JPH0541718B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to an aluminum plate material having an extremely thin electrodeposited coating and having excellent corrosion resistance and workability. More specifically, regarding pre-coated fin materials for heat exchangers made of aluminum or aluminum alloy used for heat exchangers such as indoor and outdoor heat exchangers or automobile radiators, the material has excellent corrosion resistance, hydrophilicity, and workability on the surface. The present invention relates to a precoated fin material for heat exchangers on which an organic coating layer is formed. [Prior Art] Aluminum or aluminum alloys, which have excellent workability and thermal conductivity, are widely used as fin materials for heat exchangers. Conventionally, fin materials for heat exchangers have often been used as thin sheet bases without surface treatment. However, when fin materials without surface treatment are used in heat exchangers, the aluminum reacts with water vapor in the air and moisture generated by the cooling action, causing early corrosion of the aluminum and the formation of so-called white rust (aluminum hydroxide). There was a problem that occurred. To prevent this white rust, aluminum fins for heat exchangers are made by forming inorganic coatings such as boehmite, chromate, and water glass on the surface of aluminum or aluminum alloy thin plates, or aluminum fins for heat exchangers are roll-coated with organic coatings. It has come to be used. However, with inorganic coatings such as boehmite coatings and chromate coatings, water that condenses on the aluminum fins of the heat exchanger becomes coarse water droplets and stays on the fin surfaces, and these water droplets create bridges between the fins and narrow the gaps. This results in increased ventilation resistance and a significant decrease in thermal efficiency. On the other hand, inorganic coatings such as water glass are generally relatively hydrophilic, so coarse water droplets are difficult to form, and although there is little decrease in thermal efficiency in this respect, the coating is extremely hard. There were problems in that the coating film was prone to cracking and peeling during fin forming such as press working, and the mold for forming the fins wore out in a short period of time. When roll-coating an organic paint film, there is a risk of foreign matter getting mixed in during the painting process, and there may be many defects such as pinholes or missing coatings on the paint film surface, or local variations in film thickness on the paint film surface. is likely to occur,
Therefore, there were drawbacks such as the desired corrosion resistance could not be obtained unless the film thickness was increased. However, increasing the film thickness tends to cause cracking and peeling of the coating during molding, and also causes a decrease in thermal conductivity. [Problems to be Solved by the Invention] The first invention of the present invention is to form an ultra-thin electrodeposited coating film with good corrosion resistance on the surface of an aluminum or aluminum alloy thin plate, thereby improving corrosion resistance and improving the fin forming process after forming the coating film. The purpose of the present invention is to provide an aluminum precoated fin material with excellent workability (less cracking and peeling of the coating film and less mold wear during press working). The second invention of the present invention provides corrosion resistance and
An object of the present invention is to provide an aluminum precoated fin material that has excellent workability during fin molding after coating film formation and also has good hydrophilicity. [Means for Solving the Problems] As a result of repeated experiments to find a method for forming an organic coating film on the surface of an aluminum fin material and obtaining excellent corrosion resistance, the present inventors have developed an extremely thin electrodeposition coating. It is effective to impart corrosion resistance to thin aluminum sheets without losing the processability (cracking or peeling) of the coating film, and it is also effective to add water-soluble cellulose resin (e.g. cellulose and its esters or It was discovered that uniform hydrophilicity could be imparted by using ether (a general term for derivatives such as ether), and this invention was completed. This water-soluble cellulose resin has excellent chemical resistance to lubricating oil and trichlene cleaning, which are used when processing raw aluminum sheets into heat exchanger fins, and has a large number of hydroxyl groups, so it has extremely good hydrophilicity. . In addition, polyvinyl alcohol (including its derivatives), polyimide resin, polyamide resin, poly(meth)acrylic acid resin (including its derivatives), polyethylene oxide resin (including its derivatives), or copolymers thereof, and Mixtures of two or more of these can also be used. That is, the precoated fin material for heat exchangers of the first aspect of the present invention is basically an aluminum or aluminum alloy thin plate, and a corrosion-resistant coating film with excellent workability is formed on the surface by ultra-thin electrodeposition coating. The second invention is further characterized in that a thin aluminum plate on which a hydrophilic organic coating film is formed on the electrodeposited coating film is used as a fin material of the heat exchanger. The electrodeposition coating used here can be either anionic or cationic, derived from water-soluble polymers, emulsions, colloidal dispersions, etc. Resin types include acrylic, epoxy, and urethane. Based on resins, oil-based resins, polybutadiene resins, fluororesins, polyethylene resins, etc. can be used, and depending on the purpose, various pigments, neutralizing agents (organic acids), solvents (hydrophilic, hydrophobic),
It may be added with various additives (dispersant, antifoaming agent, leveling, etc.), or may be added with an inorganic electrolyte such as chromic acid or chromate. Various types of water-soluble resins can be used for the hydrophilic organic coating, and among them, it is particularly desirable to use one or both of water-soluble cellulose resins and polyvinyl alcohol. The corrosion resistance of the heat exchanger fin material of the present invention is basically achieved by an extremely thin electrodeposited coating film formed as a base coat. Electrodeposition coating involves electrophoretically depositing paint resin ionized in an aqueous solution onto the object to be coated, which is an electrode.
It was confirmed that there is a method of forming an insoluble coating film, and that a coating film with strong adhesion can be obtained. moreover,
It is easier to control the coating thickness than the roll coating method, and a uniform coating can be obtained without any local increase or decrease in the coating thickness. In addition, there are no factors that can cause paint film defects such as foreign matter being mixed in during painting, which eliminates wasted paint, and it has been discovered that corrosion resistance equivalent to or better than that of roll coating can be obtained with a much thinner film thickness. It was found that this is a very effective coating method for applying to corrosion-resistant aluminum sheets. In all cases, heat exchanger fins are first required to have a high degree of corrosion resistance, as mentioned above. The hydrophilicity of the heat exchanger fin material of the second invention is basically expressed by the organic coating film made of a water-soluble resin formed on the electrodeposited coating film. Moreover, since the electrodeposition coating film used as a base coat is a coating film with high uniformity, it is quite effective as a base coat, as it can improve the uniformity of the upper layer coating film when the upper organic coating film is formed. Therefore, by combining the two, this second invention has excellent corrosion resistance and hydrophilicity, and since it is an organic coating film, it also has excellent processability during fin molding after coating film formation. It has now become possible to obtain a fin material for heat exchangers that has a membrane. Therefore, bridging of condensed water can be prevented, making it possible to realize a compact, highly efficient air conditioner with a narrow fin pitch. [Detailed Description of the Invention] The aluminum thin plate to which this invention is applied may be either a JIS 1100, JIS 1050 pure aluminum plate or an aluminum alloy plate containing various alloying elements depending on the purpose. The shape may be either a sheet or a coil. In manufacturing the pre-coated fin material for heat exchangers of this invention, the surface of the aluminum thin plate described above is cleaned by degreasing, washing with water, and drying, and then a corrosion-resistant organic coating is formed by electrodeposition coating, and moisture is removed by drying. remove. When using an anionic paint, an aluminum plate is used as an anode to form an electrodeposited coating.
Electrolyze at 20-110V using a stainless steel plate as the counter electrode. The thickness of the coating film can be controlled by the current application time, bath temperature, and bath concentration. When using cationic paint, use an aluminum plate as the cathode and a stainless steel plate as the counter electrode.
~100V is electrolyzed, and the thickness of the coating film can be controlled by the current application time, bath temperature, and bath concentration. The thickness of the coating film in the present invention is much thinner than that in ordinary electrodeposition coating, and is sufficient to achieve the purpose, with a dry film thickness of 0.2 per side.
A thickness of about 4.0 μm is necessary and sufficient, and therefore, even when this electrodeposition-coated aluminum plate material is subjected to fin processing, the coating film itself will not crack or peel. However, if the dry film thickness is set to about 20 to 25 μm on one side as usual, apart from corrosion resistance, it will not only lose economic efficiency but also processability, and the coating will be prone to cracking and peeling, greatly reducing processability. It is necessary to avoid this as it is limited. Thereafter, this electrodeposition coating film is dried with warm air at a temperature ranging from room temperature to less than 150°C, and then a water-soluble resin having hydrophilic properties is applied and baked. After forming the electrodeposition coating film in the above-mentioned process, instead of drying, baking may be performed at a temperature of 150 to 320° C., and then a hydrophilic water-soluble resin may be applied and baking may be performed. Electrodeposition coating to form a corrosion-resistant organic coating film can be either anionic or cationic, and the resin type used can be acrylic, epoxy, or urethane-based resins. The film thickness of electrodeposition coating can be arbitrarily selected by changing the electrolytic conditions, but the dry film thickness is 0.2 on one side.
The range is ~4.0μm, and from the standpoint of performance and economy, the optimum dry film thickness is 0.3~1.5μm on one side.
If the thickness is less than 0.2 μm, the film thickness will be too thin and the corrosion resistance will deteriorate significantly. On the other hand, if the film thickness exceeds 4.0 μm, no further improvement in corrosion resistance can be expected, and the heat transfer properties of the heat exchanger will decrease. For drying of electrodeposited coatings, it is sufficient to remove moisture from the coating using warm air from room temperature to less than 150℃, but if you perform baking treatment at a temperature of 150 to 320℃ beforehand, the hydrophilic water-soluble The hydrophilicity of the formed resin is further improved. The baking temperature and time for electrodeposited coatings vary depending on the type and composition of the coating, but usually the baking temperature is about 150-320℃ and the baking time is 1-320℃.
It is preferable to set the time to about 120 seconds. If it is less than 150°C, curing will be insufficient, and if it exceeds 320°C, the resin will thermally decompose, and there is a risk that sufficient corrosion resistance will not be ensured. If the baking time is less than 1 second, poor curing is likely to occur, and even if the baking time is longer than 120 seconds, the performance of the coating film will not change, so it is virtually meaningless. This time is extremely short compared to conventional electrodeposition coating and is sufficient. Note that a hot air oven or an infrared oven can be used for this baking. Further, when applying a hydrophilic organic coating film on an electrodeposition coating film, the cost can be reduced by baking the organic coating film after coating (2 coats/1 bake). After forming a corrosion-resistant organic coating film, it is desirable to use a water-soluble cellulose resin as disclosed in JP-A-61-101798 as the hydrophilic water-soluble resin formed on the surface. Hydrophilicity can be further improved by adding 0.05 to 5 wt % of a sea surfactant whose hydrophobic group moiety has a molecular weight of 400 or less as shown in the figure below. [Example] Examples of the present invention are shown below. (Example 1) After degreasing an aluminum alloy rolled plate coil equivalent to JIS3003 with a thickness of 0.115 mm and a width of 250 mm,
After washing with water and drying, electrodeposit the anionic type: acrylic resin, product name SVIER ED AL-50B, manufactured by Shinto Toyo Co., Ltd., and the cationic type: product name Sexade #1000, manufactured by Shinto Toyo Co., Ltd. was used to bake at 250°C for 20 seconds to form a coating film with a dry film thickness of 0.2 to 4.0 μm on one side. The corrosion resistance of the precoated fin material thus obtained was evaluated by a salt spray test. (Comparative Example 1) Regarding the same rolled aluminum alloy plate coil as in Example 1, after degreasing, washing with water, and drying, a water-soluble acrylic resin was baked at 250°C for 20 seconds, and one side was coated with a dry film thickness.
It was coated with a bar coater to a thickness of 0.4 to 3.0 μm. The corrosion resistance of the precoated fin material thus obtained was evaluated in the same manner as in Example 1.
Table 1 shows the evaluation results of the corrosion resistance of the coating film of each heat exchanger fin material of Example 1. Table 2 shows the evaluation results of the corrosion resistance of Comparative Example 1. As can be seen from Tables 1 and 2, even with the method of roll coating water-soluble acrylic resin,
The thicker the film, the better the corrosion resistance. However, the film thickness of electrodeposition coating is much thinner than the roll coating method, for example, the roll coating method has a dry film thickness of 1.5 μm on one side.
It can be seen that good results are obtained with electrodeposition coating, but good results are obtained with a dry film thickness of 0.4 μm on one side in electrodeposition coating.

【table】

[Table] * Standard

[Table] (Example 2) An aluminum alloy rolled plate coil equivalent to JIS 3003 with a thickness of 0.115 mm and a width of 250 mm was degreased, washed with water, dried, and then electrocoated with anion type: acrylic resin, product name: Esbia AL- 50B, Shinto paint
Co., Ltd. and cationic type: Acrylic resin, product name Succeed #1000, made by Shinto Toyo Co., Ltd., was dried with warm air to form a coating film of 0.2 to 4.0 μm, and then water-soluble Coat with cellulose resin and heat at 230℃ for 20 minutes.
It was baked for seconds to form a coating film of 0.6 μm on one side. The hydrophilicity of the thus obtained pre-coated fin material was evaluated by measuring the water contact angle of the coating film. Corrosion resistance was also evaluated using a salt spray test. Table 3 shows the evaluation results of the hydrophilicity and corrosion resistance of the coating film of each heat exchanger fin material of Example 2. (Comparative Example 2) After degreasing, washing, and drying the same aluminum alloy rolled plate coil as in Example 2, a water-soluble acrylic resin was applied using a bar coater, and baked at 250°C for 20 seconds to form a coil with a thickness of 0.4 to 2.0 μm on one side. A coating film was formed.
After that, apply water-soluble cellulose resin and heat at 230°C.
Baked for 20 seconds to form a coating film of 0.6 μm on one side. The precoated fin material thus obtained was evaluated for hydrophilicity and corrosion resistance in the same manner as in Example 2. Table 4 shows the evaluation results of hydrophilicity and corrosion resistance of Comparative Example 2. Tables 3 and 4 show that the coating film obtained by forming an electrodeposition coating film (anionic type or cationic type) on the base coat and applying a water-soluble cellulose resin on the coating film has a small water contact angle and good hydrophilicity. It also showed excellent corrosion resistance even with a thin base coat.

【table】

【table】

[Table] (Example 3) Anionic type of Example 2: Using acrylic resin and Svia ED AL-50B, drying the electrodeposition coating film,
Experiments were conducted in which the conditions for baking the water-soluble cellulose coating were changed, and an experiment was conducted in which the electrodeposited coating was once baked and then the water-soluble cellulose coating was baked again. The thickness of the electrodeposited film was 0.7 μm on one side when dried, and the thickness of the water-soluble cellulose resin was 0.6 μm on one side when dried.

[Table] From the above results, it can be seen that the hydrophilicity increases once the electrodeposited coating is baked. Corrosion resistance was good and unchanged. (Example 4) Sample Examples 2-4, 2-5, 2-6 of Example 2
In the step, 0.8% by weight of a surfactant (trade name: Elenon No. 19M, Daiichi Kogyo Seiyaku Co., Ltd.) whose hydrophobic group moiety has a molecular weight of 180 was added to the water-soluble cellulose resin. As a result, the contact angle changed as shown in Table 6.
Corrosion resistance was good or very good and remained unchanged.

[Table] (Example 5) Anion type of Example 2: Using acrylic resin and Asvia ED AL-50B, dry film thickness on one side is 10 μm
After drying with warm air, a water-soluble cellulose resin was applied and baked at 230°C for 20 seconds to form a coating film with a dry thickness of 0.6 μm.
For the samples obtained in this way, we visually observed the wear status of the tools (punch and die) after fin pressing and the molding defects of the fin material after forming, and determined the continuous formability by determining the number of punches until wear or defects occurred. However, after 4,000 punches, scratches and peeling of the coating occurred on the coating surface of the fin material after molding, and scratches also occurred on the tools (punch and die). On the other hand, sample Example 2-3 of Example 2 (electrodeposition coating film
When similar tests were conducted on 0.7μm, water-soluble cellulose film (0.6μm) and 2-8 (electrodeposited film thickness: 4.0μm, water-soluble cellulose film: 0.6μm), no scratches were observed on the paint film even after 1 million punches. , no peeling occurred,
No changes were observed in the tools (punch and die), which were in very good condition. [Effects of the Invention] The precoated fin material for heat exchangers according to the first aspect of the present invention is suitable for industrial production, and has excellent corrosion resistance and processability despite the extremely thin coating film. The product is free from defects. In particular, the conventional technique of electrodeposition coating has a thick coating film (e.g.
20~25μ), painting time: several minutes, baking time: several tens of minutes, electrodeposition voltage: 150~400V, perhaps because it is thinner, painting time: several seconds, baking time: several dozen seconds, electrodeposition voltage: 20 to 100V is sufficient,
Furthermore, it is possible to perform two coats and one bake, which is a great advantage in terms of cost, such as the omission of steps. In addition, the fin material of the second invention provides a fin material that has excellent workability, thermal conductivity, and high hydrophilicity in addition to the above-mentioned performance, and is therefore extremely suitable for use in heat exchangers. It exhibits excellent performance.

Claims (1)

[Scope of Claims] 1. A precoated fin material for a heat exchanger, characterized in that an electrodeposition coating film of 0.2 to 4.0 μm is formed on the surface of an aluminum or aluminum alloy thin plate. 2. A precoated fin material for a heat exchanger, comprising an electrodeposition coating film of 0.2 to 4.0 μm on the surface of an aluminum or aluminum alloy thin plate, and a hydrophilic organic coating film formed thereon.