JP7246207B2 - inkjet ink - Google Patents

Description

TECHNICAL FIELD The present invention relates to an edible inkjet ink for directly printing characters, symbols, etc. for identification on the surface of solid preparations such as tablets taken as foods or pharmaceuticals. .

BACKGROUND ART Techniques for directly printing on the surfaces of tablets, capsules, and other solid formulations taken as foods, pharmaceuticals, etc., by ink-jet printing are becoming widespread.
As an inkjet ink for printing on the surface of a solid preparation or the like by an inkjet printing method, a water-based edible inkjet ink containing water and an edible dye is used.

In addition, it has also been studied to adjust the properties of such an edible inkjet ink by blending a surface tension modifier that can be used for foods, such as decaglyceryl laurate (Patent Document 1). ).
However, conventional edible inkjet inks such as those described in Patent Document 1, which use only water as a solvent or use water in combination with a high-boiling water-soluble organic solvent such as propylene glycol, dry out. Due to its low durability, it is necessary to heat it after printing.

In addition, if it is not heated, it may bleed and the sharpness of the print may deteriorate.
When a water-soluble organic solvent with a low boiling point such as ethanol is used together with water as a solvent, the ink-jet ink can be dried quickly, and heating after printing can be omitted.
However, according to the inventor's study, conventional inkjet inks that use water and ethanol in combination, especially when used in on-demand type inkjet printers, when printing is resumed after the decap time is over, the lack of printing occurs. There is a problem that deformation, scattering, etc. are likely to occur.

Decapation time refers to the amount of time the inkjet ink inside the nozzles in the on-demand inkjet printer is exposed to the atmosphere during intermittent printing. refers to the time when
Inkjet printers are usually provided with a function to close (cap) the nozzles when the operation is stopped in order to prevent the inkjet ink in the nozzles from drying out due to exposure to the outside air and causing clogging. It is common that

However, since all the nozzles are uncapped during printing, the nozzles that are on standby especially during intermittent printing are not closed (decapped) until the next ink droplet is ejected. state) continues.
During a standby period in which no ink droplets are ejected, a meniscus is formed at the air-liquid interface between the inkjet ink and the outside air in the nozzle of the inkjet printer, and the inkjet ink is kept stationary.

However, when the decap time is long, a water-soluble organic solvent with a low boiling point such as ethanol evaporates from the inkjet ink, so that the meniscus position gradually retreats in the nozzle in the direction opposite to the ejection direction.
Immediately after the end of the standby state, the flying distance of the ink droplets ejected from the tip of the nozzle for the first time increases, and the landing position of the ink droplets on the surface of the formulation shifts, and the first dot of printing is not printed in the correct position. Sometimes.

In other words, the tip of the print may be missing or the print may be deformed as if it were compressed.
In addition, the solid content contained in the inkjet ink precipitates on the inner peripheral surface of the nozzle exposed by the receding position of the meniscus, and the concentration of the inkjet ink remaining on the inner peripheral surface increases, resulting in high viscosity. Adhesion may occur.

In some cases, solid content and adhering matter affect the trajectory and volume of ink droplets ejected from the tip of the nozzle, making it impossible to perform normal printing.
That is, when solids and deposits adhere to the exposed inner peripheral surface of the nozzle, the interface of the meniscus is drawn to the adhered solids and deposits and becomes deformed.
When an ink droplet is ejected in this state, the ink droplet flies in a direction that deviates from the correct trajectory, or the volume of the ink droplet fluctuates greatly from a predetermined value. Inkjet ink may splatter.

After the decap time, the property of being less likely to cause chipping, deformation, scattering, etc. of the print will be evaluated as the quality of "intermittent printability" below.
The longer the decap time at which no print defects, deformation, or scattering occurs, the better the intermittent printability of the inkjet ink can be evaluated.
Patent Literature 2 describes an edible inkjet ink in which a pigment is used as a colorant and sodium lauryl sulfate is added as a dispersant to enhance the dispersibility of the pigment.

However, in printing with inkjet inks that use pigments, the pigments are only attached to the surface of the formulation and do not penetrate inside like dyes, so the abrasion resistance is low, and if rubbed with fingers, etc. , The print is faint or comes off, making it easy to become unclear.
In particular, this tendency is conspicuous on the surface of FC (film-coated) tablets coated with hydroxypropylcellulose or the like and the surface of capsules made of water-soluble plastic or the like.

In addition, since the pigment is a solid substance that is insoluble in water and water-soluble organic solvents, it remains on the exposed inner peripheral surface of the nozzle as the meniscus retreats during the decap time, causing chipping, deformation, or scattering of the print. etc.
Therefore, the intermittent printing property of the inkjet ink tends to deteriorate.

JP 2017-57344 A Japanese Patent Application Laid-Open No. 2017-165900

It is an object of the present invention to provide printing that can be used, in particular, for printing on the surface of solid preparations, etc., and that has excellent drying properties and intermittent printing properties, as well as excellent clarity and abrasion resistance compared to conventional ones. An object of the present invention is to provide an inkjet ink which can also

The present invention
・ Food coloring (excluding pigments) ,
- At least one alkyl sulfate salt selected from the group consisting of an alkyl sulfate salt having 12 carbon atoms and an alkyl sulfate ester salt having 16 carbon atoms,
An inkjet ink containing ethanol and water.

INDUSTRIAL APPLICABILITY According to the present invention, it can be used for printing on the surface of solid preparations, etc., and in addition to being excellent in drying properties and intermittent printing properties compared to conventional ones, it prints with excellent clarity and abrasion resistance. Ink jet inks can also be provided.

The present invention, as described above,
・ Food coloring (excluding pigments) ,
- At least one alkyl sulfate salt selected from the group consisting of an alkyl sulfate salt having 12 carbon atoms and an alkyl sulfate ester salt having 16 carbon atoms,
An inkjet ink containing ethanol and water.

Among the above components, all of the above specific alkyl sulfate salts are known as surfactants that can be used as food additives or pharmaceutical additives.
Moreover, according to the study of the inventors, it is possible to improve the intermittent printing property of the inkjet ink by selecting and blending at least one of the alkyl sulfate ester salts.

That is, all of these alkyl sulfate ester salts have melting points exceeding room temperature (5 to 35° C.), which is the normal operating temperature range for inkjet printers, are solid at room temperature, and are soluble in water. It has the property of being slightly soluble in ethanol .
Therefore, the alkyl sulfate ester salt has moderate solubility that is not too strong in a mixed solvent of water and ethanol . Dissolve.

In this state, when the inkjet ink in the nozzle is in a standby state and a meniscus is formed, the alkyl sulfate quickly precipitates on the liquid surface of the formed meniscus to form a very thin film. .
Further, receding of the meniscus due to volatilization of ethanol or the like is suppressed.

As a result, the meniscus recedes and the inner peripheral surface of the nozzle is exposed, solids and deposits adhere to the exposed inner peripheral surface, and the meniscus is deformed by the influence of the adhering solids and deposits. can be suppressed to always maintain the meniscus in the correct position and correct shape.
Also, the inkjet ink inside the membrane can be maintained in a jettable low-viscosity state during the standby state.

Moreover, all of the above alkyl sulfate salts are also hard and brittle components with almost no film-forming properties.
Therefore, the thin film made of the alkyl sulfate can be easily broken by the ejection pressure applied to the inkjet ink in the nozzle during the next ejection.
Therefore, immediately after the standby state is completed, ink droplets of a predetermined volume can be ejected in a normal direction, thereby suppressing missing or deformed printing and scattering of inkjet ink in printing. Printability can be improved.

Moreover, all of the above alkyl sulfate ester salts also function as original surfactants, and can suppress ink-jet ink from blurring on the surface of solid formulations and the like.
Therefore, it is possible to improve the quick-drying property by using ethanol together with water, and to improve the sharpness of printing.

Furthermore, food coloring not only adheres to the surface of the formulation like pigments, but also penetrates into the coating of FC tablets, for example, so it improves abrasion resistance and can be easily rubbed with fingers. However, it is also possible to prevent the printing from being blurred or removed and becoming unclear.
<Alkyl sulfate salt>
As the alkyl sulfate, as described above, an alkyl sulfate with 12 carbon atoms and/or an alkyl sulfate with 16 carbon atoms, which can be used as a food additive or pharmaceutical additive, is used.

Of these, the C12 alkyl sulfate salt is preferably a lauryl sulfate salt in which the C12 alkyl group is a linear lauryl group (dodecyl group).
The lauryl sulfate is selected from the group consisting of lauryl sulfate alkali metal salts such as sodium lauryl sulfate and potassium lauryl sulfate; lauryl sulfate alkaline earth metal salts such as magnesium lauryl sulfate; and ammonium lauryl sulfate. At least 1 type is mentioned.

As the C16 alkyl sulfate salt, a cetyl sulfate salt in which the C16 alkyl group is a linear cetyl group (hexadecyl group) is preferable.
As the cetyl sulfate, at least one selected from the group consisting of cetyl sulfate alkali metal salts such as sodium cetyl sulfate and potassium cetyl sulfate; cetyl sulfate alkaline earth metal salts such as magnesium cetyl sulfate; and ammonium cetyl sulfate. seeds.

Among them, sodium lauryl sulfate is preferred.
Sodium lauryl sulfate has an excellent effect of forming a film on the liquid surface of the meniscus to suppress receding of the meniscus, thereby improving intermittent printing performance.
Sodium lauryl sulfate is also widely accepted as a pharmaceutical excipient in three pharmacopoeias: the Japanese Pharmacopoeia, the United States Pharmacopeia (USP), and the European Pharmacopoeia (EP). .

Therefore, by selectively using sodium lauryl sulfate, the versatility of the inkjet ink of the present invention can be enhanced.
One or more of these alkyl sulfate salts can be used.
The ratio of the alkyl sulfate is preferably 0.03% by mass or more, particularly 0.05% by mass or more, and preferably 7% by mass or less, particularly 5% by mass or less, in the total amount of the inkjet ink.

If the ratio of the alkyl sulfate is less than this range, the effects of improving the intermittent printing property and improving the sharpness of the print, which are obtained by blending the alkyl sulfate, cannot be sufficiently obtained. Sometimes.
On the other hand, if the proportion of the alkyl sulfate exceeds the above range, the fixability of the inkjet ink may be insufficient, resulting in a decrease in the abrasion resistance of the print.

On the other hand, by setting the proportion of the alkyl sulfate within the above range, it is possible to further improve the drying property, intermittent printing property, sharpness of printing, abrasion resistance, and the like of the ink jet ink.
As a surfactant that can be used as a food additive or pharmaceutical additive, for example, decaglyceryl laurate and the like are known.

However, when a surfactant such as decaglyceryl laurate that has a melting point below room temperature and is liquid at room temperature is used, a film is formed on the liquid surface of the meniscus as described above to suppress the receding of the meniscus. However, the effect of improving the intermittent printing performance cannot be obtained.
In addition, when decaglyceryl laurate or the like is used in combination with an alkyl sulfate ester salt, the decaglyceryl laurate or the like functions as a compatibilizer and inhibits the formation of the above-described film, which also has the effect of improving intermittent printing. is not obtained.

Therefore, liquid surfactants such as decaglyceryl laurate are preferably not included (excluded) in the present invention.
<Food coloring>
Food dyes include, for example, one or more of various synthetic or natural food dyes.

Among them, the synthetic food coloring is, for example, one of various dyes such as azo, triphenylmethane, xanthene, and indigoid dyes that are approved for use as food additives or pharmaceutical additives, or Two or more kinds can be used.
Specific examples of synthetic food dyes include Food Red No. 2, Food Red No. 40, Food Red No. 102, Food Yellow No. 4 and Food Yellow No. 5 (above, azo dyes); Food Blue No. 1 and Food Green. Food Red No. 3 (above, triphenylmethane dye); Food Red No. 3, Food Red No. 104, Food Red No. 105, Food Red No. 106 (above, xanthene dye); Food Blue No. 2 (above, indigoid dye) etc.

Examples of natural food coloring include caramel coloring, tomato coloring, turmeric coloring, gardenia coloring, β-carotene coloring, palm oil carotene, marigold coloring, safflower coloring, hot pepper coloring , annatto coloring, lac coloring, and cochineal coloring. , Benicouji pigment (monascus pigment) , beet red pigment, red cabbage pigment, purple sweet potato pigment, red radish pigment, grape skin pigment, anthocyanin pigment, perilla pigment, elderberry pigment, purple corn pigment , cacao pigment, oyster pigment, sorghum pigment Pigment, spirulina pigment, paprika pigment, squid ink pigment, riboflavin, riboflavin butyrate, riboflavin sodium phosphate, chlorophyll, copper chlorophyll and its metal salts (sodium salts, etc.), iron chlorophyll and its metal salts (sodium salts, etc.), etc. mentioned.

In particular, as the food coloring matter for red ink-jet ink commonly used overseas, such as in Europe and the United States, Food Red No. 40, which is approved for use in the aforementioned USP and EP, is preferable.
Food Red No. 40 is not compatible with, for example, vitamin C and sugar and reacts with them, making it difficult to select materials such as surfactants to be used in combination.
However, both C12 alkyl sulfate and/or C16 alkyl sulfate have good compatibility with Food Red No. 40 and do not react with it.

Therefore, the combined use of Food Red No. 40 and the above alkyl sulfate salt can further improve the drying property, intermittent printing property, sharpness of printing, abrasion resistance, and the like of the ink-jet ink.
In the case of printing in red on the surface of pharmaceutical preparations in Japan, for example, Food Red No. 102, which is approved for use in Ministry of Health, Labor and Welfare Ordinance No. 30, may be used.

Food Red No. 102 also has good compatibility with C12 alkyl sulfate and/or C16 alkyl sulfate and does not react.
Therefore, the combined use of Food Red No. 102 and the above alkyl sulfate can further improve the drying property, intermittent printing property, sharpness of printing, abrasion resistance, and the like of the ink-jet ink.

However, for applications where safety is not critical enough to be commonly used for pharmaceuticals, such as foods and food packaging materials, any of the above food colorings may be used as long as they comply with the laws and regulations of each country applicable to the applicable application. may be used.
The type and proportion of the food coloring can be appropriately set according to the color, color density, and the like.
However, the proportion of the edible colorant in the total amount of the inkjet ink is preferably 0.5% by mass or more, particularly 1% by mass or more, and is 10% by mass or less, especially 5% by mass or less, particularly 3% by mass or less. is preferred.

If the ratio of the food coloring is less than this range, the ink-jet ink may have insufficient color development.
On the other hand, if the ratio of the food coloring exceeds the above range, the viscosity of the inkjet ink becomes too high, and the undissolved food coloring causes ejection failure when the inkjet ink is ejected from the nozzle of the inkjet printer. It may happen.

On the other hand, by setting the ratio of the edible coloring matter within the above range, the inkjet ink can be colored with a sufficient density while suppressing the increase in viscosity and the occurrence of ejection failure.
In addition to food coloring, it is also possible to use pigments that can be used as food additives or pharmaceutical additives. Printability may deteriorate.

Therefore, pigments are not included (excluded) in the present invention.
<Ethanol>
Inkjet inks that use only water as a solvent require heating after printing as described above, but by using ethanol together with water, quick-drying properties can be imparted to the ink jet inks.

Further, even if heating after printing is omitted, bleeding can be suppressed and the sharpness of printing can be improved.
Further, by using ethanol together with water, as described above, the solubility of the alkyl sulfate can be adjusted to improve the intermittent printing property .

Ethanol is also excellent in terms of volatility, versatility, safety and the like.
The proportion of ethanol in the total amount of ethanol and water is preferably 8% by mass or more, particularly preferably 10% by mass or more, and 61% by mass or less, particularly preferably 51% by mass or less.
If the proportion of ethanol is less than this range, the ink-jet ink dries quickly, and when heating is omitted, printing tends to blur, and the sharpness of the printing may deteriorate.

In addition, since the amount of water is relatively large, the solubility of the alkyl sulfate salt becomes too strong, and the effect of improving the intermittent printing performance due to the mechanism described above may not be obtained sufficiently.
On the other hand, when the proportion of ethanol is higher than the above range, the amount of water is relatively small, so the solubility of the alkyl sulfate ester salt is reduced, and the effect of improving intermittent printing performance is also due to the mechanism described above. may not be obtained sufficiently.

In addition, the undissolved alkyl sulfate may cause ejection failure when the inkjet ink is ejected from nozzles of an inkjet printer.
On the other hand, by setting the proportion of ethanol within the above range, it is possible to further improve the drying properties of the inkjet ink, the intermittent printability, the sharpness of the print, etc. while suppressing the occurrence of ejection failure.

It is conceivable to use other water-soluble organic solvents such as alcohols having 4 or more carbon atoms or propylene glycol together with ethanol .
However, since these other water-soluble organic solvents have a high boiling point, the ink-jet ink dries quickly, and when heating is omitted, printing tends to bleed, and the sharpness of printing may deteriorate.

Therefore, the other water-soluble organic solvents are not included (excluded) in the present invention.
The inkjet ink of the present invention is prepared by adding water (for example, ultrapure water) to each of the above components to make the total amount 100% by mass.
The inkjet ink of the present invention can be suitably used in the aforementioned on-demand inkjet printer.

In particular, it is possible to print directly on the surface of tablets, capsules, and other solid preparations by using an on-demand thermal inkjet printer.

EXAMPLES The present invention will be described below based on examples and comparative examples, but the configuration of the present invention is not necessarily limited to these examples.
<Example 1>
After blending each of the following components, the mixture was filtered using a 1 μm membrane filter to prepare an inkjet ink.

Each component in the table is as follows.
Food coloring: Food Red No. 40 Surfactant: Sodium lauryl sulfate (Melting point: 204°C, solid at room temperature.)
Water-soluble organic solvent: ethanol (boiling point: 78.3°C)
The proportion of sodium lauryl sulfate was 2.0% by weight in the total amount of the inkjet ink, and the proportion of ethanol was 18.8% by weight in the total amount of ethanol and water.

<Example 2>
An inkjet ink was prepared in the same manner as in Example 1, except that the same amount of magnesium lauryl sulfate (melting point: 207° C., solid at room temperature) was added as a surfactant instead of sodium lauryl sulfate.
The ratio of magnesium lauryl sulfate was 2.0% by weight in the total amount of the inkjet ink, and the ratio of ethanol was 18.8% by weight in the total amount of ethanol and water.

<Example 3>
An inkjet ink was prepared in the same manner as in Example 1, except that the same amount of sodium cetyl sulfate (melting point: 191° C., solid at room temperature) was added as a surfactant instead of sodium lauryl sulfate.
The proportion of sodium cetyl sulfate was 2.0% by weight in the total amount of the inkjet ink, and the proportion of ethanol was 18.8% by weight in the total amount of ethanol and water.

<Comparative Example 1>
An inkjet ink was prepared in the same manner as in Example 1, except that the same amount of decaglyceryl laurate (melting point: 10° C., liquid at room temperature) was added as a surfactant instead of sodium lauryl sulfate.
The proportion of decaglyceryl laurate was 2.0% by weight in the total amount of the inkjet ink, and the proportion of ethanol was 18.8% by weight in the total amount of ethanol and water.

<Comparative Example 2>
An inkjet ink was prepared in the same manner as in Comparative Example 1, except that the same amount of propylene glycol (boiling point: 188.2° C.) was added as the water-soluble organic solvent instead of ethanol.
This corresponds to the conventional inkjet ink described in Patent Document 1.

<Comparative Example 3>
An inkjet ink was prepared in the same manner as in Example 1 except that sodium lauryl sulfate was not blended as a surfactant, the amount of ethanol was 18.4% by mass, and the amount of ultrapure water was 79.6% by mass. bottom.
The proportion of sodium lauryl sulfate was 0.0% by weight in the total amount of the inkjet ink, and the proportion of ethanol was 18.8% by weight in the total amount of ethanol and water.

<Example 4>
In the same manner as in Example 1, except that the amount of sodium lauryl sulfate as a surfactant was 0.03% by mass, the amount of ethanol was 18.38% by mass, and the amount of ultrapure water was 79.59% by mass. An inkjet ink was prepared.
The proportion of sodium lauryl sulfate was 0.03% by weight in the total amount of the inkjet ink, and the proportion of ethanol was 18.8% by weight in the total amount of ethanol and water.

<Example 5>
In the same manner as in Example 1, except that the amount of sodium lauryl sulfate as a surfactant was 0.05% by mass, the amount of ethanol was 18.45% by mass, and the amount of ultrapure water was 79.5% by mass. An inkjet ink was prepared.
The proportion of sodium lauryl sulfate was 0.05% by weight in the total amount of the inkjet ink, and the proportion of ethanol was 18.8% by weight in the total amount of ethanol and water.

<Example 6>
In the same manner as in Example 1, except that the amount of sodium lauryl sulfate as a surfactant was 3.0% by mass, the amount of ethanol was 17.9% by mass, and the amount of ultrapure water was 77.1% by mass. An inkjet ink was prepared.
The proportion of sodium lauryl sulfate was 3.0% by weight in the total amount of the inkjet ink, and the proportion of ethanol was 18.8% by weight in the total amount of ethanol and water.

<Example 7>
In the same manner as in Example 1, except that the amount of sodium lauryl sulfate as a surfactant was 4.0% by mass, the amount of ethanol was 17.7% by mass, and the amount of ultrapure water was 76.3% by mass. An inkjet ink was prepared.
The proportion of sodium lauryl sulfate was 4.0% by weight in the total amount of the inkjet ink, and the proportion of ethanol was 18.8% by weight in the total amount of ethanol and water.

<Example 8>
In the same manner as in Example 1, except that the amount of sodium lauryl sulfate as a surfactant was 5.0% by mass, the amount of ethanol was 17.5% by mass, and the amount of ultrapure water was 75.5% by mass. An inkjet ink was prepared.
The proportion of sodium lauryl sulfate was 5.0% by weight in the total amount of the inkjet ink, and the proportion of ethanol was 18.8% by weight in the total amount of ethanol and water.

<Example 9>
In the same manner as in Example 1, except that the amount of sodium lauryl sulfate as a surfactant was 7.0% by mass, the amount of ethanol was 17.1% by mass, and the amount of ultrapure water was 73.9% by mass. An inkjet ink was prepared.
The proportion of sodium lauryl sulfate was 7.0% by weight in the total amount of the inkjet ink, and the proportion of ethanol was 18.8% by weight in the total amount of ethanol and water.

<Example 10>
An inkjet ink was prepared in the same manner as in Example 1, except that Food Red No. 40 was replaced with Food Red No. 102 as the food coloring in the same amount.
The proportion of sodium lauryl sulfate was 2.0% by weight in the total amount of the inkjet ink, and the proportion of ethanol was 18.8% by weight in the total amount of ethanol and water.

<Comparative Example 4>
An inkjet ink was prepared in the same manner as in Example 1, except that the same amount of edible pigment was added instead of the edible pigment.
The proportion of sodium lauryl sulfate was 2.0% by weight in the total amount of the inkjet ink, and the proportion of ethanol was 18.8% by weight in the total amount of ethanol and water.

This corresponds to the conventional inkjet ink described in Patent Document 2.
<Comparative Example 5>
An inkjet ink was prepared in the same manner as in Example 1, except that ethanol was not blended and the amount of ultrapure water was 96.0% by mass.
The proportion of sodium lauryl sulfate was 2.0% by mass in the total amount of the inkjet ink, and the proportion of ethanol was 0.0% by mass in the total amount of ethanol and water.

<Example 11>
An inkjet ink was prepared in the same manner as in Example 1, except that the amount of ethanol was 8.0% by mass and the amount of ultrapure water was 88.0% by mass.
The proportion of sodium lauryl sulfate was 2.0% by mass in the total amount of the inkjet ink, and the proportion of ethanol was 8.3% by mass in the total amount of ethanol and water.

<Example 12>
An inkjet ink was prepared in the same manner as in Example 1, except that the amount of ethanol was 10.0% by mass and the amount of ultrapure water was 86.0% by mass.
The proportion of sodium lauryl sulfate was 2.0% by weight in the total amount of the inkjet ink, and the proportion of ethanol was 10.4% by weight in the total amount of ethanol and water.

<Example 13>
An inkjet ink was prepared in the same manner as in Example 1, except that the amount of ethanol was 15.5% by mass and the amount of ultrapure water was 80.5% by mass.
The proportion of sodium lauryl sulfate was 2.0% by weight in the total amount of the inkjet ink, and the proportion of ethanol was 16.1% by weight in the total amount of ethanol and water.

<Example 14>
An inkjet ink was prepared in the same manner as in Example 1, except that the amount of ethanol was 30.0% by mass and the amount of ultrapure water was 66.0% by mass.
The proportion of sodium lauryl sulfate was 2.0% by mass in the total amount of the inkjet ink, and the proportion of ethanol was 31.3% by mass in the total amount of ethanol and water.

<Example 15>
An inkjet ink was prepared in the same manner as in Example 1, except that the amount of ethanol was 48.5% by mass and the amount of ultrapure water was 47.5% by mass.
The proportion of sodium lauryl sulfate was 2.0% by weight in the total amount of the inkjet ink, and the proportion of ethanol was 50.5% by weight in the total amount of ethanol and water.

<Example 16>
An inkjet ink was prepared in the same manner as in Example 1, except that the amount of ethanol was 58.0% by mass and the amount of ultrapure water was 38.0% by mass.
The proportion of sodium lauryl sulfate was 2.0% by weight in the total amount of the inkjet ink, and the proportion of ethanol was 60.4% by weight in the total amount of ethanol and water.

<Comparative Example 6>
An inkjet ink was prepared in the same manner as in Example 1, except that the amount of ethanol was 96.0 mass % and no ultrapure water was added.
The proportion of sodium lauryl sulfate was 2.0% by mass in the total amount of the inkjet ink, and the proportion of ethanol was 100.0% by mass in the total amount of ethanol and water.

<Intermittent printing test>
Using an on-demand thermal inkjet printer [Print Mail Wide Array manufactured by Videojet Co., Ltd.], the inkjet inks prepared in Examples and Comparative Examples are applied to the surface of the FC tablet with a semi-voiced sound of 2 points. An "°" was printed, and the same printing was performed again after standing for 20 minutes or 60 minutes in the decapped state.

After standing still, the state of print defects, deformation, scattering, etc. was observed, and the intermittent printability was evaluated according to the following criteria.
◯: No chipping, deformation, scattering, or the like of the print was observed even after standing for 60 minutes.
Δ: Missing, deformation, scattering, etc. of printing were observed after standing for 60 minutes, but chipping, deformation, scattering, etc. of printing were not observed after standing still for 20 minutes.

x: Missing, deformation, scattering, etc. of printing were observed even after standing still for 20 minutes.
<Scratch resistance test>
Using the same inkjet printer as used in the intermittent printing test, the inkjet inks prepared in Examples and Comparative Examples were printed on the surface of FC tablets.
After rubbing the surface of the FC tablet 30 times with a lard-tipped finger under a load of 1 kgf, the print was visually observed and fixability was evaluated according to the following criteria.

◯: No change was observed in printing compared to before rubbing.
Δ: The print was slightly blurred, but could be read.
x: Printing was blurred and could not be read.
<Print clarity test>
Using the same inkjet printer as that used in the intermittent printing test, 1 dot was printed on the surface of the FC tablet with the inkjet inks prepared in Examples and Comparative Examples.

Then, the dot diameter was measured, and the sharpness of printing was evaluated according to the following criteria.
◯: The dot diameter was 80 μm or more and 100 μm or less.
Δ: The dot diameter was 50 μm or more and less than 80 μm, or more than 100 μm and 150 μm or less.
x: The dot diameter was less than 50 μm or greater than 150 μm.

<Drying test>
Using the same inkjet printer as that used in the intermittent printing test, 300×600 dpi printing was performed on the surface of the FC tablet with the inkjet inks prepared in Examples and Comparative Examples.
After a certain period of time has passed since the printing, when the operation of rubbing the printing once with a cotton swab is repeated with the elapsed time extended by 1 second from 1 second after printing, the printing does not stretch or blur. The elapsed time required was recorded, and the dryness was evaluated according to the following criteria.

◯: 8 seconds after printing, printing did not stretch or blur.
Δ: Printing did not stretch or blur between 9 seconds and 12 seconds after printing.
x: It took 13 seconds or longer for the print to stop stretching or blurring.
The above results are shown in Tables 2 to 6.

From the results of Examples 1 to 16 and Comparative Examples 1 to 6 in Tables 2 to 6, the combination of food coloring, alkyl sulfate with 12 carbon atoms and/or alkyl sulfate with 16 carbon atoms, ethanol , and water By doing so, it can be used for printing on the surface of solid preparations, etc., and moreover, it has excellent drying properties and intermittent printing properties compared to conventional ones, and it is also possible to print with excellent clarity and abrasion resistance. It turned out that the inkjet ink which can be made can be provided.

Further, from the results of Examples 1 to 3, it was found that it is preferable to select and use sodium lauryl sulfate as the alkyl sulfate salt.
From the results of Examples 1 and 4 to 9, it was found that the ratio of alkyl sulfate such as sodium lauryl sulfate is 0.03% by mass or more, particularly 0.05% by mass or more in the total amount of the inkjet ink. It was found that the amount is preferably 7% by mass or less, particularly preferably 5% by mass or less.

From the results of Examples 1 and 10, it was found that it is preferable to use Food Red No. 40 or Food Red No. 102 as the red food coloring.
From the results of Examples 1 and 11 to 16, the proportion of ethanol in the total amount of alcohol and water is preferably 8% by mass or more, particularly 10% by mass or more, and 61% by mass or less, particularly 51% by mass. % or less was found to be preferable.

Claims (5)

・ Food coloring (excluding pigments) ,
- At least one alkyl sulfate salt selected from the group consisting of an alkyl sulfate salt having 12 carbon atoms and an alkyl sulfate ester salt having 16 carbon atoms,
Inkjet inks containing ethanol and water. The inkjet ink of claim 1, wherein the alkyl sulfate salt is sodium lauryl sulfate. 3. The inkjet ink according to claim 1, wherein the proportion of the alkyl sulfate ester salt is 0.05% by mass or more and 5% by mass or less in the total amount of the inkjet ink. The inkjet ink according to any one of claims 1 to 3 , wherein the ethanol content is 10% by mass or more and 51% by mass or less in the total amount of the ethanol and the water. 5. The inkjet ink of any one of claims 1 to 4 , wherein the food coloring is Food Red No. 40.