JP2006096932A - Inkjet ink and recording method by using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet ink capable of obtaining a printed material improved in scratch resistance and image smoothness of the formed characters and images, and excellent in ejection stability on printing, and a recording method by using the same. <P>SOLUTION: This inkjet ink containing at least a pigment, water and polymer fine particles is characterized in that an ink viscosity ratio (η<SB>2</SB>/η<SB>1</SB>) satisfies the condition prescribed by the following formula (1): 0.8<(η<SB>2</SB>/η<SB>1</SB>)<5.0, by taking ink viscosity at 25°C as η<SB>1</SB>and ink viscosity at 25°C on vaporizing water equivalent to the 10 mass% of the total amount of the ink as η<SB>2</SB>. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ink-jet ink which can provide a printed matter with improved formed characters, image scratch resistance and image smoothness, and has excellent emission stability during printing, and a recording method using the same.

  In recent years, inkjet recording methods can form images easily and inexpensively, and thus have been widely applied to various printing and printing fields such as photographic image fields, various printing fields, special printing fields such as marking and color filters. In particular, inkjet recording devices that can emit and control fine dots, ink with improved color gamut, durability, and emission suitability, ink absorbency, coloring material color development, surface gloss, etc. are dramatically improved. Inkjet paper has been developed, and it is becoming possible to obtain image quality comparable to silver salt photography.

  However, an inkjet image recording system that requires inkjet dedicated paper has problems such as limitations on the recording media that can be used and the relatively high cost of the recording media used. On the other hand, in an office environment, there is a demand for a new system that can perform full-color printing at high speed on various recording media without being restricted by recording media (for example, plain paper, coated paper, art paper, double-sided printing on plain paper, etc.). Is growing.

  In response to the above requirements, the ink-jet ink configuration is compatible with various recording media, can perform high-speed printing, has excellent character reproducibility and image quality, and has excellent storability against scratches, etc. Inkjet inks have been required to be developed.

  Various methods for solving the above problems have been proposed. One of the methods is a solvent-based ink, which is an oil-based ink (solvent-based inkjet ink) containing a volatile solvent and having improved drying properties. By using it, since the penetration into the recording medium is fast and the drying time is short, a printed matter having excellent fixability can be obtained. However, there are odors such as ethyl acetate and methyl ethyl ketone as the solvent, and a large amount of volatile solvents that affect the human body are used, so that it is difficult to apply in the present situation where the office environment is more demanding.

  Other methods include hot melt type ink. This hot-melt type ink uses a wax that becomes a solid state at room temperature and melts and lowers its viscosity when heated. The ink melted by heating with an ink jet recording head is ejected and landed on the recording paper. Then, it is cooled and solidified to form a printed image. This hot-melt type ink has advantages such as not using a volatile solvent, but since wax is used as a main component, scratches are easily generated when the formed image surface is rubbed, and the scratch resistance is improved. It has challenges and is difficult to apply to permanent prints. Further, since the solid content ratio of wax or the like as the ink component is high, there is a drawback that formed characters, images, and the like are raised on the recording medium.

  As another method, an ultraviolet curable ink-jet ink is known. This ultraviolet curable ink-jet ink is an ink mainly composed of a monomer curable by ultraviolet rays and an ultraviolet curing initiator, and is printed on a recording medium and then cured by irradiating the landed ink droplets with ultraviolet rays. is there. This cure has the advantage of improving scratch resistance against scratches and the like, and further eliminating the need for volatile solvents, but many of the UV curable monomers used have skin irritation and sensitization. In addition, there are problems in that the safety of the ink itself has a problem, or because the solid content ratio in the ink component is high, the formed characters, images, and the like rise on the recording medium.

As other methods, many latex inks containing polymer fine particles have been disclosed and proposed (see, for example, Patent Documents 1 to 4). This latex ink has excellent environmental friendliness and scratch resistance by adding polymer fine particles to an ink containing water as a main component. When printing on various recording media, the formed characters and images are recorded on the recording media. It is said that a printed matter that does not rise is obtained. However, in such a latex ink, when continuous printing or intermittent printing is performed in an environment where the ink typified by a low humidity environment is very easy to dry, the ink viscosity increases as the ink dries, and the ink from the recording head increases. There is a problem that it is impossible to perform stable emission due to poor emission, and the content of polymer fine particles is naturally limited, so it is not possible to obtain sufficient image durability required for printed materials It is.
JP-A-9-87560 JP-A-9-176533 Japanese Patent Laid-Open No. 10-60353 JP 2000-85238 A

  SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and its object is to improve characters formed on various recording media, scratch resistance of images, image smoothness, and excellent emission stability during printing. To provide an inkjet ink and a recording method using the same.

  The above object of the present invention is achieved by the following configurations.

(Claim 1)
In an inkjet ink containing at least a pigment, water and polymer fine particles, the ink viscosity at 25 ° C. is η _1, and the ink viscosity at 25 ° C. when water corresponding to 10% by mass of the total mass of the ink is evaporated is η ₂ . Ink jet ink, wherein the ink viscosity ratio η ₂ / η ₁ satisfies the condition defined by the following formula (1):

Formula (1)
0.8 <η ₂ / η ₁ <5.0
(Claim 2)
The inkjet ink according to claim 1, comprising an amphiphilic substance.

(Claim 3)
The inkjet ink according to claim 2, wherein the amphiphilic substance is an N-substituted acrylamide compound or a vinyl ether compound.

(Claim 4)
The inkjet ink according to claim 2 or 3, wherein an average particle diameter of the amphiphile is 10 to 300 nm.

(Claim 5)
The inkjet ink according to claim 2, wherein the amphiphilic substance is an amphiphilic polymer compound and has a core-shell structure.

(Claim 6)
The inkjet ink according to any one of claims 1 to 5, wherein the polymer fine particles have an average particle size of 10 to 300 nm.

(Claim 7)
The ink-jet ink according to any one of claims 1 to 6, wherein a content of the polymer fine particles is 5 to 30% by mass.

(Claim 8)
The ink-jet ink according to any one of claims 1 to 7, wherein the ink viscosity at 25 ° C is 10 mPa · s or more and 300 mPa · s or less.

(Claim 9)
An ink jet ink according to any one of claims 1 to 8 is ejected from an ink jet recording head to record an image.

(Claim 10)
The recording method according to claim 9, wherein the ejection amount of the inkjet ink ejected from the inkjet recording head is 0.1 to 2.0 pl per droplet.

  According to the present invention, there are provided an ink-jet ink which is improved in scratch resistance and image smoothness of characters and images formed on various recording media and has excellent emission stability during printing, and a recording method using the same. be able to.

  Hereinafter, the best mode for carrying out the present invention will be described in detail.

As a result of intensive studies in view of the above problems, the present inventor has determined that an ink viscosity at 25 ° C. is η ₁ in an ink-jet ink containing at least a pigment, water, and polymer fine particles, and corresponds to 10% by mass of the total mass of the ink. When the ink viscosity at 25 ° C. when water is evaporated is η ₂ , the ink viscosity ratio η ₂ / η ₁ satisfies the condition defined by the above formula (1). As soon as the present invention has been found, it has been found that an ink-jet ink can be realized which has improved scratch resistance and image smoothness of characters and images formed on a recording medium and is excellent in emission stability during printing.

  Details of the present invention will be described below.

  The ink-jet ink of the present invention contains at least a pigment, water, and polymer fine particles, and has a viscosity behavior with respect to a volume change defined by the formula (1).

That is, in the inkjet ink of the present invention, the ink viscosity at 25 ° C. is η _1, and the ink viscosity at 25 ° C. when water equivalent to 10% by mass of the total mass of the ink is evaporated is η _2. The ratio η ₂ / η ₁ is in the range of 0.8 <η ₂ / η ₁ <5.0, and more preferably 0.8 <η ₂ / η ₁ <2.5.

Normally, the amount of ink ejected from the recording head increases as the viscosity decreases, and the print density increases accordingly. Conversely, when the ink viscosity increases, the ink discharge amount decreases and the print density decreases. Therefore, when water corresponding to 10% by mass of the total mass of the ink is evaporated, if the ink viscosity ratio η ₂ / η ₁ is less than 08, the viscosity difference from the reference ink viscosity (η ₁ ) becomes too large. Since the dot density is different between the image portion that is continuously emitted and the case where the image is re-emitted from the recording head that has stopped emitting, a problem occurs in image reproducibility. When the viscosity due to drying exceeds 5.0, the viscosity accompanying drying of the ink becomes too high, and it becomes difficult to stably eject ink droplets from the recording head.

As a measuring method of η ₂ / η ₁ defined by the above formula (1), after measuring the viscosity (η ₁ ) and mass of the ink at 25 ° C., Fine Oven DF42 manufactured by Yamato Scientific Co., Ltd. was used. When the ink mass is reduced by an amount equivalent to 10% by mass except for the ink evaporation component (water, etc.) under the condition of a fan air volume of 1000 rpm, the above operation is stopped, and the viscosity (η ₂ ) of the ink is measured. determine the ₂ / _{η 1.}

The means for setting the ink viscosity ratio η ₂ / η ₁ within the range defined in the present invention is not particularly limited, but in the present invention, it is preferable to add a viscosity inhibitor.

  The amphiphilic substance according to the present invention is a part of a substance that reversibly changes its hydrophilicity and hydrophobicity. In an environment with a lot of water, the substance and water are bonded by hydrogen bonds. In this case, the material is bonded with hydrogen bonds, and the viscosity is lowered.

  Examples of such amphiphilic substances include poly N-substituted acrylamides such as polyisopropyl acrylamide, hydrophobized pullulan, modified polyethylene oxide, amphiphilic star polymers described in JP-A No. 2002-146256, 11-322866, JP-A-11-322742, JP-A-2000-319473, JP-A-2001-19770, etc., and a compound selected from poly-modified vinyl, poly-modified vinyl ether compounds, etc. The form may be either a linear polymer or a star polymer emulsion having a polymer nucleus.

  Among them, the monomer is particularly preferably an N-substituted acrylamide compound or a vinyl ether compound. Specific examples of the compound include N-substituted (meth) acrylamide derivatives and vinyl methyl ether derivatives. Among them, preferred monomers for obtaining the effects of the present invention are N-substituted (meth) acrylamide derivatives, such as N-ethylmethacrylamide, Nn-propylacrylamide, N-isopropylacrylamide, and N-isopropylmethacrylamide. N-cyclopropylacrylamide, N-cyclopropylmethacrylamide, N, N-diethylmethacrylamide, N-methyl-N-isopropylacrylamide, and N-methyl-Nn-propylacrylamide are particularly preferable.

  In the present invention, it is more preferable that the amphiphilic substance has a core-shell structure. For example, (meth) acrylic heavy polymers described in JP-A-7-33224, JP-A-2003-40916, and the like. Examples thereof include polymer fine particles having a core-shell structure having a core portion made of a coalescence and an outer shell portion made of an N-alkylacrylamide polymer.

  The average particle size of the viscosity-suppressing substance according to the present invention is preferably 10 to 300 nm. If the average particle size is 10 nm or more, an increase in viscosity due to drying of the ink can be suppressed, and if it is 500 nm or less, stable emission can be achieved without causing clogging during emission from the recording head. preferable. The average particle size of the viscosity-inhibiting substance can be determined by a commercially available particle size measuring instrument using a light scattering method, an electrophoresis method, or a laser Doppler method.

  Moreover, in the inkjet ink of the present invention, the content of the viscosity inhibitor according to the present invention is set to 0.2% by mass or more and 30% by mass or less from the viewpoint of further achieving the object effect of the present invention. preferable.

  Next, the polymer fine particles according to the present invention will be described.

  The polymer fine particles that can be used in the present invention are not particularly limited. For example, styrene-butadiene copolymer, polystyrene, acrylonitrile-butadiene copolymer, acrylate copolymer, polyurethane, silicon-acrylic copolymer. Examples thereof include latex such as coalescence and acrylic-modified fluororesin. The latex may be obtained by dispersing polymer particles using an emulsifier, or may be dispersed without using an emulsifier. A surfactant is often used as an emulsifier, but a polymer having a water-soluble group such as a sulfonic acid group or a carboxylic acid group (for example, a polymer in which a solubilizing group is graft-bonded, a single group having a solubilizing group). It is also preferable to use a polymer obtained from a monomer and a monomer having an insoluble part.

  In the ink-jet ink of the present invention, it is particularly preferable to use soap-free latex. Soap-free latex is a latex that does not use an emulsifier and a polymer having a water-soluble group such as a sulfonic acid group or a carboxylic acid group (for example, a polymer in which a solubilizing group is graft-bonded, a solubilizing group) A polymer obtained from a monomer having an insoluble part and a monomer having an insoluble part).

  In recent years, as latex polymer particles, there are also latexes in which core-shell type polymer particles having different compositions at the center and outer edge of the particles are dispersed in addition to the latex in which the polymer particles are uniform throughout. However, this type of latex can also be preferably used.

  In the inkjet ink of the present invention, the average particle size of the polymer fine particles is preferably 10 nm or more and 300 nm or less, and more preferably 10 nm or more and 200 nm or less from the viewpoint of ink stability and ejection stability. If the average particle size of the polymer fine particles is 300 nm or less, good glossiness of the formed image can be obtained, and if it is 10 nm or more, good water resistance and scratch resistance can be obtained. The average particle size of the polymer fine particles can be determined by a commercially available particle size measuring instrument using a light scattering method, an electrophoresis method, a laser Doppler method or the like.

  In the ink-jet ink of the present invention, the content of the polymer fine particles according to the present invention is preferably 5% by mass or more and 30% by mass or less from the viewpoint of further achieving the object effect of the present invention. If the content of the polymer fine particles according to the present invention is 5% by mass or more, sufficient scratch resistance can be obtained, and if it is 30% by mass or less, the ink viscosity is in an appropriate range and stable ink ejection properties. Can be obtained.

  The polymer fine particles according to the present invention preferably have a glass transition point of −20 ° C. or higher and 80 ° C. or lower, more preferably −10 ° C. or higher and 60 ° C. or lower. If the glass transition point is too low, the scratch resistance is improved, but conversely, if the images are left on top of each other, adhesion occurs and the image portion is peeled off. Further, if the glass transition point is too high, the scratching property is inferior.

  The polymer fine particles according to the present invention exhibit an effect of fixing a pigment after being ejected onto a recording medium and then forming a film after removing water and an organic solvent to some extent from the system by drying and permeation.

  Next, the pigment will be described.

  As the pigment that can be used in the present invention, conventionally known organic and inorganic pigments can be used. For example, azo pigments such as azo lakes, insoluble azo pigments, condensed azo pigments, chelate azo pigments, phthalocyanine pigments, perylene and perylene pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, etc. Examples include polycyclic pigments, dye lakes such as basic dye lakes, and acid dye lakes, organic pigments such as nitro pigments, nitroso pigments, aniline black, and daylight fluorescent pigments, and inorganic pigments such as carbon black.

  Specific organic pigments are exemplified below.

  Examples of pigments for magenta or red include C.I. I. Pigment red 2, C.I. I. Pigment red 3, C.I. I. Pigment red 5, C.I. I. Pigment red 6, C.I. I. Pigment red 7, C.I. I. Pigment red 15, C.I. I. Pigment red 16, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 53: 1, C.I. I. Pigment red 57: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 123, C.I. I. Pigment red 139, C.I. I. Pigment red 144, C.I. I. Pigment red 149, C.I. I. Pigment red 166, C.I. I. Pigment red 177, C.I. I. Pigment red 178, C.I. I. And CI Pigment Red 222.

  Examples of the orange or yellow pigment include C.I. I. Pigment orange 31, C.I. I. Pigment orange 43, C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 13, C.I. I. Pigment yellow 14, C.I. I. Pigment yellow 15, C.I. I. Pigment yellow 17, C.I. I. Pigment yellow 74, C.I. I. Pigment yellow 93, C.I. I. Pigment yellow 94, C.I. I. Pigment yellow 128, C.I. I. And CI Pigment Yellow 138.

  Examples of pigments for green or cyan include C.I. I. Pigment blue 15, C.I. I. Pigment blue 15: 2, C.I. I. Pigment blue 15: 3, C.I. I. Pigment blue 16, C.I. I. Pigment blue 60, C.I. I. And CI Pigment Green 7.

  As a method for dispersing the pigment, for example, various dispersing machines such as a ball mill, a sand mill, an attritor, a roll mill, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, a wet jet mill, and a paint shaker can be used. It is also preferable to use a centrifugal separator or a filter for the purpose of removing the coarse particles of the pigment dispersion.

  In the ink according to the present invention, a self-dispersed pigment in which polar groups such as sulfonic acid and carboxylic acid are pendant on the pigment surface, or a pigment dispersed using a polymer dispersant is preferable.

  The polymer dispersant according to the present invention is not particularly limited, and a water-soluble resin or a water-insoluble resin is used. Examples of these polymers include styrene, styrene derivatives, vinyl naphthalene derivatives, acrylic acid, acrylic acid derivatives, methacrylic acid, methacrylic acid derivatives, maleic acid, maleic acid derivatives, itaconic acid, itaconic acid derivatives, fumaric acid, fumaric acid. Examples thereof include a polymer composed of a single monomer selected from acid derivatives, a copolymer composed of two or more monomers, and salts thereof. Water-soluble polymers such as polyvinyl alcohol, polyvinyl pyrrolidone, cellulose derivatives, gelatin, and polyethylene glycol can also be used.

  The content of these water-soluble resins with respect to the total amount of ink is preferably 0.1 to 10% by mass, and more preferably 0.3 to 5% by mass. These water-soluble resins can be used in combination of two or more.

  The pigment content used in the inkjet ink of the present invention is preferably 0.3 to 20% by mass, more preferably 2.0 to 15% by mass, based on the total mass of the ink.

  The inkjet ink of the present invention contains at least water as a solvent, but an aqueous liquid medium can be further used.

Examples of the water-soluble organic solvent preferably used include alcohols (for example, methanol, ethanol, propanol, isopropanol, n-butanol, isobutanol, secondary butanol, tertiary butanol), polyhydric alcohols (for example, ethylene glycol, Diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, thiodiglycol), polyhydric alcohol ethers (eg, ethylene glycol monomethyl ether) , Ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol Cole monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, ethylene glycol Monophenyl ether, propylene glycol monophenyl ether), amines (for example, ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, diethylenediamine, triethylene) Tetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, tetramethylpropylenediamine), amides (eg, formamide, N, N-dimethylformamide, N, N-dimethylacetamide, etc.), heterocycles (eg, 2 -Pyrrolidone, N-methyl-2-pyrrolidone, cyclohexyl pyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone, etc.), sulfoxides (for example, dimethyl sulfoxide), etc. Various surfactants can be used from the viewpoint of adjusting the surface tension of the ink or improving the dispersion stability of the pigment.

  The surfactant that can be used in the present invention is not particularly limited, and examples thereof include anionic surfactants such as dialkyl sulfosuccinates, alkyl naphthalene sulfonates, fatty acid salts, polyoxyethylene alkyl ethers, polyoxyethylene alkyl ethers, and polyoxyethylene alkyl ethers. Nonionic surfactants such as oxyethylene alkyl allyl ethers, acetylene glycols, polyoxyethylene / polyoxypropylene block copolymers, and cationic surfactants such as alkylamine salts and quaternary ammonium salts. In particular, an anionic surfactant and a nonionic surfactant can be preferably used.

  In the present invention, a polymer surfactant can also be used. For example, styrene-acrylic acid-acrylic acid alkyl ester copolymer, styrene-acrylic acid copolymer, styrene-maleic acid-acrylic acid alkyl ester. Copolymer, styrene-maleic acid copolymer, styrene-methacrylic acid-acrylic acid alkyl ester copolymer, styrene-methacrylic acid copolymer, styrene-maleic acid half ester copolymer, vinylnaphthalene-acrylic acid copolymer Examples thereof include vinyl compounds and vinyl naphthalene-maleic acid copolymers.

  In addition to the above description, the inkjet ink of the present invention is publicly known depending on the purpose of improving the emission stability, print head and ink cartridge compatibility, storage stability, image storage stability, and other various performances as necessary. Various additives, such as viscosity modifiers, specific resistance regulators, film forming agents, UV absorbers, antioxidants, anti-fading agents, anti-fouling agents, rust inhibitors, etc. can be appropriately selected and used, For example, oil droplet fine particles such as liquid paraffin, dioctyl phthalate, tricresyl phosphate, silicone oil, ultraviolet absorbers described in JP-A-57-74193, JP-A-57-87988, and JP-A-62-261476, 57-74192, 57-87989, 60-72785, 61-146591, JP-A-1-95091 and 3-13376. Fluorescent whitening described in JP-A-59-42993, JP-A-59-52689, JP-A-62-280069, JP-A-61-228771, JP-A-4-219266 and the like An agent etc. can be mentioned.

  The ink-jet ink of the present invention having the above-described configuration preferably has an ink viscosity at 25 ° C. of 10 mPa · s or more and 300 mPa · s or less, more preferably 10 mPa · s or more and 200 mPa · s or less. By setting the ink viscosity to 10 mPa · s or more, preferable ink fluidity at the time of image recording can be obtained, and high image sharpness can be realized. Further, by setting it to 300 mPa · s or less, an appropriate ink viscosity can be obtained, and stable emission from the recording head can be performed.

  Next, the recording method of the present invention will be described.

  In the recording method using the inkjet ink of the present invention, for example, an inkjet recording image is formed by ejecting ink as droplets from an inkjet head based on a digital signal and adhering to a recording medium by a printer loaded with inkjet ink. It is formed.

  The ink jet recording head that can be used in the recording method using the ink jet ink of the present invention may be an on-demand system or a continuous system. In addition, as an ink ejection method, an electro-mechanical conversion method (for example, a single cavity type, a double cavity type, a bender type, a piston type, a shear mode type, a shared wall type, etc.), an electro-thermal conversion method (for example, Any ejection method such as a thermal ink jet type or a bubble jet (registered trademark) type may be used.

  In the recording method of the present invention, the discharge amount of the ink jet ink discharged from the ink jet recording head is set to 0.1 to 2.0 pl per droplet from the viewpoint that the object and effects of the present invention can be fully exhibited. preferable.

  As a recording medium that can be used in the recording method using the ink-jet ink of the present invention, for example, plain paper, coated paper, cast-coated paper, glossy paper, glossy film, OHP film, ink jet dedicated paper, etc. are widely used. Among them, the effect can be exhibited by inkjet image recording using plain paper, coated paper, cast coated paper, glossy paper or the like which is an absorbent support.

The paper, coated paper, there is a non-coated paper, as the coated paper, the coating amount per 1m ² is one side 20g before and after of art paper, 1m ² per coated amount on one side 10g before and after the coated paper Examples include a light-weight coated paper having a coating amount per 1 m ^{2 of} about 5 g on one side, a finely coated paper, a mat-like finished mat-coated paper, a dull-like finished dull-coated paper, and a newsprint. Non-coated paper includes printing paper A using 100% chemical pulp, printing paper B using 70% or more chemical pulp, printing paper C using 40% or more and less than 70% chemical pulp, and printing using less than 40% chemical pulp. Examples thereof include paper D, gravure paper containing mechanical pulp and subjected to calendar treatment. More details are described in detail in “Latest Paper Processing Handbook” edited by the Paper Processing Handbook Editorial Committee, published by Tech Times, “Printing Engineering Handbook” edited by the Japan Printing Society.

  The plain paper is 80 to 200 μm uncoated paper belonging to a part of uncoated paper, special printing paper and information paper. The plain paper used in the present invention includes, for example, high-grade printing paper, intermediate-grade printing paper, low-grade printing paper, thin-like printing paper, fine-coating printing paper, special printing paper such as fine-quality printing paper, foam paper, PPC paper, and others There are information sheets and the like. Specifically, there are the following sheets and various modified / processed sheets using these sheets, but the present invention is not particularly limited thereto. High quality paper and colored high quality paper, recycled paper, copy paper / colored paper, OCR paper, carbonless paper / colored paper, synthetic paper such as YUPO 60, 80, 110 microns, YUPO COAT 70, 90 microns, etc. Coated paper 90kg, Foam mat paper 70, 90, 110kg, Foamed PET 38 microns, Mitsuori-kun (above, Kobayashi recording paper), OK fine paper, New OK fine paper, Sunflower, Phoenix, OK Royal White, Export fine paper ( NPP, NCP, NWP, Royal White) OK Book Paper, OK Cream Book Paper, Cream Premium Paper, OK Map Paper, OK Ishikari, Cucumber, OK Foam, OKH, NIP-N (above, Shin Oji Paper), Gold Wang, Toko, export quality paper, special demand quality paper, book paper, book paper L, light cream book paper, elementary textbook Paper, continuous slip paper, high quality NIP paper, silver ring, gold yang, gold yang (W), bridge, capital, silver ring book, harp, harp cream, SK color, securities paper, opera cream, opera, KYP medical record, silvia HN, Excellent Foam, NPI Foam DX (Nippon Paper), Pearl, Kinryo, Uscream fine paper, Special Book Paper, Super Book Paper, Book Paper, Diamond Foam, Inkjet Foam (Mitsubishi Paper), Carpet V, carpet SW, white elephant, luxury publication paper, cream carpet, cream white elephant, securities / voucher paper, book paper, map paper, copy paper, HNF (above, Hokuetsu), phone book cover, Book paper, cream shirairai, cream shirairaifu, cream shirairaifu, DSK (above, Daishowa Paper), Sendai MP fine paper, Jiang, Thunderbird fine, hanging paper, colored paper base, dictionary paper, cream book, white book, cream fine paper, map paper, continuous slip paper (above, Chuetsu Pulp), OP gold cherry (Chuetsu), gold sand, reference book paper, Replacement certificate paper (white), form printing paper, KRF, white foam, color foam, (K) NIP, fine PPC, Kishu inkjet paper (above, made by Kishu Paper), Taiou, Bright Foam, Kant, Kant White, Dante , CM paper, Dante Comic, Heine, paperback book paper, Heine S, New AD paper, Utrilo Excel, Excel Super A, Kant Excel, Excel Super B, Dante Excel, Heine Excel, Excel Super C, Excel Super D, AD Excel, Excel Super E, New Bright Foam, New Bright NI P (above, made by Daio Paper), Sun Ring, Moon Ring, Cloud Pass, Galaxy, Baiyun, Wyeth, Moon Ring Ace, Baiyun Ace, Cloud Pass Ace (above, Nippon Paper Industries), Taiou, Bright Foam, Bright Nip (Nagoya Pulp), Peony A, Golden Pigeon, Special Peony, White Peony A, White Peony C, Silver Pigeon, Super White Peony A, Light Cream White Peony, Special Medium Quality Paper, White Pigeon, Super Medium Quality Paper, Blue Pigeon, Red Pigeon, Gold Pigeon M Snow Vision, Snow Vision, Gold Pigeon Snow Vision, White Pigeon M, Super DX, Hamanasu O, Red Pigeon M, HK Super Printing Paper (above, Honshu Paper), Stalinden (A・ AW), Star Elm, Star Maple, Star Laurel, Star Poplar, MOP, Star Cherry I, Cherry I Super, Cherry II Super, Star Cherry III, Star Cherry IV, Cherry III Super, Cheri -IV Super (above, made by Maruzumi Paper), SHF (above, made by Toyo Pulp), TRP (above, made by Tokai Pulp) and the like.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In the following examples, “%” and “part” represent “% by mass” and “part by mass”, respectively, unless otherwise specified.

《Preparation of amphiphile》
(Preparation of amphiphile 1)
A monomer liquid 1 was prepared by mixing 10 parts of styrene, 10 parts of n-butyl methacrylate, 10 parts of 2-hydroxyethyl acrylate, and 0.5 part of ethylene glycol dimethacrylate.

  To a four-necked flask, 0.2 part of dodecyl sulfate and 180 parts of ion-exchanged water were added and dissolved, and then purged with nitrogen. In this, 5 parts of monomer liquid 1 was added, and it heated up at 60 degreeC, stirring. After the temperature rise, 3 parts of a 2% aqueous ammonium persulfate solution was added dropwise, and the temperature was further raised to 80 ° C., and the remaining monomer solution 1 (25.5 parts) and 40 parts of a 2% aqueous ammonium persulfate solution were added over 3 hours. The core part was prepared by dripping and aging for 2 hours.

  While maintaining the above reaction solution at 80 ° C., a mixture of 100 parts of N-isopropylacrylamide and 1000 parts of ion-exchanged water and 240 parts of 0.2% ammonium persulfate were added dropwise over 2 hours. After aging for a while, centrifugal separation was performed to remove coarse particles, and an aqueous dispersion containing amphiphilic substance 1 having a core-shell structure with an average particle diameter of 153 nm was prepared. The average particle diameter was measured using a Zetasizer 1000HS manufactured by Malvern.

(Preparation of amphiphilic substance 2)
In the preparation of the amphiphile 1, the average particle size is the same except that 0.2 part of C ₁₂ H ₂₅ O (CH ₂ CH ₂ O) ₉ H is used instead of 0.2 part of dodecyl sulfate. An aqueous dispersion containing amphiphilic substance 2 having a core-shell structure with a diameter of 350 nm was obtained.

(Preparation of amphiphile 3)
In the preparation of the amphiphilic substance 1, an aqueous dispersion containing the amphiphilic substance 3 having a core-shell structure with an average particle size of 124 nm is used except that N-ethylacrylamide is used instead of N-isopropylacrylamide. I got a thing.

(Preparation of amphiphilic substance 4)
In the preparation of the amphiphilic substance 1, an aqueous dispersion containing the amphiphilic substance 4 having a core-shell structure with an average particle size of 138 nm is used except that N-acryloylpiperidine is used instead of N-isopropylacrylamide. I got a thing.

(Preparation of amphiphile 5)
In the preparation of the amphiphilic substance 1, water containing the amphiphilic substance 5 having a core-shell structure with an average particle size of 218 nm was used in the same manner except that 2-ethoxyethyl vinyl ether was used instead of N-isopropylacrylamide. A dispersion was obtained.

(Preparation of amphiphile 6)
10 parts of styrene, 10 parts of n-butyl methacrylate, 10 parts of 2-hydroxyethyl acrylate, 0.5 part of ethylene glycol dimethacrylate, and 100 parts of N-isopropylacrylamide were mixed to prepare monomer liquid 2.

  After adding dodecyl sulfate 0.2 and 1180 parts of ion-exchanged water to a four-necked flask and dissolving, it was purged with nitrogen. To this, 5 parts of the monomer liquid 2 was added, and the temperature was raised to 60 ° C. while stirring. After the temperature rise, 43 parts of 2% ammonium persulfate aqueous solution was dropped, and the temperature was further raised to 80 ° C. The remaining monomer liquid 2 and 40 parts of 2% ammonium persulfate aqueous solution were dropped over 4 hours, and the mixture was aged for 2 hours. Thus, an aqueous dispersion containing the amphiphilic substance 6 having an average particle diameter of 155 nm was obtained.

(Preparation of amphiphile 7)
3 parts of styrene, 3 parts of methyl methacrylate, 10 parts of 2-hydroethyl acrylate, 10 parts of methacrylic acid and 100 parts of N-isopropylacrylamide were mixed to prepare a monomer liquid 3.

  In a four-necked flask, 0.2 part of dodecyl sulfate and 1180 parts of ion exchange water were added and dissolved, and then the atmosphere was replaced with nitrogen. To this, 5 parts of the monomer liquid 3 was added, and the temperature was raised to 60 ° C. while stirring. After the temperature rise, 43 parts of 2% ammonium persulfate aqueous solution was added dropwise, and the temperature was further raised to 80 ° C. The remaining monomer solution 3 and 40 parts of 2% ammonium persulfate aqueous solution were added dropwise over 4 hours, and aged for 2 hours. Then, the solution was neutralized with N, N-dimethylethanolamine to prepare an aqueous solution in which the amphiphile 7 was in a dissolved state.

<Preparation of inkjet ink>
[Carbon black dispersion]
Talker Black # 8500 (Tokai Carbon Co., Ltd.) 120g
Jongkrill 62 (Johnson Polymer Co., Ltd.) 59g
Lebenol WX (Kao Corporation) 3g
Diethylene glycol 100g
Ion exchange water 300g
After the above additives were mixed, the mixture was dispersed using a sand grinder filled with 50% by volume of 0.5 mm zirconia beads, and then a coarse product was removed with a centrifugal separator to obtain a black pigment dispersion.

[Preparation of black inks 1-22]
Carbon black dispersion 10 parts as solid content Amphiphile (type listed in Table 1) Amount listed in Table 1 (solid content)
Ethylene glycol 10 parts Polymer fine particles (types listed in Table 1) Amounts listed in Table 1 (solid content)
Orphin E1010 (manufactured by Nissin Chemical) 0.3 part Proxel GXL (manufactured by Avicia) 0.1 part Water was added to make 100 parts in total.

  The details of the comparative additives and polymer fine particles described in abbreviations in Table 1 are as follows.

[Comparison additive]
A: Hydroxypropyl cellulose (Nippon Soda Co., Ltd. HPC-M No viscosity maximum)
B: Polyethylene glycol (average molecular weight: 10,000, no viscosity maximum)
[Polymer fine particles]
LxA: Composition = St / BA / 2EHA / MAA, average molecular weight = 55000, average particle size 105 nm, Tg = 15 ° C.
LxB: Composition = St / BA / 2EHA / MAA, average molecular weight = 50000, average particle size 250 nm, Tg = 15 ° C.
LxC: composition = St / BA / 2EHA / MAA, average molecular weight = 55000, average particle size 350 nm, Tg = 15 ° C.
LxD: composition = St / BMA / HEMA / MAA, average molecular weight = 30000, average particle size 87 nm, Tg = 45 ° C.
LxE: composition = St / 2EHA / HEMA / MAA, average molecular weight = 100000, average particle size 120 nm, Tg = 30 ° C.
LxF: Composition = St / BMA / HEMA / MAA, average molecular weight = 120,000, average particle size 156 nm, Tg = 50 ° C.
St: Styrene 2EHA: 2-ethylhexyl acrylate HEMA: 2-hydroxyethyl acrylate MAA: methacrylic acid BA: n-butyl acrylate BMA: n-butyl methacrylate << Evaluation of inkjet ink >>
[Measurement of ink viscosity ratio η ₂ / η ₁ ]
The viscosity (η ₁ ) at 25 ° C. of each prepared ink was measured using a B-type viscometer BL manufactured by Tokyo Keiki Co., Ltd. Next, the ink was set in a Fine Oven DF42 manufactured by Yamato Scientific Co., Ltd., and when the ink mass was reduced by an amount equivalent to 10% by mass, the ink evaporation component (water, etc.) was removed under the conditions of 30 ° C. and a fan air volume of 1000 rpm. The operation was stopped, and the viscosity (η ₂ ) of the ink was measured using the above viscometer to obtain η ₂ / η ₁ .

[Inkjet image formation]
Each of the black inks prepared above was converted into 0 per droplet by an ink jet printer PXG-900 manufactured by Seiko Epson Corporation or an ink jet printer equipped with an electrostatic suction type ink jet recording head described in JP-A No. 2004-136656. It was emitted onto art paper (Tokuhishi Art, manufactured by Mitsubishi Paper Industries, Ltd., basis weight: 127.9 g / m ² ) with an emission amount of .5 pl, and line drawings and solid images were created.

[Evaluation]
(Evaluation of scratch resistance)
As for the scratch resistance, the black solid image created above was subjected to five reciprocal scratches on the surface with an office eraser (manufactured by MONNO Tonbo Pencil Co., Ltd.), and the remaining density was visually checked by 20 general evaluators. Evaluation was made and judged according to the following criteria.

A: 16 or more people evaluated that the density of the original image remained almost. ○: 12 to 15 people evaluated that the density of the original image remained. Δ: Almost the density of the original image remained. 8 to 11 people evaluated as being X: No more than 7 people evaluated that the density of the original image remained (evaluation of image smoothness)
For each printed image, the image surface was visually observed, and the image smoothness was evaluated according to the following criteria.

◎: There is no image swell and smoothness is very good. ○: Swelling is observed in some images, but there is almost no problem in practical use. △: Image swelling is recognized and the quality is practically acceptable. Yes x: Strong image swell, image quality deteriorates, and has a practical problem (evaluation of output stability)
Depending on the ink jet image formation conditions, line art and solid images are printed on art paper at intervals of 40 ° C, 30% RH, 20 ° C, and 70% RH, respectively. After stopping, the 10th print was made. The emission state of the nozzle at the time of printing the tenth sheet was visually observed, and the emission stability was evaluated according to the following criteria.

◎: No change in emission state for all nozzles ○: Diagonal emission is observed with 1 or 2% by number of nozzles, but there is no ink shortage △: Ink shortage occurs with 3 to 10% or less nozzles X: Ink out occurred in 10% or more nozzles. Table 1 shows the results obtained as described above.

As is apparent from the results shown in Table 1, the ink of the present invention in which the ink viscosity ratio η ₂ / η ₁ is in the range specified by the present invention is higher than the comparative example in the scratch resistance and image smoothness of the formed image. It can be seen that even if intermittent emission is performed under the conditions of excellent performance and different temperature and humidity environments, no emission failure occurs.

Example 2
The black inks 3 and 20 prepared in Example 1 were prepared by using an ink jet printer PXG-900 manufactured by Seiko Epson Corporation or an ink jet printer provided with an electrostatic suction type ink jet recording head described in JP-A No. 2004-136656. Emitted onto art paper (basket weight: 127.9 g / m ² ) with the amount of emission per droplet listed in Table 2, creating line drawings and solid images In the same manner as described in the examples, the emission stability, scratch resistance and image smoothness were evaluated, and the obtained results are shown in Table 2.

  As is apparent from the results shown in Table 2, by performing emission and image formation with an emission amount per droplet in the range of 0.2 to 2.0 pl, scratch resistance, image smoothness, and emission stability. Is more preferable.

Claims (10)

In an inkjet ink containing at least a pigment, water and polymer fine particles, the ink viscosity at 25 ° C. is η _1, and the ink viscosity at 25 ° C. when water corresponding to 10% by mass of the total mass of the ink is evaporated is η ₂ . Ink jet ink, wherein the ink viscosity ratio η ₂ / η ₁ satisfies the condition defined by the following formula (1):
Formula (1)
0.8 <η ₂ / η ₁ <5.0 The inkjet ink according to claim 1, comprising an amphiphilic substance. The inkjet ink according to claim 2, wherein the amphiphilic substance is an N-substituted acrylamide compound or a vinyl ether compound. The inkjet ink according to claim 2 or 3, wherein an average particle diameter of the amphiphile is 10 to 300 nm. The inkjet ink according to any one of claims 2 to 4, wherein the amphiphilic substance is an amphiphilic polymer compound and has a core-shell structure. The inkjet ink according to any one of claims 1 to 5, wherein the polymer fine particles have an average particle size of 10 to 300 nm. The ink-jet ink according to any one of claims 1 to 6, wherein a content of the polymer fine particles is 5 to 30% by mass. The ink-jet ink according to any one of claims 1 to 7, wherein the ink viscosity at 25 ° C is 10 mPa · s or more and 300 mPa · s or less. An ink jet ink according to any one of claims 1 to 8 is ejected from an ink jet recording head to record an image. The recording method according to claim 9, wherein the ejection amount of the inkjet ink ejected from the inkjet recording head is 0.1 to 2.0 pl per droplet.