JP2010159379A - Coating composition and method for producing the same and fin for heat exchanger - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coating composition whose hydrophilicity is not deteriorated over a long period of time as a result of contamination being washed away by dew drops during the operation of an air conditioner even when the contamination such as fats and oils are deposited, and a fin for a heat exchanger. <P>SOLUTION: The coating composition includes 15 wt.% or more, in a solid component, of an acrylic polymer (A) including a sulfonic acid group-containing monomer and a carboxy group-containing monomer, each of which being 40 mol% or more, and also 40 wt.% or more, in the solid component, of an acrylic polymer (B) including 65 mol% or more of a carboxy group-containing monomer. The coating composition is adjusted by adding ammonia or one or two or more of amines, of which a molar ratio to the total carboxy group-containing monomers is 0.3 or more, and an alkali metal hydroxide, of which a molar ratio to the sulfonic acid group-containing monomer is 0.5-2.0, to an aqueous solution of a mixture of the acrylic polymers. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a coating composition, a manufacturing method thereof, and a fin for a heat exchanger having a coating film formed of the coating composition, and particularly relates to a coating composition applied to the surface of aluminum.

Aluminum for air conditioner heat exchangers is mainly made of aluminum because of its light weight and high thermal conductivity.
When used on the evaporator side in a heat exchanger such as an air conditioner, water vapor in the air is condensed and condensed water is generated in the fins. When dew condensation water exists as water droplets, the ventilation resistance increases, pressure loss increases, and the capacity of the heat exchanger decreases. For this reason, in order to make the water condensed on the fins flow down easily, imparting hydrophilicity to the surface has been performed.
As a method for imparting hydrophilicity to the surface of aluminum or aluminum alloy, there is a method of applying an inorganic surface treatment agent such as water glass to the surface. However, they tend to adsorb odor components in the environment, and the odor components may be detached at the start of operation to generate odor.

  In order to solve such a problem, in the technique described in Patent Document 1, a chromate film is formed on the surface of aluminum, and an alumina sol film is formed thereon to impart hydrophilicity. In addition, as in the technique described in Patent Document 2, there is a method using an organic surface treatment agent mainly composed of a hydrophilic resin. As the surface treatment agent having a hydrophilic resin as a main component, an acrylic resin or a cellulose-based one is used.

Japanese Patent Laid-Open No. 8-200903 JP 7-268274 A

Even if paints having these compositions are used, depending on the environment in which they are used, various types of dirt may adhere and the original performance may be lost. In particular, when oil droplets or the like generated during cooking adhere, the effect is remarkable. Among the dirt that adheres, aldehydes have a relatively high solubility in water, so they naturally dissolve in condensed water, but oils and fats (floor wax and oil droplets generated during cooking), etc. are in water. Since it hardly dissolves, once it adheres to the coating film surface, it does not easily fall off.
In order to make it difficult for oil droplets or the like to adhere, a method of making the surface tension of the coating film extremely low is conceivable, but at the same time, the surface becomes water-repellent and the pressure loss becomes large. Further, a method of making it easy to remove adhered substances such as oil by preliminarily mixing a substance having a surface active action in the coating film is also conceivable. However, this method loses its action after all the surface-active substances are eluted.

  The present invention has been made in view of such circumstances, and even if contaminants such as fats and oils adhere, the contaminants are washed away by the condensed water during the cooling operation, and as a result, the hydrophilicity is lowered over a long period of time. It is an object to provide a non-coating composition and a fin for a heat exchanger.

  The coating composition of the present invention contains 15% by weight or more of the acrylic polymer (A) containing 40 mol% or more of each of the sulfonic acid group-containing monomer and the carboxyl group-containing monomer in the solid content, and 65 mol% of the carboxyl group-containing monomer. The acrylic polymer (B) containing at least 40% by weight in the solid content is contained in an aqueous solution of these acrylic polymer mixture, and one or more of ammonia or amine is added to the total carboxyl group-containing monomer. A molar ratio of 0.3 or more is prepared by adding an alkali metal hydroxide to the sulfonic acid group-containing monomer at a molar ratio of 0.5 to 2.0.

  Moreover, the manufacturing method of the coating composition of the present invention includes an acrylic polymer (A) containing 40 mol% or more of sulfonic acid group-containing monomer and carboxyl group-containing monomer, and an acrylic system containing 65 mol% or more of carboxyl group-containing monomer. The polymer (B) is mixed with water or water in such a ratio that the acrylic polymer (A) is 15% by weight or more in the solid content and the acrylic polymer (B) is 40% by weight or more in the solid content. While being dissolved and mixed in the main solvent, one or more of ammonia or amine is added to the aqueous solution of these acrylic polymer mixtures in a molar ratio of 0.3 or more with respect to the total carboxyl group-containing monomer. The alkali metal hydroxide is adjusted by adding a molar ratio of 0.5 to 2.0 with respect to the sulfonic acid group-containing monomer.

In order to be washed away by condensed water even if dirt such as oil adheres, (1) the coating film has a low affinity with oil-stained substances and (2) has a high affinity with water At the same time, (3) the coating film itself needs to have high water permeability.
It is thought that the mechanism by which the contaminants such as oil are washed away by the condensed water is as shown in FIG.
That is, as shown in FIG. 1A, the oil stain substance 2 does not form a chemical bond on the surface of the coating film 1 having a very high hydrophilicity (hydrophilic coating film) 1, and does not form on the surface of the coating film 1. It is simply a riding condition. And as shown in (c), when the dew condensation water 3 adheres to the surface of the coating film 1 around the oil-stained substance 2 as shown in (b), the coating film 1 has high water permeability and high hydrophilicity. The water 3 passes through the coating film 1 and reaches the interface between the surface of the coating film 1 and the oil stain substance 2. For this reason, the adhesion of the oily soil material 2 is reduced, and the oily soil material 2 falls together with the condensed water 3 from the surface of the coating film 1.

The coating composition of the present invention comprises two types of acrylics, an acrylic polymer (A) having 40 mol% or more of sulfonic acid groups and carboxyl groups, and an acrylic polymer (B) having 65 mol% or more of carboxyl groups. The polymer is dissolved in water or a solvent mainly composed of water.
A polymer containing a large amount of an alkali metal sulfonate has a very low affinity with oils and fats, so that the oils and fats are difficult to stick and have an excellent affinity with water. However, such a polymer alone is difficult to cure even when baked, and only a coating film having poor water resistance can be obtained. Moreover, if the ratio of the sulfonic acid-containing monomer is lowered in order to facilitate curing, the affinity with fats and oils increases. When a coating film is prepared using the coating composition of the present invention, the two polymers are dissolved, but the polymer (A) containing more sulfonic acid groups having higher solubility in water is more preferable. It will be unevenly distributed on the surface. Further, alkali metal ions in the aqueous solution are also preferentially bonded to the sulfonic acid group. As a result, the alkali metal sulfonate group is present at a high density on the coating surface. Therefore, the oil and fat has extremely low affinity and can be obtained with excellent affinity with water. On the other hand, the polymer (B) containing a lot of carboxyl groups dissolves to some extent, and the carboxyl groups in the polymers (A) and (B) react with each other to be baked and cured, so that the water resistance is also excellent. A coating film can be obtained. In addition, since a crosslinking agent such as an amino-based resin is not used and crosslinking is performed only with an ester bond, the water permeability of the coating film itself is excellent.

  The present invention includes a polymer (A) containing a large amount of sulfonic acid having a low affinity with fats and oils and the like, and a polymer containing a large amount of carboxyl groups having a certain degree of hydrophilicity and capable of reacting with the polymer (A). It is the coating composition which mixed the molecular body (B). This mixture is prepared with alkali metal hydroxide and ammonia or amine. Among these regulators, after the alkali metal hydroxide is baked to form a coating film, it mainly binds to a sulfonic acid group and exists as an alkali metal sulfonate group, and plays a major role in improving hydrophilicity. In addition, ammonia or amines are volatilized during baking and hardly remain in the coating film, but it is considered that carboxyl groups are connected to each other during volatilization and contribute to the crosslinking reaction.

If the sulfonic acid-containing group of the polymer (A) is less than 40 mol%, the oil and oil removal properties are not sufficient, and if the carboxyl group is less than 40 mol%, the compatibility with the polymer (B) is insufficient. In addition, the crosslinking reaction does not proceed sufficiently. Moreover, when the carboxyl group of the polymer (B) is also less than 65 mol%, the bake-curing is not sufficient and the water resistance is poor.
The reason why the amount of ammonia or amines is 0.3 or more in terms of the molar ratio with respect to the carboxyl group-containing monomer is that the reaction between the carboxyl groups does not proceed sufficiently when the molar ratio is less than 0.3, and the crosslinking is insufficient. Thus, the coating film is inferior in water resistance. On the other hand, although there is no upper limit, even if it is added in a large amount, it volatilizes during baking, so there is no problem even if it is added too much. The reason why the amount of the alkali metal hydroxide is limited to 0.5 to 2.0 in terms of mol ratio with respect to the sulfonic acid-containing monomer is that the oil / fat removal property is not sufficient when it is less than 0.5. When it exceeds 0, the compatibility of the polymers (A) and (B) is lost, only the resin (B) is cured, and the resin (A) is present in an uncrosslinked state on the surface and dissolved in water. Will end up.

In the coating composition of the present invention, the cellulose polymer may be contained in an amount of 30% by weight or less in the solid content.
In addition to the polymers (A) and (B), the addition of 30% by weight or less of a cellulose polymer improves the hydrophilicity. The reason for this is considered to be that surface roughening is promoted. However, if it exceeds 30% by weight, the initial hydrophilicity is excellent, but the oil and oil removal properties are lowered, which is not preferable.

The fin for a heat exchanger of the present invention is obtained by forming a coating film formed from the coating composition on the surface of an aluminum plate material or on the surface of an organic corrosion-resistant film applied on the aluminum plate material. .
The coating film formed using the adjusted coating solution composed of the polymers (A) and (B) is not so high in corrosion resistance because of its high water permeability. In applications where corrosion resistance is not so required, it can be fully used by coating on the surface of an aluminum plate that has been subjected to a corrosion-resistant surface treatment such as phosphate chromate. However, when the usage environment is severe and corrosion resistance is required, the requirement can be satisfied by applying the coating solution on the organic corrosion-resistant film. In this case, the corrosion-resistant film is not particularly limited, but resin-based films such as epoxy-based, urethane-based, acrylic-based, and polyester-based films can be used.

  According to the coating composition of the present invention, even if contaminants such as fats and oils adhere, the contaminants are washed away by the condensed water during the cooling operation, and as a result, the hydrophilicity does not decrease over a long period of time. The heat exchanger fin coated with can prevent a long-term decline in the capacity as a heat exchanger without increasing the ventilation resistance due to contaminants such as oil and fat.

It is sectional drawing which showed typically the mechanism by which the oil stain substance adhering on the coating film consisting of the coating composition which concerns on this invention is washed off.

Hereinafter, an embodiment of the present invention will be described.
The fin for a heat exchanger includes an aluminum plate, an organic corrosion-resistant coating formed on the plate, and a hydrophilic coating formed on the organic corrosion-resistant coating.
As the aluminum plate material, for example, JIS standard alloy numbers 1100, 1200, 1050, 3003, 7072, etc. are used. In the present invention, aluminum includes both pure aluminum and aluminum alloy.
As a resin used for the organic corrosion-resistant film, an epoxy resin is generally used, but an acrylic resin or a polyester resin can also be used. The film thickness is not particularly limited, but is preferably 0.5 to 5 μm. If it is less than 0.5 μm, it does not have sufficient corrosion resistance for applications that require corrosion resistance. When the thickness exceeds 5 μm, not only the corrosion resistance is not improved any more, but also the cutting workability when processing into a fin material may be adversely affected.

The coating composition used for the hydrophilic coating film contains an acrylic polymer (A) containing 40 mol% or more of a sulfonic acid group-containing monomer and 40 mol% or more of a carboxyl group-containing monomer, and 65 mol% or more of a carboxyl group-containing monomer. An aqueous solution obtained by mixing the acrylic polymer (B) is adjusted with ammonia or an amine and an alkali metal hydroxide.
As the sulfonic acid group-containing monomer used in the acrylic polymer (A), at least one selected from vinyl sulfonic acid, methallyl sulfonic acid, and allyl sulfonic acid can be used. As the carboxyl group-containing monomer used in the acrylic polymer (A), at least one selected from methacrylic acid, acrylic acid, and itaconic acid is used. In addition to the sulfonic acid group-containing monomer and the carboxyl group-containing monomer, other monomers may be included as long as hydrophilicity is not impaired. Other monomers include 2-hydroxy acrylate, 2 methoxyethyl acrylate, acrylamide and the like.
In addition, the carboxyl group-containing monomer used in the acrylic polymer (B) is at least one selected from methacrylic acid, acrylic acid, and itaconic acid, and contains other monomers as long as the hydrophilicity is not inhibited. Also good. As the other monomer, a monomer containing a sulfonic acid group together with 2-hydroxyacrylate, 2-methoxyethyl acrylate, acrylamide and the like may be used as in the acrylic polymer (A).

And these two kinds of acrylic polymers (A) and (B) are such that the polymer (A) contains 15% by weight or more in the solid content and the polymer (B) contains 40% by weight or more in the solid content. In an aqueous solution of the polymer mixture, one or more of ammonia or amine is added in a molar ratio to the total carboxyl group-containing monomer in a molar ratio of 0.001. A coating composition is prepared by adjusting the alkali metal hydroxide to a molar ratio of 0.5 to 2.0 with respect to the sulfonic acid group-containing monomer.
In addition, the polymer mixture may further include a cellulose polymer in a solid content of 30% by weight or less. In that case, the cellulose polymer may include a carboxymethyl cellulose salt (sodium salt, Potassium salts, ammonium salts, etc.), hydroxymethylcellulose and the like can be suitably used.
The film thickness of the hydrophilic coating film formed by applying this coating composition is, for example, 0.3 to 3 μm. When the coating thickness is less than 0.3 μm, the phenomenon that the water 3 passes through the coating film 1 and reaches the interface between the coating film 1 and the oily soil substance 2 as shown in FIG. Therefore, when it exceeds 3 μm, it takes a considerable amount of time to swell after being swollen in water and dry, so that the tendency of breeding of straw and the like appears.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, the organic corrosion-resistant film is formed according to the required quality of corrosion resistance. It may be omitted or replaced with a surface treatment such as phosphate chromate.

Examples will be described below.
<Synthesis of acrylic polymer>
Polymerization was carried out in water at the monomer ratio shown in Table 1 to obtain a polymer (A). As examples, five types were prepared: one composed of a sulfonic acid group-containing monomer and a carboxyl group-containing monomer, and one added with other monomers. In addition, as a comparative example, one in which either the sulfonic acid group-containing monomer or the carboxyl group-containing monomer was less than 40 mol% and deviated from the scope of the present invention was also created.

Moreover, it superposed | polymerized in water with the monomer composition shown in Table 2, and obtained the polymeric body (B). As examples, four types were prepared: those composed of a carboxyl group monomer and those added with other monomers. In addition, as a comparative example, a monomer having a carboxyl group monomer of less than 65 mol% and out of the scope of the present invention was also prepared.

<Adjustment of paint>
The polymers shown in Tables 1 and 2 were mixed at the ratios shown in Table 3, and paints were prepared using various pH adjusters. Moreover, what added the cellulose polymer was also created. In Table 3, DMEA is dimethylethanolamine, TEA is triethanolamine, and DMA is dimethylamine. CMC-Na is carboxymethylcellulose sodium, CMC-ammonium is carboxymethylcellulose ammonium, and HMC is hydroxymethylcellulose.

<Evaluation of coating film performance>
On the surface of the aluminum plate that has been subjected to phosphate chromate treatment and the aluminum plate that has been pre-coated with an organic corrosion-resistant film at a thickness of 1 μm, apply the paint prepared in the above-mentioned <Preparation of paint> column and bake. An evaluation sample was obtained. The coating thickness was 1 μm for all. Epoxy resin, urethane resin, or polyester resin was used as the resin for the organic corrosion-resistant film. As evaluation items, the following film adhesion, oil spillage, and corrosion resistance were used.
(1) Film adhesion The presence or absence of coating film peeling after rubbing the surface of the coating film 10 times with a cloth moistened with water was visually determined. The state without peeling was marked with ◯, the state with slight peeling was marked with Δ, and the state with large peeling was marked with ×.
(2) Evaluation of oil spillability After immersing in oleic acid and dropping excess oil over 10 minutes, the contact angle after immersing in pure water for 1 minute and lifting and drying was measured. When the contact angle was 20 ° or less, it was evaluated as “good”, when it exceeded 20 ° and was 40 ° or less, Δ was relatively good, and when it exceeded 40 °, it was evaluated as “poor”.
(3) Corrosion resistance A salt spray test for 480 hours is performed based on JIS Z 2371, the degree of corrosion of the surface is confirmed, and corrosion is performed using a rating number (Rating Number, hereinafter referred to as RN) described in JIS H 8679. Was evaluated. ○ is RN 9.8 or more, Δ is 9.5 or more and less than 9.8, and x is less than 9.5.

As shown in Table 4, the examples were generally good in coating film adhesion, oil spillability, and corrosion resistance. Moreover, what formed the organic corrosion-resistant film | membrane as a surface treatment was also favorable. In the comparative example, any of coating film adhesion, oil spillage, and corrosion resistance was poor.
<Analysis of coating composition>
Apply the coating film of Sample B shown in <Preparation of paint> above to the surface of the aluminum plate material subjected to the phosphoric acid chromate treatment, and then dissolve the aluminum plate material in dilute hydrochloric acid solution. Obtained.
About the surface and the back surface (surface which was adhere | attached on the board | plate material made from aluminum) of this film, the surface analysis was performed with the X-ray photoelectron spectroscopy analyzer (ESCA). Since the surface is contaminated with dirt, the surface was analyzed by performing ion sputtering equivalent to 200 angstroms in thickness in terms of SiO ₂ for 1 minute to clean the surface. The results are shown in Table 5 below.

  From the results shown in Table 5, it can be seen that S derived from the sulfonic acid in the polymer (A) has a high concentration on the coating surface and a low concentration on the back surface. Further, it is presumed that K added as KOH is linked to it and mainly bonded to the sulfonic acid group. In other words, the sulfonic acid alkali metal salt group is present at high density on the surface side of the coating film, so that it has low affinity with fats and oils, excellent affinity with water, and also has good adhesion. It is recognized as an excellent coating film.

1 Coating (hydrophilic coating)
2 Oil stains 3 Water (condensation water)

Claims (4)

  An acrylic polymer (A) containing 40 mol% or more of sulfonic acid group-containing monomer and carboxyl group-containing monomer, respectively, in an amount of 15 wt% or more in solid content and containing 65 mol% or more of carboxyl group-containing monomer B) is contained in a solid content of 40% by weight or more, and in the aqueous solution of these acrylic polymer mixture, one or more of ammonia or amine is in a molar ratio of 0.3 or more with respect to the total carboxyl group-containing monomer, A coating composition prepared by adding an alkali metal hydroxide to a sulfonic acid group-containing monomer in a molar ratio of 0.5 to 2.0.   The coating composition according to claim 1, comprising a cellulose polymer in a solid content of 30% by weight or less.   An acrylic polymer (A) containing 40 mol% or more of a sulfonic acid group-containing monomer and a carboxyl group-containing monomer, and an acrylic polymer (B) containing 65 mol% or more of a carboxyl group-containing monomer, While the body (A) is 15% by weight or more in solid content and the acrylic polymer (B) is in a ratio of 40% by weight or more in solid content, it is dissolved and mixed in water or a solvent mainly containing water, In an aqueous solution of these acrylic polymer mixtures, one or more of ammonia or amine is used in a molar ratio of 0.3 or more with respect to the total carboxyl group-containing monomer, and an alkali metal hydroxide is used as the sulfonic acid group-containing monomer. A method for producing a coating composition, wherein the molar ratio is adjusted by adding 0.5 to 2.0.   The coating film formed from the coating composition according to claim 1 or 2 is formed on the surface of the aluminum plate or on the surface of the organic corrosion-resistant film applied on the aluminum plate. Features heat exchanger fins.

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