Image forming apparatus

Abstract

The invention provides an image forming apparatus. The image forming apparatus includes an ink print head unit, a pre-coating print head unit, and a control unit. The ink head unit discharges ink to a printing base material conveyed in a predetermined conveying direction. The pre-coating head unit is disposed on the upstream side of the ink head unit in the conveyance direction, and discharges a pre-coating liquid to the printing base material. The control unit controls the head unit for the pre-coating liquid so that the head unit discharges the pre-coating liquid. When the surface tension of the printing base material is lower than a predetermined value, the control unit controls the head unit for the pre-coating liquid so as to discharge a predetermined amount of the pre-coating liquid. Therefore, the pre-coating treatment can be performed according to the characteristics of the printing base material.

Description

Technical Field

[0001] The present invention relates to an image forming device which forms an image on a printing substrate by inkjet method. Background Art

[0002] In an inkjet image forming apparatus, a pre-coating treatment of applying a pre-coating liquid is generally performed in order to improve the adhesion between a printing substrate and ink.

[0003] The discharge amount of the pre-coating liquid may be determined according to the type of ink and the amount of ink deposited per unit area on the printing substrate. This improves the scratch resistance of the printing substrate on which the image is formed.

[0004] Furthermore, it is considered that the adhesion between the printing substrate and the ink depends not only on the type of ink and the adhesion amount per unit area of ​​the discharged ink, but also on the characteristics of the printing substrate. Summary of the invention

[0005] Therefore, in view of the above circumstances, an object of the present invention is to provide an inkjet image forming apparatus capable of performing a pre-coating process according to the characteristics of a printing substrate.

[0006] In order to achieve the above-mentioned object, the image forming device of the present invention comprises an ink print head unit, a pre-coating print head unit and a control unit. The ink print head unit discharges ink to a printing substrate transported along a specified conveying direction. The pre-coating print head unit is arranged at a position on the upstream side of the conveying direction than the ink print head unit, and is used to discharge a pre-coating liquid to the printing substrate. The control unit controls the pre-coating liquid print head unit to discharge the pre-coating liquid. When the surface tension of the printing substrate is lower than a specified value, the control unit controls the pre-coating liquid print head unit in a manner of discharging a specified amount of the pre-coating liquid. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 It is a front view schematically showing an image forming apparatus according to an embodiment of the present invention.

[0008] Figure 2 It is a plan view showing a print head unit in the image forming apparatus according to one embodiment of the present invention.

[0009] Figure 3 This is a diagram for explaining the behavior of a liquid droplet with respect to a printing substrate having different surface tensions in the image forming apparatus according to one embodiment of the present invention.

[0010] Figure 4This is a table showing the results of evaluation tests of line width reproducibility and ink drying state in the image forming apparatus according to one embodiment of the present invention.

[0011] Figure 5A It is a diagram (photograph) showing an image of Example 1 in the image forming apparatus according to one embodiment of the present invention.

[0012] Figure 5B It is a diagram (photograph) showing an image of Comparative Example 2 in the image forming apparatus according to one embodiment of the present invention. DETAILED DESCRIPTION

[0013] Next, refer to the attached Figure 1 An image forming apparatus according to an embodiment of the present invention will be described.

[0014] Reference Figure 1 , the overall structure of the image forming apparatus 1 is described. Figure 1 It is a front view schematically showing the internal structure of the image forming apparatus 1 .

[0015] The image forming device 1 includes a supply roller 3, an image forming unit 5, a drying unit 7 and a winding roller 9, wherein the supply roller 3 is wound with a long printing substrate M; the image forming unit 5 forms an image on the printing substrate M supplied from the supply roller 3 by inkjet method; the drying unit 7 dries the image formed by the image forming unit 5; and the winding roller 9 winds up the printing substrate M dried by the drying unit 7.

[0016] The printing base material M is wound and mounted on the supply roller 3. As the supply roller 3 rotates, the printing base material M is fed in a predetermined conveying direction.

[0017] The image forming section 5 is arranged downstream of the supply roller 3 in the conveying direction. The image forming section 5 includes a pre-coating liquid print head unit 11, four ink print head units 13B, 13C, 13M, and 13Y (collectively referred to as 13), and a conveying plate 15 for conveying the printing substrate M along the surface.

[0018] The one pre-coat liquid print head unit 11 is arranged upstream in the conveying direction of the four ink print head units 13. The pre-coat liquid print head unit 11 has the same structure as the four ink print head units 13. The print head units 11 and 13 are electrically connected to the control unit 19.

[0019] like Figure 2 As shown, the pre-coat liquid print head unit 11 and the four ink print head units 13 each include three print heads 21 and a plate 23 that supports the three print heads 21 . Figure 2 It is a plan view showing the print head units 11 and 13 .

[0020] like Figure 2 As shown, the three print heads 21 are arranged in a staggered manner along the width direction Y (line scan head method) in a manner equal to the width of the printing substrate M (the length along the width direction Y intersecting the conveying direction X), and are supported by the plate 23. Each print head 21 has a plurality of nozzles (not shown). The discharge ports of the nozzles open on the lower surface of the print head 21.

[0021] The pre-coating liquid is supplied to each print head 21 of the pre-coating liquid print head unit 11. The supplied pre-coating liquid is discharged downward from the discharge port of each print head 21. The components of the pre-coating liquid are, for example, 10% of polyester resin (trade name PESRESIN A-640, manufactured by TAKAMATSU OIL & FAT Co., LTD.), 0.04% of surfactant (trade name Surfynol 440, manufactured by Nissin Chemical Co., Ltd.), 25% of propylene glycol, and 64.96% of water.

[0022] The four ink head units 13B, 13C, 13M, and 13Y are arranged in sequence along the transport direction X, and are supplied with black, cyan, magenta, and yellow inks, respectively. The supplied inks are discharged downward from the discharge ports of the respective print heads 21 .

[0023] Refer again Figure 1 The conveying plate 15 is disposed below one pre-coating liquid print head unit 11 and four ink print head units 13. The upper surface of the conveying plate 15 is formed flat. Figure 2 As shown, the width of the conveying plate 15 is wider than the width of the printing substrate M and all the print head units 11 and 13. A heat source (not shown) is provided below the conveying plate 15 to heat the conveying plate 15 to a predetermined temperature. The conveying plate 15 is made of metal, for example.

[0024] The printing substrate M fed from the supply roller 3 is transported along the upper surface of the transport plate 15 below the pre-coat liquid print head unit 11 and the ink print head unit 13 .

[0025] The drying section 7 is arranged on the downstream side of the image forming section 5 in the conveying direction. The drying section 7 includes a heating drum 31, and an upstream tension roller 33 and a downstream tension roller 35 respectively arranged on the upstream side and the downstream side of the heating drum 31. The printing substrate M passing through the image forming section 5 is wound around the heating drum 31 between the upstream tension roller 33 and the downstream tension roller 35. The heating drum 31 dries the printing substrate M conveyed along the surface by heating.

[0026] The winding roller 9 is arranged on the downstream side of the drying section 7 in the conveying direction. One end of the printing substrate M is fixed to the winding roller 9. The winding roller 9 is connected to a motor (not shown) for rotation. The winding roller 9 is rotated in a predetermined direction at a predetermined rotation speed by the motor, whereby the printing substrate M is fed from the supply roller 3. The fed printing substrate M passes through the image forming section 5 and the drying section 7 and is wound on the winding roller 9.

[0027] As described above, the control unit 19 controls the print head unit 13. In addition, the control unit 19 includes an input unit 19a such as a display panel. The input unit 19a includes a surface tension input unit for inputting the value of the surface tension of the printing substrate M. The value of the surface tension is, for example, a value measured in accordance with "JIS K 6768:1999 Plastics-Film and Sheet-Wetting Tension Test Method".

[0028] The image forming operation of the image forming apparatus 1 having the above-mentioned structure will be described. During the image forming operation, first, the user inputs the surface tension of the printing substrate M to the input unit 19a of the control unit 19. When the input surface tension value is less than 38 mN / m, the control unit 19 discharges a predetermined amount (for example, 2.0 g / m 2 ) by controlling the pre-coating liquid using the print head unit 11.

[0029] After that, the motor is driven to rotate the take-up roller 9, and the printing substrate M is sent out from the supply roller 3 to the image forming unit 5. In the image forming unit 5, the printing substrate M is transported along the upper surface of the transport plate 15. When the printing substrate M is transported below the pre-coating liquid print head unit 11, the control unit 19 controls the pre-coating liquid print head unit 11 to discharge a predetermined amount of pre-coating liquid to the printing substrate M according to the image data. On the other hand, when the input surface tension value is higher than 38mN / m, the control unit 19 controls the pre-coating liquid print head unit 11 so as not to discharge the pre-coating liquid. That is, when the input surface tension value is 38mN / m or more, the pre-coating process is not performed.

[0030] After that, the printing substrate M is conveyed to the bottom of the ink print head unit 13, and the ink of the specified color is discharged from the corresponding print head unit 13 according to the image data. At this time, the printing substrate M is assisted in drying by the heated conveying plate 15. The ink reacts with the pre-coating liquid and is not easy to move from the landing position. The printing substrate M with the image formed in this way is conveyed to the drying section 7. In the drying section 7, the ink is completely dried. After that, the printing substrate M is wound up on the winding roller 9.

[0031] As described above, according to the present invention, the pre-coating treatment is performed only when the surface tension of the printing substrate M is less than 38 mN / m. Thus, when the surface tension of the printing substrate M is low, the surface energy of the printing substrate M is low and stable, so that the landed ink droplets are easily moved from the landing position on the printing substrate M. As a result, Figure 3 As shown in the figure on the left side of , sometimes two ink droplets are pulled together and become one large droplet after drying. As a result, the size of the droplets is uneven, and as a result, the line width is uneven. On the other hand, when the pre-coating treatment is performed, the adhesion between the ink and the printing substrate M is improved, and it is difficult for the landed ink droplets to move from the landing position on the printing substrate M. As a result, Figure 3 As shown in the figure on the right side of , two ink droplets merge with the printing substrate M and are not pulled closer to each other. In addition, when the surface tension of the printing substrate M is high (for example, when it is 38 mN / m or more), the surface energy of the printing substrate M is high and unstable, so it is easy for other objects (ink, etc.) to adhere to the surface. In other words, the ink and the printing substrate M are easy to merge.

[0032] Therefore, by performing the pre-coating process only when the surface tension of the printing substrate M is less than 38 mN / m, the adhesion between the printing substrate M and the ink can be improved and the pre-coating process can be performed efficiently. The printing substrate having a surface tension of less than 38 mN / m refers to a plastic film made of PET or polypropylene, for example.

[0033] Next, a test for evaluating the relationship between the surface tension of the printing substrate and the line width reproducibility and the drying state in the image forming apparatus 1 of the present embodiment is described. As the pre-coating liquid, the above-mentioned components (polyester resin (trade name PESRESIN A-640, manufactured by Takamatsu Oil & Fats Co., Ltd.) 10%, surfactant (trade name Surfynol 440, manufactured by Nissin Chemical Industry Co., Ltd.) 0.04%, propylene glycol 25%, water 64.96%) are used.

[0034] The surface tension of the evaluated printing substrate was measured in accordance with "JIS K 6768:1999 Plastics - Film and Sheet - Wetting Tension Test Method". Printing substrates with different surface tensions were prepared, and the pre-coating treatment was performed by changing the coating amount of the pre-coating liquid. The line width reproducibility and drying state of the image formed by printing an image with 600 dpi as one dot line on each printing substrate using cyan ink were evaluated, and the results were reported in Figure 4 As shown in the table.

[0035] Line width reproducibility was determined from observation results using a microscope (trade name, MM-800 (manufactured by Nikon Corporation)). Line widths less than 45 μm were set to 0, 45 μm or more and less than 50 μm were set to △, and 50 μm or more were set to ×. In the dry state, hot air at a temperature of 120 degrees and a wind speed of 37 m / s was brought into contact with the printed substrate for 10 seconds, and then, when the image was touched with a finger, the state in which the ink did not adhere to the finger was set to 0, and the state in which the ink adhered was set to ×.

[0036] In Examples 1 to 6, the surface tension value was 22.6 to 38.0 mN / m, and the pre-coating treatment was performed by changing the coating amount of the pre-coating liquid. In Comparative Examples 1 to 3, the surface tension value was 22.6 mN / m, and the coating amount of the pre-coating liquid was less than that of the Example (Comparative Example 1), more than that of the Example (Comparative Example 3), and no pre-coating treatment was performed (Comparative Example 2). The images of Example 1 and Comparative Example 2 were respectively Figure 5A , Figure 5B Shown in.

[0037] according to Figure 4 As shown in the table, in Examples 1 to 6, when the surface tension value is 22.6 to 38.0 mN / m, by applying the coating amount of 1.0 to 3.0 g / m 2 Pre-coating in the range of 2000 to 20000 can obtain good results in line width reproducibility and drying state. Figure 5A As shown, the lines are of uniform width.

[0038] On the other hand, in Comparative Example 1, although the surface tension value is the same as that of Examples 1 to 4, the coating amount is less than that of Examples 1 to 4. Therefore, it is considered that the effect of the pre-coating treatment cannot be fully exerted, and good line width reproducibility cannot be obtained. In addition, in Comparative Example 2, although the surface tension value is the same as that of Examples 1 to 4, since the pre-coating treatment is not performed, as described above, the droplets of the landed ink are pulled closer to widen the line width, and good line width reproducibility cannot be obtained. Figure 5B As shown, Figure 5A In comparison, the line width is not uniform. In Comparative Example 3, although the surface tension value is the same as that of Examples 1 to 4, the coating amount is larger than that of Examples 1 to 4. Therefore, it is considered that the amount of the pre-coating treatment liquid is excessive, and a good dry state cannot be obtained.

[0039] From these evaluation results, it was confirmed that, when the surface tension value was less than 38.0 mN / m, good line width reproducibility and dry state could be obtained by performing the pre-coating treatment.

[0040] In the above-mentioned embodiment, a print head unit 13 of four colors is used, but the present invention is not limited to four colors, and may be more or less than four colors. In addition, the print head units 11 and 13 are not limited to the line scan head method. However, the line scan head method is preferred because it can increase the printing speed. In addition, as the printing substrate M, a long plastic film (PET film) is used, but a cut film may also be used. In addition, the printing substrate M may be synthetic paper or the like.

[0041] Although the present invention describes specific embodiments, the present invention is not limited to the above-described embodiments. A person skilled in the art can modify the above-described embodiments without departing from the scope and spirit of the present invention.

Claims

1. An image forming device, characterized in that: It has a print head unit for ink, a print head unit for pre-coating liquid, and a control unit, wherein: The ink print head unit discharges ink toward a printing substrate transported in a predetermined transport direction; The pre-coating liquid print head unit is arranged at a position upstream of the ink print head unit in the conveying direction, and is used to discharge the pre-coating liquid toward the printing substrate; The control unit controls the pre-coating liquid print head unit to discharge the pre-coating liquid. The control unit controls the pre-coat liquid print head unit so as to discharge a predetermined amount of the pre-coat liquid when the surface tension of the printing substrate is lower than a predetermined value.

2. The image forming apparatus according to claim 1, wherein: The control unit includes an input unit for inputting the surface tension of the printing substrate.

3. The image forming apparatus according to claim 1, wherein: The control unit controls the pre-coat liquid print head unit so as to discharge a predetermined amount of the pre-coat liquid when the surface tension of the printing substrate is less than 38 mN / m.

4. The image forming apparatus according to claim 1, wherein: The printing substrate is a plastic film.

5. The image forming apparatus according to claim 1, wherein: The pre-coat liquid print head unit has the same structure as the ink print head unit.

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