JP2011202029A - Ink set for inkjet recording - Google Patents

Abstract

To provide an ink composition set for ink jet recording capable of matching the temperature characteristics of the viscosity of a dark ink composition having a high pigment concentration and a light ink composition having a low pigment concentration.
An ink set comprising: a first ink composition comprising at least a pigment, glycerin and water; and a second ink composition comprising at least a pigment, glycerin, a thickener and water. The pigment contained in the first ink composition and the pigment contained in the second ink composition are the same type of pigment, and the pigment concentration of the first ink composition is the same as the second ink composition. The ratio of the viscosity value at the same temperature of the first ink composition and the second ink composition (viscosity value of the first ink composition / viscosity value of the second ink composition) is higher than the pigment concentration of An ink set for ink-jet recording, wherein the temperature is from 0.95 to 1.05 in a temperature range of from 10 ° C to 40 ° C.
[Selection figure] None

Description

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

  The ink jet recording method is a recording method in which printing is performed by ejecting ink droplets from an ink jet head and landing on a recording medium such as paper. Due to recent advances in ink jet recording technology, the ink jet recording system has come to be used for high-definition image recording (printing), which has been the field of photography and offset printing.

  In recent years, a color image is formed using a plurality of color ink compositions by such an ink jet recording method. In general, a color image is formed by three colors of a yellow ink composition, a magenta ink composition, and a cyan ink composition, four colors obtained by adding a black ink composition to the three colors, and a color shade ( The color type is classified according to the concentration of the colorant, and an ink set containing these dark and light ink compositions is used. For example, there are inks having four ink compositions of black, cyan, magenta, and yellow as dark inks, and three ink compositions of light black, light cyan, and light magenta as light inks.

  In the ink jet recording method in which a color image is formed using a plurality of color ink compositions, the viscosity of each ink composition constituting the ink set is substantially the same from the viewpoint of controlling the ink discharge weight from the same head. It is desirable. Further, the viscosity of the ink has a temperature characteristic that varies depending on the temperature, and it is desirable that the temperature characteristic is substantially the same for each ink composition. This is because if the temperature characteristics of the viscosity of each ink composition are different, it may cause variations in the ink discharge weight, which in turn may cause deterioration in graininess or unevenness of the recorded image. As a technique for controlling the temperature characteristic of the viscosity of the ink, for example, Patent Document 1 discloses an ink for inkjet recording in which the ratio of the viscosity at 5 ° C. to the viscosity at 40 ° C. of the ink when the colorant is a dye is specified. ing.

JP-A-10-53737

  However, when the colorant is a pigment, there is a problem that it is difficult to match the temperature characteristics of the viscosity between a dark ink composition having a high pigment concentration and a light ink composition having a low pigment concentration. The reason for this is that the dark ink composition with a high pigment concentration has a large interaction between the pigments, so the temperature characteristic is small, whereas the light ink composition with a low pigment concentration has a small interaction between the pigments. Therefore, it is considered that the temperature characteristic is increased.

  Such temperature characteristics of viscosity may be adjusted by adjusting the amount of a humectant such as glycerin contained in the ink composition, but in such a case, another problem occurs. The ink jet head is entirely covered with a cap in order to prevent ink from drying during storage other than use. When ink compositions with different amounts of humectant are used, a phenomenon occurs in which an ink composition with a large amount of humectant draws out moisture from an ink composition with a small amount of humectant when stored for a long period of time. As a result, ink clogging may occur in the inkjet head.

  In some embodiments according to the present invention, by solving the above-described problems, an ink for inkjet recording capable of matching the temperature characteristics of the viscosity of a dark ink composition having a high pigment concentration and a light ink composition having a low pigment concentration can be achieved. A composition set is provided. In addition, some aspects of the present invention provide an ink composition set for ink jet recording that can prevent the clogging of the ink jet head during long-term storage by solving the above problems.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following aspects or application examples.

[Application Example 1]
One aspect of the ink set for inkjet recording according to the present invention is:
A first ink composition comprising at least a pigment, glycerin and water;
A second ink composition comprising at least a pigment, glycerin, a thickener and water;
An ink set comprising:
The pigment contained in the first ink composition and the pigment contained in the second ink composition are the same type of pigment, and the pigment concentration of the first ink composition is the same as that of the second ink composition. Higher than the pigment concentration,
The ratio of the viscosity values of the first ink composition and the second ink composition at the same temperature (viscosity value of the first ink composition / viscosity value of the second ink composition) is 10 ° C. or higher and 40 ° C. or lower. It is 0.95 or more and 1.05 or less in the temperature region.

  According to the application example 1, the viscosity characteristics of the first ink composition having a high pigment concentration and the second ink composition having a low pigment concentration are adjusted by adding a thickener to the second ink composition to adjust the viscosity. Can be obtained.

[Application Example 2]
In application example 1,
The thickener may be at least one selected from sodium alginate, carboxymethylcellulose, and pectin.

[Application Example 3]
In application example 1 or application example 2,
The thickener concentration of the second ink composition may be 0.1% by mass or more and 1.5% by mass or less.

[Application Example 4]
In any one of Application Examples 1 to 3,
Both of the first ink composition and the second ink composition may have a glycerin concentration of 20% by mass or less.

[Application Example 5]
In any one of Application Examples 1 to 4,
The difference between the glycerin concentration of the first ink composition and the glycerin concentration of the second ink composition may be 2% by mass or less.

  According to Application Example 5, not only can the temperature characteristics of the viscosity of the first ink composition having a high pigment concentration and the second ink composition having a low pigment concentration be easily matched, but also the inkjet head is clogged during long-term storage. An ink set for ink-jet recording can be obtained.

[Application Example 6]
In any one of Application Examples 1 to 5,
The pigment concentration of the first ink composition may be 6% by mass or more and 15% by mass or less, and the pigment concentration of the second ink composition may be 0.5% by mass or more and 4% by mass or less.

  Hereinafter, preferred embodiments of the present invention will be described. The embodiment described below describes an example of the present invention. In addition, the present invention is not limited to the following embodiments, and includes various modifications that are implemented within a range that does not change the gist of the present invention.

1. Ink set for ink jet recording An ink set for ink jet recording according to an embodiment of the present invention includes at least one set of a first ink composition and a second ink composition containing the same type of pigment. The first ink composition has a higher pigment concentration than the second ink composition. Therefore, the first ink composition may be expressed as a “dark ink composition” and the second ink composition may be expressed as a “light ink composition”. Hereinafter, the first ink composition and the second ink composition will be described in detail.

1.1. First ink composition The first ink composition contains at least a pigment, glycerin and water. The first ink composition is preferably a water-based ink composition containing water as a main solvent from the viewpoint of safety and ease of handling. As the water, pure water such as ion exchange water, ultrafiltration water, reverse osmosis water, distilled water or ultrapure water is preferably used, and water sterilized by ultraviolet irradiation or addition of hydrogen peroxide is used. Is more preferable. By using sterilized water, generation of mold and bacteria can be prevented and ink can be stored for a long time. The content of water in the first ink composition is 50% by mass with respect to the total mass of the first ink composition from the viewpoint of ensuring appropriate physical properties (such as viscosity) of the ink and ink stability and reliability. The content is preferably 80% by mass or less.

  As the pigment used in the first ink composition, known inorganic pigments and organic pigments can be used, and are not particularly limited. Examples of the pigment include pigments such as pigment yellow, pigment red, pigment violet, pigment blue, and pigment black described in the color index, as well as phthalocyanine, azo, anthraquinone, azomethine, and condensed ring systems. Pigments. Further, organic pigments such as yellow No. 4, 5, 205, 401; orange 228, 405; blue No. 1, 404, etc., titanium oxide, zinc oxide, zirconium oxide, iron oxide, ultramarine blue, bitumen, Inorganic pigments such as chromium oxide may be used. Specifically, C.I. I. Pigment Yellow 1, 3, 12, 13, 14, 17, 24, 34, 35, 37, 42, 53, 55, 74, 81, 83, 95, 97, 98, 100, 101, 104, 108, 109, 110, 117, 120, 128, 138, 150, 153, 155, 174, 180, 198, C.I. I. Pigment Red 1, 3, 5, 8, 9, 16, 17, 19, 22, 38, 57: 1, 90, 112, 122, 123, 127, 146, 184, 202, C.I. I. Pigment violet 1, 3, 5: 1, 16, 19, 23, 38, C.I. I. Pigment Blue 1, 2, 15, 15: 1, 15: 2, 15: 3, 15: 4, 16, C.I. I. Pigment black 1, 7 and the like. These pigments may be used alone or in combination of two or more.

  These pigments are firstly used as pigment dispersions dispersed in an aqueous medium using a ball mill, roll mill, bead mill, high-pressure homogenizer, high-speed stirring disperser, etc., together with a dispersant such as a polymer dispersant and a surfactant. You may add in an ink composition.

  Examples of the polymer dispersant include natural polymer compounds such as glue, gelatin and saponin, polyvinyl alcohols, polypyrrolidones, acrylic resins (polyacrylic acid, acrylic acid-acrylonitrile copolymer, vinyl acetate- Acrylic acid copolymer, vinyl acetate-acrylic acid ester copolymer, etc.), styrene-acrylic acid resins (styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer, styrene-methacrylic acid-alkyl acrylate) Ester copolymer, styrene-α-methylstyrene-acrylic acid copolymer, styrene-α-methylstyrene-acrylic acid-alkyl acrylate copolymer, styrene-vinyl acetate-acrylic acid copolymer, etc.), styrene -Maleic acid resins, vinyl acetate-fatty acid vinyl-fatty acid vinyl- Synthetic polymers such as resins of tyrene copolymer and salts thereof may be mentioned. The constitution of the copolymer may be any of random type, block type and graft type.

  Examples of the surfactant include anionic surfactants such as fatty acid salts, higher alkyl dicarboxylates, higher alcohol sulfates, and higher alkyl sulfonates; and cationic surfactants such as fatty acid amine salts and fatty acid ammonium salts. Nonionic surfactants such as polyoxyalkyl ethers, polyoxyalkyl esters, sorbitan alkyl esters and the like.

  Among these dispersants, water-insoluble resins are particularly preferable. The water-insoluble resin is a block copolymer resin of a monomer having a hydrophobic group and a monomer having a hydrophilic group, and contains at least a monomer having a salt-forming group. After neutralization, 100 g of water at 25 ° C. Refers to a resin having a solubility of less than 1 g. As a monomer having a hydrophobic group, methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, n-amyl (meth) acrylate, isoamyl ( (Meth) acrylate, n-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, octadecyl (meth) acrylate, cyclohexyl (meth) acrylate, (Meth) acrylic acid ester salts such as phenyl (meth) acrylate, benzyl (meth) acrylate, glycidyl (meth) acrylate; vinyl esters such as vinyl acetate; acrylonitrile, methacrylo Vinylcyan compounds such as tolyl; aromatic vinyl monomers such as styrene, α-methylstyrene, vinyltoluene, 4-t-butylstyrene, chlorostyrene, vinylanisole, vinylnaphthalene, etc. Two or more kinds can be mixed and used. Examples of the monomer having a hydrophilic group include polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, ethylene glycol / propylene glycol mono (meth) acrylate, and each of them is used alone or in combination of two or more. be able to. Examples of the monomer having a salt-forming group include acrylic acid, methacrylic acid, styrene carboxylic acid, maleic acid and the like, and each can be used alone or in admixture of two or more. Furthermore, macromonomers such as styrene macromonomer and silicone macromonomer having a polymerizable functional group at one end, and other monomers can be used in combination.

  The water-insoluble resin is preferably used as a salt neutralized with a tertiary amine such as ethylamine or trimethylamine, or an alkali neutralizer such as lithium hydroxide, sodium hydroxide, potassium hydroxide or ammonia, and has a weight average molecular weight of 10 From about 15,000 to 150,000, the pigment can be stably dispersed.

  The pigment has a dispersibility-imparting group (hydrophilic functional group and / or salt thereof) bonded to the pigment surface directly or via an alkyl group, alkyl ether group, aryl group, etc., and is dispersed in an aqueous medium without a dispersant. Or what was processed as a self-dispersion type pigment which dissolves may be added.

  The self-dispersing pigment is produced, for example, by binding (grafting) an active species having a dispersibility-imparting group or a dispersibility-imparting group to the surface of the pigment by subjecting the pigment to physical treatment or chemical treatment. Examples of the physical treatment include vacuum plasma treatment. Examples of the chemical treatment include a wet oxidation method in which the pigment surface is oxidized with an oxidizing agent in water, a method in which p-aminobenzoic acid is bonded to the pigment surface to bond a carboxyl group via a phenyl group, and the like. Is mentioned. Inks containing self-dispersing pigments do not need to contain a dispersant as described above to disperse ordinary pigments, so there is almost no foaming due to a decrease in defoaming properties caused by the dispersant, and stable ejection It is easy to prepare ink with excellent properties. Further, since a significant increase in viscosity due to the dispersant can be suppressed, more pigment can be contained, and the print density can be sufficiently increased.

  In the present invention, self-dispersing pigments that are surface-treated by oxidation treatment with hypohalous acid and / or hypohalite, or oxidation treatment with ozone are preferred in terms of high color development. Moreover, a commercial item can also be used as a self-dispersion type pigment, for example, microjet CW-1 (trade name, manufactured by Orient Chemical Industry Co., Ltd.), CAB-O-JET200, CAB-O-JET300 (above trade names, Cabot Corporation).

  These pigments preferably have a volume average particle diameter in the range of 50 nm or more and 200 nm or less from the viewpoint of storage stability of the ink and prevention of nozzle clogging. The average particle size can be measured by a particle size distribution measuring apparatus such as Microtrac UPA150 (manufactured by Nikkiso Co., Ltd.), LPA3100 (manufactured by Otsuka Electronics Co., Ltd.), etc., which uses a dynamic light scattering method as a measurement principle.

  The pigment concentration (solid content concentration) in the first ink composition is preferably 6% by mass or more and 15% by mass or less, and preferably 6% by mass or more and 10% by mass or less with respect to the total mass of the first ink composition. More preferably. If the pigment concentration is less than 6% by mass, the color developability may be inferior, and if it exceeds 15% by mass, the storage stability and clogging performance of the ink may be affected.

  Glycerin used in the first ink composition has the effect of improving the permeability of the ink into the recording medium and preventing clogging of the inkjet head. However, since the viscosity of glycerin has a large temperature characteristic that varies depending on the temperature, the temperature characteristic of the first ink composition increases as the glycerin concentration in the first ink composition increases. From the viewpoint of making the temperature characteristics as small as possible and preventing clogging of the inkjet head, the glycerin concentration in the first ink composition may be 20% by mass or less with respect to the total mass of the first ink composition. preferable.

  Further, the first ink composition may further contain a water-soluble organic solvent other than glycerin, a surfactant, a pH adjuster, an antiseptic / antifungal agent and the like, if necessary.

  By adding a water-soluble organic solvent other than glycerin to the first ink composition, it is possible to control the permeability and bleeding of the ink into the recording medium, and to improve the drying of the ink and clogging in the vicinity of the nozzles of the inkjet head. be able to. As such a water-soluble organic solvent, 1,2-alkanediols, glycol ethers, and pyrrolidones are preferably used. Specific examples of 1,2-alkanediols include 1,2-pentanediol, 4-methyl-1,2-pentanediol, 1,2-hexanediol, 1,2-octanediol, and the like. . Specific examples of glycol ethers include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-propyl ether, Ethylene glycol mono-iso-propyl ether, diethylene glycol mono-iso-propyl ether, ethylene glycol mono-n-butyl ether, ethylene glycol mono-t-butyl ether, diethylene glycol mono-t-butyl ether, triethylene glycol mono-t-butyl ether, 1 -Methyl-1-methoxybutanol, propylene glycol Monoethyl ether, propylene glycol monoethyl ether, propylene glycol mono-t-butyl ether, propylene glycol mono-n-propyl ether, propylene glycol mono-iso-propyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, Examples include dipropylene glycol mono-n-propyl ether and dipropylene glycol mono-iso-propyl ether. Specific examples of pyrrolidones include 2-pyrrolidone and N-methyl-2-pyrrolidone. These water-soluble organic solvents can be used alone or in combination of two or more. The concentration of the water-soluble organic solvent in the first ink composition is 1% by mass or more based on the total mass of the first ink composition from the viewpoint of ensuring appropriate physical properties (such as viscosity) of the ink and ensuring reliability. It is preferable that it is 50 mass% or less.

  By adding a surfactant to the first ink composition, the wettability of the ink to the recording medium can be controlled, and the permeability to the recording medium and the printing stability in the ink jet recording method can be improved. Examples of the surfactant include an anionic surfactant, a cationic surfactant, an amphoteric surfactant, and a nonionic surfactant. From the viewpoint of reducing the foaming property of the ink composition, the nonionic surfactant is used. Agents are preferred.

  Among the nonionic surfactants, acetylene glycol surfactants and polyether-modified siloxane surfactants are more preferable. Specific examples of acetylene glycol surfactants include Surfynol 420, 440, 465, 485, 104, STG (above Air Products), Orphin PD-001, SPC, E1004, E1010 (above Nissin Chemical). Kogyo Co., Ltd.), acetylenol E00, E40, E100, LH (above Kawaken Fine Chemical Co., Ltd.) and the like. Specific examples of the polyether-modified siloxane-based surfactant include BYK-346, 347, 348, UV3500 (manufactured by Big Chemie). These surfactants can be used singly or in combination of two or more. The concentration of the surfactant in the first ink composition is preferably 0.1% by mass to 3% by mass with respect to the total mass of the first ink composition.

  The first ink composition is preferably adjusted to a pH of 6 or more and 10 or less by adding a pH adjuster. When the pH is within the above range, the clogging recovery property of the ink jet head is improved without adversely affecting the material constituting the ink jet printer. Specific examples of the pH adjusting agent include alkali hydroxides such as lithium hydroxide, potassium hydroxide and sodium hydroxide; alkanolamines such as triethanolamine, tripropanolamine, diethanolamine and monoethanolamine; ammonia and the like. It is done.

  The first ink composition is benzoic acid, dichlorophene, hexachlorophene, sorbic acid, p-hydroxybenzoic acid ester, ethylenediaminetetraacetic acid (EDTA) and salts thereof (ethylenediaminetetraacetic acid disodium ( EDTA2Na)), triazoles such as sodium dehydroacetate and benzotriazole, 1,2-benchazolin-3-one (trade name “Prosecyl XL” manufactured by Avicia), 3,4-isothiazoline-3-one, 4, 4-dimethyloxazolidine or the like may be added.

  Moreover, you may further add an antifoamer, antioxidant, a ultraviolet absorber, a solubilizing agent, etc. to a 1st ink composition as needed.

1.2. Second ink composition The second ink composition contains at least a pigment, glycerin, a thickener, and water. Since the second ink composition is common to the first ink composition in many respects, the description regarding the first ink composition described above can be applied mutatis mutandis except for the differences described below. Hereinafter, differences from the first ink composition will be described in detail.

  The second ink composition contains the same type of pigment as the pigment contained in the first ink composition. The pigment concentration of the second ink composition is lower than the pigment concentration of the first ink composition. Therefore, the first ink composition can be expressed as a “dark ink composition” and the second ink composition as a “light ink composition”. In the examples described later, the first ink composition and the second ink composition are expressed as “dark ink composition” and “light ink composition”, respectively. The pigment concentration in the second ink composition is preferably 0.5% by mass or more and 4% by mass or less, and preferably 1% by mass or more and 3% by mass or less with respect to the total mass of the second ink composition. More preferred. When the pigment concentration is less than 0.5% by mass, the balance of gradation may be deteriorated when used in combination with the first ink composition. On the other hand, when the pigment concentration exceeds 4% by mass, the visibility of the ink dots is increased, and the granularity of the ink may be conspicuous.

  As in the first ink composition, the glycerin concentration in the second ink composition is preferably 20% by mass or less with respect to the total mass of the second ink composition. The difference between the glycerin concentration of the first ink composition and the glycerin concentration of the second ink composition is preferably 2% by mass or less, and more preferably 1% by mass or less. By reducing the difference in glycerin concentration to 2% by mass or less, not only can the temperature characteristics of the viscosity of the first ink composition having a high pigment concentration and the second ink composition having a low pigment concentration be easily matched, It is also possible to prevent clogging of the inkjet head during long-term storage.

  In the present invention, “matching the temperature characteristics of the viscosity of the first ink composition and the second ink composition” means the ratio of the viscosity values of the first ink composition and the second ink composition at the same temperature (first (Viscosity value of one ink composition / viscosity value of the second ink composition) is 0.95 or more and 1.05 or less in a temperature range of 10 ° C. or more and 40 ° C. or less. The viscosity of each ink composition can be measured using, for example, a Canon Fensuke backflow viscometer (manufactured by Rouai Co., Ltd., model “VM-252C”).

  The clogging mechanism of the ink jet head is considered as follows. The ink jet head is entirely covered with a cap in order to prevent ink from drying during storage other than use. When ink compositions with different amounts of humectant are used, an ink composition with a large amount of humectant will extract moisture from an ink composition with a small amount of humectant when stored for a long period of time. Clogging may occur. If the difference in glycerin concentration is 2% by mass or less, the occurrence of such a phenomenon can be effectively suppressed, and as a result, clogging of ink in the inkjet head can be prevented.

  By adding an appropriate amount of the thickener used in the second ink composition, the temperature characteristic of the viscosity of the second ink composition can be adjusted to that of the first ink composition. Examples of the thickener include polymers such as alginic acid, sodium alginate, carboxymethylcellulose, sodium carboxymethylcellulose, hydroxyethylcellulose, hydroxylpropylcellulose, sodium polyacrylate, xanthan gum, carrageenan, and pectin. However, if the weight average molecular weight of these polymers is too high, there is a problem that the interaction between molecules becomes large and the viscosity characteristic becomes too small. Therefore, the weight average molecular weight of these polymers is preferably several hundred thousand or less. Among these thickeners, sodium alginate, carboxymethylcellulose, and pectin are more preferable in terms of low molecular weight, and sodium alginate is particularly preferable in terms of storage stability and discharge characteristics. These thickeners may be used individually by 1 type, and may be used in mixture of 2 or more types.

  The concentration of the thickener in the second ink composition varies depending on the type of the thickener, but the ratio of the viscosity values at the same temperature of the first ink composition and the second ink composition (viscosity of the first ink composition). (Value / viscosity value of the second ink composition) may be appropriately adjusted so as to be 0.95 or more and 1.05 or less in a temperature range of 10 ° C. or more and 40 ° C. or less.

1.3. Applications and physical properties of ink composition set for ink jet recording The ink composition set according to the present embodiment can be applied to an ink jet recording system. In the present invention, the ink jet recording system means a system in which an ink composition is ejected as droplets from a fine nozzle, and the droplets adhere to a recording medium. Hereinafter, the ink jet recording method will be specifically described.

  The first method is an electrostatic suction method. In this method, a strong electric field is applied between the nozzle and the acceleration electrode placed in front of the nozzle, ink is ejected continuously from the nozzle in the form of droplets, and printing information is printed while the ink droplets fly between the polarizing electrodes. This is a method in which a signal is supplied to a deflection electrode for recording, or a method in which an ink droplet is ejected in response to a print information signal without being deflected.

  The second method is a method of forcibly ejecting ink droplets by applying pressure to the ink liquid with a small pump and mechanically vibrating the nozzle with a crystal resonator or the like. The ejected ink droplet is charged simultaneously with the ejection, and a print information signal is applied to the deflection electrode and recorded while the ink droplet flies between the deflection electrodes.

  As a third method, there is a method using a piezoelectric element. This method is a method in which a pressure and a print information signal are simultaneously applied to an ink liquid by a piezoelectric element to eject and record ink droplets.

  The fourth method is a method in which the ink liquid is rapidly expanded in volume by the action of thermal energy, and is a system in which the ink liquid is heated and foamed with a microelectrode in accordance with a print information signal to eject and record ink droplets.

  The ink composition set for ink jet recording according to the present embodiment can be applied to any of the ink jet recording methods described above.

2. EXAMPLES Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

2.1. Production of pigment dispersion 2.1.1. Black pigment dispersion B1
100 g of color black S170 (trade name, manufactured by Degussa Huls), which is a commercially available carbon black, was mixed with 1 kg of water and pulverized by a ball mill using zirconia beads. 1400 g of sodium hypochlorite (effective chlorine concentration 12%) was added dropwise to this pulverized stock solution, reacted for 5 hours while pulverizing with a ball mill, and further boiled for 4 hours with stirring to perform wet oxidation. The obtained dispersion stock solution was filtered with glass fiber filter paper GA-100 (trade name, manufactured by Advantech Toyo Co., Ltd.), and further washed with water. The obtained wet cake was redispersed in 5 kg of water, desalted and purified with a reverse osmosis membrane until the conductivity reached 2 mS / cm, and further concentrated until the pigment concentration reached 20% by mass to obtain a black pigment dispersion. B1 was obtained. The average particle size of the pigment in the dispersion was measured using a particle size distribution measuring device (manufactured by Microtrac, model “Microtrac UPA150”), and was 110 nm.

2.1.2. Magenta pigment dispersion M1
Using 20 parts by mass of methyl ethyl ketone, 0.03 parts by mass of 2-mercaptoethanol, a polymerization initiator, and a monomer mixture shown in Table 1, the mixture was placed in a reaction vessel sufficiently substituted with nitrogen gas and polymerized with stirring at 75 ° C. Thereafter, 0.9 part by mass of 2,2′-azobis (2,4-dimethylvaleronitrile) dissolved in 40 parts by mass of methyl ethyl ketone was added to 100 parts by mass of the monomer mixture, and aged for 1 hour at 80 ° C. Got.

  5 parts by mass obtained by drying the obtained polymer solution under reduced pressure was dissolved in 15 parts by mass of methyl ethyl ketone, and the polymer was neutralized using an aqueous sodium hydroxide solution. Furthermore, C.I. I. 15 parts by mass of Pigment Red 122 was added and kneaded with a disperser while adding water. After adding 100 parts by mass of ion-exchanged water to the obtained kneaded material and stirring, methylene pigment having a solid content of 20% by mass is removed by removing methyl ethyl ketone at 60 ° C. under reduced pressure and further removing a part of water. Dispersion M1 was obtained. The average particle size of the pigment in the dispersion was measured using a particle size distribution measuring apparatus (manufactured by Microtrac, model “Microtrac UPA150”), and found to be 140 nm.

2.1.3. Cyan pigment dispersion C1
C. I. In place of Pigment Red 122, C.I. I. A cyan pigment dispersion C1 was obtained in the same manner as in the production method of the magenta pigment dispersion M1, except that CI Pigment Blue 15: 4 was used. The average particle size of the pigment in this dispersion was measured using a particle size distribution measuring apparatus (manufactured by Microtrac, model “Microtrac UPA150”), and was 80 nm.

2.2. Ink Preparation and Ink Set Each component was mixed in the proportions shown in Table 2, stirred at room temperature for 2 hours, and then filtered through a membrane filter having a pore size of 5 μm to produce ink production examples 1-12. Ink Production Examples 1 to 4 are dark ink compositions (first ink compositions), and Ink Production Examples 5 to 12 are light ink compositions (second ink compositions). In addition, all the addition amount shown in Table 2 is represented as a mass% density | concentration, and the number in () of a pigment dispersion liquid represents the solid content density | concentration of a pigment. The remaining amount of ion-exchanged water means adding ion-exchanged water so that the total amount of ink becomes 100% by mass. Also, ink sets 1 to 8 shown in Table 3 were prepared by combining the dark ink composition and the light ink composition of Production Example.

2.3. Evaluation of ink set 2.3.1. Evaluation of Granularity An ink jet printer PX-B500 (manufactured by Seiko Epson Corporation) was filled with a dark ink composition in the magenta and cyan columns and a light ink composition in the black and yellow columns according to each ink set. For OK Top Coat N (Oji Paper Co., Ltd.), with a resolution of 720 x 720 dpi, Duty from 100% (Duty amount at 100% Duty: 1.0 mg / cm ² ) to 10% every 10% The changed patch pattern was printed. The granularity of the obtained patch pattern was evaluated according to the following criteria. The evaluation results were as shown in Table 4 below.
A: The graininess of the ink cannot be confirmed at all visually.
B: Almost no granularity of the ink can be visually confirmed.
C: The graininess of the ink can be clearly confirmed visually.

2.3.2. Storage stability evaluation The ink composition was put in an aluminum pack and left in an environment at 70 ° C. for 1 week in a state where the ink composition was put in the aluminum pack. After standing, changes in physical properties (viscosity, surface tension, pH, average particle diameter) were confirmed. Ink storage stability was evaluated according to the following criteria. The evaluation results were as shown in Table 4 below.
A: There is almost no change in physical properties.
B: Physical properties change.

2.3.3. Evaluation of ejection characteristics According to each ink set, the ink jet printer PX-B500 (manufactured by Seiko Epson Corporation) was filled with a dark ink composition in the magenta and cyan columns and a light ink composition in the black and yellow columns. With respect to OK Top Coat N (manufactured by Oji Paper Co., Ltd.), 100 pages were printed at a rate of 400 characters / page with a standard of font size 11 with MS Word and 400 characters / page with MSP Gothic to evaluate the ejection characteristics. The ink ejection characteristics were evaluated according to the following criteria. The evaluation results were as shown in Table 4 below.
A: Printing disorder cannot be confirmed at all.
B: One to five printing irregularities can be confirmed.
C: Six or more printing irregularities can be confirmed.

2.3.4. Evaluation of clogging Using an ink jet printer similar to the above, printing was continued for 10 minutes, and after confirming that ink was ejected normally from all nozzles, the recording head was capped with the ink cartridges loaded. And left in an environment of 25 ° C. and 50% Rh for 3 months. After leaving, the cleaning operation was repeated until all nozzles ejected at the same level as the initial stage. The evaluation criteria were as follows. The evaluation results were as shown in Table 4 below.
A: Recovered to the same level as the initial state after one cleaning operation B: Recovered to the same level as the initial level after two cleaning operations C: Recovered to the same level as the initial level after 3 cleaning operations

2.3.5. Temperature characteristics of viscosity The viscosity at 10 ° C., 25 ° C., and 40 ° C. of each ink composition of each ink set was measured with a Canon Fenceke backflow viscometer (manufactured by Rouai Co., Ltd., model “VM-252C”). Thereafter, the ratio of the viscosity values at the same temperature of the ink composition of each ink set (viscosity value of the dark ink composition / viscosity value of the light ink composition) was determined. The temperature characteristics depending on the ink temperature were evaluated according to the following criteria. The evaluation results were as shown in Table 4 below.
A: Ratio is 0.97 or more and 1.03 or less at any temperature B: Ratio is 0.95 or more and 1.05 or less at any temperature (excluding the range of A)
C: Ratio is outside the range of A and B at any temperature

  As is clear from Table 4, according to the ink set for ink jet recording according to the example, generally good results were obtained in any evaluation items of graininess, storability, ejection characteristics, clogging, and temperature characteristics. . From the above, it was found that the ink set according to the example is suitable for use in the ink jet recording method.

  In addition, in the ink set 5 which concerns on an Example, it turned out that the preservability of a light ink composition is impaired a little by making the thickener added to a light ink composition into carboxymethylcellulose.

  In addition, in the ink set 6 according to the example, by using pectin as the thickener added to the light ink composition, the ejection characteristics and the temperature characteristics were somewhat impaired, but it was found to be in the category of non-defective products.

  In addition, in the ink set 7 according to the example, when the amount of sodium alginate in the light ink composition is 0.1% by mass, clogging and temperature characteristics are somewhat impaired, but this is a category of non-defective product. I found out.

  On the other hand, in the ink set 8 according to the comparative example, since the thickener is not added to the light ink composition, the inkjet head is clogged due to long-term storage, and the temperature between the dark ink composition and the light ink composition The characteristics did not match.

  The present invention is not limited to the embodiments described above, and various modifications are possible. For example, the present invention includes substantially the same configuration (for example, a configuration having the same function, method, and result, or a configuration having the same purpose and effect) as the configuration described in the embodiment. In addition, the invention includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. In addition, the present invention includes a configuration that achieves the same effect as the configuration described in the embodiment or a configuration that can achieve the same object. In addition, the invention includes a configuration in which a known technique is added to the configuration described in the embodiment.

Claims (6)

A first ink composition comprising at least a pigment, glycerin and water;
A second ink composition comprising at least a pigment, glycerin, a thickener and water;
An ink set comprising:
The pigment contained in the first ink composition and the pigment contained in the second ink composition are the same type of pigment, and the pigment concentration of the first ink composition is the same as that of the second ink composition. Higher than the pigment concentration,
The ratio of the viscosity values of the first ink composition and the second ink composition at the same temperature (viscosity value of the first ink composition / viscosity value of the second ink composition) is 10 ° C. or higher and 40 ° C. or lower. An ink set for ink-jet recording having a temperature range of 0.95 to 1.05. In claim 1,
The ink set for inkjet recording, wherein the thickener is at least one selected from sodium alginate, carboxymethylcellulose, and pectin. In claim 1 or claim 2,
An ink set for ink-jet recording, wherein the thickener concentration of the second ink composition is 0.1% by mass or more and 1.5% by mass or less. In any one of Claims 1 to 3,
An ink set for ink-jet recording, wherein the glycerin concentrations of the first ink composition and the second ink composition are both 20% by mass or less. In any one of Claims 1 thru | or 4,
An ink set for inkjet recording, wherein a difference between a glycerin concentration of the first ink composition and a glycerin concentration of the second ink composition is 2% by mass or less. In any one of Claims 1 thru | or 5,
Ink for ink jet recording, wherein the pigment concentration of the first ink composition is 6% by mass or more and 15% by mass or less, and the pigment concentration of the second ink composition is 0.5% by mass or more and 4% by mass or less. set.