JP2006182864A - Aqueous pigment dispersion and aqueous ink for inkjet-recording - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aqueous pigment dispersion for preparing an aqueous ink of inkjet-recording, capable of obtaining a colored image having excellent scratch resistance and luster, and holding excellent dispersion stability, and the aqueous ink for the inkjet-recording containing the aqueous pigment dispersion. <P>SOLUTION: This aqueous pigment dispersion for preparing the aqueous ink for inkjet-recording, containing a styrene-acrylic monomer-based copolymer containing each of polymerization units of a styrene-based monomer, a (meth)acrylic acid ester-based monomer and (meth)acrylic acid, a pigment and a basic compound as essential components is provided so that the styrene-acrylic monomer-based copolymer has 100,000 to 3,500,000 (Mw) weight-average molecular weight based on the polystyrene and non-localized cross-linked parts. The aqueous ink for the inkjet-recording is prepared from the aqueous pigment dispersion having 1-10% by mass pigment content. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an aqueous pigment dispersion and an aqueous ink for ink jet recording prepared using the aqueous pigment dispersion.

  Conventionally, dyes have been used as coloring materials for writing instruments such as sign pens and water-based markers, and water-based inks for inkjet recording. A water-based ink for ink jet recording using a dye is excellent in coloring power and sharpness, but has problems in light resistance, water resistance and the like.

  In order to solve the problems of light resistance and water resistance, in recent years, in the field of use described above, particularly in the field of water-based ink for ink jet recording, it has been actively studied to convert a color material from a dye to a pigment. However, water-based ink for inkjet recording has an upper limit on the amount of dispersant such as an organic polymer compound to ensure ejection stability, so that the coating film may be peeled off when the recording surface is rubbed after printing, or non-recording There is a problem that the recorded matter is damaged by fouling the surface, which is inferior in so-called scratch resistance. In addition, the water-based ink for ink jet recording is a recording material such as glossy paper having an ink receiving layer supported by paper or resin-coated paper, and the colorant pigment hardly penetrates the ink receiving layer on the recording paper. As a result, there is a problem that it is not only inferior in scratch resistance but also inferior in gloss due to scattered light on the printing surface as compared with the case of using a dye-based water-based ink for ink jet recording penetrating into the ink receiving layer. It was.

  Examples of water-based inks for inkjet recording that have improved ejection image quality, such as ejection stability, are polymerizable ethylenically unsaturated in one molecule such as divinylbenzene and ethylene glycol di (meth) acrylate. Average particle diameter of 0.01 obtained by polymerizing a polymerizable monomer mixture containing 5% by weight or more of a crosslinkable monomer containing 2 or more double bonds and 2% by weight or more of a hydrophilic group-containing monomer A water-based ink for ink-jet recording containing polymer fine particles of ˜0.1 μm is known (see Patent Document 1).

  However, Patent Document 1 uses a copolymer obtained by emulsion polymerization using a polymerization initiator as a styrene-acrylic copolymer for preparing an inkjet recording water-based ink. For this reason, this copolymer is not controlled in molecular weight, and is a very high molecular weight copolymer that is practically impossible to measure. For such an ink jet recording prepared using such a copolymer. The gloss of the colored image was still unsatisfactory when the recording was performed from the water-based ink onto the dedicated paper for inkjet recording.

  Similarly, water-based inks for inkjet recording with improved ejection stability and dispersion stability include polymerizable ethylenically unsaturated double bonds in one molecule such as divinylbenzene and trimethylolpropane tri (meth) acrylate. Inkjet recording containing fine particles having an average particle size of 200 nm or less obtained by polymerizing a polymerizable monomer mixture containing 0.1 to 5% by weight of a crosslinkable monomer containing two or more and an acid group-containing monomer Water-based inks are known (see Patent Document 2).

  However, in Patent Document 2, a copolymer having a Mw of 3,000 to 70,000 obtained by solution polymerization using a polymerization initiator as a styrene-acrylic copolymer for preparing an inkjet recording aqueous ink. Use coalescence. For this reason, this copolymer is a copolymer having a relatively low molecular weight equivalent to that conventionally used, and an inkjet recording from an aqueous ink for inkjet recording prepared using such a copolymer. The scratch resistance and gloss of the colored image when recorded on the special paper for printing were still unsatisfactory.

  Furthermore, an ink-jet ink using a star polymer as an additive for improving water resistance and image color density is known (Patent Document 3). This star polymer is a polymer with linear arms that radiate from the central core, such as two or more polymerizable ethylenically unsaturated double bonds in one molecule, such as ethylene glycol di (meth) acrylate. It consists of a polymer in which polymerized units of the crosslinkable monomer contained are concentrated in a specific part of the polymer molecular structure and the cross-linked part is localized in the polymer molecule.

  However, in Patent Document 3, this star polymer is not allowed to function as a dispersant, and the dispersant is separately used as a dispersant, and the star polymer is used as an additive in the dispersant. . In the star polymer of Patent Document 3, the cross-linked portion is localized in the polymer molecule, and it is difficult to obtain the pigment dispersibility by the star polymer itself, and the pigment is stably and finely dispersed by such a star polymer itself. It has been difficult to prepare a water-based ink for inkjet recording.

JP-A-7-278479 JP 2003-268288 A JP 2000-169771 A

  The present invention provides an aqueous pigment dispersion for preparing a water-based ink for ink-jet recording, which can provide a colored image having excellent scratch resistance and gloss on a special paper for ink-jet recording while maintaining excellent dispersion stability, Another object of the present invention is to provide a water-based ink for inkjet recording comprising the water-based pigment dispersion.

As a result of synthesizing copolymers having various compositions and characteristics in order to solve the above-mentioned problems, and intensively examining the relationship between them and dispersion stability and colored image characteristics, the present inventors have found that styrene-acrylic copolymer. As a coalescence, a crosslinked part is present and the crosslinked part is delocalized, and a copolymer having a weight average molecular weight in an appropriate range without being too small or too small is excellent in dispersed particles in an aqueous pigment dispersion. The inventors have found that a water-based ink for ink-jet recording of a colored image that can maintain stability and has excellent scratch resistance and gloss on a special paper for ink-jet recording can be prepared, and the present invention has been completed.
That is, the present invention requires a styrene-acrylic copolymer, a pigment, and a basic compound each containing a styrene monomer, a (meth) acrylic acid ester monomer, and a (meth) acrylic acid polymerization unit. In the aqueous pigment dispersion for preparing an aqueous ink for ink-jet recording, which is contained in an aqueous medium as a component, the styrene-acrylic copolymer has a polystyrene-equivalent weight average molecular weight (Mw) = 100,000 to An aqueous pigment dispersion for preparing a water-based ink for ink-jet recording, which is a 3,500,000 styrene-acrylic copolymer having a crosslinked part and having a crosslinked part delocalized provide.
The present invention also provides an aqueous ink for inkjet recording prepared from the above-described aqueous pigment dispersion, wherein the pigment content is 1 to 10% in terms of mass.

In the water-based ink for ink-jet recording of the present invention, the styrene-acrylic copolymer contained therein has a polystyrene-equivalent weight average molecular weight (Mw) = 100,000 to 3,500,000 and has a cross-linked portion. Since the cross-linked portion is a delocalized styrene-acrylic copolymer, a colored image having excellent scratch resistance and gloss can be obtained, and it has a particularly remarkable effect of being excellent in dispersion stability. Play.
The water-based pigment dispersion of the present invention has a particularly remarkable effect that the water-based ink for ink jet recording as described above can be easily prepared.

Details of the present invention will be described below.
The present invention includes a styrene monomer, a (meth) acrylic acid ester monomer, and a styrene-acrylic copolymer containing each polymerization unit of (meth) acrylic acid, a pigment, and a basic compound as essential components. In the aqueous pigment dispersion for preparing an aqueous ink for inkjet recording, which is contained in an aqueous medium, the styrene-acrylic copolymer has a polystyrene-equivalent weight average molecular weight (Mw) = 100,000-3. , 500,000, a water-based pigment dispersion for preparing a water-based ink for ink-jet recording, which is a styrene-acrylic copolymer having a cross-linked portion and a delocalized cross-linked portion .

  The pigment in the aqueous pigment dispersion of the present invention is an organic pigment or an inorganic pigment, and any known pigment can be used. These pigments can be used in any form such as dry powder or wet cake.

  In the present invention, the aqueous medium refers to a liquid medium containing 60% or more of water in terms of mass with only water or a mixture of water and a water-soluble organic solvent.

  In the aqueous pigment dispersion of the present invention, the particles dispersed in the aqueous medium (hereinafter referred to as dispersed particles) may be pigment particles and copolymer particles, but the pigment is coated with the copolymer. It may be in the form of a composite particle. In the aqueous pigment dispersion, the dispersed particles are dispersed so that the average dispersed particle diameter (median diameter) is 50 to 200 nm.

  In the present invention, (meth) acrylic acid is a technical term including both acrylic acid and methacrylic acid. Similarly, the styrene-acrylic copolymer in the present invention contains polymerized units of a styrene monomer, a (meth) acrylic acid ester monomer and (meth) acrylic acid, and is a weight average in terms of polystyrene. This is a technical term that means a styrene-acrylic copolymer having a molecular weight (Mw) = 100,000 to 3,500,000 and having a cross-linked portion, and the cross-linked portion being delocalized.

  The styrene-acrylic copolymer in the present invention can be obtained by copolymerizing a styrene monomer, a (meth) acrylic acid ester monomer, and (meth) acrylic acid as essential components. .

  The weight average molecular weight (hereinafter abbreviated as Mw) of the styrene-acrylic copolymer is a polystyrene equivalent weight molecular weight. It can be measured by gel permeation chromatography (hereinafter abbreviated as GPC). In this measurement, polystyrene of various Mw is used as a standard substance, and the maximum peak by GPC of the styrene-acrylic copolymer is defined as the Mw.

  Moreover, the styrene-acrylic copolymer in the present invention has a cross-linked portion, and the cross-linked portion is delocalized. In order to make the styrene-acrylic copolymer contain a cross-linked moiety, for example, a cross-linkable monomer containing two or more polymerizable ethylenically unsaturated double bonds in one molecule described later is a comonomer. As long as they are used together. If the monomer mixture containing the crosslinkable monomer, styrene monomer, (meth) acrylic acid ester monomer and (meth) acrylic acid is randomly copolymerized, they are block copolymerized. Thus, a copolymer having a localized crosslinked part is obtained, whereas a styrene-acrylic copolymer in which the crosslinked part is present at random, that is, the crosslinked part is delocalized. Whether or not the styrene-acrylic copolymer has a cross-linked portion can be estimated from the decomposition pattern obtained by decomposing the copolymer by pyrolysis chromatography, for example. Whether or not the shape of the polymer is a star polymer can be determined by determining the molecular weight distribution of the copolymer by gel permeation chromatography (GPC). The star polymer as described above substantially depends on the molecular weight distribution of the side chain. Therefore, it has only one peak and shows a smooth curve shape close to a normal distribution centered on it, whereas two polymerizable ethylenically unsaturated double bonds are present in one molecule as described above. A copolymer obtained by random copolymerization using the crosslinkable monomer contained above as a comonomer is characterized by having a large number of peaks and a curved shape in which these peaks appear irregularly. Using this feature, it is possible to distinguish between the two.

  Examples of the styrene monomer include styrene, α-methyl styrene, o-methyl styrene, m-methyl styrene, p-methyl styrene, tert-butyl styrene, etc., among which styrene, α-methyl styrene, One or more styrenic monomers selected from the group consisting of tert-butylstyrene are preferred in that they contribute more to the technical effects of the present invention and are readily available and inexpensive.

  Copolymers containing a large number of polymer units of styrenic monomers are susceptible to cracking of the colored image and peeling of the colored image itself from the recording medium due to weighted contact. Used in combination with acid esters. In addition, the copolymer containing a large number of styrene monomer polymerization units, due to the interaction with the ink discharge nozzle interface of the printer or the like, the discharge response is insufficient, the color image may be blurred, It may cause nozzle clogging.

  On the other hand, a copolymer containing (meth) acrylic acid and (meth) acrylic ester polymerized units that do not contain polymerized units of styrenic monomers enhances the adhesion of colored images onto the recording medium. This is effective in preventing the occurrence of scratches on the surface of a colored image due to simple contact. Specifically, it is excellent in affinity with a recording medium (dedicated paper) having a hydrophilic surface such as an inkjet photographic paper, and is effective in developing the fixing property and glossiness there. . However, the color image density on the recording medium cannot be improved as much as expected.

  Therefore, when a higher color image density on the recording medium is required, a copolymer containing styrene monomer, (meth) acrylic acid ester monomer, and (meth) acrylic acid as essential components is copolymerized. Styrene-acrylic copolymer is used.

  When trying to satisfy both the characteristics of the colored image density on the recording medium and the fixing property on the special paper, a part of the polymerization unit of the styrene monomer in the polymerization unit of the copolymer is described below. It is effective to substitute a polymerization unit of a benzyl (meth) acrylate monomer that is one of (meth) acrylate monomers. In this case, the charge ratio of each monomer is that of the styrene monomer and the benzyl (meth) acrylate monomer when the total monomer total of the styrene-acrylic copolymer is 100 mol%. The total number of moles is 40 to 80 mol%, and the number of moles of styrene monomer to be tightened to the total number of moles of styrene monomer and benzyl (meth) acrylate monomer is 50 to 90 mol%. It is effective to do. More preferred is a styrene-acrylic copolymer having a total of 50 to 80 mol% of the styrene monomer and the benzyl (meth) acrylate monomer.

  Examples of the benzyl (meth) acrylate monomer include benzyl acrylate and benzyl methacrylate. Among them, benzyl methacrylate is easily available because it contributes more to the technical effect of the present invention. It is preferable in that it is inexpensive.

  As the styrene-acrylic copolymer in the present invention, the polymerization unit of the styrene monomer is a polymerization unit of styrene or tert-butylstyrene, and the polymerization unit of the (meth) acrylic acid ester monomer described below. Is a styrene-acrylic copolymer which is a polymerized unit of benzyl methacrylate, and in particular, the charge ratio is 50 moles of styrene with respect to the total moles of styrene or tert-butylstyrene and benzyl methacrylate. Most preferably, it is -80% styrene-acrylic copolymer.

  Examples of (meth) acrylic acid include acrylic acid and methacrylic acid. (Meth) acrylic acid is preferable in terms of availability, price, etc., because the coexistence range of the electrically neutral state and the anion state can be controlled widely.

  Examples of copolymerizable (meth) acrylic acid ester monomers and other monoethylenically unsaturated monomers include methyl (meth) acrylate, n-butyl (meth) acrylate, and (meth) acrylic. 2-ethylhexyl acid, n-octyl (meth) acrylate, dodecyl (meth) acrylate, octadecyl (meth) acrylate, cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, dimethyl maleate, dimethyl fumarate, Unsaturated fatty acid esters such as (meth) acrylic acid 2-aminoethyl; Unsaturated fatty acid amides such as (meth) acrylamide and N-methyl (meth) acrylamide; Unsaturated nitriles such as (meth) acrylonitrile; Vinyl acetate Unsaturated ethers such as vinyl propionate; ethylene, propylene, 1-butene, -Unsaturated hydrocarbons such as octene, vinylcyclohexane, 4-vinylcyclohexene; unsaturated halogenated hydrocarbons such as vinyl chloride, vinylidene chloride, tetrafluoroethylene, 3-chloropropylene; 4-vinylpyridine, N -Vinyl-substituted heterocyclic compounds such as vinyl carbazole and N-vinyl pyrrolidone; monomers containing a substituent containing an active hydrogen such as a carboxyl group, a hydroxyl group and an amino group in the exemplified monomers and ethylene oxide; Reaction products with epoxides such as propylene oxide and cyclohexene oxide; monomers containing a substituent containing a hydroxyl group, an amino group, etc. in the above exemplified monomers and acetic acid, propionic acid, butanoic acid, hexanoic acid, Examples include reaction products with carboxylic acids such as decanoic acid and dodecanoic acid.

  The styrene-acrylic copolymer may be a copolymer obtained by copolymerizing a styrene monomer, a (meth) acrylic acid ester monomer, and (meth) acrylic acid. It may be a copolymer obtained by copolymerizing a (meth) acrylic acid ester-based monomer.

  Examples of the (meth) acrylic acid ester monomer having a hydroxyl group include hydroxy such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, and 3-hydroxypropyl (meth) acrylate. Alkyl (meth) acrylate, diethylene glycol mono (meth) acrylate, triethylene glycol mono (meth) acrylate, polyethylene glycol mono (meth) acrylate, propylene glycol mono (meth) acrylate, dipropylene glycol mono (meth) acrylate, tripropylene glycol Mono (meth) acrylate, tetramethylene ether glycol mono (meth) acrylate, polyethylene oxide-polypropylene oxide random polymer glycol or the same block poly Chromatography glycol mono (meth) acrylate, polyethylene oxide - alkylene glycol mono (meth) acrylate mono (meth) acrylate random polymer glycol or the block polymers glycol polytetramethylene ether. Of these, hydroxyalkyl (meth) acrylate is preferred because it is easy to prepare water-soluble styrene-acrylic copolymer and adjust the glass transition temperature, and is easily available and inexpensive. Hereinafter, the glass transition temperature is referred to as Tg.

  Although the content rate of the polymerization unit of the (meth) acrylic acid ester monomer having a hydroxyl group in all the polymerization units of the styrene-acrylic copolymer is not particularly limited, it is usually 3 to 20%, preferably 5 to 15 %. Here,% is based on mass. The (meth) acrylic acid ester monomer having a hydroxyl group may be 3 to 15 mol% on a molar basis.

  In preparation of the water-soluble styrene-acrylic copolymer, a terminal alkyl or terminal arylated polyalkylene glycol (meth) acrylate may be used. The repeating unit of the oxyalkylene group of the polyalkylene glycol may consist of only one kind of oxyalkylene group. For example, two or more kinds of oxyalkylene groups may be randomly selected such as a combination of an oxyethylene group and an oxypropylene group. Or you may contain in a block. In this case, the repeating unit of the oxyalkylene group is preferably 4 to 50. When this repeating unit becomes large, the viscosity of the styrene-acrylic copolymer increases, and it tends to be difficult to easily prepare an aqueous pigment dispersion or an aqueous ink for inkjet recording.

  Examples of the (meth) acrylic acid ester of such a terminal alkyl or terminal arylated polyalkylene glycol include methoxy polyethylene glycol, methoxy polyethylene polypropylene glycol, ethoxy polyethylene glycol, ethoxy polyethylene polypropylene glycol, propoxy polyethylene glycol, and propoxy polyethylene. Polyalkylene having one terminal alkyl or arylated, such as polypropylene glycol, 2-ethylhexyloxypolyethylene glycol polypropylene glycol, lauryloxypolyethylene glycol, stearyloxypolyethylene glycol, nonylphenyloxypolyethylene glycol, nonylphenyloxypolyethyleneglycol polypropylene glycol, etc. (Meth) acrylic acid esters of glycol. However, from the viewpoint of environmental hormones, it is preferable to use a terminal alkylated (meth) acrylic acid ester of polyalkylene glycol rather than a terminal arylated polyalkylene glycol (meth) acrylic acid ester.

  The styrene-acrylic copolymer in the present invention can be produced by charging and reacting the respective monomers in a reaction vessel so that the content ratio of the respective polymerization units is obtained. In the present invention, the reaction rate of each monomer described above is considered to be substantially the same, and the charging ratio of each monomer is regarded as the content ratio of the polymerization unit of each monomer in terms of mass. The same applies to the case of molar conversion. The copolymer in the present invention can be synthesized by various conventionally known reaction methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization.

  In order to obtain a water-based ink for inkjet recording in which an image excellent in scratch resistance and gloss is obtained, the weight average molecular weight of the styrene-acrylic copolymer in the present invention is Mw = 100, 000-3,500,000. Until now, a relatively low molecular weight copolymer of about 3,000 to 70,000 has been used in many water-based inks for inkjet recording. On the other hand, the styrene-acrylic copolymer obtained as an emulsion has an ultra-high molecular weight that cannot be measured by GPC such as 3,800,000 or more. If the molecular weight is increased to this extent, the viscosity of the water-based ink for ink jet recording prepared therefrom tends to be high, and the dispersibility is lowered due to a decrease in wettability to the pigment.

  In the present invention, in order to improve the point that the viscosity is increased and the decrease in dispersion ability, the styrene-acrylic copolymer is a cross-link containing two or more polymerizable ethylenically unsaturated double bonds in one molecule. A polymerization unit of a polymerizable monomer (crosslinkable monomer) was further contained. Compared to a linear copolymer composed only of a monofunctional monomer, a branched copolymer partially containing such a crosslinkable monomer polymerization unit is required for an aqueous pigment dispersion. High molecular weight can be achieved while maintaining the low viscosity. Thereby, the water-based ink for inkjet recording using this water-based pigment dispersion can obtain a colored image having excellent scratch resistance and gloss on the recording medium and is excellent in dispersion stability.

  Examples of the crosslinkable monomer include crosslinkable monomers containing 2 to 6 polymerizable ethylenically unsaturated double bonds in one molecule. For example, ethylene glycol di (meth) acrylate, diethylene glycol di ( (Meth) acrylate, triethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate (4 to 30 repeating units of oxyethylene group), polypropylene glycol di (meth) acrylate (4 to 4 repeating units of oxypropylene group) 30), tritetramethylene glycol di (meth) acrylate, polytetramethylene glycol di (meth) acrylate (4 to 30 repeating units of oxytetramethylene group), poly (ethylene glycol-propylene glycol) di (meth) acrylate ( Oxyethylene Group and oxypropylene group each having a repeating unit of 4 to 30), poly (ethylene glycol-tetramethylene glycol) di (meth) acrylate (oxyethylene group and oxytetramethylene group each having 4 to 30 repeating units), Poly (propylene glycol-tetramethylene glycol) di (meth) acrylate (4-30 units of each of oxypropylene group and oxytetramethylene group), poly (ethylene glycol-propylene glycol-tetramethylene glycol) di (meth) A crosslinkable monomer having two polymerizable ethylenically unsaturated double bonds in one molecule, such as acrylate (each repeating unit of oxyethylene group, oxypropylene group and oxytetramethylene group is 4 to 30) The body is mentioned.

  Other crosslinkable monomers include, for example, trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, trimethylolpropane alkylene oxide adduct tri (meta) 3) Polymerizable ethylenically unsaturated double bonds in one molecule such as tetra (meth) acrylate of alkylene oxide adduct of acrylate, pentaerythritol, hexa (meth) acrylate of alkylene oxide adduct of dipentaerythritol Examples thereof include 6 crosslinkable monomers. The repeating unit of the oxyalkylene group may consist of only one kind of oxyalkylene group. For example, it contains two or more kinds of oxyalkylene groups in a random or block manner, such as a combination of an oxyethylene group and an oxypropylene group. It may be what you do.

  The polymerizable unsaturated bond of such a crosslinkable monomer is suitable in that the unsaturated bond of α, β-unsaturated carbonyl group is excellent in reactivity in radical polymerization. good.

  The charge ratio of the crosslinkable monomer is not particularly limited, but is usually 0.001 to 5%, preferably 0.001 to 3% of the total monomer amount in terms of mass. More preferably, it is 0.01 to 3%. If the amount added is too large, the degree of branching will increase too much, making it difficult to control the polymerization reaction. On the other hand, if the amount is too small, it is difficult to obtain the effect of improving the gloss and abrasion resistance of the colored image on the recording medium.

  The styrene-acrylic copolymer in the present invention has a specific Mw as described above. The molecular weight of the styrene-acrylic copolymer can be controlled by adjusting the addition amount of the polymerization initiator, the reaction concentration, etc., but considering the economy, the combined use of a chain transfer catalyst is effective. In addition, if the molecular weight is the same with the same monomer composition, the colored image on the recording medium is more scratch-resistant and glossy with the styrene-acrylic copolymer using a chain transfer catalyst. It will be better.

  Examples of the chain transfer catalyst include thiols such as n-dodecyl mercaptan, n-octyl mercaptan, thioglycerol, octyl 3-mercaptopropionate, 2,4-diphenyl-4-methyl-1-pentene (α-styrene dimer). ) And the like. The amount added is 0.5 to 10% equivalent, preferably 0.8 to 5% equivalent of all monomers for preparing a styrene-acrylic copolymer in terms of mass.

  Further, the styrene-acrylic copolymer in the present invention contains a polymerization unit of (meth) acrylic acid as an essential component. This polymerized unit is an indispensable polymerized unit for dispersing the styrene-acrylic copolymer in an aqueous medium, and this polymerized unit can increase the affinity of the styrene-acrylic copolymer for water, Dispersibility in an aqueous medium and dispersion stability of dispersed particles when an aqueous pigment dispersion is obtained can be further improved.

  The type and amount of other copolymerizable ethylenically unsaturated monomers used in combination with the styrene monomer in the styrene-acrylic copolymer and the molecular weight of the copolymer under certain conditions In contrast, if the acid value of the styrene-acrylic copolymer is too small, the dispersion stability of the dispersed particles tends to decrease, and conversely, if the acid value of the styrene-acrylic copolymer is too large, the colored image Water resistance and color image density tend to decrease, both of which are not preferred.

  From such a viewpoint, the styrene-acrylic copolymer has, for example, an acid value of 60 to 150 mgKOH / g, preferably an acid value of 85 to 135 mgKOH / g, more preferably an acid value of 85 to 110 mgKOH / g. Thus, it is particularly preferable when a plain paper is used as a recording medium in that a particularly high colored image density can be obtained. Here, the acid value means the number of mg of potassium hydroxide necessary for neutralizing 1 g of the styrene-acrylic copolymer. In order to make the styrene-acrylic copolymer have such an acid value, the content ratio of the polymerization units of (meth) acrylic acid in the total polymerization units in terms of mass is usually 8 to 25%, preferably 10 to 10%. 21%, more preferably 10 to 17%. Although different depending on other monomer species to be used, when the total monomer is 100%, (meth) acrylic acid may be about 12 to 30 mol% on a molar basis.

  When the styrene-acrylic copolymer in the present invention has the above acid value, the copolymer neutralized with a basic compound described later has good dispersibility in an aqueous medium, and an aqueous pigment dispersion is obtained. The contribution of the dispersed particles to the dispersion stability is remarkable. More specifically, this aqueous pigment dispersion is preferable because the dispersion stability of dispersed particles becomes good when applied to the preparation of an aqueous ink for inkjet recording.

  The styrene-acrylic copolymer in the present invention contains a polymerization unit of (meth) acrylic acid, but in preparing the aqueous pigment dispersion of the present invention, at least a part of the carboxyl group is formed by a basic compound described later. By adopting an ionized form, the dispersibility of the styrene-acrylic copolymer in the aqueous medium and the dispersion stability of the dispersed particles are expressed. The optimum proportion of ionized carboxyl groups is usually set in the range of 30 to 100%, particularly 70 to 100%. The content ratio of the ionized carboxyl group does not mean the molar ratio of the carboxyl group to the basic compound but takes into account the dissociation equilibrium. Even if a stoichiometric equivalent of a strongly basic compound is used, the carboxyl group contains less than 100% of the ionized group (carboxylate group) by dissociation equilibrium. State.

  By comparing the types of monomers in the styrene-acrylic copolymer, the ratio of their use, the molecular weight of the copolymer, and the acid value, etc. under certain conditions, the carboxyl groups in the copolymer are ionized. The smaller the amount of the basic compound used, the more the water resistance and the color image density of the colored image tend to improve, while the dispersion stability of the dispersed particles tends to decrease. Therefore, it is preferable that the amount of the basic compound used is selected so that these characteristics are balanced, together with the acid value of the copolymer used.

  As the basic compound used for ionizing at least a part of the carboxyl group of the styrene-acrylic copolymer in this manner, any known and conventional compounds can be used. Examples of such a basic compound include compounds selected from the group consisting of ammonia, organic amines such as primary amines, secondary amines, and tertiary amines, and alkali metal hydroxides. In the present invention, the basic nitrogen-containing heterocyclic compound is a tertiary amine.

  By ionizing at least part of the carboxyl group of the styrene-acrylic copolymer with a basic compound, the counter ion of the carboxylate group becomes a cation selected from the group consisting of ammonium ions or alkali metal ions. In the present invention, when a basic nitrogen-containing heterocyclic compound is used as the basic compound, the heterocyclic compound becomes a protonated cation of the basic nitrogen-containing heterocyclic compound.

  For example, when an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide is used as the basic compound, the dispersed particles in the aqueous pigment dispersion are compared with the case where ammonia or the organic amine is used. This is preferable because of good dispersion stability.

  When ammonia or the above organic amines are used, they are excellent in volatility at low temperatures. Therefore, the dryness of the colored image on the recording medium of the aqueous pigment dispersion and the aqueous pigment recording liquid, and the preparation of the aqueous ink for inkjet recording are used. Excellent discharge stability immediately after.

  On the other hand, however, ammonia and the organic amine volatilize when left for a long time and / or in a high-temperature atmosphere, so that the dispersion stability of the dispersed particles in the aqueous pigment dispersion and the aqueous ink for inkjet recording is gradually impaired. In some cases, sedimentation of dispersed particles is observed. It is not preferable to prepare a water-based ink for inkjet recording as it is from such a water-based pigment dispersion because the settled particles in the ink cause a discharge failure of ink droplets from the nozzles of the printer.

  In the present invention, the styrene-acrylic copolymer is a styrene-acrylic copolymer containing both a carboxyl group and a carboxylate group in which a part of the carboxyl group is neutralized with a basic compound. Is optimal.

  If necessary, the styrene-acrylic copolymer is different from the radical polymerizability such as a monoethylenically unsaturated monomer containing an epoxy group represented by 2,3-epoxypropyl (meth) acrylate. It may contain a cross-linked moiety by the reactive functional group.

  In the case of a copolymer containing a polymerized unit of a monoethylenically unsaturated monomer containing an epoxy group, the epoxy group can be subjected to a ring-opening reaction for crosslinking. If necessary for crosslinking of the epoxy group, a curing catalyst may be used in combination.

The aqueous pigment dispersion of the present invention can be produced, for example, by the methods 1) to 4) as described later.
1) A method for producing an aqueous pigment dispersion in which a pigment is mechanically forcedly dispersed in an aqueous emulsion containing a styrene-acrylic copolymer and a basic compound.
2) A method for producing an aqueous pigment dispersion in which the above-mentioned monomers are polymerized using a dispersant and a basic compound in water in the presence of a pigment to form a styrene-acrylic copolymer, if necessary.
3) A method for producing an aqueous pigment dispersion in which a mixture of a pigment, a styrene-acrylic copolymer, and an organic solvent is gradually phase-inverted from an oil phase to an aqueous phase using water and a basic compound and then desolvated .
4) Solvent removal from a uniform mixture of pigment, styrene-acrylic copolymer, basic compound, organic solvent, and water, acid compounding, acid precipitation, washing the precipitate, A method for producing an aqueous pigment dispersion which is dispersed in an aqueous medium together with a compound.

  As described above, in the aqueous pigment dispersion of the present invention, the dispersed particles are preferably those in which the interaction between the pigment and the styrene-acrylic copolymer acts strongly in terms of dispersion stability, etc. The aqueous pigment dispersions produced by 3) and 4) have not only high dispersion stability of the dispersed particles, but also the aqueous pigment dispersions of the aqueous pigment dispersions produced by the methods 1) and 2). It is preferable because the viscosity becomes lower. In the ink jet recording system, in order to eject ink droplets from a nozzle, it is desired that the ink droplet has a low viscosity. Therefore, it is preferable that the viscosity of the aqueous pigment dispersion itself for preparing it is also low.

  In the present invention, it is preferable to include a step of dispersing a mixture comprising a pigment, a styrene-acrylic copolymer, a basic compound and an aqueous medium, regardless of which production method is used. This mixture preferably contains a water-soluble organic solvent. More specifically, it is preferable to include a step (dispersion step) of dispersing a mixture of at least a pigment, a styrene-acrylic copolymer, a basic substance, a water-soluble organic solvent, and water. By using a water-soluble organic solvent in combination with water, the liquid viscosity in the dispersion step may be reduced.

  Examples of the water-soluble organic solvent include ketones such as acetone, methyl ethyl ketone, methyl butyl ketone, and methyl isobutyl ketone; methanol, ethanol, 2-propanol, 2-methyl-1-propanol, 1-butanol, and 2-methoxyethanol. Alcohols such as tetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, and the like; amides such as dimethylformamide, N-methylpyrrolidone, and the like. It is preferable to use a compound selected from the group consisting of a ketone and an alcohol having 1 to 5 carbon atoms. These water-soluble organic solvents may be used as the styrene-acrylic copolymer solution, or may be separately contained in the mixture during the dispersion step.

  The aqueous pigment dispersion of the present invention preferably has a pigment / styrene-acrylic copolymer (nonvolatile content) = 100/10 to 100/100 in terms of mass. Optimally, it can be produced using the above-mentioned raw materials so that the non-volatile content of the styrene-acrylic copolymer is 20 to 65 parts and the aqueous medium is 835 to 880 parts per 100 parts of the pigment in terms of mass.

  As a dispersion apparatus that can be used in the dispersion step, any of various known apparatuses can be used and is not particularly limited. Examples of such a dispersing device include a method using kinetic energy of a spherical dispersion medium having a diameter of about 0.1 to 10 mm made of steel, stainless steel, zirconia, alumina, silicon nitride, glass, etc., shearing by mechanical stirring. Examples of the dispersion device include a dispersion method such as a force utilization method, a pressure change of a dispersed flow bundle supplied at high speed, a flow passage change, or a force utilization force generated by a collision.

  By carrying out such a dispersion step, a state in which the pigment is dispersed in the liquid medium containing the styrene-acrylic copolymer is formed. Further, by using a larger amount of the basic compound in such a dispersion step, the copolymer contained in the liquid medium can be changed from a dispersed state to a dissolved state.

  Subsequent to the dispersion step, when an organic solvent is used in the dispersion step, a step of removing the organic solvent and a step of removing excess water (distillation step) to obtain a desired solid concentration can be performed. As the aqueous pigment dispersion of the present invention, those containing no organic solvent are preferred because they have no odor and can improve the working environment.

  In the aqueous pigment dispersion of the present invention, the pigment and the styrene-acrylic copolymer interact more effectively when exhibiting superior properties in all aspects of dispersion arrival level, dispersion time, and dispersion stability. Is preferably strongly dispersed.

  In order to enhance the interaction of the dispersed particles, it is preferable to incorporate a step of bringing the styrene-acrylic copolymer in a dissolved state into close contact with the pigment surface as a subsequent step of the dispersing step.

  As a step of bringing the styrene-acrylic copolymer in a dissolved state into close contact with the pigment surface, the liquid medium containing the pigment and the basic compound and the dissolved copolymer is acidified to produce styrene- A step (acid precipitation step) in which the anionic group in the acrylic copolymer is returned to the functional group before being neutralized and the copolymer is precipitated is preferable.

  In the acid precipitation process, an acidic compound such as hydrochloric acid, sulfuric acid, acetic acid or the like is added to the aqueous pigment dispersion obtained through the dispersion process and the distillation process performed as necessary to acidify, thereby forming a basic compound and a salt. This is a step of precipitating the styrene-acrylic copolymer in a dissolved state on the surface of the pigment particles. By this step, the interaction between the pigment and the styrene-acrylic copolymer can be enhanced. After the precipitate obtained by increasing the interaction in this manner is filtered off, more preferably, the precipitate is washed, and then dispersed again in an aqueous medium together with the basic compound, whereby an aqueous pigment having superior dispersion stability. It can be a dispersion.

  The filtration step is a step of filtering a precipitate obtained by enhancing the interaction between the pigment and the styrene-acrylic copolymer. This deposit is a solid content composed of a pigment and a styrene-acrylic copolymer. This step is a step of filtering the solid content after the acid precipitation step with a filter press, a Nutsche filtration device, a pressure filtration device or the like.

  The washing step is a step of washing and filtering the precipitate separated in the filtration step. By performing this step, inorganic salts contained in the finally obtained aqueous pigment dispersion can be reduced or removed. become. Commercially available organic pigments may contain a large amount of inorganic salts, and aqueous inks for ink jet recording obtained from aqueous pigment dispersions prepared using such organic pigments may clog printer nozzles. Ejection failure due to etc. is likely to occur. However, this problem can be solved by preparing a water-based ink for inkjet recording from the water-based pigment dispersion that has undergone the washing step.

  When an aqueous pigment dispersion is produced according to the above method 4), inorganic salts contained in commercially available organic pigments and inorganic salts mixed due to other factors can be collectively reduced or removed in this washing step. In addition, there is an advantage that the unit operation is simpler because it is not necessary to independently perform the pre-cleaning of the organic pigment itself, which is necessary when the same problem occurs in other production methods.

  The redispersion step is a step in which a basic compound and, if necessary, water and additives are added to the solid content obtained by the acid precipitation step and the filtration step to form an aqueous pigment dispersion again. In this step, the counter ion of the ionized carboxyl group in the styrene-acrylic copolymer can be changed to a basic compound different from the basic compound used in the dispersion step.

  When an aqueous pigment dispersion is produced by a production method including an acid precipitation step and a redispersion step as essential steps, preferably including a filtration step and a washing step, the pigment and the styrene-acrylic copolymer are dispersed as described above. It is possible to easily form a state in which the interaction with the water is further increased, and as an aqueous pigment dispersion, it is more excellent in terms of physical properties such as dispersion reaching level and dispersion stability and suitability for use such as solvent resistance. The characteristics can be exhibited.

  To the aqueous pigment dispersion of the present invention containing a styrene-acrylic copolymer thus obtained, for example, at least one aqueous resin selected from the group consisting of aqueous polyurethane, aqueous polyester, and aqueous acrylic is added. You can also As this aqueous resin, a resin that can be dispersed in an aqueous medium by itself without containing a surfactant or the like is preferable. Such an aqueous polyurethane is produced by combining a dimethylolpropionic acid, a diol, an organic diisocyanate and, if necessary, a diamine, and performing a polyaddition reaction to obtain a carboxyl group-containing polyurethane, which is neutralized with a basic compound as described above. The aqueous polyester can be esterified or transesterified by combining trimellitic acid, pyromellitic acid, sulfosuccinic acid and their derivatives with diol and dicarboxylic acid to form a carboxyl group or sulfo group-containing polyester as described above. The aqueous acryl has a monomer composition different from that of the styrene-acrylic copolymer, and (meth) acrylic acid can be copolymerized with other monoethylene. Carboxylation reaction with a photopolymerizable unsaturated monomer Containing acrylic resin to be prepared by neutralizing with a basic compound such as mentioned above it.

  It is preferable that the dispersed particles of these aqueous resins are relatively smaller than those of the dispersed particles in the aqueous pigment dispersion serving as a base in the range of an average dispersed particle diameter (median diameter) of 10 to 100 nm. Addition of these water-based resins to the water-based pigment dispersion of the present invention has an effect of improving the scratch resistance when touching the special paper. Among these water-based resins, water-based polyurethane is preferable because it has a greater effect of improving scratch resistance when touched with a finger. Scratch resistance at the time of touching means the color bleeding when a colored image on a recording medium is rubbed with a finger at regular intervals immediately after printing. The addition of water-based polyurethane is effective in improving the scratch resistance immediately after printing and 10 minutes after printing.

  Examples of such an aqueous polyurethane include polyester-based polyurethane, polyether-based polyurethane, polyetherester-based polyurethane, and polycarbonate-based polyurethane. These can be easily obtained by using a corresponding polymer diol such as polyester diol or polyether diol as the diol in the production method described above.

  The above-mentioned aqueous resin can be added to the aqueous pigment dispersion of the present invention so that it becomes 5 to 30 parts in terms of non-volatile content per 100 parts of pigment. This aqueous resin may be added to the aqueous pigment dispersion of the present invention to prepare an aqueous ink for inkjet recording, but after preparing the aqueous ink for inkjet recording from the aqueous pigment dispersion of the present invention, The aqueous resin can be added to the above amount.

  The aqueous ink for inkjet recording of the present invention contains the aqueous pigment dispersion of the present invention. Such a water-based ink for ink-jet recording can be prepared from the water-based pigment dispersion so that the pigment content is 1 to 10% in terms of mass. At this time, if necessary, water or a water-soluble organic solvent is added to the thick aqueous pigment dispersion exceeding the above-mentioned pigment content to dilute it to the required pigment content within the above range. Various additives necessary for the preparation of water-based inks such as wetting agents, fungicides and pH adjusters can be used in combination. In addition, the obtained water-based ink for ink-jet recording can be extremely clogged with nozzle clogging or the like by filtering through a microfilter as necessary, or by performing a centrifugal separation (ultracentrifugation) under more severe conditions than usual. It can be reduced.

  Further, by appropriately selecting and preparing the composition according to the ejection method, it is possible to obtain an aqueous ink for ink jet recording that can be applied to either the piezo method or the thermal method from the aqueous pigment dispersion of the present invention.

  The water-based ink for ink jet recording of the present invention can be used for recording on a known and commonly used recording medium. Examples of such a recording medium include plain paper, resin-coated paper, mixed paper, and synthetic resin film. Among them, the water-based ink for ink-jet recording of the present invention can give a colored image with higher gloss on a special paper for ink-jet recording such as a photographic paper, and a colored image with a clearer color density on a plain paper. In particular, as a plain paper for recording media, plain paper made of thick fibers made from conifer pulp is the most effective in improving color development.

  In the following synthesis examples, examples and comparative examples, “parts” and “%” are all in terms of mass.

[Synthesis Example 1] (tBST system)
Methyl ethyl ketone is added to the reaction vessel of an automatic polymerization reactor [polymerization tester DSL-2AS type, manufactured by Sakai Sangyo Co., Ltd.] having a reaction vessel equipped with a stirring device, a dropping device, a temperature sensor, and a reflux device having a nitrogen introducing device at the top. 1,100 parts were charged, and the inside of the reaction vessel was purged with nitrogen while stirring. After raising the temperature inside the reaction vessel to 80 ° C. while maintaining a nitrogen atmosphere, 187 parts of butyl acrylate, 75 parts of 2-hydroxyethyl methacrylate, 138 parts of methacrylic acid, 300 parts of p-tert-butylstyrene from a dropping device, A mixed solution of 300 parts of benzyl methacrylate and 80 parts of “Perbutyl (registered trademark) O” (active ingredient tert-butyl peroxy 2-ethylhexanoate) manufactured by NOF Corporation was dropped over 4 hours. After completion of the dropping, the reaction was further continued at the same temperature for 15 hours to obtain a solution of a styrene-acrylic copolymer (B-1) having an acid value of 90, Mw of 27,100, and a resin nonvolatile content of 47.2% [ Total mol% of styrene monomer and benzyl (meth) acrylate monomer = 50 mol%, mol number of styrene monomer / (mol number of styrene monomer and (meth) acrylic acid Sum of moles of benzylic monomer) = 52%].

[Synthesis Example 2] (Same as above)
As a mixed liquid dropped from the dropping device, 157 parts of butyl acrylate, 75 parts of 2-hydroxyethyl methacrylate, 138 parts of methacrylic acid, 300 parts of p-tert-butylstyrene, 300 parts of benzyl methacrylate, manufactured by NOF Corporation The copolymer was prepared under the same conditions as in Synthesis Example 1 except that a mixed solution of 3 parts of “Blemmer (registered trademark) PDE-50” [active component ethylene glycol dimethacrylate] and 100 parts of “perbutyl (registered trademark) O” was used. Synthesized. In this way, a solution of a styrene-acrylic copolymer (B-2) having an acid value of 90, Mw of 477,300, and a resin non-volatile content of 46.9% was obtained [styrene monomer and benzyl (meth) acrylate single monomer. Total mol% with the monomer = 50 mol%, number of moles of styrene monomer / (sum of moles of styrene monomer and moles of benzyl (meth) acrylate monomer) = 52% ].

[Synthesis Example 3] (Same as above)
A copolymer was synthesized under the same composition and conditions as in Synthesis Example 2 except that 100 parts of “Perbutyl (registered trademark) O” was changed to 80 parts. A solution of a styrene-acrylic copolymer (B-2) having an acid value of 90 and a resin non-volatile content of 47.3% was obtained [total mole of styrene monomer and benzyl (meth) acrylate monomer % = 50 mol%, the number of moles of styrene monomer / (sum of the number of moles of styrene monomer and the number of moles of benzyl (meth) acrylate monomer) = 52%]. Mw exceeded the measurement limit of the measuring instrument and could not be measured (Mw was estimated to be 3,800,000 or more).

[Synthesis Example 4] (Same as above)
100 parts of “Perbutyl® O” was converted to 10 parts of 2,4-diphenyl-4-methyl-1-pentene (chain transfer catalyst, α-styrene dimer) and 80 parts of “Perbutyl® O”. A copolymer was synthesized under the same composition and conditions as in Synthesis Example 2 except for the above. Thus, a solution of a styrene-acrylic copolymer (B-4) having an acid value of 90, Mw of 2,931,600 and a resin non-volatile content of 46.4% was obtained [styrene monomer and benzyl (meth) acrylate. Total mol% with the monomer based monomer = 50 mol%, mole number of styrene monomer / (sum of mole number of styrene monomer and mole number of benzyl (meth) acrylate monomer) = 52%].

[Synthesis Example 5] (Same as above)
A copolymer was synthesized under the same composition and conditions as in Synthesis Example 4 except that 10 parts of 2,4-diphenyl-4-methyl-1-pentene was changed to 20 parts. A solution of a styrene-acrylic copolymer (B-5) having an acid value of 90, Mw 444,700, and a resin non-volatile content of 47.0% was obtained [styrene monomer and benzyl (meth) acrylate monomer. And the total number of moles of styrene monomer / (sum of moles of styrene monomer and moles of benzyl (meth) acrylate monomer) = 52%].

[Synthesis Example 6] (Same as above)
A copolymer was synthesized under the same composition and conditions as in Synthesis Example 4 except that 10 parts of 2,4-diphenyl-4-methyl-1-pentene was changed to 30 parts. A solution of a styrene-acrylic copolymer (B-6) having an acid value of 90, Mw of 165,400, and a resin non-volatile content of 47.3% was obtained [styrene monomer and benzyl (meth) acrylate monomer. And the total number of moles of styrene monomer / (sum of moles of styrene monomer and moles of benzyl (meth) acrylate monomer) = 52%].

[Synthesis Example 7] (Same as above)
A copolymer was synthesized under the same composition and conditions as in Synthesis Example 4 except that 10 parts of 2,4-diphenyl-4-methyl-1-pentene was changed to 40 parts. A solution of a styrene-acrylic copolymer (B-7) having an acid value of 90, Mw of 138,100, and a resin non-volatile content of 45.4% was obtained [styrene monomer and benzyl (meth) acrylate monomer. And the total number of moles of styrene monomer / (sum of moles of styrene monomer and moles of benzyl (meth) acrylate monomer) = 52%].

[Synthesis Example 8] (Same as above)
A copolymer was synthesized under the same composition and conditions as in Synthesis Example 4 except that 10 parts of 2,4-diphenyl-4-methyl-1-pentene was changed to 80 parts. A solution of a styrene-acrylic copolymer (B-8) having an acid value of 90, Mw of 26,200, and a resin nonvolatile content of 45.3% was obtained [a styrene monomer and a benzyl (meth) acrylate monomer. And the total number of moles of styrene monomer = (sum of moles of styrene monomer and moles of benzyl (meth) acrylate monomer) = 52%].

[Synthesis Example 9] (ST system)
Methyl ethyl ketone is added to the reaction vessel of an automatic polymerization reactor [polymerization tester DSL-2AS type, manufactured by Sakai Sangyo Co., Ltd.] having a reaction vessel equipped with a stirring device, a dropping device, a temperature sensor, and a reflux device having a nitrogen introducing device at the top. 1,100 parts were charged, and the inside of the reaction vessel was purged with nitrogen while stirring. After raising the temperature inside the reaction vessel to 80 ° C. while maintaining a nitrogen atmosphere, 75 parts of 2-hydroxyethyl methacrylate, 138 parts of methacrylic acid, 500 parts of styrene, 257 parts of benzyl methacrylate, “Blemmer (registered) A mixed solution of 3 parts of “PDE-50” and 160 parts of “Perbutyl (registered trademark) O” was added dropwise over 4 hours. After completion of the dropwise addition, the reaction was further continued at the same temperature for 15 hours to obtain a solution of a styrene-acrylic copolymer (B-9) having an acid value of 90, Mw of 24,400, and a resin nonvolatile content of 46.4% [ Total mol% of styrene monomer and benzyl (meth) acrylate monomer = 73 mol%, mol number of styrene monomer / (mol number of styrene monomer and (meth) acrylic acid Sum of moles of benzylic monomer) = 77%].

[Synthesis Example 10] (Same as above)
A copolymer was synthesized under the same composition and conditions as in Synthesis Example 9 except that 160 parts of “Perbutyl (registered trademark) O” was changed to 100 parts. A solution of a styrene-acrylic copolymer (B-10) having an acid value of 90, Mw of 104,700 and a resin non-volatile content of 46.8% was obtained [a styrene monomer and a benzyl (meth) acrylate monomer. And the total number of moles of styrene monomer = (sum of moles of styrene monomer and moles of benzyl (meth) acrylate monomer) = 77%].

[Synthesis Example 11] (Same as above)
A copolymer was synthesized under the same composition and conditions as in Synthesis Example 9 except that 160 parts of “Perbutyl (registered trademark) O” was changed to 80 parts. A solution of a styrene-acrylic copolymer (B-11) having an acid value of 90, Mw 557,600, and a resin non-volatile content of 47.2% was obtained [styrene monomer and benzyl (meth) acrylate monomer And the total number of moles of styrene monomer = (sum of moles of styrene monomer and moles of benzyl (meth) acrylate monomer) = 77%].

[Synthesis Example 12] (Same as above)
The same composition and conditions as in Synthesis Example 9 except that 160 parts of “Perbutyl® O” were changed to 10 parts of 2,4-diphenyl-4-methyl-1-pentene and 80 parts of “Perbutyl® O”. The copolymer was synthesized with Thus, a solution of a styrene-acrylic copolymer (B-12) having an acid value of 90, Mw 136,400, and a resin non-volatile content of 46.7% was obtained [styrene monomer and benzyl (meth) acrylate single monomer. Total mol% with respect to the monomer = 73 mol%, number of moles of styrene monomer / (sum of moles of styrene monomer and moles of benzyl (meth) acrylate monomer) = 77% ].

  The respective copolymers synthesized in the above synthesis examples are summarized in Table 1 together with Mw data. In Synthesis Examples 1 to 12, random copolymerization was carried out, and all of the obtained copolymers had a styrene-acrylic system in which crosslinked portions were present at random, that is, the crosslinked portions were delocalized. It is a copolymer.

Abbreviations in Table 1 are as follows.
tBST: p-tert-butylstyrene, ST: styrene, PDE-50: Blemmer (registered trademark) PDE-50, MSD: 2,4-diphenyl-4-methyl-1-pentene (α-styrene dimer)

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, these Examples demonstrate this invention concretely and an aspect is not limited by this.

  In a plastic container with a lid, 116 parts of the copolymer (B-2) obtained in Synthesis Example 2, 93 parts of a 5% aqueous potassium hydroxide solution, water and C.I. I. Pigment Blue 15: 3 [manufactured by Dainippon Ink & Chemicals, Inc.] 182 parts, 30 parts of methyl ethyl ketone, and 579 parts of water were charged, stirred, and mixed. Here, the amount of each charge is based on the pigment, the amount of copolymer methyl ethyl ketone solution is 30% of the resin non-volatile content with respect to the pigment, and the 20% aqueous sodium hydroxide solution is styrene-acrylic copolymer. The amount by which the acid value was neutralized by 95%, and methyl ethyl ketone was determined to be 50% of the pigment by adding the amount of methyl ethyl ketone contained in the copolymer and the amount of methyl ethyl ketone added additionally. Water is an amount necessary to make the non-volatile content of the mixed solution 24%.

  4,554 parts of zirconia beads having a diameter of 0.5 mm were added to the mixed solution, the lid was put on, and the mixture was attached to a paint shaker dispersing apparatus (manufactured by Toyo Seiki Seisakusho Co., Ltd.) and dispersed for 2 hours. After the completion of dispersion, 1,000 parts of water was added and zirconia beads were separated using a 200-mesh sheet to obtain a diluted dispersion. The diluted dispersion was put into a glass distillation apparatus, and the whole amount of methyl ethyl ketone and a part of water were removed by atmospheric distillation.

  From this dispersion, coarse particles were removed with a centrifuge [50A-IV type, Sakuma Seisakusho] over 6,000 G for 30 minutes to obtain an aqueous pigment dispersion.

  The obtained aqueous pigment dispersion had a nonvolatile content of 12.3% and an average dispersed particle size (median diameter) of 107.1 nm. The viscosity was 2.20 mPa / s.

(Appropriate evaluation of water-based ink for inkjet recording)
A water base ink for ink jet recording was prepared with reference to Example 1 described in JP-A-7-228808. The ink composition is shown below. Using this ink, solid printing was carried out on several recording media with a piezo ink jet printer, and evaluation was performed.

Aqueous pigment dispersion Amount of 4% solid pigment in the ink Triethylene glycol monobutyl ether 10 parts Diethylene glycol 15 parts Surfinol 465 (Air Products) 0.8 parts Ion-exchanged water Remaining amount

(Ink storage stability test)
This ink was stored in a glass container at 70 ° C. for 3 days, and the average particle size and viscosity before and after that were measured. The case where the storage stability was Δ, and the case where it was less than + 10% was evaluated as ◯. The results are shown in Table 2.

  As recording media, two types of paper, Canon PB paper manufactured by Canon Inc. and Xerox 4024 manufactured by Xerox, were used as plain paper. As the exclusive paper, Canon photo gloss film HG201 and Seiko Epson photo paper (gloss) were used.

(Color density on plain paper)
The color image density is a value obtained by measuring the color image density of 5 points on a single sample using GRETAG (registered trademark) D196 manufactured by Gretag Macbeth and averaging them. Of these average values, the results for Xerox 4024 paper are summarized in Table 2 as plain paper coloring. The larger the number, the better the color developability.
For Canon PB paper manufactured by Canon Co., Ltd., printing was performed on 5 sheets of the same lot product, and for each of the 5 samples, the color image density was measured per 5 points in the same manner as described above, and the average value was obtained. However, since the result was almost the same as the case of measuring 5 points for the single sample, the color image density was measured for 5 points for a single sample in any plain paper and averaged.

(Abrasion resistance test)
In the scratch resistance test, solid printing was performed on a photo gloss film HG201 manufactured by Canon, and the color smearing was observed by rubbing with a finger at regular intervals (immediately, 10 minutes, 1 hour later) after printing, Scratch resistance was evaluated. The evaluation criteria were evaluated in five stages: A: no bleeding, B: no bleeding, the finger is colored, C: lightly blotting, D: bleeding, E: heavy bleeding. The results are shown in Table 2.

(Glossiness in photo paper)
The gloss of photographic paper was solid printed on photographic paper (glossy) manufactured by Seiko Epson Corporation, and the 20 ° gloss value was measured with a haze-gloss meter manufactured by BYK Gardner. The results are shown in Table 2.

  An aqueous pigment dispersion was prepared in the same mixing ratio and operation as in Example 1 except that the styrene-acrylic copolymer was changed to the B-4 copolymer prepared in Synthesis Example 4. The obtained aqueous pigment dispersion had a nonvolatile content of 12.3% and an average dispersed particle diameter (median diameter) of 127.5 nm. The viscosity was 2.38 mPa / s. Inks were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 2.

  An aqueous pigment dispersion was prepared by the same mixing ratio and operation as in Example 1, except that the styrene-acrylic copolymer was changed to the B-5 copolymer prepared in Synthesis Example 5. The obtained aqueous pigment dispersion had a nonvolatile content of 12.3% and an average dispersed particle diameter (median diameter) of 119.8 nm. The viscosity was 2.12 mPa / s. Inks were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 2.

  An aqueous pigment dispersion was prepared in the same mixing ratio and operation as in Example 1 except that the styrene-acrylic copolymer was changed to the B-6 copolymer prepared in Synthesis Example 6. The obtained aqueous pigment dispersion had a nonvolatile content of 12.4% and an average dispersed particle size (median diameter) of 110.1 nm. The viscosity was 2.06 mPa / s. Inks were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 2.

  An aqueous pigment dispersion was prepared in the same mixing ratio and operation as in Example 1, except that the styrene-acrylic copolymer was changed to the B-7 copolymer prepared in Synthesis Example 7. The obtained aqueous pigment dispersion had a nonvolatile content of 12.5% and an average dispersed particle diameter (median diameter) of 108.1 nm. The viscosity was 2.22 mPa / s. Inks were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 2.

Comparative Example 1
An aqueous pigment dispersion was prepared in the same mixing ratio and operation as in Example 1 except that the styrene-acrylic copolymer was changed to the B-1 copolymer prepared in Synthesis Example 1. The obtained aqueous pigment dispersion had a non-volatile content of 12.3% and an average dispersed particle diameter (median diameter) of 106.8 nm. The viscosity was 2.32 mPa / s. Inks were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 2.

Comparative Example 2
An aqueous pigment dispersion was prepared in the same mixing ratio and operation as in Example 1 except that the styrene-acrylic copolymer was changed to the B-3 copolymer prepared in Synthesis Example 3. The obtained aqueous pigment dispersion had a nonvolatile content of 12.4% and an average dispersed particle diameter (median diameter) of 257.8 nm. The viscosity was 3.70 mPa / s. Inks were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 2.

Comparative Example 3
An aqueous pigment dispersion was prepared in the same mixing ratio and operation as in Example 1 except that the styrene-acrylic copolymer was changed to the B-8 copolymer prepared in Synthesis Example 8. The obtained aqueous pigment dispersion had a nonvolatile content of 12.3% and an average dispersed particle size (median diameter) of 169.3 nm. The viscosity was 3.16 mPa / s. Inks were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 2.

  The three alphabets of scratch resistance in Table 2 are the evaluation results immediately after the left, 10 minutes later, and 1 hour later.

  An aqueous pigment dispersion was prepared in the same mixing ratio and operation as in Example 1 except that the styrene-acrylic copolymer was changed to the B-10 copolymer prepared in Synthesis Example 10. The obtained aqueous pigment dispersion had a nonvolatile content of 12.3% and an average dispersed particle size (median diameter) of 109.5 nm. The viscosity was 1.92 mPa / s. Inks were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 3.

  An aqueous pigment dispersion was prepared by the same mixing ratio and operation as in Example 1, except that the B-11 copolymer prepared in Synthesis Example 11 was used as the styrene-acrylic copolymer. The obtained aqueous pigment dispersion had a non-volatile content of 12.3% and an average dispersed particle diameter (median diameter) of 114.3 nm. The viscosity was 2.04 mPa / s. Inks were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 3.

  An aqueous pigment dispersion was prepared in the same mixing ratio and operation as in Example 1, except that the styrene-acrylic copolymer was changed to the B-12 copolymer prepared in Synthesis Example 12. The obtained aqueous pigment dispersion had a nonvolatile content of 12.3% and an average dispersed particle size (median diameter) of 106.8 nm. The viscosity was 1.90 mPa / s. Inks were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 3.

Comparative Example 4
An aqueous pigment dispersion was prepared in the same mixing ratio and operation as in Example 1 except that the styrene-acrylic copolymer was changed to the B-9 copolymer prepared in Synthesis Example 9. The obtained aqueous pigment dispersion had a non-volatile content of 12.4% and an average dispersed particle size (median diameter) of 124.8 nm. The viscosity was 2.36 mPa / s. Inks were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 3.

(Dispersion method different from Examples 1-8 and disperser)
In a mixing vessel equipped with a cooling jacket, 645 parts of the copolymer (B-4) obtained in Synthesis Example 4, 98 parts of a 20% aqueous sodium hydroxide solution, water and C.I. I. Pigment Blue 15: 3 (Dainippon Ink Chemical Co., Ltd.) 1000 parts, 153 parts of methyl ethyl ketone, and 3568 parts of water were charged, stirred and mixed. Here, the amount of each charged is 1,000 parts of pigment, the amount of copolymer is 30% of the non-volatile content with respect to the copper phthalocyanine pigment, and the 20% sodium hydroxide aqueous solution is a styrene-acrylic copolymer. The amount of acid is 100% neutralized and water is the amount necessary to make the non-volatile content of the mixed solution 24%.

The mixed solution was passed through a dispersing device (SC mill SC100 / 32 type, manufactured by Mitsui Mining Co., Ltd.) filled with zirconia beads having a diameter of 0.3 mm, and dispersed for 4 hours by a circulation method. The number of revolutions of the dispersing device was 2700 rpm, and the temperature of the dispersion liquid was kept at 40 ° C. or less through the cooling jacket through cold water.
After the dispersion, the dispersion stock solution was extracted from the mixing tank, and then the mixing tank and the dispersion device flow path were washed with 10,000 parts of water, and the diluted dispersion liquid was obtained together with the dispersion stock solution. The diluted dispersion was put into a glass distillation apparatus, and the whole amount of methyl ethyl ketone and a part of water were removed by atmospheric distillation.

  The dispersion from which methyl ethyl ketone was removed was cooled, and then 10% hydrochloric acid was added dropwise with stirring to adjust the pH to 4.5, and then the solid content was filtered with a Nutsche filter and washed with water. Take the cake in a container, add 20% potassium hydroxide aqueous solution and water in such an amount that the acid value of the styrene-acrylic copolymer is 90% neutralized, and add a dispersion stirrer [TK Homodispa Model 20, Special Machine Industries Co., Ltd. The product was dispersed again.

  To this dispersion, pure water was added to adjust the non-volatile content to 23%. After removing coarse particles over 6,000 G for 30 minutes from this dispersion with a centrifuge [50A-IV type, Sakuma Seisakusho], pure water was added to adjust the non-volatile content. A 20% aqueous pigment dispersion was obtained. The dispersed particles of this aqueous pigment dispersion were composite particles in which the pigment was coated with a copolymer.

The obtained aqueous pigment dispersion had a pH of 9.82, a non-volatile content of 20.0%, and an average dispersed particle diameter (median diameter) of 128.0 nm. The viscosity was 4.56 mPa / s. Inks were prepared and evaluated in the same manner as in Example 1. The plain paper color density was 1.73, the scratch resistance CBB, the average particle size and the viscosity were both storage stability ○ and the gloss value was 18.6. Although the conditions of Example 2 were different from those of the disperser and the dispersion method, the scratch resistance and storage stability were also good. The gloss value was also excellent when compared with the dispersion method under the same conditions.

Claims (7)

Styrene monomer, (meth) acrylic acid ester monomer, and styrene-acrylic copolymer containing each polymerization unit of (meth) acrylic acid, pigment, basic compound as an essential component in an aqueous medium In the aqueous pigment dispersion for preparing an inkjet recording water-based ink, the styrene-acrylic copolymer has a polystyrene-equivalent weight average molecular weight (Mw) = 100,000 to 3,500,000. A water-based pigment dispersion for preparing a water-based ink for ink-jet recording, which is a styrene-acrylic copolymer having a cross-linked portion and a de-localized cross-linked portion. The styrene-acrylic copolymer contains a polymerized unit of a crosslinkable monomer containing two or more polymerizable ethylenically unsaturated double bonds in one molecule, and the crosslinked portion is delocalized. The aqueous pigment dispersion according to claim 1, which is an acrylic copolymer. The styrene-acrylic copolymer is polymerized into a styrene monomer, (meth) acrylic acid ester monomer, (meth) acrylic acid and one molecule in the presence of a chain transfer catalyst in an organic solvent. The aqueous pigment dispersion according to claim 1, which is a styrene-acrylic copolymer obtained by polymerizing a crosslinkable monomer containing two or more polymerizable ethylenically unsaturated double bonds and having a delocalized cross-linked portion. . The styrene-acrylic copolymer has polymerized units of a styrene monomer, benzyl (meth) acrylate, and (meth) acrylic acid, and has a cross-linked portion, and the cross-linked portion is delocalized. The aqueous pigment dispersion according to any one of claims 1 to 3, which is a styrene-acrylic copolymer. In the styrene-acrylic copolymer, the total number of styrene monomers and benzyl (meth) acrylate occupied when the total amount of all monomers is 100 mol% is 40 to 80 mol%, and styrene A styrene-acrylic copolymer in which the number of moles of the styrene monomer in the total moles of the monomer and benzyl (meth) acrylate is 50 to 90 mol% and the crosslinked part is delocalized. The aqueous pigment dispersion according to any one of claims 1 to 4, which is a polymer. The styrene-acrylic copolymer contains a tert-butylstyrene polymer unit as a polymer unit of a styrene monomer, has a cross-linked portion, and the cross-linked portion is delocalized. The aqueous pigment dispersion according to any one of claims 1 to 5, which is a coalescence. The aqueous ink for inkjet recording prepared from the aqueous pigment dispersion according to any one of claims 1 to 6, wherein the pigment content is 1 to 10% in terms of mass.