JP5258535B2 - Maintenance liquid for ink jet recording, ink set, and maintenance method - Google Patents

Description

  The present invention relates to a maintenance liquid for ink jet recording, an ink set, and a maintenance method that are preferably used in an ink jet recording apparatus.

  With the rapid development of the information technology industry in recent years, various information processing systems have been developed, and recording methods and apparatuses suitable for each information processing system have been put into practical use.

  Among these, the ink jet recording method is widely used because it can be recorded on various materials, the hardware (device) is relatively inexpensive and compact, and has excellent quietness. . In the recording using the ink jet recording method, it has become possible to obtain a so-called photographic-like high quality recorded matter. In addition, an ink jet recording method using pigment ink is generally considered to have better storage stability than an ink jet recording method using dye ink.

  However, the pigment ink does not re-dissolve when the water in the ink evaporates and solidifies. Therefore, solidifying at the nozzle tip of the ink jet head causes clogging and causes non-ejection of the ink. . Further, when the ink is solidified at the cap, the wipe portion, etc., there is a problem that wiping becomes difficult and a burden is imposed on the maintenance system.

In order to solve such a problem, a maintenance liquid for ink jet recording containing 0.1 to 10% by weight of a resin solvent having a solubility in water at 25 ° C. of 3% by weight or more and 1 to 50% by weight of a humectant (for example, Patent Document 1) and an inkjet recording maintenance liquid containing a resin solvent that is insoluble or hardly soluble in water and a humectant are disclosed (for example, see Patent Document 2).
JP 2007-119658 A JP 2007-169314 A

  However, in the above-described conventional technology, the amount of solvent is not sufficient in terms of detergency, and for example, when the ink used for recording contains fine resin particles or is prepared with a hydrophobic solvent, the cleaning effect is insufficient. Met. Further, since the humectant is contained, if the humectant is mixed into the ink through the nozzles during maintenance, the recording medium may be curled when recording on the recording medium.

  The present invention has been made in view of the above, and provides a maintenance liquid excellent in cleaning properties, an ink set using the same, and a maintenance method while suppressing adverse effects on a recording head and ejected ink. It is an object to achieve this purpose.

Specific means for achieving the above object are as follows.
<1> Inkjet recording maintenance comprising at least water, 8% by mass or more of (mono or di) propylene alkyl ether and an anionic surfactant which is insoluble or hardly soluble in water and based on the total mass. It is a liquid.

  In the present invention, “maintenance” includes maintaining a recording head that discharges ink for inkjet recording and its discharge performance at or near an expected state, and cleaning the recording head (cleaning). Maintenance and maintenance in a better condition.

<2> The maintenance liquid for inkjet recording according to <1>, wherein the anionic surfactant is sodium alkylcarboxylate or sodium alkylsulfonate .
<3> The Sodium alkyl carboxylic acid and said alkyl sulfonic acid, carbon atoms in the alkyl portion is an ink jet recording maintenance liquid according to SL before in the range of 10 to 20 <2>.
< 4 > For inkjet recording according to any one of <1> to < 3 >, wherein the inkjet recording apparatus includes an ejection nozzle that ejects pigment ink and is used for cleaning the ejection nozzle. Maintenance liquid.

< 5 > An ink set comprising an aqueous ink composition containing a pigment, and the inkjet recording maintenance liquid according to any one of <1> to < 4 >.
< 6 > The ink set according to < 5 >, wherein the water-based ink composition further contains a resin compound.
< 7 > The ink set according to < 5 > or < 6 >, wherein the pigment is dispersed by a pigment dispersant.

< 8 > An inkjet recording maintenance liquid according to any one of <1> to < 4 >, wherein at least a part of an inkjet recording head that performs recording by discharging an aqueous ink composition containing at least a pigment. This is a maintenance method for cleaning using
< 9 > The maintenance method according to < 8 >, wherein the water-based ink composition includes water and the pigment dispersed with a pigment dispersant and a resin compound.

  According to the present invention, it is possible to provide a maintenance liquid excellent in cleanability, an ink set using the same, and a maintenance method, in which adverse effects on the recording head and ejected ink are suppressed. When applied to cleaning an inkjet recording apparatus using pigment ink, that is, an inkjet recording head for discharging pigment ink, particularly excellent cleaning properties can be obtained.

  Hereinafter, the maintenance liquid for inkjet recording of the present invention, the ink set using the same, and the maintenance method will be described in detail.

The inkjet recording maintenance liquid of the present invention (hereinafter also simply referred to as “maintenance liquid”) includes at least water, (mono or di) propylene alkyl ether which is an organic solvent insoluble or hardly soluble in water, and anionic. In addition to containing a surfactant , the content of the organic solvent is 8% by mass or more with respect to the total mass. Further, the maintenance liquid of the present invention can be constituted using other components such as a surfactant.

In the present invention, by containing an organic solvent that is insoluble or hardly soluble in water together with water, the solubility or redispersibility of the ink adhering to the recording head or the like is improved, so that the ink adhering to the ejection head or the like is thickened. -Excellent in cleaning property of solidified ink, and it is possible to avoid problems such as unstable ejection after nozzle cleaning and nozzle clogging. Also, when mixed into the ink through the discharge nozzle, there is little concern about the aggregation of the ink, and the adverse effect on the head member is low. In particular, when a pigment ink containing a pigment is used as a coloring material, the cleaning property is excellent when problems such as thickening and solidification due to drying of the pigment ink occur.
As a result, when a recording device such as an ink jet printer is used for a long time after it has been used, it is possible to avoid the occurrence of ejection failures such as ejection instability and nozzle clogging, and the associated decrease in reliability. The discharge performance and image quality can be kept stable.

The reason why the above-described problems can be effectively suppressed / resolved by the maintenance liquid of the present invention is not clear, but is presumed as follows, for example.
For example, in the case of a pigment ink containing a pigment and a resin compound, the organic solvent contained in the maintenance liquid of the present invention is a good solubilizer / softener for the resin compound in the ink, and is generated when the pigment ink is dried. Quickly permeates the thickened / solidified product and softens, re-disperses or dissolves it, and is excellent in the effect of quickly dissolving or re-dispersing solids (pigments, resin compounds, etc.) in the maintenance liquid. . It is considered that by dissolving or redispersing the solid matter from the surface, the lump of the dried ink is loosened and easily dropped from the nozzle surface of the head.

Hereinafter, components of the maintenance liquid for inkjet recording of the present invention will be described.
(Organic solvent)
The maintenance liquid for inkjet recording of the present invention contains at least one propylene alkyl ether (mono or di) which is an organic solvent insoluble or hardly soluble in water. By including this organic solvent, it is possible to improve the washability of the dried ink. Specifically, for example, in the case of pigment ink, the resin compound particles normally contained in the pigment ink have a characteristic of being well redispersed.

  A general water-based pigment ink has water and a pigment as a color material and a resin dispersant that disperses the pigment in water as main components, and a water-soluble organic solvent, a resin compound, and the like are added as necessary. When this pigment ink is dried in the ink flow path of the printer, water and water-soluble organic solvent gradually evaporate, resulting in a thickened / solidified product with the pigment and resin compound mainly remaining. Cause problems such as ink clogging. This thickened / solidified product does not easily dissolve or disperse in water. In the case of using the above-described conventional maintenance liquid, although there are some effects in comparison with water, there are many cases where the cleaning performance / recovery performance that can solve problems such as clogging is insufficient. On the other hand, the maintenance liquid for inkjet recording of the present invention is excellent in the performance of dissolving or redispersing the above thickened / solidified product in the maintenance liquid quickly by the action of the organic solvent contained therein. The recovery performance is high, and as a result, problems such as ink clogging can be solved.

  The organic solvent having such an action effect is selected from those which are insoluble or hardly soluble in water, more specifically those having a solubility in water at 20 ° C. of less than 10% by mass.

  The content of the organic solvent contained in the maintenance liquid for inkjet recording of the present invention is in the range of 8% by mass or more with respect to the total mass of the maintenance liquid. Especially, the range of 8-50 mass% is preferable, as for content of an organic solvent, 8-25 mass% is more preferable, and 8-15 mass% is especially preferable. When the content of the organic solvent is less than 8% by mass, the above-described effects, that is, the thickening of the ink, the dissolution or redispersibility of the solidified product, and the cleaning performance / recovery performance are not sufficiently exhibited. The discharge performance cannot be stably maintained for a long time at a desired state or a state close thereto.

The organic solvent can be appropriately selected and used as long as it is insoluble or hardly soluble in water, and examples thereof include ethers and alcohols.
The ethers can be selected without particular limitation, for example, diethyl ether, dibutyl ether, ethyl methyl ether, dihexyl ether, furan, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, dipropylene glycol t-butyl ether, diethylene glycol Examples include monohexyl ether, ethylene glycol mono-2-ethylhexyl ether, and diethylene glycol mono-2-ethylhexyl ether.
The alcohol is not particularly limited and can be selected from linear or branched alcohols having 4 or more carbon atoms, and examples thereof include butanol, pentanol, hexanol, octanol and the like. Among them, the alcohol is preferably a non-cyclic linear or branched alcohol having 4 or more carbon atoms.

  Among these, from the viewpoint of thickening of the ink and dissolution or redispersibility of the solidified product, it is preferably selected from the group consisting of the ethers.

Among ethers, an ether solvent having both one hydroxyl group and one or more ether bonds is more preferable. Examples of such ether solvents include (mono or di) propylene alkyl ethers such as propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, dipropylene glycol t-butyl ether, diethylene glycol monohexyl ether, ethylene glycol mono-2- (Mono or di) ethylene alkyl ethers such as ethyl hexyl ether and diethylene glycol mono-2-ethyl hexyl ether may be mentioned.
Among the above, propylene alkyl ether is particularly preferable from the viewpoints of thickening of the ink, dissolution or redispersibility of the solidified product, and ejection properties.

(water)
The maintenance liquid for inkjet recording of the present invention contains water. Preferable water can be pure water such as ion exchange water, ultrafiltration water, reverse osmosis water, distilled water, or ultrapure water for the purpose of reducing ionic impurities as much as possible.
The maintenance liquid of the present invention preferably has a composition mainly containing water from the viewpoints of safety, versatility, ease of handling, etc., and the ratio of the maintenance liquid to the total mass of the water in the composition mainly containing water as a solvent. Is preferably in the range of 50 to 92 mass%, more preferably in the range of 75 to 92 mass%.

(Surfactant)
Jet recording maintenance liquid of the present invention, rather preferable to contain at least one surfactant, in the present invention contain an anionic surfactant. A surfactant that solubilizes and / or emulsifies the organic solvent described above in water may be included.
Moreover, since the above-mentioned organic solvent is insoluble or hardly soluble in water, it easily forms two layers with coexisting water, and a composition form in which a surfactant is added to form one layer from the viewpoint of easy handling. More preferred.

  As the surfactant that can be contained in the maintenance liquid of the present invention, particularly, the above-mentioned organic solvent can be solubilized and / or emulsified in water and itself can be dissolved and / or dispersed in water. Although there is no limitation, an anionic surfactant or a nonionic surfactant is preferably used from the viewpoint of not causing an aggregation reaction with the ink.

  Specific examples of the anionic surfactant include sodium methyl taurate oleate, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium lauryl sulfate, sodium alkyldiphenyl ether disulfonate, sodium alkylnaphthalene sulfonate, sodium dialkylsulfosuccinate. , Sodium stearate, potassium oleate, sodium dioctyl sulfosuccinate, sodium polyoxyethylene alkyl ether sulfate, sodium polyoxyethylene alkyl ether sulfate, sodium polyoxyethylene alkyl phenyl ether sulfate, sodium dialkylsulfosuccinate, sodium stearate Sodium oleate, t-octylphenoxyethoxypolyethoxyethyl sulfate Potassium salt and the like, it is possible to select these one.

  Specific examples of the nonionic surfactant include acetylenic diol derivatives such as ethylene oxide adducts of acetylene diol, polyoxyethylene lauryl ether, polyoxyethylene octyl phenyl ether, polyoxyethylene oleyl phenyl ether, polyoxyethylene nonyl phenyl. Examples include ether, oxyethylene / oxypropylene block copolymer, t-octylphenoxyethyl polyethoxyethanol, nonylphenoxyethyl polyethoxyethanol, and the like, and one of these can be selected.

Among the above, the surfactant contains an anionic surfactant, more preferably an alkyl carboxylate or sodium alkyl sulfonate, in this case further, if the carbon number of the alkyl moiety is in the range of 10 to 20 Particularly preferred.

  The content of the surfactant in the maintenance liquid of the present invention is not particularly limited, but is preferably 0.1% by mass or more from the viewpoint of detergency, and more preferably 0.5 to 10% by mass.

  The maintenance liquid of the present invention preferably has a small amount of moisturizing agent in order to avoid curling of the recording medium after recording due to mixing into the ink during maintenance, and the content of the moisturizing agent is the maintenance liquid. It is preferable that it is 1 mass% or less with respect to the total mass of this, and it is especially preferable not to contain a humectant.

  A humectant is a water-soluble compound with low volatility and relatively high water retention ability. Specifically, polyols (eg glycerin, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene) Glycol, dipropylene glycol, polypropylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, pentaerythritol, etc.), lactams (eg 2-pyrrolidone, N-methyl-2- Pyrrolidone, etc.), and water-soluble solid humectants (eg, 1,6-hexanediol, 1,8-octanediol, 2,2-dimethyl-1,3-propanediol, 2,2-diethyl-1, Diols such as 3-propanediol, trimethylolethane, Monosaccharides such as limethylolpropane, glucose, mannose, fructose, ribose, xylose, arabinose, galactose, aldonic acid, glucitol (sorbitol), maltose, cellobiose, lactose, sucrose, trehalose, maltotriose, disaccharides, oligosaccharides And polysaccharides, and derivatives of these sugars such as reducing sugars, oxidized sugars, amino acids and thio sugars).

-Physical property values of maintenance liquid-
The maintenance liquid of the present invention is preferably a liquid that does not cause aggregation when mixed with the aqueous ink composition. If the aggregation occurs, components such as pigments in the ink composition are further fixed to the ink jet head or the like, thereby reducing the effect of the present invention.

The pH of the maintenance liquid of the present invention is not particularly limited, but is preferably in the range of pH 6 to 10 and in the range of pH 7 to 9 in terms of rust prevention in the ink jet recording apparatus and prevention of liquid repellent film deterioration of the head. More preferred.
In order to adjust the pH of the maintenance liquid to the above range, a pH adjuster such as a water-soluble basic substance can be used as necessary.

  Specific examples of the water-soluble basic substance include alcohol amines (for example, diethanolamine, triethanolamine, 2-amino-2-ethyl-1,3-propanediol), alkali metal hydroxide (for example, water Lithium oxide, sodium hydroxide, potassium hydroxide, etc.), ammonium hydroxide (for example, ammonium hydroxide, quaternary ammonium hydroxide), phosphonium hydroxide, alkali metal carbonate and the like.

The viscosity at 25 ° C. of the maintenance liquid of the present invention is preferably 1 mPa · s or more and 1000 mPa · s or less, more preferably 1 mPa · s or more and less than 500 mPa · s, more preferably, from the viewpoint of workability. 2 mPa · s or more and less than 100 mPa · s.
The viscosity is a value measured under conditions of 25 ° C. using VISCOMETER TV-22 (manufactured by TOKI SANGYO CO. LTD).

  The maintenance liquid in the present invention may be colored by including a color material such as a pigment, but the content of the color material such as a pigment is a maintenance point in order to avoid the risk of damaging the hue of the ink (that is, the ink image). It is preferably 1% by mass or less of the total mass of the liquid, and particularly preferably a colorless liquid not containing a pigment.

  The maintenance liquid of the present invention is preferably applied to an inkjet recording apparatus that uses pigment ink as an ink for image recording, and is used for maintenance of an ejection nozzle of an inkjet recording apparatus that includes an ejection nozzle that ejects pigment ink. As described above, since the maintenance liquid of the present invention has excellent cleaning properties, it is suitable for an ink jet recording apparatus using pigment ink, which has been increasingly used in recent years.

  The maintenance liquid for inkjet recording of the present invention is preferably used in combination with an aqueous ink composition containing a pigment. The ink set of the present invention is configured by providing the aqueous ink composition containing a pigment and the above-described maintenance liquid for inkjet recording of the present invention. In the ink set of the present invention, since the ink-jet recording maintenance liquid described above has excellent ink cleaning properties, a recording head for discharging ink and its discharge performance are maintained and maintained during image recording using pigment-based ink. However, it can be maintained and maintained at or close to the desired state.

Here, the water-based ink composition (hereinafter sometimes simply referred to as “ink” or “pigment ink”) will be described.
The water-based ink composition in the present invention is a pigment ink containing a pigment as a coloring material, and generally contains water together with the pigment, is excellent in dischargeability, and from the viewpoint of fixability of an image to be formed, is further a resin compound, It is preferable to contain a pigment dispersant. The pigment ink in the present invention is preferably an ink in which a pigment is dispersed using a pigment dispersant. In addition to the pigment, water, the resin compound, and the pigment dispersant, the pigment ink may be configured using other components such as an organic solvent and a surfactant as necessary.

<Pigment>
The pigment ink in the present invention contains at least one kind of pigment. There is no restriction | limiting in particular as a pigment contained in an ink, According to the objective, it can select suitably. The pigment may be an organic pigment or an inorganic pigment. In addition to the pigment, the ink may contain other coloring material such as a dye for adjusting the hue.

Examples of the organic pigment include azo pigments, polycyclic pigments, dye chelates, nitro pigments, nitroso pigments, and aniline black. Among these, azo pigments and polycyclic pigments are more preferable. Examples of the azo pigments include azo lakes, insoluble azo pigments, condensed azo pigments, and chelate azo pigments. Examples of the polycyclic pigment include phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, indigo pigments, thioindigo pigments, isoindolinone pigments, and quinofullerone pigments. Examples of the dye chelates include basic dye chelates and acidic dye chelates.
Examples of the inorganic pigment include titanium oxide, iron oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, chrome yellow, and carbon black. Among these, carbon black is particularly preferable.

  In addition, as said carbon black, what was manufactured by well-known methods, such as a contact method, a furnace method, and a thermal method, is mentioned, for example. When a pigment is used as the coloring material, it is preferable to use a dispersant together with the pigment from the viewpoint of dispersion stability in the ink, or to use a surface-treated pigment as the pigment.

  The above pigments may be used alone or in combination of a plurality selected from the above-mentioned groups or between the groups.

  In the water-based ink composition of the present invention, the content of the pigment in the total mass of the ink is preferably 0.1% by mass or more and 15% by mass or less in that the effect of improving the detergency is more exhibited. It is more preferably 0.5% by mass or more and 12% by mass or less, and particularly preferably 1% by mass or more and 10% by mass or less. You may use a pigment individually by 1 type or in combination of 2 or more types.

<Resin compound>
The aqueous ink composition in the invention is preferably constituted using at least one resin compound. This effectively improves the abrasion resistance of the formed image. The resin compound is preferably contained as resin compound particles (hereinafter also referred to as “polymer particles”). When the water-based ink composition contains a resin compound, the cleaning effect of the maintenance liquid is liable to be reduced due to the increase in viscosity or solidification of the ink. Therefore, the effect of the present invention can be achieved by using the ink containing the resin compound. .

  Examples of polymer particles include thermoplastic, thermosetting or modified acrylic, epoxy, polyurethane, polyether, polyamide, unsaturated polyester, phenol, silicone, or fluorine resins, chlorides, and the like. Amino resins such as polyvinyl resins such as vinyl, vinyl acetate, polyvinyl alcohol, or polyvinyl butyral, polyester resins such as alkyd resins and phthalic resins, melamine resins, melamine formaldehyde resins, aminoalkyd co-condensation resins, urea resins, urea resins, etc. Examples thereof include particles of a resin having an anionic group such as a system material, a copolymer or a mixture thereof. Among these, anionic acrylic resins include, for example, an acrylic monomer having an anionic group (anionic group-containing acrylic monomer) and, if necessary, other monomers copolymerizable with the anionic group-containing acrylic monomer. Obtained by polymerization in a solvent. Examples of the anionic group-containing acrylic monomer include an acrylic monomer having one or more selected from the group consisting of a carboxyl group, a sulfonic acid group, and a phosphonic group. Among them, an acrylic monomer having a carboxyl group (for example, acrylic acid) Methacrylic acid, crotonic acid, ethacrylic acid, propylacrylic acid, isopropylacrylic acid, itaconic acid, fumaric acid and the like), and acrylic acid or methacrylic acid is particularly preferred.

  The polymer particles are preferably self-dispersing polymer particles, more preferably self-dispersing polymer particles having a carboxyl group, from the viewpoints of ejection stability and liquid stability (particularly dispersion stability) when a pigment is used. Self-dispersing polymer particles are water-insoluble polymers that can be dispersed in an aqueous medium by the functional groups (particularly acidic groups or salts thereof) of the polymer itself in the absence of other surfactants, By means of water-insoluble polymer particles containing no free emulsifier.

  The dispersed state is both an emulsified state (emulsion) in which a water-insoluble polymer is dispersed in a liquid state in an aqueous medium and a dispersed state (suspension) in which a water-insoluble polymer is dispersed in a solid state in an aqueous medium. Is included. The water-insoluble polymer in the present invention is preferably a water-insoluble polymer that can be in a dispersed state in which the water-insoluble polymer is dispersed in a solid state.

  The dispersion state of the self-dispersing polymer particles refers to a solution in which 30 g of a water-insoluble polymer is dissolved in 70 g of an organic solvent (for example, methyl ethyl ketone), a neutralizing agent that can neutralize the salt-forming group of the water-insoluble polymer 100% If the group is anionic, sodium hydroxide, acetic acid if it is cationic) and 200 g of water are mixed and stirred (apparatus: stirring apparatus with stirring blades, rotation speed 200 rpm, 30 minutes, 25 ° C.), and then mixed. It means a state in which even after removing the organic solvent from the liquid, it can be visually confirmed that the dispersed state exists stably at 25 ° C. for at least one week.

  The water-insoluble polymer means a polymer having a dissolution amount of 10 g or less when the polymer is dried at 105 ° C. for 2 hours and then dissolved in 100 g of water at 25 ° C., and the dissolution amount is preferable. Is 5 g or less, more preferably 1 g or less. The dissolution amount is the dissolution amount when neutralized with sodium hydroxide or acetic acid according to the kind of the salt-forming group of the water-insoluble polymer.

  The aqueous medium is configured to contain water, and may contain a hydrophilic organic solvent as necessary. In the present invention, it is preferably composed of water and 0.2% by mass or less of a hydrophilic organic solvent with respect to water, and more preferably composed of water.

  The main chain skeleton of the water-insoluble polymer is not particularly limited. For example, a vinyl polymer or a condensation polymer (epoxy resin, polyester, polyurethane, polyamide, cellulose, polyether, polyurea, polyimide, polycarbonate, etc.) is used. it can. Of these, vinyl polymers are particularly preferred.

Preferable examples of the vinyl polymer and the monomer constituting the vinyl polymer include those described in JP-A Nos. 2001-181549 and 2002-88294. In addition, radical transfer of vinyl monomers using dissociable groups (or substituents that can be induced to dissociable groups), polymerization initiators, and iniferters, or dissociable groups on either initiators or terminators A vinyl polymer in which a dissociable group is introduced at the end of a polymer chain by ionic polymerization using a compound having (or a substituent that can be derived from a dissociable group) can also be used.
Moreover, as a suitable example of the monomer which comprises a condensation type polymer and a condensation type polymer, what is described in Unexamined-Japanese-Patent No. 2001-247787 can be mentioned.

  The self-dispersing polymer particles are derived from a hydrophilic constituent unit and an aromatic group-containing monomer or alicyclic (meth) acrylate from the viewpoint of self-dispersibility and the improvement of the detergency of the low-cleaning ink. It is preferable to include a water-insoluble polymer containing units. An alicyclic (meth) acrylate is a methacrylate or acrylate having an alicyclic hydrocarbon group.

The hydrophilic structural unit is not particularly limited as long as it is derived from a hydrophilic group-containing monomer, and even if it is derived from one kind of hydrophilic group-containing monomer, it contains two or more hydrophilic groups. It may be derived from a monomer. The hydrophilic group is not particularly limited, and may be a dissociable group or a nonionic hydrophilic group.
In the present invention, the hydrophilic group is preferably a dissociable group and more preferably an anionic dissociable group from the viewpoint of promoting self-dispersion and the stability of the formed emulsified or dispersed state. Examples of the dissociable group include a carboxyl group, a phosphoric acid group, and a sulfonic acid group. Among them, a carboxyl group is preferable from the viewpoint of fixability when an ink composition is configured.

The hydrophilic group-containing monomer is preferably a dissociable group-containing monomer from the viewpoint of self-dispersibility and aggregability, and is preferably a dissociable group-containing monomer having a dissociable group and an ethylenically unsaturated bond. .
Examples of the dissociable group-containing monomer include an unsaturated carboxylic acid monomer, an unsaturated sulfonic acid monomer, and an unsaturated phosphoric acid monomer.

Specific examples of the unsaturated carboxylic acid monomer include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, and 2-methacryloyloxymethyl succinic acid. Specific examples of the unsaturated sulfonic acid monomer include styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, 3-sulfopropyl (meth) acrylate, and bis- (3-sulfopropyl) -itaconate. It is done. Specific examples of unsaturated phosphoric acid monomers include vinylphosphonic acid, vinyl phosphate, bis (methacryloxyethyl) phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, dibutyl-2- Examples include acryloyloxyethyl phosphate.
Among the dissociable group-containing monomers, unsaturated carboxylic acid monomers are preferable and acrylic acid and methacrylic acid are more preferable from the viewpoints of dispersion stability and ejection stability.

The self-dispersing polymer particles preferably contain a polymer having a carboxyl group from the viewpoint of self-dispersibility and the aggregation rate when contacting with the treatment liquid, and have a carboxyl group and an acid value of 25 to 100 mgKOH / g. More preferably, it contains a polymer. Furthermore, the acid value is more preferably from 25 to 80 mgKOH / g, particularly preferably from 30 to 65 mgKOH / g, from the viewpoints of self-dispersibility and aggregation rate when contacting with the treatment liquid.
In particular, when the acid value is 25 mgKOH / g or more, the stability of self-dispersibility is improved, and when it is 100 mgKOH / g or less, the cohesiveness is improved.

The aromatic group-containing monomer is not particularly limited as long as it is a compound containing an aromatic group and a polymerizable group. The aromatic group may be a group derived from an aromatic hydrocarbon or a group derived from an aromatic heterocycle. In the present invention, an aromatic group derived from an aromatic hydrocarbon is preferable from the viewpoint of particle shape stability in an aqueous medium.
The polymerizable group may be a condensation polymerizable polymerizable group or an addition polymerizable polymerizable group. In the present invention, from the viewpoint of particle shape stability in an aqueous medium, an addition polymerizable group is preferable, and a group containing an ethylenically unsaturated bond is more preferable.

  The aromatic group-containing monomer is preferably a monomer having an aromatic group derived from an aromatic hydrocarbon and an ethylenically unsaturated bond. The aromatic group-containing monomer may be used alone or in combination of two or more.

Examples of the aromatic group-containing monomer include phenoxyethyl (meth) acrylate, benzyl (meth) acrylate, phenyl (meth) acrylate, and a styrene monomer. Of these, aromatic group-containing (meth) acrylate monomers are preferred from the viewpoint of the balance between the hydrophilicity and hydrophobicity of the polymer chain and the ink fixability, and include phenoxyethyl (meth) acrylate, benzyl (meth) acrylate, and phenyl (meth). At least one selected from acrylates is more preferable, and phenoxyethyl (meth) acrylate and benzyl (meth) acrylate are more preferable.
“(Meth) acrylate” means acrylate or methacrylate.

The alicyclic hydrocarbon group contained in the alicyclic (meth) acrylate is not particularly limited as long as it contains a cyclic non-aromatic hydrocarbon group, a monocyclic hydrocarbon group, a bicyclic carbon group. Examples thereof include a hydrogen group and a tricyclic or higher polycyclic hydrocarbon group. Examples of the alicyclic hydrocarbon group include a cycloalkyl group such as a cyclopentyl group and a cyclohexyl group, a cycloalkenyl group, a bicyclohexyl group, a norbornyl group, an isobornyl group, a dicyclopentanyl group, a dicyclopentenyl group, and an adamantyl group. , Decahydronaphthalenyl group, perhydrofluorenyl group, tricyclo [5.2.1.0 ^2,6 ] decanyl group, and bicyclo [4.3.0] nonane.

Specific examples of the alicyclic (meth) acrylate include [1] monocyclic (meth) acrylate such as cyclopropyl (meth) acrylate, cyclobutyl (meth) acrylate, cyclopentyl (meth) acrylate, and cyclohexyl (meth). Cycloalkyl (meth) acrylates having 3 to 10 carbon atoms in the cycloalkyl group such as acrylate, cycloheptyl (meth) acrylate, cyclooctyl (meth) acrylate, cyclononyl (meth) acrylate, and cyclodecyl (meth) acrylate are [ 2] Examples of the bicyclic (meth) acrylate include isobornyl (meth) acrylate and norbornyl (meth) acrylate, and [3] Examples of the tricyclic (meth) acrylate include adamantyl (meth) acrylate and dicyclohexane. Ntaniru (meth) acrylate, dicyclopentenyl oxyethyl (meth) acrylate.
Among these, from the viewpoint of dispersion stability of the self-dispersing polymer particles, bicyclic (meth) acrylate or tricyclic or higher polycyclic (meth) acrylate is preferable, isobornyl (meth) acrylate, adamantyl (meth) acrylate, and More preferably, it is at least one selected from dicyclopentanyl (meth) acrylate.

The self-dispersing polymer particles include a structural unit derived from an aromatic group-containing (meth) acrylate or alicyclic (meth) acrylate, and the content thereof is preferably 10% by mass to 95% by mass. When the content of the aromatic group-containing (meth) acrylate or alicyclic (meth) acrylate is 10% by mass to 95% by mass, self-emulsification or dispersion stability is improved, and ink viscosity is further increased. Can be suppressed.
In the present invention, the stability of the self-dispersed state, the stabilization of the particle shape in an aqueous medium due to the hydrophobic interaction between aromatic rings or alicyclic rings, and the decrease in the amount of water-soluble components due to the appropriate hydrophobicity of the particles From the viewpoint of the viewpoint and the cleaning effect, it is more preferably 15% by mass to 90% by mass, more preferably 15% by mass to 80% by mass, and particularly preferably 25% by mass to 70% by mass.

  The self-dispersing polymer particles can be constituted using, for example, a structural unit derived from an aromatic group-containing monomer or an alicyclic (meth) acrylate and a structural unit derived from a dissociable group-containing monomer. Furthermore, other structural units may be further included as necessary.

The monomer that forms the other structural unit is not particularly limited as long as it is a monomer copolymerizable with the aromatic group-containing monomer and the dissociable group-containing monomer. Among these, an alkyl group-containing monomer is preferable from the viewpoint of flexibility of the polymer skeleton and ease of control of the glass transition temperature (Tg).
Examples of the alkyl group-containing monomer include methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, alkyl (meth) acrylates such as t-butyl (meth) acrylate, hexyl (meth) acrylate, ethylhexyl (meth) acrylate; hydroxymethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) Ethylenically unsaturated monomers having a hydroxyl group such as acrylate, 4-hydroxybutyl (meth) acrylate, hydroxypentyl (meth) acrylate, hydroxyhexyl (meth) acrylate; Dialkylaminoalkyl (meth) acrylates such as ru (meth) acrylate; N-hydroxyalkyl (meth) such as N-hydroxymethyl (meth) acrylamide, N-hydroxyethyl (meth) acrylamide, N-hydroxybutyl (meth) acrylamide Acrylamide; N-methoxymethyl (meth) acrylamide, N-ethoxymethyl (meth) acrylamide, N- (n-, iso) butoxymethyl (meth) acrylamide, N-methoxyethyl (meth) acrylamide, N-ethoxyethyl (meta And (meth) acrylamides such as N-alkoxyalkyl (meth) acrylamides such as acrylamide and N- (n-, iso) butoxyethyl (meth) acrylamide.

  The molecular weight range of the water-insoluble polymer constituting the self-dispersing polymer particles is preferably 3000 to 200,000, more preferably 5000 to 150,000, and more preferably 10,000 to 100,000 in terms of weight average molecular weight. Further preferred. By setting the weight average molecular weight to 3000 or more, the amount of water-soluble components can be effectively suppressed. Moreover, self-dispersion stability can be improved by making a weight average molecular weight into 200,000 or less.

  The weight average molecular weight was measured by gel permeation chromatography (GPC). GPC uses HLC-8220GPC (manufactured by Tosoh Corporation), and as a column, TSKgel SuperHZM-H, TSKgel SuperHZ4000, TSKgel SuperHZ200 (both trade names made by Tosoh Corporation) are connected in series, THF (tetrahydrofuran) was used as an eluent. The conditions were as follows: the sample concentration was 0.35 / min, the flow rate was 0.35 ml / min, the sample injection amount was 10 μl, the measurement temperature was 40 ° C., and an IR detector was used. In addition, the calibration curve is “standard sample TSK standard, polystyrene” manufactured by Tosoh Corporation: “F-40”, “F-20”, “F-4”, “F-1”, “A-5000”, It produced from eight samples of "A-2500", "A-1000", and "n-propylbenzene".

The water-insoluble polymer constituting the self-dispersing polymer particles is a structural unit derived from an aromatic group-containing (meth) acrylate (preferably a structural unit derived from phenoxyethyl (meth) acrylate) from the viewpoint of controlling hydrophilicity / hydrophobicity of the polymer. And / or a structural unit derived from benzyl (meth) acrylate) or a structural unit derived from alicyclic (meth) acrylate as a copolymerization ratio, it contains 15 to 80% by mass of the total mass of the self-dispersing polymer particles. preferable.
In addition, the water-insoluble polymer has 15 to 80% by mass of a structural unit derived from an aromatic group-containing (meth) acrylate or alicyclic (meth) acrylate as a copolymerization ratio from the viewpoint of controlling the hydrophilicity / hydrophobicity of the polymer, It preferably contains a structural unit derived from a group-containing monomer and a structural unit derived from an alkyl group-containing monomer (preferably a structural unit derived from an alkyl ester of (meth) acrylic acid), and phenoxyethyl (meth) acrylate And / or a structural unit derived from at least one selected from benzyl (meth) acrylate or isobornyl (meth) acrylate, adamantyl (meth) acrylate, and dicyclopentanyl (meth) acrylate. 15 to 80% by mass as a polymerization ratio, carboxyl More preferably, it contains a structural unit derived from the containing monomer and a structural unit derived from the alkyl group-containing monomer (preferably a structural unit derived from an alkyl ester having 1 to 4 carbon atoms of (meth) acrylic acid), In addition, the acid value is preferably 25 to 100 mgKOH / g and the weight average molecular weight is preferably 3000 to 200,000, the acid value is 25 to 95 mgKOH / g and the weight average molecular weight is 5000 to 150,000. More preferably.

  Hereinafter, specific examples (exemplary compounds A-01 to A-19 and B-01 to B-13) of water-insoluble polymers constituting the self-dispersing polymer particles will be given. However, the present invention is not limited to these. In addition, the parenthesis represents the mass ratio of the copolymerization component.

A-01: Phenoxyethyl acrylate / methyl methacrylate / acrylic acid copolymer (50/45/5)
A-02: Phenoxyethyl acrylate / benzyl methacrylate / isobutyl methacrylate / methacrylic acid copolymer (30/35/29/6)
A-03: Phenoxyethyl methacrylate / isobutyl methacrylate / methacrylic acid copolymer (50/44/6)
A-04: Phenoxyethyl acrylate / methyl methacrylate / ethyl acrylate / acrylic acid copolymer (30/55/10/5)
A-05: benzyl methacrylate / isobutyl methacrylate / methacrylic acid copolymer (35/59/6)
A-06: Styrene / phenoxyethyl acrylate / methyl methacrylate / acrylic acid copolymer (10/50/35/5)
A-07: benzyl acrylate / methyl methacrylate / acrylic acid copolymer (55/40/5)
A-08: Phenoxyethyl methacrylate / benzyl acrylate / methacrylic acid copolymer (45/47/8)
A-09: Styrene / phenoxyethyl acrylate / butyl methacrylate / acrylic acid copolymer (5/48/40/7)
A-10: benzyl methacrylate / isobutyl methacrylate / cyclohexyl methacrylate / methacrylic acid copolymer (35/30/30/5)
A-11: Phenoxyethyl acrylate / methyl methacrylate / butyl acrylate / methacrylic acid copolymer (12/50/30/8)
A-12: benzyl acrylate / isobutyl methacrylate / acrylic acid copolymer (93/2/5)
A-13: Styrene / phenoxyethyl methacrylate / butyl acrylate / acrylic acid copolymer (50/5/20/25)
A-14: Styrene / butyl acrylate / acrylic acid copolymer (62/35/3)
A-15: Methyl methacrylate / phenoxyethyl acrylate / acrylic acid copolymer (45/51/4)
A-16: Methyl methacrylate / phenoxyethyl acrylate / acrylic acid copolymer (45/49/6)
A-17: Methyl methacrylate / phenoxyethyl acrylate / acrylic acid copolymer (45/48/7)
A-18: Methyl methacrylate / phenoxyethyl acrylate / acrylic acid copolymer (45/47/8)
A-19: Methyl methacrylate / phenoxyethyl acrylate / acrylic acid copolymer (45/45/10)

B-01: Methyl methacrylate / isobornyl methacrylate / methacrylic acid copolymer (20/72/8)
B-02: Methyl methacrylate / isobornyl methacrylate / benzyl methacrylate / methacrylic acid copolymer (30/50/14/6)
B-03: Methyl methacrylate / dicyclopentanyl methacrylate / methacrylic acid copolymer (40/50/10)
B-04: Methyl methacrylate / dicyclopentanyl methacrylate / phenoxyethyl methacrylate / methacrylic acid copolymer (30/50/14/6)
B-05: Methyl methacrylate / isobornyl methacrylate / methoxypolyethylene glycol methacrylate (n = 2) / methacrylic acid copolymer (30/54/10/6)
B-06: Methyl methacrylate / dicyclopentanyl methacrylate / methoxy polyethylene glycol methacrylate (n = 2) / methacrylic acid copolymer (54/35/5/6)
B-07: Methyl methacrylate / adamantyl methacrylate / methoxy polyethylene glycol methacrylate (n = 23) / methacrylic acid copolymer (30/50/15/5)
B-08: Methyl methacrylate / isobornyl methacrylate / dicyclopentanyl methacrylate / methacrylic acid copolymer (20/50/22/8)
B-09: Ethyl methacrylate / cyclohexyl methacrylate / acrylic acid copolymer (50/45/5)
B-10: Isobutyl methacrylate / cyclohexyl methacrylate / acrylic acid copolymer (40/50/10)
B-11: n-butyl methacrylate / cyclohexyl methacrylate / styrene / acrylic acid copolymer (30/55/10/5)
B-12: Methyl methacrylate / dicyclopentenyloxyethyl methacrylate / methacrylic acid copolymer (40/52/8)
B-13: Lauryl methacrylate / dicyclopentenyloxyethyl methacrylate / methacrylic acid copolymer (25/65/10)

  The method for producing the water-insoluble polymer constituting the self-dispersing polymer particles in the present invention is not particularly limited. For example, emulsion polymerization is carried out in the presence of a polymerizable surfactant to obtain a surfactant and a water-insoluble polymer. Examples include a method of covalent bonding, and a method of copolymerizing a monomer mixture containing the hydrophilic group-containing monomer and the aromatic group-containing monomer by a known polymerization method such as a solution polymerization method or a bulk polymerization method. Among the polymerization methods, a solution polymerization method is preferable and a solution polymerization method using an organic solvent is more preferable from the viewpoint of aggregation rate and droplet ejection stability when an ink composition is used.

  The self-dispersing polymer particles include a polymer synthesized in an organic solvent from the viewpoint of the aggregation rate, and the polymer has a carboxyl group (preferably having an acid value of 20 to 100 mgKOH / g). It is preferable that some or all of the carboxyl groups are neutralized and prepared as a polymer dispersion having water as a continuous phase. That is, the production of the self-dispersing polymer particles in the present invention includes a step of synthesizing a polymer in an organic solvent and a dispersion step of making an aqueous dispersion in which at least a part of the carboxyl groups of the polymer is neutralized. It is preferable to do so.

The dispersion step preferably includes the following step (1) and step (2).
Step (1): Step of stirring a mixture containing a polymer (water-insoluble polymer), an organic solvent, a neutralizing agent, and an aqueous medium Step (2): Step of removing the organic solvent from the mixture

The step (1) is preferably a treatment in which a polymer (water-insoluble polymer) is first dissolved in an organic solvent, then a neutralizing agent and an aqueous medium are gradually added, mixed and stirred to obtain a dispersion. In this way, by adding a neutralizing agent and an aqueous medium to a water-insoluble polymer solution dissolved in an organic solvent, a self-dispersing polymer having a particle size with higher storage stability without requiring strong shearing force. Particles can be obtained.
There is no restriction | limiting in particular in the stirring method of this mixture, Dispersing machines, such as a generally used mixing stirring apparatus and an ultrasonic disperser, a high-pressure homogenizer, can be used as needed.

Preferred examples of the organic solvent include alcohol solvents, ketone solvents, and ether solvents.
Examples of the alcohol solvent include isopropyl alcohol, n-butanol, t-butanol, ethanol and the like. Examples of the ketone solvent include acetone, methyl ethyl ketone, diethyl ketone, and methyl isobutyl ketone. Examples of ether solvents include dibutyl ether and dioxane. Among these solvents, ketone solvents such as methyl ethyl ketone and alcohol solvents such as isopropyl alcohol are preferable. It is also preferable to use isopropyl alcohol and methyl ethyl ketone in combination for the purpose of moderating the polarity change during the phase inversion from oil to water. By using this solvent in combination, it is possible to obtain self-dispersing polymer particles having a fine particle size with high dispersion stability without aggregation and sedimentation and fusion between particles.

  The neutralizing agent is used so that a part or all of the dissociable group is neutralized and the self-dispersing polymer forms a stable emulsified or dispersed state in water. When the self-dispersing polymer has an anionic dissociative group (for example, a carboxyl group) as a dissociable group, examples of the neutralizing agent used include basic compounds such as organic amine compounds, ammonia, and alkali metal hydroxides. It is done. Examples of organic amine compounds include monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine, monopropylamine, dipropylamine, monoethanolamine, diethanolamine, triethanolamine, N, N-dimethyl-ethanolamine, N, N-diethyl-ethanolamine, 2-dimethylamino-2-methyl-1-propanol, 2-amino-2-methyl-1-propanol, N-methyldiethanolamine, N-ethyldiethanolanine, monoisopropanolamine, di Examples include isopropanolamine and triisopropanolamine. Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Among these, sodium hydroxide, potassium hydroxide, triethylamine, and triethanolamine are preferable from the viewpoint of stabilizing the dispersion of the self-dispersing polymer particles in water.

  These basic compounds are preferably used in an amount of 5 to 120 mol%, more preferably 10 to 110 mol%, still more preferably 15 to 100 mol%, based on 100 mol% of the dissociable group. . By making it 5 mol% or more, further 10 mol% or more, and especially 15 mol% or more, the effect of stabilizing the dispersion of particles in water is exhibited, 120 mol% or less, further 110 mol% or less, especially By setting it to 100 mol% or less, there is an effect of reducing the water-soluble component.

  In the step (2), the aqueous dispersion of the self-dispersing polymer particles is obtained by distilling off the organic solvent from the dispersion obtained in the step (1) by a conventional method such as distillation under reduced pressure and phase-inversion into an aqueous system. A dispersion can be obtained. The organic solvent in the obtained aqueous dispersion has been substantially removed, and the amount of the organic solvent is preferably 0.2% by mass or less, more preferably 0.1% by mass or less.

The average particle size of the polymer particles (particularly self-dispersing polymer particles) is preferably in the range of 10 to 400 nm, more preferably in the range of 10 to 200 nm, still more preferably in the range of 10 to 100 nm, and particularly preferably in terms of volume average particle size. It is the range of 10-50 nm. Manufacturability is improved by having an average particle diameter of 10 nm or more. Moreover, storage stability improves by setting it as an average particle diameter of 400 nm or less. Moreover, there is no restriction | limiting in particular regarding the particle size distribution of a polymer particle, Any of what has a wide particle size distribution or a monodispersed particle size distribution may be sufficient. Further, two or more water-insoluble particles may be mixed and used.
The average particle size and particle size distribution of the polymer particles are determined by measuring the volume average particle size by a dynamic light scattering method using a nanotrack particle size distribution measuring device UPA-EX150 (manufactured by Nikkiso Co., Ltd.). It is

  The content of the polymer particles (particularly self-dispersing polymer particles) in the ink composition is preferably 1 to 30% by mass with respect to the ink composition from the viewpoint of the glossiness of the image. More preferably, it is 15 mass%. The polymer particles (particularly self-dispersing polymer particles) can be used singly or in combination of two or more.

<Pigment dispersant>
The water-based ink composition in the invention preferably has a configuration in which a pigment is dispersed by a pigment dispersant by using at least one pigment dispersant. Thereby, the pigment particles can be present in a fine particle size, and high dispersion stability can be obtained after dispersion. In the present invention, if the water-based ink composition contains a resin dispersant, the cleaning effect by the maintenance liquid tends to be reduced due to increase in viscosity or solidification of the ink. The effect of.

The pigment does not necessarily need to be coated on the entire particle surface, and may be in a state where at least a part of the particle surface is coated.
The pigment resin dispersant (hereinafter also simply referred to as a dispersant) may be either a polymer dispersant or a low molecular surfactant type dispersant. The polymer dispersant may be either a water-soluble dispersant or a water-insoluble dispersant.

  The low molecular surfactant type dispersant can stably disperse the pigment in the aqueous solvent while keeping the ink at a low viscosity. The low molecular surfactant type dispersant is a low molecular dispersant having a molecular weight of 2,000 or less. The molecular weight of the low molecular surfactant type dispersant is preferably 100 to 2,000, and more preferably 200 to 2,000.

  The low molecular surfactant type dispersant has a structure including a hydrophilic group and a hydrophobic group. Moreover, the hydrophilic group and the hydrophobic group should just be independently contained 1 or more in 1 molecule, respectively, and may have multiple types of hydrophilic group and hydrophobic group. In addition, a linking group for linking a hydrophilic group and a hydrophobic group can be appropriately included.

The hydrophilic group is anionic, cationic, nonionic, or a betaine type that combines these.
The anionic group may be any one as long as it has a negative charge, and may be a phosphoric acid group, a phosphonic acid group, a phosphinic acid group, a sulfuric acid group, a sulfonic acid group, a sulfinic acid group, or a carboxylic acid group. Preferably, it is a phosphoric acid group or a carboxylic acid group, and more preferably a carboxylic acid group. The cationic group may be any as long as it has a positive charge, but is preferably an organic cationic substituent, and more preferably a nitrogen or phosphorus cationic group. Further, it is more preferably a pyridinium cation or an ammonium cation. Examples of the nonionic group include polyethylene oxide, polyglycerin, and a part of a sugar unit.
The hydrophilic group is preferably an anionic group.

  When the low molecular surfactant type dispersant has an anionic hydrophilic group, the pKa is preferably 3 or more from the viewpoint of promoting the aggregation reaction by contacting with an acidic treatment liquid. The pKa of the low molecular surfactant type dispersant is titrated with a solution of 1 mmol / L of the low molecular surfactant type dispersant in a tetrahydrofuran-water (3: 2 = V / V) solution with an acid or alkaline aqueous solution. The value obtained experimentally from the titration curve. When the pKa of the low-molecular surfactant type dispersant is 3 or more, 50% or more of the anionic groups are in a non-dissociated state when in contact with a liquid having a theoretical pH of about 3. Therefore, the water solubility of the low-molecular surfactant type dispersant is remarkably lowered, and an agglomeration reaction occurs. That is, the aggregation reactivity is improved. From this viewpoint, the low molecular surfactant type dispersant preferably has a carboxylic acid group as an anionic group.

The hydrophobic group has a hydrocarbon-based, fluorocarbon-based, silicone-based or the like structure, and is particularly preferably a hydrocarbon-based group. Further, the hydrophobic group may have a linear structure or a branched structure. Further, the hydrophobic group may have a single chain structure or a chain structure of more than this, and in the case of a structure of two or more chains, it may have a plurality of types of hydrophobic groups.
The hydrophobic group is preferably a hydrocarbon group having 2 to 24 carbon atoms, more preferably a hydrocarbon group having 4 to 24 carbon atoms, and further preferably a hydrocarbon group having 6 to 20 carbon atoms.

  Among the polymer dispersants, examples of the water-soluble dispersant include hydrophilic polymer compounds. For example, natural hydrophilic polymer compounds include plant polymers such as gum arabic, tragan gum, guar gum, karaya gum, locust bean gum, arabinogalactone, pectin, quince seed starch, seaweeds such as alginic acid, carrageenan and agar. Examples include molecules, animal polymers such as gelatin, casein, albumin and collagen, and microorganism polymers such as xanthene gum and dextran.

  In addition, in hydrophilic polymer compounds modified from natural products, fiber polymers such as methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, carboxymethylcellulose, starch such as sodium starch glycolate and sodium starch phosphate And seaweed polymers such as sodium alginate, propylene glycol alginate, and the like.

  Further, synthetic hydrophilic polymer compounds include vinyl polymers such as polyvinyl alcohol, polyvinyl pyrrolidone, and polyvinyl methyl ether, non-crosslinked polyacrylamide, polyacrylic acid or alkali metal salts thereof, water-soluble styrene acrylic resins, and the like. Acrylic resin, water-soluble styrene maleic acid resin, water-soluble vinyl naphthalene acrylic resin, water-soluble vinyl naphthalene maleic resin, polyvinyl pyrrolidone, polyvinyl alcohol, alkali metal salts of β-naphthalene sulfonic acid formalin condensate, quaternary ammonium and amino And a polymer compound having a salt of a cationic functional group such as a group in the side chain, a natural polymer compound such as shellac, and the like.

  Among these, water-soluble dispersants introduced with carboxyl groups are hydrophilic polymers such as homopolymers of acrylic acid, methacrylic acid, styrene acrylic acid, and copolymers with monomers having other hydrophilic groups. Preferred as a compound.

  Among the polymer dispersants, as the water-insoluble dispersant, a polymer having both a hydrophobic portion and a hydrophilic portion can be used. For example, styrene- (meth) acrylic acid copolymer, styrene- (meth) acrylic acid- (meth) acrylic acid ester copolymer, (meth) acrylic acid ester- (meth) acrylic acid copolymer, polyethylene glycol ( Examples thereof include (meth) acrylate- (meth) acrylic acid copolymers, vinyl acetate-maleic acid copolymers, and styrene-maleic acid copolymers.

  The weight average molecular weight of the polymer dispersant is preferably 3,000 to 100,000, more preferably 5,000 to 50,000, still more preferably 5,000 to 40,000, and particularly preferably 10,000. 000 to 40,000.

  The acid value of the polymer dispersant is preferably 100 or less mgKOH / g or less from the viewpoint of good aggregation when the treatment liquid comes into contact. Furthermore, the acid value is more preferably from 25 to 100 mgKOH / g, further preferably from 25 to 80, and particularly preferably from 30 to 65. When the acid value of the polymer dispersant is 25 or more, the stability of self-dispersibility is improved.

  The polymer dispersant preferably contains a polymer having a carboxyl group from the viewpoint of self-dispersibility and aggregation rate when the treatment liquid comes into contact. The polymer dispersant has a carboxyl group and an acid value of 25 to 80 mgKOH / g. More preferably.

  The mixing mass ratio (p: s) between the pigment (p) and the dispersant (s) is preferably in the range of 1: 0.06 to 1: 3, more preferably in the range of 1: 0.125 to 1: 2. Preferably, it is 1: 0.125 to 1: 1.5.

  In the present invention, from the viewpoint of image light resistance and quality, it is preferable to contain a pigment and a dispersant, more preferably an organic pigment and a polymer dispersant, and a polymer dispersant containing an organic pigment and a carboxyl group. It is particularly preferred that Moreover, it is preferable that a pigment is coat | covered with the polymer dispersing agent which has a carboxyl group from a cohesive viewpoint, and is water-insoluble.

The average particle size of the pigment is preferably 10 to 200 nm, more preferably 10 to 150 nm, and even more preferably 10 to 100 nm. When the average particle size is 200 nm or less, the color reproducibility is good, the droplet ejection characteristics when droplets are ejected by the ink jet method are good, and when it is 10 nm or more, the light resistance is good. Further, the particle size distribution of the color material is not particularly limited, and may be either a wide particle size distribution or a monodisperse particle size distribution. Two or more color materials having a monodisperse particle size distribution may be mixed and used.
The average particle size and particle size distribution of the polymer particles are determined by measuring the volume average particle size by a dynamic light scattering method using a nanotrack particle size distribution measuring device UPA-EX150 (manufactured by Nikkiso Co., Ltd.). It is

-Ratio of pigment and pigment dispersant-
The ratio of the pigment to the pigment dispersant is preferably 100: 25 to 100: 140, more preferably 100: 25 to 100: 50, by mass ratio. When the ratio of the pigment dispersant is 100: 25 or more, the dispersion stability and the abrasion resistance tend to be improved, and when it is 100: 140 or less, the dispersion stability tends to be improved.

<Water>
The water-based ink composition in the invention can be constituted using water. Although there is no restriction | limiting in particular in the quantity of water, Preferably it is 10 to 99 mass% from the point of ensuring stability and discharge reliability.

<Other ingredients>
The water-based ink composition in the invention may contain other components as necessary in addition to the above components. Other components include, for example, surfactants, ultraviolet absorbers, antifading agents, antifungal agents, pH adjusters, rust inhibitors, antioxidants, emulsion stabilizers, antiseptics, antifoaming agents, viscosity modifiers. And known additives such as dispersion stabilizers and chelating agents.

  The maintenance liquid and ink set for ink jet recording of the present invention are used for ink jet recording. Specifically, energy is given to ink for ink jet recording, and a known image receiving material (for example, plain paper, resin) is used. (Coated paper, inkjet paper, film, electrophotographic co-paper, fabric, glass, metal, ceramics, etc.).

  The ink jet method is not particularly limited, and is a known method, for example, a charge control method for ejecting ink using electrostatic attraction, a drop-on-demand method (pressure pulse method) using vibration pressure of a piezo element. ), An acoustic ink jet system that converts electrical signals into acoustic beams, irradiates the ink and ejects ink using radiation pressure, and thermal ink jet (bubble jet) that uses the pressure generated by heating the ink to form bubbles (Registered trademark)) method or the like. As an inkjet head, either an on-demand method or a continuous method may be used, and an ejection method may be an electro-mechanical conversion method (for example, a single cavity type, a double cavity type, a vendor type, a piston type, a shear mode type, Shared wall type, etc.), electrical-thermal conversion system (for example, thermal ink jet type, bubble jet (registered trademark) type, etc.), electrostatic attraction system (for example, electric field control type, slit jet type, etc.), and discharge system (for example, , Spark jet type, etc.).

In the present invention, there is no particular limitation on the nozzle or the like that ejects ink when recording is performed by the ink jet method, and can be appropriately selected according to the purpose.
As an inkjet head, a single serial head is used, and a shuttle system that performs recording while scanning the head in the width direction of the recording medium, and a line in which recording elements are arranged corresponding to the entire area of one side of the recording medium. There is a line system using a head. In the line system, an image can be recorded on the entire surface of the recording medium by scanning the recording medium in a direction orthogonal to the arrangement direction of the recording elements, and a carriage system such as a carriage for scanning a short head is not necessary. Further, since complicated scanning control of the carriage movement and the recording medium is not required, and only the recording medium is moved, the recording speed can be increased as compared with the shuttle system. The present invention is applicable to any of these forms.

  The maintenance method of the present invention is to wash at least a part of an inkjet recording head that performs recording by discharging an aqueous ink composition containing at least a pigment, using the above-described maintenance liquid for inkjet recording of the present invention. is there. The above-described maintenance liquid for inkjet recording is easy to dissolve or re-disperse even in a thickened / solidified state after recording, etc., and has high ink cleaning and removal properties, so a recording head for ejecting ink and its ejection performance are maintained. It can be maintained and maintained at or close to its intended state. This is particularly effective in the case of recording an image using an aqueous ink composition containing water, a pigment dispersed with a pigment dispersant, and a resin compound.

The maintenance using the maintenance liquid of the present invention is a method in which the maintenance liquid is applied to a desired portion and the attached ink can be removed by adhering from the viewpoint of preventing ink contamination and clogging. Any method may be selected. For example, it can be performed by a method of wiping the nozzle surface after applying the maintenance liquid to the nozzle surface of the recording head of the ink jet recording apparatus.
At this time, the maintenance liquid can be applied by, for example, roller coating, spraying, or the like. In addition, in the removal process for removing the fixed ink (ink-fixed matter), after applying the maintenance liquid, the nozzle surface is rubbed (wiping) with a wiper blade, the ink fixed matter is scraped off, wind pressure, maintenance liquid, etc. A method of removing by hydraulic pressure or the like and a method of wiping with a cloth or paper are preferable. Among them, scraping with a blade and wiping with a cloth or paper are preferable. The amount, temperature, and the like of the maintenance liquid at the time of application can be appropriately selected depending on the liquid composition, ink type, adhesion amount, and the like.

  In the ink jet recording method, ink is ejected from a nozzle having a small diameter of about 20 to 50 μm, and therefore, near the tip of the nozzle, the ink is thickened due to volatilization of a low-boiling solvent or water, separation of a coloring material, aggregation, and the like. Is likely to occur, and may cause problems such as printing disturbance and nozzle clogging. These problems are likely to occur when the apparatus is stopped for a long period of time, and the maintenance liquid of the present invention is excellent in ink cleaning properties, and can solve problems such as printing disturbance and nozzle clogging.

  The maintenance liquid of the present invention is used as a method for solving problems such as thickening and solidification due to drying of the ink. It can be preferably used.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist thereof. Unless otherwise specified, “part” is based on mass.

(Examples 1-3 , 6-7 , 11-14 , Reference Examples 4-5, 8-10 Comparative Examples 1-6)
(1) Preparation of maintenance liquid The maintenance liquid of this invention and the maintenance liquid for a comparison were prepared with the composition shown to the following Table 1-2. Each maintenance liquid was prepared by mixing each component and stirring sufficiently.

(2) Preparation of water-based ink composition <Preparation of self-dispersing polymer B-01>
In a 2 liter three-necked flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas introduction tube, 540.0 g of methyl ethyl ketone was charged and heated to 75 ° C. While maintaining the temperature in the reaction vessel at 75 ° C., 108 g of methyl methacrylate, 388.8 g of isobornyl methacrylate, 43.2 g of methacrylic acid, 108 g of methyl ethyl ketone, and “V-601” (manufactured by Wako Pure Chemical Industries, Ltd.) ) A mixed solution consisting of 2.16 g was added dropwise at a constant speed so that the addition was completed in 2 hours. After completion of the dropwise addition, a solution consisting of 1.08 g of “V-601” and 15.0 g of methyl ethyl ketone was added, stirred for 2 hours at 75 ° C., and then a solution consisting of 0.54 g of “V-601” and 15.0 g of methyl ethyl ketone was added. After further stirring at 75 ° C. for 2 hours, the temperature was raised to 85 ° C., and stirring was further continued for 2 hours. In this way, a copolymer polymerization solution was obtained.

  The weight average molecular weight (Mw) of the obtained copolymer was 61000 [calculated in terms of polystyrene by gel permeation chromatography (GPC), and the columns used were TSKgel SuperHZM-H, TSKgel SuperHZ4000, TSKgel SuperHZ200 (manufactured by Tosoh Corporation). Used; the same applies hereinafter), and the acid value was 52.1 mgKOH / g.

  Next, 588.2 g of the polymerization solution was weighed, 165 g of isopropanol and 120.8 ml of 1 mol / L sodium hydroxide aqueous solution were added, and the temperature in the reaction vessel was raised to 80 ° C. Subsequently, 718 g of distilled water was added dropwise thereto at a rate of 20 ml / min to disperse in water. Thereafter, the temperature in the reaction vessel was maintained at 80 ° C. for 2 hours, 85 ° C. for 2 hours, and 90 ° C. for 2 hours under atmospheric pressure, and the solvent was distilled off. Further, the inside of the reaction vessel was decompressed to distill off isopropanol, methyl ethyl ketone, and distilled water, and self-dispersing polymer particles [B-01; methyl methacrylate / isobornyl methacrylate / methacrylic acid having a solid content concentration of 26.0%. An aqueous dispersion of a copolymer (= 20/72/8 [mass ratio])] was obtained.

<Preparation of Cyan Pigment Dispersion C1>
-Synthesis of water-insoluble polymer dispersant-
In a reaction vessel, 6 parts of styrene, 11 parts of stearyl methacrylate, 4 parts of styrene macromer AS-6 (manufactured by Toa Gosei Co., Ltd.), 5 parts of Plenmer PP-500 (manufactured by NOF Corporation), 5 parts of methacrylic acid, 2-mercaptoethanol 0 A mixed solution of 0.05 part and 24 parts of methyl ethyl ketone was prepared.

  On the other hand, 14 parts of styrene, 24 parts of stearyl methacrylate, 9 parts of styrene macromer AS-6 (manufactured by Toa Gosei Co., Ltd.), 9 parts of Plenmer PP-500 (manufactured by NOF Corporation), 10 parts of methacrylic acid, 0.13 of 2-mercaptoethanol Part mixture, 56 parts of methyl ethyl ketone, and 1.2 parts of 2,2′-azobis (2,4-dimethylvaleronitrile) were prepared and placed in a dropping funnel.

  Next, under a nitrogen atmosphere, the mixed solution in the reaction vessel was heated to 75 ° C. while stirring, and the mixed solution in the dropping funnel was gradually dropped over 1 hour. After 2 hours from the end of dropping, a solution prepared by dissolving 1.2 parts of 2,2′-azobis (2,4-dimethylvaleronitrile) in 12 parts of methyl ethyl ketone was added dropwise over 3 hours, and further at 75 ° C. for 2 hours, The solution was aged at 80 ° C. for 2 hours to obtain a methyl ethyl ketone solution of a water-insoluble polymer dispersant.

  For a part of the solution of the obtained water-insoluble polymer dispersant, the solid content obtained by isolation by removing the solvent was diluted to 0.1% by mass with tetrahydrofuran, and the weight average molecular weight was determined with GPC. It was measured. As a result, the isolated solid had a polystyrene equivalent weight average molecular weight of 25,000.

-Preparation of cyan pigment dispersion-
Methyl ethyl ketone solution of the obtained water-insoluble polymer dispersant in terms of solid content is 5.0 g, Pigment Blue 15: 3 (cyan pigment, manufactured by Dainichi Seika Co., Ltd.) 10.0 g, methyl ethyl ketone 40.0 g, 1 mol / L water 8.0 g of sodium oxide and 82.0 g of ion-exchanged water were supplied to the vessel together with 300 g of 0.1 mm zirconia beads, and dispersed at 1000 rpm for 6 hours with a ready mill disperser (manufactured by Imex). The obtained dispersion was concentrated under reduced pressure using an evaporator until methyl ethyl ketone was sufficiently distilled off. The pigment concentration was adjusted to 10% by mass, and a cyan pigment dispersion C1 was obtained as a dispersion of colored particles made of a pigment whose surface was coated with a water-insoluble polymer dispersant. The average particle diameter of the obtained cyan pigment dispersion C1 was 77 nm.

<Preparation of cyan ink C-01>
The cyan pigment dispersion C1, the aqueous dispersion of the self-dispersing polymer particles B-01, and water, Sanix GP250 (manufactured by Sanyo Chemical Industries), and diethylene glycol monoethyl ether ( Cyan ink was prepared using Wako Pure Chemical Industries, Ltd.) and a surfactant so as to have the following ink composition. After the preparation, coarse particles were removed with a 5 μm membrane filter to prepare cyan ink C-01 as an aqueous ink composition.
<Ink composition of cyan ink C-01>
・ Cyan pigment (Pigment Blue 15: 3, manufactured by Dainichi Seika Co., Ltd.): 4% by mass
・ The water-insoluble polymer dispersant: 2% by mass
-Aqueous dispersion of the self-dispersing polymer particles B-01 (in terms of solid content): 8% by mass
・ Sanix GP250 ... 10% by mass
・ Diethylene glycol monoethyl ether: 5% by mass
・ Orphine E1010 (manufactured by Nissin Chemical Industry Co., Ltd.) ... 1% by mass
・ Ion-exchanged water (added so that the total is 100% by mass)

(3) Evaluation-1. Redispersibility-
Prepare a dried product of Cyan Ink C-01, add 100 times the amount of cleaning liquid (maintenance liquid prepared above) to the dried product, stir, and determine the remaining amount of dried product after 1 minute and the color of the cleaning solution. The way of attaching was examined and evaluated according to the following evaluation criteria. The evaluation results are shown in Tables 1 and 2 below.
<Evaluation criteria>
A: The dried ink was almost redispersed and hardly remained.
○: About half of the dried ink was redispersed.
Δ: The cleaning solution was lightly colored.
X: The washing liquid was not colored at all.

-2. Maintainability
The cyan ink C-01 is applied to an ink jet recording apparatus [Dimatics Material Printer DMP-2831 manufactured by FUJIFILM Daimatics Co., Ltd. (the cartridge is modified so that liquid for 10 pl discharge (DMC-11610) can be supplied from the outside)]. In addition, each of the maintenance liquids is sequentially loaded, and after the cyan ink C-01 is discharged under the conditions (1) to (3) below, the maintenance liquid is applied to the nozzle surface of the head with a roller, and then a cloth wipe (Toraysee, The nozzle surface of the inkjet head was wiped with Toray Industries, Inc. Pass / fail was judged from the subsequent re-ejectability evaluation, and the maintainability was evaluated according to the following evaluation criteria. The evaluation results are shown in Tables 1 and 2 below.
-Evaluation conditions for re-ejectability-
(1) Immediately after the end of continuous discharge for 45 minutes, the cloth is wiped once, and when the ink discharge rate of all nozzles thereafter is 90% or more, it passes.
(2) Pause for 30 minutes after ejection for 1 minute, perform cloth wipe once after pause, and pass if the ink ejection rate of all nozzles after that is 90% or more.
(3) Immediately after the end of discharge for 15 minutes, the cloth is wiped once, and if the image recorded thereafter is not uneven, it passes.
~ Measurement method of ink discharge rate ~
After confirming that ink was discharged from all nozzles at the start of the experiment, the number of discharge nozzles after the end of the experiment including maintenance was counted, and the discharge rate was calculated from the following formula.
Discharge rate (%) = [number of discharge nozzles after maintenance] / [total number of nozzles] × 100
<Evaluation criteria>
◎: When all three items are acceptable ○: When two items are acceptable △: When only one item is acceptable ×: When all three items are unacceptable

  As shown in Tables 1 and 2, in the examples, excellent redispersibility and maintainability were exhibited. On the other hand, Comparative Examples 1, 2, and 6 in which the content of the organic solvent in the maintenance liquid is less than 8% by mass, and Comparative Examples 3 and 3 that do not include a water-insoluble organic solvent (an organic solvent that is insoluble or hardly soluble in water). No. 5 was inferior in redispersibility and maintainability, and as a result, the discharge stability was deteriorated.

  As described above, by using the maintenance liquid having the configuration of the present invention, the colorant concentration is high, and the ink contains a pigment, in particular, the ink having an increased amount of resin fine particles and the low SP value solvent as the ink solvent. Even when it is applied to an ink jet recording apparatus using this, it exhibits excellent cleaning properties and does not attack members. Further, the maintenance liquid of the present invention can be used for an existing ink jet recording apparatus.

Claims (9)

A maintenance liquid for inkjet recording comprising at least water, 8% by mass or more (mono or di) propylene alkyl ether which is insoluble or hardly soluble in water and an anionic surfactant with respect to the total mass. The maintenance liquid for inkjet recording according to claim 1, wherein the anionic surfactant is sodium alkylcarboxylate or sodium alkylsulfonate. The maintenance liquid for ink jet recording according to claim 2, wherein the sodium alkylcarboxylate and the sodium alkylsulfonate have an alkyl moiety having 10 to 20 carbon atoms. The maintenance liquid for inkjet recording according to any one of claims 1 to 3 , wherein the maintenance liquid is used for cleaning the ejection nozzle of an inkjet recording apparatus provided with an ejection nozzle for ejecting pigment ink. An aqueous ink composition comprising a pigment;
An ink set comprising the maintenance liquid for inkjet recording according to any one of claims 1 to 4 . The ink set according to claim 5 , wherein the water-based ink composition further contains a resin compound. The ink set according to claim 5 or 6 , wherein the pigment is dispersed by a pigment dispersant. At least a part of an inkjet recording head that performs recording by discharging an aqueous ink composition containing at least a pigment is washed using the maintenance liquid for inkjet recording according to any one of claims 1 to 4. Maintenance method. The maintenance method according to claim 8 , wherein the water-based ink composition contains water and the pigment and a resin compound dispersed with a pigment dispersant.