JP2013253185A - Magnetic color ink composition and method for producing the magnetic color ink composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic color ink composition in which dulling of the color of a coloring material due to magnetic particles is suppressed, so that the original color tone of the coloring material can be reproduced.SOLUTION: A magnetic color ink composition contains magnetic particles, a basic dye and a vehicle, wherein the magnetic particles constitute coated particles by being surface-coated with the coating film of the basic dye, the coating film having a thickness of 20-50 nm.

Description

  The present invention relates to a magnetic ink composition that contains magnetic particles and a vehicle, and is structured such that after printing, magnetic particles are aggregated by application of magnetic energy, and the magnetic particles and the vehicle are separated. More specifically, the present invention relates to a magnetic color ink composition containing a dye as a coloring material in addition to magnetic particles and a vehicle, and a method for producing the magnetic color ink composition.

  Conventionally, as a printing technology capable of performing full color printing on a recording medium (for example, plain paper, coated paper, art paper, newspaper, etc.), an inkjet method, an electrophotographic method, a dot matrix method, a thermal recording method, an offset printing method, Various image recording methods such as a lithographic printing method, a relief printing method, and a gravure printing method have been proposed.

  Particularly in recent years, in these image recording methods, there has been an increasing need to perform high-speed printing, and there has been a problem of shortening the ink drying time and the fixing time to the recording medium.

  As a technique for shortening the ink drying time and fixing time, a technique (magnetic ink) using magnetic energy for fixing the ink has been proposed. For example, after a data image is printed using liquid ink in which magnetic particles are dispersed, the liquid ink is dried while orienting the magnetic particles by applying magnetism in a certain direction by an external magnetic field, and the magnetic particles are the data. There has been proposed an ink-jet printing method that is permanently stored in an image (see Patent Document 1).

  Also proposed is a water-based magnetic ink for bubble jets containing water, a water-soluble organic solvent, a magnetic dispersion, a nonionic-anionic surfactant and a base (see Patent Document 2).

  The technique described in Patent Document 1 or 2 is an effective technique when applied to black ink. However, when the above technique is applied to color ink for full-color printing, the following problems occur.

  In the technique, inorganic magnetic particles such as ferrite and magnetite are used as the magnetic material. These inorganic magnetic particles are black or dark brown particles. For this reason, when the inorganic magnetic particles are contained in the color ink for full-color printing, there is a problem that the color of the color material is dull and the original color tone of the color material cannot be reproduced. Therefore, when the magnetic ink technology is applied to the color ink, it is a problem to suppress the dull color of the color material due to the magnetic particles and to reproduce the original color tone of the color material.

  As a technique for suppressing the dullness of the color material due to the magnetic particles and reproducing the original color tone of the color material, for example, a transparent resin layer is provided on the surface of the magnetic particles, and a dye is mixed into the transparent resin layer, A method has been proposed in which the transparent resin layer is colored with the dye to conceal the color unique to the magnetic material (see Patent Document 3).

  A magnetic toner containing an organic magnetic substance such as a ferrocene polymer dehydrogenated compound and a dye has also been proposed (see Patent Document 4). This technology uses an organic magnetic material (that is, does not use an inorganic magnetic material), so that all ink components are composed of organic materials, and a clear image can be obtained by improving the compatibility and dispersibility of the ink components. It is intended.

Japanese Patent Laid-Open No. 6-126953 JP-A-9-12948 JP-A-51-42539 Japanese Patent Laid-Open No. 5-134451

  However, even with the technique described in Patent Document 3 or 4, it is difficult to reproduce the original color tone of the color material by suppressing the dullness of the color material due to the magnetic particles.

  That is, since the technique described in Patent Document 3 is a method of kneading a dye into the transparent resin layer formed on the surface of the magnetic particles, the color unique to the magnetic material is completely obtained unless the film thickness of the transparent resin layer is increased. I couldn't hide it. When the film thickness of the transparent resin layer is increased, the particle diameter of the entire magnetic particle including the transparent resin layer is increased, which is not preferable in terms of reduction in image definition and sharpness.

  In addition, since the technique described in Patent Document 4 is a method of simply mixing an organic magnetic substance and a pigment, the effect of suppressing the dull color of the color material due to the magnetic particles and reproducing the original color tone of the color material. It was insufficient. Moreover, since it is a technique using an organic magnetic material, it cannot be a solution when using an inorganic magnetic material.

  The present invention has been made to solve the above-described problems of the prior art, and suppresses the dullness of the color material due to the magnetic particles, and can reproduce the original color tone of the color material. And a method for producing a magnetic color ink composition.

  As a result of intensive studies on the above problems, the present inventors have found that the above problems can be solved by forming a film of a basic dye on the surface of the magnetic particles and concealing the color inherent to the magnetic substance by the film. The headline and the present invention were completed.

[1] Magnetic color ink composition:
That is, according to the present invention, the magnetic particles contain a basic dye and a vehicle, the magnetic particles are coated with the basic dye film to form the coated particles, and the film of the film A magnetic color ink composition having a thickness of 20 nm or more and 50 nm or less is provided.

  In the composition of the present invention, the basic dye is deposited on the surface of the magnetic particles by changing the pH of the acidic solution containing the magnetic particles and the basic dye to the basic side. It is preferable that it is formed.

In the composition of the present invention, the magnetic particles are preferably magnetic particles selected from the group consisting of Fe ₃ O ₄ , Ni and Co. Furthermore, the pH of the composition of the present invention is preferably adjusted to 7 or higher.

[2] Method for producing magnetic color ink composition:
According to the present invention, a magnetic color ink composition comprising magnetic particles, a basic dye and a vehicle, wherein the magnetic particles are coated with the basic dye film to form coated particles. In this method, the basic dye is deposited on the surface of the magnetic particle by changing the pH of the acidic solution containing the magnetic particle and the basic dye to the basic side, and is deposited on the surface of the magnetic particle. A method for producing a magnetic color ink composition is provided, wherein the film is formed.

In the production method of the present invention, an acidic solution containing the magnetic particles and the basic dye is dropped into a basic solution of Fe ²⁺ sulfate and Fe ³⁺ sulfate, and Fe ₃ O ₄ It is preferable that the magnetic dye is formed and the pH of the acidic solution is changed to the basic side to precipitate the basic dye on the surface of the magnetic particle.

  In the production method of the present invention, after the basic dye is dissolved in the acidic dispersion of the magnetic particles, the pH of the acidic dispersion is changed to the basic side, and the basic dye is converted into the magnetic particles. It is also preferable to deposit on the surface.

  According to the magnetic color ink composition of the present invention, it is possible to suppress the color dullness of the color material due to the magnetic particles and reproduce the original color tone of the color material.

  Further, according to the method for producing a magnetic color ink composition of the present invention, a basic dye can be effectively deposited on the surface of magnetic particles by utilizing a change in solubility based on a change in pH. Therefore, the surfaces of the magnetic particles are efficiently coated, and the color unique to the magnetic material (black or dark brown) can be effectively concealed.

It is a schematic explanatory drawing which shows typically the structure of an inkjet recording device. It is a schematic explanatory drawing which shows typically the mechanism which isolate | separates a coating particle and a vehicle in the magnetic color ink composition of this invention.

  The present invention will be described in detail below. However, the present invention is not limited to the following embodiment, and includes all objects having the invention-specific matters.

[1] Magnetic color ink composition:
The magnetic color ink composition of the present invention is a composition containing at least magnetic particles, a basic dye, and a vehicle.

[1-1] Basic dye:
The basic dye is a dye having a basic group such as an amino group or an imino group in a pigment molecule and forming a cationic pigment ion in an aqueous solution. In the composition of the present invention, this basic dye becomes a coloring material.

  The structure of the basic dye is not particularly limited as long as it is a compound having an appropriate color tone and concentration. Any of conventionally known basic dyes and newly synthesized basic dyes can be used.

  Examples of basic dyes include C.I. I. Basic Yellow 2 and 11; C.I. I. C. Basic Red 1 and 13; I. Basic Blue 5, 7, 9 and 26; all of the following trade names are “CARTSOL (yellow) MRL.LIQ”, “Cartasol Red Bk.LIQ”, “Cartasol Blue Bk.LIQ” <any May also be made by Clariant Japan Ltd.>;

[1-2] Magnetic particles:
Magnetic particles are magnetic particles. In the composition of the present invention, the magnetic particles are present in the form of coated particles whose surfaces are coated with a basic dye film.

  The magnetic material is a substance that can be magnetized, and includes a diamagnetic material, a paramagnetic material, and a ferromagnetic material. However, in the present invention, it is preferable to use a ferromagnetic material as the magnetic material. In addition to the inorganic magnetic material, the magnetic material includes an organic magnetic material. In the present invention, these magnetic materials may be used alone or in combination of two or more.

As the inorganic magnetic material, it is preferable to use a ferromagnetic material exhibiting ferromagnetism or ferrimagnetism. Examples of the ferromagnetic material include Fe, Ni, Co and alloys thereof, and oxides such as CrO ₂ . Examples of ferrimagnetic materials include spinel ferrite (MnFe ₂ O ₄ , Fe ₃ O ₄ , γ-Fe ₂ O ₃ , NiZnFe ₂ O ₄ ), garnet (Y ₃ Fe ₆ O ₁₂ ), and the like.

  Organic magnetic materials obtained by heat-treating indanthrone compounds (for example, see JP-A-5-326244), ferrocene polymers (for example, see JP-A-5-134451), and phthalocyanine compounds by heat-treatment What can be obtained (for example, refer to Japanese Patent Application Laid-Open No. Hei 6-271796).

The magnetic particles are preferably magnetic particles selected from the group consisting of Fe ₃ O ₄ , Ni and Co, because the particle size and particle size distribution can be easily controlled, and are Fe ₃ O ₄ particles. Is particularly preferred.

The method for preparing the magnetic material is not particularly limited. For example, Fe ₃ O ₄ can be obtained by a method of oxidizing a mixture of Fe ²⁺ sulfate and Fe ³⁺ sulfate using a hydroxide such as NaOH.

The average particle diameter of the magnetic particles is preferably 30 to 200 nm, and more preferably 30 to 100 nm. By setting it to 30 nm or more, the magnetic responsiveness of the magnetic particles can be improved. By setting the thickness to 200 nm or less, the apparent specific gravity can be reduced by coating with a color material described later, and the sedimentation rate of particles can be suppressed. Further, it is possible to prevent clogging at the ink jet nozzles and stably discharge. In addition, the average particle diameter here means 50% particle diameter (median diameter) d ₅₀ in the particle size distribution obtained by the laser diffraction / scattering method.

Regarding the particle size distribution of the magnetic particles, the 10% particle diameter d10 is preferably ₁₀ to 100 nm, and more preferably 30 to 80 nm. On the other hand, the 90% particle diameter d ₉₀ is preferably 100 to 300 nm, and more preferably 100 to 200 nm. Here, the particle size distribution means a particle size distribution obtained by a laser diffraction / scattering method.

  In the composition of the present invention, the magnetic particles are coated with a basic dye film to form coated particles. The film thickness is 20 nm or more and 50 nm or less, and preferably 20 nm or more and 40 nm or less. By setting the film thickness to 20 nm or more, the surface of the magnetic particles can be sufficiently covered, and the color unique to the magnetic material can be reliably concealed. On the other hand, by setting the film thickness to 50 nm or less, the magnetic responsiveness of the magnetic particles can be improved. Accordingly, when magnetic energy is applied after printing, the coated particles rapidly aggregate and the basic dye and the vehicle can be easily separated. Thereby, the drying time and fixing time of the ink can be shortened.

  The film thickness of the coating can be controlled by the amount ratio (mass basis) of the magnetic particles and the basic dye. The amount ratio of the magnetic particles to the basic dye is preferably in the range of 1: 0.5 to 1: 4. By making the amount of the basic dye 0.5 times or more of the magnetic particles, the film thickness of the coating can be made 20 nm or more. On the other hand, when the amount of the basic dye is 4 times or less that of the magnetic particles, the film thickness of the coating can be 50 nm or less.

  The method for forming the film is not particularly limited. However, it is preferable to form the basic solution by depositing the basic dye on the surface of the magnetic particles by changing the pH of the acidic solution containing the magnetic particles and the basic dye to the basic side. According to such a method, the surface of the magnetic particles can be coated with the basic dye using the change in solubility based on the pH change. Therefore, the surface of the magnetic particle is covered without any spots, and the color unique to the magnetic material (black or dark brown) can be effectively concealed.

As a method of changing the pH of the acidic solution to the basic side, an acidic solution containing magnetic particles and a basic dye is dropped into a basic solution of Fe ²⁺ sulfate and Fe ³⁺ sulfate, A method of forming magnetic particles made of Fe ₃ O ₄ and changing the pH of the acidic solution to the basic side to precipitate the basic dye on the surface of the magnetic particles can be mentioned. This method is preferable in that the surface of the magnetic particle can be coated with a basic dye simultaneously with the formation of the magnetic particle.

  In addition, it is possible to employ a method in which a basic dye is dissolved in an acidic dispersion of magnetic particles, and then the pH of the acidic dispersion is changed to the basic side to precipitate the basic dye on the surface of the magnetic particles. . This method can form a basic dye film having a uniform film thickness on magnetic particles having a stable particle size distribution. Therefore, it is preferable in that coated particles having uniform particle size distribution and dye coating thickness can be obtained.

  “Change the pH to the basic side” means that at least the pH is 7 or more, preferably the pH is 8 or more, more preferably 9.5 or more, and the pH is 10 or more. It is particularly preferable that By setting the pH to a high value (that is, strongly basic), the basic dye can be sufficiently precipitated, and a basic dye film can be reliably formed.

  What is necessary is just to determine suitably content of a coating particle according to the characteristic etc. which are required for ink. Generally, it is preferably 0.2 to 20%, more preferably 0.5 to 10%, and more preferably 1 to 5% with respect to the total amount (mass basis) of the composition. Particularly preferred.

[1-3] Vehicle:
The vehicle is a medium for dissolving or dispersing the coloring material and other additives. The vehicle imparts appropriate viscosity and fluidity to the ink composition.

  The composition of the vehicle is not particularly limited. A conventionally known vehicle, for example, a vehicle containing at least one selected from the group of water and various organic solvents can be used. However, when the composition of the present invention is used as an aqueous inkjet ink, it is preferable to use an aqueous medium containing at least water and a water-soluble organic solvent as a vehicle.

  As water, it is preferable to use ion-exchanged water (deionized water) instead of general water (tap water, mineral water, etc.) containing various ions.

  Examples of the water-soluble organic solvent include alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol; ethylene glycol, propylene glycol, butylene glycol, Polyhydric alcohols such as triethylene glycol, thiodiglycol, hexylene glycol, diethylene glycol, glycerin, trimethylolpropane, 1,2,6-hexanetriol;

  Lower alkyl ethers of polyhydric alcohols such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether; polyethylene glycol, polypropylene glycol, etc. Polyalkylene glycols;

  Ethers such as tetrahydrofuran and dioxane; Ketones such as acetone; Amides such as dimethylformamide and dimethylacetamide; Cyclic amide compounds such as N-methyl-2-pyrrolidone, 2-pyrrolidone and ε-caprolactam; Imide compounds such as succinimide Other examples include 1,3-dimethyl-2-imidazolidinone, triethanolamine, sulfolane, dimethyl sulfoxide, and the like.

  Among the water-soluble organic solvents, polyhydric alcohols, particularly trimethylol, are provided because the ink composition has sufficient moisture retention (prevents ink sticking) and maintains a viscosity that can be stably discharged by an inkjet head. Propane, diethylene glycol, and glycerin are preferably used. These water-soluble organic solvents may be used alone or in a combination of two or more.

  The amount (mass basis) of the water-soluble organic solvent is preferably 60% or less, more preferably 30% or less, based on the total mass of the composition of the present invention. By setting the amount of the water-soluble organic solvent to 60% or less, the amount of water in the composition of the present invention is relatively increased, the viscosity of the composition is lowered, and the ink ejection property can be improved.

[1-4] Surfactant:
The composition of the present invention preferably contains a surfactant. The surfactant is an amphiphilic substance having a hydrophilic group and a hydrophobic group, and has an effect of maintaining the surface tension of the composition at an appropriate level and promoting ink absorption into the recording medium.

  The kind of surfactant is not specifically limited. For example, conventionally known surfactants such as an anionic surfactant, a cationic surfactant, a nonionic surfactant, and an amphoteric surfactant can be used.

  Examples of the anionic surfactant include alkyl sulfocarboxylates, α-olefin sulfonates, polyoxyethylene alkyl ether acetates, N-acyl amino acids and salts thereof, N-acyl methyl taurates, alkyl sulfates, polysulfates. Oxyalkyl ether sulfate, polyoxyethylene alkyl ether phosphate, rosin acid soap, castor oil sulfate ester, lauryl alcohol sulfate ester, alkylphenol type phosphate ester, alkyl type phosphate ester, alkylallyl sulfone hydrochloride, diethyl sulfosuccinate , Diethylhexyl sulfosuccinate, dioctyl sulfosuccinate and the like.

  Examples of the cationic surfactant include quaternary ammonium salt surfactants such as 2-vinylpyridine derivatives and poly-4-vinylpyridine derivatives.

  Nonionic surfactants include polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether; polyoxyethylene alkenyl ethers such as polyoxyethylene oleyl ether; polyoxyethylene nonyl phenyl ether, polyoxyethylene octyl phenyl ether, polyoxy Polyoxyethylene alkyl phenyl ethers such as ethylene dodecyl phenyl ether; other ethers such as polyoxyalkyl alkyl ethers;

  Ester systems such as polyoxyethylene oleate, polyoxyethylene distearate, sorbitan laurate, sorbitan monostearate, sorbitan monooleate, sorbitan sesquioleate, polyoxyethylene monooleate, polyoxyethylene stearate;

  2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, 3,5-dimethyl-1-hexyn-3-ol Acetylene glycol series (hereinafter, all trade names are “acetylenol EH”, “E100”, “manufactured by Kawaken Fine Chemical Co., Ltd.”, “Surfinol 104”, “82”, “465”, “Orphine STG”) And the like.

  Examples of amphoteric surfactants include betaine surfactants such as lauryldimethylaminoacetic acid betaine, 2-alkyl-N-carboxymethyl-N-hydroxyethylimidazolinium betaine, coconut oil fatty acid amidopropyldimethylaminoacetic acid betaine; Amino acid surfactants such as octyl polyaminoethyl glycine; other imidazoline derivatives;

  Among the surfactants, nonionic surfactants are preferable, acetylene glycol surfactants are more preferable, and ethylene oxide adducts of acetylene glycol (for example, trade name “acetylenol EH” manufactured by Kawaken Fine Chemical Co., Ltd.) Is particularly preferred.

[1-5] Other additives:
Furthermore, you may add additives other than surfactant to the composition of this invention in the limit which does not inhibit the effect of this invention. For example, various organic amines such as diethanolamine and triethanolamine; inorganic alkali agents such as alkali metal hydroxides (sodium hydroxide, lithium hydroxide, potassium hydroxide, etc.); pH adjusters such as organic acids and mineral acids; etc. , Dispersants, viscosity modifiers, surface tension modifiers, antifoaming agents, rust inhibitors, preservatives, antifungal agents, ultraviolet absorbers, fluorescent brighteners, water-soluble polymers, and the like may be added.

[1-6] Magnetic color ink composition:
In the magnetic color ink composition of the present invention, coated particles (magnetic particles whose particle surfaces are coated with a basic dye film), surfactants, and other additives are dispersed or dissolved in a vehicle. . The dispersed state of the coated particles is stabilized by a surfactant or a water-soluble polymer.

  The magnetic color ink composition of the present invention preferably has a pH adjusted to 7 or higher. By setting the pH to a high value (that is, strongly basic), the basic dye can be sufficiently precipitated, and a basic dye film can be reliably formed. In addition, it is possible to effectively prevent a situation in which the surface of the magnetic particles is exposed by re-dissolving the basic dye film.

[2] Application, usage, etc .:
The composition of the present invention can be suitably used as an inkjet ink, particularly an inkjet aqueous ink. “Inkjet” is a printing method that performs printing by spraying fine ink particles onto a recording medium, and “inkjet ink” is ink that is used in an inkjet printer. The “water-based ink” is an ink containing a dye (water-soluble dye) and an aqueous medium.

  Moreover, since the composition of this invention contains a magnetic particle, it can be used as a magnetic ink. Specifically, after printing on the surface (printing surface) of a recording medium such as paper using the composition of the present invention, the coated particles are applied by applying magnetic energy from the back surface (non-printing surface) side of the recording medium. That is, the magnetic particles and the basic dye constituting the coating are migrated and fixed on the surface of the recording medium.

  The magnetic energy can be applied by, for example, an ink jet recording apparatus as shown in FIG.

  FIG. 1 is a schematic explanatory view schematically showing the configuration of an ink jet recording apparatus. The ink jet recording apparatus shown in FIG. 1 includes a recording head 2 that ejects ink, a supply unit (not shown) for supplying ink to the recording head 2, a transport unit 4 for transporting a recording medium 3, and a recording unit. A sensor (not shown) for detecting the position and conveying speed of the medium 3, magnetic field generating means 5 for applying magnetic energy from the back side of the recording medium 3, and a vehicle installed downstream of the recording head 2 A liquid removing means 6 for removing is provided, and these components are covered with the frame body 1. Each element such as the magnetic field generating means 5 is managed by a computer via the control panel 7.

  In the ink jet recording apparatus shown in FIG. 1, the recording medium 3 is conveyed in the X direction in the drawing by the conveying means 4, and the magnetic color ink composition of the present invention is ejected from the recording head 2 onto the recording medium 3. Printing is performed by landing the magnetic color ink composition on the surface of the medium 3.

  After printing, as shown in FIG. 2, the coated particles 8 (and thus the basic dye (coloring material) covering the surface of the magnetic particles) are applied to the surface of the recording medium 11 by the magnetic force generated from the magnetic field generating means 10. Attract and aggregate. As a result, the coated particles 8 and the vehicle 9 are rapidly solid-liquid separated, the ink can be dried quickly, and the coated particles 8 and the coloring material can be fixed on the surface of the recording medium 11 at high speed.

  The magnetic energy is preferably applied by applying a magnetic force of 1000 gauss or more in a direction perpendicular to the printing surface of the recording medium. The coated particles are stably dispersed in the ink composition. However, when a magnetic force of 1000 gauss or more is applied, the force that attracts the magnetic particles in the coated particles to the application means exceeds the force that stabilizes the dispersion, and the basic dye (coloring material) present on the coated particle surface ) And the solid-liquid separation of the vehicle is sufficiently promoted.

  The application of magnetic energy is preferably performed in a state where the magnetic application means is in contact with the back surface (non-printing surface) of the recording medium. Thereby, magnetic energy can be applied efficiently.

  The structure of the recording head 2 is not particularly limited. For example, a thermal recording head that generates bubbles by heating and discharges ink by the bubbles, a piezoelectric recording head that discharges ink by applying a voltage and deforming a piezoelectric element (piezoelectric element), an electrical signal And a magnetic recording head that ejects ink by magnetizing ink in the tube can be used.

  The structure of the magnetic field generating means 5 is not particularly limited. However, it is preferable to use a flat magnet or a magnet pulley. Further, if necessary, an electromagnet capable of arbitrarily applying magnetic energy can be used.

  The structure of the liquid removing means 6 is not particularly limited. For example, a porous roller, an air knife, a water-absorbing roller in which a highly water-absorbing material (such as microfiber) is wound around the surface, or the like can be used.

  Examples of recording media include plain paper, high-quality paper, medium-quality paper, coated paper, art paper, cast-coated paper, synthetic paper, newsprint paper, postcard paper, business card paper, label paper, cardboard paper, inkjet paper, etc. The inkjet exclusive paper is more preferable. The ink jet dedicated paper has a coating layer (liquid absorption layer) that receives ink and absorbs ink components on at least one surface, and is therefore suitable for ink jet printing.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. However, the present invention is not limited to the configurations of the following examples. In the following description, “parts” and “%” are based on mass unless otherwise specified.

In the examples and comparative examples, those shown in Table 1 were used.

  The ink compositions of Examples and Comparative Examples were prepared by the following method.

<Example 1>
To a mixture of 16.68 parts of iron (II) sulfate and 24.0 parts of iron (III) sulfate, 19.6 parts of 10% NaOH aqueous solution was added dropwise and stirred for about 30 minutes. Thereafter, washing by decantation was performed to obtain 13.92 parts of iron oxide fine particles as magnetic particles.

  A magnetic particle dispersion was prepared by dispersing 10 parts of the iron oxide fine particles in an aqueous hydrochloric acid solution adjusted to pH 5.0. Separately, a basic dye solution was prepared by dissolving the basic dye 1 (20 parts) in an aqueous hydrochloric acid solution adjusted to pH 4.5. Then, the basic dye solution was added to the magnetic particle dispersion to obtain a mixed solution.

  While stirring the mixed solution strongly, a 10% NaOH aqueous solution is added, and the pH of the acidic solution is changed to 10.0 to precipitate a basic dye on the surface of the magnetic particles. Magnetic particles (coated particles) coated with a coating were obtained. The coated particles were collected by a filter.

  Next, 3 parts of the coated particles are added and dispersed in a solution obtained by adding 0.5 part of the acetylene glycol surfactant to 96.5 parts of the aqueous medium and mixing the resulting mixture, whereby the ink composition of Example 1 is obtained. Obtained.

<Example 2>
An ink composition of Example 2 was obtained in the same manner as Example 1 except that the basic dye 1 was changed to the basic dye 2.

<Example 3>
An ink composition of Example 3 was obtained in the same manner as in Example 1 except that the basic dye 1 was changed to the basic dye 3.

<Example 4>
Except that the magnetic particles were changed from the iron oxide fine particles to the Ni particles, and the basic dye was precipitated on the surface of the magnetic particles by changing the pH to 9.5, the same as in Example 1. Thus, an ink composition of Example 4 was obtained.

<Example 5>
The ink composition of Example 5 was obtained in the same manner as Example 1 except that the basic dye was precipitated on the surface of the magnetic particles by changing the pH to 8.0.

<Example 6>
An ink composition of Example 6 was obtained in the same manner as in Example 1 except that the addition amount of the basic dye 1 was changed to 40 parts.

<Example 7>
Except that the basic dye 1 was added in an amount of 10 parts and the pH was changed to 9.5, the basic dye was precipitated on the surface of the magnetic particles. Thus, an ink composition of Example 7 was obtained.

<Comparative Example 1>
A magnetic color ink composition of Comparative Example 1 was obtained in the same manner as in Example 1 except that the basic dye was precipitated on the surface of the magnetic particles by changing the pH to 6.7.

<Comparative example 2>
An ink composition of Comparative Example 2 was obtained in the same manner as Example 1 except that 10% NaOH aqueous solution was not added.

<Comparative Example 3>
An ink composition of Comparative Example 3 was obtained in the same manner as in Example 1, except that the magnetic particles were changed from the iron oxide fine particles to the Ni particles, and no 10% NaOH aqueous solution was added.

<Comparative example 4>
Except that the basic dye 1 was added to 3 parts, and the pH was changed to 9.6, the basic dye was precipitated on the surface of the magnetic particles, as in Example 1. Thus, an ink composition of Comparative Example 4 was obtained.

<Comparative Example 5>
A magnetic color ink composition of Comparative Example 5 was obtained in the same manner as in Example 1 except that the addition amount of the basic dye 1 was changed to 80 parts.

<Comparative Example 6>
The ink of Comparative Example 6 was prepared by adding and dispersing the basic dye 1 (6 parts) in a solution obtained by adding 0.5 parts of the acetylene glycol surfactant to 93.5 parts of the aqueous medium and mixing. A composition was obtained.

<Comparative Example 7>
An ink composition of Comparative Example 7 was obtained in the same manner as Comparative Example 6 except that the basic dye 1 was changed to the basic dye 2.

<Comparative Example 8>
An ink composition of Comparative Example 8 was obtained in the same manner as Comparative Example 6 except that the basic dye 1 was changed to the basic dye 3.

<Comparative Example 9>
The ink composition of Comparative Example 9 was prepared by adding and dispersing the iron oxide fine particles (3 parts) in a solution in which 0.5 part of the acetylene glycol surfactant was added to 96.5 parts of the aqueous medium and mixed. I got a thing.

Table 2 shows the raw materials and production conditions of the compositions of Examples and Comparative Examples.

<Evaluation>
The ink compositions of Examples and Comparative Examples were evaluated by the following methods.

(1) Particle size of coated particles:
The ink composition was diluted 100 times in concentration, and the particle size was measured with a concentrated system particle size analyzer (trade name “FPAR” manufactured by Otsuka Electronics Co., Ltd.).

(2) Film thickness:
The film thickness of the coated particles was determined by the following general formula (1).
Coating thickness = (particle diameter of coated particles−particle diameter of magnetic particles) / 2: (1)

(3) Absorption spectrum:
The absorption spectrum of the ink composition was measured using a spectrophotometer (trade name “V-550” manufactured by JASCO Corporation). This absorption spectrum was compared with the absorption spectrum measured with the basic dye alone, and evaluated according to the following criteria.
○: The absorption spectrum of the ink composition is equivalent to that of the basic dye.
X: The absorption spectrum of the ink composition is different from that of the basic dye (the absorption spectrum of the ink composition is broad or does not show an absorption spectrum).

(4) Aggregation characteristics:
Printing and application of magnetic energy were performed by the ink jet recording apparatus shown in FIG. 1, and the ink aggregation properties were evaluated.

  As the recording head 2, an on-demand type multi-recording head 600 dpi was used. This recording head is a thermal recording head that applies thermal energy according to a recording signal, generates bubbles by heating, and discharges ink by the bubbles. As the magnetic field generating means 5, a super magnet bar roller was used. As the recording medium 3, A4 size plain paper (trade name “CANON EXTRA80” <manufactured by Canon Inc.>) having a basis weight of 80 g was used.

  Using the ink composition of Example or Comparative Example, solid printing was performed with the recording head 2 under the condition of a single color and an ink amount of 100%. At this time, the conveyance speed of the recording medium 3 was set to 30 m / min. After the solid printing, in a state where the magnetic field generating means 5 is in direct contact with the non-printing surface of the recording medium 3, a magnetic force of 3000 gauss is applied in a direction perpendicular to the printing surface of the recording medium 3 to apply magnetic energy. Went.

When magnetic energy was applied as described above, the state of separation between the colorant and the vehicle was visually observed, and the aggregation characteristics were evaluated according to the following criteria.
○: Color material and vehicle are separated within 0.5 seconds from application of magnetic energy.
Δ: Color material and vehicle are separated after 0.5 seconds from the application of magnetic energy.
X: Color material and vehicle do not separate at 3 seconds from application of magnetic energy.

(5) Color dullness:
The printed matter obtained when evaluating the aggregation property of the ink was visually observed, and the color dullness was evaluated according to the following criteria. The results are shown in the table.
○: Coloring of the color material in the printed matter is equivalent to that of the basic dye alone.
(Triangle | delta): The color development of the coloring material in a printed matter becomes dull with the black of magnetic particles.
X: The black color of the magnetic particles is visible in the printed matter.

Table 3 shows the evaluation results of the compositions of Examples and Comparative Examples.

  As is clear from the results shown in Table 3, the compositions of Examples 1 to 7 showed good results in the evaluation of absorption spectra, aggregation characteristics, and color dullness. On the other hand, the compositions of Comparative Examples 1 to 3 were poor in evaluation of absorption spectrum, aggregation characteristics, and color dullness because the basic dye film was not formed sufficiently or not formed at all.

  In the composition of Comparative Example 4, the film thickness of the basic dye film was thin, and the evaluation of color dullness was not good. In the composition of Comparative Example 5, the film thickness of the basic dye film was too thick, and the aggregation property was poor.

  In addition, since the composition of Comparative Examples 6-8 did not contain magnetic particles, it did not exhibit agglomeration characteristics. Furthermore, since the composition of Comparative Example 9 did not contain a coloring material, it could not be used as a color ink composition.

1: frame, 2: recording head, 3: recording medium, 4: transport means, 5: magnetic field generating means, 6: liquid removing means, 7: control panel, 8: coated particles, 9: vehicle, 10: magnetic field generation Means 11: Recording medium.

Claims (7)

Containing magnetic particles, basic dye and vehicle,
The magnetic color ink composition, wherein the magnetic particles are coated with the basic dye film to form coated particles, and the film thickness is 20 nm or more and 50 nm or less.   The coating film is formed by changing the pH of an acidic solution containing the magnetic particles and the basic dye to the basic side to precipitate the basic dye on the surface of the magnetic particles. Item 2. The magnetic color ink composition according to Item 1. The magnetic color ink composition according to claim 1 or 2, wherein the magnetic particles are magnetic particles selected from the group consisting of Fe ₃ O ₄ , Ni and Co.   The magnetic color ink composition according to any one of claims 1 to 3, wherein the pH is adjusted to 7 or more.   A method for producing a magnetic color ink composition comprising magnetic particles, a basic dye and a vehicle, wherein the magnetic particles are covered with a coating of the basic dye to form coated particles. By changing the pH of the acidic solution containing the magnetic particles and the basic dye to the basic side, the basic dye is deposited on the surface of the magnetic particles, and the coating is formed on the surface of the magnetic particles. A method for producing a magnetic color ink composition. An acidic solution containing the magnetic particles and the basic dye is dropped into a basic solution of Fe ²⁺ sulfate and Fe ³⁺ sulfate to form magnetic particles made of Fe ₃ O ₄ , The method for producing a magnetic color ink composition according to claim 5, wherein the pH of the acidic solution is changed to the basic side to deposit the basic dye on the surface of the magnetic particles.   The basic dye is dissolved in the acidic dispersion of the magnetic particles, and then the pH of the acidic dispersion is changed to the basic side to precipitate the basic dye on the surface of the magnetic particles. A method for producing a magnetic color ink composition.

Images