Surface processing method for aluminum heat exchanger
Provided is a surface processing method for an aluminum heat exchanger, by which odor can be suppressed and which enables the aluminum heat exchanger to exhibit corrosion resistance and moisture resistance that are excellent to conventional art. The surface processing method for an aluminum heat exchanger uses a chemical conversion treatment agent that includes: one, or two or more type of a metallic element (A) selected from a group comprising of zirconium, titanium, and hafnium; vanadium element (B); and a resin (C). The resin (C) includes a polyvinyl alcohol resin (C1). The ratio (Wa/Wb) of the weight-based total content (Wa) of the metallic element (A) relative to the weight-based content (Wb) of vanadium element (B) is 0.1-15, and the ratio ((Wa+Wb)/Wc1) of the weight-based total content (Wa+Wb) of the metallic element (A) and vanadium element (B) relative to the weight-based total content (Wc1) of the polyvinyl alcohol resin (C1) is 0.25-15.
1. A surface treatment method for an aluminum heat exchanger, the method comprising the steps of:
(a) treating a surface of the aluminum heat exchanger with a chemical conversion agent to form a chemical conversion coating film on the surface of the aluminum heat exchanger,
(b) allowing the aluminum heat exchanger on the surface of which the chemical conversion coating film has been formed in the step (a) to contact with a hydrophilic agent including a hydrophilic resin, and
(c) performing a baking treatment on the aluminum heat exchanger which has been allowed to contact with the hydrophilic agent in the step (b) to form a hydrophilizing coating film,
wherein the chemical conversion agent comprises one, or two or more metal elements (A) selected from the group consisting of zirconium, titanium and hafnium,
vanadium element (B), and
a resin (C), and
the resin (C) comprises a polyvinyl alcohol based resin (C 1 ) comprising at least of one of polyvinyl alcohol and a derivative thereof, and
the value of a ratio (Wa/Wb) of the mass-based total content (Wa) of the metal element (A) to the mass-based content (Wb) of the vanadium element (B) is 0.1 to 15, and
the value of a ratio ((Wa+Wb)/Wc 1 ) of the mass-based total content (Wa+Wb) of the metal element (A) and the vanadium element (B) to the mass-based total content (Wc 1 ) of the polyvinyl alcohol based resin (C 1 ) is 0.25 to 15.
2. The surface treatment method for an aluminum heat exchanger according to claim 1 , wherein the resin (C) further comprises one, or two or more metal ion-cross linkable polymers (C 2 ), and
wherein the value of a ratio (Wc 2 /(Wc 1 +Wc 2 )) of the mass-based total content (Wc 2 ) of the metal ion-cross linkable polymer (C 2 ) to the mass-based total content (Wc 1 +Wc 2 ) of the polyvinyl alcohol based resin (C 1 ) and the metal ion-cross linkable polymer (C 2 ) is 0.4 or less.
3. The surface treatment method for an aluminum heat exchanger according to claim 2 , wherein the chemical conversion agent comprises one, or two or more selected from the group consisting of polyacrylic acid, phosphoric acid polymer, phosphonic acid polymer, water-soluble or water-dispersible epoxy polymer, water-soluble or water-dispersible urethane based polymer and polyester as the metal ion-cross linkable polymer (C 2 ).
4. The surface treatment method for an aluminum heat exchanger according to claim 1 , wherein the total concentration of the metal element (A) in the chemical conversion agent is 50-100,000 ppm by mass, and the concentration of the vanadium element (B) is 50-100,000 ppm by mass, and the total concentration of the resin (C) is 50-100,000 ppm by mass, and pH is 0.5-6.5.
5. The surface treatment method for an aluminum heat exchanger according to claim 1 , wherein the average saponification degree of the polyvinyl alcohol based resin (C 1 ) is 80% or more.
6. The surface treatment method for an aluminum heat exchanger according to claim 1 , wherein the chemical conversion agent further comprises a surfactant.
7. The surface treatment method for an aluminum heat exchanger according to claim 1 , wherein the chemical conversion agent further comprises one, or two or more sources of free fluorine selected from the group consisting of hydrofluoric acid, ammonium fluoride, ammonium hydrogendifluoride and fluorides of alkali metals.