Surface treatment method for aluminum heat exchangers

Abstract

A surface treatment method for aluminum heat exchangers including (a) a step wherein a chemical conversion coating film is formed on the surface of an aluminum heat exchanger by subjecting the aluminum heat exchanger to chemical conversion using a chemical conversion agent; (b) a step wherein the aluminum heat exchanger, the surface of which has been provided with a chemical conversion coating film in step (a), is brought into contact with a hydrophilizing agent that contains a hydrophilic resin; and (c) a step wherein a hydrophilized coating film is formed on the surface of the aluminum heat exchanger by baking the aluminum heat exchanger, which has been subjected to a contact treatment in step (b). The chemical conversion agent used in step (a) contains zirconium and/or titanium in an amount of 5-5,000 ppm by mass in total, vanadium in an amount of 10-1,000 ppm by mass and a metal stabilizer in an amount of 5-5,000 ppm by mass. In addition, the chemical conversion agent used in step (a) has a pH of 2-6.

Claims

1. A surface treatment method for an aluminum heat exchanger, comprising: (a) a step of forming a chemical conversion film on a surface of the aluminum heat exchanger using a chemical conversion treatment agent; (b) a step of bringing the aluminum heat exchanger on which the chemical conversion film was formed on the surface in the step (a) into contact with a hydrophilization treatment agent containing a hydrophilic resin; and (c) a step of forming a hydrophilized film on the surface by baking the aluminum heat exchanger that was contact treated in the step (b), wherein the chemical conversion treatment agent used in the step (a) contains both zirconium and titanium, wherein a content thereof is 10 to 2,500 ppm by mass in total, contains vanadium, wherein a content thereof is 100 to 500 ppm by mass, contains a metal stabilizer, wherein a content thereof is 10 to 2,000 ppm by mass, and has a pH of 3 to 5.

2. The surface treatment method for aluminum heat exchanger according to claim 1, wherein the metal stabilizer is at least one selected from the group consisting of organic compounds having reducibility and iminodiacetic acid derivatives.

3. The surface treatment method for aluminum heat exchanger according to claim 2, wherein: in the chemical conversion film formed in the step (a), a total of an amount of zirconium and an amount of titanium is 5 to 300 mg/m.sup.2, an amount of vanadium is 1 to 150 mg/m.sup.2, and an amount of metal stabilizer is 0.5 to 200 mg/m.sup.2 in terms of carbon, and a film amount of the hydrophilized film formed in the step (c) is 0.05 to 5 g/m.sup.2.

4. The surface treatment method for aluminum heat exchanger according to claim 2, wherein the hydrophilization treatment agent used in the step (b) further comprises at least one of a guanidine compound represented by general formula (1) below and a salt thereof, ##STR00008## wherein, in formula (1), Y represents —C(═NH)—(CH.sub.2).sub.m—, —C(═O)—NH—(CH.sub.2).sub.m—, or —C(═S)—NH—(CH.sub.2).sub.m—; m represents an integer of 0 to 20; n represents a positive integer; k represents 0 or 1; X represents hydrogen, an amino group, hydroxyl group, methyl group, phenyl group, chlorophenyl group or methylphenyl group; Z represents hydrogen, an amino group, hydroxyl group, methyl group, phenyl group, chlorophenyl group, methylphenyl group, or a polymer represented by general formula (2) below having a mass average molecular weight of 200 to 1,000,000; and ##STR00009## wherein p in formula (2) represents a positive integer.

5. The surface treatment method for aluminum heat exchanger according to claim 4, wherein the guanidine compound and salt thereof are a compound having a biguanide structure represented by general formula (3) below and a salt thereof ##STR00010##

6. The surface treatment method for aluminum heat exchanger according to claim 4, wherein the hydrophilization treatment agent used in the step (b) further comprises at least one selected from the group consisting of phosphoric acid, condensed phosphoric acid, phosphonic acid, derivatives thereof and lithium ion.

7. The surface treatment method for aluminum heat exchanger according to claim 4, wherein the hydrophilic resin in the hydrophilization treatment agent used in the step (b) further comprises at least one of a polyvinyl alcohol and a modified-polyvinyl alcohol having a degree of saponification of at least 90%.

8. The surface treatment method for aluminum heat exchanger according to claim 4, wherein the aluminum heat exchanger is flux brazed.

9. The surface treatment method for aluminum heat exchanger according to claim 4, wherein the aluminum heat exchanger is flux brazed according to the Nocolok brazing process.

10. The according to claim 1, wherein the hydrophilization treatment agent used in the step (b) further comprises at least one of a guanidine compound represented by general formula (1) below and a salt thereof, ##STR00011## wherein, in formula (1), Y represents —C(═NH)—(CH.sub.2).sub.m—, —C(═O)—NH—(CH.sub.2).sub.m—, or —C(═S)—NH—(CH.sub.2).sub.m; m represents an integer of 0 to 20; n represents a positive integer; k represents 0 or 1; X represents hydrogen, an amino group, hydroxyl group, methyl group, phenyl group, chlorophenyl group or methylphenyl group; Z represents hydrogen, an amino group, hydroxyl group, methyl group, phenyl group, chlorophenyl group, methylphenyl group, or a polymer represented by general formula (2) below having a mass average molecular weight of 200 to 1,000,000; and ##STR00012## wherein p in formula (2) represents a positive integer.

11. An aluminum heat exchanger, comprising: a chemical conversion film formed on a surface of the aluminum heat exchanger using a chemical conversion treatment agent; a hydrophilized film formed by baking treatment, after bringing the aluminum heat exchanger on which the chemical conversion film was formed into contact with a hydrophilization treatment agent containing a hydrophilic resin, wherein the chemical conversion film is formed by the chemical conversion treatment agent that contains both zirconium and titanium, wherein a content thereof is 10 to 2,500 ppm by mass in total, contains vanadium, wherein a content thereof is 100 to 500 ppm by mass, contains a metal stabilizer, wherein a content thereof is 10 to 2,000 ppm by mass, and has a pH of 3 to 5, wherein the metal stabilizer is at least one selected from the group consisting of organic compounds having reducibility and iminodiacetic acid derivatives, and wherein the chemical conversion film includes the metal stabilizer.

12. The aluminum heat exchanger according to claim 11, wherein in the chemical conversion film, a total of an amount of zirconium and an amount of titanium is 5 to 300 mg/m.sup.2, an amount of vanadium is 1 to 150 mg/m.sup.2, and an amount of metal stabilizer is 0.5 to 200 mg/m.sup.2 in terms of carbon, and a film amount of the hydrophilized film is 0.05 to 5 g/m.sup.2.

13. The aluminum heat exchanger according to claim 11, wherein the hydrophilization treatment agent further comprises at least one of a guanidine compound represented by general formula (1) below and a salt thereof, and the chemical conversion film includes the hydrophilic resin and at least one of a guanidine compound represented by general formula (1) below and a salt thereof, ##STR00013## wherein, in formula (1), Y represents —C(═NH)—(CH.sub.2).sub.m—, —C(═O)—NH—(CH.sub.2).sub.m—, or —C(═S)—NH—(CH.sub.2).sub.m; m represents an integer of 0 to 20; n represents a positive integer; k represents 0 or 1; X represents hydrogen, an amino group, hydroxyl group, methyl group, phenyl group, chlorophenyl group or methylphenyl group; Z represents hydrogen, an amino group, hydroxyl group, methyl group, phenyl group, chlorophenyl group, methylphenyl group, or a polymer represented by general formula (2) below having a mass average molecular weight of 200 to 1,000,000; and ##STR00014## wherein p in formula (2) represents a positive integer.

14. The aluminum heat exchanger according to claim 13, wherein the guanidine compound and salt thereof are a compound having a biguanide structure represented by general formula (3) below and a salt thereof ##STR00015##

15. The aluminum heat exchanger according to claim 11, wherein the hydrophilic resin further comprises at least one of a polyvinyl alcohol and modified-polyvinyl alcohol having a degree of saponification of at least 90%.

16. The aluminum heat exchanger according to claim 11, wherein the aluminum heat exchanger is flux brazed.

17. The aluminum heat exchanger according to claim 11, wherein the aluminum heat exchanger is flux brazed according to the Nocolok brazing process.

Description

EXAMPLES

(1) Next, the present invention will be explained in further detail based on examples; however, the present invention is not to be limited thereto. Parts, % and ppm are all mass based unless otherwise specified.

Examples 1 to 38 and Comparative Examples 1 to 6

Preparation of Chemical Conversion Treatment Agent

(2) Following a preparation method known heretofore, chemical conversion treatment agents were prepared by formulating and mixing the respective components so that the contents of zirconium, titanium, vanadium and metal stabilizer as well as pH become as shown in Table 1 to Table 3. Fluorozirconic acid was used as the zirconium supply source, fluorotitanic acid was used as the titanium supply source, and vanadyl sulfate was used as the vanadium supply source. The respective concentrations in Table 1 to Table 3 are calculated from the formulation.

(3) Preparation of Hydrophilization Treatment Agent

(4) Following a preparation method known heretofore, hydrophilization treatment agents with a solid content concentration of 2.5% were prepared by formulating and mixing the respective components so that the contents of hydrophilic resin, guanidine compound represented by the above general formula (1), phosphorus-based compound, lithium ion and additives become as shown in Table 1 to Table 3, and using water as the solvent. However, in Example 13 only, a hydrophilization treatment agent with a solid content concentration of 5% was prepared.

(5) Manufacture of Test Heat Exchanger

(6) In Examples 1 to 33 and Comparative Examples 1 to 6, an aluminum heat exchanger (NB heat exchanger) for automobile air-conditioning brazed with KAlF.sub.4 and K.sub.3AlF.sub.6 flux by the Nocolok brazing process was used as the heat exchanger. In addition, in Examples 34 to 38, an aluminum heat exchanger (VB heat exchanger) for automobile air-conditioning brazed by way of a vacuum brazing method was used. The flux amount on the fin surface of the NB heat exchanger was 50 mg/m.sup.2 as potassium.

(7) These heat exchangers were acid washed by dipping for 20 seconds in an acid bath containing 1% sulfuric acid and 0.4% KAlF.sub.4 and K.sub.3AlF.sub.6 flux at 40° C.

(8) After acid washing, the heat exchangers were subjected to chemical conversion treatment by dipping for 60 seconds in the chemical conversion treatment agent prepared as mentioned above at 50° C.

(9) After chemical conversion treatment, the heat exchangers were washed with water for 30 second, followed by dipping for 10 seconds in the hydrophilization treatment agent prepared as mentioned above at room temperature. After dipping, the wet film amount was adjusted by way of air blowing.

(10) Next, baking treatment was conducted in a drying oven for 5 minutes at a baking temperature at which the temperature of the heat exchanger itself became 150° C., thereby manufacturing the test heat exchangers.

(11) Evaluation

(12) For the test heat exchangers manufactured in each of the Examples and Comparative Examples, the physical property evaluations shown below were performed.

(13) Corrosion Resistance (White Rust Resistance)

(14) For the test heat exchangers manufactured in each of the Examples and Comparative Examples, evaluation of corrosion resistance (white rust resistance) based on JIS Z 2371 was conducted. More specifically, a 5% saline solution was sprayed at 35° C. onto the test heat exchangers manufactured in each of the Examples and Comparative Examples, followed by visually evaluating an area of white rust occurrence after the elapse of 2,000 hours in accordance with the evaluation criteria described below. Two people served as evaluators, and corrosion resistance was evaluated based on the average value of the evaluations of the two people.

(15) (Evaluation Criteria)

(16) 10: No white rust generation

(17) 9: White rust observed, but area of white rust generation less than 10%

(18) 8: Area of white rust generation at least 10% to less than 20%

(19) 7: Area of white rust generation at least 20% to less than 30%

(20) 6: Area of white rust generation at least 30% to less than 40%

(21) 5: Area of white rust generation at least 40% to less than 50%

(22) 4: Area of white rust generation at least 50% to less than 60%

(23) 3: Area of white rust generation at least 60% to less than 70%

(24) 2: Area of white rust generation at least 70% to less than 80%

(25) 1: Area of white rust generation at least 80% to less than 90%

(26) Moisture Resistance (Blackening Resistance)

(27) For the test heat exchangers manufactured in each of the Examples and Comparative Examples, a moisture resistance test of 3,000 hours was conducted under an environment at a temperature of 70° C. and humidity of at least 98%. The area of blackening occurrence after the test was visually evaluated based on the evaluation criteria described below. Two people served as evaluators, and moisture resistance was evaluated based on the average value of the evaluations of the two people.

(28) Hydrophilicity

(29) The contact angles with water droplets were measured after bringing the test heat exchangers manufactured in each of the Examples and Comparative Examples into contact with running water for 72 hours. The measurement of contact angle was conducted using an automatic contact angle meter “CA-Z” (manufactured by Kyowa Interface Science Co., LTD.). The hydrophilicity is higher as the contact angle decreases, and the hydrophilicity is evaluated as favorable so long as the contact angle is no more than 40°.

(30) Odor

(31) After bringing the test heat exchangers manufactured in each of the Examples and Comparative Examples into contact with running tap water for 72 hours, the odor thereof was evaluated by the evaluation criteria described below. Two people served as evaluators, and odor was evaluated based on the average value of the evaluations of the two people. The odor resistance was evaluated as favorable so long as the odor was no more than 1.5.

(32) (Evaluation Criteria)

(33) 0: No odor

(34) 1: Slight odor sensed

(35) 2: Odor easily sensed

(36) 3: Odor distinctly sensed

(37) 4: Strong odor sensed

(38) 5: Very strong odor sensed

(39) Film Amount

(40) With the fins joined together so as to be at least 10 mm×10 mm, the zirconium amount, titanium amount and vanadium amount in the chemical conversion film formed on the surface of the test heat exchangers manufactured in each of the Examples and Comparative Examples were calculated from the measurement results of an X-ray fluorescence spectrometer “XRF-1700” (manufactured by SHIMADZU Corp.).

(41) In addition, the metal stabilizer amount in the chemical conversion film was calculated from the measurement results of a TOC apparatus “TOC-VCS” (manufactured by SHIMADZU Corp.) as the organic carbon amount in the chemical conversion film (i.e. in terms of carbon).

(42) The film amount of the hydrophilized film formed on the surface of the test heat exchangers manufactured in each of the Examples and Comparative Examples was calculated from the measurement results of the TOC apparatus “TOC-VCS” (manufactured by SHIMADZU Corp.), using a conversion factor calculated from the relationship between the hydrophilized film amount of a standard film sample and an organic carbon amount contained therein.

(43) The compositions of the chemical conversion treatment agents and hydrophilization treatment agents prepared in each of the Examples and Comparative Examples and the evaluations results of the test heat exchangers manufactured in each of the Examples and Comparative Examples are collectively shown in Table 1 to Table 3.

(44) TABLE-US-00001 TABLE 1 Example 1 2 3 4 5 6 7 8 9 10 Chemical Zr Concentration: ppm 30 — 5 5 3000 — 1000 2000 1000 100 conversion Ti Concentration: ppm — 10 5 5 — 500 150 500 10 50 treatment V Concentration: ppm 100 100 100 100 50 10 500 500 300 100 agent Metal Ascorbic acid Concentration: ppm 100 — — 50 — — — — — 500 stabilizer Oxalic acid Concentration: ppm — 100 — — — — — — — — Aruberi L Concentration: ppm — — 100 50 — — — — — — Pyrogallol Concentration: ppm — — — — 100 — — — — — Pancil FG-70 Concentration: ppm — — — — — 100 — — — — PL-6757 Concentration: ppm — — — — — — 100 — — — Iminodiacetic acid Concentration: ppm — — — — — — — 100 — — Baypure CX-100 Concentration: ppm — — — — — — — — 100 — pH 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 Hydro- Hydro- Polyvinyl alcohol Solid content % 50 50 50 50 50 50 50 50 50 50 philization philic Ethylene oxide- Solid content % 20 20 20 20 20 20 20 20 20 20 treatment resin modified agent polyvinyl alcohol Carboxymeth- Solid content % — — — — — — — — — — ylcellulose Sodium polyvinyl Solid content % — — — — — — — — — — sulfonate Polyacrylic acid Solid content % — — — — — — — — — — Chitosan Solid content % — — — — — — — — — — Guanidine 1-o-tolyl biguanide Solid content % — — — — — — — — — — compound Polyhexamethylene Solid content % 10 10 10 10 10 10 10 10 10 10 biguanide Phosphorus- Phosphoric acid Solid content % — — — — — — — — — — based Condensed Solid content % — — — — — — — — — — compound phosphoric acid Phytic acid Solid content % — — — — — — — — — — PBTC Solid content % — — — — — — — — — — Lithium Lithium hydroxide Solid content % — — — — — — — — — — Additives Silica Solid content % 20 20 20 20 20 20 20 20 20 20 Phenol resin Solid content % — — — — — — — — — — Citric acid Solid content % — — — — — — — — — — Film Chemical Zr mg/m.sup.2 9 — 3 3 80 — 57 71 37 4 amount conversion Ti mg/m.sup.2 — 10 9 8 — 101 39 103 7 20 film V mg/m.sup.2 10 18 14 15 7 10 48 50 16 16 C(metal stabilizer) mg/m.sup.2 5 4 6 6 7 5 5 3 7 15 Hydrophilized film g/m.sup.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Heat exchanger NB NB NB NB NB NB NB NB NB NB Evaluation results Corrosion resistance (2000 h) 7.0 7.5 8.5 9.0 8.0 8.5 9.5 9.5 9.0 9.0 Moisture resistance 7.5 7.0 7.5 8.0 7.0 7.0 8.0 8.5 9.5 9.0 (70° C. 98% RH3000 h) Hydrophilicity 20 20 20 20 20 20 20 20 20 20 Odor 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 Example 11 12 13 14 15 16 17 18 19 Chemical Zr Concentration: ppm 500 500 500 500 500 500 500 500 500 conversion Ti Concentration: ppm 50 50 50 50 50 50 50 50 50 treatment V Concentration: ppm 100 100 100 100 100 100 100 100 100 agent Metal Ascorbic acid Concentration: ppm 500 500 500 500 500 500 10 2000 500 stabilizer Oxalic acid Concentration: ppm — — — — — — — — — Aruberi L Concentration: ppm — — — — — — — — — Pyrogallol Concentration: ppm — — — — — — — — — Pancil FG-70 Concentration: ppm — — — — — — — — — PL-6757 Concentration: ppm — — — — — — — — — Iminodiacetic acid Concentration: ppm — — — — — — — — — Baypure CX-100 Concentration: ppm — — — — — — — — — pH 3.5 3.5 3.5 3 3.5 5 3.5 3.5 3.5 Hydro- Hydro- Polyvinyl alcohol Solid content % 50 50 50 40 40 40 40 40 45 philization philic Ethylene oxide- Solid content % 20 20 20 20 20 20 20 20 20 treatment resin modified agent polyvinyl alcohol Carboxymeth- Solid content % — — — — — — — — — ylcellulose Sodium polyvinyl Solid content % — — — — — — — — — sulfonate Polyacrylic acid Solid content % — — — — — — — — — Chitosan Solid content % — — — — — — — — — Guanidine 1-o-tolyl biguanide Solid content % — — — — — — — — — compound Polyhexamethylene Solid content % 10 10 10 20 20 20 20 20 10 biguanide Phosphorus- Phosphoric acid Solid content % — — — — — — — — 5 based Condensed Solid content % — — — — — — — — — compound phosphoric acid Phytic acid Solid content % — — — — — — — — — PBTC Solid content % — — — — — — — — — Lithium Lithium hydroxide Solid content % — — — — — — — — — Additives Silica Solid content % 20 20 20 20 20 20 20 20 20 Phenol resin Solid content % — — — — — — — — — Citric acid Solid content % — — — — — — — — — Film Chemical Zr mg/m.sup.2 23 23 23 25 22 20 32 14 22 amount conversion Ti mg/m.sup.2 16 16 16 19 17 13 27 8 17 film V mg/m.sup.2 14 14 14 15 15 10 25 6 14 C(metal stabilizer) mg/m.sup.2 12 16 13 19 16 11 1 32 13 Hydrophilized film g/m.sup.2 0.1 0.2 2 0.2 0.2 0.2 0.2 0.2 0.2 Heat exchanger NB NB NB NB NB NB NB NB NB Evaluation results Corrosion resistance (2000 h) 9.0 9.0 9.0 9.5 9.5 8.5 9.5 8.5 9.5 Moisture resistance 8.5 9.0 8.5 8.5 9.5 9.0 8.5 9.5 9.0 (70° C. 98% RH3000 h) Hydrophilicity 20 20 20 22 22 22 22 22 20 Odor 1.0 1.0 1.0 1.5 1.5 1.5 1.5 1.5 1.0

(45) TABLE-US-00002 TABLE 2 Example 20 21 22 23 24 25 26 27 28 29 Chemical Zr Concentration: ppm 500 500 500 500 500 500 500 500 500 500 conversion Ti Concentration: ppm 50 50 50 50 50 50 50 50 50 50 treatment V Concentration: ppm 100 100 100 100 100 100 100 100 100 100 agent Metal Ascorbic acid Concentration: ppm 500 500 500 500 500 500 500 500 500 500 stabilizer Oxalic acid Concentration: ppm — — — — — — — — — — Aruberi L Concentration: ppm — — — — — — — — — — Pyrogallol Concentration: ppm — — — — — — — — — — Pancil FG-70 Concentration: ppm — — — — — — — — — — PL-6757 Concentration: ppm — — — — — — — — — — Iminodiacetic acid Concentration: ppm — — — — — — — — — — Baypure CX-100 Concentration: ppm — — — — — — — — — — pH 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 Hydro- Hydro- Polyvinyl alcohol Solid content % 45 45 45 49 — 50 40 — 70 70 philization philic Ethylene oxide- Solid content % 20 20 20 20 — — 20 — — 20 treatment resin modified agent polyvinyl alcohol Carboxymeth- Solid content % — — — — 60 — — — — — ylcellulose Sodium polyvinyl Solid content % — — — — — 20 — — — — sulfonate Polyacrylic acid Solid content % — — — — 30 — 10 — — — Chitosan Solid content % — — — — — — — 60 — — Guanidine 1-o-tolyl biguanide Solid content % — — — — 5 — 10 — — — compound Polyhexamethylene Solid content % 10 10 10 10 — 10 — 10 — 10 biguanide Phosphorus- Phosphoric acid Solid content % — — — — — — — — — — based Condensed Solid content % 5 — — — — — — — — — compound phosphoric acid Phytic acid Solid content % — 5 — — — — — — — — PBTC Solid content % — — 5 — — — — — — — Lithium Lithium hydroxide Solid content % — — — 1 — — — — — — Additives Silica Solid content % 20 20 20 20 — 20 20 20 30 — Phenol resin Solid content % — — — — 5 — — — — — Citric acid So id contents — — — — — — — 10 — — Film Chemical Zr mg/m.sup.2 21 23 22 23 22 21 22 23 22 21 amount conversion Ti mg/m.sup.2 16 15 15 14 15 15 17 15 14 17 film V mg/m.sup.2 13 14 15 11 13 14 15 15 14 15 C(metal stabilizer) mg/m.sup.2 15 12 16 17 15 14 12 16 16 14 Hydrophilized film g/m.sup.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Heat exchanger NB NB NB NB NB NB NB NB NB NB Evaluation results Corrosion resistance (2000 h) 9.5 9.5 9.5 9.5 9.0 9.0 9.0 9.0 9.0 9.0 Moisture resistance 9.0 9.0 9.0 8.5 7.5 8.5 7.5 8.5 7.5 7.5 (70° C. 98% RH3000 h) Hydrophilicity 20 20 20 20 22 21 20 20 20 20 Odor 1.0 1.0 1.0 1.0 1.5 1.5 1.0 1.5 1.5 1.5 Example 30 31 32 33 34 35 36 37 38 Chemical Zr Concentration: ppm 500 500 500 500 500 100 500 500 500 conversion Ti Concentration: ppm 50 50 50 50 50 — 50 50 50 treatment V Concentration: ppm 100 100 100 100 100 100 100 100 100 agent Metal Ascorbic acid Concentration: ppm 500 500 500 500 100 100 — — — stabilizer Oxalic acid Concentration: ppm — — — — — — — — — Aruberi L Concentration: ppm — — — — — — 100 — — Pyrogallol Concentration: ppm — — — — — — — — — Pancil FG-70 Concentration: ppm — — — — — — — — — PL-6757 Concentration: ppm — — — — — — — — — Iminodiacetic acid Concentration: ppm — — — — — — — 100 — Baypure CX-100 Concentration: ppm — — — — — — — — 100 pH 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 Hydro- Hydro- Polyvinyl alcohol Solid content % — 60 55 — 50 50 45 49 — philization philic Ethylene oxide- Solid content % — — 20 — 20 20 20 20 — treatment resin modified agent polyvinyl alcohol Carboxymeth- Solid content % 60 — — — — — — — 70 ylcellulose Sodium polyvinyl Solid content % — 30 — — — — — — — sulfonate Polyacrylic acid Solid content % 20 — 20 — — — — — 20 Chitosan Solid content % — — — 70 — — — — — Guanidine 1-o-tolyl biguanide Solid content % — — — — — — — — — compound Polyhexamethylene Solid content % — — — — 10 10 10 10 — biguanide Phosphorus- Phosphoric acid Solid content % — — 5 — — — — — — based Condensed Solid content % — — — — — — 5 — — compound phosphoric acid Phytic acid Solid content % — — — — — — — — — PBTC Solid content % — — — — — — — — — Lithium Lithium hydroxide Solid content % — — — — — — — 1 — Additives Silica Solid content % 20 — — 20 20 20 20 20 — Phenol resin Solid content % — 10 — — — — — — 10 Citric acid So id contents — — — 10 — — — — — Film Chemical Zr mg/m.sup.2 23 23 21 22 29 15 25 27 27 amount conversion Ti mg/m.sup.2 15 17 16 15 11 — 10 13 11 film V mg/m.sup.2 13 15 14 14 18 9 15 16 14 C(metal stabilizer) mg/m.sup.2 15 13 16 14 17 5 13 11 10 Hydrophilized film g/m.sup.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Heat exchanger NB NB NB NB VB VB VB VB VB Evaluation results Corrosion resistance (2000 h) 9.0 9.0 9.0 9.0 7.5 7.0 7.5 75 7.5 Moisture resistance 7.5 7.5 7.5 7.5 8.5 7.5 8.0 8.5 7.5 (70° C. 98% RH3000 h) Hydrophilicity 20 20 20 20 22 21 20 21 20 Odor 1.0 1.5 1.0 1.5 1.0 1.0 1.0 1.0 1.5

(46) TABLE-US-00003 TABLE 3 Comparative Example 1 2 3 4 5 6 Chemical Zr Concentration: ppm — 500 — 1000 500 500 conversion Ti Concentration: ppm — — 200 100 50 50 treatment V Concentration: ppm 100 — — — 100 100 agent Metal Ascorbic acid Concentration: ppm 100 100 100 100 100 — stabilizer pH 3.5 3.5 3.5 3.5 1.5 3.5 Hydro- Hydro- Polyvinyl alcohol Solid content % 50 50 50 50 50 50 philization philic Ethylene oxide- Solid content % 20 20 20 20 20 20 treatment resin modified agent polyvinyl alcohol Carboxymeth- Solid content % — — — — — — ylcellulose Sodium polyvinyl Solid content % — — — — — — sulfonate Polyacrylic acid Solid content % — — — — — — Chitosan Solid content % — — — — — — Guanidine 1-o-tolyl biguanide Solid content % — — — — — — compound Polyhexamethylene Solid content % 10 10 10 10 10 10 biguanide Phosphorus- Phosphoric acid Solid content % — — — — — — based Condensed Solid content % — — — — — — compound phosphoric acid Phytic acid Solid content % — — — — — — PBTC Solid content % — — — — — — Lithium Lithium hydroxide Solid content % — — — — — — Additives Silica Solid content % 20 20 20 20 20 20 Phenol resin Solid content % — — — — — — Film Chemical Zr mg/m.sup.2 — 37 — 53 7 34 amount conversion Ti mg/m.sup.2 — — 41 36 9 27 film V mg/m.sup.2 4 — — — 5 25 C (metal stabilizer) mg/m.sup.2 4 6 3 4 2 — Hydrophilized film g/m.sup.2 0.2 0.2 0.2 0.2 0.2 0.2 Heat exchanger NB NB NB NB NB NB Evaluation results Corrosion resistance (2000 h) 3.0 5.0 4.0 5.0 4.0 9.0 Moisture resistance 2.0 3.0 3.0 3.0 3.0 3.0 (70° C. 98% RH3000 h) Hydrophilicity 20 20 20 20 20 20 Odor 1.0 1.0 1.0 1.0 1.0 1.0

(47) The details of each component in Table 1 to Table 3 are as follows.

(48) (1) In the chemical conversion treatment agent, Zr concentration represents the zirconium content in the chemical conversion treatment agent (concentration of various ions in terms of the metal element)), Ti concentration represents the titanium content in the chemical conversion treatment agent (concentration of various ions in terms of the metal element), and V concentration represents the vanadium content in the chemical conversion treatment agent (concentration of various ions in terms of the metal element).

(49) (2) The concentration of metal stabilizer in the chemical conversion treatment agent is the content of metal stabilizer relative to the chemical conversion treatment agent.

(50) (3) Aruberi L of the metal stabilizer is the anthocyanin.

(51) (4) Pancil FG-70 of the metal stabilizer is the catechin.

(52) (5) PL-6757 of the metal stabilizer is the polyphenol.

(53) (6) Baypure CX-100 of the metal stabilizer is the tetrasodium iminodisuccinate.

(54) (7) Solid content % of each component in the hydrophilization treatment agent represents the content of each component relative to the solid content of the hydrophilization treatment agent.

(55) (8) Degree of saponification of polyvinyl alcohol is 99%, and the number average molecular weight thereof is 60,000.

(56) (9) Degree of saponification of ethyleneoxide-modified polyvinyl alcohol is 99%, the number average molecular weight thereof is 20,000, and the content ratio of polyoxyethylene groups (proportion of polyvinyl alcohol relative to total pendant groups) is 3%.

(57) (10) The number average molecular weight of carboxymethylcellulose is 10,000.

(58) (11) The number average molecular weight of sodium polyvinyl sulfonate is 20,000.

(59) (12) The number average molecular weight of polyacrylic acid is 20,000.

(60) (13) The weight average molecular weight of chitosan is 430,000. Since it is necessary for chitosan to dissolve in citric acid, citric acid is also simultaneously contained in the case of using chitosan.

(61) (14) The condensed phosphoric acid is tripolyphosphoric acid.

(62) (15) PBTC represents phosphonobutane tricarboxylic acid.

(63) (16) The phenol resin is an organic cross-linker consisting of resol-type phenol resin, and the number average molecular weight thereof is 300.

(64) As shown in Table 1 to Table 3, all of Examples 1 to 38 are superior in corrosion resistance and moisture resistance compared to Comparative Examples 1 to 5, and are superior in moisture resistance even when comparing with Comparative Example 6; the hydrophilicity and odor (odor resistance) were found to be favorable without any inferiority. From these results, it has been confirmed that more superior corrosion resistance and moisture resistance than conventionally were obtained by forming a hydrophilized film by chemical conversion treating the NB heat exchanger and VB heat exchanger with a chemical conversion treatment agent containing at least one among zirconium and titanium, the content thereof being 5 to 5,000 ppm by mass in total, containing vanadium, the content thereof being 10 to 1,000 ppm by mass, containing metal stabilizer, the content thereof being 5 to 5,000 ppm by mass, as well as having a pH of 2 to 6 to form a chemical conversion film, followed by bringing into contact with a hydrophilization treatment agent containing hydrophilic resin and baking.

INDUSTRIAL APPLICABILITY

(65) According to the surface treatment method of aluminum heat exchanger of the present invention, since it is possible to impart superior corrosion resistance and moisture resistance even to a heat exchanger on which flux remains on the surfaces of fins, etc., the surface treatment method of the present invention is preferably applied to the surface treatment of aluminum heat exchanger for automobile air-conditioning.