JP5496927B2 - Ink set, cleaning method and image forming method - Google Patents

Description

  The present invention relates to an ink set, a maintenance liquid, a cleaning method, and an image forming method.

  The ink jet recording method is a method of performing recording by ejecting droplet-shaped ink from a large number of nozzles formed on an ink jet recording head toward a recording medium and fixing the ink to the recording medium. The ink used in the ink jet recording method is generally composed mainly of water and containing at least a coloring component and an organic solvent. However, the ink contains a pigment as a coloring component for the purpose of improving the storage stability of the image. Inks containing resin particles have been proposed for the purpose of improving film quality.

In the ink jet recording method, a part of the ink ejected from the ink jet recording head adheres to the nozzle surface of the ink jet recording head and thickens and solidifies, resulting in ejection abnormalities such as abnormal ink ejection amount and ejection direction abnormality. There is. In particular, in a commercial inkjet printer, since ink is continuously ejected for a relatively long time, a large amount of ink is misted around the nozzle surface, and the ambient temperature around the nozzle surface is increased by continuous operation. When the above conditions overlap, the thickened product and the solidified product (ink-adhered product) generated by drying the ink are likely to adhere to the nozzle surface.
Therefore, in the ink jet recording apparatus, it is necessary to clean the ink jet recording head including the nozzle surface, and various maintenance liquids (also referred to as “cleaning liquids”) have been developed in accordance with the ink composition. (For example, refer patent documents 1-9).

JP 2010-137458 A JP 2009-096113 A JP 2007-119658 A Japanese Patent Laid-Open No. 2005-007703 JP 2001-113727 A JP-A-11-157087 JP 11-152499 A Japanese Patent Laid-Open No. 4-115595 Japanese Patent No. 2650284

  Among inks for inkjet recording, ink containing pigments and resin particles tends to thicken and solidify when attached to the nozzle surface, etc., and is difficult to re-dissolve after solidification. Improvement was desired. Further, in the market, there has been a demand for further increase in the processing speed of the ink jet recording apparatus, and a reduction in the time required for cleaning the ink jet recording head with the maintenance liquid has been demanded.

In view of the above, an object of the present invention is to provide an ink set and a maintenance liquid that are excellent in cleaning properties of an ink-fixed matter, and to achieve the object.
Another object of the present invention is to provide a cleaning method and an image forming method using the ink set, and to achieve the object.

Specific means for solving the above-described problems are as follows.
<1> At least an ink composition containing a pigment, resin particles, and water, at least 50% by mass to 75% by mass water based on the total mass, and an alkylene glycol monoalkyl ether having an alkyl group with 4 or less carbon atoms. And a maintenance liquid containing at least one selected from alkylene glycol monoalkyl ether and alkylene glycol monoaryl ether having 5 or more carbon atoms in the alkyl group.
<2> The total content of the alkylene glycol monoalkyl ether having 4 or less carbon atoms in the alkyl group is 20% by mass or more and 40% by mass or less with respect to the total mass of the maintenance liquid. Ink set.
<3> The total content of the alkylene glycol monoalkyl ether having 5 or more carbon atoms in the alkyl group and the alkylene glycol monoaryl ether is 1% by mass to 10% by mass with respect to the total mass of the maintenance liquid. The ink set according to <1> or <2>.
<4> The ink set according to any one of <1> to <3>, wherein the maintenance liquid further contains at least one alkylene glycol monoalkyl ether acetate.
< 5 > The ink set according to any one of <1> to <4> is used, and a maintenance liquid in the ink set is provided on a nozzle surface of an inkjet recording head that discharges an ink composition in the ink set. Giving a cleaning method.
< 6 > The cleaning method according to < 5 >, wherein the nozzle surface is wiped after the maintenance liquid is applied.
< 7 > An ink that uses the ink set according to any one of <1> to <4>, and that applies ink onto a recording medium by ejecting an ink composition in the ink set from an inkjet recording head. An image forming method comprising: an applying step; and a cleaning step of applying a maintenance liquid in the ink set to a nozzle surface of the inkjet recording head.

  According to the present invention, it is possible to provide an ink set and a maintenance liquid that are excellent in the washability of the fixed ink. Further, according to the present invention, it is possible to provide a cleaning method and an image forming method using the ink set.

The perspective view which showed schematic structure of the cleaning apparatus of the inkjet recording head with which implementation of the cleaning method of this invention is carried out The front view which showed schematic structure of the cleaning apparatus of the head for inkjet recording used for implementation of the cleaning method of this invention

Hereinafter, although the form for implementing this invention is demonstrated in detail, this invention is not limited to this, A various deformation | transformation can be implemented within the range of the meaning.
In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.

  In the present specification, the ink fixed product refers to a thickened product and a solidified product produced by removing at least a part of the solvent from the ink composition.

≪Ink set≫
The ink set of the present invention is
An ink composition containing a pigment, resin particles, and water;
50% by mass to 75% by mass of water based on the total mass, at least one alkylene glycol monoalkyl ether having an alkyl group having 4 or less carbon atoms, and alkylene glycol monoalkyl ether having an alkyl group having 5 or more carbon atoms And a maintenance liquid containing at least one selected from alkylene glycol monoaryl ethers.
In the ink set of the present invention, the maintenance liquid contained in the ink set is excellent in the cleaning property of the ink fixed matter derived from the ink composition contained in the ink set. Therefore, the ink set of the present invention can maintain and maintain the recording head that discharges the ink composition and the discharge performance thereof, and can maintain and maintain the desired state or a state close thereto.

  The ink set of the present invention provides a known image receiving material (for example, plain paper, resin-coated paper, inkjet paper, film, electrophotographic co-paper, fabric, glass, metal, ceramics, etc.) by applying energy to the ink composition. ) Is suitable for inkjet recording.

<Maintenance liquid>
The maintenance liquid contained in the ink set of the present invention comprises 50% by mass or more and 75% by mass or less of water, at least one alkylene glycol monoalkyl ether having an alkyl group having 4 or less carbon atoms, and alkyl. And at least one selected from alkylene glycol monoalkyl ether and alkylene glycol monoaryl ether having 5 or more carbon atoms in the group.
By adopting such a configuration, the maintenance liquid is excellent in the cleaning property of the ink fixed matter derived from the ink composition, maintains and maintains the recording head for discharging the ink composition and its discharge performance, and is in an intended state. Or it can be kept close to it and sustained.
The maintenance liquid may further contain other components such as a surfactant.

(water)
The maintenance liquid contains water. Water content is 50 mass%-75 mass% with respect to the total mass of a maintenance liquid. If the water content is less than 50% by mass with respect to the total mass of the maintenance liquid, it is difficult to dissolve or redisperse the fixed ink in the maintenance liquid. On the other hand, when the content of water is more than 75% by mass with respect to the total mass of the maintenance liquid, the content of glycol ethers is reduced, and the effect of penetrating into the fixed ink and dissolving or redispersing is poor. The content of water is preferably 55% by mass to 70% by mass and more preferably 60% by mass to 70% by mass with respect to the total mass of the maintenance liquid.

  The water contained in the maintenance liquid is preferably pure water such as ion exchange water, ultrafiltration water, reverse osmosis water, distilled water, or ultrapure water for the purpose of reducing ionic impurities as much as possible.

(Alkylene glycol monoalkyl ether and alkylene glycol monoaryl ether)
The maintenance liquid is at least one selected from alkylene glycol monoalkyl ethers having an alkyl group having 4 or less carbon atoms, and alkylene glycol monoalkyl ethers and alkylene glycol monoaryl ethers having an alkyl group having 5 or more carbon atoms. Contains seeds.
Alkylene glycol monoalkyl ethers having an alkyl group with 4 or less carbon atoms have high penetrability, such as gaps between fixed inks, cracks and cracks in fixed inks, and boundaries between fixed inks and fixed objects. Easy to penetrate.
On the other hand, alkylene glycol monoalkyl ethers and alkylene glycol monoaryl ethers having an alkyl group with 5 or more carbon atoms dissolve well in resin particles (particularly acrylic resin particles) in ink containing pigments and resin particles. It is an agent / softening agent, and it is easy to soften and dissolve the ink fixed matter derived from the ink containing the pigment and the resin particles.
Accordingly, the maintenance liquid contains both of these two groups of glycol ethers, so that it quickly penetrates into and around the fixed ink material derived from the ink composition contained in the ink set of the present invention. Excellent in rapidly dissolving or redispersing solids (pigments, resin compounds, etc.) in the maintenance liquid. Then, the ink fixed object to which the maintenance liquid is applied softens the lump or becomes small and easily peels off from the fixed object. In particular, the maintenance liquid remarkably exhibits the above-described effect on an ink fixed substance derived from an ink composition containing a pigment and acrylic resin particles.

<Alkylene glycol monoalkyl ether having an alkyl group with 4 or less carbon atoms>
Specific examples of the alkylene glycol monoalkyl ether having 4 or less carbon atoms in the alkyl group include 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 monobutyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol mono Ethyl ether, diethylene glycol Monopropyl ether, diethylene glycol monobutyl 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, tripro Glycol monopropyl ether, tripropylene glycol monobutyl ether, and the like.
The alkylene glycol monoalkyl ether having 4 or less carbon atoms in the alkyl group may be used alone or in combination of two or more.

  The alkylene glycol monoalkyl ether having 4 or less carbon atoms in the alkyl group has 1 to 4 carbon atoms in the alkylene moiety and 1 to 6 repetitions in the alkylene moiety from the viewpoint of permeability of the maintenance liquid to the fixed ink. More preferred is a compound having 1 to 3 carbon atoms in the alkylene moiety and 1 to 4 repeats in the alkylene moiety, 2 or 3 carbon atoms in the alkylene moiety, and 1 to 3 repeats in the alkylene moiety. More preferred are compounds.

The content of the alkylene glycol monoalkyl ether having 4 or less carbon atoms in the alkyl group is preferably 20% by mass to 40% by mass with respect to the total mass of the maintenance liquid. When the content is 20% by mass or more, the maintenance liquid has good penetrability with respect to the fixed ink. When the content is 40% by mass or less, the solubility or redispersibility of the fixed ink in the maintenance liquid is good. From the above viewpoint, the content is more preferably 22% by mass to 35% by mass, and further preferably 25% by mass to 30% by mass.
In addition, when using together 2 or more types of alkylene glycol monoalkyl ethers whose carbon number of an alkyl group is 4 or less, the said content is the total amount of alkylene glycol monoalkyl ether whose carbon number of an alkyl group is 4 or less.

<Alkylene glycol monoalkyl ether and alkylene glycol monoaryl ether having 5 or more carbon atoms in the alkyl group>
Specific examples of the alkylene glycol monoalkyl ether having 5 or more carbon atoms in the alkyl group include dimethylene glycol monopentyl ether, dimethylene glycol monohexyl ether, dimethylene glycol mono-2-ethylhexyl ether, and trimethylene glycol monopentyl ether. , Trimethylene glycol monohexyl ether, trimethylene glycol mono-2-ethylhexyl ether, ethylene glycol monopentyl ether, ethylene glycol monohexyl ether, ethylene glycol mono-2-ethylhexyl ether, diethylene glycol monopentyl ether, diethylene glycol monohexyl ether, diethylene glycol Mono-2-ethylhexyl ether, triethylene glycol monope Tyl ether, triethylene glycol monohexyl ether, triethylene glycol mono-2-ethylhexyl ether, propylene glycol monopentyl ether, propylene glycol monohexyl ether, propylene glycol mono-2-ethylhexyl ether, dipropylene glycol monopentyl ether, dipropylene glycol Examples include monohexyl ether, dipropylene glycol mono-2-ethylhexyl ether, tripropylene glycol monopentyl ether, tripropylene glycol monohexyl ether, tripropylene glycol mono-2-ethylhexyl ether, and the like.

  Specific examples of the alkylene glycol monoaryl ether include dimethylene glycol monophenyl ether, dimethylene glycol monobenzyl ether, dimethylene glycol monotolyl ether, trimethylene glycol monophenyl ether, trimethylene glycol monobenzyl ether, trimethylene glycol mono Tolyl ether, ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, ethylene glycol monotolyl ether, diethylene glycol monophenyl ether, diethylene glycol monobenzyl ether, diethylene glycol monotolyl ether, triethylene glycol monophenyl ether, triethylene glycol monobenzyl ether, Triethylene glycol Tolyl ether, propylene glycol monophenyl ether, propylene glycol monobenzyl ether, propylene glycol monotolyl ether, dipropylene glycol monophenyl ether, dipropylene glycol monobenzyl ether, dipropylene glycol monotolyl ether, tripropylene glycol monophenyl ether, tripropyl ether And propylene glycol monobenzyl ether and tripropylene glycol monotolyl ether.

  The alkylene glycol monoalkyl ether and alkylene glycol monoaryl ether having 5 or more carbon atoms in the alkyl group may be used alone or in combination of two or more.

  As the alkylene glycol monoalkyl ether and alkylene glycol monoaryl ether having 5 or more carbon atoms in the alkyl group, from the viewpoint of the stability of the maintenance liquid, the alkylene moiety has 1 to 4 carbon atoms and the alkylene moiety has 1 to 5 repetitions. 6 is preferable, a compound having 1 to 4 carbon atoms in the alkylene moiety and 1 to 4 alkylene moieties is more preferable, and 2 or 3 carbon atoms in the alkylene moiety and 1 to 3 alkylene moieties in the alkylene moiety. The compound of is more preferable.

In the alkylene glycol monoalkyl ether in which the alkyl group has 5 or more carbon atoms, the upper limit of the carbon number of the alkyl group is not particularly limited. From the viewpoint of solubility in the maintenance liquid, the alkyl group preferably has 5 to 10 carbon atoms, more preferably 6 to 8 carbon atoms, and still more preferably 6 to 7 carbon atoms.
In the alkylene glycol monoaryl ether, the upper limit of the carbon number of the aryl group is not particularly limited. From the viewpoint of solubility in the maintenance liquid, the aryl group preferably has 6 to 48, more preferably 6 to 24, and still more preferably 6 to 12 carbon atoms. Specifically, the aryl group is preferably a phenyl group or a benzyl group, and particularly preferably a phenyl group.

The content of the alkylene glycol monoalkyl ether and alkylene glycol monoaryl ether having 5 or more carbon atoms in the alkyl group is preferably 1% by mass to 10% by mass with respect to the total mass of the maintenance liquid. When the content is 1% by mass or more, the solubility or redispersibility of the fixed ink in the maintenance liquid is good. When the content is 10% by mass or less, the solubility in the maintenance liquid is good and the stability of the liquid is good. From the above viewpoint, the content is more preferably 2% by mass to 8% by mass, and further preferably 3% by mass to 6% by mass.
When two or more alkylene glycol monoalkyl ethers and alkylene glycol monoaryl ethers having 5 or more carbon atoms in the alkyl group are used in combination, the content is alkylene glycol monoalkyl ether having 5 or more carbon atoms in the alkyl group and This is the total amount of alkylene glycol monoaryl ether.

In the present invention, from the viewpoint of improving the cleaning properties of the ink set,
The alkylene glycol monoalkyl ether having 4 or less carbon atoms in the alkyl group includes at least one alkylene glycol monoalkyl ether having 2 or 3 carbon atoms in the alkylene moiety and 1 to 3 repeating alkylene moieties,
As alkylene glycol monoalkyl ether and alkylene glycol monoaryl ether having 5 or more carbon atoms in the alkyl group, the alkylene moiety has 2 or 3 carbon atoms, the alkylene moiety has 1 to 3 repetitions, and the alkyl group has 6 to 6 carbon atoms. 7 alkylene glycol monoalkyl ether and at least 1 selected from alkylene glycol monoaryl ethers having 2 or 3 carbon atoms in the alkylene moiety, 1 to 3 repeating alkylene moieties, and 6 to 12 carbon atoms in the aryl group A maintenance liquid containing seeds is preferred.

(Alkylene glycol monoalkyl ether acetate)
The maintenance liquid preferably contains at least one alkylene glycol monoalkyl ether acetate. The alkylene glycol monoalkyl ether acetate is a good solubilizer / softener for the resin particles in the ink containing the pigment and the resin particles, and the fixed ink is easily softened and dissolved. Therefore, the maintenance liquid further contains an alkylene glycol monoalkyl ether acetate, thereby improving the efficiency of dissolving or redispersing the fixed ink in the maintenance liquid. When an ink set containing such a maintenance liquid is used, even if the time from when the maintenance liquid is applied to the ink ejection head to the time when wiping is short, the fixed ink is easily peeled off from the nozzle surface of the ink ejection head and is washed. Good properties.

Examples of the alkylene glycol monoalkyl ether acetate include dimethylene glycol monomethyl ether acetate, dimethylene glycol monoethyl ether acetate, dimethylene glycol monopropyl ether acetate, dimethylene glycol monobutyl ether acetate, trimethylene glycol monomethyl ether acetate, trimethylene Glycol monoethyl ether acetate, trimethylene glycol monopropyl ether acetate, trimethylene glycol monobutyl ether acetate, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monopropyl ether acetate, ethylene glycol monobutyl ether acetate Over DOO, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monopropyl ether acetate, diethylene glycol monobutyl ether acetate,
Triethylene glycol monomethyl ether acetate, triethylene glycol monoethyl ether acetate, triethylene glycol monopropyl ether acetate, triethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, propylene glycol monopropyl ether acetate, Propylene glycol monobutyl ether acetate, dipropylene glycol monomethyl ether acetate, dipropylene glycol monoethyl ether acetate, dipropylene glycol monopropyl ether acetate, dipropylene glycol monobutyl ether acetate, tripropylene glycol monomethyl ether acetate Tate, tripropylene glycol monoethyl ether acetate, tripropylene glycol monopropyl ether acetate, tripropylene glycol monobutyl ether acetate, 3-methoxy-3-methyl-1-butyl acetate, and the like.
An alkylene glycol monoalkyl ether acetate may be used individually by 1 type, and may use 2 or more types together.

The alkylene glycol monoalkyl ether acetate is a compound having 1 to 4 carbon atoms in the alkylene moiety and 1 to 6 repeating alkylene moieties from the viewpoint of improving the efficiency of dissolving or redispersing the fixed ink in the maintenance liquid. More preferably, a compound having 1 to 3 carbon atoms in the alkylene moiety and 1 to 4 carbon atoms in the alkylene moiety is more preferable, and a compound having 2 or 3 carbon atoms in the alkylene moiety and 1 to 3 carbon atoms in the alkylene moiety is further included. preferable.
The carbon number of the alkyl group of the alkylene glycol monoalkyl ether acetate is not particularly limited. From the viewpoint of improving the efficiency of dissolving or redispersing the fixed ink in the maintenance liquid, the alkyl group preferably has 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms, further preferably 1 to 6 carbon atoms, and particularly preferably 1 to 4 carbon atoms. preferable.

The content of the alkylene glycol monoalkyl ether acetate is preferably 1% by mass to 10% by mass with respect to the total mass of the maintenance liquid. When the content is 1% by mass or more, the solubility or redispersibility of the fixed ink in the maintenance liquid is good. When the content is 10% by mass or less, the content of glycol ethers can be increased, which is advantageous. From the above viewpoint, the content of the alkylene glycol monoalkyl ether acetate is more preferably 2% by mass to 8% by mass, and further preferably 3% by mass to 6% by mass.
In addition, when using 2 or more types of alkylene glycol monoalkyl ether acetate together, the said content is the total amount of alkylene glycol monoalkyl ether acetate.

(Other organic solvents)
From the viewpoint of improving wettability and permeability, the maintenance liquid is within the range not impairing the effects of the present invention, and other than alkylene glycol monoalkyl ether, alkylene glycol monoaryl ether, and alkylene glycol monoalkyl ether acetate. An organic solvent may be used in combination. Examples of the organic solvent that can be used in combination include water-soluble organic solvents such as alcohols and polyhydric alcohols.
Specific examples of the alcohol include linear or branched alkyl alcohols such as ethanol, butanol and isopropanol. Specific examples of the polyhydric alcohol include ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, dipropylene glycol, 2-butene-1,4-diol, 2-ethyl-1,3- Alkanediols such as hexanediol, 2-methyl-2,4-pentanediol, 1,2-octanediol, 1,2-hexanediol, 1,2-pentanediol, 4-methyl-1,2-pentanediol And triols such as glycerin, 1,2,4-butanetriol, and 1,2,6-hexanetritriol.
In addition, 2-pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, formamide, acetamide, dimethyl sulfoxide, sorbit, sorbitan, acetin, diacetin, triacetin, sulfolane, glycerin, etc. are also water-soluble It can be used as an organic solvent.

(Other additives)
In addition to the above-mentioned components, the maintenance liquid may contain, for example, a surfactant, an antifading agent, an emulsion stabilizer, a penetration accelerator, an ultraviolet absorber, an antiseptic, an antifungal agent, a rust inhibitor, and a pH. Other additives such as a regulator, an antifoaming agent and a viscosity modifier can be included.

(Physical properties etc. of maintenance liquid)
The maintenance liquid is preferably a liquid that does not cause aggregation when mixed with the ink composition of the present invention. This is because when aggregation occurs, components such as pigments in the ink composition further adhere to the ink discharge head and the like, thereby reducing the effects of the present invention.

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

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

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

  The maintenance liquid may be colored by including a coloring material such as a pigment, but the content of the coloring material such as a pigment is the amount of the maintenance liquid in order to avoid the risk of damaging the hue of the ink (that is, the ink image). It is preferably 1% by mass or less of the total mass, and in particular, it is preferably a colorless liquid containing no pigment.

<Ink composition>
The ink composition (hereinafter also referred to as “ink”) included in the ink set of the present invention contains at least a pigment, resin particles, and water. The ink may further contain other components such as a water-soluble organic solvent and a surfactant.

A general water-based pigment ink contains water, a pigment, and resin particles as main components, and a water-soluble organic solvent or the like is added as necessary. When the pigment ink adheres to the nozzle surface of the ink ejection head, the pigment ink thickens or solidifies by drying, generating an ink-fixed material mainly composed of the pigment and the resin particles, resulting in ink ejection failure.
In the ink set of the present invention, the maintenance liquid contained in the ink set is excellent in the performance of dissolving or redispersing the ink fixed matter mainly composed of the pigment and the resin particles, and therefore the cleaning performance is high. Discharge defects can be suppressed or eliminated.

(Pigment)
The ink contained in the ink set of the present invention contains at least one pigment. There is no restriction | limiting in particular as a pigment contained in the said ink, According to the objective, it can select suitably. The pigment may be an organic pigment or an inorganic pigment. In addition to the pigment, the ink may contain other coloring materials such as dyes for hue adjustment and the like.

Examples of organic pigments include azo pigments, polycyclic pigments, dye chelates, nitro pigments, nitroso pigments, and aniline black. Among these, azo pigments and polycyclic pigments are more preferable. Examples of the azo pigments include azo lakes, insoluble azo pigments, condensed azo pigments, and chelate azo pigments. Examples of the polycyclic pigment include phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, indigo pigments, thioindigo pigments, isoindolinone pigments, and quinofullerone pigments. Examples of dye chelates include basic dye chelates and acidic dye 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, carbon black is particularly preferable. Examples of carbon black include those produced by known methods such as a contact method, a furnace method, and a thermal method.

  The average particle diameter of the pigment is preferably 10 nm to 200 nm, more preferably 10 nm to 150 nm, and even more preferably 10 nm to 100 nm. When the average particle size is 200 nm or less, the color reproducibility is good, the droplet ejection characteristics when droplets are ejected by the ink jet method are good, and when it is 10 nm or more, the light resistance is good. The average particle size and particle size distribution of the pigment are determined by measuring the volume average particle size by a dynamic light scattering method using a nanotrack particle size distribution measuring device UPA-EX150 (manufactured by Nikkiso Co., Ltd.).

From the viewpoint of dispersion stability in the ink, it is preferable to use a dispersant together with the pigment or use a surface-treated pigment as the pigment.
A single pigment may be used, or a plurality of pigments may be selected from within or between each group described above and used in combination.

  In the ink, the content of the pigment with respect to the total mass of the ink is preferably 0.1% by mass to 15% by mass, more preferably 0.5% by mass to 12% by mass in terms of the effect of improving detergency. % Is more preferable, and 1% by mass to 10% by mass is particularly preferable.

(Resin particles)
The ink contained in the ink set of the present invention contains at least one kind of resin particles (hereinafter also referred to as “polymer particles”). This effectively improves the abrasion resistance of the formed image.

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

The polymer particles are preferably self-dispersing polymer particles, and more preferably self-dispersing polymer particles having a carboxyl group, from the viewpoint of ejection stability and pigment dispersion stability. Self-dispersing polymer particles are water-insoluble polymers that can be dispersed in an aqueous medium by the functional groups (particularly acidic groups or salts thereof) of the polymer itself in the absence of other surfactants, By means of water-insoluble polymer particles containing no free emulsifier.
Here, the dispersed state refers to both an emulsified state (emulsion) in which a water-insoluble polymer is dispersed in an aqueous medium and a dispersed state (suspension) in which a water-insoluble polymer is dispersed in an aqueous medium in a solid state. It includes the state of. The water-insoluble polymer in the present invention is preferably a water-insoluble polymer that can be in a dispersed state in which the water-insoluble polymer is dispersed in a solid state.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

  The weight average molecular weight was measured by gel permeation chromatography (GPC). GPC uses HLC-8220GPC (manufactured by Tosoh Corp.), and columns are connected in series with three TSKgel SuperHZM-H, TSKgel SuperHZ4000, TSKgel SuperHZ200 (both trade names made by Tosoh Corp.), and eluent Used THF (tetrahydrofuran) and an IR detector. The conditions were a sample concentration of 0.35 / 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" n-propylbenzene ".

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

  Hereinafter, specific examples (exemplary compounds A-01 to A-19 and B-01 to B-13) of water-insoluble polymers constituting the self-dispersing polymer particles will be given. However, the present invention is not limited to these. The values in parentheses represent the mass ratio of the copolymer component.

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

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

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

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

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

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

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

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

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

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

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

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

(Pigment dispersant)
The ink contained in the ink set of the present invention preferably contains a pigment dispersed using at least one pigment dispersant. Thereby, the pigment particles can be present in a fine particle size, and high dispersion stability can be obtained after dispersion. In general, when the ink contains a resin dispersant, the effect of the ink set of the present invention is remarkable because the cleaning effect of the maintenance liquid tends to be reduced along with the thickening and solidification of the ink.

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

  The low molecular surfactant type dispersant can stably disperse the pigment in the aqueous solvent while keeping the ink at a low viscosity. The low molecular surfactant type dispersant is a low molecular dispersant having a molecular weight of 2000 or less. The molecular weight of the low molecular surfactant type dispersant is preferably 100 to 2000, and more preferably 200 to 2000.

  The low molecular surfactant type dispersant has a structure including a hydrophilic group and a hydrophobic group. One or more hydrophilic groups and hydrophobic groups may be independently contained in one molecule, and may have plural kinds of hydrophilic groups and hydrophobic groups. The low molecular surfactant type dispersant may appropriately have a linking group for linking a hydrophilic group and a hydrophobic group.

The hydrophilic group is anionic, cationic, nonionic, or a betaine type that combines these. The hydrophilic group is preferably an anionic group.
The anionic group may be any as long as it has a negative charge, but is preferably a phosphate group, phosphonic acid group, phosphinic acid group, sulfuric acid group, sulfonic acid group, sulfinic acid group or carboxylic acid group. More preferably a phosphoric acid group or a carboxylic acid group, and even more preferably a carboxylic acid group. The cationic group may be any one having a positive charge, but is preferably an organic cationic substituent, more preferably a nitrogen or phosphorus cationic group, a pyridinium cation or an ammonium cation. More preferably. Nonionic groups are, for example, polyethylene oxide, polyglycerin, a part of sugar units, and the like.

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

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

Among the polymer dispersants, examples of the water-soluble dispersant include hydrophilic polymer compounds. For example, natural hydrophilic polymer compounds include plant gums such as gum arabic, tragan gum, guar gum, karaya gum, locust bean gum, arabinogalactone, pectin, quince seed starch, seaweeds such as alginic acid, carrageenan, agar, etc. Examples thereof include polymer polymers, animal polymers such as gelatin, casein, albumin and collagen, and microbial polymers such as xanthene gum and dextran.
Examples of hydrophilic polymer compounds modified from natural products include fiber polymers such as methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, carboxymethylcellulose, starch-based compounds such as sodium starch glycolate and sodium starch phosphate Examples include polymers, seaweed polymers such as sodium alginate and propylene glycol alginate.
Synthetic hydrophilic polymer compounds include vinyl polymers such as polyvinyl alcohol, polyvinyl pyrrolidone, and polyvinyl methyl ether, non-crosslinked polyacrylamides, polyacrylic acid or alkali metal salts thereof, and acrylics such as water-soluble styrene acrylic resins. Resin, water-soluble styrene maleic acid resin, water-soluble vinyl naphthalene acrylic resin, water-soluble vinyl naphthalene maleic resin, polyvinyl pyrrolidone, polyvinyl alcohol, alkali metal salt of β-naphthalene sulfonic acid formalin condensate, quaternary ammonium, amino group, etc. And a polymer compound having a cationic functional group salt in the side chain, a natural polymer compound such as shellac, and the like.
Among these, water-soluble dispersants introduced with carboxyl groups are hydrophilic polymers such as homopolymers of acrylic acid, methacrylic acid, styrene acrylic acid, and copolymers with monomers having other hydrophilic groups. Preferred as a compound.

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

The weight average molecular weight of the polymer dispersant is preferably 3000 to 100,000, more preferably 5000 to 50000, still more preferably 5000 to 40000, and particularly preferably 10,000 to 40000.
The acid value of the polymer dispersant is preferably 100 mgKOH / g or less from the viewpoint of good cohesiveness when the treatment liquid comes into contact, and 25 mgKOH / g or more from the viewpoint of good self-dispersibility stability. preferable. The acid value is more preferably from 25 to 80 mgKOH / g, still more preferably from 30 to 65 mgKOH / g.
The polymer dispersant preferably contains a polymer having a carboxyl group from the viewpoint of self-dispersibility and aggregation rate when the treatment liquid comes into contact, and the polymer dispersant has a carboxyl group and an acid value of 25 to 80 mgKOH / g. It is more preferable to contain.

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

The average particle size of the pigment dispersed by the polymer dispersant is preferably in the range of 30 to 200 nm, and more preferably in the range of 50 to 150 nm. When the average particle size is 30 nm or more, the production suitability is improved, and when it is 200 nm or less, the storage stability is improved. The particle size distribution of the pigment dispersed by the polymer dispersant is not particularly limited, and may be either a wide particle size distribution or a monodisperse particle size distribution. A mixture of two or more pigments having a monodispersed particle size distribution may be used.
Here, the average particle size and the particle size distribution are determined by measuring the volume average particle size by a dynamic light scattering method using a nanotrack particle size distribution measuring device UPA-EX150 (manufactured by Nikkiso Co., Ltd.). It is.

  The mixing ratio of the pigment and the pigment dispersant is preferably 100: 25 to 100: 140, more preferably 100: 25 to 100: 50 in terms of mass ratio. When the ratio of the pigment dispersant is 25 or more with respect to the pigment 100, it is advantageous in that the dispersion stability and abrasion resistance are improved, and when it is 140 or less with respect to the pigment 100, the dispersion stability is improved. Is advantageous.

(water)
The ink contained in the ink set of the present invention contains water. The amount of water is not particularly limited, but is preferably 10% by mass to 99% by mass from the viewpoint of ink stability and ejection reliability.

(Water-soluble organic solvent)
The ink contained in the ink set of the present invention preferably contains a water-soluble organic solvent.
Examples of water-soluble organic solvents include glycerin, 1,2,6-hexanetriol, trimethylolpropane, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, dipropylene glycol, 2- Butene-1,4-diol, 2-ethyl-1,3-hexanediol, 2-methyl-2,4-pentanediol, 1,2-octanediol, 1,2-hexanediol, 1,2-pentanediol Alkanediols (polyhydric alcohols) such as 4-methyl-1,2-pentanediol; C1-C4 alkyl alcohols such as ethanol, methanol, butanol, propanol, isopropanol; ethylene glycol monomethyl ether Ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene 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 ethylene glycol monomethyl ether acetate, etc. Chromatography ethers; 2-pyrrolidone, N- methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, formamide, acetamide, dimethyl sulfoxide, sorbitol, sorbitan, acetin, diacetin, triacetin, and sulfolane. These may be used alone or in combination of two or more.

  Polyhydric alcohols are useful in terms of preventing drying and imparting moisture. For example, glycerin, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, 1,3-butanediol, 2,3-butanediol, 1,4-butanediol, 3-methyl-1 , 3-butanediol, 1,5-pentanediol, tetraethylene glycol, 1,6-hexanediol, 2-methyl-2,4-pentanediol, polyethylene glycol, 1,2,4-butanetriol, 1,2 , 6-hexanetriol and the like. These may be used alone or in combination of two or more. From the viewpoint of permeability, a polyol compound is preferable, and examples of the aliphatic diol include 2-ethyl-2-methyl-1,3-propanediol, 3,3-dimethyl-1,2-butanediol, 2,2 -Diethyl-1,3-propanediol, 2-methyl-2-propyl-1,3-propanediol, 2,4-dimethyl-2,4-pentanediol, 2,5-dimethyl-2,5-hexanediol , 5-hexene-1,2-diol, 2-ethyl-1,3-hexanediol, and the like. Of these, 2-ethyl-1,3-hexanediol and 2,2,4-trimethyl-1,3-pentanediol are preferable. These may be used alone or in combination of two or more.

  The content of the water-soluble organic solvent contained in the ink composition is preferably 1 to 50% by mass, more preferably 5 to 40% by mass from the viewpoint of preventing drying of the ink and imparting wetness. 10 to 30% by mass is particularly preferable.

(Other ingredients)
The ink contained in the ink set of the present invention may contain other components as necessary in addition to the above components. Other components include, for example, surfactants, ultraviolet absorbers, antifading agents, antifungal agents, pH adjusters, rust inhibitors, antioxidants, emulsion stabilizers, antiseptics, antifoaming agents, viscosity modifiers. And known additives such as dispersion stabilizers and chelating agents.

≪Cleaning method≫
In the cleaning method of the present invention, the ink set of the present invention described above is used, and the maintenance liquid in the ink set is applied to the nozzle surface of the inkjet recording head that discharges the ink composition in the ink set. The nozzle surface of the inkjet recording head is cleaned. The cleaning method of the present invention is excellent in the detergency of the adhered ink adhered to the nozzle surface of the inkjet recording head.
The details of the configuration and preferred embodiments of the ink set used in the cleaning method of the present invention are as described above.

In the cleaning method of the present invention, the maintenance liquid can be applied to the nozzle surface of the inkjet recording head by, for example, ejection by an inkjet method, coating using a roller, spraying, or the like. The application amount of the maintenance liquid, dissolved ink adhering matter is not particularly limited as long as it is an amount capable of swelling or the like, preferably to a ^{1kg / m 2 ~100kg / m 2} .
The temperature of the maintenance liquid at the time of application to the nozzle surface can be appropriately selected according to the maintenance liquid composition, the ink composition, the amount of adhered ink, and the like, but preferably 20 to 40 ° C.

  The cleaning method of the present invention uses a wiping means (wiping means) for wiping the nozzle surface (before or after applying maintenance liquid to the nozzle surface of the inkjet recording head for the purpose of improving the removal efficiency of the adhered ink. It is preferable to remove the fixed ink or its softened material by wiping. Examples of the wiping means and wiping method include scraping with a blade and wiping with a cloth or paper. In the present invention, it is preferable to perform wiping after applying the maintenance liquid to remove the fixed ink or its softened material.

There is no particular limitation on the time from when the maintenance liquid is applied until the wiping by the wiping means is performed, that is, when the maintenance liquid is left in contact with the fixed ink on the nozzle surface of the inkjet recording head. , Can be set to an appropriate length for the cleaning process.
In the cleaning method of the present invention, the maintenance liquid used is applied with the maintenance liquid because it is excellent in the effect of rapidly dissolving or redispersing the ink fixed substance while the ink is rapidly penetrating into the ink fixed substance and its periphery. The ink sticking matter is quickly softened or reduced in size and easily peeled off from the nozzle surface of the inkjet recording head. Therefore, from the viewpoint of increasing the processing speed of the ink jet recording apparatus, the standing time may be, for example, 10 seconds or less, preferably 7 seconds or less, more preferably 5 seconds or less, still more preferably 3 seconds or less, and particularly preferably 2 seconds or less. preferable. The standing time may be as short as this, and according to the present invention, the time required for cleaning the inkjet recording head can be shortened compared to the conventional case, and the processing efficiency of the inkjet recording apparatus can be improved. On the other hand, the lower limit of the standing time is preferably 0.5 seconds or more, and more preferably 1 second or more, from the viewpoint of securing the time required for the dissolution or redispersion of the ink fixed substance by the maintenance liquid.

  When the wiping means is a blade (hereinafter also referred to as “wiper blade”), the material of the wiper blade is preferably elastic rubber, and specific materials include butyl rubber, chloroprene rubber, ethylene propylene rubber, silicone rubber, urethane. Examples thereof include rubber and nitrile rubber. In order to impart ink repellency to the wiper blade, a wiper blade coated with a fluorine resin or the like may be used.

  The cleaning method of the present invention is suitable when the temperature of the nozzle surface of the inkjet recording head is 40 ° C. or higher. When the temperature is 40 ° C. or higher, the ink ejected from the ink jet recording head is likely to be dried and thickened or solidified easily, and an ink fixed matter is likely to be generated on the surface of the nozzle surface. The cleaning method of the present invention is excellent in the ability of the maintenance liquid to be used to dissolve or redisperse the ink-fixed matter, so that the cleaning performance of the ink-fixed matter is higher than that of the conventional cleaning method at the temperature of 40 ° C. It is remarkable.

  Hereinafter, an embodiment of the cleaning method of the present invention will be described with reference to the drawings of an inkjet recording head cleaning device used for carrying out the cleaning method of the present invention. However, this method is not limited to the embodiment. In the following description, the maintenance liquid is referred to as “cleaning liquid”, the wiping means as “wiping means”, and the wiping as “wiping”.

  FIG. 1 is a perspective view showing a schematic configuration of an ink jet recording head cleaning device (hereinafter referred to as “cleaning device”) 10 used for carrying out the cleaning method of the present invention, and FIG. 2 is a front view thereof. It is.

  As shown in FIGS. 1 and 2, the cleaning device 10 applies a cleaning liquid to a liquid ejection surface (nozzle surface) 12 a of a liquid ejection head (inkjet recording head) 12 provided in a liquid ejection device such as an inkjet recording device. A cleaning liquid application unit 14 and a discharge surface wiping unit 16 that wipes a liquid discharge surface (hereinafter referred to as “discharge surface”) 12 a of a liquid discharge head (hereinafter referred to as “head”) 12 with a wiping means. After a predetermined time (that is, the time for which the cleaning liquid is left) has elapsed since the cleaning liquid was applied to the ejection surface 12a of the head 12, the ejection surface 12a to which the cleaning liquid has been applied is wiped with a wiping means. The discharge surface 12a is cleaned. The cleaning apparatus 10 is connected to a cleaning process control unit 70 that controls the operation of each unit, and various operations related to the cleaning process are executed under the control of the cleaning process control unit 70.

  The cleaning device 10 is configured to be movable relative to the head 12 between a maintenance position immediately below the head 12 and a retracted position retracted from just below the head 12. That is, the cleaning device 10 may be configured to be movable, or the cleaning device 10 may be configured to be fixed and the head 12 to move. When the liquid is discharged by the head 12, the cleaning device 10 is disposed at the retracted position, and when the discharge surface cleaning process of the head 12 is performed, the cleaning device 10 is disposed at the maintenance position immediately below the head 12. 1 and 2 show a state in which the cleaning device 10 is disposed at the maintenance position.

  In this example, the cleaning liquid application unit 14 and the ejection surface wiping unit 16 are mounted on the same carriage 18, and the longitudinal direction (mainly) of the head 12 is within a plane parallel to the ejection surface 12 a using a motor (not shown) as a drive source. It is configured to be capable of reciprocating relative to the head 12 in the scanning direction (horizontal direction in FIG. 1).

  A cap 20 is provided at the periphery of the head 12 as a means for preventing drying of the nozzle formed on the ejection surface 12a of the head 12 or preventing an increase in ink viscosity near the nozzle (see FIG. 1). The cap 20 is configured to be movable relative to the head 12 by a moving mechanism (not shown). By moving the cap 20 or the head 12 to a predetermined position when the power is turned off or when waiting for printing, the cap 20 is brought into close contact with the head 12 (however, there is a space between the ejection surface 12a and the cap 20). The discharge surface 12 a is covered with the cap 20. In addition, in a state where the ejection surface 12a of the head 12 is covered with the cap 20, the ink in the head 12 is pressurized so that the deteriorated ink in the vicinity of the nozzle (ink having increased viscosity) is discharged toward the cap 20 in advance. Discharging (pressurizing purge) is performed.

  The cleaning liquid application unit 14 includes a spraying device 30 as cleaning liquid spraying means that mists and sprays the cleaning liquid onto the discharge surface 12a of the head 12, and the cleaning liquid sprayed from the spraying device 30 without adhering to the discharge surface 12a. A liquid collection container 42 is provided for collecting the cleaning liquid or the like that has fallen downward in the vertical direction.

  In the ejection device 30, an ejection port 32 that ejects the cleaning liquid is formed in an upper portion (on the discharge surface 12 a side), and a liquid flow path 34 that communicates with the ejection port 32 is provided therein. The ejection port 32 has a slit shape, and the width thereof is the same as the wiping width of the wiping means (blade 60 in this example) disposed in the ejection surface wiping portion 16. The shape of the injection port 32 is not limited to the slit shape, and various shapes such as a circular shape and a square shape can be applied. Moreover, the injection port 32 may be comprised by the several hole part.

  A supply port (not shown) is provided at one end of the liquid channel 34, and one end of the supply tube 36 is connected to the supply port. The other end of the supply tube 36 is connected to a supply tank 38, and a supply pump 40 is provided in the middle thereof. An air communication hole 38a is formed in the supply tank 38, and the inside of the supply tank 38 is released to the atmosphere. A cleaning liquid that dissolves or redisperses the ink used in the head 12 is stored in the supply tank 38, and the cleaning liquid in the supply tank 38 flows through the supply tube 36 according to the driving of the supply pump 40. Supplied to the passage 34.

  Although not shown, vibration generating means such as a piezoelectric element is provided in the liquid flow path 34, and the cleaning liquid in the liquid flow path 34 is misted using ultrasonic vibration generated by the vibration generating means. And injected from the injection port 32. According to the ejection device 30 of the present example, the fine droplets are ejected only by the excitation pressure (excitation energy) when the liquid is misted without using pressurization by a pump or the like. The liquid droplets do not penetrate deep inside the meniscus and destroy the meniscus.

  The liquid collection container 42 is a container that is disposed between the ejection port 32 and the carriage 18 and has a concave shape that opens toward the upper part (the discharge surface 12a side), and the side wall of the liquid collection container 42 in plan view. The portion is formed so as to surround the injection port 32. As a result, of the cleaning liquid ejected from the ejection port 32, the cleaning liquid or the like (including ink dissolved or redispersed by the cleaning liquid) that does not adhere to the discharge surface 12a and falls downward in the vertical direction is contained in the liquid collection container 42. The liquid is collected and the contamination of the liquid ejection apparatus due to the cleaning liquid or the like is prevented.

In the present embodiment, when the cleaning liquid is ejected from the ejection port 32, the ejection port 32 is preferably disposed at a position close to the ejection surface 12 a of the head 12. Specifically, the distance _{L 1} between the injection port 32 and the ejection surface 12a is preferably 0.5 to 2.0 mm, 0.7 to 1.0 mm is more preferable. In this example, it is set to 0.8 mm. By disposing the ejection port 32 at a position close to the ejection surface 12a of the head 12 in this way, the mist-like cleaning liquid (microdroplets) ejected from the ejection port 32 adheres to the ejection surface 12a without loss. Can be made.
If the ejection port 32 is too close to the ejection surface 12a, there is a concern that the ejection device 30 may come into contact with the head 12. Therefore, the carriage 18 needs to be transported with high accuracy and cost. Therefore, from the viewpoint of microdroplets generation capability and cost of the injector 30, the distance L ₁ between the injection port 32 and the ejection surface 12a is preferably set within the range mentioned above.

In this embodiment, the injector 30 relatively vertically movable injectors lifting mechanism 44 is provided for the head 12, the distance L ₁ between the injection port 32 and the ejection surface 12a is made variable. For this reason, if there is little injection amount of the cleaning liquid by the injection apparatus 30, the application amount of the cleaning liquid with respect to the discharge surface 12a can be increased by bringing the injection port 32 close to the discharge surface 12a. On the other hand, if the amount of cleaning liquid ejected is large, the amount of cleaning liquid applied to the ejection surface 12a can be reduced by separating the ejection port 32 from the ejection surface 12a. Thus in accordance with the injection amount of the cleaning liquid, by varying the distance L ₁ between the injection port 32 and the discharge surface 12a, it is possible to optimize the deposition volume of the cleaning solution with respect to the ejection surface 12a. Further, the misted cleaning liquid (fine droplets) can be efficiently attached to the ejection surface 12a of the head 12, and contamination in the liquid ejection apparatus due to the cleaning liquid or the like is prevented.

In the present embodiment, the moving speed of the carriage 18 on which the ejection device 30 is mounted is variable according to the amount of cleaning liquid ejected by the ejection device 30. For this reason, if the amount of the cleaning liquid ejected by the ejection device 30 is small, the amount of the cleaning liquid applied to the ejection surface 12a can be increased by slowing the moving speed of the carriage 18 and extending the time for ejecting the cleaning liquid onto the ejection surface 12a. it can. Conversely, if the amount of cleaning liquid sprayed is large, the amount of cleaning liquid applied to the discharge surface 12a can be reduced by increasing the moving speed of the carriage 18 and shortening the time for spraying the cleaning liquid onto the discharge surface 12a. Thus in accordance with the injection amount of the cleaning liquid, not only changing the distance L ₁ between the injection port 32 and the discharge surface 12a, also by changing the moving speed of the carriage 18 the injection device 30 is mounted, for the ejection surface 12a The application amount of the cleaning liquid can be optimized more closely.

As a more preferable embodiment in the present embodiment, in accordance with the injection amount of the cleaning liquid by the injector 30, the manner in which the moving speed of the aspects in which the distance L ₁ between the injection port 32 and the discharge surface 12a to the variable and the carriage 18 to the variable Although a combined configuration is shown, the present invention is not limited to this, and a configuration including any one of these aspects is also suitable. In the case of this configuration, the control of the amount of cleaning liquid applied to the ejection surface 12a of the head 12 can be simplified.

  The ejection surface wiping unit 16 is provided with a blade 60 as wiping means, a blade holder 62 that holds the blade 60, and a liquid collection container 64 that collects ink wiped by the blade 60.

  The blade 60 is a plate-like member having substantially the same width as the liquid discharge surface 12a of the head 12 (length in a direction perpendicular to the paper surface of FIG. 1), and has elasticity such as silicone rubber and silicone resin, for example. It is made of an ink repellent (liquid repellent) material.

The blade holder 62 is a member that holds the base end portion (the lower portion in FIG. 1) of the blade 60. In this example, the tip of the blade 60 (the portion excluding the base end portion of the blade 60 held by the blade holder 62, i.e., the portion that protrudes from the blade holder 62 of the blade 60) the length L ₂ of about 6mm It has become.

  In the present embodiment, a blade lifting mechanism 66 that moves the blade holder 62 holding the blade 60 in the liquid discharge direction (vertical direction in FIG. 2) of the head 12 is provided, and the distance between the blade 60 and the discharge surface 12a is as follows. It is variable. By moving the blade holder 62 upward, the blade 60 contacts (abuts) the discharge surface 12a, and the discharge surface 12a is wiped by the blade 60 as the carriage 18 moves. On the other hand, by moving the blade holder 62 downward, the blade 60 is separated from the discharge surface 12a, and even if the carriage 18 is moved when the cleaning liquid is ejected by the ejection device 30, the ejection surface 12a is not wiped by the blade 60. In this manner, the blade lifting mechanism 66 can switch between the state in which the blade 60 is in contact (contact) with the discharge surface 12a and the state in which the blade 60 is separated from the discharge surface 12a, and the spraying device 30 sprays the cleaning liquid onto the discharge surface 12a. It is possible to vary the time from when the discharge surface 12a is wiped off by the blade 60 (that is, the cleaning liquid leaving time).

  The liquid collection container 64 is a container that is disposed between the blade 60 and the carriage 18 and has a concave shape that opens toward the upper part (the discharge surface 12a side), and the side wall portion of the liquid collection container 64 in plan view. Is formed so as to surround the blade 60. For this reason, the ink wiped by the blade 60 is collected in the liquid collection container 64, and the inside of the liquid ejection device is prevented from being contaminated by the ink wiped by the blade 60. .

  One end of the collection tube 46 is branched into two flow paths (branch flow paths) 46a and 46b, and the tips of the branch flow paths 46a and 46b are formed on the bottoms of the liquid collection containers 42 and 64, respectively. Connected to a discharge port (not shown). A recovery tank 48 is connected to the other end of the recovery tube 46, and a recovery pump 50 is provided in the middle thereof. An air communication hole 48a is formed in the recovery tank 48, and the inside thereof is in an open state. Then, according to the driving of the recovery pump 50, the liquid (ink, cleaning liquid) collected in the liquid collection containers 42 and 64 is recovered in the recovery tank 48 via the recovery tube 46.

The cleaning processing control unit 70 functions as a control unit that controls each part of the cleaning device 10 such as the ejection device 30, the carriage 18, the ejection device lifting mechanism 44, the blade lifting mechanism 66, the supply pump 40, and the recovery pump 50. For example, depending on the injection quantity of the washing liquid, or by varying the distance L ₁ by controlling the driving of the injector lift mechanism 44 and the injection port 32 and the discharge surface 12a, and controls the drive mechanism of the carriage 18 (not shown) Thus, the moving speed of the carriage 18 is varied.

  In the present embodiment, the aspect in which the cleaning liquid ejecting means (the ejecting device 30) is provided as the means for applying the cleaning liquid to the ejection surface 12a of the head 12 is illustrated. However, the present invention is not limited thereto, and for example, replaced with the cleaning liquid ejecting means. In addition, a cleaning liquid application unit that applies the cleaning liquid by bringing the application roller into contact with the discharge surface 12a may be provided, or a cleaning liquid discharge unit that discharges the cleaning liquid by an inkjet method may be provided.

  In this embodiment, the aspect provided with the blade member (blade 60) as the wiping means for wiping the ejection surface 12a of the head 12 was illustrated, but the present invention is not limited to this, and for example, a nonwoven fabric or the like instead of the blade member. The web-shaped member may be provided.

  In this embodiment, the cleaning liquid application unit 14 and the ejection surface wiping unit 16 are mounted on the same carriage 18, but they may be mounted on different carriages. According to this aspect, the cleaning liquid application unit 14 and the ejection surface wiping unit 16 can reciprocate independently of each other in the longitudinal direction of the head 12, and the ejection surface 12 a is wiped after the cleaning liquid is applied to the ejection surface 12 a of the head 12. The setting range of time until wiping by means is widened, and the cleaning efficiency can be further improved.

  Next, the operation of the cleaning device 10 will be described.

  When the cleaning process of the ejection surface 12 a of the head 12 is performed, the cleaning device 10 is disposed at a maintenance position directly below the head 12. Then, while moving the carriage 18 relative to the head 12, the cleaning liquid is ejected from the ejection device 30 of the cleaning liquid application unit 14, and the cleaning liquid is applied to the ejection surface 12 a of the head 12. At this time, the blade 60 is disposed at a position separated from the discharge surface 12a, and the blade 60 does not wipe the discharge surface 12a.

  Subsequently, after the cleaning liquid is applied to the ejection surface 12a of the head 12, a standby state is maintained until a predetermined time (leaving time) elapses. This standing time is set longer than the minimum time required to dissolve or redisperse the ink adhering to the ejection surface 12a of the head 12 and remove it from the ejection surface 12a by wiping with the blade 60.

  Then, after the above-described standing time has elapsed, the blade lifting mechanism 66 is disposed at a position where the blade 60 contacts (contacts) the ejection surface 12a, and the blade 18 moves relative to the head 12 while moving the carriage 18 relative to the head 12. The ejection surface 12a is wiped by 60, and the ink attached to the ejection surface 12a is removed. The relative movement of the carriage 18 with respect to the head 12 is such that the blade 60 moves once from one end in the longitudinal direction of the head 12 to the other end, or the blade 60 moves one or more times in the longitudinal direction of the head 12. Set to move back and forth.

In this embodiment, temperature / humidity detection means 72 for detecting the temperature and humidity in the vicinity of the ejection surface 12a of the head 12 is provided, and the detection result by the temperature / humidity detection means 72 is notified to the cleaning processing control unit 70. It has become. The cleaning process control unit 70 optimizes the discharge surface cleaning process based on the temperature and humidity detected by the temperature / humidity detecting means 72.
Further, a job time notifying unit 74 is provided for notifying the execution time (hereinafter referred to as “job time”) of the print job performed immediately before by the head 12. In the present embodiment, the job time is notified to the cleaning processing control unit 70 by the job time notification means 74. The cleaning process control unit 70 determines the required leaving time A according to the job time, and optimizes the ejection surface cleaning process based on the result.

≪Image formation method≫
In the image forming method of the present invention, the ink set described above is used,
An ink application step of applying ink onto a recording medium by discharging the ink composition in the ink set from an inkjet recording head;
And a cleaning step of applying a maintenance liquid in the ink set to the nozzle surface of the inkjet recording head.
The image forming method of the present invention can be appropriately provided with other steps (dry removal step, heat fixing step, etc.) as necessary.

<Ink application process>
In the ink application process of the present invention, the ink composition is ejected from an ink jet recording head to apply ink onto a recording medium. The details of the configuration and preferred embodiments of the ink composition used in this step are as described above.
Examples of the recording medium include known image receiving materials, that is, plain paper, resin-coated paper, ink jet exclusive paper, film, electrophotographic co-paper, fabric, glass, metal, ceramics, and the like.

There is no particular limitation on the ink jet method for discharging the ink composition from the ink jet recording head. Known methods, for example, charge control method that ejects ink using electrostatic attraction force, drop-on-demand method (pressure pulse method) that uses vibration pressure of piezo element, electric signal is converted into acoustic beam and ink is irradiated The acoustic ink jet method that ejects ink using radiation pressure, and the thermal ink jet (bubble jet (registered trademark)) method that uses ink to form bubbles by heating the ink, Also good.
The inkjet method uses a method of ejecting a large number of low-density inks called photo inks in a small volume, a method of improving image quality using a plurality of inks having substantially the same hue and different concentrations, and colorless and transparent inks. The method used is included.

  As the inkjet recording head (hereinafter also referred to as “inkjet head” or “head”), a known one can be applied. For example, a continuous type or a dot-on-demand type can be used. Among the dot-on-demand types, the thermal head is preferably a type having an operation valve as described in JP-A-9-323420 for discharging. As the piezo head, for example, heads described in European Patent A277703, European Patent A278590, and the like can be used. The head preferably has a temperature control function so that the temperature of the ink can be controlled. In the ink application step, it is preferable to control the ink temperature so that the fluctuation range of the ink viscosity is within ± 5%. Further, the drive frequency is preferably 1 kHz to 500 kHz. The shape of the nozzle is not necessarily circular, and may be oval, rectangular, or the like. The nozzle diameter is preferably in the range of 10 μm to 100 μm. In addition, although the opening part of a nozzle is not necessarily a perfect circle, the nozzle diameter assumes the circle | round | yen equivalent to the area of this opening part in that case, and makes it the diameter.

  The nozzle surface of the head is preferably subjected to ink repellent treatment in order to suppress ink adhesion. By coating the nozzle surface with a perfluoropolymer such as PTFE, PFA, or FEP, the liquid repellency is particularly good.

  The temperature of the ink during ink ejection is preferably 30 ° C. or higher from the viewpoint of improving maintainability, and more preferably 35 ° C. or higher. Further, from the viewpoint of ink stability and ejection reliability, 70 ° C. or lower is preferable.

In the image forming method of the present invention, it is preferable to further provide a step of heating and drying the ink on the recording medium after the ink application step. The ink aggregation rate can be increased by heating and drying the ink after the ink application step.
Heating and drying can be performed by a known heating means such as a heater, a blowing means using blowing air such as a dryer, or a combination of these. As a heating method, for example, a method of applying heat with a heater or the like from the side opposite to the ink application surface of the recording medium, a method of applying warm air or hot air to the ink application surface of the recording medium, a heating method using an infrared heater These may be mentioned, and a plurality of these may be combined and heated.

  In the image forming method of the present invention, for the purpose of improving the scratch resistance of the image, it is preferable to further provide a step of fixing the image recorded by applying the ink to the recording medium by heating and pressing. Heating is preferably performed at a temperature equal to or higher than the minimum film-forming temperature (MFT) of the polymer particles in the image. By heating to MFT or higher, the polymer particles become a film and the image is enhanced. The method of heating and pressing is not particularly limited, and for example, a method of passing a pair of heating and pressing rollers is preferable.

<Cleaning process>
In the cleaning step of the present invention, the maintenance liquid is applied to the nozzle surface of the ink jet recording head, thereby removing the ink adhering matter derived from the ink composition adhering to the nozzle surface. Details, such as a structure of a maintenance liquid used at this process, and a preferable aspect, are as having stated already.

In the cleaning step, a maintenance liquid is applied to at least the head surface of the head in order to remove ink or ink adhering matter from the nozzle surface of the head. By applying the maintenance liquid to the head surface, the fixed ink is dissolved or swollen.
The application of the maintenance liquid can be performed, for example, by ejection using an ink jet method, application using a roller, spraying, or the like. The application amount of the maintenance liquid and the liquid temperature at the time of application are as described above in the section of the cleaning method.

  In the cleaning process, wiping of the nozzle surface using a wiping means (wiping means) is performed before or after the maintenance liquid is applied to the nozzle face of the inkjet recording head for the purpose of improving the removal efficiency of the adhered ink. It is preferable to remove the adhered ink or its softened material. The forms of the wiping means and the wiping method are as described above in the section of the cleaning method.

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

In the following examples, the weight average molecular weight was measured by gel permeation chromatography (GPC) and calculated in terms of polystyrene. GPC uses HLC-8220GPC (manufactured by Tosoh Corp.), and columns are connected in series with three TSKgel SuperHZM-H, TSKgel SuperHZ4000, TSKgel SuperHZ200 (both trade names made by Tosoh Corp.), and eluent Used THF (tetrahydrofuran) and an IR detector. The conditions were a sample concentration of 0.35 / 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" n-propylbenzene ".
The acid value of the polymer was determined by the method described in JIS standard (JIS K0070: 1992).

(Examples 1-18, Comparative Examples 1-8)
[1] Preparation of water-based ink composition <Preparation of self-dispersing polymer particles B-01>
In a 2 liter three-necked flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas introduction tube, 540.0 g of methyl ethyl ketone was charged and heated to 75 ° C. While maintaining the temperature in the reaction vessel at 75 ° C., 108 g of methyl methacrylate, 388.8 g of isobornyl methacrylate, 43.2 g of methacrylic acid, 108 g of methyl ethyl ketone, and “V-601” (manufactured by Wako Pure Chemical Industries) 2 .16 g of the mixed solution was added dropwise at a constant speed so that the addition was completed in 2 hours. After completion of the dropwise addition, a solution consisting of 1.08 g of “V-601” and 15.0 g of methyl ethyl ketone was added, stirred for 2 hours at 75 ° C., and then a solution consisting of 0.54 g of “V-601” and 15.0 g of methyl ethyl ketone was added. After further stirring at 75 ° C. for 2 hours, the temperature was raised to 85 ° C. and stirring was continued for 2 hours. In this way, a copolymer polymerization solution was obtained. The weight average molecular weight (Mw) of this copolymer was 61000, and the acid value was 52.1 mgKOH / g.

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

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

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

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

  A part of the solution of the water-insoluble polymer dispersant obtained above is taken, and the solid content obtained by removing the solvent is diluted to 0.1% by mass with tetrahydrofuran, and the weight average molecular weight (Mw) is determined by GPC. It was 25000 when measured.

-Preparation of cyan pigment dispersion-
Methyl ethyl ketone solution of water-insoluble polymer dispersant in terms of solid content is 5.0 g, Pigment Blue 15: 3 (cyan pigment, manufactured by Dainichi Seika Co., Ltd.) 10.0 g, methyl ethyl ketone 40.0 g, 1 mol / L sodium hydroxide 8 0.0 g and 82.0 g of ion-exchanged water were supplied to the vessel together with 300 g of 0.1 mm zirconia beads, and dispersed at 1000 rpm for 6 hours with a ready mill disperser (manufactured by Imex). The obtained dispersion was concentrated under reduced pressure using an evaporator until methyl ethyl ketone was sufficiently distilled off. The pigment concentration was adjusted to 10% by mass, and a cyan pigment dispersion C1 was obtained as a pigment dispersion whose surface was coated with a water-insoluble polymer dispersant. The average particle size of the particles contained in the cyan pigment dispersion C1 was 77 nm.

<Preparation of cyan ink C-01>
Using cyan pigment dispersion C1, aqueous dispersion of self-dispersing polymer particles B-01, ion-exchanged water, Sannix GP250, diethylene glycol monoethyl ether, olphine E1010, and urea, cyan ink was formed to have the following ink composition. Was prepared. After the preparation, coarse particles were removed with a 5 μm membrane filter to prepare cyan ink C-01.
"Ink composition"
・ Cyan pigment (Pigment Blue 15: 3, manufactured by Dainichi Seika Co., Ltd.): 4% by mass
・ Water-insoluble polymer dispersant: 2% by mass
-Aqueous dispersion of self-dispersing polymer particles B-01 (in terms of solid content): 8% by mass
・ Sanix GP250 (manufactured by Sanyo Chemical Industries) ... 10% by mass
・ Diethylene glycol monoethyl ether: 5% by mass
・ Orphine E1010 (manufactured by Nissin Chemical Industry Co., Ltd.) ... 1% by mass
・ Urea: 3% by mass
・ Ion-exchanged water: the remaining amount of total 100% by mass

[2] Preparation of Maintenance Liquid With the compositions shown in Tables 1 and 2 below (numbers are mass%), alkylene glycol monoalkyl ether, alkylene glycol monoaryl ether, other organic solvents, nitric acid (concentration 67. 5%), imidazole, and ultrapure water were mixed and sufficiently stirred to prepare a maintenance liquid of the present invention and a comparative maintenance liquid.

[3] Evaluation Detergency (1)
For evaluation of detergency, as an ink jet recording apparatus, a DIMA-Materials Printer DMP-2831 manufactured by FUJIFILM Daimatics Co., Ltd. (the cartridge is remodeled so that DMC-11610 for 10 pl discharge can be supplied from the outside) is used. did. The ink jet recording apparatus includes a cleaning device having a configuration similar to that of the cleaning device illustrated in FIGS. 1 and 2.

The ink jet recording apparatus was loaded with cyan ink C-01 and either the present invention or a comparative maintenance liquid. Cyan ink C-01 was discharged under the following conditions (1) to (3), and cleaning was performed as follows.
First, a maintenance liquid at 25 ° C. was made into a mist and sprayed, and applied to the nozzle surface of the inkjet head. At this time, the amount of maintenance liquid applied to the nozzle surface was set to 20.0 kg / m ² . Next, 5 seconds after the application of the maintenance liquid, the blade was brought into contact with the nozzle surface and immediately moved once from one end in the longitudinal direction of the nozzle surface to the other end.
Immediately after the cleaning was performed in this manner, re-ejection was performed to determine whether the re-ejectability was acceptable, and the detergency (1) was evaluated according to the following evaluation criteria. The evaluation results are shown in Tables 1 and 2 below.

-Pass / fail judgment for re-ejectability-
(1) When the ink is continuously discharged for 45 minutes and cleaning is performed once immediately after completion, and the subsequent ink discharge rate is 90% or more, it is passed.
(2) Continuous discharge for 1 minute, 30 minutes after the end, cleaning is performed once after the stop, and if the subsequent ink discharge rate is 90% or more, it passes.
(3) After 15 minutes of continuous discharge, cleaning is performed once immediately after completion, and if the recorded image does not show unevenness, it passes.

-Measurement method of ink discharge rate-
At the start of the experiment, it was confirmed that ink was ejected from all nozzles, the number of ejection nozzles after cleaning was counted, and the ejection rate was calculated from the following formula.
Discharge rate (%) = [number of discharged nozzles after cleaning] / [total number of nozzles] × 100

-Evaluation criteria for cleanability-
A: 3 items pass B: 2 items pass C: 1 item pass D: 3 items fail B or higher is a level that can be put to practical use.

2. Detergency (2)
In the same manner as the evaluation method of the cleaning property (1), however, after the maintenance liquid is applied to the nozzle surface of the inkjet head, the time until the blade is brought into contact with the nozzle surface is changed to 2 seconds. 2) was evaluated. The evaluation results are shown in Tables 1 and 2 below.

  As is apparent from Tables 1 and 2, the maintenance liquid and ink set of the present invention are excellent in the cleaning property of the fixed ink.

DESCRIPTION OF SYMBOLS 10 ... Cleaning apparatus 12 ... Liquid discharge head, 12a ... Liquid discharge surface 14 ... Cleaning liquid provision part 16 ... Discharge surface wiping part 18 ... Carriage 20 ... Cap 30 ... Injection apparatus 32 ... Injection port 60 ... Blade 62 ... Blade holder

Claims (7)

An ink composition containing a pigment, resin particles, and water;
50% by mass to 75% by mass of water based on the total mass, at least one alkylene glycol monoalkyl ether having an alkyl group having 4 or less carbon atoms, and alkylene glycol monoalkyl ether having an alkyl group having 5 or more carbon atoms And a maintenance liquid containing at least one selected from alkylene glycol monoaryl ethers;
An ink set. 2. The ink set according to claim 1, wherein the total content of the alkylene glycol monoalkyl ether having 4 or less carbon atoms in the alkyl group is 20% by mass or more and 40% by mass or less with respect to the total mass of the maintenance liquid . The total content of the alkylene glycol monoalkyl ether having 5 or more carbon atoms in the alkyl group and the alkylene glycol monoaryl ether is 1% by mass or more and 10% by mass or less based on the total mass of the maintenance liquid. The ink set according to claim 1 or 2.   The ink set according to any one of claims 1 to 3, wherein the maintenance liquid further contains at least one alkylene glycol monoalkyl ether acetate. The ink set according to any one of claims 1 to 4, is used,
A cleaning method of applying a maintenance liquid in the ink set to a nozzle surface of an ink jet recording head that discharges an ink composition in the ink set. The cleaning method according to claim 5 , wherein the nozzle surface is wiped after the maintenance liquid is applied. The ink set according to any one of claims 1 to 4, is used,
An ink application step of applying ink onto a recording medium by discharging the ink composition in the ink set from an inkjet recording head;
A cleaning step of applying a maintenance liquid in the ink set to the nozzle surface of the inkjet recording head;
An image forming method comprising: