ink

Abstract

We provide an ink that achieves both low viscosity and curl suppression. [Solution] The ink contains a pigment, water, a first curl inhibitor consisting of betaines, and a second curl inhibitor consisting of pyridinium sulfobetaines, wherein the water content is 60% by weight or more.

Description

Technical Field

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[0001] The present technology relates to ink for inkjet printing.

Background Art

[0002] In inkjet printing, if the ink has a high viscosity, the ejected droplets become unstable. Also, there is a problem that the force required for ejection increases and the power consumption increases. Therefore, reducing the viscosity of the ink is required, and as a method, increasing the ink moisture content has been proposed. However, increasing the moisture content of the ink induces paper elongation and makes the paper prone to curl during drying.

[0003] In contrast, Patent Document 1 discloses an ink in which betaines, which are N-trialkyl-substituted derivatives of amino acids and exist as zwitterions, are added as curl inhibitors to suppress the occurrence of curl. Also, Patent Document 2 discloses an ink in which pyridinium sulfobetaines are used as a humectant to achieve ejection stability. Pyridinium sulfobetaines are the same zwitterions as betaines and also have a curl suppressing effect. Also, pyridinium sulfobetaines have an advantage that logP (octanol / water partition coefficient) is largely negative compared to betaines, are selectively soluble in water, and are less likely to precipitate crystals.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the ink described in Patent Document 1 suffers from problems such as crystal precipitation because the betaine is amphiphilic and does not have good solubility in water. Furthermore, as in the ink described in Patent Document 2, directly replacing the betaine with pyridinium sulfobetaine results in a decrease in the curl-suppressing effect.

[0006] In light of the above circumstances, the objective of this technology is to provide an ink that achieves both low viscosity and curl suppression. [Means for solving the problem]

[0007] To achieve the above objective, an ink according to one embodiment of the present invention contains a pigment, water, a first curl inhibitor consisting of betaines, and a second curl inhibitor consisting of pyridinium sulfobetaines, wherein the water content is 60% by weight or more.

[0008] The above ink contains 60% or more by weight of water and has low viscosity. Furthermore, as a curl inhibitor, it contains both betaines, which have excellent curl-inhibiting properties, and pyridinium sulfobetaines, which have excellent selective solubility in water. Therefore, it is possible to prevent the precipitation of the curl inhibitor while maintaining its curl-inhibiting effect. Thus, the above ink can achieve both low viscosity and curl-inhibiting properties.

[0009] The logP values ​​of the octanol / water partition coefficients of the first curl inhibitor, the second curl inhibitor, and the components other than water may be +0.1 or less.

[0010] The betaines and pyridinium sulfobetaines may be non-surfactant types with a linear alkane portion having 3 or fewer carbon atoms.

[0011] The ink may have a viscosity of 6.0 mPa·s or less. [Effects of the Invention]

[0012] As described above, the present invention can provide an ink that achieves both low viscosity and curl suppression. [Brief explanation of the drawing]

[0013] [Figure 1] This graph shows the curl measurement results according to an embodiment of the present invention. [Figure 2] This graph shows the curl measurement results according to an embodiment of the present invention. [Figure 3] This graph shows the curl measurement results according to an embodiment of the present invention. [Modes for carrying out the invention]

[0014] Embodiments of the present invention will be described below.

[0015] [Ink composition] (Schematic configuration) An ink according to one embodiment of the present invention contains a first curl inhibitor a, a second curl inhibitor b, a pigment c, and water. Table 1 below shows an example of the composition of the ink according to this embodiment. 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.

[0016] [Table 1]

[0017] In the ink according to this embodiment, by using two types of curl inhibitors, a first curl inhibitor a and a second curl inhibitor b, it is possible to suppress curling even with a high water content, thereby achieving both low viscosity and curl suppression. The details of each component of the ink according to this embodiment will be described below.

[0018] (First curl inhibitor) The first curl inhibitor a consists of betaines. Betaines are N-trialkyl-substituted derivatives of amino acids and have the structure shown in the following formula (1). In formula (1), R1, R2, R3 and R4 are each a hydrocarbon group. The first curl inhibitor a is preferably a non-surfactant type in which the linear alkane part (R1) has 3 or less carbon atoms.

[0019]

Chemical formula

[0020] Specifically, as the first curl inhibitor a, a betaine having the structure shown in the following formula (2) can be used. The betaine shown in formula (2) is also called N,N,N-trimethylglycine.

[0021]

Chemical formula

[0022] In the ink according to this embodiment, in order to sufficiently obtain the effect of curl suppression, the content of the first curl inhibitor a is 5% by weight or more, and in order to prevent precipitation of the first curl inhibitor a, the content of the first curl inhibitor a is preferably 10% by weight or less.

[0023] (The second curl inhibitor) The second curl inhibitor b consists of pyridinium sulfobetaines. Pyridinium sulfobetaines have the structure shown in the following formula (3). In formula (1), R5 is a hydrocarbon group. Although pyridinium sulfobetaines are named betaines, they have a structure different from that of N-trialkyl-substituted derivatives of amino acids, and thus belong to a different group of compounds from ordinary betaines. The second curl inhibitor b is preferably a non-surfactant type in which the linear alkane part (R5) has 3 or less carbon atoms.

[0024]

Chemical formula

[0025] Specifically, as the second curl inhibitor b, 1-(3-sulfopropyl)pyridinium-betaine having the structure shown in formula (4) below can be used.

[0026] [ka]

[0027] In the ink according to this embodiment, it is preferable that the content of the second curl inhibitor b is 7% by weight or more in order to sufficiently obtain the curl-suppressing effect, and that the content of the second curl inhibitor b is 20% by weight or less in order to prevent the precipitation of the second curl inhibitor b.

[0028] (Pigment) Pigment c may be either a resin-dispersed pigment or a self-dispersing pigment. Specifically, examples of pigment c include inorganic pigments such as 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.

[0029] Examples of pigment c include organic pigments such as azo pigments, diazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, and quinophthalone pigments.

[0030] The hue of the ink according to this embodiment is not particularly limited, and any of the chromatic pigments such as yellow, magenta, cyan, blue, red, orange, and green can be used as pigment c. 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. Pigment c may be one or more selected from these chromatic pigments.

[0031] (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, it is preferable that the water content be 60% by weight or more in order to reduce viscosity, and it is preferable that the water content be 70% by weight or less in order to suppress curling.

[0032] (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. As a dispersant, pigment dispersion resins and surfactants can be used. As a pigment dispersion resin, acrylic resins and urethane resins can be used. As a surfactant, nonionic surfactants and silicone surfactants can be used.

[0033] Furthermore, the ink according to this embodiment may contain a flocculant that has the effect of agglomerating pigments on the paper surface. Examples of flocculants that can be used include 1,5-pentadiol, 1,4-butanediol, and 3-methyl-1,5-pentadiol.

[0034] The ink according to this embodiment preferably has a viscosity of 6.0 mPa·s or less. The viscosity of the ink can be made 6.0 mPa·s or less by increasing the water content to 60% by weight or more.

[0035] [Regarding the octanol / water partition coefficient] In the ink according to this embodiment, the logP values ​​of the octanol / water partition coefficients of components other than the first curl inhibitor a, the second curl inhibitor b, and water c are preferably +0.1 or less. By setting the logP values ​​of the octanol / water partition coefficients to +0.1 or less, mixing of the materials becomes easier, and the precipitation of the first curl inhibitor a and the second curl inhibitor b can be suppressed.

[0036] [About the effects of the ink] The ink according to this embodiment has the configuration described above. As stated above, the ink according to this embodiment contains a first curl inhibitor a which is a betaine, a second curl inhibitor b which is a pyridinium sulfobetaine, and 60% by weight or more of water. By making the water content 60% by weight or more, it is possible to make the ink low viscosity.

[0037] On the other hand, if the water content is 60% by weight or more, the betaines become difficult to dissolve, and crystal precipitation may occur. Pyridinium sulfobetaines have excellent selective solubility in water and are less prone to crystal precipitation, but their curl-suppressing effect is weaker than that of betaines. Therefore, by including both betaines and pyridinium sulfobetaines in the ink, it is possible to prevent crystal precipitation while maintaining the curl-suppressing effect. For this reason, the ink according to this embodiment can achieve low viscosity and excellent curl-suppressing effect (see Examples). [Examples]

[0038] Inks according to the examples and comparative examples of the present invention were prepared. Table 2 below shows the composition of the inks according to the examples and comparative examples. As shown in Table 2, each ink contains carbon black as a pigment, methacrylic acid-methyl methacrylate-butyl acrylate-styrene copolymer (mass average molecular weight 20000, acid value 100) as a dispersion resin, 3-methyl-1,5-pentadiol as a flocculant, and Orphine EXP4200 (manufactured by Nisshin Chemical Industry Co., Ltd.) as a surfactant. Furthermore, inks 1 and 2 contain glycerin as a curl inhibitor, and ink 3 contains betaines as a curl inhibitor. Ink 4 contains pyridinium sulfobetaines as a curl inhibitor, and ink 5 contains betaine and pyridinium sulfobetaines as curl inhibitors. Note that betaine is used as the betaine, and 1-(3-sulfopropyl)pyridinium-betaine is used as the pyridinium sulfobetaine.

[0039] [Table 2]

[0040] Various measurements were performed on each of the inks listed above. Table 3 below shows the measurement results.

[0041] [Table 3]

[0042] The viscosity of each of the above inks was measured using a Lovis 2000ME (manufactured by Anton Paar). As shown in Table 3, compared to a conventional ink with a water content of approximately 50% (Ink 1), increasing the water content to approximately 60% reduced the viscosity (Inks 2-5). Furthermore, it was found that the viscosity of inks using pyridinium sulfobetaine (Ink 4) decreased more significantly than that of inks using betaine (Ink 3) as a curl inhibitor.

[0043] Furthermore, each of the above inks was placed in a petri dish and heated at 40°C for 40 hours, and the presence or absence of crystal precipitation was visually confirmed. As a result, as shown in Table 3, crystal precipitation was confirmed only in ink 3. This indicates that crystal precipitation occurs when betaines alone are used as curl inhibitors, but crystal precipitation can be suppressed when betaines and pyridinium sulfobetaines are used in combination.

[0044] Furthermore, each of the above inks was printed on C2 paper (A6 size, manufactured by Fujifilm) at room temperature. To assess the curl of the paper over time, the height of the raised corners was measured with a metal ruler, and the average of these measurements was taken to determine the curl height. Figures 1 to 3 are graphs showing the relationship between the number of days elapsed since printing and the curl height. As shown in Figure 1, a comparison between ink 1 and ink 2 reveals that increasing the moisture content worsens the curl.

[0045] Furthermore, as shown in Figure 2, a comparison of inks 2 to 4 reveals that both betaines and pyridinium sulfobetaines have a curl-suppressing effect, with betaines being superior. Additionally, as shown in Figure 3, a comparison of inks 3 to 5 confirms that mixing betaines and pyridinium sulfobetaines maintains a curl-suppressing effect almost equivalent to that of betaines alone. Therefore, it can be concluded that using inks combining betaines and pyridinium sulfobetaines allows for both low ink viscosity and curl suppression.

Claims

1. Pigments and Water and, A first curl inhibitor consisting of betaines, A second curl inhibitor consisting of pyridinium sulfobetaines and It contains the above, and the water content is 60% by weight or more. ink.

2. The ink according to claim 1, The logP values ​​of the octanol / water partition coefficients of the first curl inhibitor, the second curl inhibitor, and the components other than water are +0.1 or less. ink.

3. The ink according to claim 1, The betaines and pyridinium sulfobetaines are non-surfactant types, with the linear alkane portion having 3 or fewer carbon atoms. ink.

4. The ink according to claim 1, The viscosity is 6.0 mPa·s or less. ink.

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