Metallic colloidal solution and inkjet-use metallic ink
A metallic colloidal solution (a) includes a water-based dispersion medium that is easy in handling with regard to safety and environment and metallic particles having a uniform particle diameter and being excellent in properties such as conductivity and (b) has properties suitable for various printing methods and ink-applying methods. In addition, an inkjet-use metallic ink incorporating the metallic colloidal solution has properties suitable for the inkjet printing method. The metallic particles are deposited by reducing metallic ions in water and have a primary-particle diameter of at most 200 nm. The dispersion medium is made of a mixed solvent of water and a water-soluble organic solvent. The metallic particles are dispersed in the dispersion medium under the presence of a dispersant having a molecular weight of 200 to 30,000.
1. A metallic colloidal solution comprising:
(a) metallic particles selected from the group consisting of nickel, copper, silver, gold, platinum, palladium, and an alloy of these metals that:
(a1) are deposited by reducing metallic ions in water; and
(a2) have a primary-particle diameter of at most 200 nm;
(b) a dispersant having a molecular weight of 200 to 30,000; and
(c) a dispersion medium made of a mixed solvent of water and a water-soluble organic solvent,
wherein the water-soluble organic solvent is a glycol ether, and the ratio of the water-soluble organic solvent to the mixed solvent is at least 70 percent, but less than 100 percent by weight.
2. A metallic colloidal solution as defined by claim 1 , the metallic colloidal solution being produced:
(a) by using as a starting material a water-based metallic colloidal solution obtained by depositing metallic particles through the reduction of metallic ions in water; and
(b) without undergoing a process that completely separates the metallic particles from water.
3. A metallic colloidal solution as defined by claim 1 , wherein the content of the metallic particles is 0.1 to 90 wt. %.
4. A metallic colloidal solution as defined by claim 1 , wherein the dispersant is an organic compound that does not contain any of sulfur, phosphorus, boron, and a halogen atom.
5. A metallic colloidal solution as defined by claim 1 , wherein the amount of the dispersant is 2 to 30 weight parts per 100 weight parts of the metallic particles.
6. An inkjet-use metallic ink incorporating a metallic colloidal solution comprising:
(a) metallic particles selected from the group consisting of nickel, copper, silver, gold, platinum, palladium, and an alloy of these metals that:
(a1) are deposited by reducing metallic ions in water; and
(a2) have a primary-particle diameter of at most 200 nm;
(b) a dispersant having a molecular weight of 200 to 30,000; and
(c) a dispersion medium made of a mixed solvent of water and a water-soluble organic solvent,
wherein the water-soluble organic solvent is a glycol ether, and the ratio of the water-soluble organic solvent to the mixed solvent is at least 70 percent by weight, but less than 100 percent by weight.
7. An inkjet-use metallic ink as defined by claim 6 , the inkjet-use metallic ink having a surface tension of 20 to 60 mN/m at 25° C. and a viscosity of 0.5 to 40 mPa·s at 25° C.
8. An inkjet-use metallic ink as defined by claim 6 , wherein the metallic colloidal solution is produced:
(a) by using as a starting material a water-based metallic colloidal solution obtained by depositing metallic particles through the reduction of metallic ions in water; and
(b) without undergoing a process that completely separates the metallic particles from water.