JPH04149286A - Water-base recording ink - Google Patents

Abstract

PURPOSE:To provide the subject ink containing at least specific carbon black, dispersing agent and a specific pH buffering solution, having excellent drying characteristics and fixing property to plain paper, free from trouble of nozzle clogging in recording and having excellent storage stability and high safety. CONSTITUTION:The objective ink contains at least (A) preferably 1-30wt.% (especially 3-12wt.%) of carbon black having pH of <=6, (B) preferably 0.3-30wt.% (especially 1-15wt.%) of a dispersing agent composed of conventional anionic surfactant and a polymer dispersing agent and (C) preferably 1-35wt.% of a buffering solution having pH of 6-8 and composed of potassium dihydrogen phosphate-sodium hydroxide, sodium tetraborate-hydrochloric acid, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an aqueous recording ink used in an inkjet printer that performs recording using liquid ink.

[Conventional technology]

Conventionally, examples of using carbon black for coloring recording liquid ink are JP-A-61-285875 and JP-A-6
．． 1. -6074. It is described in JP-A-1-51881 and the like.

[Problem to be solved by the invention]

Conventionally, when recording on plain paper with water-based recording ink that uses carbon black as a colorant, the ink liquid does not have sufficient drying and fixing properties, making high-speed recording virtually impossible. Ta. Further, depending on the recording paper, print quality deterioration such as blurring may occur, and this tendency is even more pronounced during high-resolution recording. Furthermore, compared to uniform ink systems that use dyes as colorants, carbon black is more likely to aggregate (clogging, etc.) and it is difficult to ensure reliability during recording, which is also a major factor in achieving low-resolution recording. Similarly, when storing a single ink, ensuring long-term storage stability was a major issue.

SUMMARY OF THE INVENTION The present invention is intended to solve these problems, and one of its objects is to provide a new aqueous recording ink.

Another object of the present invention is to provide an aqueous recording ink that has good drying properties and porous properties and is capable of high-speed recording on plain paper.

Another object of the present invention is to provide an aqueous recording ink that can prevent clogging during recording, ensure reliability, achieve high resolution recording, and obtain high quality printing. There is a particular thing.

Another object of the present invention is to provide an aqueous recording ink which does not cause aggregation of Kerr-Zen black in the ink during storage and has excellent stability.

[Means to solve the problem]

The aqueous recording ink of the present invention is characterized in that it contains at least carbon black with a pH of 6 or less, a dispersant, and a buffer solution with a pH of 6 to 8.

〔Example〕

Examples of the present invention will be described in detail below. Conventionally, water has been mainly used as a solvent for ink because of its low viscosity, excellent safety, ease of handling, low cost, and lack of odor. In addition, water-soluble organic solvents such as alcohols such as ethanol and propatool, polyhydric alcohols such as ethylene glycol, diethylene glycol, and glycerin, or their ethers and esters are added for the purpose of improving properties. I can do that.

Carbon black, which is a coloring agent, is desired to have good affinity with water, which is the main solvent. It has many coating layers of substances and has a pH of 6 or less. The pH of this carbon black refers to a value obtained by the following measuring method. That is, 52 carbon blacks and 100 distilled water to be measured.
Put 1 into a beaker, measure the total weight, and boil it for 1 hour. After cooling to room temperature, measure the weight of the gold, add distilled water equal to the flow rate due to boiling, stir, and let stand for 10 minutes. (Measure with a meter.

Commercially available carbon blacks with a pH of 6 or less according to the above measurement method are, for example, #2400B manufactured by Jōkaku Kasei Kogyo Co., Ltd.
215D, #2200B, $10DO, MA100. M
A7. MA8. MA11 Texa special black 550. Special 7' Rank 55D, Sue: Sial Flak 250° Special Black 100. U-Pen 1255m Raven 12oo manufactured by Columbian Carbon Co., Ltd.
, Sieben 11f 0. Raven 1060. Sieben 10
401 Raven 1030. Cabot Monarch 13
00. Mogul L, Ji-Gal 400. Palcan 10-F2 and the like can be used, but the carbon black of the present invention with a pH of 6 or less is not limited to the commercially available ones mentioned above, and can be treated with various oxidizing agents and surface modification methods such as plasma treatment, Those with a pH of 6 or less can also be used. The amount added is preferably 1 to 50% by weight, more preferably 5 to 12% by weight based on the total weight of the ink.

The dispersant that can be used in the present invention is a conventional anionic surfactant or a polymeric fractional agent. Examples of polymeric dispersants include proteins such as gelatin and casein, natural gums such as gum arabic, cellulose derivatives such as glucoquine methyl cellulose such as saponin, carboxymethyl cellulose and hydroxymethyl cellulose, and lignin sulfonates.

Natural polymers such as ceramics, polyacrylic m salts.

Styrene-acrylic acid copolymer salt, vinyl naphtha V7-
Akvrurl copolymer salt, styrene-maleic acid copolymer salt, vinylnaphthalene-maleic acid copolymer salt, β
- Sodium salt of naphthalene sulfonic acid formalin condensate, anionic polymers such as polyphosphoric acid, nonionic polymers such as polyvinyl alcohol, polyvinylpyrrolidone, polyethyl/glycol, and one of these,
Alternatively, two or more types can be used in combination. The amount added is preferably 0.5 to 50% by weight, more preferably 1 to 15% by weight, based on the total weight of the ink.The buffer solution with a pH of 6 to 8 used in the present invention generally contains hydrogen ions. Potassium dihydrogen phosphate-sodium hydroxide, potassium decachloride-sodium hydroxide,
Mix appropriate amounts of sodium tetraphosphate-hydrochloric acid, potassium dihydrogen phosphate-sodium tetraphosphate, potassium dihydrogen phosphate-disodium hydrogen phosphate, ammonium dihydrogen phosphate-aqueous ammonia, oxalic acid + potassium chloride-sodium carbonate, etc. Such systems are known and can be used in various ways. The amount added is preferably 1 to 65% by weight based on the total weight of the ink. When the pH of the buffer solution is 6 or less, it is expected that the electrical repulsion of carbon black with a pH of 6 or less will decrease.
The dispersion state becomes unstable and particle aggregation is likely to occur due to changes in the environmental temperature at 1%.Also, in the case of a buffer solution with a pH of 8 or higher, it may interfere with the protective colloid effect of the dispersant and inhibit the stability of the dispersion. In addition, alcohol-based water-soluble organic solvents and alcoholates may be generated in the ink, leading to deterioration of ink performance.Furthermore, the ink of the present invention has a high possibility of coming into contact with the human body, so from the viewpoint of safety, It is reasonable to adjust the pH to around neutrality of 6-8.

In addition to the above, if necessary, a fungicide, a preservative, a rust preventive, an antifoaming agent, and a nozzle prevention agent such as urea, urea, ethylene urea, etc. can be contained.

Table 1 shows the ink compositions of Examples 1 to 5 of the present invention and Comparative Examples 1 to 5. All numerical values in Table 1 are weight %.

Buffer 1 in Table 1 is potassium dihydrogen phosphate 0025
0.025 moles of disodium hydrogen phosphate are dissolved in 1 liter of pure water, and the pH is -68. Buffer 2 contains 02 mol of oxalic acid, 0.2 mol of potassium chloride,
It is made by dissolving 042 moles of sodium hydroxide in 1 liter of pure water, and the pH is 78. Buffer 6 is made by dissolving 02 moles of potassium hydrogen phthalate and 02 moles of sodium hydroxide in 1 liter of pure water, and has a pH of 4.1.Furthermore, buffer solution 4 contains 02 moles of sodium tetraborate. , 01 mol of sodium hydroxide dissolved in 1 liter of pure water, pH=92.

In addition, the carbon black with a pH of 6 or less used was
The Raven series is made by Columbian Carbon, MA1.
00 is manufactured by Mitsubishi Chemical Industries, Ltd., and p used as a comparative example.
The aa[l carbon bra #950 is manufactured by Mitsubishi Chemical Industries, Ltd.

Furthermore, Denkapoval B-03 is used as a dispersant.
' Partially saponified polyvinyl alcohol manufactured by Ki Kagaku Kogyo Co., Ltd., Labelin F HL c, Sodium salt of β-naphthalene sulfonic acid formalin condensate manufactured by Dai-Ko M Pharmaceutical Co., Ltd.
Di-Nkuriru 61J is a 5% aqueous solution of styrene-acrylic acid copolymer Dan3α manufactured by Jinson Co., Ltd., and shellac GBN.
is seven lac resin manufactured by Chufu Shellac Manufacturing Co., Ltd. For the ink sample, first, double the predetermined amount of dispersant is dissolved in pure water, and after complete dissolution, carbon black is added in the same amount twice the predetermined amount. This dispersant and carbon black mixture is dispersed for 8 hours using a sand mill.Then, to remove large particles, it is filtered through Toyo Roshi No. 2 to obtain a dispersion.Next, this dispersion is diluted with pure water and glycerin is added. In addition, a buffer solution was added at a rate of 2 occ per minute while stirring to prepare an ink sample.

The ink samples of Examples 1 to 5 and Comparative Examples 1 to 5 thus obtained were prototyped with a discharge nozzle diameter of 50 μm, a piezoelectric element drive voltage of 120 cm, a drive frequency of 5 KHz, and a resolution of 200 dots/inch. Using a nozzle evaluation machine, we evaluate print quality by observing a print sample under a microscope at 200x magnification, and after solid printing, we measure the drying time by aligning the recording paper with the printing surface to check the time it takes for ink transfer, and solid printing. After leaving it for 2 hours, we conducted a fixation evaluation by rubbing it strongly with a finger, and a continuous ejection stability evaluation to check for the presence or absence of dots during continuous printing for 12 hours.In addition, the environmental temperature and humidity were set at 70°C and humidity while the glass sample bottle was sealed. A storage stability evaluation was conducted to investigate the degree of aggregation of carbon black particles in a constant temperature and humidity chamber for 50 days at 85%.The results are shown in Table 2.

Note that Xerox PP○ paper was used as the recording paper. In addition, the symbols in Table 2 are: ○: No problem, △: Slight problem.
×: Indicates the results of a three-level subjective evaluation: There is clearly a problem.

At least, the ink samples of Examples 1 to 5 containing carbon black with a pH of 6 or less, a dispersant, and a buffer with a pH of 6 to 8 had high printing quality with no smearing in all evaluations conducted this time, and had good drying properties. The fixing properties were also sufficient, and the dispersion stability during discharge and long-term storage was also satisfactory.

However, ink samples using carbon black with a pH higher than 6 as in Comparative Example 1, and ink samples with a pH of 6 or more as in Comparative Example 2,
In the ink sample containing a smaller buffer solution, dispersion stability could not be ensured, and agglomeration of carbon black was observed relatively early in the storage stability evaluation. In an ink sample containing a buffer solution with a pH higher than 8 as in Comparative Example 6, the print quality deteriorated significantly, and the polymeric material used as a dispersant tended to precipitate. Comparative examples 4 and 5
For ink samples that do not contain a buffer or a fractionating agent, the former may cause carbon braation during long-term storage.

In the latter case, the carbon black particles were not sufficiently crushed during dispersion, and many large particles were observed during filtration.

Furthermore, when the above-mentioned print quality evaluation was performed using the aqueous recording ink of the present invention on recycled paper such as Xerox's New OK Paper, R Paper, and Honshu Paper Co.'s Yamayuri Paper, the above five types of recycled paper also showed the same results. Good print quality with little bleeding etc. could be obtained.

Although the embodiments of the present invention have been described in detail above, the aqueous recording ink of the present invention is not limited to these configurations, materials, and manufacturing methods.

〔Effect of the invention〕

According to the present invention, it is possible to provide an aqueous recording ink used in an inkjet printer, which has a pH maintained around neutrality of 6 to 8 and has excellent safety.

Further, it has the effect that it is possible to provide an aqueous recording ink that has excellent drying properties and fixing properties on plain paper and can perform high-speed recording. Furthermore, it is possible to provide an aqueous recording ink that prevents clogging during recording, ensures reliability, achieves high resolution recording, and provides print quality of production quality.

Further, even during long-term storage, the carbon black in the ink does not aggregate, making it possible to provide an aqueous recording ink with excellent stability. Furthermore, even on recycled paper, there is an effect that high quality printing with less bleeding etc. can be obtained.

that's all

Claims (1)

[Claims] An aqueous recording ink comprising at least carbon black having a pH of 6 or less, a dispersant, and a buffer having a pH of 6 to 8.