Compositions: coating or plastic – Coating or plastic compositions – Marking
Reexamination Certificate
1999-04-27
2001-06-05
Klemanski, Helene (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Marking
C106S031860, C106S031890
Reexamination Certificate
active
06241811
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for producing an ink composition which is preferably used in ink jet recording, and an ink composition prepared thereby.
2. Background Art
An ink prepared by adding a dye as a water-soluble colorant component to an aqueous medium is generally known as an ink for ink jet recording. On the other hand, however, there are not a few dyes having poor lightfastness, waterfastness and other various properties. Utilization of an ink composition comprising a pigment as a colorant component has recently been studied from the viewpoint of improving the above properties.
Since the pigment is generally insoluble in water, utilization thereof in water-based ink compositions requires that the pigment is mixed with a polymer called a “dispersant” and the like to prepare a mixture which is then stably dispersed in water followed by preparation of an ink composition using the dispersion.
Stable dispersion of the pigment in an aqueous system requires studies on type and particle diameter of pigments, type of dispersants, dispersion methods and the like. Up to now, various dispersion methods and ink compositions for ink jet recording have been proposed in the art.
Japanese Patent Laid-Open No. 157954/1994 discloses that a pigment and a polymeric dispersant are charged into a two-roll milling (two-roll mill) device to prepare a pigment dispersion that is then dispersed in an aqueous carrier medium to prepare an ink composition for ink jet recording.
Japanese Patent Publication No. 55548/1986 discloses that a polymer (a dispersant) previously prepared by polymerizing a monomer is dispersed together with a pigment and a water-soluble polyhydric alcohol (ethylene glycol) in a ball mill, a sand mill or the like to prepare a pigment dispersion for the preparation of an ink composition for ink jet recording.
Japanese Patent Laid-Open No. 227668/1992 discloses a process for producing an ink composition, comprising the steps of: providing a previously prepared block polymer as a dispersant, using this dispersant in combination with a pigment, a water-soluble organic solvent, such as diethylene glycol, and water in a horizontal Mini mill or the like to prepare a dispersion; and diluting the dispersion to prepare an ink composition.
In ink jet recording, an improvement in response frequency of a recording head is necessary from the viewpoint of improving recording speed. To this end, the amount of the ink ejected is preferably small. For this, preferably, a larger dot diameter is provided using a smaller amount of the ink ejected. On the other hand, however, particularly in a blotted recorded image (solid image), a larger amount of ink should be ejected in order to eliminate the creation of white streaks caused by lack of dot diameter.
A commonly used method for solving this problem is to add a surfactant or a glycol ether to an ink to impart a penetrating property. In the case of pigment-based inks, for example, Japanese Patent Laid-Open No. 147861/1981 proposes utilization of triethylene glycol monomethyl ether as a pigment.
Further, the ink for ink jet recording has generally been prepared by dispersing a pigment together with a dispersant to prepare a pigment dispersion and adding various components to the pigment dispersion.
SUMMARY OF THE INVENTION
The present inventors have now found that, in producing a pigment-based ink composition, a change in sequence of dispersion of additive components leads to a change in properties of the resultant ink composition. They have further found that dispersion of specific components together with a pigment enables the production of an ink composition which, when printed on a recording medium, is less likely to cause feathering or bleeding and can realize a large dot diameter in a reduced amount of the ink ejected. The present invention has been made based on such finding.
Accordingly, an object of the present invention is to provide a process for producing an ink composition for ink jet recording which can increase the dot diameter in a smaller amount of ink ejected, and an ink composition produced by the above process.
According to one aspect of the present invention, there is provided a process for producing an ink composition according to the present invention, said ink composition comprising at least a pigment, a dispersant, water, and an alkyl ether derivative, with 3 or more carbon atoms, of a polyhydric alcohol and/or an acetylene glycol compound represented by the following formula (I):
wherein R
1
, R
2
, R
3
, and R
4
each independently represent an alkyl group having 1 to 6 carbon atoms; and n and m are an integer, provided that the sum of n and m is 0 to 30,
said process comprising the steps of:
dispersing a mixture comprising at least a pigment, a dispersant, water, and an alkyl ether derivative, with 3 or more carbon atoms, of a polyhydric alcohol and/or an acetylene glycol compound represented by the formula (I) to prepare a dispersion or an ink composition; and
optionally preparing an ink from the dispersion.
According to another aspect of the present invention, there is provided an ink composition produced by the above process.
DETAILED DESCRIPTION OF THE INVENTION
Ink Composition
The ink composition according to the present invention may be used in recording methods using an ink composition. Recording methods using an ink composition include, for example, an ink jet recording method, a recording method using writing utensils, such as pens, and other various printing methods. Particularly preferably, the ink composition according to the present invention is used in the ink jet recording method.
In the process for producing an ink according to the present invention, a mixture comprising a pigment, a dispersant, water, and an alkyl ether derivative, with 3 or more carbon atoms, of a polyhydric alcohol and/or an acetylene glycol compound represented by the formula (I) is subjected to the dispersing step. According to a conventional process for producing a pigment-based ink composition comprising an alkyl ether derivative, with 3 or more carbon atoms, of a polyhydric alcohol or an acetylene glycol compound represented by the formula (I), a pigment is first dispersed together with water and a dispersant to prepare a pigment dispersion to which an alkyl ether derivative, with 3 or more carbon atoms, of a polyhydric alcohol or an acetylene glycol compound represented by the formula (I) is added. By contrast, according to the process of the present invention, all of these components are simultaneously subjected to the dispersing step.
The ink composition prepared by simultaneously subjecting all the components to the dispersing step has an advantage that, as compared with an ink composition prepared by first preparing a dispersion from a pigment and a dispersant and then adding an alkyl ether derivative, with 3 or more carbon atoms, of a polyhydric alcohol or an acetylene glycol compound represented by the following formula (I) to the dispersion, a recorded image suffering from a lesser degree of feathering or bleeding can be realized on a recording medium and, in addition, the same dot diameter can be realized in a smaller amount of the ink ejected. In other words, the ink composition according to the present invention, when the amount of the ink composition ejected is identical, can provide a larger dot diameter. In particular, a relatively large dot diameter can be realized in a smaller amount of ink on a recording medium designed so as to yield a high-quality image, that is, a recording medium (a gloss film) comprising a transparent coating provided on the surface of a white film as a substrate.
It is surprising that the sequence of dispersion of components can greatly improve the properties of the ink composition. Although the reason why the properties of the ink composition can be improved has not been elucidated yet, it is considered that, in the dispersing step, sufficient interaction between the dispersant and the alkyl ether derivative of a polyhydr
Faison Veronica F.
Klemanski Helene
Ladas & Parry
Seiko Epson Corporation
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