JP7367534B2 - inkjet ink - Google Patents

Description

The present invention relates to an inkjet ink.

In inkjet recording printing, inkjet ink is ejected from a recording head of an inkjet recording apparatus to print an image on a recording medium. For example, Patent Document 1 describes an inkjet ink containing a wax emulsion with an average particle diameter of 150 nm or more and 200 nm or less.

Japanese Patent Application Publication No. 2013-170198

However, the inkjet ink disclosed in Patent Document 1 leaves room for improvement in printing images with excellent scratch resistance while ensuring storage stability and ejection stability.

The present invention has been made in view of the above problems, and its purpose is to provide an inkjet ink that can print images with excellent scratch resistance while ensuring storage stability and ejection stability.

The inkjet ink according to the present invention includes an aqueous medium, a pigment, 2.00% by mass or more and 7.00% by mass of polyhydric alcohol monoalkyl ether, and 30.00% by mass or more and 35.00% by mass or less. It contains a diol compound, 2-pyrrolidone of 6.00% by mass or more and 7.00% by mass or less, and wax particles of 0.14% by mass or more and 2.86% by mass or less. The polyhydric alcohol monoalkyl ether is at least one selected from the group consisting of diethylene glycol monobutyl ether and triethylene glycol monobutyl ether. The diol compound is at least one selected from the group consisting of ethylene glycol and propylene glycol. The volume median diameter of the wax particles is 30 nm or more and 50 nm or less.

According to the inkjet ink according to the present invention, it is possible to print an image with excellent scratch resistance while ensuring storage stability and ejection stability.

Hereinafter, preferred embodiments of the present invention will be described. First, terms used in this specification will be explained. Unless otherwise specified, the content of each component in the inkjet ink is the content (unit: mass %) of each component relative to the total mass of the inkjet ink.

"Volume median diameter" is a particle diameter (volume-based median diameter) at which the cumulative frequency from the small particle size side in the volume-based particle size distribution is 50%. The method for measuring the volume median diameter is the same method as in the examples described later or a method similar thereto.

When measuring the volume median diameter of the wax particles in the inkjet ink, for example, after separating the wax particles in the inkjet ink by centrifugation, the separation is performed using the same method as in the examples described later or a method similar thereto. The volume median diameter of the wax particles is measured.

Hereinafter, the compound and its derivatives may be collectively referred to by adding "system" after the compound name. When a polymer name is expressed by adding "system" after the compound name, it means that the repeating unit of the polymer is derived from the compound or its derivative.

<Inkjet ink>
The inkjet ink of this embodiment (hereinafter sometimes simply referred to as "ink") is suitably used for recording on a recording medium. For example, the ink according to this embodiment is ejected from a nozzle of a recording head of an inkjet recording apparatus toward a printing surface of a recording medium, and is printed on the recording medium. Examples of the recording medium include printing paper (more specifically, plain paper, copy paper, recycled paper, thin paper, thick paper, glossy paper, etc.).

The ink according to the present embodiment includes an aqueous medium, a pigment, a polyhydric alcohol monoalkyl ether of 2.00% by mass or more and 7.00% by mass or less, and a diol of 30.00% by mass or more and 35.00% by mass or less. compound, 6.00% by mass or more and 7.00% by mass or less of 2-pyrrolidone, and 0.14% by mass or more and 2.86% by mass or less of wax particles. The polyhydric alcohol monoalkyl ether is at least one selected from the group consisting of diethylene glycol monobutyl ether and triethylene glycol monobutyl ether. The diol compound is at least one selected from the group consisting of ethylene glycol and propylene glycol. The volume median diameter of the wax particles is 30 nm or more and 50 nm or less.

Hereinafter, at least one polyhydric alcohol monoalkyl ether selected from the group consisting of diethylene glycol monobutyl ether and triethylene glycol monobutyl ether may be referred to as "specific alcohol ether." Furthermore, at least one diol compound selected from the group consisting of ethylene glycol and propylene glycol may be referred to as a "specific diol compound."

According to the ink according to the present embodiment, by having the above-described configuration, it is possible to print an image with excellent scratch resistance while ensuring storage stability and ejection stability. The reason is assumed to be as follows.

The ink according to the present embodiment contains 2.00% by mass or more of a specific alcohol ether, 30.00% by mass or more of a specific diol compound, and 0.14% by mass or more of wax particles. The wax particles contained in the ink according to this embodiment have a volume median diameter of 30 nm or more. For these reasons, in the ink according to this embodiment, the affinity between the wax particles and the specific alcohol ether and specific diol compound tends to be low. Therefore, when the ink according to this embodiment lands on a recording medium, wax particles tend to be easily arranged on the surface of the landed ink. This increases the slipperiness of the image printed on the recording medium, so that the ink according to this embodiment can print an image with excellent scratch resistance.

On the other hand, if the amount of wax particles in the ink is too large, or if the volume median diameter of the wax particles in the ink is too large, the nozzles of the recording head tend to become clogged when printing with the ink. . Furthermore, if the amount of the specific alcohol ether in the ink is too large, or if the amount of the specific diol compound in the ink is too large, the nozzles of the recording head tend to become clogged when printing with the ink. In contrast, in the ink according to the present embodiment, the wax particle content is 2.86% by mass or less, the volume median diameter of the wax particles is 50 nm or less, and the specific alcohol ether content is 7.00 nm or less. % by mass or less, and the content of the specific diol compound is 35.00% by mass or less. As described above, in the ink according to the present embodiment, the upper limit of the content of wax particles, the upper limit of the volume median diameter of wax particles, the upper limit of the content of specific alcohol ether, and the upper limit of the content of specific An upper limit is set for the content of diol compounds. Therefore, according to this embodiment, ink ejection stability can be ensured.

In addition, if the amount of specific alcohol ether in the ink is too large, or if the amount of specific diol compound in the ink is too large, the dispersion stability of the pigment in the ink will decrease, and the storage stability of the ink will be affected. It may decrease. On the other hand, in the ink according to the present embodiment, the content of the specific alcohol ether is 7.00% by mass or less, and the content of the specific diol compound is 35.00% by mass or less. Furthermore, the ink according to this embodiment contains 2-pyrrolidone at a content of 6.00% by mass or more. 2-pyrrolidone has stronger hydrophilicity than specific alcohol ethers and stronger hydrophilicity than specific diol compounds. For these reasons, in the ink according to the present embodiment, aggregation of the pigment can be suppressed even though the specific alcohol ether and the specific diol compound are contained. As a result, the dispersion stability of the pigment increases in the ink according to this embodiment. Therefore, according to the ink according to this embodiment, the storage stability of the ink can be ensured.

Note that if the amount of 2-pyrrolidone in the ink is too large, when the ink lands on the recording medium, for example, the cellulose fibers contained in the printing paper will swell, resulting in a decrease in the scratch resistance of the printed image. There are cases. On the other hand, in the ink according to this embodiment, the content of 2-pyrrolidone is 7.00% by mass or less. As described above, in the ink according to the present embodiment, the upper limit of the content of 2-pyrrolidone is set to an extent that does not reduce the scratch resistance of the printed image. Therefore, when using the ink according to this embodiment, it is possible to both ensure the storage stability of the ink due to 2-pyrrolidone and print an image with excellent scratch resistance.

Each component contained in the ink according to this embodiment will be described in more detail below. Note that among the components described below, components other than 2-pyrrolidone may be used alone or in combination of two or more.

[Aqueous medium]
An aqueous medium is a medium containing water as a main component. The aqueous medium may function as a solvent or a dispersion medium. Specific examples of the aqueous medium include water or a mixture of water and a polar solvent. Examples of polar solvents contained in the aqueous medium include methanol, ethanol, isopropyl alcohol, butanol, and methyl ethyl ketone. The content of water in the aqueous medium is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. The aqueous medium is preferably water, more preferably ion-exchanged water.

The content of the aqueous medium is preferably 5% by mass or more and 99% by mass or less, more preferably 40% by mass or more and 90% by mass or less. When the content of the aqueous medium is within this range, an ink having an appropriate viscosity can be obtained. In addition, when using the pigment dispersion liquid mentioned later as a material of an ink, the mass of the aqueous medium in the pigment dispersion liquid is also included in the mass of the aqueous medium when calculating the preferable content of the aqueous medium.

[Pigment]
Examples of pigments include yellow pigments, orange pigments, red pigments, blue pigments, violet pigments, and black pigments. Examples of yellow pigments include C.I. I. pigment yellow (74, 93, 95, 109, 110, 120, 128, 138, 139, 151, 154, 155, 173, 180, 185, and 193). Examples of orange pigments include C.I. I. Pigment Orange (34, 36, 43, 61, 63, and 71). Examples of red pigments include C.I. I. Pigment Red (122 and 202). Examples of blue pigments include C.I. I. Pigment Blue (15, more specifically 15:3). Examples of the purple pigment include C.I. I. pigment violet (19, 23, and 33). Examples of black pigments include C.I. I. Pigment Black (7).

In order to print an image having a desired image density, the pigment content is preferably 4% by mass or more and 8% by mass or less.

Further, in this embodiment, pigment particles constituting the pigment in the ink may be coated with a coating resin. Hereinafter, a composite containing pigment particles and a coating resin that covers the surface of the pigment particles may be referred to as a pigment dispersion.

In order to print an image having a desired image density while increasing the dispersion stability of the pigment dispersion in the ink, the volume median diameter of the pigment dispersion is preferably 30 nm or more and 200 nm or less, and preferably 70 nm or more. More preferably, the thickness is 130 nm or less. For the same reason, the content of the pigment dispersion is preferably 5% by mass or more and 10% by mass or less. The coating resin that covers the surface of the pigment particles will be described below.

(coating resin)
In order to improve the dispersion stability of the pigment dispersion in the ink, the coating resin may be a styrene-acrylic acid resin, a styrene-maleic acid copolymer, a vinylnaphthalene-acrylic acid copolymer, or a vinylnaphthalene-maleic acid resin. It is preferably at least one of the copolymers, more preferably a styrene-acrylic acid resin, and even more preferably a styrene-acrylic acid resin having anionic properties.

Styrene-acrylic acid resin is a resin containing repeating units derived from styrene and repeating units derived from acrylic acid, methacrylic acid, acrylic ester, or methacrylic ester. In order to further enhance the dispersion stability of the pigment dispersion in the ink, the styrene-acrylic acid resin is a copolymer of styrene, acrylic acid, and an acrylic acid alkyl ester, or a copolymer of styrene, methacrylic acid, and a methacrylic acid alkyl ester. Copolymers of acrylic acid alkyl ester, styrene and acrylic acid copolymers, styrene, maleic acid and acrylic acid alkyl ester copolymers, styrene and methacrylic acid copolymers, and styrene and methacrylic acid Preferably, it is at least one copolymer with an alkyl ester. For the same reason, the styrene-acrylic acid resin is more preferably a copolymer of styrene, methacrylic acid, alkyl methacrylate, and alkyl acrylate; A copolymer with -butyl is more preferable. Note that among the specific examples of the styrene-acrylic acid resins listed above, for the styrene-acrylic acid resins having a carboxyl group, the carboxyl group may be present in the form of a salt.

In order to print an image having a desired image density, the amount of the coating resin is preferably 15 parts by mass or more and 100 parts by mass or less based on 100 parts by mass of the pigment (powder of pigment particles).

(Preparation method of pigment dispersion)
Next, an example of a method for preparing a pigment dispersion will be described. First, a coating resin is synthesized. Specifically, a monomer or prepolymer capable of synthesizing the coating resin by polymerization and a polymerization initiator are added to a predetermined solvent, and the mixture is heated to reflux at a predetermined temperature. In this way, the coating resin is synthesized.

Next, the synthesized coating resin and pigment (powder of pigment particles) are dispersed in an aqueous medium using a media type dispersion machine. In this way, a dispersion liquid (hereinafter sometimes referred to as a pigment dispersion liquid) in which a large number of pigment dispersions are dispersed is obtained.

The amount of the aqueous medium used when dispersing the coating resin and pigment is preferably 1 time or more and 10 times or less, and 1 time or more and 5 times or less, relative to the total mass of the pigment and coating resin. It is more preferable.

The volume median diameter of the pigment dispersion can be adjusted by changing the particle size of the media used in the media-type dispersion machine (for example, the particle size of beads). For example, the smaller the particle size of the media, the smaller the volume median diameter of the pigment dispersion tends to be.

[Specified alcohol ether]
The content of the specific alcohol ether is 2.00% by mass or more and 7.00% by mass or less. If the content of the specific alcohol ether is less than 2.00% by mass, it becomes difficult to print an image with excellent scratch resistance. On the other hand, if the content of the specific alcohol ether exceeds 7.00% by mass, it becomes difficult to ensure the storage stability and ejection stability of the ink. In order to print images with better scratch resistance, triethylene glycol monobutyl ether is preferred as the specific alcohol ether.

[Specific diol compound]
The content of the specific diol compound is 30.00% by mass or more and 35.00% by mass or less. If the content of the specific diol compound is less than 30.00% by mass, it becomes difficult to print an image with excellent scratch resistance. On the other hand, if the content of the specific diol compound exceeds 35.00% by mass, it becomes difficult to ensure the storage stability and ejection stability of the ink. In order to print images with better scratch resistance, propylene glycol is preferred as the specific diol compound.

[2-pyrrolidone]
The content of 2-pyrrolidone is 6.00% by mass or more and 7.00% by mass or less. When the content of 2-pyrrolidone is less than 6.00% by mass, it becomes difficult to ensure the storage stability of the ink. On the other hand, if the content of 2-pyrrolidone exceeds 7.00% by mass, it becomes difficult to print an image with excellent scratch resistance.

[Wax particles]
The content of wax particles is 0.14% by mass or more and 2.86% by mass or less. If the content of wax particles is less than 0.14% by mass, it becomes difficult to print an image with excellent scratch resistance. On the other hand, if the content of wax particles exceeds 2.86% by mass, it becomes difficult to ensure the ejection stability of the ink. Note that the wax particles may contain components other than wax, but in order to print images with better scratch resistance, the wax content in the wax particles should be 80% by mass or more and 100% by mass or less. More preferably, the wax particles are composed of wax (ie, composed only of wax).

The volume median diameter of the wax particles is 30 nm or more and 50 nm or less. If the volume median diameter of the wax particles is less than 30 nm, it becomes difficult to print an image with excellent scratch resistance. On the other hand, if the volume median diameter of the wax particles exceeds 50 nm, it becomes difficult to ensure ink ejection stability.

Examples of the waxes contained in the wax particles include aliphatic hydrocarbon waxes, oxides of aliphatic hydrocarbon waxes, vegetable waxes, animal waxes, mineral waxes, waxes containing fatty acid esters as a main component, and fatty acid ester-based waxes. Waxes that are partially or completely deoxidized may be mentioned.

Examples of the aliphatic hydrocarbon wax include polyolefin wax (more specifically, polyethylene wax, polypropylene wax, polyolefin copolymer wax, etc.), microcrystalline wax, paraffin wax, and Fischer-Tropsch wax.

Examples of oxides of aliphatic hydrocarbon wax include oxidized polyethylene wax and block copolymers of oxidized polyethylene wax. Examples of vegetable waxes include candelilla wax, carnauba wax, pyril wax, jojoba wax, and rice wax. Animal waxes include, for example, beeswax, lanolin, and spermaceti. Mineral waxes include, for example, ozokerite, ceresin, and petrolatum.

Examples of waxes containing fatty acid ester as a main component include montanic acid ester wax and castor wax. Examples of waxes in which part or all of the fatty acid esters are deoxidized include deoxidized carnauba wax.

In order to print an image with better scratch resistance, the wax contained in the wax particles is preferably at least one selected from the group consisting of polyethylene wax and oxidized polyethylene wax.

Wax particles can be contained in the ink, for example, by using a wax particle dispersion described below as a material when producing the ink.

[Surfactant]
The ink of this embodiment preferably contains a surfactant. The surfactant improves the wettability of the ink to the recording medium. Examples of the surfactant include nonionic surfactants and anionic surfactants. In order to further improve the wettability of the ink to the recording medium, the surfactant is preferably a nonionic surfactant, and more preferably a glycol compound having an acetylene group.

In order to further improve the wettability of the ink to the recording medium, the content of the surfactant is preferably 0.10% by mass or more and 0.80% by mass or less, and 0.40% by mass or more and 0.60% by mass. It is more preferable that it is less than % by mass.

[Other ingredients]
The ink of this embodiment may further contain known additives (more specifically, dissolution stabilizers, desiccation inhibitors, antioxidants, viscosity modifiers, pH adjusters, antifungal agents, etc.) as necessary. May be contained. Further, the ink of the present embodiment may further contain at least one selected from the group consisting of polyhydric alcohol monoalkyl ethers other than specific alcohol ethers and diol compounds other than specific diol compounds, if necessary. good.

[Preferred combination of materials]
In this embodiment, in order to print an image with even better scratch resistance while ensuring the storage stability and ejection stability of the ink, it is preferable that the following condition 1 is satisfied, and the following conditions 1 and 2 are satisfied. is more preferable, and it is even more preferable that conditions 1, 2, and 3 below are satisfied.
Condition 1: The ink contains triethylene glycol monobutyl ether as the specific alcohol ether and propylene glycol as the specific diol compound.
Condition 2: The ink contains a nonionic surfactant.
Condition 3: The content of nonionic surfactant is 0.40% by mass or more and 0.60% by mass or less.

<Ink manufacturing method>
Next, a preferred method for manufacturing the ink according to the embodiment described above will be described. Hereinafter, explanations of components that overlap with those of the ink according to the embodiment described above will be omitted.

First, materials (components) for preparing ink are placed in a container so that the content of each component becomes a desired content. Materials for preparing the ink include pigments (or pigment dispersions), specific alcohol ethers, specific diol compounds, 2-pyrrolidone, wax particles (or wax particle dispersions), and aqueous media (e.g., ion-exchanged water). ) is included at least. Examples of the wax particle dispersion include a dispersion in which wax particles are dispersed in ion-exchanged water.

Next, the contents of the container are stirred using a stirrer (for example, "Three-One Motor BL-600" manufactured by Shinto Kagaku Co., Ltd.) to uniformly mix the contents of the container. The stirring speed (rotation speed) when stirring the contents of the container is, for example, 300 rpm or more and 500 rpm or less.

Next, foreign matter and coarse particles contained in the container contents are removed by filtering the container contents using a filter. In this way, an ink is obtained.

Examples of the present invention will be described below, but the present invention is not limited to the scope of the examples in any way. First, a method for measuring the volume median diameter of each component, and a method for measuring the mass average molecular weight (Mw) and acid value of the coating resin (specifically, coating resin P described later) will be explained.

<Measurement method of volume median diameter>
The volume median diameter of each component (specifically, the volume median diameter of the pigment dispersion and the volume median diameter of the wax particles) was determined using dynamic light scattering particle size distribution in an atmosphere at a temperature of 25°C. The measurement was performed using a measuring device ("Zetasizer Nano ZS" manufactured by Sysmex Corporation). In the measurement of the volume median diameter of the pigment dispersion, a solution obtained by diluting the pigment dispersion obtained by the preparation method described below with ion-exchanged water (dilution ratio: 300 times by volume) was used as a measurement sample. In addition, in the measurement of the volume median diameter of wax particles, a wax particle dispersion (more specifically, one of AQUACER (registered trademark) 515, AQUACER (registered trademark) 531, Hitech E-5403P, and MYE-35G), which will be described later, was used. After diluting with ion-exchanged water until the wax particle concentration (solid content concentration) became 0.1% by mass, the obtained diluted liquid was used as a measurement sample.

<Method for measuring mass average molecular weight (Mw) of coating resin P>
The mass average molecular weight (Mw) of the coating resin P was measured using gel filtration chromatography ("HLC-8020GPC" manufactured by Tosoh Corporation) under the following conditions.

[conditions]
Column: “TSKgel SuperMultiporeHZ-H” manufactured by Tosoh Corporation (4.6mm I.D. x 15cm semi-micro column)
Number of columns: 3 Eluent: Tetrahydrofuran Flow rate: 0.35 mL/min Sample injection volume: 10 μL
Measurement temperature: 40℃
Detector: IR detector

The calibration curve used to measure the mass average molecular weight (Mw) was based on TSKgel standard polystyrene manufactured by Tosoh Corporation (F-40, F-20, F-4, F-1, A-5000, A-2500, and A-1000) and n-propylbenzene.

<Method for measuring acid value of coating resin P>
The acid value of the coating resin P was measured according to the neutralization titration method specified in "JIS (Japanese Industrial Standard) K0070-1992".

<Synthesis of coating resin P>
A stirrer, a nitrogen introduction tube, a condenser, and a dropping funnel were set in a four-necked flask (capacity: 1000 mL). The flask was then charged with 100 g of isopropyl alcohol and 300 g of methyl ethyl ketone. Next, the monomer solution was added dropwise to the contents of the flask over 2 hours while heating to reflux at a temperature of 70° C. while bubbling nitrogen. The monomer solution added dropwise contained 40.0 g of styrene, 10.0 g of methacrylic acid, 10.0 g of n-butyl acrylate, 40.0 g of methyl methacrylate, and 0.4 g of azobisisobutyrochloride. It was a mixture with nitrile (AIBN, polymerization initiator).

After dropping the monomer solution, the contents of the flask were further heated to reflux at a temperature of 70° C. for 6 hours.

Next, 50 mL of a methyl ethyl ketone solution containing 0.2 g of AIBN was dropped into the flask over 15 minutes, and then the flask contents were further heated to reflux at a temperature of 70° C. for 5 hours. In this way, a coating resin P (styrene-acrylic acid resin, weight average molecular weight (Mw): 20,000, acid value: 100 mgKOH/g) was obtained.

<Preparation of pigment dispersion L>
Pigment Blue 15:3 as a pigment (Toyo Color Co., Ltd. "Lionol (registered trademark) Blue FG-7330" manufactured by Co., Ltd., components: 15 parts by mass of copper phthalocyanine), 6 parts by mass of coating resin P, 0.5 parts by mass of 1,2-octanediol, and 78 parts by mass of ion-exchanged water. 5 parts by mass were added.

Additionally, an amount of sodium hydroxide necessary for neutralizing the coating resin P was added to the vessel. More specifically, an aqueous sodium hydroxide solution containing 1.1 times the mass of sodium hydroxide as the neutralization equivalent was added to the vessel. Note that the amount of the coating resin P, 6 parts by mass, also includes the amount of sodium added for neutralization. Furthermore, the amount of ion-exchanged water, 78.5 parts by mass, also includes the amount of water contained in the aqueous sodium hydroxide solution added for neutralization and the amount of water generated in the neutralization reaction.

Next, the vessel was filled with media (zirconia beads having an average particle diameter of 0.5 mm) so that the filling amount was 70% by volume based on the capacity of the vessel. The solid content in the vessel was then dispersed in ion-exchanged water for 240 minutes at a temperature of 10° C. and a circumferential speed of 8 m/sec using the above-mentioned media-type wet disperser. As a result, a pigment dispersion L containing a pigment dispersion (a pigment dispersion in which pigment particles were coated with coating resin P) with a volume median diameter of 100 nm was obtained.

<Preparation of ink>
Inks A1 to A8 and B1 to B13 were prepared using the pigment dispersion L obtained by the above procedure and by the preparation method described below. The compositions of inks A1 to A8 and B1 to B13 are shown in Tables 1 to 4.

The meaning of each term in Tables 1 to 4 will be explained below. "TGMB" means triethylene glycol monobutyl ether. "DGMB" means diethylene glycol monobutyl ether. "DGME" means diethylene glycol monoethyl ether. "EG" means ethylene glycol. "PG" means propylene glycol. "PD" means 1,3-propanediol. "TG" means triethylene glycol.

Moreover, "Surfynol 420" means a nonionic surfactant ("Surfynol (registered trademark) 420" manufactured by Nissin Chemical Industry Co., Ltd., component: glycol compound having an acetylene group).

Moreover, "515", "5403P", "531" and "35G" each mean the wax particles in the wax particle dispersion shown in Table 5 below. "Diameter" in Table 5 means the volume median diameter (unit: nm) of the wax particles. "AQUACER" in Table 5 is a registered trademark. The wax particle content in Tables 1 to 4 is the content of solid content (wax particles) contained in the wax particle dispersion in the ink. Furthermore, "ion-exchanged water" in Tables 1 to 4 includes water in the wax particle dispersion.

In Tables 1 to 4, "-" means that the corresponding component was not used. The meaning of each term in Tables 1 to 4 has been explained above.

[Preparation of ink A1]
Pigment dispersion L, triethylene glycol monobutyl ether, ethylene glycol, 2-pyrrolidone, wax particle dispersion ("AQUACER (registered trademark) 515" manufactured by BIC Chemie Japan Co., Ltd., solid content concentration: 35% by mass) , a nonionic surfactant ("Surfynol (registered trademark) 420" manufactured by Nissin Chemical Industry Co., Ltd., component: a glycol compound having an acetylene group), and ion-exchanged water, the content of each component being as shown in Table 1. It was placed in a beaker so that the content was as shown in the "A1" column. Next, the contents of the beaker were stirred for 60 minutes at a rotational speed of 400 rpm using a stirrer ("Three-One Motor BL-600" manufactured by Shinto Kagaku Co., Ltd.) to uniformly mix the contents of the beaker. Next, the contents of the beaker were filtered using a filter (pore size: 5 μm) to remove foreign matter and coarse particles contained in the contents of the beaker, thereby obtaining ink A1.

[Preparation of inks A2 to A8 and B1 to B13]
Inks A2 to A8 and B1 to B13 were obtained in the same manner as ink A1, except that the components shown in Tables 1 to 4 were used at the content rates shown in Tables 1 to 4. Ta.

<Evaluation method>
Inks A1 to A8 and B1 to B13 were evaluated for storage stability, ejection stability, and image density and scratch resistance of printed images using the methods shown below. Note that in each evaluation of ejection stability, image density, and scratch resistance, an inkjet printer (prototype manufactured by Kyocera Document Solutions Co., Ltd.) equipped with a piezo-type line-type recording head was used as an evaluation machine. The inkjet printer was equipped with three recording heads (KJ4B-QA manufactured by Kyocera Document Solutions Co., Ltd., resolution: 600 dpi).

[Storage stability]
After putting ink (specifically, any one of inks A1 to A8 and B1 to B13) into a glass container, the container was sealed. Next, the sealed container containing the above ink was allowed to stand for 4 weeks in an environment with a temperature of 60°C, and the ink was visually observed after standing, and the storage stability of the ink was determined using the following criteria. did. When the evaluation was A, it was evaluated that "storage stability was ensured." Moreover, when the judgment was B, it was evaluated that "storage stability could not be ensured".

(Judgment criteria for storage stability)
A: No precipitation of ink components was observed.
B: Precipitation of ink components was observed.

[Discharge stability]
The recording head of the evaluation machine was filled with ink (specifically, any one of inks A1 to A8 and B1 to B13). Ink ejection conditions were set so that the amount of ink ejected per droplet was 9 pL. Next, in an environment with a temperature of 25° C. and a humidity of 50% RH, a solid image of 10 cm x 10 cm in size was printed on plain paper (“ColorCopy (registered trademark)” manufactured by Mondi, A4 size, basis weight: 90 g/m ² ) and 100 sheets were printed continuously. Then, the printed solid image was visually observed, and the ejection stability of the ink was determined based on the following criteria. When the judgment was A, it was evaluated that "discharge stability was ensured." Moreover, when the judgment was B, it was evaluated that "discharge stability could not be ensured".

(Judgment criteria for discharge stability)
A: No image defects due to nozzle clogging were observed in all of the 100 printed solid images.
B: Image defects due to nozzle clogging were observed in at least one of the 100 printed solid images.

[Image density]
The recording head of the evaluation machine was filled with ink (specifically, any one of inks A1 to A8 and B1 to B13). Ink ejection conditions were set so that the amount of ink ejected per droplet was 9 pL. Next, in an environment with a temperature of 25° C. and a humidity of 50% RH, a solid image of size 10 cm x 10 cm was printed on a sheet of plain paper (“ColorCopy (registered trademark)” manufactured by Mondi, A4 size, Printed on a basis weight of 90 g/m ² ). Then, the image density of the printed solid image was measured using a reflection densitometer ("RD-19" manufactured by X-Rite). Specifically, 10 image density measurement locations were randomly selected in the printed solid image, and the image density was measured at each of the selected measurement locations. Then, the arithmetic mean value of the measured image densities at 10 locations was taken as the evaluation value of the image density of the evaluation target (ink). When the image density (evaluation value) was 0.90 or more, it was evaluated as "good". On the other hand, when the image density (evaluation value) was less than 0.90, it was evaluated as "not good".

[Abrasion resistance]
The recording head of the evaluation machine was filled with ink (specifically, any one of inks A1 to A8 and B1 to B13). Ink ejection conditions were set so that the amount of ink ejected per droplet was 9 pL. Next, in an environment with a temperature of 25° C. and a humidity of 50% RH, a solid image of size 10 cm x 10 cm was printed on a sheet of plain paper (“ColorCopy (registered trademark)” manufactured by Mondi, A4 size, Printed on a basis weight of 90 g/m ² ). After 10 seconds have elapsed since the printing of the solid image, the unprinted plain paper ("ColorCopy (registered trademark)" manufactured by Mondi) is placed on the surface of the plain paper on which the solid image has been printed (the surface on the solid image side). , A4 size, basis weight: 90 g/m ² ) were stacked on top of each other. Next, while applying a load of 1 kg to the unprinted plain paper using a weight, one side of the unprinted plain paper was rubbed back and forth over the solid image 5 times (rubbing test). After 5 minutes had elapsed from the end of the scratch test, the image density of the above-mentioned surface of the unprinted plain paper was measured using a reflection densitometer ("RD-19" manufactured by X-Rite). Specifically, three image density measurement locations were randomly selected in the area of the above-mentioned surface that was in contact with the solid image, and the image density was measured at each of the selected measurement locations. Then, the arithmetic mean value of the measured image densities at the three locations was taken as the evaluation value of the scratch resistance of the evaluation target (ink). When the image density (evaluation value) was less than 0.020, it was evaluated that "an image with excellent scratch resistance was printed." On the other hand, when the image density (evaluation value) was 0.020 or more, it was evaluated that "an image with excellent scratch resistance could not be printed."

<Evaluation results>
For each of the inks A1 to A8 and B1 to B13, the storage stability and ejection stability evaluation results, as well as the image density and scratch resistance evaluation values of the printed images are shown in Table 6.

Inks A1 to A8 contained an aqueous medium (ion-exchanged water), a pigment, a specific alcohol ether, a specific diol compound, 2-pyrrolidone, and wax particles. In Inks A1 to A8, the content of specific alcohol ether was 2.00% by mass or more and 7.00% by mass or less. In Inks A1 to A8, the content of the specific diol compound was 30.00% by mass or more and 35.00% by mass or less. In Inks A1 to A8, the content of 2-pyrrolidone was 6.00% by mass or more and 7.00% by mass or less. In Inks A1 to A8, the wax particle content was 0.14% by mass or more and 2.86% by mass or less. In Inks A1 to A8, the volume median diameter of wax particles was 30 nm or more and 50 nm or less.

As shown in Table 6, the storage stability of inks A1 to A8 was evaluated as A. Therefore, inks A1 to A8 were able to ensure storage stability. For inks A1 to A8, the ejection stability was evaluated as A. Therefore, inks A1 to A8 were able to ensure ejection stability. The scratch resistance evaluation value for images printed using each of inks A1 to A8 was less than 0.020. Therefore, when each of inks A1 to A8 was used, images with excellent scratch resistance could be printed.

In ink B1, the content of wax particles exceeded 2.86% by mass. In inks B2 and B13, the volume median diameter of wax particles exceeded 50 nm. Ink B3 contained diethylene glycol monoethyl ether as a polyhydric alcohol monoalkyl ether, but did not contain any specific alcohol ether. Ink B4 had a specific alcohol ether content of less than 2.00% by mass. In ink B5, the content of specific alcohol ether exceeded 7.00% by mass. Ink B6 contained 1,3-propanediol as a diol compound, but did not contain any specific diol compound. Ink B7 contained triethylene glycol as a diol compound, but did not contain any specific diol compound. In ink B8, the content of the specific diol compound was less than 30.00% by mass. In Ink B9, the content of the specific diol compound exceeded 35.00% by mass. Ink B10 had a 2-pyrrolidone content of less than 6.00% by mass. In ink B11, the content of wax particles was less than 0.14% by mass. In Ink B12, the content of 2-pyrrolidone exceeded 7.00% by mass.

As shown in Table 6, the storage stability of inks B5, B9, and B10 was evaluated as B. Therefore, inks B5, B9, and B10 could not ensure storage stability. For inks B1, B2, B5, B9, B10, and B13, the ejection stability was evaluated as B. Therefore, inks B1, B2, B5, B9, B10, and B13 could not ensure ejection stability. The scratch resistance evaluation value of the images printed using each of inks B3, B4, B6 to B8, B11, and B12 was 0.020 or more. Therefore, when each of inks B3, B4, B6 to B8, B11, and B12 were used, an image with excellent scratch resistance could not be printed.

The above results indicate that the ink according to the present invention can print images with excellent scratch resistance while ensuring storage stability and ejection stability.

The ink according to the present invention can be used, for example, to print images using a printer.

Claims (5)

an aqueous medium;
pigment and
2.00% by mass or more and 7.00% by mass or less of polyhydric alcohol monoalkyl ether;
A diol compound of 30.00% by mass or more and 35.00% by mass or less,
2-pyrrolidone of 6.00% by mass or more and 7.00% by mass or less,
Containing wax particles of 0.14% by mass or more and 2.86% by mass or less,
The polyhydric alcohol monoalkyl ether is at least one selected from the group consisting of diethylene glycol monobutyl ether and triethylene glycol monobutyl ether,
The diol compound is at least one selected from the group consisting of ethylene glycol and propylene glycol,
An inkjet ink, wherein the wax particles have a volume median diameter of 30 nm or more and 50 nm or less. The inkjet ink according to claim 1, further comprising a surfactant. The inkjet ink according to claim 2, wherein the content of the surfactant is 0.10% by mass or more and 0.80% by mass or less. The inkjet ink according to any one of claims 1 to 3, wherein the wax contained in the wax particles is at least one selected from the group consisting of polyethylene wax and oxidized polyethylene wax. Containing the triethylene glycol monobutyl ether as the polyhydric alcohol monoalkyl ether,
The inkjet ink according to any one of claims 1 to 4, containing the propylene glycol as the diol compound.