Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-07-09
2004-05-25
Shosho, Callie (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S284000
Reexamination Certificate
active
06740690
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a water-based ink composition, and more specifically to a water-based ink composition which can be suitably used for a water-based ink for inkjet recording.
2. Discussion of the Related Art
As a colorant for a water-based ink composition, a water-soluble dye or an aqueous pigment dispersion has been used. In the case of the water-soluble dye, however, the ink composition is poor in water resistance and light fastness. Also, in the case of the aqueous pigment dispersion, an ink composition obtained has a high degree of coloration, but the ink composition is poor in fixing ability on a paper surface, rubbing resistance and high-lighter fastness.
For the purposes of improving water resistance and fixing ability, there has been proposed a use of an aqueous dispersion of polymer particles containing a dye or pigment and a water-insoluble polymer as a colorant as disclosed in Japanese Patent Laid-Open Nos. Hei 8-183920 and Hei 10-140065.
However, in order to improve water resistance or fixing ability to a sufficiently satisfiable level, the water-insoluble polymer should be usually used in an amount of not less than 40% by weight based on the entire colorant. Therefore, when the amount of the colorant in the ink is adjusted to the same amount as a conventional water-soluble dye or pigment dispersion ink, there is a defect that printed density is relatively lowered because the content of the coloring agent, namely the dye or pigment in the ink, is so low.
In view of the above prior art, there has been proposed the addition of polymer particles containing a dye or pigment to an ink composition in a large amount in order to increase printed density. In this process, however, the viscosity of the ink composition increases. Therefore, when the ink is used as a water-based ink for inkjet printing, jetting failure is sometimes caused by the increased viscosity, so that the amount of the polymer particles containing a dye or pigment in an ink is inevitably restricted.
An object of the present invention is to provide a water-based ink composition excellent in printed density, water resistance, high-lighter fastness and rubbing resistance.
Another object of the present invention is to provide a water-based ink for inkjet printing excellent in jetting ability.
These and other objects of the present invention will be apparent from the following description.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a water-based ink composition comprising a polybasic acid, an ionic polymer and a colorant.
DETAILED DESCRIPTION OF THE INVENTION
When the polybasic acid and the ionic polymer are used for a water-based ink composition, printed density of the water-based ink composition is remarkably increased. It is thought that this phenomenon would be based upon the followings: During the course of jetting a water-based composition on paper to permeate the water-based ink composition into the paper, the paper absorbs water contained in the water-based ink composition. Therefore, the concentration of the water-based ink composition increases to a high level, resulting in that the ionic polymer and/or the ionic polymer particle containing a coloring agent [hereinafter referred to as “ionic polymer (particle)”], contained in the water-based ink composition, is rapidly and strongly aggregated by the polybasic acid. Therefore, the coloring agent finally remains on the surface of the paper in a large amount, so that high printed density is exhibited.
On the other hand, when the polybasic acid and the ionic polymer (particle) are contained in the water-based ink composition, it is apprehensive that storage stability of the water-based ink composition would be lowered. However, the storage stability can be increased by controlling the kinds or concentration of the polybasic acid and the kinds or concentration of the ionic polymer (particle), which are contained in the water-based ink composition.
Also, the polybasic acid can be used as a neutralizing agent for the cationic polymer (hereinafter referred to as “the use of polybasic acid as a neutralizing agent”). Alternatively, the cationic polymer is neutralized with a monovalent acid or the combination of the monovalent acid and the polybasic acid, and thereafter the polybasic acid can be further added to the neutralized cationic polymer (hereinafter referred to as “the further addition of polybasic acid.”). When the polybasic acid is used as a neutralizing agent, the neutralization degree, that is, the percentage of the neutralized salt-forming group in the salt-forming group of the ionic polymer is preferably not more than 30% by mol, more preferably not more than 20% by mol, from the viewpoint of storage stability.
In the case of the further addition of polybasic acid, the pH of the ink composition is preferably not less than 3, more preferably not less than 4, from the viewpoint of corrosion resistance of the metal members in the head. In addition, the pH of the ink composition is preferably not more than 7, more preferably not more than 6, from the viewpoint of storage stability. Specifically, the pH of the ink composition is preferably 3 to 7, more preferably 4 to 6. In this case, the amount of the polybasic acid is preferably not more than 2 mol, more preferably not more than 1 mol, per one mol of the ionic functional group of the cationic polymer. The amount of the polybasic acid is prioritized over the pH of the ink composition.
In the case of the further addition of polybasic acid, when the cationic polymer is neutralized with the combination of the monovalent acid and the polybasic acid, the neutralization degree based upon the polybasic acid is preferably not more than 30% by mol, more preferably not more than 20% by mol, from the viewpoint of storage stability.
When the anionic polymer is neutralized and thereafter the polybasic acid is further added to a neutralized anionic polymer, it is preferable that the polybasic acid is added to the neutralized anionic polymer so that the pH of the ink composition becomes not less than 6, preferably not less than 7, still more preferably not less than 8, from the viewpoint of storage stability. In addition, the pH of the ink composition is preferably not more than 12, more preferably not more than 10, still more preferably not more than 9, from the viewpoint of corrosion resistance of the metal members in the head. Specifically, the pH of the ink composition is preferably 6 to 12, more preferably 7 to 10, still more preferably 8 to 9. In this case, the amount of the polybasic acid is preferably not more than 2 mol, more preferably not more than 1 mol, per one mol of the ionic functional group of the anionic polymer. The amount of the polybasic acid is prioritized over the pH of the ink composition.
The term “polybasic acid” is intended to mean an acid having two or more acidic groups. The polybasic acid can be any of organic acids and inorganic acids.
The organic acid includes, for instance, oxalic acid, malonic acid, glutaconic acid, glutaric acid, tartronic acid, pimelic acid, succinic acid, DL-malic acid, tartaric acid, citric acid, trimellitic acid, polyethylene oxide (n=2 to 60) dicarboxylic acids, glycerol dicarboxylic acids, polyglycerol (n=2 to 10) dicarboxylic to decacarboxylic acids and the like.
The inorganic acid includes, for instance, carbonic acid, sulfuric acid, sulfonic acid, phosphoric acid, pyrophosphoric acid, tripolyphosphoric acid, phosphonic acid and the like.
Among the polybasic acids, polybasic organic acids having a water solubility of not less than 1% by weight at 20° C., preferably not less than 10% by weight, more preferably not less than 50% by weight are desirable, from the viewpoints of dispersion stability and jetting stability of the ink composition. Preferred examples of the polybasic organic acid are oxalic acid, malonic acid, polyethylene oxide dicarboxylic acids, the number of moles of ethylene oxide of which is 2 to 30, glycerol dicar
Nakano Yukihiro
Shiga Fumihide
Kao Corporation
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Shosho Callie
LandOfFree
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