JP2975550B2 - Pre-coated fin material for heat exchanger - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to aluminum or aluminum alloy (hereinafter referred to as aluminum or aluminum alloy) used for heat exchangers used for condensers and evaporators of commercial and home air conditioners and radiators for automobiles. The present invention relates to a precoated fin material for a heat exchanger, and more particularly to a precoated fin material for a heat exchanger having a coating layer having excellent hydrophilicity formed on the surface.

[0002]

2. Description of the Related Art As a fin material for a heat exchanger, aluminum, which is lightweight and excellent in workability and heat conductivity, has been widely used. In recent years, due to demands for downsizing and energy saving of room air conditioners and the like, measures have been devised to further increase the conduction efficiency, such as raising louvers and shortening the distance between fins. For this reason, when water condenses on the fins, the water droplets form a bridge between the fins, thereby increasing the ventilation resistance and causing the water droplets to resonate with the ventilation and generate noise. Problems such as corrosion of the fin material began to occur at the same time. Therefore, in order to improve this, the fin material is subjected to a corrosion resistance treatment and a hydrophilic treatment (a contact angle at the time of condensation of water is reduced to prevent water droplets). Further, in order to increase productivity, instead of the conventional fin molding, post-coating after assembling and post-assembly treatment, an aluminum sheet is preliminarily subjected to hydrophilization treatment and pre-coating to form the same. As a result, aluminum fin materials for heat exchangers are required to have moldability as well as hydrophilicity.

[0003] In response to such demands, various kinds of hydrophilic resin compositions, hydrophilic inorganic compound compositions, and fin materials coated with the following have been proposed. It can be broadly classified into an organic type mainly composed of an organic resin and an inorganic type mainly composed of an inorganic type such as silica. Regarding organic compounds, a resin composition (Japanese Patent Laid-Open No. 3-252461) in which N-methylolamide is blended as a crosslinking agent with a carboxymethylcellulose salt such as sodium, potassium, ammonium or the like, a water-soluble organic compound having a sulfonic acid group or a salt thereof introduced. Composition comprising a polymer compound and a water-soluble organic polymer compound
-50690), a cross-linking agent is added to a hydrophilic resin or a hydrophilic substance, polymerized during application and baking, and water resistant while maintaining hydrophilicity (prevention of elution into water)
The idea of trying to balance both is common.

[0004] However, such a resin composition exhibits good hydrophilicity immediately after the formation of a coating film, but when moisture adheres to the surface for a long time, the crosslinked bond is broken and the low molecular weight hydrophilicity is reduced. Since the active substance elutes and the crosslinking agent component remains on the coating surface, the concentration of the crosslinking agent component on the coating surface gradually increases. As a result, the cross-linking agent remaining in the coating film forms a cross-linking bond with another hydrophilic group in the coating film.As a result, the cross-linking density of the resin composition becomes too high, and the hydrophilicity gradually decreases, Causes a reduction in hydrophilic persistence. On the other hand, various proposals have also been made regarding an inorganic hydrophilic composition or a fin material coated with the composition. The inorganic hydrophilic composition is basically a composition in which a small amount of an organic resin is added as a binder to an alkali silicate as disclosed in JP-A-62-235377, or a fin material coated with the composition. is there. However, since such an inorganic hydrophilic composition contains a large amount of hard silica particles, it is harder to mold than an organic hydrophilic resin composition, and abrasion of a mold is large. Further, at present, a volatile press oil which does not require cleaning after molding has been used instead of a press oil which requires cleaning after molding, which has been conventionally used to reduce environmental pollution. When such a volatile press oil is used, molding difficulty and mold wear are promoted, so that it is difficult to simultaneously satisfy long-term stable hydrophilicity and moldability requirements with an inorganic hydrophilic composition. Met.

[0005]

According to the present invention, even when water is condensed on aluminum fins even when used for a long time, the water does not stop as coarse water droplets on the fin surface but flows down as a thin water layer. It has a coating film, and this coating film has excellent corrosion resistance, can prevent corrosion due to moisture and humidity, and has good moldability even when a low boiling point, low viscosity volatile press oil is used. An object of the present invention is to develop a precoated fin material for a heat exchanger and a method for producing the same.

[0006]

According to the present invention, there is provided a thin plate of aluminum or the like coated with a hydrophilic resin mainly containing an acrylic resin and a polyvinyl alcohol resin not containing a crosslinking agent other than an intramolecular crosslinking agent. It is baked and has a structure in which tile-like protrusions having a surface of 0.05 to 0.2 μm are laid, and the number of such tile-like protrusions is 0.5 to 1.5 / μm ^2.
The above-mentioned problem was solved by developing a pre-coated fin material for a heat exchanger which is present at a ratio of (1). Further, this pre-coated fin material for a heat exchanger is coated on a thin plate of aluminum or the like with a hydrophilic resin mainly composed of an acrylic resin and a polyvinyl alcohol-based resin not containing a crosslinking agent other than an intramolecular crosslinking agent. It can be obtained by a method for producing a precoated fin material for a heat exchanger by performing a baking time of 5 seconds or more at 250 ° C.

As a thin plate made of aluminum or the like used for the fin material for a heat exchanger of the present invention, 110
0, 1050, pure aluminum plate such as 1N30, 201
7, 2024, etc., Al-Cu alloy plates, 3003, 30
Al-Mn alloy plates such as 04, 5052, 5083, etc., and Al-Mg plates such as 6061
Any of a -Si alloy plate or the like may be used, and the shape may be any of a sheet and a coil. In producing the heat exchanger fin material of the present invention, the above-described thin plate such as aluminum is degreased, washed with water, and dried, and then mainly contains an acrylic resin and a polyvinyl alcohol resin containing no crosslinking agent. Is coated and baked.

In this case, prior to the hydrophilic resin coating, a base treatment for improving corrosion resistance and coating film adhesion may be performed.
For example, a thin plate of aluminum or the like is subjected to a current density of 4 to 5 in an alkaline aqueous solution having a pH of 9 to 13 and a bath temperature of 35 to 85 ° C.
A method of forming an oxide film having a thickness of 500 to 5000 ° on a thin plate made of aluminum or the like by conducting an alternating current electrolytic treatment at 0 A / dm ² for a time when the amount of electricity exceeds 80 C / dm ² (Japanese Patent Application No. Hei. No. 109341) or polyacrylic acid, polymethacrylic acid polyacrylic acid derivative, polymethacrylic acid derivative, urethane resin, urethane resin derivative, epoxy resin, epoxy resin derivative, polyamide, polyamide derivative, etc.
Or a paint containing at least 0.4 or 5 μm of a copolymer or mixture of two or more of these, or a paint containing trivalent chromium, hexavalent chromium, SiO ₂ , silicate, zirconium salt, etc., A method of forming a corrosion-resistant film by baking (JP-A-61-107198, JP-A-1-2579)
No. 5) or a method in which an aluminum plate material is subjected to phosphoric acid chromate or chromate chromate treatment by a method such as spraying or dipping to form a film having a chromium adhesion amount of 5 to 100 mg / m ² (Japanese Patent Application Laid-Open No. 62-105629). However, the method is not limited to these methods.

The hydrophilic resin used in the present invention does not contain a crosslinking agent component such as a melamine resin, a urea resin, an epoxy resin, an isocyanate compound, and an acrylic resin and a polyvinyl alcohol which do not contain a surfactant. This is a solution of water, alcohol, or a mixed solvent thereof containing a base resin as a main component. Acrylic resins include acrylic acid; acrylates such as alkali metal salts, ammonium salts and lower alkylamine salts; lower acrylates such as methyl acrylate, ethyl acrylate and propyl acrylate; methacrylic acid; Examples thereof include polymers or copolymers of methacrylates such as salts, ammonium salts and lower alkylamine salts, and lower methacrylates such as methyl methacrylate, ethyl methacrylate and butyl methacrylate.

Examples of the polyvinyl alcohol-based resin include polyvinyl alcohol or a copolymer of an ester compound having a carboxyl group or a sulfonic group such as acrylic acid, methacrylic acid, maleic acid, vinyl sulfonic acid or the like, a part of which has a hydroxyl group; A resin modified with an anionic substituent such as a hydrolyzate of an acid ester polymer or a cationic substituent such as a primary to tertiary amino group or a quaternary ammonium group is preferable. The hydrophilic resin of the present invention is used in the form of a mixture of the above acrylic resin and polyvinyl alcohol resin. This mixing ratio is more than 20% by weight and less than 70% by weight as the acrylic resin, more than 30% by weight as the polyvinyl alcohol-based resin, and
A hydrophilic resin mixed with less than 0% by weight (total 100% by weight), preferably 30 to 60% by weight of acrylic resin and 70 to 40% by weight of polyvinyl alcohol resin, and handled as a solution in which water or alcohol is dissolved. It is applied to a thin plate such as aluminum as a solvent having an easy viscosity, for example, a concentration of about 5% by weight. The coating method is not particularly limited, such as generally used roll coating and spray coating. As for the coating thickness, the projection height after baking is 0.05-0.2μ
m, but the coating is applied to a thickness of at least 0.1 μm, preferably 0.2 to 2.0 μm. If the thickness of the coating film is less than 0.1 μm, there will be portions where irregularities of sufficient height are not formed. Also 2.
Even if it exceeds 0 μm, the performance does not change and is useless.

After baking is performed after coating on a thin plate such as aluminum, the hydrophilic resin undergoes phase separation at the time of baking to form irregularities on the surface. In this case, the surface is a tile-shaped protrusion, height 0.05-0.2 μm, size 0.5-
1.5 pieces / μm ² (the diameter is 0.5 to 1.5
(inhomogeneous one having an order of μm).
The baking temperature may be a temperature at which self-crosslinking of the coating film is promoted and thermal decomposition does not occur. The temperature is preferably about 150 to 250 ° C, particularly preferably about 170 to 230 ° C. The baking time is determined in consideration of productivity, and may be 5 seconds or more. If the time is less than 5 seconds, a portion where the self-crosslinking of the coating film is not sufficient occurs. When a coating film on a thin plate of aluminum or the like is baked under such conditions, tile-like projections of an appropriate size are formed on the surface. It should be noted that suitable conditions for the size and shape of the unevenness can be determined by a simple test.

Since the hydrophilic resin of the present invention is a self-crosslinking hydrophilic resin containing no other compound as a crosslinking agent,
Even if a part of the cross-linking is broken and the low-molecular-weight hydrophilic resin part is eluted, the surface is only renewed constantly. For this reason, the functional group concentration of the crosslinking agent is increased, the crosslinking density is increased, and the hydrophilicity is not reduced. The acrylic resin, the polyvinyl alcohol resin, the copolymer resin or the acryl-modified polyvinyl alcohol resin used for the hydrophilic resin of the present invention can be of a self-crosslinking type, and the structure has a sufficiently high hydrophilic group density. It is extremely excellent as a base resin.

[0013]

A hydrophilic coating material for a thin plate such as aluminum used as a conventional precoated fin material is obtained by cross-linking a hydrophilic (water-soluble) resin with a cross-linking agent. The low molecular weight hydrophilic resin flows out into the water and the crosslinker component (hydrophobic) having a long molecular chain at the other end remains on its surface. Then, the functional group bonds to the functional group (hydrophilic group) of the hydrophilic resin. As a result, it is considered that a coating film having a high crosslinking density and a low hydrophilicity was left on the fin material surface, and good hydrophilicity could not be maintained for a long period of time. Since the hydrophilic resin of the present invention is a self-crosslinking type, a part of the cross-linking is broken, and even if the low-molecular-weight hydrophilic resin flows out, the surface having the same properties is regenerated, so that the above-mentioned problems can be avoided.

The surface of the coating film of the present invention has tile-shaped fine projections. When the surface of the coating film is roughened, the contact angle with water decreases as compared with the case of a smooth surface. This is derived from the Weuzel equation, and the unevenness on the surface of the hydrophilic resin of the present invention acts very effectively also in increasing the hydrophilicity of the fin material surface.

[0015] Recently, since low-boiling and low-viscosity press oils called cleaning-less press oils or volatile press oils are used to prevent environmental pollution, the press oil volatilizes during molding and loses lubrication. Tends to be high. Therefore, in the formability of the precoated fin material, it is necessary to consider the formability when the lubricating oil runs out = the formability in a non-lubricated state. When corrugated, tower-shaped or mountain-shaped irregularities are imparted to the coating film surface, the frictional resistance increases, and the point of contact between the mold and the coating film surface increases. Molding defects such as film peeling are likely to occur. On the other hand, when the lubricating oil (press oil) volatilizes on a smooth surface, the mold and the coating film surface come into surface contact with each other, so that the overall frictional resistance increases and molding defects easily occur. Since the entire surface of the coating film is easily peeled off, the thickness of the hydrophilic coating film layer is reduced, and the hydrophilicity, in particular, the hydrophilicity after aging (hydrophilic persistence) is likely to be reduced. Therefore,
It is preferable to provide irregularities so that the mold and the coating film surface come into contact with an appropriate area. In other words, it is presumed that it is preferable to have a surface shape in which an appropriate number of tile-shaped projections (= plateau-shaped projections) having a smooth portion area and a height within a certain appropriate range are arranged per unit area. The mechanism could not be clarified because it was not examined in detail, but the surface of a thin plate such as aluminum was coated with a hydrophilic resin and the surface was tiled with a height of about 0.05 to 0.2 μm. In the case where the projections have projections and depressions, a precoated fin material having good formability can be obtained even if a cleaning-less press oil or a volatile press oil is used because of low frictional resistance, no galling or peeling of the coating film.

In the present invention, the hydrophilic resin of the present invention is coated and baked to form tile-like projections having a diameter of 0.5 to 1.5 μm and a height of 0.05 to 0.2 μm. Having a tile-like projection of 0.5 to
It is very preferable because a shape having a shape of 1.5 particles / μm ² can be obtained. Although it is estimated, when the size (diameter) of the protrusion exceeds 1.5 μm, a smooth portion (plateau-shaped portion)
Becomes too large, resulting in the same surface as a smooth surface, and the effect decreases because the contact area with the mold becomes too large. If it is less than 0.5 μm, the size of the smooth portion is too small, so that the effect of the unevenness is not sufficiently exhibited. On the other hand, if the height of the unevenness exceeds 0.2 μm, the unevenness penetrates through the volatile press oil film, so that the lubricity is reduced. If the height is less than 0.05 μm, the effect of holding the volatile press oil is small, so that the lubricity also decreases. If the density of the tile-like projections is less than 0.5 / μm ² or exceeds 1.5 / μm ² , the area of the smooth portion becomes too large, so that the contact area with the mold increases and the moldability decreases. It is believed that.

[0017]

【Example】

(Measurement method) Tile-shaped protrusion size: The surface shape and size were measured with a scanning electron microscope at a magnification of 5,000 and 10,000 times. Projection height: After the test piece was solidified with a resin, an ultra-thin section was formed with an ultramicrotome, and the cross section was measured with a transmission electron microscope. Film thickness: The aluminum of the test piece before coating was counted by X-ray fluorescence, the test piece was counted from the coated surface after coating, and the thickness of the coating film was converted from the decrease in the count before and after the coating. Initial hydrophilicity: The water contact angle immediately after painting and baking was measured. Hydrophilicity persistence: After painting and baking, immersion in pure water for 200 hours and then measuring the water contact angle. The moldability was evaluated in a situation where drawless molding was performed using an actual fin press. (Molding conditions) Volatile press oil: RF190 (Showa Shell Sekiyu) was used, ironing rate was 55%, and molding speed was 250 sp.
m. (Evaluation) ：: very good ：: good ：: scratches on the inner surface of the color part ×: bad (buckling, color fly-out)

(Example 1, Comparative Example 1) After degreasing an IN30 aluminum plate (300 μm), the coating thickness of a 50:50 mixture of a hydrophilic resin aqueous solution of an acrylic resin and a polyvinyl alcohol resin was reduced. Change and paint,
It was baked at 200 ° C. for 15 seconds to obtain a test material, and the moldability, initial hydrophilicity, and hydrophilic durability were evaluated. For comparison, a pre-coated fin material coated with a conventionally used cellulosic hydrophilic resin containing a plate cross-linking agent and baked in the same manner was evaluated for moldability, initial hydrophilicity, and hydrophilic persistence in the same manner as in the example. went. Table 1 shows the results.
If the coating thickness of the hydrophilic resin is less than 0.1 μm, the moldability is poor, but if it is 0.1 μm or more, there seems to be no particular problem. However, since the heat conductivity is deteriorated, the thickness is preferably about 2.0 μm or less.

[0019]

[Table 1]

Example 2 The same aluminum plate as in Example 1 was degreased and then baked with a hydrophilic resin aqueous solution in which the mixing ratio of an acrylic resin and a polyvinyl alcohol resin was changed to a coating film thickness of 1.0 μm. The test materials were evaluated for moldability and hydrophilic sustainability. Table 2 shows the results. Acrylic resin ratio in hydrophilic resin is 2
If it is 0% or less, there are small tile-shaped protrusions, the height of which is low, the number of the protrusions is reduced, and the moldability is reduced. On the other hand, when the acrylic resin ratio is 70% or more, large ones increase, so that the number of projections decreases and the moldability decreases.

[0021]

[Table 2]

Example 3 After the same aluminum plate as in Example 1 was degreased, a hydrophilic resin aqueous solution having a blend ratio of 45% of an acrylic resin and 55% of a polyvinyl alcohol resin was applied to a coating film thickness of 1.0 μm. Then, the moldability and hydrophilicity persistence of the test materials obtained by changing the baking temperature and the baking time were evaluated. Table 3 shows the results. In the case of low baking temperature and low temperature baking, a reasonable coating film is formed in workability, but the self-crosslinking rate is low and the hydrophilicity persistence is insufficient. On the other hand, baking temperature 30
At 0 ° C. high-temperature baking, the thermal decomposition reaction proceeds, the tile-like projections are small and the number is reduced, and the moldability is significantly reduced.

[0023]

[Table 3]

[0024]

According to the present invention, the surface of a thin plate such as aluminum is coated and baked with a hydrophilic resin mainly composed of an acrylic resin and a polyvinyl alcohol resin without using a crosslinking agent. It has irregularities. Since the fin material of the present invention does not use a crosslinking agent, it is excellent in the long-term low contact angle hydrophilicity persistence in which the breaking of the cross-linking does not occur even if it is in contact with water for a long time, and the hydrophilicity does not decrease due to an increase in the cross-linking density. It is a fin material such as aluminum. In particular, it has the feature that good moldability can be maintained even when a volatile press oil is used during press molding, and because it is an organic polymer-based hydrophilic treatment agent, a volatile press oil is used. Even at this time, it is possible to suppress the wear of the entire press die, and it is a material with high productivity because it is a pre-coated fin material.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F28F 1/32 F28F 13/18

Claims (3)

(57) [Claims] 1. A thin plate made of aluminum or an aluminum alloy is coated and baked with a hydrophilic resin mainly composed of an acrylic resin and a polyvinyl alcohol resin not containing a crosslinking agent other than an intramolecular crosslinking agent, so that the surface is high. 0.0
A precoated fin material for a heat exchanger having a structure in which tile-shaped projections of 5 to 0.2 μm are spread, and the tile-shaped projections are present at a ratio of 0.5 to 1.5 / μm ² . 2. A thin plate of aluminum or an aluminum alloy is coated with a hydrophilic resin mainly containing an acrylic resin and a polyvinyl alcohol resin not containing a crosslinking agent other than an intramolecular crosslinking agent, and a baking temperature of 150 to 250.
A method for producing a precoated fin material for a heat exchanger, wherein a baking treatment is performed at a temperature of 5 ° C. for a baking time of 5 seconds or more. 3. The mixing ratio of the acrylic resin and the polyvinyl alcohol resin as hydrophilic resins is more than 20% by weight and less than 70% by weight of the acrylic resin, more than 30% by weight and less than 80% by weight of the polyvinyl alcohol resin, 3. The method for producing a precoated fin material for a heat exchanger according to claim 2, wherein the thickness of the coated film is at least 0.1 [mu] m.