JP4389317B2 - Black aqueous ink composition and method for producing the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an aqueous ink composition, in particular, a black aqueous ink and a method for producing the same.
[0002]
[Prior art]
Black ink for inkjet recording is roughly classified into oil-based inks and water-based inks, but oil-based inks have problems in terms of odor and toxicity, and water-based inks are becoming mainstream.
However, since many conventional water-based inks use a water-soluble dye as a colorant, they have a drawback of poor water resistance and light resistance. In addition, when printing on so-called plain paper such as commonly used copy paper, bleeding called so-called feathering occurs, which causes a significant decrease in print quality.
[0003]
In order to remedy the above disadvantages, various water-based inks using carbon black having excellent water resistance and light resistance as a coloring material have been proposed in the past. For example, a water-soluble resin having a function as a binder and a dispersant can be used together with a water-soluble resin. -Various resin-dissolved inks and polymer latexes in which bon black is dispersed in an aqueous medium, or resin-dispersed inks containing carbon black as microcapsules have been proposed.
[0004]
As a water-based pigment ink for an inkjet printer, it is necessary to disperse the pigment as finely as possible. As an example of a specific resin-soluble water-based ink, Japanese Patent No. 2512861 discloses:
(A) Fill a 2-roll milling device with pigment and polymer dispersant;
(B) grinding to obtain a dispersion of pigment and polymer dispersant;
(C) comprising the step of dispersing this pigment dispersion in an aqueous carrier medium,
A method of adjusting an aqueous pigment ink for inkjet has been proposed.
In Japanese Patent Laid-Open No. 3-153775,
a) a solid pigment preparation containing a pigment and an acrylic resin having a carboxyl group,
b) an organic solvent dilutable with water,
c) consisting of water, and d) a wetting agent.
An aqueous ink composition for inkjet printing has been proposed.
However, even when these techniques are used, the ejection stability of ink in pigment fine particle formation and ink jet recording is not always sufficient.
[0005]
On the other hand, as a means for improving nozzle clogging and ink ejection stability in dye ink, Japanese Patent Application Laid-Open No. 57-145168 discloses an ink for an ink jet printer in which a water-soluble dye and a wetting agent are dissolved in water. Ink for inkjet printers has been proposed in which the concentration of the oil-soluble substance contained is 100 ppm or less, and specifically, purification of dyes is disclosed. However, as described above, water-soluble dyes have problems in water resistance and light resistance, and the influence of impurities in ink components in pigment ink has not been clarified so far.
[0006]
[Problems to be solved by the invention]
The problem to be solved by the present invention is to provide a black aqueous ink composition having excellent particle size, excellent dispersion stability, high density recording in ink jet recording, and excellent ejection stability, and a method for producing the same. It is in.
[0007]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present inventors have completed the present invention. That is, the present invention
(1) In a black aqueous ink containing at least carbon black and a water-soluble resin, a black ink composition characterized by using carbon black from which an organic solvent-soluble component has been removed is provided.
(2) By mixing and stirring carbon black and an organic solvent that is incompatible with water, the organic solvent soluble components adsorbed on the surface of the carbon black particles are extracted and removed, and then dispersed in an aqueous medium together with at least a water-soluble resin. The present invention provides a method for producing black aqueous ink.
[0008]
A commercially available general product can be used as the carbon black used in the present invention. Specifically, Mitsubishi Chemical Corporation products # 5, # 10, # 30, # 33, # 40, # 42, # 45, # 48, # 52, # 95, # 960B, # 2600, MA7, Products such as MA8, MA11, MA100, MA230, MA600, and # 260 (all are trade names) are listed.
The amount of carbon black to be used is not particularly defined, but it is preferably prepared so that the amount is usually 0.5 to 20% by mass in the finally obtained aqueous ink composition.
[0009]
Carbon black often adsorbs hydrophobic organic solvent-soluble components on the particle surface, and when dispersed in an aqueous medium as it is, the dispersion becomes insufficient. As a result, when an ink composition using the ink composition is used in an ink jet printer, non-ejection tends to occur. In particular, when the recording method is thermal ink jet recording, if the dispersion is insufficient, the boiling characteristics of the ink are greatly affected, and the print density is liable to decrease. The present invention improves these problems and enables a significant improvement in print quality.
[0010]
The hydrophobic organic solvent-soluble component adsorbed on the surface of the carbon black particles can be extracted and removed by mixing and stirring carbon black with an organic solvent incompatible with water. Although there is no restriction | limiting in particular about mixing stirring processing time, 0.5 to 2 hours are preferable at room temperature. The higher the processing temperature, the shorter the processing time.
The organic solvent that is not compatible with water is not particularly limited as long as it dissolves the hydrophobic organic solvent-soluble component adsorbed on the surface of the carbon black particles, but preferably has a low boiling point if possible. An aromatic organic solvent such as toluene or xylene is preferred.
[0011]
As the water-soluble resin, various resins such as a natural resin and a synthetic resin can be used. For example, natural resins include gelatin and shellac resins, and synthetic resins include styrene resins, acrylic resins, polyester resins, polyurethane resins, polyvinyl alcohol, polyvinyl pyrrolidone, and cellulose resins.
In the present invention, a water-soluble polymer electrolyte obtained by neutralizing a resin having an acid group with a basic substance is used. That is, the water-soluble resin used in the present invention is, for example, an acid having a radical copolymer of (meth) acrylic acid with at least one monomer selected from the group consisting of styrene, substituted styrene, and (meth) acrylic acid ester. It is obtained by neutralizing the group with a basic substance.
The acid value range of the resin having an acid group is preferably 50 to 280, and the molecular weight range is preferably 1000 to 50000.
Although content in the ink of the said water-soluble resin is not specifically limited, The range of 1-20 mass% is preferable.
[0012]
Examples of the basic substance for neutralizing the acid group of the resin include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide and lithium hydroxide, amines such as ammonia, triethylamine and morpholine, and triethanol. Alcohol amines such as amine, diethanolamine, and N-methyldiethanolamine can be used, but if the basic substance is highly volatile, nozzle clogging is likely to occur in ink jet recording. It is preferable to use the alcohol amine.
The amount of the basic substance used is not particularly limited as long as the resin having an acid group is water-soluble, but an amount corresponding to 50 to 200 mol% with respect to the number of moles of the acid group is preferable.
[0013]
In an aqueous medium for dispersing carbon black together with at least the water-soluble resin, it is preferable to use ion-exchanged water as the main component of water. If necessary, an organic solvent compatible with water may be added as a subcomponent.
[0014]
Moreover, various additives can be added as needed. For example, when used as an ink for an ink jet printer, it is preferable to add an anti-drying agent for the purpose of preventing clogging due to drying of the ink jet spray nozzle opening. As the drying inhibitor, an organic solvent having a boiling point equal to or higher than that of water and compatible with water is usually used. In the present invention, any conventionally known one can be used. For example, polyhydric alcohols such as ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, glycerin or their alkyl ethers.
Although the usage-amount of a drying inhibiting agent changes with the kinds, it is normally selected suitably from the range of 1-150 mass parts with respect to 100 mass parts of water.
In addition, when quick drying is required depending on the application, it is not always necessary to add an anti-drying agent. Conversely, for the purpose of accelerating drying, low-boiling organics such as lower alcohols, ketones and esters compatible with water are used. A solvent can also be used.
[0015]
Examples of additives other than drying inhibitors include water-soluble organic solvents and surfactants that have the effect of allowing the ink to penetrate into paper better, pH adjusters, dispersants, antifoaming agents, preservatives, chelating agents, and the like. . These additives may be added at the time of pigment dispersion or may be added after the pigment dispersion.
[0016]
The pigment dispersion method in the present invention is preferably a wet dispersion method. Specifically, a known wet dispersion apparatus such as a bead mill such as a paint shaker, a ball mill or a sand mill, or a beadless mill such as a nanomizer or a homogenizer can be used alone or in combination.
A pigment dispersion having a desired particle diameter can be obtained using the wet dispersion apparatus. The average particle diameter range of the dispersed pigment is preferably 0.01 to 1 μm, and more preferably 0.2 μm or less.
The black aqueous ink composition and the method for producing the same of the present invention can be applied to other inks in general, paints, color filters, electronic devices and the like in addition to aqueous inks for inkjet printers.
[0017]
【Example】
Next, the present invention will be described more specifically with reference to examples and comparative examples. In the following examples, “part” represents “part by mass”.
[0018]
(Purification of carbon black)
After adding 50 parts of Mitsubishi Carbon Black # 45L to 150 parts of toluene and stirring at room temperature for 1 hour, the carbon black was filtered off and vacuum dried.
[0019]
Example 1
10 parts of carbon black obtained by the above operation, aqueous solution of styrene-acrylic acid-methacrylic acid copolymer [copolymer composition (mass ratio): styrene / acrylic acid / methacrylic acid = 77/10/13, molecular weight: 8300, Acid value: 150, neutralizing agent: NaOH, neutralization rate: 100%, resin solid content: 12.5% by mass] 25 parts, diethylene glycol 20 parts, and ion-exchanged water 45 parts are mixed, and paint shaker (beads: 1 mm) The mixture was stirred for 3 hours using zirconia to obtain a carbon black dispersion.
[0020]
50 parts of the carbon black dispersion, 7 parts of glycerin, 3 parts of propylene glycol monopropyl ether, and 40 parts of ion-exchanged water were mixed and stirred, and filtered using a 1 μm membrane filter to obtain the black aqueous ink composition of the present invention. .
As a result of measuring the volume average particle size of carbon black in the obtained black aqueous ink with a laser Doppler particle size distribution meter “Microtrac UPA-150” manufactured by Nikkiso Co., Ltd., it was 0.08 μm, no aggregates, Even after standing at 60 ° C. for 3 days in a constant temperature tester, it had the same volume average particle size and showed stable dispersion.
In addition, using the ink left at 60 ° C. for 3 days and simultaneously driving all the nozzles using an inkjet printer “NOVAJET PRO” manufactured by ENCAD USA, a solid print image of 100 cm × 50 cm was printed. A homogeneous image with no printing unevenness was obtained. As a result of measuring the optical density of this image using a reflection densitometer “RD-918” manufactured by Macbeth, it was 1.22.
[0021]
(Comparative Example 1)
A black aqueous ink composition was obtained in the same manner as in Example 1 except that unpurified carbon black was used.
The volume average particle diameter of carbon black in the obtained ink is 0.10 μm, which is larger than that of Example 1. Also, after standing at 60 ° C. for 3 days in a constant temperature tester, it is caused by aggregation. Sedimentation of carbon black particles was observed.
In addition, when the solid print image was printed in the same manner as in Example 1 using the ink after being left at 60 ° C. for 3 days, the density unevenness occurred, and the average value of the optical density measured at an arbitrary plurality of positions of the image was also obtained. It was as low as 1.11. Innumerable white spots due to nozzle discharge failure were also observed.
[0022]
The ink of Example 1 had a smaller particle size and excellent dispersion stability, and was excellent in ejection stability even in printing by an ink jet printer, and a high-density and homogeneous image was obtained.
[0023]
【The invention's effect】
(1) A black aqueous ink composition using carbon black from which an organic solvent-soluble component that is incompatible with water is removed, and (2) carbon black, in a black aqueous ink containing at least carbon black and a water-soluble resin. And a hydrophobic organic solvent-soluble component adsorbed on the surface of the carbon black particles are extracted and removed by mixing and stirring an organic solvent that is incompatible with water and then dispersed in an aqueous medium together with at least a water-soluble resin. By the black aqueous ink production method characterized by the above, a black aqueous ink composition is obtained that is excellent in dispersion stability with fine particle size, excellent in ejection stability in ink jet recording, and capable of uniform recording at high concentration.

Claims (5)

In a black aqueous ink containing at least carbon black and a water-soluble resin, carbon black mixed and stirred with toluene is used, and the water-soluble resin is at least one selected from the group consisting of styrene, substituted styrene, and (meth) acrylic acid ester. and monomers, (meth) radical copolymer group having the ink jet printer for black aqueous ink composition, characterized in der Rukoto those obtained by neutralizing with a basic substance with acrylic acid. Carbon black and toluene are mixed and stirred, and the toluene is filtered off and dried. Then, the carbon black is dispersed in an aqueous medium together with at least a water-soluble resin. The water-soluble resin is styrene, substituted styrene, (meta ) at least one monomer selected from the group consisting of acrylic acid ester, a der Rukoto those obtained by neutralizing a (meth) an acid group having a radical copolymer of acrylic acid, with a basic substance A method for producing a black aqueous ink for an ink jet printer . The method for producing a black aqueous ink for an ink jet printer according to claim 2, wherein the basic substance is an alkali metal hydroxide. The method for producing a black aqueous ink for an ink jet printer according to claim 2 or 3, wherein an organic solvent having a boiling point equal to or higher than that of water and compatible with water is added to the aqueous medium. The method for producing a black aqueous ink for an inkjet printer according to any one of claims 2 to 4, wherein the black aqueous ink is used for thermal ink jet recording.