JPH06904B2 - Surface treatment agent for heat exchanger fins - Google Patents

Description

TECHNICAL FIELD The present invention relates to a surface treatment agent for heat exchanger fins, and more particularly to an aqueous surface treatment agent for forming a corrosion resistant and persistent hydrophilic coating on aluminum fins of a heat exchanger. .

2. Description of the Related Art Aluminum and its alloys are widely used in the heat exchanger field due to their light weight and excellent workability and thermal conductivity. With the spread of air conditioning systems, the number of air conditioners for both cooling, dehumidification, and heating / heating has increased.
Generally, aluminum alloy fins are used.

In the air conditioner, water in the air adheres to the fin surface as condensed water during cooling operation. The attached condensed water exists in a semi-circular shape or a bridge shape between the fins, so that the smooth flow of air is hindered and the ventilation resistance is increased. Therefore, if the fin surface is water-repellent, condensed water during cooling may cause a bridge between the fins, which significantly increases ventilation resistance and reduces heat exchange efficiency.

On the other hand, aluminum and its alloys are originally excellent in corrosion resistance, but when condensed water stays on the fin surface for a long period of time, formation of oxygen concentration cells or pollutants in the atmosphere are gradually adsorbed and concentrated to cause a hydration reaction, The corrosion reaction is accelerated. This corrosion product is, of course, deposited on the surface of the fins and impairs the heat exchange characteristics, but has a drawback that white fine powder is discharged together with warm air by the blower during the heating operation in winter.

Therefore, in order to improve these problems, it has been attempted to form a film having both of the above properties on the fin surface for the purpose of improving the corrosion resistance of the fin and also increasing the hydrophilicity of the surface. Has been done.

Such a method is roughly divided into a method of forming an inorganic film and a method of forming an organic film, and as a method of forming an inorganic film, for example, after applying a corrosion-resistant film by a chromate treatment, a boehmite-based ( JP-A-56
-108071) or chlorine silicate (JP-A-59-1307).
A typical method is to form a hydrophilic film described in JP-A No. 8 and 50-38645). However, although such an inorganic film is excellent in both hydrophilicity and corrosion resistance, it requires a wastewater treatment facility because it contains harmful heavy metals such as chromium when it is industrially processed in large quantities and continuously, and that it is a two-coat system. Therefore, the processing equipment is generally larger than the one-coat type, and the processing cost is relatively high. Furthermore, in the case of chlorine silicate treatment, the odor peculiar to silica is emitted from the air conditioner and there is discomfort.In addition, when it is applied to precoat treatment, cracks are formed in the coating at the time of cutting, the corrosion resistance is reduced, and at the time of cutting. However, there is a drawback that the tool wear is remarkable.

On the other hand, as a method for forming an organic film, for example, a method in which a water-soluble or water-dispersible polymer resin is coated with an aqueous solution containing silica fine particles and then a heat-cured hydrophilic film is formed (JP-A-55- 99976, 553-125437, 5
5-164264) is typical, but when it is applied to pre-coating treatment because it contains silica fine particles, the coating cracks during cutting, corrosion resistance decreases, and tool wear during cutting is significant, There is a problem that the hydrophilicity is slightly inferior, and although it is slight, the odor peculiar to silica is emitted from the air conditioner, which causes discomfort. Incidentally, JP-A-55-164264 discloses that water-soluble melamine, alkyd, polyester and acrylic are used for the same purpose, but their performance is not yet sufficient.

Problems to be Solved by the Invention As described above, the conventional surface treatment technology for heat exchanger fins requires a waste water treatment facility or treatment when trying to solve hydrophilicity or corrosion resistance of the heat exchanger fins. There are problems that the cost is high, cracks are formed in the film during processing, and an unpleasant odor is emitted. Therefore, the present invention solves the above problems and has a hydrophilic surface, a corrosion resistance, a water solubility, a solvent resistance, etc., which does not generate cracks during processing, and which does not generate an unpleasant odor. The purpose is to develop a drug.

Means for Solving the Problems According to the present invention, a heat treatment containing an addition reaction product of at least one selected from the group of urea, thiourea and guanidine with a formalin or a condensation product of the addition reaction product and an alkali metal salt. A surface treatment for the exchanger fin is provided.

According to the present invention, there is further provided a surface treatment agent for a heat exchanger fin containing an addition reaction product of at least one selected from the group of urea, thiourea and guanidine with formalin or the addition reaction product and water-soluble nylon. To be done.

The conventional surface treatment agent for heat exchanger fins has an acrylic resin as a main component, but since the acrylic resin consumes hydrophilic functional groups in the curing reaction, the hydrophilicity of the formed film was insufficient. . Therefore, in order to obtain sufficient hydrophilicity, it is necessary to prevent reaction curing at all or to make it insufficient, but in this case, the formed film is eluted in water and the adhesion to the substrate is also obtained. There was a problem of not having.

On the other hand, urea resin has a large amount of hydrophilic functional groups in the molecule. Therefore, it is convenient to obtain a hydrophilic film, but these functional groups are also consumed when the thermosetting reaction occurs, and the hydrophilicity becomes insufficient. From this point of view, when the present inventors thermally cure the urea resin in the presence of an alkali metal salt, a cured film having good adhesion to the substrate is obtained in a form in which the hydrophilic functional group remains. The present invention has been completed by finding that the hydrophilicity and the elution resistance to water are also good. Although the detailed reaction mechanism is unclear, it is presumed that the thermosetting in an alkaline atmosphere allows the condensation reaction of the urea resin to proceed to form a gelled film with a hydrophilic functional group appropriately left.

The present inventors further found that the water-soluble nylon itself is hard to cure and the film obtained is redissolvable in water, but when it is mixed with urea resin, it is redissolved in water. It was found that a good hydrophilic film was obtained with almost no occurrence. When a mixture of urea resin and water-soluble nylon is heat-cured in the presence of an alkali metal salt, a cured film with better hydrophilicity can be obtained, and the adhesion with an aluminum substrate is good, and the redissolvability in water is good. Was small, and the corrosion resistance was good.

The resin used in the present invention is, as described above, obtained by addition-reacting one or two or more kinds selected from the group of urea, thiourea and guanidine with formalin, or by further condensing these resins. It is a resinous substance to be used, and it is particularly preferable to use a condensate. In addition, these resinous materials,
Usually, it is obtained as a mixture of condensates obtained by condensation reaction of monomethylol urea, dimethylol urea, monomethylene urea, dimethylene urea and the like.

In the present invention, urea, thiourea and / or guanidine are used as a surface treating agent by addition or addition condensation with formalin. This is because urea, thiourea and guanidine are comparatively more effective than melamine and the like. A low molecular weight addition condensate is obtained, the content ratio of the hydrophilic group in the molecule is high, and since the hydrophilic methylol group remains even after condensation and curing, the hydrophilicity of the obtained film is improved. Because it will be. In the present invention, the use ratio of urea, thiourea and / or guanidine and formalin is not particularly critical, but it is preferable to add 150 to 400 parts by weight of formalin (as a 40% aqueous solution) to 100 parts by weight of the former. Is preferred.

According to the present invention, the resin comprising the addition product or addition condensation product of urea, thiourea and / or guanidine and formalin has an alkali metal salt and a polymerization ratio of 1 / 0.0005 to 0.
5, preferably adjusted to 1 / 0.001 to 0.05 and blended in the surface treatment agent. If the ratio of the resin to the alkali metal is less than 1 / 0.0005, a film having desired hydrophilicity cannot be obtained, and conversely, if it exceeds 1 / 0.5, the film swells and the adhesiveness deteriorates, which is not preferable. As the alkali metal salt, for example, sodium hydroxide, potassium hydroxide, hydroxides such as lithium hydroxide, sodium phosphate, lithium phosphate, potassium phosphate and modified products thereof, pyrophosphoric acid condensed with these, tripolyphosphoric acid, Sodium, lithium, potassium carbonate, hydrogen carbonate, borate and the like can be used.

According to a second aspect of the present invention, a surface treating agent for heat exchanger fins, which comprises water-soluble nylon and the above-mentioned addition or condensation-condensation resinous product of urea, thiourea and / or guanidine and formalin, is provided. Provided.

The water-soluble nylon used in this embodiment is, for example, nylon-6 solubilized in water and / or alcohol, and is a commercially available resin such as AQ-nylon A.
-90, A-70, A-50, P-70, P-50 etc. (made by Toray Industries, Inc.) can be used conveniently. In this case, the alkali metal salt is not an essential component, but the weight ratio of the resin component to the alkali metal salt is 1 / 0.0005 to 0.
5, especially preferable because blending adjustment so as to be 1 / 0.001 to 0.05 further improves hydrophilic durability, and addition of the above urea, thiourea and / or guanidine or formalin or addition condensation condensation resinous material and water-soluble nylon The mixing ratio is not particularly limited, but generally 1 to 100 parts by weight of water-soluble nylon, preferably 1 part by weight with respect to 100 parts by weight of the resinous material.
Add 0 to 40 parts by weight. If the amount of the water-soluble nylon is too small, the effect of improving the hydrophilicity, which is the purpose of blending the water-soluble nylon, cannot be obtained. On the contrary, if the amount is too large, the water solubility is increased and the cost is increased.

The surface treatment agent for heat exchanger fins according to the present invention may include general-purpose optional components such as a surfactant, a color pigment, an alcohol solvent, and an amine solvent, in addition to the above-mentioned essential components. As the surfactant, for example, nonionic,
The surfactant may be appropriately selected from anionic surfactants, cationic surfactants, amphoteric surfactants and the like in consideration of workability such as stability, foaming property and coating property of the treatment liquid. Representative surfactants are as follows.

Nonionic polyoxyethylene glycol, polyoxypropylene glycol, polyoxyethylene polyoxypropylene glycol, polyoxyethylene alkylphenyl ether, glycerin fatty acid partial ester, sorbitan fatty acid partial ester, pentaerythritol fatty acid partial ester, polyoxyethylene sorbitan fatty acid partial Ester, polyoxyethylene alkyl ether, anionic dialkyl sulfosuccinate, alkane sulfonate, alkylbenzene sulfonate, alkylnaphthalene sulfonate, polyoxyethylene alkylsulfophenyl ether salt, alkyl phosphate ester salt, polyoxyethylene alkyl Ether phosphate ester salt, fatty acid alkyl ester sulfate ester salt, alkyl sulfate ester salt, Lioxyethylene alkyl ether sulfate ester salt, fatty acid monoglyceride sulfate ester salt Cationic alkylamine salt, dialkylamine salt Amphoteric system N, N, N-trialkyl-N-sulfoalkyleneammonium betaine Coating and baking can be carried out by a conventional method. For example, the desired coating is obtained by bringing the fin base material and the surface treatment agent into contact with each other by roll coating, spray coating and roll squeezing, dipping, etc., and then baking under appropriate baking conditions, for example, at a temperature of 100 to 300 ° C for 10 seconds to 30 minutes. Can be obtained. The temperature at the time of coating is not particularly limited, but if the temperature is too high, the surface treatment agent gels with time, so it is preferable to coat at a temperature of room temperature to 50 ° C.

Examples The present invention will be further described according to the following examples and comparative examples, but it goes without saying that the technical scope of the present invention is not limited to these examples.

Examples 1 to 10 and Comparative Examples 1 to 8 As an aluminum thin plate, thickness 0.1 mm, width 100 mm and length
Various surface treatment agents shown in Table 1 were evaluated using JIS A-110 H 24 of 200 mm. A weak alkaline degreasing agent (trade name "Rydrin manufactured by Nippon Paint Co., Ltd."
322 N-8 "), washed with water and dried. afterwards,
The water-based surface treatment agent shown in Table 1 was formed, and the coating amount was 1 g / m ^2.
Was coated with a bar coater so that the coating film was heated to a temperature of 240 ° C. for 30 seconds, and dried by heating to form a film. Punch oil (trade name "Idemitsu Punch Oil" manufactured by Idemitsu Petroleum Co., Ltd.) is applied to the aluminum plate hydrophilized in this way by brushing, and after cutting for about 24 hours, 1,1,1-trichloroethane (Toyo Soda Co., Ltd. The solvent was degreased under the trade name of "Toyoclean") and subjected to the following evaluation test.

The evaluation results of the obtained film are as shown in Table 1.
The resins used in Table 1 are as follows.

* 1 Yuria resin (48% solids) manufactured by Gunei Chemical Co., Ltd. * 2 Urya resin (65%) manufactured by Dainippon Ink and Chemicals, Inc.
Solids) * 3 Mitsui Toatsu Chemical Co., Ltd. Yuria resin (52% solids) * 4,5 Toray Co., Ltd. water-soluble nylon resin (100% solids) * 6 Daiichi Kogyo Seiyaku Co., Ltd. Dialkyn sulfosuccinate [Evaluation Test] Corrosion resistance: JIS Z 2371 The salt spray test was evaluated by the area ratio of white rust generation on the flat surface after 300 hours.

◎: White rust occurrence area ratio 0% ○: White rust occurrence area ratio 0% to less than 10% △: White rust occurrence area ratio 10% to less than 50% ×: White rust occurrence area ratio 50% or more Adhesion: Flat surface Cut 100 pieces of 1 mm square goggles with a knife, then press cellophane tape on the goggles, and then quickly peel it off. The area ratio of the film remaining at this time was evaluated.

Primary adhesion: evaluated by heating and drying and then allowed to cool. Secondary adhesion: evaluated after being immersed in tap water for 24 hours and dried (at room temperature). Hydrophilicity: 5 cycles of the hydrophilized aluminum plate in the following cycle test. Then, the water wet area ratio immediately after entering from drying to immersion in running water was evaluated.

[7 hours running water immersion (flow rate 5 / Hr, tap water) → 17 hours room temperature drying] cycle ◎: Water wetting area ratio 100% ○: Water wetting area rate 90 to less than 100% △: Water wetting area rate 50 to 90 Less than%: Water wetting area ratio less than 50% Water solubility: Calculated from the weight difference before and after immersion in tap water for 24 hours.

Water dissolution rate = [(initial amount of film-amount of film after immersion for 24 hours) / initial amount of film] x 100 ◎: Water dissolution rate less than 5% ○: Water dissolution rate 5 to less than 10% △: Water dissolution rate 10 to Less than 20% x: Water solubility less than 20% Effect of the invention As described above, when the surface treatment agent according to the present invention is applied to the heat exchanger fins, the initial hydrophilicity and the hydrophilic continuity due to the dry-wet cycle are improved. Both are good and have good corrosion resistance as well as good water solubility and solvent resistance. Further, since the surface treatment agent according to the present invention does not contain silica, there is no discomfort such as a bad odor, cracks do not occur during processing, the tool is less likely to wear such as dies, and hydrophilicity of the precoat after solvent degreasing It is possible to obtain an excellent effect that does not decrease.

Claims (6)

[Claims] 1. A heat exchanger fin comprising an addition reaction product of at least one selected from the group of urea, thiourea and guanidine with formalin or a condensate of the addition reaction product, and an alkali metal salt. Surface treatment agent. 2. The ratio of the addition reaction product or the condensation product of the addition reaction product to the alkali metal is 1 / 0.0005 to 0.5 (weight ratio).
The surface treatment agent according to claim 1, which is 3. A heat exchanger fin comprising an addition reaction product of at least one selected from the group of urea, thiourea and guanidine with formalin or a condensation product of the addition reaction product and water-soluble nylon. Surface treatment agent. 4. A ratio of the addition reaction product of at least one selected from the group of urea, thiourea and guanidine with formalin or the condensation product of the addition reaction product and water-soluble nylon is 1 /.
The surface treatment agent according to claim 3, wherein the surface treatment agent is 0.001 to 1 (weight ratio). 5. A heat comprising an addition reaction product of at least one selected from the group of urea, thiourea and guanidine with formalin or a condensation product of the addition reaction product, water-soluble nylon and an alkali metal salt. Surface treatment of exchanger fins. 6. The ratio of the addition reaction product or the condensation product of the addition reaction product, the aqueous nylon and the alkali metal salt is 1: 0.
The surface treatment agent according to claim 5, which is 001 to 1: 0.0005 to 0.5.