JP2018076400A - Aqueous ink, ink cartridge, and inkjet recording method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aqueous ink having such properties that a development time for marker pen resistance is reduced, an image having excellent marker pen resistance can be recorded and excellent recovery property of an ink from a solidified state is obtained.SOLUTION: An inkjet aqueous ink comprising a pigment, an urethane resin and a water-soluble organic solvent is provided, in which the urethane resin has units respectively derived from a polyisocyanate and a polyol comprising a polyol having no acid group. In the polyol, a proportion (mol%) of polyol having an acid group is 10 mol% or less. The water-soluble organic solvent comprises a first water-soluble organic solvent having a specific permittivity of 30.0 or less.SELECTED DRAWING: None

Description

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

  In recent years, plain paper or the like is used as a recording medium, and the ink jet recording method is also used for printing business texts including characters and charts, and the frequency of use for such applications has increased remarkably. In such applications, a high level of color developability and fastness (resistance to light, ozone gas, water, etc.) is required, so inks using pigments as pigments (pigment inks) must be used. There are many.

  The reason why the color developability of the image recorded with the pigment ink is higher than the ink using the dye as the color material is that the amount of the color material present on the surface of the recording medium is large. This is because the dye penetrates into the inside of the recording medium, while the pigment has the property of rapidly agglomerating due to the process in which the ink is applied to the recording medium and the evaporation of the liquid component that occurs after the ink is applied. is there. However, in pigment inks, pigments that are coloring materials are likely to be present on the surface of a recording medium, so if a recorded image is immediately traced with a marker pen, the image and the marker pen are contaminated. It has a problem of low nature.

  In order to improve image characteristics and the like recorded with pigment ink, it has been studied to add a urethane resin to the ink (see Patent Documents 1 and 2).

JP 2008-179657 A JP 2008-266595 A

  The present inventors have examined the pigment ink again. When an image is recorded with the inks described in Patent Documents 1 and 2, the marker resistance of the image does not develop early after recording, and the level of the marker resistance of the image is still insufficient, and there is room for further improvement. Turned out to be.

  Furthermore, when the inks of Patent Documents 1 and 2 are left in a state where they are mounted on an ink jet recording apparatus for a long period of time, depending on the type of water-soluble organic solvent in the ink, along with the evaporation of water in the vicinity of the ejection port of the recording head It was found that the ink fixing / recovering property was insufficient.

  Accordingly, an object of the present invention is to provide a water-based ink that can shorten the time required for the development of marker resistance, record an image excellent in marker resistance, and is excellent in adhesion recovery. 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, the ink of the present invention is a water-based inkjet ink containing a pigment, a urethane resin, and a water-soluble organic solvent, wherein the urethane resin includes a polyisocyanate and a polyol containing a polyol having no acid group. The proportion (mol%) of the polyol having an acid group in the polyol is 10 mol% or less, and the water-soluble organic solvent has a relative dielectric constant at a temperature of 25 ° C. The present invention relates to a water-based ink containing a first water-soluble organic solvent of 30.0 or less.

  The present invention also relates to an ink cartridge comprising an ink and an ink storage portion that stores the ink, wherein the ink is the water-based ink.

  The present invention is also an ink jet recording method for recording an image on a recording medium by ejecting ink from an ink jet recording head, wherein the ink is a water-based ink having the above-described configuration. Regarding the method.

  ADVANTAGE OF THE INVENTION According to this invention, the time required for expression of marker resistance is shortened, an image excellent in marker resistance is recorded, and an aqueous ink excellent in ink fixation and recovery, an ink cartridge using the aqueous ink, and an inkjet A recording method 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 may be dissociated into ions in the ink, but for convenience, it is expressed as “contains a salt”. In addition, water-based ink for inkjet may be simply referred to as “ink”. The physical property values are values at a temperature of 25 ° C. unless otherwise specified.

  A urethane resin is a resin synthesized using (poly) isocyanate in a broad sense. A urethane resin generally used for water-based inks for inkjet is synthesized using a polyisocyanate and a component (polyol or polyamine) that reacts with the polyisocyanate, and a crosslinking agent or a chain extender is also used as necessary. Urethane resins synthesized using such components are mainly composed of two segments, a hard segment and a soft segment.

  The hard segment is composed of units derived from a compound having a relatively low molecular weight, such as polyisocyanate, polyamine or polyol having an acid group, and a crosslinking agent or chain extender. Since the hard segment has many urethane bonds, and the hard segment portion tends to be dense due to hydrogen bonds between the urethane bonds, the hard segment mainly contributes to the strength of the urethane resin. On the other hand, the soft segment is composed of units derived from a compound having a relatively large molecular weight, such as a polyol having no acid group. Since the soft segment is less dense than the hard segment, the soft segment mainly contributes to the flexibility of the urethane resin. As described above, the urethane resin has both strength and flexibility and exhibits high elasticity.

  First, in order to shorten the time required for the expression of marker resistance (marker resistance expression time), the present inventors examined the configuration of the urethane resin. When the ink adheres to the recording medium and the water in the ink evaporates, the water present in the vicinity of the resin is separated, and the hydrophobic interaction between the hydrophobic portion of the resin and the pigment particle surface causes the resin to become a pigment. By covering with, the marker resistance of the image is improved. In this process, the marker resistance of the image is manifested by the separation of water present in the vicinity of the resin.

  However, since the urethane resin has a urethane bond (—NH—CO—) having a strong hydrogen bonding force, water tends to exist in the vicinity of the urethane resin. Furthermore, in the urethane resin having an acid group, the urethane resin easily spreads due to repulsion between the acid groups, and water tends to exist around the acid group. Immediately after the ink adheres to the recording medium, even if a part of the water present in the vicinity of the urethane resin is separated, a large amount of water is still present in the vicinity of the urethane resin. Therefore, the marker resistance of the image does not appear early.

  Therefore, it was decided to use a urethane resin with as few acid groups as possible. That is, the ink of the present invention contains a urethane resin in which the proportion of the polyol having an acid group is 10 mol% or less in the polyol of the resin. Since this urethane resin has few acid groups, water leaves quickly. Immediately after the ink adheres to the recording medium and the water in the ink evaporates, the water quickly leaves the urethane resin, so that the marker resistance of the image is developed early.

  However, if the ink containing urethane resin with reduced acid groups as much as possible is filled up to the discharge port of the recording head, if the device is left for a long period of time, the urethane resin will evaporate due to the evaporation of water in the ink near the discharge port. Agglomerates with the pigment. As a result, it was found that the viscosity of the ink was increased and the ink fixing recovery property could not be obtained. The reason is as follows.

  Urethane resins with as few acid groups as possible have few units having acid groups. For this reason, when the water in the ink evaporates, the distance between the urethane resins is reduced, and the urethane resin interacts with the polyol. When the urethane resin is aggregated, the pigment is entrained to form a large aggregate, so that the ink is thickened and fixed to the ejection port. Even if the recovery operation is performed, the ink is fixed near the ejection port, and thus the ink fixing recovery property cannot be obtained.

Therefore, the inventors of the present invention, when the water-soluble organic solvent contained in the ink together with the urethane resin with reduced acid groups as much as possible contains the first water-soluble organic solvent having a relative dielectric constant of 30.0 or less, It was found that agglomeration was suppressed and ink fixing recovery was obtained.
When the relative dielectric constant exceeds 30.0, the hydrogen atom and oxygen atom of the polyol are difficult to polarize to δ ⁺ and δ ⁻ , respectively, and the polyol interacts and becomes easily entangled. The entangled polyol entrains the pigment and becomes a large agglomerate, so that the ink fixing recovery property cannot be obtained.

  Since there is a lot of water in the ink in the vicinity of the ejection port and the resin is less likely to aggregate, the first water-soluble organic solvent can suppress the aggregation of the resin. On the other hand, in the recording medium, the amount of water is less than in the vicinity of the discharge port and the resin is likely to aggregate. Therefore, even if the first water-soluble organic solvent is present, it is difficult to suppress the aggregation of the resin. If the urethane resin hardly penetrates into the recording medium together with the water in the ink and the urethane resin tends to remain on the recording medium, the water can be quickly separated from the urethane resin by using a urethane resin with reduced acid groups as much as possible. Therefore, the marker resistance of the image is developed early regardless of the presence or absence of the first water-soluble organic solvent in the ink.

  When the ink contains a urethane resin having a reduced acid group as much as possible and the first water-soluble organic solvent, the marker resistance is not only exhibited at an early stage, but also the marker resistance level is improved. Since there are few polyols which have an acid group, the hydrophobic part of a urethane resin and the particle surface of a pigment are easy to carry out a hydrophobic interaction. Thereby, since the urethane resin tends to be present in the vicinity of the pigment, the urethane resin can cover the pigment. However, since there are few polyols which have an acid group, it interacts between polyols and a urethane resin tends to aggregate. When the ink contains the first water-soluble organic solvent, aggregation of the urethane resin is suppressed, and the resin can uniformly coat the pigment. This improves the marker resistance of the image.

When the relative dielectric constant exceeds 30.0, the hydrogen atoms and oxygen atoms of the polyol are difficult to polarize to δ ⁺ and δ ⁻ , respectively, so that the polyol interacts and the urethane resin aggregates. Since the urethane resin cannot uniformly cover the pigment, the marker resistance of the image cannot be obtained.

<Ink>
The ink of the present invention is a water-based ink containing a pigment, a urethane resin, and a water-soluble organic solvent. Hereinafter, “(meth) acrylic acid” and “(meth) acrylate” represent “acrylic acid, methacrylic acid” and “acrylate, methacrylate”.

(Pigment)
The ink of the present invention contains a pigment such as an inorganic pigment or an organic pigment. Examples of the pigment species include inorganic pigments such as carbon black, calcium carbonate, and titanium oxide; organic pigments such as azo, phthalocyanine, and quinacdrine. In addition to pigments, dyes may be used in combination for purposes such as toning. The content (% by mass) of the pigment in the ink is preferably 0.5% 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. More preferably.

  Examples of the pigment dispersion method include a resin dispersion pigment using a resin dispersant and a self-dispersion pigment that does not require a resin dispersant.

  As the resin dispersant used for the resin-dispersed pigment, any known (co) polymer that can be used for ink-jet ink can be used. Suitable resin dispersants include copolymers (such as acrylic resins) having hydrophilic units and hydrophobic units as described below. Examples of the hydrophilic unit include units derived from hydrophilic monomers such as (meth) acrylic acid and salts thereof. Hydrophobic units include monomers having an aromatic ring such as styrene and its derivatives, benzyl (meth) acrylate; monomers having an aliphatic group such as (meth) acrylic acid ester Examples include units derived from the body.

As the self-dispersing pigment, one having an anionic group bonded to the particle surface of the pigment directly or via another atomic group (-R-) can be used. Examples of the anionic _group, -COOM, -SO 3 M, and the like _-PO 3 _{M 2.} Examples of M include a hydrogen atom; an alkali metal; ammonium (NH ₄ ); and an 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;

  Among these, it is preferable to use a self-dispersing pigment. The resin-dispersed pigment has less exposure of the pigment particle surface than the self-dispersed pigment. Therefore, the hydrophobic portion of the urethane resin and the particle surface of the pigment are less likely to interact with each other in a hydrophobic manner, and the urethane resin is less likely to coat the pigment. Thereby, the marker resistance of the image may not be sufficiently obtained.

(Urethane resin)
As described above, the urethane resin generally used for inkjet ink is synthesized using at least a polyisocyanate and a component (polyol or polyamine) that reacts with the polyisocyanate, and if necessary, a crosslinking agent or a chain extender. Is also used. The urethane resin used in the ink of the present invention has units derived from each of a polyisocyanate and a polyol containing a polyol having no acid group. In the present invention, the “unit” for the urethane resin refers to a repeating unit derived from one monomer. Hereinafter, each monomer which becomes a structural unit of a urethane resin is demonstrated. In addition, in order to exhibit the effect | action by a urethane resin efficiently, it is not much preferable to set it as urethane resin (what is called urethane-acrylic composite resin) in which the acrylic resin chain is incorporated. Moreover, it is not so preferable to use an active energy ray-curable urethane resin, that is, a urethane resin having a polymerizable group.

[Polyisocyanate]
The “polyisocyanate” in the present invention means a compound having two or more isocyanate groups in the molecule in order to react with a polyol or polyamine. The proportion of units derived from polyisocyanate in the resin is preferably 10 mol% or more and 80 mol% or less. Examples of the polyisocyanate include aliphatic and aromatic polyisocyanates.

  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-methyl-1,5-pentane 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.

  Among these, the polyisocyanate is preferably an aliphatic polyisocyanate, and more preferably at least one selected from the group consisting of isophorone diisocyanate and hexamethylene diisocyanate.

[Polyol]
A polyol can be used as a component which becomes a unit constituting the urethane resin by the reaction with the polyisocyanate. “Polyol” in the present invention means a compound having two or more hydroxy groups in the molecule, such as polyether polyol, polyester polyol, polycarbonate polyol and the like having no acid group; Can be mentioned. A polyol can use 1 type, or 2 or more types as needed. The proportion (mol%) of units derived from polyol in the resin is preferably 10 mol% or more and 80 mol% or less.

[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 that undergo addition polymerization 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 Diols such as dihydroxyphenylmethane, hydrogenated bisphenol A, dimethylolurea and derivatives thereof; glycerin, trimethylolpropane, 1,2,5-hexanetriol, 1,2,6-hexanetriol, pentaerythritol, trimethylolmelamine and Its derivatives, polyoxypropy Triols such as Ntorioru; 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; and the like.

  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 aromatic dicarboxylic acids; malonic 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. 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 above 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, diaryl carbonate, and dialkyl carbonate, and phosgene, and an aliphatic diol component react are mentioned.

  Especially, it is preferable that the polyol which does not have an acid group contains polyether polyol. Polyester polyols and polycarbonate polyols are less hydrophilic than polyether polyols. For this reason, when the urethane resin aggregates due to the interaction of the polyol in the urethane resin, the pigment is entrained and a large aggregate is generated, so that the viscosity of the ink is increased and the ink fixing / recovering property may not be sufficiently obtained. Furthermore, the polyether polyol preferably contains polyethylene glycol or polypropylene glycol having a small number of carbon atoms and higher hydrophilicity.

  The proportion (mol%) of the polyol having no acid group in the polyol is preferably 90 mol% or more, and more preferably 100 mol%.

[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 cations forming the salt include ions of alkali metals such as lithium, sodium and potassium, ammonium ions, and cations of organic amines such as dimethylamine. Can be mentioned. Among these, the polyol having an acid group is preferably a polyol having a carboxylic acid group, and more preferably dimethylolpropionic acid. In addition, since the molecular weight of the polyol which has a general purpose acid group is about 400 at the highest, the unit derived from the polyol which has an acid group becomes a hard segment of a urethane resin fundamentally.

  The proportion (mol%) of the polyol having an acid group in the polyol is 10 mol% or less, and preferably 0 mol%. That is, the polyol is preferably only a polyol having no acid group. When a unit derived from a polyol having an acid group is present, water tends to be present in the vicinity of the urethane resin, so that the marker resistance of the image may be difficult to express early. Furthermore, when there is a unit derived from a polyol having an acid group, the hydrophobic part of the urethane resin and the particle surface of the pigment are less likely to interact with each other, so that the urethane resin is less likely to coat the pigment. Thereby, the marker resistance of the image may not be sufficiently obtained.

[Chain extender, Crosslinker]
A crosslinking agent or a chain extender may be used for the urethane resin. 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, as a crosslinking agent or a chain extender, depending on the purpose such as crosslinking or chain extension, in addition to water, the polyisocyanate and polyol mentioned above, a polyamine and the like can be appropriately selected and used. Can do. Examples of polyamines include ethylenediamine, propylenediamine, hexylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, isophoronediamine, xylylenediamine, diphenylmethanediamine, hydrogenated diphenylmethanediamine, hydrazine, polyamide polyamine, and polyethylene polyimine. It is done. In addition, since the molecular weight of general-purpose polyamine is about 400 at most as well as the polyol having general-purpose acid groups, the unit derived from polyamine is basically a hard segment of urethane resin. As the chain extender, those capable of crosslinking the urethane resin can also be used.

[Content]
The content (% by mass) of the urethane 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 4.0% by mass based on the total mass of the ink. More preferably, it is as follows. Further, the content (mass%) of the urethane resin is a mass ratio with respect to the content (mass%) of the pigment, and is preferably 0.1 times or more and 2.0 times or less. If the ratio is less than 0.1 times, the amount of the urethane resin is too small relative to the pigment, so that the marker resistance of the image may not be sufficiently obtained. When the ratio exceeds 2.0 times, since the urethane resin is more than the pigment, the urethane resin is likely to agglomerate between the urethane resins, and the ink fixing / recovering property may not be sufficiently obtained.

[Synthesis method]
As a method for synthesizing the urethane resin, any of those conventionally conventionally used as a method for synthesizing the urethane resin can be used. For example, the following method is mentioned. A prepolymer is synthesized using a polyisocyanate and a compound (polyol or polyamine) that reacts with the polyisocyanate. At this time, if necessary, an organic solvent having a boiling point of 100 ° C. or less may be used, and the acid group of the prepolymer is neutralized using a neutralizing agent. Thereafter, a prepolymer is added to a liquid containing a chain extender or a crosslinking agent to carry out a chain extension reaction or a crosslinking reaction. Next, when an organic solvent is used, it is removed to obtain a urethane resin.

  Examples of neutralizers include organic bases such as N, N-dimethylethanolamine, N, N-diethylethanolamine, diethanolamine, triethanolamine, trimethylamine, and triethylamine; inorganic bases such as sodium hydroxide, potassium hydroxide, and ammonia; Etc. The neutralizing agent is preferably used in an amount of 0.5 to 1.0 mol, more preferably 0.8 to 1.0 mol, per 1 mol of acidic groups in the prepolymer. Outside this range, the liquid containing the urethane resin may become unstable and increase in viscosity, and the workability of ink preparation may be slightly reduced.

  The number of reactive groups (isocyanate group, hydroxy group, amino group, imino group, etc.) per molecule of the compound (polyisocyanate, polyol, polyamine, etc.) used for the synthesis of the urethane resin matches the desired characteristics of the urethane resin. To decide. For example, a compound having one reactive group per molecule becomes a unit present at the end of the urethane resin. In addition, a compound having two or more reactive groups per molecule becomes a unit existing at a position sandwiched between other units constituting the urethane resin. Among them, a compound having three or more reactive groups per molecule is It becomes a unit for crosslinking urethane resin. When it is desired to crosslink the urethane resin, a unit derived from a compound having three or more reactive groups per molecule may be used as a constituent unit depending on the desired degree of crosslinking. On the contrary, when it is not desired to crosslink the urethane resin, only a unit derived from a compound having two reactive groups per molecule may be used as a constituting unit.

[Analysis method]
The composition of the urethane resin can be analyzed by the following method. First, a method for extracting the urethane resin from the ink containing the urethane resin will be described. Specifically, an excess acid (such as hydrochloric acid) is added to the supernatant obtained by centrifuging the ink at 80,000 rpm to extract the precipitated urethane resin. Moreover, urethane resin can also be fractionated by drying the said supernatant liquid. In addition, the urethane resin can be extracted from the ink using an organic solvent (such as hexane) that does not dissolve the pigment but dissolves the urethane resin. In addition, although analysis can also be performed from ink, more accurate analysis can be performed by using the urethane resin (solid content) extracted by the above-described method.

The urethane resin collected as described above is dried and then dissolved in deuterated dimethyl sulfoxide to prepare a sample to be measured. Then, for this sample, it can be confirmed from the position of peak obtained by performing an analysis by proton nuclear magnetic resonance method ^{(1 H-NMR),} a polyisocyanate, a polyol, a type, such as a polyamine. Furthermore, the composition ratio can also be calculated from the ratio of the integrated values of the chemical shift peaks of the respective components. Moreover, even if the urethane resin is analyzed by pyrolysis gas chromatography, the types of polyisocyanate, polyol, polyamine, and the like can be confirmed. Furthermore, it can analyze by carbon nuclear magnetic resonance spectroscopy (< ¹³ > C-NMR), calculates | requires the repeating number of the unit unit of the polyol which does not have an acid group, and can calculate a number average molecular weight.

  Furthermore, the dried acid precipitate is dissolved in tetrahydrofuran, and the ratio of the polyol having an acid group in the polyol can be measured by potentiometric titration using an ethanol titration solution of potassium hydroxide.

(Water-soluble organic solvent)
Usually, the “water-soluble organic solvent” refers to a liquid, but in the present invention, the water-soluble organic solvent includes those that are solid at a temperature of 25 ° C. Specific examples of the water-soluble organic solvent include those shown below (the numerical values in parentheses represent the relative dielectric constant at a temperature of 25 ° C.). 1 to 4 carbon atoms such as methyl alcohol (33.1), ethyl alcohol (23.8), n-propyl alcohol, isopropyl alcohol (18.3), n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol Monohydric alcohols. 1,2-propanediol (28.8), 1,3-butanediol (30.0), 1,4-butanediol (31.1), 1,5-pentanediol (27.0), 1, Such as 2-hexanediol (14.8), 1,6-hexanediol (7.1), 2-methyl-1,3-propanediol, 3-methyl-1,5-pentanediol (23.9), etc. Dihydric alcohols. Polyhydric alcohols such as 1,2,6-hexanetriol (28.5), glycerin (42.3), trimethylolpropane (33.7) and trimethylolethane. Alkylene glycols such as ethylene glycol (40.4), diethylene glycol (31.7), triethylene glycol (22.7), tetraethylene glycol, butylene glycol, hexylene glycol and thiodiglycol; Glycol ethers such as diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether (9.8). Polyalkylene glycols having a number average molecular weight of 200 to 1,000, such as polyethylene glycol (11.5) having a number average molecular weight of 600, polyethylene glycol (4.6) having the same number, and polypropylene glycol. 2-pyrrolidone (28.0), N-methyl-2-pyrrolidone (32.0), 1,3-dimethyl-2-imidazolidinone, N-methylmorpholine, urea (110.3), ethylene urea (49 .7) and nitrogen-containing compounds such as triethanolamine (31.9). Sulfur-containing compounds such as dimethyl sulfoxide (48.9) and bis (2-hydroxyethylsulfone); The water-soluble organic solvent contained in the ink preferably has a relative dielectric constant of 3.0 or more, and preferably has a vapor pressure at a temperature of 25 ° C. lower than that of water.

The relative dielectric constant of the water-soluble organic solvent can be measured under the condition of a frequency of 10 kHz using a dielectric constant meter (for example, BI-870, manufactured by BROOKHAVEN INSTRUMENTS CORPORATION). The relative permittivity of a solid water-soluble organic solvent at a temperature of 25 ° C. can be calculated from the following formula (A) by measuring the relative permittivity of a 50.0 mass% aqueous solution.
ε _sol = 2ε _50% −ε _water (1)
ε _sol : relative dielectric constant of a water-soluble organic solvent solid at a temperature of 25 ° C. ε _50% : relative dielectric constant of a 50.0% by mass aqueous solution of the water-soluble organic solvent solid at a temperature of 25 ° C. ε _water : relative dielectric constant of _water The reason for calculating the relative dielectric constant of a solid water-soluble organic solvent at a temperature of 25 ° C. from the relative dielectric constant of a 50.0 mass% aqueous solution is as follows. Among the water-soluble organic solvents that are solid at a temperature of 25 ° C., there are those that can be constituents of ink, and it is difficult to prepare a high-concentration aqueous solution exceeding 50.0 mass%. On the other hand, in a low-concentration aqueous solution of 10.0% by mass or less, the relative dielectric constant of water is dominant, and it is difficult to obtain a certain (effective) relative dielectric constant value of the water-soluble organic solvent. As a result, the inventors have studied that most of the water-soluble organic solvents that are solid at a temperature of 25 ° C. used in the ink can prepare an aqueous solution to be measured, and the calculated dielectric constant is also high. It was found to be consistent with the effect of the present invention. For the above reasons, in the present invention, the relative permittivity of a solid water-soluble organic solvent at a temperature of 25 ° C. is calculated from the relative permittivity of a 50.0 mass% aqueous solution and used. Even if it is a solid water-soluble organic solvent at a temperature of 25 ° C., the above-mentioned ε _sol is calculated using an aqueous solution with a saturated concentration for a solution in which the solubility in water is low and a 50.0 mass% aqueous solution cannot be prepared. The relative dielectric constant value calculated according to the case is used for convenience.

[First water-soluble organic solvent]
The ink contains a first water-soluble organic solvent having a relative dielectric constant of 30.0 or less. The relative dielectric constant of the first water-soluble organic solvent is preferably 10.0 or more. When the relative dielectric constant is less than 10.0, repulsion due to the hydrophilic group in which the pigment is dispersed is less likely to occur, and the pigment is likely to aggregate. As a result, there may be a case where sufficient ink fixing recovery is not obtained. Furthermore, if the relative dielectric constant is less than 10.0, the water-soluble organic solvent itself easily penetrates into the recording medium, so that the urethane resin also penetrates together with the water-soluble organic solvent, and the urethane resin exists in the vicinity of the pigment. It becomes difficult. The urethane resin cannot cover the pigment, and the marker resistance of the image may not be sufficiently obtained. The content (% by mass) of the first water-soluble organic solvent in the ink is preferably 3.5% by mass or more and 20.0% by mass or less based on the total mass of the ink.

  As the first water-soluble organic solvent, 1,3-butanediol (30.0), 1,2-propanediol (28.8), 1,2,6-hexanetriol (28.5), 2-pyrrolidone (28.0), 1,5-pentanediol (27.0), ethyl alcohol (23.8), triethylene glycol (23.7), isopropyl alcohol (18.3), 1,2-hexanediol ( 14.8), polyethylene glycol (11.5) having a number average molecular weight of 600, triethylene glycol monobutyl ether (9.8), 1,6-hexanediol (7.1), polyethylene glycol having a number average molecular weight of 1,000 (4.6). Among these, the first water-soluble organic solvent is preferably triethylene glycol (23.7). If the ink contains a first water-soluble organic solvent having a relative dielectric constant of 30.0 or less, a water-soluble organic solvent having a relative dielectric constant exceeding 30.0 can also be used in combination.

  The content (% by mass) of the first water-soluble organic solvent is a mass ratio with respect to the content (% by mass) of the urethane resin, and is preferably 2.0 times or more and 10.0 times or less. When the ratio is less than 2.0 times, since the first water-soluble organic solvent is less than the urethane resin, the urethane resin is likely to aggregate, and ink fixing and recoverability may not be sufficiently obtained. If the ratio exceeds 10.0 times, the amount of the first water-soluble organic solvent is greater than that of the urethane resin, so that there is a large amount of the first water-soluble organic solvent in addition to the vicinity of the urethane resin, and the viscosity of the ink is likely to increase. . As a result, there may be a case where sufficient ink fixing recovery is not obtained.

(Aqueous medium)
The ink of the present invention contains an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent. It is preferable to use deionized water (ion exchange water) as water. The water-soluble organic solvent is not particularly limited except that it contains the first water-soluble organic solvent. As the water-soluble organic solvent, any of those usable for water-based inks such as other alcohols, glycols, glycol ethers, and nitrogen-containing compounds can be used. Further, one or more of these water-soluble organic solvents can be contained in the ink.

  The content (% by mass) of water in the ink is preferably 45.0% by mass or more and 95.0% by mass or less based on the total mass of the ink. The content (% by mass) of the water-soluble organic solvent in the ink is preferably 3.0% by mass or more and 55.0% by mass or less based on the total mass of the ink. This content is a value including the first water-soluble organic solvent. When the content of the water-soluble organic solvent is less than 3.0% by mass, reliability such as ejection stability may not be sufficiently obtained when the ink is used in an ink jet recording apparatus. Further, when the content of the water-soluble organic solvent is more than 55.0% by mass, the viscosity of the ink increases, and ink supply failure may occur.

(Other ingredients)
In the ink of the present invention, various kinds of surfactants, pH adjusters, antifoaming agents, rust preventives, antiseptics, antifungal agents, antioxidants, anti-reducing agents, chelating agents, and the like are included as necessary. An additive may be contained.

(Ink physical properties)
In the present invention, the pH, static surface tension, and viscosity of the ink at 25 ° C. are preferably in the following ranges. The pH 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 is preferably 30 mN / m or more and 45 mN / m or less, and more preferably 35 mN / m or more and 40 mN / m or less. The viscosity 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. In addition, what is described as “parts” and “%” with respect to the component amounts is based on mass unless otherwise specified.

  Abbreviations are as follows. HDI: hexamethylene diisocyanate, IPDI: isophorone diisocyanate, TDI: tolylene diisocyanate, MDI: diphenylmethane diisocyanate, PPG: polypropylene glycol, PTMG: polytetramethylene glycol, PEG: polyethylene glycol, PC: polyhexamethylene carbonate diol, PES: polyester Polyol, DMPA: dimethylolpropionic acid, EDA: ethylenediamine.

<Synthesis of urethane resin>
After the polyol having no acid group described in Table 1 was dissolved in methyl ethyl ketone, the polyisocyanate described in Table 1 was added. Furthermore, if necessary, a polyol having an acid group shown in Table 1 was added and reacted at a temperature of 75 ° C. for 1 hour to obtain a prepolymer solution. The obtained prepolymer solution was cooled to a temperature of 60 ° C., and an aqueous potassium hydroxide solution was added to neutralize acid groups. Then, it cooled to the temperature of 40 degreeC, ion-exchange water was added, and it emulsified by stirring at high speed with a homomixer. After emulsification, a chain extender was added, and a chain extension reaction was performed at a temperature of 30 ° C. for 12 hours. When the presence of isocyanate groups was no longer confirmed by a Fourier transform infrared spectrophotometer (FT-IR), methyl ethyl ketone was distilled off from the solution under heating and reduced pressure, and the urethane resin content was 20.0%. A liquid containing a certain urethane resin was obtained. In the lower part of Table 1, the ratio (mol%) of the polyol having an acid group in the polyol (described as “the ratio of the polyol having an acid group” in the table) and the acid value (mgKOH / g) of the urethane resin are described. To do.

  The method for measuring the acid value of the urethane resin is as follows. Using a potentiometric automatic titrator (AT-510, manufactured by Kyoto Denshi Kogyo Co., Ltd.) equipped with a streaming potential titration unit (PCD-500), the acid value of urethane resin dissolved in tetrahydrofuran is measured by colloidal titration using the potential difference. did. At this time, an ethanol solution of potassium hydroxide was used as a titration reagent. The numerical values given to polypropylene glycol, polyethylene glycol, polyhexamethylene carbonate diol, polyester polyol, and polytetramethylene glycol are number average molecular weights.

<Preparation of pigment dispersion>
(Pigment dispersion 1)
A commercially available pigment dispersion (Cab-O-Jet300, manufactured by Cabot) containing a self-dispersing pigment was prepared. The pigment type of this self-dispersing pigment is carbon black. Pigment dispersion 1 was obtained by preparing the pigment content with an appropriate amount of water. The pigment dispersion 1 contained a self-dispersing pigment in which benzenecarboxylic acid groups were bonded to the particle surface, and the pigment content was 10.0%.

(Pigment dispersion 2)
A commercially available pigment dispersion (Cab-O-Jet260, manufactured by Cabot) containing a self-dispersing pigment was prepared. The pigment type of this self-dispersing pigment is C.I. I. Pigment Red 122. The pigment content was prepared with an appropriate amount of water to obtain pigment dispersion 2. The pigment dispersion 2 contained a self-dispersed pigment in which a functional group containing a sulfonic acid group was bonded to the particle surface, and the pigment content was 10.0%.

(Pigment dispersion 3)
10.0 parts of pigment, 20.0 parts of liquid containing resin, and 70.0 parts of ion-exchanged water were mixed to obtain a mixture. As the pigment, carbon black (Black Pearls 880, manufactured by Cabot) was used. As the liquid containing the resin, the styrene-acrylic acid copolymer is neutralized with an equimolar amount of sodium hydroxide aqueous solution with respect to the acid value of the copolymer, and the resin content is 20.0%. A liquid was used. The styrene-acrylic acid copolymer has an acid value of 140 mgKOH / g and a weight average molecular weight of 10,000. The obtained mixture was dispersed for 3 hours using a batch type vertical sand mill (manufactured by Imex), and then pressure filtered through a microfilter (manufactured by Fuji Film) having a pore size of 1.2 μm. Subsequently, ion-exchanged water was added to obtain a pigment dispersion 3 having a pigment content of 10.0% and a resin content of 4.0%.

<Preparation of ink>
Each component described in Tables 2 to 4 was mixed. The numerical value attached to polyethylene glycol is the number average molecular weight. Acetylenol E100 is a nonionic surfactant manufactured by Kawaken Fine Chemicals. In the table, the numerical value in parentheses represents the relative dielectric constant at a temperature of 25 ° C. In the lower part of Tables 2 to 4, the content (%) of the urethane resin, the content (%) of the first water-soluble organic solvent, and the content (times) of the first water-soluble organic solvent relative to the content of the urethane resin (Described as “first water-soluble organic solvent / urethane resin (times)” in the table).

<Evaluation>
Each ink obtained above was filled in an ink cartridge and mounted on an ink jet recording apparatus (PIXUS MG8130, manufactured by Canon) that ejects ink from the recording head by the action of thermal energy. In this embodiment, the recording duty of a solid image recorded under the condition that one ink droplet having a mass per droplet of 30 ng ± 10% is applied to a unit area of 1/600 inch × 1/600 inch is 100. It is defined as%. The recording conditions were temperature: 23 ° C. and relative humidity: 55%. In the present invention, in the evaluation criteria of the following evaluation items, levels AA to B are acceptable and C is an unacceptable level. The evaluation results are shown in Table 5.

(Marker resistance development time)
Using the ink jet recording apparatus described above, vertical ruled lines having a recording duty of 100% and a thickness of 1/10 inch were recorded on plain paper (PPC paper GF-500, manufactured by Canon). With yellow line markers (OPTEX, manufactured by Zebra), different portions of the vertical ruled lines were traced 30 seconds and 1 minute after recording, respectively. Thereafter, the non-recorded part was immediately traced, and the contamination state of the line marker was visually confirmed.
A: When traced after 30 seconds, the pen tip was slightly stained, but the non-recorded portion was hardly stained even when the non-recorded portion was traced.
B: When traced after 1 minute, the pen tip was slightly stained, but the non-recorded portion was hardly stained even when the non-recorded portion was traced.
C: When traced after 1 minute, the pen tip was stained, and when the non-recording part was traced, the non-recording part was soiled.

(Marker resistance)
Using the ink jet recording apparatus described above, vertical ruled lines having a recording duty of 100% and a thickness of 1/10 inch were recorded on plain paper (PPC paper GF-500, manufactured by Canon). Vertical ruled lines were traced 5 minutes after recording with a yellow line marker (OPTEX, manufactured by Zebra). Thereafter, the non-recorded part was immediately traced, and the contamination state of the line marker was visually confirmed.

    A: Even after 5 minutes, the pen tip was not stained and the non-recorded portion was not stained even when the non-recorded portion was traced.

    B: When traced after 5 minutes, the pen tip was slightly colored and contaminated, but the non-recorded portion was hardly stained even when the non-recorded portion was traced.

    C: When traced after 5 minutes, the tip of the pen was stained, and when the non-recording part was traced, the non-recording part was soiled.

(Adhesive recovery)
A nozzle check pattern of PIXUS MG8130 was recorded on plain paper (PPC paper GF-500, manufactured by Canon) using the inkjet recording apparatus. Thereafter, the recording head (head cartridge) on which the ink cartridge was mounted was removed from the ink jet recording apparatus and left for 7 days in an environment of a temperature of 30 ° C. and a relative humidity of 10%. Then, the head cartridge was mounted again on the ink jet recording apparatus, and a nozzle check pattern was recorded. When the nozzle check pattern was not normally recorded and clogging occurred, the nozzle check pattern was recorded again after cleaning from the printer driver. If clogging occurred even at this time, after cleaning from the printer driver, after further powerful cleaning, the nozzle check pattern was recorded again. If clogging still occurred, powerful cleaning and a nozzle check pattern were repeatedly recorded. In this way, the sticking recoverability was evaluated based on the number of strong cleanings required until the nozzle check pattern could be recorded normally.
AA: The nozzle check pattern was recorded normally after one powerful cleaning.
A: The nozzle check pattern was normally recorded by two powerful cleanings.
B: A nozzle check pattern was normally recorded by three powerful cleanings.
C: Four or more powerful cleanings were required until the nozzle check pattern was normally recorded.

  In the evaluation results of Examples 27 and 28, the marker resistance expression time, the marker resistance, and the fixation recovery property were all B, but were inferior to the other Bs.

Claims (8)

A water-based ink for ink-jet containing a pigment, a urethane resin, and a water-soluble organic solvent,
The urethane resin has a unit derived from each of a polyisocyanate and a polyol containing a polyol having no acid group,
Of the polyol, the proportion (mol%) of the polyol having an acid group is 10 mol% or less,
The water-based ink, wherein the water-soluble organic solvent contains a first water-soluble organic solvent having a relative dielectric constant of 30.0 or less at a temperature of 25 ° C.   The aqueous ink according to claim 1, wherein the polyol having no acid group contains a polyether polyol.   The water-based ink according to claim 1 or 2, wherein the polyether polyol contains polyethylene glycol or polypropylene glycol.   The content (mass%) of the first water-soluble organic solvent is 2.0 to 10.0 times in mass ratio with respect to the content (mass%) of the urethane resin. The water-based ink according to item 1.   The water-based ink according to claim 1, wherein the pigment is a self-dispersing pigment.   The aqueous ink according to claim 1, wherein the polyol is only a polyol having no acid group. 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 6. 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 6.