JPH06264003A - Method of surface treatment for imparting mildewproofness and hydrophilicity to aluminum material - Google Patents

Abstract

PURPOSE:To provide a surface treatment which forms a hydrophilic coating film excellent in mildewproofness on the surface of metallic material and does not contain any harmful chromium (VI) compound. CONSTITUTION:A surface treatment for rendering metallic material hydrophilic which basically consists of a water-soluble resin and a silica source and has a mildewproofing component comprising butyl p-hydroxybenzoate incorporated therein. The amount of the p-hydroxybenzoate to be incorporated is preferably 0.1-1.0wt.% A hydrophilic coating film is formed by degreasing the surface of aluminum material, drying it, coating it with the surface treatment, and then drying it by heating. The coating film formed on the surface of metallic material is excellent in mildewproofness, hydrophilicity, corrosion resistance, adhesiveness, durability, etc., and is effecitive as a hydrophilic surface film in assembling fins with narrow gaps to increase heat exchange capacity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface treatment agent for imparting antifungal properties and hydrophilicity to the surface of a metal material, a surface treatment method using this surface treatment agent, and a fin for a heat exchanger to which hydrophilicity is imparted. Aluminum products such as.

[0002]

2. Description of the Related Art A metal material may be required to have a surface having a good wettability with water depending on its use.
For example, aluminum or aluminum alloy (hereinafter,
When this is used as a fin of a heat exchanger, etc., heat is exchanged with the atmosphere on the fin surface, but during cooling, moisture in the atmosphere condenses on the back surface of the fin. In a heat exchanger in which the fin gap is narrowed in order to increase the heat exchange capacity, the condensed water becomes spherical and forms a bridge between the fins. As a result, ventilation resistance between the fins increases, and defects such as a decrease in heat exchange capacity, noise generation, and reduction in energy consumption efficiency occur. The bridge of condensed water generated between the fins can be prevented by increasing the hydrophilicity of the fin surface. The water attached to the highly hydrophilic surface spreads and evaporates over the entire surface of the surface without aggregating in a spherical shape.

In addition to the heat exchanger, when water in the atmosphere is prevented from dew condensation on the surface of the metal member arranged in a wet atmosphere, water is used to prevent defrosting of the metal member requiring a glossy surface. Even when the amount of water evaporated from the metal surface is increased by improving the wettability with respect to the metal surface treatment, a surface treatment for imparting hydrophilicity to the metal surface is required. Known methods for imparting hydrophilicity to the surface of an aluminum material include, for example, boehmite treatment, phosphoric acid chromate treatment, and application of hydrophilic paint. The present applicants have introduced in JP-B-61-40305 a surface treating agent having a hydrophilic property and a durability improved by compounding a chromium compound, an acrylic acid polymer, silica and hydrofluoric acid. This surface treatment agent improves the hydrophilicity by adding silica powder, and improves the corrosion resistance by adding hexavalent chromium. In addition, the elution of chromium from the film is prevented by regulating the ratio of hexavalent chromium to the total chromium.

When the surface treating agent disclosed in JP-B-61-40305 is used, a film having excellent hydrophilicity and durability can be formed on the metal surface. Moreover, harmful metals such as hexavalent chromium do not elute over a long period of time. However, this surface treatment agent has a problem in that it contains hexavalent chromium, which is a harmful substance, as one component. Therefore, it is possible to develop a component that is harmless to hexavalent chromium and exhibits a crosslinking action equivalent to that of hexavalent chromium. desired.

As a hydrophilic surface-treating agent containing no hexavalent chromium, for example, in JP-A-2-103133, a zirconium compound, a titanium compound, a silicon compound or the like is used. However, the cross-linking action comparable to that of hexavalent chromium is not exhibited, and the durability of the formed film is poor. In addition, there is a problem with the adhesion to the metal surface, and it is necessary to devise a coating method. In this regard, the present inventors have found that when a vanadium compound is used as a cross-linking agent to convert to hexavalent chromium, a hydrophilic film having excellent adhesion is formed,
The application was filed as Japanese Patent Application No. 4-283887.

[0006]

By the way, when mold is generated on the surface of Al, which is a heat exchanger member such as fins, an unpleasant odor peculiar to the start of cooling operation is emitted. The generation of mold is a phenomenon which is remarkably observed on the Al surface which has been surface-treated with an alkali silicate-based coating material which is highly hydrophilic.
From this point, Al that has been rendered hydrophilic by the surface treatment
It is required to suppress the generation of mold on the surface. As a means for imparting antifungal properties to fins, a method of applying a hydrophilic precoat containing an antifungal agent to the fins has been adopted (JP-A-1-240688 and JP-A-4-3).
39869, JP-A-4-76394, etc.). The hydrophilic precoat improves hydrophilicity and corrosion resistance, and exhibits an action of suppressing the growth of mold, bacteria and the like.

However, many of the commercially available antifungal agents and industrial antifungal agents are expensive and tend to be shunned as a cause of increasing the cost of an inexpensive hydrophilic precoat. Moreover, there are many unsolved problems in terms of safety for the human body and the environment, compatibility with paints, and the like. Furthermore, conventional fungicides do not exhibit a growth-suppressing effect on Kumonosubi which easily proliferate in paints. The present invention has been devised to solve such problems, and by using butyl parahydroxybenzoate as an active ingredient imparting antifungal properties, the corrosion resistance, durability, workability, etc. are impaired. The purpose is to form a hydrophilic coating on the metal surface that is mild to the environment and is harmless to the environment.

[0008]

In order to achieve the object, a hydrophilic metal surface treatment agent for mold prevention of the present invention has a water-soluble resin as a film-forming component, a silica source as a hydrophilicity-imparting component and a mold-proofing property. It is characterized by containing butyl parahydroxybenzoate as a component. As a typical water-soluble resin, a water-soluble or water-dispersible acrylic acid polymer such as polyacrylic acid or its ester is used. For example, acrylic acid, methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate,
There are 2-ethyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, maleic acid, itaconic acid and the like.

The acrylic acid polymer undergoes a crosslinking reaction with a crosslinking agent such as a vanadium compound and becomes insoluble in water. Therefore, when a crosslinking agent is used in combination, the water-soluble acrylic acid polymer has an average molecular weight of 10,000 to 300,
Those with 000 are desirable. The water-dispersion emulsion type acrylic acid polymer has no particular restriction on the molecular weight. The amount of the acrylic acid polymer compounded is preferably set so that the solid content of the polymer precursor is in the range of 1 to 50 g / l. The silica source that imparts hydrophilicity to the film is used in the form of silica powder and / or silicate. Examples of silica include anhydrous silica, colloidal silica, fumed silica, and amorphous silica. Examples of silicates include sodium silicate, potassium silicate, alkaline earth metal salts of silicic acid, and aluminum silicate. When the silica source is added as a powder, it is preferable to use both the primary particles and the secondary particles as fine particles having 50% or more and 1 μm or less.

If the silica source is less than 1 g / l in terms of SiO ₂ , the improvement of hydrophilicity is insufficient. Conversely, 50g / l
If the content exceeds 1, the formed film becomes hard and becomes a cause of promoting wear of the mold in the subsequent molding step and the like.
Butyl parahydroxybenzoate has the following structural formula:
Improves the antifungal properties of hydrophilic coatings. The amount of butyl parahydroxybenzoate added is preferably set in the range of 0.1 to 1% by weight in order to obtain a given antifungal activity. When the amount of butyl parahydroxybenzoate added is less than 0.1% by weight, the antifungal effect is small, and the antibacterial action is deteriorated particularly by the baking process. The improvement of antifungal action by butyl parahydroxybenzoate is saturated at 1% by weight. Further, when a large amount of butyl parahydroxybenzoate exceeding 1% by weight is contained, not only the cost of the surface treatment agent rises but also the solubility in the coating composition decreases.

[Chemical 1]

The hydrophilic metal surface treating agent used in the present invention may further contain one or more of vanadium compounds, alkali carbonates, surfactants and hydrofluoric acid as auxiliary components. The vanadium compound is a component that cross-links with polyacrylic acid to form a film having an excellent anti-corrosion action and excellent adhesion on the metal surface. Typical vanadium compounds that can be used include ammonium vanadate and vanadium pentoxide. Further, metal vanadium is dissolved in an acid solution such as nitric acid, hydrofluoric acid, or hydrofluoric acid to volatilize excess acid, and vanadyl oxychloride, vanadyl chloride, potassium vanadate, sodium vanadate, etc. are used. You can also

When the vanadium compound is added, it is desirable to set the content in the range of 1 to 10 g / l in terms of V. If the content of the vanadium compound is less than 1 g / l, the crosslinking reaction does not proceed sufficiently and the formed film has poor corrosion resistance. The addition effect of the vanadium compound saturates at about 10 g / l, and even if it is added more, the effect commensurate with the increase in amount cannot be obtained. If the solid content (resin part) of the acrylic acid polymer is less than 1 g / l, a film that contributes to corrosion resistance is not sufficiently formed, and conversely, if the amount added exceeds 50 g / l, the hydrophilicity of the film decreases.

When a water-soluble carbonate is added as a pH adjusting agent to the hydrophilic metal surface treating agent of this system, the stability of the solution is improved and the hydrophilicity of the formed film is also improved. As the water-soluble carbonate, potassium hydrogen carbonate, sodium hydrogen carbonate, ammonium hydrogen carbonate, sodium sesquicarbonate, or the like is used. In particular, when colloidal silica is used as the silica source, it is preferable to add the water-soluble carbonate in an amount such that the pH is 7 to 11 in order to obtain good hydrophilicity. Further, when the water-soluble carbonate is further applied and dried after the film is formed, the hydrophilicity of the film is further improved. In this case, a surfactant may be used instead of the water-soluble carbonate. In order to improve the initial hydrophilicity of the formed coating film, an appropriate surfactant may be added. As the surfactant, anionic surfactants such as sodium alkylbenzene sulfonate and sodium alkyldiphenyl ether disulfonate, and fluorine-based surfactants are used.

The hydrofluoric acid or soluble hydrofluoric acid salt contained as an auxiliary agent improves the adhesion of the coating by etching the surface of the base material, and at the same time, the coating mainly contains the reaction product of the base metal and the vanadium compound. Exhibits a good corrosion resistance. Although the detailed mechanism thereof is unknown, hydrofluoric acid or soluble hydrofluoric acid acts on the base metal in cooperation with the vanadium compound, and imparts a slight dissolving action to the silica particles to form the silica particles in the acrylic acid polymer. It is presumed that it is finely dispersed to form a dense hydrophilic film having excellent durability and corrosion resistance. Examples of soluble hydrofluoric acid salts that can be used include silicon fluoride, boron fluoride, titanium fluoride, zirconium fluoride, and zinc fluoride. If the amount of F ⁻ ions derived from fluoride is less than 0.1 g / l, the amount of etching on the aluminum surface will be insufficient and adhesion will not be improved. On the contrary, if it exceeds 5 g / l, the metal surface will be overetched. Prone.

The hydrophilic metal surface treating agent of the present invention may further contain cellulose as a thickening agent imparting corrosion resistance. For example, an appropriate amount of a thickener such as sodium salt, potassium salt, ammonium salt of carboxymethyl cellulose, hydroxyethyl cellulose and the like is added to adjust the surface treatment agent to have a viscosity suitable for the application form. Each of these components is added to water, deionized water, pure water or the like to prepare a surface treatment agent. If necessary, a thickener such as sodium carboxymethyl cellulose (CMC) is added to adjust the surface treatment agent to have a viscosity suitable for the application form. The coating amount on the metal surface is preferably 250 mg after drying.
/ M ² or more is set to an amount at which a coating film is formed. As a coating means, roll coating, brush coating, dipping method, spraying or the like is adopted.

The temperature of the metal surface coated with the hydrophilic metal surface treatment agent is 50 to 260 ° C., preferably 180 to 250.
Dry by holding at a temperature of ° C for 20 seconds to 30 minutes. In order to avoid thermal decomposition of butyl parahydroxybenzoate, air drying at room temperature is preferable. Air drying is particularly effective when the amount of butyl parahydroxybenzoate added is small. However, in air-drying, it takes a long time to completely dry the metal surface, and workability cannot be denied. Further, when natural drying in the line is adopted, a long drying zone is required although the dryer itself is unnecessary. In this respect,
The drying temperature is preferably 50 ° C or higher. 180 ~
When the drying temperature is set high in the temperature range of 250 ° C, the drying can be completed in a short time. For example, at a high drying temperature of 180 ° C. or higher, a short drying time of 20 to 60 seconds may be sufficient. However, at drying temperatures above 260 ° C,
An effect commensurate with the increase in temperature cannot be obtained, and decomposition of butyl parahydroxybenzoate is promoted, which adversely affects the material strength of the base metal.

If the drying is insufficient, the hydrophilic metal surface treatment agent applied to the metal surface will be insufficiently and nonuniformly formed. As a result, a film that does not exhibit the desired performance is formed. Therefore, depending on the drying temperature, the metal surface is subjected to a drying treatment for 20 seconds or more. However, if the drying time is longer than 30 minutes, the work efficiency is lowered. Therefore, the temperature is set to be high to shorten the drying time. A hydrophilic coating film is formed on the metal surface after drying. The adhesion amount of the hydrophilic coating film is preferably 250 mg / m ² or more from the viewpoint of obtaining given properties such as hydrophilicity, corrosion resistance and durability. If the amount of adhesion is less than 250 mg / m ² , sufficient hydrophilicity cannot be imparted to the metal surface. Further, the formed hydrophilic coating film tends to be island-shaped, and the adhesion to the metal surface is also reduced. A water-soluble carbonate, a surfactant or the like may be further applied to the formed hydrophilic coating film and dried. This post-treatment further improves the hydrophilicity of the coating film.

[0018]

The butyl parahydroxybenzoate contained in the hydrophilic metal surface treating agent of the present invention is acceptable as a food additive so as to satisfy the physical properties required for the hydrophilic film formed on the Al surface. It is selected from various antifungal agents and does not adversely affect the human body or environment. Butyl parahydroxybenzoate has a good antifungal property as compared with ethyl hydroxybenzoate and propyl hydroxybenzoate without inhibiting solubility, hydrophilicity, etc., as will be specifically shown in Examples described later. Present. In addition, butyl parahydroxybenzoate also effectively acts on Kumonosukabi that could not be suppressed by conventional fungicides. Therefore, it is possible to maintain a hydrophilic metal surface having excellent durability without causing surface deterioration due to mold generation, odor generation and hydrophilicity reduction.

[0019]

【Example】

Example 1: As a hydrophilic film forming solution, polyacrylic acid 0.5% by weight, water glass 2.5% by weight, carboxymethyl cellulose 0.15% by weight, ammonium vanadate 0.1% by weight, hydrofluoric acid Paint A whose basic composition is 0.04% by weight and the balance water, and polyacrylic acid 0.3
A coating material B having a basic composition of 0% by weight, 4% by weight of colloidal silica, 0.15% by weight of carboxymethyl cellulose, 0.1% by weight of ammonium vanadate and the balance water was prepared. To these paints A and B, 0.1% of various fungicides
Wt% was added.

The prepared hydrophilic film-forming solution was applied to a 0.10 mm thick aluminum alloy foil AA3102 and air dried. At this time, the coating amount was adjusted so that the adhesion amount of the hydrophilic film after drying was 250 mg / m ² . The hydrophilicity of the hydrophilic film is that water droplets on the Al surface after film formation are 10μ
It was investigated by measuring the diameter of the water drop after 1 minute of loading. Water droplets having a diameter of 8 mm or more have good wettability, that is, hydrophilicity, as compared with conventional hydrophilic metal surfaces.

The antifungal property was investigated as follows. The mold suspension is sprinkled on an Al plate test piece having a hydrophilic film formed from various fungicide-added solutions on its surface, and the mixture is kept at 30 ° C. for 3 days.
Molds were cultured by standing still for 0 days. Then, observing the mold growth condition on the surface of the test piece, 0 indicates that no mold growth is observed, 1 indicates that mold growth is 10 or less in terms of area ratio to the surface of the test piece, 1 indicates mold growth area. 10-2
0% range is 2, mold growth area is 30-60
% In the range of 3%, mold growth rate is 60% area rate
From 4 to 5, the test piece was evaluated as 5 grades. The results of these tests are shown in Table 1. The solubility in Table 1 was evaluated as ◯ when completely dissolved when 0.1% by weight of various antifungal agents was added to the aqueous solution, and as x when a suspension was detected.

As is clear from Table 1, butyl parahydroxybenzoate forms a film having excellent antifungal properties without causing a substantial decrease in hydrophilicity as compared with other antifungal agents. It turns out to be effective. Also, paint A and paint B
As is clear from the comparison of the test results of 1., the antifungal ability is maintained even if the component system of the paint is slightly changed. On the other hand, 2 (4thiazoyl) benzimidazole and 2mercaptobenzothiazole, which are effective in antifungal properties in the component system of paint A, significantly reduce the hydrophilicity of the formed film, and in the component system of paint B, Mold is not also effectively exhibited. On the contrary, p-chloro-m-cresol is inferior in antifungal ability in the component system of coating material A. With other antifungal agents added, sufficient decrease in hydrophilicity was not observed, but sufficient antifungal properties were not obtained.

[Table 1]

Example 2: 0.5% by weight of polyacrylic acid,
Water glass 2.5% by weight, carboxymethyl cellulose 0.15% by weight, ammonium vanadate 0.1% by weight
Further, butyl parahydroxybenzoate was added to the solution prepared by dissolving 0.04% by weight of hydrofluoric acid in water in the amounts shown in Table 2. Adhesion amount of each solution on the Al surface in terms of dry coating 2
It was applied at a rate of 50 mg / m ² and dried by heating at 240 ° C. for 1 minute. The test piece on which the hydrophilic film was formed,
Salt spray test (SST) according to JIS Z2371
I went to That is, a 5% concentration saline solution kept at 35 ° C. was continuously sprayed on the surface of the test piece for 21 days.

The surface of the test piece after the salt spray test was observed to examine the adhesion state of the hydrophilic film. As a result, all the test pieces had a hydrophilic film with excellent adhesion which was substantially the same as that immediately after formation. Further, when the corrosion resistance was judged based on the observation result of the surface of the test piece, all the test pieces exhibited excellent corrosion resistance with the same initial gloss as before the salt spray. Corrosion resistance was also investigated by the wet test. In the wet test, the test piece on which the hydrophilic film was formed was placed in a constant temperature and humidity chamber at a temperature of 50 ° C. and a relative humidity of 98%, left for 21 days, and then the corrosion resistance was similarly determined from the surface state of the test piece. From these test results, it was confirmed that even if a solution containing butyl parahydroxybenzoate was used, a hydrophilic film having no difference in corrosion resistance and adhesion was formed.

Further, the fungicidal property was investigated by the test method according to JIS Z2911 and the same test method as in Example 1. In the former test method, the agar medium (nutrient) is placed in the center, and a mold suspension is sprayed on it for 30 days for 7 days.
After culturing at 0 ° C., the mold growth condition was adjusted to 5 as in Example 1.
Graded. The results obtained by the test method according to JIS Z2911 are shown as the antifungal property 1, and the results obtained by the same test method as in Example 1 are shown as the antifungal property 2 in Table 2. In addition, in Table 2, the initial hydrophilicity measured by the same test method as in Example 1 is also shown.

[Table 2]

As is clear from Table 2, 0.1 to 1.0
It can be seen that the hydrophilic film formed from the solution to which butyl parahydroxybenzoate is added in the amount of% by weight exhibits sufficiently excellent antifungal property although the initial hydrophilicity is not substantially decreased or slightly decreased. . In this regard, in Test No. 15 in which the amount of butyl parahydroxybenzoate added was small,
Although the initial hydrophilicity was not reduced as compared to Test No. 14 in which no additives were added, no noticeable improvement in antifungal property was performed.
On the other hand, in Test No. 19 in which a large amount of butyl parahydroxybenzoate was added, although excellent mold resistance was obtained,
The tendency of decrease in hydrophilicity becomes remarkable.

Example 3: 0.3% by weight of polyacrylic acid,
Colloidal silica 0.8% by weight, carboxymethyl cellulose 0.15% by weight, ammonium vanadate 0.1
To a solution of 1% by weight and 0.5% by weight potassium carbonate dissolved in water, butyl parahydroxybenzoate was added at various concentrations, and corrosion resistance and film adhesion were examined in the same manner as in Example 2. Also in this case, it was confirmed that the addition of butyl parahydroxybenzoate did not deteriorate the corrosion resistance and the film adhesion. In addition, Table 3 shows the results of similarly examining the antifungal property and the initial hydrophilicity. As is clear from Table 3,
A hydrophilic film formed from a solution to which 0.1 to 1.0% by weight of butyl parahydroxybenzoate is added has a sufficiently excellent anti-protection property, although the initial hydrophilic property is not or substantially decreased. It turns out that it exhibits moldiness.

[Table 3]

[0028]

As described above, in the present invention, the addition of butyl parahydroxybenzoate as an antifungal agent prevents the deterioration of hydrophilicity, corrosion resistance, film adhesion, etc. Al with a hydrophilic film with excellent moldability
It can be formed on a metal surface such as. Since the hydrophilic metal surface treatment agent used does not contain harmful metals such as hexavalent chromium, it does not adversely affect the environment. Also,
When using a metal material to which hydrophilicity is given, for example, as fins of a heat exchanger, condensed moisture accumulates spherically on the fin surface to increase ventilation resistance and an unpleasant odor caused by mold formation. It is possible to maintain the heat exchange capacity in the initial high state without generation of heat. Further, the metal material treated with the hydrophilic metal surface treatment agent is used as a structure around water, for example, other than the fin, by utilizing its excellent surface properties, hydrophilicity, durability and the like.

Continuation of the front page (72) Inventor Yutaka Mochizuki 1-34-1 Kambara, Kambara-cho, Anbara-gun, Shizuoka Prefecture

Claims (10)

[Claims] 1. A hydrophilic metal surface treating agent for antifungal which comprises a water-soluble resin as a film forming component, a silica source as a hydrophilicity imparting component, and butyl parahydroxybenzoate as a mildewproofing component. 2. The hydrophilic antifungal agent according to claim 1, wherein one or more polyacrylic acid selected from water-soluble acrylic acid, water-dispersible acrylic acid and esters thereof is used as the water-soluble resin. Metal surface treatment agent. 3. A hydrophilic metal surface treatment for mold prevention according to claim 1, wherein one or more selected from ultrafine particulate anhydrous silica, colloidal silica and alkali metal silicate is used as a silica source. Agent. 4. The hydrophilic metal surface treating agent for mold prevention according to claim 1, wherein the content of butyl parahydroxybenzoate is 0.1 to 1% by weight. 5. The hydrophilic metal surface treating agent for mold prevention according to claim 1, which comprises one or more of a vanadium compound, an alkali carbonate, a surfactant and hydrofluoric acid as an auxiliary component. 6. The hydrophilic metal surface treating agent for mold prevention according to claim 1, wherein a thickening agent such as sodium salt, potassium salt, ammonium salt of carboxymethyl cellulose, hydroxyethyl cellulose or the like is added. 7. The surface of an aluminum material is degreased and dried, and then the hydrophilic metal surface treating agent for mold prevention according to claim 1 is applied and air-dried or heat-dried. Surface treatment method for aluminum material. 8. A surface treatment method for an aluminum material, which comprises subjecting the aluminum material to a surface treatment by the method according to claim 7, and further applying a water-soluble carbonate and drying the surface. 9. A surface treatment method for an aluminum material, which comprises subjecting the aluminum material to a surface treatment by the method according to claim 7, and further applying a surfactant and drying the surface. 10. An aluminum product in which a coating film formed from the hydrophilic metal surface treating agent for mold prevention by the method according to any one of claims 7 to 9 is formed with an adhesion amount of 250 mg / m ² or more.