JPH01299877A - Surface treating agent for heat exchanger aluminum fin and its treatment - Google Patents

Abstract

PURPOSE:To obtain the title surface-treating agent which can give a film which is excellent in initial hydrophilicity and retentivity of hydrophilicity after immersion in flowing water and can control or prevent the formation of water drops, by using fully saponified PVA, a water-soluble polyamide resin, a urea resin and water as essential components. CONSTITUTION:Fully saponified PVA is mixed with a water-soluble polyamide resin formed by making, for example, nylon-6 soluble in water and/or alcohol and a urea resin which is preferably an alkyl-etherified urea resin in which at least part of the methylol groups are alkyl-etherified in a ratio among solid matters of, desirably, 1:0.5-2:0.01-0.5, and water in an amount to give a solid concentration of, preferably, 2-10wt.% is added to the mixture to dissolve or disperse and dilute said three components.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to surface treatment of aluminum heat exchanger fin materials, and more specifically, the present invention relates to surface treatment of aluminum heat exchanger fin materials. This invention relates to a certain surface treatment agent and treatment method.

[Prior Art] Heat exchangers for air conditioners are made of aluminum as a measure to prevent problems caused by condensation of condensed water during cooling, such as loss of power due to increased ventilation resistance, generation of noise, and scattering of water droplets. The surface of the fin material has been treated to make it hydrophilic. As a method for performing such processing, fins are created by molding aluminum material, and after this is assembled,
There is a method of dip coating a surface treatment agent. This method has been put into practical use, for example, as a method for forming an inorganic film, chromate film - alkali silicate treatment (Japanese Patent Application Laid-open No. 13078/1982), and as a method for forming an organic film, chromate film - polyamide treatment. Examples include resin film formation (Japanese Unexamined Patent Publication No. 61-250495). The former silicate-based treatment has good wood-philicity and maintains a contact angle with water of 20 degrees or less, but it has a unique odor, and furthermore, it causes the scattering of fine powder due to the decomposition of the film, and it is also susceptible to bacteria. There are problems in that molds are likely to grow, and molds are likely to generate unpleasant odors. On the other hand, the latter method, which involves forming a polyamide resin film, has fewer odor problems, but does not have sufficient water resistance.
Another problem is that the cost is high.

[Problem to be solved by the invention] Air conditioners have become smaller and lighter in recent years, and heat exchangers have also become compact in design, so the spacing between fins has become smaller, and higher hydrophilicity is required, with a contact angle of 30° with water. The following has become essential.

Furthermore, since the purpose is to provide a comfortable living space, the generation of odor has recently become a problem. As mentioned above, the immersion-type treatment agents currently in practical use cannot sufficiently meet such demands. Therefore, the present invention aims to develop an organic resin system that is advantageous in terms of odor and has better hydrophilicity. The purpose is to develop surface treatment agents and surface treatment methods by dipping.

[Means for Solving the Problems] According to the present invention, a film with excellent hydrophilic properties can be formed by dipping and baking a heat exchanger with a surface treatment agent containing polyvinyl alcohol, water-soluble polyamide, and urea resin. can be formed on aluminum surfaces.

That is, the present invention provides a surface treatment agent for heat exchanger aluminum fins containing completely saponified polyvinyl alcohol, water-soluble polyamide resin, urea resin, and water, and the above surface treatment agent at a solid content of 2 to 10% by weight. The present invention provides a method for surface treatment of aluminum fins of a heat exchanger, which is characterized in that the aluminum fins are dip-coated in a bath with a concentration of 50%.

Polyvinyl alcohol (hereinafter abbreviated as rPVAJ), which is one of the components of the surface treatment agent in the present invention, plays a major role as a film-forming component and has a large amount of secondary hydroxyl groups in its molecules, so it is difficult to interact with water. Compatible with this purpose is generally one with a degree of saponification of 98% or more, which has a high affinity and also maintains water resistance and parent tree sustainability through the interaction of this hydroxyl group with other constituent components. It is saponified type PVA. This material has low solubility in water at room temperature, and exhibits desirable properties as a film formed on aluminum heat exchangers used below room temperature.
Further, it is preferable that the degree of polymerization of PVA is 500 or more, from the viewpoint of maintaining hydrophilicity due to molecular entanglement with the polyamide resin described below and water resistance.

The water-soluble polyamide resin, which is another component of the treatment agent of the present invention, plays an important role in imparting hydrophilicity in the present invention.The above-mentioned PVA, when used alone, undergoes partial crystallization when heated and exhibits hydrophobicity. However, by adding an appropriate second component, crystallization due to heating can be suppressed and hydrophilicity can be maintained. The present inventors have found that water-soluble polyamide resin is optimal as a component that plays such a role. Furthermore, the mixing ratio of PVA and polyamide resin is 1:0.
．． It has been found that in the range of 5 to 2, high hydrophilicity can be imparted and water resistance can also be maintained. The water-soluble polyamide resin used for this purpose is nylon-6 soluble in water and/or alcohol, and commercially available resins such as AQ nylon A-90, A-70, P-70, etc. (
(manufactured by Toshi ■) can be suitably used. Although a water-soluble polyamide resin alone forms a film with excellent hydrophilic properties, it is redissolved in water. In order to stably dissolve the polyamide resin, it is preferable to add an appropriate amount of a neutralizing agent (such as phosphoric acid) or an alcoholic solvent.

Although it is possible to form a hydrophilic film with fairly good water resistance using just the PVA and polyamide resin mentioned above, in order to further improve the water resistance and the persistence of parent wood, in the present invention, a urea resin is used as a crosslinking agent. Commonly used water-soluble melamine resins, phenolic resins, epoxy resins, etc. significantly impair hydrophilicity due to the influence of non-polar components in their skeletons, whereas urea resins have highly polar skeletons that impede hydrophilicity. is small. Urea resin is generally an addition condensation product of urea and formalin, but when the addition condensation reaction is not carried out sufficiently and a large amount of low molecular weight methylol urea is present, or when the amount of formalin during the reaction is small and there is a large amount of insoluble methylene urea. If this is the case, the water solubility or water dispersibility will be poor and precipitation will occur, which is not preferable. The urea resin used in the present invention needs to be water-soluble or water-dispersible, and in particular, lower alcohol (
For example, those in which some or all of the methylol groups are converted into alkyl ethers by adding methanol, ethanol, etc. have excellent water solubility and good dilution stability, and are preferred at low solid content concentrations, generally 10% by weight or less. In the dipping treatment used, it is particularly preferable to use the alkyl etherified urea resin as the urea resin from the viewpoint of dilution stability.

The blending ratio of urea resin is solid content weight ratio: PVA:urea resin: 1:0. Of~0.5. Furthermore, it is preferable that 1 is in the range of 0.1 to 0.3.

Water is used to dissolve, disperse, and dilute the PVA, water-soluble polyamide resin, and urea resin.

In addition to the above-mentioned essential ingredients, the surface treatment agent for heat exchanger aluminum fins according to the present invention includes pigments, surfactants, antifoaming agents, alcoholic solvents, pH adjusters (acids, alkalis, etc.). It can contain any general purpose ingredients.

Although the surface treatment agent according to the present invention shows particularly excellent suitability for dip coating, it can also be applied to roll coating and spray coating by appropriately adjusting the concentration of the treatment agent.

When applying dip coating, the solid content concentration of the treatment agent is usually 2 to 2.
A bath is adjusted to a range of 10% by weight, and aluminum fins are dip coated in this bath. The aluminum fins to be dip coated are usually pre-formed and assembled heat exchanger aluminum fins, which are immersed in water, pulled up, and baked under appropriate baking conditions, for example, at 150 to 200°C for 10 to 30 minutes. By applying a coating amount of 0.2 to 5μ layer, preferably 0.2μ layer.
A hydrophilic film of 5 to 3 μI can be obtained.

The surface treatment agent according to the present invention forms a practical hydrophilic film by applying it to untreated aluminum fin materials that have been degreased and cleaned. It is preferable from the viewpoint of corrosion resistance etc. to use a chemical conversion treated aluminum fin material which has been subjected to chemical conversion treatment, and to apply the surface treatment agent of the present invention to this material to form a hydrophilic film.

EXAMPLES The present invention will be specifically explained below using examples and comparative examples. Hereinafter, "1%" means "wt%".

Examples 1 to 7 and Comparative Examples 1 to 4 An aluminum base material with a thickness of 0. 1 dragon, width 7
Using a thin piece of AA3003 with a length of 0+u+ and a length of 150 mm, it was washed with hot water at 40°C, and then immersed in a 2% caustic soda aqueous solution at 40°C for 2 minutes to degrease and wash.
I washed it with water.

As shown in Table 1, this material was used as is without any chemical conversion treatment, and was treated with phosphoric acid chromate (Alchromate 3701J, manufactured by Nippon Parker Co., Ltd.) so that the amount of Cr deposited was approximately 100 mg/rr? Use it so that it becomes, or ■
The chromic acid chromate method was used.

Next, the above-mentioned untreated or chemically treated board was dip-coated in a surface treatment agent having the composition shown in Table 1, and then baked in a hot air drying oven at 150°C for 30 minutes to achieve a coating weight of 1.
A hydrophilic film of g/rn' was formed.

Table 1 shows the test results of the surface treated plate obtained.

Notes in the formulation shown in Table 1 are as follows.

*1. Manufactured by ZKikagaku Kogyo ■, fully saponified (>98%)
Poval (100% solids) *2. Manufactured by Denki Kagaku Kogyo ■, partially saponified (88-9%)
Poval (100% solids) Made by Hon 3.4 Toshi ■, water-soluble polyamide resin (100% solids) *5. Manufactured by Dainippon Ink & Chemicals ■, water-soluble methyl etherified urea resin (70% solids) *6. Water-soluble methyl etherified urea resin (65% solids) manufactured by Mitsui Toatsu Chemical ■ The test methods and evaluation methods in Table 1 are as follows.

[Test and evaluation method] Water wettability: Water wettability was evaluated by the water wet area ratio when a test plate was immersed in tap water for 30 seconds and pulled out.

0: Water wet area ratio 100% O: l/ less than 90-100% Δ: 〃
50 to less than 90%
The contact angle of the water droplet was measured at 0° C. using a contact angle meter DCAA model manufactured by Kyowa Kagaku ■. The water wettability and contact angle were determined by immersing the initial test plate in running tap water for 500 hours, pulling it up, and then placing it in an environment of 20°C, 75% R, H for 24 hours.
The tests were also carried out on test plates immersed in running water that had been left for an extended period of time.

Water solubility = Calculated from the weight difference before and after immersion in tap water at about 15° C. for 24 hours.

Water dissolved weight (%) = ((Initial film weight - Film weight after 24 hours immersion) /Initial film weight) Less than X: // 20% or more Corrosion resistance: JIS Z 2371 salt spray test 300
Evaluation was made based on the area ratio of white rust on the flat surface after a period of time.

0: White rust occurrence area rate 0 to less than 1% Q:
/l l -w l Less than 0% Stability of treatment solution: Place the surface treatment agent in a glass container, cover with a lid, and let it cool to room temperature.
After standing for 0 days, changes such as aggregation and the presence or absence of sediment were evaluated.

0: No change ○: Slight turbidity observed [Effects of the invention] As explained above, when the surface treatment agent according to the present invention is applied to heat exchanger aluminum fins, initial hydrophilicity and hydrophilicity after immersion in running water A film can be obtained that has both good durability on wood and good water and solubility resistance.

Moreover, by combining the chemical conversion treatment, a hydrophilic treated plate with excellent corrosion resistance can be obtained. Furthermore, since the surface treatment agent according to the present invention does not contain silicate, there is no unpleasant odor or other unpleasant sensations, and it also has excellent dilution stability, making it excellently applicable as a treatment agent for dip coating used at low concentrations. It indicates gender.

Claims (1)

[Claims] 1) A surface treatment agent for heat exchanger aluminum fins containing completely saponified polyvinyl alcohol, water-soluble polyamide resin, urea resin, and water. 2) The surface treatment agent according to claim 1, wherein the solid content weight ratio of polyvinyl alcohol: polyamide resin: urea resin is 1:0.5 to 2:0.01 to 0.5. 3) A heat exchange method characterized by dip-coating aluminum fins in a surface treatment agent bath containing completely saponified polyvinyl alcohol, water-soluble polyamide resin, urea resin, and water with a solid content concentration of 2 to 10% by weight. Surface treatment method for aluminum fins. 4) The surface treatment method according to claim 3, wherein the aluminum fin to be dip coated is previously treated with chromate phosphate or chromate chromate.