Highly hydrophilic baked antifouling coating film, method for producing the same, aluminum fin material for heat exchangers, heat exchangers and heating-cooling systems

Abstract

A highly hydrophilic, baked-on antifouling coating film for formation on an outer surface of a heat exchanger, wherein the coating film contains: Aluminum oxide particles contained in an aluminum oxide sol; a water-soluble acrylic resin containing a sulfonic acid; Polyethylene glycol; and Fluorinated resin particles where the coating film quantity is 0.3 to 0.8 g / m² 2 is, and where the amount of water-soluble sulfur components is 0.5 mg / m³ 2 or less.

Description

[Technical field]

[0001] The present invention relates to a highly hydrophilic, baked-on antifouling coating film, a method for producing the same, an aluminum fin material for a heat exchanger comprising the coating film, a heat exchanger, and a heating / cooling system. Priority is claimed in Japanese patent application no. 2016-243686, filed on December 15, 2016, and Japanese patent application no. 2017-220447, filed on November 15, 2017, the contents of which are incorporated herein by reference. [Background on the state of the art]

[0002] In an air conditioning heat exchanger, a problem arises when hydrophilic contaminants, such as dust, and hydrophobic contaminants, such as oil, adhere to the fin surface, making it water-repellent. This leads to condensation splashing, which is the scattering of condensate by bubbles. To eliminate this condensation splashing, it is necessary to make it more difficult for both hydrophilic and hydrophobic contaminants to adhere to the fins.

[0003] A technique known for imparting hydrophilicity to the surface of a fin for a heat exchanger is one in which a surface of a fin material is surface-treated with an organic polymer resin solution containing silica particles; and a technique in which an aluminum fin material is coated with a coating formed by mixing an aqueous composition containing an organic polymeric substance from an acrylic resin and the like, and SiO2 or TiO2, and applying and drying the mixture.

[0004] The patent literature described below 1 discloses an organic resin, such as a polyacrylic acid metal-crosslinked using a Zr compound, in which a hydrophilic coating film containing silica particles and polyethylene glycol is formed on a surface made of a base material of an aluminum alloy. The patent literature described below 2 discloses that an underlying coating layer containing a resin and zirconium is formed on an aluminum plate, and a hydrophilic coating layer containing a resin, colloidal silicon dioxide, and a zirconium compound is formed on top of this.

[0005] As a means of solving the condensation spattering described above, it is effective to apply a mixed film of hydrophilic and hydrophobic particles to the surfaces of aluminum fins, but when using colloidal silicon dioxide, which is known to be hydrophilic particles, the particle hardness is high, and this creates the problem where mold wear can easily occur if a fin material is produced by pressing from an aluminum sheet material.

[0006] Accordingly, the inventors of the present application, as described in patent literature 3 below, proposed first using an aluminum oxide sol with a lower Mohs hardness than that of colloidal silicon dioxide as hydrophilic particles and mixing in a fluorinated resin as hydrophobic particles, thereby obtaining a coating film structure that makes it difficult for both hydrophilic and hydrophobic contaminants to adhere to it. Patent literature 4 discloses a coating composition comprising silicon dioxide microparticles and fluorinated resin particles and discloses an article comprising a silica film on its surface consisting of silica microparticles, wherein fluorinated resin particles are embedded and distributed in the silica film such that they are partially exposed on a surface of the silica film. [List of citations][Patent literature] [Patent Literature 1] Japanese Unexamined Patent Application, First Publication JP 2010-96 416 A [Patent Literature 2] Japanese Patent JP 4 667 978 B2 [Patent Literature 3] Japanese Unexamined Patent Application, First Publication JP 2016-90 105 A [Patent literature 4] EP 2 105 470 A2 [Summary of the invention][Technical problem]

[0007] By forming the coating film described in patent literature 3 on an aluminum fin material, it is possible to provide a fin material that is effective against both hydrophilic and hydrophobic fouling and exhibits less deformation. Accordingly, to manufacture a heat exchanger using the aluminum fin material including the coating film described above, a variety of aluminum fin materials were prepared, these fin materials were arranged parallel to one another, a heat transfer tube made of a copper alloy was provided for insertion into these materials, and thus a heat exchanger core was assembled. Subsequently, an environmental test was carried out.

[0008] However, when a large number of heat exchanger cores, prepared for environmental testing, were stored for several months, it was observed that green-discolored sections formed on the outer circumference of the heat transfer tube of the heat exchanger core, depending on the storage conditions. The inventors of the present invention analyzed the green-discolored sections of the heat transfer tube using an electron beam microanalysis (EPMA) and X-ray photoelectron spectroscopy (ESCA) and found that chlorine, which was not present in normal sections, was present in the discolored sections, and that more sodium and sulfur were present than in the normal sections. Furthermore, Fourier-transform infrared spectroscopy (FT-IR analysis) of these discolored sections revealed a peak value that is nearly equivalent to that of a patina.Based on the above results, it was determined that a patina occurs in the discolored sections and that corrosion occurs in a surface layer of part of the heat transfer pipe.

[0009] In view of these circumstances, an objective of the invention of the present application is to provide a highly hydrophilic, baked-on antifouling coating film that is effective against both hydrophilic and hydrophobic contaminants, that also does not cause problems with regard to mold wear, and that does not cause the problem of corrosion and the like occurring in a copper heat transfer tube, even if the highly hydrophilic, baked-on antifouling coating film is stored for a longer period of time; a method for producing the same; an aluminum fin material containing the coating film; a heat exchanger; and a heating-cooling system.Against this background, a further objective of the invention of the present application is to provide a heating and cooling system with a heat exchanger which has a highly hydrophilic, baked-on antifouling coating film with the excellent properties described above. [Solution to the problem]

[0010] A highly hydrophilic, baked-on antifouling coating film of the present invention is a baked-on coating film formed on an outer surface of a heat exchanger, wherein the film contains: aluminum oxide particles contained in an aluminum oxide sol; a water-soluble acrylic resin containing a sulfonic acid, polyethylene glycol, and fluorinated resin particles, in which an amount of water-soluble sulfur components is 0.5 mg / m². 2 or less, and a coating film quantity of 0.3 to 0.8 g / m² 2 amounts.

[0011] In the present invention, it is preferred that the average particle diameter of the aluminium oxide particles is 0.02 to 20 µm and that 5 to 45 mass-% of the aluminium oxide particles are contained in 100 mass-% of the solids content of the baked-on coating film.

[0012] In the present invention, it is preferred that the dynamic coefficient of friction of a surface is 0.2 or less.

[0013] In the present invention, it is preferred that 0.05 to 3 mass-% of the fluorinated resin particles with an average particle diameter of 0.1 to 0.5 µm are contained in 100 mass-% of the solids content of the baked-on coating film.

[0014] It is preferred that the area ratio of the aluminium oxide particles on the surface of the baked-on coating film of the present invention is 90% or more.

[0015] In an aluminum rib material of the present invention, it is preferred that the above-described baked-on coating film is formed on an outer surface made of a sheet material of aluminum or an aluminum alloy.

[0016] In a heat exchanger of the present invention, it is preferred that a plurality of the aluminum fin materials described above are arranged parallel to each other, that a through-hole is formed in each of the aluminum fin materials, and that a heat transfer tube made of copper or a copper alloy is provided to be inserted into the through-hole and integrated with the aluminum fin material.

[0017] A heating and cooling system of the present invention is formed from the heat exchanger described above.

[0018] A method of the present invention for producing a highly hydrophilic, baked-on antifouling coating film to be applied to an outer surface of a fin material or a heat transfer tube comprises: applying an aqueous coating obtained by mixing an aluminum oxide sol, a water-soluble acrylic resin, polyethylene glycol, and fluorinated resin particles to the outer surface of the fin material or the heat transfer tube, such that a coating film quantity of 0.3 to 0.8 g / m² is achieved. 2 is; heating and drying the coating to obtain the highly hydrophilic, baked-on antifouling coating film; and washing the film with water or hot water so that an amount of water-soluble sulfur components in the highly hydrophilic, baked-on antifouling coating film of 0.5 mg / m² 2or less. The method of the present invention further comprises the use of aluminum oxide particles with an average particle diameter of 0.02 to 20 µm, such that 5 to 45 wt% of the aluminum oxide particles are contained in 100 wt% of the solids content of the baked-on coating film.

[0019] The method of the present invention further comprises that 100 mass-% of the solids content of the baked-on coating film may contain 0.05 to 3 mass-% of the fluorinated resin particles with an average particle diameter of 0.1 to 0.5 µm. [Advantageous effects of the invention]

[0020] According to the highly hydrophilic, baked-on antifouling coating film of the present invention, it is possible to provide a highly hydrophilic, baked-on antifouling coating film that is effective against both hydrophilic and hydrophobic contaminants, that can prevent the formation of condensation splashes, and that does not cause any problems with regard to mold wear when the coating film is processed as a rib material.

[0021] Furthermore, according to the baked-on coating film of the present invention, no problems such as corrosion and the like occur in the heat transfer tube even when the baked-on coating film is provided on the surface of the fin material and the fin material is combined with the heat transfer tube made of copper or a copper alloy for mounting the heat exchanger and is then stored for a longer period of time.

[0022] According to the manufacturing process of the present invention, it is possible to obtain the excellent, highly hydrophilic, baked-on antifouling coating film described above, in which an amount of water-soluble sulfur components is reduced to 0.5 mg / m². 2 or less reduced.

[0023] Furthermore, according to the heating / cooling system with the heat exchanger which has the aforementioned properties, it is possible to obtain a heating / cooling system in which the occurrence of condensation splashing can be suppressed and corrosion in the heat transfer tube is not caused even when the fin material is combined with the heat transfer tube and stored for a longer period of time during a manufacturing step. [Brief description of the drawings] Fig. Figure 1 is a partial cross-sectional view of an aluminum rib material with a highly hydrophilic, baked-on antifouling coating film according to the present invention. Fig. Figure 2 is a perspective view showing an example of a heat exchanger core in which an aluminum fin with the highly hydrophilic, baked-on antifouling coating film according to the invention is mounted with a heat transfer tube. Fig. Figure 3 is a microphotograph showing a surface condition of the baked-on coating film before washing with hot water, containing the fluorinated resin particles obtained in the examples. Fig. Figure 4 is a micrograph showing a surface condition of the baked-on coating film after washing with hot water, containing the fluorinated resin particles obtained in the examples. [Description of the embodiments]

[0024] The present invention will now be described in detail with reference to the embodiments illustrated in the accompanying drawings. As shown in the cross-sectional view in Fig. Figure 1 shows a fin material 1 for a heat exchanger of the present embodiment comprising a base material 2 made of aluminium or an aluminium alloy, a chemical conversion coating 3 applied to a surface of the base material 2 and a highly hydrophilic, baked-on antifouling coating film 5 designed to cover the chemical conversion coating 3.

[0025] The aluminum or aluminum alloy forming the base material 2 is not particularly restricted, and it is possible to use, appropriately, an aluminum material with a composition generally applied to a base material for a heat exchanger. Examples include aluminum alloys such as A1050, A1100, A1200, and A3003 according to JIS, and the like. As a chemical conversion coating 3, it is possible to use a chromated thin chromate coating and the like.

[0026] The highly hydrophilic, baked-on antifouling coating film 5 is a baked-on coating film obtained by applying an aqueous coating containing an aluminum oxide sol, a water-soluble acrylic resin containing a sulfonic acid, and polyethylene glycol or a modified polyethylene glycol product to the chemical conversion coating 3 as a coating film and then baking at 150 to 300 °C for a predetermined time, for example, several seconds to several minutes.

[0027] The aluminum oxide sol represents a state in which the aluminum oxide particles are dispersed in a liquid dispersion medium. Accordingly, the highly hydrophilic, baked-on antifouling coating film 5 obtained after the baking of the aqueous coating has a structure in which the aluminum oxide particles 7 are dispersed in a resin layer 6, which was produced from a baked-on substance consisting of a mixture of the water-soluble acrylic resin and polyethylene glycol or a modified polyethylene glycol product.

[0028] Furthermore, a structure can be assumed in which fluorinated resin particles 8 are added to the highly hydrophilic, baked-on coating film 5. To add the fluorinated resin particles 8 to the highly hydrophilic, baked-on antifouling coating film 5, a necessary quantity of a PTFE dispersion, an FEP dispersion, or the like, in which the fluorinated resin particles 8 are dispersed in water, is mixed with the aqueous coating.

[0029] It is possible to obtain the highly hydrophilic, baked-on antifouling coating film 5 by adding the required amount of fluorinated resin particles 8. This can be achieved by mixing the fluorinated resin particles 8, in the state of a PTFE dispersion, an FEP dispersion, or the like, into the aqueous coating and then baking the aqueous coating. During the baking process, the moisture in the coating evaporates and is eliminated, while the solids contained in the coating remain to form the highly hydrophilic, baked-on antifouling coating film 5.

[0030] In this example, it is necessary to remove most of the sulfur components contained in the resin layer 6 by washing the coating film with water or hot water (using hot water at 60 °C to 80 °C, e.g. with hot water at 60 °C) after baking in order to elute the sulfur components contained in the resin layer 6 of the highly hydrophilic, baked-on antifouling coating film 5.

[0031] The aluminum oxide sol is in a state where dispersed particles (aluminum oxide particles) are transferred from an amorphous gel to boehmite (hydrate), and this state does not change under agglomeration processes or normal curing conditions of a coating film. Aluminum oxide particles of the aluminum oxide sol in the transition stage from this amorphous gel to boehmite are softer than colloidal silicon dioxide. For example, their Mohs hardness is low. Accordingly, the processability during the pressing of the rib material 1, including the highly hydrophilic, cured antifouling coating film 5 containing the aluminum oxide particles derived from this aluminum oxide sol, is excellent, and the durability of a mold can also be increased.

[0032] A water-soluble acrylic resin is preferably obtained by copolymerizing an α,β-unsaturated monomer A with a sulfonic acid group or a salt thereof, an α,β-unsaturated monomer B with a carboxylic acid group and an α,β-unsaturated monomer C with an alcoholic hydroxyl group (a desirable ratio: A: 1 to 80 wt.% (preferably 30 to 50 wt.%), B: 1 to 50 wt.% (preferably 20 to 50 wt.%) and C: 1 to 50 wt.% (preferably 20 to 40 wt.%) with A + B + C = 100 wt.%).

[0033] Preferred examples of the α,β-unsaturated monomer A with a sulfonic acid group or a salt thereof include vinylsulfonic acid, arylsulfonic acid, 2-acrylamido-2-methylsulfonic acid, styrenesulfonic acid, methacryloyloxyethylsulfonic acid, or a salt, such as a sodium salt, potassium salt, lithium salt, and the like, of the aforementioned acids. This monomer A exhibits anionic hydrophilicity and thus improves the water wettability of the coating film.

[0034] Preferred examples of the α,β-unsaturated monomer B with a carboxylic acid group include acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, and the like. This monomer B improves the water wettability and adhesion of the coating film. Preferred examples of the α,β-unsaturated monomer C with an alcoholic hydroxyl group include 2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate, N-methylol(meth)acrylamide, and the like. This monomer C improves the water wettability of the coating film and plays a role in the fixation of particles originating from the aluminum oxide sol.

[0035] The coating film quantity of the aqueous coating is preferably in the range of 0.3 to 0.8 g / m². 2as the coating film quantity (corresponding to a coating film quantity of the solids content) excluding moisture, which is removed from the aqueous coating at the time of curing. Where an upper and lower limit of a range are expressed using "to" in the following description, the lower and upper limits are included unless otherwise stated. Accordingly, the range of 0.3 to 0.8 g / m² means 2 then 0.3 g / m² 2 or more and 0.8 g / m² 2 or less. By adjusting the coating film quantity of the aqueous paint within the aforementioned range of 0.3 to 0.8 g / m². 2 The highly hydrophilic, baked-on antifouling coating film 5 will be obtained with excellent coating film adhesion, hydrophilicity, contamination resistance, and antifouling properties. A coating film quantity of less than 0.3 g / m² is required. 2This can lead to poor hydrophilicity, poor contamination resistance, and poor antifouling properties of the baked-on antifouling coating film 5. Furthermore, a coating film quantity exceeding 0.8 g / m² can 2 leading to poor adhesion and an increase in the cost of the highly hydrophilic, baked-on antifouling coating film 5.

[0036] The average particle diameter of the aluminum oxide particles contained in the aluminum oxide sol is preferably in the range of 0.02 to 20 µm. An average particle diameter of less than 0.02 µm causes the problem of adsorption odors due to an increase in a certain surface area, and an average particle diameter of more than 20 µm causes the problem of increased mold wear during pressing. The amount of added aluminum oxide particles is preferably in the range of 5 to 45 wt% in 100 wt% of the solids content of the coating. By adding the amount of aluminum oxide particles in this range, the highly hydrophilic, baked-on antifouling coating film 5 is obtained with excellent coating film adhesion, hydrophilicity, contamination resistance, and antifouling properties.An added quantity of less than 5 wt% of aluminum oxide particles can lead to poor hydrophilicity, poor contamination resistance, and poor antifouling properties. An added quantity of more than 45 wt% of aluminum oxide particles can easily lead to poor adhesion and an increase in the cost of the highly hydrophilic, baked-on antifouling coating film. In addition to solid components such as aluminum oxide particles and fluorinated resin, the aqueous coating contains approximately 40 to 60% water-soluble acrylic resin, which contains a sulfonic acid, and approximately 20 to 40% polyethylene glycol as solid components.

[0037] The average particle diameter of the fluorinated resin particles 8 is preferably in the range of 0.1 to 0.5 µm, and the added amount is preferably in the range of 0.05 to 3 wt%, based on 100 wt% of the solids content in the coating. Particles contained in a PTFE dispersion, an FEP dispersion, and the like can be used for the fluorinated resin particles 8.

[0038] Favorable antifouling properties are observed when the amount of added fluorinated resin particles 8 is in the range of 0.05 to 3 wt%. An added amount of less than 0.05 wt% leads to a deterioration of the antifouling properties of the baked-on antifouling coating film 5, and an added amount of more than 3 wt% easily leads to poor hydrophilicity of the baked-on antifouling coating film 5.

[0039] An average particle diameter of the fluorinated resin particles 8 of less than 0.1 µm causes the problem that specified antifouling properties cannot be demonstrated, and an average particle diameter of the fluorinated resin particles 8 of more than 0.5 µm causes the problem that the particles are difficult to disperse homogeneously in the coating.

[0040] The dynamic coefficient of friction of the surface of the highly hydrophilic, baked-on antifouling coating film 5 is preferably 0.20 or less. If the dynamic coefficient of friction of the highly hydrophilic, baked-on antifouling coating film 5 is greater than 0.20, poor mold wear can easily occur. If the dynamic coefficient of friction of the highly hydrophilic, baked-on antifouling coating film 5 is 0.20 or less, press workability is excellent and poor mold wear is unlikely.

[0041] The surface area of ​​the highly hydrophilic, baked-on antifouling coating film 5 occupied by the aluminum oxide particles is preferably 90% or more. The aluminum oxide particles must be dispersed within the antifouling coating film 5, and to achieve this dispersion, the amount of aluminum oxide particles added must be adjusted to 40% by mass or less in 100% by mass of the coating's solids content. By adjusting the amount to 40% by mass or less, the surface area of ​​the aluminum oxide particles on the coating surface can be 90% or more, thereby reducing the dynamic coefficient of friction and mold wear.If the surface area ratio of the aluminium oxide particles present on the surface of the antifouling coating film 5 is less than 90%, the aluminium oxide particles are easily brought into an aggregated state on the surface of the highly hydrophilic, baked-on antifouling coating film 5 and the aggregation increases the dynamic coefficient of friction to over 0.2, and thus the mold wear worsens.

[0042] The amount of sulfur components contained in the resin layer 6 of the highly hydrophilic, baked-on antifouling coating film 5 is preferably 0.5 mg / m². 2 or less. The amount of sulfur components contained in resin layer 6 can be reduced to 0.5 mg / m². 2or less by washing with water or hot water for about 1 second to 10 minutes as described above to elute the sulfur components contained in resin layer 6 in water or hot water.

[0043] If the amount of sulfur components contained in resin layer 6 is 0.5 mg / m² 2 If the fin material is combined with a copper or copper alloy heat transfer tube to configure the heat exchanger as described later, the sulfur components contained in resin layer 6 reach the surface of the heat transfer tube due to condensed water, moisture, and the like, and react with the copper, forming a patina. As shown in the examples described later, as long as the amount of sulfur components is, for example, in the range of 0.05 to 0.48 mg / m², this can be achieved. 2This prevents corrosion of the heat transfer pipe. When washing with hot water, it is preferable to perform the washing with hot water at approximately 60 to 80 °C for approximately 1 second to 60 seconds. When washing with water, it is preferable to perform the washing for approximately 10 seconds to 60 minutes.

[0044] The rib material 1 with the above-described highly hydrophilic, baked-on antifouling coating film 5 on its surface is characterized by excellent adhesion of the coating film, excellent hydrophilicity, excellent contamination resistance, a small dynamic coefficient of friction and less mold wear, thereby extending the service life of the mold.

[0045] This is because by using the aluminum oxide sol, which contains aluminum oxide particles with a lower Mohs hardness than the colloidal silicon dioxide from the related prior art, and by mixing in the fluorinated resin particles 8 as hydrophobic particles, thus making it difficult for both hydrophilic and hydrophobic contaminants to adhere to it, the antifouling properties of the baked-on coating film 5 with excellent hydrophilicity are improved; and by allowing 90% or more of the surface area of ​​the aluminum oxide particles derived from the aluminum oxide sol to be present on the surface of the highly hydrophilic, baked-on antifouling coating film 5, mold wear at the time of pressing can be reduced.

[0046] The rib material 1 with the above structure can be widely applied to heat exchangers for room air conditioners, heat exchangers for packed air conditioners, heat exchangers for vending machines, heat exchangers for freezer display cases, heat exchangers for refrigerators and the like.

[0047] Furthermore, the highly hydrophilic, baked-on antifouling coating film 5 can be formed on both the front and back surfaces of the fin material 1, with the chemical conversion coating 3 positioned between them. In addition, the highly hydrophilic, baked-on antifouling coating film 5 can be applied not only to the front and back surfaces of the fin material 1 of the heat exchanger, but also to the entire heat exchanger, including the heat transfer tube. For example, the highly hydrophilic, baked-on antifouling coating film 5 can be formed on the entire surface of the heat exchanger core by combining the fin material 1 and the heat transfer tube 11 to assemble the heat exchanger core, and then applying and baking on the aforementioned aqueous coating to the entire heat exchanger core.In this case, the highly hydrophilic, baked-on antifouling coating film 5 can be used as a post-coating for the heat exchanger.

[0048] Fig. Figure 2 shows a configuration in which a plurality of rectangular, plate-shaped fins (radiator plates) 15 made of fin material 1 are arranged parallel to one another at predetermined intervals, and the U-shaped heat transfer tube 11 is inserted into an insertion hole 15a formed in each fin 15 to partially mount the heat exchanger core 16 through it. The U-shaped heat transfer tube 11 is inserted into the insertion hole 15a of the plurality of fins 15 such that a curved section 11a is positioned on one side of a parallel body of the fin 1 and one side of an opening end 11b is positioned on the other side of the parallel body of the fin 1.

[0049] Into these heat transfer tubes 11, a tube-expanding plug (not shown) is inserted from the side of the opening end 11b to expand the tubes, which improves the connection strength between the heat transfer tubes 11 and the fins 15, and then a U-shaped elbow tube (not shown) is connected to the side of the opening end of the heat transfer tube 11, thus completing the heat exchanger core 16.

[0050] In this heat exchanger core 16, the heat transfer tube 11 and the elbow tube are made of copper or a copper alloy.

[0051] The highly hydrophilic, baked-on antifouling coating film 5 is formed on the front and back surfaces of the fin 15 in the heat exchanger core 16. For this reason, the highly hydrophilic, baked-on antifouling coating film 5 and the heat transfer tube 11 are brought into contact with each other at a circumferential edge section of the inlet hole 15a. In a coating film of the related technology, if a condition persists in which condensate adheres to a contact section, as in a case where the heat exchanger core 16 is stored in a warehouse or the like, the sulfur content from the coating film can leach into the condensate, leading to corrosion of the heat exchanger tube 16. On the other hand, since the highly hydrophilic, baked-on antifouling coating film 5 formed on the fin material 1, as described above, contains only 0.5 mg / m² 2or contains less sulfur, elution of the sulfur content onto the condensate side is less likely, even if condensate is present near the contact area between the highly hydrophilic, baked-on antifouling coating film 15 and the heat transfer tube 11, and thus corrosion, such as patina, does not occur in the heat transfer tube 11. The heat exchanger with the heat exchanger core 16 described above can be used in a wide variety of applications, e.g., as a heating / cooling system. [Examples]

[0052] Aluminum oxide sol (average particle diameter of aluminum oxide particles: 0.8 µm) under the trade name (CATALOID AS-3), manufactured by JGC Catalysts and Chemicals Ltd., a water-soluble acrylic resin (2-acrylamide-2-methylpropanesulfonic acid), polyethylene glycol (PEG #6000), and a fluorinated resin (PTFE fluorine dispersion) under the trade name (PTFE AD911E), manufactured by Asahi Glass Co. Ltd., were mixed in the ratios specified in Table 1 below to prepare an aqueous coating. In Table 1, an added quantity is denoted by the quantity of fluorinated resin particles contained in the PTFE fluorine dispersion.

[0053] An aluminum alloy plate with a thickness of 100 µm, made of JIS A 1050 alloy, was subjected to a chromate phosphate process to form a chemical conversion coating with a thickness of 0.3 µm. An aqueous coating of various compositions, shown in Table 1 below, was then applied to this chemical conversion coating using a stick coater in the application quantity (total amount of moisture and solids remaining in the coating before curing) as shown in Table 1. The coating was then cured for 30 seconds in an oven at 220 °C (target temperature), forming a highly hydrophilic, cured antifouling coating film. This curing process causes the moisture in the aqueous coating to evaporate, leaving only the solids in the aqueous coating on the aluminum alloy plate.

[0054] After baking, a hot water washing process was carried out to wash the highly hydrophilic, baked-on antifouling coating film for 10 seconds under running hot water at 60 °C.

[0055] With regard to the large number of rib materials obtained, the adhesion of a coating film, the hydrophilicity after washing under running water, a contact angle after wet / dry cycles, the contamination resistance, a dynamic coefficient of friction, a powder adhesion rate, the mold wear, an area ratio of the aluminium oxide particles and the presence or absence of discoloration in a copper tube were measured and are shown in Table 1 below.

[0056] The adhesion shown in Table 1 is the result of observing the adhesion of an antifouling coating after placing a paper towel (registered trademark) affixed to a 1-pound hammer on the surface of the antifouling coating of samples and then applying 10 back-and-forth rubs. A sample from which the antifouling coating did not detach is designated A, a sample where a layer remained while a skin layer detached is designated B, a sample from which approximately 50% of the coating detached is designated C, and a sample from which 100% of the coating detached is designated D.

[0057] Hydrophilicity after washing under running water refers to the measurement of the contact angle of the antifouling coating surface after immersion of the samples in running water at room temperature, with a flow rate of 3 l / min for 24 hours. A sample with a contact angle of 20° or less is designated B, and a sample with a contact angle greater than 20° is designated D.

[0058] The contact angle after the wet / dry cycle represents the result of measuring the contact angle of the antifouling coating surface after 14 cycles of immersion of the samples in running water at room temperature, with a flow rate of 3 l / min for 24 hours, and drying at 80 °C for 16 hours. A sample with a contact angle of 40° or less is designated B, and a sample with a contact angle greater than 40° is designated D.

[0059] In a contamination resistance test to assess contamination resistance, 6 g of palmitic acid were placed as the contaminant and a sample was added to a beaker. The contact angle of the antifouling coating surface was measured after heating and exposure to 100 °C for 6 days. A sample with a contact angle of 60° or less is designated B, and a sample with a contact angle greater than 60° is designated D.

[0060] The dynamic coefficient of friction was obtained using a Bowden-type friction measuring device by measuring the frictional force when pressing a contactor with a steel ball of size φ 9 / 32 and a load of 200 g against the surface of the antifouling coating of the samples, to which no pressing oil had been applied, and moving the sample (1 cycle).

[0061] A sample with a dynamic coefficient of friction of 0.2 or less is designated B, and a sample with a dynamic coefficient of friction above 0.2 is designated D. Regarding powder adhesion, an adhesion area ratio was measured by image analysis by immersing a 100 mm × 100 mm sample (aluminum fin material) in running water at a flow rate of 3 l / min for 1 hour at room temperature, and then bonding each of eleven and twelve types of test powders specified in JIS Z 8901 to the surface of the sample's antifouling coating. A sample with an adhesion area ratio of 3% or less is designated A, a sample with an adhesion area ratio of 3% or more up to 10% or less is designated B, and a sample with an adhesion area ratio greater than 10% is designated D.

[0062] Regarding die wear, a sample (aluminum rib material) was die-cut one million times by press machining, and the wear condition of a cutting die (slot edge) was observed. Regarding the hardness of the slot edge, slot edges with HRC 37 to 41 were used to quantitatively measure the wear zone of the metal die edge (slot edge) using a laser microscope. A sample with a wear zone of 100 µm 2 or less in a two-dimensional cross-section is designated by B, and a sample with a wear area of ​​more than 100 µm 2 is designated with D.

[0063] Regarding the surface area ratio of the aluminum oxide particles, the surface of the antifouling coating was quantitatively evaluated using a laser microscope at 100x objective lens magnification. The surface area ratio of the aluminum oxide particles was then measured by particle analysis of a binary image within a 50 µm × 50 µm field of view. A sample with an aluminum oxide particle surface area ratio of 90% or higher is designated B, and a sample with a surface area ratio of less than 90% is designated D.

[0064] To measure the amount of water-soluble sulfur components in the coating film, the rib was cut into four A4-sized sheets (8 pages) and placed in a container. 100 ml of pure water was added, heated to 40 °C, and stirred for 10 minutes. This water was analyzed by ICP emission spectroscopy, and a value was assumed to be obtained by converting a measured amount of sulfur into an original amount per coating film. In the copper tube decolorization test, the aforementioned ribs were cut to a height of 10 cm and a width of 5 cm and placed in the bottom of a beaker, clipped to a copper tube of the same length. Water was added to the bottom of the beaker, and one opening of the beaker was sealed with foil.The environmental conditions consisted of seven cycles of 35 °C × 16 hrs → 20 °C × 4 hrs → 35 °C × 1 hr → 20 °C × 3 hrs, performed as one cycle. The presence or absence of discoloration in the copper pipe was then observed. A case in which discoloration of the copper pipe was observed was designated D, and a case in which no discoloration was observed was designated B.

[0065] Based on the results shown in Table 1, samples No. 1 to 20, in which a coating film quantity of the aqueous coating was in the range of 0.3 to 0.8 g / m², showed 2This resulted in a favorable balance between the properties, as these samples exhibited excellent adhesion of the coating film and also performed excellently in numerous tests, including hydrophilicity after washing under running water, contact angle after wet / dry cycles, contamination resistance, dynamic coefficient of friction, powder adhesion rate, mold wear, and particle area ratio. Furthermore, in all samples Nos. 1 to 20, the amount of water-soluble sulfur components in the coating film was 0.5 mg / m². 2 or less, and no discoloration (corrosion) occurred in the copper heat transfer pipe.

[0066] Among samples No. 1 to 20, samples No. 1 to 14, which had a coating film quantity in the range of 0.3 to 0.8 g / m², showed the following: 2With an amount of added aluminium oxide ranging from 5 to 45% by mass in the solids content of the coating and an amount of added fluorinated resin ranging from 0.05 to 3.0% by mass in the solids content of the coating, excellent results were achieved in all test areas.

[0067] Regarding these samples, sample no. 28, with an excessive amount of added aluminum oxide particles, had a higher dynamic coefficient of friction and showed poor results in terms of shape wear and particle area ratio. Sample no. 21 of the comparison sample, with a low application rate of the aqueous coating, exhibited deteriorated hydrophilicity after washing under running water, a worsened contact angle after the wet / dry cycle, and reduced contamination resistance. Furthermore, samples no. 23 and 24 of the comparison sample, with an excessive amount of coating film in the aqueous coating, showed adhesion problems.

[0068] Furthermore, samples No. 25, 26 and 27 were samples in which the amount of coating applied was appropriate, the amount of aluminum oxide added and the amount of fluorinated resin added were also appropriate, but the amount of water-soluble sulfur components in the coating film was large, and thus discoloration occurred in the copper heat transfer pipe.

[0069] Samples No. 29 to 31 were samples in which the coating film quantity of the paint was appropriate, the quantity of added aluminium oxide and the quantity of added fluorinated resin were also appropriate, but the quantity of water-soluble sulfur components in the coating film was large, and thus discoloration occurred in the copper pipe.

[0070] Although sample No. 32 was a sample with an extremely small amount of added fluorinated resin and a sample with a large amount of the water-soluble sulfur components in the coating film, the powder adhesion rate deteriorated and corrosion of the copper heat transfer tube also occurred.

[0071] Although sample No. 33 was a sample with an extremely large amount of added fluororesin and a sample with a large amount of water-soluble sulfur components in the coating film, the hydrophilicity deteriorated after washing under running water, as did the wet / dry cycles and contamination resistance, and corrosion of the copper heat transfer pipe also occurred.

[0072] Based on the results shown in Table 1, it was determined that when forming the highly hydrophilic, baked-on antifouling coating film on the rib material, it is important to apply it at a rate in the range of 0.3 to 0.8 g / m². 2 to apply the aqueous coating described above and, after baking, to wash with hot water so that the amount of water-soluble sulfur components decreases by 0.5 mg / m² 2 reduced.

[0073] Based on the aforementioned results, it is possible to provide a rib material with a favorable balance of properties, as this material exhibits excellent coating film adhesion and also performs exceptionally well in numerous tests, including hydrophilicity, contamination resistance, dynamic coefficient of friction, powder adhesion rate, mold wear, and particle area ratio. Furthermore, this rib material is characterized by the absence of corrosion within the copper pipe, even when the material is adhered to it.

[0074] Furthermore, by using a coating film in which the average particle diameter of the aluminum oxide particles in the coating film is 0.02 to 20 µm and the content of aluminum oxide particles is 5 to 45 wt%, based on 100 wt% of the solids content of the baked-on coating film, a rib can be provided in which the adhesion of a coating film, the hydrophilicity, the contact angle, the contamination resistance and the area ratio of the particles are excellent, in which little mold wear occurs and in which corrosion of the copper tube is unlikely.

[0075] Fig. Figure 3 is a micrograph showing the aluminium oxide and fluorine particles contained in the baked-on antifouling coating film before hot water washing, which forms on the surface of sample No. 3 of the example in Table 1. Fig.Figure 4 is a photomicrograph showing the aluminum oxide and fluorine particles contained in the baked-on antifouling coating film after hot water washing, which forms on the surface of sample No. 3 of the example in Table 1. A large number of irregularly shaped aluminum oxide particles with a variety of pointed projections are in a state of mixing with rice-grain-like fluorine resin particles. Thus, the structure in which these particles are embedded within the resin layer can be understood as an articulated structure of the antifouling coating. [Applicability to industry]

[0076] A heat exchanger and a heating / cooling system with less condensation splashing can be provided. [List of reference symbols] 1 Rib material 2 Base material 3 Chemical Conversion Coating 5. Highly hydrophilic, baked-on antifouling coating film 6 resin layer 7 aluminum oxide particles 8 fluorinated resin particles 11 Heat transfer pipe 11a Curved section 15th rib 15a Entry hole 16 heat exchanger core

Claims

[1] A highly hydrophilic, baked-on antifouling coating film for formation on an outer surface of a heat exchanger, wherein the coating film contains: Aluminum oxide particles contained in an aluminum oxide sol; a water-soluble acrylic resin containing a sulfonic acid; Polyethylene glycol; and Fluorinated resin particles where the coating film quantity is 0.3 to 0.8 g / m² 2 is, and where the amount of water-soluble sulfur components is 0.5 mg / m³ 2 or less. [2] Highly hydrophilic, baked-on antifouling coating film according to claim 1, where the average particle diameter of the aluminium oxide particles is 0.02 to 20 µm, and 5 to 45% by mass of the aluminium oxide particles are contained in 100% by mass of the solids content of the baked-on coating film. [3] A highly hydrophilic, baked-on antifouling coating film according to claim 1 or 2, wherein the coefficient of kinetic friction of a surface is 0.2 or less. [4] A highly hydrophilic, baked-on antifouling coating film according to any one of claims 1 to 3, wherein 0.05 to 3 wt% of the fluorinated resin particles having an average particle diameter of 0.1 to 0.5 µm are contained in 100 wt% of the solids content of the baked-on coating film. [5] A highly hydrophilic, baked-on antifouling coating film according to any one of claims 1 to 4, wherein the surface area fraction of the aluminium oxide particles on the surface of the baked-on coating film is 90% or more. [6] Aluminium rib material, wherein the baked-on coating film according to any one of claims 1 to 5 is formed on an outer surface of a plate material made of aluminium or an aluminium alloy. [7] Heat exchanger, wherein a plurality of aluminium rib materials according to claim 6 are arranged parallel to each other, a through hole is formed in each of the aluminum rib materials and A heat transfer tube, made of copper or a copper alloy, is intended to be inserted into the through-hole and integrated with the aluminum fin material. [8] Heating and cooling system comprising the heat exchanger according to claim 7. [9] Method for producing a highly hydrophilic, baked-on antifouling coating film for application to an outer surface of a fin material or a heat transfer tube, the method comprising: Mixing an aluminum oxide sol, a water-soluble acrylic resin, polyethylene glycol and fluorinated resin particles to obtain an aqueous coating; After the mixing step: Apply the aqueous coating to the outer surface of the fin material or the heat transfer pipe in a coating film quantity of 0.3 to 0.8 g / m². 2 ; Dry heating of the fin material or heat transfer tube to obtain a highly hydrophilic, baked-on antifouling coating film after the application step; and Washing the coating film with water or hot water, so that a quantity of water-soluble sulfur components in the highly hydrophilic, baked-on antifouling coating film of 0.5 mg / m² 2 or lessens. [10] Method for producing a highly hydrophilic, baked-on antifouling coating film according to claim 9, wherein 5 to 45 wt% of the aluminium oxide particles are contained in 100 wt% of the solids content of the baked-on coating film by using aluminium oxide particles with an average particle diameter of 0.02 to 20 µm. [11] Method for producing a highly hydrophilic, baked-on antifouling coating film according to claim 9 or 10, wherein 0.05 to 3 wt% of the fluorinated resin particles with an average particle diameter of 0.1 to 0.5 µm are contained in 100 wt% of the solids content of the baked-on coating film.

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