JP2018104561A - Aqueous ink, ink cartridge and inkjet recording method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aqueous ink excellent in storage stability as well as capable of recording an image excellent in scratch resistance.SOLUTION: An aqueous ink is a water-based inkjet ink containing a pigment and a urethane resin. The urethane resin has a unit derived from a polyisocyanate having an allophanate structure with an addition of a hydroxy acid.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, the pigment ink has a problem that the scratch resistance of the image is low because the pigment as the color material is likely to be present on the surface of the recording medium.

  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 to 3). The inks described in Patent Documents 1 and 2 contain a urethane resin modified with allophanate added with polyethylene glycol monomethyl ether. The ink described in Patent Document 3 contains a urethane resin modified with allophanate added with a monohydric alcohol having 1 to 5 carbon atoms.

JP 2006-022132 A JP 2012-140602 A Japanese Patent Laying-Open No. 2015-025122

  The inventor conducted a new study on the pigment ink. As a result, when the inks described in Patent Documents 1 to 3 are stored for a long period of time, the particle diameter of the pigment increases or the viscosity of the ink increases due to precipitation of the urethane resin, resulting in insufficient storage stability. I found out. Further, the inks described in Patent Documents 1 and 2 have insufficient scratch resistance of recorded images.

  Accordingly, an object of the present invention is to provide a water-based ink capable of recording an image having excellent storage stability and excellent scratch resistance. 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 ink jet ink containing a pigment and a urethane resin, and the urethane resin has a unit derived from a polyisocyanate having an allophanate structure to which a hydroxy acid is added. It is characterized by.

  ADVANTAGE OF THE INVENTION According to this invention, while being excellent in storage stability, the water-based ink which can record the image excellent in abrasion resistance can be provided. In addition, according to the present invention, an ink cartridge using the water-based ink and an ink jet 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 normal temperature (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. A film formed of a urethane resin (hereinafter sometimes referred to as a urethane resin film) has a microphase separation structure formed by a hard segment and a soft segment, and thus has both strength and flexibility and exhibits high elasticity. . Such characteristics of the urethane resin film are closely related to the development of the scratch resistance of the image.

  First, the present inventor studied various urethane resins in order to improve the scratch resistance of images recorded with pigment ink. As a result, it was found that the scratch resistance of the recorded image is improved by adding urethane resin to the ink. In order to further improve the scratch resistance, an investigation was made to incorporate a unit derived from a polyisocyanate having an allophanate structure into a urethane resin. As a result, it was found that the storage stability of the ink was lowered. Therefore, the present inventor has studied to increase the hydrophilicity of the urethane resin by increasing the acid value in order to suppress a decrease in storage stability. As a result, it was found that when the acid value of the urethane resin is increased, the storage stability of the ink is improved, but the scratch resistance of the image is lowered.

  As described above, the urethane resin is mainly synthesized using a polyisocyanate and a component that reacts with the polyisocyanate. When raising the acid value of the urethane resin used in the water-based ink, the amount of a compound having a relatively small molecular weight such as a polyol having an acid group is usually increased. Then, the usage-amount of the polyol which does not have an acid group inevitably decreases. Thereby, while the urethane bond in a urethane resin increases, a soft segment will reduce and it will become the tendency for the softness | flexibility of a urethane resin film to fall. As described above, when the hydrophilicity of the urethane resin is increased by increasing the acid value, the storage stability of the ink is improved, but the scratch resistance of the image is decreased.

  This inventor examined not using the technique of improving the hydrophilic property of a urethane resin by increasing the usage-amount of the polyol which has an acid group, but using polyisocyanate which has an acid group. As a result, it was found that it is effective to use a polyisocyanate having an allophanate structure to which a hydroxy acid is added. A mechanism that can achieve both storage stability and scratch resistance with an ink containing a urethane resin having a unit derived from a polyisocyanate having an allophanate structure to which a hydroxy acid is added is presumed as follows.

  The storage stability of the ink decreases when the urethane resin, which is unstable in the ink, aggregates while entraining the pigment. Therefore, in order to suppress a decrease in storage stability, it is important to suppress the aggregation of the urethane resin in the ink and to maintain its existence state stably. The urethane resin used in the ink of the present invention has a hydroxy acid acid group at the position of a unit derived from polyisocyanate. That is, there is an acid group having an action of relaxing the denseness in the hard segment having the characteristic that it is likely to be densely present due to hydrogen bonds of urethane bonds. Since this acid group hydrates in the ink, the aggregation of the urethane resin is suppressed, so that the presence state is easily maintained stably, and the storage stability of the ink can be improved.

  On the other hand, when ink is applied to the recording medium, water decreases due to evaporation and penetration. Then, since the water hydrated to the acid group disappears, the urethane resin starts to aggregate abruptly. At this time, the unit derived from the polyisocyanate having an allophanate structure exhibits a strong hydrophobic interaction and aggregates while involving the pigment. As a result, the urethane resin tends to be present in the vicinity of the pigment, and the scratch resistance of the image can be improved.

<Ink>
Hereafter, each component which comprises the aqueous ink for inkjets of this invention is demonstrated in detail.

(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 can be synthesized using a polyisocyanate having an allophanate structure to which a hydroxy acid is added as a polyisocyanate. 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 constituent unit of the urethane resin by synthesis will be described.

  In addition, in order to efficiently exhibit the action of the unit derived from the specific polyisocyanate possessed by the urethane resin, it is not easy to use a urethane resin (so-called urethane-acrylic composite resin) in which an acrylic resin chain is incorporated. It is not preferable. 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 urethane resin used in the ink of the present invention has a unit derived from a polyisocyanate having an allophanate structure to which a hydroxy acid is added as a unit derived from a polyisocyanate. The proportion (mol%) of units derived from polyisocyanate in the urethane resin is preferably 10.0 mol% or more and 80.0 mol% or less.

[Polyisocyanate having an allophanate structure to which a hydroxy acid is added]
The “polyisocyanate having an allophanate structure added with a hydroxy acid” in the present invention is the following compound. That is, it means a compound having a structure derived from two or more molecules of polyisocyanate and an allophanate structure to which a hydroxy acid is added, and having two or more isocyanate groups in the molecule in order to react with a polyol or polyamine. To do.

The polyisocyanate having an allophanate structure to which a hydroxy acid is added is formed by adding an isocyanate to a urethane bond. The allophanate structure is a structure of a portion surrounded by a broken line in the following formula (1). R ₁ represents a polyisocyanate residue, that is, a structure other than NCO, and a plurality of R ₁ present in one molecule may be the same as or different from each other. R ₂ is a residue of a hydroxy acid used for forming a urethane bond, and an acid group is present here.

  Examples of the acid group of the hydroxy acid include a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, and a phosphonic acid group. Of these, a carboxylic acid group and a sulfonic acid group are preferable. Examples of the hydroxy acid include aliphatic monohydroxycarboxylic acids such as glycolic acid, 3-hydroxypropionic acid and 2-hydroxybutyric acid; aromatic monohydroxycarboxylic acids such as hydroxybenzoic acid; dimethylolpropionic acid and dimethylolbutanoic acid. Aliphatic dihydroxycarboxylic acid; aliphatic monohydroxysulfonic acid such as hydroxyethanesulfonic acid; aromatic monohydroxysulfonic acid such as hydroxybenzenesulfonic acid; and the like. Since the scratch resistance of the recorded image can be further improved, it is particularly preferable that the acid group of the hydroxy acid is a carboxylic acid group. This is due to the following reason. Carboxylic acid groups tend to form dimers due to intermolecular hydrogen bonding. Therefore, when the water content in the ink is reduced by evaporation or penetration, the viscosity of the ink is likely to increase when the acid group of the hydroxy acid is a carboxylic acid group compared to other acid groups. This is because the urethane resin present on the surface tends to increase.

  In addition, examples of the acid group of the hydroxy acid include a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, and a phosphonic acid group. The acid group of the hydroxy acid may be in a salt form, and examples of the cation forming the salt include alkali metal ions such as lithium, sodium and potassium, ammonium ions, and organic amine cations such as dimethylamine.

  Examples of the polyisocyanate that becomes a part of the polyisocyanate having an allophanate structure to which a hydroxy acid is added 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-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.

  Among these, aliphatic polyisocyanates are preferable, and hexamethylene diisocyanate is more preferable among them. This is due to the following reason. By adding a hydroxy acid to the polyisocyanate used as a raw material, a urethane bond is formed between the hydroxy group and the isocyanate group. Therefore, hexamethylene diisocyanate having an allophanate structure to which a hydroxy acid is added has a urethane bond in the structure in advance. The urethane resin synthesized by further reacting this isocyanate with other components has more urethane bonds in the molecular chain than the urethane resin synthesized using polyisocyanate to which no hydroxy acid is added. It will be. For this reason, when an ink containing such a urethane resin is applied to a recording medium, a urethane resin film having excellent strength is formed. However, since hexamethylene diisocyanate has a linear structure, it is rich in flexibility. That is, since the strength and flexibility of the urethane resin film can be improved in a balanced manner, the scratch resistance of the recorded image can be further improved.

  The ratio (mol%) of “units derived from polyisocyanate having an allophanate structure added with hydroxy acid” in the total amount of units derived from polyisocyanate in the urethane resin is preferably as follows. . That is, it is preferably 70.0 mol% or more, more preferably 90.0 mol% or more, and particularly preferably 95.0 mol% or more. The said ratio may be 100.0 mol%. In this case, the unit derived from the polyisocyanate contained in the urethane resin is only “a unit derived from the polyisocyanate having an allophanate structure to which a hydroxy acid is added”.

  Moreover, the ratio (mol%) of "the unit derived from the polyisocyanate which has the allophanate structure which the hydroxy acid added" which occupies the total amount of the unit which has an acid group which a urethane resin has should be as follows. preferable. That is, it is preferably 70.0 mol% or more, more preferably 90.0 mol% or more, and particularly preferably 95.0 mol% or more. The said ratio may be 100.0 mol%. In this case, the unit having an acid group that the urethane resin has is only “a unit derived from a polyisocyanate having an allophanate structure to which a hydroxy acid is added”. Examples of the unit having an acid group include a unit derived from a polyol having an acid group in addition to a unit derived from a polyisocyanate having an allophanate structure to which a hydroxy acid is added.

[Other polyisocyanates]
The urethane resin may have a unit derived from “another polyisocyanate” in addition to a unit derived from a polyisocyanate having an allophanate structure to which a hydroxy acid is added. Examples of other polyisocyanates include the above-described aliphatic and aromatic polyisocyanates.

  The ratio (mol%) of “units derived from other polyisocyanates” in the total amount of units derived from polyisocyanate in the urethane resin is preferably 5.0 mol% or less. The ratio may be 0.0 mol%. In this case, the unit derived from the polyisocyanate contained in the urethane resin is only “a unit derived from the polyisocyanate having an allophanate structure to which a hydroxy acid is added”.

[Polyol, polyamine]
Polyols and polyamines can be used as the component that 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. The “polyamine” in the present invention means a compound having two or more “amino groups and imino groups” in the molecule. One or two or more polyols and polyamines can be used as necessary. The proportion (mol%) of units derived from polyol and polyamine in the urethane resin is preferably 1.0 mol% or more and 50.0 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.

  The number average molecular weight of the polyol having no acid group is preferably from 450 to 4,000. Among these, it is particularly preferable to use a polyether polyol having a number average molecular weight of 450 to 4,000. When the number average molecular weight decreases, the number of urethane bonds in the urethane resin increases and the rigidity of the polyol increases, whereby the strength of the urethane resin film tends to increase. In addition, when the number average molecular weight increases, the number of polyols that are reaction partners of polyisocyanate decreases, so the number of urethane bonds in the urethane resin decreases, and the extensibility of the polyol increases, thereby increasing the flexibility of the urethane resin film. Tend to increase. Therefore, by setting the number average molecular weight of the polyol having no acid group within the range of 450 or more and 4,000 or less, the balance between strength and flexibility of the urethane resin film is improved. Can be further improved. On the other hand, if the number average molecular weight of the polyol having no acid group is less than 450, the urethane resin film is hard and brittle, and thus the scratch resistance may not be sufficiently obtained. Further, if the number average molecular weight is more than 4,000, the flexibility of the urethane resin film becomes too high, so that the scratch resistance may not be sufficiently obtained.

  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 of the urethane resin is preferably as follows. That is, it is preferably 70.0 mol% or more, more preferably 90.0 mol% or more, and particularly preferably 95.0 mol% or more. The said ratio may be 100.0 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. 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 ratio (mol%) of the unit derived from the polyol having an acid group in the total amount of the unit derived from the polyol in the urethane resin is preferably as follows. That is, it is preferably 30.0 mol% or less, more preferably 10.0 mol% or less, and particularly preferably 5.0 mol% or less. The ratio may be 0.0 mol%.

[Polyamine]
Polyamines include monoamines having multiple hydroxy groups such as dimethylolethylamine, diethanolmethylamine, dipropanolethylamine, dibutanolmethylamine; ethylenediamine, propylenediamine, hexylenediamine, isophoronediamine, xylylenediamine, diphenylmethanediamine, hydrogen And bifunctional polyamines such as added diphenylmethanediamine and hydrazine; trifunctional or higher functional polyamines such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, polyamide polyamine, and polyethylenepolyimine. For convenience, compounds having a plurality of hydroxy groups and one “amino group, imino group” are also listed as “polyamines”. 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.

  The proportion (mol%) of units derived from polyamine in the urethane resin is preferably as follows. That is, it is preferably 30.0 mol% or less, more preferably 10.0 mol% or less, and particularly preferably 5.0 mol% or less. The ratio may be 0.0 mol%.

  Among the above polyols and polyamines, a polyol having no acid group is preferably used because of excellent balance between strength and flexibility of the urethane resin film, and polyether polyol is more preferably used. Among the polyether polyols, it is particularly preferable to use polypropylene glycol. The reason is considered as follows. Polypropylene glycol has an intermediate number of carbon atoms between polyethylene glycol and polytetramethylene glycol, so that the urethane resin film has almost intermediate characteristics when using them. Therefore, the characteristics of the urethane resin film using polypropylene glycol have a good balance between strength and flexibility, and the degree thereof becomes higher. In addition, since polypropylene glycol has a structure in which methyl groups are branched, it is considered that polypropylene glycol easily interacts with the pigment. Therefore, the urethane resin tends to exist in the vicinity of the pigment after the ink is applied to the recording medium. For these reasons, it is considered that the scratch resistance of the recorded image is further improved.

[Crosslinking agent, chain extender]
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, the crosslinking agent or chain extender can be appropriately selected from water, the above-mentioned 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.

[Neutralizer]
The acid group of the urethane resin is preferably neutralized with a cation. Examples of acid group neutralizers include organic bases such as N, N-dimethylethanolamine, N, N-diethylethanolamine, diethanolamine, triethanolamine, trimethylamine, and triethylamine; lithium hydroxide, sodium hydroxide, potassium hydroxide And inorganic bases such as ammonia. Of these, alkali metal hydroxides such as lithium hydroxide, sodium hydroxide and potassium hydroxide are preferred. 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 mol of the acidic group contained 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.

[Physical properties and properties of urethane resin]
[Acid value]
The acid value of the urethane resin is preferably 5 mgKOH / g or more and 200 mgKOH / g or less. Furthermore, it is preferable that they are 40 mgKOH / g or more and 140 mgKOH / g or less. Especially, it is preferable that they are 30 mgKOH / g or more and 90 mgKOH / g or less. If the acid value is low, the hydrophilicity of the urethane resin is low, so there is a tendency that the storage stability of the ink cannot be sufficiently obtained, and the flexibility of the urethane resin film becomes too high, so the scratch resistance of the image is sufficient. It tends to be impossible to obtain. On the other hand, if the acid value is high, the urethane resin film becomes hard and brittle, and thus there is a tendency that sufficient scratch resistance of the image cannot be obtained. The acid value of the urethane resin can be adjusted by the ratio of units derived from a polyisocyanate having an allophanate structure to which a hydroxy acid is added or units derived from a polyol having an acid group to the urethane resin.

  The acid value of the urethane resin can be measured by a titration method. In Examples described later, an automatic potentiometric titrator (trade name: AT-510; manufactured by Kyoto Electronics Industry) equipped with a streaming potential titration unit (PCD-500) is used, and dissolved in tetrahydrofuran by colloid titration using the potential difference. The acid value of the urethane resin was measured. At this time, an ethanol solution of potassium hydroxide was used as a titration reagent.

  As described above, the ratio (mol%) of “units derived from polyisocyanate having an allophanate structure to which a hydroxy acid is added” in the total amount of units having acid groups in the urethane resin is as follows. It is preferable. That is, it is preferably 70.0 mol% or more, more preferably 90.0 mol% or more, and particularly preferably 95.0 mol% or more. This ratio can also be expressed as a ratio of an acid value based on a unit derived from a polyisocyanate having an allophanate structure added with a hydroxy acid, based on the acid value of the urethane resin. This ratio is preferably 70% or more, more preferably 90% or more, and particularly preferably 95% or more. When the proportion is less than 70%, it is difficult to suppress aggregation of the urethane resin in the ink, and thus storage stability may not be sufficiently obtained. The ratio may be 100%.

  The ratio of the acid value based on the unit derived from the polyisocyanate having an allophanate structure to which a hydroxy acid is added, based on the acid value of the urethane resin, can be confirmed as follows. An acid value based on a unit derived from a polyisocyanate having an allophanate structure added with a hydroxy acid is determined from the composition of the urethane resin analyzed by the method described later. Moreover, the acid value of a urethane resin is measured by the above-mentioned method. The ratio is calculated from the two acid values thus determined.

(Weight average molecular weight)
The weight average molecular weight of the urethane resin is preferably 3,000 or more and 100,000 or less, and more preferably 5,000 or more and 50,000 or less. The weight average molecular weight is a value in terms of polystyrene obtained by gel permeation chromatography (GPC).

[Mole ratio of urethane bond / urea bond]
In the present invention, the molar ratio of urethane bond / urea bond means that the total of the ratio of the urethane bond (mol%) and the ratio of the urea bond (mol%) in the urethane resin is 100.0 mol%. The ratio is expressed in the form of a fraction. And that the said molar ratio is 85.0 / 15.0 or more means that the ratio for which a urethane bond accounts is 85.0 mol% or more. Therefore, the ratio occupied by urea bonds is 15.0 mol% or less (100.0 mol% of the total minus 85.0 mol% of urethane bonds or less). In addition, for the sake of simplicity, “the molar ratio of the urethane bond occupying ratio (mol%) to the ratio of the urea bond occupying (mol%) in the urethane resin” is described as “urethane bond / urea bond molar ratio”. Sometimes.

  In the urethane resin, the ratio (mol%) occupied by the urethane bond is a molar ratio with respect to the ratio (mol%) occupied by the urea bond, and is preferably 85.0 / 15.0 or more. Storage stability can be further improved by making the molar ratio of urethane bond / urea bond within this range. This is because strong hydrogen bonds between urea bonds are less likely to occur, the entanglement of urethane resin chains is reduced, and water molecules are likely to be present in the vicinity of the urethane resin. The upper limit of the molar ratio is preferably 100.0 / 0.0 or less.

  Examples of the method for adjusting the molar ratio of urethane bond / urea bond in the urethane resin include the following two methods. As a 1st method, the method of adjusting the usage-amount of the amine compound at the time of synthesize | combining a urethane resin is mentioned. In this method, the amount of urea bonds generated by the reaction between an amine compound and an isocyanate group is controlled. Specifically, the urethane resin is synthesized by the following method. First, a plurality of types of urethane resins are synthesized by using different amounts of amine compounds, and the molar ratio of urethane bond / urea bond is calculated by the method described later. From the obtained molar ratio, the relationship between the amount of amine compound used and the molar ratio was examined to create a calibration curve, and this calibration curve was used to synthesize a urethane resin having a desired molar ratio. The amount of the amine compound used is determined. The reason why the calibration curve is prepared in advance is that even if the same kind of amine compound is used, the reaction rate may change if the other components are different, so the molar ratio is not the same.

  The second method includes a method of adjusting the residual ratio of unreacted isocyanate groups when the urethane resin is phase-shifted into water. In this method, the amount of urea bonds generated by the reaction between water and isocyanate groups is controlled. Specifically, the urethane resin is synthesized by the following method. In the middle of the synthesis reaction of the urethane resin, the residual ratio of the isocyanate group relative to the amount of polyisocyanate used is confirmed by a Fourier transform infrared spectrophotometer (FT-IR). The residual ratio of isocyanate groups can be adjusted by changing the reaction time and the amount of polyisocyanate used. Then, ion-exchanged water is added to the reaction system when the residual ratio of isocyanate groups reaches the same value as the desired molar ratio of urethane bond / urea bond. For example, when synthesizing a urethane resin having a urethane bond / urea bond molar ratio of 95.0 / 5.0, when the residual ratio of the isocyanate group derived from the charged polyisocyanate is 5.0 mol%. Add ion exchange water at In the examples described later, the molar ratio of urethane bond / urea bond in the urethane resin was adjusted by the second method.

  When an isocyanate group reacts with an amine, a urea bond is formed. Therefore, when polyamine is used, it is preferable to determine the amount of use so that the molar ratio of urethane bond / urea bond in the urethane resin becomes a desired ratio.

The molar ratio of urethane bond / urea bond in the urethane resin can be confirmed as follows. Specifically, the urethane resin dissolved in deuterated dimethyl sulfoxide was calculated by analyzing the carbon nuclear magnetic resonance method ( ¹³ C-NMR) and calculated from the ratio of the integrated values of the peaks of the urethane bond and the urea bond. Ask. However, the positions of the peaks of the urethane bond and the urea bond vary depending on the type of compound used for the synthesis of the urethane resin. Therefore, it is necessary to examine the positions of the urethane bond and urea bond peaks of the compounds used in the synthesis of the urethane resin. The method is shown below.

First, the composition of the urethane resin, specifically, the polyisocyanate and the components (polyol, polyamine, etc.) that react with the polyisocyanate are analyzed. In addition, about the analysis method of a composition of a urethane resin, the method mentioned later can be utilized. Subsequently, in order to confirm the chemical shift of the urethane bond and urea bond corresponding to the said polyisocyanate, the following operation is performed. A reaction product is prepared using a polyisocyanate and components (polyol, polyamine, water) that react with the polyisocyanate one by one. For example, when a polyol having no acid group and a polyamine are used in combination, (i) a reaction product of a polyisocyanate and a polyol not having an acid group, (ii) a reaction product of a polyisocyanate and a polyamine, (iii) a polyisocyanate Water reactants are prepared respectively. The reactants thus prepared were dissolved in deuterated dimethyl sulfoxide and analyzed by carbon nuclear magnetic resonance ( ¹³ C-NMR) to confirm the chemical shift of urethane bonds and urea bonds for each reactant. To do.

  In the above example, the chemical shift of the urethane bond is confirmed from the reactant (i), and the chemical shift of the urea bond is confirmed from the reactants (ii) and (iii). Then, from the obtained chemical shifts, the peak of urethane bond and urea bond is specified, and the molar ratio of urethane bond / urea bond in the urethane resin is calculated from the ratio of the integrated values of these peaks. For example, the chemical shift of the urethane resin using Compound 1 described later as the isocyanate is slightly different depending on the measurement conditions and the composition of the urethane resin, but peaks are detected at around 155 ppm for the urethane bond and around 158 ppm for the urea bond. .

In Examples described later, the molar ratio of urethane bond / urea bond in the urethane resin was determined as follows. Excess acid (hydrochloric acid) was added to the liquid containing the synthesized urethane resin, and the precipitated urethane resin was collected and dried. A sample dissolved in deuterated dimethyl sulfoxide was used as a sample. And about this sample, the peak integrated value of the chemical shift of a urethane bond and a urea bond is calculated | required with the nuclear magnetic resonance apparatus (Brand name "Avance500", the product made from BRUKER BioSpin) by carbon nuclear magnetic resonance method ( ^13C -NMR). It was. The molar ratio of urethane bond / urea bond was determined from the ratio of these peak integrated values.

[Gel fraction]
The gel fraction of the urethane resin is preferably 5% by mass or less. The “gel fraction” indicates the solubility of the urethane resin in tetrahydrofuran, which is a solvent that easily dissolves the resin, and is an index indicating the degree of crosslinking in the urethane resin. The lower the gel fraction, the lower the degree of crosslinking and the higher the steric freedom of the urethane resin. The higher the gel fraction, the higher the degree of crosslinking and the lower the steric freedom of the urethane resin. When the gel fraction of the urethane resin is 5% by mass or less, the storage stability can be further improved. This is because the entanglement of the urethane resin chain is reduced and water molecules are likely to be present in the vicinity of the urethane resin.

  The gel fraction of the urethane resin means that when the urethane resin is dissolved in tetrahydrofuran, the component that remains without being dissolved is referred to as “gel”, and the mass of this gel is equal to the mass of the urethane resin used as a sample. It is obtained by calculating the proportion (mass%). The gel fraction is calculated as follows. A liquid containing urethane resin is prepared by mixing urethane resin and water. Using this liquid, a film (mass B) of urethane resin having a uniform thickness is prepared and dried. This film is immersed in tetrahydrofuran and placed in an environment at a temperature of 23 ° C. for 24 hours. Thereafter, the gel fraction (mass%) is calculated from the urethane resin (gel, mass A) remaining without being dissolved based on the formula of A / B × 100 (%). The lower limit of the gel fraction is 0% by mass, and the upper limit is 100% by mass.

[State of urethane resin]
Even if the urethane resin is dissolved in the aqueous medium constituting the ink and does not have a particle size (water-soluble urethane resin), the urethane resin is dispersed in the aqueous medium constituting the ink and has a particle size. (Water dispersible urethane resin) existing in a state having The water-insoluble urethane resin is present in the ink in the form of resin particles.

  Whether the urethane resin is “water-soluble” or “water-dispersible” can be determined according to the following method. First, a liquid (resin solid content: 10% by mass) containing a urethane resin neutralized with an alkali corresponding to an acid value (sodium hydroxide, potassium hydroxide, etc.) is prepared. Next, the prepared liquid is diluted 10 times (volume basis) with pure water to prepare a sample solution. Then, when the particle diameter of the resin in the sample solution is measured by the dynamic light scattering method, when the particles having the particle diameter are measured, it can be determined that the resin is “resin particles”. The measurement conditions at this time can be, for example, SetZero: 30 seconds, number of measurements: 3, measurement time: 180 seconds, shape: true sphere, refractive index: 1.59. As the particle size distribution measuring device, a particle size analyzer (for example, trade name “UPA-EX150”, manufactured by Nikkiso) using a dynamic light scattering method can be used. Of course, the particle size distribution measuring apparatus and measurement conditions to be used are not limited to the above.

[Method of synthesizing urethane resin]
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 polyisocyanate and a compound (polyol or polyamine) that reacts with the polyisocyanate are reacted in such an amount that the isocyanate groups increase, thereby synthesizing a prepolymer having an isocyanate group at the end of the molecule. 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.

  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. About this sample, from the position of the peak obtained by analyzing by proton nuclear magnetic resonance ( ¹ H-NMR), the types of polyisocyanate, polyol, polyamine and the like including those having an allophanate structure to which a hydroxy acid is added are selected. Can be confirmed. Furthermore, the composition ratio can also be calculated from the ratio of the integrated values of the chemical shift peaks of the respective components. 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. In addition, even if it analyzes by pyrolysis gas chromatography, types, such as a polyisocyanate, a polyol, a polyamine containing what has an allophanate structure which the hydroxy acid added, can be confirmed.

About the urethane resin, the structure of polyisocyanate can be confirmed from the infrared absorption spectrum obtained by analyzing by infrared spectroscopic analysis (IR). The allophanate structure, mainly, NH stretching vibration absorption at 3300cm ^-1, 1750~1710cm ^-1, and two C = O stretching vibration absorption is present in 1708~1653cm ^-1.

〔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 3.0% by mass based on the total mass of the ink. More preferably, it is as follows. Further, the content (% by mass) of the urethane resin based on the total mass of the ink is preferably 0.05 times or more and 10.0 times or less as a mass ratio with respect to the content (% by mass) of the pigment. If the mass ratio is less than 0.05 times, the scratch resistance of the image may not be sufficiently obtained. On the other hand, when the mass ratio is more than 10.0 times, there may be a case where the ejection stability cannot be sufficiently obtained.

(Pigment)
The color material used in the ink of the present invention is 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.

  As a pigment dispersion method, any method such as a resin dispersion pigment using a resin dispersant or a self-dispersion pigment which does not require a resin dispersant may be adopted. In order to efficiently exhibit the film properties of the urethane resin and increase the scratch resistance of the image, it is preferable to suppress the interaction between the urethane resin and the pigment to some extent. Therefore, it is preferable to use a resin-dispersed pigment using a resin different from the urethane resin, such as an acrylic resin, as a dispersant, or a self-dispersed pigment that does not require a 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;

(Aqueous medium)
The ink of the present invention is an aqueous ink containing at least water as an aqueous medium. 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 may further contain a water-soluble organic solvent. The water-soluble organic solvent is not particularly limited as long as it is water-soluble, and monohydric or 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 components described above, the ink of the present invention is a water-soluble organic substance that is solid at room temperature, such as polyhydric alcohols such as trimethylolpropane and trimethylolethane, and urea derivatives such as urea and ethyleneurea, if necessary. A compound may be contained. Furthermore, the ink of the present invention contains 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 a water-soluble agent as necessary. Various additives such as a functional resin 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, PEG: polyethylene glycol, PTMG: polytetramethylene glycol, PC: polyhexamethylene carbonate diol, NPG: neo Pentyl glycol, EDA: ethylenediamine, DETA: diethylenetriamine, DMPA: dimethylolpropionic acid, TMP: trimethylolpropane. In addition, the numerical value attached | subjected to PPG, PEG, PTMG, and PC is a number average molecular weight.

<Synthesis of polyisocyanate>
(Compounds 1-11)
In a reactor equipped with a stirrer, a thermometer, a cooler, and a nitrogen gas introduction tube, the amount (parts) of polyisocyanate, hydroxy acid (or NPG), and 0.1 shown in Table 1 under a nitrogen atmosphere Part of the tin-based catalyst was added and reacted at a temperature of 80 ° C. for 2 hours. Subsequently, 0.01 part of zirconium 2-ethylhexanoate was added, and the reaction was performed at a temperature of 130 ° C. to obtain a reaction product. This reaction product was distilled with a thin film distillation apparatus to remove unreacted polyisocyanate, and thus compounds 1 to 11 were obtained. The obtained compounds 1 to 11 were all polyisocyanates having an allophanate structure.

(Compound 12)
In a reactor equipped with a stirrer, thermometer, cooler, and nitrogen gas inlet tube, under a nitrogen atmosphere, 863.0 parts HDI, 137.0 parts polyethylene glycol monomethyl ether (number average molecular weight 400), and 0.2 part of zirconium 2-ethylhexanoate was charged and reacted at a temperature of 90 ° C. for 2 hours. Next, 0.1 part of phosphoric acid was added and a stop reaction was performed at a temperature of 50 ° C. for 1 hour to obtain a reaction product. This reaction product was distilled with a thin film distillation apparatus under the conditions of a temperature of 130 ° C. and a pressure of 0.04 kPa to remove unreacted HDI, and thus Compound 12 was obtained. The resulting compound 12 was HDI having an allophanate structure.

(Compound 13)
Compound 13 was obtained by the same procedure except that polyethylene glycol monomethyl ether was changed to one having a number average molecular weight of 600 in the synthesis of compound 12. The obtained compound 13 was HDI having an allophanate structure.

(Compound 14)
In a reactor equipped with a stirrer, a thermometer, a cooler, and a nitrogen gas inlet tube, 186.0 parts of HDI, 14.0 parts of isopropanol, and 0.1 part of a tin-based catalyst are added under a nitrogen atmosphere. The mixture was allowed to react at a temperature of 80 ° C. for 2 hours. Next, 0.01 part of zirconium 2-ethylhexanoate was added, and the reaction was performed at a temperature of 100 ° C. to obtain a reaction product. This reaction product was distilled with a thin-film distillation apparatus under conditions of a temperature of 130 ° C. and a pressure of 0.04 kPa to remove unreacted HDI, and thus compound 14 was obtained. The resulting compound 14 was HDI having an allophanate structure.

<Synthesis of urethane resin>
(Urethane resin 1-29)
In a four-necked flask equipped with a stirrer, a thermometer, a cooler, and a nitrogen gas introduction tube, the amount of polyisocyanate used in Table 2, a polyol having no acid group, 0.1 part of a tin-based catalyst, and 300.0 parts of methyl ethyl ketone were added. And it was made to react at the temperature of 80 degreeC under nitrogen gas atmosphere for 3 hours. Next, other components in the amounts used shown in Table 2 were added, the residual ratio of isocyanate groups was confirmed by FT-IR, and the reaction was performed at a temperature of 80 ° C. until the desired residual ratio was obtained, thereby obtaining a reaction solution. After cooling the obtained reaction liquid to a temperature of 40 ° C., ion exchange water was added, and an aqueous potassium hydroxide solution was added while stirring at high speed with a homomixer to obtain a liquid containing a resin. From the obtained liquid, methyl ethyl ketone was distilled off under reduced pressure by heating to obtain liquids containing water-soluble urethane resins 1 to 29 each having a urethane resin (solid content) content of 42.9%. .

(Urethane resin 30)
In a four-necked flask equipped with a stirrer, thermometer, condenser, and nitrogen gas inlet tube, 128.6 parts of PTMG 2,000, 8.0 parts of NPG are put, and the temperature is 100 ° C. until uniform. Mixed. Further, 165.6 parts of Compound 12 and 0.05 parts of dibutyltin dilaurate were added and reacted at a temperature of 80 ° C. for 3 hours to obtain a solution containing a prepolymer. After 702.0 parts of water was added to the resulting solution to emulsify, a chain extension reaction of the isocyanate group present at the end of the prepolymer with water was performed at a temperature of 40 ° C. When it was confirmed by FT-IR that the isocyanate group was no longer present, the reaction was terminated, the concentration was adjusted, and the urethane resin (solid content) content was 42.9%. A liquid containing was obtained.

(Urethane resin 31)
In a four-necked flask equipped with a stirrer, a thermometer, a cooler, and a nitrogen gas introduction tube, 303.6 parts of PPG 2,000 was placed and dissolved. Further, 485.6 parts of Compound 13, 115.3 parts of IPDI, and 95.5 parts of DMPA were added and reacted at a temperature of 75 ° C. for 1 hour to obtain a solution containing a prepolymer. After cooling the obtained solution to a temperature of 60 ° C., an aqueous potassium hydroxide solution was added and emulsified by stirring at high speed with a homomixer. Thereafter, 10.4 parts of EDA was added and the chain extension reaction was carried out at a temperature of 30 ° C. for 12 hours. The reaction was terminated when it was confirmed by FT-IR that the isocyanate group no longer existed, and a liquid containing a resin was obtained. From the obtained liquid, methyl ethyl ketone was distilled off under reduced pressure by heating to obtain a liquid containing the urethane resin 31 having a urethane resin (solid content) content of 42.9%.

(Urethane resin 32)
In a four-necked flask equipped with a stirrer, thermometer, condenser, and nitrogen gas inlet tube, 57.1 parts of Compound 14, 136.3 parts of PPG 2,000, and 300.0 parts of methyl ethyl ketone were placed. The reaction was carried out at a temperature of 80 ° C. for 7 hours in a nitrogen gas atmosphere. Next, 2.4 parts of DMPA, 3.8 parts of TMP, and 0.4 parts of EDA were added, and the residual ratio of isocyanate groups was confirmed by FT-IR. To obtain a reaction solution. After cooling the obtained reaction liquid to a temperature of 40 ° C., ion exchange water was added, and an aqueous potassium hydroxide solution was added while stirring at high speed with a homomixer to obtain a liquid containing a resin. From the obtained liquid, methyl ethyl ketone was distilled off under reduced pressure by heating to obtain a liquid containing urethane resin 32 having a urethane resin (solid content) content of 42.9%.

(Synthesis conditions and characteristics of urethane resin)
Table 2 shows the synthesis conditions and characteristics of the urethane resin described above. “The ratio of the acid value based on the unit derived from the polyisocyanate having an allophanate structure to which a hydroxy acid is added, based on the acid value of the urethane resin” is referred to as “the ratio of the acid value based on the allophanate”.

<Preparation of pigment dispersion>
(Pigment dispersion 1)
Mix 20.0 g carbon black, 7.0 mmol ((4-aminobenzoylamino) -methane-1,1-diyl) bisphosphonic acid monosodium salt, 20.0 mmol nitric acid, and 200.0 mL pure water. did. And it mixed at 6,000 rpm at room temperature using the Silverson mixer. After 30 minutes, 20.0 mmol of sodium nitrite dissolved in a small amount of water was slowly added to the mixture. By this mixing, the temperature of the mixture reached 60 ° C., and the reaction was performed in this state for 1 hour. Thereafter, the pH of the mixture was adjusted to 10 using an aqueous sodium hydroxide solution. After 30 minutes, 20.0 mL of pure water was added, and diafiltration was performed using a spectrum membrane. After performing ion exchange treatment and replacing the counter ion of the anionic group of the self-dispersing pigment from sodium ion to potassium ion, the pigment solid concentration was adjusted to obtain Pigment Dispersion Liquid 1. The pigment dispersion 1 contains a self-dispersing pigment in which —C ₆ H ₄ —CONH—CH (PO (OK) ₂ ) ₂ groups are bonded to the particle surface, and the pigment content is 30.0%. there were.

(Pigment dispersion 2)
To a solution prepared by dissolving 5.0 g of concentrated hydrochloric acid in 5.5 g of water, 1.5 g of 4-amino-1,2-benzenedicarboxylic acid was added while being cooled to a temperature of 5 ° C. Next, the container containing the solution is placed in an ice bath and the solution is stirred to keep the solution constantly at 10 ° C. or lower, and 1.8 g of sodium nitrite is dissolved in 9.0 g of water at 5 ° C. Solution was added. After stirring the solution for an additional 15 minutes, 6.0 g of carbon black was added with stirring. Thereafter, the mixture was further stirred for 15 minutes to obtain a slurry. The obtained slurry was filtered with a filter paper (trade name “standard filter paper No. 2”, manufactured by Advantech), and then the pigment particles were sufficiently washed with water and dried in an oven at 110 ° C. to prepare a self-dispersing pigment. After performing ion exchange treatment and replacing the counter ion of the anionic group of the self-dispersing pigment from sodium ion to potassium ion, the pigment solid concentration was adjusted to obtain Pigment Dispersion Liquid 2. The pigment dispersion 2 contained a self-dispersing pigment having —C ₆ H ₃ — (COOK) ₂ groups bonded to the particle surface, and the pigment content was 30.0%.

(Pigment dispersion 3)
500.0 g of carbon black, 45.0 g of aminophenyl (2-sulfoethyl) sulfone (APSES), 900.0 g of distilled water were placed in the reactor. And it stirred for 20 minutes at the temperature of 55 degreeC, and rotation speed 300rpm. Here, 40.0 g of a 25.0% sodium nitrite aqueous solution was dropped over 15 minutes, and then 50.0 g of distilled water was further added. And it was made to react at the temperature of 60 degreeC for 2 hours, and the reaction material was obtained. The obtained reaction product was taken out while being diluted with distilled water, and the concentration of pigment solids was adjusted to obtain a dispersion having a pigment content of 15.0%. Thereafter, impurities were removed by centrifugation to obtain dispersion A. This dispersion A contained a pigment in which APSES was bonded to the pigment particle surface.

  In order to determine the number of moles of the functional group bonded to the pigment in the dispersion A, the following operation was performed. Using a sodium ion electrode (1512A-10C; manufactured by HORIBA, Ltd.), the sodium ion concentration in dispersion A was measured and converted to the number of moles (mol / g) per solid content of the pigment. Next, dispersion A having a pigment content of 15.0% was added dropwise to the pentaethylenehexamine (PEHA) solution at room temperature over 1 hour with vigorous stirring to obtain a mixture. The concentration of PEHA in the PEHA solution at this time was 1 to 10 times the number of moles of sodium ions measured above, and the amount of solution was the same as that of dispersion A. After stirring this mixture for 18 to 48 hours, impurities were removed to obtain dispersion B. Dispersion B contained a pigment having PEHA bound to the particle surface via APSES, and the pigment content was 10.0%.

  A styrene-acrylic acid copolymer (weight average molecular weight 8,000, acid value 140 mg KOH / g, dispersity Mw / Mn 1.5 [Mw: weight average molecular weight, Mn: number average molecular weight]), which is a water-soluble resin, was prepared. . 190.0 g of this water-soluble resin was added to 1,800 g of distilled water, potassium hydroxide required to neutralize the resin was added, and dissolved by stirring to obtain an aqueous resin solution. To the obtained aqueous resin solution, 500.0 g of Dispersion B having a pigment content of 10.0% was added dropwise with stirring to obtain a mixture. Then, the above mixture was transferred to an evaporating dish and heated at a temperature of 150 ° C. for 15 hours to evaporate the liquid component, and then the dried product was cooled to room temperature. Next, the dried product was added to distilled water whose pH was adjusted to 9.0 with potassium hydroxide and dispersed using a disperser. Furthermore, 1.0 mol / L potassium hydroxide aqueous solution was added under stirring to adjust the pH of the liquid to 10-11. Thereafter, impurities and coarse particles were removed by desalting and purification to obtain pigment dispersion 3. The pigment dispersion 3 contains a resin-bound pigment in which an organic group containing a polymer (a styrene-acrylic acid copolymer that is a water-soluble resin) is bonded to the particle surface. Was 30.0%, and the resin content was 15.0%.

(Pigment dispersion 4)
500.0 g of ion exchange water and 15.0 g of carbon black were mixed and stirred at 15,000 rpm for 30 minutes to pre-wet the pigment. To this, 4,485 g of ion-exchanged water was added and dispersed with a high-pressure homogenizer to obtain dispersion C. The average particle size of the pigment in dispersion C was 110 nm. The obtained dispersion C was transferred to a high-pressure vessel and pressurized at a pressure of 3.0 MPa, and then ozone ozone treatment of the pigment was performed by introducing ozone water having an ozone concentration of 100 ppm to obtain dispersion D. After adjusting the pH of the dispersion D to 10.0 using potassium hydroxide, the pigment solid content was adjusted to obtain the pigment dispersion 4. The pigment dispersion 4 contained a self-dispersing pigment having —COOK groups bonded to the particle surface, and the pigment content was 30.0%.

(Pigment dispersion 5)
10.0 g of carbon black, 20.0 g of a water-soluble resin, and 70.0 g of water were mixed to obtain a mixture. As the water-soluble resin, a styrene-acrylic acid copolymer having an acid value of 200 mgKOH / g and a weight average molecular weight of 10,000 neutralized with a 10.0% aqueous sodium hydroxide solution was used. This mixture was dispersed for 1 hour using a sand grinder, and then impurities were removed by centrifugation, followed by pressure filtration with a microfilter (manufactured by Fuji Film) having a pore size of 3.0 μm. Next, the pigment solid content was adjusted to obtain a pigment dispersion 5 having a pH of 10.0. The pigment dispersion 5 contained a pigment dispersed with a water-soluble resin (resin dispersant), and the pigment content was 30.0% and the resin content was 15.0%.

(Pigment dispersion 6)
10.0 g of carbon black, a liquid containing 46.6 g of urethane resin 1 and 43.4 g of water were mixed to obtain a mixture. This mixture was dispersed for 1 hour using a sand grinder, and then impurities were removed by centrifugation, followed by pressure filtration with a microfilter (manufactured by Fuji Film) having a pore size of 3.0 μm. Subsequently, the pigment solid content was adjusted to obtain a pigment dispersion 6 having a pH of 10.0. The pigment dispersion 6 contained the pigment dispersed by the urethane resin 1, and the pigment content was 30.0% and the resin content was 15.0%.

<Preparation of ink>
Each component shown below was mixed and stirred sufficiently, followed by pressure filtration with a micro filter (manufactured by Fuji Film) having a pore size of 3.0 μm to prepare each ink. Acetylenol E100 is a nonionic surfactant (acetylene glycol ethylene oxide adduct) manufactured by Kawaken Fine Chemical Co., Ltd., and the balance of ion-exchanged water is such that the total amount of all components of the ink is 100.0%. That is.
Pigment dispersion (type shown in Table 3): 10.0%
-Liquid containing urethane resin (types shown in Table 3): Amount used (%) shown in Table 3
・ Glycerin: 9.0%
・ Triethylene glycol: 5.0%
-Acetylenol E100: 0.1%
-Ion exchange water: the balance.

<Evaluation>
Each ink obtained above was filled in an ink cartridge and mounted on an ink jet recording apparatus (trade name “PIXUS iP3100”, manufactured by Canon Inc.) that discharges 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 28 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 3. Table 3 also shows the characteristics of each ink.

(Abrasion resistance)
Using the inkjet recording apparatus, a solid image of 1.0 inch × 0.5 inch having a recording duty of 100% was recorded on plain paper (trade name “PPC paper GF-500”, manufactured by Canon). A record was obtained. After 10 minutes and 1 day of recording, respectively, a sillbon paper and a weight with a surface pressure of 40 g / cm ² were placed on the solid image of the recorded material, and the solid image and the sylbon paper were rubbed together. Thereafter, the sylbon paper and the weight were removed, the state of the non-recorded portion was visually checked, and the scratch resistance was evaluated according to the following evaluation criteria.
AA: There was no stain on the white background portion after 10 minutes.
A: There was almost no stain on the white background after 10 minutes, and there was no stain on the white background after 1 day. B: There was almost no stain on the white background after 10 minutes, and there was almost no stain on the white background after 1 day. C: The white background was stained after 10 minutes, but it was inconspicuous, and the white background was hardly stained after 1 day.

(Storage stability)
The inks obtained above, the volume average particle diameter (D ₅₀₎ of the _pigment, and to measure the viscosity of the ink. Thereafter, 100 g of ink was put into a 180 mL capacity polytetrafluoroethylene sealed container, sealed, and placed in an oven at a temperature of 60 ° C. and stored for one month. Thereafter, the ink was taken out and returned to 25 ° C., and then the volume average particle diameter (D ₅₀ ) of the pigment and the viscosity of the ink were measured again. The volume average particle size of the pigment was determined using a particle size analyzer (trade name “UPA-EX150”, manufactured by Nikkiso) by a dynamic light scattering method, Set zero: 60 seconds, measurement time: 120 seconds, measurement frequency: 3 times The refractive index was measured under the condition of 1.8. Further, the viscosity of the ink was measured using an E-type viscometer (trade name “RE80L”, manufactured by Toki Sangyo Co., Ltd.) under the conditions of the number of rotations: 20 rpm and the number of measurements: 3. Then, the volume average particle diameter and the ink viscosity change rate before and after storage were determined, and storage stability was evaluated according to the evaluation criteria shown below.
A: Volume average particle size and change rate of viscosity were both less than 15% B: Only one of volume average particle size and change rate of viscosity was 15% or more C: Volume average particle size, The viscosity change rate was 15% or more.

  The storage stability of Examples 1 to 5 was relatively better than that of Example 6.

Claims (12)

A water-based ink jet ink containing a pigment and a urethane resin,
The water-based ink, wherein the urethane resin has a unit derived from a polyisocyanate having an allophanate structure to which a hydroxy acid is added.   The aqueous ink according to claim 1, wherein the hydroxy acid is a hydroxycarboxylic acid.   The water-based ink according to claim 1, wherein the urethane resin has a unit derived from a polyol.   The water-based ink according to claim 3, wherein the polyol includes a polyether polyol.   The water-based ink according to claim 4, wherein the polyether polyol contains polypropylene glycol.   6. The water-based ink according to claim 1, wherein the urethane resin has an acid value of 30 mgKOH / g or more and 90 mgKOH / g or less.   The ratio (%) of the acid value based on the unit derived from the polyisocyanate having an allophanate structure added with the hydroxy acid, based on the acid value of the urethane resin, is 70% or more. The water-based ink according to item 1.   The ratio (mol%) which a urethane bond accounts in the said urethane resin is a molar ratio with respect to the ratio (mol%) which a urea bond occupies, and is 85.0 / 15.0 or more, Any one of Claim 1 thru | or 7 The water-based ink described in 1.   The water-based ink according to any one of claims 1 to 8, wherein a gel fraction of the urethane resin is 5% by mass or less.   The content (% by mass) of the urethane resin based on the total mass of the ink is 0.05 to 10.0 times by mass ratio with respect to the content (% by mass) of the pigment. 10. The water-based ink according to any one of 9 above. 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 10. An inkjet recording method for recording an image on a recording medium by discharging ink from an inkjet recording head,
An inkjet recording method, wherein the ink is the water-based ink according to any one of claims 1 to 10.