JP2006057032A - Pigment dispersion liquid for ink-jet recording and ink-jet recording ink produced by using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pigment dispersion liquid for ink-jet recording having high image density and excellent ejection stability and liquid stability and provide a technique relating to a pigment-based ink-jet recording ink produced by using the dispersion liquid. <P>SOLUTION: The pigment dispersion liquid for ink-jet recording at least contains carbon black, a dispersing agent and water. The carbon black has an average particle diameter (D50) of 50-120 nm and a PVC blackness of 10-30. The dispersing agent preferably contains at least one kind of compound expressed by general formula (1) (n is an integer of 20-300; R is a 1-20C alkyl, allyl or an aralkyl; and m is an integer of 0-7). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an inkjet pigment dispersion and an inkjet ink using the same, 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 simpler in process than other recording methods, so that it is easy to achieve full color, and there is an advantage that a high-resolution image can be obtained even with an apparatus having a simple configuration. As ink-jet inks, dye-based inks in which various water-soluble dyes are dissolved in water or a mixture of water and an organic solvent are used. Dye-based inks have excellent color tone, but are resistant to light. There was a disadvantage that was inferior in nature. 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 cause nozzle clogging more easily than dye-based inks. The 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.

  On the other hand, in recent years, it has been desired to reduce the particle size of the ink in order to increase the density of the image and improve the fineness. However, in dispersing the pigment ink, depending on the selection of the disperser method, the dispersion process conditions, etc. When the particle size is reached, the liquid tends to aggregate and the ejection stability cannot be guaranteed.

  In order to improve nozzle clogging and color gamut, it is necessary to reduce the average particle diameter of the pigment. However, styrene-acrylic copolymers and styrene-maleic acid copolymers (patent documents 1 and the like) that are currently widely used. ), An ink using a polymer dispersant such as sodium naphthalene sulfonate formalin condensate (Patent Document 2, etc.), polyethylene glycol alkylphenyl ether (Patent Document 3, etc.), polyethylene glycol alkylphenyl ether sulfate (Patent Document 4, etc.) ), Polyethylene glycol alkyl phenyl ether phosphate (Patent Document 5 etc.) and other inks using surfactants, the average particle size of the pigment is large, image density, color tone sharpness, ejection stability and liquid It was inferior in stability.

As for black ink, various proposals have been made for pigment-based ink liquids using carbon black. Self-dispersing carbon black (Patent Document 6), improvement of yellowing property of carbon black (Patent Document 7), reactive ink (Patent Document 8) as a black ink, etc. have been proposed, but it is still not sufficient. .
JP-A-56-147863 Japanese Patent Laid-Open No. 61-083267 JP-A-5-105837 JP-A-10-168367 Japanese Patent Laid-Open No. 10-88050 Japanese Patent Laid-Open No. 2002-3767 JP 2002-256193 A Japanese Patent Laid-Open No. 2002-241652

  The present invention has been made in view of the above circumstances, and has a high image density, an ink jet pigment dispersion excellent in ejection stability and liquid stability, and a technology related to a pigment-based ink jet ink using the same. 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 physicochemical characteristics of carbon black and the average particle diameter (D50) of the pigment dispersion, and have reached the present invention.
That is, this invention is the following (1)-(15).

(1) A pigment dispersion containing at least carbon black, a dispersant, and water, wherein the carbon black has an average particle diameter (D50) of 50 nm to 120 nm and the carbon black has a PVC blackness of 10 to 30. This is a pigment dispersion for inkjet.

（一般式（１）中、ｎは２０以上２００以下の整数を、Ｒは炭素数１〜２０のアルキル基、アリル基、又はアラルキル基を、ｍは０〜７の整数を表す。） (2) The inkjet pigment dispersion described in (1) above, wherein the dispersant contains at least one compound represented by the following general formula (1).

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

（一般式（２）中、ｎは２０以上２００以下の整数を表す。） (3) The inkjet pigment dispersion according to (2), wherein the dispersant contains at least one compound represented by the following general formula (2).

(In general formula (2), n represents an integer of 20 or more and 200 or less.)

(4) The inkjet pigment dispersion according to (3), wherein the dispersant contains a compound represented by the following formula.

(5) The inkjet pigment according to any one of (1) to (4), wherein the dispersant is contained in a ratio of 0.3 to 2 with respect to the carbon black 1 on a weight basis. It is a dispersion.
(6) The inkjet pigment dispersion according to any one of (1) to (5), wherein the content of the carbon black is 5% by weight to 50% by weight.

(7) A pigment-based inkjet ink comprising the pigment dispersion according to any one of (1) to (6).
(8) The pigment-based inkjet ink according to (7), wherein the content of carbon black in the pigment-based inkjet ink is 1% by weight to 20% by weight.

(9) An ink cartridge containing the pigment-based inkjet ink according to (7) or (8).
(10) An ink jet printing apparatus, wherein recording is performed by discharging the pigment-based ink-jet ink described in (7) or (8) onto an image support.
(11) The inkjet printing apparatus according to (10), wherein the inkjet printing apparatus is a piezo type.
(12) The inkjet printing apparatus according to (10), wherein the inkjet printing apparatus is a thermal type.

(13) An image forming method characterized in that printing is performed by an inkjet printing apparatus using the pigment-based inkjet ink described in (7) or (9).
(14) An image formed product printed by an inkjet printing apparatus using the pigment-based inkjet ink described in (7) or (9).
(15) The image formed product according to (14), wherein the image support of the image formed product is paper.

  The ink-jet pigment dispersion of the present invention and the ink-jet ink using the same 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 feature of the present invention is that the average particle diameter (D50) of the carbon black (pigment) particles is 50 nm to 120 nm. Even if the average particle diameter (D50) is less than 50 nm or exceeds 120 nm, the image density is lowered.
The average particle diameter (D50) in the present invention is a volume average particle diameter, and can be measured by a conventional method. For example, it is measured using a particle size analyzer UPA150 manufactured by Nikkiso Co., Ltd. Can do.
When the pigment is dispersed using a disperser, the average particle diameter (D50) can be controlled by the peripheral speed of the disperser rotating portion, the dispersion time, the dispersion flow rate, and the dispersion temperature. In the present invention, the average particle diameter (D50) of the pigment particles is 50 nm to 120 nm. If the peripheral speed of the rotating part of the disperser is too high, the pigment dispersion tends to aggregate, and if it is too low, the dispersion efficiency is poor and the productivity is lowered, so that it is preferably 6 m / s to 13 m / s.

Further, it is desirable that the dispersion is completed when the change in the average particle diameter of the dispersion liquid in the media mill for 5 minutes is less than 2%.
Furthermore, the dispersion flow rate is preferably 300 ml / min or more, and if it is less than 300 ml / min, the dispersion temperature rises, which is not preferable for dispersion stability. Further, the circulation type dispersion is not preferable because the particle diameter standard deviation tends to be large in short-time dispersion. Further, the dispersion temperature is preferably less than 10 ° C. during dispersion, and more preferably 4 ° C. to 8 ° C. has good dispersion stability.
When a bead mill is used as the disperser described below, the particle size can be controlled by adjusting the size of the dispersion medium (beads). In this case, in order to make the average particle diameter (D50) 50 nm to 120 nm, it is preferable to use beads having a diameter of about 0.1 mm to 1.0 mmφ, and more preferably 0.1 mm to 0.5 mmφ.

In the pigment dispersion of the present invention, the dispersant is preferably contained in a proportion of 0.3 to 2 with respect to the carbon black 1 on a weight basis. More preferably, the said ratio is 0.5-2 with respect to carbon black 1. FIG. By adopting the use amount of such a dispersant, the average particle diameter (D50) can be 50 nm to 120 nm, thereby providing a pigment dispersion having good image density, ejection stability, and liquid stability. be able to.
In addition, if the amount of the dispersant used is less than 0.3, the above effect is difficult to be achieved, and the storage stability of the pigment dispersion and the ink is inferior, and as a result, nozzle clogging tends to occur easily. If it is large, the viscosity of the pigment dispersion and ink tends to be too high, and printing by the ink jet system tends to be difficult.

（一般式（１）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、又はアラルキル基、ｍは０〜７の整数を表す。） 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 average particle diameter (D50) is 50 nm to 120 nm in a short time. It is preferable to obtain a pigment dispersion.

(In General Formula (1), n is an integer of 20 or more and 200 or less, R is an alkyl group having 1 to 20 carbon atoms, an allyl group, or an aralkyl group, and m is 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 50 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. Examples of the compound represented by the general formula (1) include POE (n = 40) β naphthyl ether, POE (n = 40) 1-methyl β naphthyl ether, POE (n = 60) 1,5-dimethyl β naphthyl ether. Among them, POE (n = 40) β naphthyl ether is more preferable.

Examples of the carbon black used in the pigment dispersion of the present invention include carbon black produced by a furnace method or a channel method.
The PVC blackness of the carbon black used in the present invention is preferably 10 to 30, more preferably 15 to 25, and is excellent in high image density, ejection stability, and liquid storage stability.
The PVC blackness in the present invention refers to the PVC blackness referred to in the physicochemical test method described on page 8 in the Mitsubishi Chemical Corporation carbon catalog “Mitsubishi Carbon Black / Mitsubishi Conductive Carbon Black”. Each of the values when kneading PVC resin with a roll and setting it as # 5: 1, # 40: 10, # 45: 20, MCF88: 30, # 900: 35, relative to the standard sample after sheeting. This is the index value of the blackness of the brand.

  In the pigment dispersion of the present invention, the concentration of carbon black 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.

The pigment dispersion of the present invention can be obtained by dispersing the carbon black, a dispersant, water, and various additives as necessary with a known disperser such as a sand mill, a ball mill, a roll mill, a bead mill, a nanomizer, or a homogenizer.
At this time, it is preferable that the amount of the dispersant used is set to a ratio of 0.3 or more and 2 or less with respect to the carbon black 1 on the weight basis as described above, and wet dispersion treatment is employed. The wet dispersion treatment referred to in the present invention is a so-called wet dispersion method in which a mixture of carbon black, a dispersant, water, and a water-soluble organic solvent as necessary is mixed with the sand mill, ball mill, roll mill, bead mill, nanomizer, homogenizer, etc. It is a process of pulverizing 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 and degassed with a filter, a centrifugal separator or the like. Can be obtained. The concentration of carbon black in the ink is preferably 1% by weight to 15% by weight with respect to the total amount of ink. If the amount is less than 1% by weight, the image density is low and the printed image lacks sharpness. If the amount is more than 15% 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 or more and 50% by weight or less, 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) the image on 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 further demonstrate this invention, this invention is not limited to these examples. In addition, the part in an Example is a basis of weight.

Example 1
Formula 1
Carbon black MCF88 (Mitsubishi Chemical Corporation) 150 parts Compound of general formula (1) (n = 40, m = 0) 110 parts Piionin A-51-B (Takemoto Yushi Co., Ltd.) 2 parts Distilled water 738 parts After premixing the mixture, it was dispersed in a disk-type bead mill (Shinmaru Enterprises KDL type) using 0.3 mm zirconia beads at a peripheral speed of 10 m / s and a liquid temperature of 8 ° C. for 120 minutes to obtain a pigment dispersion (A). Obtained.

Examples 2-5
The pigment dispersions (B), (C), (D), (E) were similarly prepared except that the carbon black of Example 1 was sequentially changed to # 850, # 45, # 990, and MA600 (manufactured by Mitsubishi Chemical Corporation). )

Examples 6-10
The dispersion times of Examples 1 to 5 were changed, and the particle size (D50) of each pigment dispersion was adjusted as shown in Table 1, and the pigment dispersions (F), (G), (H), (I), (J) Got.

Comparative Examples 1 and 2
Pigment dispersions (K) and (L) were obtained in the same manner except that the carbon black of Example 1 was sequentially changed to # 2300 and # 260 (manufactured by Mitsubishi Chemical Corporation).

Comparative Examples 3-7
The dispersion times of Examples 1 to 5 were changed and the particle size (D50) of each pigment dispersion was adjusted as shown in Table 1 to prepare pigment dispersions (M), (N), (O), (P), (Q). Got.

Comparative Example 8
Except for changing the dispersion time of Comparative Example 1, the particle size (D50) of the pigment dispersion was adjusted as shown in Table 1 to obtain a pigment dispersion (R).

Comparative Example 9
Except for changing the dispersion time of Example 4, the particle size (D50) of the pigment dispersion was adjusted as shown in Table 1 to obtain a pigment dispersion (S).

Comparative Example 10
Except for changing the dispersion time of Example 2, the particle size (D50) of the pigment dispersion was adjusted as shown in Table 1 to obtain a pigment dispersion (T).

The average particle diameter (D50) of carbon black at the end of dispersion of the pigment dispersions (A) to (T) was measured with a particle size analyzer UPA150 manufactured by Nikkiso Co., Ltd. The results are shown in Table 1.
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 the ink formulation 1, stirred for 30 minutes, filtered through a membrane filter having a pore size of 0.8 μm, and vacuum degassed to compare (k) to (t). An example ink was obtained.
Ink formula 1
Pigment dispersion (pigment concentration 15% by weight) 40.0 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 parts Distilled water 73.55 parts

  The average particle diameter (D50) of carbon black contained in the ink liquids (a) to (t) was measured in the same manner as in the case of the pigment dispersion. 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 results are shown in Table 1.

Image Density Image density is measured with a Xrite densitometer for color measurement of a solid image of an image sample.
Regarding ejection stability, after printing a printed matter, the printer was left in a 40 ° C. environment for one month with the printer head capped. 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 placed in a polyethylene container and sealed, and after storing at 70 ° C. for 3 weeks, 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 (15)

  A pigment dispersion containing at least carbon black, a dispersant, and water, wherein the carbon black has an average particle diameter (D50) of 50 nm to 120 nm, and the carbon black has a PVC blackness of 10 to 30, Inkjet pigment dispersion. 2. The inkjet pigment dispersion according to claim 1, wherein the dispersant contains at least one compound represented by the following general formula (1).

(In general formula (1), n represents an integer of 20 or more and 200 or less, R represents an alkyl group, an allyl group, or an aralkyl group having 1 to 20 carbon atoms, and m represents an integer of 0 to 7). The inkjet pigment dispersion according to claim 2, wherein the dispersant contains at least one compound represented by the following general formula (2).

(In general formula (2), n represents an integer of 20 or more and 200 or less.) 4. The inkjet pigment dispersion according to claim 3, wherein the dispersant contains a compound represented by the following formula.

  5. The inkjet pigment dispersion according to claim 1, wherein the dispersant is contained in a ratio of 0.3 to 2 with respect to the carbon black 1 on a weight basis.   The inkjet pigment dispersion according to any one of claims 1 to 5, wherein the content of the carbon black is 5 to 50% by weight.   A pigment-based inkjet ink comprising the inkjet pigment dispersion according to any one of claims 1 to 6.   The pigment-based inkjet ink according to claim 7, wherein the content of carbon black in the pigment-based inkjet ink is 1% by weight to 20% by weight.   An ink cartridge containing the pigment-based inkjet ink according to claim 7 or 8.   9. An ink jet printing apparatus, wherein recording is performed by discharging the pigment-based ink jet ink according to claim 7 or 8 onto an image support.   The inkjet printing apparatus according to claim 10, wherein the inkjet printing apparatus is a piezo type.   The inkjet printing apparatus according to claim 10, wherein the inkjet printing apparatus is a thermal type.   9. An image forming method comprising printing with an ink jet printing apparatus using the pigment-based ink jet ink according to claim 7.   An image formed product printed by an inkjet printing apparatus using the pigment-based inkjet ink according to claim 7 or 8.   The image formed article according to claim 14, wherein the image support of the image formed article is paper.