JP5391092B2 - Rust prevention treatment method for heat exchanger - Google Patents

Description

  The present invention relates to a rust preventive treatment for a heat exchanger used in an air conditioner for automobiles, particularly a heat exchanger (hereinafter also referred to as NB heat exchanger) that is flux brazed by a Nocolok brazing method (hereinafter referred to as NB method). With respect to the (corrosion resistance treatment) method, the rust heat resistance (corrosion resistance) and hydrophilicity of the NB heat exchanger are improved.

In heat exchangers used for air conditioners for automobiles, aluminum fins are usually held at a narrow interval in order to obtain as much heat exchange surface area as possible, and furthermore, aluminum tubes for supplying refrigerant to these fins are arranged in a complicated manner. It has a complicated structure. Moisture in the air adheres to the fin surface as condensed water when the air conditioner is operating, but on the fin surface with poor wettability, it becomes a substantially hemispherical water droplet or it exists in a bridge shape between the fins, so that intake of air is smooth This hinders the flow and increases the draft resistance. Thus, if the wettability of the fin surface is poor, the heat exchange efficiency is lowered.
Furthermore, aluminum and its alloys constituting aluminum fins and aluminum tubes (hereinafter referred to as “aluminum fins”) are usually excellent in rust prevention, but if condensed water stays on the fin surface for a long time, oxygen Concentration cells are formed, or pollutants in the atmosphere are gradually attached and concentrated to promote hydration and corrosion reactions. This corrosion product accumulates on the fin surface and impairs heat exchange characteristics. In addition, during the heating operation in winter, the corrosion product becomes white fine powder and is discharged together with warm air by the blower.

Therefore, in order to improve these problems, for example, after heat cleaning an aluminum heat exchanger, it is immersed in a zirconium-based chemical conversion treatment solution and subjected to zirconium chemical conversion treatment, and then modified polyvinyl alcohol, phosphorus compound salt, boron compound salt In addition, a surface treatment method has been proposed in which a hydrophilic treatment is performed by immersing in a hydrophilic treatment liquid in which a hydrophilic organic compound, a crosslinking agent and the like are mixed, and the aluminum surface is excellent in hydrophilicity and deodorization (see Patent Document 1). .
In recent years, NB heat exchangers assembled by joining aluminum fins and aluminum tubes by the NB method of brazing in nitrogen gas using fluxes such as KAlF ₄ and K ₂ AlF ₅ have been used in automobile air conditioners. It has been used as an exchanger. As a method for surface-treating this NB heat exchanger, for example, the NB heat exchanger is immersed in a zirconium-based chemical conversion treatment solution and subjected to zirconium chemical conversion treatment, and thereafter, polyvinyl alcohol, polyoxyalkylene-modified polyvinyl alcohol, an inorganic crosslinking agent, A surface treatment method or the like has been proposed in which a hydrophilic treatment is performed by immersing in a hydrophilic treatment liquid mixed with a guanidine compound and the like, and a deodorizing effect is imparted in addition to a good antirust / hydrophilic effect (see Patent Document 2). ).

However, since such NB heat exchangers use fluxes such as KAlF ₄ and K ₂ AlF ₅ , the flux remains on the surface of aluminum fins, etc., the surface state becomes non-uniform, chemical conversion treatment with zirconium, etc. However, there is a problem that the uniform surface treatment cannot be performed and the rust prevention property is insufficient.
This is because in the NB heat exchanger, the flux does not exist uniformly on the surface of aluminum fins or the like, but a portion where the flux remains and a portion where the flux does not remain are generated. When the chemical conversion treatment with zirconium is performed in such a state, a zirconium chemical conversion film is formed on the surface portion not covered with the flux residue, but the zirconium chemical conversion film is formed on the portion covered with the flux residue or in the vicinity thereof. This is due to the fact that the flux residue, which is inferior in rust prevention from the zirconium conversion coating, gradually dissolves and the surface of aluminum fins appears and rust begins to appear.

Therefore, in order to perform uniform surface treatment of the zirconium conversion coating, a method of removing the flux residue from the surface of the NB heat exchanger has been considered.
However, for example, in the method of removing the flux residue by etching with an acid or alkali, there is a problem that only the flux residue cannot be removed, and the joint portion between the aluminum fin and the aluminum tube is etched.
Further, a method has been proposed in which the amount of flux residue is reduced to bring the surface state closer to a uniform state. For example, the flux residue is reduced by adding cesium (Cs) to the flux to increase the activity of the flux and melting in the process of raising the temperature to the brazing temperature (about 600 ° C.) of aluminum fins or the like. In this method, the wettability of aluminum to the aluminum surface is improved, so that the entire product can be covered with a small amount of flux (see Patent Document 3).

  However, even if the amount of the flux residue is reduced, as long as the flux residue is present, a portion where the flux residue is present and a portion where the flux residue is not present are generated, so that the surface state becomes uneven, The problem that it was difficult to obtain good rust prevention properties still remained. Further, there has been a demand for a method capable of obtaining good rust prevention properties even in a state where a large amount of flux remains without performing a method of reducing the flux residue in advance.

JP 2003-003282 A JP 2006-069197 A JP 2005-188788 A

  Therefore, the present invention has been made to solve the above-described problems. In the NB heat exchanger, even if a flux residue is present on the surface of the aluminum fin or the like constituting the NB heat exchanger, the NB heat exchanger can be prevented. It aims at providing the method which can improve rust property.

  In the present invention, when a zirconium-based chemical conversion treatment and a hydrophilic treatment are performed on an NB heat exchanger made of aluminum, a predetermined surface treatment using lithium is performed prior to the chemical conversion treatment, thereby preventing the NB heat exchanger. The present invention provides a method for further increasing rustability. That is, by a predetermined surface treatment using lithium, a surface layer having high rust prevention property containing lithium is formed on the surface of the flux residue, and aluminum having no flux residue is exposed by the subsequent zirconium chemical conversion treatment. Providing a method for remarkably improving the rust prevention property of the NB heat exchanger by forming a zirconium chemical conversion film on a portion of the NB heat exchanger by combining the surface layer containing lithium and the chemical conversion film It is.

The present invention
(1) After heat treating the heat exchanger flux-brazed by the Nocolok brazing method with a lithium treatment solution containing lithium and having a pH of 7 or higher, the heat treatment is performed with a zirconium chemical treatment solution having a pH of 3 to 5 and containing zirconium. Antirust treatment method of heat exchanger,
(2) The antirust treatment method for a heat exchanger according to (1), wherein the lithium content in the lithium treatment liquid is 50 to 5000 ppm,
(3) The rust prevention of the heat exchanger according to (1) or (2) above, wherein the temperature of the lithium treatment liquid is 20 to 90 ° C. and the time of the surface treatment with the lithium treatment liquid is 5 to 900 seconds. Processing method,
(4) The rust preventive treatment method for a heat exchanger according to any one of (1) to (3), wherein the zirconium content in the zirconium chemical conversion treatment solution is 50 to 5000 ppm.
(5) The temperature of the zirconium chemical conversion treatment solution is 50 to 70 ° C., and the time for the zirconium chemical conversion treatment is 20 to 900 seconds, the heat exchanger prevention according to any one of (1) to (4) above Rust treatment method,
(6) The rust preventive treatment method for a heat exchanger according to any one of (1) to (5), wherein the zirconium conversion treatment is followed by a hydrophilic treatment.
Is to provide.

  According to the rust preventive treatment method of the heat exchanger of the present invention, in the NB heat exchanger, even if a flux residue is present on the surface of aluminum fins constituting the NB heat exchanger, the rust preventive property of the NB heat exchanger is improved. Can do.

Hereinafter, the antirust treatment method for the heat exchanger of the present invention will be described.
This form is specifically described in order to make the gist of the invention better understood, and does not limit the present invention.
The heat exchanger used for this invention is a heat exchanger especially used for the air-conditioner of a motor vehicle. This heat exchanger is assembled by joining fins and tubes made of aluminum or aluminum alloy by a known NB method in which brazing is performed in nitrogen gas. Hereinafter, unless otherwise specified, the term “aluminum” includes both aluminum and aluminum alloys.
The flux used in the NB method is not particularly limited as long as it contains a salt composed of Li and an anion that forms a poorly soluble salt, and a normal halogen-based flux used in the NB method can be used. Examples of the halogen-based flux include KAlF ₄ , K ₂ AlF ₅ , K ₃ AlF ₆ , CsAlF ₄ , Cs ₃ AlF ₆ , and Cs ₂ AlF ₅ , and a mixture of two or more thereof.

[Surface treatment with lithium treatment solution]
In the surface treatment with the lithium treatment liquid of the present invention, the NB heat exchanger assembled by the NB method is subjected to surface treatment with a lithium treatment liquid containing lithium and having a pH of 7 or higher.
Inferring the mechanism of surface treatment with this lithium treatment liquid, the film is formed by utilizing the ion exchange reaction (formula 1) between alkali metal ions such as potassium in the flux, particularly halogen-based flux, and lithium ions in the lithium treatment liquid. To form.
K _x AlF _y + xLi ⁺ → Li _x AlF _y + xK ⁺
However, x and y are x = 1, y = 4, x = 2, y = 5 or x = 3, y = 6.
The flux residue is mainly a compound compound of potassium fluoride, cesium fluoride and aluminum fluoride. KAlF ₄ , K ₃ AlF ₆ , K ₂ AlF ₅ , CsAlF ₄ , Cs ₃ AlF ₆ and Cs ₂ AlF ₅ are It is highly soluble and easily soluble in water. On the other hand, Li ₂ AlF ₅ has lower solubility than K ₂ AlF ₅ or the like.

By the surface treatment with the lithium treatment liquid, a layer containing a sparingly soluble lithium salt is formed at least on the surface of the flux residue by an ion exchange reaction between potassium ions and the like in the flux residue and lithium ions in the treatment liquid. It improves the rust resistance (corrosion resistance) of the residue.
The lithium treatment liquid of the present invention can be prepared by dissolving a lithium compound in a solvent, and the lithium compound as a raw material is not particularly limited, but lithium hydroxide, lithium sulfate, lithium nitrate, lithium carbonate, lithium silicate, It is preferable to use a water-soluble lithium compound such as lithium chloride, lithium nitrite, lithium bromide, lithium hydride, or lithium metal.

Although content of lithium in this lithium processing liquid is not specifically limited, 50-5000 ppm is preferable, 100-2000 ppm is more preferable, 400-1000 ppm is further more preferable. This is because if it is 50 ppm or more, the amount is sufficient for ion exchange, and even if it is contained in excess of 5000 ppm, the ion exchange time cannot be shortened. For example, the economics associated with the increase in the content cannot be obtained. .
Moreover, the pH of a lithium processing liquid is 7 or more, and preferable pH is 7-12. Adjustment of pH can be performed with common acids and alkalis, such as a sulfuric acid, nitric acid, and ammonia.

The surface treatment with the lithium treatment liquid can be performed, for example, by bringing the NB heat exchanger into contact with the lithium treatment liquid, and examples thereof include dipping and spraying. At that time, the temperature of the lithium treatment liquid and the surface treatment time are not particularly limited. However, even if the flux residue is etched by the zirconium chemical conversion treatment described later, the lithium treatment solution remains so that a layer containing sufficient lithium remains on the surface of the flux residue. The liquid temperature and surface treatment time should be determined.
When the temperature of the lithium treatment liquid is low or the surface treatment time is short, the amount of ion exchange of lithium is small, and when the temperature of the lithium treatment liquid is high or the surface treatment time is long, the surface of the flux residue or the aluminum surface Is not preferable because it is excessively etched to prevent the formation of a lithium film. The temperature of a preferable lithium processing liquid is 20-90 degreeC, More preferably, it is 30-70 degreeC. The preferable surface treatment time is 5 to 900 seconds, more preferably 15 to 600 seconds. If the temperature of the lithium treatment liquid and the surface treatment time are within this range, even if zirconium conversion treatment is performed, a layer containing sufficient lithium can be left on the surface of the flux residue, and the rust prevention property is improved. A flux residue that does not cause problems in the hydrophilicity, adhesion, and other performances of the hydrophilic film formed thereon can be obtained. In particular, in terms of adhesion, since dissolution of the flux in a harsh environment can be suppressed, an improvement in adhesion can be expected.

  In the present invention, since it is not necessary to remove the flux residue from the NB heat exchanger assembled and assembled by the NB method, before the surface treatment with the lithium treatment liquid of the present invention, the NB heat exchanger is treated with acid or alkali. There is no need to clean with.

[Zirconium conversion treatment]
In the zirconium chemical conversion treatment of the present invention, the NB heat exchanger surface-treated with the above lithium treatment liquid is treated with a zirconium chemical conversion liquid having a pH of 3 to 5 containing zirconium. This zirconium conversion treatment is performed to form a zirconium conversion coating on the aluminum surface of the NB heat exchanger.
This zirconium conversion treatment forms a zirconium conversion coating while etching the surface of aluminum. Even if there is a flux residue that is insufficiently surface-treated with the above-mentioned lithium treatment liquid, even if the portion is etched and the flux residue disappears, a zirconium chemical conversion film is formed on the exposed aluminum surface. By performing the surface treatment and the zirconium chemical conversion treatment, the rust prevention property of the NB heat exchanger can be improved.

The zirconium chemical conversion treatment solution containing zirconium used in the present invention is a solution in which a zirconium-based compound is dissolved in water and zirconium ions are used as active species. Zirconium compounds include zirconium compounds such as fluorozirconic acid and zirconium fluoride, and salts thereof such as lithium, sodium, potassium, and ammonium. A zirconium compound such as zirconium oxide may be dissolved with a fluoride such as hydrofluoric acid.
The zirconium content of the zirconium chemical conversion treatment liquid is not particularly limited, but is preferably 50 to 5000 ppm, more preferably 100 to 3000 ppm, and further preferably 300 to 1500 ppm. From the viewpoint of rust prevention, the amount of the zirconium conversion coating on the aluminum surface of the flux-brazed NB heat exchanger is preferably 1 to 200 mg / m ² , more preferably ² to 150 mg / m ² . is there.

The zirconium chemical conversion treatment solution has a pH in the range of 3-5. If the pH is 3 or more, a zirconium conversion coating can be formed without causing excessive etching with the zirconium conversion treatment solution. If the pH exceeds 5, it is difficult to obtain a sufficient amount of zirconium conversion coating due to insufficient etching. This is because there is a possibility that the rust prevention property is lowered. A more preferable pH is 3.5 to 4.5.
In addition to the above zirconium-based compounds, this zirconium chemical conversion treatment liquid is used to improve rust prevention properties, such as titanium, manganese, zinc, cerium, vanadium, trivalent chromium, and other metal ions, and phenol resin. An agent; a silane coupling agent for improving adhesion; phosphoric acid or the like for promoting a chemical conversion reaction may be contained.

The method of the zirconium chemical conversion treatment of the present invention is not particularly limited, and any of a spray method, an immersion method and the like may be used.
The temperature of the zirconium chemical conversion treatment liquid is preferably 50 to 70 ° C, more preferably 55 to 65 ° C. Moreover, the time of a zirconium chemical conversion treatment becomes like this. Preferably it is 20 to 900 second, More preferably, it is 30 to 600 second. This is because if the temperature of the treatment liquid and the treatment time are in this range, a zirconium conversion coating having rust prevention properties can be formed.

[Hydrophilic treatment]
In the present invention, it is preferable to perform a hydrophilic treatment after the zirconium chemical conversion treatment. The hydrophilic treatment agent and the hydrophilic treatment method used for the hydrophilic treatment are not particularly limited, and known hydrophilic treatment agents and hydrophilic treatment methods can be used.
As the hydrophilization treatment agent, for example, the modified polyvinyl alcohol, phosphorus compound salt, boron compound salt, hydrophilic organic compound, cross-linking agent and the like described in Patent Document 1 (Japanese Patent Application Laid-Open No. 2003-003282) are mixed. A treatment agent, a hydrophilic treatment agent in which polyvinyl alcohol, polyoxyalkylene-modified polyvinyl alcohol, an inorganic crosslinking agent, a guanidine compound and the like described in Patent Document 2 (Japanese Patent Application Laid-Open No. 2006-069197) are mixed can be used.

Various additives other than the above can be used for the hydrophilization treatment agent as necessary. Examples of the additive include lubricants, antibacterial agents, fungicides, antiseptics, antibacterial agents, surfactants, pigments, dyes, and inhibitors for imparting corrosion resistance.
This hydrophilic treatment agent can be prepared by a conventionally known method. For example, a modified polyvinyl alcohol, a phosphorus compound salt, a boron compound salt, a hydrophilic organic compound, a crosslinking agent, or the like is dissolved or dispersed. For the dispersion, a method of forcibly dispersing with an ultrasonic disperser, a fine medium disperser, or the like can be used as necessary. The solvent or the dispersion medium is not particularly limited, but those mainly composed of water are preferable from the viewpoint of waste liquid treatment and the like.
The solid content concentration of the solution or dispersion containing the hydrophilizing agent is selected within a suitable range from the viewpoint of workability, economy and the like, but is usually used in a 1 to 10% by mass solution.

The method for the hydrophilic treatment using the solution or dispersion containing the hydrophilic treatment agent is not particularly limited, and examples thereof include a dipping method and a coating method. Since the NB heat exchanger has a complicated shape, the dipping method is preferable. In this hydrophilization treatment, in the case of the dipping method, the temperature of the solution or dispersion is preferably about 10 to 60 ° C., and the treatment time is preferably about 3 seconds to 5 minutes. A film having a solid film amount of 0.02 to 3 g / m ² is formed by this hydrophilization treatment.
And after this hydrophilization process, a hydrophilic membrane | film | coat can be obtained by baking at 100-220 degreeC for 10 to 60 minutes. When the baking temperature is less than 100 ° C., the film forming property is insufficient, and when it exceeds 220 ° C., the hydrophilic sustainability is lowered. Preferably, it is 120-200 degreeC.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in more detail, this invention is not limited only to these Examples.
[Preparation of lithium treatment solution]
Using lithium hydroxide, sulfuric acid for adjusting pH and ammonia, a lithium treatment solution adjusted to the lithium concentration and pH shown in Table 1 was prepared.
[Preparation of zirconium conversion treatment solution]
Using a zirconium-based chemical conversion treatment agent (Alsurf 95, manufactured by Nippon Paint Co., Ltd.), sulfuric acid and ammonia for pH adjustment, a zirconium chemical conversion treatment liquid adjusted to the zirconium concentration and pH shown in Table 1 was prepared.
[Preparation of hydrophilization solution]
An organic type hydrophilic treatment agent for aluminum (Surf Alcoat 2100, manufactured by Nippon Paint Co., Ltd.) was used.

Examples 1-20 and Comparative Examples 1-3
As the heat exchanger, an automotive heat exchanger made of aluminum brazed with an aluminum fluoride fluoride flux was used. The flux residue amount brazed was 20 mg / m ² (fin surface) as K.
And after cutting this heat exchanger into a size of 0.1 m ² as a test piece, immersing it in the above-mentioned lithium treatment liquid at the temperature and surface treatment time of the lithium treatment liquid shown in Table 1, and pulling it up Washed thoroughly with tap water. However, in the case of Comparative Example 1, an aqueous sulfuric acid solution was used instead of the lithium treatment solution.
The test pieces of Examples 1 to 20 and Comparative Examples 2 to 3 were subjected to X-ray photoelectron spectroscopic analysis (XPS apparatus: AXIS-NOVA manufactured by KRATOS, X-ray source: mono-Al), and a lithium film was formed on the surface. Confirmed that.
Furthermore, this test piece was immersed in said zirconium chemical conversion treatment liquid at the temperature of the zirconium treatment liquid and the chemical conversion treatment time shown in Table 1, pulled up, and then sufficiently washed with tap water. However, in the case of Comparative Example 2, the zirconium chemical conversion treatment was not performed.
Next, this test piece was immersed in the hydrophilization treatment solution at 20 ° C. for 1 minute, pulled up, and then heated at an ultimate temperature of 140 ° C. for 30 minutes to obtain a hydrophilic test piece.

Evaluation about said Example and a comparative example was performed as follows.
[Rust prevention evaluation]
The hydrophilized test piece was sprayed with 5% saline at 35 ° C. based on JIS Z 2371 and allowed to stand for 1000 hours (SST test).
The dried test piece was struck 30 times with a metal bat so that all the generated white rust was dropped, and the amount of white rust obtained was measured. The measurement results are shown in Table 1.
[Evaluation of hydrophilicity]
After contacting the hydrophilized test piece with running water for 72 hours, the contact angle of water droplets was measured using an automatic contact angle meter (CA-Z, manufactured by Kyowa Interface Chemical Co., Ltd.). As the hydrophilicity, the contact angle is preferably 40 ° or less, but the contact angles were 40 ° or less in both Examples and Comparative Examples.

According to Examples 1-20, the amount of white rust generation was 0.32-0.53 g / cm < ² >. On the other hand, in Comparative Example 1 in which the surface treatment with the lithium treatment liquid was not performed (treated with sulfuric acid), the amount of white rust generated was 0.73 g / cm ² , and Comparative Example 2 in which no zirconium conversion treatment was performed. The amount of white rust generated was 0.67 g / cm ² .
Further, in Comparative Example 3 in which the pH of the zirconium chemical conversion treatment is less than 3 (pH 2.0), the amount of white rust generated is 0.80 g / cm ² , and when the pH of the zirconium chemical conversion treatment solution is less than 3, the zirconium chemical conversion film It was found that the formation was not sufficient.
From these Examples and Comparative Examples, it was found that if the surface treatment and the zirconium chemical conversion treatment with the lithium treatment liquid of the present invention were performed, the rust prevention property was improved.

  According to the rust preventive treatment method of the heat exchanger of the present invention, even if a flux residue is present on the surface of the NF heat exchanger such as aluminum fins, the rust preventive property and hydrophilicity of the NB heat exchanger. Therefore, the NB heat exchanger treated by this method can be suitably used as a heat exchanger in an automobile air conditioner.

Claims (6)

  A heat exchanger in which flux heat brazing by the Nocolok brazing method is subjected to surface treatment with a lithium treatment solution containing lithium and having a pH of 7 or higher, and then subjected to zirconium conversion treatment with a zirconium chemical treatment solution having a pH of 3 to 5 containing zirconium. Rust prevention treatment method.   The rust preventive treatment method for a heat exchanger according to claim 1, wherein a content of lithium in the lithium treatment liquid is 50 to 5000 ppm.   The temperature of the said lithium processing liquid is 20-90 degreeC, and the time of the surface treatment by the said lithium processing liquid is 5-900 second, The rust prevention processing method of the heat exchanger of Claim 1 or 2.   The rust preventive treatment method for a heat exchanger according to any one of claims 1 to 3, wherein a content of zirconium in the zirconium chemical conversion treatment solution is 50 to 5000 ppm.   The temperature of the said zirconium chemical conversion liquid is 50-70 degreeC, and the time of the said zirconium chemical conversion process is 20-900 second, The rust prevention processing method of the heat exchanger in any one of Claims 1-4.   The rust preventive treatment method for a heat exchanger according to any one of claims 1 to 5, further comprising a hydrophilic treatment after the zirconium chemical conversion treatment.