JP2012021120A - Aqueous pigment dispersion for inkjet ink, and aqueous pigment ink for inkjet printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aqueous pigment dispersion in which a pigment is finely dispersed, and an agglomerated pigment precipitated in a head-cleaning operation can be made resoluble easily when applying to an inkjet printer, and by which an ink discharge stability is retained and the ink having excellent storage stability can be provided.SOLUTION: The aqueous pigment dispersion for inkjet ink includes the pigment, a pigment derivative and a polymeric dispersant. In the pigment derivative, one or more acidic groups in the molecule thereof are chemically modified. The polymeric dispersant is a diblock polymer comprising a hydrophilic block and a hydrophobic block, and PDI (polydispersivity) of the diblock polymer is ≤1.5. The dispersant contains at least benzyl methacrylate or cyclohexyl methacrylate as a monomer composing the hydrophobic block. The number-average molecular weight of the hydrophobic block is 500 to 50,000.

Description

  The present invention relates to an aqueous pigment dispersion for ink-jet ink and an ink. More specifically, when the pigment is highly finely dispersed, maintains good storage stability, and is applied to an inkjet printer, the head is not clogged even after a long pause, and the inkjet printer has good ejection stability. The present invention relates to an aqueous pigment ink and an aqueous pigment dispersion for an inkjet ink used in the ink.

  Color materials used in ink for inkjet printers are roughly classified into dyes and pigments. Ink for ink jet printers that use pigments as color materials are characterized in that the printed matter has excellent fastness, such as water resistance and light resistance, compared to inks that use dyes as color materials. In addition, dye ink is used by dissolving a dye as a coloring material in an ink medium, whereas pigment ink is used as a pigment dispersion in which a pigment as a coloring material is finely dispersed in an ink medium. The

  In particular, an inkjet printer is a printing method that records an image by ejecting ink droplets from a very thin nozzle of several tens of μm. There are problems of re-dissolvability and ejection stability, such as not clogging the nozzle, and even if nozzle clogging occurs after a long pause, the causative substance is re-dissolved by a simple cleaning operation and recovered immediately. Furthermore, it is necessary for the ink to maintain these properties for a long time, i.e. to have high stability.

  With regard to the high re-solubility, ejection stability, and storage stability of water-based ink-jet inks, pigment encapsulation methods have been studied, and water-insoluble resins (see Patent Document 1) and polymers having urethane bonds (Patent Document) 2) is used. Further, a method of combining an acidic pigment derivative and a dispersant having an amino group in order to strengthen the bond between the pigment and the dispersant (see Patent Documents 3 and 4) is also disclosed. In addition, a method of adding a nozzle clogging preventive agent (see Patent Documents 5 and 6) and a method of combining a pigment derivative and a nonionic dispersant (see Patent Document 7) are also disclosed so as not to cause nozzle clogging. The level of re-dissolvability, ejection stability and storage stability is increasing. However, there is a need for inks that are still inadequate and have all of the higher performance.

JP 2003-191864 A JP 2002-167536 A Japanese Patent Laid-Open No. 6-136411 JP 2004-51813 A JP 2006-8881 A JP 2010-18742 A JP 2003-171574 A

  For all ink jet printers, there is ejection stability as a problem derived from ink. This problem is a nozzle failure during operation or after long-term operation interruption, which may be caused by foreign matter in the ink, etc., but the medium in the ink evaporates during the long-term pause and the ink at the air / liquid interface. This is often because the solid component of the material precipitates or crystallizes. In particular, in aqueous pigment inks, dispersed pigments may agglomerate due to solvent composition changes caused by evaporation. At this time, the precipitated pigment aggregate needs to be easily redissolved in the head cleaning operation.

  Therefore, an object of the present invention is to achieve ejection stability, which is a problem derived from ink that occurs in an ink jet printer. Specifically, the provision of ink that is less likely to clog the head even after a long pause, can easily re-dissolve pigment aggregates deposited in the head cleaning operation, maintains ink ejection stability, and is excellent in ink storage stability. It is an object of the present invention to provide an aqueous pigment dispersion that makes it possible.

  The present inventors use an organic pigment containing a specific acidic pigment derivative in the aqueous pigment dispersion and a block polymer having a narrow monomolecular dispersibility with a narrow molecular weight distribution and a hydrophobic block composed of a specific monomer. It has been found that the above problems can be solved.

That is, this invention consists of the following structures.
1. An aqueous pigment dispersion comprising a pigment, a pigment derivative, and a polymer dispersant, wherein the pigment derivative is an acidic pigment derivative obtained by chemically modifying one or more acidic groups in the molecule, The polymer dispersant is a diblock polymer comprising a hydrophilic block and a hydrophobic block, the PDI of the diblock polymer is 1.5 or less, and at least benzyl as a monomer constituting the hydrophobic block An aqueous pigment dispersion for ink-jet inks containing methacrylate or cyclohexyl methacrylate, wherein the hydrophobic block has a number average molecular weight of 500 to 50,000.

2. 2. The aqueous pigment dispersion for inkjet ink according to 1 above, wherein the acidic pigment derivative is obtained by chemically modifying one or more sulfonic acid groups that are acidic groups in the molecule.
3. 3. The aqueous pigment dispersion for inkjet ink according to 1 or 2 above, comprising the acidic pigment derivative at a ratio of 0.1 to 20 parts by mass with respect to 100 parts by mass of the pigment.

4). 4. The aqueous pigment dispersion for inkjet ink according to any one of 1 to 3 above, wherein the polymer dispersant has an acid value of 40 to 200 mg KOH / g.
5. The aqueous pigment dispersion for inkjet ink according to any one of 1 to 4 above, wherein the polymer dispersant is contained at a ratio of 5 to 50 parts by mass with respect to 100 parts by mass of the pigment.

6). An aqueous pigment ink for inkjet printers, comprising the aqueous pigment dispersion for inkjet according to any one of 1 to 5 above.

  Since the aqueous pigment dispersion of the present invention is highly finely dispersed and maintains good storage stability, it has good ejection stability, re-dissolvability and storage stability required when applied to an ink jet printer. It is an excellent one. The water-based pigment ink for inkjet comprising the aqueous pigment dispersion of the present invention is less likely to clog the head even after a long pause, is likely to occur after a long pause, and foreign matters that cause nozzle clogging are easily redissolved by the head cleaning operation. And its performance is maintained for a long time.

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. Each component constituting the aqueous pigment dispersion of the present invention will be described.
[Aqueous pigment dispersion]
<Pigment>
First, the pigment used in the present invention will be described. Conventionally known organic pigments and inorganic pigments can be used as the pigment, and there is no particular limitation. For example, organic pigments include phthalocyanine, azo, azomethine azo, azomethine, anthraquinone, perinone / perylene, indigo / thioindigo, dioxazine, quinacridone, isoindoline, isoindolinone, diindole. Chromatic pigments such as ketopyrrolopyrrole, quinophthalone, and induslen pigments, and carbon black pigments such as furnace black, lamp black, acetylene black, and channel black. Examples of inorganic pigments include extender pigments, titanium oxide pigments, iron oxide pigments, and spinnel pigments.

  It is desirable to select and use the pigment type, particle size, and treatment type according to the purpose. Organic fine-particle pigments are preferred unless the colorant requires a hiding power. On the other hand, when high clarity and transparency are desired, it is desirable to refine the pigment by wet grinding such as salt milling or dry grinding. In that case, in consideration of nozzle clogging at the time of printing, it is desirable to remove the organic pigment having a particle size of more than 0.5 μm and to make the average particle size 0.15 μm or less.

  More specific examples of such pigments by color index (CI) numbers include C.I. I. Pigment Yellow 12, 13, 14, 17, 20, 24, 74, 83, 86, 93, 94, 95, 97, 109, 110, 117, 120, 125, 128, 129, 137, 138, 147, 148, 150, 151, 153, 154, 155, 166, 168, 175, 180, 181, 185, 191, C.I. I. Pigment orange 16, 36, 43, 51, 55, 59, 61, 64, 71, 73, C.I. I. Pigment Red 4, 5, 9, 23, 48, 49, 52, 53, 57, 97, 112, 122, 123, 144, 146, 147, 149, 150, 166, 168, 170, 177, 180, 184, 185, 192, 202, 207, 214, 215, 216, 217, 220, 221, 223, 224, 226, 227, 228, 238, 240, 242, 254, 255, 264, 272, C.I. I. Pigment violet 19, 23, 29, 30, 37, 40, 50, C.I. I. Pigment blue 15, 15: 1, 15: 3, 15: 4, 15: 6, 22, 60, 64, C.I. I. Pigment green 7, 36, and the like. In addition, these pigments may be used alone or in combination of two or more. As a mixing method, mixing with a powder pigment, mixing with a paste pigment, mixing by pigmentation is performed. For example, creating a solid solution.

  Among these, as a pigment for water-based inkjet ink, blue is C.I. from the color development property, dispersibility, and weather resistance. I. Pigment Blue 15: 3, red is C.I. I. Pigment red 122, C.I. I. Pigment Violet 19, yellow is C.I. I. Pigment Yellow 74, 155, green is C.I. I. Pigment Green 7 is most preferable.

<Pigment derivative>
Next, the pigment derivative used in the present invention will be described. This pigment derivative adsorbs on the pigment surface and changes the properties of the pigment surface. However, when added in a large amount, the properties as a pigment are weakened, and problems such as bleeding at the time of printing occur. Therefore, those that can change the properties of the pigment surface with a small amount of addition are preferable. The pigment derivative used in the present invention is an acidic pigment derivative in which at least one acidic group is chemically modified in the molecule. Examples of the acidic group include a carboxyl group, a phosphoric acid group, and a sulfonic acid group. As described above, in order to change the polarity of the pigment surface with a small amount, the sulfonic acid group must be strongly acidic. It is advantageous.

  The acidic pigment derivative used in the present invention may have, for example, at least one sulfonic acid group in the pigment itself, or may have a pigment surface modified by a chemical having a sulfonic acid group. The pigments that can be used in this case are all the above-mentioned conventionally known organic pigments and inorganic pigments. Further, the pigment-like structure may have at least one sulfonic acid group. These acidic pigment derivatives are not limited to single use, and may be used in combination.

  The method for producing an acidic pigment derivative having an acidic group such as a sulfonic acid group used in the present invention is not particularly limited, but is generally obtained as follows. First, the pigment is sulfonated with fuming sulfuric acid, concentrated sulfuric acid, chlorosulfuric acid or the like. The obtained sulfonated product is dispersed in water to form a slurry, which is then filtered and washed to remove residual acid such as sulfuric acid, and recovered in a paste form. The recovered paste may be used as it is, but may be dried and pulverized as necessary. When performing this drying and pulverization, it is common to wash with hydrochloric acid once. If direct sulfonation is difficult, an acidic pigment derivative may be synthesized using a starting material containing a sulfonic acid group.

  The number of sulfonic acid groups in the molecule in the acidic pigment derivative obtained as described above has a distribution, and is represented by an average value unless particularly separated and purified. The average number is preferably 1 or more and 2 or less. If the ratio is less than 1, the effect on the pigment surface polarity change intended by the present invention is diminished. If the ratio exceeds 2, the effect is high, but the hydrophilicity is too strong, causing bleeding. This is not preferable.

  Examples of acidic pigment derivatives that can be used in the present invention are shown below, but the present invention is not limited to these.

  In the derivatives (5) and (6), x and y represent 0 or 1. X + y = n (Formula 1), and in the derivatives (1), (2), (3), (7) and (Formula 1), n represents 1 or 2.

  The addition amount of the acidic pigment derivative is preferably 0.1% by mass to 20% by mass with respect to the pigment. More preferably, it is 0.5 mass%-15 mass% with respect to a pigment, Furthermore, it is 1 mass%-10 mass% with respect to a pigment. If the amount is less than 0.1% by mass, the effect of changing the pigment surface properties is hardly recognized. On the other hand, if the amount exceeds 20% by mass, the properties as a pigment are weakened, and the pigment has poor weather resistance and water resistance. Since it tends to become, it is not preferable.

  The combination of the pigment and the pigment derivative used in the present invention is not particularly limited, but it is desirable that the chemical structures of the two are similar, and the acidic pigment derivative is preferably used in combination with the base pigment. Specifically, it is preferable to use a phthalocyanine derivative for the phthalocyanine pigment and a quinacridone derivative for the quinacridone. This is because the acidic pigment derivative used in the present invention is adsorbed to the pigment by hydrophobic interaction in water, but if the structures of both are similar, they are likely to overlap sterically and contain an aromatic ring. This is because the structure can be firmly adsorbed by π-π stacking of both.

<Polymer dispersant>
Next, the polymer dispersant used in the present invention will be described. The polymer dispersant is a diblock polymer composed of a hydrophilic block and a hydrophobic block, and the PDI of the diblock polymer is required to be 1.5 or less. Further, the polymer dispersant needs to contain at least benzyl methacrylate or cyclohexyl methacrylate as a monomer constituting the hydrophobic block, and the hydrophobic block has a number average molecular weight of 500 to 50,000.

(AB diblock polymer)
The polymer dispersant used in the present invention is a diblock polymer, which is represented by [General Formula 1] AB, and is hereinafter described as an AB diblock polymer. Here, A and B in the general formula 1 each represent a polymer block of one or more addition polymerizable monomers. The A block is a hydrophilic polymer block including at least a monomer having an acid group, and the B block is a polymer block of a hydrophobic monomer. Examples of the AB diblock polymer include (meth) acrylate polymers composed of (meth) acrylate monomers. In the case of producing a (meth) acrylate-based polymer, the conventional radical polymerization method could not obtain an acrylate-based polymer having a controlled structure such as a block polymer and a narrow molecular weight distribution. On the other hand, in recent years, a living radical polymerization method has been invented, the molecular weight distribution is narrow, and a structure like an AB diblock polymer can be controlled. Therefore, the living radical polymerization method is useful as a method for producing the AB diblock polymer used in the present invention. This point will be described later.

  However, the method for obtaining the AB diblock polymer used in the present invention is not particularly limited, and the AB diblock polymer can also be produced by the following methods. For example, an atom transfer radical polymerization method in which a metal complex such as copper or ruthenium is used as a catalyst, an organic halide as an initiating compound, and oxidation and reduction thereof, a nitroxide method in which a nitroxide -NO radical is transferred, a dithiocarboxylic acid There are a reversible addition-fragmentation chain transfer polymerization method using an ester and the like, an iodine transfer polymerization method, a method using organic tellurium and organic bismuth, and an addition-cleavage type chain transfer polymerization method using a cobalt compound as a catalyst.

  Next, the effect | action in pigment dispersion of each polymer block of A and B is demonstrated. The hydrophobic B polymer block is adsorbed on the pigment surface, and the hydrophilic A polymer block on the opposite side is dissolved in water or an aqueous solution containing a water-soluble organic solvent (hereinafter referred to as an aqueous medium). When a diblock polymer is contained, a stable dispersion system is established. Specifically, the B polymer block is a polymer block that is insoluble in an aqueous medium, and by utilizing this property, the B polymer block is significantly adsorbed and deposited on a pigment hydrophobic surface in the aqueous medium to coat the pigment, The encapsulated state can be maintained. The A polymer block on the opposite side is a polymer block having an acid group such as a carboxyl group, and can be dissolved in an aqueous medium by neutralizing and ionizing the acid group such as a carboxyl group with an alkali. Become. As a result, the A polymer block is ionized to exhibit the effects of electrical repulsion and steric hindrance, enhance storage stability, and prevent aggregation and sedimentation of pigment particles. Pigments that are highly stabilized by encapsulation do not form strong agglomerates when dried, can be easily re-dissolved with the addition of a new aqueous medium, and are self-dispersible. ing. This self-dispersibility is an effective property for ensuring ejection stability over a long period of time in an operation for recovering nozzle clogging caused by dried ink and pigment aggregates generated during ink jet printing.

Next, each component of the AB diblock polymer will be described.
(A polymer block)
The A polymer block is a hydrophilic polymer block containing a monomer having an acid group. Examples of the acid group of the monomer include a conventionally known carboxyl group, sulfonic acid group, and phosphoric acid group, with a carboxyl group being particularly preferred. This is because in the present invention, when a pigment is dispersed with a polymer dispersant, a carboxyl group which is a weak acid group can provide a stable dispersion without inhibiting the hydrophobic bond between the pigment and the dispersant. is there.

  A conventionally well-known thing is mentioned as a monomer which has an acid group. Examples of the monomer having a carboxyl group include acrylic acid, acrylic acid dimer, methacrylic acid, maleic acid, itaconic acid, fumaric acid, and crotonic acid. Moreover, the monomer which made maleic anhydride, succinic anhydride, and phthalic anhydride react with hydroxyalkyl (meth) acrylates, such as 2-hydroxyethyl (meth) acrylate and 4-hydroxybutyl (meth) acrylate, is mentioned. Examples of the monomer having a sulfonic acid group include styrene sulfonic acid, dimethylpropyl sulfonic acid (meth) acrylamide, ethyl sulfonate (meth) acrylate, ethyl sulfonate (meth) acrylamide, and vinyl sulfonic acid. Examples of the monomer having a phosphoric acid group include methacryloyloxyethyl phosphate ester.

  In particular, as the material for forming the A polymer block constituting the AB diblock polymer useful as the polymer dispersant used in the present invention, the aforementioned monomer having a carboxyl group is preferable. More preferred is acrylic acid or methacrylic acid. Since these have a low molecular weight, the amount used in the monomer composition for polymerization can be increased, and the acid value of the resulting polymer dispersant can be increased.

  The A polymer block is synthesized by copolymerizing other (meth) acrylate monomers on the skeleton in addition to the monomer having an acid group. A conventionally well-known thing is used as another (meth) acrylate type monomer. For example, aliphatic such as methyl (meth) acrylate, butyl (meth) acrylate, cyclohexyl (meth) acrylate, and hydroxyl group-containing (meth) acrylate such as alicyclic alkyl (meth) acrylate, 2-hydroxyethyl, 2-hydroxypropyl, etc. Examples include amino group-containing (meth) acrylates such as dimethylaminoethyl (meth) acrylate, and glycol-based (meth) acrylates such as polyethylene glycol monomethyl ether (meth) acrylate. One or more types can be used.

(B polymer block)
Next, the constituent material of the B polymer block constituting the AB diblock polymer useful as a polymer dispersant will be described. The B polymer block is a polymer block insoluble in an aqueous medium. The block is adsorbed and deposited on the pigment, whereby the pigment is encapsulated.

  As the component constituting the B polymer block, for example, a conventionally known monomer such as a vinyl monomer, aliphatic, alicyclic, aromatic alkyl (meth) acrylate, a monomer having a hydroxyl group or an amino group can be used. . In the present invention, at least benzyl methacrylate or cyclohexyl methacrylate is contained as a constituent component, and the number average molecular weight of the hydrophobic block is required to be 500 to 50,000. That is, by having these components and not having an acid group such as a carboxyl group, the B polymer block is insoluble in an aqueous medium and is effective in encapsulating the pigment.

  Particularly preferred B polymer block for use in the present invention is 100% by mass of benzyl methacrylate, 100% by mass of cyclohexyl methacrylate, or 100% by mass in combination of benzyl methacrylate and cyclohexyl methacrylate. However, it is not limited to these, For example, you may copolymerize the (meth) acrylate type monomer which can be used for A polymer block. In this case, it is necessary to reduce the amount of polyethylene glycol monomer, sulfonic acid, carboxyl group and the like that can provide solubility in water as much as possible. The amount of the (meth) acrylate-based monomer that can provide solubility in water used in combination is preferably 20% by mass or less, more preferably 10% by mass, in 100% by mass of the monomer formed by the B polymer block. It is as follows.

  Also, if the molecular weight of the B polymer block is less than the number average molecular weight of 500, the site adsorbed to the pigment is too small to produce an accurate capsule, so a stable dispersion cannot be created, and the stability over time deteriorates. End up. On the other hand, if the number average molecular weight is too large, control of PDI (polydispersity), which will be described later, becomes difficult, and at the same time, hydrophobicity is too strong, water resolubility is deteriorated, and discharge stability is adversely affected. End up. Therefore, the B polymer block has a number average molecular weight of 500 to 50,000, more preferably 1,000 to 10,000.

(Molecular weight distribution)
Next, the AB diblock polymer used in the present invention is characterized in that its PDI (ratio of weight average molecular weight to number average molecular weight) is 1.5 or less. The smaller the PDI, the narrower the molecular weight distribution and the higher the molecular weight of the polymer. When the value is 1.0, the molecular weight distribution is the narrowest. On the other hand, if the PDI is large, the polymer having a molecular weight that is too large or too small as compared with the designed high molecular weight polymer is included. If the molecular weight is too large, fine particles may not be dispersed due to adsorption between multiparticulates, and the viscosity will also increase, surface tension will decrease, and jetting stability may be adversely affected. On the other hand, a resin having a molecular weight that is too small is dissolved, resulting in a resin that does not contribute to dispersion in the pigment dispersion. The resin increases the viscosity of the pigment dispersion, impairs the dispersion stability, and exhibits non-Newtonian behavior in jetting ink jet ink, thereby impairing jetting stability.

  In addition, a large PDI means that a block polymer as designed is often not synthesized, and in the present invention, in consideration of this point, an AB diblock polymer having a PDI of 1.5 or less is used. It was. That is, when the PDI is large, a hydrophobic block smaller than the design is bound to a larger hydrophilic block than the design, and conversely, a hydrophobic block is bound to a small hydrophilic block, There may be a mixture of things, only hydrophobic blocks. In particular, when small hydrophilic blocks or only hydrophobic blocks without hydrophilic blocks are mixed, they do not contribute to pigment encapsulation or self-dispersibility, and once dried, It becomes difficult to form a strong dry film, inhibit re-dissolution, and ensure long-term ejection stability.

  Therefore, a polymer with a narrow polydispersity (PDI) is preferred in order to have a molecular weight highly designed to encapsulate the pigment and to have a large number of AB diblock polymers of that molecular weight. Therefore, the AB diblock polymer used in the present invention has a molecular weight distribution of PDI of 1.5 or less, more preferably 1.4 or less.

(Acid value)
Next, the acid value of the AB diblock polymer used in the present invention is preferably 40 to 200 mgKOH / g. If the acid value is less than 40 mgKOH / g, the solubility in water is poor, and the stability over time and the head cleaning characteristics tend to deteriorate. On the other hand, if the acid value exceeds 200 mgKOH / g, the solubility in water is too high and the ink becomes poor in water resistance, which is not preferable.

(Mixing amount)
Next, if the amount of AB diblock polymer in the aqueous pigment dispersion of the present invention is too small, it is not preferable because the pigment cannot be sufficiently encapsulated and self-dispersing ability is not imparted. On the other hand, if the blending amount is too large, it is possible to encapsulate the pigment sufficiently, but this is not preferable because an excessive dispersant is present in the liquid. That is, such a free dispersant that is not adsorbed to the pigment adversely affects the ejection stability such as an increase in ink viscosity, a decrease in surface tension, and a decrease in Newtonian property, and also causes a problem such as a decrease in density even when printed. . Accordingly, the blending amount of the AB diblock polymer is preferably 5 to 50% by mass, and more preferably 10 to 30% by mass with respect to the pigment.

<Preparation method of aqueous pigment dispersion>
The aqueous pigment dispersion of the present invention contains a pigment, a pigment derivative (acid pigment derivative), and a polymer dispersant (AB diblock polymer) as described above. Below, the preparation methods of an aqueous pigment dispersion are demonstrated.

  First, as the process of adsorbing the acidic pigment derivative to the pigment, a method performed during pigment miniaturization such as a salt milling process or a dry pulverization process, a method of mixing powders, a method of mixing slurries, or a dispersion And a method performed during the dispersion step of the pigment using the agent. In particular, in order to perform uniform adsorption treatment on the pigment surface, it is most preferable to carry out during the dispersion step.

  As a method for dispersing a pigment or the like using a dispersant, a conventionally known method can be applied and is not particularly limited. A pigment, an acidic pigment derivative, a polymer dispersant neutralized with an alkali, and an aqueous medium are mixed and stirred, and the pigment is dispersed by a conventionally known disperser. As the aqueous medium, water or a mixed medium of water and a water-soluble organic solvent is used.

  The alkali to be used is not particularly limited, but for example, selected from the group consisting of ammonia, primary, secondary or tertiary organic amines (including basic nitrogen-containing heterocyclic compounds) and alkali metal hydroxides. Can be preferably used.

  The water used as the aqueous medium in the present invention is preferably ion-exchanged water (deionized water). In particular, a divalent metal ion needs to be removed because it inhibits dispersion in an aqueous system.

  As the water-soluble organic solvent used as the aqueous medium in the present invention, any of the water-miscible organic solvents listed below can be used. For example, alkyl alcohols having 1 to 4 carbon atoms such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol; ethylene glycol, propylene glycol, butylene glycol , Triethylene glycol, 1,2,6-hexanetriol, thiodiglycol, hexylene glycol, diethylene glycol and other alkylene glycols containing 2 to 6 carbon atoms; glycerin, ethylene glycol monomethyl (or ethyl) Ether, diethylene glycol methyl (or ethyl) ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene Lower alkyl ethers of polyhydric alcohols such as glycol monobutyl ether; N- methyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone.

  The dispersion step is preferably performed separately for pre-dispersion and main dispersion. In particular, when using dried pigments or pigment derivatives, pre-dispersion is important, which wets the surface of the hydrophobic pigment and replaces the air layer on the surface with water. proceed. If this pre-dispersion is insufficient, the progress of the dispersion is slow, a wasteful mechanical impact is imparted to the pigment, the pigment crystal structure itself is destroyed, and the dispersion becomes poor in stability. The pre-dispersion is usually possible with a general dissolver, but is preferably performed with a high-speed stirrer. High-speed stirrers include TK homomixer, TK Robomix, TK Philmix (trade name, Primics Co., Ltd.), Clear Mix (trade name, MTechnic Co., Ltd.), Ultra Disper (trade name, Asada Steel Co., Ltd.) Etc. are preferable.

  Examples of the disperser that performs the main dispersion include a kneader such as a kneader, a two-roll, a three-roll, SS5 (trade name, M Technique Co., Ltd.), Miracle KCK (trade name, Asada Steel Co., Ltd.), and an ultrasonic wave. Dispersers and high-pressure homogenizers such as microfluidizer (trade name, Mizuho Industrial Co., Ltd.), nanomizer (trade name, Yoshida Kikai Kogyo Co., Ltd.), starburst (trade name, Sugino Machine Co., Ltd.), G-Smasher (Trade name, Rix Corporation). In the case of using a bead medium such as glass or zircon, a ball mill, a sand mill, a horizontal media mill disperser, a colloid mill, or the like can be used. As a medium used in the bead mill, a bead medium having a diameter of 1 mm or less is preferable, and a bead having a diameter of 0.5 mm or less is more preferable.

  The obtained aqueous pigment dispersion may be used as it is, but coarse particles that may be slightly present may be removed by a centrifuge, an ultracentrifuge, or a filter. The coarse particles become a sediment in the ink and accumulate on the bottom, or cause nozzle clogging in ink jet printing.

  In addition, the pigment concentration in the aqueous pigment dispersion of the present invention is preferably 5% to 30%, more preferably 10% to 20% by mass. This is because if it is less than 5% by mass, the degree of freedom to add an additive or the like is reduced during the subsequent ink preparation, and if it exceeds 30% by mass, the pigment density increases in the liquid. There is a concern that problems such as concentration aggregation occur due to hindering the free movement of.

  As described above, the aqueous pigment dispersion for inkjet according to the present invention is obtained. By adding a viscosity modifier, a surface tension modifier, a penetrating agent, water and the like to this, an inkjet aqueous pigment ink is prepared. The

  Anionic, cationic, nonionic, and amphoteric surfactants and polymer surfactants can be used to adjust surface tension and paper permeability. May be damaged. The compounding quantity in an ink is 0.01-5 mass% normally, Preferably it is 0.1-2 mass%.

[Water-based pigment ink for inkjet printer]
The ink of the present invention uses an aqueous pigment dispersion composed of the above-mentioned components. In addition, a surfactant, an antifoaming agent, a preservative, etc. are used in order to obtain an ink having desired physical properties as required. Can be added. Furthermore, urea, thiourea, ethylene urea or derivatives thereof may be contained as a nozzle drying inhibitor.

  The pigment concentration in the ink of the present invention is preferably 0.1% to 20% by mass%, more preferably 1% to 10%. When the pigment concentration is less than 0.1% by mass, a problem occurs in the density at the time of printing. When the pigment concentration exceeds 20% by mass, it is influenced by the surface tension adjusting agent and the paper penetrating agent added during ink preparation, Dispersion stability may be impaired.

  Next, although a synthesis example, an Example, and a comparative example are given and this invention is demonstrated further more concretely, this invention is not limited at all by these examples. In the text, “part” or “%” is based on mass.

[Synthesis Example 1] Synthesis of AB Diblock Polymer Type Polymer Dispersant Diethylene glycol dimethyl ether (hereinafter referred to as diglyme) 125 was added to a reaction apparatus of a separable flask equipped with a stirrer, a reverse flow condenser, a thermometer and a nitrogen introduction tube. Part, 2-iodo-2-cyanopropane (hereinafter abbreviated as CP-1) 3 parts, methyl methacrylate (hereinafter abbreviated as MMA) 65 parts, methacrylic acid (hereinafter abbreviated as MAA) 35 parts, azobisiso 2.5 parts of butyronitrile (hereinafter abbreviated as AIBN) and 0.1 part of iodosuccinimide (hereinafter abbreviated as NIS) were added and stirred while flowing nitrogen. The reaction temperature was raised to 40 ° C. and polymerization was performed for 3 hours.

  After 3 hours, a part was sampled and the solid content was measured. As a result, it was 42.1%, and it was confirmed that most of the monomers were polymerized. When the molecular weight was measured by GPC, the number average molecular weight (hereinafter referred to as Mn) was 3,500, the PDI was 1.22, the molecular weight distribution was narrow, the molecular weight was uniform, MMA / A MAA polymer block (polymer block of A) could be obtained.

  Subsequently, a mixture of 50 parts of benzyl methacrylate (hereinafter abbreviated as BzMA) and 0.2 part of AIBN was added to the polymerization solution having the MMA / MAA polymer block, and polymerization was performed at that temperature for 3 hours. When solid content was measured, it was 49.0%, and it was confirmed that most monomers were polymerized, Mn was 5,400, and PDI was 1.36. Moreover, UV absorption coming from a benzyl group was confirmed, Mn by UV absorption was 5,400, and PDI was 1.37. The molecular weight in the visible region of GPC and the molecular weight in the UV region are almost the same, and the molecular weight is increased by binding the BzMA polymer block (B polymer block) to the MMA / MAA polymer block. It is considered that the BzMA polymer block is copolymerized with the / MAA polymer block.

  The acid value of the diblock polymer (polymer dispersing agent) obtained above was 146 mgKOH / g.

  Next, an aqueous potassium hydroxide solution was added to the copolymer solution to neutralize the carboxyl groups in the polymer in an equivalent amount for neutralization. The polymer solution whose solid content was adjusted to 40% with pure water was transparent, and there was no precipitation of the polymer dispersant. That is, the BzMA polymer block was dissolved without precipitation. Subsequently, it was made to react at 50 degreeC for 2 hours, and the iodine of the polymer terminal was decomposed | disassembled. As described above, an AB diblock polymer type polymer dispersant-1 was obtained.

[Synthesis Examples 2 to 8]
Except having used the raw material and compounding quantity which were described in Table 1-1, 1-2, it synthesize | combined like the synthesis example 1, and obtained the polymer dispersing agent-2-8 of AB diblock polymer type | mold. Each molecular weight, PDI, and acid value are also listed in the table.

The meanings of the abbreviations in Tables 1-1 and 1-2 are as follows.
(1) MMA; methyl methacrylate (2) MAA; methacrylic acid (3) BzMA; benzyl methacrylate (4) CHMA; cyclohexyl methacrylate (5) HEMA; hydroxyethyl methacrylate (6) St; styrene (7) BMA; butyl methacrylate

[Synthesis Example 9]
Experiments were performed in the same manner as in Synthesis Example 1 except that CP-1 and NIS in Synthesis Example 1 were not used. In the polymerization of MMA / MAA, the solid content was 42.0% in 3 hours, and most of the monomers were polymerized. Subsequently, the molecular weight of GPC was 3,400 for Mn and 2.10 for PDI. This polymer does not have a uniform molecular weight and is a normal radical polymerization polymer. Further, after the polymerization, a mixture of BzMA and AIBN was added and polymerized as the next monomer in the same manner as in Synthesis Example 1. The polymerization solution was transparent. After 3 hours, when the solid content was measured, it was confirmed that most of the monomers were polymerized at 49.9%. Moreover, when the molecular weight was measured, Mn was 5,400 and PDI was 2.40. Further, Mn in UV absorption was 5,400, and PDI was 2.42. As in Synthesis Example 1, the molecular weight in the visible region of GPC and the molecular weight in the UV region are almost the same, and the molecular weight is increased by binding the BzMA polymer block to the MMA / MAA polymer block, which is a radical polymerization polymer. The BzMA polymer block is considered to be block copolymerized with the MMA / MAA polymer block.

[Synthesis Examples 10 and 11]
Synthesis was performed in the same manner as in Synthesis Example 9 except that the raw materials and blending amounts shown in Table 2 were used to obtain AB diblock polymer type polymer dispersants-10 and 11. Each molecular weight, PDI, and acid value are also listed in the table.

  Polymer Dispersant-9,10,11 and Polymer Dispersant 1,2,3 are designed to have the same monomer composition and acid value, although PDI is different due to the difference in synthesis method. The molecular weight is also similar.

[Example 1]
175 parts of the polymer dispersant-1 obtained in Synthesis Example 1, 70 parts of diethylene glycol monobutyl ether and 370 parts of pure water were mixed to obtain a uniform solution. The solution was clear and free from precipitation and turbidity. Add 350 parts of copper phthalocyanine blue (cyanine blue KBM, manufactured by Dainichi Seika Kogyo Co., Ltd.) (hereinafter abbreviated as blue pigment 1) and 35 parts of the derivative (1) shown below. A mill base was prepared by 30 cracking.

  Next, after sufficiently dispersing the pigment using a horizontal media disperser, add 316 parts of pure water to this mill base, take out the pigment content from the disperser in a state of about 18%, add water and glycerin. A blue aqueous pigment dispersion for ink-jet of this example having a pigment concentration of 10% and a glycerin concentration of 30% was obtained. At this time, the particle diameter of the pigment was 80.0 nm, the viscosity of the dispersion liquid was 6.50 mPa · s, and the pH was 8.8. When this was stored at 70 ° C. for one week, the particle diameter of the pigment was 81.0 nm, the viscosity of the dispersion was 6.31 mPa · s, and the storage stability was good.

  Next, this blue aqueous pigment dispersion was dropped on a glass plate and dried overnight in a thermostatic chamber set at 60 ° C. and humidity of 40%. When pure water was added dropwise to the dried dispersion residue, it returned to the original pigment dispersion, and even when confirmed with a microscope, no coarse particles, dry film, or pigment aggregates were found. That is, even if the aqueous pigment dispersion of this example is once dried, the dried product has good re-solubility. In this dispersion, the polymer dispersant is encapsulated in the pigment. It is thought that self-dispersibility was imparted to the pigment.

Next, using this blue aqueous pigment dispersion for inkjet, an ink was obtained by the following formulation. This is the blue aqueous inkjet ink of this example.
・ Aqueous pigment dispersion 100 parts ・ Water 115 parts ・ 1,2-hexanediol 12.5 parts ・ Glycerin 20 parts ・ Surfinol 465 (manufactured by Air Products) 2.5 parts

  The pigment particle diameter in the obtained ink was 80.0 nm, the viscosity of the ink was 3.16 mPa · s, and the pH was 8.8. When this ink was stored at 70 ° C. for one week, the particle diameter of the pigment was 76.0 nm, and the viscosity of the dispersion liquid was 3.05 mPa · s. The storage stability was good.

  Next, the blue aqueous inkjet ink obtained above was dropped onto a glass plate and dried overnight in a thermostatic chamber set to 60 ° C. and humidity 40%. When pure water was dropped onto the dried dispersion residue, it returned to the original ink neatly, and even when confirmed with a microscope, no coarse particles, dry film, pigment aggregates were found. That is, the blue water-based inkjet ink of the present invention has a concentration of a paper penetrant such as an aqueous solvent in the ink or a paper penetrant such as Surfinol that generally promotes pigment aggregation when added in large amounts by removing moisture by drying. It was confirmed that the pigment particles did not agglomerate and the re-solubility was good even when the swell increased. That is, in this blue water-based ink-jet ink, it is considered that the polymer dispersant firmly covers and encapsulates the pigment, which is considered to impart solvent resistance and self-dispersibility to the pigment.

[Examples 2 and 3]
In the same manner as in Example 1, using the polymer dispersants-2 and 3 respectively, the blue aqueous pigment dispersion of Examples 2 and 3 and the blue aqueous inkjet ink containing the dispersion were prepared. . Each of the obtained inks was subjected to a storage stability and re-dissolution test in the same manner as in Example 1.

[Comparative Examples 1-3]
In the same manner as in Example 1, polymer dispersants-9, 10, and 11 were used to prepare blue aqueous pigment dispersions and blue aqueous inkjet inks of Comparative Examples 1 to 3, respectively. And the preservability and re-dissolvability test about the obtained ink were done. The results are shown in Table 3 together with Examples 1-3.

[Evaluation Criteria] Hereinafter, the same evaluation criteria are used for similar tests.
(Storability)
○: Change in viscosity and particle size after standing at 70 ° C. for 1 week within ± 5% Δ: Change in viscosity and particle size after standing for 24 hours at 70 ° C. within ± 5% after 1 week Change: ± 5% or more X: Change in viscosity and particle size after standing at 70 ° C. for 24 hours is ± 5% or more

(Re-solubility)
When a drop of the test sample was dropped on a glass plate and dried overnight in a thermostatic chamber set at 60 ° C. and humidity of 40%, and pure water was dropped on the dried dispersion residue,
○: Returning to a uniform ink by visual inspection, and even when confirmed with a microscope, there are no coarse particles, dry film, or pigment aggregates.
Δ: The ink returned to a uniform ink by visual observation, but foreign matter was observed by microscopic observation.
X: Foreign matter is visually observed.

  As shown in Table 3, when a polymer dispersant having a PDI of 1.5 or less and 1.4 or less in Examples 1 to 3 was used, all good results were obtained. On the other hand, when the polymer dispersant of Comparative Examples 1 to 3 having a large PDI synthesized with a normal radical polymerization polymer was used, the storage stability was good, but there was a problem in re-dissolution, and PDI was re-dissolved. It can be seen that it greatly contributes to sex. It is inferred that polymer dispersants having a large PDI are mixed with dispersants that do not work effectively for dispersion and encapsulation, and that these deteriorate the re-solubility.

[Examples 4 and 5]
In the same manner as in Example 1, polymer dispersants-4 and 5 were used to prepare the blue aqueous pigment dispersion and the blue aqueous inkjet ink of Examples 4 and 5, respectively.

[Comparative Examples 4 to 8]
The same procedure as in Example 1, except that the polymer dispersants -1 to 5 were used except for the pigment derivative (1), and the blue aqueous pigment dispersions and blue aqueous inkjet inks of Comparative Examples 4 to 8 were prepared. They were tested for storage and re-dissolution. The results are shown in Table 4 together with Examples 1-5.

  From Table 4, with respect to the polymeric dispersants 1 to 5, all of Examples 1 to 5 in which pigment derivatives are used in combination have good results. On the other hand, in Comparative Examples 4 to 8 in which no pigment derivative was used, the storage stability of the pigment dispersion was all good, but when ink was used, only the ink of Comparative Example 8 was good. The others were inferior in storage stability. The polymer dispersant-5 used in Comparative Example 8 is considered to have a certain degree of resin coating because the hydrophobic B block polymer has a large molecular weight. However, the ink of Comparative Example 8 was NG in the re-solubility test in which the conditions were more severe than the storability and the moisture was forcibly removed. Regarding re-dissolvability, the pigment dispersion was good only in the case of the pigment dispersion of Comparative Example 6. This is considered to be due to the introduction of HEMA into the hydrophobic B block polymer in the polymer dispersant-3 used in Comparative Example 6. However, in the case of ink, all five of Comparative Examples 4 to 8 that did not use a pigment derivative were NG. From these facts, it can be seen that the coexistence of the pigment derivative in the ink achieves firm encapsulation of the pigment and ensures re-dissolvability of the ink.

[Comparative Examples 9 to 11]
In the same manner as in Example 1, polymer dispersants-6, 7, and 8 were used to prepare blue aqueous pigment dispersions and blue aqueous inkjet inks, respectively, and their storability and resolubility tests were performed. . The results are shown in Table 5 together with Examples 1 to 3.

  As shown in Table 5, when the aqueous pigment dispersion was used, the storage stability was good in all cases, and the re-solubility was also practical. However, in the case of ink, the hydrophobic part of the polymer dispersant does not contain benzyl methacrylate or cyclohexyl methacrylate, and is composed of St or BMA, or even if it contains benzyl methacrylate, the molecular weight is less than 500 As for thing, the re-solubility became NG. This also shows that the selection of the monomer type of the hydrophobic part of the polymer dispersant and the molecular weight control affect the resolubility.

[Examples 6 to 13]
In the same manner as in Example 1, an aqueous pigment dispersion and an aqueous inkjet ink were prepared using a combination of the pigment, derivative and polymer dispersant described in the formulation column of Table 6, and the results of their storage stability and resolubility test Is described in the evaluation column of Table 6.

Each pigment in the table is as follows.
Red pigment 1; dimethylquinacridone pigment (CI Pigment Red 122)
Yellow pigment 1; monoazo yellow pigment (CI Pigment Yellow 74)
Yellow pigment 2; disazo yellow pigment (CI Pigment Yellow 155)
Green pigment 1; phthalocyanine pigment (CI Pigment Green 7)

  The same tendency as blue is observed in all of red, yellow, and green, and the combination of the polymer dispersant-1 or the polymer dispersant-3 and the acidic pigment derivative is excellent in storage stability and resolubility. It was possible to produce an ink, and it was confirmed that it was a useful composition in general chromatic pigments used in inkjet inks.

  The aqueous pigment ink for inkjet printers comprising the aqueous pigment dispersion of the present invention has a high degree of storage stability and dispersion stability, as well as good re-dissolvability when dried, and is less likely to clog the head even after a long pause. , Stable discharge is possible over a long period of time.

Claims (6)

An aqueous pigment dispersion comprising a pigment, a pigment derivative, and a polymer dispersant,
The pigment derivative is an acidic pigment derivative obtained by chemically modifying one or more acidic groups in the molecule,
The polymer dispersant is a diblock polymer comprising a hydrophilic block and a hydrophobic block, the PDI of the diblock polymer is 1.5 or less, and at least benzyl as a monomer constituting the hydrophobic block An aqueous pigment dispersion for ink-jet inks containing methacrylate or cyclohexyl methacrylate, wherein the hydrophobic block has a number average molecular weight of 500 to 50,000.   The aqueous pigment dispersion for inkjet ink according to claim 1, wherein the acidic pigment derivative is obtained by chemically modifying one or more sulfonic acid groups that are acidic groups in the molecule.   The aqueous pigment dispersion for inkjet ink according to claim 1 or 2, comprising the acidic pigment derivative at a ratio of 0.1 to 20 parts by mass with respect to 100 parts by mass of the pigment.   The aqueous pigment dispersion for inkjet ink according to any one of claims 1 to 3, wherein the polymer dispersant has an acid value of 40 to 200 mgKOH / g.   The aqueous pigment dispersion for inkjet ink according to any one of claims 1 to 4, wherein the polymer dispersant is contained in a proportion of 5 to 50 parts by mass with respect to 100 parts by mass of the pigment.   An aqueous pigment ink for an inkjet printer comprising the aqueous pigment dispersion for inkjet according to any one of claims 1 to 5.