Rugged structure, and method of manufacturing rugged structure

Abstract

To provide a rugged structure that has excellent effect of reducing fluid resistance, and also has durability.SOLUTION: A rugged structure has a base material and a plurality of protrusions provided on a surface of the base material. Each of at least some of the plurality of protrusions (1) has a gradient in Martens hardness in at least one of the height direction, width direction, and inward / outward directions, and / or (2) has portions with Martens hardness different from each other in the width direction.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a concave-convex structure and a method for manufacturing a concave-convex structure. [Background technology]

[0002] In recent years, in the fields of technology such as moving objects, rotating objects, and fluid transport, research into reducing fluid resistance has been actively conducted in order to achieve energy conservation and carbon dioxide reduction.In addition, the wind noise of high-speed moving objects such as aircraft and bullet trains, and rotating blades in wind power generation, has become a noise pollution problem, and the application of technologies to reduce fluid resistance is being considered.

[0003] One known technique for reducing fluid resistance is to provide a surface with irregularities called riblets, which mimic shark skin, on the base material. The riblets are known to reduce turbulent frictional resistance of fluids.

[0004] Previously, a multilayer riblet applique has been reported as a structure for reducing fluid resistance, comprising a fluorosilicone riblet structure including riblet raised portions and a base from which the riblet raised portions extend, a fluorosilicone layer adjacent to the fluorosilicone riblet structure, and a support layer adjacent to the base, the support layer including a metal underlayer, an adhesive underlayer, and at least one thermoplastic underlayer (see, for example, Patent Document 1).

[0005] In addition, an uneven resin film with an uneven structure on the surface that can reduce pressure resistance has been reported (see, for example, Patent Document 2), and specifically, a method has been reported in which a resin film such as vinyl chloride with uneven portions formed thereon is attached. Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a concavo-convex structure that is excellent in the effect of reducing fluid resistance and also has durability. [Means for solving the problem]

[0007] The concave-convex structure of the present invention, which is a means for solving the above-mentioned problems, comprises a substrate and a plurality of convex portions provided on the surface of the substrate, and each of at least some of the convex portions (1) has a gradient of Martens hardness in at least one of the height direction, width direction, and inner / outer direction, and / or (2) has portions in the width direction where the Martens hardness differs from one another. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a concavo-convex structure that is excellent in the effect of reducing fluid resistance and also has durability. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic perspective view showing an example of the concavo-convex structure of this embodiment. [Figure 2] FIG. 2 is a cross-sectional view of the concave-convex structure of FIG. [Figure 3] FIG. 3 is a cross-sectional view showing another example of the concavo-convex structure of this embodiment. [Figure 4] FIG. 4 is a cross-sectional view showing another example of the concavo-convex structure of this embodiment. [Figure 5] FIG. 5 is a cross-sectional view showing another example of the concavo-convex structure of this embodiment. [Figure 6] FIG. 6 is an explanatory diagram showing an example of a convex portion having a gradient of Martens hardness. [Figure 7] FIG. 7 is an explanatory diagram of a convex portion having a gradient of Martens hardness. [Figure 8] FIG. 8 is an explanatory diagram of a convex portion having a gradient of Martens hardness. [Figure 9] FIG. 9 is an explanatory diagram of a convex portion having a gradient of Martens hardness. [Figure 10] FIG. 10 is an explanatory diagram of a convex portion having portions with different Martens hardness. [Figure 11]FIG. 11 is a diagram showing an example of a method for manufacturing a concavo-convex structure according to this embodiment. [Figure 12] FIG. 12 is a diagram showing an example of a method for manufacturing a concavo-convex structure according to this embodiment. [Figure 13] FIG. 13 is a diagram showing an example of a method for manufacturing a concavo-convex structure according to this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] (Uneven structure) The protrusion-recess structure in this embodiment has a substrate and a plurality of protrusions provided on the surface of the substrate, and each of at least some of the plurality of protrusions (1) has a gradient of Martens hardness in at least one of the height direction, width direction, and inner / outer direction, and / or (2) has portions in the width direction where the Martens hardness differs from one another. In one embodiment, the concave-convex structure preferably further has a support layer from the viewpoints of adhesion to the substrate and durability, and in another embodiment, it is preferable that the concave-convex structure does not have a support layer from the viewpoints of weight reduction and fuel efficiency of the object, and either embodiment can be suitably selected. The concavo-convex structure may further include other members as necessary. The concave-convex structure can be suitably used as a concave-convex structure for reducing fluid resistance.

[0011] The concave-convex structure of this embodiment is based on the discovery of problems in the prior art. That is, in a multilayer structure such as that described in Patent Document 1, durability is improved by strong interlayer bonding, but the manufacturing process is complicated by the use of dispenser application, heating processes, masking, etc., and in addition, there are restrictions on the shape of the riblets in order to satisfy manufacturing constraints. Furthermore, when forming riblets on large structures such as aircraft, balancing with productivity is a major issue.

[0012] According to the concave-convex structure of this embodiment, by having multiple protrusions on the surface of the substrate, the overall resistance (referred to as fluid resistance), including pressure resistance and viscous resistance due to fluids (e.g., gases and liquids), is effectively reduced compared to the substrate surface. This reduces the power required for an object having the substrate to move through a fluid, thereby significantly reducing fuel costs. Furthermore, at least some of the multiple protrusions (1) have a Martens hardness gradient in at least one of the height direction, width direction, and inner / outer direction, and / or (2) have portions with different Martens hardness in the width direction. Therefore, the low-hardness elastic portions of each protrusion can cushion the impact of impinging particles, providing advantages in terms of durability, such as abrasion resistance, compared to the substrate itself and substrates with protrusions without a Martens hardness gradient. Therefore, a concave-convex structure can be provided that is both effective in reducing fluid resistance and durable. This may, in certain embodiments, result in a higher maximum speed for a given thrust input, improving the performance of the propulsion system. Furthermore, by using the method for producing a concave-convex structure of the present embodiment described below, photocurable compositions prepared by controlling the mixing ratio of a first photocurable composition and a second photocurable composition whose cured product has a different Martens hardness from that of the first photocurable composition are applied separately, and it is possible to produce a concave-convex structure having the desired shape, gradient, etc. with high productivity while adjusting the desired shape, gradient, etc. of the convex portions.

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings, in which: Figure 1 is a schematic perspective view showing an example of a concavo-convex structure according to this embodiment. The concave-convex structure 100 shown in FIG. 1 has a substrate 1 and a plurality of convex portions 2 provided on the surface of the substrate 1. At least some of the protrusions 2' have a Martens hardness gradient in at least one of the height direction, width direction, and inner / outer direction, and / or (2) have portions in the width direction that have different Martens hardnesses. The protrusions 2 may have protrusions that do not satisfy the above (1) and / or (2), but in the embodiment shown in FIG. 1, all of the protrusions 2 have a Martens hardness gradient. The substrate 1 is the substrate of the surface of the object where fluid resistance occurs, and the multiple convex portions 2 have a periodic uneven shape with a convex portion length L parallel to the fluid flow direction represented by arrow F in the figure.

[0014] The cross-sectional shape of the convex portion will be explained with reference to FIGS. Fig. 2 is a cross-sectional view of the concave-convex structure 100 of Fig. 1. Figs. 3 to 5 are cross-sectional views showing other examples of the concave-convex structure of this embodiment. Here, in FIG. 2, "h" indicates the height of the convex portion, "w" indicates the width of the convex portion, "p" indicates the distance between the convex portions, and "L" shown in FIG. 1 indicates the length of the convex portion.

[0015] The cross-sectional shape of the multiple protrusions 2 is not particularly limited and can be selected appropriately depending on the purpose. For example, it may be triangular as shown in FIG. 2, may have sizes that change alternately or periodically as shown in FIG. 3, or may be rectangular as shown in FIG. 4. As shown in FIG. 5, the protrusion-recess structure 100 may further include a support layer 4 between the substrate 1 and the plurality of protrusions 2.

[0016] When the surface of the substrate 1 has only a plurality of protrusions 2 as shown in FIGS. 2 to 4, this is advantageous from the viewpoint of weight reduction, and can be suitably manufactured by the method for manufacturing a concave-convex structure described later. On the other hand, further including a support layer 4 as shown in Figure 5 provides advantages in terms of adhesion to the substrate (object), good conformability to curved surfaces, and improved durability in terms of impact resistance and abrasion resistance. In particular, when the plurality of protrusions 2 and the support layer 4 are formed using a photocurable silicone, which will be described later, the low surface energy of the cured product of the photocurable silicone prevents adhesion of dirt, which is advantageous in preventing performance degradation.

[0017] <Base material> The substrate is an object on which a plurality of convex portions are to be provided, and is not particularly limited and can be appropriately selected depending on the purpose. The substrate may be a substrate for a portion of the surface that comes into contact with the fluid of the object for which the effect of reducing fluid resistance is to be obtained, or may be a transfer substrate for transferring to the surface of the object. The target object is not particularly limited and can be appropriately selected depending on the purpose. Examples include moving objects such as aircraft, automobiles, trains, ships, vehicles, and flying objects; rotating objects such as fans, turbines, and windmills; and fluid transfer components such as pipelines. The material of the substrate is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include metal materials such as aluminum, organic materials, inorganic materials, etc. The organic material may be, for example, the material of the object, such as various resins, or, if the object is painted, a coating material such as a urethane material, an epoxy material, or an acrylic material.

[0018] <Multiple protrusions> The plurality of protrusions are also called riblets, and are preferably arranged so as to form a periodic uneven shape parallel to the direction of fluid flow. The shape, size, and arrangement of the plurality of convex portions are not particularly limited and can be appropriately selected depending on the desired aspect, for example, the type of fluid, flow rate, and other hydrodynamic characteristics. Examples of the cross-sectional shape of each convex portion include a triangle such as an equilateral triangle, an isosceles triangle, or a right-angled triangle; a quadrangle such as a square, a rectangle, or a trapezoid; and a semicircle.

[0019] The size and arrangement of each convex portion can be appropriately set by the height h of the convex portion, the width w of the convex portion, the interval p between the convex portions, and the length L of the convex portion. The height h of the convex portion is preferably 20 μm or more and 200 μm or less, and more preferably 50 μm or more and 200 μm or less. The width w of the convex portion is preferably 10 μm or more and 1000 μm or less, and more preferably 20 μm or more and 500 μm or less. The distance p between the adjacent protrusions is preferably 10 μm or more and 1000 μm or less, and more preferably 20 μm or more and 500 μm or less. The length L of the convex portion is preferably 30 mm or more, more preferably 50 mm or more. The length can be appropriately selected to be optimal from the viewpoint of the shape of the object and productivity.

[0020] [Gradient and localization of Martens hardness] At least some of the plurality of protrusions have, in the cross section of each protrusion, (1) a gradient in Martens hardness in at least one of the height direction, width direction, and inner / outer direction, and / or (2) portions in the width direction having different Martens hardnesses from each other. Specifically, in the case of (1) above, the cross section of the convex portion shown in FIG. 2 may have a gradient of Martens hardness in at least one of the height h direction, width w direction, and any radial direction from the center of each convex portion (for example, the center of gravity of the cross-sectional shape). Here, "gradient" refers to a gradual increase and / or decrease in Martens hardness when plotted against the direction, with a monotonically increasing or decreasing Martens hardness being preferred. Rather than simply having two regions with different hardnesses, it is preferable to have three or more adjacent regions, with the hardness between those regions increasing or decreasing in the desired direction. The difference in Martens hardness between those regions is preferably within 10%, more preferably within 5%, and particularly preferably within 1%. Most preferred is an embodiment in which the hardness increases or decreases continuously, without a clear interface that makes such regions indistinguishable. This is expected to disperse stress and more effectively suppress fracture due to stress concentration during deformation when a load from a fluid or a colliding object is applied. Note that, for example, embodiments in which convex portions formed of a material with a specific Martens hardness are coated with a coating material with a different Martens hardness, or embodiments in which a support layer and convex portions have different Martens hardnesses, are not included in the "gradient" of this application.

[0021] In the case of (2) above, the cross section of the convex portion shown in FIG. 2 may have portions with different Martens hardness in the width w direction. Here, "areas with different Martens hardness" means that, when the Martens hardness of a certain area (for example, the central area in the width direction) is taken as the reference (100%), the Martens hardness of the adjacent area is preferably 90% or less or 110% or more, and more preferably 80% or less or 120% or more. Furthermore, as shown in Figure 10 described later, it is preferable that the central region in the width direction is a low elasticity region 5 and the distal region in the width direction is a high elasticity region 6, and when the Martens hardness of the low elasticity region 5 is taken as the reference (100%), it is preferable that the Martens hardness of the high elasticity region 6 is 110% or more, and more preferably 120% or more.

[0022] The plurality of convex portions may have convex portions at least some of which satisfy (1) and / or (2) above, and may have convex portions without a Martens hardness gradient, or may have convex portions whose Martens hardness changes stepwise in either the height h direction or the inner / outer direction. The proportion of the number of convex portions that satisfy (1) and / or (2) above is preferably 30% by number or more, 40% by number or more, 50% by number or more, 60% by number or more, 70% by number or more, 80% by number or more, or 90% by number or more, and more preferably 100% by number, relative to the total number of the plurality of convex portions.

[0023] The Martens hardness of the convex portions is not particularly limited and can be appropriately selected depending on the purpose. For example, at least a part (low elasticity part) of each convex portion that satisfies (1) and / or (2) above has a Martens hardness of 100 N / mm 2 or less, and the entirety of each of the convex portions that satisfy (1) and / or (2) above may be 100 N / mm 2 or less, and all of the plurality of protrusions may be 100 N / mm 2 The following may be used, and any of the embodiments can be suitably selected depending on the purpose.

[0024] -Martens hardness- Specifically, the Martens hardness of the convex portions can be measured using a measurement sample of the convex portions and a microhardness tester (for example, FISCHERSCOPE HM2000, manufactured by FISCHER) under the following measurement conditions. As for the method of preparing and measuring the sample for measuring the convex portions, since it is necessary to flatten the measurement surface, examples include: (i) a method of preparing a flat sample (for example, an average thickness of 20 μm to 40 μm) using the same photocurable composition and measuring it; (ii) a method of preparing a flat surface by cutting the convex portions in a plane horizontal to at least one of the height direction, width direction, and inner / outer direction, measuring the flat surface, and evaluating the gradient and localization of the Martens hardness from the distribution of measured values ​​and inflection points; (iii) a method of preparing a plurality of samples (for example, an average thickness of 10 μm or more) cut to a constant thickness in a plane perpendicular to at least one of the height direction, width direction, and inner / outer direction of the convex portions, and evaluating the gradient and localization of the Martens hardness from the distribution of measured values ​​and inflection points for each sample; and combinations of these methods. -Measurement conditions- Number of measurements: 7 measurements, averaged over 5 points excluding the upper and lower values Indenter type: Vickers Pressure conditions: constant pressure 5mN / 20sec, creep: 5sec Decompression conditions: constant pressure 5mN / 20sec, creep: 5sec (same as pressurization conditions)

[0025] From the viewpoint of achieving both the fluid reduction effect and durability (impact resistance, abrasion resistance, anti-fouling properties, etc.) of the concave-convex structure, it is effective for at least some of the plurality of convex portions to (1) have a gradient of Martens hardness in at least one of the height direction, width direction, and inner / outer direction, and / or (2) have portions in the width direction that have different Martens hardnesses from each other. Examples of convex portions having a gradient in Martens hardness include structures shown in Figures 6 to 9. Examples of convex portions having regions with different Martens hardness in the width direction include a structure shown in Figure 10. Figures 6 to 9 are explanatory diagrams showing specific examples of convex portions having a Martens hardness gradient, and are diagrams that schematically show convex portions 2' having a Martens hardness gradient in the cross-sectional view of the concave-convex structure 100 in Figure 2. Figure 10 is an explanatory diagram showing a specific example of convex portions having regions with different Martens hardness. In Figures 6 to 10, dots with different shading shown in the cross-section of convex portions 2' schematically represent the relative high and low Martens hardness.

[0026] 6 shows an embodiment in which the Martens hardness has a gradient in the height direction of the convex portions, with the shade of grayscale in the figure indicating high and low Martens hardness, and the gradient in which the Martens hardness monotonically decreases in the direction of the arrow. Each convex portion has, in its cross section, a region with a relatively low Martens hardness (low elasticity region 5) and a region with a relatively high Martens hardness (high elasticity region 6).

[0027] In the manufacturing process, a photocurable composition prepared by controlling the mixing ratio of the first composition and the second composition is applied to predetermined positions by, for example, inkjet printing, whereby convex portions having a desired gradient in Martens hardness can be suitably formed. For example, as shown in Figure 6, by providing a low elasticity region 5 at the tip of the convex portion, it is possible to provide excellent impact resistance and abrasion resistance, and by providing a high elasticity region 6 at the base of the convex portion, it is possible to provide rigidity to the convex portion and appropriately suppress deformation due to fluid load. Here, "fluid load" includes, for example, fluid and colliding objects (pebbles, sand, hail, etc.) and maintenance load (when washing a car, etc.). Therefore, for example, by mixing two liquids containing the same components but in different compositions, it is possible to form convex portions with a Martens hardness gradient integrally using the same material, which is advantageous in terms of achieving both the effect of reducing fluid resistance and durability.

[0028] FIG. 7 shows an embodiment in which the Martens hardness has a gradient in the width direction of the convex portion, and FIGS. 8 and 9 show embodiments in which the Martens hardness has a gradient in the inner and outer directions of the convex portion. As shown in Figure 7, the low elasticity regions 5 at the tip and center of the convex portion provide excellent impact resistance and abrasion resistance, and the high elasticity regions 6 at both ends of the base of the convex portion provide rigidity to the convex portion, making it possible to appropriately suppress deformation due to fluid load.

[0029] In order to form such a gradient in Martens hardness, in the manufacturing process, the mixing ratio of the two liquids, the first composition and the second composition, is controlled for each region corresponding to each voxel in the three-dimensional shape data representing the shapes of multiple convex portions, and the curing timing is controlled to control the degree to which the compositions of adjacent voxels mix together, thereby making it possible to preferably and more precisely form convex portions with a gradient in Martens hardness. In particular, inkjet printing makes it possible to apply two or more liquid compositions separately, which allows for the Martens hardness gradient to be adjusted according to the fluid load that may be applied to the target object, thereby obtaining a concavo-convex structure that combines the effect of reducing fluid resistance with durability.

[0030] FIG. 10 shows an embodiment in which the convex portion has a region with different Martens hardness in the width direction. As shown in Figure 10, the low elasticity regions 5 at the tip and center of the convex portion provide excellent impact resistance and abrasion resistance, and the high elasticity regions 6 at both ends of the base of the convex portion provide rigidity to the convex portion, making it possible to appropriately suppress deformation due to fluid load. In the manufacturing process, a first photocurable composition and a second photocurable composition, the cured product of which has a different Martens hardness from that of the first photocurable composition, are separately applied to predetermined positions by, for example, inkjet printing, thereby making it possible to suitably form convex portions having portions with different Martens hardness.

[0031] [Micro Slurry Jet Erosion (MSE) Wear Amount] The micro slurry jet erosion (MSE) wear amount of the convex portions is preferably 3 μm or less, more preferably 2 μm or less, and even more preferably 1.5 μm or less, in terms of excellent wear resistance. Furthermore, the MSE wear amount at the convex portion after the durability test is preferably 3 μm or less, more preferably 2 μm or less, and even more preferably 1.5 μm or less, in terms of excellent durability.

[0032] Specifically, the micro slurry jet erosion (MSE) wear amount at the convex portion can be measured under the following conditions using an abrasion tester (MSE tester MSE-A: manufactured by Palmeso Co., Ltd.) on a flat cured product of the photocurable composition as a test sample prepared by the following procedure. -Measurement conditions- Projectile: Alumina (average particle size 1.2 μm, polygonal) Air: Pressure 0.214 MPa, Flow rate: 6.1 L / min Slurry: Pressure 0.213 MPa, Flow rate: 125 L / min Pump pressure: 0.295MPa ·Projection amount: 3g

[0033] -Preparation of test samples- The photocurable composition for forming the convex portions was heated to a viscosity suitable for inkjet ejection, and was applied by ejection from an inkjet head (RICOH MH5420, manufactured by Ricoh Co., Ltd.) to form a flat film with an average thickness of 40 μm on a SUS substrate. The droplets were then irradiated with UV LED (wavelength 365 nm, 1,500 mJ / cm) using a Honle LEDcube100 (manufactured by Honle UV Technology). 2 ) and light-curing to prepare test samples.

[0034] [Pure water contact angle] The pure water contact angle of the convex portions is preferably 90° or more, and more preferably 100° or more. Furthermore, the pure water contact angle of the convex portions after the durability test is preferably 90° or more, and more preferably 100° or more.

[0035] Specifically, the pure water contact angle on the convex portion can be measured as a static contact angle using a contact angle meter (DropMaster 500, manufactured by Kyowa Interface Science Co., Ltd.) on a flat cured product of the photocurable composition as a test sample prepared by the above procedure under the following conditions: -Measurement conditions- Number of measurements: Average of 3 measurements ·Liquid: Pure water ·Environment: Temperature 25℃, humidity 60% Stabilization time: 500ms Volume: 1 μL

[0036] [Durability test and durability] The durability of the concave-convex structure and the convex portions can be evaluated by carrying out the following durability test and comparing the rate of change in abrasion resistance between the initial state and after durability testing, and the rate of change in contact angle between the initial state and after durability testing. -Durability test- The sample is left in a thermostatic chamber (LH43-13P, manufactured by Nagano Science Co., Ltd.) at a temperature of 85°C and a humidity of 85% for two weeks.

[0037] The MSE wear amount after the durability test (W) compared to the initial MSE wear amount (W0) T The rate of change of (%) can be calculated by the following formula (1), and is preferably 40% or less, more preferably 30% or less, and even more preferably 20% or less. ((W0-W T ) / W0)×100[%]...Equation (1)

[0038] The pure water contact angle after the durability test (C T The rate of change of (%) can be calculated by the following formula (2), and is preferably 10% or less, more preferably 5% or less, and even more preferably 2.5% or less. ((C0-C T ) / C0)×100[%]...Equation (2)

[0039] The material of the plurality of convex portions is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include a cured resin, a resin coating, and a metal. Among these, a cured resin product is preferred, and a cured product of a curable composition is more preferred. Examples of the curable composition include a moisture-curable composition, a heat-curable composition, and a photo-curable composition (for example, an ultraviolet-curable composition). Among these, a cured product of a photocurable composition is more preferred in that it allows for the production of a concavo-convex structure having a desired shape and gradient with high productivity.

[0040] When the material for the plurality of convex portions is a cured product of a photocurable composition, the method for producing a concave-convex structure of this embodiment, which will be described later, makes it possible to form a plurality of concave portions by applying and curing the photocurable composition directly to the substrate of the object. For example, when applying the composition by inkjet, the deposited droplets of the photocurable composition can be instantly cured by a light irradiation means such as a UV LED, thereby enabling the formation of concave-convex portions with high precision. Furthermore, when convex portions are directly formed on the surface of an object that has a curved shape in a direction perpendicular to the direction of gravity, dripping can be a problem, but applying and curing the photocurable composition can suppress dripping and improve productivity.

[0041] -Cured product of photocurable composition- The cured product of the photocurable composition is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include resins, rubbers, etc. Among these, silicone is preferred because it has excellent weather resistance and low-temperature properties, can ensure impact resistance and abrasion resistance due to the elasticity specific to rubber, and has excellent antifouling properties due to its low surface energy.

[0042] In many cases, the object preferably has durability such as weather resistance, low-temperature characteristics, impact resistance, and abrasion resistance, and more preferably has antifouling properties to prevent dirt and adhesions in order to maintain the effect. Materials with poor weather resistance, low-temperature characteristics, impact resistance, and abrasion resistance may be denatured by the effects of ultraviolet rays and water, and the convex portions may be crushed, scraped, or chipped by impacts from pebbles or hail. Furthermore, it is thought that the accumulation of dirt and adhesions on the convex portions will cause the unevenness to disappear, reducing the effect of reducing fluid resistance. On the other hand, in the concave-convex structure of this embodiment, the plurality of convex portions have the Martens hardness gradient, and therefore the convex portions have elastic portions with a relatively low hardness, resulting in good impact resistance and abrasion resistance. The effect of having the elastic portions is expected to be that small stones or the like are prevented from getting caught between the convex portions, thereby maintaining the effect of reducing fluid resistance.

[0043] <Support layer> The concave-convex structure preferably further has a support layer between the substrate and the plurality of convex portions, from the viewpoint of adhesiveness to the substrate (object). The support layer is preferably a cured product of a photocurable composition, and more preferably a cured product of a photocurable silicone in terms of its antifouling properties.

[0044] The photocurable composition in the support layer may be the same as or a similar composition containing the same components as the photocurable composition in the convex portions, or may be a different composition containing different components, and either embodiment can be selected appropriately depending on the purpose. The photocurable composition and its cured product in the support layer can be appropriately selected based on the details described above regarding the convex portions.

[0045] The support layer is preferably a flat layer. The average thickness of the support layer is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 10 μm or more and 200 μm or less, and more preferably 10 μm or more and 100 μm or less.

[0046] (Method for manufacturing a concave-convex structure and apparatus for manufacturing a concave-convex structure) The method for producing a concave-convex structure of this embodiment includes an application step and a light irradiation step, preferably includes a support layer formation step, and further includes other steps as necessary.

[0047] The manufacturing apparatus for a concave-convex structure of this embodiment includes a container, an application means, and a light irradiation means, and further includes other means as required.

[0048] The method for producing the concave-convex structure is not particularly limited and can be selected appropriately depending on the purpose. Examples include (1) a method in which a sheet-like concave-convex structure for transfer is transferred and adhered to a substrate, which is the surface of the object; and (2) a method in which multiple recesses are directly formed on a substrate, which is the surface of the object. Either method can be suitably selected depending on the purpose. The concave-convex structure for transfer in (1) is one embodiment of the concave-convex structure, and includes a substrate for transfer, a plurality of recesses, and, if necessary, a support layer. It can be produced by the method for producing a concave-convex structure of this embodiment. Moreover, the above (2) can be implemented by the method for manufacturing a concave-convex structure of this embodiment.

[0049] From the viewpoint of productivity and durability, the method (2) of forming directly on the substrate is preferable to the method (1) of attaching a sheet. In the method of attaching a sheet described above (1), when the shape of the convex portions is changed to match the shape of the object or the flow speed of the fluid, it can take a lot of work to change the setup of multiple types of concave-convex structures for transfer, etc. Furthermore, when transferring a concave-convex structure for transfer to the curved surface of an object, flexibility is required, and if the conformability is poor, peeling or deformation of the convex portions may occur due to various environmental loads, which could reduce the effect of reducing fluid resistance.

[0050] On the other hand, the method (2) of forming directly on a substrate is advantageous in that the shape can be changed on demand to match the shape of the object or the flow rate of the fluid, and productivity is high. However, since the target object often has a curved shape, it is required that the multiple convex portions conform to the curved surface without peeling, and that a process be able to form the multiple convex portions on demand according to the curved surface and the fluid dynamics characteristics. Furthermore, when the target object is large, it is necessary to form the multiple convex portions over a certain surface area in order to exert the effect of reducing fluid resistance, and considering the lead time for manufacturing and maintenance, a highly productive formation process is required. According to the method for producing a concave-convex structure of this embodiment, dripping can be suppressed by applying and curing a photocurable composition, and productivity can be improved.

[0051] <Containment Unit> The storage section has a first storage section that stores a first photocurable composition and a second storage section that stores a second photocurable composition. The storage section is not particularly limited as long as it is a container that can store the first photocurable composition and the second photocurable composition, respectively, and its shape, structure, size, material, etc. can be appropriately selected depending on the purpose. Examples include those that have at least an ink storage container, an ink tank, an ink bag formed from an aluminum laminate film, a resin film, etc.

[0052] <Application step and application means> The application step is a step of applying a first photocurable composition and a second photocurable composition, the cured product of which has a different Martens hardness from that of the first photocurable composition, to each region on the substrate while controlling the mixing ratio, to form a plurality of convex portions (1) having a Martens hardness gradient in at least one of the height direction, width direction, and inner / outer direction after curing, and / or (2) having portions with different Martens hardness from each other in the width direction after curing, and can be suitably performed by the application means. The application means applies a first photocurable composition and a second photocurable composition, the cured product of which has a different Martens hardness from that of the first photocurable composition, at a controlled mixing ratio to each region on the substrate, thereby forming a plurality of convex portions (1) having a Martens hardness gradient in at least one of the height direction, width direction, and inner / outer direction after curing, and / or (2) having portions with different Martens hardnesses from each other in the width direction after curing. The regions on the substrate may be regions corresponding to voxels in three-dimensional shape data representing the shapes of a plurality of convex portions.

[0053] By controlling the mixing ratio of the first photocurable composition and the second photocurable composition, the cured product of which has a different Martens hardness from that of the first photocurable composition, it is possible to prepare a photocurable composition having a desired mixing ratio for each region. By curing a photocurable composition having a concentration gradient with a controlled mixing ratio, the resulting cured product can satisfy the desired (1) and / or (2) above. wherein the Martens hardness of the cured product of the first photocurable composition is 10 N / mm 2the Martens hardness of the cured product of the second photocurable composition is 100 N / mm or less, 2 Thus, by controlling the mixing ratio, it is possible to form convex portions that satisfy (1) and / or (2) and have any Martens hardness between the minimum and maximum values ​​of the Martens hardness.

[0054] Instead of the combination of the first photocurable composition and the second photocurable composition, a combination including a composition that is not photocurable may be used. Specifically, in addition to the first composition and the second composition, a third composition may be included as needed, as long as the photocurable composition can be prepared by mixing these compositions. Each composition may contain a photocurable compound and a photopolymerization initiator, or may contain only one of them, or may contain only other components such as a solvent.

[0055] -Photocurable composition- The photocurable composition contains a photocurable compound and a photopolymerization initiator, and may further contain other components such as a solvent as required. The photocurable composition preferably contains a photocurable silicone and a photopolymerization initiator. The photocurable silicone can be appropriately selected from common silicone monomers depending on the purpose, and examples thereof include silicone compounds having reactive groups at one or both ends of polydimethylsiloxane. These may be used alone or in combination of two or more.

[0056] Examples of the photopolymerization initiator include a photoradical polymerization initiator, a photocationic polymerization initiator, etc. These may be used alone or in combination of two or more. The photoradical polymerization initiator is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include alkylphenone compounds, acylphosine oxide compounds, and oxyphenylacetic acid ester compounds. The photocationic polymerization initiator is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include photoacid generators such as onium salts having a sulfonium ion or an iodonium ion as the cation moiety. Among the above-mentioned cationic photopolymerization initiators, compounds having an anion moiety that are less corrosive to metal parts are preferred.

[0057] [viscosity] The photocurable composition has a low viscosity, which allows the formation of a uniform film. The viscosity of the photocurable composition under the temperature conditions when the photocurable composition is applied is preferably 30 mPa·s or less, and more preferably 20 mPa·s or less, in order to enable stable application.

[0058] The temperature conditions when applying the photocurable composition are not particularly limited and can be appropriately selected depending on the purpose. For example, in the case of inkjet printing, a temperature condition of 20°C to 60°C can be used. In the case of a non-Newtonian fluid, it is preferable that the viscosity be within the above range in a high shear region corresponding to the time when the photocurable composition is applied, such as when it is ejected by inkjet.

[0059] The viscosity of the photocurable composition can be measured using an E-type viscometer (TVE-25L, manufactured by Toki Sangyo Co., Ltd.) under the following conditions. -Measurement conditions- Temperature: 20℃~60℃ (varies depending on material) Rotation speed: 50 rpm

[0060] The method and means for applying the photocurable composition are not particularly limited and can be appropriately selected depending on the purpose. For example, various printing methods and printing devices such as a spray coating method, a dispense coating method, and an inkjet printing method can be used. Among these, an inkjet printing system in which a UV LED array as a light curing means is mounted on an inkjet head as an application means is preferred, and by integrating the application means and light curing means, it becomes possible to form convex portions with high precision by instantly curing the ejected droplets that have landed with the UV LED.

[0061] <Photocuring step and photocuring means> The photo-curing step is a step of irradiating the plurality of convex portions with light, and can be suitably performed by the photo-curing means, thereby forming a plurality of convex portions that (1) have a gradient in Martens hardness in at least one of the height direction, width direction, and inner / outer direction, and / or (2) have portions in the width direction that have different Martens hardnesses from one another. The light curing means is a means for irradiating the plurality of convex portions with light.

[0062] The method and device for irradiating light are not particularly limited and can be appropriately selected depending on the purpose. Examples include a UV lamp and a UV LED.

[0063] <Support layer formation process> In the case where the concave-convex structure has a support layer, the method for producing the concave-convex structure preferably includes the support layer forming step. The support layer forming step is a step of forming a support layer between the base material and the plurality of convex portions, and is carried out prior to the application step and the light irradiation step. The support layer forming step is preferably a step of applying a photocurable composition to the base material, curing the composition by irradiating the composition with light, and forming a support layer, which is a cured product of the photocurable composition, between the base material and the plurality of convex portions. The support layer forming step can be carried out using the application means and the light irradiation means.

[0064] The photocurable composition in the support layer may be the same as or a similar composition containing the same components as the photocurable composition in the convex portions, or may be a different composition containing different components, and either embodiment can be selected appropriately depending on the purpose.

[0065] [Embodiment of the method for manufacturing a concave-convex structure] An embodiment of the method for manufacturing a concave-convex structure of this embodiment will be described with reference to Figures 11 to 13. Figures 11 to 13 are diagrams showing an example of the method for manufacturing a concave-convex structure of this embodiment. FIG. 11 is an explanatory diagram of the application process and application means, FIG. 12 is an explanatory diagram of the process of controlling the mixing ratio of the first composition and the second composition, and FIG. 13 is an explanatory diagram of each voxel in three-dimensional shape data representing the shapes of multiple convex portions.

[0066] 11 shows a process for manufacturing a concave-convex structure 100 using a concave-convex structure manufacturing apparatus 200. The concave-convex structure manufacturing apparatus 200 is an inkjet system that integrally includes an inkjet head 10 as an application means and a UV LED unit 20 as a photo-curing means.

[0067] In the application step, droplets of a first photocurable composition 11 and a second photocurable composition 12 are respectively ejected from a plurality of ejection holes of an inkjet head 10. As illustrated in FIG. 12, adjacent droplets are mixed to control the mixing ratio of the first photocurable composition 11 and the second photocurable composition 12, thereby preparing a photocurable composition that achieves the desired Martens hardness for each region on the substrate. To form three-dimensional convex portions, the photocurable composition can be applied to regions corresponding to each voxel, as illustrated in FIG. 13.

[0068] In the photo-curing step, the droplets that have landed on the desired areas on the substrate are cured by the UV LED unit 20 at the desired timing (for example, immediately), thereby forming the convex portions 2 with high precision. The shape of the multiple convex parts to be formed, the method of applying the two materials, and the mixing ratio can be controlled by a program recorded on a computer. By further combining a device for transporting the concave-convex structure manufacturing device 200, it becomes possible to form the convex portions 2 directly on the substrate 1, for example, even when forming a concave-convex structure on a large target substrate.

[0069] 12 is an illustration of two photocurable compositions, a first photocurable composition 21 and a second photocurable composition 22, applied to different regions of a substrate. By applying the compositions in this manner, a mixed composition 23 is formed in the region where the two compositions are mixed, and a photocurable composition that achieves the desired Martens hardness can be prepared for each region of the substrate. Furthermore, by combining the first photocurable composition 21 and the second photocurable composition 22, which are highly compatible, the adhesion between the materials forming the convex portions is improved, thereby suppressing delamination between the multiple convex portions and / or between the multiple convex portions and the substrate. In the inkjet system of Figure 11, it is possible to control the application of the first photocurable composition 11 and the second photocurable composition 12, and it is also possible to control the mixing ratio of the two types of photocurable compositions by controlling the curing timing of the UV LED.

[0070] FIG. 13 is an explanatory diagram of each voxel in three-dimensional shape data representing the shapes of a plurality of convex portions. Here, "voxel" is a term that combines volume and pixel, and refers to a regular lattice unit in three dimensions. The size of each voxel can be expressed as the number of voxels per mm (resolution) in vpm (voxel / mm), for example, and may be 100 vpm or less.

[0071] The desired convex shape is created using three-dimensional shape data, and by changing the mixing ratio of the first photocurable composition 11 and the second photocurable composition 12 applied to each voxel indicated by symbols 31 to 36, data can be created so that the Martens hardness of the photocurable composition obtained by mixing these compositions has a gradient. By inputting the three-dimensional shape data obtained in FIG. 13 and the mixing ratio data of the two liquids into the inkjet system shown in FIG. 11 as a program, it is possible to form convex portions with the desired Martens hardness gradient.

[0072] The present invention includes, for example, the following aspects. <1> A substrate; A plurality of protrusions provided on the surface of the substrate, The concave-convex structure is characterized in that at least some of the plurality of convex portions (1) have a gradient of Martens hardness in at least one of the height direction, width direction, and inner / outer direction, and / or (2) have portions in the width direction that have different Martens hardness from each other. <2> At least some of the protrusions that satisfy (1) and / or (2) above have a resistance of 100 N / mm 2 The above <1> 1. The concavo-convex structure according to claim 1. <3> The convex portion is a cured product of a photocurable composition. <1> or <2> 1. The concavo-convex structure according to claim 1. <4> The micro slurry jet erosion (MSE) wear amount at the convex portion is 3 μm or less. <1> from <3> 1. The concavo-convex structure according to any one of the above items. <5> The pure water contact angle of the convex portion is 90° or more. <1> from <4> 1. The concavo-convex structure according to any one of the above items. <6> The method further includes providing a support layer between the substrate and the plurality of convex portions, the support layer being a cured product of a photocurable composition. <1> from <5> 1. The concavo-convex structure according to any one of the above items. <7> The above-mentioned for reducing fluid resistance <1> from <6> 1. The concavo-convex structure according to any one of the above items. <8> a step of applying a first photocurable composition and a second photocurable composition, the cured product of which has a different Martens hardness from that of the first photocurable composition, to each region on the substrate while controlling the mixing ratio, thereby forming a plurality of convex portions (1) having a gradient in Martens hardness in at least one of the height direction, width direction, and inner / outer direction after curing, and / or (2) having portions with different Martens hardness from each other in the width direction after curing; irradiating the plurality of convex portions with light; The method for producing a concave-convex structure is characterized by comprising the steps of: <9> The Martens hardness of the cured product of the first photocurable composition is 10 N / mm 2 is as follows: The Martens hardness of the cured product of the second photocurable composition is 100 N / mm 2 The above <8> 2. A method for producing a concave-convex structure according to claim 1. <10> The photocurable composition has a viscosity of 30 mPa·s or less at any temperature between 20°C and 60°C. <8> or <9> 2. A method for producing a concave-convex structure according to claim 1. <11> The photocurable composition contains a photocurable silicone and a photopolymerization initiator. <8> from <10> 1. A method for producing a concavo-convex structure according to any one of the above. <12> The method further comprises a step of forming a support layer between the substrate and the plurality of convex portions. <8> from <11> 1. A method for producing a concavo-convex structure according to any one of the above.

[0073] The aforementioned <1> from <7> The concavo-convex structure according to any one of the preceding claims, <8> from <12> The method for manufacturing a concave-convex structure according to any one of the above can solve the above-mentioned problems in the prior art and achieve the object of the present invention. [Prior art documents] [Patent documents]

[0074] [Patent Document 1] Japanese Patent Application Publication No. 2018-001746 [Patent Document 2] Japanese Patent Application Publication No. 2022-188898 [Explanation of symbols]

[0075] 1 Base material 2 Multiple protrusions 2´ Convex part 4 Support layer 10 Inkjet head 11, 21 First photocurable composition 12, 22 Second photocurable composition 20 UV LED section 30 Conveying section 100 uneven structure 200 Manufacturing equipment for concave-convex structures F Fluid flow direction

Claims

1. A substrate; A plurality of protrusions provided on the surface of the substrate, A concave-convex structure characterized in that at least some of the plurality of convex portions (1) have a gradient of Martens hardness in at least one of the height direction, width direction, and inner / outer direction, and / or (2) have portions in the width direction having different Martens hardnesses from each other.

2. At least some of the protrusions that satisfy (1) and / or (2) above have a strength of 100 N / mm ２ The concavo-convex structure according to claim 1, wherein:

3. 3. The concavo-convex structure according to claim 1, wherein the convex portions are formed from a cured product of a photocurable composition.

4. 3. The concavo-convex structure according to claim 1, wherein the micro slurry jet erosion (MSE) wear amount of the convex portions is 3 μm or less.

5. 3. The concavo-convex structure according to claim 1, wherein the convex portions have a contact angle with pure water of 90° or more.

6. The concave-convex structure according to claim 1 or 2, further comprising a support layer between the substrate and the plurality of convex portions, the support layer being a cured product of a photocurable composition.

7. The concavo-convex structure according to claim 1 or 2, which is used to reduce fluid resistance.

8. a step of applying a first photocurable composition and a second photocurable composition, the cured product of which has a different Martens hardness from that of the first photocurable composition, to each region on the substrate while controlling the mixing ratio, thereby forming a plurality of convex portions (1) having a gradient in Martens hardness in at least one of the height direction, width direction, and inner / outer direction after curing, and / or (2) having portions with different Martens hardness from each other in the width direction after curing; irradiating the plurality of convex portions with light; A method for producing a concave-convex structure, comprising:

9. The Martens hardness of the cured product of the first photocurable composition is 10 N / mm ２ is as follows: The Martens hardness of the cured product of the second photocurable composition is 100 N / mm ２ The method for producing a concave-convex structure according to claim 8, wherein the method is as described above.

10. 10. The method for producing a concave-convex structure according to claim 8, wherein the photocurable composition has a viscosity of 30 mPa·s or less at any temperature from 20°C to 60°C.

11. The method for producing a concave-convex structure according to claim 8 or 9, wherein the photocurable composition contains a photocurable silicone and a photopolymerization initiator.

12. The method for manufacturing a concave-convex structure according to claim 8 or 9, further comprising the step of forming a support layer between the substrate and the plurality of convex portions.

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