JP6408957B2 - 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, the pigment has a small average dispersed particle size, excellent dispersibility, and is directly printed by an inkjet method on tablets such as pharmaceuticals and foods. The present invention relates to an edible pigment composition and an aqueous ink composition for inkjet.

  For foods such as pharmaceuticals and supplements in tablets, product information is displayed not only on the package but also on the tablet body, thereby improving their distinguishability and preventing dispensing errors and accidental ingestion. Tablets with a coated surface can be printed by a contact method such as gravure printing, so information with high discrimination is displayed on the one hand, but uncoated or OD (orally disintegrating) tablets with poor surface smoothness are in contact. Printing by the method is difficult. Therefore, for these tablets, a marking method that can display only simple characters has become the mainstream. As a result, in the pharmaceutical industry in particular, there is an increasing need for a new printing method capable of displaying highly discriminating information even for uncoated tablets, OD tablets and the like.

  As such a printing method, for example, ink jet printing using a water-based ink composition using a dye can be cited (see Patent Document 1 below). However, when printing on a pharmaceutical tablet or the like using the aqueous ink composition, there is a problem that a printed image is blurred and inferior in light resistance. As one method for solving such a problem, there is a method of improving the light resistance by performing stamp printing using a pigment instead of a dye or the like and eliminating the bleeding problem.

  However, in the case of stamp printing using a pigment, it is necessary to prepare a printing plate, and there is a problem that workability is poor in small lot production. Therefore, a method of direct printing by an ink jet method is conceivable, 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 (2000 nm to 10,000 nm in D99), and the ink jet method is used. 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-mentioned problems, and the object thereof is to print directly on an ink jet system on tablets such as pharmaceuticals and foods with a small average dispersed particle size of pigments and excellent dispersibility. An object of the present invention is to provide an edible pigment composition and an aqueous ink composition for inkjet.

  In order to solve the above problems, the inventors of the present application have studied a pigment composition and an aqueous ink composition for inkjet. As a result, the inventors have found that the above problems can be solved by adopting the following configuration, and have completed the present invention.

  That is, the pigment composition according to the present invention includes carbon black and a polysorbate represented by the following chemical formula (1) in order to solve the above problems, and the content ratio of the carbon black and the polysorbate is: It is 1: 0.4 to 1: 3 on a mass basis, and the average dispersed particle diameter D50 of the dispersed carbon black is 50 nm to 200 nm.

（式中、前記ｗ、ｘ、ｙ及びｚはそれぞれ整数であり、ｗ＋ｘ＋ｙ＋ｚ＝２０を満たす。また、前記Ｒは炭素数が１１〜１７の親油性基を表す。）

(In the formula, w, x, y and z are each integers and satisfy w + x + y + z = 20, and R represents a lipophilic group having 11 to 17 carbon atoms.)

  According to the above configuration, since a pigment made of carbon black is used instead of a dye, when the pigment composition of the present invention is used, for example, in an aqueous inkjet ink composition, an ink composition using a dye. Compared with, light resistance can be improved.

  Moreover, according to the said structure, the polysorbate represented by the said Chemical formula (1) is used as a pigment dispersant of carbon black, and the content ratio of carbon black and polysorbate is 1: 0.4-1 on a mass basis. : By making it within the range of 3, the average dispersed particle diameter of carbon black in the pigment composition can be controlled within the range of 50 nm to 200 nm, and the dispersibility can be improved. Thereby, for example, it is possible to print on tablets such as pharmaceuticals by an inkjet method. Moreover, since it is excellent also in light resistance as above-mentioned, generation | occurrence | production of the blur of a printed image can also be prevented.

  In order to solve the above-mentioned problems, an aqueous ink composition for inkjet according to the present invention comprises the pigment composition described above and has edible properties.

  According to the above configuration, since a pigment made of carbon black is used instead of a dye, for example, even if printing is performed on a tablet surface of a pharmaceutical product or the like by an ink jet method, the printed image is excellent in light resistance and bleeding. Occurrence can be prevented.

  Moreover, according to the said structure, since polysorbate is used as a pigment dispersing agent of carbon black, and the content ratio of carbon black and polysorbate is within a range of 1: 0.4 to 1: 3 on a mass basis. An aqueous ink composition capable of controlling the average dispersed particle size of carbon black within a range of 50 nm to 200 nm and capable of being directly printed by an ink jet method on tablets of pharmaceuticals, foods, and the like. it can. In addition, edible means that it consists only of the substance recognized as oral administration as a pharmaceutical or a pharmaceutical additive, and / or the substance recognized as a food or a food additive.

  According to the present invention, a polysorbate that imparts good dispersibility to a pigment made of carbon black is contained so that the carbon black and the polysorbate have a mixing ratio of 1: 0.4 to 1: 3, and carbon Since the average dispersed particle size D50 of black is in the range of 50 nm to 200 nm, a pigment composition and an aqueous ink composition for inkjet that enable printing by using an inkjet method for tablets such as pharmaceuticals and foods are provided. can do. Further, an aqueous ink composition for ink jet using a pigment made of carbon black is superior in light resistance to that using a dye or the like, and can prevent bleeding of a printed image.

(Pigment composition)
The pigment composition according to the present embodiment is a composition including at least a pigment made of carbon black as a pigment and polysorbate as a pigment dispersant.

  Examples of the carbon black include channel black, furnace black, acetylene black, and thermal black. Moreover, it is also possible to use a commercial item as carbon black of this Embodiment, As such a commercial item, # 900, # 970, # 100, # 2200, # 2300, # 2350, # 2600, MA-7, MA-8, MA-100, MA-11, MCF88, # 45L, # 50, # 10, # 33, # 40, # 4000, # 52, CF9, etc. (trade names, all Mitsubishi Chemical Co., Ltd.), Niteron, HTC (trade names, all manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.), Asahi # 55, Asahi # 51, Asahi # 50U, Asahi # 50, Asahi # 35, Asahi # 15, Asahi Thermal (product) Name, all manufactured by Asahi Carbon Co., Ltd.), Raven700, 5750, 5250, 5000, 3500, 1255 (trade names, all manufactured by Columbia), REGAL400R, 330R, 660R, ogulL, Monarch 700, 800, 880, 900, 1000, 1100, 1300, Monarch 1400 (product names, all manufactured by Cabot), Color Black FW1, FW2, FW2V, FW18, FW200, S150, S160, S170 (product names, any Also manufactured by Degussa), PRINTEX35, U, V, 140U, 140V (trade names, all manufactured by Degussa), Special Black 6, 5, 4A, 4 (trade names, all manufactured by Degussa), TOKABLACK # 8500, # 8300, # 7550, # 7400, # 7350, # 7240, # 7100, # 7050, # 5500, # 4500, # 4400, # 4300 (trade names, all manufactured by Tokai Carbon Co., Ltd.) and the like. These pigments can be used alone or in admixture of two or more as required. However, when the pigment composition of the present embodiment is used for printing on the surface of tablets such as pharmaceuticals and supplements, carbon black may be a pharmaceutical additive specified by the Pharmaceutical Affairs Law or a food additive specified by the Food Sanitation Law. preferable.

  The average primary particle diameter of the carbon black is preferably 10 nm to 40 nm. In addition, an average primary particle diameter means the arithmetic average particle diameter calculated | required by observing the said carbon black particle before making it disperse | distribute in a solvent with a dispersing agent with an electron microscope.

  The carbon black content has a direct effect on the image density, and when printing on a water-based ink composition, which will be described later, when printing on a tablet or the like, it has an effect on the printing density. Therefore, it may be set appropriately in consideration of these points. Usually, the range of 0.5% by mass to 20% by mass is preferable with respect to the total mass of the pigment composition, more preferably within the range of 1% by mass to 15% by mass, and particularly preferably in the range of 1% by mass to 3% by mass. preferable. By setting the carbon black content to 0.5% by mass or more, a decrease in image density can be suppressed. On the other hand, by setting the carbon black content to 20% by mass or less, it is possible to prevent a decrease in gloss, nozzle clogging, and a decrease in ejection stability.

  The average dispersed particle diameter D50 of the carbon black in a dispersed state is preferably in the range of 50 nm to 200 nm, and more preferably in the range of 85 nm to 140 nm. The 99% cumulative value (D99) of the particle size distribution of the carbon black is preferably in the range of 100 nm to 500 nm. By setting the D50 to 50 nm or more, it is possible to prevent the dispersion stability, light resistance and ejection stability from deteriorating and to prevent the printing density from being lowered. On the other hand, by setting the D50 to 200 nm or less, separation and sedimentation of the carbon black can be prevented and dispersion stability can be maintained. The average dispersed particle size D50 or D99 of carbon black is a value measured by a dynamic light scattering method using Microtrac UPA-EX150 (trade name, manufactured by Nikkiso Co., Ltd.).

  The polysorbate is intended to improve the dispersibility of carbon black as a pigment. In addition, polysorbate conforms to the pharmaceutical additives defined in the Pharmaceutical Affairs Law and the standards of the 16th Japanese Pharmacopoeia, and therefore can be suitably used for printing on tablets or the like of drugs or foods.

  The polysorbate is represented by the following chemical formula (1).

（式中、前記ｗ、ｘ、ｙ及びｚはそれぞれ整数であり、ｗ＋ｘ＋ｙ＋ｚ＝２０を満たす。また、前記Ｒは炭素数が１１〜１７の親油性基を表す。）

(In the formula, w, x, y and z are each integers and satisfy w + x + y + z = 20, and R represents a lipophilic group having 11 to 17 carbon atoms.)

The lipophilic group R in the polysorbate has a carbon number in the range of 11-17. Specific examples of the lipophilic group R include an undecyl group (—C ₁₁ H ₂₃ ), a pentadecyl group (—C ₁₅ H ₃₁ ), a heptadecyl group (—C ₁₇ H ₃₅ ), and a heptadecenyl group (—C ₁₇ ). H ₃₃ ) and the like.

  Specific examples of the polysorbate include polysorbate 20 (polyoxyethylene sorbitan monolaurate (20E.O.)), polysorbate 40 (polyoxyethylene sorbitan monopalmitate (20E.O.)), polysorbate 60 ( Examples thereof include polyoxyethylene sorbitan monostearate (20E.O.)), polysorbate 80 (polyoxyethylene sorbitan monooleate (20E.O.)), and the like.

  Commercially available products of the polysorbate 20 include, for example, New Calgen D-941 (trade name, Takemoto Yushi Co., Ltd.), Ionette T-20-C (trade name, Sanyo Chemical Industries, Ltd.), Oimulgin SML20 (trade name). , Henkel Japan Co., Ltd.), Rheodor TW-L120 (trade name, Kao Corporation), Nikkor TL-10 (trade name, Nikko Chemicals Co., Ltd.), Adeka Estor T-2 (trade name, Asahi Denka Kogyo Co., Ltd.) Stock)).

  Examples of commercially available products of the polysorbate 40 include Nikkor TP-10EX (trade name, Nikko Chemicals Co., Ltd.), Rheodor TW-P120 (trade name, Kao Corp.), and New Calgen D-943-D (trade name). , Takemoto Yushi Co., Ltd.) can be used.

  Examples of commercially available products of the polysorbate 60 include Nikkor TS-10MV (trade name, Nikko Chemicals Co., Ltd.), Nonion (trade name, Nippon Oil & Fats Co., Ltd.), Rheodor TW-S120 (trade name, Kao Corporation). , Euglegin SMS20 (trade name, Henkel Japan Co., Ltd.), New Calgen D-944 (trade name, Takemoto Yushi Co., Ltd.), Adeka Estor T-62 (trade name, Asahi Denka Kogyo Co., Ltd.) it can.

  Examples of commercially available products of the polysorbate 80 include Nikkor TO-10MV (trade name, Nikko Chemicals Co., Ltd.), Rheodor TW-0120 (trade name, Kao Corp.), and Euglegin SMO20 (trade name, Henkel Japan Co., Ltd.). )), New Calgen D-945 (trade name, Takemoto Yushi Co., Ltd.), Adeka Estor T-82 (trade name, Asahi Denka Kogyo Co., Ltd.) can be used.

  The content ratio of the carbon black and the polysorbate is preferably 1: 0.4 to 1: 3 on a mass basis. When the content ratio is 1: 0.4 or more, it is possible to prevent a decrease in dispersibility of carbon black. On the other hand, when the content ratio is 1: 3 or less, for example, when used in an aqueous inkjet ink composition, it is possible to prevent a decrease in ejection stability due to adhesion of the nozzle plate.

  In the pigment composition according to the present embodiment, a dispersion medium for dispersing carbon black is included. Examples of the dispersion medium include water, and more specifically, pure water such as ion-exchanged water, ultrafiltrated water, reverse osmosis water, and distilled water, or those obtained by removing ionic impurities such as ultrapure water. . In particular, water sterilized by ultraviolet irradiation or addition of hydrogen peroxide is preferable because generation of mold and bacteria can be prevented over a long period of time. Moreover, it is not specifically limited as content of a dispersion medium, It can set as needed suitably.

  Further, 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 specifically, for example, alcohols such as methyl alcohol, ethyl alcohol, n-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, n-propyl alcohol, 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 , Diethylene glycol, dipropylene glycol, triethylene glycol, 1,2,6-hexanetriol, thiodiglycol, polyethylene glycol, polypropylene glycol, glycerin, diglycerin, polyglycerin and other polyhydric alcohols; N-methylpyrrolidone 1,3-dimethyl-2-imidazolidinone and the like. You may use these individually by 1 type or in mixture of 2 or more types. Among the water-soluble organic solvents listed above, in the present embodiment, ethyl alcohol, n-butyl alcohol, isobutyl alcohol, n-propyl alcohol, isopropyl alcohol, acetone, propylene glycol, polyethylene glycol, glycerin Is preferred. Furthermore, 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 necessary.

  In the method for producing the pigment composition of the present embodiment, the mixing method and the order of addition of carbon black, polysorbate, dispersion medium, and other additives blended as necessary are not particularly limited. For example, carbon black, polysorbate, water as a dispersion medium, and the like may be mixed at a time, and the mixed solution may be subjected to a dispersion treatment using an ordinary disperser. The dispersion time at this time is not particularly limited, but is preferably set so that the average dispersed particle diameter of the pigment is within the above numerical range. For example, when a paint shaker is used, it is preferably in the range of 2 hours to 48 hours, more preferably in the range of 6 hours to 20 hours, depending on the mass of the pigment composition. By setting the dispersion time to 2 hours or longer, the large amount of coarse particles of carbon black is reduced, and the adsorption of polyoxyethylene alkyl ether on the carbon black surface becomes insufficient, resulting in dispersion stability and storage stability. It is possible to prevent the performance from deteriorating. On the other hand, by reducing the dispersion time to 48 hours or less, the occurrence of many pigment fine particles having an average dispersed particle diameter smaller than the above numerical range is reduced, and dispersion stability, storage stability, and ejection stability are further reduced. A decrease can be prevented. In addition, a decrease in printing density can be suppressed. In addition, it does not specifically limit as a disperser used in the case of the dispersion process of a pigment, What is generally used can be used. Specific examples include a ball mill, a roll mill, a sand mill, a bead mill, a paint shaker, and a nanomizer.

  The pigment composition of the present embodiment has a form of a pigment dispersion for preparing the water-based ink composition in addition to a form of a water-based ink composition for inkjet (details will be described later) as a final product. It is included.

(Water-based ink composition for inkjet)
The aqueous inkjet ink composition (hereinafter referred to as “aqueous ink composition”) according to the present embodiment is an aqueous ink containing at least the pigment composition and having a main solvent of water. Further, the water-based ink composition of the present embodiment has edible properties and is suitably used for inkjet recording. Furthermore, since a pigment is used as a coloring material, the water-based ink composition is superior in terms of color developability, 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 0.5% by mass to 20% by mass in terms of solid content, more preferably in the range of 1% by mass to 15% by mass with respect to the total mass of the aqueous ink composition. By making the content of the pigment composition 0.5% by mass or more, the coloring power can be improved. On the other hand, dispersibility can be improved by making the content of the pigment composition 20% by mass or less.

  The water-based ink composition according to this embodiment contains water (water as a main solvent). As the water, it is preferable to use water from which ionic impurities such as ion-exchanged water, ultrafiltered water, reverse osmosis water, distilled water, or ultrapure water have been removed. In particular, water sterilized by ultraviolet irradiation or addition of hydrogen peroxide is preferable because generation of mold and bacteria can be prevented over a long period of time. Moreover, it does not specifically limit as content of water, It can set suitably as needed.

  In the aqueous ink composition of the present embodiment, other additives may be blended. However, when used as an ink-jet ink for tablets of pharmaceuticals, etc., it must comply with the pharmaceutical additives defined in the Pharmaceutical Affairs Law, etc., and the standards of the 16th Japanese Pharmacopoeia, or the food additives. preferable. Examples of the additive include a surface tension adjusting agent, a wetting agent, a water-soluble resin, an organic amine, a surfactant, a pH adjusting agent, a chelating agent, an antiseptic, a viscosity adjusting agent, and an antifoaming agent. The content of these additives is not particularly limited, and can be appropriately set as necessary.

  Among the additives, as the surface tension adjuster, those that comply with the standards of pharmaceutical additives and the 16th Japanese Pharmacopoeia, or food additives defined by the Food Sanitation Law, and a water-based ink composition There is no particular limitation as long as the surface tension can be adjusted. Specifically, for example, caprylic acid decaglycerin ester, capric acid decaglycerin ester, lauric acid decaglycerin ester, oleic acid decaglycerin ester, lauric acid hexaglycerin ester, oleic acid hexaglycerin ester, condensed linolenic acid tetraglycerin ester, Fatty acid ester palm palm, capric acid decaglycerin ester, lauric acid decaglycerin ester, myristic acid decaglycerin ester, stearic acid decaglycerin ester, oleic acid decaglycerin ester, myristic acid hexaglycerin ester, glycerin fatty acid ester mixture, stearic acid glycerin ester (Self-emulsifying type), pyroglutamic acid POE, polyethylene glycol monolaurate (10EO), monoole Polyethylene glycolate (6EO), polyoxyethylene coconut oil fatty acid sorbitan (20EO), polyoxyethylene sorbitan monostearate (20EO), polyoxyethylene sorbitan monooleate (20EO), polyoxyethylene sorbitan monopalmitate (20EO) ), POE (4.2) lauryl ether, POE (9) lauryl ether, and the like. You may use these individually by 1 type or in mixture of 2 or more types.

  Among these surface tension modifiers, caprylic acid decaglycerin ester (trade name; Ryoto polyglycerin CE19D, manufactured by Mitsubishi Chemical Foods), caprylic acid decaglycerin ester ( Trade name: SY glyceric MCA750, Sakamoto Yakuhin Kogyo), lauric acid decaglycerin ester (trade name: NIKKOL DECAGLLYN 1-L, manufactured by Nikko Chemicals Co., Ltd.), lauric acid decaglycerin ester (trade name: SY glycerase ML-750, Sakamoto Yakuhin Kogyo Co., Ltd.), oleic acid decaglycerin ester (trade name; NIKKOL DECGLYN 1-OV, manufactured by Nikko Chemicals Co., Ltd.), oleic acid decaglycerin ester (brand name: SY Glister MO-7S, Sakamoto Pharmaceutical Co., Ltd.) ), Laurin Hexaglycerin ester (trade name: NIKKOL HEXAGLYN 1-L, manufactured by Nikko Chemicals Co., Ltd.), lauric acid hexaglycerin ester (trade name: SY Glyster ML-500, manufactured by Sakamoto Pharmaceutical Co., Ltd.), oleic acid hexaglycerin ester (Trade name: SY Glister MO-5S, manufactured by Sakamoto Pharmaceutical Co., Ltd.), condensed linolenic acid tetraglycerin ester (trade name: SY Glister CR-310, manufactured by Sakamoto Pharmaceutical Co., Ltd.), fatty acid ester palm palm (product) Name: It is preferable to use commercially available products such as Tirabazole W-01, manufactured by Taiyo Kagaku Co., Ltd.

  The content of the surface tension adjusting agent is preferably in the range of 0.2% by mass to 10% by mass and more preferably in the range of 1% by mass to 4% by mass with respect to the total mass of the aqueous ink composition. By setting the content of the surface tension adjusting agent to 0.2% by mass or more, it is possible to suppress a decrease in discharge performance. On the other hand, storage stability can be ensured by setting the content of the surface tension modifier to 10% by mass or less.

  Moreover, the above-mentioned water-soluble organic solvent is mentioned as a wetting agent among the said additives. The content of the wetting agent 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. By setting the content of the wetting agent to 3% by mass or more, clogging in the vicinity of the nozzle of the inkjet head can be prevented, and the discharge performance can be improved. On the other hand, by setting the content of the wetting agent to 50% by mass or less, the viscosity of the aqueous ink composition can be appropriately controlled.

  The water-based ink composition of the present embodiment can be produced by mixing the aforementioned components by an appropriate method. That is, for example, the additive is separately added to the dispersion of the pigment composition, and further diluted with water. Thereafter, the mixture is sufficiently stirred, and if necessary, filtration is performed to remove coarse particles and foreign matters that cause clogging. Thereby, the water-based ink composition which concerns on this Embodiment can be obtained.

  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 disper, a homomixer, a mechanical stirrer, a magnetic stirrer, and the like and stirred. 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 inks and paints. In addition, since the water-based ink composition of the present embodiment is excellent in dispersibility of carbon black as a pigment, it can be suitably used for inkjet ink. In particular, the water-based ink composition of the present embodiment includes carbon black and a pigment dispersant that meet the pharmaceutical additives defined by the Pharmaceutical Affairs Law and the like, and the standards of the 16th Japanese Pharmacopoeia or fall under food additives. Therefore, it is edible and can be printed directly on the surface of tablets such as pharmaceuticals and supplements. In addition, non-contact printing by an inkjet method is possible even for tablets with poor surface smoothness such as uncoated tablets and OD tablets. Furthermore, since the water-based ink composition is excellent in light resistance, the occurrence of bleeding can be prevented even if it is directly printed on the surface of a tablet such as a pharmaceutical or a supplement.

  Hereinafter, preferred embodiments of the present invention will be described in detail by way of example. However, materials, contents, and the like described in the following examples are not intended to limit the scope of the present invention only to those unless otherwise specified. In addition, each of the materials described in the following Examples and Comparative Examples are those that conform to the pharmaceutical additives defined in the Pharmaceutical Affairs Law and the standards of the 16th Japanese Pharmacopoeia, or correspond to food additives. is there.

(Examples 1-6)
The pigment compositions of Examples 1 to 6 were prepared with the composition shown in Table 1 below. Moreover, the pigment composition of each Example was prepared by the following operation. That is, each material shown in Table 1 was put in a container and dispersed at room temperature for 7 hours (dispersion time) with a paint shaker (manufactured by Asada Tekko Co., Ltd.). This obtained the pigment composition of each Example. The numerical values in Table 1 below are all expressed in mass% unless otherwise specified.

(Comparative Examples 1-4)
The pigment compositions of Comparative Examples 1 to 4 were prepared with the composition shown in Table 2 below. These comparative examples are experimental examples when the content ratio of carbon black and polysorbate does not satisfy the range of 1: 0.4 to 1: 4 on a mass basis. In addition, the pigment composition of each comparative example was obtained by putting each material shown in Table 2 in a container and dispersing it at room temperature for 7 hours (dispersion time) with a disperser. Moreover, the numerical values in Table 2 below are all expressed in mass% unless otherwise specified.

(Comparative Examples 5 and 6)
The pigment compositions of Comparative Examples 4 and 5 were prepared with the composition shown in Table 2. These comparative examples are experimental examples in the case where a carbon black dispersant other than polysorbate is used. In addition, the pigment composition of each comparative example was obtained by putting each material shown in Table 2 in a container and dispersing it at room temperature for 7 hours (dispersion time) with a disperser.

(Examples 7 to 10)
Aqueous ink compositions of Examples 7 to 10 were prepared with the composition shown in Table 3 below. Moreover, the water-based ink composition of each Example was prepared by the following operation. First, a pigment composition was prepared according to the same procedure as in Example 1, and then a surface tension adjusting agent, a wetting agent and water were added and mixed so as to have the composition shown in Table 3 below. 7-10 aqueous ink compositions were obtained. The numerical values in Table 3 below are all expressed in mass% unless otherwise specified.

(Measurement of average dispersed particle size of pigment)
The average dispersed particle diameters D50 and D99 of the pigments in the pigment compositions and water-based ink compositions of each Example and Comparative Example were measured using a dynamic light scattering method using Microtrac UPA-EX150 (trade name, manufactured by Nikkiso Co., Ltd.). It was measured by. The results are shown in Tables 1 to 3.

(Flying property)
Matt paper (trade name: Superfine paper, manufactured by Epson Corporation) was prepared as a recording medium, and printing was performed using the aqueous ink composition prepared in Examples 7 to 10. Printing was performed using an inkjet printer.

  Evaluation of nozzle omission and fading was performed by checking whether nozzle omission or fading was observed in the printed image when the ink jet printer was stopped after discharging the aqueous ink composition from the head and then printing was performed again. . The results are shown in Table 3 above. A circle in the table means a case where neither nozzle missing nor blurring was observed. The term “nozzle missing” means that an ink droplet made of a water-based ink composition is not ejected from a nozzle where clogging has occurred. Fading means fading of an image at the initial stage of printing.

(result)
As can be seen from the experimental results of Examples 1 to 6 shown in Table 1, a polysorbate having a lipophilicity of 11 to 17 carbon atoms is used as a dispersant for a pigment composed of carbon black, and further, the inclusion of carbon black and polysorbate When the ratio is in the range of 1: 0.4 to 1: 3 on a mass basis, the average dispersed particle diameters D50 and D99 of carbon black can be reduced, and a pigment composition excellent in dispersibility can be obtained. It was confirmed that it could be manufactured.

  On the other hand, as can be seen from the experimental results of Comparative Examples 1 to 4 shown in Table 2, even when polysorbate is used as the dispersant, the content ratio of carbon black and polysorbate is outside the range of 1: 0.4 to 1: 3. In some cases, the average dispersed particle size D99 of carbon black was increased. Thereby, when printing by the inkjet system using the water-based ink composition of Comparative Examples 1-4, it was confirmed that nozzle clogging may occur and ejection stability may become poor.

  Further, as can be seen from the experimental results of Comparative Examples 5 and 6 shown in Table 2, when a dispersant other than polysorbate is used, the content ratio of carbon black and dispersant is 1: 0.4 to 1: 3. Even within this range, it was confirmed that both of the average dispersed particle diameters D50 and D90 of carbon black increase in value.

Further, as can be seen from the experimental results of Examples 7 to 10 shown in Table 3, the average dispersed particle diameters D50 and D99 of carbon black can be reduced also in the aqueous ink composition to which the surface tension adjusting agent is added. It was confirmed that an aqueous ink composition having excellent dispersibility can be produced. Furthermore, it was confirmed that the water-based ink composition of each example exhibits excellent dispersibility and also has good flight properties during printing by the inkjet method.

Claims (3)

Carbon black, the carbon black pigment dispersant containing only polysorbate represented by the following chemical formula (1), and a dispersion medium ,
The content ratio of the carbon black and the polysorbate is 1: 0.4 to 1: 3 on a mass basis,
A pigment dispersion having an average dispersed particle diameter D50 of 50 nm to 200 nm of the carbon black being dispersed .

(In the formula, w, x, y and z are each integers and satisfy w + x + y + z = 20, and R represents a lipophilic group having 11 to 17 carbon atoms.)   The pigment dispersion according to claim 1,
  A pigment dispersion in which D99 of the carbon black is 100 nm to 500 nm. An aqueous inkjet ink composition comprising the pigment dispersion according to claim 1 and 2 and having edible properties.