JP2004256915A - Composite metallic colloidal particle and solution, and production method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide metallic colloidal particles capable of producing a design hitherto impossible to obtain. <P>SOLUTION: The composite metallic colloidal solution can be obtained by reducing a compound of a second metal in a colloidal solution of a first metal containing a polymeric pigment dispersant, and the above colloidal solution of the first metal can be obtained by reducing a compound of the first metal in the presence of the above polymeric pigment dispersant. The above first metal and the above second metal are selected from the group consisting of gold, silver and copper. From the viewpoint of design characteristics, it is preferable that, in the case where the first metal is gold, the second metal is silver or copper; and it is preferable that, in the case where the first metal is silver, the second metal is gold. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to composite metal colloid particles and a solution, and a method for producing the same.

It is known that noble metal colloid particles called so-called nanoparticles having a particle size of about several nm to several tens nm show a unique color by a coloring mechanism called plasmon absorption.
Therefore, a coating film having a plating-like metallic luster can be obtained by using the noble metal colloid solution containing the noble metal colloid particles as a coloring material for a paint, or by applying the noble metal colloid solution itself on a substrate. Are known (for example, see Patent Documents 1 and 2).
However, since the types of noble metal colloid solutions are limited, it has been difficult to express a variety of designs.
JP-A-11-080647 (Claim 21) Japanese Patent Application Laid-Open No. 2000-239853 (Claim 3)

  An object of the present invention is to provide a composite metal colloid particle having a possibility of expressing an unprecedented design.

  The composite metal colloid particles of the present invention are composed of two kinds of metals selected from the group consisting of gold, silver and copper. Here, the composite metal colloid particles may have a structure in which gold is covered with silver, a structure in which silver is covered with gold, or a structure in which gold is covered with copper. Further, the volume ratio of the two selected metals may be 10/1 to 1/10.

  The composite metal colloid solution of the present invention contains the above composite colloid particles and a solvent. Here, the composite metal colloid solution may further contain a protective colloid, and the protective colloid may be a polymer pigment dispersant.

  The method for producing a composite metal colloid solution of the present invention is characterized in that a second metal compound is reduced in a first metal colloid solution containing a polymer pigment dispersant. Here, the first metal colloid solution may be obtained by reducing the first metal compound in the presence of the polymer pigment dispersant. Here, the first metal and the second metal may be selected from the group consisting of gold, silver and copper. Further, the second metal may be more noble than the first metal, wherein the first metal is gold, the second metal may be silver, and the first metal is It may be gold and the second metal may be copper. Also, the first metal may be lower than the second metal, and at this time, the first metal may be silver and the second metal may be gold.

The composite metal colloid solution of the present invention is obtained by the above-mentioned production method.
The coating method of the present invention is characterized by coating the above-mentioned composite metal colloid solution on a substrate. Here, the base material may have transparency.
The coating film of the present invention is obtained by the above coating method.

  The one coated with the metal composite colloid particles of the present invention can exhibit an unprecedented design. This is because the metal composite colloid particles of the present invention have a so-called core / shell structure, and the characteristics of the metal colloid constituting the shell portion appear for reflected light, while the core portion for transmitted light. This is probably because the characteristics of the metal colloid constituting the appear. This is particularly remarkable when the core portion is colloidal particles made of gold and the shell portion is made of silver or copper, and the shell portion sufficiently covers the core portion.

  Until now, there is no material having a different design property between the reflected light and the transmitted light, and the design property is exhibited by applying this material to a skeleton type substrate. The coating film of the present invention is expected to be used in fields requiring high designability such as mobile phones.

  Further, since the composite metal colloid solution of the present invention has a wider absorption region than the simple noble metal colloid solution, application of the coating film obtained therefrom to an optical recording medium can be considered.

Composite Metal Colloid Particles The composite metal colloid particles of the present invention are composed of two types of metals selected from the group consisting of gold, silver and copper. The average particle diameter of the composite metal colloid particles is preferably 5 to 100 nm, more preferably 10 to 50 nm. It is difficult to obtain those having a particle size of less than 5 nm from the viewpoint of production, and there is a possibility that the expression of the design may not be sufficient. If the particle size exceeds 100 nm, a problem may occur in the stability of the particles.

  The composite metal colloid particles of the present invention have a structure in which one of the two metals covers the other. Although there are six such combinations, it is preferable in terms of manufacturing that the structure be one in which gold is covered with silver, the structure in which silver is covered with gold, or the structure in which gold is covered with copper. Such a difference in structure can be controlled by a manufacturing method described later. The above structure can be confirmed by observing the composite metal colloid particles using a transmission electron microscope.

  In the composite metal colloid particles of the present invention, the volume ratio of the two selected metals is preferably 10/1 to 1/10. If it is out of these ranges, the production becomes difficult, and there is a possibility that the difference from the metal colloid particles alone cannot be recognized. A more preferred range is from 8/1 to 1/8.

Composite Metal Colloid Solution The composite metal colloid solution of the present invention contains the composite metal colloid particles and a solvent. The composite metal colloid particles are more stable when they are in the form of a so-called colloid solution dispersed in a solvent than when they are present alone. At this time, it is preferable that the composite metal colloid particles have a concentration of 1 to 50% by mass in the solvent. If the amount is less than 1% by mass, the efficiency of forming the coating film is poor, and if it exceeds 50% by mass, a problem may occur in the stability as a colloid solution.

  The composite metal colloid solution preferably further contains a protective colloid. By including the protective colloid, the stability of the composite metal colloid particles in the solution can be enhanced. The protective colloid is not limited as long as it can stably disperse the metal colloid particles in a solvent, and generally known are those which can be referred to as surfactants and polycarboxylic acids. I have. The protective colloid is preferably a polymer pigment dispersant. This polymer pigment dispersant will be described later in the method for producing a composite metal colloid solution.

  The content of the protective colloid in the composite metal colloid solution of the present invention is preferably 0.05 to 25% by mass. If the amount is less than 0.05% by mass, the stability of the composite metal colloid particles in the solvent may not be improved. If the amount is more than 25% by mass, the concentration of the noble metal may decrease, which may be inefficient. When the protective colloid is a polymer pigment dispersant, a preferable concentration of the protective colloid is 0.1 to 20% by mass.

  The composite metal colloid solution of the present invention may contain, in addition to the above components, metal colloid particles composed of one of the two selected types or composite metal colloid particles that do not satisfy the above-mentioned specifications. In the composite metal colloid solution of the present invention, these colloid particles are present as raw materials and by-products, and the content thereof is preferably 10% by mass or less based on the composite metal colloid particles.

Method for Producing Composite Metal Colloid Solution The method for producing a composite metal colloid solution of the present invention is characterized in that a second metal compound is reduced in a first metal colloid solution containing a polymer pigment dispersant. The first metal and the second metal are different types, and the metal is selected from the group consisting of gold, silver, and copper. From a manufacturing point of view, a combination in which the first metal is gold and the second metal is silver, a combination in which the first metal is gold and the second metal is copper, and wherein the first metal is copper Preferred is a combination in which silver is used and the second metal is gold.

  The first metal colloid solution containing the polymer pigment dispersant may be a solution obtained by forming a single metal colloid particle into a colloid solution using a polymer pigment dispersant. It is preferable that the first metal compound is reduced in a solvent from the viewpoint of production, stability and the like.

  The reduction of the first metal compound in the presence of the polymer pigment dispersant is performed as follows. That is, first, a first metal compound is prepared. The first metal compound used here is a compound that generates a metal ion when dissolved in a solvent. Specific examples include tetrachloroaurate (III) tetrahydrate (chloroaurate), gold sulfite, potassium aurate, silver nitrate, silver acetate, silver (I) perchlorate, copper (II) chloride dihydrate And copper (II) acetate monohydrate, copper (II) sulfate, copper (II) perchlorate hexahydrate and the like.

  The solvent is not particularly limited as long as it dissolves the first metal compound. Examples thereof include water, alcohols having 1 to 4 carbon atoms such as ethanol, ethylene glycol and methoxypropanol, ketones such as acetone, and ethyl acetate. And the like. Two or more of these can be used as long as they are mixed. When the solvent is a mixture of water and a water-soluble solvent, examples of the water-soluble solvent include acetone, methanol, ethanol, ethylene glycol, and methoxypropanol. When using ultrafiltration as a post-treatment, it is preferable to use water, alcohol, and a mixed solution of water and alcohol as a solvent.

  The first metal compound used for preparing the first metal colloid solution is preferably used such that the molar concentration of the metal in the solvent is 0.01 mol / l or more. If it is less than 0.01 mol / l, the obtained first metal colloid solution has too low a molar concentration of metal and is not efficient. It is preferably at least 0.05 mol / l, more preferably at least 0.1 mol / l.

  On the other hand, the high-molecular pigment dispersant is an amphiphilic copolymer having a structure including a solvation portion, in which a high-molecular-weight polymer is introduced with a functional group having a high affinity for the pigment surface, It is usually used as a pigment dispersant during the production of a pigment paste and is commercially available. The molecular weight is preferably 1,000 to 1,000,000. If it is less than 1,000, the stability may not be sufficient, and if it exceeds 1,000,000, the viscosity may be too high and handling may be difficult. More preferably, it is 2000 to 500,000, and still more preferably 4000 to 500,000.

  Commercially available products of such polymeric pigment dispersants include, for example, Solsperse 20000, Solsperse 24000, Solsperse 26000, Solsperse 27000, Solsperse 28000, Solsperse 32500, Solsperse 32550, Solsperse 35100, Solsperse 37500, Solsperse 41090 (all manufactured by Abisia) ), Dispervic 160, Dispervic 161, Dispervic 162, Dispervic 163, Dispervic 166, Dispervic 170, Dispervic 180, Dispervic 181, Dispervic 182, Dispervic 183, Dispervic 184, Dispervic 190, Dispervik 191, Dispervik 192, Dispervik 2 00, Dispervic 2001 (all manufactured by Big Chemie), polymer 100, polymer 120, polymer 150, polymer 400, polymer 401, polymer 402, polymer 403, polymer 450, polymer 451, polymer 452, polymer 453, EFKA-46, EFKA-47, EFKA-48, EFKA-49, EFKA-1501, EFKA-1502, EFKA-4540, EFKA-4550 (all manufactured by EFKA Chemical Co., Ltd.), Floren DOPA-158, Floren DOPA-22, Floren DOPA-17 , Floren G-700, Floren TG-720W, Floren-730W, Floren-740W, Floren-745W, (all manufactured by Kyoeisha Chemical Co., Ltd.), Azispar PA111, Azispar PB 11, Ajisper PB811, Ajisper PB821, Ajisper PW911 (manufactured by Ajinomoto Co.), Joncryl 678, Joncryl 679, Joncryl 62 (manufactured by Johnson Polymer Co.), and the like. Among these, Dispervic 191, EFKA-4550, and Dispervic 184 are suitable for producing colloidal gold particles, and Dispervic 190 and Dispervic 192 are suitable for producing colloidal silver particles. These may be used alone or in combination of two or more.

  In the reduction of the first metal compound, the amount of the polymer pigment dispersant used is 5% by mass or more based on the total amount of the metal and the polymer pigment dispersant in the first metal compound. preferable. If it is less than 5% by mass, the dispersion stability during reduction may be reduced. Although the upper limit is not particularly defined, for example, the upper limit can be 10 times or less the mass of the metal in the metal compound used for preparing the first metal colloid solution.

  The reduction of the first metal compound is efficiently performed by adding a reducing compound. Here, various compounds can be used as the reducing compound. However, by using an amine, there is no need to use a highly dangerous or harmful reducing agent, and heating or special The first metal compound can be reduced at a reaction temperature of about 5 to 100 ° C., preferably about 20 to 80 ° C. without using any light irradiation device.

  The amine is not particularly limited, and for example, those exemplified in JP-A-11-80647 can be used, and propylamine, butylamine, hexylamine, diethylamine, dipropylamine, dimethylethylamine, diethylmethyl Amine, triethylamine, ethylenediamine, N, N, N ', N'-tetramethylethylenediamine, 1,3-diaminopropane, N, N, N', N'-tetramethyl-1,3-diaminopropane, triethylenetetramine Alicyclic amines such as piperidine, N-methylpiperidine, piperazine, N, N'-dimethylpiperazine, pyrrolidine, N-methylpyrrolidine, morpholine; aniline, N-methylaniline; N, N-dimethylaniline Aromatic amines such as toluidine, anisidine, and phenetidine; benzylamine, N-methylbenzylamine, N, N-dimethylbenzylamine, phenethylamine, xylylenediamine, N, N, N ', N'-tetramethylxylylenediamine and the like Aralkylamine and the like. Examples of the amine include methylaminoethanol, dimethylaminoethanol, triethanolamine, ethanolamine, diethanolamine, methyldiethanolamine, propanolamine, 2- (3-aminopropylamino) ethanol, butanolamine, hexanolamine, and dimethylamine. Alkanolamines such as aminopropanol can also be mentioned. Of these, alkanolamines are preferred, and dimethylethanolamine is more preferred.

  Examples of the reducing agent having a stronger reducing power than the above amine include dithionite, sodium formaldehyde sulfoxylate (referred to as Rongalite) which is a derivative of dithionite, zinc formaldehyde sulfoxylate, and carbon dioxide. Examples include thiourea, sodium borohydride, lithium borohydride, sodium aluminum hydride, dimethylamine borane, hydrazine, hydrazine carbonate, hypophosphorous acid, and hydrosulfite. When using relatively mild reducing agents such as citric acid, tartaric acid, ascorbic acid and malic acid, the reducing ability can be reduced by using iron (II) sulfate, tin (II) chloride and titanium (III) chloride together. Can be improved and can be used preferably. Of these, sodium formaldehyde sulfoxylate (Rongalit) and hydrazine carbonate are preferred from the viewpoint of safety and reaction efficiency. These reducing agents, which have a stronger reducing power than the amine, are useful when the first metal is copper.

  The amount of the reducing compound to be added is preferably not less than the amount necessary for reducing the metal in the first metal compound. If the amount is less than this amount, the reduction may be insufficient. The upper limit is not particularly limited, but is preferably 30 times or less, more preferably 10 times or less, of the amount required to reduce the metal in the metal compound.

  The solution after the reduction contains, in addition to the first metal colloid particles and the polymer pigment dispersant, miscellaneous ions such as chloride ions derived from the raw material, salts generated by the reduction, and optionally an amine. Since these miscellaneous ions, salts and amines may adversely affect the stability of the obtained first metal colloid solution, it is desirable to remove them. For the removal of these components, electrodialysis, centrifugation, and ultrafiltration are used as post-treatments. As described below, when the centrifugation and ultrafiltration are used, the metal concentration is reduced at the same time. It is preferable because it can be increased.

  In the ultrafiltration, the substance to be separated usually has a diameter of 1 nm to 5 μm. By targeting the diameter, the polymer pigment dispersant can be removed along with the unnecessary ions, salts and amines, and the metal concentration in the solid content of the first metal colloid solution can be increased. If it is less than 1 nm, unnecessary components may not pass through the filtration membrane and cannot be eliminated. If it exceeds 5 μm, most of the first metal colloid particles will pass through the filtration membrane and the desired first metal colloid solution May not be obtained. The filtration membrane for the ultrafiltration is not particularly limited, but usually, for example, a resin membrane such as polyacrylonitrile, vinyl chloride / acrylonitrile copolymer, polysulfone, polyimide, or polyamide is used. Of these, polyacrylonitrile and polysulfone are preferred, and polyacrylonitrile is more preferred. It is preferable to use a filtration membrane that can be back-washed in order to efficiently perform the filtration membrane that is usually performed after the end of the ultrafiltration. The ultrafiltration membrane preferably has a molecular weight cut-off of 3000 to 80000. If it is less than 3,000, the unnecessary polymer pigment dispersant or the like is not sufficiently removed, and if it is more than 80000, the first metal colloid particles easily pass through the filtration membrane. Solution may not be obtained. More preferably, it is 10,000 to 60,000.

  The form of the filtration module for the ultrafiltration is not particularly limited, and examples thereof include a hollow fiber module (also called a capillary module), a spiral module, a tubular module, and a plate module depending on the form of the filtration membrane. Among them, the larger the membrane area, the shorter the time required for filtration can be. Therefore, a hollow fiber module having a compact form for the filtration area is preferable in terms of efficiency. When the amount of the first metal colloid solution to be treated is large, it is preferable to use a large number of ultrafiltration membranes. The ultrafiltration is performed, for example, by passing a solution containing the first metal colloid particles and the polymer pigment dispersant obtained by the above-described reduction through an ultrafiltration membrane. Filtrate containing salts, amines and polymeric pigment dispersants is eliminated. The ultrafiltration is usually repeated until the above-mentioned miscellaneous ions in the filtrate are removed to a desired concentration or less. At that time, it is preferable to add the same amount of the solvent as the amount of the removed filtrate in order to keep the concentration of the first metal colloid solution to be treated constant. By using a solvent different from that used at the time of reduction as the solvent added at this time, it is possible to replace the solvent of the first metal colloid solution. The ultrafiltration can be performed by a usual operation, for example, a so-called batch method. This batch method is a method in which the first metal colloid solution to be treated is added as much as the ultrafiltration has progressed. It should be noted that the ultrafiltration can be performed further after the miscellaneous ions have been removed to a desired concentration or less to increase the solid content concentration.

  On the other hand, in the centrifugation, the unnecessary components can be removed by removing the supernatant. The first metal colloid particles thus left are washed by adding a solvent, and the centrifugal separation is repeatedly performed, whereby the removal effect can be enhanced. Preferably, the centrifugation is performed at 1000 G or more. If it is less than 1000 G, it may be difficult to remove a part of the polymer pigment dispersant. The conditions for centrifugation differ depending on the particle size of the first metal colloid particles. For example, in order to settle particles having a particle size on the order of several nanometers, it is necessary to perform so-called ultracentrifugation conditions. Standard conditions include 3000 G for 5 to 60 minutes, preferably 15 to 45 minutes. The centrifugation can be fractionated based on the particle diameter of the first metal colloid particles by appropriately changing the conditions of the above-described gravitational acceleration, time, and / or number of operations. By the fractionation, the particle diameter of the first metal colloid particles can be made uniform to some extent. The first metal colloid solution obtained by the centrifugation is concentrated and usually takes the form of a paste. In general, the concentration is preferably 80% or more on a mass basis. The upper limit is not particularly defined, but is 90% or less in consideration of ease of handling. Thus, the first metal colloid solution obtained by centrifugation and ultrafiltration is specifically determined by the value of the metal concentration in the solid content in the solution containing the first metal colloid particles and the polymer pigment dispersant before the treatment. Although the typical values are different, the metal concentration in the solid content is higher than before the treatment. The solid content of the first metal colloid solution obtained by the centrifugation tends to be higher than that obtained by the ultrafiltration. Preferably, the amount is adjusted to 1 to 50% by mass. Also in this case, it is possible to replace the solvent of the first metal colloid solution by using a different type of solvent from that used at the time of the reduction.

  By performing the post-treatment in this manner, a solution containing the polymer pigment dispersant and the first metal colloid particles can be obtained.

  The average particle diameter of the first metal colloid particles is usually about 2 to 30 nm, preferably 10 to 20 nm. The average particle diameter of the first metal colloid particles is determined by observation with an electron microscope. On the other hand, the first metal colloid solution has a solid content of 50% by mass or less, preferably 1 to 50% by mass. The metal concentration of the first metal colloid solution, that is, the proportion of metal in the solid content of the first metal colloid solution is not particularly limited, but is 50% by mass or more when used as a conductive film material. Is preferred. More preferably, it is 50 to 95% by mass. Here, the content of the polymer pigment dispersant can be determined by determining the amount of metal by suggestive thermal analysis and subtracting this from the amount of solid content.

  In the present invention, the solid content and the metal content can be determined by measuring the residue obtained by heating at 100 to 150 ° C. and several hundreds ° C., respectively. Specifically, the temperature is raised to 140 ° C. at a rate of 10 ° C./min using TG-DTA, and then maintained at 140 ° C. for 30 minutes to determine the solid content first. Thereafter, the temperature is raised again to 500 ° C. at a rate of 10 ° C./min, and then the metal amount can be determined while maintaining the temperature at 500 ° C. for 30 minutes. The measurement of the metal concentration in the present specification is performed using this method unless otherwise specified.

  In the method for producing a composite metal colloid solution of the present invention, the dissolved second metal compound is reduced in the first metal colloid solution containing the polymer pigment dispersant thus obtained.

  As the above-mentioned second metal compound, those described above for the first metal compound are applied as they are. However, the second metal compound is selected such that the type of the second metal is different from the type of the metal of the first metal colloid. When the first metal is gold, the second metal is silver or copper, and when the first metal is silver, the second metal is gold from the viewpoint of design. preferable.

  The method for reducing the second metal compound is slightly different depending on which of the first metal and the second metal is more base. That is, when the second metal is lower than the first metal, such as when the first metal is gold and the second metal is silver, the second metal including the polymer pigment dispersant is used. A method of adding a second metal compound solution to a first metal colloid solution and adding a reducing compound thereto, or a method of adding a reducing compound to a first metal colloid solution containing a polymer pigment dispersant, Can be adopted. Here, as for the former method of adding a reducing compound, a method of reducing using a high-pressure mercury lamp instead of the reducing compound is also possible. From the viewpoint of stability, the former method is preferable.

  On the other hand, when the first metal is more noble than the second metal, such as when the first metal is silver and the second metal is gold, a metal consisting only of the second metal is used. After the second metal compound solution and the reducing compound are gradually added simultaneously to the first metal colloid solution containing the polymer pigment dispersant so that the colloid particles are not formed, the second metal colloid particles are formed. It is preferable to take a method of further adding another polymer pigment dispersant suitable for the above.

  In any case, as for the amount of the first and second metals, the volume ratio of the first metal / the second metal is preferably 10/1 to 1/10. If it is less than 10/1, there is a possibility that the difference from the first metal colloid particle alone may not be recognized, and if it is more than 1/10, precipitation may occur. A more preferred range is from 8/1 to 1/8.

The amount of the polymer pigment dispersant is preferably 5% by mass or more based on the total amount of the metal and the polymer pigment dispersant in the second metal compound. If it is less than 5% by mass, the dispersion stability during reduction may be reduced. Although the upper limit is not particularly defined, for example, the upper limit may be 10 times or less the mass of the metal contained in the second metal compound. The amount of the polymer pigment dispersant as referred to herein means the total amount of the amount contained in the first metal colloid solution and the amount further added thereto. When the polymer pigment dispersant is further added when the first metal is more noble than the second metal, the amount added is, for example, based on the mass of the metal contained in the second metal compound. 5 times or less.
Note that, even when the first metal is lower than the second metal, another or the same polymer pigment dispersant can be further added at any stage as needed.

  On the other hand, the second metal compound solution is obtained by dissolving the second metal compound in the solvent described above. The concentration of the second metal compound in the above solution is preferably such that the molar concentration of the metal is 0.01 mol / l or more. Less than 0.01 mol / l is not efficient. It is preferably at least 0.05 mol / l, more preferably at least 0.1 mol / l.

  When an amine is used as the reducing compound, the reduction can be performed under milder conditions, for example, around room temperature than when the first metal colloid particles are not present. The amount of the reducing compound to be added is preferably not less than the amount necessary for reducing the metal in the second metal compound contained in the solution. If the amount is less than this amount, the reduction may be insufficient. The upper limit is not particularly limited, but is preferably 30 times or less, more preferably 10 times or less, of the amount required to reduce the metal in the metal compound. When the first metal and the second metal are gold and silver, it is preferable to use an amine as the reducing compound. On the other hand, when copper is used as the second metal, it is preferable to use a reducing agent having a stronger reducing power than the amine described above, particularly, sodium formaldehyde sulfoxylate (Rongalit) as the reducing compound.

  The solid content concentration of the composite metal colloid solution obtained by the production method of the present invention is not particularly limited, and can be, for example, 1 to 50% by mass. The composite metal colloid solution obtained by the production method of the present invention is subjected to post-treatment when it is necessary to remove salts generated by reduction, raw materials added in excess, and the like. The post-treatment can be performed in the same manner as the post-treatment performed with the first metal colloid solution.

  By observing the composite metal colloid solution obtained by the production method of the present invention using, for example, an electron microscope, the composite metal colloid particles contained in the solution are covered with the first metal by the second metal. That is, it can be confirmed that it has a so-called core / shell structure.

  The average particle diameter of the composite metal colloid particles is preferably from 5 to 100 nm, more preferably from 10 to 50 nm, in consideration of the appearance of design and ease of production. At this time, the thickness of the core portion made of the first metal is, for example, 1 to 15 nm, and the thickness of the shell portion made of the second metal is 0.5 to 50 nm. Here, the thickness of the core portion means the radius of the core portion, while the thickness of the shell portion means the radius of the composite metal colloid particles minus the radius of the core portion.

  The average particle diameter may gradually increase from the value immediately after the reaction toward the value of the calculated particle diameter based on the amount of the second metal compound used. At this time, comparing the absorption curves of the one obtained immediately after the reaction and the one that almost reached the value of the calculated particle size, the one obtained immediately after the reaction is close to the first metal, Those almost reaching the value of the particle diameter approach those of the second metal colloid solution. From this, it is inferred that almost the entire surface of the first metal is covered by the second metal. Conversely, it is possible to determine whether the ripening is in progress by measuring the absorption curve of the composite metal colloid solution.

  When the composite metal colloid solution is to be used for forming a conductive film, the metal concentration is preferably 80% by mass or more. It is more preferably at least 90% by mass, particularly preferably at least 95% by mass.

Coating Method and Coating Film The coating method of the present invention is characterized by coating the above-mentioned composite metal colloid solution on a substrate. Various substrates can be used, but it is preferable that the coating film has transparency since the resulting coating film has different design characteristics depending on transmitted light and reflected light. Here, having transparency means a state in which the other side is not completely concealed, and for example, may have a light transmittance of 1% or more.

  The coating can be performed by any method such as flow coating, brush coating, spin coater, and dipping, and a machine well known to those skilled in the art, depending on the required film thickness. After coating, the coating is dried for an appropriate time by heating from room temperature to a temperature at which the substrate is not denatured, and a coating film is obtained.

  The coating film of the present invention thus obtained has a thickness of, for example, 0.05 μm to 0.5 μm. Outside these ranges, coating may be difficult. Compared with those obtained from a single noble metal colloid solution, the coating film of the present invention shows a change in color depending on the viewing angle as a partial gloss or transmission color in addition to the conventional color development based on plasmon absorption. It has an unprecedented design property that cannot be obtained with other materials.

  Hereinafter, a production example for obtaining a material used in an example of the present invention will be described.

Production Example 1 Preparation of Gold Colloid Solution 27 g of chloroauric acid (HAuCl ₄ .4H ₂ O) was placed in a reaction vessel containing 230 g of ethanol, and dissolved by stirring. Further, 19 g of Dispervic 191 manufactured by Big Chemie was added as a polymer pigment dispersant, and the mixture was stirred. After the polymer pigment dispersant was dissolved, the mixture was heated using a water bath until the liquid temperature reached 50 ° C. Next, while stirring was continued, 29 g of dimethylaminoethanol was added instantaneously. After the addition, the mixture was stirred for 2 hours while maintaining the liquid temperature at 50 ° C., to obtain a vivid and thick red colloidal ethanol solution of gold. Using an ultrafiltration pencil type module AHP-0013 manufactured by Asahi Kasei Corporation, the ethanol solution of the obtained colloidal gold was filtered to remove residual ions, and ethanol was added to the obtained filtrate, followed by further filtration. The procedure was repeated to obtain 83 g of an ethanol solution of colloidal gold having a solid content of 20% by mass and comprising colloidal gold particles and a polymer pigment dispersant, from which residual ion components had been removed. The average particle size of the colloidal gold particles in this solution obtained from observation with an electron microscope was 15.0 nm. Moreover, as a result of TG-DTA measurement, the metal content in the solid content was 70% by mass.

Production Example 2 Preparation of silver colloid solution 50 g of silver nitrate was placed in a reaction vessel containing 883 g of water, and dissolved by stirring. As a polymer pigment dispersant, a solution prepared by dissolving 119 g of Dispervic 190 manufactured by Big Chemie in a mixed solvent of 294 g of 1N nitric acid and 294 g of water was added and stirred. After the polymer pigment dispersant was dissolved, the mixture was heated using a water bath until the liquid temperature reached 70 ° C. Next, 131 g of dimethylaminoethanol was added instantaneously while continuing stirring. After the addition, the mixture was stirred for 2 hours to obtain a silver colloid aqueous solution exhibiting a thick yellow color. This was post-treated by ultrafiltration in the same manner as in Production Example 1 to obtain 192 g of a silver colloid aqueous solution having a solid content of 30% by mass. The average particle diameter of the silver colloid particles in this solution was 11 nm. Moreover, as a result of TG-DTA measurement, the metal content in the solid content was 55% by mass.

Preparation of gold / silver composite colloid solution 1
After dissolving 60 g of silver nitrate in 120 g of water, 1666 g of ethanol was further added to prepare a mixed solution of silver nitrate water and ethanol. This solution was added to 44 g of the gold colloid solution obtained in Production Example 1 and stirred. 158 g of dimethylaminoethanol was instantaneously added thereto, and the mixture was stirred at room temperature for 2 hours to obtain an orange gold / silver composite colloid solution.

Preparation of gold / silver composite colloid solution 2
A gold / silver composite colloid solution was obtained in the same manner as in Example 1, except that the amount of silver was reduced to one-fourth in volume ratio, and the amounts of the respective components were changed accordingly.

Preparation of silver / gold composite colloid solution Part 1
To 40 g of the silver colloid solution obtained in Production Example 2, 1997 g of ethanol was added. A solution prepared by dissolving 201 g of chloroauric acid in 999 g of ethanol and a solution of 217 g of dimethylaminoethanol in 999 g of ethanol were added dropwise at a rate of 0.2 ml / min at room temperature. After completion of the dropwise addition, stirring was continued at room temperature for 1 hour. Further, 97 g of Dispervic 191 manufactured by BYK-Chemie was added, and stirring was continued at room temperature for 1 hour to obtain a purple-red silver / gold composite colloid solution. This was subjected to ultrafiltration in the same manner as in Production Example 1 to obtain a post-treated silver / gold composite colloid solution.

Preparation of silver / gold composite colloid solution 2
A silver / gold composite colloid solution was obtained in the same manner as in Example 3, except that the amount of silver was reduced by half and the amounts of the respective components were changed accordingly.

Preparation of silver / gold composite colloid solution 3
A silver / gold composite colloid solution was obtained in the same manner as in Example 3, except that the amount of silver was reduced to one-fourth and the amounts of the respective components were changed accordingly.

Preparation of gold / copper composite colloid solution An aqueous copper sulfate solution obtained by dissolving 8 g of copper sulfate in 345 g of water was added to 60 g of the gold colloid solution obtained in Production Example 1 and stirred. An aqueous Rongalit solution in which 40 g of Rongalite was dissolved in 50 g of water was instantly added, and the mixture was stirred at room temperature for 2 hours. Thereafter, the mixture was allowed to stand at room temperature for 2 weeks to obtain a purple gold / silver composite colloid solution. This was subjected to ultrafiltration in the same manner as in Production Example 1 to obtain a post-treated gold / copper composite colloid solution.

<Characterization of composite metal colloid solution>
The composite metal colloid obtained in the above example was subjected to electron microscope observation, absorbance measurement, and differential thermal analysis using the following equipment. The results are shown in Tables 1, 2 and 3 together with the composition of each example. The gold / silver composite colloid solution was observed with an electron microscope and measured for absorbance for each of the solution immediately after the reaction and the solution after standing in order to observe changes with time.

Equipment used Transmission electron microscope: JEM-2000 manufactured by JEOL Ltd.
Spectrophotometer: UV-visible absorption spectrophotometer U-3500 manufactured by Hitachi, Ltd.
Differential thermal analysis: TG-DTA manufactured by Seiko Instruments Inc.

For various combinations using gold, silver and copper as the first or second metal as the metal species, composite metal colloids could be obtained.
When the first metal was gold and the second metal was silver, it was confirmed from an electron micrograph that a silver shell part was formed around gold as a core part. It was also confirmed at the same time that the thickness of the silver shell increased with time. Since the particle size after two weeks of standing was almost the same as the particle size calculated from the particle size of the gold colloid used and the amount of silver nitrate, the formation of the silver shell portion with respect to the gold core portion was not observed. It seems to progress gradually.

  In addition, looking at the change with time in the absorbance curve shown in FIG. 1, when the ratio of gold / silver is 1/8, the one immediately after the reaction has a maximum absorption wavelength at 493 nm and 480 nm. A gentle peak could be confirmed from about 400 nm. When the thickness of the silver shell portion was increased by standing, the maximum absorption wavelength was shifted to 419 nm, and the peak at 493 nm was hardly observed.

  On the other hand, in the case where the amount of silver is reduced to one-fourth and the ratio of gold / silver is １ ／, the maximum absorption wavelength is 512 nm immediately after the reaction, and the amount of silver is The gentle peaks seen in many are only slightly visible. When this was left standing, the same absorbance curve as that obtained immediately after the reaction where the gold / silver ratio was 1/8 was obtained.

  Considering these results together with the fact that the maximum absorption wavelength of the gold colloid particles alone is 530 nm and the maximum absorption wavelength of the silver colloid particles is 420 nm, the production of the gold / silver composite colloid particles of the present invention can be carried out in a solution. It is expected that a layer of silver colloid particles is gradually formed around the existing gold colloid particles. This is inferred from the fact that the absorbance curves of the sample immediately after the reaction when the amount of silver is large and the one after standing where the amount of silver is small are almost the same.

  If the amount of silver colloid formed as the shell part is large, most of its outer surface is covered with silver colloid, and the resulting gold / silver composite colloid particles have light absorption characteristics similar to silver colloid particles. It is thought that.

  On the other hand, in the silver / gold composite colloid solution, gold, which is darker than silver in the electron micrograph, constitutes the shell part, so that there is no clear difference as compared with gold / silver, but the particle size increases. Since no colloidal particles of gold and silver alone were observed, it is considered that silver / gold composite colloidal particles were generated by the same process.

Production of Coating Film The gold / silver composite colloid solution obtained in Example 1 was flow-coated on a transparent glass plate and dried at room temperature to obtain a coating film. This coating film had a metallic luster very similar to the coating film obtained from the silver colloid solution. Although this coating film has a property like a half mirror, it was confirmed that when light was applied from the back side of the glass plate, a red-purple color was formed. This coloring was not observed in the coating film obtained from the silver colloid solution.

  This phenomenon is considered as follows. As described above, the gold / silver composite colloid particles obtained in Example 1 had the outer surface of the gold colloid particles covered with silver colloid, and thus resembled a coating film obtained from silver colloid particles. It appears to have a metallic luster. On the other hand, color development by transmitted light is expected to be based on plasmon color development by colloidal gold particles. That is, the surface covered with the silver colloid has pores that allow light to pass through, and it is considered that the color development as described above is caused by the light transmitted through the pores and the gold colloid particles.

  The composite metal colloid solution of the present invention is used as a coating film in a field where a high design property is required, and can be applied to an optical recording medium.

3 is an absorbance curve for the gold / silver composite colloidal particle solutions obtained in Examples 1 and 2 of the present invention. The horizontal axis represents wavelength (nm), and the vertical axis represents absorbance. 9 is an absorbance curve for the gold / copper composite colloid particle solution obtained in Example 6 of the present invention. The horizontal axis represents wavelength (nm), and the vertical axis represents absorbance.

Claims (12)

  Composite metal colloid particles comprising two kinds of metals selected from the group consisting of gold, silver and copper.   2. The composite metal colloid particles according to claim 1, wherein a volume ratio of the two selected metals is 10/1 to 1/10.   A composite metal colloid solution comprising the composite metal colloid particles according to claim 1 and a solvent.   The composite metal colloid solution according to claim 5, further comprising a protective colloid.   5. The composite metal colloid solution according to claim 3, wherein the protective colloid is a polymer pigment dispersant.   A method for producing a composite metal colloid solution, comprising reducing a second metal compound in a first metal colloid solution containing a polymer pigment dispersant.   The method for producing a composite metal colloid solution according to claim 6, wherein the first metal colloid solution is obtained by reducing the first metal compound in the presence of the polymer pigment dispersant.   The method according to claim 6, wherein the first metal and the second metal are selected from the group consisting of gold, silver, and copper.   A composite metal colloid solution obtained by the production method according to claim 6.   A coating method comprising coating a substrate with the composite metal colloid solution according to any one of claims 4, 5 and 9.   The coating method according to claim 10, wherein the substrate has transparency.   A coating film obtained by the coating method according to claim 10.

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