JP2015193922A - Liquid repellent surface fine structure, production method thereof, heat exchanger, and component of air conditioner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a more concrete surface fine structure capable of achieving liquid repellency such as water repellency or oil repellency, and to provide a production method thereof.SOLUTION: The surface fine structure 10A of a fin 10 of a heat exchanger includes the surface 11 of a material, and a plurality of grooves 12 formed on the surface 11. When the contact angle formed between a smooth surface of the material and a droplet is expressed as θe, the shape of the groove 12 is determined so that the ratio of a depth to a width is larger than a basic criteria Cr1 expressed as 1/tanθe so as to express liquid repellency.

Description

  The present invention relates to a surface microstructure that is water repellent, a method for manufacturing the surface microstructure, a fin of a heat exchanger having the surface microstructure, and a heat exchanger.

The heat exchanger constituting the air conditioner includes a tube through which a refrigerant flows and fins that are thermally coupled to the tube, and heat is generated between the refrigerant in the tube and the air passing between the fins. Exchange.
The surface of the fin is hydrophilic in order to avoid a decrease in efficiency due to increased ventilation resistance between the fins due to condensation and frost formation on the heat exchanger fins, and to prevent water splashing from the fins to the air-conditioned space. Or the coating which gives water repellency is given. The fins are typically formed using aluminum, and the surface of the aluminum material is slightly hydrophilic, but it is desired that the fins have a higher hydrophilicity or sufficient water repellency.
If the hydrophilicity is sufficiently high, water spreads along the surface of the fin, so that the airflow resistance between the fins can be suppressed even if condensation or frost forms. Moreover, since water is hold | maintained on the surface of a fin because hydrophilicity is high enough, water jumping can be suppressed.
On the other hand, if the water repellency is sufficiently high, moisture hardly adheres to the surface of the fin, so that water and frost do not form a large lump, so that airflow resistance between the fins can be suppressed.

Here, a water-repellent coating using a water-repellent material typified by a fluorine-based resin or a hydrophilic coating using a hydrophilic material such as a silicone-based resin is applied to the surface of the material, so that the necessary water-repellent or hydrophilic property is obtained. Getting sex is done.
Further, hydrophilicity and water repellency depend not only on the chemical properties of the material but also on the surface roughness of the material. It is known that as the surface roughness is increased by forming fine irregularities on the surface, the hydrophilicity / water repellency exhibited when the surface of the material is smooth is emphasized (Wenzel's formula).
In Patent Document 1, an aluminum member (fin) is immersed in an acid to form an uneven structure on the surface, and then a water-repellent coating is applied using a fluorine-based resin material or the like, thereby applying the water-repellent coating alone. Water repellency than the case.

JP 2010-174269 A

The fin of the heat exchanger is coated by immersing a sheet material for forming the fin or an assembly in which the fin and the tube are assembled in a coating solution.
Therefore, in order to perform coating, a liquid tank that stores a coating liquid that matches the size of the fin and a coating liquid that fills the liquid tank are required, and these coating liquids and liquid tanks require a corresponding cost.
In addition, a step of coating is required separately from the formation of the fin and the assembly with the tube. Before coating, acid washing, washing with water, chemical conversion treatment of the base, etc. are required, and baking is performed after coating, so the process is bulky and takes time.
Furthermore, particularly when coating is applied to the fins of heat exchangers installed outdoors, it is difficult to ensure the durability of the coating that can withstand long-term use.
Accordingly, an object of the present invention is to provide a surface microstructure that can be made water repellent and not a coating, and a method for manufacturing the same.

  In addition, depending on the environment where the air conditioner is used, there is a case where oil repellency of a portion to which oil droplets adhere is required from the viewpoint of antifouling. The object of the present invention is not limited to water repellency but also includes oil repellency. An object of the present invention is to make a member in contact with a liquid repellent widely.

As described above, it is known that when unevenness is formed on the surface, it is useful for sufficiently obtaining water repellency or hydrophilicity. In order to maximize water repellency or hydrophilicity, research has been conducted to simulate fractal structures that theoretically provide ultimate surface roughness and surface area.
However, conventional research has been directed to the overall surface roughness of the surface structure, and what is the specific shape of the individual elements such as recesses or protrusions that make up the uneven surface structure? Whether it is effective for water repellency or hydrophilicity has not yet been specified.
By the way, as a result of the liquid droplets adhering to the tip of the needle in the air being gathered so as to avoid the surrounding air so that the surface energy is stable, the droplets become spherical. The contact angle of air is 180 ° (maximum contact angle).
A Cassie-Baxter equation (the following equation (1)) that defines a contact angle when one component of a composite surface formed from two components having different contact angles is air is known.

Here, r is the ratio of the actual surface area to the projected area (surface roughness) and takes a value exceeding 1 (r> 1).
f is the ratio of the area where the droplet contacts the material (solid) on the composite surface, and takes a value of 0 or more and 1 or less (0 ≦ f ≦ 1).
θ _CB is the actual contact angle between the material and the droplet.
θe is a contact angle when a droplet is allowed to stand on a material.
θ _air is a contact angle (180 °) between the air and the droplet.
From the above formula (1), when air is caught between the material and the droplet (f> 0), θ _CB > θe, so that water repellency is achieved. When the droplet is in point contact with the material (f is small), the water repellent property is obtained.

As described above, when air is entrained between the material and the liquid droplets, it becomes water repellent. If so, it can be considered that the contact angle can be controlled if the surface shape can be specifically determined whether or not the air entrainment phenomenon occurs.
Based on the above idea, the inventor of the present invention diligently searched while conducting experiments, and as a result, the present invention was completed.

The surface structure of the present invention includes a surface of a material and a plurality of grooves formed on the surface.
In the present invention, when the contact angle between the smooth surface of the material and the liquid droplet is θe, the ratio of the depth to the groove width is larger than the basic criterion of 1 / tan θe and expresses water repellency. It is characterized by doing.
Hereinafter, the material may be referred to as a contact target, and the ratio of the depth to the groove width may be referred to as an aspect ratio.

The basic criteria are set by capturing an event that determines whether air entrainment occurs or not according to the shape of the groove (depth-width relationship) that forms the surface microstructure. This basic criteria determines the boundary between water repellency and hydrophilization of the surface microstructure where the grooves are formed, and water repellency increases as the ratio of the depth to the groove width exceeds the basic criteria, and decreases as it decreases. Turn into.
Therefore, the required water repellency can be obtained by determining the depth with respect to the width of the groove within a region larger than the basic criteria.

According to the present invention, it is possible to provide necessary water repellency by forming a groove having a shape guided from the basic criteria on the surface without the need to provide a coating that imparts water repellency.
If the coating is abolished, the cost of the coating liquid and the liquid tank is not required, and the base treatment, baking, etc. associated with the coating are not required, so that the manufacturing can be efficiently performed while suppressing the manufacturing cost.
In addition, the durability and strength of the base material typically made of metal is often higher than the durability and strength of the resin coating, so it can withstand long-term outdoor use. In addition, the strength to withstand impact can be easily secured.

  In the above basic criteria, the droplet placed on the surface of the material enters the groove from one edge in the width direction of the groove and does not reach the bottom of the groove and reaches the other edge of the groove. It is set by capturing the event that arrives. When the droplet does not reach the bottom of the groove but reaches the other end of the groove so as to cross the groove (bridge), it corresponds to a larger (water-repellent) than the basic criteria.

Since the measured value of the contact angle tends to vary, it includes an error. Therefore, the ratio of the depth to the groove width can be determined so as to be larger than the basic criteria when the contact angle is increased by 10% with respect to the measured contact angle. That is, if the basic criteria are formulated by reading the contact angle measurement value (or the data sheet value, etc.) with an increase of 10%, the bridging phenomenon can surely occur and the water repellency can be expressed.
Alternatively, it is allowed to set the ratio of the depth to the groove width so as to be larger than the basic criteria when the contact angle is reduced by 10%. Even in such a case, the water repellency can be expressed by the bridge phenomenon.

In the surface structure of the present invention, if the inclination angle formed between the perpendicular to the surface of the material and the inner wall of the groove is θw, the ratio of the depth to the groove width is larger than the inclination criteria represented by the following formula. Preferably there is.

When the inner wall of the groove is inclined with respect to the normal of the surface, an extra depth is required to form a droplet bridge as compared with the case where the inner wall is along the vertical.
When the tilt angle becomes larger than a certain value, the droplet bridge is not established.
The inclination criteria are determined by determining the relationship between the inclination angle θw and the depth / width of the groove by geometric calculation using a trigonometric function.
By using the inclined criteria, the basic criteria can be extended and applied to a groove having an inner wall inclined with respect to the surface.

The surface structure of the present invention exhibits water repellency, and the groove width is preferably 5 μm or more and 200 μm or less.
Since the width of the groove is sufficiently small with respect to the diameter of the water droplet on the order of mm, the shape of the water droplet in the groove when the water droplet bridges across the groove can be approximated by a straight line. Therefore, the accuracy of the basic criteria can be ensured.

  The surface structure of the present invention exhibits water repellency and can realize a contact angle of 100 ° or more.

  In the surface structure of the present invention, the plurality of grooves are preferably formed by nanoimprinting. As a result, a groove having a minute width and depth can be formed.

The surface structure of the present invention exhibits oil repellency, and the plurality of grooves are preferably formed on the surface of the resin material in which oil droplets form the contact angle of 40 ° or more.
Even for a contact target having a contact angle θe smaller than 40 °, if the aspect ratio is larger than that of the basic criteria or the inclined criteria, oil repellency can be obtained. However, in the range where the contact angle θe is small, since the inclination of the 1 / tan θe line segment that defines the criteria is large, it is necessary to strictly control the aspect ratio for reliably obtaining oil repellency. On the other hand, if the contact angle θe is 40 ° or more, since the inclination of the line segment is small, the oil repellency can be reliably obtained without controlling the aspect ratio so strictly. Since the resin material generally has a larger contact angle θe than the metal material, the surface structure of the present invention is built in the resin material, and the member made of the metal material is covered with this, so that the metal member is substantially Excellent oil repellency can be added. Of course, the resin material can be used alone without covering the metal member.

The surface structure of the present invention exhibits oil repellency, and the ratio P / D of the groove pitch P to the diameter D of the oil droplet contacting the material is preferably 1/5 or less.
By using nanoimprinting with P / D of 1/5 or less or as described above, a groove with a width of 0.1 to 10 μm can be easily formed even with oil droplets having a diameter of 50 to 100 μm. , Excellent oil repellency can be imparted to the contact object.

The fin of the heat exchanger of the present invention is characterized in that the refrigerant is thermally coupled to the tube through which the refrigerant flows and has the above-described surface structure.
By having the above-mentioned surface structure, sufficiently high water repellency can be realized, so that condensation and frost formation can be suppressed and the efficiency of the heat exchanger can be improved.
From the viewpoint of heat exchange performance, it is preferable to finely process the fins of the heat exchanger by direct transfer or the like on the fins that are metal materials, regardless of the technique using nanoimprint described later.

  A heat exchanger according to the present invention includes the above-described fin and a tube through which a refrigerant flows.

  The component of the air conditioner of this invention has the above-mentioned surface structure, and expresses oil repellency. For example, it is preferable to apply the surface structure described above to the outer plate of an air conditioner where oil may adhere. If the components of an air conditioner have oil repellency, oil adhesion to the components can be suppressed, reducing the burden of cleaning the oil itself and dirt that sticks to the area where the oil has adhered. Can do.

  In the constituent elements of the air conditioner of the present invention, the material that the oil droplets contact is provided with a base material and a film that is formed of a resin material and covers the surface of the base material, and the contact angle of the film is 40 ° or more. It is preferable that the plurality of grooves are formed on the surface of the film by nanoimprinting. If it does so, the water repellency by the fine surface structure formed in the resin film with a large contact angle of 40 degrees or more will be added.

The surface structure manufacturing method of the present invention includes a step of forming a shape corresponding to the groove of the surface structure described above in a mold, and a step of plastically processing a material using the mold.
By transferring using a mold, it is possible to cope with mass production while reliably forming the groove shape on the surface of the member.

  According to the present invention, by providing the basic criteria specified by 1 / tan θe, it is possible to provide a specific surface structure that achieves liquid repellency such as water repellency and oil repellency.

It is a perspective view which expands and shows typically the fin of the heat exchanger which concerns on 1st Embodiment of this invention. It is a figure which shows the basic criteria which prescribes | regulates the boundary of water repellency and hydrophilization about the depth / width of the groove | channel of the surface microstructure formed in the fin. It is a figure which shows the form factor used for the sensitivity evaluation with respect to a contact angle. It is a figure which shows the result of a sensitivity evaluation. It is a figure which shows a mode that a water droplet contacts a surface fine structure and spreads. It is a figure for demonstrating that the entrainment of air arises when a groove | channel is deep. It is a figure for demonstrating that air entrainment does not arise when a groove | channel is shallow. (A) is a figure which shows the model of the groove | channel of the surface fine structure used for formulation of the basic criteria, (b) is a reprint of FIG. It is a figure for demonstrating the case where the inner wall of a groove | channel inclines with respect to the surface of a groove | channel. It is a figure which shows the inclination criteria which prescribes | regulates the boundary of water repellency and hydrophilicity about the case where the inner wall of a groove | channel is inclined like FIG. (A) is a digital microscope photograph of a surface microstructure, and (b) is a photograph showing a state in which air is involved in the surface microstructure and water repellent. It is a schematic diagram which shows the line which manufactures a fin. It is a figure which shows the manufacturing line which can be substituted for the manufacturing line shown in FIG. It is a perspective view which expands and shows typically the surface part of the outer plate | board of the air conditioner which concerns on 2nd Embodiment of this invention. It is a figure which shows the basic criteria which prescribes | regulates the boundary of oil repellency and oleophilicity about the depth / width of the groove | channel of the surface microstructure formed in the outer plate | board of an air conditioner. It is a perspective view which expands and typically shows the surface part of the outer plate | board of the air conditioner which concerns on the modification of 2nd Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[First Embodiment]
FIG. 1 shows a surface microstructure 10A of the fin 10 of the heat exchanger according to the present embodiment.
The heat exchanger of the present embodiment is a plate fin type, and a large number of plate-like fins 10 are stacked in parallel. The heat exchanger is configured by assembling the laminated body of the fins 10 and a tube (not shown) through which the refrigerant flows. This heat exchanger constitutes an air conditioner.

The fin 10 is made of an aluminum alloy material and includes a surface microstructure 10A on both the front and back surfaces.
The surface microstructure 10 </ b> A includes a surface 11 of a material that is not coated with water repellency and hydrophilicity, and a large number of grooves 12 formed on the surface 11.
Each groove 12 has a rectangular cross section and extends linearly, and is arranged in parallel with each other at a predetermined interval. The dimension (width 12W) in the direction orthogonal to the length direction of the groove 12 is sufficiently small with respect to the diameter of the water droplet. Here, the diameter of the water droplet is assumed to be about 1 mm to 3 mm.

  On the front side 101 and the back side 102 of the fin 10, the grooves 12 are alternately arranged. That is, the groove 12 on the back surface side 102 is located between the grooves 12 adjacent to each other on the front surface side 101, and the groove 12 on the surface side 101 is positioned between the grooves 12 and 12 adjacent to each other on the back surface side 102. Is located.

In the surface microstructure 10A, the material itself has hydrophilicity with a contact angle of about 45 ° to 84 °, but the ratio (aspect ratio) of the depth 12D to the width 12W of the groove 12 is a predetermined basic criteria Cr1 ( The water repellency is acquired by being determined based on FIG.
The basic criteria Cr1 (depth / width of the groove 12) is 1 / tan θe, where θe is the contact angle between the smooth surface (surface 11) of the material of the fin 10 and the water droplets. The shape of the groove 12 is determined so that the ratio of the depth 12D to the width 12D of the groove 12 is larger than the basic criteria Cr1.
That is, the depth / width of the groove 12 is one of the factors that influence the contact angle of the surface microstructure 10A, and the basic criteria Cr1 that defines the depth / width of the groove 12 is the surface on which the groove 12 is formed. The boundary between water repellency and hydrophilization of the microstructure 10A is determined.

FIG. 2 shows the relationship between the contact angle θe formed by the smooth surface of the material and the water droplets and the depth / width of the groove 12. The contact angle θe is a contact angle formed between a smooth surface on which the groove 12 is not formed and a water droplet, and is constant regardless of the size of the water droplet or the posture in which the material is installed.
Here, in order to deal with the error of the basic criteria Cr1, the basic criteria band B1 including the basic criteria Cr1 and values near the upper side and the lower side is set. Then, the depth / width of the groove 12 is determined so as to be larger than the basic criteria band B1.
Basic Criteria zone B1 is in the range from the basic criteria Cr1 ₁ when the contact angle θe is 10% less with respect to the measurement value, to the basic criteria Cr1 ₂ when the contact angle θe is 10% larger than the measured value.
Even if the contact angle θe includes a measurement error, the surface microstructure 10A is water-repellent in the region F1 in which the depth / width of the groove 12 is larger than the basic criteria band B1.
On the other hand, in the region F2 where the depth / width of the groove 12 is smaller than the basic criteria Cr1, the surface microstructure 10A is hydrophilized. However, (ranging from Cr1 ₁ to Cr1) is greater than the lower limit value Cr1 ₁ of the basic criteria band B1 be less than the depth / width basic criteria Cr1 groove 12, a bridge phenomenon to be described later are satisfied surface Since the fine structure 10A can be made water-repellent, it is allowed to set the depth / width of the groove 12 within the range.

The measured value of the contact angle θe is about 45 ° to about 90 ° in the case of a material formed using aluminum. In the case of a chemically treated aluminum material, the contact angle is about 50 to about 70 °.
In the case of a stainless steel material, the contact angle θe is about 80 ° to about 90 °.

The process that led to the identification of the basic criteria Cr1 will be described below.
As one of the factors that affect the contact angle, the present inventor has focused on the entrainment of air between the material and the water droplets.
On the other hand, the sensitivity of the form factor with respect to the contact angle was evaluated using Taguchi method (quality engineering).
As shown in FIG. 3, the shape factor used for the evaluation is as follows: the width 12W of the groove 12, the depth 12D, the pitch 12P, the cross-sectional shape of the groove 12 (rectangular, U-shaped (including arc shape), V-shaped), and It is a pattern (lattice shape, stripe shape, dot shape) formed by a plurality of grooves 12.
For the sensitivity evaluation, 18 specimens were used based on Taguchi Method L18. The width, depth, and pitch of the groove 12 are varied in three stages. Moreover, although it was not a shape factor, the test body formed from Al alloy, stainless steel (SUS), and the Al alloy which carried out the chemical conversion treatment was tried.
The result shown in FIG. 4 was obtained by the sensitivity evaluation. The vertical axis in FIG. 4 indicates the degree (sensitivity) of the influence of each factor on the contact angle, and water repellency is shown in the upper part of the figure and hydrophilicity is given in the lower part of the figure. According to the result of FIG. 4, the width, depth, and pattern sensitivity of the groove 12 are larger than the other factors with respect to the contact angle.

Here, the smaller the width of the groove 12 or the deeper the depth of the groove 12, the more water-repellent, and vice versa, the wider the width of the groove 12 or the shallower the groove 12, the more hydrophilic it becomes.
Thus, the following conditions are set in order to consider why the water repellency or hydrophilicity is caused by the difference in the width and depth of the groove 12.
Condition 1: The uneven structure (width, depth, pitch, etc. of the groove 12) of the surface fine structure 10A is sufficiently small with respect to the diameter of the water droplet.
Condition 2: The contact angle θe formed by the smooth surface of the material and the water droplets is always constant.
Condition 3: A water droplet behaves so that its surface area becomes small (minimization of surface energy).

Then, as shown in FIG. 5, it is assumed that the water droplet 14 is allowed to stand on the surface microstructure 10 </ b> A and spreads by its own weight while entraining the air 15 between the materials.
The water droplet 14 is spherical before contacting the surface microstructure 10A (FIG. 5A), and a part of the spherical surface of the water droplet 14 contacts the surface 11 of the surface microstructure 10A (FIG. 5B). .
Thereafter, the water droplet 14 also contacts the adjacent surfaces 11B and 11C across the grooves 12 and 12 on both sides from the contacted location (surface 11A) (FIG. 5C). The water droplet 14 spreads and stabilizes as it is repeated the number of times corresponding to the volume of the water droplet (FIG. 5 (d)). In the state of FIG. 5D, the contact angle θ actually formed by the surface microstructure 10A and the water droplet 14 is measured.

As described above, the mechanism of water repellency and hydrophilicity will be considered by grasping the behavior of the water droplet 14 immediately after coming into contact with the surface microstructure 10A.
First, a case where the groove 12 is sufficiently deep will be described.
As shown in FIG. 6A, the water droplet 14 contacts the surface 11A of the surface microstructure 10A. Since the uneven structure of the surface microstructure 10A is sufficiently small with respect to the diameter of the water droplet 14 (condition 1), the water droplet 14 contacts the surface 11A which is the top surface of the convex portion between the grooves 12 and 12, It extends to one end edge 121 of the opening of the groove 12.
Then, as shown in FIG. 6B, a part of the water droplet 14 enters from the end edge 121 along the inner wall 123 of the groove 12. At this time, the angle formed by the material and the water droplet 14 is θe (condition 2). The contact angle θe is also constant for the vertical surface of the material, and does not change through FIGS. 6A to 6D (the same applies to FIGS. 7A to 7D).

Thereafter, as shown in FIG. 6C, the water droplet 14 tries to penetrate deeper into the groove 12, but the water droplet 14 does not reach the bottom 124 of the groove 12 and the other edge of the groove 12. Reach 122 (opposite side). Thus, the cross-sectional shape of the water droplet 14 in the groove 12 when the water droplet 14 straddles the groove 12 and reaches the surface 11B on the opposite bank can be approximated by a straight line as shown in FIG.
When the water droplet 14 reaches the opposite shore, the inside and the outside of the groove 12 are partitioned by the water droplet 14, so that the air 15 is caught between the water droplet 14 and the material.

The water droplet 14 further spreads on the surface 11B as shown in FIG. 6 (d). At this time, since the water droplet 14 behaves so as to reduce the surface area (Condition 3), it can be estimated that the water droplet 14 maintains a linear shape without swelling downward in the groove 12.
Then, while air 15 is engulfed in the groove 12, the operations shown in FIGS. 6A to 6D are repeated and stabilized (see FIG. 5D).
Although only the right side of the water droplet 14 is illustrated, the water droplet 14 is similarly spread on the left side of the drawing.
Further, the water droplet 14 spreads in the length direction of the groove 12 (the direction orthogonal to the paper surface), and is stable in a state where its own weight and surface tension are balanced.

Next, a case where the groove 12 is shallow will be described.
As shown in FIG. 7A, the water droplet 14 contacts the surface 11A of the surface microstructure 10A. Since the uneven structure of the surface microstructure 10A is sufficiently small with respect to the diameter of the water droplet 14 (condition 1), the water droplet 14 contacts the surface 11A which is the top surface of the convex portion between the grooves 12 and 12, It extends to one end edge 121 of the opening of the groove 12.
Then, as shown in FIG. 7B, a part of the water droplet 14 enters from the edge 121 along the inner wall 123 of the groove 12. At this time, the angle formed by the material and the water droplet 14 is θe (condition 2).
Although only the right side of the water droplet 14 is illustrated, the water droplet 14 is similarly spread on the left side of the drawing.

Up to this point, it is the same as in the case where the groove 12 is deep (FIG. 6). However, when the depth of the groove 12 is shallow, as shown in FIG. 7C, the water droplet 14 reaches the bottom 124 of the groove 12, It extends along the bottom 124. At this time, the water droplet 14 also spreads in the length direction of the groove 12.
Then, as shown in FIG. 7D, the water droplet 14 overflows from the other end 122 (opposite side) of the groove 12 to the surface 11B. That is, when the groove 12 is shallow, no air is caught between the water droplet 14 and the material. Thereafter, FIGS. 7A to 7D are repeated and stabilized.

Based on the above consideration when the groove 12 is deep (FIG. 6) and when the groove 12 is shallow (FIG. 7), the wettability (water repellency and hydrophilicity) depends on the width and depth of the groove 12. The difference is whether the water droplet 14 bridges from one end 121 of the groove 12 to the other end 122 so as to straddle the groove 12 (FIG. 6C) or not (FIG. 6). 7 (c)) is presumed to be related.
That is, since the groove 12 is deep, if the water droplet 14 bridges to the opposite bank of the groove 12 without reaching the bottom 124 of the groove 12 (FIG. 6C), the air 15 is caught between the water droplet 14 and the material. It is. Then, it is estimated that water repellency is achieved.
On the other hand, if the groove 12 is shallow enough to reach the bottom 124 earlier than the water droplet 14 reaches the opposite shore of the groove 12 (FIG. 7C), the water droplet 14 sufficiently enters the groove 12, Presumed to be hydrophilic.

Based on the above consideration, a model of the groove 12 constituting the surface microstructure 10A was drawn (FIG. 8A). Based on this model, a geometric relationship for the width and depth of the groove 12 is determined.
Here, for the sake of simplicity, it is assumed that the two-dimensional shape representing the cross section of the groove 12 is handled, and the shape of the water droplet that has entered the groove 12 can be represented by a straight line.
If the value of the width 12W of the groove 12 is A, the value of the depth 12D can be expressed as A / tan θe, so the depth / width of the groove 12 is 1 / tan θe. In this 1 / tan θe (basic criteria Cr1), water repellency and hydrophilicity can be drawn.
That is, in the process in which the water droplet 14 enters the groove 12, if it reaches the opposite shore (edge 122) before the bottom portion 124 (FIG. 6 (c)), it becomes water repellent (region F1 in FIG. 2), and more than the opposite shore. If the bottom portion 124 is reached first (FIG. 7 (c)), it will become hydrophilic (region F2 in FIG. 2), and the boundary between water repellency / hydrophilization will be established on the brink of whether it is attached to the opposite bank / bottom or not. Can be set.

8B (similar to FIG. 2), for example, if the smooth surface of the aluminum alloy material of the fin 10 exhibits a contact angle θe of 84 °, the basic criteria Cr1 (depth / width) is about 0.1. It is.
Even in other materials (for example, stainless steel material, chemical-treated aluminum material, copper), the basic criteria Cr1 is determined according to the contact angle θe.

As described above, the contact angle can be controlled by using the basic criteria Cr1 set based on the event that determines whether or not the air entrainment occurs depending on the shape of the groove 12 (the relationship between the depth and the width). .
For example, when the contact angle is 84 °, the ratio of the depth to the width of the groove 12 (aspect ratio) becomes water repellent (see the upward arrow) when the ratio of the basic criteria Cr1 is 0.1 (see the upward arrow). If it falls below 0.1, it becomes hydrophilic (see downward arrow).
Therefore, when the fin 10 is desired to exhibit water repellency as in this embodiment, the depth / width of the groove 12 may be set to be larger than 0.1. Since the water repellency increases as the distance from the basic criteria Cr1 increases in the region F1 larger than the basic criteria Cr1, the required water repellency can be obtained by adjusting the depth / width of the groove 12.

As described above, according to the present embodiment, the groove 12 having a shape guided from the basic criteria Cr1 is formed on the surface of the fin 10 without the need for applying a water-repellent coating or a hydrophilic coating. It becomes possible to impart the necessary water repellency or hydrophilicity to the surface of the fin 10.
By eliminating the coating, the cost of the coating liquid and the liquid tank is no longer necessary, and the base treatment, baking, etc. associated with the coating are also unnecessary, so that the manufacturing can be efficiently performed while suppressing the manufacturing cost.
In addition, since the durability and strength of the metal base are generally higher than the durability and strength of the resin coating, durability that can withstand long-term outdoor use and strength that can withstand impact can be easily secured.

The basic criteria Cr1 described above is set for the groove 12 (FIG. 8A) having an inner wall 123 perpendicular to the surface 11 and having a rectangular cross-sectional shape.
Hereinafter, the case where the inner wall 123 is inclined with respect to the perpendicular perpendicular to the surface 11 will be described.
The inner wall 123 shown in FIGS. 9A and 9B is inclined by θw with respect to the perpendicular L1 perpendicular to the surface 11.
FIG. 9A shows a case where the inclination angle θw is small, and FIG. 9B shows a case where the inclination angle θw is large.

When the inner wall 123 is inclined with respect to the vertical line L1, an extra depth is required to establish a bridge for the water droplet 14 as compared with the case where the inner wall 123 is along the vertical line L1 (FIG. 9A). )).
Then, due to the geometric relationship between the contact angle θe and the inclination angle θw, when the inclination angle θw increases beyond a certain level (FIG. 9B), a bridge of the water droplet 14 is established as can be read from the graph of FIG. Disappear.
When the relationship between the inclination angle θw and the depth / width of the groove 12 is determined by geometric calculation using a trigonometric function, the inclination criterion Cr2 (FIG. 10) that determines whether or not the water droplet 14 is bridged can be determined. .

The inclined criteria Cr2 (depth / width) is expressed by the following equation (2).

FIG. 10 shows the inclined criteria Cr2 when the contact angle θe is 84 ° (aluminum material). As described above, as the inclination angle θw increases from 0, the depth required to establish the bridge increases, and when the inclination angle θw exceeds a certain value (here, about 45 ° or more), no bridge is generated. .
For example, when the inclination angle θw is 20 °, the depth / width (aspect ratio) of the groove 12 becomes water repellent (see the upward arrow) when the depth / width (aspect ratio) exceeds 0.4 which is the inclination criterion Cr2, and the ratio is 0. When it is less than 4, it becomes hydrophilic (see downward arrow).

Here, as in the case of the basic criteria Cr1, it is preferable to set the inclined criteria band B2 including the inclined criteria Cr2 and values near the upper side and the lower side.
Inclined Criteria band B2 refers to the range from the inclined criteria Cr2 ₁ when the contact angle θe is 10% less with respect to the measurement value, to the inclined Criteria Cr2 ₂ when the contact angle θe is 10% larger than the measured value.
Even if the contact angle θe includes a measurement error, it is surely water-repellent in a region where the depth / width of the groove 12 is larger than the inclined criteria band B2.
Even if the depth / width of the groove 12 is smaller than the slope criterion Cr2, if the slope 12 is larger than the lower limit value Cr2 ₁ of the slope criteria band B2 (range from Cr2 ₁ to Cr2), a bridging phenomenon can be established and water repellency can be achieved. Therefore, it is allowed to set the depth / width of the groove 12 within the range.
In the hydrophilic region F _B separated from the water repellent region F _A by the inclined criteria Cr2, the hydrophilicity is emphasized when the aspect ratio is increased (the upper right portion in FIG. 10). This is because the specific surface area increases because the groove 12 is deep (increase in surface roughness r).

The cross-sectional shape of the groove 12 of the surface microstructure 10A is not limited to a rectangle (FIG. 8A) or a trapezoid (FIG. 9), but may be a U-shape or a V-shape. In the case of a U-shape or V-shape, by setting the inclination angle θw along the inner wall 123, the depth / width of the groove 12 can be determined using the inclination criteria Cr2.
According to the cross-sectional shape of the groove 12 (FIG. 3) used for the sensitivity evaluation of the shape factor shown in FIG. 4 and the evaluation result of FIG. 4, the smaller the inclination angle θw, the easier the water droplet 14 bridge is formed. It is suggested that the larger the inclination angle θw, the more hydrophilic it becomes.

The width of the groove 12 can be set to about 1/4 or less of the diameter of the water droplet in order to establish a bridge, and can be set to about 5 μm to about 200 μm, for example. More preferably, it is about 30 μm to about 100 μm.
The pitch between the grooves 12 can be arbitrarily set to a value greater than zero. When the experiment was performed by changing the pitch between the grooves 12, the best water repellency was exhibited in a region where the pitch was less than twice the width of the groove 12. The result is Therefore, the pitch between the grooves 12 can be set to a value of about twice or less the width of the grooves 12. For example, the pitch between the grooves 12 can be set to about 5 μm to about 400 μm.
The pitch between the grooves 12 may be non-uniform.

The pattern of the groove 12 is arbitrary, such as a long one continuous from one end to the other end of the fin 10, an intermittent short one, a straight line, a curved line, etc., but in the sensitivity evaluation of the shape factor shown in FIG. Since the striped and latticed patterns are more water-repellent, a pattern having elongated sections can be preferably used.
In the case of a lattice, a water droplet moves obliquely from one straight line to the other at a portion where the straight line and the straight line intersect. Therefore, at the intersection of the straight lines, the width of the groove 12 (diagonal line intersecting the vertical line and the horizontal line) is relatively large with respect to the depth of the groove 12, whereas in the case of a striped pattern, The width of the groove 12 is constant throughout. For this reason, it is guessed that it is one of the factors that a striped pattern is excellent in the effect of water repellency that a bridge is easily formed over the entire striped pattern.

  When a water droplet having a volume of 1 μl is allowed to stand on the surface microstructure 10A (FIG. 11 (a)) including the groove 12 formed under the above conditions, as shown in FIG. 11 (b), the water droplet 14 and the material It exhibits water repellency when air 15 is caught between them. The contact angle θ at this time is 133 °.

The four plots shown in FIG. 10 show the data of the samples prepared in the form factor sensitivity evaluation described with reference to FIG.
All of these samples have grooves 12 formed by cutting.
The inclination angle θw of the sample corresponding to plots 1 to 3 (P1 to P3) is 0 °. Moreover, the pattern of the groove | channel 12 of these samples (P1-P3) is striped.
The inclination angle θw of the sample corresponding to the plot 4 (P4) is 26 °. The pattern of the grooves 12 of this sample (P4) is a lattice.

In the sample corresponding to plot 1, the width of the groove 12 is 200 μm, the depth of the groove 12 is 200 μm, and the depth / width is 1. The pitch between the grooves 12 is 200 μm.
In the sample corresponding to plot 2, the width of the groove 12 is 100 μm, the depth of the groove 12 is 10 μm, and the depth / width is 0.1. The pitch between the grooves 12 is 50 μm.
In the sample corresponding to plot 3, the width of the groove 12 is 100 μm, the depth of the groove 12 is 25 μm, and the depth / width is 0.25. The pitch between the grooves 12 is 200 μm.
In the sample corresponding to plot 4, the width of the groove 12 is 100 μm, the depth of the groove 12 is 100 μm, and the depth / width is 1. The pitch between the grooves 12 is 100 μm.
As can be seen from FIG. 10, each of the plots P1 to P4 belongs to a region above the slope criterion Cr2.
And the contact angle of the sample corresponding to plot 1 is 147 °,
The sample contact angle corresponding to plot 2 is 128 °,
The sample contact angle corresponding to plot 3 is 116 °.
The sample contact angle corresponding to plot 4 is 123 °,
From the above plot data, when the aspect ratio is determined to be equal to or greater than the slope criterion Cr2, the wettability is lowered and the water repellency is exhibited.

Next, a method suitable for manufacturing the surface microstructure 10A having the groove 12 deeper than a certain level based on the basic criteria Cr1 and the inclined criteria Cr2 described above will be described.
FIG. 12A shows a line for manufacturing the fin 10.
The aluminum alloy sheet material 21 having a thickness of about 100 μm used for the fin 10 is fed from a roll 22 and passes between the transfer rollers 23 and 24, and is formed into a predetermined shape in consideration of heat transfer rate, pressure loss, and the like. After being molded by the mold 25, it is cut into individual fins 10.

The transfer rollers 23 and 24 function as a mold that plastically processes the surface microstructure 10A on both surfaces of the fin 10. The transfer rollers 23 and 24 are manufactured by cutting a material having high rigidity used for a mold.
Concavities and convexities corresponding to the plurality of grooves 12 of the surface microstructure 10A (FIG. 1) are formed on the outer peripheral surfaces of the transfer rollers 23 and 24 (mold forming step). On the outer peripheral surfaces of the transfer rollers 23 and 24, convex portions corresponding to the grooves 12 and concave portions (grooves) corresponding to the adjacent grooves 12 and 12 are alternately arranged.

The height of the outer peripheral surfaces of the transfer rollers 23 and 24 with respect to the width of the convex portion 16 (FIG. 12B) is determined to be larger than the basic criteria band B1. Moreover, when the wall surface of the convex part 16 inclines with respect to the top | upper surface of the convex part 16, the height / width of the convex part 16 is defined so that it may become larger than inclination criteria belt | band | zone B2.
As shown in FIG. 12B, the transfer rollers 23 and 24 are provided with a phase shifted by the half cycle (1 / 2T) of the unevenness. Therefore, when the sheet material 21 passes between the transfer rollers 23 and 24, the grooves 12 are alternately transferred to the front and back of the sheet material 21 (transfer step).

According to the production line described above, since the step of imparting water repellency can be continuously performed by forming the surface microstructure 10A, it is possible to deal with mass production.
Further, since the phases of the unevenness of the transfer roller 23 and the unevenness of the transfer roller 24 are shifted (FIG. 12B), the transfer roller is less damaged and the sheet is less likely to be distorted.

By forming the groove 12 by the transfer rollers 23 and 24, the entire surface of the fin 10 can be sufficiently water-repellent.
In consideration of wear of a tool for cutting the sheet material 21 into individual fins 10, distortion of the fins 10, etc., it is possible to prevent a pattern from being formed at the boundary between the fins 10 and the fins 10 in the sheet material 21. . In that case, unevenness is not formed in a part of the circumferential direction of the transfer rollers 23 and 24 corresponding to the boundary between the fins 10 and 10.

Instead of the transfer rollers 23 and 24, molds 26 and 27 can be used as shown in FIG. By pressing the sheet material 21 between the molds 26 and 27 and pressing, the grooves 12 can be transferred to both surfaces of the sheet material 21.
Similar to the transfer rollers 23 and 24 (FIG. 12B), a plurality of convex portions 16 corresponding to the grooves 12 are arranged in the molds 26 and 27 with the concave portion 17 therebetween. The unevenness of the mold 26 and the unevenness of the mold 27 are alternately arranged.

The method for manufacturing the surface microstructure 10A is not limited to the method using the pair of transfer rollers 23 and 24 and the pair of molds 26 and 27.
For example, it is allowed to use one mold and form the surface microstructure 10A on the surface of the fin 10 by pressing the mold, and then turn the fin 10 over to form the surface microstructure 10A on the back surface.
In addition, it is allowed to form the surface microstructure 10A by laser processing, cutting, etching, or shot blasting.

The surface microstructure 10A of the above embodiment expresses water repellency by achieving water repellency using the basic criteria Cr1 and the inclined criteria Cr2, but the surface microstructure 10A achieves hydrophilicity using the basic criteria Cr1 and the inclined criteria Cr2. Thus, it goes without saying that the surface microstructure 10A that exhibits hydrophilicity can be provided.
According to the present invention, sufficiently high water repellency or hydrophilicity can be ensured by using the basic criteria Cr1 that defines the depth / width of the groove 12 and the inclined criteria Cr2 that considers the inclination of the inner wall of the groove 12. it can.

The present invention allows the surface microstructure 10 </ b> A to be provided only on one side of the fin 10.
Moreover, the shape of the fin 10 of this invention is not ask | required, The fin 10 may be formed in the corrugated shape (corrugated plate shape).
Further, similarly to the fins, it is also useful to provide the surface microstructure 10A on the surface of the tube that may come into contact with water or ice.
Furthermore, the surface microstructure 10A of the present invention can be applied to various members that require wettability control in addition to the fins of the heat exchanger.

  The length of the groove in the present invention is not limited. The groove in the present invention includes a concave portion (dimple) formed in a dot shape.

[Second Embodiment]
Next, a second embodiment of the present invention will be described with reference to FIGS. 14 and 15.
The second embodiment is characterized by imparting oil repellency to the constituent elements of the air conditioner.
In the first embodiment and the second embodiment, the types of liquids to be contacted are different between water and oil, but can basically be configured similarly based on the same concept.

A component 30 of the air conditioner shown in FIG. 14 is, for example, an outer plate that constitutes a housing, and is formed of a metal material such as stainless steel.
The surface structure 30 </ b> A of the component 30 includes a surface 31 with which oil droplets come into contact and a number of grooves 32 formed on the surface 31.
The grooves 32 have a rectangular cross section and extend in a straight line, and are arranged in parallel with each other at a predetermined interval. The dimension (width 32W) of the direction orthogonal to the length direction of the groove | channel 32 is sufficiently small with respect to the diameter of an oil droplet.
The contact angle formed between the smooth surface (surface 31) of the metal material of the component 30 and the oil droplet is assumed to be θe.

The pitch between the adjacent grooves 32 can be arbitrarily set to a value larger than zero. When the experiment was performed with the pitch between the grooves 32 changed, the best oil repellency was exhibited in a region where the pitch was less than twice the width 32W, and the oil repellency was obtained even when the pitch was twice the width 32W. Has been obtained. Therefore, the pitch between the grooves 32 can be set to a value that is about twice or less the width 32W. For example, the pitch between the grooves 32 can be set to about 5 μm to about 400 μm. The pitch may be uniform or non-uniform.
The pattern of the groove 32 is arbitrary, such as a long one extending linearly, a short one intermittently, a curved shape, or a dimple shape. A pattern having an elongated section can be suitably employed.

  The surface structure 30 </ b> A can be manufactured by using a transfer mold, a transfer roller, or the like corresponding to the groove 32. The surface microstructure 30A can also be formed by laser processing, cutting, etching, or shot blasting.

In the first embodiment, the behavior of the water droplets described with reference to FIGS. 5 to 7 and FIG. 9 applies to all of the droplets, and of course to the oil droplets.
As shown in FIG. 15A, if the value of the width 32W of the groove 32 is A, the value of the depth 32D can be expressed as A / tan θe, so the depth / width of the groove 32 is 1 / tan θe. . With this as the basic criterion Cr1 (FIG. 15B), the oil repellency and the oleophilicity can be drawn.
The reference numerals shown in FIG. 15B represent the same meaning as the reference numerals shown in FIG.

  The width 32W of the groove 32 is preferably set to about 1/5 or less of the diameter of the oil droplet in order to establish a bridge of the oil droplet. Further, regarding the relationship between the size of the oil droplets and the number of grooves 32, referring to FIG. 5 (d) showing the water droplets 14, at least four grooves 32 are included for the oil droplets as shown in this figure. It is preferable from the viewpoint of establishing a bridge. That is, the ratio P / D of the pitch P of the groove 32 to the diameter D of the oil droplet is preferably 1/5 or less. For example, assuming an oil droplet having a diameter of about 50 μm to about 100 μm, the width 32W of the groove 32 is preferably set to 0.1 to 10 μm.

In the present embodiment, the depth ratio (aspect ratio) of the groove 32 to the width 32W is set to be larger than that of the basic criteria Cr1. Thereby, the surface structure 30A has oil repellency.
Therefore, even if the air conditioner is used in an environment where oil may adhere, such as a kitchen, it is possible to suppress oil from adhering to the surface of the component 30, so that the oil or the location where the oil has adhered It is possible to reduce the burden of cleaning dirt that is sticky.

If the inner wall 123 of the groove 32 is inclined with respect to a perpendicular perpendicular to the surface 31 as shown in FIG. 9A, the aspect is higher than the inclined criteria Cr2 described with reference to FIG. The ratio should be large.
The inclination criteria Cr2 can be obtained by the above-described equation (2) using the contact angle θe and the inclination angle θw of the inner wall 123. The water repellent area F _{A in} FIG. 10 can be read as the oil repellent area F _A and the hydrophilic area F _{B as} the oleophilic area F _B.

[Modification of Second Embodiment]
Although the surface structure 30A can be formed on the material itself of the component 30 of the air conditioner, the surface 31 of the resin film 34 covering the surface of the metal material 33 (base material) of the component 30 as shown in FIG. The surface structure 30A can also be formed.
The surface structure 30A of the resin film 34 is preferably formed by nanoimprinting.
Nanoimprint is a technique for transferring minute irregularities formed in a mold to a resin or glass, and is applied to a material having a glass transition point. By the nanoimprint, the groove 32 can be formed with a depth and width of a scale of about 0.1 μm to 10 μm that exhibits a function of preventing adhesion of mist-like oil droplets.
A sufficient oil repellency can be obtained by forming the groove 32 having a depth of a certain level or more based on the basic criteria Cr1 and the inclined criteria Cr2 described above.

  In addition to the components of the air conditioner exemplified above, the surface structure 30A can be applied to an appropriate member that can contact oil droplets. For example, the surface structure of the present invention can be applied to machine tools, transport machines, building materials, packing materials, and clothing.

Hereinafter, an experimental example in which the oil repellency of a surface structure applied to a component (for example, a tool) constituting a machine tool is evaluated will be described.
The following three types of test materials A, B, and C were prepared, and the contact angle θ of the following cutting oil was measured.
Specimen A: Stainless steel (JIS SUS)
Specimen B: Fluororesin film (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer; PFA)
Specimen C: Groove 32 having an aspect ratio of 2 was formed in specimen B by nanoimprinting. The depth 32D of the groove 32 is 1 μm, the width 32W is 0.5 μm, and the pitch is 1 μm.
Cutting oil: DEE Oil Heavy Medium (trade name) Oil droplet diameter is 1mm

The measurement results of the contact angle are as follows.
Sample A: 12 °
Specimen B: 53 °
Specimen C: 103 °

According to the above, the fluororesin film (test material B) having a contact angle of 53 ° is sufficiently oil-repellent by forming the groove 32 deeper than a certain level (test material C).
Therefore, the surface of stainless steel (sample A) having a small contact angle θ is covered with the resin film 34 on which the fine surface structure 30A having the grooves 32 is formed, so that the stainless steel is substantially oil-repellent. Can be given. Therefore, it is possible to realize a machine tool part having both required rigidity and strength and oil repellency.

As is clear from the basic criteria Cr1 shown in FIG. 15B, the larger the contact angle θe formed by the smooth surface of the resin film 34 to be coated and the oil droplets, the greater the oil repellency even if the groove 32 is shallow. be able to.
The groove 32 is preferably formed on the surface of the resin film 34 in which oil droplets form a contact angle θe of 40 ° or more.

In the above, PFA is exemplified as the oil-repellent member, but fluorine resin such as PTFE (polytetrafluoroethylene) and FEP (perfluoroethylene propene copolymer (tetrafluoroethylene / hexafluoropropylene copolymer)), silicone resin, A resin material such as polyethylene can be used. These resin materials have a larger contact angle than metal materials, and can be expected to exhibit excellent oil repellency, similar to the PFA described above. By the way, although it is for water, the contact angle of the resin material is as follows.
PTFE: 114 ° PFA: 109 ° FEP: 115 °
Silicone resin: 110 ° Polyethylene: 88 °
In addition to the above, as long as the gist of the present invention is not deviated, the configuration described in the above embodiment can be selected or changed to another configuration as appropriate.
In the present specification, the description related to water repellency basically applies to oil repellency, and the description related to oil repellency basically applies to water repellency.
In addition, the present invention is not limited to water repellency and oil repellency, and can be used to develop the liquid repellency characteristics of any liquid.
The shape of the member provided with the surface structure of the present invention is not limited. For example, the present invention also applies to a member having a step formed on the surface, a member having a curved surface, a member having a undulation on the surface, and the like. The surface structure can be applied.

10 Fin 10A, 30A Surface structure 11, 31 Surface 12, 32 Groove 12D, 32D Width 12P Pitch 12W, 32W Width 14 Water drop 15 Air 21 Sheet material 22 Roll 23, 24 Transfer roller 25 Mold 26, 27 Mold 30 Component 33 metallic material 34 resin film 11A~11C surface 121 edge 122 edge 123 inner wall 124 bottom B1 basic criterion band B2 inclined criteria band Cr1 basic criterion Cr2 inclined criteria F1 region F2 region _{F A} region _{F B} region L1 perpendicular θe contact angle θw Angle of inclination

Claims (16)

The surface of the material,
A plurality of grooves formed on the surface,
When the contact angle between the smooth surface of the material and the droplet is θe,
The ratio of the depth to the width of the groove is greater than the basic criteria of 1 / tan θe, and exhibits liquid repellency.
A surface structure characterized by that. The ratio of the depth to the width of the groove is larger than the basic criteria when the contact angle is increased by 10%.
The surface structure according to claim 1. The surface of the material,
A plurality of grooves formed on the surface,
When the contact angle between the smooth surface of the material and the droplet is θe,
The ratio of the depth to the width of the groove is large with respect to the basic criteria which is 1 / tan θe when the contact angle is reduced by 10%.
A surface structure characterized by that. In the process in which a droplet disposed on the surface of the material enters the groove from one edge in the width direction of the groove,
Reach the other edge of the groove without reaching the bottom of the groove;
The surface structure according to any one of claims 1 to 3. When the inclination angle formed between the perpendicular to the surface of the material and the inner wall of the groove is θw,
The ratio of the depth to the width of the groove is larger than the slope criteria represented by the following formula:

The surface structure according to any one of claims 1 to 4. Expresses water repellency,
The width of the groove is 5 μm or more and 200 μm or less.
The surface structure according to any one of claims 1 to 5. Expresses water repellency,
The contact angle is 100 ° or more,
The surface structure according to any one of claims 1 to 6. A plurality of the grooves are formed by nanoimprinting.
The surface structure according to any one of claims 1 to 7. Expresses oil repellency,
The plurality of grooves are formed on the surface of the resin material in which oil droplets form the contact angle of 40 ° or more.
The surface structure according to any one of claims 1 to 5. Expresses oil repellency,
The ratio P / D of the pitch P of the groove to the diameter D of the oil droplet contacting the material is 1/5 or less.
The surface structure according to any one of claims 1 to 9. Expresses oil repellency,
Assuming that the diameter of the oil droplet contacting the material is 50 μm or more and 100 μm or less, the width of the groove is 0.1 μm or more and 10 μm or less.
The surface structure according to any one of claims 1 to 10. The refrigerant is thermally coupled to the tube through which it flows,
Having a surface structure according to any one of claims 1 to 7,
The fin of the heat exchanger characterized by the above-mentioned. A fin according to claim 12;
A tube through which the refrigerant flows,
A heat exchanger characterized by that. It has the surface structure according to any one of claims 1 to 5, 8, 9, 10, and 11,
Expresses oil repellency,
A component of an air conditioner characterized by that. The material in contact with the oil drop is
With the base material,
A film formed from a resin material and covering the surface of the base material,
The contact angle of the film is 40 ° or more;
On the surface of the film,
A plurality of the grooves are formed by nanoimprinting,
The component of the air conditioner of Claim 14. Forming a shape corresponding to the groove of the surface structure according to any one of claims 1 to 10 in a mold;
Plastically processing the material using the mold, and
A method for producing a surface structure, wherein:

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