Inkjet type image formation device

Abstract

To provide an inkjet type image formation device which can appropriately perform corona treatment even if a printing base material is conveyed at high speed.SOLUTION: An inkjet type image formation device includes head units for discharging ink onto a printing base material M conveyed in a predetermined conveyance direction, and a corona treatment unit which is arranged on the upstream side in the conveyance direction of the head units, and performs corona discharge on the printing base material, wherein the corona treatment unit includes an opposite roller 23 opposite to a corona discharge electrode 21, and the opposite roller 23 has such a reverse crown shape that a diameter of a central part is smaller than diameters of both ends, in a width direction of the printing base material M crossing the conveyance direction.SELECTED DRAWING: Figure 3

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, corona discharge may be applied to the printing substrate in order to improve adhesion between the printing substrate and the ink.

[0003] In the corona treatment electrode structure described in Patent Document 1, the discharge surface is formed as a curved surface in an arc shape centered on the axis of the earth roll. This ensures sufficient discharge time even when the conveying speed of the printing substrate increases. The corona discharge treatment device described in Patent Document 2 is equipped with an adjustment mechanism that adjusts the clearance between the corona discharge electrode and the treatment roll by bending the electrode due to heat generated during corona discharge. The adjustment mechanism prevents variations in corona treatment. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2004-103289 A [Patent Document 2] Japanese Patent Application Publication No. 6-163143 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the corona treatment electrode structure described in Patent Document 1, when the transport speed is increased for a thin and stiff printed substrate, wrinkles are likely to occur on the printed substrate. If corona discharge treatment is performed on a printed substrate with wrinkles, the corona treatment may vary and image quality may deteriorate. Moreover, the corona discharge treatment device described in Patent Document 2 does not have the effect of suppressing wrinkles when the transport speed is increased for a thin and stiff printed substrate.

[0006] SUMMARY OF THE PRESENT DISCLOSURE In view of the above circumstances, an object of the present invention is to provide an ink-jet image forming apparatus capable of performing appropriate corona treatment even when a printing substrate is transported at high speed. [Means for solving the problem]

[0007] In order to achieve the above-mentioned object, the inkjet image forming apparatus of the present invention comprises a head unit that ejects ink onto a printing substrate transported along a predetermined transport direction, and a corona treatment unit that is arranged upstream of the head unit in the transport direction and performs corona discharge on the printing substrate, the corona treatment unit comprising an opposing roller that faces a corona discharge electrode, and the opposing roller has an inverted crown shape in which the diameter of the central portion is smaller than the diameters of both ends in the width direction of the printing substrate that intersects with the transport direction.

[0008] In the ink jet image forming apparatus of the present invention, the corona discharge electrode may be supported so that a distance between the corona discharge electrode and the opposing roller is constant in the width direction.

[0009] The inkjet image forming apparatus of the present invention may be characterized in that it includes adjustment screws arranged at multiple locations in the width direction for pressing the corona discharge electrode toward the opposing roller, and the corona discharge electrode is deformed by changing the amount of screwing of the adjustment screws, thereby making the distance between the corona discharge electrode and the opposing roller constant in the width direction.

[0010] The ink jet type image forming apparatus of the present invention may be characterized in that the printing substrate is a plastic film. Effect of the Invention

[0011] According to the present invention, by forming the opposing roller in an inverted crown shape, it is possible to transport a non-absorbent printing substrate such as a plastic film without forming wrinkles. Therefore, even if a thin and stiff printing substrate is transported at high speed, the corona treatment can be performed uniformly in the width direction. [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] FIG. 2 is a diagram illustrating a corona treatment unit in an ink jet image forming apparatus according to one embodiment of the present invention. [Diagram 3] FIG. 2 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. [Figure 4] 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 5] 1 is a top view of 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; [Figure 6] 5 is a table showing the results of an evaluation test of wrinkles in the ink jet 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 type image forming apparatus 1 includes a supply roller 3 around which a long length of printing substrate M is wound, a corona treatment unit 5 that applies corona discharge to the printing substrate M supplied from the supply roller 3, an image forming section 7 that forms an image on the printing substrate M that has been subjected to corona discharge using an inkjet method, a drying section 9 that dries the image formed in the image forming section 7, and a take-up roller 11 that takes up the printing substrate M dried in the drying section 9.

[0016] First, a description will be given of the supply roller 3. The printing substrate M is wound around and attached to 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 corona treatment unit 5 will be described with reference to Fig. 2 and Fig. 3. Fig. 2 is a schematic diagram of the corona treatment unit 5, and Fig. 3 is a front view showing the corona discharge electrode 21 and the opposing roller 23. The corona treatment unit 5 is disposed downstream of the supply roller 3 in the conveying direction X. The corona treatment unit 5 includes the corona discharge electrode 21 and the opposing roller 23 disposed 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 long in the width direction of the printing substrate. The corona discharge electrode 21 is covered with an electrode cover 25 that is open at the bottom. 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 AC current. The high-frequency AC current is, for example, 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 depending on the atmospheric pressure, temperature, humidity, etc., it is set according to the environmental conditions when the corona discharge process is actually performed. The high-voltage transformer 27 amplifies the generated high-frequency AC current and converts it into discharge power, which is applied to the corona discharge electrode 21. The high-frequency power source 29 is electrically connected to a control unit 31, and generates a high-frequency AC current based on an instruction from the control unit 31.

[0019] The opposing roller 23 is made of, for example, a stainless steel cylinder and is grounded. The opposing roller 23 has an inverted crown shape with a smaller diameter at the center than at both ends in the width direction Y of the printing substrate M that intersects with the transport direction X. The difference between the diameter at the center and the diameter at both ends is, for example, 1 mm to 5 mm.

[0020] The corona discharge electrode 21 and the opposing roller 23 will be described with reference to Figure 3. Both ends of the corona discharge electrode 21 are fixed to the side plates of the electrode cover 25. Three adjustment screws 35 are screwed into the top plate of the electrode cover 25 at regular intervals in the width direction Y. The three adjustment screws 35 protrude downward from the top plate and are in contact with the center 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 pressed downward by the adjustment screws 35, and is deformed so as to bend downward.

[0021] The corona discharge electrode 21 is supported so that the distance between it and the opposing roller 23 is constant in the width direction Y. In detail, by making the amount of tightening of the central adjustment screw 35 larger than the amounts of tightening of the adjustment screws 35 at both ends, the corona discharge electrode 21 is bent so that the central portion is curved downward. As a result, the distance between the corona discharge electrode 21 and the opposing roller 23 is constant in the width direction Y. The distance is, for example, 0.5 to 2.0 mm.

[0022] Upstream and downstream tension rollers 37, 39 are disposed on the upstream and downstream sides of the opposing roller 23.

[0023] Next, the image forming unit 7 will be described with reference to Fig. 1. The image forming unit 7 is disposed downstream in the transport direction X from the corona treatment unit 5. The image forming unit 7 includes four head units 41B, 41C, 41M, and 41Y (collectively referred to as head unit 41) corresponding to four colors (black, cyan, magenta, and yellow) of ink, and a transport plate 43 along whose surface the printing substrate M is transported.

[0024] The head unit 41 will be described with reference to Fig. 4. Fig. 4 is a plan view showing the head unit 41. Each head unit 41 includes three print heads 45 and a plate 47 that supports the three print heads 45.

[0025] 4, the three print heads 45 are arranged in a staggered manner (line head system) along the width direction Y so that the width is approximately the same as the width of the printing substrate M, and are supported by a plate 47. The print head 45 is equipped with a large number of nozzles (not shown). The nozzle outlets are 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 supplied with black, cyan, magenta, and yellow ink, respectively. The supplied ink is ejected downward from the ejection openings of the nozzles of each print head 45.

[0027] The transport plate 43 is disposed below the four head units 41, as shown in Fig. 1. The upper surface of the transport plate 43 is formed flat. Also, as shown in Fig. 4, the width of the transport plate 43 is wider than the width of the printing substrate M and all of the head units 41. A heat source (not shown) is provided below the transport plate 43, and heats the transport plate 43 to a predetermined temperature. The transport plate 43 is made of, for example, metal.

[0028] Next, the drying section 9 will be described. The drying section 9 is disposed downstream of the image forming section 7 in the transport direction X. The drying section 9 includes a heat drum 51, and upstream and downstream tension rollers 53, 55 disposed upstream and downstream of the heat drum 51. The printing substrate M that has passed through the image forming section 7 is wound around the heat drum 51 between the upstream and downstream tension rollers 53, 55. The heat drum 51 dries the printing substrate M transported along its surface by being heated.

[0029] Next, the winding roller 11 will be described. The winding roller 11 is disposed downstream of the drying unit 9 in the transport direction X. 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 winding roller 11 is rotated in a predetermined direction at a predetermined rotation speed by the motor, whereby the printing substrate M is fed from the supply roller 3.

[0030] The sent printing substrate M passes between the corona discharge electrode 21 and the opposing roller 23 of the corona treatment unit 5 and is transported to the image forming section 7. In the image forming section 7, the printing substrate M is transported below the four head units 41 along the upper surface of the transport plate 43 toward the drying section 9. Then, in the drying section 9, the printing substrate M is wound around the heat drum 51 and then taken up by the take-up roller 11.

[0031] 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 generate a high-frequency current of a predetermined intensity. The control unit 31 is also electrically connected to the head unit 41, and controls the head unit 41 based on input image data.

[0032] In the inkjet image forming apparatus 1 having the above configuration, an image forming operation on a non-absorbent substrate (plastic film) will be described. During the image forming operation, the control unit 19 controls the corona treatment unit 5 to perform corona discharge treatment. As a result, in the corona treatment unit 5, corona discharge is generated between the corona discharge electrode 21 and the opposing roller 23. Note that if the printing substrate M is not non-absorbent, the corona treatment unit 5 does not perform corona discharge treatment.

[0033] Thereafter, the motor is driven to rotate the take-up roller 11, and the printing substrate M is sent from the supply roller 3 to the corona treatment unit 5. In the corona treatment unit 5, a corona discharge is generated 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.

[0034] Thereafter, the printing substrate M is transported below the head units 41, and ink of a predetermined color is ejected from the corresponding head units 41 based on image data to form an image 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 ink is completely dried. Thereafter, the printing substrate M is taken up by the take-up roller 11.

[0035] As described above, according to the present invention, by forming the opposing roller 23 in an inverted crown shape, it is possible to transport a non-absorbent printing substrate M such as a plastic film without forming wrinkles. That is, because the opposing roller 23 has an inverted crown shape, the linear speed at both ends is faster than the linear speed at the center. Therefore, as shown in FIG. 5, the printing substrate M that has passed the tension roller 37 on the upstream side is transported so as to be pulled by both ends by the opposing roller 23. As a result, the printing substrate M is stretched in the width direction Y, and wrinkles are eliminated. Therefore, even if a thin and stiff printing substrate M is transported at high speed, the corona treatment can be performed uniformly in the width direction Y.

[0036] Next, a test for evaluating the occurrence of wrinkles in the inkjet image forming apparatus 1 of this embodiment will be described with reference to the table in FIG. 6. In Examples 1 to 3, inverted crown type opposing rollers in which the outer diameter of the center portion is smaller than the outer diameter of both ends were prepared. In Example 1, the difference between the outer diameter of the center portion and the outer diameter of both ends was 5 mm, in Example 2, 2 mm, and in Example 3, 1 mm. On the other hand, in the opposing roller of Comparative Example 1, the difference between the outer diameter of the center portion and both ends was 0, and in the opposing roller of Comparative Example 2, the outer diameter of the center portion was 1 mm larger than the outer diameter of both ends.

[0037] The corona discharge electrode was adjusted with the adjustment screw shown in the figure so that the distance between the electrode and the opposing roller was 1.0 mm. The conveying speed of the printing substrate was 25 m / min, and the corona discharge amount was 80 W·min / m. 2 Then, a solid cyan image was printed.

[0038] First, the occurrence of wrinkles when the printed substrate entered the opposing roller was visually evaluated. In addition, the density of the solid image was measured to evaluate the density unevenness. The density measurement was performed using a CM-25cG colorimeter (manufactured by Konica Minolta).

[0039] As shown in the table of FIG. 6, no wrinkles were observed in Examples 1 to 3. The density unevenness was about 0.01, and was barely noticeable to the naked eye. On the other hand, wrinkles were observed in Comparative Example 1, and the number of wrinkles increased in Comparative Example 2. The density unevenness was about 0.03 in both Comparative Examples 1 and 2, and was noticeable to the naked eye. In other words, when wrinkles are present in the printing substrate, there are areas where the corona treatment is applied strongly and areas where it is applied weakly, and in the areas where it is applied weakly, the effect of obtaining compatibility (adhesion) with the ink by the corona discharge treatment is not fully exerted, so the ink is easily repelled and the density becomes low. As a result, density unevenness occurs.

[0040] Moreover, it was confirmed from the results of Examples 1 to 3 that the appropriate difference in diameter between the central portion and both end portions of the opposing roller 23 was 1 mm to 5 mm.

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

[0042] In addition, an example has been described in which the corona discharge electrode 21 is deformed in order to keep the distance to the inverted crown-shaped opposing roller 23 constant, but the shape of the part of the corona discharge electrode 21 facing the opposing roller 23 may be formed to match the shape of the opposing roller 23 so that the central part is more convex than both ends.

[0043] 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]

[0044] 1. Inkjet image forming device 5 Corona Treatment Unit 21 Corona discharge electrode 23 Opposing Roller 31 Control Unit 35 Adjustment screw 41 Head Unit

Claims

1. a head unit that ejects ink onto a printing substrate transported along a predetermined transport direction; a corona treatment unit that is disposed upstream of the head unit in the transport direction and that performs corona discharge on the printing substrate, The corona treatment unit comprises: A corona discharge electrode and an opposing roller are provided. The opposing roller has an inverted crown shape in which the diameter at the center is smaller than the diameter at both ends in a width direction of the printing substrate that intersects with the transport direction.

2. 2. The ink-jet image forming apparatus according to claim 1, wherein the corona discharge electrode is supported so that a distance between the corona discharge electrode and the opposing roller is constant in the width direction.

3. a plurality of adjustment screws arranged at a plurality of positions in the width direction for pressing the corona discharge electrode toward the opposing roller; 3. The ink-jet image forming apparatus according to claim 2, wherein the corona discharge electrode is deformed by changing the amount of screwing of the adjustment screw, thereby making the gap between the corona discharge electrode and the opposing roller constant in the width direction.

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

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