Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-07-16
2004-04-20
Shosho, Callie (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S590000, C524S601000, C523S160000
Reexamination Certificate
active
06723785
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for preparing an aqueous dispersion of pigment-containing polymer particles, and more specifically to a process for preparing an aqueous dispersion of pigment-containing polymer particles, which can be suitably used for a water-based ink for inkjet printing, an aqueous dispersion of pigment-containing polymer particles prepared by the above process, and a water-based ink comprising the aqueous dispersion.
2. Discussion of the Related Art
Development of a water-based ink has been desired in order to avoid the global environmental pollution caused by organic solvents. However, there are some defects in a water-based ink containing a water-soluble dye such that the ink is poor in water resistance and light fastness. Inkjet printing is carried out by directly jetting ink droplets from very fine nozzles to deposit the ink droplets on a recording medium, to form characters or images. The inkjet printing is advantageous in that its printing device produces noise at a low level. Also, the inkjet printing is excellent in operability, facilitates coloration and enables to use plain paper as a recording medium. Therefore, the inkjet printing has been widely used in these years.
In an ink used for inkjet printers, water-soluble dyes and polyhydric alcohols are used in order to prevent the ink from being clogged in the nozzles. However, this ink is poor in water resistance and light fastness. Especially, when the ink is used as an ink for thermal jet printing, there are some defects in the ink such that the dye is oxidized due to the heat of a heater, and that the ink is easily scorched on the heater surface, thereby lowering the discharging ability.
A water-based pigment ink has been proposed in order to eliminate this defect. As the water-based pigment ink, there has been proposed a pigment dispersion-type ink prepared by dispersing a pigment in water with a surfactant or a water-soluble polymer. However, there are some defects in the pigment dispersion-type ink such that the ink is insufficient in water resistance and light fastness.
Therefore, as an ink which is excellent in water resistance and light fastness, there has been proposed a pigment-containing ink prepared by incorporating a pigment into a water-insoluble polymer, and dispersing the resulting pigment-incorporated water-insoluble polymer in water.
During the preparation of the pigment-containing ink, the formation of fine particles of a pigment is generally carried out in an organic solvent or a mixed solvent of water and an organic solvent (dispersion treatment), as disclosed in, for instance, Japanese Patent Laid-Open Nos. Hei 8-183920 and Hei 8-218013. When this ink is prepared, a roll-mill, a beads-mill, a high-pressure homogenizer or the like has been used as a dispersion device.
However, there are some defects in the above process such that as materials used in the device, particularly a packing, ones which endure the organic solvent used should be selected in accordance with the kinds of the organic solvent, and that the durability of the packing for the organic solvent is generally poorer as compared to that for water.
Also, when the dispersion device is disassembled for washing, there are necessitated the prevention of evaporation of an organic solvent or collection of an organic solvent from a waste liquid obtained by washing. Moreover, there arises a defect in working environment such that the organic solvent would impart wrong influences to human bodies (for instance, skin, throat, or the like) when the organic solvent is contacted with skin or orally inhaled upon evaporation.
In addition, when a roll-mill is used, there are some defects in the roll-mill such that a treated product is dried because an organic solvent is evaporated from its roller surface, and that working environment is stained. When a beads-mill or a high-pressure homogenizer is used, there are some defects such that an entire device including a feeding tank and a manufactured product tank should be tightly sealed in order to prevent evaporation of an organic solvent contained in the treatment solution, and that an explosion-proof device should be provided for an electric motor or the like.
As described above, when an organic solvent is contained in a dispersion treatment liquid, equipments and means for handling the organic solvent are necessitated for from small-scale experimental equipments to large-scale industrial production equipments. Therefore, there has been desired the development of a water-based dispersion in which an organic solvent is not used.
Therefore, there has been proposed a process comprising dispersing a solid polymer in water, adding a pigment to the resulting dispersion and subjecting the mixture to a dispersion treatment as disclosed in Japanese Patent Laid-Open No. Hei 8-231906. However, there are some defects in this process such that the solid polymer is not dispersed in water unless it has an appropriate composition, and that heating or dispersion treatment with a stronger dispersion device is additionally necessitated in order to disperse the solid polymer in water, thereby making its industrial productivity poor.
As mentioned above, a process which does not necessitate an organic solvent at all is idealistic. However, the realization of such a process is actually difficult. Therefore, the polymer must be used in the form of a solution of an organic solvent in order to disperse the water-insoluble polymer in water, and effectively contact the water-insoluble polymer with a pigment. At a final stage, the organic solvent is removed. As mentioned above, when an organic solvent is used during the dispersion treatment, it would be difficult to deal with the organic solvent because a complicated apparatus is necessitated. Therefore, there has been desired for developing a process for preparing an aqueous dispersion not using an organic solvent in a dispersion process, which can remove the organic solvent in a process easily removing the organic solvent with a relatively convenient apparatus prior to the dispersion process.
An object of the present invention is to provide a process for efficiently preparing an aqueous dispersion of pigment-containing polymer particles without using an organic solvent in a dispersion step, giving no crookedness to a printed matter, and having excellent water resistance.
Another object of the present invention is to provide an aqueous dispersion of pigment-containing polymer particles prepared by the above process.
Still another object of the present invention is to provide a water-based ink comprising the above aqueous dispersion.
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 are provided:
(1) a process for preparing an aqueous dispersion of pigment-containing polymer particles, comprising the steps of:
(A) removing an organic solvent from a mixture (I) comprising an organic solvent solution of a polymer, water and optionally a neutralizing agent to give a solvent-removed product; and
(B) subjecting the solvent-removed product obtained in step (A) to a dispersion treatment, wherein a pigment is added to the mixture (I) or the solvent-removed product;
(2) a process for preparing an aqueous dispersion of pigment-containing polymer particles, comprising the steps of:
(C) mixing an organic solvent solution of a polymer, water and optionally a neutralizing agent with each other to give a mixture (II);
(D) removing an organic solvent from the mixture (II) obtained in step (C);
(E) mixing a solvent-removed product obtained in step (D) with a pigment to give a mixture (III); and
(F) subjecting the mixture (III) obtained in step (E) to a dispersion treatment;
(3) a process for preparing an aqueous dispersion of pigment-containing polymer particles, comprising the steps of:
(G) mixing an organic solvent solution of a polymer, water, pigment and optionally a neutralizing agent with each o
Hama Yoshinori
Kano Kenji
Ueyama Norio
Umehara Masahiro
Kao Corporation
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Shosho Callie
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