ink

Abstract

Provided is an ink that ensures wetting and spreading properties on a recording medium while suppressing curling on the recording medium. The ink contains a surfactant represented by general formula (1), a water-soluble solvent having a log Kow of -1.0 or more and 0.85 or less, a pigment, and water, where the content of the water-soluble solvent is 20% by mass or more and 50% by mass or less. TIFF2026040861000008.tif17164 (In general formula (1), m and n are integers that satisfy the relationship 12≦m+n≦14, and x is an integer of 1 or more and 10 or less.)

Description

[Technical Field]

[0001] The present invention relates to ink for recording an image on a recording medium. [Background technology]

[0002] Inkjet recording devices record images on a recording medium, such as paper, by repeatedly ejecting small droplets of ink from nozzles onto the recording medium. Inkjet recording devices can form high-quality images without unevenness by allowing the ink to wet and spread to a certain extent on the recording medium. Patent Document 1 discloses a technology for improving the wetting and spreading properties of ink on a recording medium by using a surfactant with a specific structure. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4815818 Summary of the Invention [Problem to be solved by the invention]

[0004] When an image is recorded on a recording medium made of fibers such as cellulose fibers using ink that has high wetting and spreading properties, the recording medium is prone to curling due to partial expansion and contraction of the fibers. For this reason, it is generally believed that a technique for improving the wetting and spreading properties of the ink using a surfactant, such as the technique described in Patent Document 1, makes the recording medium on which the image is recorded with the ink more likely to curl.

[0005] In view of the above circumstances, an object of the present invention is to provide an ink that can suppress the occurrence of curling on a recording medium while ensuring good wetting and spreading properties on the recording medium. [Means for solving the problem]

[0006] In order to achieve the above object, an ink according to one embodiment of the present invention contains a surfactant represented by general formula (1), a water-soluble solvent having a log Kow of −1.0 or more and 0.85 or less, a pigment, and water. The content of the water-soluble solvent is 20% by mass or more and 50% by mass or less. [ka] (In the general formula (1), m and n are integers that satisfy the relationship 12≦m+n≦14, and x is an integer of 1 or more and 10 or less.)

[0007] This ink has a log Kow of -1.0 or more and 0.85 or less, and by using a water-soluble solvent that is relatively highly hydrophobic, it is possible to suppress the occurrence of curling on the recording medium. Furthermore, even in a configuration in which this ink uses a water-soluble solvent with relatively high hydrophobicity, by using a surfactant that contains a balanced amount of alkyl chains and butylene oxide chains and has a relatively high overall hydrophobicity, it is possible to ensure wetting and spreading properties on the recording medium. Therefore, with this ink, it is possible to suppress the occurrence of curling on the recording medium while ensuring good wetting and spreading properties on the recording medium.

[0008] The water-soluble solvent may have a log Kow of 0.4 or more and 0.85 or less. [Effects of the Invention]

[0009] As described above, the present invention can provide an ink that ensures wetting and spreading properties on a recording medium while suppressing the occurrence of curling on the recording medium. DETAILED DESCRIPTION OF THE INVENTION

[0010] An embodiment of the present invention will be described.

[0011] [Ink Configuration] (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 onto a recording medium from a recording head of an inkjet recording device to record an image on the recording medium. The recording medium on which an image is recorded using the ink according to this embodiment is made of fibers such as cellulose fiber, and examples thereof include plain paper, copy paper, recycled paper, thin paper, and cardboard.

[0012] In the ink according to this embodiment, the use of a surfactant a having a specific composition ensures wetting and spreading properties on the recording medium, and the use of a water-soluble solvent b having a specific composition makes it possible to suppress the occurrence of curling on the recording medium. In other words, in the ink according to this embodiment, the action of surfactant a and water-soluble solvent b ensures wetting and spreading properties on the recording medium while suppressing the occurrence of curling on the recording medium. Each component of the ink according to this embodiment will be described in detail below.

[0013] (Water-soluble solvent b) In the ink according to this embodiment, the use of a water-soluble solvent b, which has a relatively high hydrophobicity, suppresses penetration into the recording medium. As a result, the ink according to this embodiment can suppress curling caused by local expansion and contraction of the recording medium. From the viewpoint of effectively suppressing curling on the recording medium, the water-soluble solvent b preferably has a log Kow of -1.0 or more and 0.4 or more. Furthermore, from the viewpoint of ensuring solubility in water, the water-soluble solvent b has a log Kow of 0.85 or less.

[0014] In the ink according to this embodiment, the content of water-soluble solvent b is 20% by mass or more in order to fully obtain the effect of the water-soluble solvent b. In addition, in the ink according to this embodiment, the content of water-soluble solvent b is 50% by mass or less in order to ensure ejection stability and to prevent a decrease in ejection stability due to aggregation of the pigment.

[0015] (Surfactant a) The ink according to this embodiment uses surfactant a represented by the following general formula (1): Surfactant a has an alkyl chain and a butylene oxide chain. Surfactant a contains a balanced amount of alkyl chain and butylene oxide chain so that the overall hydrophobicity is relatively low. This allows surfactant a to reduce the dynamic surface tension of the ink without impairing the effect of suppressing curling due to the relatively high hydrophobicity of water-soluble solvent b. Specifically, the dynamic surface tension of the ink at a surface life of 10 msec is preferably 30 mN / m or more and 40 mN / m or less.

[0016] [ka] (In the general formula (1), m and n are integers that satisfy the relationship 12≦m+n≦14, and x is an integer of 1 or more and 10 or less.)

[0017] In general formula (1), when m+n is 11 or less, the contribution of the hydrophobic alkyl chain is insufficient, making it difficult for surfactant a to achieve the effect of reducing dynamic surface tension. In general formula (1), when m+n is 15 or more, the contribution of the hydrophobic alkyl chain is excessive, making it difficult for surfactant a to dissolve in water. In general formula (1), when x is 11 or more, the contribution of the hydrophilic butylene oxide chain is excessive, making it difficult for surfactant a to achieve the effect of reducing dynamic surface tension.

[0018] In the ink according to this embodiment, the content of surfactant a is preferably 0.1% by mass or more in order to fully obtain the effects of surfactant a. Furthermore, in the ink according to this embodiment, the content of surfactant a is preferably 1.0% by mass or less in order to prevent foaming and suppress deterioration of ejection stability due to the intrusion of air bubbles into the recording head.

[0019] (Pigment C) The ink according to this embodiment contains pigment c as a colorant from the viewpoint of preventing color mixing and improving water resistance in an image recorded on a recording medium. Pigment c may be either an inorganic pigment or an organic pigment. Furthermore, as pigment c, these pigments may be used in combination with an extender pigment, if necessary.

[0020] Specific examples of inorganic pigments that can be used in the ink according to this embodiment include carbon black and metal oxides, and carbon black is particularly preferred for black inks. Examples of carbon black include furnace black, thermal lamp black, acetylene black, and channel black.

[0021] 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.

[0022] The ink according to this embodiment is not particularly limited in hue, and any chromatic pigment such as yellow, magenta, cyan, blue, red, orange, or 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. The ink according to this embodiment can use one or more pigments selected from these chromatic pigments as pigment c.

[0023] (water) In the ink according to this embodiment, the water may be, for example, ion-exchanged water, purified water, distilled water, etc. In terms of drying properties and ejection reliability, the water content of the ink according to this embodiment is preferably 40% by mass or more and 70% by mass or less.

[0024] (Other ingredients) The ink according to this embodiment may contain other components as needed. For example, the ink according to this embodiment may contain a dispersant that enhances the dispersibility of the pigment c in the solvent. Examples of dispersants that can be used include pigment dispersing resins and surfactants.

[0025] The pigment dispersion resin is a fine resin particle that adsorbs to the surface of the pigment c, thereby improving the dispersibility of the pigment c in the solvent. The molecular weight of the pigment dispersion resin is preferably in the order of tens of thousands. Examples of pigment dispersion resins include acrylic resins, styrene-acrylic resins, styrene-maleic acid resins, and urethane resins, with styrene-acrylic resins being preferred. The pigment dispersion resin preferably has an acid value of 150 mgKOH / g or more from the viewpoints of improving the dispersibility of the pigment c in the solvent, reducing the particle size, and improving the color development and coloring power of the pigment c. On the other hand, the pigment dispersion resin preferably has an acid value of 300 mgKOH / g or less from the viewpoint of improving the storage stability of the ink.

[0026] The surfactant blended as a dispersant is blended separately from surfactant A, and it reduces the interfacial tension between pigment C and the solvent, thereby increasing the dispersibility of pigment C in the solvent. Examples of such surfactants that can be used include nonionic surfactants and anionic surfactants.

[0027] In addition to the dispersant, the ink according to this embodiment may contain various additives, such as a dissolution stabilizer, an anti-drying agent, an antioxidant, a viscosity adjuster, a pH adjuster, a neutralizing agent, and an anti-mold agent, as needed.

[0028] [Examples and Comparative Examples] Inks were prepared and evaluated as examples of the present invention and comparative examples.

[0029] (Ink Preparation) First, a pigment dispersion liquid was prepared by dispersing pigment c in water. The pigment dispersion liquid was prepared by blending pigment c, a pigment dispersing resin, sodium hydroxide, Olfine (registered trademark) E1010, and water in the amounts shown in Table 1.

[0030] [Table 1]

[0031] The pigment dispersion resin used was a styrene-acrylic resin with a molecular weight of 20,000 and an acid value of 100 mgKOH / g. Sodium hydroxide was added as a neutralizing agent to neutralize the pigment dispersion resin. Olfine (registered trademark) E1010 is a surfactant added as a dispersant and is a nonionic surfactant manufactured by Nissin Chemical Industry Co., Ltd. Ion-exchanged water was used as the water.

[0032] The pigment dispersion was prepared by mixing the above components using a media-type wet disperser. Examples of media-type wet dispersers include wet dispersers (more specifically, the "Nano Grain Mill" manufactured by Asada Iron Works Co., Ltd., the "MSC Mill" manufactured by Nippon Coke and Engineering Co., Ltd., and the "Dyno Mill" manufactured by Shinmaru Enterprises Co., Ltd.).

[0033] For wet dispersion using a media-type wet disperser, media (zirconia beads with a diameter of 0.5 mm) were placed in the vessel and the discharge rate was controlled at 200-600 g / min, adjusting the average particle size of the pigment dispersion, in which dispersant adhered to pigment c dispersed in water, to be 70-130 nm. The particle size distribution of the pigment dispersion was measured using a Zetasizer Nano manufactured by Sysmex Corporation, using a diluted solution prepared by diluting the pigment dispersion 300 times with ion-exchanged water.

[0034] Next, inks according to Examples and Comparative Examples were prepared. The inks according to Examples and Comparative Examples were prepared by blending the above-mentioned pigment dispersion, surfactant a, water-soluble solvent b, and water in the amounts shown in Table 2. The surfactant a and water-soluble solvent b used in the Examples and Comparative Examples are shown in Table 3. Note that m, n, and x in Table 3 represent m, n, and x in the above general formula (1). Table 3 also shows the log Kow for water-soluble solvent b, taken from the calculation software "HSPiP." Ion-exchanged water was used as the water.

[0035] [Table 2]

[0036] [Table 3]

[0037] In preparing each ink, the components shown in Table 2 were added in order while stirring the solvent with a stirrer. In addition, the ink obtained after stirring was filtered using a filter with a pore size of φ5 μm to remove foreign matter, dust, coarse particles, etc.

[0038] (Ink measurement and evaluation) The inks according to the examples and comparative examples were subjected to measurement of dynamic surface tension, and evaluation of curl and wetting / spreading properties.

[0039] Dynamic surface tension measurement method The dynamic surface tension of each ink was measured using the bubble pressure method. Dynamic surface tension was measured using a RUSS "Bubble Pressure Dynamic Surface Tensiometer BP100" with a capillary of 0.4 mm diameter. The bubble pressure method involves inserting a capillary of known diameter into a liquid, pumping gas into the capillary, and calculating the surface tension from the pressure of the bubble formed at the tip of the capillary. By changing the amount of gas pumped into the capillary, the speed at which an interface forms can be changed, and the change in surface tension for each speed at which the interface forms can be measured. The time from when the interface begins to form until the pressure reaches its maximum is called the surface life. The dynamic surface tension of each ink was measured after a surface life of 10 msec.

[0040] How to evaluate curls For the evaluation of curl, an inkjet recording device (line type, manufactured by Kyocera Document Solutions Inc.) was used as the tester, and A4-sized plain paper ("C2" manufactured by Fujifilm Business Innovation Co., Ltd.) was used as the recording medium. Each ink was filled into the black ink tank of the tester. Then, using the tester, a 10 cm x 10 cm solid image was formed in the center of one side of the recording medium in an environment of 32°C temperature and 50% RH. Immediately after the solid image was formed, the recording medium was placed on a horizontal table with the side on which the solid image was formed facing downwards.

[0041] Ten seconds after the solid image was formed, the distance from the platform to each of the four corners of the recording medium (the height to which the four corners were raised due to the recording medium curling) was measured. The average of the measured distances from the platform to the four corners of the recording medium was used as the curl evaluation value. The curl evaluation value of each ink was evaluated according to the following criteria of A, B, and C. Inks with a curl evaluation of A or B passed, and inks with a curl evaluation of C failed. A (good): 15mm or less B (acceptable): More than 15mm and less than 20mm C (defective): More than 20mm

[0042] Wetting and spreading properties To evaluate the wetting and spreading properties, an inkjet recording device (line type, manufactured by Kyocera Document Solutions Inc.) was used as the tester, and copy paper ("CC90" manufactured by Mondi) was used as the recording medium. Each ink was filled into the black ink tank of the tester. Then, using the tester, a straight line (one-dot line) was formed on the recording medium at a discharge speed of 8 m / s under an environment of a temperature of 32°C and a humidity of 15%.

[0043] The width of the straight line formed on the recording medium was measured using a microscope. The measured line width was used as the evaluation value for the wet spreadability of each ink. The evaluation value for the wet spreadability of each ink was evaluated according to the following criteria, A and B. For wet spreadability, inks rated A passed, and inks rated B failed. A (good): 75μm or more B (bad): Less than 75 μm

[0044] Evaluation results Table 4 shows the measurement results of the dynamic surface tension of the inks according to the examples and comparative examples, as well as the evaluation results of curl and wetting and spreading properties.

[0045] [Table 4]

[0046] The inks according to Examples 1 to 7 all passed the test for both curl and wetting and spreading properties. Furthermore, the inks according to Examples 2 to 7 obtained particularly high evaluation results for curl. This is thought to be because the inks according to Examples 2 to 7, in which the water-soluble solvent b is highly hydrophobic, were able to effectively suppress the occurrence of curl on the recording medium.

[0047] On the other hand, the ink according to Comparative Example 1 failed the test for curling. This is thought to be because the ink according to Comparative Example 1, in which the water-soluble solvent b is highly hydrophilic, was unable to sufficiently suppress the occurrence of curling on the recording medium.

[0048] The ink of Comparative Example 2 failed the test for wetting and spreading. This is thought to be because the ink of Comparative Example 2, in which the water-soluble solvent b is highly hydrophobic, did not sufficiently exhibit the effect of surfactant a in reducing the dynamic surface tension.

[0049] In the ink of Comparative Example 3, surfactant a did not dissolve in the solvent, and evaluation was not possible. This is thought to be because the hydrophobic alkyl chain in surfactant a was too long, resulting in insufficient solubility in water.

[0050] The ink of Comparative Example 4 failed the test for wetting and spreading. This is thought to be because the ink of Comparative Example 4, in which the alkyl chain of surfactant a is short, does not contribute enough to reduce the dynamic surface tension due to the insufficient contribution of the hydrophobic alkyl chain.

[0051] The ink of Comparative Example 5 failed the test for wetting and spreading. This is thought to be because the ink of Comparative Example 5, in which the butylene oxide chain in surfactant a is long, makes an excessive contribution of the hydrophilic butylene oxide, and therefore does not sufficiently reduce the dynamic surface tension.

Claims

1. A composition comprising a surfactant represented by general formula (1), a water-soluble solvent having a log Kow of −1.0 or more and 0.85 or less, a pigment, and water, The content of the water-soluble solvent is 20% by mass or more and 50% by mass or less. ink. 【Chemistry 1】 (In general formula (1), m and n are positive integers satisfying the relationship 12≦m+n≦14, and x is an integer of 1 or more and 10 or less.)

2. 10. The ink of claim 1, The water-soluble solvent has a log Kow of 0.4 or more and 0.85 or less. ink.

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