JP5871716B2 - Thermal insulation paint - Google Patents

Description

  The present invention relates to a novel heat insulating paint.

  Conventionally, an inorganic or organic fine foam or a fine hollow body used as an aggregate as a paint capable of forming a heat-insulating coating has been used. Examples of inorganic fine hollow bodies include shirasu balloons, glass balloons and silica balloons, but these fine hollow bodies have low compressive strength, and most of them are destroyed in the vacuum degassing and kneading step of the paint. It was not possible to obtain a paint exhibiting sufficient heat insulation. Moreover, in the coating material which used the organic fine foam and the fine hollow body for the aggregate, the surface hardness of the coating film was remarkably lowered and easily damaged, and the weather resistance was also inferior.

  On the other hand, for example, Patent Document 1 discloses an invention for obtaining a coating material having a high heat insulating property by blending ceramic fine hollow particles having a high compressive strength so as to withstand a high stress / shearing force in the coating process. In addition, for example, in Patent Document 2, a fireproof material having excellent fireproof performance is obtained by laminating a sheet laminated material composed of an inorganic hollow particle layer and a foamable fireproof paint layer on the surface of a base material of a fireproof member. An invention of a member and its manufacturing method is disclosed.

  However, since the ceramic fine hollow particles and inorganic hollow particles described in Patent Document 1 and Patent Document 2 are both large in average particle diameter of 6 μm or more, in order to obtain a sufficient heat insulating effect, 100 layers or more are to be laminated. Then, it has to be applied to a thickness of 0.6 mm or more, and the thickness of the heat-insulating coating film and the refractory member becomes unnecessarily thick, which increases the cost and easily peels off. Further, the ceramic fine hollow particles and inorganic hollow particles described in Patent Document 1 and Patent Document 2 are not always sufficient in strength.

  Therefore, in Patent Document 3, for example, a heat insulating paint using nano hollow particles made of silica shells utilizing the heat insulation and transparency of hollow particles made of silica shells having an outer diameter in the range of about 10 nm to about 300 nm. Although a production method has been proposed, the nano hollow particles composed of the silica shell proposed here are complicated and expensive to produce, and there is still room for improvement in terms of strength.

JP-A-8-127736 JP 2000-96737 A JP, 2007-70458, A

  In view of the state of the prior art as described above, an object of the present invention is to provide a heat insulating paint having a sufficient heat insulating effect using particles that are simple to manufacture, low in cost, and excellent in strength.

  In order to solve the above-mentioned problems, the present inventor uses natural and / or artificial quartz crystals in order to obtain a heat-insulating coating having a sufficient heat-insulating effect using particles that are easy to manufacture, low in cost, and excellent in strength. In particular, it has been found that it is effective to use natural quartz, and as a result of repeated experiments on the specifications and content of the quartz powder, the present invention has been completed.

That is, the present invention
A heat insulating paint comprising: a synthetic resin emulsion; and a crystal powder having an average particle size of 150 to 500 μm and a maximum particle size of less than 1000 μm, wherein the content of the crystal powder is 45 to 50% by weight Is to provide.

  According to the heat insulating paint of the present invention having such a configuration, since natural and / or artificial quartz powder is used, it is mined in large quantities in the People's Republic of China and can be obtained at low cost. Is simple and low in cost, and natural and / or artificial quartz is excellent in strength and can exhibit a sufficient heat insulating effect. The “average particle diameter” in the present invention is measured by a dynamic light scattering method.

  According to the present invention, a heat insulating paint having a sufficient heat insulating effect can be obtained by using particles that are simple to manufacture, low in cost, and excellent in strength.

  In the following, the synthetic resin emulsion of the present invention and a crystal powder having an average particle size of 150 to 500 μm and a maximum particle size of less than 1000 μm, and the content of the crystal powder is 45 to 50% by weight The heat-insulating paint characterized by the above will be described.

  As described above, as a result of repeated experiments by the inventor, the use of quartz powder having an average particle size of 150 to 500 μm and a maximum particle size of less than 1000 μm makes it possible to produce particles that are easy to manufacture, low in cost, and excellent in strength. It has been found that a heat insulating paint having a sufficient heat insulating effect can be obtained.

  If the average particle size of the quartz powder is less than 150 μm, the quartz powder is too fine and sufficient heat insulation cannot be obtained. In addition, if the average particle size of the crystal powder is more than 500 μm, the dispersibility of the crystal powder may be reduced or the crystal powder may be easily ejected from the coating film (particularly a thin coating film). It will be inferior. Especially, in order to acquire the effect of this invention more reliably, it is especially preferable that the average particle diameter of quartz powder is 300-350 micrometers (especially 330-340 micrometers).

  The maximum particle size of the quartz powder in the present invention is preferably less than 1000 μm. When the maximum particle size of the quartz powder is 1000 μm or more, the quartz powder is likely to jump out of the coating film and easily come out, resulting in poor heat insulation. The maximum particle size of the quartz powder in the present invention is particularly preferably less than 1000 μm.

  The content of the quartz powder in the heat insulating paint of the present invention is 45 to 50% by weight (preferably 48.1 to 48.8% by weight, more preferably 48.3 to 48.5% by weight) of the heat insulating paint. If the content of the quartz powder is 45% by weight or more of the heat insulating paint, the heat insulating effect can be obtained more reliably, and if it is 50% by weight or less, the coating film forming ability is not impaired and the coating has excellent heat insulating properties. A film can be obtained more reliably.

  Next, the synthetic resin emulsion contained in the heat insulating paint of the present invention is a synthetic resin emulsion having a hydroxyl group as a functional group and having a hydroxyl value of 0.1 to 100 mgKOH / g in the resin solid content. By using such a synthetic resin emulsion having a hydroxyl group, it is possible to form a foamed carbonized layer that is excellent in foamability and has high density in the foamed state and high strength and excellent heat insulation. As the hydroxyl group, those bonded to a carbon atom are preferred.

  The hydroxyl value in the resin solid content of the synthetic resin emulsion is 0.1 to 100 mgKOH / g, preferably 1 to 80 mgKOH / g, more preferably 2 to 60 mgKOH / g. When the hydroxyl value of the synthetic resin emulsion is too small, the density of the foamed carbonized layer cannot be increased, and the strength of the foamed carbonized layer becomes insufficient. On the contrary, when the hydroxyl value is too large, the expansion ratio of the foamed carbonized layer is lowered, and it is difficult to obtain sufficient performance in heat insulation. The hydroxyl value in the present invention is a value represented by the number of mg of potassium hydroxide equimolar to the hydroxyl group contained in 1 g of resin solid content.

  As the synthetic resin emulsion in the present invention, those satisfying the above conditions can be used, for example, (meth) acrylic resin emulsions can be used, and more specifically, (meth) acrylic acid alkyl esters and / or aromatics. It is an emulsion polymer of a monomer group mainly composed of a monomer, and preferably contains a hydroxyl group-containing monomer in a ratio of 0.5 to 15% by weight in the monomer group. If such a synthetic resin emulsion is used, the effect of this invention can be acquired stably. Moreover, various physical properties such as water resistance and durability of the coating film can be enhanced. In the present invention, the acrylic acid alkyl ester and the methacrylic acid alkyl ester are collectively referred to as (meth) acrylic acid alkyl ester.

  Specific examples of the (meth) acrylic acid alkyl ester include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, n-amyl ( (Meth) acrylate, isoamyl (meth) acrylate, n-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, octadecyl (meth) acrylate, Examples include cyclohexyl (meth) acrylate, phenyl (meth) acrylate, and benzyl (meth) acrylate. The weight ratio of the (meth) acrylic acid alkyl ester in the monomer group is usually 30% by weight or more, preferably 40% by weight or more, and more preferably 50% by weight or more. Although an upper limit is not specifically limited, Usually, it is about 99.5 weight% or less (preferably 99 weight% or less) grade.

  Specific examples of the aromatic monomer include styrene, 2-methylstyrene, vinyltoluene, t-butylstyrene, chlorostyrene, vinylanisole, vinylnaphthalene, divinylbenzene, and the like. The weight ratio of the aromatic monomer in the monomer group is usually 5 to 70% by weight, preferably 10 to 50% by weight.

  In the synthetic resin emulsion in the present invention, one containing either (meth) acrylic acid alkyl ester, aromatic monomer or both in the monomer composition can be used. In particular, if both (meth) acrylic acid alkyl ester and aromatic monomer are used, advantageous effects in water resistance, fire resistance and the like are obtained.

  In the synthetic resin emulsion in the present invention, it is desirable to impart a hydroxyl group with a hydroxyl group-containing monomer. In the present invention, by using a synthetic resin emulsion in which such a hydroxyl group-containing monomer is copolymerized, it is possible to form a foamed carbonized layer that is excellent in foamability and dense in the foamed state and excellent in heat insulation. Is possible. Specific examples of the hydroxyl group-containing monomer include 2-hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, 4-hydroxyethyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, and the like.

  In addition, monomers having both a hydroxyl group and a polyalkylene oxide group, such as polyethylene glycol (meth) acrylate, polypropylene glycol (meth) acrylate, polyethylene glycol-polypropylene glycol (meth) acrylate, polyethylene glycol-polytetramethylene glycol (meth) acrylate Polypropylene glycol-polytetramethylene glycol (meth) acrylate and the like can also be used as the hydroxyl group-containing monomer. When such a monomer having both a hydroxyl group and a polyalkylene oxide group is used, coating stability such as storage stability and mechanical stirring stability can be enhanced in addition to the above effects.

  The ratio of the hydroxyl group-containing monomer in the monomer group is usually 0.5 to 15% by weight, preferably 1 to 10% by weight. When the hydroxyl group-containing monomer is less than 0.5% by weight, it is difficult to increase the density of the foamed carbonized layer, and the strength of the foamed carbonized layer tends to be insufficient. When the amount of the hydroxyl group-containing monomer is more than 15% by weight, the expansion ratio becomes insufficient, which may adversely affect water resistance and the like.

  The synthetic resin emulsion in the present invention preferably contains a nonionic monomer selected from a polyalkylene oxide group-containing monomer, a carbonyl group-containing monomer, and a nitrile group-containing monomer as the monomer component. By using such a monomer, coating stability such as storage stability and mechanical stirring stability can be enhanced while maintaining foaming performance at high temperatures.

  Specifically, examples of the polyalkylene oxide group-containing monomer include methoxypolyethylene glycol (meth) acrylate, methoxypolypropylene glycol (meth) acrylate, methoxypolyethylene glycol-polypropylene glycol (meth) acrylate, etc. (however, having a hydroxyl group) Excluding things.) Examples of the carbonyl group-containing monomer include acrolein, diacetone (meth) acrylamide, vinyl methyl ketone, vinyl ethyl ketone, and vinyl butyl ketone. Examples of the nitrile group-containing monomer include acrylonitrile and methacrylonitrile.

  The ratio (total weight ratio) of the nonionic monomers in the monomer group is usually 0.5 to 15% by weight, preferably 1 to 10% by weight. If it is in such a range, the effect excellent in the point of paint stability can be acquired.

  In the synthetic resin emulsion in the present invention, a polymerizable monomer other than the above may be used as a constituent component if necessary. Examples of such polymerizable monomers include carboxyl group-containing monomers such as acrylic acid, methacrylic acid, crotonic acid, maleic acid or a monoalkyl ester thereof, itaconic acid or a monoalkyl ester thereof, fumaric acid or a monoalkyl ester thereof; Phosphoric group-containing monomers such as monoethyl phosphate of hydroxyethyl (meth) acrylate, monophosphate ester of hydroxypropyl (meth) acrylate, monophosphate ester of hydroxybutyl (meth) acrylate; allyl sulfonic acid, styrene sulfonic acid, vinyl sulfone Acid, sulfonic acid group-containing monomers such as 2-methylpropane sulfonic acid; N-methylaminoethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, dimethylaminoethyl vinyl ether and the like Mino group-containing monomers; vinyl ester monomers such as vinyl acetate and vinyl propionate; amide group-containing monomers such as acrylamide, methacrylamide, maleate amide, and N-methylol (meth) acrylamide; glycidyl (meth) acrylate, diglycidyl (meta ) Epoxy group-containing monomers such as acrylate and allyl glycidyl ether; alkoxysilyl group-containing monomers such as vinyltrimethoxysilane, vinyltriethoxysilane, and γ- (meth) acryloyloxypropyltrimethoxysilane; vinylidene chloride, vinylidene fluoride, etc. Other vinylidene halide monomers; ethylene, propylene, isoprene, butadiene, vinyl pyrrolidone, vinyl chloride, vinyl ether, vinyl ketone, vinyl amide, chloroprene, etc. And the like.

  Among these, an ionic monomer selected from a carboxyl group-containing monomer, a phosphate group-containing monomer, and a sulfonic acid group-containing monomer is 2% by weight or less (preferably 1% by weight or less, more preferably 0.8% by weight) in the monomer group. % Or less, more preferably 0.5% by weight or less). An embodiment that does not contain such an ionic monomer in the monomer group is also suitable.

  The synthetic resin emulsion in the present invention is an emulsion polymer of a monomer group mainly composed of a hydrophobic monomer having a solubility in water of 1 g / 100 ml or less. In the monomer group, 0.5 to 15 wt. It is preferable to include it in a ratio of%. In general, a foamable fire-resistant paint using a synthetic resin emulsion as a binder does not provide sufficient water resistance, and the original foaming performance may not be exhibited due to the influence of rainfall, condensation, and the like.

  On the other hand, if a synthetic resin emulsion composed of such constituents is used, a coating film having excellent water resistance can be formed, and the foaming performance is prevented from being lowered due to the influence of rainfall, condensation, etc., and stable foaming is achieved. It becomes possible to demonstrate performance. The water solubility here refers to the weight of the monomer dissolved in 100 ml of water at a temperature of 20 ° C.

  Examples of such a hydrophobic monomer include n-butyl (meth) acrylate, isobutyl (meth) acrylate, n-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, decyl (meth) ) Acrylate, dodecyl (meth) acrylate, octadecyl (meth) acrylate, cyclohexyl (meth) acrylate, phenyl (meth) acrylate, benzyl (meth) acrylate, styrene and the like. Such a hydrophobic monomer has a water solubility of 1 g / 100 ml or less, preferably 0.9 g / 100 ml or less, more preferably 0.8 g / 100 ml or less.

  The weight ratio of the hydrophobic monomer in the monomer group is preferably 50% by weight or more, and more preferably 55% by weight or more. Although an upper limit is not specifically limited, Usually, it is about 99.5 weight% or less (preferably 99 weight% or less) grade.

  The synthetic resin emulsion in the present invention can be produced by emulsion polymerization of a monomer group in which the polymerizable monomers are appropriately mixed. As the polymerization method, a known method may be employed, and soap-free emulsion polymerization, feed emulsion polymerization, seed emulsion polymerization, etc. may be employed in addition to ordinary emulsion polymerization. During the polymerization, an emulsifier, an initiator, a dispersant, a polymerization inhibitor, a polymerization inhibitor, a buffer, a chain transfer agent, and the like can be used.

  As an emulsifier when performing emulsion polymerization, an anionic emulsifier, a cationic emulsifier, a nonionic emulsifier, an amphoteric emulsifier, and the like can be used. These may be reactive types (reactive emulsifiers) having polymerizable unsaturated groups. As the emulsifier, one or more of these emulsifiers can be used as appropriate. Usually, an anionic emulsifier and a nonionic emulsifier may be used alone or in combination.

  Specific examples of the emulsifier include alkyl benzene sulfonates such as sodium dodecylbenzene sulfonate and sodium dodecyl sulfate, fatty acid salts, rosinates, alkyl sulfates, alkyl sulfosuccinates, α-olefin sulfonates, and alkyl naphthalenes. Anionic emulsifiers such as sulfonates and polyoxyethylene alkyl (aryl) sulfates; quaternary ammonium salts such as lauryl trialkyl ammonium salts, stearyl trialkyl ammonium salts, trialkyl benzyl ammonium salts, primary to primary Cationic emulsifiers such as tertiary amine salt, lauryl pyridinium salt, benzalkonium salt, benzethonium salt or lauryl amine acetate; polyoxyethylene alkyl ether, polyoxyethylene alkyl Nonionic emulsifiers such as phenol ether, polyoxyethylene alkyl ester, polyoxyethylene sorbitan alkyl ester; amphoteric surfactants such as carboxybetaine type, sulfobetaine type, aminocarboxylic acid type, imidazoline derivative type; Eleminol JS-2 (Sanyo) Kasei Kogyo), Eleminol RS-30 (Sanyo Kasei Kogyo), Latemuru S-180A (Kao), Aqualon HS-05 (Daiichi Kogyo Seiyaku), Aqualon RN-10 (Daiichi Kogyo Seiyaku), Aqualon Examples include reactive emulsifiers such as KH-10 (Daiichi Kogyo Seiyaku Co., Ltd.) and Adeka Soap SE-10N (Asahi Denka Co., Ltd.).

  The glass transition temperature of the synthetic resin emulsion can be adjusted by selecting the kind of the polymerizable monomer, the mixing ratio, and the like. The glass transition temperature may be appropriately set in consideration of final required performance and the like, but is usually about −50 to 80 ° C., preferably about −40 to 60 ° C. In the present invention, two or more kinds of synthetic resin emulsions having different glass transition temperatures can also be used. In addition, the glass transition temperature of a synthetic resin emulsion can be calculated | required with the formula of Fox. Moreover, the average particle diameter of a synthetic resin emulsion is 50-500 nm normally, Preferably it is 100-300 nm. This average particle diameter can be measured by a dynamic light scattering method.

  In the heat insulating paint of the present invention, such a synthetic resin emulsion is used as a binder, but other binders can be used in combination as long as the effects of the present invention are not impaired. When a plurality of binders are used, the ratio of the synthetic resin emulsion may be 50% by weight or more (preferably 70% by weight or more, more preferably 90% by weight or more) in the solid content of the binder.

  The heat insulating paint of the present invention may contain a phosphorus compound. The phosphorus compound is a component that exhibits at least one effect such as a dehydration cooling effect, an incombustible gas generation effect, and a binder carbonization promotion effect in a fire, and an effect of suppressing the combustion of the resin. Examples of such phosphorus compounds include tricresyl phosphate, diphenyl cresyl phosphate, diphenyl octyl phosphate, tri (β-chloroethyl) phosphate, tributyl phosphate, tri (dichloropropyl) phosphate, triphenyl phosphate. , Tri (dibromopropyl) phosphate, chlorophosphonate, bromophosphonate, diethyl-N, N-bis (2-hydroxyethyl) aminomethylphosphate, di (polyoxyethylene) hydroxymethylphosphate, three Examples thereof include phosphorus compounds such as phosphorus chloride, phosphorus pentachloride, ammonium phosphate, and ammonium polyphosphate. Of these, ammonium polyphosphate is particularly preferred in the present invention.

  These phosphorus compounds may be subjected to surface treatment or surface coating. The mixing ratio of the phosphorus compound is 33 to 95% by weight (preferably 50 to 90% by weight) of the heat insulating paint.

  Further, the heat insulating paint of the present invention may contain a polyhydric alcohol. The polyhydric alcohol has a function of forming a thick foamed carbonized layer having excellent heat insulation properties by dehydrating and carbonizing itself together with carbonization of the binder due to fire. Examples of the polyhydric alcohol include pentaerythritol, dipentaerythritol, tripentaerythritol, neopentaerythritol, trimethylolpropane, sorbitol, inositol, mannitol, glucose fructose, starch, and cellulose. The mixing ratio of the polyhydric alcohol is usually 5 to 85% by weight (preferably 10 to 80% by weight) of the heat insulating paint.

  In addition to the above-described components, a filler can be added to the heat insulating paint of the present invention. Examples of the filler include silicates such as talc; carbonates such as calcium carbonate and sodium carbonate; metal oxides such as aluminum oxide, titanium dioxide, and zinc oxide; natural minerals such as clay, clay, shirasu, mica, and silica. Class; hollow bodies such as glass balloons and the like. The average particle diameter of the filler is usually 0.1 to 100 μm, preferably 0.2 to 50 μm. In the present invention, the physical properties of the coating film, the coating film surface condition, etc. at the time of film formation or after film formation can be adjusted by appropriately combining different types of fillers or appropriately combining fillers having different average particle diameters. You can also. The mixing ratio of the filler is 5 to 85% by weight (preferably 10 to 80% by weight) of the heat insulating paint.

  Moreover, a foaming agent can also be mix | blended with the heat insulation coating material of this invention as needed. Examples of the foaming agent include melamine and derivatives thereof, dicyandiamide and derivatives thereof, azobistetrazole and derivatives thereof, azodicarbonamide, adipic acid dihydrazide, urea, thiourea, and ethylene urea. The mixing ratio of the foaming agent is 5 to 85% by weight (preferably 10 to 80% by weight) of the heat insulating paint.

  In the heat-insulating paint of the present invention, various additives that can be used in ordinary paints can be blended as components other than those described above. Examples of such components include pigments, fibers, thickeners, film-forming aids, leveling agents, wetting agents, plasticizers, antifreezing agents, pH adjusters, antiseptics, antifungal agents, antialgae agents, and antibacterial agents. Agents, dispersants, antifoaming agents, adsorbents, crosslinking agents, ultraviolet absorbers, antioxidants, catalysts and the like. Moreover, expansive substances, such as expansive graphite and unexpanded vermiculite, can also be mix | blended.

  The heat insulating paint of the present invention can be produced by uniformly mixing the above components by a conventional method. Usually, a one-pack type may be used. Moreover, what is necessary is just to set the viscosity of the heat insulation coating material of this invention normally to about 5-50 Pa.s. In addition, the viscosity here is a viscosity in 20 rpm by a BH type viscometer, and measurement temperature is 23 degreeC.

  The heat-insulating paint of the present invention can exert its effect by applying and laminating the object to be heat-insulated. Examples of the object to be coated include a wall, a pillar, a floor, a beam, a roof, and a staircase. Such an object to be coated is formed of a base material such as concrete or steel, and may be subjected to rust prevention treatment or the like. Moreover, the heat insulation coating material of this invention can also be applied to the base material to not only concrete and steel materials but a wooden member, a resin-type member, etc.

  When applying the heat-insulating paint to the object to be coated, the coating material may be applied once or several times using a coating device such as a spray, a roller, a brush, a trowel, or a spatula. At the time of painting, the paint can be diluted with water as necessary. The film thickness of the foamed fireproof paint finally formed may be appropriately set depending on the desired fireproof performance, application site, etc., and is, for example, about 0.2 to 5 mm.

  In this invention, in order to protect the coating film formed with a heat insulation coating material, an overcoat layer can also be laminated | stacked as needed. Such an overcoat layer can be formed by applying a known water-based or solvent-type paint. As the overcoat layer, for example, an acrylic resin-based, urethane resin-based, acrylic silicon resin-based, or fluororesin-based paint can be used. These coatings may be performed by a known coating method, and a coating tool such as a spray, a roller, or a brush can be used.

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

  Quartz powder was mixed with an exterior finishing material (Shipokaken DO manufactured by SK Co., Ltd.) mainly composed of an acrylic resin emulsion to obtain a heat insulating paint. The content of the quartz powder in the heat insulating paint was 48.4% by weight, the average particle size of the quartz powder was 334 μm, and the maximum particle size was less than 1000 μm. These particle sizes were measured using an automatic dry sonic sieving measuring instrument (robot shifter) RPS-105.

  The heat insulating paint prepared as described above was applied to the wall surface with a brush with a brush, and a coating film was obtained by natural drying (described as “Crystal” in Table 1). For comparison, a coating film was obtained using the exterior finishing material (Sipokaken DO manufactured by SK Co., Ltd.) as it was without using crystal powder (described as “normal” in Table 1).

  The temperature at a position about 20 cm and 1 m away from the surface of these coating films was measured. The results are shown in Table 1 together with the temperature. For comparison, the temperature at a position about 20 cm and 1 m away from the marble wall was also measured and shown in Table 1.

  From the results shown in Table 1, it can be seen that when the heat insulating paint of the present invention is used, the temperature in the vicinity of the coating film is remarkably lowered, and a good heat insulating effect is obtained.

Claims (4)

  A heat insulating paint comprising: a synthetic resin emulsion; and a crystal powder having an average particle size of 150 to 500 μm and a maximum particle size of less than 1000 μm, wherein the content of the crystal powder is 45 to 50% by weight .   The heat insulating paint according to claim 1, wherein the synthetic resin emulsion has a hydroxyl group as a functional group, and a hydroxyl value in a resin solid content is 0.1 to 100 mgKOH / g.   The synthetic resin emulsion is an emulsion polymer of a monomer group mainly composed of a (meth) acrylic acid alkyl ester and / or an aromatic monomer, and the proportion of the hydroxyl group-containing monomer in the monomer group is 0.5 to 15% by weight. The heat-insulating paint according to claim 1 or 2, wherein The synthetic resin emulsion contains 50% by weight or more of a hydrophobic monomer having a water solubility of 1 g / 100 ml or less in the monomer group,
The heat insulating paint according to any one of claims 1 to 3.