Hydrophilic coating film, heat exchanger, and coating composition

Abstract

A hydrophilic coating is equipped with a first hydrophilic layer and a second hydrophilic layer formed on the first hydrophilic layer. The second hydrophilic layer includes: a spherical particle aggregate layer covering the first hydrophilic layer and composed of a plurality of spherical particles; binder particles in which a plurality of small-particle-size particles having a particle size smaller than that of the large-particle-size particles are bound to the surface of large-particle-size particles having a particle size larger than that of the spherical particles, and some of the small-particle-size particles are embedded in the spherical particle aggregate layer; and a connecting body formed on the spherical particle aggregate layer and the binder particles and in which a plurality of connecting body particles having a particle size smaller than that of the large-particle-size particles are connected.

Description

Hydrophilic coating, heat exchanger and coating composition

[0001] The present disclosure relates to hydrophilic coatings, heat exchangers, and coating compositions.

[0002] Air conditioners use heat exchangers in which copper tubes and aluminum fins are mechanically joined. When the heat exchanger is used as an evaporator, water vapor in the air condenses and the resulting condensed water adheres to the fins as droplets. This prevents the condensed water from being discharged, increasing ventilation resistance and reducing the heat transfer performance of the heat exchanger. To prevent this condensed water from causing ventilation resistance, a technique for forming a coating made of a hydrophilic resin has long been used in heat exchangers. There is a demand for improved drainage of condensed water in such heat exchangers.

[0003] For example, Patent Document 1 describes that since the hydrophilic coating composition contains an organic binder component, the coating film of the hydrophilic coating composition can be fixed to the substrate after drying, preventing peeling from the substrate. Furthermore, Patent Document 1 also describes that since the hydrophilic coating composition contains an antibacterial inorganic powder, it is possible to provide a hydrophilic coating composition that can form a hydrophilic coating film with excellent antibacterial properties, and that it is possible to form a hydrophilic coating film that is in close contact with the substrate.

[0004] For example, Patent Document 2 describes that the hydrophilicity of a resin coating film can be increased by increasing the concentration of an acrylamide polymer on the surface side of a precoated fin material.

[0005] For example, Patent Document 3 discloses a hydrophilic layer having bound inorganic particles, spherical inorganic particles, and fluororesin particles. It describes that the surface of an aluminum fin on which the hydrophilic layer is formed has high hydrophilicity and can drain condensation water generated on the surface of the aluminum fin. It also describes that the spherical inorganic particles have the effect of increasing adhesion between the bound inorganic particles and the corrosion-resistant resin layer and maintaining hydrophilicity for a long period of time.

[0006] JP 2023-35239 A JP 2019-100675 A International Publication No. 2022 / 130620

[0007] However, in the configuration of Patent Document 1, because the material that provides hydrophilicity is covered with an organic binder, the contact angle of the hydrophilic coating becomes equal to the contact angle of the organic binder, and the water contact angle cannot be made 10 degrees or less. Furthermore, the component that provides hydrophilicity flows out due to, for example, condensation or water aggregation that occurs over long-term use, and the hydrophilicity gradually decreases. For this reason, it is not possible to make the water contact angle 10 degrees or less, and it is also not possible to maintain hydrophilicity over the long term.

[0008] Furthermore, in the acrylamide polymer used in the hydrophilic layer in Patent Document 2, components that contribute to hydrophilicity are washed away by running water, resulting in a decrease in hydrophilicity. In addition, in the structure of Patent Document 3, the bound inorganic particles fall off with long-term use, resulting in a decrease in hydrophilicity with long-term use.

[0009] An object of the present disclosure is to provide a hydrophilic film, a heat exchanger, and a coating composition that can maintain high hydrophilicity.

[0010] The hydrophilic coating according to the present disclosure comprises a first hydrophilic layer and a second hydrophilic layer formed on the first hydrophilic layer, the second hydrophilic layer covering the first hydrophilic layer and including a spherical particle assembly layer composed of a plurality of spherical particles, binder particles each having a larger particle diameter than the spherical particles and a plurality of small particle diameter particles having a smaller particle diameter than the large particle diameter particles bound to the surface of the large particle diameter particles, and part of the binder particles embedded in the spherical particle assembly layer, and linkages formed on the spherical particle assembly layer and the binder particles and each having a particle diameter smaller than the large particle diameter particles.

[0011] Furthermore, the heat exchanger according to the present disclosure has the above-described hydrophilic coating formed on the surface of a substrate.

[0012] The coating composition according to the present disclosure also includes a plurality of spherical particles, linked particles formed by a plurality of linked particles connected in a chain, large-diameter particles having a larger particle size than the spherical particles and the linked particles, and bound particles formed by small-diameter particles bound to the surfaces of the large-diameter particles and having a smaller particle size than the large-diameter particles.

[0013] According to the present disclosure, a hydrophilic coating, a heat exchanger, and a coating composition can be provided in which binder particles that impart hydrophilicity are covered with linkage particles that are integrated by linkage particles, and a portion of the linkage particles is embedded in the spherical particles and does not flow out, thereby maintaining high hydrophilicity.

[0014] Fig. 1 is a perspective view showing a heat exchanger according to embodiment 1. Fig. 2 is a schematic diagram of a hydrophilic coating according to embodiment 1. Fig. 3 is a cross-sectional view of bound particles that constitute the hydrophilic coating according to embodiment 1. Fig. 4 is a cross-sectional view of a linked body that constitutes the hydrophilic coating according to embodiment 1. Fig. 5 is a cross-sectional view of a first hydrophilic layer that constitutes the hydrophilic coating according to a modified example of embodiment 1. Fig. 6 is a cross-sectional view of a hydrophilic coating according to a modified example of embodiment 1.

[0015] Embodiments of the present disclosure will be described below with reference to the drawings. The present disclosure is not limited to the following embodiments and can be modified in various ways without departing from the spirit and scope of the present disclosure. Furthermore, the present disclosure includes all possible combinations of the configurations shown in the following embodiments. In particular, the combinations of components are not limited to those in each embodiment; components described in one embodiment can be applied to another embodiment. The configurations shown in the drawings are merely examples of the configurations of the present disclosure, and the present disclosure is not limited to the configurations shown in the drawings. In the following description, directional terms (e.g., "up," "down," "right," "left," "front," "rear," etc.) are used as appropriate to facilitate understanding, but these are for explanatory purposes and do not limit the present disclosure. In each drawing, components designated with the same reference numerals are identical or equivalent, and this applies throughout the entire specification. The relative dimensional relationships or shapes of the components in each drawing may differ from those in the actual product.

[0016] Embodiment 1. <Heat Exchanger 1> Fig. 1 is a perspective view showing a heat exchanger 1 according to embodiment 1. Fig. 1 is a perspective view showing a heat exchanger 1 according to embodiment 1. The heat exchanger 1 performs heat exchange between, for example, a refrigerant and air. The heat exchanger 1 is, for example, a fin-tube heat exchanger. The heat exchanger 1 includes heat transfer tubes 2 and fins 3.

[0017] The heat transfer tubes 2 are tubes through which a refrigerant flows, and a plurality of them are arranged side by side. The heat transfer tubes 2 are made of aluminum or an aluminum alloy. In the first embodiment, the heat transfer tubes 2 are circular tubes having a circular cross section and a single flow path formed therein through which the refrigerant flows. However, the heat transfer tubes 2 may also be flat tubes having a flat cross section and having a plurality of flow paths formed therein through which the refrigerant flows. Furthermore, the heat exchanger 1 may have a configuration in which the fins 3 are corrugated.

[0018] The fins 3 are made of aluminum or an aluminum alloy and are components that transfer heat from the refrigerant flowing inside the heat transfer tubes 2. The fins 3 are, for example, plate fins with holes formed in advance into which the heat transfer tubes 2 are inserted. The fins 3 may also be, for example, corrugated fins that are bent and disposed between the heat transfer tubes 2. Because the fins 3 are made of aluminum, which has high thermal conductivity, and have a large area, heat exchange between the refrigerant and air is carried out efficiently.

[0019] <Hydrophilic Coating 9> Fig. 2 is a schematic diagram of the hydrophilic coating 9 according to the first embodiment. As shown in Fig. 2, the hydrophilic coating 9 is formed on the fin 3. The hydrophilic coating 9 is formed by applying a coating composition for a heat exchanger to a substrate such as the fin 3 or the heat transfer tube 2. The hydrophilic coating 9 is formed on the surface of the fin 3 or the heat transfer tube 2, thereby improving the drainage of condensation water adhering to the fin 3 or the heat transfer tube 2. The hydrophilic coating 9 is composed of a first hydrophilic layer 7 and a second hydrophilic layer 8.

[0020] <First hydrophilic layer 7> The first hydrophilic layer 7 is a coating that covers the surface of the fins 3 or the heat transfer tubes 2. The first hydrophilic layer 7 enhances the hydrophilicity of the fins 3 or the heat transfer tubes 2 and has hydrophilic properties. The first hydrophilic layer 7 also has the effect of covering and smoothing processing scratches on the surface of the fins 3 or the heat transfer tubes 2. The first hydrophilic layer 7 may be configured to contain an acrylic resin and an epoxy resin, or may be configured to contain substantially only one of them. The first hydrophilic layer 7 may also be configured to contain a silica-based material using polysilicate or polysilazane.

[0021] Examples of resins that can be used include polysaccharide polymer compounds such as carboxymethyl cellulose and hydroxyethyl cellulose, and alkali metal salts or ammonium salts thereof; acrylic acid polymers such as polyacrylic acid, sodium polyacrylate, polyacrylamide, methyl polyacrylate, copolymers of methacrylic acid and maleic acid, and alkali metal salts or ammonium salts thereof; and polyvinyl alcohol.

[0022] The crosslinking agent used in the first hydrophilic layer 7 has a functional group such as an isocyanate group, an oxazoline group, a methylene group, a carbodiimide group, or an aziridine group. The crosslinked structure may be formed from a compound such as melamine. The resin composition containing an acrylic resin may be selected from commercially available products capable of forming a resin layer with metal adhesion. Examples of crosslinked structures include the Boncoat series manufactured by DIC Corporation and the TOP series manufactured by Nippon Parkerizing Co., Ltd.

[0023] Epoxy resins are polymers containing structural units derived from monomers having epoxy groups in their molecules. The epoxy resins may contain crosslinked structures, and the crosslinked structures are formed from monomers having crosslinkable functional groups. Resin compositions containing epoxy resins may be selected from commercially available products capable of forming resin layers with metal adhesion. Examples of resin compositions containing epoxy resins include EPICRON manufactured by DIC Corporation.

[0024] Silica-based materials include polysilicate, alkyl silicate, polysilazane, etc. as raw materials. Polysilicate and alkyl silicate have low surface tension, that is, high hydrophilicity, because the -(Si-O)n- molecular chain has alkoxyl groups with low surface free energy. Coatings made from polysilazane are compounds consisting only of silicon (Si), nitrogen (N), and hydrogen (H), and are inorganic polymers that do not contain organic substances such as carbon (C). Silica-based materials are capable of forming dense silicon dioxide (SiO ２ ) and develops hydrophilicity.

[0025] The thickness of the first hydrophilic layer 7 is 10 μm or less, preferably 5 μm or less, and more preferably 3 μm or less. If the thickness of the first hydrophilic layer 7 exceeds 10 μm, cracking or peeling occurs due to shrinkage during the formation of the hydrophilic layer, making it impossible to maintain hydrophilicity. The thickness of the first hydrophilic layer 7 can be adjusted by the concentration, viscosity, etc. of the coating composition used to form the first hydrophilic layer 7.

[0026] <Second Hydrophilic Layer 8> The second hydrophilic layer 8 is a hydrophilic layer similar to the first hydrophilic layer 7. The second hydrophilic layer 8 is formed on the first hydrophilic layer 7. The second hydrophilic layer 8 includes links 4, binder particles 5, and spherical particles 6. The binder particles 5 in the second hydrophilic layer 8 increase the contact area between the second hydrophilic layer 8 and condensation water formed on the fins 3. The increased contact area is achieved because the surface structure of the second hydrophilic layer 8 has two fractal-like structures: a large uneven structure due to the presence of the binder particles 5 themselves, and fine unevenness on the surface of the binder particles 5. The two fractal-like structures in this way make the surfaces of the fins 3 and heat transfer tubes 2 on which the second hydrophilic layer 8 is formed highly hydrophilic, allowing condensation water formed on the surfaces to be drained. The spherical particles 6 also cover the first hydrophilic layer 7, thereby enhancing the adhesion between the first hydrophilic layer 7 and the binder particles 5, and improving the hydrophilicity and maintaining the hydrophilicity for a long period of time.

[0027] In the second hydrophilic layer 8, the links 4 cover the bound particles 5, some of which are embedded in the aggregate of spherical particles 6, forming countless fine gaps. The countless gaps formed in the second hydrophilic layer 8 exhibit capillary action, causing water droplets adhering to the second hydrophilic layer 8 to spread into the gaps. As water spreads into the fine gaps, the second hydrophilic layer 8 exhibits high hydrophilicity. Furthermore, the structure in which the links 4 cover the bound particles 5 and the links 4 are partially embedded in the spherical particle aggregate layer 60 prevents the bound particles 5 from peeling off, and has the effect of maintaining hydrophilicity for a long period of time.

[0028] The second hydrophilic layer 8 maintains a hydrophilic state, i.e., water spreads easily. The surfaces of the fins 3 and heat transfer tubes 2 with such properties facilitate the movement of moisture during moisture absorption and drying, and have the effect of lifting hydrophilic and hydrophobic substances attached to the surfaces of the fins 3 and heat transfer tubes 2, making them less likely to adhere. In other words, the surfaces of the fins 3 and heat transfer tubes 2 exhibit excellent antifouling properties. Furthermore, the second hydrophilic layer 8 has the property of allowing water to flow and spread easily, which provides the following effect. Specifically, in situations where water flows over the surfaces of the fins 3 and heat transfer tubes 2, such as during condensation, rainfall, and cleaning, substances attached to the surfaces of the fins 3 and heat transfer tubes 2 flow away with the water flowing over the surfaces of the fins 3 and heat transfer tubes 2, making them more easily removed.

[0029] <Spherical particles 6> The spherical particles 6 are small diameter particles that are one of the elements constituting the second hydrophilic layer 8, and the spherical particles 6 are aggregated to form a spherical particle assembly layer 60. The spherical particle assembly layer 60 is an example of a small diameter particle assembly layer.

[0030] The spherical particles 6 are SiO ２ , Al ２ O ３ , Sb ２ O ５ , ZrO ２ , TiO ２ , Fe ２ O ３ , CeO ２ , AgO, CuO, Cu ２ The spherical particles 6 are composed of one selected from the group consisting of ZnO, ZnO, and composite oxides or mixtures thereof. The spherical particles 6 can exhibit further improved hydrophilicity by having functional groups such as hydroxyl groups, carbonyl groups, carboxyl groups, amino groups, and one or more of these groups on the surface.

[0031] The spherical particles 6 can be prepared according to a method known in the art. Alternatively, a commercially available dispersion in which the second inorganic particles are dispersed in water can be used as the raw material for the coating composition as the spherical particles 6. Examples of commercially available dispersions include "Snowtex (registered trademark)-XL," "Snowtex (registered trademark)-YL," "Snowtex (registered trademark)-ZL," "PST-2," "Snowtex (registered trademark)-20," "Snowtex (registered trademark)-30," "Snowtex (registered trademark)-C," "Snowtex (registered trademark)-O," "Snowtex (registered trademark)-OS," "Snowtex (registered trademark)-OL," and "Snowtex (registered trademark)-50," all manufactured by Nissan Chemical Industries, Ltd. Other examples of commercially available dispersions include "Adelite AT-30," "Adelite AT-40," and "Adelite AT-50" manufactured by ADEKA Corporation, and "Cataloid SI-550" and "Cataloid SI-50" manufactured by JGC Catalysts and Chemicals Co., Ltd.

[0032] The spherical particles 6 may be made of one selected from acrylic, urethane, styrene, polyol, epoxy, polyester, melamine, silicone, phenol, polyacrylonitrile, polyimide, cellulose, olefin, polyvinyl, and complex oxides or mixtures thereof.

[0033] The average particle diameter of the spherical particles 6, as measured by a light scattering method, is preferably 5 nm or more and 50 nm or less. The second hydrophilic layer 8 is formed by applying a hydrophilic composition, which is a liquid coating solution, to the heat exchanger 1 and drying it. Hydrophilic particles with an average particle diameter in the range of 5 nm or more and 50 nm or less are partially dissolved in water. However, for hydrophilic particles with an average particle diameter of less than 5 nm, the proportion of the component partially dissolved in water in the hydrophilic composition increases too much, causing the particles to aggregate. If the particles aggregate, the hydrophilicity of the resulting second hydrophilic layer 8 will be reduced.

[0034] On the other hand, particles with an average particle diameter of 5 nm or more and 50 nm or less scatter light reflected by the second hydrophilic layer 8, thereby improving the transparency of the second hydrophilic layer 8. The improved transparency of the second hydrophilic layer 8 suppresses changes in the color and texture of the heat exchanger 1, preventing the color and texture of the heat exchanger 1 from being impaired. Furthermore, the second hydrophilic layer 8 obtained by using spherical particles 6 with an average particle diameter of 5 nm or more and 50 nm or less has dense particles with fine gaps between the particles. The second hydrophilic layer 8 obtained in this manner also has a finely textured surface. The fine gaps between the particles and the surface texture reduce the intermolecular forces, i.e., adhesive forces, between the particles and contaminant-causing substances, making the second hydrophilic layer 8 less likely to adhere to the contaminant-causing substances. Additionally, the second hydrophilic layer 8 exhibits hydrophilic properties.

[0035] <Bound Particles 5> Figure 3 is a cross-sectional view of a bound particle 5 constituting the hydrophilic coating 9 according to embodiment 1. As shown in Figure 3, the bound particle 5 has a configuration in which a plurality of bound small particles 52 are bound to the surface of a bound large particle 51. In other words, the plurality of bound small particles 52 are firmly bound to the surface of the bound large particle 51. The bound particle 5 has a particle diameter larger than that of the spherical particle 6 and includes a bound large particle 51 that serves as a base, and a plurality of bound small particles 52 that are bound to the surface of the bound large particle 51 and have a particle diameter smaller than that of the bound large particle 51. The bound large particle 51 is an example of a large diameter particle, and the bound small particle 52 is an example of a small diameter particle.

[0036] The bound particles 5 have high hydrophilicity due to a fractal structure formed by two types of unevenness: a large uneven structure caused by the presence of the bound large particles 51 themselves, and fine unevenness caused by the fine bound small particles 52 on the surfaces of the bound large particles 51. In particular, the bound particles 5 are likely to have a fractal structure because the bound small particles 52, which have a uniform particle size, are arranged on the bound large particles 51. For this reason, it is believed that the bound particles 5 exhibit greater hydrophilicity than other particles.

[0037] The binder particles 5 are composed of inorganic particles or resin particles. The inorganic particles are composed of silica particles or titanium particles. The inorganic particles are composed of SiO ２, Al ２ O ３ , Sb ２ O ５ , ZrO ２ , TiO ２ , Fe ２ O ３ , CeO ２ , AgO, CuO, Cu ２ The resin particles may be composed of one selected from the group consisting of ZnO, ZnO, and composite oxides or mixtures thereof. The resin particles may be composed of one selected from acrylic, urethane, styrene, polyol, epoxy, polyester, melamine, silicone, phenol, polyacrylonitrile, polyimide, cellulose, olefin, polyvinyl, and composite oxides or mixtures thereof. The resin particles may be a hydrophilic resin such as acrylamide or polyethylene oxide.

[0038] The binder particles 5 can further exhibit hydrophilicity by having a hydroxy group, a carbonyl group, a carboxy group, an amino group, or one or more of these functional groups on the surface. The hydrophilicity of the surfaces of the binder particles 5 improves as the number of hydrophilic functional groups on the particle surfaces increases.

[0039] The shape of the bound particles 5 is not limited, and may be snowman-shaped, raspberry-shaped, golf ball-shaped, or a shape that has been made porous to increase the surface area.

[0040] The particle diameter of the large bound particles 51 is preferably 80 nm or more and 350 nm or less. If the particle diameter of the large bound particles 51 is less than 80 nm, the effect of improving drainage cannot be obtained, which is undesirable. Furthermore, if the particle diameter of the large bound particles 51 exceeds 350 nm, adhesion to the substrate decreases and the composition becomes cloudy, which is undesirable. The particle diameter of the small bound particles 52 connected to the large bound particles 51 is preferably 5 nm or more and 50 nm or less. If the particle diameter of the small bound particles 52 is less than 5 nm, manufacturing is difficult, which is undesirable. Furthermore, if the particle diameter of the small bound particles 52 exceeds 50 nm, adhesion to the substrate decreases, which is undesirable.

[0041] <Linked bodies 4> FIG. 4 is a cross-sectional view of the linked bodies 4 constituting the hydrophilic coating 9 according to embodiment 1. As shown in FIG. 4, the linked bodies 4 are formed by linking a plurality of linked body particles 41, which are small-diameter particles. In FIG. 4, (a) indicates a structure in which the linked body particles 41 are linked in a beaded pattern, (b) indicates a structure in which the linked body particles 41 are linked in a chain pattern, and (c) indicates a structure in which the linked body particles 41 are linked in a beaded pattern to form a three-dimensional network structure. The linked bodies 4 are formed on a spherical particle assembly layer 60 formed by spherical particles 6 and on binder particles 5. The linked bodies 4 cover the spherical particle assembly layer 60 formed by spherical particles 6 and the binder particles 5. The linked bodies 4 have a structure in which a plurality of linked body particles 41 are linked in a chain, beaded, or spider web shape. Note that the structure of the linked bodies 4 shown in the figure is a representative example, and it goes without saying that any structure is possible as long as a plurality of linked body particles 41 are linked in a chain or beaded pattern.

[0042] The linker particles 41 constituting the linker 4 are, for example, inorganic particles. The linker particles 41 are not particularly limited and may be, for example, particles of elements such as silicon, magnesium, aluminum, titanium, cerium, tin, zinc, germanium, indium, and antimony, or oxides of these elements such as silica, alumina, and titania, or nitride particles. These may be used alone or in combination of two or more. Among these, silica particles are preferred as the linker particles 41. This is because silica particles function as a binder in coating films. Furthermore, silica particles have a refractive index closer to that of plastics and glass commonly used as substrates than titania and alumina particles. Having similar refractive indices between the substrate and the coating film reduces whitening or glare caused by light reflection at their interface or surface, and is less likely to impair the color tone of the substrate.

[0043] The connector particles 41 constituting the connectors 4 may be resin particles. The resin particles may be made of one type selected from the group consisting of acrylic, urethane, styrene, polyol, epoxy, polyester, melamine, silicone, phenol, polyacrylonitrile, polyimide, cellulose, olefin, polyvinyl, and composite oxides or mixtures thereof.

[0044] The linker 4 can further exhibit hydrophilicity by having a hydroxy group, a carbonyl group, a carboxy group, an amino group, or one or more of these functional groups on the surface.

[0045] The average particle size of the linkers 4 is 50 nm or more and 10 μm or less, preferably 100 nm or more and 5 μm or less, and more preferably 120 nm or more and 1 μm or less. Here, the average particle size refers to the average particle size measured by a laser Doppler method (dynamic electrophoretic light scattering method) using an Otsuka Electronics "Zeta Potential / Particle Size Measurement System ELSZ-1000ZS." If the average particle size of the linkers 4 is less than 50 nm, the linkers 4 will not be able to cover most of the binder particles 5. In addition, a structure in which the linkers 4 covering the binder particles 5 are partially embedded in the spherical particles 6 will not be achieved. On the other hand, if the particle size of the linkers 4 exceeds 10 μm, adhesion to the substrate and durability will decrease.

[0046] The average particle size of the linker particles 41 constituting the linkers 4 is not particularly limited, but is preferably 5 nm to 50 nm, more preferably 6 nm to 30 nm, and even more preferably 8 nm to 20 nm. When the linker particles 41 are inorganic particles, an average particle size of less than 5 nm may prevent the formation of linkers 4 in which the linker particles 41 are bonded in a chain or beaded pattern. On the other hand, if the average particle size of the linker particles 41 exceeds 20 nm, the average particle size of the linkers 4 increases, resulting in an increase in the thickness of the coating film, which may be prone to defects such as cracks.

[0047] The linker 4 can be prepared by a method known in the art. Furthermore, dispersions in which linker particles 41 are dispersed in water are commercially available, and these dispersions can also be used as raw materials for coating compositions. Examples of commercially available dispersions include the "Snowtex (registered trademark)-PS" series manufactured by Nissan Chemical Industries, Ltd.

[0048] The linker particles 41 can also be referred to as first particles, primary particles, or first inorganic particles.

[0049] <Coating Composition> The coating composition contains linkers 4, spherical particles 6, and binder particles 5. The linkers 4 are configured such that linker particles 41 are randomly bonded two-dimensionally or three-dimensionally in the form of a chain, a bead, or a spider web. The binder particles 5 are configured such that large binder particles 51 have small binder particles 52 bonded to the surfaces of the large binder particles 51. The respective contents of the linkers 4, the spherical particles 6, and the binder particles 5 are preferably 0.01 wt % or more and 10 wt % or less, more preferably 0.02 wt % or more and 5 mt % or less, and even more preferably 0.05 wt % or more and 3 wt % or less.

[0050] If the content of each of the linkers 4, spherical particles 6, and binder particles 5 is less than 0.01 wt%, the particles will break apart, making it impossible to form a hydrophilic film. Furthermore, if the content of each of the linkers 4, spherical particles 6, and binder particles 5 exceeds 10 wt%, the hydrophilic layer will become too thick and cracks will be more likely to occur, which is undesirable. Furthermore, if the content of each of the linkers 4, spherical particles 6, and binder particles 5 is too high, odors will be more likely to occur, which is undesirable.

[0051] In the coating composition, the mass ratio of the linkers 4 to the spherical particles 6 is 99:1 to 1:99, preferably 97:3 to 3:97, more preferably 95:5 to 5:95, and most preferably 90:10 to 10:90. When the mass ratio is within this range, an uneven structure can be formed on the surface of the coating film. This reduces the intermolecular forces between the dirt and the coating film, thereby improving the drainage performance of the coating film. Furthermore, when the mass ratio is within this range, the linkers 4 can reduce the cohesive force of the spherical particles 6 during coating film formation, thereby preventing the occurrence of defects such as cracks in the coating film. This allows the coating film to maintain its drainage performance and adhesion to the substrate for a long period of time, even when exposed to physical stresses such as abrasion. If the proportion of the linkers 4 is too high, defects such as cracks are more likely to occur and drainage performance will also be reduced. On the other hand, if the proportion of the spherical particles 6 is too high, the adhesion between the coating film and the substrate will be reduced, making it unable to adequately withstand physical stresses such as abrasion. In terms of the mass ratio of the links 4 to the spherical particles 6, a case where the proportion of the links 4 is too high is, for example, 99.9:0.01, and a case where the proportion of the spherical particles 6 is too high is, for example, 0.01:99.9. At this order, the coating composition cannot exert its effects, and it becomes difficult to control the coating film.

[0052] The coating composition contains a water-soluble solvent having a boiling point of 150°C or higher and 300°C or lower. The water-soluble solvent is a component that controls the drying rate of the coating composition during the formation of the coating film, i.e., the hydrophilic coating 9, and facilitates the presence of a large number of spherical particles 6 in the lower layer of the coating film and a large number of linker particles 41 that constitute the linkers 4 in the upper layer of the coating film. The lower layer of the coating film is the fin 3 side, which is the substrate side of the coating film, and is the first hydrophilic layer 7 side. The surface layer of the coating film is the surface side of the coating film. Furthermore, when the substrate on which the coating film is formed is a plastic substrate, the water-soluble solvent can swell the surface of the plastic substrate and improve adhesion between the coating film and the plastic substrate.

[0053] If the boiling point of the water-soluble solvent is less than 150°C, the drying speed becomes too fast, making it impossible to allow many spherical particles 6 to be present in the lower layer of the coating film, and the effect of improving the adhesion between the substrate and the coating film cannot be obtained. The spherical particles 6 can also be referred to as second inorganic particles. In addition, defects such as cracks are likely to occur in the coating film. On the other hand, if the boiling point of the water-soluble solvent exceeds 300°C, the water-soluble solvent is likely to remain in the coating film, making it impossible to obtain a coating film with the desired properties. Here, the water-soluble solvent generally means a solvent with a solubility in water of 70% by mass or more. If the solubility in water is less than 70% by mass, the particles are likely to separate or aggregate in water, and the above-mentioned effects may not be fully obtained.

[0054] The specific gravity of the water-soluble solvent is not particularly limited, but is preferably 0.9 or more and 1.2 or less. If the specific gravity of the water-soluble solvent is less than 0.9, the effect of improving the adhesion between the substrate and the coating film may not be sufficiently obtained. On the other hand, if the specific gravity of the water-soluble solvent is more than 1.2, the water-soluble solvent is likely to remain in the coating film, and a coating film having the desired properties may not be obtained.

[0055] The KB value (Kauri-butanol value) of the water-soluble solvent is not particularly limited, but is preferably 20 or more and 100 or less. If the KB value of the water-soluble solvent is less than 20, even if the substrate on which the coating film is formed is a plastic substrate, the effect of swelling the surface of the plastic substrate will be poor. As a result, the effect of improving the adhesion between the coating film and the plastic substrate may not be sufficiently achieved. On the other hand, if the KB value of the water-soluble solvent exceeds 100, the substrate may dissolve.

[0056] Examples of water-soluble solvents include propylene glycol monomethyl ether, ethylene glycol monomethyl ether, ethylene glycol monomethyl ether acetate, ethyl lactate, diethylene glycol dimethyl ether, dipropylene glycol dimethyl ether, dipropylene glycol dimethyl ether, diethylene glycol ethyl methyl ether, diethylene glycol isopropyl methyl ether, dipropylene glycol monomethyl ether, diethylene glycol diethyl ether, diethylene glycol monomethyl ether, diethylene glycol butyl methyl ether, tripropylene glycol dimethyl ether, triethylene glycol dimethyl ether, diethylene glycol monobutyl ether, ethylene glycol monophenyl ether, triethylene glycol monomethyl ether, diethylene glycol dibutyl ether, triethylene glycol butyl methyl ether, polyethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol monomethyl ether, and N-methyl-2-pyrrolidone. These may be used alone or in combination of two or more.

[0057] The content of the water-soluble solvent in the coating composition is 0.01% by mass or more and 10% by mass or less, preferably 0.05% by mass or more and 8% by mass or less, and more preferably 0.1% by mass or more and 5% by mass or less. If the content of the water-soluble solvent is less than 0.01% by mass, the effect of improving the adhesion between the substrate and the coating film may not be sufficiently obtained. On the other hand, if the content of the water-soluble solvent exceeds 10% by mass, the water-soluble solvent is likely to remain in the coating film, and a coating film having the desired properties may not be obtained.

[0058] The water contained in the coating composition is not particularly limited, and tap water, pure water, RO water, deionized water, or the like can be used. In particular, from the viewpoint of improving the dispersion stability of the linked bodies 4, the bound particles 5, and the spherical particles 6 in the coating composition, it is preferable that the amount of ionic impurities such as calcium ions or magnesium ions is small. Specifically, the amount of divalent or higher ionic impurities contained in the water is preferably 200 ppm or less, more preferably 50 ppm or less. If the amount of divalent or higher ionic impurities is greater than 200 ppm, and if the linked bodies 4 or the spherical particles 6 are composed of inorganic particles, the inorganic particles may aggregate and precipitate, or the strength or transparency of the coating film may decrease.

[0059] The water content in the coating composition is not particularly limited, but is preferably 80% by mass or more and 99% by mass or less. More preferably, it is 83% by mass or more and 98% by mass or less, even more preferably, 85% by mass or more and 97% by mass or less, and most preferably, it is 87% by mass or more and 96% by mass or less. If the water content is less than 80% by mass, the coating film may become thick and defects such as cracks may easily occur. On the other hand, if the water content exceeds 99% by mass, the amount of solids in the coating composition may become too small, making it difficult to efficiently form a coating film.

[0060] The coating composition may further contain a surfactant to adjust the stability, application property, and drying property of the coating composition. The surfactant is not particularly limited, and any surfactant known in the art may be used. Specifically, any of anionic, nonionic, and cationic surfactants may be used. The content of the surfactant in the coating composition is not particularly limited as long as it does not impair the effects of the present disclosure.

[0061] Examples of anionic surfactants include higher alcohol sulfates (Na salts or amine salts), alkyl allyl sulfonates (Na salts or amine salts), alkyl naphthalene sulfonates (Na salts or amine salts), alkyl naphthalene sulfonate condensates, alkyl phosphates, dialkyl sulfosuccinates, rosin soaps, and fatty acid salts (Na salts or amine salts).

[0062] Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkylphenol ethers, polyoxyethylene alkyl esters, polyoxyethylene alkylamines, polyoxyethylene alkylolamines, polyoxyethylene alkylamides, sorbitan alkyl esters, and polyoxyethylene sorbitan alkyl esters.

[0063] Examples of cationic surfactants include octadecylamine acetate, imidazoline derivative acetate, polyalkylene polyamine derivatives or salts thereof, octadecyltrimethylammonium chloride, trimethylaminoethyl alkylamido halogenides, alkylpyridinium sulfates, alkyltrimethylammonium halogenides, etc. Each of the above surfactants can be used alone or in combination of two or more.

[0064] The water contact angle of the hydrophilic coating 9 is preferably 30° or less. The water contact angle of the hydrophilic coating 9 is more preferably 15° or less. Furthermore, the water contact angle of the hydrophilic coating 9 is most preferably 10° or less. A small water contact angle improves the ability of water droplets to wet and spread in the surface direction of the fins 3 and heat transfer tubes 2, thereby achieving the effect of quickly draining water.

[0065] In this way, the hydrophilic coating 9 is configured such that the bound particles 5 that impart hydrophilicity are covered by the bound bodies 4 that are bound together, and the bound particles 5 do not flow out. Therefore, even if the hydrophilic coating 9 is continuously exposed to water, the hydrophilicity does not decrease, and the hydrophilic coating 9 with excellent drainage properties can be provided, and the heat exchanger 1 to which the hydrophilic coating 9 is formed and imparted with hydrophilicity can be obtained.

[0066] <Modification> FIG. 5 is a cross-sectional view of a first hydrophilic layer 7 constituting a hydrophilic coating 9 according to a modification of embodiment 1. FIG. 6 is a cross-sectional view of a hydrophilic coating 9 according to a modification of embodiment 1. In the hydrophilic coating 9 according to the modification, particles are added to the first hydrophilic layer 7. By adding particles to the first hydrophilic layer 7, a configuration with fine irregularities can be achieved. Spherical particles 6 of the second hydrophilic layer 8 are embedded in recesses 71 formed in the first hydrophilic layer 7. Specifically, particles of several nanometers to several micrometers are added to form a coating having a fine irregularity structure on the surface of the coating. This improves adhesion between the first hydrophilic layer 7 and the second hydrophilic layer 8, allowing the hydrophilicity of the hydrophilic coating 9 to be maintained.

[0067] <Example> Next, hydrophilic coatings 9 were prepared based on the first embodiment and a comparative example, and their performances were compared and evaluated.

[0068] (Common Conditions) First, the common conditions for both the Examples and Comparative Examples will be described. The aluminum substrate used was a 1 mm thick plate made of aluminum alloy alloy number 3003 specified in JIS H4000. The aluminum substrate was cleaned by gently wiping the surface with cotton soaked in acetone.

[0069] The hydrophilic coating 9, i.e., the layer formed by the first hydrophilic layer 7 and the second hydrophilic layer 8, was formed by applying a coating composition for forming the hydrophilic coating 9 to an aluminum substrate and drying it. The coating composition was composed of SNOWTEX series manufactured by Nissan Chemical Industries, Ltd. as the spherical particles 6, SFR-80V manufactured by JGC Catalysts and Chemicals Co., Ltd. as the bound particles 5, and SNOWTEX ST-UP manufactured by Nissan Chemical Industries, Ltd. as the linker 4. Polyoxyethylene lauryl ether was used as the surfactant, and xanthan gum was used as the thickener.

[0070]

[0071] Table 1 shows the coating compositions for Examples 1-7 and Comparative Examples 1-3.

[0072] Example 1 In Example 1, the coating composition used was the composition shown in "Example 1" in Table 1. For the spherical particles 6, Snowtex ST-O manufactured by Nissan Chemical Industries, Ltd. was used.

[0073] Example 2 Example 2 differs from Example 1 in the content of the spherical particles 6 constituting the coating composition, but the rest was the same as Example 1. That is, the coating composition of Example 2 has the composition ratio shown in "Example 2" in Table 1, and the content of the spherical particles 6 is lower than that of Example 1.

[0074] Example 3 Example 3 differs from Example 1 in the content of the spherical particles 6 constituting the coating composition, but the rest was the same as Example 1. That is, the coating composition of Example 3 has the composition ratio shown in "Example 3" in Table 1, and the content of the spherical particles 6 is higher than that of Example 1.

[0075] Example 4 Example 4 differs from Example 1 in the content of binder particles 5 constituting the coating composition, but the rest was the same as Example 1. That is, the coating composition of Example 4 had the composition ratio shown in "Example 4" in Table 1, and the content of binder particles 5 was lower than that of Example 1.

[0076] Example 5 Example 5 differs from Example 1 in the content of binder particles 5 constituting the coating composition, but the rest was the same as Example 1. That is, the coating composition of Example 5 has the composition ratio shown in "Example 5" in Table 1, and the content of binder particles 5 is higher than that of Example 1.

[0077] Example 6 Example 6 differs from Example 1 in the content of connector 4 constituting the coating composition, but the rest was the same as Example 1. That is, the coating composition of Example 6 had the composition ratio shown in "Example 5" in Table 1, and the content of connector 4 was lower than that of Example 1.

[0078] Example 7 Example 7 differs from Example 1 in the content of connector 4 constituting the coating composition, but the rest was the same as Example 1. That is, the coating composition of Example 7 had the composition ratio shown in "Example 7" in Table 1, and the content of connector 4 was higher than that of Example 1.

[0079] Comparative Example 1 Comparative Example 1 is an example in which the coating composition does not contain the spherical particles 6. That is, the coating composition of Comparative Example 1 has the composition ratio shown in "Comparative Example 1" in Table 1.

[0080] Comparative Example 2 Comparative Example 2 is an example in which the coating composition does not contain binder particles 5. That is, the coating composition of Comparative Example 2 has the composition ratio shown in "Comparative Example 2" in Table 1.

[0081] Comparative Example 3 Comparative Example 3 is an example in which the coating composition does not contain connectors 4. That is, the coating composition of Comparative Example 3 has the composition ratio shown in "Comparative Example 3" in Table 1.

[0082]

[0083] Table 2 shows the evaluation results of hydrophilic performance in Examples 1 to 7 and Comparative Examples 1 to 3. As shown in Table 2, coating compositions were prepared as described in Examples 1 to 7 and Comparative Examples 1 to 3, and the initial hydrophilicity, initial drainage property, sustained hydrophilicity, and sustained drainage property of the resulting hydrophilic coating 9 were evaluated. The hydrophilic coating 9 was formed by applying the coating composition prepared as described in Examples 1 to 7 and Comparative Examples 1 to 3 to an aluminum substrate and drying it.

[0084] The initial hydrophilicity was evaluated using an aluminum substrate that had been left at room temperature (25°C) for 1 hour. A water droplet of approximately 5 μL was dropped onto the surface of the aluminum fin from the tip of a PTFE (polytetrafluoroethylene)-coated needle with an inner diameter of 0.1 mm, and the contact angle was measured using a contact angle meter. The contact angle meter used was a CX-150 model manufactured by Kyowa Interface Science Co., Ltd. The contact angle measured here is the initial water contact angle. The smaller the contact angle, the better the hydrophilicity. The initial hydrophilicity was evaluated according to the following criteria.

[0085] 1: Contact angle of 10° or less 2: Contact angle of 10° or more and less than 15° 3: Contact angle of 15° or more and less than 30° 4: Contact angle of 30° or more and less than 50° 5: Contact angle of 50° or more

[0086] The initial drainage property was evaluated using an aluminum substrate that had been left at room temperature (25°C) for 1 hour. Using a micropipette, a 10 μL drop of water was dropped from the tip of a needle onto the surface of a vertically standing aluminum fin, and the drainage rate [cm / s], which is the rate at which the water flows down, was calculated. The faster the drainage rate, the better the drainage property. The initial drainage property was evaluated according to the following criteria.

[0087] 1: Drainage speed: 6 cm / s or more 2: Drainage speed: Less than 6 cm / s, 4 cm / s or more 3: Drainage speed: Less than 4 cm / s, 2 cm / s or more 4: Drainage speed: Less than 2 cm / s, 1 cm / s or more 5: Drainage speed: Less than 1 cm / s

[0088] The sustained hydrophilicity and sustained drainage property were evaluated by conducting an accelerated test that simulated the phenomenon of repeated condensation and drying of the heat exchanger 1. In the accelerated test, the aluminum substrate was left in an ion-exchanged water environment for 7 hours, and then exposed to an 80°C constant temperature bath for 17 hours, which constituted one cycle. After 14 cycles, the initial hydrophilicity and initial drainage property were evaluated using the same criteria as for the initial hydrophilicity and initial drainage property.

[0089] As shown in Table 2, the hydrophilic coatings 9 of Examples 1 to 7 had evaluation results of 3 or less for initial hydrophilicity and initial drainage, and were good in hydrophilicity based on contact angle and drainage based on drainage rate. Furthermore, the evaluation results of sustained hydrophilicity and sustained drainage after an accelerated test simulating the phenomenon of repeated condensation and drying were also 3 or less, indicating a high sustainability of the drainage effect. Among these, the hydrophilic coating 9 formed using the coating composition of Example 1 showed the best results.

[0090] The hydrophilic coating 9 of Comparative Example 1 did not contain spherical particles 6 and did not form aggregates of spherical particles 6, resulting in poor initial hydrophilicity. Furthermore, Comparative Example 1 had good initial drainage properties, but sustained drainage properties deteriorated in an accelerated test simulating condensation and drying. This is thought to be because the absence of aggregates of spherical particles 6 resulted in poor adhesion of the bound particles 5 and the links 4 to the substrate, causing the bound particles 5 and the links 4 to detach from the substrate, resulting in a decrease in the drainage rate.

[0091] The hydrophilic coating 9 of Comparative Example 2 does not contain the binder particles 5 and does not form a fractal structure, resulting in good hydrophilicity but poor drainage.

[0092] The hydrophilic coating 9 of Comparative Example 3 does not include the linkers 4 and does not form a structure that covers the binder particles 5. Therefore, in the accelerated test simulating condensation and drying, the binder particles 5 were detached from the substrate, resulting in a deterioration in sustained drainage.

[0093] The hydrophilic coating 9 according to the first embodiment described above includes a first hydrophilic layer 7 and a second hydrophilic layer 8 formed on the first hydrophilic layer 7 and having spherical particles 6 constituting a spherical particle assembly layer 60, binder particles 5, and linkage bodies 4. The binder particles 5 are composed of large binder particles 51 and small binder particles 52 bound to the surfaces of the large binder particles 51, forming a fractal structure. Some of the binder particles 5 are embedded in the spherical particles 6 and covered by the linkage bodies 4. This suppresses the outflow of the binder particles 5 themselves and prevents the outflow of the spherical particles 6 or the linkage bodies 41 constituting the linkage bodies 4, thereby improving the hydrophilicity of the hydrophilic coating 9 and maintaining high hydrophilicity.

[0094] The first hydrophilic layer 7 has an uneven surface, and the spherical particles 6 that form part of the spherical particle assembly layer 60 are embedded in the recesses 71. This improves the adhesion between the first hydrophilic layer 7 and the second hydrophilic layer 8, and makes it possible to maintain the hydrophilicity of the hydrophilic coating 9.

[0095] Furthermore, by adjusting the particle diameters of the large and small particles 51 and 52 constituting the binder particles 5, it is possible to improve drainage properties, maintain constant adhesion to the substrate, suppress cloudiness, and facilitate production.

[0096] The large and small particles 51 and 52 constituting the binder particles 5 are made of inorganic materials such as silica, alumina, or titania, or hydrophilic resins such as acrylamide or polyethylene oxide. By preparing the materials in this manner, the hydrophilicity of the hydrophilic coating 9 can be improved.

[0097] Furthermore, the hydrophilic coating 9 does not include a hydrophobic region on the surface, thereby improving the hydrophilicity.

[0098] In addition, a hydrophilic coating 9 is formed on the surface of the heat exchanger 1. This makes it easier to drain condensed water that has adhered to the heat exchanger 1, suppresses an increase in ventilation resistance in the heat exchanger 1 due to the adhesion of condensed water, and maintains the heat transfer performance of the heat exchanger 1.

[0099] Furthermore, a coating composition containing a plurality of spherical particles 6, linkages 4, and binder particles 5 can produce a hydrophilic coating 9 that maintains its hydrophilicity.

[0100] REFERENCE SIGNS LIST 1 heat exchanger, 2 heat transfer tube, 3 fin, 4 connected body, 5 bound particles, 6 spherical particles, 7 first hydrophilic layer, 8 second hydrophilic layer, 9 hydrophilic coating, 41 connected body particles, 51 bound large particles, 52 bound small particles, 60 spherical particle aggregate layer, 71 recess.

Claims

1. A hydrophilic coating comprising: a first hydrophilic layer; and a second hydrophilic layer formed on the first hydrophilic layer, wherein the second hydrophilic layer comprises: a spherical particle assembly layer covering the first hydrophilic layer and composed of a plurality of spherical particles; binder particles formed by binding a plurality of small particles having a particle diameter smaller than that of the large particles to the surfaces of large particles having a particle diameter larger than that of the spherical particles, and the binder particles being partially embedded in the spherical particle assembly layer; and linked bodies formed on the spherical particle assembly layer and the bound particles, the linked bodies being composed of a plurality of linked body particles having a particle diameter smaller than that of the large particles.

2. The hydrophilic coating according to claim 1, wherein the first hydrophilic layer has an uneven surface, and a portion of the spherical particle assembly layer is embedded in the recesses of the first hydrophilic layer.

3. The hydrophilic coating according to claim 1 or 2, wherein the large particle diameter particles of the binding particles have a particle diameter of 80 nm or more and 350 nm or less, and the small particle diameter particles of the binding particles have a particle diameter of 5 nm or more and 50 nm or less.

4. The hydrophilic coating according to any one of claims 1 to 3, wherein the large particle diameter particles and the small particle diameter particles are each made of an inorganic material such as silica, alumina, or titania, or a hydrophilic resin such as acrylamide or polyethylene oxide.

5. The hydrophilic coating according to any one of claims 1 to 4, which does not contain a hydrophobic region on the surface.

6. A heat exchanger having the hydrophilic coating according to any one of claims 1 to 5 formed on the surface of a substrate.

7. A coating composition comprising: a plurality of spherical particles; linked particles formed by linking a plurality of linked particles in a chain; large-diameter particles having a larger particle size than the spherical particles and the linked particles; and bound particles formed by small-diameter particles bound to the surfaces of the large-diameter particles and having a smaller particle size than the large-diameter particles.

Images