Inkjet image forming apparatus

Abstract

The invention provides an inkjet image forming apparatus. An inkjet image forming apparatus includes an image forming section, a pre-coating processing unit, and a control section. The image forming unit forms an image by discharging ink to a printing base material conveyed in a predetermined conveyance direction according to image data. The pre-coating processing unit is disposed on the upstream side of the image forming section in the conveyance direction and discharges the pre-coating liquid to the printing base material. The control unit controls the amount of the pre-coating liquid discharged from the pre-coating processing unit. The control unit makes the amount of the pre-coating liquid applied to a region where pixels of different colors are adjacent to each other greater than the amount of the pre-coating liquid applied to a region where pixels of the same color are adjacent to each other. Therefore, color mixing of the ink can be inhibited through the pre-coating treatment.

Description

Technical Field

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

[0002] In an inkjet image forming apparatus, in order to improve the adhesion between the printing substrate and the ink, the printing substrate is sometimes subjected to a pre-coating treatment (pre-treatment).

[0003] In the pre-coating process, the coating amount of the pre-coating liquid is sometimes determined according to the type of ink and the adhesion amount per unit area of ​​the ink discharged onto the printing substrate. In addition, in the pre-coating process, a pre-treatment liquid that makes the coloring material in the ink insoluble or condensed is sometimes used.

[0004] However, when the printing substrate is a plastic film with a smooth surface, the ink landed on the printing substrate moves easily. Therefore, even if the pre-coating process is performed as described above, it is easy to produce poor images such as color mixing caused by the movement of the landed ink. 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 suppressing color mixing of ink by pre-coating processing.

[0006] The inkjet image forming apparatus of the present invention comprises an image forming unit, a pre-coating processing unit and a control unit. The image forming unit discharges ink to a printing substrate transported along a predetermined transport direction according to image data to form an image. The pre-coating processing unit is arranged at a position on the upstream side of the transport direction relative to the image forming unit, and is used to discharge pre-coating liquid to the printing substrate. The control unit controls the amount of pre-coating liquid discharged from the pre-coating processing unit. The control unit makes the amount of pre-coating liquid applied to the area adjacent to pixels of different colors greater than the amount of pre-coating liquid applied to the area adjacent to pixels of the same color. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0009] Figure 3 It is a diagram for explaining the landing state of ink in the inkjet image forming apparatus according to one embodiment of the present invention.

[0010] Figure 4This is a table showing the results of observing the degree of color mixing in the inkjet image forming apparatus according to one embodiment of the present invention.

[0011] Figure 5A An image showing an example of an inkjet image forming apparatus according to an embodiment of the present invention.

[0012] Figure 5B An image of a comparative example in an inkjet image forming apparatus according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

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

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

[0015] The inkjet image forming apparatus 1 includes a supply roller 3, a pre-coating unit 5, an image forming section 7, a drying section 9, and a winding roller 11 in this order along the conveying direction of the printing substrate M. Furthermore, the inkjet image forming apparatus 1 includes a conveying plate 13 disposed below the pre-coating unit 5 and the image forming section 7 between the supply roller 3 and the drying section 9.

[0016] First, the supply roller 3 will be described. A long printing base material M is wound around the supply roller 3. The printing base material M is fed out in the conveying direction X as the supply roller 3 rotates.

[0017] Next, the pre-coating unit 5 will be described. The pre-coating unit 5 performs pre-coating on the printing substrate M fed from the supply roller 3. The pre-coating unit 5 includes a pre-coating head unit 21 that discharges a pre-coating liquid. The pre-coating head unit 21 is electrically connected to a control unit 51.

[0018] Reference Figure 2 , the pre-coating head unit 21 will be described. Figure 2 2 is a top view showing the pre-coating head unit 21. The pre-coating head unit 21 has three print heads 23 and a plate 25 supporting the three print heads 23. The three print heads 23 are arranged in a staggered manner (line head method) along the width direction Y in a manner that is the same as 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 25. The pre-coating liquid is supplied to the three print heads 23 from a pre-coating liquid supply source.

[0019] The print head 23 has a plurality of nozzles and a piezoelectric element provided in each nozzle. The discharge port of the nozzle opens at the lower surface of the print head 23. When a voltage is applied to the piezoelectric element, the piezoelectric element is deformed, and the pre-coat liquid in the nozzle is discharged downward from the discharge port.

[0020] The components of the pre-coating liquid are, for example, 10% polyester resin (trade name PESRESIN A-640, manufactured by Takamatsu Resin Co., Ltd.), 0.04% surfactant (trade name Surfynol 440, manufactured by Nissin Chemical Industry Co., Ltd.), 25% propylene glycol, and 64.96% water.

[0021] Next, refer to Figure 1 The image forming unit 7 is described below. The image forming unit 7 forms an image on the printing substrate M by inkjet method. The image forming unit 7 has four image forming head units 31B, 31C, 31M, and 31Y (collectively referred to as image forming head units 31) corresponding to four colors of ink (black, cyan, magenta, and yellow). The four image forming head units 31 are arranged in sequence along the conveying direction X. The four image forming head units 31 are electrically connected to the control unit 51.

[0022] The image forming head unit 31 has Figure 2 The pre-coating processing unit 5 shown has the same structure as the pre-coating head unit 21, and has three print heads 33 and a plate 35 supporting the three print heads 33. Black, cyan, magenta, and yellow inks are supplied to the three print heads 33 of the four image forming head units 31, respectively.

[0023] The print head 33 has a plurality of nozzles and a piezoelectric element provided in each nozzle. The discharge port of the nozzle opens at the lower surface of the print head 33. When a voltage is applied to the piezoelectric element, the piezoelectric element is deformed, and the ink in the nozzle is discharged downward from the discharge port.

[0024] Next, refer to Figure 1 The drying section 9 is described below. The drying section 9 dries the image formed on the printing substrate M in the image forming section 7. The drying section 9 includes a heating drum 41, and an upstream tension roller 43 and a downstream tension roller 45 respectively arranged on the upstream side and the downstream side of the heating drum 41. The printing substrate M passing through the image forming section 7 is wound around the heating drum 41 between the upstream tension roller 43 and the downstream tension roller 45. The heating drum 41 heats the printing substrate M conveyed along the surface by heating.

[0025] Next, the winding roller 11 is described. The end of the printing substrate M is fixed to the winding roller 11. The winding roller 11 is connected to a motor (not shown) and rotates. The motor rotates the winding roller 11 in a predetermined direction at a predetermined rotation speed, thereby feeding the printing substrate M from the supply roller 3. The fed printing substrate M passes through the pre-coating treatment unit 5, the image forming unit 7, and the drying unit 9, and is wound up on the winding roller 11.

[0026] Next, the conveying plate 13 will be described. Figure 1 As shown in FIG. 1 , the conveying plate 13 is disposed below the pre-coating unit 5 and the image forming unit 7. The upper surface of the conveying plate 13 is formed flat. Figure 2 As shown, the width of the conveying plate 13 is wider than the width of the printing substrate M and all the head units 21 and 31. A heat source (not shown) is provided below the conveying plate 13 to heat the conveying plate 13 to a predetermined temperature. The conveying plate 13 is made of metal, for example.

[0027] Next, the control unit 51 will be described. Figure 1 As shown, the control unit 51 controls the pre-coating head unit 21 of the pre-coating processing unit 5 and the four image forming head units 31 of the image forming unit 7. In addition, the image data of the printed image is input to the control unit 51. The control unit 51 determines whether the colors of adjacent pixels (dots) are the same or different based on the input image data.

[0028] The image forming operation of the inkjet image forming apparatus 1 having the above configuration will be described. During the image forming operation, image data is input to the control unit 51. The control unit 51 determines whether adjacent pixels are of the same color or different colors based on the image data.

[0029] After that, the motor is driven to rotate the take-up roller 11, and the printing substrate M is sent out from the supply roller 3. When the printing substrate M reaches the bottom of the pre-coating treatment unit 5, the pre-coating liquid is discharged from the print head 23 of the pre-coating head unit 21 of the pre-coating treatment unit 5 to the printing substrate M. At this time, the control unit 51 controls the pre-coating treatment unit 5 in such a way that the amount of pre-coating liquid discharged in the area adjacent to pixels of different colors is greater than the amount of pre-coating liquid discharged in the area adjacent to pixels of the same color. As an example, the amount of pre-coating liquid per unit area discharged in the area adjacent to pixels of different colors is 1.5 to 2 times the amount of pre-coating liquid per unit area discharged in the area adjacent to pixels of the same color. In addition, the amount of pre-coating liquid per unit area discharged in the area adjacent to pixels of the same color is the amount set when performing normal pre-coating treatment.

[0030] One pixel is formed by ink discharged from one nozzle of the print head 33 of the image forming head unit 31. Therefore, the control unit 51 determines whether adjacent pixels are the same color or different colors based on the image data. Then, when it is determined that they are different colors, the pre-coating processing unit 5 is controlled to increase the amount of pre-coating liquid discharged from the nozzle corresponding to the adjacent pixel. Specifically, the voltage applied to the piezoelectric element provided on the nozzle is increased. In addition, the amount of pre-coating liquid can be increased not only in two adjacent pixels, but also in a specified range including two pixels.

[0031] After that, the printing substrate M is conveyed to the lower side of the image forming section 7. In the image forming section 7, ink of a predetermined color is discharged from the print head 33 of the image forming head unit 31 according to the image data, and an image is formed on the printing substrate M. The printing substrate M with the image formed in this way is conveyed to the drying section 9. In the drying section 9, the image (ink) is completely dried. After that, the printing substrate M is wound up by the winding roller 11.

[0032] As described above, according to the present invention, the amount of pre-coat liquid discharged in the region where pixels of different colors are adjacent is larger than the amount of pre-coat liquid discharged in the region where pixels of the same color are adjacent.

[0033] Generally speaking, since the surface energy of the printing substrate M is low and stable, the ink droplets landed on the printing substrate M are easy to move from the landing position on the printing substrate M. As a result, Figure 3 As shown in the figure on the left, sometimes two adjacent droplets are pulled together and become one large droplet after drying. In the case where the colors of the two adjacent droplets are different, the two colors of ink are mixed and become one droplet of mixed colors. As a result, the boundaries of images of different colors are blurred and the image quality is reduced. 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, the two ink droplets merge with the printing substrate M and are not pulled closer to each other. Therefore, the two colors of ink are not easily mixed.

[0034] Furthermore, by making the amount of pre-coating liquid discharged in the region adjacent to pixels of different colors larger than the amount of pre-coating liquid in a normal pre-coating process, color mixing can be prevented without excessively increasing the amount of pre-coating liquid used.

[0035] Next, refer to Figure 4 The test for evaluating the degree of color mixing in the inkjet image forming apparatus 1 of the present embodiment will be described with reference to the table. Figure 4This is a table showing the color mixing (bleeding) of the embodiments and comparative examples. A test image consisting of rectangular full-surface images of cyan and magenta arranged adjacently was printed on an OPP film at 600 dpi. After the ink dried, a microscope (trade name MM-800, manufactured by Nikon) was used to visually observe the boundary between the two full-surface images of the test image, and no color mixing was observed as 0, a color mixing width of less than 10 μm was set to △, and a color mixing width of more than 10 μm was set to ×.

[0036] As described above, in Examples 1 to 3, the pre-coating treatment is performed in such a manner that the amount of pre-coating liquid (M1) discharged in the region adjacent to pixels of different colors is greater than the amount of pre-coating liquid (M2) discharged in the region adjacent to pixels of the same color. The ratio of the amount of pre-coating liquid per unit area discharged in the region adjacent to pixels of different colors to the amount of pre-coating liquid per unit area discharged in the region adjacent to pixels of the same color is 2 in Example 1, 1.5 in Example 2, and 1.05 in Example 3.

[0037] On the other hand, in Comparative Example 1, the amount of pre-coating liquid per unit area discharged in the area adjacent to pixels of different colors is less than the amount of pre-coating liquid discharged in the area adjacent to pixels of the same color. In the embodiments and comparative examples, the discharge amount is adjusted by the voltage applied to the piezoelectric element of the print head. The discharge amount represents the value obtained by dividing the difference in weight of the printed substrate before and after the discharge of the pre-coating liquid by the discharge area.

[0038] like Figure 4 As shown in the table, no color mixing was observed in Examples 1 and 2, and the degree of color mixing was low in Example 3. That is, by increasing the amount of pre-coating liquid discharged to the area adjacent to pixels of different colors, as described above, it is known that the ink is not easily moved from the landing position, and color mixing is reduced. In addition, it is known that the ratio of the coating amount is preferably 1.5 to 2 (Examples 1 and 2).

[0039] Reference Figure 5A and Figure 5B To illustrate other test results, a test image with different color images next to each other was printed at 600 dpi. Figure 5A The test image of the embodiment is printed after the pre-coating process is performed so that the amount of the pre-coating liquid discharged in the area adjacent to pixels of different colors is greater than the amount of the pre-coating liquid discharged in the area adjacent to pixels of the same color. Figure 5B The figure shows a test image of a comparative example which is printed after a pre-coating process is performed by applying a certain amount of paint regardless of the colors of adjacent pixels.

[0040] like Figure 5A As shown in FIG. 1 , in the embodiment, the boundary between images of different colors is clear. Figure 5BAs shown, in the comparative example, it can be seen that the boundary portion of the images of different colors is blurred and the colors are mixed.

[0041] In the above-mentioned embodiment, the image forming head unit 31 of 4 colors is used, but the present invention is not limited to 4 colors, and can be more than 4 colors or less than 4 colors. In addition, the head units 21 and 31 are not limited to the line head method. However, the line 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 it can also be a cut film.

[0042] 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 inkjet image forming device, characterized in that: It has an image forming unit, a pre-coating processing unit and a control unit, wherein: The image forming unit discharges ink onto a printing substrate transported in a predetermined transport direction to form an image according to image data; The pre-coating processing unit is arranged at an upstream side of the conveying direction relative to the image forming unit, and is used to discharge the pre-coating liquid toward the printing substrate; The control unit controls the amount of the pre-coating liquid discharged from the pre-coating treatment unit. The control unit controls the amount of the pre-coating liquid applied to a region adjacent to pixels of different colors to be larger than the amount of the pre-coating liquid applied to a region adjacent to pixels of the same color.

2. The inkjet image forming apparatus according to claim 1, wherein: The control unit determines whether colors of adjacent pixels are different based on the image data.

3. The inkjet image forming apparatus according to claim 1, wherein: The image forming unit includes a head unit for discharging ink. The pre-coating treatment unit has a head unit for discharging the pre-coating liquid, and the two head units have the same structure.

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

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