JP2010222405A - Method for producing pigment dispersion, pigment dispersion and ink for inkjet recording - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pigment dispersion for producing ink for inkjet recording, having a low viscosity and excellent jetting characteristics, to provide a method of production of the dispersion, and to provide the ink for the inkjet recording. <P>SOLUTION: The method for producing the pigment dispersion at least containing an aqueous medium, a pigment and a dispersing resin for dispersing the pigment in the aqueous medium includes a base-adding step for adding a base in an amount exceeding the equivalent of an ionic group possessed by the dispersing resin to a dispersion containing the pigment and the dispersing resin, a dispersion step for carrying out the mechanical dispersion of the dispersion obtained in the base-adding step, and a removing step for removing at least a part of the base and at least a part of the floating dispersing resin from the dispersion obtained in the dispersion step. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing a pigment dispersion, a pigment dispersion, and an inkjet recording ink.

  As means for improving the water resistance and weather resistance of an ink jet recorded image, there is a technique of using a pigment as an ink coloring material and dispersing the pigment in water to obtain an ink. However, in this case, it is difficult to achieve both pigment dispersion stability and ink jet recording ejection stability.

  Therefore, a technique for coating the pigment to be contained in the ink with a dispersion resin has been proposed. Patent Document 1 proposes a technique for dispersing a pigment with a dispersion resin having a hydrophobic part and a hydrophilic part.

JP-A-6-264017

  However, in the conventional method, since a certain amount or more of the dispersion resin is used in order to ensure the dispersion stability of the pigment, a free dispersion resin that floats without adsorbing to the pigment may remain in the system. It was. Alternatively, entanglement between the polymer chains of the dispersion resin and the polymer chains may cause an increase in the viscosity of the ink or impair the ink discharge performance.

  Accordingly, an object of the present invention is to provide a method for producing a pigment dispersion for producing an inkjet recording ink having a low viscosity and excellent ejection characteristics, and a pigment dispersion and an inkjet recording ink obtained thereby. is there.

  The above object is achieved by the present invention described below. That is, the first aspect of the present invention includes at least the aqueous medium, the pigment, and the method for producing a pigment dispersion containing the dispersion resin in which the pigment is dispersed in the aqueous medium. A base addition step of adding a base exceeding the equivalent of the ionic group of the dispersion resin to the dispersion, a dispersion step of mechanically dispersing the dispersion obtained by the base addition step, and a dispersion step obtained by the dispersion step. And a removal step of removing at least part of the base and at least part of the suspended dispersion resin from the dispersion.

  The second of the present invention is a method for producing a pigment dispersion containing at least an aqueous medium, a pigment, and a dispersion resin for dispersing the pigment in the aqueous medium, and a dispersion containing the pigment and the dispersion resin. To the dispersion obtained by the neutralization step of neutralizing at least part of the ionic groups of the dispersion resin by adding a base equivalent to or less than the equivalent of the ionic groups of the dispersion resin A dispersion step for performing mechanical dispersion, a base addition step for adding a base to the dispersion obtained by the dispersion step, and at least a part of the base and a suspended dispersion resin from the dispersion obtained by the base addition step It has the removal process which removes at least one part of this, It is a manufacturing method of the pigment dispersion characterized by the above-mentioned.

  The third of the present invention is a pigment dispersion produced by the production method of the first invention and the second invention.

  A fourth aspect of the present invention is an ink for ink jet recording produced using the pigment dispersion according to the third aspect of the present invention.

  According to the present invention, it is possible to provide a pigment dispersion and ink jet recording ink (hereinafter sometimes simply referred to as “ink”) having low viscosity and good ejection characteristics at low cost.

It is a longitudinal cross-sectional view which shows an example of the head of an inkjet recording device. It is a cross-sectional view showing an example of the head of the ink jet recording apparatus. FIG. 2 is an external perspective view of a head in which the head shown in FIG. It is a schematic perspective view which shows an example of an inkjet recording device. It is a longitudinal cross-sectional view which shows an example of an ink cartridge. It is a perspective view which shows an example of a recording unit. FIG. 3 is a diagram illustrating an example of a configuration of a recording head.

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. The details of the present invention will be described for each constituent material.
(1) Pigment Examples of the pigment that can be used in the present invention include, but are not limited to, the following. Of the pigment dispersion or ink (hereinafter, both may be referred to as “ink”), carbon black is preferably used as the pigment used in the black ink. For example, carbon black pigments such as furnace black, lamp black, acetylene black, channel black, for example, Raven 7000, Ray Van 5750, Ray Van 5250, Ray Van 5000, Ray Van 3500, Ray Van 2000, Ray Van 1500, Ray Van 1250, Ray Van 1200, Ray Van 1190 ULTRA II, Ray Van 1170, Ray Van 1255 (above, manufactured by Columbia). Black Pearls L, Regal 400R, Regal 330R, Legal 660R, Mogul L, Monarch 700, Monak 800, Monak 880, Monak 900, Monak 1000. Monak 1100, Monak 1300, Monak 1400, Vulcan XC-72R (above, 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 (Special Black) 6, Special Black 5, Special Black 4A, Special Black 4 (above, Degussa). No. 25, no. 33, no. 40, no. 47, no. 52, no. 900, no. Commercially available products such as 2300, MCF-88, MA600, MA7, MA8, MA100 (above, manufactured by Mitsubishi Chemical Corporation) or newly prepared products can also be used.

  Specific examples of organic pigments include insoluble azo pigments such as toluidine red, toluidine maroon, Hansa Yellow, Benzidine Yellow, and pyrazolone red, and soluble azo pigments such as Ritol Red, Helio Bordeaux, Pigment Scarlet, and Permanent Red 2B. Derivatives from vat dyes such as alizarin, indanthrone and thioindigo maroon, phthalocyanine pigments such as phthalocyanine blue and phthalocyanine green, quinacridone pigments such as quinacridone red and quinacridone magenta, and perylene red. Perylene pigments such as perylene scarlet, isoindolinone pigments such as isoindolinone yellow and isoindolinone orange, imidazolone pigments such as benzimidazolone yellow, benzimidazolone orange and benzimidazolone red. Pilanthrone pigments such as pyranthrone red and pyranthrone orange, thioindigo pigments, condensed azo pigments, thioindigo pigments, diketopyrrolopyrrole pigments, flavanthrone yellow, acylamide yellow, quinophthalone yellow, nickel azo yellow. Copper azomethine yellow. Other pigments such as perinone orange, anthrone orange, dianthraquinonyl red, dioxazine violet can be exemplified.

  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, 97, 109, 110, 117, 120, 125, 128, 137, 138, 147. 148, 150, 151, 153, 154, 166, 168, 180, 185, C.I. I. Pigment orange 16, 36, 43, 51, 55, 59, 61, 71, 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, 254, 255, 272, C.I. I. Pigment violet 19, 23, 29, 30, 37, 40, 50. C. I. Pigment blue 15, 15: 1, 15: 3, 15: 4, 15: 6, 22, 60, 64, C.I. I. Pigment green 7, 36, C.I. I. Pigment Brown 23, 25, 26 and the like can be exemplified.

  In particular, among these pigments, C.I. I. Pigment Yellow 74, 93, 97, 110, 120, 128, 138, 147, 148, 150, 151, 154, 155, 180, 185. C. I. Pigment red 122, C.I. I. Pigment violet 19, C.I. I. Pigment Blue 15, 15: 1, 15: 3, 15: 4 and the like are more preferable.

  In addition, pigments that are self-dispersible in water can be used. Water-dispersible pigments include those using the steric hindrance effect in which a polymer is adsorbed on the pigment surface and those using electrostatic repulsion. Examples of commercially available products include CAB-O-JET200, CAB-O-JET300 (manufactured by Cabot Corporation), Microjet Black CW-1 (manufactured by Orient Chemical Co., Ltd.), and the like.

  The pigment used in the ink of the present invention is preferably 0.1% by mass or more and 50% by mass or less based on the total mass of the ink. When the amount of the pigment is less than 0.1% by mass, a sufficient image density cannot be obtained, and when it exceeds 50% by mass, the pigment aggregates and cannot be dispersed. A more preferable range is 0.5% by mass or more and 30% by mass or less.

  The pigment used in the ink of the present invention is preferably one in which primary particles are finely divided. Examples of the fine particles include a method of applying strong grinding with a bead mill and a mechanical method using a jet mill. Alternatively, there are a method such as a method of synthesizing a pigment having a primary particle diameter as small as possible and a low surface activity at the time of pigment synthesis, and a method of atomization by an evaporation method in an inert gas, that is, a gas phase method.

(2) Dispersing resin The dispersing resin used in the present invention may be any resin as long as it can disperse the pigment in an aqueous medium. In particular, an amphiphilic block copolymer is preferably used, but is not limited thereto. The amphiphilic block copolymer has an ionic functional group characteristically. Amphiphilic is a property that has the property of being dissolved in two types of solvents that are not soluble together, a property that is soluble in a certain solvent and a property that is insoluble in a certain solvent, or a region that is incompatible with a certain solvent. Say nature with. In the present invention, a block copolymer having both a site that is compatible with water or an aqueous solvent and a site that is not compatible with water or an aqueous solvent is preferable. Moreover, each segment of a block copolymer may be a copolymer segment, and the form of the copolymerization is not limited. For example, it may be a random segment or a gradient segment.

  Further, the block copolymer is preferably a block copolymer having a structure in which a hydrophobic block segment, a nonionic hydrophilic segment, and an ionic hydrophilic segment are arranged in this order. In addition, the copolymer which the polymer segment which consists of a repeating unit structure different from a block copolymer couple | bonded with the covalent bond, and is also called a block copolymer and a block polymer.

  Specific examples of the block copolymer include acrylic, methacrylic block copolymers, polystyrene and other addition polymerization or condensation polymerization block copolymers. A conventionally known block copolymer such as a block copolymer having a polyoxyethylene or polyoxyalkylene block can also be used. In the present invention, the block copolymer 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. The block copolymer used in the present invention preferably contains a polyvinyl ether structure as a repeating unit structure. Specific examples of the ionic hydrophilic block segment (C segment) include a repeating unit represented by the following general formula (1).

（式中、Ｒ⁰は−Ｘ−（ＣＯＯＨ）_r、−Ｘ−（ＣＯＯ−Ｍ）_r又は−Ｘ²−（ＣＯＯ）₂−Ｍ²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カンジイル若しくはアルカントリイル基を表す。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から２を表す。Ｘ²はＸのうちｒが２の基を表す。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は一価のカチオンを表す。Ｍ²は二価のカチオンを表す。Ｒ⁵及び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 formula, R ⁰ represents —X— (COOH) _r , —X— (COO—M) _r or —X ² — (COO) ₂ —M ² , where X is a straight chain having 1 to 20 carbon atoms. . Jo, a branched or cyclic alkanediyl or alkanetriyl 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 -CH 3-r - or, .r representing at least one is substituted with a carbonyl group or an aromatic ring structure the structure of those of the methylene groups from 1 2 X ² represents a group in which r is 2 in X. p represents an integer of 1 to 18. m represents an integer of 0 to 35. n represents 1 or 0. q represents 0. to .M represents an integer of 17 .M ² representing a monovalent cation represents the .R ⁵ and R ⁶ represents a divalent cation group .R ^5, R ⁶ It may be the same or different.)

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

（式中、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。芳香環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基を表す。ｐは１乃至１８の整数、ｍは１乃至３６の整数、ｎは０又は１を表す。Ｒ⁵及びＲ⁶はそれぞれ独立に水素原子若しくは−ＣＨ₃を表す。Ｒ⁵及びＲ⁶が複数ある場合はそれぞれ同じでも異なっていてもよい。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及び−ＣＯ−Ｃ（ＣＨ₃）＝ＣＨ₂から選ばれる。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。Ｐｈはフェニル基、Ｐｙｒはピリジル基を表わす。）

(Wherein 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 )- Selected from CH (R ⁶ ) —O) _p —R ⁷ and — (CH ₂ ) _m — (O) _n —R ^7, wherein the hydrogen atom bonded to the carbon atom in the aromatic ring has 1 to 4 carbon atoms. A linear or branched alkyl group, and a carbon atom in the aromatic ring which may be substituted with a nitrogen atom, p is an integer of 1 to 18, m is an integer of 1 to 36, n is optionally also different case .R ⁵ and R ⁶ represents 0 or 1 there are a plurality of .R ⁵ and R ⁶ each independently represent a hydrogen atom or -CH ₃ are respectively the same .R ⁷ is hydrogen , A linear, branched or cyclic alkyl group having 1 to 18 carbon atoms, -Ph, -Pyr, -Ph-Ph, -Ph- yr, -CHO, if _{-CH 2 CHO, -CO-CH =} CH 2 and _{-CO-C (CH 3) =} .R 7 selected from CH ₂ is other than hydrogen atom, the carbon atoms in R ⁷ The bonded hydrogen atom can be substituted with a linear or branched alkyl group having 1 to 4 carbon atoms or -F, -Cl, -Br, and the carbon atom in the aromatic ring can be substituted with a nitrogen atom. Ph represents a phenyl group, and Pyr represents a pyridyl group.)

  Specific examples of the repeating unit structure represented by the general formula (1) constituting the ionic hydrophilic block segment (C segment) are given below.

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

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

などが挙げられる。

Etc.

  Each block segment of the block copolymer used in the present invention may be composed of a single repeating unit or may be composed of a plurality of repeating unit structures. Examples of the block segment composed of a plurality of repeating units include a random copolymer and a gradation copolymer whose composition ratio gradually changes. The block copolymer of the present invention 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 copolymer is 0.01 mol% or more and 99 mol with respect to the entire block copolymer. % Or less, preferably in the range of 1 mol% or more and 90 mol% or less.

  If the content is less than 0.01 mol%, there may be insufficient polymer interaction with which the ionic functional group or hydrophobic functional group or nonionic hydrophilic group should work, while the content is less than 99 mol%. On the other hand, there are cases where the interaction is excessive and the function is insufficient.

  The number average molecular weight (Mn) of the block copolymer of the present invention 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. When the molecular weight exceeds 10,000,000, the entanglement within the polymer chain and between the polymer chains becomes excessive, and it is difficult to disperse in the solvent. On the other hand, when the molecular weight is less than 200, the steric effect as a polymer may be difficult due to the low molecular weight. The preferable degree of polymerization of each block segment 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.

  Further, in order to improve the dispersion stability of the pigment and to improve the inclusion property (inclusion property), it is preferable that the molecular mobility of the block copolymer is more flexible. This is because the molecular mobility of the block copolymer is flexible, so that the block copolymer is likely to physically entangle with the surface of the functional substance and to have an affinity. Furthermore, as described later in detail, it is preferable that the coating layer is flexible in that a coating layer can be easily formed on the recording medium. For this purpose, the glass transition temperature Tg of the main chain is preferably 40 ° C. or lower, more preferably 0 ° C. or lower, and further preferably −20 ° C. or lower. Also in this respect, a polymer having a polyvinyl ether structure is preferably used because it generally has a low glass transition point and flexible properties. In the case of the above repeating unit structure example, the glass transition temperature is often about −20 ° C. or lower.

Polymerization of the block copolymer having a polyvinyl ether repeating unit structure preferably used in the present invention is often carried out mainly by cationic polymerization. Examples of the initiator include protonic acids such as hydrochloric acid, sulfuric acid, methanesulfonic acid, trifluoroacetic acid, trifluoromethanesulfonic acid, and perchloric acid. In addition, a combination of a Lewis acid such as BF ₃ , AlCl ₃ , TiCl ₄ , SnCl ₄ , FeCl ₃ , RAlCl ₂ , R _1.5 AlCl _1.5 (R represents alkyl) and a cation source (protonic acid, water, Examples include adducts of alcohol, 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. A number of methods for synthesizing block copolymers containing a polyvinyl ether structure have been reported. For example, Japanese Patent Application Laid-Open No. 11-080221, a method by cationic living polymerization by Aoshima et al. Is. By synthesizing the polymer by the above polymerization, various polymers such as homopolymers and copolymers composed of two or more monomers, as well as block copolymers, graft polymers, gradation polymers, etc. can be accurately measured in length (molecular weight). It can be synthesized to match. In addition, living polymerization can also be carried out in the HI / I ₂ system, HCl / SnCl ₄ system, or the like.

(4) Aqueous medium, other additives, etc. The aqueous medium contained in the ink of the present invention comprises a mixed solvent (aqueous medium) of water and a water-soluble organic solvent. Those having a preventive effect are particularly preferred. Moreover, it is preferable to use deionized water instead of general water containing various ions.

  Specific examples of the water-soluble organic solvent used in the present invention include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, and tert-butyl alcohol. Alkyl alcohols having 1 to 5 carbon atoms such as isobutyl alcohol and n-pentanol; amides such as dimethylformamide and dimethylacetamide; ketones or ketoalcohols such as acetone and diacetone alcohol; tetrahydrofuran. Ethers such as dioxane, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, polyethylene glycol. Oxyethylene such as polypropylene glycol or oxypropylene copolymer, ethylene glycol, propylene glycol, trimethylene glycol, triethylene glycol. Alkylene glycols in which an alkylene group such as 1,2,6-hexanetriol contains 2 to 6 carbon atoms; glycerin. Ethylene glycol monomethyl (or ethyl) ether, diethylene glycol monomethyl (or ethyl) ether. Lower alkyl ethers such as triethylene glycol monomethyl (or ethyl) ether; lower dialkyl ethers of polyhydric alcohols such as triethylene glycol dimethyl (or ethyl) ether and tetraethylene glycol dimethyl (or ethyl) ether; Examples include alkanolamines such as monoethanolamine, diethanolamine, and triethanolamine, sulfolane, N-methyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, and the like. The water-soluble organic solvents as described above can be used alone or as a mixture.

  The content of the water-soluble organic solvent as described above contained in the ink of the present invention is not particularly limited, but is preferably in the range of 3% by mass to 50% by mass with respect to the total mass of the ink. The content 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 the ink. In addition to the above-described components, the pigment dispersion or water-based ink of the present invention may have, as necessary, additives such as a viscosity modifier, an antifoaming agent, Preservatives, fungicides, surfactants, antioxidants and the like can be added. The selection of the surfactant is preferably determined so that the surface tension of the ink is 30 mN / m or more.

(5) Base In the present invention, a base is used in the base addition step and the neutralization step. The base used is not particularly limited, and preferred examples include potassium hydroxide. In the first invention, the amount of the base used is an amount that exceeds the equivalent of the ionic group that the dispersion resin has, and in the second invention, the amount is equal to or less than the equivalent of the ionic group that the dispersion resin has (neutralization step). And any amount (base addition step). In particular, the total amount of the base in the dispersion obtained by the base addition step is preferably such that the pH of the dispersion is 11 or more. Thus, by including the step of adding an excess base, the dissociation degree of the dispersion resin is promoted, and as a result, the entanglement within or between the polymer chains of the dispersion resin is reduced, thereby reducing the pigment dispersion. It is estimated that the viscosity decreases. Further, it is preferable that the pH of the pigment dispersion is set to between 8 and 10 by removing at least a part of the base and the suspended dispersion resin at the same time.

(6) Mechanical dispersion The dispersion apparatus used in the dispersion step in the present invention may be any apparatus as long as mechanical dispersion is possible. For example, colloid mill, flow jet mill, slasher mill, high speed disperser, ball mill, attritor, sand mill, sand grinder, ultra fine mill, Eiger motor mill, dyno mill, pearl mill, aji data mill. There are a cobol mill, three rolls, two rolls, an extruder, a kneader, a microfluidizer, a laboratory homogenizer, an ultrasonic homogenizer, etc., and these may be used alone or in combination. Alternatively, after mixing a predetermined solvent, water, and a dispersant, a pigment may be added and dispersed using a disperser.

(7) Removal In the present invention, at least a part of the base and the suspended dispersion resin from the dispersion obtained in the dispersion step (first invention) or the dispersion obtained in the base addition step (second invention). Remove at least a portion of The pH of the pigment dispersion obtained in the removing step is preferably 8 or more and 10 or less. If the pH is less than 10, the reliability tends to decrease, and if it is less than 8, the viscosity tends to increase.

  In the present invention, the viscosity of the pigment dispersion is further reduced by removing at least a part of the suspended dispersion resin. Since the present invention achieves the above-described effects at low cost, low-viscosity ink can be provided at low cost.

  A predetermined solvent, an additive, and the like are added to the prepared pigment dispersion, followed by stirring, mixing, and filtration, whereby the ink for inkjet recording of the present invention can be obtained.

(8) Inkjet recording As the inkjet recording method of the present invention, there are a recording method in which mechanical energy is applied to the ink and ink is ejected, and an ink jet recording method in which thermal energy is applied to the ink and ink is ejected by foaming of the ink. is there. The ink of the present invention is particularly suitable for those ink jet recording methods.

  Next, an example of the ink jet recording apparatus of the present invention suitable for performing recording using the ink of the present invention will be described below. First, FIG. 1 and FIG. 2 show an example of a head configuration which is a main part of an ink jet recording apparatus using thermal energy.

FIG. 1 is a cross-sectional view of the head 13 along the ink flow path, and FIG. 2 is a cross-sectional view taken along line AB in FIG. The head 13 is obtained by adhering a heating element substrate 15 and a glass, ceramic, silicon or plastic plate having a flow path (nozzle) 14 through which ink passes. The heating element substrate 15 includes a protective layer 16 formed of silicon oxide, silicon nitride, silicon carbide, etc., electrodes 17-1 and 17-2 formed of aluminum, gold, aluminum-copper alloy, etc., HfB ₂ , TaN, TaAl From a heating resistor layer 18 formed from a high melting point material such as, a heat storage layer 19 formed from thermal silicon oxide, aluminum oxide, or the like, and a substrate 20 formed from a material with good heat dissipation such as silicon, aluminum, aluminum nitride, etc. It has become.

  When a pulsed electric signal is applied to the electrodes 17-1 and 17-2 of the head 13, the region indicated by n of the heating element substrate 15 rapidly generates heat, and bubbles are generated in the ink 21 in contact with the surface. Will occur. The meniscus 23 protrudes due to the pressure, and the ink 21 is ejected through the nozzle 14 of the head, becomes an ink droplet 24 from the ejection orifice 22, and flies toward the recording medium 25. FIG. 3 shows an external view of an example of a multi-head in which a large number of heads shown in FIG. 1 are arranged. This multi-head is made by adhering a glass plate 27 having multi-nozzles 26 and a heating head 28 similar to that described in FIG.

  FIG. 4 shows an example of an ink jet recording apparatus incorporating this head. In FIG. 4, reference numeral 61 denotes a blade as a wiping member, one end of which is held and fixed by a blade holding member, and forms a cantilever. The blade 61 is disposed at a position adjacent to the recording area by the recording head 65, and in this example, is held in a form protruding in the moving path of the recording head 65.

  Reference numeral 62 denotes a cap on the projection port surface of the recording head 65, which is disposed at a home position adjacent to the blade 61, moves in a direction perpendicular to the moving direction of the recording head 65, contacts the ink ejection port surface, and performs capping. The structure to perform is provided. Further, reference numeral 63 denotes an ink absorber provided adjacent to the blade 61 and, like the blade 61, is held in a form protruding in the moving path of the recording head 65. The blade 61, the cap 62, and the ink absorber 63 constitute an ejection recovery unit 64, and the blade 61 and the ink absorber 63 remove moisture, dust, and the like from the ejection port surface.

  Reference numeral 65 denotes a recording head which has discharge energy generating means and performs recording by discharging ink onto a recording medium facing the discharge port surface where the discharge port is arranged. Reference numeral 66 denotes a movement of the recording head 65 by mounting the recording head 65. It is a carriage for performing. The carriage 66 is slidably engaged with the guide shaft 67, and a part of the carriage 66 is connected to a belt 69 (not shown) driven by a motor 68. As a result, the carriage 66 can move along the guide shaft 67, and the recording area and its adjacent area can be moved by the recording head 65.

  51 is a paper feed section for inserting a recording medium, and 52 is a paper feed roller driven by a motor (not shown). With these configurations, the recording medium is fed to a position facing the discharge port surface of the recording head 65, and is discharged to a paper discharge portion provided with a paper discharge roller 53 as recording progresses.

  In the above configuration, when the recording head 65 finishes recording and returns to the home position, the cap 62 of the ejection recovery unit 64 is retracted from the moving path of the recording head 65, but the blade 61 protrudes into the moving path. As a result, the ejection port of the recording head 65 is wiped.

  When the cap 62 is in contact with the ejection surface of the recording head 65 to perform capping, the cap 62 moves so as to protrude into the moving path of the recording head. When the recording head 65 moves from the home position to the recording start position, the cap 62 and the blade 61 are at the same position as that at the time of wiping described above. As a result, the ejection port surface of the recording head 65 is wiped even during this movement. The above-mentioned movement of the recording head to the home position is not only at the end of recording or at the time of ejection recovery, but also to the home position adjacent to the recording area at a predetermined interval while the recording head moves the recording area for recording. Then, the wiping is performed with this movement.

  FIG. 5 is a diagram illustrating an example of an ink cartridge that contains ink supplied to the recording head via an ink supply member, for example, a tube. Here, reference numeral 40 denotes an ink container, for example, an ink bag, in which supply ink is stored, and a rubber plug 42 is provided at the tip thereof. By inserting a needle (not shown) into the stopper 42, the ink in the ink bag 40 can be supplied to the head. An ink absorber 44 receives waste ink. The ink container preferably has a liquid contact surface made of polyolefin, particularly polyethylene.

  The ink jet recording apparatus used in the present invention is not limited to the one in which the head and the ink cartridge are separated as described above, but is preferably used in an apparatus in which they are integrated as shown in FIG. It is done. In FIG. 6, reference numeral 70 denotes a recording unit, in which an ink storage portion that stores ink, for example, an ink absorber is stored, and the ink in the ink absorber from the head portion 71 having a plurality of orifices. It is configured to be ejected as ink droplets. It is preferable for the present invention to use polyurethane as the material of the ink absorber. Alternatively, a structure in which the ink container is an ink bag with a spring or the like inside without using an ink absorber may be used. Reference numeral 72 denotes an atmosphere communication port for communicating the inside of the cartridge with the atmosphere. The recording unit 70 is used in place of the recording head 65 shown in FIG. 4 and is detachable from the carriage 66.

  EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples. However, the present invention is not limited to the following examples unless it exceeds the gist. In the following description, “part” or “%” is based on mass unless otherwise specified.

<Example 1>
As dispersion resin, from poly-4-methylphenylethyl vinyl ether (A block), poly-2- (2-methoxyethyl) ethyl vinyl ether (B block) and poly-4- (2-vinyloxy) ethoxybenzoic acid (C block) The triblock copolymer-1 (the polymerization ratio was A: B: C = 98: 90: 14) (Mn = 27,200, Mw / Mn = 1.36) was used.

  5 parts of the above dispersion resin and 5 parts of copper phthalocyanine pigment (manufactured by Toyo Ink) are co-dissolved in 100 parts of tetrahydrofuran, and contain 1 stoichiometric amount of potassium hydroxide with respect to the amount of carboxylic acid of triblock copolymer-1. 100 parts of ion exchange water was added. Then, it disperse | distributed using Nanomizer YSNM-2000AR (made by Yoshida Kikai Kogyo Co., Ltd.).

  Then, the triblock copolymer and the copper phthalocyanine pigment were converted into an aqueous phase by evaporating tetrahydrofuran. Thereafter, 2 stoichiometric amounts of potassium hydroxide were further added to the amount of carboxylic acid in triblock copolymer-1. After the pH is adjusted to 11.6, the dispersion is treated with a centrifuge (10,000 rpm × 30 minutes), and the step of replacing the supernatant with ion-exchanged water is repeated, whereby the base and the suspension are suspended. The dispersion resin was removed to obtain a pigment dispersion having a pH of 9.6. Appropriate amounts of an aqueous solvent, ion-exchanged water, and additives were added to the pigment dispersion, followed by pressure filtration through a 1 μm filter to prepare the following ink-1.

Copper phthalocyanine pigment (manufactured by Toyo Ink) 2.5 parts Triblock copolymer-1 2.5 parts Diethylene glycol 5.0 parts Glycerin 4.5 parts Trimethylolpropane 5.0 parts Acetylenol EH (river Manufactured by Ken Fine Chemical Co., Ltd.) 0.1 parts ・ Ion-exchanged water 80.4 parts

<Example 2>
As dispersion resin, from poly-4-methylphenylethyl vinyl ether (A block), poly-2- (2-methoxyethyl) ethyl vinyl ether (B block) and poly-4- (2-vinyloxy) ethoxybenzoic acid (C block) Triblock copolymer-2 (with a polymerization ratio of A: B: C = 98: 130: 14) (Mn = 31,200, Mw / Mn = 1.36) was used.

  5 parts of the above dispersion resin and 5 parts of copper phthalocyanine pigment (manufactured by Toyo Ink) are co-dissolved in 100 parts of tetrahydrofuran, and contain 3 stoichiometric amounts of potassium hydroxide with respect to the amount of carboxylic acid of triblock copolymer-2. 100 parts of ion exchange water was added. Thus, the pH was adjusted to 11.4, and then dispersed using Nanomizer YSNM-2000AR (manufactured by Yoshida Kikai Kogyo Co., Ltd.). Then, the triblock copolymer-2 and the copper phthalocyanine pigment were converted into an aqueous phase by evaporating tetrahydrofuran.

  Thereafter, the dispersion is treated with a centrifuge (10,000 rpm × 60 minutes), and the step of replacing the supernatant with ion-exchanged water is repeated to remove the base and the suspended dispersion resin. A pigment dispersion of 9.4 was obtained. Appropriate amounts of an aqueous solvent, ion-exchanged water, and additives were added to the pigment dispersion, followed by pressure filtration through a 1 μm filter to prepare the following inkjet ink-2.

-Copper phthalocyanine pigment (manufactured by Toyo Ink) 2.5 parts-Triblock copolymer-2 2.5 parts-Diethylene glycol 5.0 parts-Glycerin 4.5 parts-Trimethylolpropane 5.0 parts-Acetylenol EH (river Manufactured by Ken Fine Chemical Co., Ltd.) 0.1 parts ・ Ion-exchanged water 80.4 parts

<Example 3>
As dispersion resin, from poly-4-methylphenylethyl vinyl ether (A block), poly-2- (2-methoxyethyl) ethyl vinyl ether (B block) and poly-4- (2-vinyloxy) ethoxybenzoic acid (C block) The triblock copolymer-1 (the polymerization ratio was A: B: C = 98: 90: 14) (Mn = 27,200, Mw / Mn = 1.36) was used.

  5 parts of the above dispersion resin and 5 parts of a copper phthalocyanine pigment (manufactured by Toyo Ink) are co-dissolved in 100 parts of tetrahydrofuran and contain 3 stoichiometric amounts of potassium hydroxide with respect to the amount of carboxylic acid in triblock copolymer-1. 100 parts of ion exchange water was added. Thus, the pH was adjusted to 11.4, and then dispersed using Nanomizer YSNM-2000AR (manufactured by Yoshida Kikai Kogyo Co., Ltd.).

  Then, the triblock copolymer-1 and the copper phthalocyanine pigment were converted into an aqueous phase by evaporating tetrahydrofuran. Thereafter, the dispersion is treated with a centrifuge (10,000 rpm × 60 minutes), and the step of replacing the supernatant with ion-exchanged water is repeated to remove the base and the suspended dispersion resin. A pigment dispersion of 9.1 was obtained. Appropriate amounts of an aqueous solvent, ion-exchanged water, and additives were added to the pigment dispersion, followed by pressure filtration through a 1 μm filter to prepare the following inkjet ink-3.

Copper phthalocyanine pigment (manufactured by Toyo Ink) 2.5 parts Triblock copolymer-1 2.5 parts Diethylene glycol 5.0 parts Glycerin 4.5 parts Trimethylolpropane 5.0 parts Acetylenol EH (river Manufactured by Ken Fine Chemical Co., Ltd.) 0.1 parts ・ Ion-exchanged water 80.4 parts

<Example 4>
Styrene acrylic acid 1: 1 random copolymer-1 (Mn = 22,000, Mw / Mn = 1.98) was used as a dispersion resin.

  Ion containing 5 parts of the above dispersion resin and 5 parts of copper phthalocyanine pigment (manufactured by Toyo Ink) in 100 parts of tetrahydrofuran and containing 1 stoichiometric amount of potassium hydroxide with respect to the amount of carboxylic acid of random copolymer-1. 100 parts of exchange water was added. Then, it disperse | distributed using Nanomizer YSNM-2000AR (made by Yoshida Kikai Kogyo Co., Ltd.).

  And the random copolymer-1 and the copper phthalocyanine pigment were converted into the water phase by evaporating tetrahydrofuran. Thereafter, the pH was adjusted to 11.6 by further adding 2 stoichiometric amounts of potassium hydroxide to the amount of carboxylic acid in random copolymer-1. Thereafter, the dispersion is treated with a centrifuge (10,000 rpm × 30 minutes), and the step of replacing the supernatant with ion-exchanged water is repeated to remove the base and the suspended dispersion resin, and pH Of 9.6 was obtained. Appropriate amounts of an aqueous solvent, ion-exchanged water, and additives were added to the pigment dispersion, followed by pressure filtration through a 1 μm filter to prepare the following ink-4.

・ Copper phthalocyanine pigment (manufactured by Toyo Ink) 2.5 parts ・ Random copolymer-1 2.5 parts ・ Diethylene glycol 5.0 parts ・ Glycerin 4.5 parts ・ Trimethylolpropane 5.0 parts ・ Acetylenol EH (Kawaken) Fine chemicals) 0.1 parts ・ Ion-exchanged water 80.4 parts

<Example 5>
As dispersion resin, from poly-4-methylphenylethyl vinyl ether (A block), poly-2- (2-methoxyethyl) ethyl vinyl ether (B block) and poly-4- (2-vinyloxy) ethoxybenzoic acid (C block) Triblock copolymer-2 (with a polymerization ratio of A: B: C = 98: 130: 14) (Mn = 31,200, Mw / Mn = 1.36) was used.

  5 parts of the above dispersion resin and 5 parts of copper phthalocyanine pigment (manufactured by Toyo Ink) were co-dissolved in 100 parts of tetrahydrofuran, and 1.5 stoichiometric amount of potassium hydroxide with respect to the amount of carboxylic acid of triblock copolymer-2. 100 parts of ion exchange water containing was added. Thus, the pH was adjusted to 9.7, and then dispersed using Nanomizer YSNM-2000AR (manufactured by Yoshida Kikai Kogyo Co., Ltd.).

  Then, the triblock copolymer-2 and the copper phthalocyanine pigment were converted into an aqueous phase by evaporating tetrahydrofuran. Thereafter, the dispersion is treated with a centrifuge (10,000 rpm × 60 minutes), and the step of replacing the supernatant with ion-exchanged water is repeated to remove the base and the suspended dispersion resin. A pigment dispersion of 9.1 was obtained. Appropriate amounts of an aqueous solvent, ion-exchanged water, and additives were added to the pigment dispersion, followed by pressure filtration through a 1 μm filter to prepare the following inkjet ink-5.

-Copper phthalocyanine pigment (manufactured by Toyo Ink) 2.5 parts-Triblock copolymer-2 2.5 parts-Diethylene glycol 5.0 parts-Glycerin 4.5 parts-Trimethylolpropane 5.0 parts-Acetylenol EH (river Manufactured by Ken Fine Chemical Co., Ltd.) 0.1 parts ・ Ion-exchanged water 80.4 parts

<Example 6>
As dispersion resin, from poly-4-methylphenylethyl vinyl ether (A block), poly-2- (2-methoxyethyl) ethyl vinyl ether (B block) and poly-4- (2-vinyloxy) ethoxybenzoic acid (C block) The triblock copolymer-1 (the polymerization ratio was A: B: C = 98: 90: 14) (Mn = 27,200, Mw / Mn = 1.36) was used.

  5 parts of the above dispersion resin and 5 parts of copper phthalocyanine pigment (manufactured by Toyo Ink) are co-dissolved in 100 parts of tetrahydrofuran, and contain 1 stoichiometric amount of potassium hydroxide with respect to the amount of carboxylic acid of triblock copolymer-1. 100 parts of ion exchange water was added. Then, it disperse | distributed using Nanomizer YSNM-2000AR (made by Yoshida Kikai Kogyo Co., Ltd.). Then, the triblock copolymer and the copper phthalocyanine pigment were converted into an aqueous phase by evaporating tetrahydrofuran.

  Thereafter, the pH was adjusted to 11.6 by further adding 2 stoichiometric amounts of potassium hydroxide to the amount of carboxylic acid in triblock copolymer-1, and then the dispersion was treated with a centrifuge ( 15,000 rpm x 60 minutes). By repeating the step of replacing the supernatant with ion-exchanged water, the base and the suspended dispersion resin were removed, and a pigment dispersion having a pH of 7.8 was obtained. Appropriate amounts of an aqueous solvent, ion-exchanged water, and additives were added to the pigment dispersion, followed by pressure filtration through a 1 μm filter to prepare the following ink-6.

Copper phthalocyanine pigment (manufactured by Toyo Ink) 2.5 parts Triblock copolymer-1 2.5 parts Diethylene glycol 5.0 parts Glycerin 4.5 parts Trimethylolpropane 5.0 parts Acetylenol EH (river Manufactured by Ken Fine Chemical Co., Ltd.) 0.1 parts ・ Ion-exchanged water 80.4 parts

<Comparative Example 1>
As dispersion resin, from poly-4-methylphenylethyl vinyl ether (A block), poly-2- (2-methoxyethyl) ethyl vinyl ether (B block) and poly-4- (2-vinyloxy) ethoxybenzoic acid (C block) Triblock copolymer-1 (polymerization ratio is A: B: C = 98: 90: 14) (Mn = 27,200, Mw / Mn = 1.36) and 5 parts of copper phthalocyanine pigment (manufactured by Toyo Ink) Was used.

  5 parts of the above dispersion resin were co-dissolved in 100 parts of tetrahydrofuran, and 100 parts of ion-exchanged water containing 1 stoichiometric amount of potassium hydroxide was added to the amount of carboxylic acid of triblock copolymer-1. Then, it disperse | distributed using Nanomizer YSNM-2000AR (made by Yoshida Kikai Kogyo Co., Ltd.).

  Then, the triblock copolymer and the copper phthalocyanine pigment were converted into an aqueous phase by evaporating tetrahydrofuran, and a pigment dispersion having a pH of 8.3 was obtained. Appropriate amounts of an aqueous solvent, ion-exchanged water, and additives were added to the pigment dispersion, followed by pressure filtration through a 1 μm filter to prepare the following ink-5.

Copper phthalocyanine pigment (manufactured by Toyo Ink) 2.5 parts Triblock copolymer-1 2.5 parts Diethylene glycol 5.0 parts Glycerin 4.5 parts Trimethylolpropane 5.0 parts Acetylenol EH (river Manufactured by Ken Fine Chemical Co., Ltd.) 0.1 parts ・ Ion-exchanged water 80.4 parts

<Comparative example 2>
As dispersion resin, 5 parts of styrene acrylic acid 1: 1 random copolymer-1 (Mn = 22,000, Mw / Mn = 1.98) and copper phthalocyanine pigment (manufactured by Toyo Ink) were used.

  5 parts of the above dispersion resin was co-dissolved in 100 parts of tetrahydrofuran, and 100 parts of ion-exchanged water containing 1 stoichiometric amount of potassium hydroxide was added to the amount of carboxylic acid of random copolymer-1. Then, it disperse | distributed using Nanomizer YSNM-2000AR (made by Yoshida Kikai Kogyo Co., Ltd.).

  Then, the random copolymer-1 and the copper phthalocyanine pigment were converted to an aqueous phase by evaporating tetrahydrofuran, and a pigment dispersion having a pH of 8.0 was obtained. Appropriate amounts of an aqueous solvent, ion-exchanged water, and additives were added to the pigment dispersion, followed by pressure filtration through a 1 μm filter to prepare the following ink-6.

・ Copper phthalocyanine pigment (manufactured by Toyo Ink) 2.5 parts ・ Random copolymer-1 2.5 parts ・ Diethylene glycol 5.0 parts ・ Glycerin 4.5 parts ・ Trimethylolpropane 5.0 parts ・ Acetylenol EH (Kawaken) Fine chemicals) 0.1 parts ・ Ion-exchanged water 80.4 parts

<Evaluation>
(viscosity)
The viscosity of the ink was measured with an E-type viscometer manufactured by Toki Sangyo Co., Ltd. The evaluation results are shown in Table 1 below. The evaluation criteria are as follows.
○: Less than 3.5 mPa · s Δ: 3.5 mPa · s or more and less than 4.5 mPa · s ×: 4.5 mPa · s or more

(Discharge characteristics)
Fill the ink tank of the ink jet recording device (Canon, BJF-900) with the above ink, print alphanumeric characters in an environment of 15 ° C and 10%, stop the printer, and remove the atmosphere without caps. The head was exposed inside and printed again, and evaluated according to the following criteria. The evaluation results are shown in Table 1 below.
○: Disturbance of characters occurs after an exposure time of 60 seconds or more.
Δ: Character disturbance occurs when the exposure time is 30 seconds or more and less than 60 seconds.
X: Disturbance of characters occurs when the exposure time is less than 30 seconds.

(Long-term storage stability)
The above ink is stored in a Teflon (registered trademark) container at 60 ° C. for 5 months, and changes in particle size distribution, surface tension, viscosity, pH, presence or absence of precipitates, and influence on ejection are investigated. evaluated. The evaluation results are shown in Table 1 below.
◯: There is almost no change in physical properties, no precipitate is confirmed, and discharge is not affected.
(Triangle | delta): Either a physical property change, a deposit is confirmed, or discharge is affected.

Claims (9)

  In the method for producing a pigment dispersion containing at least an aqueous medium, a pigment, and a dispersion resin in which the pigment is dispersed in the aqueous medium, the dispersion resin has the dispersion liquid containing the pigment and the dispersion resin. A base addition step of adding a base exceeding the equivalent of the ionic group, a dispersion step of mechanically dispersing the dispersion obtained by the base addition step, and at least a part of the base from the dispersion obtained by the dispersion step And a method for producing a pigment dispersion, comprising a removal step of removing at least a part of the suspended dispersion resin.   In the method for producing a pigment dispersion containing at least an aqueous medium, a pigment, and a dispersion resin in which the pigment is dispersed in the aqueous medium, an ion of the dispersion resin in the dispersion containing the pigment and the dispersion resin Neutralization step of neutralizing at least part of the ionic groups of the dispersion resin by adding a base equal to or less than the equivalent of the functional group, and dispersion step of mechanically dispersing the dispersion obtained by the neutralization step A base addition step of adding a base to the dispersion obtained by the dispersion step, and removing at least a portion of the base and at least a portion of the suspended dispersion resin from the dispersion obtained by the base addition step. The manufacturing method of the pigment dispersion characterized by having a removal process.   The method for producing a pigment dispersion according to claim 1 or 2, wherein the total amount of the base in the dispersion obtained by the base addition step is an amount such that the pH of the dispersion becomes 11 or more.   The method for producing a pigment dispersion according to any one of claims 1 to 3, wherein the pH of the pigment dispersion obtained by the removing step is set to 8 or more and 10 or less.   The method for producing a pigment dispersion according to any one of claims 1 to 4, wherein the dispersion resin is an amphiphilic block copolymer having an ionic functional group.   The method for producing a pigment dispersion according to claim 5, wherein the block copolymer has a structure in which a hydrophobic block segment, a nonionic hydrophilic segment, and an ionic hydrophilic segment are arranged in this order.   The method for producing a pigment dispersion according to claim 5 or 6, wherein the block copolymer contains a polyvinyl ether structure as a repeating unit structure.   A pigment dispersion produced by the method for producing a pigment dispersion according to any one of claims 1 to 7.   An ink for ink-jet recording produced using the pigment dispersion according to claim 8.

Images