JP2010248420A - Ink, water-based ink set for inkjet recording, and method for inkjet recording - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide ink having properties to aggregate other ink to form an image improved in the indistinctness of an outline and a color bleeding and improved in printing density, having excellent discharge stability. <P>SOLUTION: The ink includes at least a polyvalent metal salt, a water-insoluble color material and a block polymer, wherein the block polymer is that having a hydrophobic unit, a nonionic hydrophilic unit, and an ionic hydrophilic unit. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an ink having a property of aggregating another ink by contacting and reacting with the other ink, an aqueous ink set for ink jet recording composed of the ink, and an ink jet recording method using the set. .

  The ink jet recording method has the following problems because the ink is liquid. That is, when ink lands on a recording medium such as plain paper, ink droplets permeate into the recording medium, the outline becomes unclear, and the border between adjacent different colors blurs ( A phenomenon such as so-called color bleed) has been observed.

  In order to solve these problems, a method of applying an ink containing a dye having at least one carboxyl group after applying a polyvalent metal salt solution to a recording medium has been proposed (see Patent Document 1). . That is, according to this method, an insoluble material is formed by contacting a reaction liquid containing a polyvalent metal ion and a dye capable of reacting with the polyvalent metal ion with a recording medium. As a result, the ambiguity of the outline is improved, color bleeding does not occur, and a high-quality image with excellent anti-through-through resistance can be obtained.

  In addition, by using a combination of a black ink that thickens or aggregates due to the action of salt and a color ink containing the salt, a high-quality color image with high image density and no color bleeding can be obtained. Means are also disclosed (see Patent Document 2). That is, it is possible to obtain a good image by printing two liquids of the first liquid containing salt and the ink.

JP-A-5-202328 JP-A-6-106735

  However, when the above-described techniques are used, the print density of the printed matter is improved and the color bleed is improved. On the other hand, the ejection stability of the ink and reaction liquid used in these techniques is still insufficient. However, it was not possible to say that both characteristics were combined. That is, from the viewpoint of achieving both the reactivity of the ink and the reaction liquid on the paper surface and the ejection stability, the ink set used in the ink jet recording method is insufficient. Further, conventionally, it has been difficult to realize that an ink containing a pigment as a colorant further contains a polyvalent metal ion because the ink itself aggregates.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and its purpose is to have the property of aggregating other inks in order to form an image in which the ambiguity of the contour portion and color bleeding are improved and the print density is improved. It is to provide an ink having excellent ejection stability. Also, an object of the present invention is an aqueous ink jet recording ink capable of forming an excellent image as described above, comprising the first ink as the ink and the second ink aggregated by the first ink. To provide an ink set. Another object of the present invention is to provide an ink jet recording method using the ink set and a recorded matter obtained by the ink jet recording method.

  The above object is achieved by the present invention described below. That is, the first of the present invention contains at least a polyvalent metal salt, a water-insoluble colorant, and a block polymer, and the block polymer has a hydrophobic unit, a nonionic hydrophilic unit, and an ionic property. It is an ink characterized by having a hydrophilic unit.

  A second aspect of the present invention is an ink set comprising a combination of a plurality of inks having at least one or more of the inks of the present invention as the first ink, and containing at least a water-insoluble colorant and an anion. A water-based ink set for ink-jet recording, comprising a second ink containing a component.

  In the third aspect of the present invention, in the ink jet recording method for recording on a recording medium using an ink set comprising a combination of at least a plurality of colors of ink, the ink jet recording aqueous ink set of the present invention is used as the ink set. A first ink and a second ink constituting the water base ink set for ink jet recording are applied to a recording medium to cause the second ink to aggregate.

  According to the present invention, it is possible to provide an ink having excellent ejection stability that forms an image with improved print density by improving the ambiguity of the outline and color bleeding by aggregating other inks. Further, according to the present invention, the ink is composed of the first non-ionic strong ink and the strong second ionic ink, and can perform excellent image formation as described above. An aqueous ink set is provided. The present invention also provides an ink jet recording method using the ink set.

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments of the present invention.
The ink of the present invention contains at least a polyvalent metal salt, a water-insoluble colorant, and a block polymer, and the block polymer includes a hydrophobic unit, a nonionic hydrophilic unit, and an ionic hydrophilic property. It has a unit. The ink of the present invention (sometimes referred to as the first ink) includes an aqueous ink set for inkjet recording (hereinafter simply referred to as an ink set) together with a second ink containing at least a water-insoluble colorant and containing an anionic component. ) Can be used. Since the first ink contains a polyvalent metal salt, the metal cation reacts with the anion component in the second ink to aggregate the second ink. Thereby, the ambiguity of the outline portion and the color bleed are improved, and an image having an improved printing density is formed. On the other hand, although the first ink contains a polyvalent metal salt, since the water-insoluble colorant is formed in a microcapsule state by a block polymer, it is stably ejected in ink jet recording.

[ink]
In the following, ink components such as the water-insoluble colorant, the block polymer, and the solvent that are contained in the first ink and the second ink, respectively, and the polyvalent metal salt that is contained only in the first ink. However, the present invention is not limited to these.

(Water-insoluble colorant)
In the present invention, a pigment will be described as a water-insoluble colorant, but the present invention is not limited to this. Specific examples of the pigment include preferably a black pigment and three primary color pigments of cyan, magenta, and yellow. Color pigments other than those described above, colorless or light color pigments, metallic luster pigments, and the like may be used. In addition, a newly synthesized pigment may be used for the present invention.

Examples of commercially available pigments for black, cyan, magenta, and yellow are shown below.
Raven1060, Raven1080, Raven1170, Raven1200, Raven1250, Raven1255, Raven1500, Raven2000, Raven3500, Raven5250, Raven5750, Raven7000, Raven5000, Raven5000, Raven5000, Raven5000, Raven5000, Raven5000, Raven5000, Raven5000, Raven5000 MOGUL-L, Regal 400R, Regal 660R, Regal 330R, Monarch 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1300, Monarch 1400 (above, manufactured by Cabot), Color Black FW1, Color Black FW2, Color Black FW200, Color Black 18, Color Black S160, Color Black S170, Special Black 4, Special Vr, ExP, 35P 25, no. 33, no. 40, no. 47, no. 52, no. 900, no. 2300, MCF-88, MA600, MA7, MA8, MA100 (above, manufactured by Mitsubishi Chemical Corporation) and the like can be mentioned, but are not limited thereto.

  Examples of cyan pigments include C.I. I. Pigment Blue-1, C.I. I. Pigment Blue-2, C.I. I. Pigment Blue-3, C.I. I. Pigment Blue-15, C.I. I. Pigment Blue-15: 2, C.I. I. Pigment Blue-15: 3, C.I. I. Pigment Blue-15: 4, C.I. I. Pigment Blue-16, C.I. I. Pigment Blue-22, C.I. I. Pigment Blue-60 and the like, but are not limited thereto.

  Examples of magenta pigments include C.I. I. Pigment Red-5, C.I. I. Pigment Red-7, C.I. I. Pigment Red-12, C.I. I. Pigment Red-48, C.I. I. Pigment Red-48: 1, C.I. I. Pigment Red-57, C.I. I. Pigment Red-112, C.I. I. Pigment Red-122, C.I. I. Pigment Red-123, C.I. I. Pigment Red-146, C.I. I. Pigment Red-168, C.I. I. Pigment Red-184, C.I. I. Pigment Red-202, C.I. I. Pigment Red-207 and the like, but are not limited thereto.

  Examples of yellow pigments include C.I. I. Pigment Yellow-12, C.I. I. Pigment Yellow-13, C.I. I. Pigment Yellow-14, C.I. I. Pigment Yellow-16, C.I. I. Pigment Yellow-17, C.I. I. Pigment Yellow-74, C.I. I. Pigment Yellow-83, C.I. I. Pigment Yellow-93, C.I. I. Pigment Yellow-95, C.I. I. Pigment Yellow-97, C.I. I. Pigment Yellow-98, C.I. I. Pigment Yellow-114, C.I. I. Pigment Yellow-128, C.I. I. Pigment Yellow-129, C.I. I. Pigment Yellow-151, C.I. I. Pigment Yellow-154 and the like, but are not limited thereto.

(Block polymer)
Next, the block polymer used in the present invention will be described. The polymers contained in each of the first ink and the second ink have different functionally desirable forms. However, in the unit structure constituting the block polymer in the first ink and the second ink, the same kind of polymer is contained. A monomer component may be contained. The block polymer is a copolymer in which polymer segments (units) having different repeating unit structures are bonded by a covalent bond, and is also referred to as a block copolymer or a block copolymer.

  In the present invention, the block polymer contained in the first ink has a hydrophobic unit, a nonionic hydrophilic unit, and an ionic hydrophilic unit. Thereby, the pigment can be made into a microcapsule state in the first ink, and stable ink ejection is realized in the ink jet recording. Further, in order to prevent the first ink itself from being aggregated by including the polyvalent metal salt in the first ink, the hydrophobic unit, the nonionic hydrophilic unit and the ionic component in the block polymer are used. The ratio of the degree of polymerization of the hydrophilic unit is preferably in the following range. That is, in order not to increase the ionicity of the block polymer, when the degree of polymerization of the hydrophobic unit is 10, the degree of polymerization of the nonionic hydrophilic unit is 2 or more, and the ionic hydrophilic unit The degree of polymerization is preferably 3 or less. More preferably, the ratio of the degree of polymerization of the hydrophobic unit, nonionic hydrophilic unit and ionic hydrophilic unit is such that when the degree of polymerization of the hydrophobic unit is 10, the degree of polymerization of the nonionic hydrophilic unit. Is 4 or more, and the degree of polymerization of the ionic hydrophilic unit is 2 or less. The ratio of the degree of polymerization of units mentioned above means the ratio of the number of polymerized monomers constituting the unit.

  In the present invention, the block polymer in which the second ink can contain as an anionic component and which disperses the pigment has a hydrophobic unit and an anionic (ionic) hydrophilic unit. Accordingly, the pigment can be in a microcapsule state in the second ink, and stable ink ejection is realized in the ink jet recording. In addition, the block polymer further has a nonionic hydrophilic unit as in the case of the first ink, so that ink ejection is further stabilized. In order for the second ink to further promote aggregation due to the reaction with the first ink, the hydrophobic unit, the nonionic hydrophilic unit, and the ionic hydrophilic in the block polymer in each ink. It is preferable that the polymerization degree of the sex unit has the following relationship. That is, it is preferable that the degree of polymerization of the nonionic hydrophilic unit is smaller in the block polymer in the second ink than in the block polymer in the first ink. In this case, the degree of polymerization of the ionic hydrophilic unit is preferably larger in the block polymer in the second ink than in the first ink.

  Hereinafter, properties common to the block polymer in the first ink and the block polymer in the second ink will be described. In the present invention, as a block polymer, the following known block polymers can be used as specific examples. That is, acrylic, methacrylic block copolymers, polystyrene and other addition polymerization or condensation polymerization block copolymers, block copolymers having polyoxyethylene and polyoxyalkylene blocks, and the like. In the present invention, the block polymer is more preferably a block form such as AB, ABA, ABC. A, B, and C indicate different block segments. In the present invention, the block copolymer may be bound to a copolymer chain in a T shape to form a graft copolymer. In the present invention, the block polymer preferably contains a polyvinyl ether structure as a repeating unit structure from the viewpoint of stable polymer design.

  Specific examples of the repeating unit of the ionic hydrophilic unit include a repeating unit represented by the following general formula (1).

（一般式（１）中、Ｒ⁰は−Ｘ−(ＣＯＯＨ)_r、−Ｘ−(ＣＯＯ−Ｍ)_rを表す。Ｘは炭素数１乃至２０までの直鎖状、分岐状又は環状のアルキレン基、又は−(ＣＨ(Ｒ⁵)−ＣＨ(Ｒ⁶)−Ｏ)_p−(ＣＨ₂)_m−ＣＨ_3-r−若しくは−(ＣＨ₂)_m−(Ｏ)_n−(ＣＨ₂)_q−ＣＨ_3-r−。又は、それらのメチレン基の少なくとも一つがカルボニル基又は芳香環構造で置換された構造を表す。ｒは１乃至２を表す。ｐは１乃至１８までの整数を表す。ｍは０乃至３５までの整数を表す。ｎは１又は０を表す。ｑは０乃至１７の整数を表す。Ｍは一価又は多価のカチオンを表す。Ｒ⁵、Ｒ⁶はアルキル基を表す。Ｒ⁵、Ｒ⁶は同じでも又は異なっていてもよい。）

(In the general formula (1), R ⁰ represents —X— (COOH) _r , —X— (COO-M) _r , where X is a linear, branched or cyclic alkylene having 1 to 20 carbon atoms. group, or ^{- (CH (R 5) -CH} (R 6) -O) p - (CH 2) m -CH 3-r - or _{- (CH 2) m - (} O) n - (CH 2) q -CH3 _-r-, or a structure in which at least one of the methylene groups is substituted with a carbonyl group or an aromatic ring structure, r represents 1 to 2, and p represents an integer of 1 to 18. m represents an integer of 0 to 35. n represents 1 or 0. q represents an integer of 0 to 17. M represents a monovalent or polyvalent cation. R ⁵ and R ⁶ represent an alkyl group. R ⁵ and R ⁶ may be the same or different.)

  Furthermore, specific examples of the repeating unit of the hydrophobic unit or the nonionic hydrophilic unit include a repeating unit represented by the following general formula (2).

（一般式（２）中、Ｒ¹は炭素数１乃至１８までの直鎖状、分岐状又は環状のアルキル基、−Ｐｈ、−Ｐｙｒ、−Ｐｈ−Ｐｈ、−Ｐｈ−Ｐｙｒ、−(ＣＨ（Ｒ⁵)−ＣＨ(Ｒ⁶)−Ｏ)_p−Ｒ⁷及び−(ＣＨ₂)_m−(Ｏ)_n−Ｒ⁷から選ばれる基である。また、該基における、芳香環中の水素原子は、炭素数１乃至４の直鎖状又は分岐状のアルキル基と、また、芳香環中の炭素原子は、窒素原子とそれぞれ置換していてもよい。ｐは１乃至１８の整数、ｍは１乃至３６の整数、ｎは０又は１である。Ｒ⁵、Ｒ⁶はそれぞれ独立に水素原子若しくは−ＣＨ₃である。Ｒ⁷は水素原子、炭素数１乃至１８までの直鎖状、分岐状又は環状のアルキル基、−Ｐｈ、−Ｐｙｒ、−Ｐｈ−Ｐｈ、−Ｐｈ−Ｐｙｒ、−ＣＨＯ、−ＣＨ₂ＣＨＯ、−ＣＯ−ＣＨ＝ＣＨ₂、−ＣＯ−Ｃ(ＣＨ₃)＝ＣＨ₂、−ＣＨ₂ＣＯＯＲ⁸からなる。また、Ｒ⁷が水素原子以外である場合、Ｒ⁷中の炭素原子に結合している水素原子は炭素数１乃至４の直鎖状又は分岐状のアルキル基又は−Ｆ、−Ｃｌ、−Ｂｒと、また、芳香環中の炭素原子は窒素原子とそれぞれ置換することができる。Ｒ⁸は水素原子又は炭素数１乃至５のアルキル基である。Ｐｈはフェニル基、Ｐｙｒはピリジル基を表す。）

(In the general formula (2), R ¹ is a linear, branched or cyclic alkyl group having 1 to 18 carbon atoms, -Ph, -Pyr, -Ph-Ph, -Ph-Pyr,-(CH ( R ⁵ ) —CH (R ⁶ ) —O) _p —R ⁷ and — (CH ₂ ) _m — (O) _n —R ⁷ , and a hydrogen atom in the aromatic ring in the group Is a linear or branched alkyl group having 1 to 4 carbon atoms, and the carbon atom in the aromatic ring may be substituted with a nitrogen atom, p is an integer of 1 to 18, and m is An integer of 1 to 36, n is 0 or 1. R ⁵ and R ⁶ are each independently a hydrogen atom or —CH ₃ , R ⁷ is a hydrogen atom, a straight chain having 1 to 18 carbon atoms, branched Jo or cyclic alkyl group, -Ph, -Pyr, -Ph-Ph , -Ph-Pyr, -CHO, -CH 2 CHO, -CO-CH = CH 2, -C _{-C (CH 3) = CH 2} , consisting of -CH ₂ COOR ^8. Also, when R ⁷ is other than hydrogen atom, the hydrogen atom bonded to a carbon atom in R ⁷ is from 1 to 4 carbon atoms A linear or branched alkyl group or —F, —Cl, —Br, and a carbon atom in the aromatic ring can be substituted with a nitrogen atom, and R ⁸ is a hydrogen atom or a carbon number of 1 to 5. (Ph represents a phenyl group, and Pyr represents a pyridyl group.)

  Hereinafter, the hydrophobic unit may be referred to as A segment, the nonionic hydrophilic unit as B segment, and the ionic hydrophilic unit as C segment. Specific examples of the repeating unit structure of the C segment (ionic hydrophilic unit) represented by the general formula (1) include those described below.

  Specific examples of the repeating unit structure of the A segment (hydrophobic unit) represented by the general formula (2) include those described below.

  Specific examples of the repeating unit structure of the B segment (nonionic hydrophilic unit) represented by the general formula (2) include those described below.

  In the present invention, each block segment (unit) constituting the block polymer may have a single structure selected from the above repeating units or a structure having a plurality of repeating units. Good. Examples of the block segment having a structure having a plurality of repeating units include a random copolymer and a gradient copolymer whose composition ratio gradually changes. In the present invention, the block polymer may be a polymer having a block copolymer structure grafted to another polymer.

  In the present invention, the content of the repeating unit structure represented by the general formula (1) or the general formula (2) contained in the block polymer is 0.01 mol% or more and 99 mol% or less with respect to the entire block polymer, preferably Is preferably in the range of 1 mol% to 90 mol%. If it is less than 0.01 mol%, the polymer interaction that the ionic functional group, hydrophobic functional group, or nonionic hydrophilic group should work may be insufficient, and if it exceeds 99 mol%, the interaction will work too much. The function may be insufficient. In the present invention, the number average molecular weight (Mn) of the block polymer is 200 or more and 10,000,000 or less, and the range preferably used is 1,000 or more and 1,000,000 or less. If it exceeds 10,000,000, the entanglement between the polymer chains and between the polymer chains becomes excessive, and it may be difficult to disperse in the solvent. If it is less than 200, the steric effect as a polymer may be difficult to obtain due to the low molecular weight. The preferable degree of polymerization of each block segment (unit) is 3 or more and 10,000 or less. More preferably, it is 5 or more and 5,000 or less. More preferably, it is 10 or more and 4,000 or less.

Polymerization of a block copolymer having a polyvinyl ether structure preferably used as a repeating unit structure in the present invention is often carried out mainly by cationic polymerization. Examples of the initiator include proton acids such as hydrochloric acid, sulfuric acid, methanesulfonic acid, trifluoroacetic acid, trifluoromethanesulfonic acid, perchloric acid, BF ₃ , AlCl ₃ , TiCl ₄ , SnCl ₄ , FeCl ₃ , RAlCl ₂ , R An example is a combination of a Lewis acid such as _1.5 AlCl _1.5 (R represents alkyl) and a cation source. Examples of the cation source include proton acid, water, alcohol, adduct of vinyl ether and carboxylic acid. By allowing these initiators to coexist with a polymerizable compound (monomer), the polymerization reaction proceeds, and a block copolymer can be synthesized. The block copolymer having a polyvinyl ether repeating unit structure preferably used in the present invention preferably contains 50 mol% or more, preferably 70 mol% or more, more preferably 90 mol% or more of the polyvinyl ether repeating unit structure.

The polymerization method that is more preferably used in the present invention will be described. Many methods for synthesizing polymers containing a polyvinyl ether structure have been reported (for example, JP-A-11-080221). Among them, the method by cation living polymerization by Aoshima et al. (Polymer Bulletin, Vol. 15, 1986, page 417, JP-A Nos. 11-322942 and 11-322866) is representative. By conducting polymer synthesis by cationic living polymerization, various polymers such as homopolymers, copolymers composed of two or more monomers, as well as block copolymers, graft polymers, and gradient polymers can be obtained in length (molecular weight). ) Can be combined accurately. In addition, living polymerization can also be carried out in the HI / I ₂ system, HCl / SnCl ₄ system, or the like.

  In the present invention, the content of the block polymer in the first ink and the second ink is 0.1% by mass or more and 20% by mass based on the total mass of each ink in consideration of the effect of the present invention described above. It is preferable that it is the range of the mass% or less. More preferably, it is the range of 0.5 mass% or more and 10 mass% or less.

(Self-dispersing pigment)
In the present invention, a pigment that is self-dispersible in water can also be used as the colorant for the second ink. In order to react with the metal cations in the first ink and aggregate, an anionic self-dispersing pigment is preferable. As pigments that can be self-dispersed in water, there are pigments that utilize the steric hindrance effect in which a polymer is adsorbed on the pigment surface, and pigments that utilize electrostatic repulsion. Examples of commercially available products include CAB-0-JET200, CAB-0-JET300 (manufactured by Cabot Corporation), Microjet Black CW-1 (manufactured by Orient Chemical Co., Ltd.), and the like.

(solvent)
Next, in the present invention, the solvent used for the first ink and the second ink will be described. In the present invention, various organic hydrocarbons such as linear, branched and cyclic aliphatic hydrocarbons, aromatic hydrocarbons, heteroaromatic hydrocarbons and halogen-containing solvents, aqueous solvents, water and the like are included as solvents. In particular, in the ink of the present invention, water and an aqueous solvent can be used together. Examples of the aqueous solvent include, for example, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, polyhydric alcohols such as glycerin and trimethylolpropane, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, Examples thereof include polyhydric alcohol ethers such as ethylene glycol monobutyl ether, diethylene glycol monoethyl ether and diethylene glycol monobutyl ether, and nitrogen-containing solvents such as N-methyl-2-pyrrolidone, substituted pyrrolidone and triethanolamine. In addition, monohydric alcohols such as methanol, ethanol, and isopropyl alcohol can be used for the purpose of accelerating drying on paper.

(Polyvalent metal salt)
In the present invention, the first ink contains a polyvalent metal salt. When the first ink contains the polyvalent metal salt, the metal cation comes into contact with the second ink on the paper surface, and the second ink is aggregated. Further, in order to improve the aggregation reactivity, the valence of the metal cation needs to be 2 or more. For example, if an excessively reactive cation such as a tetravalent cation is used, the first ink itself is In some cases, agglomeration reaction may occur before printing. Examples of the polyvalent metal salt used in the present invention include the following in order to aggregate the second ink after printing and recording without causing the aggregation reaction of the first ink itself. For example, divalent metal ions such as Ca ²⁺ , Cu ²⁺ , Ni ²⁺ , Mg ²⁺ , Zn ²⁺ and Ba ²⁺ , Al ³⁺ , which are safe for use in ink jet recording, ^Examples thereof include trivalent metal ions such as Fe ³⁺ , Cr ³⁺ and Y ³⁺ . Examples of the anion include SO ₄ ²⁻ , Cl ⁻ , NO ₃ ⁻ , I ⁻ , Br ⁻ , ClO ₃ ⁻ , CO ₃ ²⁻ , CH ₃ COO ⁻ , and HCOO ^−. It is not limited.

  In the present invention, the content of the polyvalent metal salt in the first ink is in the range of 0.01% by mass or more and 20% by mass or less based on the total mass of the first ink in consideration of the effect of the present invention. It is preferable that More preferably, it is the range of 1 mass% or more and 5 mass% or less.

(Other ingredients)
In the present invention, the first ink and the second ink include, in addition to the above components, a surfactant, an antifoaming agent, a preservative, as necessary, in order to obtain an ink having a desired physical property value. A dustproof agent or the like can be added.

[Ink set]
The color tone of the ink constituting the ink set containing the first ink and the second ink is not particularly limited, and for example, at least one selected from yellow, magenta, cyan, red, green, blue and black An ink showing a color tone may be used. Specifically, it can be used by appropriately selecting from the above-mentioned color materials so as to obtain an ink having a desired color tone. Here, the content of the coloring material in each ink, for example, when used for inkjet recording, can be appropriately selected so that the ink has excellent inkjet ejection characteristics and has a desired color tone and density. Good. As a standard, for example, a range of 1% by mass to 50% by mass with respect to the total mass of each ink is preferable. The amount of water contained in the ink is preferably in the range of 50% by mass to 95% by mass with respect to the total mass of each ink. The amount of the aqueous solvent contained in the ink is preferably in the range of 3% by mass to 40% by mass with respect to the total mass of each ink.

  The second ink is not limited to one type, and it is more preferable to combine two or more inks having different color tones to form an ink set suitable for forming a multicolor image. In this case, at least one of the two or more second inks only needs to react with the first ink. As long as there is an ink in which a water-insoluble colorant is dispersed in an aqueous medium, the other ink may be an ink containing a dye as a colorant. It is also possible to use dispersed ink. Further, the ink set of the present invention may be configured such that the first ink has one or more. According to such an ink set, it is possible to suppress bleeding when inks of different color tones are applied adjacently on a recording medium, which is a problem when a multicolor image is formed by an ink jet recording apparatus.

  More specifically, bleeding, which is a problem in inkjet multicolor images, tends to be particularly noticeable between black ink and other color inks. Examples of the other color inks include at least one ink selected from yellow ink, magenta ink, cyan ink, red ink, green ink, and blue ink. For this reason, also in the present invention, the black ink is combined as the second ink in which the water-insoluble colorant is dispersed in the aqueous medium by the action of the ionic group so as to interact with the first ink. Is preferred. In other words, when considering the conspicuousness of the printed matter in the bleed, the second ink is preferably a black ink containing a black pigment, in which the bleed is conspicuous. The first ink containing a polyvalent metal salt is preferably not a black ink because the first ink itself does not aggregate. Preferably, the ink is at least one water-insoluble colorant ink selected from cyan ink, yellow ink, magenta ink, red ink, green ink, and blue ink. The color ink other than the first ink and the second ink may be an ink in which a dye is dissolved in an aqueous medium. Of course, a water-insoluble colorant is dispersed in an aqueous medium in the same manner as a black ink. Ink may be used. For example, the first ink may be a pigment-based cyan ink, the second ink may be a pigment-based black ink, and the other color ink may be a four-color system using a dye-based yellow ink and a dye-based magenta ink. An ink set may be used.

[Inkjet recording method]
In the ink jet recording method of the present invention, the first ink reacts with at least one component in the second ink to destabilize the dissolved or dispersed state of the color material in the second ink. And an ink set formed by combining a plurality of colors of ink including the above ink. And (i) a step of applying a second ink to the recording medium; and (ii) a step of applying the first ink to at least a region of the recording medium to which the second ink is applied. Is adopted. As a result, it is possible to obtain an image with a high image density in which the ambiguity of the contour portion is improved and color bleeding does not occur. The reason why printing quality can be improved with high image density and high color development by using such an ink set is not clear, but the following may be considered. For example, when the first ink and the second ink are respectively ejected onto the paper surface by the ink jet method and both are adhered, a coloring material such as a pigment that is stably present in the second ink is After adhering to the ink, it is rapidly destabilized by the first ink. And it is considered that this causes the pigment to remain at the landing position on the paper surface due to the rapid aggregation or gelation of the ink.

  A plurality of ink sets composed of the first ink and the second ink, or a combination of the ink set composed of the first ink and the second ink and another ink, thereby forming a color image. An ink set that can be suitably used can be provided. Using such an ink set, for example, an ink set containing black ink as the second ink whose color material is destabilized by the first ink, recording is performed adjacent to the black image portion and the color image portion. Occurrence of bleeding can be extremely effectively suppressed.

  The first ink and the second ink used in the present invention preferably have characteristics that can be ejected from an inkjet head, but from the viewpoint of stable ejection from the inkjet head, the following characteristics are required. Is preferred. For example, it is preferable that the viscosity is 1 mPa · s (cps) to 15 mPa · s (cps) and the surface tension is 25 mN / m (dyne / cm) or more. In particular, it is more preferable that the viscosity is 1 mPa · s (cps) to 5 mPa · s (cps) and the surface tension is 25 mN / m (dyne / cm) to 50 mN / m (dyne / cm). In order to further exhibit the effects of the present invention, it is most preferable that the surface tension of the ink be in the range of 35 mN / m (dyne / cm) to 50 mN / m (dyne / cm).

  The ink jet recording method used may be a known method such as a piezo ink jet method using a piezoelectric element or a thermal ink jet method in which heat energy is applied to perform foaming and recording. In addition, although either a continuous type or an on-demand type method may be used, an on-demand type inkjet method is preferable.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated concretely, this invention is not limited to these. In this embodiment and the comparative example, all the Cy inks are used as the first ink, and all the Bk inks are used as the second ink. However, the present invention is not limited to these colors. In the following description, “%” is based on mass unless otherwise specified.

[Synthesis of block polymer]
The block polymer used for each of the first ink and the second ink is a unit structure constituting each unit, the A segment is A-i (hereinafter simply referred to as A), the B segment is B-e (hereinafter simply B). The C segment was synthesized as C-sa (hereinafter simply referred to as C).

[Preparation of first ink]
(Preparation of Cy ink 1)
As the block polymer, a triblock polymer having the above three monomer components, having a polymerization degree of A of 90, a polymerization degree of B of 60, and a polymerization degree of C of 10 was used. This is simply expressed as A90-B60-C10. Hereinafter, the same notation is used, but each number indicates the degree of polymerization of each unit. The triblock polymer and the Cy pigment were dissolved in THF, and the KOH solution was mixed to invert the phase, followed by dispersion and evaporation to prepare an aqueous pigment dispersion Cy. Next, it mixed with the solvent and additive with the composition shown below, and it stirred sufficiently and melt | dissolved, The Cy ink 1 which is the Example of the 1st ink for inkjets containing the pigment was obtained.

・ Cy pigment 2.5%
・ Block polymer 2.5%
・ Magnesium nitrate 2.5%
・ Glycerin 7%
・ Diethylene glycol 5%
・ Trimethylolpropane 7%
・ Acetylene glycol ethylene oxide adduct (trade name: acetylenol EH, manufactured by Kawaken Fine Chemical Co., Ltd.) 0.3%
・ Water 73.2%

(Preparation of Cy inks 2 to 5)
Examples of the first ink, Cy inks 2 to 5, are the same as those of the Cy ink 1 except that the block polymers shown in Table 1 below are used as the block polymers used for the Cy inks 2 to 5, respectively. Was prepared.

(Preparation of Cy inks 6 and 7)
As block polymers used for Cy inks 6 and 7, the block polymers shown in Table 1 below were used. The block polymer was dissolved in THF, the KOH solution was combined, and the phase was inverted. Then, after evaporation, each component was mixed with the following composition, sufficiently stirred and dissolved, then filtered under pressure, and is a comparative example of the first ink that does not contain a polyvalent metal salt. Inks 6 and 7 were prepared.

・ Cy pigment 2.5%
・ Block polymer 2.5%
・ Glycerin 7%
・ Diethylene glycol 5%
・ Trimethylolpropane 7%
・ Acetylene glycol ethylene oxide adduct (trade name: acetylenol EH, manufactured by Kawaken Fine Chemical Co., Ltd.) 0.3%
・ Water 75.7%

[Preparation of second ink]
(Preparation of Bk ink 1)
As the block polymer, a block polymer (A45-B0-C20) having a hydrophobic unit and an ionic hydrophilic unit was used. The block polymer and the Bk pigment were dissolved in THF, the KOH solution was mixed and the phase was inverted, and then dispersion and evaporation were performed to prepare an aqueous pigment dispersion Bk. Next, it mixed with the solvent and additive with the composition shown below, and fully stirred and melt | dissolved, and the Bk ink 1 for inkjets containing the pigment was obtained.

・ Bk pigment 4%
・ Block polymer 4%
・ Glycerin 7%
・ Diethylene glycol 5%
・ Trimethylolpropane 7%
・ Acetylene glycol ethylene oxide adduct (trade name: acetylenol EH, manufactured by Kawaken Fine Chemical Co., Ltd.) 0.3%
・ Water 72.7%

(Preparation of Bk ink 2-5)
Bk inks 2 to 5 were prepared in the same manner as Bk ink 1 except that the block polymers shown in Table 1 below were used as the block polymers used for Bk inks 2 to 5, respectively.

(Preparation of Bk ink 6)
Instead of dispersing the pigment with the polymer, the self-dispersing pigment CAB-0-JET200 (manufactured by Cabot) was used as a colorant, and the components were mixed in the following composition, sufficiently stirred and dissolved, and then filtered under pressure. Bk ink 6 using a self-dispersing pigment was prepared.

・ Self-dispersion pigment 4%
・ Glycerin 7%
・ Diethylene glycol 5%
・ Trimethylolpropane 7%
・ Acetylene glycol ethylene oxide adduct (trade name: acetylenol EH, manufactured by Kawaken Fine Chemical Co., Ltd.) 0.3%
・ Water 76.7%

[Preparation of ink set]
Using the Cy ink and Bk ink obtained above in the combinations shown in Table 1 below, and further combining four inks with BCI-6M (Mg ink, manufactured by Canon) and BCI-6Y (Ye ink, manufactured by Canon) An ink set of Example and Comparative Example consisting of

[Evaluation]
Using the ink set obtained above, an inkjet recording apparatus BJF-900 (manufactured by Canon Inc.) having an on-demand type multi-recording head that ejects ink by applying thermal energy corresponding to a recording signal to the ink. Formed. The first ink and the second ink were brought into contact with each other in the same scan. As a printing material, A4 plain paper SW-101 (manufactured by Canon) was used.

(Color bleed)
On the recording medium, Cy ink as the first ink, and Mg ink and Ye ink were first ejected as the ink for undercoating, and then Bk ink as the second ink was ejected. The printed image is divided into 5 x 5 squares (1 square size: 2 cm x 2 cm) inside a 10 cm square, and the black print section and each color are printed with Bk ink and each color ink alternately. The degree of bleeding and color mixing at the boundary with the printed part was evaluated. The evaluation criteria are as follows. The evaluation results are shown in Table 2.
〔Evaluation criteria〕
○: The boundary line between other colors is clear in each part, and no blur or color mixing is seen in the boundary part.
Δ: Some blurring or color mixing is seen at the boundary.
X: Bleeding or color mixing can be clearly confirmed at the boundary.

(OD)
The optical density (OD value) was measured using a Gretag densitometer (manufactured by Gretag Macbeth Co., Ltd.) for the Bk ink print portion of the print image used in the color bleed evaluation. The measurement results were evaluated based on the following criteria. The evaluation results are shown in Table 2.
〔Evaluation criteria〕
○: OD value is 1.3 or more.
(Triangle | delta): OD value is 1.1 or more and less than 1.3.
X: OD value is less than 1.1.

(Discharge stability)
For the Cy ink, which is the first ink, continuous discharge was performed for 5 hours at an ink discharge frequency of 5 kHz, and the change in discharge amount before and after continuous discharge was measured. The measurement results were evaluated based on the following criteria. The evaluation results are shown in Table 2.
〔Evaluation criteria〕
○: The ratio of the change in discharge amount before and after continuous discharge is less than 5%.
(Triangle | delta): The ratio of the discharge amount change before continuous discharge and after continuous discharge is 5% or more and less than 10%.
X: The rate of change in the discharge amount before and after continuous discharge is 10% or more.

  As the above evaluation results, it was shown that in the examples, an image having excellent characteristics was formed. Further, among the examples, in Examples 1, 2, 6, 7, 26, and 27, it is shown that excellent characteristics can be obtained with good balance in each of OD, color bleed, and ejection stability. It was.

Claims (11)

  At least a polyvalent metal salt, a water-insoluble colorant, and a block polymer are contained, and the block polymer has a hydrophobic unit, a nonionic hydrophilic unit, and an ionic hydrophilic unit. Ink characterized by that.   When the ratio of the degree of polymerization in the hydrophobic unit, the nonionic hydrophilic unit, and the ionic hydrophilic unit is 10 as the degree of polymerization of the hydrophobic unit, polymerization of the nonionic hydrophilic unit is performed. The ink according to claim 1, wherein the degree is 2 or more, and the degree of polymerization of the ionic hydrophilic unit is 3 or less.   The ink according to claim 1, wherein the block polymer contains a polyvinyl ether structure as a repeating unit structure. The cation of the polyvalent metal salt is Ca ²⁺ , Cu ²⁺ , Ni ²⁺ , Mg ²⁺ , Zn ²⁺ , Ba ²⁺ , Al ³⁺ , Fe ³⁺ , Cr ³⁺ , and Y ³⁺ . The ink according to any one of claims 1 to 3, which is any one of the above.   An ink set comprising a combination of a plurality of inks having at least one of the inks according to any one of claims 1 to 4 as a first ink, comprising at least a water-insoluble colorant, and an anion A water-based ink set for inkjet recording, comprising a second ink containing a component.   The inkjet according to claim 5, wherein the anionic component in the second ink is a block polymer in which a water-insoluble colorant is dispersed, and the block polymer has a hydrophobic unit and an ionic hydrophilic unit. Water-based ink set for recording.   The block polymer in the second ink has a hydrophobic unit, a nonionic hydrophilic unit, and an anionic hydrophilic unit, and the degree of polymerization of the nonionic hydrophilic unit is the first polymer. The water-based ink set for ink-jet recording according to claim 6, wherein the block polymer of the second ink is smaller than the block polymer in one ink.   The aqueous ink set for inkjet recording according to claim 6 or 7, wherein the block polymer in the second ink contains a polyvinyl ether structure as a repeating unit structure.   The water-based ink set for ink-jet recording according to any one of claims 5 to 8, wherein the water-insoluble colorant in the second ink is a black pigment.   The aqueous ink set for inkjet recording according to claim 5, wherein the second ink contains a self-dispersing pigment as a colorant as the anion component.   In the ink jet recording method for recording on a recording medium using an ink set comprising a combination of at least a plurality of colors of ink, the water base ink set for ink jet recording according to any one of claims 5 to 10 is used as the ink set. An ink jet recording method comprising: applying a first ink and a second ink constituting the water base ink set for ink jet recording to a recording medium to aggregate the second ink.