Water-based inks for inkjet printers - Patents - Printi...

Water-based inks for inkjet printers

Water-based inks for inkjet printers
Patent Agent: Harness, Dickey & Pierce, P.L.C - Reston, VA, US
Patent Inventors: Hitoshi Inoue, Tomoya Yamamoto, Yukiko Tachibana, Takayuki Ookawa, Junko Morioka
Applicaton #: 20070004822
Class: 523160000 (USPTO)
Related Patents: Synthetic Resins Or Natural Rubbers -- Part Of The Class 520 Series, Involving Inert Gas, Steam, Nitrogen Gas, Or Carbon Dioxide, Processes Of Preparing A Desired Or Intentional Composition Of At Least One Nonreactant Material And At Least One Solid Polymer Or Specified Intermediate Condensation Product, Or Product Thereof, Printing Ink Composition For Glass Or Ceramic Substrate Or Process Of Preparing
01/04/07

A water-based ink for inkjet printers contains at least a water-insoluble colorant, a block copolymer of a polyvinyl ether structure comprising at least one kind of hydrophilic segments and at least one kind of hydrophobic segments, water and an alkali. Each of the hydrophilic segments contains acidic groups. A content of the alkali is such that, when an infrared absorption intensity ascribable to ionic groups to be formed upon addition of an excess amount of the alkali to the block copolymer is supposed to be 100%, an infrared absorption intensity ascribable to ionic groups formed by dissociation of the acidic groups contained in the block copolymer becomes at least 80%, with a proviso that the content does not exceed twice as much as a smallest amount of the alkali that an infrared absorption intensity ascribable to ionic groups to be formed from the block copolymer becomes 100%.

DISCLOSURE OF THE INVENTION
[0008] The above-described object can be achieved by the present invention to be described hereinafter. Specifically, the present invention provides a water-based ink for inkjet printers, said water-based ink comprising at least a water-insoluble colorant, a block copolymer of a polyvinyl ether structure comprising at least one kind of hydrophilic segments each of which contains acidic groups and at least one kind of hydrophobic segments, water and an alkali, characterized in that a content of the alkali is such that, when the intensity of an infrared absorption (which may hereinafter be referred to as "infrared absorption intensity") ascribable to ionic groups to be formed upon addition of an excess amount of the alkali to the block copolymer is supposed to be 100%, an infrared absorption intensity ascribable to ionic groups formed by dissociation of the acidic groups contained in the block copolymer becomes at least 80%, with a proviso that the content does not exceed twice as much as a smallest amount of the alkali that an infrared absorption intensity ascribable to ionic groups to be formed from the block copolymer becomes 100%.
[0009] In the present invention, it is preferred that the acidic groups contained in the block copolymer are carboxyl groups and that the colorant is a pigment or a water-insoluble dye.
[0010] In the present invention, the infrared absorption intensity ascribable to ionic groups formed by dissociation of the acidic groups contained in the block copolymer reflects the amount of the existing ionic groups, and serves as an effective index which indicates the degree of neutralization. Described specifically, when the alkali is added in an excess amount, the acidic groups in the block copolymer are completely neutralized and are dissociated substantially 100%. In the case of such an alkali content that the infrared absorption intensity ascribable to ionic groups is smaller than 80% when the infrared absorption intensity ascribable to ionic groups to be formed upon complete neutralization of acidic groups in the block copolymer is supposed to be 100%, on the other hand, there are still a number of acidic groups which have not dissociated yet. Accordingly, the block copolymer is provided with lower hydrophilicity so that the dispersion of fine particles of the colorant in the aqueous medium becomes unstable.
[0011] If the alkali is contained in an amount greater than twice as much as the smallest amount of the alkali required to achieve complete neutralization (100% neutralization), on the other hand, the alkali exists in excess of the amount equivalent to the ionic groups. In this case, the ionic strength in the solution increases so that the static repulsive force between particles, which the block copolymer forms with the colorant included therein, becomes weaker to facilitate mutual flocculation of dispersed particles.
[0012] When the content of the alkali is such that the infrared absorption intensity ascribable to groups neutralized to have ionic property is at least 80% of the infrared absorption intensity available upon complete neutralization (100% neutralization) and the content of the alkali is not more than twice as much as the smallest amount of the alkali required for complete neutralization, the dissociation of the acidic groups in the block copolymer is sufficient and extra ions formed by the alkali are not much, thereby making it possible to obtain a water-based ink excellent in dispersion stability.
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