inkjet ink

Abstract

This invention provides an inkjet ink that can achieve both solvent resistance and print density. [Solution] An inkjet ink according to one embodiment of the present invention contains a pigment, an aqueous solvent, an alkaline agent, and a dispersion resin. The dispersion resin is a block polymer having a hydrophobic polymer block containing benzyl methacrylate and a hydrophilic polymer block containing methacrylic acid. The acid value of the block polymer is 120 mg KOH / g or more and 200 mg KOH / g or less. The logKow of the aqueous solvent is 0 or more.

Description

Technical Field

[0001] The present invention relates to an ink for inkjet printers.

Background Art

[0002] With the improvement in quality of inkjet printers in recent years, further high quality of ink for inkjet printers is required. For example, in Patent Document 1, by using a block polymer composed of a methacrylate-based hydrophobic polymer block and a hydrophilic polymer block containing methacrylic acid, an aqueous pigment dispersion for inkjet printers is disclosed which has excellent long-term storage stability and ejection stability of the ink, and furthermore has excellent printing quality with high color development property on plain paper.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In order to improve the printing density by inkjet, there are methods such as retaining the pigment on the paper or reacting the pigment with the filler of the paper. When the printing density is expressed by reacting the pigment with the filler of the paper, there are limitations on the paper. On the other hand, when the pigment is retained on the paper, the printing density can be expressed without depending on the paper. However, when the pigment is retained on the paper, generally there are many methods of aggregating the pigment on the paper surface. As one of the means for aggregating this pigment, there is a method of adding a relatively hydrophobic solvent to the solvent composition of the ink. By adding a hydrophobic solvent to the solvent composition of the ink, it becomes easier for the dispersion resin to be released from the pigment, and when the dispersion resin is released, the pigments aggregate with each other.

[0005] However, in this case, the ink will also contain hydrophobic solvents, making it a major challenge to achieve both solvent resistance in liquid and print density. Furthermore, in the invention described in Patent Document 1, the solvent type is limited to hydrophilic organic solvents with a LogKow of 0 or less, and the selection of the solvent type is not considered when manufacturing the ink.

[0006] In view of the above circumstances, the object of the present invention is to provide an inkjet ink that can achieve both solvent resistance and print density. [Means for solving the problem]

[0007] An inkjet ink according to one embodiment of the present invention contains a pigment, an aqueous solvent, an alkaline agent, and a dispersion resin. The aforementioned dispersion resin is a block polymer having a hydrophobic polymer block containing benzyl methacrylate and a hydrophilic polymer block containing methacrylic acid. The acid value of the block polymer is between 120 mg KOH / g and 200 mg KOH / g. The logKow of the aforementioned aqueous solvent is 0 or greater. [Effects of the Invention]

[0008] According to the present invention, it is possible to achieve both solvent resistance and print density. [Modes for carrying out the invention]

[0009] Embodiments of the present invention will be described below.

[0010] [Ink composition] (Schematic configuration) An inkjet ink (hereinafter also simply referred to as "ink") according to one embodiment of the present invention is ejected from the recording head of an inkjet recording device onto a recording medium and records an image on the recording medium. Examples of recording media on which an image is recorded with the ink according to this embodiment include plain paper, copy paper, recycled paper, thin paper, thick paper, glossy paper, and OHP.

[0011] The ink of this embodiment is an aqueous ink containing a pigment, an aqueous solvent, an alkaline agent, and a dispersion resin. The dispersion resin is a block polymer having a hydrophobic polymer block containing benzyl methacrylate and a hydrophilic polymer block containing methacrylic acid. The acid value of the block polymer is 180 mg KOH / g or more and 200 mg KOH / g or less, and the logKow of the aqueous solvent is 0 or more.

[0012] For example, if a solvent with a LogKow of 0 or higher is used, the dispersion resin will be released from the pigment in the liquid, causing the pigment to aggregate and settle. However, by using the dispersion resin of the present invention, the adsorption to the pigment is strengthened, ensuring solvent resistance. On the other hand, on the paper surface, water evaporates, and the mixture becomes rich in relatively hydrophobic solvents with a LogKow of 0 or higher, causing the pigment to aggregate and resulting in good print density. This makes it possible to provide an ink that ensures solvent resistance in the liquid and exhibits good print density on the paper surface due to pigment aggregation. The details are described below.

[0013] (Pigment) The water-based ink used in this embodiment contains a pigment as a coloring agent, from the viewpoint of improving the color mixing prevention and water resistance of the printed material. The pigment may be either an inorganic pigment or an organic pigment. In addition, if necessary, these may be used in combination with an extender pigment.

[0014] Examples of inorganic pigments include carbon black and metal oxides, with carbon black being particularly preferred for black inks. Examples of carbon black include furnace black, thermal lamp black, acetylene black, and channel black.

[0015] Specific examples of organic pigments include azo pigments, diazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, and quinophthalone pigments.

[0016] The hue is not particularly limited, and any chromatic pigment such as yellow, magenta, cyan, blue, red, orange, and green can be used. Specific examples of preferred organic pigments include one or more products selected from CI Pigment Yellow, CI Pigment Red, CI Pigment Orange, CI Pigment Violet, CI Pigment Blue, and CI Pigment Green.

[0017] (Dispersed resin) The dispersion resin used in this embodiment is a polymeric dispersant (hereinafter also referred to as AB block polymer) in which block A is a hydrophobic block polymer and block B is a hydrophilic block polymer. Here, block A is benzyl methacrylate, which is a hydrophobic block polymer, and block B is methacrylic acid, which is a hydrophilic block polymer. This AB block polymer can be obtained by living radical polymerization.

[0018] Regarding polymer blocks A and B, the hydrophobic A block adsorbs onto the pigment surface, coating the pigment. On the other hand, the hydrophilic B block has its carboxyl groups ionized by an alkaline agent and dissolves in an aqueous solvent. The ionized carboxyl groups have an electrostatic repulsive force, which, combined with the steric hindrance of the dispersion resin structure, maintains dispersion stability in liquid. By using such AB block polymers, the pigment adsorption function of the hydrophobic A block and the electrostatic repulsion and steric repulsion functions of the hydrophilic B block can be specialized.

[0019] The acid value of the AB block polymer, which is the dispersion resin used in this embodiment, is 120 mg KOH / g or more and 200 mg KOH / g or less.

[0020] In the low acid value range where the acid value is less than 120 mg KOH / g, since there is less methacrylic acid as the acid component, the electrostatic repulsion force and steric repulsion force become small, and solvent resistance cannot be ensured when a hydrophobic solvent is included. Also, in the high acid value range where the acid value exceeds 200 mg KOH / g, there is a large amount of methacrylic acid as the acid component, and it becomes difficult for the pigment to aggregate even on the paper surface, and the printing density cannot be ensured. That is, the acid value of the dispersion resin that can achieve both solvent resistance and printing density is 120 mg KOH / g or more and 200 mg KOH / g or less.

[0021] The acid value can be determined by a method conforming to, for example, JIS K 0070:1992 "Test Methods for Acid Value, Saponification Value, Ester Value, Iodine Value, Hydroxyl Value and Unsaponifiable Matter of Chemical Products".

[0022] Even if the acid value of the dispersion resin is within the above range, when the dispersion resin is a random polymer, if the aqueous solvent is hydrophobic, the pigment will aggregate and the solvent resistance will be poor, and the printing density cannot be ensured either. Therefore, when using a hydrophobic solvent in the aqueous solvent, the dispersion resin is preferably a benzyl methacrylate / methacrylic acid block polymer as described above.

[0023] (Aqueous solvent) The solvent used is a water-soluble solvent, and a relatively hydrophobic solvent with log Kow of 0 or more is preferred. Examples of this type of solvent include 1,2-pentanediol (logLow: 0.01), butyl triglycol (same, 0.02), 3-methyl-1,5-pentanediol (same, 0.03), 2-propanol (same, 0.05), dimethyl ether (same, 0.1), 1-propanol (same, 0.25), diethylene glycol diethyl ether (same, 0.39), triethylene glycol monobutyl ether (same, 0.44), and the like.

[0024] Note that log Kow is the water / octanol coefficient. The above log Kow numerical values are the values calculated from the Hansen solubility parameter software "HSPiP".

[0025] (Alkaline agent) In this embodiment, the alkaline agent constituting the pigment dispersion is used to solubilize the dispersion resin, which consists of the block polymer, in a water-soluble solvent. The alkaline agent used is not particularly limited, but compounds selected from the group consisting of alkali metal hydroxides, such as NaOH and KOH, can be suitably used.

[0026] (Other ingredients) The ink according to this embodiment may contain other components besides those mentioned above, such as water, surfactants, and humectants.

[0027] For example, ion-exchanged water, purified water, or distilled water can be used as the water source.

[0028] Surfactants enhance the wettability of ink to the storage medium and improve the compatibility and dispersion stability of the various components contained in the ink. Nonionic surfactants are preferred as surfactants. Furthermore, surfactants impart appropriate dynamic surface tension to the ink.

[0029] [Ink adjustment] The ink preparation method of this embodiment includes, for example, a dispersion step of preparing a pigment particle dispersion by dispersing a dispersion resin and a pigment in water, and an addition step of preparing the ink by adding an aqueous medium to the pigment particle dispersion.

[0030] (Distributed processing process) In this process, a pigment dispersion is prepared by dispersing the pigment and dispersion resin in water. The ratio of pigment to dispersion resin (mass ratio of pigment / dispersion resin) is preferably 60 / 40 to 90 / 10.

[0031] In other words, the ratio of the mass of the dispersion resin to the mass of the pigment is preferably 0.1 or more and 0.4 or less. When the ratio of the mass of the dispersion resin to the mass of the pigment is 0.4 or less, the viscosity of the pigment dispersion and ink can be easily adjusted to the desired value. When the ratio of the mass of the pigment dispersion resin to the mass of the pigment is 0.1 or more, an ink with excellent dispersion stability can be obtained.

[0032] A pigment dispersion was prepared with the composition shown in Table 1. In this dispersion, the dispersion resin was 6% by mass, the alkaline agent was 0-1% by mass, the pigment was 15% by mass, Olphine® E1010 was 0.5% by mass, and the remainder was water.

[0033] [Table 1]

[0034] The pigment used was CI Pigment Blue 15:3 (PB15:3) (Toyo Color Co., Ltd. "Lionol Blue FG-7351"). Olfin® E1010 (ethylene oxide adduct of acetylenediol) is a dispersant or surfactant used to improve the dispersibility of the pigment. An amount of alkaline agent (NaOH) was added to neutralize the dispersion resin by 105% equivolence.

[0035] Examples of dispersion equipment used in the dispersion process include wet dispersion devices such as media-type dispersers like the NanoGlen Mill manufactured by Asada Steel Co., Ltd., the MSC Mill manufactured by Mitsui Mining Co., Ltd., and the Dyno Mill manufactured by Shinmaru Enterprises, Ltd. For the dispersion conditions, small-diameter beads (0.5 mmφ zirconia beads) were set in the vessel, the discharge rate was controlled to 200 to 600 g / min, and the pigment dispersion was adjusted so that the average particle size of the dispersed pigment dispersion was 90 to 110 nm.

[0036] Furthermore, the degree of dispersion and the amount of free resin were altered by changing the bead type. Naturally, using smaller bead diameters makes it easier to create fine particles, and also strengthens the resin's coating on the pigment. For particle size distribution measurement, a solution diluted 300 times with deionized water was measured using a Zetasizer Nano manufactured by Sysmex Corporation.

[0037] (addition process) In this step, an aqueous solvent is added to the pigment dispersion prepared as described above. This allows ink to be obtained. The aqueous solvent content is preferably 20 to 35% by mass. In this step, other components (more specifically, at least one of surfactants, dissolving stabilizers, drying inhibitors, antioxidants, pH adjusters, humectants, penetrating agents, antifungal agents, and viscosity modifiers) may be added as needed. In this step, it is preferable to stir the resulting mixture with a stirrer after adding the aqueous medium. The obtained ink may be filtered to remove foreign matter and coarse particles (for example, a filter with a pore size of 5 μm or less).

[0038] Ink was prepared by sequentially adding each solvent to the pigment dispersion while stirring with a stirrer, to achieve the composition shown in Table 2. In this case, the pigment dispersion was 53.3% by mass (8% by mass of pigment), the surfactant was 0.5% by mass, the aqueous solvent was 30% by mass, glycerin was 10% by mass as a humectant, and the remainder was water.

[0039] [Table 2] [Examples]

[0040] The following describes embodiments of the present invention.

[0041] First, as shown in Table 3, several dispersion resins 1 to 6 with different acid values ​​were prepared, and pigment dispersions containing the prepared dispersion resins 1 to 6 were prepared with the compositions shown in Table 1.

[0042] [Table 3]

[0043] Dispersion resin 1 is a random polymer with an acid value of 160 mgKOH / g. Dispersion resin 2 is a block polymer with an acid value of 80 mgKOH / g. Dispersion resin 3 is a block polymer with an acid value of 120 mgKOH / g. Dispersion resin 4 is a block polymer with an acid value of 160 mgKOH / g. Dispersed resin 5 is a block polymer with an acid value of 200 mgKOH / g. Dispersion resin 6 is a block polymer with an acid value of 240 mgKOH / g.

[0044] [Example 1] A pigment dispersion containing dispersion resin 3 was prepared, and its solvent resistance was evaluated under the following conditions. Furthermore, inks with the compositions shown in Table 2 were prepared using the pigment dispersion containing dispersion resin 3, and their print density was evaluated under the following conditions. Note that 3-methyl-1,5-pentanediol (logKow: 0.03) was used as the aqueous solvent in Table 2.

[0045] (Evaluation of solvent resistance) In evaluating solvent resistance, first, the particle size distribution of pigment particles is measured, and the 50% cumulative volume particle size (initial D 50 Next, the 50% cumulative volume particle size (D after heating) was determined. Then, a solution was prepared in a 9 mL screw tube containing 1% by mass of the pigment dispersion, 40% by mass of 3-methyl-1,5-pentanediol and 40% by mass of butyl triglycol as hydrophobic solvents, and the remainder as water. After being left at 40°C for 1 hour, the particle size was measured, and the 50% cumulative volume particle size (D after heating) was determined. 50 ) and determine the particle size of the pigment dispersion only (initial D 50 The amount of change was compared with the original particle size. A particle size change of 5 nm or less was considered a pass (○), and a particle size change exceeding 5 nm was considered a fail (×).

[0046] (Evaluation of print density) For the evaluation of print density, the drive voltage was adjusted to 12 pl per dot, and a 10 x 10 cm solid image was created on A4 size copy paper (Mondi "CC90"). After 12 hours, the image density (ID) of the solid image was measured again using a reflectance densitometer (FD-9, Konica Minolta). An ID of 1.3 or higher was considered a pass (○), and an ID exceeding 1.3 was considered a fail (×).

[0047] [Example 2] A pigment dispersion containing dispersion resin 4 was prepared, and its solvent resistance was evaluated under the same conditions as in Example 1. In addition, inks with the compositions shown in Table 2 were prepared using the pigment dispersion containing dispersion resin 4, and their print density was evaluated under the same conditions as in Example 1.

[0048] [Example 3] A pigment dispersion containing dispersion resin 5 was prepared, and its solvent resistance was evaluated under the same conditions as in Example 1. Furthermore, inks with the compositions shown in Table 2 were prepared using the pigment dispersion containing dispersion resin 5, and their print density was evaluated under the same conditions as in Example 1.

[0049] [Comparative Example 1] A pigment dispersion containing dispersion resin 1 was prepared, and its solvent resistance was evaluated under the same conditions as in Example 1. Furthermore, inks with the compositions shown in Table 2 were prepared using the pigment dispersion containing dispersion resin 1, and their print density was evaluated under the same conditions as in Example 1.

[0050] [Comparative Example 2] A pigment dispersion containing dispersion resin 2 was prepared, and its solvent resistance was evaluated under the same conditions as in Example 1. Furthermore, inks with the compositions shown in Table 2 were prepared using the pigment dispersion containing dispersion resin 2, and their print density was evaluated under the same conditions as in Example 1.

[0051] [Comparative Example 3] A pigment dispersion containing dispersion resin 6 was prepared, and its solvent resistance was evaluated under the same conditions as in Example 1. Furthermore, inks with the compositions shown in Table 2 were prepared using the pigment dispersion containing dispersion resin 6, and their print density was evaluated under the same conditions as in Example 1.

[0052] (summary) Table 4 summarizes the evaluation results for solvent resistance and print density for Examples 1-3 and Comparative Examples 1-3.

[0053] [Table 4]

[0054] As shown in Table 4, in Examples 1 to 3, both solvent resistance and print density passed the test (〇), confirming that both solvent resistance and print density can be achieved simultaneously. In other words, it can be said that by using a benzyl methacrylate / methacrylic acid block polymer with an acid value of 120 mg KOH / g or more and 200 mg KOH / g or less, it is possible to achieve both solvent resistance and print density.

[0055] On the other hand, in Comparative Example 1, where the dispersion resin was a random polymer, the pigment aggregated when the aqueous solvent was hydrophobic, resulting in poor solvent resistance and inability to secure sufficient print density. Furthermore, in Comparative Example 2, which had a low acid value (less than 120 mg KOH / g), solvent resistance was poor, and in Comparative Example 3, which had a high acid value (greater than 200 mg KOH / g), print density could not be secured.

[0056] [Example 4] A pigment dispersion containing dispersion resin 4 was prepared, and its solvent resistance was evaluated under the same conditions as in Example 1. Furthermore, inks with the compositions shown in Table 2 were prepared using the pigment dispersion containing dispersion resin 4, and their print density was evaluated under the same conditions as in Example 1. For the aqueous solvent in Table 2, butyl triglycol (logKow: 0.02) was used.

[0057] [Example 5] A pigment dispersion containing dispersion resin 4 was prepared, and its solvent resistance was evaluated under the same conditions as in Example 1. Furthermore, inks with the compositions shown in Table 2 were prepared using the pigment dispersion containing dispersion resin 4, and their print density was evaluated under the same conditions as in Example 1. Note that 2-propanol (logKow: 0.05) was used as the aqueous solvent in Table 2.

[0058] [Comparative Example 4] A pigment dispersion containing dispersion resin 4 was prepared, and its solvent resistance was evaluated under the same conditions as in Example 1. Furthermore, inks with the compositions shown in Table 2 were prepared using the pigment dispersion containing dispersion resin 4, and their print density was evaluated under the same conditions as in Example 1. For the aqueous solvent in Table 2, propylene glycol (logKow: -0.92) was used.

[0059] [Comparative Example 5] A pigment dispersion containing dispersion resin 4 was prepared, and its solvent resistance was evaluated under the same conditions as in Example 1. Furthermore, inks with the compositions shown in Table 2 were prepared using the pigment dispersion containing dispersion resin 4, and their print density was evaluated under the same conditions as in Example 1. Note that 2-pyrrolidone (logKow: -0.71) was used as the aqueous solvent in Table 2. (summary) Table 5 summarizes the evaluation results for solvent resistance and print density for Examples 4 and 5 and Comparative Examples 4 and 5.

[0060] [Table 5]

[0061] Examples 4 and 5 contained a hydrophobic aqueous solvent in the ink, causing the pigment to aggregate on the paper surface, resulting in a print density of 1.3 or higher. On the other hand, Comparative Examples 4 and 5 did not contain a hydrophobic aqueous solvent, so pigment aggregation did not occur, and sufficient print density could not be ensured. Thus, with the ink according to this embodiment, by including an aqueous solvent with a logKow of 0 or higher, the print density can be improved by causing the pigment to aggregate on the paper surface.

Claims

1. It contains a pigment, an aqueous solvent, an alkaline agent, and a dispersion resin. The aforementioned dispersion resin is a block polymer having a hydrophobic polymer block containing benzyl methacrylate and a hydrophilic polymer block containing methacrylic acid. The acid value of the block polymer is 120 mg KOH / g or more and 200 mg KOH / g or less. The logKow of the aqueous solvent is 0 or greater. Inkjet ink.

2. An inkjet ink according to claim 1, The ratio of the mass of the dispersion resin to the mass of the pigment is 0.1 or more and 0.4 or less. Inkjet ink.

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