JP2018104681A - Aqueous ink, ink cartridge and inkjet recording method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aqueous ink capable of recording an image having excellent intermittent ejection stability and excellent scratch resistance. An aqueous inkjet ink containing a pigment and a urethane resin, wherein the urethane resin includes a polyisocyanate, a polyol having no acid group, an isocyanate reactive group, and a carboxylic acid group. The urethane resin has a weight average molecular weight of 5,000 or more and 30,000 or less, an acid value of 20 mgKOH / g or more and 200 mgKOH / g or less, and A water-based ink, wherein a ratio (%) of an acid value based on a unit derived from the compound in an acid value of a urethane resin is 60% or more. [Selection figure] None

Description

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

  In recent years, 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 5). The oil-based ink described in Patent Document 1 contains a urethane resin having units derived from glycolic acid. The ink described in Patent Document 2 contains a urethane resin having a polylactic acid segment and a sulfonic acid group-containing segment. The inks described in Patent Documents 3 and 4 contain a urethane resin having a carboxylic acid group and a sulfonic acid group. The ink described in Patent Document 5 contains a urethane resin in which many units derived from a diol having an acid group are present at the end of the molecular chain.

Japanese Patent Laid-Open No. 05-222332 JP 2010-174170 A Special table 2013-536274 gazette JP 2011-144355 A JP 2012-214712 A

  The inventor conducted a new study on the pigment ink. All the inks described in Patent Documents 1 to 5 have low intermittent ejection stability, and the scratch resistance of recorded images is insufficient. Here, the intermittent ejection stability will be described. When an image is recorded by the ink jet recording method, if the state where ink is not ejected from a certain ejection port of the recording head for a certain period of time continues, evaporation of water in the ink proceeds from the ejection port. Thereafter, when the next first drop of ink is ejected from the ejection port, the phenomenon that the ejection of the ink becomes unstable or the ejection cannot be performed occurs. The ink in which such a phenomenon occurs has low intermittent ejection stability. An ink that can record an image excellent in scratch resistance while satisfying intermittent ejection stability has not yet been found.

  Accordingly, an object of the present invention is to provide a water-based ink capable of recording an image having excellent intermittent ejection 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 water-based ink of the present invention is an ink-jet water-based ink containing a pigment and a urethane resin, and the urethane resin has a polyisocyanate, a polyol having no acid group, and 1 isocyanate reactive group. The urethane resin has a weight average molecular weight of 5,000 or more and 30,000 or less, and an acid value of 20 mgKOH / g or more and 200 mgKOH / g or less. The ratio (%) of the acid value based on the unit derived from the compound in the acid value of the urethane resin is 60% or more.

  ADVANTAGE OF THE INVENTION According to this invention, while being excellent in intermittent discharge stability, the aqueous 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 view of this, an attempt was made to increase the acid value and increase the hydrophilicity of the urethane resin in an attempt to improve the intermittent ejection stability of the ink. As a result, it was found that when the acid value of the urethane resin was increased, the intermittent ejection stability of the ink was improved, but the scratch resistance of the image was lowered.

  As described above, the urethane resin is mainly composed of polyisocyanate and a component that reacts with it. In the case where the acid value of the urethane resin is increased in order to improve the intermittent ejection stability of the ink, the proportion of units derived from the polyol having an acid group is increased. Then, the ratio which the unit derived from the polyol which does not have an acid group which is a component of the object reacting with polyisocyanate like the polyol which has an acid group inevitably becomes small. In this case, the urethane bond in the urethane resin is increased and the soft segment is reduced, and the flexibility of the urethane resin film is impaired. That is, if the hydrophilicity is increased by increasing the acid value of the urethane resin, the intermittent ejection stability of the ink is improved, but the scratch resistance of the image is decreased.

  In view of this, the present inventor has studied a method for achieving both the intermittent ejection stability of ink and the scratch resistance of an image. At this time, instead of increasing the hydrophilicity of the urethane resin by increasing the acid value, it was decided to devise the film characteristics of the urethane resin while keeping the hydrophilicity of the urethane resin high and keeping the molecular weight small. For this reason, the acid value of the urethane resin is kept within a high range of 20 mgKOH / g or more and 200 mgKOH / g or less, and the weight average molecular weight is controlled to a low value of 5,000 or more and 30,000 or less. It was. As a result, the urethane resin having a configuration in which the ratio of the acid value based on the unit derived from the “compound having one isocyanate reactive group and the carboxylic acid group” in the acid value of the urethane resin is 60% or more is effective. I found out. Here, the isocyanate reactive group is a group capable of reacting with an isocyanate group, and specific examples thereof include a hydroxy group, a thiol group, and an amino group.

  The “compound having one isocyanate reactive group and a carboxylic acid group” has only one group in the molecule that reacts with an isocyanate group, and therefore acts as a reaction terminator for synthesizing a urethane resin. Therefore, the urethane resin having a unit derived from the compound tends to have a low molecular weight, and many of the carboxylic acid groups are present at the ends of the molecular chain of the urethane resin. Since such a urethane resin has a low molecular weight, physical entanglement between molecules or within a molecule hardly occurs. Further, in the water-based ink, the carboxylic acid group of the urethane resin may exist by ion dissociation. Since water molecules are hydrated to ion-dissociated carboxylic acid groups, urethane resins having many carboxylic acid groups at the ends of the molecular chains are present in the ink in a state where the molecular chains are extended. Together, these facilitate hydrogen bonding between urethane bonds. As a result, despite the low molecular weight, film properties comparable to urethane resins having a relatively high molecular weight are exhibited, and the scratch resistance of the image can be improved.

  The reason why the intermittent discharge stability is improved is estimated as follows. Here, the intermittent ejection stability decreases due to the evaporation of water from the ejection port of the recording head. Therefore, in order to improve the intermittent ejection stability, even if the distance between the urethane resin and the pigment particles is reduced when water evaporates to some extent from the ink existing in the vicinity of the ejection opening of the recording head, the pigment aggregates. It is important to maintain a stable dispersion state. The urethane resin used in the ink of the present invention not only has a low molecular weight, but also exists in a state where the molecular chain is extended in the aqueous ink, so that hydrogen bonds are easily formed three-dimensionally. Due to this hydrogen bond and the carboxylic acid group present at the end of the molecular chain, the urethane resin has micelles in a state in which a part assembled by intermolecular hydrogen bonds is arranged inside and a carboxylic acid group is arranged outside. Take the structure. Many carboxylic acid groups capable of ion dissociation are present on the surface of the micelle. Therefore, a stable dispersion state is easily maintained even when water evaporates due to electrostatic repulsion generated between the surface of the micelle and a component (such as an anionic group) for dispersing the pigment. In this way, intermittent discharge stability is improved.

  On the other hand, if the ratio of the acid value based on the unit derived from the compound having one isocyanate reactive group and the carboxylic acid group in the acid value of the urethane resin is less than 60%, the above-mentioned action does not occur, and the abrasion resistance is reduced. May be insufficient, and the intermittent ejection stability may be reduced.

  As described above, in the present invention, the acid value of the urethane resin needs to be within a certain range, such as 20 mgKOH / g or more and 200 mgKOH / g or less. If the acid value of the urethane resin is less than 20 mgKOH / g, it is difficult to take a state in which the molecular chain is elongated, and therefore both the scratch resistance and the intermittent ejection stability are insufficient. Further, when the acid value of the urethane resin is more than 200 mgKOH / g, the ratio of the polyol having no acid group decreases, so that the scratch resistance becomes insufficient, and the viscosity of the ink is increased by hydration of water molecules to the acid group. As a result, the intermittent discharge stability becomes insufficient. Moreover, as above-mentioned, the weight average molecular weight of a urethane resin needs to be a certain range as low as 5,000 or more and 30,000 or less. If the weight average molecular weight of the urethane resin is less than 5,000, the flexibility is insufficient and the scratch resistance becomes insufficient. Further, if the weight average molecular weight of the urethane resin is more than 30,000, physical entanglement of molecular chains cannot be suppressed, and intermittent ejection stability becomes insufficient.

  In the present invention, the acid group that is present at the end of the molecular chain of the urethane resin and occupies 60% or more of the acid value is required to be a carboxylic acid group. Examples of the anionic group that can impart a certain degree of hydrophilicity to the resin include a sulfonic acid group and a carboxylic acid group. However, since the sulfonic acid group has a higher pKa than the carboxylic acid group, it not only easily causes ionic dissociation, but also has a high hydrophilicity. When a urethane resin having many sulfonic acid groups at the end of the molecular chain is used, the sulfonic acid group is easily maintained in an ion-dissociated state even when ink is applied to the recording medium, and the hydrophilicity is high. Does not progress, and easily penetrates into the recording medium. As a result, the urethane resin remaining on the surface of the recording medium is reduced, resulting in insufficient scratch resistance.

  Note that the ink described in Patent Document 5 containing a urethane resin in which many units derived from a diol having an acid group are present at the end of the molecular chain has insufficient intermittent ejection stability. The reason is presumed as follows. In the above urethane resin, although the acid group present at the end of the molecular chain is a carboxylic acid group, it is derived from dimethylolpropionic acid, which is a compound having two hydroxyl groups that are isocyanate reactive groups at the end of the molecular chain. Unit exists. In this urethane resin, the acid group occupying 60% or more of the acid value is a carboxylic acid group, but the same mole of the hydroxy group is present at the end of the molecular chain. In this case, when water is evaporated from the ink to some extent, hydrogen bonds are formed between the surplus hydroxy groups via water molecules, so that the viscosity of the ink increases rapidly and the aggregation of the pigment is not suppressed. Discharge stability becomes insufficient.

<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, a polyol having no acid group, and a compound having one isocyanate reactive group and a carboxylic acid group. The urethane resin has a weight average molecular weight of 5,000 or more and 30,000 or less and an acid value of 20 mgKOH / g or more and 200 mgKOH / g or less. Furthermore, the ratio (%) of the acid value based on a unit derived from a compound having one isocyanate reactive group and a carboxylic acid group in the acid value of the urethane resin is required to be 60% or more. 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 polyisocyanate. The “polyisocyanate” in the present invention means a compound having two or more isocyanate groups in the molecule. Examples of the polyisocyanate include aliphatic and aromatic polyisocyanates. Of these, aliphatic polyisocyanates are preferable, and aliphatic polyisocyanates having a cyclic structure are more preferable. As the polyisocyanate, diisocyanate is preferably used. In addition, for example, when a polyfunctional polyisocyanate having an allophanate structure, a uretdione structure, an isocyanurate structure, a biuret structure or the like is used, the amount is preferably small or not used.

  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.

  The proportion (mol%) of the unit derived from polyisocyanate in the urethane resin is preferably 10.0 mol% or more and 80.0 mol% or less, and preferably 20.0 mol% or more and 50.0 mol% or less. More preferably it is.

[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.

  The proportion (mol%) of the unit derived from polyol and polyamine in the urethane resin is preferably 10.0 mol% or more and 80.0 mol% or less, and preferably 20.0 mol% or more and 70.0 mol%. More preferably, it is as follows.

[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. 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. Moreover, since it is excellent in abrasion resistance, it is preferable that the polyol which does not have an acid group is a polycarbonate polyol.

  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 preferable that it is 10.0 mol% or more and 50.0 mol% or less.

[Polyol having an acid group]
Examples of the polyol having an acid group include polyols having an acid group such as a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, and a phosphonic acid group. The acid group is preferably a carboxylic acid group. Examples of the polyol having a carboxylic acid group include dimethylolacetic acid, dimethylolpropionic acid, dimethylolbutanoic acid, and dimethylolbutyric acid. Of these, dimethylolpropionic acid and dimethylolbutanoic acid are preferable. The acid group of the polyol having an acid group may be in a salt form. Examples of 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 85.0 mol% or less, and more preferably 60.0% mol or less. The ratio may be 0.0 mol%. In this case, the unit having an acid group that the urethane resin has is only “a unit derived from a compound having one isocyanate reactive group and a carboxylic acid group”.

[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%.

[Compound having one isocyanate reactive group and a carboxylic acid group]
The “compound having one isocyanate reactive group and a carboxylic acid group” in the present invention means a compound having one group capable of reacting with an isocyanate group and a carboxylic acid group. Examples of the group capable of reacting with an isocyanate group include a hydroxy group, a thiol group, and an amino group. That is, the compound having one isocyanate reactive group and the carboxylic acid group is at least one compound selected from the group consisting of monohydroxycarboxylic acid, monothiolcarboxylic acid, and monoaminocarboxylic acid. The molecular weight of the compound having one isocyanate reactive group and a carboxylic acid group is preferably 50 to 200, and more preferably 50 to 150.

  As monohydroxycarboxylic acid (compound having one hydroxy group and carboxylic acid group), glycolic acid, lactic acid, malic acid, tartronic acid, citric acid, 2-hydroxybutyric acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, Examples include ricinoleic acid, p-hydroxybenzoic acid, salicylic acid, vanillic acid, syringic acid, mandelic acid, benzylic acid, furoretic acid, coumaric acid, ferulic acid, and sinapinic acid.

  Examples of the monothiolcarboxylic acid group (compound having one thiol group and a carboxylic acid group) include mercaptoacetic acid, 3-mercaptopropionic acid, 2-mercaptopropionic acid, 3-mercaptoisobutyric acid, N-acetylcysteine, N- (2-mercaptopropionyl) glycine, thiosalicylic acid and the like can be mentioned.

  Monoaminocarboxylic acids (compounds having one amino group and a carboxylic acid group) include glycine, 3-aminopropanoic acid, 4-aminobutanoic acid, 5-aminopentanoic acid, 6-aminohexanoic acid, and 7-aminoheptane. Acid, 8-aminooctanoic acid, 12-aminododecanoic acid, DL-norvaline, 3-aminocyclohexanecarboxylic acid, 4-aminocyclohexanecarboxylic acid, 4- (aminomethyl) cyclohexanecarboxylic acid, 5-amino-2-methylbenzoic acid Acid, 4-aminobenzoic acid, 6-amino-2-naphthoic acid, 4- (methylamino) benzoic acid, 3-aminobenzoic acid, 2-aminobenzoic acid, 4-amino-3-methylbenzoic acid, 4- Amino-2-methylbenzoic acid, 3-amino-4-methylbenzoic acid, 4-amino-3-chlorobenzoic acid, 4- (amino Methyl) benzoic acid, 4-amino-2-chlorobenzoic acid, 2- (2-aminophenyl) ethanol, 4-aminophenyl acetic acid.

  Among the above, monohydroxycarboxylic acid and monoaminocarboxylic acid are preferable. Hydroxy groups react with isocyanate groups to form urethane bonds, and amino groups react with isocyanate groups to form urea bonds. Since the urethane bond and the urea bond form hydrogen bonds between molecules, the strength of the urethane resin film can be increased, and the scratch resistance of the recorded image can be further improved. Of these, monohydroxycarboxylic acid is preferable because of intermittent discharge stability, and glycolic acid, lactic acid, p-hydroxybenzoic acid, and salicylic acid are more preferable.

  The carboxylic acid group of a compound having one isocyanate reactive group and a carboxylic acid group may be in the form of a salt. Examples of cations that form a salt include alkali metal ions such as lithium, sodium, and potassium, ammonium ions, and dimethyl. And cations of organic amines such as amines. Of these, ions of alkali metals such as lithium, sodium and potassium are preferred. Since these cations can dissociate the carboxylic acid group more efficiently, the molecular chain of the urethane resin is more likely to be in an extended state. As a result, physical entanglement between molecules or within a molecule is not particularly likely to occur, and intermolecular hydrogen bonds are easily formed, whereby the scratch resistance and intermittent ejection stability can be further improved.

  The ratio (%) of the acid value based on the unit derived from the compound having one isocyanate reactive group and the carboxylic acid group in the acid value of the urethane resin needs to be 60% or more. When this ratio is 60% or more, the scratch resistance of the recorded image and the intermittent ejection stability of the ink can be improved from the above-described mechanism. The proportion is preferably 70% or more, and even if it is 100%, that is, all of the acid values of the urethane resin are derived from a compound having one isocyanate reactive group and a carboxylic acid group. The acid value based on However, if the acid value is too high, the ink tends to be hydrated in the water in the ink, the viscosity of the ink increases, and the intermittent ejection stability may be slightly reduced. Therefore, in order to make the intermittent ejection stability of the ink higher, the ratio is preferably 95% or less.

  The proportion (mol%) of units derived from the compound having one isocyanate reactive group and a carboxylic acid group in the urethane resin is preferably 1.0 mol% or more and 80.0 mol% or less. More preferably, it is 0 mol% or more and 60.0 mol% or less.

[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 polyisocyanates, polyols, polyamines and the like for the purpose of 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 by alkali metal ions and at least one ammonium ion of ammonium ions and organic ammonium ions. And while the neutralization rate on the basis of all the acid groups which a urethane resin has is 80% or more, it is preferable that the neutralization rate by ammonium ion is 1% or more and less than 45%. If the neutralization rate based on all acid groups is less than 80%, the cohesiveness of the urethane resin in the ink may increase, and the intermittent ejection stability of the ink may decrease. The neutralization rate based on all acid groups is preferably 100% or less.

  Also, if the neutralization rate by ammonium ions is less than 1%, the pH drop of the ink due to protons caused by the decomposition of the urethane resin cannot be suppressed, and the urethane resin becomes unstable in the ink and the cohesiveness is increased. Rise. As a result, the intermittent ejection stability of the ink may be reduced. Further, when the neutralization rate by ammonium ions is 45% or more, the cohesiveness of the urethane resin at the time of ink evaporation is increased, and the intermittent ejection stability may be lowered. The neutralization rate with ammonium ions is preferably 2% or more and 40% or less.

  The neutralization rate with alkali metal ions may be determined based on the balance between the neutralization rate based on all acid groups and the neutralization rate with ammonium ions. Specifically, the neutralization rate with alkali metal ions is preferably 45% or more and less than 99%, and more preferably 46% or more and 98% or less.

  Examples of alkali metal ions include lithium ions, sodium ions, and potassium ions. In order to neutralize the acid groups of the urethane resin with alkali metal ions, alkali metal hydroxides (lithium hydroxide, sodium hydroxide, potassium hydroxide, etc.) can be used. In this case, the acid group of the urethane resin is neutralized by alkali metal ions generated by ion dissociation of the alkali metal hydroxide. More preferably, potassium ions are used as the alkali metal ions.

Examples of ammonium ions include ammonium ions (NH ₄ ⁺ ) and organic ammonium ions (NX ₄ ⁺ , X represents a hydrogen atom or an organic group, and at least one of X is an organic group). It is done. In order to neutralize the acid group of the urethane resin with ammonium ions, a compound represented by the formula (1) or a compound represented by the formula (2) can be used. In this case, the acid group of the urethane resin is neutralized by ammonium ions generated by ionization or ion dissociation of these compounds. In the following description, “mono to tri” represents mono, di, and tri, and “mono to tetra” represents mono, di, tri, and tetra.

Formula (1): NR ₁ R ₂ R ₃
In Formula (1), R ₁ , R ₂ , and R ₃ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a hydroxyalkyl group having 1 to 6 carbon atoms.

  Examples of the compound represented by the formula (1) include ammonia; aliphatic amines such as mono-trimethylamine, mono-triethylamine, mono-tripropylamine, mono-tributylamine, mono-tripentylamine, mono-trihexylamine; Alkanolamines such as mono to triethanolamine, mono to triisopropanolamine, dimethylethanolamine, methyldiethanolamine; and the like.

  The compound represented by the formula (1) is ionized in the ink as follows, and the acid group of the urethane resin is neutralized by the produced ammonium ion.

_{NR 1 R 2 R 3 + H} 2 O → N + HR 1 R 2 R 3 + OH -.

Equation ^{_{(2): N + R 1}} R 2 R 3 R 4 A -
In Formula (2), R ₁ , R ₂ , R ₃ , and R ₄ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a hydroxyalkyl group having 1 to 6 carbon atoms. A ⁻ represents a monovalent anion.

Examples of the compound represented by the formula (2) include ammonium salts; mono-tetramethylamine salts, mono-tetraethylamine salts, mono-tetrapropylamine salts, mono-tetrabutylamine salts, mono-tetrapentylamine salts, mono-tetrapentylamine salts, Aliphatic amine salts such as tetrahexylamine salts; alkanolamine salts such as mono to tetraethanolamine salts and mono to tetraisopropanolamine salts; Examples of the monovalent anion (A ⁻ ) constituting the compound represented by the formula (2) (ammonium salt, amine salt) include hydroxide ion; halide ion; monovalent inorganic acid anion; It is done. Examples of the halide ion include fluorine ion (F ⁻ ), chloride ion (Cl ⁻ ), bromide ion (Br ⁻ ), iodide ion (I ⁻ ), and the like. Examples of the anion of the monovalent inorganic acid include nitrate ion (NO ₃ ⁻ ).

  The compound represented by the formula (2) is ionically dissociated in the ink as follows, and the acid group of the urethane resin is neutralized by the generated ammonium ion.

N ⁺ R ₁ R ₂ R ₃ R ₄ A ⁻ → N ⁺ R ₁ R ₂ R ₃ R ₄ + A ⁻ .

In order to neutralize the acid group of the urethane resin, it is preferable to use an ammonium ion generated by ionization of the compound represented by the formula (1), and N ⁺ H (CH ₂ CH ₂ OH) ₃ (triethanol It is more preferable to use an amine-derived cation). By using N ⁺ H (CH ₂ CH ₂ OH) ₃ , it is possible to effectively suppress the pH drop of the ink due to protons generated due to the decomposition of the urethane resin, and therefore the intermittent discharge stability is reduced to a particularly high level. Can be suppressed.

  The type of the acid group neutralizing agent in the urethane resin can be analyzed by using the urethane resin separated from the ink. Using a diluted urethane resin diluted with water as a sample, the neutralizing agent is separated by electrophoresis chromatography, and then the type of neutralizing agent is identified and quantified using mass spectrometry or NMR. I do. And the neutralization rate by each neutralizing agent is computable from the value of the acid value measured by the above-mentioned method. In Examples described later, analysis was performed as follows. First, a liquid containing a urethane resin was diluted with water to prepare a sample. Using this sample, the neutralizing agent was separated by electrophoresis chromatography (trade name “Agilent 1600 CE”, manufactured by Agilent Technologies), and the type of neutralizing agent was identified and quantified by mass spectrometry. The neutralization rate of each neutralizing agent was calculated from the type and quantitative value of the neutralizing agent thus obtained and the acid value measured by the above-described method. In addition, if it is in the range of about pH 5.0-10.0 which is the general pH of the water-based ink for inkjet, even if it performs the normal procedure which prepares an ink, the neutralizing agent of the acid group of a urethane resin Can never be changed.

[Physical properties and properties of urethane resin]
[Acid value]
The acid value of the urethane resin needs to be 20 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 120 mgKOH / g or less. As described above, if the acid value is less than 20 mgKOH / g or more than 200 mgKOH / g, both the scratch resistance and the intermittent ejection stability are insufficient. The acid value of the urethane resin can be adjusted by the ratio of units derived from a compound having one isocyanate reactive group and a carboxylic acid group, or units derived from a polyol having an acid group, in 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.

[Ratio of the acid value based on the unit derived from a compound having one isocyanate reactive group and a carboxylic acid group in the acid value of the urethane resin]
The ratio (%) of the acid value based on the unit derived from the compound having one isocyanate reactive group and the carboxylic acid group in the acid value of the urethane resin needs to be 60% or more. As described above, if this ratio is less than 60%, the scratch resistance tends to be insufficient, and the intermittent ejection stability tends to decrease. This ratio may be 100% and is preferably 95% or less.

  Examples of a method for adjusting the ratio of the acid value based on a unit derived from a compound having one isocyanate reactive group and a carboxylic acid group in the acid value of the urethane resin include the following two methods. As a first method, when a urethane resin is synthesized, a method in which a compound having one isocyanate reactive group and a carboxylic acid group is reacted in multiple stages. Moreover, as a 2nd method, when synthesize | combining a urethane resin, the method of adjusting the residual rate of an unreacted isocyanate group and making the polyol which does not have an acid group react with less molar ratio is mentioned. Specifically, when synthesizing a prepolymer, use of a compound having one isocyanate reactive group and a carboxylic acid group in order to obtain a residual ratio of an isocyanate group present at the terminal and a desired acid value ratio Based on the amount, the amount of the polyol having an acid group is adjusted. The amount of the polyol having an acid group and the acid value based on the “unit derived from a compound having one isocyanate-reactive group and a carboxylic acid group” present at the end of the molecular chain cause a chain extension reaction. The relationship is inversely proportional. Therefore, when the amount of the polyol having an acid group is increased, the ratio of the acid value is decreased. Conversely, when the amount of the polyol having an acid group is decreased, the ratio of the acid value is increased. In the examples described later, the ratio of the acid value based on the unit derived from the compound having one isocyanate reactive group and the carboxylic acid group in the acid value of the urethane resin was adjusted by the second method.

The ratio of the acid value based on the unit derived from the compound having one isocyanate reactive group and the carboxylic acid group in the acid value of the urethane resin can be confirmed as follows. A sample prepared by dissolving a urethane resin fractionated by the method described later in deuterated dimethyl sulfoxide is analyzed by carbon nuclear magnetic resonance spectroscopy ( ¹³ C-NMR), and carboxylic acids existing inside and at the end of the molecular chain. The peak integrated value derived from the group is calculated. And the ratio of the peak integrated value derived from the carboxylic acid group which exists in the terminal of a molecular chain in the peak integrated value derived from all the carboxylic acid groups is calculated. Thus, the ratio of the acid value based on the unit derived from the compound having one isocyanate reactive group and the carboxylic acid group in the acid value of the urethane resin can be calculated.

(Weight average molecular weight)
The weight average molecular weight of the urethane resin is required to be 5,000 or more and 30,000 or less. As described above, when the weight average molecular weight of the urethane resin is less than 5,000, the scratch resistance becomes insufficient, and when it exceeds 30,000, the intermittent ejection stability becomes insufficient. The weight average molecular weight is a value in terms of polystyrene obtained by gel permeation chromatography (GPC).

[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. In particular, it is preferable to use a water-insoluble urethane resin (urethane resin particles) present in the ink in the state 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, the prepolymer is added to a liquid containing a compound having one isocyanate reactive group and a carboxylic acid group, a chain extender, a crosslinking agent, and the like, and a termination reaction, a chain extension reaction, a crosslinking reaction, and the like are performed. 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 other hand, when it is not desired to crosslink the urethane resin, only a unit derived from a compound having one or 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, this sample is analyzed by a proton nuclear magnetic resonance method ( ¹ H-NMR) to obtain a peak position. From the obtained peak position, types such as polyisocyanate, polyol, polyamine, a compound having one isocyanate reactive group and a carboxylic acid group can be confirmed. Further, the sample is analyzed by carbon nuclear magnetic resonance spectroscopy ( ¹³ C-NMR), and a bond-derived peak existing at the end of the molecular chain is measured. And from the presence or absence of a peak, the kind of isocyanate reactive group in the compound which has one isocyanate reactive group and a carboxylic acid group 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, the compound which has one isocyanate reactive group, and a carboxylic acid group, can be confirmed.

〔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, if the mass ratio is more than 10.0 times, intermittent ejection stability may not 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 quinacridone. 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. Among these, it is particularly preferable to use a resin dispersed pigment using a resin different from the urethane resin as 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. IPDI: isophorone diisocyanate, H12MDI: 4,4′-dicyclohexylmethane diisocyanate, HDI: hexamethylene diisocyanate, TDI: tolylene diisocyanate, MDI: diphenylmethane diisocyanate, XDI: xylylene diisocyanate, T6002: 1,6-hexanediol polycarbonate ( Asahi Kasei), T5652: 1,6-hexanediol + 1,5-pentanediol polycarbonate (Asahi Kasei), T4672: 1,6-hexanediol + 1,4-butanediol polycarbonate (Asahi Kasei), PES: Polyester polyol , PPG: polypropylene glycol, PTMG: polytetramethylene glycol, PEG: polyethylene glycol,
PC1-PC4: 1,6-hexanediol-based polycarbonate synthesized by a conventional method, NPG: neopentyl glycol, EDA: ethylenediamine, DETA: diethylenetriamine, TMP: trimethylolpropane, DMPA: dimethylolpropionic acid.

<Synthesis of urethane resin>
(Urethane resin 1-50)
In a four-necked flask equipped with a stirrer, a thermometer, a cooler, and a nitrogen gas introduction tube, the amounts of polyisocyanate and polyol having no acid group shown in Table 1 are placed, and the temperature is 100 ° C. in a nitrogen gas atmosphere. For 2 hours. The amount of the polyisocyanate and the polyol having no acid group were determined so that “the number of moles of isocyanate group”> “the number of moles of hydroxy group”.

  Then, the amount of chain extender shown in Table 1, a compound having one isocyanate reactive group and a carboxylic acid group, DMPA, and 150.0 parts of methyl ethyl ketone were added. And the residual rate of the isocyanate group was confirmed by FT-IR, it was made to react at the temperature of 80 degreeC until it became a desired residual rate, and the reaction liquid was obtained. After cooling the resulting reaction solution to a temperature of 40 ° C., ion-exchanged water was added, and the neutralization rate of acid groups was changed to Table 1 with the neutralizing agents shown in Table 1 while stirring at high speed with a homomixer. The liquid was added in the amount used to give the value shown in FIG. By distilling off methyl ethyl ketone from the obtained liquid under heating and reduced pressure, liquids containing water-dispersible urethane resins 1 to 50 having a urethane resin (solid content) content of 42.9% are obtained. It was.

  A sample was prepared by diluting an aqueous solution of urethane resins 1 to 50 with pure water so that the resin content was 1.0%. About this sample, using a particle size analyzer by a dynamic light scattering method (trade name “UPA-EX150”, manufactured by Nikkiso Co., Ltd.), the particle size was measured under the conditions of SetZero: 30 seconds, number of measurements: 3 times, measurement time: 180 seconds. It was measured. As a result, the particle diameters of all of the urethane resins 1 to 50 were detected and confirmed to be water-insoluble.

(Urethane resin 51)
After synthesizing a urethane resin according to Production Example 9 (excluding components relating to neutralization) of Patent Document 1, ion-exchanged water is added and the neutralizing agent is shown in Table 1 while stirring at high speed with a homomixer. It added in the usage-amount used as a sum, and obtained the liquid containing resin. The liquid containing the urethane resin 51 whose content of urethane resin (solid content) is 42.9% was obtained by distilling a solvent off under heating and pressure reduction from the obtained liquid.

(Urethane resin 52)
After synthesizing urethane resin according to the preparation method of water-based emulsion (E-1) of Patent Document 2 (excluding components related to neutralization), neutralize while adding ion-exchanged water and stirring at high speed with a homomixer. The agent was added in a use amount that gave a neutralization rate shown in Table 1 to obtain a liquid containing a resin. The liquid containing the urethane resin 52 whose content of urethane resin (solid content) is 42.9% was obtained by distilling a solvent off under heating and pressure reduction from the obtained liquid.

(Urethane resin 53)
After synthesizing the urethane resin according to the method for synthesizing the polyurethane dispersant 3 of Patent Document 3 (excluding components related to neutralization), ion-exchanged water is added and the neutralizer is displayed while stirring at high speed with a homomixer. A liquid containing resin was obtained by adding in a use amount that gave a neutralization rate shown in 1. The liquid containing the urethane resin 53 whose content of urethane resin (solid content) is 42.9% was obtained by distilling a solvent off under heating and pressure reduction from the obtained liquid.

(Urethane resin 54)
After synthesizing a urethane resin according to the PU-9 synthesis method of Patent Document 4 (excluding components relating to neutralization), ion-exchanged water was added, and the neutralizing agents were added while stirring at high speed with a homomixer. The liquid was added in the amount used to give the neutralization rate shown in (2) to obtain a liquid containing a resin. The liquid containing the urethane resin 54 whose content of urethane resin (solid content) is 42.9% was obtained by distilling off the solvent from the obtained liquid under heating and reduced pressure.

(Urethane resin 55)
After synthesizing a urethane resin according to the synthesis method of PU-24 (excluding components relating to neutralization) of Patent Document 5, ion-exchanged water was added, and the neutralizing agents were added while stirring at high speed with a homomixer. The liquid was added in the amount used to give the neutralization rate shown in (2) to obtain a liquid containing a resin. The liquid containing the urethane resin 55 having a urethane resin (solid content) content of 42.9% was obtained by distilling off the solvent from the obtained liquid under heating and reduced pressure.

(Synthesis conditions and characteristics of urethane resin)
Tables 1 and 2 show the synthesis conditions and characteristics of the urethane resin described above. “Ratio of acid value based on a unit derived from a compound having one isocyanate reactive group and a carboxylic acid group in the acid value of the urethane resin” is expressed as “ratio of terminal acid value (%)”.

<Preparation of pigment dispersion>
(Pigment dispersion 1)
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. Subsequently, the pigment solid content 1 was adjusted to obtain a pigment dispersion 1 having a pH of 10.0. The pigment dispersion 1 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 2)
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 2. The pigment dispersion 2 contains a self-dispersing pigment having —C ₆ H ₄ —CONH—CH (PO (OK) ₂ ) ₂ groups bonded to the particle surface, and the pigment content is 30.0%. there were.

(Pigment dispersion 3)
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 content was adjusted to obtain pigment dispersion 3. The pigment dispersion 3 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 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. 4,485 g of ion exchange water was added thereto and dispersed with a high-pressure homogenizer to obtain a dispersion A. The average particle size of the pigment in this dispersion A was 110 nm. The obtained dispersion A was transferred to a high-pressure vessel and pressurized with 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, whereby dispersion B was obtained. After adjusting the pH of dispersion B to 10.0 using potassium hydroxide, the concentration of pigment solids was adjusted to obtain 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)
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, and dispersion C was obtained. This dispersion C contained a pigment in which APSES was bonded to the pigment particle surface.

  In order to obtain the number of moles of the functional group bonded to the pigment in the dispersion C, the following operation was performed. Using a sodium ion electrode (1512A-10C; manufactured by HORIBA, Ltd.), the sodium ion concentration in dispersion C was measured and converted to the number of moles (mol / g) per pigment solid content. Next, dispersion C 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 C. After stirring this mixture for 18 to 48 hours, impurities were removed, and dispersion D was obtained. In the dispersion D, a pigment having PEHA bound to the particle surface via APSES was contained, 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 D 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, and a pigment dispersion 5 was obtained. The pigment dispersion 5 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%.

<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 Tables 3 and 4): Amount used (%) shown in Tables 3 and 4
・ 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, A and B are acceptable levels, and C is an unacceptable level. The evaluation results are shown in Tables 3 and 4. Tables 3 and 4 also show 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 60 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.
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.

(Intermittent discharge stability)
Using the above inkjet recording apparatus, 10,000 drops of ink were ejected from all ejection ports of the recording head at a driving frequency of 5 kHz in an environment of a temperature of 15 ° C. ± 2 ° C. and a relative humidity of 10%. . Then, after providing a blank for 0.5 inch, ink was ejected from one ejection port, and a horizontal ruled line having a width of 4 dots (for 4 drops of ink) was recorded. Further, after the ink ejection was stopped for 1.5 seconds, the ink was ejected from the same one ejection port as described above, and a horizontal ruled line having a width of 4 dots was recorded again. Thus, the state of the two horizontal ruled lines recorded before and after the discharge pause for 1.5 seconds was visually confirmed, and the intermittent discharge stability was evaluated according to the following evaluation criteria.
AA: The horizontal ruled line after the discharge pause was not disturbed, and the line widths of the two horizontal ruled lines before and after the discharge pause were the same. A: The horizontal ruled line after the discharge pause was disturbed, but the two The line width in the horizontal ruled line was the same. B: The horizontal ruled line after the discharge stop was disordered, and the line width in the horizontal ruled line after the discharge stop was narrower than the line width before the discharge stop. The horizontal ruled line after the pause was disturbed, and the line width of the horizontal ruled line after the discharge pause was considerably narrower than the line width before the discharge pause.

Claims (11)

A water-based ink jet ink containing a pigment and a urethane resin,
The urethane resin has units derived from polyisocyanate, a polyol having no acid group, and a compound having one isocyanate reactive group and a carboxylic acid group,
The urethane resin has a weight average molecular weight of 5,000 or more and 30,000 or less, an acid value of 20 mgKOH / g or more and 200 mgKOH / g or less, and occupies the acid value of the urethane resin. A water-based ink having a ratio (%) of an acid value based on a unit of 60% or more.   2. The water-based ink according to claim 1, wherein a ratio (%) of an acid value based on a unit derived from the compound in an acid value of the urethane resin is 95% or less.   The aqueous ink according to claim 1 or 2, wherein the compound is at least one compound selected from the group consisting of monohydroxycarboxylic acid, monothiolcarboxylic acid, and monoaminocarboxylic acid.   The water-based ink according to any one of claims 1 to 3, wherein the compound is at least one selected from the group consisting of a monohydroxycarboxylic acid and a monoaminocarboxylic acid.   5. The water-based ink according to claim 1, wherein the compound is at least one selected from the group consisting of glycolic acid, lactic acid, p-hydroxybenzoic acid, and salicylic acid.   The water-based ink according to any one of claims 1 to 4, wherein the polyol having no acid group is a polycarbonate polyol.   6. The water-based ink according to claim 1, wherein the polyol having no acid group has a number average molecular weight of 450 or more and 4,000 or less.   The acid group of the urethane resin is neutralized with an alkali metal ion and at least one ammonium ion of an ammonium ion and an organic ammonium ion, and based on all the acid groups of the urethane resin. The water-based ink according to any one of claims 1 to 7, wherein a neutralization rate is 80% or more and a neutralization rate by the ammonium-based ions is 1% or more and less than 45%.   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. 9. The water-based ink according to any one of 8 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 9. 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 9.