Inkjet inks and printed materials

Abstract

The present invention aims to provide an inkjet ink that can print with stable colors with little discoloration over time, not only when printed on the surface of a printing substrate with relatively low ink permeability, but also when printed on the surface of a printing substrate with relatively high ink permeability, and a printed material having a printed portion printed with the inkjet ink. The gray ink according to this embodiment is an edible inkjet ink that contains at least a first coloring matter that is a food dye and a second coloring matter that is also a food dye, and the first coloring matter is at least one of Red No. 3, Red No. 40, Red No. 104, Red No. 105, and Red No. 106.

Description

[Technical field]

[0001] The present invention relates to ink-jet inks and substrates. [Background technology]

[0002] Some inkjet inks (hereinafter simply referred to as "inkjet inks") used in inkjet printing are edible. Patent Document 1, for example, describes a technique related to edible inkjet inks. Among the inkjet inks according to the conventional technology, there are some which are prone to change in color (tone) of printed characters, images, etc. over time, i.e., tend to discolor over time. When the printed color of the inkjet ink changes over time, the printed color intended by the ink designer is not expressed, and this can result in reduced readability and changes in color. In particular, when the inkjet ink according to the conventional technology is printed on the surface of a printing object (printed material) that has relatively high ink permeability, there is a tendency for discoloration over time to be significant. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2006-169301 A Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention has been made in consideration of the above circumstances, and has an object to provide an inkjet ink that discolors little over time and can print in a stable color, not only when printed on the surface of a printing object having relatively low ink permeability, but also when printed on the surface of a printing object having relatively high ink permeability, in particular an inkjet ink that exhibits gray or black, and a printed material having a printed portion printed with the inkjet ink. [Means for solving the problem]

[0005] According to one embodiment of the present invention, a gray or black inkjet ink contains at least a first dye which is a food dye (edible colorant) and a second dye which is also an edible dye and has a different color tone from the first dye, and the first dye is at least one of Red No. 3, Red No. 40, Red No. 104, Red No. 105, and Red No. 106. Effect of the Invention

[0006] In one aspect of the present invention, when the inkjet ink is printed on the surface of a printing object having relatively low ink permeability, as well as when the ink is printed on the surface of a printing object having relatively high ink permeability, the printed color can be maintained as gray or black, with little discoloration over time and a stable color tone. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a conceptual diagram for explaining discoloration of an ink-jet ink over time. [Diagram 2] FIG. 1 is a schematic cross-sectional view showing an example of a tablet (plain tablet) according to an embodiment of the present invention. [Diagram 3] FIG. 1 is a schematic cross-sectional view showing an example of a tablet (film-coated tablet) according to an embodiment of the present invention. [Figure 4] 1 is an example of a printed image of a tablet (plain tablet) according to an embodiment of the present invention. [Diagram 5] 1 is an example of a printed image of a tablet (film-coated tablet) according to an embodiment of the present invention. [Figure 6] 10A to 10C are conceptual diagrams illustrating a printing process of inkjet ink in a modified example of an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] The inkjet ink according to the embodiment of the present invention relates to an inkjet ink capable of improving discoloration over time of a printed image, for example, applied by an inkjet printing method to the surface of a medical tablet. Hereinafter, the configuration of the gray or black inkjet ink according to the embodiment of the present invention (hereinafter, for convenience, also referred to as "gray ink") and the tablet (printed material) having a printed portion printed with the gray ink will be described in detail.

[0009] [Gray ink tone] The "gray" or "black" exhibited by the inkjet ink according to this embodiment is a color (tone) defined as follows. First, a piezoelectric ceramic-driven drop-on-demand inkjet head with a printing resolution of 600 dpi in the main scanning direction, 600 dpi in the sub-scanning direction (the direction in which the tablet or other recording medium is transported), and a total of 2,656 nozzles is used to create a solid image on the substrate, printed with a printing drop volume of 12 pl per drop and no overprinting.

[0010] Next, an X-rite spectrodensitometer "X-rite530" is placed on top of the printed solid image, and the color tone of the reflected light (L*a*b* color system) is measured under the following conditions: viewing angle 2°, light source D50. Among the colors measured under the above conditions and expressed in the L*a*b* color system, L* Any (0~100) a* -15~+15 b* -15~+15 In this embodiment, a color tone (hue) that falls within this range is defined as "gray" or "black."

[0011] The printing substrate is preferably, for example, a tablet with a white surface (whiteness of 70 degrees or more). The whiteness can be measured by placing an X-rite spectrodensitometer "X-rite eXact" on the top surface of a substrate such as a tablet or paper, and determining the whiteness from the spectrum of reflected light. The setting conditions comply with TAPPI-T452 defined by the Technical Association of the Pulp and Paper Industry (TAPPI). As long as the whiteness is 70 degrees or more, it is also possible to use paper, etc., as well as tablets, as the printing substrate.

[0012] [Gray Ink Composition] The gray ink according to this embodiment is an inkjet ink having edibility, and contains at least a first dye, which is an edible dye (edible dye), and a second dye, which is an edible dye and has a different color tone from the first dye. The ratio of the penetration speed of the first dye into the printing object to the penetration speed of the second dye into the printing object (penetration speed of the first dye / penetration speed of the second dye) is in the range of 0.5 to 1.7. Here, the "penetration speed of the dye" refers to the distance from the surface of the printing object, such as a tablet, to the bottom end of the ink permeation portion (the position farthest from the surface of the tablet), measured after a certain time (e.g., 140 hours) has elapsed since printing, divided by the elapsed time (e.g., 140 hours) since printing.

[0013] The distance from the surface of the printing object, such as a tablet, to the bottom end of the ink permeation portion (the position farthest from the surface of the tablet) measured a certain time after printing is generally referred to as the "penetration amount." Therefore, in the gray ink according to this embodiment, it can be said that the ratio of the penetration amount of the first dye into the printing object to the penetration amount of the second dye into the printing object (penetration amount of the first dye / penetration amount of the second dye) is set within the range of 0.5 to 1.7. Moreover, the above-mentioned "second colorant" refers to the colorant contained in the gray ink according to this embodiment that is present in the greatest amount.

[0014] More specifically, the gray ink of this embodiment is an edible inkjet ink that contains at least a first pigment that is an edible dye, and a second pigment that is also an edible dye and has a different hue from the first pigment. The first dye is at least one of Erythrosine (FDA Name: FD&C Red No.3, Color Index Name: Acid Red 51, CAS Number: 16423-68-0), Allura Red AC (FDA Name: FD & C Red No.40, Color Index Name: Food Red 17, CAS Number: 25956-17-6), Phloxine B (FDA Name: D & C Red No.28, Color Index Name: Acid Red 92, CAS Number: 18472-87-7), Rose Bengal (Color Index Name: Acid Red 94, CAS Number: 632-69-9), and Acid Red (Color Index Name: Acid Red 52, CAS Number: 3520-42-1). The second dye is, for example, sodium copper chlorophyllin. With this configuration, the gray ink according to the present embodiment can be printed on the surface of a printing object having a relatively low ink permeability, and even when the gray ink is printed on the surface of a printing object having a relatively high ink permeability, the inkjet ink can be prevented from discoloring over time while maintaining the print color as gray or black. This point will be described below with reference to FIG.

[0015] FIG. 1 is a conceptual diagram for explaining discoloration over time of ink-jet ink. FIG. 1(a) is a cross-sectional view in the thickness direction of a tablet in a state where a tablet having relatively low ink permeability is printed with a gray ink according to the conventional technology and a certain time (e.g., 140 hours) has elapsed. FIG. 1(b) is a cross-sectional view in the thickness direction of a tablet in a state where a tablet having relatively high ink permeability is printed with a gray ink according to the conventional technology and a certain time (e.g., 140 hours) has elapsed. FIG. 1(c) is a cross-sectional view in the thickness direction of a tablet in a state where a tablet having relatively high ink permeability is printed with a gray ink according to the present embodiment and a certain time (e.g., 140 hours) has elapsed.

[0016] In addition, "tablets with relatively high ink permeability" refer to tablets in which the amount of ink permeation 140 hours after printing is 10 μm or more, regardless of the type of ink. On the other hand, "tablets with relatively low ink permeability" refer to tablets in which the amount of ink permeation 140 hours after printing is 5 μm or less, regardless of the type of ink. Examples of tablet types with relatively high ink permeability include plain tablets with a coarse particle size and a structure with many voids on the surface. Examples of tablet types with relatively low ink permeability include tablets with a film-coated portion with few voids, i.e., film-coated tablets.

[0017] An example of a conventional gray ink is one that contains Red No. 102 (New Coccine (Color Index Name: Acid Red 18, CAS Number: 2611-82-7)), a food dye, as a red pigment, Blue No. 1 (Brilliant Blue FCF (FDA Name: FD & C Blue No. 1, Color Index Name: Food Blue 2, CAS Number: 3844-45-9)), a food dye, as a blue pigment, and sodium copper chlorophyllin, a food dye, as a green pigment. Another conventional gray ink is one that contains Red No. 102, Blue No. 1, and Yellow No. 4 (Tartrazine (FDA Name: FD & C Yellow No. 5, Color Index Name: Acid Yellow 23, CAS Number: 1934-21-0)), a food dye, as a yellow pigment. Below, an example of a conventional gray ink containing Red No. 102, Blue No. 1, and sodium copper chlorophyllin will be described.

[0018] The above-mentioned "Color Index Name" is established by the American Association of Textile Chemists and Colorists. The above-mentioned "FDA Name" is established by the US FDA (Food and Drug Administration). In this embodiment, each usable dye (each substance) is specified using a CAS Number, but the present invention is not limited to this. For example, a dye (substance) having the same substance name as the dye (substance) described in this embodiment but a different CAS Number can be used in this embodiment because it is a geometric isomer, a stereoisomer, a substance containing an isotope, or a salt thereof. In addition, when there is no isomer or the usable dye (substance) is specified (limited), the substance (compound) itself with the CAS Number described in this embodiment can be used.

[0019] When the gray ink according to the conventional technology is printed on the surface of a tablet with low ink permeability, the permeation speed of each of the red pigment 4R, blue pigment 4B, and green pigment 4G is almost the same due to the low ink permeability. Therefore, as shown in FIG. 1(a), even after a certain time has passed after printing, the red pigment 4R, blue pigment 4B, and green pigment 4G each remain near the surface 1S of the tablet, and the printed color is gray (black). In other words, when the gray ink according to the conventional technology is printed on a tablet with low ink permeability, it can exhibit the same gray (black) color tone as immediately after printing, even after a certain time has passed after printing.

[0020] However, when the gray ink according to the conventional technology is printed on a tablet with high ink permeability, the high ink permeability may cause a difference in the permeation speed of each of the red pigment 4R, blue pigment 4B, and green pigment 4G. This is because the permeation speed of the red pigment 4R is generally faster than the permeation speed of each of the blue pigment 4B and green pigment 4G. Therefore, as shown in FIG. 1(b), after printing, the red pigment 4R permeates (moves) into the inside of the tablet over time, but the blue pigment 4B and green pigment 4G tend to remain near the surface 1S of the tablet even after time has passed. As a result, the printed color, which was gray (black) immediately after printing, becomes less red over time and becomes green overall. In other words, when the gray ink according to the conventional technology is printed on the surface of a tablet with high ink permeability, it tends to discolor significantly over time. In addition, this tendency is greater when the red pigment 4R is Red No. 102.

[0021] In contrast, the gray ink according to this embodiment contains at least a first dye and a second dye having a different hue from the first dye. The ratio of the penetration rate of the first dye into the tablet to the penetration rate of the second dye into the tablet (penetration rate of the first dye / penetration rate of the second dye) is in the range of 0.5 to 1.7. More specifically, the gray ink according to this embodiment contains at least one of Red No. 3, Red No. 40, Red No. 104, Red No. 105, and Red No. 106, which are red dyes 4R, as the first dye, and contains copper chlorophyllin sodium (copper chlorophyllin Na), which is green dye 4G, as the second dye having a different hue from the first dye. In other words, the gray ink according to this embodiment does not substantially contain Red No. 102 as red dye 4R.

[0022] The permeation rate of each of the red pigments 4R in Red No. 3, Red No. 40, Red No. 104, Red No. 105, and Red No. 106 used in this embodiment is lower than that of Red No. 102 described above, and is approximately the same as that of other pigments such as sodium copper chlorophyllin. Here, "approximately the same permeation rate" means that the ratio of the permeation rate of the red pigment 4R into the tablet to the permeation rate of the green pigment 4G into the tablet (permeation rate of red pigment 4R / permeation rate of green pigment 4G) is within the range of 0.5 to 1.7.

[0023] Therefore, even if the gray ink according to this embodiment is printed on the surface of a tablet with high ink permeability, the permeation speeds of the red pigment 4R and the green pigment 4G are almost the same. Therefore, as shown in FIG. 1(c), after printing, the red pigment 4R and the green pigment 4G permeate into the inside of the tablet at almost the same speed over time. Therefore, no specific pigment remains on the surface of the tablet, and the printed color can be almost the same gray (black) as immediately after printing even after a certain time has passed after printing. In addition, Figure 1 (c) describes the case where the gray ink of this embodiment is printed on the surface of a tablet with high ink permeability, but when the gray ink of this embodiment is printed on the surface of a tablet with low ink permeability, the red pigment 4R and the green pigment 4G each remain in the vicinity of the tablet surface 1S, so that the printed color can remain almost the same gray (black) as immediately after printing even after a certain amount of time has passed after printing.

[0024] As described above, the gray ink according to this embodiment may contain at least one of Red No. 3, Red No. 40, Red No. 104, Red No. 105, and Red No. 106 as a red pigment, with Red No. 3 being the most preferable. Red No. 3 has a penetration speed closer to that of sodium copper chlorophyllin than other red pigments, and therefore discolors less over time. The content of the red pigment is preferably in the range of 0.05% by mass to 5.0% by mass, more preferably in the range of 0.1% by mass to 3.0% by mass, based on the total mass of the gray ink according to this embodiment. If the content of the red pigment is within the above numerical range, the gray (black) tone is further emphasized.

[0025] The content of the green pigment, sodium copper chlorophyllin, is preferably in the range of 0.4% by mass to 15.0% by mass, more preferably in the range of 0.8% by mass to 12.0% by mass, based on the total mass of the gray ink according to this embodiment. If the content of the green pigment is within the above numerical range, the gray (black) tone is further emphasized. Furthermore, in the gray ink according to this embodiment, the amount of red pigment contained may be less than the amount of green pigment contained, so that the gray (black) tone is emphasized. Furthermore, the gray ink according to this embodiment may contain a third pigment, a blue pigment, which has a different hue from the red pigment as the first pigment and the green pigment as the second pigment. The third pigment, the blue pigment, is, for example, Blue No. 1, which is a food dye. By including the blue pigment in the red and green pigments, the gray (black) tone is further emphasized.

[0026] The content of the blue pigment is preferably in the range of 0.05% by mass to 1.5% by mass, more preferably in the range of 0.1% by mass to 1.2% by mass, based on the total mass of the gray ink according to this embodiment. If the content of the blue pigment is within the above numerical range, the gray (black) tone is further emphasized. Furthermore, in the gray ink according to this embodiment, the content of the blue pigment may be equal to or less than the content of the red pigment. If the content of the blue pigment is equal to or less than the content of the green pigment, the gray (black) tone is further emphasized. Furthermore, in the gray ink according to this embodiment, the content of the blue pigment may be equal to or less than the content of the red pigment. If the content of the blue pigment is equal to or less than the content of the green pigment, the gray (black) tone is further emphasized.

[0027] The total content of each food dye contained in the gray ink according to this embodiment may be in the range of 1.0% by mass or more and 15.0% by mass or less of the total ink. If the total content of each food dye is within the above numerical range, the gray (black) color tone is further emphasized. If the total content of each food dye is less than 1.0% by mass, the overall printed color tends to be lighter and visibility tends to decrease. If the total content of each food dye is more than 15.0% by mass, the viscosity of the ink increases and the nozzles of the printer are clogged, increasing the possibility of not being able to print.

[0028] (dye) The pigments (coloring materials) contained in the gray ink according to this embodiment are not particularly limited as long as they are edible, except for the pigments described above. Pigments that can be added to the gray ink according to this embodiment can be appropriately selected from, for example, conventionally known synthetic food pigments and natural food pigments. Examples of synthetic food dyes include tar-based dyes, natural dye derivatives, and natural synthetic dyes. Examples of tar-based dyes include Red No. 2 (Amaranth, FDA Name: FD & C Red No. 2, Color Index Name: Acid Red 27, CAS Number: 915-67-3), Yellow No. 4 (Tartrazine, FDA Name: FD & C Yellow No. 5, Color Index Name: Acid Yellow 23, CAS Number: 1934-21-0), Yellow No. 5 (Sunset Yellow FCF, FDA Name: FD & C Yellow No. 6, Color Index Name: Food Yellow 3, CAS Number: 2783-94-0), Blue No. 2 (Indigo Carmine, FDA Name: FD & C Blue No. 2, Color Index Name: Acid Blue 74, CAS Number: 860-22-0), Red No. 2 Aluminum Lake (FD & C Red No. 2 Aluminum Lake), Red No. 3 Aluminum Lake (FD & C Red No. 3 Aluminum Lake), Red No. 40 Aluminum Lake (FD & C Examples of the natural pigment derivatives include potassium norbixin, etc. Examples of the natural synthetic pigments include β-carotene, riboflavin, etc.

[0029] Examples of natural food dyes include anthocyanin dyes, carotenoid dyes, quinone dyes, chlorophyll dyes, flavonoid dyes, betaine dyes, monascus dyes, and other dyes derived from natural products. Examples of anthocyanin dyes include red radish dyes, red cabbage dyes, red rice dyes, elderberry dyes, cowberry dyes, gooseberry dyes, cranberry dyes, salmonberry dyes, perilla dyes, sweet blueberry dyes, strawberry dyes, dark sweet cherry dyes, cherry dyes, hibiscus dyes, huckleberry dyes, grape juice dyes, grape skin dyes, blackcurrant dyes, blackberry dyes, blueberry dyes, plum dyes, white wortberry dyes, boysenberry dyes, mulberry dyes, purple sweet potato dyes, purple corn dyes, purple yam dyes, raspberry dyes, redcurrant dyes, loganberry dyes, and other anthocyanin dyes. Examples of carotenoid pigments include annatto pigment, gardenia yellow, 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, sorghum pigment, onion pigment, and other flavonoid pigments. Examples of betaine pigments include beet red pigment. Examples of monascus pigments include red koji pigment and red koji yellow. Examples of pigments derived from other natural products include turmeric pigment, clover pigment, gardenia red pigment, spirulina blue pigment, and the like.

[0030] (dispersion medium) In addition to the above-mentioned pigments, the gray ink according to this embodiment may contain a dispersion medium (solvent) to disperse (dissolve) the above-mentioned pigments. Examples of dispersion media that can be added to the gray ink according to this embodiment include purified water, ethanol, glycerin, propylene glycol, polyethylene glycol 300 (average molecular weight 300), 1-propanol (n-propyl alcohol), 2-propanol (isopropyl alcohol), and ethyl lactate. The blending ratio is not particularly limited, but it is more preferable to include any of glycerin, propylene glycol, and polyethylene glycol 300 in the ink in a range of 1% by mass to 30% by mass in order to prevent the ink from drying at the nozzle. If the content is less than 1% by mass, the ink is more likely to dry out, causing clogging of the nozzle, and if it exceeds 30% by mass, the drying of the printed surface on the medical tablet surface becomes too slow, and when the printed tablets come into contact with each other, the undried ink may adhere to the other tablet and cause a stain, which may cause a problem.

[0031] Furthermore, among the above-mentioned dispersion media, propylene glycol can disperse Red No. 3 more easily than other dispersion media. Furthermore, of the above-mentioned dispersion media, glycerin has a higher viscosity than other dispersion media, which reduces the overall ink penetration amount, making it possible to make the penetration speed of each pigment approximately the same. As a result, the gray ink according to this embodiment has relatively high ink penetration, and can be used to print on objects that generally suffer from ink discoloration over time while reducing discoloration over time.

[0032] There is no limitation on medical tablets and the like which are the printing objects in this embodiment, but the effect tends to be particularly high in plain tablets whose surfaces are not coated with a film coating layer. Plain tablets whose surfaces are not coated with a film coating layer tend to have higher ink permeability than film-coated tablets whose surfaces are coated with a film coating layer. For this reason, in plain tablets, the difference in the permeation speed of each dye tends to be larger than in film-coated tablets. Since the gray ink according to this embodiment can reduce the difference in permeation speed, specific dye components do not remain on the tablet surface, and the discoloration over time in the printed printed part can be reduced. Note that even in the case of a film-coated tablet, if the film coating layer is formed of a material with high ink permeability, the gray ink according to this embodiment can reduce the difference in the permeation speed of each dye, so that specific dye components do not remain on the tablet surface and the change in color tone in the printed part can be reduced.

[0033] [Printing method] The gray ink according to this embodiment is not particularly limited in the printing method, and can be printed using an inkjet device such as a commercially available inkjet printer. Therefore, 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 by a so-called drop-on-demand type inkjet device that uses a piezoelectric element (piezoelectric ceramics) as an actuator, and can also be printed by other types of inkjet devices.

[0034] Examples of drop-on-demand inkjet devices include devices that employ a thermal inkjet method in which inkjet ink is ejected by the water vapor pressure generated by momentarily heating a micro-heating element to a high temperature (200 to 300°C), electrostatic type devices that eject inkjet ink by electrostatically vibrating an actuator, devices that employ an ultrasonic method that utilizes the cavitation phenomenon of ultrasonic waves, etc. In addition, if the gray ink according to this embodiment has charging properties, it is also possible to use a device that employs a continuous ejection method.

[0035] 〔tablet〕 In this embodiment, the gray ink according to this embodiment may be printed or printed on, for example, the surface of a tablet using the printing method described above. In other words, the gray ink according to this embodiment can improve the discoloration of the printed portion, i.e., the printed image, applied to the surface of a medical tablet using an inkjet printing method. Hereinafter, the configuration of a tablet having a printed image printed with the gray ink according to the embodiment will be described. The tablet according to the present embodiment is, for example, a medical tablet. Here, the term "medical tablet" refers to, for example, plain tablets (plain 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.

[0036] Fig. 2 is a schematic cross-sectional view showing an example of a medical tablet (plain tablet) on which printing (printing, image printing) has been performed. Fig. 2 shows, in cross-sectional view, a plain tablet print 5 in which a printed image 3 such as letters is printed on the upper surface of a base material 1 of the tablet. Fig. 3 is a schematic cross-sectional view showing an example of a medical tablet (film-coated tablet) on which printing (printing of characters, printing of pictures) has been performed. Fig. 3 shows, in cross-sectional view, a film-coated tablet print 9 in which a printed image 3 such as letters is printed on the upper surface of a substrate 1 of a tablet on which a film-coated layer 7 has been formed on the surface. In this embodiment, as shown in FIG. 4, a solid image may be printed as the plain tablet print image 11, and as shown in FIG. 5, a two-dimensional barcode may be printed as the film-coated tablet print image 13.

[0037] The active ingredient contained in the medical tablet is not particularly limited, and includes, for example, substances effective for the prevention and treatment of various diseases (e.g., substances having sleep-inducing action, tranquilizing activity, antibacterial activity, antihypertensive action, antianginal activity, analgesic action, anti-inflammatory activity, tranquilizing action, antidiabetic activity, diuretic action, anticholinergic activity, anti-gastric hyperacidity action, anti-epileptic action, ACE inhibitory activity, β-receptor antagonist or agonist activity, anesthetic action, appetite suppressant action, antiarrhythmic action, antidepressant action, anticoagulant activity, antidiarrheal action, antihistamine activity, antimalarial action, antitumor activity, immunosuppressant activity, antiparkinsonian action, antipsychotic action, antiplatelet activity, antihyperlipidemic action, etc.), substances having a cleaning action, fragrances, substances having a deodorant action, etc., but are not limited thereto.

[0038] The tablet according to the present embodiment can be mixed with a carrier acceptable for its use together with the active ingredient as necessary. For example, if it is a medical tablet, a medicamentically acceptable carrier can be mixed. As the medicamentically acceptable carrier, various organic or inorganic carrier substances commonly used as tablet materials are used, and for example, excipients, lubricants, binders, disintegrants, thickeners, etc. are appropriately mixed in appropriate amounts. In addition, additives such as preservatives, antioxidants, colorants, and sweeteners can be used as necessary. In this embodiment, a medical tablet is used as an example of a tablet, but the present invention is not limited to this. There is no particular limit to the printing target of the gray ink according to this embodiment, and the gray ink may be printed on the surface of various tablets, such as feed, fertilizer, cleaning agent, and food such as Ramune candy. In addition, there is no particular limit to the size of the printing target of the gray ink according to this embodiment, and the gray ink can be applied to tablets of various sizes.

[0039] [Composition of inkjet ink that exhibits colors below gray (black)] In this embodiment, the composition of the inkjet ink that exhibits gray or black has been described, but the present invention is not limited to this. For example, discoloration over time can be reduced by using an inkjet ink containing at least two kinds selected from the group of food dyes consisting of copper chlorophyllin sodium, Blue No. 1, Red No. 3, Red No. 40, Red No. 104, Red No. 105, and Red No. 106. This is because the penetration speed of each of the above-mentioned dyes is approximately the same even when the ink is printed on the surface of a printing object having a relatively high ink permeability. The blending amount of the pigment and the ink solvent in the inkjet ink described above are the same as in the case of the gray ink, and therefore a description thereof will be omitted here.

[0040] [Other Modifications] In this embodiment, the "dye permeation speed" is calculated by dividing the distance from the surface of the tablet to the bottom end of the ink permeated portion measured after a certain time (e.g., 140 hours) has elapsed since printing by the time elapsed since printing, but the present invention is not limited to this. For example, the mobility (Rf value) of a sample used in thin-layer chromatography (TLC) may be used. The "dye permeation speed" may be calculated by dividing this mobility (Rf value) by the time required for the dye to migrate. In addition, in this embodiment, a tablet with a white surface (whiteness of 70 degrees or more) is used as the printing substrate, but the present invention is not limited to this. The printing substrate may be, for example, a tablet with a red surface. Even in this case, discoloration over time can be reduced. Specifically, when printing is performed on a tablet with a red surface with ink containing copper chlorophyllin sodium and Blue No. 1, the printing color appears gray or black, and discoloration of the ink over time is reduced.

[0041] [Measurement method] In addition, examples of physical property measurements and tests of printed tablets and inks include the following: (Light resistance test) This is done by exposing the tablet to sunlight or using a tester that can give equivalent results (e.g., a xenon weather meter (Toyo Seiki Co., Ltd. Ci4000)) to irradiate a cumulative 1.2 million lux of visible light, and evaluate the color difference ΔE before and after irradiation. This is done for printed tablets. (Moisture resistance test) This is in accordance with the stability test (accelerated test) for pharmaceutical ingredients notified by the Ministry of Health, Labor and Welfare, and is evaluated by the color difference ΔE before and after exposure to 40℃±2℃ and 75%RH±5%RH (RH: relative humidity) for printed tablets. Exposure method: constant temperature and humidity chamber (e.g. Espec CSH series)

[0042] (surface tension) Ink is measured using the platinum plate method. (Example of measuring device: Kyowa Interface Science Co., Ltd. DY-700) (viscosity) Ink viscosity is measured using a cone-plate viscometer. (Example of measuring device: Brookfield DV1MCP) (transmitted absorbance) Ink is measured using a spectrophotometer. (Example of measuring device: Shimadzu UV-2450 visible-ultraviolet spectrophotometer)

[0043] In the present embodiment, the inkjet ink having edibility is described as a gray ink containing at least a first coloring matter which is an edible dye and a second coloring matter which is an edible dye and has a different color tone from the first coloring matter, that is, an ink containing the first coloring matter and the second coloring matter in advance, and is printed on a tablet or the like, but the present invention is not limited to this. For example, even if a first inkjet ink containing at least the first coloring matter and a second inkjet ink containing at least the second coloring matter are printed separately so as to be superimposed, the same effect as that of the above-mentioned embodiment can be obtained. That is, even if two types of single-color inkjet inks are printed separately so as to be superimposed, the printed color can be maintained as gray or black, and a stable color tone with little discoloration over time can be presented. Below, a modified example of this embodiment will be described.

[0044] The printed material according to the modified example of this embodiment is a printed material having a printed surface formed by inkjet printing, the printed surface being gray or black, and the printed surface being printed by overlapping a first inkjet ink containing at least a first coloring matter that is an edible dye and a second inkjet ink containing at least a second coloring matter that is an edible dye and has a different color tone from the first coloring matter, the first coloring matter being at least one of Red No. 3, Red No. 40, Red No. 104, Red No. 105, and Red No. 106. For example, the printed surface of the printed material according to the modified example of this embodiment may be printed using a second inkjet ink containing at least copper chlorophyllin sodium as shown in FIG. 6(a), and then overprinted (overprinted) using a first inkjet ink containing at least one of Red No. 3, Red No. 40, Red No. 104, Red No. 105, and Red No. 106 as shown in FIG. 6(b). The above-mentioned printed surface may be formed by printing using a first inkjet ink, and then printing using a second inkjet ink so as to overlap the first printing. In other words, the order of the inkjet inks used when forming the above-mentioned printed surface does not matter.

[0045] In addition, in the printing substrate according to the modified example of this embodiment, the second dye may be sodium copper chlorophyllin. In addition, in the printed material according to the modified example of this embodiment, the first dye may be Red No. 3. Furthermore, the printed material according to the modified example of this embodiment has a printed surface which is printed by overlapping the first inkjet ink, the second inkjet ink, and a third inkjet ink containing at least a third pigment which is an edible dye and has a different hue from the first pigment and the second pigment, and the third pigment may be Blue No. 1. For example, the printed surface of the printed material according to the modified example of this embodiment may be printed by printing using the second inkjet ink containing at least copper chlorophyllin sodium as shown in FIG. 6(a), and then overlapping (overprinting) using the first inkjet ink containing at least one of Red No. 3, Red No. 40, Red No. 104, Red No. 105, and Red No. 106 as shown in FIG. 6(b), and then overlapping (overprinting) using the third inkjet ink containing at least Blue No. 1 (not shown).

[0046] The above-mentioned printed surface may be formed by printing using a first inkjet ink, then printing using a second inkjet ink so as to overlap the first printing, and then printing using a third inkjet ink so as to overlap the first printing. The above-mentioned printed surface may be formed by printing using a third inkjet ink, then printing using a second inkjet ink so as to overlap the first printing, and then printing using a first inkjet ink so as to overlap the first printing. In other words, the order of the inkjet inks used when forming the above-mentioned printed surface does not matter. Furthermore, the printed material according to the modified example of this embodiment may have a color change over time (ΔE) of 5 or less 140 hours after the printing surface is formed. Furthermore, the printing substrate according to the modified example of this embodiment may contain at least one of glycerin, propylene glycol, water, ethanol, and isopropyl alcohol as a solvent contained in the ink. Furthermore, the printing substrate according to the modified example of this embodiment may contain at least glycerin as a solvent contained in the ink. EXAMPLES

[0047] (First Example) The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples in any way. (Inkjet ink manufacturing) First, a printing ink was prepared. The inkjet ink contains the following components: dye (coloring material), organic solvent, water (purified water), leveling agent, and bactericide. The preparation order was as follows: first, water and organic solvent were mixed to obtain a mixed solvent. Next, a leveling agent and bactericide were added to the mixed solvent to obtain a transparent base liquid. Finally, a coloring material was added to the transparent base liquid. In this way, the ink according to this embodiment was prepared. The various components will be specifically described below.

[0048] The leveling agent is a material that adjusts the surface tension of the ink so that the ejection drops from the inkjet head can be formed well. Specifically, the surface tension of the ink is preferably in the range of 24 mN / m to 34 mN / m. However, in consideration of the wettability of the surface layer of the tablet and the permeability to the inside, it is necessary to select a surface tension value that is as small as possible, that is, a surface tension value that has good wettability. Therefore, in this embodiment, the ink was prepared so that the surface tension is 24 mN / m to 28 mN / m. Note that the smaller the surface tension value, the better it is. For example, if the surface tension value is less than 24 mN / m, the ink will not form droplets, and ejection defects such as mist defects and splash phenomenon (ejection ball breakage) may occur. In this embodiment, ion-exchanged water was used as the water (purified water) constituting the ink, and at least one of glycerin, propylene glycol, and ethanol was used as the organic solvent.

[0049] Ethylparaben was added as a disinfectant to the mixed solvent of water and organic solvent described above, followed by glycerin fatty acid ester (product name: "A-121E", manufactured by Taiyo Kagaku Co., Ltd.) as a leveling agent, and the mixture was stirred for about an hour to obtain a transparent base liquid. Coloring materials were added to the above-mentioned transparent base liquid in different ratios to obtain inks of Examples 1 to 22 and Comparative Examples 1 and 2. The composition of each ink is shown in Table 1. In addition, a "blank" shown in Table 1 means that the corresponding coloring matter was not added. The color tone of the inks of Examples 1 to 16, 20 to 22 and Comparative Examples 1 and 2 is gray (black). The color tone of the ink of Example 17 is blue-green, the color tone of the ink of Example 18 is red, and the color tone of the ink of Example 19 is purple. Here, "blue-green" is a color tone expressed in the L*a*b* color system measured under the conditions of a viewing angle of 2° and a light source of D50. L* 30~90 a* -80~0 b* -50~0 This refers to a color tone that falls within the range of "gray" and "black" and does not fall within the range of "gray" and "black" mentioned above.

[0050] In addition, "red" is a color tone expressed in the L*a*b* color system measured under the conditions of a viewing angle of 2 degrees and a light source of D50. L* 30~90 a* +15~+100 b* -10~+15 This refers to a color tone that falls within the range of "gray" and "black" and does not fall within the range of "gray" and "black" mentioned above.

[0051] In addition, "purple" is a color tone expressed in the L*a*b* color system measured under the conditions of a viewing angle of 2 degrees and a light source of D50. L* 30~90 a* 0~+80 b* -50~-10 This refers to a color tone that falls within the range of "gray," "black," "blue-green," or "red" mentioned above.

[0052] [Table 1]

[0053] The inks of Examples 1 to 22 and Comparative Examples 1 and 2 were each passed through a membrane filter to remove solid foreign matter from the liquid. Specifically, each ink was passed through a membrane filter (cellulose acetate membrane) with a diameter of 5.0 μm once, and then through a membrane filter (cellulose acetate membrane) with a diameter of 0.8 μm once to obtain purified inks.

[0054] (printing) Using the above-mentioned refined ink, a circular solid image (diameter 4.0 mm) was printed on test tablets A to D having a surface whiteness of 70 degrees or more by an inkjet printer equipped with a bending mode piezoelectric inkjet head. As a result, plain tablets and film-coated tablets printed with each of the inks of Examples 1 to 22 and Comparative Examples 1 and 2 were obtained, respectively. The ingredients of the test tablets A to D are as follows: Test tablet A Tablet type: plain tablet Ingredients: Lactose (Tabletose 80, Maigret) 80%, Cellulose 20% Test tablet B Tablet type: sustained release tablets Ingredients: Lactose (Tabletose 80, Maigret) 50%, Glyceryl Behenate 15%, Cellulose 35% Test tablet C Tablet type: White film-coated tablets Base ingredients: Lactose (Tabuletose 80, manufactured by Megret) 80%, cellulose 20% Surface coating ingredients: 70% hypromellose, 20% titanium dioxide, 10% talc Test tablet D Tablet type: Clear film-coated tablets Base ingredients: Lactose (Tabuletose 80, manufactured by Megret) 75%, Cellulose 25% Surface coating ingredient: 100% hypromellose

[0055] (Measurement of ΔE discoloration over time) <How to store test tablets after printing> The printed test tablets were each sealed in a light-shielding aluminum pouch and stored in a room at room temperature of 25°C. The printed test tablets were taken out only when measuring the color change over time ΔE (24, 72, and 140 hours after printing), and were immediately returned to the light-shielding aluminum pouch (within 1 minute) after the measurement. The reason for selecting "after 140 hours" when measuring the color change over time ΔE in this example is briefly explained below. Discoloration over time occurs when the dye penetrates into the inside of the tablet over time, but it was confirmed that the change in color (tone) saturates between 100 and 140 hours after printing for all of the inks in Examples 1 to 22 and Comparative Examples 1 and 2. Therefore, we decided to measure the final discoloration over time ΔE at the point 140 hours after printing.

[0056] <Measurement method and measuring device> A circular solid image (diameter 4.0 mm) was printed on the test tablet using each of the inks of Examples 1 to 22 and Comparative Examples 1 to 2. Next, a spectrodensitometer "X-rite530" manufactured by X-rite was placed on the top surface of the printed solid image, and the color tone of the reflected light (L*a*b* color system) was measured. The setting conditions were a viewing angle of 2° and a light source of D50.

[0057] <Evaluation of discoloration over time> The evaluation of discoloration over time was determined based on the difference between the color tone immediately after printing and the color tone 140 hours after printing, i.e., the value of discoloration over time ΔE 140 hours after printing. Note that the smaller the value of discoloration over time ΔE, the smaller the discoloration over time. ◎: Less than 3 ○: 3 or more and less than 4 △: 4 or more but less than 5 ×:5 or more In addition, if the evaluation of the color change over time ΔE was "◎", "◯" or "△", there was no inconvenience in use and it was judged to be acceptable.

[0058] Tables 2 to 5 show the results of the color change over time ΔE in the printed areas printed on the surfaces of test tablets A to D using the inks of Examples 1 to 22 and Comparative Examples 1 and 2. Here, "initial color" in each table means the color tone immediately after printing. The values ​​in the "initial color" column are the values ​​of "L*", "a*", and "b*" measured immediately after printing. Table 2 shows the results when test tablet A was used as the tablet. Table 3 also shows the results when test tablet B was used as the tablet. Table 4 also shows the results when test tablet C was used as the tablet. Table 5 also shows the results when test tablet D was used as the tablet.

[0059] [Table 2]

[0060] [Table 3]

[0061] [Table 4]

[0062] [Table 5]

[0063] (Measuring the amount of penetration) In this example, the penetration amount of each dye used in Examples 1 to 22 and Comparative Examples 1 and 2 was also measured. The penetration amount of each dye used in Examples 1 to 22 and Comparative Examples 1 and 2 will be briefly described below. First, an inkjet ink containing only one type of dye used in Examples 1 to 22 and Comparative Examples 1 to 2, i.e., a monochromatic inkjet ink, was produced. Next, the test tablet A that had been printed using the inkjet ink and then left for 140 hours was embedded in paraffin and cut out using a microtome so that the cross section could be seen. Next, the test tablet A was observed at a magnification of 2000 times using an optical microscope equipped with a camera, and a cross-sectional image of the test tablet A was taken.

[0064] Finally, in the photographed cross-sectional image, the distance from the surface of test tablet A to the bottom end of the ink-permeated portion (the position farthest from the surface of the test tablet) was measured. This measurement was performed on 10 samples and averaged to determine the permeation amount of each dye used in Examples 1 to 22 and Comparative Examples 1 and 2. Table 6 shows the thus obtained penetration amounts of each dye used in Examples 1 to 22 and Comparative Examples 1 and 2. In addition, the "penetration speed" of each dye used in Examples 1 to 22 and Comparative Examples 1 and 2 can also be calculated by dividing the distance (penetration amount) measured by the above method by the elapsed time after printing (140 hours).

[0065] [Table 6]

[0066] As is clear from the results in Table 6, the penetration amounts (penetration rates) of Red No. 3, Red No. 40, Red No. 104, Red No. 105, Red No. 106 and Blue No. 1 are in the range of 0.5 to 1.7 times the penetration amount (penetration rate) of sodium copper chlorophyllin. In addition, the penetration amount (penetration rate) of Red No. 102 is 2.8 times that of sodium copper chlorophyllin.

[0067] As is clear from the results in Tables 2 to 6, when the gray ink contains at least a first dye and a second dye, and the dye contained in the gray ink with the highest content is the second dye, if the ratio of the penetration rate of the first dye into the tablet, which is the printing target, to the penetration rate of the second dye into the tablet, which is the printing target (penetration rate of the first dye / penetration rate of the second dye) is within the range of 0.5 to 1.7, discoloration over time can be reduced, as in the case of printing on the surface of a film-coated tablet, which is a printing target with relatively low ink permeability, even when printing is performed on the surface of a plain tablet, which is a printing target with relatively high ink permeability.

[0068] Furthermore, even if the ink is of a color tone other than gray (black), as long as it contains at least a first dye and a second dye, and the dye contained in the ink with the highest content is the second dye, if the ratio of the penetration rate of the first dye into the tablet, which is the printing target, to the penetration rate of the second dye into the tablet, which is the printing target (penetration rate of the first dye / penetration rate of the second dye) is within the range of 0.5 to 1.7, discoloration over time can be reduced even when the ink is printed on the surface of a plain tablet, which is a printing target with relatively high ink permeability, as in the case of printing on the surface of a film-coated tablet, which is a printing target with relatively low ink permeability.

[0069] Furthermore, when the gray ink contains at least a first dye and a second dye, and the first dye is at least one of Red No. 3, Red No. 40, Red No. 104, Red No. 105, and Red No. 106, even when printing on the surface of a plain tablet, which is a printing target with relatively high ink permeability, discoloration over time can be reduced, just as when printing on the surface of a film-coated tablet, which is a printing target with relatively low ink permeability. Furthermore, even if the ink is of a color tone other than gray (black), as long as it contains at least a first dye and a second dye, and the first dye is at least one of Red No. 3, Red No. 40, Red No. 104, Red No. 105, and Red No. 106, discoloration over time can be reduced even when printed on the surface of a plain tablet, which is a printing target with relatively high ink permeability, as in the case of printing on the surface of a film-coated tablet, which is a printing target with relatively low ink permeability.

[0070] (Second Example) The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples in any way. (Inkjet ink manufacturing) First, the printing ink was prepared. The inkjet ink contains the following components: dye (coloring material), organic solvent, water (purified water), leveling agent, and bactericide. The preparation order was as follows: first, water and organic solvent were mixed to obtain a mixed solvent. Next, a leveling agent and bactericide were added to the mixed solvent to obtain a transparent base liquid. Finally, a coloring material was added to the transparent base liquid. In this way, the ink according to this embodiment was prepared. Note that the organic solvent, water (purified water), leveling agent, and bactericide components were the same as those described in the first embodiment. Therefore, in this embodiment, the description of the organic solvent, water (purified water), leveling agent, and bactericide components will be omitted.

[0071] Ethylparaben was added as a disinfectant to the mixed solvent of water and organic solvent described above, followed by glycerin fatty acid ester (product name: "A-121E", manufactured by Taiyo Kagaku Co., Ltd.) as a leveling agent, and the mixture was stirred for about an hour to obtain a transparent base liquid. A coloring material was added to the above-mentioned transparent base liquid to obtain inks of Examples 23 to 28 and Comparative Example 3. The composition of each ink is shown in Table 7. Note that a "blank" in Table 7 means that the corresponding coloring matter was not added.

[0072] [Table 7]

[0073] Solid foreign matter in the liquid was removed by passing each of the inks of the above-mentioned Examples 23 to 28 and Comparative Example 3 through a membrane filter. Specifically, the ink was passed once through a membrane filter (cellulose acetate membrane) with a diameter of 5.0 μm, and then once through a membrane filter (cellulose acetate membrane) with a diameter of 0.8 μm to obtain purified inks.

[0074] (printing) Using the refined ink, so-called "overprinting" was performed using each of the inks listed in Table 8 in an inkjet printer equipped with three bending mode piezoelectric inkjet heads. The printer used in this embodiment has head A, head B, and head C arranged in parallel, and the table on which the heads are placed moves so that multiple prints (multiple prints) can be made on the same substrate. Each head was filled with each ink in the combination shown in Table 8, and printing was performed at 600 dpi with a uniform discharge amount of 12 pL from each head. A circular solid image (diameter 4.0 mm) was printed on the test tablet A. As a result, plain tablets printed with each ink of Examples 23 to 28 and Comparative Example 3 were obtained. The ingredients of the test tablet A are as explained in the first embodiment.

[0075] [Table 8]

[0076] (Measurement of ΔE discoloration over time) <How to store test tablets after printing> The printed test tablets were each sealed in a light-shielding aluminum pouch and stored at room temperature of 25°C. The printed test tablets were taken out only when measuring the color change over time ΔE (24, 72, and 140 hours after printing), and were immediately (within 1 minute) returned to the light-shielding aluminum pouch after the measurement.

[0077] <Evaluation of discoloration over time> The evaluation of discoloration over time was determined based on the difference between the color tone immediately after printing and the color tone 140 hours after printing, i.e., the value of discoloration over time ΔE 140 hours after printing. Note that the smaller the value of discoloration over time ΔE, the smaller the discoloration over time. ◎: Less than 3 ○: 3 or more and less than 4 △: 4 or more but less than 5 ×:5 or more In addition, if the evaluation of the color change over time ΔE was "◎", "◯" or "△", there was no inconvenience in use and it was judged to be acceptable. As described above, even when the single-color ink described in this embodiment is applied (overprinted) onto the same substrate, discoloration over time can be reduced, just as in the case of using ink formed by mixing single-color inks (just like the first embodiment). [Explanation of symbols]

[0078] 1: Tablet base material 1S: Tablet substrate surface 3: Print image 4R: Red pigment 4G: Green pigment 4B: Blue pigment 5: Printed plain tablet 7: Film coating layer 9: Film-coated tablet printout 11: Plain tablet print image (solid image) 13: Film-coated tablet print image (2D barcode)

Claims

1. A gray or black inkjet ink, comprising: The food coloring material contains only a first coloring material which is a food dye, a second coloring material which is a food dye and has a different color tone from the first coloring material, and a third coloring material which is a food dye and has a different color tone from the first coloring material and the second coloring material, the first dye is at least one of Red No. 3, Red No. 40, Red No. 104, Red No. 105, and Red No. 106; the second dye is sodium copper chlorophyllin; the third dye is Blue No. 1; The content of the second dye is within a range of 0.3% by mass to 14.0% by mass with respect to the total mass of the ink.

2. 2. The ink-jet ink according to claim 1, wherein the content of the third dye is equal to or less than the content of the first dye.

3. The dye contains at least one selected from the group of food dyes consisting of Red No. 3, Red No. 40, Red No. 104, Red No. 105, and Red No. 106, sodium copper chlorophyllin, and Blue No. 1, The content of the sodium copper chlorophyllin in the ink-jet ink is in the range of 0.3% by mass to 14.0% by mass based on the total mass of the ink.

4. 4. The ink-jet ink according to claim 1, wherein a total content of the food dye is within a range of 1% by mass to 15% by mass of the entire ink.

5. 3. The ink-jet ink according to claim 1, wherein a total content of the first coloring matter is within a range of 3.0% by mass to 7.0% by mass with respect to the total mass of the ink.

6. 6. The ink-jet ink according to claim 1, further comprising at least one of glycerin, propylene glycol, water, ethanol, and isopropyl alcohol as a solvent for the ink.

7. 6. The ink-jet ink according to claim 1, wherein the ink contains, as a solvent, glycerin, propylene glycol, water, and ethanol, but does not contain isopropyl alcohol.

8. A printing substrate comprising a printed portion printed with the ink-jet ink according to any one of claims 1 to 7.

9. A solid tablet, characterized in that the color change over time (ΔE) 140 hours after the formation of the printed portion on the printed material according to claim 8 is 5 or less.

10. 9. The printing substrate according to claim 8, which is a solid tablet.

Images