JP2007091920A - Water-based ink for inkjet recording - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide water-based ink for inkjet recording excellent in printing density when printed on plain paper and a water-based dispersion used for the ink and to provide a method for improving a print density by using the water-based ink. <P>SOLUTION: The water-based dispersion for inkjet recording comprises a pigment, metal oxide fine particles having 110-400 nm average particle diameter and a water-soluble polymer, wherein the ratio of average particle diameter of metal oxide fine particles to average particle diameter of pigment is 0.8-8. Water-based ink for inkjet recording comprises the water-based dispersion. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an aqueous ink for inkjet recording.

The ink jet recording method is a recording method in which characters and images are obtained by ejecting ink droplets directly from a very fine nozzle onto a recording member and attaching them. This method is easily spread at a full color and is inexpensive, and can be used as a recording member, and can be used as a recording member.
With regard to such an ink jet recording method, for example, Patent Document 1 discloses an ink jet ink composition in which a dye / pigment is dispersed in a medium, and a dye / pigment dispersed substantially by an anionic surfactant. An invention relating to an ink-jet ink composition, which is an ink-jet ink composition containing colorless fine particles, is capable of forming a clear image with little ink bleeding.
Patent Document 2 discloses a water-based inkjet including a pigment and colloidal silica with the object that print quality is good and high-quality printing is possible, and the printed matter has sufficient water resistance and light resistance. A recording liquid is disclosed.
Further, Patent Document 3 discloses that a water-based ink containing a coloring material and a water-soluble medium has a center line average roughness (Ra) of a print image of the water-based ink formed on a substantially smooth recording paper. The water-based ink which becomes 3-50 nm is disclosed.
However, the water-based inks disclosed in each of the above patent documents still have insufficient print density when printed on plain paper.

JP-A-8-319442 JP-A-9-227812 Japanese Patent Laid-Open No. 11-080628

  An object of the present invention is to provide a water-based ink for inkjet recording excellent in print density when printing on plain paper, an aqueous dispersion used for the ink, and a method for improving print density using the water-based ink. .

The present invention
(1) It contains a pigment, metal oxide fine particles having an average particle diameter of 110 to 400 nm, and a water-soluble polymer, and the ratio of the average particle diameter of the metal oxide fine particles to the average particle diameter of the pigment (the average particle diameter of the metal oxide particles) Water dispersion for inkjet recording, wherein the diameter / average pigment particle diameter is from 0.8 to 8,
(2) A water-based ink for ink-jet recording containing the water dispersion of (1), and (3) A method for improving print density using the water-based ink of (2) for ink-jet recording,
About.

  A high printing density can be achieved when printing on plain paper by the aqueous ink containing the aqueous dispersion for inkjet recording of the present invention.

(Metal oxide fine particles)
In the present invention, the metal oxide fine particles are used from the viewpoint of improving the printing density. Elements constituting the metal oxide fine particles are derived from the 2A group, 2B group, 3A group, 3B group, 4A group, 4B group, 5A group, 6A group, 7A group, or 8 group of the periodic table (long period type). belongs to. The metal may be a semimetal. Specific examples of the metal oxide are selected from the group consisting of silicon oxide (hereinafter referred to as silica), aluminum oxide (hereinafter referred to as alumina), manganese oxide, magnesium oxide, zinc oxide, titanium oxide, cerium oxide, and zirconium oxide. One or more types are preferable, and the surface of these oxides may be modified or surface-modified with a functional group, or may be formed into composite particles with a surfactant. The metal oxide fine particles can contain these metal oxides alone or in combination of two or more.
As the metal oxide fine particles, colloidal particles are preferable from the viewpoint of dispersibility, and among these, at least one selected from the group consisting of colloidal silica, colloidal ceria, and colloidal alumina is more preferable. Colloidal silica obtained by the production method is particularly preferred.

The average particle diameter of the metal oxide fine particles is 110 nm or more, preferably 125 nm or more, more preferably 140 nm or more, still more preferably 160 nm or more, and further preferably 170 nm or more, from the viewpoint of improving printing density. From the viewpoint of ejection properties, etc., it is 400 nm or less, preferably 360 nm or less, more preferably 300 nm or less, and from the viewpoint of printing density, dispersion stability, ejection properties, etc., it is 110-400 nm, preferably 125-360 nm, More preferably, it is 140-360 nm, More preferably, it is 160-360 nm, More preferably, it is 170-300 nm. By using the metal oxide fine particles having an average particle diameter within this range, for example, the metal oxide fine particles contained in the water-based ink ejected from the inkjet recording nozzle have a higher specific gravity than the pigment. It is considered that the printing density is improved by suppressing the sinking and the sinking of the pigment.
The average particle diameter of the metal oxide fine particles can be measured by a light scattering method by a measurement method described later. When the metal oxide fine particles are powder, about 0.1 parts by weight of polyacrylate (for example, Poise 530A, manufactured by Kao Corporation) is added to water with respect to 1 part by weight of the metal oxide fine particles. The dispersed aqueous dispersion can also be measured by the light scattering method.

The particle size distribution of the metal oxide fine particles is preferably a value of D90 / D50, preferably 1 to 3, more preferably 1 to 5 by the measurement method from the viewpoints of improving printing density, improving glossiness, and improving image clarity. 2, more preferably 1 to 1.5. D90 is a particle size at which the cumulative particle size distribution (number basis) from the small particle size side of the primary particles is 90%, and D50 is an integrated particle size distribution from the small particle size side of the primary particles. The particle size (based on the number) is 50%.
From the viewpoint of suppressing aggregation of the metal oxide fine particles in the aqueous dispersion and the water-based ink, the zeta potential (25 ° C.) of the metal oxide fine particles is preferably pH 4.5 to 10, more preferably pH 5 to 10, and further. Preferably, it is not 0 within the range of pH 7 to 10, that is, the metal oxide fine particles do not have an isoelectric point. The zeta potential can be obtained by a general measurement method.

(Pigment)
The pigment used in the aqueous dispersion of the present invention is used for exhibiting water resistance, high weather resistance, and the like that have recently been strongly demanded.
From the viewpoint of ease of production, the pigment is made into fine particles that are stable in the ink using a water-soluble polymer.

As the pigment, either an inorganic pigment or an organic pigment can be used. If necessary, they can be used in combination with extender pigments.
Examples of the inorganic pigment include carbon black, metal oxide, metal sulfide, and metal chloride. Of these, carbon black is preferred particularly for black aqueous inks. Examples of carbon black include furnace black, thermal lamp black, acetylene black, and channel black.
Examples of the organic pigment include azo pigments, disazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, and quinophthalone pigments.
The hue is not particularly limited, and any chromatic pigment such as a red organic pigment, a yellow organic pigment, a blue organic pigment, an orange organic pigment, and a green orange organic pigment can be used.

Specific examples of preferred organic pigments include C.I. I. Pigment Yellow 13, 17, 74, 83, 97, 109, 110, 120, 128, 139, 151, 154, 155, 174, 180; I. Pigment Red 48, 57: 1, 122, 146, 176, 184, 185, 188, 202; I. Pigment violet 19, 23; C.I. I. Pigment Blue 15, 15: 1, 15: 2, 15: 3, 15: 4, 16, 60; I. One or more products selected from the group consisting of CI Pigment Green 7 and 36 are listed.
Examples of extender pigments include silica, calcium carbonate, and talc.
The pigment may be a self-dispersing pigment. Self-dispersing pigments are those that bind one or more anionic or cationic hydrophilic groups directly or through other atomic groups to the surface of the pigment and can be used in aqueous media without using surfactants or resins. It means a pigment that is dispersible.
The above pigments can be used alone or in combination of two or more.

The average primary particle diameter of the pigment is preferably 40 to 180 nm, more preferably 50 to 170 nm, and particularly preferably 70 to 140 nm from the viewpoints of pigment dispersibility, printing density, and prevention of clogging of printer nozzles.
The average primary particle diameter of the pigment can be measured using a transmission electron microscope. Specifically, the number average particle is obtained by measuring 500 pieces by image analysis of a transmission electron microscope of JEOL Ltd. and calculating the average. Is the diameter. In addition, when a pigment has a major axis and a minor axis, the major axis is used for calculation.

(Water-soluble polymer)
The water-soluble polymer is used for improving the dispersion stability of the pigment and optionally the metal oxide fine particles.
In the present invention, the water-soluble polymer means a polymer having a dissolution amount of more than 10 g, preferably 20 g or more, more preferably 30 g or more when dissolved in 100 g of water at 25 ° C. When the water-soluble polymer has a salt-forming group such as a carboxy group or an ammonium group, the above-mentioned dissolution amount is 100% neutralized with acetic acid or sodium hydroxide according to the type of the water-soluble polymer. The amount of dissolution.

As the water-soluble polymer, (1) a water-soluble polymer obtained by subjecting a sulfonated product obtained by sulfonating a polynuclear aromatic compound or a mononuclear aromatic compound to formalin condensation, and preferably neutralizing, (2) a carboxy group Water-soluble polymers having are preferred.
Examples of the polynuclear aromatic compound of the above (1) include: Or a compound in which two or more aromatic rings or heterocyclic rings share two or more carbon atoms to form a condensed ring, such as trialkyl-substituted products, mono- or dialkylnaphthalene, and the like Derivatives, (ro) fluorene, diphenyl, dibenzofuran and the like, and compounds and derivatives thereof in which two or more aromatic rings or heterocycles are bonded via a direct bond or an alkylene group. Specific examples include polynaphthalene sulfonic acid (salt) typified by sodium salt of β-naphthalenesulfonic acid formalin condensate, such as DEMAL NL, DEMAL N, DEMAL MS (trade name) manufactured by Kao Corporation. Commercial products can be used.

Examples of the water-soluble polymer (2) include (meth) acrylic acid (salt) polymers represented by polyacrylic acid and copolymers thereof, sodium salts of styrene and maleic acid copolymers, diisobutylene and maleic acid copolymers. Maleic acid (salt) polymer represented by sodium salt of polymer and its copolymer, (meth) acryloyloxyethyl represented by copolymer of (meth) acrylic acid and (meth) acryloyloxyethyl phosphoric acid Examples thereof include a polymer of phosphoric acid, a sodium alginate, a polysaccharide having an anionic group represented by carboxymethylcellulose, and derivatives thereof. As such a water-soluble polymer, specifically, commercially available products such as DEMOL EP (trade name) manufactured by Kao Corporation can be used.
Examples of other water-soluble polymers include polymelamine sulfonic acid (salt), sulfonated styrene (salt) polymer, and a copolymer thereof.

The water-soluble polymer preferably has a weight average molecular weight of 2,000 to 50,000 from the viewpoint of dispersibility. The weight average molecular weight of the water-soluble polymer was measured using polystyrene as a standard substance by gel chromatography using dimethylformamide in which 60 mmol / L phosphoric acid and 50 mmol / L lithium bromide were dissolved as a solvent. can do. The water-soluble polymer is preferably anionic, nonionic or amphoteric from the viewpoint of dispersibility.

(Aqueous dispersion for inkjet recording, water-based ink)
The aqueous dispersion of the present invention containing the pigment, the metal oxide fine particles and the water-soluble polymer may be prepared by mixing the above components in any order. From the viewpoint of dispersion stability, preferably the pigment and It is preferable to preliminarily disperse a mixture containing a water-soluble polymer and an aqueous medium, then apply a shear stress to perform the main dispersion, and mix the resulting dispersion with metal oxide fine particles. Further, the metal oxide fine particles may be first mixed with the pigment. As the aqueous medium, water, a water-soluble solvent such as alcohol, and the like can be used.
When preliminarily dispersing the mixture, a commonly used mixing and stirring device such as an anchor blade can be used. Among the mixing and stirring devices, Ultra Disper [Asada Steel Co., Ltd., trade name], Ebara Milder [Ebara Seisakusho Co., Ltd., trade name], TK Homomixer, TK Pipeline Mixer, TK Homojetter, TK Homomic Line Flow, High-speed agitating and mixing devices such as Filmix [Special Machine Industry Co., Ltd., trade name], Clear Mix [M Technique Co., Ltd., trade name], KD Mill [Kinetic Dispersion Co., Ltd., trade name] and the like are preferable.

  As means for giving the shear stress of this dispersion, for example, a kneader such as a roll mill, a bead mill, a kneader, an extruder, a high-pressure homogenizer (Izumi Food Machinery Co., Ltd., trade name), a minilab 8.3H type (Rannie Co., trade name) Representative homo-valve type high-pressure homogenizer, microfluidizer (Microfluidics, trade name), nanomizer (Nanomizer, trade name), optimizer (Sugino Machine Co., trade name), Genus PY (Shiramizu Chemical Co., Ltd.) Product name], DeBEE2000 [Japan EE Co., Ltd., product name] and the like chamber type high-pressure homogenizer. Among these, a high-pressure homogenizer is preferable from the viewpoint of reducing the particle size of the pigment contained in the mixture.

The content of each component in the aqueous dispersion and aqueous ink of the present invention is as follows.
The content of the metal oxide fine particles is preferably 1 to 30% by weight, more preferably 2 to 20% by weight, and further preferably 3 to 15% by weight from the viewpoint of increasing the printing density.
The content of the pigment is preferably 1 to 10% by weight, more preferably 2 to 10% by weight, still more preferably 3 to 10% by weight, and still more preferably, from the viewpoint of increasing the printing density and imparting good dispersion stability. Is 4-8 weight.
The metal oxide fine particle / pigment content ratio [(metal oxide fine particle / pigment) weight ratio] exhibits the effect of improving the printing density by the metal oxide fine particles, and obtains dispersion stability in an aqueous dispersion or aqueous ink. In addition, from the viewpoint of low cost, it is preferably 0.3 to 10, more preferably 0.4 to 8, more preferably 0.7 to 8, still more preferably 0.8 to 5, and particularly preferably 0. .9-5.

The content of the water-soluble polymer is preferably 0.2 to 10% by weight, more preferably 1 to 8% by weight, and still more preferably 1 to 5% by weight, from the viewpoint of printing density and pigment dispersion stability.
The content ratio of the pigment to the water-soluble polymer is preferably 50/50 to 90/10 in terms of [(pigment / water-soluble polymer) weight ratio] from the viewpoint of printing density and dispersion stability. More preferably, it is -80/20.
The ratio of the average particle size of the metal oxide fine particles to the average particle size of the pigment (average particle size of metal oxide particles / average particle size of pigment) is set to 0. It is 8-8, Preferably it is 1.0-6, More preferably, it is 1.1-5, More preferably, it is 1.2-4. By using metal oxide fine particles having an average particle diameter in this range, it is considered that the metal oxide fine particles that have already submerged in the plain paper can improve the printing density by effectively suppressing the sinking of the pigment. .

The water dispersion of the present invention may be used as a water-based ink containing water as a main solvent as it is, but a wetting agent, a penetrating agent, a dispersant, a viscosity modifier, an antifoaming agent, which are usually used in water-based inks for inkjet recording, An antifungal agent, an antirust agent, etc. may be added.
The water content in the aqueous dispersion and the water-based ink of the present invention is preferably 30 to 90% by weight, more preferably 40 to 80% by weight.

The preferred surface tension (20 ° C.) of the aqueous dispersion and aqueous ink of the present invention is 30 to 65 mN / m, more preferably 35 to 60 mN / m as the aqueous dispersion, and 25 to 50 mN / m as the aqueous ink. m, more preferably 27 to 45 mN / m.
The viscosity (20 ° C.) of 20% by weight (solid content) of the aqueous dispersion of the present invention is preferably 1 to 12 mPa · s, and more preferably 1 to 9 mPa · s in order to obtain a preferable viscosity when used as a water-based ink. Preferably, 2 to 6 mPa · s is more preferable, and 2 to 5 mPa · s is particularly preferable.
The viscosity (20 ° C.) of the aqueous ink of the present invention is preferably 2 to 12 mPa · s, more preferably 2.5 to 10 mPa · s, and further preferably 2.5 to 6 mPa · s in order to maintain good ejection properties. Particularly preferred.

(Print density improvement method)
In the printing density improving method of the present invention, the printing density of the printed matter can be improved by using the water-based ink of the present invention for inkjet recording. In this case, the printing medium is not limited, and both commonly available plain paper and special paper can be used, but plain paper is preferably used from the viewpoint of exerting the effect of the present invention by the metal oxide fine particles.
The printing density improvement method of the present invention can be applied to any ink jet recording method as long as it uses the water-based ink of the present invention. In particular, the water-based ink of the present invention is used for plain paper with a high printing speed printer. For example, it is suitable for printing at a printing speed of preferably 3 to 30 sheets / minute, more preferably 5 to 30 sheets / minute, and particularly preferably 10 to 30 sheets / minute. The printing speed is assumed to be when the standard pattern (J6) (A4 size) provided by the Japan Electronics and Information Technology Industries Association (JEITA) is used and the printer is printed at a high speed (fine).

In the following examples and comparative examples, “parts” and “%” are “parts by weight” and “% by weight” unless otherwise specified.
Example 1
Demol NL (sodium salt of formalin condensate of sulfonate of polynuclear aromatic compound, manufactured by Kao Corporation) 25 parts, water 400 parts, dimethylquinacridone pigment (CI Pigment Violet 19, Clariant Japan Co., Ltd., trade name) : Hostaperm Red E5B02, average particle diameter 110 nm) was added and mixed with a disper blade at 20 ° C. for 1 hour. The obtained mixture was subjected to 10-pass dispersion treatment at a pressure of 200 MPa with a microfluidizer (trade name, manufactured by Microfluidics).

After adding 250 parts of ion-exchanged water to the obtained dispersion and stirring, a part of water was removed under reduced pressure, and a 5 μm filter (acetylcellulose membrane, outer diameter: 2.5 cm, Fuji Photo Film Co., Ltd.) The aqueous dispersion having a solid content concentration of 20% was obtained by filtering with a 25 mL needleless syringe (manufactured by Terumo Corp.) attached to the product and removing coarse particles.
To 40 parts of the resulting aqueous dispersion, 10 parts of glycerin, 7 parts of triethylene glycol monobutyl ether, 1 part of Surfynol 465, 0.3 part of Proxel XL2, colloidal silica (MP-1040, average particle size 131 nm, Nissan Chemical Industries) 16.75 parts (6.7 parts by solid content) and 24.95 parts of ion-exchanged water were mixed, and the resulting mixture was mixed with a 1.2 μm filter (acetylcellulose membrane, outer diameter: 2). .. 5 cm, manufactured by Fuji Photo Film Co., Ltd.) and filtered with a 25 mL needleless syringe to remove coarse particles, thereby obtaining an aqueous ink.

Example 2
In Example 1, water-based ink was used in the same manner as in Example 1 except that colloidal silica (MP-2040, average particle size 210 nm, manufactured by Nissan Chemical Industries, Ltd.) was used instead of colloidal silica (MP-1040). Got.

Example 3
In Example 1, water-based ink was used in the same manner as in Example 1 except that colloidal silica (MP-3040, average particle size 355 nm, manufactured by Nissan Chemical Industries, Ltd.) was used instead of colloidal silica (MP-1040). Got.

Example 4
In Example 1, instead of colloidal silica (MP-1040) 16.75 parts (6.7 parts by solid content) and ion exchange water 24.95 parts, colloidal silica (MP-2040, average particle size 210 nm, Nissan) A water-based ink was obtained in the same manner as in Example 1 except that 10.8 parts (2.7 parts as solid content) and 30.9 parts of ion-exchanged water were used.

  In Example 1, instead of 75 parts of the dimethylquinacridone pigment, 26.7 parts of a cyan pigment (CI Pigment Blue 15: 4, manufactured by Dainichi Seika Kogyo Co., Ltd., average particle size 100 nm) was used. Instead of 16.75 parts of silica (MP-1040) (6.7 parts in solid content) and 24.95 parts of ion-exchanged water, colloidal silica (MP-2040, average particle size 210 nm, manufactured by Nissan Chemical Industries, Ltd.) A water-based ink was obtained in the same manner as in Example 1 except that 41.5 parts (solid content 16.6 parts) and ion-exchanged water 1.95 parts were used.

Comparative Example 1
In Example 1, instead of colloidal silica (MP-1040) 16.75 parts (6.7 parts by solids) and ion exchange water 24.95 parts, colloidal silica (SI-80P, average particle size 100 nm, catalyst) A water-based ink was obtained in the same manner as in Example 1 except that 10.8 parts (made by Kasei Kogyo Co., Ltd.) (2.7 parts as a solid content) and 30.9 parts of ion-exchanged water were used.

Comparative Example 2
In Example 1, water-based ink was used in the same manner as in Example 1 except that colloidal silica (MP-4540M, average particle size 467 nm, manufactured by Nissan Chemical Industries, Ltd.) was used instead of colloidal silica (MP-1040). Got.
Comparative Example 3
In Example 1, in place of using 16.75 parts of colloidal silica (MP-1040) (6.7 parts by solid content) and 24.95 parts of ion-exchanged water, except that 41.7 parts of ion-exchanged water was used. A water-based ink was obtained in the same manner as in Example 1.

The performance of the ink obtained in each of the above Examples and Comparative Examples was measured and evaluated according to the following method. The results are shown in Table 1-1 and Table 1-2 below.
Printing density Solid printing on high-quality plain paper (Seiko Epson Corp., trade name: KA4250NT) using a Seiko Epson printer (model number: EM-930C) [printing condition = paper type: plain paper, mode Set: Fine], and let stand at 25 ° C. for 24 hours, then print density is 5 points in the center and four corners of printed matter (5.1 cm × 8.0 cm) with Macbeth densitometer (Creetkumakbeth, product number: RD914). Was measured and the average value was obtained. Since the mode setting is fine and ink is not overprinted, the print density is preferably 0.88 or more.

Measuring method of average particle diameter of silica The average particle diameter of silica was measured by a laser particle analysis system ELS-8000 (cumulant analysis) manufactured by Otsuka Electronics Co., Ltd. The measurement conditions are a temperature of 25 ° C., an angle between incident light and a detector of 90 °, and an integration count of 100. The refractive index of water (1.333) is input as the refractive index of the dispersion solvent. The measurement concentration is usually about 5 × 10 ⁻³ wt%.

Claims (6)

  A pigment, metal oxide fine particles having an average particle diameter of 110 to 400 nm, and a water-soluble polymer, and a ratio of the average particle diameter of the metal oxide fine particles to the average particle diameter of the pigment (average particle diameter of metal oxide particles / pigment An aqueous dispersion for inkjet recording having an average particle size of 0.8 to 8.   The aqueous dispersion according to claim 1, wherein the content ratio [(metal oxide fine particles / pigment) weight ratio] of the metal oxide fine particles and the pigment is 0.3 to 10. The aqueous dispersion according to claim 1 or 2, wherein the metal oxide fine particles are colloidal silica.   The water dispersion according to any one of claims 1 to 3, wherein the content of the metal oxide fine particles is 1 to 30% by weight.   An aqueous ink for inkjet recording, comprising the aqueous dispersion according to claim 1. A method for improving print density, wherein the water-based ink according to claim 5 is used for inkjet recording.