JP2023159466A - Ink set and maintenance method - Google Patents

Abstract

To provide an ink set and a maintenance method, which enable, during a maintenance operation of an ink-jet head, suppression of residue deposits on a discharge surface and suppression of abrasion of the discharge surface.SOLUTION: There is provided an ink set and a maintenance method, wherein the ink contains a pigment and the maintenance solution contains polymer particles. The contained amount of the polymer particles is 3 mass% to 25 mass% with respect to the total amount of the maintenance solution. The average particle size of the polymer particles is at least 3.5 times that of the average particle size of the pigment.SELECTED DRAWING: None

Description

The present disclosure relates to an ink set and a maintenance method.

An image recording method using an inkjet recording method is a method of recording an image by ejecting ink droplets onto a substrate from a large number of nozzles provided in an inkjet head. Image recording methods using inkjet recording methods are widely used because high-quality images can be recorded on a wide variety of substrates.

In an inkjet recording system in which ink is ejected from fine nozzles, if ink, dust, etc. adhere to the vicinity of the nozzles, the stability of ink ejection may be impaired. Further, as the ink adhering to the vicinity of the nozzle thickens or solidifies over time, the ejection opening of the nozzle may be blocked, causing ink ejection failure.

Therefore, in order to remove the deposits adhering to the vicinity of the nozzles, a method is known in which the ejection surface of the inkjet head is wiped with a wipe member to clean it before, during, or after image recording.

As a cleaning liquid (also referred to as a cleaning liquid or a maintenance liquid) used for cleaning, for example, Patent Document 1 describes a recording method for ejecting an aqueous ink containing a pigment dispersed by the action of an anionic group or a nonionic group. A cleaning liquid supplied to the ejection port surface of the head, the cleaning liquid containing a resin having an anionic unit or a nonionic unit, the content of the resin being based on the total mass of the cleaning liquid, 5. A cleaning liquid characterized in that the content of the cleaning liquid is 00% by mass or more and 30.00% by mass or less is described.

Japanese Patent Application Publication No. 2017-155119

By wiping the ejection surface of the inkjet head with a wipe member, it is possible to remove deposits adhering to the ejection surface (for example, near the nozzles). However, when the ink contains a pigment, if the ejection surface of the inkjet head is wiped with a wipe member, wear of the ejection surface may progress.

The present disclosure has been made in view of the above circumstances, and an object to be solved by the embodiments of the present invention is to suppress the residue of deposits on the ejection surface during maintenance operations of the inkjet head, and to An object of the present invention is to provide an ink set and a maintenance method that can suppress wear on an ejection surface.

The present disclosure includes the following aspects.
<1> Ink containing pigment and maintenance liquid containing polymer particles, the content of the polymer particles is 3% to 25% by weight based on the total amount of the maintenance liquid, and the average content of the polymer particles is 3% to 25% by weight based on the total amount of the maintenance liquid. An ink set in which the particle diameter is 3.5 times or more the average particle diameter of the pigment.
<2> The ink set according to <1>, wherein the pigment is an inorganic pigment.
<3> The ink set according to <1> or <2>, wherein the pigment is carbon black or titanium dioxide.
<4> The polymer particles include a polymer containing at least one type selected from the group consisting of a structural unit derived from a vinyl compound and a structural unit derived from a vinylidene compound, a urethane resin, an ether resin, an ester resin, an amino resin, an amide resin, The ink set according to any one of <1> to <3>, comprising at least one polymer selected from the group consisting of a phenol resin, a fluororesin, and a silicone resin.
<5> The polymer particles consist of a structural unit derived from a (meth)acrylic compound, a structural unit derived from styrene, a structural unit derived from ethylene, a structural unit derived from propylene, a structural unit derived from vinyl chloride, and a structural unit derived from vinyl acetate. The polymer according to any one of <1> to <4>, comprising at least one polymer selected from the group consisting of a polymer containing at least one selected from the group consisting of a urethane resin, and an ester resin. ink set.
<6> The ink set according to any one of <1> to <5>, wherein the polymer particles have an average particle diameter of 400 nm to 5000 nm.
<7> The ink set according to any one of <1> to <6> is used, and after the ink is ejected from the nozzle of the inkjet head, the ejection surface of the inkjet head and a wipe member that wipes the ejection surface. A maintenance method comprising: a step of applying a maintenance liquid to at least one side; and a step of wiping the ejection surface with a wipe member after applying the maintenance liquid.
<8> The maintenance method according to <7>, wherein the wipe member is at least one selected from the group consisting of cloth, nonwoven fabric, blade, and sponge.
<9> The maintenance method according to <7> or <8>, wherein the inkjet head has a liquid-repellent film.
<10> The maintenance method according to <9>, wherein the liquid-repellent film contains a fluorine compound.

According to the present disclosure, an ink set and a maintenance method are provided that can suppress the residue of deposits on the ejection surface and suppress the wear of the ejection surface during maintenance operations for an inkjet head.

The ink set and maintenance method of the present disclosure will be described in detail below.

In this specification, a numerical range indicated using "~" means a range that includes the numerical values listed before and after "~" as the minimum and maximum values, respectively.
In the numerical ranges described stepwise in this specification, the upper limit or lower limit described in a certain numerical range may be replaced with the upper limit or lower limit of another numerical range described stepwise. Moreover, in the numerical ranges described in this specification, the upper limit or lower limit described in a certain numerical range may be replaced with the value shown in the Examples.

In the present specification, if there are multiple substances corresponding to each component in the composition, unless otherwise specified, the amount of each component in the composition refers to the total amount of the multiple substances present in the composition. means.
In this specification, a combination of two or more preferred embodiments is a more preferred embodiment.
As used herein, the term "process" is used not only to refer to an independent process, but also to include a process that is not clearly distinguishable from other processes, as long as the intended purpose of the process is achieved. It will be done.

As used herein, "image" refers to films in general, and "image recording" refers to the formation of images (ie, films). Further, the concept of "image" in this specification also includes a solid image.

In this specification, "(meth)acrylate" is a concept that includes both acrylate and methacrylate. Moreover, "(meth)acrylic" is a concept that includes both acrylic and methacrylic.

In this specification, "silicone resin" is a concept that includes silicone rubber.

In this specification, "the ejection surface of the inkjet head" means the surface of the inkjet head on which ink is ejected. In an inkjet head, when a liquid-repellent film is provided on the surface from which ink is ejected (for example, the surface of a nozzle plate), the surface of the liquid-repellent film is referred to as the "ejection surface."

[Ink set]
The ink set of the present disclosure includes an ink containing a pigment and a maintenance liquid containing polymer particles. The content of the polymer particles is 3% by mass to 25% by mass based on the total amount of the maintenance liquid. The average particle diameter of the polymer particles is 3.5 times or more the average particle diameter of the pigment.

Conventionally, by wiping the ejection surface of an inkjet head with a wipe member, it is possible to remove deposits attached to the ejection surface (for example, near the nozzle). There were cases where it progressed. This is considered to be because when the ejection surface of the inkjet head is wiped with the wipe member, the ejection surface is rubbed by the pigment contained in the ink.

In the ink set of the present disclosure, the maintenance liquid contains polymer particles, the content of the polymer particles is 3% by mass to 25% by mass based on the total amount of the maintenance fluid, and the average particle diameter of the polymer particles is It is 3.5 times or more the average particle diameter of the pigment. As a result, during maintenance operations for the inkjet head, deposits on the ejection surface are suppressed and abrasion of the ejection surface is suppressed. When the average particle diameter of the polymer particles is 3.5 times or more the average particle diameter of the pigment, the polymer particles function as a cushioning material, and when the ejection surface of the inkjet head is wiped with a wipe member, the pigment Chafing is reduced. As a result, it is thought that wear on the ejection surface can be suppressed. Further, it is considered that by setting the content of polymer particles to 3% by mass to 25% by mass based on the total amount of maintenance liquid, the remaining of deposits on the discharge surface is suppressed.

<Maintenance liquid>
(polymer particles)
The maintenance liquid in the ink set of the present disclosure contains polymer particles. The polymer particles contained in the maintenance liquid are polymers containing at least one kind selected from the group consisting of a structural unit derived from a vinyl compound and a structural unit derived from a vinylidene compound, from the viewpoint of stability and cleaning properties of the maintenance liquid. It is preferable that at least one polymer selected from the group consisting of resin, ether resin, ester resin, amino resin, amide resin, phenol resin, fluororesin, and silicone resin is included. Hereinafter, a polymer containing at least one type selected from the group consisting of a structural unit derived from a vinyl compound and a structural unit derived from a vinylidene compound will be referred to as a "specific polymer."

A vinyl compound is a compound having a vinyl group (CH ₂ =CH-). Examples of the vinyl compound include (meth)acrylic compounds, styrenes, olefins, vinyl halides, vinyl ethers, vinyl esters, vinyl alcohols, allyl compounds, and (meth)acrylonitrile.

A (meth)acrylic compound is a compound having an acryloyl group (CH ₂ =CH-C(=O)-) or a methacryloyl group (CH ₂ =C(CH ₃ )-C(=O)-). Examples of the (meth)acrylic compound include (meth)acrylic acid, (meth)acrylic acid ester, and (meth)acrylamide.

Examples of styrenes include styrene, α-methylstyrene, o-methoxystyrene, m-methoxystyrene, p-methoxystyrene, o-t-butoxystyrene, m-t-butoxystyrene, pt-butoxystyrene, o-chloromethylstyrene, m-chloromethylstyrene, p-chloromethylstyrene, p-hydroxymethylstyrene, p-(2-hydroxyethyl)styrene, p-(2-hydroxyethyloxycarbonyl)styrene, o-methoxystyrene , m-methoxystyrene, p-methoxystyrene, o-t-butoxystyrene, m-t-butoxystyrene, pt-butoxystyrene, o-chloromethylstyrene, m-chloromethylstyrene, p-chloromethylstyrene, Examples include p-hydroxymethylstyrene, p-(2-hydroxyethyl)styrene, and p-(2-hydroxyethyloxycarbonyl)styrene.

Examples of olefins include ethylene, propylene, 1-butene, and 1,3-butadiene.

Examples of vinyl halides include vinyl chloride and vinyl fluoride.

Examples of the vinyl ether include methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, and stearyl vinyl ether.

Examples of vinyl esters include vinyl acetate and isopropenyl acetate.

Examples of allyl compounds include allyl acetate and allyl chloride.

A vinylidene compound is a compound having a vinylidene group (CH ₂ =C<). Examples of vinylidene compounds include vinylidene chloride and vinylidene fluoride.

Urethane resin is a polymer having urethane bonds in its molecules. The urethane resin can be obtained, for example, by reacting a polyol, a polyisocyanate, and, if necessary, a polyamine. As the polyol, polyisocyanate and polyamine, known compounds can be used. The polyol may be a polyether polyol or a polyester polyol. Note that even when the polymer contains an ether bond or an ester bond in addition to the urethane bond, it is classified as a urethane resin and is distinguished from the ether resin and ester resin described below.

Ether resins are polymers that have ether bonds within their molecules. Examples of the ether resin include polyether sulfone resin.

Ester resins are polymers that have ester bonds within their molecules. The ester resin is obtained by reacting a polycarboxylic acid derivative with a polyol. As the polycarboxylic acid derivative and polyol, known compounds can be used.

Examples of the amino resin include benzoguanamine resin, urea resin, and melamine resin.

Examples of the amide resin include nylon.

Phenol resins can be obtained, for example, by reacting phenols and aldehydes. As the phenols and aldehydes, known compounds can be used.

Silicone resins are polymers that have siloxane bonds within their molecules. It is preferable that the silicone resin has a structure in which dimethylpolysiloxane is crosslinked.

The specific polymer is preferably a polymer containing a structural unit derived from a vinyl compound, a structural unit derived from a (meth)acrylic compound, a structural unit derived from styrene, a structural unit derived from ethylene, a structural unit derived from propylene, and a structural unit derived from chloride. More preferably, it is a polymer containing at least one type selected from the group consisting of a vinyl-derived structural unit and a vinyl acetate-derived structural unit.

Specifically, specific polymers include homopolymers consisting of structural units derived from (meth)acrylic esters, and copolymers containing structural units derived from (meth)acrylic acid and structural units derived from (meth)acrylic esters. Polymers, copolymers containing structural units derived from two or more types of (meth)acrylic acid esters, copolymers containing structural units derived from styrene and structural units derived from (meth)acrylic acid, structural units derived from styrene A copolymer containing a structural unit derived from (meth)acrylic acid and a (meth)acrylic acid ester, a copolymer containing a structural unit derived from ethylene and a structural unit derived from propylene, a structural unit derived from styrene. and 1,3-butadiene-derived structural units, copolymers containing ethylene-derived structural units and vinyl chloride-derived structural units, polyethylene, polypropylene, and polyvinyl chloride.

Among these, the specific polymer preferably contains a structural unit derived from (meth)acrylic acid ester, and more preferably contains a structural unit derived from (meth)acrylic acid alkyl ester. In the (meth)acrylic acid alkyl ester, the alkyl group preferably has 1 to 6 carbon atoms, more preferably 1 to 4 carbon atoms. Specifically, the specific polymer preferably contains a structural unit derived from methyl (meth)acrylate. Furthermore, when the specific polymer includes a structural unit derived from methyl (meth)acrylate, the specific polymer may have a crosslinked structure. For example, a copolymer having a crosslinked structure can be obtained by copolymerizing methyl (meth)acrylate and a polyfunctional monomer.

The polymer particles are selected from the group consisting of structural units derived from (meth)acrylic compounds, structural units derived from styrene, structural units derived from ethylene, structural units derived from propylene, structural units derived from vinyl chloride, and structural units derived from vinyl acetate. It is preferable to include at least one polymer selected from the group consisting of a polymer containing at least one type of resin, a urethane resin, and an ester resin.

The polymer particles may be core-shell type particles. Examples of core-shell type particles include particles in which the shell part is made of urethane resin and the core part is made of a polymer containing a structural unit derived from a (meth)acrylic compound.

The weight average molecular weight of the polymer contained in the polymer particles is not particularly limited, and is, for example, 1000 to 100,000. Weight average molecular weight means a value measured by gel permeation chromatography (GPC). For measurement by GPC, HLC (registered trademark)-8020GPC (manufactured by Tosoh Corporation) was used as a measuring device, and TSKgel (registered trademark) Super Multipore HZ-H (4.6 mm ID x 15 cm, manufactured by Tosoh Corporation) was used as a column. In this case, THF (tetrahydrofuran) is used as the eluent. Further, the measurement is performed using an RI detector with a sample concentration of 0.45% by mass, a flow rate of 0.35 ml/min, a sample injection amount of 10 μl, and a measurement temperature of 40° C. The calibration curve is "standard sample TSK standard, polystyrene" manufactured by Tosoh Corporation: "F-40", "F-20", "F-4", "F-1", "A-5000", "A- 2500'', ``A-1000'', and 8 samples of ``n-propylbenzene''.

The average particle diameter (in other words, the average primary particle diameter) of the polymer particles is preferably from 400 nm to 5000 nm, more preferably from 400 nm to 4000 nm, even more preferably from 400 nm to 3000 nm. When the average particle diameter of the polymer particles is 400 nm or more, the ratio of the average particle diameter of the polymer particles to the average particle diameter of the pigment is likely to be 3.5 times or more. Therefore, when the average particle diameter of the polymer particles is 400 nm or more, the residue of deposits on the ejection surface is suppressed, and wear of the ejection surface is suppressed. Further, when the average particle diameter of the polymer particles is 5000 nm or less, the maintenance liquid has excellent storage stability.

The average particle diameter of the polymer particles is measured by a dynamic light scattering method using a Nanotrac particle size distribution analyzer (product name "UPA-EX150", manufactured by Nikkiso Co., Ltd.), and is obtained as a volume average particle diameter. After adjusting the solid content concentration of polymer particles in the maintenance liquid to 2% by mass, measurement is performed.

Further, the average particle diameter of the polymer particles is 3.5 times or more, preferably 4.0 times or more, the average particle diameter of the pigment contained in the ink described below. The upper limit of the ratio of the average particle diameter of the polymer particles to the average particle diameter of the pigment (ie, the average particle diameter of the polymer particles/the average particle diameter of the pigment) is not particularly limited, and is, for example, 50 times. When the ratio of the average particle diameter of the polymer particles to the average particle diameter of the pigment is 3.5 times or more and 10 times or less, deposits on the ejection surface are suppressed from remaining, and wear on the ejection surface is suppressed.

The content of polymer particles contained in the maintenance liquid is 3% by mass to 25% by mass, preferably 3% to 20% by mass, and preferably 5% to 15% by mass, based on the total amount of the maintenance fluid. It is more preferable that there be. When the content is 3% by mass or more, wear on the ejection surface is suppressed. This is considered to be because the polymer particles function as a cushioning material when the content is 3% by mass or more. On the other hand, when the content is 25% by mass or less, deposits on the discharge surface are suppressed from remaining. This means that if the content is 25% by mass or less, deposits (e.g., dried ink) adhering to the ejection surface will be removed during inkjet maintenance operations, and deposits originating from the maintenance liquid will be removed. This is thought to be because it becomes difficult to remain on the surface.

(water)
Preferably, the maintenance liquid contains water. The content of water is not particularly limited, and for example, it is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more based on the total amount of the maintenance liquid. . The upper limit of the water content is adjusted as appropriate depending on the content of other components. The upper limit of the water content is, for example, 80% by mass.

(Organic solvent)
Preferably, the maintenance liquid contains at least one organic solvent. When the maintenance liquid contains water, the organic solvent is preferably a water-soluble organic solvent. Water-soluble means that the solubility in water at 25° C. is 1% by mass or more.

Examples of the organic solvent include ester solvents, ketone solvents, alcohol solvents, amide solvents, ether solvents, and hydrocarbon solvents. Among these, the organic solvent is preferably at least one selected from the group consisting of ether solvents and alcohol solvents, and more preferably a combination of ether solvents and alcohol solvents.

Examples of ether solvents include alkyl ethers such as diethyl ether, ethyl methyl ether, and tetrahydrofuran;
Dimethylene glycol monomethyl ether, dimethylene glycol monoethyl ether, dimethylene glycol monopropyl ether, dimethylene glycol monobutyl ether, trimethylene glycol monomethyl ether, trimethylene glycol monoethyl ether, trimethylene glycol monopropyl ether, trimethylene glycol mono Butyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol mono-2-ethylhexyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether , diethylene glycol monohexyl ether, diethylene glycol mono-2-ethylhexyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monopropyl ether, triethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, Propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monoethyl ether, (Poly)alkylene glycol monoalkyl ethers such as tripropylene glycol monopropyl ether and tripropylene glycol monobutyl ether;
Dimethylene glycol monophenyl ether, dimethylene glycol monobenzyl ether, dimethylene glycol monotril ether, trimethylene glycol monophenyl ether, trimethylene glycol monobenzyl ether, trimethylene glycol monotril ether, ethylene glycol monophenyl ether, ethylene glycol Monobenzyl ether, ethylene glycol monotril ether, diethylene glycol monophenyl ether, diethylene glycol monobenzyl ether, diethylene glycol monotril ether, triethylene glycol monophenyl ether, triethylene glycol monobenzyl ether, triethylene glycol monotril ether, propylene glycol monophenyl Ether, propylene glycol monobenzyl ether, propylene glycol monotril ether, dipropylene glycol monophenyl ether, dipropylene glycol monobenzyl ether, dipropylene glycol monotril ether, tripropylene glycol monophenyl ether, tripropylene glycol monobenzyl ether, tripropylene glycol monobenzyl ether (Poly)alkylene glycol monoallyl ether such as propylene glycol monotolyl ether;
(Poly)alkylene glycol dialkyl ether such as ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether; and
Examples include glycerin derivatives such as polyoxyethylene glyceryl ether and polyoxypropylene glyceryl ether.

Among these, from the viewpoint of improving cleaning properties, the ether solvent is preferably a (poly)alkylene glycol monoalkyl ether.

From the viewpoint of stability of the maintenance liquid, the alkyl group in the (poly)alkylene glycol monoalkyl ether preferably has 1 to 6 carbon atoms, more preferably 2 to 4 carbon atoms. Furthermore, in the alkylene glycol monoalkyl ether, the number of carbon atoms in the alkylene chain is preferably 1 to 4, the number of repeats in the alkylene chain is preferably 1 to 6, and the number of carbon atoms in the alkylene chain is 1 to 3, and the number of carbon atoms in the alkylene chain is preferably 1 to 6. The number of repeats in the alkylene chain is more preferably 1 to 4, the number of carbon atoms in the alkylene chain is 2 or 3, and the number of repeats in the alkylene chain is 1 to 3.

Examples of alcohol solvents include alcohols such as methanol, n-propanol, iso-propanol, n-butanol, and tert-butanol; ethylene glycol, propylene glycol, butylene glycol, hexylene glycol, diethylene glycol, triethylene glycol, and tetraethylene. Glycol, pentaethylene glycol, dipropylene glycol, 2-butene-1,4-diol, 2-ethyl-1,3-hexanediol, 2-methyl-2,4-pentanediol, 1,2-octanediol, 1 (Poly)alkylene glycols such as , 2-hexanediol, 1,2-pentanediol, 4-methyl-1,2-pentanediol; and glycerin, 1,2,4-butanetriol, 1,2,6- Triols such as hexanetriol can be mentioned.

Among these, from the viewpoint of improving cleaning properties, the alcohol solvent is preferably (poly)alkylene glycol. In the (poly)alkylene glycol, the number of carbon atoms in the alkylene chain is 1 to 4, and the number of repeating alkylene chains is preferably 1 to 6. The number of carbon atoms in the alkylene chain is 1 to 3, and the number of repeating alkylene chains is preferably 1 to 6. More preferably, the number is 1 to 4, the number of carbon atoms in the alkylene chain is 2 or 3, and the number of repeats in the alkylene chain is 1 to 3.

The organic solvent contained in the maintenance liquid is preferably a combination of (poly)alkylene glycol monoalkyl ether and (poly)alkylene glycol. The proportion of (poly)alkylene glycol monoalkyl ether in the organic solvent contained in the maintenance liquid is preferably 50% by mass or more, more preferably 60% by mass or more, and preferably 65% by mass or more. More preferred. The upper limit of the above ratio is not particularly limited, and is, for example, 95% by mass. When the maintenance liquid contains (poly)alkylene glycol monoalkyl ether and (poly)alkylene glycol, the solubility of deposits in the inkjet head in the maintenance liquid is improved, and residual deposits are suppressed.

The content of the organic solvent contained in the maintenance liquid is preferably 15% to 50% by weight, more preferably 20% to 40% by weight, based on the total amount of the maintenance liquid.

(basic compound)
Preferably, the maintenance liquid contains at least one basic compound. By containing a basic compound in the maintenance liquid, a pH buffering effect can be imparted to the maintenance liquid.

The basic compound is not particularly limited as long as it has a pH buffering ability within the range of 6.0 to 9.0, which is the preferred pH of the maintenance solution.

The basic compound has a pKa value of preferably 6.0 to 9.0, preferably 6.5 to 8.4, in that it has an effective pH buffering ability in the pH range of 6.0 to 9.0. More preferably, it is 6.8 to 8.3.

Examples of basic compounds having a pKa value of 6.0 to 8.5 include cacodylic acid (pKa: 6.2), 2,2-bis(hydroxymethyl)-2,2',2''-nitrilotriethanol (pKa: 6.5), piperazine-N,N'-bis-(2-ethane sulfate) (pKa: 6.8), phosphoric acid (pKa2: 6.86), imidazole (pKa: 7.0), N'-2-hydroxyethylpiperazine-N-2-ethane sulfate (pKa: 7.6), N-methylmorpholine (pKa: 7.8), triethanolamine (pKa: 7.8), hydrazine (pKa: 8.11) and trishydroxymethylaminomethane (pKa: 8.3).

The basic compound may be either an inorganic base or an organic base. The basic compound is preferably an organic base from the viewpoint of ease of obtaining a pKa in the desired range and solubility in the maintenance liquid. The pKa value when the basic compound is an organic base is the pKa value of the conjugate acid.

The content of the basic compound contained in the maintenance solution is 0.05% by mass to 0.5% by mass based on the total amount of the maintenance solution, from the viewpoint of maintaining detergency and imparting a pH buffering effect. It is preferably 0.1% by mass to 0.3% by mass.

(acidic compound)
It is preferable that the maintenance liquid contains at least one kind of acidic compound along with the basic compound. By using a basic compound and an acidic compound in combination, the pH buffering effect of the maintenance liquid can be enhanced. In particular, by using a basic compound with a pKa value of 6.0 to 8.5 in combination with an acidic compound, the pH buffering effect of the maintenance liquid in a preferable pH range can be enhanced.

The acidic compound may be either an inorganic acid or an organic acid. Examples of inorganic acids include hydrochloric acid, sulfuric acid, sulfurous acid, nitric acid, and phosphoric acid. Organic acids include acetic acid, tartaric acid, salicylic acid, sulfosalicylic acid, and benzoic acid. Among these, the acidic compound is preferably an inorganic acid. Further, the acidic compound may be either a strong acid or a weak acid. From the viewpoint of enhancing the pH buffering effect, the acidic compound is preferably a strong acid.

A preferred combination of a basic compound and an acidic compound is an organic base and an inorganic acid having a pKa value of 6.0 to 8.5.

The content of the acidic compound contained in the maintenance liquid is preferably 0.05 equivalent to 0.95 equivalent of the basic compound in terms of acid equivalent, and 0.10 equivalent to 0.95 equivalent, from the viewpoint of enhancing the pH buffering effect of the maintenance liquid. More preferably 90 equivalents, and even more preferably 0.15 to 0.85 equivalents.

(surfactant)
Preferably, the maintenance liquid contains at least one surfactant. The surfactant may be a nonionic surfactant, a cationic surfactant, an anionic surfactant, or a betaine type surfactant. From the viewpoint of storage stability of the maintenance liquid, the surfactant is preferably a nonionic surfactant.

Examples of nonionic surfactants include polyoxyethylene alkyl ether, polyoxyethylene alkyl allyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, acetylene diol derivative, polyoxyethylene alkyl amine, and glycerin. Fatty acid esters and oxyethylene oxypropylene block copolymers are included.

The content of the surfactant contained in the maintenance liquid is preferably 0.5% to 10% by weight, more preferably 1% to 4% by weight, based on the total amount of the maintenance liquid.

(antifoaming agent)
Preferably, the maintenance liquid contains at least one antifoaming agent. Examples of antifoaming agents include silicone antifoaming agents. The silicone antifoaming agent is preferably a compound having a polysiloxane structure.

The content of the antifoaming agent contained in the maintenance liquid is preferably 0.005% by mass to 0.05% by mass based on the total amount of the maintenance fluid.

(colloidal silica)
Preferably, the maintenance liquid contains at least one type of colloidal silica. The colloidal silica is preferably a colloid made of particles of an inorganic oxide containing silicon.

Colloidal silica contains silicon dioxide or a hydrate of silicon dioxide as a main component, and may contain an aluminate as a minor component. Aluminates that may be included as minor components include, for example, sodium aluminate and potassium aluminate.

Further, colloidal silica may contain an inorganic salt such as sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonium hydroxide, or an organic salt such as tetramethylammonium hydroxide. Inorganic and organic salts act as stabilizers for the colloid.

The dispersion medium for colloidal silica is not particularly limited, and examples include water, organic solvents, and mixtures thereof. The organic solvent serving as the dispersion medium may be either a water-soluble organic solvent or a water-insoluble organic solvent, but is preferably a water-soluble organic solvent. Examples of water-soluble organic solvents include methanol, ethanol, isopropanol, and n-propanol.

The average particle diameter of the particles contained in colloidal silica is not particularly limited, but from the viewpoint of storage stability of the maintenance liquid, it is preferably 1 nm to 200 nm, more preferably 1 nm to 100 nm, and more preferably 2 nm to 50 nm. The thickness is preferably 3 nm to 25 nm, more preferably 5 nm to 20 nm.

When the average particle diameter of the particles is 200 nm or less, the storage stability of the maintenance liquid is excellent and the durability of the inkjet head is improved. In particular, when an inkjet nozzle plate includes a silicon layer, colloidal silica exhibits the effect of repairing the nozzle plate. On the other hand, when the average particle diameter of the particles is 1 nm or more, productivity is improved and colloidal silica with less variation in performance can be obtained.

The average particle size of colloidal silica is measured by a dynamic light scattering method using a Nanotrack particle size distribution analyzer (product name "UPA-EX150", manufactured by Nikkiso Co., Ltd.), and is obtained as a volume average particle size. Note that colloidal silica and polymer particles can be distinguished by using a transmission electron microscope (TEM).

The shape of colloidal silica is not particularly limited, and includes, for example, spherical shape, elongated shape, needle shape, and bead shape.

Colloidal silica may be a commercially available product. Commercially available products include, for example, Ludox AM, Ludox AS, Ludox LS, Ludox TM, and Ludox HS (manufactured by E.I. Du Pont de Nemouvs &Co); Snowtex S, Snowtex XS, Snowtex 20, Snowtex 30, Snowtex 40, Snowtex N, Snowtex C, and Snowtex O (manufactured by Nissan Chemical Co., Ltd.); Syton C-30, and SytonZOO (manufactured by Mons anto Co); Nalcoag-1060, and Nalcoag-ID21 to 64 ( (manufactured by Nalco Chem Co); methanol sol, IPA sol, MEK sol, and toluene sol (manufactured by Fuso Chemical Industry Co., Ltd.); Cataloid-S, Cataloid-F120, Cataloid SI-350, Cataloid SI-500, Cataloid SI-30, Cataloid S -20L, Cataloid S-20H, Cataloid S-30L, Cataloid S-30H, Cataloid SI-40, and OSCAL-1432 (manufactured by JGC Catalysts &Chemicals); and Adelite (manufactured by ADEKA). In addition, as bead-shaped colloidal silica, for example, Snowtex ST-UP, Snowtex PS-S, Snowtex PS-M, Snowtex ST-OUP, Snowtex PS-SO, and Snowtex PS-MO (Nissan Chemical (manufactured by the company).

The content of colloidal silica contained in the maintenance liquid is preferably 0.005% by mass to 5% by mass, more preferably 0.01% by mass to 3% by mass, based on the total amount of the maintenance fluid. More preferably, it is 0.02% by mass to 1% by mass.

(Additive)
In addition to the above ingredients, the maintenance liquid may contain other ingredients as necessary, such as anti-fading agents, emulsion stabilizers, penetration enhancers, ultraviolet absorbers, preservatives, anti-mold agents, pH adjusters, viscosity adjusters, etc. It may also contain additives.

(physical properties)
The pH of the maintenance liquid is preferably 6.0 to 9.0, more preferably 7.5 to 8.8, and even more preferably 8.0 to 8.5. The pH is measured at 25° C. using a pH meter, for example, a tabletop pH meter (product name: LAQUAF-74S, manufactured by Horiba, Ltd.).

When the pH of the maintenance liquid is 7.0 or higher, aggregation when mixed with ink can be suppressed. When the pH is 9.5 or less, deterioration of the inkjet head can be suppressed.

From the viewpoint of workability, the viscosity of the maintenance liquid is preferably 1 mPa·s to 50 mPa·s, more preferably 1 mPa·s to 10 mPa·s, and preferably 2 mPa·s to 5 mPa·s. More preferred.

The viscosity is measured at 30° C. using a viscometer, for example, a viscometer (product name “TVB-22L”, manufactured by Toki Sangyo Co., Ltd.).

Preferably, the maintenance liquid does not substantially contain pigment. The maintenance liquid does not substantially contain pigments, or if the maintenance liquid contains pigments, the pigment content is 1 mass based on the total amount of the maintenance liquid. means less than %.

<Ink>
(pigment)
The ink included in the ink set of the present disclosure includes a pigment. The number of pigments contained in the ink may be one, or two or more.

The pigment may be either an organic pigment or an inorganic pigment that is normally commercially available. Examples of pigments include "Dictionary of Pigments" edited by Seishiro Ito (published in 2000), W. Herbst, K. Examples include pigments described in "Industrial Organic Pigments" by Hunger, JP 2002-12607, JP 2002-188025, JP 2003-26978, and JP 2003-342503.

Further, the pigment may be a water-insoluble pigment that can be dispersed in water using a dispersant, or a self-dispersing pigment. A self-dispersing pigment is a pigment that can be dispersed in water without using a dispersant. A self-dispersing pigment is, for example, a pigment in which at least one selected from the group consisting of hydrophilic groups such as a carbonyl group, a hydroxyl group, a carboxyl group, a sulfo group, a phosphoric acid group, and their salts is directly or in combination with another group. It is a compound that is chemically bonded to the surface of the pigment via.

Examples of organic pigments include azo pigments, polycyclic pigments, dye chelates, nitro pigments, nitroso pigments, and aniline black. Examples of azo pigments include azo lakes, insoluble azo pigments, condensed azo pigments, and chelate azo pigments. Examples of polycyclic pigments include phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, indigo pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone pigments. Examples of the dye chelate include basic dye-type chelates and acidic dye-type chelates.

Examples of inorganic pigments include titanium oxide, iron oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, chrome yellow, and carbon black.

Among these, the pigment contained in the ink is preferably an inorganic pigment, and more preferably carbon black or titanium dioxide.

Inorganic pigments have higher hardness than organic pigments. Therefore, when the ink contains an inorganic pigment, when the inkjet head maintenance operation involves wiping away deposits (for example, dried ink) on the ejection surface with a wipe member, the ejection surface is rubbed by the inorganic pigment. In some cases, the wear of the discharge surface progressed. In the ink set of the present disclosure, even when the ink contains an inorganic pigment, wear on the ejection surface can be suppressed.

The average particle diameter of the pigment is preferably 30 nm to 300 nm, more preferably 80 nm to 250 nm, from the viewpoint of ink ejection properties and ink storage stability. The average particle diameter of the pigment is measured, for example, by the following method.

First, the ink is diluted with a solvent, and the solid concentration of the pigment in the ink is adjusted to 2% by mass. The diluted ink is measured at 25° C. by a dynamic light scattering method using a Nanotrac particle size distribution analyzer (product name "UPA-EX150", manufactured by Nikkiso Co., Ltd.). The average particle diameter of the pigment is obtained as a volume average particle diameter.

In addition, when the pigment is coated with a dispersant mentioned later, the average particle diameter of the pigment means the average particle diameter of the pigment coated with the dispersant.

The content of pigment contained in the ink is preferably 0.5% by mass to 15% by mass, and 1% by mass to 12% by mass, based on the total amount of the ink, from the viewpoint of the obtained image density and storage stability. %, more preferably 2% by mass to 10% by mass. When the ink contains two or more types of pigments, it is preferable that the total content of the two or more types of pigments is within the above range. In addition, when the pigment is titanium dioxide, the content of the pigment contained in the ink is 5% by mass to 20% by mass with respect to the total amount of the ink, from the viewpoint of the obtained image density and storage stability. It is preferably 8% by mass to 15% by mass.

(dispersant)
When a water-insoluble pigment is used as the pigment, the ink preferably contains at least one dispersant. For example, the pigment can be incorporated into the ink by mixing a pigment and a dispersant to prepare a pigment dispersion, and then mixing the pigment dispersion and other components.

As the dispersant, commonly known ones can be used. From the viewpoint of dispersion stability, the dispersant is preferably a compound having both a hydrophilic structure and a hydrophobic structure.

Examples of dispersants include higher fatty acid salts, alkyl sulfates, alkyl ester sulfates, alkyl sulfonates, sulfosuccinates, naphthalene sulfonates, alkyl phosphates, polyoxyalkylene alkyl ether phosphates, polyoxy Examples include low molecular weight dispersants having a molecular weight of less than 1000, such as alkylene alkylphenyl ether, polyoxyethylene polyoxypropylene glycol, glycerin fatty acid ester, sorbitan fatty acid ester, polyoxyethylene fatty acid amide, and amine oxide.

Further, examples of the dispersant include high molecular weight dispersants having a molecular weight of 1000 or more obtained by copolymerizing a hydrophilic monomer and a hydrophobic monomer. From the viewpoint of dispersion stability, the hydrophilic monomer is preferably a dissociative group-containing monomer, and is preferably a dissociative group-containing monomer having a dissociative group and an ethylenically unsaturated bond. Examples of the dissociative group-containing monomer include carboxy group-containing monomers, sulfonic acid group-containing monomers, and phosphoric acid group-containing monomers. From the viewpoint of dispersion stability, the hydrophobic monomer is an aromatic group-containing monomer having an aromatic group and an ethylenically unsaturated bond, or an aliphatic hydrocarbon having an aliphatic hydrocarbon group and an ethylenically unsaturated bond. A group-containing monomer is preferred. The polymer may be either a random copolymer or a block copolymer.

The dispersant may be a commercially available product. Commercially available products include, for example,
DISPERBYK-101, DISPERBYK-102, DISPERBYK-103, DISPERBYK-106, DISPERBYK-110, DISPERBYK-111, DISPERBYK-161, DISPERBYK-162, DISPERBYK -163, DISPERBYK-164, DISPERBYK-166, DISPERBYK-167, DISPERBYK- 168, DISPERBYK-170, DISPERBYK-171, DISPERBYK-174, DISPERBYK-182 (manufactured by BYK Chemie); and SOLSPERSE3000, SOLSPERSE5000, SOLSPERSE9000, SOLSPERSE 12000, SOLSPERSE13240, SOLSPERSE13940, SOLSPERSE17000, SOLSPERSE22000, SOLSPERSE24000, SOLSPERSE26000, SOLSPERSE28000, SOLSPERSE320 00, SOLSPERSE36000 , SOLSPERSE39000, SOLSPERSE41000, SOLSPERSE71000 (manufactured by Lubrizol)
can be mentioned.

As a dispersion device for dispersing the pigment, a known dispersion device can be used, and examples thereof include a ball mill, a sand mill, a bead mill, a roll mill, a jet mill, a paint shaker, an attritor, an ultrasonic dispersion machine, and a disper.

In the ink, the ratio of the dispersant content to the pigment content (i.e., dispersant content/pigment content) is 0.05 to 1.0 on a mass basis from the viewpoint of dispersion stability. It is preferably from 0.1 to 0.8.

(water)
The ink included in the ink set of the present disclosure may be a water-based ink or an active energy ray-curable ink. Water-based ink is ink containing water. In the case of water-based ink, when the ink is applied onto a substrate, the solvent such as water evaporates during drying, thereby solidifying the ink and fixing it on the substrate. On the other hand, an active energy ray-curable ink is an ink that does not contain water. In the case of active energy ray type ink, when the ink is applied onto a substrate and then irradiated with active energy rays, the ink is cured and fixed on the substrate.

When the ink included in the ink set of the present disclosure is a water-based ink, the ink contains water. The content of water is not particularly limited, and for example, it is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more based on the total amount of the maintenance liquid. . The upper limit of the water content is adjusted as appropriate depending on the content of other components. The upper limit of the water content is, for example, 80% by mass.

(polymer particles)
Preferably, the ink contains at least one polymer particle. When the ink contains polymer particles, the scratch resistance of the resulting image is improved.

The polymer constituting the polymer particles is preferably a water-insoluble polymer. "Water-insoluble" in a water-insoluble polymer means a property in which the amount dissolved in 100 g of distilled water at 25° C. is less than 2 g.

The polymer particles are selected from the group consisting of structural units derived from (meth)acrylic compounds, structural units derived from styrene, structural units derived from ethylene, structural units derived from propylene, structural units derived from vinyl chloride, and structural units derived from vinyl acetate. It is preferable to include at least one polymer selected from the group consisting of a polymer containing at least one type of resin, a urethane resin, and an ester resin. Moreover, it is more preferable that the polymer particles are particles made of a polymer containing a structural unit derived from a (meth)acrylic compound. Hereinafter, a polymer containing a structural unit derived from a (meth)acrylic compound may be referred to as an "acrylic resin."

The polymer constituting the polymer particles has a structural unit derived from (meth)acrylate having an aromatic ring structure or alicyclic structure, a structural unit derived from (meth)acrylic acid, and an alkyl group having 1 to 4 carbon atoms. It is preferable that the acrylic resin contains a structural unit derived from an alkyl (meth)acrylate.

The (meth)acrylate having an alicyclic structure is preferably an alkyl (meth)acrylate having a cycloalkyl group having 3 to 10 carbon atoms, such as cyclohexyl (meth)acrylate), isobornyl (meth)acrylate, adamantyl (meth)acrylate, etc. ) acrylate, and dicyclopentanyl (meth)acrylate, preferably at least one selected from the group consisting of isobornyl (meth)acrylate, adamantyl (meth)acrylate, and dicyclopentanyl (meth)acrylate. More preferably, it is at least one selected from the group consisting of:

The (meth)acrylate having an aromatic ring structure is preferably phenoxyethyl (meth)acrylate or benzyl (meth)acrylate.

Examples of the polymer constituting the polymer particles include phenoxyethyl acrylate/methyl methacrylate/acrylic acid copolymer (50/45/5), phenoxyethyl acrylate/benzyl methacrylate/isobutyl methacrylate/methacrylic acid copolymer (30/35) /29/6), phenoxyethyl methacrylate/isobutyl methacrylate/methacrylic acid copolymer (50/44/6), phenoxyethyl acrylate/methyl methacrylate/ethyl acrylate/acrylic acid copolymer (30/55/10/5) , benzyl methacrylate/isobutyl methacrylate/methacrylic acid copolymer (35/59/6), styrene/phenoxyethyl acrylate/methyl methacrylate/acrylic acid copolymer (10/50/35/5), benzyl acrylate/methyl methacrylate/ Acrylic acid copolymer (55/40/5), phenoxyethyl methacrylate/benzyl acrylate/methacrylic acid copolymer (45/47/8), styrene/phenoxyethyl acrylate/butyl methacrylate/acrylic acid copolymer (5/ 48/40/7), benzyl methacrylate/isobutyl methacrylate/cyclohexyl methacrylate/methacrylic acid copolymer (35/30/30/5), phenoxyethyl acrylate/methyl methacrylate/butyl acrylate/methacrylic acid copolymer (12/50) /30/8), benzyl acrylate/isobutyl methacrylate/acrylic acid copolymer (93/2/5), methyl methacrylate/methoxyethyl acrylate/benzyl methacrylate/acrylic acid copolymer (44/15/35/6), Styrene/butyl acrylate/acrylic acid copolymer (62/35/3), methyl methacrylate/phenoxyethyl acrylate/acrylic acid copolymer (45/51/4), methyl methacrylate/isobornyl methacrylate/methacrylic acid copolymer combination (20/72/8), methyl methacrylate/isobornyl methacrylate/methacrylic acid copolymer (40/52/8), methyl methacrylate/isobornyl methacrylate/methacrylic acid copolymer (65/25/10) , methyl methacrylate/isobornyl methacrylate/dicyclopentanyl methacrylate/methacrylic acid copolymer (20/62/10/8), methyl methacrylate/dicyclopentanyl methacrylate/methacrylic acid copolymer (20/72/8) ) and methyl methacrylate/isobornyl methacrylate/methacrylic acid/sodium methacrylate (70/20/5/5). Note that the value in parentheses represents the mass ratio of structural units derived from monomers.

The acid value of the polymer constituting the polymer particles is preferably 25 mgKOH/g to 100 mgKOH/g, more preferably 30 mgKOH/g to 90 mgKOH/g, and even more preferably 35 mgKOH/g to 80 mgKOH/g. preferable. The acid value is measured according to the method described in JIS K0070:1992.

The weight average molecular weight of the polymer constituting the polymer particles is preferably 1,000 to 300,000, more preferably 2,000 to 200,000, and preferably 5,000 to 100,000. More preferred. Weight average molecular weight means a value measured by gel permeation chromatography (GPC). For measurement by GPC, HLC (registered trademark)-8020GPC (manufactured by Tosoh Corporation) was used as a measuring device, and TSKgel (registered trademark) Super Multipore HZ-H (4.6 mm ID x 15 cm, manufactured by Tosoh Corporation) was used as a column. In this case, THF (tetrahydrofuran) is used as the eluent. Further, the measurement is performed using an RI detector with a sample concentration of 0.45% by mass, a flow rate of 0.35 ml/min, a sample injection amount of 10 μL, and a measurement temperature of 40° C. The calibration curve is "standard sample TSK standard, polystyrene" manufactured by Tosoh Corporation: "F-40", "F-20", "F-4", "F-1", "A-5000", "A- 2500'', ``A-1000'', and 8 samples of ``n-propylbenzene''.

The average particle diameter of the polymer particles is preferably from 1 nm to 200 nm, more preferably from 3 nm to 200 nm, even more preferably from 5 nm to 50 nm, from the viewpoint of ink ejection properties. The average particle diameter of the polymer particles is measured by a dynamic light scattering method using a Nanotrac particle size distribution analyzer (product name "UPA-EX150", manufactured by Nikkiso Co., Ltd.), and is obtained as a volume average particle diameter.

The content of polymer particles contained in the ink is preferably 0.1% to 15% by mass, more preferably 0.5% to 10% by mass, and 2% by mass based on the total amount of the ink. % to 8% by mass is more preferable.

(Organic solvent)
Preferably, the ink contains at least one organic solvent. When the ink contains an organic solvent, the ejectability of the ink improves. When the ink contains water, the organic solvent is preferably a water-soluble organic solvent. Water-soluble means that the solubility in water at 25° C. is 1% by mass or more.

Examples of the organic solvent include ester solvents, ketone solvents, alcohol solvents, amide solvents, ether solvents, and hydrocarbon solvents. Among these, the organic solvent is preferably at least one selected from the group consisting of ether solvents and alcohol solvents.

Examples of the ether solvent and the alcohol solvent include the compounds exemplified in the maintenance liquid section above.

The content of the organic solvent contained in the ink is preferably 5% by mass to 50% by mass, more preferably 10% by mass to 30% by mass, based on the total amount of the ink.

(water soluble polymer)
In the case of a water-based ink, the ink preferably contains a water-soluble polymer. When the ink contains a water-soluble polymer, the ejection properties of the ink are improved.

(antifoaming agent)
Preferably, the ink contains at least one antifoaming agent. Examples of antifoaming agents include silicone antifoaming agents. The silicone antifoaming agent is preferably a compound having a polysiloxane structure.

The content of the antifoaming agent contained in the ink is preferably 0.005% by mass to 0.05% by mass based on the total amount of the ink.

(Other ingredients)
In addition to the above components, the ink may contain, if necessary, a solid wetting agent, wax, surfactant, anti-fading agent, emulsion stabilizer, penetration enhancer, ultraviolet absorber, preservative, antifungal agent, pH It may also contain other additives such as regulators and viscosity regulators.

Further, in the case of an active energy ray-curable ink, the ink preferably contains a polymerizable compound. The polymerizable compound is not particularly limited as long as it is a compound that has a polymerizable group, and any known compound can be used.

(physical properties)
From the viewpoint of storage stability of the ink, the pH of the ink is preferably 6.0 to 11.0, more preferably 7.0 to 10.0, and more preferably 7.0 to 9.0. It is even more preferable.

The pH is measured at 25° C. using a pH meter, for example, a tabletop pH meter (product name: LAQUAF-74S, manufactured by Horiba, Ltd.).

From the viewpoint of ink ejection properties, the viscosity of the ink is preferably 1.0 mPa·s to 15.0 mPa·s, more preferably 2.0 mPa·s to 10.0 mPa·s, and 3. More preferably, it is 0 mPa·s to 8.0 mPa·s.

The viscosity is measured at 30° C. using a viscometer, for example, a viscometer (product name “TVB-22L”, manufactured by Toki Sangyo Co., Ltd.).

The surface tension of the ink is preferably 20 mN/m to 60 mN/m, more preferably 25 mN/m to 45 mN/m, from the viewpoint of ink ejection properties.

The surface tension is measured at 25° C. using a surface tension meter, for example, by the plate method using an automatic surface tension meter (product name “DY-300”, manufactured by Kyowa Interface Science Co., Ltd.).

The ink included in the ink set of the present disclosure is used to record an image using an inkjet recording method. That is, the ink included in the ink set of the present disclosure is an inkjet recording ink.

The method of ejecting ink in the inkjet recording method is not particularly limited, and may be a known method, such as a charge control method that uses electrostatic attraction to eject ink, or a drop-on-demand method that uses the vibration pressure of a piezo element. The acoustic inkjet method uses radiation pressure to eject ink by converting an electrical signal into an acoustic beam and irradiating the ink with radiation pressure. Thermal inkjet method uses the pressure generated by heating the ink to form bubbles. It may be a bubble jet (registered trademark) method.

As an inkjet recording method, in particular, there is a method described in Japanese Unexamined Patent Publication No. 54-59936, in which ink subjected to the action of thermal energy undergoes a rapid volume change, and the acting force due to this state change causes the ink to be removed from the nozzle. An inkjet recording method that uses ejection can be effectively used. As an inkjet recording method, the method described in paragraph numbers 0093 to 0105 of JP-A No. 2003-306623 can also be applied.

Application of ink onto a substrate by an inkjet recording method is performed by ejecting ink from a nozzle of an inkjet head. An inkjet head typically has a nozzle substrate on which a plurality of nozzles are formed. It is preferable that a liquid-repellent film containing a fluorine-containing polymer or the like be formed on the surface of the nozzle substrate on the side from which ink is ejected in order to suppress adhesion of ink.

<Maintenance method>
The maintenance method of the present disclosure uses the above-mentioned ink set, and after the ink is ejected from the nozzle of the inkjet head, the maintenance liquid is applied to at least one of the ejection surface of the inkjet head and a wipe member that wipes the ejection surface. and a wiping step of wiping the discharge surface with a wipe member after applying the maintenance liquid.

(Maintenance liquid application process)
The maintenance liquid application process is a process of applying maintenance liquid to at least one of the ejection surface of the inkjet head and the wipe member that wipes the ejection surface, after the ink is ejected from the nozzle of the inkjet head.

Examples of methods for applying the maintenance liquid include coating using a roller and spraying.

The maintenance liquid may be applied to the ejection surface of the inkjet head, may be applied to a wipe member that wipes the ejection surface, or may be applied to both the ejection surface of the inkjet head and the wipe member.

The inkjet head preferably includes a nozzle plate, and the nozzle plate preferably has a liquid-repellent film. Preferably, the liquid-repellent film contains a fluorine compound.

Examples of the nozzle plate include the nozzle plate described in paragraphs 0206 to 0214 of JP-A No. 2013-223958 and FIGS. 3 and 4, and the nozzle plate described in FIG. 1C of Japanese Patent Publication No. 2008-544852. It will be done.

The SP value of the liquid-repellent film is not particularly limited, but from the viewpoint of further improving ink cutting properties, it is preferably 16.00 MPa ^1/2 or less, more preferably 15.00 MPa ^1/2 or less, and 13.00 MPa ^1/2 The following are particularly preferred. Note that the SP value here is a value calculated by the Okitsu method.

The fluorine compound contained in the liquid-repellent film is preferably a compound having a fluorinated alkyl group.

The liquid-repellent film is preferably a liquid-repellent film made using a fluorinated alkylsilane compound or a compound having a perfluoropolyether structure.

The fluorinated alkylsilane compound is preferably a fluorinated alkylsilane compound represented by the following formula (F). The fluorinated alkylsilane compound represented by formula (F) is a silane coupling compound.
C _n F _2n+1 -C _m H _2m -Si-X ₃ ...(F)
In formula (F), n represents an integer of 1 or more, and m represents 0 or an integer of 1 or more. X represents an alkoxy group, an amino group, or a halogen atom. Note that a part of X may be substituted with an alkyl group.

Examples of fluorinated alkylsilane compounds include C ₈ F ₁₇ C ₂ H ₄ SiCl ₃ (also referred to as "1H, 1H, 2H, 2H-perfluorodecyltrichlorosilane" or "FDTS"), CF ₃ (CF ₂ ) ₈ Fluoroalkyltrichlorosilane such as C ₂ H ₄ SiCl ₃ ; CF ₃ (CF ₂ ) ₈ C ₂ H ₄ Si(OCH ₃ ) ₃ , 3,3,3-trifluoropropyltrimethoxysilane, tridecafluoro-1 , 1,2,2-tetrahydrooctyltrimethoxysilane, and heptadecafluoro-1,1,2,2-tetrahydrodecyltrimethoxysilane.

Among them, from the viewpoint of liquid repellency and durability, the fluorinated alkylsilane compound represented by the formula (F) has a compound in which n is an integer of 1 to 14, and m is an integer of 0 or 1 to 5. , compounds in which X is an alkoxy group or a halogen atom are preferred, and compounds in which n is an integer of 1 to 12, m is an integer of 0 to 3, and X is an alkoxy group or a halogen atom are more preferred. In particular, _the fluorinated alkylsilane compound represented _by formula _{( F} ) is preferably _{C8F17C2H4SiCl3} .

Examples of the perfluoropolyether structure include structures represented by the following formulas 1 to 3. Among these, the perfluoropolyether structure is preferably a structure represented by the following formula 1.

CF ₃ O-(CF ₂ O) _n -(CF ₂ CF ₂ O) _m -*...(1)
In Formula 1, m represents an integer from 0 to 200, n represents an integer from 0 to 300, and m+n is 1 or more. * indicates the bonding position with other structures in the compound.

In Formula 1, m is preferably an integer of 0 to 50, more preferably an integer of 1 to 50. Further, n is preferably an integer of 0 to 50, more preferably an integer of 1 to 50.

CF ₃ -(CF ₂ OCF ₂ O) _n -*...(2)
In Formula 2, n represents an integer from 1 to 100. * indicates the bonding position with other structures in the compound.

CF ₃ -(CF ₂ O) _n -*...(3)
In Formula 3, n represents an integer from 1 to 300. * indicates the bonding position with other structures in the compound.

The thickness of the liquid-repellent film is not particularly limited, but is preferably 0.2 nm to 30 nm, more preferably 0.4 nm to 20 nm. Although there is no particular problem with the thickness of the liquid-repellent film in a range exceeding 30 nm, a thickness of 30 nm or less is advantageous in terms of film uniformity, and a thickness of 0.2 nm or more provides good water repellency to ink. be.

Examples of the liquid-repellent film include a monomolecular film of a fluorinated alkylsilane compound (in other words, a SAM film) and a laminated film of a fluorinated alkylsilane compound. The laminated film of a fluorinated alkylsilane compound includes a film in which a fluorinated alkylsilane compound is laminated without being polymerized, as well as a polymerized film of a fluorinated alkylsilane compound.

The liquid-repellent film can be formed, for example, by the method described in paragraphs 0114 to 0124 of JP-A No. 2011-111527.

Specifically, the liquid-repellent film is formed by chemical vapor deposition, coating with fluororesin, eutectoid plating with fluoropolymer, etc., fluorine silane treatment, aminosilane treatment, or fluorocarbon plasma polymerization. be able to.

More specifically, the method for forming the liquid-repellent film includes the following method.

A first example is a method in which a fluoroalkyltrichlorosilane such as CF ₃ (CF ₂ ) ₈ C ₂ H ₄ SiCl ₃ is reacted with a base material to form a water-repellent monomolecular film or polymer film ( For example, see Japanese Patent No. 2500816 and Japanese Patent No. 2525536).

In CF ₃ (CF ₂ ) ₈ C ₂ H ₄ SiCl ₃ , CF ₃ (CF ₂ ) ₈ C ₂ H ₄ - is a fluoroalkyl group, and -SiCl ₃ is a trichlorosilyl group.

In this method, a base material on which active hydrogen exists is exposed to a solution in which fluoroalkyltrichlorosilane is dissolved, and the chlorosilyl group (-SiCl) and active hydrogen are reacted to form a Si-O bond with the base material. . As a result, the fluoroalkyl group is fixed to the substrate via Si--O. Here, the fluoroalkyl group imparts liquid repellency to the membrane. Depending on the film formation conditions, the liquid-repellent film can be a monomolecular film or a polymeric film.

As a second example, a porous substrate impregnated with a compound having a fluoroalkyl group such as a fluoroalkylalkoxysilane such as CF ₃ (CF ₂ ) ₈ C ₂ H ₄ Si(OCH ₃ ) ₃ is prepared in a vacuum. Examples include a method of heating to evaporate a compound having a fluoroalkyl group to make the surface of the substrate water repellent (see, for example, Japanese Patent Application Laid-Open No. 6-143586).

In this method, an intermediate layer such as silicon dioxide may be provided in order to improve the adhesion between the liquid-repellent film and the base material.

A third example is a method of forming fluoroalkylsilane on the surface of a substrate by chemical vapor deposition using a compound such as fluoroalkyltrichlorosilane such as CF ₃ (CF ₂ ) ₈ C ₂ H ₄ SiCl ₃ . (For example, see Japanese Patent Application Laid-Open No. 2000-282240).

A fourth example is a method in which fine particles of oxide such as zirconia or alumina are formed on the surface of a base material, and then a compound such as fluoroalkylchlorosilane or fluoroalkylalkoxysilane is applied thereon (for example, JP-A-6 -Refer to Publication No. 171094).

As a fifth example, by hydrolyzing and dehydrating a mixed solution of fluoroalkylalkoxysilane and metal alkoxide, and then applying this solution to a base material and baking it, fluoroalkyl chains are formed in the metal oxide. (For example, see Japanese Patent No. 2687060, Japanese Patent No. 2874391, Japanese Patent No. 2729714, and Japanese Patent No. 2555797).

In this method, the fluoroalkyl chains impart water repellency to the membrane and the metal oxides impart high mechanical strength to the membrane.

Among the above formation methods, the chemical vapor deposition method mentioned as the third example is preferred.

In the chemical vapor deposition method, a container containing a fluorinated alkylsilane compound and a nozzle plate (for example, a nozzle plate made from a silicon substrate) are placed in a closed container made of Teflon (registered trademark). One example is an embodiment in which molecules of the fluorinated alkylsilane compound are deposited on the surface of the nozzle plate by placing the whole in an electric furnace and raising the temperature to evaporate the fluorinated alkylsilane compound.

For example, a monomolecular film of a fluorinated alkylsilane compound can be formed on a nozzle plate by chemical vapor deposition. In this case, the vapor deposition surface of the nozzle plate is preferably made hydrophilic. For example, by cleaning the surface of a nozzle plate made from a silicon substrate using ultraviolet light (wavelength: 172 nm), organic impurities are removed and a clean surface is obtained. At this time, since the silicon surface is naturally oxidized and covered with a SiO ₂ film, water vapor in the atmosphere is immediately adsorbed to the surface, and the surface is covered with hydroxyl groups, making it a hydrophilic surface.

Another embodiment of the chemical vapor deposition method includes the following method.

That is, a lyophobic film is deposited on the surface of a silicon substrate by introducing a fluoroalkyltrichlorosilane compound such as CF ₃ (CF ₂ ) ₈ C ₂ H ₄ SiCl ₃ and water vapor into a CVD reactor at low pressure. I can do it.

The partial pressure of the fluoroalkyltrichlorosilane compound such as CF ₃ (CF ₂ ) ₈ C ₂ H ₄ SiCl ₃ is preferably from 0.05 torr to 1 torr (that is, from 6.67 Pa to 133.3 Pa), (more preferably from 6.67 Pa to 133.3 Pa). is preferably 0.1 to 0.5 torr (13.3 to 66.5 Pa)), and the partial pressure of H ₂ O is preferably between 0.05 torr and 20 torr (preferably 0.1 torr to 2 torr). .

The deposition temperature can be between room temperature and 100°C. The coating process can be performed, for example, by Applied Micro Structures, Inc. It can be carried out using a Molecular Vapor Deposition (MVD) TM machine from Co., Ltd.

(wiping process)
The wiping process is a process of wiping the discharge surface with a wipe member. The wipe member is preferably at least one selected from the group consisting of fabric, nonwoven fabric, blade, and sponge. Further, the material forming the wipe member may be at least one selected from the group consisting of resin, rubber, and composite materials thereof.

EXAMPLES Hereinafter, the present disclosure will be explained in more detail with reference to Examples, but the present disclosure is not limited to the following Examples unless the gist thereof is exceeded.

In the examples, weight average molecular weights were measured by gel permeation chromatography (GPC). Specifically, the measurement by GPC uses HLC (registered trademark)-8020GPC (manufactured by Tosoh Corporation) as a measuring device, and TSKgel (registered trademark) Super Multipore HZ-H (4.6 mm ID x 15 cm, manufactured by Tosoh Corporation) as a column. Three bottles of THF (Tetrahydrofuran) were used as the eluent. Further, the measurement was performed using an RI detector with a sample concentration of 0.45% by mass, a flow rate of 0.35 ml/min, a sample injection amount of 10 μl, and a measurement temperature of 40° C. The calibration curve is "standard sample TSK standard, polystyrene" manufactured by Tosoh Corporation: "F-40", "F-20", "F-4", "F-1", "A-5000", "A- 2500'', ``A-1000'', and 8 samples of ``n-propylbenzene''.

The acid value was measured according to the method described in JIS K0070:1992.

The average particle diameter of the pigment contained in the ink was measured by the following method. First, the ink was diluted with water, and the solid concentration of the pigment in the ink was adjusted to 2% by mass. Next, the diluted ink was measured at 25° C. by a dynamic light scattering method using a Nanotrac particle size distribution analyzer (product name "UPA-EX150", manufactured by Nikkiso Co., Ltd.).

The pH of the ink was measured at 25° C. using a desktop pH meter (product name: LAQUAF-74S, manufactured by Horiba, Ltd.).

The surface tension of the ink was measured at 25° C. by the plate method using an automatic surface tension meter (product name “DY-300”, manufactured by Kyowa Interface Science Co., Ltd.).

The viscosity of the ink was measured at 30° C. using a viscometer (product name “TVB-22L”, manufactured by Toki Sangyo Co., Ltd.).

<Preparation of black ink K1>
First, an aqueous dispersion of polymer particles B1 used for preparing black ink K1 was prepared.

-Preparation of aqueous dispersion B1 of polymer particles-
A 2-liter three-neck flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube was charged with 293 g of methyl ethyl ketone, and the temperature was raised to 80°C. While maintaining the temperature inside the reaction vessel at 80°C, 165.7 g of methyl methacrylate, 63.7 g of isobornyl methacrylate, 25.5 g of methacrylic acid, 48 g of methyl ethyl ketone, and dimethyl 2,2'-azobis(isobutyrate) (product name: A mixed solution consisting of 1.25 g of "V-601" (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) was added dropwise at a constant speed so that the addition was completed in 2 hours. After the dropwise addition was completed, a mixed solution of 0.60 g of "V-601" and 5.0 g of methyl ethyl ketone was added, and the mixture was further stirred for 2 hours. Thereafter, the process of adding the above mixed solution and stirring for 2 hours was repeated 4 times, and then a mixed solution of 0.60 g of "V-601" and 5.0 g of methyl ethyl ketone was added and stirred for 3 hours. Thereby, a polymer solution was obtained. The weight average molecular weight (Mw) of the polymer was 72,000, and the acid value was 62.9 mgKOH/g.
Next, 588.2 g of the polymer solution was weighed, 165 g of isopropanol and 120.8 mL of a 1 mol/L aqueous sodium hydroxide solution were added to the polymer solution, and the temperature inside the reaction vessel was raised to 80°C. Next, 718.0 g of distilled water was dropped into the reaction container at a rate of 20 mL/min. Thereafter, the temperature inside 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 then the pressure inside the reaction vessel was reduced and the isopropanol, methyl ethyl ketone, and distilled water were combined. A total of 913.7g was distilled off. Thereby, an aqueous dispersion B1 of polymer particles having a solid content concentration of 23.0% by mass was obtained. In the polymer contained in the polymer particles, the ratio (mass ratio) of structural units derived from methyl methacrylate, structural units derived from isobornyl methacrylate, and structural units derived from methacrylic acid was 65:25:10. .

-Preparation of black ink K1-
After mixing and stirring the following components, the mixture was filtered under pressure using a microfilter with a pore size of 0.2 μm (manufactured by Fuji Film Corporation) to prepare black ink K1.
- Cyan pigment dispersion: Pigment dispersion containing Pigment Blue 15:3 (product name "Pro-jet Cyan APD1000", manufactured by FUJIFILM Imaging Colorants, pigment concentration 14.0% by mass)...3.40% by mass
- Magenta pigment dispersion: Pigment dispersion containing Pigment Red 122 (product name "Pro-Jet Magenta APD1000", pigment concentration 14.0% by mass)...5.00% by mass
・Black pigment dispersion: Pigment dispersion containing Pigment Black 7 (product name "Pro-Jet Black APD1000", pigment concentration 14.0% by mass) ...18.30% by mass
・Aqueous dispersion of polymer particles B1 (solid content concentration: 23.0% by mass) ...28.40% by mass
・1,2-propanediol...2.40% by mass
・Polyoxypropylene glyceryl ether: Product name “SANNIX GP-250”, manufactured by Sanyo Chemical Industries, Ltd.…6.40% by mass
・Polyethylene glycol: Product name “PEG200”, manufactured by Sanyo Chemical Industries, Ltd.…2.50% by mass
・Tripropylene glycol monomethyl ether: Product name “MFTG”, manufactured by Nippon Nyukazai Co., Ltd.…2.00% by mass
・Polyvinylpyrrolidone: Product name “PVP K15”, manufactured by Tokyo Kasei Kogyo Co., Ltd.…0.10% by mass
・Urea...5.00% by mass
・Acetylene glycol surfactant: Product name “OLFINE E1020”, manufactured by Nissin Chemical Industry Co., Ltd.…1.30% by mass
・Aqueous dispersion of ester wax: Product name "Cellosol 524D", manufactured by Chukyo Yushi Co., Ltd., solid content concentration 20% by mass...6.50% by mass
・Aqueous dispersion of colloidal silica: Product name “Snowtex
・Silicone antifoaming agent: Product name “BYK-024”, manufactured by BYK-Chemie Japan Co., Ltd.…0.01% by mass
・Fluorine surfactant: Product name "Capstone FS-63", manufactured by DuPont...0.02% by mass
・Water…18.40% by mass

The average particle diameter of the pigment contained in black ink K1 was 110 nm. Black ink K1 had a pH of 8.2, a viscosity of 5.0 mPa·s, and a surface tension of 37.2 mN/m.

<Preparation of white ink W1>
First, a dispersion liquid T1 of titanium dioxide used for preparing white ink W1 was prepared. Further, a dispersant P1 was prepared to be used for preparing a titanium dioxide dispersion T1.

-Preparation of dispersant P1-
Dipropylene glycol in an amount equal to the total amount of monomers described below was added to a three-necked flask equipped with a stirrer and a cooling tube, and the temperature was raised to 85° C. under a nitrogen atmosphere. 9.1 molar equivalents of stearyl methacrylate, 34.0 molar equivalents of benzyl methacrylate, 31.9 molar equivalents of hydroxyethyl methacrylate, 25.0 molar equivalents of methacrylic acid, and 0.8 molar equivalents of 2-mercaptopropionic acid were mixed to form a solution. I got 1. In addition, t-butylperoxy-2-ethylhexanoate (product name "Perbutyl O", manufactured by NOF Corporation) was added in an amount of 1% by mass based on the total mass of the above monomers, and 20% by mass based on the total mass of the above monomers. Solution 2 was obtained by dissolving it in dipropylene glycol. Solution 1 was added dropwise to the three-necked flask over a period of 4 hours, and solution 2 was added dropwise over a period of 5 hours. After the dropwise addition was completed, the reaction was continued for another 2 hours, the temperature was raised to 95°C, and the mixture was stirred for 3 hours to allow all of the monomers to react. Disappearance of the monomer was confirmed by ¹ H-NMR (nuclear magnetic resonance). The temperature of the obtained reaction solution was raised to 70° C., and 20.0 molar equivalents of dimethylethanolamine were added to the reaction solution, followed by the addition of propylene glycol and stirring. This resulted in a 30% by mass solution of the polymer. The obtained polymer was designated as dispersant P1. The weight average molecular weight (Mw) of the dispersant P1 was 22,000. The dispersant P1 has a ratio (mass ratio) of structural units derived from stearyl methacrylate, structural units derived from benzyl methacrylate, structural units derived from hydroxyethyl methacrylate, and structural units derived from methacrylic acid of 20:39:27. :14. The above mass ratio was confirmed by ¹ H-NMR. The above mass ratio is a value that does not include dimethylaminoethanol.

-Preparation of titanium dioxide dispersion T1-
In a zirconia container, 45 parts by mass of titanium dioxide (trade name "PF-690", manufactured by Ishihara Sangyo Co., Ltd., average primary particle diameter: 210 nm), 15 parts by mass of a 30% by mass solution of the dispersant P1, and ultrapure. 40 parts by mass of water was added. Furthermore, 40 parts by mass of 0.5 mmφ zirconia beads (product name "Treceram beads", manufactured by Toray Industries, Inc.) were added and mixed lightly with a spatula. Dispersion was carried out for 5 hours at a rotation speed of 1,000 rpm (revolutions per minute) using a dispersing machine (product name: "Ready Mill Model LSG-4U-08", manufactured by Imex). After the dispersion was completed, the beads were removed by filtration with a filter cloth to obtain a titanium dioxide dispersion T1 having a solid content concentration of 45% by mass.

-Preparation of white ink W1-
The following components were mixed, stirred, and filtered under pressure using a microfilter with a pore size of 0.2 μm (manufactured by Fuji Film Corporation) to prepare white ink W1.
・Titanium dioxide dispersion T1 (solid content concentration: 45% by mass) ...22.50% by mass
・Aqueous dispersion of polymer particles B1 (solid content concentration: 23.0% by mass) ...21.00% by mass
・1,2-propanediol...27.00% by mass
・Polyvinylpyrrolidone: Product name “PVP K15”, manufactured by Tokyo Kasei Kogyo Co., Ltd.…0.10% by mass
・Acetylene glycol surfactant: Product name “OLFINE E1020”, manufactured by Nissin Chemical Industry Co., Ltd.…1.30% by mass
・Aqueous dispersion of colloidal silica: Product name “Snowtex
・Silicone antifoaming agent: Product name “BYK-024”, manufactured by BYK-Chemie Japan Co., Ltd.…0.01% by mass
・Water…27.80% by mass

The average particle diameter of the pigment contained in white ink W1 was 220 nm. White ink W1 had a pH of 8.1, a viscosity of 5.6 mPa·s, and a surface tension of 36.0 mN/m.

<Preparation of maintenance liquids CL1 to CL13>
The components listed in Tables 1 and 2 were mixed so as to have the contents (mass%) listed in Tables 1 and 2. Thereafter, sodium hydrogen carbonate or acetic acid was added as necessary to adjust the pH to 8.0 to 8.8. The obtained mixture was filtered using a polyvinylidene fluoride (PVDF) 5 μm filter (product name "Millex SV", manufactured by Millipore, diameter: 25 mm) connected to a plastic disposable syringe to obtain maintenance solutions CL1 to CL13. I got it.

Details of the components listed in Tables 1 and 2 are as follows. In Tables 1 and 2, the contents of colloidal silica and polymer particles indicate the contents as solid content. Further, the total content of the maintenance liquid is 100% by mass, and the remaining amount is the content of water. Components that are not included are marked with a "-".

・DEG: Diethylene glycol ・DEGmBE: Diethylene glycol monobutyl ether ・Nonionic surfactant: Product name "Pionin D-1706-N", manufactured by Takemoto Yushi Co., Ltd., main component polyoxyethylene decyl ether Colloidal silica: Product name "Snowtex XS" (Aqueous dispersion of colloidal silica, solid content concentration 20% by mass), manufactured by Nissan Chemical Industries, Ltd., average particle size 5 nm
・Silicone antifoaming agent 1: Product name “BYK-024”, manufactured by BYK-Chemie Japan Co., Ltd. ・Polymer particle 1: Product name “Eposter MX050W” (aqueous dispersion of acrylic crosslinked particles, solid content concentration 10% by mass, Japan) (manufactured by Shokubai Co., Ltd.), average particle size 70 nm
・Polymer particle 2: Product name "Eposter MX100W" (aqueous dispersion of acrylic crosslinked particles, solid content concentration 10% by mass, manufactured by Nippon Shokubai Co., Ltd.), average particle size 150 nm
- Polymer particles 3: Product name "Eposter MX200W" (aqueous dispersion of acrylic crosslinked particles, solid content concentration 10% by mass, manufactured by Nippon Shokubai Co., Ltd.), average particle size 350 nm
・Polymer particles 4: Product name "Eposter MX300W" (aqueous dispersion of acrylic crosslinked particles, solid content concentration 10% by mass, manufactured by Nippon Shokubai Co., Ltd.), average particle size 450 nm

[Example 1 to Example 6, Comparative Example 1 to Comparative Example 7]
When the inkjet head was maintained using black ink K1 and maintenance liquids CL1 to CL13, the degree of wear on the ejection surface of the inkjet head and the cleanability were evaluated. The evaluation results are shown in Table 3. The evaluation method is as follows.

(Degree of wear on the discharge surface)
An inkjet head was prepared in which a liquid-repellent film containing a compound having a perfluoroalkyl structure was formed on the surface of the ejection side. Before performing the abrasion operation described below, the contact angle (°) between the liquid-repellent film and water was measured. Next, a silicone rubber roller with a diameter of 40 mm was prepared, and a fabric (product name: Toraysee (registered trademark), manufactured by Toray Industries, Inc.) was wrapped around the outer circumferential surface of the roller.Next, black ink was applied to the fabric wrapped around the roller. K1 (1 mL) and maintenance liquid (1 mL) were soaked in. Next, the fabric and the liquid-repellent film were brought into contact, and a roller was pressed against the liquid-repellent film so that the contact pressure between the two was 40 kPa. In this state, the fabric was rubbed against the liquid-repellent film by reciprocating the roller 3500 times at a speed of 50 reciprocations per minute.Hereinafter, this operation will be referred to as "abrasion operation." During the 3500 reciprocating movements in the abrasion operation, the fabric was additionally impregnated with black ink K1 (0.5 mL) every 50 reciprocations, and the fabric was replaced with a fresh one every 1000 reciprocations. After the abrasion operation was completed, the contact angle (° C.) between the liquid-repellent film and water after the abrasion operation was measured.
The degree of decrease in contact angle was calculated by subtracting the contact angle after the abrasion operation from the contact angle before the abrasion operation. The degree of wear on the ejection surface was evaluated based on the calculated degree of decrease in the contact angle. The evaluation criteria are as follows. It was determined that the smaller the degree of decrease in the contact angle, the more the progress of wear on the ejection surface was suppressed. A and B are at levels that pose no practical problems.
A: The degree of decrease in contact angle was less than 10°.
B: The degree of decrease in contact angle was 10° or more and less than 15°.
C: The degree of decrease in contact angle was 15° or more and less than 25°.
D: The degree of decrease in contact angle was 25° or more and less than 30°.
E: The degree of decrease in contact angle was 30° or more.

(Cleanability)
An inkjet head having a liquid-repellent film formed on the surface of the ejection side was prepared. 1 mL of black ink K1 was dropped on the liquid-repellent film. The ink was allowed to dry for two days at room temperature. A silicone rubber roller with a diameter of 40 mm was prepared, and a fabric (product name: Toraysee (registered trademark), manufactured by Toray Industries, Inc.) was wrapped around the outer circumferential surface of the roller. Next, maintenance liquid (2 mL) was applied to the fabric wrapped around the roller. The fabric and the liquid-repellent film were brought into contact, and a roller was pressed against the liquid-repellent film so that the contact pressure between the two was 40 kPa.In this state, the roller was moved at a speed of 50 reciprocations per minute. The dried ink formed on the liquid-repellent film was rubbed with the cloth impregnated with the maintenance liquid by reciprocating the ink three times.Then, the residue on the liquid-repellent film was visually observed. The cleaning performance was evaluated based on the amount of material.The evaluation criteria are as follows.The smaller the amount of residual material, the better the cleaning performance.A to C are levels that pose no problem in practical use. It is.
A: There was no residue at all.
B: The amount of residual material was extremely small.
C: The amount of residual material was small.
D: The amount of residual material was slightly large.
E: The amount of residual material was extremely large.

As shown in Table 3, in Examples 1 to 6, the ink contained a pigment, the maintenance liquid contained polymer particles containing an acrylic resin, and the content of polymer particles was 3% relative to the total amount of the maintenance liquid. % to 25% by mass, and the average particle diameter of the polymer particles is 3.5 times or more larger than the average particle diameter of the pigment, so that the residue of deposits on the discharge surface is suppressed, and the It was found that wear was suppressed.

On the other hand, in Comparative Example 1, the maintenance liquid did not contain polymer particles, and it was found that wear of the discharge surface progressed.

In Comparative Examples 2 to 4, the average particle diameter of the polymer particles was less than 3.5 times the average particle diameter of the pigment, and it was found that wear of the ejection surface progressed.

In Comparative Example 5, the content of polymer particles was less than 3% by mass based on the total amount of maintenance liquid, and it was found that wear of the discharge surface progressed.

In Comparative Examples 6 and 7, the content of polymer particles was more than 25% by mass based on the total amount of maintenance liquid, and it was found that deposits remained on the discharge surface.

<Preparation of maintenance liquids CL14 to CL17>
Each component listed in Table 4 was mixed to have the content (mass%) listed in Table 4, and maintenance solutions CL14 to CL17 were prepared in the same manner as maintenance solution CL1.

Details of the components listed in Table 4 are as follows. Description of the same components as those of maintenance liquids CL1 to CL13 will be omitted. In Table 4, the contents of colloidal silica and polymer particles indicate the contents as solid content. Further, the total content of the maintenance liquid is 100% by mass, and the remaining amount is the content of water. Components that are not included are marked with a "-".

・DEGmEE: diethylene glycol monoethyl ether ・Silicone antifoaming agent 2: Product name "BYK-093", manufactured by BYK Chemie Japan Co., Ltd. ・Polymer particles 5: Product name "Tufftic F-167" (aqueous dispersion of acrylic particles, Solid content concentration 27% by mass, manufactured by Nippon Exlan Kogyo Co., Ltd.), average particle size 0.3 μm
・Polymer particles 6: Product name "Toughtic F-200" (aqueous dispersion of acrylic particles, solid content concentration 30% by mass, manufactured by Nippon Exlan Kogyo Co., Ltd.), average particle size 3.0 μm

[Example 7 to Example 8, Comparative Example 8 to Comparative Example 13]
When the inkjet head was maintained using black ink K1, white ink W1, and maintenance liquids CL14 to CL17, the degree of wear on the ejection surface of the inkjet head and the cleanability were evaluated. The evaluation results are shown in Table 5. The evaluation method was the same as in Example 1.

As shown in Table 5, in Examples 7 and 8, the ink contained a pigment, the maintenance liquid contained polymer particles containing an acrylic resin, and the content of the polymer particles was 3% relative to the total amount of the maintenance liquid. % to 25% by mass, and the average particle diameter of the polymer particles is 3.5 times or more larger than the average particle diameter of the pigment, so that the residue of deposits on the discharge surface is suppressed, and the It was found that wear was suppressed.

On the other hand, in Comparative Example 8 and Comparative Example 11, the average particle diameter of the polymer particles was less than 3.5 times the average particle diameter of the pigment, and it was found that wear of the ejection surface progressed.

In Comparative Example 9 and Comparative Example 12, the content of polymer particles was less than 3% by mass based on the total amount of maintenance liquid, and it was found that wear of the discharge surface progressed.

In Comparative Example 10 and Comparative Example 13, the content of polymer particles was more than 25% by mass based on the total amount of maintenance liquid, and it was found that deposits remained on the discharge surface.

<Preparation of maintenance liquids CL18 to CL24>
Each component listed in Table 6 was mixed to have the content (mass%) listed in Table 6, and maintenance solutions CL18 to CL24 were prepared in the same manner as maintenance solution CL1.

Details of the components listed in Table 6 are as follows. Description of the same components as those of maintenance liquids CL1 to CL13 will be omitted. In Table 6, the contents of colloidal silica and polymer particles indicate the contents as solid content. Further, the total content of the maintenance liquid is 100% by mass, and the remaining amount is the content of water. Components that are not included are marked with a "-".

・TEG: Triethylene glycol Polymer particle 7: Product name "SB Latex 0561" (aqueous dispersion of styrene-butadiene copolymer, solid content concentration 69% by mass, manufactured by JSR Corporation), average particle size 700 nm
・Polymer particles 8: Product name "KM-9729" (aqueous dispersion of silicone rubber, solid content concentration 52% by mass, manufactured by Shin-Etsu Chemical Co., Ltd.), average particle size 2.0 μm
・Polymer particles 9: Product name "X-52-1133" (aqueous dispersion of silicone rubber, solid content concentration 51% by mass, manufactured by Shin-Etsu Chemical Co., Ltd.), average particle size 5.0 μm
・Polymer particle 10: Product name "Tospearl 130" (silicone resin particles, manufactured by Momentive Performance Materials Japan), average particle size 3.0 μm
・Polymer particles 11: Product name "Tospearl 145" (silicone resin particles, manufactured by Momentive Performance Materials Japan), average particle size 4.5 μm
・Polymer particles 12: Product name "FLUOTRON115" (aqueous dispersion of fluororesin, solid content concentration 42% by mass, manufactured by Nippon Lubrizol Co., Ltd.), average particle size 2.8 μm
- Polymer particles 13: Product name "Hydran WLI-611" (urethane resin aqueous dispersion, solid content concentration 39.5% by mass, manufactured by DIC Corporation), average particle size 0.4 μm

[Example 9 to Example 21]
When the inkjet head was maintained using black ink K1, white ink W1, and maintenance liquids CL18 to CL24, the degree of wear on the ejection surface of the inkjet head and the cleaning performance were evaluated. The evaluation results are shown in Table 7. The evaluation method was the same as in Example 1.

As shown in Table 7, in Examples 9 to 21, the ink contained a pigment, the maintenance liquid contained polymer particles containing a styrene-butadiene copolymer, a silicone resin, a fluororesin, or a urethane resin, and Since the particle content is 3% to 25% by mass based on the total amount of maintenance liquid, and the average particle diameter of the polymer particles is 3.5 times or more the average particle diameter of the pigment, It was found that the residue of deposits was suppressed and the wear of the discharge surface was suppressed.

In Example 1, similar effects were obtained when the water-repellent film was changed to a compound having a perfluoropolyether structure.

Claims (10)

an ink containing a pigment;
a maintenance liquid containing polymer particles;
Equipped with
The content of the polymer particles is 3% by mass to 25% by mass based on the total amount of the maintenance liquid,
An ink set, wherein the average particle diameter of the polymer particles is 3.5 times or more the average particle diameter of the pigment. The ink set according to claim 1, wherein the pigment is an inorganic pigment. The ink set according to claim 1 or 2, wherein the pigment is carbon black or titanium dioxide. The polymer particles include a polymer containing at least one member selected from the group consisting of a structural unit derived from a vinyl compound and a structural unit derived from a vinylidene compound, a urethane resin, an ether resin, an ester resin, an amino resin, an amide resin, and a phenol resin. The ink set according to any one of claims 1 to 3, comprising at least one polymer selected from the group consisting of , fluororesin, and silicone resin. The polymer particles are selected from the group consisting of structural units derived from (meth)acrylic compounds, structural units derived from styrene, structural units derived from ethylene, structural units derived from propylene, structural units derived from vinyl chloride, and structural units derived from vinyl acetate. The ink set according to any one of claims 1 to 4, comprising at least one polymer selected from the group consisting of at least one polymer selected from the group consisting of a urethane resin, and an ester resin. . The ink set according to any one of claims 1 to 5, wherein the polymer particles have an average particle diameter of 400 nm to 5000 nm. The ink set according to any one of claims 1 to 6 is used,
After the ink is ejected from the nozzle of the inkjet head, a maintenance liquid applying step of applying the maintenance liquid to at least one of the ejection surface of the inkjet head and a wipe member that wipes the ejection surface;
A maintenance method comprising the step of wiping the discharge surface with the wipe member after applying the maintenance liquid. The maintenance method according to claim 7, wherein the wipe member is at least one member selected from the group consisting of cloth, nonwoven fabric, blade, and sponge. The maintenance method according to claim 7 or 8, wherein the inkjet head has a liquid-repellent film. The maintenance method according to claim 9, wherein the liquid-repellent film contains a fluorine compound.