JP2011162620A - Ink set, inkjet recording method and recorded matter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ink set that suppresses curling and cockling, attains an image of high qualities with little rough texture and exhibits excellent temperature characteristics of its viscosity. <P>SOLUTION: The ink set comprises a thick ink composition and a thin ink composition having a different pigment concentration, where each of the thick ink composition and the thin ink composition comprises a pigment, a humectant composed of a mixture of compounds (A), (B) and (C) below and 60-10 wt.%, based on the whole ink, of water and the weight ratio of the content of the compounds in the humectants in the thick ink composition is such that (A):(B):(C)=1:(0.1-1):(1-3) while the weight ratio of the content of the compounds in the humectants in the thin ink composition is such that ((A)+(B)):(C)=1:(1-2). (A) At least one compound selected from among glycerine, 1,2,6-hexanetriol, diethylene glycol, triethylene glycol, tetraethylene glycol and dipropylene glycol. (B) Either one or both of trimethylolpropane and trimethylolethane. (C) At least one compound having a molecular weight within the range of 100-200 from among betaines, saccharides and ureas. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an ink set, a recording method using the ink set, and a recorded matter. More specifically, an ink set capable of suppressing curling and cockling and obtaining a high-quality image free from roughness, an ink set excellent in viscosity characteristics depending on the temperature of the ink composition, an ink jet recording method, and a recorded matter About.

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 method 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 this, and further, the color density ( The color type is classified according to the concentration of the colorant, and the 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.

By using an ink set equipped with this dark and light ink in glossy inkjet paper, and changing the amount of colorant landing per unit area of the recording medium, the graininess due to ink dots is reduced, High-quality color images comparable to silver halide photography can be output.
According to the highly water-absorbing inkjet paper, a high-quality image can be realized. However, if the absorbing layer for absorbing ink is not provided thick, the amount of absorption is reduced, and the amount of coating is increased. In addition, since powdered silica, alumina or the like is used as a raw material to make the absorption layer transparent, the cost has been high. This high cost has become a barrier that narrows the user's applications.

Further, as cheap paper, there is a coated paper for printing (also called coated paper or printing paper). Coated paper is a composite sheet in which a coating color, which is a kind of paint, is applied to both sides or one side of a base paper for the purpose of improving printability, and is exclusively used for printing paper. The coated paper is used in a recording method using a high-viscosity printing ink and does not require water absorption. For this reason, optimization has been performed to improve the fixing property and color developability, and a thick absorption layer and high-quality fine particles with high transparency are not required. Moreover, supported by vigorous demand of several million tons per year, mass production facilities are in place and high-quality coated paper is supplied at a very low price.
The coated paper has been considered to be inappropriate as a recording medium for the ink jet recording method because the water absorption is lower than that of the ink jet. However, since the image quality of coated paper is extremely high, a technique using this as a recording medium for an ink jet recording method has also been proposed (see, for example, Patent Document 1).

Since coated paper is poor in water absorption, when printing on coated paper using a conventional ink composition, wrinkles that cause the coated paper to swell after discharging ink occur, so-called "cockling" or There is a problem that a phenomenon such as so-called “curling” occurs in which the coated paper itself warps.

In the ink jet recording method, it is preferable that the viscosity of each ink composition constituting the ink set is substantially the same in order to control the ink discharge weight with the same head. Variations in the ink discharge weight cause deterioration in graininess and unevenness of the recorded image. However, the viscosity of the ink varies with temperature. At this time, if the viscosity characteristics of each ink composition differ depending on the temperature, it becomes one cause of variation in ink discharge weight.
In order to compensate for this, image processing correction considering the variation of each ink for each temperature, or a signal given to the head for each ink is required, which complicates processing and increases costs.

JP 2007-277342 A

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an ink set that can suppress curling and cockling and obtain a high-quality image with little roughness and an ink composition. It is an object of the present invention to provide an ink set having excellent viscosity characteristics depending on the temperature of the product, a recording method using the ink set, and a recorded product.

  As a result of intensive studies, the present inventor, as an ink set using a dark and light ink containing a moisturizing agent, by adjusting the weight ratio of the moisturizing agent, curling and cockling are suppressed, and a high-quality image without roughness is obtained. It was found that an ink set having excellent viscosity characteristics depending on the temperature of the ink composition can be realized, and the present invention has been achieved.

The present invention is based on such knowledge, and the configuration of the present invention is as follows.
(1) An ink set having a dark ink composition and a light ink composition having different pigment concentrations,
Each of the dark ink composition and the light ink composition includes a pigment, a humectant in which the following compounds (A), (B), and (C) are mixed, and 60% by weight to 10% by weight of water in the total amount of the ink. And comprising
The weight ratio of the humectant content of the dark ink composition is (A) :( B) :( C) = 1: 0.1 to 1: 1-3, and the humectant of the light ink composition An ink set in which the weight ratio of the contents is (A) + (B) :( C) = 1: 1 to 2.
(A) At least one compound selected from glycerin, 1,2,6-hexanetriol, diethylene glycol, triethylene glycol, tetraethylene glycol and dipropylene glycol (B) either or both of trimethylolpropane and trimethylolethane (C) At least one compound that is a compound of betaines, saccharides, and ureas and has a molecular weight in the range of 100 to 200.

  (2) The pigment concentration of the dark ink composition is 6% by weight to 15% by weight, and the pigment concentration of the light ink composition is 1.5% by weight to 4% by weight. Ink set.

  (3) The ink set according to (1) or (2), wherein each of the dark ink composition and the light ink composition further comprises a resin emulsion having a minimum film forming temperature of less than 20 ° C.

  (4) The ink set according to any one of (1) to (3), wherein each of the dark ink composition and the light ink composition has a viscosity value at 20 ° C. of 5 to 20 mPa · s.

  (5) An ink jet recording method, wherein recording is performed by ejecting the droplets of the ink set according to any one of (1) to (4) and attaching the droplets to a recording medium.

  (6) Recorded matter recorded by the recording method described in (5) above.

FIG. 1 is a graph showing the ink usage rate (ink generation rate) of dark and light inks in the same color in the example. FIG. 2 is a graph showing the ink usage rate (ink generation rate) when only dark ink is used in the example.

Hereinafter, the ink set of the present invention will be described in detail based on preferred embodiments thereof.
The dark ink composition and the light ink composition of the present embodiment are preferably water-based inks in which the main solvent of the ink is water from the viewpoint of safety and handling, and the water is ion-exchanged water or ultrafiltered water. It is preferable to use pure water or ultrapure water such as reverse osmosis water or distilled water. In particular, it is preferable to use water sterilized by ultraviolet irradiation or addition of hydrogen peroxide in order to prevent the generation of mold and bacteria and to enable long-term storage of the ink. From the viewpoints of ensuring appropriate physical property values (viscosity, etc.) of the ink, ensuring the stability and reliability of the ink, it is preferably contained in the ink in an amount of 60% by weight to 10% by weight.
By defining the content of water contained in the ink composition within the above range, even on paper with poor ink water absorption, the amount of water absorbed is less than that of conventional ink compositions. Curling can be suppressed.

In the present embodiment, “paper with poor ink absorbency” means a recording having an absorption layer of a paper support in which the water absorption within 30 msec ^1/2 from the start of contact in the Bristow method is 30 ml / m ² or less. Say medium. Further, in this embodiment, conventionally, any coated paper (also referred to as printing book paper) that has been used as a printing paper for letterpress printing, flat printing (for example, offset printing), or intaglio printing (for example, gravure printing). ) Can be used. This coated paper includes ordinary coated paper, cast coated paper, and matte coated paper. Also included are printing book paper defined by JIS P 0001 number 6122, OK topcoat paper defined by JIS P 0001 number 6059, and the like. Furthermore, a paper having high absorbability such as an ink-jet paper that has been used for a long time can also be used.

  When the water content is less than 10% by weight, the fixability to the recording medium may be lowered. On the other hand, when the water content exceeds 60% by weight, cockling and curling are likely to occur when printing on paper with poor ink absorbency, as in the case of conventional aqueous ink compositions.

An existing pigment can be used as a colorant used in the dark ink composition and the light ink composition of the present invention.
Pigments are superior in weather resistance such as water resistance compared to dyes, and dyes tend to permeate with inks, especially in recording media such as plain paper, where inks penetrate easily, but pigments tend to stay on the surface of the recording medium. It has the advantage that it is difficult to get through and easily obtain high color development. In this respect, any of known inorganic pigments and organic pigments can be used. In addition to pigments such as pigment yellow, pigment red, pigment violet, pigment blue, and pigment black described in the color index, phthalocyanine-based, azo Examples thereof include pigments such as azomethine, anthraquinone, azomethine, and condensed ring systems. 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, Examples thereof include inorganic pigments such as chrome oxide. For example, 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 Bio Red 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, and an ink composition can be formed using a plurality of pigments.

  In the ink set of the present embodiment, the dark ink composition is a cyan ink composition and / or a magenta ink composition, and the light ink composition is a light cyan ink composition and / or a light magenta ink composition. Is preferred. That is, it is preferable to use a combination of a cyan ink composition and a light cyan ink composition, a combination of a magenta ink composition and a light magenta ink composition, or both of them as the dark and light ink composition. Further, a combination of a yellow ink composition and a light yellow ink composition, or a combination of a black ink composition and a light black ink composition may be used.

  These pigments are dispersed in an aqueous medium using a ball mill, a roll mill, a bead mill, a high-pressure homogenizer, a high-speed stirring disperser, or the like, together with a dispersant such as a polymer dispersant or a surfactant, or , Dispersibility imparting group (hydrophilic functional group and / or salt thereof) is directly or indirectly bonded to the pigment surface via an alkyl group, alkyl ether group, aryl group, etc., and dispersed in an aqueous medium without a dispersant In addition, it is preferable that the ink composition is blended in the ink composition as a pigment dispersion liquid which is processed as a self-dispersing pigment that dissolves and is dispersed in an aqueous medium.

  Examples of dispersants include polymer dispersants such as 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- Acrylic acid alkyl 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 resins, vinyl acetate-fatty acid vinyl ester There are synthetic polymer compounds such as resins of tyrene copolymer and salts thereof, and the copolymer may be of random type, block type, or graft type.

  In addition, surfactants used as dispersants include anionic surfactants such as fatty acid salts, higher alkyl dicarboxylates, higher alcohol sulfate esters, higher alkyl sulfonates, and cation such as fatty acid amine salts and fatty acid ammonium salts. Surface active agents, polyoxyalkyl ethers, polyoxyalkyl esters, and nonionic surfactants such as sorbitan alkyl esters.

  Among these dispersants, a water-insoluble resin is particularly preferable. Specifically, the dispersant is composed of a block copolymer resin of a monomer having a hydrophobic group and a monomer having a hydrophilic group, and at least a monomer having a salt-forming group. And a resin having a solubility in 100 g of water at 25 ° C. of less than 1 g after neutralization. Monomers having hydrophobic groups are methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, decyl methacrylate, dodecyl. Methacrylates such as methacrylate, octadecyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, benzyl methacrylate, glycidyl methacrylate, vinyl esters such as vinyl acetate, vinylcyan compounds such as acrylonitrile and methacrylonitrile, styrene, α-methylstyrene, Vinyltoluene, 4-t-butylstyrene, chlorost Emissions, vinyl anisole, include aromatic vinyl monomers such as vinyl naphthalene, may also be used alone, or a combination of two or more kinds. Examples of the monomer having a hydrophilic group include polyethylene glycol monomethacrylate, polypropylene glycol monomethacrylate, and ethylene glycol / propylene glycol monomethacrylate. These may be used alone or in admixture of two or more. Monomers having a salt-forming group include acrylic acid, methacrylic acid, styrene carboxylic acid, maleic acid, etc., and each can be used alone or in combination of two or more. Furthermore, a macromonomer such as a styrene macromonomer or a silicone macromonomer having a polysynthetic functional group at one end, or other monomers can be used in combination.

  This 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 10,000. About ˜150,000 is preferable from the viewpoint of stably dispersing the pigment.

  Furthermore, the self-dispersing pigment that can be dispersed and / or dissolved in water without a dispersant is, for example, the dispersibility-imparting group or the dispersibility-imparting group by subjecting the pigment to physical treatment or chemical treatment. It is produced by bonding (grafting) an active species having 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, and a method in which a carboxyl group is bonded via a phenyl group by bonding p-aminobenzoic acid to the pigment surface. It can be illustrated. Inks containing self-dispersing pigments do not need to contain dispersants as described above to disperse ordinary pigments, so there is almost no foaming due to a decrease in defoaming properties caused by dispersants, and stable ejection It is easy to prepare ink with excellent properties. In addition, since a significant increase in viscosity due to the dispersant can be suppressed, it is possible to contain more pigment, and the printing density can be sufficiently increased, and there are advantages such as easy handling. In particular, black ink that requires a high concentration is effective, and the black ink used in the ink set of the present invention contains at least a self-dispersing pigment that can be dispersed and / or dissolved in water without a dispersant. Is preferred.

  In the present invention, a self-dispersing pigment that is surface-treated by oxidation treatment with hypohalous acid and / or hypohalite or ozone is preferred in terms of high color development. Commercially available products can also be used as the self-dispersing pigment, such as Microjet CW-1 (trade name; manufactured by Orient Chemical Co., Ltd.), CAB-O-JET200, CAB-O-JET300 ( Examples of the above are trade names such as those manufactured by Cabot Corporation.

  These pigments preferably have a volume average particle diameter in the range of 50 to 200 nm from the viewpoint of storage stability of the ink and prevention of nozzle clogging. These average particle diameters can be obtained by particle diameter measurement using a Microtrac UPA150 (manufactured by Microtrac) or a particle size distribution analyzer LPA3100 (manufactured by Otsuka Electronics Co., Ltd.).

  The amount of these pigments added is 6 to 15% by weight in the dark ink composition. If it is less than 6% by weight, the color developability is inferior, and if it exceeds 15% by weight, it may affect the storage stability and clogging performance of the ink. The light ink composition contains 1.5 to 4% by weight. If it is less than 1.5% by weight, the balance of gradation will be poor when used in combination with dark ink, and if it is more than 4% by weight, the visibility of ink dots will increase, and the purpose of suppressing roughness Is not suitable.

In the present embodiment, the humectant used in the dark ink composition and the light ink composition is from the viewpoint of maintaining an appropriate balance of curling, cockling suitability, showthrough suitability, clogging suitability, and viscosity characteristics depending on the ink temperature. ,
(A) at least one compound selected from glycerin, 1,2,6-hexanetriol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol,
(B) Any one or a mixture of trimethylolpropane and trimethylolethane, and (C) a compound of betaines, saccharides and ureas, and at least one compound having a molecular weight in the range of 100 to 200.
The weight ratio of the content of the dark ink composition is (A) :( B) :( C) = 1: 0.1 to 0.5: 1 to 3, and the content of the light ink composition The weight ratio of the amounts is preferably (A) + (B) :( C) = 1: 1-2.

The humectant selected from the group (A) is a substance that has an effect on clogging and also has an effect on curling and cockling. However, it is a substance that is inferior in see-through suitability due to its excellent permeability to recording media.
The moisturizing agent selected from the group (B) is effective in preventing clogging, and is a substance that has excellent penetration suitability since it has a permeation suppressing effect.

  In the dark ink composition, since the pigment concentration is high, the color of the surface of the recording medium is good. For this reason, it is necessary to control the permeability by properly balancing the content ratio of (A) and (B) against the back side of the recording medium through which the back surface of plain paper or the like is transparent. In the light ink composition, since the concentration of the pigment is lower than that in the dark ink composition, the color development on the surface of the recording medium is low, and the degree of show-through is good, so that this is not a big problem.

  The humectant selected from the group selected from (A) and (B) has a characteristic that the viscosity difference between 10 ° C. and 40 ° C. of the substance is large, so that the viscosity due to temperature increases as the content in the ink increases. The ink greatly affects the characteristics, and the viscosity difference between 10 ° C. and 40 ° C. is increased.

  The humectant selected from the group (C) is a substance that is particularly excellent in curling and cockling suitability. In addition, it is a substance having excellent viscosity characteristics depending on temperature. Specifically, glycine betaine (molecular weight 117), γ-butyrobetaine (145), homarine (137), trigonelin (137), carnitine (161), homoserine betaine (161), valine betaine (159) ), Lysine betaine (188), ornithine betaine (176), alanine betaine (117), stachydrin (185), betaine glutamic acid betaine (189) Sugars such as glucose (180), mannose (180), fructose (180), ribose (150), xylose (150), arabinose (150), galactose (180), sorbitol (182) Allylurea (100), N, N-dimethylolurea 120), malonyl urea (128), carbamyl urea (103), 1,1-diethylurea (116), n-butylurea (116), creatinine (113), benzylurea (150) Of urea. When the molecular weight is less than 100, the tendency for the viscosity difference at 10 ° C. to 40 ° C. to increase becomes strong. In addition, when the molecular weight is 200 or more, the viscosity of the ink is likely to increase with respect to the added amount in the ink, and thus the molecular weight is preferably in the range of 100 to 200. Among these, glycine betaine is particularly preferable because it has a high curl suppressing effect, and a commercially available product such as amino coat (manufactured by Asahi Kasei Chemicals Corporation) can also be used.

  From the viewpoints of curling, cockling suitability, back-through suitability, and clogging suitability, these humectants may be added in an amount of 10 to 40% by weight in combination with (A), (B) and (C). preferable.

  In addition, the dark ink composition and the light ink composition of the present embodiment prevent clogging in the vicinity of the nozzles of the inkjet head, appropriately control the penetrability and bleeding of the ink in the recording medium, and dry the ink. For the purpose of imparting water, it is preferable to contain a water-soluble organic solvent, and it is particularly preferable to contain 1,2-alkanediol and / or glycol ether. Specific examples of 1,2-alkanediol include 1,2-octanediol, 1,2-hexanediol, 1,2-pentanediol, 4-methyl-1,2-pentanediol and the like. Specific examples of the glycol ether 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, 1-methyl-1-methoxybutanol, Propylene glycol monomethyl 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, dipropylene glycol mono-n- And propyl ether and dipropylene glycol mono-iso-propyl ether. These water-soluble organic solvents can be used alone or in combination of two or more, and 1 to 50 weights in the ink from the viewpoint of ensuring proper physical properties (such as viscosity) of the ink, ensuring print quality, and reliability. % Is preferably included.

  Furthermore, it is preferable to contain a surface tension adjusting agent in order to control the wettability of the ink to the recording medium, and to obtain the permeability to the recording medium and the printing stability in the ink jet recording method. As the surface tension adjusting agent, acetylene glycol surfactants and polyether-modified siloxanes are preferable. Examples of acetylene glycol surfactants include Surfynol (registered trademark) 420, 440, 465, 485, 104, STG (product of Air Products), Olphine (registered trademark) PD-001, SPC, E1004, E1010 ( Nissin Chemical Industry Co., Ltd.), acetylenol (registered trademark) E00, E40, E100, LH (product of Kawaken Fine Chemical Co., Ltd.) and the like. Examples of the polyether-modified siloxanes include BYK-346, 347, 348, and UV3530 (Bic Chemie product). A plurality of these may be used in the ink composition, and the surface tension is preferably adjusted to 20 to 40 mN / m, and the ink contains 0.1 to 3.0% by weight.

  Further, an antifoaming agent, an antioxidant, an ultraviolet absorber, an antiseptic / antifungal agent and the like can be added as necessary.

  The dark ink composition and the light ink composition used in the exemplary embodiment include a resin emulsion having a minimum film forming temperature of less than 20 ° C. from the viewpoint of securing fixability to a recorded material. By using a resin emulsion having a minimum film forming temperature of less than 20 ° C., resin fine particles that form a film at 20 ° C. or more are formed into a film at an ambient temperature, thereby improving fixability and abrasion resistance.

  These resin emulsions are preferably one or more selected from the group consisting of acrylic resins, methacrylic resins, vinyl acetate resins, vinyl chloride resins, and styrene-acrylic resins. These resins may be used as a homopolymer or may be used as a copolymer, and any of a single phase structure and a multiphase structure (core-shell type) can be used.

  Furthermore, at least one of the resin emulsions contained in the dark and light ink composition used in the present embodiment is blended in the ink composition in the form of an emulsion of resin fine particles obtained by emulsion polymerization of unsaturated monomers. It is preferable. The reason for this is that even if the resin fine particles are added as they are to the ink composition, the dispersion of the resin fine particles may be insufficient, so that the emulsion form is preferable for the production of the ink composition. The emulsion is preferably an acrylic emulsion from the viewpoint of storage stability of the ink composition.

An emulsion of resin fine particles (such as an acrylic emulsion) can be obtained by a known emulsion polymerization method. For example, it can be obtained by emulsion polymerization of an unsaturated monomer (such as an unsaturated vinyl monomer) in water containing a polymerization initiator and a surfactant.
Examples of unsaturated monomers include acrylic acid ester monomers, methacrylic acid ester monomers, aromatic vinyl monomers, vinyl ester monomers, vinyl cyanide compounds generally used in emulsion polymerization. Examples include monomers, halogenated monomers, olefin monomers, and diene monomers. Furthermore, specific examples include methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-amyl acrylate, isoamyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, decyl acrylate. , Acrylic acid esters such as dodecyl acrylate, octadecyl acrylate, cyclohexyl acrylate, phenyl acrylate, benzyl acrylate, glycidyl acrylate; methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-amyl methacrylate, isoamyl Methacrylate, n-hexyl methacrylate, 2-ethyl Methacrylic esters such as hexyl methacrylate, octyl methacrylate, decyl methacrylate, dodecyl methacrylate, octadecyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, benzyl methacrylate, glycidyl methacrylate; and vinyl esters such as vinyl acetate; vinyl such as acrylonitrile, methacrylonitrile Cyanide compounds; halogenated monomers such as vinylidene chloride and vinyl chloride; aromatic vinyl monomers such as styrene, α-til styrene, vinyl toluene, 4-t-butyl styrene, chlorostyrene, vinyl anisole, vinyl naphthalene Olefins such as ethylene and propylene, dienes such as butadiene and chloroprene, vinyl ether, vinyl ketone, vinyl pyrrolidone Vinyl monomers such as; unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid and maleic acid; acrylamides such as acrylamide, methacrylamide and N, N′-dimethylacrylamide; 2-hydroxyethyl Examples thereof include hydroxyl group-containing monomers such as acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, and 2-hydroxypropyl methacrylate, and these can be used alone or in combination of two or more.

  A crosslinkable monomer having two or more polymerizable double bonds can also be used. Examples of the crosslinkable monomer having two or more polymerizable double bonds include polyethylene glycol diacrylate, triethylene glycol diacrylate, 1,3-butylene glycol diacrylate, 1,4-butylene glycol diacrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, 1,9-nonanediol diacrylate, polypropylene glycol diacrylate, 2,2′-bis (4-acryloxypropyloxyphenyl) propane, 2,2 ′ -Diacrylate compounds such as bis (4-acryloxydiethoxyphenyl) propane; triacrylate compounds such as trimethylolpropane triacrylate, trimethylolethane triacrylate, tetramethylolmethane triacrylate Tetraacrylate compounds such as ditrimethylol tetraacrylate, tetramethylolmethane tetraacrylate, pentaerythritol tetraacrylate; Hexaacrylate compounds such as dipentaerythritol hexaacrylate; Ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, polyethylene glycol Dimethacrylate, 1,3-butylene glycol dimethacrylate, 1,4 butylene glycol dimethacrylate, 1,6-hexanediol dimethacrylate, neopentyl glycol dimethacrylate, dipropylene glycol dimethacrylate, polypropylene glycol dimethacrylate, polybutylene glycol dimethacrylate Methacrylate, 2 Dimethacrylate compounds such as 2′-bis (4-methacryloxydiethoxyphenyl) propane; trimethacrylate compounds such as trimethylolpropane trimethacrylate and trimethylolethane trimethacrylate; methylenebisacrylamide; divinylbenzene and the like. It can be used alone or in combination of two or more.

  In addition to the polymerization initiator and surfactant used in emulsion polymerization, a chain transfer agent, further a neutralizing agent, and the like may be used according to a conventional method. In particular, ammonia and inorganic alkali hydroxides such as sodium hydroxide and potassium hydroxide are preferred as the neutralizing agent.

In the present embodiment, the resin emulsion is a dark ink in the range of 1 to 10% by weight from the viewpoint of more effectively obtaining ink jet proper physical property values, reliability (clogging, ejection stability, etc.), fixing properties and the like. It is preferably contained in the composition and the light ink composition.
On the other hand, the volume average particle diameter of the resin emulsion used in the dark ink composition and the light ink composition is preferably 20 to 200 nm from the viewpoint of dispersion stability in the ink.

  The ink set of the present embodiment can be suitably used for writing instruments such as pens, stamps and the like, but can be more suitably used as an ink composition for inkjet recording. 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 are attached to a recording medium. This will be specifically described below.

As a first method, there is an electrostatic suction method, which applies a strong electric field between the nozzle and the acceleration electrode placed in front of the nozzle, and continuously ejects ink from the nozzle in the form of droplets. This is a method in which a print information signal is applied to the deflection electrode while the ink droplet is flying between the deflection electrodes for recording, or a method in which the ink droplet is ejected in response to the print information signal without being deflected.
The second method is a method in which ink droplets are forcibly ejected 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 printing information signal is given to the deflection electrode and recorded while the ink droplet flies between the deflection electrodes.
The third method is a method using a piezoelectric element, 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 heat energy, and the ink liquid is heated and foamed with a microelectrode in accordance with a print information signal to eject and record ink droplets.

Any of the above methods can be used in the ink jet recording method using the ink set of the present embodiment.
The recorded matter of the present embodiment is recorded at least using the above ink set. This recorded matter is an ink set that can suppress curling and cockling on a sheet having low water absorption by using the ink set of the present invention, and can obtain a high-quality image without roughness. Ink sets having excellent viscosity characteristics depending on the temperature, a recording method using the ink set, and recorded matter can be provided.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail using an Example, this invention is not limited to these Examples.

[Adjustment of colorant dispersion]
(Pigment dispersion B1)
100 g of commercially available carbon black Color Black S170 (trade name: manufactured by Degussa Huls) was mixed with 1 kg of water and pulverized with 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 electric conductivity reached 2 mS / cm, and further concentrated until the pigment concentration reached 20% by weight. Was prepared.
The average particle size of the pigment in this dispersion was 110 nm as measured by measuring the particle size distribution of Microtrac UPA150 (manufactured by Microtrac).

(Pigment dispersion M1)
In a reaction vessel sufficiently substituted with nitrogen gas using 20 parts by weight of an organic solvent (methyl ethyl ketone), 0.03 part by weight of a polymerization chain transfer agent (2-mercaptoethanol), a polymerization initiator, and each monomer shown in Table 1. The mixture was polymerized with stirring at 75 ° C., and 0.9 part by weight of 2,2′-azobis (2,4-dimethylvaleronitrile) dissolved in 40 parts by weight of methyl ethyl ketone was added to 100 parts by weight of the monomer component. The polymer solution was obtained by aging for 1 hour.

5 parts obtained by drying the obtained polymer solution under reduced pressure were dissolved in 15 parts of methyl ethyl ketone, and the polymer was neutralized with an aqueous sodium hydroxide solution. Furthermore, C.I. I. 15 parts of Pigment Red 122 was added and kneaded with a disperser while adding water.
After 100 parts of ion-exchanged water was added to the kneaded mixture and stirred, methyl ethyl ketone was removed at 60 ° C. under reduced pressure, and a part of the water was further removed, whereby a yellow pigment having a solid content concentration of 20% by weight was removed. An aqueous dispersion was obtained.
The average particle size of the pigment in this dispersion was measured by measuring the particle size distribution of Microtrac UPA150 (manufactured by Microtrac), and found to be 140 nm.

(Pigment dispersion C1)
In the pigment dispersion M1, C.I. I. In place of Pigment Red 122, C.I. I. A pigment dispersion C1 was obtained in the same manner as in the pigment dispersion M1, except that CI Pigment Blue 15: 4 was used.
The average particle size of the pigment in this dispersion was measured by particle size distribution measurement of Microtrac UPA150 (manufactured by Microtrac), and was 80 nm.

[Preparation of ink and ink set]
Each component was mixed in the ratio 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 prepare ink production examples 1 to 13. However, the addition amounts shown in Table 2 are all expressed as weight percent concentrations, and the numbers in parentheses in the colorant dispersion represent the solid content concentration of the colorant. The “remaining amount” of ion-exchanged water means adding ion-exchanged water so that the total amount of ink becomes 100 parts. Also, ink sets 1 to 10 shown in Table 3 were prepared by combining the light ink composition and the dark ink composition of Production Example.

<Evaluation of ink set>
(Test 1) Graininess Evaluation According to each ink set, the ink jet printer PX-B500 (manufactured by Seiko Epson) was filled with a dark ink composition in the magenta and cyan columns and a light ink composition in the black and yellow columns. For OK Top Coat N (Oji Paper Co., Ltd.), with a resolution of 720 × 720 dpi, every 10% from 100% Duty (ink injection amount at 100% Duty: 1.0 mg / cm ² ) to 10% The patch pattern changed to was printed. The ink usage rate (ink generation rate) of dark and light inks in the same color is shown in FIG. FIG. 2 shows the ink usage rate (ink generation rate) when only dark ink is used (ink set 6). The granularity of the obtained patch pattern was evaluated according to the following criteria.
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.
The evaluation results were as shown in Table 4 below.

(Test 2) Evaluation of strike-through Using the same inkjet printer as described above, the same patch pattern as in Test 1 was printed on the following three types of plain paper at the same ink usage rate. As plain paper, Xerox P (manufactured by Fuji Xerox), Xerox 4024 (manufactured by Xerox Co.), and recycle cut R-100 (manufactured by Oji Paper Co., Ltd.) were used. The printed matter was allowed to stand for 24 hours in an environment of 24 ° C., and then the through-through state of the ink on the back side of the printed surface was visually evaluated. The evaluation criteria were as follows.
A: Almost no ink breakthrough is observed.
B: Back-through of ink is recognized, but there is no problem in reprinting on the back side.
C: There was considerable ink back-through, which hindered reprinting on the back side.
The evaluation results were as shown in Table 4 below.

(Test 3) Cockling evaluation Using the same ink jet printer as above, a patch pattern similar to Test 1 having an area of 10 cm × 10 cm is printed at the same ink usage rate on OK Top Coat N (manufactured by Oji Paper Co., Ltd.). did. Thereafter, the degree of unevenness (cockling) of the recording medium was measured using a laser displacement meter LK-010 (manufactured by Keyence Corporation), and judged according to the following evaluation criteria.
A: Less than 1.0 mm B: 1.0 mm or more and less than 2.0 mm C: 2.0 mm or more Evaluation results were as shown in Table 4 below.

(Test 4) Curl Evaluation Using the same ink jet printer as described above, with respect to OK Topcoat N (manufactured by Oji Paper Co., Ltd.), the same patch pattern as in Test 1 with margins of 0.5 cm on all sides was used. Was printed. After printing, the amount of curling at the four corners when left in an environment of 24 ° C. for 24 hours was measured, and an average amount was determined according to the following evaluation criteria.
A: Less than 1.0 cm B: 1.0 cm or more and less than 3.0 cm C: 3.0 cm or more The evaluation results were as shown in Table 4 below.

(Test 5) Fixability evaluation immediately after printing Using the same ink jet printer as described above, immediately after printing the sample used in Test 3, the printed surface was rubbed strongly with a finger, and the state of the printed surface was visually observed. The evaluation criteria were as follows.
A: Some ink is removed, but the fingers are not soiled.
B: Ink is removed and the finger is also soiled.
The evaluation results were as shown in Table 4 below.

(Test 6) Evaluation of viscosity temperature characteristics The viscosity of each ink composition at 10 ° C., 25 ° C., and 40 ° C. was measured with a Canon Fenceke reverse flow viscometer VM-252C (manufactured by Kogaisha). 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 viscosity characteristics depending on the ink temperature were evaluated according to the following criteria.
A: The ratio is 0.95 to 1.05 at any temperature.
B: Ratio is 0.90 to 0.95 or 1.05 to 1.10 at any temperature
C: The ratio was 0.90 or less, or 1.10 or more at any temperature. The evaluation results were as shown in Table 4 below.

  As is apparent from Table 4, according to the ink set of the present embodiment, the ink set can suppress curling and cockling even on paper having low water absorption, and can obtain a high-quality image without roughness. It is possible to provide an ink set having excellent viscosity characteristics depending on the temperature of the ink composition, and is an ink set suitable for use in an ink jet recording system.

  The present invention is not limited to the above-described embodiment, but can be applied to uses such as ink for writing instruments and ink for offset printing.

Claims (6)

An ink set having a dark ink composition and a light ink composition having different pigment concentrations,
Each of the dark ink composition and the light ink composition includes a pigment, a humectant in which the following compounds (A), (B), and (C) are mixed, and 60% by weight to 10% by weight of water in the total amount of the ink. And comprising
The weight ratio of the humectant content of the dark ink composition is (A) :( B) :( C) = 1: 0.1 to 1: 1-3, and the humectant of the light ink composition An ink set in which the weight ratio of the contents is (A) + (B) :( C) = 1: 1 to 2.
(A) At least one compound selected from glycerin, 1,2,6-hexanetriol, diethylene glycol, triethylene glycol, tetraethylene glycol and dipropylene glycol.
(B) Either or both of trimethylolpropane and trimethylolethane.
(C) At least one compound that is a compound of betaines, saccharides, and ureas and has a molecular weight in the range of 100 to 200.   The ink set according to claim 1, wherein the concentration of the pigment in the dark ink composition is 6 wt% to 15 wt%, and the concentration of the pigment in the light ink composition is 1.5 wt% to 4 wt%.   3. The ink set according to claim 1, wherein each of the dark ink composition and the light ink composition further comprises a resin emulsion having a minimum film forming temperature of less than 20 ° C. 4.   The ink set according to any one of claims 1 to 3, wherein the dark ink composition and the light ink composition each have a viscosity value at 20 ° C of 5 to 20 mPa · s.   An ink jet recording method comprising: performing recording by ejecting droplets of the ink set according to any one of claims 1 to 4 and attaching the droplets to a recording medium.   A recorded matter recorded by the recording method according to claim 5.

Images