FIN MATERIAL AND HEAT EXCHANGER

Abstract

A heat-exchanger fin material (1) has a coating film (3) formed on at least one surface of an aluminum substrate (2). An outermost surface of the coating film (3) is a positively-chargeable coating (31) that is essentially composed of only one or more resins selected from the group consisting of cellulose-based resins, acrylic-based resins, vinyl alcohol-based resins, acrylamide-based resins, and ester-based resins. The surface roughness Ra of the coating film (3) is 100 nm or less. A heat exchanger (5) includes a plurality of fins composed of the fin material (1) and at least one metal tube (7) passing through the plurality of fins (1).

Claims

1. A heat-exchanger fin material comprising: a substrate composed of aluminum; and a coating film formed on at least one surface of the substrate and composed of a coating having one layer or two or more layers; wherein the coating film has a positively-chargeable coating on its outermost surface; the positively-chargeable coating is essentially composed of only at least one resin selected from the group consisting of cellulose-based resins, acrylic-based resins, vinyl alcohol-based resins, acrylamide-based resins, and ester-based resins; and the surface roughness Ra of the coating film is 100 nm or less.

2. The heat-exchanger fin material according to claim 1, wherein the surface roughness Ra of the coating film is 50 nm or less.

3. The heat-exchanger fin material according to claim 1, wherein the surface roughness Ra of the coating film is 20 nm or less.

4. The heat-exchanger fin material according to claim 1, wherein the water-contact angle on the surface of the coating film is 40 or less.

5. The heat-exchanger fin material according to claim 1, wherein the water-contact angle on the surface of the coating film is 30 or less.

6. The heat-exchanger fin material according to claim 1, wherein the film thickness of the positively-chargeable coating is 0.1-6 m.

7. A heat exchanger comprising: a fin composed of the heat-exchanger fin material according to claim 1.

8. The heat-exchanger fin material according to claim 3, wherein: the water-contact angle on the surface of the coating film is 30 or less, and the film thickness of the positively-chargeable coating is 0.1-6 m.

9. The heat-exchanger fin material according to claim 8, wherein the film thickness of the positively-chargeable coating is 0.5-1.5 m.

10. The heat-exchanger fin material according to claim 9, wherein at least 99 mass % of the positively-chargeable coating is composed of one or more of carboxymethyl cellulose, polyacrylic acid, polyacrylamide, polyvinyl alcohol, and/or polyester.

11. A fin comprising: a substrate composed of pure aluminum or an aluminum alloy; and a coating film formed on at least one surface of the substrate and composed of a coating having one layer or two or more layers; wherein an outermost layer of the coating film consists essentially of one or more resins selected from the group consisting of cellulose-based resins, acrylic-based resins, vinyl alcohol-based resins, acrylamide-based resins, and ester-based resins; and the coating film has an average surface roughness Ra of 100 nm or less.

12. The fin according to claim 11, wherein: the coating film exhibits a water-contact angle of 40 or less, and the coating film has a thickness of 0.1-6 m.

13. The fin according to claim 12, wherein the average surface roughness Ra of the coating film is 50 nm or less.

14. The fin according to claim 13, wherein at least 99 mass % of the outermost layer of the coating film is composed of one or more compound(s) selected from the group consisting of carboxymethyl cellulose, polyacrylic acid, polyacrylamide, polyvinyl alcohol, and polyester.

15. The fin according to claim 13, wherein at least 99.5 mass % of the outermost layer of the coating film is composed of one or more compound(s) selected from the group consisting of carboxymethyl cellulose, polyacrylic acid, polyacrylamide, polyvinyl alcohol, and polyester.

16. The fin according to claim 15, wherein the coating film has a surface electric potential of +0.01 V to +10 V.

17. The fin according to claim 16, wherein the thickness of the coating film is 0.5-1.5 m.

18. The fin according to claim 17, wherein: the coating film exhibits a water-contact angle of 30 or less, and the average surface roughness Ra of the coating film is 20 nm or less.

19. A heat exchanger comprising: a plurality of fins according to claim 18; and a metal tube passing through holes in the plurality of fins and in contact with the plurality of fins.

20. A heat exchanger comprising: a plurality of fins according to claim 11; and a metal tube passing through holes in the plurality of fins and in contact with the plurality of fins.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG. 1 is a cross-sectional view of a fin material, which has a substrate and a positively-chargeable coating, according to working example 1.

[0024] FIG. 2 is an explanatory diagram that shows a water-contact angle according to working example 1.

[0025] FIG. 3 is an explanatory diagram that shows inhibition of the adhesion of contaminants to a surface of the fin material according to working example 1.

[0026] FIG. 4A shows, according to working example 1, a cross-sectional view of the fin material having a chemical-conversion coating or a primer layer between the substrate and a coating film; FIG. 4B shows a cross-sectional view of the fin material having a coating-film layer comprising a positively-chargeable coating as well as another coating, such as a corrosion-resistant coating.

[0027] FIG. 5 is a schematic diagram of a heat exchanger according to working example 2.

DETAILED DESCRIPTION OF THE INVENTION

[0028] Embodiments of a fin material and a heat exchanger using the same will now be explained. The fin material comprises a substrate composed of aluminum. In the present specification, aluminum is a general term for a metal or an alloy in which aluminum is the principal constituent and is a general concept that includes pure aluminum and aluminum alloys.

[0029] A coating film formed on the substrate includes a coating having one layer or two or more layers. A coating formed by a single application of one coating material is one layer; furthermore, a coating that is formed by multiple applications of a coating material in which the composition is the same for each application is also one layer. The coating film has a positively-chargeable coating on its outermost surface.

[0030] Examples of resins that form the positively-chargeable coating are cellulose-based resins, acrylic-based resins, vinyl alcohol-based resins, acrylamide-based resins, and ester-based resins. At least one of these can be used. These resins have a carboxy group or a hydroxy group as the functional group.

[0031] The positively-chargeable coating is essentially composed only of the resins described above; it does not contain, for example, silica-based or titanium-based inorganic particles, water-soluble resins, or the like; it may contain unavoidable impurities, such as a resin cross-linking agent (e.g., a metal compound such as a Zr compound). As described above, the positively-chargeable coating is essentially composed of at least one resin selected from the group consisting of cellulose-based resins, acrylic-based resins, vinyl alcohol-based resins, acrylamide-based resins, and ester-based resins. The content of these resins in the positively-chargeable coating is preferably 99 mass % or more and more preferably 99.5 mass % or more.

[0032] The surface of the positively-chargeable coating will positively charge upon contact (by friction) with air. The surface electrical potential of the positively-chargeable coating varies depending on the type of resin in the positively-chargeable coating, the composition, the film thickness, the surface roughness, and the like and is within a range of, for example, +0.01 V to +10 V. In addition, the absolute value of the surface electrical potential varies not only in accordance with the coating but also with the external environment, such as the temperature and the humidity of the air.

[0033] The thickness of the positively-chargeable coating is preferably 0.1-6 m. In this case, the positive charge on the positively-chargeable coating is more readily retained, and surface smoothness is more easily increased. From the same viewpoint, the thickness of the positively-chargeable coating is preferably 0.3-3 m and more preferably 0.5-1.5 m.

[0034] The coating film may have another coating in addition to the positively-chargeable coating. An example of such a coating is a corrosion-resistant coating composed of, for example, a urethane-based resin, an epoxy-based resin, or the like. Even if the coating film has another coating, the coating of the outermost surface is the positively-chargeable coating described above.

[0035] In addition, a primer layer may be formed between the coating film and the substrate. Thereby, adhesion between the substrate and the coating film can be further improved. The primer layer can be formed of at least one type selected from the group consisting of a urethane-based primer, an acrylic-based primer, and an epoxy-based primer.

[0036] In addition, a chemical-conversion coating may be formed between the coating film and the substrate or between the primer layer and the substrate. Adhesion between the coating film and the substrate or adhesion between the primer layer and the substrate can be improved by the chemical-conversion coating. The chemical-conversion coating can be formed by subjecting the aluminum substrate to a phosphate-chromate treatment, a phosphate-zirconium treatment, a boehmite treatment, or the like.

[0037] The surface roughness Ra of the coating film on the fin material is preferably 100 nm or less. If the surface roughness Ra is more than 100 nm, then uncharged contaminants and the like tend to adhere and, furthermore, adhered contaminants tend not to come off. The surface roughness Ra of the coating film is preferably 50 nm or less and more preferably 20 nm or less. The surface roughness of the coating film is an arithmetic-mean roughness Ra as stipulated in JIS B0601-2001. The surface roughness Ra of the coating film can be controlled by adjusting the thickness of the coating film, the surface roughness of the substrate, and the like.

[0038] The contact angle of water on the surface of the coating film is preferably 40 or less. In this case, the surfaces of the fin material can sufficiently exhibit excellent hydrophilic properties. In addition, both immediately after the manufacture of a fin material, as well as after the repeated immersion in water and drying according to the aging procedure described below, the water-contact angle on the coating-film surface is, as described above, preferably 40 or less and more preferably 30 or less.

[0039] Fin materials are used in the manufacture of the heat exchanger as, for example, described below. Specifically, first, a coil-shaped fin material is cut to prescribed dimensions, and thereby a plurality of sheet-shaped fins is obtained. Subsequently, the fins are subject to slit (hole) formation, louver molding, and collar formation using a press. Next, the fins are arranged such that they are stacked in the state in which they are spaced apart from one another by a prescribed spacing while metal tubes, which are disposed at prescribed locations, are passed through holes provided in the fins. Subsequently, tube-expanding plugs are inserted into the metal tubes to enlarge the outer diameter of the metal tubes, and thereby the metal tubes and the fins are caused to closely contact each other. Thus, the heat exchanger can be obtained. The heat exchanger can be used in, for example, an indoor unit or an outdoor unit of an air conditioner.

WORKING EXAMPLES

Working Example 1

[0040] In the present example, multiple fin materials (specifically, sample E1 to sample E13 and sample C1 to sample C7) pertaining to working examples and comparative examples were prepared, and their characteristics were compared and evaluated. As shown in FIG. 1, a fin material 1 according to the working examples comprises: a substrate 2 composed of aluminum; and a coating film 3 formed on the surface(s) thereof. The coating film 3 comprises a positively-chargeable coating 31, which is essentially composed of at least one resin selected from the group consisting of cellulose-based resins, acrylic-based resins, vinyl alcohol-based resins, acrylamide-based resins, and ester-based resins. The surface roughness Ra of the coating film 3 is 100 nm or less. The substrate 2 is an aluminum sheet having a sheet thickness of 0.1 mm as stipulated in JIS A 1050-H26. It is noted that the fin material of the comparative example has a configuration that is the same as the working examples, except that the composition and surface roughness of the coating film differ, as shown in Table 1, which is discussed below.

[0041] The fin materials 1 of the samples were manufactured by applying coating materials, which contained the resin components of the compositions shown in Table 1 (discussed below), onto the substrates, thereby forming the coating films 3. Each coating film 3, i.e., the positively-chargeable coating 31, in the present example was formed directly on the substrate 2. In the manufacture of sample C7, a coating material containing a resin component and silica particles was used (refer to Table 1). It is noted that, in Table 1, CMC indicates carboxymethyl cellulose, PAA indicates polyacrylic acid, PAM indicates polyacrylamide, PVA indicates polyvinyl alcohol, PES indicates polyester, EPO indicates polyepoxy, PU indicates polyurethane, and PEG indicates polyethylene glycol.

[0042] As the surface roughness Ra of the coating film 3 for each of the samples, the arithmetic-mean roughness Ra according to JIS B0601-2001 was measured using a probe-type, surface-roughness measuring instrument (specifically, the scanning probe microscope JSPM-5200 made by JEOL Ltd.) compliant with JIS B0651-2001. The visual field during measurement was 25 m25 m. For each sample, arbitrary visual fields were selected at ten locations, the measurement described above was performed at each location, and the arithmetic mean of these ten locations was taken as the surface roughness Ra.

[0043] Next, the surface electrical potential of the coating film of each sample in the dry state was measured as follows, and the results are shown in Table 1. The measurements were performed using the scanning probe microscope (i.e., SPM) JSPM-5200 made by JEOL Ltd. Specifically, a bias voltage was applied between the probe of the scanning probe microscope and an arbitrary location of the coating-film surface, and the surface electrical potential was calculated based on the change in frequency when the bias voltage was changed. The measuring method, the calculating method, and the like were in accordance with the manual of the JSPM-5200 made by JEOL Ltd. For each sample, the surface electrical potential was measured at ten locations, and the arithmetic-mean value thereof is shown in Table 1. It is noted that the surface electrical potentials shown in the table are representative values, and it was confirmed that, even for the same sample, variations arise in the measurement values due to external factors and the like, such as temperature and humidity. However, inversion of positive or negative in the charged state of the surface did not occur.

TABLE-US-00001 TABLE 1 Surface Film Surface Potential Sample Roughness Ra Thickness Component Content Component Content Component Content Surface of Coating Film No. [nm] [m] 1 [mass %] 2 [mass %] 3 [mass %] Charge [V] E1 50 1 CMC 100 + +0.5 E2 10 1 CMC 100 + +0.5 E3 20 1 CMC 100 + +0.5 E4 100 1 CMC 100 + +0.5 E5 50 0.1 CMC 100 + +0.01 E6 50 6 CMC 100 + +10 E7 50 1 PAA 100 + +5 E8 50 1 PAM 100 + +8 E9 50 1 PVA 100 + +10 E10 50 1 PES 100 + +2 E11 50 1 PVA 90 PES 10 + +8 E12 50 1 CMC 75 PAA 25 + +6 E13 50 1 CMC 75 PAA 20 PAM 5 + +7 C1 50 1 EPO 100 10 C2 50 1 CMC 50 PU 50 4 C3 120 1 CMC 100 + +0.5 C4 150 7 CMC 100 + +15 C5 150 1 CMC 50 PEG 50 + +0.25 C6 50 1 PU 100 8 C7 150 1 CMC 50 Silica particles 50 + +8

[0044] For each sample, evaluations of the hydrophilic properties, the contamination-adhesion properties, the contamination-removing properties, corrosion resistance, and moisture resistance were performed as below. The results thereof are shown in Table 2.

[0045] (1) Hydrophilic Properties

[0046] After the manufacture of each sample, the initial water-contact angle was measured. Specifically, as shown in FIG. 2, a water droplet 19 having a volume of 2 l was dropped onto the coating film 3 of the fin material 1 of each sample. Then, the contact angle of the water droplet 19 on the coating film 3 was measured. This was taken as the initial water-contact angle. Next, each sample was aged, and the water-contact angle was measured again after the aging. Specifically, aging was performed by repeating a cycle, in which every sample was immersed in ion-exchanged water for 2 min and then dried by air blowing for 6 min, 300 times. Subsequently, the water-contact angle after the aging was measured. This was taken as the post-aging water-contact angle. In addition, each sample was subjected to a contamination treatment, and the water-contact angle was measured again. Specifically, the samples were placed inside a sealed bottle together with a contaminant composed of a higher fatty acid such that the contaminant and the samples were not in contact with one another. The interior of the sealed bottle was then heated to a temperature of 60-100 C., whereby the higher fatty acid inside the sealed bottle was vaporized and some of the contaminant adhered to the coating-film surface of the samples. This state was maintained for a long time (specifically, 100 hours), and then the temperature inside the bottle was cooled to room temperature while the sealed state was maintained. Then, the fin materials of the samples were taken out of the bottle, and the water-contact angles were measured again. If the contact angle was 30 or less, then the sample was evaluated as excellent; if the contact angle was more than 30 and 40 or less, then the sample was evaluated as satisfactory; and if the contact angle was more than 40, then the sample was evaluated as unsatisfactory.

[0047] (2) Contamination-Adhesion Properties

[0048] The contamination-adhesion properties were evaluated by assessing the adhesion of electrically charged dust and electrically conductive dust to the coating-film surface of each sample. Specifically, the electrically charged dust and the electrically conductive dust were each blown against the surface of the coating film of each sample via air. Subsequently, the amount of the electrically charged dust and the amount of the electrically conductive dust adhered to the coating-film surface were each measured. The measurements of the adhered amounts were performed by measuring the weight of each sample before and after the dust was blown against each sample, calculating the amount of adhered dust of each sample based on the weight difference, and then converting the weight difference into the amount of adhered dust per unit of area. If the adhered amount of the electrically charged dust was less than 0.2 g/m.sup.2, then the sample was evaluated as excellent; if the adhered amount of the electrically charged dust was 0.2 g/m.sup.2 or more and 0.5 g/m.sup.2 or less, then the sample was evaluated as satisfactory; and if the adhered amount of the electrically charged dust was more than 0.5 g/m.sup.2, then the sample was evaluated as unsatisfactory. The evaluation of the adhered amount of the electrically conductive dust was also performed in the same manner. It is noted that Kanto loam dust, which is a powder stipulated in JIS Z8901-2006, was used as the electrically charged dust, and carbon black, which is a powder stipulated in JIS Z8901-2006, was used as the electrically conductive dust.

[0049] (3) Contamination Removability

[0050] Contamination removability was evaluated by assessing removability of electrically charged dust and electrically conductive dust from the coating-film surface of each sample. Specifically, as in the evaluation of contamination-adhesion properties described above, samples were prepared by adhering electrically charged dust and electrically conductive dust to the coating-film surfaces. Next, each sample was cooled to a prescribed temperature by cooling the surface on the opposite side that the dust is adhered to, thereby causing condensed water to form on the surface having the adhered dust. Then, the state in which condensed water formed and flowed off was maintained for a prescribed period of time. Subsequently, the surfaces of each sample were sufficiently dried, after which the amount of the remaining dust that was not removed by the condensed water was measured in the same manner as the evaluation of the adhesion properties described above. If the residual amount of each dust was less than 0.1 g/m.sup.2, then the sample was evaluated as excellent; if the residual amount of each dust was 0.1 g/m.sup.2 or more and less than 0.5 g/m.sup.2, then the sample was evaluated as satisfactory; and if the residual amount of each dust was 0.5 g/m.sup.2 or more, then the sample was evaluated as unsatisfactory.

[0051] (4) Corrosion Resistance

[0052] Using each sample, the salt spray test stipulated in JIS Z2371 was performed for 500 hours, and post-test corrosion resistance was evaluated. Observation was performed visually; after the test, if the surface of the coating film did not whiten, then the sample was evaluated as excellent; if part of the surface whitened, then the sample was evaluated as satisfactory; and if the entire surface whitened, then the sample was evaluated as unsatisfactory.

[0053] (5) Moisture Resistance

[0054] Using each sample, the moisture-resistance test stipulated in JIS H4001 was performed for 960 hours, and post-test moisture resistance was evaluated. Observation was performed visually; after the test, if the surface of the coating film did not whiten, then the sample was evaluated as excellent; if part of the surface whitened, then the sample was evaluated as satisfactory; and if the entire surface whitened, then the sample was evaluated as unsatisfactory.

TABLE-US-00002 TABLE 2 Hydrophilic Properties Initial Post-Aging Water Water Contamination-Adhesion Properties Contamination Removability Contact Contact Post-Aging Electrically Electrically Sample Angle Angle Hydrophilic Electrostatic Conductive Electrostatic Conductive Corrosion Moisture No. [] [] Properties Dust Dust Dust Dust Resistance Resistance E1 15 33 Satisfactory Satisfactory Satisfactory Satisfactory Satisfactory Satisfactory Satisfactory E2 18 36 Satisfactory Satisfactory Excellent Satisfactory Satisfactory Satisfactory Excellent E3 17 36 Satisfactory Satisfactory Excellent Satisfactory Satisfactory Satisfactory Excellent E4 12 37 Satisfactory Satisfactory Satisfactory Satisfactory Satisfactory Satisfactory Satisfactory E5 22 38 Satisfactory Satisfactory Satisfactory Satisfactory Satisfactory Satisfactory Satisfactory E6 15 32 Satisfactory Satisfactory Satisfactory Satisfactory Satisfactory Excellent Excellent E7 18 36 Excellent Satisfactory Excellent Satisfactory Satisfactory Satisfactory Excellent E8 20 36 Satisfactory Satisfactory Excellent Satisfactory Satisfactory Satisfactory Excellent E9 34 37 Satisfactory Satisfactory Satisfactory Satisfactory Satisfactory Satisfactory Satisfactory E10 18 38 Satisfactory Satisfactory Satisfactory Satisfactory Satisfactory Satisfactory Satisfactory E11 30 40 Satisfactory Satisfactory Satisfactory Satisfactory Satisfactory Excellent Excellent E12 20 28 Excellent Satisfactory Satisfactory Satisfactory Satisfactory Excellent Satisfactory E13 20 27 Excellent Satisfactory Satisfactory Satisfactory Satisfactory Satisfactory Satisfactory C1 40 65 Unsatisfactory Unsatisfactory Satisfactory Unsatisfactory Satisfactory Satisfactory Satisfactory C2 20 40 Unsatisfactory Unsatisfactory Satisfactory Unsatisfactory Satisfactory Satisfactory Satisfactory C3 10 37 Satisfactory Satisfactory Unsatisfactory Satisfactory Unsatisfactory Satisfactory Satisfactory C4 10 40 Satisfactory Satisfactory Unsatisfactory Satisfactory Unsatisfactory Satisfactory Satisfactory C5 20 35 Unsatisfactory Satisfactory Satisfactory Unsatisfactory Satisfactory Satisfactory Satisfactory C6 60 80 Unsatisfactory Unsatisfactory Satisfactory Unsatisfactory Satisfactory Satisfactory Satisfactory C7 25 30 Unsatisfactory Satisfactory Unsatisfactory Satisfactory Unsatisfactory Satisfactory Satisfactory

[0055] As can be understood from Table 1 and Table 2, each fin material having the positively-chargeable coating on its outermost surface, which, as in sample E1 to sample E13, is essentially composed only of one or more resins selected from the group consisting of cellulose-based resins, acrylic-based resins, vinyl alcohol-based resins, acrylamide-based resins, and ester-based resins, excels in the contamination-adhesion-inhibition effect. This is because, as shown in FIG. 3, the surface of the positively-chargeable coating 31 is positively charged by contact with air, and therefore the adhesion of positively charged dust 91 and the like can be inhibited. In addition, because the surface roughness of the coating film 3 of sample E1 to sample E13 is 100 nm or less and the samples excel in surface smoothness, the adhesion of uncharged dust 92 and the like also can be inhibited. Furthermore, because dusts 91, 92 adhered to the surface of the smooth coating film 3 are easily washed away by condensed water or the like, they also excel in contamination removability.

[0056] The surface of each positively-chargeable coating 31 in sample E1 to sample E13 is positively charged upon contact (by friction) with air, as described above. If condensed water or the like adheres to the positively-chargeable coating 31, then the surface electrical potential decreases and becomes zero, but it carries a positive charge once again upon drying and contact with air. Charging by this drying and the charge dissipation by the condensed water are reversible and performed repeatedly.

[0057] In addition, the sample E1 to sample E13 also excel in hydrophilic properties and in post-aging hydrophilic properties (i.e., hydrophilicity durability). Furthermore, they also excel in post-contamination hydrophilic properties. In addition, they also excel in corrosion resistance and moisture resistance.

[0058] In contrast, the surface of the sample C1, which has a coating composed of an epoxy resin as the coating film, the surface of the sample C2, which has a coating that contains both carboxymethyl cellulose and polyurethane as the coating film, and the surface of the sample C6, which has a coating composed of polyurethane as the coating film, are negatively charged by contact with air. Consequently, the adhesion properties with respect to contaminants, such as dust, the removability of contaminants, and the like were insufficient. In particular, the adhesion properties and removability of positively charged electrically charged dust were poor. In addition, the hydrophilic propertiesparticularly the post-aging hydrophilicity durability and the post-contamination hydrophilicity durabilityof sample C1 to sample C6 were also insufficient. The post-contamination hydrophilicity durability was also insufficient for sample C2.

[0059] In addition, with regard to sample C3 and sample C4, in which the surface roughness Ra of the coating film was large and the smoothness was insufficient, the adhesion properties, the removability, etc. of contaminants, such as electrically conductive dust, were insufficient. In addition, with regard to sample C5, which contains a water-soluble resin, such as PEG, in the coating, the removability of electrically charged dust and the like were insufficient. Furthermore, the post-contamination hydrophilicity durability was also insufficient. In addition, the post-contamination hydrophilicity durability of sample C7, which has silica particles in the coating, was insufficient. Furthermore, the surface roughness of sample C7, which has the silica particles, became large and, as in sample 3 and sample 4, the adhesion properties, the removability, etc. of contaminants, such as electrically conductive dust, were insufficient.

[0060] In the present example, although a fin material was described in which the coating film 3, which comprises the positively-chargeable coating 31, was formed directly on the substrate 2, as shown in FIG. 1, the fin material may have at least one of a chemical-conversion coating 41 and a primer layer 42 between the substrate 2 and the coating film 3, which comprises the positively-chargeable coating 31, as shown in FIG. 4A. In addition, as shown in FIG. 4B, the outermost surface of the coating film 3 should have the positively-chargeable coating 31 and furthermore may have a corrosion-resistant coating 32.

Working Example 2

[0061] Working example 2 is a heat exchanger comprising fins composed of the fin materials of working example 1. As shown in FIG. 5, the heat exchanger 5 is a cross-fin-tube type and comprises: numerous sheet-shaped fins 6, each composed of the fin material 1, and metal tubes 7 that pass through these and are for transferring heat. The fins 6 are spaced apart by a prescribed spacing and are disposed in parallel. The width of each plate fin is, for example, 25.4 mm; the height is, for example, 290 mm; the fin-stacking pitch is, for example, 1.4 mm; and the width of the entire heat exchanger is, for example, 300 mm. The height direction of the fin 6 is the rolling-parallel direction of the substrate. There are two columns of the metal tube 7 in the width of the fins, and there are 14 stages of the metal tube 7 in the fin height. It is noted that, for simplicity of illustration, several of the metal tubes 7 are not shown in FIG. 5. In addition, the metal tube is a copper tube having a helical groove on its inner surface. The dimensions of the metal tube are outer diameter: 7.0 mm, bottom-wall thickness: 0.45 mm, fin height: 0.20 mm, fin vertical angle: 15.0, and helix angle: 10.0.

[0062] Each of the heat exchangers 5 was prepared as follows. First, assembly holes (not shown), each having a fin-collar part with a height of 1-4 mm for inserting the metal tubes 7 therethrough and fixing such, were formed by press working the fins 6, each composed of the fin material 1. After stacking the plate fins 6, the separately prepared metal tubes 7 were inserted through the assembly holes. A copper tube having a groove formed on its inner surface by rolling or the like was cut to a standard length and hairpin bent, to form the metal tubes 7. Next, by inserting tube-expanding plugs into one end of the metal tubes 7 and widening the outer diameter of the metal tubes 7, the metal tubes 7 were secured to the plate fins 6. After the tube-expanding plugs were removed, U-bent tubes were joined, by braising, to the metal tubes 7, and thereby each of the heat exchangers 5 was obtained.

[0063] By using samples E1-E13 according to working example 1 as the fin materials 1, contaminants, such as dust, tend not to adhere to the fins 6 of the heat exchanger 5 and, even if these contaminants adhere, they are easily removed by condensed water or the like. Furthermore, the fins 6 also excel in hydrophilic properties, hydrophilicity durability, and the like.