JP2021038295A - Ink for inkjet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inkjet ink which is excellent in ejection stability in high-speed printing, can be appropriately wetted and spread after landing on a recording medium, and can suppress the occurrence of offset and bleeding of an image to be formed.
An inkjet ink has a dynamic surface tension γ ₀ at a surface life of 0 msec of 55 mN / m or more and 60 mN / m or less, and a dynamic surface tension γ ₁₀ at a surface life of 10 msec of 40 mN / m. _{The dynamic surface tension γ 100} at m or more and 50 mN / m or less and the surface life of 100 msec is more than 30 mN / m and 33 mN / m or less, and the dynamic surface tension γ _{1000 at the surface life of 1000 msec is 30 mN / m.} It is m or more and less than 33 mN / m, and the dynamic surface tension γ ₁₀₀₀ is smaller than the dynamic surface tension γ _100.
[Selection diagram] None

Description

The present invention relates to an ink for an inkjet.

Ink for inkjet is required to have excellent ejection stability, to appropriately wet and spread after landing on a recording medium, and to suppress the occurrence of offset and bleeding of an image to be formed. These requirements are particularly important for inkjet inks used in an inkjet recording device that performs high-speed printing (for example, an inkjet recording device including a piezo recording head having a drive frequency of 18 kHz or more).

In response to such demands, for example, it has been proposed to adjust the dynamic surface tension of an inkjet ink to a specific range. Specifically, Patent Document 1 proposes an inkjet ink having a specific range of dynamic surface tension at a surface life of 50 ms and a specific range of dynamic surface tension at a surface life of 5000 ms. Has been done. Further, Patent Document 2 proposes an inkjet ink in which the dynamic surface tension at a surface life of 10 ms is within a specific range and the dynamic surface tension at a surface life of 100 ms is within a specific range. ..

Japanese Unexamined Patent Publication No. 2008-1891 Japanese Unexamined Patent Publication No. 2003-231838

However, even with the inkjet inks described in Patent Documents 1 and 2, it is difficult to satisfy all the above requirements in high-speed printing.

The present invention has been made in view of the above problems, and an object of the present invention is to provide excellent ejection stability in high-speed printing, to appropriately wet and spread after landing on a recording medium, and to prevent offset and blurring of formed images. The purpose of the present invention is to provide an ink for an inkjet that can suppress the generation.

The ink for inkjet according to the present invention has a dynamic surface tension γ ₀ of 55 mN / m or more and 60 mN / m or less at _{a surface life of 0 ms, and a dynamic surface tension γ 10} of 40 mN / m at a surface life of 10 ms. _{The dynamic surface tension γ 100} at m or more and 50 mN / m or less and the surface life of 100 ms is more than 30 mN / m and 33 mN / m or less, and the dynamic surface tension γ _{1000 at the surface life of 1000 ms is 30 mN / m.} It is m or more and less than 33 mN / m, and the dynamic surface tension γ ₁₀₀₀ is smaller than the dynamic surface tension γ _100.

The inkjet ink according to the present invention has excellent ejection stability in high-speed printing, can be appropriately wetted and spread after landing on a recording medium, and can suppress the occurrence of offset and bleeding of the formed image.

Hereinafter, embodiments of the present invention will be described. In the following, unless otherwise specified, the measured value of the medium volume diameter (D ₅₀ ) is a dynamic light scattering type particle size distribution measuring device (“Zetasizer Nano ZS” manufactured by Sysmex Co., Ltd.). It is a measured value.

In the following, the measured value of the acid value is a value measured according to "JIS (Japanese Industrial Standards) K0070-1992" unless otherwise specified. Further, the measured value of the mass average molecular weight (Mw) is a value measured by using gel permeation chromatography, unless otherwise specified.

In the present specification, acrylic and methacrylic may be collectively referred to as "(meth) acrylic".

In the present specification, the dynamic surface tension and the static surface tension both indicate the dynamic surface tension and the static surface tension at a temperature of 25 ° C. In the present specification, the dynamic surface tension can be measured by the method described in Examples or a method similar thereto.

<Ink>
Hereinafter, the inkjet ink of the present invention (hereinafter, may be simply referred to as ink) will be described. The ink of the present invention has a dynamic surface tension γ ₀ of 55 mN / m or more and 60 mN / m or less at _{a surface life of 0 msec, and a dynamic surface tension γ 10} of 40 mN / m or more and 50 mN at a surface life of 10 msec. _{/ M or less, the dynamic surface tension γ 100} at a surface life of 100 msec is more than 30 mN / m and 33 mN / m or less, and the dynamic surface tension γ _{1000 at a surface life of 1000 msec is 30 mN / m or more and 33 mN.} It is less than / m and the dynamic surface tension γ ₁₀₀₀ is smaller than the dynamic surface tension γ _100.

By providing the above-mentioned configuration, the ink of the present invention has excellent ejection stability in high-speed printing (for example, an inkjet recording device including a piezo recording head having a drive frequency of 18 kHz or more), and is suitable after landing on a recording medium. It is possible to suppress the occurrence of offset and bleeding of the image that is wet and spreads and is formed. Here, the ejection stability of the inkjet ink can be evaluated by observing the formed image. Specifically, the inkjet ink can be evaluated to be excellent in ejection stability when satellite droplets and white streaks due to ejection defects do not occur in the formed image.

It is presumed that the reason why the ink of the present invention exerts the above-mentioned effect by having the above-mentioned constitution is as follows. _{First, the dynamic surface tension γ 0 when} the surface life of the ink is 0 ms is an index showing the ink properties immediately before the ink is ejected from the nozzle of the recording head and immediately after the ink is ejected. Ink with a dynamic surface tension γ ₀ of less than 55 mN / m cannot be grouped as a single droplet after being ejected from a nozzle, and tends to generate satellite droplets. Further, an ink having a dynamic surface tension γ ₀ of more than 60 mN / m tends to have low wettability with respect to the inner wall of the nozzle when moving through the flow path to the nozzle of the recording head. Therefore, an ink having a dynamic surface tension γ ₀ of more than 60 mN / m tends to be inferior in the property (refillability) of being smoothly refilled in the nozzle after being ejected from the nozzle. Ink with poor refillability causes non-ejection and tends to generate white streaks in the formed image. On the other hand, since the ink of the present invention has a dynamic surface tension γ ₀ of 55 mN / m or more and 60 mN / m or less, satellite droplets and white streaks caused by ejection defects are formed in the formed image even in high-speed printing. Is unlikely to occur.

_{Next, the dynamic surface tension γ 10} at the surface life of the ink of 10 ms is an index showing the properties of the ink immediately after the ink ejected from the nozzle lands on the recording medium. An ink having a dynamic surface tension γ ₁₀ of less than 40 mN / m tends to quickly permeate in the thickness direction of the recording medium before permeating in the surface direction of the recording medium, and thus is difficult to wet and spread in the recording medium. Ink with a dynamic surface tension γ ₁₀ of more than 50 mN / m is difficult to penetrate in both the surface direction and the thickness direction of the recording medium. Since the ink of the present invention has a dynamic surface tension γ ₁₀ of 40 mN / m or more and 50 mN / m or less, it can be appropriately wetted and spread on a recording medium even in high-speed printing. As a result, the ink of the present invention can form moderately large pixels.

_{Next, the dynamic surface tension γ 100 when} the surface life of the ink is 100 ms is an index showing the properties of the ink contained in the image while the recording medium after image formation is being conveyed in the inkjet recording device. is there. Ink having a dynamic surface tension γ ₁₀₀ of more than 33 mN / m cannot be sufficiently fixed on a recording medium and tends to adhere to various members (for example, various rollers) in an inkjet recording device. Since the ink of the present invention has a dynamic surface tension γ ₁₀₀ of 33 mN / m or less, it is possible to suppress the occurrence of offset of the formed image even in high-speed printing. Further, an ink having a dynamic surface tension γ ₁₀₀ of 30 mN / m or less tends to have an excessively low _{dynamic surface tension γ 1000} at a surface life of 1000 ms, which will be described later. Since the ink of the present invention has a dynamic surface tension γ ₁₀₀ of more than 30 mN / m, the dynamic surface tension γ ₁₀₀₀ can be adjusted to an appropriate range.

_{Next, the dynamic surface tension γ 1000} at a surface life of 1000 milliseconds of the ink is an index showing the properties of the ink contained in the image after the recording medium after image formation is discharged from the inkjet recording device. Ink with a dynamic surface tension γ ₁₀₀₀ of less than 30 mN / m tends to cause bleeding in the formed image due to excessive penetration of the ink into the recording medium. Since the ink of the present invention has a dynamic surface tension γ ₁₀₀₀ of 30 mN / m or more, it is possible to suppress the occurrence of blurring of the formed image. Further, an ink having a dynamic surface tension γ ₁₀₀₀ of 33 mN / m or more tends to have an excessively high _{dynamic surface tension γ 100} at the above-mentioned surface life of 100 ms. _{Since the dynamic surface tension γ 1000} of the ink of the present invention is less than 33 mN / m, the dynamic surface tension γ ₁₀₀ can be adjusted to an appropriate range.

_{The dynamic surface tension γ 0} of the ink of the present invention at a surface life of 0 ms is preferably 56 mN / m or more and 58 mN / m or less. _{The dynamic surface tension γ 10} of the ink of the present invention at a surface life of 10 ms is preferably 43 mN / m or more and 47 mN / m or less. _{The dynamic surface tension γ 100} of the ink of the present invention with a surface life of 100 ms is preferably 32 mN / m or more and 33 mN / m or less. _{The dynamic surface tension γ 1000} of the ink of the present invention at a surface life of 1000 ms is preferably 30 mN / m or more and 31 mN / m or less.

The ink of the present invention contains, for example, a pigment, water, an octanediol, an acetylene glycol surfactant, and a silicone surfactant. The ink of the present invention preferably further contains pentanediol. The recording medium for forming an image with the ink of the present invention is not particularly limited, but recording paper is preferable. Hereinafter, the ink of the present invention will be described in more detail. In addition, each component described below may be used individually by 1 type, and may be used in combination of 2 or more type.

[Pigment]
In the ink of the present invention, the pigment exists, for example, as particles dispersed in a solvent (hereinafter, may be referred to as pigment particles). The D ₅₀ of the pigment particles is preferably 30 nm or more and 200 nm or less, and more preferably 70 nm or more and 130 nm or less.

Examples of the pigment include a yellow pigment, an orange pigment, a red pigment, a blue pigment, a purple pigment, and a black pigment. Examples of the yellow pigment 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 the orange pigment include C.I. I. Pigment oranges (34, 36, 43, 61, 63, and 71). Examples of the red pigment include C.I. I. Pigment Red (122 and 202). Examples of the blue pigment 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 the black pigment include C.I. I. Pigment Black (7) can be mentioned.

When the ink of the present invention contains a pigment, the content ratio of the pigment in the ink of the present invention is preferably 0.3% by mass or more and 5.0% by mass or less, and 1.0% by mass or more and 3.0% by mass or less. The following is more preferable. By setting the content ratio of the pigment to 0.3% by mass or more, the scratch resistance of the formed image can be improved. By setting the pigment content to 5.0% by mass or less, the fluidity of the ink of the present invention can be improved.

The pigment particles may contain only the pigment. Further, the pigment particles may contain a pigment and a resin. Examples of the pigment particles containing the pigment and the resin include pigment particles containing a pigment core containing a pigment and a resin that coats the surface of the pigment core (hereinafter, may be referred to as a coating resin). Examples of the coating resin include a copolymer of at least one monomer of (meth) acrylic acid alkyl ester, styrene and vinylnaphthalene, and at least one monomer of (meth) acrylic acid and maleic acid. Be done.

The coating resin includes a repeating unit derived from (meth) acrylic acid ((meth) acrylic acid unit), a repeating unit derived from (meth) acrylic acid alkyl ester ((meth) acrylic acid alkyl ester unit), and styrene. A resin having a unit is preferable. In this case, the ratio of the (meth) acrylic acid unit to the total repeating units of the coating resin is preferably 20% by mass or more and 60% by mass or less. The ratio of the (meth) acrylic acid alkyl ester unit to the total repeating units of the coating resin is preferably 30% by mass or more and 65% by mass or less. The ratio of the styrene unit to the total repeating unit of the coating resin is preferably 5% by mass or more and 25% by mass or less. As the coating resin, a resin having a repeating unit derived from methacrylic acid, a repeating unit derived from methyl methacrylate, a repeating unit derived from butyl acrylate, and a styrene unit is more preferable.

When the ink of the present invention contains a coating resin, the content of the coating resin in the ink of the present invention is preferably 10 parts by mass or more and 100 parts by mass or less, and 30 parts by mass or more and 50 parts by mass or more, based on 100 parts by mass of the pigment. More preferably, it is by mass or less. By setting the content of the coating resin to 10 parts by mass or more, the dispersibility of the pigment particles can be improved. By setting the content of the coating resin to 100 parts by mass or less, the occurrence of nozzle clogging can be suppressed.

The acid value of the coating resin is, for example, 50 mgKOH / g or more and 150 mgKOH / g or less. By setting the acid value of the coating resin to 50 mgKOH / g or more and 150 mgKOH / g or less, it is possible to improve the storage stability of the ink of the present invention while more effectively suppressing the aggregation of pigment particles.

The acid value of the coating resin can be adjusted by the amount of the monomer used when synthesizing the coating resin. For example, when synthesizing a coating resin, the acid value of the coating resin is increased by using a monomer having an acidic functional group (for example, a carboxy group) (more specifically, acrylic acid, methacrylic acid, etc.). Can be made to.

The Mw of the coating resin is, for example, 10,000 or more and 50,000 or less. By setting the Mw of the coating resin to 10,000 or more and 50,000 or less, it is possible to improve the image density of the formed image while suppressing an increase in the viscosity of the ink of the present invention.

[water]
When the ink of the present invention contains water, the content ratio of water in the ink of the present invention is, for example, 30.0% by mass or more and 60.0% by mass or less.

[Pentane diol]
The pentane diol adjusts the surface tension of the ink of the present invention (particularly, the dynamic surface tension γ _{0 at a surface life of 0 ms).} Specifically, the ink of the present invention tends to have a lower _{dynamic surface tension γ 0 as it contains more pentanediol.} As the pentane diol, 1,3-pentane diol is preferable.

When the ink of the present invention contains pentanediol, the content ratio of pentanediol in the ink of the present invention is preferably 19.0% by mass or more and 35.0% by mass or less, and 25.0% by mass or more and 32.0% by mass. More preferably, it is mass% or less. By setting the content ratio of pentanediol to 19.0% by mass or more and 35.0% by mass or less, it _{becomes easy to adjust the dynamic surface tension γ 0} of the ink of the present invention within the above range.

[Octanediol]
Octanediol adjusts the surface tension of the ink of the present invention (particularly, the dynamic surface tension γ _{0 at a surface life of 0 ms).} Specifically, the ink of the present invention tends to have a lower _{dynamic surface tension γ 0 as it contains more octane diol.} As the octane diol, 1,8-octane diol is preferable.

When the ink of the present invention contains octanediol, the content ratio of octanediol in the ink of the present invention is preferably 0.3% by mass or more and 3.5% by mass or less, and 0.7% by mass or more and 1.5% by mass. More preferably, it is by mass or less. By setting the content ratio of octane diol to 0.3% by mass or more and 3.5% by mass or less, it _{becomes easy to adjust the dynamic surface tension γ 0} of the ink of the present invention within the above range.

[Acetylene glycol surfactant]
The acetylene glycol surfactant adjusts the surface tension of the ink of the present invention (particularly, the dynamic surface tension γ _{10 at a surface life of 10 ms).} It is determined that this is because the acetylene glycol surfactant moves to the interface of the ink droplets in about 10 milliseconds after the ink droplets are ejected from the nozzle. Specifically, the ink of the present invention tends to increase the _{dynamic surface tension γ 10} as the amount of the acetylene glycol surfactant is contained. As the acetylene glycol surfactant, an ethylene oxide adduct of acetylene diol is preferable.

When the ink of the present invention contains an acetylene glycol surfactant, the content ratio of the acetylene glycol surfactant in the ink of the present invention is preferably 0.8% by mass or more and 1.2% by mass or less. By setting the content ratio of the acetylene glycol surfactant to 0.8% by mass or more and 1.2% by mass or less, it _{becomes easy to adjust the dynamic surface tension γ 10} of the ink of the present invention within the above range.

[Silicone surfactant]
The silicone surfactant adjusts the surface tension of the ink of the present invention (particularly, the dynamic surface tension γ _{100 at} a surface life of 100 ms and the dynamic surface tension γ _{1000 at a surface life of 1000 ms).} It is determined that this is because the silicone surfactant moves to the interface of the ink droplets in about 100 ms to 1000 ms after the ink droplets are ejected from the nozzle. Specifically, the more the ink of the present invention contains a silicone surfactant, the _{lower the dynamic surface tension γ 100} and the dynamic surface tension γ ₁₀₀₀ tend to be. As the silicone surfactant, a polyether-modified siloxane (siloxane compound having a polyether group) is preferable.

When the ink of the present invention contains a silicone surfactant, the content ratio of the silicone surfactant in the ink of the present invention is preferably 0.08% by mass or more and 0.11% by mass or less. By setting the content ratio of the silicone surfactant to 0.08% by mass or more and 0.11% by mass or less, the dynamic surface tension γ ₁₀₀ and the dynamic surface tension γ ₁₀₀₀ of the ink of the present invention are adjusted within the above ranges. It will be easier.

[Other ingredients]
The ink of the present invention may further contain a surfactant other than the acetylene glycol surfactant and the silicone surfactant, if necessary. Further, the ink of the present invention is a known additive (more specifically, for example, a dissolution stabilizer, a drying inhibitor, an antioxidant, a viscosity regulator, a pH regulator and a fungicide), if necessary. May be further contained.

(Dissolution stabilizer)
The dissolution stabilizer promotes the compatibility of each component contained in the ink of the present invention, and stabilizes the dissolved state of the ink of the present invention. Examples of the dissolution stabilizer include 2-pyrrolidone, N-methyl-2-pyrrolidone and γ-butyrolactone. As the dissolution stabilizer, 2-pyrrolidone is preferable. When the ink of the present invention contains a dissolution stabilizer, the content ratio of the dissolution stabilizer in the ink of the present invention is preferably 1.0% by mass or more and 15.0% by mass or less, and 4.0% by mass or more 9 More preferably, it is 0.0% by mass or less.

(Anti-drying agent)
Glycerin is preferable as the anti-drying agent. When the ink of the present invention contains an anti-drying agent, the content ratio of the anti-drying agent in the ink of the present invention is preferably 1.0% by mass or more and 15.0% by mass or less, and 4.0% by mass or more 9 More preferably, it is 0.0% by mass or less.

[Ink manufacturing method]
The ink of the present invention contains, for example, a pigment dispersion containing pigment particles, water, pentanediol, octanediol, an acetylene glycol surfactant, a silicone surfactant, and other components such as additives. It can be manufactured by uniformly mixing with a stirrer. In the production of the ink of the present invention, after each component is uniformly mixed, foreign matter and coarse particles may be removed by a filter (for example, a filter having a pore size of 5 μm or less).

(Pigment dispersion)
The pigment dispersion is a dispersion containing pigment particles. Water is preferable as the dispersion medium of the pigment dispersion liquid. The pigment dispersion can be prepared by dispersing the pigment in water. In the preparation of the pigment dispersion liquid, it is preferable to add a coating resin from the viewpoint of improving the dispersibility of the pigment particles.

In the preparation of the pigment dispersion liquid, the ratio of the addition amount of the pigment to the addition amount of all the raw materials of the pigment dispersion liquid is, for example, 5.0% by mass or more and 25.0% by mass or less. When a coating resin is used in the preparation of the pigment dispersion liquid, the ratio of the addition amount of the coating resin to the addition amount of all the raw materials of the pigment dispersion liquid is, for example, 2.0% by mass or more and 10.0% by mass or less.

When the pigment dispersion liquid is added in the production of the ink of the present invention, the ratio of the pigment dispersion liquid to all the raw materials of the ink is, for example, 5.0% by mass or more and 20.0% by mass or less.

Hereinafter, examples of the present invention will be described. However, the present invention is not limited to the following examples. First, the raw materials used for producing each ink will be described.

(Preparation of coating resin)
Repeat unit derived from methacrylic acid (MAA unit), repeating unit derived from methyl methacrylate (MMA unit), repeating unit derived from butyl acrylate (BA unit), and repeating unit derived from styrene (ST unit). ) And an alkali-soluble resin was prepared. This alkali-soluble resin had a mass average molecular weight (Mw) of 20000 and an acid value of 100 mgKOH / g. The mass ratio of each repeating unit in this alkali-soluble resin was "MAA unit: MMA unit: BA unit: ST unit = 40:15: 30: 15". 100 parts by mass of this alkali-soluble resin and an aqueous potassium hydroxide solution containing 10.5 parts by mass of potassium hydroxide were mixed. Thereby, the alkali-soluble resin was neutralized with an equal amount (strictly, 105% amount) of KOH. As a result, a coating resin solution containing a coating resin and water was obtained.

(Preparation of pigment dispersion)
Pigments (“Lionol® Blue FG-7330” manufactured by Toyo Color Co., Ltd., component: copper phthalocyanine, color index: Pigment Blue 15: 3) and the above-mentioned coating resin so as to have the compositions shown in Table 1 below. The solution, "Orphine (registered trademark) E1010" (ethylene oxide adduct of acetylenediol) manufactured by Nisshin Chemical Industry Co., Ltd. as a surfactant, and ion-exchanged water were put into a vessel having a capacity of 0.6 L. Next, the contents of the vessel were wet-dispersed using a media-type wet disperser (“DYNO®-MILL” manufactured by Willie et Bacoffen (WAB)).

The content ratio of "water" in Table 1 below is the ion-exchanged water charged into the above-mentioned vessel and the water contained in the coating resin solution (specifically, potassium hydroxide used for neutralizing the alkali-soluble resin). The total content ratio of the water contained in the aqueous solution and the water produced by the neutralization reaction of the alkali-soluble resin and potassium hydroxide) is shown.

Subsequently, media (zirconia beads) was filled in the vessel. The amount of media input was 70% by volume with respect to 100% by volume of vessel capacity. Then, the contents of the vessel were dispersed under the condition of a peripheral speed of 8 m / sec while maintaining the temperature inside the vessel at 10 ° C. by water cooling. As a result, a pigment dispersion was obtained.

_{The volume median diameter (D 50} ) of the pigment particles contained in the obtained pigment dispersion was measured. Specifically, the obtained pigment dispersion was diluted 300-fold with ion-exchanged water, and this was used as a measurement sample. _{The D 50} of the pigment particles in the measurement sample was measured using a dynamic light scattering type particle size distribution measuring device (“Zetasizer Nano ZS” manufactured by Sysmex Corporation). The D ₅₀ of the pigment particles in the measurement sample, and a D ₅₀ of the pigment particles contained in the pigment dispersion. _{The D 50} of the pigment particles contained in the pigment dispersion was 100 nm.

<Ink manufacturing>
[Ink A]
Ion-exchanged water was poured into a beaker equipped with a stirrer (“Three One Motor (registered trademark) BL-600” manufactured by Shinto Kagaku Co., Ltd.). While stirring the contents with the above-mentioned stirrer (stirring speed: 400 rpm), the above-mentioned pigment dispersion, glycerin, 2-pyrrolidone, 1,3-pentanediol, 1,8-octanediol, and acetylene glycol Surfactant ("Orfin (registered trademark) E1010" manufactured by Nissin Chemical Industry Co., Ltd., ethylene oxide adduct of acetylenediol) and silicone surfactant ("BYK (registered trademark) 348" manufactured by Big Chemie Japan Co., Ltd., poly Ether-modified siloxane) was added. The ratio of the input amount of each raw material is as shown in Table 2 below. In order to remove foreign matter and coarse particles from the obtained mixed solution, the mixed solution was filtered using a filter having a pore size of 5 μm. As a result, ink A was obtained.

[Ink B to Ink N]
Ink B to Ink N were produced by the same method as that for Ink A, except that the following points were changed. In the production of inks B to N, the ratio of the input amount of each raw material was as shown in Table 2 below. In Table 2 below, "pentanediol" and "octanediol" represent 1,3-pentanediol and 1,8-octanediol, respectively. The amount of ion-exchanged water input is from 100% by mass of the total amount of the ink raw material to other components (specifically, pigment dispersion, glycerin, 2-pyrrolidone, 1,3-pentanediol, 1,8-octanediol). , Acetylene glycol surfactant and silicone surfactant), which corresponds to the remaining amount after subtracting the input amount. For example, in ink A, the input amount of ion-exchanged water is 43.9% by mass.

[Measurement of dynamic surface tension]
_{The dynamic surface tension γ 0} at the surface life of 0 ms of each ink was determined by the following method. First, among the components used as raw materials for ink, glycerin, 2-pyrrolidone, 1,3-pentanediol, 1,8-octanediol, and water 25, which are components that mainly contribute to _{the dynamic surface tension γ 0.} The static surface tension at ° C is shown in Table 3 below.

Next, for each ink, a value (product A) obtained by multiplying the ratio of the amount of glycerin input and the static surface tension of glycerin was obtained. Further, for each ink, a value (product B) obtained by multiplying the ratio of the input amount of 2-pyrrolidone and the static surface tension of 2-pyrrolidone was obtained. Further, for each ink, the value (product C) obtained by multiplying the ratio of the input amount of 1,3-pentanediol by the static surface tension of 1,3-pentanediol was determined. Further, for each ink, a value (product D) obtained by multiplying the ratio of the input amount of 1,8-octanediol and the static surface tension of 1,8-octanediol was obtained. Further, for each ink, a value (product E) obtained by multiplying the ratio of the amount of water input and the static surface tension of water was obtained. Then, for each ink, the sum of the products A to E was regarded as _{the dynamic surface tension γ 0 of the ink.} The dynamic surface tension γ ₀ of each ink is shown in Table 4 below.

For example, in ink A, the products A to E were obtained by the following formulas. Then, the products A to E were added up, and the value obtained by rounding off the decimal point of the obtained sum was taken as the dynamic surface tension γ _{0 of the ink A.} The water content in the ink A was the total value (51.8% by mass) of the ion-exchanged water (43.9% by mass) and the water in the pigment dispersion (7.9% by mass).
Product A (glycerin): 62.0 mN / m x 0.070 = 4.34 mN / m
Product B (2-pyrrolidone): 32.5 mN / m x 0.070 = 2.275 mN / m
Product C (1,3-pentanediol): 41.0 mN / m x 0.3000 = 12.30 mN / m
Product D (1,8-octanediol): 35.7 mN / m x 0.010 = 0.357 mN / m
Product E (water): 73.0 mN / m x 0.518 = 37.814 mN / m
Dynamic surface tension γ ₀ : 4.34 mN / m + 2.275 mN / m + 12.30 mN / m + 0.357 mN / m + 37.814 mN / m = 57.086 mN / m

Next, for each ink, using a dynamic surface tension measuring device (“BP-100” manufactured by KRUSS), a dynamic surface tension γ ₁₀ with a surface life of 10 ms and a motion with a surface life of 100 ms The target surface tension γ _{100 and the dynamic surface tension γ 1000} at a surface life of 1000 ms were measured by the maximum compression method. The measurement temperature was 25 ° C. The measurement results are shown in Table 4 below.

The inks A to C, F to G, J and L have a dynamic surface tension γ ₀ at a surface life of 0 msec of 55 mN / m or more and 60 mN / m or less, and a dynamic surface tension at a surface life of 10 msec. γ ₁₀ is 40 mN / m or more and 50 mN / m or less, dynamic surface tension at a surface life of 100 msec γ ₁₀₀ is more than 30 mN / m and 33 mN / m or less, and dynamic surface tension at a surface life of 1000 msec. The γ ₁₀₀₀ was 30 mN / m or more and less than 33 mN / m, and the dynamic surface tension γ ₁₀₀₀ was smaller than the dynamic surface tension γ _100. On the other hand, the inks D to E, H to I, K and M to N did not satisfy the above-mentioned constitution. Hereinafter, the inks A to C, F to G, J and L may be referred to as the inks of Examples 1 to 7. Further, the inks D to E, H to I, K and M to N may be described as the inks of Comparative Examples 1 to 7.

<Evaluation>
For each ink, the ejection stability, the wettability and spreadability after landing on the recording medium, and the occurrence of offset and bleeding of the formed image were evaluated by the following methods. The evaluation results are shown in Table 5 below. The evaluation was carried out in an environment of a temperature of 25 ° C. and a humidity of 60% RH.

As an evaluation machine, an inkjet recording system (prototype manufactured by Kyocera Document Solutions Co., Ltd.) equipped with a piezo recording head having a drive frequency of 18 kHz was used. This evaluation machine was equipped with a PTFE driven roller for ejecting the recording paper after image formation. The evaluation machine had a structure in which the driven roller described above was in contact with the image formed on the recording paper. The dot density of the evaluator was 600 dpi.

The recording head of the evaluation machine was filled with ink to be evaluated (specifically, any of ink A to ink N). Then, the excess ink dripping from the nozzle of the piezo recording head was scraped off by the wipe blade. The distance between the piezo recording head and the recording paper was fixed at 1 mm. The transport speed of the recording paper was set to 846.7 mm / sec.

[Discharge stability]
A 5 cm × 5 cm solid image was formed on a recording paper (“Epson genuine photo paper <gloss>” manufactured by Seiko Epson Corporation) using an evaluation machine. In forming the solid image, the amount of ink ejected per unit area was set to 15 g / m ² . Each ink can be evaluated as having good ejection stability when both the following white streaks and satellite droplets are evaluated well.

(White streaks)
The above solid image was observed with a microscope, and the occurrence of white streaks due to non-ejection of ink was confirmed. White streaks were evaluated based on the following criteria.
Good (A): White streaks are not confirmed Bad (B): White streaks are confirmed

(Satellite drops)
The solid image described above was observed under a microscope and 10 dots were randomly selected. Then, for each dot, it was confirmed whether or not minute dots (dots formed by satellite droplets) exist at positions more than 10 μm away from the outer edge of the dots. Satellite drops were evaluated based on the following criteria:
Good (A): No minute dots are present at a position more than 10 μm away from the outer edge of the dot Poor (B): Fine dots are present at a position more than 10 μm away from the outer edge of the dot.

[offset]
Using an evaluation machine, a solid image of 10 cm × 10 cm was formed on recording paper (paper obtained by cutting "IJW" manufactured by Oji Paper Co., Ltd. into A4 size). In forming the solid image, the amount of ink ejected per unit area was set to 15 g / m ² . The formed solid image was confirmed, and it was confirmed whether or not the offset was caused by the contact with the driven roller of the evaluation machine. Offsets were evaluated based on the following criteria:
Good (A): Offset is not confirmed Bad (B): Offset is confirmed

(Wet spread)
A straight line was formed on the recording paper (paper obtained by cutting "IJW" manufactured by Oji Paper Co., Ltd. into A4 size) using an evaluation machine. The line width of the straight line was set to a thickness corresponding to one pixel (theoretically 59.4 μm). The line width of the drawn straight line was precisely measured by the following method. First, using an image processing system device (“Da-6000” manufactured by Oji Measuring Instruments Co., Ltd.), a grayscale image of an image composed of a straight line portion and a non-printing portion (blank paper portion) formed on recording paper is obtained. It was captured as (256 gradations). Next, using the image processing system apparatus, among the pixels of the grayscale image, the pixels having a brightness of 128 or more and 255 or less were regarded as the pixels constituting the straight line portion. Then, the line width of the drawn straight line was obtained based on the number of pixels constituting the straight line portion. The line width of the drawn straight line indicates that the larger the value is, the more preferable it is because the ink is appropriately wetted and spread on the recording medium. The wet spread of the ink was evaluated based on the following criteria.
Good (A): Line width 59.4 μm or more Bad (B): Line width less than 59.4 μm

(Blur)
The bleeding width (degree of bleeding) of the drawn straight line was precisely measured from the grayscale image described above by the following method. First, among the pixels of the above-mentioned grayscale image, the pixels having a brightness of 40 or more and less than 128 were regarded as a blurring region around the straight line portion. Then, the bleeding width was determined based on the number of pixels constituting the bleeding region. As for the bleeding width, the smaller the value, the more preferable the occurrence of bleeding can be suppressed. The bleeding width was evaluated based on the following criteria.
Good (A): Bleeding width is 5 μm or less Poor (B): Bleeding width is over 5 μm

In the inks A to C, F to G, J and L of Examples 1 to 7, the dynamic surface tension γ ₀ at a surface life of 0 msec is 55 mN / m or more and 60 mN / m or less, and the surface life is 10 msec. The dynamic surface tension γ ₁₀ is 40 mN / m or more and 50 mN / m or less, and the dynamic surface tension γ ₁₀₀ at a surface life of 100 msec is more than 30 mN / m and 33 mN / m or less, and the surface life is 1000 msec. The dynamic surface tension γ ₁₀₀₀ was 30 mN / m or more and less than 33 mN / m, and the dynamic surface tension γ ₁₀₀₀ was smaller than the dynamic surface tension γ _100. The inks A to C, F to G, J and L of Examples 1 to 7 are excellent in ejection stability in high-speed printing, can be appropriately wetted and spread after landing on a recording medium, and are formed. The occurrence of offset and bleeding could be suppressed.

On the other hand, since the inks D to E, HI, K and M to N of Comparative Examples 1 to 7 did not have the above-mentioned configurations, they were inferior in ejection stability in high-speed printing or were moderately after landing on the recording medium. The image did not get wet and spread, or the formed image was offset or blurred.

Specifically, the ink D of Comparative Example 1 had a dynamic surface tension γ ₀ of more than 60 mN / m at a surface life of 0 ms. As a result, the ink D was inferior in ejection stability, and white streaks were generated in the formed image.

Ink E of Comparative Example 2 had a dynamic surface tension γ ₀ of less than 55 mN / m at a surface life of 0 ms. As a result, the ink E was inferior in ejection stability, and satellite droplets were generated in the formed image.

Ink H of Comparative Example 3 and Ink I of Comparative Example 4 had a dynamic surface tension γ ₁₀ at a surface life of 10 ms, which was less than 40 mN / m or more than 50 mN / m. As a result, the inks H and I did not spread appropriately after landing on the recording medium.

Ink K of Comparative Example 5 had a dynamic surface tension γ ₁₀₀ of more than 33 mN / m at a surface life of 100 ms. As a result, the ink K was offset in the formed image.

Ink M of Comparative Example 6 had a dynamic surface tension γ ₁₀₀₀ of less than 30 mN / m at a surface life of 1000 ms. As a result, the ink M caused blurring in the formed image.

Ink N of Comparative Example 7 has a dynamic surface tension γ ₁₀₀ at a surface life of 100 ms less than 30 mN / m and a dynamic surface tension γ ₁₀₀₀ at a surface life of 1000 ms less than 30 mN / m. It was. As a result, the ink N caused offset and blurring in the formed image.

The ink according to the present invention can be used to form an image.

Claims (3)

_{The dynamic surface tension γ 0} at a surface life of 0 ms is 55 mN / m or more and 60 mN / m or less.
_{The dynamic surface tension γ 10} at a surface life of 10 ms is 40 mN / m or more and 50 mN / m or less.
_{The dynamic surface tension γ 100} at a surface life of 100 ms is more than 30 mN / m and 33 mN / m or less.
_{The dynamic surface tension γ 1000} at a surface life of 1000 ms is 30 mN / m or more and less than 33 mN / m, and the dynamic surface tension γ ₁₀₀₀ is smaller than the dynamic surface tension γ _100. .. Contains pigments, water, octane diols, acetylene glycol surfactants, and silicone surfactants.
The content ratio of the octane diol is 0.3% by mass or more and 3.5% by mass or less.
The content ratio of the acetylene glycol surfactant is 0.8% by mass or more and 1.2% by mass or less.
The inkjet ink according to claim 1, wherein the content ratio of the silicone surfactant is 0.08% by mass or more and 0.11% by mass or less. Further containing pentanediol,
The inkjet ink according to claim 2, wherein the content ratio of the pentane diol is 19.0% by mass or more and 35.0% by mass or less.