JP5481039B2 - Coating composition, fins and heat exchanger - Google Patents

Description

  The present invention relates to a coating composition, a fin and a heat exchanger, and more particularly to a coating composition applied to the surface of aluminum or an aluminum alloy.

Aluminum and aluminum alloys are widely used for fins of heat exchangers such as air conditioners and industrial heat exchangers because of their light weight, workability, and thermal conductivity.
In addition, in a heat exchanger such as an air conditioner, when water droplets condensed from the air adhere to the fins, ventilation resistance increases, pressure loss increases, and the capacity of the heat exchanger decreases. In addition, water droplets attached to the fins may be scattered outside the heat exchanger. For this reason, conventionally, it has been attempted to form a hydrophilic film on the surface of the fin in order to prevent water droplets from adhering to the fin and to allow the water attached to the fin to flow down easily.

In recent years, in order to reduce the size of the heat exchanger and improve the energy consumption efficiency (COP), the shape of the fins is complicated and the pitch of the fins tends to be narrowed. The adverse effect of water droplets adhering to the fin becomes more pronounced as the shape of the fin becomes more complicated and the pitch of the fin becomes narrower. In recent years, it has been required to further improve the hydrophilicity of the fin surface. ing.
In order to solve this problem, a technique has been proposed in which a plurality of resins having different compatibility are used to make the surface form of the resin-based film rough and increase the surface area (see, for example, Patent Document 1).
Japanese Patent No. 2967855

  However, in the technique described in Patent Document 1, the initial hydrophilicity is high, but it has been a problem that the hydrophilic effect cannot be maintained for a long time.

  This invention is made | formed in view of such a situation, and provides the coating composition apply | coated to the surface of aluminum or aluminum alloy which can form the coating film from which sufficiently high hydrophilicity is obtained over a long period of time. It is an issue.

In addition, the present invention provides a fin having a coating film that is lightweight, excellent in workability and thermal conductivity, and that has a sufficiently high hydrophilic property over a long period of time. It is an issue.
In addition, the present invention has a small pressure loss due to water droplets condensed from the air adhering to the fins, and even when used over a long period of time, the heat exchange capacity is not easily lowered, and the water droplets adhering to the fins are scattered outside. The challenge is to provide a difficult heat exchanger.

The coating composition of the present invention is a coating composition comprising a hydrophilic resin and water-soluble cellulose and applied to the surface of aluminum or an aluminum alloy, wherein the hydrophilic resin is a compound represented by the following general formula (1) acrylic polymer (however, R1 is H or CH3.) containing the, the alkali metal hydroxide is obtained by adding pH adjusted to the range of pH3.0~5.0 It is characterized by that.

The coating composition of the present invention may contain 1 to 3 parts by mass of an anionic surfactant with respect to 100 parts by mass of the acrylic polymer.
Moreover, the said coating composition of this invention shall contain 10-40 mass parts of said water-soluble cellulose with respect to 100 mass parts of said acrylic polymers.

  The fin of the present invention is made of aluminum or an aluminum alloy, and is characterized in that a coating film formed from any one of the above-described coating compositions is formed on the surface.

  Moreover, the heat exchanger of this invention is equipped with the fin of this invention, It is characterized by the above-mentioned.

The coating composition of the present invention, a hydrophilic resin, and a water-soluble cellulose, the hydrophilic resin is an acrylic polymer containing compound represented by the general formula (1), the hydroxides of alkali metals, Since the pH is adjusted to be in the range of 3.0 to 5.0, the coating is excellent in paintability, adhesion, and corrosion resistance, has no odor, and has a small coating surface roughness. Te, the surface of the aluminum or aluminum alloy, sufficiently high hydrophilicity becomes capable of forming a coating film obtained over a long period.

In addition, the fin of the present invention is made of aluminum or an aluminum alloy, and has a coating film formed from any of the above-described coating compositions on the surface. The obtained coating film is formed on the surface. In addition, since the fin of the present invention is made of aluminum or an aluminum alloy, it is lightweight and has excellent workability and thermal conductivity.
In addition, since the heat exchanger of the present invention includes the fin of the present invention, even when used for a long period of time, water droplets condensed from the air are less likely to adhere to the fin, and pressure loss due to water droplets adhering to the fin Decrease and scattering of water droplets adhering to the fins are less likely to occur.

Next, the coating composition, fins and heat exchanger of the present invention will be described in detail.
"Paint composition"
The coating composition of the present invention is a coating composition applied to the surface of aluminum or an aluminum alloy, and includes a hydrophilic resin and water-soluble cellulose.

"Hydrophilic resin"
The hydrophilic resin constituting the coating composition of the present invention includes an acrylic polymer containing the compound (1) represented by the following general formula (where R1 is H or CH ₃ ), an alkali metal hydroxide, Is included. The weight average molecular weight (Mw) of the hydrophilic resin is desirably 50,000 to 1,000,000. If it is less than 50,000, the adhesion of the coating film is inferior, and if it exceeds 1,000,000, the viscosity becomes very high, so that it is difficult to handle at the time of coating production, and it is easy to entrain air bubbles with a roll during coating. In addition, streaky coating defects caused by bubbles occur.

  Examples of the alkali metal hydroxide include sodium hydroxide and potassium hydroxide, and any of the above can be used alone or in combination.

Moreover, pH of hydrophilic resin is the range of 3.0-5.0, and it is more preferable that it is the range of 3.0-4.0. When the pH of the hydrophilic resin is in the range of 3.0 to 4.0, the adhesion of the coating film formed from the coating composition becomes more excellent, and the contaminants adhere to the coating film. The hydrophilicity is further improved.
When the pH of the hydrophilic resin is less than 3.0, the amount of alkali metal hydroxide is insufficient, and the effect of ionizing alkali metal ions from the carboxyl group constituting the acrylic polymer cannot be sufficiently obtained. The amount of acid anion is insufficient, and the hydrophilicity of the coating film formed from the coating composition cannot be obtained sufficiently.

  Further, when the pH of the hydrophilic resin exceeds 5.0, irregularities are formed on the surface of the coating film formed from the coating composition. The unevenness formed on the surface of the coating film reduces the ionization degree of protons of carboxyl groups constituting the acrylic polymer of the coating composition in the process of drying the coating composition to form a coating film, and the coating composition. When the alkali metal hydroxide concentration in the product becomes higher than necessary and the pH is made alkaline, the solubility of water-soluble cellulose in the coating composition decreases, and the coating film in a semi-dried state during baking It is considered that water-soluble cellulose is produced by precipitation before the acrylic resin. If the surface of the coating film is uneven, the surface exhibits excellent hydrophilicity at the beginning, but the surface becomes water-repellent at the stage where contaminants such as fats and oils adhere to some extent, and the surface of the coating film is smooth. Compared with the case, the hydrophilicity is significantly deteriorated, which is not desirable. Moreover, when the surface of a coating film is uneven | corrugated, when processing the fin by which the coating film was formed on the surface, there exists a tendency for the drying rate of the volatile oil apply | coated to a coating film to become slow, and it is unpreferable.

If the pH of the hydrophilic resin exceeds 5.0, the alkali metal hydroxide concentration in the coating composition becomes excessively high in the process of drying the coating composition to form a coating film. As a result, when the pH of the coating composition is made alkaline, the water-soluble cellulose is likely to be thermally decomposed. When water-soluble cellulose is thermally decomposed, a peculiar odor is generated. Therefore, in a heat exchanger provided with fins having a coating film formed on the surface, an odor problem may occur during use.
On the other hand, when the pH of the hydrophilic resin exceeds 5.0, the functional group that undergoes a crosslinking reaction with water-soluble cellulose is reduced, so that sufficient adhesion cannot be obtained.

"Water-soluble cellulose"
Examples of the water-soluble cellulose constituting the coating composition of the present invention include carboxymethylcellulose, hydroxymethylcellulose, hydroxypropylcellulose, and methylcellulose.

  The ratio of the acrylic polymer and the water-soluble cellulose constituting the coating composition of the present invention is not particularly limited, but the water-soluble cellulose is contained in an amount of 10 to 40 parts by mass with respect to 100 parts by mass of the acrylic polymer. Preferably it is. If the concentration of the water-soluble cellulose relative to 100 parts by mass of the acrylic polymer is less than the above range, the crosslinking reaction between the water-soluble cellulose and the acrylic polymer becomes insufficient, and sufficient hydrophilicity may not be obtained. Moreover, when the density | concentration of the water-soluble cellulose with respect to 100 mass parts of acrylic polymers exceeds the said range, an odor may generate | occur | produce after baking. Moreover, when the concentration of the water-soluble cellulose with respect to 100 parts by mass of the acrylic polymer exceeds the above range, the amount of the water-soluble cellulose with respect to the amount of the acrylic polymer becomes excessive, and the excessive water-soluble cellulose may cause unevenness on the coating film surface. is there.

Moreover, in the coating composition of this invention, it is desirable that 1-3 mass parts anionic surfactant is contained with respect to 100 mass parts of acrylic polymers. If the amount of the anionic surfactant is less than the above range, sufficient wettability may not be obtained depending on the state of the surface of the aluminum or aluminum alloy to which the coating composition is applied. Defects may occur. On the other hand, when the amount of the anionic surfactant exceeds the above range, the adhesion of the coating film may be lowered.
Among the anionic surfactants, an anionic surfactant having a benzene ring is particularly desirable. An anionic surfactant having a benzene ring is less likely to reduce the adhesion of the coating film and has improved water-solubility as compared to an anionic surfactant having no benzene ring. Examples of the anionic surfactant having a benzene ring include sodium dodecyl diphenyl ether disulfonate and sodium dodecyl sulfate.

  Further, the coating composition of the present invention may further contain other components as necessary. Other components include water-soluble resins, fungicides, antibacterial agents, deodorants, etc. for the purpose of preventing the corrosion of aluminum or aluminum alloys and the generation of unpleasant odors. Can be added as long as the maintenance and corrosion resistance are not impaired.

  The coating composition of the present invention is obtained by dissolving a hydrophilic resin and water-soluble cellulose in water or a solvent mainly containing water. Then, 1 to 3 parts by mass of an anionic surfactant is added to 100 parts by mass of the acrylic polymer as necessary, to the obtained coating composition.

  The coating composition of the present invention includes a hydrophilic resin and water-soluble cellulose, and the hydrophilic resin includes an acrylic polymer including the compound (1) represented by the above general formula, and an alkali metal hydroxide. In addition, since the pH is in the range of 3.0 to 5.0, as shown below, a film capable of forming a sufficiently high hydrophilic property over a long period on the surface of aluminum or an aluminum alloy can be formed. It becomes.

  FIG. 1 is a diagram for explaining a hydrophilic function in a coating film formed from the coating composition of the present invention. FIG. 1 (a) is a schematic view showing the surface state of a coating film formed from the coating composition of the present invention, and FIG. 1 (b) shows water on the surface of the coating film shown in FIG. 1 (a). It is the schematic which showed the surface state of the coating film when was attached. In FIGS. 1A and 1B, the symbol Me indicates an alkali metal. Further, FIG. 1 (c) does not include an alkali metal hydroxide, and instead of Me in FIG. 1 (a), a metal Me2 other than an alkali metal is bonded, as shown in FIG. 1 (a). It is the schematic which showed the surface state of the coating film when water adheres to the surface of the coating film which is the same as that shown in FIG.

In the coating film 1 formed from the coating composition of the present invention shown in FIG. 1 (a), the hydrophilic resin includes an acrylic polymer containing the compound (1) represented by the above general formula, an alkali metal hydroxide, include, are those pH is in the range of 3.0 to 5.0, the amount of alkali metal hydroxide with respect to a acrylic polymer is an appropriate amount of water in the coating film 1 formed from the coating composition As shown in FIG. 1B, the alkali metal ion Me + bonded to the carboxyl group constituting the acrylic polymer is immediately ionized and becomes a carboxylate anion that functions as a hydrophilic group. . Thereby, in the coating film 1 formed from the coating composition of this invention, high hydrophilicity is obtained over a long period of time.

  In contrast, for example, by adjusting the pH using a hydroxide of a metal other than an alkali metal instead of the alkali metal hydroxide constituting the coating composition of the present invention, FIG. 1 (c), when a metal Me2 other than an alkali metal is bonded, the metal Me2 does not ionize as metal ions even if water adheres to the coating surface. High hydrophilicity cannot be obtained.

  Further, for example, when pH is adjusted using ammonia or amines instead of the alkali metal hydroxide constituting the coating composition of the present invention, in the coating film formed from the coating composition, Crosslinking or hydrogen bonding between the carboxyl groups that should form the hydrophilic nature of the acrylic polymer is likely to occur, and the number of carboxyl groups that function as hydrophilic groups decreases, and the carboxyl group shown in FIG. Since acid anions are not generated, sufficient hydrophilicity cannot be obtained.

  In the coating composition of the present invention, since the pH of the hydrophilic resin is in the range of 3.0 to 5.0, the coating film formed from the coating composition of the present invention has a sufficiently smooth surface. As compared with the case where the surface of the coating film is uneven, the drying speed of the volatile oil applied to the coating film when the fin having the coating film formed on the surface is processed is sufficiently high. Moreover, since the coating film formed from the coating composition of the present invention has a sufficiently smooth surface, the plasticizer contained in the adhesive for building materials and wallpaper, and fatty acids and fatty acid esters generated as mist during cooking In addition to being difficult to adsorb contaminants such as oils and fats, excellent hydrophilicity can be maintained even if contaminants adhere. Therefore, the coating film formed from the coating composition of the present invention is excellent in stain resistance and becomes a coating film that provides excellent hydrophilicity maintenance over a long period of time.

  Moreover, since the pH of the hydrophilic resin is in the range of 3.0 to 5.0, the coating composition of the present invention can prevent generation of odor due to thermal decomposition of water-soluble cellulose and is sufficiently high. It becomes what can form the coating film which has adhesiveness.

  Further, in the coating composition of the present invention, when the water-soluble cellulose is contained in an amount of 10 to 40 parts by mass with respect to 100 parts by mass of the acrylic polymer, the water-soluble cellulose and the acrylic polymer undergo a crosslinking reaction, whereby the coating composition Since the water-soluble solubility of a coating film formed from a product can be improved, a coating film with high hydrophilicity can be formed over a longer period of time.

  In the coating composition of the present invention, when 1 to 3 parts by mass of an anionic surfactant is contained with respect to 100 parts by mass of the acrylic polymer, the surface of the aluminum or aluminum alloy to which the coating composition is applied Since sufficient wettability can be obtained regardless of the state, it is possible to prevent defects such as film repellency during coating.

Since the coating composition of the present invention is acidic, it is better to use a cationic surfactant or a nonionic surfactant than to use an anionic surfactant. In addition, the effect of reducing the surface tension is great, and the wettability is improved. However, when a cationic surfactant or a nonionic surfactant is used, it tends to foam when a coating composition is applied using a roll coat or the like. Poor coating is likely to occur.
On the other hand, when an anionic surfactant is used, it becomes difficult to foam during coating, so compared to the case of using a cationic surfactant or a nonionic surfactant, It is preferable because it is difficult to cause poor coating.

"fin"
FIG. 2A is a perspective view showing an example of the fin of the present invention, and FIG. 2B is an enlarged cross-sectional view showing a part of the fin shown in FIG.
The fin 10 has an elongated strip shape, and flares 11 through which copper heat transfer tubes pass are arranged at equal intervals in a single row or multiple rows in the length direction. Moreover, the surface of the fin 10 may be provided with slits 12 and the like for the purpose of improving heat transfer performance.
As shown in FIG. 2 (b), the fin 10 shown in FIG. 2 (a) has a coating film 14 formed from the coating composition of the present invention formed on the surface of a fin base 13 made of aluminum or an aluminum alloy. It has been made.
As the fin base material 13, an aluminum or aluminum alloy plate on which a base treatment layer made of a phosphoric acid chromate film or an epoxy resin film is formed is preferably used. Moreover, it is preferable that the film thickness of the coating film 14 formed on the surface of the fin base material 13 is about 0.5 to 2.0 μm.

  The fin 10 shown in FIG. 2 (a) forms a coating film 14 by applying and baking the coating composition of the present invention on the surface of a flat fin substrate 13 made of, for example, aluminum or an aluminum alloy. After that, it is obtained by making the fin base material 13 into a predetermined shape by a method of pressing. Although baking temperature is not specifically limited, In order to obtain the coating film 14 excellent in water resistance and hydrophilicity, it is preferable to set it as the range of 200-280 degreeC.

  The fin 10 shown in FIG. 2 (a) is made of aluminum or an aluminum alloy, and has a coating film 14 formed from the coating composition of the present invention on the surface. It is excellent in conductivity, and sufficiently high hydrophilicity can be obtained over a long period of time.

"Heat exchanger"
FIG. 3 is a perspective view showing an example of the heat exchanger of the present invention.
A heat exchanger 20 illustrated in FIG. 3 includes the fin 10 illustrated in FIG. 2A and a plurality of heat transfer tubes 30. The fins 10 are arranged in parallel at regular intervals, and air flows between the fins 10. The heat transfer tube 30 passes through the collar of the fin 10, and the refrigerant flows through the inside thereof.
Since the heat exchanger 20 shown in FIG. 3 includes the fin 10 shown in FIG. 2A, even when used for a long period of time, water droplets condensed from the air are less likely to adhere to the fin 10, and water droplets do not adhere to the fin 10. Decrease in pressure loss due to adhesion and scattering of water droplets adhering to the fin 10 to the outside hardly occur.

"Experimental example"
Examples of the present invention and comparative examples will be described below.
Using acrylic polymers and pH adjusters shown in Table 1, A to I hydrophilic resins having pH shown in Table 1 were obtained.

  And the hydrophilic resin of A to I shown in Table 1, the water-soluble cellulose of A to C shown in Table 2, and the surfactant of I to I shown in Table 3 are the masses shown in Table 4 to Table 6. The coating composition of Examples 1-25 and Comparative Examples 1-12 which consist of the aqueous solution contained in a part was obtained.

  The thus obtained coating compositions of Examples 1 to 25 and Comparative Examples 1 to 12 were subjected to degreasing and washing with an aluminum alloy material (material condition) in which the base treatment layers a to c shown in Table 7 were formed. The film thickness is obtained by applying a bar coater to the surface of a test body having a quality of 1200-H24, a size of 240 mm, a length of 350 mm, and a thickness of 0.1 mm, and baking at 200 ° C. for 30 seconds. A 1 μm coating film was formed, and the paintability and film performance shown below were evaluated as shown below. The results are shown in Tables 4-6.

"Paintability"
◎ There is no paint repelling and no paint surface streak unevenness ○ Paint repelling and paint surface streak unevenness are slight, but there is no problem in visual appearance Paint splash is bad and painting is impossible

(Film performance)
"Adhesion"
Using a rubbing tester (manufactured by Taihei Rika Kogyo Co., Ltd.), a water rubbing test was conducted with a load of 500 g.
◎ No film peeling after 20 round trips ○ No film peeling at 10 round trips, film peeling at less than 20 round trips △ No film peeling at 5 round trips, film peeling at less than 10 round trips × film peeling at less than 5 round trips

"Hydrophilicity"
The specimens of Examples 1 to 25 and Comparative Examples 1 to 12 were immersed in press oil (trade name: AF-3C: manufactured by Idemitsu Kosan Co., Ltd.), dried at 160 ° C. for 4 minutes, and immersed in running water for 480 hours. I let you. Thereafter, the water contact angle was measured.
◎ Water contact angle is less than 20 ° ○ Water contact angle is 20 ° or more and less than 30 ° △ Water contact angle is 30 ° or more and less than 40 ° × Water contact angle is 40 ° or more

"Corrosion resistance"
A salt spray test for 480 hours was performed based on JIS Z 2301.
◎ RN (rating number) 10
○ RN 9.8 or more △ 9.5 or more and less than RN 9.8 × less than RN 9.5

"Contamination resistance"
The specimens of Examples 1 to 25 and Comparative Examples 1 to 12 were immersed in press oil (trade name: AF-3C: manufactured by Idemitsu Kosan Co., Ltd.), dried at 160 ° C. for 4 minutes, and immersed in running water for 72 hours. I let you. Thereafter, the specimens of Examples 1 to 25 and Comparative Examples 1 to 12 and the contaminant (palmitic acid + hexadecanol) were placed in a sealed glass container having a capacity of 15 L and exposed at 100 ° C. for 24 hours. Thereafter, the water contact angle was measured.
◎ Water contact angle is less than 20 ° ○ Water contact angle is from 20 ° to less than 35 ° △ Water contact angle is from 35 ° to less than 50 ° × Water contact angle is more than 50 °

"Odor"
By sensory test.
◎ Almost no odor can be felt ○ Slightly odor △ Smell × Feels a very harsh odor “Surface roughness: uneven surface of coating film”
The centerline average roughness Ra of the coating film was calculated using a 3D laser microscope (trade name: VK-9700: manufactured by Keyence).
In addition, when surface roughness Ra is 0.1 or more, it is a rough surface (it can confirm also visually and there is a problem), and when surface roughness Ra is less than 0.05-0.1, it is somewhat. When the surface is rough (not visually observable) and the surface roughness Ra is less than 0.05, the surface is almost smooth.

As shown in Tables 4 and 5, in each of Examples 1 to 25, the evaluation of paintability is ◎ or ◯, all the evaluations of the film performance are ◎ or ◯, and the surface roughness Ra is 0. It became less than 1.
On the other hand, in Comparative Examples 1 and 2 in which the pH of the hydrophilic resin exceeds 5, the evaluation of odor, corrosion resistance, and contamination resistance was x, and the surface roughness Ra was 0.1 or more.
Further, in Comparative Examples 3 to 4 in which the pH of the hydrophilic resin is less than 3, the evaluation of hydrophilicity retention, corrosion resistance, and contamination resistance was evaluated as x.

Further, in Comparative Examples 5 to 6 in which an acrylic polymer other than the present invention was used, the evaluation of corrosion resistance, contamination resistance, and odor was Δ or ×.
In Comparative Examples 7 to 8 using a pH adjuster that was not an alkali metal hydroxide, the hydrophilicity retention, corrosion resistance, contamination resistance, and odor were all evaluated as Δ or ×.

  In Comparative Examples 9 to 12, which did not contain water-soluble cellulose, the hydrophilicity retention, corrosion resistance, stain resistance, and odor were evaluated as Δ or ×.

FIG. 1 is a diagram for explaining a hydrophilic function in a coating film formed from the coating composition of the present invention. FIG. 2A is a perspective view showing an example of the fin of the present invention, and FIG. 2B is an enlarged cross-sectional view showing a part of the fin shown in FIG. FIG. 3 is a perspective view showing an example of the heat exchanger of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Fin, 11 ... Flare, 12 ... Slit, 13 ... Fin base material, 14 ... Coating film, 20 ... Heat exchanger, 30 ... Heat exchanger tube.

Claims (5)

A coating composition comprising a hydrophilic resin and water-soluble cellulose and applied to the surface of aluminum or an aluminum alloy,
Wherein the hydrophilic resin is a compound represented by the following general formula (1) acrylic polymer (however, R1 is H or CH _3.) Containing the, alkali metal hydroxides, PH3.0～5.0 A coating composition characterized in that it is added so as to have a pH range of

  The coating composition according to claim 1, wherein 1 to 3 parts by mass of an anionic surfactant is contained with respect to 100 parts by mass of the acrylic polymer.   The said water-soluble cellulose is 10-40 mass parts with respect to 100 mass parts of said acrylic polymers, The coating composition of Claim 1 characterized by the above-mentioned.     A fin made of aluminum or an aluminum alloy, and having a coating film formed from the coating composition according to any one of claims 1 to 3 formed on a surface thereof.     A heat exchanger comprising the fin according to claim 4.

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