JPH0297578A - Ink for ink jet recording - Google Patents

Abstract

PURPOSE:To obtain the title ink prevented from causing formation of during transportation and storage and missing of dots during use by specifying the range of the nitrite ion concentration of the ink containing an azo linkage- containing dye. CONSTITUTION:An ink for ink jet recording is obtained by mixing 0.5-10 pts.wt. dye having at least one azo linkage in the molecule and a high solubility in a wetting agent and water (e.g., a compound of the formula), 5-80 pts.wt. water- soluble organic solvent (e.g., glycerol) as a wetting agent and water as a solvent. This ink is admitted through an ion exchange resin or an ultrafiltration membrane to remove nitrite ions by adsorption or separation to a nitrite ion concentration of 0.2-10ppm, deaerated, and sealed in a container made of a lowly gas-permeable member.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to an inkjet that compresses ink using vibrations of an electromechanical transducer or a valve generated by an electrothermal transducer and ejects ink particles from a nozzle for recording. This invention relates to Blink recording ink.

[Conventional technology 1 Inkjet printers have many advantages in printing waves 1; i, such as noiseless, high-speed printing, high-quality printing, and color printing, but due to the principle of printing by compressing liquid ink, ,
If air bubbles or bubble nuclei exist in the pressure generating part of the inkjet blink, the generated pressure will be absorbed by the air bubbles, making it impossible to apply sufficient pressure to the ink (and eventually the ink will no longer be able to be ejected from the nozzle). For this reason, inkjet ink has traditionally been degassed in the final manufacturing process or subjected to high-precision filtration to remove the air C capsule core, and then placed in containers with low air permeability. ,
Although such processing is initially effective, the effect disappears over time. Especially when a container containing ink is placed in a high-temperature environment, even if the ink is initially degassed, gas is generated from the ink itself and bubbles are formed.
These air bubbles caused dots to drop out, which is fatal to inkjet printers.

[Problems to be Solved by the Invention] For this reason, ink for inkjet printers has limitations on storage ζ temperature and short shelf life, which imposes major restrictions on transportation, storage, and use.

In view of the conventional problems, the present invention has been developed to prevent the generation of gas to the point of forming bubbles even if the ink is placed in a high-temperature environment during transportation and storage, thereby preventing dots from falling out during use. The purpose of the present invention is to provide an inkjet recording ink with high printing stability.

[Means to solve the problem]

In order to achieve the above object, the present invention provides an inkjet recording ink that contains a dye having at least one azo bonding group in its molecule, and that the nitrite ion concentration in the recording ink is from 0.2 ppm to loppm or less. It is characterized by

As shown in FIG. 1, the ink path of an inkjet printer includes an ink tank 12 that stores recording ink 11.
, an ink supply pipe 13 that connects the ink 11 to the print head 14, and a filter 15 for removing dust and air bubbles flowing from the ink tank 12. If air bubbles are generated in this path, the air bubbles will flow along with the flow of ink, and when the air bubbles reach the pressure generating section, the nozzles of the print head will no longer be able to eject ink, making printing impossible.

In addition, in inkjet recording inks, cavitation occurs in the ink as pressure is generated, and gas dissolved in the ink may become bubbles. Therefore,
As disclosed in Japanese Patent Publication No. 52-74406, attempts have been made to reduce the gas concentration in the ink by adding sulfite to the ink to reduce dissolved oxygen in the ink. has no effect at all. Moreover, the nitrogen concentration in the ink remains low, even if dissolved nitrogen is initially completely removed and the ink is sealed in a container with a low gas permeability coefficient.
As shown in Figure 2, the nitrogen concentration in the ink increases over time.

(a) shows the increase in nitrogen when pure water is sealed in an aluminum laminated bag, and (b) shows the increase in nitrogen when a 3% aqueous solution of Dye Direct Black 154, which has three azo bonding groups, is sealed in the same bag as ink. Indicates the amount of increase. Dissolved nitrogen] was measured using gas chromatography (the column was Molec
ular 5ieve 5A Gas Kuro Kogyo (manufactured by Fukiku) was used. Therefore, even if the ink is sealed with a highly gas-barrier bag after degassing, or even if an oxygen reducing agent is added to the ink, if the generation of nitrogen from the ink itself is not suppressed, air bubbles in the ink will The occurrence cannot be prevented, in Figure 2 (b)
The amount of dissolved nitrogen in the ink was saturated at about 14 ppm, and it was confirmed that there were actually bubbles in the ink above this concentration.

The inventor of the present invention focused on the fact that the cause of nitrogen generation is impurities in the ink, and as a result of analysis and experiments, it was found that nitrite ions and dyes with azo bonding groups contained in the ink are the cause of nitrogen generation. I found out that it is. Furthermore, when the ink contains a dye with an azo bond group, if the nitrite ion concentration in the ink is adjusted to below loppm, air bubbles will not form from the ink bag even if the ink is kept at 70°C for 15 days. It completely disappeared, satisfying the most severe usage conditions imaginable. However, when the nitrite ion concentration is less than 0.2 ppm, the flight of ink droplets tends to bend when printing after the printer has not been used for a long period of time, reducing print quality. In addition, with dyes that do not contain azo bonding groups, this flying-targeting phenomenon is observed in printing after a long period of time without blinking, regardless of the nitrite ion concentration. contains an azo bonding group in the molecule, and the nitrite ion concentration in the ink is 0.22
-1 Opp.

As a method for reducing nitrite ions to 0.2-Loppm according to the present invention, -jlQ is a method for removing nitrite ions.
Although the sulfamic acid neutralization method known in the art can be used,
With this method, it is difficult to control nitrite ions to 0.22-1 Opp, and sulfate radicals also remain in the ink. Easy-to-manage methods include passing the ink through an ion exchange resin to adsorb and remove nitrous acid, and passing the ink through an ultrafiltration membrane to separate and remove nitrite ions. In this way, the nitrite ions in the ink are reduced to 0.22-1 Opp.
One of the objects of the present invention can be achieved by deaerating the ink and sealing it in a bag or container made of a material with low gas permeability.

The recording ink of the present invention is basically composed of a dye as a coloring agent, a wetting agent to prevent nozzle clogging, and water as a solvent. In order to obtain 22-1 Opp, it is preferable that the nitrite contained in the material constituting the ink be at a low concentration.In particular, the dye having an azo bond group according to the present invention is not used in the synthesis process when diazo, such as an aromatic amine, is used. Since sodium nitrite is used during dye synthesis, it must be reduced to a sufficiently low concentration after dye synthesis.

The dye used in the present invention preferably has at least one azo bonding group in the molecule and has high solubility in water and a wetting agent.

Examples include dyes shown in structural formulas 1 to 23. If the proportion of dye in the ink is high, the concentration of nitrite ions in the ink tends to increase, so it is necessary to remove the nitrite ions by passing the aqueous dye solution through an ion exchange resin or the like in advance.

The amount of dye added should be 0.5 to obtain sufficient printing density.
-10 parts by weight is optimal.

A humectant is an important component for preventing recording ink from drying in the nozzle portion of an inkjet printer head. In the recording ink of the present invention, water-soluble organic solvents can be used, and among them, polyhydric alcohols, ether derivatives and ester derivatives of polyhydric alcohols, water-soluble amines, nitrogen-containing cyclic compounds, and the like are suitable. These compounds are mostly nitrite-free and do not require any specific removal treatment.

Polyhydric alcohols such as ethylene glycol, diethylene glycol, tonoethylene glycol, propylene glycol, polyethylene glycol, glycerin, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether,
Alkyl ether derivatives of polyhydric alcohols such as diethylene glycol dimethyl ether, diethylene glycol methyl ethyl ether, and triethylene glycol monomethyl ether; polyhydric alcohols such as ethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, glyceryl monoacetate, and glyceryl diacetate; Examples include ester derivatives, water-soluble amines such as (mono, di, and tri) ethanolamine, and polyoxyethylene amine, and nitrogen-containing cyclic compounds such as N-methyl-2-pyrrolidone. The amount of these water-soluble organic solvents to be added is to prevent the recording ink from drying out, so the larger the amount, the better the effect, but it is not preferable to add a large amount because it also increases the viscosity of the recording ink. The viscosity greatly affects the ejection cycle of ink droplets, and as the viscosity increases, the ejection cycle does not increase and the ejection characteristics become unstable. Therefore, the ink viscosity is 50mPa
, s or less, and considering this viscosity range, the water-soluble organic solvent is preferably added in an amount of 5 to 80 parts by weight.

Further, in order for the recording ink of the present invention to quickly penetrate into recording paper, the PH value of the ink is adjusted as proposed in JP-A-56-57862. It can be adjusted to 12-14. Furthermore, additives such as preservatives, fungicides, chelating agents, and pH adjusters can be added as appropriate.
Some of these additives are nitrite-based, so they must be added with care.

[Example] Example 1 Composition/No. Dye with the structure shown in 4... 1 part by weight Glycerin... 15 parts by weight Ultrapure water
...84 parts by weight of ink having the above composition was heated to obtain 500 g of ink. After cooling this ink, anion exchange resin (Amberlite I RA
61! Approved. After this, the ink was filtered through a 1 micron meter membrane filter.

After degassing, the mixture was filled into an aluminum-laminated polyethylene bag with low gas permeability, and the polyethylene was sealed in the liquid to obtain an ink-tight ink bag. The capacity of one ink bag is 120cc. After the four ink bags were placed in a 70° C. environment for 15 days, the nitrogen concentration was measured by gas chromatography and found to be 9 ppm on average. As a result of printing with this ink using an inkjet printer HG-2500 (manufactured by Seiko Epson), stable printing was achieved without any missing dots on all four prints.Furthermore, with this ink still in the head, it was possible to print at room temperature for 10 minutes. After leaving the printer without a cap to prevent clogging, I discharged it again and was able to print well without any clogging.

Comparative Example 1 The ink having the composition of Example 1 that did not pass through the anion exchange resin had a nitrite ion concentration of 32 ppm. As in Example 1, this ink was filtered and degassed, sealed in an aluminum laminated bag, and stored in an environment of 70°C for 15 days.The nitrogen concentration was measured and showed an average of 14 ppm. When the bag was opened underwater, it was confirmed that air bubbles had formed inside the ink bag. Further, when printing was performed on the remaining ink bags in the same manner as in Example 1, dots frequently fell out on all three bags, and stable printing could not be obtained.

Example 2 Dye having the structure shown in Composition No. 017: 2 parts by weight, polyethylene glycol #200 10 parts by weight, triethylene glycol: 5 parts by weight, ultrapure water: 83 parts by weight An ink with the above composition was used. Preparation was carried out in the same manner as in Example 1, and after cooling it was passed through an ultrafiltration membrane (HF 1-41-43-P manufactured by Romicon).
After supplementing the amount concentrated by ultrafiltration with ultrapure water, it was confirmed that the nitrite ion concentration in the ink was 2 ppm. After filtering and degassing this ink, it was sealed in an ink bag and evaluated in the same manner as in Example 1, and the amount of nitrogen generated was 5 ppm. In addition, printing stability is also good, with 1
It was in good condition with no clogging after the test.

Comparative Example 2-1 After preparing the ink of Example 2, 0.1 g of sulfamic acid
The nitrite ion concentration was measured after cooling, and the result was 0. It was lppm. After filtering and deaerating this ink, it was sealed in an ink bag and Example 1
When the same evaluation was performed, the amount of nitrogen generated was 1.5p.
It was pm. Furthermore, the printing stability was stable without causing any dot dropout. However, when clogging was evaluated after being left at room temperature for one month, although clogging did not occur completely, re-ejection was unstable and the flight of ink particles was also curved, so good printing could not be obtained.

Comparative Example 2-2 Instead of the dye used in Example 2, an ink was prepared in the same manner as in Example 2 using the dye shown in No. 25 that does not have an azo bond group, and then heat loss was performed. After cooling, the nitrite ion concentration was measured and found to be 2.5 ppm. After filtering and degassing this ink, it was sealed in an ink bag and evaluated in the same manner as in Example 1, and the amount of nitrogen generated was 3.5 pp.
It was m.

Furthermore, the printing stability was stable without causing any dot dropout. However, when clogging was evaluated after being left at room temperature for one month, although clogging did not occur completely, re-ejection was unstable and the flight of ink particles was also curved, so good printing could not be obtained.

Example 3 Example 3 was carried out using the same processing power method as Example 1 or Example 2.
-1 to 3-5 inks with nitrite ions of 0.22-1
As six comparative examples adjusted to Opp, inks 3-6 to 3-8 were used without adjusting the nitrite ion.

Moreover, Comparative Examples 3-9 and 3-10 are inks in which nitrite ions were neutralized with sulfamic acid. Comparative example 3-1
1 and 3-12 are inks containing the above-mentioned dyes IEI No. 26 and 27, which do not have an azo bonding group in one molecule.

In the table below, the numbers in the composition represent parts by weight, and the concentration represents the nitrite ion concentration.

The inks shown in 3-1 to 3-12 were filtered and degassed in the same manner as in Example 1, and then sealed in an ink bag and stored in a 70°C environment for 15 days. Thereafter, in the same manner as in Example 1, the ejection stability (A) when these inks were printed with an inkjet printer, and the clogging when the print head was filled with Irikitsu ink without a cap and left at room temperature. The results of performance (B) are shown in Table 1.

Table 1 condition refers to a condition in which dots drop out five or more times when 120cc of ink is printed continuously, and flight deflection refers to a condition in which blanks appear in the print or the print is disordered when seen with the naked eye. .

〔Effect of the invention〕

The recording ink of the present invention contains a dye having at least one azo bond group in one molecule, and the nitrite ion concentration in the ink is adjusted from 0.2 ppm to 10 ppm, so that the ink can withstand high-temperature environments. Since the ink itself does not generate nitrogen gas even when stored, it is durable even during transportation and storage at high temperatures, making it possible to significantly extend the life of the ink, as well as improve printing stability in inkjet printers. This is highly effective as it can prevent the phenomenon of deflection of ink particles, which deteriorates print quality and is a sign of clogging.

In addition, in Table 1, there are cases where dots frequently drop out.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the principle of an ink path in an inkjet printer. FIG. 2 is a graph showing temporal changes in dissolved nitrogen concentration in ink and water at 70°C. 11... Ink 14... Head 15... Filter and above Distributor Seiko Epson Co., Ltd. agent Patent attorney Kizobe Suzuki (and 1 other person) Figure 1 Gin Seki (h) Figure 2 44: 70°C

Claims (1)

[Claims] The inkjet recording ink contains a dye having at least one azo bond group in the molecule, and the nitrite ion concentration in the recording ink is from 0.2 ppm to 10 ppm.
An inkjet recording ink characterized by having a content of ppm or less.