JP2019202417A - Ink jet recording method and ink jet recording device - Google Patents

Abstract

To provide an inkjet recording method which can record an image having high optical density and excellent fastness such as marker resistance, hardly causes ejection deviation even when long-time recording is performed and has excellent continuous recording property.SOLUTION: There is provided an inkjet recording method for recording an image on a recording medium by ejecting an aqueous ink from a recording head by the action of thermal energy. The aqueous ink contains a self-dispersible pigment, a resin having an anionic group, a salt and wax particles and the salt is composed by bonding a cation such as an alkali metal ion and an anion such as Cl.SELECTED DRAWING: None

Description

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

  With the improvement of image quality and recording speed, ink jet recording apparatuses are used not only for output of home photographic images and Web, but also for use in business fields such as offices. Ink for inkjet recording apparatuses used in the business field is required to be able to record high-quality images in addition to reliability such as ejection stability. For example, it is required to be able to record high-quality images with high optical density and images that are resistant to smearing even if they are rubbed or pulled with a marker pen and that have excellent robustness (abrasion resistance and marker resistance). Yes.

  Various proposals have been made so far to meet such demands. For example, an aqueous ink containing a self-dispersing pigment and a resin has been proposed in order to record an image having a high optical density and excellent scratch resistance (Patent Document 1). Patent Document 1 also describes that the optical density of a recorded image can be improved by adding a salt of a monovalent cation to the ink. In addition, an aqueous ink for inkjet that can record an image excellent in scratch resistance, containing a self-dispersing pigment, acrylic resin particles, and wax particles has been proposed (Patent Document 2).

JP 2012-214713 A JP2015-124379A

  The present inventors examined water-based inks proposed in Patent Documents 1 and 2. As a result, it was found that using these water-based inks, an image having high optical density and excellent fastness such as marker resistance can be recorded. However, when these water-based inks are ejected from a recording head using thermal energy for a long time, ejection problems are likely to occur, and a new problem such that the frequency of occurrence of ejection problems increases as the number of recording sheets increases. It was found to occur.

  Accordingly, an object of the present invention is to record an image having high optical density and excellent fastness such as marker resistance, and it is difficult to cause ejection distortion even when recorded for a long time, so that continuous recording is possible. Another object of the present invention is to provide an excellent ink jet recording method. Another object of the present invention is to provide an ink jet recording apparatus used in the above ink jet recording method.

The above object is achieved by the present invention described below. That is, according to the present invention, an inkjet recording method for recording an image on a recording medium by discharging aqueous ink from a recording head by the action of thermal energy, wherein the aqueous ink is a pigment, a resin having an anionic group, Salt and wax particles, and the pigment is a self-dispersing pigment in which an anionic group is bonded to the particle surface directly or through another atomic group, and the salt includes an alkali metal ion, an ammonium ion, and an organic At least one cation selected from the group consisting of ammonium ions, Cl ⁻ , Br ⁻ , I ⁻ , ClO ⁻ , ClO ₂ ⁻ , ClO ₃ ⁻ , ClO ₄ ⁻ , NO ₂ ⁻ , NO ₃ ⁻ , SO ₄ ^{2 −} , CO ₃ ²⁻ , HCO ₃ ⁻ , HCOO ⁻ , (COO ⁻ ) ₂ , COOH (COO ⁻ ), CH ₃ COO ⁻ , C ₂ H ₄ (COO ⁻ ) ₂ , C ₆ H ₅ COO ⁻ , C ₆ H ₄ (COO ⁻ ) ₂ , PO ₄ ³⁻ , HPO ₄ ²⁻ , and at least one anion selected from the group consisting of H ₂ PO ₄ ⁻ An ink jet recording method is provided.

  According to the present invention, an image having high optical density and excellent fastness such as marker resistance can be recorded, and even when recorded for a long time, it is less likely to cause jetting and excellent in continuous recordability. Inkjet recording methods can be provided. Moreover, according to this invention, the inkjet recording device used for the said inkjet recording method can be provided.

FIG. 2 is a diagram schematically illustrating an example of an ink jet recording apparatus used in the ink jet recording method of the present invention, in which (a) is a perspective view of a main part of the ink jet recording apparatus, and (b) is a perspective view of a head cartridge.

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

  When the inks proposed in Patent Document 1 and Patent Document 2 are ejected from a recording head using thermal energy for a long time, the ink is liable to be ejected and the number of recordings is increased. Along with this, the cause of the increase in the frequency of occurrence of ejection shaking was examined in detail. As a result, it has been found that there are inks that cause ink ejection and inks that do not cause ink ejection. Further, it has been found that in the recording head where the ejection distortion has occurred, aggregates are generated on the heater for applying thermal energy to the ink and in the vicinity of the ink ejection port. Further investigation revealed that agglomerates on the heater and in the vicinity of the discharge port are generated when a self-dispersing pigment, a resin containing an anionic group, and an ink containing a salt are discharged for a long time, and contain any component. It was found that the ink does not occur when ink that is not used is ejected. Based on the above results, the present inventors presumed the mechanism of occurrence of ejection shaking as follows.

  When the water in the ink evaporates from the ejection port and the concentration of the water-soluble organic solvent in the ink in the vicinity of the ejection port increases, the self-dispersing pigment moves toward the back of the ink flow path where more water is present. It moves (hereinafter also referred to as “retraction phenomenon”), and the dispersion state of the pigment is stably maintained. However, in the case of inks containing self-dispersing pigments, resins containing anionic groups, and salts, when water evaporates, the ink viscosity increases rapidly due to the increase in the resin concentration, and the pigment agglomerates due to the increase in the salt concentration. By promoting this, the retreat phenomenon is delayed. When the backward phenomenon becomes slow, the self-dispersed pigment whose dispersion state has become unstable is likely to accumulate as an aggregate on the heater or in the vicinity of the discharge port, and it is considered that discharge distortion occurs.

  When an ink containing a resin dispersed pigment is used instead of the self-dispersed pigment, it becomes difficult to record an image having a high optical density. When an ink that does not contain an anionic group-containing resin is used, it becomes difficult to record an image with improved marker resistance. Further, when an ink containing no salt is used, it becomes difficult to record an image having a high optical density.

As a result of the study, the present inventors can record an image having high optical density and excellent fastness such as marker resistance by satisfying the following requirements (1) to (3): It has been found that even when recording is performed for a long time, it is difficult for ink jetting to occur.
(1) An image is recorded on a recording medium by ejecting water-based ink from the recording head by the action of thermal energy.
(2) The ink contains a self-dispersing pigment in which an anionic group is bonded to the particle surface directly or through another atomic group, a resin having an anionic group, a salt, and wax particles.
(3) salt, a monovalent cation such as an alkali metal ion, Cl ^- is an anion and is bonded to formed salt such.

  Some of the wax particles in the ink to which thermal energy is applied cannot maintain the particle state. As a result, the hydrophobic part of the wax is exposed, and a part of the wax is considered to be dissolved in the ink. Since the hydrophobic part of the wax is very low in polarity, the receding phenomenon is remarkably accelerated. Since the ink existing in the back of the ink flow path contains a lot of water, it is considered that the dispersion state of the self-dispersing pigment becomes stable and the generation of aggregates is suppressed.

<Ink>
The ink used in the inkjet recording method of the present invention is a water-based inkjet ink containing a self-dispersing pigment, a resin having an anionic group, a salt, and wax particles. Hereinafter, each component constituting the ink will be described in detail.

(Self-dispersing pigment)
The coloring material used in the ink is a self-dispersing pigment in which an anionic group is bonded to the pigment particle surface directly or via another atomic group. By using a self-dispersing pigment as a coloring material, it is not necessary to add a dispersant for dispersing pigment particles in the ink, or the amount of the dispersant added can be reduced. An ink containing a self-dispersing pigment is likely to undergo a state change such as an increase in viscosity or pigment association or aggregation due to evaporation of water or the like after being applied to a recording medium. For this reason, when an ink containing a self-dispersing pigment is used, an image having a high optical density can be recorded.

  The anionic group may be partially dissociated in the ink or may be completely dissociated. Examples of the anionic group include 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 a hydrogen atom, an alkali metal, ammonium, or organic ammonium. In particular, the counter ion is preferably an alkali metal cation such as lithium, sodium, or potassium because the ink ejection stability is improved as compared with a cation such as ammonium or organic ammonium.

  The anionic group may be bonded to the pigment particle surface via another atomic group. Examples of other atomic groups include alkylene groups, arylene groups, amide groups, sulfonyl groups, imino groups, carbonyl groups, ester groups, ether groups, and groups obtained by combining these groups.

  Examples of the pigment include inorganic pigments such as carbon black and organic pigments. Moreover, you may further contain dye as a coloring material for purposes, such as toning.

  The pigment content (% by mass) in the aqueous ink is preferably 1.00% by mass or more and 10.00% by mass or less based on the total mass of the ink. When the pigment content is less than 1.00% by mass, the effect of improving the optical density of the recorded image may be slightly reduced. On the other hand, when the pigment content is more than 10.00% by mass, the effect of suppressing the occurrence of jetting after long-time recording may be slightly reduced.

(Resin having an anionic group)
The ink contains a resin having an anionic group (hereinafter also simply referred to as “resin”). Examples of the anionic group include a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, and a phosphonic acid group. Of these, a carboxylic acid group is preferred.

  The weight average molecular weight in terms of polystyrene of the resin measured by gel permeation chromatography (GPC) is preferably 8,000 or more and 60,000 or less. When the weight average molecular weight of the resin is less than 8,000, the marker resistance of the recorded image may be slightly lowered. When the weight average molecular weight of the resin is more than 60,000, the effect of suppressing the occurrence of ejection after a long recording may be slightly lowered.

  The resin having an anionic group is preferably a water-soluble resin. Whether or not the resin is water-soluble can be determined according to the following method. First, a liquid (resin solid content: 10% by mass) containing a resin neutralized with an alkali corresponding to an acid value (sodium hydroxide, potassium hydroxide, etc.) is prepared. Next, the prepared liquid is diluted 10 times (volume basis) with pure water to prepare a sample solution. And when the particle diameter of resin in a sample solution is measured by a dynamic light scattering method, if the particle | grains which have a particle diameter are not measured, it can be judged that the resin is water-soluble. The measurement conditions at this time can be as follows, for example.

[Measurement condition]
SetZero: 30 seconds Number of measurements: 3 times Measurement time: 180 seconds

  As the particle size distribution measuring apparatus, a particle size analyzer (for example, trade name “UPA-EX150”, manufactured by Nikkiso) using a dynamic light scattering method can be used. Of course, the particle size distribution measuring apparatus and measurement conditions to be used are not limited to the above.

  The acid value of the resin is preferably 60 mgKOH / g or more and 130 mgKOH / g or less. When the acid value of the resin is less than 60 mgKOH / g, the ink ejection stability tends to be shifted, or the ink ejection stability is somewhat difficult, for example, it is difficult to achieve a desired ejection amount without forming an appropriate ink droplet. May be lower. On the other hand, if the acid value of the resin is more than 130 mgKOH / g, the effect of suppressing the occurrence of ejection after a long recording may be slightly lowered.

  The content (% by mass) of the resin in the aqueous ink is preferably 0.10% by mass or more and 3.00% by mass or less based on the total mass of the ink. If the resin content is less than 0.10% by mass, the amount of resin remaining in the recorded image (pigment layer) decreases, and the marker resistance of the image may be slightly lowered. On the other hand, if the resin content is more than 3.00% by mass, aggregation of self-dispersing pigments due to evaporation of water or the like tends to be promoted. May be slightly lower.

  Examples of the resin include an acrylic resin, a polyester resin, a urethane resin, and a urea resin. These resins can be used alone or in combination of two or more. Especially, it is preferable to make an ink contain an acrylic resin and a urethane resin.

[acrylic resin]
As an acrylic resin, what has a hydrophilic unit and a hydrophobic unit as a structural unit is preferable. The acrylic resin is preferably water-soluble. In the following description, “(meth) acryl” means “acryl” and “methacryl”, and “(meth) acrylate” means “acrylate” and “methacrylate”.

  The hydrophilic unit is a unit formed by polymerizing a monomer having a hydrophilic group such as an acid group, a hydroxy group, or an ethylene oxide group. Examples of the monomer having a hydrophilic group include acidic monomers having a carboxylic acid group such as (meth) acrylic acid, itaconic acid, maleic acid and fumaric acid; ethyl (meth) acrylic acid-2-phosphonate Acidic monomers having phosphonic acid groups; anionic monomers such as anhydrides and salts of these acidic monomers; (meth) acrylic acid-2-hydroxyethyl, (meth) acrylic acid-3-hydroxypropyl Monomers having a hydroxy group such as; monomers having an ethylene oxide group 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. Examples of the cation constituting the salt of the anionic group include cations such as lithium, sodium, potassium, ammonium and organic ammonium.

  The hydrophobic unit is a unit formed by polymerizing a monomer having no hydrophilic group such as an acid group, a hydroxy group or an ethylene oxide group. Monomers having no hydrophilic group include monomers having an aromatic ring such as styrene, α-methylstyrene, and benzyl (meth) acrylate; ethyl (meth) acrylate, methyl (meth) acrylate, (n−, Examples thereof include monomers having an aliphatic group such as iso-) propyl (meth) acrylate, (n-, iso-, t-) butyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate.

  As the acrylic resin, there is a copolymer having a hydrophilic unit derived from a monomer having a carboxylic acid group and a hydrophobic unit derived from a monomer having an aromatic ring or a monomer having an aliphatic group. preferable.

[Urethane resin]
As the urethane resin, it is preferable to use those having units derived from polyisocyanate, polyol having no acid group, polyol having acid group, and polyamine. The urethane resin is preferably water-soluble.

[Polyisocyanate]
Polyisocyanate is a compound having two or more isocyanate groups in its molecular structure. Examples of the polyisocyanate include aliphatic polyisocyanate and aromatic polyisocyanate. 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.

  As aromatic polyisocyanates, tolylene diisocyanate, 2,2′-diphenylmethane diisocyanate, 2,4′-diphenylmethane diisocyanate, 4,4′-diphenylmethane diisocyanate, 4,4′-dibenzyl diisocyanate, 1,5-naphthylene diene Examples include isocyanate, xylylene diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, α, α, α ′, α′-tetramethylxylylene diisocyanate. . As the polyisocyanate, it is preferable to use a polyisocyanate having a cyclic structure, and it is more preferable to use isophorone diisocyanate.

[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.

(1) Polyol having no acid group Examples of polyether polyols include addition polymers of alkylene oxides and polyols; glycols such as (poly) alkylene glycols; and the like. Examples of the alkylene oxide include ethylene oxide, propylene oxide, butylene oxide, α-olefin oxide and the like. Examples of polyols 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, etc. (Poly) alkylene glycol; ethylene glycol-propylene glycol copolymer; and the like.

  Examples of the polyester polyol include acid esters. Examples of the acid component constituting the acid ester include aromatic dicarboxylic acids such as phthalic acid, naphthalenedicarboxylic acid, biphenyldicarboxylic acid, and tetrahydrophthalic acid; alicyclic dicarboxylic acids such as hydrogenated 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, alkyl succinic acid, linolenic acid, maleic acid, fumaric acid, mesaconic acid, citraconic acid, itaconic acid, etc. An aliphatic dicarboxylic acid; and the like. These anhydrides, salts, derivatives (alkyl esters, acid halides) and the like can also be used as the acid component. Examples of the component that forms an ester with an acid component include polyols such as diol and triol; glycols such as (poly) alkylene glycol; Examples of the polyols and glycols include those exemplified as the components constituting the polyether polyol.

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

  The proportion (mol%) of the unit derived from the polyol having no acid group in the total amount of the units derived from the polyol in the urethane resin is preferably 1.0% or more and 100.0 mol% or less. . Moreover, it is more preferable that it is 5.0 mol% or more and 50.0 mol% or less, and it is especially preferable that it is 10.0 mol% or more and 30.0 mol% or less.

  Polypropylene glycol is preferably used as the polyol. That is, it is preferable to use a urethane resin having a unit derived from polypropylene glycol.

(2) 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 a urethane resin can be adjusted with the usage-amount of the polyol which has an acid group, for example.

  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.

(3) Polyamines As polyamines, monoamines having a plurality of hydroxy groups such as dimethylolethylamine, diethanolmethylamine, dipropanolethylamine, dibutanolmethylamine; ethylenediamine, propylenediamine, hexylenediamine, isophoronediamine, xylylenediamine, Bifunctional polyamines such as diphenylmethanediamine, hydrogenated diphenylmethanediamine, and hydrazine; polyfunctional 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.

(salt)
The ink contains a predetermined salt. “Salt” means a compound formed by combining a cation and an anion. When an ink containing a salt is used, aggregation of the pigment on the recording medium can be promoted, so that the optical density of the recorded image can be remarkably improved.

The salt contained in the ink is a compound formed by binding at least one cation and at least one anion so as to neutralize the electric charge. The cation is at least one selected from the group consisting of alkali metal ions, ammonium ions, and organic ammonium ions. Anions include Cl ⁻ , Br ⁻ , I ⁻ , ClO ⁻ , ClO ₂ ⁻ , ClO ₃ ⁻ , ClO ₄ ⁻ , NO ₂ ⁻ , NO ₃ ⁻ , SO ₄ ²⁻ , CO ₃ ²⁻ , HCO ₃ ⁻ , and HCOO. ⁻ , (COO ⁻ ) ₂ , COOH (COO ⁻ ), CH ₃ COO ⁻ , C ₂ H ₄ (COO ⁻ ) ₂ , C ₆ H ₅ COO ⁻ , C ₆ H ₄ (COO ⁻ ) ₂ , PO ₄ ³⁻ , HPO ₄ ²⁻ , and H ₂ PO ₄ ⁻ .

  The salt content (mass%) in the water-based ink is preferably a mass ratio with respect to the pigment content (mass%) of 0.03 to 0.40 times. When the above-mentioned mass ratio is less than 0.03 times, the effect of improving the optical density of the recorded image may be slightly lowered. On the other hand, if the mass ratio is more than 0.40 times, the effect of suppressing the occurrence of jetting after recording for a long time may be slightly reduced.

(Wax particles)
The ink contains wax particles. By using ink containing wax particles, it is possible to record an image with high optical density and excellent fastness such as marker resistance, and it is also possible to make it difficult for ink jetting to occur even when recorded for a long time. it can.

  The wax particles are present in a state of being dispersed in the ink. Examples of the wax include natural wax and synthetic wax.

  Examples of natural waxes include petroleum waxes, plant waxes, and animal and plant waxes. Examples of petroleum waxes include paraffin wax, microcrystalline wax, and petrolatum. Examples of plant waxes include carnauba wax, candelilla wax, rice wax, and wood wax. Examples of animal and plant waxes include lanolin and beeswax.

  Examples of synthetic waxes include synthetic hydrocarbon waxes and modified waxes. Examples of the synthetic hydrocarbon wax include polyolefin wax and Fischer-Tropsch wax. Examples of the modified wax include paraffin wax derivatives, montan wax derivatives, and microcrystalline wax derivatives.

  These waxes can be used singly or in combination of two or more. The wax particles are preferably formed of at least one of paraffin wax and polyolefin wax.

  The wax particles may be dispersed in the ink using a dispersant, or may be dispersed in the ink without using a dispersant. Especially, it is preferable that the ink contains a dispersant for dispersing the wax particles, and the wax particles are dispersed in the ink by the dispersant. Examples of the dispersant include a surfactant; a resin having a hydrophilic group such as a sulfonic acid group or a carboxylic acid group; Examples of the resin having a hydrophilic group include a resin having a hydrophilic group graft-bonded; a resin having a unit derived from a hydrophilic monomer and a monomer having a hydrophobic portion; Can do. The content (% by mass) of the dispersant for dispersing the wax particles is preferably 5.0% by mass or more and 25.0% by mass or less based on the total of the dispersant and the wax particles.

  The content (% by mass) of the wax particles in the aqueous ink is preferably 0.05% by mass or more and 3.00% by mass or less based on the total mass of the ink. Further, the content (mass%) of the wax particles in the water-based ink is preferably 0.01 times or more and 1.00 times or less as a mass ratio with respect to the pigment content (mass%). When the above-mentioned mass ratio is less than 0.01 times, the amount of wax particles relative to the amount of pigment is relatively small, and thus the effect of promoting the reverse phenomenon may be slightly reduced. On the other hand, if the above mass ratio is more than 1.00 times, the ink droplet deposition position is likely to be shifted, or the ink ejection is stable because it is difficult to achieve a desired ejection amount without forming an appropriate ink droplet. Sexuality may be slightly lower.

(Aqueous medium)
The ink used in the inkjet recording method of the present invention is an aqueous ink containing at least water as an aqueous medium. As water, it is preferable to use deionized water (ion exchange water). The content (% by mass) of water in the ink is preferably 10.00% 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 may further contain a water-soluble organic solvent. The water-soluble organic solvent is not particularly limited as long as it is water-soluble, and monohydric 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 ink may contain water-soluble organic compounds that are solid at room temperature, such as polyhydric alcohols such as trimethylolpropane and trimethylolethane, and urea derivatives such as urea and ethyleneurea. You may make it contain. In addition, various additions such as surfactants, pH adjusters, antifoaming agents, rust preventives, antiseptics, antifungal agents, antioxidants, anti-reducing agents, and evaporation accelerators are added to the ink as necessary. An agent may be included.

(Ink physical properties)
The viscosity of the ink at 25 ° C. is preferably 1.0 mPa · s or more and 5.0 mPa · s or less, and more preferably 1.0 mPa · s or more and 3.0 mPa · s or less. The static surface tension of the ink at 25 ° C. is preferably 28 mN / m or more and 45 mN / m or less. Furthermore, the pH of the ink at 25 ° C. is preferably 5 or more and 9 or less.

<Inkjet recording method and inkjet recording apparatus>
The ink jet recording method of the present invention is a method for recording an image on a recording medium by discharging the above-described ink from a recording head by the action of thermal energy. Other than using the ink described above, the steps of the ink jet recording method may be known. The ink jet recording apparatus of the present invention includes the above-described ink, and a recording head that is filled with the ink and discharges the ink by the action of thermal energy. The configuration of the ink jet recording apparatus may be a known one except that the recording head is filled with the ink described above.

  1A and 1B are diagrams schematically showing an example of an ink jet recording apparatus used in the ink jet recording method of the present invention. FIG. 1A is a perspective view of a main part of the ink jet recording apparatus, and FIG. 1B is a perspective view of a head cartridge. It is. The ink jet recording apparatus is provided with a conveying means (not shown) for conveying the recording medium 32 and a carriage shaft 34. A head cartridge 36 can be mounted on the carriage shaft 34. The head cartridge 36 includes recording heads 38 and 40, and is configured such that an ink cartridge 42 is set. While the head cartridge 36 is conveyed along the carriage shaft 34 in the main scanning direction, ink (not shown) is ejected from the recording heads 38 and 40 toward the recording medium 32. Then, the recording medium 32 is conveyed in the sub-scanning direction by a conveying unit (not shown), whereby an image is recorded on the recording medium 32.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further in detail, this invention is not limited at all by the following Example, unless the summary is exceeded. 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 2.5 g of concentrated hydrochloric acid in 5.5 g of water was cooled to 5 ° C., and 0.7 g of 4-aminophthalic acid was added. The container containing this solution was placed in an ice bath and cooled to 10 ° C. or lower, and a solution obtained by dissolving 0.9 g of sodium nitrite in 9.0 g of ion-exchanged water at 5 ° C. was added. After stirring for 15 minutes, 10.0 g of carbon black (specific surface area 220 m ² / g, DBP oil absorption 105 mL / 100 g) was added with stirring, and stirring was further performed 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 particles were sufficiently washed with water and dried in an oven at 110 ° C. Thereafter, sodium ions were replaced with potassium ions by an ion exchange method to obtain a self-dispersed pigment in which —C ₆ H ₃ — (COOK) ₂ groups were bonded to the surface of carbon black particles. An appropriate amount of water was added to adjust the pigment content to obtain Pigment Dispersion Liquid 1 having a pigment content of 20.0%.

(Pigment dispersion 2)
A solution obtained by dissolving 2.5 g of concentrated hydrochloric acid in 5.5 g of water was cooled to 5 ° C., and 0.8 g of p-aminobenzoic acid was added. The container containing this solution was placed in an ice bath and cooled to 10 ° C. or lower, and a solution obtained by dissolving 0.9 g of sodium nitrite in 9.0 g of ion-exchanged water at 5 ° C. was added. After stirring for 15 minutes, 9.0 g of carbon black (specific surface area 220 m ² / g, DBP oil absorption 105 mL / 100 g) was added with stirring, and stirring was further performed 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 particles were sufficiently washed with water and dried in an oven at 110 ° C. Thereafter, sodium ions were replaced with potassium ions by an ion exchange method to obtain a self-dispersing pigment in which —C ₆ H ₄ —COOK groups were bonded to the surface of carbon black particles. An appropriate amount of water was added to adjust the pigment content to obtain Pigment Dispersion Liquid 2 having a pigment content of 20.0%.

(Pigment dispersion 3)
C. instead of carbon black I. Pigment dispersion 3 was prepared in the same manner as in the case of pigment dispersion 1 except that CI Pigment Blue 15: 3 was used. The pigment content in Pigment Dispersion Liquid 3 was 20.0%.

(Pigment dispersion 4)
C. instead of carbon black I. A pigment dispersion 4 was prepared in the same manner as in the case of the pigment dispersion 1 except that Pigment Red 122 was used. The pigment content in the pigment dispersion 4 was 20.0%.

(Pigment dispersion 5)
C. instead of carbon black I. A pigment dispersion 5 was prepared in the same manner as in the case of the pigment dispersion 1 except that CI Pigment Yellow 74 was used. The pigment content in the pigment dispersion 5 was 20.0%.

(Pigment dispersion 6)
A styrene-butyl acrylate-acrylic acid copolymer having an acid value of 120 mgKOH / g and a weight average molecular weight of 10,000 was neutralized with a 10% aqueous potassium hydroxide solution. 20.0 parts of carbon black having a specific surface area of 210 m ² / g, DBP oil absorption of 74 mL / 100 g, 5.0 parts (solid content) of a neutralized styrene-butyl acrylate-acrylic acid copolymer, and 75.0 pure water Parts were mixed to obtain a mixture. The mixture obtained using a sand grinder was dispersed for 1 hour, and then centrifuged to remove coarse particles. Further, the mixture was filtered under pressure with a micro filter having a pore size of 3.0 μm (manufactured by Fuji Film), and an appropriate amount of water was added to obtain a pigment dispersion 6 in which carbon black was dispersed in water with a resin dispersant. . The pigment dispersion 6 thus obtained had a pigment content of 20.0% and a resin dispersant content of 4.7%.

<Synthesis of urethane resin>
A four-necked flask equipped with a thermometer, a stirrer, a nitrogen introduction tube, and a reflux tube was prepared. In this four-necked flask, a polyisocyanate of the type and amount used shown in Table 1, a polyol having no acid group, a polyol having an acid group, 0.02 part of dibutyltin dilaurate, and 120 parts of methyl ethyl ketone were placed in a nitrogen gas atmosphere. The reaction was carried out at 80 ° C. for 6 hours. After cooling to 40 ° C. and adding ion-exchanged water, an aqueous potassium hydroxide solution was added while stirring at high speed with a homomixer to obtain a resin solution. Methyl ethyl ketone was distilled off from the resin solution obtained by heating under reduced pressure to obtain a liquid containing water-soluble urethane resins 1 to 10 having a resin (solid content) content of 20.0%. Table 2 shows the characteristics of the urethane resin. Moreover, the detail of each component in Table 1 is shown below.
IPDI: isophorone diisocyanate TDI: tolylene diisocyanate PPG: polypropylene glycol (number average molecular weight 2,000)
DMPA: dimethylolpropionic acid

<Synthesis of acrylic resin>
After monomers of the types and amounts used shown in Table 2 were copolymerized by a conventional method, anionic groups were neutralized using an aqueous potassium hydroxide solution. Ion exchange water was added to prepare a liquid containing water-soluble acrylic resins 1 and 2 having a resin (solid content) content of 20.0%. Table 2 shows the characteristics of the acrylic resin. Moreover, the detail of each component in Table 2 is shown below.
St: Styrene BA: Butyl acrylate AA: Acrylic acid

<Preparation of aqueous dispersion of wax particles>
(Synthesis of ethylene-acrylic resin)
A 500 mL four-necked flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube was prepared. In this four-necked flask, 100.0 parts of polyethylene and 100.0 parts of diethylene glycol monoethyl ether acetate were placed. The mixture was melted in an oil bath maintained at 180 ° C. in a nitrogen atmosphere, and the temperature of the oil bath was adjusted with stirring so that the temperature in the system became 170 ° C. While stirring, 10.0 parts of benzyl acrylate, 5.0 parts of acrylic acid, and 0.4 part of di-t-butyl peroxide were added. After the system was kept at 170 ° C. and reacted for 30 minutes, the same amounts of benzyl acrylate, acrylic acid, and di-t-butyl peroxide were added. Similarly, benzyl acrylate, acrylic acid, and di-t-butyl peroxide were added a total of 5 times every 30 minutes.

  The temperature in the system is lowered to 50 ° C., and the pressure in the flask is reduced by an aspirator for 1 hour to remove the solvent, unreacted monomer, di-t-butyl peroxide, and di-t-butyl peroxide decomposition products. Removed. After aging for 2 hours, ethylene glycol monobutyl ether was distilled off under reduced pressure to obtain a resin. To the obtained resin, potassium hydroxide in an amount equivalent to the acid value and an appropriate amount of ion-exchanged water were added and heated to 80 ° C. to dissolve. Thereby, the liquid containing ethylene-acrylic resin whose content of ethylene-acrylic resin (solid content) is 20.0% was obtained.

(Aqueous dispersion of wax particles 1-6)
A four-necked flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube was prepared. To this four-necked flask, 450 g of ion-exchanged water and the wax (unit: part) shown in the upper part of Table 3 were added, held at 90 to 95 ° C., melted, and stirred. Subsequently, the dispersing agent (unit: part) shown in the upper part of Table 3 was added and dispersed at the temperature of 90 to 95 ° C. for 15 minutes using an ultrasonic homogenizer, and then cooled to room temperature and dispersed. Got. Ion exchange water was added to the obtained dispersion to obtain an aqueous dispersion of wax particles 1 to 6 having a wax particle (solid content) content of 10.0%. Table 3 shows the characteristics of the obtained aqueous dispersion of wax particles.

(Aqueous dispersion of wax particles 7)
A commercially available aqueous dispersion of polyolefin wax particles (trade name “CHEMIPARL W4005”, manufactured by Mitsui Chemicals, content of wax (solid content) 40.0%) is diluted with ion-exchanged water, and the content of wax particles is 10 An aqueous dispersion of wax particles 7 of 0.0% was obtained.

<Preparation of ink>
(Ink 1 to 46)
Each component (unit:%) shown in the upper part of Tables 4-1 to 4-5 was mixed and sufficiently stirred, and then pressure filtration was performed with a micro filter (manufactured by Fuji Film) having a pore size of 3.0 μm. An ink was prepared. In Tables 4-1 to 4-5, “acetylenol E100” is a trade name of a non-ionic surfactant (ethylene oxide adduct of acetylene glycol) manufactured by Kawaken Fine Chemicals. Pigment content P (%), wax particle content W (%), salt content S (%), resin content R (%), W / P value (times) in the prepared ink And S / P values (times) are shown in the lower part of Tables 4-1 to 4-5.

(Ink 47)
The ink of “Example 33” described in Patent Document 1 was designated as “ink 47”. This ink contains a self-dispersing pigment, a resin having an anionic group, and a predetermined salt, but does not contain wax particles.

(Ink 48)
The ink of “Example 1” described in Patent Document 2 was designated as “ink 48”. This ink contains a self-dispersing pigment, a resin having an anionic group, and wax particles, but does not contain a predetermined salt.

<Evaluation>
Each evaluation shown below was performed using a modified machine of an ink jet recording apparatus (trade name “PIXUS Pro 9500”, manufactured by Canon Inc.). The recording environment was a temperature of 25 ° C. and a relative humidity of 55%. In this embodiment, an image recorded under the condition that about 16 ng of ink is applied to a unit area (1 pixel) of 1/600 inch × 1/600 inch is defined as a recording duty of 100%. In the present invention, “AA”, “A”, and “B” are acceptable levels, and “C” is unacceptable levels in the following evaluation criteria. The evaluation results are shown in Table 5.

(Discharge)
The cartridge filled with the prepared ink was attached to the ink jet recording apparatus. A nozzle check pattern was recorded, and it was confirmed that ink was normally discharged from all the discharge ports. Thereafter, the process of recording 250 solid images with a recording duty of 5% on the entire surface of an A4 size recording medium (plain paper, product name “GF-500”, manufactured by Canon) and leaving it for 10 hours is defined as one cycle. It was repeated 200 cycles. The nozzle check pattern after 200 cycles was confirmed, and the ejection run was evaluated according to the following evaluation criteria.
AA: The nozzle check pattern was recorded normally.
A: The nozzle check pattern was slightly distorted.
B: The nozzle check pattern was slightly disturbed. C: The nozzle check pattern was significantly disturbed.

(Marker resistance)
The cartridge filled with the prepared ink was attached to the ink jet recording apparatus. A vertical ruled line having a thickness of 1/10 inch was recorded on a recording medium (plain paper, trade name “GF-500”, manufactured by Canon Inc.). Three minutes after recording, the recorded vertical ruled line was marked with a yellow line marker (trade name “OPTEX2”, manufactured by Zebra), and immediately after that, marked on the white background of the PPC paper. Marking of the marker nib and white background was confirmed, and the marker resistance of the image was evaluated according to the following evaluation criteria.
A: The marker nib was not contaminated, and the marking on the white background was not contaminated.
B: Although the marker nib is contaminated, the marking on the white background hardly occurred.
C: The marker pen tip was contaminated, and the white background marking was also contaminated.

(Optical density)
The cartridge filled with the prepared ink was attached to the ink jet recording apparatus. Then, a solid image of 2 cm × 2 cm (recording duty 100%) was recorded on four types of recording media. The four types of recording media used are as follows.
・ Product name "PPC paper GF-500" (Canon)
・ Product name "PPC paper 4024" (Xerox)
・ Product name "PPC Paper Bright White" (manufactured by Hured Packard)
・ Product name "PPC paper hammer mill jet print" (made by International Paper)

The recorded solid image was allowed to stand for one day, and then the optical density of the solid image was measured using a spectrophotometer (trade name “Spectorolino”, manufactured by Gretag Macbeth) under the conditions of light source: D50 and field of view: 2 °. From the average value and the maximum value of the optical density of the solid images recorded on the four types of recording media, the optical density of the image was evaluated according to the following evaluation criteria.
A: The average value was 1.50 or more, and the maximum value was 1.60 or more.
B: The average value was 1.50 or more, and the maximum value was 1.50 or more and less than 1.60.
C: The average value was less than 1.50.

Claims (7)

An inkjet recording method for recording an image on a recording medium by discharging aqueous ink from a recording head by the action of thermal energy,
The water-based ink contains a pigment, a resin having an anionic group, a salt, and wax particles,
The pigment is a self-dispersing pigment in which an anionic group is bonded to the particle surface directly or through another atomic group,
The salt is at least one cation selected from the group consisting of alkali metal ions, ammonium ions, and organic ammonium ions, and Cl ⁻ , Br ⁻ , I ⁻ , ClO ⁻ , ClO ₂ ⁻ , ClO ₃ ⁻ , ClO _4. ⁻ , NO ₂ ⁻ , NO ₃ ⁻ , SO ₄ ²⁻ , CO ₃ ²⁻ , HCO ₃ ⁻ , HCOO ⁻ , (COO ⁻ ) ₂ , COOH (COO ⁻ ), CH ₃ COO ⁻ , C ₂ H ₄ (COO ^- ) ₂ , C ₆ H ₅ COO ⁻ , C ₆ H ₄ (COO ⁻ ) ₂ , PO ₄ ³⁻ , HPO ₄ ²⁻ , and H ₂ PO ₄ ^−. An ink jet recording method comprising a salt constituted by bonding.   2. The inkjet recording method according to claim 1, wherein the content (mass%) of the wax particles in the water-based ink is 0.01 times or more in terms of a mass ratio with respect to the content (mass%) of the pigment.   The inkjet recording method according to claim 1, wherein the wax particles are formed of at least one of a paraffin wax and a polyolefin wax.   The inkjet recording method according to any one of claims 1 to 3, wherein the water-based ink further contains a dispersant for dispersing the wax particles.   5. The ink jet recording method according to claim 1, wherein the acid value of the resin is 60 mgKOH / g or more and 130 mgKOH / g or less.   The content (mass%) of the salt in the water-based ink is 0.03 times or more and 0.40 times or less as a mass ratio with respect to the content (mass%) of the pigment. The ink jet recording method according to claim 1. An ink jet recording apparatus comprising: a water-based ink; and a recording head filled with the water-based ink and discharging the water-based ink by the action of thermal energy,
The water-based ink contains a pigment, a resin having an anionic group, a salt, and wax particles,
The pigment is a self-dispersing pigment in which an anionic group is bonded to the particle surface directly or through another atomic group,
The salt is at least one cation selected from the group consisting of alkali metal ions, ammonium ions, and organic ammonium ions, and Cl ⁻ , Br ⁻ , I ⁻ , ClO ⁻ , ClO ₂ ⁻ , ClO ₃ ⁻ , ClO _4. ⁻ , NO ₂ ⁻ , NO ₃ ⁻ , SO ₄ ²⁻ , CO ₃ ²⁻ , HCO ₃ ⁻ , HCOO ⁻ , (COO ⁻ ) ₂ , COOH (COO ⁻ ), CH ₃ COO ⁻ , C ₂ H ₄ (COO ^- ) ₂ , C ₆ H ₅ COO ⁻ , C ₆ H ₄ (COO ⁻ ) ₂ , PO ₄ ³⁻ , HPO ₄ ²⁻ , and H ₂ PO ₄ ^−. An ink jet recording apparatus comprising a salt constituted by bonding.

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