JP5714246B2 - Encapsulated pigment and water-based ink using the same - Google Patents

Description

  The present invention relates to an encapsulated pigment excellent in water dispersibility, a method for producing the same, and an aqueous ink using the same.

  Inkjet printers can easily perform full-color printing on plain paper. In this case, a water-based ink containing a water-based dye as a coloring material is often used. However, dyes have poor light resistance and have the drawback of being colored when exposed to sunlight. Recently, pigments have been used instead of dyes.

  Examples of the pigment include a pigment aqueous dispersion in which the pigment is dispersed in water with a dispersant (for example, a water-soluble resin and a surfactant), and a pigment-containing resin in which the pigment is contained in water-insoluble polymer fine particles and dispersed in water. There are used aqueous dispersions of fine particles (that is, encapsulated pigments), self-dispersed pigment aqueous dispersions in which the surface of the pigment is treated to form hydrophilic groups and dispersed in water.

  Although the light resistance can be improved by using a pigment, there is a problem of dispersion stability of the pigment. In particular, an aqueous pigment dispersion in which a pigment is dispersed with a dispersant is inferior in long-term dispersion stability. Self-dispersed pigments have good dispersion stability but poor water resistance. On the other hand, the encapsulated pigment is excellent in both storage stability and water resistance.

  However, in order to use encapsulated pigments as ink-jet inks, it is a problem to make fine particles. In addition, when printing is performed on a non-permeable medium such as a plastic sheet with an aqueous ink containing an encapsulated pigment, it is difficult to ensure image fixability.

  Conventionally, as a method for producing an encapsulated pigment, an acid precipitation re-dissolution method, a phase inversion method, and a miniemulsion polymerization method are known (see Patent Document 1).

  The acid precipitation re-dissolution method comprises neutralizing an anionic group-containing resin, dispersing the pigment in an aqueous medium, acidifying the pH to precipitate the resin and the pigment, fixing the resin to the pigment, In this method, the anionic group is neutralized using a functional compound and redissolved in an aqueous medium (see Patent Document 2).

  In the phase inversion method, a pigment is dispersed in an organic solvent of an anionic group-containing resin, a basic compound is added, water is added while irradiating ultrasonic waves, phase inversion emulsification is performed, and then the solvent is distilled off. It is a method (refer patent document 2).

  In the miniemulsion polymerization method, the dye is dissolved in the monomer or the pigment is dispersed in the monomer, the hydrophobe is added and emulsified with an emulsifier in water to obtain an O / W type miniemulsion, and then the radical polymerization is performed as it is. Is a method of making an encapsulated pigment containing a resin in a resin (see Patent Document 3 and Patent Document 4).

  In both the acid precipitation re-dissolution method and the phase inversion method, the resin that coats the pigment needs to be excellent in the balance between hydrophilicity and hydrophobicity and adsorbability with the pigment, and the resins that can be used are considerably limited.

  In addition, the miniemulsion polymerization method has the disadvantage that if the performance of the hydrophobe is poor, emulsion polymerization occurs only with the monomer, or the emulsion particle size becomes coarse, and an encapsulated pigment having a particle size that can be used in ink jet cannot be obtained. there were.

JP 2004-155818 A JP-A-9-151342 Japanese Patent Laid-Open No. 2001-131213 JP 2008-163059 A

  An object of the present invention is to easily obtain fine particles of an encapsulated pigment having a small average particle size (for example, an average particle size of 0.2 μm or less) in a method for producing an encapsulated pigment by a miniemulsion polymerization method, and a PET sheet It is an object to provide an encapsulated pigment suitable for use in water-based inks, as well as a method for obtaining an encapsulated pigment excellent in fixability to a plastic sheet.

  As a result of diligent research under the above object, the present inventor has found that the above object can be achieved by using a mixture of a specific oligomer and an oil-soluble monomer as a resin component for coating a pigment by a miniemulsion polymerization method. The headline and the present invention were completed.

  That is, according to one aspect of the present invention, a pigment dispersion obtained by dispersing a pigment in an oily solvent is emulsified in water to obtain an O / W emulsion, and then dispersed in the O / W emulsion. A method for producing an encapsulated pigment obtained by polymerizing an oil phase, wherein the oily solvent comprises a radical polymerizable oligomer having two or more acryloyl groups or methacryloyl groups in one molecule and an oil-soluble radical polymerizable monomer The manufacturing method characterized by including these is provided.

According to a preferred embodiment of the present invention, a radical polymerizable monomer having two or more acryloyl groups or methacryloyl groups in one molecule is used as the radical polymerizable monomer.
According to another preferred embodiment of the present invention, the polymerization is performed by adding a radical polymerization initiator to the oil phase and / or the aqueous phase of the O / W emulsion.

According to another aspect of the present invention, an encapsulated pigment obtained by the production method of the present invention is provided.
According to still another aspect of the present invention, an aqueous ink, particularly an inkjet ink, containing the encapsulated pigment of the present invention is provided.

  According to the present invention, not only an oil-soluble radically polymerizable monomer but also a radically polymerizable oligomer having two or more acryloyl groups or methacryloyl groups in one molecule is used as a resin component for coating a pigment by a miniemulsion polymerization method. Therefore, since this oligomer functions as a hydrophobe and the emulsion during polymerization is stabilized, the particle diameter of the encapsulated pigment is increased and aggregation is prevented, and the plastic sheet such as a PET sheet can be used. It is considered that an encapsulated pigment excellent in fixing can be obtained.

  Hereinafter, the present invention will be described in more detail. In the present specification, “(meth) acryl” and “(meth) acrylate” mean “acryl and / or methacryl” and “acrylate and / or methacrylate”, respectively.

  The production process of the encapsulated pigment of the present invention comprises (1) a pigment dispersion preparation process, (2) an O / W emulsion preparation process, and (3) an O / W emulsion polymerization process. (4) A solvent removal step may be provided.

(1) Preparation Step of Pigment Dispersion The preparation step of the pigment dispersion is performed by dispersing the pigment in an oily solvent.
As the pigment, both inorganic pigments and organic pigments can be used. Specifically, carbon black, cadmium red, chrome yellow, cadmium yellow, chromium oxide, viridian, titanium cobalt green, ultramarine blue, Prussian blue, cobalt blue, azo pigment, phthalocyanine pigment, quinacridone pigment, isoindo Rinone pigments, dioxazine pigments, selenium pigments, perylene pigments, thioindigo pigments, quinophthalone pigments, metal complex pigments and the like can be suitably used. These pigments may be used alone or in appropriate combination. The pigment preferably has an affinity for the following oily solvent, that is, preferably has a hydrophobic surface.
The blending amount of the pigment is not particularly limited as long as the pigment is dispersed in the oily solvent, but is preferably 10 to 50% by mass as 100% by mass of the entire pigment dispersion.
The particle diameter of the pigment is preferably 60 to 150 nm.

  The oily solvent needs to be able to form oil phase particles of an O / W type emulsion in the following step (2). However, in the present invention, a radical polymerizable oligomer having two or more acryloyl groups or methacryloyl groups in one molecule. And an oil-soluble radical-polymerizable monomer as essential components.

  The oil-soluble radical polymerizable monomer can be used without limitation as long as it is a monomer capable of radical polymerization. Specifically, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate , (Meth) acrylic acid isopropyl, (meth) acrylic acid (n-, i-, t-) butyl, (meth) acrylic acid hexyl, (meth) acrylic acid 2-ethylhexyl, (meth) acrylic acid n -Alkyl or cycloalkyl esters of (meth) acrylic acid such as octyl, decyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, cyclohexyl (meth) acrylate; (meth) acrylic acid (Meth) acrylic such as methoxyethyl, ethoxyethyl (meth) acrylate, ethoxybutyl (meth) acrylate, etc. Alkoxyalkyl esters of acids; carboxyl group-containing unsaturated compounds such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid; 2-hydroxyethyl (meth) acrylate, 2- or 3-hydroxypropyl (meta ) (Meth) acrylic acid hydroxyalkyl ester of (meth) acrylic acid such as acrylate; nitrogen-containing alkyl (meth) such as N, N-dimethylaminoethyl (meth) acrylate and N, N-diethylaminoethyl (meth) acrylate Acrylates; polymerizable amides such as acrylamide, methacrylamide, N-butoxymethyl (meth) acrylamide, N, N-dimethylaminopropyl (meth) acrylamide, N, N-dimethylaminoethyl (meth) acrylamide; glycidyl (meth) Acrylate Epoxy group-containing unsaturated compound such as allyl glycidyl ether, vinyl acetate, styrene, alpha-chlorostyrene, and acrylonitrile.

  Of these oil-soluble radically polymerizable monomers, polyfunctional radically polymerizable monomers having two or more acryloyl groups or methacryloyl groups in one molecule are preferable. By using such a polyfunctional monomer, three-dimensional crosslinking proceeds when copolymerizing the monomer and oligomer in the miniemulsion particles, and a copolymer resin having a strong network structure is obtained. An encapsulated pigment having excellent resistance to an organic solvent such as a glycol ether solvent can be obtained. Since water-based inks often contain water-soluble organic solvents such as glycol ether solvents, such encapsulated pigments with excellent solvent resistance are suitable for use as pigments in water-based inks.

Examples of such polyfunctional radical polymerizable monomers include diacrylated isocyanurate, 1,3 butylene glycol di (meth) acrylate, 1,4 butanediol di (meth) acrylate, EO-modified 1,6-hexanediol di ( (Meth) acrylate, ECH-modified 1,6-hexanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, allyloxypolyethylene glycol (meth) acrylate, 1,9 nonanediol di (meth) acrylate, EO modified bisphenol A di (meth) acrylate, modified bisphenol A di (meth) acrylate, EO, PO modified bisphenol A (meth) acrylate, PO, tetramethylene oxide modified bisphenol A di (meth) acrylate, bisphenol A-diepoxy (meta ) Acrylic acid adduct, EO-modified bisphenol F di (meth) acrylate , Diethylene glycol di (meth) acrylate, epoxy (meth) acrylate, ECH-modified hexahydrophthalic acid di (meth) acrylate, hydroxypivalic acid neobendyl glycol di (meth) acrylate, neobendyl glycol di (meth) acrylate, EO Modified neobentyl glycol di (meth) acrylate, PO modified neopenterglycol di (meth) acrylate, caprolactone modified hydroxypivalate ester neopentyl glycol, stearic acid modified pentaerythritol di (meth) acrylate, ECH modified phthalic acid di (meth) ) Acrylate, poly (ethylene glycol-tetramethylene glycol) di (meth) acrylate, poly (polypropylene glycol-tetramethylene glycol) di (meth) acrylate, polyethylene glycol di (meth) acrylate Relate, polyethylene glycol-polypropylene glycol-polyethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, polytetramethylene glycol di (meth) acrylate, ECH-modified propylene glycol epoxy ester di (meth) acrylate, PO-modified bisphenol A Diglycidyl ether di (meth) acrylate, silicone di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate tricyclodecane dimethanol (meth) acrylate, neopentyl glycol modified trimethylolpropane Di (meth) acrylate, tripropylene glycol di (meth) acrylate, EO-modified tripropylene glycol di (meth) acrylate, triglycero Rudi (meth) acrylate, dipropylene glycol di (meth) acrylate, zinc di (meth) acrylate, EHC modified glycerol tri (meth) acrylate, EO modified glycerol tri (meth) acrylate, PO modified glycerol tri (meth) acrylate, Pentaerythritol triacrylate, EO-modified tri (meth) acrylate, EO-modified tri (meth) acrylate, trimethylolpropane tri (meth) acrylate, caprolactone-modified trimethylolpropane tri (meth) acrylate, HPA-modified trimethylolpropane Tri (meth) acrylate, EO-modified trimethylolpropane tri (meth) acrylate, PO-modified trimethylolpropane tri (meth) acrylate, trimethylolpropane benzoate (meth) acrylate, tris (acryloxyethyl) iso Anurate, alkoxy-modified trimethylolpropane tri (meth) acrylate, dipentaerythritol hexa (meth) acrylate, caprolactone-modified dipentaerythritol hexa (meth) acrylate, dipentaerythritol hydroxypenta (meth) acrylate, alkyl-modified dipentaerythritol tri ( (Meth) acrylate dipentaerythritol poly (meth) acrylate, alkyl-modified dipentaerythritol penta (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, pentaerythritol ethoxytetra (meth) acrylate, pentaerythritol tetra (meth) acrylate, etc. Can be mentioned.
The blending amount of the monomer is not particularly limited as long as the pigment is dispersed in the oily solvent, but is preferably 5 to 50% by mass with respect to 100% by mass of the entire pigment dispersion.

Examples of the radical polymerizable oligomer having two or more acryloyl groups or methacryloyl groups in one molecule include at least one selected from the group consisting of urethane acrylate, epoxy acrylate and polyester acrylate. Examples of the urethane acrylate oligomer include Beamset 505A-6 (manufactured by Arakawa Chemical), Photomer 6210 (manufactured by Sannopco), Ebecryl 270 (manufactured by Daicel), UV3200B, UV6300B, UV7550B (manufactured by Nippon Synthetic Chemical). Examples of the epoxy acrylate include Van Beam 22C (manufactured by Harima Chemicals), Laromar LR8765 (manufactured by BASF), Photomer 3005 (manufactured by San Nopco), Ebecryl 3500 (manufactured by Daicel), and the like. Examples of the polyester acrylate include Aronix M7100, M6100 (manufactured by Toagosei) and Ebecryl 80 (manufactured by Daicel).
When the oil-based solvent is composed only of the oil-soluble radically polymerizable monomer, the monomer is easily transferred to micelles in the polymerization step (3) below, so that resin fine particles containing no pigment are formed or pigment aggregation It becomes easy to cause. As a result of intensive studies, the present inventors have used an oligomer having an acryloyl group or a methacryloyl group having a molecular weight larger than that of the monomer and having good compatibility with the monomer in combination with the monomer, so that the oligomer serves as a hydrophobe, Furthermore, since the polymerization reaction with the monomer proceeds, it functions to positively suppress the removal of the monomer from the mini-emulsion during polymerization, thereby suppressing the generation of resin fine particles, increasing the particle size of the encapsulated pigment, preventing aggregation, etc. I found what I could do. Moreover, it is difficult to ensure the performance (flexibility and fixability to a plastic sheet) of the target resin film only by radical polymerization of the monomer, but the desired performance is imparted to the resin film by using an oligomer. It becomes easy. Further, when a polyfunctional oligomer and a polyfunctional monomer are used in combination, the three-dimensional crosslinking proceeds by the copolymerization reaction between the two, so that the solvent resistance of the encapsulated pigment can be improved.
The blending amount of the oligomer is not particularly limited as long as the pigment is dispersed in the oily solvent, but is preferably 5 to 50% by mass as 100% by mass of the entire pigment dispersion.

  The oily solvent may further contain an organic solvent having no radical polymerizability in order to adjust the viscosity of the pigment dispersion. Such an organic solvent is not particularly limited as long as it is insoluble in water and miscible with the monomer and oligomer, but may be a low-boiling water-insoluble organic solvent in order to facilitate removal after polymerization. preferable. As the low-boiling water-insoluble organic solvent, those having a boiling point of 100 ° C. or less are preferable. Specific examples include ketone solvents and ester solvents (for example, ethyl acetate). Such an organic solvent need not be added if the pigment dispersion composed of the oligomer, monomer and pigment has a low viscosity. However, as the viscosity of the solution is lower, the dispersibility of the pigment is improved, and the particle size of the oil phase particles of the O / W emulsion in the following step (2) can be reduced. Therefore, the addition of such an organic solvent is useful. The blending amount of the organic solvent is preferably 0 to 80% by mass as 100% by mass of the entire pigment dispersion.

  The oily solvent may further contain a pigment dispersant in order to improve the dispersibility of the pigment in the pigment dispersion. The pigment dispersant is not particularly limited as long as it is suitable for the pigment and solvent to be used.

  The pigment dispersion can be prepared by adding a pigment to the oily solvent and mixing using a known disperser. For example, a bead mill or an ultrasonic disperser can be used as the disperser.

(2) Preparation process of O / W type emulsion
The step of preparing the O / W type emulsion can be performed by adding the pigment dispersion obtained in the step (1) to water and homogenizing it.

The emulsifier is not particularly limited as long as it is an emulsifier used for emulsion polymerization. Preferably, a reactive emulsifier is used as such an emulsifier. The reactive emulsifier is preferable in that it is taken into the resin after the polymerization step (3) below and the emulsifier is not released from the encapsulated pigment. In particular, an anionic reactive emulsifier can be preferably used, and when an anionic reactive emulsifier and a nonionic reactive emulsifier are mixed and used, the solvent resistance of the encapsulated pigment is improved, which is more preferable. . Examples of the anionic reactive emulsifier include Aqualon KH-10, Aqualon HS-10, Aqualon BC-10, Aqualon BC-20 (trade name: manufactured by Daiichi Kogyo Seiyaku), Antox-MS-60, RA-1000. , Antox-MS-2N (manufactured by Nippon Emulsifier Co., Ltd.), Adekalia Soap SE-10N, Adekalia Soap SE-20N, Adekalia Soap SR-10 (Adeka), Teramul S-180A (Kao), Eleminol JS-2 (Manufactured by Sanyo Kasei Kogyo Co., Ltd.), and those made of sulfonate are preferable. Examples of the nonionic reactive emulsifier include, for example, the general formula H ₂ C═CR ₁ COO (CH ₂ CH ₂ O) _n R ₂ (wherein R ₁ and R ₂ are H or CH ₃ , and n is 2 to 90). ) Is preferable, and specific examples include Blemmer PE-200, Blemmer PE-350, and Blemmer PE-400 (manufactured by NOF Corporation). Other nonionic reactive emulsifiers include, for example, Adeka Soap NE-10, Adeka Soap NE-20, Adeka Soap ER-10 (manufactured by Adeka), AQUALON RN-10, AQUALON RN-30 (1st Manufactured by Kogyo Seiyaku).

In the production method of the present invention, in order to facilitate the polymerization step (3) below, it is preferable to add a radical polymerization initiator to the pigment dispersion at a stage before the step (3) below. . The radical polymerization initiator added to the pigment dispersion is preferably an oil-soluble polymerization initiator.
Examples of the oil-soluble polymerization initiator include 2,2′-azobisisobutyronitrile, 2,2′-azobis- (2-methylpropanenitrile), 2,2′-azobis- (2,4-dimethylpentane). Nitrile), 2,2′-azobis- (2-methylbutanenitrile), 1,1′-azobis- (cyclohexanecarbonitrile), 2,2′-azobis- (2,4-dimethyl-4-methoxyvaleronitrile) ), 2,2′-azobis- (2,4-dimethylvaleronitrile), 2,2′-azobis- (2-amidinopropane) hydrochloride and other azo (azobisnitrile) type initiators, benzoyl peroxide , Cumene hydroperoxide, hydrogen peroxide, acetyl peroxide, lauroyl peroxide, persulfates (eg ammonium persulfate), peracid esters (eg t-butyl peroxide) And peroxide type initiators such as octate, α-cumyl peroxypivalate and t-butyl peroctate).

The homogenization treatment in the preparation process of the O / W emulsion can be performed using a normal emulsifier, for example, a homomixer or an ultrasonic disperser.
In this step, the blending amounts of water and the pigment dispersion are 10 to 90% by mass of water and 90 to 10% by mass of the pigment dispersion, with the total of both being 100% by mass.

(3) O / W emulsion polymerization process
The polymerization step of the O / W emulsion can be performed by heating and stirring the O / W emulsion obtained in the step (2). This polymerization is preferably performed in a nitrogen atmosphere. Moreover, when the radical polymerization initiator has not yet been added to the reaction system, it is preferable to perform polymerization by adding a radical polymerization initiator at this point. The polymerization temperature is preferably 40 to 90 ° C., and it is necessary to adjust the temperature and the polymerization time depending on the kind of the polymerization initiator.

Thus, a dispersion is obtained in which the oil phase particles dispersed in the O / W emulsion are dispersed in water as encapsulated pigment fine particles. The particle size of the fine particles is preferably 60 to 200 nm.
In the O / W type emulsion, since the pigment has an affinity for the oil phase, it is included in the oil phase particles. Therefore, the fine particles are encapsulated pigments in which the pigment is coated with a resin composed of the above oligomer and monomer polymer. Construct particles.

(4) Solvent removal step When a low-boiling water-insoluble organic solvent is used as the oily solvent in the step (2), the capsule obtained in the step (3) is used to remove the organic solvent. It is preferable to heat and depressurize the aqueous dispersion of the fluorinated pigment with an evaporator. If the low-boiling water-insoluble organic solvent is not used, this solvent removal step may not be performed.

(5) Manufacturing process of ink The water dispersion of the encapsulated pigment obtained as described above can be used as an aqueous ink as it is, but when used as an inkjet ink, it is contained in the water dispersion. It is necessary to remove coarse particles and aggregates of emulsion particles generated during polymerization. Therefore, an inkjet ink can be prepared by applying the aqueous dispersion of the encapsulated pigment obtained as described above to a centrifuge or a filter.

  In order to adjust the surface tension of the inkjet ink to 40 mN / m or less suitable for ink ejection, a surfactant or an additional solvent is added to the aqueous dispersion of the encapsulated pigment obtained as described above. You can also In addition, in order to improve the storage stability and on-machine stability of inkjet ink, or to adjust the ink viscosity, a high boiling water-soluble organic solvent (glycerin, glycol solvent, glycol ether solvent) may be added. Good.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to this Example.

Example 1
(1) Preparation Step of Pigment Dispersion The following components were mixed in the following blending amounts and dispersed with a bead mill to obtain a pigment dispersion. The molecular weight of the urethane acrylate oligomer (UV3200B (trade name), manufactured by Nippon Synthetic Chemical) was 10,000. The average particle size of carbon black (MA11 (trade name) manufactured by Mitsubishi Chemical Corporation) was 126.8 nm as measured by a dynamic light scattering method (particle size distribution measuring device LB-500 manufactured by Horiba, Ltd.).

Carbon black (MA11 (trade name) manufactured by Mitsubishi Chemical) 7g
Pigment dispersant (Solsperse 32000 (trade name) manufactured by Lubrizol) 2g
Pigment dispersant (Solsperse 5000 (trade name) manufactured by Lubrizol) 0.5g
9 g of methyl methacrylate (made by Wako Pure Chemical Industries)
Urethane acrylate oligomer (UV3200B (trade name) manufactured by Nippon Synthetic Chemical) 4g
25 g of ethyl acetate
Total 45.5g

(2) Preparation process of O / W type emulsion The following components were mixed with the following compounding quantity, and the water phase was obtained.

60g of pure water
Reactive emulsifier (AQUALON KH-10 (trade name), manufactured by Daiichi Kogyo Seiyaku) 1g
Total 61g

  After adding 0.3 g of an initiator (azobisisobutyronitrile) to the pigment dispersion obtained in the above (1), it is added to the aqueous phase and emulsified with an ultrasonic disperser. A W-type emulsion was obtained.

(3) Polymerization step of O / W type emulsion The O / W type emulsion prepared in (2) above was heated to 70 ° C. under a nitrogen atmosphere and stirred for 4 hours to prepare an aqueous dispersion of encapsulated pigment fine particles. .

(4) Solvent Removal Step The aqueous dispersion of encapsulated pigment fine particles prepared in (3) above was heated under reduced pressure with an evaporator to remove ethyl acetate.

(5) Ink production process The aqueous dispersion of encapsulated pigment fine particles obtained in (4) above was centrifuged at 10,000 G for 1 minute to remove aggregates and coarse particles, and then a filter with an inner diameter of φ25 mm and an average pore diameter of 3 μm was added. I passed. The filterability of this aqueous dispersion was good.
The average particle size of the obtained encapsulated pigment was 138.5 nm as measured by a dynamic light scattering method (particle size distribution measuring device LB-500, manufactured by Horiba, Ltd.), and the weight of the aggregates precipitated during polymerization and by centrifugation was 2.9 g. Met.

  The following components were mixed in the following blending amounts to create an ink.

Water dispersion of encapsulated pigment fine particles obtained above 3 parts Diethylene glycol 1 part
Glycerin 1 part total 5 parts

When the obtained ink was applied to a PET sheet and dried by heating, the coating film was rubbed strongly with a tissue.
Moreover, the obtained ink was able to be discharged favorably with a commercially available printer (manufactured by Epson Corporation).

Example 2
The experiment was conducted in the same manner as in Example 1 except that the urethane acrylate oligomer of Example 1 (UV3200B (trade name) manufactured by Nippon Synthetic Chemical) was replaced with a polyester acrylate oligomer (Aronix M6100 (trade name) manufactured by Toagosei). .
The average dispersed particle size of carbon black was 121.2 nm, and the average particle size of the encapsulated pigment obtained was 129.3 nm. Moreover, the sedimentation aggregate was 3.6 g. The filterability of the obtained aqueous dispersion was also good. The ink performance was the same as in Example 1.

Example 3
The experiment was performed in the same manner as in Example 1 except that the urethane acrylate oligomer of Example 1 (UV3200B (trade name) manufactured by Nippon Synthetic Chemical Co., Ltd.) was replaced with an epoxy acrylate oligomer (Van Beam 22C (trade name) manufactured by Harima Kasei). .
The average dispersed particle size of carbon black was 122.7 nm, and the average particle size of the encapsulated pigment obtained was 131.8 nm. Moreover, the sedimentation aggregate was 4.3 g. The filterability of the obtained aqueous dispersion was also good. The ink performance was the same as in Example 1.

Comparative Example 1
An experiment was performed in the same manner as in Example 1 except that the urethane acrylate oligomer of Example 1 (UV3200B (trade name), manufactured by Nippon Synthetic Chemical) was replaced with hexadecane.
The average dispersed particle size of carbon black was 142.7 nm, and the average particle size of the encapsulated pigment obtained was 146.2 nm. Moreover, the sedimentation aggregate was 3.1 g. The filterability of the obtained aqueous dispersion was very poor.
When the obtained ink was applied to a PET sheet and dried by heating, the coating film was rubbed strongly with a tissue, and a slight rub-off was observed.

Comparative Example 2
The same method as in Example 1 except that the urethane acrylate oligomer of Example 1 (UV3200B (trade name) manufactured by Nippon Synthetic Chemical) was replaced with a vinyl chloride / vinyl acetate copolymer resin (Solvine C5R (trade name) manufactured by Nissin Chemical Industry). The experiment was conducted.
The average dispersed particle size of carbon black was 123.2 nm, and the average particle size of the encapsulated pigment obtained was 147.1 nm. Moreover, the amount of precipitated aggregates was as large as 7.8 g. The obtained water dispersion had good filterability. The ink performance was the same as in Example 1. However, the concentration was very light.

  The results of Examples 1-3 and Comparative Examples 1-2 are summarized in Table 1.

Note: In Table 1, abbreviations and symbols mean the following.
MMA: methyl methacrylate.
Average particle size: x for 0.2 μm or more, o for less than 0.2 μm.
Aggregate during polymerization: x when 20% or more of the solid content is aggregated, o when less than 20% is aggregated.
Filter passage: After centrifuging at 10000G for 1 minute, the filter passage with an inner diameter of 25 mm and an average pore diameter of 3 μm is 5 cc or less x, when it is more than 5 cc.
Coating film performance: A thing where the coating film falls by rubbing the coating film strongly with a tissue x, a thing which does not fall.

  From the results of Table 1, in Examples 1 to 3, radical polymerization using methyl methacrylate as a monomer constituting the oil phase of the O / W emulsion and having two or more acryloyl groups or methacryloyl groups in one molecule as an oligomer. Since a functional oligomer was used, various performances were excellent. In contrast, in Comparative Example 1, since non-radical reactive hexadecane was used instead of the radical polymerizable oligomer, the filter passability and the coating film performance were inferior. In Comparative Example 2, since a non-radical reactive vinyl chloride / vinyl acetate copolymer resin was used in place of the radical polymerizable oligomer, a large amount of aggregates were generated during polymerization, and a high concentration pigment dispersion could not be obtained. It was.

Examples 4-14
(1) Preparation process of pigment dispersion The components shown in Table 2 were mixed in the blending amounts shown in the same table, and a pigment dispersion was obtained in the same manner as in Example 1.

(2) Preparation process of O / W type emulsion After adding 0.1 g of radical polymerization initiator (azobisisobutyronitrile) to the pigment dispersion shown in Table 3, emulsifier and water (distilled water) shown in Table 3 ) Was added in the amounts shown in Table 3, and emulsified with an ultrasonic disperser to obtain an O / W emulsion.

(3) O / W emulsion polymerization process The O / W emulsion prepared in (2) above was heated to 70 ° C. with stirring in a nitrogen atmosphere and reacted for 4 hours to disperse the encapsulated pigment fine particles in water. The body was made.

(4) Solvent Removal Step The aqueous dispersion of encapsulated pigment fine particles prepared in (3) above was heated under reduced pressure with an evaporator to remove ethyl acetate.

(5) Storage Stability Evaluation The aqueous dispersion of encapsulated pigment fine particles obtained in (4) above was centrifuged at 20000 G for 6 minutes to remove aggregates and coarse particles. Add 8 g of diethylene glycol (DEG), 2 g of tetraethylene glycol monobutyl ether (TEGBE), or 1 g of DEG and TEGBE to 8 g of the resulting aqueous dispersion, and leave it at 70 ° C. for 1 month to change the viscosity. It was measured. The change rate within ± 5% of the initial viscosity was evaluated as ◯, the change greater than ± 5% and 20% or less was evaluated as Δ, and the change greater than 20% was evaluated as ×. The results are shown in Table 3.

(6) Ink production process The aqueous dispersion of encapsulated pigment fine particles obtained in (4) above was centrifuged at 10,000 G for 5 minutes to remove aggregates and coarse particles, and then passed through a 3 μm filter. The following components were mixed in the following proportions to obtain an inkjet ink.
Water dispersion of encapsulated pigment fine particles obtained above 80 parts diethylene glycol 10 parts triethylene glycol monobutyl ether 9 parts
Surfinol 465 (trade name; manufactured by Air Products Japan) 1 part Total 100 parts of ink obtained were ejected with a commercially available printer (manufactured by Epson). The case was evaluated as x. The results are shown in Table 3.

(7) Other physical properties The pigment particle size, emulsion particle size and capsule pigment particle size were measured by the following methods, and the results are also shown in Table 3.
-Pigment particle diameter It is the average particle diameter obtained by measuring the pigment dispersion produced in (1) above with a particle size distribution measuring device LB-500 manufactured by Horiba.
-Emulsion particle diameter It is the average particle diameter obtained by measuring the O / W type emulsion produced by said (2) with the particle size distribution measuring device LB-500 by Horiba.
-Capsule pigment particle size The aqueous dispersion prepared in (4) above was centrifuged at 10,000 G for 5 minutes to remove aggregates and coarse particles, passed through a 3 μm filter, and then a particle size distribution measuring device LB manufactured by Horiba, Ltd. It is an average particle diameter obtained by measurement at −500.

The abbreviations in Table 2 indicate the following.
MA11: Carbon black "MA11 (trade name)" manufactured by Mitsubishi Chemical
UV3200: Nippon Synthetic Chemical's urethane acrylate oligomer "UV3200 (trade name)"
UV7510: Nippon Synthetic Chemical's urethane acrylate oligomer "UV7510 (trade name)" molecular weight 3500
UV7550: Nippon Synthetic Chemical's urethane acrylate oligomer "UV7550 (trade name)" molecular weight 2400
UV7600: Nippon Synthetic Chemical's urethane acrylate oligomer “UV7600 (trade name)” molecular weight 1400
MMA: Methyl methacrylate manufactured by Wako Pure Chemical Industries
1,9NAD: 1,9 nonane diacrylate made by Kyoeisha Chemical
M405: Dipentaerythritol Hexaacrylate Solsperse 32000 manufactured by Toagosei Co., Ltd .: Pigment dispersant “Solsperth 32000 (trade name)” manufactured by Lubrizol
Solthverse 5000: Lubrizol pigment dispersant “Solsperth 5000 (trade name)”

The abbreviations in Table 3 indicate the following.
(A): Daiichi Kogyo Seiyaku Anionic Reactive Emulsifier “AQUALON KH-10 (trade name)”
(B): Daiichi Kogyo Seiyaku's anionic reactive emulsifier “AQUALON BC2020 (trade name)”
(C): Non-fat emulsifier “PE200 (trade name)” manufactured by NOF Corporation
(D): Nonionic emulsifier “AE400 (trade name)” manufactured by NOF Corporation
(E): Nonionic emulsifier “PME1000 (trade name)” made by NOF

  From Table 3, it can be seen that according to the present invention, an encapsulated pigment having excellent storage stability and suitable as a pigment for aqueous ink can be obtained. Further, from the comparison between Examples 4 to 11 and Examples 12 to 14, by using a polyfunctional radical polymerizable monomer and a polyfunctional radical polymerizable oligomer in combination, a water-soluble organic solvent such as a glycol ether solvent can be used. It can be seen that a highly resistant encapsulated pigment is obtained.

  Since the present invention provides fine particles of encapsulated pigment having a small average particle size and excellent fixability to a plastic sheet such as a PET sheet, it can be used in the field of printing using water-based ink, particularly in the field of inkjet printing. .

Claims (6)

Encapsulation obtained by emulsifying a pigment dispersion obtained by dispersing a pigment in an oily solvent in water to obtain an O / W emulsion, and then polymerizing the oil phase dispersed in the O / W emulsion a manufacturing method of a pigment, wherein the oily solvent is Ri Na and a radical polymerizable monomer of the radical polymerizable oligomer and an oil-soluble having two or more acryloyl groups or methacryloyl groups in the molecule, the O / W type emulsion method which is characterized in der Rukoto those emulsified using a reactive emulsifier comprising a mixture of an anionic reactive emulsifier and a nonionic reactive emulsifier. The nonionic reactive emulsifier has the general formula H ₂ C═CR ₁ COO (CH ₂ CH ₂ O) _n R _2.
(Wherein R ₁ and R ₂ are H or CH ₃ , n is 2 to 90)
The method for producing an encapsulated pigment according to claim 1 , comprising: The method for producing an encapsulated pigment according to claim 1 , wherein the anion-reactive emulsifier comprises sulfonate sulfate. An encapsulated pigment obtained by the production method according to any one of claims 1 to 3 . An aqueous ink containing the encapsulated pigment according to claim 4 . The water-based ink according to claim 5 , which is an inkjet ink.