Inkjet image forming apparatus

Abstract

The invention provides an inkjet image forming apparatus. An inkjet image forming apparatus includes a head unit, a corona processing unit, and a control unit. The head unit discharges ink to a printing base material conveyed in a predetermined conveying direction. The corona treatment unit is disposed on the upstream side of the head unit in the conveyance direction, and performs corona discharge on the printing base material. The control unit controls the amount of discharge of the corona discharge by the corona treatment unit. The control unit controls the discharge amount in accordance with the glossiness of the printing base material. Therefore, corona discharge treatment can be performed according to the characteristics of the printing base material.

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, corona discharge is sometimes performed on the printing substrate.

[0003] The corona discharge amount may be set by referring to a table in which the paper substrate (corresponding to the printing substrate) and the type of ink and the corona discharge amount are associated with each other.

[0004] However, the corona discharge treatment performed in the above case is to compensate for the difference in gloss between the printed portion and the non-printed portion, without taking the characteristics of the printed substrate into consideration. 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 corona discharge treatment according to the characteristics of a printing substrate.

[0006] The inkjet image forming apparatus of the present invention comprises a head unit, a corona treatment unit and a control unit. The head unit discharges ink to a printing substrate conveyed along a predetermined conveying direction. The corona treatment unit is arranged on the upstream side of the conveying direction relative to the head unit, and is used to perform corona discharge on the printing substrate. The control unit controls the discharge amount of the corona discharge performed by the corona treatment unit. The control unit controls the discharge amount according to the glossiness of the printing substrate. 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 FIG. 1 is a diagram schematically showing a corona treatment unit in an inkjet image forming apparatus according to an embodiment of the present invention.

[0009] Figure 3 It is a plan view showing a head unit in an inkjet image forming apparatus according to an embodiment of the present invention.

[0010] Figure 4A This is a diagram showing the results (Example) of a tape peeling test in an inkjet image forming apparatus according to an embodiment of the present invention.

[0011] Figure 4BThis is a diagram showing the results of a tape peeling test in an inkjet image forming apparatus according to an embodiment of the present invention (comparative example). DETAILED DESCRIPTION

[0012] Below, while referring to the attached Figure 1 An inkjet image forming apparatus according to an embodiment of the present invention will be described.

[0013] 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 .

[0014] The inkjet image forming apparatus 1 comprises a supply roller 3, a corona treatment unit 5, an image forming section 7, a drying section 9 and a winding roller 11, wherein the supply roller 3 is wound with a long printing substrate M; the corona treatment unit 5 applies corona discharge to the printing substrate M supplied from the supply roller 3; the image forming section 7 forms an image on the printing substrate M after the corona discharge by inkjet method; the drying section 9 dries the image formed by the image forming section 7; and the winding roller 11 winds up the printing substrate M dried by the drying section 9.

[0015] First, the supply roller 3 will be described. The printing base material M is wound and mounted on the supply roller 3. The printing base material M is fed out in a predetermined conveying direction X by the rotation of the supply roller 3.

[0016] Next, refer to Figure 2 The corona treatment unit 5 will be described. Figure 2 : is a diagram schematically illustrating a corona treatment unit 5. The corona treatment unit 5 is arranged on the downstream side of the conveying direction X relative to the supply roller 3. The corona treatment unit 5 has a corona discharge electrode 21 and an opposing roller 23, and the opposing roller 23 is arranged at a predetermined interval from the corona discharge electrode 21. The corona discharge electrode 21 is made of, for example, a rod-shaped ceramic or an aluminum cylinder coated with ceramic that is longer in the width direction Y of the printing substrate M. The opposing roller 23 is made of, for example, a stainless steel cylinder and is grounded. The interval between the corona discharge electrode 21 and the opposing roller 23 is, for example, 0.5 to 2.0 mm. In addition, tension rollers can be arranged on the upstream and downstream sides of the opposing roller 23.

[0017] The corona discharge electrode 21 is covered by an electrode cover 25 with an opening on the lower surface. The corona discharge electrode 21 is connected to a high-frequency power supply 29 via a high-voltage transformer 27. The high-frequency power supply 29 generates a high-frequency alternating current. An example of a high-frequency alternating current is 5.5kV to 6.5kV. The higher the discharge power, the higher the discharge voltage (discharge amount). However, since the discharge voltage varies depending on air pressure, temperature, humidity, etc., it is actually set according to the environmental conditions when the corona discharge treatment is performed. The high-voltage transformer 27 amplifies the generated high-frequency alternating current and converts it into discharge power, which is applied to the corona discharge electrode 21. Accordingly, corona discharge is generated between the corona discharge electrode 21 and the opposing roller 23.

[0018] The high-frequency power source 29 is electrically connected to the control unit 31 , and generates a high-frequency alternating current according to an instruction from the control unit 31 .

[0019] Next, refer to Figure 1 The image forming unit 7 is described below. The image forming unit 7 is arranged on the downstream side of the corona treatment unit 5 in the conveying direction X. The image forming unit 7 has four head units 41B, 41C, 41M, and 41Y (collectively referred to as head units 41) corresponding to inks of four colors (black, cyan, magenta, and yellow) and a conveying plate 43 that conveys the printing substrate M along the surface.

[0020] Also refer to Figure 3 The head unit 41 will be described. Figure 3 1 is a plan view showing the head unit 41. The head unit 41 includes three print heads 45 and a plate 47 that supports the three print heads 45.

[0021] like Figure 3 As shown, three print heads 45 are arranged in a staggered manner along the width direction Y (line head method) in a manner equal to the width of the printing substrate M, and are supported by a plate 47. The print head 45 has a plurality of nozzles (not shown). The nozzle outlets open on the bottom surface of the print head 45.

[0022] The four head units 41 are arranged in sequence along the transport direction X, and are respectively supplied with black, cyan, magenta, and yellow inks. The supplied inks are discharged downward from the discharge ports of the nozzles of the respective print heads 45 .

[0023] like Figure 1 As shown in FIG. 1 , the conveying plate 43 is arranged below the four head units 41. The upper surface of the conveying plate 43 is formed flat. Figure 3 As shown, the width of the conveying 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 conveying plate 43 to heat the conveying plate 43 to a predetermined temperature. The conveying plate 43 is made of metal, for example.

[0024] Next, the drying section 9 is described. The drying section 9 is arranged on the downstream side of the image forming section 7 in the conveying direction X. The drying section 9 includes a heating drum 51, and an upstream tension roller 53 and a downstream tension roller 55 arranged on the upstream and downstream sides of the heating drum 51. The printing substrate M passing through the image forming section 7 is wound around the heating drum 51 between the upstream tension roller 53 and the downstream tension roller 55. The heating drum 51 dries the printing substrate M conveyed along the surface by heating.

[0025] Next, the winding roller 11 is described. The winding roller 11 is arranged on the downstream side of the drying section 9 in the conveying direction X. 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) for rotation. The winding roller 11 is rotated in a predetermined direction at a predetermined rotation speed by the motor, and the printing substrate M is fed from the supply roller 3.

[0026] The fed printing substrate M passes between the corona discharge electrode 21 and the facing roller 23 of the corona treatment unit 5 and is fed to the image forming unit 7. In the image forming unit 7, the printing substrate M is fed to the drying unit 9 along the upper surface of the feeding plate 43 below the four head units 41. Then, in the drying unit 9, the printing substrate M is wound around the heating drum 51 and then wound up by the winding roller 11.

[0027] Next, the control unit 31 will be described. Figure 2 As shown, the control unit 31 controls the high-frequency power supply 29 of the corona treatment unit 5 to generate a high-frequency current of a specified intensity. In addition, the control unit 31 has an input unit 31a such as a display panel. The input unit 31a includes a glossiness input unit for inputting the glossiness (for example, 20-degree glossiness) of the printing substrate M. In addition, the control unit 31 is also electrically connected to the head unit 41 and controls the head unit 41 according to the input image data.

[0028] The image forming operation of the inkjet image forming apparatus 1 having the above-mentioned structure will be described. During the image forming operation, first, the user inputs the glossiness (20 degree glossiness) of the printing substrate M to the input unit 31a of the control unit 31. When the input glossiness is 25 or more, the control unit 31 controls the corona treatment unit 5 to perform the corona discharge.

[0029] After that, the motor is driven to rotate the winding roller 11, and the printed substrate M is sent from the supply roller 3 to the corona treatment unit 5. In the corona treatment unit 5, corona discharge is generated between the corona discharge electrode 21 and the facing roller 23, and the upper surface of the printed substrate M is subjected to corona treatment. On the other hand, when the input glossiness is lower than 25, the control unit 31 controls the corona treatment unit 5 in a manner not to perform corona discharge treatment. That is, when the input glossiness is lower than 25, the corona discharge treatment is not performed.

[0030] After that, the printing substrate M is conveyed to the bottom of the head unit 41, and ink of a predetermined color is discharged from the corresponding head unit 41 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 ink is completely dried. After that, the printing substrate M is wound up on the winding roller 11.

[0031] As described above, according to the present invention, when the glossiness of the printing substrate M is above a certain level, specifically, when the 20-degree glossiness is above 25, corona discharge is applied to the printing substrate M. The printing substrate M with low glossiness has fine concavities and convexities on the surface, so that the ink easily enters the concavities and convexities (anchor effect), thereby improving the adhesion between the ink and the printing substrate M. For example, in the case of a printing substrate M such as ordinary paper having a 20-degree glossiness lower than 25, corona discharge treatment is not required.

[0032] However, the adhesion between the printing substrate M and the ink is low, such as a plastic film or synthetic paper having a 20-degree glossiness of 25 or more. Therefore, the adhesion between the printing substrate M and the printing substrate M can be improved by performing a corona discharge treatment. That is, when the printing substrate M is subjected to a corona discharge treatment, fine concave and convex surfaces are formed on the surface of the printing substrate M, thereby obtaining the above-mentioned anchoring effect. Moreover, hydrophilic polar groups such as carbonyl, carboxyl, and nitride are formed on the surface of the printing substrate M. Such polar groups improve the wettability of the surface of the printing substrate M. Therefore, the physical and chemical effects achieved by the corona discharge treatment improve the adaptability (adhesion) between the printing substrate M and the ink.

[0033] In addition, in order to improve the adaptability (adhesion) of the printing substrate M and the ink, a pre-coating process using a pre-coating liquid is sometimes also implemented. However, since the liquid is applied in the pre-coating process, it is necessary to dry the printing substrate M, thereby it is necessary to extend the processing time by the amount of drying time or to set a dryer. In the corona discharge treatment, the same effect as the pre-coating process can be obtained without using liquid. However, the pre-coating process can also be used in combination according to the type of ink, etc.

[0034] Next, a test for evaluating the relationship between glossiness and adhesion in the inkjet image forming apparatus 1 of the present embodiment is described. Regarding glossiness, the printed substrate M is placed on the white portion of a concealment test paper (manufactured by TP Giken Co., Ltd.), and the 20-degree glossiness is measured using a gloss meter (trade name J480T-268, manufactured by Elcometer Limited). Adhesion is evaluated by a peel test.

[0035] The peeling test was performed by the following method: First, a cyan full-surface image was printed at 600 dpi on a printing substrate M. The printing substrate was an OPP film, the width of the printing substrate was 210 mm, and the conveying speed of the printing substrate was 3 m / min.

[0036] The printed image was subjected to a peel test according to JIS K5600 (no cross cut). The tape (trade name CT, manufactured by NICHIBAN Co., Ltd.) was firmly rubbed against the image with the fingertips and the tape was torn off within 5 minutes, or the end of the tape was grasped at an angle close to 60 degrees and torn off reliably within 0.5 to 1.0 seconds. The torn image was placed on a Figure 4A and Figure 4B The torn tape is attached to the right side of the printed substrate on the left. Figure 4A Showing an embodiment of the present invention, Figure 4B Shows a comparative example.

[0037] In the embodiment, the printed substrate is subjected to corona discharge by the corona treatment unit. The discharge power is 100 W (the discharge voltage is 6.3 kV). In the comparative example, the printed substrate is not subjected to corona discharge. Figure 4A and Figure 4B It is known that in the example, the ink was not peeled off from the printed substrate, and the ink was not attached to the removed tape. On the other hand, in the comparative example, the ink was peeled off from the printed substrate and attached to the tape.

[0038] In addition, the control unit 31 can control the corona treatment unit 5 in a manner that the higher the glossiness, the higher the voltage applied to the corona discharge electrode. In this case, even when the glossiness of the printing substrate is high and the adhesion to the ink is low, the adhesion to the ink can be improved. In addition, a measuring unit (not shown) for measuring the glossiness of the printing substrate M can be provided in the image forming device 1. In this case, after the printing substrate M is provided, the glossiness of the printing substrate M is measured by the measuring unit. The control unit 31 can control the corona treatment unit 5 to implement corona discharge according to the measured value. In this case, the operation of the user inputting the glossiness can be omitted.

[0039] In the above-mentioned embodiment, the head unit 41 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 head unit 41 is not limited to the line scanning head method. However, the line scanning head method can increase the printing speed, so it is preferred. In addition, as the printing substrate M, a long plastic film (PET film) is used, but a cut film may be used.

[0040] 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 a head unit, a corona treatment unit and a control unit, wherein: The head unit discharges ink toward a printing substrate transported in a predetermined transport direction; The corona treatment unit is arranged on the upstream side of the head unit in the conveying direction, and is used to perform corona discharge on the printing substrate; The control unit controls the discharge amount of the corona discharge performed by the corona treatment unit. The control unit controls the discharge amount according to the glossiness of the printing base material.

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

3. The inkjet image forming apparatus according to claim 1, wherein: The control unit controls the corona treatment unit to perform the corona discharge when the glossiness of the printing base material is higher than a predetermined value.

4. The inkjet image forming apparatus according to claim 3, wherein: When the 20-degree glossiness of the printed substrate is 25 or more, the control unit controls the corona treatment unit to perform the corona discharge.

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

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