JP2005060815A - Production method of gold colloid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem associated with a gold colloid whose use has been considered for achieving a fading-resistant red color, wherein the gold colloid, despite of its excellent light fastness, has a low stability which leads to discoloration or sedimentation in a liquid state and often requires a strong emulsifier as a colloid protective agent or a stabilizer to stabilize the colloid, which limits its use as a pigment. <P>SOLUTION: The colloid liquid in a vivid reddish to purple-red color can be obtained through an extremely easy method wherein chloroauric acid and chitosan are heated and stirred for a prescribed time and subsequently treated with a reductant. A light red pigment exerting an extremely high light fastness can be achieved through an easy method. The pigment has a high potential as a raw material for cosmetics and, since it does not use any surfactant, is highly safe and has a wide range of application. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a stable colloidal gold as a red-colored pigment that is difficult to fade.

Japanese Patent No. 2834400 is a patent for a colloidal gold solution which is difficult to fade. In this method, the colloid is stabilized by adding a nonionic surfactant and ethanol before and after the reduction of gold with citrate or ascorbate. Japanese Patent Application Laid-Open No. 10-68008 and Japanese Patent Application Laid-Open No. 10-176207 disclose methods for preparing noble metal colloids, particularly platinum colloids. This is a method of preparing a platinum colloid by adding sodium hydrogen carbonate in the presence of ethanol and a nonionic surfactant. In the case of platinum, it becomes a black colloid, but it is said that this method can also be applied to colloid preparation of other elements of the platinum group.
Japanese Patent No. 2834400 Japanese Patent Laid-Open No. 10-68008 Japanese Patent Laid-Open No. 10-176207

  In addition to being used as a catalyst, a noble metal colloid may be used as a dye that hardly changes color, depending on the type of metal and the size of the particles. While colloids such as platinum are often studied for the purpose of use as a highly active catalyst, gold colloids and the like have been studied for the purpose of obtaining a red color that does not fade. .

  These colloids vary in stability and catalytic activity mainly depending on their particle size. Since the catalytic activity is often proportional to the surface area of the particles, in order to make a highly active catalyst, there are many preparations in the direction of increasing the surface area as a whole by devising the manufacturing method to make the particles as fine as possible. However, high catalytic activity means high reactivity, and in many cases lacks stability in the state as it is, and a colloid protective agent or stabilizer is required. Even when producing color, the problem is the stability of the colloid, which often requires a colloidal protective or stabilizing agent.

  A gold colloid that produces a red color is generally excellent in light resistance, but due to its stability as a colloid, color change and sedimentation are likely to occur in a liquid state. As a stabilizer for preventing this, a strong emulsifier is often used, which may limit the use as a pigment.

  The present invention was completed as a result of intensive studies on a simple method capable of producing a stable colloid without using a surfactant as a colloid protective agent. That is, it is a method in which chloroauric acid and chitosan are mixed and stirred for a predetermined time while heating, and then a reducing agent is used.

  The concentration of chloroauric acid used in the present invention is 0.01 mM to 10 mM, preferably 0.2 to 20 mM. The concentration of chitosan in the reaction solution is preferably 0.01 to 5.0% by weight, more preferably 0.5 to 2.5% by weight. The chitosan used preferably has a chitin deacetylation degree of 50 to 100% and a molecular weight of 2 million or less.

  The noble metal chloride and chitosan are heated to 70-80 ° C. with mixing and stirring in purified water, and then a reducing agent is added. As the reducing agent, common reducing agents such as sodium borohydride and hydrazine can be used. The concentration in the reaction solution is preferably the same molar concentration as the noble metal chloride to several tens of times.

  As described above, a bright red colloid solution can be obtained by an extremely simple method. By changing the amount of chitosan, it is possible to obtain gold colloid solutions having different colors from slightly red to reddish purple. Some reducing agents show alkalinity depending on the type, but due to the nature of chitosan that is alkaline and gelled, it becomes turbid by adjusting the pH so that the pH becomes acidic after the addition of the reducing agent. A transparent color without any color can be obtained.

  In the present invention, a bright red dye having light resistance can be obtained by a simple method. Since it does not require the use of a strong surfactant, it is highly safe for the human body, and therefore has a wide range of applications including cosmetic raw materials. Ordinary purification operation by dialysis or the like can be performed to obtain a form for oral use.

  0.5 g of chitosan was stirred and dissolved in 500 mL of purified water. Separately, 82.36 mg of chloroauric acid was dissolved in 100 mL of purified water and then added to the chitosan solution, and purified water was added to make the total amount 950 mL. This solution was heated with stirring, stirred at 70 ° C. for 30 minutes, then the heating was terminated, and 50 mL of sodium borohydride 0.7566 g / L was added, followed by stirring to obtain a slightly red gold colloidal solution. It was. FIG. 1 is an electron micrograph of this gold colloid solution.

  1 g of chitosan was dissolved in 500 mL of purified water with stirring. Separately, 82.36 mg of chloroauric acid was dissolved in 100 mL of purified water and then added to the chitosan solution, and purified water was added to make the total amount 950 mL. This solution was heated with stirring, stirred at 70 ° C. for 30 minutes, and then the heating was terminated, and 50 mL of sodium borohydride 0.7566 g / L was added, followed by stirring to obtain a red colloidal gold solution. .

  5 g of chitosan was dissolved in 500 mL of purified water with stirring. Separately, 82.36 mg of chloroauric acid was dissolved in 100 mL of purified water and then added to the chitosan solution, and purified water was added to make the total amount 950 mL. This solution was heated with stirring, stirred at 70 ° C. for 30 minutes, then the heating was terminated, and 50 mL of sodium borohydride 0.7566 g / L was added, followed by stirring to obtain a red-purple gold colloidal solution. It was.

Electron micrograph of colloidal gold solution (× 50,000)

Claims (3)

  Method for producing noble metal colloid characterized by using chitosan as colloid protective agent   The method for producing a noble metal colloid according to claim 1, wherein the noble metal is gold.   The method for producing a noble metal colloid according to claim 1, wherein the concentration of chitosan used is 0.01 to 5.0% by weight.