inkjet ink

Abstract

We provide inkjet inks that offer both high image density and scratch resistance. [Solution] The inkjet ink contains a pigment, a cyclohexyl methacrylate / methacrylic acid copolymer having a weight-average molecular weight of 10,000 to 30,000 and an acid value of 160 mg KOH / g to 200 mg KOH / g, a surfactant represented by general formula (1), and water. TIFF2026067773000011.tif28164(In general formula (1), x, y, and z are integers determined to satisfy the conditions that the number average molecular weight of the surfactant is 2,000 or more and 2,750 or less, and the ratio of the number average molecular weight of the propylene oxide chain alone in the surfactant to the number average molecular weight of the surfactant is 0.82 or more and 0.91 or less.)

Description

Technical Field

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

Background Art

[0002] Patent Documents 1 to 4 disclose ink for inkjet for recording an image on a recording medium such as paper. In ink for inkjet, a resin can be blended as a binder for retaining a pigment on the recording medium. Thereby, it becomes possible to record a clear image with a high image density regardless of the type of the recording medium in the ink for inkjet.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the ink for inkjet that adheres a pigment to a recording medium via a resin, since the pigment tends to remain on the surface of the recording medium, it becomes difficult to ensure sufficient rub resistance as the image density of the image recorded on the recording medium is increased. Therefore, it is difficult to achieve both high image density and rub resistance in such ink for inkjet.

[0005] In view of the above circumstances, an object of the present invention is to provide an ink for inkjet capable of achieving both high image density and rub resistance.

Means for Solving the Problems

[0006] To achieve the above objective, an inkjet ink according to one embodiment of the present invention contains a pigment, a cyclohexyl methacrylate / methacrylic acid copolymer having a weight-average molecular weight of 10,000 or more and 30,000 or less and an acid value of 160 mgKOH / g or more and 200 mgKOH / g or less, a surfactant represented by general formula (1), and water. [ka] (In general formula (1), x, y, and z are integers determined to satisfy the conditions that the number average molecular weight of the surfactant is 2,000 or more and 2,750 or less, and the ratio of the number average molecular weight of the propylene oxide chain alone in the surfactant to the number average molecular weight of the surfactant is 0.82 or more and 0.91 or less.)

[0007] This inkjet ink achieves high image density by incorporating a pigment dispersion resin with a sufficiently large weight-average molecular weight and an acid value within a predetermined range. Furthermore, by keeping the weight-average molecular weight of the pigment dispersion resin from being excessively large, this inkjet ink minimizes the reduction in abrasion resistance caused by the pigment dispersion resin. Furthermore, this inkjet ink achieves high scratch resistance by incorporating a surfactant whose number-average molecular weight is not too large and whose propylene oxide chain ratio is within a predetermined range. In addition, by keeping the number-average molecular weight of the surfactant in this inkjet ink at a level that is not too small, a decrease in image density due to the effect of the surfactant is less likely to occur. These features make it possible to achieve both high image density and scratch resistance with 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 scratch resistance. [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 surfactant 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 of fibers such as cellulose fibers, and examples include plain paper, copy paper, recycled paper, thin paper, and thick paper.

[0011] In the ink according to this embodiment, a combination of a pigment dispersion resin b with a specific configuration and a surfactant c with a specific configuration can be used to achieve both image density and scratch resistance. 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 contains 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. The pigment dispersion resin b also functions as a binder to retain pigment a on the recording medium. In the ink according to this embodiment, fine particles of a cyclohexyl methacrylate / methacrylic acid copolymer are used as the pigment dispersion resin b. In the pigment dispersion resin b, cyclohexyl methacrylate constitutes a hydrophobic segment, and methacrylic acid constitutes a hydrophilic segment.

[0017] Also, in the ink according to this embodiment, the weight average molecular weight of the pigment-dispersed resin b is 10,000 or more and 30,000 or less. In the ink according to this embodiment, by setting the weight average molecular weight of the pigment-dispersed resin b to 10,000 or more, high image density can be obtained. Further, in the ink according to this embodiment, by setting the weight average molecular weight of the pigment-dispersed resin b to 30,000 or less, it is possible to make it difficult for the rubbing resistance to decrease due to the influence of the pigment-dispersed resin b. In this embodiment, the weight average molecular weight and the number average molecular weight are measured under the following conditions using gel permeation chromatography (manufactured by Tosoh Corporation, "HLC-8020GPC"). · Column: "TSKgel SuperMultiporeHZ-H" manufactured by Tosoh Corporation (semi-micro column of 4.6 mm I.D. × 15 cm) · Number of columns: 3 · Eluent: Tetrahydrofuran · Flow rate: 0.35 mL / min · Sample injection volume: 10 μL · Measurement temperature: 40 °C · Detector: IR detector The calibration curve is prepared by selecting seven types of F-40, F-20, F-4, F-1, A-5000, A-2500, and A-1000 and n-propylbenzene from TSKgel standard polystyrene manufactured by Tosoh Corporation.

[0018] Furthermore, in the ink according to this embodiment, the acid value of the pigment-dispersed resin b is 160 mgKOH / g or more and 200 mgKOH / g or less. Thereby, in the ink according to this embodiment, the image density can be increased without impairing the rubbing resistance. In this embodiment, the acid value is determined by a method conforming to JIS K0070:1992.

[0019] In the ink according to this embodiment, the content of the pigment-dispersed resin b is preferably 4% by mass or more in order to sufficiently obtain the above-described action of the pigment-dispersed resin b. Further, in the ink according to this embodiment, the content of the pigment-dispersed resin b is preferably 5% by mass or less in order to ensure high dispersion stability.

[0020] (Surfactant c) The ink according to this embodiment uses a surfactant c represented by the following general formula (1). Surfactant c has a propylene oxide chain (PO chain) constituting the central part and ethylene oxide chains (EO chains) arranged on both sides of the PO chain. In the ink according to this embodiment, surfactant c has the effect of increasing the wettability to the recording medium, thereby allowing pigment a to penetrate the recording medium appropriately. As a result, the ink according to this embodiment makes it easier to maintain the retention state of pigment a constituting the image recorded on the recording medium, and high scratch resistance is easily obtained even when the image density is high.

[0021] [ka] (In general formula (1), x, y, and z are integers determined to satisfy the conditions that the number-average molecular weight of surfactant c is between 2,000 and 2,750, and the ratio of the number-average molecular weight of only the PO chain in surfactant c to the number-average molecular weight of surfactant c (hereinafter also simply referred to as the "PO chain ratio") is between 0.82 and 0.91.)

[0022] If the number-average molecular weight of surfactant c is less than 2,000, excessive penetration into the recording medium is likely, making it difficult to obtain high image density. Furthermore, if the number-average molecular weight of surfactant c exceeds 2,750, insufficient penetration into the recording medium occurs, leading to lateral spreading along the recording medium, making it difficult to obtain high abrasion resistance. Additionally, if the ratio of PO chains is less than 0.82 or greater than 0.91, the wettability to the recording medium is not sufficiently high, making it difficult to obtain high abrasion resistance.

[0023] In the ink according to this embodiment, it is preferable that the content of surfactant c is 0.2% by mass or more in order to fully obtain the effect of surfactant c. Furthermore, in the ink according to this embodiment, it is preferable that the content of surfactant c is 1.0% by mass or less in order to ensure high discharge performance.

[0024] (water) In the ink according to this embodiment, for example, ion-exchanged water, purified water, or distilled water can be used as water. In the ink according to this embodiment, from the viewpoint of drying properties and ejection reliability, it is preferable that the water content is 30% by mass or more and 60% by mass or less.

[0025] (Other ingredients) The ink according to this embodiment may contain other components as needed. For example, a surfactant may be used in the ink according to this embodiment as a dispersant that enhances the dispersibility of pigment a in the solvent. The surfactant added as a dispersant is added separately from surfactant c and enhances the dispersibility of pigment a in the solvent by reducing the interfacial tension between pigment a and the solvent. Examples of such surfactants include nonionic surfactants and anionic surfactants.

[0026] Furthermore, in addition to surfactants, the ink according to this embodiment may contain various additives as needed, such as water-soluble humectants, penetrating agents, dissolution stabilizers, drying inhibitors, antioxidants, viscosity modifiers, pH adjusters, neutralizing agents, and antifungal agents.

[0027] [Examples] In Examples 1 to 4 of the present invention, inks were prepared and evaluated.

[0028] (Ink preparation) In Examples 1 to 4, 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, Olphine® E1010, and water in the amounts shown in Table 1.

[0029] [Table 1]

[0030] Sodium hydroxide was added as a neutralizing agent to neutralize pigment dispersion resin b. Olfin® E1010 was added as a dispersant to improve the dispersibility of pigment a in the solvent, and is a nonionic surfactant manufactured by Nisshin Chemical Industry Co., Ltd. In all of Examples 1 to 4, pigment a was pigment blue 15:3 (Toyo Color Co., Ltd. "Lionol Blue FG-7351"), and deionized water was used as the water.

[0031] 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.).

[0032] 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.

[0033] Next, 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, surfactant c, water-soluble humectant, and water in the amounts shown in Table 2. In all three Examples 1 to 3, 3-methyl-1,5-pentanediol was used as the water-soluble humectant.

[0034] [Table 2]

[0035] 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.

[0036] Furthermore, an ink according to Example 4 was prepared. The ink according to Example 4 was prepared by blending the above-mentioned pigment dispersion, surfactant c, 1,3-propanediol, triethylene glycol monobutyl ether, and water in the amounts shown in Table 3.

[0037] [Table 3]

[0038] In the preparation of the ink according to Example 4, the components shown in Table 3 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.

[0039] (Ink evaluation) The inks used in Examples 1 to 4 were evaluated for image density and scratch resistance.

[0040] • Method for evaluating image density For the evaluation of image density, an inkjet recording device (line type, manufactured by Kyocera Document Solutions Inc.) was used as the test machine. The drive voltage of the test machine was set so that the amount of ink ejected from one recording head was 12 pL. A 10 cm x 10 cm solid image was formed on a recording medium (Xerox "Vitality") using the test machine. After leaving the recording medium with the formed image for 12 hours, the image density of the solid image formed on the recording medium was measured using a fluorescence spectrophotometer (FD-5, manufactured by Konica Minolta, Inc.). Ink with an image density of 1.3 or higher was judged as passing, and ink with an image density of less than 1.3 was judged as failing.

[0041] • Method for evaluating abrasion resistance For the evaluation of abrasion resistance, an inkjet recording device (line type, manufactured by Kyocera Document Solutions Inc.) was used as the test machine. The drive voltage of the test machine was set so that the amount of ink ejected from one recording head was 12 pL. A 10 cm x 10 cm solid image was formed on the recording medium (Xerox "Vitality") using the test machine. Immediately after the solid image was formed, a sheet of paper was pressed against the solid image with a load of 500 g and slid back and forth five times. The image density of the sliding surface of the paper was then measured using a fluorescence spectrophotometer (FD-5, manufactured by Konica Minolta, Inc.). Ink with a maximum image density of 0.2 or less was judged as passing, and ink with a maximum image density exceeding 0.2 was judged as failing.

[0042] (Example 1) In Example 1, ink samples 1 to 3 were prepared using pigment dispersion resin b with various hydrophobic segments by the method described above, and the above evaluation was performed on samples 1 to 3. In all samples 1 to 3 of Example 1, "Orphine® E1010" manufactured by Nisshin Chemical Industry Co., Ltd. was used as the surfactant c.

[0043] Table 4 shows the hydrophobic segment, hydrophilic segment, molecular weight distribution, and acid value of the pigment dispersion resin b used in samples 1 to 3, as well as the evaluation results for image density and scratch resistance for samples 1 to 3. Sample 1 showed good evaluation results for both image density and scratch resistance. On the other hand, samples 2 and 3, in which the hydrophobic segment of the pigment dispersion resin b was not cyclohexyl methacrylate, failed to meet the image density standards. This is thought to be because samples 2 and 3 had excessive penetration into the recording medium.

[0044] [Table 4]

[0045] (Example 2) In Example 2, ink samples 4-8 were prepared using pigment dispersion resin b with various weight-average molecular weights by the method described above, and the above evaluation was performed on samples 4-8. In all samples 4-8 of Example 2, cyclohexyl methacrylate / methacrylic acid copolymer was used as the pigment dispersion resin b, and "Orphine® E1010" manufactured by Nisshin Chemical Industry Co., Ltd. was used as the surfactant c.

[0046] Table 5 shows the weight-average molecular weight and acid value of pigment dispersion resin b used in samples 4-8, as well as the evaluation results for image density and scratch resistance for samples 4-8. Samples 5-7 all showed good evaluation results for both image density and scratch resistance. On the other hand, sample 4, which had a small weight-average molecular weight of pigment dispersion resin b, failed in terms of image density. This is thought to be because sample 4 had excessive penetration into the recording medium. Furthermore, sample 8, which had a large weight-average molecular weight of pigment dispersion resin b, failed in terms of scratch resistance. This is thought to be because sample 8 had insufficient penetration into the recording medium.

[0047] [Table 5]

[0048] (Example 3) In Example 3, ink samples 9 to 13 were prepared using pigment dispersion resin b with various acid values ​​by the method described above, and the above evaluation was performed on samples 9 to 13. In all samples 9 to 13 of Example 3, cyclohexyl methacrylate / methacrylic acid copolymer was used as the pigment dispersion resin b, and "Orphine® E1010" manufactured by Nisshin Chemical Industry Co., Ltd. was used as the surfactant c.

[0049] Table 6 shows the weight-average molecular weight and acid value of pigment dispersion resin b used in samples 9-13, as well as the evaluation results for image density and scratch resistance for samples 9-13. Samples 10-12 all showed good evaluation results for both image density and scratch resistance. On the other hand, sample 9, in which pigment dispersion resin b had a low acid value, failed to meet the requirements for scratch resistance. This is thought to be due to insufficient penetration into the recording medium in sample 9. Furthermore, sample 13, in which pigment dispersion resin b had a high acid value, failed to meet the requirements for both image density and scratch resistance. This is thought to be due to unstable dispersion of pigment a in sample 13.

[0050] [Table 6]

[0051] (Example 4) In Example 4, ink samples 14 to 23 were prepared using various different surfactants c by the method described above, and the above evaluation was performed on samples 14 to 23. Specifically, in sample 14, Sanyo Chemical Industries, Ltd.'s "Newpol PE-61" was used as surfactant c. In sample 15, Sanyo Chemical Industries, Ltd.'s "Newpol PE-71" was used as surfactant c. In sample 16, ADEKA Corporation's "ADEKA Pluronic L-31" was used as surfactant c. In sample 17, ADEKA Corporation's "ADEKA Pluronic L-61" was used as surfactant c. In sample 18, ADEKA Corporation's "ADEKA Pluronic L-81" was used as surfactant c. In sample 19, Sanyo Chemical Industries, Ltd.'s "Newpol PE-62" was used as surfactant c. In sample 20, Sanyo Chemical Industries, Ltd.'s "Newpol PE-34" was used as surfactant c. In sample 21, Sanyo Chemical Industries, Ltd.'s "Newpol PE-64" was used as surfactant c. In Sample 22, Sanyo Chemical Industries, Ltd.'s "Newpol PE-74" was used as surfactant c. In Sample 23, polypropylene glycol was used as surfactant c. In all of Samples 14 to 23 related to Example 4, cyclohexyl methacrylate / methacrylic acid copolymer was used as pigment dispersion resin b.

[0052] Table 7 shows the number-average molecular weight of surfactant c, the number-average molecular weight of the PO chain, and the ratio of PO chains used in samples 14-23, as well as the evaluation results for image density and abrasion resistance for samples 14-23. Samples 14, 15, 17, and 18 all received good evaluation results for both image density and abrasion resistance. On the other hand, sample 16, which had a small number-average molecular weight of surfactant c, failed to meet the requirements for image density. This is thought to be because the surfactant in sample 16 penetrated the recording medium excessively. Furthermore, samples 19-22, which had a low ratio of PO chains in surfactant c, and sample 23, which had a high ratio of PO chains, all failed to meet the requirements for abrasion resistance. This is thought to be because the wettability of samples 19-23 to the recording medium was not sufficiently high.

[0053] Table 7

Claims

[Claim 1] Pigments and A cyclohexyl methacrylate / methacrylic acid copolymer having a weight-average molecular weight of 10,000 or more and 30,000 or less, and an acid value of 160 mg KOH / g or more and 200 mg KOH / g or less, A surfactant represented by general formula (1), Water and, Inkjet ink containing [this ingredient]. 【Chemistry 1】 (In general formula (1), x, y, and z are integers determined to satisfy the conditions that the number average molecular weight of the surfactant is 2,000 or more and 2,750 or less, and the ratio of the number average molecular weight of the propylene oxide chain alone in the surfactant to the number average molecular weight of the surfactant is 0.82 or more and 0.91 or less.)

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