Inkjet type image formation device

Abstract

To provide an inkjet type image formation device which can prevent color mixture of ink by precoat treatment.SOLUTION: An inkjet type image formation device 1 includes an image formation part 7 for discharging ink onto a printing base material M conveyed in a predetermined conveyance direction and forming an image thereon on the basis of image data, a precoat treatment unit 5 which is arranged on the upstream side in the conveyance direction of the image formation part 7, and discharges a precoat liquid onto the printing base material M, and a control part 51 for controlling an amount of the precoat liquid discharged from the precoat treatment unit 5, wherein the control part 51 sets the amount of the precoat liquid coated onto a region where pixels of different colors are adjacent to each other to be larger than the amount of the precoat liquid coated onto a region where pixels of the same color are adjacent to each other.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an inkjet image forming apparatus that forms an image on a printing substrate by an inkjet method. [Background technology]

[0002] In an inkjet image forming apparatus, a precoat treatment (pretreatment) is sometimes performed on a printing substrate in order to improve adhesion between the printing substrate and the ink.

[0003] The image forming apparatus described in Patent Document 1 determines the amount of precoat liquid to be applied based on the type of ink and the amount of ink per unit area to be deposited on the recording medium. The inkjet recording apparatus described in Patent Document 2 uses a pretreatment liquid that insolubilizes or aggregates color materials in the ink. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6163797 [Patent Document 2] Patent No. 3181850 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when the printing substrate is a plastic film having a smooth surface, the ink that has landed on the printing substrate is likely to move, and therefore, even if a precoat treatment is performed as described in Patent Documents 1 and 2, image defects such as color mixing due to the movement of the landed ink are likely to occur.

[0006] SUMMARY OF THE PRESENTLY PREFERRED EMBODIMENTS In consideration of the above circumstances, an object of the present invention is to provide an ink-jet image forming apparatus capable of suppressing ink color mixing by a precoat process. [Means for solving the problem]

[0007] In order to achieve the above-mentioned object, the inkjet image forming apparatus of the present invention comprises an image forming section that ejects ink based on image data onto a printing substrate transported along a predetermined transport direction to form an image, a precoat processing unit that is positioned upstream of the image forming section in the transport direction and ejects precoat liquid onto the printing substrate, and a control section that controls the amount of precoat liquid ejected from the precoat processing unit, wherein the control section makes the amount of precoat liquid applied to an area where pixels of different colors are adjacent greater than the amount of precoat liquid applied to an area where pixels of the same color are adjacent.

[0008] In the present invention, the control unit may determine whether or not adjacent pixels have different colors based on the image data.

[0009] In the present invention, the image forming section may include a head unit that ejects ink, and the precoat processing unit may include a head unit that ejects the precoat liquid, and both head units may have the same structure.

[0010] In the present invention, the printing substrate may be a plastic film. Effect of the Invention

[0011] According to the present invention, by making the amount of precoat liquid ejected into an area where pixels of different colors are adjacent greater than the amount of precoat liquid ejected into an area where images of the same color are adjacent, the ink droplets that land are less likely to move from their landing positions, thereby suppressing the mixing of two colors of ink. [Brief description of the drawings]

[0012] [Figure 1] 1 is a front view showing a schematic diagram of an ink jet type image forming apparatus according to an embodiment of the present invention; [Diagram 2]1 is a plan view showing a head unit in an ink jet type image forming apparatus according to an embodiment of the present invention. [Diagram 3] 3A and 3B are diagrams illustrating the landing state of ink in an ink jet type image forming apparatus according to one embodiment of the present invention. [Figure 4] 4 is a table showing the results of observing the degree of color mixing in an ink jet type image forming apparatus according to one embodiment of the present invention. [Figure 5A] 1 shows images in an example of an ink jet type image forming apparatus according to one embodiment of the present invention. [Figure 5B] 4 shows an image in a comparative example in the ink jet type image forming apparatus according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An ink jet type image forming apparatus according to an embodiment of the present invention will now be described with reference to the drawings.

[0014] The overall configuration of an inkjet image forming apparatus 1 will be described with reference to Fig. 1. Fig. 1 is a front view showing a schematic internal configuration of the inkjet image forming apparatus 1.

[0015] The inkjet image forming apparatus 1 includes, in this order along the transport direction of the printing substrate M, a supply roller 3, a precoat processing unit 5, an image forming section 7, a drying section 9, and a take-up roller 11. The inkjet image forming apparatus 1 further includes a transport plate 13 disposed between the supply roller 3 and the drying section 9, below the precoat processing unit 5 and the image forming section 7.

[0016] First, a description will be given of the supply roller 3. A long piece of printing substrate M is wound around the supply roller 3. The printing substrate M is sent out in a predetermined transport direction X as the supply roller 3 rotates.

[0017] Next, the precoat processing unit 5 will be described. The precoat processing unit 5 performs a precoat processing on the printing substrate M sent out from the supply roller 3. The precoat processing unit 5 includes a precoat head unit 21 that ejects a precoat liquid. The precoat head unit 21 is electrically connected to a control unit 51.

[0018] The precoat head unit 21 will be described with reference to Fig. 2. Fig. 2 is a plan view showing the precoat head unit 21. The precoat head unit 21 includes three print heads 23 and a plate 25 that supports the three print heads 23. The three print heads 23 are arranged in a staggered manner along the width direction Y (line head system) so as to be approximately the same as the width of the printing substrate M (the length along the width direction Y intersecting with the transport direction X), and are supported by the plate 25. The three print heads 23 are supplied with precoat liquid from a precoat liquid supply source.

[0019] The print head 23 has a large number of nozzles and a piezoelectric element provided in each nozzle. The nozzle outlets open on the bottom surface of the print head 23. When a voltage is applied to the piezoelectric element, the piezoelectric element deforms, and the precoat liquid in the nozzle is ejected downward from the outlet.

[0020] The components of the precoat 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, the image forming unit 7 will be described with reference to FIG. 1. The image forming unit 7 forms an image on the printing substrate M by an inkjet method. The image forming unit 7 is equipped with 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 transport direction X. The four image forming head units 31 are electrically connected to a control unit 51.

[0022] 2, and includes three print heads 33 and a plate 35 that supports 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 large number of nozzles and a piezoelectric element for each nozzle. The nozzle outlets open on the bottom surface of the print head 33. When a voltage is applied to the piezoelectric element, the piezoelectric element deforms, causing ink in the nozzle to be ejected downward from the outlet.

[0024] Next, the drying section 9 will be described with reference to Fig. 1. 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 heat drum 41, and upstream and downstream tension rollers 43, 45 arranged on the upstream and downstream sides of the heat drum 41. The printing substrate M that has passed through the image forming section 7 is wound around the heat drum 41 between the upstream and downstream tension rollers 43, 45. The heat drum 41 dries the printing substrate M transported along its surface by being heated.

[0025] Next, the winding roller 11 will be described. An 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 precoat processing unit 5, the image forming section 7, and the drying section 9, and is wound up by the winding roller 11.

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

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

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

[0029] Thereafter, 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 lower part of the precoat processing unit 5, the print head 23 of the precoat head unit 21 of the precoat processing unit 5 ejects the precoat liquid onto the printing substrate M. At this time, the control unit 51 controls the precoat processing unit 5 so that the amount of precoat liquid ejected onto the area where pixels of different colors are adjacent is greater than the amount of precoat liquid ejected onto the area where pixels of the same color are adjacent. As an example, the amount of precoat liquid ejected per unit area onto the area where pixels of different colors are adjacent is set to 1.5 to 2 times the amount of precoat liquid ejected per unit area onto the area where pixels of the same color are adjacent. Note that the amount of precoat liquid ejected per unit area onto the area where pixels of the same color are adjacent is the amount set when performing normal precoat processing.

[0030] One pixel is formed by ink ejected from one nozzle of the print head 33 of the image forming head unit 31. Therefore, the control unit 51 judges whether adjacent pixels are the same color or different colors based on the image data. If it is judged that the colors are different, the control unit 5 controls the precoat processing unit 5 to increase the amount of precoat liquid ejected from the nozzle of the print head 23 of the precoat head unit 21 that corresponds to the adjacent pixel. Specifically, the voltage applied to the piezoelectric element provided in the nozzle is increased. Note that the amount of precoat liquid may be increased not only for two adjacent pixels, but also within a predetermined range including the two pixels.

[0031] Thereafter, the printing substrate M is transported below the image forming section 7. In the image forming section 7, ink of a predetermined color is ejected from the print head 33 of the image forming head unit 31 based on image data, and an image is formed on the printing substrate M. The printing substrate M on which the image has been formed in this manner is transported to the drying section 9. In the drying section 9, the image (ink) is completely dried. Thereafter, the printing substrate M is taken up by the take-up roller 11.

[0032] As described above, according to the present invention, the amount of precoat liquid discharged to an area where pixels of different colors are adjacent is greater than the amount of precoat liquid discharged to an area where images of the same color are adjacent.

[0033] In general, a printing substrate M with low surface tension such as a plastic film has a low and stable surface energy of the printing substrate M, so that the ink droplets that land on the printing substrate M tend to move from the landing position on the printing substrate M. As a result, as shown in the left diagram of FIG. 3, two adjacent ink droplets may be attracted to each other and become one large droplet after drying. If the two adjacent inks are different colors, the two ink colors are mixed to become one mixed droplet. Then, the boundary between the images of different colors becomes blurred and the image quality deteriorates. On the other hand, when a pre-coat process is performed, the adhesion between the ink and the printing substrate M is increased, and the ink droplets that land on the printing substrate M tend to move from the landing position on the printing substrate M. As a result, as shown in the right diagram of FIG. 3, the two ink droplets blend with the printing substrate M and are not attracted to each other. Therefore, the two ink colors are less likely to mix.

[0034] Furthermore, by making the amount of precoat liquid discharged into an area where pixels of different colors are adjacent larger than the amount of precoat liquid used in normal precoat processing, color mixing can be prevented without unnecessarily increasing the amount of precoat liquid used.

[0035] Next, a test for evaluating the degree of color mixing in the inkjet image forming apparatus 1 of this embodiment will be described with reference to the table in FIG. 4. FIG. 4 is a table showing color mixing (bleeding) in examples and comparative examples. A test image in which rectangular solid images of cyan and magenta were arranged adjacent to each other was printed on an OPP film at 600 dpi. After the ink dried, the boundary between both solid images of the test image was visually observed using a microscope (product name MM-800, manufactured by Nikon Corporation). Those with no color mixing were marked with ◯, those with a color mixing width of less than 10 μm were marked with △, and those with a color mixing width of 10 μm or more were marked with ×.

[0036] As described above, in Examples 1 to 3, the precoat process was performed so that the amount of precoat liquid (M1) discharged to the area where pixels of different colors are adjacent was greater than the amount of precoat liquid (M2) discharged to the area where images of the same color are adjacent. The ratio of the amount of precoat liquid per unit area discharged to the area where pixels of different colors are adjacent to the amount of precoat liquid per unit area discharged to the area where images of the same color are adjacent was 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 precoat liquid per unit area discharged to an area where pixels of different colors are adjacent is smaller than the amount of precoat liquid discharged to an area where images of the same color are adjacent. The discharge amount was adjusted by the voltage applied to the piezo element of the print head. The discharge amount is calculated by dividing the difference in weight of the printing substrate before and after discharging the precoat liquid by the discharge area.

[0038] As shown in the table in Fig. 4, no color mixing was observed in Examples 1 and 2, and the degree of color mixing was low in Example 3. In other words, by increasing the amount of precoat liquid ejected in the area where pixels of different colors are adjacent, it is found that the ink is less likely to move from the landing position as described above, and color mixing is reduced. Furthermore, it is found that the ratio of the application amount is preferably 1.5 to 2 (Examples 1 and 2).

[0039] Other test results will be described with reference to Figures 5A and 5B. Test images in which different color images were adjacent were printed at 600 dpi. Figure 5A shows a test image of an embodiment in which a precoat process was performed in which the amount of precoat liquid discharged to an area in which pixels of different colors were adjacent was greater than the amount of precoat liquid discharged to an area in which images of the same color were adjacent, and Figure 5B shows a test image of a comparative example in which a precoat process was performed in which a constant amount was applied regardless of the color of the adjacent pixels.

[0040] As shown in Fig. 5A, the boundary between the images of different colors is clear in the example, whereas as shown in Fig. 5B, the boundary between the images of different colors is blurred and mixed in the comparative example.

[0041] In the above embodiment, four-color image forming head units 31 are used, but the present invention is not limited to four colors, and more or less than four colors may be used. In addition, the head units 21, 31 are not limited to the line head type. However, the line head type is preferable because it can increase the printing speed. In addition, a long plastic film (PET film) is used as the printing substrate M, but a cut film may also be used.

[0042] Although the present invention has been described with reference to specific embodiments, the present invention is not limited to the above embodiments, and those skilled in the art may modify the above embodiments without departing from the scope and spirit of the present invention. [Explanation of symbols]

[0043] 1. Inkjet image forming device 5 Pre-coat processing unit 7 Image forming section 21 Pre-coat head unit 31 Image forming head unit 51 Control section

Claims

1. an image forming unit that ejects ink based on image data onto a printing substrate transported along a predetermined transport direction to form an image; a precoat processing unit disposed upstream of the image forming unit in the transport direction and configured to eject a precoat liquid onto the printing substrate; a control unit for controlling an amount of the precoat liquid discharged from the precoat processing unit, The control unit is characterized in that the amount of precoat liquid applied to areas where pixels of different colors are adjacent is greater than the amount of precoat liquid applied to areas where pixels of the same color are adjacent.

2. 2. The ink jet image forming apparatus according to claim 1, wherein the control unit determines whether adjacent pixels have different colors based on the image data.

3. the image forming unit includes a head unit that ejects ink, the precoat processing unit includes a head unit that ejects the precoat liquid, 2. The ink-jet image forming apparatus according to claim 1, wherein both of said head units have the same structure.

4. 2. The ink-jet image forming apparatus according to claim 1, wherein the printing substrate is a plastic film.

Images