JP6538165B2 - Pigment composition and aqueous ink composition for inkjet - Google Patents

Description

  The present invention relates to a pigment composition and an aqueous ink composition for ink jet recording, and more specifically, an edible pigment which is excellent in dispersibility and can be directly printed by ink jet printing on tablets of medicines, food and the like. The present invention relates to a composition and an aqueous ink composition for inkjet.

  By displaying the product information not only on the package but also on the tablet body, food products such as tablet medicines and supplements are improved in their identification to prevent dispensing errors and accidental drinking. Since tablets coated on the surface can be printed by contact method such as gravure printing, while highly distinguishable information is displayed, contact is made with uncoated tablets or OD (orally disintegrating) tablets with poor surface smoothness. Printing by the method is difficult. Therefore, for these tablets, a marking method that can display only simple characters has become mainstream. As a result, particularly in the pharmaceutical industry, there is an increasing need for new printing methods capable of highly distinguishable information display even for uncoated tablets and OD tablets.

  As such a printing method, the printing of the inkjet system by the aqueous ink composition using dye is mentioned, for example (refer following patent document 1). However, printing on tablets and the like of pharmaceuticals using the aqueous ink composition has a problem that the printed image is blurred and the light resistance is poor. As one of the methods for solving such a problem, there is a method of improving the light resistance and eliminating the problem of bleeding by performing stamp printing using a pigment instead of a dye or the like.

  However, in the case of stamp printing using a pigment, it is necessary to create a printing plate, and there is a problem that the workability in small-lot production is poor. Therefore, a method of direct printing by an inkjet method is considered, but the pigment of the aqueous ink composition used for stamp printing has a large average dispersed particle diameter D50 of about 400 nm to 2000 nm (D9: 2000 nm to 10000 nm), and the inkjet method There is a problem that it is not suitable for printing.

JP 2011-236279 A

  The present invention has been made in view of the above problems, and the object thereof is to print directly on a tablet or the like of a medicine, food or the like by an ink jet method, since the average dispersed particle diameter of the pigment is small and the dispersibility is excellent. It is an object of the present invention to provide an edible pigment composition that can be used and an aqueous ink composition for inkjet.

  As a result of examining the pigment composition and the aqueous ink composition for inkjets in order to solve the above-mentioned problems, the inventors of the present invention have found that the above-mentioned problems can be solved by adopting the following constitution. It came to complete.

  That is, in order to solve the above problems, the pigment composition according to the present invention comprises a colored pigment comprising iron oxide and sodium polyacrylate having a mass average molecular weight of 1,500 to 10,000, and comprises the colored iron oxide. The content ratio of the pigment to the sodium polyacrylate is 1: 0.05 to 1: 1.5 on a mass basis, and the average dispersed particle diameter D50 of the colored pigment made of iron oxide is 10 nm to 300 nm. It is characterized by

  According to the above configuration, since a colored pigment consisting of iron oxide 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, an ink composition using the dye The light resistance can be improved as compared with the object.

  Further, according to the above configuration, since sodium polyacrylate having a mass average molecular weight in the range of 1,500 to 10,000 is used as the pigment dispersant of the colored pigment made of iron oxide, the average dispersed particle diameter is in the range of 10 nm to 300 nm. Thus, it is possible to prevent the reaggregation of the pigment and to improve the dispersibility and maintain the good storage stability. Furthermore, by setting the content ratio of the colored pigment to the sodium polyacrylate in the range of 1: 0.05 to 1: 1.5 on a mass basis, it is possible to prevent the decrease in the pigment dispersibility and It is also possible to prevent a drop in discharge stability caused by clogging or the like. Therefore, according to the pigment composition of the above-mentioned constitution, for example, direct printing with an ink jet system is possible even for solid preparations such as pharmaceuticals, and as described above, since it is excellent in light resistance, printed images The occurrence of bleeding can also be prevented.

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

  In the pigment composition, since the pharmaceutical additive defined by the Pharmaceutical Affairs Law, sodium polyacrylate conforming to the criteria of the Japanese Pharmacopoeia or the official regulations of food additives are used as a pigment dispersant, the pigment composition is contained. The aqueous ink composition for inkjet can be suitably used for an ink material which is directly printed by an inkjet method with respect to a solid preparation such as pharmaceuticals and food. Further, in the pigment composition, a colored pigment made of iron oxide is used instead of the dye, so that the printed image is excellent in light fastness even when printed on the surface of a solid preparation such as pharmaceuticals by an inkjet method, And, it is possible to prevent the occurrence of bleeding. In addition, edible means that it consists only of a substance which is approved for oral administration as a medicine or a medicine additive and / or a substance which is recognized as a food or a food additive.

  Further, in the method for producing an aqueous ink composition for inkjet according to the present invention, in order to solve the above-mentioned problems, a colored pigment consisting of iron oxide and sodium polyacrylate are simultaneously added to the dispersion medium or in any order. And a step of preparing a pigment composition, and is characterized by not including a defoaming step for reducing or eliminating bubbles.

  For example, when the ink is ejected from the ink jet head, air bubbles cause nozzle omission, ejection failure, and decrease in open time, but according to the above configuration, the generation of air bubbles is suppressed as a pigment dispersant. Since sodium polyacrylate that can be used is used, it is possible to prevent a drop in the discharge stability such as the nozzle missing. In addition, since the defoaming step for reducing or eliminating air bubbles can be omitted, the number of manufacturing steps can be reduced and the manufacturing efficiency can be improved, as compared with the conventional method of manufacturing an aqueous ink composition for inkjet. Is taken.

  In order to solve the above problems, the solid preparation according to the present invention is a solid preparation comprising a tablet or a capsule and having a dry film of an aqueous ink for ink jet on the surface, wherein the aqueous ink for ink jet is a claim. It consists of the water-based ink composition for inkjet as described in 2.

  According to the above configuration, since the aqueous ink composition for ink jet containing the colored pigment of iron oxide and sodium polyacrylate is used as the aqueous ink for ink jet, direct printing by the ink jet recording method using the aqueous ink for ink jet It is possible to realize a printed image which is excellent in light resistance and in which the occurrence of bleeding is prevented. As a result, it becomes possible to display product information also on the solid preparation body, and the identification can be improved, and a solid preparation capable of preventing dispensing errors and accidental ingestion can be provided. The solid preparation of the present invention is meant to include food preparations and pharmaceutical preparations.

  According to the present invention, a poly which meets the criteria of pharmaceutical additives defined by the Pharmaceutical Affairs Act, the Japanese Pharmacopoeia or the official document of food additives and imparts good dispersibility and storage stability to iron oxide colored pigments. Abstract: To provide a pigment composition and an aqueous ink composition for inkjet that can be directly printed by an inkjet method with good ejection stability for solid preparations such as pharmaceuticals and foods because sodium acrylate is contained. Can. Moreover, the aqueous ink composition for inkjets using the colored pigment of iron oxide is excellent in light resistance compared with the thing using dye etc., and can also prevent the blur of a printing image.

  Furthermore, according to the present invention, since sodium polyacrylate can also suppress the generation of bubbles, the defoaming step for reducing or eliminating the bubbles can be omitted. As a result, the method for producing a pigment composition and the method for producing an aqueous ink composition for inkjet according to the present invention can reduce the number of production steps as compared with the conventional production method, and the production efficiency can be improved.

(Pigment composition and method for producing the same)
The pigment composition according to the present embodiment is a composition containing at least a colored pigment of iron oxide (hereinafter sometimes referred to as "pigment") and sodium polyacrylate.

Examples of colored pigments of iron oxide include bengala and the like. Furthermore, as the bengara, for example, red α-Fe ₂ O ₃ (hematite), brown γ-Fe ₂ O ₃ (magma hate), black Fe ₃ O ₄ (magnetite), yellow α-FeOOH, etc. It can be mentioned. These pigments may be used alone or in combination of two or more, as needed. However, when the pigment composition of the present embodiment is used for printing on the surface of a solid preparation such as a medicine or a supplement, the colored pigment of iron oxide is a pharmaceutical additive, Japanese Pharmacopoeia or food additive official regulations specified by the Pharmaceutical Affairs Law. It is preferable that the material conforms to the standard of the letter (hereinafter referred to as “standard of the Pharmaceutical Affairs Law and the like”). In the present embodiment, a colored pigment means a pigment other than a white pigment which absorbs any light in the visible light wavelength range (380 to 780 nm).

  The average primary particle size (volume average particle size) of the pigment is preferably 30 nm to 800 nm, more preferably 75 nm to 250 nm, and particularly preferably 75 nm to 210 nm. The fall of light resistance can be suppressed as the said average primary particle diameter is 30 nm or more. On the other hand, when the average primary particle diameter is 800 nm or less, high coloring can be achieved. The average primary particle size is an arithmetic mean size determined by observing the pigment with an electron microscope. Further, in the present embodiment, a pigment having a monodispersed particle size distribution is used, but the present invention is not limited to this, and a pigment having a broad particle size distribution may be used. Further, two or more pigments having a monodispersed particle size distribution may be mixed and used.

  The content of the pigment directly affects the image density, and affects the storability, viscosity, pH and the like of the aqueous ink composition described later. Just do it. Usually, the range of 2% by mass to 20% by mass is preferable with respect to the total mass of the pigment composition, and the range of 5% by mass to 15% by mass is more preferable. By setting the content of the pigment to 2% by mass or more, the decrease in image density can be suppressed. On the other hand, by setting the content of the pigment to 20% by mass or less, it is possible to prevent the decrease in the gloss, the clogging of the nozzle, and the decrease in the ejection stability.

  The average dispersed particle diameter D50 of the pigment in the dispersed state is in the range of 10 nm to 300 nm, and preferably in the range of 25 nm to 200 nm. In addition, the dispersed particle diameter D99 (the particle diameter of 99% in cumulative particle size distribution in the volume integrated particle size distribution) of the pigment is preferably in the range of 100 nm to 800 nm, and more preferably in the range of 100 nm to 600 nm. By setting the D50 to 10 nm or more, it is possible to prevent the deterioration of the storage stability, the light resistance, and the discharge stability, and to prevent the reduction of the printing density. On the other hand, by setting the D50 to 300 nm or less, or the D99 to 800 nm or less, separation, sedimentation and aggregation of the pigment can be prevented, and storage stability can be maintained. The average dispersed particle diameter D50 and D99 of the pigment is a value measured by a dynamic light scattering method using Microtrac UPA-EX 150 (trade name, manufactured by Nikkiso Co., Ltd.).

  The sodium polyacrylate has a function as a pigment dispersant. By blending sodium polyacrylate, the dispersibility of the colored pigment of iron oxide can be improved. In addition, sodium polyacrylate conforms to the standard defined by the Pharmaceutical Affairs Law. Therefore, sodium polyacrylate can be suitably used for printing on tablets and the like of pharmaceuticals and foods.

  In addition, sodium polyacrylate, for example, when added to a dispersion medium to be described later, does not generate bubbles as in other conventional pigment dispersants. Therefore, the addition of the antifoaming agent can be omitted in the pigment composition of the present embodiment.

  The mass average molecular weight of sodium polyacrylate is 1500 to 10000, preferably 2000 to 8000. By setting the mass average molecular weight to 1,500 or more, the sodium polyacrylate adsorbed on the pigment surface can sufficiently exhibit the repulsive force due to steric hindrance and the like, thereby suppressing reaggregation of the pigments. Can. On the other hand, by setting the mass average molecular weight to 10000 or less, the average dispersed particle diameter D50 of the pigment can be set to 300 nm or less, and it is possible to prevent the dispersibility from being lowered.

  The content ratio of the colored pigment of the iron oxide to the sodium polyacrylate is 1: 0.05 to 1: 1.5 on a mass basis, preferably 1: 0.1 to 1: 1. The fall of the dispersibility of a colored pigment can be prevented as the said content ratio is 1: 0.05 or more. On the other hand, when the content ratio is 1: 1.5 or less, for example, when it is used for an aqueous ink composition for inkjet, it is possible to prevent a decrease in ejection stability due to adhesion of the nozzle plate.

  The pigment composition according to the present embodiment includes a dispersion medium for dispersing the colored pigment. Examples of the dispersion medium include water, and more specifically, those obtained by removing ionic impurities such as deionized water, ultrafiltered water, reverse osmosis water, pure water such as distilled water, or ultrapure water. . In particular, water sterilized by ultraviolet irradiation or hydrogen peroxide addition is preferable because it can prevent the generation of mold and bacteria over a long period of time. Further, the content of the dispersion medium is not particularly limited, and can be set as necessary.

  As the dispersion medium, a mixed solution of the water and the water-soluble organic solvent may be used. The water-soluble organic solvent is not particularly limited, and specific examples thereof include alcohols such as methyl alcohol, ethyl alcohol, n-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, n-propyl alcohol and isopropyl alcohol; Amides such as dimethylformamide and dimethylacetamide; ketones such as acetone and methyl ethyl ketone; 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 ether; ethylene glycol, propylene glycol, butylene glycol Polyalcohols such as diethylene glycol, triethylene glycol, 1,2,6-hexanetriol, thiodiglycol, polyethylene glycol, polypropylene glycol, glycerin, diglycerin and polyglycerin; N-methylpyrrolidone, 1,3 -Dimethyl-2- imidazolidinone etc. are mentioned. You may use these individually by 1 type or in mixture of 2 or more types. In addition, among these water-soluble organic solvents, as pharmaceutical additives specified by the Pharmaceutical Affairs Law, the Japanese Pharmacopoeia or Food Additives Standards, ethyl alcohol, n-butyl alcohol, isobutyl alcohol, n-propyl Alcohol, isopropyl alcohol, acetone, propylene glycol, polyethylene glycol and glycerin are preferred. Furthermore, the compounding amount in the case of using a water-soluble organic solvent as the dispersion medium is not particularly limited, and can be appropriately set as needed.

  In the method for producing the pigment composition of the present embodiment, the mixing method and the addition order of the pigment, sodium polyacrylate, the dispersion medium and the other additives to be blended if necessary are not particularly limited. For example, a pigment, sodium polyacrylate and water as a dispersion medium may be mixed at one time, and the mixture may be subjected to dispersion treatment using a conventional disperser.

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

  The dispersion time in the dispersion process is not particularly limited, and can be set as needed. The disperser used in the dispersion treatment of the pigment is not particularly limited as long as it is a commonly used disperser. Specifically, for example, a ball mill, a roll mill, a sand mill, a bead mill, a paint shaker, a nanomizer and the like can be mentioned.

  The pigment composition of the present embodiment is not only in the form of an aqueous ink composition for ink jet (details will be described later) as a final product, but also in the form of a pigment dispersion for preparing the aqueous ink composition. It is included.

(Aqueous ink composition for ink jet and method for producing the same)
An aqueous ink composition for inkjet according to the present embodiment (hereinafter, referred to as “aqueous ink composition”) is an aqueous ink containing at least the pigment composition and the main solvent is water. In addition, the aqueous ink composition of the present embodiment is edible and is suitably used for inkjet recording. Furthermore, since a water-based ink composition uses a pigment as a coloring material, it is superior to the ink composition using a dye in terms of color developability, light resistance, water resistance, and the like.

  The content of the pigment composition is preferably in the range of 2% by mass to 20% by mass, and more preferably in the range of 5% by mass to 15% by mass, in terms of pigment content with respect to the total mass of the aqueous ink composition. The coloring power can be improved by setting the content of the pigment composition to 2% by mass or more. On the other hand, the dispersibility can be improved by setting the content of the pigment composition to 20% by mass or less.

  The aqueous ink composition according to the present embodiment contains water (water as a main solvent). As said water, it is preferable to use what removed ionic impurities, such as pure waters, such as ion-exchange water, ultrafiltration water, reverse osmosis water, distilled water, or ultrapure water. In particular, water sterilized by ultraviolet irradiation or hydrogen peroxide addition is preferable because it can prevent the generation of mold and bacteria over a long period of time. Moreover, it does not specifically limit as content of water, It can set suitably as needed.

  Other additives may be blended in the aqueous ink composition of the present embodiment. However, when used as an ink jet ink for solid preparations such as pharmaceuticals, it is preferable that the ink conforms to the standards of the Pharmaceutical Affairs Law. Further, in the present embodiment, the generation of air bubbles can be suppressed even when sodium polyacrylate which is a pigment dispersant is added, so that the addition of an antifoaming agent can be omitted. Furthermore, when the water-based ink composition of the present embodiment is discharged from the ink jet head, since the air bubbles do not exist in the water-based ink composition, it is also possible to suppress the nozzle omission, the discharge failure, and the decrease in open time. Can.

  The additives include a surface tension regulator, a wetting agent (anti-drying agent), an anti-fading agent, an emulsion stabilizer, a penetration accelerator, an ultraviolet absorber, an antiseptic, a mildew agent, a pH regulator, a viscosity regulator, Well-known additives, such as a dispersion stabilizer, an antirust agent, a chelating agent, etc. are mentioned. The contents of these various additives are not particularly limited, and can be set as needed.

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

  The addition amount of the surface tension regulator 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 that can be adjusted to 27 to 36 mN / m. When the addition amount is within the above range, it is possible to ensure the discharge stability and the like in the printing by the inkjet method.

  The wetting agent is not particularly limited as long as it meets the standards such as the Pharmaceutical Affairs Law, 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, and more preferably 10% by mass to 40% by mass, with respect to the total mass of the aqueous ink composition.

  The aqueous ink composition of the present embodiment can be produced by mixing the above-mentioned components by an appropriate method. That is, for example, the additives and the like are separately added to the dispersion of the pigment composition, and then diluted with water. After that, the solution is sufficiently stirred, and if necessary, filtration is performed to remove coarse particles and foreign substances that cause clogging. Thus, the aqueous ink composition according to the present embodiment can be obtained.

  Further, in the present embodiment, by using sodium polyacrylate as a pigment dispersant, the generation of air bubbles in the aqueous ink composition can be suppressed. Therefore, the defoaming step for reducing or eliminating the bubbles can be omitted, and the production efficiency can be improved, and the inclusion of the antifoaming agent can also be omitted. The manufacture of objects becomes even easier.

  In addition, it does not specifically limit as a mixing method of each material, For example, materials are sequentially added to the container provided with stirring apparatuses, such as a mechanical stirrer and a magnetic stirrer, and stirring and mixing are performed. Moreover, it does not specifically limit as a filtration method, For example, centrifugal filtration, filter filtration, etc. are employable.

  The aqueous ink composition of the present embodiment can be applied to ink and paint. Further, since the aqueous ink composition of the present embodiment is excellent in the dispersibility of the colored pigment of iron oxide, it can be suitably used for an inkjet ink. In particular, since the aqueous ink composition of the present embodiment uses a pigment and a pigment dispersant that conforms to the standards of the Pharmaceutical Affairs Law, etc., it is edible, and it is possible to use tablets and capsules such as pharmaceuticals and supplements. Directly on the surface of the solid formulation. In addition, non-contact printing using an inkjet method is enabled even for tablets having poor surface smoothness such as uncoated tablets and OD tablets. Furthermore, since the aqueous ink composition is also excellent in light resistance, the occurrence of bleeding can be prevented even when printed directly on the surface of a solid preparation such as a medicine or a supplement.

(Solid preparation)
The solid preparation of the present embodiment comprises a tablet or a capsule, and the surface of the solid preparation is directly printed by the ink jet recording method using the aqueous ink for ink jet comprising the aqueous ink composition. . As described above, since the aqueous ink composition is excellent in light resistance and does not cause bleeding, the solid preparation can be printed with various information for improving the user's identification such as product information, and as a result, It becomes possible to prevent dispensing errors and accidental ingestion.

  The tablet is solid at normal temperature, and for example, it is preferable that the tablet material containing the active ingredient is produced by compression and / or molding into a certain shape. The capsule is preferably prepared by filling a powdery, granular, liquid or other medicine or the like into a capsule made of gelatin, a cellulose derivative or the like, or by encapsulating with a capsule base. The shape of the tablet and capsule is not particularly limited, and any shape can be adopted. The tablets and capsules may be for pharmaceutical use or 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 solid preparation is not particularly limited. Specifically, for example, the aqueous ink composition can be discharged as droplets from a fine nozzle, and the droplets can be attached to the surface of the solid preparation. The discharge method is not particularly limited, and for example, known methods such as continuous injection type (charge control type, spray type, etc.), on demand type (piezo type, thermal type, electrostatic suction type, etc.) can be adopted. .

  Hereinafter, preferred embodiments of the present invention will be described in detail by way of example. However, the materials, contents, and the like described in the following examples do not limit the scope of the present invention to them unless otherwise specified.

(Examples 1 to 19)
In Examples 1 to 19, each material was put in a container and dispersed for 64 hours (dispersion time) under normal temperature with a paint shaker so that the pigment and the dispersing agent had the mixing ratio shown in Table 1. In addition, zirconia beads were mixed at the time of dispersion.

  Next, a surface tension regulator, propylene glycol (PG) as a wetting agent, and water are added to each pigment composition, and an aqueous ink composition is prepared so as to achieve the blending ratio shown in Tables 2 to 5, and Disper, Stir at. Thus, the aqueous ink composition of each example was produced. In the preparation process of the pigment composition and the aqueous ink composition, no bubble was generated, and the defoaming step by the addition of the antifoam agent was not performed.

  Moreover, the numerical value in following Table 1-Table 5 is represented by mass% unless there is particular description. In addition, each material conforms to the standards of the Pharmaceutical Affairs Law and the like.

(Comparative Examples 1 to 5)
In Comparative Examples 1 to 5, the composition of the aqueous ink composition was changed to those shown in Tables 1 to 6 below. Each pigment composition and aqueous ink composition were produced by the method similar to the said Example 1 grade | etc., Except it.

(Examples 20 to 25)
In Examples 20 to 25, pigment compositions were prepared with the compositions shown in Tables 7 and 8 below. Moreover, preparation of the pigment composition of each Example was performed by the following operation. That is, the pigment and the dispersant were mixed so as to obtain the mixing ratio shown in Tables 7 and 8, water was further added, and the mixture was dispersed for 64 hours (dispersion time) under normal temperature with a paint shaker. In addition, zirconia beads were mixed at the time of dispersion. This produced the pigment composition of each Example. In the preparation process of the pigment composition, no bubble was generated at all, and the defoaming step by the addition of the antifoam agent was not performed.

(Comparative Examples 6 to 8)
In Comparative Examples 6 to 8, the composition of the pigment composition was changed to that shown in Table 8 below. Each pigment composition was manufactured by the method similar to the said Example 20 grade | etc., Except it.

(Measurement of average dispersed particle size of pigment)
The average dispersed particle diameters D50 and D99 of the pigments in the aqueous ink compositions of the respective Examples and Comparative Examples were measured by a dynamic light scattering method using Microtrac UPA-EX 150 (trade name, manufactured by Nikkiso Co., Ltd.).

(Discharge stability (flyability))
Matte paper (trade name: Super Fine Paper, manufactured by Epson Corporation) was prepared as a recording medium, and printing was performed using the aqueous ink compositions prepared in Examples 1 to 19 and Comparative Examples 1 to 5, respectively. Printing was performed by a single pass (one pass) method using an ink jet printer (KC 600 dpi head mounted printing jig).

  The evaluation of nozzle chipping increase number and sleepiness was performed by stopping the ink jet printer after discharging the aqueous ink composition from the head and then observing how much the nozzle chipping increased in the printed image when printing again, and the sleepiness was observed It went by whether it was done or not. The term “nozzles” means that ink droplets consisting of the aqueous ink composition are not ejected from the nozzles where clogging has occurred. Sleeping means that the printed image is blurred and blurred at the early stage of printing.

The evaluation of the nozzle increase number was performed using the following criteria.
○: The increase in the number of missing nozzles at 15 minutes in open time
X: The number of missing nozzles increased one or more at an open time of 15 minutes

In addition, evaluation of sleepiness was performed using the following criteria.
○: The rubbing portion of the image writing portion in the open time 15 minutes is less than 1 mm. ×: The rubbing of the image writing portion in the open time 15 minutes is 1 mm or more

  In addition, the evaluation of the open time was stopped after the aqueous ink composition was first ejected from the head, and printed again after 15 minutes, and the printed image at that time was evaluated for the presence or absence of the nozzle missing and the writing-out rubbing. It is a thing. A circle in the table means a case where there is no rubbing of the nozzle omission and the writing. The rubbing means that the printed image is rubbed at the initial stage of printing.

(Storage stability)
The storage stability of each of the aqueous ink compositions prepared in Examples 1 to 19 and Comparative Examples 1 to 5 was evaluated.
That is, the average particle diameter d1 of the pigment in each aqueous ink composition was measured. The particle size of the pigment was measured using the Microtrac UPA-EX150. Thereafter, each aqueous ink composition was stored for a long time at 70 ° C. for 14 days.

Furthermore, after the aqueous ink composition was returned to the temperature before long-term storage, the average particle diameter d2 of the pigment in the aqueous ink composition was measured in the same manner as described above. Then, the value of each D was computed by the formula of D (%) = (d2-d1) / d1 x 100 using the value of the particle size of the pigment before and behind long-term storage. Then, the storage stability of the pigment during long-term storage was evaluated using the following evaluation criteria. The smaller the value of D below, the higher the storage stability of the pigment during long-term storage.
○: D is less than 10% ×: D is 10% or more

(Air bubble evaluation)
The foam evaluation was performed on each of the aqueous ink compositions of Examples 1 to 19 and Comparative Examples 1 to 5. That is, 100 ml of each aqueous ink composition was placed in a 100 ml measuring cylinder and the liquid level was measured. Subsequently, each aqueous ink composition was put into a 200 ml glass sample bottle and shaken ten times longitudinally, and then the aqueous ink composition was transferred to the measuring cylinder. Finally, the measuring cylinder containing the aqueous ink composition was allowed to stand for 5 minutes, and the liquid level of the aqueous ink composition was measured.

In addition, bubble evaluation was performed using the following evaluation criteria.
○: The liquid level height is less than 10 mm compared to the initial liquid level height Δ: The liquid level is 10 mm or more and less than 30 mm compared to the initial liquid level height ×: The liquid level is the initial liquid level 30 mm or more compared to

(result)
As can be seen from the experimental results of Examples 1 to 19 shown in Tables 2 to 5, when sodium polyacrylate is blended as a pigment dispersant with respect to various iron oxide pigments, the average dispersed particle size of the pigment is It was confirmed that the value of D50 can be in the range of 10 nm to 300 nm, and an aqueous ink composition excellent in dispersibility, ejection stability (flyability) and storage stability can be produced.

  On the other hand, even when sodium polyacrylate is used as the pigment dispersant, in Comparative Examples 1, 3 and 4 in which the mass average molecular weight of the sodium polyacrylate is 50000, the particle diameter of the pigment is large and the storage stability is Decreased (see Tables 2 to 4). In Comparative Examples 2 and 5 in which pigment dispersants other than sodium polyacrylate were used, storage stability was low and bubbles were also generated (Tables 2 and 6). In the water-based ink compositions of Comparative Examples 2 and 4, the evaluation of ejection stability was not performed because the value of D99 of the pigment was too large. In addition, in the aqueous ink compositions of Comparative Examples 2 and 5, reducing or eliminating air bubbles by adding a silicone antifoam (silicone resin emulsion (trade name; KM 72, Shin-Etsu Chemical Co., Ltd. product)) Can.

Further, as seen from the experimental results of Examples 20 to 25 shown in Tables 7 and 8, the value of the average dispersed particle diameter D50 of the pigment is obtained by setting the dispersant / pigment ratio within the range of 0.05 to 1.5. Can be in the range of 10 nm to 300 nm. On the other hand, when the dispersant / pigment ratio is 2 or more as in the aqueous ink compositions of Comparative Examples 6 to 8, the value of D50 exceeds 300 nm or the pigment is not dispersed.

Claims (5)

An aqueous inkjet ink composition comprising a pigment composition and being edible.
The pigment composition contains a colored pigment consisting only of iron oxide, a mass average molecular weight of 1,500 to 10,000 , a pigment dispersant of the colored pigment and sodium polyacrylate as a bubble generation inhibitor, and a dispersion medium. ,
The content ratio of the colored pigment consisting only of the iron oxide to the sodium polyacrylate is 1: 0.05 to 1: 1.5 on a mass basis,
The aqueous ink composition for inkjets whose average dispersed particle diameter D50 of the colored pigment which consists only of said iron oxide is 10 nm-300 nm. The aqueous ink composition for inkjet according to claim 1, further comprising a surface tension regulator and a wetting agent . In a dispersion medium, a colored pigment consisting only of iron oxide and sodium polyacrylate having a mass average molecular weight of 1,500 to 10,000, and a content ratio of the colored pigment to the sodium polyacrylate is 1: 0.05 to 1 on a mass basis And the step of adding a pigment composition having an average dispersed particle diameter D50 of 10 nm to 300 nm of the colored pigment added simultaneously or in any order so as to be 1.5 , and reducing or eliminating bubbles. A method for producing an aqueous ink composition for ink jet which does not include a bubble process. The method for producing an aqueous ink composition for inkjet according to claim 3, wherein in the step of preparing the pigment composition, a surface tension regulator and a wetting agent are further added . What is claimed is: 1. A solid preparation comprising a tablet or a capsule and having a dry film of an aqueous ink for ink jet on its surface,
A solid preparation comprising the aqueous ink composition for ink jet according to claim 1 or 2, wherein the aqueous ink for ink jet.