JP2006225510A - Pigment dispersion for inkjet and inkjet ink using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pigment dispersion having high image density, good discharge and liquid stability, and to provide techniques related to the pigment dispersion and inkjet ink using the same. <P>SOLUTION: The pigment dispersion comprises at least carbon black, a dispersant, and water, wherein in the particle size measurement by the dynamic light scattering, the accumulated volume percent of a carbon black particle size of 150 nm or more is 40% or more and that of 550 nm or more is 0%. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an inkjet pigment dispersion and an ink, and more particularly to an inkjet ink excellent in ejection stability and liquid stability. More specifically, the present invention relates to a black ink for ink jet which is improved in clogging of an ink jet head, provides a high image density, and has excellent storage stability.

The inkjet recording method is easy to make full color because the process is simpler than other recording methods, and there is an advantage that a high-resolution image can be obtained even with an apparatus having a simple configuration.
As an ink-jet ink, a dye-based ink in which various water-soluble dyes are dissolved in water or a mixture of water and an organic solvent is used, but the dye-based ink has excellent color tone sharpness, There was a disadvantage of poor light resistance.
On the other hand, pigment-based inks in which carbon black and various organic pigments are dispersed are actively studied because they are superior in light resistance compared to dye-based inks.
However, pigment-based inks tend to clog nozzles more easily than dye-based inks.
A pigment ink is generally prepared by preparing a dispersion in which a coloring material and a dispersant are pre-dispersed in an aqueous solvent such as water or alcohol, and then using a media-type disperser such as a sand mill. The dispersion is adjusted by performing a dispersion step and then diluting to a predetermined concentration.

  In a pigment-based water-based ink, a surfactant or a water-soluble resin is generally used to disperse a hydrophobic pigment, but the reliability of an obtained image is extremely poor. Thus, a technique for adding film-forming resin fine particles to the ink liquid for the purpose of improving the image quality is disclosed, but it is difficult to disperse a plurality of components finely and stably over a long period of time, and these fine particles are stably dispersed. If a large amount of a dispersing agent such as a surfactant is used for this purpose, problems such as generation of bubbles in the ink tank and the head and deterioration of the image quality may occur. In addition, for the purpose of improving the dispersibility, methods of changing the pigment surface to hydrophilic groups and using resins containing hydrophilic groups are being studied. There is a problem that dispersion becomes unstable and storage stability deteriorates.

  For the purpose of stabilizing dispersion, a method of dispersing a water-dispersible resin having a carboxyl group and a nonionic hydrophilic group in the molecule in water (see Patent Document 1), whether the water-soluble polymer and the surfactant have the same polarity Nonionic addition method (see Patent Document 2), Colored ionicity-containing polyester resin in water-based recording liquid and coloring agent having the same hydrophilic group polarity (see Patent Document 3), Dispersion polarity of pigment and resin fine particles The same method (see Patent Document 4) has been reported.

  Also, pigment particles having a particle size distribution in which at least 70% of the particles in the dispersion have a diameter of less than 0.1 μm and the other particles in the dispersion have a diameter equal to or less than 0.1 μm. A pigment dispersion containing aldehyde, naphthalene sulfonate dispersant, and / or an aqueous inkjet ink composition containing at least one sulfone solvent (see Patent Document 5). A recording liquid composed of an aqueous medium containing an ionic surfactant has been proposed. In Patent Documents 7 and 8, it is proposed to use AB or BAB block copolymer as a pigment dispersant. Further, Patent Document 9 proposes to use a specific pigment, a water-soluble resin, and a solvent.

On the other hand, as a pigment dispersion method using no dispersant, Patent Document 10 discloses a method of introducing a substituent containing a water-solubilizing group into carbon black, and Patent Document 11 discloses a method of polymerizing a water-soluble monomer or the like on the surface of carbon black. Patent Document 12 discloses a method for oxidizing carbon black. Further, Patent Document 13 discloses a method for ensuring water resistance and ejection stability with an ink containing carbon black subjected to oxidation treatment and a terpolymer composed of acrylic acid, styrene, and α-methylstyrene.
In addition, an inkjet recording liquid (see Patent Document 14) is proposed in which the volume average particle diameter of dispersed particles in the inkjet recording liquid is 30 to 200 nm.
However, although the above-described conventional ink liquid can obtain a high image density with respect to the color pigment ink, it is not yet satisfactory with respect to the black pigment ink.

JP-A-5-239392 JP-A-8-283633 JP 2000-63727 A JP 2001-81366 A JP-A-8-333531 Japanese Patent Laid-Open No. 56-147871 US Pat. No. 5,085,698 US Pat. No. 5,221,334 US Pat. No. 5,172,133 US Pat. No. 5,571,311 Japanese Patent Laid-Open No. 8-81646 JP-A-8-3498 JP-A-9-194775 JP 2000-144028 A

  The present invention has been made in view of the circumstances as described above, and has a high image density, a pigment dispersion excellent in ejection stability and liquid stability, and a technology related to the pigment dispersion and an inkjet ink using the pigment dispersion. The purpose is to provide.

As a result of intensive studies, the present inventors have found that the above problems can be solved by specifying the distribution range of the particle size of carbon black, and have reached the present invention.
That is, the above-mentioned problem is (1) of the present invention, “In the particle size measurement by dynamic light scattering method, which consists of at least carbon black, a dispersant, and water, the cumulative volume percentage of carbon black particle diameter of 150 nm or more is 40% or more. And a cumulative percentage of 550 nm or more is 0%.
(2) “Inkjet pigment dispersion according to item (1), wherein the dispersant is a surfactant”;
(3) “Inkjet pigment dispersion according to item (1) or (2), wherein the dispersant uses at least one compound represented by the following general formula (1): ;

（式中、ｎは２０以上２００以下の整数、Ｒは炭素数１〜２０のアルキル基、アリル基、アラルキル基、ｍは０〜７の整数を表わす。）」；
（４）「前記分散剤が、重量基準として顔料１に対し０．１以上２以下の割合で含まれることを特徴とする前記第（１）項乃至第（３）項のいずれかに記載のインクジェット用顔料分散液」；
（５）「前記カーボンブラックの含有量が５重量％から５０重量％であることを特徴とする前記第（１）項乃至第（４）項のいずれかに記載のインクジェット用顔料分散液」によって解決される。

(Wherein n is an integer of 20 to 200, R is an alkyl group having 1 to 20 carbon atoms, an allyl group, an aralkyl group, and m is an integer of 0 to 7).
(4) “The dispersant is contained in a ratio of 0.1 to 2 with respect to the pigment 1 on a weight basis, according to any one of the items (1) to (3),” Inkjet pigment dispersion ";
(5) By the “inkjet pigment dispersion according to any one of (1) to (4) above, wherein the carbon black content is from 5 wt% to 50 wt%” Solved.

In addition, the above-mentioned problem is (6) of the present invention “consisting of at least carbon black, a dispersant, and water, and the cumulative volume percentage of the carbon black particle diameter of 150 nm or more in the particle diameter measurement by the dynamic light scattering method is 40% or more. Ink-jet ink, characterized in that the cumulative percentage of 550 nm or more is 0% ";
(7) “The inkjet ink according to item (6), wherein the dispersant is a surfactant”;
(8) “The inkjet ink according to item (6) or (7), wherein the dispersant uses at least one of compounds represented by the following general formula (1);

（式中、ｎは２０以上２００以下の整数、Ｒは炭素数１〜２０のアルキル基、アリル基、アラルキル基、ｍは０〜７の整数を表わす。）」；
（９）「前記分散剤が、重量基準として顔料１に対し０．１以上２以下の割合で含まれることを特徴とする前記第（６）項乃至第（８）項のいずれかに記載のインクジェット用インク」；
（１０）「前記カーボンブラックの含有量が、１重量％から２０重量％であることを特徴とする前記第（６）項乃至第（９）項のいずれかに記載のインクジェット用インク」により解決される。

(Wherein n is an integer of 20 to 200, R is an alkyl group having 1 to 20 carbon atoms, an allyl group, an aralkyl group, and m is an integer of 0 to 7).
(9) “The dispersant is contained in a ratio of 0.1 to 2 with respect to the pigment 1 on a weight basis, according to any one of the items (6) to (8),” Inkjet ink ";
(10) Solved by “ink jet ink according to any one of items (6) to (9), wherein content of carbon black is 1 wt% to 20 wt%” Is done.

Furthermore, the above-mentioned problem is (11) “an ink cartridge containing the ink-jet ink according to any one of (6) to (10)”;
(12) “Inkjet printing apparatus, wherein recording is performed by ejecting the inkjet ink according to any one of (6) to (10) above onto an image support”;
(13) "The inkjet printing apparatus according to (12), wherein the inkjet printing apparatus is a piezo system";
(14) "The inkjet printing apparatus according to item (12), wherein the inkjet printing apparatus is a thermal system";
(15) “An image forming method characterized by printing with an inkjet printing apparatus using the inkjet ink according to any one of (6) to (10)”;
(16) “Image formed product printed with an inkjet printing apparatus using the inkjet ink according to any one of (6) to (10)”;
(17) The problem is solved by “the image formed article according to item (16), wherein the image support of the image formed article is paper”.

  The pigment dispersion and ink of the present invention have a high image density, and are superior to conventional ones in ejection stability and ink storage stability.

The present invention will be described in more detail below.
As described above, the present invention is characterized in that the ink liquid is composed of at least carbon black, a dispersant, and water, and the cumulative volume percentage of the carbon black particle diameter of 150 nm or more is 40% or more in the particle diameter measurement by the dynamic light scattering method. And the cumulative percentage of 550 nm or more is 0%.
When the cumulative volume percentage of 150 nm or more of the carbon black particle diameter is less than 40%, a high image density cannot be obtained, and when the cumulative percentage of 550 nm or more exceeds 0%, ejection stability such as nozzle clogging is deteriorated.
In addition, the particle size measurement in this invention is measured using the Nikkiso Co., Ltd. particle size analyzer UPA150. The particle diameter of the present invention is a particle diameter by volume distribution.
When the pigment is dispersed using a disperser, the particle size can be controlled by the peripheral speed of the rotating part of the disperser, the dispersion time, the dispersion flow rate, and the dispersion temperature.

  In the pigment dispersion of the present invention, the dispersant is preferably contained in a ratio of 0.1 to 2 with respect to the carbon black 1 on a weight basis. More preferably, the ratio is 0.37 to 1 with respect to carbon black 1. By adopting such a use amount of the dispersant, the cumulative volume percentage of 150 nm or more of the pigment particles can be 40% or more and the cumulative percentage of 550 nm or more can be 0%. A pigment dispersion having good stability and liquid stability can be provided.

  In addition, it is difficult to achieve the above effect when the amount of the dispersant used is less than 0.1, and the storage stability of the pigment dispersion and the ink is inferior, and as a result, nozzles tend to clog. If it is greater than 2, the viscosity of the pigment dispersion and the ink tends to be too high, and printing by the ink jet method tends to be difficult.

  The dispersant used in the pigment dispersion of the present invention is not particularly limited, but by using at least one compound represented by the following general formula (1), the pigment particles have a cumulative volume percentage of 150 nm or more in a short time. The cumulative percentage of 40% or more and 550 nm or more can be 0%, and a stable dispersion state can be maintained for a long period of time, which is preferable.

（式中、ｎは２０以上２００以下の整数、Ｒは炭素数１〜２０のアルキル基、アリル基、アラルキル基、ｍは０〜７の整数を表わす。）

(In the formula, n represents an integer of 20 to 200, R represents an alkyl group having 1 to 20 carbon atoms, an allyl group, an aralkyl group, and m represents an integer of 0 to 7).

In the general formula (1), n is preferably 20 or more and 200 or less, more preferably 30 or more and 60 or less. When n is less than 20, the dispersion stability tends to decrease. When n is greater than 200, the viscosity of the dispersion liquid and ink tends to increase.
Among them, POE (n = 40) β-naphthyl ether in which n is 40 and m is 0, POE (n = 40) 1-methyl β-naphthyl ether in which n is 40 and m is 1, n is 60 POE (n = 60) 1-5 dimethyl β naphthyl ether and the like in which m is 2 is more preferable.

Examples of the carbon black pigment used in the pigment dispersion of the present invention include carbon black produced by a furnace method or a channel method.
For example, use commercially available products such as # 45L, MCF88, # 990, MA600, # 850 (more from Mitsubishi Chemical), NIPEX150, NIPEX160, NIPEX180 (more from Degussa), REGAL400R, REGAL600R, MOGUULL (more from Cabot) Can do.

  In the pigment dispersion of the present invention, the pigment concentration is preferably 5% by weight or more and 50% by weight or less based on the total amount of the dispersion. If it is less than 5% by weight, the productivity is inferior, and if it is more than 50% by weight, the viscosity of the pigment dispersion tends to be too high and dispersion tends to be difficult.

  Moreover, various additives other than water can be mix | blended with the pigment dispersion liquid of this invention. For example, as water-soluble organic media, alcohols such as methanol, ethanol, 1-propanol and 2-propanol, polyhydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol and glycerin, N-methylpyrrolidone, 2-pyrrolidone and the like Pyrrolidone derivatives, ketones such as acetone and methyl ethyl ketone, alkanolamines such as monoethanolamine, diethanolamine, and triethanolamine, and nonionic, anionic, cationic, amphoteric surfactants and preservatives.

Carbon blacks with a primary average particle size of 10 nm to 0.9 μm (900 nm) are generally known, but those with a small primary average particle size have high surface activity and are usually secondary agglomerated. The carbon black dispersion of the present invention is different from the conventional method for preparing a carbon black dispersion, and the carbon black, dispersant, water, and various additives as necessary are mixed with a sand mill or ball mill. It can be obtained by sufficiently dispersing with a known disperser such as a roll mill, a bead mill, a nanomizer, a homogenizer or the like and, when necessary, filtration using a predetermined mesh.
At this time, it is preferable that the amount of the dispersing agent is 0.1 to 2 with respect to the pigment 1 on the weight basis as described above, and wet dispersion treatment is employed. The wet dispersion treatment referred to in the present invention means that a mixture of a pigment, a dispersant, water and, if necessary, a water-soluble organic solvent is finely divided by a so-called wet dispersion method using the sand mill, ball mill, roll mill, bead mill, nanomizer, homogenizer or the like. It is a process of crushing and dispersing.

The pigment dispersion of the present invention thus obtained can be suitably used particularly as a pigment-based inkjet ink.
The pigment-based ink-jet ink is a known method, for example, the pigment dispersion of the present invention, water, a water-soluble organic solvent, a surfactant and the like are stirred and mixed, and coarse particles are filtered with a filter, a centrifugal separator or the like. And obtained by degassing. The concentration of carbon black in the ink is preferably 1% by weight to 20% by weight with respect to the total amount. If the amount is less than 1% by weight, the image density is low, so that the printing is not clear. If the amount is more than 20% by weight, not only the viscosity of the ink tends to increase but also nozzle clogging tends to occur. Further, the ink can be blended with a material equivalent to the material described as the additive to the pigment dispersion as required.
For example, the content of the water-soluble organic solvent is 0% by weight to 50% by weight, preferably 5% by weight to 40% by weight, and more preferably 10% by weight to 35% by weight with respect to the total amount of the ink.

  The pigment-based inkjet ink of the present invention thus obtained contains, for example, an inkjet recording ink set that forms an image on an image support by superimposing a plurality of different hue inks in order to form a color image. The ink cartridge can be suitably used.

The pigment-based ink-jet ink of the present invention can be image-formed by an ink-jet printing apparatus that forms an image by discharging (recording) it onto an image support such as paper.
Examples of the printing method include a continuous jet type and an on-demand type. Examples of the on-demand type include a piezo method, a thermal method, and an electrostatic method.

EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further, this invention is not limited to these examples. The parts in the examples are based on weight.
Example 1
(Prescription 1)
Carbon black # 45L (Mitsubishi Chemical Co., Ltd.) 150 parts POE (n = 40) β-naphthyl ether 56 parts Pionein A-51-B (Takemoto Yushi Co., Ltd.) 2 parts Distilled water 792 parts Disc after premixing the above mixture After dispersing for 5 minutes at a peripheral speed of 10 m / s and a liquid temperature of 8 ° C. using 0.3 mm zirconia beads in a type bead mill (Shinmaru Enterprises KDL type batch type), a centrifuge (manufactured by Kubota Corporation) Coarse particles were centrifuged with Model-3600), and the cumulative volume percentage of 150 nm or more and the cumulative percentage of 550 nm or more of the particle diameter of the carbon black dispersion were adjusted as shown in Table 2 to obtain a pigment dispersion (A). For the particle size, the dispersion time was changed (the other conditions were the same in each example), and the target particle size was controlled.

Examples 2-5
Pigment dispersions (B) and (C) in the same manner except that the carbon black of Example 1 was changed to MCF88, # 990, (Mitsubishi Chemical Corporation), NIPEX160-IQ, NIPEX180-IQ (Degussa). , (D), (E) were obtained.

Examples 6-10
The dispersion time of Example 1 was changed, and the cumulative volume percentage of 150 nm or more and the cumulative percentage of 550 nm or more of the particle diameter of each pigment dispersion liquid were adjusted as shown in Table 2, and the pigment dispersion liquids (F), (G), (H) , (I), (J) were obtained.
The average particle size of the dispersion was measured with a particle size analyzer UPA150 manufactured by Nikkiso Co., Ltd. The results are shown in Table 2.

Comparative Examples 1-5
By changing the dispersion time of Example 1 and adjusting each pigment dispersion as shown in Table 2, pigment dispersions (K), (L), (M), (N), and (O) were obtained.

Comparative Examples 6-10
Each pigment dispersion was similarly adjusted as shown in Table 2 except that the dispersion time in Example 1 was changed and centrifugation was not performed, and pigment dispersions (P), (Q) (R), (S), (T )
The dispersion conditions in each of these examples are as shown in the following table.

  Using the pigment dispersion liquids (A) to (J) obtained by the above method, an ink liquid was prepared according to the following ink formulation 1, and after stirring for 30 minutes, filtered through a membrane filter having a pore size of 0.8 μm and vacuum degassed. Ink liquids of Examples (a) to (j) were obtained. Similarly, an ink was prepared from the pigment dispersions (K) to (T) according to ink formulation 1, stirred for 30 minutes, filtered through a membrane filter having a pore size of 1.2 μm, and vacuum degassed to compare (k) to (t). An example ink was obtained.

(Ink formula 1)
Pigment dispersion (pigment concentration 15%) 100.0 parts Glycerin 7.5 parts Diethylene glycol 22.5 parts 2-ethyl-1,3-hexanediol 3.0 parts 2-pyrrolidone 3.0 parts Polyoxyethylene (3) Alkyl (C13) ether sodium acetate
0.45 part distilled water 13.55 part The average particle diameter of the pigment contained in the ink liquids (a) to (t) was measured. Further, printing was performed on a PPC paper 4024 manufactured by Xerox Co., Ltd. using an inkjet printer MJ-930C manufactured by EPSON, and the ejection stability and the printed image were measured with an Xrite densitometer.

The image density is measured with an Xrite densitometer for color measurement of a solid image of an image sample.
-Discharge stability About discharge stability, after printing printed matter, the printer was left to stand in a 40 degreeC environment for one month in the state capped with the printer head. Whether the discharge state of the printer after being left is restored to the initial discharge state was evaluated by the following number of cleaning operations.
○: Recovered by one operation.
Δ: Recovered by 2 to 3 operations.
X: No recovery was observed even after three or more operations.
-Ink storage stability Each ink was put in a polyethylene container, sealed, stored at 70 ° C. for 3 weeks, and the particle size, surface tension, and viscosity were measured and evaluated according to the rate of change from the initial physical properties as follows.
A: Less than 5% (all items of particle size, surface tension, viscosity)
○: 5 to 10% (all items of particle size, surface tension, viscosity)
Δ: Within 30% (all items of particle size, surface tension, viscosity)
X: Over 50% (particle size, viscosity)

Claims (17)

It consists of at least carbon black, a dispersant, and water, and in the particle size measurement by dynamic light scattering method, the cumulative volume percentage of the carbon black particle diameter of 150 nm or more is 40% or more and the cumulative percentage of 550 nm or more is 0%. An inkjet pigment dispersion characterized by comprising: The inkjet pigment dispersion according to claim 1, wherein the dispersant is a surfactant. 3. The inkjet pigment dispersion according to claim 1, wherein the dispersant uses at least one compound represented by the following general formula (1).

(In the formula, n represents an integer of 20 to 200, R represents an alkyl group having 1 to 20 carbon atoms, an allyl group, an aralkyl group, and m represents an integer of 0 to 7). The inkjet pigment dispersion according to any one of claims 1 to 3, wherein the dispersant is contained in a ratio of 0.1 to 2 with respect to the pigment 1 on a weight basis. 5. The inkjet pigment dispersion according to claim 1, wherein a content of the carbon black is 5% by weight to 50% by weight. It consists of at least carbon black, a dispersant, and water, and the cumulative volume percentage of carbon black particle diameter of 150 nm or more is 40% or more and the cumulative percentage of 550 nm or more is 0% in the particle size measurement by dynamic light scattering method. Ink-jet ink characterized by that. The inkjet ink according to claim 6, wherein the dispersant is a surfactant. The inkjet ink according to claim 6 or 7, wherein the dispersant uses at least one of the compounds represented by the following general formula (1).

(In the formula, n represents an integer of 20 to 200, R represents an alkyl group having 1 to 20 carbon atoms, an allyl group, an aralkyl group, and m represents an integer of 0 to 7). The ink-jet ink according to any one of claims 6 to 8, wherein the dispersant is contained in a ratio of 0.1 to 2 with respect to the pigment 1 on a weight basis. The ink-jet ink according to any one of claims 6 to 9, wherein the content of the carbon black is 1 wt% to 20 wt%. An ink cartridge containing the ink-jet ink according to any one of claims 6 to 10. 11. An ink jet printing apparatus that performs recording by ejecting the ink jet ink according to claim 6 onto an image support. The inkjet printing apparatus according to claim 12, wherein the inkjet printing apparatus is a piezo type. The inkjet printing apparatus according to claim 12, wherein the inkjet printing apparatus is a thermal type. 11. An image forming method, wherein printing is performed by an ink jet printing apparatus using the ink jet ink according to any one of claims 6 to 10. An image formed product printed by an ink jet printing apparatus using the ink jet ink according to claim 6. The image formed article according to claim 16, wherein the image support of the image formed article is paper.