Inkjet image forming apparatus

Abstract

The invention provides an inkjet image forming apparatus. An inkjet image forming apparatus includes a head unit and a corona processing 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 corona treatment unit has a facing roller that faces the corona discharge electrode. The opposing roller has an inverted crown shape in which the diameter of the center portion is smaller than the diameter of both end portions in the width direction of the printing base material intersecting the conveyance direction. Accordingly, corona treatment can be appropriately performed even when the printing base material is conveyed at a high speed.

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 discharge surface has a corona treatment electrode structure formed into an arc-shaped curved surface with the axis of the ground roller as the center. Accordingly, the discharge time can be ensured even if the conveying speed of the printed substrate reaches a high speed. In addition, there is a corona treatment device, which has an adjustment mechanism that adjusts the gap (clearance) between the corona discharge electrode and the treatment roller by bending the electrode using the heat during corona discharge.

[0004] However, in the former corona treatment electrode structure, in the case of a thin and non-rigid printing substrate, wrinkles easily occur in the printing substrate when the conveying speed is increased. If the corona discharge treatment is implemented in the state where the printing substrate is wrinkled, the corona treatment will produce deviations, which may lead to image quality degradation. In addition, even in the latter corona discharge treatment device, the effect of suppressing (preventing) the thin and non-rigid printing substrate from wrinkling when the conveying speed is increased cannot be obtained. 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 appropriately performing corona treatment even when a printing substrate is conveyed at high speed. [Technical solutions for solving technical problems]

[0006] The inkjet image forming device of the present invention has a head unit and a corona treatment unit. The head unit discharges ink to a printing substrate transported along a specified 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 corona treatment unit has opposing rollers that face the corona discharge electrodes. The opposing rollers have an inverted crown shape in which the diameter of the central portion in the width direction of the printing substrate intersecting the conveying direction is smaller than the diameter of the two end portions. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1It is a front view schematically showing an inkjet image forming apparatus according to an 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 front view showing a corona discharge electrode and an opposing roller in an ink jet image forming apparatus according to an embodiment of the present invention.

[0010] Figure 4 It is a plan view showing a head unit in an inkjet image forming apparatus according to an embodiment of the present invention.

[0011] Figure 5 This is a diagram showing a recording medium passing through an upstream tension roller, an opposing roller, and a downstream tension roller in an inkjet image forming apparatus according to an embodiment of the present invention, as viewed from top to bottom.

[0012] Figure 6 This is a table showing the results of a wrinkle evaluation test in the inkjet image forming apparatus according to one embodiment of the present invention. DETAILED DESCRIPTION

[0013] Below, while referring 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 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.

[0016] 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.

[0017] Next, refer to Figure 2 and Figure 3 The corona treatment unit 5 will be described. Figure 22 is a diagram schematically illustrating a corona treatment unit 5. Figure 3 2 is a front view showing the corona discharge electrode 21 and the facing roller 23. The corona treatment unit 5 is arranged downstream of the supply roller 3 in the conveying direction X. The corona treatment unit 5 includes the corona discharge electrode 21 and the facing roller 23 which is arranged at a predetermined interval from the corona discharge electrode 21.

[0018] 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 of the printed substrate. 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 5.5 kV to 6.5 kV. The higher the discharge power, the higher the discharge voltage (discharge amount). However, since the discharge voltage varies according to 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 a discharge power, which is applied to the corona discharge electrode 21. The high-frequency power supply 29 is electrically connected to the control unit 31, and generates a high-frequency alternating current according to instructions from the control unit 31.

[0019] The facing roller 23 is made of, for example, a stainless steel cylinder and is grounded. The facing roller 23 has an inverted crown shape, in which the diameter of the central portion is smaller than the diameter of the two end portions in the width direction Y of the printing substrate M intersecting the conveying direction X. An example of the difference between the diameter of the central portion and the diameter of the two end portions is 1 mm to 5 mm.

[0020] Reference Figure 3 The corona discharge electrode 21 and the facing roller 23 are described below. Both ends of the corona discharge electrode 21 are fixed to the side plates of the electrode cover 25. On the top plate of the electrode cover 25, three adjustment screws 35 are screwed at a certain interval along the width direction Y. The three adjustment screws 35 protrude downward from the top plate and contact the central part and both ends of the corona discharge electrode 21. By screwing the adjustment screws 35 into the top plate, the corona discharge electrode 21 is pushed downward by the adjustment screws 35 and deformed in a downwardly flexed manner.

[0021] The corona discharge electrode 21 is supported so that the interval between the corona discharge electrode 21 and the opposing roller 23 is constant in the width direction Y. Specifically, the central portion of the corona discharge electrode 21 is bent downward by making the screwing amount (screwing depth) of the central adjustment screw 35 greater than the screwing amount (screwing depth) of the adjustment screws 35 at both ends. As a result, the interval between the corona discharge electrode 21 and the opposing roller 23 is constant in the width direction Y. The interval is, for example, 0.5 to 2.0 mm.

[0022] An upstream tension roller 37 and a downstream tension roller 39 are arranged on the upstream side and the downstream side of the facing roller 23 .

[0023] 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.

[0024] Also refer to Figure 4 The head unit 41 will be described. Figure 4 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.

[0025] like Figure 4 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.

[0026] 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 .

[0027] 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 4 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.

[0028] Next, the drying section 9 will be 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.

[0029] 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.

[0030] 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.

[0031] Next, the control unit 31 will be described. Figure 2 As shown, the control unit 31 controls the high frequency power source 29 of the corona treatment unit 5 to generate a high frequency current of a predetermined intensity. In addition, 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.

[0032] The image forming operation with respect to the non-absorbent substrate (plastic film) in the inkjet image forming apparatus 1 having the above-mentioned structure is described. During the image forming operation, the control unit 19 controls the corona treatment unit 5 in a manner of performing corona discharge treatment. Accordingly, in the corona treatment unit 5, corona discharge is generated between the corona discharge electrode 21 and the facing roller 23. In addition, when the printing substrate M is not a non-absorbent substrate, the corona discharge treatment is not performed by the corona treatment unit 5.

[0033] Then, the motor is driven to rotate the take-up roller 11, and the printed substrate M is fed 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.

[0034] 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.

[0035] As described above, according to the present invention, by making the facing roller 23 in the shape of an inverted crown, a non-absorbent printing substrate M such as a plastic film can be conveyed in a manner that does not cause wrinkles. That is, since the facing roller 23 is in the shape of an inverted crown, the linear speed at the two end portions is faster than the linear speed at the center portion. Figure 5As shown, the printing substrate M passing through the tension roller 37 on the upstream side is conveyed by the facing roller 23 in a manner stretched toward both ends. Accordingly, the printing substrate M is stretched without wrinkling in the width direction Y. Therefore, even if the printing substrate M having a thin thickness and no rigidity is conveyed at a high speed, the corona treatment can be uniformly applied in the width direction Y.

[0036] Next, refer to Figure 6 The table below illustrates an experiment for evaluating the generation of wrinkles in the inkjet image forming apparatus 1 of the present embodiment. As Examples 1 to 3, inverted crown-shaped opposing rollers were prepared in which the outer diameter of the center portion was smaller than the outer diameter of the two ends. The difference between the outer diameter of the center portion and the outer diameter of the two ends was 5 mm in Example 1, 2 mm in Example 2, and 1 mm in Example 3. On the other hand, the difference between the outer diameter of the center portion and the outer diameter of the two ends of the opposing roller of Comparative Example 1 was 0, and the outer diameter of the center portion of the opposing roller of Comparative Example 2 was 1 mm larger than the outer diameter of the two ends.

[0037] The distance between the corona discharge electrode and the facing roller was adjusted by the adjustment screw shown in the figure so that it was 1.0 mm. The conveying speed of the printed substrate was 25 m / min and the corona discharge amount was 80 W·min / m 2 , prints a cyan full-surface image.

[0038] First, the occurrence of wrinkles when the printed substrate enters the opposing rollers was visually evaluated. Then, the density of the entire image was measured to evaluate the density unevenness. The density was measured using a spectrophotometer CM-25cG (manufactured by Konica Minolta, Inc.).

[0039] like Figure 6 As shown in the table, in Examples 1 to 3, no wrinkling was observed. In addition, the concentration unevenness was about 0.01, which is a degree at which the concentration unevenness is almost unrecognizable by visual observation. On the other hand, in Comparative Example 1, wrinkling was observed, and in Comparative Example 2, the number of wrinkles increased. In addition, the concentration unevenness of Comparative Examples 1 and 2 was about 0.03, which is a degree that can be recognized by visual observation. That is, if wrinkles exist in the printed substrate, there are parts where the corona treatment is implemented more strongly and parts where it is implemented more weakly. In the part where the corona discharge treatment is implemented more weakly, the effect of adaptability (adhesion) to the ink achieved by the corona discharge treatment cannot be fully exerted, so the ink is easily bounced off and the concentration is thinned. As a result, concentration unevenness occurs.

[0040] Furthermore, from the results of Examples 1 to 3, it was confirmed that the appropriate difference between the diameter of the center portion and the diameter of both end portions of the facing roller 23 is 1 mm to 5 mm.

[0041] 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 scan head method. However, the line scan 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.

[0042] In addition, an example is described in which corona discharge electrode 21 is deformed so that the interval with inverse crown-shaped opposing roller 23 is constant. The shape of the portion of corona discharge electrode 21 facing opposing roller 23 can be formed so that the center portion is convex compared to both end portions in accordance with the shape of opposing roller 23.

[0043] 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 and a corona treatment 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 corona treatment unit has a facing roller, which faces the corona discharge electrode. The facing roller has an inverted crown shape in which a diameter of a central portion is smaller than a diameter of both end portions in a width direction of the printing substrate intersecting the conveying direction.

2. The inkjet image forming apparatus according to claim 1, wherein: The corona discharge electrode is supported so that the interval between the corona discharge electrode and the opposing roller is constant in the width direction.

3. The inkjet image forming apparatus according to claim 2, wherein: An adjustment screw is provided, and the adjustment screw is arranged at a plurality of positions in the width direction, and the adjustment screw pushes the corona discharge electrode toward one side of the opposing roller, The corona discharge electrode is deformed by changing the screwing amount of the adjustment screw so that the interval between the corona discharge electrode and the opposing roller becomes constant in the width direction.

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

Images