High hardness micro prism mold for retroreflective film formation and its manufacturing method

Abstract

The present invention improves hardness characteristics by using an alloy of Ni-Co, Ni-W, Ni-Cr, Ni-Fe, Ni-Mo, Ni-P, or Ni-Cu as the material for a microprism mold.

Description

Technology Field

[0001] The present invention relates to a high-hardness microprism mold and a method for manufacturing the same, and more specifically, to a manufacturing technology for a microprism mold required for molding a retroreflective film. Background Technology

[0002] Retroreflective film is a film (sheet) formed with microprisms and is used in road signs, vehicle license plates, industrial safety equipment, etc. Retroreflective film is manufactured through a continuous process using a roll mold or belt mold based on the production of a cast mold. That is, retroreflective film is manufactured by extruding a film using a mold formed with microprisms (hereinafter referred to as a microprism mold). During the film extrusion process, a decrease in the thickness uniformity of the microprism mold leads to a deterioration in the quality of the retroreflective film. Specifically, when manufacturing large-area microprism molds, overall thickness uniformity is not achieved, and the thickness at both ends is made thicker than the center; consequently, when mounted on a roll, the mold takes on a shape where the ends bulge and the center is sunken. The film produced under these conditions has the problem of exhibiting a bulging shape in the center. Additionally, cracks form at the connection points of the mold, rendering the corresponding parts of the film unusable (see Fig. 1). Total or partial product defects (using only a portion of the film and discarding the rest) lower productivity.

[0003] Meanwhile, the material used for these microprism molds is known to be Ni. Microprism molds made of Ni require replacement due to deformation of the original microprism shape after prolonged use. Replacing the mold implies the shutdown and restart of the production line, which also reduces productivity.

[0004] Registered Patent No. 10-0495977 discloses a method for making a mold belt for manufacturing optical films by electroforming technology. In the above publication as well, the mold belt is formed of Ni. The problem to be solved

[0005] The objective of the present invention is to provide a plating technology for a microprism mold having a uniform thickness and excellent mechanical properties.

[0006] In other words, the present invention aims to provide a high-hardness micro-prism mold that can be used for a long period of time.

[0007] In addition, we aim to manufacture large-area microprism molds with high thickness uniformity.

[0008] Accordingly, the present invention seeks optimal results by exploring each variable of the electro-casting solution, electro-casting process, and electro-casting equipment. means of solving the problem

[0009] In accordance with the above objective, the present invention improves hardness characteristics by using an alloy of Ni-Co, Ni-W, Ni-Cr, Ni-Fe, Ni-Mo, Ni-P, or Ni-Cu as the material of a microprism mold.

[0010] In the above, the Ni ratio of the alloy is set to 70 to 95 wt%.

[0011] In addition, to maintain the thickness uniformity of the large-area mold, the electroplating solution is prepared and maintained homogeneously, the current applied to the electrode in the electroplating process is made into a pulsed current, and the electroplating process is optimized by placing an anode shielding plate and an auxiliary cathode to make the equipotential lines of the electric field formed between the anode and the cathode constant.

[0012] That is, the present invention is,

[0013] The present invention provides a micro prism mold for forming retroreflective films, characterized by being composed of any one of the alloys of Ni-Co, Ni-W, Ni-Mo, Ni-P, and Ni-Cu, with the Ni ratio of the alloy being 70 to 95 wt% to improve hardness characteristics.

[0014] In the above, a micro prism mold for forming a retroreflective film is provided, characterized in that the thickness of the micro prism mold for forming a retroreflective film is 300 µm or more and the thickness deviation is ±5% or less.

[0015] In the above, a micro prism mold for forming a retroreflective film is provided, characterized in that the hardness of the micro prism mold for forming a retroreflective film is 350 Hv or higher.

[0016] In the above, a micro prism mold for forming a retroreflective film is provided, characterized in that the outer surface area of ​​the micro prism mold for forming a retroreflective film is 35cm × 35cm or larger.

[0017] In the above, a micro prism mold for forming a retroreflective film is provided, characterized in that, in the case of a Ni-Co alloy, Co is included in an amount of 5 to 30 wt%.

[0018] As a manufacturing system for the microprism mold for forming the above retroreflective film,

[0019] Plating tank;

[0020] An anode and a cathode arranged at a distance from each other in the above plating bath;

[0021] Solution control unit for maintaining the uniformity of the solution filling the plating bath;

[0022] A power supply unit that supplies and controls the current to be applied to the positive and negative electrodes; and

[0023] Includes an anode shielding plate installed to maintain the equipotential plane of the electric field formed between the anode and the cathode during the plating process as a horizontal plane;

[0024] The above solution control unit includes a stirrer, a chemical supply unit, and a flow rate control unit, and

[0025] The above-mentioned anode shielding plate is installed near the anode and spaced apart from the anode, and

[0026] The above power supply unit applies a current having a predetermined current density to the positive and negative electrodes, and

[0027] A manufacturing system for a micro prism mold for forming a retroreflective film is provided, characterized in that, to maintain the uniformity of the solution, a flow control unit controls the flow rate of the solution at a predetermined speed according to the stirring of a stirrer, and a chemical supply unit senses the real-time solution concentration to maintain a constant solution concentration and adds the necessary chemicals to ensure plating with a uniform thickness.

[0028] In the above, a manufacturing system for a micro prism mold for retroreflective film molding is provided, further comprising a jig that fixes the cathode by applying tension to maintain a flat surface, wherein the jig is characterized by having a plurality of fixing members at predetermined intervals.

[0029] In the above, it further includes an electrode plate position control unit that controls the positions of the positive electrode, the negative electrode, and the positive shielding plate, and

[0030] The plating process is designed with a step coverage consisting of multiple steps for the final target thickness, and the power supply unit, solution control unit, and electrode plate position control unit organically control the applied current, stirrer speed, chemical supply amount, the positions of the anode and cathode, and the position of the anode shielding plate for each step coverage stage to uniformly form the thickness of the plating film over a large area, thereby providing a manufacturing system for a micro prism mold for forming a retroreflective film.

[0031] In the above, a manufacturing system for a micro-prism mold for retroreflective film molding is provided, characterized by precisely controlling the plating film thickness from the initial stage at each process step.

[0032] In the above, a manufacturing system for a micro prism mold for retroreflective film molding is provided, characterized by controlling the flow rate of the solution supplied into the plating bath to 1 to 100 Liter / min (LPM).

[0033] In the above, the distance range between the anode and the cathode is 10-300 mm, and the size ratio between the anode and the cathode is A manufacturing system for a micro prism mold for retroreflective film molding is provided, characterized in that this is 0.5 to 3.0.

[0034] In the above, the shielding plate is arranged at a position spaced 1 to 50 mm from the anode toward the cathode, and the shielding area covered by the shielding plate is 1 to 30% of the anode area. second A manufacturing system for a micro prism mold for retroreflective film molding is provided. Effects of the invention

[0035] According to the present invention, the material of the microprism mold is made of an alloy to improve hardness characteristics and extend the mold life.

[0036] In addition, according to the present invention, the overall thickness uniformity of a large-area microprism mold is increased by homogenizing the electroplating solution.

[0037] In addition, according to the present invention, the current applied to the electrode in the electroplating process is pulsed current to precisely control the overall shape of a large-area microprism mold.

[0038] In addition, according to the present invention, an anode shielding plate and an auxiliary cathode are arranged in an electric pole manufacturing system to control electron flow and electron distribution, thereby maintaining a large-area equipotential plane between the anode and cathode as a uniform plane. Brief explanation of the drawing

[0039] Figure 1 shows the problem of thickness non-uniformity and cracks occurring at the connection points of a micro-prism mold according to the prior art. Figure 2 shows a cross-sectional view of a microprism mold and an image of a retroreflective film according to the present invention. Figure 3 is a table showing the physical properties of Ni and Ni alloys. Figure 4 shows a defective image of a retroreflective film manufactured by a conventional microprism mold and an image of a product according to the present invention that improves upon it. Figure 5 shows the manufacturing equipment and product of the microprism mold of the present invention. Figure 6 shows graphs illustrating the reflective performance of a retroreflective film manufactured by the microprism mold of the present invention compared to the prior art. Figure 7 is a table showing the thickness variation of the entire large area compared with the prior art (left) when the thickness of the micro prism mold of the present invention is manufactured to be 343 µm. Figure 8 shows the three-dimensional shape of the microprism mold of the present invention as a contour graph compared with the prior art (left). Figure 9 shows that the composition ratio of the electroplating solution has been improved to be kept constant for thickness uniformity of a large-area microprism mold. Figure 10 is a table showing the physical properties of the alloy mold of the present invention compared to a conventional Ni mold. Specific details for implementing the invention

[0040] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings.

[0041] As shown in Fig. 1, the microprism mold manufactured according to the prior art has a non-uniform thickness, so when mounted on a roll and rolled to form a retroreflective film, defective products are produced. This is because the diameter of the cylindrical microprism mold is about 1000φ, and it is difficult to make it have a uniform thickness over the entire area, which is a large area of ​​about 3140 mm in width and 1500 mm in length when the mold is unfolded.

[0042] Since electroforming technology is mostly applied to small items, manufacturing large-area items is inherently difficult. Furthermore, micro-prism molds require thick films reaching 300 µm (with a margin of error of ±5%), making it very challenging to uniformly manufacture large-area thick films. If a mold with poor thickness uniformity is welded to form a cylindrical shape, cracks are generated at the welded area due to stress. Retroreflective films manufactured using such molds become defective products that fail to reflect light along the desired path. Therefore, there is a need to provide electroforming technology capable of manufacturing large-area thick films with uniform thickness.

[0043] FIG. 2 shows a cross-sectional view of a microprism mold and a product image according to the present invention. By manufacturing the thickness of the microprism mold uniformly, the retroreflective film produced thereby has a fine microprism shape and causes retroreflection.

[0044] Furthermore, conventional microprism molds are made of Ni material. When the process of extruding a retroreflective film using a Ni microprism mold continues, the shape of the microprism deforms as shown in Fig. 3. Due to continuous pressure, the ends of the microprisms become blunt and deformed, resulting in defective products that have lost their retroreflective ability. Consequently, the Ni microprism mold must be replaced. Replacing the mold requires a complete shutdown of the production line, which negatively impacts productivity. Therefore, a high-hardness mold is required that can maintain the shape of the microprism even after long-term use. Accordingly, the present invention provides a microprism mold using electroforming technology, made of a Ni alloy with a hardness higher than that of Ni.

[0045] Figure 3 is a table showing the physical properties of Ni and Ni alloys.

[0046] 300 The manufacture of microprism molds with a thickness of up to 600 µm entails the following requirements.

[0047] First, there is the uniformity of reflective performance; that is, when manufacturing retroreflective films, they must meet specifications suitable for mass production.

[0048] Second, the alloy must possess superior performance; that is, it must have better mechanical properties compared to existing Ni molds. Properties such as tensile strength, hardness, and elongation must be superior.

[0049] Third, it must ensure consistency in plating quality, that is, uniformity in the mold appearance and alloy layer composition.

[0050] More specifically, based on a mold thickness of 300 μm produced by electroplating, the thickness deviation must be within ±5%, the hardness of the mold must be 350 Hv or higher, the elongation must be 7.0% or higher, and the reflectance of the anti-reflective film produced by the mold must be 700 or higher based on a representative front angle (0.2º / -4).

[0051] As nickel alloys capable of satisfying these requirements, the properties of Ni-W, Ni-Cr, Ni-Fe, and Ni-Co were investigated as shown in Fig. 10, and all alloys were superior to Ni in terms of tensile strength and hardness. In the case of Ni-P, the hardness is excellent with 733–1148 Hv, and Ni-Cu exhibits superior hardness compared to Ni with 200–500 Hv.

[0052] While more alloy materials could be listed, the range of choices can be narrowed to the following limitations.

[0053] In other words, alloys that lack advantages in mechanical properties, alloys that are difficult to peel off after electroplating, and alloys with large compositional variations within the plating layer are excluded.

[0054] Ni-Co is the most desirable alloy, as it has superior tensile strength, hardness, and elongation characteristics compared to Ni materials and allows for compositional analysis and the maintenance of the alloy composition even in thick films. The proportion of Ni in the alloy is set to 70 to 95 wt%.

[0055] Figure 4 shows a defective image of a retroreflective film manufactured by a conventional microprism mold and an image of a product according to the present invention that improves upon it.

[0056] In order to produce large-area microprism molds with a uniform thickness of about 300 µm or more, the solution, process, and electrical equipment must be designed organically. That is, the chemical composition and characteristics of the solution must be stably managed, and the current density, current waveform, and step coverage must be designed. In terms of equipment, geometric design of the equipment including the gap distance, flow rate control, and shielding installation is required.

[0057] Figure 5 shows the manufacturing equipment and product of the microprism mold of the present invention.

[0058] The left side is a basic schematic diagram explaining the plating technology, and the central photo shows a large-area electrode plate (10) and a jig (20) that fixes the electrode plate. In the plating tank, a nickel alloy electrode plate is arranged as an anode, and a cathode made of a material such as SUS is arranged at a predetermined distance from it.

[0059] The jig (20) is provided with a plurality of fixing members at predetermined intervals to apply tension and fix the electrode plate, particularly the negative electrode (10) where plating lamination occurs, so that it maintains a flat surface.

[0060] To plate a thick film of uniform thickness over a large area, a solution control unit is installed to maintain the uniformity and homogeneity of the solution during the plating process. The solution control unit includes a stirrer and a chemical supply unit. The stirrer agitates the solution to ensure uniform deposition throughout the process. It manages the composition of the solution—specifically, its concentration—by sensing it in real time to ensure it remains constant throughout the process. In other words, it monitors the concentration of additives, stress relievers, etc., to maintain a constant level, and the chemical supply unit adds chemicals to adjust variables such as concentration and pH as needed. Since the agitation of the solution affects the control of the desired alloy composition, the solution control unit includes a flow rate control unit to control the flow rate of the solution supplied to the plating tank for agitation to 1 to 100 Liter / min (LPM).

[0061] In addition, the power control unit that supplies the current applied to the electrode in the electroplating process must be able to adjust the intensity of the current applied to the electrode plate. The intensity of the electroplating current must be in the range of 5-100 mA / ㎠.

[0062] In order to uniformly plate a large area during the electroplating process, the electric field formed between the electrode plates and the resulting equipotential plane must be controlled. This is because the equipotential plane between the plates must be controlled to form a horizontal plane across the entire front surface of the plates to ensure that a uniform thickness is achieved over the entire large area. Otherwise, as demonstrated in the prior art, a so-called "dog bone" shaped plating occurs, where both ends are thicker. To control the equipotential plane, it is necessary to adjust the distance between the anode and cathode and the size ratio between them. The distance range between the anode and cathode is 10–300 mm, and the size ratio between the anode and cathode is This must be 0.5 to 3.0.

[0063] The installation of shielding plates is also useful for equipotential surface control.

[0064] Accordingly, the present invention arranges anode shielding plates near the upper and lower portions of the anode. The position of the shielding plates is spaced 1 to 50 mm from the anode toward the cathode, and the shielding area covering the anode plates is 1 to 30% of the anode area. The shielding plates arranged at the upper and lower portions of the anode block areas where current is concentrated, allowing the current to be distributed uniformly. This can improve the uniformity of the plating thickness. The spacing and area of ​​the anode shielding plates that control the aforementioned equipotential lines are organically related to the size, spacing, and applied current of the electrode plates. Therefore, the position can be adjusted through practical experiments within the above range. To this end, an electrode plate position control unit is installed to control the position of the anode shielding plates by organically linking them to the size of the anode and cathode, the spacing between the electrode plates, and the applied current.

[0066] Figure 5 shows a photograph of a microprism mold of Ni alloy produced in this way.

[0067] Figure 6 shows graphs illustrating the reflective performance of a retroreflective film manufactured by the microprism mold of the present invention compared to the prior art.

[0068] It was confirmed that the frontal angle reflectivity of retroreflective films manufactured by microprism molds made of conventional Ni material can be increased up to 160% and all exceed ASTM IX standards.

[0069] The mold specimens used in the performance test were 10cm×10cm with a thickness of 600um, 35cm×35cm with a thickness of 350um, and 35cm×35cm with a thickness of 600um, and the results were compared based on the average of three measurements.

[0070] Figure 7 is a table showing the thickness variation of the entire large area compared with the prior art (left) when the thickness of the micro prism mold of the present invention is manufactured to be 343 µm.

[0071] The plating thickness deviation (%) of the prior art is an average of 34.6%, and the plating thickness deviation of the present invention is an average of 0.36%, showing a nearly uniform thickness.

[0072] Figure 8 shows the three-dimensional shape of the microprism mold of the present invention as a contour graph compared with the prior art (left).

[0073] It can be easily confirmed that while the conventional technology has a shape with a thick, raised outer edge, the present invention exhibits an almost perfectly flat surface.

[0074] Figure 9 shows that the composition ratio of the electroplating solution has been improved to be kept constant for thickness uniformity of a large-area microprism mold.

[0075] The amount of chemical used for alloy mold production is determined and replenished to maintain a uniform solution composition ratio. A 20-step coverage is applied to the electroplating solution to analyze the solution composition at each step and replenish it in response to changes, thereby maintaining the composition ratio of Ni and alloy metals almost constant.

[0076] Based on this, through the repeated fabrication of alloy molds and analysis of the actual alloy, it can be confirmed that the composition in the actual alloy mold is maintained uniformly according to the metal ratio in the solution (chemical). As a result, the alloy composition is maintained uniformly even at plating thicknesses of approximately 300 µm to 600 µm.

[0077] FIG. 10 is a table showing the physical properties of a Ni alloy mold containing Co among the alloys of the present invention compared to a conventional Ni mold as an example. As described above, the content of Co is 5 to 30 wt%, and in particular, this example shows the physical properties for a sample containing 18-20 wt% of Co.

[0078] Compared to the tensile strength and hardness of conventional Ni material microprism molds being 700 MPa and 150 Hv, respectively, the tensile strength and hardness of the Ni alloy material microprism mold of the present invention are significantly improved to 1741 MPa and 449 Hv, respectively.

[0079] The cutting, welding, and reflection characteristics all possess sufficient properties to be used as a mold required for retroreflective films.

[0081] Unless otherwise defined in the foregoing, all technical and scientific terms used herein have the same meaning as commonly understood by a skilled expert in the art to which the present invention pertains. Furthermore, terms defined in commonly used dictionaries are not to be interpreted ideally or excessively unless explicitly and specifically defined otherwise. Throughout the specification, when a part is described as "comprising" or "having" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components. Additionally, the singular form may include the plural form depending on the context.

[0082] In addition, in this specification, the terms "on" or "on" include cases where, in addition to cases where the object is directly placed on the object, there is another part in between.

[0083] In addition, in this specification, "on top of, on top of, or above," "below," or "below" means being located above or below the target part, and does not necessarily mean being located on the upper or lower side with respect to the direction of gravity.

[0084] In addition, in this specification, the terms "between" or "between" include cases where there is another part in between, in addition to cases where there is a gap between the objects.

[0085] The rights of the present invention are not limited to the embodiments described above but are defined by the claims, and it is obvious that a person skilled in the art may make various modifications and adaptations within the scope of the rights described in the claims. Explanation of the symbols

[0086] No drawing symbol.

Claims

Claim 1 A method for manufacturing a micro prism mold for forming a retroreflective film made of any one alloy of Ni-Co, Ni-W, Ni-Mo, Ni-P, and Ni-Cu, wherein the manufacturing method is an electroplating technique, and during the plating process, the equipotential plane of the electric field formed between the anode and the cathode installed in the plating bath is made constant as a horizontal plane, and to maintain the uniformity of the solution, the solution is stirred with a stirrer and the flow rate of the solution is controlled at a predetermined speed, and the solution concentration is sensed in real time to maintain the solution concentration constant and the necessary chemicals are added to ensure plating with a uniform thickness, and to make the equipotential plane of the electric field formed between the anode and the cathode a constant horizontal plane, an anode shielding plate is placed near the anode and spaced apart from the anode. Claim 2 delete Claim 3 A method for manufacturing a micro prism mold for forming a retroreflective film according to claim 1, wherein the plating process is designed with a step coverage consisting of multiple steps for the final target thickness, and the applied current, stirrer speed, chemical supply amount, the positions of the anode and cathode, and the position of the anode shielding plate are organically controlled for each step coverage stage to uniformly form the thickness of the plating film over a large area. Claim 4 A method for manufacturing a micro prism mold for retroreflective film molding, characterized in that, in claim 1, the flow rate of the solution supplied into the plating bath is controlled to 1 to 100 Liter / min (LPM).

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