JP2003327879A - Ink for ink-jet recording - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain ink for an ink-jet recording, which keeps excellent nozzle drying properties while maintaining continuous printability, color development, bleeding prevention, fixing properties, etc., on a medium to be printed. <P>SOLUTION: In the ink for the ink-jet recording containing at least a water- soluble dye, purified water and a water-soluble organic solvent, the ink contains formamide as the water-soluble organic solvent. The ink preferably contains at least one kind selected from diethylene glycol, diethylene glycol monobutyl ether, glycerol and 2-pyrrolidone as the water-soluble organic solvent except formamide. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water-based ink used in an ink jet recording type recording apparatus.

[0002]

2. Description of the Related Art Ink jet recording is one of the image recording technologies which have recently become more important due to their excellent recording stability and the ability to easily obtain full-color image recording.

Ink jet recording inks are generally classified into water-based inks that use purified water as a main solvent and oil-based inks that use an organic solvent as a main solvent.

Images recorded with water-based inks generally have poor water resistance. However, since the solvent is water and is excellent in safety, water-based inks have become the mainstream of inks used in inkjet recording systems.

The basic performance required of this water-based ink is that it develops color on plain paper (non-coated paper such as PPC, report paper, notebook, notepaper, and bond paper) commonly used in business and home. Excellent, clear full-color recording is possible and there is no blur in the recorded image,
Fast drying and excellent fixability on the print medium,
No clogging of the nozzle head (hereinafter abbreviated as nozzle) of the inkjet device due to ink drying,
Ink ejection characteristics are stable over a wide temperature range (nozzle drying resistance), printing colors printed on plain paper are stable and do not deteriorate over a long period of time, and the physical properties of the ink itself do not change and environmental changes It is stable and stable, there is no problem with the safety of the user, and no special odor is generated.

As a conventional technique for satisfying the above plurality of required performances, for example, a method has been proposed in which a specific surfactant is added to the ink to lower the surface tension and enhance the permeability into the inside of the recording paper. Has been done.

Further, a method of controlling the dot diameter expansion and penetrability by adding a strongly basic material to the ink and chemically dissolving the sizing material and the pulp material of the recording paper, the molecular weight in the ink is 40,000 or more. There is proposed a method of adding polyvinylpyrrolidone, a method of controlling the enlargement of the dot diameter and the permeability by adding a specific microemulsion to the ink.

Further, a method has been proposed in which dimethylsulfoxides, which dissolves a water-soluble dye well and have extremely strong hygroscopicity, are added to enhance the drying resistance of the ink itself.

Further, in order to prevent the nozzles from being clogged due to the drying of the ink, a device for regularly or forcibly cleaning the surface of the nozzle or a device for sucking the ink from the nozzle, or always when recording is stopped. There has been proposed a device for sealing the nozzle surface to prevent the ink from drying.

[0010]

However, the conventional water-based ink for ink jet recording has the following problems.

That is, among the above-mentioned conventional techniques, the method of adding a surfactant lowers the surface tension of the ink and enhances the permeability into the inside of the recording paper, so that the fixing property is improved, but the ink is used as the recording paper. Since it penetrates deeply into the interior, there is a problem that the color developability is likely to be remarkably lowered, and the ink containing a surfactant is apt to foam.

In addition, in the method of adding the strongly basic material,
Bleeding occurs on a print-receiving medium using a specific size material, for example, neutral paper, and the quick-drying property is insufficient.

Further, in the method of adding polyvinylpyrrolidone or microemulsion, it is possible to enhance the fixing property and the drying property because it has the property of penetrating into the paper, but the spread not only on the inside of the recording paper but also on the surface. Since it is large, the breakage of dots deteriorates, so that the effect cannot be expected when the recording density of ink is large, as in full-color recording.

Further, in the method of adding dimethyl sulfoxides having a strong hygroscopicity as an ink component, although the nozzle has excellent drying resistance, the drying on the plain paper at the time of low temperature recording becomes extremely slow, and the fixing property becomes poor. As it is inferior, it cannot maintain the printing quality. In addition, dimethylsulfoxides generally generate a strong odor and are difficult to handle.

Frequent cleaning using a head protector or the like during printing operation or recording stop is effective for improving the nozzle drying resistance, but is unnecessary. There is a problem in that the amount of ink used increases and economic efficiency decreases.

Therefore, the object of the present invention is to improve the above-mentioned drawbacks of the conventional water-based ink and to maintain continuous printability, color developability, prevention of bleeding, and fixability on a print medium.
An object of the present invention is to provide an ink for ink jet recording that can maintain excellent nozzle drying resistance.

[0017]

Means for Solving the Problems As a result of intensive studies for achieving the above-mentioned object, the present inventors have found that formamide, which is one of the water-soluble organic solvents, has hygroscopicity similar to that of dimethylsulfoxides. However, they have no odor, have excellent fixability (dryability) on plain paper even at low temperature printing, and have found that problems such as head clogging due to ink drying do not occur, and have completed the present invention. .

That is, the ink-jet recording ink of the present invention is an ink-jet recording ink containing at least a water-soluble dye, purified water, and a water-soluble organic solvent, and contains formamide as the water-soluble organic solvent. Characterize.

According to the ink of the present invention, since formamide has a hygroscopic property, it is possible to suppress the ink drying inside the nozzle and improve the nozzle drying resistance. As a result, the frequency of cleaning the nozzle can be reduced. Further, even if the head end surface of the nozzle is not sealed with the protective device, the nozzle can be prevented from clogging for a certain period of time.

Formamide is also water-soluble, has a low viscosity,
Since it is a transparent liquid and also acts as a regulator for reducing the large surface tension of purified water, it is possible to improve the quick-drying property to the printing medium, that is, the fixing property, and prevent the occurrence of bleeding. Printing quality can be improved.

Furthermore, since formamide is a colorless and odorless liquid, it does not have the odor of dimethyl sulfoxide, is easy to handle, and is safe for the user.

In the present invention, it is preferable that the water-soluble organic solvent further contains at least one selected from diethylene glycol, diethylene glycol monobutyl ether, glycerin and 2-pyrrolidone.

According to this aspect, the above substance is a water-soluble organic solvent having a high boiling point, and functions as an adjusting agent when determining the physical properties of the ink such as surface tension and viscosity. Therefore, by using the above water-soluble organic solvent in combination, the surface tension and the viscosity can be adjusted within the optimum range for the water-based ink.

Further, in the present invention, it is preferable that the purified water content is 25 to 70% by mass, and the formamide content is 10 to 60% by mass.

According to this aspect, by setting the content of formamide within the above range, ink fading (decrease in color developability) when the ink is stored for a long period of time while maintaining the nozzle drying resistance is achieved. Can be prevented. Further, by setting the content of purified water in the above range, it is possible to stably dissolve the water-soluble dye and form a stable ink composition while maintaining the nozzle drying resistance.

[0026]

The present invention will be described in more detail below. The inkjet recording ink of the present invention is characterized by containing at least a water-soluble dye, purified water, and a water-soluble organic solvent, and further containing formamide as the water-soluble organic solvent.

As the water-soluble dye, conventionally known water-soluble dyes can be used, and examples thereof include acid dyes, basic dyes, reactive dyes, disperse dyes, direct dyes, and food dyes. The content of water-soluble dye is 0.5 to the total amount of ink.
It is preferably 15% by mass.

Further, the purified water is preferably purified water having a purity higher than that of ion-exchanged water so as not to be influenced by heavy metals. The content of purified water is preferably 25 to 70 mass% with respect to the total amount of ink. If it is less than 25% by mass, the water-soluble dye cannot be stably dissolved, which is not preferable, and if it exceeds 70% by mass, the nozzle drying resistance in the inkjet device is deteriorated, which is not preferable.

Next, the water-soluble organic solvent will be described.
The present invention is characterized by containing formamide as a water-soluble organic solvent.

Formamide has a boiling point of 210 ° C. and is odorless,
It is a low-viscosity, transparent liquid with mildew resistance and hygroscopicity.
As a result, it is possible to suppress ink drying at the head nozzles of the inkjet apparatus, prevent clogging of the head due to ink drying even in printing at low temperatures, and improve nozzle drying resistance.

The surface tension of formamide is about 40 m.
N / m, the surface tension of dimethyl sulfoxide is about 6
Low compared to 0 mN / m. For this reason, formamide reduces the surface tension of purified water, so that the ink is excellent in fixing property (drying property) to paper as a print medium, particularly plain paper.

Further, formamdo stably dissolves in a water-soluble dye like dimethyl sulfoxides, and has no special odor. Therefore, it is easier to handle than dimethyl sulfoxides. It is also highly safe for users.

The content of formamide is preferably 10 to 60% by mass with respect to the total amount of the ink, and in consideration of nozzle drying resistance for a long period of time, 45 to 45% by mass.
It is more preferably 60% by mass.

If the content of formamide is less than 10% by mass, the effect of suppressing ink drying at the head nozzle becomes insufficient, so that it is not preferable, and if it exceeds 60% by mass, when the ink is stored for a long period of time. Ink fading (decrease in color developability) is likely to occur, which is not preferable.

In the present invention, it is preferable to use other water-soluble organic solvent in addition to the above formamide. This makes it possible to more optimally adjust the physical properties of the ink as a whole, such as viscosity, surface strength, penetrability (fixability), and dryness. For example, in the case of water-based ink, its viscosity is usually 1.5 to 4.0 mPa · s and its surface tension is 35 to
It is preferable to adjust to the range of 55 mN / m, and the above range can be easily adjusted by using the above water-soluble organic solvent in combination.

Examples of such water-soluble organic solvents other than formamide include alcohols such as ethyl alcohol, methyl alcohol, propyl alcohol, isopropyl alcohol, N-butyl alcohol, isobutyl alcohol, cyclohexanol, benzyl alcohol, and the like. Glycols such as ethylene glycol, diethylene glycol, propylene glycol, polyethylene glycol and glycerin; glycol ethers such as ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, ethylene glycol monobutyl ether and diethylene glycol monobutyl ether; and 1,3-dimethyl-2- Imidazolidinone,
Five-membered cyclic compounds such as 5,5-dimethylhydantoin, 3,5-dimethylpyrazole and 2,5-dimercapto-1,3,4-thiadiazole, and pyrrolidone such as 2-pyrrolidone and N-methyl-2-pyrrolidone And alkanolamines such as triethanolamine.

Of the above, diethylene glycol, diethylene glycol monobutyl ether, glycerin, 2
-It is preferable to include at least one selected from pyrrolidone.

In this case, the viscosity and surface tension of the ink can be adjusted by the combined use of at least one selected from glycerin, diethylene glycol and 2-pyrrolidone. Further, the combined use of at least one kind selected from diethylene glycol and 2-pyrrolidone can further enhance the effect of preventing the nozzle of the inkjet device from drying. Further, the combined use of diethylene glycol monobutyl ether can enhance the penetrability (fixability) of the ink to the printing medium.

The content of the water-soluble organic solvent other than the above formamide may be appropriately selected so as to achieve the quality required for the above purpose and application, but it is 10 to 30% by mass with respect to the total amount of the ink. It is preferable to contain.

The compounding ratio of formamide and the water-soluble organic solvent other than formamide is 1 to formamide and 0.15 to 2.5 of the water-soluble organic solvent other than formamide. It is preferable.

The above water-soluble organic solvents other than formamide may be used alone, but it is preferable to use two or more kinds in combination, and it is particularly preferable to use glycerin and diethylene glycol monobutyl ether in combination. In this case, the specific content is preferably 3 to 7% by mass in the case of glycerin and 5 to 10 in the case of diethylene glycol monobutyl ether.
It is preferably contained in an amount of 5% by mass, and preferably 5 to 15% by mass in the case of diethylene glycol and 2-pyrrolidone.

In addition to the above, an antifoaming agent, an antiseptic agent, an antifungal agent and the like may be appropriately added to the ink jet recording ink of the present invention.

The ink jet recording ink of the present invention having the above composition can be made into an ink by a conventionally known method. For example, the above compositions are mixed and sufficiently dissolved at room temperature to form a membrane filter or the like. Can be produced by pressure filtration.

The ink jet recording ink of the present invention thus obtained is excellent in continuous printability, color developability and prevention of bleeding on a print medium such as plain paper, and also has fixability (drying property) in low temperature printing. ) Is improved. Furthermore, since it has the same hygroscopicity as inks using dimethyl sulfoxides, it has excellent nozzle drying resistance, and is safe, odorless, and easy to handle.

[0045]

EXAMPLES The present invention will be described more specifically below with reference to Examples and Comparative Examples.

Example 1 As a water-soluble organic solvent, formamide, glycerin and diethylene glycol monobutyl ether were used in combination, and Table 1
The respective raw materials were mixed in a blending ratio of mass% shown in Table 1, sufficiently dissolved at room temperature, and pressure-filtered using a 0.45 μm membrane filter to obtain four color inks of Examples 1A to 1D. Created.

As the dye of Example 1A, C.I.
I. Direct Black 9 (black) was used as the dye of Example 1B, and C.I. I. Acid Blue 9 (cyan)
As the dye of Example 1C, C.I. I. Acid Red 35 (magenta color) was used as the dye of Example 1D.
C. I. Direct Yellow 86 (yellow color) was used.

[0048]

[Table 1]

Example 2 Formamide, glycerin, diethylene glycol monobutyl ether and 2-pyrrolidone were used together as the water-soluble organic solvent, and the respective raw materials were mixed at the compounding ratio shown in Table 1. As the dye, C.I. I. A black ink was prepared under the same conditions as in Example 1 except that Direct Black 9 (black) was used.

Example 3 As a water-soluble organic solvent, formamide, diethylene glycol monobutyl ether, diethylene glycol, 2
-A black ink was prepared under the same conditions as in Example 2 except that pyrrolidone was used in combination and each raw material was mixed in the mixing ratio shown in Table 1.

Example 4 As a water-soluble organic solvent, formamide, glycerin and diethylene glycol monobutyl ether were used in combination, and Table 1
A black ink was prepared under the same conditions as in Example 2 except that the raw materials were mixed in the mixing ratio shown in.

Example 5 The same conditions as in Example 2 except that formamide, glycerin, diethylene glycol monobutyl ether, diethylene glycol and 2-pyrrolidone were used in combination as the water-soluble organic solvent and the respective raw materials were mixed in the mixing ratio shown in Table 1. I made black ink with.

Comparative Example 1 A black ink was prepared under the same conditions as in Example 2 except that ethyl alcohol, glycerin, and diethylene glycol monobutyl ether were used in combination as the water-soluble organic solvent, and the raw materials were mixed in the proportions shown in Table 1. did.

Comparative Example 2 Same as Example 1B except that glycerin, diethylene glycol monobutyl ether, and 1,3-dimethylimidazolidinone were used together as the water-soluble organic solvent, and the raw materials were mixed in the mixing ratio shown in Table 1. Cyan ink was created under the conditions.

Comparative Example 3 A magenta ink was prepared under the same conditions as in Comparative Example 2 except that the dye used in Example 1C was used as the dye.

Comparative Example 4 A yellow ink was prepared under the same conditions as in Comparative Example 2 except that the dye used in Example 1D was used as the dye.

Comparative Example 5 A black ink was prepared under the same conditions as in Example 2 except that diethylene glycol monobutyl ether and dimethyl sulfoxide were used together as the water-soluble organic solvent, and the respective raw materials were mixed in the mixing ratio shown in Table 1. did.

Test Example <Physical Properties of Ink> The surface tension, viscosity and pH of the inks of Examples 1-5 and Comparative Examples 1-5 were measured. The surface tension was measured by using an automatic surface tension meter (trade name: CBVP-A3, manufactured by Kyowa Interface Science Co., Ltd.) to measure the surface tension of the ink at 25 ° C., and the viscosity of the ink at 25 ° C. was measured by an E-type viscometer ( Product name: VISCONIC ED, manufactured by Tokimec Co., Ltd.). The results are summarized in Table 1.

<Print Evaluation> The apparatus used for evaluation is a piezo type ink jet recording apparatus equipped with a four-color integrated printer head, the resolution is 300 dpi, and the ink ejection amount per nozzle is controlled to be about 60 pl. did. The test paper used for evaluation was plain paper (Xerox # 4024) manufactured by Xerox. The evaluation items are the following 6
I did about the item. The results are summarized in Table 2.

[Continuous printing test] Using the above-mentioned apparatus, a continuous printing test of 500 sheets (paper size B5) of a printing pattern having a printing density of 15% with each color ink was conducted, and no ejection failure was observed after 500 sheets. Those that were found to have a "○", and those that caused a problem even with one sheet were marked as "X".

[Coloring test] The dissolution stability of the dye in the ink and the optical reflection density of the solid printed portion were evaluated. The optical reflection density was measured with a Macbeth reflection densitometer, and black is 1.0
As described above, the cyan color is 1.2 or more, the magenta color is 1.1 or more, and the yellow color is 0.9 or more. The one satisfying the dissolution stability and the optical reflection density was marked with "O", and the one not satisfying any one was marked with "X".

[Bleeding Test] Solid printing of each color was performed, and the bleeding (including feathering) at the solid printed end was visually inspected. If there was no bleeding, it was marked with "O", and if there was bleeding, it was marked with "X".

[Fixability Test] Solid monochromatic printing of each color is performed,
After printing for 10 seconds, the printed portion was rubbed with a filter paper to check the presence or absence of ink rub. If there was no rubbing of the ink, it was marked with "O", and if there was rubbing, it was marked with "X".

[Nozzle Drying Test] A head filled with ink of each color was mounted on a notation device, the end face of the nozzle was sealed with a cap, left at 25 ° C. for 5 days and at 40 ° C. for 5 days, and then cleaned ( An ink ejection test was conducted without performing ink suction by the device protection device. If there was no ejection failure, it was marked as "○", and if there was ejection failure even with one nozzle at both temperatures, it was marked as "X". did.

[Ink Fading Test] Each color ink was filled in a required ink bag and stored at 60 ° C. for 1 month, and then solid monochromatic printing of each color was performed by the above-mentioned apparatus and head, and its optical reflection density was measured before storage. If it is 80% or more of the value of
When discolored to 0% or less, it was marked as "x".

[0066]

[Table 2]

From Table 2, it can be seen that the inks of Examples 1 to 3 of the present invention gave good results in all evaluation items.

Further, in Example 4 in which the content of formamide exceeds 10 to 60% by mass, which is the preferred range of the present invention, the reaction between the formamide and the dye proceeds, and the fading of the ink during high temperature storage was observed. . Further, in Example 5 in which the content of formamide was less than the preferred range of the present invention, a reduction in nozzle drying resistance was observed.

On the other hand, in Comparative Examples 1 to 4 which did not contain formamide, the printing characteristics were good, but the nozzle drying resistance was high, especially ejection failure occurred frequently after standing at 40 ° C. for 5 days. . Further, it can be seen that Comparative Example 5, which contains dimethyl sulfoxide, has excellent nozzle drying resistance due to its hygroscopicity, but bleeding and fixing ability are deteriorated.

[0070]

As described above, according to the present invention,
Inkjet recording ink containing water-soluble dye, purified water and water-soluble organic solvent, since formamide is contained as a water-soluble organic solvent, continuous printability, color developability, and prevention of bleeding on the print medium. It is possible to provide an inkjet recording ink that can maintain excellent nozzle dryness while maintaining fixability and the like.

Continued front page    (72) Inventor Nobuko Kiyono             1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa             Within Fuji Electric Co., Ltd. F-term (reference) 2C056 EA04 FC01                 2H086 BA52 BA53 BA56 BA62                 4J039 BC07 BC11 BC15 BC36 BC50                       BE12 CA03 EA27 EA42 EA43                       EA46 EA47 GA24

Claims (3)

[Claims] 1. An inkjet recording ink containing at least a water-soluble dye, purified water, and a water-soluble organic solvent, wherein formamide is contained as the water-soluble organic solvent. 2. The ink for ink jet recording according to claim 1, further comprising at least one selected from diethylene glycol, diethylene glycol monobutyl ether, glycerin, and 2-pyrrolidone as the water-soluble organic solvent. 3. The ink for ink jet recording according to claim 1, wherein the purified water content is 25 to 70 mass%, and the formamide content is 10 to 60 mass%.