JP2006232887A - Colored fine particle dispersion, water-based ink and image-forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a colored fine particle dispersion that is comprised of fine particles, exhibits excellent dispersion stability, provides an ink excellent in preservation property and jetting stability and gives a print excellent in printing density, light resistance and gloss, and to provide a water-based ink using the colored fine particle dispersion, and an image-forming method using the water-based ink for inkjet. <P>SOLUTION: The core-shell structured colored fine particle dispersion comprises a fine particle comprised of a resin containing a coloring material covered with a resin containing no coloring material, where the colored fine particles give a mean value of the aspect ratio (projected area diameter/maximum height) of each colored fine particle of 1.0-5.0 as measured by an Atomic Force Microscopy (AFM) after drying the colored fine particle dispersion on a smooth base plate. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a colored fine particle dispersion, an aqueous ink, and an image forming method using the same.

  In recent years, recording materials used for printers, printing presses, markers, writing instruments, etc., and inking materials have been made solvent-free and water-based, as well as water-based recording materials used especially for ink-jet recording. And those mainly composed of fine dispersions of pigments are widely used.

  Further, in order to solve the problem of water resistance and light fastness of water-based inks using water-soluble dyes, a proposal for coloring a water-dispersible resin with an oil-soluble dye or a hydrophobic dye is disclosed in, for example, JP-A-55. -139471, 58-45272, JP-A-3-250069, 8-253720, 8-92513, 8-183920, JP2001-11347, etc. Has been made.

  In fact, not only the water-dispersible resin is colored with oil-soluble dyes and hydrophobic dyes, but also colorants and colored fine particles composed of the resin covering them, and colorant particles composed of the colorant and the resin are further formed into a film. Attempts have also been made to use colored fine particles coated with a resin.

  On the other hand, even with pigment inks mainly composed of fine pigment dispersions, the light resistance is further improved in order to reduce problems such as low density and the tendency of color reproducibility problems such as bronzing. For the purpose of improving dispersion stability, ejection stability, etc., it has been disclosed in, for example, JP-A-8-269374, JP-A-9-151342, JP-A-10-88045, and JP-A-10-292143. Thus, an attempt has been made to coat the surface of a pigment with a film-forming resin.

  However, particles obtained by coloring water-dispersible resins colored with these oil-soluble dyes or hydrophobic dyes, particles obtained by mixing fine particles of a coloring material such as a pigment with a resin, or colored fine particles obtained by further coating these particles with a resin are prepared. In many cases, the dispersion or affinity of the coloring material such as dyes and pigments and the resin with respect to the organic solvent is insufficient, so that it is often impossible to stably produce a fine particle dispersion containing a high concentration coloring material. Even if the dye is easily deposited, the pigment and the resin are difficult to mix, or the coloring material such as the dye or the pigment is present on the particle surface (not completely covered with the resin). Dispersion stability of the colored fine particles themselves was impaired, and it was difficult to improve various properties such as dispersion stability and ejection stability required for ink jet ink, and effects such as improvement of light resistance were reduced. There is a problem in that.

  Several techniques have been proposed in which a coloring material and a resin are mixed and dispersed in water to form a colored fine particle dispersion, which is used as an ink for inkjet.

  Among these, as a characteristic of the resin, Japanese Patent Application Laid-Open No. 2001-98194 uses a copolymer resin composed of a hydrophilic polymerization chain portion and a hydrophobic polymerization chain portion, and Japanese Patent Application Laid-Open No. 2000-191968. JP-A-9-157508 discloses one using a vinyl polymer polymerizable unsaturated acid monomer, a hydroxyl group-containing monomer, a styrene macromer, etc., and one using a polyester resin containing cyclohexene dicarboxylic acid.

  However, the colored fine particles are still insufficient in terms of performance such as a large particle size around 100 nm, ink storage stability, ejection stability, low print density, color development, light resistance, etc. Nothing has been obtained.

  Also described is an aqueous dispersion of composite colored fine particles having a core-shell structure obtained by dissolving and emulsifying a polyester resin and an oil-soluble dye and then further polymerizing an ethylenically unsaturated monomer. (See Patent Document 1).

  However, the above-described colored fine particles having a core-shell structure have a large particle size and have a problem in dispersion stability, and are not practical.

  JP-A-2002-47440, 2002-88294, 2002-97395, and the like describe small colored particles having a particle size of 50 nm or less, but dispersion stability is not sufficient and storage stability is low. Secondary agglomeration when printed or the effect of fine particles is insufficient, and there is no description about the core-shell type. Japanese Patent Application Laid-Open Nos. 2002-80746 and 2002-80772 disclose compositions in which an oil-soluble dye dissolved in an organic solvent having a high boiling point is dispersed in an aqueous medium. Otherwise, it is unstable and ink ejection is not stable.

As described above, storability and ejection stability have problems in terms of print density, color reproducibility, light resistance of images, gloss, and the like, and the development of an immediate solution is desired.
Japanese Patent Laid-Open No. 9-157508

  The present invention has been made in view of the above problems, and an object of the present invention is to obtain fine particles, excellent dispersion stability, and excellent ink storage stability and ejection stability when ink is prepared. The present invention provides a colored fine particle dispersion excellent in print density, light resistance and gloss of a print, an aqueous ink using the colored fine particle dispersion, and an image forming method using the aqueous ink for inkjet. .

  The above object of the present invention can be achieved by the following constitution.

(Claim 1)
In a core-shell type colored fine particle dispersion in which fine particles containing a resin containing a coloring material are coated with a resin not containing a coloring material, the colored fine particle dispersion is dried on a smooth substrate, and an atomic force microscope ( When the aspect ratio (projected area diameter / maximum height) of each colored fine particle is measured by atomic force microscopy (AFM), the average aspect ratio of the colored fine particle is 1.0 to 5.0. Colored fine particle dispersion.

(Claim 2)
The colored fine particle dispersion is dried on a smooth substrate, and the perimeter (l) and area (S) of the projected image of each colored fine particle are measured by an atomic force microscope (AFM). ^2. The colored fine particle dispersion according to claim 1, wherein the average roundness of the colored fine particles is in the range of 100 to 150 when ((πl 2/4 / S) × 100) is obtained.

(Claim 3)
The colored fine particle dispersion according to claim 1 or 2, wherein an average volume particle size of the colored fine particles of the colored fine particle dispersion is in the range of 5 to 1000 nm.

(Claim 4)
A water-based ink comprising the colored fine particle dispersion according to any one of claims 1 to 3.

(Claim 5)
The water-based ink according to claim 4, wherein the water-based ink is an ink-jet water-based ink.

(Claim 6)
6. An image forming method, wherein the water-based ink according to claim 5 is ejected as droplets from an ink-jet head based on a digital signal, and adhered to an ink receiving medium.

  According to the present invention, fine particles are excellent in dispersion stability, and when ink is prepared, the ink storage stability and emission stability are excellent, and the print density, light resistance, and gloss of the obtained print are excellent. , A colored fine particle dispersion, an aqueous ink using the colored fine particle dispersion, and an image forming method using the aqueous ink for inkjet.

  Hereinafter, although the best mode for carrying out the present invention will be described, the present invention is not limited to these.

  Hereinafter, the present invention will be described in detail.

  The colored fine particle dispersion of the present invention will be described.

  The colored fine particle dispersion according to the present invention has the following characteristics, and is fine and excellent in dispersion stability. When an ink is produced, the ink has excellent storage stability and emission stability, and the obtained print has A colored fine particle dispersion excellent in print density, light resistance, and gloss can be obtained.

  The colored fine particles in the colored fine particle dispersion in the present invention are spherical in which spherical colored fine particles made of a resin containing a coloring material are uniformly coated with a resin not containing a coloring material in a liquid, and have a diameter of 5 to 5. It is preferable that the thickness is 1000 nm, and a spherical shape is maintained even when dried on a flat substrate.

  When actually printed on paper for inkjet printers or the like, it has the same shape, and colored fine particles made of a resin containing a color material are coated with a resin not containing a color material. As a result, it is estimated that the print density, light resistance, and gloss are excellent.

  In the liquid of the present invention, spherical colored fine particles are uniformly coated with a resin not containing a colorant, which means that individual particles are dropped on a flat substrate and dried on the substrate. It means that a circle is observed and a protrusion is formed at the center.

(Aspect ratio of colored fine particles)
In addition, the feature of the present invention is that the spherical shape is maintained even when dried on a flat substrate, and the aspect ratio is 1.0 to 5.0, which is observed from directly above the substrate. The roundness of individual particles is preferably in the range of 100 to 150.

  It is spherical in liquid and has an aspect ratio of 1.0 to 5.0 when dried on a flat substrate while maintaining its shape.

  When the aspect ratio is less than 1.0, there is a large repulsive force from the substrate or adjacent particles, and it is expected to be colored fine particles that are difficult to adhere to the substrate or ink jet printer paper. Not suitable for ink jet ink. Also, when the aspect ratio exceeds 5.0, no projection is formed at the center on the flat substrate, it is close to the state of adhering in a plate shape, and the core shell is on the flat substrate or paper dedicated for inkjet printers. It can be judged that it does not have a structure. Therefore, when an ink for an ink jet printer is prepared, a colored fine particle dispersion excellent in print density, light resistance, and gloss of the obtained print cannot be obtained.

(Roundness of colored fine particles)
The roundness of the colored fine particles in the present invention is preferably in the range of 100 to 150. More preferably, it is 100-140, More preferably, it is 100-130.

  From the measurement method and the calculation method, the roundness cannot be less than 100. Further, when the roundness exceeds 150 on a flat substrate, the spherical shape is not retained in the dispersion, and several colored fine particles form aggregates. In this case, the aggregates of colored fine particles are expected to expand in the liquid due to disturbances such as long-term storage, so that the dispersion stability is excellent, and the ink storage stability and emission stability are excellent when the ink is prepared. It is difficult to obtain a colored fine particle dispersion.

  As described in claims 1 to 2, the aspect ratio and the roundness are preferably evaluated based on the obtained values in an image obtained by measurement with an atomic force microscope (AFM).

  The aspect ratio, roundness, and volume particle diameter in the present invention are values obtained by the calculation method described below.

(Aspect ratio of colored fine particles)
Aspect ratio (A) when measuring the shape of one particle with an atomic force microscope (AFM) and measuring the projected area (S) of the particle and the maximum height (h) from the substrate surface AR) is given by:

Projected area diameter (2r) = 2 × (S / π) ^0.5
AR = 2r / h
(Roundness of colored fine particles)
Roundness (RC) when the shape of one particle is measured by an atomic force microscope (AFM), and the projected area (S) of one particle and the perimeter (1) of one particle are measured. ) Is given by:

^{RC = (πl 2/4 /} S) × 100
(Volume particle size of colored fine particles)
The volume particle size when measuring the shape of one particle with an atomic force microscope (AFM) and measuring the integrated value of one particle at a height from the substrate surface as a volume (V) ( R) is given by:

R = 2 × (3V / 4π) ^1/3
Alternatively, the coefficient of variation can be obtained using a dynamic light scattering method. For example, it can be determined using a laser particle size analysis system manufactured by Otsuka Electronics or a Zetasizer 1000HS manufactured by Malvern.

(Volume particle size of colored fine particles)
The average volume particle size of the colored fine particles in the present invention is required to be in the range of 5 to 1000 nm, preferably 5 to 300 nm, and more preferably 5 to 150 nm. When the average volume particle diameter is 5 nm or less, the surface area per unit volume becomes very large, so that the effect of encapsulating the coloring material in the core-shell polymer becomes small. On the other hand, particles that are larger than 1000 nm tend to clog the head, and are liable to settle in the ink, so that the stagnation stability deteriorates.

  The colored fine particle dispersion is fine and has excellent dispersion stability. When image formation is performed using the aqueous ink of the present invention prepared using the colored fine particle dispersion, the maximum density is high, and In addition, an image having excellent image storage stability and light resistance can be obtained.

  Further, when water-based inks or ink-jet inks using the colored fine particle dispersion of the present invention, which are stable fine particles, are used, surface scattering is suppressed, so that they are not found in conventional inks using colored fine particle dispersions. A glossy texture with a sense of quality is obtained.

  In the present invention, each shape parameter was evaluated as follows.

  In accordance with the following method, atomic force microscope (AFM) measurement is performed, and the aspect ratio, volume particle size, and roundness are calculated for 50 or more, preferably 100 or more colored fine particles, and the average aspect ratio is calculated. The average roundness was calculated.

(Measurement method)
The sample used is a product obtained by naturally drying a colored fine particle dispersion or a solution obtained by diluting a colored fine particle dispersion on a smooth sample base.

  The atomic force microscope (AFM) used is an SPI3800N probe station and SPA4000 multifunctional unit manufactured by Seiko Instruments Inc., and a smooth base coated with a dispersion of colored fine particles cut into a size of about 1 cm square is applied to a piezoelectric substrate. The sample was set on a horizontal sample stage on the scanner, and when it reached the region where the interatomic action was reached, it was scanned in the XY direction, and the unevenness of the sample at that time was detected by the displacement of the piezo in the Z direction. A piezo scanner that can scan XY 20 μm and Z 2 μm was used. The cantilever was a silicon cantilever SI-DF20 manufactured by Seiko Instruments Inc., which had a resonance frequency of 120 to 150 kHz and a spring constant of 12 to 20 N / m, and was measured in a DFM mode (Dynamic Force Mode). A measurement area of 500 μm square was measured with 1 (or 2) field of view and a frequency of 2 Hz. Further, the obtained three-dimensional data was approximated by least squares to correct a slight inclination and distortion of the sample, and the substrate surface was obtained from a portion where no colored fine particles were present.

"measurement"
From the three-dimensional data measured by the above operation, the maximum height (h), projected area (S), and perimeter length (l) are measured for individual colored fine particles that are not in contact with each other. For the measurement, three-dimensional data was converted into a gray scale image having a gradation of 16 bits, and image analysis software “Image-Pro Plus” manufactured by Media Cybernetics was used.

"resin"
The resin (polymer) according to the present invention will be described.

  As the resin according to the present invention, a generally known resin (polymer) can be used, but a preferable resin (polymer) is obtained by radical polymerization of a vinyl monomer having a polymerizable ethylenically unsaturated double bond. Polymers are preferably used.

  Examples of the polymer obtained by radical polymerization of a vinyl monomer having a polymerizable ethylenically unsaturated double bond preferably used in the present invention include acrylic acid ester, styrene-acrylic acid ester, vinyl acetate-acrylic acid ester and the like. A copolymer or the like is preferred.

  Specific monomers that give the above polymers include vinyl acetate, methyl acrylate, ethyl acrylate, n-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, isononyl acrylate, dodecyl acrylate, Octadecyl acrylate, 2-phenoxyethyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, 2-ethylhexyl methacrylate, 2-hydroxyethyl methacrylate, dodecyl methacrylate, octadecyl methacrylate, methacryl Cyclohexyl acid, stearyl methacrylate, benzyl methacrylate, glycidyl methacrylate, phenyl methacrylate, styrene, α-methylstyrene, acrylonitrile, etc., and acetoacetoxy Chill methacrylate, glycidyl methacrylate of soybean oil fatty acid modified products: include (Blenmer G-FA manufactured by NOF Corporation) and the like.

By combining the above-mentioned monomers, the solubility parameter (SP value) is preferably 16 to 20 (MPa) ^1/2 and the weight average molecular weight is preferably 2,000 to 50,000, more preferably 2, By setting it to 000 to 30,000, the resin for colored fine particles of the present invention can be obtained.

  As a more preferred combination, styrene or methyl methacrylate as a main component, acetoacetoxyethyl methacrylate, glycidyl methacrylate modified with soybean oil fatty acid (Blemmer G-FA: manufactured by NOF Corporation), and n-butyl acrylate, Add at least one selected from long-chain (meth) acrylates such as stearyl methacrylate and 2-ethylhexyl acrylate, and add acrylonitrile, divinylbenzene, diethylene glycol dimethacrylate, etc. as necessary to improve physical properties. The copolymer which can be mentioned can be mentioned.

The above polymer may have a substituent, and the substituent may have a linear, branched, or cyclic structure. Various polymers having the above functional groups are commercially available, but can also be synthesized by a conventional method. These copolymers can also be obtained, for example, by introducing an epoxy group into one polymer molecule and then performing polycondensation with another polymer or graft polymerization using light or radiation.

(Weight average molecular weight of resin)
The weight average molecular weight of the resin according to the present invention is preferably in the range of 2,000 to 50,000. More preferably, it is 2,000 to 30,000, and particularly preferably 2,000 to 15,000.

  The method for measuring the weight average molecular weight of the resin according to the present invention is determined by measurement by GPC (gel permeation chromatography) using THF (tetrahydrofuran) as a solvent. That is, 1.0 ml of THF is added to 0.5 to 5 mg of a measurement sample, more specifically 1 mg, and the mixture is sufficiently dissolved by stirring with a magnetic stirrer at room temperature. Subsequently, after processing with a membrane filter having a pore size of 0.45 to 0.50 μm, the solution is injected into GPC. The measurement conditions of GPC are measured by stabilizing the column at 40 ° C., flowing THF at a flow rate of 1.0 ml / min, and injecting about 100 μl of a sample having a concentration of 1 mg / ml. The column is preferably used in combination with a commercially available polystyrene gel column. For example, Shodex GPC KF-801, 802, 803, 804, 805, 806, 807 manufactured by Showa Denko KK, TSKgel G1000H, G2000H, G3000H, G4000H, G5000H, G6000H, G7000H, TSK guard column manufactured by Tosoh Corporation Combinations can be mentioned. As a detector, a refractive index detector (IR detector) or a UV detector may be used. In the measurement of the molecular weight of a sample, the molecular weight distribution of the sample is calculated using a calibration curve created using monodisperse polystyrene standard particles. About 10 points may be used as polystyrene for preparing a calibration curve.

<< Solubility parameter >>
The resin according to the present invention preferably has a solubility parameter (SP value) of 16 to 20 (MPa) ^1/2 in order to develop the above-described good compatibility state during the production of the colored fine particles. More preferably, it is 17-19 (MPa) ^1/2 , Most preferably, it is 17.5-18.5 (MPa) ^1/2 .

  The solubility parameter according to the present invention will be described.

  The solubility parameter is a value obtained from the solubility parameter of Hildebrand, which is often used when evaluating the ease of dissolution of the non-electrolyte in an organic solvent. This solubility parameter is described in J. Org. H. Hildebrand, J.M. M.M. Prausnitz. R. L. “Regular and Related Solutions” by Scott, Van Nostrand-Reinhold, Princeton (1970), “Polymer Data Handbook Fundamentals” Polymer Science Society can be referred to. The solubility parameter values of various solvents are as follows. F. M.M. Barton, “Handbook of Solrity Parameters and Other Cohesion Parameters”, CRC Press, Boca Raton / Florida (1983), “Polymer Data Handbook Fundamentals”, Polymer Society.

The solubility parameter of the substance is
SP = (δE / V) ^1/2
Where δE is the cohesive energy per mole and V is the molar volume.

  The solubility parameter can be determined by several methods, such as a method for determining from solubility, or a latent heat of vaporization method, a vapor pressure method, a swelling method, a surface tension method, a thermal swelling coefficient method, and a refractive index method.

In the present invention, any solubility parameter determined by the following method is used. The unit is represented by (MPa) ^1/2 in the present invention.

  The solubility parameter can be determined from the solubility of various SP values in known solvents. This method for determining the solubility parameter based on the solubility in a solvent is effective when the structure of the dye or the like is unknown.

  In the dye of the present invention, for example, various solvents with known SP values such as ethanol, acetone, methyl ethyl ketone, ethyl acetate, etc. are used, and a dissolution method for obtaining the SP value of the dye as a solute from the SP value of the solvent having the highest solubility is used. Use. In this method, δd (dispersion force term), δp (polarity term), and δh (hydrogen bond term), which are each component of the SP value of each solvent of the highest solubility group, are plotted separately for each term, Find the center value for each term. The SP value of the dye can be determined by using the central value as the value of each term of the SP value of the dye (C. M. Hansen, J. Paint Technol., 39 (505) 104 (1967), C.I. M. Hansen, J. Paint Technol., 39 (511) 505 (1967)).

  Although it is difficult to accurately determine the SP value by a dissolution method with a pigment having low solubility in a solvent, the above-mentioned document shows measurement using a suspended state. That is, the closer the SP value is to the solvent, the better the pigment is wetted. After mixing the solvent and the pigment, shake well and use a solvent that is well suspended (does not settle) such as ethanol, acetone, methyl ethyl ketone, ethyl acetate, etc. The solvent is selected from a plurality of solvents (may be plural), and the δd (dispersion force term), δp (polarity term), and δh (hydrogen bond term) of each solvent in good suspension state are divided for each term. Plot, calculate the central value of each δd (dispersion force term), δp (polarity term), δh (hydrogen bond term), respectively, and calculate the central value of each term with each term of the SP value of the pigment to be obtained By doing so, the SP value of the pigment can be obtained.

  The solubility parameter can be obtained by calculation when the structure is known.

  Small related chemical composition and SP value, and proposed a calculation method in which SP value is obtained by dividing the sum of molar attractive constants ΔF in a molecule by molar volume V. In this method, ΔF can be easily calculated because it can be assigned to each atomic group.

S = (ΣΔF) / V
However, since the Small equation includes only the cohesive energy generated from the dispersion force, Rheineck, Hoy, Krebelen, and Fedors have proposed different modified ΔFs in order to further improve the accuracy of the above calculation method. Hansen also proposed three-dimensional decomposed parameters. The numerical value slightly varies depending on each correction parameter, but the error when viewed as the difference between the two colorants defined in the present invention is small. When the structure is known, the solubility parameter obtained by the calculation using the correction parameter can be used. The calculation program used in the present invention is Project Leader in a molecular calculation package called CAChe manufactured by Fujitsu Limited.

  The solubility parameter calculated by any of these methods is used in the present invention. For example, when the solubility parameter value is determined from the solubility in the solvent, the solubility parameter value of the solvent to be used may be slightly different depending on the method to be obtained, and the SP value of the color material is slightly different accordingly. . However, since the difference in the values is not so large, it is sufficient to adopt the one having the smallest difference as the SP value difference between the color materials.

Therefore, in the case of dyes or pigments having a known structure, it is preferable to use the above-described calculation method. If the difference in solubility parameter between two or more kinds of color materials obtained in this way is within 4.0 (MPa) ^1/2 , the color materials have an appropriate affinity and only one kind of color material is present. The affinity with the resin does not decrease due to the strength of cohesion between molecules as in the case of a coloring material, and this is preferable because the compatibility with the resin is improved.

  In the present invention, specific numerical values of the solubility parameter according to the present invention are, BRANDRUP and E. H. Numerical values described in IMMERGUT, “POLYMER HANDBOOK”, THIRD EDITION, JOHN WILEY & SONS (1989) were used. However, the numerical value calculated | required by calculation (simulation) was used about the thing which is not described in the said literature.

(Tg of resin (glass transition point))
Various types of Tg can be used as the Tg of the resin (polymer), but it is preferable to use at least one polymer having a Tg of 10 ° C. or higher. Further, from the viewpoint of improving the dispersion stability of the colored fine particle dispersion of the present invention, the resin Tg is preferably in the range of 0 ° C to 100 ° C.

<Colored fine particle dispersion>
The colored fine particle dispersion of the present invention will be described.

  The colored fine particle aqueous dispersion of the present invention dissolves (or disperses) the above resin (may be used in plural) and a dye (or pigment) in an organic solvent, and removes the organic solvent after emulsification in water. It is obtained by forming by the method to do. Alternatively, for example, a resin fine particle aqueous dispersion is formed in advance by emulsion polymerization, an organic solvent solution in which a dye is dissolved is mixed with the resin fine particle aqueous dispersion, and the dye is then impregnated into the resin fine particles. Can be obtained by various methods.

  Such an aqueous dispersion of colored fine particles can be used to form an ink-jet ink. However, the colored fine particle dispersion is prevented from agglomerating for a long period of time, and the stability of the fine particles as an ink suspension is improved. In order to give image fastness such as color tone and gloss when printed on media, and light fastness, a shell made of an organic polymer is formed using the colored fine particles in the colored fine particle dispersion as a core. It is preferable to do this.

As a method for forming the shell, there is a method in which a polymer dissolved in an organic solvent is gradually dropped and adsorbed on the surface of the colored fine particle core at the same time as precipitation. In the present invention, a core containing a colorant and a resin is used. After forming colored fine particles, a monomer having a polymerizable unsaturated double bond is added, emulsion polymerization is performed in the presence of an activator, and a shell is formed by depositing on the core surface simultaneously with polymerization. Even when formed by this method, for example, when a dye is used as a color material, there is some phase mixing at the core / shell interface, and the color material content in the shell is not necessarily zero. However, less mixing is preferable, and the color material content (concentration) in the shell is preferably 0.8 or less of the color material content (concentration) in the core not subjected to core / shell formation. Preferably it is 0.5 or less.

  Examples of the monomer having a polymerizable unsaturated double bond that forms a polymer covering the colorant particle as a shell include ethylene, propylene, butadiene, vinyl chloride, vinylidene chloride, vinyl acetate, styrene, (meth) acrylic acid esters, A compound selected from (meth) acrylic acid, acrylamides and the like, particularly (meth) acrylic acid esters such as styrene, ethyl (meth) acrylate, butyl (meth) acrylate, and ethylhexyl (meth) acrylate are preferable. In addition to these monomers, a raw material monomer that forms a shell with a polymerizable unsaturated monomer containing a hydroxyl group in the molecule, for example, an ester such as hydroxyalkyl (meth) acrylate such as hydroxyethyl (meth) acrylate Up to 50% of total, other ethylenic unsaturations It is preferably used in admixture with monomers having a double bond. In addition, for reasons such as increasing the stability of the shell, an ethylenic group containing a dissociable group having a pKa value of 3 to 7 such as a monomer containing a carboxylic acid such as acrylic acid or methacrylic acid or a monomer containing a sulfonic acid. You may use 10% or less of unsaturated monomers. By using such a monomer component having a hydroxyl group (specifically, a monomer having a hydration layer-forming group such as acrylic acid or methacrylic acid) for shell formation, water of the core / shell colored fine particles can be obtained. The stability of the dispersion can be significantly improved.

(Reactive emulsifier)
Moreover, the group which forms a hydration layer can be introduce | transduced by adding and copolymerizing a reactive emulsifier at the time of a polymerization reaction, water dispersion is stronger, and stable shell formation can be performed.

  Examples of the reactive emulsifier used in the present invention include, for example, Aqualon RN-10, RN-20, RN-30, RN-50 (above, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) NE-10, NE-20, NE-30 (above, manufactured by Asahi Denka Co., Ltd.) and the like, and anionic compounds such as Aqualon HS-10, HS-20, HS-1025, Aqualon KH-05, KH-10 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), Latemul S-180 (manufactured by Kao Co., Ltd.), Adekaria Soap SE-10N, SE-20N (manufactured by Asahi Denka Co., Ltd.), etc. Is mentioned.

  In order to obtain an appropriate particle size in the colored fine particle dispersion of the present invention, optimization of the formulation and selection of an appropriate emulsification method are important. The formulation differs depending on the color material and polymer used, but since it is a suspension in water, it is generally necessary that the polymer constituting the shell is more hydrophilic than the polymer constituting the core. Further, the color material contained in the polymer constituting the shell is preferably less than the polymer constituting the core as described above, and the color material is also required to be less hydrophilic than the polymer constituting the shell. . The hydrophilicity and hydrophobicity can be estimated using, for example, the solubility parameter (SP) described above.

(Solubility parameters of core polymer and shell polymer)
From the viewpoint of improving the formation of the compatible state between the polymer in the core part and the polymer in the shell part, the solubility parameter a (SP) of the polymer in the shell part of the colored fine particles forming the core-shell structure in the colored fine particle dispersion described later. Value) and the solubility parameter b (SP value) of the core polymer of the core part is preferably 2 (MPa) ^1/2 or less, more preferably 1 ( MPa) ^1/2 or less.

Further, as described above, by adjusting the absolute value | a−b | to be preferably 2 (MPa) ^1/2 or less, there is no expression of new particles when forming a core-shell, and further stability is achieved. Particles can be obtained.

(Solubility of resin in ethyl acetate)
Moreover, it discovered together that the solubility with respect to the ethyl acetate of the resin which concerns on this invention is 50 mass% or more is preferable for formation of the compatible state of an oil-based dye and resin.

<Coloring materials (dyes, pigments, etc.)>
The coloring material encapsulated by the polymer will be described.

  As the hue of the color material used in the present invention, yellow, magenta, cyan, black, blue, green, and red are preferably used, and yellow, magenta, cyan, and black dyes are particularly preferable. Oil-soluble dyes are usually dyes that are soluble in organic solvents that do not have water-soluble groups such as carboxylic acids and sulfonic acids and are insoluble in water. However, oil-soluble dyes are oil-soluble by salting water-soluble dyes with long-chain bases. Also included are dyes designed to indicate For example, acid dyes, direct dyes, and salt-forming dyes of reactive dyes and long chain amines are known. The oil-soluble dye is not limited to the following, and particularly preferable specific examples include, for example, Valifast Yellow 4120, Valifast Yellow 3150, Varifast Yellow 3108, Varifast Yellow 2310N, and Valifast Yell 1101 manufactured by Orient Chemical Industry Co., Ltd. , Valentine Red 3320, Valentine Red 3304, Valentine Red 1306, Valentine Blue 2610, Valentine Blue 2606, Valentine Blue 1603, Oil Yellow GG-S, Oil Yellow GG-S, Oil Yellow GG-S, Oil Yellow GG-S, Oil Yellow GG-S, Oil Yellow GG-S, Oil Yellow GG-S, Oil Yellow GG-S, Oil Yellow GG-S, Oil Yellow GG-S w 105, Oil Scallet 308, Oil Red RR, Oil Red OG, Oil Red 5B, Oil Pin 312, Oil Blue BOS, Oil Blue 613, Oil Blue 2N, Oil Black BY, Oil Black BS, Oil Black BS, Oil 70 Bac , Oil Black 5906, Oil Black 5905; Kayset Yellow SF-G, Kayase Yellow K-CL, Kayase Yellow AG, Kayset Yellow A-G, Kayset Yellow A-G, Kayset Yellow 2K, Kayset Yellow 2G -BL, Kayset Red A-BR, K ayaset Magenta 312, Kayase Blue K-FL; FS Yellow 1015, FS Magenta 1404, FS Cyan 1522, FS Blue 1504, C.I. I. Solvent Yellow 88, 83, 82, 79, 56, 29, 19, 16, 14, 04, 03, 02, 01, C.I. I. Solvent Red 84: 1, C.I. I. Solvent Red 84, 218, 132, 73, 72, 51, 43, 27, 24, 18, 01, C.I. I. Solvent Blue 70, 67, 44, 40, 35, 11, 02, 01, C.I. I. Solvent Black 43, 70, 34, 29, 27, 22, 7, 3, C.I. I. Solvent Violet 3, C.I. I. Solvent Green 3 and 7, Plast Yellow DY352, Plast Red 8375; Mitsui Chemicals MS Yellow HD-180, MS Red G, MS Magenta HM-1450H, MS Blue HM-1384; Sumitomo Chemical Co., Ltd. ES Red 3001, ES Red 3002, ES Red 3003, TS Red 305, ES Yellow 1001, ES Yellow 1002, TS Yellow 118, ES Orange 2001, ES Blue 6001, TS Turq Blue 618 Ner Elu Yellow 6G, Cer Yellow Yellow 6G, CerB GN, MACROLEX Red V olet R, and the like. In addition, metal complex dyes such as those disclosed in JP-A Nos. 9-277893, 10-20559, and 10-30061 are also preferably used. Preferred structures are those represented by the following general formula (2). is there.

General formula (2)
M (Dye) _l (A) _m
In the formula, M represents a metal ion, and Dye represents a dye capable of coordinating with a metal. A represents a ligand other than a dye, l represents 1 to 3, and m represents 0, 1, 2, 3. When m is 0, l represents 2 or 3, in which case Dye may be the same or different.

  Examples of the metal ion represented by M include metals belonging to Groups 1 to 17 of the periodic table, such as Al, Co, Cr, Cu, Fe, Mn, Mo, Ni, Sn, Ti, Pt, Pd, Zr, and the like. An ion such as Zn can be used. Ni, Cu, Cr, Co, Zn, and Fe ions are particularly preferable from the viewpoint of color tone and various durability. Particularly preferred are Ni ions.

  Various dye structures are conceivable as the dye capable of coordinating with the metal represented by Dye, but conjugated methine dyes, azomethine dyes, and those having a coordination group in the azo dye skeleton are preferred.

  A disperse dye can be used as the oil-soluble dye, and the disperse dye is not limited to the following, but as a particularly preferred specific example, C.I. I. Disperse Yellow 5, 42, 54, 64, 79, 82, 83, 93, 99, 100, 119, 122, 124, 126, 160, 184: 1, 186, 198, 199, 204, 224 and 237; C . I. Disperse Orange 13, 29, 31: 1, 33, 49, 54, 55, 66, 73, 118, 119 and 163; C.I. I. Disperse Red 54, 60, 72, 73, 86, 88, 91, 92, 93, 111, 126, 127, 134, 135, 143, 145, 152, 153, 154, 159, 164, 167: 1, 177 , 181, 204, 206, 207, 221, 239, 240, 258, 277, 278, 283, 311, 323, 343, 348, 356 and 362; I. Disperse violet 33; C.I. I. Disperse Blue 56, 60, 73, 87, 113, 128, 143, 148, 154, 158, 165, 165: 1, 165: 2, 176, 183, 185, 197, 198, 201, 214, 224, 225 257, 266, 267, 287, 354, 358, 365 and 368 and C.I. I. Disperse Green 6: 1 and 9 etc. are mentioned.

  Other oil-soluble dyes include phenols, naphthols, cyclic methylene compounds such as pyrazolone and pyrazolotriazole, or so-called couplers such as open-chain methylene compounds, p-phenylenediamines or p-diaminopyridines, and the like. Also preferred are azomethine dyes, indoaniline dyes and the like obtained by oxidative coupling of compounds. An azomethine dye having a pyrazolotriazole ring is particularly preferable as a magenta dye.

  The pigment is not limited to the following, but as a particularly preferred specific example, as a carbon black pigment, No. manufactured by Mitsubishi Kasei Corporation. 2300, no. 900, MCF-88, no. 33, no. 40, no. 45, no. 52, MA7, MA8, MA100, no. 2200B; Columbia Raven 700, Raven 5750, Raven 5250, Raven 5000, Raven 3500, Raven 1255; Cabot Regal 400R, Regal 330R, Regal 660R, Mull L, Monch 800, Mon900 Monorch 1000, Monarch 1100, Monarch 1300, Monarch 1400; Color Black FW2, Color Black FW2, Color Black FW18, Color Black FW200, Color Black FW200, Color Black FW200, Col Black FW200C S160, Color Black S170, Printex 35, Printex U, Printex V, Printex 140U, Printex 140V, Special Black 6, Special Black 4 Heat, Special Black 4A, Speck 4A, Speck 4A, Speck Maxsorb G-15, Maxsorb G-08, etc. can be used.

  Examples of yellow pigments include C.I. I. Pigment Yellow 1, C.I. I. Pigment Yellow 2, C.I. I. Pigment Yellow 3, C.I. I. Pigment Yellow 12, C.I. I. Pigment Yellow 13, C.I. I. Pigment Yellow 14, C.I. I. Pigment Yellow 16, C.I. I. Pigment Yellow 17, C.I. I. Pigment Yellow 73, C.I. I. Pigment Yellow 74, C.I. I. Pigment Yellow 78, C.I. I. Pigment Yellow 83, C.I. I. Pigment Yellow 93, C.I. I. Pigment Yellow 95, C.I. I. Pigment Yellow 97, C.I. I. Pigment Yellow 98, C.I. I. Pigment Yellow 114, C.I. I. Pigment Yellow 128, C.I. I. Pigment Yellow 129, C.I. I. Pigment Yellow 138, C.I. I. Pigment Yellow 154, magenta pigments include C.I. I. Pigment Red 5, C.I. I. Pigment Red 7, C.I. I. Pigment Red 12, C.I. I. Pigment Red 48 (Ca), C.I. I. Pigment Red 48 (Mn), C.I. I. Pigment Red 57 (Ca), C.I. I. Pigment Red 57: 1, C.I. I. Pigment Red 122, C.I. I. Pigment Red 123, C.I. I. Pigment Red 168, C.I. I. Pigment Red 184, C.I. I. Pigment Red 202, cyan pigments include C.I. I. Pigment Blue 1, C.I. I. Pigment Blue 2, C.I. I. Pigment Blue 3, C.I. I. Pigment Blue 15: 3, C.I. I. Pigment Blue 15:34, C.I. I. Pigment Blue 16, C.I. I. Pigment Blue 22, C.I. I. Pigment Blue 60, C.I. I. Vat Blue 4, C.I. I. Vat Blue 60, etc. are mentioned.

  The colored fine particle dispersion according to the present invention and the colored fine particles having a more preferable core / shell form have a spherical shape and a particle size of 5 to 1000 nm.

  On the other hand, it is preferable that 1-30 mass% is mix | blended in this ink as coloring materials, such as the said dye and a pigment, and it is still more preferable that 1.5-25 mass% is mix | blended. If the blending amount of the coloring material is less than 1% by mass, the printing density is insufficient, and if it exceeds 30% by mass, the suspension stability with time decreases and the particle size tends to increase due to aggregation. It is preferable to be within the range.

(Difference in solubility parameter between colorants)
In the present invention, a colored fine particle aqueous dispersion in which two or more kinds of coloring materials are simultaneously contained in the resin may be used. In that case, two or more different kinds of coloring materials may be selected from the above-described coloring materials. Select and use. It is particularly preferable to select two or more types in which the difference in solubility parameter (SP) value between the colorants is within 4.0 (MPa) ^1/2 .

(Water-based ink)
The water-based ink of the present invention will be described.

  The water-based ink of the present invention comprises a suspension of a polymer containing water as a medium and encapsulating the coloring material. The suspension includes various conventionally known additives such as wetting agents such as polyhydric alcohols, inorganic salts, emulsifiers, Dispersants, surfactants, preservatives, antifungal agents, pH adjusters, silicone-based antifoaming agents, viscosity adjusting agents or chelating agents such as EDTA, oxygen absorbers such as sulfites, etc. as necessary May be added.

  Here, as the wetting agent, for example, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, glycerin, diethylene glycol diethyl ether, diethylene glycol mono n-butyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl Polyhydric alcohols such as ether, ethylene glycol monobutyl ether, methyl carbitol, ethyl carbitol, butyl carbitol, ethyl carbitol acetate, diethyl carbitol, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, propylene glycol monomethyl ether And its ethers, acetates, N Can be used methyl-2-pyrrolidone, 1,3-dimethylimidazolidinone, triethanolamine, formamide, nitrogen-containing compounds such as dimethyl formamide, dimethyl monkey sulfoxide one or two or more kinds. Although there is no restriction | limiting in particular in the compounding quantity of these wetting agents, Preferably 0.1-50 mass% can be mix | blended in the said water-based ink, More preferably, 0.1-30 mass% can be mix | blended.

  In addition, an inorganic salt may be added to the ink in order to keep the viscosity of the ink stable and improve color development. Examples of inorganic salts include sodium chloride, sodium sulfate, magnesium chloride, magnesium sulfide and the like. When implementing this invention, it is not limited to these.

  Further, the emulsifier and the dispersant are not particularly limited, but the HLB value of 8 to 18 is preferable from the viewpoint of manifesting the effect or from the effect of suppressing the increase in the particle diameter of the suspension. .

(Surfactant)
As the surfactant, any of cationic, anionic, amphoteric and nonionic can be used.

  The emulsifier or dispersant is preferably an anionic surfactant or a polymer surfactant, and an anionic surfactant is particularly preferable.

  The surfactant for adjusting the surface tension of the ink is preferably a nonionic surfactant.

  Examples of the cationic surfactant include aliphatic amine salts, aliphatic quaternary ammonium salts, benzalkonium salts, benzethonium chloride, pyridinium salts, imidazolinium salts, and the like.

  Examples of anionic surfactants include fatty acid soap, N-acyl-N-methylglycine salt, N-acyl-N-methyl-β-alanine salt, N-acyl glutamate, alkyl ether carboxylate, acylated peptide , Alkyl sulfonate, alkyl benzene sulfonate, alkyl naphthalene sulfonate, dialkyl sulfosuccinate, alkyl sulfoacetate, α-olefin sulfonate, N-acylmethyl taurine, sulfated oil, higher alcohol sulfate Salts, secondary higher alcohol sulfates, alkyl ether sulfates, secondary higher alcohol ethoxy sulfates, polyoxyethylene alkylphenyl ether sulfates, monoglyculates, fatty acid alkylolamide sulfates, alkyl ether phosphates Salt, alkyl phosphate ester salt and the like.

  Examples of amphoteric surfactants include carboxybetaine type, sulfobetaine type, aminocarboxylate, imidazolinium betaine and the like.

  Nonionic surfactants include polyoxyethylene alkyl ether, polyoxyethylene secondary alcohol ether, polyoxyethylene alkylphenyl ether (eg, Emulgen 911), polyoxyethylene sterol ether, polyoxyethylene lanolin derivative, polyoxyethylene Polyoxypropylene alkyl ether (for example, Newpol PE-62), polyoxyethylene glycerin fatty acid ester, polyoxyethylene castor oil, hydrogenated castor oil, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, polyethylene glycol fatty acid ester, Fatty acid monoglyceride, polyglycerin fatty acid ester, sorbitan fatty acid ester, propylene glycol fatty acid ester , Sucrose fatty acid esters, fatty acid alkanolamides, polyoxyethylene fatty acid amides, polyoxyethylene alkyl amines, alkyl amine oxides, acetylene glycol, acetylene alcohol, and the like. In addition, examples of the surfactant include dispersants Demol SNB, MS, N, SSL, ST, and P (trade names) manufactured by Kao Corporation.

  When these surfactants are used, they can be used singly or as a mixture of two or more kinds. By adding 0.001 to 1.0% by mass with respect to the total amount of the ink, the surface of the ink can be used. Tension can be adjusted arbitrarily. When implementing this invention, it is not limited to these. In order to maintain the long-term storage stability of the ink, an antiseptic and an antifungal agent may be added to the ink.

  Moreover, the following water-soluble resins can be used as the polymer surfactant, which is preferable from the viewpoint of ejection stability. As the water-soluble resin, styrene-acrylic acid-acrylic acid alkyl ester copolymer, styrene-acrylic acid copolymer, styrene-maleic acid-acrylic acid alkyl ester copolymer, styrene-maleic acid copolymer are preferably used. Polymer, styrene-methacrylic acid-acrylic acid alkyl ester copolymer, styrene-methacrylic acid copolymer, styrene-maleic acid half ester copolymer, vinyl naphthalene-acrylic acid copolymer, vinyl naphthalene-maleic acid copolymer Etc. Other examples of the polymer surfactant include Jonkrill, an acrylic-styrene resin (Johnson Corporation). Two or more of these polymer surfactants can be used in combination.

  The addition amount of each of the above polymer surfactants with respect to the total amount of the water-based ink is preferably 0.1 to 10% by mass, and more preferably 0.3 to 5% by mass. If the blending amount is less than 0.01% by mass, it is difficult to reduce the particle size of the suspension, and if it exceeds 10% by mass, the particle size of the suspension may increase or the suspension stability may decrease and gelation may occur. .

  Examples of the antiseptic / antifungal agent include aromatic halogen compounds (eg, Preventol CMK, chloromethylphenol, etc.), methylene dithiocyanate, halogen-containing nitrogen sulfur compounds, 1,2-benzisothiazolin-3-one (eg, PROXEL GXL). However, the present invention is not limited to these.

  In order to keep the aqueous ink of the present invention stable, a pH adjusting agent may be added to the aqueous ink. As the pH adjuster, hydrochloric acid, acetic acid, citric acid, sodium hydroxide, potassium hydroxide or the like can be diluted with water or used as it is.

  Moreover, as said antifoamer, a commercial item can be used without a restriction | limiting in particular. Examples of such commercially available products include KF96, 66, 69, KS68, 604, 607A, 602, 603, KM73, 73A, 73E, 72, 72A, 72C, 72F, 82F, 70, 71, manufactured by Shin-Etsu Silicone. 75, 80, 83A, 85, 89, 90, 68-1F, 68-2F (trade name) and the like. Although there is no restriction | limiting in particular in the compounding quantity of these compounds, It is preferable to mix | blend 0.001-2 mass% in the water-based ink of this invention. If the compounding amount of the compound is less than 0.001% by mass, bubbles are likely to be generated at the time of preparing the ink, and it is difficult to remove small bubbles in the ink. During printing, repellency may occur in the ink and the print quality may be deteriorated.

  Next, the emulsification method used in the production of the ink of the present invention will be described.

  In the ink of the present invention, various methods can be used as an emulsification method, for example, in the production of core color material particles or in the production of core / shell colored fine particles directly from pigment particles and a polymer. . Examples thereof are summarized in the description on page 86 of “Advances in Functional Emulsifier / Emulsification Technology and Application Development CMC”. In the present invention, it is particularly preferable to use an emulsifying and dispersing apparatus using ultrasonic waves, high-speed rotational shearing, and high pressure for forming the dye core. For pigments, a media disperser is preferred.

  In the emulsification dispersion using ultrasonic waves, two types of so-called batch type and continuous type can be used. The batch method is suitable for producing a relatively small amount of sample, and the continuous method is suitable for producing a large amount of sample. In the continuous type, for example, a device such as UH-600SR (manufactured by SMT Co., Ltd.) can be used. In the case of such a continuous system, the ultrasonic wave irradiation time can be obtained by the volume of the dispersion chamber / flow velocity × the number of circulations. In the case where there are a plurality of ultrasonic irradiation apparatuses, the total irradiation time is obtained. In practice, the ultrasonic irradiation time is usually 10000 seconds or less. Further, if it is necessary for 10000 seconds or more, the load on the process is large, and in practice, it is necessary to shorten the emulsification dispersion time by reselecting the emulsifier. Therefore, more than 10,000 seconds are not necessary. More preferably, it is 10 seconds or more and 2000 seconds or less.

  As an emulsifying and dispersing device by high-speed rotational shearing, it is described in Disper Mixer as described in pages 255 to 256 of "Functional emulsifier / emulsification technology and application development CMC", or page 251. Such a homomixer and an ultramixer as described on page 256 can be used. These types can be properly used depending on the liquid viscosity at the time of emulsification dispersion. In the emulsification disperser using these high-speed rotary shears, the rotational speed of the stirring blade is important. In the case of an apparatus having a stator, the clearance between the stirring blade and the stator is usually about 0.5 mm and cannot be made extremely narrow, so the shearing force mainly depends on the peripheral speed of the stirring blade. If the peripheral speed is preferably 5 m / S or more and 150 m / S or less, it can be used for emulsification and dispersion in the present invention. This is because when the peripheral speed is low, it is often impossible to reduce the particle size even if the emulsification time is extended, and in order to achieve 150 m / S, it is necessary to extremely improve the performance of the motor. More preferably, the peripheral speed is 20 to 100 m / S.

For emulsification and dispersion by high pressure, LAB2000 (manufactured by SMT) can be used, but the emulsification and dispersion ability depends on the pressure applied to the sample. The pressure is preferably in the range of 10 ⁴ kPa to ⁵ × 10 ⁵ kPa. Moreover, it can emulsify and disperse | distribute several times as needed, and can obtain the target particle size. If the pressure is too low, the desired particle size cannot be achieved in many cases by carrying out emulsification and dispersion many times, and in order to make the pressure 5 × 10 ⁵ kPa, the apparatus is heavily loaded and is not practical. . More preferably, it is the range of 5 * 10 < ⁴ > kPa-2 * 10 < ⁵ > kPa.

  These emulsifying / dispersing devices may be used alone or in combination as necessary. Colloid mills, flow jet mixers, etc. alone cannot achieve the object of the present invention, but by combining with the apparatus of the present invention, it is possible to enhance the effects of the present invention, such as enabling emulsification and dispersion in a short time. is there.

  When forming an image by ejecting the aqueous ink for inkjet recording of the present invention, the inkjet head to be used may be an on-demand system or a continuous system. In addition, as a discharge method, an electro-mechanical conversion method (for example, a single cavity type, a double cavity type, a bender type, a piston type, a shear mode type, a shared wall type, etc.), an electro-thermal conversion method (for example, thermal ink jet) Any ejection method such as a mold, a bubble jet (registered trademark) mold, or the like may be used.

  The aqueous ink of the present invention is preferably used as an ink for ink jet.

(Image forming method)
The image forming method of the present invention will be described.

  In the image forming method of the present invention, an image forming method using an aqueous ink as an inkjet aqueous ink (also referred to as an inkjet recording aqueous ink) is preferable.

  For example, an ink jet recording image is formed on an ink jet image recording medium, for example, by ejecting ink as droplets from an ink jet head based on a digital signal and attaching it to an ink receptor with a printer loaded with water-based ink for ink jet recording. An ink jet print is obtained.

  As the inkjet image recording medium, for example, any of plain paper, coated paper, cast coated paper, glossy paper, glossy film, and OHP film can be used, and for example, a so-called void layer in which a porous layer is formed, for example. It is preferable if the recording medium has It is not particularly limited to the material or shape of the support described above, and for example, it may have a three-dimensional structure other than those formed in a sheet shape.

  The water-based ink of the present invention can be used as ink for writing instruments such as general fountain pens, ballpoint pens, sign pens, etc., in addition to water-based inks for inkjet recording. The aqueous ink of the present invention can be dried to obtain fine powder. The obtained powder can be used for toner for electrophotography.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.

Example 1
<< Synthesis of Resins P-1 to P-6 >>
A dropping device, a thermometer, a nitrogen gas introduction tube, a stirring device, and a reflux condenser were attached to a 3 liter four-necked flask, and 1000 g of ethyl acetate was heated to reflux. Weigh out so that the total amount of monomers is 1000 g at the composition ratio shown in Table 1, and then add dropwise a monomer mixture solution containing 1 g of N, N'-azobisisovaleronitrile over 2 hours. Then, the solvent was distilled off under reduced pressure to obtain resins P-1 to P-6 shown in Table 1, respectively.

  Details of the abbreviations indicating the monomers (also referred to as monomers) listed in Table 1 are as follows.

ST: Styrene MMA: Methyl methacrylate SMA: Stearyl methacrylate EHA: 2-ethylhexyl acrylate BA: Butyl acrylate AAEM: 2-acetoacetoxyethyl methacrylate (manufactured by Nippon Synthetic Chemical)
GFA: Reactant monomer of glycidyl methacrylate and soybean fat fatty acid (Blemmer G-FA manufactured by NOF Corporation)
<< Preparation of Colored Fine Particle Dispersion CP-7 >>: Core / Shell Type Step (1): Preparation of Colorant-Containing Polymer (a): Core Polymer Creamix CLM-0.8S (MTechnic Co., Ltd.) Pot Into this, 12 g of FSB 1504 as a dye, 12 g of resin P-3 and 120 g of ethyl acetate as a resin were added and stirred to completely dissolve the dye and the resin.

  Subsequently, 270 g of an aqueous solution containing 3 g of sodium lauryl sulfate (SDS) as a surfactant was added, followed by emulsification for 5 minutes at a rotational speed of 20000 rpm. Thereafter, ethyl acetate was removed under reduced pressure to prepare a colorant-containing polymer (a).

Step (2): Preparation of shell polymer After replacing the inside of the separable flask containing the colorant-containing polymer (a) prepared above with nitrogen gas and heating to 80 ° C. with a heater, the shell polymer is prepared. 3.5 g of styrene and 1.5 g of 2-hydroxyethyl methacrylate were weighed to prepare a mixed solution of 0.3 g of N, N′-azobisisovaleronitrile. The solution was added dropwise and allowed to react for 6 hours to obtain colored fine particle dispersion CP-7 having a core-shell type particle structure.

<< Preparation of Colored Fine Particle Dispersion CP-2-4, 6, 8-12 >>: Core / Shell Type In the preparation of colored fine particle dispersion CP-7, dye (used amount 12 g), resin (used amount 12 g), interface Dispersion of colored fine particles having a core-shell type particle structure in the same manner except that the activator, shell monomer composition (total monomer amount is 5 g), and initiator (usage amount 0.3 g) are set as shown in Table 2. Body CP-2-4, 6, 8-12 were prepared respectively.

<< Preparation of Colored Fine Particle Dispersions CP-1 and 5 >>: Core Type As shown in Table 2, only the core polymer was prepared.

  That is, in “Colorant-containing polymer (a) (core polymer)”, the types of dyes, resins, and surfactants are as shown in Table 2 (the same amounts used), and the same as the preparation of colorant-containing polymer (a) Thus, a dispersion of the colorant-containing polymer (core polymer) was prepared. These are referred to as colored fine particle dispersions CP-1 and CP-5, respectively.

<Evaluation of shape of colored fine particles>
<Volume particle size>
The volume particle size of the obtained colored fine particles was measured by an average volume particle size with a Zetasizer 1000HS manufactured by Malvern. Moreover, it was confirmed that the data obtained from transmission electron microscope (TEM) observation also coincided with the average volume particle diameter.

<Aspect ratio, roundness>
The obtained colored fine particle dispersion was diluted 100 times, coated on a silicon wafer and sufficiently dried, and then the average aspect ratio and average true circle of an atomic force microscope (AFM) for 50 or more colored fine particles were obtained. The degree was evaluated.

  The atomic force microscope (AFM) used is an SPI3800N probe station and SPA4000 multifunctional unit manufactured by Seiko Instruments Inc., and a smooth base coated with a dispersion of colored fine particles cut into a size of about 1 cm square is applied to a piezoelectric substrate. The sample was set on a horizontal sample stage on the scanner, and when it reached the region where the interatomic action was reached, it was scanned in the XY direction, and the unevenness of the sample at that time was detected by the displacement of the piezo in the Z direction. A piezo scanner that can scan XY 20 μm and Z 2 μm was used. The cantilever was a silicon cantilever SI-DF20 manufactured by Seiko Instruments Inc., which had a resonance frequency of 120 to 150 kHz and a spring constant of 12 to 20 N / m, and was measured in a DFM mode (Dynamic Force Mode). A measurement area of 500 μm square was measured with a 1 (or 2) field of view and a frequency of 2 Hz. Further, the obtained three-dimensional data was approximated by least squares to correct a slight tilt and distortion of the sample, and the substrate surface was obtained from a portion where no colored fine particles were present.

  From the three-dimensional data measured by the above operation, the maximum height (h), projected area (S), and perimeter length (l) were measured for each colored fine particle not in contact with each other. For the measurement, three-dimensional data was converted into a gray scale image having a gradation of 16 bits, and image analysis software “Image-Pro Plus” manufactured by Media Cybernetics was used.

  In addition, when individual colored fine particles develop on the substrate and adhere to other colored fine particles during coating and drying, or when individual colored fine particles develop on the substrate and have the maximum and minimum heights within the measurement surface. When the difference (Rz) was less than 1/10 of the average volume particle size, it was determined that the particle shape was not on the substrate, and measurement was impossible.

  The above results are also shown in Table 2.

  Details of the abbreviations indicating the types of dyes listed in Table 2 are as follows.

FSY1015: FS Yellow 1015 (Arimoto Chemical)
DY1352: Plast Yellow DY-352 (Arimoto Chemical)
PR8375: Last Red 8375 (Arimoto Chemical)
MRG: MS Red G (Mitsui Chemicals)
FSB-1504: FS Blue 1504 (Arimoto Chemical)
OB860: Oil Black 860 (manufactured by Orient Chemical)
Details of the abbreviations indicating the surfactants listed in Table 2 are as follows.

SDS: Sodium lauryl sulfate KH-10: Aqualon KH-10 (Daiichi Kogyo Seiyaku)
Details of the abbreviations indicating the monomers (also referred to as monomers) listed in Table 2 are as follows.

ST: Styrene HEMA: 2-Hydroxyethyl methacrylate Details of abbreviations indicating the initiators shown in Table 2 are as follows.

KPS: Potassium persulfate AIVN: N, N′-azobisisovaleronitrile << Preparation of water-based inks I-1 to I-12 for inkjet use >>
Each of the dispersions of the colored fine particle dispersions CP-1 to CP-12 produced above was weighed in the amounts shown in Table 3, and the solvent, surfactant, and preservative Proxel GX shown in Table 3 were set to 0.00. The inks I-1 to I-12 were prepared by mixing 100 g each so that 1% and the remainder became pure water. The obtained ink was filtered using a 0.8 μm membrane filter to remove dust and coarse particles, thereby preparing aqueous inkjet aqueous inks I-1 to I-12.

  Details of the abbreviations indicating the ink solvent and the surfactant shown in Table 3 are as follows.

EG: Ethylene glycol Gly: Glycerin E1010: Olfine E1010 (manufactured by Nissin Chemical)
[Performance evaluation]
In order to evaluate the storability of the water-based ink (dispersion stability of the contained colored fine particle dispersion), each of the obtained water-based inks I-1 to I-12 for inkjet was subjected to forced deterioration conditions (60 ° C.) described below. 168 hours), and the following particle size change rate (%) and filterability were evaluated.

<Change rate of particle size (%)>
Before and after storing each prepared ink at 60 ° C. for 168 hours, the average volume particle size was measured with a Zetasizer 1000HS manufactured by Malvern (average particle size after heat storage / average volume particle size before heat storage). X100 (%) was determined as the particle size change rate.

<Filterability>
After storing the ink at 60 ° C. for 168 hours, 5 ml was collected from each ink and filtered through a 0.8 μm cellulose acetate membrane filter. Level), what could be filtered only in an amount less than half, was marked as x (impossible level).

  Next, the ink-jet water-based inks I-1 to I-12 prepared above are packed in genuine color ink cartridges (manufactured by Epson), respectively, and ink-jet paper Photolique QP by an ink-jet printer (manufactured by Epson, model number CL-750). Printed on glossy paper (Konica Co., Ltd.) with an image sample (wedge) with the density changed in 10 steps from 0% to 100% with the print driver turned off. The light resistance was evaluated as shown below. The injection stability was also evaluated as shown below.

《Maximum concentration》
Each maximum density measured by X-Rite 900 (manufactured by Nippon Flat Plate Equipment) is described.

《Light resistance》
A low temperature Xe weather meter XL75 (manufactured by Suga Test Instruments Co., Ltd.) was used as a tester (illuminance 70000 lx, 7 days, 20 ° C., 50 RH). The reflection density remaining rate was measured by measuring the change in density in the vicinity of the print density 1 using X-Rite 900 (manufactured by Nippon Flat Equipment). For samples with insufficient concentration, the change in concentration at the highest concentration portion was measured. The level of light resistance was evaluated as follows.

A: Reflection density remaining rate is 85% or more B: Reflection density remaining rate is less than 70 to less than 85% C: Reflection density remaining rate is less than 50 to 70% D: Reflection density remaining rate is less than 50% The above is practical.
<< Outgoing stability >>
With the inkjet printer, 10 images of 1 cm × 10 cm wedge charts spaced apart on an A4 large page were printed continuously with the printer, the state was observed, and the rank was evaluated as follows.

A: No change in the emission state (good)
B: Oblique emission is observed, but there is no ink shortage (allowable)
C: Ink shortage occurs approximately 10% D: Ink shortage occurs approximately several tens of percent In the present invention, rank B or higher is practical.

  The results are shown in Table 4.

Y: Yellow, M: Magenta, C: Cyan, BK: Black As is clear from Table 4, the water-based ink for ink jet prepared using the colored fine particle dispersion of the present invention has a change in particle size as compared with the comparison. It can be seen that the ink is a low-rate ink and excellent in filterability, and is an ink-jet aqueous ink having excellent physical properties such that clogging and the like are unlikely to occur during printing.

  Further, when the ink-jet aqueous ink is used for image formation by a printer, it reflects the filterability and is excellent in ejection stability from the ink-jet nozzle, and the obtained image has a high maximum density and light resistance. It turns out that it is also excellent.

  The present inventors presume that this result is derived from the high degree of completeness of the coating with the shell polymer in the colored fine particle dispersion.

  As described above, by using the colored fine particle dispersion of the present invention, the rate of change in particle size is small, the filterability is excellent, the discharge stability from the inkjet nozzle is excellent, the maximum density of the image is high, and It turns out that the water-based ink for inkjets excellent also in light resistance can be provided.

Claims (6)

In a core-shell type colored fine particle dispersion in which fine particles containing a resin containing a coloring material are coated with a resin not containing a coloring material, the colored fine particle dispersion is dried on a smooth substrate, and an atomic force microscope ( When the aspect ratio (projected area diameter / maximum height) of each colored fine particle is measured by atomic force microscopy (AFM), the average aspect ratio of the colored fine particle is 1.0 to 5.0. Colored fine particle dispersion. The colored fine particle dispersion is dried on a smooth substrate, and the perimeter (l) and area (S) of the projected image of each colored fine particle are measured by an atomic force microscope (AFM). ^2. The colored fine particle dispersion according to claim 1, wherein the average roundness of the colored fine particles is in the range of 100 to 150 when ((πl 2/4 / S) × 100) is obtained. The colored fine particle dispersion according to claim 1 or 2, wherein an average volume particle size of the colored fine particles of the colored fine particle dispersion is in the range of 5 to 1000 nm. A water-based ink comprising the colored fine particle dispersion according to any one of claims 1 to 3. The water-based ink according to claim 4, wherein the water-based ink is an ink-jet water-based ink. 6. An image forming method, wherein the water-based ink according to claim 5 is ejected as droplets from an ink-jet head based on a digital signal, and adhered to an ink receiving medium.