Compositions: coating or plastic – Coating or plastic compositions – Marking
Reexamination Certificate
1998-07-07
2001-01-09
Klemanski, Helene (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Marking
C106S031680, C106S031690, C106S031700, C106S031710, C106S031950
Reexamination Certificate
active
06171381
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention provides an aqueous metallic ink composition. More particularly, the aqueous metallic ink composition of the invention has utility in the ink for writing instruments, for printing, for coating, and the like.
2. Description of Related Arts
It has been a conventional practice to prepare an aqueous metallic ink composition by adding to an aqueous solution with a metallic powder pigment and a colorant, a water-soluble organic solvent, if required, and a water-soluble resin as a bonding agent (a binder resin), a viscosity controlling agent, or a dispersant, and the like. For example, Japanese Unexamined Patent Publication No.8-199108 (1996) discloses an aqueous ink composition for ball-point pens comprising a metallic powder pigment, a resin, a specific compound capable of providing lubricity, a water-soluble organic solvent, and water. In this report, the resin is used as the bonding agent (the binder resin) and the viscosity controlling agent. The binder resin includes, for example, a water-soluble acrylic resin, an acrylic emulsion and the like. Examples of thickening agents include a microbial polysaccharide or derivatives thereof such as xanthan gum or dextran, a water-soluble vegetable polysaccharide or derivatives thereof, and a water-soluble seaweed polysaccharide or derivatives thereof, water-soluble cellulose derivatives, and a water-soluble synthetic polymer. Frequently, an anionic polymer such as the acrylic resin is used as a pigment dispersant.
However, when the aqueous metallic ink composition containing the conventional water-soluble resin is used for coating (writing or printing) on an absorbent surface (the surface capable of absorbing aqueous ink or being penetrated by aqueous ink) such as a paper (for example, a paper for copy), the pigment (the colorant) penetrates into the paper and the density of the color development at the ink film such as prints or images decreases with the passage of time (for example, from the moment of writing to a few minutes after writing). Also the problem arises that the ink film such as prints or images blurs easily. At the same time, the ink film fixability to a nonabsorbent surface (the surface which neither absorbs the aqueous ink nor be penetrated by the aqueous ink) is low. Moreover, using only the cellulose derivative as a water-soluble resin, the dispersibility falls off because of gelation. These ink compositions have low viscosity stability with time, so the viscosity increases or decreases after storage. Therefore, it is difficult to keep the adequate viscosity for a long time. Accordingly, it is difficult to control the viscosity of the ink composition for each purpose.
The anionic polymer as the pigment dispersant also may cause a viscosity change of the ink (such as an increase of the viscosity) with aggregation or precipitation. The metallic powder pigment (particularly, an aluminum powder pigment) tends to ionize in the ink and the pH of the ink changes because of the ion element which is produced by the metallic powder pigment. Specifically, when the pH of the ink decreases, the aggregation or the precipitation of the anionic polymer changes the viscosity of the ink. Furthermore, the change of the viscosity, which is caused by the aggregation or the precipitation of the anionic polymer in the ink, is often the increase of the viscosity. Accordingly, the writing characteristic deteriorates in some cases.
Thus, the conventional aqueous metallic ink composition has problems in that the density of color development at the ink film decreases while the viscosity stability with time is low.
SUMMARY OF THE INVENTION
The present invention provides an aqueous ink composition comprising a metallic powder pigment, a colorant, water and a water-soluble organic solvent, and further including a natural polysaccharide and at least one compound selected from the group consisting of cellulose derivatives, a cyclodextrin, cyclodextrin derivatives, a water-soluble soy polysaccharide and water-soluble soy polysaccharide derivatives.
As a result of intensive study to solve the foregoing problems, the present inventors completed the invention by finding that in case that an aqueous metallic ink composition comprising at least a metallic powder pigment, a colorant, water, and a water-soluble organic solvent, and further including a natural polysaccharide and cellulose derivatives is used, the stability with time to the density of the color development at an ink film is increased, and the ink film fixability to nonabsorbent surface is improved. The present invention provides an aqueous ink composition comprising at least a metallic powder pigment, a colorant, water, and a water-soluble organic solvent, and further including natural polysaccharide and cellulose derivatives. The aqueous metallic ink composition of the invention comprises both the natural polysaccharide and cellulose derivatives so that the colorant has difficulty in penetrating into the absorbent surface (such as drawing paper). Therefore, the decrease of the density of the color development at the ink film can be restrained. The metallic powder pigment is coated by cellulose derivatives which are used together with the natural polysaccharide so that cellulose derivatives can act effectively on the metallic powder pigment. That is, a carboxyl group and/or a hydroxyl group of cellulose derivatives acts on the metallic powder pigment and a hydrophilic characteristic of the metallic powder pigment increases. Then, the intimacy (linkage) between the metallic powder pigment and the colorant becomes strong. As a result, the colorant is caught or adsorbed by the metallic powder pigment, and then the absorption of the colorant into the absorbent surface is restrained. Moreover, because the composition comprises the natural polysaccharide and cellulose derivatives, the ink film fixability to the nonabsorbent surface (for example, the surface of art paper) is improved. The cause of these phenomena appears to be that a carboxyl group and/or a hydroxyl group of cellulose derivatives are linked with the nonabsorbent surface by a hydrogen bond. Accordingly, because the aqueous metallic ink composition of the invention comprises the natural polysaccharide and cellulose derivatives, the decrease of the density of the color-development at the ink film can be restrained and the ink film fixability to the nonabsorbent surface is excellent. Also, the presence of natural polysaccharide and cellulose derivatives enables control of the viscosity of the aqueous metallic ink composition and improves the dispersibility in a high degree. The cause of these phenomena appears to be that the metallic powder pigment is coated by cellulose derivatives so that the influence of a metallic ion on the natural polysaccharide can be restrained or prevented by controlling the elution of metallic ion into the ink composition. Even though the composition contains cellulose derivatives, the aqueous metallic ink composition has high stability to the dispersion because cellulose derivatives are used with the natural polysaccharide.
In accordance with another embodiment of the invention, and as a result of intensive study, the inventors completed the invention by discovering that in case that aqueous metallic ink compositions comprising at least a metallic powder pigment, a colorant, water, and a water-soluble organic solvent, and further including both a natural polysaccharide and a cyclodextrin or cyclodextrin derivatives is used, the stability with time to the density of the color development is improved, and the viscosity change of the ink after storage is restrained or prevented. The present invention provides an aqueous ink composition, comprising at least a metallic powder pigment, a colorant, water, and a water-soluble organic solvent, and further including a natural polysaccharide and a cyclodextrin or cyclodextrin derivatives.
This aqueous metallic ink composition contains both the natural polysaccharide, and the cyclodextrin or cyclo
Matsumoto Kaoru
Murata Naoshi
Shibuya Ken-ichi
Yoshimura Yasuyuki
Armstrong, Westerman Hattori, McLeland & Naughton
Klemanski Helene
Sakura Color Products Corporation
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