Resin-coated aluminum alloy sheet and resin composition for resin-coated aluminum alloy sheet

Abstract

To provide a resin-coated aluminum alloy plate provided with excellent heat dissipation and high humidity resistance.SOLUTION: A resin-coated aluminum alloy plate comprises a coated resin layer formed from a cured material of a resin composition containing an epoxy -based resin and a curing agent, wherein the coated resin layer contains 5.0 to 25.0 pts.mass of graphite particles relative to a total of 100.0 pts.mass of the epoxy-based resin and the curing agent and 3.0 to 28.0 pts.mass of silica particles relative to 100.0 pts.mass of the epoxy-based resin and the curing agent, and a thickness of the coated resin layer is 2.0 to 25.0 μm.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a resin-coated aluminum alloy sheet which is suitable as a material for housings, heat sinks, reflectors, etc. for heat-generating electronic components and home appliances and which has processability, heat dissipation properties, and high-humidity resistance, and to a resin composition for a resin-coated aluminum alloy sheet which is used for forming a resin layer of the resin-coated aluminum alloy sheet. [Background technology]

[0002] In recent years, as electronic devices have become smaller and more powerful, the amount of heat generated by components can increase locally. This increase in heat generated by components can impair the performance of the electronic device and also reduce its reliability. Methods for quickly dissipating this heat include heat dissipation measures such as ventilation holes and cooling fans. However, these measures have the drawbacks of increasing costs and reducing environmental friendliness by increasing CO2 emissions due to the energy required to power the fans.

[0003] On the other hand, heat dissipation measures based on thermal radiation are low-cost because they do not require power, and are environmentally friendly because they can be made quieter by eliminating the need for a cooling fan, and can also be applied to space-saving applications.Amid this trend, a heat-dissipating resin-coated aluminum alloy sheet has been proposed, in which high heat dissipation properties are imparted by applying a coating to the surface of an aluminum alloy substrate with excellent thermal conductivity (Patent Document 1), and expectations for heat-dissipating resin-coated aluminum alloy sheets are expected to grow even more in the future.

[0004] As a low-cost material with good processability and heat dissipation properties, a thermally emissive surface treatment material has been proposed (Patent Document 2), which comprises an outer coating film and an inner coating film on the surface of a substrate made of metal or the like, and the inner coating film contains 0.03 to 70 mass % of a pigment with a thermal emissivity of 70% or more, relative to the dry mass of the inner coating film. However, in a resin-coated aluminum alloy plate as in Patent Document 2, the resin is prone to softening, and therefore, when the aluminum alloy plate is wound and stored in a coil during production, a blocking phenomenon occurs in which the resin coating films adhere to each other, which can be a problem.

[0005] In response to this, a heat-dissipating resin-coated aluminum alloy plate has been proposed that achieves excellent heat dissipation, is less susceptible to blocking, and has excellent processability (Patent Document 3). However, because the coating film in Patent Document 3 uses a resin that is easily hydrolyzed, there is a possibility that the coating film will deteriorate in a high-humidity environment. Furthermore, while the selection of a resin that does not hydrolyze has been considered, it has been extremely difficult to achieve both heat dissipation properties and durability (moisture resistance) in a high-humidity environment because the resin itself has low emissivity. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-201001 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-228085 [Patent Document 3] Japanese Patent Application Laid-Open No. 2005-305993 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a resin-coated aluminum alloy sheet that has both good heat dissipation and high humidity resistance. [Means for solving the problem]

[0008] As a result of extensive research, the present inventors have found that high humidity resistance can be improved without reducing heat dissipation by providing a chemical conversion coating on an aluminum alloy plate and then providing a coating resin layer thereon consisting of a cured product of a resin composition containing an epoxy resin, a curing agent, a predetermined amount of graphite particles, and a predetermined amount of silica particles, thereby completing the present invention.

[0009] The above problems are solved by the present invention described below. That is, the present invention (1) has a coating resin layer formed of a cured product of a resin composition containing an epoxy resin and a curing agent, the coating resin layer contains 5.0 to 25.0 parts by mass of graphite particles relative to 100.0 parts by mass of the epoxy resin and the curing agent in total, and 3.0 to 28.0 parts by mass of silica particles relative to 100.0 parts by mass of the epoxy resin and the curing agent in total, and the coating resin layer has a thickness of 2.0 to 25.0 μm; The present invention provides a resin-coated aluminum alloy sheet characterized by the above.

[0010] The present invention (2) provides the resin-coated aluminum alloy sheet according to (1), characterized in that the coating resin layer is formed from a cured product of a resin composition containing, as resin components, the epoxy resin and the curing agent, and containing, as fillers, 5.0 to 25.0 parts by mass of the graphite particles relative to 100.0 parts by mass of the epoxy resin and the curing agent in total, and 3.0 to 28.0 parts by mass of the silica particles relative to 100.0 parts by mass of the epoxy resin and the curing agent in total.

[0011] The present invention (3) also provides the resin-coated aluminum alloy sheet according to (1) or (2), characterized in that the molecular weight of the epoxy resin is 40,000 to 60,000.

[0012] The present invention (4) provides the resin-coated aluminum alloy sheet according to any one of (1) to (3), wherein the curing agent is an amino resin-based curing agent.

[0013] The present invention (5) also provides the resin-coated aluminum alloy sheet according to any one of (1) to (4), characterized in that the coating resin layer has a thickness of 5.0 to 15.0 μm.

[0014] The present invention (6) also provides the resin-coated aluminum alloy sheet according to any one of (1) to (5), wherein the graphite particles have an average particle size of 1.0 to 8.0 μm.

[0015] The present invention (7) also provides a resin-coated aluminum alloy sheet according to (6), characterized in that the graphite particles have an average particle size of 1.0 to 5.0 μm.

[0016] The present invention (8) also provides the resin-coated aluminum alloy sheet according to any one of (1) to (7), characterized in that the arithmetic mean roughness Ra of the surface of the coating resin layer is 0.100 to 2.500 μm.

[0017] The present invention (9) also provides the resin-coated aluminum alloy sheet according to any one of (1) to (8), characterized in that the coating resin layer has a glossiness of 0.1 to 4.5.

[0018] The present invention (10) also provides a resin composition for a resin-coated aluminum alloy sheet, comprising an epoxy resin, a curing agent, 5.0 to 25.0 parts by mass of graphite particles relative to a total of 100.0 parts by mass of the epoxy resin and the curing agent, 3.0 to 28.0 parts by mass of silica particles relative to a total of 100.0 parts by mass of the epoxy resin and the curing agent, and a solvent. [Effects of the Invention]

[0019] According to the present invention, it is possible to provide a resin-coated aluminum alloy sheet that has both good heat dissipation properties and high moisture resistance. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a schematic cross-sectional view of an embodiment of a resin-coated aluminum alloy sheet of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] The resin-coated aluminum alloy sheet according to the present invention has a coating resin layer formed of a cured product of a resin composition containing an epoxy resin and a curing agent, the coating resin layer contains 5.0 to 25.0 parts by mass of graphite particles relative to 100.0 parts by mass of the epoxy resin and the curing agent in total, and 3.0 to 28.0 parts by mass of silica particles relative to 100.0 parts by mass of the epoxy resin and the curing agent in total, and the coating resin layer has a thickness of 2.0 to 25.0 μm; The resin-coated aluminum alloy sheet is characterized by the following. The resin-coated aluminum alloy sheet of the present invention is a heat-dissipating resin-coated aluminum alloy sheet having heat dissipation properties.

[0022] The resin-coated aluminum alloy sheet of the present invention has a coating resin layer formed on the surface of the aluminum alloy sheet directly or via a chemical conversion coating, the coating layer being made of a cured product of a resin composition containing an epoxy resin, a curing agent, graphite particles, and silica particles.

[0023] The resin-coated aluminum alloy sheet of the present invention will be described with reference to FIG. 1. FIG. 1 is a schematic cross-sectional view of an example of the resin-coated aluminum alloy sheet of the present invention. In FIG. 1, the resin-coated aluminum alloy sheet 1 comprises a chemical conversion coating 3 formed on the surface of an aluminum alloy sheet (aluminum sheet) 2 and a coating resin layer 4 formed on the surface of the chemical conversion coating 3. Note that the resin-coated aluminum alloy sheet of the example shown in FIG. 1 has a chemical conversion coating as a base for the coating resin layer, but in the present invention, the chemical conversion coating is optional, and the coating resin layer may be formed directly on the surface of the aluminum alloy sheet (aluminum sheet). For example, the coating resin layer may be formed directly on the surface of an aluminum alloy sheet (aluminum sheet) that has been washed with an organic solvent, alkali, or acid. The resin-coated aluminum alloy sheet of the present invention includes (i) a resin-coated aluminum alloy sheet consisting of an aluminum alloy sheet (including aluminum sheet), a chemical conversion coating formed on the surface of the aluminum alloy sheet, and a coating resin layer formed on the surface of the chemical conversion coating, and (ii) a resin-coated aluminum alloy sheet consisting of an aluminum alloy sheet (for example, an aluminum alloy sheet cleaned with an organic solvent, alkali, or acid) (including aluminum sheet) and a coating resin layer formed on the surface of the aluminum alloy sheet. Organic solvents used for cleaning aluminum alloy sheets include acetone, methylene chloride, and methyl ethyl ketone. Alkalis include aqueous sodium hydroxide solutions and commercially available aluminum degreasing solutions (containing alkali builders, chelating agents, surfactants, etc.). Acids include nitric acid and sulfuric acid.

[0024] (aluminum alloy plate) The aluminum alloy sheet according to the resin-coated aluminum alloy sheet of the present invention is a sheet made of either aluminum or an aluminum alloy. The material of the aluminum alloy sheet is not particularly limited, but 1000 series aluminum materials, 3000 series aluminum alloy materials, and 5000 series aluminum alloy materials are suitable. The thickness of the aluminum alloy sheet is appropriately selected depending on the application, but is preferably in the range of 0.6 to 2.0 mm, more preferably in the range of 1.0 to 1.5 mm.

[0025] (conversion coating) The resin-coated aluminum alloy sheet of the present invention may or may not have a chemical conversion coating on the aluminum alloy sheet. When the resin-coated aluminum alloy sheet of the present invention has a chemical conversion coating, the chemical conversion coating is formed on the surface of the aluminum alloy sheet before forming a coating resin layer on the aluminum alloy sheet.

[0026] The chemical conversion coating is not particularly limited, but a chromate chemical conversion coating formed with a chromate phosphate treatment solution or a non-chromate chemical conversion coating formed with an environmentally friendly non-chromate treatment solution is preferred. The non-chromate chemical conversion coating is not particularly limited, but a zirconium phosphate-based chemical conversion coating or a zirconium-molybdenum-based chemical conversion coating is preferred.

[0027] The amount of Cr or Zr in the chemical conversion coating is measured by fluorescent X-ray. If the chemical conversion coating contains Cr, the amount of Cr is 5 to 45 mg / m2 in terms of Cr atoms. 2 When the chemical conversion coating contains Zr, the coating amount of Zr is preferably 0.5 to 15 mg / m in terms of Zr atoms. 2 The coating amount of Cr in terms of Cr atoms is preferably 5 mg / m 2 Less than or equal to 0.5 mg / m2 of Zr film equivalent to Zr atoms 2 If the thickness is less than 45mg / m, corrosion resistance may be poor. 2 or the amount of Zr film in terms of Zr atoms is 15 mg / m 2 If it exceeds this value, the adhesion during processing may be poor.

[0028] When forming a chemical conversion coating on an aluminum alloy sheet, it is preferable to perform a degreasing treatment to remove dirt from the surface of the aluminum alloy sheet and to adjust the surface properties. The degreasing treatment is preferably alkaline washing, and is carried out using, for example, caustic soda, sodium phosphate, sodium silicate, or the like. Such degreasing treatment by alkaline washing is carried out by spraying a predetermined surface treatment liquid onto the aluminum alloy sheet or immersing the aluminum alloy sheet in the treatment liquid at a predetermined temperature for a predetermined time. After the alkaline washing, it is preferable to perform acid washing in order to remove smut generated by the alkaline washing. The acid is not particularly limited, but examples include sulfuric acid and nitric acid, with 0.5 to 5.0 mass % sulfuric acid being particularly preferred.

[0029] The surface of the obtained degreased aluminum alloy plate is then subjected to a chemical conversion treatment to form a chemical conversion coating on the surface of the aluminum alloy plate. Examples of chemical conversion treatments include immersing the degreased aluminum alloy plate in a treatment liquid such as a chromate phosphate treatment liquid or a non-chromate treatment liquid at a predetermined temperature for a predetermined time, and spraying the treatment liquid such as a chromate phosphate treatment liquid or a non-chromate treatment liquid onto the degreased aluminum alloy plate, followed by drying.

[0030] (Coating resin layer) The resin-coated aluminum alloy sheet according to the present invention has a coating resin layer on the surface of the aluminum alloy sheet, either directly or via a chemical conversion coating. The coating resin layer of the resin-coated aluminum alloy sheet according to the present invention is formed of a cured product of a resin composition containing an epoxy-based resin and a curing agent. That is, the coating resin layer of the resin-coated aluminum alloy sheet according to the present invention is obtained by curing a resin composition containing an epoxy-based resin and a curing agent. The coating resin layer formed of a cured product of a resin composition containing an epoxy-based resin and a curing agent contains graphite particles and silica particles.

[0031] The epoxy resin is not particularly limited as long as it is a thermosetting epoxy resin that can be cured with a curing agent to form a resin layer. Examples of epoxy resins include glassy epoxy resins at room temperature. Examples of epoxy resins include bisphenol A, bisphenol F, and novolac resins, as well as those synthesized using amines and carboxylic acids. The epoxy resin contributes to the moisture resistance of the resin-coated aluminum alloy sheet, achieving high moisture resistance. The number-average molecular weight of the epoxy resin is preferably in the range of 40,000 to 60,000. If the number-average molecular weight of the epoxy resin is less than 40,000, the processability may be poor. If the number-average molecular weight of the epoxy resin is more than 60,000, the coatability may be poor. In the present invention, the number-average molecular weight is measured using gel permeation chromatography (GPC).

[0032] The curing agent is a curing agent for epoxy resins, and examples of the curing agent include amino resin curing agents. Examples of the amino resin curing agent include compounds having a urea skeleton such as urea, urea derivatives, compounds having a guanamine skeleton such as guanamine, methylated benzoguanamine, butylated benzoguanamine, methylbutylated benzoguanamine, and ethylated benzoguanamine, and compounds having a melamine skeleton such as melamine, methylated melamine, butylated melamine, and butylmethylated melamine.

[0033] The graphite particles have the function of emitting infrared rays, and examples thereof include known materials having the function of emitting infrared rays. The inclusion of graphite particles in the coating resin layer imparts heat dissipation properties to the coating resin layer. Examples of graphite particles include graphite particles having aggregating properties, such as graphite. Graphite is a hexagonal, hexagonal plate-like crystal with a turtle-shell-like structure, where carbon atoms are connected within the plane of each layer by strong covalent bonds, and layers are bonded by weak van der Waals forces. The type of graphite particles is not particularly limited, and examples thereof include scaly graphite, flake graphite, granular graphite, and amorphous graphite.

[0034] The average particle size of the graphite particles is preferably 1.0 to 8.0 μm. By having the average particle size of the graphite particles be 1.0 to 8.0 μm, the surface area of ​​the pigment in the coating resin layer is increased, resulting in high emissivity and excellent bending workability. On the other hand, if the average particle size of the graphite particles is less than 1.0 μm, no further effect on bending workability is observed and costs may increase. On the other hand, if the average particle size of the graphite particles is more than 8.0 μm, bending workability may be inferior. The average particle size of the graphite particles is more preferably 1.0 to 5.0 μm. By having the average particle size of the graphite particles be 1.0 to 5.0 μm, emissivity can be further increased. In the present invention, graphite particles such as graphite exist in the resin composition and the coating resin layer in the form of secondary particles formed by aggregation of primary particles, and the average particle size of the graphite particles refers to the average particle size of the secondary particles of the graphite particles. The average particle size of the secondary particles of the graphite particles refers to the particle size of the particles at 50% of the volume accumulated as measured by laser diffraction.

[0035] The content of graphite particles in the coating resin layer is 5.0 to 25.0 parts by mass, preferably 10.0 to 20.0 parts by mass, per 100.0 parts by mass of the total of the epoxy resin and curing agent. Having the content of graphite particles in the coating resin layer within this range allows for the production of a uniform coating resin layer with excellent heat dissipation properties. On the other hand, if the content of graphite particles in the coating resin layer is less than this range, the absolute amount of graphite particles in the coating resin layer may be insufficient, resulting in poor heat dissipation properties. On the other hand, if the content of graphite particles in the coating resin layer exceeds this range, a uniform coating resin layer may not be produced.

[0036] The silica particles are not particularly limited, but examples include wet-process silica and dry-process silica, with wet-process silica being preferred. Wet-process silica has more silanol groups on its surface than dry-process silica. These silanol groups function as a filler to reinforce and adsorb. Furthermore, for the purpose of improving the transparency, water resistance, etc. of the coating resin layer, the silica particles may be surface-treated to be hydrophobic with silanes or silicones. When the coating resin layer contains hard silica particles, the coating resin layer becomes hard, improving the blocking resistance and hardness of the coating resin layer.

[0037] The content of silica particles in the coating resin layer is 3.0 to 28.0 parts by mass, preferably 3.0 to 25.0 parts by mass, more preferably 5.0 to 18.0 parts by mass, and even more preferably 10.0 to 15.0 parts by mass, per 100.0 parts by mass of the total of the epoxy resin and curing agent. Having the content of silica particles in the coating resin layer within this range provides excellent heat dissipation. On the other hand, if the content of silica particles in the coating resin layer is less than 3.0 parts by mass, the heat dissipation may be poor, while if it exceeds the above range, the alkali resistance becomes extremely low. Furthermore, from the viewpoint of excellent alkali resistance, it is preferable that the content of silica particles in the coating resin layer be 15.0 parts by mass or less per 100.0 parts by mass of the total of the epoxy resin and curing agent.

[0038] The coating resin layer may contain wax to impart lubricity. The wax is not particularly limited, but lanolin, polyethylene wax, and carnauba wax are preferably used. The polyethylene wax preferably has a number average molecular weight of 600 to 12,000 and a melting point of 80 to 130°C. Carnauba wax is a vegetable wax whose main component is a higher fatty acid ester, and preferably has a melting point of 80 to 86°C. The wax content in the resin composition layer is 1.0 to 15.0% by mass, preferably 2.0 to 12.0% by mass, based on the total amount of the epoxy resin and the curing agent.

[0039] The coating resin layer is a cured resin composition containing an epoxy resin, a curing agent, graphite particles, and silica particles. The resin composition for forming the coating resin layer contains, as resin components, an epoxy resin and a curing agent, and, as fillers, 5.0 to 25.0 parts by mass of graphite particles per 100.0 parts by mass of the epoxy resin and curing agent combined, and 3.0 to 28.0 parts by mass of silica particles per 100.0 parts by mass of the epoxy resin and curing agent combined. The epoxy resin, curing agent, graphite particles, silica particles, and wax in the resin composition are the same as those in the coating resin layer.

[0040] The content of the curing agent in the resin composition is appropriately selected depending on the type of epoxy resin, the epoxy equivalent, etc., and the type of curing agent, but is preferably 0.5 to 11.0 parts by mass, more preferably 0.5 to 7.0 parts by mass, per 100.0 parts by mass of the epoxy resin.

[0041] The content of graphite particles in the resin composition is 5.0 to 25.0 parts by mass, preferably 10.0 to 20.0 parts by mass, per 100.0 parts by mass of the total of the epoxy resin and curing agent. By having the content of graphite particles in the resin composition within this range, a uniform coating resin layer with excellent heat dissipation properties can be obtained. On the other hand, if the content of graphite particles in the resin composition is less than this range, the absolute amount of graphite particles in the resin film may be insufficient, resulting in poor heat dissipation properties. On the other hand, if the content of graphite particles in the resin composition exceeds this range, a uniform coating resin layer cannot be obtained.

[0042] The content of silica particles in the resin composition is 3.0 to 28.0 parts by mass, preferably 3.0 to 25.0 parts by mass, more preferably 5.0 to 18.0 parts by mass, and even more preferably 10.0 to 15.0 parts by mass, per 100.0 parts by mass of the total of the epoxy resin and curing agent. Having the content of silica particles in the resin composition within this range results in excellent heat dissipation. If the content of silica particles in the resin composition is less than 3.0 parts by mass, the heat dissipation may be poor, while if it exceeds the above range, the alkali resistance will be extremely low. Furthermore, from the viewpoint of excellent alkali resistance, it is preferable that the content of silica particles in the coating resin layer be 15.0 parts by mass or less, per 100.0 parts by mass of the total of the epoxy resin and curing agent.

[0043] The resin composition may contain wax to impart lubricity. The wax is not particularly limited, but polyethylene wax and carnauba wax are preferably used. The polyethylene wax preferably has a number-average molecular weight of 600 to 12,000 and a melting point of 80 to 130°C. Carnauba wax is a vegetable wax whose main component is a higher fatty acid ester and preferably has a melting point of 80 to 86°C. The wax content in the resin composition is 1.0 to 15.0 mass%, preferably 2.0 to 12.0 mass%, based on the total weight of the epoxy resin and curing agent. The average particle size of the wax is preferably 1 to 5 μm. When the average particle size of the wax falls within the above range, the wax is less soluble in solvents and tends to protrude from the surface of the coating resin layer when applied in a wet state. By baking and drying the wax, the protruding portions melt, and the wax covers the surface of the coating resin layer, resulting in a uniform wax distribution. Furthermore, when the coating resin layer is composed of two or more layers of cured resin compositions, it is preferable that only the uppermost resin layer contains wax. The number average molecular weight is measured using gel permeation chromatography (GPC). The melting point is measured in accordance with JIS K7121. The average particle size is measured by laser diffraction / scattering.

[0044] The resin composition may contain a solvent. When the resin composition contains a solvent, the epoxy resin, curing agent, graphite particles, silica particles, and other components that are optionally contained are dispersed or dissolved in the solvent. The solvent is not particularly limited, and examples thereof include water, esters, glycol ethers, glycols, ketones, aromatic hydrocarbons, aliphatic hydrocarbons, and alcohols. Among these, xylene, toluene, and mixtures thereof are particularly preferred as the solvent. The resin composition is usually prepared so that the solid content is 1.0 to 50.0 mass%.

[0045] The coating resin layer is made of a cured product of a resin composition, and is formed by applying the resin composition to an aluminum alloy plate in a predetermined thickness to form a coating layer of the resin composition, and then heating to cure the resin composition.

[0046] The thickness of the coating resin layer is preferably 2.0 to 25.0 μm. When the thickness of the coating resin layer is within the above range, high emissivity is obtained and processability is excellent. The thickness of the coating resin layer is preferably 5.0 to 25.0 μm in terms of improving heat dissipation. The thickness of the coating resin layer is more preferably 5.0 to 15.0 μm in terms of improving paintability. Furthermore, the thickness of the coating resin layer is preferably 5.0 μm or more in terms of improving alkali resistance, and more preferably 10.0 μm or more in terms of even higher alkali resistance. When the coating resin layer is made up of two or more resin layers, the thickness of the coating resin layer refers to the total thickness of all the resin layers.

[0047] The coating resin layer may consist of one resin layer, two resin layers, or three or more resin layers. When the coating resin layer consists of two or more resin layers, each resin layer may be made of a cured product of a resin composition having the same composition, or may be made of a cured product of a resin composition having a different composition within the composition range of the resin composition of the resin-coated aluminum alloy sheet of the present invention. When the coating resin layer consists of two resin layers, the thickness of the upper layer is preferably 3.0 to 10.0 μm, and the thickness of the lower layer is preferably 3.0 to 10.0 μm. The thickness of the coating resin layer is measured using a strand gauge, an electromagnetic film thickness meter, an eddy current film thickness meter, a gravimetric method, or the like.

[0048] The arithmetic mean roughness of the surface of the coating resin layer is preferably 0.7 to 2.5 μm, more preferably 1.2 to 2.3 μm. When the surface roughness of the coating resin layer is within the above range, the surface area of ​​the coating film surface increases, and the emissivity increases.

[0049] The glossiness of the surface of the coating resin layer is preferably 0.1 to 4.5, more preferably 0.3 to 2.0. When the glossiness of the coating resin layer is in the above range, a high emissivity can be obtained. When the glossiness of the coating resin layer is in the above range, the coating film surface becomes rough and the surface area of ​​the coating film increases, thereby improving heat dissipation properties.

[0050] The emissivity of the coating resin layer is preferably 0.70 to 0.95, more preferably 0.80 to 0.95, and even more preferably 0.80 to 0.95. When the emissivity of the coating resin layer is within the above range, heat dissipation properties are improved.

[0051] Examples of methods for forming a coating resin layer include the following. First, an epoxy resin and a curing agent are mixed in a solvent, and then graphite particles and silica particles are added. These components are dissolved or dispersed in the solvent to prepare a coating material (resin composition). Next, this coating material (resin composition) is applied directly to the surface of the aluminum alloy plate or onto a chemical conversion coating formed on the surface of the aluminum alloy plate. The coating material is then baked and dried in an oven at a predetermined temperature for a predetermined time to form a coating film of the resin composition, which is then cured. This results in the formation of a coating resin layer. The solvent is not particularly limited, but examples include water, esters, glycol ethers, glycols, ketones, aromatic hydrocarbons, aliphatic hydrocarbons, and alcohols. Among these, xylene, toluene, and mixtures thereof are particularly preferred. Typically, the coating material is prepared to have a solids content of 1 to 50% by mass.

[0052] When forming a resin coating layer consisting of two resin layers, a paint (resin composition) is applied directly to the surface of the aluminum alloy plate or onto a chemical conversion coating formed on the surface of the aluminum alloy plate, and baked and dried in an oven at a predetermined temperature for a predetermined time to form a lower resin layer, and then the paint (resin composition) is applied to the surface of the lower resin layer and baked and dried in an oven at a predetermined temperature for a predetermined time to form an upper resin layer.

[0053] The coating method for the coating material (resin composition) is not particularly limited, but examples thereof include a roll coater method, a roll squeeze method, an air knife method, a chemi-coater method, a dipping method, a spray method, and a bar coater method. To form a coating resin layer on an aluminum alloy plate at low cost, the most suitable method is to continuously apply the coating material (resin composition) using a coil with a roll coater. When applying the coating material using this method, the coating material is baked, for example, in a baking oven divided into 3 to 7 zones. The total baking time is preferably 10 to 60 seconds, more preferably 20 to 45 seconds. The maximum baking temperature is preferably 200 to 290°C.

[0054] Furthermore, when forming a thick resin coating layer with a thickness of 10.0 to 25.0 μm, the thickness of the resin composition to be applied must be large in order to form a thick resin coating layer in one application. Furthermore, if the resin composition is thick, the solvent in the resin composition is less likely to evaporate after application, and the evaporation of the solvent is hindered by the curing of the resin, which may result in a problem of impairing the flatness of the coating surface. Therefore, when forming a thick resin coating layer, it is preferable to first use the resin composition to form a lower resin layer with a thickness of 3.0 to 15.0 μm, and then form an upper resin layer with a thickness of 3.0 to 15.0 μm, as this makes it less likely to hinder the evaporation of the solvent and suppresses the occurrence of unevenness on the coating surface.

[0055] The resin composition for resin-coated aluminum alloy sheets of the present invention contains an epoxy resin, a curing agent, 5.0 to 25.0 parts by mass, preferably 10.0 to 20.0 parts by mass, of graphite particles per 100.0 parts by mass of the epoxy resin and the curing agent combined, 3.0 to 28.0 parts by mass, preferably 3.0 to 25.0 parts by mass, more preferably 5.0 to 18.0 parts by mass, and even more preferably 10.0 to 15.0 parts by mass of silica particles per 100.0 parts by mass of the epoxy resin and the curing agent combined, and a solvent. The resin composition for resin-coated aluminum alloy sheets of the present invention may optionally contain 1.0 to 15.0% by mass, preferably 2.0 to 12.0% by mass, of wax per 100.0 parts by mass of the epoxy resin and the curing agent combined.

[0056] The resin composition for a resin-coated aluminum alloy sheet of the present invention is a resin composition for forming a resin coating layer on an aluminum alloy sheet by applying the resin composition directly to the surface of the aluminum alloy sheet or onto a chemical conversion coating formed on the surface of the aluminum alloy sheet to form a coating film of the resin composition, and then curing the coating film of the resin composition. The resin composition for a resin-coated aluminum alloy sheet of the present invention is a resin composition for a heat-dissipating resin-coated aluminum alloy sheet.

[0057] The epoxy-based resin, curing agent, graphite particles, silica particles, solvent, and wax in the resin composition for resin-coated aluminum alloy sheet of the present invention are the same as the epoxy-based resin, curing agent, graphite particles, silica particles, solvent, and wax in the resin composition in the resin-coated aluminum alloy sheet of the present invention described above.

[0058] Next, the present invention will be explained in more detail by way of examples, but these are merely illustrative and do not limit the present invention. [Example]

[0059] (Examples 1 to 12, Comparative Examples 1 and 2) An aluminum alloy plate (material: JIS A1050, plate thickness: 0.6 mm) was degreased with a commercially available aluminum degreaser, washed with water, and then subjected to a chemical conversion treatment with a commercially available phosphate chromate treatment solution to form a chemical conversion coating. Next, as shown in Table 1, an epoxy resin, an amino-based curing agent (resin component), heat-dissipating particles, and silica particles (wet-process silica) were added to an organic solvent (a mixed solvent of toluene, methyl ethyl ketone, and cyclohexanone) and dispersed or dissolved to prepare a coating material. The resulting coating material was applied to one surface of the aluminum alloy plate on which the chemical conversion coating had been formed using a bar coater and baked in a hot air oven to form a coating resin layer. The baking conditions were a maximum temperature of 272°C and a baking time of 84 seconds. In Example 12, a two-coat method was used in which a lower resin layer was formed first, and then an upper resin layer was formed. In addition, when the amount of chemical conversion coating was measured using fluorescent X-rays, the Cr content was 20 to 30 g / m 2 The thickness of the coating resin layer after drying was measured using an eddy current film thickness meter, and the results are shown in Table 1.

[0060] (Test Method) The resin-coated aluminum alloy sheets thus obtained were subjected to performance tests according to the following test methods. (Emissivity) The emissivity of the surface of the coating resin layer was measured using a portable emissivity meter (DandSAERD, manufactured by Kyoto Electronics Manufacturing Co., Ltd.) in accordance with ASTM C1371 (Standard Test Method for Measuring the Emittance of Materials at Near Room Temperature Using a Portable Emitometer). (glossiness) The glossiness of the surface of the coating resin layer was measured using a handy glossmeter (IG-410, manufactured by Horiba, Ltd.). (bending workability) The test piece was bent 180 degrees 3 times with the evaluation surface facing outward, and the cracks in the coating resin layer were visually inspected to evaluate the bending workability using the following criteria: 1: no cracks in the coating resin layer, 2: very minor cracks in the coating resin layer but good, 3: small cracks in the coating resin layer but usable, 4: large cracks in the coating film and unusable. (Tape Test) A cross-cut peel test was conducted in accordance with JIS K5400 to test adhesion. Test materials were used in the initial stage (untreated after painting) and after a high-temperature, high-humidity test (120°C, 96 hours). The test method involved making 100 1mm x 1mm squares (11 cuts vertically and horizontally) with a utility knife, adhering cellophane tape to the surface, and then rapidly peeling the tape off to count the number of squares where the coating film remained. (Chemical resistance test) An immersion test was conducted in accordance with JIS K5600-6-1 to test for chemical resistance. The immersion liquids used were a 5% by mass aqueous solution of sodium hydroxide and 5% by mass sulfuric acid. The test pieces were immersed in the immersion liquid for 24 hours, after which they were rinsed with water and dried. The condition of the coating was visually observed and rated according to the following criteria: 1: no peeling of the coating; 2: very slight peeling of the coating, but good; 3: minor peeling of the coating, but usable; and 4: major peeling of the coating, unusable. (Arithmetic mean roughness Ra of the coating resin layer surface) The arithmetic mean roughness Ra (μm) of the surface of the resin layer of the resin-coated aluminum alloy sheet was measured in accordance with JIS B0601. (Measurement of the average particle size of graphite particles) The particle size distribution and average particle size (D50, particle size of particles at 50% cumulative volume) were calculated by laser diffraction method. The obtained performance test results are shown in Table 1. In Table 1, the amounts added are shown in parts by mass based on 100.0 parts by mass of the total of the epoxy resin and curing agent.

[0061] [Table 1]

[0062] (Examples 13 to 16) An aluminum alloy plate (material: JIS A1050, plate thickness: 0.6 mm) was degreased with a commercially available aluminum degreaser, washed with water, and then subjected to a chemical conversion treatment with a commercially available phosphate chromate treatment solution to form a chemical conversion coating. Next, as shown in Table 2, an epoxy resin, an amino curing agent (resin component), heat-dissipating particles, and silica particles (wet-process silica) were added to an organic solvent (a mixed solvent of toluene, methyl ethyl ketone, and cyclohexanone) and dispersed or dissolved to prepare a coating material. The resulting coating material was applied to one surface of the aluminum alloy plate on which the chemical conversion coating had been formed using a bar coater, and baked in a hot air oven to form a coating resin layer. The baking conditions were a maximum temperature of 272°C and a baking time of 84 seconds. In addition, when the amount of chemical conversion coating was measured using fluorescent X-rays, the Cr content was 20 to 30 g / m 2 The thickness of the coating resin layer after drying was measured using an eddy current film thickness meter, and the results are shown in Table 2. The emissivity of the resulting resin-coated aluminum plate was measured, and the results are shown in Table 2.

[0063] [Table 2]

[0064] The resin types in Tables 1 and 2 are as follows. A Epoxy resin (molecular weight 50,000) and amino-based hardener B High molecular weight polyester The types of heat-dissipating particles in Tables 1 and 2 are as follows: A1 Graphite particles: average particle size 3.0 μm, A2 graphite particles: average particle size 5.0μm, A3 Graphite particles: average particle size 7.0 μm, A4 Graphite particles: average particle size 8.0 μm, B Existing graphite particles C Carbon black [Explanation of symbols]

[0065] 1. Resin-coated aluminum alloy plate 2. Aluminum alloy plate 3. Chemical conversion coating 4. Coating resin layer

Claims

1. a coating resin layer formed of a cured product of a resin composition containing an epoxy resin and a curing agent; The resin-coated aluminum alloy plate is characterized in that the coating resin layer contains 5.0 to 25.0 parts by mass of graphite particles relative to a total of 100.0 parts by mass of the epoxy-based resin and the curing agent, and 3.0 to 28.0 parts by mass of silica particles relative to a total of 100.0 parts by mass of the epoxy-based resin and the curing agent, and the coating resin layer has a thickness of 2.0 to 25.0 μm.

2. The resin-coated aluminum alloy sheet according to claim 1, wherein the coating resin layer is formed from a cured product of a resin composition containing, as resin components, the epoxy resin and the curing agent, and, as fillers, 5.0 to 25.0 parts by mass of the graphite particles per 100.0 parts by mass of the epoxy resin and the curing agent in total, and 3.0 to 28.0 parts by mass of the silica particles per 100.0 parts by mass of the epoxy resin and the curing agent in total.

3. 3. The resin-coated aluminum alloy sheet according to claim 1, wherein the number average molecular weight of the epoxy resin is 40,000 to 60,000.

4. 4. The resin-coated aluminum alloy sheet according to claim 1, wherein the curing agent is an amino resin-based curing agent.

5. The resin-coated aluminum alloy sheet according to any one of claims 1 to 4, wherein the coating resin layer has a thickness of 5.0 to 15.0 µm.

6. The resin-coated aluminum alloy sheet according to any one of claims 1 to 5, characterized in that the graphite particles have an average particle size of 1.0 to 8.0 µm.

7. The resin-coated aluminum alloy sheet according to claim 6, wherein the graphite particles have an average particle size of 1.0 to 5.0 μm.

8. The resin-coated aluminum alloy sheet according to any one of claims 1 to 7, characterized in that the arithmetic mean roughness Ra of the surface of the coating resin layer is 0.100 to 2.500 µm.

9. The resin-coated aluminum alloy sheet according to any one of claims 1 to 8, characterized in that the coating resin layer has a glossiness of 0.1 to 4.

5.

10. A resin composition for a resin-coated aluminum alloy sheet, comprising: an epoxy resin; a curing agent; 5.0 to 25.0 parts by mass of graphite particles relative to a total of 100.0 parts by mass of the epoxy resin and the curing agent; 3.0 to 28.0 parts by mass of silica particles relative to a total of 100.0 parts by mass of the epoxy resin and the curing agent; and a solvent.

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