JP2007161846A - Method for producing pigment dispersion, ink composition and ink set for ink-jet recording, method for forming image and apparatus for recording image - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ink for ink jets suppressing an increase in viscosity even when a larger amount of a polymer is added, having good jetting characteristics and achieving high image quality by adding a block copolymer after a dispersion treatment. <P>SOLUTION: A method for producing a pigment dispersion comprising an aqueous medium, a water-insoluble colorant and a dispersed resin is provided. The method for producing the pigment dispersion is characterized as comprising a step of carrying out the dispersion treatment of the water-insoluble colorant in the aqueous medium with the dispersed resin and a step of adding the block copolymer different from the dispersed resin used in the dispersion treatment as a post-added dispersed resin to a dispersion obtained by the dispersion treatment. An ink composition and an ink set for ink-jet recording comprise the pigment dispersion. A method for forming the image and an apparatus for recording the image use the ink composition. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ink composition for ink jet recording suitable for recording color images and storing recorded images, an ink set formed by combining the ink compositions, and a method for producing a pigment dispersion used in the ink composition. Furthermore, the present invention relates to an image forming method for forming an image using the ink composition or ink set, and an image recording apparatus for performing the method.

  In the ink jet recording method, an ink droplet is ejected from a nozzle provided in a recording head by pressure due to thermal energy or vibration by a piezoelectric element, and fixed on a recording medium to form an image. Such an ink jet recording method is excellent in quietness, and can perform high-resolution image formation at high speed without using a special fixing means. The ink jet recording method is also suitable for forming a color image from the viewpoint of structural ease and running cost. For this reason, in recent years, inkjet recording methods and apparatuses effective for color image formation have been provided for output for personal computers, graphic printing, and many other applications.

  When forming a color image by the ink jet recording method, it is common to use at least three primary colors of a cyan ink composition, a magenta ink composition, and a yellow ink composition. Furthermore, image formation is widely performed using four colors obtained by adding a black ink composition to these three primary colors. For example, a red image is expressed in a pseudo manner by applying magenta and yellow inks to the same point on the recording medium or adjoining them. Similarly, a blue image is represented by magenta and cyan inks, and a green image is represented by cyan and yellow inks. These can be expressed with further gradation by adjusting the amount of ink droplets and the number of applied inks or combining black.

  Recently, in addition to the above-mentioned four colors of cyan, magenta, yellow and black, two colors with reduced concentrations of cyan ink composition and magenta ink composition are added to form a color image with six colors of ink. Sometimes it is done. Each ink composition used for the formation of such a color image has a good color developability in itself and develops a good intermediate color when combined with a plurality of ink compositions. Is required.

  In addition, the ink compositions constituting the ink set composed of a combination of a plurality of colors used in the ink jet recording method as described above are required to have the performances listed below. For example, the ink physical properties such as viscosity and surface tension are appropriate. In addition, the optical density is high, a clear color tone and an image are given, and an image excellent in fastness such as water resistance, scratch resistance and light resistance is given. In addition, the ink is excellent in storage stability, and further, it is difficult to cause clogging of the nozzle. Furthermore, there is no problem in odor and no problem in safety.

  A dye aqueous solution is usually used for the ink composition used in the ink jet recording method. For this reason, there are cases where bleeding occurs during color superimposition or a phenomenon called feathering appears in the fiber direction of the paper at the recording location on the recording medium. Patent Document 1 discloses the use of a pigment-dispersed ink to improve these problems. As other inks in which a pigment is dispersed in a water-soluble medium composed of water or a water-soluble organic solvent, there are various proposals as listed below. For example, there is a method of using a polymer dispersant and an anionic surfactant in combination (Patent Document 2), or a method of using a polymer dispersant and a nonionic surfactant in combination (Patent Document 3). Further, for example, there is a method using a block copolymer as a dispersant (Patent Document 4) and a method using a graft copolymer as a dispersant (Patent Document 5). For example, there is a method of using a polymer dispersant obtained by copolymerizing a monomer having a nonionic group with respect to a polymer dispersant having a hydrophilic structure portion and a hydrophobic structure portion (Patent Documents 6 and 7).

  However, the conventional method as described above has not yet obtained an ink composition in which a pigment satisfying all the requirements listed above is dispersed. In particular, there are problems such as deterioration in storage stability due to aggregation of pigments, occurrence of clogging at the tip of a fine nozzle, and ink jet recording properties. In particular, the ink composition may not have sufficient discharge durability over a long period of time. In a specific example, when ink is continuously ejected by an ink jet recording head, a situation such as a decrease in ejection amount or ejection speed may occur, and ejection may be difficult to perform stably. As described above, in the pigment-dispersed ink, many improvements are still desired.

US Pat. No. 5,085,698 JP-A-56-147868 Japanese Patent Laid-Open No. 56-147871 US Pat. No. 5,221,334 JP-A-6-100810 JP-A-6-264017 JP-A-6-306317

  The present invention has been made in view of the above-described problems of the prior art, and an object of the present invention is to provide a pigment-dispersed ink that is excellent in any of the various performances described above. Specifically, the present invention provides an ink composition and an ink set that satisfy various characteristics as an ink composition for ink jet recording and satisfy satisfactory image formation and ejection stability during ink jet ejection. is there. Another object of the present invention is to provide an image forming method using these and an image recording apparatus thereof. Another object of the present invention is to provide a method for producing a pigment dispersion that makes it possible to provide an ink composition having excellent performance as described above.

  The above object is achieved by the present invention described below. That is, according to a first aspect of the present invention, in a method for producing a pigment dispersion containing an aqueous medium, a water-insoluble colorant and a dispersion resin, the water-insoluble colorant is dispersed in the aqueous medium using the dispersion resin. And a step of adding a block copolymer different from the dispersion resin used in the dispersion treatment to the dispersion obtained by the dispersion treatment as a post-addition dispersion resin. is there.

  That is, in the present invention, after a water-insoluble colorant is dispersed in an aqueous medium using a dispersion resin, a block copolymer different from the first dispersion resin is added to the dispersion obtained by the dispersion treatment. Is added as a post-added dispersion resin. In the present invention, an excellent pigment dispersion is prepared by performing a two-stage process of adding a second dispersion resin different from the first dispersion resin after the pigment dispersion process. By using the above-mentioned second dispersion resin, the present inventors have good discharge stability without increasing the viscosity when compared with the case of only the first dispersion resin and the amount of the resin is equivalent. The present inventors have found that a pigment dispersion exhibiting the following can be prepared, and reached the present invention.

  As a preferable aspect of the manufacturing method of the above-mentioned pigment dispersion, each form of the manufacturing method of the pigment dispersion enumerated below is mentioned. A form in which different acid values are used for the dispersion resin used at the time of dispersion and the block copolymer added after the dispersion treatment. A form in which the acid value of the block copolymer added after the dispersion treatment is lower than the acid value of the dispersion resin used during dispersion. A configuration in which the average value of the acid value of the dispersion resin and the acid value of the post-addition dispersion resin is in the range of 3 KOHmg / g or more and 150 KOHmg / g or less.

  The second aspect of the present invention is the above-described method for producing a pigment dispersion. In particular, the polymer used during dispersion is a triblock copolymer, and the dispersion resin added after the dispersion treatment is a hydrophobic segment and a hydrophilic segment. It is a diblock copolymer which has these.

  As a preferable aspect of the manufacturing method of the said pigment dispersion liquid, each form of the manufacturing method of the pigment dispersion liquid enumerated below is mentioned. A mode in which the molecular weight of the diblock copolymer added after the dispersion treatment is smaller than the molecular weight of the triblock copolymer used during the dispersion treatment. The form using the block copolymer which contains a polyvinyl ether structure as a repeating unit structure as a triblock copolymer used at the time of a dispersion process.

  According to a third aspect of the present invention, there is provided a combination of an ink composition for ink-jet recording, comprising the pigment dispersion obtained by any one of the above methods, a polyhydric alcohol as an organic solvent, and the ink composition. Is an ink set.

  Further, in the image forming method of forming an image by ejecting the ink composition onto a recording medium by applying energy to the ink composition, the ink composition or the ink set is used as the ink composition. This is an image forming method. More preferred is an image forming method in which the ink composition is discharged by a heating means. Further, the present invention is an image recording apparatus characterized by having a configuration for performing the above-described image forming method.

  According to the present invention, by adding the block copolymer as the post-added dispersion resin, more dispersion resin can be added to the pigment dispersion in a state where the increase in viscosity is suppressed. As a result, it is possible to provide an inkjet ink that has good ejection characteristics and can provide a high-quality image.

  Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. As the water-insoluble colorant used in the present invention, a pigment is used, and the pigment may be either an organic pigment or an inorganic pigment. The pigment used in the ink is preferably a black pigment and three primary color pigments of cyan, magenta, and yellow. Note that pigments other than those described above, colorless or light pigments, or metallic luster pigments may be used. In the present invention, commercially available pigments may be used, or newly synthesized pigments may be used. Moreover, you may use together with dye.

The following are examples of commercially available pigments for black, cyan, magenta, and yellow.
Examples of the black pigment include, but are not limited to, the following.
Raven 1060, Raven 1080, Raven 1170, Raven 1200, Raven 1250, Raven 1255, Raven 1500, Raven 2000, Raven 3500, Raven 5250, Raven 5750, Raven 7000, Raven 7000, Raven 7000, Raven 7000, Raven 7000, Raven 7000 Manufactured);
Black Pearls L, MOGUL-L, Regal 400R, Regal 660R, Regal 330R, Monarch 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1300, Monarch 1400 (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 Black 4A, Special Black 6, Printex35, PrintexU, Printex140U, PrintexV, Printex140V (more than Degussa AG );
No. 25, no. 33, no. 40, no. 47, no. 52, no. 900, no. 2300, MCF-88, MA600, MA7, MA8, MA100 (manufactured by Mitsubishi Chemical)

Examples of cyan pigments include, but are not limited to, the following.
C. 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 etc.

Examples of magenta pigments include, but are not limited to, the following.
C. 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, etc.

Examples of yellow pigments include, but are not limited to, the following.
C. 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, etc.

  In the present invention, a pigment that is self-dispersible in water can also be used as the water-insoluble colorant. 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 Corp.), Microjet Black CW-1 (manufactured by Orient Chemical Co., Ltd.), and the like.

  The pigment used in the present invention is preferably used in the range of 0.1 to 50% by mass with respect to the total mass of the ink composition. 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 to 30% by mass. More preferably, it is 0.7-10 mass%. The average particle diameter of the pigment ink composition of the present invention is preferably in the range of 50 to 200 nm, and preferably 100 nm or less in order to obtain better image quality. In addition, FPAR-1000 (Otsuka Electronics) was used for the measurement of the pigment particle diameter.

  Any dispersion resin can be used for the dispersion treatment of pigment particles used in the present invention, but the weight average molecular weight is preferably in the range of 1,000 to 30,000. Furthermore, it is preferable to use a material in the range of 3,000 to 15,000. Specific examples of the dispersion resin include a block copolymer composed of at least two monomers selected from the monomers listed below (at least one is a hydrophilic monomer), or random or graft copolymer. Examples thereof include salts and salts thereof.

Examples of the monomer include, but are not limited to, the following.
Styrene, styrene derivatives, vinyl naphthalene, vinyl naphthalene derivatives, aliphatic alcohol esters of α, β-ethylenically unsaturated carboxylic acids, acrylic acid, acrylic acid derivatives, maleic acid, maleic acid derivatives, itaconic acid, itaconic acid derivatives, Fumaric acid, fumaric acid derivative, etc. In the present invention, a triblock copolymer containing a polyvinyl ether structure described later as a repeating unit structure can be particularly preferably used. These resins are alkali-soluble resins that are soluble in an aqueous solution in which a base is dissolved. When the obtained pigment dispersion is used as an ink composition, the dispersion resin as described above is contained in an amount of 0.1 to 10% by mass with respect to the total amount of the ink. It is preferable to use it.

  Next, the post-added dispersion resin used after dispersion of the pigment used in the present invention will be described. The present invention is characterized in that after the dispersion treatment, a block copolymer different from the dispersion resin (polymer) described above used for the pigment dispersion treatment is added as a post-added dispersion resin, followed by stirring treatment. Therefore, not only when the dispersion resin used for dispersing the pigment is a random copolymer or a graft copolymer, but also when the dispersion resin used for dispersing the pigment is a block copolymer different from the post-added dispersion resin. Good. According to the study by the present inventors, from the viewpoint of ink suitability, a triblock copolymer is used as a dispersion resin, and a diblock copolymer having a hydrophobic segment and a hydrophilic segment is used as a post-added dispersion resin. Particular preference is given to pigment dispersions obtained by use.

  As the block copolymer used as the post-added dispersion resin, those having at least a hydrophobic block segment and a hydrophilic segment and having a structure capable of forming micelles are preferable. More preferably, a triblock copolymer having a structure in which a hydrophobic segment (A segment), a nonionic hydrophilic segment (B segment), and an ionic hydrophilic segment (C segment) are arranged in this order, or a hydrophobic segment And a diblock copolymer having an ionic segment. Here, the block copolymer used in the present invention is a copolymer in which polymer segments having different repeating unit structures are bonded by a covalent bond, and is also called a block copolymer or a block polymer. When a diblock copolymer is used, it is possible to prepare a pigment dispersion having a lower viscosity. For this reason, a favorable result is obtained when it is used as the forming material of the ink for ink jet recording.

  Specific examples of the block copolymer that can be used in the present invention include the following conventionally known block copolymers. Examples thereof include acrylic, methacrylic block copolymers, polystyrene and other addition polymerization or condensation polymerization block copolymers, and block copolymers having polyoxyethylene and polyoxyalkylene blocks. In the present invention, it is particularly preferable to use a block copolymer containing a polyvinyl ether structure as a repeating unit structure as the dispersion resin.

  Specific examples of the ionic hydrophilic block segment (C segment) constituting the block copolymer include a repeating unit represented by the following general formula (1).

（上記式中、Ｒ⁰は、−Ｘ−ＣＯＯＨ、−Ｘ−ＣＯＯＭ、−Ｘ−ＣＨ（ＣＨ₂ＣＯＯＨ）₂、−Ｘ−ＣＨ（ＣＨ₂ＣＯＯ）₂Ｍ、−Ｘ−Ｏ−（ＣＨ₂）_q−ＣＯＯＨ、−Ｘ−Ｏ−（ＣＨ₂）_q−ＣＯＯＭ、−Ｘ−Ｏ−Ｐｈ−（ＣＨ₂）_q−ＣＯＯＨ、−Ｘ−（Ｏ）_n−Ｐｈ−（ＣＨ₂）_q−ＣＯＯＭを表す。ここで、−Ｘ−は、炭素数１から２０までの直鎖状、分岐状又は環状のアルキレン基を表す。ｎは１又は０を表す。ｑは０から１７の整数を表す。Ｍは、一価又は多価のカチオンを表す。Ｐｈは、フェニレン基を表す。）

(In the above formula, R ⁰ is —X—COOH, —X—COOM, —X—CH (CH ₂ COOH) ₂ , —X—CH (CH ₂ COO) ₂ M, —X—O— (CH _{2 ) q -COOH, -X-O- (} CH 2) q -COOM, -X-O-Ph- (CH 2) q -COOH, -X- (O) n -Ph- (CH 2) q -COOM Here, -X- represents a linear, branched or cyclic alkylene group having 1 to 20 carbon atoms, n represents 1 or 0, and q represents an integer of 0 to 17. M represents a monovalent or polyvalent cation, and Ph represents a phenylene group.)

  Specific examples of the repeating unit structure represented by the general formula (1) are given below. In the formula, Ph represents a phenylene group.

  Furthermore, specific examples of the repeating unit structure of the hydrophobic segment or nonionic hydrophilic segment constituting the block polymer used in the present invention include a repeating unit represented by the following general formula (2).

（式中、Ｒ¹は、炭素数１から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からなる群から選ばれ、芳香環中の水素原子は、炭素数１から４の直鎖状又は分岐状のアルキル基と、又、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から１８の整数、ｍは１から３６の整数、ｎは０又は１である。Ｒ⁵及び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から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、−Ｐｈ−ＣＨ₃、−ＣＨＯ、−ＣＨ₂ＣＨＯ、−ＣＯ−ＣＨ＝ＣＨ₂、−ＣＯ−Ｃ（ＣＨ₃）＝ＣＨ₂、−ＣＨ₂ＣＯＯＲ⁸からなり、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から４の直鎖状又は分岐状のアルキル基又は−Ｆ、−Ｃｌ、−Ｂｒと、又、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から５のアルキル基である。Ｐｈはフェニル基又はフェニレン基、Ｐｙｒはピリジル基を表わす。）

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

  Specific examples of the repeating unit structure represented by the general formula (2) constituting the hydrophobic segment (A segment) constituting the block copolymer used in the present invention include those described below.

  Specific examples of the unit structure represented by the general formula (2) constituting the nonionic hydrophilic segment (B segment) constituting the block copolymer used in the present invention are as follows. 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 gradient copolymer whose composition ratio gradually changes. The block copolymer used in the present invention may be a polymer having a block copolymer structure graft-bonded to another polymer.

  The content of the repeating unit structure represented by the general formula (1) or (2) in the block copolymer used in the present invention is 0.01 to 99 mol% with respect to the entire block polymer compound, preferably 1 The range of 90 mol% or less is desirable. That is, 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. On the other hand, if it exceeds 99 mol%, the function may be insufficient due to excessive interaction.

  The block copolymer used in the present invention preferably has a number average molecular weight (Mn) of 200 or more and 10,000,000 or less. More preferably, the range is 1,000 or more and 1,000,000 or less. When it 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 to obtain due to a small molecular weight. The preferred degree of polymerization of each block segment constituting the block copolymer used in the present invention is 3 or more and 10,000 or less. The more preferable range of the polymerization degree is 5 or more and 5,000 or less, and more preferably 10 or more and 4,000 or less.

  In the method for producing a pigment dispersion according to the present invention, a polymer having an acid value different from that of the dispersion resin used at the time of dispersion is used as a block copolymer which is a post-added dispersion resin used after the dispersion treatment. It is preferable to use it. Further, in that case, it is desirable to use a block copolymer which is a post-added dispersion resin having an acid value lower than that of the polymer used for the dispersion treatment. The reason is as follows. First, when a polymer having a low acid value is used during the dispersion treatment, it is difficult to disperse and the dispersion stability of the pigment dispersion is deteriorated. Therefore, it is necessary to use a dispersion resin having a high acid value to some extent. On the other hand, when the acid value of the obtained pigment dispersion is too high, there is a problem that the discharge characteristics deteriorate when the ink is used for inkjet recording using the pigment dispersion and the ink is discharged using a heating means. is there. For this reason, the acid value of the block copolymer, which is a post-added dispersion resin used after the dispersion treatment, is made lower than the acid value of the dispersion resin used during the dispersion treatment, so that the total acid value (the resulting pigment dispersion is obtained) It is preferable to adjust the acid value).

  At this time, it is preferable that the average value of the acid value of the dispersion resin used at the time of dispersion and the acid value of the post-added dispersion resin added after the dispersion treatment be 3 KOHmg / g or more and 150 KOHmg / g or less. More preferably, it is 30 or more and 90 KOHmg / g or less.

The average value of the acid value mentioned above means a value obtained as follows.
Acid value of dispersion resin used for pigment dispersion treatment: A (KOHmg / g)
Acid value of post-added dispersion resin used after dispersion treatment: B (KOHmg / g)
Dispersing resin (polymer) amount in pigment dispersion used for dispersion treatment: w _A (mass%)
Amount of post-added dispersion resin in pigment dispersion used after dispersion treatment: w _B (mass%)
Average acid value = (Aw _A + Bw _B ) / (w _A + w _B )

  The production method of the pigment dispersion according to the present invention may be the same as the production method of the ordinary pigment dispersion, as long as the configuration and addition method of the dispersion resin to be used are specified. For example, a pigment dispersion can be easily obtained by a normal dispersion method as described below, using an aqueous medium, a pigment, and a polymer as a dispersion resin as raw materials. For example, a method using a physical treatment such as a sand mill, a bead mill, or a kneader can be used in order for the polymer to be physically adsorbed on the pigment to be stably finely dispersed. In addition, it is also possible to use a method in which a pigment and a polymer are allowed to coexist in a solvent, and the solubility of the polymer is reduced in the solvent to deposit on the pigment surface. In addition, when the pigment is once dissolved and re-pigmented, a chemical treatment method such as a method of dispersing in a polymer can be used at the same time. In the present invention, a dispersion method appropriately selected from the methods listed above may be used.

  In the present invention, the ratio of the pigment and the polymer in the pigment dispersion is not particularly limited as long as the minimum necessary pigment dispersion stability is obtained. Further, the range of the amount of the preferred polymer used in the present invention is, in terms of mass ratio, a polymer that is a dispersion resin used for the dispersion treatment and a polymer that is a post-addition dispersion resin added after the dispersion treatment with respect to the pigment. In total, it is from 0.1 to 5, more preferably from 0.3 to 1.5.

  In the production method of the present invention, it is preferable to use a polymer which is a post-added dispersion resin added after the pigment dispersion step and which has been previously dissolved in an aqueous medium. At this time, the amount of the post-added dispersed resin to be contained in the aqueous medium is 0.5 to 50% by mass, more preferably 3 to 25% by mass. At this time, if the resin concentration in the polymer aqueous solution is high, the viscosity of the polymer aqueous solution increases, and therefore it may be difficult to make uniform when added to the pigment dispersion.

  The amount of the polymer, which is the post-added dispersion resin used after the dispersion treatment in the present invention, is suppressed to the same amount or less as the pigment content in the dispersion, thereby obtaining a low-viscosity pigment dispersion that can be applied to ink jet ink. . More preferably, the effect of the present invention is obtained even in an amount of 0.3 or less with respect to the pigment content.

  An ink composition for inkjet recording according to the present invention comprises the pigment dispersion obtained by the method for producing a pigment dispersion according to the present invention described above, and a polyhydric alcohol as an organic solvent. To do. Examples of the aqueous medium suitably used in the present invention include a mixed solvent of water, a buffer solution, and a water-soluble organic solvent. As water contained in water and a buffer solution, it is preferable to use ion-exchanged water (deionized water) instead of general water containing various ions.

Further, the water-soluble organic solvent used in the ink composition according to the present invention is not particularly limited as long as it is soluble in water, but includes the following.
Multivalents such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, propylene glycol, butylene glycol, 1,2,6-hexanetriol, thioglycol, hexylene glycol, glycerin, trimethylolethane, trimethylolpropane, etc. Alcohols,
Alkyl ethers of polyhydric alcohols such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether,
Urea, 2-pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, triethanolamine, etc.

  Next, an image forming method and an image recording apparatus using the ink composition according to the present invention described above will be described. FIG. 1 is a schematic perspective view showing a main part of an example of a liquid ejection head as an ejection type inkjet head that communicates bubbles with the atmosphere during ejection, and an inkjet printer as an inkjet image recording apparatus using the head.

  The ink jet printer shown in FIG. 1 has the following configuration. Reference numeral 1030 shown in FIG. 1 is a conveying device that intermittently conveys a sheet 1028 serving as a recording medium provided in the casing 1008 along the longitudinal direction in a direction indicated by an arrow P shown in the drawing. A recording unit 1010 shown in FIG. 1 is reciprocally moved substantially in parallel with the guide shaft 1014 in the arrow S direction substantially orthogonal to the conveyance direction P of the paper 1028 by the conveyance device 1030. Reference numeral 1006 denotes a movement drive unit as drive means for reciprocating the recording unit 1010.

  The transfer device 1030 has the following structure. That is, it includes a pair of roller units 1022a and 1022b arranged to face each other substantially parallel to each other, a pair of roller units 1024a and 1024b, and a drive unit 1020 for driving these roller units. When the drive unit 1020 of the transport device 1030 is activated, the paper 1028 is sandwiched between the two pairs of roller units and transported intermittently in the arrow P direction. The movement drive unit 1006 has the following structure. A belt 1016 is wound around pulleys 1026a and 1026b arranged on a rotating shaft opposed to each other with a predetermined interval, and is arranged substantially parallel to the roller units 1022a and 1022b and connected to the carriage member 1010a of the recording unit 1010. , And a motor 1018 that is driven in the forward direction and the reverse direction.

  When the motor 1018 is activated and the belt 1016 rotates in the direction of arrow R shown in the drawing, the carriage member 1010a of the recording unit 1010 is moved in the direction of arrow S by a predetermined amount of movement. When the motor 1018 is activated and the belt 1016 rotates in the direction opposite to the arrow R direction, the carriage member 1010a of the recording unit 1010 is moved by a predetermined amount of movement in the direction opposite to the arrow S direction. . Further, a recovery unit 1026 for performing discharge recovery processing of the recording unit 1010 is provided at one end of the movement driving unit 1006 at a position serving as the home position of the carriage member 1010a so as to face the ink discharge port array of the recording unit 1010. It has been.

  The recording unit 1010 includes an ink jet cartridge (hereinafter sometimes simply referred to as a cartridge) that contains ink. The cartridges 1012Y, 1012M, 1012C, and 1012B contain ink of each color, for example, yellow, magenta, cyan, and black. Ink tanks for each color are detachably attached to the carriage member 1010a. The effect of the ink composition according to the present invention is not limited to a specific color. For example, it is also a preferred aspect that two or more selected from the yellow, magenta, cyan and black inks are the ink composition according to the present invention.

  FIG. 2 is a perspective view showing an example of an ink jet cartridge that can be mounted on the above-described ink jet recording apparatus. A cartridge 1012 shown in FIG. 2 is of a serial type, and a main part is composed of an inkjet head 100 and a liquid tank 1001 that stores a liquid such as ink.

  The inkjet head 100 has a large number of ejection ports 832 for ejecting liquid. A liquid such as ink is guided from a liquid tank 1001 to a common liquid chamber (not shown) of the liquid discharge head 100 via a liquid supply passage (not shown). In the cartridge 1012 shown in FIG. 2, the ink jet head 100 and the liquid tank 1001 are integrally formed so that the liquid can be supplied into the liquid tank 1001 as necessary. However, the present invention is not limited to this, and a structure in which the liquid tank 1001 is connected to the liquid discharge head 100 in a replaceable manner may be adopted.

  EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these examples. In the text, “parts” and “%” are based on mass unless otherwise specified. Further, the remaining amount is the remainder obtained by subtracting each component from 100% as a whole.

[Synthesis of dispersion resin]
Polymers used in Examples and Comparative Examples were obtained as follows.

(Random polymer)
As the random polymer, RP1 and RP2 which are random copolymers of styrene acrylic acid were used. These random polymers were synthesized by conventional methods. Table 1 shows data on the number average molecular weight Mw and molecular weight distribution Mw / Mn of the polymer.

(Block polymer)
As the block polymer, a total of three types of BP1, BP2 and BP3 synthesized by living cationic polymerization using an aluminum catalyst were used. A specific synthesis method will be described later. The structures of these block polymers are as shown in Table 1, and each segment constituting the block polymer is as follows.

The hydrophobic segment (A) is composed of the following unit structure (27).

Moreover, a nonionic hydrophilic segment (B) consists of the following unit structure (32).

The ionic hydrophilic segment (C) has the following unit structure (11).

  A method for synthesizing the block polymer will be described. First, after the inside of the glass container with the three-way cock attached was replaced with nitrogen, the adsorbed water was removed by heating to 250 ° C. in a nitrogen gas atmosphere. Next, after returning the system to room temperature, the A block monomer was added to 16 mmol of ethyl acetate, 0.1 mmol of 1-isobutoxyethyl acetate, and 11 ml of toluene, and the reaction system was cooled. When the internal temperature reached 0 ° C., 0.2 mmol of ethylaluminum sesquichloride (an equimolar mixture of diethylaluminum chloride and ethylaluminum dichloride) was added to initiate polymerization. The molecular weight was monitored in a time-sharing manner using molecular sieve column chromatography (GPC) to confirm the completion of polymerization of the A block.

  The B block monomer was then added and polymerization continued. After confirming the completion of the polymerization of the B block by monitoring using GPC, a toluene solution of the C block component was added and the polymerization was continued. After 20 hours, the polymerization reaction was stopped. The polymerization reaction was stopped by adding 0.3% ammonia / methanol aqueous solution to the system. The reaction mixture solution was diluted with dichloromethane and washed 3 times with 0.6M hydrochloric acid and then 3 times with distilled water. The organic phase obtained was concentrated and dried with an evaporator, and then vacuum-dried, then repeatedly dialyzed in a methanol solvent using a cellulose semipermeable membrane to remove the monomeric compound, and the target ABC A triblock polymer (BP1) consisting of the following segments was obtained. The compound was identified using NMR and GPC.

In the above, BP2 was synthesized by polymerizing by the same method using each ABC block monomer similar to BP1.
Moreover, in the above, the diblock polymer (BP3) which consists of an A segment and a C segment by polymerizing by the same method as the above using an A block monomer and a C block monomer without using a B block monomer. Synthesized. Table 1 shows data of the number of polymerizations, the number average molecular weight Mw, and the molecular weight distribution Mw / Mn for each segment of the block copolymers (BP1) to (BP3) prepared above.

[Preparation of pigment dispersion]
<Example 1>
300 mL Kolben equipped with a mechanical stirrer was placed in the tank of the ultrasonic generator, and 8.0 g of the previously synthesized styrene-acrylic acid random copolymer (RP1) was used as a pigment and C.I. I. 10 g of Pigment Blue 15: 3 was added. Furthermore, 100 mL of tetrahydrofuran was added thereto, and mixed well until the pigment surface was sufficiently wetted with the solvent. Next, purified water was injected, premixed for 30 minutes, and then charged into a bead mill and dispersed for 3 hours. Thereafter, tetrahydrofuran was distilled off using a rotary evaporator, and the concentration was adjusted to obtain a pigment dispersion having a pigment concentration of 5% and P / B = 1.25. Next, the triblock polymer (BP1) synthesized earlier was dissolved in an alkaline aqueous solution containing KOH so that the neutralization rate was 100%. This triblock polymer aqueous solution was mixed with the previously obtained pigment dispersion to obtain a cyan pigment dispersion with a pigment concentration of 5% and P / B = 1. In the present invention, P / B represents pigment amount / dispersed resin amount.

<Example 2>
The pigment is C.I. I. A pigment dispersion for magenta color was obtained in the same manner as in Example 1 except that the pigment red 122 was used. Tables 2-1 and 2-2 collectively show the manufacturing conditions. That is, using two types of polymers and pigments shown in Table 2-1 and Table 2-2 in the amounts and ratios shown in the table, a pigment dispersion having a pigment concentration of 5% and P / B = 1 was obtained. . More specifically, a pigment dispersion was obtained by dispersing the pigment using a bead mill and then adding and mixing a polymer aqueous solution added later.

<Example 3>
The pigment is C.I. I. A pigment dispersion for yellow was obtained in the same manner as in Example 1 except that the pigment yellow 128 was used. Tables 2-1 and 2-2 collectively show the manufacturing conditions. That is, using two types of polymers and pigments shown in Table 2-1 and Table 2-2 in the amounts and ratios shown in the table, a pigment dispersion having a pigment concentration of 6.5% and P / B = 1 was prepared. Obtained. More specifically, a pigment dispersion was obtained by dispersing the pigment using a bead mill and then adding and mixing a polymer aqueous solution added later.

<Example 4>
A black pigment dispersion was obtained in the same manner as in Example 1 except that the pigment was replaced with carbon black. Tables 2-1 and 2-2 collectively show the manufacturing conditions. That is, using two types of polymers and pigments shown in Table 2-1 and Table 2-2 in the amounts and ratios shown in the table, a pigment dispersion having a pigment concentration of 6.0% and P / B = 1 was prepared. Obtained. More specifically, a pigment dispersion was obtained by dispersing the pigment using a bead mill and then adding and mixing a polymer aqueous solution added later.

<Example 5>
300 mL Kolben equipped with a mechanical stirrer was placed in a tank of an ultrasonic generator, and 8.0 g of the previously synthesized triblock polymer (BP1) was added thereto. I. 10 g of Pigment Blue 15: 3 was added. Furthermore, 100 mL of tetrahydrofuran was added thereto, and mixed well until the pigment surface was sufficiently wetted with the solvent. Next, phase inversion was performed by dropping and injecting an aqueous alkali solution containing KOH so that the neutralization rate of the block polymer was 100%. Thereafter, premixing was performed for 30 minutes, and dispersion was performed using Nanomizer YSNM-2000AR (manufactured by Yoshida Kikai Kogyo Co., Ltd.) until the average particle size of the pigment became 100 nm or less. Tetrahydrofuran was distilled off from this dispersion using a rotary evaporator, and the concentration was adjusted to obtain a pigment dispersion having a pigment concentration of 5% and P / B = 1.25. Next, the previously prepared block polymer (BP2) was dissolved in an alkaline aqueous solution containing KOH so that the neutralization rate was 100%. This block polymer aqueous solution was mixed with the previously obtained pigment dispersion to obtain a pigment dispersion having a pigment concentration of 5% and P / B = 1.

<Example 6>
The pigment is C.I. I. A pigment dispersion for magenta color was obtained in the same manner as in Example 5 except that the pigment red 122 was used. Tables 2-1 and 2-2 collectively show the manufacturing conditions. That is, using two types of polymers and pigments shown in Table 2-1 and Table 2-2 in the amounts and ratios shown in the table, a pigment dispersion having a pigment concentration of 5% and P / B = 1 was obtained. . More specifically, a pigment dispersion was obtained by dispersing the pigment using a nanomizer and then adding and mixing a polymer aqueous solution added later.

<Example 7>
The pigment is C.I. I. A pigment dispersion for yellow was obtained in the same manner as in Example 5 except that the pigment yellow 128 was used. Tables 2-1 and 2-2 collectively show the manufacturing conditions. That is, using two types of polymers and pigments shown in Table 2-1 and Table 2-2 in the amounts and ratios shown in the table, a pigment dispersion having a pigment concentration of 6.5% and P / B = 1 was prepared. Obtained. More specifically, a pigment dispersion was obtained by dispersing the pigment using a nanomizer and then adding and mixing a polymer aqueous solution added later.

<Example 8>
A black pigment dispersion was obtained in the same manner as in Example 5 except that the pigment was replaced with carbon black. Tables 2-1 and 2-2 collectively show the manufacturing conditions. That is, using two types of polymers and pigments shown in Table 2-1 and Table 2-2 in the amounts and ratios shown in the table, a pigment dispersion having a pigment concentration of 6.0% and P / B = 1 was prepared. Obtained.

<Example 9>
300 mL Kolben equipped with a mechanical stirrer was placed in a tank of an ultrasonic generator, 7.0 g of styrene-acrylic acid random copolymer (RP2) was contained therein, and C.I. I. 10 g of Pigment Blue 15: 3 was added. Furthermore, 100 mL of tetrahydrofuran was added thereto, and mixed well until the pigment surface was sufficiently wetted with the solvent. Next, purified water was injected, premixed for 30 minutes, and then charged into a bead mill and dispersed for 3 hours. Thereafter, tetrahydrofuran was distilled off using a rotary evaporator, and the concentration was adjusted to obtain a pigment dispersion having a pigment concentration of 5% and P / B = 1.42. Next, the previously prepared block polymer (BP2) was dissolved in an alkaline aqueous solution containing KOH so that the neutralization rate was 100%. This block polymer aqueous solution was mixed with the previously obtained pigment dispersion to obtain a cyan pigment dispersion with a pigment concentration of 5% and P / B = 1.

<Example 10>
The pigment is C.I. I. A pigment dispersion liquid for magenta color was obtained in the same manner as in Example 9 except that the pigment red 122 was used. Tables 2-1 and 2-2 collectively show the manufacturing conditions. That is, using two types of polymers and pigments shown in Table 2-1 and Table 2-2 in the amounts and ratios shown in the table, a pigment dispersion having a pigment concentration of 5% and P / B = 1 was obtained. . More specifically, a pigment dispersion was obtained by dispersing the pigment using a bead mill and then adding and mixing a polymer aqueous solution added later.

<Example 11>
The pigment is C.I. I. A pigment dispersion for yellow was obtained in the same manner as in Example 9 except that the pigment yellow 128 was used. Tables 2-1 and 2-2 collectively show the manufacturing conditions. That is, using two types of polymers and pigments shown in Table 2-1 and Table 2-2 in the amounts and ratios shown in the table, a pigment dispersion having a pigment concentration of 6.5% and P / B = 1 was prepared. Obtained. More specifically, a pigment dispersion was obtained by dispersing the pigment using a bead mill and then adding and mixing a polymer aqueous solution added later.

<Example 12>
A black pigment dispersion was obtained in the same manner as in Example 9 except that the pigment was replaced with carbon black. Tables 2-1 and 2-2 collectively show the manufacturing conditions. That is, using two types of polymers and pigments shown in Table 2-1 and Table 2-2 in the amounts and ratios shown in the table, a pigment dispersion having a pigment concentration of 6.0% and P / B = 1 was prepared. Obtained. More specifically, a pigment dispersion was obtained by dispersing the pigment using a bead mill and then adding and mixing a polymer aqueous solution added later.

<Example 13>
300 mL Kolben equipped with a mechanical stirrer was placed in a tank of an ultrasonic generator, and 8.0 g of the previously synthesized triblock polymer (BP1) was added thereto. I. 10 g of Pigment Blue 15: 3 was added. Furthermore, 100 mL of tetrahydrofuran was added thereto, and mixed well until the pigment surface was sufficiently wetted with the solvent. Next, phase inversion was performed by dropping and injecting an aqueous alkali solution containing KOH so that the neutralization rate of the block polymer was 100%. Thereafter, premixing was performed for 30 minutes, and dispersion was performed using Nanomizer YSNM-2000AR (manufactured by Yoshida Kikai Kogyo Co., Ltd.) until the average particle size of the pigment became 100 nm or less. Tetrahydrofuran was distilled off from this dispersion using a rotary evaporator, and the concentration was adjusted to obtain a pigment dispersion having a pigment concentration of 5% and P / B = 1.25. Next, the previously prepared diblock polymer (BP3) was dissolved in an alkaline aqueous solution containing KOH so that the neutralization rate was 100%. This block polymer aqueous solution was mixed with the previously obtained pigment dispersion to obtain a pigment dispersion having a pigment concentration of 5% and P / B = 1.

<Example 14>
The pigment is C.I. I. A pigment dispersion for magenta color was obtained in the same manner as in Example 13 except that the pigment red 122 was used. Tables 2-1 and 2-2 collectively show the manufacturing conditions. That is, using two types of polymers and pigments shown in Table 2-1 and Table 2-2 in the amounts and ratios shown in the table, a pigment dispersion having a pigment concentration of 5% and P / B = 1 was obtained. . More specifically, a pigment dispersion was obtained by dispersing the pigment using a nanomizer and then adding and mixing a polymer aqueous solution added later.

<Example 15>
The pigment is C.I. I. A pigment dispersion for yellow was obtained in the same manner as in Example 13 except that the pigment yellow 128 was used. Tables 2-1 and 2-2 collectively show the manufacturing conditions. That is, using two types of polymers and pigments shown in Table 2-1 and Table 2-2 in the amounts and ratios shown in the table, a pigment dispersion having a pigment concentration of 6.5% and P / B = 1 was prepared. Obtained. More specifically, a pigment dispersion was obtained by dispersing the pigment using a nanomizer and then adding and mixing a polymer aqueous solution added later.

<Example 16>
A black pigment dispersion was obtained in the same manner as in Example 13 except that the pigment was replaced with carbon black. Tables 2-1 and 2-2 collectively show the manufacturing conditions. That is, using two types of polymers and pigments shown in Table 2-1 and Table 2-2 in the amounts and ratios shown in the table, a pigment dispersion having a pigment concentration of 6.0% and P / B = 1 was prepared. Obtained.

<Comparative Example 1>
300 mL Kolben equipped with a mechanical stirrer was placed in the tank of the ultrasonic generator, and 10.0 g of the previously synthesized styrene-acrylic acid random copolymer (RP1) was added to the C.I. I. 10 g of Pigment Blue 15: 3 was added. Furthermore, 100 mL of tetrahydrofuran was added thereto, and mixed well until the pigment surface was sufficiently wetted with the solvent. Next, purified water was injected, premixed for 30 minutes, and then charged into a bead mill and dispersed for 3 hours. Thereafter, tetrahydrofuran was distilled off using a rotary evaporator, and the concentration was adjusted to obtain a cyan pigment dispersion having a pigment concentration of 5% and P / B = 1.0.

<Comparative example 2>
The pigment is C.I. I. A pigment dispersion for magenta color was obtained in the same manner as in Comparative Example 1 except that the pigment red 122 was used. Tables 2-1 and 2-2 collectively show the manufacturing conditions. That is, the pigment dispersion of the polymer and pigment shown in Table 2-1 and Table 2-2 in the amount and ratio shown in the table, using a bead mill as a dispersing means, and having a pigment concentration of 5% and P / B = 1. A liquid was obtained.

<Comparative Example 3>
The pigment is C.I. I. A pigment dispersion for yellow was obtained in the same manner as in Comparative Example 1 except that the pigment yellow 128 was used. Tables 2-1 and 2-2 collectively show the manufacturing conditions. That is, the polymer and pigment shown in Table 2-1 and Table 2-2 were used in the amounts and ratios shown in the table, using a bead mill as a dispersing means, and having a pigment concentration of 6.5% and P / B = 1. A pigment dispersion was obtained.

<Comparative example 4>
A black pigment dispersion was obtained in the same manner as in Comparative Example 1 except that the pigment was replaced with carbon black. Tables 2-1 and 2-2 collectively show the manufacturing conditions. That is, the polymer and pigment shown in Table 2-1 and Table 2-2 were used in the amounts and ratios shown in the table, using a bead mill as a dispersing means, and having a pigment concentration of 6.0% and P / B = 1. A pigment dispersion was obtained.

<Comparative Example 5>
300 mL Kolben equipped with a mechanical stirrer was placed in the tank of the ultrasonic generator, and 10.0 g of the previously synthesized triblock polymer (BP1) was added thereto. I. 10 g of Pigment Blue 15: 3 was added. Further, 100 mL of tetrahydrofuran was added thereto, and mixed well until the pigment surface was sufficiently wetted with the solvent. Next, phase inversion was performed by dropping and injecting an alkaline aqueous solution containing KOH so that the neutralization rate of the block polymer was 100%. Thereafter, premixing was performed for 30 minutes, and dispersion was performed using Nanomizer YSNM-2000AR (manufactured by Yoshida Kikai Kogyo Co., Ltd.) until the average particle size of the pigment became 100 nm or less. Tetrahydrofuran was distilled off from this dispersion using a rotary evaporator, and the concentration was adjusted to obtain a pigment dispersion having a pigment concentration of 5% and P / B = 1.0.

<Comparative Example 6>
The pigment is C.I. I. A pigment dispersion for magenta color was obtained in the same manner as in Comparative Example 5 except that the pigment red 122 was used. Tables 2-1 and 2-2 collectively show the manufacturing conditions. That is, a pigment dispersion having a pigment concentration of 5% and P / B = 1 in the amount and ratio shown in Table 2-1 and Table 2-2 using a nanomizer as a dispersing means. A liquid was obtained.

<Comparative Example 7>
The pigment is C.I. I. A pigment dispersion for yellow was obtained in the same manner as in Comparative Example 5 except that CI Pigment Yellow 128 was used. Tables 2-1 and 2-2 collectively show the manufacturing conditions. That is, the amount and ratio of the polymer and pigment shown in Table 2-1 and Table 2-2 in the amount and ratio shown in the table, using a nanomizer as a dispersing means, a pigment concentration of 6.5% and P / B = 1. A pigment dispersion was obtained.

<Comparative Example 8>
A pigment dispersion for black color was obtained in the same manner as in Comparative Example 5 except that the pigment was replaced with carbon black. Tables 2-1 and 2-2 collectively show the manufacturing conditions. That is, the polymer and pigment shown in Table 2-1 and Table 2-2 were mixed in the amount and ratio shown in the table using a nanomizer as the dispersing means, and the pigment concentration was 6.0% and P / B = 1. A pigment dispersion was obtained.

  In Tables 2-1 and 2-2, the polymer types used in Examples 1 to 16 and Comparative Examples 1 to 8 described above, the amount of polymer added at the time of dispersion or after the dispersion treatment, the pigment type and the amount thereof The average acid values are shown together. In the examples, the polymer is added after mechanical dispersion in each dispersion treatment method. On the other hand, in the comparative example, the polymer is added and dispersed before the dispersion treatment without adding the polymer after the dispersion. For comparison, all P / B ratios were set to 1.

(Preparation of ink composition and composition of ink set)
Glycerin, diethylene glycol, trimethylolpropane, and acetylenol EH (manufactured by Kawaken Fine Chemical Co., Ltd.) were added to the pigment dispersions of Examples and Comparative Examples obtained above, and inks of the respective colors were prepared with the compositions shown in Tables 3 to 8 below. . Then, ink sets 1 to 6 were prepared by combining a plurality of ink compositions having the respective compositions shown in Tables 3 to 8 below. Of these, ink sets 1 to 4 are examples of the present invention configured using four color ink compositions of black, magenta, cyan, and yellow, and ink sets 5 and 6 correspond to the comparative examples. . The viscosity of each ink composition is also shown.

  In general, it is desirable that the viscosity of an ink used for inkjet is adjusted to 3.5 mPa · s or less. When the viscosity is high, the refill cannot catch up, and when the drive frequency is high, there are cases where the ejection cannot be performed. In the ink sets 1 to 4 as examples, all inks are suppressed to 3.5 mPa · s or less. On the other hand, in ink sets 5 and 6, there is an ink having a viscosity exceeding 3.5 mPa · s. When the polymer is added to the dispersion treatment, it can be seen that such a viscosity can be kept low even though the solid content concentration in the ink is the same when compared with the ink using the same pigment.

(Image evaluation)
Each ink set produced above was evaluated for color unevenness, glossiness, and ejection stability as follows. The evaluation was obtained by mounting each ink set on an inkjet printer BJF-930 (manufactured by Canon Inc.) and printing on professional photo paper PR101 (manufactured by Canon Inc.) under predetermined conditions. I went about the image.

[Color unevenness evaluation]
For black, cyan, magenta, and yellow, 100% duty solid patches (5 × 5 cm) were printed, and the presence or absence of color unevenness was confirmed.
Evaluation A: Color unevenness is not visible.
Evaluation B: Some color unevenness occurs.
Evaluation C: Color unevenness occurs remarkably.

  In the evaluation this time, the printed samples of the results corresponding to the evaluations B and C were streaky unevenness on the writing start side. The obtained results are shown in Table 9.

[Glossiness evaluation]
Table 10 shows the results of performing solid printing in the same manner as the color unevenness evaluation and evaluating the 20 ° gloss using a gloss meter GMX-203 (Murakami Color Research Laboratory).
Evaluation A: All colors 50 or more Evaluation B: All colors 40 or more and less than 50 Evaluation C: All colors 40 or less

[Discharge stability evaluation]
Using an inkjet printer BJF-930 (manufactured by Canon Inc.), each ink is regularly ejected from the head, and the ejection amount is calculated from the mass of the ink every 1 × 10 ⁶ times, up to 1 × 10 ⁸ The change in the discharge amount was investigated. The obtained results are shown in Table 11.
Evaluation A: No change in discharge amount up to 1 × 10 ⁸ .
Evaluation B: No change in discharge amount up to 5 × 10 ⁷ .
Evaluation C: Discharge amount fluctuation below that.

  In the ink sets 1 to 4, although there was an ink with a slight change in the discharge amount with yellow, it was in a range that had no practical problem.

  As an application example of the present invention, the present invention can provide a pigment dispersion liquid that suppresses the increase in viscosity even when more dispersion resin is added. It is effective in applications where compatibility with characteristics is required.

It is a schematic perspective view which shows the principal part of an example of the inkjet printer which can mount an inkjet head. It is a schematic perspective view which shows an example of the inkjet cartridge provided with the inkjet head.

Explanation of symbols

100: inkjet recording head 832: discharge port 1001: liquid tank 1006: moving drive unit 1008: casing 1010: recording unit 1010a: carriage member 1012: cartridge 1012Y, M, C, B: inkjet cartridge 1014: guide shaft 1016: belt 1018 : Motor 1020: Drive unit 1022a, 1022b, 1024a, 1024b: Roller unit 1026: Recovery unit 1026a, 1026b: Pulley 1028: Paper 1030: Transport device P: Paper transport direction R: Belt rotation direction S: Paper transport direction Direction approximately perpendicular to

Claims (12)

  In a method for producing a pigment dispersion containing an aqueous medium, a water-insoluble colorant and a dispersion resin, a step of dispersing the water-insoluble colorant in the aqueous medium using the dispersion resin, and a dispersion obtained by the dispersion treatment A method for producing a pigment dispersion, comprising adding a block copolymer different from the dispersion resin used for the dispersion treatment to the liquid as a post-addition dispersion resin.   The method for producing a pigment dispersion according to claim 1, wherein the dispersion resin and the post-addition dispersion resin are resins having different acid values.   The method for producing a pigment dispersion according to claim 2, wherein the acid value of the post-added dispersion resin is lower than the acid value of the dispersion resin.   The pigment dispersion liquid according to claim 2 or 3, wherein an average value of the acid value of the dispersion resin and the acid value of the post-addition dispersion resin is in a range of 3 KOHmg / g or more and 150 KOHmg / g or less. Production method.   The dispersion resin contains a triblock copolymer, and the post-addition dispersion resin contains a diblock copolymer having a hydrophobic segment and a hydrophilic segment. A method for producing a pigment dispersion.   The method for producing a pigment dispersion according to claim 5, wherein the molecular weight of the diblock copolymer is smaller than the molecular weight of the triblock copolymer.   The method for producing a pigment dispersion according to any one of claims 1 to 6, wherein the dispersion resin contains a triblock copolymer containing a polyvinyl ether structure as a repeating unit structure.   An ink composition for ink jet recording, comprising: a pigment dispersion obtained by the method for producing a pigment dispersion according to any one of claims 1 to 7; and a polyhydric alcohol as an organic solvent. .   An ink set comprising a combination of a plurality of ink-jet recording ink compositions, wherein the ink set comprises the ink-jet recording ink composition according to claim 8.   In an image forming method for forming an image by ejecting an ink composition onto a recording medium by applying energy to the ink composition, the ink composition for ink jet recording according to claim 8 or claim 10 as the ink composition. An image forming method using the ink set according to Item 9.   The image forming method according to claim 10, wherein the means for discharging the ink composition onto the recording medium is a heating means.   An image recording apparatus having a configuration for performing the image forming method according to claim 10.

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