Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2000-02-03
2002-03-26
Owens, Amelia (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C549S205000, C549S218000, C536S004100
Reexamination Certificate
active
06362348
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an additive for inkjet printing, a recording solution, a method for preventing discoloration and fading of an image and a recording sheet.
BACKGROUND OF THE INVENTION
Inkjet printing is characterized in that the printer itself is inexpensive, the running cost is low and the color recording is facilitated, therefore, the inkjet printer is rapidly prevailing in recent years as an output device of digital signals from computer, digital camera and the like. As the ink for inkjet printing, various types of recording solutions such as an ink obtained by dissolving a dye in an aqueous medium or non-aqueous medium, an ink obtained by dispersing a pigment in an aqueous or oily solvent and a solid ink capable of thermal fusion have been heretofore put into practice or proposed. At the present time, an ink obtained by dissolving a dye in an aqueous medium is mainly prevailing and this ink is characterized by beautiful color and high safety to human body and to environment.
Particularly in recent years, an inkjet printer capable of easy printing at home or office is popularized and a printer capable of forming an image almost like a silver salt photograph has been developed. However, the aqueous dye is readily discolored or faded and accordingly, is inferior in the storage stability to the silver salt photograph. Due to this, the image formed and the hue thereof are disadvantageously liable to deteriorate in aging.
As a technique for solving such a problem, a method of using a pigment dispersion-type ink has been proposed and this is already used in practice for black ink and has succeeded in achieving excellent storage stability as compared with conventional inks using a dye. However, the inkjet printer has a tendency in recent years to have finer and finer nozzles for jetting out an ink so as to obtain a high-quality image and the pigment particle itself is also becoming small in the particle size for preventing the clogging of nozzles. As the pigment particle size is smaller, the light fastness is more inferior and the image is more easily discolored or faded. Accordingly, the change of ink into a pigment dispersion cannot be necessarily a countermeasure for the discoloration or fading. Moreover, a pigment dispersion-type ink has not yet been put into practice for color inks which are more outstandingly discolored or faded than the black ink in a photographic image.
Other than the above-described technique, various methods have been proposed to prevent the deterioration of a dye. For example, a method for preventing discoloration or fading by incorporating an ascorbic acid or the like into an ink is disclosed in JP-A-2-228379 (the term “JP-A” as used herein means an “unexamined Japanese patent application”), JP-A-7-331150, JP-A-9-95634 and JP-A-9-302294. The ascorbic acid or an inorganic salt thereof is relatively stable in the crystal and dry state, however, is colored and decomposed when it absorbs moisture. Furthermore, in the region of from neutral to alkaline condition, the ascorbic acid is accelerated to oxidize due to oxygen in air and easily decomposed. Accordingly, it is difficult to use the oxidation resistant effect of the ascorbic acid and, even if there is such an effect, the effect does not continue because the ascorbic acid is readily oxidized. Thus, the effect of preventing the discoloration or fading of a dye is not satisfactory.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an additive for inkjet printing, capable of preventing discoloration or fading (in the present invention, referred to as “color change”) of an image formed by the inkjet printing.
Another object of the invention is to provide a recording solution containing the additive.
A still other object of the invention is to provide a method for preventing color change of image using the additive.
A further other object of the invention is to provide a recording sheet containing the additive.
Other objects and effects of the present invention will become apparent from the following description.
As a result of extensive investigations for solving the problems encountered in conventional techniques, the present inventors have found that the color change can be remarkably improved by incorporating a specific compound into an inkjet-printed image.
More specifically, the above described objectives of the present invention have been achieved by providing the following additives, recording solutions, methods for preventing image discoloration and image fading, and recording sheets.
(1) An additive for inkjet printing, comprising a stabilized ascorbic acid derivative.
(2) The additive according to item (1) above, wherein said stabilized ascorbic acid derivative is:
an ascorbic acid derivative wherein at least one of the groups derived from the hydroxyl groups at the 2- and 3-positions of ascorbic acid is an ester with an inorganic or organic acid or a glycoside with a saccharide and at least one of the groups derived from the hydroxyl groups at the 5- and 6-positions of ascorbic acid may form an ester with an inorganic or organic acid; or a salt thereof.
(3) The additive according to item (2) above, wherein said stabilized ascorbic acid derivative is:
an ascorbic acid derivative wherein the group derived from the hydroxyl group at the 2-position of ascorbic acid is an ester with a phosphoric acid or a glucoside with a glucose and at least one of the groups derived from the hydroxyl groups at the 3-, 5- and 6-positions of ascorbic acid may form an ester with an inorganic or organic acid; or a salt thereof.
(4) The additive according to item (2) above, wherein said stabilized ascorbic acid derivative is an alkali metal, alkaline earth metal or transition metal salt of ascorbic acid-2-phosphate, an ascorbic acid-2-glucoside or a 6-ester thereof with an organic acid.
(5) A recording solution for inkjet printing, comprising a recording agent for forming a printing image, a liquid medium for dissolving or dispersing said recording agent and the additive according to any one of items (1) to (4) above.
(6) The recording solution according to item (5) above, wherein said liquid medium is an aqueous medium.
(7) The recording solution according to item (6) above, wherein said recording agent is a dye.
(8) The recording solution according to item (7) above, wherein the recording solution has a pH of from 7 to 12.
(9) The recording solution according to any one of items (6) to (8) above, wherein the additive is an ascorbic acid-2-phosphate alkali metal salt.
(10) A method for preventing discoloration and fading of an image, comprising providing the additive according to any one of items (1) to (4) above for an image formed by an inkjet printing method.
(11) The method according to item (10) above, wherein said provision of the additive is carried out by incorporating the additive into a recording solution to form an image.
(12) The method according to item (10) above, wherein said provision of the additive is carried out by incorporating the additive into a recording sheet onto which an image to be formed.
(13) The method according to item (10) above, wherein said provision of the additive is carried out by incorporating the additive into an image formed on a recording sheet.
(14) A recording sheet for inkjet printing, containing the additive according to any one of items (1) to (4) above.
(15) A recording sheet for inkjet printing, having an image formed thereon, which image contains the additive according to any one of items (1) to (4) above.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in detail below.
The ascorbic acid is relatively stable in the crystal and dry state, however, is colored and decomposed when it absorbs moisture. Furthermore, in the region of from neutral to alkaline conditions, the ascorbic acid is accelerated to oxidize due to oxygen in air and is readily decomposed. Accordingly, the use of ascorbic acid itself as an additive for an inkjet printing ink is not effective in bringing out the ascorbic
Itoh Yuji
Koshikawa Toshio
Takahashi Hiroshi
Uotani Nobuo
Owens Amelia
Seiko Epson Corporation
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