JPH02233781A - 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 Application Field) The present invention provides a recording liquid for writing instruments (fountain pens, felt pens, etc.)
Regarding inks suitable for the so-called inkjet recording method in which recording is performed by ejecting ink as droplets from fine ejection ports (ejection orifices) provided in the recording head, it is particularly suitable for recording on plain paper. This invention relates to yellow 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. In particular, when performing color recording, the most important thing is the color reproducibility of each color of the printed matter.

C.I., which is generally well known as a yellow dye for writing instruments and inkjet inks. I. Direct Yellow 86 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 carried out on paper with a low pH (pH), there is a problem that the bright yellow color changes to dark yellow. This problem is particularly important in Japan, where acidic paper is used at a higher rate than in Western countries, and it is a major problem that must be solved.

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-62-116676, the print quality on plain paper is better as the amount of water-soluble organic solvents such as glycols is smaller. However, C. I. On the contrary, discoloration of Direct Yellow 86 is less likely to occur when the amount of water-soluble organic solvent is large. Usually, C.I. ! ．． The color tone of Direct Yellow 86 is dark yellow. Therefore, the cause of discoloration is thought to be due to the dye being 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 unlikely to occur even after printing, and discoloration may occur. There are few trends. In other words, 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, C.
I. There is a problem in that Direct Yellow 86 has a tendency to discolor.

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. The purpose of the present invention is to provide an ink that provides sufficient color reproducibility and print quality even when printed on highly acidic paper. (Means for solving the problems) The above object is 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 C.I. I. Contains Direct Yellow 86, contains at least one water-soluble organic solvent selected from the group consisting of diethylene glycol, glycerin, polyethylene glycol and ethylene glycol in a range of 4 to 20% by weight, and further contains 1 dissociation stage. This is a recording liquid characterized by containing an alkali metal salt of an organic carboxylic acid having an acid dissociation index (pKa) of 4.3 or more at 25°C.

(Function) Certain dyes, namely C.I. I. By using Direct Yellow 86, containing a specific amount of a specific water-soluble organic solvent, and further containing an alkali metal salt of an organic carboxylic acid with a specific pκa, when printing on plain paper, especially paper with high acidity. Furthermore, an ink with sufficient color reproducibility, 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 code layer on its surface containing fillers such as silica, alumina, and calcium carbonate, thereby sufficiently reproducing the color properties of dyes.

However, ordinary plain paper does not have such a coating layer, and therefore sufficient color reproducibility of dyes cannot be obtained, and when printing is performed on so-called acid paper, which has a particularly high surface acidity, C.I. l
Direct Yellow 86 turned dark yellow, making it impossible to obtain an ideal color image.

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 Since organic carboxylic acid salts are generally solid (powder) at room temperature, it is desirable that the amount added be as small as possible in consideration of clogging at the tip of the printer head.

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, pKa4,3
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. Further, among the types of 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 C.I. I. Direct Yellow 86 and an alkali metal salt of an organic carboxylic acid are dissolved in a mixed solvent of the above-mentioned specific water-soluble organic solvent and water. Preferably, ionized water is used.

In addition, for the purpose of toning, etc., C. l. direct yellow 8
Yellow dyes other than 6 can also be used in combination.

C. in the present invention. I. As a color tone improver for direct yellow 86 printing on plain paper, the following pKa
Preferred examples include alkali metal salts of organic carboxylic acids having the following values (as described in Chemical Handbook, Basic Edition, edited by the Chemical Society of Japan).

Place at 25°C 2 κa acetic acid 4.8 Butyric acid 4.8 Adipic acid 4.4 Crotonic acid 4.7 Vinyl acetic acid 4.3 Trimethylacetic acid 5,0 Cyclohexanecarboxylic acid 4.9 Brobionic acid 4.9 Octanoic acid 4 .9 In general, the larger the content of the organic carboxylic acid alkali metal salt at this time, 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 0.05% 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. 1 to 15%, preferably 05 to 10%, more preferably 1
This accounts for between 8% and 8%.

In the method of adjusting the pH of ink as described above, the alkali metal salt of an organic carboxylic acid itself can be used as a ρH adjuster;
Furthermore, sodium hydroxide, potassium hydroxide,
It can be carried out by adding a general alkaline agent such as lithium hydroxide or an acid such as hydrochloric acid or carboxylic acid.
The range of t is 5.0 to 10.0, considering safety to the human body, stability to wetted materials used in recording devices and instruments, etc.
It is in the range of 0.

The ink of the present invention, which is formulated from these components, not only has excellent color properties and print quality when recorded on plain paper, but also has excellent recording properties (signal response, droplet formation stability, ejection stability). It is well-balanced and excellent in terms of performance, long-term continuous recording performance), fixing performance on 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. For example, viscosity modifiers such as polyvinyl alcohol, cellulose, and water-soluble resins; various anionic or nonionic surfactants; surface tension modifiers such as diethanolamine and triethanolamine; and antifungal agents. .

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 described in more detail with reference to Examples, Comparative Examples, and Usage Examples. In the text, parts or percentages are based on weight unless otherwise specified.

Examples 1 to 5 Inushikeyu C. I. Direct Yellow 86 2 parts diethylene glycol 15 rin water
82.4 parts lithium acetate (
Acetic acid pKa・4.8) 0. 6th part of the test C. I. Direct Yellow 86 2 parts C.
I. Direct Yellow 1421 parts Polyethylene glycol (average molecular weight 300) 5 parts Ethylene glycol 10 parts Water
81.2 parts Sodium vinyl acetate (vinyl acetate pKa 4,3) 0.9 parts Length 1 C. I. Direct Yellow 86 Glycerin N-methyl-2-pyrrolidone water Lithium propionate 4.9) Dog A fake 4 (:.I. Direct Yellow 86 C.I. Direct Yellow 23 Ethylene glycol Glycerin water Trimethyl lithium acetate (topKa=5) .0) Inuse ■1 C.I. Direct Yellow 86 Diethylene glycol glycerin water 3 parts 10 parts 3 parts 83, 6 parts (brobionic acid pKa = 0.4 parts 2 parts 1 part 8 parts 7 parts 81.2 parts Limethylacetic acid 0.8 parts 4 parts 12 parts 3 parts 80.1 parts Sodium adibate (adipate pKa=4.4) 0
．． Mix 9 parts of each of the above components, and then add an average pore size of 0.45 μm.
Each aqueous ink of the present invention was obtained by pressure filtration using a fluorine tree filter.

Comparative Examples 1 to 5 (manufacturing method is same as Example) ! ．． Direct Yellow 86 5 parts Polyethylene glycol (average molecule i 300) 21 parts Water 73.1 parts Sodium succinate (succinic acid pKa = 4.2) 0.9
Part Comparative Example I C. l. Direct Yellow 86 4 parts C.
I. Direct Yellow 1422 parts Ethylene glycol 10 parts Water
81.5 parts Lithium citrate (citrate pK
a=3.2) 2.5 part Le pattern example l C. I. Direct Yellow 86 Glycerin water monochrome sodium acetate PEA-2.9) 5 parts 9 parts 81 parts (monochrome acetic acid 5 parts Pine Example A CI Direct Yellow 86 4 parts ethylene glycol 3 parts water
92.8 parts Sodium acetate (acetic acid pKa -4.8) 0. Part 2 Mosquito Case 1 C. 1. Direct Yer:. -86
Part 3C. ! ．． acid red 23 1
part polyethylene glycol (average molecule l 300) 15
6 parts glycerin 6 parts water
74.2 parts Lithium propionate (bropionate pKa-4.9)
0. 8-part usage example An on-demand type in which recording is performed by applying thermal energy to the ink in the recording head to generate droplets using the yellow ink obtained in Examples 1 to 5 and Comparative Examples 1 to 5 above. multi-head (discharge orifice diameter 25μm,
The resistance value of the heating resistor is 120 ohms, the driving voltage is "IOV,"
The following (Test 1) to (Test 3) were investigated using a recording device having a frequency of 4 Kl1z). The results are shown in Table 2 below.

Color defined by the following formula between inkjet paper IJ Matte Coat NM (manufactured by Mitsubishi Paper Mills) having a silica coating layer of Test 1- and a rough print image (2 x 2 cm) recorded on the recording material shown in Table 1 below. The average value of the phase difference ΔH@ (CIEI976 recommended) was determined using a color analyzer (manufactured by Murakami Color Research Institute),
The color properties of the recorded images were evaluated.

Δ]age = ((ΔEゝab) 2- (Δpi)2-(Δji)2) 2/1○: ΔH”=5.0 or less △・ΔH”=5.0 to 10.0 ×: Δ}I'' = 10.0 or more Test 2° 300 dots were continuously printed on the recording material shown in Table 1 below so that they did not touch each other, and after air drying indoors for 24 hours,
The number of dots in which amorphous or irregular bleeding occurred was counted using a microscope, and the percentage was evaluated based on the following criteria.

○: 20% or less △: 20 to 40% After that, it was printed and evaluated based on the following criteria.

O: Returns to normal printing state within 5 recovery operations.

Δ: Returns to normal printing state after 6 to 10 recovery operations.

×: Non-discharge or irregular printing occurred after 6 to 10 recovery operations.

γ−’; 1 ”’) Canon NP-DRY Tidal MX M paper Cascade Bond rpc paper rpc paper bond paper canon poetry Hachin 7-mil company Fuji Xerox ■ Takashi Cascade Co., Ltd. Note that the recording material is a trade name.

*: The value of surface acidity was determined according to TAPPI standard OM-82.

to T529 (Margin below)

Claims (2)

[Claims] (1) In a recording liquid containing at least a water-soluble dye and a water-soluble organic solvent, at least C.I. I
．． Contains Direct Yellow 86, contains at least one water-soluble organic solvent selected from the group consisting of diethylene glycol, glycerin, polyethylene glycol and ethylene glycol in a range of 4 to 20% by weight, and further contains 1 dissociation stage. Acid dissociation index (pK) at 25°C
A recording liquid characterized in that a) contains an alkali metal salt of an organic carboxylic acid having a value of 4.3 or more. (2) The recording liquid according to claim 1, wherein the content of the water-soluble organic solvent is 4 to 15% by weight.