JP2001262015A - Pigment ink - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pigment ink which, when used in continuous ink jet recording, is excellent in delivery stability and in redispersibility into a solvent after dried. SOLUTION: This pigment ink at least contains a pigment, a resin, and water, and its product F of electrical conductivity (mS/cm) by surface tension (mN/m) is in the range represented by 50<=F<=400.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pigment ink, and in particular, relates to an ink jetting stability suitable for a continuous ink jet recording system in which ink droplets are ejected from a print head to perform recording, and re-use in a solvent after drying. The present invention relates to a pigment-dispersed ink having excellent dispersibility.

[0002]

2. Description of the Related Art In recent years, an ink jet recording system having features such as non-contact printing and easy colorization has been used in various applications from homes / offices to industrial fields. In particular, the continuous ink jet recording method enables high-speed printing even when printing is not used, because ink is circulated to generate ink droplets.

In the continuous ink jet recording system,
The ink particles are charged, continuously ejected by the vibration effect, and the trajectory is controlled by an intermediate electric field, thereby forming an image on a recording medium. The ink particles not used for image formation are collected and reused.

[0004] Inks used include dye inks and pigment inks. Dye inks are excellent in resolubility and have good ink ejection characteristics, but are inferior in water resistance and weather resistance. On the other hand, a pigment-dispersed ink needs to disperse water-insoluble pigment particles and maintain a stable storage state. Pigment inks are excellent in water resistance and weather resistance, but because the pigment is dispersed in the solution, it is difficult to re-disperse the ink once dried. If the ink has a bad influence and is dried in the nozzle from which the ink is ejected, there is a problem that the shape of the droplet and the ejection direction of the droplet are disturbed and the ejection stability of the ink is deteriorated. Examples of such a pigment ink for a continuous inkjet recording system include, for example, JP-A-10-306.
No. 247 describes an ink using a dispersion composed of acid carbon black and a resin. In addition, Japanese Patent Application Laid-Open
No. 310733 describes an ink containing a dye, a pigment and a resin. In these inks, the dispersion of the pigment is stabilized by utilizing the electrostatic repulsion caused by the surface charge of the pigment and the charge of the dye.However, dispersion breakdown due to the addition of a conductive agent and aggregation due to drying during circulation of the ink are not observed. However, the ink cannot be completely suppressed, and sedimentation occurs when used for a long time, and the ink has poor re-dispersibility.

[0005]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a pigment ink used for ink jet recording,
An object of the present invention is to provide a pigment ink excellent in ink ejection stability and redispersibility in a solvent after drying.

[0006]

SUMMARY OF THE INVENTION The present inventor has conducted extensive experiments and studies over many years. As a result, at least in a pigment ink containing a pigment, a resin, and water, the electrical conductivity and the surface of the pigment-dispersed ink were measured. When the product F of the tension is in the range of 50 ≦ F ≦ 400, it has been found that the ejection stability and the redispersibility are excellent, and the present invention has been accomplished.

The above pigment ink is particularly effective in a continuous ink jet recording system.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A continuous ink jet recording system is described in, for example, JP-A-8-207288, in which ink particles formed by a print head are charged and continuously ejected by a vibration effect. By controlling the trajectory by deflecting it in the middle of the electric field, an image is formed on the recording medium,
On the other hand, ink particles not used for image formation are collected and reused. At this time, the pigment ink needs to have conductivity in order to induce charges required for deflection in the ink particles. In addition, it is important for the ejection stability of the pigment ink that the ink droplets are formed at equal intervals and the droplets are highly uniform, and the surface tension of the pigment ink has a great influence.
For this reason, in the continuous ink jet recording system, the relationship F between the conductivity and the surface tension of the pigment ink is 50 ≦ F ≦ 40.
The pigment ink in the range of 0 shows characteristics excellent in ejection stability and redispersibility.

When the F value defined in the present invention is less than 50,
Ink droplets are not sufficiently deflected to collect ink droplets, so that ink leaks from the print head, and the shape of ink droplets becomes unstable when ink droplets are generated, resulting in deterioration of print quality. On the other hand, when the F value is larger than 400, the ink particles are greatly deflected and come into contact with the charging portion, so that insulation failure occurs and the safety device operates to stop the device, or the dispersion stability of the pigment-dispersed ink is reduced. Disadvantages such as a decrease in

The conductivity of the ink of the present invention is 1 to 15 (mS / c
m) is preferred. If the conductivity is 1 (mS / cm) or more, ink leakage due to insufficient charging can be prevented. The conductivity is 1
If it is 5 (mS / cm) or less, it is possible to prevent the occurrence of insulation failure due to excessive deflection of ink particles and to prevent the dispersion stability from lowering.

The primary particle size of the pigment used in the ink of the present invention is preferably in the range of 10 nm to 150 nm. If the primary particle size of the pigment is within this range, the effect of the present invention can be remarkably exhibited. Primary particle size is 150nm
Within this range, sedimentation of the pigment in the ink can be prevented, and a decrease in print quality can be suppressed. When the thickness is 10 nm or more, deterioration of light resistance is prevented.

In order to maintain a good printing state continuously by the continuous ink jet recording method, it is preferable that the pigment particle size when the dried ink is redispersed in a solvent is 10 to 250 nm. When the thickness is within 250 nm, sedimentation of the pigment can be prevented, and when the thickness is 10 nm or more, a decrease in optical density during printing can be prevented. A more preferred range is 50 to 200 nm.

As a method for evaluating redispersibility, for example,
0.2 g of ink was dropped on a weighing dish with a dropper, and
There is a method of measuring the dispersion particle diameter of the ink which is dried at ℃ and then re-dispersed by dropping the ink solvent by a laser Doppler method. As described above, if the pigment particle diameter in the above-described range during re-dispersion is exceeded, when the circulating ink is rapidly formed into droplets, aggregation of the pigment due to concentration and drying of the solvent occurs, and the pigment aggregates in the conduit. In some cases, the ink flow is adversely affected, and the shape of the droplet or the direction in which the droplet is ejected is disturbed in the nozzle from which the ink is ejected, so that stable ejection of the ink may not be achieved.

In the continuous ink jet recording system, the ink is continuously formed into droplets at a high speed, and ink particles not used for image formation are collected and the ink is circulated stably.
The pigment-dispersed ink preferably maintains a viscosity of 1 to 10 cP at 25 ° C. When the viscosity is 10 cP or less, it is possible to prevent the ejection stability from deteriorating due to the decrease in the fluidity of the ink droplets. In addition, since water is usually used as a solvent, the viscosity of the ink is preferably maintained at 1 cP or more. A more preferred range is 2-5 cP.

The number average molecular weight of the resin used in the ink of the present invention is preferably in the range of 1,000 to 100,000.
When the molecular weight is within this range, the dispersion and dispersion stability of the pigment in the pigment-dispersed ink can be enhanced. When the molecular weight is 1,000 or more, a decrease in long-term storage stability due to an increase in pigment particle size can be suppressed. Molecular weight 10
When the viscosity is 0000 or less, an increase in the viscosity of the ink due to an increase in the viscosity of the resin can be suppressed. The more preferable molecular weight of the resin is 3000 to 50,000.

The resins used in the present invention include, for example, polyester resins, polyether resins, polyurethane resins, vinyl acetate resins, rosin ester resins, cellulose resins, epoxy resins, and maleic resins. , A polyethylene glycol-based resin, an acrylic resin and the like, and an acrylic resin is particularly preferred. However, other resins can of course be used. Acrylic resin is particularly preferred as the resin used in the pigment-dispersed ink of the present invention because it is easy to control the acid value and glass transition temperature of the resin, and it becomes possible to design the resin according to the pigment. is there.

The acrylic resin-forming monomers used in the present invention include, for example, methyl acrylate, ethyl acrylate, isopropyl acrylate, and n-acrylic acid.
Propyl, n-butyl acrylate, t-acrylic acid
Butyl, benzyl acrylate, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, tridecyl methacrylate, benzyl methacrylate 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, octyl acrylate, octyl methacrylate, lauryl acrylate, lauryl methacrylate, cetyl acrylate, cetyl methacrylate, stearyl acrylate,
(Meth) acrylates such as stearyl methacrylate, behenyl acrylate, behenyl methacrylate; styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, pt
styrene-based monomers such as tert-butylstyrene;
Itaconic esters such as benzyl itaconate; maleic esters such as dimethyl maleate; fumaric esters such as dimethyl fumarate; acrylonitrile, methacrylonitrile, vinyl acetate;
-Hydroxyl-containing monomers such as hydroxyethyl, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate; acrylamide, aminoethyl acrylate, aminopropyl acrylate, methacrylamide A basic monomer having a primary amino group such as aminoethyl methacrylate, aminopropyl methacrylate, methylaminoethyl acrylate, methylaminopropyl acrylate, ethylaminoethyl acrylate,
Basic monomers having a secondary amino group, such as ethylaminopropyl acrylate, methylaminoethyl methacrylate, methylaminopropyl methacrylate, ethylaminoethyl methacrylate, and ethylaminopropyl methacrylate; dimethylaminoethyl acrylate; Monomers having a tertiary amino group such as diethylaminoethyl acrylate, dimethylaminopropyl acrylate, diethylaminopropyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, dimethylaminopropyl methacrylate, diethylaminopropyl methacrylate, etc., acrylic Acid dimethylaminoethyl methyl chloride salt, methacrylic acid dimethylaminoethyl methyl chloride salt, acrylate dimethylaminoethylbenzyl chloride De salts, basic monomers having such quaternary amino group such as dimethylaminoethyl methacrylate benzyl chloride salt. And α-olefins such as ethylene. Other monomers include, for example, acrylic acid, methacrylic acid, crotonic acid, ethacrylic acid, propylacrylic acid, isopropylacrylic acid, itaconic acid, fumaric acid, acroyloxyethyl phthalate, acroyloxysuccinate, and the like. . Further, another acidic group monomer can be used in combination. For example, ethyl acrylate 2-ethyl sulfonate,
Monomers having a sulfonic acid group, such as ethyl methacrylate 2-ethyl sulfonic acid, butyl acrylamide sulfonic acid, ethyl methacrylate 2-ethyl phosphonate, acrylic acid 2
And monomers having a phosphonic acid group such as ethyl phosphonate.

The method of polymerizing the resin in the present invention includes known general methods such as bulk polymerization, solution polymerization, suspension polymerization, emulsion polymerization, and redox polymerization. Among them, solution polymerization is simple because the reaction method is simple. preferable. As the polymerization initiator, a known initiator in each polymerization method can be used. For example, di-tert-butyl perphthalate, tert-
Butyl hydroperoxide, dicumyl peroxide, benzoyl peroxide, tert-butyl peroxybenzoate, tert-butyl peroxyethyl hexanoate, tert-butyl peroxypivalate, methyl ethyl ketone peroxide, di-tert-butyl peroxide , Peroxides such as cumene peroxide, acetyl peroxide, lauroyl peroxide and the like, and azobisisobutyronitrile, azobisisopropylnitrile, azobis-2,4-dimethylvaleronitrile, azobiscyclohexanecarbonitrile and the like. Examples include inorganic salts such as azonitrile and potassium persulfate, and two-component systems of benzoyl peroxide and dimethylaniline.

In the pigment-dispersed ink of the present invention using the acrylic resin, in order to achieve redispersibility in a solvent after drying, the acid value of the resin in which the pigment is dispersed is 50 KOH mg.
/ G to 300 KOHmg / g, and more preferably 50 KOHmg / g to 200 KOHmg / g. When the acid value of the resin falls within this range, the dispersion and dispersion stability of the pigment in the pigment-dispersed ink can be improved. When the acid value is 50 KOHmg / g or more, aggregation of the pigments due to insufficient electric charge in water can be suppressed. When the acid value is 300 KOHmg / g or less, the solubility of the resin in water is suppressed and the dispersion of the pigment can be suppressed. A decrease in stability can be prevented. The resin is lithium hydroxide,
The resin is preferably neutralized with a monovalent alkali metal ion such as sodium hydroxide and potassium hydroxide. Further effect is obtained by using at least one selected from water-soluble inorganic salts or hydroxides as a pH adjuster and adjusting the pH of the prepared aqueous pigment-dispersed ink to fall within the range of 7 to 10. It is a target. Examples of the water-soluble inorganic salt include sodium carbonate and calcium carbonate, and examples of the water-soluble inorganic hydroxide include lithium hydroxide, sodium hydroxide, potassium hydroxide, magnesium hydroxide, and calcium hydroxide.

The amount of the resin added to the pigment-dispersed ink of the present invention is in the range of 0.1 to 20% by weight, preferably 0.1 to 10% by weight, based on the whole ink composition. When the amount of the resin added is within this range, the dispersibility of the pigment or disperse dye particles and the storage stability of the ink can be improved. If the amount of resin added is 0.1% by weight or more,
The effect of improving the dispersibility of the pigment or disperse dye particles and the storage stability of the ink is obtained. On the other hand, when the addition amount of the resin is 20% by weight or less, the increase in the viscosity of the ink can be suppressed, and a decrease in the ejection stability can be prevented.

The pigment-dispersed ink of the present invention contains at least one or more water-soluble organic solvents selected from the group consisting of water-soluble polyhydric alcohols to suppress drying, and after drying, the pigment is converted into the solvent. Preferably, redispersibility for dispersion is achieved. The amount of the water-soluble organic solvent to be added is preferably in the range of 4 to 30% by weight, more preferably 4 to 20% by weight, based on the whole ink composition. When the amount of the water-soluble organic solvent is at least 4% by weight, the effect of improving the property of preventing clogging of the print head will be sufficient. On the other hand, when the blending amount of the water-soluble organic solvent is 30% by weight or less, it is possible to prevent defects such as dispersibility of the pigment by lowering the organicity of the solution.

The water-soluble solvent used in the present invention includes, for example, ethylene glycol, diethylene glycol and glycerin. Further, other organic solvents and various additives can be used in combination. For example,
Triethylene glycol, tripropylene glycol,
Dimethyl sulfoxide, diacetone alcohol, glycerin monoallyl ether, propylene glycol, polyethylene glycol, thiodiglycol, N-methyl-
2-pyrrolidone, 2-pyrrolidone, γ-butyrolactone, 1,3-dimethyl-2-imidazolidinone, sulfolane, trimethylolpropane, neopentyl glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether , Ethylene glycol monoallyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, β-dihydroxyethylurea, urea, acetonyl Acetone, pentaerythritol, hexylene glycol, ethylene Glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, ethylene glycol monophenyl ether, diethylene glycol diethyl ether, diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, triethylene glycol monobutyl ether, triethylene glycol dimethyl ether, triethylene glycol Diethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol Coal monomethyl ether, glycerin monoacetate, glycerin diacetate, glycerin triacetate, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether acetate, cyclohexanol, 1-butanol, 2,5-hexanediol, ethanol, n-propanol, 2-propanol, 1-methoxy-2-propanol, furfuryl alcohol, tetrahydrofurfuryl alcohol, 1,2-
Butanediol, 1,4-butanediol, 1,3-butanediol, 2,4-pentanediol, 1,5-pentanediol, 2-methyl-2,4-pentanediol, 1,2-cyclohexanediol, 1 , 4-cyclohexanediol, trimethylolethane, trimethylolpropane, 1,2,4-butanetriol, 1,
2,6-hexanetriol, 1,2,5-pentanetriol, 3-methyl-1,5-pentanediol, 3
-Hexene-2, 5-diol and the like. Also,
If necessary, polyethylene glycol can be added.

The pigment-dispersed ink of the present invention comprises a pigment, a resin,
A liquid mixture containing water may be dispersed, or at least one water-soluble organic solvent selected from the group consisting of water-soluble polyhydric alcohols may be added and dispersed. Various additives are added as needed to form an ink. It is also possible to first prepare a dispersion having a high pigment concentration, dilute it by adding a solvent, various additives, and the like, and use the resulting dispersion as an ink.

The pigment used in the present invention is not particularly limited. In addition to conventionally used pigments, pigments newly synthesized therefrom can be equally used.

The pigment which can be used in the pigment-dispersed ink of the present invention includes inorganic pigments, organic pigments, dyes which do not dissolve in solvents, fillers, medicines, polymerization initiators, catalysts, ultraviolet absorbers and the like. It is not limited to these, as long as it is not dissolved in a solvent. Examples include quinacridone, phthalocyanine-based, threne-based, perylene-based, phthalone-based, dioxazine-based, isoindolinone-based, methine-azomethine-based, diketopyrrolopyrrole-based, azochelate-based, insoluble azo-based, and condensed azo-based compound pigments. Among them, one or more organic pigments selected from the group consisting of quinacridone-based, phthalocyanine-based, selen-based, perylene-based, phthalone-based, dioxazine-based, methine-azomethine-based, and diketopyrrolopyrrole-based compound pigments are preferable.

Examples of the inorganic pigment include carbon black, titanium oxide, zinc white, zinc oxide, tripon, iron oxide, aluminum oxide, silicon dioxide, kaolinite,
Montmorillonite, talc, barium sulfate, calcium carbonate, silica, alumina, cadmium red, red iron oxide, molybdenum red, chrome vermillion, molybdate orange, graphite, chrome yellow, cadmium yellow, yellow iron oxide, titanium yellow, chromium oxide, pyridian , Cobalt green, titanium cobalt green,
Examples thereof include cobalt chrome green, ultramarine blue, ultramarine blue, navy blue, cobalt blue, cerulean blue, manganese violet, cobalt violet, and mica.

Examples of the organic pigment include azo, azomethine, polyazo, phthalocyanine, quinacridone, anthraquinone, indigo, thioindigo, quinophthalone, benzimidazolone, isoindoline, and isoindolinone. And the like.

Examples of the dye which does not dissolve in a solvent include, for example,
Examples include azo-based, anthraquinone-based, indigo-based, phthalocyanine-based, carbonyl-based, quinone-imine-based, methine-based, quinoline-based, and nitro-based ones, and among these, disperse dyes are particularly preferred.

Examples of the dye that does not dissolve in a solvent include, for example,
Examples include azo-based, anthraquinone-based, indigo-based, phthalocyanine-based, carbonyl-based, quinone-imine-based, methine-based, quinoline-based, and nitro-based ones, and among these, disperse dyes are particularly preferred.

The amount of the pigment-dispersed ink of the present invention is preferably 0.1 to 20% by weight based on the total amount of the ink composition.
More preferably, it is 1.0 to 11% by weight. When it is within this range, the color tone and optical density of the ink can be satisfied, and the viscosity and storage stability of the aqueous dispersion ink can be satisfied.

In the pigment-dispersed ink composition of the present invention,
Various types of inks conventionally used in ink jet printer inks such as surfactants, anti-clogging agents for print heads, defoamers for inks, bactericides, fungicides, and agents for imparting water resistance to prints, as required. Additives can also be included.
Antifoaming agents include alkyl benzene sulfonic acid type, alkyl sulfate type, fatty acid salt type and quaternary ammonium salt type cationic activators, or alkyl betaine,
Examples include amphoteric surfactants such as amine oxides, nonionic surfactants, and organic silicone-based nonionic surfactants such as methylpolysiloxane copolymer. Examples of fungicides and fungicides include benzoates, alkylamine salts, and quaternary ammonium salts. Antifoaming agents include fatty acid esters such as sorbitan acid esters, polyoxyethylene alkyl ethers, and silicone oils.

In order to adjust the electric conductivity of the pigment-dispersed ink of the present invention to a predetermined value, an electrolyte may be added. However, the required conductivity varies depending on the printer model, and the conductivity of the ink also varies depending on other components in the ink. Therefore, an electrolyte is appropriately added as necessary. Electrolytes that can be used for such purposes include, for example, ammonium chloride, sodium chloride, lithium nitrate,
Inorganic salts such as ammonium nitrate, ammonium thiocyanate, potassium thiocyanate, sodium thiocyanate, ammonium nitrite, lithium acetate, potassium acetate, ammonium acetate, etc., triethanolamine hydrochloride, triethanolamine nitrate, triethanolamine sulfate, etc. .

As the dispersing machine for producing the pigment-dispersed ink of the present invention, any commonly used dispersing machine may be used. Examples thereof include a container driving medium mill such as a roll mill, a ball mill, a centrifugal mill, and a planetary ball mill. A high-speed rotation mill such as a sand mill or a medium stirring mill such as a stirring tank type mill may be used. As a specific method for producing a pigment-dispersed ink, there is a method of dispersing the ink using a planetary ball mill or a sand mill using ceramic beads having a particle diameter of 0.01 to 1.0 mm. In this case, the acceleration is preferably performed at an acceleration of 5 to 50 G in a planetary ball mill, at a filling ratio of ceramic beads of 50 to 90%, and at a peripheral speed of 5 to 20 m / s in a sand mill.

The pigment-dispersed ink of the present invention can be used in all printers without any particular limitation, as long as it is a commercially available continuous ink jet recording system.
For example, printing can be performed by using a printer described in JP-A-08-109343 and U.S. Pat. No. 4,255,754.

Hereinafter, the present invention will be described in more detail with reference to specific examples. In the following examples, unless otherwise specified, the particle diameters of pigments and disperse dyes used were measured by a laser Doppler type particle size distribution meter N4P manufactured by Coulter.
The measurement was performed with LUS.

[0036]

EXAMPLES (Example 1) The following composition was prepared with a particle size of 0.3 mm.
Was dispersed in a sand mill for 1 hour using the zirconia beads described above to obtain a dispersion.・ 15 parts by weight of black pigment (made by Degussa, trade name: Printex 75) ・ 5 parts by weight of acrylic acid-containing acrylic resin A (molecular weight: 20,000, acid value: 200) ・ 80 parts by weight of ion-exchanged water 30 parts by weight of this dispersion While stirring, glycerin 10
Parts by weight and 60 parts by weight of ion-exchanged water were added dropwise over 30 minutes to obtain a pigment-dispersed ink. By adding lithium nitrate to this ink composition, the conductivity of the ink was 5 mS / cm.
It was adjusted to become.

The dispersed particle size of the pigment was 80 nm. The surface tension of this ink composition was 60 mN / m. Therefore, the F value of the obtained pigment-dispersed ink was 300. As a result of printing evaluation using this ink, as shown in Table 1, very excellent characteristics were obtained.

(Comparative Example 1) The following composition was prepared by changing the particle size to 0.3 m.
The dispersion is obtained by using a zirconia bead of m for 1 hour with a sand mill for dispersion.・ 15 parts by weight of black pigment (manufactured by Degussa, trade name: Printex 75) ・ 5 parts by weight of acrylic acid-containing acrylic resin A (molecular weight: 20,000) ・ 80 parts by weight of ion-exchanged water While stirring 30 parts by weight in this dispersion, Glycerin 1
0 parts by weight and 60 parts by weight of ion-exchanged water were dropped over 30 minutes to obtain an ink. Lithium nitrate was added to this ink to adjust the conductivity of the ink to 8 mS / cm. The dispersed particle size of the pigment was 83 nm. The surface tension of this ink was 55 mN / m. Therefore, the F value of the obtained pigment-dispersed ink was 440. As a result of printing evaluation using this ink, as shown in Table 1, Example 1 was used.
The characteristics were inferior to those of.

Comparative Example 2 The following composition was dispersed in a sand mill for 1 hour using zirconia beads having a particle size of 0.3 mm to obtain a dispersion.・ 15 parts by weight of black pigment (manufactured by Degussa, trade name: Printex 75) ・ 7 parts by weight of acrylic acid-containing acrylic resin B (molecular weight: 17,000) ・ 80 parts by weight of ion-exchanged water While stirring 30 parts by weight in this dispersion, Glycerin 1
0 parts by weight and 60 parts by weight of ion-exchanged water were dropped over 30 minutes to obtain an ink. Lithium nitrate was added to this ink to adjust the conductivity of the ink to 1 mS / cm. The pigment dispersion particle size was 85 nm.

The surface tension of this ink was 40 mN / m. Therefore, the F value of the obtained pigment-dispersed ink was 40. Table 1 shows the results of printing evaluation using this ink.
As shown in the figure, the characteristics were inferior to those of Example 1.

Example 2 The following composition was dispersed in a sand mill for 1 hour using zirconia beads having a particle size of 0.3 mm to obtain a dispersion. 15 parts by weight of cyan pigment (CI Pigment Blue 15: 3) 7 parts by weight of acrylic acid-containing acrylic resin A 78 parts by weight of ion-exchanged water While stirring 30 parts by weight of this dispersion, glycerin 10
A part by weight and 70 parts by weight of ion-exchanged water were dropped over 30 minutes to obtain an ink. Lithium nitrate was added to this ink to adjust the conductivity of the ink to 5 mS / cm.

The dispersed particle size of the pigment was 82 nm. The surface tension of this ink was 55 mN / m. Accordingly, the F value of the obtained pigment-dispersed ink was 275. As a result of performing ink evaluation using this ink, as shown in Table 1, very excellent ink characteristics were obtained.

Example 3 The following composition was dispersed in a sand mill using zirconia beads having a particle diameter of 0.3 mm for 3 hours to obtain a dispersion.・ 15 parts by weight of magenta pigment (CI Pigment Red 122) ・ 8 parts by weight of acrylic acid-containing acrylic resin A ・ 77 parts by weight of ion-exchanged water While stirring 30 parts by weight of this dispersion, glycerin 10
The ink was obtained by dropping 30 parts by weight of ion-exchanged water over 30 minutes. Lithium nitrate was added to this ink to adjust the conductivity of the ink to 5 mS / cm.

The dispersed particle size of the pigment was 98 nm. The surface tension of this ink was 50 mN / m. Therefore, the F value of the obtained pigment-dispersed ink was 250. As a result of printing evaluation using this ink, as shown in Table 1, very excellent characteristics were obtained.

Example 4 The following composition was dispersed in a sand mill for 4 hours using zirconia beads having a particle size of 0.3 mm to obtain a dispersion. 15 parts by weight of yellow pigment (CI Pigment Yellow 74) 9 parts by weight of acrylic acid-containing acrylic resin A 76 parts by weight of ion-exchanged water While stirring 30 parts by weight of this dispersion, glycerin 10
The ink was obtained by dripping 30 parts by weight and 64 parts by weight of ion-exchanged water over 30 minutes. Lithium nitrate was added to this ink to adjust the conductivity of the ink to 5 mS / cm.

The pigment particle size was 143 nm. The surface tension of this ink was 53 mN / m. Therefore, the F value of the obtained pigment-dispersed ink was 265. As a result of printing evaluation using this ink, as shown in Table 1, very excellent characteristics were obtained.

Example 5 The following composition was prepared by changing the particle size to 0.3 m.
m of zirconia beads was dispersed in a sand mill for 1 hour to obtain a dispersion. -15 parts by weight of black pigment (manufactured by Degussa, trade name: Printex 75)-8 parts by weight of acrylic acid-containing acrylic resin A-80 parts by weight of ion-exchanged water 30 parts by weight of this dispersion were stirred with 10 parts of glycerin.
Parts by weight and 60 parts by weight of ion-exchanged water were added dropwise over 30 minutes to obtain a pigment-dispersed ink composition. Lithium nitrate was added to this ink, and the conductivity of the ink was 6 mS / cm.
It was adjusted to become.

The particle size of the pigment was 80 nm. The surface tension of this ink was 40 mN / m. Therefore, the F value of the obtained pigment-dispersed ink was 240. As a result of printing evaluation using this ink, as shown in Table 1, very excellent characteristics were obtained.

(Comparative Example 3) The following composition was used, and the particle size was 0.3 m
m of zirconia beads was dispersed in a sand mill for 1 hour to obtain a dispersion.・ 15 parts by weight of black pigment (manufactured by Degussa, trade name: Printex 75) ・ 5 parts by weight of acrylic resin containing acrylic resin C (molecular weight: 130,000) ・ 80 parts by weight of ion-exchanged water While stirring 30 parts by weight of this dispersion, glycerin 10
Parts by weight and 60 parts by weight of ion-exchanged water were added dropwise over 30 minutes to obtain a pigment-dispersed ink. Lithium nitrate was added to this ink to adjust the conductivity of the ink to 10 mS / cm.

The particle size of the pigment was 80 nm. The surface tension of this ink composition was 60 mN / m. Therefore, the F value of the obtained pigment-dispersed ink was 600. As a result of printing evaluation using this ink, as shown in Table 1, the properties were inferior to those of Example 5.

Table 1 shows the storage stability, ejection stability, viscosity, and pigment particle size after redispersion of the inks obtained in each of the examples and comparative examples.

[0052]

[Table 1]

In this table, the storage stability is as follows.
After standing at 7 ° C. for 7 days, a sample having a viscosity of 1.5 times or more that before standing was rated as X, a sample having a viscosity of 1.1 to 1.5 times that before standing was rated as Δ, and the others were rated as ○. The viscosity was measured at 25 ° C. using a viscometer (R100, manufactured by Toki Sangyo). Regarding the ejection stability, a recording pattern in which the inks of Examples 1 to 5 and Comparative Examples 1 to 3 were printed on plain paper by a continuous ink jet printer was observed.も の indicates that there was no dot disturbance, and X indicates that the dot disturbance was 5% or more of the whole. The pigment particle size after redispersion was determined by dispensing 0.5 g of the prepared ink composition on a glass plate, drying the mixture in a 60 ° C. environment for 30 minutes, and then ion-exchanged water containing 15% by weight of glycerin. To 50 parts by weight of an aqueous solution adjusted to pH 8 by adding sodium hydroxide thereto, and the pigment particle size when redispersed was measured. From the results shown in Table 1, it can be understood that the pigment-dispersed ink according to the present invention has excellent ejection stability and re-dispersibility after drying.

[0054]

As described above, according to the present invention, a pigment-dispersed ink having excellent ejection stability and dispersion stability can be obtained.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C056 EA26 FA05 FC01 2H086 BA52 BA53 BA55 BA59 BA60 BA61 4J039 AB02 AB08 AD08 AD10 AD14 AE04 AE05 AE06 AE07 BC07 BE01 BE12 CA06 EA24 EA44 EA46 GA24

Claims (10)

[Claims] 1. A pigment ink containing at least a pigment, a resin, and water, wherein the conductivity of the pigment ink (mS / cm)
And a product F of surface tension (mN / m) within a range of 50 ≦ F ≦ 400. 2. The redispersion pigment particle size after drying is 250 nm.
The pigment ink according to claim 1, wherein: 3. The pigment ink according to claim 1, wherein the viscosity is in the range of 1 mPa · s to 10 mPa · s. 4. The resin having an acid value of 50 KOHmg / g or more.
The pigment ink according to claim 1, wherein the content is within a range of 300 KOHmg / g. 5. A resin having a number average molecular weight of 1,000 to 1,
The pigment ink according to claim 1, wherein the value is in the range of 00000. 6. The pigment ink according to claim 1, wherein the resin is neutralized with a monovalent alkali metal ion. 7. The pigment ink according to claim 1, wherein the resin is an acrylic resin. 8. The pigment ink according to claim 1, further comprising at least one or more water-soluble organic solvents selected from the group consisting of polyhydric alcohols. 9. The pigment ink according to claim 1, further comprising a pH adjuster, wherein the pH adjuster comprises a water-soluble inorganic salt and / or hydroxide. 10. The pigment-dispersed ink according to claim 1, which is used for continuous ink jet recording in which recording is performed by discharging ink droplets from a print head.