JPH0574625B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a composition for coating the surface of a fin material of a heat exchanger. [Prior Art] and [Problems to be Solved by the Invention] Conventionally, aluminum has been widely used as a fin material in heat exchangers, particularly heat exchangers with fins. In such a heat exchanger with fins, it is necessary to increase the heat transfer area of the fins in order to improve the efficiency, but at the same time, due to space constraints, it is necessary to reduce the fin pitch at the same time. This is due to an increase in ventilation resistance, especially an increase in wind pressure loss due to condensed water on the fins, and a decrease in ventilation volume.
Problems such as noise generation and front splashing of condensed water occur. Therefore, in order to improve the efficiency and save space of heat exchangers with fins, the method of reducing wind pressure loss due to condensed water in the fins is an important deciding factor. Wind pressure loss due to condensed water on the fins is caused by the fact that when the heat exchanger is used as an evaporator, the surface temperature of the fins becomes below the dew point of the air, moisture in the air condenses, and this condensed water adheres to the surface of the fins, resulting in damage between the fins. This occurs when the air passage is narrowed due to the bridging phenomenon of condensed water. Therefore, in order to reduce the pressure loss, it is sufficient to constantly remove the condensed water on the fin surface.
There are two possible ways to do this: Specifically, there are two methods: one is to make the fin surface completely water-repellent so that the condensed water droplets roll off, and the other is to make the fin surface hydrophilic (impart water wettability) so that the water droplets flow down as a thin water film. In reality, normally obtained water repellent fins are often found to be insufficient in removing condensed water when tested in actual equipment. On the other hand, hydrophilic treatment involves causing condensed water to flow down the fin surface as a thin water film through expansion wetting, and various methods such as chromate treatment, boehmite treatment, and water-soluble polymer coating methods have actually been proposed. There is. In such hydrophilized fins, there is a strong risk that the aluminum or aluminum alloy of the base material will be corroded by moisture due to the hydrophilic treatment, so corrosion resistance is particularly strongly required. This is because when aluminum materials are corroded by moisture, white powder (so-called white rust), which is a type of aluminum hydroxide, is generated, and in dry conditions, it escapes into the room and poses a sanitary problem. Therefore, it is important for the aluminum fin material for heat exchangers to have high hydrophilicity on its surface to form a thin film for condensed water, to minimize wind pressure loss due to condensed water, and to have strong corrosion resistance. be. Conventionally, various aluminum materials with hydrophilic and corrosion-resistant film layers have been proposed for use as fin materials, but these require long periods of time at high temperatures to form the film; for example, salt spray tests have been conducted to test corrosion resistance. In terms of processability, for example, it cannot withstand processing of more than 1 million products, resulting in cracks in the product. Alternatively, there are still many problems such as complicated processing steps such as neutralization and water washing steps after film formation. In view of these problems, the inventors of the present invention aimed to economically provide an aluminum material for heat exchangers that has good water wettability, excellent corrosion resistance, workability, and solvent resistance. Table 2-b group, 3-b
A fin material coating comprising an inorganic compound which is a compound of an element of Group 6 or Group 6-b and is soluble in water under an alkali together with a silicon compound, and a thermosetting water-soluble polymer compound. As a result of further intensive research, we have arrived at the invention of a composition for coating fin materials, which has particularly excellent processability among the above properties. [Means for solving the problem] and [effect] That is, the present invention provides an aqueous solution comprising polyvinyl alcohol, zirconium nitrate, a water-soluble melamine resin, and a curing catalyst thereof, and a water-soluble inorganic powder dispersed in the aqueous solution. A composition for coating a fin material, characterized in that: As the polyvinyl alcohol of the present invention, any commercially available completely saponified type, intermediate saponified type, or partially saponified type can be used, but it is preferable to use the completely saponified type for the purpose of manufacturing with good reproducibility of performance as a fin material. . The water-soluble melamine resin of the present invention may be either a commercially available monomer resin or a dimer type resin with a certain degree of condensation polymerization. Curing catalysts for melamine resin include ammonium salt catalysts such as ammonium chloride, diammonium phosphate, and ammonium sulfamate, hydrochloric acid or sulfamate salts of organic amino alcohols, dimethylaniline hydrochloride, pyridine-hydrochloric acid, and pyricone.
Examples include organic amine salt catalysts such as monochloroacetic acid, and inorganic metal catalysts such as magnesium chloride, zinc chloride, and zinc sulfate. Among them, it is preferable to use an organic amine salt catalyst. The water-insoluble inorganic powder in the present invention includes:
Any powder that is insoluble or has extremely low solubility in water and has hydrophilic properties may be used, such as zinc hydroxide, aluminum hydroxide, calcium hydroxide, iron hydroxide, copper hydroxide, magnesium hydroxide, colloidal silica, etc. I can list them. Among these inorganic powders, colloidal silica is particularly suitable. In preparing the composition of the present invention, for example, polyvinyl alcohol and zirconium nitrate are dissolved in water to prepare a solution A. Separately from liquid A, a water-soluble melamine resin and its curing catalyst are dissolved in water to obtain liquid B. Next, liquid A and liquid B are mixed, water-insoluble inorganic powder, metal chelating agents, pigments, dyes, thickeners, etc. are added as needed, and vigorous stirring is performed to defoam. do it. The quantitative proportions of each component in the composition of the present invention are:
Although not particularly specified, the amount of zirconium nitrate is 2 to 10 parts by weight, preferably 4 to 7 parts by weight, based on 100 parts by weight of polyvinyl alcohol. If the amount of this component is too small, the insolubilization of polyvinyl alcohol will be incomplete, and if it is too large, the hydrophilicity of the film will be insufficient and the removal of condensed water will be insufficient. The amount of water-soluble melamine resin is 50 to 200 parts by weight, preferably 80 to 180 parts by weight, based on 100 parts by weight of polyvinyl alcohol. If the amount of this component is too small, the adhesive force with the fin material tends to decrease, and if it is too large, the hydrophilicity of the coating will be insufficient, resulting in insufficient removal of condensed water as described above. The amount of the inorganic powder is 50 to 200 parts by weight, preferably 70 to 150 parts by weight, based on 100 parts by weight of polyvinyl alcohol. If the amount of this component is too small, the film tends to lose its hydrophilicity as it repeats wetting and drying, and if it is too large, it loses transparency and impairs its value as a product. The particle size of this component is normally one that passes through a 320 mesh sieve, but better results can be obtained by using a finer powder than that. A metal chelating agent such as 5-sulfosalicic acid, ethylenediaminetetraacetic acid, trans-cyclohexane-1,2diaminetetraacetic acid, etc. may be added to the composition of the present invention for the purpose of enhancing the adhesive strength with the fin material. In order to form a hydrophilic film on the surface of a fin material made of aluminum or an aluminum alloy thin plate using the composition of the present invention, the water solubility of the composition of the present invention prepared as described above is determined on the surface of the fin material. A coating film of the composition of the present invention is formed on the surface of the fin material by coating the fin material or by immersing the fin material in the aqueous solution, and if necessary, remove excess by ironing with a roller, air blowing, etc. The aqueous solution is removed, and the coating film is finally cured by heat treatment. This heat treatment is carried out at 200°C to 250°C, for example.
It can be dried for 30 to 60 seconds in a hot air dryer set at ℃. The fin material does not need to be pretreated prior to application of the composition of the present invention, unless the surface thereof is contaminated with oily substances. [Example] Next, the present invention will be described in more detail based on Examples. Experimental examples 1 to 14 JIS A-1100 with a thickness of 0.15m/m after degreasing
Aluminum thin plate, dimensions 200m/m x 300m/m
It was cut into On the other hand, add 5 g of melamine resin (manufactured by Nippon Carbide Kogyo Co., Ltd.; product Ni-Resin) to 30 ml of water.
5% of polyvinyl alcohol (Shin-Etsu Chemical Co., Ltd. product type C-17) and 0.05% to 0.5% of zirconium nitrate were dissolved in 5% of polyvinyl alcohol (Shin-Etsu Chemical Co., Ltd. product type C-17) and 1g of guanidine sulfamate was added as a catalyst.
melamine resin in a range of 50 to 200 parts by weight per 100 parts by weight of polyvinyl alcohol, and colloidal silica (Japan Aerosil Industries Co., Ltd. product type).
COK84) was added to 100 parts by weight of polyvinyl alcohol in an amount ranging from 20 to 200 parts by weight to prepare an aqueous solution with a total component concentration of 10% having the component composition shown in Table 1-1. Next, the aluminum thin plate mentioned above was immersed in this aqueous solution, then taken out, excess aqueous solution was removed, and then dried in a hot air dryer at 250°C for 30 minutes.
A treated product was obtained by drying for a second. Regarding the treated products obtained as described above, contact angle measurement was performed as an indicator of wettability, salt spray test was performed as an indicator of corrosion resistance, trichlene immersion test was performed as an indicator of solvent resistance, and oil test was performed as an indicator of workability. Processing tests were conducted on each, and cold and heat resistance tests were also conducted to measure quality characteristics.
The results of these tests are shown in Table 1-2.

【table】

【table】

[Table] Experimental Examples 13 to 17 The compositions shown in Table 2-1 below were prepared and coated on the surface of an aluminum plate in the same manner as Experimental Examples 1 to 12 to create an aluminum fin material, and its performance was measured. As shown in Table 2-2, all of the fin materials exhibited good properties.

【table】

[Table] The meanings of *1 to *6 are the same as in Table 1-2 [Effects of the invention] As described above, the present invention has excellent properties such as water wettability, corrosion resistance, processability, and solvent resistance. , provides a novel composition for coating fin materials, which has high industrial applicability.

Claims (1)

[Claims] 1. A composition for coating fin materials, comprising an aqueous solution comprising polyvinyl alcohol, zirconium nitrate, a water-soluble melamine resin, and a curing catalyst thereof, and a water-insoluble inorganic powder dispersed in the aqueous solution.