JP6847754B2 - Pigment composition and water-based ink composition for inkjet - Google Patents

Description

The present invention relates to a pigment composition and an aqueous ink composition for inkjet, and more specifically, an edible pigment having excellent dispersibility and capable of being directly printed on tablets of pharmaceuticals, foods, etc. by an inkjet method. The present invention relates to a composition and an aqueous ink composition for inkjet.

For foods such as tablets of pharmaceuticals and supplements, by displaying product information not only on the packaging but also on the tablet itself, dispensing mistakes and accidental ingestion are prevented. It is possible to print on tablets whose surface is coated by a contact method such as gravure printing, but it is difficult to print by contact method with uncoated tablets and OD (orally disintegrating) tablets with poor surface smoothness. There is. Therefore, for these tablets, the engraving method that can display only simple characters has become the mainstream. Therefore, in the pharmaceutical industry, there is an increasing need for a new printing method capable of displaying product information even on uncoated tablets and OD tablets.

Examples of such a printing method include inkjet printing using an aqueous ink composition using a dye (see Patent Document 1 below). However, in the conventional water-based ink composition, there is no one using an edible white dye. Therefore, it is conceivable to use an aqueous ink composition using a white pigment such as titanium oxide. However, since titanium oxide is an inorganic pigment having a heavy specific gravity, it is difficult to secure a level of dispersibility that can be applied to water-based ink jet inks. Further, as a pigment dispersant for satisfactorily dispersing titanium oxide, it is necessary to use a pigment dispersant that conforms to the standards such as pharmaceutical additives specified by the Pharmaceutical Affairs Law, and it is difficult to select a material. As a result, so far, no water-based ink composition using a white pigment has been put on the market that solves these problems.

Japanese Unexamined Patent Publication No. 2011-236279

The present invention has been made in view of the above problems, and an object of the present invention is that the average dispersed particle size of the pigment is small, the dispersibility is excellent, and the pigment is directly printed on tablets of pharmaceuticals, foods, etc. by an inkjet method. It is an object of the present invention to provide an edible pigment composition and an aqueous ink composition for inkjet.

As a result of examining the pigment composition and the water-based ink composition for inkjet in order to solve the above-mentioned problems, the inventors of the present application have found that the above-mentioned problems can be solved by adopting the following configuration, and have found that the present invention can be solved. It came to be completed.

That is, in order to solve the above-mentioned problems, the pigment composition according to the present invention comprises a pigment composed of titanium oxide particles and / or zinc oxide particles whose surface is not hydrophilic, and a pigment having a mass average molecular weight of 10,000 or less. The ratio of the average primary particle size of the titanium oxide particles or the zinc oxide particles to the average dispersed particle size D50 of the dispersed titanium oxide particles or zinc oxide particles containing sodium polyacrylate as a dispersant is 1: 0. It is characterized in that it is in the range of 3 to 1: 3.

According to the above configuration, as a pigment dispersant for a pigment composed of titanium oxide particles and / or zinc oxide particles whose surface is not hydrophilized by hydrate of silicon dioxide, poly having a mass average molecular weight in the range of 10,000 or less. By using sodium acrylate, the ratio of the average primary particle size of the titanium oxide particles or zinc oxide particles to the average dispersed particle size D50 of the dispersed titanium oxide particles or zinc oxide particles is set to 1: 0.3 to 1: 3. Within the range, the average dispersed particle size of the pigment can be reduced to a level close to the average primary particle size. Thereby, it is possible to prevent the reaggregation of the pigment and provide a pigment composition having excellent dispersibility.

Further, according to the above configuration, since a pigment composed of titanium oxide particles and / or zinc oxide particles is used instead of the dye, when the pigment composition of the present invention is used, for example, in an aqueous ink composition for inkjet. Can improve the light resistance as compared with the ink composition using a dye.

In the above configuration, it is preferable that the surface of the titanium oxide particles is hydrophilic. Thereby, the ratio of the average primary particle size of the titanium oxide particles to the average dispersed particle size D50 of the dispersed titanium oxide particles can be set in the range of 1: 0.3 to 1: 3.

In the above configuration, the average primary particle size of the titanium oxide particles or the zinc oxide particles is preferably in the range of 20 nm to 400 nm. By setting the average primary particle size of the titanium oxide particles or zinc oxide particles to 20 nm or more, it is possible to suppress a decrease in the light resistance of the printed image. On the other hand, by setting the average primary particle size to 400 nm or less, it is possible to prevent the pigment from settling in the ink and the nozzle from clogging.
High color can be achieved.

Further, in the above configuration, it is preferable that the average dispersed particle size D50 of the dispersed titanium oxide particles or zinc oxide particles is in the range of 20 nm to 500 nm. By setting the D50 of the dispersed titanium oxide particles or zinc oxide particles to 20 nm or more, it is possible to suppress deterioration of storage stability, light resistance and ejection stability, and also prevent reduction of printing density. On the other hand, by setting the D50 to 500 nm or less, separation, sedimentation and aggregation of the pigment composed of titanium oxide particles or zinc oxide particles can be prevented, and storage stability can be maintained.

Further, in the above configuration, the content ratio of the pigment composed of the titanium oxide particles and / or the zinc oxide particles to the sodium polyacrylate is 1: 0.05 to 1: 1.5 on a mass basis. It is preferably within the range. As a result, it is possible to prevent a decrease in the dispersibility of the pigment and also prevent a decrease in discharge stability due to clogging of the nozzle or the like. Therefore, when the pigment composition having the above constitution is applied to the water-based ink composition, printing by an inkjet method is possible. Further, as described above, since it is also excellent in light resistance, it is possible to prevent the occurrence of blurring of the printed image.

The water-based ink composition for inkjet according to the present invention is characterized in that it contains the pigment composition and is edible in order to solve the above-mentioned problems.

The pigment composition contains a pharmaceutical additive specified by the Pharmaceutical Affairs Law, sodium polyacrylate conforming to the standards of the Japanese Pharmacy and Food Additives Official Standards as a pigment dispersant, and therefore for inkjets containing the pigment composition. The water-based ink composition can be suitably used as an ink material for direct printing on tablets such as pharmaceuticals and foods by an inkjet method. Further, in the pigment composition, instead of the dye, a pigment composed of titanium oxide particles and / or zinc oxide particles whose surface is not hydrophilized by a hydrate of silicon dioxide is used, so that, for example, a pharmaceutical product or the like is used. Even if the printed image is printed on the surface of the tablet by an inkjet method, the printed image has excellent light resistance and can prevent the occurrence of bleeding. In addition, edible means that it consists only of a substance approved for oral administration as a drug or a pharmaceutical additive, and / or a substance approved as a food or a food additive.

According to the present invention, it conforms to the standards of pharmaceutical additives, Japanese Pharmacopoeia or Food Additives Official Standards stipulated by the Pharmaceutical Affairs Law, and the titanium oxide particles and / or the surface are hydrophilized by hydrate of silicon dioxide. Since it contains sodium polyacrylate, which imparts good dispersibility to pigments composed of zinc oxide particles, it is possible to print directly on tablets of pharmaceuticals, foods, etc. with good ejection stability by the inkjet method. It is possible to provide a pigment composition and an aqueous ink composition for inkjet. Further, the water-based ink composition for inkjet using a pigment composed of titanium oxide particles and / or zinc oxide particles has excellent light resistance as compared with those using a dye or the like, and can prevent bleeding of a printed image. ..

(Pigment composition and its manufacturing method)
The pigment composition according to the present embodiment is a pigment composed of titanium oxide (TiO ₂ ) particles and / or zinc oxide (ZnO) particles whose surface is not hydrophilized by a hydrate of silicon dioxide, and a pigment dispersant. It is a composition of a pigment dispersion containing at least sodium polyacrylate (hereinafter, "titanium oxide particles and / or zinc oxide particles whose surface is not hydrophilized by a hydrate of silicon dioxide" are referred to as "titanium oxide". A pigment composed of titanium oxide particles or the like is sometimes referred to as a "pigment".)

The pigment composed of titanium oxide particles is a white pigment, which has a smaller specific gravity and a higher refractive index than other known white pigments. In addition, titanium oxide pigments are chemically and physically stable. Therefore, the pigment composed of titanium oxide particles is excellent in hiding property and coloring property, and is also excellent in durability against acids, alkalis and other environments. Further, the pigment composed of the zinc oxide particles is also a white pigment, which is an inorganic pigment having an ultraviolet shielding property. In addition to the pigment, the pigment composition of the present embodiment may contain a known pigment.

In the present embodiment, the titanium oxide particles having a crystal structure of anatase type (tetragonal crystal), rutile type (tetragonal crystal) or blue kite type (orthorhombic crystal) can be used. However, when the pigment composition of the present embodiment is applied to an aqueous ink composition for inkjet, titanium oxide having a rutile crystal structure is preferable from the viewpoint of improving the concealing property of a printed image. This makes it possible to prevent the printed image from being visually observed from the surface to be printed (formed). Further, titanium oxide having a rutile-type crystal structure has a high refractive index of visible light (wavelength range 360 nm to 830 nm), so that color development can be improved. On the other hand, since titanium oxide having an anatase-type crystal structure has a function as a photocatalyst, when it is used in the pigment composition of the present embodiment, the photocatalyst material can be applied by an inkjet method. As a result, as compared with the coating of the photocatalyst material by the conventional spray method, the loss due to the scattering of the sprayed photocatalyst material can be significantly reduced, and the coating accuracy can be improved. In the present invention, the titanium oxide particles mean crystalline titanium oxide particles unless otherwise specified.

The surface of the titanium oxide particles is preferably hydrophilic. This makes it possible to bring the average dispersed particle size of the dispersed titanium oxide particles close to the average primary particle size of the titanium oxide particles (details will be described later). Hydroxylation groups are usually present on the surface of the titanium oxide particles, which makes the surface of the titanium oxide particles hydrophilic. In the present invention, "hydrophilic" means that a functional group or the like having an affinity for water is present on the surface of the titanium oxide particles.

Further, in the present invention, the hydrophilic treatment may be performed from the viewpoint of improving or maintaining the hydrophilicity of the surface of the titanium oxide particles. When the surface of the titanium oxide particles is hydrophilized, for example, an inorganic compound and / or an organic compound surface treatment agent can be used.

The surface treatment agent for the inorganic compound is not particularly limited, and examples thereof include aluminum hydroxide, aluminum oxide, zirconium oxide, silica, and cerium oxide. The surface treatment agent for the organic compound is not particularly limited, and for example, dimethylpolysiloxane, methylhydrogenpolysiloxane, (dimethicone / methicone) copolymer, methylphenylsilicone, amino-modified silicone, hydrogendimethicone, triethoxysilylethyl. Silicone oils such as polydimethylsiloxyethyl dimethicone and triethoxysilylethyl polydimethylsiloxyethylhexyl dimethicone; higher fatty acids such as stearic acid and lauric acid; Polyhydric alcohols such as; alkanolamines such as triethanolamine and tripropanolamine, or derivatives such as hydrochlorides or organic acid salts thereof; alkylsilanes such as caprylylsilane, decylsilane, perfluorooctylsilane, alkyltitanates, alkylaluminum. Amines such as nate, polyolefin, polyester, lauroyl lysine; organic metal compounds such as titanium-based coupling agents, aluminum-based coupling agents, and zirconium-based coupling agents can be mentioned. The surface treatment can be performed with at least one compound selected from these organic compounds. Further, the hydrophilic treatment may be performed by combining an inorganic compound and an organic compound.

Commercially available products can also be used as the titanium oxide particles, and such commercially available products include, for example, STR-100N (trade name, manufactured by Sakai Chemical Industry Co., Ltd., rutile type), TTO-51A (trade name). , Ishihara Sangyo Co., Ltd., rutile type), TTO-55A (trade name, Ishihara Sangyo Co., Ltd., rutile type), TTO-55A (trade name, Ishihara Sangyo Co., Ltd., rutile type), TTO-80A (commodity) Name, Ishihara Sangyo Co., Ltd., rutile type), MPT-140 (trade name, Ishihara Sangyo Co., Ltd., rutile type), MPT-141 (trade name, Ishihara Sangyo Co., Ltd., rutile type), MKR-1 (trade name, Ishihara Sangyo Co., Ltd., rutile type) Product names, Sakai Chemical Industry Co., Ltd., rutile type), KA-10 (trade name, Titanium Industry Co., Ltd., anatase type) and the like can be mentioned.

In the present embodiment, as the zinc oxide particles, those whose surface is not hydrophilized with silicon dioxide hydrate (hydrophilic silica) are used. That is, when zinc oxide particles obtained by forming a film made of silicon dioxide hydrate (hydrous silica) on the surface and hydrophilized are used together with sodium polyacrylate described later as a pigment dispersant, the zinc oxide particles are used. The average dispersed particle size of the pigment becomes large, and the storage stability may decrease. By using zinc oxide particles whose surface is not hydrophilized with silicon dioxide hydrate, the average dispersed particle size of the dispersed zinc oxide particles is brought close to the average primary particle size of the zinc oxide particles. Will be possible. In the present invention, the zinc oxide particles mean crystalline zinc oxide particles unless otherwise specified. Further, the zinc oxide particles of the present invention include those whose surface is coated with a compound other than the hydrate of silicon dioxide and hydrophilized.

Commercially available products can be used as the zinc oxide particles, and examples of such commercially available products include FINEX-50 (trade name, manufactured by Sakai Chemical Industry Co., Ltd.) and FINEX-30 (trade name, Sakai Chemical Co., Ltd.). Examples include (manufactured by Kogyo Co., Ltd.) and FINEX-25 (trade name, manufactured by Sakai Chemical Industry Co., Ltd.).

The pigment of the titanium oxide particles and / or the zinc oxide particles whose surface is not hydrophilized (hereinafter, may be referred to as “titanium oxide particles or the like”) is the pigment composition of the present embodiment, such as a pharmaceutical product or a supplement. When used for printing on the surface of tablets, it must comply with the standards of the Pharmaceutical Additives, Japanese Pharmacy Law or Food Additives Official Standards (hereinafter referred to as "Standards of the Pharmaceutical Affairs Law, etc.") specified by the Pharmaceutical Affairs Law. preferable.

The average primary particle size (volume average particle size) of the titanium oxide particles or the like is preferably 20 nm to 400 nm, more preferably 30 nm to 200 nm, and particularly preferably 40 nm to 100 nm. By setting the average primary particle size to 20 nm or more, the decrease in light resistance of the printed image can be suppressed, the concentration of the pigment can be increased, and the transparency can be improved. In addition, sufficient concealment can be ensured. On the other hand, by setting the average primary particle diameter to 400 nm or less, it is possible to achieve high coloration and prevent sedimentation of titanium oxide particles and the like and clogging of nozzles. In addition, when pigment particles having a large average primary particle size are usually selected, the pigment particles are sufficiently ground to enable pigment dispersion at the level of the average dispersed particle size required for printing by an inkjet method. The process time for this is long. However, as described above, by setting the average primary particle size to 400 nm or less, it is possible to suppress the lengthening of the process time.

In the present invention, the "average primary particle size" means the average particle size of the primary particles, and the primary particles generally mean the smallest particles constituting the powder, and are single crystals or crystals close to them. It means that it includes particles formed by gathering together.

The average primary particle diameter is an arithmetic mean diameter obtained by observing titanium oxide particles or the like with an electron microscope. In the present embodiment, titanium oxide particles or the like having a monodisperse particle size distribution are used, but the present invention is not limited to this, and titanium oxide particles or the like having a multi-dispersion particle size distribution may be used. Good. Further, two or more kinds of pigments having a monodisperse particle size distribution may be mixed and used.

The shape of the titanium oxide particles and the like is not particularly limited, and any shape such as a spherical shape, a rod shape, a needle shape, a spindle shape, and a plate shape can be used. In the present embodiment, titanium oxide particles having the same shape may be used, or two or more different shapes may be mixed and used. The average primary particle diameter in the case of rod-shaped, needle-shaped, or spindle-shaped particles is defined by a geometric mean value of the length (or height) of the major axis and the length (or width) of the minor axis.

Since the content of the pigment directly affects the image density and affects the storage stability, viscosity, pH, etc. of the water-based ink composition described later, it should be appropriately set in consideration of these points. Just do it. Usually, it is preferably in the range of 2% by mass to 20% by mass, more preferably in the range of 5% by mass to 15% by mass, based on the total mass of the pigment composition. By setting the content of the pigment composed of titanium oxide particles and / or zinc oxide particles to 2% by mass or more, it is possible to suppress a decrease in image density. On the other hand, by reducing the content of the pigment composed of titanium oxide particles and / or zinc oxide particles to 20% by mass or less, it is possible to prevent a decrease in glossiness, clogging of nozzles, and a decrease in discharge stability.

The sodium polyacrylate functions as a pigment dispersant for the pigment of the present embodiment. By blending sodium polyacrylate, the dispersibility of the pigment can be improved. In addition, sodium polyacrylate conforms to the standards stipulated by the Pharmaceutical Affairs Law and the like. Therefore, sodium polyacrylate can be suitably used for printing on tablets and the like of pharmaceuticals or foods.

The mass average molecular weight of sodium polyacrylate is 10,000 or less, preferably 1500 to 10000, and more preferably 2000 to 8000. By setting the mass average molecular weight of sodium polyacrylate to 10,000 or less, it is possible to prevent the molecular chain of sodium polyacrylate adsorbed on the surface of titanium oxide particles or the like from becoming excessively long. As a result, it is possible to reduce the possibility that pigments made of titanium oxide particles or the like are crosslinked and aggregated. By setting the mass average molecular weight of sodium polyacrylate to 1500 or more, it is possible for sodium polyacrylate adsorbed on the surface of titanium oxide particles or the like to sufficiently exert a repulsive force due to steric hindrance or the like. As a result, it is possible to prevent the titanium oxide particles and the like from reaggregating with each other. The mass average molecular weight of sodium polyacrylate is, for example, a value obtained by the measuring method described in Examples described later.

The content ratio of the pigment of the present embodiment to the sodium polyacrylate is preferably 1: 0.05 to 1: 1.5 on a mass basis, and is 1: 0.1 to 1: 1. Is more preferable. By setting the content ratio to 1: 0.05 or more, it is possible to prevent a decrease in the dispersibility of the pigment of the titanium oxide particles. On the other hand, by setting the content ratio to 1: 1.5 or less, it is possible to prevent a decrease in ejection stability due to adhesion of the nozzle plate, for example, when used in an inkjet water-based ink composition. ..

When sodium polyacrylate is added to a dispersion medium described later, for example, bubbles are relatively less likely to be generated as compared with other conventional pigment dispersants. Therefore, in the pigment composition of the present embodiment, the addition of the antifoaming agent can be omitted.

The pigment composition according to the present embodiment contains a dispersion medium for dispersing the pigment of titanium oxide particles and / or zinc oxide particles whose surface has not been hydrophilized with silicon dioxide hydrate. .. Examples of the dispersion medium include water, and more specifically, pure water such as ion-exchanged water, ultrafiltration water, reverse osmosis water, and distilled water, or those from which ionic impurities such as ultrapure water have been removed can be mentioned. .. In particular, water that has been sterilized by irradiation with ultraviolet rays or addition of hydrogen peroxide is suitable because it can prevent the growth of mold and bacteria for a long period of time. Further, the content of the dispersion medium is not particularly limited and can be appropriately set as needed.

Further, as the dispersion medium, a mixed solution of the water and a water-soluble organic solvent may be used. The water-soluble organic solvent is not particularly limited, and specifically, for example, alcohols such as methyl alcohol, ethyl alcohol, n-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, n-propyl alcohol, and isopropyl alcohol; Amidos such as dimethylformamide and dimethylacetamide; ketones such as acetone and methylethylketone; tetrahydrofuran, dioxane, ethylene glycol methyl ether, ethylene glycol ethyl ether, diethylene glycol methyl ether, diethylene glycol ethyl ether, triethylene glycol monomethyl ether, triethylene glycol mono Ethers such as ethyl ethers; ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, triethylene glycol, 1,2,6-hexanetriol, thiodiglycol, polyethylene glycol, polypropylene glycol, glycerin, diglycerin, polyglycerin, etc. Polyhydric alcohols; N-methylpyrrolidone, 1,3-dimethyl-2-imidazolidinone and the like. These may be used alone or in combination of two or more. In addition, among these water-soluble organic solvents, ethyl alcohol, n-butyl alcohol, isobutyl alcohol, and n-propyl are classified as those that meet the standards of the Pharmaceutical Additives, Japanese Pharmacy, or Food Additives Official Standards stipulated by the Pharmaceutical Affairs Law. Alcohol, isopropyl alcohol, acetone, propylene glycol, polyethylene glycol and glycerin are preferable. Further, the blending amount when a water-soluble organic solvent is used as the dispersion medium is not particularly limited, and can be appropriately set as needed.

The average dispersed particle diameter D50 of the dispersed titanium oxide particles and the like is preferably in the range of 20 nm to 500 nm, and more preferably in the range of 40 nm to 100 nm. Further, the dispersed particle size D99 of the pigment (the particle size of 99% in the integrated particle size distribution in the volume integrated particle size distribution) is preferably 1000 nm or less, more preferably 500 nm or less. By setting the D50 to 20 nm or more, deterioration of storage stability, light resistance and ejection stability can be prevented, and a decrease in print density can also be prevented. On the other hand, by setting D50 to 500 nm or less or D99 to 1000 nm or less, separation, precipitation and aggregation of the pigment can be prevented, and storage stability can be maintained. The average dispersed particle diameters D50 and D99 of the pigment are values measured by a dynamic light scattering method using Microtrac UPA-EX150 (trade name, manufactured by Nikkiso Co., Ltd.).

The ratio of the average primary particle size of the titanium oxide particles and the like to the average dispersed particle size D50 of the titanium oxide particles dispersed in the dispersion medium is in the range of 1: 0.3 to 1: 3. In the present embodiment, by using sodium polyacrylate having a mass average molecular weight of 10,000 or less as a pigment dispersant for a pigment such as titanium oxide particles, the average dispersed particle size of the titanium oxide particles or the like can be adjusted to the titanium oxide particles or the like. The level can be almost the same as the average primary particle size of. As a result, for example, when titanium oxide particles having a small average primary particle size are used, a pigment composition having a small average dispersed particle size D50 can be obtained, and separation, precipitation, and aggregation of the pigment are prevented and stored. Stability can be maintained. The ratio of the average primary particle size of the titanium oxide particles and the like to the average dispersed particle size D50 of the titanium oxide particles is preferably 1: 0.5 to 1: 2.5, more preferably 1: 0.8. ~ 1: 2.

In the method for producing a pigment composition of the present embodiment, a pigment composed of titanium oxide particles and / or zinc oxide particles whose surface is not hydrophilized, sodium polyacrylate, a dispersion medium, and other additions to be blended as necessary. The mixing method and the order of addition of the agents are not particularly limited. For example, a pigment of titanium oxide particles and / or zinc oxide particles, sodium polyacrylate, water as a dispersion medium, or the like may be mixed at once, and the mixed solution may be subjected to a dispersion treatment using a normal disperser. ..

However, in the present embodiment, the generation of bubbles in the pigment composition can be suppressed by using sodium polyacrylate as the pigment dispersant. Therefore, the defoaming step for reducing or eliminating the bubbles can be omitted, and the manufacturing efficiency can be improved. Further, since the inclusion of the antifoaming agent can be omitted, the production of a pigment composition conforming to the standards of the Pharmaceutical Affairs Law and the like becomes easier.

The dispersion time in the dispersion processing is not particularly limited, and can be appropriately set as needed. The disperser used in the dispersal treatment of the pigment is not particularly limited as long as it is a generally used disperser. Specific examples thereof include ball mills, roll mills, sand mills, bead mills, paint shakers, nanomizers and the like.

The pigment composition of the present embodiment includes not only the form of the water-based ink composition for inkjet which is the final product (details will be described later) but also the form of the pigment dispersion liquid for preparing the water-based ink composition. It includes.

(Aqueous ink composition for inkjet and its manufacturing method)
The water-based ink composition for inkjet (hereinafter referred to as "water-based ink composition") according to the present embodiment is a water-based ink containing at least the pigment composition and whose main solvent is water. Further, the water-based ink composition of the present embodiment has edible properties and is suitably used for inkjet recording. Further, since the water-based ink composition uses a pigment as a coloring material, it is superior in color development, light resistance, water resistance and the like as compared with an ink composition using a dye.

The content of the pigment composition is preferably in the range of 2% by mass to 40% by mass, more preferably in the range of 5% by mass to 30% by mass, in terms of pigment content, with respect to the total mass of the aqueous ink composition. By setting the content of the pigment composition to 2% by mass or more, the coloring power can be improved. On the other hand, the dispersibility can be improved by setting the content of the pigment composition to 40% by mass or less.

The water-based ink composition according to the present embodiment contains water (water as a main solvent). As the water, it is preferable to use pure water such as ion-exchanged water, ultrafiltration water, reverse osmosis water, distilled water, or water from which ionic impurities such as ultrapure water have been removed. In particular, water that has been sterilized by irradiation with ultraviolet rays or addition of hydrogen peroxide is suitable because it can prevent the growth of mold and bacteria for a long period of time. The water content is not particularly limited and can be set as needed.

In the water-based ink composition of the present embodiment, other additives may be blended. However, when used as an inkjet ink for tablets such as pharmaceuticals, it is preferable that the ink conforms to the standards of the Pharmaceutical Affairs Law and the like. Further, in the present embodiment, since the generation of air bubbles can be suppressed by adding sodium polyacrylate as a pigment dispersant, the addition of an antifoaming agent can be omitted. Further, when the water-based ink composition of the present embodiment is ejected from the inkjet head, since the bubbles do not exist in the aqueous ink composition, nozzle omission, ejection failure, and decrease in open time can be suppressed. Can be done.

Examples of the additive include a surface tension regulator, a wetting agent (antidrying agent), a fading inhibitor, an emulsion stabilizer, a penetration accelerator, an ultraviolet absorber, a preservative, a fungicide, a pH adjuster, and a viscosity regulator. Known additives such as dispersion stabilizers, rust preventives, chelating agents and the like can be mentioned. The contents of these various additives are not particularly limited and can be appropriately set as needed.

The surface tension adjusting agent is not particularly limited as long as it conforms to the standards of the Pharmaceutical Affairs Law and the like, and specific examples thereof include glycerin fatty acid ester and the like. Examples of the glycerin fatty acid ester include decaglyceryl caprylate and decaglyceryl laurate.

The amount of the surface tension adjusting agent added is preferably in the range in which the surface tension of the aqueous ink composition can be adjusted to 25 to 40 mN / m, and more preferably in the range in which the surface tension can be adjusted to 27 to 36 mN / m. When the addition amount is within the above range, it is possible to secure the ejection stability at the time of printing by the inkjet method.

The wetting agent is not particularly limited as long as it conforms to the standards of the Pharmaceutical Affairs Law and the like, and specific examples thereof include propylene glycol and glycerin.

The amount of the wetting agent added is preferably 3% by mass to 50% by mass, more preferably 10% by mass to 40% by mass, based on the total mass of the aqueous ink composition.

The viscosity of the aqueous ink composition of the present embodiment is preferably 2 mPa · s to 7 mPa · s, more preferably 3 mPa · s to 5 mPa · s at the time of ejection from the inkjet nozzle, considering the ejection stability from the inkjet nozzle. .. By setting the viscosity of the water-based ink composition within the above numerical range, it is possible to suppress the occurrence of clogging in the inkjet nozzle, maintain good ejection stability, and suppress a decrease in flight performance. The viscosity of the aqueous ink composition can be obtained by measuring, for example, using a viscometer (trade name: VISCOMATE MODEL VM-10A, manufactured by SEKONIC CORPORATION) under the condition of a measurement temperature of 25 ° C.

The water-based ink composition of the present embodiment can be produced by mixing the above-mentioned components by an appropriate method. That is, for example, the additive or the like is separately added to the dispersion liquid of the pigment composition, and the mixture is further diluted with water. Then, the mixture is sufficiently stirred, and if necessary, filtration is performed to remove coarse particles and foreign substances that cause clogging. Thereby, the water-based ink composition according to the present embodiment can be obtained.

Further, in the present embodiment, by using sodium polyacrylate as a pigment dispersant, it is possible to suppress the generation of bubbles in the aqueous ink composition. Therefore, the defoaming step for reducing or eliminating the bubbles can be omitted, the manufacturing efficiency can be improved, and the inclusion of the defoaming agent can be omitted. Therefore, the water-based ink composition conforming to the standards of the Pharmaceutical Affairs Law and the like. Manufacture of goods becomes easier.

The mixing method of each material is not particularly limited, and for example, the materials are sequentially added to a container equipped with a stirring device such as a mechanical stirrer or a magnetic stirrer to perform stirring and mixing. The filtration method is not particularly limited, and for example, centrifugal filtration, filter filtration, or the like can be adopted.

The water-based ink composition of the present embodiment can be applied to inks and paints. Further, the water-based ink composition of the present embodiment has excellent dispersibility of a pigment composed of titanium oxide particles and / or zinc oxide particles whose surface is not hydrophilic, and is therefore preferably used for inkjet inks. be able to. In particular, since the aqueous ink composition of the present embodiment uses a pigment and a pigment dispersant conforming to the standards of the Pharmaceutical Affairs Law and the like, it has edible properties and is directly applied to the surface of tablets such as pharmaceuticals and supplements. It is possible to print. In addition, non-contact printing by the inkjet method is possible even for tablets having poor surface smoothness such as uncoated tablets and OD tablets. Further, since the water-based ink composition is also excellent in light resistance, it is possible to prevent the occurrence of bleeding even when directly printed on the surface of tablets such as pharmaceuticals and supplements.

(Solid preparation)
The tablet of the present embodiment is directly printed on the surface of the tablet by an inkjet recording method using an inkjet water-based ink composed of the water-based ink composition. As described above, since the water-based ink composition has excellent light resistance and does not cause bleeding, various information for improving user identification such as product information can be printed on the tablet, and as a result, dispensing is performed. It is possible to prevent mistakes and accidental ingestion.

The tablets are solid at room temperature, and for example, those produced by compressing and / or molding a tablet material containing an active ingredient into a certain shape are preferable. The shape of the tablet is not particularly limited, and any shape can be adopted. Further, the tablet may be a tablet for pharmaceutical use or a tablet for food use. Examples of tablets for food use include health foods such as tablets and supplements.

The inkjet recording method for the surface of the tablet is not particularly limited. Specifically, for example, the water-based ink composition can be ejected as droplets from a fine nozzle, and the droplets can be adhered to the tablet surface. The discharge method is not particularly limited, and for example, a known method such as a continuous injection type (charge control type, spray type, etc.), an on-demand type (piezo method, thermal method, electrostatic suction method, etc.) can be adopted. ..

(Other matters)
In the present embodiment, the case where the pigment composition is applied to the water-based ink composition for inkjet has been described as an example, but the present invention is not limited to this application example. The pigment composition of the present embodiment can be composed of all components conforming to the standards of the pharmaceutical additive, the Japanese Pharmacopoeia or the official standard of food additives specified by the Pharmaceutical Affairs Law, and has low biotoxicity. Therefore, for example, The pigment composition of the present embodiment can also be applied to cosmetics and the like. Specifically, since the titanium oxide and zinc oxide also function as an ultraviolet shielding agent, the pigment composition of the present embodiment can be blended with a sunscreen agent having an O / W (Oil in Water) formulation. .. Further, the pigment composition of the present embodiment can be applied as an oral administration agent having an ultraviolet shielding function.

Hereinafter, preferred embodiments of the present invention will be described in detail exemplary. However, the materials, contents, etc. described in the following examples are not limited to those of the present invention unless otherwise specified.

(Pigment)
In each Example and Comparative Example, various titanium oxide nanoparticles or zinc oxide nanoparticles were used as pigments. The details are as shown in Tables 1 and 2 below. As the titanium oxide nanoparticles 1, those having a rod-like shape were used. Further, as the titanium oxide nanoparticles 2 to 9 and the zinc oxide nanoparticles 1 to 5, those having a substantially spherical shape were used. The hydrous silica in the zinc oxide nanoparticles 4 and 5 means a film made of silicon dioxide hydrate formed on the surface of zinc oxide by the hydrophilic treatment, whereby the zinc oxide nanoparticles 4 and 5 have. Has a hydrophilic surface.

(Examples 1 to 8)
In Examples 1 to 8, each material is placed in a container so that the pigment, the pigment dispersant, and the pure water as the dispersion medium have the blending ratios shown in Table 3 below, and the disperser (paint shaker, Asada Iron Works Co., Ltd.) The mixture was dispersed at room temperature for 24 hours (dispersion time). In addition, zirconia beads were mixed at the time of dispersion. As sodium polyacrylate as the pigment dispersant, TEGO Dispers 715W (mass average molecular weight 3000) manufactured by Evonik Industries, Inc. was used. Further, unless otherwise specified, the numerical values in Table 3 below are expressed in mass% with respect to the total mass of the pigment composition. Furthermore, each material conforms to the standards of the Pharmaceutical Affairs Law and the like.

(Comparative Example 1)
In this comparative example, the blending ratios of the pigment, the pigment dispersant, and the pure water as the dispersion medium are set as shown in Table 3 below. A pigment composition according to this comparative example was prepared in the same manner as in Example 1 and the like except for the above.

(Examples 9 to 11)
In Examples 9 to 11, each material is placed in a container so that the pigment, the pigment dispersant, and the pure water as the dispersion medium have the blending ratios shown in Table 4 below, and the disperser (paint shaker, Asada Iron Works Co., Ltd.) The mixture was dispersed at room temperature for 24 hours (dispersion time). In addition, zirconia beads were mixed at the time of dispersion. As sodium polyacrylate as the pigment dispersant, TEGO Dispers 715W (mass average molecular weight 3000) manufactured by Evonik Industries, Inc. was used. Further, the numerical values in Table 4 below are expressed in mass% with respect to the total mass of the pigment composition unless otherwise specified. Furthermore, each material conforms to the standards of the Pharmaceutical Affairs Law and the like.

(Comparative Examples 2 and 3)
In Comparative Examples 2 and 3, the blending ratios of the pigment, the pigment dispersant, and the pure water as the dispersion medium were set as shown in Table 4 below. Other than that, pigment compositions according to these Comparative Examples were prepared in the same manner as in Example 9 and the like.

(Examples 12 to 22)
In Examples 12 to 22, a pigment, a pigment dispersant, and pure water as a dispersion medium are placed in a container and dispersed in a disperser (paint shaker, manufactured by Asada Iron Works Co., Ltd.) for 24 hours (dispersion time) at room temperature. I let you. In addition, zirconia beads were mixed at the time of dispersion. As a result, the pigment composition according to each example was prepared. As sodium polyacrylate as the pigment dispersant, TEGO Dispers 715W (mass average molecular weight 3000) manufactured by Evonik Industries, Inc. was used.

Next, a surface tension adjusting agent, propylene glycol as a wetting agent, and pure water are added to each pigment composition, and the water-based ink composition for inkjet (hereinafter, "" An aqueous ink composition ”) was prepared and stirred with a disper. As a result, the water-based ink compositions of each example were prepared. In the process of producing the pigment composition and the water-based ink composition, since no bubbles were generated, the defoaming step by adding the defoaming agent was not performed. Unless otherwise specified, the numerical values in Tables 5 and 6 below are expressed as% by mass with respect to the total mass of the water-based ink composition. In addition, each material conforms to the standards of the Pharmaceutical Affairs Law and the like.

(Measurement of mass average molecular weight of sodium polyacrylate)
The mass average molecular weight of sodium alginate is a value determined by gel permeation chromatography (GPC) using polyethylene oxide (PEO) / polyethylene glycol (PEG) as a standard product.

(Measurement of average primary particle size and average dispersed particle size of titanium oxide nanoparticles and zinc oxide nanoparticles)
The average primary particle diameters of the titanium oxide nanoparticles and zinc oxide nanoparticles and the average dispersed particle diameters D50 and D99 in each Example and Comparative Example were determined by using Microtrac UPA-EX150 (trade name, manufactured by Nikkiso Co., Ltd.). It was measured by a dynamic light scattering method. Since the titanium oxide nanoparticles 1 used in Examples 1 and 9 have a rod-like shape, the average primary particle diameter is the length (height) of the major axis and the length (width) of the minor axis. The geometric mean value was used.

(Measurement of viscosity)
The viscosities of the aqueous ink compositions of Examples 12 to 22 were measured. The viscosity was measured using a viscometer (VISCOMATE MODEL VM-10A, manufactured by SEKONIC CORPORATION) under the condition of a measurement temperature of 25 ° C. The results are shown in Tables 5 and 6 above.

(Discharge stability (flying property))
Matte paper (trade name: Super Fine Paper, manufactured by Epson Corporation) was prepared as a recording medium, and printing was performed using the water-based ink compositions prepared in Examples 12 to 22, respectively. Printing was performed by a single-pass (one-pass) method using an inkjet printer (a printing jig equipped with a KC 600 dpi head).

The number of nozzle chips increased and the evaluation of sleepiness were evaluated by stopping the inkjet printer after ejecting the water-based ink composition from the head, and then observing how much nozzle chipping increased in the printed image when printing again. I went depending on whether it was done or not. Note that the nozzle chipping means that ink droplets made of the water-based ink composition are not ejected from the nozzle in which the clogging occurs. Sleeping means that the printed image becomes blurry and unclear in the early stage of printing.

The number of nozzles increased was evaluated using the following criteria.
◯: The number of nozzle omission increases at 15 minutes of open time is 0
X: The number of nozzle omissions increased by 1 or more in the open time of 15 minutes

In addition, the evaluation of sleepiness was performed using the following criteria.
◯: The rubbing of the image export part at the open time of 15 minutes is less than 1 mm ×: The rubbing of the image export part at the open time of 15 minutes is 1 mm or more.

In addition, the evaluation of the open time was performed by first ejecting the water-based ink composition from the head, then stopping, and printing again after 15 minutes, and evaluating the presence or absence of nozzle omission and writing rubbing in the printed image at that time. It is a thing. ◯ in Tables 5 and 6 means that there is no nozzle omission or rubbing of writing. The rubbing means that the printed image is rubbed at the initial stage of printing.

(result)
As can be seen from the experimental results of Examples 1 to 8 shown in Table 3, sodium polyacrylate having a mass average molecular weight of 3000 was blended as a pigment dispersant with the pigment composed of titanium oxide nanoparticles 1 to 8 having a hydrophilic surface. In this case, the ratio of the average primary particle size of the titanium oxide nanoparticles to the average dispersed particle size of the dispersed titanium oxide nanoparticles is 1: 0.3 regardless of the value of the average primary particle size of the titanium oxide nanoparticles and the crystal structure. It was within the range of ~ 1: 3. Further, as can be seen from the experimental results of Examples 9 to 11 shown in Table 4, the sodium polyacrylate is also added as a pigment dispersant to the pigment composed of zinc oxide nanoparticles 1 to 3 whose surface is not hydrophilic. Then, regardless of the value of the average primary particle size of the zinc oxide nanoparticles, the ratio of the average primary particle size of the zinc oxide nanoparticles to the average dispersed particle size of the dispersed zinc oxide nanoparticles was within the above numerical range. .. As a result, it was shown that in the pigment compositions according to Examples 1 to 11, titanium oxide nanoparticles or zinc oxide nanoparticles can be dispersed at a level close to the average primary particle size.

On the other hand, in Comparative Example 1 in which titanium oxide nanoparticles having a hydrophobically treated surface were used as the pigment, the average dispersed particle size was increased, and the possibility of lowering the storage stability was shown. Further, in Comparative Examples 2 and 3, although zinc oxide nanoparticles whose surface was treated to be hydrophilic were used as the pigment, the average dispersed particle size became large, and the result showed the possibility of deterioration of storage stability. ..

Further, as can be seen from the experimental results of Examples 12 to 22 shown in Tables 5 and 6, the average primary particle size and the average dispersed particles of the titanium oxide nanoparticles or the zinc oxide nanoparticles also in the aqueous ink composition containing the pigment composition. The ratio with the diameter could be maintained within the above numerical range, and good pigment dispersibility was maintained. It was also confirmed that an aqueous ink composition having excellent ejection stability (flying property) was obtained.

Claims (8)

And Ranaru pigment or titanium oxide particles, mass average molecular weight and a sodium polyacrylate as 10,000 of the pigment dispersing agent,
Wherein an average primary particle size of the titanium oxide particles, the ratio of the mean dispersed particle diameter D50 of the dispersed titanium oxide particles, 1: 0.3 to 1: Ri der range of 3,
The average primary particle size of the titanium oxide particles is in the range of 20 nm to 200 nm.
A pigment composition in which the average dispersed particle size D50 of the dispersed titanium oxide particles is in the range of 20 nm to 100 nm. The pigment composition according to claim 1, wherein the surface of the titanium oxide particles is hydrophilic. Content ratio of said titanium oxide particles or Ranaru pigment and the sodium polyacrylate, 1 by weight: 0.05: pigment composition according to claim 1 or 2 in the range of 1.5 .. It contains a pigment composed of zinc oxide particles whose surface is not hydrophilized by a hydrate of silicon dioxide, and sodium polyacrylate as a pigment dispersant having a mass average molecular weight of 10,000 or less.
A pigment composition in which the ratio of the average primary particle size of the zinc oxide particles to the average dispersed particle size D50 of the dispersed zinc oxide particles is in the range of 1: 0.3 to 1: 3. The pigment composition according to claim 4, wherein the average primary particle size of the zinc oxide particles is in the range of 20 nm to 400 nm. The pigment composition according to claim 4 or 5, wherein the average dispersed particle size D50 of the dispersed zinc oxide particles is in the range of 20 nm to 500 nm. The invention according to any one of claims 4 to 6, wherein the content ratio of the pigment composed of the zinc oxide particles to the sodium polyacrylate is in the range of 1: 0.05 to 1: 1.5 on a mass basis. Pigment composition. An inkjet water-based ink composition containing the pigment composition according to any one of claims 1 to 7 and having edible properties.