inkjet ink

Abstract

This technology provides a low-cost solution that achieves both ejection stability and wettability in inkjet inks. [Solution] The inkjet ink contains a pigment, a pigment dispersion resin, and a surfactant represented by general formula (1). In the above inkjet ink, the number of coarse particles with a particle size of 0.6 μm or more is 1.0 × 10 9 pcs / mL or more 1.0×10 11 The number of particles / mL is less than or equal to 1 / mL. TIFF2026066796000011.tif17164(In general formula (1), m and n are positive integers satisfying the relationship 9 ≤ m + n ≤ 10, and x and y are integers satisfying all of the following relationships: 5 ≤ x ≤ 15, 7 ≤ y ≤ 10, and 1.5 ≤ y / x ≤ 2.0.)

Description

[Technical Field]

[0001] This invention relates to inkjet ink. [Background technology]

[0002] Patent documents 1 and 2 disclose inkjet inks for recording images on recording media such as paper. With inkjet inks, the more coarse particles there are, the more difficult it becomes to obtain stable ejection performance. On the other hand, the less coarse particles there are in inkjet inks, the higher the manufacturing cost becomes. In contrast, a technique is known that improves ejection stability without increasing cost by increasing the surface tension of the inkjet ink. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2010-024313 [Patent Document 2] Japanese Patent Publication No. 2011-236424 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, with inkjet inks, increasing surface tension makes it difficult to achieve sufficient wetting and spreading properties on the recording medium, which in turn makes it difficult to form gapless, high-quality images. Therefore, there is a need for inkjet ink technology that can achieve both ejection stability and wetting and spreading properties, even if some coarse particles remain.

[0005] In view of the above circumstances, the object of the present invention is to provide a technology that can achieve both ejection stability and wettability in inkjet inks at a low cost. [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, and a surfactant represented by general formula (1). In the above inkjet ink, the number of coarse particles with a particle size of 0.6 μm or more is 1.0 × 10 9 pcs / mL or more 1.0×10 11 The number of particles / mL is less than or equal to 1 / mL.

[0007] [ka] (In general formula (1), m and n are positive integers satisfying the relationship 9 ≤ m + n ≤ 10, and x and y are integers satisfying all of the following relationships: 5 ≤ x ≤ 15, 7 ≤ y ≤ 10, and 1.5 ≤ y / x ≤ 2.0.)

[0008] This inkjet ink incorporates a surfactant in which the balance of hydrophobic and hydrophilic groups in general formula (1) is controlled, thereby achieving both ejection stability and wettability even in a composition with a relatively large amount of coarse particles.

[0009] The number of coarse particles is 5.0 × 10 10 The number of cells / mL or more may be higher. [Effects of the Invention]

[0010] As described above, the present invention provides a technology that can achieve both ejection stability and wettability in inkjet inks at a low cost. [Modes for carrying out the invention]

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

[0012] [Inkjet 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.

[0013] In the ink according to this embodiment, by incorporating a surfactant c of a specific composition, it is possible to achieve both discharge stability and wettability even in a composition with a relatively large number of coarse particles. In this embodiment, coarse particles refer to particles with a particle diameter of 0.6 μm or more. Examples of coarse particles that may be contained in the ink include pigment dispersions in which pigment a and pigment dispersion resin b are integrated, intermediates produced in the process of synthesizing pigment a, and catalysts used to synthesize pigment a.

[0014] In the ink according to this embodiment, the number of coarse particles is 1.0 × 10 9 pcs / mL or more 1.0×10 11 The number of coarse particles is less than or equal to 1.0 × 10¹⁶ particles / mL. In the ink according to this embodiment, the number of coarse particles is 1.0 × 10¹⁶ 11 By keeping the number of particles / mL or less, high discharge stability can be easily obtained. In addition, in the ink according to this embodiment, the number of coarse particles is 1.0 × 10 9 By setting the number of particles / mL or higher, it becomes easier to obtain a high image density in the image formed on the recording medium. Furthermore, in the ink according to this embodiment, the number of coarse particles is 5.0 × 10 10 A particularly significant advantage is that it can achieve both discharge stability and wetting spread even in compositions of pcs / mL or higher. The details of each component of the ink according to this embodiment will be described below.

[0015] (Pigment a) The ink according to this embodiment contains pigment a as a colorant from the viewpoint of improving the anti-color mixing property and water resistance in the image recorded on the recording medium. Pigment a may be either an inorganic pigment or an organic pigment. Further, as pigment a, these may be used in combination with a extender pigment as needed.

[0016] Specific examples of the inorganic pigment that can be used in the ink according to this embodiment include, for example, carbon black, metal oxides, etc. Among them, in particular, for black ink, carbon black is preferable. Examples of carbon black include furnace black, thermal lamp black, acetylene black, channel black, etc.

[0017] Specific examples of the organic pigment 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.

[0018] In the ink according to this embodiment, the hue is not particularly limited, and any of the chromatic pigments such as yellow, magenta, cyan, blue, red, orange, green, etc. can be used. Specific examples of preferable chromatic pigments include C.I. Pigment Yellow, C.I. Pigment Red, C.I. Pigment Orange, C.I. Pigment Violet, C.I. Pigment Blue, and C.I. Pigment Green, etc. The ink according to this embodiment can use one or more selected from these chromatic pigments as pigment a.

[0019] [[ID=1 / 5]] (Pigment dispersion resin b) The pigment dispersion resin b is fine particles of a resin that has water solubility and suppresses the aggregation of pigment a by adhering to the surface of pigment a. Examples of the pigment dispersion resin b include copolymers of at least one monomer selected from (meth)acrylic acid alkyl esters, styrene, and vinyl naphthalene, and at least one monomer selected from (meth)acrylic acid and maleic acid.

[0020] As the pigment dispersion resin b, a resin having repeating units derived from (meth)acrylic acid ((meth)acrylic acid units), repeating units derived from (meth)acrylate alkyl ester ((meth)acrylate alkyl ester units), and styrene units is preferred. In this case, the proportion of (meth)acrylic acid units among the total repeating units of the pigment dispersion resin b is preferably 4.5% by mass or more and 8.0% by mass or less. The proportion of (meth)acrylate alkyl ester units among the total repeating units of the pigment dispersion resin b is preferably 35% by mass or more and 70% by mass or less. The proportion of styrene units among the total repeating units of the pigment dispersion resin b is preferably 27% by mass or more and 60% by mass or less. As the pigment dispersion resin b, a resin having repeating units derived from methacrylic acid, repeating units derived from methyl methacrylate, repeating units derived from butyl acrylate, and styrene units is more preferred.

[0021] In the ink according to this embodiment, the content of pigment dispersion resin b is preferably 0.5% by mass or more and 8.0% by mass or less, and more preferably 1.5% by mass or more and 4.0% by mass or less. By setting the content of pigment dispersion resin b to 0.5% by mass or more, aggregation of pigment a can be more effectively suppressed. By setting the content of pigment dispersion resin b to 8.0% by mass or less, nozzle clogging of the recording head can be suppressed.

[0022] (Surfactant c) The surfactant c incorporated into the ink according to this embodiment is represented by general formula (1).

[0023] [ka]

[0024] In general formula (1), m and n are positive integers satisfying the relationship 9 ≤ m + n ≤ 10. Also, x and y are integers satisfying all of the following relationships: 5 ≤ x ≤ 15, 7 ≤ y ≤ 10, and 1.5 ≤ y / x ≤ 2.0. "m + n" represents the amount of the first hydrophobic portion. "x" represents the amount of the hydrophilic portion. "y" represents the amount of the second hydrophobic portion. In other words, in the ink according to this embodiment, the balance between discharge stability and wetting spreadability is controlled by the amount of the first hydrophobic portion, the amount of the hydrophilic portion, the amount of the second hydrophobic portion, and the ratio of the hydrophilic portion to the hydrophilic portion in the surfactant c.

[0025] (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.

[0026] (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.

[0027] 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.

[0028] [Examples] In Examples 1 and 2 of the present invention, ink preparation and evaluation were carried out.

[0029] (Ink adjustment) In Examples 1 and 2, 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.

[0030] [Table 1]

[0031] 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 both Examples 1 and 2, pigment a was pigment blue 15:3 (Toyo Color Co., Ltd. "Lionol Blue FG-7351"), pigment dispersion resin b was benzyl methacrylate / methacrylic acid, and deionized water was used as water.

[0032] 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, "NanoGlenMill" manufactured by Asada Iron Works Co., Ltd., "MSC Mill" manufactured by Nippon Coke Industries Co., Ltd., and "DinoMill" manufactured by Shinmaru Enterprises, Ltd.). In the wet dispersion using the media-type wet disperser, media (zirconia beads with a diameter of 0.5 mm) were set in the vessel, and the discharge rate was set to 200 g / min or more and 600 g / min or less.

[0033] Next, the ink according to Example 1 was prepared. The ink according to Example 1 was prepared by blending the above-mentioned pigment dispersion, surfactant c, 3-methyl-1,5-pentanediol, and water in the quantities shown in Table 2.

[0034] [Table 2]

[0035] In preparing the ink according to Example 1, the components shown in Table 2 were added in order while stirring the solvent with a stirrer. Each ink after stirring was then filtered using a filter (pore size determined for each sample).

[0036] Furthermore, the ink according to Example 2 was prepared. The ink according to Example 2 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 preparing the ink according to Example 2, the components shown in Table 3 were added in order while stirring the solvent with a stirrer. Furthermore, each ink after stirring was filtered using a filter with a pore size of φ1 μm.

[0039] (Measurement of coarse particle number) To measure the number of coarse particles in each ink, an Accusizer particle size analyzer was used to count the number of particles between 0.6 μm and 200 μm in a diluted solution prepared by diluting the ink 10,000 times. The number of coarse particles obtained from the measurement was converted to the original solution equivalent, i.e., multiplied by 10,000, to obtain the number of coarse particles in the ink.

[0040] (Ink evaluation) The inks used in Examples 1 and 2 were evaluated for ejection stability, wetting properties, and image density.

[0041] • Method for evaluating discharge stability In evaluating the ejection stability, the length of the droplets that appeared in the image recorded on the recording medium with each ink was measured. In other words, it was assumed that droplets were formed by satellite droplets for each ink, and the shorter the droplet length, the higher the ejection stability, and the longer the droplet length, the lower the ejection stability. For measuring the droplet length, an inkjet recording device (Kyocera Document Solutions Inc.'s "TASKalfa Pro 15000c") was used to form a straight line image (dot line) on the recording medium (Mondi Corporation's "CC90"). The length of the droplets extending from the dot line in the transport direction was measured, and the maximum value was used as the evaluation value for ejection stability. The evaluation value for the ejection stability of each ink was evaluated according to the following A and B criteria. For ejection stability, inks with an evaluation of A were considered to pass, and inks with an evaluation of B were considered to fail. A (good): 60μm or less B (defective): More than 60μm

[0042] • Method for evaluating wetting spread In the evaluation of wetting spreadability, an inkjet recording device (line type, manufactured by Kyocera Document Solutions Inc.) was used, with an ejection rate of 11 pL per dot, to form an image of 10 straight lines (1-dot lines) on a recording medium (Mondi Corporation "CC90"). The dried straight line images 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 wetting spreadability. The evaluation value of the wetting spreadability of each ink was evaluated according to the following A and B criteria. For wetting spreadability, an A rating indicates a pass, and a B rating indicates a fail. A (good): 80μm or more B (Defective): Less than 80 μm

[0043] • Method for evaluating image density An inkjet recording apparatus (manufactured by Kyocera Document Solutions Inc., "TASKalfa Pro 15000c") was used to form a solid image on a recording medium (manufactured by Mondi, "CC90"). Then, the image density of the dried solid image was measured using a fluorescence spectrophotometer (FD-5, manufactured by Konica Minolta Inc.). For each ink, the average value of the image density obtained from five measurements was used as the evaluation value of the image density. The evaluation values of the image density of each ink were evaluated according to the following criteria A and B. Regarding the image density, an ink with an evaluation of A is considered qualified, and an ink with an evaluation of B is considered unqualified. A (Good): 1.20 or more B (Poor): Less than 1.20

[0044] (Example 1) In Example 1, in the above method, by changing the discharge amount during the preparation of the pigment dispersion liquid and the pore diameter of the filter during the preparation of the ink, samples 1 to 5 of inks with variously different numbers of coarse particles were prepared, and the above evaluations were performed on samples 1 to 5. In samples 1 to 5, a copolymer represented by the general formula (1) (m + n = 10, x = 5, y = 9, y / x = 1.8) was used as surfactant c.

[0045] Table 4 shows the discharge amount during the preparation of the pigment dispersion liquid, the pore diameter of the filter during the preparation of the ink, and the number of coarse particles for samples 1 to 5. In samples 2 to 4, the number of coarse particles was within the range of not less than 1.0×10 9 particles / mL and not more than 1.0×10 11 particles / mL. On the other hand, in sample 1, the number of coarse particles exceeded 1.0×10 11 particles / mL, and in sample 5, the number of coarse particles was less than 1.0×10 9 particles / mL.

[0046] [Table 4]

[0047] Table 5 shows the evaluation results for ejection stability, wetting spread, and image density for samples 1-5. Samples 2-4 all passed in all aspects: ejection stability, wetting spread, and image density. On the other hand, sample 1, which had a large number of coarse particles, failed in terms of ejection stability. Also, sample 5, which had a small number of coarse particles, failed in terms of image density.

[0048] [Table 5]

[0049] (Example 2) In Example 2, ink samples 6 to 15 were prepared using the above method with surfactant c in which m+n, x, y, and y / x in general formula (1) varied, and the above evaluation was performed on samples 6 to 15. In all samples 6 to 15, the number of coarse particles was 1.0 × 10⁻⁶. 9 pcs / mL or more 1.0×10 11 The values ​​were kept within the range of 1 / mL or less. Table 6 shows the m+n, x, y, and y / x for surfactant c used in samples 6 to 15. Samples 7 and 10 both have the configuration of the above embodiment. On the other hand, in samples 12 and 14, m+n is less than 9, and in samples 11, 13, and 15, m+n is greater than 10. Also, in samples 6 and 11, x is less than 5, and in samples 8, 9, 13, and 15, y is greater than 10. Furthermore, in sample 15, y / x is greater than 2.0.

[0050] [Table 6]

[0051] Table 7 shows the evaluation results for ejection stability, wetting spread, and image density for samples 6-15. Samples 7 and 10 both passed in all aspects: ejection stability, wetting spread, and image density. On the other hand, samples 6, 8, 9, and 11-15 failed in at least one of the three aspects: ejection stability, wetting spread, and image density.

[0052] Table 7

Claims

1. It contains a pigment, a pigment dispersion resin, and a surfactant represented by general formula (1), The number of coarse particles with a particle size of 0.6 μm or larger is 1.0 × 10 ９ pcs / mL or more 1.0×10 １１ It is less than or equal to 1 cell / mL. Inkjet ink. 【Chemistry 1】 (In general formula (1), m and n are positive integers satisfying the relationship 9 ≤ m + n ≤ 10, and x and y are integers satisfying all of the following relationships: 5 ≤ x ≤ 15, 7 ≤ y ≤ 10, and 1.5 ≤ y / x ≤ 2.0.)

2. An inkjet ink according to claim 1, The number of coarse particles is 5.0 × 10 １０ It is more than one cell per mL. Inkjet ink.

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