JP2015193848A - Heat-radiating coating material, and light-emitting diode (led) illumination, heat sink and solar cell module back sheet each coated therewith - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat-radiating coating material which can enhance emissivity in the infrared region, and efficiently radiating heat; and a light-emitting diode (LED) illumination, a heat sink, and a solar cell module back sheet each coated therewith.SOLUTION: The heat-radiating coating material includes: (a) a ceramic powder with an average particle size of 0.1-50 μm, containing a zinc oxide powder and/or a titanium oxide powder; and (b) a binder. The content of the (a) component is 25-100 pts.mass based on 100 pts.mass of the (b) component.

Description

  The present invention relates to a heat-radiating paint that has high heat radiation and efficiently releases generated heat as infrared rays to the outside of the system, and to a light emitting diode (LED) illumination, a heat sink, and a solar cell module backsheet coated with the same.

  As is known in black body radiation, thermal radiation is a phenomenon in which heat energy is emitted from an object as electromagnetic waves, particularly infrared rays. In contrast, the phenomenon in which an object is warmed by electromagnetic waves radiated from a heat source is called thermal energy absorption. Thermal radiation and heat absorption have opposite energy conversion directions, which follow the second law of thermodynamics. In order to advance thermal radiation advantageously, it is possible to absorb electromagnetic waves at a wide wavelength range and to increase the surface area. However, the heat generation temperature of LED (light emitting diode) illumination, electronic components, etc. is about 70 to 200 ° C., and since this heat is radiated in the infrared region, it is not necessary to be a complete black body. Ceramics have been widely used so far because they have a feature of selectively emitting heat in the infrared region (see Patent Documents 1 to 3).

JP-A-3-136807 Japanese Patent Laid-Open No. 10-279845 JP 2004-43612 A

However, with conventional techniques, it may be difficult to achieve both thermal radiation and coating film adhesion.
It is an object of the present invention to provide a thermal radiation coating, a light emitting diode (LED) illumination, a heat sink, and a solar cell module back sheet on which the emissivity in the infrared region is increased and heat can be efficiently radiated.

  As a result of investigations to solve the above problems, the present inventors have used specific ceramics, and further made the mixing ratio of ceramic powder (hereinafter also referred to as ceramics) and binder a certain specific ratio, It has been found that the radiation and coating film adhesion are improved.

  The present invention includes (a) a ceramic powder having an average particle diameter of 0.1 to 50 μm and containing zinc oxide powder and / or titanium oxide powder, and (b) a binder which is a thermosetting resin or colloidal silica. Further, the present invention relates to a thermal radiation coating material containing 30 to 100 parts by mass of zinc oxide powder or titanium oxide powder or a total of both to 100 parts by mass of the binder.

  In the present invention, (b) the binder is phenol resin, alkyd resin, melamine urea resin, epoxy resin, polyurethane resin, silicon resin, vinyl acetate resin, acrylic resin, chlorinated rubber resin, vinyl chloride resin, fluororesin, cellulose The present invention relates to the above-mentioned thermal radiation paint which is at least one of gum and colloidal silica.

  The present invention also relates to the above-mentioned thermal radiation paint having an emissivity of 0.90 or more in a wavelength range of 2 to 22 μm.

  Moreover, this invention relates to the light emitting diode (LED) illumination which apply | coated the said heat radiation coating material with the average film thickness of 1-50 micrometers.

  The present invention also relates to a heat sink in which the thermal radiation paint is applied with an average film thickness of 1 to 50 μm.

  Moreover, this invention relates to the solar cell module backsheet which apply | coated said thermal radiation coating material with the average film thickness of 1-50 micrometers.

  According to the present invention, it has become possible to provide a thermal radiation paint that can increase the emissivity in the infrared region and efficiently dissipate heat, and a light emitting diode (LED) illumination, a heat sink, and a solar cell module backsheet coated with the same.

It is the schematic diagram which showed the measuring method of the temperature of the LED bulb which applied the coating material. It is the schematic diagram which showed the heat sink which applied the coating material. It is the expanded view which showed the solar cell module backsheet which applied the coating material.

Embodiments of the present invention will be described below.
The present invention includes (a) a ceramic powder having an average particle diameter of 0.1 to 50 μm and containing zinc oxide powder and / or titanium oxide powder, and (b) a binder which is a thermosetting resin or colloidal silica. The heat-radiating paint contains 30 to 100 parts by mass of zinc oxide powder or titanium oxide powder or a total of both with respect to 100 parts by mass of the binder.

  A conventionally well-known thing can be used as a zinc oxide powder and titanium oxide powder used by this invention, It does not specifically limit. For example, commercially available 23-K (manufactured by Hakusuitec Co., Ltd., zinc oxide), TIG R-900 (manufactured by DuPont Co., Ltd., titanium oxide), JR-1000 (manufactured by Teika Co., Ltd., titanium oxide) and the like are preferably used. be able to. Moreover, the ceramic powder which has another heat radiation characteristic may be included, a conventionally well-known thing can be used and it does not specifically limit. Hereinafter, the ceramic powder is used as a generic term including zinc oxide powder and titanium oxide powder. Other ceramic powders that can be used include, for example, powders of silicon oxide, zirconium oxide, magnesium oxide, iron oxide, copper oxide, nickel oxide, and cobalt oxide.

The average particle diameter of the zinc oxide powder and titanium oxide powder in the present invention is 0.1 to 50 μm from the viewpoint of thermal radiation, but is preferably 1 to 45 μm from the viewpoint of coating properties. The average particle diameter of the ceramic powder that can be used in addition to these is also preferably 0.1 to 50 μm, more preferably 1 to 45 μm. If the average particle size of the ceramic powder exceeds 50 μm, it penetrates through a film with a recommended film thickness of 50 μm for efficient thermal radiation, and there is a risk that the strength of the coating film, the adhesive strength with the object to be coated, and the adhesive strength will be reduced. is there. On the other hand, if the average particle size of the ceramic powder is less than 0.1 μm, the ceramic powder is completely covered with the binder, which may reduce the emissivity of the surface of the coating film of the thermal radiation paint. These ceramic powders may be used alone or in combination of two or more. It is also possible to use titanium oxide with excellent far-infrared radiation, silicon oxide or zinc oxide with high radiation in the near-infrared region. It is.
The average particle size of the ceramic powder can be measured by, for example, a laser diffraction particle size distribution measurement method.

  The ceramic powder in the present invention may have pores. Further, pores may be formed by agglomeration of primary particles of the ceramic powder. Inclusion of ceramics having pores tends to improve the emissivity. In this regard, the inventors of the present application think that the emissivity can be increased by increasing the surface area of the coating film of the thermal radiation paint by floating on the coating film surface after painting due to having pores. Yes. Further, it is considered that the emissivity inherent in ceramics can be expressed by increasing the proportion of ceramic powder on the surface and decreasing the proportion of resin (binder).

  The thermal radiation coating material of the present invention preferably has an emissivity of 0.90 or more in a wavelength range of 2 to 22 μm. In order to obtain the emissivity (also referred to as thermal emissivity), an emissivity measuring device TSS-5X (manufactured by Japan Sensor Co., Ltd., wavelength range 2 to 22 μm) is generally used, and the measurement is performed in an acrylic case. Do. If the emissivity (thermal emissivity) is less than 0.90, the heat dissipation effect may be insufficient for non-metals.

  As the binder used in the present invention, conventionally known binders can be used, and are not particularly limited, and examples thereof include emulsion resins such as synthetic resins and aqueous emulsion resins. Synthetic resins include alkyd resin, amino alkyd resin, acrylic resin, phenol resin, urea resin, melamine resin, epoxy resin, polyurethane, polyvinyl chloride, polyvinyl acetate, etc., and acrylic resin from the viewpoint of price. Is preferred. Examples of the water-based emulsion resin include silicon acrylic emulsion, acrylic emulsion, urethane emulsion, urethane acrylic emulsion, and the like. Among them, silicon acrylic emulsion is preferable from the viewpoint of dispersibility and heat resistance. Furthermore, the synthetic resin preferably has good mechanical stability and a glass transition temperature (hereinafter abbreviated as Tg) of 0 to 70 ° C. Below 0 ° C., the adhesion is good, but the coating film is too flexible and the wear resistance, stain resistance, drying property, and coating film strength are poor. When the temperature exceeds 70 ° C., excessive film-forming aids are added, the viscosity of the paint is remarkably increased, cracks are caused by a decrease in the flexibility of the coating film, and the water resistance of the coating film tends to decrease. If it is the range of 0-70 degreeC, the above thing does not arise and it becomes a favorable coating film.

  Moreover, the average molecular weight (weight average molecular weight in terms of standard polystyrene by gel permeation chromatography) of the synthetic resin used as the binder is preferably 100,000 to 200,000. If a polymer having an average molecular weight of less than 100,000 is used, the coating film strength is too weak, and the coating film may be peeled off such that the coating film is torn off or the stain resistance tends to be poor. On the other hand, if it exceeds 200,000, there is no problem in coating strength and stain resistance, but the viscosity tends to increase. More preferably, it is 130,000-170,000. If the weight average molecular weight is in the above range, the above-mentioned phenomenon does not occur and a good coating film is obtained. In the case of an aqueous emulsion resin, the solid content concentration (hereinafter abbreviated as NV) is preferably 43 to 62% by mass. When the amount is less than 43% by mass, the NV in the coating tends to be low and the drying property tends to be inferior. When the amount exceeds 62% by mass, the viscosity of the coating tends to increase or the crack resistance tends to decrease. 10-70 mass% is preferable with respect to a thermal radiation coating material, and, as for the compounding quantity of binders, such as a synthetic resin and water-system emulsion resin, 20-60 mass% is more preferable, and 30-50 mass% is further more preferable. If it is less than 10% by mass, the workability tends to increase due to an increase in the viscosity of the paint, while if it exceeds 70% by mass, the drying property and the contamination tend to be inferior.

  In addition, in the case of application to a high temperature region exceeding 200 ° C., it is particularly preferable to include a thermosetting resin as a binder in order to impart heat resistance. Such a thermosetting resin is commercially available and can be synthesized by a conventional method. As a thermosetting resin, Preferably an epoxy resin is mentioned, YDCN-700-10, YSLV-80XY (the Toto Kasei Co., Ltd. make, brand name) etc. are mentioned. As a curing agent for this resin, a known curing agent that is usually used can be used. For example, bisphenols having two or more phenolic hydroxyl groups in one molecule such as amines, polyamides, acid anhydrides, polysulfides, boron trifluoride, bisphenol A, bisphenol F, bisphenol S, phenol novolac resins, bisphenol A Examples thereof include phenolic resins such as novolak resin and cresol novolak resin. These are used singly or in combination of two or more. Such a phenol resin is commercially available and can be synthesized by a conventional method. Examples of the commercially available phenol resins include the Millex XLC series and the Millex XL series (trade name, manufactured by Mitsui Chemicals, Inc.), and HE-200C-10 (produced by Nippon Air Water Co., Ltd., phenol resin, trade name). )).

  In addition, the coating film after sintering by the sol-gel method using colloidal silica or the like as a binder can be made into a ceramic, and can have high heat radiation and high heat resistance.

  The present invention includes (a) a ceramic having an average particle diameter of 0.1 to 50 μm and containing zinc oxide powder and / or titanium oxide powder, and (b) a binder, On the other hand, it is a thermal radiation coating containing 25 to 100 parts by mass of the component (a). Moreover, it is preferable that the ceramic (powder) containing one or both of the oxide powder and the titanium oxide powder is 30 to 100 parts by mass with respect to 100 parts by mass of the binder (b). Furthermore, it is preferable that it is 40-90 mass parts from a thermal radiation viewpoint, and it is especially preferable that it is 50-85 mass parts from a coating-film viewpoint. When the component (a) is less than 25 parts by mass, the component is buried in the binder and the heat radiation performance may be deteriorated. Moreover, when the said (a) component exceeds 100 mass parts, many irregular irregularities appear on the coating-film surface, and there exists a possibility of impairing an external appearance.

  In general, the heat-radiating paint used in the present invention may be produced by filling or kneading other components together with the above components. Examples of such components include a film forming aid, a plasticizer, a pigment, a silane coupling agent, a dispersant, and an antifoaming agent.

  As film-forming aids, butyl carbitol acetate, butyl carbitol, butyl cellosolve, butyl cellosolve acetate, benzyl acetate, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, 2,2,4-trimethyl 1,3-pentanediol diisobutyrate, 2,2,4-trimethyl-1,3-pentanediol 2-ethylhexanoate isobutyrate, 2,2,4-trimethyl-1,3-pentanediol di-2- Examples include ethyl hexanoate, 2-ethylhexyl glycol, and propylene glycol monobutyl ether. The content of the film-forming auxiliary is preferably 0.1 to 20% by mass, more preferably 0.5 to 10% by mass, and 1 to 5% by mass in the thermal radiation coating. Is more preferable. Here, if the content of the film-forming auxiliary is less than 0.1% by mass, there is a tendency that film formation at the time of coating cannot be obtained, and if it exceeds 20% by mass, the film formation is good but the drying of the coating film is deteriorated. Tend.

  Examples of the plasticizer include phthalic acid esters such as dioctyl phthalate (DOP), phosphoric acid esters such as triethyl phosphate (TEP) and tributyl phosphate (TBP), phenyl glycidyl ether (PGE), benzyl alcohol, acetyl citrate plasticizer, An epoxy plasticizer, a trimet plasticizer, etc. are mentioned. 0.5-5 mass% is preferable in a thermal radiation coating material, and, as for the compounding quantity of a plasticizer, 1-4 mass% is more preferable, and 1.5-2.5 mass% is further more preferable. If it is less than 0.5% by mass, the flexibility at low temperature tends to be inferior, whereas if it exceeds 5% by mass, the drying property and the contamination tend to be inferior.

  Examples of silane coupling agents include various ones having functional groups such as epoxy groups, styryl groups, methacryloxy groups, acryloxy groups, amino groups, ureido groups, chloropropyl groups, mercapto groups, isocyanate groups, and sulfide groups. An epoxy group is preferable. The silane coupling agent is preferably contained in the thermal radiation paint in an amount of 0.01 to 5% by mass, more preferably 0.02 to 4% by mass, and 0.03 to 3% by mass. More preferably. Here, if the content of the silane coupling agent is less than 0.01% by mass, the effect of improving the coating film strength and water resistance tends to be insufficient. There is a tendency to decrease in strength, viscosity, crack resistance, etc. and increase in viscosity over time.

  Examples of dispersants include polycarboxylic acid alkylamine salts, alkylammonium salts, alkylroll aminoamides, polycarboxylic acid polyaminoamides, acrylic copolymer ammonium salts, polycarboxylic acid sodium salts, polycarboxylic acid ammonium salts, polycarboxylic acid salts. Examples thereof include carboxylic acid amino alcohol salts, polyaminoamide carboxylates, and polyaminoamide polar acid ester salts.

  Antifoaming agent includes modified silicone antifoaming agent, special silicone antifoaming agent, silicone antifoaming agent, silica antifoaming agent, silica silicone antifoaming agent, hydrophobic silica, hydrophobic silicone, wax, special Examples thereof include wax and polysiloxane.

  The blending amount of the dispersant and the antifoaming agent is preferably 0.1 to 5% by mass, more preferably 0.3 to 4% by mass, and still more preferably 0.5 to 3% by mass in the thermal radiation coating. If it is less than 0.1% by mass, the dispersion and antifoaming properties of the paint tend to be low. On the other hand, if it exceeds 5% by mass, the dispersion and defoaming properties are good, but repellency and cocoon skin phenomenon tend to occur on the coating surface during coating.

  When producing a paint using the thermal radiation paint of the present invention, the production method of the paint is not particularly limited, but first, it is necessary to disperse ceramic powder in a binder. As this method, a binder and ceramic powder are usually mixed with water or an organic solvent, and this mixture is dispersed and kneaded using various dispersing and kneading devices such as a three roll, ball mill, sand mill, bead mill, kneader and the like. It can be carried out. In the case where the binder is an emulsion resin, water or an organic solvent is not always necessary, and can be appropriately used as necessary.

In addition, it is preferable to use the above-mentioned dispersant when dispersing the ceramic because the dispersibility and dispersion stability of the pigment are improved. Examples of the pigment include inorganic pigments such as zinc white, lead white, lithopone, titanium dioxide, ultramarine blue, prussian blue (potassium ferrocyanide), carbon black, or organic pigments containing azo compounds as components. Can be mentioned.
The dispersant is preferably used in an amount of 50 parts by mass or less with respect to 100 parts by mass of the pigment when the ceramic powder is dispersed. The large particle diameter titanium dioxide, silica powder or silicate powder, and other components may be added at the time of pigment dispersion or after dispersion. Similarly, water or an organic solvent may be used in its entirety when the ceramic powder is dispersed, or a part thereof may be added after the dispersion. However, it is preferable to use at least 50 parts by weight of water or organic solvent at the time of dispersion with respect to 100 parts by weight of the total amount of binder and ceramic powder at the time of dispersion. If it is less than 50 parts by mass, the viscosity at the time of dispersion is too high, and it may be difficult to disperse particularly when dispersed with a ball mill, sand mill, bead mill or the like.

  There is no restriction | limiting in particular as water or the organic solvent used at the time of dispersion | distribution, As an organic solvent, a ketone type, alcohol type, an aromatic type etc. are mentioned, for example. Specific examples include acetone, methyl ethyl ketone, cyclohexane, ethylene glycol, propylene glycol, methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butyl alcohol, benzene, toluene, xylene, ethyl lactate, and ethyl acetate. These may be used alone or in combination of two or more.

  However, the selection of water or an organic solvent is appropriately determined in combination with other materials such as ceramics and a dispersant, and in some cases, when a certain organic solvent is used, the heat radiation performance that is a feature of the present invention Obviously, the organic solvent cannot be used in the system. Therefore, although there is no restriction | limiting in the organic solvent to be used, You must select the organic solvent suitable for the type | system | group.

  Next, the application method of the thermal radiation paint thus obtained is preferably brush application, spray application, roll coater application, but depending on the object to be applied, electrostatic coating, curtain coating, dipping method, electrodeposition coating Etc. are also applicable. Further, after coating, the method of drying to form a coating film may be a method such as natural drying or baking, which is appropriately selected depending on the paint properties and the like.

  Although it does not specifically limit regarding the average film thickness after application | coating of a thermal radiation coating material, It is preferable that it is 50 micrometers or less. If it exceeds 50 μm, the influence of the thermal resistance in the film cannot be ignored, and heat may not be sufficiently transmitted to the surface of the coating film, which may reduce the heat radiation efficiency. Moreover, it is preferable that an average film thickness is 1 micrometer or more. If it is less than 1 μm, the heat dissipation effect may not be sufficiently exhibited.

The system for applying the thermal radiation paint is not particularly limited, but can be applied to heat sinks for LED bulbs (LED lighting), back chassis of liquid crystal televisions, and the like. For example, the heat sink 2 made of Al is mentioned. The coating method is performed by the above-described method, and it is preferable to coat a portion not in contact with the heat source as shown in FIG. In general, metal has a very low emissivity, and heat radiation by heat radiation cannot be expected. Therefore, coating on a metal surface with a heat radiation paint is useful for heat radiation.
Moreover, even if it is a non-metal, the effect of this invention can be anticipated if it is a to-be-coated body whose emissivity is lower than the emissivity of a coating film. For example, as shown in FIG. 3, a solar cell module backsheet can be mentioned. In addition, as shown in FIG. 3, the coating part is preferably a back sheet surface.
Moreover, it is preferable that the average film thickness of the thermal radiation coating material apply | coated to appropriate parts, such as LED lighting, a heat sink, and a solar cell module backsheet, is 1-50 micrometers.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

(Examples 1-6, Comparative Examples 1-3, Reference Example 1)
Tables 1 and 2 show trade names and blending ratios (mass ratios). Each component was stirred until uniform to obtain a paint.

Below, the detail of each component is shown.
23-K (trade name): manufactured by Hakusuitec Co., Ltd., zinc oxide, average particle size 5.5 μm
TIG R-900 (trade name): manufactured by DuPont, titanium oxide, average particle size 0.2 μm
JR-1000 (trade name): manufactured by Teika Co., Ltd., titanium oxide, average particle size 1.0 μm
Primal AC-3001 (trade name): manufactured by Rohm and Haas Japan Co., Ltd., acrylic emulsion SN Dispersant 5029 (trade name): manufactured by San Nopco Co., Ltd., ammonium polycarboxylate CS16 (trade name): Chisso Petrochemical Co., Ltd. Manufactured by 2,2,4-trimethyl-1,3-pentadiolisobutyrate Nopco 8034 (trade name): manufactured by San Nopco Co., Ltd., hydrophobic silica polyethylene glycol Adeka Sizer NRS-602 (trade name): Asahi Denka Kogyo Co., Ltd. Adipic acid diester KBM-403 (trade name): Shin-Etsu Chemical Co., Ltd. 3-glycidoxypropyltrimethoxysilane

(Evaluation)
The following evaluation items were evaluated using the paints obtained in Examples 1 to 6 and Comparative Examples 1 to 3.

[Preparation of thermal emissivity sample plate]
As a sample for measuring the thermal emissivity, a paint was applied to an aluminum plate having a thickness of 1 mm with a desktop coater, followed by heating and drying at 80 ° C. for 30 minutes. The film thickness after drying was 40 μm.

[Thermal emissivity]
The thermal emissivity is a value representing the ability to release thermal energy in comparison with a complete black body. Also, from Kirchhoff's law, heat radiation and heat absorption are equivalent, and the relationship of heat emissivity = heat absorption rate holds. In addition, since energy incident on an opaque substance performs reflection and absorption at the same time, the relationship of reflectivity + absorption rate (emissivity) = 1 holds. Therefore, if the reflectance is measured, the thermal emissivity can be obtained indirectly.
In order to obtain the thermal emissivity based on the above principle, an emissivity measuring device TSS-5X (manufactured by Japan Sensor Co., Ltd., wavelength range 2 to 22 μm) was used. The measurement was performed in an acrylic case.

[Temperature measurement of LED bulb]
Using the paints obtained in Examples 1 to 6 and Comparative Examples 1 to 3, the surface of the Al heat sink 2 and the vicinity of the LED bulb 1 were coated with a film thickness of 25 μm by spraying, and dried by heating at 80 ° C. for 30 minutes. The temperature was measured at two points (measurement points) shown in FIG. 1 in the vicinity of the heat sink 2 and the LED bulb 1 coated with this paint. The temperature was measured by fixing a thermocouple with a polyimide tape cut to 3 × 5 mm at two points (measurement points) as shown in FIG. 1 and measuring temperatures before lighting and 1 hour after lighting. The temperature difference before and after lighting was determined.

[Coating film adhesion test]
Using the paints obtained in Examples 1 to 6 and Comparative Examples 1 to 3, the paint is applied to an aluminum plate having a thickness of 1 mm with a desktop coater and dried by heating at 80 ° C. for 30 minutes. The thickness of the coating was adjusted to 40 μm after drying. Only this coating film part was cut in parallel in both vertical and horizontal directions at intervals of 2 mm, and 25 squares were cut at 5 × 5. A cellophane tape (manufactured by Nichiban Co., Ltd.) was strongly pressure-bonded to the lattice pattern portion, and then peeled off to determine whether the coating film was peeled off. When four samples were used and the number of peeled pieces was less than 10 squares, the case where the number was 10 squares or more was indicated as x.

When comparing Comparative Examples 1 and 3, when the ceramic content is less than or not included in the above range, the emissivity is 0.90 or less and the heat dissipation is reduced, whereas all of Examples 1 to 6 have the emissivity. It was greater than 0.90 and the temperature could be reduced by 1 ° C. or more. Further, when compared with Comparative Example 2, it was found that the coating film adhesion was good when the ceramic was in the above range.
Reference Example 1 is a case where no paint is applied.

1: LED bulb, 2: heat sink, 3: coating film, 4: heat source, 5: cover glass, 6: filler, 7: cell, 8: tab wire, 9: backsheet.

Claims (5)

  (A) a ceramic powder having an average particle size of 0.1 to 50 μm and containing zinc oxide powder and / or titanium oxide powder, and (b) a binder which is a thermosetting resin or colloidal silica, and the binder 100 The thermal radiation coating material which contains 30-100 mass parts of zinc oxide powder or a titanium oxide powder or the total of both with respect to a mass part.   The thermal radiation paint according to claim 1, wherein the emissivity in a wavelength range of 2 to 22 µm is 0.90 or more.   Light emitting diode (LED) illumination in which the thermal radiation paint according to claim 1 or 2 is applied with an average film thickness of 1 to 50 µm.   A heat sink in which the heat-radiating paint according to claim 1 or 2 is applied with an average film thickness of 1 to 50 µm.   A back sheet for a solar cell module, wherein the thermal radiation paint according to claim 1 or 2 is applied with an average film thickness of 1 to 50 µm.

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