Metal image forming method

Abstract

To solve the problem in which: in a subtractive method, a method using a toner image formed on a photoreceptor as a resist pattern is proposed in order to reduce the cost and time required for a resist pattern forming step; however, an etching step requiring cost and time is still necessary in this method, and thus a new metal image forming method is demanded which does not need the resist pattern forming step and the etching step.SOLUTION: A toner image is used as a resist pattern for metal image formation in a known lift-off method rather than using the toner image as a resist pattern for an etching step. The toner image is formed by forming and developing an electrostatic pattern directly on a substrate without using a photoreceptor. A surface on which the toner image is formed is covered with a metal layer by using a physical manufacturing method, and subsequently the toner image is removed together with the metal layer on the toner image, thereby obtaining a metal image.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for forming metal images. [Background technology]

[0002] The subtractive method is widely used as a method for forming a metal image. The process of the subtractive method is outlined below. That is, the metal image is formed through a process of laminating a photosensitive and etching-resistant resist on the metal layer of an object having a metal layer provided on an insulating base material (resist lamination process), a process of exposing the resist layer through a photomask, developing it, and forming a resist pattern on the metal layer (resist pattern formation process), a process of removing the metal layer not covered by the resist layer by etching and washing it (etching process), and a process of removing the resist layer from the metal layer, washing it, and obtaining a metal image (resist removal process).

[0003] The subtractive method requires large-scale exposure equipment and development equipment in the resist pattern formation process, and the production and storage of photomasks is costly. To solve these problems, a method has been proposed in which a toner image formed on a photoreceptor is used as a resist pattern (see Patent Document 1). That is, a toner image formed on a photoreceptor using a wet toner having etching resistance is transferred onto a conductive layer (copper foil, ITO film) of a target object by electrostatic transfer, and then fixed to form a resist pattern on the conductive layer. After the resist pattern is formed, an etching process and a resist removal process are performed to form a conductive layer image. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2008-270398 A Summary of the Invention [Problem to be solved by the invention]

[0005] The above-mentioned method of using a toner image formed on a photoreceptor as a resist pattern can reduce the equipment cost, manufacturing cost, and manufacturing time required for the resist pattern formation process. However, the etching process is still required. The etching process also requires large-scale equipment, and requires manufacturing costs and manufacturing time. There is a demand for a new metal image formation method that does not require an etching process in addition to the resist pattern formation process.

[0006] The present invention proposes a method for forming a metal image to solve the above problems. [Means for solving the problem]

[0007] The present inventors have changed their concept and investigated using a toner image as a resist pattern for forming a metal image in a known lift-off method, instead of using a toner image as a resist pattern for an etching process. As a result, they have found that a metal image can be obtained on an insulating layer by forming an electrostatic pattern directly on an insulating layer of a substrate consisting of an insulating layer and a conductive layer without using a photoreceptor, developing the electrostatic pattern with charged particles called toner to form a toner image on the insulating layer, covering the surface on which the toner image is formed with a metal layer by a physical preparation method, and then removing the toner image together with the metal layer on the toner image, thereby achieving the present invention.

[0008] The present invention provides a method for forming a metal image which overcomes the above problems. (I) (1) a step of forming a static electricity pattern on an insulating layer of a substrate S including an insulating layer and a conductive layer (a static electricity pattern forming step); (2) developing the electrostatic pattern with charged particles called toner to form a toner image on the insulating layer of the substrate S (developing step); (3) a step of coating the surface of the substrate S on which the toner image is formed with a metal layer by a physical preparation method (metal layer coating step); (4) A method for forming a metal image, comprising a step of removing the toner image together with the metal layer on the toner image (toner removing step). (II) The method for forming a metal image described in item 1 above, characterized in that an original plate having a printing layer on which a letterpress, intaglio, or gravure-like pattern is formed and a first electrode, and a substrate S having an insulating layer and a conductive layer that becomes a second electrode are used, the printing layer of the original plate and the insulating layer of the substrate S are brought into close contact with each other, and an appropriate voltage sufficient to discharge the gap between the pattern of the printing layer and the insulating layer is applied between the first electrode of the original plate and the second electrode of the substrate S, thereby forming an electrostatic pattern corresponding to the pattern of the printing layer on the insulating layer of the substrate S. (III) A method for forming a metal image as described in item 1 above, characterized in that a substrate S is used, which is made of a molded body of only a conductive material or a laminate of an insulating material and a conductive material, and which comprises a mask sheet having a predetermined ion-permeable opening, an insulating layer, and a conductive layer that serves as a back electrode, and the mask sheet and the insulating layer of the substrate S are brought into close contact with each other, ions are irradiated through the mask sheet, and then the mask sheet is peeled off from the substrate S, thereby forming a static electricity pattern on the insulating layer of the substrate S corresponding to the ion-permeable openings and ion-shielding parts of the mask sheet. (IV) The method for forming a metallic image as described in the above item 3, wherein the ion irradiation means is an ion irradiation method using corona discharge. Effect of the Invention

[0009] The method of the present invention does not require the resist pattern forming step and etching step as in the conventional technology, and therefore does not require the equipment related to these steps, and can reduce the production costs and production time required for these steps. [Brief description of the drawings]

[0010] [Figure 1] Static electricity pattern formation process [Diagram 2] Development process [Diagram 3] Metal layer coating process [Figure 4] Toner removal process [Diagram 5] An example of a static electricity pattern formation process [Figure 6] Another example of the static electricity pattern formation process DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] FIG. 1 shows the static electricity pattern forming step of the present invention, in which a static electricity pattern is formed and maintained on an insulating layer 22 of a substrate S. The substrate S is composed of a conductive layer 21 and an insulating layer 22, which become electrodes in the static electricity pattern forming process. The insulating layer 22 must have high electrical insulation because it must retain the static electricity pattern. Molded products such as polyimide, polycarbonate, PET (polyethylene terephthalate), cycloolefin polymer, cycloolefin copolymer, and fluorine-based resin can be used as the insulating layer 22. The thickness of the insulating layer 22 is preferably 5 to 300 μm. If the thickness is less than 5 μm, handling is difficult. Furthermore, if the thickness exceeds 300 μm, it becomes difficult to apply means for improving productivity such as the roll-to-roll method.

[0012] The conductive layer 21 only needs to serve to supply an electric field in the electrostatic pattern formation process or to stabilize the electric charge on the insulating layer 22, and therefore may be made of any conductive material, such as a metal, a conductive oxide, carbon, graphite, or a conductive polymer. The conductive layer 21 is disposed on the surface of the insulating layer 22 opposite to the surface on which the static electricity pattern is formed. The conductive layer 21 can fulfill the above-mentioned role if it is pressed against the insulating layer 22, but if it is integrated with the insulating layer 22, it becomes easier to handle in the static electricity pattern forming process and the development process. If the conductive layer 21 is formed on the surface of the insulating layer 22 opposite to the surface on which the static electricity pattern is formed by a method such as sputtering a metal film, a conductive oxide film, or the like, coating a conductive polymer film, or laminating a metal foil, the insulating layer 22 and the conductive layer 21 can be integrated. Conversely, the insulating layer 22 and the conductive layer 21 can be integrated by providing the insulating layer 22 on the conductive layer 21 made of metal foil or the like by a coating method or the like. Alternatively, the insulating layer 22 and the conductive layer 21 can be integrated by laminating a sheet with a conductive layer, which is an insulating material sheet previously provided with a conductive layer 21 such as a metal film, a conductive oxide film, or a conductive polymer film, on the surface of the insulating layer 22 opposite to the surface on which the static electricity pattern is formed, using an adhesive layer.

[0013] An example of the electrostatic pattern formation process is shown in FIG. 5. This method is an application of the high-definition electrostatic printing method proposed by the present inventors (see the specification of Japanese Patent Application No. 2018-188998). Using an original plate 10 having a plate layer 12 on which a relief, intaglio, or gravure-like pattern is formed (FIG. 5 shows an example in which the portion where a toner image is formed is intaglio) and a first electrode 11, and a substrate S having an insulating layer 22 and a conductive layer 21 that becomes a second electrode, the plate layer 12 of the original plate 10 and the insulating layer 22 of the substrate S are brought into close contact with each other, and an appropriate voltage is applied between the first electrode 11 of the original plate 10 and the second electrode 21 of the substrate S to discharge the gap between the pattern of the plate layer 12 and the insulating layer 22, thereby forming an electrostatic pattern corresponding to the pattern of the plate layer 12 on the insulating layer 22.

[0014] The conditions under which a gap discharges can be calculated using Paschen's law. The discharge inception voltage for gaps of 8 μm or more can be expressed as a straight line, and is approximated by the following formula, where gap: d (μm) and gap discharge inception voltage: Vb. Vb=312+6.2d (1) The gap (the gap between the pattern of the printing layer 12 and the insulating layer 22) is 20 μm, and the discharge start voltage is 436 V. In other words, when an external voltage of 436 V or more is applied to the gap, a discharge occurs and ions are generated. Of the generated ions, positive ions move toward the negative electrode and negative ions move toward the positive electrode in accordance with the electric field. The ions charge the insulating layer 22, which acts to weaken the electric field in the gap. The discharge ends when the voltage applied to the gap reaches the discharge start voltage of 436 V.

[0015] In the example of FIG. 5, the insulating layer 22 is PET with a thickness of 25 μm and a relative dielectric constant of 3.2, which is converted to an air thickness of 25÷3.2=7.8. In this example, the entire surface of the insulating layer 22 is pre-charged with +300V. This pre-charge process ensures that the substrate S adheres to the original plate 10. With the plate layer 12 and the insulating layer 22 in close contact, the second electrode 21 is set to ground potential, and a voltage is applied so that −723V is applied to the first electrode 11. The voltage applied to the 20 μm gap is (723+300)×20÷(20+7.8)V=736V. Since this is greater than the discharge start voltage of 436V for a 20 μm gap obtained from formula (1), discharge ions are generated in the gap, negative ions move toward the electrode 21 and charge the insulating layer 22, and positive ions flow to the electrode 11. When the insulating layer 22 is charged to -(736-436) = -300V, the electric field applied to the gap reaches the discharge start voltage of 436V, and the discharge stops. Thereafter, the applied power is turned off and the electrode 21 is set to 0V, and then the substrate S is peeled off from the original 10. This results in a static electricity pattern being created on the insulating layer 22 in which the areas corresponding to the gaps in the intaglio (areas where the toner image is formed) are charged to -300V, and the other areas are charged to +300V. The electrode 21 is set to 0V before peeling in order to create conditions that prevent any part of the entire surface from discharging upon peeling.

[0016] Another example of the electrostatic pattern formation process is shown in FIG. 6. This method is an application of the electrostatic printing method proposed by the present inventors (see the specification of Japanese Patent Application No. 2021-132875). A substrate S is used that includes a mask sheet M made of only a conductive material or a laminate of an insulating material and a conductive material and has a predetermined ion-permeable opening, an insulating layer 22, and a conductive layer 21 that becomes a back electrode, and the mask sheet M and the insulating layer 22 of the substrate S are closely attached to each other. After ion irradiation is performed through the mask sheet M, the mask sheet M is peeled off from the substrate S to form a static electricity pattern on the insulating layer 22 of the substrate S that corresponds to the ion-permeable opening and ion shielding portion of the mask sheet M.

[0017] In the example of FIG. 6, a conductive layer 21, which becomes a back electrode, is adhered to the surface of the insulating layer 22 opposite to the surface on which the static electricity pattern is formed, and the conductive layer 21 is grounded. Before the mask sheet M is adhered to the insulating layer 22, a preliminary charging process is performed on the entire surface of the insulating layer 22 at -300V. This preliminary charging process ensures that the mask sheet M adheres to the insulating layer 22. With the mask sheet M having the ion permeable openings 31 adhered to the insulating layer 22, ion irradiation is performed through the mask sheet M by the ion irradiation means 40. After the ion irradiation, the surface of the mask sheet M and the ion irradiation parts corresponding to the ion permeable openings 31 of the insulating layer 22 are charged to +300V. The mask sheet M is peeled off from the insulating layer 22 while being grounded. The ion irradiation parts (parts other than those where the toner image is formed) corresponding to the ion permeable openings 31 of the insulating layer 22 are charged to +300V, and the non-ion irradiation parts (parts where the toner image is formed) corresponding to the ion shielding parts are charged to -300V, forming a static electricity pattern.

[0018] Figure 2 shows the development process. The electrostatic pattern created in the electrostatic pattern formation process is developed with charged particles called toner. In the present invention, the toner image must be removed together with the metal layer on top of it in the final process, and the material is selected in combination with the solution used for removal (alkaline aqueous solution or organic solvent). For example, if the toner is a material mainly composed of polyvinyl acetate, methanol should be selected as the solution. As the toner, the liquid toner for electrophotography proposed by the present inventors can also be applied (see the specification of Japanese Patent Application No. 2019-209237). Liquid toner is advantageous in forming a high-resolution toner image compared to dry toner. 2 shows an example in which a positively charged toner is used. The drying conditions immediately after development are 110°C for 3 minutes. In this case, the toner does not adhere to the parts of the insulating layer 22 that are charged to +300V (parts other than those where a toner image is to be formed), but adheres to the parts that are charged to -300V (parts where a toner image is to be formed), and a toner image 24 is formed on the insulating layer 22.

[0019] 3 shows a metal layer coating step. The surface of the substrate S on which the toner image 24 is formed on the insulating layer 22 is coated with a metal layer 50 by a physical preparation method. A physical fabrication method, i.e., PVD (Physical Vapor Deposition), is a film formation method that utilizes physical phenomena in a vacuum, and is classified into sputtering methods (DC sputtering, DC magnetron sputtering, RF sputtering, RF magnetron sputtering, etc.), vacuum deposition methods (resistance heating, electron beam heating, etc.), and ion plating methods (activated reactive deposition, high density plasma assisted deposition, etc.). When forming a metal layer, DC magnetron sputtering or vacuum deposition is preferred from the viewpoint of film formation speed. Before forming the metal layer, the surface to be coated with the metal layer may be modified by plasma treatment or the like.

[0020] FIG. 3 shows an example in which a DC magnetron sputtering method was used as a physical fabrication method. A copper target was set on the cathode of a DC magnetron sputtering device, and the substrate S was attached to a substrate holder. The deposition chamber was opened for 10 -4 After evacuating the chamber to 100 Pa, argon gas was introduced and the pressure was adjusted to 0.2 Pa. After sputtering was performed by applying a voltage to the cathode, the film formation chamber was broken and the substrate S was removed. The toner image 24 on the insulating layer 22 and the surface of the insulating layer 22 without the toner image were both covered with a copper layer 50.

[0021] 4 shows the toner removal step. The toner image 24 on the substrate S is removed together with the metal layer 50 on the toner image. As a result, the metal layer 50 that directly covered the insulating layer 22 remains, forming a metal image. In the example of FIG. 4, the toner image was removed by immersing the sample in methanol for 1 minute while applying ultrasonic vibration, and then the sample was washed with water for 1 minute. The copper image formed on the substrate S had a thickness of 100 nm, a line width of 50 μm, and a line spacing of 50 to 150 μm.

[0022] If necessary, the metal image formed by the above method may be subjected to an electroless plating process, or an electroless plating process and an electroplating process, to laminate the same or a different metal on the metal image formed by the above method. By performing such an electroless plating process, or an electroless plating process and an electroplating process, it is possible to improve the strength, conductivity, and other properties of the entire metal image including the laminated portion. Industrial Applicability

[0023] The present invention can be used in various industrial fields such as commercial printing, card business, and cosmetic containers, in addition to the electronics field. [Explanation of symbols]

[0024] 10:Original version 11: 1st electrode 12: Plate layer S: Substrate S 21: Conductive layer 22: Insulating layer 24: Toner image M: Mask sheet 31: Ion-permeable opening 32: Ion shielding section 40: Ion irradiation means 50: Metal image

Claims

1. (1) A step of forming a static electricity pattern on an insulating layer of a substrate S including an insulating layer and a conductive layer (a static electricity pattern forming step); (2) developing the electrostatic pattern with charged particles called toner to form a toner image on the insulating layer of the substrate S (developing step); (3) a step of coating the surface of the substrate S on which the toner image is formed with a metal layer by a physical preparation method (metal layer coating step); (4) A method for forming a metal image, comprising a step of removing the toner image together with a metal layer on the toner image (toner removing step).

2. The method for forming a metal image according to claim 1, further comprising the steps of: using an original plate having a plate layer on which a relief, intaglio or gravure-like pattern is formed and a first electrode; and a substrate S having an insulating layer and a conductive layer which becomes a second electrode; bringing the plate layer of the original plate into close contact with the insulating layer of the substrate S; and applying an appropriate voltage between the first electrode of the original plate and the second electrode of the substrate S sufficient to discharge the gap between the pattern of the plate layer and the insulating layer, thereby forming an electrostatic pattern corresponding to the pattern of the plate layer on the insulating layer of the substrate S.

3. The method for forming a metal image according to claim 1, further comprising the steps of: using a substrate S, which is made of a molded body of only a conductive material or a laminate of an insulating material and a conductive material, and which is provided with a mask sheet having a predetermined ion-permeable opening, an insulating layer, and a conductive layer which serves as a back electrode, the mask sheet and the insulating layer of the substrate S are brought into close contact with each other; irradiating ions through the mask sheet; and then peeling the mask sheet from the substrate S, thereby forming a static electricity pattern on the insulating layer of the substrate S which corresponds to the ion-permeable openings and ion-shielding portions of the mask sheet.

4. 4. The method for forming a metal image according to claim 3, wherein the ion irradiation means is an ion irradiation method using corona discharge.

Images