JP6641990B2 - Water repellent substrate and method for producing the same - Google Patents

Description

  The present invention relates to a water-repellent substrate provided with a water-repellent aluminum substrate and a method for producing the same.

  2. Description of the Related Art In an air conditioning system of an electric vehicle, a plug-in hybrid vehicle, or the like, a heat pump system (hereinafter, an HP system) using air as a heat source is used. In the HP system, the refrigerant is compressed to a high temperature and a high pressure by a compressor, radiated by an evaporator, passes through an expansion valve to a low temperature and a low pressure, and reaches an outdoor unit. At this time, the outdoor unit is cooled by absorbing heat from the outside air by the refrigerant, and when the outside of the vehicle becomes high in humidity, condensed water is generated on the surface of the aluminum fins of the outdoor unit. If the condensed water is not removed, it will eventually freeze and turn into frost.

  2. Description of the Related Art As a technique for preventing frost formation on fins for heat exchangers such as outdoor units, there is known a coating method in which unevenness is provided on the surface of a base material to coat a water-repellent coating. In the film system, the condensed water is in a super-water-repellent state on the film surface, so that it can be easily removed by external force such as running wind. For example, Patent Document 1 discloses a water-repellent substrate provided with water repellency by forming an uneven portion made of boehmite on a surface of an aluminum substrate and forming a film made of fluorinated alkylsilane or the like. It has been disclosed.

JP 2013-036733 A

  However, it has been found that when a water-repellent substrate of a film type is used as a fin for a heat exchanger such as an outdoor unit, the water-repellent performance gradually decreases. As a result, the generated water droplets are frozen without being removed and become frost. When the amount of frost increases, the amount of air passing between the fins decreases. Furthermore, since the heat conductivity to the refrigerant also decreases, a defrosting operation is required, and the operation efficiency is reduced. In addition, in order to obtain desired water repellency, it is necessary to use an expensive fluorine-based water repellent material, and the productivity is reduced.

  The present invention has been made in view of such a background, removes condensed water generated in a low-temperature and high-humidity environment, can maintain super water repellency to prevent frost formation, and has a high productivity water repellent base. It is intended to provide a material and a manufacturing method thereof.

One embodiment of the present invention provides an aluminum substrate (2),
An alumite layer (3) provided on the surface of the aluminum substrate;
A water-repellent film (4) provided on the surface of the alumite layer;
The alumite layer has a concavo-convex structure (33) composed of a base layer (31) integral with the aluminum base and a number of pin-like projections (32) arranged in parallel on the surface of the base layer . A structure in which the pin-like projections are arranged at the apexes of the hexagonal cells surrounding the pores by etching the alumite having a hexagonal cell structure having pores (34);
With respect to the ten-point average roughness Rzjis of the concavo-convex structure, the contact area ratio of the pin-like projections is 0 on the virtual cut surface (A) having a height of 20% from the maximum height position of the concavo-convex structure. .01 or less,
The water-repellent film is a film made of a hydrocarbon-based water-repellent material, which is on the water-repellent substrate (1).

Another embodiment of the present invention provides an aluminum substrate (2),
An alumite layer (3) provided on the surface of the aluminum substrate;
A water-repellent film (4) provided on the surface of the alumite layer;
The alumite layer has a concavo-convex structure (33) composed of a base layer (31) integral with the aluminum base and a number of pin-like projections (32) arranged in parallel with the surface of the base layer. The contact area ratio of the pin-like projections is 0.01 or less on the virtual cut surface (A) having a height of 20% Rzjis cut ratio from the maximum height position of the uneven structure with respect to the point average roughness Rzjis. ,
The method for producing a water-repellent substrate (1), wherein the water-repellent film is a film made of a hydrocarbon-based water-repellent material,
Forming the alumite layer having the concavo-convex structure on the surface of the aluminum base by alumite treatment and etching treatment (S1, S2);
Preparing a coating liquid containing the hydrocarbon-based water-repellent material (S11);
A step of adding a hydrocarbon solvent to the coating liquid to separate and remove water (S12);
A step of immersing the aluminum substrate on which the alumite layer is formed in the coating liquid from which water has been removed (S13);
Baking the aluminum substrate to which the coating liquid has been applied (S15).
In addition, the code | symbol in a parenthesis is attached for reference, and this invention is not limited by these codes.

  In the water-repellent substrate according to the above aspect, the alumite layer serving as the surface layer of the aluminum substrate has a fine concavo-convex structure having a small contact area ratio. It becomes possible to develop aqueous properties. In addition, a regular uneven structure in which pin-like projections are arranged side by side, and a portion where a water-repellent film is not formed is unlikely to be formed, so that good water repellency can be obtained on the entire surface. Thereby, the condensed water is pushed out to the surface of the uneven structure, and the generated water droplet can be easily slid off by an external force or the like and removed. In addition, it is possible to prevent the condensed water from remaining inside the uneven structure and the water repellency from gradually decreasing. The hydrocarbon-based water-repellent material has the second lowest surface free energy next to the fluorine-based water-repellent material, contributes to improvement in water repellency, is less expensive than the fluorine-based water-repellent material, and improves productivity.

  Such a water-repellent substrate is formed by forming a water-repellent film using a coating liquid from which moisture is separated on an alumite layer having a concavo-convex structure formed by subjecting an aluminum substrate to alumite treatment and etching. Is further improved. Therefore, in a low-temperature and high-humidity environment, the condensed water generated is removed by making it super-water-repellent, and a water-repellent substrate that can maintain high water-repellent performance for a long time and prevent problems due to frosting can be obtained. .

FIG. 2 is an enlarged sectional view of a main part showing a schematic structure of a water-repellent substrate in the first embodiment. FIG. 2 is an enlarged perspective view of a main part schematically showing a concavo-convex structure of the alumite layer of the water-repellent substrate in the first embodiment. FIG. 2 is a schematic diagram showing a water-repellent film molecular structure of a water-repellent substrate in the first embodiment. FIG. 3 is an enlarged perspective view of a main part of the alumite layer schematically showing a method of measuring a contact area ratio in the first embodiment. FIG. 3 is an enlarged perspective view showing an alumite layer forming step by an alumite forming step and an etching step of the aluminum base material in the first embodiment. FIG. 2 is an enlarged sectional view of a main part showing a state in which water droplets adhere to the surface of the water-repellent substrate in the first embodiment. FIG. 4 is a diagram illustrating a relationship between a contact area ratio and a contact angle with water according to the first embodiment. FIG. 4 is a model diagram showing a relationship between the concavo-convex structure of the alumite layer and drainage of generated condensed water in the first embodiment. FIG. 3 is a diagram showing a step of covering an alumite layer formed on an aluminum substrate with a water-repellent film in the first embodiment. FIG. 4 is a model diagram showing a method for calculating a dynamic θ difference indicating the sliding property of a water droplet attached to the surface of a water-repellent substrate in the first embodiment. FIG. 5 is a cross-sectional view of a main part showing behavior of water droplets attached to the surface of the water-repellent substrate in the first embodiment. FIG. 5 is an enlarged cross-sectional view of a principal part showing a method for observing an image of the concavo-convex structure of the alumite layer of Example 1 in Experimental Example 1. FIG. 13 is a tilt observation image obtained by a scanning electron microscope viewed from the direction of arrow XIV in FIG. 12, showing the surface shape of the concave-convex structure of Example 1 in Experimental Example 1. 13 is a cross-sectional observation image of the XIV-XIV cross section of FIG. 12 by a transmission electron microscope, showing a cross-sectional shape of the concavo-convex structure of Example 1 in Experimental Example 1. FIG. 7 is an enlarged cross-sectional view of a principal part showing a method for observing an image of a concave-convex structure of a boehmite layer in Comparative Example 1 in Experimental Example 1. FIG. 16 is a surface observation image by a scanning electron microscope viewed from the direction of arrow XVI in FIG. 15, showing the surface shape of the uneven structure of Comparative Example 1 in Experimental Example 1. FIG. 16 is a cross-sectional observation image of the XVII-XVII cross section of FIG. 15 by a transmission electron microscope, showing a cross-sectional shape of the concavo-convex structure of Comparative Example 1 in Experimental Example 1. The figure which shows the relationship between Rzjis cut rate and contact area rate in Experimental example 1. The figure which shows the relationship between the condensed water test frequency and the maximum condensed water droplet diameter in Experimental example 2. FIG. 9 is a cross-sectional view of a principal part showing the behavior of water droplets attached to the surface of the water-repellent substrate of Comparative Example 1 in Experimental Example 2. Surface observation by a scanning electron microscope showing the change of the maximum condensed water droplet diameter on the surface of the water-repellent substrates of Example 1 and Comparative Examples 1 and 2 in Experimental Example 2 after performing the condensed water test once to three times. image. FIG. 9 is a diagram showing a relationship between the number of carbon atoms of an alkyl group and a dynamic θ difference in Experimental Example 3. The figure which shows the relationship between C molar ratio which is the molar ratio of the main agent which comprises a water-repellent film in Experiment 3, and a dynamic (theta) difference.

(Embodiment 1)
Next, an embodiment of a water-repellent substrate will be described with reference to the drawings. The water-repellent substrate of the present embodiment can be used, for example, as a fin material for a heat exchanger, and is applied to an outdoor unit or the like of a vehicle-mounted heat pump system to prevent frost formation in a low-temperature and high-humidity environment. As shown in FIG. 1, a water-repellent substrate 1 is a plate-shaped aluminum substrate 2, an alumite layer 3 formed on a surface of the aluminum substrate 2, and a water-repellent film formed on a surface of the alumite layer 3. And 4. The aluminum base 2 is made of aluminum or an aluminum alloy.

  The alumite layer 3 forms a surface layer of the aluminum base 2 and includes a base layer 31 integrated with the aluminum base 2 and a large number of pin-like projections 32. The numerous pin-like projections 32 project from the surface of the base layer 31 in the thickness direction X of the aluminum base material 2 in a substantially parallel manner. The air layer 11 is formed between the adjacent pin-shaped projections 32. As shown in FIG. 2, the alumite layer 3 has a predetermined concavo-convex structure 33 composed of a base layer 31 and a large number of pin-like projections 32 juxtaposed on the surface of the base layer 31.

  The water-repellent film 4 is made of a hydrocarbon-based water-repellent material, and forms the outermost layer of the aluminum substrate 2. The water-repellent film 4 covers the surface of the base layer 31 of the alumite layer 3 and the surfaces of the numerous pin-like projections 32, and covers the entire surface of the uneven structure 33. As shown in FIG. 3, the water-repellent film 4 specifically includes a main agent 41 made of a metal alkoxide having an alkyl group 43 and a cross-linking agent 42 made of an organic silane, and is a hydrocarbon-based water-repellent containing no fluorine. It is configured using materials. Such a hydrocarbon-based water-repellent material becomes an organic-inorganic hybrid film having a three-dimensional matrix structure by co-hydrolysis and dehydration condensation of a metal alkoxide and an organic silane.

The water-repellent film 4 exhibits water repellency by arranging a large number of hydrophobic alkyl groups 43 on the outermost surface of the organic-inorganic hybrid film, and promotes discharge of condensed water. The molecular length of the main agent 41 affects the molecular mobility of the alkyl group 43, and the molecular interval d is determined according to the molar ratio between the main agent 41 and the crosslinking agent 42, and the distance between the length of the alkyl group 43 and the adjacent alkyl group 43. Is equivalent to For example, FIG. 3 illustrates a structure in which the ratio of the main agent 41 to the crosslinking agent 42 is 1: 3 and the ratio of the main agent 41 is 25 mol%.
Hereinafter, the detailed structure of the water-repellent substrate 1 will be described in detail.

  In FIG. 2, the width W of the pin-shaped protrusion 32, the height H of the pin-shaped protrusion 32, and the protrusion interval D between the adjacent pin-shaped protrusions 32 determine the uneven structure 33 in the alumite layer 3. At this time, the height H of each pin-shaped protrusion 32 represents the depth of the concavo-convex structure 33, and is controlled by the film thickness of the alumite layer 3 and the etching depth. The width W and the projection interval D represent the size of the concavo-convex structure 33, and the projection interval D corresponds to the width of the air layer 11 between the pin-shaped projections 32. Since the pin-like projections 32 are regularly arranged, and the air layer 11 is uniformly formed in the depth direction between the pin-like projections 32, the condensed water generated in the air layer 11 is appropriately discharged, and the water repellency is maintained well. Is done.

  In the alumite layer 3, the smaller the width W of the pin-shaped projections 32 with respect to the repetition period of the concavo-convex structure 33, the smaller the contact area with water droplets generated by condensation of water and the higher the water repellency. Therefore, the smaller the area ratio of the pin-shaped projections 32 on the outermost surface of the uneven structure 33, the better the alumite layer 3 is. Therefore, the contact area ratio on the surface of the alumite layer 3 is defined as follows. That is, the ten-point average roughness of the concavo-convex structure 33 is Rzjis, and the cut rate of the height from the maximum height position, which is the outermost surface of the concavo-convex structure 33, in the depth direction is Rzjis cut rate. At this time, a virtual cut surface is set to a height at which the Rzjis cut rate becomes 20% from the maximum height, and a contact area per unit area of the pin-shaped projection 32 on the virtual cut surface is defined as a contact area ratio. The ten-point average roughness Rzjis is a surface roughness measured according to JIS B0601-2001.

Specifically, as shown in FIG. 4, the alumite layer 3 is cut at a height of 20% Rzjis cut rate from the outermost surface of the concavo-convex structure 33 in a virtual cutting plane parallel to the plate surface of the aluminum base material 2. Then, a predetermined measurement area A is set. Then, from the total area of the pin-shaped protrusions 32 appearing in the measurement area A, the contact area ratio at an Rzjis cut rate of 20% can be calculated using the following equation 1.
Formula 1: Contact area ratio = [total area of pin-shaped projections 32 in measurement area A (unit: μm ² )] / [area of measurement area A (unit: μm ² )]
By configuring the contact area ratio to be 0.01 or less, preferably 0.005 or less, super-water repellency can be exhibited by combination with the water-repellent film 4 which is the outermost layer. .
The relationship between the contact area ratio and the super water repellency will be described later.

The alumite layer 3 is a layer made of porous aluminum oxide (that is, Al ₂ O ₃ ) formed by performing a surface treatment on the aluminum substrate 2. As shown in FIG. 5, the alumite layer 3 is formed by an anodizing process step S1 and an etching process step S2. As shown in the left diagram of FIG. 5, the alumite generated by the alumite treatment has a hexagonal cell structure having pores 34, and grows from the surface of the aluminum substrate 2 in the thickness direction X thereof. As shown in the middle diagram of FIG. 5, the pores 34 of the alumite are etched to be gradually expanded, and as shown in the right diagram of FIG. Becomes At this time, the many pin-shaped projections 32 are located at the apexes of the hexagonal cells of alumite, and a regular uneven structure 33 is formed.

Specifically, in the alumite treatment step S1, the surface of the aluminum substrate 2 is washed with an acid in advance, and then anodized by applying a voltage in a phosphoric acid bath. Thus, an alumite layer having a hexagonal cell structure is formed on the entire surface. As the acid cleaning agent, for example, nitric acid is used. In anodic oxidation, an alumite film forming reaction represented by the following reaction formula proceeds, and pores 34 are formed in many hexagonal cells along their axis.
[Alumite film formation reaction formula]
_{Anode: 2Al + 3H 2 O → Al} 2 O 3 + 6H + + 6e -
・ Cathode: 2H ⁺ + 2e ⁻ → H ₂ ↑

  In the etching step S2, the alumite layer formed in the alumite processing step is etched in a phosphoric acid bath. As a result, the pores 34 are etched from the inside, the pores 34 are expanded, and the walls defining adjacent hexagonal cells are thinned. As described above, when the thin wall portion of the alumite layer is removed by repeating the alumite-forming and etching, the nano-order pin-shaped protrusions 32 are arranged at the apexes of the hexagonal cells, and the irregularities of the nano-pin structure are formed. It is formed.

  As shown in FIG. 6, the water-repellent substrate 1 exhibits super-water-repellency due to the uneven structure 33 of the alumite layer 3 and the water-repellent film 4 on the surface. Condensed water generated by condensation of water on the surface of the water-repellent substrate 1 is extruded to the outermost surface by the outermost water-repellent film 4 to become water droplets 5. At this time, the air layer 11 is formed between the adjacent pin-shaped projections 32, and the water droplets 5 are applied to the pin-shaped projections 32 covered with the water-repellent film 4 on the outermost surface of the uneven structure 33 of the alumite layer 3. Are supported in point contact with Generally, when the surface of the water-repellent substrate 1 is in a super-water-repellent state, a contact angle θ with respect to water, which is an angle formed between the surface of the water-repellent substrate 1 and the surface of the water droplet 5, is 150 ° or more, and the water droplet 5 For example, it is possible to slide down from the surface by an external force such as its own weight or blowing.

When the water-repellent substrate 1 has irregularities on its surface, the contact angle θ with respect to water can be obtained by the following equation 2.
Equation 2: cos θ = [A1 / (A1 + A2)] cos θ1 + [A2 / (A1 + A2)] cos θ2
In the formula, A1: the contact area of the water-repellent film 4 with the water droplet 5, A2: the contact area of the air layer 11 with the water droplet 5, θ1: the contact angle of water on the surface of the water-repellent film 4 with no unevenness, θ2: the air layer 11 Since the alumite layer 3 has a regular uneven structure 33 in which the pin-like projections 32 are juxtaposed, A 1 and A 2 are substantially constant, and the water repellency of the surface of the water repellent substrate 1 is uniform. Further, since θ1 and θ2 are constants, for example, θ2 = 180 ° (that is, cos θ2 = −1), a highly water-repellent material is used for the water-repellent film 4 as the outermost layer, and the area of A1 with respect to A2 The smaller the ratio, the larger the water contact angle θ.
At this time, as shown in Expression 3, the coefficient of the first term of Expression 2 is the contact area ratio of the water-repellent substrate 1 and the contact area ratio of the water-repellent film 4 in contact with the water droplet 5 on the outermost surface. is there.
Formula 3: Contact area ratio of water-repellent substrate 1 = A1 / (A1 + A2)
This contact area ratio has a correlation with the above-mentioned contact area ratio of the concavo-convex structure 33 of the alumite layer 3, and the smaller the contact area ratio of the Rzjis cut ratio of 20%, the smaller the contact area ratio of the water-repellent substrate 1.

Then, based on these formulas 2 and 3, the conditions having super water repellency were studied.
Assuming that the contact angle of water with respect to the surface of the hydrocarbon-based water-repellent coating 4 having no irregularities is θ1 = 90 °, as shown in FIG. becomes large, and theoretically, the contact angle θ with respect to water becomes 150 ° or more when the contact area ratio is 0.13 or less. That is, when the pin-shaped projections 32 are arranged at regular intervals, it is preferable that the width W of the pin-shaped projections 32 in contact with the water droplets 5 be smaller and the projection interval D be larger. The contact area of the coating 4 becomes smaller. Specifically, when the contact area ratio of the above-described Rzjis cut rate of 20% is 0.01 or less, the water contact angle θ is set to 150 by combination with the water-repellent film 4 made of a hydrocarbon-based water-repellent material. ° can be larger.

Further, as shown in FIG. 8, a simulation using a model diagram of the concavo-convex structure 33 of the alumite layer 3 has revealed the conditions under which the condensed water 51 is drained well.
In the left diagram of FIG. 8, when the opposing walls corresponding to the pin-shaped projections 32 are arranged at a uniform interval in the depth direction from the surface, with respect to the concave portions 12 forming the air layer 11 between the opposing walls, The width w of the air layer 11 generated by the condensed water 51 (that is, equivalent to the protrusion interval D) affects the discharge performance. For example, when the lengths Lx and Ly of one side of the cube including the concave portion 12 having a height h are in a relationship of Lx = Ly = 2h, and are changed in the range of h: w = 20: 2 to 13, FIG. 8 As shown in the right diagram, there is a width w (for example, w2 = 6) from which the condensed water 51 is discharged without causing clogging or stagnation. If the width w is smaller than this, the condensed water 51 is clogged (for example, w1 = 3), and if the width w is larger than this, the condensed water 51 stays (for example, w3 = 11).

  Based on the simulation result, based on the test result of examining the sliding property of the condensed water using the test piece in which the protrusion interval D of the concave-convex structure 33 is changed, it is preferable that the protrusion interval D is D = 75 nm to 100 nm. It has been confirmed that high water repellency can be obtained. Further, the width W and the height H of the pin-shaped protrusion 32 are preferably W = 20 nm or less and H = 200 nm to 600 nm. The irregular structure 33 of the alumite layer 3 can be formed to have a desired projection interval D, width W, and height H by adjusting the conditions of the alumite treatment for forming the alumite layer 3 and the etching treatment. .

  The material of the water-repellent film 4 as the outermost layer of the water-repellent substrate 1 determines θ1 in the above equation (2). More specifically, an organic-inorganic hybrid film composed of a hydrocarbon-based water-repellent material has a hydrophobic alkyl group 43 on the outermost surface serving as a free end surface, and undergoes molecular motion by thermal energy to form water droplets. Move 5 and slide down. The main agent 41 of the hydrocarbon-based water-repellent material is a metal alkoxide having an alkyl group 43 in a side chain, preferably an alkylalkoxysilane having a siloxane bond (that is, a Si—O—Si bond) in the main chain. Can be In addition, tetraethoxysilane (hereinafter, referred to as TEOS) can be used as the organic silane serving as the crosslinking agent 42. Such a film has the second highest water repellency next to a film made of a fluorine-based water-repellent material, and acts in the direction of increasing the contact angle θ with respect to water in the above equation (2).

  The water repellency of the water repellent film 4 is affected by the molecular length and the molecular interval d of the main agent 41 located on the outermost surface. For example, when the molecular length of the main agent 41 is short and the molecular interval d is wide, the alkyl group 43 is easy to move and the water droplet 5 is easy to move. The water droplet 5 is easily hydrogen-bonded to the hydroxyl group contained in the crosslinking agent 42. For this purpose, the number of carbon atoms of the alkyl group 43 that determines the molecular length of the main agent 41 and the mixing ratio of the crosslinking agent 42 may be appropriately set so as to obtain a desired sliding property.

  For example, the alkyl group 43 included in the main agent 41 is preferably a chain alkyl group having 3 to 18 carbon atoms (that is, C3 to C18). Preferably, the alkyl group 43 is a chain alkyl group having a molecular length of 5 to 11 carbon atoms (that is, C5 to C11). The main agent 41 having the C3 to C18 alkyl group 43 is a liquid at room temperature, and the adjustment of the coating liquid for immersing the aluminum base material 2 is facilitated. When the carbon number of the alkyl group 43 is in the range of C5 to C11, the dynamic θ difference indicating the adhesive force of the water droplet 5 is reduced to 0.01 or less, and the sliding property of the water droplet 5 is improved, which is more preferable.

  As the main agent 41, specifically, trimethoxypropylsilane (ie, C3), hexyltrimethoxysilane (ie, C6), octyltriethoxysilane (ie, C8), decyltrimethoxysilane (ie, C10) ), Dodecyltriethoxysilane (ie, C12), octadecyltriethoxysilane (ie, C18).

  The water-repellent film 4 is formed by immersing the aluminum base material 2 on which the alumite layer 3 of the uneven structure 33 is formed in a coating solution in which the main agent 41 and the crosslinking agent 42 are dissolved in a solvent. Specifically, as shown in FIG. 9, a preparation step S11 for preparing a coating liquid, a dehydration step S12 for removing moisture in the coating liquid, and a dipping step S13 for dipping the aluminum base material 2 in the coating liquid, After a washing step S14 for washing the coated aluminum substrate 2 and a firing step S15 for firing the aluminum substrate 2, the surface of the uneven structure 33 of the alumite layer 3 is covered with the water-repellent film 4.

  In the preparation step S11, when preparing the coating liquid, the mixing ratio between the alkylalkoxysilane serving as the main agent 41 and the TEOS serving as the cross-linking agent 42 is set, for example, so as to have a desired molecular interval d. For example, a molar ratio of the main agent 41: crosslinking agent 42 = 5 to 15:95 to 85 is preferable because the dynamic θ difference indicating the adhesive force of the water droplet 5 becomes small, and the sliding property of the water droplet 5 increases. More preferably, the ratio of the main agent 41 to the crosslinking agent 42 is 7 to 13: 93 to 87 (that is, the molar ratio of the main agent 41 is 7 to 13 mol%).

Here, a description will be given of a dynamic θ difference that indicates the sliding property of a water droplet, which is an index of the water repellency of the water repellent film 4. As shown in FIG. 10, for example, the adhesive force F of the water droplet 5 attached to the vertical wall W is expressed by the following Expression 4, and the smaller the adhesive force F with respect to the gravity mg, the more easily it slides down.
Formula 4: F = kwγ (cos θR−cos θA)
In the formula, k: coefficient, w: contact width, γ: surface tension, cos θA: advancing contact angle, cos θ R: receding contact angle From Equation 4, from the equation 4, the advancing contact angle cos θA on the side where gravity mg acts and the receding contact on the opposite side. The smaller the dynamic θ difference (ie, cos θR−cos θA), which is the difference from the angle cos θR, the smaller the adhesive force F, and the easier it is to slide down. At this time, the condensed water that grows is desirably smaller than the fin interval, for example, so as not to block the passage between the fins for the heat exchanger. Preferably, the water droplet diameter is not more than half the size of the fin interval (for example, 0.7 mm). For example, when the dynamic θ difference is 0.01 or less, the water droplet diameter is smaller than 0.7 mm. It will be small enough.

  As a solvent for preparing the coating liquid, for example, ethanol can be used. Further, the total content of the main agent 41 and the crosslinking agent 42 with respect to the solvent is preferably set to 40 to 60% by mass. A predetermined concentration of hydrochloric acid is mixed into the coating liquid as a catalyst for crosslinking and polymerizing the main agent 41 and the crosslinking agent 42. At this time, in order to prevent a large amount of water contained in the coating liquid from being taken into the water-repellent film 4, a dehydration step S12 of adding a hydrocarbon solvent after adding hydrochloric acid to remove water is provided. Good.

  In the immersion step S13, the aluminum substrate 2 is immersed in the dehydrated coating liquid, applied to the entire surface of the uneven structure 33, and then rinsed in the cleaning step S14 to remove excess coating liquid. After that, in the firing step S15, by firing at a predetermined temperature, the water-repellent film 4 containing no water is obtained, and the water repellency is further improved.

  As shown in FIG. 11, the water-repellent substrate 1 obtained in this manner has an alumite layer 3 having a fine concavo-convex structure 33 formed on a surface layer of an aluminum substrate 2, and is regularly formed with the base layer 31. The entire surface of the concavo-convex structure 33 composed of the pin-like projections 32 arranged in parallel is covered with a water-repellent film 4 made of a hydrocarbon-based water-repellent material, thereby forming a super water-repellent film. Therefore, when condensed water 51 is generated between the pin-shaped protrusions 32 arranged at a predetermined protrusion interval D in a low-temperature and high-humidity environment (for example, see FIG. 11A), the water-repellent substrate 1 Is pushed out of the air layer 11 to the outermost surface by the effect of the shape of the water droplet 5 to generate a water droplet 5 (for example, see FIG. 11B). On the outermost surface, the water droplet 5 becomes a super water repellent state by the effect of the contact area ratio of the concavo-convex structure 33 and the composition of the water repellent film 4, and the dynamic θ difference indicating the sliding property of the water droplet of the formula 4 is reduced. Easily slide down (for example, see FIG. 11C). Next, water drops 5 are generated again in the same manner (see, for example, FIG. 11D), and sliding down is repeated.

  At this time, in the alumite layer 3 formed by anodizing and etching, the water-repellent film 4 is uniformly formed inside the uneven structure 33, particularly, up to the surface near the base layer 31, so that even if condensed water is repeatedly generated, Does not remain inside. Therefore, even if a relatively inexpensive hydrocarbon-based water-repellent material is used, sufficiently high water-repellency can be obtained, and good dischargeability and slipperiness from the concavo-convex structure 33 can be maintained for a long period of time to prevent a decrease in water-repellency I do. Accordingly, the water-repellent substrate 1 is used as a heat exchanger fin or the like, has both super water repellency and high productivity, prevents frost formation, and improves operation efficiency.

  Next, with respect to the water-repellent substrate 1 of the present embodiment, the water-repellent performance of the uneven structure 33 of the alumite layer 3 and the water-repellent film 4 was evaluated. For comparison, the same evaluation was performed for an example in which a boehmite layer was formed by a conventional boehmite treatment. These experimental examples will be described.

(Experimental example 1)
By the method shown in FIG. 5 described above, the alumite treatment step S1 and the etching treatment step S2 are sequentially performed to form an alumite layer 3 composed of a base layer 31 and a number of pin-shaped projections 32 on the surface of the aluminum base material 2. did. As the aluminum substrate 2, an Al-Mg-Si-based aluminum alloy (for example, BA4104) used for a fin material for a heat exchanger was used. First, in the alumite treatment step S1, the surface of the aluminum substrate 2 was acid-cleaned. Nitric acid (for example, a concentration of 67% by mass) was used as an acid cleaning agent, and immersion treatment was performed at room temperature for 1 minute. Thereafter, by applying a voltage in a phosphoric acid bath and performing anodization, an alumite layer 3 having a hexagonal cell structure was formed on the entire surface of the aluminum substrate 2. Anodizing was performed under the following conditions.
[anodization]
・ Drug: phosphoric acid, concentration 2% by mass
・ Voltage: 50V
・ Time: 50 seconds

The surface of the anodized aluminum substrate 2 was rinsed with pure water, and then etched in a phosphoric acid bath in an etching step S2 to expand the pores 33 of the alumite layer 3. The etching process was performed under the following conditions.
[etching]
・ Drug: phosphoric acid, concentration 2% by mass
・ Temperature: 40 ° C
Time: 10 minutes The alumite and etching were repeatedly performed to form the alumite layer 3 having the uneven structure 33 on the surface of the aluminum substrate 2 (that is, Example 1).

  With respect to the alumite layer 3 of Example 1, as shown in FIG. 12, an image observation of the surface shape and the cross-sectional structure of the obtained concavo-convex structure 33 was performed. As shown in FIG. 13, in the image obtained by obliquely observing the uneven structure of the surface of the alumite layer 3 using a scanning electron microscope (hereinafter, referred to as SEM), a structure in which many pin-like projections 32 are regularly arranged. Was confirmed. Further, as shown in FIG. 14, in an image obtained by observing the cross-sectional structure of the alumite layer 3 using a transmission electron microscope (hereinafter, referred to as a TEM), the width W, the height H, and the interval D was measured. As a result, W = 8 nm, H = 600 nm, and D = 100 nm, and the concavo-convex structure 33 having a desired height and a width W sufficiently smaller than the protrusion interval D was obtained.

  For comparison, a boehmite layer 61 made of aluminum oxide was formed on the surface of the aluminum substrate 2 by a conventional boehmite-forming process, and the uneven structure 63 was similarly evaluated (Comparative Example 1). The boehmite treatment was performed by immersing the aluminum substrate 2 in water at a temperature in the range of 80C to 100C for about 5 minutes.

  As for the boehmite layer 61 of Comparative Example 1, as shown in FIG. 15, an image observation of the surface shape and the sectional structure of the obtained concavo-convex structure 63 was performed. As shown in FIG. 16, in the image obtained by observing the uneven structure 63 on the surface of the boehmite layer 61 using an SEM, a structure having a large number of needle-like projections 62 was confirmed. Further, as shown in FIG. 17, in an image obtained by observing the cross-sectional structure of the boehmite layer 61 using a TEM, a large number of needle-like projections 62 have an uneven structure 63 extending in an irregular direction. It has been found that the lower layer 611 on the second side has a constriction structure in which the width of the needle-like projections 62 is smaller than that of the upper layer 612 on the front side.

  Further, as Comparative Example 2, by forming the alumite layer 3 on the surface of the aluminum base material 2 in the same manner as in Example 1, and reducing the number of times of the alumite treatment and the etching treatment, the irregularities having different contact area ratios were obtained. Structure 33 was adopted. When the cross-sectional structure of the alumite layer 3 of Comparative Example 2 was observed using a TEM in the same manner as in Example 1, it was confirmed that the cross-sectional structure was a concavo-convex structure 33 in which the pin-like projections 32 were juxtaposed. However, while the projection interval D of the pin-like projections 32 is around 100 nm, the width W is wide, around 40 nm, and the height H is lower than 400 nm.

  For these Example 1 and Comparative Examples 1 and 2, the contact area ratio at an Rzjis cut rate of 10% to 50% was measured by the method shown in FIG. First, with respect to the alumite layer 3 of Example 1, a three-dimensional uneven image was obtained by scanning the surface of the uneven structure 33 using a scanning probe microscope (hereinafter, referred to as SPM). The ten-point average roughness Rzjis is calculated based on the obtained three-dimensional unevenness image, and the contact of the pin-shaped projection 32 in the measurement area A at each virtual cut surface with the Rzjis cut rate of 10% to 50% from the maximum height. The area ratio was calculated. Similarly, for Comparative Examples 1 and 2, the contact area ratio at an Rzjis cut ratio of 10% to 50% was measured.

  As shown in FIG. 18, in the entire range of the Rzjis cut ratio of 10% to 50%, the contact area ratio of Example 1 was the smallest, and the Rzjis cut ratio of 20% was 0.002. . In both Example 1 and Comparative Examples 1 and 2, the contact area ratio was the smallest at an Rzjis cut rate of 10%, and the contact area rate increased with an increase in the Rzjis cut rate. The increase in the area ratio is relatively slow compared to Comparative Examples 1 and 2. Therefore, at the Rzjis cut rate of 10%, the contact area ratio is 0.01 or less in both the example 1 and the comparative examples 1 and 2. However, at the Rzjis cut rate of 20% and 30%, only the example 1 has the contact area rate. The area ratio is 0.01 or less.

  As described above, in Comparative Examples 1 and 2, the contact area ratio is large as a whole. In particular, the concavo-convex structure 63 of the boehmite layer 61 of Comparative Example 1 is slightly smaller than that of Comparative Example 2 at an Rzjis cut ratio of 10%, but reversed at an Rzjis cut ratio of 20%. This is thought to be due to the unevenness in the height of the uneven structures 33 and 63, and the pin-like projections 32 and the needle-like projections 62 that do not appear in the measurement area A when the Rzjis cut rate is 10%. In the boehmite layer 61 of Comparative Example 1, since the width of the needle-like protrusions 62 of the upper layer 612 is larger and irregular, it is considered that the contact area ratio increases after the Rzjis cut rate of 20% or more.

(Experimental example 2)
On the aluminum base material 2 of Example 1 obtained in Experimental Example 1, a water-repellent coating 4 for covering the uneven structure 33 of the alumite layer 3 was further formed in the step shown in FIG. First, in the preparation step S11, as shown below, ethanol was used as a solvent, octylalkoxysilane having C8 carbon atoms and TEOS as a crosslinking agent 42 were added as the main agent 41, and the mixture was stirred for 30 minutes (ie, S111). Furthermore, 0.05 mol / L hydrochloric acid was added as a catalyst, and the mixture was stirred for 30 minutes to cause a cross-linking reaction between the main agent 41 and the cross-linking agent 42 to gel (ie, S112).
Solvent: ethanol (for example, manufactured by Wako Pure Chemical Industries, Ltd.)
Main agent 41: octyltriethoxysilane (for example, L04407; manufactured by Johnson Matthey Japan GK, trade name)
Crosslinking agent 42: TEOS (for example, KBE-04; manufactured by Shin-Etsu Chemical Co., Ltd., trade name)
Catalyst: hydrochloric acid 0.05 mol / L (for example, manufactured by Wako Pure Chemical Industries, Ltd.)

  The molar ratio between the main agent 41 and the crosslinking agent 42 was octylalkoxysilane: TEOS = 10: 90 (that is, the molar ratio of the main agent 41 was 10%). The gel concentration, which is the ratio of the mass of the main agent 41 and the mass of the crosslinking agent 42 to the total mass including the solvent and the catalyst, was 50% by mass.

  Next, in the dehydration step S12, a hydrocarbon-based cleaning agent (trade name: NS Clean, manufactured by JX Nippon Oil & Energy) was added, stirred for 30 minutes, and allowed to stand for 10 minutes (ie, S121). Thereafter, the supernatant was extracted and water was separated, and the obtained extract was used as a coating liquid (that is, S122). In the immersion step S13, the aluminum substrate 2 of Example 1 was immersed in the obtained coating liquid for 30 minutes. Further, in the cleaning step S14, the aluminum substrate 2 was cleaned for 1 minute using a hydrocarbon-based cleaning agent. Thereafter, in a firing step S15, the water-repellent substrate 1 in which the surface of the alumite layer 3 was coated with the water-repellent film 4 was obtained by firing at 150 ° C. for 30 minutes.

  With respect to the water-repellent substrate 1 of Example 1 thus obtained, the sliding property of the water droplet 5 was evaluated by the dynamic θ difference shown in FIG. For the measurement of the dynamic θ difference, a contact angle measuring device using an expansion-shrinkage method (that is, DM-501, manufactured by Kyowa Interface Science Co., Ltd.) was used. As a result, the dynamic θ difference was 0.0003, and it was confirmed that the sample had a sliding property of 0.001 or less, which is the value obtained in Comparative Example 1.

  Further, a condensed water test was performed on the water-repellent substrate 1 of Example 1 by repeating dry and wet to measure the maximum condensed water diameter. In the condensed water test, the test piece of the water-repellent substrate 1 is cooled to 0 ° C. or less (for example, −5 ° C. or less), placed in a high-humidity constant temperature and humidity chamber, and blown to the surface of the test piece (for example, , Wind speed 1 m / sec), and condensed water generated on the surface was observed for 60 minutes using a CCD camera. At this time, the maximum diameter of the condensed water generated was measured, and then the test piece was cooled again, and observation of the condensed water on the surface was repeatedly performed.

  For comparison, a fluorine-based water-repellent film made of a fluorine-based water-repellent material was formed on the surface of the boehmite layer 61 for the aluminum substrate 2 of Comparative Example 1. The fluorine-based water-repellent film is immersed in a coating liquid prepared in the same manner using a water-repellent material (OPTOOL DSX; manufactured by Daikin Industries, Ltd., trade name) mainly containing a silane compound containing perfluoropolyether. , And formed by firing. Further, with respect to the aluminum substrate 2 of Comparative Example 2, a hydrocarbon-based water-repellent film 4 similar to that of Example 1 was formed on the surface of the uneven structure 33 of the alumite layer 3. For Comparative Examples 1 and 2, test pieces of the obtained water-repellent substrate were produced, and a condensed water test was performed in the same manner.

  As shown in FIG. 19, the water-repellent substrate 1 of Example 1 had a maximum condensed water droplet diameter of 0.4 mm after one condensed water test, and even after three condensed water tests, 0.7 mm or less required for the fin material was satisfied. In contrast, in Comparative Example 1 in which a fluorine-based water-repellent film was formed on the boehmite layer 61, the maximum condensed water droplet diameter after one dry / wet repetition test was equal to that in Example 1, but the condensed water test was repeated. As a result, the condensed water diameter increased, and the maximum condensed water droplet diameter after three times of the condensed water test increased to around 2.0 mm.

  As shown in FIG. 20, the boehmite layer 61 of Comparative Example 1 has a film made of a fluorine-based water-repellent material because the needle-like projections 62 constituting the concavo-convex structure 63 have constrictions in the lower layer 611. It is difficult to cover the entire surface of the concavo-convex structure 63. Therefore, when condensed water 51 is generated between the needle-like projections 62 in a low-temperature and high-humidity environment (see, for example, FIG. 20E), the outermost surface is initially formed by the effect of the uneven structure 63 and the fluorine-based water-repellent film. The water droplets 5 are extruded onto the surface to form (for example, see FIG. 20 (f)) and slide down easily (for example, see FIG. 20 (g)). However, by repeating this, it is considered that the condensed water remains inside the uneven structure 63 (for example, see FIG. 20 (h)), and the water repellency decreases.

  In Comparative Example 2 in which the hydrocarbon-based water-repellent coating 4 was formed on the alumite layer 3 having a large contact area ratio, the maximum condensed water droplet diameter after one condensed water test exceeded 1.0 mm, and three times. The subsequent maximum condensed water droplet diameter increased to about 1.5 mm. As shown in comparison with FIG. 21, when the condensed water test is repeated three times, the diameter of the condensed water generated on the surface of the water-repellent substrate 1 of Example 1 is smaller than that of Comparative Example 1, and the number of tests is one. It does not change much even if it increases up to 3 times. On the other hand, in Comparative Example 1, the diameter of the condensed water was increased by repeating the condensed water test, and the water repellency was reduced.

(Experimental example 3)
A water-repellent coating 4 was formed on the aluminum base material 2 of Example 1 obtained in Experimental Example 1 in the same manner as in Experimental Example 2. At this time, in the preparation step S11, as the main agent 41 of the water-repellent film 4, alkylalkoxysilanes having different numbers of carbon atoms were used as shown below.
Carbon number C3: trimethoxypropylsilane (for example, B21033; manufactured by Johnson Matthey Japan GK, trade name)
Carbon number C6: hexyltrimethoxysilane (for example, KBM-3063; manufactured by Shin-Etsu Chemical Co., Ltd., trade name)
Carbon number C8: octyltriethoxysilane (for example, L04407; manufactured by Johnson Matthey Japan GK, trade name)
Carbon number C10: decyltrimethoxysilane (for example, KBM-3103; manufactured by Shin-Etsu Chemical Co., Ltd., trade name)
Carbon number C12: dodecyltriethoxysilane (for example, D3383; trade name, manufactured by Tokyo Chemical Industry Co., Ltd.)
Carbon number C18: octadecyltriethoxysilane (for example, S12325; trade name, manufactured by Wako Pure Chemical Industries, Ltd.)

  The aluminum substrate 2 of Example 1 was immersed in a coating liquid prepared in the same manner as in Experimental Example 2 and baked to obtain a water-repellent substrate 1 on which water-repellent films 4 having different carbon numbers were formed. With respect to the obtained water-repellent substrate, the dynamic θ difference was measured using the contact angle measuring device described above, and the sliding property of the water droplet 5 was evaluated.

  For comparison, in the method shown in FIG. 9 above, the aluminum substrate 2 of Example 1 was subjected to the same steps (that is, the steps shown on the left side in the drawing) except that the dehydration step S12 and the washing step S14 were omitted. A water-repellent film 4 was formed on the substrate to obtain a water-repellent substrate of Comparative Example 3. At this time, the above-mentioned alkylalkoxysilane having 6 to 18 carbon atoms was used as the main agent 41 of the water-repellent film 4. With respect to the obtained water-repellent substrate, the dynamic θ difference was measured using the contact angle measuring device described above, and the sliding property of the water droplet 5 was evaluated.

  As shown in FIG. 22, in Comparative Example 3 in which dehydration of the prepared coating liquid and cleaning after coating were not performed, the dynamic θ difference of the obtained water-repellent substrate exceeded 0.01. On the other hand, in the water-repellent substrate 1 of Example 1, the dynamic θ difference is smaller than that of Comparative Example 3 using the main agent 41 having the same carbon number. In those, the dynamic θ difference was 0.01 or less.

  Further, with respect to the water-repellent substrate 1 of Example 1, the molar ratio of the main agent 41 and the crosslinking agent 42 constituting the water-repellent film 4 was changed in the range of octylalkoxysilane: TEOS = 5 to 30:95 to 70, Otherwise, the water-repellent substrate 1 was produced in the same manner. With respect to the obtained water-repellent substrate, the dynamic θ difference was measured using the contact angle measuring device described above, and the sliding property of the water droplet 5 was evaluated.

  As shown in FIG. 23, the dynamic θ difference changes depending on the molar ratio of the main agent 41 contained in the water-repellent film 4 (that is, the C molar ratio in the figure). When the C molar ratio is around 10%, the dynamic θ difference becomes the minimum, and the dynamic θ difference tends to increase even if it is smaller or larger than this. Specifically, when the C molar ratio of the main agent 41 is in the range of 7% to 13%, the dynamic θ difference is 0.01 or less.

  The water-repellent substrate 1 of the present invention is not limited to the contents described in the embodiment and the examples, and various modifications can be made without departing from the gist of the present invention. For example, in the above embodiment, the description has been given as an application example to an HP system used for a vehicle air conditioning system. However, as an air conditioning system other than a vehicle, an outdoor unit of an HP system for a water heater, and other fins for a heat exchanger. It is preferably used. Further, it can be arbitrarily used for applications other than the heat exchanger fins.

DESCRIPTION OF SYMBOLS 1 Water-repellent base material 2 Aluminum base material 3 Alumite layer 32 Pin-shaped projection 33 Uneven structure 4 Water-repellent film 43 Alkyl group 5 Condensed water A Virtual cut surface

Claims (7)

An aluminum substrate (2);
An alumite layer (3) provided on the surface of the aluminum substrate;
A water-repellent film (4) provided on the surface of the alumite layer;
The alumite layer has a concavo-convex structure (33) composed of a base layer (31) integral with the aluminum base and a number of pin-like projections (32) arranged in parallel on the surface of the base layer . A structure in which the pin-like projections are arranged at the apexes of the hexagonal cells surrounding the pores by etching the alumite having a hexagonal cell structure having pores (34);
With respect to the ten-point average roughness Rzjis of the concavo-convex structure, the contact area ratio of the pin-like projections is 0 on the virtual cut surface (A) having a height of 20% from the maximum height position of the concavo-convex structure. .01 or less,
The water-repellent film is a film made of a hydrocarbon-based water-repellent material.   The water-repellent substrate according to claim 1, wherein the contact area ratio is 0.005 or less.   The water-repellent substrate according to claim 1 or 2, wherein the hydrocarbon-based water-repellent material includes a main agent (41) composed of a metal alkoxide having an alkyl group (43) and a crosslinking agent (42) composed of an organic silane.   The water-repellent substrate according to claim 3, wherein the metal alkoxide is an alkylalkoxysilane having an alkyl group having 3 to 18 carbon atoms, and the organic silane is a tetraalkoxysilane.   The water-repellent substrate according to claim 3 or 4, wherein the molar ratio of the main agent and the crosslinking agent is 7 to 13:93 to 87. An aluminum substrate (2);
An alumite layer (3) provided on the surface of the aluminum substrate;
A water-repellent film (4) provided on the surface of the alumite layer;
The alumite layer has a concavo-convex structure (33) composed of a base layer (31) integral with the aluminum base and a number of pin-like projections (32) arranged in parallel with the surface of the base layer. The contact area ratio of the pin-like projections is 0.01 or less on the virtual cut surface (A) having a height of 20% Rzjis cut ratio from the maximum height position of the uneven structure with respect to the point average roughness Rzjis. ,
The method for producing a water-repellent substrate (1), wherein the water-repellent film is a film made of a hydrocarbon-based water-repellent material,
Forming the alumite layer having the concavo-convex structure on the surface of the aluminum base by alumite treatment and etching treatment (S1, S2);
Preparing a coating liquid containing the hydrocarbon-based water-repellent material (S11);
A step of adding a hydrocarbon solvent to the coating liquid to separate and remove water (S12);
A step of immersing the aluminum substrate on which the alumite layer is formed in the coating liquid from which water has been removed (S13);
Baking the aluminum substrate to which the coating liquid has been applied (S15).   In the step of forming the alumite layer, the step of anodizing the surface of the aluminum base by anodizing (S1) and the step of etching the aluminum base after the anodization (S2) The method for producing a water-repellent substrate according to claim 6, wherein the method is repeated.