JP2018150412A - Ink set and inkjet recording method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink set which does not impair respective characteristics of ink using a self-dispersible pigment and ink using a resin-dispersible pigment, and prevents lowering of discharge stability occurring when brought into contact with the inks.SOLUTION: An ink set is used for an inkjet recording device having a cap for capping discharge ports each corresponding to first ink and second ink collectively with the same member. The first ink contains a self-dispersible pigment and has an introduction amount of a functional group of 0.1 mmol/g or more and 0.3 mmol/g or less, and the second ink contains an urethane resin and a resin-dispersible pigment, and has a difference (first ink to second ink) of dynamic surface tension at a life time of the first ink of 10 msec to dynamic surface tension at a life time of the second ink of 10 msec of 10 mN/m or more.SELECTED DRAWING: None

Description

  The present invention relates to an ink set and an ink jet recording method.

  In recent years, pigment inks used in ink jet recording apparatuses have been developed for various purposes as functions are improved. Specifically, it has been developed into ink for plain paper in the business field, ink suitable for store poster use, and ultra-high image quality ink for professional photographers. Further, the type and dispersion form of the pigment are appropriately selected according to the application. Examples of the dispersion form of the pigment include a self-dispersion pigment and a resin dispersion pigment. In addition, pigment inks having different dispersion forms may be simultaneously loaded in an ink jet recording apparatus that can be used for various purposes (Patent Document 1).

  On the other hand, when a plurality of types of pigment inks having different dispersion forms are used together in one ink jet recording apparatus, it is assumed that a certain phenomenon occurs. For example, the resin dispersant used in the resin-dispersed pigment is strictly designed for the balance of adsorption and desorption from the pigment particle surface. For this reason, when it comes into contact with inks having different dispersion forms, the balance between adsorption and desorption of the resin dispersant to the pigment particle surface may be easily lost, and the dispersion state of the pigment may become unstable.

JP 2005-264115 A

  When an ink using a self-dispersing pigment and an ink using a resin-dispersed pigment are mounted and used in one inkjet recording apparatus, it is necessary to particularly consider the influence on reliability due to contact. For example, it is known that self-dispersed pigments become unstable in dispersion due to an increase in electrolyte concentration in the system. Moreover, the resin dispersant used for the resin dispersion pigment usually has an anionic group for imparting hydrophilicity. When such a resin dispersant is mixed in an ink using a self-dispersing pigment, there arises a problem that the dispersion state of the self-dispersing pigment becomes unstable due to an increase in electrolyte concentration.

  On the other hand, the resin dispersant used for the resin-dispersed pigment is designed strictly for the balance of adsorption and desorption from the particle surface of the pigment. It is known that when this balance is biased in the direction of desorption, the dispersion state of the pigment becomes unstable. When a resin-dispersed pigment is mixed in an ink containing a self-dispersed pigment having a low functional group introduction amount (the amount of functional groups bonded to the pigment particle surface), the resin dispersant is detached from the pigment and self-dispersed. It is adsorbed on the particle surface where the functional group of the pigment is not bonded. As a result, the dispersion state of the resin-dispersed pigment becomes unstable, causing problems such as a decrease in ejection stability.

  Furthermore, the ink using the resin-dispersed pigment is not very suitable for improving the optical density of images recorded on plain paper because the aggregation of the pigment after adhering to the recording medium is relatively slow. However, ink using a resin-dispersed pigment is easy to wet and spread, and is easy to improve the smoothness between ink dots, and is therefore suitable for improving the glossiness of an image recorded on glossy paper. In consideration of wettability to glossy paper, the surface tension of the ink using the resin dispersed pigment is preferably designed to be low by blending a highly water-soluble organic solvent or surfactant. However, the presence of highly water-soluble water-soluble organic solvents and surfactants tends to bias the adsorption and desorption balance of the resin dispersant to the pigment particle surface in the desorption direction. For this reason, the ink using the resin-dispersed pigment containing excessively water-soluble organic solvents and surfactants has a problem that the storage stability is insufficient.

  Therefore, the object of the present invention is to suppress the deterioration of the ejection stability that occurs when these inks come into contact with each other without impairing the characteristics of the inks using the self-dispersing pigment and the ink using the resin-dispersed pigment. It is to provide an ink set. Another object of the present invention is to provide an ink jet recording method using the ink set.

  The above object is achieved by the present invention described below. That is, according to the present invention, the recording head including the first ink and the second ink, and having the discharge port for discharging the ink, and the discharge port corresponding to each of the first ink and the second ink are the same member. An ink set for use in an ink jet recording apparatus including a cap that is collectively capped with a self-dispersing pigment in which a functional group including an anionic group is bonded to the particle surface of the first pigment. A resin in which the functional group is introduced in an amount of 0.10 mmol / g or more and 0.30 mmol / g or less, and the second ink disperses the urethane resin, the second pigment, and the second pigment. A dispersant (excluding the urethane resin) is contained, and the urethane resin has a polyisocyanate, a polyether polyol having no acid group, and an acid group. The urethane resin has a unit derived from each of the polyols, and the proportion of the urethane bond in the total of urethane bonds and urea bonds in the urethane resin is 85.0 mol% or more and 99.0 mol% or less, The weight average molecular weight of the second ink is 20,000 or less, and the content (mass%) of the urethane resin in the second ink is a mass ratio with respect to the content (mass%) of the second pigment. 10 times or more and 2.00 times or less, and the difference between the dynamic surface tension of the first ink at the lifetime of 10 milliseconds and the dynamic surface tension of the second ink at the lifetime of 10 milliseconds (first ink-first 2 ink) is provided with an ink set of 10 mN / m or more.

  According to the present invention, an ink in which a decrease in ejection stability that occurs when these inks come into contact with each other is suppressed without impairing the characteristics of the ink using the self-dispersing pigment and the ink using the resin-dispersed pigment. Set can be offered. Moreover, according to the present invention, an ink jet recording method using the ink set can be provided.

It is sectional drawing which shows typically one Embodiment of an ink cartridge. 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. It is a schematic diagram which shows an example of the cleaning part of an inkjet recording device.

  Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is dissociated into ions in the ink, but it is expressed as “contains a salt” for convenience. Ink jet ink may be simply referred to as “ink”. Physical property values are values at normal temperature (25 ° C.) unless otherwise specified.

  When an ink using a self-dispersing pigment (self-dispersing pigment ink) is applied to a recording medium, the pigment quickly aggregates with moisture evaporation. Since the aggregated pigment tends to stay near the surface of the recording medium, the optical density of an image recorded on plain paper can be increased. On the other hand, the ink using the resin dispersed pigment (resin dispersed pigment ink) has a steric hindrance of the resin dispersant, and therefore the pigment in the ink adhering to the recording medium aggregates relatively slowly. For this reason, the resin-dispersed pigment ink tends to be unsuitable for enhancing the color developability of the image recorded on plain paper, but imparts gloss to the image recorded on glossy paper because of the gradual aggregation of the pigment. It is suitable in the above. Further, by optimizing the amount of the resin dispersant to be used, the image surface becomes smoother and an image having excellent gloss can be recorded. By using an ink set in which two types of inks having different characteristics are combined in this way, a multipurpose recorded matter can be provided.

  However, as a result of the study by the present inventors, it has been found that when the self-dispersed pigment ink and the resin-dispersed pigment ink are simply used in combination, there are problems in securing the reliability of the ink jet recording apparatus. In particular, it has been found that the problem becomes more prominent in the case of an ink jet recording apparatus provided with a cap for capping the ejection openings corresponding to each ink together with the same member.

  The first problem is a problem caused by the self-dispersing pigment. In the self-dispersing pigment, the dispersion state of the pigment becomes unstable due to the increase of the electrolyte concentration in the system. The present inventors evaluated various reliability after performing the recovery operation in a state where the discharge ports corresponding to the self-dispersed pigment ink and the resin-dispersed pigment ink were collectively capped with the same cap. As a result, it has been found that the ejection stability of the self-dispersed pigment ink after long-term storage is lowered. This is because the dispersion of the self-dispersed pigment gradually becomes unstable due to the resin dispersant having a charge mixed in the self-dispersed pigment ink, and the ink aggregates and thickens during long-term storage. This is thought to be due to a decline in sex. In particular, the ejection stability of the ink using the self-dispersing pigment with a large amount of functional group introduced tends to be remarkably lowered. This is presumably because the self-dispersing pigment with a large amount of functional group introduction has a relatively small particle surface area of the pigment that can be solvated with the water-soluble organic solvent in the ink.

  The present inventors set the amount of functional group introduction of the self-dispersing pigment to a certain value or less, so that even when the electrolyte concentration of the self-dispersing pigment ink is increased and the dispersion state of the pigment becomes unstable, the solvent We examined how to keep the dispersion state to some extent stable by summation. As a result, it was found that although the deterioration of the ink ejection stability due to long-term storage was suppressed to some extent, the level was still insufficient and there was room for further improvement.

  The second problem is a problem caused by the resin dispersed pigment. By setting the introduction amount of the functional group of the self-dispersing pigment to a certain value or less, the dispersion state of the resin-dispersed pigment mixed in the self-dispersing pigment ink becomes unstable, and the ejection stability of the ink is lowered. The resin dispersing agent is designed strictly for the balance of adsorption and desorption from the pigment particle surface. When the functional group introduction amount of the self-dispersing pigment is lowered, the particle surface to which the functional group of the self-dispersing pigment is not bonded increases, and the resin dispersant detached from the pigment is adsorbed thereto. As a result, the balance between adsorption and desorption of the resin dispersant is lost, the dispersion state of the resin dispersed pigment becomes unstable, the ink is thickened, and it is considered that the ejection stability is lowered.

  The third problem is a problem caused by the resin-dispersed pigment ink. In order to further improve the glossiness of images recorded on glossy paper using resin-dispersed pigment ink, the surface tension of the resin-dispersed pigment ink is designed to be low when considering the wettability of the resin-dispersed pigment ink to the recording medium. It is preferable. That is, the glossy paper suitability of the resin-dispersed pigment ink can be further enhanced by containing a large amount of a highly water-soluble organic solvent or surfactant. However, the presence of highly water-soluble water-soluble organic solvents and surfactants tends to bias the adsorption and desorption balance of the resin dispersant to the pigment particle surface in the desorption direction. That is, it has been found that there is a trade-off relationship between improvement in glossy paper suitability of resin-dispersed pigment ink and improvement in storage stability.

As a result of the study, the present inventors have found that the above three problems can be solved by the following two means. The first means is to satisfy the following conditions 1 to 4.
Condition 1: The second ink containing the second pigment and the resin dispersant for dispersing the second pigment is further made to contain a urethane resin having a unit derived from a polyether polyol having no acid group.
Condition 2: A urethane resin having a urethane bond ratio of 85.0 mol% to 99.0 mol% in the total of urethane bonds and urea bonds is used.
Condition 3: A urethane resin having a weight average molecular weight of 20,000 or less is used.
Condition 4: The content (mass%) of the urethane resin in the second ink is 0.10 times or more and 2.00 times or less as a mass ratio with respect to the content (mass%) of the second pigment.

  By satisfying Condition 1, it is possible to suppress a decrease in ejection stability of the self-dispersed pigment ink (first ink) even after a long time has passed since the second ink containing the resin-dispersed pigment was mixed. This is presumably because the decrease in the ejection stability of the first ink was suppressed by the urethane resin having a highly hydrophilic ether bond. Moreover, the above three problems can be solved by satisfying condition 2. The urea bond is a bond having a very high hydrogen bonding property. The first problem is that the urea bond in the urethane resin mixed in the first ink strongly interacts with the anionic group of the self-dispersing pigment, thereby reducing the instability of the dispersed state of the pigment over time. Can be solved. In addition, when the urethane resin which does not contain a urea bond was used, the fall of the discharge stability of the 1st ink by long-term progress was not able to be improved.

  The second problem is solved by suppressing the decrease in the ejection stability of the second ink by adsorbing the urethane resin to the second pigment which has become unstable due to desorption of the resin dispersant. Can do. Note that when a urethane resin containing no urea bond was used, it was not possible to improve the decrease in ejection stability of the second ink. For this reason, it turns out that a urethane resin adsorb | sucks to a 2nd pigment because a urea bond functions effectively. The third problem is that the urethane resin is adsorbed instead of the resin dispersant released from the second pigment by the highly permeable water-soluble organic solvent and the surfactant, thereby lowering the ejection stability of the second ink. This can be solved by suppressing the problem.

  The second means is to set the surface tension difference between the first ink and the second ink to a certain value or more. Thereby, a 1st subject and a 2nd subject can be solved. Specifically, the difference (first ink-second ink) between the dynamic surface tension of the first ink at a lifetime of 10 milliseconds and the dynamic surface tension of the second ink at a lifetime of 10 milliseconds is set to 10 mN / m. That's it. In general, when two different kinds of liquids are mixed, the liquid having the lower surface tension flows into the liquid having the higher surface tension as the difference in the surface tension at the interface increases. By using the first ink and the second ink in which the difference in dynamic surface tension is set to a certain level or more, the second ink having a low dynamic surface tension flows into the first ink having a high dynamic surface tension, and the second ink It is thought that the urethane resin in the ink functioned more effectively.

<Ink set>
The ink set of the present invention includes a first ink and a second ink. An ink set used in an ink jet recording apparatus including a recording head having an ejection port for ejecting ink and a cap for collectively capping ejection ports corresponding to the first ink and the second ink with the same member. is there. The first ink is a so-called self-dispersing pigment ink containing a self-dispersing pigment in which a functional group containing an anionic group is bonded to the particle surface of the first pigment. The second ink is a so-called resin-dispersed pigment ink containing a urethane resin, a second pigment, and a resin dispersant (excluding the urethane resin) that disperses the second pigment. Hereinafter, each component constituting the first ink and the second ink included in the ink set of the present invention will be described in detail.

(Self-dispersing pigment)
The first ink contains a self-dispersing pigment in which a functional group including an anionic group is bonded to the particle surface of the first pigment directly or through another atomic group. The anionic group may be partially dissociated in the ink, or all may be dissociated. Examples of the first pigment include inorganic pigments such as carbon black and organic pigments. As the first pigment, any known pigment that can be used for ink-jet ink can be used. Urethane resin is easy to physically adsorb on carbon black. For this reason, it is preferable to use carbon black as the first pigment because discharge stability after long-term storage is further improved as compared with the case of using an organic pigment.

  The content (% by mass) of the first pigment (self-dispersing pigment) in the ink is preferably 0.10% by mass or more and 15.00% by mass or less based on the total mass of the ink, and is 1.00% by mass. % To 8.00% by mass is more preferable. When the content of the first pigment is less than 0.10% by mass, the optical density of the recorded image may be slightly lowered. On the other hand, if the content of the first pigment is more than 15.00% by mass, ink jet characteristics such as anti-sticking property may be slightly lowered.

  Examples of the anionic group bonded to the particle surface of the pigment include hydrophilic groups such as a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, and a phosphonic acid group. Examples of the counter ion of the anionic group include cations such as hydrogen atom, alkali metal, ammonium and organic ammonium. The counter ion is preferably a cation of an alkali metal such as lithium, sodium, or potassium, because the ejection stability of the ink is better than in the case of ammonium or organic ammonium. The anionic group may be directly bonded to the pigment particle surface or may be bonded via another atomic group (—R—). Other atomic groups (—R—) include linear or branched alkylene groups having 1 to 12 carbon atoms, arylene groups such as phenylene groups and naphthylene groups, amide groups, sulfonyl groups, amino groups, carbonyl groups, and esters. Groups and ether groups. Moreover, the group etc. which combined these groups can be mentioned.

  The amount of functional group introduced into the self-dispersing pigment (functional group introduced amount) is 0.10 mmol / g or more and 0.30 mmol / g or less. When the functional group introduction amount is less than 0.10 mmol / g, the ejection stability after long-term storage decreases. On the other hand, when the functional group introduction amount is more than 0.30 mmol / g, the ink tends to thicken due to the influence of the electrolyte such as the mixed resin dispersant, and the ejection stability of the ink after long-term storage is lowered. The unit of the functional group introduction amount is the number of millimoles of functional group per 1 g of pigment solid content.

  The amount of functional group introduced can be determined by colloid titration. In Examples described later, a pigment dispersion is obtained by colloidal titration using a potential difference using a potentiometric automatic titration apparatus (trade name “AT-510”, manufactured by Kyoto Electronics Industry Co., Ltd.) equipped with a streaming potential titration unit (PCD-500). The surface charge amount of the self-dispersing pigment was measured. Methyl glycol chitosan was used as a titration reagent. It is also possible to measure the surface charge amount of the pigment extracted from the ink by an appropriate method.

  Whether or not the pigment is a self-dispersing pigment can be determined by the following method. First, after an acid is added to the ink or pigment dispersion, the precipitate is collected by centrifugation. The collected precipitate is taken in a petri dish, poured into water and stirred to redisperse the precipitate. If no precipitate is formed in the petri dish after being left for 1 day and the pigment is dispersed, the pigment in the ink or pigment dispersion can be determined to be a self-dispersing pigment.

(Resin dispersion pigment)
The second ink contains a second pigment and a resin dispersant other than the urethane resin in which the second pigment is dispersed. That is, the second ink contains a resin dispersed pigment. Examples of the second pigment include inorganic pigments such as carbon black and organic pigments. As the first pigment, any known pigment that can be used for ink-jet ink can be used.

  The content (% by mass) of the second pigment in the ink is preferably 0.10% by mass or more and 15.00% by mass or less, based on the total mass of the ink, and is 1.00% by mass or more and 8.00% by mass. More preferably, it is at most mass%. When the content of the second pigment is less than 0.10% by mass, the optical density of the recorded image may be slightly lowered. On the other hand, if the content of the second pigment is more than 15.00% by mass, ink jet characteristics such as anti-sticking property may be slightly lowered.

  Whether or not the pigment is dispersed by the resin can be determined by the following method. The liquid prepared by concentrating or diluting the ink so that the total solid content is about 10% by mass is centrifuged at 12,000 rpm for 1 hour to recover the precipitated components including the pigment. The liquid layer contains a water-soluble organic solvent, a resin that does not contribute to pigment dispersion, and the like. And when resin is contained in the sedimentation component, it can be judged that the pigment was disperse | distributed with resin. Note that the resin contained as a main component in the sediment component is a resin that contributes to the dispersion of the pigment, and the resin contained as a main component in the liquid layer is a resin that does not contribute to the dispersion of the pigment. be able to. It is preferable that the resin contained as a main component in the sedimentation component is not a urethane resin. Moreover, although a trace amount urethane resin may be contained in the sedimentation component, it is preferable that content of resin other than urethane resin is larger than content of urethane resin.

[Resin dispersant]
As the resin dispersant, any known resin dispersant that can be used for ink-jet ink can be used. The resin dispersant is preferably an acrylic resin having at least an acrylic component such as a unit derived from (meth) acrylic acid or a unit derived from (meth) acrylic ester, and is preferably a water-soluble acrylic resin. . In the present invention, “the resin is water-soluble” means that the resin is neutralized with an alkali equivalent to the acid value and does not form particles whose particle diameter can be measured when measured by a dynamic light scattering method. Means. In the following description, “(meth) acryl” means “acryl” and “methacryl”, and “(meth) acrylate” means “acrylate” and “methacrylate”.

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

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

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

  The weight average molecular weight in terms of polystyrene of the resin dispersant measured by gel permeation chromatography (GPC) is preferably 1,000 or more and 30,000 or less, and preferably 3,000 or more and 15,000 or less. Further preferred. The acid value of the resin dispersant is preferably 90 mgKOH / g or more and 180 mgKOH / g or less. When a resin dispersant having an acid value within the above range is used, the dispersion stability of the second pigment can be improved, and the ejection stability of the second ink can be further improved.

  The content (% by mass) of the resin dispersant in the second ink is preferably 0.10% by mass or more and 5.00% by mass or less, and 0.50% by mass or more based on the total mass of the second ink. More preferably, it is 3.00 mass% or less. Further, the content (% by mass) of the second pigment in the second ink is preferably a mass ratio with respect to the content (% by mass) of the resin dispersant and is 0.30 times or more and 5.00 times or less. More preferably, it is 0.50 times or more and 2.00 times or less.

[Urethane resin]
The second ink contains a urethane resin having units derived from polyisocyanate, polyether polyol having no acid group, and polyol having an acid group.

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

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

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

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

[Polyether polyol having no acid group]
Polyether polyol having no acid group is used as a component that reacts with polyisocyanate to form a urethane bond and becomes a unit constituting the urethane resin. By using a polyether polyol having no acid group, it is possible to improve the glossiness of an image recorded with the second ink, and the first ink after long-term storage even when mixed with the first ink. It is possible to suppress a decrease in discharge stability. The proportion (% by mass) of units derived from the polyether polyol having no acid group in the urethane resin is preferably 0.1% by mass or more and 80.0% by mass or less.

  Examples of polyether polyols having no acid group include addition polymers of alkylene oxides and polyols; glycols such as (poly) alkylene glycols; and the like. Examples of the alkylene oxide include ethylene oxide, propylene oxide, butylene oxide, α-olefin oxide and the like. Examples of polyols to be addition-polymerized with alkylene oxide include 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl- 1,5-pentanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 4,4-dihydroxyphenylpropane, 4,4-dihydroxy Diols such as phenylmethane, hydrogenated bisphenol A, dimethylolurea and derivatives thereof; glycerin, trimethylolpropane, 1,2,5-hexanetriol, 1,2,6-hexanetriol, pentaerythritol, trimethylolmelamine and derivatives thereof , Polyoxypropylene Triols such as polyol; and the like. Examples of glycols include tetramethylene glycol, hexamethylene glycol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol, (poly) tetramethylene glycol, (Poly) alkylene glycol such as neopentyl glycol; ethylene glycol-propylene glycol copolymer; Among these polyether polyols having no acid group, polyethylene glycol, polypropylene glycol, poly (1,2-butylene glycol), poly (1,3-butylene glycol) and the like are preferably used. The number average molecular weight of the polyether polyol having no acid group is preferably 400 or more and 4,000 or less.

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

  The proportion (mass%) of units derived from the polyol having an acid group in the urethane resin is preferably 5.0 mass% or more and 40.0 mass% or less. The proportion (mol%) of units derived from polyol having an acid group in the total amount of units derived from polyol in the urethane resin is preferably 0.0 mol% or more and 100.0 mol% or less. . Moreover, it is more preferable that they are 30.0 mol% or more and 90.0 mol% or less, and it is especially preferable that they are 50.0 mol% or more and 90.0 mol% or less.

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

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

[Ratio of urethane bond]
The ratio of the urethane bond in the total of the urethane bond in the urethane resin and the urea bond derived from the polyamine is 85.0 mol% or more and 99.0 mol% or less. If the ratio of urethane bonds is less than 85.0 mol%, the ratio of urea bonds is too high, and the discharge accuracy of the second ink is lowered. On the other hand, if the ratio of urethane bonds is more than 99.0 mol%, the ratio of urea bonds is too small, so that the adsorptive power of the urethane resin to the particle surface of the second pigment is reduced, and the storage stability of the second ink. Decreases. Moreover, since the adsorption | suction power with respect to the particle | grain surface of a 1st pigment also falls, the discharge stability after long-term storage falls.

  Examples of the method for adjusting the proportion of urethane bonds in the urethane resin include the following first method and second method. A 1st method is a method of adjusting the quantity of the chain extender (amine compound) made to react with polyisocyanate at the time of manufacture of a urethane resin. In this method, the amount of urea bonds formed by the reaction between an amine compound and an isocyanate group is controlled. Specifically, first, a plurality of types of urethane resins are synthesized by changing the amount of the amine compound used. And the ratio (mol%) of the urethane bond of each urethane resin synthesize | combined is calculated by the method mentioned later. A calibration curve is created from the relationship between the calculated urethane bond ratio (mol%) and the amount of amine compound used. Using the prepared calibration curve, it is possible to determine the amount of amine compound used to produce a urethane resin in which the proportion of urethane bonds is the desired mol%. Even if the same kind of amine compound is used, the reaction rate may change if the types of other components are different, so the ratio of urethane bonds in the obtained urethane resin is not necessarily the same. For this reason, by preparing a calibration curve in advance, it is possible to manufacture a urethane resin in which the proportion of urethane bonds is a desired mol%.

  The second method is a method of adjusting the residual ratio of unreacted isocyanate groups when the urethane resin is phase-inverted to water. In this method, the amount of urea bonds formed by the reaction between water and isocyanate groups is controlled. Specifically, first, in the process of producing a urethane resin (in the course of synthesis), analysis is performed using a Fourier transform infrared spectrophotometer (FT-IR). Check the survival rate. The residual ratio of isocyanate groups can be adjusted by changing the reaction time and the amount of polyisocyanate used. And when the residual rate of an isocyanate group becomes the ratio of the desired urethane bond, ion-exchange water is added to the reaction system. For example, when producing a urethane resin having a urethane bond ratio of 95 mol%, when the residual ratio of isocyanate groups derived from the polyisocyanate used is 5 mol%, ion-exchanged water is used as a reaction system. What is necessary is just to add. In the examples described later, the ratio (mol%) of the urethane bond in the total of the urethane bond and the urea bond in the urethane resin was adjusted by the second method.

[Characteristics of urethane resin]
The content (mass%) of the urethane resin in the second ink is a mass ratio with respect to the content (mass%) of the second pigment, and is 0.10 times or more and 2.00 times or less. When the above-mentioned mass ratio is less than 0.10 times, the storage stability of the second ink containing a large amount of a surfactant or a penetrating solvent is lowered. In addition, when an image is recorded on glossy paper, the wettability of the other ink applied over the recording portion of the second ink is lowered, and the smoothness of the image is impaired, so that the glossiness is lowered. On the other hand, when the mass ratio is more than 2.00 times, the discharge stability of the first ink after long-term storage is lowered due to the salting-out effect of the urethane resin mixed in the first ink. Further, since the amount of solid content in the second ink increases, the smoothness of the image recorded with the second ink is impaired, and the glossiness is lowered.

  The content (% by mass) of the urethane resin in the second ink is preferably 0.10% by mass or more and 10.00% by mass or less based on the total mass of the second ink. When the content of the urethane resin in the second ink is less than 0.10% by mass, the scratch resistance of an image recorded on glossy paper may be slightly lowered. On the other hand, when the content of the urethane resin in the second ink is more than 10.00% by mass, the ejection stability of the second ink may be slightly lowered. The second ink may further contain a resin other than the resin dispersant and the urethane resin as long as the effects of the present invention are not impaired.

  The urethane resin may be contained in the first ink. When the urethane resin of the first ink is contained, the content (% by mass) of the urethane resin in the first ink is preferably 0.50% by mass or less based on the total mass of the first ink. More preferably, one ink does not contain a urethane resin. When the content of the urethane resin in the first ink is more than 0.50% by mass, the dispersion state of the self-dispersing pigment is likely to be unstable. Also, depending on the type of urethane resin, the surface tension of the first ink is likely to be greatly reduced, so it may be somewhat difficult to increase the optical density of the image.

  Urethane resin cannot be said to be suitable as a resin dispersant for dispersing the second pigment in the second ink. Therefore, it is important that the second ink contains a resin dispersant for dispersing the second pigment together with the urethane resin. The urethane resin in the second ink is considered to be because the effect of the present invention is more easily obtained when the urethane resin is present in a free state than that related to adsorption and desorption of the particle surface of the second pigment.

  The weight average molecular weight in terms of polystyrene of the urethane resin measured by GPC is 20,000 or less. If the weight average molecular weight of the urethane resin is more than 20,000, the mixed first ink tends to thicken, and the ejection stability after long-term storage of the first ink is lowered. Further, the glossiness of the image recorded on the glossy paper with the second ink is lowered. The weight average molecular weight of the urethane resin is preferably 10,000 or more.

  The acid value of the urethane resin is preferably 40 mgKOH / g or more and 140 mgKOH / g or less. When the acid value of the urethane resin is less than 40 mgKOH / g, ink jet aptitude such as ejection stability may be slightly lowered. On the other hand, when the acid value of the urethane resin is more than 140 mgKOH / g, the adsorptive power of the second pigment to the particle surface tends to be lowered, and the dispersion stability of the second pigment may be slightly lowered.

[Analytical method of urethane resin]
The physical properties such as the composition, molecular weight, and acid value of the urethane resin can be measured according to a conventionally known method. Specifically, the physical property value of the urethane resin can be measured by analyzing a sediment and a supernatant obtained by centrifuging the ink. Since the pigment is insoluble in an organic solvent, the urethane resin can be separated from the pigment by solvent extraction. Although the urethane resin can be analyzed even in the ink state, analysis of the urethane resin extracted from the ink is preferable because the measurement accuracy can be improved. Specifically, the urethane resin can be precipitated and extracted by adding excess acid (such as hydrochloric acid) to the supernatant obtained by centrifuging the ink at 80,000 rpm. Moreover, the above-mentioned supernatant liquid can be dried to separate the urethane resin. Further, the urethane resin can be extracted from the ink using an organic solvent (such as hexane or chloroform) that does not dissolve the pigment and the resin dispersant (preferably an acrylic resin) but dissolves the urethane resin. Although the urethane resin can be analyzed even in the ink state, analysis of the urethane resin extracted from the ink is preferable because the measurement accuracy can be improved. Hereinafter, examples of methods for measuring various physical property values of the urethane resin will be described.

(1) Composition of urethane resin After drying the fractionated urethane resin, it is dissolved in deuterated dimethyl sulfoxide (heavy DMSO) and analyzed by proton nuclear magnetic resonance ( ¹ H-NMR). And from the position of the obtained peak, the kind of polyisocyanate, the polyol which does not have an acid group, the polyol which has an acid group, and a polyamine can be confirmed. It is also possible to confirm the types of polyisocyanates, polyols having no acid groups, polyols having acid groups, and polyamines by drying the separated urethane resin and analyzing by pyrolysis gas chromatography. it can. Furthermore, the composition ratio can be calculated from the ratio of the integrated values of the peaks.

(2) Ratio of urethane bond The ratio of urethane bond in the total of urethane bond and urea bond in the urethane resin can be measured as follows. That is, a measurement sample is prepared by dissolving a urethane resin in deuterated dimethyl sulfoxide. And the sample prepared by the carbon nuclear magnetic resonance method ( ^13C -NMR) is analyzed, and the ratio of the urethane bond in the urethane resin is calculated from the integrated value of each peak of the obtained urethane bond and urea bond. Can do. However, the positions of the respective peaks of the urethane bond and the urea bond vary depending on the type of compound used for the production of the urethane resin. For this reason, it is necessary to investigate the position of the peak of a urethane bond and a urea bond for every compound used for the synthesis | combination of a urethane resin. The method will be described below.

First, a compound (polyisocyanate, polyether polyol having no acid group, polyol having an acid group) to be a raw material of the urethane resin is prepared. Then, (i) a reaction product of a polyisocyanate and a polyether polyol having no acid group, (ii) a reaction product of a polyisocyanate and a polyol having an acid group, and (iii) a reaction product of polyisocyanate and water are prepared. The dried reaction product prepared is dissolved in deuterated DMSO and analyzed by carbon nuclear magnetic resonance ( ¹³ C-NMR).

  In the case of the above example, the chemical shift of the urethane bond is confirmed from the reactant (i) and the reactant (ii), and the chemical shift of the urea bond is confirmed from the reactant (iii). From each confirmed chemical shift, the peak of urethane bond and the peak of urea bond are identified, and the ratio of the integrated value of these peaks indicates the ratio of urethane bond to the total of urethane bond and urea bond in the urethane resin. calculate. For example, in the case of a urethane resin obtained using isophorone diisocyanate, the urethane bond peak is detected in the vicinity of 155 ppm, although some deviation occurs depending on the measurement conditions and the composition of the urethane resin. Further, the peak of urea bond is detected around 158 ppm.

(3) Acid value of urethane resin After drying the collected urethane resin, it was dissolved in THF and titrated with potassium hydroxide using a potentiometric automatic titrator (trade name “AT510”, manufactured by Kyoto Electronics Industry Co., Ltd.). The acid value of the urethane resin can be measured by potentiometric titration using the liquid.

Moreover, the acid value derived from the polyol (dimethylol propionic acid (DMPA) and dimethylol butanoic acid (DMBA)) which has an acid group can be measured with the following method. First, after the separated urethane resin is dried, it is dissolved in heavy DMSO, and ¹³ C-NMR is measured. From the ratio of the integrated value of the peak derived from the quaternary carbon atom of DMPA and DMBA and the integrated value of the peak of the acid group derived from other compounds (for example, acrylic acid), DMPA and DMBA, and the acid group The molar ratio with the other compounds having is calculated. The acid value derived from DMPA and DMBA can be obtained by multiplying the acid value of the entire urethane resin by the molar ratio of DMPA and DMBA. In addition, the peak of the acid group derived from the quaternary carbon atom of DMPA and DMBA appears at around 65 ppm and around 60 ppm, respectively. In addition, when it is known that a compound having an acid group other than DMPA and DMBA is not used, the acid value derived from the polyol having an acid group can also be measured by the titration method described above.

(4) Weight average molecular weight of urethane resin The weight average molecular weight of the urethane resin can be measured by GPC. An example of GPC measurement conditions is as follows.

Apparatus: Alliance GPC 2695 (manufactured by Waters)
Column: 4-column column of Shodex KF-806M (Showa Denko)
・ Mobile phase: Tetrahydrofuran (special grade)
・ Flow rate: 1.0 mL / min
・ Oven temperature: 40.0 ℃
-Sample solution injection volume: 0.1 mL
・ Detector: RI (refractive index)
Polystyrene standard samples: PS-1 and PS-2 (manufactured by Polymer Laboratories)

(Dynamic surface tension)
The difference between the dynamic surface tension of the first ink at a lifetime of 10 milliseconds and the dynamic surface tension of the second ink at a lifetime of 10 milliseconds (first ink-second ink) is 10 mN / m or more, preferably Is 15 mN / m or more. The difference from the dynamic surface tension is preferably 30 mN / m or less, and more preferably 25 mN / m or less.

  In general, when two different kinds of liquids are mixed, the liquid having the lower surface tension flows into the liquid having the higher surface tension as the difference in the surface tension at the interface increases. By using the first ink and the second ink in which the difference in dynamic surface tension is set to a certain level or more, the second ink having a low dynamic surface tension flows into the first ink having a high dynamic surface tension. . Thereby, the urethane resin in the second ink can function more effectively.

  The dynamic surface tension of the first ink and the second ink at a lifetime of 10 milliseconds is a value measured by the maximum bubble pressure method. The maximum bubble pressure method is a method for measuring the maximum pressure required to release bubbles generated at the tip of a probe (thin tube) immersed in the liquid to be measured, and determining the surface tension of the liquid from this maximum pressure. The maximum pressure is measured while bubbles are continuously generated at the tip of the probe. At this time, the time from when the surface of a new bubble is generated at the tip of the probe until the maximum bubble pressure is reached (when the radius of curvature of the bubble is equal to the radius of the probe tip) is called a lifetime. The dynamic surface tension of the ink is a value measured at 25 ° C.

  The dynamic surface tension of the second ink at a lifetime of 10 milliseconds is preferably 40 mN / m or less. When the dynamic surface tension of the second ink is 40 mN / m or less, the wettability to the recording medium is improved, so that the glossiness of the obtained image is improved. The dynamic surface tension of the second ink at a lifetime of 10 milliseconds is preferably 25 mN / m or more, and more preferably 30 mN / m or more. The dynamic surface tension of the first ink at a lifetime of 10 milliseconds is preferably 40 mN / m or more and 60 mN / m or less, and more preferably 45 mN / m or more and 55 mN / m or less. The dynamic surface tension of each ink can be easily controlled by appropriately selecting the amount and type of a highly water-soluble organic solvent or surfactant.

(Aqueous medium)
The first ink and the second ink are aqueous inks containing an aqueous medium containing water. As water, it is preferable to use deionized water (ion exchange water). The content (% by mass) of water in the ink is preferably 10.00% by mass or more and 90.00% by mass or less, preferably 50.00% by mass or more and 90.00% by mass or less, based on the total mass of the ink. More preferably.

  The aqueous medium can further contain a water-soluble organic solvent. As the water-soluble organic solvent, monohydric alcohol, polyhydric alcohol, (poly) alkylene glycol, glycol ether, nitrogen-containing polar solvent, sulfur-containing polar solvent and the like can be used. The content (% by mass) of the water-soluble organic solvent in the ink is preferably 3.00% by mass or more and 50.00% by mass or less based on the total mass of the ink.

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

  The first ink preferably further contains a surfactant. The HLB value of the surfactant determined by the Griffin method is preferably 15.0 or more. By containing a surfactant having an HLB value within the above range in the second ink, the thickening of the first ink and the decrease in ejection stability caused by the mixing of the second ink and the first ink are further effectively suppressed. can do. The HLB value obtained by the Griffin method is 20.0 or less by definition, and the upper limit of the HLB value of the surfactant that can be contained in the first ink is also 20.0.

  As surfactants having an HLB value of 15.0 or more, the following trade names are NIKKOL BC-20, BC-30, BC-40, BO-20V, BO-50V (above, manufactured by Nikko Chemicals); EMALEX 125, 130, 550, 630, 640, 720, 725, 730, 750, 1625 (above, manufactured by Nihon Emulsion); Emalmin CC-200, CO-200, L380 (above, manufactured by Sanyo Kasei); Emulgen 147, 430, 920, 985 (above, manufactured by Kao); DP-20 (made by Aoki Yushi).

  The content (% by mass) of the surfactant in the first ink is preferably 0.05% by mass or more and 0.50% by mass or less based on the total mass of the first ink. By setting the content of the surfactant in the first ink within the above range, the optical density of the image recorded on the plain paper with the first ink can be further increased, and the ejection stability of the first ink can be improved. The decrease can be more effectively suppressed.

(Ink physical properties)
The pH of the first ink and the second ink at 25 ° C. is preferably 5.0 or more and 10.0 or less, and more preferably 7.0 or more and 9.5 or less. The static surface tension of the first ink and the second ink at 25 ° C. 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 of the first ink and the second ink at 25 ° C. is preferably 1.0 mPa · s to 5.0 mPa · s.

<Ink cartridge>
The ink cartridge includes ink and an ink storage unit that stores the ink. And the ink accommodated in this ink accommodating part is the ink (1st ink and 2nd ink) which comprises the ink set of this invention demonstrated above. FIG. 1 is a cross-sectional view schematically showing an embodiment of an ink cartridge. 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 inkjet recording method of the present invention is a method of recording an image on a recording medium by ejecting the first ink and the second ink contained in the ink set of the present invention described above from an inkjet recording head, respectively. 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 first ink and the second ink included in the ink set 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.

  Next, a configuration for covering the ejection port of the recording head in the ink jet recording apparatus to which the ink set of the present invention is applied will be described. In the following description, for the sake of simplicity, it is described as a (1) discharge port. However, in general, an inkjet recording apparatus is provided with a plurality of discharge ports for discharging one ink to form a discharge port array. . When a plurality of types of ink are used, a row of ejection openings is provided according to the number of inks.

  FIG. 3 is a schematic diagram illustrating an example of the cleaning unit of the ink jet recording apparatus. The cleaning unit covers the ejection port by bringing the cap M5010 into contact with the surface of the recording head (not shown) having the ejection port, thereby suppressing ink evaporation. More specifically, capping is performed by raising the cap holder M5060 by a vertically movable mechanism (not shown) and bringing the cap M5010 into contact with the surface of the recording head having the ejection port with an appropriate adhesion force. When the pump M5000 is operated in the capped state, a negative pressure is generated between the surface having the discharge port and the cap M5010. By this negative pressure, ink is sucked from the ejection ports via tubes M5090 and M5100 connected to the suction ports M5070 and M5080, and the recording head is cleaned. Further, the ink is fixed to the recording head by discharging ink (preliminary discharge) to the suction chambers M5020 and M5030, or by sucking ink existing on the cap M5010 with the cap M5010 opened. And other harmful effects. An ink absorbing member or the like may be provided inside the suction chamber.

  As described above, FIG. 3 shows a configuration in which the suction chamber formed by the peripheral wall portion M5040 is divided into two suction chambers M5020 and M5030 having the same volume at the partition wall M5050. In the recording head, an ejection port array corresponding to a plurality of inks is provided on one recording element substrate. In order to increase the efficiency of suction, suction chambers are provided corresponding to the number of recording element substrates. The volumes of these suction chambers may be different from each other, and may be configured by one suction chamber without having a partition wall. Furthermore, it is good also as a structure which covers each discharge port row | line | column which discharges multiple types of ink collectively with one cap, or may provide a cap for each discharge port row | line | column which discharges multiple types of ink.

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

<Preparation of pigment dispersion>
(Pigment dispersion 1)
A solution obtained by dissolving 5 g of concentrated hydrochloric acid in 5.5 g of water was cooled to 5 ° C., and 1.5 g of 4-amino-1,2-benzenedicarboxylic acid (treatment agent) was added. A container containing this solution was placed in an ice bath and cooled to 10 ° C. or lower, and a solution obtained by dissolving 1.8 g of sodium nitrite in 9.0 g of water at 5 ° C. was added. After stirring for 15 minutes, 6.0 g of carbon black having a specific surface area of 250 m ² / g and a DBP oil absorption of 140 mL / 100 g was added with stirring, and the mixture was further stirred for 15 minutes to obtain a slurry. The obtained slurry was filtered with a filter paper (trade name “filter paper for standard No. 2”, manufactured by Advantech), and the obtained particles were sufficiently washed with water. The washed particles were dried in an oven at 110 ° C. to obtain a self-dispersing pigment. Water was added to the obtained self-dispersing pigment so that the pigment content was 10.0% to obtain a dispersion. A pigment in a state where a self-dispersed pigment in which —C ₆ H ₃ — (COOK) ₂ groups are bonded to the surface of carbon black particles is dispersed in water by exchanging sodium ions in the dispersion with potassium ions by an ion exchange method. Dispersion 1 was obtained. The functional group introduction amount of the self-dispersing pigment in the pigment dispersion 1 was 0.20 mmol / g. The functional group introduction amount is a value obtained by conversion from the potassium ion concentration in the pigment dispersion 1 measured using an ion meter (manufactured by DKK).

(Pigment dispersion 2)
A pigment dispersion 2 was obtained in the same manner as in the case of the pigment dispersion 1 except that the amount of the treating agent was changed to 0.75 g. The pigment content in the pigment dispersion 2 was 10.0%, and the functional group introduction amount was 0.10 mmol / g.

(Pigment dispersion 3)
A pigment dispersion 3 was obtained in the same manner as in the case of the pigment dispersion 1 except that the amount of the treating agent was changed to 2.25 g. The pigment content in Pigment Dispersion Liquid 3 was 10.0%, and the functional group introduction amount was 0.30 mmol / g.

(Pigment dispersion 4)
C. I. Pigment blue 15: 4 particle surface pigment dispersion liquid in which self-dispersed pigment having —C ₆ H ₃ — (COONa) ₂ group bonded thereto is dispersed in water (trade name “CAB-O-JET250C”, manufactured by Cabot ) Was prepared. Water was added to this pigment dispersion to disperse the pigment so that the pigment content was 10.0%, thereby preparing pigment dispersion 4. The amount of the functional group introduced into the self-dispersing pigment in the pigment dispersion 4 was 0.25 mmol / g.

(Pigment dispersion 5)
C. I. A pigment dispersion liquid (trade name “CAB-O-JET260C”, manufactured by Cabot) in which a self-dispersing pigment having —C ₆ H ₃ — (COONa) ₂ groups bonded to the particle surface of Pigment Red 122 is dispersed in water. Prepared. Water was added to this pigment dispersion to disperse the pigment so that the pigment content would be 10.0%, thereby preparing pigment dispersion 5. The functional group introduction amount of the self-dispersing pigment pigment in the pigment dispersion 5 was 0.10 mmol / g.

(Pigment dispersion 6)
A pigment dispersion 6 was obtained in the same manner as in the case of the pigment dispersion 1 except that the amount of the treating agent was changed to 0.70 g. The pigment content in the pigment dispersion 6 was 10.0%, and the functional group introduction amount was 0.09 mmol / g.

(Pigment dispersion 7)
A pigment dispersion 7 was obtained in the same manner as in the case of the pigment dispersion 1 except that the amount of the treating agent was changed to 2.30 g. The pigment content in the pigment dispersion 7 was 10.0%, and the functional group introduction amount was 0.31 mmol / g.

(Pigment dispersion 8)
15.0 parts of pigment, 30.0 parts of an aqueous solution of a resin dispersant, and 55.0 parts of water were mixed and dispersed with a sand grinder for 1 hour, and then centrifuged to remove non-dispersed materials including coarse particles. . As the pigment, carbon black (trade name “Printex85”, manufactured by Orion Engineered Carbons) was used. As an aqueous solution of the resin dispersant, a styrene-acrylic acid copolymer (composition (molar ratio) = 33: 67) is neutralized with a 10% aqueous potassium hydroxide solution in an equimolar amount with respect to the acid value, and an appropriate amount of ion-exchanged water. An aqueous solution having a resin (solid content) content of 20.0%, obtained by adding s. The styrene-acrylic acid copolymer had an acid value of 150 mgKOH / g and a weight average molecular weight of 8,000. After pressure filtration with a microfilter having a pore size of 3.0 μm (manufactured by Fuji Film), an appropriate amount of ion-exchanged water was added to prepare a pigment dispersion 8. The pigment content in the pigment dispersion 8 was 10.0%, and the resin content was 3.0%.

(Pigment dispersion 9)
The type of pigment is C.I. I. A pigment dispersion 9 was obtained in the same manner as in the case of the pigment dispersion 8 except that Pigment Blue 15: 3 (manufactured by Clariant) was used. The pigment content in the pigment dispersion 9 was 10.0%, and the resin content was 3.0%.

(Pigment dispersion 10)
The type of pigment is C.I. I. A pigment dispersion 10 was obtained in the same manner as in the case of the pigment dispersion 8 except that the pigment was changed to Pigment Red 122 (manufactured by Clariant). The pigment content in the pigment dispersion 10 was 10.0%, and the resin content was 3.0%.

(Pigment dispersion 11)
The type of pigment is C.I. I. A pigment dispersion 11 was obtained in the same manner as in the preparation of the pigment dispersion 8 except that the pigment was changed to Pigment Yellow 74 (manufactured by Clariant). The pigment content in the pigment dispersion 11 was 10.0%, and the resin content was 3.0%.

<Synthesis of urethane resin>
A four-necked flask equipped with a stirrer, a thermometer, a nitrogen gas introduction tube, and a reflux tube was prepared. In this four-necked flask, the type and amount of polyisocyanate shown in Table 1, a polyol having no acid group, a polyol having an acid group, and 300.0 parts of methyl ethyl ketone were placed. And it was made to react at 80 degreeC under nitrogen gas atmosphere for 6 hours. Subsequently, the polyamine of the quantity shown in Table 1 was added, and it was made to react at 80 degreeC until a product became a predetermined | prescribed weight average molecular weight, and the reaction liquid was obtained. After cooling the obtained reaction liquid to 40 degreeC, ion-exchange water was added and potassium hydroxide aqueous solution was added, stirring at high speed with a homomixer, and the liquid was obtained. Methyl ethyl ketone was distilled off from the liquid obtained by heating under reduced pressure to obtain liquids containing urethane resins 1 to 12 each having a urethane resin (solid content) content of 20.0%. Table 1 shows the properties of the urethane resin. The acid value of the urethane resin was measured by potentiometric titration using a potassium hydroxide-methanol titrant. The weight average molecular weight of the urethane resin was measured by GPC. The ratio (mol%) of urethane bonds in the total of urethane bonds and urea bonds in the urethane resin was measured and calculated by ¹³ C-NMR. did). Moreover, the detail of each component in Table 1 is shown below.

IPDI: isophorone diisocyanate H12MDI: dicyclohexylmethane-4,4′-diisocyanate PPG: polypropylene glycol (number average molecular weight: 2,000)
PTMG: Polytetramethylene glycol (number average molecular weight: 2,000)
PC: Polycarbonate polyol (number average molecular weight: 2,000)
DMPA: dimethylolpropionic acid DMBA: dimethylolbutanoic acid EDA: ethylenediamine IPDA: isophoronediamine

The ratio of urethane bonds in the total of urethane bonds and urea bonds in the obtained urethane resin was measured as follows. First, HCl was added to a liquid containing a urethane resin to precipitate the urethane resin. The dried resin was dissolved in heavy DMSO to prepare a measurement sample. And the sample prepared by ¹³ C-NMR (device name “Avance500”, manufactured by BRUKER Bio Spin) was analyzed, and from the integrated value of each peak of the obtained urethane bond and urea bond, the urethane bond in the urethane resin was analyzed. The percentage was calculated. For example, in the case of a urethane resin obtained using isophorone diisocyanate, the urethane bond peak is detected in the vicinity of 155 ppm, although some deviation occurs depending on the measurement conditions and the composition of the urethane resin. Further, the peak of urea bond is detected around 158 ppm.

  The proportion of urethane bonds in the total of urethane bonds and urea bonds in the urethane resin was adjusted as follows. The isocyanate groups in the polyisocyanate are gradually reduced by reacting with polyols having no acid groups and hydroxyl groups in polyols having acid groups. By confirming the residual ratio of isocyanate groups as needed, when a predetermined residual ratio is reached, polyamine (chain extender) is added, and the remaining isocyanate groups and amino groups are reacted to form urea bonds. Adjusted the ratio.

The measurement conditions of GPC for measuring the weight average molecular weight of the urethane resin are as shown below. Apparatus: Alliance GPC 2695 (manufactured by Waters)
Column: 4-column column of Shodex KF-806M (Showa Denko)
・ Mobile phase: Tetrahydrofuran (special grade)
・ Flow rate: 1.0 mL / min
・ Oven temperature: 40.0 ℃
-Sample solution injection volume: 0.1 mL
・ Detector: RI (refractive index)
Polystyrene standard samples: PS-1 and PS-2 (manufactured by Polymer Laboratories, molecular weight: 7,500,000, 2,560,000, 841,700, 377,400, 320,000, 210,500, 148,000, (17 types of 96,000, 59,500, 50,400, 28,500, 20,650, 10,850, 5,460, 2,930, 1,300, 580)

<Preparation of ink>
After mixing each component (unit:%) shown in the upper part of Tables 2-1 and 2-2 and 3-1 to 3-3 and stirring sufficiently, with a micro filter (manufactured by Fuji Film) having a pore size of 3.0 μm. Each ink was prepared by pressure filtration. “NIKKOL BO-50V” and “NIKKOL BC-20” in Tables 2-1 and 2-2 are trade names of surfactants manufactured by Nikko Chemicals. “Emalmine CO-200” in Tables 2-1 and 2-2 is a trade name of a surfactant manufactured by Sanyo Chemical Industries. "Acetyleneol E100" in Tables 2-1 and 2-2 and 3-1 to 3-3 is a trade name of a nonionic surfactant (acetylene glycol ethylene oxide adduct) manufactured by Kawaken Fine Chemicals. The HLB values determined by the Griffin method for these surfactants are shown in parentheses. The dynamic surface tension γ ₁₀ was measured by a maximum bubble pressure method under a condition of 25 ° C. using a dynamic surface tension meter (trade name “BUBLE PRESSURE TENSIOTER BP-2”, manufactured by KRUSS).

<Evaluation>
Each evaluation shown below was performed using the ink obtained above and the ink set combining them. In the present invention, according to the evaluation criteria shown below, “A” and “B” are acceptable levels, and “C” is an unacceptable level.

(Optical density of the image recorded with the first ink)
The first ink obtained above was filled in an ink cartridge and set in an ink jet recording apparatus (trade name “PIXUS Pro 9500”, manufactured by Canon Inc.), and a solid image of 2 cm × 2 cm was recorded on three types of recording media. The three types of recording media are “CAD standard paper 2” (Canon), “CAD special paper IJM021” (Ose), and “LED plotter paper THL-P300” (Toyo Sangyo). Paper was cut into A4 size. The recording conditions were temperature: 23 ° C., relative humidity: 55%, discharge amount per drop: within 3.5 ng ± 10%. Further, the ink application amount was adjusted so that about 18 ng of ink was applied to 600 dpi × 600 dpi. After leaving the recorded solid image for one day, the optical density was measured using a reflection densitometer (trade name “Macbeth RD-918”, manufactured by Macbeth) to calculate the average value of the three recording media. The optical density was evaluated according to the evaluation criteria shown in FIG. The results are shown in Table 4. The numerical values in parentheses in the evaluation criteria shown below are values used as evaluation criteria when the pigment type is an organic pigment.
A: The average value of the optical density was 1.3 or more (0.8 or more).
B: The average value of the optical density was 1.2 or more and less than 1.3 (0.7 or more and less than 0.8).
C: The average value of optical density was less than 1.2 (less than 0.7).

(Storage stability of the second ink)
The viscosity of the second ink obtained above at 25 ° C. was measured (viscosity before storage). The second ink was put in a sealed container and allowed to stand in a constant temperature bath at 70 ° C. for 1 week, and then returned to 25 ° C. to measure the viscosity (viscosity after storage). The viscosity of the ink was measured using an E-type viscometer (“RE-80L type”, manufactured by Toki Sangyo). Then, “increase rate of viscosity = viscosity after storage / viscosity before storage” was calculated, and storage stability was evaluated according to the evaluation criteria shown below. The results are shown in Table 4.
A: The increase rate of the viscosity was 1.1 or less.
B: The increase rate of the viscosity exceeded 1.1 and was 1.3 or less.
C: The increase rate of the viscosity exceeded 1.3.

(Glossiness of images recorded with the second ink)
The second ink obtained above was filled in an ink cartridge, set in an ink jet recording apparatus (trade name “PIXUS Pro 9500”, manufactured by Canon Inc.), and a solid image of 3 cm × 3 cm was recorded on a recording medium. As the recording medium, “Premium Glossy Paper” (manufactured by Canon) cut to A4 size was used. The recording conditions were temperature: 23 ° C., relative humidity: 55%, discharge amount per drop: within 3.5 ng ± 10%. Further, the ink application amount was adjusted so that about 22 ng of ink was applied to 600 dpi × 600 dpi. After leaving the recorded solid image for one day, 20 ° gloss was measured using a digital haze meter (trade name “Micro Haze Plus”, manufactured by BYK), and the optical density was evaluated according to the evaluation criteria shown below. The results are shown in Table 4.
A: The 20 ° gloss was 40 or more.
B: The 20 ° gloss was 30 or more and less than 40.
C: The 20 ° gloss was less than 30.

(Second ink ejection accuracy)
The second ink obtained above was filled in an ink cartridge and set in an ink jet recording apparatus (trade name “PIXUS MX7600”, manufactured by Canon Inc.). The process of recording two 19cm x 26cm solid images on A4 size PPC paper (product name "PB Paper", manufactured by Canon), leaving them for 30 minutes, and recording two similar solid images again in one cycle Image recording was performed. The recording conditions were temperature: 23 ° C., relative humidity: 55%, discharge amount per drop: within 4.5 ng ± 10%. Further, the ink application amount was adjusted so that about 18 ng of ink was applied to 600 dpi × 600 dpi. After repeating the above cycle 10 times, one nozzle check pattern was recorded, and the discharge accuracy of the obtained nozzle check pattern was visually confirmed. Moreover, the recording head was removed after recording, and the periphery of the discharge port was observed with a microscope to observe the presence or absence of deposits, and the discharge accuracy was evaluated according to the following evaluation criteria. The results are shown in Table 4.
A: Slight deposits were generated, but the nozzle check pattern was not disturbed.
B: Some deposits were generated, and the nozzle check pattern was slightly disturbed.
C: Many deposits were generated, and the nozzle check pattern was significantly disturbed.

(Discharge stability)
Each of the first ink and the second ink obtained above was filled in an ink cartridge to form an ink set with the combinations shown on the left side of Table 5, and set in an ink jet recording apparatus (trade name “PIXUS Pro 9500”, manufactured by Canon Inc.). In order to cover the ejection openings corresponding to the first ink and the second ink with the same cap, the ink cartridge for the first ink is set at the position of the MBk ink, and the ink cartridge for the second ink is set. Set to PBk ink position. After performing the suction recovery operation at the time of tank replacement and the two cleaning operations using the printer driver, the recording apparatus was allowed to stand for one week with the power on. One week later, a nozzle check pattern of the first ink was recorded via a printer driver, and ejection stability was evaluated according to the following evaluation criteria. The results are shown in Table 5.
A: The nozzle check pattern was recorded normally.
B: A part of the ruled line portion of the nozzle check pattern was faint.
C: Non-ejection or fading was observed in the ruled line portion of the nozzle check pattern, and “streaks” were present in the solid image portion.

Claims (7)

A recording head including a first ink and a second ink and having an ejection port for ejecting the ink; and a cap for collectively capping the ejection ports corresponding to each of the first ink and the second ink with the same member. An ink set used for an inkjet recording apparatus provided,
The first ink contains a self-dispersing pigment in which a functional group including an anionic group is bonded to the particle surface of the first pigment, and the introduced amount of the functional group is 0.10 mmol / g or more and 0.30 mmol / g. And
The second ink contains a urethane resin, a second pigment, and a resin dispersant (excluding the urethane resin) for dispersing the second pigment,
The urethane resin has units derived from polyisocyanate, a polyether polyol having no acid group, and a polyol having an acid group,
The proportion of urethane bonds in the total of urethane bonds and urea bonds in the urethane resin is 85.0 mol% or more and 99.0 mol% or less,
The urethane resin has a weight average molecular weight of 20,000 or less,
The content (mass%) of the urethane resin in the second ink is a mass ratio with respect to the content (mass%) of the second pigment, and is 0.10 times or more and 2.00 times or less,
The difference (first ink-second ink) between the dynamic surface tension of the first ink at a lifetime of 10 milliseconds and the dynamic surface tension of the second ink at a lifetime of 10 milliseconds is 10 mN / m or more. An ink set characterized by that.   The ink set according to claim 1, wherein the dynamic surface tension of the second ink at a lifetime of 10 milliseconds is 40 mN / m or less.   The difference between the dynamic surface tension of the first ink at a lifetime of 10 milliseconds and the dynamic surface tension of the second ink at a lifetime of 10 milliseconds (first ink-second ink) is 15 mN / m or more. Item 3. The ink set according to Item 1 or 2.   The ink set according to claim 1, wherein the first pigment is carbon black. The first ink further contains a surfactant;
The ink set according to any one of claims 1 to 4, wherein the surfactant has an HLB value determined by a Griffin method of 15.0 or more.   The ink set according to claim 5, wherein the content of the surfactant in the first ink is 0.05% by mass or more and 0.50% by mass or less. 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 a first ink and a second ink included in the ink set according to any one of claims 1 to 6.

Images