JPH0225580A - Surface-treated aluminum sheet for heat exchanger and production thereof - Google Patents

Abstract

PURPOSE:To produce a surface-treated Al sheet for a heat exchanger having superior hydrophilic property, corrosion resistance and antimold property by coating an Al sheet with an aq. soln. contg. a specified alkali silicate and an antimold agent and by successively carrying out baking, neutralization, washing and dealkalization. CONSTITUTION:An aq. soln. contg. an alkali silicate having >=1 ratio of SiO2 to M2O (M is an alkali metal such as Li, Na or K) and an antimold agent is used as a treating bath. The surface of an Al or Al alloy sheet is coated with the treating bath so as to regulate the amt. of SiO2 to 100-1,000mg/m<2> and the coated surface is baked at >=150 deg.C, neutralized with an aq. acid soln., washed and dealkalized. The resulting surface-treated Al sheet having a formed coating film has superior hydrophilic property, corrosion resistance and antimold property and a heat exchanger made of the Al sheet maintains the antimold property and generates no offensive odor even when used in a dusty atmosphere at high temp. and humidity.

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention is based on I! It relates to a surface-treated aluminum plate for heat exchangers that is water-based, has excellent corrosion resistance, and mold growth prevention properties, and more specifically, an aluminum plate that is suitable for aluminum fin materials for heat exchangers used in high temperatures, high temperatures, or dusty atmospheres. and its manufacturing method. Note that in the present invention, the aluminum plate is a general term for industrial pure aluminum plates and aluminum alloy plates. (Prior art and issues to be solved)Currently, aluminum fin materials for heat exchangers include 1050.11
Pure aluminum fin materials such as 00 are used, but in recent years, moisture in the atmosphere has condensed in this type of aluminum fin material. The formation of so-called bridges that accumulate between the fins can reduce heat exchange performance, generate noise when blowing air, and cause water to fly.To prevent this, we have created water leakage properties on the fin surfaces, and In order to prevent the formation of white rust, surface treatment is widely performed to impart corrosion resistance. As a surface-treated aluminum fin material, it is common to provide a corrosion-resistant film such as a chromate treatment film or a resin coating film.
As shown in Japanese Patent No. 62-129695, there have been attempts to provide a corrosion-resistant film and a hydrophilic film. However, even with such surface-treated fin materials,
Similar to conventionally used untreated fin materials, high temperatures,
In the case of heat exchangers that are exposed to high humidity and are used in particularly dusty atmospheres, mold may grow on the fin surface, which may cause an unpleasant odor during use. In order to prevent the growth of mold, attempts have been made to add an anti-mold agent to resin-based corrosion-resistant coatings or hydrophilic coatings; However, there is a problem that the antifungal agent is easily washed away when the product falls, and the effect only lasts for a short time.Also, in the case of a corrosion-resistant film, there are problems such as a decrease in corrosion resistance due to the addition of the antifungal agent. It was very difficult to fully satisfy the requirements of hydrophilicity, corrosion resistance, and mold resistance. The present invention has been made in view of the above circumstances, and
Made of heat exchanger A heat exchanger that does not cause mold to grow on the fin surface even when used at high temperatures, in high temperatures, or in an atmosphere with a lot of dirt or dust, and this mold-resistant property remains and does not generate unpleasant odors. The object of the present invention is to provide a dexterous aluminum plate and a method for manufacturing the same. (Means for Solving the Problems) In order to achieve the above object, the present inventors have devised a measure that can impart not only corrosion resistance and hydrophilicity but also mold resistance and its sustainability to this type of surface-treated fin material. I have conducted extensive research on the subject. As a result, the S x O-Z M z O ratio (where M is L
i, Na. After painting and baking with an aqueous solution containing at least one alkali silicate (alkali metal such as K) and a fungicide as a treatment bath,
Neutralization with acid provides not only hydrophilicity and corrosion resistance, but also
It was discovered that a film with excellent anti-mold properties (hereinafter referred to as "anti-mold properties") and durability can be obtained, and the present invention has been made based on this discovery. That is, the method for manufacturing a surface-treated aluminum plate for a heat exchanger according to the present invention is an alkali silicate with a 310 z / M z O ratio (where M is an alkali metal such as Li, Na, etc.) of 1 or more. An aqueous solution containing a fungicide and an antifungal agent is used as a treatment bath, and the surface of the aluminum and aluminum alloy plate is heavily loaded with S10□ in the range of 100 to 1000 mg/+++, and then baked at a temperature of 150°C or higher. A heat exchanger with excellent hydrophilicity, corrosion resistance, and anti-mold property, characterized in that it is then neutralized and washed with an acid aqueous solution to perform a dealkalization treatment, and if necessary, a hydrophilic film is further provided as a second layer. The gist of the present invention is a method for producing a surface-treated aluminum plate for use in heat exchangers according to the present invention, in which a surface-treated aluminum plate obtained by the above method is provided on the surface, and if necessary, The present invention is characterized in that a hydrophilic film is provided as the 21st J.Hereinafter, the present invention will be explained in more detail.As mentioned above, the surface treatment film according to the present invention has the following features:
After applying a mixed aqueous solution of an alkali silicate with a specific composition and a fungicide as a treatment bath by a roll coating method, dip coating method, brush coating method, etc., it is baked at a temperature of 150°C or higher,
Next, it is obtained by neutralizing and washing with an aqueous acid solution such as nitric acid, phosphoric acid, or acetic acid, and then performing a dealkalization treatment. As the alkali silicate, SiO2/M20 (however,
M must have an alkali metal (Lj, Na, etc.) ratio of 1 or more, and a ratio of 3 or more is particularly preferred because it has a high SiO□ content and is advantageous for film formation. As the fungicide, commercially available fungicide 1, for example, those containing tetrachloroisophthalnitrile, N-(fluorodichloromethylthio)-phthalimide, thiabendazole, etc. as main components can be used. However, since the fungicide is used at the same time as the alkali silicate, it is desirable to use one with excellent alkali resistance or to add it before painting. The amount of antifungal agent added is 1 to 30% based on the weight of the dry film.
It is preferable to add it so that This is because if it is less than 1%, sufficient mildewproofing properties and mildewproofing durability cannot be obtained, and if it exceeds 30%, the corrosion resistance of the film decreases. The amount of captured film is in the range of 100 to 1000 mg/floor 2 in terms of Sin. This is because sufficient corrosion resistance cannot be obtained with less than 100 mg/*", and
This is because if it exceeds "g/m", processing defects are likely to occur during molding. For baking after painting, the baking temperature should be 150° C. or higher. It is necessary to bake for an appropriate time (5 seconds to 1 minute). In addition, 1
If the baking time is longer than 1 minute, the neutralization and cleaning by the acid in the first process will not be carried out effectively, and the alkali salt will remain in the film.
Sufficient corrosion resistance cannot be obtained. Further, although it is not as noticeable as the baking time, a similar tendency occurs in high-temperature baking, so it is preferable to avoid baking at temperatures of 300° C. or higher. Next, dealkalization treatment is performed with an acid aqueous solution to remove the alkali component in the alkali silicate and stabilize the film. The type of acid, the concentration and temperature of the acid aqueous solution are not particularly limited, but
It is preferable to use nitric acid or phosphoric acid as a 10 to 30% aqueous solution, which has little effect on corrosion resistance even if it remains in the film, because it is easy to handle. Immediately after dealkalization with an acid, the surface treatment film structure of the present invention is completed by washing with water and drying. The surface treated film obtained has not only corrosion resistance and hydrophilicity, but also excellent mold resistance and durability. Further, in the present invention, if necessary, the above-mentioned surface treatment film can be used as the first layer, and a hydrophilic film can be provided thereon as the second layer. The structure of the hydrophilic film is not particularly limited; for example, it may be a water glass-based hydrophilic film, or a resin-based hydrophilic film such as acrylic resin or polyvinyl alcohol resin. Thereby, hydrophilicity can be further improved. Next, examples of the present invention will be shown. (Example) Aluminum plate (JIS 1100H26, plate thickness 0.
12no*) was degreased and washed with water according to a conventional method, and then an aqueous solution of alkali silicate (1
00g/Q) to which an antifungal agent was added in an amount of 10% based on the weight of the dry film, was applied as a treatment bath using a roll coater, baked under the conditions shown in the same table, and dealkalized. , wash with water. Dry. In addition, in dealkalization treatment, the liquid temperature is kept at room temperature (approximately 2
(0°C), and the immersion time was 20 seconds. Further, for some samples, the coating shown in the same table was provided as the second M. The obtained samples were examined for corrosion resistance, hydrophilicity, and mold resistance. The results are also listed in the same table. In addition, the corrosion resistance was evaluated by performing a salt spray test based on JIS Z 2371 for 500 hours and checking the occurrence of corrosion after the test. Mildew resistance was measured at the initial stage and after 24 hours of running water (flow rate: 5 Q/min) using the attached method with additions to JIS Z 2911. Specifically, each test piece was injected with three types of mold spores (A spsrgillus niger).
I F 04414), Penicillium
citrinu+m (IFO7784), Clad
osporium cladosporioides (
Spray a mixed spore suspension containing IFO6348) and
Check the reproductive rate with the naked eye after culturing at ℃ for 7 days! I guess, ○(
Evaluation was performed on a five-level scale from excellent to poor. This leveling is 0 if no mold growth is observed on the sample surface with the naked eye, O if slight mold growth is observed, Δ if mold growth is observed to the extent of 1/3, and Δ if mold growth is observed to be around 2/3. A. Items where mold growth is observed on the entire surface ×
As the fungicidal agent, commercially available thiabendazole type agents, which are relatively stable even at high pH, were selected and used. Hydrophilicity was evaluated by observing the water wet state after immersion in water.

[Left below]

In Table 1, rods 1 to Nn7 are examples of the present invention. N118 to Na12 are comparative examples. In contrast to the examples of the present invention, which provide good corrosion resistance, hydrophilicity, anti-mold properties, and their sustainability, the anti-mold agent is added to the conventional resin-based film (corrosion-resistant film or hydrophilic film). Methods (Comparative Examples 8 to 9), namely 1 In the present invention, when the amount of film is small (Comparative Example Halo), when baking at low temperature (Comparative Example Mail), and when dealkalization is not performed (Comparative Example It can be seen that in case 12), either the corrosion resistance, the mold resistance, or the durability of the mold resistance is insufficient. Here, the reason why the surface treatment film according to the present invention provides better anti-mold durability than when a mold preventive agent is added to a resin-based film as in the conventional method is because of the amorphous 8102 film. Antifungal agent is moderately dispersed inside. This is because the anti-mold agent is fixed and does not easily flow out, and the effect of the anti-mold agent is gradually exerted. Due to this effect, as shown in Examples 6 to NQ7 of the present invention, even when the surface treatment film according to the present invention is used as a base treatment film (first layer) and a hydrophilic film is further provided, it has excellent mold and mildew resistance. Mold persistence is obtained. (Effects of the Invention) As explained above, according to the present invention, a surface-treated aluminum plate for a heat exchanger not only has corrosion resistance and hydrophilicity, but also has excellent mold resistance and durability. Therefore, when used as a fin material for a heat exchanger used at high temperatures or in an atmosphere with a lot of dust, mold will not occur even if dust in the atmosphere adheres to it. Therefore, generation of unpleasant odors can be suppressed. Patent applicant Hisashi Nakamura, patent attorney representing Kobe Steel, Ltd.

Claims (4)

[Claims] (1) SiO_2/M_2O ratio (where M is Li, N
Using an aqueous solution containing at least one alkali silicate and a fungicide (alkali metals such as
Hydrophilic, corrosion resistant and A method for manufacturing surface-treated aluminum plates for heat exchangers that have excellent mold growth prevention properties. (2) A surface-treated aluminum plate for a heat exchanger having excellent hydrophilicity, corrosion resistance, and mold growth prevention property, characterized in that the surface treatment film according to claim 1 is provided on the surface of the aluminum or aluminum alloy plate. (3) In an aluminum plate for a heat exchanger in which a corrosion-resistant film is provided as a first layer and a hydrophilic film is provided as a second layer on the surface of an aluminum or aluminum alloy plate, the surface treatment film according to claim 1 is provided as the first layer. A method for manufacturing an aluminum plate for a heat exchanger, characterized by: (4) Hydrophilicity, corrosion resistance and mold growth prevention properties characterized by providing the surface treatment film according to claim 1 as the first layer on the surface of the aluminum and aluminum alloy plate and providing the hydrophilic film as the second layer. Superior surface-treated aluminum plate for heat exchangers.