JP6127943B2 - Aqueous silver colloidal liquid, method for producing the same, and paint using aqueous silver colloidal liquid - Google Patents

Description

  The present invention is, for example, an electronic device such as an automobile, a bicycle, and a mobile phone, an OA device, a home appliance such as a heating cooker or an air conditioning device, or a coating material for metallic coating for parts thereof, and a raw material thereof. The present invention relates to an aqueous silver colloid solution and a method for producing the same.

  Industrial paints that give a high-class metallic feel to the coating film of various products such as electronic equipment such as automobiles, bicycles, mobile phones, OA equipment, home appliances such as heating cookers and air-conditioning equipment, and their parts. Conventionally, compositions containing aluminum flake pigments have been widely used. However, since coating compositions containing aluminum flake pigments are difficult to obtain a coating film that exhibits a glittering and strong radiance, development of coating materials containing scaly inorganic powders different from aluminum flake pigments and their coating methods has been actively developed. Has been done. As a result, many highly distinctive products born with a strong metallic feeling that cannot be obtained with conventional colored coated metal plates have come to market.

  For example, Patent Document 1 discloses metal flakes such as aluminum, zinc, copper, bronze, nickel, titanium, and stainless steel and alloy flakes thereof, flakes such as non-metallic flakes such as pearl mica, transparent pearl mica, colored mica, and interference mica. There is shown a flake pigment comprising known flake particles known as pigment base particles, a coating film covering the surface of the flake particles, and fine particles having a property of imparting triboelectric charging properties to the flake pigment.

  And the said film is equipped with the 1 or more types of 1st coupling unit derived from the fluorine-type polymerizable monomer which outermost layer has a fluorine, and the 1 or more types of 2nd coupling unit derived from the polymerizable monomer which has a phosphate group. It is a copolymer, and fine particles are fixed through the outermost layer, whereby a coating film can be obtained by applying a powder coating composed of flake pigment with a triboelectric electrostatic coater and baking it. It is described. Moreover, the coating film obtained by this has the outstanding metallic feeling and high-intensity feeling, and it is shown that there is no color nonuniformity.

  Patent Document 2 discloses an aluminum alloy composed of 99 to 80% by weight of aluminum and 1 to 20% by weight of one or two metals selected from nickel, magnesium, tin, copper, manganese, titanium, and silver. A metallic paint composition containing powder as a metallic pigment is shown. Since this aluminum alloy is harder than aluminum flakes having an aluminum content of 99.7% by weight or more, which is usually used as a metallic pigment, conventional aluminum is used when it is extended with a lubricant and a spreading medium liquid in a ball mill. Unlike flakes, it is not flattened flatly and produces warping and unevenness, and this warpage and unevenness does not decrease the brightness of the highlight part, and it also has excellent brightness of the shade part, and also excellent smoothness. Have been described.

  On the other hand, various organic resin paints such as urethane, polyolefin, and fluorine are used for clear coating for protecting the coating film. Acrylic, epoxy, or other organic resin paints may be used for relatively high transparency, and this technology prevents long-term deterioration of metallic feel and discoloration from corrosive gases such as sulfides and chlorides and sunlight. Is also progressing.

For example, Patent Document 3 discloses semi-transparent scale-like inorganic powder (aluminum flakes, stainless steel flakes, glass flakes, alumina flakes, mica powder, talc powder, plate kaolin, barium sulfate flakes, etc. And coated with a transparent oxide such as TiO ₂ , SiO ₂ , ZrO ₂ , Fe ₂ O ₃ , Fe ₃ O ₄ , SnO ₂ , Cr ₂ O ₃ , ZnO, Al ₂ O _{3 as} necessary. A clear coating of an alkyl silicone resin (one or a mixture of two or more selected from methyl silicone resin, phenyl silicone resin, methyl phenyl silicone resin) and a metallic glossy substrate -The heat-resistant clear precoat metal plate formed on the metal plate is described.

  Patent Document 4 discloses composite metal oxides such as Black 25: Co—Ni, Black 26: Cu—Mn—Fe, Black 27: Co—Cr—Fe, and Black 28: Cu—Cr having a primary particle diameter of 5 nm to 100 nm. A coating composition containing a pigment and a scaly aluminum pigment is shown. Then, L * a based on the spectral reflectance obtained by receiving the light irradiated so as to be 45 degrees with respect to the coating film obtained by applying this coating composition at 15 degrees with respect to the regular reflection light. It is shown that the type and amount of the pigment are determined so that the lightness L * 15 ° in the * b * color system is in the range of 80 to 160.

  Further, the lightness L * 110 ° in the L * a * b * color system based on the spectral reflectance obtained by receiving the specularly reflected light at 110 degrees is in the range of 5 to 30, and FF = L * 15. The hue h * 45 ° obtained by receiving the FF value calculated by ° / L * 110 ° within the range of 4.0 to 12.0 and 45 degrees with respect to the regular reflection light is 235 to 280. It is also shown that it is preferable to be within the range. Furthermore, by applying clear paint, it is excellent in weather resistance when applied to the outer panel of automobiles, which are popular for silver or gray metallic paint, and it has high brightness in highlights (near specular reflection light) and shade. In (oblique direction), the lightness is low, and it is described that it is possible to form a coating film that does not feel yellow in the shade from the highlight.

  By the way, in recent years, various sensors have been built into automobiles, home appliances, mobile phones, and the like that require the above-mentioned high-class feeling of painting, and the above-mentioned strong glitter feeling is expressed in the coating film. In addition to the above, it has been required to have a property of transmitting electromagnetic waves. However, since the flaky metal powder and the flaky inorganic powder described above have a property of reflecting electromagnetic waves, each particle of the powder is substantially the same as the surface of the substrate to be coated with a paint containing these powders as a pigment. In the case of painting by arranging them in parallel, complicated processing such as fine drilling for electromagnetic wave transmission is required in the vicinity of the sensor. Accordingly, there has been a demand for an industrial coating that gives a high-grade metallic feeling while transmitting electromagnetic waves that do not require such drilling.

  For example, Patent Document 5 includes gold, silver, ruthenium, rhodium, palladium, osmium, iridium, platinum, etc., or copper, nickel, bismuth, indium, cobalt, zinc, tungsten, chromium, iron, molybdenum, tantalum, manganese, A coating film comprising a metal nanoparticle having a particle diameter of about 1 to 100 nm containing one or more metals such as tin and titanium, a resin component, a method for forming the same, and a coating composition thereof are shown. Yes.

  And it is described that this coating film has electromagnetic wave permeability, adhesiveness and high brightness appearance, and is excellent in balance. Moreover, it is described that this resin component consists of resin (polymer) (a) containing an oxazoline group and resin (b) containing a carboxyl group. Furthermore, it is described that the resin (b) is an amphiphilic high molecular weight copolymer including a functional group having a high affinity for nanoparticles and a solvent-affinity moiety, and preferably has a number average molecular weight of 1,000 to 1,000,000. Has been.

  In Patent Document 6, metal nanoparticles containing 72 to 99% by mass of silver nanoparticles are dispersed in a composition excluding the dispersion medium, and polyvinyl pyrrolidone, a polyvinyl pyrrolidone copolymer, polyvinyl alcohol are further dispersed in the dispersion medium. And an electrode-forming composition prepared by adding and mixing 0.1 to 20% by mass of metal nanoparticles with one or more organic polymer additives selected from the group consisting of cellulose ethers. Has been.

JP 2009-215411 A JP 2003-64315 A JP 2004-50772 A JP 2013-40257 A Japanese Patent No. 5163715 Japanese Patent No. 5309521

  However, since the paints shown in Patent Documents 1 to 4 are obtained by arranging metal flakes or scaly inorganic powders substantially parallel to the surface of the base material to be coated in order to obtain a high-quality metallic feeling, In addition, the reflection from the scaly powder was still large, and as a result, the brightness difference was insufficient, so that the metal texture required in the market was not achieved. Moreover, good electromagnetic wave permeability could not be expected.

  Further, the metal nanoparticles shown in Patent Document 5 include a resin containing an oxazoline group and a resin containing a carboxyl group in order to be suitable for use in an automobile body and an automobile part. For this reason, the substance which can be added, heating temperature, a use, etc. will be limited. Moreover, the composition for electrode formation of patent document 6 does not have the process of removing it, after adding organic polymer. Therefore, it is expected that the organic polymer not adsorbed on the silver particles remains. Residues of polyvinyl pyrrolidone and polyvinyl alcohol cause a strong yellow or orange hue modulation in each of the particles, and when stored for a long period of time, there is also a change in hue over time due to decomposition. It is not suitable for the intended use.

  As described above, a coating composition containing metal fine particles capable of forming a coating film having a high metal texture and electromagnetic wave permeability is desired. In particular, such metal fine particles often take the form of a colloid in order to prevent agglomeration. In this case, excellent dispersibility and high storage stability that does not settle even if the colloid is stored for a long period of time are required. The present invention has been made in view of these problems, and is an aqueous silver colloid liquid that has a high dispersibility and storage stability, and that can provide a coating film excellent in metal texture and electromagnetic wave permeability when used as a paint. The purpose is to provide.

In order to achieve the above object, the aqueous silver colloidal solution provided by the present invention contains an organic substance containing at least polyvinylpyrrolidone and polyvinyl alcohol (excluding a protective agent for an organic molecular main chain having a carbon skeleton of 1 to 3 carbon atoms). From substantially spherical silver particles having an average particle size (D50) of 45 to 100 nm and a minimum particle size (Dmin) of 15 nm or more adsorbed on the surface , and water as a solvent containing impurities other than the silver particles adsorbed by the organic matter An aqueous silver colloid liquid for coating , wherein the organic substance adheres in an amount of 1 to 10% by mass with respect to silver particles, and the total amount of impurities other than the silver particles adsorbed by the organic substance is in the aqueous silver colloid liquid. 1 mass% or less. In the above-described aqueous silver colloid liquid for paint of the present invention, the molecular weights of polyvinylpyrrolidone and polyvinyl alcohol are preferably 3,000 to 25,000 .

  Moreover, this invention provides the coating material using the above-mentioned aqueous silver colloid liquid. The coating film obtained by applying this paint preferably has a specular reflectance of 97% or more with respect to light having a wavelength of 400 to 800 nm. In addition, this coating film is an L * a * b * table based on the spectral reflectance obtained by receiving the light irradiated at 45 degrees with respect to the coating film surface at 25 degrees with respect to the regular reflection light. Spectral spectrum obtained by receiving the light L * 25 in the color system in the range of 25 to 120 and receiving the light irradiated at 45 degrees with respect to the coating film surface at 75 degrees with respect to the regular reflection light. The lightness L * 75 in the L * a * b * color system based on the reflectance is in the range of 10 to 40, and the FF value calculated by “FF = L * 25 / L * 75” is 2.5. L * C * h ° color system obtained by receiving light irradiated at 45 degrees with respect to specular reflection light within a range of 6.0 and 45 degrees with respect to the coating film surface It is preferable that hue h ° 45 in the range of 0 to 120 or 330 to 360. Furthermore, this coating film preferably has an electromagnetic wave transmission loss at 76 GHz of 1 dB or less.

In addition, the method for producing an aqueous silver colloid solution provided by the present invention comprises an aqueous solution of a silver ammine complex salt in which a silver compound is dissolved in an ammonia solution, hydrazine as a reducing agent, polyvinylpyrrolidone, and polyvinyl alcohol. And a step of adsorbing an organic substance containing at least polyvinylpyrrolidone and polyvinyl alcohol on the surface of the silver particles, and a step of filtering and washing the aqueous solution containing the precipitated silver particles. In the mixing, the polyvinyl pyrrolidone is mixed so as to be 1 to 10% by mass and the polyvinyl alcohol is 1 to 40% by mass with respect to silver.

  In the above-mentioned method for producing an aqueous silver colloidal solution, it is preferable that the molecular weights of polyvinylpyrrolidone and polyvinyl alcohol are 3,000 to 25,000. In the above-described method for producing an aqueous silver colloid solution, it is preferable that the silver compound is silver chloride, an ultrafiltration device is used for filtration, and pure water is used for the washing.

  According to the present invention, an aqueous silver colloid liquid excellent in dispersibility and storage stability in the liquid can be obtained, and the coating film formed using the paint has a good metallic texture and transmits electromagnetic waves. It has the characteristic to do.

It is the SEM image which observed the silver particle in the aqueous silver colloid liquid obtained with the sample 1 of the Example by the scanning electron microscope (magnification 20,000 times). It is the SEM image which observed the silver particle in the aqueous silver colloid liquid obtained with the sample 2 of the Example by the scanning electron microscope (magnification 10,000 times).

(Aqueous silver colloid solution)
Hereinafter, embodiments of the aqueous silver colloid solution of the present invention will be described in detail, but the present invention is not limited to the following embodiments. The aqueous silver colloidal liquid of the embodiment of the present invention is composed of silver particles having a spherical shape and an average particle diameter (D50) of 45 to 100 nm and water as a solvent containing impurities inevitably mixed in the production. Become. The surface of the silver particles is coated with at least two kinds of organic substances such as polyvinyl pyrrolidone and polyvinyl alcohol, and the adhesion amount thereof is 1 to 10% by mass with respect to the silver particles. On the other hand, the total amount of inevitable impurities is 1% by mass or less with respect to the aqueous silver colloid solution. In addition, the case where it is coat | covered with the modified | denatured substance derived from organic substance is also included with being covered with organic substance.

  Both polyvinylpyrrolidone and polyvinyl alcohol have the property of being easily adsorbed on the surface of silver particles. In particular, polyvinyl pyrrolidone has a property of being easily adsorbed on the surface of silver particles as compared with polyvinyl alcohol, but on the other hand, it also has a characteristic that it is difficult to remain. Therefore, with polyvinyl pyrrolidone alone, the amount of organic matter attached may become 0.03 mass% or less with respect to silver particles by washing with pure water or the like. If it is about 0.03% by mass, there is no problem with the initial amount of polyvinylpyrrolidone deposited, but since polyvinylpyrrolidone gradually deviates over time, aggregation gradually proceeds as it is stored, which causes a problem in storage stability. May occur.

  On the other hand, polyvinyl alcohol alone is adsorbed on the surface of silver particles although not as much as polyvinyl pyrrolidone, and in this case, it has a characteristic that it tends to remain. However, since polyvinyl alcohol has a property of swelling with water, if it is adsorbed in a large amount, it may be difficult to clean the inside of the swollen portion.

  However, when silver chloride is reduced when silver chloride is reduced by mixing a silver complex salt solution in which silver chloride is dissolved in aqueous ammonia with a dispersant containing at least two kinds of polyvinylpyrrolidone and polyvinyl alcohol and hydrazine. Higher properties of polyvinylpyrrolidone are preferentially adsorbed on silver particles, and polyvinyl alcohol is adsorbed on the outer position. Since polyvinyl alcohol has the property of swelling with water as described above, even if polyvinyl pyrrolidone deviates from the surface of silver particles by utilizing this property, the surrounding polyvinyl alcohol inhibits liberation, and the desorbed polyvinyl pyrrolidone Is immediately adsorbed on the surface of the silver particles, so that an aqueous silver colloidal solution excellent in dispersibility and storage stability can be obtained.

  In addition, since polyvinyl alcohol has a property of swelling with water, dispersibility is maintained even when drying proceeds to some extent by positioning the polyvinyl alcohol outside the polyvinyl pyrrolidone. When this aqueous silver colloidal solution is applied to a paint, it is possible to prevent silver particles from being unevenly arranged due to local variations in drying speed during drying. That is, it is difficult to obtain good dispersibility in the dry state of polyvinyl pyrrolidone, but dispersibility is maintained while the polyvinyl alcohol occupying the surroundings is swollen, and the arrangement time is increased by extending the time for arranging silver particles. Unevenness is reduced.

  In order to obtain these properties, it is desirable to preferentially adsorb polyvinylpyrrolidone to silver particles in an aqueous silver colloidal solution and adsorb polyvinyl alcohol so that it is located outside, but formation of silver particles by reduction When polyvinyl alcohol is sometimes added without forming polyvinyl alcohol and after adding silver colloid, uniform adsorption is difficult, and the above-described good dispersibility and storage stability are not obtained so much. Also, these properties do not appear after complete drying or after fixing with a clear coat or the like.

  Since the silver particles contained in the aqueous silver colloidal liquid of the embodiment of the present invention are substantially spherical in shape, the coating film obtained when this aqueous silver colloidal liquid is applied as a paint has little irregular reflection and is in the form of scaly Compared with (flat plate) particles, the reflection on the shade is kept low, so the metal texture is excellent, and the electromagnetic wave permeability is high. Furthermore, the silver particles contained in the aqueous silver colloidal liquid according to the embodiment of the present invention have a particle size that is large as a nanopowder and high in uniformity of particle size, so that there are few particles that are too fine, and thus non-sinterable, ie, sintered. It is also excellent in that it is hard to tie.

  However, since the silver particles contained in the aqueous silver colloidal liquid of the embodiment of the present invention become conductive when sintered, the electromagnetic wave permeability is lost as in the case of using flake powder or scaly inorganic powder, so that the conductive paste It can also be used as a raw material. In the present invention, the silver particles in the aqueous silver colloid liquid refer to single crystal particles, polycrystalline particles, or aggregates thereof.

  The inevitable impurities contained in the aqueous silver colloid liquid (that is, silver particles to which organic substances are attached and components other than water as a solvent) cause the metallic texture to be poor when the aqueous silver colloid liquid is applied to a paint, Cause the smoothness of the film to deteriorate. Therefore, it is necessary to reduce the total amount of impurities to such an extent that the above-mentioned adverse effects are not substantially affected. Specifically, the total amount of inevitable impurities should be 1% by mass or less with respect to the aqueous silver colloid liquid. is necessary.

(spherical)
Silver particles in the aqueous silver colloidal liquid according to the embodiment of the present invention were observed with an SEM image (for example, 20,000 times) using an FE-SEM (Field Emission Scanning Electron Microscope, Hitachi, Ltd., model S-4700). The shape at the time is substantially spherical. Specific examples of non-spherical shapes include dendrites (including leaves and needles), needles, etc., ellipses, flakes, etc. with an aspect ratio (major axis / minor axis) of 1.5 or more The difficult thing can be mentioned.

  The non-spherical silver particles as described above may be contained in the aqueous silver colloid liquid as long as the effect of the spherical silver particles is not hindered. In that sense, it is important that the spherical silver particles occupy 80% by mass or more of the total silver particles, preferably 90% by mass or more, and most preferably about 100% by mass. An aqueous silver colloidal solution containing more spherical silver particles can be prepared by adjusting the charging time of the reducing solution and the dispersion.

(Average particle size (D50))
The silver particles contained in the aqueous silver colloidal liquid of the embodiment of the present invention are required to have an average particle diameter (D50) of 45 to 100 nm, and preferably 45 to 80 nm. The average particle diameter (D50) here is a volume cumulative particle diameter D50 measured by a laser diffraction / scattering particle size distribution measuring apparatus. If this D50 is less than 45 nm, the non-sintering characteristics cannot be obtained sufficiently. On the other hand, when D50 is larger than 100 nm, not only the electromagnetic wave permeability is lowered, but the film thickness of the coating film is increased, leading to an increase in cost.

  The average particle diameter of the silver particles described above can be adjusted by the respective concentrations of polyvinyl pyrrolidone and polyvinyl alcohol with respect to silver during reduction. Specifically, the average particle diameter of silver particles can be reduced by increasing the concentration of polyvinylpyrrolidone, and conversely, the average particle diameter of silver particles can be increased by increasing the concentration of polyvinyl alcohol. . Of these, polyvinylpyrrolidone has a higher contribution to the average particle diameter of silver particles. Of course, the concentration of polyvinyl pyrrolidone and polyvinyl alcohol also has a close influence on the amount of organic matter deposited, as will be described later, and therefore the concentrations of polyvinyl pyrrolidone and polyvinyl alcohol are adjusted in consideration of the desired amount of organic matter deposited and the average particle size.

(Minimum particle size (Dmin))
The minimum particle diameter (Dmin) of the silver particles contained in the aqueous silver colloidal liquid of the embodiment of the present invention is preferably 15 nm or more, and more preferably 30 nm or more. When this Dmin is smaller than 15 nm, for example, the non-sinterability of the coating film after the aqueous silver colloid liquid is applied as a paint and dried is deteriorated, and the film is baked due to the influence of sunlight (ultraviolet rays) or the temperature of the use environment. This is not preferable because it may lead to deterioration of electromagnetic wave permeability and change in hue.

(Non-sedimentation)
The aqueous silver colloidal solution of the embodiment of the present invention is excellent in high dispersibility and storage stability as described above. There is non-sedimentation as an index for measuring these characteristics. For example, an aqueous silver colloid solution is diluted with an appropriate amount of room temperature pure water and stirred, and then has a non-sedimentation property so that silver particles do not settle as colloidal particles even after standing for 1 week or more, preferably 3 weeks or more. It is preferable.

  Since the silver particles contained in the aqueous silver colloidal liquid of the embodiment of the present invention are fine and substantially spherical, the density (bulk density) with respect to the apparent size (also referred to as particle size) of the particles is increased, but the surrounding polyvinyl chloride Since the alcohol can be sufficiently present, the dispersion effect of polyvinyl pyrrolidone can be sufficiently exhibited. As a result, the sedimentation speed when the colloid is dispersed becomes slow, and a characteristic capable of floating for a long time is obtained.

(Amount of organic matter)
The aqueous silver colloidal solution containing silver particles described above can be prepared by mixing at least two types of dispersants of polyvinyl pyrrolidone and polyvinyl alcohol and hydrazine in a silver complex salt aqueous solution, and reducing the silver complex salt. In that case, since the above-mentioned organic substances such as polyvinyl pyrrolidone and polyvinyl alcohol are particularly easily attached to the generated silver particles, silver particles to which a large amount of these organic substances are attached are obtained. The adhesion amount of these organic substances to the silver particles needs to be 1 to 10% by mass with respect to the silver particles.

  The reason is that when the organic matter adhesion amount is in the range of 1 to 10% by mass, the non-sinterability and non-sedimentability can be enhanced without significantly impairing the metal texture of the coating film. That is, when the organic substance adhesion amount is less than 1% by mass, the non-sintering property may be deteriorated and the electromagnetic wave permeability of the coating film may be reduced. The texture may be poor and the design may be reduced.

(Use)
As described above, the aqueous silver colloidal liquid according to the embodiment of the present invention is excellent in non-sedimentation, that is, dispersibility and storage stability, and also excellent in non-sinterability. Furthermore, the coating film formed using it as a coating material is excellent in design, that is, metal texture, and excellent in electromagnetic wave permeability. Therefore, it is preferably used as a raw material for paints of articles that are electromagnetic wave transmission type and require an excellent appearance design. Specifically, it can be suitably used for paintings for home appliances such as automobiles, bicycles, electronic devices, OA devices, heating cooking appliances and air-conditioning devices, and parts thereof.

(Production method)
The aqueous silver colloidal liquid of the embodiment of the present invention is not limited, but can be prepared by, for example, the following method. That is, a silver ammine complex salt aqueous solution (also referred to as a silver ammine complex salt aqueous solution or a silver complex salt aqueous solution) is prepared by dissolving a silver compound in ammonia water, and at least two kinds of dispersants such as polyvinylpyrrolidone and polyvinyl alcohol, and a hydrazine solution. And the silver compound is reduced to precipitate silver particles. An aqueous silver colloidal solution can be obtained by filtering and washing the resulting aqueous solution containing silver particles.

  As the silver compound to be reduced, silver chloride, silver oxide, silver nitrate, silver carbonate, or the like can be used. Among these, silver chloride is preferable. The reason is that when silver chloride is used as a raw material, the reduction reaction is slow compared to other silver compounds, so that the generation of fine particles having a minimum particle size of less than 15 nm is suppressed, and the particle size distribution is more stable. is there.

  When using silver chloride as the silver compound, it is preferable to adjust the silver concentration of the silver complex aqueous solution obtained by dissolving silver chloride in aqueous ammonia to 0.1 to 30 g / L, and to 1 to 15 g / L. More preferably. When this silver concentration is less than 0.1 g / L, productivity deteriorates and it becomes difficult to obtain silver powder efficiently. On the other hand, if the silver concentration is higher than 30 g / L, the shape of the silver particles to be produced becomes unstable, and the particle size distribution becomes particularly unstable.

  The pH of the aqueous silver complex salt solution obtained by dissolving silver chloride in aqueous ammonia is preferably adjusted to 10 to 13, more preferably about pH 12. When this pH is lower than 10, silver chloride is precipitated, and the characteristics such as the particle size distribution of the product are not stable. On the other hand, even if the pH exceeds 13, the characteristics of the silver particles produced are not particularly improved, and a large amount of ammonia gas may volatilize and cause bad odor. In particular, by adjusting the pH of the aqueous silver complex salt solution to about 12, a more stable aqueous silver colloidal solution can be prepared in terms of the uniformity of the particle shape and particle size distribution.

  As the dispersant used in the embodiment of the present invention, two types of polyvinyl pyrrolidone and polyvinyl alcohol are essential, but a dispersant other than these may be further added as necessary. At that time, it is expected that the added other dispersing agent will remain slightly on the surface of the silver particles. Therefore, when stored for a long period of time, the coating is designed to cause discoloration due to ultraviolet rays or to reduce transparency. It is desirable that it does not impair the properties and does not promote sintering.

  Examples of such a dispersant include fatty acids such as stearic acid, palmitic acid, oleic acid and stearic acid, and polyoxyethylene alkyl ethers such as polyoxyethylene (7) oleyl ether and polyoxyethylene (23) lauryl ether. And carboxylic acids such as succinic acid, lactic acid and formic acid, azo compounds such as imidazole and benzotriazole, amino compounds such as diethanolamine and polyethyleneimine, and surfactants. Dispersibility can be further improved by adding one or more of these.

  The molecular weight of polyvinyl pyrrolidone used for the dispersant is preferably 3,000 to 25,000. If the molecular weight is less than 3,000, the function as steric hindrance is poor, and as a result, the dispersibility may be deteriorated. On the other hand, if the molecular weight exceeds 25,000, the smoothness of the coating film may be lowered. Because there is. As described above, it is desirable that the polyvinyl alcohol used in the dispersant has a swelling property. For that purpose, it is preferable that the hydrophilic property is high, that is, the molecular weight is relatively small, and the polyvinyl alcohol is adsorbed on the surface of the silver particles. However, since it occupies the periphery of polyvinyl pyrrolidone, it is inevitably preferable to have a molecular weight comparable to that of polyvinyl pyrrolidone.

  Polyvinylpyrrolidone is added so that it may become 1-10 mass% with respect to silver. When this amount is less than 1% by mass, the amount adsorbed on the surface of the silver particles becomes insufficient, and the dispersibility is deteriorated to cause a problem in design when a coating film is formed. There is a risk of lowering electromagnetic wave permeability. On the other hand, when the amount exceeds 10% by mass, the adsorption of polyvinyl alcohol is hindered, and there is a problem in design properties when a coating film is formed, or the effect of extending the time of silver particle arrangement to obtain sufficient electromagnetic wave permeability May be insufficient.

  Polyvinyl alcohol is added so that it may become 1-40 mass% with respect to silver. If this amount is less than 1% by mass, it cannot be sufficiently present around the polyvinyl pyrrolidone on the surface of the silver particles, and unevenness is likely to occur during drying, resulting in non-uniform film thickness, reduced design, There is a possibility of causing a problem that the electromagnetic wave permeability is lowered due to the scattering. On the other hand, when the amount exceeds 40% by mass, it takes too much time to wash the silver particles, and the productivity is lowered, which is not preferable.

  The hydrazine used as the reducing agent is preferably adjusted to a molar ratio of 0.6 or more with respect to the silver compound, and more preferably adjusted within the range of 1 to 3. If this molar ratio is less than 0.6, the reduction is insufficient, and unreduced silver may precipitate in the aqueous silver colloid solution after reduction. On the other hand, if this molar ratio is greater than 3, it becomes uneconomical and the working environment may be deteriorated by the generation of hydrazine gas.

  In the method described above, after adding a dispersant containing at least polyvinylpyrrolidone and polyvinyl alcohol to the reducing solution, the reducing solution containing the dispersant is added to the silver complex aqueous solution in which a silver compound such as silver chloride is dissolved in ammonia water. However, the present invention is not limited to this method, and a dispersant containing at least polyvinylpyrrolidone and polyvinyl alcohol may be added to the silver complex aqueous solution together with or separately from the reducing agent, and both the reducing agent and the silver complex salt may be added. Silver particles may be generated by dissolving a dispersant containing at least polyvinylpyrrolidone and polyvinyl alcohol in the third liquid not included, and adding and mixing the third liquid together with the reducing liquid or separately into the silver complex aqueous solution. .

  In any case, as a reducing condition, the temperature of the mixture obtained by mixing the dispersant containing at least polyvinyl alcohol and polyvinylpyrrolidone and the reducing solution in the silver complex aqueous solution is preferably 15 to 50 ° C, and preferably 20 to 45 ° C. More preferred is 25 to 40 ° C. If this temperature is less than 15 ° C., the reduction performance of hydrazine is lowered and the production of silver particles is delayed, so that the reduction time becomes longer and the productivity is lowered. On the other hand, when the temperature is higher than 50 ° C., not only the volatilization amount of ammonia increases, but also the particle size of silver powder may vary.

  After confirming the completion of the reduction reaction by the completion of foaming by the reduction reaction, or by reducing the oxidation-reduction potential, the aqueous silver colloid liquid is obtained by filtering and washing the aqueous solution containing the precipitated silver particles. It is done. The filtration and washing methods are not particularly limited as long as the silver particles are not dissolved or the polyvinylpyrrolidone or polyvinyl alcohol adsorbed on the surface is not removed, and a general method can be adopted. it can.

  For example, since silver particles have an average particle size of 100 nm or less, concentration using an ultrafiltration device having a molecular weight cut off of about 25,000 to 100,000, and dilution of the resulting concentrate with pure water By repeating the above, filtration and washing treatment can be performed. Thereby, impurities such as polyvinyl pyrrolidone, polyvinyl alcohol, ammonia, hydrazine, and surfactant dissolved in the liquid without adsorbing on the surface of the silver particles can be sufficiently removed. Thereafter, an aqueous silver colloidal solution can be obtained by concentrating the silver concentration to 1 g / mL, for example. In order to accelerate the removal of polyvinyl pyrrolidone and polyvinyl alcohol that are not adsorbed on the silver particles, it is effective to add an alcohol such as ethanol to the pure water used for the washing.

  Polyvinylpyrrolidone and polyvinyl alcohol adsorbed on the surface of the silver particles are easily decomposed below the combustion temperature and decomposition temperature of the single substance by the catalytic effect of silver, respectively, and a metallic luster peculiar to silver can be easily obtained. On the other hand, polyvinylpyrrolidone, polyvinyl alcohol, and surfactant remaining in the liquid hardly come into contact with the surface of the silver particles, so that the catalytic effect of silver is not obtained, and combustion or decomposition of each single substance is not possible. Unless it is carried out, yellow or orange color resulting from them is exhibited, and the design is impaired. Therefore, in the aqueous silver colloid liquid, impurities such as polyvinyl pyrrolidone and polyvinyl alcohol remaining in the liquid without adsorbing on the surface of the silver particles are sufficiently removed by the above washing treatment, and the total amount of impurities contained in the water is aqueous. It should be 1% by mass or less based on the colloidal liquid.

(paint)
Since the aqueous silver colloid of the embodiment of the present invention is applied as a paint and then has a metallic texture in the coating film obtained by drying and is excellent in electromagnetic wave permeability, it has not only excellent design properties but also electromagnetic wave permeability. It is preferable to apply it to a paint for metallic coating of required articles. In such a coating material, a resin component, a solvent, and other additives can be appropriately blended in order to adjust the viscosity necessary for coating. Moreover, you may add the component of clear coating mentioned later previously.

  Further, the aqueous silver colloidal solution obtained as described above may be further subjected to organic surface treatment. By subjecting the silver particles in the aqueous colloidal silver solution to an organic surface treatment, the cohesiveness can be further suppressed or the non-sinterability can be improved. In addition, the affinity with other materials can be controlled by appropriately selecting the organic surface treatment agent.

  As the organic surface treatment agent, for example, an organic compound such as a surfactant, a saturated fatty acid, an unsaturated fatty acid, a nitrogen-containing organic compound, a sulfur-containing organic compound, and a silane coupling agent can be used. As described above, since the surface of silver particles is occupied by highly hydrophilic polyvinyl alcohol, it is difficult to form a film of these organic surface treatment agents in water. For this reason, for example, when oleic acid, capric acid or stearic acid is used as the organic compound, the organic compound is mixed with an aqueous silver colloid solution in a paint, applied to a substrate, and then formed on the particle surface during drying. There is a way to show the sex.

(Color of coating film)
The coating film formed with the paint using the above aqueous silver colloidal liquid has a high specular reflectance and an excellent brightness feeling, and has a flip-flop property (hereinafter referred to as FF property) indicating that there is a difference in brightness depending on the visual direction. In addition, it has a dense feeling that does not make the grainy feel of particles more, so that it expresses a metal texture with excellent design.

  Specifically, the coating film formed with the paint using the aqueous silver colloidal liquid according to the embodiment of the present invention has a specular reflectance of 97% or more and was irradiated so as to be 45 degrees with respect to the coating film surface. The lightness L * 25 in the L * a * b * color system based on the spectral reflectance obtained by receiving the light at 25 degrees with respect to the regular reflection light is in the range of 25 to 120, On the other hand, the lightness L * 75 in the L * a * b * color system based on the spectral reflectance obtained by receiving the light irradiated so as to be 45 degrees at 75 degrees with respect to the regular reflection light is 10 to 40. Irradiated so that the FF value calculated by FF = L * 25 / L * 75 is in the range of 2.5 to 6.0 and is 45 degrees to the coating surface. The hue h ° 45 in the L * C * h ° color system obtained by receiving the light at 45 degrees with respect to the regular reflection light is 0 to 120 or 330. It is in the range of 360.

  In order to obtain a desired value within the range indicated for the above index, the average particle diameter of the silver particles in the aqueous silver colloid contained in the silver ink, the amount of organic matter adhered, the amount of the aqueous silver colloid, the resin component The type and amount of the are appropriately adjusted. Specifically, the influence of plasmons can be adjusted by changing the average particle diameter of the silver particles. If the particle size is reduced, the influence of plasmons increases and the hue h ° 45 increases (in the range of −30 to 120). Moreover, since the coating film also increases, the influence of the base color also decreases. The reflectance can be adjusted by changing the amount of organic matter attached. If the organic substance adhesion amount is decreased, the lightness L * 75 increases, but since the sinterability increases, the FF value may decrease at the same time, and adjustment within a range where sintering is not required is necessary. Further, the light reflection characteristics may be adjusted by irradiating ultraviolet rays or the like.

(Electromagnetic wave transmission)
The average particle diameter of the silver particles contained in the aqueous silver colloidal liquid according to the embodiment of the present invention is a fine spherical shape of 45 to 100 nm, and an organic substance adheres to the surface, and the non-sinterability is high. The coating film formed by the paint has excellent electromagnetic wave transmission, and specifically, the electromagnetic wave transmission loss at 76 GHz is 1 dB or less.

(Composition of coating film)
The substrate to which the paint using the aqueous silver colloidal liquid according to the embodiment of the present invention is applied is subjected to plating or vapor deposition with a metal such as iron, zinc, aluminum, magnesium, an alloy containing these, or these metals. Or a molded product made of plastic or foam, or glass. These materials may be subjected to degreasing treatment or surface treatment as necessary. Further, it is preferable to form an undercoat film or an intermediate coat film on the base material, apply the coating material to form a coating film, and apply clear coating thereon.

  Here, the undercoat film is formed to conceal the surface of the material, or to give the material anticorrosion and rustproofness, etc., which is applied by applying the undercoat paint and drying and curing. Obtained by. There are no particular limitations on the type of undercoat paint, and examples thereof include electrodeposition paints and solvent-type primers. On the other hand, the intermediate coating film is formed to conceal the material surface and the undercoat coating film, to provide adhesion and chipping resistance, and to adjust the lightness in the multilayer coating film. Yes, this can be obtained by applying an intermediate coating on the material surface or undercoat, drying and curing. There is no limitation in particular in the kind of intermediate coating material, A well-known thing can be used. For example, an organic solvent-based or water-based paint containing a thermosetting resin composition or a color pigment as an essential component can be suitably used.

  When the above-described undercoat film or intermediate coat film is formed on a substrate, the aqueous silver colloid liquid of the embodiment of the present invention is used after the undercoat film and the intermediate coat film are heated and crosslinked and cured. The intermediate coating film is formed after the undercoating film is heated and cross-linked and cured, and the intermediate coating film remains uncured and the aqueous silver colloidal liquid according to the embodiment of the present invention is applied. Alternatively, a paint using the aqueous silver colloid liquid of the embodiment of the present invention may be applied while both the undercoat film and the intermediate coat film are uncured.

  The clear paint is a paint that is applied to an uncured or cured coating surface of a paint film that uses the aqueous silver colloidal liquid according to the embodiment of the present invention, and is mainly composed of a resin component and a solvent, and further required. Depending on the above, it is a liquid paint that forms a colorless or colored transparent coating film by blending other paint additives and the like. There is no restriction | limiting in particular as a clear coating material, A well-known thing can be used. For example, a liquid or powdery coating composition containing a base resin and a crosslinking agent can be applied.

  Examples of the base resin include resins containing a crosslinkable functional group such as a hydroxyl group, a carboxyl group, a silanol group, and an epoxy group, that is, an acrylic resin, a polyester resin, an alkyd resin, a fluororesin, a urethane resin, a silicon-containing resin, and the like. Can be mentioned. Examples of the crosslinking agent include melamine resin, urea resin, polyisocyanate compound, block polyisocyanate compound, epoxy compound or resin, carboxyl group-containing compound or resin, acid anhydride, alkoxysilane group-containing compound or resin, etc. The thing which can react with the functional group of base resin can be mentioned. Further, if necessary, additives such as a solvent such as water and an organic solvent, a curing catalyst, an antifoaming agent, an ultraviolet absorber, a rheology control agent, an antioxidant, and a surface conditioner can be appropriately blended.

  The clear paint can be blended with a color pigment within a range that does not impair the transparency. As the coloring pigment, one or more of those known for ink and paint can be used. The addition amount is preferably blended so that the solid content is 30% by mass or less with respect to the resin solid content in the clear coating film, more preferably in the range of 0.01 to 15% by mass, and 0.1 to 0.1%. A range of 10% by mass is particularly preferable.

  The clear paint can be applied by a method such as electrostatic coating, air spray, or airless spray, and is preferably formed so that the coating film after curing has a thickness in the range of 15 to 70 μm. The clear coating film itself can be crosslinked and cured usually at a temperature of about 50 to about 180 ° C. in the case of a baking dry type, and is usually in the range of room temperature drying to about a normal drying type or forced drying type. It can be crosslinked and cured at a temperature of 80 ° C.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated more concretely, this invention is not limited to these Examples. In addition, the particle size measurement, the measurement of the organic substance adhesion amount, the sedimentation evaluation, the electromagnetic wave permeability evaluation, the metal texture evaluation, and the reflectance evaluation in the following examples were respectively performed in the following manner.

<Particle size measurement>
The particle size of the silver particles contained in the aqueous silver colloid solution was measured by taking a small amount of the aqueous silver colloid solution in a beaker and adding 50 mL of a 0.2% aqueous sodium hexametaphosphate solution. Then, the dispersion | distribution process was carried out for 10 second using the ultrasonic disperser US-300T (Nippon Seiki Seisakusho make, OUTPUT: 6, TUNING: 5), and the sample for a measurement was prepared. This measurement sample was introduced into a dynamic light scattering particle size distribution analyzer UPA-EX150 (manufactured by Nikkiso), and volume cumulative average particle diameters D50 and Dmin were measured.

<Measurement of organic matter adhesion amount>
The measurement of the amount of organic matter adhering to the surface of the silver particles was performed using a thermogravimetric / thermal differential analyzer (manufactured by Bruker AXS, TG-DTA2000SR), dry air 100 mL / min, temperature rising rate 10 ° C./min. The temperature was measured by raising the temperature from room temperature to 1,000 ° C. In this measurement method, the aqueous silver colloidal liquid of the present invention had a large mass reduction region from room temperature to 200 ° C. and a small mass reduction region from 220 ° C. to 400 ° C. The mass loss from room temperature to 200 ° C. is due to the evaporation of water in the colloid, and the mass loss from 220 ° C. to 1,000 ° C. is due to decomposition and volatilization of attached organic matter. The mass can be regarded as a single silver particle. Therefore, the mass reduction amount from 220 ° C. to 1,000 ° C. divided by the remaining mass at 1,000 ° C. was defined as the ratio of the amount of organic matter attached to silver.

<Evaluation of sedimentation>
At room temperature, 25 g of an aqueous silver colloidal solution was diluted with 30 mL of pure water and stirred for 1 minute, and then collected in a glass beaker.
○: It did not sink for more than 3 weeks.
Δ: Sedimentation was observed after 1 week to 3 weeks.
X: Sedimentation was observed within one week.

<Evaluation of electromagnetic wave transmission>
A colorless and transparent glass flat plate (length: 150 mm × 150 mm) as a substrate was set in a photoresist spinner (K359SD-2, manufactured by Kyowa Riken Co., Ltd.), and the glass surface was degreased with ethanol. About 0.5 g was hung on the substrate with a dropper. Thereafter, spin coating was performed by rotating at 250 rpm for 30 seconds.

  Next, using a microwave network analyzer (manufactured by Agilent Technologies, 8510C), according to the KEC method (Kansai Electronics Industry Promotion Center method), the sample is fixed with a jig for measuring the shield effect, and the applied frequency of the in-vehicle millimeter wave radar The electromagnetic wave transmission loss at 76 GHz was measured.

<Evaluation of metal texture>
Based on the spectral reflectance measured using a multi-angle spectrocolorimeter MA-68II manufactured by X-Rite, each sample was irradiated with light irradiated at 45 degrees to the coating surface. Light L * 25 in the L * a * b * color system obtained by receiving light at 25 degrees with respect to specular reflection light, and light irradiated so as to be 45 degrees with respect to the coating surface is used as specular reflection light. On the other hand, the light L * 75 in the L * a * b * color system based on the spectral reflectance obtained by receiving light at 75 degrees, and the light irradiated so as to be 45 degrees with respect to the coating surface is a regular reflection light. The hue h ° 45 in the L * C * h ° display system obtained by receiving light at 45 degrees was measured, and the FF value obtained by FF = L * 25 / L * 75 was calculated.

<Evaluation of reflectance>
Similarly, the specular reflectance (gross,%) of light having an incident angle and a light receiving angle of 25 ° and a wavelength of 400 to 800 nm was measured.

[Example]
Aqueous silver colloid solutions of Samples 1 to 5 were prepared by the following method. First, 35 g of silver chloride and 0.35 L of 25% aqueous ammonia were added to 6.65 L of pure water and dissolved to prepare a silver ammine complex salt aqueous solution (silver concentration 3.8 g / L, 35 ° C., pH 12.23). ). On the other hand, 7 mL of hydrazine monohydrate (manufactured by Kanto Chemical Co., Ltd., deer grade 1) is diluted with 1.8 L of pure water. 2 g was dissolved to obtain a reducing solution. The molecular weight of POVAL 203 was 13,000, and the molecular weight of polyvinylpyrrolidone K15 was 10,000.

  The reducing solution was added while stirring the silver ammine complex salt aqueous solution at 300 rpm using a stirrer. After completion of the reduction by stirring for 1 hour, impurities are removed by repeating washing and concentration with pure water using an ultrafiltration kit Vivaflow 200 VF20P3 (manufactured by Sartorius Mechatronics, molecular weight cut off 50,000). Removed. Thus, an aqueous silver colloid of Sample 1 having a silver concentration of 1 g / mL and a total amount of impurities of 0.15% by mass was obtained. A scanning electron microscope (FE-SEM) observation image of the silver particles in the aqueous silver colloidal solution of Sample 1 obtained is shown in FIG.

  Next, 35 g of silver chloride and 0.35 L of 25% ammonia water were added and dissolved in 1.65 L of pure water to prepare a silver ammine complex salt aqueous solution (silver concentration 13.2 g / L, 35 ° C., pH 12.2. 93). On the other hand, 7 mL of hydrazine monohydrate (manufactured by Kanto Chemical Co., Ltd., deer grade 1) was diluted with 1.8 L of pure water to obtain a reducing solution. Furthermore, 7 g of POVAL 203 (manufactured by Kuraray), 1 g of polyvinylpyrrolidone K15 (manufactured by Tokyo Chemical Industry) and 9 g of polyoxyethylene (7) stearyl ether (manufactured by Wako Pure Chemical Industries) as polyvinyl alcohol were dissolved in 5 L of pure water and did.

  The dispersion and the reducing solution were added while stirring the silver ammine complex salt aqueous solution at 300 rpm using a stirrer. After completion of reduction by stirring and holding for 1 hour, impurities are obtained by repeating washing with pure water and concentration using an ultrafiltration kit Vivaflow 200 VF20P3 (manufactured by Sartorius Mechatronics, molecular weight cut off 50,000). Removed. As a result, an aqueous silver colloid of Sample 2 having a silver concentration of 1 g / mL and a total amount of impurities of 0.16% by mass was obtained. A scanning electron microscope (FE-SEM) observation image of the silver particles in the aqueous silver colloidal solution of Sample 2 obtained is shown in FIG.

  Next, the amount of addition of POVAL 203 (manufactured by Kuraray) was changed to 0.3 g instead of 10 g, and the amount of polyvinyl pyrrolidone K15 (manufactured by Tokyo Chemical Industry) was changed to 2.4 g instead of 2 g. An aqueous silver colloid solution of Sample 3 was prepared in the same manner as in the case. The aqueous silver colloid solution of Sample 3 had a silver concentration of 1 g / mL and an impurity total amount of 0.13% by mass.

  Next, the aqueous silver of Sample 4 was the same as Sample 1 described above except that polyvinylpyrrolidone K15 (manufactured by Tokyo Chemical Industry) was not added and VF20P4 having a molecular weight cut off of 100,000 was used in the ultrafiltration kit. A colloidal solution was prepared. The aqueous silver colloidal solution of Sample 4 had a silver concentration of 1 g / mL and an impurity total amount of 0.19% by mass.

  Next, the amount of polyvinylpyrrolidone K15 (manufactured by Tokyo Chemical Industry) was changed to 5 g instead of 2 g, and the sample 1 described above except that 9 g of polyoxyethylene (23) lauryl ether (manufactured by Wako Pure Chemical Industries) was added to the reducing solution. An aqueous silver colloid solution of Sample 5 was prepared in the same manner as in. The aqueous silver colloidal solution of Sample 5 had a silver concentration of 1 g / mL and a total impurity amount of 0.20% by mass.

  Table 1 below summarizes the preparation conditions of the aqueous silver colloid solutions of Samples 1 to 5 described above. Moreover, the measurement result of the organic substance adhesion amount performed with respect to the silver particle in the aqueous silver colloid liquid of the samples 1-5 obtained by this, the average particle diameter D50 and Dmin using the dynamic light scattering type particle size distribution measuring apparatus In addition, Table 2 shows the evaluation results of sedimentation properties. Further, 5% ethylene glycol monobutyl ether (Wako Pure Chemical Industries) is added to each of the aqueous silver colloid solutions of Samples 1 to 5 to form a coating material, and the coating metal obtained by applying each coating material. The texture and electromagnetic wave transmission loss were evaluated. The evaluation results are also shown in Table 2.

  From the results of Table 2 above, the aqueous silver colloidal solutions of Samples 1 to 3 have a spherical shape by electron microscope observation, an average particle size (D50) of 45 to 100 nm, high uniformity, and an organic matter adhesion amount of silver. It turned out that the silver particle which is 1-10 mass% with respect to it is obtained. Moreover, it turned out that the silver particle contained in the aqueous silver colloid liquid of samples 1-3 is equipped with the outstanding non-sedimentation property which does not sink for 3 weeks or more in a sedimentation test. Moreover, the aqueous silver colloid liquids of Samples 1 to 3 were excellent in metal texture and electromagnetic wave permeability.

  On the other hand, in the aqueous silver colloid liquid of Sample 4, the D50 of the silver particles exceeded 100 nm due to the insufficient amount of polyvinylpyrrolidone added to the silver, so that the electromagnetic wave permeability was deteriorated, the amount of attached organic substances was large, and the metal texture was also deteriorated. On the other hand, in the aqueous silver colloid solution of Sample 5, the amount of polyvinyl pyrrolidone added to silver was excessive, so that this excessive adsorption of polyvinyl pyrrolidone hinders the adhesion of polyvinyl alcohol, the organic matter adhesion amount is less than 1%, Dmin Became 15 nm or less, and the non-sedimentation property deteriorated. In addition, the metal texture and electromagnetic wave permeability deteriorated.

Claims (10)

Average particle diameter (D50) of 45 to 100 nm and the minimum particle diameter on which organic substances containing at least polyvinylpyrrolidone and polyvinyl alcohol (excluding organic molecular main chain protecting agents having a carbon skeleton of 1 to 3 carbon atoms) are adsorbed on the surface (Dmin) An aqueous silver colloid liquid for paint comprising substantially spherical silver particles of 15 nm or more and water as a solvent containing impurities other than the silver particles adsorbed by the organic matter ,
The adhesion amount of the organic substance is 1 to 10% by mass with respect to the silver particles, and the total amount of impurities other than the silver particles adsorbed by the organic substance is 1% by mass or less with respect to the aqueous silver colloid liquid. Aqueous silver colloid liquid for paint . The aqueous silver colloidal liquid for paint according to claim 1, wherein the molecular weight of the polyvinylpyrrolidone and polyvinyl alcohol is 3,000 to 25,000. A paint comprising the aqueous silver colloid liquid for paint according to claim 1 or 2.   It is a coating film obtained by apply | coating the coating material of Claim 3, Comprising: A mirror surface reflectance is 97% or more with respect to the light of wavelength 400-800 nm, The coating film characterized by the above-mentioned. Lightness L * 25 in the L * a * b * color system based on the spectral reflectance obtained by receiving the light irradiated at 45 degrees with respect to the coating surface at 25 degrees with respect to the regular reflection light. Is within the range of 25 to 120, and L * a based on the spectral reflectance obtained by receiving the light irradiated so as to be 45 degrees with respect to the coating film surface at 75 degrees with respect to the regular reflection light. * B * The lightness L * 75 in the color system is in the range of 10 to 40, the FF value calculated by the following formula (1) is in the range of 2.5 to 6.0, and the coating surface The hue h ° 45 in the L * C * h ° color system obtained by receiving the light irradiated so as to be 45 ° with respect to the regular reflection light at 45 ° is 0 to 120 or 330 to 360. The coating film according to claim 4, which is within the range of
[Equation 1]
FF = L * 25 / L * 75   The coating film according to claim 4 or 5, wherein an electromagnetic wave transmission loss at 76 GHz is 1 dB or less. An aqueous solution of a silver ammine complex salt obtained by dissolving a silver compound in an ammonia solution, hydrazine as a reducing agent, and at least two kinds of dispersants such as polyvinyl pyrrolidone and polyvinyl alcohol are mixed to precipitate silver particles by reduction and polyvinyl pyrrolidone. And adsorbing an organic substance containing at least polyvinyl alcohol on the surface of the silver particles ;
And a step of filtering and washing the aqueous solution containing the precipitated silver particles,
A method for producing an aqueous silver colloidal solution, wherein the mixture is mixed so that the polyvinyl pyrrolidone is 1 to 10% by mass and the polyvinyl alcohol is 1 to 40% by mass with respect to silver.   The method for producing an aqueous silver colloidal solution according to claim 7, wherein the molecular weight of the polyvinyl pyrrolidone and polyvinyl alcohol is 3,000 to 25,000.   The method for producing an aqueous silver colloidal solution according to claim 7 or 8, wherein the silver compound is silver chloride.   The method for producing an aqueous silver colloidal solution according to any one of claims 7 to 9, wherein an ultrafiltration device is used for the filtration and pure water is used for the washing.