JP2998189B2 - Aqueous inkjet recording ink - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aqueous recording ink used in an ink jet printer that performs recording using a liquid ink.

[Conventional technology]

Conventionally, examples in which carbon black is used as a colorant for a recording liquid ink are described in JP-A-61-283875, JP-A-64-6074, and JP-A-1-31881.

[Problems to be solved by the invention]

Conventionally, when recording is performed on plain paper with an aqueous recording ink using carbon black as a coloring agent, the drying and fixing properties of the ink liquid were not sufficiently obtained, and high-speed recording was practically impossible. Also, depending on the recording paper, print quality deterioration such as bleeding occurred, and the tendency was more remarkable during high-resolution recording. Furthermore, compared to a uniform ink system using a dye as a colorant, aggregation of carbon black is more likely to occur and it is difficult to ensure reliability during recording such as clogging, which is also a major factor in achieving high resolution printing. It was an obstacle.
Similarly, when storing ink, securing long-term storage stability has been a major issue.

Therefore, the present invention solves such a problem,
One object is to provide a novel aqueous recording ink.

Another object of the present invention is to provide an aqueous recording ink capable of high-speed recording with excellent drying and fixing properties on plain paper.

Another object of the present invention is to provide an aqueous recording ink capable of preventing clogging at the time of recording, ensuring reliability, achieving high-resolution recording, and obtaining high-quality printing quality. It is in.

Another object of the present invention is to provide an aqueous recording ink which is excellent in stability without causing aggregation of carbon black in the ink during storage.

[Means for solving the problem]

The aqueous inkjet recording ink of the present invention comprises at least carbon black having a pH of 6 or less, a dispersant, and a pH of 6 or less.
A buffer which is higher and less than 8.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail. Conventionally, water has been mainly used as a solvent for ink because of its low viscosity, excellent safety, easy handling, low cost, and no odor. For the purpose of improving various properties, alcohols such as ethanol and propanol, polyhydric alcohols such as ethylene glycol, diethylene glycol and glycerin, or water-soluble organic solvents such as etherified products and esterified products thereof can be added. .

It is desired that carbon black as a coloring agent has good affinity for water as a main solvent, and has a hydrophilic functional group such as a hydroxyl group, a carboxyl group, or a sulfone group on its surface.
A material having many coating layers made of a substance having a hydrophilic functional group and having a pH of 6 or less is used. The pH of this carbon black refers to a value obtained by the following measurement method. That is, 3 g of carbon black to be measured and 100 g of distilled water are put into a beaker, the total weight is measured, and the whole is boiled for 1 hour.
After allowing to cool to room temperature, the total weight is measured, distilled water corresponding to the amount reduced by boiling is added, and the mixture is stirred and left standing for 10 minutes. The pH of the supernatant is measured with a glass electrode type pH meter.

Commercially available carbon black having a pH of 6 or less according to the above measurement method is, for example, # 2400B, # 2350, manufactured by Mitsubishi Kasei Kogyo Co., Ltd.
# 2200B, # 1000, MA100, MA7, MA8, MA11, Degussa special black 550, special black 350, special black 250, special black 100, columbian carbon raben 1255, raben 1200, raben 1170, raben 1060, Raven 1040, Raven 1030, Cabot Monarch 1300, Mogal L, Regal 400, Vulcan XC-72
However, the carbon black having a pH of 6 or less according to the present invention is not limited to the above-mentioned commercially available ones, and may be treated with various oxidizing agents and a surface modification method such as a plasma treatment to have a pH of 6 or less. Can also be used. The addition amount is preferably 1 to 30% by weight based on the total weight of the ink, and more preferably 3 to 12% by actual amount.

The dispersant that can be used in the present invention is an ordinary anionic surfactant or a polymer dispersant. Examples of the polymer dispersant include proteins such as gelatin and casein, natural gums such as gum arabic, glucoxides such as savonin, cellulose derivatives such as methylcellulose, carboxymethylcellulose and hydroxymethylcellulose, lignin sulfonates, and natural polymers such as ceramics. Polyacrylate, styrene-acrylic acid copolymer salt, vinylnaphthalene-acrylic acid copolymer salt, styrene-maleic acid copolymer salt, vinylnaphthalene-maleic acid copolymer salt, β
-Anionic polymers such as sodium salt of naphthalenesulfonic acid formalin condensate, polyphosphoric acid and the like, and nonionic polymers such as polyvinyl alcohol, polyvinylpyrrolidone and polyethylene glycol. One or more of these are used. They can be used in combination. The addition amount is preferably 0.3 to 30% by weight based on the total weight of the ink.
More preferably, it is 1 to 15% by weight.

The buffer having a pH of higher than 6 and lower than 8 used in the present invention is generally used variously for the purpose of preventing a decrease in pH due to contamination of hydrogen ions. Sodium, potassium borate dechloride-sodium hydroxide, sodium tetraborate-hydrochloric acid, potassium dihydrogen phosphate-sodium tetraborate, potassium dihydrogen phosphate-disodium hydrogen phosphate, ammonium chloride-aqueous ammonia, potassium borate borate- A system in which an appropriate amount of sodium carbonate or the like is mixed is known, and various systems can be used. The addition amount is 1 to 1 based on the total weight of the ink.
35% by weight is preferred. If the pH of the buffer is 6 or less,
It is expected that the electrical repulsion of the following carbon blacks is reduced, the dispersion state becomes unstable, and the aggregation of the particles is likely to occur particularly due to a change in the environmental temperature. Also, pH
If the buffer is 8 or more, it may hinder the protective colloid action of the dispersant and impede the dispersion stability, or may form alcohol-based water-soluble organic solvents and alcoholates in the ink, leading to deterioration of the ink performance. is there. Further, since the ink of the present invention has a high possibility of touching the human body, the pH is adjusted to 6 to 6 from the viewpoint of safety.
It is reasonable to adjust to around 8 neutral.

In addition to the above, if necessary, fungicides, preservatives, rust inhibitors,
It may contain an antifoaming agent, urea, thiourea, ethylene urea, etc. for nozzle drying prevention. Example 1 of the present invention
Table 1 shows the ink compositions of Comparative Example Nos. 5 and Comparative Examples 1 to 5. All numerical values in Table 1 are% by weight.

Buffer 1 in Table 1 was prepared by dissolving 0.025 mol of potassium dihydrogen phosphate and 0.025 mol of disodium hydrogen phosphate in 1 liter of pure water, and had a pH of 6.8. Buffer 2
Is a solution prepared by dissolving 0.2 mol of boric acid, 0.2 mol of potassium chloride and 0.2 mol of sodium hydroxide in 1 liter of pure water.
H = 7.8. Buffer 3 contains potassium hydrogen phthalate 0.2
Mol, 0.2 mol of sodium hydroxide dissolved in 1 liter of pure water, pH = 4.1. In addition, buffer 4
0.2 mol of sodium tetraborate and 0.1 mol of sodium hydroxide are dissolved in 1 liter of pure water, and the pH is 9.2.

In addition, as the carbon black having a pH of 6 or less,
Raven series made by Colombian Carbon, MA100
Is manufactured by Mitsubishi Kasei Kogyo Co., Ltd.
Carbon Black # 950 is manufactured by Mitsubishi Chemical Corporation.

Denkapovar B-03 further used as a dispersant
Is a partially saponified polyvinyl alcohol manufactured by Denki Kagaku Kogyo Co., Ltd., Labelin FHL is a sodium salt of β-naphthalenesulfonic acid formalin condensate manufactured by Daiichi Kogyo Seiyaku Co., Ltd., Joncryl-61J is a styrene-acrylic acid copolymer manufactured by Johnson Co. Shellac GBN, a 30.5% aqueous solution of salt, is a shellac resin manufactured by Gifu Shellac Works. The ink sample is prepared by dissolving twice as much a predetermined amount of dispersant in pure water, and after completely dissolving, carbon black is similarly added in twice the amount.
This mixed solution of the dispersant and carbon black is dispersed for 8 hours using a sand mill. Thereafter, the mixture is filtered through Toyo Filter Paper No. 2 to remove the giant particles to obtain a dispersion. Next, this dispersion was diluted with pure water, glycerin was added, and the buffer was added at a rate of 20 cc per minute with stirring to obtain an ink sample.

For the ink samples of Examples 1 to 5 and Comparative Examples 1 to 6 thus obtained, using a prototype 9-nozzle evaluator having a discharge nozzle diameter of 50 μm, a piezoelectric element drive voltage of 120 V, a drive frequency of 5 KHz, and a resolution of 200 dots / inch, 200 of print samples
Evaluation of print quality by observation with a microscope at × 2 magnification, evaluation of drying time to investigate the time until ink transfer stops after aligning the recording paper with the print surface after solid printing, and evaluation of fixability by strongly rubbing with a finger after leaving for 2 hours after solid printing Then, continuous ejection stability evaluation for investigating the presence or absence of missing dots during continuous printing for 12 hours was performed. In addition, when the glass sample bottle is closed, the ambient temperature is
The storage stability was evaluated by investigating the degree of aggregation of carbon black particles in a thermo-hygrostat at 85% for 30 days. Table 2 shows the results.

The recording paper used was Xerox PPC paper. The symbols in Table 2 are: ○: no problem, Δ: slightly problematic,
×: The result of a three-stage subjective evaluation of clearly having a problem is shown.

Samples of Examples 1 to 5 containing at least carbon black having a pH of 6 or less, a dispersant, and a buffer having a pH of higher than 6 and lower than 8 were all printed with high bleeding in all evaluations performed this time. The quality, drying property and fixing property were sufficient, and sufficient results were obtained in terms of dispersion stability during ejection and long-term storage. However, in the ink sample using carbon black having a pH of more than 6 as in Comparative Example 1 and the ink sample containing a buffer solution having a pH of 6 or less as in Comparative Example 2, dispersion stability could not be ensured, and storage stability was evaluated. Also, aggregation of carbon black was observed relatively early. In the ink sample containing the buffer solution having a pH of 8 or more as in Comparative Example 3, the print quality was significantly deteriorated, and the polymer material used as the dispersant tended to precipitate. In ink samples containing no buffer solution or dispersant as in Comparative Examples 4 and 5, carbon black aggregation during long-term storage in the former,
In the latter case, the carbon black particles were not sufficiently pulverized at the time of dispersion, and a large number of giant particles were observed at the time of filtration.

Furthermore, when the above-described print quality evaluation was performed on Xerox's new CK paper, R paper, and Honshu Paper's Yamayuri paper which are recycled paper with the aqueous recording ink of the present invention, the above three types of recycled paper were also evaluated. Good printing quality with little bleeding was obtained.

As mentioned above, although the Example of this invention was described in detail, the aqueous recording ink of this invention is not limited to these structures, materials, and manufacturing methods.

〔The invention's effect〕

ADVANTAGE OF THE INVENTION According to this invention, it has the effect that it can provide the aqueous recording ink excellent in safety which kept pH around 6-8 neutrality in the aqueous recording ink used for an inkjet printer. Further, there is an effect that it is possible to provide a water-based recording ink capable of performing high-speed recording with excellent drying and fixing properties on plain paper. Further, there is an effect that it is possible to provide a water-based recording ink that can prevent clogging at the time of recording, secure reliability, achieve high-resolution recording, and obtain high-quality printing quality. Further, even during long-term storage, there is an effect that aggregation of carbon black in the ink does not occur and an aqueous recording ink having excellent stability can be provided. Further, the present invention has an effect that high-quality printing quality with little bleeding or the like can be obtained on recycled paper.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-64-6074 (JP, A) JP-A-57-209972 (JP, A) JP-A-4-189878 (JP, A) JP-A-Heisei 4- 149285 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C09D 11/00-11/20

Claims (2)

(57) [Claims] 1. An aqueous ink jet recording ink comprising at least carbon black having a pH of 6 or less, a dispersant, and a buffer having a pH higher than 6 and lower than 8. 2. The aqueous ink jet recording ink according to claim 1, wherein the pH of the buffer is 6.8 to 7.8.