JP2010094888A - Ink set and inkjet recording method - Google Patents

Abstract

The present invention provides an ink set comprising a reaction liquid excellent in re-dissolvability and the reaction liquid and ink that form an image with high color developability.
SOLUTION: An ink (1) containing an anionic color material, a reaction liquid (2) containing a cationic substance (4) for promoting aggregation of the anionic color material and a water-soluble polymer compound (5). The water-soluble polymer compound has at least a repeating structural unit having monomethyl maleate as a monomer component and a repeating structural unit having vinyl alcohol as a monomer component. It is.
[Selection] Figure 1

Description

  The present invention relates to an ink set and an ink jet recording method suitable for an ink jet printer. In particular, the present invention relates to an ink set and an ink jet recording method effective for plain paper.

Inkjet recording is used as a means for easily forming a high-quality color image, and in recent years, there is an increasing demand for a higher-quality color image. Conventionally, various proposals have been made for the purpose of forming a high-quality color image. For example, for the purpose of improving color developability, a proposal regarding a reaction solution containing a polyvalent metal salt has been made (see Patent Document 1). Moreover, the proposal regarding the reaction liquid containing a polyvalent metal salt and nonionic resin is made | formed with the objective of improving color developability and water resistance (refer patent document 2).
JP-A-10-095941 Japanese Patent Laid-Open No. 11-078211

  The present inventors have also confirmed that the color development is improved when a nonionic resin is added to the reaction solution. However, the demand for higher image quality is increasing year by year. For the purpose of forming a higher quality image than before, droplets of the recording head that ejects ink have been reduced, but depending on the resin added to the reaction liquid, clogging etc. may occur in the nozzle of the recording head. There was a problem that it was easy to wake up. Therefore, it is desired to design a resin having high re-dissolvability so as not to cause clogging while improving the color developability of the recorded image. An object of the present invention is to provide an ink set and an ink jet recording method that solve the above-described problems.

  The present invention is an ink set comprising an ink containing an anionic color material, and a reaction liquid containing a cationic substance that promotes aggregation of the anionic color material and a water-soluble polymer compound, the water-soluble The polymer compound has at least a repeating structural unit represented by the formula (1) and a repeating structural unit represented by the formula (2), and the repeating structural unit represented by the formula (1) is 5 of all repeating structural units. The ink set is characterized by being at least mol%, and the repeating structural unit represented by the formula (2) is at least 60 mol% of all the repeating structural units.

(Z ₁ is any _one of —H, —COOH, and COOCH ₃ .

Z ₂ is any one of —SO ₃ H, —R ₃ —SO ₃ H, —COOH, and —R ₄ —COOH.

R ₁ and R ₂ are any one of a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, and a benzene ring.

R ₃ and R ₄ are any one of an alkyl group having 1 to 5 carbon atoms and a benzene ring. )

  The present invention is also an ink jet recording method using the above ink set.

  By using the ink set of the present invention, the reaction liquid in the ink set can have excellent re-solubility, and clogging and the like can be prevented. In addition, it is possible to provide an ink set for forming an image with excellent color development and an ink jet recording method using the ink set.

  Hereinafter, the present invention will be described in detail with reference to preferred embodiments. The present invention more effectively aggregates color materials on a recording medium by using an ink containing an anionic color material and a reaction liquid containing a water-soluble polymer compound and a cationic substance defined by the present invention. It made it possible.

  The reason why such an effect is manifested is that the present inventor presumes that the following mechanism is manifested on the recording medium.

  Prior to ink application, the reaction liquid is applied onto the recording medium. (FIG. 1 (a)). Here, an ink having an anionic coloring material is applied so as to come into contact with the reaction liquid in a liquid-liquid state. When contacted, the water-soluble polymer compound in the reaction solution is affected by the anionic coloring material, so that the acid component in the water-soluble polymer compound is ionized. (FIG. 1 (b)).

  Since the ionized water-soluble polymer compound exhibits an anionic property, it reacts with a cationic substance that has existed in the reaction solution until then. Since the water-soluble polymer compound becomes unstable when it reacts with a cationic substance, the water-soluble polymer compound present on the recording medium is likely to precipitate. The water-soluble polymer compound deposited on the recording medium can efficiently trap the anionic coloring material on the recording medium. The cationic substance not only functions as a component that destabilizes the water-soluble polymer compound, but also functions as a component that promotes aggregation of the anionic coloring material. Therefore, in the present invention, color development superior to that of the prior art can be obtained by trapping the anionic color material with the water-soluble polymer compound and aggregating the anionic color material itself (FIG. 1 (c)). Here, the destabilization of the water-soluble polymer compound in the present invention does not mean a phenomenon such as gelation of the water-soluble polymer compound by crosslinking or the like, but an anionic water-soluble polymer compound and a cationic substance. This refers to a phenomenon based on the electrostatic interaction. That is, in the present invention, insolubilization of the water-soluble polymer compound due to crosslinking can be suppressed, and the re-solubility of the water-soluble polymer compound can be improved. In the present invention, “on the recording medium” means the surface of the recording medium or the vicinity thereof.

  Next, each component constituting the ink and reaction liquid set according to the present invention will be described, and the present invention will be described in more detail.

<Constituent components of reaction solution>
(Water-soluble polymer compound)
The water-soluble polymer compound contained in the reaction solution of the present invention has a repeating structural unit represented by formula (1) and formula (2). Such a water-soluble polymer compound can be synthesized by a conventionally known method. As a typical synthesis method, for example, a method of combining radical copolymerization and hydrolysis is exemplified. Such a synthesis method is specifically disclosed in JP-A No. 2004-265637.

(Z ₁ is any _one of —H, —COOH, and COOCH ₃ .

Z ₂ is _{-SO 3 H, -R 3 -SO 3} H, -COOH, among -R 4 -COOH, is any one.

R ₁ and R ₂ are any one of a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, and a benzene ring.

R ₃ and R ₄ are any one of an alkyl group having 1 to 5 carbon atoms and a benzene ring. )

Specific examples of the monomer component that forms the repeating structural unit represented by the formula (1) in the water-soluble polymer compound of the present invention include those shown below. Sulfonic acid group-containing monomers such as vinyl sulfonic acid or its salt, allyl sulfonic acid or its salt, methallyl sulfonic acid or its salt, styrene sulfonic acid or its salt; and acrylic acid, methacrylic acid, itaconic acid, monomethyl maleate , Carboxyl group-containing monomers such as crotonic acid and paravinylbenzoic acid. Of these, monomethyl maleate is preferred from the viewpoint of relatively easy synthesis of a polymer having a narrow molecular weight distribution and easy control of the water solubility of the polymer. In addition, the water-soluble polymer compound of the present invention may be any of a block polymer, a random polymer, a graft polymer, and a gradient polymer. The repeating structural unit in the present invention refers to a unit in which the carbon-carbon double bond portion of the monomer component becomes a single bond and the polymerization arm is expanded. That is, when monomethyl maleate is a monomer component that forms a repeating structural unit, the repeating structural unit is represented by R ₁ in formula (1) being H, R ₂ being H, and Z ₁ being COOCH ₃ And indicates that Z ₂ is COOH. In the present invention, the monomer component forming the repeating structural unit represented by the formula (2) refers to vinyl alcohol.

  In the water-soluble polymer compound of the present invention, the ratio of the repeating structural unit represented by the formula (1) is required to be 5 mol% or more of all repeating structural units. In addition, the repeating structural unit represented by the formula (1) is preferably 30 mol% or less of all repeating structural units. Further, in order to sufficiently obtain the hydrophilicity of the water-soluble polymer compound, the repeating structural unit represented by the formula (2) is required to be 60 mol% or more of all repeating structural units. The repeating structural unit represented by the formula (2) is preferably 95 mol% or less of all repeating structural units. Of course, the total number of repeating structural units, which is the total of each repeating structural unit, is 100 mol%.

  As long as the repeating structural unit represented by the formula (1) is 5 mol% or more of all repeating structural units and the repeating structural unit represented by the formula (2) is 60 mol% or more of all repeating structural units, An effect can be obtained. That is, in the present invention, it may be a water-soluble polymer compound having only the repeating structural units represented by the formulas (1) and (2), and the repeating structures represented by the formulas (1) and (2). In addition to the unit, it may be a water-soluble polymer compound containing a repeating structural unit other than the formulas (1) and (2).

  Specific examples of the monomer component forming the repeating structural unit other than those represented by formula (1) and formula (2) include the following. Styrene monomers such as styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-tert-butylstyrene; ethyl acrylate, isopropyl acrylate, acrylic acid-n-propyl, acrylic Acid-n-butyl, acrylate-t-butyl, benzyl acrylate, ethyl methacrylate, isopropyl methacrylate, methacrylate-n-propyl, methacrylate-n-butyl, isobutyl methacrylate, methacrylate-t-butyl, Tridecyl methacrylate, benzyl methacrylate, acrylonitrile, methacrylonitrile, vinyl acetate.

  In particular, it is preferable to have a repeating structural unit having vinyl acetate as a monomer component as a repeating structural unit other than those represented by formulas (1) and (2). In other words, it is preferable to have a repeating structural unit represented by Formula (3). This is because the repeating structural unit represented by the formula (2) is obtained by saponifying the repeating structural unit represented by the formula (3). By controlling the saponification of the repeating structural unit represented by the formula (3), it becomes easy to change the ratio (mol%) of the repeating structural unit represented by the formula (2) with respect to all the repeating structural units.

  In the case of the water-soluble polymer compound as described above, the repeating structural unit represented by the formula (1) is 5 mol% or more and 30 mol% or less of all repeating structural units, and the repeating structural unit represented by the formula (2) is It is preferable that 60 mol% or more and 95 mol% or less of all repeating structural units and the repeating structural unit represented by the formula (3) is 0 mol% or more and 15 mol% or less of all repeating structural units. As described above, in the present invention, since it may be a water-soluble polymer compound having only the repeating structural units represented by the formulas (1) and (2), it is represented by the formula (3) for all repeating structural units. It is not excluded that the ratio of the repeating structural unit is 0%.

  The composition ratio of the monomer units in the water-soluble polymer compound can be calculated using an analyzer such as NMR. The molecular weight can be measured by GPC analysis. The molecular weight of the water-soluble polymer compound is preferably 5000 to 100,000 in terms of weight average molecular weight. Furthermore, 10,000 or more and 50000 or less are preferable. In order to sufficiently obtain the effects of the present invention, the amount of the water-soluble polymer compound added to the reaction solution is preferably 0.1% by mass or more. Further, from the viewpoint of adjusting the viscosity of the reaction solution, the addition amount is preferably 10% by mass or less. The addition amount of the water-soluble polymer compound is more preferably 0.5% by mass or more and 5% by mass or less.

(Cationic substance)
The reaction liquid of the present invention is required to contain a cationic substance that insolubilizes or aggregates the coloring material in the ink. Examples of the cationic substance include cationic polymers, polyvalent metal ions, and salts thereof. Of these, polyvalent metal ions are preferred, and the viscosity increase is relatively small when used with the aqueous water-soluble polymer compound of the present invention.

(Polyvalent metal ions and their salts)
Specific examples of the polyvalent metal ions that can be used in the reaction solution include divalent metal ions such as Ca ²⁺ , Cu ²⁺ , Ni ²⁺ , Mg ²⁺ , Zn ^2+, and Ba ²⁺ , Al ³⁺ , And trivalent metal ions such as Fe ³⁺ , Cr ³⁺ , and Y ³⁺ . The salt is a polyvalent metal salt composed of the polyvalent metal ions and the anions bonded to these polyvalent metal ions as mentioned above, but is soluble in water. It is required to be. Examples of the anion for forming a salt include SO ₄ ²⁻ , Cl ⁻ , CO ₃ ²⁻ , NO ₃ ⁻ , I ⁻ , Br ⁻ , ClO ₃ ^−, CH ₃ COO ⁻ , HCOO ^{− and the} like. Of course, the present invention is not limited to the above compounds.

  When polyvalent metal ions are used as the cationic substance, the content of polyvalent metal ions in the reaction solution is preferably 0.01% by mass or more and 10% by mass or less. In addition, when a polyvalent metal ion is used as the cationic substance, the content of the polyvalent metal salt in the reaction solution may be 0.01% by mass or more and 20% by mass or less considering the effect of the present invention. preferable. More preferably, it is 10 mass% or more and 15 mass% or less. The reaction solution preferably contains no coloring material and is transparent, but does not necessarily have to exhibit no absorption in the visible region. That is, even if absorption is shown in the visible range, absorption may be shown in the visible range as long as it does not affect the image.

(Cationic polymer)
Specific examples of the cationic polymer that can be used in the reaction solution include polyallylamine hydrochloride, polyaminesulfone hydrochloride, polyvinylamine hydrochloride, chitosan acetate, and the like. Other than these, a copolymer of vinylpyrrolidone and aminoalkyl alkylate quaternary salt obtained by cationizing a part of a nonionic polymer substance, a copolymer of acrylamide and aminomethylacrylamide quaternary salt, etc. Can be mentioned. Moreover, it is preferable that content of a cationic substance is 0.1 to 20 mass% with respect to the reaction liquid whole quantity.

(Aqueous medium)
Examples of the aqueous medium that can be used for the reaction liquid include water or a mixed solvent of water and a water-soluble organic solvent. As the water-soluble organic solvent, those having an effect of preventing the reaction solution from drying are particularly preferable. Specifically, for example, alkyl alcohols having 1 to 4 carbon atoms such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol; dimethylformamide, Amides such as dimethylacetamide; Ketones or ketoalcohols such as acetone and diacetone alcohol; Ethers such as tetrahydrofuran and dioxane; Polyalkylene glycols such as polyethylene glycol and polypropylene glycol; Ethylene glycol, propylene glycol, butylene glycol, tri 2 to 6 alkylene groups such as ethylene glycol, 1,2,6-hexanetriol, thiodiglycol, hexylene glycol and diethylene glycol Alkylene glycols containing 5 carbon atoms; lower alkyl ether acetates such as polyethylene glycol monomethyl ether acetate; glycerin; ethylene glycol monomethyl (or ethyl) ether, diethylene glycol methyl (or ethyl) ether, triethylene glycol monomethyl (or ethyl) ether, etc. Lower alkyl ethers of polyhydric alcohols; polyhydric alcohols such as trimethylolpropane and trimethylolethane; N-methyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone and the like. . The water is preferably deionized water.

  The content of the water-soluble organic solvent as described above is not particularly limited, but is preferably 3% by mass or more and 50% by mass or less with respect to the total amount of the reaction solution. The water content is preferably 50% by mass or more and 95% by mass or less based on the total amount of the reaction solution. Furthermore, in addition to the above components, surfactants, antifoaming agents, preservatives, antifungal agents and the like may be added as necessary.

  The pH of the reaction solution of the present invention is preferably adjusted to less than 7.0. The water-soluble polymer compound of the present invention does not ionize in an acidic pH environment and hardly reacts with a cationic substance, so that the water-soluble polymer compound and the cationic substance coexist stably in the reaction solution. can do. Moreover, it is more preferable if the reaction solution is prepared at pH 5.0 or more and less than 7.0.

<Constituent components of ink>
(Coloring material)
Examples of the color material that can be used in the water-based ink of the present invention include an anionic color material. In the present invention, the anionic coloring material is a coloring material that exhibits anionicity when added to ink. Specific examples include an anionic dye, a pigment having an anionic group chemically bonded to the surface, and a pigment dispersed with an anionic dispersant. Further, a microencapsulated pigment or a colored resin may be used as long as it is an anionic color material in the ink.

  Further, the content of the color material in the ink is preferably in the range of 1% by mass to 50% by mass with respect to the total amount of the ink, and more preferably in the range of 1% by mass to 10% by mass. preferable. In the present invention, the pigment dispersed with the anionic dispersant refers to a dispersion containing both the anionic dispersant and the pigment. Hereinafter, these color materials will be described in detail.

(Pigment)
Examples of the pigment that can be used in the present invention include carbon black and organic pigments.

  Examples of the carbon black include carbon black pigments such as furnace black, lamp black, acetylene black, and channel black. For example, Raven 7000, Ray Van 5750, Ray Van 5250, Ray Van 5000, Ray Van 3500, Ray Van 2000, and Ray Van 1500. , Ray Van 1250, Ray Van 1200, Ray Van 1190 ULTRA-II, Ray Van 1170, Ray Van 1255 (made by Columbia), Black Pearls L, Legal 400R, Legal 330R, Legal 660R, Mogul L, Monak (Monarch) 700, Monak 800, Monak 880, Monak 900, Monak 1000, Nak 1100, Monak 1300, Monak 1400, Vulcan XC-72R (manufactured by Cabot), Color Black FW1, Color Black FW2, Color Black FW2V, Color Black FW18, Color Black FW200, Color Black S150, Color Black S160, Color Black S170, Printex 35, Printex U, Printex V, Printex 140U, Printex 140V, Special Black 6, Special Black 5, Special Black 4A, Special Black 4 ( Degussa), No. 25, no. 33, no. 40, no. 47, no. 52, no. 900, no. 2300, MCF-88, MA600, MA7, MA8, MA100 (manufactured by Mitsubishi Chemical Co., Ltd.) and the like, but are not limited thereto, and conventionally known carbon black can be used. . In addition, magnetic fine particles such as magnetite and ferrite, titanium black and the like can be used as the black pigment.

  Examples of organic pigments include insoluble azo pigments such as toluidine red, toluidine maroon, Hansa yellow, benzidine yellow, and pyrazolone red, soluble azo pigments such as ritole red, heliobordeaux, pigment scarlet, and permanent red 2B, alizarin, and indanthrone. Derivatives from vat dyes such as thioindigo maroon, phthalocyanine pigments such as phthalocyanine blue and phthalocyanine green, quinacridone pigments such as quinacridone red and quinacridone magenta, perylene pigments such as perylene red and perylene scarlet, isoindolinone yellow , Isoindolinone pigments such as isoindolinone orange, imidazoles such as benzimidazolone yellow, benzimidazolone orange and benzimidazolone red Pigments, pyranthrone pigments such as pyranthrone red, pyranthrone orange, thioindigo pigments, condensed azo pigments, thioindigo pigments, flavanthrone yellow, acylamide yellow, quinophthalone yellow, nickel azo yellow, copper azomethine yellow, peri Other pigments such as non-orange, anthrone orange, dianslaquinonyl red, dioxazine violet and the like can be mentioned.

  Further, when the organic pigment is represented by a color index (CI) number, C.I. I. Pigment Yellow 12, 13, 14, 17, 20, 24, 74, 83, 86, 93, 109, 110, 117, 120, 125, 128, 137, 138, 147, 148, 151, 153, 154, 166, 168, C.I. I. Pigment orange 16, 36, 43, 51, 55, 59, 61, C.I. I. Pigment Red 9, 48, 49, 52, 53, 57, 97, 122, 123, 149, 168, 175, 176, 177, 180, 192, 215, 216, 217, 220, 223, 224, 226, 227, 228, 238, 240, C.I. I. Pigment violet 19, 23, 29, 30, 37, 40, 50, C.I. I. Pigment blue 15, 15: 3, 15: 1, 15: 4, 15: 6, 22, 60, 64, C.I. I. Pigment green 7, 36, C.I. I. Examples thereof include CI Pigment Brown 23, 25, 26, and the like. Of course, conventionally known organic pigments other than those described above can be used.

(Anionic dispersant)
Examples of the anionic dispersant for dispersing the pigment that can be used in the present invention include a copolymer having an anionic group. Specifically, for example, styrene-acrylic acid copolymer, styrene-acrylic acid-acrylic acid alkyl ester copolymer, styrene-maleic acid copolymer, styrene-maleic acid-acrylic acid alkyl ester copolymer, styrene. -Methacrylic acid copolymer, styrene-methacrylic acid-acrylic acid alkyl ester copolymer, styrene-maleic acid half ester copolymer, vinylnaphthalene-acrylic acid copolymer, vinylnaphthalene-maleic acid copolymer, styrene- Examples thereof include maleic anhydride-maleic acid half ester copolymers or salts thereof.

  These dispersants are preferably those having a weight average molecular weight in the range of 1,000 to 30,000, and particularly preferably in the range of 3,000 to 15,000. The mass ratio of pigment to dispersant in the ink (pigment: dispersant) is preferably 1:10 to 10: 1.

(Pigments with anionic groups chemically bonded to the surface)
As the anionic coloring material of the present invention, a pigment having an anionic group chemically bonded to the surface, a so-called self-dispersing pigment can also be used. The self-dispersing pigment can be obtained by oxidizing the above-described pigment or introducing a hydrophilic substituent on the surface. Specific examples include those in which an anionic group is bonded to the surface of carbon black (anionic CB). Hereinafter, an anionic carbon black will be described as an example.

(Anionic CB)
The anionic carbon black is selected from the group consisting of —COO (M2), —SO ₃ (M2), —PO ₃ H (M2), —PO ₃ (M2) _{2 on} the surface of the carbon black, Examples include those having at least one anionic group bonded thereto. M2 described in the above group represents a hydrogen atom, an alkali metal, ammonium, or organic ammonium. Among these, carbon black obtained by bonding —COO (M2) or —SO ₃ (M2) to the carbon black surface and anionicly charged is preferable because of its excellent dispersibility in the ink.

  Of the M2, specific examples of the alkali metal include Li, Na, K, Rb and Cs. Specific examples of organic ammonium include methyl ammonium, dimethyl ammonium, trimethyl ammonium, ethyl ammonium, diethyl ammonium, triethyl ammonium, methanol ammonium, dimethanol ammonium, and trimethanol ammonium. When M2 is ammonium or organic ammonium, the water resistance of the recorded image is further improved, which is preferable.

  Examples of the method for producing self-dispersing carbon black in which M2 is ammonium include the following. For example, self-dispersing carbon black in which M2 is an alkali metal is replaced with ammonium using an ion exchange method, M2 is converted to a hydrogen atom by adding an acid, and then ammonium hydroxide is added to convert M2 to ammonium. And the like.

  Examples of the method for producing anionic carbon black include a method of oxidizing carbon black with sodium hypochlorite. For example, this method can chemically bond —COONa groups to the surface of carbon black.

Even if the anionic group described above is directly bonded to the surface of the carbon black, other atomic groups are interposed between the surface of the carbon black and the anionic group, and the anionic group is indirectly attached to the surface of the carbon black. It may be combined with. Here, specific examples of the other atomic group include, for example, a linear or branched alkylene group having 1 to 12 carbon atoms, a substituted or unsubstituted phenylene group, and a substituted or unsubstituted naphthylene group. . Moreover, as a substituent of a phenylene group and a naphthylene group, a C1-C6 linear or branched alkyl group is mentioned, for example. Specific examples of combinations of other atomic groups and anionic groups include, for example, —C ₂ H ₄ COO (M2), —Ph—SO ₃ (M2), —Ph—COO (M2) and the like ( However, Ph represents a phenyl group).

(Colored fine particles / microencapsulated pigment)
In addition to the color materials described above, pigments microencapsulated with a polymer or the like, or colored fine particles in which resin particles are coated with a color material can be used. When used as a microencapsulated pigment anionic colorant, it is preferable to use the above-described pigment and an anionic dispersant.

(Aqueous medium)
The aqueous medium that can be used in the ink of the present invention is not particularly limited, and the same aqueous media as described above can be used as the aqueous medium that can be used in the reaction liquid. The contents of the water-soluble organic solvent and water in the ink of the present invention are not particularly limited, but the amount of the water-soluble organic solvent relative to the total amount of the ink is preferably 3% by mass or more and 50% by mass or less. The amount of water relative to the total amount of ink is preferably 50% by mass or more and 95% by mass or less.

  Further, in order to make the role of the anionic coloring material in the ink destabilizing the water-soluble polymer compound in contact with the reaction liquid more effectively, the ink of the present invention has a pH of 7. It is preferable to adjust to 0 or more. The specific pH range is preferably pH 7.0 or more and pH 10.0 or less, and more preferably pH 9.0 or more and pH 10.0 or less.

  In addition, when the reaction liquid and the ink of the present invention are mixed at a mass ratio of reaction liquid: ink = 1: 4 and the pH of the liquid mixture becomes 7.0 or more, the ink and the reaction liquid come into contact with each other. It is preferable because destabilization of the water-soluble polymer compound can be promoted. For the purpose of setting the pH of the mixed solution to 7.0 or more, a substance having a buffering action against pH in an alkaline region may be added to the ink of the present invention. Such a buffering action can be obtained by adding an appropriate amount of a substance such as dipotassium hydrogen phosphate or boric acid to the ink together with a strong alkaline substance such as sodium hydroxide or potassium hydroxide. In addition to the above components, the ink of the present invention may further contain a humectant, a surfactant, an antifoaming agent, an antiseptic, an antifungal agent, and the like as necessary.

(Ink set)
The color of the ink in the case of constituting the ink and reaction liquid set of the present invention is not particularly limited, and for example, it is an ink showing one color tone selected from yellow, magenta, cyan, red, green, blue and black. That's fine. Further, the ink combined with the reaction liquid is not limited to one type, and two or more different color inks may be combined to form an ink set suitable for forming a multicolor image. In this case, at least one of the two or more inks may react with the reaction liquid. Of course, all the inks constituting the ink set may be inks that react with the reaction liquid. With such an ink set, bleeding that occurs when inks of different colors are applied adjacently on the recording medium can be suppressed. More specifically, bleeding that is a problem in an inkjet multicolor image is at least one selected from black ink and other color inks (for example, yellow ink, magenta ink, cyan ink, red ink, green ink, and blue ink). In the present invention, at least black ink is preferably configured as ink that reacts with the reaction liquid.

(Image forming method)
The image forming method of the present invention includes at least a step of applying ink onto a recording medium and a step of applying a reaction liquid onto the recording medium. Further, in the above step, it is required to apply the ink and the reaction liquid so that the ink and the reaction liquid come into contact with each other in a liquid-liquid state on the recording medium. With such a configuration, it is possible to form an image with high color developability. When applying the reaction liquid and the ink on the recording medium, it is preferable to apply the ink to at least the area of the recording medium to which the reaction liquid is applied, and the ink is applied to the area of the recording medium to which the reaction liquid is applied. More preferably.

  In the step of applying the ink and the reaction liquid of the present invention, the method for applying the ink and the reaction liquid onto the recording medium may be any method. Specifically, an ink jet recording method can be used for the ink and the reaction liquid. The inkjet recording method is preferable because the reaction liquid can be applied only to the ink application position. However, the present invention is not limited to this, and the reaction solution may be applied by a known method such as roll coating.

  In the present invention, the order of applying the ink and the reaction liquid is not particularly limited. Specifically, the ink may be applied after the reaction liquid is applied, or the reaction liquid may be applied after the ink is applied. In addition, the reaction liquid may be applied after ink is applied, and further ink may be applied. After the reaction liquid is applied, ink may be applied, and further the reaction liquid may be applied.

The amount of ink applied on the recording medium is preferably 1 g / m ² or more and 20 g / m ² or less. Further, the amount of the reaction solution applied on the recording medium is preferably 1 g / m ² or more and 20 g / m ² or less, more preferably 2 g / m ² or more and 5 g / m ² or less.

  Hereinafter, although it demonstrates more concretely using an Example and a comparative example, this invention is not limited by the following Example, unless the summary is exceeded. Unless otherwise specified, “%” and “part” mean “% by mass” and “part by mass”. In the examples, AIBN refers to azobisisobutyronitrile.

<Synthesis of water-soluble polymer compound 1>
A reactor equipped with a stirrer, reflux condenser, nitrogen inlet tube, thermometer, and pressure gauge was purged with nitrogen, and then deoxygenated 1500 parts by weight of vinyl acetate monomer, 800 parts by weight of monomethyl maleate, and 1000 parts by weight of methanol were charged. . Thereafter, the temperature was raised under stirring, and when the internal temperature reached 60 ° C., a solution in which 2 parts by mass of AIBN was dissolved as an initiator in 50 parts by mass of methanol was gradually added dropwise to initiate polymerization. After polymerization at 60 ° C. for 4 hours, the polymerization was stopped by cooling. 18 parts by mass of 2% sodium hydroxide-methanol solution was added to 1000 parts by mass of the polyvinyl acetate resin-methanol solution obtained by polymerization, and the mixture was mixed well and allowed to stand at 40 ° C. for 1 hour. The gel obtained after saponification was purified several times with a large amount of water and then dried with a blow dryer at 60 ° C. to obtain the water-soluble polymer compound 1 (polyvinyl alcohol-monomethyl maleate copolymer) of the present invention. It was. As a result of GPC measurement, the weight average molecular weight was 30,000. This water-soluble polymer compound 1 was dissolved in water to obtain a 10% aqueous solution. Table 1 shows the repeating structural units possessed by the water-soluble polymer compound 1.

<Synthesis of water-soluble polymer compound 2>
A reactor equipped with a stirrer, reflux condenser, nitrogen inlet tube, thermometer, and pressure gauge was purged with nitrogen, and then deoxygenated 1500 parts by weight of vinyl acetate monomer, 800 parts by weight of monomethyl maleate, and 1000 parts by weight of methanol were charged. . Thereafter, the temperature was raised under stirring, and when the internal temperature reached 60 ° C., separately, a solution in which 2 parts by mass of AIBN was dissolved as an initiator in 50 parts by mass of methanol was gradually added dropwise to initiate polymerization. After polymerization at 60 ° C. for 4 hours, the polymerization was stopped by cooling. 10 parts by mass of 2% sodium hydroxide-methanol solution was added to 1000 parts by mass of the polyvinyl acetate resin-methanol solution obtained by polymerization, and the mixture was mixed well and allowed to stand at 40 ° C. for 1 hour. The gel obtained after saponification is purified several times with a large amount of water and then dried with a blow dryer at 60 ° C. to obtain the water-soluble polymer compound 2 (polyvinyl alcohol-monomethyl maleate copolymer) of the present invention. It was. As a result of GPC measurement, the weight average molecular weight was 30,000. This water-soluble polymer compound 2 was dissolved in water to obtain a 10% aqueous solution. The repeating structural units possessed by the water-soluble polymer compound 2 are shown in Table 1.

<Synthesis of water-soluble polymer compound 3>
A reactor equipped with a stirrer, reflux condenser, nitrogen inlet tube, thermometer, and pressure gauge was purged with nitrogen, and then deoxygenated vinyl acetate monomer 2500 parts by mass and methanol 1000 parts by mass were charged. Thereafter, the temperature was raised under stirring, and when the internal temperature reached 60 ° C., separately, a solution in which 2 parts by mass of AIBN was dissolved as an initiator in 50 parts by mass of methanol was gradually added dropwise to initiate polymerization. After polymerization at 60 ° C. for 4 hours, the polymerization was stopped by cooling. 10 parts by weight of 2% sodium hydroxide-methanol solution was added to 1000 parts by weight of the polyvinyl acetate resin-methanol solution obtained by polymerization, and the mixture was mixed well and allowed to stand at 40 ° C. for 1 hour. The gel obtained after saponification was purified several times with a large amount of water, and then dried with a blow dryer at 60 ° C. to obtain a water-soluble polymer compound 3. As a result of GPC measurement, the weight average molecular weight was 30,000. This water-soluble polymer compound 3 was dissolved in water to obtain a 10% aqueous solution. The repeating structural units possessed by the water-soluble polymer compound 3 are shown in Table 1.

<Preparation of reaction solution>
The following components were mixed, sufficiently stirred and dissolved, and then filtered under pressure with a microfilter (manufactured by Fuji Film) having a pore size of 0.2 μm to prepare reaction solutions 1 to 4. As the acetylene glycol ethylene oxide adduct (surfactant) used in each reaction solution, acetylenol E100 (trade name, manufactured by Kawaken Fine Chemical Co., Ltd.) was used.

(Reaction solution 1)
・ Calcium nitrate tetrahydrate 10% by mass
-10% aqueous solution of 10% water-soluble polymer compound 1
・ Glycerin 10% by mass
・ Acetylene glycol ethylene oxide adduct 0.2% by mass
・ Remaining amount of water (69.8% by mass)
(Reaction solution 2)
・ Calcium nitrate tetrahydrate 10% by mass
-10% aqueous solution of 10% water-soluble polymer compound 2
・ Glycerin 10% by mass
・ Acetylene glycol ethylene oxide adduct 0.2% by mass
・ Remaining amount of water (69.8% by mass)
(Reaction solution 3)
・ Calcium nitrate tetrahydrate 10% by mass
-10% aqueous solution of 10% water-soluble polymer compound 3
・ Glycerin 10% by mass
・ Acetylene glycol ethylene oxide adduct 0.2% by mass
・ Remaining amount of water (69.8% by mass)
(Reaction solution 4)
・ Calcium nitrate tetrahydrate 10% by mass
・ Glycerin 10% by mass
・ Acetylene glycol ethylene oxide adduct 0.2% by mass
・ Remaining amount of water (79.8% by mass)
<Preparation of ink>
10 parts of pigment [# 990 (manufactured by Mitsubishi Chemical Corporation)], 80 parts of an anionic dispersant, and 10 parts of pure water were mixed. The anionic dispersant is a 10% by mass aqueous resin solution obtained by neutralizing a styrene-acrylic acid copolymer having an acid value of 150 mg / KOH and having a weight average molecular weight of 11,000 with 1 equivalent of potassium hydroxide. . The materials shown below were charged into a batch type vertical sand mill (manufactured by IMEX), filled with 150 parts of 0.3 mm diameter zirconia beads, and dispersed for 5 hours while cooling with water. Further, this dispersion was centrifuged to remove coarse particles. As a final preparation, a pigment dispersion Bk1 having a solid content of about 18% by mass and a weight average particle size of 100 nm was obtained. Using the obtained pigment dispersion Bk1, Bk ink 1 and Bk ink 2 were prepared as follows.

(Bk ink 1)
The following components were mixed, sufficiently stirred and dissolved / dispersed, followed by pressure filtration with a microfilter (manufactured by Fuji Film) having a pore size of 3.0 μm to prepare Bk ink 1.
-Pigment dispersion Bk1 obtained above 30% by mass
・ Glycerin 10% by mass
・ Acetylene glycol ethylene oxide adduct 1% by mass
・ Remaining amount of water (59% by mass)
(Bk ink 2)
The following components were mixed, sufficiently stirred and dissolved / dispersed, followed by pressure filtration with a microfilter having a pore size of 3.0 μm (manufactured by Fuji Film) to prepare Bk ink 2.
-Dispersion Bk1 30% by mass
・ 10% by mass of 10% aqueous solution of water-soluble polymer compound 1
・ Glycerin 10% by mass
・ Acetylene glycol ethylene oxide adduct 1% by mass
・ Remaining amount of water (49% by mass)
Table 2 shows the physical properties of the ink and the reaction liquid and the pH when the ink and the reaction liquid are mixed.

<Evaluation of re-solubility of reaction solution>
The reaction liquids 1 to 4 were weighed 5 g at a petri dish and left in an oven set at 60 ° C. for 24 hours. After 24 hours, the petri dish was taken out of the oven, and 5 g of each reaction solution was again measured and added to the petri dish containing each reaction solution. The resolvability of the reaction solution was evaluated by putting a stir bar in each petri dish and stirring with a magnetic stirrer. The evaluation criteria are as follows. The results are shown in Table 3.
A: Redissolved within 10 minutes.
○: Redissolved for more than 10 minutes within 1 hour.
X: Not re-dissolved even after 1 hour.

<Evaluation of color development of ink set>
A solid image of 3 cm × 3 cm was formed using the ink jet recording apparatus BJF900 (manufactured by Canon Inc.) with the combination of Bk ink 1, Bk ink 2 and reaction liquids 1 to 4 shown in Table 4 below. At this time, printing was performed so that the reaction liquid was first applied to the recording medium, and printing was performed so as to apply Bk ink 1 by simultaneous scanning. The applied amount on the recording medium was adjusted so that the reaction liquid was 2.4 g / m ^{2 in} all cases and the Bk ink 1 was 10 g / m ² . Canon office paper (manufactured by Canon Inc.) was used as the recording medium. The optical density (OD value) of the obtained solid image was measured with RD-918 (manufactured by Macbeth). The evaluation results are shown in Table 3.

It is the figure which showed typically the mode on the recording medium of the ink set in embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ink 2 Reaction liquid 3 Recording medium 4 Cationic substance 5 Water-soluble polymer compound

Claims (9)

An ink set comprising: an ink containing an anionic color material; and a reaction liquid containing a cationic substance that promotes aggregation of the anionic color material and a water-soluble polymer compound,
The water-soluble polymer compound has at least a repeating structural unit represented by the formula (1) and a repeating structural unit represented by the formula (2), and the repeating structural unit represented by the formula (1) is an all repeating structure. An ink set comprising: 5 mol% or more of units, and the repeating structural unit represented by the formula (2) is 60 mol% or more of all repeating structural units.

(Z ₁ is any _one of —H, —COOH, COOCH ₃ —SO ₃ H, —R ₃ —SO ₃ H, and —R ₄ —COOH.
Z ₂ is any one of —SO ₃ H, —R ₃ —SO ₃ H, —COOH, and —R ₄ —COOH.
R ₁ and R ₂ are any one of a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, and a benzene ring.
R ₃ and R ₄ are any one of an alkyl group having 1 to 5 carbon atoms and a benzene ring. )

The ink set according to claim 1, wherein the water-soluble polymer compound further has a repeating structural unit represented by the formula (3).

The water-soluble polymer compound is composed of a repeating structural unit represented by the formula (1), a repeating structural unit represented by the formula (2), and a repeating structural unit represented by the formula (3).
The repeating structural unit represented by the formula (1) is 5 mol% or more and 30 mol% or less of all repeating structural units, and the repeating structural unit represented by the formula (2) is 60 mol% or more and 95 mol% of all repeating structural units. The ink set according to claim 2, wherein the repeating structural unit represented by the formula (3) is 0 mol% or more and 15 mol% or less of all repeating structural units.   The ink set according to any one of claims 1 to 3, wherein the anionic colorant is a pigment in which an anionic group is chemically bonded to a surface or a pigment dispersed by an anionic dispersant.   The ink set according to claim 1, wherein the cationic substance is a polyvalent metal ion.   The pH of the mixed solution in which the pH of the ink is 7.0 or more, the pH of the reaction solution is less than 7.0, and the ink and the reaction solution are mixed at a mass ratio of 4: 1. The ink set according to claim 1, wherein the ink set is 7.0 or more. The ink set according to claim 1, wherein R ₁ in the formula (1) is H, R ₂ is H, Z ₁ is COOCH ₃ , and Z ₂ is COOH. .   An ink jet recording method using the ink set according to claim 1, wherein the ink and the reaction liquid are applied to a recording medium.   9. The ink jet recording method according to claim 8, wherein after the reaction liquid is applied on the recording medium, the ink is applied to a region where the reaction liquid is applied on the recording medium.

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