JP2012224772A - Nonaqueous ink set - Google Patents

Abstract

A non-aqueous ink set is excellent in pigment dispersion stability, can suppress back-through, and can realize a high printing density.
An ink set composed of at least two or more types of ink is used, and both the first ink and the second ink contain at least 50% by mass of a five-membered heterocyclic compound having a C═O bond in at least a pigment and an organic solvent. In addition, the content of the polymer component in the ink is 20% by mass or less of the pigment, the pigment of the first ink is pH 6 or less, and the pigment of the second ink is pH 7 or more.
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Description

  The present invention relates to a non-aqueous ink set suitable for use in an ink jet recording system, and more particularly to a non-aqueous ink set that has an excellent effect of suppressing show-through and has a high printing density.

  Inkjet recording is a method in which high-fluidity inkjet ink is ejected as ink particles from fine head nozzles, and images are recorded on printing paper placed facing the nozzles, enabling high-speed printing with low noise. Therefore, it has been spreading rapidly in recent years. As inks used in such an ink jet recording method, various so-called non-aqueous inks in which pigments are finely dispersed in a water-insoluble solvent have been proposed.

  For example, in Patent Document 1, the applicant has proposed a non-aqueous ink containing a pigment, an organic solvent, an ester solvent, a higher alcohol solvent, a hydrocarbon solvent, and the like, and further containing a soluble polymer dispersant. This ink has excellent on-machine stability, ink-jet suitability, and has the advantage that a printed surface that does not stick even when superimposed on a printed surface printed by a PPC copier or laser printer can be obtained. Yes, and excellent in toner suitability. Patent Document 2 discloses a non-aqueous ink containing a pigment, an ester solvent and a hydrocarbon solvent as organic solvents, and further containing a dispersion type polymer dispersant (NAD).

  Conventionally, pigment-dispersed non-aqueous inks are modified by using a resin or a polymer-type dispersant (dissolved type or NAD) as described in Patent Documents 1 and 2, or directly by a polymer on the pigment surface. By carrying out (grafting or microencapsulation), the dispersion stability of the pigment has been ensured. In any of these methods, the aggregation of the pigment is physically suppressed by the steric hindrance by the polymer. In other words, the pigment dispersion stability of the ink is improved by including the polymer component in the ink. I will try to let you.

  By the way, as an ink set used for the ink jet recording method, there are an ink set including cyan (C), magenta (M), and yellow (Y) ink, and an ink set including black (K). In general, a color image is formed by three colors of yellow, magenta, and cyan, and optionally four colors including black ink. In the case of such an ink set, it is required that each of the inks constituting the ink set has a good color developability and that a good image density can be realized when combined with a plurality of inks. . For example, in the patent document 3, the applicant has proposed an ink set in which a specific pigment and a pigment dispersant are combined. According to this ink set, it is possible to further improve the image density of the printed matter, particularly the black density.

JP 2007-126564 A JP 2007-197500 A JP 2009-270061 A

  When the polymer component is contained in the ink, the pigment is dragged to the polymer component after the ink is transferred to the printing paper because the affinity between the pigment and the polymer component is high or the pigment and the polymer component are bonded. Easily penetrate into the paper. For this reason, the printing density on the surface of the printing paper is lowered or the back-through occurs. This is also true for ink sets. In particular, in mixed-color black (so-called composite black), the amount of ink ejected per unit area increases, and show-through is significantly worsened.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a non-aqueous ink set that is excellent in pigment dispersion stability, can suppress back-through, and can achieve a high printing density. It is what.

The non-aqueous ink set of the present invention is an ink set comprising at least two kinds of inks, and both the first ink and the second ink are five-membered heterocyclic rings having a C═O bond in at least a pigment and an organic solvent. 50 mass% or more of the formula compound, the content of the polymer component in the ink is 20 mass% or less of the pigment, the pigment contained in the first ink is pH 6 or less, and the second ink contains The contained pigment has a pH of 7 or more.
Here, the polymer component means a polymer having a repeating structure of a monomer (monomer) and having a molecular weight of 500 or more.

The five-membered heterocyclic compound is preferably at least one selected from carbonate compounds, lactone compounds, imidazolidinone compounds, and pyrrolidone compounds.
The content of the polymer component in the ink is more preferably 5% by mass or less of the pigment, and it is preferable that the polymer component is not substantially contained.

The content of the five-membered heterocyclic compound is preferably 60 to 97% by mass with respect to the total amount of each of the first ink and the second ink.
It is preferable that the pigment of the first ink is carbon black and the pigment of the second ink is copper phthalocyanine.

The non-aqueous ink set of the present invention contains 50% by mass or more of a five-membered heterocyclic compound having a C═O bond in an organic solvent, so that the content of the polymer component in the ink is 20% by mass or less of the pigment. In addition, it is possible to achieve both pigment dispersion stability and suppression of show-through, and in addition, by setting the pH of the pigment of the first ink to 6 or less and the pH of the pigment of the second ink to 7 or more. When the pigment contained in the first ink and the second ink comes in contact with the paper surface, more pigment tends to stay on the paper surface due to the acid-base interaction, and a printed matter with a high printing density can be obtained. Can do.
Since the non-aqueous ink set of the present invention has a high printing density, it is suitable for a line-type inkjet system that forms an image in one pass.

  Moreover, since the non-aqueous ink set of the present invention has a low content of the polymer component, the temperature dependency of the viscosity is low. For this reason, by using the non-aqueous ink set of the present invention for the circulating ink jet system, the time required for temperature adjustment can be shortened, and the power required for temperature adjustment can also be reduced. Therefore, the non-aqueous ink set of the present invention can be suitably used for a circulation type inkjet system.

  The non-aqueous ink set of the present invention (hereinafter also simply referred to as an ink set) is an ink set composed of at least two kinds of inks, and a five-membered heterocyclic ring having a C═O bond in a pigment having a pH of 6 or less and an organic solvent. C = O in the first ink containing the formula compound in an amount of 50% by mass or more based on the total amount of the organic solvent, and the content of the polymer component in the ink is 20% by mass or less of the pigment, the pigment having a pH of 7 or more and the organic solvent A second ink containing a 5-membered heterocyclic compound having a bond in an amount of 50% by mass or more based on the total amount of the organic solvent, and a content of a polymer component in the ink being 20% by mass or less of the pigment. is there.

  Here, the ink set includes not only an ink cartridge itself in which a plurality of ink cartridges are integrated, but also a case where a plurality of individual ink cartridges are used in combination, and further, an ink cartridge and a recording head are integrated. Is also included. Either the first ink or the second ink may be ejected first.

  The five-membered heterocyclic compound contained in the first ink and the second ink of the present invention contains 50% by mass or more based on the total amount of the organic solvent contained in each of the first ink and the second ink, preferably The range of 60 to 97% by mass with respect to the total amount of each of the first ink and the second ink is preferable. The five-membered heterocyclic compound may be a liquid or a solid. In the case of a solid, any compound that dissolves in an organic solvent may be used. As the organic solvent to be dissolved, an organic solvent described later can be used. Preferred examples of the 5-membered heterocyclic compound include carbonate compounds, lactone compounds, imidazolidinone compounds, and pyrrolidone compounds.

Preferred examples of the carbonate compound include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, and derivatives thereof.
Preferred examples of the lactone compound include γ-butyrolactone, α-acetyl-γ-butyrolactone, pentano-4-lactone, and derivatives thereof.

Examples of the imidazolidinone compounds include 2-imidazolidinone, 1,3-dimethyl-2-imidazolidinone, 1,3-diethyl-2-imidazolidinone, 1,3-dipropyl-2-imidazolidinone, Preferable examples include 3-diisopropyl-2-imidazolidinone, 1,3-dibutyl-2-imidazolidinone and derivatives thereof.
Preferred examples of the pyrrolidone compound include 2-pyrrolidone, N-methyl-pyrrolidone, 1-ethyl-2-pyrrolidone and derivatives thereof.
Examples of the derivative include compounds in which a hydrogen atom is substituted with a fluorine atom or an alkyl group having 1 to 4 carbon atoms.

  Ordinary ink contains about 0.5 to 30% by mass of a polymer component such as a dispersant or resin (about 30 to 200% by mass with respect to the pigment) with respect to the total amount of the ink in order to achieve dispersibility of the pigment. It is necessary to let However, since the ink of the ink set of the present invention can achieve pigment dispersibility with a five-membered heterocyclic compound, sufficient pigment dispersion stability is obtained even when the content of the polymer component is 20% by mass or less of the pigment. It is possible to secure. On the other hand, five-membered heterocyclic compounds have a weaker affinity for pigments than polymers, so after ink is transferred to printing paper like polymers, there is no possibility of dragging the pigment and penetrating into the paper. As a result, high density printing can be performed.

  It is desirable that the content of the polymer component in the first ink and the second ink is 20% by mass or less, preferably 5% by mass or less, more preferably substantially free of the pigment contained in each ink. . Here, “substantially not containing” means not only containing no polymer component but also containing, for example, the polymer component as an unavoidable impurity.

  The polymer component includes a polymer component originally contained in the pigment in addition to a case where the polymer component is intentionally contained such as a polymer dispersant or a resin. When a polymer dispersant is included as a polymer component, for example, as a commercial product, Solsperse series (Solsperse 20000, 28000, 27000, 41000, 41090, 43000, 44000) manufactured by Nippon Lubrizol Co., Ltd., manufactured by BASF Japan Ltd. Jonkrill series (Johnkrill 57, 60, 62, 63, 71, 501), polyvinylpyrrolidone K-30 and K-90 made by Daiichi Kogyo Seiyaku Co., Ltd. 2000, 2001).

  When a resin is included as a polymer component, Marquide NO. 31, NO. 32, NO. 33, Marquide NO. Styrene acrylic resins such as 32-30WS maleic acid resin, Tamano 751 manufactured by Arakawa Chemical Industry Co., Ltd., phenol resin such as Tamanoru PA, Jonkrill 682 (trade name) manufactured by BASF Japan, Tachikasei Kogyo Co., Ltd. High-rack 111, 110H, etc. made of ketone resin, Nippon Steel Chemical Co., Ltd., Escron G90, V120, etc. Coumaron resin, Chisso Co., Ltd., Vinylec E type, K type, etc., Polyvinyl formal resin, Ube Industries, Ltd. Ε-caprolactam copolymer such as nylon 6 manufactured by Sekisui Chemical Co., Ltd., Polysethyl butyral resin such as ESREC BL-1 and BL-2, polystyrene such as Astyka Chemical Co., Ltd. Such as polyacrylic acid ester, polymethyl methacrylate, Polymethacrylates such as propyl methacrylate, addition polymerization resins such as chlorinated polypropylene, polyvinyl acetate, maleic anhydride polymer, acrylonitrile / butadiene / styrene resin, chlorinated polypropylene, DFK resin, polyester, polyurethane, polyamide, etc. Examples include condensation polymerization resins.

The organic solvents contained in the first ink and the second ink of the present invention may all be cyclic members of a five-membered heterocyclic compound, but may contain other organic solvents. Examples of organic solvents other than cyclic carbonates include water-soluble organic solvents, specifically, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, propylene glycol, dipropylene glycol, and tripropylene. Glycols such as glycol, glycerin, acetins, triethylene glycol monomethyl ether, triethylene glycol monobutyl ether, glycol derivatives such as tetraethylene glycol monomethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, triethanolamine, 1 -Methyl-2-pyrrolidone, β-thioglycol, sulfolane and the like can be used. These water-soluble organic solvents can be used alone or in combination of two or more.
The content of the water-soluble organic solvent is preferably 40% by mass or less based on the total amount of each of the first ink and the second ink, from the viewpoint of pigment dispersion stability and suppression of back-through.

  For the first ink and the second ink of the present invention, conventionally known inorganic pigments and organic pigments can be appropriately used as long as the pH described below is satisfied. Examples of inorganic pigments include titanium oxide, bengara, cobalt blue, ultramarine blue, bitumen, carbon black, calcium carbonate, kaolin, clay, barium sulfate, talc, and silica. Examples of the organic pigment include insoluble azo pigments, azo lake pigments, condensed azo pigments, condensed polycyclic pigments, and copper phthalocyanine pigments. These pigments may be used alone or in appropriate combination. The addition amount of the pigment is preferably 0.5 to 20% by mass with respect to the total amount of each of the first ink and the second ink.

  The pigment of the first ink in the ink set of the present invention has a pH of 6 or less, and the pigment of the second ink has a pH of 7 or more. As a result, when the pigments contained in the first ink and the second ink come in contact with each other on the paper surface, more pigments tend to stay on the paper surface due to the acid-base interaction, and the printed matter has a higher printing density. Can be obtained. More preferably, the pigment of the first ink has a pH of 2 to 6, and the pigment of the second ink has a pH of 7 to 10. If it is lower than pH 2 or higher than pH 10, oxidation or hydrolysis of the organic solvent in the ink may be accelerated, which is not preferable. From the viewpoint of considering the acid-base interaction, the pH difference between the pH of the pigment of the first ink and the pH of the pigment of the second ink is preferably 1 or more, more preferably 2 or more. The pH of the pigment can be regarded as the pH of the pigment washing water, and the pH of the pigment washing water is measured according to JIS standard K5101-17-1.

  The pigment preferably has many polar functional groups such as carboxylic acid group, sulfonic acid group, hydroxyl group and amino group on the surface. Specific examples of pigments having a pH of 6 or less (acidic) include carbon black MA100, MA11, MA8, MA7 (Mitsubishi Chemical), Raven 1040, Raven 1255 (Colombian), Regal 400 (Cabot), Cyanine Blue KRG, Cyanine Blue 4044 ( Sanyo Dye), Brilliant Carmine 6B-321, Super Red BN (DIC), AP22 (Daiichi Seika), Fast Yellow 4190 (DIC), Monoazo Yellow Fastellolow 7416 (Sanyo Dye) and the like can be preferably exemplified. In addition, in carbon black, it can also adjust by carrying out the acidic process of acidic carbon black or neutral carbon black.

  Examples of pigments having a pH of 7 or higher include monoazo yellow No. 1 Preferred examples include 55 (Daiichi Seika), cyanine blue GFR (Sanyo dye), SYMULER FAST YELLOW BY2000GT (DIC), FUJI RED5R734, FUJI RED5R729, and FUJI FAST ORANGE38R (Fujii dye).

  In addition to the above components, the ink of the ink set of the present invention may contain a conventional additive. Additives include surfactants such as anionic, cationic, amphoteric or nonionic surfactants, antioxidants such as dibutylhydroxytoluene, propyl gallate, tocopherol, butylhydroxyanisole, and nordihydroguaiare. And tic acid.

The first ink and the second ink of the ink set of the present invention are dispersed by adding all or all components into a known disperser such as a bead mill at one time or divided, and if desired, a known filtration such as a membrane filter. It can be prepared by passing through a machine.
Examples of the non-aqueous ink set of the present invention are shown below.

(Preparation of carbon black prototype)
Carbon black (MA600, particle diameter 20 nm, specific surface area 140 m ² / g (JISK6217), pH = 7, manufactured by Mitsubishi Chemical Corporation) 10 g, and KPS (persulfuric acid represented by K ₂ S ₂ O ₈ ) as a surface treatment agent 1 g of potassium (manufactured by Wako Pure Chemical Industries, Ltd.), 2 g of demole NL (β-naphthalenesulfonic acid formalin condensate sodium salt, manufactured by Kao Corporation) as a pigment dispersant, and 100 g of water as a solvent, stirring device, temperature It put in the flask which attached the meter, the nitrogen gas introducing device, and the cooling pipe.

  Next, zirconia beads (2.0 mmφ, 450 g / reaction mixture 100 g) were placed in the flask, and then nitrogen gas was blown into the flask while stirring to replace the inside of the flask. The flask was set in an oil bath set at 105 ° C. and subjected to reaction for 6 hours while stirring at 100 rpm in a nitrogen gas atmosphere. After removing the beads from the obtained reaction mixture by filtration, an equal mass of butisenol (tetraethylene glycol monobutyl ether, manufactured by Kyowa Hakko Chemical) was added to the remaining reaction mixture and stirred, and then the contents of the flask were centrifuged. To separate the solid and liquid.

The separated solid was dispersed in water, stirred at 70 ° C. for 12 hours to dissolve the unreacted surface treatment agent in water, and then filtered using a filter to isolate carbon black. The obtained carbon black was dried at 100 ° C. for 12 hours. When the obtained carbon black was analyzed using FT-IR, the presence of COOH groups and SO ₃ K groups was confirmed. Further, when the pH of the pigment washing water was measured in accordance with JIS standard K5101-17-1, the pH was 2.3.

(Preparation of ink)
After premixing the raw materials with the formulation shown in Table 1 below (the numerical values shown in Table 1 are parts by mass), the inks of Preparation Examples 1 to 9 were prepared by dispersing the raw materials for about 12 minutes.

(Evaluation)
(Storage stability)
Each of the inks of Preparation Examples 1 to 9 was put in a glass bottle, sealed, and allowed to stand at 70 ° C. for 1 month, then the change in the viscosity of the ink was measured, and the measurement result was evaluated as follows.
Viscosity change rate: [(viscosity after 4 weeks × 100) / (initial value of viscosity)] − 100 (%)
○: Viscosity change rate less than 5% Δ: Viscosity change rate 5% or more and less than 10% ×: Viscosity change rate 10% or more

(Betrayal)
The ink of the preparation example was solid-printed by overlaying each ink at a resolution of 300 dpi using ORPHIS X9050 in an ideal paper thin mouth, and the back side of the paper was visually observed and evaluated according to the following criteria.
A: No show-through is observed. ○: Some show-through is observed. Δ: There is a show-through. X: Many show-throughs are shown in Table 2 together with details of the transfer ink.

  As shown in Table 1, although the inks of Preparation Examples 1 to 7 have an overwhelmingly lower polymer content than conventional inks, as in the inks of Preparation Examples 8 and 9 having a high polymer content, No aggregation or sedimentation of the pigment was observed, and the storage stability was excellent. And as shown in Table 2, all of Examples 1 to 6 which are the ink sets of the present invention were suppressed from see-through and the resulting print density was high. As shown in Example 4, this effect did not change even when the first ink was transferred after the second ink was transferred first.

  On the other hand, even if the pH of the pigment of the first ink is 6 or less, Comparative Examples 1, 2, and 3 in which the pH of the pigment of the second ink is less than 7, Even if the pH was 7 or more, in Comparative Example 4 where the pH of the pigment of the first ink was higher than 6, the show-through was observed because the acid-base interaction was not sufficient. Comparative Examples 5 and 6 are ink sets in which the pH of the pigment of the first ink is 6 or less and the pH of the pigment of the second ink is 7 or more. In this case, an adjustment example in which the polymer ratio to the pigment is high Since the prepared inks 8 and 9 were used, it was not possible to suppress the breakthrough.

  As is clear from the above examples, the ink set of the present invention contains 50% by mass or more of a 5-membered heterocyclic compound having a C═O bond in an organic solvent, so that the content of the polymer component in the ink is a pigment. Even if it is 20% by mass or less, it is possible to achieve both the pigment dispersion stability and the suppression of back-through. In addition, the pH of the pigment of the first ink is 6 or less, and the pigment of the second ink By setting the pH to 7 or more, when the pigments contained in the first ink and the second ink contact on the paper surface, more pigment tends to stay on the paper surface due to acid-base interaction, A printed matter having a high printing density can be obtained.

Claims (5)

  An ink set comprising at least two kinds of inks, wherein both the first ink and the second ink contain at least 50% by mass of a 5-membered heterocyclic compound having a C═O bond in at least a pigment and an organic solvent, The content of the polymer component in the ink is 20% by mass or less of the pigment, the pigment contained in the first ink is pH 6 or less, and the pigment contained in the second ink is pH 7 or more. A non-aqueous ink set characterized by the above.   The non-aqueous ink set according to claim 1, wherein the five-membered heterocyclic compound is at least one selected from a carbonate compound, a lactone compound, an imidazolidinone compound, and a pyrrolidone compound.   The non-aqueous ink set according to claim 1 or 2, wherein the content of the polymer component in the ink is 5% by mass or less of the pigment.   The non-aqueous ink set according to claim 1, wherein the non-aqueous ink set is substantially free of a polymer component.   The content of the five-membered heterocyclic compound is 60 to 97 mass% with respect to the total amount of the first ink and the second ink, respectively. The non-aqueous ink set described.