Aqueous inkjet printing method and aqueous inkjet printing device

Abstract

To enable aqueous inkjet printing to be performed on a plastic film.SOLUTION: In an aqueous inkjet printing, in which a film F to be printed passes through an inkjet head part 10 and runs on a hot-air drying passage 20 while being applied with constant tension, sufficient tension for enabling the film to run stably is applied so that the film is neither flogged nor meandered by hot air during hot-air drying, and the tension and a drying temperature are adjusted so that the film is not contracted by the tension and the temperature.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an aqueous inkjet printing method and an aqueous inkjet printing device, and in particular to a printing method and device that are ideal for packaging materials made of plastic film used for packaging bags for storing food and lids for food containers when distributing food. [Background technology]

[0002] Nowadays, in the distribution of food, instead of face-to-face sales where food is prepared on the spot, packaged, and sold, a method is becoming mainstream in which processed foods, bread, sweets, etc. prepared in advance in food factories are packaged and sold at retail stores such as convenience stores and supermarkets.

[0003] In this sales method, packaged foods are displayed on shelves in retail stores, and customers pick them up and examine them before purchasing. Therefore, the packaging itself must be designed to attract customers' purchasing desire and make them more eye-catching.

[0004] In the above cases, since the primary purpose of the packaging material itself is to package food, the shape cannot be changed in a way that would impair its function, and the role of the patterns and / or letters (hereinafter referred to as "patterns, etc.") applied to the surface becomes extremely important.

[0005] Printing is a common method for applying the above-mentioned designs to packaging bags and food container lids, and there are two printing methods for printing on packaging bags and food container lids: printing on the back side (reverse printing) and printing on the front side (front printing). In this case, the Food Sanitation Act prohibits printing ink from coming into contact with food in food packaging materials, so when printing on the back side, a protective plastic film must be laminated on the printed layer side of the plastic film.

[0006] On the other hand, when printing on the front side of packaging material, there are no such restrictions, but the printed layer is exposed, so care must be taken to ensure that the printed layer does not become unclear due to physical friction or solvents (alcohol or oil) when it comes into contact with the back side of the film when it is printed and rolled up during processing into packaging bags or lids, or when it comes into contact with other packaging materials, items, or people's fingers during distribution or display.

[0007] In the above case, plastic film is a substrate that is difficult to absorb liquid, unlike paper, so gravure printing, which uses gravure ink with high coating adhesion, or flexographic printing, which uses flexographic ink, has been adopted for printing (for example, Patent Document 1).

[0008] Incidentally, inkjet printing, which does not require plate making and can generate images for printing from digital data, has excellent on-demand capabilities and would be useful for food packaging materials, which require printing of various designs at any time, but has not been adopted.

[0009] The reason is that aqueous inkjet inks that can be used for inkjet printing lack physical properties such as abrasion resistance, alcohol resistance, oil resistance, and water resistance, and the ink comes off easily and the coating adhesion is weak.In this case, gravure inks and flexographic inks, which have good coating adhesion, have too high viscosity and cannot be used in inkjet printing, which sprays the ink from a nozzle to adhere it, because they cannot be sprayed smoothly from the nozzle.

[0010] In the case of food packaging, which is not a fixed durable consumer good with a fixed design, but is consumed in a short period of time and requires printing of a wide variety of designs depending on the contents, speeding up printing is essential to improve production efficiency.

[0011] However, gravure printing and flexographic printing require plates to be prepared for new designs and set on the production line each time, which means the process of starting printing takes time, and there are limits to how quickly the process can be accelerated.

[0012] For example, in the case of food packaging materials with designs printed using gravure printing, it took a total of 12 days for the necessary pre-printing work (submitting the block copy + plate making) and printing, plus 6 days for post-processing (film lamination, finishing), for a total of 18 days.

[0013] Furthermore, as mentioned above, gravure printing requires a lot of work to separate colors and make plates, so the minimum order lot is inevitably large, forcing customers to purchase more packaging material than necessary, resulting in waste.

[0014] On the other hand, it is easy to choose to use inkjet printing when printing on the back side of the bag, but this requires a process of laminating a plastic film on the side of the printed layer of the plastic film, which creates the problem of being costly and time-consuming.

[0015] In this regard, the inventors of the present application have created the following invention. The first invention is an invention characterized in that, when printing a pattern and / or letters on the surface that is to be positioned on the front side of a plastic film that is to constitute a food packaging material during bag manufacturing, the pattern and / or letters are inkjet-printed using inkjet ink, and then a transparent inkjet ink is overprinted on the printed area by inkjet printing.

[0016] The second invention is characterized in that, when printing a pattern and / or letters on the front side of a plastic film that is to constitute food packaging material, the pattern and / or letters are inkjet-printed using inkjet ink, and then a transparent UV ink is overprinted.

[0017] Furthermore, the third invention is an invention characterized in that, when printing a pattern and / or letters on the front side of a plastic film that is to constitute a food packaging material, the pattern and / or letters are inkjet-printed using inkjet ink, and then a transparent EB ink is overprinted. [Prior art documents] [Patent documents]

[0018] [Patent Document 1] Patent Publication No. 2000-273379 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0019] According to the invention by the inventor of the present application, when printing a pattern or the like on the front surface of a packaging bag or a lid for a food container, even if inkjet printing is performed using aqueous inkjet ink, a transparent inkjet ink, or a transparent UV ink or a transparent EB ink is overprinted on the printed area to protect the printed layer of the pattern or the like, so that the printed layer of the pattern or the like is not exposed.

[0020] This prevents the printed layer of the design, etc. from being scraped off by friction and becoming unclear or generating shavings due to contact with the back side of the film when the film is wound up after printing during processing into packaging bags or lids, or contact with other packaging materials, articles, or people's fingers during distribution or display.

[0021] On the other hand, because printing is completed using inkjet printing, which has excellent on-demand capabilities, there is no time required to start printing, as with gravure printing or flexographic printing, which require preparing a plate for a new design and setting it on the production line. This makes it possible to speed up the process and dramatically improve the production efficiency of food packaging, which requires printing a wide variety of designs depending on the contents at any time.

[0022] The above invention breaks the conventional technical common sense that aqueous inkjet inks cannot be used for printing on plastic films because they lack physical properties such as abrasion resistance, alcohol resistance, oil resistance, and water resistance, the ink comes off easily, and the coating film adhesion is weak.

[0023] However, the inventors of the present invention, who carried out aqueous inkjet ink printing on plastic films, which no one had ever attempted before, faced a new problem.

[0024] The problem is that in aqueous inkjet printing, where the ink head (printing part) is non-contact, the tension of the printing ink head and the film running along the drying path are under the same conditions, so the drying temperature and the tension of the drying path cause thermal expansion and contraction of the film, making it impossible to control the registration and dimensions. [Means for solving the problem]

[0025] The present invention has been created with the objective of providing an aqueous ink jet printing method and an aqueous ink jet printing apparatus that solve the above-mentioned problems.

[0026] In other words, the aqueous inkjet printing method of the present invention is characterized in that, in aqueous inkjet printing, the film to be printed is applied with a constant tension while passing through the ink head section and traveling along a hot air drying path, a tension is applied to the film to allow stable traveling so that the film does not flap or meander due to the hot air during hot air drying, and the tension and drying temperature are adjusted to a range in which the film to be printed does not shrink due to the tension and temperature.

[0027] Furthermore, the invention described in claim 2 is characterized in that, in the aqueous inkjet printing method, a general-purpose film, OPP (biaxially oriented polypropylene), is used as the film to be printed, with a heat shrinkage rate of 150°C for 5 minutes, MD (vertical) 8-30%, TD (horizontal) 5-35%, and when the drying device is capable of sufficiently drying the specified aqueous ink and has an oven length of 5.5 m, the tension inside the drying oven is reduced to 20 N (10 N to 30 N for a width of 760 mm) under the conditions of a drying temperature of 85°C and a speed of 80 m / min, thereby limiting the finished dimensions of the printed film to ±0.2% in the vertical direction and ±0.2% in the horizontal direction.

[0028] Furthermore, the invention described in claim 3 is characterized in that, in the above-mentioned aqueous inkjet printing method, a plurality of large-diameter rotating drums are provided in the hot air drying path, and the film travels while coming into contact with the arcuate outer surface as it rotates, and the film is sent to the next rotating drum in sequence, and the film is dried by the heat from the rotating drum it comes into contact with and by a hot air device arranged on the periphery of the rotating drum, thereby realizing stable travel of the film so that it does not flap or meander, and the tension and temperature of the film are lowered to a level that keeps film shrinkage within a predetermined range.

[0029] Furthermore, the invention described in claim 4 is characterized in that in the above-mentioned aqueous inkjet printing method, after the moisture in the film is dried using an infrared heater in the hot air drying path, the film is made to run along a spiral path in a drying oven equipped with a hot air device and dried with hot air, thereby realizing stable running of the film so that it does not flap or meander, and the tension and temperature of the film are lowered to a level that keeps the film shrinkage within a specified range.

[0030] Furthermore, the invention described in claim 5 is characterized in that in the above-mentioned aqueous inkjet printing method, in the hot air drying path, both widthwise ends of the film are fixed via clips to film transport members arranged on both sides of the film in the widthwise direction, so that the film travels in conjunction with the travel of the film transport members, thereby realizing stable travel so that the film does not flap or meander, and the tension and temperature of the film are lowered to a level that keeps the film shrinkage within a specified range.

[0031] Furthermore, the invention described in claim 6 is characterized in that in the aqueous inkjet printing method, the film is adsorbed and fixed to the belt of the belt conveyor in the hot air drying route and transported, thereby realizing stable running of the film so that it does not flap or meander, and the tension and temperature of the film are reduced to a level that keeps the film shrinkage within a specified range.

[0032] The aqueous inkjet printing device described in claim 7 is an aqueous inkjet printing device in which the film to be printed is applied with a constant tension while passing through the ink head unit and traveling along a hot air drying path, and is characterized in that it applies tension to the film to allow stable traveling so that the film does not flap or meander due to the hot air during hot air drying, and is equipped with a conversion system for balancing the printing area, drying temperature, traveling speed and tension to adjust the tension and drying temperature to a range in which the film to be printed does not shrink due to the tension and temperature.

[0033] This invention is a printing method that combines non-contact inkjet printing with the function of drying water-based ink. When water-based inkjet printing is performed on a printing substrate made of OPP (biaxially oriented polypropylene), a film with low heat resistance, the heat from drying the water-based ink causes the print dimensions to expand and contract, resulting in misregistration and a significant deviation from the standard product dimensions, making printing impossible.

[0034] Since the ink head (printing part) is non-contact, it is subject to the same tension conditions as inside the drying oven. Generally, hot air drying involves blowing hot air from a nozzle onto the ink surface, so tension is required to ensure stable running of the film so that it does not flap or meander.

[0035] Through experiments described below, the inventors of this application found the optimum conditions for aqueous inkjet printing even with OPP (biaxially oriented polypropylene), a film with low heat resistance among the general-purpose films used in aqueous inkjet printing. By reproducing these optimum conditions, the temperature conditions are such that the aqueous ink can be sufficiently dried, and the film can be kept in a stable running state without flapping or meandering due to the hot air in the drying oven, preventing the OPP (biaxially oriented polypropylene) film with low heat resistance from thermally expanding or contracting, allowing for print register control and ensuring that product dimensions are within standard.

[0036] The present invention aims to develop an aqueous inkjet printing device that can suppress the thermal expansion and contraction that is a problem when using general-purpose film OPP (biaxially oriented polypropylene): heat shrinkage rate 150°C for 5 minutes, conditions: MD (vertical) 8 to 30%, TD (horizontal) 5 to 35% for aqueous inkjet printing, and can reproduce printing register and dimensions.

[0037] In this case, it was discovered that thermal expansion and contraction could be suppressed by lowering the tension inside the drying oven to 20N (10N to 30N when the width is 760mm). However, in this case, the temperature and hot air required for drying would cause the film to sag and meander in a drying oven of typical structure, making the tension unstable and preventing it from running, so an aqueous inkjet printer that can run stably even at a tension of 20N (10N to 30N when the width is 760mm) is required.

[0038] Even when using the above-mentioned aqueous inkjet printer with general-purpose OPP (biaxially oriented polypropylene) film, with a heat shrinkage rate of 150°C for 5 minutes, MD (vertical) 8-30%, TD (horizontal) 5-35%, if the drying equipment is capable of sufficiently drying the specified aqueous ink and the oven length is 5.5 m, the finished dimensions of the printed film will be within the standard (vertical ±0.2%, horizontal ±0.2%) by reducing the tension inside the drying oven to 20 N (10 N to 30 N for a width of 760 mm) under conditions of a drying temperature of 85°C and a speed of 80 m / min.

[0039] Based on the above premise, the inventors of the present invention conducted experiments combining temperature, tension, and heating time using a typical film used in aqueous inkjet printing, and found the optimal conditions for aqueous inkjet printing based on the temperature required for drying, the tension required for stable operation in the drying oven, and the heating time equivalent to the printing speed. If these optimal conditions can be reproduced, it will be possible to design an aqueous inkjet printer capable of mass production. The details of the experiment are as follows.

[0040] <Experiment content> ·Constant temperature and humidifier Yamato Scientific Co., Ltd. Model IG401 Equilibrium Temperature and Humidity Control System (GTHC System) (performance) Temperature and humidity range: +5°C to +85°C (87°C acceptable) / 40% to 95% Temperature fluctuation: ±1.0℃, temperature gradient: 5℃, spatial temperature deviation: 5℃ Humidity fluctuation: ±596 rh, humidity gradient: 10% rh, spatial humidity deviation: 1096 rh ·Base material used OPP: Tocello (U-1, 20 μm), Futamura Chemical (FOR-AQ, 20 μm) Special OPP: Toyobo (P2161, 20 μm) PET: Toyobo (E5100, 12 μm) ·jig Hanging clip (width 145mm) Weight clip (145mm wide): 350g, 950g, 1,500g Actual water-based inkjet printer: Test results for a width of 760 m converted to a sample size of 140 mm * Actual machine 20N = 350g, actual machine 50N = 950g, actual machine 80N = 1,500g specimen Size: Length (film direction) 200mm, Width (film direction) 140mm ·measurement 300mm JLS1 Grade 1 Metal Ruler + Tokai Sangyo PEAK10x Magnifying Glass (0.1mm Scale) Temperature (each temperature setting + constant humidity of 40%) and heating time 75℃ (4 seconds = 76℃, 11 seconds = 76.5℃, 18 seconds = 77℃) 80℃ (4 seconds = 81℃, 11 seconds = 81.5℃, 18 seconds = 82℃) 85℃ (4 seconds = 86℃, 11 seconds = 86.5℃, 18 seconds = 87℃) Change the set temperature for each heating time, taking into account the temperature drop in the thermostatic bath Actual water-based inkjet printer: Calculate heating time from speed and drying oven Drying oven 5.5m, speed 80m / min = 4 seconds, 30m / min = 11 seconds, 0.3m / min = 18 seconds The heating temperature is determined by combining the conditions under which water-based ink dries in the actual machine. *30m / min = 75℃, 80m / min = 85℃, 0.3m / min is not tested on actual equipment

[0041] Experimental method Samples were taken from three locations on both sides and in the center of the film substrate (MD direction of the film) Cut to a size of 200mm long and 140mm wide. Punch holes with a needle at 100mm intervals both vertically and horizontally in the center of the specimen. Before heating, measure 100mm in both length and width using a metal ruler and magnifying glass (to one decimal place) and record. Select the specified weight for the weight clip Attach a hanging clip to the top of the specimen and a weight clip to the bottom. Check that the thermostatic bath is at the specified temperature (±1°C) and hang the specimen in the bath. Close the door of the thermostatic chamber and heat for the specified time. After the specified time has passed, open the door and remove the sample. Remove the top and bottom clips After heating, measure 100mm in both length and width using a metal ruler and a magnifying glass (to one decimal place) and record the measurement. Record the dimensions after heating and subtract them from the dimensions before heating. The graph plots the difference (+ is expansion, - is contraction). Check the thermal expansion and contraction of each specimen

[0042] <Experimental Results> [Table 1] The hanging weight within the print control range of 0.296 is indicated. (1) OPP: Tocello: U-1: Passes when the paper is heated to 85°C vertically in 4 seconds, 75°C vertically, 80°C horizontally, and 85°C horizontally in 11 seconds at 350g. Since printing is done both vertically and horizontally at the same time, a low tension of 350g is required. (2) OPP: Futamura Chemical: FOR-AQ, like Tocello, requires low tension of 350g. (3) Special OPP: Toyobo: P2171 is a film that is more heat-resistant than regular OPP, so it can be printed in 11 seconds at 80°C / 85°C vertically and with a tension of 950g. (4) PET: Toyobo E5100 is a highly heat-resistant film, unlike OPP, so it can be printed at a normal tension of 1,500g.

[0043] <Graph showing detailed experimental results> (1) 75℃: Vertical heat-shrinkable OPP <Tocello U-1#20> [Table 2]

[0044] (1) 75℃: Horizontal heat-shrinkable OPP (Tocello U-1#20) [Table 3] (1) At 75°C, water-based ink dries at a speed of 30 m / min = 11 seconds on an actual machine, so the print controllable range is: vertical and horizontal expansion of 0.2% or less. A tension of 950g for 11 seconds is slightly above the limit in the vertical direction, but 350g is acceptable.

[0045] (1) 80℃: OPP vertical heat shrinkable <Tocello U-1#20> [Table 4]

[0046] (1) 80℃: Horizontal heat-shrinkable OPP (Tocello U-1#20) [Table 5] (1) At 80°C, the drying limit for water-based ink is 80 m / min = 4 seconds. Printing controllable range: Vertical and horizontal expansion and contraction of 0.2% or less Passed both vertical and horizontal tests at a tension of 950g for 4 seconds.

[0047] (1) 85℃: Vertical heat-shrinkable OPP <Tocello U-1#20> [Table 6]

[0048] (1) 85℃: Horizontal heat-shrinkable OPP (Tocello U-1#20) [Table 7] (1) At 85°C, water-based ink dries at a speed of 80 m / min (4 seconds) on an actual machine. Printing controllable range: Vertical and horizontal expansion and contraction of 0.2% or less A tension of 950g for 4 seconds is slightly above the limit in the vertical direction, but 350g is acceptable.

[0049] (2) 75℃: OPP vertical heat expansion <Futamura Chemical FOR-AQ#20> [Table 8]

[0050] (2) 75℃: OPP horizontal heat expansion <Futamura Chemical FOR-AQ#20> [Table 9] (2) At 75°C, water-based ink dries at a speed of 30 m / min = 11 seconds on an actual machine. Printing controllable range: Vertical and horizontal expansion and contraction of 0.2% or less A tension of 950g for 11 seconds exceeds the vertical limit, but 350g passes.

[0051] (2) 80℃: OPP vertical heat expansion <Futamura Chemical: FOR-AQ#20> [Table 10]

[0052] (2) 80℃: OPP horizontal thermal expansion <Futamura Chemical: FOR-AQ#20> [Table 11] (2) At 80°C, the drying limit for water-based ink is 80 m / min = 4 seconds. Printing controllable range: Vertical and horizontal expansion and contraction of 0.2% or less A tension of 950g for 4 seconds is slightly above the limit in the vertical direction, but 350g is acceptable.

[0053] (2) 85℃: OPP vertical heat expansion <Futamura Chemical: FOR-AQ#20> [Table 12]

[0054] (2) 85℃: OPP horizontal thermal expansion <Futamura Chemical: FOR-AQ#20> [Table 13] (2) At 85°C, water-based ink dries at a speed of 80 m / min = 4 seconds on an actual machine. Print controllable range: Vertical and horizontal stretching is 0.296 or less A tension of 950g for 4 seconds is slightly above the limit in the vertical direction, but 350g is acceptable.

[0055] (3) 75℃: Special OPP vertical heat shrinkable <Toyobo P2171 20μ> [Table 14]

[0056] (3) 75℃: Special OPP horizontal heat shrinkage <Toyobo P2171 20μ > [Table 15] (3) At 75°C, water-based ink dries at a speed of 30 m / min = 11 seconds on an actual machine. Print controllable range: Vertical and horizontal expansion and contraction is 0.296 or less It is heat resistant and passes both vertical and horizontal tests at a tension of 1,500g for 11 seconds.

[0057] (3) 80℃: Special OPP vertical heat shrinkable <Toyobo P2171 20μ> [Table 16]

[0058] (3) 80℃: Special OPP horizontal heat shrinkage <Toyobo P2171 20μ> [Table 17]

[0059] (3) At 80°C, the drying limit for water-based ink is 80 m / min = 4 seconds. Printing controllable range: Vertical and horizontal expansion and contraction of 0.2% or less It is heat resistant and passes both vertical and horizontal tension tests at 1,500g for 4 seconds.

[0060] (3) 85℃: Special OPP vertical heat shrinkable <Toyobo P2171 20μ> [Table 18]

[0061] (3) 85℃: Special OPP horizontal heat shrinkage <Toyobo P2171 20μ> [Table 19] (3) At 85°C, water-based ink dries at a speed of 80 m / min (4 seconds) on an actual machine. Printing controllable range: Vertical and horizontal expansion and contraction of 0.2% or less It is heat resistant and passes both vertical and horizontal tension tests at 1,500g for 4 seconds.

[0062] (4) 75℃: PET longitudinal heat shrinkage <Toyobo E5100 12μ> [Table 20]

[0063] (4) 75℃: PET horizontal heat shrinkage <Toyobo E5100 12μ> [Table 21]

[0064] (4) At 75°C, water-based ink dries at a speed of 30 m / min = 11 seconds on an actual machine. Printing controllable range: Vertical and horizontal expansion and contraction of 0.2% or less It is heat resistant and passes both vertical and horizontal tests at a tension of 1,500g for 11 seconds.

[0065] (4) 80℃: PET longitudinal heat shrinkage <Toyobo E5100 12μ> [Table 22]

[0066] (4) 80℃: PET horizontal heat shrinkage <Toyobo E5100 12μ> [Table 23] (4) At 80°C, the drying limit for water-based ink is 80 m / min = 4 seconds. Printing controllable range: Vertical and horizontal expansion and contraction of 0.2% or less It is heat resistant and passes both vertical and horizontal tension tests at 1,500g for 4 seconds.

[0067] (4) 85℃: PET vertical heat shrinkable sheet <Toyobo E510012μ> [Table 24]

[0068] (4) 85℃: PET horizontal heat shrinkage <Toyobo E510012μ> [Table 25] (4) At 85°C, water-based ink dries at a speed of 80 m / min (4 seconds) on an actual machine. Printing controllable range: Vertical and horizontal expansion and contraction of 0.2% or less It is heat resistant and passes both vertical and horizontal tension tests at 1,500g for 4 seconds. [Effects of the Invention]

[0069] According to the aqueous inkjet printing method of the present invention, even when printing on a film with low heat resistance, the hot air in the drying oven can be made to cause the film to run stably without flapping or meandering, preventing the film from thermally expanding or contracting, allowing for printing register control and ensuring that the product dimensions are within the standard.

[0070] Furthermore, the aqueous inkjet printing apparatus of the present invention is equipped with a conversion system for balancing the printing area, drying temperature, running speed and tension in order to adjust the tension and drying temperature within a range in which the film to be printed does not shrink due to the tension and temperature, making it possible to easily carry out the above printing method at the printing site. [Brief explanation of the drawings]

[0071] [Figure 1] 1 is a conceptual diagram of the aqueous inkjet printing method of the present invention. [Figure 2] FIG. 1 is a conceptual diagram of the first embodiment. [Figure 3] FIG. 10 is a conceptual diagram of the second embodiment of the same. [Figure 4] FIG. 10 is a conceptual diagram of the third embodiment of the same. [Figure 5] FIG. 10 is a conceptual diagram of the fourth embodiment of the same. [Figure 6] 1 is a print example using the aqueous inkjet printing method of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION

[0072] Specific embodiments of the present invention will be described below with reference to the accompanying drawings. Figure 1 is a conceptual diagram of the aqueous inkjet printing method of the present invention. In the figure, symbol F denotes the film to be printed, which passes through ink head unit 10 and travels along hot air drying path 20 while being subjected to a certain tension. Since ink head unit 10 is a non-contact type, the tension conditions are the same as those in drying path 20. In drying path 20, hot air is blown from a nozzle onto the ink surface in a drying oven to dry it.

[0073] As a result of the above-mentioned experiments, the inventors of the present application found that, using a general-purpose film OPP (biaxially oriented polypropylene) as the film to be printed on, with a heat shrinkage rate of 150°C for 5 minutes: MD (length) 8-30%, TD (width) 5-35%, and a drying device with an oven length of 5.5 m that can sufficiently dry a specified water-based ink, the finished dimensions of the printed film can be kept to ±0.2% lengthwise and ±0.2% widthwise by reducing the tension inside the drying oven to 20 N (10 N to 30 N for a width of 760 mm) at a drying temperature of 85°C and a speed of 80 m / min.

[0074] In the above case, a drying device is required that allows the film to run stably without flapping or meandering even when tension is low.

[0075] Figure 2 shows a first embodiment of the drying device. In this example, multiple large-diameter rotating drums 21 are provided along the hot-air drying path, with the film F traveling along the rotating drums while contacting the arcuate outer surfaces. The film is fed sequentially to the next rotating drum, and is dried by the heat from the rotating drum with which it comes into contact and by hot-air devices 23 located around the rotating drums. This ensures stable film travel without flapping or meandering, and lowers the film's tension and temperature to a level that keeps its shrinkage within a specified range. Reference numeral 22 in the figure denotes guide rollers for guiding the film.

[0076] Figure 3 shows a second embodiment of the drying device. In this example, the film F is first dried using an infrared heater (not shown) in the hot air drying path, and then the film is run along a spiral path in a drying oven equipped with a hot air device (not shown) and dried with hot air. This ensures stable running of the film without flapping or meandering, and lowers the tension and temperature of the film to a level that keeps film shrinkage within a specified range. Reference numeral 32 in the figure denotes a guide roller for guiding the film.

[0077] Figure 4 shows a third embodiment of the drying device. In this example, in the hot air drying path, both widthwise ends of the film F are fixed with clips 41 to film transport members 40 arranged on both sides of the film in the widthwise direction, so that the film travels along with the travel of the film transport members, ensuring stable travel without flapping or meandering, and lowering the tension and temperature of the film to a level that keeps film shrinkage within a specified range.

[0078] Figure 5 shows a fourth embodiment of the drying device. In this example, the film F is adsorbed and fixed to the belt 51 of the belt conveyor 50 and transported along the hot air drying path, ensuring stable running without flapping or meandering, and lowering the tension and temperature of the film to a level that keeps film shrinkage within a specified range. The adsorption means used here is a means for sucking air through numerous small holes drilled in the belt 51 of the belt conveyor 50.

[0079] Figure 6 shows an outline of the prior invention by the inventor of the present application, in which a design and / or letters 1 are first printed on film F using aqueous inkjet ink, and then a transparent printing layer 2 is overprinted on top of that using inkjet ink, UV ink, or EB ink.

[0080] In aqueous inkjet printing, where the film to be printed is applied with a constant tension while passing through the ink head unit and traveling along a hot air drying path, the present invention is characterized in that it applies tension to the film to allow it to travel stably so that it does not flap or meander due to the hot air during hot air drying, and in that the tension and drying temperature are adjusted to a range in which the film to be printed does not shrink due to the tension and temperature, and to achieve this, the aqueous inkjet printing device may also be characterized by being equipped with a conversion system for the balance between printing area, drying temperature, traveling speed and tension.

[0081] More specifically, in an aqueous inkjet printing device in which a film to be printed is applied with a certain tension and passes through an ink head unit and travels through a hot air drying path, By inputting the properties of the film to be printed and the coverage that indicates the area where the ink will be used, printing speed, drying temperature, tension, By providing a printing management system that automatically calculates the above, the aqueous inkjet printing device can run stably and prevent the film from flapping or meandering due to the hot air during hot air drying, and can also prevent shrinkage. [Explanation of symbols]

[0082] F film 1. Designs and / or letters 2 transparent printing layer 10 Ink head unit 20 Hot air drying route 21 Rotating drum 22 Guide roller 23 Hot air equipment 32 Guide roller 40 Film transport member 41 clips 50 conveyor belt 51 Belt

Claims

1. In an aqueous inkjet printing method in which a film to be printed passes through an ink head unit and travels along a hot air drying path while being given a certain tension, tension is given to the film so that the film can travel without flapping or meandering due to the hot air during hot air drying, and the tension and drying temperature are adjusted within ranges that cause little shrinkage of the film to be printed due to the tension and temperature, The aqueous inkjet printing method uses a general-purpose film, OPP (biaxially oriented polypropylene), as the film to be printed, with a heat shrinkage rate of 150°C for 5 minutes under conditions of MD (vertical) 8-30%, TD (horizontal) 5-35%, and uses a drying device that can sufficiently dry the specified aqueous ink, with an oven length of 5.5 m, a drying temperature of 85°C, a speed of 80 m / min, and a low tension in the drying oven of 10 N to 30 N at a width of 760 mm, thereby limiting the finished dimensions of the printed film to ±0.2% vertically and ±0.2% horizontally.

2. 2. The aqueous inkjet printing method according to claim 1, wherein the hot air drying path includes a plurality of large-diameter rotating drums on which the film travels while contacting the arcuate outer periphery of the rotating drum as the drum rotates, and the film is fed to the next rotating drum in sequence while being dried by heat from the rotating drum with which it comes into contact and by a hot air device disposed on the periphery of the rotating drum, thereby realizing a running motion of the film without flapping or meandering, and lowering the tension and temperature of the film to a level that keeps film shrinkage within a predetermined range.

3. 2. The aqueous inkjet printing method according to claim 1, wherein in the hot air drying path, moisture in the film is dried using an infrared heater, and then the film is run along a spiral path in a drying oven equipped with a hot air device and dried with hot air, thereby realizing a running state of the film without flapping or meandering, and lowering the tension and temperature of the film to a level that keeps the shrinkage of the film within a predetermined range.

4. The aqueous inkjet printing method according to claim 1, wherein in the hot air drying path, both widthwise ends of the film are fixed to film transport members arranged on both sides of the film in the widthwise direction via clips, and the film travels in accordance with the travel of the film transport members, thereby realizing a travel of the film without flapping or meandering, and the tension and temperature of the film are lowered to a level that keeps the film shrinkage within a predetermined range.

5. 2. The aqueous inkjet printing method according to claim 1, wherein the film is transported by adsorbing and fixing it to the belt of a belt conveyor in the hot air drying route, thereby realizing a running motion of the film without flapping or meandering, and the tension and temperature of the film are lowered to a level that keeps the shrinkage of the film within a predetermined range.

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