inkjet ink

Abstract

This invention provides an inkjet ink that can achieve both scratch resistance and print density. [Solution] An inkjet ink according to one embodiment of the present invention 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 280 mg KOH / g or less, and the neutralization rate of the block polymer is 40% or more and 60% or less.

Description

Technical Field

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

Background Art

[0002] With the improvement in quality of inkjet printers in recent years, further high quality of ink for inkjet has been demanded. For example, Patent Document 1 discloses a technique for improving printing density by using a block polymer composed of a methacrylate-based hydrophobic polymer block and a hydrophilic polymer block containing methacrylic acid.

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 rub resistance of ink for inkjet, there is a method of increasing the acid value of a polymer dispersant (dispersion resin) to enhance the affinity with paper. However, when the acid value of the polymer dispersant is increased, the printing density tends to decrease due to dispersion stability. On the other hand, in order to increase the printing density, it is necessary to reduce the dispersion stability of the pigment and cause aggregation. However, when the printing density increases, the rub resistance deteriorates, but this point is not mentioned in Patent Document 1.

[0005] In view of the above circumstances, an object of the present invention is to provide an ink for inkjet that can achieve both rub resistance and printing density.

Means for Solving the Problems

[0006] An ink for inkjet according to one embodiment of the present invention 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 between 180 mg KOH / g and 280 mg KOH / g, and the neutralization rate of the block polymer is between 40% and 60%. [Effects of the Invention]

[0007] According to the present invention, it is possible to achieve both scratch resistance and print density. [Modes for carrying out the invention]

[0008] Embodiments of the present invention will be described below.

[0009] [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.

[0010] 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 280 mg KOH / g or less, and the neutralization rate of the block polymer is 40% or more and 60% or less.

[0011] In this embodiment, abrasion resistance is ensured by increasing the acid value of the dispersion resin, and the dispersion stability of the pigment is reduced by lowering the neutralization rate of the dispersion resin, causing the pigment to aggregate. Furthermore, the block polymer used as the dispersion resin has a structure in which hydrophilic and hydrophobic parts are clearly separated, and the pigment is coated with the hydrophobic part, preventing the pigment from penetrating the paper and increasing the print density. This makes it possible to provide an ink that can achieve both abrasion resistance and print density. The details are described below.

[0012] (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.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] (Dispersed resin) The dispersion resin used in this embodiment is a polymer dispersant (hereinafter also referred to as an AB block polymer) in which the A block is a hydrophobic block polymer and the B block is a hydrophilic block polymer. Here, the A block is benzyl methacrylate which is a hydrophobic block polymer, and the B block is methacrylic acid which is a hydrophilic block polymer. That is, the AB block polymer is a benzyl methacrylate / methacrylic acid copolymer and can be obtained by living radical polymerization.

[0017] Regarding each polymer block of A and B, the hydrophobic A block adsorbs on the pigment surface and plays a role in coating the pigment. On the other hand, the hydrophilic B block has a role of being dissolved in an aqueous solvent by ionizing the carboxyl group with an alkaline agent. The ionized carboxyl group has an electrical electrostatic repulsive force, and together with the steric hindrance of the dispersion resin structure, it maintains the dispersion stability in the liquid. By using such an AB block polymer, the function of pigment adsorption by the hydrophobic A block and the functions of electrostatic repulsive force and steric repulsive force by the hydrophilic B block can be specialized respectively.

[0018] The acid value of the AB block polymer which is the dispersion resin used in this embodiment is 180 mgKOH / g or more and 280 mgKOH / g or less.

[0019] In the low acid value region where the acid value is less than 180 mgKOH / g, since there is little methacrylic acid which is an acid component, the abrasion resistance is low. Also, in the above low acid value region, the pigment dispersibility is poor and it is difficult to make fine particles, and the color development and coloring power decrease.

[0020] On the other hand, in the high acid value region where the acid value exceeds 200 mgKOH / g, there is a lot of methacrylic acid which is an acid component, and the pigment is less likely to aggregate on the paper surface, and the printing density becomes low. Also, in the above high acid value region, the storage stability of the ink deteriorates.

[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] The neutralization rate of the dispersion resin composed of benzyl methacrylate / methacrylic acid block polymer with an acid value of 180 to 280 mgKOH / g is preferably 40% or more and 60% or less. When the neutralization rate of the dispersion resin is less than 40%, the printing density increases but the abrasion resistance tends to decrease. When the neutralization rate of the dispersion resin exceeds 60%, the abrasion resistance increases but the printing density tends to decrease.

[0023] The neutralization rate indicates the ratio of neutralized acid groups when the total number of acid groups contained in the above dispersion resin is taken as 100%. The neutralization rate can be calculated, for example, from the amount of the basic compound used in the neutralization treatment of the dispersion resin when preparing the dispersion resin. Specifically, the theoretical value of the amount of the basic compound required to completely neutralize the dispersion resin is M A , and the amount of the basic compound used in the neutralization treatment of the dispersion resin is M B . When it is A , the percentage (100×M B / M B ) of the amount of use M A with respect to the theoretical value M A is shown. Note that M

[0024] When determining the image quality, a pigment dispersion coated with a fine particle resin having a molecular weight of tens of thousands is suitable as the dispersion resin. Examples of materials satisfying the above conditions include styrene acrylic resins.

[0025] 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, resulting in poor solvent resistance and inability to ensure the printing density. 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.

[0026] (Water-based solvent) The solvent used should be a water-soluble solvent, preferably a relatively hydrophobic solvent with a logKow of 0 or greater. Examples of such solvents include 1,2-pentanediol (logLow: 0.01), butyl triglycol (logLow: 0.02), 3-methyl-1,5-pentanediol (logLow: 0.03), 2-propanol (logLow: 0.05), dimethyl ether (logLow: 0.1), 1-propanol (logLow: 0.25), diethylene glycol diethyl ether (logLow: 0.39), and triethylene glycol monobutyl ether (logLow: 0.44).

[0027] Note that logKow is the water / octanol coefficient. The logKow value above is calculated using Hansen solubility parameter software "HSPiP".

[0028] (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.

[0029] (Other ingredients) The ink according to this embodiment may contain other components besides those mentioned above, such as water, surfactants, and humectants.

[0030] For example, ion-exchanged water, purified water, or distilled water can be used as the water source.

[0031] 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.

[0032] [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.

[0033] (Distributed processing process) In this process, a pigment dispersion is prepared by dispersing the pigment and the dispersion resin in water. The ratio of pigment to dispersion resin (mass ratio of pigment / dispersion resin) is preferably, for example, 60 / 40 to 90 / 10.

[0034] A pigment dispersion was prepared with the composition shown in Table 1. In this dispersion, 5.5% by mass of polymer dispersant (dispersion resin) solution, 15% by mass of pigment, 0.5% by mass of Olphine® E1010, and the remainder being water.

[0035] [Table 1]

[0036] The polymer dispersant (dispersion resin) solution was prepared by adding an amount of aqueous sodium hydroxide solution (alkaline agent) sufficient to neutralize the carboxyl groups of the block polymer or random polymer used as the dispersion resin (equivalent to a neutralization rate of 40-60%), and then adding pure water to adjust the solid content to 30%. The pigment used was CI Pigment Red (e.g., PR-112). Olphine® E1010 (ethylene oxide adduct of acetylenediol) is a dispersant or surfactant used to enhance the dispersibility of the pigment.

[0037] 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.

[0038] 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.

[0039] (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).

[0040] 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 40.0% by mass, the surfactant ("Surfinol® 420" manufactured by Nisshin Chemical Industry Co., Ltd.) was 0.3% by mass, the aqueous solvent was 24% by mass (4.0% by mass of triethylene glycol monobutyl ether, 20.0% by mass of 3-methyl-1,5-pentanediol), glycerin was 5% by mass as a humectant, and the remainder was water.

[0041] [Table 2] [Examples]

[0042] The following describes embodiments of the present invention.

[0043] [Example 1] A pigment dispersion containing a benzyl methacrylate / methacrylic acid block polymer with an acid value of 186 mgKOH / g and a neutralization rate of 58% was prepared as the dispersion resin with the composition shown in Table 1. Inks with the composition shown in Table 2 were then prepared using this pigment dispersion. The abrasion resistance and print density of the prepared inks were evaluated.

[0044] The benzyl methacrylate / methacrylic acid block polymer used had a number-average molecular weight (Mn) of 10,000 to 11,000 and a molecular weight distribution (PDI) of 1.20 to 1.23 (the same applies hereafter).

[0045] (Evaluation of abrasion resistance) In evaluating abrasion resistance, a test machine was used to print a solid image measuring 5cm x 4cm onto copy paper (Mondi CC90) using pigment ink, with the amount of ink ejected from one recording head set to 11.5pL. The printed recording paper was fixed with the printed area facing upwards, and an unprinted recording paper was placed on top. Furthermore, a 1kg weight with a base area of ​​5cm x 4cm was placed on top, and the unprinted recording paper and the weight were moved back and forth horizontally as a single unit under load. After 5 back-and-forth rubs, the area of ​​the unprinted recording paper that had been in contact with the printed area was measured using a reflectance densitometer (FD-9, Konica Minolta). The color measurement conditions were: observation light source D50, illumination condition M2, field of view 2°, and density status I. The evaluation criteria for abrasion resistance were as follows: the standard density of the recording paper before abrasion was measured, and the value obtained by subtracting the standard density from the density of the area rubbed over the printed surface (FD) was less than 0.02 if it was less than 0.02.

[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), and an ID of 1.3 or higher was considered acceptable.

[0047] [Example 2] A pigment dispersion containing a benzyl methacrylate / methacrylic acid block polymer with an acid value of 235 mgKOH / g and a neutralization rate of 51% was prepared as the dispersion resin with the composition shown in Table 1. Inks with the composition shown in Table 2 were then prepared using this pigment dispersion. The abrasion resistance and print density of the prepared inks were evaluated under the same conditions as in Example 1.

[0048] [Example 3] A pigment dispersion containing a benzyl methacrylate / methacrylic acid block polymer with an acid value of 274 mgKOH / g and a neutralization rate of 43% was prepared as the dispersion resin with the composition shown in Table 1. Inks with the composition shown in Table 2 were then prepared using this pigment dispersion. The abrasion resistance and print density of the prepared inks were evaluated under the same conditions as in Example 1.

[0049] [Comparative Example 1] A pigment dispersion containing a benzyl methacrylate / methacrylic acid block polymer with an acid value of 138 mgKOH / g and a neutralization rate of 55% was prepared as the dispersion resin with the composition shown in Table 1. Inks with the composition shown in Table 2 were then prepared using this pigment dispersion. The abrasion resistance and print density of the prepared inks were evaluated under the same conditions as in Example 1.

[0050] [Comparative Example 2] A pigment dispersion containing a benzyl methacrylate / methacrylic acid block polymer with an acid value of 287 mgKOH / g and a neutralization rate of 48% was prepared as the dispersion resin with the composition shown in Table 1. Inks with the composition shown in Table 2 were then prepared using this pigment dispersion. The abrasion resistance and print density of the prepared inks were evaluated under the same conditions as in Example 1.

[0051] [Comparative Example 3] A pigment dispersion containing a benzyl methacrylate / methacrylic acid block polymer with an acid value of 220 mgKOH / g and a neutralization rate of 32% was prepared as the dispersion resin with the composition shown in Table 1. An ink with the composition shown in Table 2 was then prepared using this pigment dispersion. The abrasion resistance and print density of the prepared inks were evaluated under the same conditions as in Example 1.

[0052] [Comparative Example 4] A pigment dispersion containing a benzyl methacrylate / methacrylic acid block polymer with an acid value of 251 mgKOH / g and a neutralization rate of 83% was prepared as the dispersion resin with the composition shown in Table 1. Inks with the composition shown in Table 2 were then prepared using this pigment dispersion. The abrasion resistance and print density of the prepared inks were evaluated under the same conditions as in Example 1.

[0053] (summary) Table 3 summarizes the evaluation results for scratch resistance and print density for Examples 1-3 and Comparative Examples 1-4.

[0054] [Table 3]

[0055] Examples 1-3 showed good scratch resistance and print density. Specifically, the inks in Examples 1-3, in which the acid value of the dispersed resin (polymer) is 180 mg KOH / g or more and 280 mg KOH / g or less, and the neutralization rate is 40% or more and 60% or less, all exhibited scratch resistance of less than 0.02 and print density of 1.3 or more, thus demonstrating that both scratch resistance and print density can be achieved.

[0056] On the other hand, Comparative Example 1 had a low acid value of 138 mgKOH / g (less than 180 mgKOH / g), resulting in lower scratch resistance compared to Examples 1-3. Comparative Example 2 had a high acid value of 287 mgKOH / g (greater than 280 mgKOH / g), resulting in lower print density compared to Examples 1-3. Furthermore, Comparative Example 3 had a low neutralization rate of 32% (less than 40%), resulting in lower scratch resistance compared to Examples 1-3. Finally, Comparative Example 4 had a high neutralization rate of 83% (greater than 60%), resulting in lower print density compared to Examples 1-3.

[0057] [Example 4] A pigment dispersion containing a benzyl methacrylate / methacrylic acid block polymer with an acid value of 192 mgKOH / g and a neutralization rate of 49% was prepared as the dispersion resin with the composition shown in Table 1. Inks with the composition shown in Table 2 were then prepared using this pigment dispersion. The abrasion resistance and print density of the prepared inks were evaluated under the same conditions as in Example 1.

[0058] [Example 5] A pigment dispersion containing a benzyl methacrylate / methacrylic acid block polymer with an acid value of 248 mgKOH / g and a neutralization rate of 55% was prepared as the dispersion resin with the composition shown in Table 1. Inks with the composition shown in Table 2 were then prepared using this pigment dispersion. The abrasion resistance and print density of the prepared inks were evaluated under the same conditions as in Example 1.

[0059] [Comparative Example 5] A pigment dispersion containing a benzyl methacrylate / methacrylic acid random polymer with an acid value of 224 mgKOH / g and a neutralization rate of 47% was prepared as the dispersion resin with the composition shown in Table 1. Inks with the composition shown in Table 2 were then prepared using this pigment dispersion. The abrasion resistance and print density of the prepared inks were evaluated under the same conditions as in Example 1.

[0060] The benzyl methacrylate / methacrylic acid random polymer used had a number-average molecular weight (Mn) of 10,000 to 11,000 and a molecular weight distribution (PDI) of 2.00 to 2.20 (the same applies hereafter).

[0061] [Comparative Example 6] A pigment dispersion containing a benzyl methacrylate / methacrylic acid random polymer with an acid value of 253 mgKOH / g and a neutralization rate of 57% was prepared as the dispersion resin with the composition shown in Table 1. Inks with the composition shown in Table 2 were then prepared using this pigment dispersion. The abrasion resistance and print density of the prepared inks were evaluated under the same conditions as in Example 1.

[0062] (summary) Table 4 summarizes the evaluation results for scratch resistance and print density for Examples 4 and 5 and Comparative Examples 5 and 6.

[0063] [Table 4]

[0064] Examples 4 and 5 showed good scratch resistance and print density, similar to Examples 1-3. Specifically, the inks in Examples 4 and 5, in which the acid value of the dispersed resin (polymer) is 180 mg KOH / g or more and 280 mg KOH / g or less, and the neutralization rate is 40% or more and 60% or less, all exhibited scratch resistance of less than 0.02 and print density of 1.3 or more, thus demonstrating that both scratch resistance and print density can be achieved.

[0065] On the other hand, in Comparative Examples 5 and 6, although the acid value of the dispersion resin (polymer) was between 180 mg KOH / g and 280 mg KOH / g, and the neutralization rate was between 40% and 60%, the print density was lower compared to Examples 4 and 5 because it was a random polymer. From this, it was confirmed that a block polymer is preferable for the dispersion resin in order to achieve both scratch resistance and print density.

Claims

1. It 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 180 mg KOH / g or more and 280 mg KOH / g or less. The neutralization rate of the block polymer is 40% or more and 60% or less. Inkjet ink.

2. An inkjet ink according to claim 1, The logKow of the aqueous solvent is 0 or greater. Inkjet ink.

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