Method for printing edible inkjet ink, method for producing tablet, discharge device, and drive waveform generation device

Abstract

The present invention provides a method for printing an edible inkjet ink and the like, which can reduce the reduction range of initial discharge performance and intermittent restart performance even when the addition amount of an alcohol solvent in the edible inkjet ink is increased and the dryness is improved. The method for printing an image with an inkjet ink according to an embodiment of the present invention is a method for printing a printed image with an inkjet ink using a device for discharging an inkjet ink containing an alcohol in a range of 30% or more and 60% or less, the device for discharging the inkjet ink comprising: an ink discharge head for discharging the inkjet ink; and a drive waveform generation device that generates a drive waveform to be applied to the pressure generation element of the ink discharge head, the drive waveform being a waveform that, when the inkjet ink is discharged, decreases from a reference potential V0 to a potential V2, then increases to a potential V3 higher than the reference potential V0, and restores to the reference potential V0.

Description

Technical Field

[0001] The present invention relates to a printing method for edible inkjet ink, a method for manufacturing tablets, a discharging device, and a driving waveform generating device. Background Art

[0002] Regarding ink for inkjet printing (hereinafter also simply referred to as "inkjet ink"), there is ink having edibility. Further, as a technique related to edible inkjet ink, for example, there is a technique described in Patent Document 1.

[0003] Regarding edible inkjet ink, for example, there is ink containing an alcohol solvent as a drying solvent for improving the drying property of the ink. Further, regarding edible inkjet ink, for example, there is ink containing vegetable charcoal black pigment as a black pigment, tar pigment as an edible dye, and the like.

[0004] Patent Document 1: Japanese Patent Application Laid-Open No. 2006-169301 Summary of the Invention

[0005] Regarding inkjet ink containing an edible pigment (hereinafter also simply referred to as "inkjet ink"), sometimes the performance of drying the printed ink, that is, so-called drying property, is required. As a method for improving this performance, for example, there is a method of adding an alcohol solvent having a higher drying property as a drying solvent to the inkjet ink and increasing the addition amount of the alcohol solvent. However, in this method, sometimes the drying of the nozzle liquid surface is promoted, and the initial discharge property and the intermittent restart property (hereinafter also referred to as printing stability) deteriorate. In particular, regarding inkjet ink in which the content (concentration) of the alcohol solvent is 30% by mass or more of the entire ink, there is a significant tendency for the above-described initial discharge property and intermittent restart property to deteriorate. Here, the "initial discharge property" refers to the property of being able to discharge the ink without non-printing portions caused by non-discharge of the ink immediately after the start of printing. Further, the "intermittent restart property" refers to the property of being able to discharge the ink without an increase in non-printing portions from the initial discharge when printing is performed using the above-described inkjet head after the ink is placed in the inkjet head without being rinsed for a predetermined time. In addition, the above-described intermittent restart property is sometimes also referred to as printing restart property or printing intermittent restart property.

[0006] On the other hand, if printing is performed using inkjet ink with a reduced addition amount of the alcohol solvent, the above-described intermittent restart property is improved, but for example, there is a tendency for the drying property of the ink to decrease. Therefore, if text or the like is printed on tablets having a low drying property such as film-coated tablets (FC tablets) or sugar-coated tablets using inkjet ink with a reduced addition amount of the alcohol solvent, there is a possibility that the ink is transferred to printing machine components or other tablets due to the low drying property of the ink.

[0007] The present invention has been made in view of the above circumstances, and an object thereof is to provide a printing method of an edible inkjet ink capable of reducing the decrease in initial ejection performance and intermittent restart performance even when the addition amount of an alcohol solvent in the edible inkjet ink is increased to improve the drying property, a tablet having a printed image printed by using the printing method, an ink ejection device for the printing method of the edible inkjet ink, and a drive waveform generation device for the ink ejection device.

[0008] A printing method of an edible inkjet ink according to one aspect of the present invention is a method of printing a printed image with the edible inkjet ink by using a device that ejects an edible inkjet ink containing an alcohol in a range of 30% or more and 60% or less. The device that ejects the edible inkjet ink includes: an ink ejection head that ejects the edible inkjet ink; and a drive waveform generation device that generates a drive waveform applied to a pressure generating element of the ink ejection head. The drive waveform is a waveform that decreases from a reference potential V0 to a potential V2 lower than the reference potential V0 when the inkjet ink is ejected, then increases to a potential V3 higher than the reference potential V0, and then returns to the reference potential V0 again.

[0009] A method for manufacturing a tablet according to one aspect of the present invention is a method for manufacturing a tablet having a printed image printed with an edible inkjet ink by using a device that ejects an edible inkjet ink containing an alcohol in a range of 30% or more and 60% or less. The device that ejects the edible inkjet ink includes: an ink ejection head that ejects the edible inkjet ink; and a drive waveform generation device that generates a drive waveform applied to a pressure generating element of the ink ejection head. The drive waveform is a waveform that decreases from a reference potential V0 to a potential V2 lower than the reference potential V0 when the inkjet ink is ejected, then increases to a potential V3 higher than the reference potential V0, and then returns to the reference potential V0 again.

[0010] An ejection device according to one aspect of the present invention is a device that ejects an edible inkjet ink containing an alcohol in a range of 30% or more and 60% or less, and includes: an ink ejection head that ejects the edible inkjet ink; and a drive waveform generation device that generates a drive waveform applied to a pressure generating element of the ink ejection head. The drive waveform is a waveform that decreases from a reference potential V0 to a potential V2 lower than the reference potential V0 when the inkjet ink is ejected, then increases to a potential V3 higher than the reference potential V0, and then returns to the reference potential V0 again.

[0011] In addition, a driving waveform generation device according to one aspect of the present invention is a device that generates a driving waveform applied to a pressure generating element of a liquid discharge head that discharges an edible inkjet ink containing an alcohol in a range of greater than or equal to 30% and less than or equal to 60%. The driving waveform is a waveform that, when the inkjet ink is discharged, decreases from a reference potential V0 to a potential V2 lower than the reference potential V0, then increases to a potential V3 higher than the reference potential V0, and then returns to the reference potential V0 again.

[0012] In addition, a printing method of an edible inkjet ink according to one aspect of the present invention is a method of printing a printed image with the edible inkjet ink using a device that discharges an edible inkjet ink containing an alcohol in a range of greater than or equal to 30% and less than or equal to 60%. The device that discharges the edible inkjet ink includes: an ink discharge head that discharges the edible inkjet ink; and a driving waveform generation device that generates a driving waveform applied to a pressure generating element of the ink discharge head. The driving waveform continuously includes, in time series: a first waveform driven when the inkjet ink is not discharged; and a second waveform driven when the inkjet ink is discharged. The first waveform is a waveform that, after decreasing from a reference potential V0 to a potential V1 lower than the reference potential V0, returns to the reference potential V0 again. The second waveform is a waveform that, after decreasing from a reference potential V0 to a potential V2 lower than the reference potential V0, increases to a potential V3 higher than the reference potential V0, and then returns to the reference potential V0 again. The potential V2 is lower than the potential V1.

[0013] In addition, a manufacturing method of a tablet according to one aspect of the present invention is a method of manufacturing a tablet having a printed image printed with the edible inkjet ink using a device that discharges an edible inkjet ink containing an alcohol in a range of greater than or equal to 30% and less than or equal to 60%. The device that discharges the edible inkjet ink includes: an ink discharge head that discharges the edible inkjet ink; and a driving waveform generation device that generates a driving waveform applied to a pressure generating element of the ink discharge head. The driving waveform continuously includes, in time series: a first waveform driven when the inkjet ink is not discharged; and a second waveform driven when the inkjet ink is discharged. The first waveform is a waveform that, after decreasing from a reference potential V0 to a potential V1 lower than the reference potential V0, returns to the reference potential V0 again. The second waveform is a waveform that, after decreasing from a reference potential V0 to a potential V2 lower than the reference potential V0, increases to a potential V3 higher than the reference potential V0, and then returns to the reference potential V0 again. The potential V2 is lower than the potential V1.

[0014] In addition, a discharging device according to one embodiment of the present invention is a device that discharges an edible inkjet ink containing an alcohol in a range of 30% or more and 60% or less, and includes: an ink discharging head that discharges the edible inkjet ink; and a driving waveform generating device that generates a driving waveform applied to a pressure generating element of the ink discharging head. The driving waveform continuously includes, in time series: a first waveform driven when the inkjet ink is not discharged; and a second waveform driven when the inkjet ink is discharged. The first waveform is a waveform that, after dropping from a reference potential V0 to a potential V1 lower than the reference potential V0, returns to the reference potential V0 again. The second waveform is a waveform that, after dropping from the reference potential V0 to a potential V2 lower than the reference potential V0, rises to a potential V3 higher than the reference potential V0 and then returns to the reference potential V0 again. The potential V2 is lower than the potential V1.

[0015] In addition, a driving waveform generating device according to one embodiment of the present invention is a device that generates a driving waveform applied to a pressure generating element of a liquid discharging head that discharges an edible inkjet ink containing an alcohol in a range of 30% or more and 60% or less. The driving waveform continuously includes, in time series: a first waveform driven when the inkjet ink is not discharged; and a second waveform driven when the inkjet ink is discharged. The first waveform is a waveform that, after dropping from a reference potential V0 to a potential V1 lower than the reference potential V0, returns to the reference potential V0 again. The second waveform is as follows

[0016] That is, after dropping from the reference potential V0 to a potential V2 lower than the reference potential V0, it rises to a potential V3 higher than the reference potential V0 and then returns to the reference potential V0 again. The potential V2 is lower than the potential V1.

[0017] Effects of the Invention

[0018] If it is a printing method of an edible inkjet ink, a discharging device for the printing method, and a driving waveform generating device for the discharging device according to one embodiment of the present invention, then even when the addition amount of the alcohol solvent in the edible inkjet ink is increased to improve the drying property, it is possible to reduce the decrease in initial discharge property and intermittent restart property.

[0019] In addition, if it is a method for manufacturing a tablet according to one embodiment of the present invention, then even when the addition amount of the alcohol solvent in the edible inkjet ink is increased to improve the drying property, it is possible to reduce the decrease in initial discharge property and intermittent restart property. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a schematic cross-sectional view schematically showing the mechanical structure of the print head according to this embodiment.

[0021] Figure 2 is a schematic diagram schematically showing the drive signal according to this embodiment.

[0022] Figure 3 is a schematic diagram schematically showing the operation of the meniscus when the first waveform according to this embodiment is applied to the piezoelectric vibrator alone.

[0023] Figure 4 is a schematic diagram schematically showing the operation of the meniscus when the second waveform according to this embodiment is applied to the piezoelectric vibrator alone.

[0024] Figure 5 is a top view and a cross-sectional view showing a first structural example of the medical tablet according to this embodiment.

[0025] Figure 6 is a top view and a cross-sectional view showing a second structural example of the medical tablet according to this embodiment.

[0026] Figure 7 is a schematic diagram schematically showing the drive waveform according to this embodiment. Detailed Embodiment

[0027] The edible inkjet ink according to the embodiment of the present invention relates to, for example, an edible inkjet ink used when printing characters, images, etc. on the surface of a medical tablet by an inkjet printing method. Hereinafter, the edible inkjet ink according to the embodiment of the present invention and the structure of a tablet having a printed portion printed with the inkjet ink will be described in detail. In addition, the printing method of the edible inkjet ink according to the embodiment of the present invention, the discharging device for the printing method, and the drive waveform generating device for the discharging device will be described in detail.

[0028] [Composition of Inkjet Ink]

[0029] The inkjet ink according to this embodiment contains at least water, an alcohol solvent, and an edible pigment.

[0030] If the alcohol solvent according to this embodiment is an alcohol solvent with a relatively high drying property, its type is arbitrary. For example, if it contains at least one of ethanol, isopropyl alcohol (IPA), and n-propyl alcohol (NPA), it is preferred.

[0031] In addition, the content (concentration) of the alcohol solvent is preferably in the range of greater than or equal to 30% by mass and less than or equal to 60% by mass with respect to the entire inkjet ink, more preferably in the range of greater than or equal to 30% by mass and less than or equal to 50% by mass, and further preferably in the range of greater than or equal to 30% by mass and less than or equal to 45% by mass. In addition, regarding the inkjet ink related to the prior art, from the viewpoint of preventing excessive drying of the ink, the content of the alcohol solvent is mostly set to less than 30% by mass with respect to the entire inkjet ink. Therefore, compared with the inkjet ink related to the prior art, the inkjet ink related to this embodiment can be called an ink with a relatively high content of the alcohol solvent.

[0032] In addition, regarding the inkjet ink related to this embodiment, it is preferable that the viscosity of the ink at a temperature of 25°C is less than or equal to 5.0 mPa·s, more preferably less than or equal to 4.5 mPa·s, and further preferably less than or equal to 4.0 mPa·s. In addition, regarding the inkjet ink related to this embodiment, the lower limit value of the viscosity of the ink at a temperature of 25°C is not particularly limited, but if it is greater than or equal to 2.3 mPa·s, it is easy to handle the ink.

[0033] In addition, regarding the inkjet ink related to this embodiment, it is preferable that the surface tension of the ink at a temperature of 25°C is in the range of greater than or equal to 23 mN / m and less than or equal to 34 mN / m, and more preferably in the range of greater than or equal to 24 mN / m and less than or equal to 34 mN / m.

[0034] Next, each component contained in the inkjet ink related to this embodiment will be described in detail.

[0035] (Edible pigment)

[0036] Examples of the edible pigment contained in the inkjet ink related to this embodiment include edible pigments and edible dyes. The edible pigment related to this embodiment is not particularly limited. For example, it is vegetable charcoal black pigment such as medicinal charcoal, binchotan charcoal or bamboo charcoal, carbon that can be orally ingested, or industrial carbon black derived from petroleum. Among the above carbons, carbon that can be orally ingested is also particularly preferred. In the case of using carbon that can be orally ingested, the inkjet ink related to this embodiment can be used for direct printing on the surface of tablets, direct printing on foods, and packaging in direct contact with pharmaceuticals and foods.

[0037] In addition, the edible dye related to this embodiment is not particularly limited. For example, it is a known synthetic food colorant or natural food colorant.

[0038] As synthetic food colors, examples include tar colors, natural pigment derivatives, natural synthetic pigments, etc. As tar colors, examples include 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. 1, Food Blue No. 2, Food Green No. 3, 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, Food Blue No. 2 Aluminum Lake, etc. As natural pigment derivatives, examples include potassium norbixin, etc. As natural synthetic pigments, examples include β-carotene, riboflavin, etc.

[0039] In addition, as natural food colors, examples include anthocyanin pigments, carotenoid pigments, quinone pigments, flavonoid pigments, betaine pigments, monascus pigments, pigments derived from other natural substances. As anthocyanin pigments, examples include beetroot pigment, red cabbage pigment, red rice pigment, elderberry pigment, blueberry pigment, currant pigment, cranberry pigment, salmonberry pigment, perilla pigment, sweet blueberry pigment, strawberry pigment, deep sweet cherry pigment, cherry pigment, hibiscus pigment, whiteberry pigment, grape juice pigment, grape peel pigment, blackcurrant pigment, blackberry pigment, blueberry pigment, plum pigment, bilberry 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. As carotenoid pigments, examples include annatto pigment, gardenia yellow pigment, and other carotenoid pigments. As quinone pigments, examples include cochineal pigment, gromwell pigment, shellac pigment, and other quinone pigments. As flavonoid pigments, examples include safflower yellow pigment, sorghum pigment, onion pigment, and other flavonoid pigments. As betaine pigments, examples include betanin. As monascus pigments, examples include monascus rice pigment, monascus yellow pigment. As pigments derived from other natural substances, examples include curcumin, morin, gardenia red pigment, spirulina blue pigment, etc.

[0040] The content (concentration) of the edible pigment is preferably, for example, in the range of greater than or equal to 0.5% by mass and less than or equal to 6% by mass, more preferably in the range of greater than or equal to 1% by mass and less than or equal to 5% by mass, relative to the whole inkjet ink. If it is such a composition, good visual confirmability can be given to the printed image, and high printing stability can be given.

[0041] On the contrary, if the content of the edible pigment is less than 0.5% by mass, there is a tendency for the overall printing color to become thinner and the visual confirmation of the printed image to deteriorate. In addition, if the content exceeds 6% by mass, the edible pigment in the inkjet ink precipitates or deposits as a solid due to the deterioration of the dissolution stability of the edible pigment, which causes clogging of the nozzles of the inkjet head during printing, showing a tendency for intermittent restart performance to decline.

[0042] (Solvent)

[0043] The inkjet ink according to this embodiment contains a solvent for dissolving or dispersing the aforementioned edible pigment. Moreover, this solvent contains water and an alcohol solvent as a drying solvent (drying property solvent). Hereinafter, this water and the drying solvent will be described.

[0044] The water contained in the inkjet ink according to this embodiment is, for example, purified water. The proportion of water contained in the inkjet ink according to this embodiment is preferably greater than or equal to 30% by mass of the entire inkjet ink, for example.

[0045] The drying solvent contained in the inkjet ink according to this embodiment is an alcohol solvent, for example, an alcohol solvent containing at least one of ethanol, isopropyl alcohol (IPA), and n-propyl alcohol (NPA). The concentration of this alcohol solvent is less than or equal to 60% by mass with respect to the entire inkjet ink. In addition, if the concentration of the alcohol solvent exceeds 60% by mass with respect to the entire inkjet ink, the drying property of the ink is excessive, showing a tendency for printing stability to decline. In addition, the lower limit value of the concentration of the alcohol solvent is greater than or equal to 30% by mass with respect to the entire inkjet ink. If it is within the above numerical range, excellent drying property can be imparted to the inkjet ink.

[0046] (Dispersant)

[0047] In addition to the aforementioned edible pigment and solvent, the inkjet ink according to this embodiment may contain a dispersant. The dispersant that can be added to the inkjet ink according to this embodiment only needs to be able to improve the dispersibility of the aforementioned edible pigment (especially edible pigments such as carbon) and be edible. For example, it is a sucrose fatty acid ester having an HLB (Hydrophilic-Lipophilic Balance) value in the range of greater than or equal to 11 and less than or equal to 20. The content of the sucrose fatty acid ester is preferably in the range of greater than or equal to 60% by mass and less than or equal to 180% by mass with respect to the aforementioned edible pigment. In addition, if the content of the sucrose fatty acid ester as a dispersant is less than 60% by mass with respect to the aforementioned edible pigment, there is a tendency for the dispersion stability of the edible pigment to decline. In addition, if the content of the sucrose fatty acid ester as a dispersant exceeds 180% by mass with respect to the aforementioned edible pigment, there is a tendency for the drying property to decline.

[0048] In addition, the sucrose fatty acid ester contained in the inkjet ink according to the present embodiment preferably has an HLB value in the range of greater than or equal to 11 and less than or equal to 20. If such a configuration is adopted, sufficient dryness can be imparted to the inkjet ink, and the decrease in printing stability can be reduced. In addition, if the HLB value of the sucrose fatty acid ester is less than 11, there is a tendency for the printing stability to decrease. Further, the upper limit value of the HLB value of the sucrose fatty acid ester is 20.

[0049] (Humectant)

[0050] In addition to the aforementioned edible pigment, solvent, and dispersant, the inkjet ink according to the present embodiment may further contain a humectant, and its content may be in the range of greater than or equal to 0.001% by mass and less than or equal to 10% by mass with respect to the entire inkjet ink. If such a configuration is adopted, sufficient dryness can also be imparted in terms of use for inkjet ink, and the decrease in printing stability can be further reduced. In addition, if the content of the humectant is less than 0.001% by mass with respect to the entire inkjet ink, there is a tendency for the printing stability to decrease. Further, if the content of the humectant exceeds 10% by mass with respect to the entire inkjet ink, there is a tendency for it to be difficult to impart sufficient dryness to the inkjet ink.

[0051] In addition, it is more preferable that the content of the humectant in the inkjet ink according to the present embodiment is less than or equal to 3% by mass with respect to the entire inkjet ink. If such a configuration is adopted, sufficient dryness can be imparted to the inkjet ink, and the decrease in printing stability can be further reduced.

[0052] The humectant that can be added to the inkjet ink according to the present embodiment may be any substance that is usually added to inkjet ink, and can be used without particular limitation. In addition, if the humectant according to the present embodiment has a high boiling point, the effect is better. Here, "high boiling point" means, for example, greater than or equal to 140 °C.

[0053] Specific examples of the humectant according to the present embodiment include, for example, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, pentylene glycol, 1,3 - propanediol, 2 - butene - 1,4 - diol, 2 - ethyl - 1,3 - hexanediol, 2 - methyl - 2,4 - pentanediol, tripropylene glycol, polyethylene glycol with a number - average molecular weight less than or equal to 2000, 1,3 - propanediol, 1,2 - propanediol, isobutylene glycol, glycerol, erythritol, pentaerythritol, 2 - pyrrolidone, N - methyl - 2 - pyrrolidone, and N - ethyl - 2 - pyrrolidone. Among the above humectants, a humectant containing at least one of propylene glycol and glycerol is particularly preferred. If such a configuration is adopted, sufficient dryness can be imparted to the inkjet ink, and the decrease in printing stability can be further reduced.

[0054] In addition, for example, one type of wetting agent related to this embodiment can be used alone, or two or more types can be used in combination.

[0055] (Binder)

[0056] In addition to the aforementioned edible pigments, solvents, dispersants, and wetting agents, the inkjet ink related to this embodiment may contain a binder (adhesive). The binder that can be added to the inkjet ink related to this embodiment is not particularly limited as long as it is a substance usually added to inkjet ink, and for example, it contains polysaccharides. In addition, the polysaccharides contained in the binder related to this embodiment preferably have a weight average molecular weight in the range of 1,000 or more and 10,000 or less. If it has such a composition, sufficient dryness can be imparted to the inkjet ink, and the decrease in printing stability can be further reduced. In addition, if the weight average molecular weight of the polysaccharide as the binder is less than 1,000, there is a tendency that it is difficult to impart sufficient dryness to the inkjet ink. In addition, if the weight average molecular weight of the polysaccharide as the binder exceeds 10,000, there is a tendency for the printing stability to decrease.

[0057] In addition, the content of the polysaccharides related to this embodiment is preferably 0.01% by mass or more and 10% by mass or less of the total mass of the inkjet ink. If the content of the binder is within the above range, the viscosity of the ink becomes a viscosity that can be appropriately used for inkjet printing.

[0058] Examples of the polysaccharides related to this embodiment include maltodextrin, erythritol, PVP (polyvinylpyrrolidone), dextran, polydextrose, trehalose, or starch substances such as corn and wheat, cellulose substances such as carboxymethyl cellulose and hydroxymethyl cellulose, sodium alginate, gum arabic, locust bean gum, tragacanth gum, guar gum, and tamarind seeds.

[0059] In addition, as the adhesive involved in the present embodiment, for example, it may contain disaccharides with a solubility of less than or equal to 39 g in 100 ml of water at 20°C. Specifically, they are lactose, cellobiose, and reduced isomaltulose. The solubility of lactose in 100 ml of water at 20°C is 16 g, the solubility of cellobiose is 14 g, and the solubility of reduced isomaltulose is 30 g. By adding the aforementioned disaccharides to the above inkjet ink, it can be solidified on the surface of a printed material (such as a tablet) containing an edible pigment (especially an edible dye). Thus, if it is an inkjet ink containing the aforementioned disaccharides, the photochromic fading of the printed image can be sufficiently suppressed, and the light resistance can be improved. In addition, the above disaccharides (lactose, cellobiose, reduced isomaltulose) used as adhesives in the present embodiment also have the function of suppressing the decomposition (photodegradation) caused by light irradiation of the inkjet ink. Therefore, the occurrence of photochromic fading itself can also be suppressed.

[0060] The mixing ratio of the above disaccharides in the inkjet ink involved in the present embodiment, that is, the total content of the above disaccharides (lactose, cellobiose, reduced isomaltulose), is preferably in the range of greater than or equal to 1% by mass and less than or equal to 20% by mass of the entire inkjet ink. If it is such a composition, the solidification effect of the inkjet ink containing the above disaccharides can be more reliably exerted, and the light resistance of the inkjet ink can be improved. In addition, relatively high printing stability can be imparted to the inkjet ink involved in the present embodiment.

[0061] On the contrary, if the mixing ratio of the above disaccharides is less than 1% by mass of the entire inkjet ink, the solidification effect of the inkjet ink can be weakened. In addition, if the mixing ratio of the above disaccharides exceeds 20% by mass of the entire inkjet ink, due to the increase in ink viscosity and the deterioration of the dissolution stability of the above disaccharides, the binder in the inkjet ink precipitates or deposits as a solid, which causes clogging of the nozzles of the inkjet head during printing and can reduce printing stability.

[0062] Furthermore, generally, sugars have the property of being difficult to dissolve in alcohols. Therefore, in the present embodiment, by making the solvent contain propylene glycol and ethanol, the solubility of the solvent with respect to the above disaccharides used as adhesives is reduced. Therefore, in the present embodiment, when a solvent containing the above alcohols (propylene glycol, ethanol) together with the above disaccharides used as adhesives is added to the inkjet ink, the solidification effect of the inkjet ink can be reliably exerted, and the edible pigment (especially an edible dye) contained in the inkjet ink can be highly concentrated and retained on the surface of the printed material (such as a tablet). Thus, for the inkjet ink, the photochromic fading of the printed image can be sufficiently suppressed, and the light resistance can be improved.

[0063] In addition, as described above, propylene glycol acts as a wetting agent, can prevent the drying of the ink in the inkjet nozzle, and can impart sufficient printing stability to the inkjet ink. In addition, ethanol has a high volatility, so it can improve the transfer resistance (drying property) of the inkjet ink.

[0064] (Leveling agent)

[0065] In addition to the above-mentioned edible pigments (especially edible dyes), solvents or internal addition resins, the inkjet ink according to the present embodiment may contain a leveling agent. The leveling agent that can be added to the inkjet ink according to the present embodiment only needs to be an edible and water-soluble surfactant. As the above leveling agent, for example, polyglycerol fatty acid esters (e.g., decaglycerol distearate Q-182S manufactured by "Taiyo Chemical Co., Ltd." (Sun Chemical Corporation), decaglycerol monolaurate Q-12S manufactured by the same company), sorbitan fatty acid esters (e.g., "Nikol Chemicals Co., Ltd." (Nikol Chemicals) NIKKOL SL-10), sucrose fatty acid esters (e.g., DK ester F-110 manufactured by "Daiichi Kogyo Seiyaku Co., Ltd." (Daiichi Kogyo Seiyaku)), polysorbates (emmazor S-120 series manufactured by "Kao Corporation") and the like can be cited.

[0066] [Printing method]

[0067] Regarding the inkjet ink according to the present embodiment, the printing method is not particularly limited, and printing can be performed using an inkjet device such as a commercially available inkjet printer. Therefore, the application range of the inkjet ink according to the present embodiment is large and very useful. For example, the inkjet ink according to the present embodiment can be obtained by printing using an inkjet device of a so-called on-demand supply method in which a piezoelectric element (piezoelectric ceramic) is used as an actuator, or can also be obtained by printing using an inkjet device of other methods.

[0068] As an on-demand supply type inkjet device, for example, the following devices can be cited: a device using a thermal inkjet method in which water vapor pressure generated by making a minute heating element become high temperature (200 - 300 °C) instantaneously is used to eject the inkjet ink; an electrostatic type device in which an actuator performs electrostatic vibration to eject the inkjet ink; a device using an ultrasonic method utilizing the cavitation phenomenon of ultrasonic waves. In addition, if the inkjet ink according to the present embodiment has a charge property, a device using a continuous jet type (continuous method) can also be used.

[0069] Next, an example of an inkjet device for ejecting the inkjet ink according to the present embodiment and printing on the surface of a printed matter (e.g., a tablet) will be described.

[0070] The inkjet device as a device for discharging inkjet ink according to this embodiment has at least: a print head (ink discharge head) that discharges inkjet ink; and a drive waveform generation device (drive signal generation circuit) that generates a drive waveform (drive signal) applied to a pressure generating element (piezoelectric oscillator) of the print head.

[0071] (Mechanical structure of the print head)

[0072] Figure 1 An example of the mechanical structure of the print head 10 is shown. The substrate unit 21 is constituted by sandwiching a flow path forming plate 24 with a nozzle plate 22 having nozzle holes 22A formed therein and a vibration plate 23 having protrusions 23A formed therein. Ink chambers 25, ink supply ports 26, and pressure generating chambers 27 are formed in the flow path forming plate 24.

[0073] A housing chamber 29 is formed in the base 28, and a piezoelectric oscillator 17 is installed in the housing chamber 29. The piezoelectric oscillator 17 is fixed via a fixed substrate 30 in such a manner that its front end abuts against the protrusion 23A of the vibration plate 23. Here, for the piezoelectric oscillator 17, for example, PZT with a longitudinal vibration transverse effect is used, which contracts when charged and expands when discharged. The charging and discharging of the piezoelectric oscillator 17 are performed via a wire 31.

[0074] In addition, the piezoelectric oscillator 17 is not limited to PZT with a longitudinal vibration transverse effect, and may also be a bending vibration type PZT. In this case, it expands when charged and contracts when discharged. Also, as an oscillator that expands and contracts according to the input drive waveform, it is not limited to the piezoelectric oscillator 17, and other oscillators such as magnetostrictive elements can be used, for example.

[0075] In this embodiment, if a waveform with a negative potential is applied to the piezoelectric oscillator 17, the piezoelectric oscillator 17 contracts and the pressure generating chamber 27 expands, the pressure in the pressure generating chamber 27 decreases, and ink flows from the ink chamber 25 into the pressure generating chamber 27. Also, in this embodiment, if a waveform with a positive potential is applied to the piezoelectric oscillator 17, the piezoelectric oscillator 17 expands and the pressure generating chamber 27 contracts, the pressure in the pressure generating chamber 27 increases, and the ink in the pressure generating chamber 27 is discharged to the outside via the nozzle holes 22A.

[0076] (Details of the drive waveform)

[0077] Next, with reference to Figure 2 each waveform (drive waveform) constituting the drive signal according to this embodiment will be described.

[0078] Figure 2 Each waveform constituting the drive signal according to this embodiment is shown. This drive signal can be generated, for example, by using a drive signal generation circuit as a known technique.

[0079] As Figure 2 shown, the drive signal involved in this embodiment has at least a first waveform and a second waveform. Here, the first waveform is used to swing the meniscus and is not used to eject ink droplets. On the other hand, the second waveform is used to eject ink droplets.

[0080] Thus, the drive signal involved in this embodiment has at least: a first waveform as a swing waveform for swinging the meniscus; and a second waveform as an ejection waveform for ejecting ink.

[0081] Next, each waveform element of the first waveform and the second waveform will be described in detail.

[0082] Regarding the first waveform, as Figure 2 shown, its voltage value starts from the reference potential V0 (P11), drops from the reference potential V0 to the lowest potential V1 at a prescribed voltage gradient θ12 (P12), and maintains the lowest potential V1 for a prescribed time (P13). Next, the voltage value of the first waveform rises again from the lowest potential V1 to the reference potential V0 at a prescribed voltage gradient θ14 (P14).

[0083] Here, it is set that the voltage gradient θ14 is greater than the voltage gradient θ12.

[0084] The voltage value of the second waveform starts from the reference potential V0 (P21) in the same manner as the first waveform, and drops to the lowest potential V2 at a prescribed voltage gradient θ22 (P22). The lowest potential V2 of this second waveform is less than (lower than) the lowest potential V1 of the first waveform. Moreover, after the voltage value of the second waveform maintains the lowest potential V2 for a prescribed time (P23), it rises to the highest potential V3 at a prescribed voltage gradient θ24 (P24).

[0085] Here, it is set that the voltage gradient θ24 is greater than the voltage gradient θ22.

[0086] Moreover, after the voltage value of the second waveform holds the highest potential V3 for a prescribed time (P25), it drops again to the reference potential V0 (P26).

[0087] Here, regarding the second waveform, it is set that the voltage gradient θ24 is greater than the voltage gradient θ26.

[0088] (Modified example of drive signal)

[0089] Next, a modified example of the drive signal involved in this embodiment will be described.

[0090] In the present embodiment, a driving signal having at least a first waveform and a second waveform has been described, but the present invention is not limited thereto. In the present embodiment, as long as the driving signal has the second waveform, for example, it may not have the first waveform. That is, in the present embodiment, if it has the second waveform for discharging ink, it may not have the swing waveform (the first waveform) for not discharging ink.

[0091] In addition, in the present embodiment, a case where the voltage gradient θ14 is set to be greater than the voltage gradient θ12 has been described, but the present invention is not limited thereto. For example, the voltage gradient θ14 may be set to be less than the voltage gradient θ12, or the voltage gradient θ12 and the voltage gradient θ14 may be set to be the same.

[0092] In addition, in the present embodiment, a case where the voltage gradient θ24 is set to be greater than the voltage gradient θ22 has been described, but the present invention is not limited thereto. For example, the voltage gradient θ24 may be set to be less than the voltage gradient θ22, or the voltage gradient θ22 and the voltage gradient θ24 may be set to be the same.

[0093] In addition, in the present embodiment, a case where the voltage gradient θ26 is set to be greater than the voltage gradient θ24 has been described, but the present invention is not limited thereto. For example, the voltage gradient θ26 may be set to be less than the voltage gradient θ24, or the voltage gradient θ24 and the voltage gradient θ26 may be set to be the same.

[0094] As long as the printing cycle is greater than or equal to 1 kHz, more preferably greater than or equal to 7 kHz. In addition, the upper limit value of the printing cycle is not particularly limited, but if it is a print head with high versatility, it is usually less than or equal to 50 kHz.

[0095] In addition, in the present embodiment, it is preferable that the potential difference between the lowest potential V1 of the first waveform and the reference potential V0 is in the range of being greater than or equal to 10% and less than or equal to 60% of the potential difference between the lowest voltage V2 of the second waveform and the reference potential V0, more preferably in the range of being greater than or equal to 15% and less than or equal to 55%, and further preferably in the range of being greater than or equal to 20% and less than or equal to 50%.

[0096] In addition, in the present embodiment, it is preferable that the potential difference between the highest voltage V3 of the second waveform and the reference potential V0 is in the range of being greater than or equal to 5% and less than or equal to 50% of the potential difference between the lowest voltage V2 of the second waveform and the reference potential V0, more preferably in the range of being greater than or equal to 10% and less than or equal to 45%, and further preferably in the range of being greater than or equal to 15% and less than or equal to 40%.

[0097] (Discharge state of ink droplets)

[0098] Next, refer to Figure 3 and Figure 4 to outline the ejection state of the ink droplets near the nozzle hole 22A for each waveform based solely on the drive signal.

[0099] First, Figure 3 is an explanatory diagram showing the ejection state of the ink droplets based on the first waveform.

[0100] In the state of P11 at the reference potential V0, the meniscus 40 is in a position slightly retracted from the ejection surface of the nozzle hole 22A. Next, in the state of P12 when the potential drops from the reference potential V0 to the lowest potential V1, the piezoelectric vibrator 17 contracts and the pressure generating chamber 27 expands, and the meniscus 40 is drawn into the nozzle hole 22A. At this time, the pressure generating chamber 27 expands at a speed corresponding to the contraction speed of the piezoelectric vibrator 17. In the state of P13, the lowest potential V1 is maintained for a time such that the temporarily retracted meniscus 40 does not return to the position before being drawn in. In the state of P14 when the potential rises from the lowest potential V1 to the reference potential V0, the piezoelectric vibrator 17 extends and the pressure generating chamber 27 contracts, and the temporarily retracted meniscus 40 returns to the position before being drawn in. At this time, the pressure generating chamber 27 contracts at a speed corresponding to the extension speed of the piezoelectric vibrator 17. Further, when the meniscus 40 is about to return to the position before being drawn in, due to inertia, the meniscus 40 does not stay at the position before being drawn in, and in the state of P21, the meniscus 40 is in a position slightly protruding from the ejection surface of the nozzle hole 22A.

[0101] In this way, the meniscus 40 oscillates due to the first waveform.

[0102] Figure 4 shows the changing state of the ink when the second waveform is continuously applied to the piezoelectric vibrator 17 with respect to the first waveform. In the state of P21 at the reference potential V0, the meniscus 40 is in a position slightly protruding from the ejection surface of the nozzle hole 22A. Next, if the potential is rapidly reduced from the reference potential V0 to the lowest potential V2, the piezoelectric vibrator 17 contracts and the pressure generating chamber 27 expands, so the meniscus 40 is drawn into the nozzle hole 22A. In the state of P23, the lowest potential V2 is maintained for a short time such that the meniscus 40 does not return to its original position.

[0103] In the state of P24, with the meniscus 40 drawn inside the nozzle hole 22A, the voltage applied to the piezoelectric vibrator 17 is rapidly boosted from the lowest potential V2 to the highest potential V3. As a result, the piezoelectric vibrator 17 elongates and the pressure generating chamber 27 contracts, and the meniscus 40 begins to protrude from the discharge surface of the nozzle hole 22A. At this time, the pressure generating chamber 27 contracts at a speed corresponding to the elongation speed of the piezoelectric vibrator 17. Even in the state of P25 where the highest potential V2 is maintained, due to inertia, the meniscus 40 continues to protrude. Moreover, in the state of P26, while the meniscus 40 is in the protruding state, the voltage applied to the piezoelectric vibrator 17 is again decreased to the intermediate potential V0. As a result, the piezoelectric vibrator 17 contracts and the pressure generating chamber 27 expands, and the ink protruding from the nozzle hole 22A is torn off to discharge ink droplets. In addition, before the state shown in P26, the ink droplets fly, for example, toward the surface of the object to be printed (e.g., a tablet).

[0104] The average speed of the ink droplets discharged in this way is not particularly limited, but for example, it is preferably greater than or equal to 3 m / s at a location 1 mm away from the discharge surface of the nozzle hole 22A. In addition, the upper limit value of the average speed of the ink droplets is not particularly limited, but for example, it is preferably less than or equal to 10 m / s at a location 1 mm away from the discharge surface of the nozzle hole 22A.

[0105] As described above, in the present embodiment, the drive waveform (drive signal) applied to the piezoelectric vibrator 17 of the print head 10 generated by the drive signal generation circuit may be any waveform as long as it is a waveform that, after dropping from the reference potential V0 to the potential V2 when discharging inkjet ink, rises to a potential V3 higher than the reference potential V0 and then returns to the reference potential V0, and the generation method thereof is arbitrary.

[0106] In addition, in the present embodiment, the drive waveform (drive signal) applied to the piezoelectric vibrator 17 of the print head 10 generated by the drive signal generation circuit continuously includes, in time series, a first waveform driven when inkjet ink is not discharged and a second waveform driven when inkjet ink is discharged. The first waveform is a waveform that, after dropping from the reference potential V0 to the potential V1, returns to the reference potential V0 again. The second waveform is a waveform that, after dropping from the reference potential V0 to the potential V2, rises to a potential V3 higher than the reference potential V0 and then returns to the reference potential V0 again. It is better if the potential V2 is lower than the potential V1, and the generation method thereof is arbitrary.

[0107] 〔Tablet〕

[0108] In this embodiment, the inkjet ink of this embodiment is used to print characters or images on, for example, the surface of a tablet using the aforementioned printing method. Furthermore, the optical density (OD value) of the printed image produced by the aforementioned printing method is preferably greater than or equal to 0.3, more preferably greater than or equal to 0.35, and even more preferably greater than or equal to 0.4.

[0109] Next, the structure of a tablet having a printed image (printed portion) printed using the inkjet ink according to the embodiment will be described.

[0110] The tablets involved in this embodiment are, for example, medical tablets. Here, "medical tablets" include, for example, plain tablets (bare tablets), sugar-coated tablets, enteric-coated tablets, orally disintegrating tablets, and film-coated tablets having a water-soluble surface layer formed on the outermost surface of the tablet.

[0111] Figure 5 (a) and (b) are a plan view showing a first configuration example of the medical tablet according to the present embodiment and a cross-sectional view taken along line X1-X'1 of the plan view. Figure 5 The medical tablets shown in (a) and (b) are plain tablets, and an image 9 is printed on the surface of the substrate 1. The image 9 is an arbitrary image such as text, a symbol, or a barcode, and is printed using the aforementioned inkjet ink and the aforementioned inkjet printing method.

[0112] Figure 6 (a) and (b) are a plan view and a cross-sectional view taken along line X2-X'2 showing a second configuration example of the medical tablet according to the present embodiment. Figure 6 The medical tablets shown in (a) and (b) are film-coated tablets, and an image 9 is printed on the surface of a film 5 covering a matrix 1 . Figure 6 The images 9 shown in (a) and (b) are also Figure 5 Images 9 shown in (a) and (b) are similarly printed using the aforementioned inkjet ink and the aforementioned inkjet printing method.

[0113] The active ingredient contained in the medical tablet is not particularly limited. For example, it includes substances effective for the prevention / treatment of various diseases (such as substances having a sleep-promoting effect, sedative activity, antibacterial activity, antihypertensive effect, antianginal activity, analgesic effect, anti-inflammatory activity, psychotropic effect, diabetes treatment activity, diuretic effect, anticholinergic activity, antihyperacid effect, antiepileptic effect, ACE inhibitory activity, β-blocker or stimulant activity, anesthetic effect, appetite suppressant effect, antiarrhythmic effect, antidepressant effect, anticoagulant activity, antidiarrheal effect, antihistamine activity, antimalarial effect, antitumor activity, immunosuppressive activity, antiparkinsonian effect, antipsychotic effect, antiplatelet activity, antihyperlipidemic effect, etc.), substances having a cleaning effect, fragrances, substances having a deodorizing effect, etc., but are not limited thereto.

[0114] The tablet according to this embodiment can be formulated with a carrier permissible for its use together with the active ingredient as needed. For example, if it is a medical tablet, a pharmaceutically acceptable carrier can be formulated. As the pharmaceutically acceptable carrier, various conventional organic or inorganic carrier substances are used as formulation materials. For example, appropriate amounts of excipients, lubricants, binders, disintegrants, thickeners, etc. are formulated. In addition, additives such as preservatives, antioxidants, colorants, sweeteners, etc. can also be used as needed.

[0115] In this embodiment, a medical tablet is exemplified as the tablet for illustration, but the present invention is not limited thereto. The printing object of the inkjet ink according to this embodiment is not particularly limited. For example, it can be printed on the surfaces of various tablets such as foods like feeds, fertilizers, detergents, and fizzy candies. In addition, regarding the inkjet ink according to this embodiment, the size of the printing object is not particularly limited, and it can be applied to tablets of various sizes. In addition, in addition to the direct printing on the surface of the aforementioned tablets, the inkjet ink according to this embodiment can be used for the direct printing on foods and the packaging in direct contact with pharmaceuticals and foods.

[0116] In addition, the medical tablet of this embodiment is not particularly limited. In particular, it tends to show a higher effect on film-coated tablets with a film coating covering the surface. This is because, on the surface of the printed tablet, compared with the plain tablet, there are fewer voids in the film-coated tablet, so the ink is more likely to remain on the tablet surface. Therefore, if it is the inkjet ink according to this embodiment, it is easier to exhibit the effect of quick drying compared with the inkjet ink according to the prior art.

[0117] In addition, if it is the printing method according to this embodiment, compared with the printing method according to the prior art, even for inks with high quick-drying properties, the decrease in initial ejection performance and intermittent restart performance can be reduced.

[0118] (Effect of this Embodiment)

[0119] (1) The method for printing an image using an inkjet ink according to this embodiment is a method for printing an image with an inkjet ink using an inkjet device that discharges an inkjet ink containing an alcohol in a range of 30% or more and 60% or less. The inkjet device has: a print head 10 that discharges the inkjet ink; and a drive signal generation circuit that generates a drive signal applied to the piezoelectric oscillator 17 of the print head 10. The waveform of the drive signal when the inkjet ink is discharged is a waveform that, after decreasing from the reference potential V0 to the potential V2, rises to a potential V3 higher than the reference potential V0 and then returns to the reference potential V0 again.

[0120] With such a structure, even when the addition amount of the alcohol solvent in the inkjet ink is increased to improve the drying property, the decrease in the initial discharge property and the intermittent restart property can be reduced compared with the prior art.

[0121] (2) Further, the method for manufacturing a tablet having a printed image printed with an inkjet ink according to this embodiment is a method for manufacturing a tablet having a printed image printed with an inkjet ink using an inkjet device that discharges an inkjet ink containing an alcohol in a range of 30% or more and 60% or less. The inkjet device has: a print head 10 that discharges the inkjet ink; and a drive signal generation circuit that generates a drive signal applied to the piezoelectric oscillator 17 of the print head 10. The waveform of the drive signal when the inkjet ink is discharged is a waveform that, after decreasing from the reference potential V0 to the potential V2, rises to a potential V3 higher than the reference potential V0 and then returns to the reference potential V0 again.

[0122] With such a structure, a tablet can be provided in which, even when the addition amount of the alcohol solvent in the inkjet ink is increased to improve the drying property, the decrease in the initial discharge property and the intermittent restart property can be reduced compared with the prior art.

[0123] (3) Further, the inkjet device for discharging an inkjet ink according to this embodiment is an inkjet device that discharges an inkjet ink containing an alcohol in a range of 30% or more and 60% or less, and has: a print head 10 that discharges the inkjet ink; and a drive signal generation circuit that generates a drive signal applied to the piezoelectric oscillator 17 of the print head 10. The waveform of the drive signal when the inkjet ink is discharged is a waveform that, after decreasing from the reference potential V0 to the potential V2, rises to a potential V3 higher than the reference potential V0 and then returns to the reference potential V0 again.

[0124] If such a structure is adopted, an inkjet device can be provided, that is, even when the addition amount of the alcohol solvent in the inkjet ink is increased to improve the drying property, the decrease in the initial ejection property and the intermittent restart property can be reduced compared with the prior art.

[0125] (4) Additionally, the drive signal generation circuit for generating a drive signal according to the present embodiment is a drive signal generation circuit that generates a drive signal applied to the piezoelectric vibrator 17 of the print head 10 that ejects inkjet ink containing alcohol in a range of greater than or equal to 30% and less than or equal to 60%. The waveform of the drive signal during inkjet ink ejection is as follows: after decreasing from the reference potential V0 to the potential V2, it rises to a potential V3 higher than the reference potential V0 and then returns to the reference potential V0 again.

[0126] If such a structure is adopted, a drive signal generation circuit can be provided, that is, even when the addition amount of the alcohol solvent in the inkjet ink is increased to improve the drying property, the decrease in the initial ejection property and the intermittent restart property can be reduced compared with the prior art.

[0127] (5) Additionally, the method for printing a printed image using inkjet ink according to the present embodiment is a method for printing a printed image with inkjet ink using an inkjet device that ejects inkjet ink containing alcohol in a range of greater than or equal to 30% and less than or equal to 60%. The inkjet device includes: a print head 10 that ejects inkjet ink; and a drive signal generation circuit that generates a drive signal applied to the piezoelectric vibrator 17 of the print head 10. The waveform of the drive signal continuously includes, in time series: a first waveform driven when the inkjet ink is not ejected; and a second waveform driven when the inkjet ink is ejected. The first waveform is as follows: after decreasing from the reference potential V0 to the potential V1, it returns to the reference potential V0 again. The second waveform is as follows: after decreasing from the reference potential V0 to the potential V2, it rises to a potential V3 higher than the reference potential V0 and then returns to the reference potential V0 again. The potential V2 is lower than the potential V1.

[0128] If such a structure is adopted, even when the addition amount of the alcohol solvent in the inkjet ink is increased to improve the drying property, the decrease in the initial ejection property and the intermittent restart property can be reduced compared with the prior art.

[0129] (6) Additionally, the method for manufacturing tablets with printed images printed using inkjet ink in this embodiment is a method for manufacturing tablets with printed images printed using an inkjet device that discharges inkjet ink containing alcohols in the range of greater than or equal to 30% and less than or equal to 60%. The inkjet device has: a print head 10 that discharges inkjet ink; and a drive signal generation circuit that generates a drive signal applied to the piezoelectric oscillator 17 of the print head 10. The waveform of the drive signal continuously includes in time series: a first waveform driven when the inkjet ink is not discharged; and a second waveform driven when the inkjet ink is discharged. The first waveform is a waveform that, after dropping from the reference potential V0 to the potential V1, returns to the reference potential V0 again. The second waveform is a waveform that, after dropping from the reference potential V0 to the potential V2, rises to a potential V3 higher than the potential V0 and then returns to the reference potential V0 again. The potential V2 is lower than the potential V1.

[0130] With such a structure, it is possible to provide tablets that can reduce the decline in initial discharge performance and intermittent restart performance compared to the prior art even when the addition amount of the alcohol solvent in the inkjet ink is increased to improve drying performance.

[0131] (7) Additionally, the inkjet device that discharges inkjet ink in this embodiment is an inkjet device that discharges inkjet ink containing alcohols in the range of greater than or equal to 30% and less than or equal to 60%. It has: a print head 10 that discharges inkjet ink; and a drive signal generation circuit that generates a drive signal applied to the piezoelectric oscillator 17 of the print head 10. The waveform of the drive signal continuously includes in time series: a first waveform driven when the inkjet ink is not discharged; and a second waveform driven when the inkjet ink is discharged. The first waveform is a waveform that, after dropping from the reference potential V0 to the potential V1, returns to the reference potential V0 again. The second waveform is a waveform that, after dropping from the reference potential V0 to the potential V2, rises to a potential V3 higher than the reference potential V0 and then returns to the reference potential V0 again. The potential V2 is lower than the potential V1.

[0132] With such a structure, it is possible to provide an inkjet device that can reduce the decline in initial discharge performance and intermittent restart performance compared to the prior art even when the addition amount of the alcohol solvent in the inkjet ink is increased to improve drying performance.

[0133] (8) Further, the driving signal generation circuit for generating a driving signal according to this embodiment is a driving signal generation circuit that generates a driving signal applied to the piezoelectric vibrator 17 of the print head 10 that discharges inkjet ink containing an alcohol in a range of greater than or equal to 30% and less than or equal to 60%. The waveform of the driving signal continuously includes, in time series: a first waveform driven when the inkjet ink is not discharged; and a second waveform driven when the inkjet ink is discharged. The first waveform is a waveform that after descending from the reference potential V0 to the potential V1, returns to the reference potential V0 again. The second waveform is a waveform that after descending from the reference potential V0 to the potential V2, rises to a potential V3 higher than the reference potential V0 and then returns to the reference potential V0 again. The potential V2 is lower than the potential V1.

[0134] If it is such a structure, a driving signal generation circuit can be provided, that is, even when increasing the addition amount of the alcohol solvent in the inkjet ink to improve the drying property, compared with the prior art, the decrease in initial discharge property and intermittent restart property can be reduced.

[0135] (9) Further, the alcohol according to this embodiment may include at least one of ethanol, NPA, and IPA.

[0136] If it is such a structure, compared with the prior art, the decrease in initial discharge property and intermittent restart property can be further reduced.

[0137] (10) Further, the viscosity of the inkjet ink according to this embodiment at 25°C may be less than or equal to 5.0 mPa·s.

[0138] If it is such a structure, compared with the prior art, the decrease in initial discharge property and intermittent restart property can be further reduced.

[0139] (11) Further, the surface tension of the inkjet ink according to this embodiment at 25°C may be in the range of greater than or equal to 23 mN / m and less than or equal to 34 mN / m.

[0140] If it is such a structure, compared with the prior art, the decrease in initial discharge property and intermittent restart property can be further reduced.

[0141] (12) Further, the optical density (OD value) of the printed image according to this embodiment may be greater than or equal to 0.3.

[0142] If it is such a structure, a printed image with sufficient visual confirmability can be obtained.

[0143] (13) Further, the discharge frequency when discharging the inkjet ink according to this embodiment may be greater than or equal to 1 kHz.

[0144] If it is this kind of structure, the printing efficiency can be improved.

[0145] (14) Additionally, for the present embodiment, the average droplet velocity at a location 1 mm away from the front end of the discharge nozzle for the inkjet ink when discharging the inkjet ink can be greater than or equal to 3 m / s.

[0146] If it is this kind of structure, a printed image with excellent visual confirmation property can be obtained.

[0147] (15) Additionally, for the present embodiment, the potential difference between the peak potential of the first waveform, i.e., potential V1, and the reference potential V0 can be within the range of 10 - 60% of the potential difference between the peak potential of the second waveform, i.e., potential V2, and the reference potential V0.

[0148] If it is this kind of structure, even when the addition amount of the alcohol solvent in the inkjet ink is increased to improve the drying property, compared with the prior art, the decrease in the initial discharge property and the intermittent restart property can be further reduced.

[0149] [Examples]

[0150] Next, the present invention will be described in more detail using examples, but the present invention is not limited by any of the examples.

[0151] (Manufacture of Inkjet Ink)

[0152] Next, the preparation process of the inkjet ink will be described.

[0153] The inkjet ink contains components such as edible pigments, organic solvents (drying accelerators), water, wetting agents, and other optional additives. As the preparation sequence, first, water and the organic solvent are mixed to obtain a mixed solvent. Next, after adding the wetting agent and the edible pigment to this mixed solvent, other additives are added. Finally, the mixed solution is injected into a disperser such as a paint stirrer and made to be refined and dispersed for a specified time. Thus, the inkjet ink according to the present embodiment is prepared. Next, each component will be specifically described.

[0154] For the edible pigment, as edible dyes, Food Red No. 2, Food Red No. 3, Food Red No. 102, Food Yellow No. 4, Food Yellow No. 5, Food Green No. 3, Food Blue No. 1, and Food Blue No. 2 are used, and carbon is used as the edible pigment.

[0155] For the organic solvent, as the drying solvent (drying accelerator), ethanol, n - propanol (NPA), and isopropyl alcohol (IPA) are used.

[0156] For the water constituting the ink, purified water (ion - exchanged water) is used.

[0157] For the wetting agent, propylene glycol and glycerol are used.

[0158] For the additive (binder), isomaltulose, lactose, sucrose fatty acid ester, trehalose, and cellobiose are used.

[0159] The above components are formulated into 37 different inks. Their components are shown in Tables 1 to 4.

[0160] In addition, each of the above inks is passed through a membrane filter to remove solid foreign substances in the liquid. Specifically, it is passed once through a membrane filter with a diameter of 5.0 μm (cellulose acetate membrane) and then once through a membrane filter with a diameter of 0.8 μm (cellulose acetate membrane), thereby obtaining a refined ink.

[0161] [Table 1]

[0162]

[0163] [Table 2]

[0164]

[0165] [Table 3]

[0166]

[0167] [Table 4]

[0168]

[0169] Thirty-seven inkjet inks (Samples 1 to 37) were produced by the above-described formulation method. The components of the 37 inkjet inks (Samples 1 to 37) are shown in Tables 1 to 4.

[0170] In addition, Samples 1 to 35 correspond to Examples 1 to 35, and Samples 36 to 37 correspond to Comparative Examples 1 to 2.

[0171] (Type of drive waveform applied to the piezoelectric oscillator)

[0172] Next, the types of drive waveforms (printing methods) applied to the piezoelectric oscillator will be described.

[0173] · Waveform A: Comparative example (waveform related to the prior art: basic waveform)

[0174] Waveform A is the drive waveform when the inkjet ink is discharged. As shown in Figure 7 (a), it is a waveform that, after decreasing from the reference potential V0 to the potential V2, returns to the reference potential V0 again.

[0175] · Waveform B: Example (waveform related to this example)

[0176] Waveform B is the driving waveform when the inkjet ink is discharged. As shown in Figure 7 (b), it is the following waveform, that is, after decreasing from the reference potential V0 to the potential V2, it rises to a potential V3 higher than the reference potential V0 and then returns to the reference potential V0 again.

[0177] · Waveform C: Example (waveform related to this example)

[0178] Waveform C is the driving waveform when the inkjet ink is discharged. As shown in Figure 7 (c), it is the first waveform and the second waveform. The first waveform is the following waveform, that is, after decreasing from the reference potential V0 to the potential V1, it returns to the reference potential V0 again. The second waveform is the following waveform, that is, after decreasing from the reference potential V0 to the potential V2, it rises to a potential V3 higher than the reference potential V0 and then returns to the reference potential V0 again. Here, the potential V2 is lower than the potential V1.

[0179] (Evaluation items and evaluation criteria)

[0180] Regarding each inkjet ink formulated in this example, evaluations of the initial dischargeability and intermittent restartability were carried out when printing with the respective driving waveforms (printing methods) shown in Figure 7 . The results of each evaluation are shown in Tables 1 to 4. In addition, the evaluation method of this example is as follows.

[0181] (1) Evaluation of initial dischargeability

[0182] For the inkjet head, a piezoelectric ceramic-driven on-demand supply type inkjet head with a printing resolution of 600 dpi in the main scanning direction, 600 dpi in the sub-scanning direction (the conveying direction of the recording medium such as tablets), and a total of 1,280 nozzles was used. Immediately after nozzle maintenance was carried out using the above inkjet head, a test pattern was printed with each driving waveform. Moreover, the readability of the printed image accompanied by the generation of non-discharge areas was confirmed according to the printing condition of the test pattern. The evaluation criteria are as follows.

[0183] ◎: No non-discharge

[0184] ○: Has readability

[0185] ×: No readability

[0186] In addition, if the evaluation of the initial dischargeability is "◎" or "○", there is no problem in use, so it is evaluated as qualified.

[0187] When printing with waveform A, the initial ejection performance of samples 1, 6, 8, 10, 12, and 17 is "〇", and that of samples 2 to 5, 7, 9, 11, 13 to 16, and 18 to 37 is "×".

[0188] In addition, when printing with waveform B, the initial ejection performance of samples 1 to 35 is "○", and that of samples 36 and 37 is "×".

[0189] In addition, when printing with waveform C, the initial ejection performance of samples 1 to 4, 6 to 10, 12 to 15, 17, 19 to 24, 26 to 29, 32, and 34 is "◎", that of samples 5, 11, 16, 18, 25, 30, 31, 33, and 35 is "○", and that of samples 36 and 37 is "×".

[0190] (2) Evaluation of intermittent restart performance

[0191] For the inkjet head, a piezoelectric ceramic-driven on-demand supply type inkjet head with a printing resolution of 600 dpi in the main scanning direction, 600 dpi in the sub-scanning direction (the conveying direction of the recording medium such as tablets), and a total nozzle number of 1,280 is used. After placing the above ink in the above inkjet head without flushing for 30 minutes, a test pattern was printed using the above inkjet head with each driving waveform. Moreover, the readability of the printed image accompanied by the generation of non-ejection areas was confirmed based on the printing condition of the test pattern. The evaluation criteria are as follows.

[0192] ◎: No non-ejection

[0193] ○: Readable

[0194] ×: Unreadable

[0195] In addition, if the evaluation of the intermittent restart performance is "◎" or "○", there is no problem in use, so it is evaluated as qualified.

[0196] When printing with waveform A, the intermittent restart performance of samples 1 to 37 is "×".

[0197] In addition, when printing with waveform B, the intermittent restart performance of samples 1 to 35 is "○", and that of samples 36 and 37 is "×".

[0198] In addition, when printing with waveform C, the intermittent restart performance of samples 1 to 3, 6 to 8, 10, 12, 14, 17, 23, 26 to 28, 32, and 34 is "◎", that of samples 4, 5, 9, 11, 13, 15, 16, 18 to 22, 24, 25, 29 to 31, 33, and 35 is "○", and that of samples 36 and 37 is "×".

[0199] According to the above results, if the driving waveform applied to the piezoelectric vibrator of a device that discharges inkjet ink containing alcohol in a range greater than or equal to 30% and less than or equal to 60% is formed into the following waveform, that is, after decreasing from the reference potential V0 to the potential V2, it increases to the potential V3 higher than the reference potential V0, and then returns to the reference potential V0 again, then even if the amount of alcohol solvent added to the inkjet ink is increased to improve the drying property, the decline in the initial discharge property and the intermittent restart property can be reduced compared with the prior art.

[0200] Description of the label

[0201] 1 Matrix

[0202] 5 films

[0203] 9 images

[0204] 10 print head

[0205] 17 Piezoelectric vibrator

[0206] 21 Base unit

[0207] 22 Nozzle Plate

[0208] 22A Nozzle hole

[0209] 23 Vibration Plate

[0210] 23A raised part

[0211] 24 Flow path forming plate

[0212] 25 Ink Room

[0213] 26 Ink supply port

[0214] 27 Pressure Generation Chamber

[0215] 28 abutment

[0216] 29 Containment Chamber

[0217] 30 Fixed base plate

[0218] 31 wires

[0219] 40 Meniscus

Claims

1. A printing method of an edible inkjet ink, which is a method of printing a printed image with the edible inkjet ink by using a device that discharges an edible inkjet ink containing an alcohol in a range of greater than or equal to 30% and less than or equal to 60%, characterized in that, The device for discharging the edible inkjet ink has: An ink discharge head that discharges the edible inkjet ink; and A drive waveform generation device that generates a drive waveform applied to a pressure generating element of the ink discharge head, The drive waveform when the inkjet ink is discharged is a waveform that, after decreasing from a reference potential V0 to a potential V2 lower than the reference potential V0, rises to a potential V3 higher than the reference potential V0 and then returns to the reference potential V0 again.

2. A method for manufacturing a tablet, which is a method for manufacturing a tablet having a printed image printed with the edible inkjet ink by using a device that discharges an edible inkjet ink containing an alcohol in a range of greater than or equal to 30% and less than or equal to 60%, characterized in that, The device for discharging the edible inkjet ink has: An ink discharge head that discharges the edible inkjet ink; and A drive waveform generation device that generates a drive waveform applied to a pressure generating element of the ink discharge head, The drive waveform when the inkjet ink is discharged is a waveform that, after decreasing from a reference potential V0 to a potential V2 lower than the reference potential V0, rises to a potential V3 higher than the reference potential V0 and then returns to the reference potential V0 again.

3. A discharging device, which is a device that discharges an edible inkjet ink containing an alcohol in a range of greater than or equal to 30% and less than or equal to 60%, characterized in that, The discharging device has: An ink discharge head that discharges the edible inkjet ink; and A drive waveform generation device that generates a drive waveform applied to a pressure generating element of the ink discharge head, The drive waveform when the inkjet ink is discharged is a waveform that, after decreasing from a reference potential V0 to a potential V2 lower than the reference potential V0, rises to a potential V3 higher than the reference potential V0 and then returns to the reference potential V0 again.

4. A drive waveform generation device, which is a device that generates a drive waveform applied to a pressure generating element of a liquid discharge head that discharges an edible inkjet ink containing an alcohol in a range of greater than or equal to 30% and less than or equal to 60%, characterized in that, The drive waveform when the inkjet ink is discharged is a waveform that, after decreasing from a reference potential V0 to a potential V2 lower than the reference potential V0, rises to a potential V3 higher than the reference potential V0 and then returns to the reference potential V0 again.

5. A printing method of an edible inkjet ink, which is a method of printing a printed image with the edible inkjet ink by using a device that discharges an edible inkjet ink containing an alcohol in a range of greater than or equal to 30% and less than or equal to 60%, characterized in that, The device for discharging the edible inkjet ink has: An ink ejection head that ejects the edible inkjet ink; and A drive waveform generation device that generates a drive waveform applied to a pressure generating element of the ink ejection head, The drive waveform continuously includes in time series: a first waveform driven when the inkjet ink is not ejected; and a second waveform driven when the inkjet ink is ejected, The first waveform is a waveform that, after dropping from a reference potential V0 to a potential V1 lower than the reference potential V0, returns to the reference potential V0 again, The second waveform is a waveform that, after dropping from a reference potential V0 to a potential V2 lower than the reference potential V0, rises to a potential V3 higher than the reference potential V0 and then returns to the reference potential V0 again, The potential V2 is a potential lower than the potential V1.

6. A method for manufacturing a tablet, which is a method for manufacturing a tablet having a printed image printed with the edible inkjet ink by a device that ejects an edible inkjet ink containing an alcohol in a range of greater than or equal to 30% and less than or equal to 60%, characterized in that The device that ejects the edible inkjet ink has: An ink ejection head that ejects the edible inkjet ink; and A drive waveform generation device that generates a drive waveform applied to a pressure generating element of the ink ejection head, The drive waveform continuously includes in time series: a first waveform driven when the inkjet ink is not ejected; and a second waveform driven when the inkjet ink is ejected, The first waveform is a waveform that, after dropping from a reference potential V0 to a potential V1 lower than the reference potential V0, returns to the reference potential V0 again, The second waveform is a waveform that, after dropping from a reference potential V0 to a potential V2 lower than the reference potential V0, rises to a potential V3 higher than the reference potential V0 and then returns to the reference potential V0 again, The potential V2 is a potential lower than the potential V1.

7. An ejection device that ejects an edible inkjet ink containing an alcohol in a range of greater than or equal to 30% and less than or equal to 60%, characterized in that The ejection device has: An ink ejection head that ejects the edible inkjet ink; and A drive waveform generation device that generates a drive waveform applied to a pressure generating element of the ink ejection head, The drive waveform continuously includes in time series: a first waveform driven when the inkjet ink is not ejected; and a second waveform driven when the inkjet ink is ejected, The first waveform is a waveform that, after dropping from a reference potential V0 to a potential V1 lower than the reference potential V0, returns to the reference potential V0 again, The second waveform is a waveform that, after dropping from a reference potential V0 to a potential V2 lower than the reference potential V0, rises to a potential V3 higher than the reference potential V0 and then returns to the reference potential V0 again, The potential V2 is a potential lower than the potential V1.

8. A driving waveform generating device, which is a device for generating a driving waveform applied to a pressure generating element of a liquid ejection head that ejects an edible inkjet ink containing an alcohol within a range of greater than or equal to 30% and less than or equal to 60%, and is characterized in that the driving waveform continuously includes, in time series: a first waveform driven when the inkjet ink is not ejected; and a second waveform driven when the inkjet ink is ejected, the first waveform is a waveform that, after dropping from a reference potential V0 to a potential V1 lower than the reference potential V0, returns to the reference potential V0 again, the second waveform is a waveform that, after dropping from a reference potential V0 to a potential V2 lower than the reference potential V0, rises to a potential V3 higher than the reference potential V0 and then returns to the reference potential V0 again, the potential V2 is a potential lower than the potential V1.

9. The printing method of the edible inkjet ink according to claim 1 or 5, characterized in that the alcohol includes at least one of ethanol, NPA, and IPA.

10. The manufacturing method of the tablet according to claim 2 or 6, characterized in that the alcohol includes at least one of ethanol, NPA, and IPA.

11. The ejection device for ejecting the edible inkjet ink according to claim 3 or 7, characterized in that the alcohol includes at least one of ethanol, NPA, and IPA.

12. The driving waveform generating device according to claim 4 or 8, characterized in that the alcohol includes at least one of ethanol, NPA, and IPA.

13. The printing method of the edible inkjet ink according to claim 1 or 5, characterized in that the viscosity of the ink at 25°C is less than or equal to 5.0 mPa·s.

14. The manufacturing method of the tablet according to claim 2 or 6, characterized in that the viscosity of the ink at 25°C is less than or equal to 5.0 mPa·s.

15. The ejection device for ejecting the edible inkjet ink according to claim 3 or 7, characterized in that the viscosity of the ink at 25°C is less than or equal to 5.0 mPa·s.

16. The driving waveform generating device according to claim 4 or 8, characterized in that the viscosity of the ink at 25°C is less than or equal to 5.0 mPa·s.

17. The printing method of the edible inkjet ink according to claim 1 or 5, characterized in that the surface tension of the ink at 25°C is in a range of greater than or equal to 23 mN / m and less than or equal to 34 mN / m.

18. The manufacturing method of the tablet according to claim 2 or 6, characterized in that the surface tension of the ink at 25°C is in a range of greater than or equal to 23 mN / m and less than or equal to 34 mN / m.

19. The ejection device for ejecting the edible inkjet ink according to claim 3 or 7, characterized in that the surface tension of the ink at 25°C is in a range of greater than or equal to 23 mN / m and less than or equal to 34 mN / m.

20. The driving waveform generating device according to claim 4 or 8, characterized in that the surface tension of the ink at 25 °C is in the range of greater than or equal to 23 mN / m and less than or equal to 34 mN / m.

21. The printing method of the edible inkjet ink according to claim 1 or 5, characterized in that the optical density of the printed image, i.e., the OD value, is greater than or equal to 0.

3.

22. The manufacturing method of the tablet according to claim 2 or 6, characterized in that the optical density of the printed image, i.e., the OD value, is greater than or equal to 0.

3.

23. The discharging device for discharging the edible inkjet ink according to claim 3 or 7, characterized in that the optical density of the printed image, i.e., the OD value, is greater than or equal to 0.

3.

24. The driving waveform generating device according to claim 4 or 8, characterized in that the optical density of the printed image, i.e., the OD value, is greater than or equal to 0.

3.

25. The printing method of the edible inkjet ink according to claim 1 or 5, characterized in that the discharging frequency when discharging the ink is greater than or equal to 1 kHz.

26. The manufacturing method of the tablet according to claim 2 or 6, characterized in that the discharging frequency when discharging the ink is greater than or equal to 1 kHz.

27. The discharging device for discharging the edible inkjet ink according to claim 3 or 7, characterized in that the discharging frequency when discharging the ink is greater than or equal to 1 kHz.

28. The driving waveform generating device according to claim 4 or 8, characterized in that the discharging frequency when discharging the ink is greater than or equal to 1 kHz.

29. The printing method of the edible inkjet ink according to claim 1 or 5, characterized in that the average droplet velocity at a location 1 mm away from the front end of the discharging nozzle for the ink when discharging the ink is greater than or equal to 3 m / s.

30. The manufacturing method of the tablet according to claim 2 or 6, characterized in that the average droplet velocity at a location 1 mm away from the front end of the discharging nozzle for the ink when discharging the ink is greater than or equal to 3 m / s.

31. The discharging device for discharging the edible inkjet ink according to claim 3 or 7, characterized in that the average droplet velocity at a location 1 mm away from the front end of the discharging nozzle for the ink when discharging the ink is greater than or equal to 3 m / s.

32. The driving waveform generating device according to claim 4 or 8, characterized in that the average droplet velocity at a location 1 mm away from the front end of the discharging nozzle for the ink when discharging the ink is greater than or equal to 3 m / s.

33. The printing method of the edible inkjet ink according to claim 5, characterized in that the potential difference between the peak potential of the first waveform, i.e., the potential V1 and the reference potential V0, is in the range of 10 - 60% of the potential difference between the peak potential of the second waveform, i.e., the potential V2 and the reference potential V0.

34. The manufacturing method of the tablet according to claim 6, characterized in that the potential difference between the peak potential of the first waveform, i.e., the potential V1 and the reference potential V0, is within the range of 10 to 60% of the potential difference between the peak potential of the second waveform, i.e., the potential V2 and the reference potential V0.

35. The discharging device for discharging the edible inkjet ink according to claim 7, characterized in that the potential difference between the peak potential of the first waveform, i.e., the potential V1 and the reference potential V0, is within the range of 10 to 60% of the potential difference between the peak potential of the second waveform, i.e., the potential V2 and the reference potential V0.

36. The driving waveform generating device according to claim 8, characterized in that the potential difference between the peak potential of the first waveform, i.e., the potential V1 and the reference potential V0, is within the range of 10 to 60% of the potential difference between the peak potential of the second waveform, i.e., the potential V2 and the reference potential V0.

Images