Chemistry: electrical and wave energy – Processes and products – Electrophoresis or electro-osmosis processes and electrolyte...
Reexamination Certificate
1997-01-30
2001-03-13
Mayekar, Kishor (Department: 1741)
Chemistry: electrical and wave energy
Processes and products
Electrophoresis or electro-osmosis processes and electrolyte...
C204S496000, C204S497000, C204S508000, C106S499000, C428S457000
Reexamination Certificate
active
06200446
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a pigment dispersion composition for fill-in coloration of an aluminum or aluminum alloy oxide film, which is adapted to fill micropores of the aluminum or aluminum alloy oxide film with a pigment for coloration thereof.
BACKGROUND ART
In an attempt to provide a colored film of high practicality, the inventor of the present invention has previously proposed a pigment dispersion composition for fill-in coloration of an aluminum or aluminum alloy oxide film, the pigment dispersion composition being adapted to fill micropores of the oxide film with a pigment by electrophoresis for coloration thereof, wherein a 50%-cumulative point (average particle diameter: D50) of the pigment particle diameter distribution in the dispersion is 200 nm or smaller. This pigment dispersion composition provides for a vivid color film having excellent weatherability and fastness and enables repetitive coloration because pigment particles are filled in the micropores of the aluminum oxide film to a great depth.
In actual use, however, the pigment is unavoidably deposited on the film surface as well as in the micropores when the electrophoresis is performed to fill the pigment into the micropores. The pigment deposited on the film surface other than in the micropores is likely to lead to an unstable color density of a thus colored material and to be brought into an electrodeposition surface coating bath in the succeeding step to contaminate the bath. With an anodic aluminum oxide film having micropores of diameters of about 50 nm or smaller, in particular, this tendency becomes more remarkable since most of the pigment is deposited on the film surface other than in the micropores, though depending on the size of the pigment particles. Even with an anodic aluminum oxide film having micropores of diameters of greater than 50 nm, the pigment is unavoidably deposited on the film surface as well as in the micropores, as stated above.
Thus, it has been required to wash away the pigment deposited on the film surface other than in the micropores irrespective of the micropore diameter of the anodic aluminum oxide film for convenience in the operational procedure in order to prevent such disadvantages. Typical means for washing away the pigment deposited on the film surface other than in the micropores are brushing, showering and like means which require cumbersome operations with time and labor. Therefore, the deposited pigment is preferably removed by simple immersion in still water or running water.
It is an object of the present invention to provide a pigment dispersion composition for fill-in coloration of an aluminum or aluminum alloy oxide film, which is adapted to fill pigment particles into micropores of the film to a great depth to provide for a vivid color film having excellent weatherability and fastness and allows repetitive coloration, and which permits the pigment deposited on the film surface other than in the micropores to be readily washed away by simple immersion in still water or running water.
DISCLOSURE OF THE INVENTION
As a result of intensive study to attain the above object, a pigment dispersion composition has been realized which, after having been applied onto an anodic aluminum oxide film for fill-in coloration, permits the pigment thereof deposited on the surface other than in micropores of the film to be advantageously removed by simple immersion in still water or running water, thereby allowing easy cleaning.
More specifically, it has been discovered that, if a pigment dispersion composition for fill-in coloration of an aluminum or aluminum alloy oxide film contains at least one compound selected from the group consisting of water-soluble amines and/or derivatives thereof, certain water-insoluble amines and/or derivatives thereof, water-soluble polyvalent alcohols, and water-soluble urea and thiourea and derivatives thereof, such compounds act to reduce the drying speed of water contained in the pigment dispersion composition. This is conceivably because such a compound dissolves in water and chemically associates with dispersed pigment or dispersant existing around the surface of each pigment particle. Further, even after the composition is dried, the pigment deposited on the surface of the aluminum film can readily be removed by simple water washing probably because the compound remains as intervening between pigment particles or between the pigment particles and the film surface. It has also been discovered that the pigment dispersion composition for fill-in coloration containing any of the foregoing compounds permits the pigment particles to be filled into micropores of the aluminum film to a great depth thereby providing for a vivid color film having excellent weatherability and fastness and, in addition, enables repetitive coloration.
The present invention provides a pigment dispersion composition for fill-in coloration of an aluminum or aluminum alloy oxide film, essentially consisting of a pigment, a pigment dispersant, a water-soluble organic solvent, water, and a water-soluble amine and/or a derivative thereof.
Examples of specific water-soluble amines and/or derivatives thereof include mono-, di- and trialkanolamines such as methanolamine and ethanolamine, and derivatives thereof. Such water-soluble amines and/or derivatives thereof are desirably those having a solubility of 1 g or greater in 100 g of water at 25° C., for example, triethanolamine (pKa at 25° C.=7.76).
The present invention also provides a pigment dispersion composition for fill-in coloration of an aluminum or aluminum alloy oxide film, essentially consisting of a pigment, a pigment dispersant, a water-soluble organic solvent, water, and a water-insoluble amine and/or a derivative thereof.
When such a water-insoluble amine and/or a derivative thereof is used, it is desired that the pigment dispersant comprise a resin acid and that the water-insoluble amine and/or derivative thereof has a pKa value between 7.1 and 12 at 25° C., the pKa value being defined as the logarithm of the reciprocal of the acid dissociation constant of a conjugate acid from the resin acid. Examples of preferred water-insoluble amines and/or derivatives thereof include mono-, di- and trialkylamines such as methylamine and ethylamine; aromatic amines such as benzylamine, and derivatives thereof; heterocyclic amines such as piperidine, piperazine and morpholine, and derivatives thereof. Such a water-insoluble amine and/or derivative thereof is used as a neutralizer for the resin acid, thereby being turned into a compound which can be homogeneously contained in water.
A compound having a pKa value of greater than 12 such as guanidine exhibits a too strong alkalinity and, hence, will provide a dispersion exhibiting an undesirably strong alkalinity, so that a coloring failure and corrosion of an aluminum plate will result. On the other hand, a compound having a pKa value of smaller than 7.1 such as pyridine or o- or p-nitroaniline exhibits a too weak alkalinity and, hence, cannot cause the resin to dissolve, resulting in an undesirable pigment dispersion. In this connection, a compound having a pKa value ranging from 7.1 to 12 is preferable such as methylamine (pKa at 25° C.=10.6), piperidine (pKa at 25° C.=11.1) or triethylamine (pKa at 25° C.=10.7). In particular, methylamine (pKa at 25° C.=10.6) and triethylamine (pKa at 25° C.=10.7) having a pKa value within a range between 7.5 and 11 are best-suited for the purpose of the invention.
It should herein be noted that, although an expression generally applied to the dissociation of a weak base represents a pH value in relation to a pKb value, the present invention uses a pKa value. The expression representing a pH value in relation to a pKb value is transformed into an expression simply representing the pH value in relation to a pKa value as follows.
pH=14−(½)pKb+(½)log
C
(1)
where C represents an electrolyte concentration,
Ka×Kb=Kw
&e
Inoue Hiroshi
Inoue Shigeyasu
Ito Seishiro
Armstrong, Westerman Hattori, McLeland & Naughton
Mayekar Kishor
Sakura Color Products Corporation
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