may be provided with a heating mechanism to improve the drying of ink during printing.

[0022] The shuttle unit 4 performs a printing process on the substrate 15. Fig. 2 is a diagram showing a schematic configuration of the shuttle unit 4. As shown in Fig. 2, the shuttle unit 4 includes a housing 21, a main scanning drive guide 22, a main scanning drive motor 23 (see Fig. 4), a head lift guide 24, a head lift motor 25 (see Fig. 4), a head unit 26, a capping unit 66, a suction unit 28, an ink supply unit 29, and a cleaning unit 30.

[0023] The housing 21 houses each part such as the head unit 26. The housing 21 is formed in a gate shape that straddles the flatbed unit 3 in the left-right direction. The housing 21 is supported by the stand portion 11 of the shuttle base unit 2, and is configured to be movable along the sub-scanning drive guides 13A and 13B.

[0024] The main scanning drive guide 22 guides the head unit 26 to move in the left-right direction (main scanning direction). The main scanning drive guide 22 is formed of an elongated member extending in the left-right direction. The head unit 26 is moved in the left-right direction by a main scanning drive motor 23.

[0025] The head lift guide 24 guides the head unit 26 to move in the vertical direction. The head lift guide 24 is formed from a member that is elongated in the vertical direction. The head lift guide 24 is configured to be movable in the left-right direction along the main scanning drive guide 22 together with the head unit 26. The head unit 26 is raised and lowered in the vertical direction by a head lift motor 25.

[0026] As described above, the head unit 26 performs a printing process by ejecting ink onto the substrate 15 while moving in the left-right direction along the main scanning drive guide 22. The head unit 26 has an inkjet head 31 as shown in Fig. 2. In this embodiment, the inkjet head 31 corresponds to the head portion of the present invention.

[0027] It is preferable to use a circulation-compatible head that can circulate ink up to the vicinity of the nozzles as the inkjet head 31. It is also preferable to use a head that can change the amount of ink ejected in many gradations by changing the waveform of the driving voltage supplied to the inkjet head 31. As the inkjet head 31, for example, the RC1536 head series manufactured by SII Printec Co., Ltd. can be used.

[0028] The capping unit 66 seals the ink ejection surface of the inkjet head 31 to prevent the ink ejection ports of each nozzle of the inkjet head 31 from drying out while the inkjet printing device 1 is on standby and not performing a printing operation. The ink ejection surface is the surface on which the ink ejection ports of each nozzle of the inkjet head 31 are arranged.

[0029] 2, the capping unit 66 is installed inside the right end of the housing 21. When the head unit 26 moves to the standby position at the right end of the housing 21, the capping unit 66 seals the ink ejection surface of the inkjet head 31.

[0030] The capping unit 66 is raised and lowered in the vertical direction by a cap lifting motor 67 (see FIG. 4). Specifically, the capping unit 66 is raised and lowered between a contact position where it contacts the ink ejection surface of the inkjet head 31 and a retracted position below the contact position.

[0031] The suction section 28 provided below the capping unit 66 is for sucking ink accumulated in the capping unit 66. The suction section 28 includes a suction tube 68, a suction pump 69, and a waste liquid tank 70.

[0032] One end of the suction pipe 68 is connected to the capping unit 66, and the other end of the suction pipe 68 is connected to a waste liquid tank 70. A suction pump 69 is provided for each of the suction pipes 68.

[0033] The ink accumulated in the capping unit 66 is sucked by the suction of the suction pump 69 and is stored in the waste liquid tank 70 via the suction pipe 68.

[0034] The ink supply unit 29, the cleaning unit 30, and the circulation unit 40 provided in the head unit 26 shown in Fig. 2 will be described below. Fig. 3 is a diagram showing specific configurations of the ink supply unit 29, the cleaning unit 30, and the circulation unit 40.

[0035] 3, the ink supply unit 29 includes a first ink tank 29a, a second ink tank 29b, and a third ink tank 29c that store ink of three process colors (basic colors), respectively, and a fourth ink tank 29d that stores density adjustment ink.

[0036] The first ink tank 29a stores yellow ink, the second ink tank 29b stores magenta ink, and the third ink tank 29c stores cyan ink. In this embodiment, a mixed color ink is produced from three process colors (yellow, magenta, and cyan), but white and black may be added as necessary.

[0037] As the process color ink, a general solvent ink or water-based ink can be used. For the solvent ink, a pigment is dispersed in a main solvent such as glycol monoacetates or glycol ethers, and a solvent in which a binder resin that provides fixation to the substrate 15 is dissolved is added. In addition, it is preferable to use a solvent with a low boiling point from among highly safe solvents.

[0038] The aqueous ink may contain 20% by weight of CAB-O-JET 450C, 12.5% ​​by weight of CAB-O-JET465M, and 20% by weight of CAB-O-JET470Y (manufactured by Cabot Corporation) as colorants ...7.9% by weight of Superflex 470 (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) as binder resin, 1.0% by weight of Surfynol 485 (manufactured by Nissin Chemical Industry Co., Ltd.) as surfactants, 15% by weight of glycerin, and 10% by weight of ethylene glycol, with the amount of water used being such that the total of the components is 100.0%.

[0039] The density adjustment ink is an ink obtained by removing the coloring material from the above-mentioned process color inks.

[0040] A first ink path 29e is connected to the first ink tank 29a, and a first supply pump 29f is provided on the first ink path 29e.

[0041] A second ink path 29g is connected to the second ink tank 29b, and a second supply pump 29h is provided on the second ink path 29g.

[0042] A third ink path 29i is connected to the third ink tank 29c, and a third supply pump 29k is provided on the third ink path 29i.

[0043] A fourth ink path 29m is connected to the fourth ink tank 29d, and a fourth supply pump 29n is provided on the fourth ink path 29m.

[0044] In this embodiment, the first ink tank 29a, the first ink path 29e, the first supply pump 29f, the second ink tank 29b, the second ink path 29g, the second supply pump 29h, the third ink tank 29c, the third ink path 29i and the third supply pump 29k correspond to the basic color supply unit of the present invention.

[0045] In this embodiment, the fourth ink tank 29d, the fourth ink path 29m, and the fourth supply pump 29n correspond to a concentration adjusting liquid supply unit of the present invention.

[0046] The cleaning unit 30 has a cleaning liquid tank 32 that stores a cleaning liquid. A cleaning liquid path 33 is connected to the cleaning liquid tank 32, and a cleaning liquid supply pump 34 is provided on the cleaning liquid path 33.

[0047] If the ink is water-based, the cleaning solution should contain water, which is the main solvent for the ink, a water-soluble solvent, a surfactant, a humectant, and optionally a pH adjuster and preservative.If the ink is solvent-based, the cleaning solution should contain the main solvent, a surfactant, a humectant, and optionally a pH adjuster and preservative.In either case, it is best to make the solution transparent and add cleaning properties using surfactants and solvent types.

[0048] The first ink path 29e, the second ink path 29g, the third ink path 29i, the fourth ink path 29m and the cleaning liquid path 33 are connected to a common path 35, and the common path 35 is connected to a first valve 41 of the circulation section 40.

[0049] The circulation section 40 is provided together with the inkjet head 31 inside the housing of the head unit 26, and moves together with the inkjet head 31 in the left-right direction (main scanning direction).

[0050] The circulation unit 40 includes the above-mentioned first valve 41, first circulation path 42, mixed color ink tank 43, second circulation path 44, second valve 45, third circulation path 46, third valve 47, recovery tank 48, fourth circulation path 49, and circulation pump 50.

[0051] One end of a first circulation path 42 is connected to the first valve 41, and the other end of the first circulation path 42 is connected to a mixed color ink tank 43. In addition, one end of a second circulation path 44 is connected to the mixed color ink tank 43, and the other end of the second circulation path 44 is connected to the inkjet head 31, and a second valve 45 is provided on the second circulation path 44.

[0052] In addition, a third circulation path 46 is provided between the ink-jet head 31 and the recovery tank 48, and a third valve 47 is provided on the third circulation path 46.

[0053] One end of a fourth circulation path 49 is connected to the recovery tank 48, the other end of the fourth circulation path 49 is connected to the first valve 41, and a circulation pump 50 is provided on the fourth circulation path 49.

[0054] In addition, a first air path 43a is connected to the mixed color ink tank 43, and a second air path 48a is connected to the recovery tank .

[0055] The ink supply unit 29 supplies process color (yellow, magenta, cyan) inks and concentration adjustment inks to produce mixed color inks, the cleaning unit 30 cleans the ink path through which the ink passes, including the inkjet head 31, and the circulation unit 40 circulates the mixed color ink; the operation of each unit will be described in detail later.

[0056] Fig. 4 is a block diagram showing a control system of the inkjet printing apparatus 1 of this embodiment. The inkjet printing apparatus 1 includes a control unit 5 that controls the entire apparatus. The control unit 5 includes a CPU (Central Processing Unit), a semiconductor memory, a hard disk, etc. The control unit 5 executes a program stored in advance in a storage medium such as the semiconductor memory or the hard disk, and controls each unit shown in Fig. 4 by operating an electric circuit.

[0057] Next, a description will be given of the operation of the inkjet printing apparatus 1 of this embodiment. The inkjet printing apparatus 1 of this embodiment performs each operation in the following order: ink preparation operation, ink circulation operation, printing operation, ink discharge operation, and cleaning operation.

[0058] First, the ink preparation operation will be described. During the ink preparation operation, the first valve 41 is controlled to open the common path 35 and the first circulation path 42, and the second valve 45 is closed. Then, the first supply pump 29f, the second supply pump 29h, the third supply pump 29k, and the fourth supply pump 29n are operated to supply the yellow, magenta, and cyan inks and the density adjustment ink at a predetermined blend ratio. The blend ratio will be described in detail later.

[0059] The yellow, magenta, cyan inks and the density adjusted ink are stored in the mixed color ink tank 43 via the common path 35, the first valve 41, and the first circulation path 42. The inks stored in the mixed color ink tank 43 are stirred by the stirrer 43b to create the mixed color ink. During the ink creation operation, the inkjet head 31 is sealed by the capping unit 66.

[0060] Next, the initial filling operation will be described. During the initial operation, the first valve 41 is controlled to open the first circulation path 42 and the fourth circulation path 49, the second valve 45 is controlled to open the mixed color ink tank 43 and the inkjet head 31, and the third valve 47 is closed.

[0061] Then, a pressure mechanism (not shown) introduces air from the first air path 43a, thereby controlling the inside of the mixed color ink tank 43 to a positive pressure, thereby initially filling the inkjet head 31 with the mixed color inks. Even during the initial filling operation, the inkjet head 31 is sealed by the capping unit 66, and the ink accumulated in the capping unit 66 is discharged into the waste ink tank 70 via the suction tube 68.

[0062] Next, the ink circulation operation will be described. During the ink circulation operation, the third valve 47 is controlled to open the inkjet head 31 and the recovery tank 48. Then, the pressure mechanism (not shown) sucks air from the second air path 48a, thereby controlling the inside of the recovery tank 48 to a negative pressure, and as a result, the mixed color inks filled in the inkjet head 31 flow into the recovery tank 48.

[0063] Then, when the liquid level of the mixed color ink stored in the recovery tank 48 becomes higher than a preset reference position, the circulation pump 50 operates to cause the mixed color ink to flow into the fourth circulation path 49. The mixed color ink flowing into the fourth circulation path 49 is returned to the mixed color ink tank 43 via the first valve 41 and the first circulation path 42, thereby circulating the mixed color ink. Note that even during the ink circulation operation, the inkjet head 31 is sealed by the capping unit 66, and the ink stored in the capping unit 66 is discharged into the waste liquid tank 70 via the suction tube 68.

[0064] Next, the printing operation will be described. While continuing the ink circulation operation described above, the head unit 26 moves over the substrate 15 placed on the flatbed unit 3, and the mixed color ink is ejected from the inkjet head 31 to perform printing. Details of the printing operation will be described later.

[0065] If the liquid level of the mixed color ink stored in the mixed color ink tank 43 falls below a preset reference position during the printing operation, the printing operation is temporarily stopped, and the head unit 26 moves again to the capping unit 66. Then, after the inkjet head 31 is capped, the ink preparation operation is performed again. Then, after the mixed color ink is replenished, the printing operation is resumed.

[0066] Next, the ink discharging operation will be described. After the printing operation is completed, the ink discharging operation is performed. During the ink discharging operation, the above-mentioned initial filling operation is performed, and mixed color inks are discharged from the inkjet head 31. It is preferable to discharge as much ink as possible from the path by repeating the initial filling operation and the above-mentioned ink circulation operation.

[0067] Next, the cleaning operation will be described. During the cleaning operation, the first valve 41 is controlled so that the common path 35 and the mixed color ink tank 43 are opened, and the cleaning liquid supply pump 34 is operated. As a result, cleaning liquid is supplied from the cleaning liquid tank 32 to the mixed color ink tank 43 via the cleaning liquid path 33, the common path 35, the first valve 41, and the first circulation path 42. The cleaning liquid is stirred by the stirrer 43b in the mixed color ink tank 43, thereby cleaning the mixed color ink tank 43. Thereafter, the initial filling operation, the ink circulation operation, the ink discharge operation, and the above-mentioned cleaning liquid supply operation are repeated, thereby cleaning all of the paths of the mixed color inks.

[0068] Next, the printing operation of the inkjet printing apparatus 1 of this embodiment will be described in detail.

[0069] In the inkjet printing apparatus 1, in a standby state before the start of a printing operation, the shuttle unit 4 is disposed at a standby position. The standby position of the shuttle unit 4 is the position of the shuttle unit 4 shown by the solid line in FIG.

[0070] When a print job is input, the control unit 5 controls the sub-scanning drive motor 12 to move the shuttle unit 4 from the standby position to the print processing start position. The print processing start position of the shuttle unit 4 is the position of the shuttle unit 4 shown by the two-dot chain line in Fig. 1, which is the front end of the stand part 11 of the shuttle base unit 2. Note that, prior to input of the print job, the substrate 15 is placed on the medium placement surface 3a of the flatbed unit 3.

[0071] Next, the control unit 5 controls the main scanning drive motor 23 to move the head unit 26 in the main scanning direction, while controlling the inkjet head 31 to eject ink from the nozzles based on the input print job, thereby printing one pass.

[0072] Next, the control unit 5 controls the sub-scanning drive motor 12 to move the shuttle unit 4 backward to the printing position of the next pass. The control unit 5 forms an image on the substrate 15 by alternately repeating the printing for one pass and the movement of the shuttle unit 4.

[0073] When printing of one sheet is completed, the control unit 5 controls the sub-scanning drive motor 12 to place the shuttle unit 4 in the standby position, thereby completing the printing operation.

[0074] As described above, by printing while reciprocating the head unit 26 in the main scanning direction, a high-resolution printed image can be obtained by increasing the number of reciprocations with a minimum number of inkjet heads 31. As a result, a smooth gradation can be expressed from high to low printing rates. The method of printing a gradation image will be described in detail later.

[0075] Also, it can be realized in a small space and at low cost because it can be realized with a minimum number of inkjet heads 31. Also, productivity can be increased by increasing the reciprocating distance of the head unit 26 and increasing the moving speed and ejection frequency of the head.

[0076] It should be noted that the process colors may be individually overprinted to operate like a normal inkjet printer.

[0077] Here, when printing on plated metal, such as that used for watch dials, the base material is colored and has a unique texture, such as reflecting light, making it difficult to accurately determine the color coordinates of the print using optical equipment.

[0078] Even if it were possible to quantify the color on the substrate, in most cases the color, including the texture of the substrate, would differ from the color of the printed ink.

[0079] Therefore, it is preferable to create a color sample using the actual substrate and ink, and store in the control unit 5 a blending ratio table that associates the type of substrate, the color of the darkest colored portion (the portion with the highest printing rate) on the substrate, and the blending ratio of the process color inks (yellow, magenta, and cyan in this embodiment) and density adjustment inks used at that time. FIG. 5 is a diagram showing an example of the blending ratio table. Note that when creating a color sample, the method of applying ink to the substrate does not have to be inkjet printing, and spray application or a bar coater may be used instead.

[0080] Then, the control unit 5 acquires information on the type of substrate and the color to be printed, which have been set and input by, for example, a user, and based on the acquired information on the type of substrate and the color, refers to a mixing ratio table to determine the mixing ratio of the process color ink and the density adjustment ink.

[0081] Then, the control unit 5 controls the ink supply unit 29 based on the determined blending ratio to supply the inks of the respective colors and the density-adjusted inks. This makes it possible to obtain a printed matter of the desired color even if the substrate is something like a clock face.

[0082] In addition, the way the ink spreads and soaks into the substrate varies depending on the combination of the substrate and the mixed color ink, so the image resolution and dot diameter required to reproduce a 100% solid image differ. The dot diameter is controlled by the waveform of the drive voltage supplied to the inkjet head 31, so it is necessary to select the waveform of the drive voltage according to the required dot diameter.

[0083] Therefore, it is preferable to store the image resolution and the driving voltage waveform when printing in correspondence with the base material and the color of the mixed ink, as in the blending ratio table shown in FIG. 5. Then, the control unit 5 determines the image resolution and the driving voltage waveform based on the information on the type of base material and the information on the color to be printed, and controls the inkjet head 31 based on these to perform printing. This makes it possible to reproduce a 100% solid image using the mixed color ink. Note that FIG. 6 is a diagram showing an example of the driving voltage waveform of the inkjet head 31, and by increasing the pulse waveform shown in FIG. 6, the ink ejection amount can be increased, and the dot diameter can be enlarged.

[0084] When printing a gradation image, the density is adjusted by gradually lowering the printing rate. The density of the gradation image can be freely selected from the density of a 100% solid image or less, and may be, for example, a gradation image with a density change of 100% to 70%, or a gradation image with a density change of 50% to 70%.

[0085] Furthermore, if the viscosity of the mixed inks of the mixed colors exceeds ±5% from the reference viscosity, dots cannot be arranged at accurate positions on the substrate. Since the viscosity of the mixed inks of the mixed colors varies depending on the mixing ratio of the mixed inks of the mixed colors, it is preferable to store the voltage values ​​of the driving voltages corresponding to the mixing ratios, as shown in the mixing ratio table in FIG. 5. The voltage value of the driving voltage is the magnitude of the driving voltage V shown in FIG. 6.

[0086] Based on the mixture ratio calculated from the information on the type of substrate and the information on the color to be printed, the control unit 5 refers to the mixture ratio table, calculates the voltage value of the drive voltage corresponding to the mixture ratio, and controls the inkjet head 31. This makes it possible to improve the positional accuracy of the dots printed on the substrate, and thereby improve image quality.

[0087] That is, based on the input information on the type of substrate and the color to be printed, the control unit 5 refers to the mixing ratio table shown in FIG. 5 to determine the mixing ratio of the mixed color inks, the image resolution when printing, and the waveform and voltage value of the driving voltage of the inkjet head 31, and controls the ink supply unit 29 and the inkjet head 31 based on these, thereby reproducing a gradation image that looks natural even when viewed from close up.

[0088] The color of the mixed ink having the mixture ratio determined from the mixture ratio table shown in Fig. 5 may be detected and quantified using a sensor such as a liquid color detection sensor or a color sensor. The sensor may be provided in the mixed color ink tank 43, for example.

[0089] According to the inkjet printing device 1 of the above embodiment, a process color ink and a density adjustment ink are mixed to generate a mixed color ink, and the mixed color ink is ejected onto a substrate to perform printing. This makes it possible to increase the number of colors other than the process colors and to express light density gradations.

[0090] Furthermore, in the inkjet printing device 1 of the above embodiment, a cleaning unit 30 is provided for cleaning the mixed color ink path including the inkjet head 31. Therefore, by performing the above-mentioned cleaning operation, the color of the mixed color ink can be changed in a short time.

[0091] Furthermore, in the inkjet printing apparatus 1 of the above embodiment, the mixing ratio of the process color ink and the concentration adjustment ink is determined based on information on the type of substrate and information on the color of the ink to be printed, and the ink supply unit 29 is controlled based on the determined mixing ratio. Therefore, as described above, a printed matter of the desired color can be obtained even if the substrate is something like a clock face.

[0092] Furthermore, in the inkjet printing device 1 of the above embodiment, the image resolution during printing and the waveform of the driving voltage applied to the inkjet head 31 are controlled based on information on the type of substrate and information on the color of the ink, so that, as described above, a 100% solid image can be reproduced using mixed color inks.

[0093] Furthermore, in the inkjet printing device 1 of the above embodiment, the voltage value of the drive voltage applied to the inkjet head 31 is controlled based on the mixing ratio of the process color inks. As a result, as described above, the positional accuracy of the dots printed on the substrate can be improved, and image quality can be improved.

[0094] Furthermore, in the inkjet printing device 1 of the above embodiment, the circulation section 40 is housed within the head unit 26 and moves together with the head unit 26 (inkjet head 31), thereby making it possible to shorten the ink path of the circulation section 40, thereby enabling the cleaning operation to be performed in a shorter time.

[0095] The present invention is not limited to the above-described embodiment, and the components can be modified and embodied in the implementation stage without departing from the gist of the invention. In addition, various inventions can be formed by appropriately combining the multiple components disclosed in the above-described embodiment. For example, all the components shown in the embodiment can be appropriately combined. Of course, various modifications and applications are possible without departing from the spirit of the invention.

[0096] The present invention further discloses the following supplementary notes.

[0097] (Appendix 1) The printing device of the present invention comprises a base color supply unit that supplies base color ink, a concentration adjustment liquid supply unit that supplies concentration adjustment liquid to adjust the concentration of the base color ink, a mixing unit that mixes the base color ink supplied by the base color supply unit with the concentration adjustment liquid supplied by the concentration adjustment liquid supply unit to generate a mixed color ink, and a head unit that ejects the mixed color ink generated by the mixing unit onto a substrate to perform printing.

[0098] (Appendix 2) The printing device described in Supplementary Note 1 may include a cleaning unit that cleans the ink path of the mixed color including the head unit.

[0099] (Appendix 3) The printing device described in Appendix 1 or Appendix 2 can be provided with a control unit that acquires information on the type of substrate and information on the color of ink to be printed on the substrate, determines a mixing ratio of the base color ink and concentration adjustment liquid based on the acquired information on the type of substrate and the information on the color of ink, and controls the base color supply unit and the concentration adjustment liquid supply unit based on the determined mixing ratio.

[0100] (Appendix 4) In the printing device described in Supplementary Note 3, the control unit can control the image resolution during printing and the waveform of the drive voltage applied to the head unit based on information on the type of substrate and information on the color of the ink.

[0101] (Appendix 5) In the printing device according to Supplementary Note 3 or Supplementary Note 4, the control unit can control the voltage value of the drive voltage applied to the head unit based on the blending ratio.

[0102] (Appendix 6) In the printing device described in any one of Supplementary Notes 1 to 5, a circulation unit is provided that supplies the mixed color ink to the head unit and collects the mixed color ink that has not been used in the head unit and supplies it again to the head unit, and the circulation unit is housed in the same housing as the head unit and can move together with the head unit. [Explanation of symbols]

[0103] 1 Inkjet printing device 2 Shuttle Base Unit 3 Flatbed unit 3a Media placement surface 4 Shuttle Unit 5. Control section 11 Mounting section 12 Sub-scanning drive motor 15 Base material 21 Case 22 Main scanning drive guide 23 Main scanning drive motor 24 Head lift guide 25 Head lift motor 13A, 13B Sub-scanning drive guide 26 Head Unit 28 Suction part 29 Ink supply unit 29a First ink tank 29b Second ink tank 29c Third ink tank 29d Fourth Ink Tank 29e First ink path 29f First supply pump 29g Second ink path 29h Second supply pump 29i 3rd ink path 29k 3rd supply pump 29m 4th ink path 29n Fourth supply pump 30 Cleaning section 31 Inkjet head 32 Cleaning solution tank 33 Cleaning fluid path 34 Cleaning solution supply pump 35 Common Route 40 Circulation section 41 First Valve 42 First Circulation Route 43 Mixed color ink tank 43a First Air Path 43b Mixer 44 Second Circulation Route 45 Second Valve 46 The third circulation route 47 Third Valve 48 Recovery Tank 48a Secondary Air Path 49 The Fourth Circulation Route 50 Circulation Pump 66 Capping Unit 67 Cap lift motor 68 Suction tube 69 Suction Pump 70 Waste Liquid Tank

Claims

1. A basic color supply unit that supplies ink of a basic color; a concentration adjusting liquid supply unit that supplies a concentration adjusting liquid for adjusting the concentration of the ink of the basic color; a mixing unit that mixes the ink of the basic color supplied by the basic color supply unit and the concentration adjustment liquid supplied by the concentration adjustment liquid supply unit to generate an ink of a mixed color; a head unit that ejects the mixed color ink produced by the mixing unit onto a substrate to perform printing.

2. The printing apparatus according to claim 1 , further comprising a cleaning unit configured to clean the ink paths of the mixed colors including the head unit.

3. 2. A printing device as described in claim 1, further comprising a control unit that acquires information on the type of substrate and information on the color of ink to be printed on the substrate, determines a mixing ratio of the ink of the basic color and the concentration adjustment liquid based on the acquired information on the type of substrate and the information on the color of ink, and controls the basic color supply unit and the concentration adjustment liquid supply unit based on the determined mixing ratio.

4. 4. The printing apparatus according to claim 3, wherein the control unit controls the image resolution and the waveform of the drive voltage applied to the head unit during printing, based on the information on the type of the base material and the information on the color of the ink.

5. 4. The printing apparatus according to claim 3, wherein the control unit controls a voltage value of a drive voltage applied to the head unit based on the mixture ratio.

6. a circulation unit that supplies the mixed color ink to the head unit, and collects the mixed color ink that has not been used in the head unit and supplies it again to the head unit; 2. The printing apparatus according to claim 1, wherein the circulation unit is accommodated in the same housing as the head unit and moves together with the head unit.

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