JP2548449B2 - Surface treatment method for aluminum heat exchanger - Google Patents

Description

The present invention relates to a surface treatment method for an aluminum (including aluminum alloy) aluminum heat exchanger surface treatment method, and particularly for an automobile car air conditioner. It is preferable for use in an evaporator.

[Prior Art] Conventionally, in an evaporator, when condensed water is generated on the surface of the evaporator, water droplets are accumulated between the fins to increase ventilation resistance and deteriorate performance. There was a problem of scattering to the downstream side.

There is also a problem that rust is likely to occur on the fins due to the accumulation of water droplets between the fins. Therefore, recently, it has been adopted to assemble an aluminum heat exchanger by brazing and then apply a surface treatment having excellent corrosion resistance and hydrophilicity. Explaining a specific example of this surface treatment, on the metal surface of the aluminum base material such as fins,
A chemical conversion film such as chromic acid or phosphate that gives corrosion resistance is formed to form a chemical conversion film, and then an inorganic substance such as silica fine particle silicate that gives a hydrophilic surface is coated on this conversion film. To form a film of an inorganic substance (JP-A-58-2596, JP-A-61-250495, JP-A-62-62495).
-272099, and Japanese Patent Publication No. 2-25692).

However, the above-mentioned inorganic substances are likely to be desorbed with the lapse of use and scatter as fine powders, resulting in deterioration of hydrophilic ability and corrosion resistance. Further, there is a problem that the scattered fine particles stimulate the user's sense of smell and give an unpleasant feeling.

On the other hand, dislike the scattering of these inorganic substances, --OH, --COO
H, -NH _2, there were some method of applying a polymer resin film having a hydrophilic group such as -NH ₄ ^+, coating by a polymer resin having a hydrophilic group is reduced durability of the easy film soluble resin in water However, if the durability of the film is improved by using a resin that is difficult to dissolve in water, the hydrophilicity is lowered, so that a film excellent in both durability and hydrophilicity could not be obtained.

Further, even in the case of a polymer resin film having hydrophilicity, it has a drawback that oil and the like adheres with the passage of time and the fresh water decreases.

[Problems to be Solved by the Invention] The present invention has been made in view of the above points, and does not cause scattering of fine powder over time, and improves corrosion resistance and hydrophilicity (water leakage) of a metal surface of an aluminum base material. It is an object of the present invention to provide an aluminum heat exchange group and a method for producing the same.

[Means for Solving the Problems] In order to achieve the above object, the present invention forms a chemical conversion film having corrosion resistance on the metal surface of an aluminum heat exchanger,
Furthermore, a resin derived from diethylenetriamine, adipic acid, and epichlorohydrin and silica particles which are charged and dispersed in a cation and polyvinylpyrodone, polyvinyl alcohol, cellulose, and an aqueous solution containing one or more kinds of starch are applied to make them hydrophilic. Form a film.

That is, the present invention provides (A) a resin derived from diethylenetriamine, adipic acid and epichlorohydrin after (B) polyvinylpyrrolidone, polyvinyl alcohol, cellulose and starch after chemical conversion film formation treatment on the metal surface of an aluminum heat exchanger. At least 1 selected from the group of
Provided is a surface treatment method for a heat exchanger made of aluminum, which comprises applying a mixed aqueous solution of a seed and (C) silica particles which are electrically charged and dispersed in cations and then drying.

The chemical conversion treatment method that can be used in the present invention is a typical alkali-chromate method as a surface treatment method for aluminum. Chromate method, chromate phosphate method, zinc phosphate and recently adopted in some parts. Examples of the chromium-free film forming method that has been used include a phosphate film forming method of titanium and zircon, and a resin film forming method containing chromic acid. INDUSTRIAL APPLICABILITY The present invention is applicable to various heat exchangers made of aluminum. Particularly, the heat exchanger for use in automobiles has a large air volume, and has a quality required for miniaturization, measurement, and heat exchange efficiency. The environment is severe as well as the environment in which it is used. Therefore, it forms a film with excellent corrosion resistance,
Since a method capable of performing as homogeneous a treatment as possible to the inside of a heat exchanger having a plurality of predominant shapes is required, the film formation method mainly containing chromic acid is most suitable.

After the above-mentioned chemical conversion coating is applied to the surface of an aluminum heat exchanger, an organic polymer resin solution containing a resin derived from diethylenetriamine, adipic acid and epichlorohydrin is applied to form a polymer resin coating.

The resin derived from the mixed component (A) of the present invention, diethylenetriamine, adipic acid and epichlorohydrin, is a resin having the following structural formula.

The average molecular weight of the resin is 2,000 to 100,000. The resin (A) of the present invention has a great feature that durability such as maintenance of hydrophilicity and avoidance of scattering of fine particles is further improved as compared with the case of using a conventional polyamide resin.

The mixed component (B) of the present invention is at least one selected from the group of polyvinylpyrrolidone, polyvinyl alcohol, cellulose and starch. The average molecular weight of polyvinylpyrrolidone is 1000 to 50,000, and the average molecular weight of polyvinyl alcohol is 2,000 to 100,000.

The fine silica particles charged with and dispersed in the cation of the mixed component (C) of the present invention are colloidal silica having a particle size of 1 to 100 mμ.

The mixing ratios of (A), (B) and (C) above are as follows. That is, the amount of the component (B) is 10 to 30 parts by weight, preferably 10 to 20 parts by weight, relative to 100 parts by weight of the component (A). The component (C) is 1 to 100 parts by weight, preferably 10 parts by weight, based on 100 parts by weight of the sum of both components (A) and (B).
~ 30 parts by weight.

The coating method of the mixed aqueous solution of (A), (B) and (C) after the chemical conversion coating treatment on the metal surface of the aluminum heat exchanger is by dip coating.

The treatment temperature of the treatment liquid in the present invention is room temperature to 80 ° C.
Usually, the temperature is set to room temperature (10 to 40 ° C.), but it is also possible to heat the bath for the purpose of improving workability. At temperatures above 80 ° C, water evaporates quickly and the concentration of the treatment liquid tends to change, which is disadvantageous. In addition, heat exchangers easily generate microorganisms in a high temperature state where condensed water is attached, and in a plurality of shapes such as heat exchangers, dust in the air is also easily attached, which causes a strange odor due to microorganisms and dust. May occur. Therefore, as a method of suppressing the generation of microorganisms in the heat exchanger in a high temperature state and preventing the generation of offensive odor, it is preferable to add an antifungal agent to the polymer resin film.

The drying condition after the application is 60 to 180 ° C. for 10 minutes to 2 hours.

The amount of the film finally obtained by the surface treatment is 50 mg / m ^{2 to 3} g / m ² .

Resin is an aqueous solution of inorganic or organic acid,
-It exhibits cationicity as NHR ₂ ⁺ and dissolves or disperses in an aqueous solution. A resin which exhibits a cationic property and is dissolved or dispersed in an aqueous solution has a property of losing its charge by an ionic compound to precipitate or become insoluble and precipitate. In addition, the polyvalent metal ions also have the property of causing the resin to associate, insolubilize, and precipitate. Therefore, when an organic polymer resin film exhibiting cation property is formed on a chemical conversion film consisting of polyvalent metal ions such as zinc, chromium and aluminum, and anions such as phosphate ions and chromate ions, it is , When the base metal or chemical conversion film is dissolved,
These polyvalent metals and anions bind to the resin and tend to diffuse less easily.

Further, the resin film containing the colloidal silica having a cationic charge that can be uniformly dispersed in the polymer resin solution according to the present invention can have improved corrosion resistance and hydrophilicity as compared with the resin alone film.

In addition, a method was adopted in which the adsorption of pollutants in the air, particularly the oil component which deteriorates the hydrophilic performance, was reduced over time. Water-soluble polyvinylpyrrolidone, which has hydrophilicity
By containing polyvinyl alcohol water-soluble cellulose, starch and the like, these substances are dissolved in water and sequentially washed off together with the surface contaminants, so that the film surface can be protected from contamination and the hydrophilic performance can be maintained.

[Examples] Examples of the present invention will be described below together with comparative examples.

Example 1 The metal surface of an aluminum heat exchanger was immersed in an alkaline degreasing detergent (trade name: Fine Cleaner 4306, manufactured by Nippon Parkerizing) at a concentration of 20 g / at a temperature of 60 ° C. for 2 minutes and then washed with water to be cleaned.

Then, for the purpose of imparting corrosion resistance to the metal surface, a chromate chromate film chemical conversion treatment agent for aluminum (registered trademark, Alchrome 713, manufactured by Nippon Parkerizing) 72 g /
Diluted in water at a ratio of 50 ° C., maintaining this aqueous solution at 50 ° C., and immersing the heat exchanger assembly previously cleaned by the above-mentioned washing step for about 2 minutes in this aqueous solution to obtain a chromium deposition amount of about 100 mg / Form a chromate chromate conversion coating of m ² .

After that, as a treatment liquid for imparting a hydrophilic film, a resin derived from diethylenetriamine, adipic acid and epiclohydrin (molecular weight: 50000) is 20 g /, polyvinylpyrrolidone (trade name: Rubiscol K17, BASF Japan molecular weight: 9000) is 10 g /, and a cation is formed. Charged and dispersed colloidal silica (registered trademark Snowtex AK NISSAN CHEMICAL) after dip coating with 2g / 30 ° C aqueous solution, then at about 130 ° C
It was dried for 20 minutes to form a film of about 500 mg / m ² .

Table 1 shows the results of performance confirmation of the main qualities of the aluminum heat exchanger. As shown in Table 1, the corrosion resistance was a value after 500 hours of a salt spray test based on JIS-Z-2371, in which almost no white rust was generated and there was no problem in practical use.

Further, as a measure of ventilation resistance due to condensed water in the evaporator, the contact angle of water on the surface was measured, and a favorable result was shown at 5 degrees or less.

Also, tap water at 0.5 / min to evaluate the durability of the film.
After immersing the object to be treated in the flowing water tank for 48 hours,
After drying for a minute, the contact angle of water was measured again, and the result was about 20 degrees, which was a good value.

Furthermore, after the processed product was installed in an actual car and put in a usable state, the odor of the initial wind when the air conditioner was in operation was sniffed, and no one felt an unpleasant odor. The test was conducted by 5 adults.

Based on the above results, a surface treatment method for an aluminum heat exchanger satisfying the four requirements of the main performance, corrosion resistance, initial contact angle, durability and odor required for the heat exchanger was completed.

Example 2 The same treatment as in Example 1 was carried out by changing the composition of the treatment liquid for imparting the hydrophilic film used in Example 1, and the performance was confirmed. As shown in Table 1. It showed good results.

Example 3 As a treatment liquid for imparting a hydrophilic film, a resin derived from diethylenetriamine, adipic acid and epichlorohydrin, a molecular weight of 50000 is 20 g /, polyvinyl alcohol, a molecular weight of 3000 is 10 g /, and 2 g of cation-charged and dispersed colloidal silica. As a result of confirming the performance by using the same aqueous solution of / at 30 ° C. and the same as in Example 1, as shown in Table 1, good results were shown.

Example 4 As a treatment liquid for imparting a hydrophilic film, a resin derived from diethylenetriamine, adipic acid and epichlorohydrin, 20 g of a molecular weight of 50000 / soluble starch (Wako Pure Chemical Industries) 10 g /, colloidal silica charged with cations and dispersed. 2 g / 30 ° C. aqueous solution was used, otherwise Example 1
As a result of performing the same treatment and confirming the performance, a good result was shown as shown in Table 1.

Example 5 As a treatment liquid for imparting a hydrophilic film, a resin molecular weight of 2000 derived from diethylenetriamine, adipic acid and epichlorohydrin is 20 g /, and the polyvinylpyrrolidone used in Example 1 is 20 g / colloidal silica 2 g /
Using the same aqueous solution at 30 ° C., and otherwise treating as in Example 1,
As a result of confirming the performance, as shown in Table 1, good results were shown.

Example 6 With the composition of the treatment liquid for imparting the hydrophilic film used in Example 1, the amount of silica charged with cations and dispersed was 10 g /
The same treatment as in Example 1 was carried out with the increased 30 ° C. aqueous solution, and the performance was confirmed. As a result, the corrosion resistance, initial contact angle and durability were almost the same as those in Example 1. In terms of odor, 1 out of 5 people felt the smell of powdered white ink. However, it was not particularly unpleasant and was not a problem in practical use.

Example 7 In place of the chromate chromate film chemical conversion treatment agent used in Example 1, a phosphoric acid chromate film chemical conversion treatment agent (registered trademark, Alchrome 701, Nippon Parkerizing) was used, and a chromium film amount of about 100 mg / m ² was obtained. A green chromate phosphate coating was formed. Others were the same as in Example 1, and the treatment was performed using the hydrophilicity-imparting treatment liquid to recognize the performance, and the results shown in Table 1 were obtained.

Corrosion resistance and odor were slightly inferior to those of Examples 1 to 5, but they were not a problem in practical use.

Example 8 After the same phosphoric acid chromate as in Example 7 was applied, the treatment liquid shown in Table 1 was used as the treatment liquid for imparting hydrophilicity,
Others were processed in the same manner as in Example 1, and the performance was confirmed.
As shown in the table, there was no problem in practical use.
A comparative example will be shown below and further compared with the examples of the present invention.

Comparative Example 1 In contrast to Comparative Examples 1 and 7, an example in which a corrosion resistant film was not applied was shown. All others were treated in the same manner as in Example 1, and the results of confirming the performance are shown in Table 1. It is inferior in corrosion resistance as compared with the present invention.

Comparative Examples 2 to 6 The treatment liquid composition shown in Table 1 was used as the treatment liquid composition for imparting hydrophilicity, and the other treatments were performed in the same manner as in Example 1, and the results of confirming the performance are shown. Compared with the present invention, the odor and the change with time of odor are inferior, and in Comparative Examples 3 to 5, the retention of hydrophilicity over time is also inferior.

Comparative Example 7 An example was shown in which the treatment for imparting hydrophilicity was not performed. Table 1 shows the results of performance confirmation performed by otherwise performing the same processes as in Example 1. It is also inferior to the present invention in hydrophilicity, odor and their properties over time.

Comparative Example 8 A polyamide resin was used instead of the component (A) of the present invention. In Comparative Example 8, the present invention resulted in inferior odor property with time.

(Note) 1) Resin derived from diethylenetriamine, adipic acid and epichlorohydrin Resin A: Molecular weight 50,000 Resin B: Molecular weight 2,000 Performance evaluation standard for treated products 2) Corrosion resistance White rust after 500 hours of salt spray test based on JIS-Z2371 Occurrence rate ◎: No abnormality ○: White rust within 5% ×: White rust on the whole surface 3), 4) Contact angle Static contact angle of water measured with a contact angle meter manufactured by Kyowa Scientific Co., Ltd. Contact angle 20 degrees or less Water splashing causes practical problems 40 degrees or more 5) Odor Equipped on a practical vehicle, 5 adults sniff the air odor when starting the air conditioner and evaluate it ○ Everyone has no unpleasant odor △ Among 5 people 1-2 people feel strange odor x 3-4 people or more feel unpleasant odor # all feel unpleasant odor [Effect of the invention] The surface coating of the aluminum heat exchanger obtained by the surface treatment method of the present invention has corrosion resistance, Hydrophilic and odor Excellent in all sexual point is further improved than conventional products in hydrophilicity retention and odor of the change (avoidance of starch raw scattering) in particular over time.

Claims (2)

(57) [Claims] 1. A metal surface of an aluminum heat exchanger is subjected to a chemical conversion film-forming treatment, and then (A) a resin derived from diethylenetriamine, adipic acid and epichlorohydrin (B) polyvinylpyrrolidone, polyvinyl alcohol, cellulose and starch At least one selected from the group consisting of: and (C) a surface treatment of an aluminum heat exchanger characterized by coating and drying a mixed aqueous solution of silica fine particles in which silica fine particles are charged with cations in water and dispersed. Method 2. The method according to claim 1, wherein the aqueous solution of the mixture has a pH of 2 to 7.