JP7364117B2 - Water-based pigment ink, printed matter and method for producing printed matter - Google Patents

Description

The present invention relates to an aqueous pigment ink, a printed matter, and a method for producing a printed matter.

The inkjet recording method is a recording method in which ink droplets are directly ejected from very fine nozzles onto a recording member and attached thereto to obtain characters or images. This method not only has the advantage that the device used has low noise and good operability, but also can be easily colored. Therefore, it is used not only as an output device in offices and homes, but also for industrial purposes.

Inks for inkjet recording methods (inkjet inks) include solvent inks, UV inks, water-based inks, and the like. Among these, demand for water-based inks is increasing from the viewpoint of environmental friendliness (for example, see Patent Document 1).

In addition, in recent years, the use of inkjet recording methods is expected to expand, and in addition to ink-absorbing recording media such as plain paper, recording media that are difficult to absorb ink, such as coated paper and coated paperboard, and ink-jet recording media are expected to expand. There is a growing need for printing on non-absorbent recording media using water-based inkjet inks.

Furthermore, there are several types of ink ejection heads used in the inkjet printing method, depending on the ejection method, recording medium, etc. Therefore, it is necessary to select and use an inkjet printing ink that has characteristics such as optimum viscosity that are suitable for the type of ink ejection head used.

Examples of methods for adjusting the viscosity of the ink include increasing the solid content of the pigment dispersion resin, binder, etc. contained in the ink.

However, ink that simply has a high solids content cannot be stably ejected from the ink ejection head during inkjet printing, which may cause clogging of the ink ejection nozzle or abnormalities in the ejection direction of ink droplets. Ta.

A method of adjusting the viscosity of the ink to increase it without impairing the ejection stability of the ink includes a method of increasing the amount of a high boiling point solvent such as glycerin or propylene glycol contained in the ink.

However, the ink obtained by the above method is difficult to dry after being printed on a recording medium, which may lead to a decrease in the production efficiency of printed matter and printing defects such as bleeding over time. In particular, when used for printing on a recording medium that is difficult to absorb the solvent in the ink, is difficult to absorb, or is non-absorbent, it may significantly reduce the production efficiency of printed matter or cause printing defects such as bleeding. It could be the cause.

Japanese Patent Application Publication No. 2011-12226

The problems to be solved by the present invention are to make it easy to adjust the viscosity of the water-based pigment ink to the optimum value for the ink ejection head, to have excellent ejection stability when printing with the inkjet printing method, and to be able to maintain the stability of the recording medium after printing. To provide an aqueous pigment ink that quickly dries on the surface.

The present inventor has proposed an aqueous pigment ink containing an acrylic thickener, a high boiling point solvent, water, a pigment, and a binder, wherein the solid content is 1 to 15% by mass with respect to the total amount of the aqueous pigment ink. The above problem has been solved by an aqueous pigment ink characterized in that the mass proportion of the high boiling point solvent to the total amount of the aqueous pigment ink is 0.1 to 35% by mass.

In the aqueous pigment ink of the present invention, the viscosity of the aqueous pigment ink can be easily adjusted to the optimum value for the ink ejection head. In particular, when it is necessary to adjust the viscosity of water-based pigment ink in the direction of increasing it, it dries quickly on the surface of the recording medium after printing without sacrificing the excellent ejection stability when printing with the inkjet printing method. It is possible to obtain an aqueous pigment ink with the property (drying property) that

Hereinafter, preferred embodiments of the present invention will be described. However, the present invention is not limited to the following embodiments. Note that in this specification, a numerical range indicated using "~" indicates a range that includes the numerical values written before and after "~" as the minimum value and maximum value, respectively. Moreover, the upper limit value and lower limit value described individually can be combined arbitrarily.

The aqueous pigment ink of the present invention is an aqueous pigment ink containing an acrylic thickener, a high-boiling point solvent, water, a pigment, and a binder, wherein the mass ratio of solid content to the total amount of the aqueous pigment ink is 1 to 15. % by mass, and the mass ratio of the high boiling point solvent to the total amount of the aqueous pigment ink is 0.1 to 35% by mass.

In the aqueous pigment ink of the present invention, by selecting and using an acrylic thickener from among various types of thickeners, the solid content and the proportion of the high boiling point solvent used can be increased. The viscosity can be adjusted to the optimum viscosity for the type of ink ejection head used without causing any deterioration in ejection stability or drying properties.

As described above, in the aqueous pigment ink of the present invention, the viscosity of the aqueous pigment ink can be easily adjusted to the optimum value for the ink ejection head. In particular, when it is necessary to adjust the viscosity of water-based pigment ink in the direction of increasing it, the viscosity is optimal for the ink ejection head used without sacrificing the excellent ejection stability and drying properties when printing with the inkjet printing method. can be adjusted to

In order to solve the above-mentioned problems, the aqueous pigment ink of the present invention uses an aqueous pigment ink in which the mass ratio of solid content to the total amount of the aqueous pigment ink is in the range of 1 to 15% by mass. Among these, for water-based pigment inks, it is more preferable that the mass proportion of the solid content is 4 to 12% by mass, and 6 to 12% by mass for excellent ejection stability when printing by inkjet printing method. This is especially preferable for maintaining the Note that the solid content refers to components other than the solvent, such as water and high-boiling point solvents, contained in the aqueous pigment ink of the present invention, and includes, for example, the pigment, binder, acrylic thickener, and other essential components of the present invention. , refers to the solid content of optional components such as pigment dispersion resin and wax.

Further, as the aqueous pigment ink of the present invention, one in which the mass proportion of the high boiling point solvent to the total amount of the aqueous pigment ink is 0.1 to 35% by mass is used. Among these, as the aqueous pigment ink, it is preferable to use one in which the mass proportion of the high boiling point solvent is in the range of 15 to 35 mass %, and it is preferable to use one in which the mass proportion of the high boiling point solvent is in the range of 15 to 30 mass %. It is particularly preferable for obtaining an aqueous pigment ink that has both excellent ejection stability when printing by a printing method and a property (dryability) that can quickly dry on the surface of a recording medium after printing. Note that the high boiling point solvent refers to an organic solvent having a boiling point of 180° C. or higher, such as glycerin or propylene glycol.

Further, the aqueous pigment ink of the present invention can be adjusted to have a viscosity that is optimal for the type of ink ejection head used, and in particular, can be easily adjusted to increase the viscosity. As the aqueous pigment ink, it is preferable to use one with a viscosity in the range of 3 to 10 mPa・s at 32°C, and it is preferable to use one in the range of 4 to 8 mPa・s to improve storage stability and ejection stability. It is possible to obtain a water-based pigment ink with excellent performance, and when used in an inkjet recording method, it reduces the apparent deviation of the landing position on the recording medium caused by flight deflection, and effectively reduces the occurrence of streaks on printed matter. It is possible to obtain printed matter that is protected against oxidation.
The above viscosity is a value measured under the following conditions using, for example, a cone-plate rotational viscometer equivalent to an E-type viscometer.
Measuring device: TVE-25 type viscometer (manufactured by Toki Sangyo Co., Ltd., TVE-25 L)
Calibration standard solution: JS20
Measurement temperature: 32℃
Rotation speed: 10-100rpm
Injection volume: 1200μL

As the acrylic thickener used in the aqueous pigment ink of the present invention, a polymer of acrylic ester or methacrylic ester is used. Any acrylic thickener can be used, but it is preferable to use one that dissolves or swells in water, rather than one that does not dissolve in water and is dispersed in water (for example, in an emulsion).

As the acrylic thickener, commercially available products can be used, such as Solthix A100 and Solthix A200 manufactured by Lubrizol.

The acrylic thickener (solid content) is preferably used in an amount of 0.01% by mass or more, more preferably 0.02% by mass or more, based on the total amount of the aqueous pigment ink of the present invention. It is particularly preferable to use 0.05% by mass or more in order to increase the viscosity of the aqueous pigment ink and adjust it to the optimum viscosity for the ink ejection head to be used. On the other hand, the acrylic thickener is preferably used in an amount of 0.3% by mass or less, and preferably 0.25% by mass or less, based on the total amount of the aqueous pigment ink of the present invention. More preferably, it is used in a range of 0.2% by mass or less in order to maintain excellent ejection stability and maintain high gloss of printed matter.

On the other hand, water-based pigment inks whose viscosity has been adjusted using, for example, a polyurethane-based thickener or a polyamide-based thickener instead of the acrylic thickener described above, do not cause agglomeration of solid content such as pigments and binders contained therein. There is a concern that sedimentation may occur or the thickener may gel, resulting in a decrease in ejection stability and storage stability. In addition, by using a water-based pigment ink whose viscosity has been adjusted using a polyurethane-based thickener or a polyamide-based thickener instead of the acrylic thickener, it is possible to use a recording medium that is difficult to absorb ink or that is non-absorbable. The printed matter obtained by printing on the paper may have a decrease in gloss.

Next, the high boiling point solvent used in the aqueous pigment ink of the present invention will be explained.

The high boiling point solvent prevents the aqueous pigment ink of the present invention from drying and sticking on the surface of the ejection port of the ink ejection head when ejecting the aqueous pigment ink of the present invention by an inkjet printing method, and provides excellent ejection stability. Used to secure. Further, the high boiling point solvent is used to adjust the viscosity of the aqueous pigment ink of the present invention.

The high boiling point solvent prevents the water-based pigment ink from drying and sticking on the surface of the ejection port of the ink ejection head, while also providing the property (drying property) that it can quickly dry on the surface of the recording medium after printing. It is used in a range of 0.1 to 35% by mass, preferably in a range of 15 to 35% by mass, more preferably in a range of 15 to 30% by mass, based on the total amount of the aqueous pigment ink. use.

As the high boiling point solvent, solvents that are highly miscible with water and have a boiling point of 180°C or higher, preferably in the range of 180 to 300°C can be used, such as ethylene glycol, diethylene glycol, triethylene glycol, and those having a molecular weight of 2000. The following polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, isopropylene glycol, isobutylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, 1, 3-butanediol, 3-methyl-1,3butanediol, 1,5-pentanediol, 3-methyl-1,5pentanediol, 2-methyl-2,4-pentanediol, 1,2-hexanediol, 1,6-hexanediol, mesoerythritol, pentaerythritol, glycerin, etc. can be used. Among them, it is preferable to use propylene glycol or glycerin as the high-boiling point solvent, and using a combination of propylene glycol and glycerin allows the pigment to have excellent dispersion stability without agglomeration or precipitation in the aqueous pigment ink. It is preferable because the viscosity can be adjusted to a desired value while maintaining the properties, and the inkjet printing method achieves excellent ejection stability when printing.

Next, water used in the aqueous pigment ink of the present invention will be explained.

As the water, specifically, pure water or ultrapure water such as ion-exchanged water, ultrafiltrated water, reverse osmosis water, distilled water, etc. can be used. The water is preferably used in an amount of 30 to 90% by mass based on the total amount of the water-based pigment ink in order to obtain a water-based pigment ink with better drying properties and even better ejection stability. , more preferably in a range of 40 to 80% by mass.

Next, the pigment used in the aqueous pigment ink of the present invention will be explained.

The pigment is not particularly limited, and organic pigments and inorganic pigments commonly used in water-based gravure inks or water-based inkjet inks can be used. The pigment may include one or both of organic and inorganic pigments. Further, as the pigment, both non-acid-treated pigments and acid-treated pigments can be used.

As the inorganic pigment, for example, iron oxide, carbon black produced by a method such as a contact method, a furnace method, or a thermal method can be used.

Examples of organic pigments include azo pigments (azo lakes, insoluble azo pigments, condensed azo pigments, chelate azo pigments, etc.), polycyclic pigments (for example, phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments). Pigments, isoindolinone pigments, quinofularone pigments, etc.), lake pigments (for example, basic dye type chelates, acidic dye type chelates, etc.), nitro pigments, nitroso pigments, aniline black, etc. can be used.

Examples of pigments (black pigments) that can be used in black ink include C.I. I. Pigment Black 1, 6, 7, 8, 10, 26, 27, 28 and the like. Among these, C. I. Pigment Black 7 is preferably used. A specific example of the black pigment is No. 1 manufactured by Mitsubishi Chemical Corporation. 2300, No. 2200B, No. 900, No. 960, No. 980, No. 33, No. 40, No. 45, No. 45L, No. 52, HCF88, MA7, MA8, MA100, etc.; Raven5750, Raven5250, Raven5000, Raven3500, Raven1255, Raven700, etc. manufactured by Columbia; Regal 400R, Regal 330R, Regal manufactured by Cabot 660R, Mogul L, Mogul 700, Monarch800, Monarch880 , Monarch900, Monarch1000, Monarch1100, Monarch1300, Monarch1400, etc.; Color Black FW1, FW2, FW2V, FW18, FW200, S150, S160, S manufactured by Degussa 170, Printex 35, same U, same V, Examples include Special Black 1400U, Special Black 6, Special Black 5, Special Black 4, Special Black 4A, NIPEX150, NIPEX160, NIPEX170, and NIPEX180.

Specific examples of pigments (yellow pigments) that can be used in yellow ink include C.I. I. Pigment Yellow 1, 2, 12, 13, 14, 16, 17, 73, 74, 75, 83, 93, 95, 97, 98, 109, 110, 114, 120, 128, 129, 138, 150, 151, 154, 155, 174, 180, 185 and the like.

Specific examples of pigments (magenta pigments) that can be used in magenta ink include C.I. I. Pigment Red 5, 7, 12, 48 (Ca), 48 (Mn), 57 (Ca), 57:1, 112, 122, 123, 146, 176, 184, 185, 202, 209, 269, 282, etc.; C. I. Pigment Violet 19 and the like.

Specific examples of pigments (cyan pigments) that can be used in cyan ink include C.I. I. Pigment Blue 1, 2, 3, 15, 15:3, 15:4, 15:6, 16, 22, 60, 63, 66 and the like. Among these, C. I. Pigment Blue 15:3 is preferably used.

Specific examples of pigments (white pigments) that can be used in white ink include sulfates of alkaline earth metals, carbonates, finely divided silicic acid, silicas such as synthetic silicates, calcium silicate, alumina, and alumina hydrate. , titanium oxide, zinc oxide, talc, clay, etc.

In order to obtain an aqueous pigment ink with excellent dispersion stability, it is preferable that the pigment is provided with a means for stably dispersing it in a solvent such as water or a high boiling point solvent. For example, on the surface of a pigment, a dispersibility-imparting group (a hydrophilic functional group and/or its salt) or an active species having a dispersibility-imparting group is present either directly or indirectly through an alkyl group, an alkyl ether group, an aryl group, etc. may be directly connected (grafted). Such self-dispersing pigments can be produced by methods such as vacuum plasma treatment, oxidation treatment with hypohalous acid and/or hypohalite salts, oxidation treatment with ozone, or oxidation of the pigment surface with an oxidizing agent in water. It can be produced by a wet oxidation method, a method in which p-aminobenzoic acid is bonded to the pigment surface to bond a carboxyl group via a phenyl group, and the like.

When using a self-dispersing pigment, there is no need to include a pigment dispersion resin, which will be described later, so foaming etc. caused by the pigment dispersion resin can be suppressed, and an aqueous pigment ink with excellent ejection stability can be easily obtained. Furthermore, when using a self-dispersing pigment, a significant increase in viscosity caused by the pigment dispersion resin is suppressed, making it possible to contain a larger amount of pigment, making it easier to produce printed matter with high print density. As the self-dispersing pigment, it is also possible to use commercially available products. Commercially available products include BONJET BLACK CW-1, BONJET BLACK CW-1S, BONJET BLACK CW-2, BONJET BLACK CW-3 (product names; manufactured by Orient Chemical Industry Co., Ltd.), CAB-O-JET200, CAB-O. - JET300 (trade name; manufactured by Cabot Corporation), SENSIJET Black SDP100, SENSIJET Black SDP1000, SENSIJET Black SDP2000 (trade name; manufactured by SENSIENT Corporation), etc.

From the viewpoint of ensuring sufficient print density, the content of the pigment is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more, based on the total amount of the aqueous pigment ink. The content of the pigment is such that streak-like printing defects occur due to misalignment of the landing position on the recording medium caused by flight curvature and the water-based pigment ink not being sufficiently wetted and spread on the recording medium. In addition, the pigment maintains excellent dispersion stability without coagulating or precipitating in the aqueous pigment ink, even when the printed matter on the recording medium is rubbed. From the viewpoint of easily obtaining superior image fastness without peeling of the aqueous pigment ink, the amount is preferably 12% by mass or less, preferably 10% by mass or less, and more preferably 8% by mass or less, based on the total amount of the aqueous pigment ink. From these viewpoints, in this embodiment, the pigment content is preferably 1 to 12% by mass, more preferably 2 to 10% by mass, and 3 to 8% by mass, based on the total amount of the aqueous pigment ink. is even more preferable.

As the pigment, pigments other than the water-dispersible pigments described above can also be used. In order to stably disperse the pigment in water, it is preferable to use a combination of the pigment and a pigment dispersion resin. The pigment dispersion resin is used to stably disperse the pigment in a solvent such as water. Therefore, unlike the binder described below, the pigment dispersion resin exists in a state where it is adsorbed onto the surface of the pigment or covers part or all of the surface of the pigment.

Further, when the pigment dispersion resin is used, the pigment dispersion resin corresponds to the solid content of the aqueous pigment ink of the present invention.
Examples of the pigment dispersion resin include polyvinyl alcohols, polyvinylpyrrolidones, acrylic resins such as acrylic acid-acrylic ester copolymers, styrene-acrylic acid copolymers, styrene-methacrylic acid copolymers, and styrene-methacrylic acid. - Styrene-acrylic resins, styrene-maleic acid copolymers, such as acrylic ester copolymers, styrene-α-methylstyrene-acrylic acid copolymers, styrene-α-methylstyrene-acrylic acid-acrylic ester copolymers Aqueous resins of polymers, styrene-maleic anhydride copolymers, vinylnaphthalene-acrylic acid copolymers, and salts of the aforementioned aqueous resins can be used. As the pigment dispersion resin, compounds exemplified as polymer (G) in WO2018/190139 pamphlet can also be used. These pigment-dispersed resins may be cross-linked with a cross-linking agent after pigment dispersion.

In order to maintain excellent dispersion stability and ejection stability, the pigment dispersion resin is preferably used in an amount of 5 to 200% by mass based on 100% by mass of the total pigment, and 5 to 100% by mass. It is more preferable to use the range.

Next, the binder used in the aqueous pigment ink of the present invention will be explained.

The binder is used for the purpose of fixing the pigment in the aqueous pigment ink to the recording medium. Unlike the pigment dispersion resin, the binder is not adsorbed on the surface of the pigment in the aqueous pigment ink, and is dispersed in a solvent such as water or a high boiling point solvent separately from the pigment or pigment dispersion resin. It exists.

The binder is not particularly limited, but for example, acrylic resins, urethane resins, olefin resins, etc. can be used singly or in combination of several types.

The above-mentioned binder suppresses the decrease in the ejection stability and the occurrence of the above-mentioned white streaks, improves the print density and image fastness of printed matter, and provides good gloss, and is effective against the total amount of the above-mentioned water-based pigment ink. It is preferably used in a range of 0.5% by mass to 5.0% by mass, and more preferably in a range of 0.5% by mass to 4.0% by mass. In addition, the aqueous pigment ink containing the binder in the above range can further improve the image fastness of printed matter by crosslinking the binder and forming a strong film through a heating step after printing. Further, even when water is dropped onto the printed matter or when it is rubbed with a water-soaked cloth, it is possible to impart good water resistance so that the aqueous pigment ink does not peel off.

In particular, the binder is used to prevent the white streaks and the aqueous pigment ink from uniformly spreading on the recording medium, resulting in uneven density in printed matter, even if the recording medium is poorly absorbent or non-absorbent. It is preferable to use a modified polyolefin from the viewpoint of suppressing the phenomenon (mottling). Examples of the modified polyolefin include acid-modified polypropylene.

Acid-modified polypropylene is a resin obtained by modifying polypropylene with one or more acidic compounds, and has a polypropylene-derived skeleton (polypropylene skeleton) and a functional group derived from the acidic compound. The polypropylene skeleton has structural units mainly derived from propylene.

The polypropylene skeleton may be a homopolypropylene (homopolymer of propylene) skeleton, a block polypropylene (block copolymer of propylene and other olefins (e.g. ethylene)) skeleton, or a random polypropylene (a homopolymer of propylene and It may also have a skeleton of a random copolymer with other olefins (for example, ethylene). Examples of other olefins include alkenes such as ethylene, isobutylene, 1-butene, 1-pentene, and 1-hexene. These components may be linear or branched. The number of carbon atoms in the other olefin components is, for example, 2 to 6.

The content of the propylene component in the polypropylene skeleton (the content of structural units derived from propylene) is, for example, 60 mol% or more, and may be 70 mol% or more. When the polypropylene skeleton is a block polypropylene skeleton or a random polypropylene skeleton, the content of propylene components in the polypropylene skeleton (content of structural units derived from propylene) is, for example, 95 mol% or less, and 90 mol% or less. Good too.

The content of the polypropylene skeleton in the acid-modified polypropylene is, for example, 50 to 99% by mass based on the total amount of the acid-modified polypropylene. The content of the polypropylene skeleton in the acid-modified polypropylene may be 50% by mass or more, 60% by mass or more, or 70% by mass or more, and 99% by mass or less, 95% by mass or less, or 90% by mass or more, based on the total amount of the acid-modified polypropylene. It may be less than % by mass.

The acidic compound is, for example, a compound having an acidic group such as a carboxy group or an acid anhydride group, or a derivative thereof. A derivative is a compound obtained by modifying (for example, esterification, amidation, or imidization) the acidic group of a compound having an acidic group. The number of acidic groups in the acidic compound may be one or more (for example, two). Examples of the acidic compound include unsaturated carboxylic acids, unsaturated carboxylic acid anhydrides, and derivatives thereof. Specifically, for example, (meth)acrylic acid, maleic acid, maleic anhydride, fumaric acid, citraconic acid, citraconic anhydride, mesaconic acid, itaconic acid, itaconic anhydride, aconitic acid, aconitic anhydride, and himic anhydride, In addition, derivatives of these compounds can be exemplified. Examples of derivatives include compounds having at least one (meth)acryloyl group in the molecule, such as methyl (meth)acrylate and ethyl (meth)acrylate. Note that (meth)acrylic means acrylic or methacryl. The same applies to (meth)acrylate and (meth)acryloyl. The acidic compound is preferably a compound having an acidic group.

The degree of acid modification (eg, graft weight) in acid-modified polypropylene is, for example, 1 to 20% by mass. The degree of acid modification in the acid-modified polypropylene may be 1% by mass or more or 3% by mass or more, and may be 20% by mass or less or 10% by mass or less. The degree of acid modification and graft weight can be determined by alkaline titration or Fourier transform infrared spectroscopy.

Examples of the acid modification method include a method of graft modification of polypropylene. Specifically, there is a method in which polypropylene is heated and melted above its melting point in the presence of a radical reaction initiator to react (melting method), and a method in which polypropylene is dissolved in an organic solvent and then heated and stirred in the presence of a radical reaction initiator. Examples include a method in which the reaction is carried out using a solution method (solution method). Examples of the radical reaction initiator include organic peroxide compounds, azonitrile, and the like.

The acid-modified polypropylene may be chlorinated. The chlorination reaction can be carried out by a conventionally known method.

The weight average molecular weight of the acid-modified polypropylene is, for example, 10,000 to 200,000. The weight average molecular weight of the acid-modified polypropylene may be 10,000 or more, 15,000 or more, or 40,000 or more, and may be 200,000 or less, 150,000 or less, or 120,000 or less. The above weight average molecular weight is a value measured by gel permeation chromatography (standard material: polystyrene).

The melting point (Tm ₁ ) of acid-modified polypropylene is, for example, 50 to 150°C. When the melting point (Tm ₁ ) of the acid-modified polypropylene is within this range, better drying properties and image fastness on the surface of the recording medium tend to be obtained. The melting point (Tm ₁ ) of the acid-modified polypropylene is preferably lower than the melting point of the oxidized polyethylene wax. The above melting point (Tm ₁ ) is a value measured using a melting point measuring device based on JIS K 0064.

Acid-modified polypropylene is, for example, particulate. The average particle diameter of the particulate acid-modified polypropylene is, for example, 10 to 200 nm from the viewpoint of preventing clogging of the inkjet head. The average particle diameter of the particulate acid-modified polypropylene may be 10 nm or more or 20 nm or more, and may be 200 nm or less or 170 nm or less. The average particle diameter is the d50 diameter in a volume-based particle size distribution, which is measured by a laser scattering method using a laser scattering particle size measuring device (for example, Microtrac).

The acid-modified polypropylene is preferably dispersed in a solvent, and more preferably in the form of an emulsion dispersed in a solvent. The above-mentioned solvent is preferably an aqueous medium, and it is more preferable to use the same solvent as the water, high boiling point solvent, etc. contained in the aqueous pigment ink.

When using the acid-modified polypropylene, the pH of the aqueous dispersion of the acid-modified polypropylene is, for example, at a liquid temperature of 25%, in order to facilitate the dispersion of the acid-modified polypropylene resin in the solvent and improve the storage stability of the aqueous pigment ink. It is preferably 6 to 10 at °C. In order to keep the pH within this range, the aqueous dispersion of acid-modified polypropylene contains an amine neutralizing agent such as aqueous ammonia, triethylamine, triethanolamine, dimethylaminoethanol, and morpholine, or sodium hydroxide, water, etc. An inorganic base such as potassium oxide may also be included.

Acid-modified polypropylene can be used alone or in combination of two or more.

Commercially available products can also be used as the acid-modified polypropylene. Preferred commercial products include Auroren (registered trademark) AE-301 and AE-502 manufactured by Nippon Paper Industries Co., Ltd.

The aqueous pigment ink of the present invention may contain the above-mentioned acrylic thickener, high boiling point solvent, water, binder, and, if necessary, other components than the pigment dispersion resin.

Examples of the other components include wax.

As the wax, for example, it is preferable to use a wax having a melting point of 150° C. or lower, and among them, it is preferable to use oxidized polyethylene wax in order to improve the image fastness of printed matter. The oxidized polyethylene wax is obtained by subjecting polyethylene wax to oxidation treatment, and has a skeleton derived from polyethylene (polyethylene skeleton). The polyethylene skeleton mainly has structural units derived from ethylene.

The polyethylene skeleton may be a homopolyethylene (homopolymer of ethylene) skeleton, a block polyethylene (block copolymer of ethylene and other olefins) skeleton, or a random polyethylene (a homopolymer of ethylene and other olefins) skeleton. A random copolymer) skeleton may also be used. Examples of other olefins include alkenes such as propylene, isobutylene, 1-butene, 1-pentene, and 1-hexene. These components may be linear or branched. The number of carbon atoms in the other olefin components is, for example, 2 to 6.

The content of the ethylene component (the content of structural units derived from ethylene) in the polyethylene skeleton is, for example, 60 mol% or more, and may be 70 mol% or more. When the polyethylene skeleton is a block polyethylene skeleton or a random polyethylene skeleton, the content of the ethylene component (the content of structural units derived from ethylene) in the polyethylene skeleton is, for example, 95 mol% or less, and 90 mol% or less. Good too.

The content of the polyethylene skeleton in the oxidized polyethylene wax is, for example, 50 to 99% by mass based on the total amount of the oxidized polyethylene wax. The content of the polyethylene skeleton in the oxidized polyethylene wax may be 50% by mass or more, 60% by mass or more, or 70% by mass or more, and 99% by mass or less, 95% by mass or less, or 90% by mass or less, based on the total amount of the oxidized polyethylene wax. It may be less than % by mass.

The oxidized polyethylene wax preferably includes high-density oxidized polyethylene wax from the viewpoint of obtaining better image fastness. In this embodiment, the synergistic effect of using acid-modified polypropylene resin and high-density oxidized polyethylene wax together provides better drying properties and image fastness on the surface of the recording medium, and better mottling suppressing effect. tends to be obtained. The density of the high-density oxidized polyethylene wax is, for example, 0.95 g/cm ³ or more, and may be 0.95 to 1.1 g/cm ³ .

The melting point (Tm ₂ ) of the oxidized polyethylene wax is, for example, 150°C or lower, preferably 140°C or lower, and may be 135°C or lower. The melting point (Tm ₂ ) of the oxidized polyethylene wax is, for example, 40°C or higher, preferably 120°C or higher, and more preferably 125°C or higher. The above-mentioned melting point (Tm ₂ ) is a value measured by a melting point measuring device based on JIS K 0064.

The oxidized polyethylene wax is, for example, in particulate form. The average particle diameter of the particulate polyethylene oxide wax is, for example, 10 to 200 nm from the viewpoint of preventing clogging of the inkjet head. The average particle diameter of the particulate oxidized polyethylene wax may be 20 nm or more or 30 nm or more, and may be 100 nm or less or 60 nm or less. The average particle diameter is the d50 diameter in a volume-based particle size distribution, which is measured by a laser scattering method using a laser scattering particle size measuring device (for example, Microtrac).

The oxidized polyethylene wax is preferably dissolved or dispersed in a solvent, and more preferably in the form of an emulsion dispersed in a solvent. It is preferable to use the same solvent as the high boiling point solvent, water, etc. used in the aqueous pigment ink of the present invention.

Oxidized polyethylene waxes can be used alone or in combination of two or more.

As the oxidized polyethylene wax, commercially available products can also be used. Preferred commercial products include AQUACER515 and AQUACER1547 manufactured by BYK.

The content of oxidized polyethylene wax is preferably 0.1% by mass or more, 0.2% by mass or more, or 0.3% by mass based on the total amount of the water-based pigment ink in order to obtain printed matter with excellent image fastness. More preferably, the amount is % by mass or more. In order to obtain a water-based pigment ink with sufficient ejection stability, the content of the oxidized polyethylene wax is preferably, for example, 5% by mass or less, more preferably 3% by mass or less, based on the total amount of the water-based pigment ink. More preferably, it is 2% by mass or less.

In order to obtain printed matter with excellent image fastness, the content of oxidized polyethylene wax is preferably 1.6 parts by mass or more, 4 parts by mass or more, or 6 parts by mass or more with respect to 100 parts by mass of pigment. There may be. In order to obtain an aqueous pigment ink with sufficient ejection stability, the content of the oxidized polyethylene wax is, for example, 500 parts by mass or less, 350 parts by mass or less, or 200 parts by mass or less, based on 100 parts by mass of the pigment. It may be. From these viewpoints, the content of the oxidized polyethylene wax may be 1.6 to 500 parts by mass based on 100 parts by mass of the coloring material.

The wax may include waxes other than the acid value polyethylene wax. The content of the oxidized polyethylene wax is preferably 80 parts by mass or more, more preferably 90 parts by mass or more, and 95 parts by mass to 100 parts by mass, based on 100 parts by mass of the total amount of the wax. Particularly preferred.

When acid-modified polypropylene resin is used as the binder and oxidized polyethylene wax is used as the wax, the ratio of the content of oxidized polyethylene wax to the content of acid-modified polypropylene resin (content of oxidized polyethylene wax/acid-modified polypropylene The resin content (resin content) is, for example, 0.03 to 10 from the viewpoint of superior drying properties and fastness, and better suppression of mottling. The ratio may be 0.03 or more, 0.1 or more, 0.2 or more, or 0.3 or more, and may be 10 or less, 2.0 or less, or 1.5 or less. In this embodiment, it is particularly preferable that the ratio of the content of the acid-modified polypropylene resin to the content of the high-density oxidized polyethylene wax is within the above range.

Further, as the other components, a solvent (penetrating agent) other than the water or the high boiling point solvent and a solid wetting agent component can be used.

The penetrating agent includes lower alcohols such as ethanol and isopropyl alcohol; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl butyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether , diethylene glycol monobutyl ether, diethylene glycol isobutyl 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 dimethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monoethyl ether , tripropylene glycol monopropyl ether, tripropylene glycol monobutyl ether, and other glycol monoethers.

The penetrating agent is preferably used from the viewpoint of suppressing the mottling, but the content of the penetrating agent is determined based on the total amount of the aqueous pigment ink in order to obtain a water-based pigment ink with sufficient ejection stability. 8% by mass or less, more preferably 4% by mass or less. That is, the content of the penetrant may be 0% by mass to 8% by mass.

Solid wetting agents include, for example, urea and urea derivatives. Examples of urea derivatives include ethylene urea, propylene urea, diethyl urea, thiourea, N,N-dimethyl urea, hydroxyethyl urea, hydroxybutyl urea, ethylene thiourea, diethyl thiourea, and the like. These can be used alone or in combination of two or more. From the viewpoint of easily obtaining printed matter with excellent drying properties, it is preferable to use at least one selected from the group consisting of urea, ethylene urea and 2-hydroxyethyl urea.

In addition to the above-mentioned components, the aqueous pigment ink of the present invention may optionally contain a surfactant, a wetting agent (drying inhibitor), a penetrant, a preservative, a viscosity modifier, a pH modifier, a chelating agent, It may further contain other additives such as plasticizers, antioxidants, and ultraviolet absorbers.

By using a surfactant, the aqueous ink composition ejected from the ejection port of the inkjet head can easily wet and spread on the surface of the printing medium after landing on the printing medium, thereby preventing the occurrence of streak-like printing defects. Cheap. Furthermore, by using a surfactant, the leveling properties of the aqueous pigment ink can be easily improved by lowering the surface tension of the aqueous pigment ink.

As the surfactant, various anionic surfactants, nonionic surfactants, cationic surfactants, amphoteric surfactants, etc. can be used. The surfactant is preferably one or more selected from the group consisting of anionic surfactants and nonionic surfactants in order to suppress the occurrence of streaky printing defects.

Examples of anionic surfactants include alkylbenzene sulfonates, alkylphenyl sulfonates, alkylnaphthalene sulfonates, higher fatty acid salts, higher fatty acid ester sulfate salts, higher fatty acid ester sulfonate salts, and higher alcohol ether sulfate salts. Examples include ester salts and sulfonates, higher alkyl sulfosuccinates, polyoxyethylene alkyl ether carboxylates, polyoxyethylene alkyl ether sulfates, alkyl phosphates, polyoxyethylene alkyl ether phosphates, etc. Specific examples include dodecylbenzenesulfonate, isopropylnaphthalenesulfonate, monobutylphenylphenol monosulfonate, monobutylphenylphenol sulfonate, dibutylphenylphenol disulfonate, and the like.

Examples of nonionic surfactants include polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, glycerin fatty acid ester, and polyoxyethylene sorbitan fatty acid ester. Oxyethylene glycerin fatty acid ester, polyglycerin fatty acid ester, sucrose fatty acid ester, polyoxyethylene alkylamine, polyoxyethylene fatty acid amide, fatty acid alkylolamide, alkyl alkanolamide, acetylene glycol, oxyethylene adduct of acetylene glycol, polyethylene glycol Examples include polypropylene glycol block copolymers, among which polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene dodecylphenyl ether, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester , polyoxyethylene sorbitan fatty acid ester, fatty acid alkylolamide, acetylene glycol, oxyethylene adduct of acetylene glycol, and polyethylene glycol polypropylene glycol block copolymer.

The aqueous pigment ink preferably contains an acetylene surfactant in order to suppress the occurrence of streaky printing defects. Acetylene surfactants are surfactants that have an acetylene structure in their molecules. The acetylene surfactant preferably contains one or more selected from the group consisting of acetylene glycol and an oxyethylene adduct of acetylene glycol in order to suppress the occurrence of streaky printing defects.

The content of the acetylene surfactant is preferably 80 to 100% by mass, and 85 to 99.9% by mass, based on the total amount of surfactant, in order to suppress the occurrence of streak-like printing defects. It is more preferably 90 to 99.5% by mass, even more preferably 95 to 99.3% by mass.

Other surfactants include silicone surfactants such as polysiloxane oxyethylene adducts; fluorine surfactants such as perfluoroalkyl carboxylates, perfluoroalkyl sulfonates, and oxyethylene perfluoroalkyl ethers; Biosurfactants such as spicrisporic acid, rhamnolipid, lysolecithin, etc. can also be used.

The content of the surfactant is preferably 0.001 to 5% by mass, more preferably 0.001 to 3% by mass, even more preferably 0.001 to 2% by mass, based on the total amount of the aqueous pigment ink. Particularly preferred is from 0.01 to 2% by weight, very preferably from 0.1 to 2% by weight, very preferably from 0.5 to 2% by weight, even more preferably from 0.8 to 2% by weight, from 1 to 1.6% by weight. Mass % is more preferred. Water-based pigment ink containing a surfactant with these contents has good wettability of the ejected droplets on the surface of the printing material, easily spreads sufficiently on the printing material, and does not form streaks. It is easy to obtain the effect of preventing the occurrence of printing defects. Furthermore, an aqueous pigment ink containing a surfactant in each of the above ranges tends to have the effect of improving the leveling properties of the coating film. From the same viewpoint, it is preferable that the content of the acetylene surfactant is within each of the above ranges.

The pH of the water-based pigment ink improves the storage stability and ejection stability of the water-based pigment ink, and improves the wetting and spreading, print density, and image fastness when printing on recording media that are poorly absorbent or non-absorbent. In terms of improvement, it is preferably 7.0 or more, more preferably 7.5 or more, and still more preferably 8.0 or more. The upper limit of the pH of water-based pigment ink is set to suppress the deterioration of the components that make up the ink application or ejection device (e.g., ink ejection openings, ink channels, etc.), and to prevent the effects of water-based pigment ink if it adheres to the skin. is preferably 11.0 or less, more preferably 10.5 or less, still more preferably 10.0 or less. From these viewpoints, the pH of the aqueous pigment ink is preferably 7.0 to 11.0. Note that the above pH is the pH at 25°C.

The surface tension of the aqueous pigment ink is, for example, 20 to 40 mN/m at 25°C. When the surface tension of the water-based pigment ink is within this range, when used in an inkjet recording method, the ejected droplets tend to have good wettability on the surface of the recording medium, and have sufficient wetting and spreading after landing. Tend. The surface tension of the aqueous pigment ink at 25° C. is preferably 25 mN/m or more, more preferably 27 mN/m or more. The surface tension of the aqueous pigment ink at 25° C. is preferably 35 mN/m or less, more preferably 32 mN/m or less.

The aqueous pigment ink of the present invention can be manufactured by mixing the above-mentioned components. The above-mentioned components may be mixed all at once or sequentially. For example, a binder (eg, acid-modified polypropylene resin) and a wax (eg, oxidized polyethylene wax) may each be dissolved or dispersed in an aqueous medium before being mixed. Further, the pigment may be mixed together after being dispersed in an aqueous medium together with a pigment dispersion resin. For mixing, a dispersing machine such as a bead mill, ultrasonic homogenizer, high-pressure homogenizer, paint shaker, ball mill, roll mill, sand mill, sand grinder, Dyno mill, Dispermat, SC mill, nanomizer, etc. can be used. After mixing, centrifugation treatment, filtration treatment, etc. may be performed as necessary.

(Printed matter and its manufacturing method)
The printed matter of the present invention is obtained by printing the aqueous pigment ink of the present invention on the surface of a recording medium.

This printed material includes a recording medium and an ink coating printed on the surface of the recording medium. The ink coating formed on the surface of the recording medium is, for example, a dried product of the aqueous pigment ink, and the solid content in the aqueous pigment ink of the present invention (for example, the pigment, the binder, and the acrylic additive) (viscous agents, etc.).

Examples of the recording medium include ink-absorbing recording media such as plain paper, and ink-poor or non-ink-absorbing recording media such as coated paper.

"Difficult to absorb ink" means that the amount of water absorbed by the recording medium is 10 g/ ^m2 or less when the recording surface of the recording medium contacts water for 100 msec, and "non-ink absorbent" means that the water absorption amount is 0 g/m ² . The amount of water absorbed is the amount of transfer at a contact time of 100 msec with pure water, which is measured using an automatic scanning absorption meter (KM500win, manufactured by Kumagai Riki Kogyo Co., Ltd.) at 23°C and 50% relative humidity. It is. The measurement conditions are shown below.
[Spiral Method]
Contact Time: 0.010~1.0 (sec)
Pitch: 7 (mm)
Length per sampling: 86.29 (degree)
Start Radius: 20 (mm)
End Radius: 60 (mm)
Min Contact Time: 10 (ms)
Max Contact Time: 1000 (ms)
Sampling Pattern: 50
Number of sampling points: 19
[Square Head]
Slit Span: 1 (mm)
Width: 5 (mm)

Examples of recording media that are poorly absorbent or non-absorbent in ink include cardboard whose surface is provided with a colored layer that does not easily absorb the solvent in the ink, art paper such as printing paper, coated paper, lightweight coated paper, Examples include slightly coated paper and plastic film.

The printed material can be manufactured by printing on the recording medium using the aqueous pigment ink using an inkjet recording method and drying the printed material.

The printed matter is produced by an inkjet recording method in which the distance from a surface (x) having an ink ejection port of an inkjet head to a position (y) where a perpendicular to the surface (x) intersects with the recording medium is 1 mm or more, It can be manufactured by discharging aqueous pigment ink, printing it on the recording medium, and drying it. From the viewpoint of suppressing the white streaks, the distance to the position (y) where the perpendicular to the surface (x) intersects with the recording medium is preferably 5 mm or less, preferably 4 mm or less, and more preferably 3 mm or less.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples.

<Preparation of pigment dispersion>
(Preparation of pigment dispersion resin (P-1))
As the pigment dispersion resin (P-1), a polymer (P-1) prepared according to Synthesis Example 1 of WO2018/190139 pamphlet was used.

Specifically, a hexane solution of BuLi and a styrene solution in which styrene was previously dissolved in tetrahydrofuran were introduced from tube reactors P1 and P2 into a T-shaped micromixer M1, and living anion polymerization was performed to obtain a polymer. .

Next, the polymer obtained in the above step is transferred to the T-shaped micromixer M2 through the tube reactor R1, and the growth end of the polymer is transferred from the reaction regulator (α-methylstyrene (α -MeSt)).

Then, a solution of tert-butyl methacrylate in which tert-butyl methacrylate was previously dissolved in tetrahydrofuran was introduced from the tube reactor P4 into the T-shaped micromixer M3, and the trapped polymer moved through the tube reactor R2 was continuously mixed with the trapped polymer. A living anionic polymerization reaction was performed. Thereafter, the living anionic polymerization reaction was quenched by supplying methanol to produce a block copolymer (PA-1) composition.

When producing the block copolymer (PA-1) composition, the reaction temperature was set at 24° C. by immersing the entire microreactor in a constant temperature bath.
The molar ratio of monomers constituting the block copolymer (PA-1) obtained by the above method is (BuLi/styrene/α-methylstyrene/tert-butyl methacrylate)=1.0/12.0/1. It was 3/8.1.

The resulting block copolymer (PA-1) composition is hydrolyzed by treatment with a cation exchange resin, then distilled off under reduced pressure, and the resulting solid is pulverized to form a powder. A pigment dispersion resin (P-1) consisting of a polymer was obtained.

(Preparation example 2-1)
Carbon black "#960" (trade name) manufactured by Mitsubishi Chemical Corporation was prepared as a black pigment, and a pigment dispersion K (pigment concentration: 20% by mass) was prepared by the following method. First, 150 g of black pigment, 60 g of pigment dispersion resin (P-1), 75 g of propylene glycol, and 19.4 g of a 34% by mass potassium hydroxide aqueous solution were charged into a 1.0 L intensive mixer (manufactured by Nippon Eirich Co., Ltd.), and the rotor The mixture was kneaded for 25 minutes at a peripheral speed of 2.94 m/s and a pan peripheral speed of 1 m/s. Subsequently, while continuing to stir, 306 g of ion-exchanged water was gradually added to the kneaded material in the container of the intensive mixer, followed by 12 g of propylene glycol and 127.0 g of ion-exchanged water so that the pigment concentration was 20% by mass. By further adding 5 g and mixing, an aqueous pigment dispersion (pigment dispersion K) having a pigment concentration of 20% by mass was obtained.

(Preparation example 2-2)
As the cyan pigment, "FASTOGEN BLUE SBG-SD" (trade name) manufactured by DIC Corporation was prepared, and the pigment was prepared in the same manner as in Preparation Example 2-1, except that the cyan pigment was used instead of the black pigment. Dispersion C (pigment concentration: 20% by mass) was prepared.

(Preparation example 2-3)
Pigment dispersion was carried out in the same manner as in Preparation Example 2-1, except that "FASTOGEN SUPER MAGENTA RY" (trade name) manufactured by DIC Corporation was prepared as a magenta pigment, and the magenta pigment was used instead of the black pigment. Body M (pigment concentration: 20% by mass) was prepared.

(Preparation example 2-4)
As a yellow pigment, "FAST YELLOW 7413" (trade name) manufactured by Sanyo Shiki Co., Ltd. was prepared, and pigment dispersion was carried out in the same manner as in Preparation Example 2-1, except that the yellow pigment was used instead of the black pigment. Body Y (pigment concentration: 20% by mass) was prepared.

<Acrylic thickener>
The following two types of acrylic thickeners were prepared.
・Soltix A100 (manufactured by Lubrizol, solid content 30% by mass)
・Soltix A200 (manufactured by Lubrizol, solid content 30% by mass)

<Binder>
As the binder, acid-modified polypropylene shown below was used.
・Auroren AE-301: Nippon Paper Industries Co., Ltd., trade name, acid-modified polypropylene resin, solid content 35% by mass

<Wax>
As the wax, the following oxidized polyethylene wax was prepared.
・AQUACER515: manufactured by BYK, trade name, high-density oxidized polyethylene wax emulsion, melting point (Tm ₂ ) 135°C, solid content 30% by mass

<Preparation of water-based pigment ink>
(Examples 1 to 13)
Using the pigment dispersion obtained above, the pigment dispersion, resin dispersion, binder and wax shown in Tables 1 and 2, an acrylic thickener, propylene glycol and glycerin as high boiling point solvents, and other components were added. Triethanolamine, TegoWET280 (manufactured by Evonik, silicone surfactant), ACTICIDE B20 (manufactured by So Japan Co., Ltd., preservative), ethylene urea, SURFYNOL 420 (manufactured by Evonik, acetylene surfactant) Aqueous pigment inks of Examples 1 to 13 were obtained by mixing and stirring the mixture and distilled water.

The content of the pigment dispersion is such that the concentration of pigment relative to the total amount of the aqueous pigment ink is 5.6% by mass for black ink, 4.3% by mass for cyan ink, 6.0% by mass for magenta ink, and 3% by mass for yellow ink. The amount necessary to adjust the content to .3% by mass was used. For example, in the aqueous pigment ink of Example 1, 22% by mass of pigment dispersion C (4.3% by mass of pigment) was used. The content of the binder was adjusted so that the content of the resin (solid content) would be the value described in the column "Auroren AE301 (solid content) [mass %]" of "Binder" in Tables 1 and 2.

The content of wax (solid content) was 1.0% by mass. The content of the acrylic thickener (solid content) was 0.06 to 0.18% by mass. The content of propylene glycol was set so that the viscosity (32°C) of the aqueous pigment inks in Examples 1 to 5 and 8 to 13 was approximately 4.8 Pa·s, and in Examples 6 and 7, the content of propylene glycol was The content was set at 6 to 20% by mass so that the viscosity (32° C.) was about 6.0 mPa·s and 7.5 mPa·s, respectively. The contents of glycerin, triethanolamine, TegoWET280, ACTICIDE B20, ethylene urea and SURFYNOL 420 are 12.0% by mass, 0.2% by mass, 0.1% by mass, 0.1% by mass, and 5.62% by mass, respectively. % by mass and 1.00% by mass. Distilled water was added so that the total content of the added components was 100% by mass. Note that all of the above contents are based on the total amount of the aqueous ink composition.

(Comparative Examples 1 to 12)
As shown in Tables 3 and 4, in Comparative Example 1, excluding the acrylic thickener, the amount of propylene glycol and the amount of distilled water were adjusted so that the viscosity of the water-based pigment ink at 32°C was around 4.8 mPa・s. A water-based pigment ink was obtained in the same manner as in Example 1, except that . In Comparative Examples 2 to 11, instead of the acrylic thickener, a thickener other than the acrylic thickener described below was used, and propylene was used so that the viscosity at 32°C was around 4.8 mPa・s. A water-based pigment ink was obtained in the same manner as in Example 1, except that the amount of glycol and the amount of distilled water were adjusted. In Comparative Example 12, the amount of binder resin (solid content) was changed to the value shown in Table 2, and the amount of propylene glycol and distilled water were changed so that the viscosity at 32°C was around 4.8 mPa・s. A water-based pigment ink was obtained in the same manner as in Example 1 except that the amount of was adjusted.

<Thickeners other than acrylic thickeners>
・DN-10L (manufactured by Daicel Fine Millize, carboxymethyl cellulose, solid content 100% by mass)
- Ceolus RC-591 (manufactured by Asahi Kasei Chemicals, crystalline cellulose mixture, solid content 100% by mass)
・Pullulan (manufactured by Hayashibara Co., Ltd., polysaccharide, solid content 100% by mass)
・ADEKA NOL UH420 (manufactured by ADEKA, polyurethane, solid content 30% by mass)
・ADEKA NOL UH438 (manufactured by ADEKA, polyurethane, solid content 30% by mass)
・ADEKA NOL UH450VF (manufactured by ADEKA, polyurethane, solid content 30% by mass)
・Disparon AQH-800 (manufactured by Kusumoto Kasei Co., Ltd., polyamide, solid content 12% by mass)
・Disparon AQH-810 (manufactured by Kusumoto Kasei Co., Ltd., polyamide, solid content 17% by mass)
・Disparon AQH-870 (manufactured by Kusumoto Kasei Co., Ltd., polyamide, solid content 17% by mass)
・Smectone-SWN (manufactured by Kunimine Industries, synthetic hectorite, solid content 100% by mass)

<Characteristics evaluation>
The storage stability, filtration performance, ejection stability (initial appearance/white streaks), coating film gloss, drying performance, and image fastness of the aqueous pigment inks of Examples and Comparative Examples were evaluated by the methods shown below. Note that filterability is an evaluation characteristic that is performed when filling an inkjet head with the aqueous pigment ink in order to prevent aggregates and precipitates in the aqueous pigment ink from clogging the inkjet head. . If the filterability is poor, it becomes difficult to fill the inkjet head.

[Evaluation of storage stability]
The water-based pigment inks of Examples and Comparative Examples were filled into plastic bottles, stored in a constant temperature bath at 60°C for 4 weeks, and the rate of change in viscosity of the water-based pigment inks was measured before and after being left in the constant temperature bath. did. The storage stability of the water-based pigment ink was evaluated based on the following criteria. The rate of change in the viscosity is [(Viscosity of the water-based pigment ink before standing - Viscosity of the water-based pigment ink after standing)/(Viscosity of the water-based pigment ink before standing)] x 100. Refers to the calculated value.
5: Rate of change with respect to the initial value (viscosity of the aqueous pigment ink before standing still) is within ±5% 4: Rate of change with respect to the initial value is within ±5% to ±10% 3: To the initial value The rate of change is over ±10% to within ±20% 2: The rate of change is over ±20% to the initial value 1: It gels or aggregates at the time of ink formation, making it impossible to create ink

The viscosity of the ink was measured using a cone-plate rotational viscometer equivalent to an E-type viscometer under the following conditions.
Measuring device: TVE-25 type viscometer (manufactured by Toki Sangyo Co., Ltd., TVE-25 L)
Calibration standard solution: JS20
Measurement temperature: 32℃
Rotation speed: 10-100rpm
Injection volume: 1200μL

[Evaluation of discharge stability (initial occurrence)]
The aqueous pigment inks of Examples and Comparative Examples were each filled into an inkjet head KJ4B-YH manufactured by Kyocera Corporation, and OK Top Coat+ (manufactured by Oji Paper Co., Ltd., basis weight 104.7 g/ A printed matter was obtained by carrying out 100% solid printing on (m ² ). The supply pressure for printing was adjusted by setting the water head difference of the ink subtank from the head nozzle plate surface to +35 cm and the negative pressure to -5.0 kPa. In addition, the shortest distance between the ink ejection opening of the inkjet head and the recording medium (from the surface (x) having the inkjet head's ink ejection opening, the perpendicular line assumed to the surface (x) intersects the recording medium) The distance (gap) to the position (y) was set to 1 mm. The driving conditions for the head were a standard voltage and temperature for an inkjet head, and a droplet size of 18 pL.

After the ink ejection was stopped upon completion of the printing, it was left for 1 minute. After the 1 minute elapsed, the same method as above was applied again to OK Top Coat + (manufactured by Oji Paper Co., Ltd., basis weight 104.7 g/m ² ) and npi high-quality paper (manufactured by Nippon Paper Industries Co., Ltd., basis weight 64 g/m ² ). 100% solid printing was performed, and the edges (2 cm vertical edges) were visually observed and evaluated based on the following criteria.

5: There were no scratches or irregularities on the edge, and the edge was on a straight line.

4: There was some scratching on the edge, but there were few irregularities, and the edge was slightly distorted.

3: The edges were noticeably scratched and uneven, and the edges were greatly distorted.

2: Ink was ejected, but the end portion was not ejected beyond 5 cm.

1: Not a single drop of ink was ejected.

[Evaluation of discharge stability (white streaks)]
The aqueous pigment inks of Examples and Comparative Examples were each filled into an inkjet head KJ4B-YH manufactured by Kyocera Corporation, and OK Top Coat+ (manufactured by Oji Paper Co., Ltd., basis weight 104.7 g/ m ² ) and an ink-absorbing recording medium, NPI high-quality paper (manufactured by Nippon Paper Industries, basis weight 64 g/m ² ), after performing 100% solid printing, at a distance of about 8 cm from the printing surface. A printed matter was obtained by drying it for 1 second using a certain 9 kW near-infrared heater.

The printed surface of the printed matter was read with a scanner, and the percentage of the area where ink was not applied (streak rate) was calculated using image analysis software "ImageJ". The streak rate indicates the ratio of the area where the aqueous pigment ink was not applied to the area where 100% solid printing was performed. The supply pressure in the printing was adjusted by setting the water head difference of the ink sub-tank from the head nozzle plate surface to +35 cm and the negative pressure to -5.0 kPa. In addition, the shortest distance between the ink ejection opening of the inkjet head and the recording medium (from the surface (x) having the inkjet head's ink ejection opening, the perpendicular line assumed to the surface (x) intersects the recording medium) The distance (gap) to the position (y) was set to 1 mm. The driving conditions for the head were a standard voltage and temperature for an inkjet head, and a droplet size of 18 pL.
5: Streak rate of printed matter less than 1% 4: Streak rate of printed matter 1% or more and less than 3% 3: Streak rate of printed matter 3% or more and less than 5% 2: Streak rate of printed matter 5% or more and less than 10% 1: Streaks of printed matter rate of 10% or more

[Evaluation of dryness]
The aqueous pigment inks of Examples and Comparative Examples were each filled into an inkjet head KJ4B-YH manufactured by Kyocera Corporation, and OK Top Coat+ (manufactured by Oji Paper Co., Ltd., basis weight 104.7 g/ m ² ) and an ink-absorbing recording medium, NPI high-quality paper (manufactured by Nippon Paper Industries, basis weight 64 g/m ² ), after performing 100% solid printing, at a distance of about 8 cm from the printing surface. It was heated for 1 second using a 9kW near-infrared heater.

After 10 seconds had elapsed from the end of the heating, the coating film on the printed matter was rubbed by hand using a cotton swab. Next, the coating film of the printed matter 60 seconds after the end of the heating was manually rubbed with a cotton swab.

The scratched coating surface was visually observed, and the drying properties were evaluated based on the following criteria.

5: After 10 seconds, the paint film does not come off at all, and the cotton swab is not colored. 4: There is no visible peeling of the paint film after 10 seconds, but the cotton swab has some color. 3: After 60 seconds, the cotton swab has color. Afterwards, the paint film does not come off at all, and the cotton swab does not get colored (there is some peeling of the paint film that can be seen visually after 10 seconds).
2: There is no visible peeling of the paint film after 60 seconds, but the cotton swab is colored (there is visible paint peeling after 10 seconds)
1: The paint film peels off even after 60 seconds have passed.

[Evaluation of paint film gloss]
The aqueous pigment inks of Examples and Comparative Examples were each filled into an inkjet head KJ4B-YH manufactured by Kyocera Corporation, and OK Top Coat+ (manufactured by Oji Paper Co., Ltd., basis weight 104.7 g/ After performing 100% solid printing on the printed surface (m ² ), it was dried for 1 second using a 9 kW near-infrared heater located approximately 8 cm from the printing surface, and then left at room temperature (25°C) for 12 hours (overnight). ) A printed matter was obtained by leaving it to dry.

Next, the printed surface of the obtained printed matter was measured using a gloss meter micro-TRI-gloss (manufactured by BYK-Gardnaer), and the coating film gloss was evaluated based on the following criteria.

The supply pressure in the printing was adjusted by setting the water head difference of the ink sub-tank from the head nozzle plate surface to +35 cm and the negative pressure to -5.0 kPa. In addition, the shortest distance between the ink ejection opening of the inkjet head and the recording medium (from the surface (x) having the inkjet head's ink ejection opening, the perpendicular line assumed to the surface (x) intersects the recording medium) The distance (gap) to the position (y) was set to 1 mm. The driving conditions for the head were a standard voltage and temperature for an inkjet head, and a droplet size of 18 pL.
5: 60° gloss is 40 or more 4: 60° gloss is 30 or more, less than 40 3: 60° gloss is 20 or more, less than 30 2: 60° gloss is 10 or more, less than 10 1: 60° gloss is less than 10

[Evaluation of image robustness]
The aqueous pigment inks of Examples and Comparative Examples were each filled into an inkjet head KJ4B-YH manufactured by Kyocera Corporation, and OK Top Coat+ (manufactured by Oji Paper Co., Ltd., basis weight 104.7 g/ After performing 100% solid printing on the printed surface (m ² ), it was dried for 1 second using a 9 kW near-infrared heater located approximately 8 cm from the printing surface, and then left at room temperature (25°C) for 12 hours (overnight). ) A printed matter was obtained by leaving it to dry.

Next, using a Gakushin type friction tester RT-300 (manufactured by Daiei Kagaku Seiki Seisakusho Co., Ltd.), the printed surface of the printed material was rubbed 200 times at a load of 100 g/cm ² using the same paper as the printing base material as a friction element. did. The degree of peeling of the coating film on the printed surface was visually observed, and the image fastness was evaluated based on the following criteria.
5: There are no scratches on the printed matter, and no coloring can be seen on the paper to be rubbed.4: There are slight scratches on the printed matter, and slightly light coloring is observed on the paper to be rubbed.3: There are slight scratches on the printed matter, and the paper to be rubbed is also observed. 2: There are many scratches on the printed matter, and dark coloring is observed on the entire surface of the paper to be rubbed. 1: There are many scratches on the printed matter, and dark coloring is observed on the entire surface of the paper to be rubbed. The supply pressure in the above printing was adjusted by setting the water head difference of the ink sub-tank from the head nozzle plate surface to +35 cm and the negative pressure to -5.0 kPa. In addition, the shortest distance between the ink ejection opening of the inkjet head and the recording medium (from the surface (x) having the inkjet head's ink ejection opening, the perpendicular line assumed to the surface (x) intersects the recording medium) The distance (gap) to the position (y) was set to 1 mm. The driving conditions for the head were a standard voltage and temperature for an inkjet head, and a droplet size of 18 pL.

[Evaluation of filterability]
50 mL of each of the aqueous pigment inks of Examples and Comparative Examples was passed through a 5 μm filtration filter, Acrodisk 25 mm w/5 μm Versapor STRL 50/pk (manufactured by Pall), using a syringe, and the amount of liquid passed was measured. Filterability was evaluated based on the following criteria.
5: Liquid passing amount is 50mL
4: The amount of liquid passed is 40 mL or more and less than 50 mL 3: The amount of liquid passed is 30 mL or more and less than 40 mL 2: The amount of liquid passed is 20 mL or more and less than 30 mL 1: The amount of liquid passed is 10 mL or more and less than 20 mL

Claims (10)

An aqueous pigment ink containing an acrylic thickener, a high boiling point solvent having a boiling point of 180° C. or higher, water, a pigment, a binder, and a surfactant,
The aqueous pigment ink has a viscosity of 3 to 10 mPa·s at 32°C,
The high boiling point solvent contains propylene glycol and/or glycerin,
The mass ratio of solid content to the total amount of the aqueous pigment ink is 1 to 12% by mass,
The mass ratio of the high boiling point solvent to the total amount of the aqueous pigment ink is 15 to 35% by mass,
An aqueous pigment ink, wherein the surfactant includes an acetylene surfactant and/or a silicone surfactant. The aqueous pigment ink according to claim 1, wherein the mass ratio of the acrylic thickener to the total amount of the aqueous pigment ink is in the range of 0.01 to 0.3 mass%. the surfactant includes an acetylene surfactant,
The aqueous pigment ink according to claim 1 or 2, wherein the content of the acetylene surfactant is 0.001 to 5% by mass based on the total amount of the aqueous pigment ink. The aqueous pigment ink according to any one of claims 1 to 3, wherein the high boiling point solvent contains propylene glycol and glycerin. The aqueous pigment ink according to any one of claims 1 to 4, wherein the pigment is contained in an amount of 1 to 12% by mass based on the total amount of the aqueous pigment ink. The aqueous pigment ink according to any one of claims 1 to 5, further comprising a wax having a melting point of 150°C or less. The aqueous pigment ink according to claim 6, wherein the wax is an oxidized polyethylene wax. The aqueous pigment ink according to any one of claims 1 to 7, which is used for printing on a recording medium that is poorly absorbent or non-absorbent. A printed matter in which the aqueous pigment ink according to any one of claims 1 to 8 is printed on the surface of a recording medium. An inkjet recording method in which the distance from a surface (x) having an ink ejection port of an inkjet head to a position (y) where a perpendicular to the surface (x) and a recording medium intersect is 1 mm or more, claims 1 to 8. A method for producing a printed matter, comprising discharging the aqueous pigment ink according to any one of the above and printing on the recording medium.