WO2017110200A1

WO2017110200A1 - Water-repellent base material and method for manufacturing same

Info

Publication number: WO2017110200A1
Application number: PCT/JP2016/079505
Authority: WO
Inventors: 康志浅野; 上仁柴田
Original assignee: 株式会社デンソー
Priority date: 2015-12-25
Filing date: 2016-10-04
Publication date: 2017-06-29
Also published as: JP2017115219A; JP6641990B2

Abstract

This water-repellent base material (1) includes an aluminum base material (2), an alumite layer (3) provided on a surface of the aluminum base material, and a water-repellent coating (4) provided on a surface of the alumite layer. The alumite layer has a base layer (31) integrated with the aluminum base material, and a surface relief structure (33) formed from a plurality of pin-like protrusions (32) provided side-by-side on a surface of the base layer. With respect to the ten-point average roughness Ｒ_zjis of the surface relief structure, the contact surface area ratio of the pin-like protrusions is 0.01 or less in a virtual cross section (A) at a height at which the Ｒ_zjis cut ratio is 20% from the position of the maximum height of the surface relief structure, and the water-repellent coating is formed from a hydrocarbon-based water-repellent material.

Description

Water-repellent substrate and method for producing the same

Cross-reference of related applications

This application is based on Patent Application No. 2015-254043 filed on December 25, 2015, the entire contents of which are incorporated herein by reference.

The present disclosure relates to a water-repellent substrate obtained by imparting water repellency to an aluminum substrate and a method for producing the same.

In air conditioning systems such as electric vehicles and plug-in hybrid vehicles, heat pump systems (hereinafter referred to as HP systems) using air as a heat source are used. In the HP system, the refrigerant is compressed to a high temperature and a high pressure by a compressor, then radiated by an evaporator, passes through an expansion valve, becomes a low temperature and a low pressure, and reaches an outdoor unit. At this time, the refrigerant absorbs heat from the outside air to cool the outdoor unit, and when the outside of the vehicle becomes highly humid, condensed water is generated on the surface of the aluminum fin of the outdoor unit. If condensed water is not removed, it will eventually freeze and turn into frost.

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

JP 2013-036733 A

However, it has been found that when a water-repellent substrate by a film method 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, and when the amount of frost increases, the amount of air passing between the fins decreases. Furthermore, since the thermal conductivity to the refrigerant is also reduced, a defrosting operation is required and the operation efficiency is reduced. Moreover, in order to obtain a desired water repellency, it has been necessary to use an expensive fluorine-based water repellent material, and a problem has been found that productivity is lowered.

An object of the present disclosure is to provide a highly productive water-repellent substrate capable of sustaining super-water repellency that removes condensed water generated in a low-temperature and high-humidity environment and prevents frost formation, and a method for producing the same. To do.

One aspect of the present disclosure includes an aluminum substrate;
An alumite layer provided on the surface of the aluminum substrate;
A water-repellent film provided on the surface of the anodized layer,
The anodized layer has a concavo-convex structure composed of a base layer integral with the aluminum base material and a large number of pin-like protrusions juxtaposed on the surface of the base layer, and the ten-point average roughness Rzjis of the concavo-convex structure is as described above. In the virtual cut surface having a height of 20% Rzjis cut rate from the maximum height position of the concavo-convex structure, the contact area rate of the pin-shaped protrusion is 0.01 or less,
The water-repellent film is on a water-repellent substrate, which is a film made of a hydrocarbon-based water-repellent material.

Another aspect of the present disclosure includes an aluminum substrate;
An alumite layer provided on the surface of the aluminum substrate;
A water-repellent film provided on the surface of the anodized layer,
The anodized layer has a concavo-convex structure composed of a base layer integral with the aluminum base material and a large number of pin-like protrusions juxtaposed on the surface of the base layer, and the ten-point average roughness Rzjis of the concavo-convex structure is as described above. In the virtual cut surface having a height of 20% Rzjis cut rate from the maximum height position of the concavo-convex structure, the contact area rate of the pin-shaped protrusion is 0.01 or less,
The water-repellent film is a film made of a hydrocarbon-based water-repellent material, a method for producing a water-repellent substrate,
Forming the alumite layer having the concavo-convex structure on the surface of the aluminum substrate by anodizing and etching; and
Preparing a coating liquid containing the hydrocarbon-based water repellent material;
Adding a hydrocarbon solvent to the coating solution to separate and remove moisture;
A step of immersing the aluminum base material on which the alumite layer is formed in the coating liquid from which moisture has been removed;
And baking the aluminum substrate to which the coating liquid has been applied.

In the water-repellent substrate according to the above aspect, since the anodized layer that is the surface layer of the aluminum substrate has a fine uneven structure with a small contact area ratio, it is super-repellent when combined with a water-repellent film made of a hydrocarbon-based water-repellent material. Aqueous can be expressed. Moreover, since it is a regular concavo-convex structure in which pin-shaped protrusions are juxtaposed and a water-repellent film is not formed, a good water repellency can be obtained on the entire surface. Thereby, the condensed water is pushed out to the surface of the concavo-convex structure, and the generated water droplets can be easily slid down and removed by an external force or the like. Moreover, it is suppressed that condensed water remains inside the concavo-convex structure and the water repellency is gradually lowered. The hydrocarbon-based water-repellent material has the lower surface free energy next to the fluorine-based water-repellent material, contributes to the improvement of water repellency, is cheaper than the fluorine-based water-repellent material, and improves the productivity.

Such a water-repellent substrate is formed by forming a water-repellent film on a concavo-convex structure anodized layer formed by anodizing and etching an aluminum substrate using a coating liquid from which moisture is separated. Is further improved. Therefore, in a low temperature and high humidity environment, a water repellent base material that can be removed by making the generated condensed water into a super water repellent state, maintaining high water repellent performance for a long period of time, and preventing problems due to frost formation can be obtained. .

The above and other objects, features, and advantages of the present disclosure will become more apparent from the following detailed description with reference to the accompanying drawings. The drawing
FIG. 1 is an enlarged cross-sectional view of a main part showing a schematic structure of a water-repellent substrate in Embodiment 1. FIG. 2 is an enlarged perspective view of a main part schematically showing the concavo-convex structure of the alumite layer of the water-repellent substrate in Embodiment 1. FIG. 3 is a schematic diagram showing the water-repellent film molecular structure of the water-repellent substrate in Embodiment 1. FIG. 4 is an enlarged perspective view of a main part of an alumite layer schematically showing a method for measuring a contact area ratio in the first embodiment. FIG. 5 is an enlarged perspective view showing an alumite layer forming step by an anodizing step and an etching step of an aluminum base material in Embodiment 1, FIG. 6 is an enlarged cross-sectional view of a main part showing a state in which water droplets adhere to the surface of the water-repellent substrate in Embodiment 1. FIG. 7 is a diagram illustrating a relationship between a contact area ratio and a water contact angle in the first embodiment. FIG. 8 is a model diagram showing the relationship between the uneven structure of the anodized layer and the discharge of condensed water generated in Embodiment 1. FIG. 9 is a diagram showing a step of coating the alumite layer formed on the aluminum base material with a water-repellent coating in Embodiment 1. FIG. 10 is a model diagram illustrating a method for calculating a dynamic θ difference indicating the sliding property of water droplets attached to the surface of a water-repellent substrate in Embodiment 1. FIG. 11 is a cross-sectional view of a main part showing the behavior of water droplets attached to the surface of the water-repellent substrate in Embodiment 1. FIG. 12 is an enlarged cross-sectional view of a main part showing an image observation method of the uneven structure of the alumite layer of Example 1 in Experimental Example 1, 13 is a tilt observation image by a scanning electron microscope viewed from the XIII arrow direction of FIG. 12, showing the surface shape of the concavo-convex structure of Example 1 in Experimental Example 1. 14 is a cross-sectional observation image by a transmission electron microscope of the XIV-XIV cross section of FIG. 12, showing the cross-sectional shape of the concavo-convex structure of Example 1 in Experimental Example 1. FIG. 15 is an enlarged cross-sectional view of a main part showing an image observation method of the uneven structure of the boehmite layer of Comparative Example 1 in Experimental Example 1, FIG. 16 is a surface observation image by a scanning electron microscope viewed from the XVI arrow direction of FIG. 15, showing the surface shape of the concavo-convex structure of Comparative Example 1 in Experimental Example 1. FIG. 17 is a cross-sectional observation image by a transmission electron microscope of the XVII-XVII cross section of FIG. 15, showing the cross-sectional shape of the concavo-convex structure of Comparative Example 1 in Experimental Example 1. FIG. 18 is a diagram showing the relationship between the Rzjis cut rate and the contact area rate in Experimental Example 1. FIG. 19 is a diagram showing the relationship between the number of condensed water tests and the maximum condensed water droplet diameter in Experimental Example 2. FIG. 20 is a cross-sectional view of the main part showing the behavior of water droplets attached to the surface of the water-repellent substrate of Comparative Example 1 in Experimental Example 2, FIG. 21 is a scanning electron graph showing a change in the maximum condensed water droplet diameter on the surface after performing the condensed water test 1 to 3 times for the water repellent substrates of Example 1 and Comparative Examples 1 and 2 in Experimental Example 2. It is a surface observation image by a microscope, FIG. 22 is a diagram showing the relationship between the carbon number of the alkyl group and the dynamic θ difference in Experimental Example 3, FIG. 23 is a diagram showing the relationship between the C molar ratio, which is the molar ratio of the main agent constituting the water repellent film, and the dynamic θ difference in Experimental Example 3.

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

The anodized 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 protrusions 32. A large number of pin-shaped protrusions 32 protrude substantially parallel to the thickness direction X of the aluminum base 2 from the surface of the base layer 31. An air layer 11 is formed between adjacent pin-shaped protrusions 32. As shown in FIG. 2, the alumite layer 3 has a predetermined concavo-convex structure 33 including a base layer 31 and a large number of pin-like protrusions 32 juxtaposed on the surface of the base layer 31.

The water repellent coating 4 is made of a hydrocarbon-based water repellent material and forms the outermost layer of the aluminum base 2. The water-repellent coating 4 covers the entire surface of the concavo-convex structure 33 by covering the surface of the base layer 31 of the alumite layer 3 and the surfaces of many pin-like protrusions 32. As shown in FIG. 3, the water-repellent coating 4 specifically includes a hydrocarbon-based water-repellent material containing 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 containing no fluorine. Constructed 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 metal alkoxide and organic silane.

The water repellent coating 4 exhibits water repellency and promotes the discharge of condensed water by arranging a large number of hydrophobic alkyl groups 43 on the outermost surface of the organic-inorganic hybrid coating. 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 of the main agent 41 and the crosslinking agent 42, and the distance between the alkyl group 43 and the adjacent alkyl group 43 is determined. It corresponds to. For example, FIG. 3 illustrates a structure in which main agent 41: crosslinking agent 42 = 1: 3, and the ratio of main agent 41 is 25 mol%.
Below, the detailed structure of the water repellent base material 1 is explained in full 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 distance D between adjacent pin-shaped protrusions 32 determine the uneven structure 33 in the alumite layer 3. At this time, the height H of each pin-like protrusion 32 represents the depth of the concavo-convex structure 33 and is controlled by the film thickness and the etching depth of the alumite layer 3. The width W and the protrusion distance D represent the size of the uneven structure 33, and the protrusion distance D corresponds to the width of the air layer 11 between the pin-shaped protrusions 32. The pin-shaped protrusions 32 are regularly arranged, and the air layer 11 is uniformly formed in the depth direction therebetween, so that 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-like protrusion 32 with respect to the repetition period of the concavo-convex structure 33, the smaller the contact area with water droplets produced by condensation of moisture, and the higher the water repellency. Therefore, the alumite layer 3 is better as the area ratio occupied by the pin-like protrusions 32 on the outermost surface of the concavo-convex structure 33 is smaller. 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 that is the outermost surface of the concavo-convex structure 33 to the depth direction is the Rzjis cut rate. At this time, a virtual cut surface is set from the maximum height to a height at which the Rzjis cut rate is 20%, and the contact area per unit area of the pin-like protrusion 32 on the virtual cut surface is defined as the contact area rate. The ten-point average roughness Rzjis is a surface roughness measured according to JIS B0601-2001 (that is, ISO 4287 1997).

Specifically, as shown in FIG. 4, in a virtual cut surface obtained by cutting the alumite layer 3 in parallel with the plate surface of the aluminum base 2 at a height position where the Rzjis cut rate is 20% from the outermost surface of the concavo-convex structure 33. 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 ratio of 20% can be calculated using the following formula 1.
Formula 1: Contact area ratio = [total area of pin-like protrusions 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, and preferably 0.005 or less, super water repellency can be exhibited by a combination with the water repellent coating 4 that is the outermost layer. .
The relationship between the contact area ratio and 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 surface treatment of the aluminum base 2. As shown in FIG. 5, the anodized layer 3 is formed by an anodizing process S1 and an etching process S2. As shown in the left diagram of FIG. 5, the alumite produced by the alumite treatment has a hexagonal cell structure having pores 34 and grows in the thickness direction X from the surface of the aluminum base 2. As shown in the middle diagram of FIG. 5, the alumite pores 34 are etched to gradually increase the diameter, and as shown in the right diagram of FIG. 5, a layer in which a large number of pin-like protrusions 32 are arranged side by side. It becomes. At this time, a large number of pin-like protrusions 32 are positioned at the apexes of the alumite hexagonal cells, and a regular uneven structure 33 is formed.

Specifically, in the anodizing treatment step S1, the surface of the aluminum substrate 2 is previously acid-washed and then anodized by applying a voltage in a phosphoric acid bath. Thereby, 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 the anodic oxidation, an alumite film forming reaction shown in the following reaction formula proceeds, and pores 34 are formed along the axial center in many hexagonal cells.
[Anodizing reaction formula]
Anode: 2Al + 3H ₂ O → Al ₂ O ₃ + 6H ⁺ + 6e ⁻
・ Cathode: 2H ⁺ + 2e ⁻ → H ₂ ↑

In the etching process S2, the anodized layer formed in the anodizing process is etched in a phosphoric acid bath. Thereby, the pore 34 is etched from the inside, the pore 34 expands, and the wall part which divides the adjacent hexagonal cell becomes thin. As described above, when the thin wall portion of the anodized layer is removed by repeating anodization and etching, nano-order pin-shaped protrusions 32 are juxtaposed at the apex position of the hexagonal cell. 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 thereof. Condensed water generated by condensation of moisture on the surface of the water-repellent substrate 1 is pushed out to the outermost surface by the outermost water-repellent film 4 to form water droplets 5. At this time, the air layer 11 is formed between adjacent pin-shaped protrusions 32, and the water droplets 5 are pin-shaped protrusions 32 covered with the water-repellent coating 4 on the outermost surface of the uneven structure 33 of the alumite layer 3. Supported by point contact. In general, when the surface of the water-repellent substrate 1 is in a super-water-repellent state, the water contact angle θ, 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. For example, it is possible to slide off the surface by an external force such as its own weight or air flow.

When the water-repellent substrate 1 has irregularities on the surface, the water contact angle θ is obtained by the following formula 2.
Formula 2: cos θ = [A1 / (A1 + A2)] cos θ1 + [A2 / (A1 + A2)] cos θ2
In the formula, A1: contact area of the water repellent film 4 with respect to the water droplet 5, A2: contact area of the air layer 11 with respect to the water drop 5, θ1: contact angle with water on the surface of the water repellent film 4 having no irregularities, θ2: air layer 11 Since the alumite layer 3 has a regular concavo-convex structure 33 with pin-like protrusions 32 arranged side by side, A1 and A2 are substantially constant, and the water repellency of the surface of the water repellent substrate 1 is uniform. Further, θ1 and θ2 are constants, for example, θ2 = 180 ° (that is, cos θ2 = −1). Therefore, a material having high water repellency is used for the water repellent coating 4 which is the outermost layer, and the area of A1 with respect to A2 When the ratio is decreased, the contact angle θ with water is increased.
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 is the contact area ratio of the water-repellent coating 4 that contacts the water droplet 5 on the outermost surface. is there.
Formula 3: Contact area ratio of the water-repellent substrate 1 = A1 / (A1 + A2)
This contact area ratio correlates with the contact area ratio of the concavo-convex structure 33 of the alumite layer 3 described above, and the smaller the contact area ratio with an Rzjis cut rate of 20%, the smaller the contact area ratio of the water-repellent substrate 1.

Therefore, based on these

formulas

2 and 3, the conditions having super water repellency were examined.
When the water contact angle with respect to the surface of the hydrocarbon-based water-repellent coating 4 having no irregularities is θ1 = 90 °, as shown in FIG. 7, the smaller the contact area ratio of the water-repellent substrate 1, the more the water contact angle. θ increases, and theoretically, the contact area ratio is 0.13 or less and the water contact angle θ is 150 ° or more. That is, when the pin-shaped protrusions 32 are arranged at regular intervals, the width W of the pin-shaped protrusions 32 in contact with the water droplets 5 should be made smaller and the protrusion interval D should be made larger. The contact area of the film 4 becomes smaller. Specifically, when the contact area ratio with the Rzjis cut rate of 20% is 0.01 or less, the contact angle θ with respect to water is set to 150 by combining with the water repellent coating 4 made of a hydrocarbon-based water repellent material. Can be larger than °.

Further, as shown in FIG. 8, the conditions under which the condensed water 51 is satisfactorily drained are found by the simulation using the model diagram of the uneven structure 33 of the alumite layer 3.
In the left diagram of FIG. 8, when the opposing wall corresponding to the pin-like protrusion 32 is arranged with a uniform interval in the depth direction from the surface, with respect to the concave portion 12 that forms the air layer 11 between the opposing walls, The width w of the air layer 11 generated by the condensed water 51 (that is, corresponding 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 a range of h: w = 20: 2 to 13, 8 As shown in the right figure, there is a width w (for example, w2 = 6) through which the condensed water 51 is discharged without causing clogging or stagnation. When the width w is smaller than this, the condensed water 51 is clogged (for example, w1 = 3), and when the width w is larger than this, the condensed water 51 is retained (for example, w3 = 11).

Based on the result of the examination of the sliding property of the condensed water using a test piece in which the projection interval D of the concavo-convex structure 33 is changed based on the simulation result, preferably, when the projection 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-like protrusions 32 are preferably W = 20 nm or less and H = 200 nm to 600 nm. The concavo-convex structure 33 of the alumite layer 3 can be formed to have a desired protrusion interval D, width W, and height H by adjusting the conditions of the anodizing process for forming the anodized layer 3 and the etching process. .

The material of the water-repellent coating 4 that is the outermost layer of the water-repellent substrate 1 determines θ1 in the above formula 2. Specifically, an organic-inorganic hybrid coating 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 cause water droplets. Move 5 and slide it down. The main agent 41 of the hydrocarbon-based water repellent material is a metal alkoxide having an alkyl group 43 in the side chain, and preferably an alkylalkoxysilane having a siloxane bond (ie, Si—O—Si bond) in the main chain. It is done. Further, as the organic silane serving as the crosslinking agent 42, tetraethoxysilane (hereinafter referred to as TEOS) can be used. Such a film has high water repellency next to a film made of a fluorine-based water repellent material, and acts in the direction of increasing the water contact angle θ in the above formula 2.

The water repellency of the water repellent film 4 is affected by the molecular length and molecular spacing d of the main agent 41 located on the outermost surface. For example, when the molecular length of the main agent 41 is shorter and the molecular interval d is wider, the alkyl group 43 is easier to move and the water droplet 5 is easier to move. The water droplet 5 is likely to hydrogen bond to the hydroxyl group contained in the crosslinking agent 42. For this purpose, the blending ratio of the carbon number of the alkyl group 43 that determines the molecular length of the main agent 41 and the crosslinking agent 42 may be set appropriately so that a desired sliding property can be obtained.

For example, the alkyl group 43 contained 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 (ie, C5 to C11). The main agent 41 having a C3 to C18 alkyl group 43 is liquid at room temperature, and the adjustment of the coating liquid for immersing the aluminum substrate 2 becomes easy. It is more preferable that the carbon number of the alkyl group 43 is in the range of C5 to C11 because the dynamic θ difference indicating the adhesion force of the water droplet 5 is as small as 0.01 or less and the sliding property of the water droplet 5 is increased.

Specific examples of the main agent 41 include 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 anodized layer 3 of the concavo-convex structure 33 is formed in a coating solution obtained by dissolving the main agent 41 and the crosslinking agent 42 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, an immersion step S13 for immersing the aluminum substrate 2 in the coating liquid, The surface of the concavo-convex structure 33 of the alumite layer 3 is covered with the water repellent coating 4 through a washing step S14 for washing the coated aluminum substrate 2 and a firing step S15 for firing the aluminum substrate 2.

In the blending step S11, when blending the coating liquid, the blending ratio of the alkyl alkoxysilane serving as the main agent 41 and the TEOS serving as the cross-linking agent 42 is set, for example, to be a desired molecular spacing d. For example, a molar ratio of 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 main agent 41: crosslinking agent 42 is in the range of 7 to 13:93 to 87 (that is, the molar ratio of the main agent 41 is 7 mol% to 13 mol%).

Here, the dynamic θ difference representing the slidability of water droplets, which is an index of water repellency of the water-repellent coating 4, will be described. As shown in FIG. 10, for example, the adhesion force F of the water droplet 5 adhered to the vertical wall W is expressed by the following formula 4. The smaller the adhesion force F against gravity mg, the easier it is to slide down.
Formula 4: F = kwγ (cos θR−cos θA)
In the equation, k: coefficient, w: contact width, γ: surface tension, cos θA: advancing contact angle, cos θR: receding contact angle From equation 4, the advancing contact angle cos θA on the side on which gravity mg acts and the receding contact on the opposite side. The smaller the dynamic θ difference (that is, cos θR−cos θA), which is the difference from the angle cos θR, the smaller the adhesion force F and the easier it is to slide down. At this time, it is desirable for the condensed water to grow to be smaller than the fin interval so as not to block the passage between the fins for the heat exchanger, for example. Preferably, the water droplet diameter is not more than half 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 less than 0.7 mm. Small enough.

As the 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 40 to 60% by mass. The coating solution is mixed with hydrochloric acid having a predetermined concentration as a catalyst for crosslinking and polymerizing the main agent 41 and the crosslinking agent 42. At this time, in order to avoid that a large amount of water contained in the coating liquid is taken into the water-repellent film 4, a dehydration step S12 is provided to remove water by adding a hydrocarbon solvent after the addition of hydrochloric acid. Good.

In the dipping step S13, the aluminum substrate 2 is dipped in the dehydrated coating solution and applied to the entire surface of the concavo-convex structure 33, and then rinsed in the washing step S14 to remove excess coating solution. Then, by baking at predetermined temperature by baking process S15, the water repellent film 4 which does not contain a water | moisture content is obtained, and water repellency is improved further.

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

At this time, the alumite layer 3 formed by anodization and etching has the water-repellent film 4 uniformly formed inside the concavo-convex structure 33, particularly the surface close to the base layer 31, so that even if condensed water is repeatedly generated, It 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 drainage and sliding properties from the concavo-convex structure 33 can be maintained for a long period of time to prevent a decrease in water repellency. To do. Therefore, it becomes the water-repellent substrate 1 that is used for fins for heat exchangers and the like, has super water repellency and high productivity, prevents frost formation and improves operating efficiency.

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

(Experimental example 1)
The alumite treatment step S1 and the etching treatment step S2 are sequentially performed by the method shown in FIG. 5 to form the alumite layer 3 including the base layer 31 and a large number of pin-like protrusions 32 on the surface of the aluminum base 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 anodizing treatment step S1, the surface of the aluminum base 2 was acid cleaned. As a chemical for acid cleaning, nitric acid (for example, concentration 67% by mass) was used, and immersion treatment was performed for 1 minute at room temperature. Thereafter, an anodized layer 3 having a hexagonal cell structure was formed on the entire surface of the aluminum base 2 by applying a voltage in a phosphoric acid bath and performing anodization. Anodization 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 the etching treatment step S2 to enlarge the pores 33 of the anodized layer 3. The etching process was performed under the following conditions.
[etching]
・ Drug: Phosphoric acid, concentration 2% by mass
・ Temperature: 40 ℃
-Time: 10 minutes This anodization and etching were repeated to form the anodized layer 3 having the concavo-convex structure 33 on the surface of the aluminum base 2 (that is, Example 1).

For the alumite layer 3 of Example 1, as shown in FIG. 12, the surface shape and the cross-sectional structure of the obtained uneven structure 33 were observed. As shown in FIG. 13, a structure in which a large number of pin-like protrusions 32 are arranged side by side in an image obtained by observing the uneven structure on the surface of the alumite layer 3 using a scanning electron microscope (hereinafter referred to as SEM). 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 TEM), the width W, the height H, and the protrusion interval of the pin-like protrusions 32. D was measured. As a result, the concavo-convex structure 33 having W = 8 nm, H = 600 nm, D = 100 nm, a desired height, and a sufficiently small width W with respect to the protrusion interval D was obtained.

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

For the boehmite layer 61 of Comparative Example 1, as shown in FIG. 15, image observation of the surface shape and cross-sectional structure of the obtained uneven structure 63 was performed. As shown in FIG. 16, a structure having a large number of needle-like protrusions 62 was confirmed in an image obtained by observing the uneven structure 63 on the surface of the boehmite layer 61 using an SEM. 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 protrusions 62 have an uneven structure 63 extending in an irregular direction, It has been found that the lower layer 611 on the two side has a constricted structure in which the width of the needle-like protrusion 62 is narrower than that of the upper layer 612 on the surface side.

Further, as Comparative Example 2, irregularities having different contact area ratios are formed by forming the alumite layer 3 on the surface of the aluminum base 2 in the same manner as in Example 1 and reducing the number of times of anodizing treatment and etching treatment. Structure 33 was obtained. When the cross-sectional structure of the alumite layer 3 of Comparative Example 2 was observed using TEM in the same manner as in Example 1, it was confirmed that the concavo-convex structure 33 in which the pin-like protrusions 32 were juxtaposed. However, while the projection interval D of the pin-like projections 32 is around 100 nm, the width W is as wide as 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 rate at an Rzjis cut rate of 10% to 50% was measured by the method shown in FIG. First, a three-dimensional concavo-convex image was obtained by scanning the surface of the concavo-convex structure 33 for the alumite layer 3 of Example 1 using a scanning probe microscope (hereinafter referred to as SPM). Based on the obtained three-dimensional concavo-convex image, the 10-point average roughness Rzjis is calculated, and the contact of the pin-like protrusion 32 in the measurement area A is measured on each virtual cut surface with an Rzjis cut rate of 10% to 50% from the maximum height. The area ratio was calculated. Similarly, for Comparative Example 1 and Comparative Example 2, the contact area ratio was measured at an Rzjis cut ratio of 10% to 50%.

As shown in FIG. 18, in the entire range of the Rzjis cut rate of 10% to 50%, the contact area rate of Example 1 was the smallest, and the Rzjis cut rate 20% contact area rate was 0.002. . Further, in both Example 1 and Comparative Examples 1 and 2, the contact area ratio is the smallest when the Rzjis cut rate is 10%, and the contact area ratio increases as the Rzjis cut rate increases. The increase in area ratio is relatively gradual with respect to Comparative Examples 1 and 2. For this reason, the contact area rate is 0.01 or less in both the example 1 and the comparative examples 1 and 2 at the Rzjis cut rate of 10%, but only the example 1 is in contact at the Rzjis cut rate of 20% and 30%. The area ratio is 0.01 or less.

Thus, in Comparative Examples 1 and 2, the overall contact area ratio is large. In particular, the uneven structure 63 of the boehmite layer 61 of Comparative Example 1 is slightly smaller than that of Comparative Example 2 at an Rzjis cut rate of 10%, but is reversed at an Rzjis cut rate of 20%. It is considered that there are variations in the heights of the concavo-

convex structures

33 and 63, and there are pin-like protrusions 32 and needle-like protrusions 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%.

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

The molar ratio of 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 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 Corporation) was added, stirred for 30 minutes, and allowed to stand for 10 minutes (that is, S121). Thereafter, the supernatant was extracted to separate water, and the obtained extract was used as a coating solution (ie, S122). In the dipping step S13, the aluminum substrate 2 of Example 1 was dipped in the obtained coating solution for 30 minutes. Further, in the cleaning step S14, the aluminum substrate 2 was cleaned for 1 minute using a hydrocarbon-based cleaning agent. Then, in baking process S15, the water-repellent base material 1 by which the surface of the alumite layer 3 was coat | covered with the water-repellent film 4 was obtained by baking at 150 degreeC for 30 minutes.

For the water-repellent substrate 1 of Example 1 obtained in this way, the sliding property of the water droplet 5 was evaluated based on the dynamic θ difference shown in FIG. For the measurement of the dynamic θ difference, a contact angle measuring device using an expansion contraction 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 film had a sliding property of 0.001 or less, which is the value obtained in Comparative Example 1.

Furthermore, the water repellent substrate 1 of Example 1 was subjected to a condensed water test by repeated wet and dry, and the maximum condensed water diameter was measured. In the condensed water test, the test piece of the water-repellent substrate 1 is cooled to 0 ° C. or lower (for example, −5 ° C. or lower), placed in a high-humidity constant temperature and humidity chamber, and blown to the surface of the test piece (for example, The wind speed was 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 generated condensed water was measured, and then the test piece was cooled again and the condensed water on the surface was observed repeatedly.

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. Fluorine-based water-repellent coating uses a water-repellent material (OPTOOL DSX; manufactured by Daikin Industries, Ltd., trade name) mainly composed of a silane compound containing perfluoropolyether, and is immersed in a coating solution prepared in the same manner. It was formed by firing. For the aluminum substrate 2 of Comparative Example 2, the same hydrocarbon-based water repellent coating 4 as that of Example 1 was formed on the surface of the concavo-convex structure 33 of the alumite layer 3. About the comparative examples 1 and 2, the test piece of the obtained water-repellent base material was produced, and the condensed water test was implemented similarly.

As shown in FIG. 19, the water-repellent substrate 1 of Example 1 has a maximum condensed water droplet diameter after one condensed water test of 0.4 mm, and even after three condensed water tests, Satisfied 0.7 mm or less required for the fin material. On the other hand, in Comparative Example 1 in which the fluorine-based water repellent film was formed on the boehmite layer 61, the maximum condensed water droplet diameter after one dry / wet repeated test was the same as that in Example 1, but the condensed water test was repeated. As a result, the diameter of the condensed water increased, and the maximum condensed water droplet diameter after three condensed water tests 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 protrusions 62 constituting the concavo-convex structure 63 have a narrowed portion in the lower layer 611. It is difficult to cover the entire surface that becomes the uneven structure 63. Therefore, when condensed water 51 is generated between the needle-like protrusions 62 in a low temperature and high humidity environment (see, for example, FIG. 20 (e)), the outermost portion is initially the outermost due to the effect of the concavo-convex structure 63 and the fluorine-based water repellent film. Water droplets 5 are generated by being pushed out onto the surface (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 concavo-convex structure 63 (see, for example, FIG. 20H), and the water repellency is lowered.

Further, in Comparative Example 2 in which the hydrocarbon-based water-repellent film 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 maximum condensed water droplet diameter later increased to about 1.5 mm. As shown in FIG. 21, when the condensed water test is repeated three times, the condensed water diameter 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 greatly even if it is increased up to 3 times. On the other hand, in Comparative Example 1, the condensed water diameter is increased by repeating the condensed water test, and the water repellency is lowered.

(Experimental example 3)
A water-repellent coating 4 was formed on the aluminum substrate 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, alkylalkoxysilanes having different carbon numbers were used as the main agent 41 of the water repellent coating 4 as shown below.
Carbon number C3: Trimethoxypropylsilane (for example, B21033; manufactured by Johnson Matthey Japan LLC, trade name)
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 G.K., 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; manufactured by Tokyo Chemical Industry Co., Ltd., trade name)
Carbon number C18: Octadecyltriethoxysilane (for example, S12325; manufactured by Wako Pure Chemical Industries, Ltd., trade name)

The aluminum substrate 2 of Example 1 was immersed in a coating solution prepared in the same manner as in Experimental Example 2 and baked to obtain a water-repellent substrate 1 having a water-repellent film 4 having a different carbon number. About the obtained water repellent base material, the dynamic (theta) difference was measured using the above-mentioned contact angle measuring apparatus, and the sliding property of the water droplet 5 was evaluated.

For comparison, in the method shown in FIG. 9, the aluminum substrate 2 of Example 1 was used in the same process (that is, the process shown on the left side in the figure) except that the dehydration process S12 and the cleaning process S14 were omitted. A water-repellent film 4 was formed on the surface to obtain a water-repellent substrate of Comparative Example 3. At this time, the above-described alkyl alkoxysilane having 6 to 18 carbon atoms was used as the main agent 41 of the water repellent coating 4. About the obtained water repellent base material, the dynamic (theta) difference was measured using the above-mentioned contact angle measuring apparatus, and the sliding property of the water droplet 5 was evaluated.

As shown in FIG. 22, in Comparative Example 3 in which the prepared coating solution was not dehydrated and washed after coating, the dynamic θ difference of the obtained water-repellent substrate exceeded 0.01. On the other hand, the water-repellent substrate 1 of Example 1 has a smaller dynamic θ difference compared to Comparative Example 3 using the main agent 41 having the same carbon number, and has 5, 8, and 10 carbon atoms. As for the thing, the dynamic (theta) difference became 0.01 or less.

Further, for 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 = 5-30: 95-70, Otherwise, the water-repellent substrate 1 was produced by the same method. About the obtained water repellent base material, the dynamic (theta) difference was measured using the above-mentioned contact angle measuring apparatus, and the sliding property of the water droplet 5 was evaluated.

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 is minimized, and the dynamic θ difference tends to increase whether it is smaller or larger. 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 disclosure is not limited to the contents described in the above embodiment and the above examples, and various modifications can be made without departing from the gist of the present invention. For example, in the said embodiment, although demonstrated as an application example to the HP system used for a vehicle-mounted air conditioning system, as an air conditioning system other than vehicle-mounted, the outdoor unit of the HP system for water heaters, and other heat exchanger fins Preferably used. Moreover, it can be used arbitrarily for applications other than heat exchanger fins.

Claims

An aluminum substrate (2);
An alumite layer (3) provided on the surface of the aluminum substrate;
A water repellent coating (4) provided on the surface of the anodized layer,
The alumite layer has a concavo-convex structure (33) composed of a base layer (31) integral with the aluminum base and a large number of pin-like protrusions (32) juxtaposed on the surface of the base layer. With respect to the point average roughness Rzjis, the contact area ratio of the pin-like protrusions is 0.01 or less at the virtual cut surface (A) having a height of 20% Rzjis cut rate from the maximum height position of the concavo-convex structure. ,
The water-repellent film is a water-repellent substrate (1) which 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) made of a metal alkoxide having an alkyl group (43) and a cross-linking agent (42) made 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 to 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 coating (4) provided on the surface of the anodized layer,
The alumite layer has a concavo-convex structure (33) composed of a base layer (31) integral with the aluminum base and a large number of pin-like protrusions (32) juxtaposed on the surface of the base layer. With respect to the point average roughness Rzjis, the contact area ratio of the pin-like protrusions is 0.01 or less at the virtual cut surface (A) having a height of 20% Rzjis cut rate from the maximum height position of the concavo-convex structure. ,
The water-repellent film is a method for producing a water-repellent substrate (1), which 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 material by anodizing and etching (S1, S2);
Preparing a coating liquid containing the hydrocarbon-based water repellent material (S11);
Adding a hydrocarbon solvent to the coating liquid to separate and remove moisture (S12);
Immersing the aluminum base material on which the alumite layer has been formed in the coating liquid from which moisture has been removed (S13);
A step (S15) of firing the aluminum substrate to which the coating liquid has been applied.
In the step of forming the alumite layer, a step (S1) of anodizing the surface of the aluminum substrate by anodizing, and a step of etching the aluminum substrate that has been anodized (S2). The method for producing a water-repellent substrate according to claim 6, which is repeated.