Abstract:
Provided is a precoated fin material for heat exchangers that allows the construction of a fin structure in which frost formation at the time of heater operation can be prevented to the extent possible, and under such a condition that condensation is liable to occur on a fin surface, a water droplet of condensed water can be quickly removed by bringing the water droplet into contact with a hydrophilic film, and as a result, a favorable heat exchange function can be maintained without any increase in ventilation resistance. Also provided is a heat exchanger including such fin structure. The precoated fin material for heat exchangers includes: a fin substrate formed of an aluminum plate material; a crosslinked hydrophobic film having a frost formation-suppressing effect, the crosslinked hydrophobic film being formed on one surface of the fin substrate and being formed of an aqueous hydrophobic coating composition containing a resin (A) having a fluorine atom-containing group, a quaternary ammonium salt group-containing modified epoxy resin (B), and an amino resin (C) at predetermined ratios; and a hydrophilic film having a condensed water-removing effect, the hydrophilic film being formed on another surface of the fin substrate. The heat exchanger includes a fin structure in which a hydrophobic surface having a frost formation-suppressing effect and a hydrophilic surface having a condensed water-removing effect are opposite to each other.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a precoated fin material for heat exchangers, having imparted with an excellent frost formation-suppressing effect and an excellent condensed water-removing effect onto a surface of an aluminum plate material formed of aluminum or an aluminum alloy, and to a heat exchanger including a fin structure constructed by using the material. 
       BACKGROUND ART 
       [0002]    A precoated fin material for heat exchangers, which is formed of an aluminum plate material, has been used as a fin material for a heat exchanger for a heat pump air conditioner by being molded into a desired fin shape. However, in a heat exchanger using the precoated fin material for heat exchangers, when the temperature of the air is low or the evaporating temperature of a refrigerant is low in an outdoor unit at the time of heater operation, frost adheres onto the surface of a fin in some cases. In addition, once the frost is formed, a gap between fins is clogged to increase a ventilation resistance. Eventually, the quantity of air to flow into the heat exchanger reduces, and hence the evaporating ability of the heat exchanger of the outdoor unit reduces. Accordingly, when the frost adheres onto the fin surface of the heat exchanger, the following problem arises. The heater operation needs to be stopped and a defrosting operation needs to be performed for removing the frost, and hence comfortability remarkably reduces. 
         [0003]    In addition, a method involving forming a hydrophobic film on the surface of the fin is available as a technology for the suppression of such frost formation. The time period during which the clogging occurs owing to the frost formation can be postponed by the method. However, after defrosting or under such a condition that the temperature of the refrigerant is relatively high so that a water droplet condenses on the surface of the fin, the method involves the following problem. Condensed water adheres to the gap between the fins, the adhering condensed water forms a bridge between the fins to increase the ventilation resistance, and as a result, heat exchange performance reduces. 
         [0004]    Accordingly, the following has been demanded for improving the thermal efficiency of the heat exchanger at the time of the heater operation. The condensed water on the fin surface is removed before the frost formation and the fin surface is turned into a surface on which the frost formation hardly occurs. In addition, the following methods each have been proposed as means for solving the problem: a hydrophilic treatment method involving forming a hydrophilic film on the fin surface to cause the condensed water to flow down as a thin water film (Patent Literatures 1 to 3); a hydrophobic treatment method involving forming a hydrophobic film on the fin surface to remove the condensed water at an early stage (Patent Literatures 4 to 6); a hydrophobic/hydrophilic treatment method involving forming a hydrophobic film and a hydrophilic film depending on the placement and site of the fin to compensate for the disadvantages of the hydrophobic film and hydrophilic film with their advantages (Patent Literatures 7 to 9); and the like. 
       CITATION LIST 
     Patent Literature 
       [0000]    
       
         [PTL 1] JP 09-014888 A 
         [PTL 2] JP 2000-028291 A 
         [PTL 3] JP 2010-223520 A 
         [PTL 4] JP 08-269367 A 
         [PTL 5] JP 09-026286 A 
         [PTL 6] JP 2009-270181 A 
         [PTL 7] JP 08-152287 A 
         [PTL 8] JP 3761262 B2 
         [PTL 9] JP 2006-046695 A 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0014]    However, in the hydrophilic treatment method of each of Patent Literatures 1 to 3, a function of causing the condensed water to flow down as a thinwater film is not sufficient and defrosting property by which frost formation is suppressed when performance of heater operation is not sufficient. In addition, in the hydrophobic treatment method of each of Patent Literatures 4 to 6 as well, water repellency is not sufficient and defrosting property by which the frost formation is suppressed through secure removal of a condensed water droplet is not sufficient. Further, in each of Patent Literatures 7 to 9, water-repelling performance and hydrophilic performance, in particular, the water-repelling performance in the hydrophobic film and hydrophilic film to be formed depending on the placement and site of the fin, in particular, the hydrophobic film are not necessarily sufficient. Accordingly, it is still unable to achieve a satisfactory frost formation-suppressing effect. In addition, it is still unable to sufficiently solve the problem of the increase of the ventilation resistance between the fins due to the condensed water. 
         [0015]    Therefore, in view of the problems of the conventional technologies, the inventors of the present invention have conducted extensive studies on the development of a precoated fin material for heat exchangers having an excellent frost formation-suppressing effect and an excellent condensed water-removing effect, and the development of a heat exchanger including a fin structure that does not cause frost formation at the time of heater operation, and does not involve the problem of an increase in ventilation resistance between fins due to condensed water through the cooperation of the frost formation-suppressing effect and condensed water-removing effect exhibited by using the precoated fin material. As a result, the inventors have found that a crosslinked hydrophobic film obtained by introducing a specific crosslinked structure into a hydrophobic film is excellent in frost formation-suppressing effect, and that a fin structure that brings together an excellent frost formation-suppressing effect and an excellent condensed water-removing effect can be constructed by placing the crosslinked hydrophobic film and a hydrophilic film excellent in condensed water-removing effect opposite to each other to cause the films to cooperate with each other. Thus, the inventors have completed the present invention. 
         [0016]    Therefore, an object of the present invention is to provide a precoated fin material for heat exchangers having, on one of its surfaces, a crosslinked hydrophobic film having an excellent frost formation-suppressing effect, and having, on the other surface, a hydrophilic film having a condensed water-removing effect. 
         [0017]    Another object of the present invention is to provide a heat exchanger including a fin structure in which a one-side hydrophobic/one-side hydrophilic fin material formed of the precoated fin material for heat exchangers is used, or a double-side hydrophobic fin material including, on each of both of its surfaces, a crosslinked hydrophobic film having an excellent frost formation-suppressing effect and a double-side hydrophilic fin material including, on each of both of its surfaces, a hydrophilic film having an excellent condensed water-removing effect are used, and the crosslinked hydrophobic film having an excellent frost formation-suppressing effect and the hydrophilic film having an excellent condensed water-removing effect are placed opposite to each other to be caused to cooperate with each other, and hence frost formation at the time of heater operation can be prevented to the extent possible, and under such a condition that condensation is liable to occur on a fin surface, a water droplet of condensed water can be quickly removed by bringing the water droplet into contact with the hydrophilic film, and as a result, a favorable heat exchange function can be maintained without any increase in ventilation resistance. 
       Solution to Problem 
       [0018]    That is, the present invention relates to a precoated fin material for heat exchangers, including: a fin substrate formed of an aluminum plate material formed of aluminum or an aluminum alloy; a crosslinked hydrophobic film having a frost formation-suppressing effect (or an anti-frost effect), the crosslinked hydrophobic film being formed on one surface of the fin substrate; and a hydrophilic film having a condensed water-removing effect, the hydrophilic film being formed on another surface of the fin substrate, in which the crosslinked hydrophobic film is formed of an aqueous hydrophobic coating composition containing a resin (A) having at least one kind of fluorine atom-containing group selected from the group consisting of a perfluoroalkyl group and a perfluoroalkenyl group, a quaternary ammonium salt group-containing modified epoxy resin (B), and an amino resin (C) in which a solid content of the resin (A) having at least one kind of fluorine atom-containing group selected from the group consisting of a perfluoroalkyl group and a perfluoroalkenyl group is 1 to 30 parts by mass with respect to 100 parts by mass of a total of solid contents of the quaternary ammonium salt group-containing modified epoxy resin (B) and the amino resin (C). 
         [0019]    The present invention also relates to a heat exchanger, including a fin structure in which a large number of flat precoated fin materials are placed at a predetermined interval to be parallel to each other, and a hydrophobic surface having a frost formation-suppressing effect (or an anti-frost effect) and a hydrophilic surface having a condensed water-removing effect are opposite to each other between precoated fin materials adjacent to each other, in which: the large number of precoated fin materials include a large number of one-side hydrophobic/one-side hydrophilic fin materials each having, on one surface of a fin substrate formed of an aluminum plate material formed of aluminum or an aluminum alloy, a crosslinked hydrophobic film forming the hydrophobic surface and each having, on another surface thereof, a hydrophilic film forming the hydrophilic surface, or include a plurality of double-side hydrophobic fin materials each having, on each of both surfaces of a fin substrate formed of an aluminum plate material formed of aluminum or an aluminum alloy, a crosslinked hydrophobic film forming the hydrophobic surface and a plurality of double-side hydrophilic fin materials each having, on each of both surfaces of a fin substrate formed of an aluminum plate material formed of aluminum or an aluminum alloy, a hydrophilic film forming the hydrophilic surface; and the crosslinked hydrophobic film is formed of an aqueous hydrophobic coating composition containing a resin (A) having at least one kind of fluorine atom-containing group selected from the group consisting of a perfluoroalkyl group and a perfluoroalkenyl group, a quaternary ammonium salt group-containing modified epoxy resin (B), and an amino resin (C) in which a solid content of the resin (A) having at least one kind of fluorine atom-containing group selected from the group consisting of a perfluoroalkyl group and a perfluoroalkenyl group is 1 to 30 parts by mass with respect to 100 parts by mass of a total of solid contents of the quaternary ammonium salt group-containing modified epoxy resin (B) and the amino resin (C). 
         [0020]    In the present invention, the aluminum plate material forming the fin substrate may be formed of pure aluminum or may be formed of an aluminum alloy, and is not particularly limited. From the viewpoint of corrosion resistance, an anticorrosive film is preferably formed on each of both surfaces of the fin substrate. 
         [0021]    The anticorrosive film to be formed on each of both surfaces of the fin substrate for the purpose is formed by applying an anticorrosive treatment agent to each of both surfaces of the fin substrate, and examples of the anticorrosive treatment agent to be used here can include a chromate treatment agent, a chromate-phosphate treatment agent, a chromium-free chemical conversion treatment agent, and an organic anticorrosive primer. Of those, a chromium-free chemical conversion treatment agent or an organic anticorrosive primer is preferred from the viewpoint of an environmentally friendly anticorrosive film. 
         [0022]    In the present invention, as a precoated fin material for heat exchangers, a one-side hydrophobic/one-side hydrophilic fin material is formed by providing the crosslinked hydrophobic film forming a hydrophobic surface on one surface of the fin substrate and providing the hydrophilic film forming a hydrophilic surface on the other surface thereof, or a double-side hydrophobic fin material is formed by providing the crosslinked hydrophobic film having a frost formation-suppressing effect on each of both surfaces of the fin substrate. With regard to the crosslinked hydrophobic film having a frost formation-suppressing effect, the hydrophobic film formed of the aqueous hydrophobic coating composition containing the resin (A) having a fluorine atom-containing group, the quaternary ammonium salt group-containing modified epoxy resin (B), and the amino resin (C) to be described later needs to form a crosslinked structure. 
         [0023]    Here, the water contact angle of the crosslinked hydrophobic film having a frost formation-suppressing effect is preferably 100° or more, more preferably 105° or more, and its thickness is typically 0.05 to 5.0 μm, preferably 0.1 to 4.0 μm, more preferably 0.2 to 2.0 μm. The water contact angle of the crosslinked hydrophobic film is desirably as large as possible. However, when the water contact angle of the crosslinked hydrophobic film is less than 100°, there arises a problem in that the frost formation-suppressing effect reduces. In addition, when the thickness of the crosslinked hydrophobic film is less than 0.05 μm, for example, the following problem arises. Variations in frost formation suppression and hydrophilicity between lots enlarge, and the deterioration of the frost formation suppression and hydrophilicity-maintaining property over time enlarges. In contrast, when the thickness exceeds 5.0 μm, neither additional frost formation suppression nor an additional improvement in hydrophilicity can be expected. In addition, for example, the following problem arises. The burn of the film due to heat upon brazing of a copper tube for a refrigerant to the fin material becomes rather conspicuous and a cost increases with increasing thickness. 
         [0024]    In the present invention, the crosslinked hydrophobic film that exhibits a frost formation-suppressing effect is formed by applying the aqueous hydrophobic coating composition, and as the aqueous hydrophobic coating composition to be used for the purpose, there can be given an aqueous hydrophobic coating composition containing the resin (A) having at least one kind of fluorine atom-containing group selected from the group consisting of a perfluoroalkyl group and a perfluoroalkenyl group, the quaternary ammonium salt group-containing modified epoxy resin (B), and the amino resin (C) from the viewpoint of long-term maintenance of the frost formation-suppressing effect. It should be noted that in the following description, the “resin (A) having at least one kind of fluorine atom-containing group selected from the group consisting of a perfluoroalkyl group and a perfluoroalkenyl group” is sometimes simply described as the “resin (A) having a fluorine atom-containing group.” 
       &lt;Resin (A) Having Fluorine Atom-Containing Group&gt; 
       [0025]    In the aqueous hydrophobic coating composition, a known resin can be used as the resin (A) having a fluorine atom-containing group as long as the resin has a perfluoroalkyl group and/or a perfluoroalkenyl group, and a resin dispersed or dissolved in water or a medium using water as a main component (hereinafter referred to as “aqueous medium”) can be used. Such resin (A) having a fluorine atom-containing group is preferably, for example, a resin obtained by subjecting a polymerizable unsaturated monomer (a-1) having at least one kind of fluorine atom-containing group selected from the group consisting of a perfluoroalkyl group and a perfluoroalkenyl group (hereinafter sometimes described as the “polymerizable unsaturated monomer (a-1) having a fluorine atom-containing group”) of a structure represented by the following general formula (I) and any other polymerizable unsaturated monomer (a-2) to a copolymerization reaction. A method of performing the polymerization reaction can be selected from known polymerization methods, and examples thereof can include bulk polymerization, solution polymerization, emulsion polymerization, suspension polymerization, and dispersion polymerization. Of those, emulsion polymerization is preferred from the viewpoint of, for example, the efficiency with which the resin dispersed or dissolved in the aqueous medium is produced. 
         [0000]    
       
                 
         
             
             
         
       
     
         [0026]    (In the formula, Rf represents a linear or branched perfluoroalkyl group or perfluoroalkenyl group having 1 to 21 carbon atoms. R represents a hydrogen atom, a halogen atom, or a methyl group. X represents an oxygen atom or an imino group. Y represents a divalent organic group having 1 to 20 carbon atoms that may contain or may not contain an oxygen atom, a sulfur atom, a nitrogen atom, or a phosphorus atom.) 
         [0027]    The fluorine atom-containing group is preferably a perfluoroalkyl group, and examples of the perfluoroalkyl group include —CF 3 , —CF 2 CF 3 , —CF 2 CF 2 CF 3 , CF(CF 3 ) 2 , —CF 2 CF 2 CF 2 CF 3 , —CF 2 CF(CF 3 ) 2 , —C(CF 3 ) 3 , —(CF 2 ) 4 CF 3 , —(CF 2 ) 2 CF (CF 3 ) 2 , —CF 2 C(CF 3 ) 3 , —CF(CF 3 )CF 2 CF 2 CF 3 , —(CF 2 ) 5 CF 3 , —(CF 2 ) 3 CF(CF 3 ) 2 , —(CF 2 ) 4 CF(CF 3 ) 2 , —(CF 2 ) 7 CF 3 , —(CF 2 ) 5 CF(CF 3 ) 2 , —(CF 2 ) 6 CF(CF 3 ) 2 , and —(CF 2 ) 9 CF 3 . The perfluoroalkyl group has 1 to 21 carbon atoms, preferably 2 to 20 carbon atoms, more preferably 4 to 16 carbon atoms. 
         [0028]    The emulsion polymerization of the polymerizable unsaturated monomer (a-1) having a fluorine atom-containing group can be performed by a known method involving subjecting a mixture of the monomer (a-1) and the other polymerizable unsaturated monomer (a-2) to emulsion polymerization with an emulsifier and a polymerization initiator in the aqueous medium. It should be noted that in the emulsion polymerization, a hydrophilic or hydrophobic organic solvent may be used as required. 
         [0029]    A conventionally known emulsifier can be used as the emulsifier, and examples thereof include an anionic surfactant, a nonionic surfactant, an amphoteric surfactant, and a combination thereof. A compound having a fluorine atom of, for example, a fluorinated alkyl group bonded thereto may be used as the surfactant as required. 
         [0030]    A conventionally known polymerization initiator can be used as the polymerization initiator, and examples thereof include: persulfates such as ammoniumpersulfate (APS), potassiumpersulfate, and sodium persulfate; and oil-soluble polymerization initiators such as diisopropyl peroxydicarbonate (IPP), benzoyl peroxide, dibutyl peroxide, and azobisisobutyronitrile (AIBN). 
         [0031]    In addition, a chain transfer agent may be used in the emulsion polymerization reaction, and examples of the chain transfer agent include: malonic acid diesters such as diethyl malonate (MDE) and dimethyl malonate; acetic acid esters such as ethyl acetate and butyl acetate; alcohols such as methanol and ethanol; mercaptans such as n-lauryl mercaptan and n-octyl mercaptan; and an α-methylstyrene dimer. 
         [0032]    An aqueous dispersion of the resin (A) having a fluorine atom-containing group can be produced by performing the polymerization reaction at a polymerization temperature of 20 to 150° C. for a polymerization time of 0.1 to 100 hr. In the aqueous dispersion, the resin (A) having a fluorine atom-containing group is obtained as particles having an average particle diameter of 10 to 500 nm, preferably 30 to 200 nm. Its solid content concentration is desirably about 5 to 50 mass %. 
         [0033]    Each of the particles of the resin (A) having a fluorine atom-containing group may be of a monolayer structure or may be of a multilayer structure including a core-shell structure. In addition, the inside of each of the particles may be crosslinked and those particles can be obtained by a known method in emulsion polymerization. 
         [0034]    A monomer having copolymerization reactivity to the polymerizable unsaturated monomer (a-1) having a fluorine atom-containing group can be used as the other polymerizable unsaturated monomer (a-2) without any particular limitation. Examples thereof can include: acrylic acid; methacrylic acid; itaconic acid; itaconic anhydride; maleic anhydride; butadiene; isoprene; chloroprene; a (meth)acrylic acid alkyl ester in which the alkyl group has 1 to 20 carbon atoms; a (meth)acrylic acid cyclohexyl ester; isobornyl (meth)acrylate; a (meth)acrylic acid benzyl ester; polyethylene glycol di(meth)acrylate; aromatic vinyl-based monomers such as styrene, α-methylstyrene, and p-methylstyrene; hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, hydroxyamyl (meth)acrylate, and hydroxyhexyl (meth)acrylate; a vinyl alkyl ether in which the alkyl group has 1 to 20 carbon atoms; a halogenated alkyl vinyl ether in which the alkyl group has 1 to 20 carbon atoms; a vinyl alkyl ketone in which the alkyl group has 1 to 20 carbon atoms; silyl group-containing unsaturated monomers such as vinyltriethoxysilane and γ-(methacryloxypropyl)trimethoxysilane; (meth)acrylamide-based monomers such as (meth)acrylamide, N-methylol(meth)acrylamide, N-methoxymethyl (meth)acrylamide, N-ethoxymethyl (meth) acrylamide, N-n-propoxymethyl (meth)acrylamide, N-isopropoxymethyl (meth)acrylamide, N-n-butoxymethyl (meth)acrylamide, N-sec-butoxymethyl (meth)acrylamide, and N-tert-butoxymethyl (meth)acrylamide; vinyl esters such as vinyl acetate and “VeoVa” (vinyl ester manufactured by Shell); acrylonitrile; methacrylonitrile ethylene; and butadiene. It should be noted that herein, the term “(meth)acrylic acid” is a collective term for acrylic acid and methacrylic acid, the term “(meth)acrylate” is a collective term for acrylate and methacrylate, and the term “(meth) acrylamide” is a collective term for acrylamide and methacrylamide. 
         [0035]    A commercial product of the resin (A) having a fluorine atom-containing group dissolved or dispersed in an aqueous medium is, for example, UNIDYNE TG-652, UNIDYNE TG-664, UNIDYNE TG-410, UNIDYNETG-5521, UNIDYNETG-5601, UNIDYNETG-8711, UNIDYNETG-470B, UNIDYNE TG-500S, UNIDYNE TG-580, UNIDYNE TG-581, or UNIDYNE TG-658 (all of which are manufactured by DAIKIN, trade name), SWK-601 (manufactured by SEIMI CHEMICAL), FS6810 (manufactured by Fluoro Technology), or NK GUARD SR-108 (manufactured by NICCA CHEMICAL CO., LTD). 
         [0036]    Instead of the method based on the copolymerization reaction between the polymerizable unsaturated monomer (a-1) having a fluorine atom-containing group and the other polymerizable unsaturated monomer (a-2), the production of the resin (A) having a fluorine atom-containing group can be similarly performed by a polymerization reaction between the polymerizable unsaturated monomers involving using a perfluoroalkyl group-containing radical generator as a polymerization initiator, and examples of the polymerization initiator can include fluorine-containing organic peroxides described in JP 2010-195937 A. 
         [0037]    &lt;Quaternary Ammonium Salt Group-Containing Modified Epoxy Resin (B)&gt; 
         [0038]    The aqueous hydrophobic coating composition contains the quaternary ammonium salt group-containing modified epoxy resin (B) to be described below from the viewpoints of the processability, adhesiveness, moisture resistance, and corrosion resistance of a coating film to be obtained. 
         [0039]    The modified epoxy resin (B) can be produced by subjecting a mixture containing an epoxy resin (b-1), a carboxyl group-containing acrylic resin (b-2), and an amine compound (b-3) to a reaction. In the reaction, a reaction for producing a quaternary ammonium salt group, and an esterification reaction between an epoxy group in the epoxy resin and a carboxyl group in the carboxyl group-containing acrylic resin progress to produce the quaternary ammonium salt group-containing modified epoxy resin (B). In addition, in the reaction, the epoxy group of the epoxy resin (b-1) opens to produce a hydroxyl group. In addition, a hydroxyl group of the quaternary ammonium salt group-containing modified epoxy resin (B) thus produced has reactivity with the amino resin (C) to be described later. 
         [0040]    A bisphenol-type epoxy resin is preferred as the epoxy resin (b-1) from the viewpoints of adhesiveness and corrosion resistance. The bisphenol-type epoxy resin is a resin obtained by a reaction between a bisphenol compound and an epihalohydrin such as epichlorhydrin. 
         [0041]    Examples of the bisphenol compound can include bis(4-hydroxyphenyl)-2,2-propane (bisphenol A), 4,4-dihydroxybenzophenone, bis(4-hydroxyphenyl)methane (bisphenol F), and 4,4-dihydroxydiphenyl sulfone (bisphenol S). Of those bisphenol-type epoxy resins (b-1), a bisphenol A-type epoxy resin is preferably used from the viewpoint of corrosion resistance. 
         [0042]    From the viewpoints of, for example, the dispersion stability in an aqueous medium and the processability and hygiene of the coating film to be obtained, it is suitable to use the bisphenol-type epoxy resin (b-1) having a number-average molecular weight in the range of 4,000 to 30,000, preferably 5,000 to 30,000, and having an epoxy equivalent of 2,000 to 10,000, preferably 2,500 to 10,000. 
         [0043]    Here, as a commercial product of a bisphenol A-type epoxy resin that can be used as the bisphenol-type epoxy resin (b-1), there can be given, for example, jER1010, jER1256B40, and jER1256 manufactured by Japan Epoxy Resins Co. Ltd. 
         [0044]    In addition, the bisphenol A-type epoxy resin may be a bisphenol A-type modified epoxy resin obtained by modifying a bisphenol A-type epoxy resin with a dibasic acid. In this case, a resin having a number-average molecular weight in the range of 2,000 to 8,000 and an epoxy equivalent in the range of 1,000 to 4,000 can be suitably used as the bisphenol A-type epoxy resin to be caused to react with the dibasic acid. In addition, a compound represented by a general formula “HOOC—(CH 2 ) n —COOH (where n represents an integer of 1 to 12),” specifically, for example, succinic acid, adipic acid, pimelic acid, azelaic acid, sebacic acid, dodecanedioic acid, or hexahydrophthalic acid can be used as the dibasic acid, and adipic acid can be particularly suitably used. 
         [0045]    The bisphenol A-type modified epoxy resin can be obtained by subjecting a mixture of the bisphenol A-type epoxy resin and the dibasic acid to a reaction in the presence of an esterification catalyst such as tri-n-butylamine and an organic solvent under the conditions of a reaction temperature of 120 to 180° C. and a reaction time of about 1 to 4 hr. 
         [0046]    The carboxyl group-containing acrylic resin (b-2) to be used in the production of the quaternary ammonium salt group-containing modified epoxy resin (B) can be produced by subjecting a mixture containing a carboxyl group-containing polymerizable unsaturated monomer and any other polymerizable unsaturated monomer to a copolymerization reaction with, for example, a radical polymerization initiator through heating in an organic solvent under the conditions of 80 to 150° C. and 1 to 10 hr. 
         [0047]    As the other polymerizable unsaturated monomer that can be used in the production of the carboxyl group-containing acrylic resin (b-2), for example, there can be given the other polymerizable unsaturated monomer (a-2) described for the resin (A) having a fluorine atom-containing group. 
         [0048]    As the radical polymerization initiator to be used in the production of the carboxyl group-containing acryl resin (b-2), for example, an organic peroxide-based or azo-based radical polymerization initiator is used. Examples of the organic peroxide-based radical polymerization initiator include benzoyl peroxide, t-butyl peroxy-2-ethylhexanoate, di-t-butyl peroxide, t-butyl peroxybenzoate, and t-amyl peroxy-2-ethylhexanoate, and examples of the azo-based radical polymerization initiator include azobisisobutyronitrile and azobisdimethylvaleronitrile. 
         [0049]    In the copolymerization reaction in the production of the carboxyl group-containing acrylic resin (b-2), a chain transfer agent may be used as required, and examples of the chain transfer agent include known agents such as an α-methylstyrene dimer and a mercaptan compound. 
         [0050]    The carboxyl group-containing acrylic resin (b-2) has a weight-average molecular weight in the range of preferably 5,000 to 100,000, more preferably 10,000 to 100,000 and a resin acid value in the range of preferably 150 to 700 mgKOH/g, more preferably 200 to 500 mgKOH/g from the viewpoints of, for example, its stability in an aqueous medium, and the processability and adhesiveness of the coating film to be obtained. 
         [0051]    The amine compound (b-3) is preferably a tertiary amine compound such as triethylamine, dimethylethanolamine, triethanolamine, monomethyldiethanolamine, or N-methylmorpholine. 
         [0052]    The quaternary ammonium salt group-containing modified epoxy resin (B) can be produced by subjecting the mixture containing the epoxy resin (b-1), the carboxyl group-containing acrylic resin (b-2), and the amine compound (b-3) to a reaction through heating in an organic solvent under the conditions of 80 to 120° C. and 0.5 to 8 hr. 
         [0053]    Here, a blending ratio between the epoxy resin (b-1) and the carboxyl group-containing acrylic resin (b-2) in the reaction, which has only to be appropriately selected depending on painting workability and coating film performance, falls within the range of preferably 10/90 to 95/5, more preferably 60/40 to 90/10 in terms of a solid content mass ratio “resin (b-1)/resin (b-2).” 
         [0054]    In addition, the usage of the amine compound (b-3) suitably falls within the range of 1 to 10 mass % with reference to the total solid content of the epoxy resin (b-1) and the carboxyl group-containing acrylic resin (b-2) from the viewpoints of, for example, the moisture resistance and corrosion resistance of the resultant film. 
         [0055]    The quaternary ammonium salt group-containing modified epoxy resin (B) obtained by the reaction has an acid value in the range of preferably 20 to 120 mgKOH/g, more preferably 30 to 100 mgKOH/g and a weight-average molecular weight in the range of preferably 1,000 to 40,000, more preferably 2,000 to 15,000 from the viewpoints of its stability in an aqueous medium, and the processability, adhesiveness, moisture resistance, and corrosion resistance of the coating film to be obtained. 
         [0056]    It should be noted that the “weight-average molecular weight” in the description is a value obtained by converting a retention time (retention volume) measured with tetrahydrofuran as a solvent by gel permeation chromatography with reference to the weight-average molecular weight of a polystyrene. In addition, the “number-average molecular weight” is a value determined from the weight-average molecular weight by calculation. 
         [0057]    “HLC8120GPC” (manufactured by Tosoh Corporation) was used as a gel permeation chromatograph. Four columns, i.e., “TSKgel G-4000HXL,” “TSKgel G-3000HXL,” “TSKgel G-2500HXL,” and “TSKgel G-2000HXL” (all of which were manufactured by Tosoh Corporation, trade name) were used, and the measurement was performed under the following conditions: mobile phase; tetrahydrofuran, measurement temperature; 40° C., flow rate; 1 ml/min, and detector; R1. 
         [0058]    The quarternary ammonium salt group-containing modified epoxy resin (B) is neutralized and dispersed in an aqueous medium, and a basic compound such as an amine or ammonia is suitably used as a neutralizer to be used in the neutralization. 
         [0059]    Typical examples of the amine to be used as the neutralizer include triethylamine, triethanolamine, dimethylethanolamine, diethylethanolamine, and morpholine. Of those, triethylamine and dimethylethanolamine are particularly suitable. In addition, for the neutralization of the quarternary ammonium salt group-containing modified epoxy resin (B), it is generally preferred that the neutralization be performed in the range of 0.2 to 2.0 equivalents with respect to carboxyl groups in the resin. 
         [0060]    In the present invention, the amount of a quaternary ammonium salt group formed at the time of the esterification reaction and by the neutralization (the number of moles of the quaternary ammonium salt group contained per 1 g of the resin) desirably falls within the range of 3.0×10 −4  mol/g or less, preferably within the range of 0.6×10 −4  to 3.0×10 −4  mol/g, more preferably within the range of 0.8×10 −4  to 2.5×10 −4  mol/g from the viewpoints of, for example, the adhesiveness, the moisture resistance, and the corrosion resistance. 
         [0061]    Here, the measurement of the quaternary ammonium salt group amount is performed as described below. That is, a sample after the initiation of the reaction is dissolved in a solvent to prepare a sample solution, and then a titration reaction is performed by dropping an indicator solution (a solution obtained by dissolving an indicator having a sulfonic group and a hydroxyl group as functional groups in a solvent) to the resultant sample solution. For each of the first stage of the titration reaction where the indicator in the indicator solution and the quaternary ammonium salt of an epoxy compound in the sample solution react with each other to form an ionized indicator in which both the sulfonic group and the hydroxyl group have been simultaneously ionized, and a carboxylic acid, and the second stage of the titration reaction where the ionized indicator produced by the first-stage titration reaction and the indicator in the indicator solution react with each other to form a sulfonic group-ionized indicator in which only the sulfonic group has been ionized, a relationship between a titer and an electric conductivity is plotted. A titer t 1  in the first stage is determined from a titer at the point of intersection between a straight line connecting the plots in the first stage and a straight line connecting the plots in the second stage, and then the amount (mol/g) of the quaternary ammonium salt in 1 g of the sample in terms of a solid content is determined from the following equation (1). 
         [0000]      Quaternary ammonium salt amount (mol/g)=t 1  (ml)×2×indicator concentration (mol/l)×( 1/1,000)×{100/(sample (g)×solid content(%))}  Equation (1)
 
         [0062]    It should be noted that an aqueous medium in which the quaternary ammonium salt group-containing modified epoxy resin (B) is dispersed may be water alone or may be a mixture of water and an organic solvent. Any one of the conventionally known solvents can be used as the organic solvent as long as the stability of the quaternary ammonium salt group-containing modified epoxy resin (B) in the aqueous medium is not impaired. 
         [0063]    &lt;Amino Resin (C)&gt; 
         [0064]    Examples of the amino resin (C) in the aqueous hydrophobic coating composition include a melamine resin, a urea resin, and a benzoguanamine resin. Of those, a melamine resin is preferred from the viewpoints of the processability and the adhesiveness. 
         [0065]    Examples of the melamine resin include a partially etherified or fully etherified melamine resin obtained by etherifying part or all of the methylol groups of methylolated melamine with a monohydric alcohol having 1 to 8 carbon atoms such as methyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol, n-butyl alcohol, i-butyl alcohol, 2-ethylbutanol, or 2-ethylhexanol. 
         [0066]    As such resin, there can be used one in which the methylol groups are fully etherified or one in which the methylol groups are partially etherified and methylol groups and imino groups remain. Examples thereof can include alkyl-etherified melamines such as methyl-etherified melamine, ethyl-etherified melamine, and butyl-etherified melamine. One kind of these malamines may be used alone, or two or more kinds thereof may be used in combination as required. Of those, a methyl-etherified melamine resin in which at least part of the methylol groups are methyl-etherified is suitable. 
         [0067]    Commercial products of the melamine resin satisfying such conditions are commercially available under, for example, the following trade names: “CYMEL 202,” “CYMEL 232,” “CYMEL 235,” “CYMEL 238,” “CYMEL 254,” “CYMEL 266,” “CYMEL 267,” “CYMEL 272,” “CYMEL 285,” “CYMEL 301,” “CYMEL 303,” “CYMEL 325,” “CYMEL 327,” “CYMEL 350,” “CYMEL 370,” “CYMEL 701,” “CYMEL 703,” “CYMEL 736,” “CYMEL 738,” “CYMEL 771,” “CYMEL 1141,” “CYMEL 1156,” “CYMEL 1158,” “MYCOAT 212,” “MYCOAT 715,” and “MYCOAT 776” (all of which are manufactured by Nihon Cytec Industries Inc.); “U-VAN 120,” “U-VAN 20HS,” “U-VAN 2021,” “U-VAN 2028,” and “U-VAN 2061” (all of which are manufactured by Mitsui Chemicals, Inc.); and “Melan 522” (manufactured by Hitachi Chemical Co., Ltd.). 
         [0068]    It should be noted that a blending ratio between the quaternary ammonium salt group-containing modified epoxy resin (B) and the amino resin (C) falls within the range of preferably 95/5 to 50/50, particularly preferably 93/7 to 60/40 in terms of a solid content mass ratio “quaternary ammonium salt group-containing modified epoxy resin (B)/amino resin (C).” When the amount of the amino resin (C) is excessively small, sufficient curability is not obtained. In contrast, when the amount is excessively large, the processability of the produced precoated fin material may reduce. 
         [0069]    The content of the resin (A) having a fluorine atom-containing group in the aqueous hydrophobic coating composition is 1 to 30 parts by mass, preferably 3 to 25 parts by mass, more preferably 10 to 22 parts by mass with respect to 100 parts by mass of the total of the quaternary ammonium salt group-containing modified epoxy resin (B) and the amino resin (C) in terms of a solid content from the viewpoints of frost formation-suppressing property, the corrosion resistance, and coating stability. 
         [0070]    It should be noted that additives such as a basic compound, a cross linking agent other than the amino resin (C) (such as a blocked polyisocyanate), colloidal silica, an antibacterial agent, a coloring pigment, a rust preventive pigment known per se (such as a chromate-based, lead-based, or molybdic acid-based pigment), and a rust preventive agent (such as: a phenolic carboxylic acid, e.g., tannic acid or gallic acid and a salt thereof; an organic phosphoric acid, e.g., phytic acid or phosphinic acid; a metal biphosphate; or a nitrite), and an aqueous medium can be added to the aqueous hydrophobic coating composition in the present invention in addition to the resin (A) having a fluorine atom-containing group, the quarternary ammonium salt group-containing modified epoxy resin (B), and the amino resin (C) as required. Here, the aqueous medium may be water or may be a mixed solvent of water and a small amount of an organic solvent or any one of the basic compounds such as amines and ammonia. In addition, the content of water in the mixed solvent is typically 80 mass % or more. 
         [0071]    In addition, in the present invention, the fin structure of a heat exchanger in which a hydrophobic surface and a hydrophilic surface are opposite to each other is constructed by using the one-side hydrophobic/one-side hydrophilic fin material, or the fin structure of the heat exchanger in which the hydrophobic surface and the hydrophilic surface are opposite to each other is constructed by using the double-side hydrophobic fin material obtained by providing each of both surfaces of the fin substrate with the crosslinked hydrophobic film forming the hydrophobic surface and the double-side hydrophilic fin material obtained by providing each of both surfaces of the fin substrate with the hydrophilic film forming the hydrophilic surface. The hydrophilic film in the one-side hydrophobic/one-side hydrophilic fin material or the double-side hydrophilic fin material is formed by applying a hydrophilic coating material to be described later. 
         [0072]    Here, the water contact angle of the hydrophilic film exhibiting a condensed water-removing effect is preferably 40° or less, more preferably 30° or less, and its thickness is typically 0.05 to 5.0 μm or less, preferably 0.1 to 4.0 μm, more preferably 0.2 to 2.0 μm. The water contact angle of the hydrophilic film is desirably as small as possible. However, when the water contact angle of the hydrophilic film is more than 40°, a problem in that condensed water hardly flows arises. In addition, when the thickness of the hydrophilic film is less than 0.05 μm, as in the case of the crosslinked hydrophobic film, for example, the following problem arises. Variations in frost formation suppression and hydrophilicity between lots enlarge, and the deterioration of the frost formation suppression and hydrophilicity-maintaining property over time enlarges. In contrast, when the thickness exceeds 5.0 μm, neither additional frost formation suppression nor an additional improvement in hydrophilicity can be expected. In addition, for example, the following problem arises. The burn of the film due to heat upon brazing of a copper tube for a refrigerant to the fin material becomes rather conspicuous and a cost increases with increasing thickness. 
         [0073]    In the present invention, examples of the hydrophilic coating material to be used for forming the hydrophilic film exhibiting a condensed water-removing effect can include: inorganic hydrophilic coating materials such as water glass-based, silica-based, and boehmite-based coating materials; an organic hydrophilic coating material containing a water-soluble acrylic resin, a water-soluble cellulose resin, a water-soluble amino resin, a polyvinyl alcohol, or the like; and an organic-inorganic composite hydrophilic coating material containing an inorganic material and an organic resin. From the viewpoints of measures against an odor and measures against the abrasion of a mold, an organic hydrophilic coating material is preferred. 
         [0074]    A known coating material can be used as the organic hydrophilic coating material and examples thereof can include the following organic hydrophilic coating compositions (E): 
         [0075]    (1) an organic hydrophilic coating composition containing a polyvinyl alcohol having a saponification degree of 87% or more and a neutralized resin obtained by neutralizing at least part of the carboxyl groups of a high-acid value acrylic resin having a resin acid value of 300 mgKOH/g or more with a basic compound that does not have a boiling point of less than 180° C. and does not decompose at less than 180° C. to form a salt; and 
         [0076]    (2) an organic hydrophilic coating composition containing a polyvinyl alcohol-based resin and a polyethylene glycol-based resin as main components, and containing a nitric acid compound having a monovalent or divalent element (see JP 2002-275407 A). 
         [0077]    &lt;Method of Forming Anticorrosive Film Crosslinked Hydrophobic Film, and Hydrophilic Film&gt; 
         [0078]    A method of forming the anticorrosive film, the crosslinked hydrophobic film, and the hydrophilic film on the surface of the fin substrate is not particularly limited. For example, a roll coater method for application with a generally used roll coater, a gravure roll method for application with a gravure roll convenient for controlling an application amount, a natural coating method convenient for thick application, a reverse coating method advantageous for neatly finishing a coating surface, a bar coating method, or a spray method can be adopted. 
         [0079]    For example, when the one-side hydrophobic/one-side hydrophilic fin material for heat exchangers is produced by forming the crosslinked hydrophobic film on one surface of the fin substrate with the aqueous hydrophobic coating composition and forming the hydrophilic film on the other surface thereof with the organic hydrophilic coating composition, first, the aqueous hydrophobic coating composition is applied to one surface of the fin substrate with a roll coater or the like and then subjected to heating with, for example, a floater oven under high-temperature ventilation, preferably heating under a high-temperature ventilation of 10 to 30 m/min at a high temperature of 60 to 300° C. for 2 sec to 30 min to form the crosslinked hydrophobic film on one surface of the fin substrate. Next, the hydrophilic coating composition is applied to the other surface of the fin substrate and then subjected to heating with, for example, a floater oven under high-temperature ventilation, preferably heating under a high-temperature ventilation of 10 to 30 m/min at a high temperature of 60 to 300° C. for 2 sec to 30 min. Alternatively, the aqueous hydrophobic coating composition is applied to one surface of the fin substrate with a roll coater or the like, then the hydrophilic coating composition is applied to the other surface of the fin substrate, and then the resultant is subjected to heating with, for example, a floater oven under high-temperature ventilation, preferably heating under a high-temperature ventilation of 10 to 30 m/min at a high temperature of 60 to 300° C. for 2 sec to 30 min. 
         [0080]    &lt;Fin Structure of Heat Exchanger&gt; 
         [0081]    The precoated fin material for heat exchangers of the present invention thus obtained is molded into a heat exchange fin having a desired fin shape before use by being subjected to ordinary molding. For example, volatile press oil for press molding is applied to the surface of the precoated fin material and then the resultant is subjected to molding such as slit processing. 
         [0082]    In addition, the fin structure of a heat exchanger formed by using the heat exchange fin is constructed so that its hydrophobic surface provided with the crosslinked hydrophobic film and its hydrophilic surface provided with the hydrophilic film may be opposite to each other. 
         [0083]    For example, when the one-side hydrophobic/one-side hydrophilic fin material is used as the precoated fin material for heat exchangers, the fin structure has only to be constructed by placing the large number of one-side hydrophobic/one-side hydrophilic fin materials so that their hydrophobic surfaces and hydrophilic surfaces may be opposite to each other, followed by fixation to a tube material. In addition, when the double-side hydrophobic fin material is used as the precoated fin material for heat exchangers, the fin structure has only to be constructed with the double-side hydrophilic fin material, which is obtained by forming a hydrophilic film on each of both surfaces of the fin substrate with the hydrophilic coating material, together with the double-side hydrophobic fin material by alternately placing the double-side hydrophobic fin material and the double-side hydrophilic fin material so that the hydrophobic surface and the hydrophilic surface may be opposite to each other, followed by fixation to the tube material. 
       Advantageous Effects of Invention 
       [0084]    According to the precoated fin material for heat exchangers formed of the one-side hydrophobic/one-side hydrophilic fin material of the present invention, the crosslinked hydrophobic film formed on one surface exhibits an excellent frost formation-suppressing effect and the hydrophilic film formed on the other surface exhibits an excellent condensed water-removing effect. Accordingly, the fin structure of a heat exchanger excellent in frost formation-suppressing characteristic and condensed water-removing characteristic can be easily constructed by using the precoated fin material for heat exchangers. 
         [0085]    In addition, according to a heat exchanger including the fin structure of the present invention, the excellent frost formation-suppressing effect exhibited by the hydrophobic surface of the crosslinked hydrophobic film and the excellent condensed water-removing effect exhibited by the hydrophilic surface of the hydrophilic film cooperate with each other to prevent frost formation at the time of heater operation to the extent possible. In addition, under such a condition that condensation is liable to occur on a fin surface, when a water droplet produced by condensation on the hydrophobic surface brought into contact with the adjacent hydrophilic surface, the water droplet can be quickly removed by being easily migrated to a hydrophilic surface side. Thus, a favorable heat exchange function can be maintained over a long time period without any increase in ventilation resistance. 
     
    
     DESCRIPTION OF EMBODIMENTS 
       [0086]    Hereinafter, a preferred embodiment of the present invention is specifically described on the basis of examples and comparative examples. 
         [0087]    It should be noted that in the following examples and comparative examples, the measurement of the water contact angles of a crosslinked hydrophobic film and a hydrophilic film, and the confirmation of a frost formation-suppressing effect were performed by the following methods. 
         [0088]    (Measurement of Water Contact Angle) 
         [0089]    Part of a precoated fin material for heat exchangers produced in each of the examples and comparative examples was cut into a piece measuring 7 cm by 15 cm. 2 μL of pure water were dropped on the film of the test piece placed horizontally and then the contact angle of a water droplet formed on the film of the test piece was measured with a contact angle meter (manufactured by Kyowa Interface Science Co., Ltd.: CA-A). 
         [0090]    (Test of Confirming Frost Formation-Suppressing/Condensed Water-Removing Effect) 
         [0091]    A one-side hydrophobic/one-side hydrophilic fin material (JIS A 1050, 500 mm by 25 mm by 0.1 mm) obtained in each of Examples 1 to 8 and Comparative Examples 1 to 8 was subjected to press working with 2 rows×12 rows of collar portions to provide a heat exchange fin, and then the heat exchange fins were laminated so that the collar portions coincided with each other, and so that a fin structure in which a hydrophobic surface and a hydrophilic surface were opposite to each other at an interval of 1.5 mm was formed. A copper tube (JIS-C1220, outer diameter: 7 mm, wall thickness: 0.3 mm) was inserted into the collar portions of the laminate, and then the copper tube was expanded with a mandrel to join the collar portions mechanically, thereby producing a cross fin tube-type heat exchanger (having external dimensions measuring 500 mm by 25 mm by 250 mm). Thus, a cross fin and tube-type test heat exchanger of each of Examples 1 to 8 and Comparative Examples 1 to 8 having the fin structure in which the hydrophobic surface and the hydrophilic surface were opposite to each other at an interval of 1.5 mm was produced. 
         [0092]    In addition, a fin material of Comparative Example 9 was subjected to press working in the same manner as in the foregoing to provide a heat exchange fin and then the heat exchange fins were laminated at an interval of 1.5 mm so that the collar portions coincided with each other. A copper tube (JIS-C1220, outer diameter: 7 mm, wall thickness: 0.3 mm) was inserted into the collar portions of the laminate, and then the copper tube was expanded with a mandrel to join the collar portions mechanically, thereby producing a cross fin tube-type test heat exchanger (having external dimensions measuring 500 mm by 25 mm by 250 mm). 
         [0093]    Further, a double-side hydrophobic fin material obtained in each of Examples 9 to 11 and a double-side hydrophilic fin material (JIS A 1050, 500 mm by 25 mm by 0.1 mm) were used and laminated in the same manner as in the foregoing so that a fin structure in which a hydrophobic surface and a hydrophilic surface were opposite to each other at an interval of 1.5 mm was formed. Then, a cross fin and tube-type test heat exchanger of each of Examples 9 to 11 having the fin structure in which the hydrophobic surface and the hydrophilic surface were opposite to each other at an interval of 1.5 mm was produced in the same manner as in the foregoing. 
         [0094]    In addition, in Comparative Example 10, a construction in which the two double-side hydrophobic fin materials (JIS A 1050, 500 mm by 25 mm by 0.1 mm) of Example 9 were laminated and then two double-side hydrophilic fin materials (JIS A 1050, 500 mm by 25 mm by 0.1 mm) were laminated was repeated a plurality of times to form a fin structure. Thus, a cross fin and tube-type test heat exchanger of Comparative Example 10 in which the fin materials were laminated so that a hydrophobic surface and a hydrophobic surface, a hydrophobic surface and a hydrophilic surface, and a hydrophilic surface and a hydrophilic surface were formed at an equal interval of 1.5 mm was produced. Further, in Comparative Example 11, a construction in which the five double-side hydrophobic fin materials (JIS A 1050, 500 mm by 25 mm by 0.1 mm) of Example 10 were laminated and then five double-side hydrophilic fin materials (JIS A 1050, 500 mm by 25 mm by 0.1 mm) were laminated was repeated a plurality of times to form a fin structure. Thus, a cross fin and tube-type test heat exchanger of Comparative Example 11 in which the fin materials were laminated so that a hydrophobic surface and a hydrophobic surface, a hydrophobic surface and a hydrophilic surface, and a hydrophilic surface and a hydrophilic surface were formed at an equal interval of 1.5 mm was produced. 
         [0095]    Next, a 50-wt % aqueous solution of propylene glycol was introduced as a refrigerant into each of the test heat exchangers of Examples 1 to 11 and Comparative Examples 1 to 11 thus produced. The refrigerant was circulated in a thermostatic chamber having a chamber temperature of 2° C. and a humidity RH of 90% or more under the conditions of a refrigerant temperature of −6° C. and a refrigerant flow rate of 1 L/min, and then the heat exchanger was operated for 45 min, followed by the observation of a frost formation state in the heat exchange fin of each test heat exchanger. In addition, after the frost formation, a defrosting operation was performed with the refrigerant at 30° C. for 3 min, followed by the observation of the presence or absence of the formation of a bridge by melt water (or condensed water) produced between heat exchange fins. 
         [0096]    The frost formation-suppressing effect was evaluated as described below. A time period required for the formation of frost on the entire surface was measured and the evaluation was performed by the following criteria: x: the case where the time period was less than 15 min, Δ: the case where the time period was 15 min or more and less than 30 min, ∘: the case where the time period was 30 min or more and less than 45 min, and ⊚: the case where no frost formation occurred even after a lapse of 45 min. In addition, a condensed water-removing effect was evaluated as described below. The state of adhesion of the melt water (or condensed water) between the fins after the defrosting operation was observed and the evaluation was performed by the following criteria: x: the case where the bridge occurred on substantially the entire surface, Δ: the case where the bridge occurred on part of the surface, and ∘: the case where the occurrence of the bridge was not observed. 
         [0097]    &lt;Production of Fin Substrates a and b&gt; 
         [0098]    An aluminum material (JIS A 1050) having a plate thickness of 100 μm was used as an aluminum fin material and subjected to a degreasing treatment. After that, an anticorrosive film was formed by painting each of both surfaces of the aluminum material with a chromate-based treatment agent (treatment agent a: manufactured by Nihon Parkerizing Co., Ltd., trade name “ALCHROM 712”) or an organic treatment agent (treatment agent b: manufactured by KANSAI PAINT CO., LTD., trade name “Cosmer 9105”) as an anticorrosive treatment agent through the use of a roll coater. Thus, fin substrates a and b to be used in the following examples and comparative examples were produced. 
         [0099]    Here, upon preparation of the fin substrate a with the treatment agent a, the substrate was formed by: painting each of both surfaces of the aluminum material with the treatment agent a through the use of the roll coater so that the amount of the agent became 20 mg/m 2  in terms of a Cr amount; and drying the agent at a peak metal temperature (PMT) of 230° C. for 15 sec. In addition, when the treatment agent b was used, the substrate was formed by: painting each of both surfaces of the aluminum plate piece with the treatment agent b through the use of the roll coater so that the thickness of the agent became 1.0 g/m 2 ; and drying the agent at a PMT of 250° C. for 10 sec. 
       PRODUCTION EXAMPLE OF AQUEOUS HYDROPHOBIC COATING COMPOSITION 
       [0100]    In the following production examples, the term “part (s)” refers to “part(s) by mass” and the term “%” refers to “mass %.” 
       (1) Production of Carboxyl Group-Containing Acrylic Resin (Ca) to be Used in Production of Ammonium Salt Group-Containing Modified Epoxy Resin (B) 
     Production Example 1 
     Solution of Carboxyl Group-Containing Acrylic Resin (ca-1) 
       [0101]    850 parts of n-butanol were heated to 100° C. in a stream of nitrogen, and then a monomer mixture and a polymerization initiator “450 parts of methacrylic acid, 450 parts of styrene, 100 parts of ethyl acrylate, and 40 parts of t-butyl peroxy-2-ethylhexanoate” were dropped therein over 3 hr. After the dropping, the resultant mixture was aged for 1 hr. Next, a mixed solution of 10 parts of t-butyl peroxy-2-ethylhexanoate and 100 parts of n-butanol was dropped to the aged product over 30 min, and after the dropping, the resultant mixture was aged for 2 hr. Next, 933 parts of n-butanol and 400 parts of ethylene glycol monobutyl ether were added to the aged product to provide a solution of a carboxyl group-containing acrylic resin (ca-1) having a solid content of about 30%. The resultant resin had a resin acid value of 300 mgKOH/g and a weight-average molecular weight of about 17,000. 
       Production Example 2 
     Solution of Carboxyl Group-Containing Acrylic Resin (Ca-2) 
       [0102]    1,400 parts of n-butanol were heated to 100° C. in a stream of nitrogen, and then a monomer mixture and a polymerization initiator “670 parts of methacrylic acid, 250 parts of styrene, 80 parts of ethyl acrylate, and 50 parts of t-butyl peroxy-2-ethylhexanoate” were dropped therein over 3 hr. After the dropping, the resultant mixture was aged for 1 hr. Next, a mixed solution of 10 parts of t-butyl peroxy-2-ethylhexanoate and 100 parts of n-butanol was dropped to the aged product over 30 min, and after the dropping, the resultant mixture was aged for 2 hr. Next, 373 parts of n-butanol and 400 parts of ethylene glycol monobutyl ether were added to the aged product to provide a solution of a carboxyl group-containing acrylic resin (ca-2) having a solid content of about 30%. The resultant resin had a resin acid value of 450 mgKOH/g and a weight-average molecular weight of about 14,000. 
       (2) Production of Ammonium Salt Group-Containing Modified Epoxy Resin (ae) 
     Production Example 3 
     Aqueous Dispersion of Ammonium Salt Group-Containing Modified Epoxy Resin (ae-1) 
       [0103]    513 parts of a jER828EL (manufactured by Japan Epoxy Resins Co., Ltd., epoxy resin, epoxy equivalent: about 190, number-average molecular weight: about 380), 287 parts of bisphenol A, 0.3 part of tetramethylammonium chloride, and 89 parts of methyl isobutyl ketone were loaded, and were then subjected to a reaction for about 4 hr while being heated to 140° C. in a stream of nitrogen. Thus, an epoxy resin solution was obtained. The resultant epoxy resin had an epoxy equivalent of 3,700 and a number-average molecular weight of about 17,000. 
         [0104]    Next, 667 parts of the solution of the carboxyl group-containing acrylic resin (ca-1) having a solid content of about 30% obtained in Production Example 1 were charged into the resultant epoxy resin solution, and were then uniformly dissolved by heating to 90° C. After that, 40 parts of deionized water were dropped to the solution at the temperature over 30 min. Next, 30 parts of dimethylethanolamine were added to the mixture and then the whole was subjected to a reaction by being stirred for 1 hr. Further, 2,380 parts of deionized water were added to the resultant over 1 hr to provide an aqueous dispersion of an ammonium salt group-containing modified epoxy resin (ae-1) having a solid content of about 25%. The resultant resin had a resin acid value of 48 mgKOH/g, a quaternary ammonium salt amount (based on the electric conductivity titration method in the description) of 1.2×10 −4  mol/g, and a weight-average molecular weight of 26,000. 
       Production Example 4 
     Aqueous Dispersion of Ammonium Salt Group-Containing Modified Epoxy Resin (Ae-2) 
       [0105]    519 parts of a jER828EL (manufactured by Japan Epoxy Resins Co., Ltd., epoxy resin, epoxy equivalent: about 190, number-average molecular weight: about 380), 281 parts of bisphenol A, 0.3 part of tetramethylammonium chloride, and 89 parts of methyl isobutyl ketone were loaded, and were then subjected to a reaction for about 4 hr while being heated to 140° C. in a stream of nitrogen. Thus, an epoxy resin solution was obtained. The resultant epoxy resin had an epoxy equivalent of 2,800 and a number-average molecular weight of about 12,000. 
         [0106]    Next, 667 parts of the solution of the carboxyl group-containing acrylic resin (ca-2) having a solid content of about 30% obtained in Production Example 2 were charged into the resultant epoxy resin solution, and were then uniformly dissolved by heating to 90° C. After that, 40 parts of deionized water were dropped to the solution at the temperature over 30 min. Next, 53 parts of dimethylethanolamine were added to the mixture and then the whole was subjected to a reaction by being stirred for 1 hr. Further, 2,350 parts of deionized water were added to the resultant over 1 hr to provide an aqueous dispersion of an ammonium salt group-containing modified epoxy resin (ae-2) having a solid content of about 25%. The resultant resin had a resin acid value of 75 mgKOH/g, a quaternary ammonium salt amount (result based on the electric conductivity titration) of 1.8×10 −4  mol/g, and a weight-average molecular weight of 18,000. 
       (3) Production of Aqueous Hydrophobic Coating Composition (D) 
     Production Example 5 
     Aqueous Hydrophobic Coating Composition (D-1)) 
       [0107]    10 parts (solid content) of a UNIDYNE TG-500S (*1 of Note 2), parts (solid content) of the quaternary ammonium salt group-containing modified epoxy resin (ae-1) obtained in Production Example 3, and 10 parts (solid content) of a MYCOAT 715 (*4 of Note 2) were added, and then deionized water was further added to the mixture to adjust its solid content. Thus, an aqueous hydrophobic coating composition (D-1) having a solid content of 10% was obtained. 
       Production Examples 6 to 12 
     Aqueous Hydrophobic Coating Compositions (D-2) to (D-8)) 
       [0108]    Respective components were sufficiently stirred with a stirring machine in accordance with formulation shown in each of Table 1 and Table 2 below, and then deionized water was added to the mixture to adjust its solid content. Thus, aqueous hydrophobic coating compositions (D-2) to (D-8) each having a solid content of 10% were produced. 
         [0000]    
       
         
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Aqueous hydrophobic coating 
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 composition 
                 D-1 
                 D-2 
                 D-3 
                 D-4 
                 D-5 
                 D-6 
                 D-7 
                 D-8 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Resin (A) having 
                 UNIDYNE 
                 10 
                 — 
                 — 
                 — 
                 — 
                  1 
                 3 
                 20 
               
               
                 fluorine 
                 TG-500S (*1) 
               
               
                 atom-containing 
                 UNIDYNE 
                 — 
                 10 
                 — 
                 10 
                 — 
                 — 
                 — 
                 — 
               
               
                 group 
                 TG-580 (*2) 
               
               
                   
                 UNIDYNE 
                 — 
                 — 
                 10 
                 — 
                 10 
                 — 
                 — 
                 — 
               
               
                   
                 TG-581 (*3) 
               
               
                 Quaternary 
                 ae-1 
                 90 
                 90 
                 90 
                 — 
                 — 
                 90 
                 90 
                 90 
               
               
                 ammonium salt 
                 ae-2 
                 — 
                 — 
                 — 
                 90 
                 90 
                 — 
                 — 
                 — 
               
               
                 group-containing 
               
               
                 modified epoxy 
               
               
                 resin (B) 
               
               
                 Amino resin (C) 
                 MYCOAT 715 (*4) 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
               
               
                   
               
               
                 (Note 1) 
               
               
                 The ratio of a blended content is represented in a “part (s) by mass” unit in terms of a solid content. 
               
               
                 (Note 2) 
               
               
                 (*1): UNIDYNE TG-500S: manufactured by DAIKIN INDUSTRIES, LTD, trade name, water dispersion of fluorine-based resin, solid content: 30 mass % 
               
               
                 (*2): UNIDYNE TG-580: manufactured by DAIKIN INDUSTRIES, LTD, trade name, water dispersion of fluorine-based resin, solid content: 30 mass % 
               
               
                 (*3): UNIDYNE TG-581: manufactured by DAIKIN INDUSTRIES, LTD, trade name, water dispersion of fluorine-based resin, solid content: 30 mass % 
               
               
                 (*4): MYCOAT 715: Nihon Cytec Industries Inc., trade name, methyl-etherified melamine resin, solid content: 80% 
               
             
          
         
       
     
       Production Examples of Hydrophilic Coating Compositions (E) 
     Production Example 13 
     Polyvinyl Alcohol Aqueous Solution (e-1) 
       [0109]    A DENKA POVAL K-05 (manufactured by DENKI KAGAKU KOGYO KABUSHIKI KAISHA, saponification degree: 99%, polymerization degree: 550) was dissolved in water to provide a polyvinyl alcohol aqueous solution (e-1) having a solid content of 14%. 
       Production Example 14 
     Acrylic Resin Aqueous Solution 
       [0110]    80 parts of a “JULIMER AC10LP” (polyacrylic acid manufactured by Nihon Junyaku Co., Ltd., weight-average molecular weight: 25,000, acid value: 779 mgKOH/g) were dissolved in 535 parts of a 3% aqueous solution of n-butanol to provide an acrylic resin aqueous solution (e-2) having a solid content of 13%. 
       Production Example 15 
     Acrylic Resin Aqueous Solution 
       [0111]    80 parts of a “JULIMER AC10LHP” (polyacrylic acid manufactured by Nihon Junyaku Co., Ltd., weight-average molecular weight: 250,000, acid value: 779 mgKOH/g) were dissolved in 920 parts of a 3% aqueous solution of n-butanol to provide an acrylic resin aqueous solution (e-3) having a solid content of 8%. 
       Production Example 16 
     Hydrophilic Coating Composition (E-2) 
       [0112]    385 parts of the acrylic resin aqueous solution (e-2) having a solid content of 13% obtained in Production Example 14 were added to 357 parts of the polyvinyl alcohol aqueous solution (e-1) having a solid content of 14% obtained in Production Example 13. Further, 146 parts of a mixed solution (solution containing lithium hydroxide monohydrate at a concentration of 10%) of 14.6 parts of lithium hydroxide monohydrate (LiOH.H 2 O) and 131.4 parts of a 3% aqueous solution of n-butanol were added to the mixture so that the neutralization degree of the carboxyl groups of the acrylic resin became 0.6 equivalent, followed by mixing and stirring. Further, 112 parts of a 3% aqueous solution of n-butanol were added to the resultant, and then the contents were mixed and stirred so as to be uniform. Thus, a hydrophilic coating composition (E-2) having a solid content of 10% was obtained. Table 2 shows coating formulation. 
       Production Example 17 
     Hydrophilic Coating Composition (E-3) 
       [0113]    385 parts of the acrylic resin aqueous solution (e-3) having a solid content of 13% obtained in Production Example 15 were added to 357 parts of the polyvinyl alcohol aqueous solution (e-1) having a solid content of 14% obtained in Production Example 13. Further, 146 parts of a mixed solution (solution containing lithium hydroxide monohydrate at a concentration of 10%) of 14.6 parts of lithium hydroxide monohydrate (LiOH.H 2 O) and 131.4 parts of a 3% aqueous solution of n-butanol were added to the mixture so that the neutralization degree of the carboxyl groups of the acrylic resin became 0.6 equivalent, followed by mixing and stirring. Further, 112 parts of a 3% aqueous solution of n-butanol were added to the resultant, and then the contents were mixed and stirred so as to be uniform. Thus, a hydrophilic coating composition (E-3) having a solid content of 10% was obtained. Table 2 shows coating formulation. 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Hydrophilic coating composition 
                 E-2 
                 E-3 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Polyvinyl alcohol aqueous solution (e-1) 
                 50 
                 50 
               
               
                   
                 Acrylic resin aqueous solution (e-2) 
                 50 
                 — 
               
               
                   
                 Acrylic resin aqueous solution (e-3) 
                 — 
                 50 
               
               
                   
                 Lithium hydroxide monohydrate (neutralization 
                 0.6 
                 0.6 
               
               
                   
                 equivalent) 
               
               
                   
                   
               
               
                   
                 (Note) 
               
               
                   
                 Contents blended in the components e-1 to e-3 are each represented in a “part(s) by mass” unit in terms of a solid content. 
               
             
          
         
       
     
       Preparation of Comparative Hydrophobic Coating Composition 
     Comparative Production Example 1 
     Modified Epoxy Resin Free of Quaternary Ammonium Salt Group 
       [0114]    513 parts of a jER828EL (manufactured by Japan Epoxy Resins, Co., Ltd., epoxy resin, epoxy equivalent: about 190, number-average molecular weight: about 380), 287 parts of bisphenol A, 0.3 part of tetramethylammonium chloride, and 89 parts of methyl isobutyl ketone were loaded, and were then subjected to a reaction for about 4 hr while being heated to 140° C. in a stream of nitrogen. Thus, an epoxy resin solution was obtained. The resultant epoxy resin had an epoxy equivalent of 3,700 and a number-average molecular weight of about 17,000. 
         [0115]    Next, 667 parts of the solution of the carboxyl group-containing acrylic resin (ca-1) having a solid content of about 30% obtained in Production Example 1 were charged into the thus obtained epoxy resin solution, and were then uniformly dissolved by heating to 90° C. After that, 40 parts of deionized water were dropped to the solution at the temperature over 30 min. Next, 0.2 part of tetramethylammonium chloride was added to the mixture and then the whole was subjected to a reaction under stirring for 3 hr. Further, a mixture of 2,380 parts of deionized water and 23 parts of 25% ammonia water was added to the resultant over 1 hr to provide an aqueous dispersion of a modified epoxy resin free of any quaternary ammonium salt group having a solid content of about 25%. The resultant resin had a resin acid value of 48 mgKOH/g and a weight-average molecular weight of 24,000. 
         [0000]    
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                 Comparative hydrophobic coating 
                   
                   
                   
                   
                   
               
               
                 composition 
                 F-1 
                 F-2 
                 F-3 
                 F-4 
                 F-5 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Resin (A) having fluorine 
                 UNIDYNE 
                 10 
                 — 
                 — 
                 — 
                 10 
               
               
                 atom-containing group 
                 TG-500S (*1) 
               
               
                   
                 UNIDYNE 
                 — 
                 10 
                 — 
                 — 
                 — 
               
               
                   
                 TG-580 (*2) 
               
               
                   
                 UNIDYNE 
                 — 
                 — 
                 10 
                 — 
                 — 
               
               
                   
                 TG-581 (*3) 
               
               
                   
                 LUMIFLON 
                 — 
                 — 
                 — 
                 10 
                 — 
               
               
                   
                 FE-2320 (*5) 
               
               
                 Quaternary ammonium salt 
                 (ae-1) 
                 90 
                 90 
                 90 
                 90 
                 — 
               
               
                 group-containing modified 
               
               
                 epoxy resin (B) 
               
             
          
           
               
                 Modified epoxy resin free of quaternary 
                   
                 90 
               
               
                 ammonium salt group (*6) 
               
             
          
           
               
                 Amino resin (C) 
                 MYCOAT 715 (*4) 
                  0 
                  0 
                  0 
                 10 
                 10 
               
               
                   
               
               
                 (Remark 1) 
               
               
                 The ratio of a blended content is represented in a “part (s) by mass” unit in terms of a solid content. 
               
               
                 (Remark 2) 
               
               
                 (*1) to (*4): The resins are identical to those of Table 1. 
               
               
                 (*5): LUMIFLON FE-2320: manufactured by ASAHI GLASS CO., LTD., trade name, an alternating copolymer of fluoroethylene and vinyl ether (that does not have any perfluoroalkyl group) 
               
               
                 (*6): The modified epoxy resin of Comparative Production Example 1 (free of any quaternary ammonium salt group) 
               
             
          
         
       
     
       Production Example of One-Side Hydrophobic/One-Side Hydrophilic Fin Material 
     Example 1 
       [0116]    The fin substrate a was used as a fin substrate and then the coating material D-1 of the aqueous hydrophobic coating composition shown in Table 1 was applied onto the anticorrosive film on one surface of the fin substrate a with a roll coater (or a bar coater) so as to have a thickness shown in Table 4. Next, the coating material was dried at a PMT of 220° C. for 10 sec to form a crosslinked hydrophobic film. 
         [0117]    Next, a carboxymethylcellulose-based coating material E-1 (manufactured by Nippon Paint Co., Ltd., trade name “SURFALCOAT 160”) was applied onto the anticorrosive film on the other surface of the fin substrate a having the crosslinked hydrophobic film formed on one of its surfaces with a roll coater so as to have a thickness shown in Table 4. Next, the coating material was dried at a PMT of 200° C. for 10 sec to form a hydrophilic film. Thus, a one-side hydrophobic/one-side hydrophilic fin material according to Example 1 was prepared. 
       Examples 2 to 8 
       [0118]    One-side hydrophobic/one-side hydrophilic fin materials according to Examples 2 to 8 were each prepared in the same manner as in Example 1 by using a fin substrate shown in Table 4 and using the coating material E-1, or the coating material E-2 or coating material E-3 shown in Table 2 as the aqueous hydrophobic coating composition and hydrophilic coating composition shown in Table 4, and when the coating material E-2 or the coating material E-3 was used, under the conditions of a PMT of 230° C. and 10 sec. 
       Comparative Example 1 
       [0119]    The fin substrate a was used as a fin substrate and then the coating material D-1 of the aqueous hydrophobic coating composition shown in Table 1 was applied onto each of the anticorrosive films formed on both surfaces of the fin substrate a with a roll coater so as to have a thickness shown in Table 4. Next, the coating material was dried at a PMT of 220° C. for 10 sec to form a double-side hydrophobic fin material of Comparative Example 1 having cross linked hydrophobic films on both surfaces of the fin material a. 
       Comparative Example 2 
       [0120]    The fin substrate a was used as a fin substrate and then the coating material E-2 of the hydrophilic coating composition shown in Table 1 was applied onto the anticorrosive films formed on both surfaces of the fin substrate a with a roll coater so as to have a thickness shown in Table 4. Next, the coating material was dried at a PMT of 230° C. for 10 sec to form a double-side hydrophilic fin material of Comparative Example 2 having hydrophilic films on both surfaces of the fin substrate a. 
       Comparative Example 3 
       [0121]    The fin substrate a was used as a fin substrate and then the coating material F-1 of the comparative hydrophobic coating composition shown in Table 3 was applied onto the anticorrosive film on one surface of the fin substrate a with a roll coater so as to have a thickness shown in Table 4. Next, the coating material was dried at a PMT of 220° C. for 10 sec to form a hydrophobic film. 
         [0122]    Next, the coating material E-1 of the hydrophilic coating composition was applied onto the anticorrosive film on the other surface of the fin substrate a having the hydrophobic film formed on one of its surfaces with a roll coater so as to have a thickness shown in Table 4. Next, the coating material was dried at a PMT of 200° C. for 10 sec to form a hydrophilic film. Thus, a one-side hydrophobic/one-side hydrophilic fin material according to Comparative Example 3 was prepared. 
       Comparative Example 4 
       [0123]    The fin substrate a was used as a fin substrate and then the coating material D-2 of the aqueous hydrophobic coating composition shown in Table 1 was applied onto the anticorrosive film on one surface of the fin substrate a with a roll coater so as to have a thickness shown in Table 4. Next, the coating material was dried at a PMT of 220° C. for 10 sec to form a crosslinked hydrophobic film. 
         [0124]    Next, the coating material E-2 of the hydrophilic coating composition was applied onto the anticorrosive film on the other surface of the fin substrate a having the crosslinked hydrophobic film formed on one of its surfaces with a roll coater so as to have a thickness shown in Table 4. Next, the coating material was dried at a PMT of 270° C. for 10 sec to form a hydrophilic film. Thus, a one-side hydrophobic/one-side hydrophilic fin material according to Comparative Example 4 was prepared. 
       Comparative Example 5 
       [0125]    The fin substrate a was used as a fin substrate and then the coating material F-2 of the comparative hydrophobic coating composition shown in Table 3 was applied onto the anticorrosive film on one surface of the fin substrate a with a roll coater so as to have a thickness shown in Table 4. Next, the coating material was dried at a PMT of 220° C. for 10 sec to form a hydrophobic film. 
         [0126]    Next, the coating material E-1 of the hydrophilic coating composition was applied onto the anticorrosive film on the other surface of the fin substrate a having the hydrophobic film formed on one of its surfaces with a roll coater so as to have a thickness shown in Table 4. Next, the coating material was dried at a PMT of 270° C. for 10 sec to form a hydrophilic film. Thus, a one-side hydrophobic/one-side hydrophilic fin material according to Comparative Example 4 was prepared. 
       Comparative Examples 6 to 9 
       [0127]    The fin substrate b was used as a fin substrate and then the comparative hydrophobic coating composition F-3, F-4, or F-5 shown in Table 3 was applied onto each of the anticorrosive films formed on both surfaces of the fin substrate b with a roll coater so as to have a thickness shown in Table 4. Next, the coating material was dried at a PMT of 220° C. for 10 sec to form a double-side hydrophobic fin material of each of Comparative Examples 6 to 8 having comparative hydrophobic films on both surfaces of the fin substrate b. 
         [0128]    In addition, in Comparative Example 9, a fin material on which a hydrophobic or hydrophilic film was not formed was prepared by using the fin substrate b as a fin substrate. 
         [0129]    Each of the one-side hydrophobic/one-side hydrophilic fin materials of Examples 1 to 8 and Comparative Examples 1 to 9 produced as described above was subjected to the measurement of water contact angles in the hydrophobic surface formed of each of the crosslinked hydrophobic films of Examples 1 to 8 and the hydrophobic films of Comparative Examples 1 to 9, and the hydrophilic surface formed of each of the hydrophilic films of Examples 1 to 8 and Comparative Examples 1 to 9. In addition, in each of Examples 1 to 8 and Comparative Examples 1 to 9, a heat exchanger was produced and then the test of confirming a frost formation-suppressing/condensed water-removing effect was performed. 
         [0130]    Table 4 shows the results. 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 4 
               
             
             
               
                   
                   
               
               
                   
                 hydrophobic surface 
                 Hydrophilic surface 
                   
               
             
          
           
               
                   
                   
                   
                   
                 Water 
                   
                   
                 Water 
                   
                   
               
               
                   
                 Kind of 
                   
                   
                 contact 
                   
                   
                 contact 
                 Frost 
                 Condensed 
               
               
                   
                 fin 
                 Coating 
                 Thickness 
                 angle 
                 Coating 
                 Thickness 
                 angle 
                 formation-suppressing 
                 water-removing 
               
               
                   
                 substrate 
                 material 
                 (μm) 
                 (°) 
                 material 
                 (μm) 
                 (°) 
                 effect 
                 effect 
               
               
                   
                   
               
             
          
           
               
                 Example 
                 1 
                 a 
                 D-1 
                 0.1 
                 100 
                 E-1 
                 0.2 
                 20 
                 ◯ 
                 ◯ 
               
               
                   
                 2 
                 a 
                 D-2 
                 0.2 
                 105 
                 E-2 
                 0.5 
                 15 
                 ◯ 
                 ◯ 
               
               
                   
                 3 
                 a 
                 D-3 
                 0.4 
                 110 
                 E-3 
                 3.0 
                 40 
                 ◯ 
                 ◯ 
               
               
                   
                 4 
                 a 
                 D-4 
                 2.0 
                 102 
                 E-1 
                 0.5 
                 15 
                 ⊚ 
                 ◯ 
               
               
                   
                 5 
                 b 
                 D-5 
                 0.7 
                 115 
                 E-2 
                 1.0 
                  5 
                 ⊚ 
                 ◯ 
               
               
                   
                 6 
                 b 
                 D-6 
                 1.0 
                 103 
                 E-3 
                 0.5 
                 30 
                 ⊚ 
                 ◯ 
               
               
                   
                 7 
                 b 
                 D-7 
                 3.0 
                 105 
                 E-1 
                 1.0 
                 10 
                 ⊚ 
                 ◯ 
               
               
                   
                 8 
                 b 
                 D-8 
                 5.0 
                 108 
                 E-1 
                 2.0 
                  7 
                 ⊚ 
                 ◯ 
               
               
                 Comparative 
                 1 
                 a 
                 D-1 
                 0.5 
                 100 
                 — 
                 — 
                 — 
                 ◯ 
                 X 
               
               
                 Example 
                 2 
                 a 
                 — 
                 — 
                 — 
                 E-2 
                 1.0 
                 20 
                 X 
                 ◯ 
               
               
                   
                 3 
                 a 
                 F-1 
                 0.2 
                  95 
                 E-1 
                 1.0 
                 10 
                 X 
                 ◯ 
               
               
                   
                 4 
                 a 
                 D-2 
                 0.5 
                 102 
                 E-2 
                 1.0 
                 55 
                 ◯ 
                 X 
               
               
                   
                 5 
                 a 
                 F-2 
                 1.0 
                  80 
                 E-1 
                 1.0 
                 45 
                 X 
                 Δ 
               
               
                   
                 6 
                 b 
                 F-3 
                 5.0 
                 100 
                 — 
                 — 
                 — 
                 Δ 
                 X 
               
               
                   
                 7 
                 b 
                 F-4 
                 2.0 
                 105 
                 — 
                 — 
                 — 
                 X 
                 X 
               
               
                   
                 8 
                 b 
                 F-5 
                 1.0 
                 100 
                 — 
                 — 
                 — 
                 Δ 
                 X 
               
               
                   
                 9 
                 b 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 X 
                 X 
               
               
                   
               
             
          
         
       
     
         [0131]    In each of the heat exchange fins used in Examples 1 to 8, frost formation occurred on the hydrophilic surface having formed thereon the hydrophilic film, but the frost did not grow until clogging occurred. In the other hydrophobic surface having formed thereon the cross linked hydrophobic film, no frost formation phenomenon occurred and the frost was not formed on the entire surface within 30 min. After a defrosting operation, the melt water of the frost adhering to the hydrophilic surface flowed down. In addition, dew condensation water on the hydrophobic surface came into contact with the hydrophilic surface to flow down and no bridge formation occurred, and hence a good ventilation state was established. The frost that adhered to the hydrophilic surface at that time also melted to flow down. 
         [0132]    In contrast, in Comparative Example 1, no frost formation phenomenon occurred because both surfaces of the heat exchange fin had only the hydrophobic films each having a frost formation-suppressing effect. However, after a defrosting operation, a bridge was formed by dew condensation water. In addition, in Comparative Example 2, both surfaces of the heat exchange fin had only the hydrophilic films and hence frost was formed on the entire surf ace within a short time period to cause clogging. Further, in each of Comparative Examples 3, 5, 6, and 8, the hydrophobic film had no frost formation suppression-maintaining effect and hence the frost was formed on the entire surface within 15 min to 30 min, and after the defrosting operation, the bridge was formed by the dew condensation water. In Comparative Example 4, no frost formation occurred within 30 min because one surface of the fin had the hydrophobic film having the frost formation-suppressing effect. However, after the defrosting operation, the melt water of the frost adhering to the hydrophilic surface did not flow down. In addition, although the dew condensation water on the hydrophobic surface was in contact with the hydrophilic surface, the dew condensation water did not flow down and the bridge was formed by the dew condensation water. Further, in Comparative Example 7, the hydrophobic film had a low frost formation-suppressing effect and hence the frost was formed on the entire surface within 15 min, and after the defrosting operation, the bridge was formed by the dew condensation water. Further, in the case of Comparative Example 9 using the untreated heat exchange fin, as in Comparative Example 7, the frost was formed on the entire surface within 15 min, and after the defrosting operation, the bridge was formed by the dew condensation water. 
       Production Example of Double-Side Hydrophobic Fin Material 
     Example 9 
       [0133]    The fin substrate a or b was used as a fin substrate and then the coating material D-2 of the aqueous hydrophobic coating composition shown in Table 1 was applied onto each of the anticorrosive films formed on both surfaces of the fin substrate a or b with a roll coater so as to have a thickness shown in Table 5. Next, the coating material was dried at a PMT of 220° C. for 10 sec to form a double-side hydrophobic fin material of Example 9 having crosslinked hydrophobic films on both surfaces of the fin substrate a. 
       Example 10 
       [0134]    The fin substrate b was used as a fin substrate and then the coating material D-3 of the aqueous hydrophobic coating composition shown in Table 1 was applied onto each of the anticorrosive films formed on both surfaces of the fin substrate b with a roll coater so as to have a thickness shown in Table 5. Next, the coating material was dried at a PMT of 220° C. for 10 sec to form a double-side hydrophobic fin material of Example 10 having crosslinked hydrophobic films on both surfaces of the fin substrate. 
       Example 11 
       [0135]    The fin substrate b was used as a fin substrate and then the coating material D-4 of the aqueous hydrophobic coating composition shown in Table 1 was applied onto each of the anticorrosive films formed on both surfaces of the fin substrate b with a roll coater so as to have a thickness shown in Table 5. Next, the coating material was dried at a PMT of 220° C. for 10 sec to form a double-side hydrophobic fin material of Example 11 having crosslinked hydrophobic films on both surfaces of the fin substrate. 
         [0136]    Each of the resultant double-side hydrophobic fin materials of Examples 9 to 11 was subjected to the measurement of a water contact angle in the same manner as in the foregoing. Table 5 shows the results. 
         [0000]    
       
         
               
               
             
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 5 
               
             
             
               
                   
                   
               
               
                   
                 hydrophobic surface 
               
             
          
           
               
                   
                   
                   
                   
                 Water 
               
               
                   
                 Kind of fin 
                 Coating 
                 Thickness 
                 contact 
               
               
                   
                 substrate 
                 material 
                 (μm) 
                 angle (°) 
               
               
                   
                   
               
             
          
           
               
                 Example 
                 9 
                 a 
                 D-2 
                 1 
                 105 
               
               
                   
                 10 
                 b 
                 D-3 
                 0.5 
                 110 
               
               
                   
                 11 
                 b 
                 D-4 
                 1 
                 100 
               
               
                   
               
             
          
         
       
     
         [0137]    &lt;Production Example of Double-Side Hydrophilic Fin Material&gt; 
         [0138]    The fin substrate a or b was used as a fin substrate and then the coating material E-1, E-2, or E-3 of the hydrophilic coating composition shown in Table 2 was applied onto each of the anticorrosive films formed on both surfaces of the fin substrate a or b with a roll coater (or a bar coater) so as to have a thickness shown in Table 6. Next, the coating material E-1 was dried at a PMT of 200° C. for 10 sec and the coating materials E-2 and E-3 were dried at a PMT of 230° C. for 10 sec to form three kinds of double-side hydrophilic fin materials (a to c) having hydrophilic films on both surfaces of the fin substrate a or b. 
         [0139]    Each of the resultant double-side hydrophilic fin materials (a to c) was subjected to the measurement of a water contact angle in the same manner as in the foregoing. Table 6 shows the results. 
         [0000]    
       
         
               
               
             
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 6 
               
             
             
               
                   
                   
               
               
                   
                 Hydrophilic surface 
               
             
          
           
               
                   
                   
                   
                   
                 Water 
               
               
                   
                 Kind of fin 
                 Coating 
                 Thickness 
                 contact 
               
               
                   
                 substrate 
                 material 
                 (μm) 
                 angle (°) 
               
               
                   
                   
               
             
          
           
               
                 Double-side 
                 a 
                 a 
                 E-1 
                 0.5 
                 15 
               
               
                 hydrophilic fin 
                 b 
                 b 
                 E-2 
                 0.8 
                 10 
               
               
                 material 
                 c 
                 b 
                 E-3 
                 0.5 
                 30 
               
               
                   
               
             
          
         
       
     
       Production of Fin Structure and Test of Confirming Frost Formation-Suppressing/Condensed Water-Removing Effect 
     Examples 9 to 11, and Comparative Examples 10 and 11 
       [0140]    Fin structures of Examples 9 to 11 were each constructed with any one of the double-side hydrophobic fin materials of Examples 9 to 11 shown in Table 5 produced as described above and any one of the double-side hydrophilic fin materials a to c shown in Table 6 by alternately placing the double-side hydrophobic fin material and the double-side hydrophilic fin material so that a hydrophobic surface and a hydrophilic surface were opposed to each other at an interval of 1.5 mm. Then, as in the case of each of Examples 1 to 8, a cross fin tube-type test heat exchanger was produced and the test of confirming a frost formation-suppressing/condensed water-removing effect was performed. 
         [0141]    In addition, in Comparative Example 10, a construction in which the two double-side hydrophobic fin materials of Example 9 were laminated and then the two double-side hydrophilic fin materials a were laminated was repeated a plurality of times to construct a fin structure. In addition, in Comparative Example 11, a construction in which the five double-side hydrophobic fin materials D-3 of Example 10 were laminated and then the five double-side hydrophilic fin materials b were laminated was repeated a plurality of times to construct a fin structure. Then, in the same manner as in the foregoing, cross fin tube-type test heat exchangers were produced and the test of confirming a frost formation-suppressing/condensed water-removing effect was performed. 
         [0142]    Table 7 shows the results of Examples 9 to 11, and Comparative Examples 10 and 11. 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 7 
               
               
                   
                   
               
               
                   
                 Double-side 
                 Double-side 
                 Frost 
                 Condensed 
               
               
                   
                 hydrophobic 
                 hydrophilic 
                 formation- 
                 water- 
               
               
                   
                 fin 
                 fin 
                 suppressing 
                 removing 
               
               
                   
                 material 
                 material 
                 effect 
                 effect 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Example 
                 9 
                 D-2 
                 a 
                 ⊚ 
                 ◯ 
               
               
                   
                 10 
                 D-3 
                 b 
                 ◯ 
                 ◯ 
               
               
                   
                 11 
                 D-4 
                 c 
                 ⊚ 
                 ◯ 
               
               
                 Compar- 
                 10 
                 D-2 
                 a 
                 Δ 
                 Δ 
               
               
                 ative 
                 11 
                 D-3 
                 b 
                 Δ 
                 X 
               
               
                 Example