Film straightening device, digital printing machine, and method for manufacturing plastic film prints

Abstract

To provide a film correction device capable of suppressing sagging and curling at both sides of a film during printing, in a digital printing method for printing information, such as characters or images, on a surface of a plastic film according to an inkjet method.SOLUTION: A film correction device suppresses sagging and / or curling at both sides of a film arranging a suctioning type belt which drives synchronously with printing speed, at a lower part of an ink head during digital printing for printing according to an inkjet method on a surface of a plastic film. Further, the film correction device corrects sagging in a direction that is orthogonal to a conveyance direction of the plastic film and curling on sides in the conveyance direction, and includes: a driving belt having suction holes for suctioning the film, and driving the film in a film conveyance direction synchronously with conveyance speed of the film; and a suction body for suctioning the film through the suction holes.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a digital printing method in which fine droplets of ink are sprayed directly onto a printing medium such as a plastic film, without the need to prepare a copy as in gravure printing or offset printing, and to an apparatus that can effectively prevent sagging of the film and curling of both sides. [Background technology]

[0002] Traditionally, gravure printing was the mainstream method for printing on plastic films, specifically multi-layer plastic films. In contrast, digital printing, which allows for high-definition, high-resolution printing, has been adopted by the film industry since around 2007. Unlike gravure printing, digital printing does not require the creation of a block copy, and is therefore characterized by low manufacturing costs. In addition, because the ink is sprayed directly onto the surface using the inkjet method, vivid, beautiful printing is possible. Furthermore, it is possible to print a wide variety of products in small lots, making it possible to provide packaging with different designs for each season, for example. Currently, it is being put to practical use mainly as reverse printing on stretched PET film, OPP, etc.

[0003] However, problems with this type of digital printing are the sagging of the plastic film, which is the printing medium, and curling on both sides. In conventional gravure printing, printing is done by pressing the film against the plate cylinder, so some sagging and curling of the film is not a problem. However, in digital printing, the film is advanced only by guide rolls, so there is nothing to suppress the sagging of the film and curling on both sides. Currently, the distance between the ink head and the film during printing is only a few millimeters, 1 to 2 mm, and the sagging parts of the film rub against the ink head. In the case of continuous type digital printing, which continuously releases ink, the distance between the ink head and the film can be made larger, so the film does not rub against the ink head, but the printed characters and images may become distorted and the product cannot be shipped.

[0004] As a method for suppressing sagging of the film and curling of both sides, various proposals have been made regarding improvements to the film itself (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2018 / 110639 [Patent Document 2] JP 2003-175543 A [Patent Document 3] JP 2015-47798 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, it would be sufficient to have a device that can suppress sagging and curling of both sides of the film without improving the film itself. Conventionally, the majority of inkjet printing is for paper, and some proposals have been made regarding paper transport devices (see, for example, Patent Document 3). However, the current situation is that no device has yet been proposed that can suppress sagging and curling of both sides of plastic films, particularly multi-layer plastic films with a large thickness (for example, 30 to 100 μm), especially for digital printing.

[0007] Therefore, an object of the present invention is to provide a film straightening device that can suppress sagging of the film and curling of both sides during printing in a digital printing method in which information such as letters or images is printed on the surface of a plastic film using an inkjet system. [Means for solving the problem]

[0008] As a result of intensive research into achieving the above object, the inventors have discovered that a specific film straightening device can be used to suppress film sagging and curling on both sides during printing. The present invention was completed based on this knowledge gained over many years.

[0009] That is, the present invention provides a film straightening device that suppresses sagging and / or curling of both sides of a plastic film during a digital printing method in which printing is performed on the surface of the film by an inkjet method.

[0010] The film straightening device is preferably provided with a suction-type drive belt (e.g., a belt conveyor) that drives in synchronization with the printing speed, below the ink head during digital printing on the surface of the plastic film using an inkjet method.

[0011] Regarding the installation position, the drive belt should be installed only under the ink head. Or, in the case of a CMYK inkjet printer or other device that has four ink heads, a belt of the same length as the total length of all four ink heads should be installed instead of only under the ink heads, in order to prevent sagging of the film and curling of both sides.

[0012] The belt length can be set to match the ink head, and the belt width is preferably set to be equal to or greater than the maximum width of the printing film. By making the belt width wider than the film width, the entire film can be sucked in, effectively preventing curling of both sides of the film.

[0013] By creating a vacuum inside the drive belt (e.g., a belt conveyor) and opening suction holes on the belt, the film can be sucked in, which is expected to reduce the film's sagging and curling on both sides. The belt conveyor can be rotated in sync with the printing speed to prevent printing misalignment.

[0014] The present invention also provides a film straightening device for straightening sagging of a plastic film in a direction perpendicular to the transport direction and / or curling of both sides in the transport direction, the film straightening device comprising: a drive belt having suction holes for sucking the film, which drives in the film transport direction in synchronization with the film transport speed, and a suction body for sucking the film through the suction holes.

[0015] The drive belt preferably has a plurality of suction holes along the film transport direction.

[0016] The drive belt preferably has suction holes at positions corresponding to both side edges in the film transport direction.

[0017] The film straightening device may include a plate-shaped body at the center in the belt width direction between the drive belt and the plastic film.

[0018] The film straightening device may have a film expanding member located upstream of the drive belt in the film transport direction, which expands both side portions of the film while transporting the film.

[0019] The plastic film is preferably a multi-layer plastic film having a thickness of 30 to 100 μm.

[0020] The present invention also provides a digital printing press comprising an upstream guide roll that unwinds and transports a roll-shaped plastic film, a film straightening device provided under the film located under the ink head with the drive belt that transports the film while sucking the unwound plastic film through a suction hole, the ink head that digitally applies ink onto the plastic film sucked through the suction hole, and a downstream guide roll that transports the inked plastic film and winds it up into a roll.

[0021] Furthermore, the present invention provides a method for producing a plastic film print, which includes a printing step in which, while transporting a plastic film, the film straightening device is used to suppress sagging of the film in a direction perpendicular to the film transport direction and / or curling of both sides of the film in the transport direction, and ink is applied to the film by digital printing to form a printed layer.

[0022] In this way, the film straightening device of the present invention can be preferably applied to plastic films, and is particularly effective for printing on multi-layer plastic films that have sagging or curls on both sides. By preventing sagging and curling of the film and improving the flatness of the film during printing, information such as images can be tightly adhered. Effect of the Invention

[0023] The film straightening device of the present invention can suppress sagging and curling of both sides of a plastic film, making it possible to perform digital printing with excellent aesthetics on plastic films with sagging and curling of both sides, particularly on multi-layer plastic films. [Brief description of the drawings]

[0024] [Figure 1] FIG. 1 is a cross-sectional view showing one embodiment of a film correction device of the present invention. [Diagram 2] FIG. 2 is an enlarged top schematic view of one embodiment of a drive belt. [Diagram 3] FIG. 13 is an enlarged schematic top view of another embodiment of the drive belt. [Figure 4] FIG. 13 is an enlarged schematic top view of another embodiment of the drive belt. [Diagram 5] FIG. 13 is an enlarged schematic top view of another embodiment of the drive belt. [Figure 6] FIG. 13 is an enlarged schematic top view of another embodiment of the drive belt. [Figure 7] FIG. 13 is an enlarged schematic top view of another embodiment of the drive belt. [Figure 8]FIG. 13 is an enlarged schematic top view of another embodiment of the drive belt. [Figure 9] FIG. 11 is a cross-sectional view showing another embodiment of the film correction device of the present invention. [Figure 10] 10 is an enlarged schematic top view of the vicinity of the film side-edge folding prevention roller in FIG. 9. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] The film straightening device of the present invention is a device for suppressing sagging and / or curling of both sides of a film, which is provided with a suction belt that drives in synchronization with the printing speed under an ink head during digital printing on the surface of a plastic film using an inkjet method. The film straightening device of the present invention is, for example, a film straightening device that straightens sagging in a direction perpendicular to the transport direction of a plastic film and / or curling of both sides in the transport direction, and is equipped with at least a drive belt having suction holes for sucking the film and driven in the film transport direction in synchronization with the film transport speed, and a suction body for sucking the film through the suction holes.

[0026] An embodiment of the film straightening device of the present invention is shown in Fig. 1. Fig. 1 shows an embodiment in which the film straightening device of the present invention is applied to an inkjet printer, which is a type of digital printer. 1 is a plastic film (hereinafter, may be simply referred to as "film"), 21 is a drive belt (endless belt) having suction holes, 22 and 23 are belt drive rolls, 2 is a belt conveyor consisting of the endless belt 21 and the belt drive rolls 22 and 23, 3 is a suction body, 4 is a film roll on the unwinding side, 5 is a film roll on the winding side, 6 and 7 are guide rolls, 8a to 8d are ink heads, 9a is an unwinding section, 9b is an application section, and 9c is a winding section.

[0027] In Fig. 1, the space is divided into an unwinding section 9a, an application section 9b, and a winding section 9c along the film transport direction D. In the unwinding section 9a, an unwinding side film roll 4 rotated and driven by an unwinding side motor (not shown) and an upstream guide roll 6 are arranged in sequence along the film transport direction D. Under the application section 9b, a film straightening device is installed, which includes an endless belt 21, a belt conveyor 2 consisting of a pair of drive rollers 22 and 23 capable of driving the endless belt 21 by rotating, and an inside of the belt conveyor 2, more specifically, an aspirator 3 installed between the endless belt 21 on the belt conveyor 2. In the winding section 9c, a guide roll 7 and a winding side film roll 5 are arranged in sequence along the film transport direction D.

[0028] In the unwinding section 9a, the film 1 to be coated with ink in the coating section 9b is wound in a roll shape around the unwinding film roll 4. The film 1 is unwound from the unwinding film roll 4, passes through the coating section 9b, and is wound up onto the take-up film roll 5 in the take-up section 9c.

[0029] In the coating section 9b, while the film 1 is transported in the transport direction D, the endless belt 21 is driven in synchronization with the transport speed of the film 1 in the transport direction D, and the film 1 is sucked toward the endless belt 21 by the suction body 3 through the endless belt 21, thereby eliminating slack and curl of the film 1, while the printing ink is discharged from the ink heads 8a to 8d, and printing is continuously performed on the film 1 by, for example, an inkjet method, and a printed layer is formed. The belt conveyor consisting of the endless belt 21 and the driving rolls 22 and 23 is connected to a power source (not shown) so that the belt facing the film 1 is driven in the transport direction D. The film straightening device of the present invention preferably includes at least such a belt conveyor 2 and the above-mentioned suction body 3. Note that FIG. 1 shows an example in which a belt conveyor equipped with the endless belt 21 is used, but the driving belt in the film straightening device of the present invention is not limited to this embodiment, and a belt with ends may be used, and may be unwound from the unwinding side roll like the film 1 and driven in the transport direction D.

[0030] 1 (i.e., the film 1 side). The endless belt 21 has suction holes that enable the suction body 3 to suck the film 1 toward the endless belt 21. The suction body 3 can suck the film 1 toward the endless belt 21 through the suction holes, thereby preventing sagging of the film and / or curling of both sides.

[0031] In the embodiment shown in FIG. 1, the belt conveyor 2 and the suction body 3 constituting the film straightening device of the present invention are installed under the film 1 at the position where the ink heads 8a to 8d are set, so that the suction body 3 sucks the film 1 through the suction holes 2a while the belt conveyor 2 rotates in the conveying direction D in synchronization with the printing speed, and sends the film 1 in the conveying direction D while sucking it. That is, the belt conveyor 2 and the suction body 3 are installed under the film 1 located under the ink heads 8a to 8d of the inkjet printer at a position where the film 1 can be sucked. This makes it possible to eliminate slack and / or curls on both sides of the film 1. Then, when digital printing is performed by the inkjet printer, the film 1 is free of slack and curls on both sides, improving the flatness of the film, preventing printing misalignment, and allowing information such as images to be uniformly attached. In this way, the film straightening device of the present invention makes it possible to perform digital printing on the film with excellent aesthetics.

[0032] FIG. 2 is a top view showing an embodiment of a drive belt having suction holes. The endless belt 21 is installed under the film 1 so that the belt surface (the belt surface having suction holes) is parallel to the film 1. The suction holes 2a are provided in a plurality of positions corresponding to both sides of the film 1 along the film conveying direction D, that is, over the entire circumferential direction of the endless belt 21. Even when driven in the film conveying direction D, the suction holes 2a are continuously present on the upper side of the endless belt 21 (the side facing the film 1). The suction holes 2a are provided in a plurality of rows in the belt width direction (direction perpendicular to the film conveying direction D), and further provided in a plurality of rows parallel to the circumferential direction, with a group of suction holes 2a provided in the belt width direction forming one row. The suction holes 2a are provided at equal intervals in the film conveying direction or circumferential direction and the belt width direction. This makes it possible to evenly suppress sagging of the film 1 and curling of both sides.

[0033] The belt width of endless belt 21 is set to be equal to or greater than the maximum width of film 1. Suction holes 2a are provided at positions corresponding to both side edges of film 1. With this configuration, suction body 3 can suck the entire width of film 1, effectively preventing curling of both side edges of the film.

[0034] When the film straightening device of the present invention is applied to a digital printer (particularly an inkjet printer), as shown in FIG. 1, it is preferable to provide the belt conveyor 2 only in the application section 9b, that is, only in the area extending before and after the ink head of the inkjet printer, under the film located under the ink head. This makes it possible to prevent the film from sagging and curling on both sides only when the ink is directly sprayed. In this case, the length of the belt conveyor 2 is appropriately set according to the size of the ink head. Also, for example, in a case where a plurality of ink heads are mounted in the film conveying direction D, such as a CMYK inkjet printer, by installing a belt conveyor 2 having a length that is approximately the same (the same or slightly longer) as the distance across the plurality of ink heads, rather than just under one ink head, it is possible to prevent the film from sagging and curling on both sides throughout the ink application. The film straightening device of the present invention may have a belt conveyor for each ink head (for example, four in the case of a CMYK inkjet printer), but if the length is approximately the same as the distance across the plurality of ink heads, it is inexpensive to prepare one belt conveyor and suction body.

[0035] The film straightening device of the present invention may be a movable type in which the drive belt is capable of sucking or contacting the film when in operation, and is in a position where the film is not sucked when not in operation. In this way, the film straightening device of the present invention may have a mechanism for moving the drive belt and the suction body between a position where the film is sucked and a position where the film is not sucked.

[0036] For example, when the area of ​​the film 1 to be coated reaches the coating section 9b, the endless belt 21 is set in a state where it can be vacuum-adsorbed through the suction holes 2a, an operation is started for applying ink to this area of ​​the film 1 to be coated, and while tension is applied to the film 1 in the conveying direction D, the endless belt 21 is operated, the film 1 is vacuum-adsorbed, and curls and sagging of the side edges are corrected. Before the area of ​​the film 1 to be coated reaches the coating section 9b and after it has passed through the coating section 9b, the operation of the belt conveyor 2 may be stopped and / or the belt conveyor 2 may be lowered, for example, to a retracted position.

[0037] As shown in FIG. 3, the suction holes 2a are provided only on both side portions 10a and 10c of the belt width direction (positions corresponding to both side portions of the film 1), and may not be provided in the width direction center portion 10b. In such a configuration, it is possible to suck only both side portions of the film 1, thereby suppressing curling of both sides of the film. For the same purpose, as shown in FIG. 4, a plate-like body 11 such as an acrylic resin plate may be provided in the belt width direction center portion 10b. The plate-like body 11 is provided between the film 1 and the endless belt 21 to prevent the film 1 from being sucked in the width direction center portion 10b. The plate-like body 11 does not have suction holes because it is provided for the purpose of preventing suction in the portion provided therein.

[0038] The hole size (diameter) of the suction holes 2a may be any size that can sufficiently suck the film and allow it to be transported in the transport direction D, and is, for example, about 3 to 5 mm. If the hole size is 3 mm or more, the suction force is sufficient and sagging and curling can be more effectively suppressed. If the hole size is 5 mm or less, the suction force is not too high and the film can be more appropriately transported in the transport direction.

[0039] The shape of the suction hole 2a is preferably circular, but may be polygonal as long as the effect of the present invention is not impaired.

[0040] When it is desired to change the strength of suction, it is preferable to increase the number of suction holes rather than increasing the size of the suction holes. For example, it is preferable to create suction holes at intervals of 5 to 50 mm.

[0041] When it is difficult to increase the number of suction holes, for example, as shown in Figs. 5 to 7, a part or all of the endless belt can be made into a halftone plate 2b. The halftone plate 2b also corresponds to a suction hole. This makes it possible to increase the suction force without changing the degree of vacuum. In the endless belt 21 shown in Figs. 5 to 7, the arrangement (number, position, arrangement, etc.) of the halftone plates 2b is not particularly limited and can be changed as appropriate.

[0042] As shown in FIG. 8, the endless belt 21 may have ultraviolet transmission holes 2c in order to cure the ultraviolet curable ink applied on the film 1 by irradiating the film 1 with ultraviolet light from the lower side of the belt surface. In inkjet printing, when curing the ultraviolet curable ink of the primer, more complete ultraviolet curing can be achieved by irradiating the film with ultraviolet light from the back side to cure the ultraviolet curable ink of the primer. The ultraviolet transmission holes 2c are provided so that ultraviolet light can easily pass through the belt, and are generally provided with an area larger than that of the suction holes 2a. If the belt is transparent or translucent enough to transmit ultraviolet light, there is no need to provide the ultraviolet transmission holes 2b.

[0043] The ultraviolet light transmitting holes 2c are arranged, for example, along the conveying direction D in the belt width direction central portion 10b of an arbitrary first row L1 and in the belt width direction central portion 10b of a second row L2 over a wider area than those in the first row L1, forming one set (set S), and the endless belt has multiple sets S at equal intervals around the circumference.

[0044] The material of the endless belt 21 is not particularly limited, but is preferably stainless steel or plastic. If it is plastic, it may be transparent or translucent. That is, the endless belt 21 may be a stainless steel belt or a plastic belt. It is more preferable that the endless belt 21 has antistatic properties.

[0045] The film straightening device of the present invention may have a film expansion member upstream of the drive belt in the film transport direction, which expands both side portions of the film while transporting the film. An example of the film expansion member is a film side folding prevention roller provided at a position that is the lower part of the film on the upstream side of the drive belt in the film transport direction. For example, as shown in FIG. 9, by providing a film side folding prevention roller 12 immediately before the belt conveyor 2, folding of the side of the film 1 being transported to the back side can be prevented or eliminated, and the side of the film 1 can be prevented from being folded inward or outward when the film is sucked by the suction body 3 thereafter.

[0046] 10 shows a view from above near the film side fold prevention roller 12 in FIG. 9. As the film side fold prevention roller 12, for example, a pair of film side fold prevention rollers 12a and 12b are provided in the film width direction. The film side fold prevention rollers 12a and 12b are each inclined so that the upper part is symmetrical with each other at an arbitrary angle toward the outside of the film width, and the upper ends of the inclined film side fold prevention rollers 12a and 12b are installed at a position higher than the conveying path of the film 1. By installing in this configuration and rotating the film side fold prevention rollers 12a and 12b in synchronization with the film conveying speed, the conveyed film 1 comes into contact with the film side fold prevention rollers 12a and 12b on the back side (belt conveyor 2 side), and at the same time, if the film 1 has a fold B on the side edge, it is pushed outward in the width direction, and the fold B is eliminated.

[0047] According to the film straightening device of the present invention, sagging of the plastic film and curling of both sides can be suppressed. Therefore, it is possible to perform digital printing with excellent aesthetics on plastic films with sagging and curling of both sides, especially on multi-layer plastic films. Since plastic films are unwound from a roll to a roll and printed on, unlike printing paper, they have self-supporting properties. Therefore, in a printing machine that performs digital printing on plastic films, there is usually no need to install a drive belt under the film under the ink head. However, the present invention has the effect of suppressing sagging of the film and curling of the sides during printing by installing a film straightening device equipped with a drive belt and a suction body under the film under the ink head, thereby enabling digital printing with excellent aesthetics.

[0048] The plastic film used in the film straightening device of the present invention is not particularly limited, but is preferably a multilayer film (particularly, a multilayer coextruded film). This is because multilayer films (particularly, multilayer coextruded films) often have an asymmetric structure in the thickness direction due to differences in the resin components and thickness ratios of each layer, and are prone to sagging and curling. The plastic film may be a sheet-like film (flat film) or a film obtained by flattening a tubular film. In addition, the plastic film is preferably a film transported by roll-to-roll.

[0049] The thickness of the plastic film is not particularly limited, but is preferably 30 to 100 μm. The film straightening device of the present invention is particularly suitable for eliminating sagging and curling of plastic films of such a thickness.

[0050] The film straightening device of the present invention can temporarily eliminate slack or curl even if the film has slack or curl, regardless of the film being improved. For this reason, it is particularly preferable to use it in combination with a digital printer such as an inkjet printer, for example, as shown in FIG. 1. The use of the film straightening device of the present invention is not limited to this, and it can be applied to any equipment for eliminating slack or side curl of a film. For example, it can be preferably used for temporarily eliminating slack or curl of a film when laminating it with another film.

[0051] A plastic film print can be produced by using the film straightening device of the present invention and a digital printer. Specifically, a plastic film print can be produced by a method having a printing step in which ink is applied onto the film by digital printing (e.g., inkjet printing) to form a print layer while the film is conveyed and the film straightening device of the present invention is used to suppress sagging of the film in a direction perpendicular to the film conveying direction and / or curling of both sides in the conveying direction.

[0052] The transport speed of the plastic film is not particularly limited, but is preferably 100 m / min or less from the viewpoint of simultaneously eliminating slack and curl and printing. When the film straightening device of the present invention is used in an inkjet printer, the printing speed can be increased to a maximum of 50 m / min when using ultraviolet curable ink (UV ink), and to a maximum of 75 m / min when using water-based ink, or further increased by devising the drying of the ink, from the viewpoint of simultaneously eliminating slack and curl and printing. In addition, it is preferable that the transport speed of the drive belt (i.e., the rotation speed of the belt conveyor) is synchronized with the transport speed of the film. In other words, it is preferable that the transport speed of the drive belt has a drive structure that can synchronize with the printing speed.

[0053] The degree of vacuum when the suction body 3 sucks the film through the suction holes is set appropriately depending on the number and hole diameter of the suction holes, but is preferably 12 to 36 kPa. The degree of vacuum does not have to be constant while the suction body 3 is in operation. Suction by the suction body 3 may be performed continuously or intermittently. Furthermore, the degree of vacuum can be adjusted according to the situation, since the degree of suction differs depending on the width and thickness of the film. EXAMPLES

[0054] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples. A plastic film was prepared as a printing medium. The details of the film are as follows. Film A: Multi-layer co-extruded flat film (composition: nylon / adhesive layer / polyethylene, thickness: 50 μm) Film B: Multi-layer co-extruded tube film (composition: nylon / adhesive layer / polyethylene, thickness: 50 μm) Film C: Multi-layer co-extruded tube film (with side seal, composition: nylon / adhesive layer / polyethylene, thickness: 50 μm)

[0055] Examples 1 to 3 For the above films A to C, digital printing was performed using the inkjet method to produce plastic film prints while eliminating slack and curls in the film using the film straightening device shown in Figure 1. The film transport speed was set to 50 mm / min to match the printing speed, the belt conveyor rotation speed was 50 mm / min, and the vacuum level was 36 kPa.

[0056] Comparative Examples 1 to 3 For the above films A to C, digital printing was carried out by the inkjet method in the same manner as in Examples 1 to 3, except that no film straightening device was used, to produce plastic film prints.

[0057] (evaluation) The film was evaluated for sagging, curling, and rubbing against the ink head during digital printing in the examples and comparative examples. The evaluation criteria were as follows. The results are shown in Table 1.

[0058] (1) Sagging and curling The evaluation was made as follows: ◯: the sagging or curling was eliminated during printing; Δ: the sagging or curling was relatively small; and ×: the sagging or curling was relatively large.

[0059] (2) Rubbing against the ink head The case where no rubbing occurred between the ink head and the film during printing was rated as ◯, and the case where rubbing occurred was rated as x.

[0060] [Table 1]

[0061] As can be seen from Table 1, by using the film straightening device of the present invention, both the flat film and the tube film were prevented from sagging and curling on both sides, and no rubbing with the ink head was observed. In addition, when the same film was used without using the film straightening device of the present invention, curling on both sides of the tube film was not observed to the same extent as with the flat film, but sagging toward the top (ink head side) was observed, as with the flat film, and rubbing with the ink head was also confirmed.

[0062] In summary, the configuration of the present invention and its variations are set forth below. [1] A film straightening device that suppresses sagging of the film and / or curling of both sides by installing a suction-type belt that moves in sync with the printing speed under the ink head during digital printing using the inkjet method to print on the surface of plastic film. [2] A film straightening device for straightening sagging of a plastic film in a direction perpendicular to the transport direction and / or curling of both sides in the transport direction, the film straightening device comprising: a drive belt having suction holes for sucking the film, which drives in the film transport direction in synchronization with the film transport speed, and a suction body for sucking the film through the suction holes. [3] The film straightening device according to [1] or [2], wherein the drive belt has a plurality of suction holes along the film transport direction. [4] The film straightening device according to any one of [1] to [3], wherein the drive belt has suction holes on both sides in the film transport direction. [5] A film straightening device according to [3] or [4], wherein the drive belt has a plurality of suction holes at equal intervals along the film transport direction at positions corresponding to both sides in the film transport direction. [6] The film straightening device according to any one of [1] to [5], wherein the drive belt has a plurality of suction holes at equal intervals in the belt width direction. [7] The film straightening device according to any one of [1] to [5], wherein the drive belt has no suction hole in the central portion in the belt width direction. [8] The film straightening device according to any one of [1] to [7], wherein the drive belt is an endless belt. [9] The film straightening device according to [8], comprising: a belt conveyor having the endless belt and a pair of drive rollers capable of driving the endless belt by rotating; and the suction body.

[10] The film straightening device according to [9], wherein the suction body is installed between the belts of the endless belt.

[11] The film straightening device according to any one of [1] to

[10] , further comprising a plate-shaped body disposed in the center in the belt width direction between the drive belt and the plastic film.

[12] A film straightening device according to any one of [1] to

[11] , further comprising a film expansion section disposed upstream of the drive belt in the film transport direction, which expands both side edges of the film while transporting the film.

[13] The film straightening device according to any one of [1] to

[12] , wherein the plastic film is a multilayer plastic film having a thickness of 30 to 100 μm.

[14] The film straightening device according to any one of [1] to

[13] , wherein the plastic film is a plastic film transported by roll-to-roll.

[15] A digital printing press comprising: an upstream guide roll that unwinds and transports a roll-shaped plastic film; a film straightening device described in any one of [1] to

[14] , in which the drive belt that transports the film while sucking the unwound plastic film through a suction hole is provided under the film located under an ink head; the ink head that digitally applies ink onto the plastic film sucked through the suction hole; and a downstream guide roll that transports the inked plastic film and winds it up into a roll.

[16] A method for producing a printed product on a plastic film, comprising a printing step of applying ink onto the film by digital printing to form a printed layer while conveying the plastic film and suppressing sagging of the film in a direction perpendicular to the film conveying direction and / or curling of both sides of the film in the conveying direction using a film straightening device in any one of [1] to

[15] . [Industrial Applicability]

[0063] The film straightening device of the present invention can perform digital printing using an inkjet method to print aesthetically pleasing information such as text or images, even on plastic film that has sagging or side curls. [Explanation of symbols]

[0064] 1. Plastic film 2. Conveyor belt 21 Endless Belt 22,23 Driving roll 2a Suction hole 2b halftone version 2c UV transmission hole 3 Suction body 4 Unwinding film roll 5. Take-up film roll 6,7 Guide roll 8a~8d Ink head 9a Unwinding section 9b Application part 9c Winding section 10a, 10c Belt width direction side edge portion 10b Belt width direction center 11 Plate-shaped body 12, 12a, 12b Film side folding prevention roller D Film transport direction L1 first row L2 second row S set B Fold in the film sides

Claims

1. A suction-type drive belt having suction holes that are driven in synchronization with the printing speed and a suction body for sucking the film through the suction holes are provided under an ink head during digital printing that uses an inkjet method to print on the surface of a multilayer plastic film including a nylon layer; a plate-shaped body is provided in the center of the belt width direction between the drive belt and the multilayer plastic film, a mechanism for moving the drive belt and the suction body between a position where the film is suctioned and a position where the film is not suctioned, the drive belt has the suction holes at positions corresponding to both side edges of the film, The suction hole has a diameter of 3 to 5 mm, and the film straightening device suppresses sagging and / or curling of both sides of the film.

2. A film straightening device for straightening slack in a direction perpendicular to the conveying direction of a multilayer plastic film including a nylon layer and / or curls on both sides in the conveying direction, the film straightening device comprising: a drive belt having suction holes for sucking the film and driven in the film conveying direction in synchronization with the conveying speed of the film; and a suction body for sucking the film through the suction holes; a plate-shaped body is provided in the center of the belt width direction between the drive belt and the multilayer plastic film, a mechanism for moving the drive belt and the suction body between a position where the film is suctioned and a position where the film is not suctioned, the drive belt has the suction holes at positions corresponding to both side edges of the film, The film straightening device, wherein the suction hole has a diameter of 3 to 5 mm.

3. 3. The film straightening device according to claim 1, wherein the drive belt has a plurality of suction holes along the film transport direction.

4. The film straightening device according to any one of claims 1 to 3, further comprising a film expansion member disposed upstream of the drive belt in the film transport direction, the film expansion member expanding both side portions of the film while transporting the film.

5. The film straightening device according to any one of claims 1 to 4, wherein the multilayer plastic film has a thickness of 30 to 100 µm.

6. A digital printing machine comprising: an upstream guide roll that unwinds and transports a roll-shaped plastic film; the film straightening device described in any one of claims 1 to 5, in which the drive belt that transports the film while sucking the unwound plastic film through a suction hole is provided under the film located under the ink head; the ink head that digitally applies ink onto the plastic film sucked through the suction hole; and a downstream guide roll that transports the plastic film coated with ink and winds it up into a roll.

7. A method for producing a plastic film print, comprising a printing step of applying ink onto the film by digital printing to form a printed layer while conveying a plastic film and suppressing sagging of the film in a direction perpendicular to the film conveying direction and / or curling of both sides of the film in the conveying direction using a film straightening device described in any one of claims 1 to 5.

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