JP2003342501A - Water-base ink - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water-base ink improving the jetting stability from a nozzle or a penpoint and clogging resistance without lowering fixing properties, abrasion, water and marker resistances of a formed image. <P>SOLUTION: The water-base ink comprises a colorant, a resin, water glass and an organic solvent. The colorant is self-dispersible carbon black having anionic hydrophilic groups on the surface. The polydispersity index obtained by analyzing the particle size distribution of the carbon black by a cumulant method is ≤0.2. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a water-based ballpoint pen,
The present invention relates to a water-based ink (water-based recording liquid) that can be suitably used for writing instruments such as fountain pens and water-based felt-tip pens, and on-demand type ink jet printers such as thermal jet systems and piezo systems.

[0002]

2. Description of the Related Art Conventionally, carbon black, which has excellent fastness such as water resistance and light resistance, has been widely used as a black color material for printing inks. It is necessary to stabilize the dispersion in the medium. However, since carbon black generally does not have good dispersibility, as a means for obtaining a uniform dispersion system, a method of adding a dispersant to an aqueous ink to disperse carbon black in an aqueous medium or carbon black by oxidation or the like is used. The method of making the surface hydrophilic is adopted.

However, in the method of adding a dispersant to obtain a high dispersibility, a large amount of a dispersant is required to stabilize and disperse the carbon black, so that the viscosity of the water-based ink becomes high and the water-based ink has a high viscosity. Discharge stability becomes poor. Also,
In the method of hydrophilizing the surface of carbon black, the fixability of the water-based ink when printed on paper is poor, and the scratch resistance and marker resistance of the obtained image are not sufficient.

In order to improve these, Japanese Patent Laid-Open No. 10-1
As disclosed in Japanese Patent Publication No. 83040, in the case where the method of dispersing the carbon black and the water-dispersible resin which have been subjected to the oxidation treatment on the surface is adopted, the scratch resistance and the marker resistance of the obtained image are not sufficient. Even if there was, there were cases where the ejection stability of the ink was unstable.

[0005]

SUMMARY OF THE INVENTION Therefore, the object of the present invention is to solve the above-mentioned problems of the prior art, and to reduce the fixing property, scratch resistance, water resistance, and marker resistance of an image to be formed, without reducing the nozzle. Another object of the present invention is to provide a water-based ink having improved ejection stability from a pen tip and resistance to clogging.

[0006]

The above object can be achieved by the present invention described below. That is, the present invention is a water-based ink containing a coloring material, a resin, water glass and an organic solvent,
The coloring material is a self-dispersing carbon black having an anionic hydrophilic group on the surface, and the polydispersity index obtained by analyzing the particle size distribution of the carbon black by the cumulant method is 0.2 or less. An aqueous ink characterized by the above is provided.

In the present invention, the water-based ink has a mass ratio of the coloring material to the resin of 1: 0.01 to 1: 2 in terms of solid content; a mass ratio of the resin to the water glass. Is a water-based ink having a solid content ratio of 1: 0.001 to 1: 1; a water-soluble or water-dispersible polyester resin or a water-dispersible polyurethane resin; and an inkjet printer. The above-mentioned water-based ink for use is provided.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail with reference to the preferred embodiments. The carbon black used as a coloring material in the present invention is a self-dispersing carbon black having an anionic hydrophilic group (such as a carboxyl group or a sulfonic acid group) on the surface thereof. It is preferable that the surface of carbon black is subjected to an oxidation treatment using a known oxidizing agent, or carbon black having an anionic hydrophilic group provided on the surface.

In the present invention, the self-dispersing carbon black as described above is used as the coloring material for the water-based ink, so that the amount of the pigment dispersant added to the water-based ink of the present invention can be reduced or the dispersant can be used. The carbon black is stably dispersed in the water-based ink even without the addition of the above. As a result, in addition to the effect of reducing the amount of the dispersant used or eliminating the dispersant, the nozzle and the pen tip The ejection stability and the anti-clogging property of the water-based ink are also improved.

The polydispersity index of the self-dispersing carbon black used in the present invention is 0.2 or less as determined by analyzing the particle size distribution by the cumulant method. The “polydispersity index” here is a value obtained by the electrophoretic light scattering method, and is a value obtained from the calculation formula of u / G ² . u is the value of the second-order coefficient of the cumulant method, and G is the damping constant of the cumulant method. When the polydispersity index exceeds 0.2, the self-dispersing carbon black has a wide particle size distribution, and carbon black having a large particle size is present in the water-based ink, which tends to deteriorate the ejection stability of the water-based ink. It is not preferable because it exists.

The zeta potential on the surface of the self-dispersion carbon black measured by a laser zeta potentiometer is preferably in the range of -100 to -30 mV.
When the zeta potential is higher than -30 mV, there may be a defect such as precipitation of the self-dispersing carbon black in the aqueous ink. Moreover, the zeta potential is -100 m.
If it is smaller than V, defects such as poor water resistance of the formed image may occur.

The average particle size of the above carbon black measured by a laser particle size analysis system is 20 to 2
It is preferably in the range of 00 nm. If the average particle size is too small, the image density of the image formed by the water-based ink will decrease, while if the average particle size is too large, the ejection stability and clogging resistance of the water-based ink from the nozzle or pen tip will be poor. It may decrease.

The above-mentioned self-dispersing carbon black is preferably produced in water by a conventionally known method to prepare an aqueous dispersion, and the dispersion or presscake is preferably used. Also, when using a commercially available product, it is preferable to use it in the state of a dispersion liquid or a press cake.
This is because if these dispersion liquids or press cakes are once dried to form powders, the self-dispersing carbon black particles aggregate, and it is not easy to perform fine dispersion again.

The resin used in the present invention has a function of fixing the self-dispersing carbon black to the recording material after the aqueous ink is applied to the recording material such as paper, and is, for example, water-soluble. Or water-dispersible acrylic resin,
Resins such as epoxy resins and silicone resins can be used. Further, water-soluble or water-dispersible polyester resins and polyurethane resins are particularly preferable.

These polyester resins have a molecular weight of 3,000 to 100,000, more preferably 4,0.
0 to 50,000, a glass transition temperature (Tg) of -20 to 100 ° C, more preferably -15 to 80 ° C, and a thermal decomposition temperature of 150 ° C or higher, further preferably 2
A resin having a temperature of 00 ° C or higher is preferable. For example, PLUSCOAT RZ105 (manufactured by Gosho Chemical Co., Ltd.), Polyester WR961, WR905 (manufactured by Nippon Gosei Co., Ltd.), M
D-1930 (manufactured by Toyobo Co., Ltd.) and the like can be obtained and used in the present invention. The water-dispersible polyurethane resin has a glass transition temperature (Tg) of -50 to.
100 ° C., more preferably −30 to 80 ° C., average particle diameter 10 to 200 nm, further preferably 15 to
Resins with a thickness of 80 nm are preferred. Such a water-dispersible polyurethane resin can be obtained in the trade name of Neosticker 400 (manufactured by Nika Kagaku Co., Ltd.) and used in the present invention.

The mass ratio of the above self-dispersible carbon black and the resin in the aqueous ink is 1: in terms of solid content.
It is preferably 0.01 to 1: 2. If the amount of the resin is too small, the image formed by the aqueous ink of the present invention may not have sufficient fixability of the aqueous ink to a recording material such as scratch resistance, water resistance, and marker resistance. If it is too large, the viscosity of the water-based ink becomes high, and the ejection stability and anti-clogging property of the water-based ink may decrease.

An object of the present invention is to use water glass, without lowering the scratch resistance, water resistance, marker resistance, etc. of the image formed by the water-based ink, and the ejection property and resistance to the water-based ink. It is to improve the clogging property.
The water glass (sodium silicate solution) used in the present invention is N
represented by a ₂ · nSiO ₂ , the diatomaceous ratio (SiO ₂ / Na
O ratio (n)) is n = 2 to 4 (reference: Kagaku Daiji Kyoritsu Shuppan Co., Ltd., issued September 15, 1938), for example, Kishida Kagaku Co., Ltd. Etc. and can be used in the present invention.

The mass ratio of the above resin to water glass in the aqueous ink is 1: 0.001 to 1: 1 in terms of solid content.
Is preferred. If the amount of water glass is too small,
The ejection stability and clogging resistance of the water-based ink may not be sufficient, and if the amount of water glass is too large, the viscosity of the water-based ink will increase and the ejection stability and clogging resistance of the water-based ink will decrease. There is a case.

The aqueous ink of the present invention requires a liquid medium in which the above carbon black, resin and water glass are dispersed or dissolved, and the liquid medium needs to contain at least a water-soluble organic solvent. Preferably, a mixed solvent of water and a water-soluble organic solvent is used as the liquid medium of the aqueous ink. In the present invention, the proportion of the water-soluble organic solvent in the total weight of the aqueous ink is, for example, 5 to 50% by mass, and further 5
It is preferably ˜40% by mass.

The above water-soluble organic solvent is used in the water-based ink of the present invention in order to prevent the water-based ink from solidifying due to drying at the nozzle and the tip of the pen. Specifically, it has 1 carbon atoms. To 4 alkyl alcohols (eg,
Methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, etc., ketones or keto alcohols (for example, amides such as dimethylformamide, dimethylacetamide, acetone) , Diacetone alcohol, etc.),
Ethers (eg, tetrahydrofuran, dioxane, etc.), polyalkylene glycols (eg, polyethylene glycol, polypropylene glycol, etc.),
Alkylene glycols in which the alkylene group contains 2 to 6 carbon atoms (for example, ethylene glycol, propylene glycol, butylene glycol, triethylene glycol, 1,2,6-hexanetriol, thiodiglycol, hexylene glycol, diethylene glycol, etc. ), Alkyl ethers such as polyhydric alcohols (for example, ethylene glycol methyl ether, ethylene glycol ethyl ether, triethylene monomethyl ether, triethylene glycol monoethyl ether, etc.), and further N-methyl-2-pyrrolidone, 2-pyrrolidone , 1,3-dimethyl-2-imidazolidinone and the like.

Particularly preferred water-soluble organic solvents are glycerin and polyhydric alcohols (for example, diethylene glycol and ethylene glycol). Polyhydric alcohols other than glycerin include, for example, diethylene glycol, ethylene glycol, polyethylene glycol and propylene glycol. Is mentioned. Two or more kinds of these aqueous organic solvents may be mixed and used in the aqueous ink.

The water-based ink of the present invention contains water in addition to the above water-soluble organic solvent. The proportion of water in the total mass of the aqueous ink is generally 20 to 95% by mass, and particularly 4
It is preferably 0 to 95% by mass, more preferably 60 to 95% by mass. Further, it is preferable to use pure water or ion-exchanged water as the water.

In the aqueous ink of the present invention, the above components are mixed to sufficiently disperse the self-dispersing carbon black in the aqueous medium, and the particle size distribution of the carbon black is calculated by the cumulant method. The dispersion index should be 0.2 or less. The dispersion method may be a method in which other components are added and mixed in the dispersion liquid of the self-dispersing carbon black. If necessary, a conventionally known dispersing device can be used, and if necessary, it is preferable to remove coarse particles that may remain in the aqueous ink by centrifugation or a filtration method.

The proportion of the self-dispersing carbon black in the aqueous ink of the present invention in the total weight of the aqueous ink is
For example, 0.1 to 20% by mass, further 1 to 10% by mass
Is preferred. When the amount of the self-dispersing carbon black is less than 0.1% by mass, a sufficient image density cannot be obtained in a printed image, and when the amount of the carbon black exceeds 20% by mass, ejection such as clogging of a nozzle or a pen tip. Not only does the stability decrease, but the image density does not improve.

The proportion of the resin in the water-based ink of the present invention with respect to the total weight of the water-based ink is generally 0.001 to 20 mass%, and more preferably 0.01 to 10 mass%. . If the amount of the resin is less than 0.001% by mass, the scratch resistance, marker resistance, etc. of the obtained image will decrease, while if the amount of the resin exceeds 20% by mass, the viscosity of the aqueous ink will increase, Discharge stability such as clogging of the water-based ink at the nozzles and the pen tip is reduced.

The ratio of the water glass in the water-based ink of the present invention to the total weight of the water-based ink is generally 0.00001 to 10 mass%, more preferably 0.0001.
It is preferably about 5% by mass. When the amount of the water glass is less than 0.00001% by mass, the ejection stability is unstable, while when the amount of the water glass is more than 10% by mass,
The viscosity of the water-based ink becomes high, and the ejection stability such as clogging of the water-based ink at the nozzles and the pen tip decreases.

In addition to the above components, the water-based ink of the present invention may contain various additives such as a surfactant, a pH adjuster, an antioxidant and an antifungal agent. The viscosity of the water-based ink of the present invention is 1.0 at 25 ° C.
It is preferably from 5.0 mPas.

[0028]

EXAMPLES Next, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples unless it exceeds the gist. In the following description, "part" or "%" is based on mass unless otherwise specified.

In the following examples, the average particle size was determined by dynamic light scattering method (trade name: Laser particle size analysis system PAR-III; manufactured by Otsuka Electronics Co., Ltd.), and the zeta potential was determined by electrophoresis. It is a value measured using a light scattering method (trade name: Laser zeta electrometer ELS-6000; manufactured by Otsuka Electronics Co., Ltd.).

The maker value is adopted as the active ingredient of the resin, and the molecular weight is GPC (detector RI-8012 (manufactured by Tosoh Corp.), column Plgel MIXED-B (manufactured by AMR Corp.)). The glass transition temperature (Tg) and the thermal decomposition temperature were measured using a differential thermogravimetric simultaneous measurement device (TG / DTA220 (manufactured by Seiko Instruments Inc.).) The molecular weight and Tg of Polyester WR961 were measured. , And Tg of Superflex 420 adopted the manufacturer's value.

First, dispersions CB-1 and CB- of self-dispersing carbon black used in Examples and Comparative Examples.
The method of creating No. 2 will be described. (CB-1) 250 g of commercially available carbon black "MA8" [manufactured by Mitsubishi Chemical Co., Ltd.] was well mixed and dispersed in 1,000 ml of ion-exchanged water (hereinafter referred to as water), and then 1,000 g of ammonium peroxodisulfate was added thereto. It was charged and stirred at 60 to 70 ° C. for 8 hours. The obtained slurry is subjected to an ultrafiltration membrane having a molecular weight cutoff of 10,000 [manufactured by Toyo Roshi Kaisha, Ltd.].
It was desalted until the electric conductivity of the filtrate was 0.5 ms / cm or less. Furthermore, the solid content concentration is concentrated to 20%,
% Potassium hydroxide (20 g) was added dropwise to adjust the pH of the dispersion to 8
Adjusted to. Finally, water was added to adjust the solid content concentration to 15%. The carbon black in the obtained dispersion is
The average particle size was 85 nm, the polydispersity index was 0.15, and the zeta potential was -50 mV.

(CB-2) Self-dispersion type carbon black CAB-O-JET200 manufactured by Cabot Corporation (solid content concentration 20%, having sulfonic acid group as surface hydrophilic group).
It was used. The average particle size is 130 nm and the polydispersity index is 0.
13, the zeta potential was -70 mV.

Examples 1 to 5 and Comparative Examples 1 to 8 As a method for producing the aqueous ink, in Examples 1 to 5, the self-dispersion type carbon black dispersion prepared as described above, each resin and water glass were used. Was stirred for 30 minutes so that each solid content becomes the ratio shown in Table 1-1 and Table 1-2, 20% of diethylene glycol and 0.15% of acetylenol EH were added, and finally self-dispersion in the aqueous ink. Water was added so that the solid content of the type carbon black was 5%, and the mixture was stirred for 1 hour. Further, the obtained water-based ink was filtered under reduced pressure using a 3 μm membrane filter [manufactured by Toyo Roshi Kaisha, Ltd.] to prepare water-based inks of Examples 1 to 5.

In Comparative Examples 1 and 2, the self-dispersing carbon black dispersion (no resin or water glass) was used.
Diethylene glycol 20% and acetylenol EH
0.15% was added, and finally water was added so that the solid content of the self-dispersion type carbon black in the aqueous ink was 5%, and the mixture was stirred for 1 hour. Further, the obtained water-based ink was filtered under reduced pressure using a 3 μm membrane filter [manufactured by Toyo Roshi Kaisha, Ltd.] to prepare water-based inks of Comparative Examples 1 and 2.

In Comparative Examples 3 to 6, diethylene glycol 20% and acetylenol EH 0.15 were added to the self-dispersion type carbon black dispersion and the resin (without water glass).
%, And finally water was added so that the solid content of the self-dispersion type carbon black in the aqueous ink was 5%, and the mixture was stirred for 1 hour. Further, the obtained water-based ink was filtered under reduced pressure using a 3 μm membrane filter [manufactured by Toyo Roshi Kaisha, Ltd.] to prepare water-based inks of Comparative Examples 3 to 6.

In Comparative Example 7, 20% of diethylene glycol and 0.15% of acetylenol EH were added to the self-dispersing carbon black dispersion and the resin (without water glass), and finally the self-dispersing carbon black in the aqueous ink was prepared. Water was added so that the solid content was 5%, and the mixture was stirred for 1 hour. Further, the obtained water-based ink was filtered under reduced pressure using a 3 μm membrane filter [manufactured by Toyo Roshi Kaisha, Ltd.] to prepare a water-based ink of Comparative Example 7.

In Comparative Example 8, the self-dispersing carbon black dispersion and water glass (no resin), 20% diethylene glycol and 0.15% acetylenol EH were added, and finally the solid dispersion of the self-dispersing carbon black in the aqueous ink. Water was added so that the content was 5%, and the mixture was stirred for 1 hour. Further, the obtained water-based ink was filtered under reduced pressure using a 3 μm membrane filter [manufactured by Toyo Roshi Kaisha, Ltd.] to prepare a water-based ink of Comparative Example 8. In addition, Table 1-2
C. shown in FIG. B / resin / water glass represents the final solids concentration of the resulting aqueous ink.

[0038]

[0039]

Recording was performed on the commercially available copy paper (plain paper) NP-PB [Nippon Paper Manufacturing Co., Ltd.] and glossy paper PR101 [Canon Co., Ltd.] using the water-based inks of the above Examples and Comparative Examples. Image formation (printing) was performed using an aqueous inkjet printer F660 [manufactured by Canon Inc.]. The printed matter was evaluated as follows.

(Scratch resistance) After leaving for 12 hours or more after printing, a Kimwipe is placed on the printed paper, and a weight of 500 g / 12.56 cm ² is placed on the Kimwipe. It was visually observed from the black solid image and the rubbing condition of the character printing portion. The evaluation criteria are as follows, and the evaluation results are shown in Table 2 below. ◯: There is no stain on the white paper part, there is no black solid image, and no rubbing on the character print part. Δ: The white paper part is slightly stained, and the black solid image and the character print part are slightly scratched. X: The white paper part is stained and the black solid image and part of the character print part are scraped off. XX: The white paper part is badly soiled, and the black solid image and the character print part are scraped off as a whole.

(Water resistance) After leaving for 12 hours or more after printing,
The printed matter was allowed to stand in tap water for 5 minutes, the reflection density of the image after drying the water was measured, and the residual ratio of the reflection density before the water resistance test and after the water resistance test was obtained to obtain a water resistance scale. did. The evaluation criteria are as follows, and the evaluation results are shown in Table 2 below. ◯: The residual ratio of image density is 90% or more. Δ: The residual ratio of image density is 80% or more and less than 90%. X: The residual ratio of image density is 70% or more and less than 80%. XX: The residual ratio of image density is less than 70%.

(Marker resistance) After the characters were printed for 12 hours or more, the characters were once marked with a normal writing pressure using a yellow highlighter manufactured by ZEBRA, and the marker resistance was evaluated according to the following evaluation criteria. did. The evaluation results are shown in Table 2 below. ◯: No bleeding or smearing of white letters was found on the printed part, and the pen tip was not dirty. Δ: The white character part is slightly stained, and the printed part is also slightly blurred. X: The white character part is dirty and the printed part has bleeding.

(Dischargeability) The state of the printed image and the heater surface of the ink head after printing were observed and evaluated according to the following evaluation criteria. ◯: The black solid image portion and the character printing portion can be printed sufficiently cleanly, and almost no deposit is seen on the heater surface. Δ: The black solid image part and the character printing part can be printed sufficiently cleanly, but there is a little deposit on the heater surface. X: A black solid image part and a character print part are faint, and many deposits are seen on the heater surface.

[0045]

As is clear from the above Examples and Comparative Examples, the images obtained with the aqueous inks of Examples in which the resin and water glass were added include the inks of Comparative Examples in which only the resin or water glass was added, and both. As compared with the image using the ink of Comparative Example, which was not used, the scratch resistance, water resistance, marker resistance, and ejection property were excellent.

[0047]

The water-based ink of the present invention is excellent in scratch resistance, water resistance, and marker resistance even when an image is formed not only on plain paper but also on glossy paper. As a result, the water-based ink has good ejection stability at the nozzle.

Claims (6)

[Claims] 1. An aqueous ink containing a coloring material, a resin, water glass and an organic solvent, wherein the coloring material is a self-dispersing carbon black having an anionic hydrophilic group on the surface,
A water-based ink having a polydispersity index of 0.2 or less obtained by analyzing a particle size distribution of the carbon black by a cumulant method. 2. The water-based ink according to claim 1, wherein a mass ratio of the coloring material and the resin is 1: 0.01 to 1: 2 in solid content ratio. 3. The mass ratio of the resin to the water glass is
The water-based ink according to claim 1, wherein the solid content ratio is 1: 0.001 to 1: 1. 4. The water-based ink according to claim 1, wherein the resin is a water-soluble or water-dispersible polyester resin. 5. The water-based ink according to claim 1, wherein the resin is a water-dispersible polyurethane resin. 6. The water-based ink according to claim 1, which is for an inkjet printer.