JPH1046076A - Water-based pigment-based printing liquid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject printing liquid good in pigment dispersibility, storage stability, water resistance and weatherability by mutually blending a pigment, dispersant and aqueous medium so that the absolute value of the ξ-potential on the surface of the pigment being dispersed comes to a specified level or higher. SOLUTION: This printing liquid which comprises a pigment, dispersant and aqueous medium is obtained by the following process: the pigment such as carbon black is added to a dispersion medium composed of a dispersant such as polyethylene glycol, water, and a water-soluble organic solvent such as glycerol or diethylene glycol, and the resultant mixture is preliminarily dispersed by use of a homogenizer under ultrasonication and then further dispersed by use of a hydraulic-type ultra-high-pressure homogenizer, thus affording the objective printing liquid excellent in pigment dispersibility, storage stability, water resistance and weatherability, with the absolute value of the ξ-potential on the surface of the pigment being dispersed at >=38mV.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording liquid, and more particularly to a recording liquid used for ink jet recording.

[0002]

2. Description of the Related Art Ink jet recording is a recording method capable of high-speed printing with low noise, and is a recording method that has been rapidly spreading recently. In such ink jet recording, recording is performed by discharging a recording liquid as small droplets by a method such as heating or pressurization and attaching the recording liquid to a recording material such as paper.

[0003] Dyes have been used as coloring materials for recording liquids. However, from the viewpoint of water resistance and weather resistance of the recorded matter, it is more advantageous to use a pigment than a dye. As the liquid medium, an aqueous liquid medium is more advantageous than a non-aqueous liquid medium from the viewpoint of bleeding on plain paper.

Therefore, an attempt has been made to prepare a recording liquid by using a pigment as a coloring material of the recording liquid and dispersing the pigment in an aqueous liquid medium (Japanese Patent Publication No. 1-15542).

[0005]

However, since the recording liquid in which the pigment is dispersed in the aqueous liquid medium is a heterogeneous system, aggregation of the pigment during long-term storage becomes a problem, and clogging is liable to occur. was there. That is, a recording liquid using a pigment as a coloring material has a problem in the dispersibility of the pigment and the storage stability thereafter, and satisfactory characteristics have not been obtained.

Accordingly, an object of the present invention is to provide a pigment-based recording liquid which is excellent in dispersibility of a pigment in an aqueous liquid medium and storage stability thereafter, and is also excellent in water resistance and weather resistance. is there.

[0007]

According to the present invention, there is provided a recording liquid comprising at least a pigment, a dispersant, an aqueous liquid medium,
And the absolute value of the zeta potential on the pigment surface is 38 m
V or more.

The recording liquid of the present invention comprises at least a pigment, a dispersant, and an aqueous liquid medium, but may optionally contain various additives. These various additives are appropriately added to the recording liquid as needed. Examples of such additives include a surface tension adjuster, an antioxidant,
Examples include an ultraviolet absorber, a stabilizer, and a fungicide.

By preparing a recording liquid in the combination as described above, a recording liquid giving a recorded matter having excellent dispersibility, storage stability, water resistance and weather resistance can be obtained.

(Function) If the dispersibility of the pigment is poor, the pigment particles become large particles. Further, even if the initial dispersibility is good, the dispersibility is reduced in a short time with the passage of time, and the one in which the pigment particles become large has poor storage stability.
When used as an ink jet recording liquid, the pigment particles are 2
It is necessary that the particle size is less than 00 nm, and when the particle size exceeds the above range, problems such as clogging occur. The pigment used in the present invention has an average particle size of less than 200 nm and is dispersed in an aqueous liquid medium.

In order to improve the storage stability of the recording liquid, it is necessary to improve the dispersion stability of the pigment in an aqueous liquid medium. Therefore, there is a method in which a charge is imparted to the surface of the pigment by adsorption of a dispersant or other methods, and the dispersion of the pigment in an aqueous liquid medium is stabilized by utilizing the repulsive force.

In the present invention, by adjusting the recording liquid so that the absolute value of the zeta potential on the surface of the pigment becomes 38 mV or more, the dispersion stability due to repulsion in an aqueous liquid medium is improved, and long-term storage is possible. A recording liquid can be obtained.

[0013]

DETAILED DESCRIPTION OF THE INVENTION As described above, the recording liquid of the present invention comprises at least a pigment, a dispersant, and an aqueous liquid medium, and is characterized in that the absolute value of the zeta potential on the surface of the pigment is 38 mV or more. Things.

Further, if necessary, various additives such as a surface tension modifier, an antioxidant, an ultraviolet absorber, a stabilizer, and a fungicide may be added.

[0015]

Next, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

Example 1 A dispersion medium was prepared using an aqueous liquid medium comprising a dispersant, water and a water-soluble organic solvent. The pigment and the dispersion medium were pre-dispersed for 1 hour using a homogenizer while performing ultrasonic treatment, and then a recording liquid was prepared using a hydraulic ultra-high pressure homogenizer. The mixing ratio is shown below.

[0017] Carbon black 5% by weight Pure water 81.5% by weight Sodium dodecyl sulfate 0.5% by weight Glycerin 5% by weight Polyethylene glycol 8% by weight

Example 2 A recording liquid was prepared in the same manner as in Example 1 with the following compounding ratio. In the parenthesis of the following copolymer, the polymerization ratio of each monomer is shown.

Carbon black 5% by weight Pure water 76% by weight Diethylene glycol 15% by weight Styrene-methacrylic acid-methyl methacrylate copolymer 3% by weight (20/35/45); molecular weight of about 40,000 triethylamine 1% by weight

Comparative Example 1 A recording liquid was prepared in the same manner as in Example 1 with the following compounding ratio.

5% by weight of carbon black 82% by weight of pure water 5% by weight of glycerin 8% by weight of polyethylene glycol

Comparative Example 2 A recording liquid was prepared in the same manner as in Example 1 with the following compounding ratio.

Carbon black 5% by weight Pure water 81.99% by weight Sodium dodecyl sulfate 0.01% by weight Glycerin 5% by weight Polyethylene glycol 8% by weight

Using the recording liquid thus obtained, evaluation was made by the following evaluation method.

Zeta potential measurement Zeta potential was measured using an electrophoretic light scattering altimeter LEZA-600 (manufactured by Otsuka Electronics Co., Ltd.).

Storage stability After leaving each recording liquid at 50 ° C. for 100 hours, the presence or absence of sedimentation of the pigment was examined. The results were evaluated as follows.

Without sedimentation ○ With sedimentation ×

The results of the evaluations of the recording liquids of Examples 1 and 2 and Comparative Examples 1 and 2 are shown in Table 1 below.

[0029]

[Table 1]

The recording liquid of each of the examples had an absolute value of the zeta potential of 38 mV or more, and showed good storage stability. On the other hand, the recording liquids of the respective comparative examples all showed an absolute value of the zeta potential of 38 mV or less, and were inferior in storage stability. As described above, the results of Examples and Comparative Examples indicate that the recording liquid of the present invention has high pigment dispersing ability and excellent storage stability.

[0031]

As described above, the recording liquid of the present invention comprises:
Since the absolute value of the zeta potential is 38 mV or more, it can be seen that the pigment dispersibility is excellent and the storage stability is excellent.

Thus, according to the present invention, it is possible to provide a recording liquid in which a pigment is used as a coloring material and which has excellent pigment dispersibility and subsequent storage stability. Further, by using a pigment as a coloring material, a recording liquid having excellent water resistance and weather resistance can be provided.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Maki Takizawa, 840 Takeno, Shimotomi, Tokorozawa City, Saitama Prefecture

Claims (1)

[Claims] 1. A recording liquid comprising at least a pigment, a dispersant, and an aqueous liquid medium, wherein the absolute value of the zeta potential on the surface of the dispersed pigment is 38 mV or more.