Inkjet image forming apparatus

Abstract

To provide an inkjet image forming apparatus capable of performing corona treatment in accordance with characteristics of a printing base material.SOLUTION: An inkjet image forming apparatus 1 includes an image forming part 7 that ejects ink based on image data onto a printing base material M conveyed in a predetermined conveyance direction to form an image, a corona treatment unit 5 that is disposed on an upstream side of the image forming part 7 in the conveyance direction and performs a corona discharge on the printing base material M, and a control part 31 that controls a discharge amount of the corona discharge performed by the corona treatment unit 5. The control part 31 controls the discharge amount based on an arithmetic average roughness of the printing base material M.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] In an inkjet type image forming apparatus, corona discharge may be performed on a printing substrate in order to enhance the adhesion between the printing substrate and the ink.

[0003] The image forming apparatus described in Patent Document 1 sets the corona discharge amount with reference to a table that associates a paper substrate (corresponding to the printing substrate), the type of ink, and the corona discharge amount.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the image forming apparatus described in Patent Document 1 performs corona discharge treatment in order to compensate for the difference in glossiness between the printed portion and the non-printed portion, and the characteristics of the printing substrate are not considered.

[0006] Therefore, in consideration of the above circumstances, an object of the present invention is to provide an inkjet type image forming apparatus capable of performing corona discharge treatment according to the characteristics of a printing substrate.

Means for Solving the Problems

[0007] To achieve the above object, an inkjet type image forming apparatus of the present invention includes an image forming unit that discharges ink based on image data to form an image on a printing substrate conveyed along a predetermined conveyance direction, a corona treatment unit that is disposed upstream of the image forming unit in the conveyance direction and performs corona discharge on the printing substrate, and a control unit that controls the discharge amount of the corona discharge performed by the corona treatment unit. The control unit is characterized in that it controls the discharge amount based on the arithmetic mean roughness of the printing substrate.

[0008] In the present invention, the control unit may be characterized by including an input unit that inputs the arithmetic mean roughness of the printing substrate.

[0009] In the present invention, the control unit may be characterized in that it controls the corona treatment unit to perform the corona discharge when the arithmetic mean roughness of the printing substrate is 0.3 μm or less.

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

Advantages of the Invention

[0011] According to the present invention, since corona treatment is performed on a printing substrate having a small surface roughness, the adhesion between the ink and the printing substrate can be enhanced.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4A

Figure 4B

Figure 5

Mode for Carrying Out the Invention

[0013] Hereinafter, an inkjet type image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings.

[0014] With reference to FIG. 1, the overall configuration of the inkjet type image forming apparatus 1 will be described. FIG. 1 is a front view schematically showing the internal configuration of the inkjet type image forming apparatus 1.

[0015] The inkjet type image forming apparatus 1 includes, in order along the conveyance direction X of the printing substrate M, a supply roller 3, a corona treatment unit 5, an image forming unit 7, a drying unit 9, and a winding roller 11.

[0016] First, the supply roller 3 will be described. A long printing substrate M is wound around the supply roller 3. By rotating the supply roller 3, the printing substrate M is fed out in a predetermined conveyance direction X.

[0017] Next, the corona treatment unit 5 will be described with reference to FIG. 2. FIG. 2 is a diagram schematically illustrating the corona treatment unit 5. The corona treatment unit 5 is disposed on the downstream side of the supply roller 3 in the conveyance direction X. The corona treatment unit 5 includes a corona discharge electrode 21 and a counter roller 23 disposed at a predetermined interval from the corona discharge electrode 21. The corona discharge electrode 21 is made of, for example, a rod-shaped ceramic that is long in the width direction Y of the printing substrate M or an aluminum cylinder coated with ceramic. The counter roller 23 is made of, for example, a stainless steel cylinder and is grounded. The interval between the corona discharge electrode 21 and the counter roller 23 is, for example, 0.5 to 2.0 mm. Note that tension rollers may be disposed on the upstream side and the downstream side of the counter roller 23.

[0018] The corona discharge electrode 21 is covered with an electrode cover 25 having an open bottom surface. The corona discharge electrode 21 is connected to a high-frequency power source 29 via a high-voltage transformer 27. The high-frequency power source 29 generates a high-frequency alternating current. The high-frequency alternating current is, for example, 5.5 kV to 6.5 kV in one example. The higher the discharge power, the higher the discharge voltage (discharge amount). However, since the discharge voltage varies depending on the atmospheric pressure, temperature, humidity, etc., it is set according to the environmental conditions, etc. when actually performing the corona discharge treatment. The high-voltage transformer 27 amplifies the generated high-frequency alternating current, converts it into discharge power, and applies it to the corona discharge electrode 21. Thereby, a corona discharge occurs between the corona discharge electrode 21 and the counter roller 23.

[0019] The high-frequency power source 29 is electrically connected to the control unit 31 and generates a high-frequency alternating current based on an instruction from the control unit 31.

[0020] Next, the image forming unit 7 will be described with reference to FIG. 1. The image forming unit 7 is disposed on the downstream side of the corona treatment unit 5 in the conveyance direction X. The image forming unit 7 includes four head units 41B, 41C, 41M, and 41Y (collectively referred to as the head unit 41) corresponding to four colors (black, cyan, magenta, and yellow) of ink, and a conveyance plate 43 along which the printing substrate M is conveyed.

[0021] The head unit 41 will be described with reference to FIG. 3 as well. FIG. 3 is a plan view showing the head unit 41. The head unit 41 includes three print heads 45 each and a plate 47 that supports the three print heads 45.

[0022] As shown in FIG. 3, the three print heads 45 are arranged in a staggered pattern (line head method) along the width direction Y so as to be approximately the same as the width of the printing substrate M, and are supported by the plate 47. The print head 45 is provided with a number of nozzles (not shown). The discharge ports of the nozzles are open on the lower surface of the print head 45.

[0023] As shown in FIG. 1, the four head units 41 are arranged in order along the conveyance direction X, and black, cyan, magenta, and yellow inks are supplied thereto respectively. The supplied ink is discharged downward from the discharge ports of the nozzles of each print head 45.

[0024] The conveyance plate 43 is disposed below the four head units 41 as shown in FIG. 1. The upper surface of the conveyance plate 43 is formed flat. Also, as shown in FIG. 3, the width of the conveyance plate 43 is wider than the width of the printing substrate M and all the head units 41. A heat source (not shown) is provided below the conveyance plate 43 to heat the conveyance plate 43 to a predetermined temperature. The conveyance plate 43 is made of, for example, metal.

[0025] Next, the drying unit 9 will be described with reference to FIG. 1. The drying unit 9 is disposed on the downstream side in the conveyance direction X from the image forming unit 7. The drying unit 9 includes a heat drum 51 and upstream and downstream tension rollers 53 and 55 disposed on the upstream side and the downstream side of the heat drum 51. The printing substrate M that has passed through the image forming unit 7 is wound around the heat drum 51 between the upstream and downstream tension rollers 53 and 55. The heat drum 51 is heated to dry the printing substrate M conveyed along the surface.

[0026] Next, the take-up roller 11 will be described with reference to FIG. 1. The take-up roller 11 is disposed on the downstream side in the conveyance direction X of the drying unit 9. The end of the printing substrate M is fixed to the take-up roller 11. The take-up roller 11 is connected to a motor (not shown) and rotates. By rotating the take-up roller 11 in a predetermined direction at a predetermined rotational speed by the motor, the printing substrate M is fed out from the supply roller 3.

[0027] The fed-out printing substrate M passes between the corona discharge electrode 21 of the corona treatment unit 5 and the counter roller 23 (see FIG. 2) and is conveyed to the image forming unit 7. In the image forming unit 7, the printing substrate M is conveyed along the upper surface of the conveyance plate 43 below the four head units 41 toward the drying unit 9. Then, after being wound around the heat drum 51 in the drying unit 9, it is wound around the take-up roller 11.

[0028] Next, the control unit 31 will be described. As shown in FIG. 2, the control unit 31 controls the high-frequency power supply 29 of the corona treatment unit 5 to create a high-frequency current of a predetermined intensity. Further, the control unit 31 is provided with an input unit 31a such as a display panel. The input unit 31a includes an average roughness input unit for inputting the arithmetic average roughness of the printing substrate M (for example, the arithmetic average roughness defined in JIS B0601: 2001). The control unit 31 is also electrically connected to the head unit 41 and controls the head unit 41 based on the input image data.

[0029] The image forming operation of the inkjet type image forming apparatus 1 having the above configuration will be described. During the image forming operation, first, the user inputs the arithmetic average roughness of the printing substrate M to the input unit 31a of the control unit 31. When the input arithmetic average roughness is 3 μm or less, the control unit 31 controls the corona treatment unit 5 to execute the corona discharge treatment.

[0030] Thereafter, the motor is driven to rotate the winding roller 11, and the printing substrate M is sent out from the supply roller 3 to the corona treatment unit 5. In the corona treatment unit 5, corona discharge occurs between the corona discharge electrode 21 and the opposing roller 23, and the upper surface of the printing substrate M is subjected to corona treatment. On the other hand, when the input arithmetic average roughness is less than 0.3 μm, the control unit 31 controls the corona treatment unit 5 so as not to perform corona discharge treatment. That is, when the input arithmetic average roughness is less than 0.3 μm, the corona discharge treatment is not executed.

[0031] Thereafter, the printing substrate M is conveyed below the head unit 41, and based on the image data, ink of a predetermined color is ejected from the corresponding head unit 41, and an image is formed on the printing substrate M. The printing substrate M on which the image is thus formed is conveyed to the drying unit 9. In the drying unit 9, the ink is completely dried. Thereafter, the printing substrate M is wound around the winding roller 11.

[0032] As described above, according to the present invention, when the arithmetic average roughness of the printing substrate M is below a certain level, specifically 0.3 μm or less, corona discharge is applied to the printing substrate M. The printing substrate M with a large arithmetic average roughness has fine irregularities on its surface, and ink easily penetrates into these irregularities (anchor effect), enhancing the adhesion between the ink and the printing substrate M.

[0033] However, a printing substrate M such as a plastic film or synthetic paper with an arithmetic average roughness of 0.3 μm or less has low adhesion to ink. Therefore, by applying corona discharge treatment, the adhesion to the printing substrate M can be enhanced. That is, when corona discharge treatment is applied to the printing substrate M, fine irregularities are formed on the surface of the printing substrate M, and the aforementioned anchor effect can be obtained. Furthermore, hydrophilic polar groups such as carbonyl groups, carboxyl groups, and nitrides are formed on the surface of the printing substrate M. Such polar groups increase the wettability of the surface of the printing substrate M. Therefore, due to such physical and chemical actions by the corona discharge treatment, the compatibility (adhesion) between the printing substrate M and the ink is improved.

[0034] In addition, in order to improve the compatibility (adhesion) between the printing substrate M and the ink, a precoat treatment using a precoat solution may be performed. However, since a liquid is applied in the precoat treatment, it is necessary to dry the printing substrate M, which increases the processing time by the drying time or requires the installation of a dryer. In the corona discharge treatment, the same effect as the precoat treatment can be obtained without using a liquid. However, depending on the type of ink, etc., the precoat treatment may be used in combination.

[0035] Next, in the inkjet type image forming apparatus 1 of the present embodiment, a test for evaluating the relationship between the arithmetic mean roughness and the adhesion will be described. The printing substrate M is an OPP film having an arithmetic surface roughness of 0.08 μm. The surface roughness is a value defined by JIS B0601:2001 measured using a surface roughness measuring instrument (trade name FORMATRACER Avant FTA-H4D3000-D, manufactured by Mitutoyo Corporation). The width of the printing substrate M is 210 mm, and the conveyance speed of the printing substrate M is 3 m / min. The adhesion was evaluated by a peel test.

[0036] The peel test was performed by the following method. First, a solid cyan image was printed on the printing substrate M at 600 dpi. The printed image was subjected to a peel test based on JIS K5600 (no cross-cut was formed). A tape (trade name CT, manufactured by Nichiban Co., Ltd.) was firmly rubbed on the image with a fingertip, and within 5 minutes, the tape was peeled off, or the edge of the tape was grasped at an angle close to 60 degrees and pulled off surely within 0.5 to 1.0 seconds. The images after peeling are shown in FIGS. 4A and 4B. The peeled tape is attached to the right side of the left printing substrate. FIG. 4A shows an example of the present invention, and FIG. 4B shows a comparative example.

[0037] In the example, the printing substrate is subjected to corona discharge by the corona treatment unit 5. The discharge power is 100 W (the discharge voltage is 6.3 kV). In the comparative example, the printing substrate is not subjected to corona discharge. As is clear from FIGS. 4A and 4B, in the example (see FIG. 4A), the ink has not peeled off from the printing substrate, and the tape that has been peeled off has no ink attached thereto. On the other hand, in the comparative example (see FIG. 4B), the ink has peeled off from the printing substrate and adhered to the tape.

[0038] Next, referring to the table in FIG. 5, the results of evaluating the adhesion in the examples and the comparative examples will be described. The adhesion was evaluated by the following method. In the above-described peeling test, the unused tape and the peeled tape were attached to copy paper (trade name C2, manufactured by Fujifilm Business Innovation Corporation), and the image density was measured using an image densitometer (trade name FD-5, manufactured by Konica Minolta, Inc.). When the difference in image density between the unused tape and the peeled tape was less than 0.005, it was evaluated as ○; when it was less than 0.15, it was evaluated as Δ; and when it was 0.15 or more, it was evaluated as ×. Examples 1 to 3 show printing substrates that have been subjected to corona treatment and have an arithmetic surface roughness of 0.03 μm or less. Example 4 shows a printing substrate that has not been subjected to corona treatment and has an arithmetic surface roughness greater than 0.03 μm. Comparative Examples 1 to 3 show printing substrates that have not been subjected to precoat treatment and have an arithmetic surface roughness of 0.03 μm or less.

[0039] From the table, it was found that good adhesion can be obtained by performing corona treatment even when the arithmetic surface roughness is 0.3 μm or less (Examples 1 to 3). Also, in the case where the arithmetic surface roughness is greater than 0.3 μm (Example 4), good adhesion can be obtained without performing corona treatment. On the other hand, in the case where the arithmetic surface roughness is 0.3 μm or less (Comparative Examples 1 to 3), it was found that sufficient adhesion cannot be obtained. From these results, it can be seen that corona treatment is necessary when the arithmetic surface roughness of the printing substrate is 0.3 μm or less.

[0040] Note that the control unit 31 may control the corona treatment unit 5 so that the voltage applied to the corona discharge electrode 21 increases as the arithmetic surface roughness increases. In this case, even when the arithmetic surface roughness of the printing substrate M is large and the adhesion to the ink is low, the adhesion to the ink can be enhanced.

[0041] In the above embodiment, the four-color head unit 41 is used, but the present invention is not limited to four colors, and may be more or less than four colors. Further, the head unit 41 is not limited to the line head method. However, the line head method is preferable because the printing speed can be increased. Also, although the long plastic film (PET film) is used as the printing substrate M, a cut film may also be used.

[0042] Although the present invention has been described with respect to specific embodiments, the present invention is not limited to the above embodiments. Those skilled in the art can modify the above embodiments without departing from the scope and gist of the present invention.

Explanation of Reference Numerals

[0043] 1 Inkjet type image forming apparatus 5 Corona treatment unit 7 Image forming unit 31 Control unit 31a Input unit

Claims

1. An image forming unit that discharges ink based on image data to form an image on a printing substrate conveyed along a predetermined conveyance direction; A corona treatment unit disposed upstream of the image forming unit in the conveyance direction and performing corona discharge on the printing substrate; A control unit that controls the discharge amount of the corona discharge performed by the corona treatment unit, and The control unit controls the discharge amount based on the arithmetic mean roughness of the printing substrate. An inkjet type image forming apparatus characterized by this.

2. The inkjet type image forming apparatus according to claim 1, wherein the control unit includes an input unit for inputting the arithmetic mean roughness of the printing substrate.

3. The inkjet type image forming apparatus according to claim 1, wherein the control unit controls the corona treatment unit to perform the corona discharge when the arithmetic mean roughness of the printing substrate is 0.3 μm or less.

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

Images