Master mold used in the manufacture of molds for retroreflective sheets and method for manufacturing the same

Abstract

A master mold for manufacturing a retroreflective sheet mold and a method for manufacturing the same are disclosed. The master mold used to manufacture the disclosed retroreflective sheet mold includes a lower layer, an upper layer provided on the lower layer, and a plurality of unit master molds provided on the upper layer, the plurality of unit master molds being arranged continuously without separation from each other in the lateral and vertical directions, and each unit master mold includes first and second surfaces that are in contact with each other so as to form a first corner, and third and fourth surfaces separated from each other via the first and second surfaces, the third and fourth surfaces being inclined with respect to each other, and the first and second surfaces being in contact with the third and fourth surfaces.

Description

Technical Field

[0001] The present invention relates to the production of a mold for producing a light reflection sheet or a light reflection tape, and more particularly to a master mold used for producing a mold for a retroreflective sheet having a high reflectance for obliquely incident light and a method for producing the same.

Background Art

[0002] A light reflection sheet is a sheet that reflects incident light. A light reflection sheet is also referred to as a light reflection tape. The light reflection sheet can exhibit various colors depending on the material of the retroreflective region. Therefore, by using a light reflection sheet, the discrimination power and visibility of the object to which the light reflection sheet is attached are increased. Due to such characteristics of the light reflection sheet, the light reflection sheet is applied to various fields. For example, it may be used in transportation fields such as vehicles, transportation fields, safety fields, security fields, or may be applied to product designs.

[0003] A retroreflective sheet, which is a type of light reflection sheet, has a high light reflectance for perpendicularly incident light that is incident perpendicularly to the surface of the retroreflective sheet. On the other hand, for light that is incident obliquely to the surface of the retroreflective sheet, that is, obliquely incident light, the reflectance may be relatively low and may not be practical.

[0004] As a result, there is an increasing interest in a retroreflective sheet having a high reflectance for obliquely incident light. In order to manufacture a retroreflective sheet having a high reflectance for obliquely incident light, a mold for embossing such a retroreflective sheet is required.

Summary of the Invention

Problems to be Solved by the Invention

[0005] One embodiment of the present invention provides a master mold capable of improving the production efficiency of a mold for producing a retroreflective sheet (hereinafter referred to as a mold for a retroreflective sheet) having a relatively high reflectance for obliquely incident light.

[0006] One embodiment of the present invention provides a master mold that can improve the cost efficiency of molds for retroreflective sheets.

[0007] One embodiment of the present invention provides a master mold that can reduce the manufacturing cost of molds for retroreflective sheets.

[0008] One embodiment of the present invention provides a method for manufacturing such a master mold. [Means for solving the problem]

[0009] A master mold used to manufacture a mold for a retroreflective sheet according to an exemplary embodiment includes a lower layer, an upper layer provided on the lower layer, and a plurality of unit master molds provided on the upper layer, wherein the plurality of unit master molds are arranged continuously without separation from each other in the lateral and vertical directions, and each unit master mold includes first and second surfaces that are in contact with each other so as to form a first corner, and third and fourth surfaces that are separated from each other via the first and second surfaces, wherein the third and fourth surfaces are inclined with respect to each other, and the first and second surfaces are in contact with the third and fourth surfaces.

[0010] For example, one of the third and fourth faces is a vertical face, while the other two form an acute angle with respect to the vertical face.

[0011] For example, an edge created by the contact of the first and second faces may connect the upper vertex of the third face to the upper vertex of the fourth face. One of the third and fourth faces is a vertical face, and the length of the edge is equal to the height of the vertical face.

[0012] As an example, the distance between the vertex of the upper end of the vertical surface of the first unit master mold and the vertex of the upper end of the non-vertical faces among the third and fourth faces of the second unit master mold adjacent to the first unit mast mold is the same as the edge length.

[0013] A method for manufacturing a master mold according to an exemplary embodiment includes the steps of forming a first symmetrical pattern on one surface of a substrate in a first direction, and asymmetrically removing a portion of the first pattern in a second direction perpendicular to the first direction, wherein the first pattern is a pattern that forms a second pattern with a triangular cross-section on one surface of the substrate, and a portion of the second pattern is also removed in the process of removing a portion of the first pattern, and the removal of a portion of the second pattern forms a vertical surface and an inclined surface inclined thereto.

[0014] As an example, a process can be carried out at least twice in which a symmetrical first pattern is formed on one surface of the substrate in a first direction, and then a process can be carried out in which a portion of the first pattern is asymmetrically removed.

[0015] For example, the process of removing a portion of the first pattern can be performed at least twice.

[0016] For example, in the process of forming the first pattern, the first engraving machine is used, and the first pattern is a V-shaped groove.

[0017] For example, in the process of asymmetrically removing a portion of the first pattern, a second engraving machine is used, and the chip in contact with the substrate of the second engraving machine may include a vertical surface and an inclined surface that forms an acute angle with respect to it. [Effects of the Invention]

[0018] The master mold used in the manufacture of the retroreflective sheet mold according to the present disclosure is completed by directly forming the mold pattern on the plane of a substrate. The mold pattern can be formed simply by sequentially moving two separate engraving machines in directions orthogonal to each other.

[0019] As described above, the mold pattern is formed on the plane of the substrate simply by moving two engraving machines in mutually orthogonal directions, making the pattern formation process easy and the resulting pattern simple. Therefore, the process of transferring the mold pattern formed on the master mold to another mold substrate is easy, and the transfer of the mold pattern is achieved completely. Furthermore, because the mold pattern is simple and formed on a plane, the transferred mold pattern does not get damaged even after repeated transfers. Therefore, it is cost-effective. [Brief explanation of the drawing]

[0020] [Figure 1] This is a step-by-step perspective view showing a method for manufacturing a master mold used in the production of a mold for a retroreflective sheet with high reflectivity to obliquely incident light, according to an exemplary embodiment of the present invention. [Figure 2] This is a perspective view showing an example of a first engraving machine used in a method for manufacturing a master mold, according to one exemplary embodiment of the present invention. [Figure 3] This is a step-by-step perspective view showing a method for manufacturing a master mold used in the production of a mold for a retroreflective sheet with high reflectivity to obliquely incident light, according to an exemplary embodiment of the present invention. [Figure 4] This is a step-by-step perspective view showing a method for manufacturing a master mold used in the production of a mold for a retroreflective sheet with high reflectivity to obliquely incident light, according to an exemplary embodiment of the present invention. [Figure 5] This is a step-by-step perspective view showing a method for manufacturing a master mold used in the production of a mold for a retroreflective sheet with high reflectivity to obliquely incident light, according to an exemplary embodiment of the present invention. [Figure 6] This is a step-by-step perspective view showing a method for manufacturing a master mold used in the production of a mold for a retroreflective sheet with high reflectivity to obliquely incident light, according to an exemplary embodiment of the present invention. [Figure 7]It is a perspective view showing step by step a method for manufacturing a master mold used for manufacturing a mold for a retroreflective sheet having a high reflectance for obliquely incident light according to an exemplary embodiment of the present invention. [Figure 8] It is a perspective view showing an example of a second engraving machine used for a method for manufacturing a master mold according to an exemplary embodiment of the present invention. [Figure 9] It is a perspective view of a unit master mold included in the master mold of FIG. 7. [Figure 10] It is a plan view of the master mold of FIG. 7. [Figure 11] It is a cross-sectional view taken along line 11-11' of FIG. 10. [Figure 12] It is a cross-sectional view taken along line 12-12' of FIG. 10.

BEST MODE FOR CARRYING OUT THE INVENTION

[0021] A master mold used for manufacturing a mold for a retroreflective sheet according to an embodiment includes a lower layer portion, an upper layer portion provided on the lower layer portion, and a plurality of unit master molds provided on the upper layer portion. The plurality of unit master molds are continuously arranged without being separated from each other in the horizontal and vertical directions. Each unit master mold has a first surface and a second surface that form a first angle and are in contact with each other, and a third surface and a fourth surface that are separated from each other via the first surface and the second surface. The third surface and the fourth surface are inclined with respect to each other, and the first surface and the second surface are in contact with the third surface and the fourth surface.

[0022] Hereinafter, a master mold used for manufacturing a mold for a retroreflective sheet having a high reflectance for obliquely incident light according to an exemplary embodiment and a method for manufacturing the same will be described in detail with reference to the accompanying drawings. The size of each component shown in each drawing and the thickness of a layer or region are shown exemplarily for clarity and convenience of explanation, and may be exaggerated. Further, the embodiments described below are merely exemplary, and various modifications are possible from such embodiments. Also, in the layer structure described below, the expressions "upper side" or "upper" include not only those directly above in contact but also those above other members without contact.

[0023] Figures 1 to 8 are perspective views illustrating, step by step, a method for manufacturing a master mold used in the production of a mold for a retroreflective sheet with high reflectivity to obliquely incident light, according to an exemplary embodiment of the present invention, and perspective views showing the elements used in this manufacturing method.

[0024] To manufacture a master mold, first, a mold substrate 40 is prepared as shown in Figure 1. In one embodiment, the mold substrate 40 includes a lower layer 40A and an upper layer 40B that are sequentially stacked. The lower layer 40A is also referred to as the lower substrate. The upper layer 40B is also referred to as the upper substrate. In one embodiment, the lower layer 40A includes a first metal layer, and the upper layer 40B includes a material layer containing metal. In one embodiment, the first metal layer is a stainless steel layer or includes a stainless steel layer. In one embodiment, the upper layer 40B includes a second metal layer or an alloy layer. In one embodiment, the constituent material of the second metal layer may be the same as or different from the constituent material of the first metal layer. In one embodiment, the second metal layer may include a copper (Cu) layer, but is not limited to this. In one embodiment, the alloy layer may include nickel-phosphorus (NiP), but is not limited to this.

[0025] In order to process the mold substrate 40 into a master mold, first, the first engraving machine 100 is moved in a first direction (for example, in the X-axis direction) on the surface of the upper layer 40B. In one embodiment, the surface of the upper layer 40B is a plane parallel to the plane defined by the X-axis and Y-axis (XY plane).

[0026] The tip 100b of the first engraving machine 100 is moved from one end to the other of the surface of the upper layer 40B while in contact with the surface of the upper layer 40B. The contact state between the tip 100b of the first engraving machine 100 and the surface of the upper layer 40B during such movement is set considering the pattern formed on the surface of the upper layer 40B. For example, if the pattern formed on the surface of the upper layer 40B is a first pattern 3G1 having an inverted triangular or V-shaped cross-section, i.e., formed as a V-shaped groove, as shown in Figure 3, the degree or state of contact between the tip 100b of the first engraving machine 100 and the surface of the upper layer 40B is set considering the shape of the first pattern 3G1 formed on the surface of the upper layer 40B. The shape of the first pattern 3G1 is determined by the shape of the tip portion 100b of the first engraving machine 100, while the size of the first pattern 3G1 is determined based on the degree or state of contact between the tip portion 100b of the first engraving machine 100 and the surface of the upper portion 40B.

[0027] The first engraving machine 100 is moved in a first direction on the surface of the upper layer 40B to form a single pattern, and then the first engraving machine 100 is moved back to its original position. Then, the first engraving machine 100 is moved a predetermined distance in a second direction (for example, the Y-axis direction) perpendicular to the first direction, and then moved again in the first direction to form another single pattern on the surface of the upper layer 40B. By repeating the above process, as shown in Figure 4, multiple patterns parallel to the first direction, i.e., multiple V-shaped first patterns 3G1, are formed on the entire surface of the upper layer 40B.

[0028] Referring to Figure 3 or Figure 4, a single V-shaped first pattern 3G1 is formed linearly from one end to the other of the surface of the upper layer 40B in a first direction. The width 3W1 of the upper end of the first pattern 3G1 in a second direction is constant or substantially constant along the entire length of the first pattern 3G1.

[0029] "Substantially constant" means that the width error of the first pattern 3G1 is within the tolerance range or within a range of width variation that does not affect the operating characteristics of a product manufactured using a mold manufactured according to the manufacturing method of the present disclosure.

[0030] In one embodiment, the width 3W1 at the upper end of the first pattern 3G1, i.e., the maximum width of the first pattern 3G1, may be approximately 1 μm to 500 μm, although this is not limited to this range. For example, the width 3W1 at the upper end of the first pattern 3G1 may be approximately 100 μm, although this is not limited to this range.

[0031] The first pattern 3G1 is formed as a V-shaped groove and has a V-shaped (inverted triangle) cross-section. Therefore, the width 3W1 of the first pattern 3G1 narrows as the depth of the first pattern 3G1 increases. In other words, the width 3W1 of the first pattern 3G1 gradually widens from the bottom to the top of the first pattern 3G1.

[0032] In one embodiment, the depth 3D1 of the first pattern 3G1 may be approximately 50 μm to 150 μm, but is not limited to this. In one embodiment, the depth 3D1 of the first pattern 3G1 may be approximately 90 μm.

[0033] Multiple first patterns 3G1 are formed adjacent to each other, and two adjacent first patterns 3G1 are formed so that they touch each other. For example, two adjacent first patterns 3G1 are formed so that their boundaries touch each other.

[0034] The first pattern 3G1 is formed as a V-shaped groove and has a V-shaped (inverted triangle) cross-section. Consequently, a second pattern 150 with a triangular cross-section is formed between two adjacent first patterns 3G1. In other words, when multiple first patterns 3G1 with an inverted triangle cross-section are formed on the surface of the upper layer 40B, multiple second patterns 150 with a triangular cross-section are formed on the surface of the upper layer 40B. Therefore, multiple second patterns 150 exist between multiple first patterns 3G1, and multiple first patterns 3G1 exist between multiple second patterns 150.

[0035] Since the second pattern 150 is formed as a result of forming the V-shaped first pattern 3G1, the change in the width of the second pattern 150 is opposite to the change in the width 3W1 of the first pattern 3G1. That is, the width of the second pattern 150 is widest at the bottom and narrows towards the top. Also, the width of the bottom end (maximum width) of the second pattern 150 is the same as the width of the top end (maximum width) of the first pattern 3G1.

[0036] The second pattern 150 has a first inclined surface 3S1 and a second inclined surface 3S2. The first inclined surface 3S1 and the second inclined surface 3S2 are surfaces parallel to a first direction (for example, the X-axis direction), that is, perpendicular to the plane defined by the Y-axis and Z-axis (YZ-plane).

[0037] The first inclined surface 3S1 and the second inclined surface 3S2 are also the two inclined inner surfaces of the V-shaped groove of the first pattern 3G1. In other words, the first inclined surface 3S1 and the second inclined surface 3S2 are located at the boundary between the first pattern 3G1 and the second pattern 150, and are surfaces shared by the first pattern 3G1 and the second pattern 150.

[0038] The first inclined surface 3S1 and the second inclined surface 3S2 of the first pattern 3G1 are inclined at a first angle θ1 relative to each other. That is, the angle between the first inclined surface 3S1 and the second inclined surface 3S2 in the first pattern 3G1 is the first angle θ1. This means that the angle between the first inclined surface 3S1 and the second inclined surface 3S2 in the second pattern 150 is also the first angle θ1.

[0039] The areas of the first inclined surface 3S1 and the second inclined surface 3S2 are identical or substantially identical to each other.

[0040] The first engraving machine 100 is also called an engraving tool, engraving knife, bit, or cutting tool. The first engraving machine 100 includes a main body 100a and a tip 100b provided at the lower end of the main body 100a. The main body 100a is also called a handle. The tip 100b is also called a contact end, contact part, blade, etc. The main body 100a is the part that is directly coupled to a drive device (e.g., a machine tool) that moves the first engraving machine 100. The tip 100b is the part that is in direct contact with the surface of the upper layer 40B and is directly used to form the first pattern 3G1 on the surface of the substrate 40. Depending on the degree to which the tip 100b initially contacts the surface of the upper layer 40B (e.g., contact area), the size of the cross-section of the first pattern 3G1 formed on the substrate 40 differs.

[0041] Figure 2 shows a three-dimensional example of the first engraving machine 100.

[0042] Referring to Figure 2, the main body 100a of the first engraving machine 100 has a rectangular prism shape, and the tip 100b is attached (joined) to the bottom surface of the rectangular prism. The main body 100a has a first width Wx in the X-axis direction and a second width Wy in the Y-axis direction. In one embodiment, the first width Wx and the second width Wy have a predetermined ratio. In one embodiment, the first width Wx and the second width Wy may be the same as or different from each other. The tip 100b covers the entire bottom surface of the main body 100a. The width of the tip 100b in the X-axis direction is constant and the same as the width of the main body 100a. The width of the tip 100b in the Y-axis direction or in the direction parallel to the Y-axis is not constant and narrows towards the lower end of the tip 100b. The change in the width of the tip 100b in the Y-axis direction is constant towards the lower end of the tip 100b. Therefore, the tip portion 100b has two triangular faces spaced apart from each other by a distance corresponding to a first width Wx in the X-axis direction, a first quadrilateral inclined surface 2S1 interposed between the two triangular faces and connecting the first hypotenuses of the two triangles, and a second quadrilateral inclined surface 2S2 interposed between the two triangular faces and connecting the second hypotenuses of the two triangles.

[0043] In other words, the first inclined surface 2S1 and the second inclined surface 2S2 touch each other at the lower end of the tip portion 100b and share one side. The side shared by the first inclined surface 2S1 and the second inclined surface 2S2 is parallel to the X-axis and has a length corresponding to the first width Wx. Also, the side shared by the first inclined surface 2S1 and the second inclined surface 2S2 connects each vertex of the two triangles to each other. That is, the first inclined surface 2S1 and the second inclined surface 2S2 are located between the faces of the two triangles and have a shape that widens from the lower end to the upper end of the tip portion 100b. In one embodiment, the first inclined surface 2S1 and the second inclined surface 2S2 spread out at a first angle θ1. The first angle θ1 is also referred to as the angle between the first inclined surface 2S1 and the second inclined surface 2S2. The first angle θ1 is acute (i.e., an angle less than 90 degrees). In one embodiment, the first angle θ1 may be an angle of 45 degrees or more and less than 90 degrees.

[0044] As the first engraving machine 100 forms the first pattern 3G1 and the second pattern 150 on the surface of the upper layer 40B, the first angle θ1 determines the angle between the two inclined inner surfaces of the V-shaped first pattern 3G1, and thereby also determines the angle between the first inclined surface 3S1 and the second inclined surface 3S2 of the second pattern 150.

[0045] In a direction perpendicular to the surface of the upper layer 40B, i.e., perpendicular to the XY plane (for example, the Z-axis direction), the main body 100a has a first length h1 and the tip portion 100b has a second length h2. The first length h1 and the second length h2 may be the same or different from each other. In one embodiment, the second length h2 is set to be smaller than the first length h1. In one embodiment, the second length h2 is determined by considering the size (depth, maximum width, etc.) of the first pattern 3G1 formed on the surface of the upper layer 40B. Also, since the angle θ1 between the first inclined surface 2S1 and the second inclined surface 2S2 differs depending on the second length h2, the second length h2 is determined by considering the angle θ1 between the first inclined surface 2S1 and the second inclined surface 2S2. Furthermore, when the second length h2 is constant, the angle θ1 between the first inclined surface 2S1 and the second inclined surface 2S2 varies depending on the width in the Y-axis direction of the upper end of the tip portion 100b (the distance between the upper edge of the first inclined surface 2S1 and the upper edge of the second inclined surface 2S2). Therefore, when the second length h2 is constant, the width in the Y-axis direction of the upper end of the tip portion 100b is determined by considering the angle between the first inclined surface 2S1 and the second inclined surface 2S2.

[0046] The second length h2 is determined by considering the depth 3D1 of the first pattern 3G1. In one embodiment, the second length h2 may be about 50 μm to 150 μm. The second length h2 may be, for example, about 90 μm. In one embodiment, the width of the upper end of the tip portion 100b that directly contacts the bottom surface of the main body portion 100a is determined by considering the maximum width 3W1 of the first pattern 3G1. The width of the upper end of the tip portion 100b is not limited to this, but may be, for example, about 1 μm to 500 μm. In one embodiment, the width of the upper end of the tip portion 100b may be about 100 μm.

[0047] The tip portion 100b is made of a material with higher hardness than the constituent material of the upper layer portion 40B. In one embodiment, the tip portion 100b is made of a carbon-containing material. For example, the tip portion 100b may be made of diamond, but is not limited to this. In one embodiment, the main body portion 100a is made of a metallic material or a non-metallic material.

[0048] After the formation of the first pattern 3G1 and the second pattern 150, in order to form a third pattern on the surface of the upper layer 40B on which the first pattern 3G1 and the second pattern 150 are formed, a second engraving machine 200, which has a different structure from the first engraving machine 100, is moved in a direction perpendicular to the longitudinal direction of the first pattern 3G1 and the second pattern 150 (i.e., a direction perpendicular to the X-axis or a direction parallel to the Y-axis), as shown in Figure 5. The second engraving machine 200 is moved from one end of the surface of the upper layer 40B to the other, traversing the first pattern 3G1 and the second pattern 150, in a direction perpendicular to the longitudinal direction of the first pattern 3G1 and the second pattern 150. The second engraving machine 200 can start from one end of the surface of the upper layer 40B at a height at which the first pattern 3G1 and the second pattern 150 can be cut, and maintain that height until the other end of the upper layer 40B. The height of the second engraving machine 200 can be vertically displaced from a height that allows cutting of the first pattern 3G1 and the second pattern 150 to a depth corresponding to the depth 3D1 of the first pattern 3G1.

[0049] By moving the second engraving machine 200 as described above, as shown in Figure 6, a portion of the first pattern 3G1 and the second pattern 150 can be removed, thereby forming a single third pattern 7G1 on the surface of the upper layer 40B. After forming the single third pattern 7G1, the second engraving machine 200 is moved back to its original position. Then, the second engraving machine 200 is moved to a second position in the first direction (X-axis direction) according to a set movement value. In one embodiment, after forming the single third pattern 7G1, the second engraving machine 200 may be moved directly to the second position without moving it back to its original position.

[0050] To form another single third pattern 7G1, the second engraving machine 200, which has been moved to the second position, is moved in a direction perpendicular to the lengths of the first pattern 3G1 and the second pattern 150 under the same moving conditions as when the previous single third pattern 7G1 was formed. In one embodiment, the second position is a position where the previously formed third pattern 7G1 and the third pattern 7G1 formed by the second engraving machine 200, which has been moved from the second position, are spaced apart from each other in a direction parallel to the first pattern 3G1 and the second pattern 150 (for example, in the X-axis direction).

[0051] By repeating the above process, multiple third patterns 7G1 are formed across the entire surface of the upper layer 40B, as shown in Figure 7. As a result, a master mold 700 is formed, which is used to manufacture a mold for a retroreflective sheet with high reflectivity to obliquely incident light.

[0052] Multiple third patterns 7G1 are formed on the surface of the master mold 700, spaced apart from each other in the X-axis direction. The distance (spacing) in the X-axis direction between each of the multiple third patterns 7G1 is constant or substantially constant, but is not limited to this.

[0053] The third pattern 7G1 is formed on each of the multiple second patterns 150. The third pattern 7G1 is a portion of the second pattern 150 that has been removed, and can be considered as a groove formed in the second pattern 150. The third pattern 7G1 has a third surface 7S1 inclined with respect to the XY and YZ planes, and a fourth surface 7S2 parallel to the YZ plane, i.e., perpendicular to the X axis and the XZ planes. Therefore, the fourth surface 7S2 is a vertical surface perpendicular to the surface of the upper layer 40B. The third surface 7S1 and the fourth surface 7S2 share a base. The third surface 7S1 is a surface inclined with respect to the fourth surface 7S2 at a second angle θ2. In other words, the angle between the third surface 7S1 and the fourth surface 7S2 is the second angle θ2. The second angle θ2 is determined by the shape of the tip 200b of the second engraving machine 200, which is used to directly contact the first pattern 3G1 and the second pattern 150 and remove portions of them. In other words, the tip 200b of the second engraving machine 200 is designed with the shape of the third pattern 7G1 in mind. The second angle θ2 is acute. For example, the second angle θ2 may be an angle greater than or equal to 30 degrees and less than 90 degrees.

[0054] The third pattern 7G1 is formed on each of the multiple second patterns 150. Each pattern of the third pattern 7G1 is spaced apart from each other by a first distance DS1. The first distance DS1 corresponds to the distance between the upper vertex of the third face 7S1 of a certain third pattern 7G1 and the upper vertex of the fourth face 7S2 of the adjacent third pattern 7G1. In one embodiment, the first distance DS1 is the same as, or substantially the same as, the depth 3D1 of the first pattern 3G1. In one embodiment, the second distance DS2, which is the distance between the upper vertex of the third face 7S1 and the upper vertex of the fourth face 7S2 in a certain third pattern 7G1, is the same as, or substantially the same as, the first distance DS1.

[0055] In a single third pattern 7G1, the third surface 7S1 and the fourth surface 7S2 are formed by cutting the second pattern 150, which has a triangular cross-section, in a direction perpendicular to its length; therefore, the shapes of the third surface 7S1 and the fourth surface 7S2 are also triangular. However, the size (or area) of the third surface 7S1 is different from the size (or area) of the fourth surface 7S2.

[0056] The depth of the third pattern 7G1 is the same as, or substantially the same as, the depth of the first pattern 3G1 or the height of the second pattern 150. The depth of the third pattern 7G1 is the height of the fourth face 7S2 of the third pattern 7G1.

[0057] The second engraving machine 200 includes a main body 200a and a tip 200b. The main body 200a is the part that is connected to or directly coupled to the drive unit (e.g., a machine tool) of the second engraving machine 200. The tip 200b is the part that is in direct contact with the surface of the upper layer 40B and is made of a material with a higher hardness than the constituent material of the upper layer 40B. For example, the constituent material of the tip 200b may be the same as or different from the tip 100b of the first engraving machine 100. For example, the tip 100b of the first engraving machine 100 is made of a carbon crystal having a first hardness (e.g., diamond), and the tip 200b of the second engraving machine 200 is made of a carbon crystal having a second hardness different from the first hardness or other material. The first and second hardnesses are set higher than the hardness of the upper layer 40B.

[0058] Figure 8 shows an example of the second engraving machine 200.

[0059] Referring to Figure 8, the main body 200a of the second engraving machine 200 has a rectangular prism shape. However, it is not limited to this shape. The tip 200b of the second engraving machine 200 is attached (connected) to the bottom surface of the main body 200a. The main body 200a has a third width 8Wx in the X-axis direction and a fourth width 8Wy in the Y-axis direction. In one embodiment, the third width 8Wx and the fourth width 8Wy have a predetermined ratio. In one embodiment, the third width 8Wx and the fourth width 8Wy may be the same as or different from each other. The third width 8Wx and the fourth width 8Wy of the main body 200a are constant from the upper end to the lower end of the main body 200a.

[0060] The upper end surface of the tip portion 200b covers the entire bottom surface of the main body portion 200a. However, it is not limited to this. For example, the area of ​​the upper end surface of the tip portion 200b may be the same as or different from the area of ​​the bottom surface of the main body portion 200a. In one embodiment, the area of ​​the upper end surface of the tip portion 200b may be smaller or larger than the bottom surface of the main body portion 200a.

[0061] The width of the tip portion 200b in the X-axis direction and the width in the Y-axis direction vary along the longitudinal direction of the tip portion 200b. For example, the width of the tip portion 200b in the X-axis direction narrows from the upper end to the lower end of the tip portion 200b, and the width of the tip portion 200b in the Y-axis direction also narrows from the upper end to the lower end of the tip portion 200b. Therefore, the tip portion 200b has an overall downward-pointing pointed shape. However, the lower end 20T of the tip portion 200b is not a pointed point, but has a blade-like straight edge 20E. The edge 20E is the part where the first surface 5S1 and the second surface 5S2 of the tip portion 200b touch each other. The first surface 5S1 and the second surface 5S2 are inclined surfaces relative to each other, and their width gradually narrows towards the lower end 20T of the tip portion 200b. The widths of the first surface 5S1 and the second surface 5S2 are narrowest at the lower end 20T of the tip portion 200b. The edge 20E can be considered as the portion formed where the narrowest parts of the first surface 5S1 and the second surface 5S2 meet. Therefore, the edge 20E is a sharp part, like the blade of a knife. The second surface 5S2 of the tip 200b is a surface parallel to the YZ plane, that is, perpendicular to the X axis and the XZ plane. The first surface 5S1 and the second surface 5S2 of the tip 200b have a shape that widens from the edge 20E toward the upper end of the tip 200b. Therefore, the first surface 5S1 and the second surface 5S2 are surfaces that are inclined toward each other. The first surface 5S1 and the second surface 5S2 form a third angle θ31. That is, the angle between the first surface 5S1 and the second surface 5S2 is a third angle θ3. In other words, the first surface 5S1 is inclined toward the second surface 5S2 at a third angle θ3, and is also inclined toward the YZ plane at a third angle θ3. In one embodiment, the third angle θ3 is acute, but is not limited to this; for example, it may be an angle of 30 degrees or more and less than 90 degrees. The third angle θ3 determines the angle θ2 between the third surface 7S1 and the fourth surface 7S2 of the third pattern 7G1. Therefore, the third angle θ3, which is the angle between the first surface 5S1 and the second surface 5S2 of the tip portion 200b, is the same as the second angle θ2, which is the angle between the third surface 7S1 and the fourth surface 7S2 of the third pattern 7G1.

[0062] The tip portion 200b is interposed between the first surface 5S1 and the second surface 5S2, and has a third surface 8S1 and a fourth surface 8S12 that are spaced apart from each other and inclined relative to each other. The third surface 8S1 is a surface located forward in the direction of travel (Y-axis direction) of the second engraving machine 200. The third surface 8S1 has a triangular shape. One side of the third surface 8S1 forms one side of the upper end surface of the tip portion 200b, and the vertex of the third surface 8S1 spaced apart from this side is connected to the edge portion 20E. The third surface 8S1 is a surface that is perpendicular to the first surface 5S1 and the second surface 5S2, and is inclined with respect to the XZ plane.

[0063] The fourth surface 8S2 is located at the rear in the direction of travel of the second engraving machine 200 and is provided symmetrically to the third surface 8S1. The fourth surface 8S2 has a triangular shape. One side of the fourth surface 8S2 forms one side of the upper end surface of the tip portion 200b, and the vertex of the fourth surface 8S2 spaced apart from this side is connected to the edge portion 20E. The fourth surface 8S2 is perpendicular to the first surface 5S1 and the second surface 5S2 and is inclined with respect to the XZ plane. The inclination angles of the third surface 8S1 and the fourth surface 8S12 with respect to the XZ plane are different from each other.

[0064] In a direction perpendicular to the surface of the upper layer 40B, i.e., perpendicular to the XY plane (for example, in the Z-axis direction), the main body 200a has a first length 8h1 and the tip portion 200b has a second length 8h2. The first length 8h1 and the second length 8h2 may be the same as or different from each other. In one embodiment, the second length 8h2 is set to be smaller than the first length 8h1. In one embodiment, the second length 8h2 is the same as, or substantially the same as, the second length h2 of the tip portion 100b of the first engraving machine 100.

[0065] The master mold 700 shown in Figure 7 includes a plurality of unit master molds 70U formed on the surface (e.g., the XY plane) of the upper layer 40B. The plurality of unit master molds 70U are arranged to have a constant period or pitch in the lateral direction (e.g., the Y axis) and the vertical direction (e.g., the X axis).

[0066] Figure 9 shows the unit master mold 70U in three dimensions. The fourth surface 7S2 on the left side of Figure 9 is shown for illustrative purposes only and does not necessarily have to be included in the unit master mold 70U.

[0067] Referring to Figure 9, the unit master mold 70U has four faces 7S1, 7S2, 3S1, and 3S2. Two of the four faces, 3S1 and 3S2, are faces formed in the process of forming the first pattern 3G1 using the first engraving machine 100, and are two inclined faces in the second pattern 150 having a triangular cross-section. The other two faces, 7S1 and 7S2, are faces formed in the process of forming the third pattern 7G1 using the second engraving machine 200, and are a fourth face 7S2 which is a vertical face and a third face 7S1 which is inclined at an acute angle to the fourth face 7S2. The fourth face 7S2 is a face perpendicular to the surface of the upper layer 40B (e.g., the XY plane). The fourth face 7S2 is perpendicular to the X axis and parallel to the YZ plane. The direction perpendicular to the fourth face 7S2, that is, the direction perpendicular to the fourth face 7S2, is parallel to the X axis. Since the fourth surface 7S2 is formed as a result of the second pattern 150 being cut by the second engraving machine 200 in a direction perpendicular to the length of the second pattern 150, the shape of the fourth surface 7S2 is triangular.

[0068] The third surface 7S1 of the unit master mold 70U is separated from the fourth surface 7S2 by a first distance DS1, but is in contact with the fourth surface 7S2 of another adjacent unit master mold via their bottom surfaces. In other words, two adjacent unit master molds 70U have a structure in which the fourth surface 7S2 and the third surface 7S1 share a bottom surface. The second distance DS2, which is the distance between the upper vertex of the third surface 7S1 of a single unit master mold 70U and the upper vertex of the fourth surface (left side 7S2) of the adjacent unit master mold, may be the same as or different from the first distance DS1. In one embodiment, the height 9H1 of the fourth surface 7S2 of the unit master mold 70U may be the same as or different from the first distance DS1 or the second distance DS2. The relationship between such values ​​(i.e., the first distance DS1, the second distance DS2, and the height 9H1) is set to increase the obliquely incident light reflectance of the retroreflective sheet.

[0069] As described above, the third surface 7S1 and the fourth surface 7S2 are formed simultaneously by the second engraving machine 200, so the shape of the third surface 7S1 is triangular, just like the fourth surface 7S2. However, since the third surface 7S1 is inclined relative to the fourth surface 7S2, although both the third surface 7S1 and the fourth surface 7S2 are triangular, their triangular shapes and areas are different. For example, the area of ​​the third surface 7S1 is set to be larger than the area of ​​the fourth surface 7S2. In the unit master mold 70U, the first surface 3S1 and the second surface 3S2 are interposed between the third surface 7S1 and the fourth surface 7S2. The first surface 3S1 and the second surface 3S2 are surfaces perpendicular to the fourth surface 7S2. The upper edges of the first surface 3S1 and the second surface 3S2 touch each other to form a single edge. This upper edge extends between the upper vertex of the third surface 7S1 and the upper vertex of the fourth surface 7S2, and is in contact with both upper vertices. The lower edge of the first surface 3S1 and the lower edge of the second surface 3S2 are spaced apart from each other. The lower edges of the first surface 3S1 and the second surface 3S2 are in contact with the lower edges of the third surface 7S1 and the fourth surface 7S2. The first surface 3S1 and the second surface 3S2 have a shape that widens downwards. In one embodiment, the first surface 3S1 and the second surface 3S2 are inclined relative to each other at a first angle θ1. Since the unit master mold 70U is the part corresponding to the unit mold of the retroreflective sheet mold, the first angle θ1 is set so that the reflectivity of the retroreflective sheet to obliquely incident light is high.

[0070] Figure 10 is a plan view of the master mold 700 shown in Figure 7.

[0071] Referring to Figure 10, multiple unit master molds 70U are arranged horizontally and vertically on the master mold 700. Unit master molds 70U adjacent to each other horizontally and vertically are connected to each other so as not to overlap.

[0072] Figure 11 is a cross-sectional view along the line 11-11' in Figure 10.

[0073] Referring to Figure 11, the unit master molds 70U are arranged repeatedly in the X-axis direction. The unit master molds 70U are arranged continuously without gaps. Adjacent unit master molds 70U are arranged so as not to overlap each other.

[0074] Figure 12 is a cross-sectional view along the line 12-12' in Figure 10.

[0075] Referring to Figure 12, the second pattern 150 is repeatedly arranged in the Y-axis direction. The second pattern 150 is arranged continuously without gaps.

[0076] In Figures 1 to 12, it is shown that six second patterns 150 are formed on the surface of the upper layer 40B, and that 20 or fewer unit master molds 70U are formed. However, this is merely for illustrative and explanatory purposes and does not limit the number of second patterns 150 and the number of unit master molds 70U. More than six second patterns 150 and more than 20 unit master molds 70U may be formed on the surface of the upper layer 40B.

[0077] Although many details are specifically described in the above explanation, these should be interpreted as examples of desirable embodiments rather than limiting the scope of the invention. Therefore, the scope of the invention is not determined by the described embodiments, but by the technical idea described in the claims. Industrial Applicability

[0078] A master mold for obtaining a mold for manufacturing a retroreflective sheet according to one embodiment of the present invention is formed by directly forming a mold pattern on one surface of a flat substrate, and the method is also completed by simply moving two types of engraving machines sequentially in directions perpendicular to each other to engrave the pattern.

[0079] Thus, the illustrated method for manufacturing a master mold simply involves moving two engraving machines perpendicular to each other to form a mold pattern on a plane, making the pattern formation process easy and the resulting pattern simple. Therefore, transferring the mold pattern formed on the master mold to another mold substrate is easy, and the transfer of the mold pattern is completed perfectly. Furthermore, because the mold pattern is simple and formed on a plane, repeated transfers do not damage the transferred mold pattern, making it economical in the production of molds for manufacturing retroreflective sheets.

Claims

1. It is a master mold, Lower section and, An upper layer provided on the lower layer, The above includes a plurality of unit master molds provided on the upper layer, The aforementioned multiple unit master molds are arranged continuously in the horizontal and vertical directions without spacing from each other. Each of the aforementioned unit master molds is The first and second surfaces, which are in contact with each other and form a first angle, It has a third surface and a fourth surface that are spaced apart from each other via the first surface and the second surface, The third and fourth surfaces are inclined relative to each other. The first and second surfaces are in contact with the third and fourth surfaces, respectively, of the master mold.

2. The master mold according to claim 1, A master mold in which one of the third and fourth surfaces is a vertical surface, and the other surface forms an acute angle with respect to the vertical surface.

3. The master mold according to claim 1, A master mold in which the edges formed by the contact of the first and second surfaces with each other are in contact with the upper vertex of the third surface and the upper vertex of the fourth surface.

4. The master mold according to claim 3, One of the third and fourth surfaces is a vertical surface. A master mold in which the length of the edge is the same as the height of the vertical surface.

5. The master mold according to claim 4, A master mold in which the distance between the upper vertex of the vertical surface of the first unit master mold among the plurality of unit master molds and the upper vertex of the non-vertical surface of the third and fourth surfaces of the second unit master mold adjacent to the first unit master mold is the same as the length of the edge.

6. A method for manufacturing a master mold, The steps include forming a first pattern on the surface of a substrate that is symmetrical in a first direction, The process includes the step of asymmetrically removing a portion of the first pattern in a second direction perpendicular to the first direction, The formation of the first pattern results in the formation of a second pattern having a triangular cross-section on the surface of the substrate. In the step of asymmetrically removing a portion of the first pattern, a portion of the second pattern is also removed. A method comprising removing a portion of the second pattern to form a vertical surface and an inclined surface inclined with respect to the vertical surface.

7. The method according to claim 6, A method comprising performing the step of asymmetrically removing a portion of the first pattern at least twice after performing the step of forming the first pattern.

8. The method according to claim 6 or 7, A method comprising the step of asymmetrically removing a portion of the first pattern, performed at least twice.

9. The method according to claim 6, The step of forming the first pattern is carried out using the first engraving machine, The first pattern is formed as a V-shaped groove, in a method.

10. The method according to claim 6, The step of asymmetrically removing a portion of the first pattern is carried out using a second engraving machine. The method wherein the tip of the second engraving machine that contacts the surface of the substrate has a vertical surface and an inclined surface that forms an acute angle with respect to the vertical surface.

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