JP4590878B2 - Pigment dispersion and ink composition using the same - Google Patents

Description

  The present invention relates to a pigment dispersion and an ink composition using the same, and more particularly to a pigment dispersion that can realize an ink composition having excellent ejection stability and storage stability.

  As a colorant for ink jet recording ink, a pigment is used because of its excellent fastness such as water resistance and light resistance. In an ink composition using a pigment, printing is performed by attaching the pigment to the surface of the recording medium, and therefore, the abrasion resistance may be inferior compared to the case where a dye ink is used. It has also been pointed out that the glossiness is lost depending on the type of recording medium used and the pigment particle size.

  In response to such problems, attempts have been made to add various additives to the ink composition. For example, in JP-A-8-295837 (Patent Document 1), by containing a urethane fine particle polymer having a crosslinked structure, a printed matter having excellent solvent resistance and hardly causing bleeding due to water or the like is realized. A possible ink composition is disclosed. Japanese Patent Application Laid-Open No. 2000-1639 (Patent Document 2) discloses an ink jet recording ink that is excellent in friction resistance and stability over time by containing a water-soluble resin made of a polyurethane resin. Furthermore, Japanese Patent Application Laid-Open No. 2002-30235 (Patent Document 3) discloses an aqueous pigment ink for ink jetting which is excellent in gloss and friction resistance by containing thermoplastic resin fine particles.

However, when such a pigment dispersion or an ink composition containing polyurethane is used, it is difficult to adjust the viscosity of the ink, or the ink ejection stability or storage stability is impaired. was there.
JP-A-8-295837 JP 2000-1639 A JP 2002-30235 A

Summary of the Invention

  The present inventors have now observed that the phenomenon as described above is due to a change in viscosity of a pigment dispersion containing a polyurethane resin and an ink composition comprising the pigment dispersion, and a predetermined environment such as high temperature and alkaline conditions. It was found to be due to hydrolysis of polyurethane molecular chains below, and by adding 1,2-hexanediol to these pigment dispersions and carrying out heat treatment, it was excellent in ejection stability and storage stability, and The inventors have obtained knowledge that an ink composition having sufficient glossiness and abrasion resistance can be obtained. The present invention is based on this finding.

  That is, an object of the present invention is a pigment dispersion containing a polyurethane resin and an ink composition comprising the pigment dispersion, which is excellent in ejection stability and storage stability, and has sufficient glossiness and abrasion resistance. It is an object to provide a pigment dispersion having properties and an ink composition using the pigment dispersion.

  The pigment dispersion according to the present invention is a pigment dispersion containing at least a pigment, a polyurethane resin, and 1,2-hexanediol, and the viscosity change of the pigment dispersion does not substantially occur. Until the heat treatment.

  Moreover, it is preferable to perform the said heat processing at 60 to 70 degreeC, and also it is preferable to carry out for 3 to 7 days.

  According to the present invention, by adding 1,2-hexanediol to a pigment dispersion containing a polyurethane resin and performing a predetermined heat treatment, an ink composition can be easily formed without causing a change in viscosity of the pigment dispersion over time. By using this pigment dispersion, an ink composition having excellent ejection stability and storage stability and sufficient glossiness and abrasion resistance can be obtained.

DETAILED DESCRIPTION OF THE INVENTION

  Hereinafter, the pigment dispersion according to the present invention and the ink composition using the same will be described.

1. Pigment dispersion The pigment dispersion according to the present invention comprises at least a pigment, a polyurethane resin, and 1,2-hexanediol, and is subjected to heat treatment until the viscosity change of the pigment dispersion does not substantially occur. It is obtained by applying. By subjecting the pigment dispersion to heat treatment at 60 to 70 ° C., preferably 70 ° C., for 3 to 7 days, preferably 3 days, the viscosity change of the pigment dispersion does not substantially occur. In this way, the pigment dispersion that has been heat-treated to such an extent that no change in viscosity occurs is unlikely to cause hydrolysis of polyurethane molecular chains even when stored in a predetermined environment such as high temperature and alkaline conditions. Accordingly, since the viscosity of the pigment dispersion does not change with time, the viscosity of the ink composition can be easily adjusted when preparing the ink composition using the pigment dispersion. In addition, the ink composition thus obtained does not change the viscosity of the ink over a long period of time and is excellent in ink ejection stability and storage stability. Here, the extent to which the viscosity change of the pigment dispersion does not substantially occur is the following formula when the solution viscosity before heat-treating the pigment dispersion is η ₀ and the solution viscosity after heat-treatment is η. The viscosity change rate (Δη) expressed is 4% or less.

Δη (%) = | η−η ₀ | / η ₀ × 100
The 1,2-hexanediol added to the pigment dispersion is preferably 2 to 8% by weight based on the pigment dispersion. If it is less than 2% by weight, the ejection stability and storage stability of the ink composition cannot be sufficiently obtained even if the pigment dispersion is subjected to heat treatment, and if it exceeds 8% by weight, it is adjusted after the heat treatment. The glossiness of the ink composition is greatly reduced.

  Hereinafter, each component constituting the pigment dispersion according to the present invention will be described.

(1) Polyurethane resin From the viewpoint of achieving color image glossiness, prevention of bronzing, and storage stability of the ink composition, and the formation of a color image with even higher glossiness, the polyurethane resin is capable of forming a urethane bond and / or Or it is preferable that it is resin which has an amide bond and an acidic group.

  In the present invention, the polyurethane resin is a resin containing a polymer obtained by reacting a diisocyanate compound and a diol compound. Examples of the diisocyanate compound include aromatic aliphatic diisocyanate compounds such as hexamethylene diisocyanate and 2,2,4-trimethylhexamethylene diisocyanate, aromatic diisocyanate compounds such as toluylene diisocyanate and phenylmethane diisocyanate, and modified products thereof. . Examples of the diol compound include polyethers such as polyethylene glycol and polypropylene glycol, polyesters such as polyethylene abido and polybutylene abates, and polycarbonates. In the present invention, the polyurethane resin preferably has a carboxyl group.

In the pigment dispersion according to the present invention, the weight ratio between the solid content of the pigment and the solid content other than the pigment such as the polyurethane resin is preferably 100: 20 to 100: 80. By containing the polyurethane resin in such a range, it is possible to form a color image having both glossiness of the color image, prevention of bronzing, and storage stability of the ink composition and excellent glossiness.

  In the present invention, from the viewpoint that the content of the polyurethane resin satisfies both the glossiness of the color image, the prevention of bronzing, and the storage stability of the ink composition and can form a color image having further excellent glossiness, the pigment is used. Preferably it is 10-40 weight part with respect to 100 weight part, More preferably, it is 10-35 weight part.

  The acid value of the polyurethane resin is preferably 10 to 300 from the viewpoint of achieving color image glossiness, prevention of bronzing, and storage stability of the ink composition and forming a color image having further excellent glossiness. More preferably, it is 20-100. The acid value is the mg amount of KOH required to neutralize 1 g of resin.

  From the viewpoint that the weight average molecular weight (Mw) before crosslinking of the polyurethane resin is compatible with the glossiness of the color image, the prevention of bronzing, and the storage stability of the ink composition and can form a color image with further excellent glossiness. Preferably it is 100-200,000, More preferably, it is 1000-50,000. Mw is measured by GPC (gel permeation chromatography), for example.

  The glass transition temperature (Tg; measured in accordance with JIS K6900) of the polyurethane resin is from the viewpoint that both color image glossiness, prevention of bronzing, and storage stability of the ink composition are compatible, and a color image with further excellent glossiness can be formed. Is preferably −50 to 200 ° C., and more preferably −50 to 100 ° C.

  The polyurethane resin is dispersed in the form of fine particles in the pigment dispersion of the present invention or adsorbed to the pigment. The glossiness of the color image, prevention of bronzing, and storage stability of the ink composition are available. From the viewpoint of forming a color image having both excellent compatibility and glossiness, the polyurethane resin preferably has a maximum particle size of 0.3 μm or less and an average particle size of 0.2 μm or less (more preferably 0). .1 μm or less) is more preferable.

  The average particle diameter is an average value of molecular diameter (volume 50% diameter) as particles actually formed in the dispersion liquid. For example, Microtrac UPA (Microtrac Inc.) is used. Can be measured.

(2) Pigment As the pigment used in the pigment dispersion according to the present invention, inorganic pigments and organic pigments can be used, and each can be used alone or in combination. As the inorganic pigment, for example, in addition to titanium oxide and iron oxide, carbon black produced by a known method such as a contact method, a furnace method, or a thermal method can be used. Examples of the organic pigment include azo pigments (including azo lakes, insoluble azo pigments, condensed azo pigments, chelate azo pigments), polycyclic pigments (for example, phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, Dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinofullerone pigments, etc.), dye chelates (for example, basic dye type chelates, acidic dye type chelates), nitro pigments, nitroso pigments, aniline black, and the like can be used.

  Specific examples of the pigment are appropriately given according to the type (color) of the ink composition to be obtained using the pigment dispersion according to the present invention. For example, as a pigment for a yellow ink composition, C.I. I. Pigment Yellow 1, 2, 3, 12, 14, 16, 17, 73, 74, 75, 83, 93, 95, 97, 98, 109, 110, 114, 128, 129, 138, 139, 147, 150, 151, 154, 155, 180, 185 and the like, and one or more of these are used. Of these, C.I. I. It is preferable to use one or more selected from the group consisting of CI Pigment Yellow 74, 110, 128 and 147. Examples of the pigment for the magenta ink composition include C.I. I. Pigment Red 5, 7, 12, 48 (Ca), 48 (Mn), 57 (Ca), 57: 1, 112, 122, 123, 168, 184, 202, 209; I. Pigment violet 19 or the like, and one or more of these may be used. Of these, C.I. I. Pigment red 122, 202, 209 and C.I. I. It is preferable to use one or more selected from the group consisting of CI Pigment Violet 19. Examples of the pigment for the cyan ink composition include C.I. I. Pigment Blue 1, 2, 3, 15: 3, 15: 4, 15:34, 16, 22, 60; I. Bat blue 4, 60, etc. are mentioned, These 1 type or 2 types or more are used. Of these, C.I. I. Pigment Blue 15: 3 and / or 15: 4 are preferably used, especially C.I. I. Pigment Blue 15: 3 is preferably used. Examples of the pigment for the black ink composition include carbon blacks such as furnace black, lamp black, acetylene black and channel black (CI pigment black 7), inorganic pigments such as iron oxide pigments; aniline black And organic pigments such as (CI Pigment Black 1).

  The concentration of the pigment in the pigment dispersion according to the present invention is not particularly limited because it may be adjusted to an appropriate pigment concentration (content) when an ink composition described below is prepared, but is usually 5 to 20% by weight. It is.

  In the present invention, the pigment is preferably a pigment kneaded with a dispersant described later, and an excellent color image can be formed even if the pigment is not surface-treated.

(3) Dispersant The pigment dispersion according to the present invention preferably comprises a copolymer resin of a hydrophobic monomer and a hydrophilic monomer as a dispersant. These copolymer resins are adsorbed on the pigment to improve dispersibility.

  Specific examples of the hydrophobic monomer include, for example, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-propyl acrylate, n-propyl methacrylate, iso-propyl acrylate, iso-propyl methacrylate, n-butyl acrylate, and n-butyl. Methacrylate, sec-butyl acrylate, sec-butyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, n-hexyl acrylate, n-hexyl methacrylate, n-octyl acrylate, n-octyl methacrylate, iso-octyl acrylate, iso-octyl Methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, decyl acrylate, decyl methacrylate, lauryl acrylate, laur Methacrylate, stearyl acrylate, stearyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 2-dimethylaminoethyl acrylate, 2-dimethylaminoethyl methacrylate, 2-diethylamino Ethyl acrylate, 2-diethylaminoethyl methacrylate, glycidyl acrylate, glycidyl methacrylate, allyl acrylate, allyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, phenyl acrylate, phenyl methacrylate, nonyl phenyl acrylate, nonyl phenyl methacrylate, benzyl acrylate, benzyl methacrylate, dicyclo Pentenyl acrylate, dicyclopentenyl methacrylate, bornyl acrylate, bornyl methacrylate, 1,3-butanediol diacrylate, 1,3-butanediol dimethacrylate, 1,4-butanediol diacrylate, 1,4-butanediol di Methacrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, diethylene glycol dimethacrylate, triethylene glycol diacrylate, triethylene glycol dimethacrylate, tetraethylene glycol diacrylate, tetraethylene glycol dimethacrylate, polyethylene glycol diacrylate, polyethylene Glycol dimethacrylate, neopentyl glycol diacrylate, 1,6 Hexanediol diacrylate, 1,6-hexanediol dimethacrylate, dipropylene glycol diacrylate, dipropylene glycol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, glycerol acrylate, glycerol methacrylate, styrene, methylstyrene, vinyl Toluene and the like can be mentioned. You may use these individually or in mixture of 2 or more types.

  Specific examples of the hydrophilic monomer include acrylic acid, methacrylic acid, maleic acid, itaconic acid and the like.

  From the viewpoint that the copolymer resin of the hydrophobic monomer and the hydrophilic monomer can form a color image having both glossiness of the color image, prevention of bronzing, and storage stability of the ink composition and excellent glossiness. , Styrene- (meth) acrylic acid copolymer resin, styrene-methylstyrene- (meth) acrylic acid copolymer resin, or styrene-maleic acid copolymer resin, (meth) acrylic acid- (meth) acrylic acid ester copolymer resin Or at least one of styrene- (meth) acrylic acid- (meth) acrylic acid ester copolymer resin.

  The copolymer resin may be a resin (styrene-acrylic acid resin) containing a polymer obtained by reacting styrene with acrylic acid or an ester of acrylic acid. Alternatively, the copolymer resin may be an acrylic acid-based water-soluble resin. Alternatively, a salt such as sodium, potassium, or ammonium may be used.

  The content of these copolymer resins is 100 parts by weight of the pigment from the viewpoint of achieving color image glossiness, prevention of bronzing, and storage stability of the ink composition and forming a color image with further excellent glossiness. The amount is preferably 10 to 50 parts by weight, and more preferably 10 to 35 parts by weight.

(4) Crosslinking agent In the pigment dispersion according to the present invention, an epoxy resin having a glycidyl ether skeleton or a resin having an oxazoline group is added as a crosslinking agent, so that glossiness of color images, prevention of bronzing, and This is particularly preferable from the viewpoint of achieving both the storage stability of the ink composition and the formation of a color image having further excellent gloss. By adding a polyurethane resin and a crosslinking agent to cause a crosslinking reaction, the copolymer resin and the polyurethane resin are crosslinked by the crosslinking agent to cover the surface of the pigment (encapsulation), improving stability over time, low Helps to increase viscosity and adhesion, and stabilize pigment dispersion.

  The crosslinking agent is preferably a resin that reacts with a carboxyl group (carboxyl group attack type resin) from the viewpoint of further improving dispersibility. For example, a polycarbodiimide type having a carbodiimide group in the molecule, an oxazoline type having an oxazoline group in the molecule, an aziridine type and the like can be mentioned.

  The addition amount of the cross-linking agent is the same as that for the polyurethane resin, from the viewpoint of achieving color image glossiness, bronzing prevention, and storage stability of the ink composition, and capable of forming a color image with further excellent glossiness. It is preferably 1 to 50% by weight.

  The addition amount of the cross-linking agent is such that the copolymer resin and the above-described copolymer resin and the above-described one can be formed from the viewpoint of achieving color image glossiness, prevention of bronze, and storage stability of the ink composition and at the same time forming a color image having further excellent glossiness. The gel fraction is preferably 20% or more, more preferably 35% or more, based on the total carboxy groups of the polyurethane resin.

  Further, the addition amount of the crosslinking agent is effective solid weight from the viewpoint of achieving color image glossiness, prevention of bronzing, and storage stability of the ink composition and forming a color image having further excellent glossiness. The ratio (crosslinking agent / (styrene-acrylic acid resin + polyurethane resin)) is preferably 1/100 to 50/100, more preferably 1/100 to 40/100.

  The weight-average molecular weight (Mw) of the polyurethane resin reacted with the cross-linking agent can form a color image having both glossiness of a color image, prevention of bronzing, and storage stability of the ink composition and excellent glossiness. From the viewpoint, it is preferably 10,000 or more, and more preferably 30,000 or more.

(5) Other Additives The pigment dispersion according to the present invention is publicly known after blending a pigment, polyurethane resin, 1,2-hexanediol, and pigment dispersant with a neutralizer and other additives as necessary. It is prepared by carrying out a dispersion treatment with a disperser or the like. In the present invention, the pigment is a pigment prepared by a bead mill or a collision type jet pulverizer, so that the gloss of the color image, the prevention of bronzing, and the storage stability of the ink composition are compatible and the gloss is further improved. It is preferable from the viewpoint that an excellent color image can be formed. Further, water is usually used as the aqueous medium used in the pigment dispersion. As the water, it is preferable to use pure or ultrapure water such as ion exchange water, ultrafiltration water, reverse osmosis water, and distilled water. In particular, water obtained by sterilizing these waters by ultraviolet irradiation or addition of hydrogen peroxide is preferable because generation of mold and bacteria is prevented for a long period of time.

  In addition, as an aqueous medium used for the pigment dispersion, an aqueous medium used in an ink composition described later, for example, a penetrating solvent, a wetting solvent, a surfactant, or the like may be used together with or separately from water. Furthermore, the pigment dispersion according to the present invention is preferably subjected to ion exchange treatment or ultrafiltration treatment.

2. Method for Producing Pigment Dispersion A pigment dispersion according to the present invention is prepared by mixing the above-described pigment and a dispersant, dispersing the pigment using a bead mill or a collision-type jet pulverizer, and then adding a polyurethane resin. Accordingly, a crosslinking agent is added to perform a crosslinking treatment to prepare an untreated pigment dispersion. Next, a predetermined amount of 1,2-hexanediol is added to the untreated pigment dispersion and heat treatment is performed. The heat treatment is performed at 60 to 70 ° C., preferably 70 ° C., for 3 to 7 days, preferably 3 days. Even if the pigment dispersion is stored in a predetermined environment such as high temperature and alkaline conditions by adding a predetermined amount of 1,2-hexanediol and performing the above heat treatment, Changes in viscosity over time are less likely to occur. Accordingly, the viscosity of the ink composition can be easily adjusted when preparing the ink composition. In addition, the ink composition thus obtained does not change the viscosity of the ink over a long period of time and is excellent in ink ejection stability and storage stability.

  In addition, after dispersing a pigment, it is preferable to add an alkaline compound to the pigment and perform a neutralization treatment. In the pigment dispersion treatment, an organic solvent may be added and kneaded as necessary. Thereby, the copolymer resin is firmly fixed on the surface of the pigment.

  Moreover, it is preferable to remove the impurities by performing an ion exchange treatment or an ultrafiltration treatment after the pigment dispersion treatment. Ion exchange treatment can remove ionic substances such as cations and anions (divalent metal ions, etc.), and by ultra-treatment, impurities dissolved substances (residual substances during pigment synthesis, excess components in dispersion composition) , Resin not adsorbed on the organic pigment, contamination components, etc.) can be removed. In the ion exchange treatment, a known ion exchange resin is used. The ultratreatment uses a known ultrafiltration membrane and may be either a normal type or a double capacity up type.

3. Ink composition The ink composition according to the present invention comprises at least the pigment dispersion described above and an aqueous medium. Thus, the ink composition of the present invention is obtained by adding a predetermined amount of 1,2-hexanediol to the above-described pigment dispersion, that is, the untreated pigment dispersion, and performing a heat treatment. It is excellent in stability and storage stability, and can realize sufficient glossiness and abrasion resistance. In the present invention, when an organic pigment for a color image is used as the pigment, a color image with particularly improved glossiness can be formed.

  The ink composition according to the present invention is obtained by blending the pigment dispersion with an aqueous medium to be described later. The pigment dispersion and the aqueous medium contain the pigment content (concentration) in the ink composition. ) Is preferably added to the ink composition in an amount of 10% by weight or less, particularly 1.0 to 7.0% by weight from the viewpoint of obtaining excellent glossiness.

  As the aqueous medium used in the ink composition of the present invention, water, a penetrating solvent, a wetting solvent, a surfactant and the like are usually used.

  Here, the water used as the aqueous medium is the same as the water used in the pigment dispersion described above. Usually, after blending a penetrating solvent, a wetting solvent, a surfactant and the like, the ink composition as a balance is used. It is made to contain.

  The penetrating solvent has a function of increasing the wettability to the recording medium to enhance the penetrability. In particular, alkanediols and / or glycol ethers are preferably used from the viewpoint of improving the penetrability.

  Examples of alkanediols include 1,2-pentanediol and 1.2-hexanediol.

  Examples of glycol ethers include ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether. Etc.

  One or more of these osmotic solvents are used.

  The penetrating solvent is preferably contained in the ink composition of the present invention in an amount of 1 to 20% by weight, more preferably 1 to 10% by weight.

  In addition, the wet solvent has a function of preventing the ink from drying and preventing clogging in the head of the ink jet printer when used for ink jet recording. Alcohols are preferred, specifically, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, propylene glycol, butylene glycol, 1.2.6-hexanetriol, thiodiglycol, hexylene glycol, glycerin, Examples include trimethylolethane and trimethylolpropane.

  In addition, as a wet solvent, saccharides such as urea, 2-pyrrolidone, N-methyl-2-pyrrolidone, 1.3-dimethyl-2-imidazolidinone, triethanolamine, and sugar alcohol can be used.

  The wet solvent is preferably contained in the ink composition of the present invention in an amount of 0.1 to 30% by weight, more preferably 0.5 to 20% by weight.

  Further, the surfactant has a function of increasing the wettability to the recording medium and improving the permeability, and acetylene glycols and / or polysiloxanes are preferably used from the viewpoint of improving the permeability.

Preferred examples of the acetylene glycols include acetylene glycol compounds represented by the following general formula (I).

(In the formula, 0 ≦ m + n ≦ 50, R ^{1 to} R ⁴ each independently represents an alkyl group having 1 to 6 carbon atoms.)
As the acetylene glycol compound represented by the general formula (I), commercially available compounds can be used. For example, Olphine Y, Surfynol 82, 440, 465, STG, E1010 (all trade names, Air Products and Chemicals Co., Ltd.), and Surfynol 465 is particularly preferable.

Preferred examples of the polysiloxane include polysiloxane compounds represented by the following general formula (II).

(Wherein R ^{1 to} R ⁹ each independently represents a C _1-6 alkyl group, j and k each independently represent an integer of 1 or more, EO represents an ethyleneoxy group, and PO represents Represents a poropyleneoxy group, and m and n represent an integer of 0 or more, provided that m + n represents an integer of 1 or more, and EO and PO are in random order in parentheses. It may be a block.)
As the polysiloxane compound represented by the general formula (II), commercially available compounds can be used, and for example, BYK348 (manufactured by BYK Japan) can be used.

  Various surfactants such as a cationic surfactant, an anionic surfactant, and a nonionic surfactant can also be used as the surfactant. One or more of these surfactants are used. The surfactant is preferably contained in the ink composition of the present invention in an amount of 0.1 to 5.0% by weight, more preferably 0.2 to 1.0% by weight.

  The ink composition according to the present invention preferably further contains an organic pH adjusting agent or an inorganic pH adjusting agent, and as the pH adjusting agent, alkanolamines or alkylamines are particularly preferably used. By including a pH adjusting agent, not only the storage stability of the ink is improved, but also the ink has a function of preventing a rapid pH change on the recording medium and improving the glossiness. By using alkanolamines or alkylamines as a regulator, the gloss can be further enhanced.

  Examples of alkanolamines include triethanolamine, monoethanolamine, diethanolamine, dimethylethanolamine, and diethylethanolamine. Examples of alkylamines include triethylamine, monoethylamine, diethylamine, dimethylethylamine, diethylmethylamine and the like.

One or more of these pH adjusters are used. The pH adjuster is preferably contained in the ink composition of the present invention in an amount of 0.1 to 5.0% by weight, more preferably 0.3 to 1.5% by weight.

  The ink composition according to the present invention has a pH of 8.0 or more from the viewpoint of achieving both color image glossiness, prevention of bronzing, and storage stability of the ink composition and formation of a color image having further excellent glossiness. It is preferable that the maximum particle size of the pigment is 0.3 μm or less and the 50% volume dispersion diameter is 0.15 nm or less.

In the present invention, since the above-described pigment dispersion is used even when the alkaline ink composition is stored or used in a high temperature environment, the polyurethane contained in the ink composition is used. Hydrolysis of the molecular chain is unlikely to occur, and therefore, the viscosity does not change with time, and is excellent in ejection stability and storage stability.

  The ink composition according to the present invention further includes a fixing agent such as a water-soluble rosin, an antifungal agent / preservative such as sodium benzoate, an antioxidant / ultraviolet absorber such as an allophanate, and a chelating agent, if necessary. Such additives can be contained, and one or more of these can be used.

4). Method for Producing Ink Composition The ink composition of the present invention can be prepared in the same manner as a conventional ink composition prepared using a pigment dispersion. In the preparation, it is preferable to remove coarse particles using a membrane filter, a mesh filter or the like.

  The ink composition of the present invention is not limited in its application and can be used as various ink compositions such as ink for ink jet printers and ink for writing instruments such as pens. In particular, ink droplets are ejected from nozzles. It is preferably used for an ink jet recording method which is a recording method for forming an image such as a character or a figure by adhering the droplet to a recording medium, and particularly preferably used for an on-demand ink jet recording method. As an on-demand type ink jet recording method, for example, a piezoelectric element recording method in which recording is performed using a piezoelectric element disposed in a printer head, or heat energy generated by a heater of a heating resistance element disposed in the printer head is used. And a thermal jet recording method for recording, and can be suitably used for any ink jet recording method.

  The number and type (color) of the ink composition according to the present invention is not particularly limited, and examples of the ink composition described above include a yellow ink composition, a magenta ink composition, a cyan ink composition, and a black ink composition. Each of them can be used alone or in combination as a ink set. In particular, since these ink sets can particularly improve the glossiness of color images, the ink composition includes at least a chromatic color ink composition such as a yellow ink composition, a magenta ink composition, or a cyan ink composition. preferable.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not restrict | limited to these.

(1) Preparation of pigment dispersion A mixture having the following composition was charged into a pressure kneader and kneaded at room temperature for 10 hours to prepare a pigment kneaded product.

CI Pigment Yellow 74 20 parts by weight Styrene-methylstyrene-acrylic acid copolymer 3 parts by weight (acid value 160, weight average molecular weight 8000, glass transition temperature 75 ° C.)
Glycerin 15 parts by weight Isopropyl alcohol 4 parts by weight Next, the obtained pigment mixture and each of the following components were charged into a stirrer and superheated at 95 ° C. for 2 hours to prepare an adjustment liquid.

Pigment kneaded material 42 parts by weight Neutralizing agent (triethanolamine) 3 parts by weight Ion-exchanged water 55 parts by weight Next, the obtained adjustment liquid is sequentially applied to a refinable bead mill (having an ability to produce 50 nm organic pigment fine particles) The resulting mixture was treated for 3 passes, adjusted to pH 8.5 with sodium hydroxide, and then centrifuged at 25000 G for 5 minutes to remove coarse particles. The obtained adjustment liquid had a solid content of 23.0%, a pH of 8.3, and a pigment particle diameter (volume 50% dispersion diameter) of 100 nm or less.

  Next, the prepared product, polyurethane resin and cross-linking agent were charged in a stirrer at the following blending ratio and stirred at 90 ° C. for 5 hours to cross-link the resin in the preparation solution to obtain a cross-linked adjustment solution. It was. The pH of the resulting crosslinked preparation was about 8. Further, a pigment dispersion was prepared by adjusting with ion-exchanged water and potassium hydroxide so that the pigment solid content concentration was 10% and the pH was about 9. The obtained pigment dispersion was about 15 parts of polyester-based polyurethane resin with respect to 100 parts of pigment as a charged theoretical amount.

Adjustment liquid 100 parts by weight Polyester polyurethane resin (solid content 30%) 10 parts by weight (acid value 50, triethylamine neutralization)
8 parts by weight of cross-linking agent (epoxy resin having 20% glycidyl ether as skeleton: epoxy equivalent 200)
To the pigment dispersion thus obtained, 5% by weight of 1,2-hexanediol was added and stirred sufficiently. The obtained pigment dispersion was heat-treated under the conditions shown in Table 1 below to obtain pigment dispersions A to E.

In addition, pigment dispersions to which 1,2-hexanediol was not added were also subjected to heat treatment under the conditions shown in Table 1 below to obtain pigment dispersions F and G.

(2) Preparation of ink composition Using the obtained treated pigment dispersion A, an ink composition A having the following composition was prepared.

Treated pigment dispersion A 61.9% by weight
Glycerin 10.0% by weight
1,2-hexanediol 5.0% by weight
BYK-348 0.5% by weight
Triethanolamine 0.9% by weight
Pure water remaining amount In the same manner as described above, ink compositions B to G were prepared in the same manner even when they were applied to the treated pigment dispersions B to G.

(3) Evaluation of Ink Composition The obtained ink compositions A to G were evaluated for ink storage stability described below. The ink storage stability was evaluated by enclosing 50 cc of the ink composition in an ink pack, leaving it in an environment of 70 ° C. for 6 days, measuring the viscosity of the ink composition before and after being left, and calculating the rate of change in viscosity. went. Viscosity measurement was performed using a reverse flow type viscosity tube (manufactured by Koiso Co., Ltd.), and the measurement temperature was 20 ° C. The viscosity change rate was calculated by the following formula.

Δη (%) = | η−η ₀ | / η ₀ × 100
Here, η ₀ represents the viscosity of the ink composition before standing, and η represents the viscosity of the ink composition after standing for 6 days in an environment of 70 ° C.

  The storage stability was evaluated according to the following criteria.

  Evaluation A: The viscosity change of the ink was less than 4%.

  Evaluation B: The change in the viscosity of the ink was 4 to 7%.

  Evaluation C: The change in the viscosity of the ink was 7% or more.

The evaluation results were as shown in Table 2.

Claims (10)

A pigment, a polyester-based polyurethane resins, 1,2-hexanediol, are facilities A pigment dispersion comprising at least comprises, the heat treatment until the viscosity change in the pigment dispersion is not substantially occur ,
A pigment dispersion , wherein the heat treatment is performed at 60 ° C to 70 ° C for 3 to 7 days . The pigment dispersion according to claim 1 , wherein the 1,2-hexanediol is contained in an amount of 2 to 8% by weight based on the pigment dispersion. The pigment dispersion liquid according to claim 1 or 2 , wherein the polyurethane resin has a urethane bond and / or an amide bond and an acidic group. The pigment dispersion according to any one of claims 1 to 3 , wherein a weight ratio between the solid content of the pigment and the solid content other than the pigment is 100: 20 to 100: 80. The pigment dispersion according to any one of claims 1 to 4 , wherein the polyurethane resin is contained in an amount of 10 to 40 parts by weight with respect to the pigment.   The pigment dispersion according to any one of claims 1 to 5, wherein the polyurethane resin has an acid value of 10 to 300. The pigment dispersion according to any one of claims 1 to 6 , further comprising an epoxy resin having a glycidyl ether skeleton or a resin having an oxazoline group as a crosslinking agent. The pigment dispersion liquid according to claim 7 , wherein the crosslinking agent is a resin that reacts with a carboxyl group. The pigment dispersion according to claim 7 or 8 , wherein the crosslinking agent is contained in an amount of 1 to 50% by weight based on the polyurethane resin. An ink composition comprising at least the pigment dispersion according to any one of claims 1 to 9 and an aqueous medium, wherein the solution viscosity change rate before and after standing at 70 ° C for 6 days is less than 4%. An ink composition.