JP5880180B2 - Inkjet recording method - Google Patents

Description

  The present invention relates to an ink jet recording method.

  In recent years, inkjet recording inks that can be directly printed on non-absorbable recording media such as vinyl chloride sheets have been developed as inkjet recording inks for industrial use. Examples of these ink jet recording inks include solvent ink jet recording inks using an organic solvent as a vehicle, and actinic ray curable ink jet recording inks mainly containing a polymerizable monomer. The solvent inkjet recording ink has a problem that there are many VOCs (volatile organic compounds) that have become a social problem in recent years because the solvent is dried and evaporated in the atmosphere. In addition, there are concerns about odors and safety impacts on workers, and sufficient facilities such as ventilation are required. On the other hand, since the actinic ray curable ink jet recording ink is cured immediately after printing, the VOC is close to zero. However, many monomers used have skin sensitization properties. In addition, there is a restriction that an expensive actinic ray irradiation light source is incorporated in the printer, and there remains a problem in terms of practical use in the printing field. From such a background, it is desired to print on a non-water-absorbing recording medium using a water-based inkjet ink which has a small environmental load and has been widely used for home use.

  When printing is performed using a water-based inkjet ink on a recording medium such as a sign for which a surface is coated with a resin or a coated paper whose surface is coated with a paint, the water absorption and fixing properties of ink droplets are lowered. As a result, there is a problem that the image quality and durability of the formed image are lowered.

  For this reason, it has been studied that the water-based inkjet ink contains a water-soluble organic solvent having a low surface tension (see Patent Document 1). The water-soluble organic solvent increases the wettability of the ink droplets that have landed on the recording medium, and suppresses deterioration in image quality.

  In addition, it has been studied to improve the fixability by heating the recording medium or by applying hot air to the ink droplets that have landed on the recording medium so that the drying of the ink droplets is accelerated. However, when performing the heat drying process, moisture evaporated from the ink droplets landed on the recording medium may be condensed on the nozzle surface, and the ejection stability from the nozzle may be reduced. On the other hand, it is studied to suppress dew condensation on the nozzle surface by blowing air to the gap between the recording medium and the inkjet recording head during inkjet recording (Patent Document 2).

JP 2011-201228 A JP 2007-190801 A

  However, depending on the type of liquid component or solid component contained in the ink-jet ink, if the heat drying process is performed, the drying of the ink droplets that have landed on the recording medium may become too fast. As the drying speeds up, the ink droplets on the recording medium are difficult to spread and the leveling of the dots is not in an appropriate state, resulting in a problem that the glossiness of the formed image is lowered.

  This invention is made | formed in view of the said situation, The water-based inkjet ink containing the propylene glycols whose boiling point is 180-300 degreeC is used. An object of the present invention is to provide an image with particularly high glossiness without impairing the ejection property and image quality by blowing air to the gap between the recording medium and the ink jet recording head during image formation using the ink jet ink.

The above object of the present invention is achieved by the following configurations.
[1] A water-soluble organic solvent selected from at least one of water, a pigment, a binder resin containing a water-soluble acrylic resin, glycol ethers and 1,2-alkanediols having 4 or more carbon atoms A step of ejecting droplets of an aqueous inkjet ink containing a propylene glycol having a boiling point of 180 ° C. or higher and lower than 300 ° C. from an inkjet recording head and landing on a recording medium;
And a step of sending air to a gap between a recording surface of the recording medium and a nozzle surface of the inkjet recording head.
[2] The inkjet recording method according to [1], wherein the propylene glycol is dipropylene glycol or tripropylene glycol.
[3] The inkjet recording method according to [1] or [2], wherein the content of the propylene glycol is 3 to 15% by mass with respect to the mass of the aqueous inkjet ink.
[4] The inkjet recording method according to any one of [1] to [3], wherein a surface tension of the water-based inkjet ink is 23 mN / m or more and less than 32 mN / m.
[5] The inkjet recording method according to any one of [1] to [4], further including a step of heating the recording medium on which the droplets land.
[6] The inkjet recording method according to any one of [1] to [5], further including a step of cleaning a nozzle discharge port of the inkjet recording head.
[7] The inkjet recording method according to any one of [1] to [6], wherein the recording medium is a non-water-absorbing recording medium.

  According to the ink jet recording method of the present invention, an image with particularly high gloss can be provided without impairing the ejection property and image quality of ink droplets.

It is a figure which shows an example of schematic structure of the recording part which discharges the inkjet ink of an inkjet recording device, and records an image. It is a figure which shows an example of principal part sectional drawing which made the inkjet recording device of FIG. 1 the cross section from the AA direction.

1. Water-based inkjet ink The water-based inkjet ink is selected from at least one of water, a pigment, a binder resin containing a water-soluble acrylic resin, glycol ethers, and 1,2-alkanediols having 4 or more carbon atoms. A water-soluble organic solvent and a propylene glycol having a boiling point of 180 ° C. or higher and lower than 300 ° C.

<Propylene glycols>
Propylene glycols contained in the inkjet ink used in the present invention have a boiling point of 180 ° C. or higher and lower than 300 ° C., and preferably 200 ° C. or higher and lower than 280 ° C. When the propylene glycol is contained in the inkjet ink, evaporation of the solvent in the ink droplets that have landed on the recording medium can be suppressed. Thereby, aggregation and precipitation of solid contents such as pigments and resin components in the ink-jet ink can be prevented.

  When an image is formed on a water-absorbing recording medium, ethylene glycol, glycerin, or the like is included in the inkjet ink to suppress evaporation of moisture in the ink droplet. However, when an image is formed on a non-water-absorbing recording medium (a recording medium that has no ink absorptivity or has a low water-absorbing property), ink droplets containing ethylene glycol or glycerin are highly hydrophilic. As a result, it is repelled on the recording medium. On the other hand, propylene glycols are less hydrophilic than ethylene glycol and glycerin. Therefore, inkjet inks containing propylene glycols can form high quality images regardless of whether the recording medium has water absorption or not.

  Examples of the propylene glycols include propylene glycol, dipropylene glycol, and tripropylene glycol. The propylene glycols contained in the inkjet ink used in the present invention are preferably dipropylene glycol or tripropylene glycol. One or more of these may be used in the ink-jet ink used in the present invention.

  The content of the propylene glycols is preferably 3 to 15% by mass, and more preferably 5 to 10% by mass with respect to the entire ink. When the content of propylene glycol is less than 3% by mass, it is difficult to suppress evaporation of the solvent in the inkjet ink when printing is performed while blowing air. On the other hand, when the content of propylene glycol is more than 15% by mass, the drying property of the ink droplets on the recording medium is inferior, and the image tends to blur.

  By incorporating propylene glycol into the ink-jet ink used in the present invention, a high-quality image can be formed. The reason for this is that ink droplets that land on a non-water-absorbing recording medium are not repelled, and the water-soluble acrylic resin and water-soluble organic solvent are compatible with each other, so that resin solids precipitate and aggregate during the drying process. It can be considered that it can be suppressed. Further, in the present invention, since propylene glycol having a boiling point of 180 ° C. or more and less than 300 ° C. is contained, even if air is sent to the gap between the recording surface of the recording medium and the nozzle surface of the inkjet recording head at the time of image formation, the ink liquid Drop drying does not become too fast. For this reason, the leveling of dots is in an appropriate state, and it is possible to suppress a decrease in gloss of the image.

<About binder resin containing water-soluble acrylic resin>
The binder resin has a function of fixing (adhering) the landed ink droplets to the recording medium. In addition, the binder resin is required not only to improve the abrasion resistance and water resistance of the ink film, but also to have a function of increasing gloss and optical density. Therefore, it is more preferable that the binder resin be easily dispersed in an aqueous solvent described later, have a certain degree of transparency, and have compatibility with other ink components.

  Since the binder resin contained in the inkjet ink used in the present invention has high solubility and stability in an aqueous solvent, a water-soluble acrylic resin is used.

  The water-soluble acrylic resin may be a homopolymer of (meth) acrylic acid ester or a copolymer of (meth) acrylic acid ester and another copolymerization monomer such as styrene or silicone. A copolymer of (meth) acrylic acid ester and another copolymerization monomer is particularly preferred because it has a high degree of freedom in designing the resin structure, is easily synthesized by a polymerization reaction, and is low in cost. In the copolymer, the total mass of the structural units derived from the (meth) acrylic acid ester is preferably 60 to 100% by mass, and 80 to 100% by mass with respect to the mass of all monomers constituting the copolymer. It is more preferable that

  Examples of (meth) acrylic acid esters include (meth) acrylic acid alkyl esters. Especially, the C1-C12 alkylester of (meth) acrylic acid is preferable. The (meth) acrylic acid ester may be one type or two or more types. Examples of preferable combinations of two or more kinds of (meth) acrylic acid esters include a combination of methyl methacrylate, acrylic acid C1-C12 alkyl ester, and methacrylic acid C2-C12 alkyl ester.

  Examples of other copolymerization monomers in the copolymer of (meth) acrylic acid ester and other copolymerization monomers include monomers having acidic groups. Examples of the monomer having an acidic group include acrylic acid, methacrylic acid, itaconic acid and the like. Among them, copolymers of (meth) acrylic acid esters and other copolymerization monomers include methyl methacrylate, acrylic acid C1-C12 alkyl ester and methacrylic acid C2-C12 alkyl ester as main monomers, and other copolymers. It is preferably a copolymer obtained by polymerizing a monomer having an acidic group as a polymer monomer. The total content of the structural units derived from the main monomers (methyl methacrylate, acrylic acid C1-C12 alkyl ester and methacrylic acid C2-C12 alkyl ester) contained in the copolymer is based on the total monomers constituting the copolymer. It is preferable that it is 80-95 mass%.

  It is preferable that at least a part of the acidic groups contained in the water-soluble acrylic resin is neutralized with a base from the viewpoint of increasing the solubility in an aqueous solvent. Examples of the base to be neutralized include alkali metal or alkaline earth metal hydroxides (for example, NaOH, KOH, etc.); amines (for example, alkanolamine, alkylamine, etc.); ammonia and the like. Among them, the resin neutralized with amines evaporates the amine together with the aqueous solvent from the ink fixed on the recording medium, so that the solubility of the resin from which the amine is removed is lowered. A cured ink film containing such a resin is preferable because it has water resistance. Specific examples of amines include ammonia, triethylamine, 2-dimethylaminoethanol, 2-di-n-butylaminoethanol, methyldiethanolamine, 2-amino-2-methyl-1-propanol, diethanolamine, triethanolamine, 2 -Methylaminoethanol and the like.

  The acid value of the water-soluble acrylic resin used in the present invention is preferably 50 to 300 mgKOH / g, and more preferably 50 to 130 mgKOH / g. If the acid value of the water-soluble resin is less than 50 mgKOH / g, the resin may not be sufficiently soluble in water and may not be sufficiently soluble in an aqueous solvent. On the other hand, if the acid value of the water-soluble resin is more than 300 mgKOH / g, the ink film becomes soft and the abrasion resistance decreases.

  The acid value of the water-soluble acrylic resin in the present invention refers to the number of milligrams of potassium hydroxide required to neutralize the acid contained in 1 g of the water-soluble resin, and the acid value measurement and hydrolysis acid value measurement of JISK 0070. It can be measured by (total acid value measurement).

  The content of the neutralizing base depends on the acid value and content of the water-soluble acrylic resin, but the number of chemical equivalents is 0.5 to 5 times the number of chemical equivalents of acidic groups contained in the water-soluble acrylic resin. It is preferable to do so. If the content of the neutralizing base is less than 0.5 times the number of chemical equivalents of the acidic groups contained in the water-soluble acrylic resin, the effect of increasing the dispersibility of the water-soluble acrylic resin is sufficient. May not be obtained. On the other hand, if the content of the neutralizing base is more than 5 times the number of chemical equivalents of the acidic groups contained in the water-soluble acrylic resin, the water resistance of the ink film is reduced, discoloration, odor, etc. May occur.

The weight average molecular weight (Mw) of the water-soluble acrylic resin is preferably 2.0 × 10 ^{4 to} 8.0 × 10 ⁴ , and more preferably 2.5 × 10 ^{4 to} 7.0 × 10 ^4. preferable. If the weight average molecular weight is less than 2.0 × 10 ⁴ , the fixing ability of the ink is small, and the resulting image may not have sufficient abrasion resistance. On the other hand, if the weight average molecular weight (Mw) is more than 8.0 × 10 ⁴ , the viscosity of the ink may be too high, and the ejectability from the nozzle may be lowered.

  The glass transition temperature (Tg) of the water-soluble acrylic resin is preferably 30 to 100 ° C. If the Tg is less than 30 ° C., the resulting image may not have sufficient abrasion resistance, or blocking may occur. On the other hand, when Tg is higher than 100 ° C., it is considered that the ink film after drying becomes too hard and brittle, and the abrasion resistance may be lowered.

  The content of the water-soluble acrylic resin is preferably 1 to 10% by mass with respect to the entire ink. If the content of the water-soluble acrylic resin is less than 1% by mass, the function of fixing a coloring material such as a pigment on a recording medium may not be sufficiently obtained. On the other hand, when the content of the water-soluble acrylic resin is more than 30% by mass, the viscosity of the ink is increased and the injection stability may be lowered.

  The aqueous inkjet ink of the present invention may further contain water-dispersed polymer fine particles in order to further improve the abrasion resistance of the ink film.

  The water-based dispersed polymer fine particles can be composed of the same water-soluble resin as described above. The average particle diameter of the water-dispersible polymer fine particles is preferably 300 nm or less, more preferably 250 nm or less, from the viewpoint of obtaining an image having good gloss without nozzle clogging of the ink jet recording head. Further, the average particle size of the polymer fine particles is preferably 10 nm or more from the viewpoint of production stability.

  The content of the water-dispersible polymer fine particles is preferably 0.7 to 6.0% by mass with respect to the entire ink, from the viewpoint of easy fixing to a recording medium and long-term storage stability of the ink. It is more preferable that it is 0-3.0 mass%.

<About a mixture of water and water-soluble organic solvent (aqueous solvent)>
The aqueous solvent in the present invention indicates a mixture of water and a water-soluble organic solvent.

  The water-soluble organic solvent in the present invention is preferably one that uniformly disperses or dissolves the water-soluble acrylic resin and other ink components. Examples of the water-soluble organic solvent used in the present invention include a water-soluble organic solvent having a low surface tension.

  A water-soluble organic solvent having a low surface tension can easily spread ink even on a non-water-absorbing recording medium (for example, printing paper, vinyl chloride sheet, etc.). Specifically, the water-soluble organic solvent having a low surface tension is preferably a water-soluble organic solvent having a surface tension at 25 ° C. of 45 mN / m or less.

  The water-soluble organic solvent contained in the inkjet ink used in the present invention includes a solvent selected from at least one of glycol ethers and 1,2-alkanediols having 4 or more carbon atoms. From the viewpoint of injection stability and the like, the 1,2-alkanediols preferably have 8 or less carbon atoms.

  Examples of glycol ethers include ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, dipropylene glycol mono Examples include propyl ether and tripropylene glycol monomethyl ether.

  Examples of 1,2-alkanediols having 4 or more carbon atoms include 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol, 1,2-octanediol, and the like. included.

  The content of the 1,2-alkanediol is preferably 3 to 15% by mass with respect to the entire ink. This is because if the content is less than 3% by mass, wetting and spreading on the recording medium is not sufficient, and if the content exceeds 15% by mass, the drying property is poor.

  The total content of the water-soluble organic solvent containing 1,2-alkanediol and glycol ethers is preferably 3 to 30% by mass with respect to the entire ink. When the total content is less than 3% by mass, wetting and spreading on the recording medium is not sufficient, and when the total content is more than 30% by mass, the storage stability of the ink tends to decrease.

  The aqueous solvent contained in the inkjet ink used in the present invention may further contain another water-soluble organic solvent, if necessary. Examples of other water-soluble organic solvents include alcohols (eg, methanol, ethanol, propanol, isopropanol, butanol, isobutanol, secondary butanol, tertiary butanol), polyhydric alcohols (eg, ethylene glycol, diethylene glycol, Ethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, thiodiglycol), amines (eg, ethanolamine, diethanolamine, triethanolamine, N -Methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine , Diethylenediamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, tetramethylpropylenediamine), amides (eg, formamide, N, N-dimethylformamide, N, N-dimethylacetamide, 2-pyrrolidone) 1,3-dimethyl-2-imidazolidinone, etc.).

  The water content is preferably 50 to 85 mass% with respect to the entire ink.

  The total amount of the aqueous solvent may be adjusted so that the surface tension and viscosity of the ink are in the ranges described later, and for example, it is preferably about 85 to 95% by mass with respect to the entire ink.

<About pigment>
The pigment may be a known organic pigment or inorganic pigment. Examples of organic pigments include azo pigments such as azo lakes, insoluble azo pigments, condensed azo pigments and chelate azo pigments; phthalocyanine pigments, perylene and perylene pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, And polycyclic pigments such as quinophthaloni pigments; dye lakes such as basic dye-type lakes and acid dye-type lakes; nitro pigments; nitroso pigments; aniline black; and daylight fluorescent pigments.

Specific examples of the pigment are shown below, but the present invention is not limited to these exemplified compounds.
Preferred examples of organic pigments for magenta or red and violet include C.I. I. Pigment red 2, C.I. I. Pigment red 3, C.I. I. Pigment red 5, C.I. I. Pigment red 6, C.I. I. Pigment red 7, C.I. I. Pigment red 8, C.I. I. Pigment red 12, C.I. I. Pigment red 15, C.I. I. Pigment red 16, C.I. I. Pigment red 17, C.I. I. Pigment red 22, C.I. I. Pigment red 23, C.I. I. Pigment red 41, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 53: 1, C.I. I. Pigment red 57: 1, C.I. I. Pigment red 112, C.I. I. Pigment red 114, C.I. I. Pigment red 122, C.I. I. Pigment red 123, C.I. I. Pigment red 139, C.I. I. Pigment red 144, C.I. I. Pigment red 146, C.I. I. Pigment red 148, C.I. I. Pigment red 149, C.I. I. Pigment red 150, C.I. I. Pigment red 166, C.I. I. Pigment red 170, C.I. I. Pigment red 177, C.I. I. Pigment red 178, C.I. I. Pigment red 220, C.I. I. Pigment red 202, C.I. I. Pigment red 222, C.I. I. Pigment red 238, C.I. I. Pigment red 245, C.I. I. Pigment red 258, C.I. I. Pigment red 282, C.I. I. Pigment violet 19, C.I. I. Pigment Violet 23 and the like are included.

  Preferred examples of organic pigments for orange or yellow and brown include C.I. I. Pigment orange 13, C.I. I. Pigment orange 16, C.I. I. Pigment orange 31, C.I. I. Pigment orange 34, C.I. I. Pigment orange 43, C.I. I. Pigment yellow 1, C.I. I. Pigment yellow 3, C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 13, C.I. I. Pigment yellow 14, C.I. I. Pigment yellow 15, C.I. I. Pigment yellow 16, C.I. I. Pigment yellow 17, C.I. I. Pigment yellow 43, C.I. I. Pigment yellow 55, C.I. I. Pigment yellow 74, C.I. I. Pigment yellow 81, C.I. I. Pigment yellow 83, C.I. I. Pigment yellow 93, C.I. I. Pigment yellow 94, C.I. I. Pigment yellow 109, C.I. I. Pigment yellow 110, C.I. I. Pigment yellow 120, C.I. I. Pigment yellow 128, C.I. I. Pigment yellow 129, C.I. I. Pigment yellow 138, C.I. I. Pigment yellow 139, C.I. I. Pigment yellow 147, C.I. I. Pigment yellow 150, C.I. I. Pigment yellow 151, C.I. I. Pigment yellow 153, C.I. I. Pigment yellow 154, C.I. I. Pigment yellow 155, C.I. I. Pigment yellow 175, C.I. I. Pigment yellow 180, C.I. I. Pigment yellow 181, C.I. I. Pigment yellow 185, C.I. I. Pigment yellow 194, C.I. I. Pigment yellow 199, C.I. I. Pigment yellow 213, C.I. I. Pigment Brown 22 and the like are included.

  Preferred examples of organic pigments for green or cyan include C.I. I. Pigment blue 15, C.I. I. Pigment blue 15: 1, C.I. I. Pigment blue 15: 2, C.I. I. Pigment blue 15: 3, C.I. I. Pigment blue 15: 4, C.I. I. Pigment blue 15: 5, C.I. I. Pigment blue 16, C.I. I. Pigment blue 29, C.I. I. Pigment blue 60, C.I. I. Pigment Green 7 etc. are included.

  Examples of organic pigments for black include C.I. I. Pigment black 5, C.I. I. Pigment black 7 and the like are included. Examples of organic pigments for white include C.I. I. Pigment White 6 etc. are included.

  Examples of inorganic pigments include carbon black and titanium oxide.

  The inkjet ink used in the present invention may further contain a pigment dispersant in order to enhance the dispersibility of the pigment. Examples of the pigment dispersant include a hydroxyl group-containing carboxylic acid ester, a salt of a long chain polyaminoamide and a high molecular weight acid ester, a salt of a high molecular weight polycarboxylic acid, and the like. Examples of the product of the pigment dispersant include TEGO Dispers 750W (manufactured by Evonik Degussa).

  The pigment is preferably added to the inkjet ink as a pigment dispersion in order to disperse stably. The pigment dispersion may be any dispersion that can be stably dispersed in an aqueous solvent. A pigment dispersion in which a pigment is dispersed with a dispersion resin; a capsule pigment in which the pigment is coated with a water-insoluble resin; a surface-modified dispersion resin And self-dispersing pigments that can be dispersed without containing.

  The dispersion resin used in the pigment dispersion in which the pigment is dispersed with the dispersion resin is preferably a water-soluble resin. Preferred examples of such water-soluble resins include styrene-acrylic acid-acrylic acid alkyl ester copolymers, styrene-acrylic acid copolymers, styrene-maleic acid copolymers, styrene-maleic acid-acrylic acid alkyl esters. Copolymer, styrene-methacrylic acid copolymer, styrene-methacrylic acid-acrylic acid alkyl ester copolymer, styrene-maleic acid half ester copolymer, vinyl naphthalene-acrylic acid copolymer, vinyl naphthalene-maleic acid copolymer Polymers and the like are included. Further, as a pigment dispersion resin, a water-soluble resin that can be used as the binder resin may be used.

  The water-insoluble resin in the capsule pigment in which the pigment is coated with a water-insoluble resin is a resin that is insoluble in water in a weakly acidic to weakly basic range. Specifically, a resin having a solubility in an aqueous solution having a pH of 4 to 10 is 2% or less. Examples of water-insoluble resins include acrylic resins, styrene-acrylic resins, acrylonitrile-acrylic resins, vinyl acetate resins, vinyl acetate-acrylic resins, vinyl acetate-vinyl chloride resins, polyurethane resins, silicon-acrylic resins, acrylic silicon resins, Polyester resin, epoxy resin and the like are included. The average particle diameter of the capsule pigment is preferably about 80 to 200 nm from the viewpoints of ink storage stability, color developability, and the like.

  The capsule pigment (pigment fine particles coated with a water-insoluble resin) can be produced by a known method. For example, a water-insoluble resin is dissolved in an organic solvent (for example, methyl ethyl ketone), and a base component is further added to partially or completely neutralize acidic groups contained in the water-insoluble resin. A pigment and ion-exchanged water are added to the obtained solution and mixed and dispersed. Thereafter, the organic solvent is removed from the obtained solution, and ion-exchanged water is further added as necessary to prepare a capsule pigment. Alternatively, there is a method in which a monomer is added to a solution in which a pigment and a polymerizable surfactant are dispersed and a polymerization reaction is performed to coat the pigment with a resin.

The weight average molecular weight (Mw) of the aforementioned dispersion resin and water-insoluble resin is preferably 3.0 × 10 ^{3 to} 5.0 × 10 ⁵ , more preferably 7.0 × 10 ^{3 to} 2.0 × 10. ⁵ . The glass transition temperature (Tg) of the dispersion resin and the water-insoluble resin is preferably about −30 to 100 ° C., more preferably about −10 to 80 ° C.

  The mass ratio of the pigment to the dispersion resin is preferably 100/150 to 100/30 for the pigment / dispersion resin. From the viewpoint of enhancing the durability of the image, the ejection stability of the ink, and the storage stability, it is more preferably 100/100 to 100/40.

  The pigment can be dispersed by, for example, a ball mill, sand mill, attritor, roll mill, agitator, Henschel mixer, colloid mill, ultrasonic homogenizer, pearl mill, wet jet mill, paint shaker, or the like.

  From the viewpoint of removing the coarse particles of the pigment dispersion and making the particle size distribution of the pigment fine particles uniform, the pigment dispersion is subjected to a centrifugal separation process or a filtration process using a filter before being added to the ink. Also good.

  The self-dispersing pigment may be a commercial product. Examples of commercially available self-dispersing pigments include CABO-JET200, CABO-JET300 (manufactured by Cabot Corp.), Bonjet CW1 (manufactured by Orient Chemical Industries Ltd.), and the like.

<About surfactants>
The surfactant has a function of making the aqueous inkjet ink easily wet and spread on the recording medium. When the inkjet ink used in the present invention contains a surfactant, there is no particular limitation, and anionic surfactants such as dialkylsulfosuccinates, alkylnaphthalenesulfonates, and fatty acid salts; polyoxyethylene alkyl ethers Nonionic surfactants such as polyoxyethylene alkyl allyl ethers, acetylene glycols, and polyoxyethylene / polyoxypropylene block copolymers; cationic surfactants such as alkylamine salts and quaternary ammonium salts; Silicon-based surfactants; fluorine-based surfactants and the like can be used.

  Among the above-mentioned surfactants, the ink-jet ink can be easily wetted and spread on a non-water-absorbing recording medium (for example, printing paper, vinyl chloride sheet, etc.), so that a silicon-based surfactant, a fluorine-based surfactant, or Nonionic surfactants such as acetylene glycol are preferred. By including a silicon-based surfactant or a fluorine-based surfactant in the ink-jet ink used in the present invention, the dot diameter of the landed ink droplets can be greatly expanded, and a high-quality image with high density and no unevenness. Can be formed.

  These surfactants may be used alone or in combination of two or more. Further, these surfactants are preferably used in combination with a water-soluble organic solvent having a low surface tension.

  Preferred examples of the silicon-based surfactant include a polyether-modified polysiloxane compound. Examples of commercially available products include KF-351A, KF-642, KF-643 manufactured by Shin-Etsu Chemical Co., Ltd., and Big Chemie BYK345, BYK347, BYK348, and the like.

  The fluorine-based surfactant may be a compound in which at least a part of hydrogen atoms bonded to the carbon atoms constituting the hydrophobic group is substituted with a fluorine atom in a normal surfactant. Of these, a fluorosurfactant having a perfluoroalkyl group is preferred.

  Examples of commercially available fluorosurfactants include DIC Corporation's trade name: Megafac F series (F-410, F-444, F-477, F-556, etc.), Asahi Glass Co., Ltd. : Surflon, manufactured by Minnesota Mining and Manufacturing Company, Inc. Product name: Fluorad FC, manufactured by Imperial Chemical Industry, Inc. Product name: Monflor, Ei Dupont Nemeras Product name: Zonyls, Farbevelke Hoechst, Inc. Product name: Ricovet VPF, Neos Inc. Product name: Footent, Big Chemie, Inc. Product name: BYK340 (surface conditioner, fluorine-modified polymer), etc. Contains Be turned.

  The content of the surfactant is such that the surface tension of the ink is within the range described below (in order to allow the ink to wet and spread well even on a coated paper or a resin recording medium whose surface energy is lower than that of ordinary paper) 23 mN / m or more and less than 32 mN / m). Specifically, the content is preferably 0.01% by mass or more and less than 2.0% by mass with respect to the entire ink.

<About other ingredients>
The inkjet ink used in the present invention may further contain other components as necessary. Examples of other components include fungicides, rust inhibitors, antiseptics, antifungal agents, antifoaming agents, viscosity modifiers, penetrants, pH adjusters, drying inhibitors (eg urea, thiourea, ethylene urea) Etc.) are included.

  The antiseptic and the antifungal agent have a function of maintaining the storage stability of the inkjet ink over a long period of time. The preservative and the antifungal agent are not particularly limited, and for example, aromatic halogen compounds (for example, Preventol CMK), methylene dithiocyanate, halogen-containing nitrogen sulfur compounds, 1,2-benzisothiazolin-3-one (for example, PROXEL) GXL).

<Physical properties of ink>
The inkjet ink used in the present invention is preferably used as an aqueous inkjet ink.

  Ink jet ink used in the present invention preferably has an ink viscosity at 25 ° C. of 1 to 40 mPa · s, more preferably 5 to 40 mPa · s, and more preferably 5 to 20 mPa · s from the viewpoint of ejection properties. More preferably.

  The surface tension at 25 ° C. of the inkjet ink used in the present invention is preferably 23 mN / m or more and less than 32 mN / m, more preferably 25 to 30 mN / m, depending on the surfactant or the like. When the surface tension of the ink is less than 23 mN / m, the ink droplets are too wet and spread on the recording medium, the dot leveling is not in an appropriate state, and the image quality is likely to deteriorate. On the other hand, when the surface tension of the ink is 32 mN / m or more, it is difficult to spread the ink droplets on the recording medium.

2. Manufacturing method of water-based ink-jet ink The ink-jet ink used in the present invention comprises the above-described propylene glycol, a binder resin containing a water-soluble acrylic resin, water, a water-soluble organic solvent, and a pigment as required. Manufactured through a step of mixing the ingredients. The mixing means is not particularly limited, and may be a three-one motor, a magnetic stirrer, a disper, a homogenizer, a line mixer, or the like.

3. Inkjet recording apparatus The inkjet recording method of the present invention can be performed using an inkjet recording apparatus. Hereinafter, each recording apparatus will be described with reference to the drawings, but the ink jet recording apparatus is not limited thereto.

  FIG. 1 shows a schematic configuration of a recording unit of an ink jet recording apparatus. The ink jet recording apparatus includes an ink jet recording head 1 (see FIG. 2), a head carriage 2 that houses a plurality of ink jet recording heads 1, a blower mechanism 3 installed on a side plate structure 2b of the head carriage 2, and a recording medium 6. Transport rollers 8 and 9, and a temperature control unit 20 disposed on the lower surface of the recording medium 6.

  The roll-shaped recording medium 4 is pulled out in the direction of arrow a in FIG. 1 by the operation of the conveying rollers 8 and 9, and the recording medium 6 is guided to the stage 7. The head carriage 2 is installed facing the upper side of the recording medium 6. Ink is ejected from the inkjet recording head 1 accommodated in the head carriage 2 onto the recording medium 6 guided to the stage 7 to form an image.

  The temperature control unit 20 is disposed in the vicinity of the head carriage 2 and heats the recording medium 6 to a predetermined temperature. For example, as shown in FIG. 1, the temperature control unit 20 is disposed on the lower surface of the stage 7. The temperature control unit 20 may be various heaters or heating rollers, or may be a lamp or the like.

  The recording medium 6 is not particularly limited, and may be a water-absorbing recording medium (recording medium having ink absorbability), a non-water-absorbing recording medium (recording medium having no or low ink absorbability), or the like. sell.

  Examples of the water-absorbing recording medium include plain paper, fabric, inkjet dedicated paper, inkjet glossy paper, cardboard, wood and the like.

  The non-water-absorbing recording medium includes not only a recording medium having no ink absorbability but also a recording medium having a low ink absorbability. Examples of non-water-absorbing recording media include coated paper such as printing paper, resin base materials, metal base materials, and glass base materials. The resin base material may be a resin base material (including plates, sheets, and films) preferably made of a hydrophobic resin, a composite base material of the resin base material and other base materials (paper, etc.), and the like. Examples of the hydrophobic resin include polystyrene, acrylonitrile-butadiene-styrene copolymer (ABS resin), vinyl chloride, polyethylene terephthalate (PET), and preferably vinyl chloride.

  Examples of the recording medium made of polyvinyl chloride include SOL-371G, SOL-373M, SOL-4701 (manufactured by Big Technos Co., Ltd.), glossy PVC (manufactured by Systemgraph Co., Ltd.), KSM-VS, KSM-VST. , KSM-VT (above, Kimoto Co., Ltd.), J-CAL-HGX, J-CAL-YHG, J-CAL-WWWG (above, Kyosho Osaka Co., Ltd.), BUSMARK V400 F vinyl, litecal V-600F VINYL (above, made by Flexcon), FR2 (made by Hanwha), LLBAU13713, LLSP20133 (above, made by Sakurai Co., Ltd.), P-370B, P-400M (above, made by Kambo Plus Co., Ltd.), S02P, S12P, S13P, S14P , S22P, S24P, S34P, S27P As described above, manufactured by Grafityp), P-223RW, P-224RW, P-249ZW, P-284ZC (hereinafter, manufactured by Lintec Corporation), LKG-19, LPA-70, LPE-248, LPM-45, LTG-11, LTG-21 (above, manufactured by Shinsei Co., Ltd.), MPI 3023 (produced by Toyo Corporation), Napoleon Gloss PVC (made by Futatsu Electronics Co., Ltd.), JV-610, Y-114 (above, made by ICC Corporation) NIJ-CAPVC, NIJ-SPVCGT (manufactured by Nichie Corporation), 3101 / H12 / P4, 3104 / H12 / P4, 3104 / H12 / P4S, 9800 / H12 / P4, 3100 / H12 / R2, 3101 / H12 / R2, 3104 / H12 / R2, 1445 / H14 / P3, 1438 / OneWay Vision (from Inetrcoat), JT5129PM, JT5728P, JT5822P, JT5829P, JT5829R, JT5829PM, JT5829RM, JT5929PM (above, manufactured by Mactac), MPI1005, MPI1200, MP12000, MP12000, MP12000, MP12000, MP12000, MP12000 (Above, manufactured by Avery), AM-101G, AM-501G (above, manufactured by Ginichi Co., Ltd.), FR2 (manufactured by Hanwha Japan Co., Ltd.), AY-15P, AY-60P, AY-80P, DBSP137GGH, DBSP137GGL ( As mentioned above, manufactured by Insight Co., Ltd., SJT-V200F, SJT-V400F-1 Company-made), SPS-98, SPSM-98, SPSH-98, SVGL-137, SVGS-137, MD3-200, MD3-301M, MD5-100, MD5-101M, MD5-105 (above, manufactured by Metamark), 640M, 641G, 641M, 3105M, 3105SG, 3162G, 3164G, 3164M, 3164XG, 3164XM, 3165G, 3165SG, 3165M, 3169M, 3451SG, 3551G, 3551M, 3631, 3641M, 3651G, 3651M, 3651SG, 3951G, 3641M Manufactured by Orafol), SVTL-HQ130 (manufactured by Lamy Corporation), SP300GWF, SPCLEARAD vinyl (above, manufactured by Catalina), RM-SJR (Manufactured by Ryoyo Shoji Co., Ltd.), HiLucky, New Lucky PVC (above, made by LG), SIY-110, SIY-310, SIY-320 (above, made by Sekisui Chemical Co., Ltd.), PRINT MI Frontlit, PRINT XL Lightweight banner (Endutex, Inc.), RIJET 100, RIJET 145, RIJET165 (above, Ritrama), NM-SG, NM-SM (Nichiei Kako Co., Ltd.), LTO3GS (Lukio Co., Ltd.), Easy Print 80, Performance Print 80 (above, manufactured by Jetgraph Corporation), DSE550, DSB 550, DSE 800G, DSE 802/137, V250WG, V300WG, V350WG (above, manufactured by Hexis), DigitalW ite 6005PE, 6010PE (manufactured by Multifix), are included IJ180-10 (manufactured by Sumitomo 3M Co., Ltd.), and the like.

  FIG. 2 illustrates the nozzle surface 5 of the inkjet recording head 1 housed inside the head carriage 2, the guide plate 10, and the end portion 10 a of the guide plate 10. The head carriage 2 incorporates a plurality of ink jet recording heads 1 according to the number of colors of images to be printed on the recording medium 6. The ink jet recording head 1 is disposed with the nozzle surface 5 facing the recording medium 6. The head carriage 2 in FIG. 2 houses four types of ink jet recording heads 1 of yellow (Y), magenta (M), cyan (C), and black (K). The number of colors of the recording head 1 is set as appropriate.

  The ink jet recording head 1 may be an on-demand type or a continuous type. In addition, the inkjet recording head discharge method is an electro-mechanical conversion method (for example, a single cavity type, a double cavity type, a bender type, a piston type, a shear mode type, a shared wall type, etc.), an electro-thermal conversion method ( For example, any discharge method such as a thermal ink jet type or a bubble jet (registered trademark) type may be used.

  A plurality of ink chambers are arranged inside the ink jet recording head 1, and each ink chamber is provided with an ejection means (not shown). The injection means is, for example, a piezo element. Ink jet ink is supplied to an ink chamber disposed inside the ink jet recording head 1 by an ink supply means (not shown). The ink-jet ink supplied to the ink chamber is ejected from the nozzle on the nozzle surface 5 toward the recording medium 6 by the operation of the ejecting means.

  The side plate structure 2 b constitutes both side surfaces of the head carriage 2. The blower mechanism 3 is provided in each of the side plate structures 2b. One blower mechanism 3 is configured to blow air onto the recording medium 6 and the other blower mechanism 3 is configured to suck air. As another example, the air blowing mechanism 3 may be provided only to one side plate structure 2b to blow air to the recording medium 6 or to suck air. Here, the blower mechanism 3 is, for example, a blower fan or the like. The air sent by the blower mechanism 3 may be room temperature or heated hot air. In the case of blowing warm air, if a film heater (not shown) with a temperature control function is provided at a predetermined position in the vicinity of an end portion 10a described later, and the film heater is held at a predetermined temperature, the air is blown. Good.

  Air sent from the blower mechanism 3 flows through a gap (referred to as a flow path X) between the nozzle surface 5 and the recording medium 6. The channel width of the channel X is preferably 0.5 to 3 mm. The end 10a end of the guide plate 10 may be bent at a predetermined angle so that the air sent from the blower mechanism 3 is smoothly sent to the flow path X.

  The air blowing mechanism 3 may be an axial flow type fan from the viewpoint of space efficiency and the like, and may have a drive configuration that can control the input pulse width ratio (PWM control) so that the air blowing amount of the air blowing mechanism 3 can be controlled stepwise.

4). Inkjet recording method The present invention is an inkjet recording method using an aqueous inkjet containing propylene glycol having a boiling point of 180 ° C. or higher and lower than 300 ° C., and includes at least the following steps (1) and (2), Steps 3) and (4) may be included.
(1) A step of ejecting water-based inkjet ink droplets from an inkjet recording head and landing on a recording medium (2) A step of sending air to a gap between a recording surface of the recording medium and a nozzle surface of the inkjet recording head 3) A step of heating the recording medium on which the liquid droplets land (4) A step of cleaning a nozzle discharge port of the ink jet recording head

<(1) Landing process>
The ink jet recording method of the present invention ejects ink droplets from an ink jet recording head using the ink jet recording apparatus shown in the drawing. The droplets of the inkjet ink ejected from the nozzle surface of the inkjet recording head land on a certain area (landable area) of the recording medium.

  The inkjet recording head is scanned as many times as necessary, and after the inkjet ink is ejected to one landing possible area, the recording medium is appropriately moved in the transport direction (the direction of arrow a in FIG. 1). Again, an ink jet ink droplet is ejected and landed on the landable area adjacent to the one landable area by the ink jet recording head. By repeating the above-described operation, an image composed of an aggregate of ink-jet ink droplets is formed on the entire landable area of the recording medium.

<(2) About the blowing process>
In the ink jet recording method, wind is sent to the gap between the recording surface of the recording medium and the nozzle surface of the ink jet recording head. Thereby, moisture evaporated from the ink droplets that have landed on the recording medium is prevented from condensing on the nozzle surface.

  When inkjet ink is ejected from the inkjet recording head and ink droplets land on the recording surface of the recording medium heated by the temperature control unit provided in the inkjet recording apparatus, the moisture (main solvent component) of the inkjet ink evaporates. . The evaporated water is condensed on the nozzle surface of the ink jet recording head.

  In order to prevent such dew condensation, the air blowing mechanism is driven to send air to the gap between the recording surface of the recording medium and the nozzle surface of the ink jet recording head. The wind sent into the gap flows in the direction of arrow d in FIG. 2 along the recording medium. It is preferable that the blowing speed flowing between the nozzle surface of each ink jet recording head and the recording medium is substantially constant. By keeping the blowing speed constant, the print quality can be kept good.

  The blowing is preferably performed continuously during the discharge of the inkjet ink. However, when the temperature of the nozzle surface is higher than or the same as the temperature around the nozzle surface, no condensation occurs on the nozzle surface, so that it is not necessary to blow.

  The air flowing through the gap between the recording surface of the recording medium and the nozzle surface of the ink jet recording head may be warm air, normal temperature air, or cold air. When sending warm air, the air flowing in from the periphery of the head carriage in the blowing mechanism on the blowing side may be warmed by the film heater.

<(3) Heating process>
In the ink jet recording method, it is preferable to heat the recording medium from the viewpoint of easily controlling the drying speed of the ink droplets landed on the recording medium.

  The heating temperature of the recording medium is preferably set so that the surface temperature is 35 ° C. or higher and lower than 100 ° C. If the surface temperature of the recording medium is less than 35 ° C., the ink film may not be sufficiently dried (solidified). On the other hand, if the surface temperature of the recording medium exceeds 100 ° C., the recording medium may be deformed and wavy.

<(4) Cleaning process>
In the ink jet recording method, the nozzle outlet of the ink jet recording head may be washed. Washing is removal of the solvent component of the ink film attached to the nozzle outlet of the ink jet recording head. The removal may be performed by wiping the nozzle outlet of the inkjet recording head with a wiping means such as a blade wipe or an ink absorbing member that absorbs ink.

  In the cleaning process, the inkjet recording apparatus is provided with wiping means (blade wipe or ink absorbing member) and a supply means for supplying a cleaning liquid containing an organic solvent to the wiping means. This can be done by wiping off the nozzle outlet with the taking means.

  The wiping member is composed of, for example, high-density fibers that are ultrafine fibers of 0.1 denier or less; the absorbing member is, for example, any one of polyester, acrylic, nylon, or a combination thereof .

  By removing the solvent component of the ink film adhering to the nozzle discharge port of the ink jet recording head by the cleaning means, it is possible to suppress a decrease in the ejectability of the ink jet ink.

  In the following, the invention will be described in more detail with reference to examples. These examples do not limit the scope of the present invention.

<Preparation of materials>
(Propylene glycols)
Propylene glycol (PG): boiling point 187.85 ° C
Dipropylene glycol (DPG): boiling point 222-236 ° C
Tripropylene glycol (TPG): boiling point 273 ° C.

(Water-soluble organic solvent)
1,2 butanediol (1,2-BDO)
1,2 hexanediol (1,2-HDO)
1,2 propanediol (1,2-PDO)
Dipropylene glycol monopropyl ether (DPGPE)
Triethylene glycol monobutyl ether (TEGBE)
Tripropylene glycol monomethyl ether (TPGME)
2-pyrrolidone (2-PDN)
Ecamide B-100 (B100) (made by Idemitsu Kosan Co., Ltd.)
1,3-dimethyl-2-imidazolidinone (DMI)
Dipropylene glycol monomethyl ether (DPGME)
Ethylene glycol (EG)

(Surfactant)
Orphin E1010 (manufactured by Nissin Chemical Industry Co., Ltd.): acetylene glycol-based surfactant Megafac F-444 (manufactured by DIC): fluorinated surfactant KF-643 (manufactured by Shin-Etsu Chemical Co., Ltd.): silicon-based surfactant KF351A (Manufactured by Shin-Etsu Chemical Co., Ltd.): Silicon surfactant Surfactant 400sw (manufactured by Neos): Fluorine surfactant

(Water-soluble acrylic resin)
Synthesis Example of Water-Soluble Acrylic Resin 186 parts of 2-propanol was placed in a flask equipped with a dropping funnel, a reflux tube, a nitrogen introduction tube, a thermometer, and a stirring device, and heated and refluxed while bubbling nitrogen. To the obtained 2-propanol, 76 parts by mass of methyl methacrylate, 13 parts by mass of 2-ethylhexyl acrylate, and 11 parts by mass of methacrylic acid were added to prepare a mixed solution. A monomer solution in which 0.5 part by mass of an initiator (AIBN) was dissolved was dropped into the obtained mixed solution with a dropping funnel over 2 hours. After the dropwise addition, the mixture was further heated and refluxed for 5 hours, then allowed to cool, and 2-propanol was distilled off under reduced pressure. Thereby, a copolymer (acrylic copolymer resin) of (meth) acrylic acid ester and another copolymerizable monomer was obtained.
To 20 parts by mass of the obtained acrylic copolymer resin, 67.8 parts by mass of ion-exchanged water and 12.2 parts by mass of N, N-dimethylaminoethanol as a neutralizing base were added, and the mixture was heated and stirred at 70 ° C. The resin was dissolved. Thereby, an aqueous solution of a water-soluble acrylic resin having a resin solid content of 20% by mass was obtained. Note that the amount of N, N-dimethylaminoethanol added was 1.05 times the number of chemical equivalents of the acidic equivalents of the acrylic copolymer resin.

<Preparation of ink>
(Preparation of cyan pigment dispersion)
As a pigment dispersant, 20 parts by mass of TEGO Dispers 750W (solid content: 40% by mass, manufactured by Evonik Degussa) was added to 65 parts by mass of ion-exchanged water. To this solution, C.I. I. After 15 parts by mass of Pigment Blue 15: 3 was added and premixed, the mixture was dispersed by a sand grinder filled with 50% by volume of 0.5 mm zirconia beads. Thereby, a cyan pigment dispersion having a pigment solid content of 15% by mass was obtained.

(Preparation of cyan ink C-1)
30 parts by mass of an aqueous solution of the water-soluble acrylic resin, 10 parts by mass of 1,2-butanediol, 20 parts by mass of propylene glycol, and 1 part by mass of Orphine E1010 as a surfactant were added and stirred. The total amount was 80 parts by mass. It was prepared by adding ion-exchanged water so that When 20 parts by mass of the cyan pigment dispersion prepared above was being stirred, 80 parts by mass of the obtained solution was added. This solution was filtered through a 1 μm filter to obtain cyan ink C-1. The water-soluble acrylic resin is contained in an amount of 6% by mass with respect to the mass of the entire ink, and the pigment is contained in an amount of 3% by mass with respect to the mass of the entire ink.

(Preparation of inks C2 to C16)
Inks C-2 to C-16 were prepared in the same manner as ink C-1, except that the ink composition was changed as shown in Table 1.

<Measurement of ink properties>
The surface tension of the ink was measured at 25 ° C. by the Wilhelmy method (plate method) using an automatic surface tension meter CVBP-Z manufactured by Kyowa Interface Science. The measurement results are shown in Table 1.

The composition of the ink used in the present invention and the mass% of each composition are shown in Table 1 below.

<Image forming method>
As an ink jet recording head, a piezo type head having a nozzle diameter of 28 μm, a driving frequency of 10 kHz, a nozzle number of 512, a minimum appropriate liquid amount of 14 pl, and a nozzle density of 180 dpi was used. The prepared ink was loaded into one of the ink jet recording heads of an on-demand ink jet printer equipped with four rows of piezo heads.

  The recording medium was heated from the back surface (the surface opposite to the surface facing the head) by a contact heater provided in the ink jet printer so that the surface temperature of the recording medium was 40 ° C. As the recording medium, a soft vinyl chloride sheet IJ180-10 (manufactured by Sumitomo 3M Limited) was used.

  The storage position of the ink jet recording head was provided with an ink emptying position and a wiping unit for an absorbing member (absorber roller). Head cleaning was performed at an arbitrary frequency.

  A blower fan was used as a blower mechanism for sending air to the gap between the recording surface of the recording medium and the nozzle surface of the inkjet recording head. One blower fan was provided on each side plate structure constituting both side surfaces of the head carriage. Using any one of the air blowing fans, air was constantly blown during image formation. However, in Comparative Example 2 only, image formation was performed without driving the blower fan.

  A solid image having a resolution of 720 dpi × 720 dpi, 20 cm × 20 cm, a printing rate of 100%, and 50% was formed on the soft vinyl chloride sheet IJ180-10 to obtain a recorded image.

<Image evaluation>
(Glossy)
The solid image of each ink prepared above was visually observed for glossiness and evaluated according to the following criteria. The obtained evaluation results are shown in Table 2.
○: There is almost no gloss difference between the printed part and the unprinted part, and the gloss is excellent. △: The gloss difference between the printed part and the unprinted part can be recognized, and the image quality is not acceptable. There is a large difference in glossiness, and there is a marked decrease in image quality.

(Injection stability)
A solid image with a printing rate of 100% was continuously printed for 30 minutes in an environment of 25 ° C. and 50% RH. After discharging for 30 minutes continuously, the influence on the solid image due to the discharge failure of each nozzle was visually observed and evaluated according to the following criteria. The obtained evaluation results are shown in Table 2.
◎: Image defects are not observed at all, and the image is uniform. ○: Slight fading is observed at the image writing portion. △: Image defects due to defective ink ejection are slightly observed. Yes: Strong image defects due to poor ink ejection are observed

(Tensile resistance of coating film)
The solid image of each ink prepared above was dried on a hot plate at 50 ° C. for 10 minutes. The next day, both sides of the solid image were pulled to about twice the original length, and the stretched portion was rubbed with a cotton swab to evaluate the degree of peeling of the coating film according to the following criteria. The obtained evaluation results are shown in Table 2.
◎: The rubbed part is not peeled off at all ○: The color of the rubbed part is slightly thin △: The rubbed part is peeled off ×: The rubbed part is easily peeled off

(Image quality (granular))
The solid images of each ink prepared above were visually observed and evaluated according to the following criteria. The obtained evaluation results are shown in Table 2.
◎: No repelling in the image at all ○: Image quality is not affected, but when the image is magnified with a loupe, a slight unevenness in the image is observed. , Inconspicuous range ×: noticeable repellency is seen in the image, and there is a problem in practical use

  As shown in Table 2, it can be seen that Examples 1 to 13 give good results in all evaluation items. Among these, an example using an ink in which the content of dipropylene glycol is 3 to 15% by mass with respect to the mass of the whole ink and the surface tension of the ink is 23 mN / m or more and less than 32 mN / m is particularly good. Results are obtained (Examples 10-13).

  On the other hand, Comparative Example 1 has poor evaluation results of “gloss”, “injection stability”, and “image quality”. The decrease in “gloss” can be caused by the fact that the ink of Comparative Example 1 does not contain propylene glycols (PG, DPG, TPG). This is because the ink droplets landed on the recording medium by the air blowing become too fast to dry and the leveling of the dots is not in an appropriate state. In addition, a decrease in “ejection stability” may occur because the ink of Comparative Example 1 contains a large amount of water. This is because a large amount of water evaporates from the ink droplets that have landed on the recording medium, so that the water cannot be removed by blowing and the nozzle surface is condensed. The decrease in “image quality” can occur when ink droplets that land on a non-water-absorbing recording medium are repelled due to the high surface tension of the ink, and the droplets coalesce.

  In Comparative Example 2, “injection stability” and “image quality” are lowered. The decrease in “injection stability” was caused by condensation on the nozzle surface because no air was blown during image formation. The decrease in “image quality” can be caused by slow drying of ink droplets and dot coalescence because no air is blown during image formation.

  In Comparative Example 3, “the tensile resistance of the coating film” and “the image quality” are lowered. The decrease in the “resistance to tensile strength of the coating film” can be caused by non-uniform formation of the resin component film because the drying speed of the ink solvent is too high. The deterioration of “image quality” can be caused by ink droplets being repelled on a non-absorbing recording medium because the surface tension of the ink is too high because the ink contains ethylene glycol.

  According to the present invention, it is possible to provide an ink jet recording method capable of providing an image with particularly high gloss without impairing the ejection property and image quality.

DESCRIPTION OF SYMBOLS 1 Inkjet recording head 2 Head carriage 2b Side plate structure 3 Blower mechanism 4 Roll-shaped recording medium 5 Nozzle surface 6 Recording medium 7 Stage 8, 9 Conveyance roller 10 Guide plate 10a End part of guide plate 20 Temperature control part

Claims (7)

A water-soluble organic solvent selected from at least one of water, a pigment, a binder resin containing a water-soluble acrylic resin, glycol ethers and 1,2-alkanediols having 4 or more carbon atoms, and a boiling point of 180 Water-based ink-jet ink containing propylene glycol having a temperature of not lower than 300 ° C. and lower than 300 ° C. , and water-soluble selected from at least one of the glycol ethers and 1,2-alkanediols having 4 or more carbon atoms An inkjet recording method using an aqueous inkjet ink, wherein the content of the volatile organic solvent is 3% by mass to 14% by mass with respect to the total mass of the aqueous inkjet ink,
Discharging the water-based inkjet ink droplets from an inkjet recording head and landing on a recording surface made of a resin of a recording medium made of a resin base ;
And a step of sending air to a gap between the recording surface made of the resin of the recording medium and the nozzle surface of the inkjet recording head.   The inkjet recording method according to claim 1, wherein the propylene glycol is dipropylene glycol or tripropylene glycol.   The inkjet recording method of Claim 1 or Claim 2 whose content of the said propylene glycol is 3-15 mass% with respect to the mass of water-based inkjet ink.   The inkjet recording method according to any one of claims 1 to 3, wherein a surface tension of the water-based inkjet ink is 23 mN / m or more and less than 32 mN / m.   The inkjet recording method according to claim 1, further comprising a step of heating the recording medium on which the droplets land.   The inkjet recording method according to claim 1, further comprising a step of cleaning a nozzle discharge port of the inkjet recording head. The resin base material is a base material made of polyvinyl chloride,
The inkjet recording method according to claim 1 , wherein droplets of the water-based inkjet ink are landed on a recording surface made of the polyvinyl chloride of the base material made of the polyvinyl chloride .

Images