JP2006342294A - Aqueous pigment dispersion for inkjet ink and aqueous ink for inkjet recording - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water-based ink for ink-jet recording using a pigment as a colorant, having excellent dispersion and storage stability, high printing density, and high glossiness particularly when special paper is used. And an aqueous pigment dispersion for the ink.
An aqueous pigment dispersion for inkjet ink containing a (meth) acrylic copolymer, a pigment, and a basic substance, wherein the (meth) acrylic copolymer comprises benzyl (meth) acrylate and (meth). Acrylic acid is an essential constituent monomer, and the total of benzyl (meth) acrylate and (meth) acrylic acid with respect to the total monomer amount constituting the acrylic copolymer is 85% by mass or more, and the acid value is 40 to 110 mgKOH / g. An aqueous pigment dispersion for inkjet inks. And an aqueous ink for inkjet recording using the aqueous pigment dispersion for inkjet ink.
[Selection figure] None

Description

  The present invention relates to an aqueous pigment dispersion for an inkjet recording aqueous ink using a pigment as a coloring material, and an inkjet recording aqueous ink.

  Conventionally, a dye ink using a dye as a coloring material has been used as a water-based ink for inkjet recording. Dye inks have many advantages such as excellent storage stability, hardly clogging the nozzles of inkjet printers, and the printed matter obtained has excellent gloss. However, it has been pointed out that there are defects derived from dyes, such as inability to store printed matter for a long time due to poor weather resistance, and poor water resistance and light resistance. In recent years, weather resistance, water resistance and light resistance have been pointed out. Development of a water-based ink for ink jet recording (hereinafter abbreviated as “pigment ink”) using an excellent pigment is in progress.

Usually, pigment ink is prepared by diluting a pigment dispersion in which a pigment is dispersed in an aqueous solvent with a dispersant such as a surfactant or a polymer dispersant with water or an aqueous solvent, and inhibiting drying as necessary. It is prepared by adding an agent, a penetrating agent, or other additives. However, it has been difficult to impart ink suitability for ink jet recording using various additives while ensuring the dispersion stability of the pigment, that is, the storage stability of the pigment ink.
Also, the pigment particles have a drawback that they are easily affected by the surface condition of the recording medium. For example, in a recording medium such as plain paper or recycled paper such as paper that is not surface-coated, the pigment particles penetrate between the paper fibers and do not remain on the paper surface, so that the print density cannot be obtained. There were drawbacks. In addition, there is a disadvantage that it is difficult to provide uniform quality because bleeding and color unevenness easily occur due to the composition of the paper fiber and the effect of a processing agent such as a sizing agent, and the degree of bleeding and color unevenness varies. there were.
In addition, in a recording medium having a surface coating such as inkjet special paper used for photographic printing, the printing density is maintained because the pigment particles do not enter between the fibers, but the glossiness which is the highest required characteristic is not sufficient. , There is a case where there is a difference in glossiness in a portion where the print duty is different.

  Numerous approaches have been taken to improve print density. For example, a self-dispersing pigment (for example, carbon black) in which an anionic group is directly bonded to the pigment surface, and a polymer dispersant made of a (meth) acrylic copolymer containing benzyl methacrylate as a monomer unit are used in an aqueous solvent. A water-based ink for inkjet recording containing a dispersed pigment in a dispersed state in an aqueous solvent is known (see Patent Document 1). In addition, a water-based ink for ink-jet recording composed of two liquids, a water-based ink and a reaction liquid, and as a polymer dispersant for the water-based ink, a (meth) acrylic copolymer as a main chain and all constituting side chains There is also known an aqueous ink for inkjet recording using a graft polymer in which 50% by mass or more of the monomer unit is a monomer unit having a hydrophobic functional group derived from an aromatic vinyl compound (see Patent Document 2).

  However, all of the polymer dispersants used in the ink described in the document have a high acid value (400 in the example of Patent Document 1 and 400 in the example of Patent Document 2). Usually, a polymer dispersant based on a (meth) acrylic copolymer is set to have a high acid value for the purpose of maintaining water solubility. However, polymer dispersants with high acid values have high viscosity, and the amount of ink added to ink jet inks that are adjusted to low viscosity is limited, so it may be difficult to disperse depending on the type of pigment, as well as dispersion stability and storage stability. There was a problem of inferiority. In addition, the ink described in any of the documents has a problem that it is not glossy when printed on ink jet dedicated paper.

As the low acid value polymer dispersant used for pigment ink, the total of the styrene monomer and the benzyl (meth) acrylate monomer is 40 to 80 mol%, and the styrene monomer A styrene-acrylic copolymer having a styrene monomer of 40 to 90% and an acid value of 85 to 135 with respect to the total number of methacrylic acid and benzyl (meth) acrylate monomer is known. (Patent Document 3). By narrowing down the constituent components of the (meth) acrylic copolymer, a water-based ink for ink jet recording having excellent dispersion stability and excellent printing density even at a low acid value can be obtained.
However, the ink also has a problem that it is not glossy when printed on ink jet paper.

Japanese Patent Laid-Open No. 2002-88,287 JP 2004-255,870 A Japanese Patent Laid-Open No. 2004-217,916

  Therefore, an aqueous ink for inkjet recording using a pigment as a colorant, which has excellent dispersion and storage stability, high printing density, and high gloss, especially when special paper is used, is obtained. The current situation has not yet been obtained.

  The problem to be solved by the present invention is a water-based ink for inkjet recording using a pigment as a colorant, which has excellent dispersion and storage stability, high printing density, and high glossiness especially when special paper is used. It is an object of the present invention to provide a water-based ink for ink-jet recording and to provide a water-based pigment dispersion for the ink.

As a result of intensive studies, the inventors of the present invention have a (meth) acrylic copolymer obtained by copolymerizing benzyl (meth) acrylate and (meth) acrylic acid with an essential constituent monomer at a specific ratio. It has been found that it is excellent in pigment dispersibility, has the above-mentioned properties as an aqueous ink for inkjet recording, and can solve the above-mentioned problems.
That is, the present invention relates to an aqueous pigment dispersion for inkjet inks containing a (meth) acrylic copolymer, a pigment, and a basic substance, wherein the (meth) acrylic copolymer comprises benzyl (meth) acrylate and (meta ) Acrylic acid as an essential constituent monomer, and the total of benzyl (meth) acrylate and (meth) acrylic acid with respect to the total amount of monomers constituting the acrylic copolymer is 85% by mass or more, and an acid value of 40 to 110 mgKOH / An aqueous pigment dispersion for inkjet inks is provided.

  The present invention also provides an aqueous ink for inkjet recording using the above-described aqueous pigment dispersion for inkjet ink.

  Since the aqueous pigment dispersion of the present invention has a low acid value, it is excellent in dispersion and storage stability. In addition, it is possible to obtain a printed matter having a high printing density and particularly excellent gloss when an inkjet paper is used.

  In the present invention, (meth) acrylic acid is a technical term including both acrylic acid and methacrylic acid. Similarly, the (meth) acrylic copolymer in the present invention is a technical term that means a copolymer obtained by polymerizing benzyl (meth) acrylate monomer and (meth) acrylic acid as essential components. An aqueous solvent refers to a mixture of water alone or a mixture of water and a water-soluble organic solvent and containing 60% or more of water in terms of mass.

((Meth) acrylic copolymer)
The (meth) acrylic copolymer used in the present invention has benzyl (meth) acrylate and (meth) acrylic acid as essential constituent monomers, and benzyl (meth) acrylate with respect to the total amount of monomers constituting the acrylic copolymer, A total with (meth) acrylic acid is 85 mass% or more, and an acid value is 40-110 mgKOH / g.
Examples of benzyl (meth) acrylate include benzyl acrylate and benzyl methacrylate, and benzyl methacrylate is preferable in that the effects of the present invention can be expressed more easily and are easily available and inexpensive.
Examples of (meth) acrylic acid include acrylic acid and methacrylic acid. (Meth) acrylic acid is preferable because it can widely control the solubility in water when neutralized with a base and is easily available and inexpensive.

As a constituent monomer of the (meth) acrylic copolymer used in the present invention, a general-purpose monomer may be used in addition to benzyl (meth) acrylate and (meth) acrylic acid, but the amount used is less than 15% by mass. It is necessary to.
Examples of the general-purpose monomer used include known vinyl polymerizable monomers such as various (meth) acrylic acid esters, vinyl monomers such as styrene, alkyl vinyl ether, and vinyl acetate. In the aqueous pigment dispersion of the present invention, the total of benzyl (meth) acrylate and (meth) acrylic acid accounts for 85% by mass or more based on the total amount of monomers constituting the (meth) acrylic copolymer, and 15% Most of the general-purpose monomers can be used because the properties unique to the general-purpose monomer are less expressed. However, when a monomer having a hydroxyl group is used in a composition having a relatively high acid value (around 100 mgKOH / g), the hydrophilicity of the resulting (meth) acrylic copolymer becomes too high, resulting in water-jet recording water. Depending on the type of aqueous solvent used in preparing the ink, the penetrability becomes too high, and the printing characteristics such as color density and gloss are rarely deteriorated. Although this can be avoided by appropriately selecting the type of aqueous solvent to be used, if the hydroxyl value of the (meth) acrylic copolymer is designed to be at least 20.0 mgKOH / g, Such a problem can be avoided, and the type of aqueous solvent to be used is also preferred.
In addition, a monomer having a long-chain aliphatic hydrocarbon group having 14 or more carbon atoms rarely has a stable color density or gloss value. Therefore, it is preferable not to use a monomer having a long-chain aliphatic hydrocarbon group having 14 or more carbon atoms as much as possible.

  Preferable examples of the (meth) acrylic copolymer used in the present invention include a (meth) acrylic copolymer using a total of 95% by mass or more of benzyl methacrylate and methacrylic acid. When the content is 95% by mass or more, it is possible to obtain an aqueous ink for inkjet recording that is particularly excellent in the print density that is the effect of the present invention. Among these, a methacrylic copolymer using 100% of benzyl methacrylate and methacrylic acid is most preferable.

By setting the acid value of the (meth) acrylic copolymer used in the present invention to an acid value in the range of 40 to 110 mgKOH / g, the affinity of the copolymer for water can be increased, and the aqueous solution can be used. The dispersibility of this copolymer and the dispersion stability of the pigment when it is made into an aqueous pigment dispersion can be further enhanced. Among these, the range of 60 to 90 mgKOH / g is preferable, and the range of 50 to 85 mgKOH / g is still more preferable. If the acid value is too small, the dispersion stability of the pigment tends to decrease. If the acid value exceeds 110, the water resistance of the colored image and the color image density tend to decrease. .
In addition, an acid value means the mg number of potassium hydroxide required in order to neutralize 1 g of (meth) acrylic copolymers.
Substantially, when benzyl (meth) acrylate: (meth) acrylic acid is used in the range of 83:17 to 95: 5, the acid value is within the range.
In the (meth) acrylic copolymer used in the present invention, benzyl (meth) acrylate and (meth) acrylic acid occupy 85% or more of the constituent components. Benzyl (meth) acrylate is a hydrophobic component, but even if it is neutralized with an acid value in this range, it is sufficiently in the form of a water-soluble resin.

  The molecular weight of the (meth) acrylic copolymer used in the present invention is preferably in the range of 5,000 to 100,000 in terms of mass average molecular weight, and particularly preferably in the range of 10,000 to 50,000. When the weight average molecular weight is less than 5,000, the dispersion stability tends to decrease. When the weight average molecular weight of the dispersant exceeds 50,000, the viscosity of the aqueous ink for inkjet recording obtained using the resin is low. When the ink jet recording is performed, the dischargeability of the ink from the ink jet nozzles is lowered, and the print density tends to be lowered. The mass average molecular weight is a value measured by a gel permeation chromatography (hereinafter abbreviated as GPC) method.

  The (meth) acrylic copolymer used in the present invention can be obtained by a known polymerization method. Examples thereof include bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. The polymerization form may be any of radical polymerization, ionic polymerization, and photopolymerization. In general, after polymerization by solution polymerization using a radical polymerization initiator, it is neutralized with a basic substance (3) described later, and dispersed in an aqueous solvent to be used as an aqueous pigment dispersion.

Although it is not certain why the aqueous pigment dispersion using the (meth) acrylic copolymer used in the present invention has both physical properties of printing density and glossiness, the benzyl ( It is presumed that (meth) acrylate has some influence on the physical properties.
Benzyl (meth) acrylate is known as a constituent monomer of a pigment dispersion for ink jet recording ink, and is known to be effective in pigment dispersibility and ink wettability with respect to the orifice surface of an ink jet nozzle.
However, as in the present invention, benzyl (meth) acrylate and (meth) acrylic acid are essential constituent monomers, and benzyl (meth) acrylate and (meth) acrylic acid with respect to the total amount of monomers constituting the acrylic copolymer By using a (meth) acrylic copolymer having a constitution in which the total amount is 85% by mass or more, a water-based ink for inkjet recording having both printing density and glossiness (especially when printed on special paper) Is obtained for the first time in the present invention. This is because the (meth) acrylic copolymer used in the present invention introduces a large amount of benzyl groups, so that an oleophilic part having high affinity with the pigment ink and an aqueous solvent which is the ink medium This is thought to be due to the balance with the hydrophilic part having high affinity.

In general, it is considered that a high printing density can be obtained if pigment particles adhere to the surface of a recording medium. For this purpose, it is desirable that the ink permeability is suppressed to some extent.
The glossiness is considered to be obtained by maintaining the smoothness of the printed surface. For this purpose, the presence of a resin component that fills the voids of the pigment after fixing the print surface is preferable.
On the other hand, inkjet inks are required to dry immediately after printing, that is, liquid components such as aqueous solvents must permeate or evaporate.

  The (meth) acrylic copolymer used in the present invention is considered to have a balance between lipophilicity and hydrophilicity that maintains dispersion stability and is easily separated from an aqueous solvent after printing. Therefore, it is considered that both dispersion stability and drying properties can be maintained. Since it is easily separated from the aqueous solvent, it is thought that after printing, it remains on the surface of the recording medium so as to surround the pigment without penetrating the recording medium, and it is considered that both printing density and glossiness can be obtained. It is done.

  This does not work for aromatic groups other than benzyl groups. Although the reason is not clear, for example, when styrene is used instead of benzyl (meth) acrylate, the printing density is maintained but the gloss value is lowered.

  When the Tg of the (meth) acrylic copolymer used in the present invention is in the range of 30 to 80 ° C., the dispersibility and dispersion stability are good, and the Tg of the (meth) acrylic copolymer used in the preparation of the water-based ink for inkjet recording is used. The printing stability is good, the water resistance of the colored image is good, and the image preservability such as the friction resistance and the sticking resistance is also good. Here, the Tg of the copolymer is a calculated value obtained arithmetically from the Tg of the homopolymer of each monomer.

(Pigment)
Examples of the pigment used for the preparation of the aqueous pigment dispersion of the present invention include inorganic pigments such as barium sulfate, lead sulfate, titanium oxide, yellow lead, bengara, chromium oxide, and carbon black, anthraquinone pigments, perylene pigments, and disazo pigments. Phthalocyanine pigments, isoindoline pigments, dioxazine pigments, quinacridone pigments, perinone pigments, benzimidazolone pigments, and the like. These can be used alone or in combination.

  As the black pigment, it is preferable to use carbon black such as furnace black, lamp black, acetylene black, channel black, etc., which has excellent light resistance and high hiding power. Specifically, for example, Raven 7000, Raven 5750, Raven 5250, Raven 5000 Ultra (ULTRA II), Raven 3500, Raven 2500 Ultra, Raven 2000, Raven 1500, Raven 1255, Raven 1250, Raven 1200, Raven 1190 Ultra II, Raven 1170, Raven 1080 Ultra, Raven 1060 Ultra, Raven 790 Ultra, Raven 780 Ultra, Raven 760 Ultra (above Colombian Carbon), Regal 400R, Legal 330R, Legal 660R, Mogul (Moul) L, Monarch 700, Monarch ) 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300, Monarch 1400 (above, manufactured by Cabot), Color Black FW1, Color Black FW2, Color Black FW2V, Color Black 18, Color Black FW200, Color Black S150, Color Black S160, Color Black S170, Printex 35, Printex U, Printex V, Printex 140U, Printex 140V, Special Black 6, Special Black 5, Special Black 4A, Special Black 4 (and above) , Manufactured by Degussa), No. 25, no. 33, no. 40, no. 45, no. 45L, no. 47, no. 52, no. 900, no. 960, no. 2300, MCF-88, MA600, MA7, MA8, MA100 (manufactured by Mitsubishi Chemical Corporation), and the like.

Furthermore, among the representative organic pigments of cyan, magenta, and yellow, which are the three primary colors, pigments that can be suitably used in the present invention are exemplified below.
Examples of cyan pigments include C.I. I. Pigment Blue 1, C.I. I. Pigment Blue 2, C.I. I. Pigment blue 3, C.I. I. Pigment blue 15, C.I. I. Pigment blue 15: 1, C.I. I. Pigment blue 15: 3, C.I. I. Pigment blue 15:34, C.I. I. Pigment blue 16, C.I. I. Pigment blue 22, C.I. I. Pigment blue 60, and the like.

  Examples of magenta pigments include C.I. I. Pigment red 5, C.I. I. Pigment red 7, C.I. I. Pigment red 12, C.I. I. Pigment red 48, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 57, C.I. I. Pigment red 112, C.I. I. Pigment red 122, C.I. I. Pigment red 123, C.I. I. Pigment red 146, C.I. I. Pigment red 168, C.I. I. Pigment red 184, C.I. I. Pigment red 202, and the like.

  Examples of yellow pigments include C.I. I. Pigment yellow 1, C.I. I. Pigment yellow 2, C.I. I. Pigment yellow 3, C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 13, C.I. I. Pigment yellow 14, C.I. I. Pigment yellow 16, C.I. I. Pigment yellow 17, C.I. I. Pigment yellow 73, C.I. I. Pigment yellow 74, C.I. I. Pigment yellow 75, C.I. I. Pigment yellow 83, C.I. I. Pigment yellow 93, C.I. I. Pigment yellow 95, C.I. I. Pigment yellow 97, C.I. I. Pigment yellow 98, C.I. I. Pigment yellow 114, C.I. I. Pigment yellow 128, C.I. I. Pigment yellow 129, C.I. I. Pigment yellow 151, C.I. I. Pigment yellow 154, and the like.

  As for the particle diameter of the pigment, the primary particle diameter is preferably in the range of 1 to 500 nm, and more preferably in the range of 20 to 200 nm. The particle diameter of the pigment after being dispersed in the medium is preferably in the range of 10 to 300 nm, and more preferably in the range of 50 to 150 nm. The primary particle diameter of the pigment can be measured by an electron microscope, a gas or solute adsorption method, an air flow method, an X-ray small angle scattering method, and the like. The pigment particle diameter after dispersion can be measured by a known and common centrifugal sedimentation method, laser diffraction method (light scattering method), ESA method, capillary method, electron microscope method, or the like. Preferable is measurement by Microtrac UPA using a dynamic light scattering method.

(Basic substance)
The (meth) acrylic copolymer used in the present invention has a form in which at least a part of the carboxyl group is ionized with a basic substance, so that the dispersibility of the copolymer in an aqueous solvent and pigment particles are reduced. To exhibit dispersion stability.
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 substance but takes into account the dissociation equilibrium. Even if a stoichiometrically equivalent strong basic substance is used, the carboxyl group has a content of groups ionized by dissociation equilibrium (carboxylate group) of less than 100%, and the carboxylate group and carboxyl group are mixed. State.

  The basic substance is not particularly limited, and a known and commonly used substance can be used. Specific examples include organic amines such as ammonia, primary amines, secondary amines, and tertiary amines, or alkali metal hydroxides.

By ionizing at least part of the carboxyl group of the (meth) acrylic copolymer with the basic substance, the counter ion of the carboxylate group becomes a cation selected from the group consisting of ammonium ions or alkali metal ions.
Among these, use of an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide is preferable because the dispersion stability of the pigment particles in the aqueous pigment dispersion becomes particularly good.
A highly volatile basic substance such as ammonia or the above organic amine is excellent in drying property after printing, or excellent in ejection stability immediately after preparation of a water-based ink for ink jet recording, but is left for a long time and / or in a high temperature atmosphere. As a result, the dispersion stability of the dispersed particles in the aqueous pigment dispersion and the inkjet recording aqueous ink is gradually impaired, and sedimentation of the dispersed particles may be observed. In the case of long-term storage or use in a high-temperature atmosphere, it is preferable to select another basic substance.

The aqueous pigment dispersion of the present invention contains the (meth) acrylic copolymer, pigment, and basic substance in an aqueous solvent.
In the aqueous pigment dispersion of the present invention, the (meth) acrylic copolymer mainly has a role of dispersing the pigment, but a part thereof may exist as particles. The pigment may exist as particles as it is, or may be coated with the (meth) acrylic copolymer, and the presence form is not particularly limited.
In the aqueous pigment dispersion, it is preferable that the dispersed particles are dispersed so that the average dispersed particle diameter (median diameter) is 50 to 200 nm because of excellent storage stability and ink transparency.

  As the aqueous solvent used in the aqueous pigment dispersion of the present invention, water or a mixed solvent composed of a water-soluble organic solvent having compatibility between water and water is preferable. 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, etc .; amides such as dimethylformamide, N-methylpyrrolidone, etc., and especially those having 3 to 6 carbon atoms 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 copolymer solution or separately contained in the mixture during the dispersion step.

  The non-volatile content concentration in the aqueous pigment dispersion is preferably 10 to 35% by mass, more preferably 10 to 25% by mass. When the nonvolatile content concentration is less than 10% by mass, the dispersion of the pigment is lowered, and when it exceeds 35% by mass, the storage stability of the aqueous pigment dispersion tends to be lowered.

  In addition to the above components, various additives used for general aqueous pigment dispersions may be added to the aqueous pigment dispersion of the present invention, as necessary, within a range that does not impair the effects of the present invention. . Examples of additives include polymer dispersants such as polyvinyl alcohol, surfactants, antifoaming agents, and antioxidants.

In the present invention, the (meth) acrylic copolymer, the pigment, the basic substance, an aqueous solvent, and an additive to be used as necessary are aqueous using a known and conventional mixer or disperser. A pigment dispersion is produced. Specific manufacturing methods include, for example,
(A) After adding the pigment to the aqueous solution or aqueous solvent solution of the (meth) acrylic copolymer neutralized with a basic substance, the pigment is dispersed using various stirring and dispersing devices, and if necessary A method of adding an additive to form an aqueous pigment dispersion,

(B) The resulting kneaded product is pulverized after melt-kneading the pigment and the (meth) acrylic copolymer before neutralization using a kneader, two rolls, or an extrusion kneader. . The pulverized kneaded product is poured into water containing a necessary amount of a basic substance, a pigment dispersion is prepared using a stirring and dispersing device, and then an additive is added as necessary to form an aqueous pigment dispersion. how to,

(C) Disperse the pigment using a stirring / dispersing device in a solution in which the (meth) acrylic copolymer before neutralization is dissolved in an organic solvent having compatibility with water, such as methyl ethyl ketone and tetrahydrofuran. Then, while stirring, water containing a necessary amount of basic substance is added to effect phase inversion emulsification. Next, after distilling off the organic solvent under reduced pressure, if necessary, an additive is added to form an aqueous pigment dispersion,
and so on.

  As a stirring / dispersing device for dispersing the pigment, for example, an ultrasonic homogenizer, a high-pressure homogenizer, a paint shaker, a ball mill, a roll mill, a sand mill, a sand grinder, a dyno mill, a dispermat, an SC mill, a nanomizer, and the like, various commonly known dispersions are used. You can use the machine.

(Water-based ink for inkjet recording)
The water-based ink for ink-jet recording of the present invention is prepared by diluting the water-based pigment dispersion of the present invention with the above-mentioned water or an aqueous solvent, and adding a drying inhibitor, a penetrating agent, or other additives as necessary. To do.

The drying inhibitor gives an effect of inhibiting drying of the water-based ink for inkjet recording at the ink jet nozzle opening of the inkjet printer head. Usually, a water-soluble organic solvent having a boiling point equal to or higher than that of water is used.
Examples of water-soluble organic solvents that can be used as drying inhibitors include polyhydric alcohols such as ethylene glycol, diethylene glycol, polyethylene glycol, and glycerol, pyrrolidones such as N-methyl-2-pyrrolidone and 2-pyrrolidone, amides, and dimethyl sulfoxide. And imidazolidinone. When the solvent is water, the amount of the drying inhibitor used is preferably in the range of 1 to 150 parts with respect to 100 parts of water.

The penetrating agent is used for facilitating penetration of the water-based ink for ink jet recording, which is ejected from the ink ejecting nozzle of the ink jet printer head and adheres to the recording medium, into the recording medium. By using the penetrating agent, it is possible to obtain a recorded matter in which the aqueous solvent quickly penetrates into the recording medium and the image does not blur.
Examples of penetrants used in the present invention include polyhydric alcohols such as ethylene glycol, 1,2,6-hexanetriol, thiodiglycol, hexylene glycol and diethylene glycol, diols such as pentanediol and hexanediol, and laurin. Glycol ethers such as propylene glycol, lower alkyl ethers of polyhydric alcohols such as diethylene glycol ethyl ether and triethylene glycol monoethyl ether, lower alcohols such as ethanol and isopropyl alcohol, glycol ethers such as diethylene glycol-N-butyl ether, propylene And water-soluble organic solvents such as glycol derivatives. These can be used alone or in admixture of two or more. More preferable permeability may be obtained by using a mixture of two or more.
In addition, since the printing density may be affected depending on the selection of the penetrant, it is preferable to adjust the composition according to the configuration and acid value of the (meth) acrylic copolymer of the present invention. For example, when a (meth) acrylic copolymer having a relatively high acid value and high hydrophilicity is used, it is preferable to select a penetrant having high hydrophobicity and low penetrability. Specifically, when a water-soluble organic solvent such as alkyldiols such as 1,2-hexanediol and 1,6-hexanediol is used, the printing density can be slightly increased.

The water-based ink for inkjet recording of the present invention uses the (meth) acrylic copolymer as a pigment dispersant, and it is not particularly necessary to add a surfactant for the purpose of improving pigment dispersibility. A slight amount of a surfactant may be added for the purpose of adjusting physical properties such as surface tension. The surfactant is not particularly limited, and anionic surfactants such as alkylbenzene sulfonates and higher fatty acid salts, nonionic surfactants such as polyoxyethylene alkyl ethers and polyoxyethylene fatty acid esters, and other cationic surfactants. The surfactant may be appropriately selected from known and commonly used surfactants such as amphoteric surfactants. These surfactants can be used alone or in combination of two or more.
Examples of other additives include antiseptics, antifungal agents, and chelating agents for preventing nozzle clogging.

  If coarse particles are present in the water-based ink for ink jet recording, the ink jet nozzles of the ink jet printer may become clogged. Therefore, it is preferable to remove the coarse particles by centrifugal separation or filtration after the dispersion treatment.

  The aqueous ink for inkjet recording of the present invention thus obtained is excellent in storage stability and dischargeability from the ink jet nozzle of the inkjet printer head, and is an ink film formed on a recording medium using the ink. Can form a uniform image with high resolution and high density.

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

[Synthesis Example 1]
100 parts of methyl ethyl ketone (hereinafter abbreviated as MEK) is kept at 80 ° C. in a nitrogen stream and is stirred with 87.8 parts of benzyl methacrylate, 12.2 parts of methacrylic acid, and a polymerization initiator (“Perbutyl (registered trademark)”). ) O ”[active ingredient peroxy 2-ethylhexanoate t-butyl, manufactured by NOF Corporation] was added dropwise over 2 hours. After completion of the dropwise addition, 0.5 part of “Perbutyl (registered trademark) O” was added every 4 hours and stirred at 80 ° C. for 12 hours. Thus, a MEK solution (1-A) of an acrylic copolymer having a carboxyl group and having a nonvolatile content of 52% was obtained. The resin had a weight average molecular weight of 25,000 and an acid value of 80 mgKOH / g.

[Synthesis Example 2]
The same procedure as in Synthesis Example 1 was performed except that 100 parts of methyl ethyl ketone was used and a mixed solution of 90.8 parts of benzyl methacrylate, 9.2 parts of methacrylic acid and 6 parts of “Perbutyl (registered trademark) O” was used. A MEK solution of an acrylic copolymer (1-B) having a value of 60 mgKOH / g and a nonvolatile content of 52% was obtained.

[Synthesis Example 3]
The same procedure as in Synthesis Example 1 was performed, except that 100 parts of methyl ethyl ketone was used and a mixed solution of 89.8 parts of benzyl acrylate, 10.2 parts of acrylic acid and 6 parts of “Perbutyl (registered trademark) O” was used. A MEK solution of an acrylic copolymer (1-C) having a value of 80 mg KOH / g and a nonvolatile content of 52% was obtained.

[Synthesis Example 4]
Synthesis Example 1 except that 100 parts of methyl ethyl ketone was used and a mixed solution of 82.8 parts of benzyl methacrylate, 5 parts of butyl acrylate, 12.2 parts of methacrylic acid and 6 parts of “Perbutyl (registered trademark) O” was used. The same operation was performed to obtain a MEK solution of an acrylic copolymer (1-D) having an acid value of 80 mgKOH / g and a nonvolatile content of 50%.

[Synthesis Example 5]
Synthesis example except using 100 parts of methyl ethyl ketone and using a mixed solution of 80.3 parts of benzyl methacrylate, 7.5 parts of methyl methacrylate, 12.2 parts of methacrylic acid and 6 parts of “Perbutyl (registered trademark) O” The same operation as 1 was performed to obtain a MEK solution of an acrylic copolymer (1-E) having an acid value of 80 mgKOH / g and a nonvolatile content of 52%.

[Synthesis Example 6]
Same as Synthesis Example 1 except that 100 parts of methyl ethyl ketone is used and a mixed solution of 75.8 parts of benzyl methacrylate, 15 parts of methyl methacrylate, 9.2 parts of methacrylic acid and 6 parts of “Perbutyl (registered trademark) O” is used. Then, an MEK solution of an acrylic copolymer (1-F) having an acid value of 60 mgKOH / g and a nonvolatile content of 50% was obtained.

[Synthesis Example 7]
100 parts of methyl ethyl ketone and 75.8 parts of benzyl methacrylate, 7.5 parts of methyl methacrylate, 7.5 parts of 2-hydroxyethyl methacrylate, 9.2 parts of methacrylic acid and “Perbutyl (registered trademark) O” A MEK of an acrylic copolymer (1-G) having an acid value of 60 mgKOH / g, a hydroxyl value of 32.5 mgKOH / g, and a non-volatile content of 51%, except that 6 parts of the mixed solution was used. A solution was obtained.

[Synthesis Example 8]
Synthesis Example 1 except that 100 parts of methyl ethyl ketone was used and a mixed solution of 79.7 parts of benzyl methacrylate, 5 parts of butyl acrylate, 15.3 parts of methacrylic acid and 6 parts of “Perbutyl (registered trademark) O” was used. The same operation was performed to obtain a MEK solution of an acrylic copolymer (1-H) having an acid value of 100 mgKOH / g and a nonvolatile content of 50%.

[Synthesis Example 9]
Same as Synthesis Example 1 except that 100 parts of methyl ethyl ketone is used and a mixed solution of 64.7 parts of benzyl methacrylate, 20 parts of methyl methacrylate, 15.3 parts of methacrylic acid and 6 parts of “Perbutyl (registered trademark) O” is used. Then, an MEK solution of an acrylic copolymer (1-I) having an acid value of 100 mgKOH / g and a nonvolatile content of 52% was obtained.

[Synthesis Example 10]
Operation similar to Synthesis Example 1 except that 100 parts of methyl ethyl ketone is used and a mixed solution of 57.8 parts of benzyl methacrylate, 30 parts of styrene, 12.2 parts of methacrylic acid and 6 parts of “Perbutyl (registered trademark) O” is used. And a MEK solution of a styrene-acrylic copolymer (1-J) having an acid value of 80 mgKOH / g and a nonvolatile content of 50% was obtained.

[Synthesis Example 11]
The same procedure as in Synthesis Example 1 was performed, except that 100 parts of methyl ethyl ketone was used and a mixed solution of 69.4 parts of benzyl methacrylate, 30.6 parts of methacrylic acid and 6 parts of “Perbutyl (registered trademark) O” was used. A MEK solution of an acrylic copolymer (1-K) having a value of 200 mgKOH / g and a nonvolatile content of 52% was obtained.

[Synthesis Example 12]
The same procedure as in Synthesis Example 1 was carried out except that 100 parts of methyl ethyl ketone was used and a mixed solution of 87.8 parts of styrene, 12.2 parts of methacrylic acid and 4 parts of “Perbutyl (registered trademark) O” was used, and an acid value of 80 mg KOH / G, MEK solution of acrylic copolymer (1-L) having a nonvolatile content of 52% was obtained.

  Table 1 shows the monomer composition ratios and acid values of the copolymers (1-A) to (1-L) synthesized in each of these synthesis examples 1 to 8.

  Note) In Table 1, St is styrene, BzMA is benzyl methacrylate, BzA is benzyl acrylate, BA is butyl acrylate, MMA is methyl methacrylate, HEMA is 2-hydroxyethyl methacrylate, MAA is methacrylic acid, and AA is It means acrylic acid. The numbers represent the number of parts of each monomer when the total monomer is 100 parts in terms of mass. MAA + BzMA means the total mass% of (meth) acrylic acid and benzyl (meth) acrylate monomer in the copolymer.

<Example 1>
Copolymer (1-A) obtained in Synthesis Example 1, 5% aqueous potassium hydroxide solution, Fastogen (registered trademark) Blue TGR (copper phthalocyanine pigment manufactured by Dainippon Ink & Chemicals, Inc.) in 250 mL of polyvin Charged and mixed. Here, the amount charged is 10 parts for the copper phthalocyanine pigment, the amount of the resin is 50% by mass with respect to the pigment, and the 5% aqueous potassium hydroxide solution is the copolymer (B-1). The amount by which the acid value is neutralized by 100%, and water is the amount necessary to make the non-volatile content of the mixed solution 30%.
The mixed solution was dispersed for 2 hours with a paint conditioner (using zirconia beads having a diameter of 0.5 mm). After the dispersion is complete, remove the ethyl ethyl ketone from the liquid obtained by removing the zirconia beads using an evaporator, and centrifuge (8200 G, 30 minutes) to remove coarse particles. And an aqueous pigment dispersion (1-A) having a nonvolatile content of 20% was obtained.

<Examples 2 to 8>
It replaced with the copolymer (1-A) obtained by the synthesis example 1, and it replaced with the copolymer (1-B)-(1-H) obtained by the synthesis example 2, and it carried out similarly to Example 1, and changed. Aqueous pigment dispersions (1-B) to (1-H) having a nonvolatile content of 20% were obtained.

<Comparative Examples 1-4>
Example except that the copolymer (1-A) obtained in Synthesis Example 1 was changed to the copolymers (1-I) to (1-L) obtained in Synthesis Example 5 to Synthesis Example 8. 1 to obtain aqueous pigment dispersions (1-I) to (1-L) having a nonvolatile content of 20%.

The aqueous pigment dispersion (1-A) obtained in Example 1 was used, adjusted according to the following composition, and filtered through a filter having a pore size of 6 μm to prepare a piezo ink jet recording aqueous ink (1-A). .

Aqueous pigment dispersion (1-A) 25.0 parts Diethylene glycol monobutyl ether 10.0 parts Diethylene glycol 15.0 parts Surfinol 465 (manufactured by Air Products) 0.8 parts Water 49.2 parts

<Examples 10 to 16>
Instead of the aqueous pigment dispersion (1-A) obtained in Example 1, the same amount of the aqueous pigment dispersions (1-B) to (1-H) obtained in Examples 2 to 8 was used. Were the same as in Example 1 to prepare water-based inks for ink-jet recording (1-B) to (1-H).

<Comparative Examples 5-8>
Aside from using the same amount of the aqueous pigment dispersions (1-I) to (1-L) obtained in Comparative Examples 1 to 4 instead of the aqueous pigment dispersion (1-A) obtained in Example 1, The same operation as in Example 1 was performed to prepare water-based inks for ink-jet recording (1-I) to (1-L).

<Performance tests and evaluation criteria>
(Determination of pigment particle size in water-based ink for inkjet recording)
After adding water to the sample ink and diluting it 1000 times, the particle size of the pigment dispersed in the sample ink is measured using a particle size analyzer (“Microtrac UPA150” manufactured by Leeds & Northrup). Measurement was made as the initial particle size, and the determination was made according to the following three-stage criteria.
○ Particle size less than 120nm.
Δ: Particle size of 120 nm or more and less than 150 nm.
X Particle size of 150 nm or more.

(Storage stability of aqueous pigment dispersion)
After the aqueous pigment dispersion was allowed to stand at 60 ° C. for 30 days, the particle size of the pigment dispersed in the sample was measured using the particle size analyzer.
When the rate of change of the measured value relative to the initial particle diameter was 10% or less, “○” was evaluated, and when the rate of change was more than 10%, “×” was evaluated.

(Inkjet recording test (print density, gloss value))
Using a piezo type ink jet printer (EM-930C, manufactured by Seiko Epson Corporation), drawing was performed on the recording medium with sample ink, and a print density test and a gloss value test were performed. As the recording medium, “Canon PB paper” manufactured by Canon Co., Ltd. or “Xerox 4024” manufactured by Xerox Co., Ltd. was used as plain paper, and “photographic paper gloss” manufactured by Seiko Epson Co., Ltd. was used as a dedicated paper for inkjet.

a) Print density
The print density was evaluated for special paper.
Print a solid image on inkjet paper, use a print density measuring machine “GRETAG (registered trademark) D196 Gretag Macbeth Co., Ltd.”, measure the color image density for 5 points of a single sample, and average the values. The printing density was used. The larger the value, the better the print density, and the determination was made according to the following four criteria for each paper.
"Photo paper gloss" manufactured by Seiko Epson Corporation
◎ Print density 2.7 or higher.
○ Printing density is 2.5 or more and less than 2.7.
Δ: Print density is 2.0 or more and less than 2.5.
× Print density less than 2.0.

b) Gloss value measurement of image
A solid image was printed on a special paper, and the gloss of the colored image was measured at a measurement angle of 20 degrees using a haze gloss meter “BYK Gardner” as a gloss value measuring machine. Three points of a single sample were measured, and a value obtained by averaging them was defined as a gloss value. The larger the value, the better the gloss, and the determination was made according to the following four levels of criteria.
◎ Gloss value 25 or more ○ Gloss value 20 or more.
Δ: Gloss value of 10 or more and less than 20.
X Gloss value less than 10.

c) Determination of visual glossiness The degree of glossiness of the printed matter obtained in the above printing test was visually determined based on the following four criteria.
◎ Glossy and almost no diffuse reflection.
○ Glossy but slightly diffused.
△ Glossy but diffuse reflection is large.
× Not glossy and hardly reflects light.

  Table 2 summarizes the performance test results of the aqueous pigment dispersion of the present invention and the aqueous ink for inkjet recording.

  In Table 2, the dispersed particle diameter is the pigment particle diameter determination in the water-based ink for ink jet recording, the stability is the storage stability of the aqueous pigment dispersion, and the print density is printed on the special paper “photo paper gloss”. The print density and gloss value mean gloss measurement of the image, and glossiness means visual glossiness determination.

From the results shown in Table 2, the aqueous pigment dispersion using the (meth) acrylic copolymer of the present invention is excellent in storage stability, and the water-based ink for ink jet recording preferably has a particle diameter of the dispersed pigment. It can be seen that the obtained inkjet printed matter is excellent in gloss and has a high color image density. In particular, in Examples 1 to 4, in which the total mass% of (meth) acrylic acid and (meth) acrylic acid benzyl monomer in the copolymer is 95% by mass or more, the print density is 2.7 or more. Yes, the gloss value was 25 or more, and the glossiness was very excellent.
On the other hand, in both Comparative Example 1 and Comparative Example 2, the total of benzyl (meth) acrylate and (meth) acrylic acid with respect to the total amount of monomers constituting the (meth) acrylic copolymer is less than 85% by mass. As an example, both the print density and gloss value were low. Comparative Example 3 is an example having a large acid value, while Comparative Example 4 is an example not containing benzyl (meth) acrylate, but this has low print density and gloss value.

Claims (5)

An aqueous pigment dispersion for inkjet inks comprising a (meth) acrylic copolymer, a pigment, and a basic substance, wherein the (meth) acrylic copolymer comprises benzyl (meth) acrylate and (meth) acrylic acid. It is an essential constituent monomer, and the total of benzyl (meth) acrylate and (meth) acrylic acid with respect to the total amount of monomers constituting the acrylic copolymer is 85% by mass or more, and the acid value is 40 to 110 mgKOH / g. A water-based pigment dispersion for ink-jet inks. The aqueous pigment dispersion for inkjet ink according to claim 1, wherein the total of benzyl (meth) acrylate and (meth) acrylic acid is 95% by mass or more based on the total amount of monomers constituting the (meth) acrylic copolymer. body. The aqueous pigment dispersion for inkjet ink according to claim 1, wherein the hydroxyl value of the (meth) acrylic copolymer is 20.0 mgKOH / g or less. The aqueous pigment dispersion for inkjet ink according to claim 1, wherein the (meth) acrylic copolymer comprises (meth) acrylic acid and benzyl methacrylate. A water-based ink for ink-jet recording using the water-based pigment dispersion for ink-jet ink according to claim 1.