Inkjet inks and tablet printing materials for tablets

Abstract

This disclosure aims to provide an inkjet ink for tablets that exhibits excellent print quality (particularly intermittent restart), lightfastness, and moisture resistance, not only when used with neutral or acidic tablets, but also when used with alkaline tablets, as well as with tablets. The disclosure also aims to provide a tablet printed material having a printed area printed with the inkjet ink. [Solution] The inkjet ink for tablets according to this embodiment comprises an edible dye, a fade inhibitor, a binder resin, and water and ethanol as solvents, wherein the binder resin is shellac.

Description

Technical Field

[0001] The present disclosure relates to inkjet ink for tablets and tablet prints.

Background Art

[0002] There is, for example, an inkjet ink for tablets (hereinafter also simply referred to as "inkjet ink") which is an inkjet ink for printing on tablets and has edibility by using, for example, a food dye as a coloring material (see, for example, Patent Document 1). Tablets to be printed can be classified into neutral tablets, acidic tablets, and alkaline tablets according to the value of pH. Here, the "neutral tablet" refers to a tablet formed from a neutral raw material or a tablet whose printed surface shows neutrality by coating the surface of the tablet with a neutral component. The "acidic tablet" refers to a tablet formed from an acidic raw material or a tablet whose printed surface shows acidity by coating the surface of the tablet with an acidic component. The "alkaline tablet" refers to a tablet formed from an alkaline raw material or a tablet whose printed surface shows alkalinity by coating the surface of the tablet with an alkaline component.

[0003] Some inkjet inks containing dyes such as Brilliant Blue No. 1 according to the prior art contain reducing isomaltulose which has relatively low solubility in ethanol as an additive (i.e., a fading inhibitor) for improving light resistance. However, inkjet inks containing reducing isomaltulose are excellent in moisture resistance against neutral tablets and acidic tablets, but may be inferior in moisture resistance against alkaline tablets.

[0004] Furthermore, some conventional inkjet inks contain shellac to improve moisture resistance (especially against alkaline tablets). Since shellac tends to have relatively low solubility in water, inkjet inks containing shellac tend to have a higher ethanol content than inkjet inks that do not contain shellac in order to reduce shellac precipitation. Therefore, while inkjet inks containing shellac have superior moisture resistance (especially against alkaline tablets), they may have inferior print quality, such as intermittent restart. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 6389506 [Overview of the project] [Problems that the invention aims to solve]

[0006] As mentioned above, conventional inkjet inks generally lacked superior print quality (especially intermittent restart), lightfastness, and moisture resistance for all types of tablets, including neutral, acidic, and alkaline tablets. The inventors have found that in order to improve the above performance of inkjet ink, it is necessary to add ethanol, a fade inhibitor, and shellac to the inkjet ink.

[0007] This disclosure has been made in view of the above, and aims to provide an inkjet ink for tablets that exhibits excellent print quality (particularly intermittent restart), lightfastness, and moisture resistance for any type of tablet, including neutral tablets, acidic tablets, and alkaline tablets, and a printed tablet material comprising a printed portion printed with said inkjet ink for tablets. More specifically, this disclosure aims to provide an inkjet ink for tablets that exhibits excellent print quality (particularly intermittent restart), lightfastness, and moisture resistance not only when used with neutral tablets and acidic tablets, but also when used with alkaline tablets, and a printed tablet material comprising a printed portion printed with said inkjet ink for tablets. [Means for solving the problem]

[0008] To achieve the above objective, an inkjet ink for tablets according to one aspect of the present disclosure comprises an edible dye, a fade inhibitor, a binder resin, and water and ethanol as solvents, wherein the binder resin is shellac.

[0009] Furthermore, in order to achieve the above objective, an inkjet ink for tablets according to one aspect of this disclosure comprises an edible dye, reduced isomaltulose as a fade inhibitor, shellac as a binder resin, and water and ethanol as solvents, wherein the amount of ethanol added to the entire inkjet ink for tablets is in the range of 1.0% by mass or more and 10.0% by mass or less, and further contains sodium carbonate as a pH adjuster, and the inkjet ink for tablets as a whole is alkaline.

[0010] Furthermore, in order to achieve the above objective, an inkjet ink for tablets according to one aspect of this disclosure is an inkjet ink for tablets for printing on magnesium oxide tablets containing magnesium oxide in a range of 0.2 g to 0.5 g per tablet, comprising an edible dye, reduced isomaltulose as a fade inhibitor, shellac as a binder resin, and water and ethanol as solvents, wherein the dye comprises only Blue No. 1, or only Yellow No. 4 and Red No. 106, and the amount of Blue No. 1 added to the entire inkjet ink for tablets is in the range of 0.5% by mass to 5.0% by mass, and the amount of Yellow No. 1 added to the entire inkjet ink for tablets is in the range of Yellow No. 4 and Red No. 106 The amount of No. 4 added is within the range of 0.25% by mass or more and 2.0% by mass or less, and the amount of Red No. 106 added to the entire inkjet ink for tablets is within the range of 0.25% by mass or more and 3.0% by mass or less, the amount of reduced isomaltulose added to the entire inkjet ink for tablets is within the range of 1.0% by mass or more and 10.0% by mass or less, the amount of shellac added to the entire inkjet ink for tablets is within the range of 1.0% by mass or more and 5.0% by mass or less, the amount of ethanol added to the entire inkjet ink for tablets is within the range of 1.0% by mass or more and 10.0% by mass or less, and the inkjet ink for tablets as a whole is alkaline.

[0011] Furthermore, in order to achieve the above objective, a tablet printout according to one aspect of this disclosure comprises a printed section printed using the above-mentioned inkjet ink for tablets. [Effects of the Invention]

[0012] According to one aspect of this disclosure, excellent print quality (particularly intermittent restart), lightfastness, and moisture resistance can be achieved for any type of tablet, whether neutral, acidic, or alkaline. In other words, according to one aspect of this disclosure, it is possible to provide an inkjet ink for tablets that has excellent print quality (particularly intermittent restart), lightfastness, and moisture resistance not only when used with neutral or acidic tablets, but also when used with alkaline tablets, as well as an inkjet ink for tablets. [Brief explanation of the drawing]

[0013] [Figure 1] This is a conceptual diagram illustrating the permeability and lightfastness of an inkjet ink according to the embodiments of this disclosure. [Figure 2] This is a schematic cross-sectional view showing an example of a tablet (plain tablet) according to the embodiments of this disclosure. [Figure 3] This is a schematic cross-sectional view showing an example of a tablet (film-coated tablet) according to the embodiments of this disclosure. [Figure 4] This is an example of a printed image of a tablet (plain tablet) according to the embodiment of this disclosure. [Figure 5] This is an example of a printed image of a tablet (film-coated tablet) according to the embodiment of this disclosure. [Modes for carrying out the invention]

[0014] The inkjet ink according to the embodiment of this disclosure (hereinafter referred to as "this embodiment") exhibits excellent print quality (especially intermittent restart), lightfastness, and moisture resistance regardless of whether it is used on neutral tablets, acidic tablets, or alkaline tablets. In other words, with the inkjet ink according to this embodiment, it is possible to effectively reduce the deterioration of print quality (especially intermittent restart), lightfastness, and moisture resistance not only when printing on neutral tablets with a neutral surface, or acidic tablets with an acidic surface, but also when printing on alkaline tablets with an alkaline surface. The configuration of the inkjet ink (inkjet ink for tablets) and the tablets (printed tablets) having a printed area printed using the inkjet ink according to this embodiment will be described in detail below.

[0015] [Inkjet ink composition] The inkjet ink according to this embodiment contains an edible dye (food coloring), a fade inhibitor, a binder resin, and water and ethanol as solvents. Furthermore, the inkjet ink according to this embodiment contains shellac as the binder resin. The shellac used in this embodiment is a natural resin, and its properties are as follows: specific gravity: 1.02~1.12, specific heat: 0.53 (0℃), softening point: 70~80℃ (ball-ring method), acid value: 60~80, saponification value: 200~260, iodine value: 15~30 (Wiiss method), heat setting time: 2~6 minutes (JIS K5909 170℃), volume resistivity: 10¹⁵~10¹⁶ Ω·cm, dielectric constant: 3.5~4.0, electrical dielectric strength: 40~80kV / mm, SP value: 12.5±2.0.

[0016] The composition of shellac varies depending on the purification method and product, but it mainly consists of resin acids such as aleuritic acid, jalaric acid, and laxijalaric acid. Examples of commercially available shellac products include those from Nippon Shellac Industry Co., Ltd., Koyo Chemical Co., Ltd., and Gifu Shellac Manufacturing Co., Ltd. Furthermore, the term "shellac" in this disclosure includes both the shellac specified in JIS K 5909 and the white shellac specified in JIS K 5911. Examples of commercially available products include BDS and Laccoat 30EA manufactured by Nippon Shellac Industries Co., Ltd.

[0017] With the above-described composition of the inkjet ink, excellent print quality (particularly intermittent restartability), light resistance, and moisture resistance can be achieved regardless of whether it is used for any type of tablets, such as neutral tablets, acidic tablets, and alkaline tablets. Hereinafter, the light resistance of the inkjet ink according to the present embodiment will be described while referring to FIG. 1.

[0018] FIG. 1 is a conceptual diagram for explaining the relationship between the adhesion of ink and light resistance on the surface of a printed material (solid preparation). Here, as the solid preparation, for example, a tablet provided with a film-coated portion having few voids, that is, a film-coated (FC) tablet is used. Note that the present disclosure is not limited thereto, and a plain tablet or a capsule tablet may also be used as the printed material. FIGS. 1(a) to 1(d) are schematic cross-sectional views in the thickness direction of tablets in a state where inkjet inks A to D having different compositions are printed on tablets (here, film-coated tablets) and a certain period of time has elapsed. In this example, the inkjet ink A is an ink using an edible dye 4 as a coloring material and using water and ethanol as solvents. As the dye 4, Brilliant Blue FCF can be exemplified.

[0019] Further, the inkjet ink B is an ink obtained by adding shellac as a binder resin to the inkjet ink A. Further, the inkjet ink C is an ink obtained by adding a predetermined saccharide as a fading inhibitor to the inkjet ink B. Here, the saccharide added as a fading inhibitor to the inkjet ink C is, for example, lactose. Further, the inkjet ink D is an ink obtained by adding reduced isomaltulose as a fading inhibitor to the inkjet ink B. That is, focusing on the binder resin and the fading inhibitor, the inkjet ink A is an inkjet ink that contains neither a binder resin nor a fading inhibitor.

[0020] Further, the inkjet ink B is an inkjet ink that contains shellac as a binder resin and does not contain a fading inhibitor. Furthermore, inkjet ink C is an inkjet ink that contains shellac as a binder resin and lactose, a disaccharide, as a fade inhibitor. Furthermore, inkjet ink D is an inkjet ink that contains shellac as a binder resin and reduced isomaltulose as a fade inhibitor.

[0021] Specifically, Figure 1(a) is a schematic cross-sectional view in the thickness direction of a tablet after printing inkjet ink A, which contains dye 4 as a colorant and water and ethanol as solvents, onto the surface 1S of the tablet substrate 1, and allowing a certain period of time (e.g., 140 hours) to elapse. Figure 1(b) is a schematic cross-sectional view in the thickness direction of a tablet after printing inkjet ink B onto the surface 1S of the tablet substrate 1, and allowing a certain period of time (e.g., 140 hours) to elapse. Figure 1(c) is a schematic cross-sectional view in the thickness direction of a tablet after printing inkjet ink C onto the surface 1S of the tablet substrate 1, and allowing a certain period of time (e.g., 140 hours) to elapse. Figure 1(d) is a schematic cross-sectional view in the thickness direction of a tablet after printing inkjet ink D onto the surface 1S of the tablet substrate 1, and allowing a certain period of time (e.g., 140 hours) to elapse.

[0022] First, we will explain the difference between the presence or absence of shellac, a resin binder, in inkjet inks and the resulting ink adhesion, using inkjet inks A and B as examples. By adding shellac, a resin binder, to the inkjet ink, a dry film 10 formed by the shellac is created on the surface of the printed ink. This makes it easier for the dye 4 to remain on the surface of the tablet, and helps to suppress discoloration and fading of the printed image.

[0023] Next, we will explain the difference between the presence or absence of sugars, which act as fade inhibitors in inkjet inks, and the penetration of dyes, using inkjet inks B and C as examples. Among the various colorants used in inkjet inks, tar-based dyes used as food dyes, for example, can cause discoloration and fading of printed text and images on surfaces such as solid formulations. For example, Blue No. 1, a type of tar-based dye, caused discoloration and fading of printed images due to penetration into solid formulations over time and photodegradation. In response to this, a method is known in which sugars, which are discoloration inhibitors, are added to inkjet ink to suppress the penetration of dyes into solid formulations and thereby suppress discoloration and fading of printed images.

[0024] As shown in Figure 1(b), when inkjet ink B, which does not contain sugars that function as a fade inhibitor, is printed, the dye 4 penetrates into the base material 1 of the tablet after a certain period of time has elapsed since printing. Here, the depth of penetration of the dye 4 in inkjet ink B after this certain period of time is denoted as the penetration depth X (μm). In contrast, as shown in Figure 1(c), when inkjet ink C, which contains sugars that function as a fade inhibitor, is printed, after a certain period of time has elapsed since printing, the penetration depth Y (μm) of inkjet ink C becomes smaller than the penetration depth X of inkjet ink B (X > Y).

[0025] In inkjet ink C, the addition of a predetermined sugar that functions as a fade inhibitor increases the viscosity of the ink, thereby suppressing the penetration of the dye 4 tablet into the substrate 1. Therefore, when inkjet ink C is printed, the dye 4 remains near the surface 1S within the substrate 1 of the tablet even after a certain period of time has elapsed since printing. In other words, inkjet ink containing a predetermined sugar that functions as a fade inhibitor can suppress the discoloration and fading of the printed image due to the penetration of the dye (e.g., Blue No. 1) compared to inkjet ink without the addition of a predetermined sugar that functions as a fade inhibitor.

[0026] As described above, the inkjet ink according to this embodiment, by selecting the type and amount of fade inhibitor, binder resin, and solvent to be added, fixes the ink to the surface of any type of substrate, whether neutral, acidic, or alkaline, thereby sufficiently suppressing light-induced fading of the printed image and improving lightfastness. The inventors have found that fixing the ink to the surface of the substrate (e.g., a tablet) is effective in suppressing light-induced fading of the printed image. In this example, by fixing the ink to the surface 1S of the tablet, the dye 4 is fixed to the surface 1S, and as a result, the dye 4 can be left on the surface 1S at a high concentration.

[0027] When the concentration of dye 4 is high on the surface 1S of the tablet substrate 1, for example, the proportion of colorants that undergo photodegradation and discoloration due to photolysis among the dye 4 on the surface 1S is reduced. In other words, even if some of the dye 4 undergoes photodegradation and discoloration, the impact is limited, and the decrease in the visibility (readability) of the printed image is suppressed. As a result, the visibility of the printed image as a whole is maintained, and as a result, photodegradation and discoloration of the printed image can be sufficiently suppressed. Therefore, the lightfastness of the inkjet ink can be improved. Furthermore, the inventors have discovered that, regardless of whether the substrate is neutral, acidic, or alkaline, certain sugars such as lactose or reduced isomaltulose function as a binder that fixes the ink containing the dye as a colorant to the surface of the substrate.

[0028] Specifically, the inkjet ink according to this embodiment contains a food dye as a colorant, sugars that function as a fade inhibitor, shellac as a binder resin, and water and ethanol that function as solvents. With this configuration, regardless of whether it is used in neutral tablets, acidic tablets, or alkaline tablets, the ink containing the dye used as a colorant can be fixed to the surface of the substrate, and the dye can remain on the surface at a high concentration. As a result, the inkjet ink according to this embodiment can sufficiently suppress light-induced discoloration of printed images and improve lightfastness.

[0029] As shown in Figure 1(d), when inkjet ink D, which is a more preferred form of inkjet ink according to this embodiment, is printed on the surface 1S of the tablet substrate 1, the dye 4 (here, Blue No. 1) in the ink is fixed to the surface 1S. Specifically, when inkjet ink D is printed, the penetration depth Z (μm) of the dye 4 after a certain period of time has elapsed since printing is further reduced than the penetration depth Y of the dye 4 in inkjet ink C containing a predetermined sugar (Y > Z). For example, the penetration depth Z of the dye 4 in inkjet ink D is reduced to about 50% of the penetration depth Y of the dye 4 in inkjet ink C. In other words, inkjet ink D can further suppress the penetration of the dye 4. As a result, the dye 4 remains on the surface 1S at a high concentration, and the decrease in the visibility of the printed image is suppressed as described above. As a result, regardless of whether inkjet ink D is used for neutral tablets, acidic tablets, or alkaline tablets, the light-induced discoloration of the printed image is sufficiently suppressed, and inkjet ink D can improve lightfastness.

[0030] On the other hand, while inkjet ink C can leave dye 4 near the surface 1S inside the tablet substrate 1, it does not sufficiently suppress the penetration of dye 4 compared to inkjet ink D, and therefore cannot fix the ink on the surface 1S. In other words, because the concentration of dye 4 remaining on the surface 1S is low with inkjet ink C, it is unable to suppress light-induced discoloration of printed images as well as with inkjet ink D, and tends to be inferior to inkjet ink D in that its lightfastness is not easily improved.

[0031] As described above, the inkjet ink according to this embodiment, by adding a predetermined sugar (for example, lactose or reduced isomaltulose) as a fade inhibitor, significantly suppresses the penetration of the dye into the substrate and fixes the ink to the surface of the substrate, regardless of whether it is used in neutral, acidic, or alkaline tablets. As a result, the inkjet ink according to this embodiment can suppress light-induced fading of printed images and improve lightfastness, and can also suppress fading of printed images caused by the penetration of the dye into the substrate.

[0032] Furthermore, as shown in Figure 1(d), the inkjet ink D can be fixed to the surface 1S of the tablet substrate 1 in a slightly raised manner. As a result, when inkjet ink D is printed, for example, the print appears to stand out more darkly on the surface 1S. Therefore, compared to inkjet inks A, B, and C, for example, inkjet ink D can improve the visibility of the printed image during printing. In other words, the inkjet ink according to this embodiment can reduce the decrease in visibility due to light discoloration of the printed image, and can also provide good visibility to the printed image at the time of printing.

[0033] The following describes the details of the lightfastness of the inkjet ink according to this embodiment. The inkjet ink according to this embodiment only needs to have a color difference ΔE of 20 or less before and after the lightfastness test, as defined in JIS Z 8781. Here, the lightfastness test is a test that compares the color difference ΔE (according to JIS Z 8781), which indicates the amount of change in chromaticity and optical color density, before and after irradiation with visible light, for a printed image printed using the inkjet ink according to this embodiment. Specifically, the color difference ΔE is measured before and after irradiating the printed image with a cumulative 1.2 million lux of visible light, and the values ​​are compared. For visible light irradiation, for example, a xenon weather meter (Toyo Seiki Seisakusho Ci4000) is used. The printed image in the lightfastness test is, for example, a solid print on a tablet (for example, a film-coated tablet) which is the object to be printed on.

[0034] Sufficient lightfastness for the formation of printed images on medical tablets and the like often refers to a color difference ΔE of 20 or less in the printed image before and after irradiation with 1.2 million lux of visible light in a lightfastness test. The decision to use a color difference ΔE of 20 or less as a criterion for sufficient lightfastness was derived from opinion tests conducted by the inventors in collaboration with various medical professionals. When the color difference ΔE exceeds 20, it is recognized that the visibility of the printed image (e.g., the readability of the print) begins to decline. In other words, if the color difference ΔE before and after visible light irradiation is 20 or less, it can be said that the inkjet ink has excellent lightfastness, with light-induced discoloration and fading sufficiently suppressed. Although this number is larger than the typical ΔE of 3-6 for commercial printed materials, this number was obtained because tablets are not usually compared before and after exposure to light, and it is assumed that the printed image on the tablet surface will naturally fade.

[0035] The reason why sugars such as lactose and reduced isomaltulose are used as fixatives (fading inhibitors) in the inkjet ink according to this embodiment is that if fixatives other than sugars such as lactose and reduced isomaltulose are added, the dye on the tablet surface will not be sufficiently fixed to the surface of the substrate, and when the above lightfastness test is performed on a solid print image, the color difference ΔE may exceed 20. By adding sugars such as lactose and reduced isomaltulose as fixatives, the dye on the tablet surface is sufficiently fixed to the surface of the substrate, so that the color difference ΔE before and after the lightfastness test falls below 20, and the inkjet ink is given excellent lightfastness.

[0036] The following describes each component that makes up the inkjet ink according to this embodiment. (Colorants) As described above, the inkjet ink according to this embodiment contains an edible dye. In the inkjet ink according to this embodiment, the blending ratio of the edible dye is preferably within the range of 0.5% by mass or more and 5.0% by mass or less relative to the total mass of the ink. With such a configuration, good visibility can be provided to the printed image, as well as high intermittent restartability (i.e., excellent print quality). Furthermore, if the content of the edible dye is within the above range, the edible dye can be reliably left at a high concentration on the surface of the printed material by adding a fixative that functions as a fade inhibitor, thereby suppressing light-induced fading in the printed image and improving the lightfastness of the inkjet ink according to this embodiment.

[0037] In contrast, if the food dye content is less than 0.5% by mass, the overall printed color tends to become lighter, reducing the visibility of the printed image. Furthermore, if the food dye content is less than 0.5% by mass, lightfastness may be reduced or absent. Furthermore, if the food dye content exceeds 5.0% by mass, the dissolution stability of the colorant deteriorates, causing the pigment in the ink to precipitate or solidify. This can lead to nozzle clogging of the inkjet head during printing, potentially resulting in a decrease in print quality (especially intermittent restart). Furthermore, the lower limit of the food dye content is more preferably 0.8% by mass or more, and even more preferably 1.0% by mass or more, relative to the total mass of the ink. Furthermore, the upper limit of the food dye content is more preferably 4.0% by mass or less, and even more preferably 3.0% by mass or less, relative to the total mass of the ink.

[0038] Furthermore, the inkjet ink according to this embodiment preferably contains at least one food dye selected from, for example, azo dyes, triphenylmethane dyes, and xanthene dyes. Examples of azo dyes include at least one of the following: Red No. 102 (New Coccine, CAS number: 2611-82-7, E number: E124) and Yellow No. 4 (Tartrazine, CAS number: 1934-21-0, E number: E102). Another example of a triphenylmethane-based dye is Brilliant Blue FCF (CAS number: 3844-45-9, E number: E133). Another example of a xanthene dye is Acid Red 52 (CAS number: 3520-42-1).

[0039] Furthermore, the inkjet ink according to this embodiment may contain only Blue No. 1 as a food dye, or it may contain only Yellow No. 4 and Red No. 106. In the case of a form containing only Blue No. 1 as a food dye, it is preferable that the amount of Blue No. 1 added to the total inkjet ink is within the range of 0.5% by mass or more and 5.0% by mass or less. Furthermore, in the form containing only Yellow No. 4 and Red No. 106 as food dyes, it is preferable that the amount of Yellow No. 4 added to the total inkjet ink is within the range of 0.25% by mass to 2.0% by mass, and the amount of Red No. 106 added to the total inkjet ink is within the range of 0.25% by mass to 3.0% by mass. It should be noted that the dyes that can be added to the inkjet ink according to this embodiment are not limited to the food dyes described above. For example, the inkjet ink according to this embodiment may also be appropriately selected and added from conventionally known synthetic food dyes and natural food dyes.

[0040] Examples of synthetic food colorings include tar-based dyes, natural pigment derivatives, and natural synthetic dyes. Examples of tar-based dyes include Food Blue No. 1, Food Red No. 2, Food Red No. 3, Food Red No. 40, Food Red No. 102, Food Red No. 104, Food Red No. 105, Food Red No. 106, Food Yellow No. 4, Food Yellow No. 5, Food Blue No. 2, Food Red No. 2 Aluminum Lake, Food Red No. 3 Aluminum Lake, Food Red No. 40 Aluminum Lake, Food Yellow No. 4 Aluminum Lake, Food Yellow No. 5 Aluminum Lake, Food Blue No. 1 Aluminum Lake, and Food Blue No. 2 Aluminum Lake. Examples of natural pigment derivatives include norbixin potassium. Examples of natural synthetic dyes include β-carotene and riboflavin.

[0041] Furthermore, natural food colorings include, for example, anthocyanin pigments, carotenoid pigments, quinone pigments, chlorophyll pigments, flavonoid pigments, betaine pigments, monascus pigments, and other pigments derived from natural sources. Examples of anthocyanin pigments include red radish pigment, red cabbage pigment, red rice pigment, elderberry pigment, cowberry pigment, gooseberry pigment, cranberry pigment, salmonberry pigment, perilla pigment, blueberry pigment, strawberry pigment, dark sweet cherry pigment, cherry pigment, hibiscus pigment, huckleberry pigment, grape juice pigment, grape skin pigment, blackcurrant pigment, blackberry pigment, blueberry pigment, plum pigment, whortleberry pigment, boysenberry pigment, mulberry pigment, purple sweet potato pigment, purple corn pigment, purple yam pigment, raspberry pigment, red currant pigment, loganberry pigment, and other anthocyanin pigments. Examples of carotenoid pigments include annatto pigment, gardenia yellow pigment, and other carotenoid pigments. Examples of quinone pigments include cochineal pigment, lithospermum pigment, lac pigment, and other quinone pigments. Examples of flavonoid pigments include safflower yellow pigment, sorghum pigment, onion pigment, and other flavonoid pigments. Examples of betaine pigments include beet red pigment. Examples of monascus pigments include red yeast rice pigment and red yeast rice yellow pigment. Examples of pigments derived from other natural products include turmeric pigment, Clerodendrum pigment, gardenia red pigment, and spirulina blue pigment.

[0042] (Adhesive) As described above, the inkjet ink according to this embodiment contains a fixing agent for fixing ink containing food dye to the surface of the substrate. In the inkjet ink according to this embodiment, this fixing agent plays the role of a fade inhibitor. Specifically, the fixing agent contained in the inkjet ink according to this embodiment is, for example, a sugar, more preferably a disaccharide, even more preferably lactose or reduced isomaltulose, and most preferably reduced isomaltulose. If the fixing agent is a sugar such as reduced isomaltulose, by adding it to the inkjet ink together with a solvent having the component composition described later, the ink containing food dye can be fixed to the surface of the substrate. As a result, the inkjet ink according to this embodiment can sufficiently suppress light-induced fading of printed images and improve lightfastness for any type of tablet, whether neutral, acidic, or alkaline. Furthermore, sugars such as reduced isomaltulose used as a fixing agent in this embodiment also have the function of suppressing the decomposition (photodegradation) of inkjet ink by light irradiation. Therefore, it is also possible to suppress the occurrence of light-induced fading itself. In the inkjet ink according to this embodiment, the blending ratio of sugars such as reduced isomaltulose, which are used as a binder, i.e., the content (mass) of the fade inhibitor, is preferably within the range of 1.0% by mass or more and 10.0% by mass or less, relative to the total mass of the ink.

[0043] If the proportion of the fade inhibitor is less than 1.0% by mass of the total ink mass, the ink's adhesion effect may be reduced. Therefore, if the proportion of the fade inhibitor is less than 1.0% by mass of the total ink mass, the lightfastness may decrease or the ink may not exhibit any lightfastness at all. Furthermore, if the proportion of the fade inhibitor exceeds 10.0% by mass relative to the total mass of the ink, the ink viscosity may increase, and the solubility stability of the fade inhibitor may deteriorate, causing the fade inhibitor in the ink to precipitate or settle as a solid. This can lead to nozzle clogging of the inkjet head during printing, potentially reducing intermittent restart performance. Furthermore, the lower limit of the fade inhibitor content is more preferably 3.0% by mass or more, and even more preferably 5.0% by mass or more, relative to the total mass of the ink. Also, the upper limit of the fade inhibitor content is more preferably 8.0% by mass or less, and even more preferably 7.0% by mass or less, relative to the total mass of the ink.

[0044] (solvent) The inkjet ink according to this embodiment contains, in addition to food dyes and fade inhibitors, a solvent (dispersion medium) for dissolving (dispersing) the food dyes and fade inhibitors. The inkjet ink according to this embodiment contains water (e.g., purified water) and ethanol as solvents. Generally, fade inhibitors, especially disaccharides such as reduced isomaltulose, have poor solubility in alcohols. Therefore, in this embodiment, the inclusion of ethanol in the solvent reduces the solubility of the fade inhibitor used as a fixative in the solvent. Accordingly, in this embodiment, by adding a solvent containing the above-mentioned alcohols (especially ethanol) together with the fade inhibitor as a fixative to the inkjet ink, the ink's fixing effect can be reliably achieved, and the edible dye contained in the ink can be left on the surface of the printed material (e.g., a tablet) at a higher concentration. As a result, the inkjet ink according to this embodiment can sufficiently suppress light-induced fading of printed images and improve lightfastness. Furthermore, because ethanol is highly volatile, it can improve the transfer resistance (drying speed) of inkjet inks.

[0045] In the inkjet ink according to this embodiment, the blending ratio of each component of the solvent is not limited, but the blending ratio of ethanol, i.e., the amount of ethanol added, is preferably in the range of 1.0% by mass or more and 10.0% by mass or less relative to the total mass of the ink. With such a configuration, the solubility of the fade inhibitor in the solvent is reliably reduced, and the fixing effect of the ink containing food dye is further improved. Therefore, the inkjet ink can be given superior lightfastness.

[0046] Furthermore, if the amount of ethanol added is less than 1.0% by mass, the effect of reducing the solubility of the fade inhibitor in the solvent may decrease. Also, if the amount of ethanol added exceeds 10.0% by mass, the ink may dry out at the inkjet nozzle, causing nozzle clogging of the inkjet head during printing, and intermittent restart performance may decrease. In addition, if the amount of ethanol added exceeds 10.0% by mass, the solubility of the fade inhibitor in the solvent decreases further (i.e., the fade inhibitor becomes less soluble in the solvent), causing the fade inhibitor to precipitate, which may result in a decrease in ink adhesion effect and a decrease in lightfastness. Furthermore, the precipitated fade inhibitor may cause nozzle clogging of the inkjet head, and intermittent restart performance may decrease. Furthermore, the lower limit of the amount of ethanol added is more preferably 2.5% by mass or more, and even more preferably 4.0% by mass or more, relative to the total mass of the ink. Also, the upper limit of the amount of ethanol added is more preferably 8.0% by mass or less, and even more preferably 7.0% by mass or less, relative to the total mass of the ink.

[0047] Furthermore, the inkjet ink according to this embodiment may contain propylene glycol as a solvent. Propylene glycol functions as a wetting agent, preventing the ink from drying out at the inkjet nozzle and providing the ink with sufficient intermittent restart properties. When propylene glycol is included in the solvent, the blending ratio of propylene glycol, i.e., the amount of propylene glycol added, is preferably within the range of 28.0% by mass or less relative to the total mass of the ink. With such a configuration, printing can be performed without impairing the drying properties of the ink, and the fixing effect of the ink containing food dyes is further improved. As a result, the inkjet ink can be given superior lightfastness.

[0048] Furthermore, if the amount of propylene glycol added exceeds 28.0% by mass, the drying time of the printed surface on the tablet surface will increase, which may cause problems (transfer failure) such as undried ink adhering to one tablet and causing smudging when printed tablets come into contact with each other. Furthermore, if the inkjet ink according to this embodiment contains propylene glycol as a solvent, it is preferable that the amount of propylene glycol added is greater than the amount of ethanol added as a solvent.

[0049] Furthermore, the inkjet ink according to this embodiment may further contain at least one of glycerin or isopropyl alcohol as a solvent. Specifically, the solvent may further contain either glycerin or isopropyl alcohol, or both glycerin and isopropyl alcohol. Glycerin functions as a wetting agent, similar to propylene glycol described above. Isopropyl alcohol, like ethanol described above, is highly volatile, and can therefore improve the transfer resistance (drying properties) of the inkjet ink.

[0050] (Binder resin) The inkjet ink according to this embodiment contains a binder resin in addition to a food dye, a fade inhibitor, and a solvent. Furthermore, the inkjet ink according to this embodiment contains shellac as the binder resin. As described above, the "shellac" used in this embodiment is a natural resin, and its properties are as follows: specific gravity: 1.02~1.12, specific heat: 0.53 (0℃), softening point: 70~80℃ (ball-ring method), acid value: 60~80, saponification value: 200~260, iodine value: 15~30 (Wiiss method), heat setting time: 2~6 minutes (JIS K5909 170℃), volume resistivity: 10¹⁵~10¹⁶ Ω·cm, dielectric constant: 3.5~4.0, electrical dielectric strength: 40~80kV / mm, SP value: 12.5±2.0.

[0051] The components of shellac vary depending on the purification method and product, but for example, it mainly consists of resin acids such as aleuritic acid, jararic acid, and laccijararic acid. More specifically, the shellac according to this embodiment may be any one of aleuritic acid, jararic acid, or laccijararic acid, or it may be a hard resin in which aleuritic acid is esterified with jararic acid or laccijararic acid. If it is a hard resin in which aleuritic acid is esterified with jararic acid or laccijararic acid, it is preferable to have 1 to 4 ester bonds in the molecule. Examples of commercially available shellac products include those from Nippon Shellac Industry Co., Ltd., Koyo Chemical Co., Ltd., and Gifu Shellac Manufacturing Co., Ltd. Furthermore, the term "shellac" in this disclosure includes both the shellac specified in JIS K 5909 and the white shellac specified in JIS K 5911. Examples of commercially available products include BDS and Laccoat 30EA manufactured by Nippon Shellac Industries Co., Ltd.

[0052] In the inkjet ink according to this embodiment, the blending ratio of the binder resin is not limited, but it is preferable that the blending ratio of the binder resin, i.e., the amount of binder resin added, is within the range of 1.0% by mass or more and 5.0% by mass or less of the total mass of the ink. With such a configuration, excellent moisture resistance is achieved not only when used in neutral tablets and acidic tablets, but also when used in alkaline tablets. Furthermore, if the amount of binder resin added is less than 1.0% by mass, the moisture resistance to alkaline tablets may decrease. Also, if the amount of binder resin added exceeds 5.0% by mass, the amount (ratio) of other components may decrease relatively, potentially reducing functions such as light resistance. In addition, the printability (especially intermittent restart) may deteriorate due to increased ink viscosity.

[0053] When considering moisture resistance, the amount of binder resin added is more preferably 2.0% by mass or more, and even more preferably 4.0% by mass or more, relative to the total mass of the ink. Furthermore, when considering moisture resistance, the amount of binder resin added is preferably 5.0% by mass or less, relative to the total mass of the ink. Furthermore, when considering print stability, the amount of binder resin added is more preferably 4.0% by mass or less of the total mass of the ink, and even more preferably 3.0% by mass or less. Also, when considering print stability, the amount of binder resin added is preferably 1.0% by mass or more of the total mass of the ink.

[0054] (pH adjuster) Shellac is known to dissolve not only in alcohols but also in alkaline aqueous solutions. Therefore, by making the ink alkaline, shellac can remain dissolved without precipitation even in solvents with a low alcohol content (i.e., inks with a low alcohol content). Thus, when adding (dissolving) shellac, which has high solubility in alcohols, to inkjet ink containing reduced isomaltulose, which has low solubility in alcohols, the coexistence of shellac and reduced isomaltulose can be achieved by adding a pH adjuster to the inkjet ink to appropriately adjust its pH. A pH adjuster that can be added to the inkjet ink according to this embodiment is, for example, sodium carbonate.

[0055] In the inkjet ink according to this embodiment, the blending ratio of the pH adjuster is not limited, but it is preferable that the blending ratio of the pH adjuster, i.e., the amount of pH adjuster added, is within the range of 0.1% by mass or more and 0.6% by mass or less of the total mass of the ink. With such a configuration, excellent moisture resistance is achieved not only when used in neutral tablets and acidic tablets, but also when used in alkaline tablets. Furthermore, if the amount of pH adjuster added is less than 0.1% by mass, the solubility of the binder resin may decrease, potentially reducing its moisture resistance to alkaline tablets. Also, if the amount of pH adjuster added exceeds 0.6% by mass, the ink itself may become strongly alkaline, potentially reducing the light resistance and other functions of neutral and acidic tablets. Furthermore, the lower limit of the amount of pH adjuster added is more preferably 0.2% by mass or more, and even more preferably 0.3% by mass or more, relative to the total mass of the ink. Also, the upper limit of the amount of pH adjuster added is more preferably 0.5% by mass or less, and even more preferably 0.4% by mass or less, relative to the total mass of the ink.

[0056] Furthermore, the inkjet ink according to this embodiment is preferably alkaline as a whole, and the pH value of the entire inkjet ink can be appropriately adjusted by adjusting the amount of pH adjusting agent added. The pH value of the inkjet ink according to this embodiment is preferably within the range of 7.5 to 9.5. With such a configuration, excellent moisture resistance is achieved not only when used in neutral or acidic tablets, but also when used in alkaline tablets. Furthermore, the lower limit of the pH value of the inkjet ink is more preferably 8.0 or higher, and even more preferably 8.3 or higher. Also, the upper limit of the pH value of the inkjet ink is more preferably 9.0 or lower, and even more preferably 8.8 or lower.

[0057] Furthermore, the pH value of the inkjet ink according to this embodiment is preferably set so that the absolute difference between it and the pH value at the printing location of the tablet to be printed is 2 or less, more preferably set to 1.8 or less, and even more preferably set to 1.5 or less. For example, if the pH value of the inkjet ink according to this embodiment is set to "7.5", then it is preferable that the pH value at the printing location on the tablet to be printed is "within the range of 5.5 to 9.5". Furthermore, when the pH value of the inkjet ink according to this embodiment is set to "9.5", it is preferable that the pH value at the printing location of the tablet to be printed is "within the range of 7.5 to 11.5".

[0058] By adding binder resin to the ink, the ink adheres to the tablets, increasing its strength after printing and providing moisture resistance to the printed tablets. Using alkali-treated binder resin also makes the inkjet ink itself more alkaline, so even when printing on alkaline tablets, the ink's performance does not change due to pH differences, resulting in improved moisture resistance. The pH value of the inkjet ink according to this embodiment may be a value obtained by measuring it with, for example, a pH meter using the glass electrode method according to known technology. Furthermore, the pH value at the printing area of ​​the tablet to be printed according to this embodiment may be a value obtained by simply measuring it by dropping a pH indicator such as phenolphthalein solution, bromophenol blue solution, or methyl orange solution onto the printing area of ​​the tablet.

[0059] (Internal resin additive) The inkjet ink according to this embodiment may contain an internal resin in addition to the dyes and solvents described above. The internal resin that can be added to the inkjet ink according to this embodiment is an edible, water-soluble powder, paste, or flake-like resin-like substance that can form a film on the tablet surface upon drying after printing. Examples of the internal resin include polyvinyl alcohol (PVA), hydroxypropyl cellulose (HPC), hydroxypropyl methylcellulose (HPMC), polyvinylpyrrolidone (PVP), high molecular weight polyethylene glycol (PEG) such as polyethylene glycol 4000 / polyethylene glycol 1540, methacrylic acid copolymer (product name: Eudragit S100), maltodextrin, and erythritol.

[0060] (Leveling agent) The inkjet ink according to this embodiment may contain a leveling agent in addition to the dyes, solvents, or internal resins described above. The leveling agent that can be added to the inkjet ink according to this embodiment may be any edible and water-soluble surfactant. Examples of the leveling agent include polyglycerin fatty acid esters (e.g., decaglycerin distearate Q-182S and decaglycerin monolaurate Q-12S from Taiyo Kagaku Co., Ltd.), sorbitan fatty acid esters (e.g., NIKKOL S-10 from Nikko Chemicals Co., Ltd.), sucrose fatty acid esters (e.g., DK ester F-110 from Daiichi Kogyo Seiyaku Co., Ltd.), and polysorbate (Emazole S-120 series from Kao Corporation).

[0061] [Printing method] The inkjet ink according to this embodiment is not particularly limited by the printing method and can be printed using commercially available inkjet devices such as inkjet printers. For this reason, the inkjet ink according to this embodiment has a wide range of applications and is very useful. For example, the inkjet ink according to this embodiment can be printed using a so-called drop-on-demand inkjet device that uses a piezoelectric element (piezoelectric ceramic) as an actuator, or it can be printed using other types of inkjet devices. Examples of drop-on-demand inkjet devices include those employing a thermal inkjet method that ejects inkjet ink using water vapor pressure generated by instantaneously heating a minute heating element to a high temperature (200-300°C), electrostatic type devices that eject inkjet ink by electrostatically vibrating an actuator, and ultrasonic devices that utilize the cavitation phenomenon of ultrasound. Furthermore, if the inkjet ink according to this embodiment has charged properties, it is also possible to use a device employing a continuous ejection method.

[0062] 〔tablet〕 In this embodiment, the inkjet ink according to this embodiment may be printed on the surface of any type of tablet, such as a neutral tablet, an acidic tablet, or an alkaline tablet, using the printing method described above. In other words, the tablet according to this embodiment only needs to have a printed area, i.e., a printed image, printed using the inkjet ink according to this embodiment. The inkjet ink according to this embodiment can, for example, improve the lightfastness of a printed image applied to the surface of a medical tablet using the inkjet printing method. The configuration of a tablet having a printed image printed with the inkjet ink according to this embodiment will be described below. The tablets according to this embodiment are, for example, medical tablets. Here, "medical tablets" include, for example, uncoated tablets, sugar-coated tablets, enteric-coated tablets, orally disintegrating tablets, as well as film-coated tablets in which a water-soluble surface layer is formed on the outermost surface of the tablet.

[0063] Furthermore, the tablets according to this embodiment are preferably alkaline tablets, at least on the surface being alkaline, and even more preferably magnesium oxide tablets, at least on the surface containing magnesium oxide. In other words, the inkjet ink according to this embodiment can be used not only for printing on neutral tablets and acidic tablets, but also for printing on alkaline tablets, at least on the surface being alkaline. Furthermore, the tablets according to this embodiment may contain magnesium oxide as a main component, and it is preferable that the tablets contain magnesium oxide in an amount of 0.2 g to 0.5 g per tablet. In other words, the inkjet ink according to this embodiment can be used not only for printing on neutral tablets and acidic tablets, but also for printing on tablets containing magnesium oxide in an amount of 0.2 g to 0.5 g per tablet.

[0064] Figure 2 is a schematic cross-sectional view showing an example of a printed (printed, imaged) medical tablet (plain tablet). In Figure 2, a printed tablet 5 is shown in cross-sectional view, with printed images 3 such as characters printed on the upper surface of the tablet base material 1. Figure 3 is a schematic cross-sectional view showing an example of a medical tablet (film-coated tablet) with printing (printing, image printing) applied. In Figure 3, a film-coated tablet printed material 9 is shown in cross-sectional view, with a printed image 3 such as characters printed on the upper surface of a tablet substrate 1 on which a film coating layer 7 has been formed on the surface. In this embodiment, as shown in Figure 4, a solid image may be printed as the plain tablet print image 11, and as shown in Figure 5, a two-dimensional barcode may be printed as the film-coated tablet print image 13.

[0065] The active ingredients contained in medical tablets are not particularly limited. For example, they include, but are not limited to, substances effective in preventing and treating various diseases (e.g., substances with sleep-inducing effects, tranquilizer activity, antibacterial activity, antihypertensive effect, anti-angina activity, analgesic effect, anti-inflammatory activity, tranquilizer effect, diabetes treatment activity, diuretic effect, anticholinergic activity, antihyperacid effect, antiepileptic effect, ACE inhibitory activity, β-receptor antagonist or agonist activity, anesthetic effect, appetite suppressant effect, antiarrhythmic effect, antidepressant effect, anticoagulant activity, antidiarrheal effect, antihistamine activity, antimalarial effect, antitumor activity, immunosuppressive activity, antiparkinson's disease effect, antipsychotic effect, antiplatelet activity, antihyperlipidemia effect, etc.), substances with cleansing effect, fragrances, substances with deodorizing effect, etc.

[0066] The tablets according to this embodiment may, if necessary, be formulated with a carrier that is permissible for their intended use, along with the active ingredient. For example, if it is a medical tablet, a pharmaceutically acceptable carrier may be formulated. As a pharmaceutically acceptable carrier, various organic or inorganic carrier substances commonly used as pharmaceutical materials may be used, and appropriate amounts of excipients, lubricants, binders, disintegrants, thickeners, etc., may be added as appropriate. In addition, additives such as preservatives, antioxidants, colorants, and sweeteners may be used as necessary. In this embodiment, medical tablets were used as an example of tablets, but the present disclosure is not limited thereto. The printing surface of the inkjet ink according to this embodiment is not particularly limited, and it may be printed on the surface of various tablets, such as tablets administered to animals other than humans (pets, livestock, poultry, etc.), feed, fertilizers, cleaning agents, candies such asラムネ (ramune) candy, and supplements. Furthermore, the size of the printing surface of the inkjet ink according to this embodiment is not particularly limited and can be applied to tablets of various sizes.

[0067] (Effects of this embodiment) (1) The inkjet ink according to this embodiment comprises an edible dye, a fade inhibitor, a binder resin, and water and ethanol as solvents, wherein the binder resin is shellac. With this configuration, compared to conventional technology, the print quality (especially intermittent restart), lightfastness, and moisture resistance are superior not only when used in neutral or acidic tablets, but also when used in alkaline tablets.

[0068] (2) The inkjet ink according to this embodiment may contain reduced isomaltulose as a fade inhibitor. With this configuration, the light resistance is superior compared to conventional technology.

[0069] (3) Furthermore, the inkjet ink according to this embodiment may contain an amount of ethanol added in the range of 1.0% by mass or more and 10.0% by mass or less. With this configuration, print quality (especially intermittent restart performance) is superior to that of conventional technologies.

[0070] (4) The inkjet ink according to this embodiment may further contain sodium carbonate as a pH adjuster. With this configuration, compared to conventional technology, the print quality (especially intermittent restart), lightfastness, and moisture resistance are superior not only when used in neutral or acidic tablets, but also when used in alkaline tablets.

[0071] (5) The inkjet ink according to this embodiment may also be an inkjet ink for use in printing on alkaline tablets whose surface is at least alkaline. This configuration offers superior moisture resistance compared to conventional technologies.

[0072] (6) The inkjet ink according to this embodiment may also be an inkjet ink for use in printing on magnesium oxide tablets, which contain magnesium oxide on at least one surface. This configuration offers superior moisture resistance compared to conventional technologies.

[0073] (7) The inkjet ink according to this embodiment may also contain a dye in an amount of 0.5% by mass or more and 5.0% by mass or less, a binder resin in an amount of 1.0% by mass or more and 5.0% by mass or less, and a fade inhibitor in an amount of 1.0% by mass or more and 10.0% by mass or less. With this configuration, compared to conventional technology, the print quality (especially intermittent restart), lightfastness, and moisture resistance are superior not only when used in neutral or acidic tablets, but also when used in alkaline tablets.

[0074] (8) In addition, the inkjet ink according to this embodiment may contain at least one dye selected from azo dyes, triphenylmethane dyes, and xanthene dyes. With this configuration, light resistance and visibility are superior compared to conventional technologies.

[0075] (9) In addition, the inkjet ink according to this embodiment may have an azo dye that is at least one of Red No. 102 and Yellow No. 4, a triphenylmethane dye that is Blue No. 1, and a xanthene dye that is Red No. 106. With this configuration, light resistance and visibility are superior compared to conventional technologies.

[0076] (10) The inkjet ink according to this embodiment also comprises an edible dye, reduced isomaltulose as a fade inhibitor, shellac as a binder resin, and water and ethanol as solvents, wherein the amount of ethanol added to the total inkjet ink is in the range of 1.0% by mass or more and 10.0% by mass or less, and further contains sodium carbonate as a pH adjuster, and the inkjet ink as a whole may be alkaline. With this configuration, compared to conventional technology, the print quality (especially intermittent restart), lightfastness, and moisture resistance are superior not only when used in neutral or acidic tablets, but also when used in alkaline tablets.

[0077] (11) Furthermore, the inkjet ink according to this embodiment is an inkjet ink for printing on magnesium oxide tablets containing magnesium oxide in a range of 0.2 g to 0.5 g per tablet, and comprises an edible dye, reduced isomaltulose as a fade inhibitor, shellac as a binder resin, and water and ethanol as solvents, and the dye comprises only Blue No. 1, or only Yellow No. 4 and Red No. 106, and the amount of Blue No. 1 added to the entire inkjet ink is in the range of 0.5% by mass to 5.0% by mass, and Yellow No. 4 in the entire inkjet ink The amount of added is within the range of 0.25% by mass to 2.0% by mass, and the amount of Red No. 106 added to the entire inkjet ink is within the range of 0.25% by mass to 3.0% by mass, the amount of reduced isomaltulose added to the entire inkjet ink is within the range of 1.0% by mass to 10.0% by mass, the amount of shellac added to the entire inkjet ink is within the range of 1.0% by mass to 5.0% by mass, and the amount of ethanol added to the entire inkjet ink is within the range of 1.0% by mass to 10.0% by mass, and the inkjet ink as a whole may be alkaline. With this configuration, compared to conventional technology, the print quality (especially intermittent restart), lightfastness, and moisture resistance are superior not only when used in neutral or acidic tablets, but also when used in alkaline tablets.

[0078] (12) The inkjet ink according to this embodiment may further contain sodium carbonate as a pH adjuster, and the amount of sodium carbonate added to the total inkjet ink may be in the range of 0.1% by mass or more and 0.6% by mass or less. With this configuration, compared to conventional technology, the print quality (especially intermittent restart), lightfastness, and moisture resistance are superior not only when used in neutral or acidic tablets, but also when used in alkaline tablets.

[0079] (13) In addition, the inkjet ink according to this embodiment may have an absolute difference of 2 or less between the pH of the inkjet ink and the pH of the printed area on the tablet to be printed. With this configuration, compared to conventional technology, the print quality (especially intermittent restart), lightfastness, and moisture resistance are superior not only when used in neutral or acidic tablets, but also when used in alkaline tablets.

[0080] (14) The tablet (tablet printout) according to this embodiment includes a printed image (an example of a printed area) 3 printed with the inkjet ink described above. With this configuration, when used with neutral or acidic tablets, and especially when used with alkaline tablets, it is possible to sufficiently suppress light-induced discoloration of printed images 3 directly printed on the surface of tablets, etc., compared to conventional technologies, and to significantly improve the light resistance of the printed images 3. Furthermore, it is possible to impart edibility to the printed image portion printed on the surface of the tablets.

[0081] (15) The tablets (printed tablets) according to this embodiment may have a printed area and may contain magnesium oxide in an amount of 0.2 g to 0.5 g per tablet. With this configuration, when used with neutral or acidic tablets, and especially when used with alkaline tablets, it is possible to sufficiently suppress light-induced discoloration of printed images 3 directly printed on the surface of tablets, etc., compared to conventional technologies, and to significantly improve the light resistance of the printed images 3. Furthermore, it is possible to impart edibility to the printed image portion printed on the surface of the tablets.

[0082] [Examples] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way by these examples. <Examples 1-29 and Comparative Examples 1-16, and Reference Examples 1-3> The following describes the preparation procedures for inkjet inks in Examples 1-29, Comparative Examples 1-16, and Reference Examples 1-3. (Manufacturing of inkjet inks) First, the printing ink was prepared. The inkjet ink contains a dye (food dye), a solvent, a fade inhibitor, a binder resin, and a pH adjuster in the amounts described below. The preparation procedure was as follows: First, the binder resin and pH adjuster were added to the solvent, and then the mixture was stirred for about 2 hours while being heated to about 60°C to obtain a mixed solvent. A fade inhibitor was then added to this mixed solvent to obtain a transparent base liquid. Next, the dye was added to this transparent base liquid. In this way, the ink according to this embodiment was prepared. The various components will be described in detail below.

[0083] In this example, purified water (ion-exchanged water), propylene glycol (PG), and ethanol were used as solvents as needed. Specifically, a solvent (mixed solvent) was obtained by adding propylene glycol (PG) and ethanol to purified water, to which a binder resin and a pH adjuster were added, and the mixture was stirred well for about 2 hours while being heated to about 60°C. A fade inhibitor was also added to the aforementioned solvent as needed, and the mixture was stirred for about 1 hour to obtain a transparent base liquid. To the aforementioned transparent base liquid, food dyes Blue No. 1, Red No. 102, Red No. 106, and Yellow No. 4 were added as dyes as needed to obtain the inkjet inks of Examples 1 to 29, Comparative Examples 1 to 16, and Reference Examples 1 to 3.

[0084] <Sample #1 (Comparative Example 1)> For Sample #1 (Comparative Example 1), the total inkjet ink content was set to 1.5% by mass of the dye Blue No. 1, the solvent content was set to 64.0% by mass of purified water, 6.5% by mass of ethanol, and 28.0% by mass of propylene glycol (PG). Note that the inkjet ink in Sample #1 (Comparative Example 1) does not contain any binder resin, pH adjuster, or fade inhibitor. In this way, we obtained the inkjet ink for Sample #1 (Comparative Example 1). Furthermore, the inkjet ink of Sample #1 (Comparative Example 1) was printed onto the surface of a tablet that exhibited acidity to obtain the tablet of Sample #1 (Comparative Example 1).

[0085] <Sample #2 (Comparative Example 2)> The inkjet ink of Sample #1 (Comparative Example 1) was printed onto the surface of a neutral tablet to obtain the tablet of Sample #2 (Comparative Example 2).

[0086] <Sample #3 (Comparative Example 3)> The inkjet ink of Sample #1 (Comparative Example 1) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of Sample #2 (Comparative Example 2).

[0087] <Sample #4 (Reference Example 1)> For Sample #4 (Reference Example 1), the total inkjet ink content was set to 1.5% by mass of the dye Blue No. 1, 54.0% by mass of the solvent (purified water), 6.5% by mass of ethanol, 28.0% by mass of propylene glycol (PG), and 10.0% by mass of reduced isomaltulose, a fade inhibitor. Note that the inkjet ink in Sample #4 (Reference Example 1) does not contain either binder resin or pH adjuster. In this way, we obtained the inkjet ink for sample #4 (reference example 1). Furthermore, the inkjet ink of Sample #4 (Reference Example 1) was printed onto the surface of a tablet that exhibited acidity to obtain the tablet of Sample #4 (Reference Example 1).

[0088] <Sample #5 (Reference Example 2)> The inkjet ink of Sample #4 (Reference Example 1) was printed onto the surface of a neutral tablet to obtain the tablet of Sample #5 (Reference Example 2).

[0089] <Sample #6 (Comparative Example 4)> The inkjet ink of Sample #4 (Reference Example 1) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of Sample #6 (Comparative Example 4).

[0090] <Sample #7 (Example 1)> For Sample #7 (Example 1), the total inkjet ink content was 1.5% by mass of the dye Blue No. 1, 50.8% by mass of the solvent purified water, 6.5% by mass of ethanol, 28.0% by mass of propylene glycol (PG), 3.0% by mass of the binder resin shellac, 0.2% by mass of the pH adjuster sodium carbonate, and 10.0% by mass of the fade inhibitor reduced isomaltulose. In this way, we obtained the inkjet ink for sample #7 (Example 1). Furthermore, the inkjet ink of Sample #7 (Example 1) was printed onto the surface of a tablet that exhibited acidity to obtain the tablet of Sample #7 (Example 1).

[0091] <Sample #8 (Example 2)> The inkjet ink of Sample #7 (Example 1) was printed onto the surface of a neutral tablet to obtain the tablet of Sample #8 (Example 2).

[0092] <Sample #9 (Example 3)> The inkjet ink of Sample #7 (Example 1) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of Sample #9 (Example 3).

[0093] <Sample #10 (Comparative Example 5)> For Sample #10 (Comparative Example 5), the total inkjet ink content was set to 1.5% by mass of the dye Blue No. 1, 54.0% by mass of the solvent (purified water), 6.5% by mass of ethanol, 28.0% by mass of propylene glycol (PG), and 10.0% by mass of reduced isomaltulose, a colorfastness inhibitor. Note that the inkjet ink in Sample #10 (Comparative Example 5) does not contain either binder resin or pH adjuster. In this way, we obtained the inkjet ink for sample #10 (comparative example 5). Furthermore, the inkjet ink of Sample #10 (Comparative Example 5) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of Sample #10 (Comparative Example 5).

[0094] <Sample #11 (Comparative Example 6)> For Sample #11 (Comparative Example 6), the total inkjet ink content was set to 1.5% by mass of the dye Blue No. 1, 51.0% by mass of the solvent purified water, 6.5% by mass of ethanol, 28.0% by mass of propylene glycol (PG), 3.0% by mass of polyethylene glycol 300 (polyethylene glycol with a mass-average molecular weight (Mw) of 300) as a binder resin, and 10.0% by mass of reduced isomaltulose as a fade inhibitor. Note that the inkjet ink in Sample #11 (Comparative Example 6) does not contain a pH adjuster. In this way, we obtained the inkjet ink for sample #11 (comparative example 6). Furthermore, the inkjet ink of Sample #11 (Comparative Example 6) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of Sample #11 (Comparative Example 6).

[0095] <Sample #12 (Comparative Example 7)> For Sample #12 (Comparative Example 7), the total inkjet ink content was set to 1.5% by mass of the dye Blue No. 1, 61.0% by mass of the solvent (purified water), 6.5% by mass of ethanol, 28.0% by mass of propylene glycol (PG), and 3.0% by mass of the binder resin polyethylene glycol 400 (polyethylene glycol with a mass-average molecular weight (Mw) of 400). Note that the inkjet ink in Sample #12 (Comparative Example 7) does not contain either a pH adjuster or a fade inhibitor. In this way, we obtained the inkjet ink for sample #12 (comparative example 7). Furthermore, the inkjet ink of Sample #12 (Comparative Example 7) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of Sample #12 (Comparative Example 7).

[0096] <Sample #13 (Comparative Example 8)> For Sample #13 (Comparative Example 8), the total inkjet ink content was set to 1.5% by mass of the dye Blue No. 1, 51.0% by mass of the solvent purified water, 6.5% by mass of ethanol, 28.0% by mass of propylene glycol (PG), 3.0% by mass of polyethylene glycol 400 (polyethylene glycol with a mass-average molecular weight (Mw) of 400) as a binder resin, and 10.0% by mass of reduced isomaltulose as a colorfastness inhibitor. Note that the inkjet ink in Sample #13 (Comparative Example 8) does not contain a pH adjuster. In this way, we obtained the inkjet ink for sample #13 (comparative example 8). Furthermore, the inkjet ink of Sample #13 (Comparative Example 8) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of Sample #13 (Comparative Example 8).

[0097] <Sample #14 (Comparative Example 9)> For Sample #14 (Comparative Example 9), the total inkjet ink content was set to 1.5% by mass of the dye Blue No. 1, 48.4% by mass of the solvent purified water, 6.5% by mass of ethanol, 28.0% by mass of propylene glycol (PG), 5.6% by mass of polyethylene glycol 400 (polyethylene glycol with a mass-average molecular weight (Mw) of 400) as a binder resin, and 10.0% by mass of reduced isomaltulose as a fade inhibitor. Note that the inkjet ink in Sample #14 (Comparative Example 9) does not contain a pH adjuster. In this way, we obtained the inkjet ink for sample #14 (comparative example 9). Furthermore, the inkjet ink of Sample #14 (Comparative Example 9) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of Sample #14 (Comparative Example 9).

[0098] <Sample #15 (Comparative Example 10)> For Sample #15 (Comparative Example 10), the total inkjet ink content was set to 1.5% by mass of the dye Blue No. 1, 51.0% by mass of the solvent purified water, 6.5% by mass of ethanol, 28.0% by mass of propylene glycol (PG), 3.0% by mass of polyethylene glycol 1540 (polyethylene glycol with a mass-average molecular weight (Mw) of 1540) as a binder resin, and 10.0% by mass of reduced isomaltulose as a fade inhibitor. Note that the inkjet ink in Sample #15 (Comparative Example 10) does not contain a pH adjuster. In this way, we obtained the inkjet ink for sample #15 (comparative example 10). Furthermore, the inkjet ink of Sample #15 (Comparative Example 10) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of Sample #15 (Comparative Example 10).

[0099] <Sample #16 (Example 4)> For Sample #16 (Example 4), the total inkjet ink content was 1.5% by mass of the dye Blue No. 1, 50.8% by mass of the solvent purified water, 6.5% by mass of ethanol, 28.0% by mass of propylene glycol (PG), 3.0% by mass of the binder resin shellac, 0.2% by mass of the pH adjuster, and 10.0% by mass of the fade inhibitor reduced isomaltulose. In this way, we obtained the inkjet ink for sample #16 (Example 4). Furthermore, the inkjet ink of Sample #16 (Example 4) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of Sample #16 (Example 4).

[0100] <Sample #17 (Comparative Example 11)> For Sample #17 (Comparative Example 11), the total inkjet ink content was set to 1.5% by mass of the dye Blue No. 1, 60.8% by mass of the solvent (purified water), 6.5% by mass of ethanol, 28.0% by mass of propylene glycol (PG), 3.0% by mass of the binder resin (shellac), and 0.2% by mass of the pH adjuster (sodium carbonate). Note that the inkjet ink in Sample #17 (Comparative Example 11) does not contain a fade inhibitor. In this way, we obtained the inkjet ink for sample #17 (comparative example 11). Furthermore, the inkjet ink of Sample #17 (Comparative Example 11) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of Sample #17 (Comparative Example 11).

[0101] <Sample #18 (Example 5)> For Sample #18 (Example 5), the total inkjet ink content was 1.5% by mass of the dye Blue No. 1, 55.8% by mass of the solvent purified water, 6.5% by mass of ethanol, 28.0% by mass of propylene glycol (PG), 3.0% by mass of the binder resin shellac, 0.2% by mass of the pH adjuster sodium carbonate, and 5.0% by mass of the fade inhibitor reduced isomaltulose. In this way, we obtained the inkjet ink for sample #18 (Example 5). Furthermore, the inkjet ink of Sample #18 (Example 5) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of Sample #18 (Example 5).

[0102] <Sample #19 (Example 6)> For Sample #19 (Example 6), the total inkjet ink content was 1.5% by mass of the pigment Red No. 102, 57.3% by mass of purified water as the solvent, 6.5% by mass of ethanol, 28.0% by mass of propylene glycol (PG), 3.0% by mass of shellac as the binder resin, 0.2% by mass of sodium carbonate as the pH adjuster, and 5.0% by mass of reduced isomaltulose as the fade inhibitor. In this way, we obtained the inkjet ink for sample #19 (Example 6). Furthermore, the inkjet ink of Sample #19 (Example 6) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of Sample #19 (Example 6).

[0103] <Sample #20 (Example 7)> For Sample #20 (Example 7), the total inkjet ink content was 1.5% by mass of the pigment Red No. 102, 57.3% by mass of purified water as the solvent, 6.5% by mass of ethanol, 28.0% by mass of propylene glycol (PG), 3.0% by mass of shellac as the binder resin, 0.2% by mass of sodium carbonate as the pH adjuster, and 5.0% by mass of lactose as the fade inhibitor. In this way, we obtained the inkjet ink for sample #20 (Example 7). Furthermore, the inkjet ink of Sample #20 (Example 7) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of Sample #20 (Example 7).

[0104] <Sample #21 (Reference Example 3)> For the inkjet ink of Sample #21 (Reference Example 3), the proportion of the pigment Red No. 102 was set to 1.5% by mass, the proportion of purified water among the solvents was set to 62.3% by mass, the proportion of ethanol was set to 6.5% by mass, the proportion of propylene glycol (PG) was set to 28.0% by mass, the proportion of shellac, a binder resin, was set to 3.0% by mass, and the proportion of sodium carbonate, a pH adjuster, was set to 0.2% by mass. Note that the inkjet ink in Sample #21 (Reference Example 3) does not contain a fade inhibitor. In this way, we obtained the inkjet ink for sample #21 (reference example 3). Furthermore, the inkjet ink of Sample #21 (Reference Example 3) was printed onto the surface of a tablet that exhibited alkaline properties to obtain the tablet of Sample #21 (Reference Example 3).

[0105] <Sample #22 (Comparative Example 12)> For Sample #22 (Comparative Example 12), the total inkjet ink content was set to 1.0% by mass of the dye Blue No. 1, 63.4% by mass of the solvent purified water, 6.5% by mass of ethanol, 28.0% by mass of propylene glycol (PG), 1.0% by mass of the binder resin shellac, and 0.1% by mass of the pH adjuster sodium carbonate. Note that the inkjet ink in Sample #22 (Comparative Example 12) does not contain a fade inhibitor. In this way, we obtained the inkjet ink for sample #22 (comparative example 12). Furthermore, the inkjet ink of Sample #22 (Comparative Example 12) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of Sample #22 (Comparative Example 12).

[0106] <Sample #23 (Example 8)> For Sample #23 (Example 8), the total inkjet ink content was 1.0% by mass of the dye Blue No. 1, 58.4% by mass of the solvent purified water, 6.5% by mass of ethanol, 28.0% by mass of propylene glycol (PG), 1.0% by mass of the binder resin shellac, 0.1% by mass of the pH adjuster sodium carbonate, and 5.0% by mass of the fade inhibitor reduced isomaltulose. In this way, we obtained the inkjet ink for sample #23 (Example 8). Furthermore, the inkjet ink of Sample #23 (Example 8) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of Sample #23 (Example 8).

[0107] <Sample #24 (Example 9)> For Sample #24 (Example 9), the total inkjet ink content was 1.0% by mass of the dye Blue No. 1, 53.4% ​​by mass of the solvent purified water, 6.5% by mass of ethanol, 28.0% by mass of propylene glycol (PG), 1.0% by mass of the binder resin shellac, 0.1% by mass of the pH adjuster sodium carbonate, and 10.0% by mass of the fade inhibitor reduced isomaltulose. In this way, we obtained the inkjet ink for sample #24 (Example 9). Furthermore, the inkjet ink of Sample #24 (Example 9) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of Sample #24 (Example 9).

[0108] <Sample #25 (Comparative Example 13)> For Sample #25 (Comparative Example 13), the total inkjet ink content was set to 1.0% by mass of the dye Blue No. 1, 62.3% by mass of the purified water solvent, 6.5% by mass of ethanol, 28.0% by mass of propylene glycol (PG), 2.0% by mass of the shellac binder resin, and 0.2% by mass of sodium carbonate pH adjuster. Note that the inkjet ink in Sample #25 (Comparative Example 13) does not contain a fade inhibitor. In this way, we obtained the inkjet ink for sample #25 (comparative example 13). Furthermore, the inkjet ink of sample #25 (comparative example 13) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of sample #25 (comparative example 13).

[0109] <Sample #26 (Example 10)> For Sample #26 (Example 10), the total inkjet ink content was 1.0% by mass of the dye Blue No. 1, 57.3% by mass of the solvent purified water, 6.5% by mass of ethanol, 28.0% by mass of propylene glycol (PG), 2.0% by mass of the binder resin shellac, 0.2% by mass of the pH adjuster sodium carbonate, and 5.0% by mass of the fade inhibitor reduced isomaltulose. In this way, we obtained the inkjet ink for sample #26 (Example 10). Furthermore, the inkjet ink of sample #26 (Example 10) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of sample #26 (Example 10).

[0110] <Sample #27 (Example 11)> For Sample #27 (Example 11), the total inkjet ink content was 1.0% by mass of the dye Blue No. 1, 47.3% by mass of the solvent purified water, 11.5% by mass of ethanol, 28.0% by mass of propylene glycol (PG), 2.0% by mass of the binder resin shellac, 0.2% by mass of the pH adjuster sodium carbonate, and 10.0% by mass of the fade inhibitor reduced isomaltulose. In this way, we obtained the inkjet ink for sample #27 (Example 11). Furthermore, the inkjet ink of sample #27 (Example 11) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of sample #27 (Example 11).

[0111] <Sample #28 (Comparative Example 14)> For Sample #28 (Comparative Example 14), the total inkjet ink content was set to 1.0% by mass of the dye Blue No. 1, 61.1% by mass of the solvent purified water, 6.5% by mass of ethanol, 28.0% by mass of propylene glycol (PG), 3.0% by mass of the binder resin shellac, and 0.4% by mass of the pH adjuster sodium carbonate. Note that the inkjet ink in Sample #28 (Comparative Example 14) does not contain a fade inhibitor. In this way, we obtained the inkjet ink for sample #28 (comparative example 14). Furthermore, the inkjet ink of Sample #28 (Comparative Example 14) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of Sample #28 (Comparative Example 14).

[0112] <Sample #29 (Example 12)> For Sample #29 (Example 12), the total inkjet ink content was 1.0% by mass of the dye Blue No. 1, 56.1% by mass of the solvent purified water, 6.5% by mass of ethanol, 28.0% by mass of propylene glycol (PG), 3.0% by mass of the binder resin shellac, 0.4% by mass of the pH adjuster sodium carbonate, and 5.0% by mass of the fade inhibitor reduced isomaltulose. In this way, we obtained the inkjet ink for sample #29 (Example 12). Furthermore, the inkjet ink of sample #29 (Example 12) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of sample #29 (Example 12).

[0113] <Sample #30 (Example 13)> For Sample #30 (Example 13), the total inkjet ink content was 1.0% by mass of the dye Blue No. 1, 46.1% by mass of the solvent purified water, 11.5% by mass of ethanol, 28.0% by mass of propylene glycol (PG), 3.0% by mass of the binder resin shellac, 0.4% by mass of the pH adjuster sodium carbonate, and 10.0% by mass of the fade inhibitor reduced isomaltulose. In this way, we obtained the inkjet ink for sample #30 (Example 13). Furthermore, the inkjet ink of sample #30 (Example 13) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of sample #30 (Example 13).

[0114] <Sample #31 (Comparative Example 15)> For Sample #31 (Comparative Example 15), the total inkjet ink content was set to 1.0% by mass of the dye Blue No. 1, 60.0% by mass of the solvent purified water, 6.5% by mass of ethanol, 28.0% by mass of propylene glycol (PG), 4.0% by mass of the binder resin shellac, and 0.5% by mass of the pH adjuster sodium carbonate. Note that the inkjet ink in Sample #31 (Comparative Example 15) does not contain a fade inhibitor. In this way, we obtained the inkjet ink for sample #31 (comparative example 15). Furthermore, the inkjet ink of Sample #31 (Comparative Example 15) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of Sample #31 (Comparative Example 15).

[0115] <Sample #32 (Example 14)> For Sample #32 (Example 14), the total inkjet ink content was 1.0% by mass of the dye Blue No. 1, 55.0% by mass of the solvent purified water, 6.5% by mass of ethanol, 28.0% by mass of propylene glycol (PG), 4.0% by mass of the binder resin shellac, 0.5% by mass of the pH adjuster sodium carbonate, and 5.0% by mass of the fade inhibitor reduced isomaltulose. In this way, we obtained the inkjet ink for sample #32 (Example 14). Furthermore, the inkjet ink of sample #32 (Example 14) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of sample #32 (Example 14).

[0116] <Sample #33 (Example 15)> For Sample #33 (Example 15), the total inkjet ink content was 1.0% by mass of the dye Blue No. 1, 50.0% by mass of the solvent purified water, 6.5% by mass of ethanol, 28.0% by mass of propylene glycol (PG), 4.0% by mass of the binder resin shellac, 0.5% by mass of the pH adjuster sodium carbonate, and 10.0% by mass of the fade inhibitor reduced isomaltulose. In this way, we obtained the inkjet ink for sample #33 (Example 15). Furthermore, the inkjet ink of sample #33 (Example 15) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of sample #33 (Example 15).

[0117] <Sample #34 (Comparative Example 16)> For Sample #34 (Comparative Example 16), the total inkjet ink content was set to 1.0% by mass of the dye Blue No. 1, 53.9% by mass of the solvent (purified water), 11.5% by mass of ethanol, 28.0% by mass of propylene glycol (PG), 5.0% by mass of the binder resin (shellac), and 0.6% by mass of the pH adjuster (sodium carbonate). Note that the inkjet ink in sample #34 (comparative example 16) does not contain a fade inhibitor. In this way, we obtained the inkjet ink for sample #34 (comparative example 16). Furthermore, the inkjet ink of sample #34 (comparative example 16) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of sample #34 (comparative example 16).

[0118] <Sample #35 (Example 16)> For Sample #35 (Example 16), the total inkjet ink content was 1.0% by mass of the dye Blue No. 1, 48.9% by mass of the solvent purified water, 11.5% by mass of ethanol, 28.0% by mass of propylene glycol (PG), 5.0% by mass of the binder resin shellac, 0.6% by mass of the pH adjuster sodium carbonate, and 5.0% by mass of the fade inhibitor reduced isomaltulose. In this way, we obtained the inkjet ink for sample #35 (Example 16). Furthermore, the inkjet ink of sample #35 (Example 16) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of sample #35 (Example 16).

[0119] <Sample #36 (Example 17)> For Sample #36 (Example 17), the total inkjet ink content was 1.0% by mass of the dye Blue No. 1, 43.9% by mass of the solvent purified water, 11.5% by mass of ethanol, 28.0% by mass of propylene glycol (PG), 5.0% by mass of the binder resin shellac, 0.6% by mass of the pH adjuster sodium carbonate, and 10.0% by mass of the fade inhibitor reduced isomaltulose. In this way, we obtained the inkjet ink for sample #36 (Example 17). Furthermore, the inkjet ink of sample #36 (Example 17) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of sample #36 (Example 17).

[0120] <Sample #37 (Example 18)> For Sample #37 (Example 18), the total inkjet ink content was 0.5% by mass of the dye Blue No. 1, 56.6% by mass of the solvent (purified water), 6.5% by mass of ethanol, 28.0% by mass of propylene glycol (PG), 3.0% by mass of the binder resin shellac, 0.4% by mass of the pH adjuster sodium carbonate, and 5.0% by mass of the fade inhibitor reduced isomaltulose. In this way, we obtained the inkjet ink for sample #37 (Example 18). Furthermore, the inkjet ink of sample #37 (Example 18) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of sample #37 (Example 18).

[0121] <Sample #38 (Example 19)> For Sample #38 (Example 19), the total inkjet ink content was 1.0% by mass of the dye Blue No. 1, 56.1% by mass of the solvent purified water, 6.5% by mass of ethanol, 28.0% by mass of propylene glycol (PG), 3.0% by mass of the binder resin shellac, 0.4% by mass of the pH adjuster sodium carbonate, and 5.0% by mass of the fade inhibitor reduced isomaltulose. In this way, we obtained the inkjet ink for sample #38 (Example 19). Furthermore, the inkjet ink of sample #38 (Example 19) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of sample #38 (Example 19).

[0122] <Sample #39 (Example 20)> For Sample #39 (Example 20), the total inkjet ink content was 3.0% by mass of the dye Blue No. 1, 54.1% by mass of the solvent purified water, 6.5% by mass of ethanol, 28.0% by mass of propylene glycol (PG), 3.0% by mass of the binder resin shellac, 0.4% by mass of the pH adjuster sodium carbonate, and 5.0% by mass of the fade inhibitor reduced isomaltulose. In this way, we obtained the inkjet ink for sample #39 (Example 20). Furthermore, the inkjet ink of sample #39 (Example 20) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of sample #39 (Example 20).

[0123] <Sample #40 (Example 21)> For Sample #40 (Example 21), the total inkjet ink content was 5.0% by mass of the dye Blue No. 1, 52.1% by mass of the solvent purified water, 6.5% by mass of ethanol, 28.0% by mass of propylene glycol (PG), 3.0% by mass of the binder resin shellac, 0.4% by mass of the pH adjuster sodium carbonate, and 5.0% by mass of the fade inhibitor reduced isomaltulose. In this way, we obtained the inkjet ink for sample #40 (Example 21). Furthermore, the inkjet ink of sample #40 (Example 21) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of sample #40 (Example 21).

[0124] <Sample #41 (Example 22)> For Sample #41 (Example 22), the total inkjet ink content was 0.5% by mass of the pigment Red No. 102, 56.6% by mass of the purified water solvent, 6.5% by mass of ethanol, 28.0% by mass of propylene glycol (PG), 3.0% by mass of the binder resin shellac, 0.4% by mass of the pH adjuster sodium carbonate, and 5.0% by mass of the fade inhibitor reduced isomaltulose. In this way, we obtained the inkjet ink for sample #41 (Example 22). Furthermore, the inkjet ink of sample #41 (Example 22) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of sample #41 (Example 22).

[0125] <Sample #42 (Example 23)> For Sample #42 (Example 23), the total inkjet ink content was 1.0% by mass of the pigment Red No. 102, 56.1% by mass of the solvent (purified water), 6.5% by mass of ethanol, 28.0% by mass of propylene glycol (PG), 3.0% by mass of the binder resin (shellac), 0.4% by mass of the pH adjuster (sodium carbonate), and 5.0% by mass of the fade inhibitor (reduced isomaltulose). In this way, we obtained the inkjet ink for sample #42 (Example 23). Furthermore, the inkjet ink of sample #42 (Example 23) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of sample #42 (Example 23).

[0126] <Sample #43 (Example 24)> For Sample #43 (Example 24), the total inkjet ink content was 3.0% by mass of the pigment Red No. 102, 49.1% by mass of purified water as the solvent, 11.5% by mass of ethanol, 28.0% by mass of propylene glycol (PG), 3.0% by mass of shellac as the binder resin, 0.4% by mass of sodium carbonate as the pH adjuster, and 5.0% by mass of reduced isomaltulose as the fade inhibitor. In this way, we obtained the inkjet ink for sample #43 (Example 24). Furthermore, the inkjet ink of sample #43 (Example 24) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of sample #43 (Example 24).

[0127] <Sample #44 (Example 25)> For Sample #44 (Example 25), the total inkjet ink content was 5.0% by mass of the pigment Red No. 102, 47.1% by mass of the solvent (purified water), 11.5% by mass of ethanol, 28.0% by mass of propylene glycol (PG), 3.0% by mass of the binder resin (shellac), 0.4% by mass of the pH adjuster (sodium carbonate), and 5.0% by mass of the fade inhibitor (reduced isomaltulose). In this way, we obtained the inkjet ink for sample #44 (Example 25). Furthermore, the inkjet ink of sample #44 (Example 25) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of sample #44 (Example 25).

[0128] <Sample #45 (Example 26)> For the inkjet ink of Sample #45 (Example 26), the proportion of Red No. 106 pigment was set to 0.3% by mass, the proportion of Yellow No. 4 pigment was set to 0.3% by mass, the proportion of purified water solvent was set to 51.6% by mass, the proportion of ethanol solvent was set to 11.5% by mass, the proportion of propylene glycol (PG) solvent was set to 28.0% by mass, the proportion of shellac binder resin was set to 3.0% by mass, the proportion of sodium carbonate pH adjuster was set to 0.4% by mass, and the proportion of reduced isomaltulose fade inhibitor was set to 5.0% by mass. In this way, we obtained the inkjet ink for sample #45 (Example 26). Furthermore, the inkjet ink of sample #45 (Example 26) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of sample #45 (Example 26).

[0129] <Sample #46 (Example 27)> For the inkjet ink of Sample #46 (Example 27), the proportion of Red No. 106 pigment was set to 0.5% by mass, the proportion of Yellow No. 4 pigment was set to 0.5% by mass, the proportion of purified water solvent was set to 51.1% by mass, the proportion of ethanol solvent was set to 11.5% by mass, the proportion of propylene glycol (PG) solvent was set to 28.0% by mass, the proportion of shellac binder resin was set to 3.0% by mass, the proportion of sodium carbonate pH adjuster was set to 0.4% by mass, and the proportion of reduced isomaltulose fade inhibitor was set to 5.0% by mass. In this way, we obtained the inkjet ink for sample #46 (Example 27). Furthermore, the inkjet ink of sample #46 (Example 27) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of sample #46 (Example 27).

[0130] <Sample #47 (Example 28)> For the inkjet ink of Sample #47 (Example 28), the proportion of Red No. 106 pigment was set to 1.5% by mass, the proportion of Yellow No. 4 pigment was set to 1.5% by mass, the proportion of purified water solvent was set to 49.1% by mass, the proportion of ethanol solvent was set to 11.5% by mass, the proportion of propylene glycol (PG) solvent was set to 28.0% by mass, the proportion of shellac binder resin was set to 3.0% by mass, the proportion of sodium carbonate pH adjuster was set to 0.4% by mass, and the proportion of reduced isomaltulose fade inhibitor was set to 5.0% by mass. In this way, we obtained the inkjet ink for sample #47 (Example 28). Furthermore, the inkjet ink of sample #47 (Example 28) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of sample #47 (Example 28).

[0131] <Sample #48 (Example 29)> For the inkjet ink of Sample #48 (Example 29), the proportion of Red No. 106 pigment was set to 2.5% by mass, the proportion of Yellow No. 4 pigment was set to 2.5% by mass, the proportion of purified water solvent was set to 47.1% by mass, the proportion of ethanol solvent was set to 11.5% by mass, the proportion of propylene glycol (PG) solvent was set to 28.0% by mass, the proportion of shellac binder resin was set to 3.0% by mass, the proportion of sodium carbonate pH adjuster was set to 0.4% by mass, and the proportion of reduced isomaltulose fade inhibitor was set to 5.0% by mass. In this way, we obtained the inkjet ink for sample #48 (Example 29). Furthermore, the inkjet ink of sample #48 (Example 29) was printed onto the surface of a tablet that exhibited alkalinity to obtain the tablet of sample #48 (Example 29).

[0132] The following describes each evaluation item and its evaluation method implemented in this embodiment. (Printing stability: initial printability and continuous printability) A piezoelectric ceramic-driven drop-on-demand inkjet head was used, with a print resolution of 600 dpi in the main scanning direction, 600 dpi in the sub-scanning direction (the direction in which recording media such as tablets are transported), and a total of 2,656 nozzles. Using the above inkjet head, a test pattern was printed immediately after nozzle maintenance. The readability of the printed image, including the occurrence of non-ejected areas, was then confirmed from the print quality of the test pattern. The evaluation criteria are as follows. In this evaluation, "initial printability" refers to the printability immediately after the start of printing, while "continuous printability" refers to the printability 30 minutes after the start of printing. ○: When missing or curved lines account for 5% or less of the total. △: When missing or curved lines account for 20% or less of the total. ×: If more than 20% of the lines are missing or curved. Furthermore, if the initial printability and continuous printability evaluations were "○" or "△", it was considered acceptable as there were no problems with its use.

[0133] (Print stability: Intermittent restart) Using a piezoelectric ceramic-driven drop-on-demand inkjet head with a print resolution of 600 dpi in the main scanning direction, 600 dpi in the sub-scanning direction (transport direction of the recording medium such as tablets), and a total of 1,280 nozzles, a test pattern was printed with a print drop rate of 6 pl per drop after being left for a specified time (15 to 60 minutes) without flushing. It was confirmed that ink was ejected from all nozzles without any failures. Tables 1 to 4 below show the evaluation results for intermittent printability (intermittent restart and ejection stability), which measured the waiting time during which ink ejection was possible. The evaluation criteria are as follows. ○: 15 minutes or more but less than 30 minutes △: 5 minutes or more but less than 15 minutes ×: Less than 5 minutes Furthermore, if the intermittent restart (discharge stability) test evaluation was "○" or "△", it was considered acceptable as there were no problems with use.

[0134] (Lightfastness) For each example and comparative example, the printed tablets, whose chromaticity and optical color density were measured, were irradiated with visible light at a cumulative illuminance of 1.2 million lux-hours in a 30% RH environment using a photostability tester (Nagano Science LT-200A-14WC). The chromaticity and optical color density of the irradiated printed tablets were measured using a spectrophotometer, and the color difference ΔE (according to JIS Z 8781), which indicates the change in chromaticity and optical color density before and after visible light irradiation, was compared. As described above, regarding the change in color before and after visible light irradiation, the inventors concluded that if the color difference ΔE according to JIS Z 8781 is 20 or less (ΔE≦20), light-induced discoloration is sufficiently suppressed, and the ink has excellent lightfastness. Furthermore, they concluded that if the color difference ΔE is 20 or less (ΔE≦20), the inkjet ink also has excellent readability. Therefore, if ΔE≦20, the inkjet ink was deemed to have excellent lightfastness and readability, and was considered to have passed this evaluation. The evaluation criteria in the table are as follows: ◎:ΔE≦10 〇:ΔE≦15 △:ΔE≦20 ×:ΔE>20

[0135] (Moisture resistance) The tablet printouts of each example, comparative example, and reference example, for which chromaticity and optical color density were measured, were left standing for 4 hours in a constant temperature and humidity chamber (Yamato Scientific IG421) set to 40°C and 90%RH. After standing, the chromaticity and optical color density of the tablet printouts were measured using a spectrophotometer, and the color difference ΔE (according to JIS Z 8781), which indicates the amount of change in chromaticity and optical color density before and after standing under high humidity conditions, was compared. As described above, regarding the change in color when standing under high humidity conditions, the inventors concluded that if the color difference ΔE according to JIS Z 8781 is 15 or less (ΔE≦15), bleeding is sufficiently suppressed and excellent moisture resistance is achieved. Furthermore, they concluded that if the color difference ΔE is 15 or less (ΔE≦15), excellent readability is also achieved. Therefore, if ΔE≦15, the inkjet ink was deemed to have excellent moisture resistance and readability, and was considered to have passed this evaluation. The evaluation criteria in the table are as follows: ◎:ΔE≦5 〇:ΔE≦10 △:ΔE≦15 ×:ΔE>15

[0136] (pH value measurement) The pH values ​​of the inks in each example, comparative example, and reference example were measured using a pH meter employing the glass electrode method. The measurement temperature was 25°C. The obtained pH values ​​are shown in the table.

[0137] [Table 1]

[0138] [Table 2]

[0139] [Table 3]

[0140] [Table 4]

[0141] [Table 5]

[0142] As shown in Tables 1-5, the inkjet inks corresponding to Examples 1-29, specifically samples #7-9, 16, 18-20, 23-24, 26-27, 29-30, 32-33, and 35-48, all meet the acceptance criteria for initial printability, continuous printability, and intermittent restart in this example. Therefore, the inkjet inks of samples #7-9, 16, 18-20, 23-24, 26-27, 29-30, 32-33, and 35-48, which correspond to Examples 1-29, exhibit excellent print quality (especially intermittent restart) not only when used with neutral and acidic tablets, but also when used with alkaline tablets.

[0143] Furthermore, as shown in Tables 1-5, the inkjet inks corresponding to Examples 1-29, specifically samples #7-9, 16, 18-20, 23-24, 26-27, 29-30, 32-33, and 35-48, meet the lightfastness requirements for this example. Therefore, the inkjet inks of samples #7-9, 16, 18-20, 23-24, 26-27, 29-30, 32-33, and 35-48, which correspond to Examples 1-29, exhibit excellent lightfastness not only when used with neutral or acidic tablets, but also when used with alkaline tablets.

[0144] Furthermore, as shown in Tables 1-5, the inkjet inks corresponding to Examples 1-29, specifically samples #7-9, 16, 18-20, 23-24, 26-27, 29-30, 32-33, and 35-48, meet the acceptance criteria for moisture resistance in these examples. Therefore, the inkjet inks of samples #7-9, 16, 18-20, 23-24, 26-27, 29-30, 32-33, and 35-48, which correspond to Examples 1-29, exhibit excellent moisture resistance not only when used with neutral or acidic tablets, but also when used with alkaline tablets.

[0145] Furthermore, as shown in Reference Examples 1-2, even inkjet inks that do not contain shellac as a binder resin exhibit excellent print quality (especially intermittent restart), lightfastness, and moisture resistance when used on neutral or acidic tablets. Furthermore, because Red No. 102 itself possesses high lightfastness, as shown in Reference Example 3, even inkjet inks that do not contain a fade inhibitor (e.g., reduced isomaltulose) exhibit excellent print quality (especially intermittent restart), lightfastness, and moisture resistance, not only when used on neutral and acidic tablets, but also when used on alkaline tablets.

[0146] As described above, the inkjet ink of this embodiment, which contains an edible dye, a fade inhibitor, a binder resin, and water and ethanol as solvents, wherein the binder resin is shellac, exhibits excellent print quality (especially intermittent restart), lightfastness, and moisture resistance not only when used on neutral or acidic tablets, but also when used on alkaline tablets.

[0147] The scope of this disclosure is not limited to the illustrative and described embodiments, but also includes all embodiments that produce an effect equivalent to that which is intended by this disclosure. Furthermore, the scope of this disclosure is not limited to the combination of features defined by the claims, but may be defined by any desired combination of specific features from each of the disclosed features.

[0148] Furthermore, for example, this disclosure can take the following configuration. (1) It comprises an edible dye, a fade inhibitor, a binder resin, and water and ethanol as solvents. The aforementioned binder resin is shellac, and the inkjet ink is for tablets. (2) The inkjet ink for tablets according to (1) above, comprising reduced isomaltulose as the colorfastness inhibitor. (3) The inkjet ink for tablets according to (1) or (2) above, wherein the amount of ethanol added is in the range of 1.0% by mass or more and 10.0% by mass or less. (4) An inkjet ink for tablets according to any one of items (1) to (3) above, further comprising sodium carbonate as a pH adjuster. (5) An inkjet ink for tablets according to any one of the above items (1) to (4), for use in printing on alkaline tablets whose surface is at least alkaline. (6) An inkjet ink for tablets according to any one of the above items (1) to (4), for use in printing on magnesium oxide tablets that contain magnesium oxide on at least one surface. (7) The aforementioned dye is blended in an amount of 0.5% by mass or more and 5.0% by mass or less. The binder resin is blended in a range of 1.0% by mass or more and 5.0% by mass or less. An inkjet ink for tablets according to any one of the above items (1) to (6), wherein the aforementioned fade inhibitor is formulated in an amount of 1.0% by mass or more and 10.0% by mass or less. (8) The inkjet ink for tablets according to any one of (1) to (7) above, wherein the dye is at least one selected from azo dyes, triphenylmethane dyes, and xanthene dyes. (9) The azo dye is at least one of Red No. 102 and Yellow No. 4. The aforementioned triphenylmethane-based dye is Blue No. 1, The inkjet ink for tablets described in (8) above, wherein the xanthene dye is Red No. 106. (10) It contains an edible dye, reduced isomaltulose as a colorfastness inhibitor, shellac as a binder resin, and water and ethanol as solvents. The amount of ethanol added to the entire inkjet ink for tablets is within the range of 1.0% by mass or more and 10.0% by mass or less. It further contains sodium carbonate as a pH adjuster. Inkjet ink for tablets is generally alkaline. (11) This is an inkjet ink for tablets used to print on magnesium oxide tablets containing magnesium oxide in a range of 0.2g to 0.5g per tablet. It contains an edible dye, reduced isomaltulose as a colorfastness inhibitor, shellac as a binder resin, and water and ethanol as solvents. The aforementioned dye may contain only Blue No. 1, or only Yellow No. 4 and Red No. 106. The amount of Blue No. 1 added to the entire inkjet ink for tablets is within the range of 0.5% by mass or more and 5.0% by mass or less. The amount of Yellow No. 4 added to the entire inkjet ink for tablets is within the range of 0.25% by mass or more and 2.0% by mass or less, and the amount of Red No. 106 added to the entire inkjet ink for tablets is within the range of 0.25% by mass or more and 3.0% by mass or less. The amount of reduced isomaltulose added to the entire inkjet ink for tablets is within the range of 1.0% by mass or more and 10.0% by mass or less. The amount of shellac added to the entire inkjet ink for tablets is within the range of 1.0% by mass or more and 5.0% by mass or less. The amount of ethanol added to the entire inkjet ink for tablets is within the range of 1.0% by mass or more and 10.0% by mass or less. The aforementioned inkjet ink for tablets is alkaline overall. (12) It further contains sodium carbonate as a pH adjuster, The tablet inkjet ink according to any one of the above items (1) to (11), wherein the amount of sodium carbonate added to the entire tablet inkjet ink is in the range of 0.1% by mass or more and 0.6% by mass or less. (13) The tablet inkjet ink according to any one of the above items (1) to (12), wherein the absolute difference between the pH of the tablet inkjet ink and the pH of the printed area on the tablet to be printed is 2 or less. (14) A tablet printout comprising a printed area printed using the inkjet ink for tablets described in any one of the above items (1) to (13). (15) The tablet printout described in (14) above, wherein each tablet on which the printed portion is printed contains magnesium oxide in an amount of 0.2 g to 0.5 g per tablet. [Explanation of Symbols]

[0149] 1. Tablet base material 3. Printed image 5. Plain printed materials 7. Film coating layer 9. Film-coated tablet printouts 10 Dry film 11. Plain tablet print image (solid color image) 13. Printed image of film-coated tablets (with 2D barcode)

Claims

1. It comprises an edible dye, a fade inhibitor, a binder resin, and water and ethanol as solvents. The aforementioned dye contains an edible pigment selected from Blue No. 1, Red No. 102, Red No. 106, and Yellow No. 4 in an amount of 0.5% by mass or more and 5.0% by mass or less relative to the total amount of ink. The binder resin contains shellac in an amount of 1.0% by mass or more and 5.0% by mass or less relative to the total amount of ink. The ink contains sodium carbonate as a pH adjuster in an amount of 0.1% to 0.6% by mass relative to the total amount of ink. The ink contains the aforementioned fade inhibitor, selected from reduced isomaltulose or lactose, in an amount of 5.0% by mass or more and 10.0% by mass or less relative to the total amount of ink. It contains 28% by mass of propylene glycol relative to the total amount of ink. The aforementioned ethanol is contained in an amount of 1.0% by mass or more and 10.0% by mass or less relative to the total amount of ink. The residue contains the aforementioned water, Inkjet ink for tablets with a pH range of 7.5 to 9.

5.

2. The inkjet ink for tablets according to claim 1, for use in printing on alkaline tablets whose surface is at least alkaline.

3. The tablet inkjet ink according to claim 1, for use in printing on magnesium oxide tablets containing magnesium oxide on at least one surface.

4. The inkjet ink for tablets according to claim 1, which is for printing on magnesium oxide tablets containing magnesium oxide in an amount of 0.2 g or more and 0.5 g or less per tablet.

5. The inkjet ink for tablets according to any one of claims 1 to 4, wherein the absolute difference between the pH of the inkjet ink for tablets and the pH of the printed area on the tablet to be printed is 2 or less.

6. A tablet printout comprising a printed portion printed using the inkjet ink for tablets described in any one of claims 1 to 4.

7. The tablet printout according to claim 6, wherein each tablet on which the printed portion is printed contains magnesium oxide in an amount of 0.2 g to 0.5 g per tablet.

8. It comprises an edible dye, a fade inhibitor, a binder resin, and water and ethanol as solvents. The aforementioned dye contains an edible pigment selected from Blue No. 1, Red No. 102, Red No. 106, and Yellow No. 4, and the total amount of the edible pigment is within the range of 0.5% by mass or more and 5.0% by mass or less relative to the total amount of ink. The binder resin contains shellac in an amount of 1.0% by mass or more and 5.0% by mass or less relative to the total amount of ink. The ink contains sodium carbonate as a pH adjuster in an amount of 0.1% to 0.6% by mass relative to the total amount of ink. The ink contains the aforementioned fade inhibitor, selected from reduced isomaltulose or lactose, in an amount of 5.0% by mass or more and 10.0% by mass or less relative to the total amount of ink. It contains 28% by mass of propylene glycol relative to the total amount of ink. The aforementioned ethanol is contained in an amount of 1.0% by mass or more and 10.0% by mass or less relative to the total amount of ink. The residue contains the aforementioned water, Inkjet ink for tablets with a pH range of 7.5 to 9.

5.

9. The aforementioned Blue No. 1 is contained in an amount of 0.5% by mass or more and 5.0% by mass or less relative to the total amount of ink. The aforementioned Red No. 102 is contained in an amount of 0.5% by mass or more and 5.0% by mass or less relative to the total amount of ink. The aforementioned Red No. 106 is contained in an amount of 0.3% by mass or more and 2.5% by mass or less relative to the total amount of ink. The inkjet ink for tablets according to claim 8, wherein the aforementioned Yellow No. 4 is contained in an amount of 0.3% by mass or more and 2.5% by mass or less based on the total amount of ink.

Images