JPH0881646A - 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, useful for an ink jet printer, etc., by using carbon black graftpolymerized with prescribed monomer components as a colorant. CONSTITUTION: This ink contains (A) a water-soluble monomer (e.g. N- acryloylmorpholine, 5-20wt.% to a dispersion medium), (B) a water-insoluble monomer (e.g. styrene, a total amount of the components A and B is 5-20 pts.wt.), (C) carbon black having the surface on which the components A and B are graft-polymerized (e.g. primary particle diameter is 15-40nm) and (D) an aqueous medium dispersing the component C. A monomer having an aromatic hydrocarbon group is used as at least one of the components A and B, and preferably the component A is graft-polymerized with (E) a polymerizable trialkoxysilane derivative and further with 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 of a printed matter and storage stability of the ink, and also excellent in fixing property of the printed matter.

[0006]

Means and Actions for Solving the Problems The ink of the present invention is characterized by containing carbon black obtained by graft-polymerizing a water-soluble monomer and a water-insoluble monomer on the surface, and an aqueous medium in which the carbon black is dispersed. It is what That is, as a result of intensive studies to solve the above technical problems, the present inventors have found that the use of carbon black as a colorant improves the water resistance of a print, while the water-soluble monomer is carbon black. When graft-polymerized on the surface of the ink, the affinity between the carbon black and the aqueous medium increases, the dispersibility of the colorant and the storage stability of the ink improve, and the water-insoluble monomer also graft-polymerizes on the surface of the carbon black. By doing so, they found a new fact that an ink having improved fixability of printed matter can be obtained, and completed the present invention.

Furthermore, another ink of the present invention is characterized by containing carbon black having a surface thereof graft-polymerized with a water-soluble monomer and a polymerizable trialkoxysilane derivative, and an aqueous medium in which the carbon black is dispersed. . Even with such an ink, the printed matter has high water resistance, the dispersibility of the colorant and the storage stability of the ink are excellent, and the fixability of the printed matter is also excellent.

As the colorant in the ink of the present invention, carbon black obtained by graft-polymerizing a predetermined monomer on the surface (hereinafter referred to as grafted carbon black) is used. To prepare this grafted carbon black,
There are (a) a method using a water-soluble monomer and a water-insoluble monomer, and (b) a method using a water-soluble monomer and a polymerizable trialkoxysilane derivative.

First, the case (a) will be described. In this case, the grafted carbon black is obtained by dispersing carbon black in water, adding a water-soluble monomer, a water-insoluble monomer and a water-soluble polymerization initiator, and carrying out graft polymerization while stirring. The graft polymerization reaction is usually performed at a temperature of 40 to 100 ° C. for 2 to 8 hours, more preferably at a temperature of 60 to 80 ° C. for 5 to 7 hours.

The carbon black used for obtaining the grafted carbon black includes the contact method,
Examples include those manufactured by a conventionally known method such as a furnace method and a thermal method. 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.

The amount of carbon black added is not particularly limited, but the concentration is 2 to 30% by weight, more preferably 5 to 20% by weight, based on the dispersion medium such as water. Examples of the water-soluble monomer include N-acryloylmorpholine, styrene sulfonate, aminoethyl methacrylate, acrylamides, and the like, and two or more kinds of these may be mixed and used.

Examples of the water-insoluble monomer include vinyl acetate-based monomers such as styrene and vinyl pivalate, and two or more kinds of these may be mixed and used. It is preferable that at least one of the water-soluble monomer and the water-insoluble monomer has an aromatic hydrocarbon group in order to improve the affinity with the carbon black surface in the aqueous medium.

The addition amount of the water-soluble monomer and the water-insoluble monomer is not particularly limited, but carbon black 100
50 to 500 parts by weight, more preferably 1 part by weight
It is from 00 to 300 parts by weight. However, the amount of the water-insoluble monomer added is 2 to 40 parts by weight in the total amount with the water-soluble monomer,
It is more preferably 5 to 20 parts by weight. Examples of the water-soluble polymerization initiator include 2,2′-azobis (2-amidinopropane) dihydrochloride, 2,2′-azobis (2-N-benzylamidinopropane) dihydrochloride, 2,2′-azobis. Examples include [2-N- (2-hydroxyethyl) amidinopropane] dihydrochloride. The addition amount of the water-soluble polymerization initiator is not particularly limited, but it is 5 with respect to all the monomer components.
-30% by weight, more preferably 10-20% by weight.

Next, the case (b) will be described. The grafted carbon black in this case is obtained by dispersing carbon black in a dispersion medium such as water, adding a water-soluble monomer, a polymerizable trialkoxysilane derivative and a water-soluble polymerization initiator, and further improving the fixing property. It can be obtained by adding a water-insoluble monomer as needed and carrying out graft polymerization while stirring. The graft polymerization reaction is usually performed at a temperature of 40 to 100 ° C. for 2 to 10 hours, more preferably 60 to 80 ° C. for 7 to 9 hours.

The carbon black, water-soluble monomer, water-insoluble monomer and water-soluble polymerization initiator include (a)
The same thing as that used in the case of can be used. The polymerizable trialkoxysilane derivative is a compound having a polymerizable group (vinyl group, allyl group, etc.) in the molecule, and examples thereof include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltripropoxysilane, and vinyltributoxysilane. Can be mentioned. These compounds function as a silane coupling agent.

The types and addition amounts of carbon black, water-soluble monomer and water-soluble polymerization initiator are the same as in (a). Furthermore, the proportion of the water-insoluble monomer in the total amount with the water-soluble monomer is the same as in the case of (a). The addition amount of the polymerizable trialkoxysilane derivative is not particularly limited, but is 10 to 300 parts by weight, more preferably 50 parts by weight with respect to 100 parts by weight of carbon black.
~ 200 parts by weight.

In the ink of the present invention, the grafted carbon black prepared by the above method (a) or (b) is added to an aqueous medium and dispersed using a dispersing means such as a ball mill, and then the particle size is adjusted. Therefore, it can be obtained by performing centrifugation or filtration with a filter as necessary. 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 ketone alcohols, tetrahydrofuran, ethers such as dioxane, glycerin, ethylene glycol, diethylene glycol,
Polyhydric alcohols such as triethylene glycol, alkyl ether derivatives of polyhydric alcohols such as triethylene glycol monomethyl ether, ester derivatives of polyhydric alcohols such as glyceryl monoacetate, N-methyl-2-pyrrolidone, 1 , 3-dimethyl-
Examples thereof include nitrogen-containing cyclic compounds such as 2-imidazolidinone.

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 3 to 30% by weight, and more preferably 5 to 20% by weight, based on the aqueous medium.

[0019]

EXAMPLES The ink of the present invention will be described below with reference to examples. Examples 1 to 2 (1) Preparation of grafted carbon black Table 1 shows each component for obtaining the grafted carbon black and the blending amount thereof.

[0020]

[Table 1]

In the table, 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 the table were reacted at 80 ° C. for 8 hours for graft polymerization to obtain grafted carbon black. (2) Preparation of Ink The above-mentioned grafted carbon black was used and blended in the following composition for each example.

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. Examples 3 to 5 Inks were obtained in the same manner as in Examples 1 to 2 except that the components shown in Table 2 were used in the proportions shown in the table to carry out the graft polymerization.

[0023]

[Table 2]

The water-soluble polymerization initiators in the table are the same as those in Examples 1 to 1 above.
The same as that used in 2. Comparative Examples 1 and 2 (1) Preparation of Dispersant A dispersant of each Comparative Example was prepared with the following composition.

[0025]

[Table 3]

The water-soluble polymerization initiators in the table are the same as in Examples 1 to 1 above.
The same as that used in 2. The dispersants of Comparative Examples 1 and 2 were heated at 80 ° C. for 5 hours for polymerization, and then the product was filtered, washed with water and dried to obtain a dispersant. (2) Preparation of Ink The above-mentioned dispersant was used and blended in the following composition for each comparative example.

Carbon black 5.0 parts by weight Dispersant 1.0 parts by weight Glycerin 1.5 parts by weight Ethanol 8.0 parts by weight Distilled water 84.5 parts by weight Then, the above composition was dispersed in a ball mill for 5 hours. I got the ink. Evaluation of Ink Properties The inks obtained in Examples 1 to 5 and Comparative Examples 1 and 2 were subjected to the following tests to evaluate their properties. (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. HOR for measurement
LA-700 manufactured by IBA was used. (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. .

[0028]

[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.

[0030]

[Equation 2]

As is clear from the above equation, the smaller the calculated value, the better the fixing property. Table 4 shows the results of the evaluation of the above characteristics.

[0032]

[Table 4]

As is clear from Table 4, the inks of Examples 1 to 5 and Comparative Examples 1 and 2 all used carbon black as a colorant and thus had excellent water resistance.
The print density also shows a sufficient value. However, the inks of Examples 1 to 5 in which a predetermined monomer component was graft-polymerized on the surface of carbon black were superior in fixability to the inks of Comparative Examples 1 and 2, and the change in dispersed particle size with time was small. Therefore, it has excellent storage stability.

[0034]

According to the present invention, since the grafted carbon black obtained by graft-polymerizing a predetermined monomer component on the surface of the water-insoluble carbon black is used as the colorant of the ink, the water resistance of the printed matter is improved. In addition to being high and showing a sufficient print density, the storage stability of the ink is good because the dispersed particle diameter of the ink has a small change over time.
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 (4)

[Claims] 1. An ink comprising carbon black having a surface thereof graft-polymerized with a water-soluble monomer and a water-insoluble monomer, and an aqueous medium in which the carbon black is dispersed. 2. The ink according to claim 1, wherein at least one of the water-soluble monomer and the water-insoluble monomer is a monomer having an aromatic hydrocarbon group. 3. An ink comprising: a carbon black having a surface thereof graft-polymerized with a water-soluble monomer and a polymerizable trialkoxysilane derivative; and an aqueous medium in which the carbon black is dispersed. 4. The ink according to claim 3, wherein a water-insoluble monomer is further added to the water-soluble monomer and the polymerizable trialkoxysilane derivative for graft polymerization.