JP2003342496A - Silica-coated gold fine particles, production method thereof and red pigment - Google Patents

Abstract

(57) [Problem] It is useful as a red pigment which does not lose sharpness or discolor even when exposed to high temperatures. SOLUTION: The average particle diameter (D _G ) is 2 nm to 50 nm.
The surface of the gold fine particles in the range of is coated with silica,
The average particle size of the silica-coated gold particles (D _P) is 4nm~1
It is in the range of 50 nm. To produce, the average particle size (D
_G ) A surfactant is added to an aqueous dispersion of gold fine particles having a range of 2 nm to 50 nm or a mixed dispersion of water and an organic solvent, and then an alkali is added to adjust the pH of the dispersion to a range of 9 to 12. It is adjusted, heat-aged if necessary, and an acidic silicic acid solution or silica sol is added.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to fine gold particles whose surfaces are coated with silica, a method for producing the fine gold particles, and a red pigment comprising the fine particles.

[0002]

BACKGROUND OF THE INVENTION Various pigments are used for coloring or color display in paints, cosmetics, printing inks, color filters for liquid crystal display devices, etc., and red pigments at this time are red iron oxide, molybdenum red, etc. Inorganic pigments such as, are generally known. However, this type of red pigment has a drawback in that it has a broad absorption region in the absorption region having a wavelength of 400 to 800 nm which exhibits a red color, and thus lacks in sharpness and transparency. On the other hand, gold particles having a particle size of several tens of nm have a sharp absorption peak near 550 nm, and are known as clear and transparent pigments. However, when gold particles are used as a pigment, when the pigment is exposed to a high temperature, there are problems such as aggregation, discoloration due to aggregation, and discoloration to black, that is, heat resistance. Has been done.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and silica-coated gold fine particles useful as a red pigment that does not deteriorate in sharpness or discolor even when exposed to high temperatures, and their production. A method and a red pigment comprising the fine particles are provided.

[0004]

Silica-coated gold particles according to the present invention SUMMARY OF THE INVENTION is characterized in that the average particle diameter (D _G) is coated with a surface of gold particles in the range of 2nm~50nm silica.
The silica-coated gold fine particles have an average particle diameter (D _P ) of 4n.
It is preferably in the range of m to 150 nm. The method for producing silica-coated gold fine particles according to the present invention has an average particle diameter (D
_G ) is in the range of 2 nm to 50 nm, a surfactant is added to an aqueous dispersion of fine gold particles or a mixed dispersion of water and an organic solvent, and then an alkali is added to adjust the pH of the dispersion to 9 to 1
It is characterized in that it is adjusted to the range of 2, and if necessary, it is heat-aged and an acidic silicic acid solution or silica sol is added.
The red pigment according to the present invention is characterized by comprising the silica-coated gold fine particles.

[0005]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be specifically described below.

[0006] Silica-coated gold particles according to the silica-coated gold particles present invention has an average particle diameter (D _G) is coated with a surface of gold particles in the range of 2nm~50nm silica, average particle gold particles The diameter is particularly preferably in the range of 2 to 30 nm. When the average particle size is less than 2 nm, the light absorption wavelength due to plasmon absorption is less than 400 nm, and the sharpness and transparency of the fine gold particles as a clear and transparent red pigment deteriorate. If the average particle size exceeds 50 nm, 550n
Absorption in the vicinity of m is reduced and the red color is not exhibited. Further, since the dispersibility is reduced, it is difficult to uniformly coat silica or obtain silica-coated gold particles in a monodispersed state,
For this reason, it becomes difficult to obtain fine particles of silica-coated gold for a clear and transparent red pigment.

As the gold fine particles, conventionally known gold fine particles having an average particle size in the above range can be used. Particularly, when gold fine particles having a uniform particle size distribution are used, it is possible to suppress the spread of the absorption region, and it is clear. Thus, it is possible to obtain transparent silica-coated gold fine particles. The fine gold particles used in the present invention are
For example, it can be produced by adding a reducing agent to the gold compound aqueous solution. It can also be obtained by irradiating the gold compound aqueous solution with ultrasonic waves.

In the present invention, the silica coating layer has a thickness of 1 to
It is preferably in the range of 50 nm, particularly 1 to 20 nm. When the fine gold particles are coated with silica, they are prevented from agglomerating even when subjected to a high temperature heat history during production and use, and discoloration due to agglomeration is suppressed, and they have a clear and transparent feeling and are excellent in heat resistance. Silica-coated gold fine particles as a red pigment are obtained. If the thickness of the silica coating layer is less than 1 nm, the effect of suppressing aggregation may be insufficient and the heat resistance may be insufficient. Thickness of silica coating is 50 nm
When it exceeds, the scattering of light by the silica coating layer becomes remarkable, and pink or even white is exhibited. Therefore, the silica-coated gold fine particles according to the present invention preferably have an average particle diameter (D _P ) of 4 to 150 nm, more preferably 4 to 100 nm.

If a red pigment having a clear and transparent feeling and excellent heat resistance can be obtained from the silica-coated gold fine particles of the present invention, other metal oxides (eg, alumina, zirconia, Titania, etc.),
Complex metal oxides (eg silica-alumina, silica-
It is also possible to use zirconia, silica-titania, etc.).

Method for producing silica-coated gold fine particles Next, a method for producing the silica-coated gold fine particles according to the present invention will be described. Method for producing a silica-coated gold particles according to the present invention, the aqueous dispersion or water and an organic solvent mixed dispersion of gold fine particles having a mean particle size of (D _G) is in the range of 2 nm to 50 nm, a surfactant is added Then, an alkali is added to adjust the pH of the dispersion to a range of 9 to 12, and the mixture is heat-aged if necessary, and an acidic silicic acid solution or silica sol is added. The gold fine particles described above can be used as the gold fine particles. Further, as the dispersion medium,
Water or water and an organic solvent are used, and as the organic solvent, alcohols such as methanol, ethanol, propanol, butanol, diacetone alcohol, furfuryl alcohol, tetrahydrofurfuryl alcohol, ethylene glycol and hexylene glycol; acetic acid methyl ester, Esters such as acetic acid ethyl ester; ethers such as diethyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether; acetone, methyl ethyl ketone,
Ketones such as acetylacetone and acetoacetate; amides such as dimethylformamide; and the like. These may be used alone or in combination of two or more. Among these, especially methanol,
Alcohols such as ethanol, propanol, butanol, diacetone alcohol, furfuryl alcohol, tetrahydrofurfuryl alcohol, ethylene glycol and hexylene glycol are preferable from the viewpoint of stably monodispersing the gold fine particles. The reason for this is not clear, but it is presumed that a uniform silica coating layer is formed due to the high affinity between the alcohol and the surfactant.

The concentration of the fine gold particles in the fine gold particle dispersion is 0.
It is preferably in the range of 1 to 5% by weight, more preferably 0.2 to 2% by weight. When the concentration of the fine gold particles is less than 0.1% by weight, the silica coating efficiency (silica utilization rate) is low and the production efficiency is low, which is not preferable. On the other hand, if the concentration of the fine gold particles exceeds 5% by weight, the stability of the dispersion is reduced, and the fine gold particles gel when the acidic silicic acid solution or silica sol is added, or the acidic silicic acid solution or silica sol gels, resulting in a uniform It may not be possible to form a silica coating layer.

As the surfactant added to the gold fine particle dispersion liquid, a cationic surfactant is preferable. The cationic surfactant is coordinated to the surface of the fine gold particles, and the surface becomes positively charged, and the acidic silicic acid solution or silica sol having a negative charge is efficiently attached and aggregated on the surface of the fine gold particles to deposit silica. , To form a silica coating layer. As the cationic surfactant, a conventionally known cationic surfactant such as an aliphatic amine salt and its ammonium salt, an aromatic quaternary ammonium salt, or a heterocyclic quaternary ammonium salt can be used.

The amount of the surfactant added may be such that the surface of the finally obtained gold fine particles is sufficiently covered with silica and the heat resistance can be improved. It depends on the average particle size of the gold fine particles to be used. It is preferable to add the fine particle water dispersion or the water / organic solvent mixture dispersion so that the concentration thereof is in the range of about 0.2 to 20% by weight, and more preferably 0.5 to 10% by weight. If the concentration of the surfactant is less than 0.2% by weight, the amount of the surfactant coordinated to the surface of the fine gold particles is small, so that silica is not sufficiently deposited, and it is difficult to form a coating layer having a thickness within the above range. . Even when the concentration of the surfactant exceeds 20% by weight, the amount of the surfactant on the surface of the gold fine particles does not increase and the positive charge does not increase, and on the contrary, the precipitation of silica is hindered and the economical efficiency is reduced. Sometimes.

As another method, a surfactant similar to the above is added to a gold compound aqueous solution or a water / organic solvent mixed solvent solution having a gold concentration of 0.1 to 5% by weight, and then added. By adding a reducing agent, a gold fine particle dispersion liquid containing the same surfactant as described above can be obtained. The reducing agent at this time is not particularly limited as long as gold of the gold compound can be reduced to obtain fine gold particles,
Examples thereof include ferrous sulfate, trisodium citrate, tartaric acid, sodium borohydride, sodium hypophosphite and the like. As the organic solvent, the same ones as described above can be used, and in this case also, it is preferable to use the alcohol solvent.

Then, an alkali is added to the gold fine particle dispersion containing a surfactant to adjust the pH of the dispersion to 9 to 12, preferably 9 to 11. As the alkali, NaOH, KOH, RbOH, CsOH or the like can be used, and the pH is adjusted by adding an aqueous solution of these alkali metals. When the pH of the gold fine particle dispersion liquid is less than 9, silica is not deposited on the surface of the gold fine particles due to the low solubility of silica, silica fine particles are generated, or silica sol is gelated to obtain silica-coated gold fine particles. Sometimes there is not. When the pH of the gold fine particle dispersion exceeds 12, the solubility of silica is high, so that the precipitation of silica on the surface of the gold fine particles may be suppressed, or the deposition rate of silica sol may be reduced or may not occur.

Next, an acidic silicic acid solution or silica sol is added to the gold fine particle dispersion liquid whose pH has been adjusted. The acidic silicic acid solution is preferably an acidic silicic acid solution obtained by dealkalizing an aqueous solution of an alkali metal silicate such as sodium silicate or potassium silicate with an ion exchange resin or the like. Further, as the silica sol, a conventionally known silica sol can be used. For example, JP-A-63-45 filed by the applicant of the present application can be used.
The silica sol disclosed in Japanese Patent Application Laid-Open No. 114 and Japanese Patent Application Laid-Open No. 63-64911 is preferable because it has a uniform silica particle diameter and is excellent in stability.

When an acidic silicic acid solution is used, the amount of the acidic silicic acid solution added varies depending on the average particle size of the gold fine particles, but 0.01 to 20 parts by weight, and more preferably 0.02 parts by weight as SiO ₂ per 1 part by weight of the gold fine particles. It is preferably in the range of 02 to 5 parts by weight. If the amount of the acidic silicic acid solution added is less than 0.01 part by weight, a silica coating layer having a thickness within the above range cannot be formed and heat resistance may be insufficient. Even if the amount of the acidic silicic acid solution added exceeds 20 parts by weight, the heat resistance does not further improve, and the silica coating layer becomes too thick, causing light scattering, giving a pink or even white color. It may happen. The addition rate of the acidic silicic acid solution is not particularly limited as long as a silica coating layer capable of exhibiting the heat resistance can be formed, and the addition should be carried out over a period of time within the range where silica fine particles that do not contribute to the formation of the silica coating layer are not formed. Is preferred.

Next, when silica sol is used, the addition amount of silica sol varies depending on the average particle diameter of gold fine particles, but 0.1 to ₂ as SiO ₂ per 1 part by weight of gold fine particles.
It is preferably 0 part by weight, more preferably 1 to 10 parts by weight. When the amount of silica sol added is less than 0.1 part by weight, heat resistance may be insufficient. Even if the amount of silica sol added exceeds 20 parts by weight, the heat resistance does not further improve, and the thickness of the silica coating layer becomes too thick, which causes light scattering, resulting in a pink or white color. May be. The addition rate of silica sol is
There is no particular limitation as long as the silica coating layer capable of exhibiting the heat resistance can be formed, and when the silica coating amount is small, it can be added at a time.

The average particle size of the silica particles in the silica sol is preferably 4 to 50 nm, more preferably 5 to 30 nm. If the average particle size of the silica particles is less than 4 nm, it is difficult to obtain a stable silica sol. On the other hand, if the average particle size exceeds 50 nm, it is difficult to deposit / precipitate on the surface of the gold fine particles. Even if it can be coated, the silica coating layer becomes too thick and causes light scattering, which may cause pink or even white. In the production method of the present invention, the acidic silicic acid solution or silica sol may be added and then aged if necessary. Specifically, 30 to 150 ° C., preferably 50 to
It suffices to perform heat treatment at 100 ° C. for several hours, and by performing such heat aging, a more dense silica coating layer or a silica coating layer having a more uniform thickness can be formed.

Red Pigment The red pigment according to the present invention comprises the silica-coated gold fine particles. The silica-coated gold fine particles have a wavelength of 480 to 6 because the average particle size of the gold fine particles is in the range of 2 to 50 nm.
Since it has an absorption peak in a narrow range of 00 nm, it is useful as a clear and transparent red pigment. Furthermore, since the fine gold particles are coated with silica, for example, 500 ° C
It is useful as a red pigment excellent in heat resistance since it can maintain a clear and transparent red color without agglomeration or discoloration due to the agglomeration even when exposed to the above high temperature.

[0021]

EFFECTS OF THE INVENTION The silica-coated gold fine particles according to the present invention show a clear and transparent red color because the average particle size of the gold fine particles is in a specific range, and the gold fine particles are coated with silica, so that they are exposed to high temperatures. Even when exposed, the fine gold particles do not aggregate or grow. For this reason, it is possible to obtain a red pigment having excellent heat resistance without deteriorating the clarity and transparency or discoloring. According to the method for producing silica-coated gold fine particles according to the present invention, the silica-coated gold fine particles can be easily and efficiently produced. The red pigment according to the present invention has excellent heat resistance and is useful as a pigment used in paints, cosmetics, printing inks, color filters for liquid crystal display devices and the like.

[0022]

EXAMPLES Preferred examples of the present invention will be given below, but the present invention is not limited to these examples.

[0023]

[Example 1]Preparation of silica-coated gold fine particles (A) Chloroauric acid tetrahydrate (HAuCl.4H) in 1410 g of distilled water
₂O) 14.25 g was dissolved and a surfactant (flower
Ou Co., Ltd .: Coatamine 24P; CH₃(CH ₂)₁₁N
(CH₃)₃Cl) 28.5 g was added. Then return
Sodium borohydride with a concentration of 1 wt% (N
aBH_Four) Addition of 7.7 g of cations on the surface of the fine gold particles
Prepare a gold fine particle dispersion with a surfactant coordinated (adsorbed)
Made The average particle size of the gold particles at this time was measured and the result
Is shown in Table 1. Next, collect 100 g of gold fine particle dispersion
Then, add 1% by weight NaOH aqueous solution to
Adjust the pH of the dispersion to 10.5 and raise to 95 ° C for 30 minutes.
Heated for a while. After that, SiO₂Acidic silica with a concentration of 3% by weight
Liquid 1.3g was added over 15 minutes to obtain silica-coated gold fine particles.
(A) A dispersion was prepared. Then, after separating the particles,
The silica-coated gold fine particles (A) are dried at 120 ° C. for 1 hour.
Prepared.

Evaluation of Silica-Coated Gold Fine Particles (1) Redness (Clearness of Red Color Tone) The silica-coated gold fine particles (A) were visually observed for redness and evaluated according to the following criteria. It was shown to. Vivid red, with transparency: ◎ Red, with a slight decrease in transparency: ○ Pink / close to pink, decreased transparency: △ Pink / white with increased whiteness, no transparency: × (2) Reflection Ratio (redness and transparency) The silica-coated gold fine particles (A) are dispersed in pure water so that the gold concentration is 0.005% by weight, and the reflectance is measured with a spectrophotometer (Otsuka Electronics Co., Ltd .: MCPD). -2000) and displayed as the average value of the reflectance in the wavelength range of 480 to 600 nm. The results are shown in Table 1. (3) The heat-resistant silica-coated gold fine particles (A) are fired at 700 ° C. for 1 hour,
The degree of redness was visually observed and evaluated according to the following criteria. The results are shown in Table 1. Vivid red, with transparency: ◎ Red, with a slight decrease in transparency: ○ Pink / close to pink, decrease in transparency: △ Black or gold: × (4) Particle-dispersible silica-coated gold fine particles (A) dispersion Was allowed to stand for 1 hour, the presence or absence of sedimentation of fine particles was observed, and the results were shown in Table 1 according to the following criteria. No settling of fine particles: ○ Fine particle settling is observed: ×

[0025]

Example 2 Preparation of silica-coated gold fine particles (B) Silica-coated gold fine particles were prepared in the same manner as in Example 1 except that 3 g of an acidic silicic acid solution having a SiO ₂ concentration of 3% by weight was added for 30 minutes. (B) Dispersion and silica-coated gold fine particles (B) were prepared. The obtained silica-coated gold fine particles (B) were evaluated for redness, reflectance, heat resistance and dispersibility, and the results are shown in Table 1.

[0026]

Example 3 Preparation of silica-coated gold fine particles (C) Silica-coated gold fine particles were prepared in the same manner as in Example 1 except that 24 g of an acidic silicic acid solution having a SiO ₂ concentration of 3% by weight was added for 30 minutes. (C) A dispersion and silica-coated gold fine particles (C) were prepared. The obtained silica-coated gold fine particles (C) were evaluated for redness, reflectance, heat resistance and dispersibility, and the results are shown in Table 1.

[0027]

[Example 4] Preparation of silica-coated gold fine particles (D) In Example 1, instead of the acidic silicic acid solution, silica sol (manufactured by Catalysts & Chemicals Industry Co., Ltd .: SI-550, average particle size 5) was used.
Silica-coated gold fine particles (D) were prepared in the same manner as in Example 1 except that 3.0 g of SiO _{2 and} 48 wt% of SiO ₂ concentration was added at one time. The silica coated gold fine particles (D) were evaluated for redness, reflectance, heat resistance and dispersibility, and the results are shown in Table 1. However, the silica-coated gold fine particles (D) were likely to settle, and the reflectance could not be measured.

[0028]

Example 5 Preparation of Silica-Coated Gold Fine Particles (E) In Example 4, silica sol (Catalyst Chemical Co., Ltd.)
Made: SI-550, average particle size 5 nm, SiO ₂ concentration 4
Silica-coated gold fine particles (E) were prepared in the same manner as in Example 1 except that 5.5 g (8% by weight) was added at one time. The silica coated gold fine particles (E) were evaluated for redness, reflectance, heat resistance and dispersibility, and the results are shown in Table 1. However,
The silica-coated gold fine particles (E) were prone to sedimentation, and the reflectance could not be measured.

[0029]

Example 6 Preparation of Silica Coated Gold Fine Particles (F) In Example 4, silica sol (Catalyst Chemical Co., Ltd.)
Made: SI-550, average particle size 5 nm, SiO ₂ concentration 4
Silica-coated gold fine particles (F) were prepared in the same manner as in Example 1 except that 9.9 g (8% by weight) was added at one time. The silica coated gold fine particles (F) were evaluated for redness, reflectance, heat resistance and dispersibility, and the results are shown in Table 1. However,
The silica-coated gold fine particles (F) were prone to sedimentation, and the reflectance could not be measured.

[0030]

[Example 7] Preparation of silica-coated gold fine particles (G) In the same manner as in Example 2 except that 2820 g of distilled water was used in Example 2, a cationic surfactant was coordinated (adsorbed) on the surface of the gold fine particles. ) A fine gold particle dispersion was prepared.
The average particle size of the fine gold particles at this time was measured, and the results are shown in Table 1.
It was shown to. Then, a silica-coated gold fine particle (G) dispersion and a silica-coated gold fine particle (G) were prepared in the same manner as in Example 1. Redness of silica-coated gold fine particles (G),
The reflectance, heat resistance and dispersibility were evaluated, and the results are shown in Table 1.

[0031]

Comparative Example 1 Preparation of Gold Fine Particles (H) In the same manner as in Example 1, a gold fine particle dispersion liquid in which a cationic surfactant was coordinated (adsorbed) was prepared. Then, this dispersion was dried at 120 ° C. to prepare gold fine particles (H). Table 1 shows the measured values of the average particle size and the evaluation of redness, reflectance, heat resistance and dispersibility of the gold fine particles (H). The color tone of the gold fine particle (H) dispersion was clear and red with a transparent feeling.

[0032]

Comparative Example 2 Preparation of Gold Fine Particles (I) In the same manner as in Example 7, a gold fine particle dispersion liquid in which a cationic surfactant was coordinated (adsorbed) was prepared. Then 120
By drying at 0 ° C., gold fine particles (I) were prepared. For the gold fine particles (I), measured values of average particle size, redness, reflectance,
The evaluation of heat resistance and dispersibility is shown in Table 1. In addition, the color tone of the gold fine particle (I) dispersion liquid was clear and was a transparent red color.

[0033]

TABLE 1 Gold fine particulate silica coated gold particle size coating layer weight ratio The particle size of the evaluation of fine gold particles reflected red heat dispersion D _G type thickness (SiO ₂ / Au) D _P of rate of resistance (nm) (* 1 ) (nm) (nm) (%) Example 1 15 L 2.6 0.08 20 ◎ 0.5 ◎ ○ Example 2 15 L 5 0.19 25 ◎ 0.5 ◎ ○ Example 3 15 L 20 1.5 55 ○ 0.8 ○ ○ Example 4 15 S 28 3.0 71 ○ − ○ × Example 5 15 S 37 5.0 89 ○ − ○ × Example 6 15 S 48 10 111 ○ − ○ × Example 7 5 L 1.5 0.19 8 ◎ 0.5 ○ ○ Comparative Example 1 15 − − 0 − × 0.5 × ○ Comparative Example 2 5 − − 0 − × 0.5 × ○ (* 1) L: Acidic silicic acid solution, S: Silica sol

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Claims (4)

[Claims] 1. An average particle diameter (D _G ) of 2 nm to 50 nm
The silica-coated gold fine particles are characterized in that the surfaces of the gold fine particles in the range are covered with silica. 2. The average particle diameter (D _P ) is 4 nm to 150 n.
The silica-coated gold fine particles according to claim 1, which are in the range of m. 3. The average particle diameter (D _G ) is 2 nm to 50 nm.
To the aqueous dispersion of fine gold particles or the mixed dispersion of water and an organic solvent in the range of, a surfactant is added, and then an alkali is added to adjust the pH of the dispersion to the range of 9 to 12, and if necessary, A method for producing silica-coated gold fine particles according to claim 1 or 2, characterized in that the acidic silicic acid solution or silica sol is added after aging by heating. 4. A red pigment comprising the silica-coated gold fine particles according to claim 1.