JPH02233780A - Recording liquid - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application)
i. (hereinafter referred to as ink) and ink passed through the so-called inkjet recording method, in which recording is performed by ejecting ink as droplets from minute ejection ports (ejection orifices) provided in the recording head, are particularly good for recording on plain paper. This invention relates to blue (cyan) ink that provides good color reproducibility.

(Prior Art) The inkjet recording method forms ink droplets using various ink ejection methods, and one of them is
Recording is performed by attaching part or all to a recording material such as paper, and the inks used in such inkjet recording methods mainly include various water-soluble dyes or pigments mixed with water or water. Those dissolved or decomposed in a liquid medium consisting of a water-soluble organic solvent are known and used.

Further, inks similar to those described above are also used as inks for writing instruments such as fountain pens, felt pens, and ballpoint pens.

(Problems to be solved by the invention) It goes without saying that conventional inks such as those described above are required to have various performances such as light resistance, water resistance, storage stability, and ejection stability after printing. The most important thing, especially when performing color recording, is the color reproducibility of each color of the printed matter. Copper phthalocyanine dyes are commonly known as cyan dyes for writing instruments and inkjet inks.
It has good light resistance, water resistance, ejection stability, etc. after printing, and is widely used.

However, when printing on so-called plain paper such as copy paper or bond paper using a printer or writing instrument, there is a problem that the color quality is lower than when printing on coated paper developed for inkjet recording. There is. This tendency is due to the surface acidity (generally referred to as acidic paper).
When printing is performed on paper with a low pH (pH), there is a problem that the colorful cyan color changes to green.

This problem is particularly important in Japan, where acidic paper is used at a higher rate than in Western countries, and is a major issue that must be resolved.

In order to solve the above problems, we applied for the patent application No. 63-2765.
In Specification No. 3, C. I. It has been proposed to adjust the pH of an ink using Direct Blue 199 as a dye to 12.5 or higher.

It is true that by using this method, it is possible to easily suppress discoloration of phthalocyanine dyes on acidic paper. However, there are problems such as the alkali resistance of the recording head and its surrounding materials and safety to the human body, and furthermore, C.I. I. When Direct Blue 86 is used, due to its high alkalinity, there are problems such as ejection stability, especially in inkjet printers that eject ink using thermal energy, and an immediate solution to these problems has been desired.

Furthermore, these problems become particularly noticeable in inks intended to provide good print quality even in plain paper recording. In other words, as described in JP-A-62-11-6676, the print quality on plain paper is better as the amount of water-soluble organic solvents such as glycols is smaller.

However, the discoloration of the phthalocyanine dye on paper (especially acidic paper) is less likely to occur when the amount of water-soluble organic solvent is large. Usually, the color tone of phthalocyanine dye in an acid-precipitated state is green. Therefore, it is thought that the cause of discoloration is that the dye is in an acidic precipitation state on the paper, but if the amount of water-soluble organic solvent in the ink is above a certain level, acidic precipitation is difficult to occur even after printing, and green discoloration occurs. There is little tendency for That is, when recording on plain paper, it is better to reduce the amount of solvent in the ink as much as possible, but on the other hand, there is a problem in that the tendency of phthalocyanine dyes to discolor is increased.

Therefore, an object of the present invention is to improve the above-mentioned drawbacks, and to improve the water resistance and light resistance of printed matter and the ejection stability of the ink, and the pH of the ink is near neutral. To provide an ink that provides sufficient color reproducibility and print quality even when printed on highly acidic paper.

(Means for solving problems) The above objects are achieved by the present invention as described below.

That is, the present invention provides a recording liquid containing at least a water-soluble dye and a water-soluble organic solvent, in which at least one of the water-soluble dyes is a phthalocyanine dye selected from the group consisting of diethylene glycol, glycerin, polyethylene glycol, and ethylene glycol. It contains at least one water-soluble organic solvent in the range of 4 to 20% by weight, and further has an acid dissociation index (pκa) at 25°C when the number of dissociation stages is 1.
) is 4.3 or more, and is a recording liquid characterized by containing an alkali metal salt of an organic carboxylic acid.

(Function) A specific dye, that is, at least one phthalocyanine dye, is used as the ink dye, a specific amount of a specific water-soluble organic solvent is used, and an alkali metal salt of an organic carboxylic acid with a specific pκa is further added. By including the ink, sufficient color reproducibility can be obtained even when printing on plain paper, especially paper with high acidity, and furthermore, an ink with good printing quality and sufficient ejection stability is provided.

(Preferred Embodiments) Next, the present invention will be described in more detail by citing preferred embodiments.

Normally, when printing on plain paper, dyes used in water-based inks are required to have various properties that are required when printing on coated paper with an ink-absorbing layer. In recording, it is extremely important to obtain sufficient color reproducibility.

Generally, inkjet recording paper used has a coating layer containing a filler such as silica, alumina, or calcium carbonate on its surface, thereby sufficiently reproducing the color properties of dyes.

However, ordinary plain paper does not have such a coating layer, and as a result, sufficient color reproducibility of dyes cannot be obtained, and when printing on so-called acid paper, which has a particularly high surface acidity, phthalocyanine-based cyan The dye turned green, making it impossible to obtain ideal color images.

This tendency is relatively rare when printing on acidic paper, but when printing on acidic paper, it is possible to suppress discoloration by adding an alkali metal salt of organic carboxylic acid to the ink. I discovered that it is possible to Generally, organic carboxylic acid salts are solid (powder) at room temperature, so in consideration of clogging at the tip of the printer head, it is desirable that the amount added be as small as possible.

Therefore, as a result of intensive research by the inventors as described above,
It has been found that the color tone improvement effect on plain paper is better when an organic carboxylic acid with an acid dissociation index (pKa) as large as possible is used. Specifically, ρKa4.3
If the alkali metal salt of the organic carboxylic acid described above is used, a sufficient color tone improvement effect can be obtained with a small amount added that does not cause clogging at the tip of the printer head.

Furthermore, in order to improve the print quality when printing on plain paper, the amount of water-soluble organic solvent contained in the ink is 4 to 2.
A range of 0% by weight is desirable. If this amount is less than 4%, the tendency for clogging to occur becomes noticeable;
If the number is larger than that, the print quality will deteriorate rapidly. Also, among the types of green water-soluble organic solvents, diethylene glycol, ethylene glycol, glycerin, and polyethylene glycol are preferable not only in terms of printing quality but also in terms of safety and clogging resistance.

The ink of the present invention is prepared by dissolving a phthalocyanine dye and an alkali metal salt of an organic carboxylic acid in a mixed solvent of the above specific water-soluble organic solvent and water, where the water is:
It is preferred to use deionized water rather than ordinary water containing various ions.

As the dye to be dissolved in the liquid medium, any phthalocyanine-based dye is suitable; for example, C.I. I. Direct Blue 86, 87, 189, 199
, 262, (:.I. acid pull-185, 197, 228, 2
43, 249, 254, 255, 275, 279, (:.I. Reactive Blue 3, 7, 11, l4, 1
5, 18, 21, 23, 25, 30, 35, 38, 41
, 48, 57, 58, 63, 71, 72, 77, 85,
Examples include 88, 91, 92, 95, etc.

Furthermore, cyan dyes other than phthalocyanine dyes may be mixed and used for the purpose of color toning.

As the color tone improving agent for plain paper printing using phthalocyanine dyes in the present invention, alkali metal salts of organic carboxylic acids having the following pKa values (as described in the Chemical Handbook, Fundamentals Edition, edited by the Chemical Society of Japan) are preferred. Can be mentioned.

At 25℃ 2 κ8 4. 8 4. 8 4. 4 4.7 4. 3 5. 0 4. 9 4. 9 4, 9 Acetate butyrate Adibate Crotonate Vinyl acetate Trimethyl acetate Cyclohexane Carboxylic acid Brobionic acid Octanoic acid In general, the larger the content of the organic carboxylic acid alkali metal salt, the greater the color tone improvement effect can be obtained. ,
0 in the total ink weight as it may affect clogging etc.
．． 01% to 2%, preferably O. OS% to 1.5%
, more preferably within the range of 0.05 to 1.0%.

The amount of dye to be dissolved in the liquid medium is determined depending on the type of liquid medium components, the characteristics required of the ink, etc., but generally it is about 0.00% by weight in the total amount of ink. The proportion is 1 to 15%, preferably 0.5 to 10%, more preferably 1 to 8%.

In the method of adjusting the pH of ink as described above, the alkali metal salt of organic carboxylic acid itself can be used as a pH adjuster, but
Furthermore, sodium hydroxide, potassium hydroxide,
This can be done by adding a general alkaline agent such as lithium hydroxide or an acid such as hydrochloric acid or carboxylic acid, and the preferred pH range depends on safety to the human body and wetted materials used in recording devices and instruments. Considering the stability etc., it is in the range of 5.0 to 10.0.

The ink of the present invention, which is formulated from such components, not only has excellent color properties and print quality when recorded on plain paper, but also has excellent recording properties (signal response, stability of FI droplet formation, and ejection stability). It is well-balanced and has excellent properties such as durability, long-term continuous recording performance), fixation to recording materials, and light resistance, weather resistance, and water resistance of recorded images. In order to further improve such properties, various conventionally known additives may be added. Examples include viscosity modifiers such as polyvinyl alcohol, celluloses, and water-soluble resins; various anionic or nonionic surfactants; surface tension modifiers such as diethanolamine and triethanolamine; antifungal agents; and the like.

Further, in order to prepare ink used in an inkjet recording method in which the ink is charged, a resistivity adjuster such as inorganic salts such as lithium chloride, ammonium chloride, and sodium chloride is added.

When applied to an inkjet recording method in which ink is ejected by the action of thermal energy, thermal physical property values (e.g., specific heat, coefficient of thermal expansion, thermal conductivity, etc.)
may be adjusted.

(Example) Next, the present invention will be explained in more detail by giving Examples, Comparative Examples, and Usage Examples. In the text, parts or percentages are based on weight unless otherwise specified.

Examples 1 to 6 Back application group 1 C. 1. Direct Pull 86 0.5 part C
, t. Direct Blue 1992 parts diethylene glycol 13 parts water
84.5 parts Lithium acetate (acetic acid pKa-4.11) 0. 5 parts (ink pH=7.8) Yuyu Kasuse C. I. Direct Blue 86 3 parts ethylene glycol 10 parts polyethylene glycol (average molecular weight 11 300) 4 parts water 83 parts lithium propionate (probionic acid pKa 4.9)
0. 6 parts (ink pH=
8.1) Urahoumawari C. I. Acid Blue-185 2.5 parts Glycerin 10 parts Ethylene glycol 4 parts Water
82.9 parts lithium acetate (butyric acid pKa=
4.8) 0. 6 parts (ink pH=8.0) 100 million A C. 1. Acid Blue-9 Part 2 C.
I. Direct Blue 87 2 parts Polyethylene glycol (average molecular weight 300) 11 parts N-methyl-2-pyrrolidone 3 parts Water
81.2 parts Lithium vinyl acetate (vinyl acetate pKa=4.:l) 0.8 parts (ink pH=7.3) Inuse A5 C. !・Reactive Blue-77 Diethylene glycol Polyethylene glycol (average molecular weight 2 parts 9 parts 5 parts 83.5 parts 0.5 parts Sodium acetate (acetic acid pKa・4.8) (ink pH=
7.0) Length example beach C. I. Direct Blue 199 Glycerin Ethylene Glycol Water Sodium Adipate 3 parts 11 parts 4 parts 81.4 parts (adibic acid pKa = 4.4) 0.9 parts (ink pH = 8.5) The above components were mixed respectively, and then Average pore size 0.45μm
Each aqueous ink of the present invention was obtained by pressure filtration using a fluororesin filter.

Comparative Examples 1 to 7 (manufacturing method is the same as in Examples) Example C. I. Reactive Blue-77 6 parts diethylene glycol 15 parts water
76.9 parts Sodium acetate (butyric acid pκa = 4.8) 4.1 parts (ink pH =
7.6) ■Mosquito cases [:. I. Direct Blue 1998 parts Polyethylene glycol (average molecular i 400) 15 parts N-methyl-2-pyrrolidone 20 parts Water
56.2 parts Lithium succinate (succinate pκa-4.2) 0 8 parts (ink pH = 8.9) c. r. Direct Blue 1893 parts Glycerin 10 parts Ethylene glycol 3 parts Water
81.5 parts Lithium citrate (Quen l'lpKa-3.2) 3.5 parts (ink pH=9.0) Mosquito Drama 4 c. r Acid Blue - 2792 parts N-methyl-2-pyrrolidone 15 parts Polyethylene glycol (average molecular weight 300) 11 parts Water 70.8 parts Lithium probionic acid (probionic acid pKa = 4.9)
1.2 parts (ink pH=8
．． 2) 5 c. r. Reactive Blue-77 5 parts Polyethylene glycol (average molecule 1: 100) 21 parts Water 72 parts Sodium succinate (succinic acid pKa - 4.2) 2.0
part (ink pH=7.3) Le pattern example l C. I. Direct Blue 86 6 parts diethylene glycol 3 parts water
90 parts Lithium brobionate (bropionate pKa-4.9)
1.0 parts (ink pH = 7.9) ■Mosquito example C. I. Direct Blue 1993 parts diethylene glycol 10 parts triethylene glycol 11 parts water
75.1 part Sodium adibate (
Azivin fip Ka-4. 4) 0.9
(Ink pH=8.0) Usage Example Using the cyan inks obtained in Examples 1 to 6 and Comparative Examples 1 to 7 above, thermal energy was applied to the ink in the recording head to generate droplets. The following (Test 1) was carried out using a recording device having an on-demand type multi-head for recording (discharge orifice diameter 25 μm, heating resistor resistance value 120 ohms, drive voltage 30 V, frequency 4 κHz).
) to (Test 3) were investigated. The results are shown in Table 2 below.

1 1 Color defined by the following formula between inkjet paper IJ Matte Coat NM (manufactured by Santsuru Paper) having a silica coating layer and a solid printed image (2 x 2 cm) recorded on the recording material shown in Table 1 below. The average value of the phase difference ΔH" (recommended by CIEl976) was determined using a color analyzer (manufactured by Murakami Color Research Institute) to evaluate the chromaticity of the recorded image. 80"=((ΔE"-b)"-(ΔL") ) ”− (Δ
Cη2) 2/IQ:AH"=5.0 or less Δ:ΔH"=5.0 to 10.0 ×:Δo"=to.o or more 2°' After printing continuously so that they do not touch each other and drying naturally indoors for 24 hours,
The number of dots with amorphous or irregular bleeding was counted using a microscope, and the percentage was evaluated based on the following criteria. O: 20% or less Δ: 20 to 40% It was then printed and evaluated using the following criteria. O: Returns to normal printing within 5 recovery operations. Δ: Returns to normal printing state after 6 to 10 recovery operations. ×: Non-discharge or irregular printing after 6 to 10 recovery operations. Tobi 1'' LJ Canon NP-DRY Tidal MX M Paper Cascade Bond PPC Paper RPC Paper Bond Paper Canon ■ Yato 7-Mill Company Fuji Xerox ■ Neys Cascade Inc. The recording material is the product name.

Book: Surface acidity value is TAPPI standard θF82
It was calculated according to T529 Example 5 Example 6 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Comparative Example 7

Claims (2)

[Claims] (1) In a recording liquid containing at least a water-soluble dye and a water-soluble organic solvent, at least one of the water-soluble dyes is a phthalocyanine dye, and at least one dye selected from the group consisting of diethylene glycol, glycerin, polyethylene glycol, and ethylene glycol. Contains a water-soluble organic solvent of 4 to 20% by weight, and further contains 1 dissociation stage.
The acid dissociation index (pKa) at 25°C is 4.3
A recording liquid characterized by containing an alkali metal salt of the above organic carboxylic acid. (2) The recording liquid according to claim 1, wherein the content of the water-soluble organic solvent is 4 to 15% by weight.