JP2019099692A - Water-based ink, ink cartridge, and inkjet recording method - Google Patents

Abstract

To provide a water-based ink for inkjet high in optical concentration, capable of recording an image excellent in marker resistance and excellent in redispersion, and an ink cartridge and an inkjet recording method using the water-based ink.SOLUTION: There is provided a water-based ink for inkjet containing a self-dispersible pigment, a first urethane resin and a second urethane resin. The first urethane resin has a crosslinked structure, and the second urethane resin has no crosslinked structure. There are provided an ink cartridge having the water-based ink and an ink housing part housing the water-based ink, and an inkjet recording method using the water-based ink.SELECTED DRAWING: None

Description

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

  In recent years, with the improvement of image quality and recording speed, the use opportunity of the ink jet recording apparatus in the business field is increasing. Performances required for water-based inks for inkjet used in the business field include reliability (such as ejection stability), image quality (such as high optical density), and fastness (such as scratch resistance and marker resistance). be able to. In order to improve these performances, for example, an aqueous ink containing a self-dispersion pigment and a urethane resin having a crosslinked structure has been proposed (Patent Document 1). Also, there is disclosed an ink using a pigment dispersed with a urethane resin not having a crosslinked structure and another urethane resin not having a crosslinked structure (Patent Documents 2 and 3).

JP, 2011-144354, A JP, 2011-202004, A Japanese Patent Publication No. 2013-535548 gazette

  The present inventors examined a conventional ink containing a urethane resin having a crosslinked structure and a conventional ink using a pigment dispersed with a urethane resin. As a result, although the reliability of the ink and the quality and the fastness of the recorded image have been improved to some extent, it was found that none of the characteristics has reached the level required in the recent business field. .

  By the way, the ink redispersion property is a very important performance from the viewpoint of the reliability, which affects the adhesion recovery property of the ink jet recording apparatus and the deposition property on the waste ink storage portion. By using the ink proposed in Patent Document 1, it was possible to record an image with good image quality and fastness. However, when the present inventors examined, it turned out that the ink proposed by patent document 1 is not favorable in redispersibility. Moreover, although the ink proposed by patent document 2 and 3 was favorable in re-dispersion property, it turned out that the cohesion of the pigment at the time of provision to a recording medium is scarce. For this reason, with the inks proposed in Patent Documents 2 and 3, it has been difficult to record an image with high optical density and an image excellent in fastness such as marker resistance.

  Accordingly, an object of the present invention is to provide an aqueous ink for inkjet having excellent redispersibility, capable of recording an image having high optical density and excellent marker resistance. Another object of the present invention is to provide an ink cartridge and an ink jet recording method using the aqueous ink.

  The above object is achieved by the present invention described below. That is, according to the present invention, it is an aqueous ink for inkjet containing a self-dispersion pigment, a first urethane resin, and a second urethane resin, wherein the first urethane resin has a crosslinked structure, An aqueous ink is provided, characterized in that the second urethane resin does not have a crosslinked structure.

  According to the present invention, it is possible to provide an aqueous ink for inkjet having excellent redispersibility, which can record an image having a high optical density and an excellent marker resistance. Further, according to the present invention, it is possible to provide an ink cartridge and an ink jet recording method using this aqueous ink.

FIG. 2 is a cross-sectional view schematically showing an embodiment of the ink cartridge of the present invention. It is a figure which shows typically an example of the inkjet recording device used for the inkjet recording method of this invention, (a) is a perspective view of the principal part of an inkjet recording device, (b) is a perspective view of a head cartridge.

  Hereinafter, the present invention will be described in more detail by way of preferred embodiments. In the present invention, when the compound is a salt, the salt is dissociated into ions in the ink, but for convenience, it is expressed as “containing a salt”. Moreover, the thing of the water-based ink for inkjets may only be described as "ink." Physical property values are values at normal temperature (25 ° C.) unless otherwise specified.

  It is already known that an ink capable of recording an image having a high optical density and improved scratch resistance and marker resistance can be obtained by blending a urethane resin having a crosslinked structure with a self-dispersion pigment. However, when the present inventors examined, it turned out that redispersion property falls about the ink which made the urethane resin which has a crosslinked structure and the self-dispersion pigment coexist. The ink redispersion is a very important performance from the viewpoint of reliability, which affects the adhesion recovery of the ink jet recording apparatus and the deposition on the waste ink storage portion.

  Urethane resin is, in a broad sense, a resin synthesized using (poly) isocyanate. The urethane resin generally used for the aqueous ink for inkjet is synthesize | combined using polyisocyanate and the component (polyol and polyamine) which reacts with polyisocyanate. Furthermore, they are synthesized using crosslinking agents and chain extenders, if necessary. The urethane resin synthesized using these components is usually mainly composed of two segments, a hard segment and a soft segment.

  The hard segment is composed of units derived from relatively low molecular weight compounds such as polyisocyanates, polyamines, polyols having acid groups, crosslinking agents, and chain extenders. A large number of urethane bonds exist in the hard segment, and the hard segment portions are easily concentrated due to hydrogen bonds between the urethane bonds. For this reason, the hard segment mainly contributes to the strength of the urethane resin. On the other hand, soft segments are composed of units derived from compounds having relatively large molecular weight, such as polyols having no acid group. Soft segments are less likely to be densely present than hard segments. Therefore, the soft segment mainly contributes to the flexibility of the urethane resin. A film formed of a urethane resin (hereinafter also referred to as a “urethane resin film”) has a microphase separation structure formed by the hard segment and the soft segment, so that it has both strength and flexibility, and exhibits high elasticity. The properties of such a urethane resin film are closely related to the development of the marker resistance of the image.

  On the other hand, since the crosslinked structure part is bulky and the crosslinked structure part in the hard segment in which the micro phase separation structure is formed is particularly bulky, it is considered that the adsorption to the pigment is physically inhibited. The resin adsorbed to the pigment has the function of stabilizing the dispersion state of the pigment, and is expected to contribute to the improvement of the redispersibility of the ink. That is, it is presumed that the decrease in the adsorptivity due to the bulkiness of the cross-linked structure portion of the urethane resin is the cause of the decrease in the redispersibility of the ink. Therefore, the present inventors further studied under the assumption that the adsorption of the urethane resin to the pigment is promoted by reducing the bulkiness of the crosslinked structure portion, and the redispersibility of the ink is improved. As a result, it has been found that the redispersibility of the ink is improved by further adding a urethane resin having a small steric hindrance, that is, having no crosslinked structure, and the composition of the ink of the present invention has been found. By bonding the hard segment of the urethane resin not having a crosslinked structure to the crosslinked structure portion of the urethane resin having a crosslinked structure, the bonding of the crosslinked structural portions in forming the microphase separation structure is suppressed, and the urethane resin Bulkiness is alleviated. As a result, it is considered that the redispersion of the ink is improved while making it possible to record an image having a high optical density and an excellent marker resistance.

<Ink>
The ink of the present invention is an aqueous ink for inkjet containing a self-dispersion pigment, a first urethane resin, and a second urethane resin. Hereinafter, each component etc. which comprise the ink of this invention are demonstrated in detail.

(Self-dispersible pigment)
The ink of the present invention contains a self-dispersible pigment as a colorant. As the self-dispersible pigment, those in which an anionic group such as an acid group is bonded to the surface of the pigment particle directly or through another atomic group (-R-) can be used. The content (% by mass) of the pigment in the ink is preferably 0.1% by mass or more and 10.0% by mass or less based on the total mass of the ink.

  As an anionic group, a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, a phosphonic acid group etc. can be mentioned. These anionic groups may form a salt. Examples of the cation forming a salt include ions of alkali metals such as lithium, sodium and potassium; and cations of organic amines such as ammonium ion and dimethylamine. When the anionic group forms a salt, the form of the salt in the ink may be either in a partially dissociated state or in a completely dissociated state.

  As another atomic group (-R-), a linear or branched alkylene group having 1 to 12 carbon atoms; an arylene group such as a phenylene group or a naphthylene group; an amide group; a sulfonyl group; an amino group; a carbonyl group; Groups; ether groups can be mentioned. Moreover, the group etc. which combined these groups can be mentioned.

  The type of pigment is not particularly limited, and any known inorganic pigment or organic pigment can be used. Specific examples of the pigment include inorganic pigments such as calcium carbonate, titanium oxide and carbon black; and organic pigments such as azo, phthalocyanine and quinacridone. In addition, a dye or the like may be further contained in the ink as a coloring material for the purpose of toning or the like.

The surface charge amount of the self-dispersing pigment is preferably 1.0 [mu] mol / m ² or more 4.5μmol / m ² or less. The amount of surface charge is defined as a value obtained by dividing the amount of hydrophilic group (mmol / g) of the self-dispersion pigment by the external specific surface area STSA (m ² / g) of the pigment. When the hydrophilic group contained in the functional group is an ionic group (anionic group or cationic group), the amount of the ionic group contained in the functional group of the self-dispersion pigment in the pigment dispersion liquid by a colloid titration method Can be measured. In the Example mentioned later, it measured by potentiometric titration, using the potentiometric automatic titration apparatus (brand name "AT-510", Kyoto Electronics Co., Ltd. make) equipped with the flow potential titration unit (PCD-500). At this time, methyl glycol chitosan was used as a titrant for analysis of the anionic group. Of course, it is also possible to measure the amount of hydrophilic groups using a pigment extracted from the ink by an appropriate method. The external specific surface area STSA (m ² / g) can be quantified under generally known conditions using, for example, a nitrogen adsorption method.

(Urethane resin)
The ink of the present invention contains a first urethane resin having a crosslinked structure and a second urethane resin having no crosslinked structure. Hereinafter, the first urethane resin and the second urethane resin are collectively referred to simply as "urethane resin". As the urethane resin, for example, a urethane resin having a unit derived from each of polyisocyanate, a polyol having no acid group, a polyol having an acid group, and a polyamine can be used. The "unit" of the urethane resin in the present invention means a repeating unit derived from one monomer.

[First urethane resin]
The first urethane resin has a crosslinked structure. "The urethane resin has a crosslinked structure" in the present invention means that the urethane resin has a three-dimensional network structure formed by three-dimensionally advancing urethanization reaction at the time of production. That is, the first urethane resin having a crosslinked structure is required to include, in its structure, a unit derived from a compound having three or more reactive groups. The three-dimensional structure formed by the hydrogen bond between urethane bonds and the three-dimensional structure formed by the hydrogen bond between the urethane bond and the hydroxyl group of the polyol are not included in the “crosslinked structure” in the present invention. In addition, the urethane resin obtained by the two-component reaction type crosslinking reaction is included in the “urethane resin having a crosslinked structure” in the present invention as long as it is added to the ink after the crosslinking reaction. On the other hand, the urethane resin that undergoes a crosslinking reaction after being applied to the recording medium is not included in the “urethane resin having a crosslinked structure” in the present invention.

  As a compound which has a 3 or more reactive group, the trifunctional or more than trifunctional polyisocyanate, the trifunctional or more than trifunctional polyol, and the trifunctional or more than trifunctional chain extender (trifunctional or more polyamine etc.) can be mentioned. Among them, as a compound having three or more reactive groups, a trifunctional or higher functional polyamine is preferable, and at least one of diethylenetriamine and triethylenetetramine is more preferable. Among them, diethylenetriamine is particularly preferable. That is, the first urethane resin preferably has a crosslinked structure crosslinked by a trifunctional or higher functional polyamine. When a trifunctional or higher functional polyisocyanate or a trifunctional or higher functional polyol is used as a compound having three or more reactive groups, urethane bonds are three-dimensionally generated to form a crosslinked structure. On the other hand, when a trifunctional or higher functional polyamine is used as a compound having three or more reactive groups, a urea bond is three-dimensionally formed to form a crosslinked structure.

  The proportion (mol%) of units derived from the compound having three or more reactive groups contained in the first urethane resin is 1.0 mol% or more and 8.0 mol% or less based on all the units. Is preferred. If the above ratio is less than 1.0 mol%, the effect of improving the marker resistance may be slightly reduced. On the other hand, if the above ratio is more than 8.0 mol%, the ink redispersibility may be slightly reduced.

  The content (% by mass) of the first urethane resin in the ink is preferably 3.0% by mass or less based on the total mass of the ink. When the content of the first urethane resin is more than 3.0% by mass, the redispersibility of the ink may be reduced. Further, the content (% by mass) of the first urethane resin in the ink is preferably 0.10 times to 0.90 times by mass ratio with respect to the content (% by mass) of the self-dispersion pigment. If the mass ratio is less than 0.10 times, the marker resistance of the image may be slightly reduced. On the other hand, if the mass ratio is more than 0.90 times, the optical density of the image may be slightly reduced.

[Second urethane resin]
The second urethane resin does not have a crosslinked structure. The "urethane resin does not have a crosslinked structure" in the present invention means that the urethane resin does not include a unit derived from a compound having three or more reactive groups in its structure. The second urethane resin may have a three-dimensional structure formed by hydrogen bonding of the urethane bond and the hydroxyl group of the polyol.

  The proportion (mol%) of the urethane bond in the total of the urethane bond and the urea bond in the second urethane resin is preferably 90 mol% or more. If the proportion of urethane bonds is less than 90 mol%, the redispersibility of the ink may be reduced. It is preferable that the said ratio is 100 mol% or less.

  The content (% by mass) of the first urethane resin in the ink is preferably 0.50 times or more and 2.00 times or less by mass ratio with respect to the content (% by mass) of the second urethane resin. When the mass ratio is less than 0.50 times, the marker resistance of the image may be slightly reduced. On the other hand, if the above mass ratio is more than 2.00 times, the ink redispersibility may be slightly reduced.

[Polyisocyanate]
The polyisocyanate is a compound having two or more isocyanate groups in its molecular structure. As polyisocyanate, aliphatic polyisocyanate, aromatic polyisocyanate, etc. can be 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 Polyisocyanate having a chain structure such as 5-diisocyanate, 3-methylpentane-1,5-diisocyanate; isophorone diisocyanate, hydrogenated xylylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 1,4-cyclohexane diisocyanate Polyoxy resins having a cyclic structure such as methyl cyclohexylene diisocyanate and 1,3-bis (isocyanate methyl) cyclohexane Cyanate; and the like.

  As aromatic polyisocyanate, tolylene diisocyanate, 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-dibenzyl diisocyanate, 1,5-naphthylene diisocyanate Isocyanate, xylylene diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, dialkyl diphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, α, α, α ', α'-tetramethyl xylylene diisocyanate and the like can be mentioned. .

  Among the above polyisocyanates, alicyclic polyisocyanates are preferable. Further, among the alicyclic polyisocyanates, isophorone diisocyanate is more preferable.

  In order to impart a crosslinked structure to the urethane resin, it is also preferable to use a polyisocyanate having three or more isocyanate groups (polyfunctional isocyanate having three or more functions). Examples of the trifunctional or higher functional polyisocyanate include various isocyanate prepolymers such as polyisocyanurate type polyisocyanate, adduct type polyisocyanate, and biuret type polyisocyanate. When a trifunctional or higher functional polyisocyanate is used, the proportion of units derived from the trifunctional or higher polyisocyanate is preferably 5.0% by mass or more and 90.0% by mass or less based on the total polyisocyanate compound. If the proportion of units derived from trifunctional or higher polyisocyanate is less than 5.0% by mass, the improvement in the marker resistance of the image may be slightly reduced. On the other hand, when the proportion of the unit derived from the trifunctional or higher polyisocyanate is more than 90.0% by mass, the urethane resin film becomes tough while the flexibility decreases, so the marker resistance improvement effect of the image is improved. It may decrease slightly.

[Polyol, polyamine]
A polyol is a compound having two or more hydroxy groups in its molecular structure. Examples of the polyol include polyols having no acid group such as polyether polyol, polyester polyol, polycarbonate polyol and the like; polyols having an acid group; and the like. In addition, a polyamine is a compound having two or more amino groups in its molecular structure.

[Polyol not having an acid group]
Examples of polyether polyols include addition polymers of alkylene oxides and polyols; glycols such as (poly) alkylene glycol; and the like. Examples of the alkylene oxide include ethylene oxide, propylene oxide, butylene oxide, α-olefin oxide and the like. As polyols to be addition-polymerized with alkylene oxide, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl- 1,5-pentanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 4,4-dihydroxyphenylpropane, 4,4-dihydroxy Diols such as phenylmethane, hydrogenated bisphenol A, dimethylol urea and derivatives thereof; glycerin, trimethylolpropane, 1,2,5-hexanetriol, 1,2,6-hexanetriol, pentaerythritol, trimethylolmelamine and derivatives thereof , Polyoxypropylene Triols such as polyol; and the like. As glycols, 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 glycols such as neopentyl glycol; ethylene glycol-propylene glycol copolymers; and the like can be mentioned.

  As polyester polyol, an acid ester etc. can be mentioned. Examples of the acid component constituting the acid ester include aromatic dicarboxylic acids such as phthalic acid, naphthalene dicarboxylic acid, biphenyl dicarboxylic acid and tetrahydrophthalic acid; alicyclic dicarboxylic acids such as hydrogenated products of these aromatic dicarboxylic acids; Acid, succinic acid, tartaric acid, oxalic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, alkylsuccinic acid, linolenic acid, maleic acid, fumaric acid, mesaconic acid, citraconic acid, etc. Aliphatic dicarboxylic acids; and the like. These anhydrides, salts, derivatives (alkyl esters, acid halides) and the like can also be used as the acid component. Moreover, as a component which forms an acid component and ester, polyols, such as diol and triol; Glycols, such as (poly) alkylene glycol; etc. can be mentioned. As the polyols and glycols, those exemplified as components constituting the above-mentioned polyether polyol can be mentioned.

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

  The number average molecular weight of the polyol having no acid group is preferably 400 or more and 4,000 or less. The polyol having no acid group is preferably a polyether polyol, and more preferably glycols such as polyethylene glycol, polypropylene glycol and polytetramethylene glycol. The proportion of units derived from glycols in units derived from a polyol having no acid group in the urethane resin is preferably 90.0% by mass or more, and more preferably 100.0% by mass . It is preferable that all of the units derived from the polyol having no acid group in the urethane resin are units derived from glycols.

[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 polyols having a carboxylic acid group include dimethylol acetic acid, dimethylol propionic acid, dimethylol butanoic acid and dimethylol butyric acid. The acid group of the polyol having an acid group may be in a salt form. Examples of the cation forming a salt include ions of alkali metals such as lithium, sodium and potassium; and cations of organic amines such as ammonium ion and dimethylamine. The molecular weight of the polyol having a general-purpose acid group is at most about 400. For this reason, a unit derived from a polyol having an acid group is usually a hard segment of a urethane resin.

  The proportion of a unit derived from a polyol having an acid group in the unit for giving an acid value to a urethane resin is preferably 90.0% by mass or more, and more preferably 100.0% by mass. That is, it is preferable that all the units which give an acid value to a urethane resin are units derived from the polyol which has an acidic radical.

  The acid value of the first urethane resin is preferably 30 mg KOH / g or more and 90 mg KOH / g or less, and more preferably 40 mg KOH / g or more and 80 mg KOH / g or less. When the acid value of the first urethane resin is less than 30 mg KOH / g, the discharge stability of the ink may be reduced. On the other hand, when the acid value of the first urethane resin is more than 90 mgKOH / g, the balance of the ratio of the hard segment and the soft segment may be lost, and the marker resistance improvement effect of the image may be slightly reduced.

  The acid value of the second urethane resin is preferably 20 mg KOH / g or more and 100 mg KOH / g or less. If the acid value of the second urethane resin is less than 20 mg KOH / g, the discharge stability of the ink may be reduced. On the other hand, when the acid value of the second urethane resin is more than 100 mg KOH / g, the amount of ions in the ink may increase, and the dispersed state of the pigment may be somewhat unstable.

[Polyamine]
Examples of polyamines include monoamines having a plurality of hydroxy groups such as dimethylolethylamine, diethanolmethylamine, dipropanolethylamine, dibutanolmethylamine, etc .; ethylenediamine, propylenediamine, hexylenediamine, isophoronediamine, xylylenediamine, diphenylmethanediamine, hydrogen Examples thereof include bifunctional polyamines such as added diphenylmethanediamine and hydrazine; and trifunctional or higher polyamines such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, polyamidepolyamine, polyethylenepolyimine and the like. For convenience, compounds having a plurality of hydroxy groups and one "amino group, imino group" are also listed as "polyamines". In addition, the molecular weight of the general-purpose polyamine is also at most about 400, similarly to the polyol having the general-purpose acid group. For this reason, units derived from polyamines usually become hard segments of urethane resin.

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

  The use of a chain extender affects the molecular weight of the resulting urethane resin. The weight average molecular weight Mw1 of the first urethane resin is preferably 5,000 or more and 30,000 or less, and more preferably 8,000 or more and 25,000 or less. When the weight average molecular weight Mw1 of the first urethane resin is less than 5,000, the thickening during ink evaporation is insufficient, and the resin remaining on the recording medium tends to decrease, and the marker resistance of the image is slightly reduced. May. On the other hand, if the weight average molecular weight Mw1 of the first urethane resin is more than 30,000, the adsorption of the resin to the pigment tends to be reduced, and the ink redispersion may be slightly reduced. The ratio (Mw1 / Mw2) of the weight average molecular weight Mw1 of the first urethane resin to the weight average molecular weight Mw2 of the second urethane resin is preferably 0.4 times or more and 0.8 times or less. When the above ratio is less than 0.4, the second urethane resin is likely to be included in the second urethane resin because the second urethane resin is too large compared to the first urethane resin. The marker resistance improvement effect may be slightly reduced. On the other hand, if the above ratio is more than 0.8 times, the second urethane resin is relatively too small, which makes it difficult to suppress the bond between the crosslinked structure parts of the first urethane resin, and the ink Dispersion may be slightly reduced.

[Method of verification]
The various physical properties and the like of the urethane resin can be verified by analyzing the sediment and the supernatant obtained by centrifuging the ink. Since the pigment is insoluble in the organic solvent, the urethane resin can also be separated by solvent extraction. Although the physical properties of the urethane resin can be verified even in the state of the ink, extraction accuracy from the ink can be further enhanced. For example, an excess acid (such as hydrochloric acid) is added to a supernatant obtained by centrifuging the ink at 80,000 rpm to precipitate a resin, and the resin is taken out and dried. The dried resin is placed in tetrahydrofuran and left for 24 hours. Since the crosslinked structure portion of the urethane resin is insoluble in tetrahydrofuran, this operation makes it possible to separate the urethane resin having a crosslinked structure from the urethane resin having no crosslinked structure.

  The composition of the urethane resin is analyzed by thermal decomposition gas chromatography or Fourier transform infrared spectrophotometer (FT-IR) for the resin separated by the above method. Thereby, types such as polyisocyanate, polyol having no acid group, and polyol having an acid group can be easily confirmed.

(I) Reactant of polyisocyanate and polyol having an acid group, (ii) Reactant of polyisocyanate and polyether polyol, and (iii) Reactant of polyisocyanate and water, as described above. Prepare each of The thus prepared reactant is dissolved in deuterated dimethyl sulfoxide and analyzed by carbon nuclear magnetic resonance ( ¹³ C-NMR) to confirm the chemical shift of the urethane bond and the urea bond for each reactant. Do. In the above example, the chemical shift of the urethane bond from the reactant of (i) and (ii) and the chemical shift of the urea bond from the reactant of (iii) are respectively confirmed. And the peak of a urethane bond and a urea bond is specified from each obtained chemical shift, and the ratio of the urethane bond in a urethane resin is computed from the ratio of the integration value of those peaks.

In addition, a polyol having an acid group, the type of which is specified as described above, is dissolved in deuterated dimethyl sulfoxide and analyzed by carbon nuclear magnetic resonance ( ¹³ C-NMR) to confirm its chemical shift. . Further, the separated urethane resin is also analyzed by carbon nuclear magnetic resonance ( ¹³ C-NMR) to confirm its chemical shift. Then, for example, the polyol having an acid group is calculated by calculating the ratio from the peak integrated value around 175 ppm derived from a carboxylic acid group in the urethane resin and the peak integrated value derived from a polyol having an acid group previously obtained. Calculate the ratio of the acid value of origin. By the way, the chemical shift derived from the polyol having an acid group is somewhat shifted depending on the measurement conditions, but, for example, it is around 65 ppm in the case of dimethylol propionic acid and around 60 ppm in the case of dimethylol butanoic acid.

  The weight average molecular weight (Mw), number average molecular weight (Mn), and polydispersity (Mw / Mn) of the urethane resin can be measured and calculated by gel permeation chromatography (GPC method).

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

  The aqueous medium can further contain a water-soluble organic solvent. As the water-soluble organic solvent, monohydric alcohol, polyhydric alcohol, (poly) alkylene glycol, glycol ether, nitrogen-containing polar solvent, sulfur-containing polar solvent and the like can be used. The content (mass%) of the water-soluble organic solvent in the ink is preferably 3.0 mass% or more and 50.0 mass% or less based on the total mass of the ink, and is 15.0 mass% or more and 40.0 It is further preferable that the content is at most mass%. If the content of the water-soluble organic solvent in the ink is out of the above range, ejection failure may easily occur.

(Physical properties of ink)
The aqueous ink of the present invention is an ink applied to an ink jet recording method. For this reason, it is preferable to control to the physical-property value suitable for the ink for inkjets. The surface tension of the ink at 25 ° C. is preferably 20 mN / m or more and 60 mN / m or less, and more preferably 30 mN / m or more and 50 mN / m or less. The viscosity of the ink at 25 ° C. is preferably 1.0 mPa · s or more and 10.0 mPa · s or less. It is particularly preferable that the viscosity of the ink is 6.0 mPa · s or less because the ejection stability is improved. The pH of the ink at 25 ° C. is preferably 5.0 or more and 10.0 or less.

(Other additives)
In the ink of the present invention, other than the above components, if necessary, water solubility of solid at room temperature such as polyhydric alcohols such as trimethylolpropane and trimethylolethane, and urea derivatives such as urea and ethylene urea An organic compound may be contained. Furthermore, in the ink of the present invention, if necessary, a surfactant, a pH adjuster, a rust inhibitor, an antiseptic, a mildew agent, an antioxidant, a reduction inhibitor, an evaporation promoter, a chelating agent, and Various additives such as water soluble resins may be contained.

<Ink cartridge>
The ink cartridge of the present invention comprises an ink and an ink storage portion for storing the ink. The ink stored in the ink storage unit is the ink of the present invention described 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 are in communication via the communication port 18. In addition, the absorber storage chamber 16 is in communication 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 portion may not have an ink storage chamber for storing liquid ink, and may be configured to hold the entire amount of ink stored by an absorber. In addition, the ink storage portion may be configured to store the entire amount of ink in a liquid state without having an absorber. Furthermore, the ink cartridge may be configured to have an ink storage portion and a recording head.

<Ink jet recording method>
The ink jet recording method of the present invention is a method of discharging an ink of the present invention described above from an ink jet recording head to record an image on a recording medium. Examples of the method of ejecting the ink include a method of applying mechanical energy to the ink and a method of applying thermal energy to the ink. In the present invention, it is particularly preferable to adopt a method of applying thermal energy to the ink to eject the ink. Except for using the ink of the present invention, the steps of the inkjet recording method may be known.

  FIG. 2 is a view schematically showing an example of an ink jet recording apparatus used in the ink jet recording method of the present invention, wherein (a) is a perspective view of the main part of the ink jet recording apparatus, and (b) is a perspective view of a head cartridge. It is. The inkjet recording apparatus is provided with conveyance 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 to set the ink cartridge 42. 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 the conveyance means (not shown), whereby the image is recorded on the recording medium 32.

  Hereinafter, the present invention will be described in more detail by way of examples and comparative examples, but the present invention is not limited at all by the following examples as long as the gist thereof is not exceeded. Those described as "parts" and "%" in terms of component amounts are on a mass basis unless otherwise specified.

<Preparation of pigment dispersion>
(Pigment dispersion 1, 5 to 8)
A solution obtained by dissolving 5.0 g of concentrated hydrochloric acid in 5.5 g of water was cooled to 5 ° C., and the amount of the treating agent (4-amino-1,2-benzenedicarboxylic acid) shown in Table 1 was added. The container containing this solution was placed in an ice bath to cool to below 10 ° C., and a solution obtained by dissolving sodium nitrite in the amount shown in Table 1 in 9.0 g of water at 5 ° C. was added. After stirring for 15 minutes, 6.0 g of carbon black (specific surface area 220 m ² / g, DBP oil absorption 105 mL / 100 g) was added under stirring, and stirring was further performed 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 Advantec), and then the obtained particles were sufficiently washed with water. The washed particles were dried in an oven at 110 ° C. to obtain a self-dispersible pigment. After ion exchange treatment was carried out to substitute the counter ion of the anionic group of the self-dispersion pigment from sodium ion to potassium ion, the concentration of the solid content was adjusted to obtain pigment dispersions 1, 5-8. The obtained pigment dispersions 1, 5 to 8 contain a self-dispersion pigment in which —C ₆ H ₃ — (COOK) ₂ group is bonded to the particle surface of the pigment, and the pigment content is 10.0 %Met.

  The surface charge of the self-dispersed pigment in the pigment dispersion was determined by potentiometric titration using 5 mmol / L methyl glycol chitosan as a titration reagent using a potentiometric automatic titration apparatus equipped with a flow potential titration unit (PCD-500). It was measured. A trade name "AT-510" (manufactured by Kyoto Denshi Kogyo Co., Ltd.) was used as a potentiometric automatic titrator. The surface charge amount of the measured self-dispersible pigment is shown in Table 1.

(Pigment dispersion 2)
A commercially available pigment dispersion (trade name "CAB-O-JET 450C", manufactured by Cabot) containing a self-dispersible pigment having a functional group containing a phosphonic acid group bonded to the particle surface is diluted with ion-exchanged water to contain the pigment A pigment dispersion 2 having an amount of 10.0% was prepared. The surface charge amount of the measured self-dispersible pigment is shown in Table 1.

(Pigment dispersion 3)
A commercially available pigment dispersion (trade name "CAB-O-JET 265M", manufactured by Cabot) containing a self-dispersing pigment having a functional group containing a phosphonic acid group bonded to the particle surface is diluted with ion-exchanged water to contain the pigment A pigment dispersion 3 having an amount of 10.0% was prepared. The surface charge amount of the measured self-dispersible pigment is shown in Table 1.

(Pigment dispersion 4)
A commercially available pigment dispersion (trade name "CAB-O-JET 740Y", manufactured by Cabot) containing a self-dispersion pigment having a functional group containing a phosphonic acid group bonded to the particle surface is diluted with ion-exchanged water to contain the pigment A pigment dispersion 4 whose amount was 10.0% was prepared. The surface charge amount of the measured self-dispersible pigment is shown in Table 1.

(Pigment dispersions 9 to 13)
The components shown in Table 2 were mixed to obtain a mixture. The resulting mixture was dispersed for 1 hour using a sand grinder and then centrifuged to remove impurities. Furthermore, after pressure-filtering with the micro filter (made by Fujifilm) of 3.0 micrometers of pore sizes, the density | concentration of solid content was adjusted and the pigment dispersion liquids 9-13 were obtained. In Table 2, "Joncril 683" is a trade name (made by BASF) of an aqueous resin solution in which the content of the acrylic resin is 20.0%.

<Synthesis of Urethane Resin>
A four-necked flask equipped with a thermometer, a stirrer, a nitrogen gas inlet tube, and a reflux tube was prepared. The four-necked flask was charged with polyisocyanate (IPDI) of the type and amount shown in Table 3 and a polyol, and reacted at a temperature of 100 ° C. for 2 hours under a nitrogen gas atmosphere. Subsequently, DMPA (polyol having an acid group), a chain extender, and 150.0 parts of methyl ethyl ketone of the type and amount shown in Table 3 are added, the residual ratio of isocyanate group is confirmed by FT-IR, and desired residual The reaction was carried out at a temperature of 80 ° C. until the reaction rate reached to obtain a reaction solution. After cooling the obtained reaction solution to a temperature of 40 ° C., an appropriate amount of ion exchange water is added, and while stirring at high speed with a homomixer, a neutralizing agent (potassium hydroxide aqueous solution) is added to neutralize the acid group , Obtained a liquid containing a resin. The methyl ethyl ketone was distilled off from the obtained liquid under heating and pressure reduction, and the liquid containing urethane resins 1 to 12 each having a urethane resin (solid content) content of 25.0% was obtained. The weight average molecular weight of the urethane resin was adjusted by appropriately changing the reaction time at a temperature of 80 ° C.

  Hydrochloric acid was added dropwise to the obtained liquid, and the precipitated urethane resin was separated and vacuum dried overnight at 40 ° C. to obtain a solid urethane resin. A solution obtained by dissolving the obtained urethane resin in tetrahydrofuran was used as a sample to be measured for the acid value and the weight average molecular weight. The acid value of the urethane resin was measured by potentiometric titration with potassium hydroxide / ethanol titration solution using a potentiometric automatic titrator (manufactured by Kyoto Denshi Kogyo Co., Ltd.). The weight average molecular weight of the urethane resin was determined by gel permeation chromatography (GPC) as a value in terms of polystyrene. GPC (trade name "Alliance GPC 2695", manufactured by Waters) was used as a measuring device. The column used was a 4-column column with a trade name "Shodex KF-806M" (manufactured by Showa Denko). As a detector, RI (refractive index) detector (brand name "2414Detector", product made from Waters) was used. As a standard polystyrene sample, PS-1 and PS-2 (manufactured by Polymer Laboratories) were used. The acid value and weight average molecular weight of the urethane resin are shown in Table 3. Further, the proportion (mol%) of units derived from the compound having three or more reactive groups contained in the urethane resin is shown in Table 3 as “proportion of crosslinking unit (mol%)”.

Details of each component in Table 3 are shown below. The numerical values assigned to PPG and PTMG are the respective number average molecular weights.
IPDI: isophorone diisocyanate PPG 1000: polypropylene glycol PPG 2000: polypropylene glycol PTMG 2000: polytetramethylene glycol DMPA: dimethylol propionic acid GLY: glycerin EDA: ethylene diamine DETA: diethylene triamine TETA: triethylene tetraamine NPG: neopentyl glycol

Preparation of Ink
Each component (unit:%) shown in the upper row of Tables 4-1 to 4-4 is mixed, and after sufficient stirring, pressure filtration is performed using a micro filter (manufactured by Fujifilm) with a pore size of 3.0 μm. Each ink of -26 and comparative example 1-11 was prepared. In Tables 4-1 to 4-4, “Acetylenol E100” is a trade name of a nonionic surfactant (acetylene glycol ethylene oxide adduct) manufactured by Kawaken Fine Chemicals. The viscosity at 25 ° C. of each ink was 6 mPa · s or less. The pigment content P (%) in the prepared ink, the first urethane resin content U ₁ (%), the second urethane resin content U ₂ (%), the value of U ₁ / P (fold) And U ₁ / U ₂ values (fold) are shown in the lower part of Tables 4-1 to 4-4.

<Evaluation>
Each evaluation shown below was performed using the ink obtained above. In the present invention, “A” and “B” are acceptable levels, and “C” is unacceptable level according to the evaluation criteria described below. The evaluation results are shown in Table 5.

(Optical density)
The prepared ink was filled in each ink cartridge, and was set in an ink jet recording apparatus (trade name "PIXUS iP3100" manufactured by Canon Inc.) which ejects the ink from the recording head by the action of thermal energy. In this embodiment, an image recorded under the condition of applying one drop of approximately 28 ng ink to a unit area of 1/600 dpi × 1/600 dpi is defined as having a recording duty of 100%. A solid image of 2 cm × 2 cm with a recording duty of 100% was recorded on the following four types of recording media (plain paper). As recording media, under the following trade names, “GF-500” (manufactured by Canon), “4024” (manufactured by Xerox), “Bright White” (manufactured by Hewlett Packard), and “Hammer Mill Jet Print” (manufactured by International Paper) Was used. One day after recording, the optical density of the solid image was measured using a reflection densitometer (trade name "Macbeth RD-918, manufactured by Macbeth). The average value of the optical density of the solid image recorded on four types of recording media was calculated, and the optical density of the image was evaluated according to the evaluation criteria shown below.
A: The average value of optical density was 1.4 or more.
B: The average value of optical density was 1.3 or more and less than 1.4.
C: The average value of the optical density was less than 1.3.

(Marker resistance)
The prepared inks were each filled in an ink cartridge and set in the same inkjet recording apparatus as that used for the evaluation of the optical density. Using the above-described ink jet recording apparatus, vertical ruled lines with a thickness of 1/10 inch were recorded on a recording medium (plain paper, trade name “GF-500”, manufactured by Canon Inc.). Five minutes after recording, the vertical ruled lines were marked using a yellow line marker (trade name "OPTEX2", manufactured by Zebra), and immediately thereafter, the white area was marked. The stains of the marker pen point and the white area were confirmed, and the marker resistance was evaluated according to the evaluation criteria shown below.
A: Neither the pen point nor the white part was dirty.
B: The pen point was dirty, but the white area was not dirty.
C: Both the pen point and the white area were dirty.

(Redispersibility)
Into a petri dish, 2.0 g of the ink was placed and placed in an environment of a temperature of 30 ° C. and a relative humidity of 10% for 20 hours to dry the ink to obtain a solid. The mass of the dried matter (dried matter before dropping the ink) was measured. 1.0 g of the same ink was dropped onto the dried product, stirred for 30 seconds, and allowed to stand for 1 minute. After removing the ink in the fluid state, the mass of the dried product was measured, and the first "solid content retention rate (%)" was calculated according to the following formula (1). Furthermore, the same operations of dropping the ink, stirring, leaving still, and removing the ink in a fluid state were repeated, and the “solid content remaining rate (%)” of the second time was calculated according to the following formula (1). Then, the redispersibility of the ink was evaluated according to the evaluation criteria shown below.
Solid content retention rate (%)
= [Mass of dry matter / mass of dry matter before dropping ink] x 100 (1)
A: The solid content retention rate for the first time was less than 100%.
B: The solid content retention rate of the 1st time was 100% or more, but the solid content retention rate of the 2nd time was less than 90%.
C: The solid content retention rate for the second time was 90% or more.

Claims (10)

An aqueous inkjet ink comprising a self-dispersing pigment, a first urethane resin, and a second urethane resin,
An aqueous ink, wherein the first urethane resin has a crosslinked structure, and the second urethane resin does not have a crosslinked structure.   The ratio (mol%) of the unit derived from the compound having three or more reactive groups contained in the first urethane resin is 1.0 mol% or more and 8.0 mol% or less. Water-based ink.   The aqueous ink according to claim 1, wherein the first urethane resin has a crosslinked structure crosslinked by a trifunctional or higher functional polyamine.   The aqueous ink according to claim 3, wherein the trifunctional or higher functional polyamine is diethylenetriamine.   The aqueous ink according to any one of claims 1 to 4, wherein the proportion (mol%) of the urethane bond in the total of the urethane bond and the urea bond in the second urethane resin is 90 mol% or more. The content (mass%) of the first urethane resin is 3.0 mass% or less based on the total mass of the ink,
The content (mass%) of said 1st urethane resin is 0.10 times or more and 0.90 times or less by mass ratio with respect to content (mass%) of said self-dispersion pigment. The aqueous ink as described in 1 or 2.   The content (mass%) of the first urethane resin is 0.50 times or more and 2.00 times or less in mass ratio with respect to the content (mass%) of the second urethane resin. The water-based ink according to any one of the above. The surface charge amount of the self-dispersion pigment, 1.0 [mu] mol / m ² or more 4.5μmol / m ² or less aqueous ink according to any one of claims 1 to 7. An ink cartridge comprising an ink and an ink storage unit for storing the ink, the ink cartridge comprising:
An ink cartridge, wherein the ink is the aqueous ink according to any one of claims 1 to 8. An ink jet recording method of discharging an ink from a recording head of an ink jet method to record an image on a recording medium, comprising:
An ink jet recording method, wherein the ink is the aqueous ink according to any one of claims 1 to 8.

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