ink

Abstract

To provide an ink that can achieve both storage stability and image density. The ink contains a surfactant having a main skeleton 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, in which the content of the water-soluble solvent is 20% by mass or more and 50% by mass or less. TIFF2026040860000008.tif7164 (In general formula (1), x is an integer of 4 or more and 10 or less, and y is an integer of 1 or more and 5 or less.)

Description

[Technical Field]

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

[0002] In inks for recording images on recording media such as paper, it is preferable that the pigment has high dispersibility in the solvent in order to improve storage stability before use. On the other hand, it is preferable that the pigment has high coagulation on the recording medium in order to improve the density of the image recorded on the recording medium. In other words, in order to achieve both storage stability and image density in such inks, the pigment must exhibit contradictory behavior in the solvent and on the recording medium.

[0003] Patent Document 1 discloses an ink that can achieve both storage stability and image density. This ink contains two types of compounds: a compound that improves storage stability, and a compound that improves image density. Specifically, the former enhances the dispersibility of the pigment in the solvent by forming π-π stacking with the pigment. The latter enhances the affinity between the pigment and the cellulose fibers that make up the recording medium. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6687899 Summary of the Invention [Problem to be solved by the invention]

[0005] The ink disclosed in Patent Document 1 uses two additional compounds to improve storage stability and image density. However, from the standpoint of the number of manufacturing steps and cost, it is advantageous to use fewer raw materials in the ink. Furthermore, Patent Document 1 does not take into consideration the compatibility between the solvent and the compounds, and it is thought that the ink disclosed in Patent Document 1 may not be able to ensure storage stability depending on the properties of the solvent.

[0006] In view of the above circumstances, an object of the present invention is to provide an ink that can achieve both storage stability and image density. [Means for solving the problem]

[0007] 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 general formula (1), x is an integer of 4 or more and 10 or less, and y is an integer of 1 or more and 5 or less.)

[0008] The surfactant used in this ink has a butylene oxide chain constituting the center and ethylene oxide chains arranged on both sides of the butylene oxide chain. In the solvent, this surfactant is oriented so that the butylene oxide chain faces the pigment and the ethylene oxide chain faces the solvent. The butylene oxide chains adsorb to the pigment, and the surfactant acts to disperse the pigment in the solvent. The action of this surfactant provides this ink with high storage stability. Furthermore, 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, the pigment tends to aggregate easily on the recording medium, resulting in high image density. Therefore, this ink can achieve both storage stability and image density.

[0009] The water-soluble solvent may have a log Kow of 0.4 or more and 0.85 or less. [Effects of the Invention]

[0010] As described above, the present invention can provide an ink that can achieve both storage stability and image density. DETAILED DESCRIPTION OF THE INVENTION

[0011] An embodiment of the present invention will be described.

[0012] [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. Examples of recording media on which images are recorded using the ink according to this embodiment include plain paper, copy paper, recycled paper, thin paper, cardboard, glossy paper, and overhead projectors.

[0013] In the ink according to this embodiment, high storage stability is achieved by using a surfactant a having a specific composition, and high image density is achieved by using a water-soluble solvent b having a specific composition. In other words, in the ink according to this embodiment, the effects of surfactant a and water-soluble solvent b enable both storage stability and image density to be achieved. Each component of the ink according to this embodiment will be described in detail below.

[0014] (Surfactant a) The ink according to this embodiment uses surfactant a represented by the following general formula (1): Surfactant a has a butylene oxide chain constituting the center and ethylene oxide chains arranged on both sides of the butylene oxide chain. In the solvent, surfactant a is oriented so that the butylene oxide chain faces the pigment c and the ethylene oxide chain faces the solvent. The butylene oxide chain adsorbs to pigment c, and surfactant a acts to disperse pigment c in the solvent. The ink according to this embodiment achieves high storage stability due to the action of surfactant a.

[0015] [ka] (In general formula (1), x is an integer of 4 or more and 10 or less, and y is an integer of 1 or more and 5 or less.)

[0016] In general formula (1), when x is 3 or less or 11 or more, the effect of surfactant a is difficult to obtain. Furthermore, in general formula (1), when y is 6 or more, the contribution of the hydrophobic butylene oxide chain becomes excessive, making surfactant a less soluble in water. Therefore, in the ink according to this embodiment, by setting x to 4 or more and 10 or less and y to 1 or more and 5 or less in general formula (1), the effect of surfactant a in improving storage stability can be effectively obtained.

[0017] 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.

[0018] (Water-soluble solvent b) In the ink according to this embodiment, the use of the water-soluble solvent b, which has a relatively high hydrophobicity, makes it easier for the pigment c to aggregate on the recording medium. As a result, the ink according to this embodiment can obtain a high image density on the recording medium, that is, can record a clear image with high visibility on the recording medium. In order to obtain a high image density 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, in order to ensure solubility in water, the water-soluble solvent b preferably has a log Kow of 0.85 or less.

[0019] 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.

[0020] (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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] (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.

[0025] (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.

[0026] 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.

[0027] The surfactant blended as a dispersant is blended separately from the surfactant A, and it reduces the interfacial tension between the pigment C and the solvent, thereby increasing the dispersibility of the pigment C in the solvent. Examples of such surfactants that can be used include nonionic surfactants and anionic surfactants.

[0028] 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.

[0029] [Examples and Comparative Examples] Inks were prepared and evaluated as examples of the present invention and comparative examples.

[0030] (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.

[0031] [Table 1]

[0032] 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.

[0033] 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.).

[0034] 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.

[0035] 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 x and y in Table 3 represent x and y 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.

[0036] [Table 2]

[0037] [Table 3]

[0038] To prepare each ink, the components shown in Table 2 were added in order while stirring the solvent with a stirrer. In addition, the ink after stirring was filtered using a filter with a pore size of φ5 μm to remove foreign matter, dust, coarse particles, etc.

[0039] (Ink evaluation) The inks according to the examples and comparative examples were evaluated for image density and storage stability.

[0040] Image density evaluation method To evaluate image density, an inkjet recording device (line type, manufactured by Kyocera Document Solutions Inc.) was used as the test machine, and copy paper ("CC90" manufactured by Mondi) was used as the recording medium. Each ink was filled into the black ink tank of the test machine. The amount of ink ejected from one recording head in the test machine was set to 11.5 pL. Then, a 2.3 cm x 11.5 cm solid image was formed on the recording medium using the test machine in an environment of 32°C temperature and 50% RH relative humidity.

[0041] The recording medium on which the image was formed was stored overnight under normal temperature and humidity conditions, after which the density of the area on which the image was formed was measured using a fluorescence spectrodensitometer (FD-5, manufactured by Konica Minolta, Inc.), and the average value of the density at three points within the solid image was used as the evaluation value for the image density of each ink. The measurement conditions were observation illuminant D50, lighting condition M2, field of view 2°, and density status I. The evaluation value for the image density of each ink was evaluated according to the following criteria: A, B, C. Inks with an image density rating of A or B passed, and inks with a rating of C failed. A (good): 1.5 or more B (Acceptable): 1.18 or more and less than 1.5 C (bad): Less than 1.18

[0042] · Evaluation method for storage stability To evaluate storage stability, the viscosity (initial viscosity V1) of each ink was first measured using an E-type viscometer ("TV-100EL" manufactured by Toki Sangyo Co., Ltd.). Next, approximately 30 g of each ink was placed in a sealed 50 mL container, which was then placed in an incubator set to an internal temperature of 60°C and stored for one month. The container was then removed from the incubator and left to stand at room temperature for three hours.

[0043] Then, each ink was taken out of each container, and the viscosity (post-treatment viscosity V2) was measured using the vibration viscometer described above. Based on the measured initial viscosity V1 and post-treatment viscosity V2, the viscosity change rate [%] was calculated using the following formula. Viscosity change rate [%]=100×(V1-V2) / V1 The calculated viscosity change rate was used as an evaluation value for the storage stability of each ink. The evaluation value for the storage stability of each ink was evaluated according to the following criteria, A and B. For storage stability, inks rated A passed, and inks rated B failed. A (good): 5% or less B (Bad): More than 5%

[0044] Evaluation results Table 4 shows the evaluation results of the image density and storage stability of the inks according to the examples and comparative examples.

[0045] [Table 4]

[0046] The inks according to Examples 1 to 7 all passed the test in terms of both image density and storage stability. Furthermore, the inks according to Examples 2 to 7 achieved particularly high image density. 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 aggregate pigment c on the recording medium.

[0047] On the other hand, the image density of the ink according to Comparative Example 1 was unacceptable. This is thought to be because the ink according to Comparative Example 1, in which the water-soluble solvent b has high hydrophilicity, was unable to obtain the effect of aggregating pigment c on the recording medium.

[0048] The ink according to Comparative Example 2 failed the storage stability test. This is thought to be because the pigment c aggregated in the water-soluble solvent b of the ink according to Comparative Example 2, which had high hydrophobicity.

[0049] The ink of Comparative Example 3 failed the storage stability test. This is thought to be because the ink of Comparative Example 3, which has a small number of ethylene oxide chains in surfactant a, caused the dispersion of pigment c in the solvent to become unstable.

[0050] The ink of Comparative Example 4 failed the storage stability test. This is thought to be because in the ink of Comparative Example 4, in which surfactant a has a large number of ethylene oxide chains, surfactant a becomes entangled with multiple pigments c, making the dispersion of pigments c in the solvent unstable.

[0051] In Comparative Example 5, surfactant a did not dissolve in the solvent, and evaluation was not possible. This is thought to be because in Comparative Example 5, surfactant a had an excessive amount of butylene oxide chains, which are hydrophobic groups, resulting in insufficient solubility in water.

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), x is an integer of 4 or more and 10 or less, and y is an integer of 1 or more and 5 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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