JP2007145889A - Ink for inkjet and method for inkjet recording - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide ink for inkjet and to provide a method for inkjet recording with high jetting reliability even when jetting the ink in a heated state thereof from a piezo head. <P>SOLUTION: The ink is used for inkjet printing for jetting the ink which is a liquid at normal temperature in the heated state thereof from the piezo type head. The ink is a water-based pigment ink comprising at least water, a water-soluble organic solvent and a pigment. The ink is deaerated so that the concentration of the dissolved oxygen in the ink is <10% of the concentration of the saturated dissolved oxygen at the ink temperature during jetting. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ink-jet ink and an ink-jet recording method, and more particularly to a degree of deaeration of ink-jet ink, wherein the ink is ejected from a piezo head in a heated state.

  An ink jet image printing method is a method in which fine droplets of ink are ejected from an ink jet recording head and attached to a target recording medium for printing. The ink jet method is advantageous in that its mechanism is relatively simple, inexpensive, and can form a high-definition and high-quality image.

  There are various types of ink jet recording systems, but on-demand recording systems, which have been mainstream in recent years, are classified into so-called piezo systems using piezo elements and thermal jets. Among them, the inkjet recording method using the piezo method repeatedly pressurizes and depressurizes a number of times during ink ejection, so that minute bubbles are likely to occur due to cavitation, leading to dot omission and landing position misalignment during ink ejection. It is known to deteriorate print image quality such as graininess.

  In general, cavitation is a physical phenomenon in which, when the pressure of a liquid at a certain temperature becomes lower than the vapor pressure determined by that temperature, the liquid evaporates and becomes bubbles. For this reason, the ink-jet ink used is usually subjected to a deaeration process so that the amount of gas contained in the ink-jet ink is reduced as much as possible to prevent generation of bubbles during ejection.

  Patents that disclose a technique for degassing ink include Patent Document 1 and Patent Document 2, but the degree of degassing is not described or even if it is described, saturated dissolution at room temperature There is no description about the amount of saturated dissolved gas at a temperature higher than room temperature.

On the other hand, Japanese Patent Application Laid-Open No. 2003-228667 discloses an ink jet method in which ink is heated and ejected from a head. Ink having a viscosity higher than 50 mPa seconds cannot be ejected stably, but it has been shown that the effect of stably ejecting ink within the viscosity range suitable for ejection is obtained by reducing the viscosity by heating. However, there is no mention of whether or not the ink is deaerated and the degree of deaeration, and there is a problem that cavitation occurs when continuous ejection is performed if only this requirement is implemented.
Japanese Patent Laid-Open No. 9-59549 Japanese Patent Laid-Open No. 5-17712 JP 2003-136756 A

  The present invention has been made in view of the above problems, and an object thereof is to provide an inkjet ink and an inkjet recording method with high ejection reliability even when the ink is ejected from a piezo head in a heated state. is there.

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

  1. Ink used for inkjet printing in which ink that is liquid at room temperature is ejected from a piezo-type head in a heated state, the ink is an aqueous pigment ink containing at least water, a water-soluble organic solvent, and a pigment, and An inkjet ink, wherein the dissolved oxygen concentration in the ink is deaerated so as to be less than 10% of the saturated dissolved oxygen concentration at the ink temperature at the time of ejection.

  2. The ink contains at least water, a water-soluble organic solvent, and a pigment, and the water content is 10% by mass or more and less than 50% by mass of the total ink mass, and is the most contained of the water-soluble organic solvent. The SP value of the water-soluble organic solvent is 16.5 or more and less than 24.6, and the content of the water-soluble organic solvent having the SP value of 16.5 or more and less than 24.6 is 30% by mass or more of the total ink mass. 2. The ink-jet ink as described in 1 above, wherein

  3. An ink jet recording method in which an ink that is liquid at normal temperature is ejected from a piezo-type head in a heated state, and the ink is an aqueous pigment ink containing at least water, a water-soluble organic solvent, and a pigment, An inkjet recording method, wherein the dissolved oxygen concentration is deaerated so as to be less than 10% of the saturated dissolved oxygen concentration at the ink temperature at the time of ejection.

  4). The ink contains at least water, a water-soluble organic solvent and a pigment, and the water content is 10% by mass or more and less than 50% by mass of the total ink mass, and the most contained of the water-soluble organic solvent. The water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6, and the content of the water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6 is 30% by mass of the total ink mass. 4. The ink jet recording method as described in 3 above, which is as described above.

  According to the present invention, it is possible to provide an inkjet ink and an inkjet recording method with high ejection reliability even when the ink is ejected from a piezo head in a heated state.

  The best mode for carrying out the present invention will be described in detail below, but the present invention is not limited thereto.

  As a result of intensive studies on the above problems, the present inventor is an ink used for ink jet printing in which an ink that is liquid at room temperature is ejected from a piezo-type head in a heated state, and the ink is at least water, water-soluble organic An ink jet ink which is a water-based pigment ink containing a solvent and a pigment and is deaerated so that the dissolved oxygen concentration in the ink is less than 10% of the saturated dissolved oxygen concentration at the ink temperature at the time of ejection. Ink for inkjet printing, and inkjet recording method using the ink, and inkjet ink and inkjet recording method with high ejection reliability even when the ink that is the object of the present invention is ejected from a piezo head in a heated state This is what we can do.

  The heating state in the present invention refers to a state where the ink is heated by some means, and the temperature for heating the ink is preferably 30 ° C. or higher and lower than 100 ° C., more preferably 40 ° C. or higher and 90 ° C. or lower. .

  As the place for heating the ink, the effect of the present invention can be obtained in any case of heating in the ink head, heating in the middle of the ink supply path, or heating the whole from the ink cartridge. The heating method in the ink head is preferable because the heating range is small and the amount of energy to be applied is small.

  In addition, although the effect of the present invention can be obtained by heating the ink by any method, a method of heating using a heater is preferable. Moreover, it is preferable not only to heat, but also to control the temperature by feeding back the temperature measured by the temperature sensor.

  As the piezo-type head that can be heated according to the present invention, for example, a piezo-type inkjet head having 256 nozzles having the same structure as the head with a heater described in Japanese Patent Application Laid-Open No. 2003-136756 is preferably used.

  The ink used in the recording method of the present invention is characterized by being deaerated. The degassing degree is characterized by being less than 10% of the saturated dissolved oxygen concentration at the temperature at which the ink is heated. The solubility of gases in water and other liquids decreases as the liquid temperature increases. The same applies to nitrogen as well as oxygen (see Table 1).

  When the saturated dissolved gas concentration is lowered by heating, the supersaturated gas becomes bubbles. The generation of bubbles causes cavitation immediately at the time of emission and becomes a problem. In addition, bubbles may adhere to the flow path, and the bubbles may flow into the ink chamber and cause cavitation.

  Continuous expansion and compression are repeated in the ink chamber of the piezo head. At this time, if there are minute bubbles (which are considered to be attached around the pigment particles in the case of pigment ink), the dissolved gas flows into the bubbles during expansion, and conversely, the gas re-enters from the bubbles into the ink during compression. Dissolve. Here, from the relationship between the surface area of the bubble during expansion and compression, the flow of dissolved gas to the bubble is superior by repeated expansion and compression, and the bubble grows. Cavitation occurs when bubbles of a certain size are formed through such bubble growth. At this time, the flow of the dissolved gas to the bubble is proportional to the partial pressure of the dissolved gas of the ink (dissolved gas concentration / saturated dissolved gas concentration). Therefore, in order to prevent cavitation accompanying this bubble growth process, a high degree of deaeration of less than 10% of the saturated dissolved oxygen concentration is required.

  Ink deaeration may be performed by any method, but a deaeration method using a hollow fiber deaeration module is preferable from the viewpoint of deaeration efficiency and ejection reliability. Furthermore, the degassing method using the external reflux type hollow fiber degassing module has a small pressure loss when degassing the pigment ink, and the dispersion stability is not deteriorated due to the high differential pressure before and after the degassing. preferable. As such an external reflux type hollow fiber deaeration module, a commercially available one can be used, and examples thereof include Dainippon Ink & Chemicals, Inc. SEPAREL EF-002A-P and SEPARELEF-004P.

  Various resins are used as the material of the hollow fiber, and in particular, poly-4 methylpentene 1 resin or polytetrafluoroethylene resin has a large amount of ink and its deaeration performance is less likely to deteriorate during processing. It is preferable because the ink component and the dispersant are less likely to adhere to the outer surface of the hollow fiber and the ink components are less likely to change.

  In the present invention, the degree of deaeration is measured by the dissolved oxygen concentration. Examples of the method for measuring the dissolved oxygen concentration include the Ostwald method (see Experimental Chemistry Course 1, Basic Operation [I], page 241, 1975, Maruzen), the method of measuring by the mass spectrum method, the galvanic cell type, and the polarograph. It can be measured using a simple oxygen concentration meter such as a mold or a colorimetric analysis method. The dissolved oxygen concentration can also be easily measured using a commercially available dissolved oxygen concentration meter (DO-30A type manufactured by Toa Denpa Kogyo Co., Ltd.).

  The ink of the present invention may be any ink as long as it is an aqueous pigment ink containing at least water, a water-soluble organic solvent, and a pigment.

  The viscosity of the ink of the present invention may be any viscosity, but is preferably 10 mPa seconds or more and less than 100 mPa seconds. The ink of 10 mPa seconds or less hardly needs to be heated, and the ink of 100 mPa seconds or more does not lower the viscosity to a region where the emission property is sufficiently stable even when the ink temperature is 95 ° C.

  Hereinafter, the ink composition of the present invention will be described in detail.

  As the pigment that can be used in the ink of the present invention, conventionally known pigments can be used without particular limitation, and any of water-dispersible pigments, solvent-dispersible pigments and the like can be used. For example, organic pigments such as insoluble pigments and lake pigments. And inorganic pigments, such as carbon black, can be used preferably. This pigment is present in a dispersed state in the ink, and the dispersion method may be any of self-dispersion, dispersion using a surfactant, polymer dispersion, and microcapsule dispersion. Dispersion is particularly preferred from the standpoint of fixability.

  The insoluble pigment is not particularly limited. Dioxazine, thiazole, phthalocyanine, diketopyrrolopyrrole and the like are preferable.

  Specific pigments that can be preferably used include the following pigments.

  Examples of the magenta or red pigment 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. Pigment red 202, C.I. I. Pigment red 222, C.I. I. Pigment violet 19 and the like.

  Examples of the pigment for orange or yellow 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 15: 3, C.I. I. Pigment yellow 17, C.I. I. Pigment yellow 74, C.I. I. Pigment yellow 93, C.I. I. Pigment yellow 128, C.I. I. Pigment yellow 94, C.I. I. And CI Pigment Yellow 138.

  Examples of the pigment 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.

  Examples of black pigments include C.I. I. Pigment black 1, C.I. I. Pigment black 6, C.I. I. Pigment black 7 and the like.

  The average particle size in the dispersed state of the pigment contained in the inkjet ink produced by the production method of the present invention is preferably 50 nm or more and less than 200 nm. When the average particle size of the pigment dispersion is less than 50 nm or 200 nm or more, the stability of the pigment dispersion tends to deteriorate, and the storage stability of the ink tends to deteriorate.

  The particle size of the pigment dispersion can be determined by a commercially available particle size measuring instrument using a dynamic light scattering method, an electrophoresis method, or the like. Accurate and often used.

  The pigment used in the ink of the present invention is preferably used after being dispersed by a disperser together with a dispersant and other additives necessary for various desired purposes. As the disperser, a conventionally known ball mill, sand mill, line mill, high-pressure homogenizer, or the like can be used. In particular, the particle size distribution of the ink produced by dispersion with a sand mill is sharp and preferable. The material of the beads used for sand mill dispersion is preferably zirconia or zircon from the viewpoint of contamination of bead fragments and ionic components. Furthermore, the bead diameter is preferably 0.3 mm to 3 mm.

  In the ink of the present invention, it is preferable to use a polymer dispersant in the dispersion.

  The polymer dispersant referred to in the present invention has a polymer component having a molecular weight of 5000 or more and 200000 or less. The polymer dispersant is selected from styrene, styrene derivatives, vinyl naphthalene derivatives, acrylic acid, acrylic acid derivatives, maleic acid, maleic acid derivatives, itaconic acid, itaconic acid derivatives, fumaric acid and fumaric acid derivatives. Examples thereof include a block copolymer comprising at least one kind of monomer, a random copolymer and salts thereof, polyoxyalkylene, and polyoxyalkylene alkyl ether.

  In the case of an acidic polymer dispersant, it is preferably added after neutralization with a neutralizing base. Here, the neutralizing base is not particularly limited, but is preferably an organic base such as ammonia, monoethanolamine, diethanolamine, triethanolamine, or morpholine.

  Moreover, in this invention, it is preferable that the addition amount of a polymer dispersing agent is 10-100 mass% with respect to a pigment.

  Examples of the water-soluble organic solvent preferably used as the solvent used in the ink of the present invention include alcohols (for example, methanol, ethanol, propanol, isopropanol, butanol, isobutanol, secondary butanol, tertiary butanol, pen) (Tanol, hexanol, cyclohexanol, benzyl alcohol, etc.), 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, 1,3-propanediol, 1,4-butanediol, 1,5 Pentanediol, 1,2-pentanediol, 1,2-hexanediol, 1,2,6-hexanetriol, etc., polyhydric alcohol alkyl ethers, amines (eg, ethanolamine, diethanolamine, triethanolamine, N -Methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, diethylenediamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, tetramethylpropylenediamine, etc.), amides (for example, formamide N, N-dimethylformamide, N, N-dimethylacetamide, etc.), heterocycles (for example, 2-pyrrolidone, N-methyl-2-pyrrolidone, cyclohexylpi Pyrrolidone, 2-oxazolidone, etc.), sulfoxides (e.g., dimethyl sulfoxide), sulfones (e.g., sulfolane), urea, acetonitrile, and acetone.

  Furthermore, in the ink of the present invention, the SP value of the most water-soluble organic solvent among the water-soluble organic solvents is 16.5 or more and less than 24.6, and the SP value is 16.5 or more and less than 24.6. It is preferable that the content of the water-soluble organic solvent is 30% by mass or more of the total ink mass. Since this solvent composition contains a large amount of a water-soluble organic solvent having a higher hydrophobicity than water, the solubility of the entire ink is high, and as a result, cavitation is unlikely to occur during continuous emission.

  The solvent solubility parameter (SP value) in the present invention is a value represented by the square root of the molecular cohesive energy. F. Fedors, Polymer Engineering Science, 14, p147 (1974). The unit is (MPa) 1/2, and refers to the value at 25 ° C.

  Hereinafter, examples of water-soluble organic solvents having an SP value of 16.5 or more and less than 24.6 are shown together with the SP value. Needless to say, the present invention is not limited to this.

Ethylene glycol monomethyl ether (SP value: 24.5)
Ethylene glycol monoethyl ether (23.5)
Ethylene glycol monobutyl ether (22.1)
Ethylene glycol monoisopropyl ether (22.3)
Diethylene glycol monomethyl ether (23.0)
Diethylene glycol monoethyl ether (22.4)
Diethylene glycol monobutyl ether (21.5)
Diethylene glycol diethyl ether (16.8)
Triethylene glycol monomethyl ether (22.1)
Triethylene glycol monoethyl ether (21.7)
Triethylene glycol monobutyl ether (21.1)
Propylene glycol monomethyl ether (23.0)
Propylene glycol monophenyl ether (24.2)
Dipropylene glycol monomethyl ether (21.3)
Tripropylene glycol monomethyl ether (20.4)
3-Dimethyl-2-imidazolidinone (21.8)
In the ink of the present invention, in addition to the above description, if necessary, the output stability, print head and ink cartridge compatibility, storage stability, image storage stability, and other various performance improvement objectives are known. Various additives such as polysaccharides, viscosity modifiers, specific resistance regulators, film forming agents, ultraviolet absorbers, antioxidants, anti-fading agents, antifungal agents, rust preventives, etc. may be appropriately selected and used. For example, oil droplet fine particles such as liquid paraffin, dioctyl phthalate, tricresyl phosphate, silicon oil, ultraviolet absorbers described in JP-A-57-74193, 57-87988, and 62-261476, As described in Kaisho 57-74192, 57-87989, 60-72785, 61-146591, JP-A-1-95091 and 3-13376, etc. Anti-fading agents, fluorescent whitening agents described in JP-A Nos. 59-42993, 59-52689, 62-280069, 61-242871, and JP-A-4-219266 Can be mentioned.

(recoding media)
The recording medium that can be used in the inkjet recording method of the present invention can be used without particular limitation, for example, an absorbent support such as plain paper and fine paper, or a low-absorbency recording medium such as art paper or coated paper, Alternatively, a non-absorbing medium such as a film or an inkjet recording medium can be widely used.

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 coated paper having a coating amount per 1 m ^{2 of} about 5 g on one side, a fine coated paper, a mat coated paper with a matte finish, a dull coated paper with a dull finish, and a newspaper. 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. Further details are described in detail in the “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 shiorai, cream shiorai, medium rough, cream shiorai large rough, DSK (above, Daishowa Paper), Sendai MP fine paper Jinjiang, 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 N IP (above, made by Daio Paper Co., Ltd.), 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, Che Examples include Lee IV Super (above, Maruzumi Paper), SHF (above, Toyo Pulp), TRP (above, Tokai Pulp) and the like.

  Further, as the non-absorbable recording medium, all of various commonly used films can be used. For example, there are a polyester film, a polyolefin film, a polyvinyl chloride film, a polyvinylidene chloride film, and the like. In addition, resin-coated paper that is photographic printing paper (RC paper in which both sides of a paper base material are coated with an olefin resin), YUPO paper that is synthetic paper, and the like can also be used.

  In addition, as various ink jet recording media, an ink receiving layer is formed on the surface using an absorbent support or a non-absorbent support as a base material. Examples of the ink receiving layer include a coating layer, a swelling layer, and a fine void layer. The swelling layer absorbs ink when the ink receiving layer made of a water-soluble polymer swells. The fine void layer is composed of inorganic or organic fine particles having a secondary particle size of about 20 to 200 nm and a binder, and fine voids of about 100 nm absorb ink.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[Preparation of Ink 1]
A bead mill (bead mill filled with 340 g of zirconia beads) after weighing a pigment, an aqueous solvent, and a polymer dispersant, adding ion-exchanged water to make 100 parts, and premixing with a dissolver as in the following dispersion formulation A pigment dispersion 1 was prepared by a dispersion treatment with Ashizawa Finetech Mini Cer).

<Pigment dispersion 1>
Pigment Blue 15: 3 15 parts BYK191 (produced by Big Chemie) (as solid content) 6 parts Dipropylene glycol monomethyl ether 20 parts Thereafter, each material is weighed and mixed according to the following ink formulation, and then with a # 1000 mesh metal mesh filter Filtration gave ink 1.

<Ink 1 prescription>
Pigment dispersion 1 20 parts Dipropylene glycol monomethyl ether 54 parts Ion-exchanged water 26 parts [Preparation of inks 2 and 3]
Thereafter, each pigment dispersion and each ink were obtained in the same manner except for the blending of the additives.

<Pigment dispersion 2>
Carbon black: Mitsubishi MA7 20 parts Jonkrill 70 (manufactured by Johnson Polymer) (as solid content) 8 parts Tripropylene glycol monomethyl ether 20 parts <Ink 2 formulation>
Pigment dispersion 2 25 parts Tripropylene glycol monomethyl ether 65 parts Ion-exchanged water 10 parts <Pigment dispersion 3>
Pigment Red 122 15 parts Jonkrill 501 (manufactured by Johnson Polymer) (as solid content) 6 parts Glycerin 20 parts <Ink 3 prescription>
Pigment dispersion 3 20 parts Glycerin 34 parts Triethylene glycol monobutyl ether 5 parts Orphine E1010 (Nisshin Chemical, nonionic surfactant) 0.6 parts Ion-exchanged water 40.4 parts [Deaeration treatment]
For the inks 1 to 3, the external circulation type hollow fiber deaeration module: Dainippon Ink & Chemicals, Inc. SEPAREL EF-002A-P is used to perform the deaeration treatment so that the dissolved oxygen concentration is as shown in Table 2. went.

[Droplet evaluation]
Using a piezo-type inkjet head having 256 nozzles having the same structure as that of the head with a heater described in Japanese Patent Application Laid-Open No. 2003-136756, the droplet ejection state was evaluated at the temperatures shown in Table 2. The ejection conditions were such that the voltage applied to the piezo was adjusted so that the droplet velocity was 6 m / second, and the ejection frequency was 8 kHz. For the evaluation of light emission, 10 nozzles were selected from a total of 256 nozzles, and droplets ejected from the nozzles were observed with a stroboscope and evaluated as follows.

○: There is no satellite, and it is flying stably as a single droplet △: There is one small satellite, but it is flying stably ×: Is there a satellite of the same size as the main droplet? , There are two or more satellites that land in a state separated from the main droplet. XX: The generation of satellite is unstable, and the size and speed of the main droplet are observed. XXX: Apply to the piezo. Even if the voltage is increased, the droplet velocity does not reach 6m / sec or cannot be ejected. [Continuous ejection evaluation]
Each continuous emission experiment was performed at the temperatures shown in Table 2 using a 256-type piezo-type inkjet head having the same structure as the head with a heater described in JP-A-2003-136756. During continuous emission, the voltage applied to the piezo was adjusted so that the droplet velocity was 6 m / second, and the emission was continued for 1 hour at a discharge frequency of 8 kHz. With respect to the evaluation of emission, the droplets ejected from all 256 nozzles were observed with a stroboscope, and the results were evaluated as follows.

◯: All 256 nozzles were able to emit with no problems after continuous 1 hour emission. Δ: All 256 nozzles were able to emit without problems until 30 minutes of continuous emission. Abnormal speed occurred due to cavitation from 30 minutes to 1 hour. X: Up to continuous 30 minutes of emission, all 256 nozzles could emit without problems. Abnormal speed was observed due to cavitation during 30 minutes to 1 hour, and then nozzles were missing. XX: Abnormal speed due to cavitation occurred during 30 minutes, leading to nozzles. Table 2 shows the parameters and the results obtained.

  1A, 2A, and 3A are experimental examples in which the ink is ejected without heating, but at this time, a lot of satellites are generated due to the effect of high ink viscosity, and the effect extends to fluctuations in the velocity of the main droplet. Ink with high viscosity cannot be ejected from a piezo head.

  1A and 1B are experimental examples of the difference in the emission test temperature of the ink that has been subjected to the same deaeration. The saturated dissolved oxygen concentration at 20 ° C. is less than 10%, but is 10% or more for the saturated dissolved oxygen concentration at 40 ° C. When the light is emitted at 20 ° C., the viscosity is slightly high, which causes a problem due to satellites. However, there is no problem of cavitation during continuous emission. On the other hand, when it was ejected at 40 ° C., it had an appropriate viscosity and the state of the ejected droplets was good, but a problem caused by cavitation occurred during continuous ejection.

  At 1C, deaeration was performed so that the saturated dissolved oxygen concentration at 40 ° C. was less than 10%. As a result, when ejected by heating to 40 ° C., the flying droplets were in good condition and no cavitation occurred during continuous ejection.

  It can also be seen that similar results are obtained for ink 2 and ink 3 having different ink compositions and viscosities.

  As described above, the degassing degree of the ink used in the ink jet recording method in which the ink is ejected from the piezo head while the ink is heated and the ink jet recording method in which the ink is heated from the piezo head is the saturated dissolved oxygen at the ink temperature at the time of ejection. By making the concentration less than 10%, an inkjet ink and an inkjet recording method with high ejection reliability could be provided.

Claims (4)

Ink used for inkjet printing in which ink that is liquid at room temperature is ejected from a piezo-type head in a heated state, the ink is an aqueous pigment ink containing at least water, a water-soluble organic solvent, and a pigment, and An inkjet ink, wherein the dissolved oxygen concentration in the ink is deaerated so as to be less than 10% of the saturated dissolved oxygen concentration at the ink temperature at the time of ejection. The ink contains at least water, a water-soluble organic solvent, and a pigment, and the water content is 10% by mass or more and less than 50% by mass of the total ink mass, and is the most contained of the water-soluble organic solvent. The SP value of the water-soluble organic solvent is 16.5 or more and less than 24.6, and the content of the water-soluble organic solvent having the SP value of 16.5 or more and less than 24.6 is 30% by mass or more of the total ink mass. The inkjet ink according to claim 1, wherein the inkjet ink is provided. An ink jet recording method in which an ink that is liquid at normal temperature is ejected from a piezo-type head in a heated state, and the ink is an aqueous pigment ink containing at least water, a water-soluble organic solvent, and a pigment, An inkjet recording method, wherein the dissolved oxygen concentration is deaerated so as to be less than 10% of the saturated dissolved oxygen concentration at the ink temperature at the time of ejection. The ink contains at least water, a water-soluble organic solvent and a pigment, and the water content is 10% by mass or more and less than 50% by mass of the total ink mass, and the most contained of the water-soluble organic solvent. The water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6, and the content of the water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6 is 30% by mass of the total ink mass. The inkjet recording method according to claim 3, which is as described above.