ink

Abstract

This invention provides an ink that can achieve both high image density and wide line width even in solvent formulations with high hydrophobicity. [Solution] The ink contains a surfactant represented by general formula (1), a water-soluble solvent with a log Kow of -1.0 or more and 0.4 or less, a pigment, and water, wherein the content of the water-soluble solvent is 30% by mass or more and 50% by mass or less. [Formula 1] TIFF2026054797000011.tif28160(In general formula (1), m and n are integers whose sum is between 12 and 14, x is an integer between 1 and 20, and y is an integer between 1 and 10.)

Description

Technical Field

[0001] This technology relates to ink for inkjet printing.

Background Art

[0002] Inks used for inkjet printing are preferably those capable of printing with a high image density and a wide line width. A high image density can be achieved by using a solvent formulation containing a large amount of a highly hydrophobic solvent and aggregating pigments on the paper surface. However, when using a highly hydrophobic solvent formulation, it is impossible to lower the surface tension using a surfactant, and the wet spreading of the ink deteriorates. Therefore, a high image density and a wide line width are in a trade-off relationship, and it is difficult to achieve both.

[0003] In contrast, Patent Document 1 discloses a technique in which an ink added with a coloring material and a predetermined compound has excellent color density on both plain paper and special paper, excellent ejection stability in inkjet recording, and can ensure a sufficient line width in printing.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the ink described in Patent Document 1, since the hydrophobicity of the above compound is low, it is difficult to obtain the effect as a surfactant for lowering the surface tension in a highly hydrophobic solvent formulation, and there is a problem that a sufficient line width cannot be obtained.

[0006] In view of the above circumstances, an object of the present technology is to provide an ink capable of achieving both a high image density and a wide line width even in a highly hydrophobic solvent formulation. [Means for solving the problem]

[0007] To achieve the above objective, an ink according to one embodiment of the present invention contains a surfactant represented by general formula (1), a water-soluble solvent with a log Kow of -1.0 or more and 0.4 or less, a pigment, and water, wherein the content of the water-soluble solvent is 30% by mass or more and 50% by mass or less. [ka] (In general formula (1), m and n are integers whose sum is between 12 and 14, x is an integer between 1 and 20, and y is an integer between 1 and 10.)

[0008] Because the above ink contains both a surfactant and a water-soluble solvent with suitable hydrophobic properties, the dynamic surface tension of the ink is within a suitable range, making it possible to achieve both high image density and wide line width.

[0009] The dynamic surface tension value at 10 msec may be between 37 mN / m and 39 mN / m. [Effects of the Invention]

[0010] As described above, the present invention can provide an ink that can achieve both high image density and wide line width even in solvent formulations with high hydrophobicity. [Modes for carrying out the invention]

[0011] Embodiments of the present invention will be described below.

[0012] [Ink composition] (Schematic configuration) An ink according to one embodiment of the present invention contains a surfactant a, a water-soluble solvent b, a pigment c, and water. The ink according to this embodiment is typically 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. Examples of recording media on which images are recorded with the ink according to this embodiment include plain paper, copy paper, recycled paper, thin paper, thick paper, glossy paper, and OHP.

[0013] In the ink according to this embodiment, by using surfactant a with a specific configuration, the dynamic surface tension of the ink can be reduced even in highly hydrophobic solvent formulations, ensuring ink wetting and spreading while maintaining high image density. The details of each component of the ink according to this embodiment will be described below.

[0014] (Surfactant a) Surfactant a is represented by the following general formula (1) and is a nonionic surfactant having an ethylene oxide chain, a butylene oxide chain positioned at one end of the ethylene oxide chain, and a hydrocarbon chain positioned at the other end of the ethylene oxide chain. Because surfactant a has a highly hydrophobic butylene oxide chain, the dynamic surface tension of the ink is reduced even in highly hydrophobic solvent formulations, and the wetting spread of the ink can be increased. In addition, since the pigment aggregates in highly hydrophobic solvent formulations, the image density can be kept high.

[0015] [ka] (In general formula (1), m+n is an integer between 12 and 14, x is an integer between 1 and 20, and y is an integer between 1 and 10.)

[0016] In the general formula (1), when m + n is 11 or less, x is 21 or more, or y is 0, the hydrophilicity of the surfactant a is too high, and the dynamic surface tension of the ink becomes high, so the line width becomes small. Also, when m + n is 15 or more, x is 0, or y is 11 or more, the hydrophobicity of the surfactant a is too high, and the dynamic surface tension of the ink becomes low, so the image density becomes thin. Therefore, in the ink according to the present embodiment, it is preferable that m + n is 12 or more and 14 or less, x is 1 or more and 20 or less, and y is 1 or more and 10 or less (see Examples).

[0017] In the ink according to the present embodiment, in order to sufficiently obtain the action of the surfactant a, the content of the surfactant a is preferably 0.1% by mass or more. Also, in the ink according to the present embodiment, the content of the surfactant a is preferably 1.0% by mass or less.

[0018] (Water-soluble solvent b) The water-soluble solvent b has an octanol / water partition coefficient (log Kow) of -1.0 or more and 0.4 or less. Thereby, the pigment c is likely to aggregate due to hydrophobic interaction on the recording medium. As a result, in the ink according to the present embodiment, a high image density can be obtained on the recording medium, that is, a clear image with high visibility can be recorded on the recording medium.

[0019] When the octanol / water partition coefficient (log Kow) of the water-soluble solvent b is less than -1.0, the hydrophilicity of the water-soluble solvent b is too high and the dynamic surface tension of the ink becomes high, so it becomes difficult to wet and spread, and the line width becomes small. On the other hand, when the octanol / water partition coefficient (log Kow) of the water-soluble solvent b exceeds 0.4, the hydrophobicity of the water-soluble solvent b is too high and the dynamic surface tension of the ink becomes low, so the pigment c becomes difficult to aggregate and the image density becomes thin. Therefore, the octanol / water partition coefficient (log Kow) of the water-soluble solvent b is preferably -1.0 or more and 0.4 or less.

[0020] Specifically, as the water-soluble solvent b, any one or more of propylene glycol, 2-pyrrolidone, 1,5-pentanediol, and 3-methyl-1,5-pentanediol can be used. Table 1 below shows the octanol / water partition coefficients (log Kow) of these substances. The numerical values in Table 1 are cited from the software "HSPiP".

[0021] [Table 1]

[0022] In the ink according to this embodiment, in order to fully obtain the action of the above water-soluble solvent b, the content of the water-soluble solvent b is preferably 30% by mass or more and 50% by mass or less.

[0023] (Pigment c) The ink according to this embodiment contains a pigment c as a colorant from the viewpoint of improving the anti-color mixing property and water resistance in an image recorded on a recording medium. The pigment c may be either an inorganic pigment or an organic pigment. Further, as the pigment c, these may be used in combination with a extender pigment as necessary.

[0024] Specific examples of the inorganic pigments that can be used in the ink according to this embodiment include, for example, carbon black, metal oxides, etc. Particularly in black ink, carbon black is preferred. Examples of carbon black include furnace black, thermal lamp black, acetylene black, channel black, etc.

[0025] Specific examples of the 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, quinophthalone pigments, etc.

[0026] 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 (Color Index International) 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 c.

[0027] (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 40% by mass or more and 70% by mass or less.

[0028] (Other ingredients) The ink according to this embodiment may contain components other than those mentioned above, as needed. For example, the ink according to this embodiment may contain a dispersant that enhances the dispersibility of pigment c in a solvent. Examples of dispersants include pigment dispersing resins and surfactants.

[0029] Pigment dispersion resin consists of fine resin particles that adsorb to the surface of pigment c, thereby improving the dispersibility of pigment c in the solvent. The molecular weight of the pigment dispersion resin is preferably around tens of thousands. Specifically, styrene-acrylic resin is an example of a material that satisfies the above conditions, and resins with an acid value in the range of 150 mgKOH / g to 300 mgKOH / g are suitable. If the acid value is low, the pigment dispersibility is poor, making it difficult to form fine particles and reducing color development and tinting power. Also, if the acid value is high, the storage stability of the ink deteriorates.

[0030] The surfactant added as a dispersant is added separately from surfactant a above, and improves the dispersibility of pigment c in the solvent by reducing the interfacial tension between pigment c and the solvent. Examples of such surfactants include nonionic surfactants and anionic surfactants.

[0031] Furthermore, in addition to the dispersant, the ink according to this embodiment may contain various additives as needed, such as dissolution stabilizers, drying inhibitors, antioxidants, viscosity modifiers, pH adjusters, neutralizing agents, and antifungal agents.

[0032] The ink according to this embodiment has the configuration described above. As described above, in the general formula (1) of surfactant a, m+n is set to 12 or more and 14 or less, x is set to 1 or more and 20 or less, and y is set to 1 or more and 10 or less, and the octanol / water partition coefficient (log Kow) of water-soluble solvent b is set to -1.0 or more and 0.4 or less, so that the dynamic surface tension of the ink is within a suitable range, specifically the dynamic surface tension at 10 msec is set to 37 mN / m or more and 39 mN / m or less. As a result, the ink according to this embodiment can achieve both a high image density and a wide line width (see Examples). [Examples]

[0033] Ink preparation and evaluation were performed as examples and comparative examples of the present invention.

[0034] (Ink adjustment) First, the pigment dispersion was prepared. The pigment dispersion was prepared by blending pigment c, pigment dispersion resin, sodium hydroxide, Olphine® E1010, and water in the quantities shown in Table 2.

[0035] [Table 2]

[0036] PR-112 was used as pigment c. A styrene-acrylic resin with a molecular weight of 20,000 and an acid value of 100 mgKOH / g was used as the pigment dispersion resin. Sodium hydroxide was added as a neutralizing agent to neutralize the pigment dispersion resin, in an amount sufficient to neutralize the pigment dispersion resin to 105% equivolence. Olphine (registered trademark) E1010 is a surfactant added as a dispersant, and is a nonionic surfactant manufactured by Nisshin Chemical Industry Co., Ltd. Ion-exchanged water was used as the water.

[0037] 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 "NanoGlen Mill" manufactured by Asada Iron Works Co., Ltd., the "MSC Mill" manufactured by Nippon Coke Industries Co., Ltd., and the "Dino Mill" manufactured by Shinmaru Enterprises, Ltd.).

[0038] 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 c dispersed in water, to 70-130 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.

[0039] Next, the inks for the examples and comparative examples were prepared. The inks for the examples and comparative examples were prepared by blending the above-mentioned pigment dispersion, surfactant a, water-soluble solvent b, and water in the quantities shown in Table 3.

[0040] [Table 3]

[0041] Tables 4 and 5 show the surfactant a and water-soluble solvent b used in the examples and comparative examples. Note that m, n, x, and y in Tables 4 and 5 represent the m, n, x, and y in the general formula (1) above. Tables 4 and 5 also show the log Kow for water-soluble solvent b, quoted from the calculation software "HSPiP". Ion-exchanged water was used as the water.

[0042] [Table 4]

[0043] [Table 5]

[0044] During the preparation of each ink, the components shown in Table 3 were added sequentially while stirring the solvent with a stirrer. Furthermore, foreign matter, debris, and coarse particles were removed by filtering the stirred ink using a filter with a pore size of φ5 μm.

[0045] (Ink evaluation) The inks used in the examples and comparative examples were evaluated for image density and storage stability.

[0046] <Dynamic surface tension measurement> The dynamic surface tension of the ink from 10 to 1000 msec was measured using the bubble pressure method (KRUSS BP100 bubble pressure dynamic surface tension meter), with a 0.4 mm diameter capillary used. The bubble pressure method is the most widely used method for measuring dynamic surface tension, in which a capillary of known diameter is inserted into a liquid, gas is introduced into the capillary, and the surface tension is calculated from the pressure of the bubbles formed at the tip. By changing the amount of gas injected, the rate at which the interface is formed is changed, and the change in surface tension for each interface formation rate is measured. The time from when the interface begins to form until the pressure reaches its maximum is called the "surface age," and it is considered a time parameter in evaluating dynamic surface tension measurements. For the inks related to the examples and comparative examples, the 10 msec value of the dynamic surface tension measured by the bubble pressure method was evaluated. The dynamic surface tension values ​​listed below are all values ​​at 10 msec.

[0047] <Evaluation unit> Image density, scratch resistance, and intermittent ejection maintenance were evaluated under conditions of 32°C and 50% RH relative humidity. For these three evaluations, an inkjet recording device (an inkjet recording device equipped with a line-type recording head, manufactured by Kyocera Document Solutions Inc.) was used as the evaluation machine. The inks used in the examples and comparative examples were filled into the black ink tank of the evaluation machine. Copy paper (Mondi "CC90") was used as the recording medium for the evaluation of image density, scratch resistance, and intermittent ejection maintenance.

[0048] <Evaluation of image density> Using the evaluation machine described above, copy paper (Mondi "CC90") was used as the recording medium, and the amount of ink ejected from one recording head was set to 11.5 pL. A solid image measuring 2.3 cm x 11.5 cm was printed. After storing the plain paper with the formed image in a normal temperature and humidity environment for 24 hours, the image density of the solid image was measured using a fluorescence spectrophotometer (FD-5: Konica Minolta), and the average of the image densities at three points within the solid image was defined as the print density. The measurement conditions were: observation light source D50, illumination condition M2, field of view 2°, and density status I. An image density of 1.18 or higher was judged as good (○), and an image density of less than 1.18 was judged as poor (×).

[0049] <Evaluation of wetting spread> The wetting spread was evaluated based on the line width of the printed material. Measuring the line width serves as an indicator of whether the solid color is filled in for each type of paper. Copy paper (Mondi "CC90") was used as the recording medium. The evaluation machine was adjusted to an ejection speed of 8 m / s, and a single-dot line (a line formed by one dot) was printed at a head temperature of 32°C and humidity of 15%. The single-dot line was observed under a microscope and the line width was measured. A line width of 75 μm or more was judged as good (○), and a line width of less than 75 μm was judged as poor (×).

[0050] <Evaluation Results> The image density and wetting spread evaluation results for the inks used in the examples and comparative examples are shown in Tables 6 and 7.

[0051] [Table 6]

[0052] [Table 7]

[0053] As shown in Tables 6 and 7, the inks from Examples 1 to 12 exhibited good image density and line width. On the other hand, the inks from Comparative Examples 1 and 3 had an octanol / water partition coefficient (log Kow) of water-soluble solvent b less than -1.0, resulting in excessive hydrophilicity. This led to high dynamic surface tension, poor wetting and spreading, and consequently, poor line width. Furthermore, the inks from Comparative Examples 2 and 4 had an octanol / water partition coefficient (log Kow) of water-soluble solvent b exceeding 0.4, resulting in excessive hydrophobicity. This led to low dynamic surface tension and poor image density.

[0054] Furthermore, the inks in Comparative Examples 5, 8, and 9 had excessively high hydrophilicity due to surfactant a, resulting in high dynamic surface tension and poor line width. Specifically, the ink in Comparative Example 5 had a small number of carbon atoms in the hydrocarbon chain (m+n = 11), the ink in Comparative Example 8 had a large number of carbon atoms in the ethylene oxide chain (x = 21), and the ink in Comparative Example 9 had a small number of carbon atoms in the butylene oxide chain (y = 0), all of which contributed to high hydrophilicity.

[0055] The inks in Comparative Examples 6, 7, and 10 suffered from poor image density because the hydrophobicity of surfactant a was too high, resulting in low dynamic surface tension. Specifically, the ink in Comparative Example 6 had a large number of carbon atoms in the hydrocarbon chain (m+n = 15), the ink in Comparative Example 7 had a small number of carbon atoms in the ethylene oxide chain (x = 0), and the ink in Comparative Example 10 had a large number of carbon atoms in the butylene oxide chain (y = 11), all of which contributed to high hydrophobicity.

[0056] From the above, the ink according to the present invention can achieve a suitable dynamic surface tension and good image density and line width by setting the hydrophobicity of both surfactant a and water-soluble solvent b to a suitable range. Specifically, it can be said that the hydrophobicity of both surfactant a and water-soluble solvent b can be set to a suitable range by setting the number of carbon atoms (m+n) of the hydrocarbon chain of surfactant a to 12 or more and 14 or less, the number of carbon atoms (x) of the ethylene oxide chain to 1 or more and 20 or less, the number of carbon atoms (y) of the butylene oxide chain to 1 or more and 10 or less, and the octanol / water partition coefficient (log Kow) of water-soluble solvent b to -1.0 or more and 0.4 or less.

Claims

1. It contains a surfactant represented by general formula (1), a water-soluble solvent with log Kw of -1.0 or more and 0.4 or less, a pigment, and water. The content of the water-soluble solvent is 30% by mass or more and 50% by mass or less. ink. 【Chemistry 1】 (In general formula (1), m and n are integers whose sum is between 12 and 14, x is an integer between 1 and 20, and y is an integer between 1 and 10.)

2. The ink according to claim 1, The dynamic surface tension value at 10 msec is between 37 mN / m and 39 mN / m. ink.

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