inkjet ink

Abstract

To provide an inkjet ink that can achieve both high image density and pigment diffusion. [Solution] The inkjet ink contains a pigment, a pigment dispersion resin, a water-soluble humectant, and water. The pigment dispersion resin is a block copolymer in which a hydrophilic polymer block X is composed of methacrylic acid, a hydrophobic polymer block Y is composed of benzyl methacrylate, the block arrangement is XYX, and the acid value is 60 mg KOH / g or more and 120 mg KOH / g or less. The water-soluble humectant contains at least one of a polyhydric alcohol monoisopropyl ether and a polyhydric alcohol monobutyl ether.

Description

TECHNICAL FIELD

[0001] The present invention relates to inkjet ink.

BACKGROUND ART

[0002] Patent Documents 1 to 4 disclose inkjet inks for recording images on recording media such as paper. Inkjet inks are required to have high image density for recording clear images with high visibility on recording media. On the other hand, inkjet inks are required to form high-quality images without gaps on recording media.

PRIOR ART DOCUMENTS

PATENT DOCUMENTS

[0003]

PATENT DOCUMENT 1

PATENT DOCUMENT 2

PATENT DOCUMENT 3

PATENT DOCUMENT 4

SUMMARY OF THE INVENTION

PROBLEM TO BE SOLVED BY THE INVENTION

[0004] In inkjet inks, it is preferable that pigments aggregate on the recording medium in order to improve the image density of images recorded on the recording medium. On the other hand, in inkjet inks, it is necessary to ensure the diffusibility of the pigments with respect to the recording medium in order to form high-quality images without gaps on the recording medium. That is, inkjet inks are required to exhibit conflicting behaviors of pigment aggregation and diffusion after landing on the recording medium.

[0005] In view of the above circumstances, the object of the present invention is to provide an inkjet ink that can achieve both image density and pigment diffusivity. [Means for solving the problem]

[0006] To achieve the above objective, an inkjet ink according to one embodiment of the present invention contains a pigment, a pigment dispersion resin, a water-soluble humectant, and water. The pigment dispersion resin consists of a block copolymer in which the hydrophilic polymer block X is composed of methacrylic acid, the hydrophobic polymer block Y is composed of benzyl methacrylate, the block sequence is XYX, and the acid value is 60 mg KOH / g or more and 120 mg KOH / g or less. The aforementioned water-soluble humectant comprises at least one of a polyhydric alcohol monoisopropyl ether and a polyhydric alcohol monobutyl ether. The inkjet ink may further contain a nonionic surfactant.

[0007] This inkjet ink uses a pigment dispersion resin made of the block copolymer described above in combination with a hydrophobic, water-soluble humectant described above. As a result, in this inkjet ink, the pigment aggregates during the stage when water evaporation progresses after impact with the recording medium, and diffuses during the stage when it penetrates the recording medium. This makes it possible to achieve both image density and pigment diffuseness in this inkjet ink. [Effects of the Invention]

[0008] As described above, the present invention can provide an inkjet ink that can achieve both image density and pigment diffusivity. [Modes for carrying out the invention]

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

[0010] [Ink composition] (Schematic configuration) An inkjet ink according to one embodiment of the present invention (hereinafter also simply referred to as "ink") contains a pigment a, a pigment dispersion resin b, a water-soluble humectant c, and water. The ink according to this embodiment is a water-based ink that is ejected from the recording head of an inkjet recording device onto a recording medium to record an image on the recording medium. The recording medium on which the image is recorded with the ink according to this embodiment is made up of hydrophilic fibers such as cellulose fibers, and examples include plain paper, copy paper, recycled paper, thin paper, and thick paper.

[0011] The ink according to this embodiment uses a combination of a pigment-dispersing resin b with a specific configuration and a water-soluble humectant c with a specific configuration. This results in a characteristic behavior where pigment a aggregates during the evaporation of moisture after impact with the recording medium, and then diffuses during the penetration into the recording medium. As a result, the ink according to this embodiment achieves a balance between image density and the diffusivity of pigment a. The details of each component of the ink according to this embodiment will be described below.

[0012] (Pigment a) The ink according to this embodiment contains pigment a as a coloring agent, from the viewpoint of improving the ability to prevent color mixing and the water resistance of images recorded on a recording medium. Pigment a 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] Specific examples of inorganic pigments usable in the ink according to this embodiment include, for example, 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 that can be used in the ink according to this embodiment 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] In the ink according to this embodiment, 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 chromatic pigments include CI pigment yellow, CI pigment red, CI pigment orange, CI pigment violet, CI pigment blue, and CI pigment green. In the ink according to this embodiment, one or more selected from these chromatic pigments can be used as pigment a.

[0016] (Pigment-dispersed resin b) The ink according to this embodiment is formulated with a pigment dispersion resin b as a dispersant to enhance the dispersibility of pigment a in the solvent by adsorbing onto the surface of pigment a. In the ink according to this embodiment, fine particles of a benzyl methacrylate / methacrylic acid copolymer are used as the pigment dispersion resin b. More specifically, the pigment dispersion resin b is a block copolymer in which the hydrophilic polymer block X is composed of methacrylic acid and the hydrophobic polymer block Y is composed of benzyl methacrylate, with a block arrangement of XYX. Furthermore, the acid value of the pigment dispersion resin b is 60 mg KOH / g or more and 120 mg KOH / g or less. In the pigment dispersion resin b, the hydrophilic polymer block X, which is methacrylic acid, has the effect of improving penetration into the recording medium, and the hydrophobic polymer block Y, which is benzyl methacrylate, has the effect of improving image density.

[0017] In the ink according to this embodiment, it is preferable that the content of pigment dispersion resin b is 0.5% by mass or more in order to fully obtain the effect of pigment dispersion resin b. Furthermore, in the ink according to this embodiment, it is preferable that the content of pigment dispersion resin b is 7.0% by mass or less in order to obtain high dispersion stability.

[0018] (Water-soluble humectant c) In the ink according to the present embodiment, a hydrophobic water-soluble humectant c is blended. The ink according to the present embodiment contains at least one of polyhydric alcohol monoisopropyl ether and polyhydric alcohol monobutyl ether as the water-soluble humectant c. In the ink according to the present embodiment, by the action of reducing the surface tension by the hydrophobic water-soluble humectant c, the pigment dispersion, which is a composite in which the pigment dispersion resin b is adsorbed on the pigment a, can be diffused on the recording medium while maintaining the image density.

[0019] In the ink according to the present embodiment, in order to sufficiently obtain the effect of the above water-soluble humectant c, the content of the water-soluble humectant c is preferably 0.3 mass% or more. Further, in the ink according to the embodiment, in order to obtain high dispersion stability, the content of the water-soluble humectant c is preferably 7.0 mass% or less.

[0020] (Water) In the ink according to the present embodiment, as the water, for example, ion-exchanged water, purified water, distilled water and the like can be used. In the ink according to the present embodiment, from the viewpoints of drying property and ejection reliability, the content of water is preferably 40 mass% or more and 60 mass% or less.

[0021] (Other Components) To the ink according to the present embodiment, components other than those described above may be blended as necessary. For example, a surfactant can be blended into the ink according to the present embodiment. The surfactant has an effect of increasing the wettability of the ink with respect to the recording medium, and an effect of increasing the compatibility and dispersion stability of each component contained in the ink. Examples of the surfactant to be blended in the ink according to the present embodiment include anionic surfactants, cationic surfactants, nonionic surfactants, and amphoteric surfactants. The surfactant is preferably a nonionic surfactant. The nonionic surfactant is preferably a surfactant having an acetylene bond, and more preferably a surfactant having an acetylene glycol structure or an acetylene alcohol structure.

[0022] Furthermore, in addition to surfactants, the ink according to this embodiment may contain various additives as needed, such as penetrating agents, dissolution stabilizers, drying inhibitors, antioxidants, viscosity modifiers, pH adjusters, neutralizing agents, and antifungal agents.

[0023] [Examples] In Examples 1 to 3 of the present invention, inks were prepared and evaluated. Below, we will first describe the common aspects of Examples 1 to 3, and then describe the individual aspects of each Example 1 to 3.

[0024] (Ink preparation) In Examples 1-3, a pigment dispersion was first prepared by dispersing pigment a in water. The pigment dispersion was prepared by blending pigment a, pigment dispersion resin b, sodium hydroxide, Surfinol® 420, and water in the quantities shown in Table 1.

[0025] [Table 1]

[0026] Sodium hydroxide was added as a neutralizing agent to neutralize pigment dispersion resin b. Surfinol® 420 was added as a dispersant to improve the dispersibility of pigment a in the solvent, and is a nonionic surfactant with an acetylene glycol structure manufactured by Nisshin Chemical Industry Co., Ltd. In all of Examples 1 to 3, pigment blue 15:3 (Toyo Color Co., Ltd. "Lionol Blue FG-7351") was used as pigment a, and deionized water was used as water.

[0027] The pigment dispersion was prepared by mixing the above components using a wet dispersion method with a media-type wet disperser. Examples of media-type wet dispersers include wet dispersers (more specifically, the "NanoGlenMill" manufactured by Asada Iron Works Co., Ltd., the "MSC Mill" manufactured by Nippon Coke Industries, Ltd., and the "DinoMill" manufactured by Shinmaru Enterprises, Ltd.).

[0028] In wet dispersion using a media-type wet disperser, media (zirconia beads with a diameter of 0.5 mm) were set in the vessel, and the discharge rate was controlled to 200-600 g / min to adjust the average particle size of the pigment dispersion, in which the dispersant adhered to pigment a dispersed in water, to 90-110 nm. The particle size distribution of the pigment dispersion was measured using a Zetasizer Nano manufactured by Sysmex Corporation, with the pigment dispersion diluted 300 times with deionized water.

[0029] Next, the inks according to Examples 1 to 3 were prepared. The inks according to Examples 1 to 3 were prepared by blending the above-mentioned pigment dispersion, Surfinol® 420, water-soluble humectant c, and water in the quantities shown in Table 2.

[0030] [Table 2]

[0031] In the preparation of the inks in Examples 1 to 3, the components shown in Table 2 were added in order while stirring the solvent with a stirrer. Furthermore, foreign matter, dirt, and coarse particles were removed by filtering each ink after stirring using a filter with a pore size of φ5 μm.

[0032] (Ink evaluation) The inks from Examples 1 to 3 were evaluated for image density and the diffusivity of pigment a.

[0033] • Method for evaluating image density A solid image was formed on a recording medium (Mondi Corporation's CC90) using an inkjet recording device (Kyocera Document Solutions Inc.'s "TASKalfa Pro 15000c"). The image density of the solid image after drying was measured using a fluorescence spectrodensitometer (FD-5, Konica Minolta Inc.). For each ink, the average of five measurements was used as the image density evaluation value. The image density evaluation value for each ink was evaluated according to the following P and F criteria. For image density, an ink with an evaluation of P was considered acceptable, and an ink with an evaluation of F was considered unacceptable. A (good): 1.20 or more B (Poor): Less than 1.20

[0034] • Method for evaluating the diffusivity of pigment a Using an inkjet recording device (Kyocera Document Solutions Inc. "TASKalfa Pro 15000c"), with an ejection rate of 11 pL per dot, images of 10 straight lines (1-dot lines) were formed on a recording medium (Mondi Corporation "CC90"). The dried images of the straight lines were then observed with an optical microscope (Nikon Corporation "MM-800"), and the line width of each straight line image was measured using the application measurement "Line Measurement". For each ink, the average line width of the 10 straight line images was used as the evaluation value for the diffusivity of pigment a. The evaluation value for the diffusivity of pigment a for each ink was evaluated according to the following A and B criteria. For the diffusivity of pigment a, inks with an evaluation of A are considered acceptable, and inks with an evaluation of B are considered unacceptable. A (good): 75μm or more B (Defective): Less than 75 μm

[0035] (Example 1) In Example 1, ink samples 1-4 were prepared using the above method with pigment dispersion resins b1, b2, b3, and b4, each consisting of benzyl methacrylate (BzMMA) / methacrylic acid (MAA) copolymers (acid value: 100 mg KOH / g) with different compositions, and the above evaluation was performed on samples 1-4. Table 3 shows the compositions of pigment dispersion resins b1, b2, b3, and b4. Pigment dispersion resin b1 has the composition of pigment dispersion resin b according to this embodiment. Pigment dispersion resins b2 and b3 have block arrangements different from pigment dispersion resin b according to this embodiment. Pigment dispersion resin b4 is a random copolymer. In all samples 1-4 of Example 1, triethylene glycol monobutyl ether was used as the water-soluble humectant c.

[0036] [Table 3]

[0037] Table 4 shows the pigment dispersion resins used in Samples 1-4, and the evaluation results for image density and pigment a diffusion for Samples 1-4. Sample 1, which used pigment dispersion resin b1, passed both the image density and pigment a diffusion tests. On the other hand, Samples 2 and 3, which used pigment dispersion resins b2 and b3, which have different block arrangements from those in this embodiment, failed both the image density and pigment a diffusion tests. Furthermore, Sample 4, which used pigment dispersion resin b4, which is made of a random copolymer, passed the pigment a diffusion test but failed the image density test.

[0038] [Table 4]

[0039] (Example 2) In Example 2, ink samples 5-9 were prepared using the above method with pigment dispersion resins b5, b6, b7, b8, and b9, which consist of benzyl methacrylate (BzMMA) / methacrylic acid (MAA) copolymers with mutually different acid values, and the above evaluation was performed on samples 5-9. Table 5 shows the composition of pigment dispersion resins b5, b6, b7, b8, and b9. The acid value of pigment dispersion resin b5 is less than 60 mgKOH / g. The acid values ​​of pigment dispersion resins b6, b7, and b8 are between 60 mgKOH / g and 120 mgKOH / g. The acid value of pigment dispersion resin b9 is greater than 120 mgKOH / g. In all samples 5-9 of Example 2, triethylene glycol monobutyl ether was used as the water-soluble humectant c.

[0040] [Table 5]

[0041] Table 6 shows the pigment dispersion resins used in samples 5-9, and the evaluation results for image density and pigment a's diffusivity for samples 5-9. Samples 6-8, using pigment dispersion resins b6, b7, and b8, passed both the image density and pigment a's diffusivity tests. On the other hand, sample 5, using pigment dispersion resin b5 with an acid value of less than 60 mgKOH / g, passed the image density test but failed the pigment a's diffusivity test. Furthermore, sample 9, using pigment dispersion resin b9 with an acid value of more than 120 mgKOH / g, passed the pigment a's diffusivity test but failed the image density test.

[0042] [Table 6]

[0043] (Example 3) In Example 3, ink samples 10-15 were prepared using the above method with mutually different water-soluble humectants c1, c2, c3, c4, c5, and c6, and the above evaluation was performed on samples 10-15. Table 7 shows the water-soluble humectants c1, c2, c3, c4, c5, and c6. Water-soluble humectants c1, c2, and c3 are glycol ether compounds corresponding to water-soluble humectant c in this embodiment. On the other hand, water-soluble humectant c4 is a glycol ether compound that does not correspond to water-soluble humectant c in this embodiment. Furthermore, water-soluble humectant c5 is a triol compound, and water-soluble humectant c6 is a diol compound. In all samples 10-15 of Example 3, a block copolymer was used as the pigment dispersion resin b, in which the hydrophilic polymer block X is composed of methacrylic acid, the hydrophobic polymer block Y is composed of benzyl methacrylate, the block sequence is XYX, and the acid value is 90 mgKOH / g.

[0044] [Table 7]

[0045] Table 8 shows the water-soluble humectants used in samples 10-15, and the evaluation results for image density and pigment a's diffusivity for samples 10-15. Samples 10-12, using water-soluble humectants c1, c2, and c3, passed both the image density and pigment a's diffusivity tests. On the other hand, sample 13, using water-soluble humectant c4, passed the image density test but failed the pigment a's diffusivity test. Furthermore, sample 13, using water-soluble humectant c5, failed both the image density and pigment a's diffusivity tests. In addition, sample 15, using water-soluble humectant c6, passed the pigment a's diffusivity test but failed the image density test.

[0046] [Table 8]

Claims

1. Pigments and A pigment dispersion resin comprising a block copolymer in which hydrophilic polymer block X is composed of methacrylic acid, hydrophobic polymer block Y is composed of benzyl methacrylate, the block arrangement is X-Y-X, and the acid value is 60 mg KOH / g or more and 120 mg KOH / g or less, A water-soluble humectant comprising at least one of polyhydric alcohol monoisopropyl ether and polyhydric alcohol monobutyl ether, Water and, Inkjet ink containing [this ingredient].

2. An inkjet ink according to claim 1, It further contains a nonionic surfactant. Inkjet ink.

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