JPH0881647A - Ink - Google Patents

Abstract

PURPOSE: To obtain an ink having high water resistance of printed matter, sufficient level of printed density and excellent conservative stabilities and fixing properties of printed matter, polymerized with a polymerizable surfactant as a colorant. CONSTITUTION: This ink contains (A) a polymerizable surfactant [e.g. a compound expressed by the formula (M is metal atom, preferably Na or K; (m) is 5-10)], (B) carbon black having the surface on which the component A is graft-polymerized and (C) an aqueous medium dispersing the component B. Preferably, at least one kind of (D) a water-soluble monomer (e.g. N- acryloylmorpholine) and (E) a water-insoluble monomer (e.g. styrene) is graft- polymerized to the component A. Preferably, 10-1000 pts.wt. of the component A is added to 100 pts.wt. of the component B.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink, and more particularly to an ink suitable for an ink jet recording system.

[0002]

2. Description of the Related Art With the recent advances in the performance of personal computers and software, higher performance is also required for character and graphic image recording devices such as printers. Examples of the image recording method include various methods such as a dot impact method, a thermal transfer method, and an ink jet method. Among them, the ink jet method ejects fine particles of ink (recording liquid) from ejection orifices (fine holes) of a recording head. Since it is ejected to form a recorded image, (1) the sound at the time of recording is small, (2) a high-resolution image can be reproduced at high speed, (3)
Color display is possible, (4) Can be recorded on plain paper,
(5) It has advantages such as low running cost.

Examples of the ink used in this ink jet system include a colorant dissolved or dispersed in water or a mixed liquid of water and a water-soluble organic solvent (hereinafter referred to as "aqueous medium"). The characteristics of the ink are taken into consideration including the relationship with the recording head, and (1) the quality of the printed matter is high,
(2) High storage stability of ink, (3) High robustness of printed matter (for example, water resistance, light resistance, fixability, etc.), (4) Ink frequency corresponding to printing speed of printing device. Responsiveness, (5) Ink dries quickly on the recording material, (6) No clogging of the ejection orifice (high ejection stability) during printing or restarting after printing is interrupted. (7) It is required that the safety of the ink is high.

However, since the conventional ink uses a water-soluble dye as a colorant, there is a problem in that the fastness of the printed matter, especially the water resistance and the light resistance, is poor. Therefore, the use of pigments such as carbon black, water-insoluble colorants such as disperse dyes and oil-soluble dyes, and dispersants for dispersing these in an aqueous medium have also been investigated. However, conventionally known dispersants are difficult to stably disperse the above water-insoluble colorant in an aqueous medium, and in particular, the colorant aggregates or precipitates when the ink is stored for a long time. In addition, there are problems that the storage stability of the ink is poor and that the ejection orifice is clogged so that the ink cannot be ejected stably.

Further, these inks have a problem of poor fixability in that the printed matter is easily separated from the surface of the printing medium. An object of the present invention is to provide an ink having excellent water resistance and fixability of printed matter and excellent storage stability.

[0006]

The ink of the present invention is characterized by containing carbon black having a surface thereof graft-polymerized with a polymerizable surfactant, and an aqueous medium in which the carbon black is dispersed. Is. That is, the present inventors have conducted intensive studies to solve the above technical problems, and as a result of using carbon black as a coloring agent, the water resistance of the printed matter is increased, while the polymerizable surfactant is added. When graft-polymerized on the surface of carbon black, the affinity between the carbon black and the aqueous medium is increased, the dispersibility of the colorant and the storage stability of the ink are improved, and an ink with improved fixability of the printed matter is obtained. The present invention has been completed by discovering the new fact that it is possible.

In the present invention, when carbon black obtained by graft-polymerizing at least one of a water-soluble monomer and a water-insoluble monomer together with a polymerizable surfactant is used, the same action as described above can be obtained. Ink is obtained. As the colorant in the ink of the present invention, carbon black obtained by graft-polymerizing a polymerizable surfactant on the surface (hereinafter referred to as grafted carbon black) is used.

As the carbon black used for obtaining the grafted carbon black, those produced by a conventionally known method such as a contact method, a furnace method and a thermal method can be used. Since functional groups such as a carboxyl group, a hydroxyl group and a carbonyl group are present on the surface of these carbon blacks, it is possible to graft polymerize the monomer on the surface. The primary particle size of carbon black is 10 to 100 nm, more preferably 15 to 40 nm
Is.

The polymerizable surfactant has a polymerizable group (vinyl group, allyl group, etc.) in the molecule, preferably at the terminal, and is represented by the following general formulas (1) to (7).
The compound represented by

[0010]

Embedded image

[0011]

Embedded image

(Wherein M is a metal atom, preferably Na,
An alkali metal atom such as K is shown. m is 5 to 10, p is 7 to 12, r is 7 to 12, s is 6 to 11, and t is 7-1.
2, u is an integer of 8 to 13, and w is an integer of 8 to 13. X represents an anion, preferably a halogen atom such as chlorine or bromine. ) Examples of the water-soluble monomer that may be graft-polymerized with the polymerizable surfactant include N-acryloylmorpholine, styrene sulfonate, aminoethyl methacrylate, acrylamides, and the like, and two or more of them are mixed. It can also be used.

Examples of the water-insoluble monomer which may be graft-polymerized with the polymerizable surfactant include styrene and
Examples thereof include vinyl acetate-based monomers such as vinyl pivalate, and two or more of these may be mixed and used. The grafted carbon black is obtained by dispersing the carbon black in water, adding a polymerizable surfactant and a water-soluble polymerization initiator, and optionally adding at least one of a water-soluble monomer and a water-insoluble monomer, and stirring the mixture. However, it is obtained by carrying out graft polymerization. The graft polymerization reaction is usually performed at a temperature of 40 to 100 ° C. for 5 to 1
It is carried out for 0 hours, more preferably for 5 to 8 hours at a temperature of 60 to 80 ° C.

The amount of carbon black added is not particularly limited, but it is preferably 2 to 30% by weight, more preferably 5%, with respect to water.
~ 20 wt% concentration. The amount of the polymerizable surfactant added is 0.1 to 10 times, and more preferably 0.25 to 4 times the weight of the carbon black. Examples of the water-soluble polymerization initiator include 2,2′-azobis (2-amidinopropane) dihydrochloride and 2,2′-azobis (2-
N-benzylamidinopropane) dihydrochloride, 2,2'-
Examples thereof include azobis [2-N- (2-hydroxyethyl) amidinopropane] dihydrochloride. The amount of the water-soluble polymerization initiator added is not particularly limited, but is 5 to 30% by weight, more preferably 5 to 20% by weight, based on all the monomer components.

The amount of the monomer components of the water-soluble monomer and the water-insoluble monomer is not particularly limited, but is 50 to 300 parts by weight, more preferably 80 to 200 parts by weight, relative to 100 parts by weight of carbon black. However, the addition amount of the water-insoluble monomer is 0 in the total amount with the water-soluble monomer.
-50% by weight, more preferably 10-25% by weight.

In the ink of the present invention, the grafted carbon black produced by the above-mentioned method is added to an aqueous medium and dispersed by using a dispersing means such as a ball mill, and then centrifugal separation is carried out if necessary in order to adjust the particle size. It is obtained by performing filtration with a filter. The aqueous medium refers to water or a mixed solution of water and a water-soluble organic solvent. The water-soluble organic solvent is not particularly limited, but examples thereof include alcohols such as methanol, ethanol, n-propanol, isopropyl alcohol, sec-butyl alcohol, amides such as dimethylformamide and dimethylacetamide, and ketones such as acetone and diacetone alcohol. Or ethers such as ketone alcohols, tetrahydrofuran, dioxane, polyhydric alcohols such as glycerin, ethylene glycol, diethylene glycol, triethylene glycol, alkyl ether derivatives of polyhydric alcohols such as triethylene glycol monomethyl ether, glyceryl monoacetate Such as ester derivatives of polyhydric alcohols, nitrogen-containing N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, etc. Jo compounds and the like.

The water-soluble organic solvent has the function of assisting the evaporation of the ink printed on the paper and adjusting the evaporation rate. The ratio of the water-soluble organic solvent to water is 30 parts by weight or less, and more preferably 5 to 20 parts by weight, relative to 100 parts by weight of water, in order to maintain the characteristics as an aqueous medium. The amount of the grafted carbon black added is not particularly limited, but is 1 to 20% by weight, more preferably 3 to 15% by weight, based on the aqueous medium.

[0018]

EXAMPLES The ink of the present invention will be described below with reference to examples. Examples 1 to 4 (1) Preparation of grafted carbon black Table 1 shows each component for obtaining the grafted carbon black and the blending amount thereof.

[0019]

[Table 1]

In the table, as the polymerizable surfactant, sodium undecylenate [a compound in which m in the general formula (1) is 8] was used. Further, as the water-soluble polymerization initiator,
2,2'-azobis (2-amidinopropane) dihydrochloride (V-50 manufactured by Wako Pure Chemical Industries, Ltd.) was used. The compositions shown in Table 1 were reacted at 80 ° C. for 5 hours to carry out graft polymerization to obtain grafted carbon black. (2) Preparation of ink An ink composition having the following composition was prepared using the above grafted carbon black.

Grafted carbon black 5.0 parts by weight Glycerin 1.5 parts by weight Ethanol 8.0 parts by weight Distilled water 85.5 parts by weight Next, the above composition was dispersed in a ball mill for 5 hours to obtain an ink. The blending amount of each component for obtaining the comparative ink is shown below.

Carbon black 5.0 parts by weight Sodium undecylenate 1.0 parts by weight Glycerin 1.5 parts by weight Ethanol 8.0 parts by weight Distilled water 84.7 parts by weight Then, the above composition was dispersed in a ball mill for 5 hours. And got the ink. Evaluation of Ink Properties Regarding the inks obtained in Examples 1 to 4 and Comparative Example,
The following tests were conducted to evaluate the characteristics. (1) Time-dependent measurement test of dispersed particle size of ink Immediately after producing the ink and after leaving at room temperature for 60 days,
Dispersion particle size of carbon black in ink [central particle size D ₅₀
(Μm)] was measured by a light scattering method. The measurement is HOR
It was performed using LA-700 manufactured by IBA. (2) Printing Density Measurement Test Using the inks of Examples and Comparative Examples, a black solid was printed on the paper surface with an inkjet printer, and the initial printing density was measured with a reflection densitometer (TC-6DS manufactured by Tokyo Denshoku Co., Ltd.). It was measured using. (3) Water resistance test of printed matter The paper used for the image density measurement test is immersed in water at 20 ° C. for 5
After left for a minute and sufficiently dried, the print density was measured using the same reflection densitometer as described above, and the water resistance of the ink was determined from the initial print density in (2) above using the following formula. .

[0023]

[Equation 1]

(4) Fixability test of printed matter After using the same printer as above to print a black solid and completely dry it, rub it with a 400 g weight with a filter paper stuck on the bottom surface, and the density of the ink adhering to the filter paper. Was measured with the same reflection densitometer as above, and the fixability was determined from the density of the filter paper as the base using the following formula.

[0025]

[Equation 2]

As is clear from the above formula, the smaller the calculated value, the better the fixing property. Table 2 shows the results of the evaluation of the above characteristics.

[0027]

[Table 2]

As is clear from Table 2, since the inks of Examples 1 to 4 and Comparative Example all used carbon black as the colorant, they were excellent in water resistance and had a sufficient print density. is there. However, Examples 1 to 1 in which a polymerizable surfactant was graft-polymerized on the surface of carbon black
The ink of No. 4 has excellent fixability as compared with the inks of Comparative Examples, and further, the change with time of the dispersed particle diameter is small,
It also has excellent storage stability.

[0029]

INDUSTRIAL APPLICABILITY According to the present invention, a grafted carbon black obtained by graft-polymerizing a polymerizable surfactant (and optionally a predetermined monomer) on the surface of water-insoluble carbon black is used as a colorant. Since it is used, not only the printed matter has high water resistance and the printing density shows a sufficient value, but also the storage stability of the ink is good because the change of the dispersed particle diameter of the ink with time is small. Further, it is also excellent in the fixing property of the printed matter.

Therefore, the ink of the present invention is particularly suitable for use as an ink for ink jet printers.

Claims (3)

[Claims] 1. An ink comprising a carbon black having a surface thereof graft-polymerized with a polymerizable surfactant, and an aqueous medium in which the carbon black is dispersed. 2. The ink according to claim 1, wherein at least one of a water-soluble monomer and a water-insoluble monomer is graft-polymerized with the polymerizable surfactant. 3. The polymerizable surfactant is carbon black 10
The ink according to claim 1, which is added in an amount of 10 to 1000 parts by weight with respect to 0 parts by weight.