JP2021085091A - Hydrophilic coating and precoated fin - Google Patents

Abstract

To provide a hydrophilic coating having excellent hydrophilicity even after brazing heat treatment and a precoated fin.SOLUTION: A hydrophilic coating is formed on the outer surface of a base material composed of aluminum or an aluminum alloy and consists of particles composed of γ-alumina alone, or consists of particles composed of alumina hydrate alone, or consists of mixed particles.SELECTED DRAWING: Figure 1

Description

The present invention relates to hydrophilic coatings and precoated fins.

As a heat exchanger for air conditioning such as an air conditioner, a heat exchanger in which a copper tube and an aluminum fin are mechanically bonded is widely used.
When the heat exchanger is used as the evaporator side, when water vapor in the air is condensed and the condensed water adheres to the fins as water droplets, the ventilation resistance increases and the pressure loss increases, which reduces the capacity of the heat exchanger. Is a problem.
Further, in recent years, a type of heat exchanger in which an aluminum tube and fins are combined and joined by brazing heat treatment is being studied, and even in such a heat exchanger, improvement in drainage of condensed water is required. ing.

For example, Patent Document 1 below describes a technique for improving the drainage of condensed water by performing surface treatment on the front and back surfaces of fins in a heat exchanger in which a copper tube and aluminum fins are mechanically coupled. Is disclosed.
Further, Patent Document 2 below describes a heat exchanger in which a plurality of flat tubes made of aluminum and a plurality of fins are brazed and joined, and a windward bulging portion is provided between the plurality of fins along the air passage direction. The leeward side bulge is provided, and the height of the flat portion formed between the bulge and the flat pipe is disclosed so that the leeward side is larger than the leeward side.

Japanese Patent No. 6111364 Japanese Patent No. 5177306

In the surface treatment technique described in Patent Document 1, a hydrophilic film made of a cured product of a coating film in which an appropriate amount of a polymer polymer, alcohol, cellulose, etc. is mixed with a water-soluble polymer compound is provided on the surface of the fin material to make it hydrophilic. It is a technology to improve. However, since this hydrophilic film is a film containing a polymer compound, there is a problem that the polymer compound deteriorates when used in a heat exchanger of the type that joins fins and tubes through brazing heat treatment such as heating at 600 ° C. Had had.
The technique described in Patent Document 2 has a structure in which a flat portion is provided on the lower surface of the bulging portion in order to smoothly drain the drain water generated during defrosting, and the flat portion is inclined to facilitate the drainage of drain water. However, it is considered that the structure is not particularly considered in terms of improving the drainage property of the condensed water itself generated on the front and back surfaces of the fins.

An object of the present invention is to provide a technique that is applicable to a heat exchanger having a brazed configuration and can improve the drainage property of dew condensation water adhering to fins.

The hydrophilic film of the present invention is formed on the outer surface of a base material made of aluminum or an aluminum alloy, and is composed of particles made of γ-alumina or particles made of alumina hydrate, either alone or mixed. It is characterized by being.
In the hydrophilic film of the present invention, it is preferable coating amount of the particles is 0.05 g / ^{m 2} or more 2.3 g / ^{m 2} or less.

In the hydrophilic film of the present invention, the film thickness is preferably 25 nm or more and 2000 nm or less.
In the hydrophilic film of the present invention, the particle size of the particles is preferably 5 nm or more and 2000 nm or less.
In the hydrophilic film of the present invention, the alumina hydrate is preferably alumina monohydrate or alumina trihydrate.

The precoated fin of the present invention is characterized in that the hydrophilic film described in any of the above is formed on at least one surface.
The precoated fin of the present invention is characterized in that the hydrophilic film described in any of the above is a clad material of aluminum or an aluminum alloy formed on at least one surface.

Since the hydrophilic film according to the present invention is a hydrophilic film mainly composed of γ-alumina particles or alumina hydrate particles formed on the outer surface of the base material, excellent hydrophilicity can be obtained by these particles. Therefore, when applied to the outer surface of the fin, it is possible to provide a fin having excellent drainage property such as dew condensation water.
Further, even when the fin is applied to a fin for a heat exchanger of a type that undergoes brazing heat treatment, excellent hydrophilicity can be exhibited after the brazing heat treatment, and the fin has excellent drainage property. Can be granted.

As a result, for both fins of a general heat exchanger in which aluminum fins are mechanically bonded to a copper tube and a heat exchanger in which aluminum fins are brazed to an aluminum tube. Can also provide a hydrophilic film that can impart excellent hydrophilicity.
Further, excellent hydrophilicity can be exhibited even after the brazing heat treatment, and drainage can be ensured by applying the coating in advance before the brazing heat treatment, so that a precoated fin having excellent surface drainage can be provided.

It is a perspective view which shows an example of the heat exchanger constructed by applying the hydrophilic film which concerns on this invention. It is sectional drawing which took the cross section in the heat exchanger shown in FIG. 1 along the plane orthogonal to the length direction of a tube. In the heat exchanger shown in FIG. 1, it is a cross-sectional view which took a vertical cross section along the length direction of a tube, and shows the state before a brazing process. In the heat exchanger shown in FIG. 1, it is a cross-sectional view which took a vertical cross section along the length direction of a tube, and shows the state after a brazing process. It is a partial cross-sectional view which shows the state which provided the hydrophilic film on both sides of the fin material which provided the brazing material layer on one side. A partial cross-sectional view showing a state in which a hydrophilic film is provided on both sides of a fin material having a brazing material layer on both sides. It is a front view which shows the other example of the heat exchanger constructed by applying the hydrophilic film which concerns on this invention. It is a partially enlarged sectional view of the heat exchanger. It is a partial cross-sectional view which shows the heat exchanger assembly before brazing the heat exchanger. The graph which shows the example of the analysis result by the Fourier transform infrared spectroscopy (FT-IR) about the example of the hydrophilic film which concerns on this invention. The graph which shows an example of the analysis result by the Fourier transform infrared spectroscopy (FT-IR) about the conventional hydrophilic film.

Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the accompanying drawings. In addition, in the drawings used in the following description, in order to make the features easy to understand, the featured parts may be enlarged for convenience, and the dimensional ratio of each component is the same as that of the actual heat exchanger. Not always.

"First embodiment"
FIG. 1 is a perspective view showing an example of a heat exchanger configured by using a fin material having a hydrophilic film according to the present invention.
The heat exchanger 11 of this example is used as a heat exchanger for indoor / outdoor units of a room air conditioner, an outdoor unit for HVAC (Heating Ventilating Air Conditioning), a heat exchanger for automobiles, and the like. It is an all-aluminum heat exchanger.

As shown in FIG. 1, the heat exchanger 11 is parallel to and vertically spaced between a pair of header pipes 14 and a pair of header pipes 14 which are vertically separated from each other and erected in parallel. , A plurality of flat tubes 22 joined at substantially right angles to the header tube 14 and the outer surface (upper surface or lower surface) 12b of the tube body 12 constituting these tubes 22 are brazed to dissipate heat to the outside air. A plurality of fins (aluminum fins) 13 and a plurality of fins (aluminum fins) 13 are provided.
A supply pipe 15 for supplying a refrigerant to the tube 22 is connected to the upper end of one of the pair of left and right header pipes 14 via the header pipe 14. A recovery pipe 16 for recovering the refrigerant via the tube 22 is connected to the lower end of the other header pipe 14. The tube 22, the fin 13, the header pipe 14, the supply pipe 15, and the recovery pipe 16 are all made of aluminum or an aluminum alloy.

FIG. 2 is a partial cross-sectional view of the heat exchanger 11 having a cross section taken along a plane orthogonal to the length direction of the tube 22. As shown in FIG. 2, a plurality of (six in this example) refrigerant flow paths 12a arranged along the width direction are formed inside the pipe body 12 constituting the tube 22. Further, as shown in FIG. 2, a plurality of notches 19 having a shape corresponding to the cross-sectional shape of the tube 22 are formed in the fin 13 at predetermined intervals (8 in this example). Tubes 22 are fitted into the notches 19 and fixed by brazing.
As an example, the tube 12 has a flat front surface (upper surface) 12A and a back surface (lower surface) 12B, and a large number of flat cross sections including a first short side surface 12C and a second short side surface 12D adjacent to the front surface 12A and the back surface 12B. The hole is formed in a tubular shape.

3 and 4 are partial cross-sectional views taken along the length direction of the tube 22 in the heat exchanger 11, and FIG. 3 shows the state of the heat exchanger assembly 11a before the brazing heat treatment. , FIG. 4 shows the state after the brazing heat treatment.
As shown in FIG. 2, the fins 13 have a vertically long rectangular plate shape, and a plurality of fins 13 are arranged in parallel along the length direction of the tube 22, and the tube 22 is inserted through the notch 19. The plurality of fins 13 are arranged in parallel with each other at regular intervals.
As shown in FIGS. 3 and 4, the fin 13 is formed with a bent portion 20 bent in the thickness direction of the fin 13 along the outer surface 12b of the tube 22 at the peripheral edge of the notch 19. These bent portions 20 can be formed by, for example, burring.

The tube 22 and the fin 13 are arranged so that the tube 22 is inserted into a plurality of fins 13 arranged at regular intervals, and the tube 22 is fitted in the notch 19 of the fin 13 and individually fixed by brazing. ing.
In the state before the brazing heat treatment shown in FIG. 3, it is preferable to adjust the gap between the bent portion 20 formed in the cutout portion 19 of the fin 13 and the upper surface or the lower surface of the tube 22 to 10 μm or less.
In the fin 13 of this example, the tube 22 is inserted through the notch 19, but the fin 13 may be provided with a slit-shaped through hole instead of the notch 19, and the tube 22 may be inserted through the through hole. good.

Hereinafter, the main components of the heat exchanger 11 will be described in more detail.
<Fin>
As shown in FIG. 4, the fins 13 are a plate-shaped base material 3 made of aluminum or an aluminum alloy, and a hydrophilic film after brazing heat treatment provided on the first surface 3a and the second surface 3b of the base material 3. Has 1a. That is, the hydrophilic film 1a after the heat treatment is provided on both the front and back surfaces of the base material 3.
<Base material>
The base material 3 is made of a pure aluminum alloy such as JIS1050 or an alloy mainly composed of JIS3003 aluminum alloy. The base material 3 may be formed of an aluminum alloy having another composition system.
The base material 3 is processed by melting the above-mentioned aluminum alloy by a conventional method and passing through a hot rolling step, a cold rolling step, a pressing step and the like. The method for producing the base material 3 is not particularly limited in the present invention, and a known production method can be appropriately adopted.

<Hydrophilic film>
In the heat exchanger assembly 11a before the brazing heat treatment shown in FIG. 3, the hydrophilic film 1 according to the present embodiment is formed on the outer surface (both front and back surfaces) of the fin 13.
The heat exchanger assembly 11a corresponds to the heat exchanger before brazing, and the left and right header tubes 14, the tubes 22, and the fins 13a are assembled so as to have an approximate shape shown in FIG. The heat exchanger 11 can be obtained by heating the heat exchanger assembly 11a to a brazing heat treatment temperature as described later.
The hydrophilic film 1 formed on the fins 13a of the heat exchanger assembly 11a is a colloid of crystalline alumina hydrates such as γ-alumina, alumina monohydrate called alumina sol, and alumina trihydrate. It is a film obtained by applying a paint in which a solution and a surfactant are dissolved in a solvent and drying the film.
Nitric acid or acetic acid may be contained as a stabilizer in the alumina sol used for the coating material forming the hydrophilic film 1. The coating material of the present embodiment is, for example, a solution obtained by adding about 3 to 6 g of a colloidal solution of crystalline alumina hydrate such as alumina monohydrate or alumina trihydrate to 30 g of water as a solvent.
As the crystalline alumina hydrate, alumina monohydrates such as dibusite, bayarite and norstrandite, alumina trihydrates such as boehmite and dispore, and todite can be applied.
As γ-alumina, powdered commercially available γ-alumina was used as a dispersion medium by mixing with water.

Nitric acid or acetic acid as a stabilizer is preferably contained in the colloidal solution in an amount of about 0.2 to 0.8% by mass in terms of mass ratio with respect to the alumina sol.
Colloidal solution, as an example, Al ₂ as principal contain about 70 wt% to 90 wt% water as blended with stabilizer dispersion medium constituting the alumina monohydrate or alumina trihydrate O A composition containing about 10 to 30% by mass of _{3 can be adopted.}

The thickness of the hydrophilic film 1 is preferably 25 nm or more and 2000 nm or less.
When the coating material is applied to the surface of the fin 13a to form the hydrophilic film 1, the amount of γ-alumina, alumina monohydrate, and alumina trihydrate adhered is 0.05 ^{g / m 2} or more and 2.3 g /. The range is preferably m ² or less (0.05 to 2.3 g / m ^2).
When configuring the hydrophilic film 1 is applied to the surface of the paint the fins 13a, the adhesion amount of the surface active agent 0.05 g / ^{m 2} or more 1.0 g / ^{m 2} or less in the range (0.05-1. It is preferably 0 g / m ^2).

In order to obtain an excellent water contact angle, the amount of adhesion of γ-alumina, alumina monohydrate, and alumina trihydrate is 0.2 g / m ² or more even within these ranges. A range of 5 g / m ² or less is desirable. The amount of the surfactant attached is preferably in the range ^{of 0.1 g / m 2} or more and 1.0 g / m ^{2 or less.}
Further, in order to obtain a particularly excellent water contact angle, the amount of adhesion of γ-alumina, alumina monohydrate, and alumina trihydrate is 0.2 g / m ² or more 1 even within these ranges. A range of .2 g / m ² or less is more desirable. The amount of the surfactant attached is more preferably in the range ^{of 0.1 g / m 2} or more and 0.5 g / m ^{2 or less.}

When the thickness of the hydrophilic film 1 is less than 25 nm, the amount of γ-alumina, the amount of alumina monohydrate, and the amount of alumina trihydrate present in the film are insufficient. The water contact angle becomes large, and the hydrophilicity of the fin 13 decreases.
When the thickness of the hydrophilic film 1 exceeds 2000 nm, the hydrophilic film 1 is too thick and the brazing property is lowered.

If the amount of adhesion of the hydrophilic film 1 is ^{less than 0.05 g / m 2} , the amount of γ-alumina, the amount of alumina monohydrate, and the amount of alumina trihydrate will be insufficient. The contact angle becomes large, and the hydrophilicity of the fin 13 decreases.
If the amount of γ-alumina, alumina monohydrate, or alumina trihydrate adhered ^{to the hydrophilic film 1 exceeds 2.3 g / m 2} , the hydrophilic film 1 is too thick and the brazing property is lowered.
When the amount of the surfactant attached ^{to the hydrophilic film 1 is less than 0.05 g / m 2} , discoloration is likely to occur on the hydrophilic film 1.
If the amount of the surfactant attached to the hydrophilic film 1 ^{exceeds 1.0 g / m 2} , there is a concern that the brazing property may be deteriorated due to the excessive amount of the surfactant present on the surface of the fin 13a.
By containing a surfactant in addition to alumina monohydrate and alumina trihydrate, it is possible to provide a hydrophilic film capable of suppressing a change with time after coating and preventing discoloration.

Further, the particles of alumina monohydrate and alumina trihydrate contained in the hydrophilic film 1 tend to have an angular shape rather than a spherical shape, and thus the alumina 1 water dispersed in the coating film. Japanese particles and alumina trihydrate particles have a major axis (length in the longitudinal direction). The major axis of the alumina monohydrate particles and the alumina trihydrate particles is preferably in the range of 5 nm or more and 2000 nm or less (5 to 2000 nm).
This major axis indicates the major axis of the alumina monohydrate particles and the alumina trihydrate particles existing in the coating film before brazing. If the length of the major axis is less than 5 nm, the contact angle increases, and conversely, if it exceeds 2000 nm, the contact angle increases and the brazing property decreases.
The measurement of these particles is an average value of 50 particles existing in the field of view based on the TEM image of the sample. The shape of these particles may be various shapes such as granular, rod-shaped, needle-shaped, and feather-shaped, and any shape may be used, but any shape has a long axis.

As a surfactant that can be contained in the hydrophilic film 1, a nonionic surfactant can be exemplified, and among them, for example, polyoxyethylene alkyl ether can be used.
In addition, as an anionic surfactant, a carboxylate, a sulfonate, a sulfate ester salt, a phosphoric acid ester salt and the like can be applied. LAS known as an alkylbenzene sulfonate, MES known as an α-sulfo fatty acid methyl ester salt, AOS known as an α-olefin sulfonate, and the like may be used. As the sulfate ester salt, AS of an alkyl sulfate ester salt, AES known as a polyoxyethylene alkyl sulfate ester salt, or the like may be used.
In addition, as a cationic surfactant, a carboxylate or a quaternary ammonium salt can be provided.
In addition, as the nonionic surfactant, glycerin fatty acid ester, sorbitan fatty acid ester, sucrose fatty acid ester, polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene polyoxypropylene glycol and the like may be used. .. Further, as the amphoteric surfactant, alkyl betaine, fatty acid amide propyl betaine, alkylamine oxide and the like may be used.

In the heat exchanger assembly 11a shown in FIG. 3, brazing material layers 5 are formed on the upper surface and the lower surface of the tube 22, and the heat exchanger assembly 11a is heated to a temperature of about 580 to 620 ° C. for several minutes to several tens of minutes. The brazing filler metal layer 5 can be melted by heating to some extent. After the heat treatment and cooling, a heat exchanger 11 in which the tube 22 and the fins 13 are brazed can be obtained by the brazing layer 5A as shown in FIG.
The hydrophilic coating film 1 formed on the fins 13a before brazing becomes a hydrophilic film 1a after the brazing heat treatment and remains on the outer surface of the fins 13.

As an example, the brazing material layer 5 can use a coating film of a brazing paint containing Si powder, a Zn-containing flux or a non-Zn-containing flux, and a binder.
As an example, the ratio of Si powder coating amount: 1.0 to 5.0 g / m ² , flux coating amount: 3.0 to 20.0 g / m ² , binder coating amount: 0.5 to 8.5 g / m ² A brazing composition coating film can be used.
When the coating film contains a Zn-containing flux, Zn diffuses on the upper surface and the lower surface of the tube 22 to form a Zn diffusion layer during the brazing heat treatment, and the Zn diffusion layer exerts an anticorrosion effect.
The brazing material layer 5 may be composed of other generally known brazing composition paints or a general brazing material layer applied to a clad material such as a brazing sheet.
Further, it can be used even in a configuration in which a brazing material layer is formed on the fin 13 side and a brazing material layer is not formed on the tube 22. At this time, a Zn sprayed layer or a flux layer may be formed on the surface of the tube 22.

The hydrophilic film 1 of this embodiment is mainly composed of γ-alumina, alumina monohydrate, alumina trihydrate and a surfactant before brazing, and after brazing heat treatment, alumina monohydrate and alumina 3 Hydrophilicity is exhibited by removing water from the hydrate, evaporating the surfactant, and then aggregating the alumina particles after heating to form an aluminum oxide film. Therefore, the hydrophilic film 1a after the brazing heat treatment also exhibits good hydrophilicity.

Since the hydrophilic film 1 of this embodiment is mainly composed of γ-alumina, alumina monohydrate, alumina trihydrate, a surfactant and a solvent, it is excellent not only before the brazing heat treatment but also after the brazing heat treatment. Expresses hydrophilicity.
Therefore, in the heat exchanger 11 shown in FIG. 1, even if water adheres to the outer surface of the fins 13, a thin water film is formed and no water droplets are generated. Therefore, the water droplets block the gap between the adjacent fins 13. There is nothing to do. Therefore, it is possible to provide the heat exchanger 11 in which the ventilation resistance between the fins does not increase due to water droplets and the heat exchange efficiency does not easily decrease.

Further, since the hydrophilic film 1 of the present embodiment contains an appropriate amount of the surfactant, there is little possibility of discoloration after coating, and discoloration of the fins 13 is unlikely to occur. Therefore, when the hydrophilic film 1 is stored after being applied, there is no problem in the appearance and aesthetics of the fins 13. Further, if the amount of the surfactant contained in the hydrophilic film 1 is too large, the brazing property may be adversely affected.
If the hydrophilic film 1 seems to discolor in a short time after coating, the heat exchanger must be assembled and brazing heat treatment or the like must be performed in a short time after coating. In this respect, if the hydrophilic film 1 does not discolor in a short time after application, it takes a long time to process fins, assemble a heat exchanger, perform brazing heat treatment, etc., so that there is a margin in the production plan. ..

In the embodiment shown in FIGS. 1 to 4, an example in which the hydrophilic film 1 is formed on the front and back surfaces of the base material 3 as the fin 13 has been described.
However, as for the structure of the fin 13, a structure in which a brazing material layer is bonded to one side of the base material 3 to form a brazing sheet, or a structure in which a brazing material layer is bonded to both sides of the base material 3 to form a brazing sheet is adopted. May be done.
FIG. 5 shows an example of the above configuration, in which the brazing material layer 3A is bonded to one side (upper surface in FIG. 5) of the base material 3, and is attached to the bottom surface side of the base material 3 and the upper surface side of the brazing material layer 3A, respectively. The fin material 25 is formed by forming the hydrophilic film 1.
FIG. 6 shows another example of the above-described configuration, in which the brazing material layer 3A is laminated on both sides of the base material 3 (both upper and lower sides in FIG. The fin material 26 is formed by forming a hydrophilic film 1 on the outer surface side (upper surface side) of the brazing material layer 3A on the bottom surface side and the upper surface side of the base material, respectively.

By processing these fin materials 25 and 26 to form fins 13a, it can be applied as fins 13 of the heat exchanger 11 shown in FIGS. 1 to 4.
Since the fin materials 25 and 26 are provided with the hydrophilic film 1 on the outer surface as in the previous example, excellent hydrophilicity can be obtained.
Further, since the hydrophilic film 1 exhibits good hydrophilicity even after undergoing brazing heat treatment, the fin 13 made of fin materials 25 and 26 exhibits good hydrophilicity. Therefore, the heat exchanger provided with the fins 13 made of the fin materials 25 and 26 can obtain the same effect as the heat exchanger 11 described in the previous example.

"Second form"
Hereinafter, a second form in which the hydrophilic film is applied to a corrugated fin type heat exchanger will be described.
As shown in FIG. 7, the heat exchanger 30 of the second form is the header tubes 31 and 32 which are separated from each other to the left and right and are oriented in the vertical direction and arranged in parallel with each other, and the header tubes 31 and 32 of these header tubes 31 and 32. A plurality of flat tubes 33 joined in parallel with each other at a right angle to the header tubes 31 and 32, and corrugated fins (corrugated fins) 34 joined to each tube 33. It is mainly composed of. The header tube 31, 32 tube 33 and the fin 34 are all made of an aluminum alloy.

More specifically, as shown in FIGS. 7 and 8, a plurality of slits 36 are formed on the opposite side surfaces of the header pipes 31 and 32 at regular intervals in the length direction of each pipe, and the header pipes 31 and 32 are formed. The tube 33 is erected between the header tubes 31 and 32 by inserting the end of the tube 33 into the slits 36 facing each other. Further, fins 34 are arranged between a plurality of tubes 33 erected between the header tubes 31 and 32 at predetermined intervals, and these fins 34 are brazed to the front surface side or the back surface side of the tubes 33.

As shown in FIG. 8, the first fillet portion 38 is formed by the brazing material at the portion where the end portion of the tube 33 is inserted through the slit 36 of the header tubes 31 and 32, and the tube 33 is brazed with respect to the header tubes 31 and 32. It is attached. Further, in the corrugated fin 34, the apex portion of the wave is opposed to the front surface or the back surface of the adjacent tube 33, and the brazing material generated in the portion between them forms the second fillet portion 39, and the surface of the tube 33 is formed. Corrugated fins 34 are brazed to the side and the back surface.

In the heat exchanger 30 of the present embodiment, the header tubes 31 and 32, a plurality of tubes 33 erected between them, and a plurality of fins 34 are assembled to form a heat exchanger assembly, and the heat exchanger is heated. It is manufactured by attaching. The Zn diffusion layer 42 is formed on the front surface side and the back surface side of the tube 33 by heating during brazing.

The tube 33 of the present embodiment is provided with a plurality of refrigerant passages 33C formed therein, a flat front surface (upper surface) 33A and a back surface (lower surface) 33B, and a short side surface adjacent to the front surface 33A and the back surface 33B. It is formed into a flat, multi-hole tubular shape.
As shown in FIG. 9, the brazing coating film 37 is applied to the front surface 33A and the back surface 33B of the tube 33 in the state of the heat exchanger assembly 41 before brazing. The Zn contained in these brazing coating films 37 is diffused to the front surface 33A and the back surface 33B by heating at the time of brazing, and the Zn diffusion layer 42 is formed. The Zn diffusion layer 42 has a lower potential than the aluminum alloy constituting the tube 33, and preferentially corrodes in a planar manner to suppress the formation of pitting corrosion in the tube 33, thereby providing an anticorrosive function to the tube 33. Play.

The fin 34 is made of a plate-shaped fin material whose cross-sectional structure is enlarged and shown in FIG. 8, and is processed into a corrugated shape. The fin material is composed of a base material 34a made of an aluminum alloy plate and a hydrophilic coating film 35a formed on its outer surface (both front and back surfaces).
The aluminum or aluminum alloy constituting the base material 34a is not particularly limited, and an aluminum material having a composition applied to the base material of a general heat exchanger fin can be appropriately used.

In this embodiment, as shown in FIG. 9, as the hydrophilic film 35 before the brazing heat treatment, a film equivalent to the hydrophilic film 1 used in the first embodiment can be applied.
In the case of the heat exchanger 30 shown in FIGS. 7 and 8, a hydrophilic film 35 can be provided as a precoat film on the fins 34 as shown in FIG. 8 before the heat exchanger is formed by brazing.
This hydrophilic film 35 becomes a hydrophilic film 35a after brazing heat treatment. This hydrophilic film 35a exhibits excellent hydrophilicity even after brazing heat treatment.

Since the heat exchanger 30 having the structure shown in FIGS. 7 and 8 has the hydrophilic film 35a, the same effect as that of the heat exchanger 11 described above can be obtained.

In the first embodiment, a structure in which a brazing coating film for brazing is provided on the front surface or the back surface of the tube 33 is adopted, but the brazing coating film is abbreviated and the brazing coating film of the tube 33 and the fin 34 is brazed. Brazing may be arranged within the range of the part to be joined, and the structure of the heat exchanger brazed using this brazing may be adopted.
The tube 33 and the fins 34 may be brazed and joined by melting the placed brazing by heating at the time of brazing and spreading the molten brazing around the boundary portion between the tube 33 and the fins 34.

Further, the fin 34 may be composed of a three-layered brazing sheet having brazing material layers provided on both the front and back surfaces of the core material layer, and the tube 33 may adopt a structure in which no brazing coating film is provided. At this time, a Zn sprayed layer or a flux layer may be formed on the outer surface of the tube 33.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.
<Preparation of sample>
A plate containing Si: 0.4 to 1.0% by mass, Mn: 1.0 to 2.0% by mass, Zn: 0.5 to 3.5% by mass, and having a composition of the balance Al and unavoidable impurities. A plurality of aluminum base materials were prepared, and these base materials were subjected to degreasing treatment.
After the degreasing treatment, the hydrophilic paints described below were applied to the front and back surfaces of each base material by bar coater coating.

<Main component of paint>
Using a colloidal solution in which crystalline alumina hydrates such as γ-alumina, alumina monohydrate or alumina trihydrate are individually or mixed and dissolved in water, this colloidal solution is dissolved in water. The obtained hydrophilic paint was applied to both sides of the substrate. Boehmite and dispore are used as the alumina monohydrate, dibsite, bayarite and norstrandite are used as the alumina trihydrate, and other toadite is used, and this coating film is heated in an atmosphere of 240 ° C. for 30 seconds. It was dried to obtain a hydrophilic film before brazing.
As γ-alumina, powdered commercially available γ-alumina was used and mixed with water as a dispersion medium.

When these hydrophilic paints are applied on an aluminum base material by bar coater coating, the coating amount of each particle is adjusted as shown in Tables 1 to 6 described later to obtain a hydrophilic film.

Next, an aluminum alloy for tubes containing Si: 0.3 to 0.5% by mass and Mn: 0.2 to 0.4% by mass and composed of the balance Al and unavoidable impurities was melted and extruded from this alloy. An aluminum alloy tube for a heat exchanger having a flat cross-sectional shape (thickness 0.26 mm × width 17.0 mm × height 1.5 mm) was formed.
Further, a coating film of a brazing material layer was formed on the flat upper surface and the lower surface of these tubes. The coating film of the brazing filler metal is 3 g of Si powder (D (99) particle size 10 μm), 6 g of Zn-containing flux (KZnF ₃ powder: D (50) particle size 2.0 μm), 1 g of acrylic resin binder, and as a solvent. A solution consisting of 16 g of a mixture of 3-methoxy-3-methyl-1butanol and isopropyl alcohol was applied with a bar coater and dried (heated in an atmosphere of 150 ° C. for 5 minutes) to form a solution.

The aluminum fin material was corrugated by corrugating to form an aluminum fin having a total length of 100 mm. The 11 tubes were combined with the 10 aluminum fins to assemble a mini-core test piece having a 10-stage structure similar to the shape of the heat exchanger shown in FIG.
Brazing heat treatment was performed under the condition that these mini-core specimens were kept in a furnace in a nitrogen atmosphere at 600 ° C. for 3 minutes. By this brazing heat treatment, sacrificial anode layers are formed on the upper and lower surfaces of the tube on which the brazing coating film was formed, and the fins having a hydrophilic film and the tube are brazed and joined to heat the tube. It was used as a exchanger test piece.

The film thickness (nm) of the hydrophilic film before brazing formed on the aluminum fin material of the mini-core test piece was measured according to the procedure described later.
The contact angle on the fin surface of the heat exchanger test piece (after brazing heat treatment) was measured based on the following conditions.
The brazing property was evaluated based on the following conditions.

[Measurement of hydrophilic film thickness before brazing]
The vicinity of the surface containing the hydrophilic film of the fin material cut out to 10 mm × 10 mm is processed with FIB (Focused Ion Beam), and the processed cross section is processed with FE-SEM (Field Emission-Scanning Electron Microscope). An image was taken at a magnification of 50,000 times with a microscope), and the thickness of the hydrophilic film before brazing was actually measured.

[Contact angle: Contact angle after repeated dry / wet test]
The sample before brazing heat treatment with the hydrophilic film coated and the sample after brazing heat treatment at 600 ° C for 3 minutes are immersed in running water for 8 hours and then dried for 16 hours, which is 14 cycles. The contact angle of the aluminum fin surface after the implementation was measured. If the contact angle at this time was 30 ° or less, it was judged to have good hydrophilicity.

[Brazing property: Fin bonding rate evaluation test]
Each of the brazed fins was peeled off from the tube, and the fin joint marks remaining on the tube surface were observed. Then, the number of unjoined parts (places where brazing was performed but no joint traces remained) was counted. 100 observations were made on one sample, and a sample in which 80 or more (80% or more) were normally brazed and joined was judged to be a sample having good brazing property.
The above measurement results and observation results are summarized in Tables 1 to 6 below.

As shown in Tables 1 to 6, Examples 1 to 9 are samples in which γ-alumina particles are contained alone in a hydrophilic film, and Examples 10 to 28 are boehmite and die spor in addition to γ-alumina particles. , Todite, dibusite, boehmite, norstrandite, any one or more of the particles are mixed and added.
Examples 29 to 37 are samples in which boehmite particles are contained alone in a hydrophilic film, and Examples 38 to 52 are any one of dispore, toadite, jibsite, bayerite, and norstrandite in addition to boehmite particles. Alternatively, it is a sample in which two or more kinds of particles are mixed and added.
Examples 53 to 61 are samples in which the die-spore particles are contained alone in the hydrophilic film, and Examples 62 to 71 are any one or 2 of todite, dibsite, bayarite, and norstrandite in addition to the die-spore particles. This is a sample in which particles of seeds or more are mixed and added.

Examples 72 to 80 are samples in which toadite particles are contained alone in a hydrophilic film, and examples 81 to 86 are one or more of dibusite, bayarite, and norstrandite in addition to toadite particles. This is a sample in which the particles of the above are mixed and added.
Examples 87 to 95 are samples in which dibusite particles are contained alone in a hydrophilic film, and Examples 96 to 98 are a mixture of one or two particles of bayarite and norstrandite in addition to dibusite particles. It is a sample added by.
Examples 99 to 107 are samples in which the bayerite particles are contained alone in the hydrophilic film, and Example 108 is a sample in which particles of norstrandite are mixed and added in addition to the bayerite particles.
Examples 109 to 117 are samples in which norstrandite particles are contained alone in a hydrophilic film.

As described in Examples 1 to 117, if the hydrophilic film (before brazing) having a film thickness of 25 to 2000 nm and a particle diameter of 5 to 2000 nm using the above-mentioned particles, the water contact angle before brazing is 10. A hydrophilic film having excellent hydrophilicity and excellent hydrophilicity at ° to 30 ° and having a water contact angle of 8 ° to 30 ° even after brazing can be obtained. I was able to.

As shown in Tables 5 and 6, the coating amount of any of γ-alumina, boehmite, dispore, toadite, dibusite, bayarite, and norstrandite particles is 0.03 g / m, which is less than ^{0.05 g / m 2. In} the comparative example set to 2, the water contact angle exceeded 30 ° and the hydrophilicity decreased. Further, in the comparative example in which the coating amount of the particles was 2.5 g / m ^{2 , which was more than 2.3 g / m 2} , the brazing property was lowered.
As shown in Tables 5 and 6, a comparative example in which the film thickness of the hydrophilic film before brazing was 20 nm The brazing property was lowered, and a comparative example in which the film thickness and the particle size were 2500 nm was the water contact angle. Both brazing properties were reduced. In addition, a comparative example in which particles of γ-alumina, boehmite, dispore, toadite, dibusite, bayarite, or norstrandite were set to 3 nm, which is less than 5 nm, had excellent brazing properties, but the water contact angle became poor and hydrophilic. The sex has decreased.
Further, as shown in Comparative Example 36 of Table 6, the conventional boehmite-treated film is inferior to the example sample in the water contact angle before and after brazing.

[FT-IR measurement: Fourier transform infrared spectroscopy]
For the fins of the present invention and the conventional hydrophilic film, using IRT-5000 manufactured by JASCO Corporation, using a polarizing reflection unit, analysis under the condition of 50 times integration by high-sensitivity RAS measurement at an incident angle of 85 degrees. Was done. A gold-deposited mirror was used to collect the background spectrum. The hydrophilic film of the present invention uses the sample of 31 in Table 2 below, and the conventional hydrophilic film is a boehmite-treated film having a thickness of 10 nm shown in Comparative Example 36 of Table 6 (5 to 10 in boiling pure water). (Soaking for minutes) was used. The measurement results are shown in FIGS. 10 and 11.

FIG. 10 shows the analysis results of the hydrophilic film according to the present invention by Fourier transform infrared spectroscopy (FT-IR).
From the analysis results of FIG. 10, the hydrophilic coating in the example, there are the absorbance (Abs) 0.1 or more peaks at a wavenumber of ^{3300cm -1 ~3399cm} -1, and, wavenumber ^{1000cm -1 ~1099cm} -1 and ^1100cm absorbance 0.2 or more peaks are present at the position of ^-1 ~1199cm -1, and the absorbance 1.0 or more peaks were found to be present at the position of the wave number ^{800cm -1 ~900cm} -1.
In contrast, in the analysis result of the boehmite coating according to the prior art shown in FIG. 11, the absorbance 0.1 or more peaks at a wavenumber of ^{3300cm -1 ~3399cm} -1 is not present, and, wavenumber ^1000cm -1 ^{~1199cm -} There was only one peak having an absorbance of 0.8 or more at the position of ¹ , and a peak having an absorbance of about 0.6 was present at the position of ^{wave number 800 cm -1 to} 900 cm ^-1.
From the comparison of the analysis results, it can be seen that the hydrophilic film according to the present invention has a structure different from that of the conventional boehmite film.

1 ... Hydrophilic film before brazing heat treatment, 1a ... Hydrophilic film after brazing heat treatment, 3 ... Base material, 3A ... Brazing material layer, 11 ... Heat exchanger, 11a ... Heat exchanger assembly, 12 ... Tube Body, 13, 13a ... Fins, 14 ... Header tube, 13 ... Fins, 19 ... Notches, 22 ... Tubes, 25, 26 ... Fin materials, 30 ... Heat exchangers, 33 ... Tubes, 34 ... Fins (Brazed fins) , 34a ... Substrate, 35 ... Hydrophilic film, 35a ... Hydrophilic film, 41 ... Heat exchanger assembly.

Claims (7)

Hydrophile formed on the outer surface of a base material made of aluminum or an aluminum alloy and composed of particles made of γ-alumina or particles made of alumina hydrate alone or mixed. Sex film. Hydrophilic film according to claim 1, wherein the coating amount of the particles is 0.05 g / ^{m 2} or more 2.3 g / ^{m 2} or less. The hydrophilic film according to claim 1 or 2, wherein the film thickness is 25 nm or more and 2000 nm or less. The hydrophilic film according to any one of claims 1 to 3, wherein the particle size of the particles is 5 nm or more and 2000 nm or less. The hydrophilic film according to any one of claims 1 to 4, wherein the alumina hydrate is alumina monohydrate or alumina trihydrate. A precoated fin characterized in that the hydrophilic film according to any one of claims 1 to 5 is formed on at least one surface. A precoated fin according to any one of claims 1 to 5, wherein the hydrophilic film is a clad material of aluminum or an aluminum alloy formed on at least one surface.

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