JP2018150413A - Aqueous ink, ink cartridge, and ink jet recording method - Google Patents

Abstract

A water-based ink capable of recording an image having a high optical density is provided. An aqueous ink containing a pigment, a first resin, and a second resin. The first resin is derived from a block A composed of units derived from a monomer having an aromatic ring, a block B composed of units derived from a (meth) acrylic acid ester, and (meth) acrylic acid. And a block copolymer having a block C composed of a unit of the second resin, wherein the second resin is a urethane resin having an acid value of 40 mgKOH / g or more. [Selection figure] None

Description

  The present invention relates to an aqueous ink, an ink cartridge, and an ink jet recording method.

  In recent years, inks used in inkjet recording methods have been required to be able to record images having a high level of fastness (resistance to light, ozone gas, water, etc.), and inks using pigments as color materials (pigment inks) Opportunities to be used are increasing. Furthermore, the ink used in the ink jet recording method is required to be able to output a high-quality image comparable to a silver salt photograph. However, the pigment ink is in the form of particles, and the recorded image has a higher image quality than the ink (dye ink) using a dye dissolved in an aqueous medium in a molecular state. There is a problem that glossiness is low. Furthermore, it is also known that bronzing is likely to occur when an image is recorded using pigment ink.

  In order to solve the above problems, for example, an ink-jet ink containing a block copolymer and a urethane resin emulsion has been proposed (Patent Document 1). In addition, an ink jet ink to which a block copolymer and a urethane resin are added has been proposed in order to improve the scratch resistance and color developability of images recorded on coated paper (Patent Document 2).

JP 2012-072357 A JP 2011-001443 A

  The present inventors examined a conventional ink to which a block copolymer was added. As a result, it has been found that although the optical density of the recorded image is slightly improved, the optical density has not reached the high level required in recent years.

  Further, it was found that when an image is recorded with the ink proposed in Patent Document 1, the glossiness of the image tends to be lowered due to the urethane resin emulsion, and the optical density of the image is also lowered due to the reduction of the glossiness. . Furthermore, it has been found that even when the ink proposed in Patent Document 2 is used, the color developability of the recorded image is not improved so much.

  Accordingly, an object of the present invention is to provide a water-based ink capable of recording an image having a high optical density. Another object of the present invention is to provide an ink cartridge and an ink jet recording method using the water-based ink.

  The above object is achieved by the present invention described below. That is, according to the present invention, a water-based ink containing a pigment, a first resin, and a second resin, wherein the first resin is composed of units derived from a monomer having an aromatic ring. Block A, block B composed of units derived from (meth) acrylic acid ester, and block C composed of units derived from (meth) acrylic acid, A water-based ink is provided in which the second resin is a urethane resin having an acid value of 40 mgKOH / g or more.

  ADVANTAGE OF THE INVENTION According to this invention, the water-based ink which can record an image with high optical density can be provided. In addition, according to the present invention, an ink cartridge and an ink jet recording method using this water-based ink can be provided.

It is sectional drawing which shows typically one Embodiment of the ink cartridge of this invention. FIG. 2 is a diagram schematically illustrating an example of an ink jet recording apparatus used in the ink jet recording method of the present invention, in which (a) is a perspective view of a main part of the ink jet recording apparatus, and (b) is a perspective view of a head cartridge.

  Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is dissociated into ions in the ink, but it is expressed as “contains a salt” for convenience. In addition, water-based ink for inkjet may be simply referred to as “ink”. Physical property values are values at normal temperature (25 ° C.) unless otherwise specified. The “unit” of the resin means a repeating unit derived from one monomer.

As a result of various investigations, the present inventors have found that a water-based ink capable of recording an image having a high optical density can be obtained by adopting the following configuration. That is, the water-based ink of the present invention is a water-based ink containing a pigment, a first resin, and a second resin. The first resin is a block copolymer having the following block A, block B, and block C. The second resin is a urethane resin having an acid value of 40 mgKOH / g or more. The present inventors presume the reason why the optical density of the recorded image is improved by adopting such a configuration as follows.
Block A: a polymer block composed of units derived from a monomer having an aromatic ring.
Block B: a polymer block composed of units derived from (meth) acrylic acid ester.
Block C: a polymer block composed of units derived from (meth) acrylic acid.

  When ink containing a pigment is applied to a recording medium such as glossy paper, the pigment does not penetrate into the recording medium and remains on the surface of the recording medium. Then, part of the pigment and resin remains on the surface of the recording medium to form a pigment layer, and an image is recorded. Here, it is considered that the closer the pigment particles are packed, the more the internal scattering of light in the pigment layer is suppressed and the optical density of the image is improved. Here, when the block copolymer in which the block A and the block B which are hydrophobic units and the block C which is a hydrophilic unit are separated is closely attached to the pigment particles, the pigment particles are more densely packed. Clogged. Thereby, the internal scattering of light in the pigment layer is suppressed, and the optical density of the image is improved.

  In addition, the adhesion between the ink dots applied to the recording medium is considered to affect the internal scattering of light in the pigment layer. By including a urethane resin having a high surface energy in the ink, the adhesion between the ink dots can be improved. For this reason, it is considered that the density of the pigment layer formed on the recording medium such as glossy paper is increased, the internal scattering of light is suppressed, and the optical density of the image is improved.

<Ink>
The ink of the present invention is a water-based ink containing a pigment, a first resin, and a second resin. Hereafter, each component which comprises the ink of this invention is demonstrated in detail.

(Pigment)
The ink of the present invention contains a pigment such as an inorganic pigment or an organic pigment as a color material. Examples of the inorganic pigment include carbon black, calcium carbonate, and titanium oxide. Examples of the organic pigment include azo, phthalocyanine, quinacdrine and the like. In addition, for purposes such as toning, a dye may be used in combination as a coloring material. The content (% by mass) of the pigment in the ink is preferably 0.1% by mass or more and 10.0% by mass or less, and 1.0% by mass or more and 10.0% by mass or less based on the total mass of the ink. It is more preferable that it is 2.0 mass% or more and 8.0 mass% or less.

  When the pigments are classified by the dispersion method, there can be mentioned resin-dispersed pigments using a resin dispersant, self-dispersed pigments that do not require a resin dispersant, and the like. Any dispersion system pigment can be used in the ink of the present invention. In order to efficiently exhibit the characteristics of the film formed of the urethane resin, which is the second resin, and improve the scratch resistance of the image, it is preferable to suppress the interaction between the urethane resin and the pigment to some extent. For this reason, it is preferable to use a resin dispersion pigment using a resin other than a urethane resin (for example, an acrylic resin) as a resin dispersant, or a self-dispersion pigment that does not require a resin dispersant.

  The resin dispersant is preferably a resin having a hydrophilic unit and a hydrophobic unit as constituent units. The resin dispersant is preferably an acrylic resin having at least an acrylic component such as a unit derived from (meth) acrylic acid or a unit derived from (meth) acrylic ester, and is a water-soluble acrylic resin. Further preferred. "Water-soluble acrylic resin" is dissolved in an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent, and can be present in an aqueous medium in a state that does not have a particle diameter when measured by a dynamic light scattering method. It means resin. In the following description, “(meth) acryl” means “acryl” and “methacryl”, and “(meth) acrylate” means “acrylate” and “methacrylate”.

  The hydrophilic unit is a unit having a hydrophilic group such as an acid group or a hydroxy group. The hydrophilic unit can be formed, for example, by polymerizing a monomer having a hydrophilic group. Specific examples of the monomer having a hydrophilic group include acidic monomers having a carboxy group such as (meth) acrylic acid, itaconic acid, maleic acid, and fumaric acid, and anionic monomers such as anhydrides and salts of these acidic monomers. Monomers having a hydroxy group such as 2-hydroxyethyl (meth) acrylate and 3-hydroxypropyl (meth) acrylate; ethylene oxide groups such as methoxy (mono, di, tri, poly) ethylene glycol (meth) acrylate; And the like. Examples of the cation constituting the salt of the anionic monomer include ions such as lithium, sodium, potassium, ammonium, and organic ammonium.

  The resin dispersant is preferably a resin having an acid value. For this reason, it is preferable to use resin containing the unit derived from said anionic monomer as a hydrophilic unit as a resin dispersing agent. The resin dispersant becomes water-soluble by being neutralized with a neutralizer such as hydroxide of alkali metal (lithium, sodium, potassium, etc.) or ammonia water.

  The hydrophobic unit is a unit having no hydrophilic group such as an acid group or a hydroxy group. The hydrophobic unit can be formed, for example, by polymerizing a monomer having a hydrophobic group. Specific examples of the monomer having a hydrophobic group include monomers having an aromatic ring such as styrene, α-methylstyrene, benzyl (meth) acrylate; ethyl (meth) acrylate, methyl (meth) acrylate, (iso) propyl (meth) And monomers having an aliphatic group such as acrylate, (n-, iso-, t-) butyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate.

  The content (% by mass) of the resin dispersant in the ink is preferably 0.1% by mass or more and 10.0% by mass or less, based on the total mass of the ink, and is 0.2% by mass or more and 4.0% by mass. More preferably, it is% or less.

As the self-dispersing pigment, one having an acid group bonded to the particle surface of the pigment directly or via another atomic group (-R-) can be used. Examples of the acid group include a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, and a phosphonic acid group. Examples of acid group counter ions include cations such as hydrogen atoms, alkali metals, ammonium (NH ₄ ), and organic ammonium. Examples of the other atomic group (—R—) include an alkylene group, an arylene group, an amide group, a sulfonyl group, an imino group, a carbonyl group, an ester group, an ether group, and a group obtained by combining these groups.

(First resin)
The ink of the present invention contains a block copolymer having block A, block B, and block C as the first resin. Block A is a polymer block composed of units derived from monomers having an aromatic ring. Examples of the monomer having an aromatic ring include benzyl (meth) acrylate, styrene, α-methylstyrene, and the like. Block B is a polymer block composed of units derived from (meth) acrylic acid esters. Examples of (meth) acrylic acid esters include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, and the like. The block C is a polymer block composed of units derived from (meth) acrylic acid. These monomers can be used individually by 1 type or in combination of 2 or more types. In this specification, “(meth) acrylic” means “acrylic” and “methacrylic”. The content (% by mass) of the first resin in the ink is preferably 0.1% by mass or more and 5.0% by mass or less, and 0.1% by mass or more and 0.5% by mass or less based on the total mass of the ink. More preferably, it is at most mass%.

  The proportion (mass%) of the block A in the first resin is preferably 50.0 mass% or less based on the total mass of the first resin. Since the block A is composed of units derived from a monomer having an aromatic ring, the block A is a polymer block that is rigid and can be strongly adhered to the pigment by π-π interaction. If the ratio of the block A in the first resin is more than 50.0% by mass, the rigid characteristics of the block A become remarkable, so that the first resin itself tends to be bulky. For this reason, the adhesiveness of the first resin to the pigment tends to be lowered, and the effect of improving the optical density of the image may be slightly lowered. The proportion (mass%) of the block A in the first resin is preferably 20.0 mass% or more based on the total mass of the first resin.

  The ratio (% by mass) of the block B in the first resin is preferably 20.0% by mass or more and 60.0% by mass or less based on the total mass of the first resin. Moreover, it is preferable that the ratio (mass%) of the block C which occupies for 1st resin is 10.0 to 40.0 mass% on the basis of 1st resin total mass.

  The content (% by mass) of the first resin in the ink is a mass ratio with respect to the content (% by mass) of the pigment, and is preferably 0.02 times or more and 0.50 times or less. If the mass ratio is less than 0.02 times, the amount of the first resin adsorbed on the pigment is reduced, and the effect of improving the optical density of the image may be slightly reduced. On the other hand, if the mass ratio is more than 0.50 times, the first resin tends to remain on a recording medium such as glossy paper, and the effect of improving the optical density of the image may be slightly reduced.

[Synthesis method]
The block copolymer used as the first resin can be synthesized according to a polymerization method that is generally used conventionally. Specific examples of the polymerization method include a living radical polymerization method and a living anion polymerization method.

[Analysis method]
The composition and molecular weight of the first resin can be analyzed by a conventionally known method. Further, the composition and molecular weight of the first resin can be confirmed by analyzing the sediment and the supernatant obtained by centrifuging the ink. Although the first resin can be analyzed even in the ink state, it is preferable to analyze the first resin extracted from the ink because the measurement accuracy can be improved. For example, an excess acid (such as hydrochloric acid) is added to the supernatant obtained by centrifuging the ink at 75,000 rpm to precipitate the resin. When chloroform is added to the precipitated resin, the urethane resin dissolves, and the first resin can be extracted by fractionating the insoluble matter. By analyzing the extracted first resin using a high temperature gas chromatography / mass spectrometer (high temperature GC / MS), the types of units constituting the block copolymer can be confirmed.

Moreover, molecular weight etc. can be confirmed by analyzing the extracted 1st resin quantitatively with a nuclear magnetic resonance method ( ^13C -NMR) or a Fourier-transform-type infrared spectrophotometer (FT-IR). . Furthermore, the acid value of the first resin can be measured by a titration method. In Examples described later, the resin was dissolved in tetrahydrofuran and measured by a potentiometric titration method using a potassium hydroxide ethanol titrant using an automatic potentiometric titrator (trade name “AT510”, manufactured by Kyoto Electronics Industry Co., Ltd.). The weight average molecular weight and number average molecular weight of the first resin can be measured by gel permeation chromatography (GPC). The measurement conditions for GPC are as follows.

Apparatus: Alliance GPC 2695 (manufactured by Waters)
Column: 4-column column of Shodex KF-806M (Showa Denko)
・ Mobile phase: Tetrahydrofuran (special grade)
・ Flow rate: 1.0 mL / min
・ Oven temperature: 40.0 ℃
-Sample solution injection volume: 0.1 mL
・ Detector: RI (refractive index)
Polystyrene standard sample: PS-1 and PS-2 (manufactured by Polymer Laboratories, molecular weight: 7,500,000, 2,560,000, 841,700, 377,400, 320,000, 210,500, 148,000 , 96,000, 59,500, 50,400, 28,500, 20,650, 10,850, 5,460, 2,930, 1,300, 580)

[Characteristic]
The weight average molecular weight (Mw) in terms of polystyrene of the first resin (block copolymer) measured by GPC is preferably 3,000 or more and 25,000 or less. If the weight average molecular weight of the first resin is less than 3,000, the first resin is small, so that it is difficult to remain on glossy paper, and the effect of improving the optical density of the image may be slightly reduced. On the other hand, if the weight average molecular weight of the first resin is more than 25,000, it may remain on a recording medium such as glossy paper and may become a factor causing internal scattering due to its bulk. For this reason, the effect of improving the optical density of the image may be slightly reduced.

  The molecular weight distribution value (Mw / Mn value) of the first resin is preferably 1.0 ≦ “Mw / Mn” ≦ 2.0. Mw means the polystyrene equivalent weight average molecular weight of the first resin measured by GPC, and Mn means the polystyrene equivalent number average molecular weight of the first resin measured by GPC. In principle, the value of Mw / Mn is 1.0 or more. The closer the Mw / Mn value is to 1.0, the more monodisperse. If the value of Mw / Mn is more than 2.0, the mixing ratio of the high molecular weight or low molecular weight block copolymer is large, so the effect of improving the optical density of the image may be slightly reduced.

  The acid value of the first resin is preferably 80 mgKOH / g or more and 250 mgKOH / g or less. When the acid value of the first resin is less than 80 mgKOH / g, it is likely to remain on a recording medium such as glossy paper due to low water solubility, and the effect of improving the glossiness of the image is slightly reduced, and the optical density There are cases where the effect of improving is slightly reduced. On the other hand, when the acid value of the first resin is more than 250 mgKOH / g, the hydrophilicity is high, and thus the first resin is difficult to be adsorbed on the pigment particle surface. In addition, since it is difficult to remain on the recording medium, the effect of improving the optical density of the image may be slightly reduced.

(Second resin)
The ink of the present invention contains a urethane resin having an acid value of 40 mgKOH / g or more as the second resin. The content (% by mass) of the second resin in the ink is preferably 0.1% by mass or more and 10.0% by mass or less, and 0.5% by mass or more and 3.0% by mass or less based on the total mass of the ink. More preferably, it is at most mass%. If the content of the second resin is less than 0.1% by mass, the effect of improving the optical density of an image recorded on a recording medium such as glossy paper may be slightly reduced. On the other hand, if the content of the second resin is more than 10.0% by mass, the effect of improving the optical density of an image recorded on a recording medium such as glossy paper may be slightly lowered.

  As the urethane resin, for example, a urethane resin having a unit derived from polyisocyanate, a polyol having no acid group, a polyol having an acid group, a polyamine, or the like can be used.

[Polyisocyanate]
Polyisocyanate is a compound having two or more isocyanate groups in its molecular structure. As the polyisocyanate, aliphatic polyisocyanate, aromatic polyisocyanate and the like can be used. The proportion (% by mass) of units derived from polyisocyanate in the urethane resin is preferably 10.0% by mass or more and 80.0% by mass or less.

  Aliphatic polyisocyanates include tetramethylene diisocyanate, hexamethylene diisocyanate, dodecamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, 2-methylpentane-1 , 5-diisocyanate, polyisocyanate having a chain structure such as 3-methylpentane-1,5-diisocyanate; isophorone diisocyanate, hydrogenated xylylene diisocyanate, 4,4′-dicyclohexylmethane diisocyanate, 1,4-cyclohexane diisocyanate, Polypropylene having a cyclic structure such as methylcyclohexylene diisocyanate and 1,3-bis (isocyanatomethyl) cyclohexane Cyanate; and the like.

  Aromatic polyisocyanates include tolylene diisocyanate, 2,2′-diphenylmethane diisocyanate, 2,4′-diphenylmethane diisocyanate, 4,4′-diphenylmethane diisocyanate, 4,4′-dibenzyl diisocyanate, 1,5-naphthylene diisocyanate. Examples include isocyanate, xylylene diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, α, α, α ′, α′-tetramethylxylylene diisocyanate. . Of these polyisocyanates, it is preferable to use an aliphatic polyisocyanate. Further, among the aliphatic polyisocyanates, those having a cyclic structure are preferable, and isophorone diisocyanate is more preferable.

[Polyol, polyamine]
A polyol is a compound having two or more hydroxy groups in its molecular structure. Examples of the polyol include a polyol having no acid group such as a polyether polyol, a polyester polyol, and a polycarbonate polyol; a polyol having an acid group; Polyamine is a compound having two or more amino groups in its molecular structure. The proportion (mol%) of units derived from polyol and polyamine in the urethane resin is preferably 10.0 mol% or more and 80.0 mol% or less, and preferably 20.0 mol% or more and 60.0 mol% or less. More preferably.

[Polyol having no acid group]
Examples of polyether polyols include addition polymers of alkylene oxides and polyols; glycols such as (poly) alkylene glycols; and the like. Examples of the alkylene oxide include ethylene oxide, propylene oxide, butylene oxide, α-olefin oxide and the like. Examples of polyols to be addition-polymerized with alkylene oxide include 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl- 1,5-pentanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 4,4-dihydroxyphenylpropane, 4,4-dihydroxy Diols such as phenylmethane, hydrogenated bisphenol A, dimethylolurea and derivatives thereof; glycerin, trimethylolpropane, 1,2,5-hexanetriol, 1,2,6-hexanetriol, pentaerythritol, trimethylolmelamine and derivatives thereof , Polyoxypropylene Triols such as polyol; and the like. Examples of glycols include tetramethylene glycol, hexamethylene glycol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol, (poly) tetramethylene glycol, (Poly) alkylene glycol such as neopentyl glycol; ethylene glycol-propylene glycol copolymer;

  Examples of the polyester polyol include acid esters. Examples of the acid component constituting the acid ester include aromatic dicarboxylic acids such as phthalic acid, naphthalenedicarboxylic acid, biphenyldicarboxylic acid, and tetrahydrophthalic acid; alicyclic dicarboxylic acids such as hydrogenated products of these aromatic dicarboxylic acids; Acid, succinic acid, tartaric acid, oxalic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, alkyl succinic acid, linolenic acid, maleic acid, fumaric acid, mesaconic acid, citraconic acid, itaconic acid, etc. An aliphatic dicarboxylic acid; and the like. These anhydrides, salts, derivatives (alkyl esters, acid halides) and the like can also be used as the acid component. Examples of the component that forms an ester with an acid component include polyols such as diol and triol; glycols such as (poly) alkylene glycol; Examples of the polyols and glycols include those exemplified as the components constituting the polyether polyol.

  As the polycarbonate polyol, a polycarbonate polyol produced by a known method can be used. Specific examples include alkanediol-based polycarbonate diols such as polyhexamethylene carbonate diol. Moreover, the polycarbonate diol etc. which are obtained by making carbonate components, such as alkylene carbonate, a diaryl carbonate, a dialkyl carbonate, and phosgene, and an aliphatic diol component react can be mentioned.

  The proportion (mol%) of the unit derived from the polyol having no acid group in the total amount of the units derived from the polyol in the urethane resin is preferably 1.0% or more and 100.0 mol% or less. . Moreover, it is more preferable that it is 5.0 mol% or more and 50.0 mol% or less, and it is especially preferable that it is 10.0 mol% or more and 30.0 mol% or less.

[Polyol having an acid group]
Examples of the polyol having an acid group include polyols having an acid group such as a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, and a phosphonic acid group. The acid group is preferably a carboxylic acid group. Examples of the polyol having a carboxylic acid group include dimethylolacetic acid, dimethylolpropionic acid, dimethylolbutanoic acid, and dimethylolbutyric acid. Of these, dimethylolpropionic acid and dimethylolbutanoic acid are preferable. The acid group of the polyol having an acid group may be in a salt form. Examples of the cation forming the salt include ions of alkali metals such as lithium, sodium and potassium; cations of organic amines such as ammonium ion and dimethylamine. Since the molecular weight of the polyol having a general acid group is about 400 at most, the unit derived from the polyol having an acid group basically becomes a hard segment of the urethane resin. The acid value of the urethane resin can be adjusted by the amount of acid group-containing diol used.

  The proportion (mol%) of units derived from polyol having an acid group in the total amount of units derived from polyol in the urethane resin is preferably 0.0 mol% or more and 100.0 mol% or less. . Moreover, it is more preferable that they are 30.0 mol% or more and 90.0 mol% or less, and it is especially preferable that they are 50.0 mol% or more and 90.0 mol% or less.

[Polyamine]
Polyamines include monoamines having multiple hydroxy groups such as dimethylolethylamine, diethanolmethylamine, dipropanolethylamine, dibutanolmethylamine; ethylenediamine, propylenediamine, hexylenediamine, isophoronediamine, xylylenediamine, diphenylmethanediamine, hydrogen Bifunctional polyamines such as added diphenylmethanediamine and hydrazine; trifunctional or higher functional polyamines such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, polyamide polyamine, and polyethylene polyimine; For convenience, compounds having a plurality of hydroxy groups and one “amino group, imino group” are also listed as “polyamines”. Since the molecular weight of polyamine is about 400 at most, the unit derived from polyamine is basically a hard segment of urethane resin. The proportion (mol%) of units derived from polyamine in the urethane resin is preferably 10.0 mol% or less, and more preferably 5.0 mol% or less. The proportion (mol%) of units derived from polyamine in the urethane resin may be 0.0 mol%.

[Crosslinking agent, chain extender]
In synthesizing the urethane resin, a crosslinking agent or a chain extender can be used. Usually, the crosslinking agent is used in the synthesis of the prepolymer, and the chain extender is used in performing the chain extension reaction on the prepolymer synthesized in advance. Basically, the crosslinking agent or chain extender can be appropriately selected from water, polyisocyanate, polyol, polyamine and the like according to the purpose such as crosslinking and chain extension. As the chain extender, those capable of crosslinking the urethane resin can also be used.

[Physical properties and properties of urethane resin]
[Acid value]
The acid value of the second resin (urethane resin) is 40 mgKOH / g or more. When the acid value of the urethane resin is less than 40 mgKOH / g, the solubility of the urethane resin in the ink is lowered and the emulsion tends to be in an emulsion state. For this reason, the optical density of the image becomes insufficient. The acid value of the second resin (urethane resin) is preferably 150 mgKOH / g or less.

  The acid value of the urethane resin can be measured by a titration method. In Examples described later, a urethane resin dissolved in tetrahydrofuran was prepared as a measurement sample. Then, by using a potentiometric automatic titration apparatus (trade name “AT510”, manufactured by Kyoto Denki Kogyo Co., Ltd.) equipped with a streaming potential titration unit (PCD-500), potentiometric titration with a potassium hydroxide ethanol titrant is used. The acid value was measured.

(Weight average molecular weight)
The polystyrene-reduced weight average molecular weight (Mw) of the second resin (urethane resin) measured by GPC is preferably 20,000 or less. If the weight average molecular weight of the urethane resin is more than 20,000, the second resin becomes too bulky and it may be difficult to sufficiently improve the adhesion between the ink dots, so the optical density of the image is improved. The effect may be slightly lower. The polystyrene equivalent weight average molecular weight (Mw) of the second resin (urethane resin) is preferably 5,000 or more.

  The weight average molecular weight of the urethane resin can be measured by GPC. In Examples described later, urethane resin dissolved in tetrahydrofuran was used as a measurement sample, and measurement was performed under the same conditions as those for measuring the molecular weight of the first resin (block copolymer) described above.

(Synthesis method)
The urethane resin can be synthesized according to a conventional general method for synthesizing a urethane resin. For example, a urethane resin can be synthesized according to the method shown below. The polyisocyanate, the polyol having no acid group, and the polyol having an acid group are reacted in an equivalent ratio such that the isocyanate group becomes excessive in the presence or absence of an organic solvent having a boiling point of 100 ° C. or less. As a result, a urethane prepolymer having an isocyanate group at the molecular end is synthesized. Next, neutralizing agents are used to neutralize acidic groups such as carboxylic acid groups and sulfonic acid groups in the synthesized urethane prepolymer. Thereafter, the urethane prepolymer neutralized with acidic groups is allowed to react in an aqueous solution containing a chain extender, and then the organic solvent remaining in the system is removed as necessary to obtain a urethane resin. be able to.

[Analysis method]
The composition of the urethane resin can be analyzed by the following method. First, a method for extracting urethane resin from ink will be described. In order to extract the urethane resin from the ink, an excess acid (such as hydrochloric acid) is added to the supernatant obtained by centrifuging the ink at 80,000 rpm to precipitate the resin. When chloroform is added to the precipitated resin, the urethane resin is dissolved, so that the second resin can be extracted from the liquid phase. In addition to chloroform, an organic solvent such as hexane that does not dissolve the pigment and block copolymer but dissolves the urethane resin may be used. Although the urethane resin can be analyzed even in the ink state, analysis of the urethane resin extracted from the ink is preferable because the measurement accuracy can be improved.

The separated urethane resin is dried and then dissolved in deuterated dimethyl sulfoxide (deuterated DMSO) and analyzed by proton nuclear magnetic resonance ( ¹ H-NMR). And from the position of the obtained peak, types, such as polyisocyanate, the polyol which does not have an acid group, the polyol which has an acid group, and a polyamine, can be confirmed. Furthermore, the composition ratio can be calculated from the ratio of the integrated values of the peaks. Further, the number average molecular weight can be calculated by analyzing by carbon nuclear magnetic resonance spectroscopy ( ¹³ C-NMR) and determining the number of repeating units derived from a polyol having no acid group. Even when analyzed by pyrolysis gas chromatography, the types of polyisocyanate, polyol, polyamine and the like can be confirmed.

(Aqueous medium)
The ink of the present invention is an aqueous ink containing an aqueous medium containing water. As water, it is preferable to use deionized water (ion exchange water). The content (% by mass) of water in the ink is preferably 10.0% by mass or more and 90.0% by mass or less, preferably 50.0% by mass or more and 90.0% by mass or less, based on the total mass of the ink. More preferably.

  The aqueous medium can further contain a water-soluble organic solvent. As the water-soluble organic solvent, monohydric alcohol, polyhydric alcohol, (poly) alkylene glycol, glycol ether, nitrogen-containing polar solvent, sulfur-containing polar solvent and the like can be used. The content (% by mass) of the water-soluble organic solvent in the ink is preferably 3.0% by mass or more and 50.0% by mass or less based on the total mass of the ink.

(Other additives)
In addition to the above-described components, the ink of the present invention is water-soluble at room temperature, such as polyhydric alcohols such as trimethylolpropane and trimethylolethane, and urea derivatives such as urea and ethyleneurea. An organic compound may be contained. Furthermore, in the ink of the present invention, a surfactant, a pH adjuster, a rust inhibitor, an antiseptic, an antifungal agent, an antioxidant, an anti-reduction agent, an evaporation accelerator, a chelating agent, and You may contain various additives, such as water-soluble resin.

(Ink physical properties)
The pH of the ink at 25 ° C. is preferably 5.0 or more and 10.0 or less, and more preferably 7.0 or more and 9.5 or less. The static surface tension of the ink at 25 ° C. is preferably 30 mN / m or more and 45 mN / m or less, and preferably 35 mN / m or more and 40 mN / m or less. The viscosity of the ink at 25 ° C. is preferably 1.0 mPa · s or more and 5.0 mPa · s or less.

<Ink cartridge>
The ink cartridge of the present invention includes ink and an ink storage unit that stores the ink. And the ink accommodated in this ink accommodating part is the ink of this invention demonstrated above. FIG. 1 is a cross-sectional view schematically showing an embodiment of the ink cartridge of the present invention. As shown in FIG. 1, an ink supply port 12 for supplying ink to the recording head is provided on the bottom surface of the ink cartridge. The inside of the ink cartridge is an ink storage portion for storing ink. The ink storage portion is composed of an ink storage chamber 14 and an absorber storage chamber 16, which communicate with each other via a communication port 18. The absorber housing chamber 16 communicates with the ink supply port 12. The ink storage chamber 14 stores liquid ink 20, and the absorber storage chamber 16 stores absorbers 22 and 24 that hold the ink in an impregnated state. The ink storage unit may have a form in which the entire amount of ink stored is held by an absorber without having an ink storage chamber for storing liquid ink. Further, the ink storage portion may have a form that does not have an absorber and stores the entire amount of ink in a liquid state. Further, the ink cartridge may be configured to have an ink storage portion and a recording head.

<Inkjet recording method>
The ink jet recording method of the present invention is a method of recording an image on a recording medium by discharging the ink of the present invention described above from an ink jet recording head. Examples of the method for ejecting ink include a method for imparting mechanical energy to the ink and a method for imparting thermal energy to the ink. In the present invention, it is particularly preferable to employ a method in which thermal energy is applied to the ink and the ink is ejected. Other than using the ink of the present invention, the steps of the ink jet recording method may be known.

  2A and 2B are diagrams schematically showing an example of an ink jet recording apparatus used in the ink jet recording method of the present invention. FIG. 2A is a perspective view of a main part of the ink jet recording apparatus, and FIG. 2B is a perspective view of a head cartridge. It is. The ink jet recording apparatus is provided with a conveying means (not shown) for conveying the recording medium 32 and a carriage shaft 34. A head cartridge 36 can be mounted on the carriage shaft 34. The head cartridge 36 includes recording heads 38 and 40, and is configured such that an ink cartridge 42 is set. While the head cartridge 36 is conveyed along the carriage shaft 34 in the main scanning direction, ink (not shown) is ejected from the recording heads 38 and 40 toward the recording medium 32. Then, the recording medium 32 is conveyed in the sub-scanning direction by a conveying unit (not shown), whereby an image is recorded on the recording medium 32.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further in detail, this invention is not limited at all by the following Example, unless the summary is exceeded. What is described as “parts” and “%” with respect to the component amounts is based on mass unless otherwise specified.

<Synthesis of block copolymer>
A four-necked flask equipped with a stirrer, thermometer, nitrogen gas inlet tube, and reflux tube was purged with nitrogen, and then 100.0 parts of dimethylformamide and 0.5 parts of pentamethyldiethylenetriamine were added. Monomer A of the type and amount shown in Table 1 and 0.07 part of a polymerization initiator (chloroethylbenzene) were added and heated to a temperature of 80 ° C. with stirring. Subsequently, copper (I) chloride was added to polymerize block A composed of units derived from monomer A. The molecular weight was monitored by molecular sieve column chromatography (GPC), and after the polymerization of monomer A was completed, the type and amount of monomer B shown in Table 1 were added to continue the polymerization.

  The molecular weight was monitored by GPC, and after the polymerization of monomer B was completed, the type and amount of monomer C shown in Table 1 were added to continue the polymerization. The monomer D was also added in the same manner to continue the polymerization. After stopping the polymerization, the carboxylic acid ester group was hydrolyzed with a methanol solution of sodium hydroxide to obtain a carboxylic acid group. 2.8 parts of a 35.0% aqueous hydrochloric acid solution was added, and the mixture was stirred at 25 ° C. for 10 minutes and then filtered. The copolymer was washed with pure water three times and dried to obtain block copolymers 1 to 21.

Using a GPC (manufactured by Tosoh Corporation) equipped with a differential refractive index detector, tetrahydrofuran was used as a developing solvent, and the polystyrene equivalent weight average molecular weight and number average molecular weight of the obtained block copolymer were measured. Moreover, < ¹ > H-NMR was measured and it confirmed that TMS ester was hydrolyzed by presence of the chemical shift (peak) of a carboxylic acid group. Furthermore, ¹ H-NMR was measured to calculate the constitutional ratio of monomers constituting each block. In addition, a measurement sample was prepared by dissolving the block copolymer in tetrahydrofuran. Then, the acid value of the block copolymer was measured using a potentiometric automatic titrator (trade name “AT510”, manufactured by Kyoto Denshi Kogyo Co., Ltd.) using a 0.5 mol / L potassium hydroxide ethanol solution as a titration reagent. Various properties of the block copolymer are shown in Table 2. Moreover, the detail of each component in Table 1 and 2 is shown below.

BzMA: benzyl methacrylate St: styrene αmSt: α-methylstyrene BzA: benzyl acrylate BMA: n-butyl methacrylate BA: n-butyl acrylate MMA: methyl methacrylate TMS-MAA: trimethylsilyl methacrylate TMS-AA: acrylic Acid trimethylsilyl MAA: methacrylic acid AA: acrylic acid

  After the obtained block copolymer was dissolved in tetrahydrofuran, an aqueous potassium hydroxide solution was added so that the acid group neutralization rate of the block copolymer was 80% on a molar basis. After adding an appropriate amount of water and stirring, tetrahydrofuran was removed under reduced pressure. An appropriate amount of water was added to obtain liquids each containing block copolymers 1 to 21. The content of the block copolymer in each liquid was 20.0%.

<Synthesis of random copolymer>
A four-necked flask equipped with a stirrer, a thermometer, a nitrogen gas introduction tube, and a reflux tube was prepared, and the inside was replaced with nitrogen. 100 parts of tetrahydrofuran, 10.4 parts of styrene, 4.7 parts of n-butyl methacrylate, 4.5 parts of methacrylic acid, and 0.16 part of azobisisobutyronitrile were added, and the system temperature was 70 ° C. with stirring. Polymerization was carried out by heating so that A potassium hydroxide aqueous solution was added to the obtained aqueous solution so that the neutralization rate of the acid groups was 80% on a molar basis. Further, an appropriate amount of water was added and stirred, and then tetrahydrofuran was removed under reduced pressure. Further, water was added to obtain a liquid containing a random copolymer. The content of the random copolymer in the obtained liquid was 20.0%. The acid value of the obtained random copolymer was 150 mgKOH / g, the weight average molecular weight was 15,000, and the molecular weight distribution (Mw / Mn) was 2.1.

<Synthesis of urethane resin>
In a four-necked flask equipped with a thermometer, a stirrer, a nitrogen introduction tube, and a reflux tube, the types and amounts of polyisocyanate shown in Table 3, a polyol having no acid group, and a polyol having an acid group were placed. Further, 0.02 part of dibutyltin dilaurate and 120 parts of methyl ethyl ketone were added and reacted at 80 ° C. for 6 hours in a nitrogen gas atmosphere. Next, polyamines of the types and amounts shown in Table 3 were added and reacted at 80 ° C. until the desired weight average molecular weight was obtained. After cooling to 40 ° C., methanol and ion-exchanged water were added, and an aqueous potassium hydroxide solution was added while stirring at high speed with a homomixer. The mixture was heated and decompressed to distill off methyl ethyl ketone to obtain liquids containing urethane resins 1 to 9, respectively. The content of the urethane resin in each liquid was 20.0%. Table 3 shows the weight average molecular weight and acid value of the obtained urethane resin. Moreover, the detail of each component in Table 3 is shown below.

IPDI: Isophorone diisocyanate PPG2000: Polypropylene glycol (number average molecular weight 2,000)
PEG2000: Polyethylene glycol (number average molecular weight 2,000)
PTMG2000: Polytetramethylene glycol (number average molecular weight 2,000)
PC2000: Polycarbonate polyol (number average molecular weight 2,000)
PES2000: Polyester polyol (number average molecular weight 2,000)
DMPA: dimethylolpropionic acid EDA: ethylenediamine

<Preparation of pigment dispersion>
(Pigment dispersion 1)
A pigment (CI Pigment Blue 15: 3) 10.0 g, a water-soluble resin 3.0 g, and water 87.0 g were mixed to obtain a mixture. As the water-soluble resin, a styrene-acrylic acid copolymer having an acid value of 120 mgKOH / g and a weight average molecular weight of 10,000 neutralized with a 10.0% aqueous potassium hydroxide solution was used. The mixture was dispersed for 1 hour using a sand grinder, and then centrifuged to remove impurities, followed by pressure filtration with a microfilter (manufactured by Fuji Film) having a pore size of 3.0 μm. Next, the pigment dispersion 1 was obtained by adjusting the concentration of the pigment solids. The obtained pigment dispersion 1 contains a pigment dispersed with a water-soluble resin (resin dispersant), the pigment content is 10.0%, and the resin dispersant content is 3.0%. Met.

(Pigment dispersion 2)
The pigment is C.I. I. A pigment dispersion 2 was obtained in the same manner as in the case of the pigment dispersion 1 except that the pigment red 122 was used. The pigment dispersion 2 contains a pigment dispersed with a water-soluble resin (resin dispersant), and the pigment content was 10.0% and the resin dispersant content was 3.0%. .

(Pigment dispersion 3)
The pigment is C.I. I. A pigment dispersion 3 was obtained in the same manner as in the case of the pigment dispersion 1 except that the pigment yellow 74 was used. The pigment dispersion 3 contains a pigment dispersed with a water-soluble resin (resin dispersant), and the pigment content was 10.0% and the resin dispersant content was 3.0%. .

(Pigment dispersion 4)
A pigment dispersion 4 was obtained in the same manner as in the case of the pigment dispersion 1 except that the pigment was changed to carbon black. The pigment dispersion 4 contains a pigment dispersed with a water-soluble resin (resin dispersant), and the pigment content was 10.0% and the resin dispersant content was 3.0%. .

<Preparation of ink>
Each component shown in Tables 4-1 to 4-3 was mixed and sufficiently stirred, and then pressure filtration was performed with a microfilter (manufactured by Fuji Film) having a pore size of 3.0 μm to prepare each ink. “Acetyleneol E100” in Tables 4-1 to 4-3 is a trade name of a nonionic surfactant (acetylene glycol ethylene oxide adduct) manufactured by Kawaken Fine Chemicals. The lower part of Table 4 shows the ink characteristics.

<Evaluation>
(Optical density)
Each of the prepared inks was filled into an ink cartridge, and mounted on an ink jet recording apparatus (trade name “PIXUS Pro10”, manufactured by Canon Inc.) that discharges ink from the recording head by the action of thermal energy. In the present embodiment, the recording duty when the applied amount of ink per 600 dpi × 600 dpi is 16.0 ng is defined as 100%. The recording conditions were a temperature of 23 ° C. and a relative humidity of 55%. A solid image of 2 cm × 2 cm having a recording duty of 100% was recorded on A4 size glossy paper (trade name “Canon Photo Paper / Glossy Gold GL-101”, manufactured by Canon). Thereafter, the optical density of the image was measured using a fluorescence spectral densitometer (trade name “FD-7”, manufactured by Konica Minolta). On the other hand, a comparative ink having the same composition as each ink is prepared except that the portion not containing the block copolymer and the urethane resin is replaced with pure water, and a solid image is recorded under the same conditions as above. At the same time, the optical density of the image was measured. Then, the optical density of the image recorded with each ink was compared with the optical density of the image recorded with the comparative ink, and the optical density of the image was evaluated according to the following evaluation criteria. The evaluation results are shown in Table 5. In the present invention, in the evaluation criteria shown below, “AA”, “A”, and “B” are acceptable levels, and “C” is an unacceptable level.
AA: The optical density increased by 0.10 or more.
A: The optical density increased by 0.05 or more and less than 0.10.
B: The optical density increased by 0.02 or more and less than 0.05.
C: The increase in optical density was less than 0.02, and the difference in optical density was hardly understood.

Claims (7)

A water-based ink containing a pigment, a first resin, and a second resin,
The first resin includes a block A composed of units derived from a monomer having an aromatic ring, a block B composed of units derived from a (meth) acrylic acid ester, and (meth) acrylic acid. A block copolymer having a block C composed of derived units,
The water-based ink, wherein the second resin is a urethane resin having an acid value of 40 mgKOH / g or more.   2. The water-based ink according to claim 1, wherein a ratio (% by mass) of the block A in the first resin is 50.0% by mass or less based on the total mass of the first resin.   The water-based ink according to claim 1 or 2, wherein the acid value of the first resin is 80 mgKOH / g or more and 250 mgKOH / g or less.   The water-based ink according to any one of claims 1 to 3, wherein the second resin has a weight average molecular weight of 20,000 or less.   The water-based ink according to any one of claims 1 to 4, wherein the first resin has a weight average molecular weight of 3,000 or more and 25,000 or less. An ink cartridge comprising ink and an ink containing portion for containing the ink,
An ink cartridge, wherein the ink is the water-based ink according to any one of claims 1 to 5. An inkjet recording method for recording an image on a recording medium by discharging ink from an inkjet recording head,
An ink jet recording method, wherein the ink is the water-based ink according to any one of claims 1 to 5.

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