Incremental printing of symbolic information – Ink jet – Fluid or fluid source handling means
Reexamination Certificate
2000-01-19
2002-06-18
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Fluid or fluid source handling means
C347S101000
Reexamination Certificate
active
06406139
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to ink, and more particularly to printing ink for use with a recording device such as a printer.
The ink of the present invention is preferably applicable to a piezo-type inkjet head in which a piezoelectric element is used for a print head or a film-boiling-type (or bubble-type) inkjet head, and can widely be employed not only for a printer (inkjet printer) as a single unit, but also for a copier, a facsimile, a computer system, word-processor, or the combination thereof which has a printing function.
The inkjet printer is currently in increasing demand due to its excellence in noiseless operation and easiness to achieve a fall-color printing. In particular, the drop-on-demand inkjet head that ejects ink droplets from an inkjet nozzle only when necessary in printing operation has become widely used.
Among inkjet heads, those using a piezoelectric element (i.e. piezo-type inkjet head) have increasingly come into the limelight in recent years for their high energy-efficiency, etc. This kind of inkjet head typically includes a piezoelectric element, one common ink chamber which receives from an external device and stores ink, a plurality of pressure chambers connected to the piezoelectric element and a nozzle plate connected to the pressure chambers so that a nozzle may be connected to each pressure chamber. Each pressure chamber is connected to the common ink chamber through an ink supply channel so that it may receive ink from the common ink chamber and increase an internal pressure by utilizing a deformation of the piezoelectric element, thereby ejecting ink from each nozzle.
Other than the piezo-type inkjet head, those which eject ink droplets by using so-called bubble-type (film-boiling-type) ink ejecting means are known too.
Conventionally, the ink employed for this kind of inkjet recoding device is basically composed of a dye and a water-soluble organic solvent, but the dye has the intrinsic disadvantages of low water resistance and inferior lightfastness. Thus, to overcome such disadvantages, aqueous dispersoid ink (or pigment ink), which uses a pigment instead of a dye, has been developed. Compared with the dye ink, the aqueous dispersoid ink (or pigment ink) has a number of advantages in high water resistant lightfast property, high optical density on a recording medium, and less blurred property, etc.
The pigment ink, however, is disadvantageously difficult to keep a pigment particle stable because the pigment itself is insoluble in water or other solvents, and likely to clog in the nozzle. Accordingly, securing the ink dispersive stability has posed the most significant challenge in the pigment ink. Various proposals have been made to deal with this challenge, but prior art proposals have been found still insufficient.
For example, seeking to provide the dispersive and preservative stabilities to writing ink for use with a pen, etc. comprising a pigment, a dispersing agent, and an aqueous medium, Japanese Patent Publication (Kokai) No. 55-35434 has proposed to employ as a dispersing agent a polymer including as a main constituent alkyl ester of acrylic or methacrylic acid sharing both hydrophilic and lipophilic portions, and to employ an aqueous medium including a nonvolatile hydrophilic organic solvent, such as ethylene glycol.
However, writing ink is intrinsically unfit for ink used for such an inkjet recording device as ejects a droplet from a micro nozzle (hereinafter referred to as “inkjet ink”), and a long-term conservation thereof would evaporate water, increase its viscosity, and flocculate its particle; therefore such writing ink cannot be considered to secure the dispersive and preservative stabilities to such an extent as to be satisfactorily applicable to inkjet ink.
BRIEF SUMMARY OF THE INVENTION
Accordingly, it is an exemplified general object of the present invention to provide novel and useful ink, an ink storage such as an ink cartridge or tank, and a recording device using the ink in which the above disadvantages are eliminated.
More specifically, it is an exemplified object of the present invention to provide such ink that maintains the dispersive and preservative stabilities fit for inkjet ink, an ink storage, and a recording device using the ink.
The present inventors, after thorough study to achieve the above objects, have discovered that the previous disadvantages may be eliminated by instant novel dispersoid ink including a specific pigment, dispersing agent and/or additive in which a dispersed particle in the ink ranges in average diameter within a specific range when measured on a specific principle by a specific detection process.
Ink set forth in claim 1 comprises water and a water-soluble organic solvent, wherein a dispersed particle included in the ink further comprises a colorant including at least a carbon black, wherein the dispersed particle has a primary particle diameter of 30 nm or smaller, a BET specific surface area of 200 m
2
/g or smaller, a DBP oil absorption amount of 80 cc/100 g or smaller, a volatilization rate of 2.0% or higher, and a pH not greater than 7, and wherein the ink further comprises as a dispersing agent an acrylic macromolecule copolymer having weight average molecular weight of 80,000 or less. A relatively small primary particle, that is 30 nm or smaller in diameter, of the dispersed particle is selected so that it may hardly be precipitated. The dispersed particle if having the BET specific surface area of 200 m
2
/g or smaller would not be porous in general. The DBP oil absorption amount of 80 cc/100 g or smaller indicates the dispersed particle is relatively not so flocculated. The carbon black having a volatilization rate of 2.0% means that the dispersed particle has an oxidized film, etc. A pH not greater than 7 indicates that the dispersed particle is acidized. The present inventors have discovered that the ink satisfying these requirements is stable dispersoid ink. Moreover, the inventers have discovered that the ink further comprising as a dispersing agent an acrylic macromolecule copolymer having weight average molecular weight of 80,000 or less may gain further improved stability.
The ink set forth in claim 2 comprises water and a water-soluble organic solvent, wherein a dispersed particle included in the ink further comprises a colorant including at least a carbon black, wherein the dispersed particle has a primary particle diameter of 30 nm or smaller, a BET specific surface area of 200 m
2
/g or smaller, a DBP oil absorption amount of 80 cc/100 g or smaller, a volatilization rate of 2.0% or higher, and a pH not greater than 7, wherein the ink further comprises as a dispersing agent a polymer indispensably including hydrophilic, cationic and lipophilic components. The dispersed particle having a primary particle larger than 30 nm, a BET specific surface area larger than 200 m
2
/g, a DBP oil absorption amount larger than 80 cc/100 g, a volatilization rate lower than 2.0%, and a pH greater than 7 would easily be flocculated and make its dispersion unstable. The present inventors have discovered that the ink further comprising as a dispersing agent a polymer indispensably including hydrophilic, cationic and lipophilic components in addition to these requirements may have further improved stability.
Because the carbon black carries negative charge, and, when the above dispersing agent is employed, the dispersing agent is adsorbed with its lipophilic component and adhered with its cationic component to a surface of the pigment, and the hydrophilic portion is dissolved in an aqueous medium. It is conceivable that a pigment particle is stably retained in the aqueous medium by the action of these three portions of the dispersing agent.
The ink set forth in claim 3 is aqueous dispersoid ink comprising at least water, a water-soluble organic solvent, and a colorant, wherein a ratio R of Kt to Ko (=Kt/Ko) satisfies R≦5 where Ko (=Dm/Do) is a ratio of a maximum particle diameter Dm to an average particle diameter Do in sai
Ozaki Mitsuo
Suzuki Shigeharu
Tokuyo Shino
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