JP5753698B2 - Aluminum fin for heat exchanger and heat exchanger - Google Patents

Description

  The present invention relates to an aluminum fin for a heat exchanger and a heat exchanger using the same. In the present specification, “aluminum” is a general term for metals and alloys mainly composed of aluminum, and is a concept including pure aluminum and aluminum alloys.

As a heat exchanger in an air conditioner or a refrigerator, a cross fin tube type heat exchanger configured by combining a large number of plate fins and tubes (heat transfer tubes) is frequently used.
Conventionally, aluminum has been used for the plate fin because it is lightweight and has excellent thermal conductivity and workability.

In producing a cross fin tube, first, an assembly hole having a fin collar portion with a height of about 1 to 4 mm for inserting and fixing the heat transfer tube into a heat exchanger fin made of an aluminum plate is pressed. Thus, the plate fin is produced.
Next, after laminating the obtained plate fins, a separately prepared heat transfer tube is inserted into the assembly hole.

As the heat transfer tube, a tube obtained by subjecting the inner surface of a copper tube or a copper alloy tube to groove processing by rolling or the like, as well as performing regular cutting and hairpin bending processing is provided.
Next, the heat exchanger tube is manufactured through a process of expanding and fixing the heat transfer tube to the aluminum plate fin and brazing the U-bend tube at the end of the heat transfer tube opposite to the side subjected to the hairpin bending process.

  In such an air conditioner heat exchanger, for example, in an outdoor unit during heating operation, moisture in the air adheres to the surface of the aluminum fin as condensed water, and the outside air temperature is low (2 ° C. or lower). The condensed water freezes and forms frost. Since the surface of the metal material is generally poor in hydrophilicity, this condensed water exists on the fin surface in a semicircular shape or in a bridge shape between the fins, and eventually forms frost. This hinders the flow of air between the fins, increases ventilation resistance, and causes a significant decrease in heat exchange efficiency. In order to improve the heat efficiency of the heat exchanger, it is necessary to quickly remove condensed water on the fin surface before freezing and to make the surface difficult to frost.

The following two measures can be considered as this solution.
(1) A highly hydrophilic film is formed on the surface of the aluminum alloy fin, and the condensed water flows down as a thin water film.
(2) A water-repellent film is formed on the surface of the aluminum alloy fin so that condensed water is removed early so that it does not easily remain on the surface.

Various proposals have been made for the water repellent coating (2) in which the surface of the aluminum alloy fin is water repellent and the condensed water is less likely to stay.
For example, Patent Document 1 discloses that a ratio of a solution composed of a silicone-based or fluorine-based resin compound and a solid content in the solution is 10 to 40% by weight, a specific surface area of 50 m ² / g or more, and an average particle There is disclosed a water-repellent coating composition comprising inorganic fine particles having a diameter of 4 μm or less and further subjected to hydrophobic treatment on the surface.
Patent Document 2 discloses a solution comprising a silicone-based resin compound, a resin modifier having at least two types of functional groups in the molecule, and a particle size of 4 μm or less, and a composition ratio of 5 to 5 for the solid content in the solution. A water-repellent coating composition comprising 60% by weight of inorganic fine particles is disclosed.

In Patent Document 3, 0.2 parts by weight or more of a fluorine-based or silicon-based water repellent agent and an average particle size of 0.5 to 1 part by weight on the surface of an aluminum plate with respect to 1 part by weight of a thermosetting resin as a binder. 1 mg / dm ² or more of a film made of a mixture prepared by mixing 4 to 8 parts by weight of one or more mixed powders selected from the group consisting of 5 μm alumina, zirconia, titania and silicon carbide. A surface-treated aluminum fin material is disclosed.

Patent Document 4 contains 0.2 part by weight or more of hydrophobic silica and 0.1 part by weight or more of a water repellent having a perfluoroalkyl group with respect to 1 part by weight of the thermosetting resin solid content. A water-repellent paint characterized by the above is disclosed.
In Patent Document 5, a base film made of an organic resin containing organic or inorganic fine particles (A) is formed on at least one surface of a metal material, and a finish film showing water repellency is formed on the base film. A water-repellent metal coating material is disclosed in which the average particle size of the fine particles (A) is 1.5 times or more larger than the film thickness of the organic resin undercoat.

JP-A-3-244680 Japanese Patent Laid-Open No. 5-222339 JP-A-8-285491 JP-A-8-269367 JP 2009-12238 A

However, although Patent Documents 1 to 5 achieve excellent water repellency, it cannot be said that characteristics that suppress frost formation, that is, difficult frost formation are sufficiently obtained. Furthermore, there are some that are difficult to maintain water repellency.
For example, the techniques described in Patent Documents 1 and 2 have a problem that particles in the water-repellent coating easily fall off. Patent Document 3 also has a problem that particles such as alumina are easily dropped, as in Patent Documents 1 and 2. The technique of Patent Document 4 needs to be in a state where the hydrophobic silica is exposed on the surface of the film, and there is a problem that the hydrophobic silica is likely to fall off.

  The technique of Patent Document 5 was made under the problem of preventing the dropout of particles such as Patent Documents 1 and 2, and the effect of preventing the particle dropout after forming the finish film can be expected. Particles may fall off before the coating is formed, leading to performance degradation and contamination of the production line.

Thus, the current situation is that a water-repellent coating suitable for stable mass production has not been obtained while maintaining the initial performance.
Furthermore, in recent years, in order to meet demands for reducing the weight of heat exchangers, improving the thermal efficiency, and further reducing the size of the heat exchanger, a design in which the intervals between aluminum fins are made increasingly narrower has been adopted. In such a cross fin tube type heat exchanger having a narrow fin interval, the aluminum fin material coated with the water-repellent coating disclosed in Patent Documents 1 to 5 has a large contact angle with water, and therefore has a smaller condensation. Even with water, a bridge of condensed water is formed between the fins, increasing ventilation resistance and frosting fast.

  Therefore, instead of focusing on obtaining a water-repellent coating film that maximizes the contact angle with water as far as possible, it has excellent anti-frosting properties by selecting an appropriate coating material composition. A new problem has been found that it is necessary to develop aluminum fins that can be obtained.

  An object of the present invention is to propose an aluminum fin having excellent anti-frosting property and a heat exchanger using the same even in a cross fin tube type heat exchanger having a narrow fin interval (fin interval of 2 mm or less). is there.

1st invention is the aluminum fin for heat exchangers which consists of the board | substrate which consists of aluminum, and the 1 layer or multiple layer coating film formed in the surface of this board | substrate,
Among the coating films, the component contained in the outermost coating film is solid mass%, and the fluororesin containing a perfluoroalkyl group is A, and the sum of one or both of the urethane resin and the epoxy resin is B. When
A + B ≧ 95%
A ≧ 5 0%, B ≧ 3 0%
Ru heat exchanger aluminum fins near, characterized in that it.

A second invention is a cross formed by laminating a large number of fins made of aluminum, and inserting and placing the fins in a cylindrical collar portion provided on the fins so that the heat transfer tube and the numerous fins are integrally assembled. A heat exchanger comprising fin tubes,
The fin is formed using the aluminum fin for heat exchanger of the first invention,
Stacking pitch of the fins, Ru heat exchanger near, characterized in that it is 2mm or less.

  The aluminum fin for a heat exchanger of the first invention (hereinafter, simply referred to as “fin” as appropriate) has a coating film of the outermost layer having the above-mentioned special component structure, and a fluororesin containing a perfluoroalkyl group The main component is one or both of a urethane resin and an epoxy resin. Thereby, the fin of this invention exhibits the characteristic that it is hard to form the bridge of condensed water between fins compared with the coating film which pursued only the conventional water repellency, and also it is hard to form frost. And by including a fluororesin containing a water-repellent perfluoroalkyl group, the contact angle with water is optimized without adding particles, an increase in ventilation resistance is suppressed, and a coating surface that is difficult to frost is obtained. It is possible.

  The heat exchanger of the second invention is configured using the above-described excellent fins. Therefore, it is excellent in sustainability of difficult frost formation, and even when the fin pitch is 2 mm or less, an increase in ventilation resistance due to frost formation is effectively suppressed, and good heat exchange performance can be maintained for a long time. .

Explanatory drawing which shows the coating-film structure of the aluminum fin for heat exchangers in an Example. Explanatory drawing which shows another example of the coating-film structure of the aluminum fin for heat exchangers in an Example. Explanatory drawing which shows the structure of the heat exchanger in an Example. Explanatory drawing shown about the water droplet contact angle (alpha) in an Example.

  As described above, the fin of the present invention has a single layer or a plurality of layers. One layer here means a layer coated with the same type of coating film, not only when the same type of coating film is applied once, but also by coating the same type of coating film a plurality of times. The film is also a single layer. Therefore, a plurality of layers means a case where different types of coating films are laminated.

  In the case of a multi-layer coating film, for example, an epoxy coating film can be provided as the first layer, and the outermost layer can be provided thereon. Moreover, it is preferable to provide a base treatment layer on one surface or both surfaces of the aluminum substrate. As the base treatment layer, for example, a coating type or reaction type phosphoric acid chromate or a chromium-free chemical conversion film layer is employed.

And the component contained in the coating film of the outermost layer, as described above, is a solid content by mass%, A is a fluororesin containing a perfluoroalkyl group, and B is the sum of one or both of a urethane resin and an epoxy resin. when a a + B ≧ 95%, and, a ≧ 5 0%, a B ≧ 3 0%. Accordingly, the outermost coating film has a fluororesin and urethane resin containing a perfluoroalkyl group as main components, a fluororesin containing a perfluoroalkyl group and an epoxy resin as main components, or a perfluoroalkyl group. One of the main components is a fluororesin containing an alkyl group, a urethane resin, and an epoxy resin.

By including a fluororesin containing a water-repellent perfluoroalkyl group, it is possible to optimize the contact angle with water without adding particles, suppress an increase in ventilation resistance, and obtain a coating surface that is difficult to frost. Is possible.
On the other hand, the urethane resin and the epoxy resin are basically hydrophilic. However, when an appropriate amount is contained in the fluororesin containing a perfluoroalkyl group, in addition to improving the adhesion of the coating film, the water droplet contact angle is remarkable. It has been found that the frost resistance is effectively improved without reduction (= without significant reduction in water repellency). By adding at least one of a hydrophilic urethane resin and an epoxy resin, it is considered that the water-repellent portion of the perfluoroalkyl group is oriented on the surface of the coating film to enhance the water-repellent effect.

When A + B is less than 95%, that is, when components other than A and B are contained in an amount of 5% or more, water repellency is lowered, or the above-mentioned frost formation in the coating film cannot be sufficiently obtained. On the other hand, components other than A and B may be added as long as they are less than 5%. Preferably, A + B ≧ 99%, more preferably A + B = 100%, and 0 except for A + B.
Further, it is possible to contain particles such as alumina as in the prior art. However, if the content is too large, there is a problem that the particles are easily dropped, which is not preferable.

In the fin, A ≧ 50%, are B ≧ 30%. When A is 50% or more, after mixing A and B, a part of the paint is hard to solidify before coating, and it is easy to apply uniformly on the substrate surface, and the paintability is excellent. Moreover, it is excellent in the adhesiveness of the formed coating film because B is 30% or more. In particular, in the case of so-called pre-coated fins in which a paint is applied on an aluminum plate in advance (before cutting into fin shapes) using a coating method such as a roll coating method or a bar coating method, by press working Even if it cut | disconnects to a fin shape, since it is excellent in the adhesiveness of a coating film, a coating film becomes difficult to peel off.

As the fluororesin containing a perfluoroalkyl group, for example, a perfluoroalkyl group-containing polyester or a perfluoroalkyl group-containing acrylic resin is desirable.
As said urethane resin, the thing more than pencil hardness HB is preferable.

Further, the coating film of the outermost layer, has preferably to be water droplet contact angle of 90 ° ~150 °. That is, it is preferable that the outermost coating film has an appropriate water repellency. When the water droplet contact angle is less than 90 °, the coating film is in a hydrophilic state, and there is a possibility that the removal of cohesive water generated on the coating film surface may be delayed. On the other hand, when the water droplet contact angle exceeds 150 °, the water repellency is too strong, and even if there is little adhesion water, there is a possibility that it becomes close to a sphere and easily forms a bridge between narrow fins.

  The method of applying the coating film is not particularly limited, and various known methods such as a roll coating method, a bar coating method, a dip coating method, and a spray method can be employed. Moreover, various conditions can be selected according to the kind of each synthetic resin paint etc. also about the hardening conditions for making it harden | cure after apply | coating a coating material to the one or both surfaces of the said board | substrate, ie, baking conditions.

An aluminum fin for a heat exchanger according to an embodiment of the present invention will be described.
As shown in FIG. 1, the heat exchanger aluminum fin 1 of this example includes a substrate 10 made of aluminum and a single layer of water-repellent coating film 2 formed on the surface of the substrate 10. In addition, sample No. described later. 2, a corrosion-resistant undercoat film 3 was formed between the water-repellent coating film 2 and the substrate 10 to form a two-layer coating film as shown in FIG. In addition, between the board | substrate 10 and the coating film 2 or the coating film 3, sample No. mentioned later is mentioned. In addition to 4, a chemical conversion film 4 made of phosphate chromate is formed.

In this example, a plurality of examples (samples No. 1 to 5, 14 , 15 ), reference examples (samples No. 10, 11 , 12, 13 ) and comparative examples in which the components of the outermost layer coating film 2 were changed were used. (Sample Nos. 6-9, 16, 17) were prepared and their performance was evaluated. As will be described later, specific evaluation was performed by preparing a heat exchanger composed of a cross fin tube and performing evaluation by preparing a flat sample having a completely similar coating film configuration.

First, Table 1 shows the components of the coating film of each sample.
In this example, the fluororesin, urethane resin and epoxy resin containing a perfluoroalkyl group were specifically selected from the following and used in combination.
<Fluorine resin containing perfluoroalkyl group>
a. EC450 made by Ohara Palladium
b. AGE060 made by Asahi Glass
<Urethane resin>
a. ADEKA HUX350
b. ADEKA H1
<Epoxy resin>
a. ADE101-50 made by ADEKA
b. ADE051R made by ADEKA

Moreover, as known from Table 1, the actual施例Sample No. 1 to 5, 14 and 15, the components contained in the outermost coating film 2 are solid mass%, and when the fluororesin containing a perfluoroalkyl group is A and the urethane resin + epoxy resin is B, a + B ≧ 95%, a ≧ 5 0%, meets all B ≧ 3 0%. Sample No. 5 contains 2% of isocyanate as a crosslinking agent in addition to the fluororesin and urethane resin, and A + B = 98%. Sample No. 1-4 , 14 and 15 are A + B = 100%.

Sample No. as a comparative example. In No. 6, the outermost coating film contains less than 10% urethane resin without containing epoxy resin.
Sample No. as a comparative example. In No. 7, the outermost coating film contains 100% of a fluororesin containing a perfluoroalkyl group, and does not contain a urethane resin or an epoxy resin.
Sample No. as a comparative example. In No. 8, the outermost coating film contains 100% urethane resin and does not contain a fluororesin containing a perfluoroalkyl group.
Sample No. as a comparative example. 9 contains the above fluororesin and urethane resin, but also contains 25% amino resin, specifically, melamine resin (DIC becamine J101), and A + B = 75%.
Sample No. as a comparative example. In No. 16, the outermost coating film contains less than 10% of a fluororesin containing a perfluoroalkyl group.
Sample No. as a comparative example. In No. 17, the outermost coating film contains less than 10% urethane resin without containing an epoxy resin.

  In preparing the sample as a flat sample, first, as a substrate, an JIS A 1050-H26, 0.1 mm thick aluminum plate is prepared, and phosphoric acid chromate is immersed in the surface of the substrate. A chemical conversion film was formed. Sample No. For No. 4, only degreasing was performed with a weak alkaline degreasing agent, and no chemical conversion film was formed.

Thereafter, sample No. About 1, 2, 4-17, the coating material used as the coating film 2 of the outermost layer was baked on the conditions hold | maintained at 100 degreeC for 20 minutes by the immersion method. The thickness of the water repellent coating film 2 was set to 1.5 μm.
Sample No. As for No. 3, an epoxy resin paint to be a corrosion-resistant coating film 3 was applied by a dipping method and baked under the condition of maintaining at 170 ° C. for 20 minutes. The thickness of the corrosion-resistant coating film 3 was set to 1.0 μm. On the upper layer of the coating film 3, the outermost coating film 2 was applied under the same conditions as described above.

Next, the manufacturing method of a heat exchanger is demonstrated.
As shown in FIG. 3, the heat exchanger 6 used in this example is a cross fin tube type in which a number of plate fins made of the aluminum fins 1 for heat exchanger and a heat transfer tube 61 that passes through these plate fins are combined. is there.

  In producing the heat exchanger 6, first, as described above, a JIS A 1050-H26, 0.1 mm thick aluminum plate was prepared as a substrate, and the substrate was subjected to immersion treatment with phosphoric acid chromate. A chemical conversion film was formed on the surface. Sample No. For No. 4, only degreasing was performed with a weak alkaline degreasing agent.

Next, an assembly hole (not shown) having a fin collar portion having a height of about 1 to 4 mm for inserting and fixing the heat transfer tube 61 into the fin 1 made of an aluminum plate is pressed to form the plate fin. Make it.
Next, after laminating the obtained plate fins, a separately prepared heat transfer tube 61 is inserted into the assembly hole.

The heat transfer tube 61 is usually provided with a copper tube or a copper alloy tube subjected to grooving by rolling or the like, and subjected to regular cutting and hairpin bending.
Next, the heat exchanger 6 is manufactured through a process of expanding and fixing the heat transfer tube 61 to the fin 1 and brazing the U-bend tube 62 at the end of the heat transfer tube opposite to the side subjected to the hairpin bending process. The
As for the size of each part, the width W of the fin 1 was 25.4 mm, the length L was 294 mm, the lamination pitch P of the fins was 1.4 mm, and the width D of the entire heat exchanger 6 was 300 mm.

The heat transfer tube 61 has an outer diameter: 7.0 mm, a bottom wall thickness: 0.45 mm, a fin height: 0.20 mm, a fin apex angle: 15.0 °, a spiral angle: 10.0 °, and an inner surface with a spiral groove A grooved copper tube was adopted.
The obtained heat exchanger 6 was heated at 140 ° C. for 20 minutes for degreasing.
The surface of the fin 1 was painted using an immersion method in which the entire heat exchanger after degreasing was immersed in a paint. The coating conditions were the same as in the case of the flat plate sample described above.

<Evaluation of water droplet contact angle>
For each sample, the water droplet contact angle was evaluated using the flat plate-shaped sample described above.
In the evaluation method, as shown in FIG. 4, 2 μl of pure water is dropped on the fin surface, and the contact angle α between the water droplet 8 and the surface of the coating film 2 is measured.
The evaluation results are shown in Table 2.

<Evaluation of difficult frost formation>
Using each of the samples and the heat exchanger described above, the evaluation of difficult frost formation was performed.
In the evaluation, the heat exchanger is installed in an environment where the atmospheric temperature (dry bulb temperature) is 2 ° C. and the wet bulb temperature is 1 ° C., and a refrigerant 91 of −5 ° C. is supplied into the heat transfer tube at a flow rate of 20 kg / hr. It carried out on the driving | running conditions that the inlet wind speed of the wind which flows and distribute | circulates shall be 1.5 m / sec. And the ventilation resistance of the wind 92 was measured by the differential pressure | voltage at the entrance side and exit side of a heat exchanger, and it evaluated by the operation time until the value became 500 Pa. The operating time until the draft resistance reaches 500 Pa is from a heat exchanger using an unpainted material prepared separately for comparison (adopting a fin that exposes the aluminum substrate surface and does not form any paint film, etc.) Also, those that extended for 20 minutes or more were regarded as acceptable (◯), and those that were less than 20 minutes were regarded as unacceptable (x).
The evaluation results are shown in Table 2.

<Evaluation of coating film adhesion>
About each sample, the coating-film adhesiveness was evaluated using the flat plate-shaped sample mentioned above.
Specifically, a hammer tip having a tip weight of 0.9 kg was wrapped with 8 sheets of Nippon Paper Crecia Co., Ltd. Kimwipe on a sample placed with the surface of the coating film 2 facing up. The surface of the coating film 2 was slid, and the number of sliding times when the aluminum plate was exposed was measured. Those having the number of sliding times of 5 or more were evaluated as “a” as having excellent adhesion. Those having the number of sliding times of 2 times or more and 4 times or less were evaluated as “b” as having adhesiveness. The said sliding frequency | count of 1 or less was evaluated as "c" not having adhered. In addition, this evaluation is relative evaluation and does not distinguish an Example and a comparative example.
The evaluation results are shown in Table 2.

<Evaluation of paintability>
The paintability of the paint was evaluated for each sample.
Specifically, after mixing A and B, a part of the paint that did not solidify before coating was designated as “a” as having excellent paintability. In addition, a solidified part of the paint was regarded as “b” because the paintability was not good. In addition, this evaluation is relative evaluation and does not distinguish an Example and a comparative example.
The evaluation results are shown in Table 2.

As is known from Table 2, the examples of the present invention (Sample Nos. 1 to 5, 14 and 15) had good frost resistance.
On the other hand, Sample No. No. 6 had a small content (B) of urethane resin + epoxy resin as a component of the coating film 2 of the outermost layer, and the hard frosting property was not good.
Sample No. of Comparative Example No. 7 contained neither the urethane resin nor the epoxy resin as a component of the outermost layer coating film 2, and the frost resistance was not good.
Sample No. of Comparative Example No. 8 did not contain a fluororesin as a component of the outermost layer coating film 2, and was difficult to form.
Sample No. of Comparative Example No. 9 had a small total amount (A + B) of the fluororesin and the urethane resin as the components of the outermost coating film 2, and the frost resistance was not good.
Sample No. of Comparative Example No. 16 had a small content (A) of the fluororesin as a component of the outermost coating film 2 and did not have good frost formation.
Sample No. of Comparative Example No. 17 had a small content (B) of urethane resin + epoxy resin as a component of the outermost-layer coating film 2, and had a poor frost formation property.

  Moreover, about the water droplet contact angle, the Example of this invention has stopped in the range which shows moderate water repellency in the range of 90 degrees-150 degrees. It can be seen that even within this range, very excellent frost formation can be obtained.

In addition, among the above samples , those in which B is 30% or more (sample Nos. 1 to 5, 10, 13 to 15) are compared with those in which B is less than 30% (samples No. 11 and 12). Thus, it can be seen that the formed coating film is excellent in adhesion.

Moreover, among the above samples , those in which A is 50% or more (sample Nos. 1 to 5, 11, 12, 14, 15) are those in which A is less than 50% (samples No. 10 and 13). In comparison, it can be seen that part of the paint is hard to solidify and is excellent in paintability.

DESCRIPTION OF SYMBOLS 1 Aluminum fin for heat exchangers 10 Board | substrate 2 Coating film of outermost layer 6 Heat exchanger

Claims (3)

A heat exchanger aluminum fin comprising a substrate made of aluminum and one or more coating films formed on the surface of the substrate,
Among the coating films, the component contained in the outermost coating film is solid mass%, and the fluororesin containing a perfluoroalkyl group is A, and the sum of one or both of the urethane resin and the epoxy resin is B. When
A + B ≧ 95%
A ≧ 5 0%, B ≧ 3 0%
An aluminum fin for a heat exchanger. The aluminum fin for heat exchangers according to claim 1, wherein the outermost-layer coating film has a water droplet contact angle of 90 ° to 150 °. Heat exchange consisting of a cross fin tube in which a large number of fins made of aluminum are laminated and inserted into a cylindrical collar portion provided on the fin, and the heat transfer tube and the fins are assembled together. A vessel,
The fin is formed using the aluminum fin for heat exchanger according to claim 1 or 2 ,
The heat exchanger according to claim 1, wherein a lamination pitch of the fins is 2 mm or less.

Images