Water-repellent material

Abstract

Conventional water-repellent materials and methods for manufacturing them, while forming minute irregularities on the substrate surface, have not been able to consistently achieve high water repellency. [Solution] The present invention relates to a metal substrate having a three-dimensionally irregular uneven surface, the surface of the metal substrate having fine irregularities smaller than the size of the uneven surface formed by anodizing the metal substrate, and a water-repellent coating on the outermost layer, wherein the fine uneven surface is formed in the recesses between a first convex portion and a second convex portion adjacent to the first convex portion of the uneven surface.

Description

Technical Field

[0001] The present invention relates to a water-repellent substrate having water-repellent properties imparted to an aluminum substrate and a method for manufacturing the same.

Background Art

[0002] In the exterior of transportation equipment such as automobiles, window glass, the roofs of buildings such as houses, mirrors, eyeglass lenses, household appliances, industrial equipment, etc., in order to prevent problems caused by water adhesion, a water-repellent film using a fluorine material or the like is applied to the substrate surface to prevent water droplet adhesion. However, simply applying a water-repellent film to the substrate surface cannot sufficiently enhance the water-repellent properties. Therefore, attempts have been made to form minute irregularities on the substrate surface to improve the water-repellent properties by the lotus effect. For example, minute irregularities are formed on the substrate surface in advance, and by applying a water-repellent film to the substrate surface on top of these minute irregularities, higher water-repellent properties can be achieved, and the water-repellent film can be firmly adhered to the substrate surface by the anchor effect, resulting in excellent durability.

[0003] In Patent Document 1, a water-repellent member is described in which a water-repellent film is formed on an anodic oxidation layer having an uneven structure formed on an aluminum substrate by anodic oxidation treatment and etching treatment, using a coating liquid from which moisture has been separated.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In conventional water-repellent members and methods for manufacturing water-repellent members, since a pin-shaped uneven structure is formed on the substrate surface, deterioration of water-repellent characteristics due to surface wear or the like has been a problem.

Means for Solving the Problems

[0006] To solve the above problems, the water-repellent member of the present invention comprises a metal substrate having a three-dimensionally irregular uneven surface, fine irregularities smaller than the size of the uneven surface formed by anodizing the metal substrate on the surface of the metal substrate, and a water-repellent coating on the outermost layer, wherein the fine uneven surface is formed in the recess between a first convex portion and a second convex portion adjacent to the first convex portion of the uneven surface. [Effects of the Invention]

[0007] The water-repellent member of the present invention can achieve high water repellency stably while using a simple method for forming a water-repellent surface. Furthermore, because the water-repellent coating can be firmly adhered to the water-repellent treated surface through an anchoring effect, a water-repellent surface with excellent durability can be obtained. [Brief explanation of the drawing]

[0008] [Figure 1] Water-repellent material manufacturing process according to the present invention [Figure 2] Surface irregularities of the water-repellent member according to the present invention [Figure 3] Combination conditions for exhibiting water repellency according to the present invention [Figure 4] Component diagram of an air conditioning system [Modes for carrying out the invention]

[0009] The following describes an embodiment of a water-repellent surface formation method according to the present invention and a water-repellent article having a water-repellent surface formed using this method.

[0010] The water-repellent surface formation method according to the present invention is a method for forming a water-repellent surface by sandblasting a substrate and then applying anodizing treatment to form a water-repellent coating on the outermost layer.

[0011] The uneven surface of this invention will now be described. As shown in Figures 1 and 2, first, first and second uneven surfaces are formed by blasting. The goal is for the first and second uneven surfaces to be uniform in height, but in reality, there is a difference in the height of the unevenness overall. There is a recess between the first uneven surface and the adjacent second uneven surface, and the sides are vertical or inclined toward the back. Next, fine pores, which form an uneven surface, are formed on the surface where the uneven surface was formed by blasting by anodizing. As a result, the uneven surface of the substrate has a fractal structure consisting of the uneven surface formed by blasting and the fine uneven surface formed by anodizing. Finally, by coating the substrate surface with a silicon compound or a fluorine compound, a water-repellent structure with good water-repellent properties is obtained.

[0012] As shown in Figure 3, the first and second uneven surfaces formed by blasting are controlled by the hard abrasive grain (media) size and the blasting pressure. Next, the fine uneven surfaces formed by anodizing are controlled by the current density.

[0013] Specifically, the method is characterized by setting the axial angle θ of the spray nozzle with respect to the perpendicular direction of the substrate surface to 0°, and the distance of the tip of the spray nozzle from the substrate surface to 200 mm, and spraying hard abrasive grains with an average particle size of 150 μm or less onto the substrate surface at a spray pressure of 0.1 MPa to 0.6 MPa to create an uneven surface, and then performing an anodizing treatment at a current density in the range of 1 A / dm² to 3 A / dm².

[0014] In the water-repellent surface formation method according to the present invention, by applying sandblasting treatment to the substrate surface under the above-described conditions, large irregularities can be formed on the substrate surface, and by applying anodizing treatment, a fractal structure in which minute irregularities are formed on the large irregularities can be easily formed, thereby improving water repellency. According to Wenzel's theory, which is generally known, such an irregular structure increases the effective surface area of ​​the substrate surface, emphasizing the change in surface energy associated with wetting, and further improving water repellency can be achieved. Furthermore, according to Cassie's theory, which is generally known, such an irregular structure prevents water from penetrating the minute recesses due to capillary action, increasing the area ratio of voids in which air is trapped between adjacent minute protrusions, and further improving water repellency can be achieved.

[0015] Furthermore, the wettability of a solid surface is primarily judged by the contact angle of a water droplet, due to the ease of measurement. Generally, water repellency is defined as a contact angle of 90° or higher for a water droplet on a solid surface, with 110° to 150° being considered highly water-repellent, and anything higher being super-water-repellent. When a solid surface is flat, the contact angle obtained by applying a water-repellent film using fluorine materials, etc., is approximately 100°.

[0016] Furthermore, the sliding angle of the water droplet is also used for evaluation. Generally, the smaller the inclination angle, the better the properties, as the water droplet rolls more easily. When the solid surface is flat, the sliding angle obtained by applying a water-repellent film using fluorine material, etc., is approximately 40°.

[0017] In the water-repellent surface formation method according to the present invention, it is necessary to satisfy the above-described sandblasting and anodizing treatment conditions in order to form the above-described fractal structure on the substrate surface. The sandblasting treatment conditions of the present invention are described below.

[0018] First, regarding preferred substrates, the present invention uses aluminum or an aluminum alloy.

[0019] For the hard abrasive grains used in the sandblasting treatment employed as a pretreatment in the present invention, those with an average particle size of 150 μm are used. Increasing the surface area by roughening the substrate surface to form an uneven structure can improve water repellency. However, in order to exhibit a visible effect, it is preferable that the average particle size of the hard abrasive grains be 5 μm or more. However, if the average particle size of the hard abrasive grains exceeds 300 μm, problems such as the unevenness on the substrate surface becoming large and the water repellent effect decreasing will occur, making it impractical.

[0020] Incidentally, when stably forming a fractal structure on the substrate surface, it is preferable to use aluminum oxide-based abrasive grains, silicon carbide-based abrasive grains, glass, or zirconia alumina abrasive grains (Z) as the hard abrasive grains used in the sandblasting treatment of the present invention. Here, the aluminum oxide-based abrasive grains have sharp corners and appropriate toughness, and include brown alumina-based (alundum: A), white alumina-based (white alundum: WA), single crystal alumina-based (hydroxyapatite: HA), etc. Also, the silicon carbide-based abrasive grains have high hardness, and include black silicon carbide-based (carborundum: C), green silicon carbide-based (green carborundum: GC), etc. Further, zirconia alumina abrasive grains (Z) having high hardness and high toughness are used.

[0021] Also, under the sandblasting treatment conditions used in the present invention, the axis angle θ of the injection nozzle with respect to the vertical direction of the substrate surface is set to 0°, and the distance from the tip of the injection nozzle to the substrate surface is set to 100 mm to 200 mm. Here, if the axis angle of the injection nozzle with respect to the vertical direction of the substrate surface exceeds 85°, an uneven shape suitable for improving water repellency cannot be formed on the substrate surface. And if the distance from the tip of the injection nozzle to the substrate surface is less than 100 mm, hard abrasive grains cannot be stably injected from the injection nozzle, and a uniform uneven shape cannot be formed on the substrate surface. Also, if the distance from the tip of the injection nozzle to the substrate surface exceeds 200 mm, the processing ability is significantly reduced and it is not suitable for practical use.

[0022] Also, under the sandblasting treatment conditions used in the present invention, the above-described hard abrasive grains are sprayed onto the surface of the substrate at an injection pressure of 0.1 MPa to 0.6 MPa. Although the optimum set values of these injection pressures and injection times vary somewhat depending on the hardness of the substrate and the type of hard abrasive grains to be sprayed, an excellent water-repellent surface can be formed within the above range. Here, if the injection pressure is less than 0.1 MPa, the processing ability is reduced and it is not practical. Further, if the injection pressure exceeds 0.6 MPa, when aluminum or an aluminum alloy is used as the substrate, there is a risk that the substrate may be deformed or damaged by that pressure.

[0023] Subsequently, the anodizing treatment conditions used in the present invention will be described.

[0024] First, aluminum or an aluminum alloy is used as the substrate. When the substrate is formed by machining such as cutting, dirt and oil adhering during processing are removed. The substrate is immersed in an organic solvent such as acetone and degreased by ultrasonic cleaning. Further, for dirt and natural oxide films that cannot be removed by ultrasonic cleaning, degreasing treatment is performed using a commercially available degreasing solution for aluminum and removed.

[0025] Next, an anodic oxidation treatment is performed on the substrate of aluminum or an aluminum alloy. When the anodic oxidation treatment is performed, a porous aluminum oxide coating layer (also referred to as a porous structure) having a plurality of pores is formed on the surface of the substrate.

[0026] For the anodizing process, an electrolyte solution is used, which is prepared by adding sulfuric acid to pure water to adjust its concentration. The anode (substrate: aluminum or aluminum alloy) and cathode are immersed in the electrolyte solution, and the anodizing process is carried out by connecting the cathode and anode to a power source and applying current. The cathode material can be anything as long as it has low reactivity with the electrolyte solution; for example, carbon, platinum, titanium, or stainless steel can be used. The electrolyte temperature is preferably in the range of 15°C to 25°C and is preferably controlled by a heater and chiller. By applying a voltage between the electrodes and performing the anodizing process for 10 to 120 minutes, an aluminum oxide film layer with pores is formed near the surface of the substrate. After that, the electrolyte solution is washed off the substrate after it is removed from the processing tank with pure water.

[0027] Finally, by coating the substrate surface with silicon compounds or fluorine compounds, water-repellent properties can be imparted to the substrate.

[0028] (Example 1) The method for manufacturing the water-repellent member of the present invention will be described below.

[0029] A 50mm x 50mm x 0.5mm thick aluminum plate was used as the base material. First, the aluminum plate was subjected to sandblasting. The hard abrasive grains used for sandblasting were white alumina-based (white alundum: WA) #100 with an average particle size of 150 μm.

[0030] The processing conditions were as follows: the axial angle θ of the spray nozzle relative to the perpendicular direction of the substrate surface was 0°, and the distance of the tip of the spray nozzle from the substrate surface was 200 mm. The spray pressure was 0.5 MPa to 0.7 MPa when sprayed onto the substrate surface.

[0031] The blast treatment conditions described above formed a textured surface with a height of 10 μm on the substrate.

[0032] Next, the blast-treated surface was subjected to anodizing.

[0033] First, the substrate was immersed in acetone and ultrasonically cleaned for 3 minutes. Then, it was degreased using an aluminum degreasing solution (Top Alclean, manufactured by Okuno Pharmaceutical Co., Ltd.) at 60°C for 5 minutes.

[0034] Next, anodizing treatment was performed on the substrate (aluminum) as the anode and a carbon plate as the cathode. The electrolyte was prepared as 180 g / L sulfuric acid. The electrolyte was maintained at a constant temperature of 20°C using a heater and chiller. The anodizing treatment was carried out by applying voltage to the anode and cathode using a power supply. The voltage was adjusted so that the current density was between 1 A / dm² and 3 A / dm² relative to the area of ​​the part to be anodized. By applying the voltage for 30 to 90 minutes, an aluminum oxide layer with a fine uneven structure of pores with a height of 0.1 μm perpendicular to the blasted surface was formed.

[0035] Next, to impart water repellency to the substrate, a hydrophobic molecular coating was applied. A fluorine compound (DURASURF DS-5841S135, manufactured by Harves Co., Ltd.) was used as the hydrophobic molecule. While the fluorine compound can be applied to the substrate by spraying or immersion, the immersion method was chosen in this case. After applying the fluorine compound to the substrate by immersion, a heat drying treatment was performed at 100°C for 60 minutes to impart water repellency to the substrate.

[0036] (Example 2) A 50mm x 50mm x 0.5mm thick aluminum plate was used as the base material. First, the aluminum plate was subjected to sandblasting. The hard abrasive grains used for sandblasting were white alumina-based (white alundum: WA) #100 with an average particle size of 150 μm.

[0037] The processing conditions were as follows: the axial angle θ of the spray nozzle relative to the perpendicular direction of the substrate surface was 0°, and the distance of the tip of the spray nozzle from the substrate surface was 200 mm. The spray pressure was 0.3 MPa when sprayed onto the substrate surface.

[0038] The blasting process described above formed an uneven surface with a height of 8 μm on the substrate surface.

[0039] Next, the blast-treated surface was subjected to anodizing.

[0040] First, the substrate was immersed in acetone and ultrasonically cleaned for 3 minutes. Then, it was degreased using an aluminum degreasing solution (Top Alclean, manufactured by Okuno Pharmaceutical Co., Ltd.) at 60°C for 5 minutes.

[0041] Next, anodizing treatment was performed on the substrate (aluminum) as the anode and a carbon plate as the cathode. The electrolyte was prepared as 180 g / L sulfuric acid. The electrolyte was maintained at a constant temperature of 20°C using a heater and chiller. The anodizing treatment was carried out by applying voltage to the anode and cathode using a power supply. The voltage was adjusted so that the current density was between 1 A / dm² and 3 A / dm² relative to the area of ​​the part to be anodized. By applying the voltage for 30 to 90 minutes, an aluminum oxide layer with a fine uneven structure of pores with a height of 0.1 μm perpendicular to the blasted surface was formed.

[0042] Next, to impart water repellency to the substrate, a hydrophobic molecular coating was applied. A fluorine compound (DURASURF DS-5841S135, manufactured by Harves Co., Ltd.) was used as the hydrophobic molecule. While the fluorine compound can be applied to the substrate by spraying or immersion, the immersion method was chosen in this case. After applying the fluorine compound to the substrate by immersion, a heat drying treatment was performed at 100°C for 60 minutes to impart water repellency to the substrate.

[0043] (Example 3) A 50mm x 50mm x 0.5mm thick aluminum plate was used as the base material. First, the aluminum plate was subjected to sandblasting. The hard abrasive grains used for sandblasting were white alumina-based (white alundum: WA) #60 with an average particle size of 300 μm.

[0044] The processing conditions were as follows: the axial angle θ of the spray nozzle relative to the perpendicular direction of the substrate surface was 0°, and the distance of the tip of the spray nozzle from the substrate surface was 200 mm. The spray pressure was 0.3 MPa to 0.7 MPa when sprayed onto the substrate surface.

[0045] The blast treatment described above formed an uneven surface with a height of 5 μm on the substrate surface.

[0046] Next, the blast-treated surface was subjected to anodizing.

[0047] First, the substrate was immersed in acetone and ultrasonically cleaned for 3 minutes. Then, it was degreased using an aluminum degreasing solution (Top Alclean, manufactured by Okuno Pharmaceutical Co., Ltd.) at 60°C for 5 minutes.

[0048] Next, anodizing treatment was performed on the substrate (aluminum) as the anode and a carbon plate as the cathode. The electrolyte was prepared as 180 g / L sulfuric acid. The electrolyte was maintained at a constant temperature of 20°C using a heater and chiller. The anodizing treatment was carried out by applying voltage to the anode and cathode using a power supply. The voltage was adjusted so that the current density was between 1 A / dm² and 3 A / dm² relative to the area of ​​the part to be anodized. By applying the voltage for 30 to 90 minutes, an aluminum oxide layer with a fine uneven structure of pores with a height of 0.1 μm perpendicular to the blasted surface was formed.

[0049] Next, to impart water repellency to the substrate, a hydrophobic molecular coating was applied. A fluorine compound (DURASURF DS-5841S135, manufactured by Harves Co., Ltd.) was used as the hydrophobic molecule. While the fluorine compound can be applied to the substrate by spraying or immersion, the immersion method was chosen in this case. After applying the fluorine compound to the substrate by immersion, a heat drying treatment was performed at 100°C for 60 minutes to impart water repellency to the substrate. (Water repellency evaluation)

[0050] As shown in Figure 3, the water repellency of the water-repellent members fabricated according to Examples 1, 2, and 3 was evaluated. Water repellency was measured by the contact angle and sliding angle in pure water.

[0051] The contact angle was measured by placing a 2.5 μl droplet of pure water on the substrate surface. As a result, Example 1 showed a contact angle of 156°, exhibiting superhydrophobicity of 150° or more, and was judged as ◎. Example 2 showed high hydrophobicity with a contact angle of 145°, but its performance tended to be slightly inferior, and was judged as ○. Example 3 also showed high hydrophobicity with a contact angle of 141°, but its performance tended to be slightly inferior, and was judged as ○.

[0052] Next, the sliding angle was measured by placing a 50 μl liquid droplet of pure water on the substrate surface and tilting the substrate, then measuring the substrate tilt angle when the droplet slid off the substrate surface. As a result, in Example 1, the water droplet slid off when the substrate tilt angle was 2° or less, and the sliding performance of the water droplet was good, so it was judged as ◎. In Example 2, compared to Example 1, the tilt angle was 10°, and the droplet tended to slide off slightly less, so it was judged as ○. In Example 3, the tilt angle was 30°, and the sliding performance was only slightly better than the sliding angle of 40° obtained by applying a water-repellent coating to a flat aluminum surface, so it was judged as △.

[0053] In Example 1, under surface irregularity formation conditions with a hard abrasive grain size of #100, an average particle size of 150 μm, a spray pressure of 0.5 MPa to 0.7 MPa, and a current density of 1 A / dm² to 3 A / dm², the material exhibits excellent properties, with a contact angle of 150° or more and an inclination angle of 2° or less, causing water droplets to slide off, resulting in the best water-repellent properties in this example. In Example 2, the sliding angle is slightly larger due to the lower spray pressure compared to Example 1, but it still exhibits good water-repellent properties as a water-repellent material. In Example 3, the hard abrasive grain size is #60 with an average particle size of 300 μm, and the water-repellent properties are only slightly better than those obtained by applying a water-repellent coating to a flat aluminum surface.

[0054] In this embodiment, since fine irregularities exist in the recessed areas between the irregularly formed first and second protrusions, the water-repellent function that would otherwise be reduced by surface wear can be maintained.

[0055] As an example of the application of the water-repellent material described above, as shown in Figure 4, by applying the uneven structure implemented in this embodiment to the inner surface of the fins 105 of the heat exchange section, which is a component of an air conditioning device that performs heating, cooling, and ventilation, or to the drain tray 106 located below the heat exchange section, it is expected that the growth of bacteria and mold that occur in places where moisture is generated or passes through can be suppressed.

[0056] By employing the process of this embodiment, it is possible to form uneven surfaces over a large area at low cost, even for complex shapes. [Explanation of symbols]

[0057] 100: Base material 101: Hard abrasive grains 102: First convex part 103: Second convex part 104: Pores 105: Fins of the heat exchange section 106: Drain tray 107: Fluorine coating

Claims

1. A metal substrate having a three-dimensionally irregular uneven surface, The surface of the metal substrate has fine irregularities smaller than the size of the uneven shape formed by anodizing the metal substrate, and the outermost layer has a water-repellent coating, wherein the fine irregularities are formed in the recesses between a first convex portion and a second convex portion adjacent to the first convex portion.

2. The water-repellent member according to claim 1, characterized in that the size of the protrusions of the uneven shape is 6 μm to 20 μm, and the size of the protrusions of the fine unevenness is 0.01 μm to 0.1 μm.

3. The water-repellent member according to claim 1, characterized in that the metal material is aluminum or an aluminum alloy.

4. The water-repellent member according to claim 1, characterized in that the aforementioned uneven shape is formed by blasting with hard abrasive grains of size #100, that is, with an average particle size of 150 μm.

5. The water-repellent member according to any one of claims 1 to 4, characterized in that the water-repellent coating is a coating made of a fluorine-based water-repellent material.

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