Aqueous inkjet printer

Abstract

To solve problems such as misregistration caused by meandering of a plastic film during movement when aqueous ink-jet printing is performed on the plastic film, distortion of printing, and dimensional change and repetitive adjustment of level differences and gaps between heads.SOLUTION: An aqueous inkjet printer is provided with: a primary unit 1 which makes prints with four color inks, CMYK, and dries the prints; and a secondary unit 10 which makes prints with a white ink and dries the prints after the primary unit. In the primary unit, an infrared ray IR heater 3 is disposed next to a print head 2 which makes prints in the four colors (CMYK) and then a hot-air dryer 4 is disposed. In the secondary unit 10, an infrared ray IR heater is disposed next to a white ink print head 12 and then a hot-air dryer 14 is disposed. The infrared ray IR heater of the primary unit limits its output to such a degree that carbon, a main material, of an india ink does not fully react to a wave length of an infrared ray IR and only moisture in the inks is evaporated. The hot-air dryer dries the inks to such a degree that the india ink does not adhere to a guide roll by low-temperature hot air of 70°C or lower. In the hot-air dryer in the secondary unit, the inks are dried with high-temperature hot air.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an aqueous inkjet printing apparatus, and particularly to an apparatus optimal for plastic films used for packaging materials such as packaging bags and lids of containers.

Background Art

[0002] As printing corresponding to printing on small-lot, multi-variety packaging materials made of plastic films, inkjet printing, which does not require plate making during printing and can generate a printing image from digital data, is excellent in on-demand properties and is useful for packaging materials that must print various patterns and the like at any time.

[0003] In the above inkjet printing, since aqueous inkjet printing contains an aqueous solvent in addition to a colorant in the ink, it is necessary to remove the aqueous solvent by heat drying after printing.

[0004] Regarding the above, Patent Document 1 describes an aqueous inkjet printing apparatus in which a printing object such as paper, a plastic film, or a fabric passes through a printing head unit that discharges ink and travels through a drying path, and a first heating unit and a second heating unit are provided at the tip of the printing head unit, and the set temperature of the second heating unit is set higher than the set temperature of the first heating unit.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Disclosure of the Invention

Problems to be Solved by the Invention

[0006] By the way, in an aqueous inkjet printing apparatus using a plastic film as a printing target, problems have occurred that do not manifest in paper or fabric. These are problems that occur chronically, such as misregistration due to the meandering of the plastic film during running, misregistration due to printing distortion, misregistration due to dimensional changes, and repeated adjustment of the head level and gap. Until now, in such situations, there have been many losses before and during printing, which has hindered normal printing.

Means for Solving the Problems

[0007] The present invention was created for the purpose of providing an aqueous inkjet printing apparatus that solves the above problems.

[0008] That is, the aqueous inkjet printing apparatus of the present application is In an aqueous inkjet printing apparatus in which a plastic film to be printed passes through a printing head unit that discharges ink while being given a certain tension and travels along a drying path, A primary unit that prints and dries CMYK four-color inks and a secondary unit that prints and dries white ink after that are provided, In the above primary unit, an infrared IR heating device is arranged next to the printing head that prints CMYK four colors, and a hot air drying device is arranged next to that, In the above secondary unit, a hot air drying device is arranged next to the printing head that prints white ink, In the infrared IR heating device in the above primary unit, the output is set so that carbon, which is the main raw material of black ink among CMYK four colors, does not completely react to the wavelength of infrared IR and only the moisture in the ink is evaporated, In the hot air drying device in the above primary unit, the hot air drying is performed at a low temperature of 70°C or lower without completely drying the black ink so that the ink does not adhere to the guide roll, In the hot air drying device in the above secondary unit, it is characterized by drying with high-temperature hot air.

[0009] Further, in the invention described in claim 2, in the secondary unit of the aqueous inkjet printing apparatus, an infrared IR heating device is arranged next to the printing head that prints white ink, and a hot air drying device is arranged next to that. The output of the infrared IR heating device in the secondary unit is characterized by being limited to 65% or less.

[0010] Further, in the invention described in claim 3, in the aqueous inkjet printing apparatus, the plastic film to be printed travels under a tension of less than 50 N.

Advantages of the Invention

[0011] In a conventional aqueous inkjet printing apparatus, hot air drying was performed in an environment of 75 to 85°C using a hot air drying device that blows hot air toward the printing surface of the object to be printed.

[0012] The inventor of the present application found through experiments that the cause of the above problems in an aqueous inkjet printing apparatus with a plastic film as the object to be printed is that the plastic film undergoes heat shrinkage due to overly high-temperature hot air drying that is normal for objects to be printed such as paper and fabric. By performing hot air drying at a high temperature of 75 to 85°C, the plastic film undergoes heat shrinkage, resulting in chronic defects such as phenomenon 1 (snaking during running), phenomenon 2 (printing distortion), phenomenon 3 (dimensional change), and the need for adjustment such as phenomenon 4 (repeated adjustment of head steps and gaps).

[0013] To fundamentally solve the above problems, it is necessary to lower the drying temperature to 70°C or less. However, if the drying temperature is lowered to 70°C or less, the aqueous ink will be insufficiently dried and adhere to the roll, making printing impossible (hereinafter referred to as "roll-up"). It is impossible to achieve drying conditions where the plastic film does not undergo heat shrinkage and the aqueous ink does not roll up, and there has been no method to solve this problem until now.

[0014] Through experiments, the inventor of the present application conceived of the temperature conditions and heating means essential for an invention that fundamentally solves this chronic problem.

[0015] First, regarding the heating means, in the present invention, the configuration in which a drying device was arranged and dried after printing CMYK four-color inks and white ink has been changed to a configuration in which each ink is dried individually every time it is printed. That is, in the present invention, a primary unit that prints and dries CMYK four-color inks and a secondary unit that then prints and dries white ink are provided, and individual drying devices are arranged in each unit.

[0016] Regarding the drying after printing CMYK four-color inks, by drying with low-temperature hot air of 70°C or less without completely drying the ink so that the ink does not adhere to the guide roll, shrinkage of the plastic film in the path until the next white ink is printed is prevented, and problems such as misregistration due to meandering during the running of the plastic film, misregistration due to printing distortion, misregistration due to dimensional changes, and repeated adjustment of the head step and gap are eliminated.

[0017] Regarding the drying in the aforementioned primary unit, the inventor of the present application conceived of adopting a known infrared IR method (such as Patent Document 1). However, when drying color ink with infrared rays, especially black ink reacts too much to the wavelength of infrared rays and the black ink gets heated and melts. Therefore, the inventor of the present application focused on the condition of stopping at the energy that only dries the moisture in the black ink because carbon, which is the main raw material of the black ink, does not completely react to the wavelength of infrared IR, and discovered it. Evaporate only the moisture in the ink of CMYK four colors with infrared IR, and dry it with low-temperature hot air below 70°C without completely drying the black ink in particular so that the ink is not taken up by the guide roll, and then use high-temperature hot air in the subsequent white ink unit to completely dry white and CMKY four colors. That is, the drying condition of evaporating only the moisture of CMYK four colors (especially black ink) at a low temperature of 70°C or lower using infrared IR was found in the primary unit of CMYK four colors mentioned above. That is, the fact that it was confirmed that drying was performed in a state where the ink was not taken up by the guide roll of the primary unit of CMYK four colors became the trigger for the invention. That is, since there was a process of drying only CMYK four colors first, it was possible to create a state where it was not completely dried with infrared IR even at a low temperature of 70°C or lower. As a result, the phenomenon in which the black ink, which was a conventional problem, reacted too much to the wavelength of infrared IR, got heated, and melted could be avoided.

[0018] According to the present invention, it becomes possible to use infrared IR for a known black ink mainly made of carbon.

Brief Description of the Drawings

[0019]

Figure 1

Best Mode for Carrying Out the Invention

[0020] Hereinafter, the chronic quality defect phenomenon when aqueous inkjet printing a plastic film clarified by the inventor of the present application will be described.

[0021] (Chronic Defect Phenomenon No. 1: Misregistration due to Snakiness during Running) During the printing process, the deviation of the meandering state for CMYK four colors with respect to white is ±0.3 to 0.5 mm in the front, back, left, and right directions. According to the experiments of the inventors of the present application, at the conventional hot air drying temperature of 75 to 85°C, both heat-resistant OPP and general-purpose OPP continue to meander slowly in the front, back, left, and right directions while running even when a constant tension is applied in the drying furnace. As a result of the experiments, it was clarified that this is due to the heat shrinkage of the plastic film at high temperatures due to the orientation during the production of the plastic film.

[0022] The water-based inkjet printing device does not control the tension in a constant manner. Instead, by adjusting the driving nip roll to a constant rotation speed, the running of the plastic film flows smoothly without problems. That is, even if there is a tension fluctuation due to the heat shrinkage of the plastic film, the driving nip roll remains at a constant rotation, so the fluctuation of the plastic film directly results in a phenomenon of meandering in the front, back, left, and right directions. Originally, it is not a tension control, but the draw ratio (rotation rate of all driving nip rolls) is set to match the target tension. In this case, the target tension is set between 20 and 50 N. Ordinarily, a high tension of 50 N or more is required to eliminate meandering, but if the tension is too strong, wrinkles are likely to appear on the plastic film, and the straight line in the width direction of the printing also curves, causing problems in terms of design. Therefore, it is necessary to use a low tension of less than 50 N (20 to 50 N). However, in this tension range, due to the influence of the heat shrinkage of the plastic film, the flow extends and the width contracts, which directly results in a phenomenon of meandering in the left, right, front, and back directions. In the gravure machine and flexo machine, the tension control method is different, and since printing is performed while being nipped by the plate, even at a high tension (50 N or more), the straight line in the width direction of the printing does not curve and is printed normally, and the phenomenon of meandering in the front, back, left, and right directions does not occur. That is, it is a phenomenon specific to the water-based inkjet printing device.

[0023] The target plastic films include both general-purpose OPP, which is prone to heat shrinkage except for PET with stable heat shrinkage, and heat-resistant OPP, which is slightly more stable than the former. General-purpose OPP is likely to cause significant heat shrinkage during running and meander left and right and back and forth at drying temperatures as high as 75 - 85°C. Similarly, heat-resistant OPP is less likely to meander, but when the alignment of CMYK four colors and white is strict (±0.3 mm) in terms of design, alignment errors will occur. Therefore, it is necessary to find the optimal conditions under which both general-purpose OPP and heat-resistant OPP can be printed stably.

[0024] (Chronic Defect Phenomenon Part 2: Alignment Error due to Printing Distortion) In water-based inkjet printing, after printing, the film directly enters the drying oven. When the plastic film undergoes heat shrinkage due to high-temperature drying in the drying oven, even if the wind speed difference of the hot air in the width direction of the nozzle, the guide roll in the drying oven, and the assembly of the machine body are within the allowable accuracy, the CMYK four-color printing will show a left-right difference in the width direction and become distorted in design. If printing white in this distorted state next, the positions of the CMYK four colors will have a left-right difference compared to the white at the normal position, resulting in a misalignment. It was a chronic defect as it was easy to produce non-adjustable distortion by the twisting roll in the machine.

[0025] The cause of this printing distortion was found to be hot air drying at too high a temperature through experimental results. Whether it is general-purpose OPP or heat-resistant OPP, drying at a high temperature (75 - 85°C) will affect the orientation during plastic film formation. For example, a shape perpendicular to the printing design will be distorted left and right and become slightly rhomboid. Of course, it is also affected to some extent by the assembly accuracy of the printing device and the left-right wind speed difference of the hot air from the drying nozzles. However, in the case of this water-based inkjet printing device, it was found that even within the accuracy of the machine manufacturer, heat shrinkage of the plastic film caused by hot air drying at too high a temperature will result in distortion.

[0026] The plastic films targeted are both general-purpose OPP, which is prone to heat shrinkage and is less stable than heat-resistant OPP, which is more stable than general-purpose OPP and is other than PET with stable heat shrinkage. General-purpose OPP is likely to cause a distortion phenomenon with a left-right difference due to significant heat shrinkage during running at a drying temperature of 75 to 85 °C, which is too high. Similarly, although heat-resistant OPP is less likely to generate distortion, misregistration occurs when the tolerance for CMYK four colors and white in terms of design is strict (±0.3 mm). Therefore, it is necessary to find the optimal conditions under which both general-purpose OPP and heat-resistant OPP can be stably printed.

[0027] (Chronic Defect Phenomenon No. 3: Misregistration Due to Dimension Change) In water-based inkjet printing, there is no printing plate in the inkjet method, and the ink is ejected non-contact for printing. The printed material is run through a drying oven at a constant tension until the ink dries. However, since it is necessary to dry the water-based ink at a high temperature (75 to 85 °C) to completely dry it, the dimensions of the CMYK four colors change significantly due to the influence of this high temperature. After drying the CMYK four colors and printing white in the next unit, there is a dimensional difference between the CMYK four colors with changed dimensions and the white in the original data, so misregistration will occur as it is. Therefore, usually, while making trial prints, the dimensions of each other are checked, and especially the dimension of white is corrected in the data to start printing.

[0028] The cause of this dimensional difference was clarified from the results of this experiment to be hot air drying at too high a temperature. When both general-purpose OPP and heat-resistant OPP are dried at a high temperature (75 to 85 °C), the plastic film undergoes heat shrinkage, causing the dimensions of the CMYK four colors to change. It was clarified that due to the conventional hot air drying at too high a temperature, the plastic film undergoes heat shrinkage, resulting in a dimensional difference between the CMYK four colors and white.

[0029] The target plastic film is both general-purpose OPP, which is prone to heat shrinkage except for PET with stable heat shrinkage, and heat-resistant OPP, which is slightly more stable. General-purpose OPP significantly undergoes heat shrinkage during running at a drying temperature as high as 75 to 85 °C, and the dimensional change of CMYK four colors is likely to be large after drying. Similarly, although heat-resistant OPP is less prone to heat shrinkage than general-purpose OPP, when the alignment of CMYK four colors and white is strict (±0.3 mm) in terms of design, alignment errors occur. Therefore, it is necessary to find the optimal conditions under which both general-purpose OPP and heat-resistant OPP can be stably printed.

[0030] (Chronic Defect Phenomenon No. 4: Repeated Adjustment of Head Step and Gap) In water-based inkjet printing, since multiple heads are used for the same color, it is necessary to individually adjust the step (alignment in the flow direction) and gap (alignment in the width direction) between adjacent heads for each head. However, even if adjusted with great effort, once the machine is stopped and printing is performed again, the adjustment results cannot be reproduced, and it is necessary to repeat the adjustment, which is not suitable for mass production.

[0031] The reason why the adjustment of this head step (alignment in the flow direction) and gap (alignment in the width direction) cannot be reproduced was clarified from the results of this experiment to be hot air drying that was too hot. Even if the step and gap were adjusted between individual heads first and confirmed by proof printing, adjustment would be required at another location and could not be reproduced repeatedly. When both general-purpose OPP and heat-resistant OPP are dried at a high temperature (75 to 85 °C), the plastic film undergoes heat shrinkage, and the plastic film changes slightly each time it is repeated, so the previous state could not be reproduced.

[0032] Figure 1 is a conceptual diagram of the water-based inkjet printing apparatus of the present invention. In the figure, reference symbol F is the plastic film to be printed. This plastic film passes through the printing head unit that discharges ink while being given a tension of 50 N here and travels through the drying path to be printed.

[0033] In the present invention, the printing head for printing CMYK four colors and the printing head 12 for printing white ink are respectively housed in the primary unit 1 and the secondary unit 10, and individual drying paths are provided within each unit.

[0034] That is, a drying path consisting of an infrared IR heating device 3 and a subsequent hot air drying device 4 is provided after the printing head 2 for printing CMYK four colors in the primary unit 1, and a drying path consisting of an infrared IR heating device 13 and a subsequent hot air drying device 14 is provided after the printing head 12 for printing white ink in the secondary unit 10.

[0035] In the above drying path, in the infrared IR heating device 3 in the primary unit 1, the output is adjusted so that carbon, which is the main raw material of the ink inks among the CMYK four colors, does not completely react to the wavelength of the infrared IR and only the moisture in the ink is evaporated, and in the hot air drying device 4, the drying is limited to such an extent that the ink does not adhere to the guide roll with hot air at a low temperature of 70°C or less without completely drying the ink.

[0036] On the other hand, in the drying path of the secondary unit 10, after printing with the CMYK four colors, the plastic film F printed with white ink by the printing head 12 is completely dried, and here, an infrared IR heating device 13 and a subsequent hot air drying device 14 are provided. In this case, if there is a sufficient distance in the drying path by the hot air drying device 14, the infrared IR heating device 13 becomes unnecessary.

[0037] The inventor of the present application conducted the following tests using the above aqueous inkjet printing device. <Test Content> ◎ Plastic Film (Printing Substrate) · Heat-resistant OPP #20 (Toyobo P2171) · General-purpose OPP #20 (Toppan U-1) (Testing Machine (1) Test Conditions) Aqueous inkjet printing conditions: speed 50 m / min, tension around 40 N, paper width 760 mm Drying conditions for CMYK four colors · Heat-resistant OPP = IR output of the primary unit is 90% or more + drying temperature is 70°C or less · General-purpose OPP = IR output of the primary unit is 90% or more + drying temperature is 70°C or less (Testing machine (2) test conditions) Water-based inkjet printing conditions: speed 50 m / min, tension around 40 N, paper width 760 mm Drying conditions for CMYK 4 colors · Heat-resistant OPP = IR output of the primary unit is 70% or more + drying temperature is 70°C or less · General-purpose OPP = IR output of the primary unit is 70% or more + drying temperature is 70°C or less ◎ Infrared IR heating device specifications · Testing machine (1): 3.8 kw × 6 units (wavelength approximately 2.0 μm) · Testing machine (2): 3.8 kw × 9 units (wavelength approximately 2.0 μm) ◎ Two types of printing designs (coverage: 4 colors 120 - 140%, white 140%) · Design A with strict registration: serpentine left - right - front - back ±0.3 mm · Design B with strict head step and gap: reproduce by repeating after adjustment ◎ White drying conditions (low IR output + high-temperature hot air drying) Same conditions for both testing machines (1) and (2): IR output of the secondary unit is 65% or less + 80°C or more

[0038] <Test results> (Results of testing machine (1)) · Heat-resistant OPP = IR output of the primary unit is 90% or more + 70°C or less → All of the above chronic defects (1 - 4) are eliminated · General-purpose OPP = IR output of the primary unit is 90% or more + 70°C or less → All of the above chronic defects (1 - 4) are eliminated (Results of testing machine (2)) · Heat-resistant OPP = IR output of the primary unit is 70% or more + 70°C or less → All of the above chronic defects (1 - 4) are eliminated · General-purpose OPP = IR output of the primary unit is 70% or more + 70°C or less → All of the above chronic defects (1 - 4) are eliminated

[0039] (Test considerations) The tests were conducted under the same conditions for both testing machines (1) and (2), except for the different specifications of the infrared IR heating devices. The difference in the specifications of the infrared IR heating devices lies in that the testing machine (1) has 6 IR lamps, while the testing machine (2) has 9 IR lamps.

[0040] In the case of the 6 IR lamps of the testing machine (1), even when the IR output was set to 90% or more, there was no damage to the plastic film. By combining drying at a low temperature of 70°C or less, it was possible to dry the water-based ink at a film running speed of 50 m / min. In the case of the 9 IR lamps of the testing machine (2), when the IR output was set to 90% or more, damage occurred to the heat-resistant OPP plastic film and strong flow wrinkles were generated. Therefore, the output was set to 70% or more to eliminate the plastic film wrinkles. For general-purpose OPP as well, when the IR output was 90% or more, damage occurred to the plastic film and strong flow wrinkles were generated. Therefore, the output was set to 70% or more to eliminate the plastic film wrinkles. For both heat-resistant OPP and general-purpose OPP, by combining drying at a low temperature of 70°C or less at the appropriate IR output, it was possible to sufficiently dry the water-based ink at a speed of 50 m / min.

[0041] By optimizing the output according to the specifications of the infrared IR heating device and combining drying at a low temperature of 70°C or less, all chronic defects such as phenomenon 1 (snaking during running), phenomenon 2 (printing distortion), phenomenon 3 (dimensional change), and phenomenon 4 (repeated adjustment of head step and gap) caused by heat shrinkage of the plastic film at high temperature were resolved.

Explanation of symbols

[0042] F Film 1 Primary unit 2 CMYK ink printing head 3 Infrared IR heating device 4 Hot air drying device 10 Secondary unit 12 CMYK ink printing head 13 Infrared IR heating device 14 Hot air drying device

Claims

1. In an aqueous inkjet printing apparatus in which a plastic film to be printed travels through a drying path while passing through a printing head unit that ejects ink while being given a constant tension, a primary unit that prints and dries CMYK four-color inks and a secondary unit that then prints and dries white ink are provided. In the primary unit, an infrared IR heating device is arranged next to the printing head that prints the CMYK four colors, and a hot air drying device is arranged next to that. In the secondary unit, a hot air drying device is arranged next to the printing head that prints white ink. In the infrared IR heating device in the primary unit, its output is limited to the extent that carbon, which is the main raw material of black ink among the CMYK four colors, does not completely react to the wavelength of infrared IR and only the moisture in the ink is evaporated. In the hot air drying device in the primary unit, drying is limited to the extent that the ink does not adhere to the guide roll with hot air at a low temperature of 70°C or less without completely drying the black ink. In the hot air drying device in the secondary unit, drying is performed with high-temperature hot air. An aqueous inkjet printing apparatus characterized by the above.

2. In the secondary unit, an infrared IR heating device is arranged next to the printing head that prints white ink, and a hot air drying device is arranged next to that. The aqueous inkjet printing apparatus according to Claim 1, wherein the output of the infrared IR heating device in the secondary unit is limited to 65% or less.

3. The aqueous inkjet printing apparatus according to Claim 1 or 2, wherein the plastic film to be printed travels with a tension of less than 50 N.

Images