JP4882607B2 - Method for producing colored microcapsule aqueous pigment dispersion - Google Patents

Description

  The present invention relates to a colored microcapsule-dispersed aqueous jet ink.

  Ink jet recording inks are roughly classified into oil-based inks and water-based inks, but oil-based inks have problems in terms of odor and toxicity, and water-based inks are becoming mainstream.

  However, many of the conventional water-based inks have a drawback that water resistance and light resistance are poor because a water-soluble dye is used as a colorant. In addition, since the dye is dissolved at the molecular level, printing on so-called plain paper such as copy paper commonly used in offices causes bleeding called wrinkle-like feathering, which causes a significant decrease in print quality. .

  Various so-called water-based pigment inks have been proposed in the past to improve the above-mentioned drawbacks. For example, resin-dissolved inks in which carbon black or organic pigments are dispersed using a water-soluble resin as a binder / dispersant. Various resin-dispersed inks containing a colorant as polymer latex or microcapsules have been proposed.

  As water-based pigment inks for jet printers, colorant particles dispersed in a fine particle size as much as possible are required. As a specific example of a resin-soluble water-based ink, Japanese Patent No. 2512861 discloses (a) a pigment and Filling a 2-roll mill with a polymeric dispersant; (b) grinding to obtain a dispersion of pigment and polymeric dispersant; and (c) dispersing the pigment dispersion in an aqueous carrier medium A method for preparing an aqueous pigmented ink-jet ink having improved properties (see Patent Document 1), and JP-A-3-153775, a) a pigment and a carboxyl group-containing polyacrylic resin. Containing solid pigment preparation b) Organic solvent dilutable with water c) Wetting agent d) Water-based ink composition for ink jet printing containing water (see Patent Document 2) It is draft.

  However, these technologies are effective for finer pigments, but due to the effect of the dissolved dispersant resin, abnormal ink jets due to increased ink viscosity near the nozzles and worst nozzle clogging occur due to the evaporation of ink moisture. It was easy and the water resistance of the printed matter was extremely inferior.

  Resin-dispersed water-based inks have the advantages of relatively little increase in viscosity due to water evaporation of the ink and excellent water resistance. Specifically, JP-A-58-45272 discloses an ink composition containing a urethane polymer latex containing a dye (see Patent Document 3), and JP-A-62-95366 discloses a polymer in a water-insoluble organic solvent. And an oil-based dye are further dissolved, mixed with an aqueous solution containing a surfactant and emulsified, and then the solvent is evaporated, and an ink containing a dye encapsulated in polymer particles is proposed (see Patent Document 4). Japanese Laid-Open Patent Application No. 62-254833 proposes a method of producing an aqueous coloring agent suspension by reducing the interfacial tension between an organic solvent and water during encapsulation to 10 dynes or less (see Patent Document 5). Similarly, JP-A-1-170672 proposes a recording liquid containing a macroencapsulated dye (see Patent Document 6). However, the dispersion stability of a colored resin dispersion obtained from the recording liquid is disclosed. Is not necessarily sufficient, also large bubble due to the influence of the surfactant to be used for encapsulation, ejection characteristics of the ink jet is not necessarily sufficient.

  Japanese Patent Application Laid-Open No. 3-240586 proposes an image forming material in which the surface of particles dispersed in a dispersion medium is coated with a resin that swells in the dispersion medium (see Patent Document 7). However, the sol-gel phase transition was likely to occur near room temperature, and the dispersion stability of the particles was not always good, and the injection abnormality was likely to occur.

Further, in JP-A-5-247370, in a coloring composition for image recording containing a pigment and a resin, the pigment is coated with a thin film of a cured polymer which is substantially insoluble in the dispersion medium and has a polar group. A coloring composition for image recording, which is characterized by being a pigment, has been proposed (see Patent Document 8). However, in the present invention, the pigment itself lacks self-dispersibility and fixing ability to recording paper. , A resin as a dispersing agent and a fixing agent is essential, so that although the dispersion stability is superior compared to a pigment not coated with a cured polymer, the jetting stability as an inkjet is insufficient and the water resistance is inferior The shortcoming was not improved.
Japanese Patent No. 2512861 JP-A-3-153775 JP 58-045272 A JP 62-095366 A JP 62-254833 A JP-A-1-170672 JP-A-3-240586 Japanese Patent Laid-Open No. 5-247370

  The problem to be solved by the present invention is to provide a colored microcapsule-dispersed water-based jet ink having a fine particle size, excellent dispersion stability, excellent ink jetting characteristics, and excellent adhesion of capsule particles to a recording medium. Another object of the present invention is to provide a method for producing an aqueous dispersion of colored macrocapsules.

  As a result of intensive research to solve the above problems, the present inventors, in short, have an influence on the ejection stability of a free-dissolved film-forming resin component that is not coated with a pigment. The above-mentioned problems have been solved by making the quantity range that does not reach and contributes to the fixation of the capsule particles to the recording medium.

That is, according to the present invention, in an ink containing colored microcapsules coated with a pigment with a film-forming resin in an aqueous medium, the resin component dissolved in the ink in the film-forming resin is 0.01 to 2% by mass. The following method for producing a colored microcapsule aqueous dispersion for providing a colored microcapsule-dispersed aqueous jet ink is provided. That is, the present invention includes (1) a kneading step of dispersing a pigment in a film-forming resin having an acid value to obtain a solid coloring compound;
(2) At least water, an organic solvent that dissolves the film-forming resin, a base, and the solid coloring compound are mixed, and dispersion is performed to obtain a pigment suspension in which at least a part of the film-forming resin is dissolved by dispersion. Turbidity process,
(3) Provided is a method for producing an aqueous dispersion of colored microcapsules, comprising a reprecipitation step of depositing a film-forming resin component dissolved in the pigment suspension on the pigment surface.

  The colored microcapsule-dispersed aqueous jet ink produced from the colored microcapsule aqueous dispersion produced by the production method of the present invention comprises 0.01 to 2 mass of a resin component dissolved in the ink in the film-forming resin. Therefore, it is possible to obtain a particularly remarkable technical effect of being excellent in dispersion stability with time, jetting characteristics, and excellent image fixing property to a recording medium.

  Therefore, in inkjet recording, for example, without sacrificing the features of resin-dispersed water-based inks with excellent print quality, water resistance, and light resistance, excellent dispersion stability, no nozzle clogging, and stable ink jet ejection characteristics are possible. To do.

  In the present invention, the SI unit system is adopted as the unit system, and the weight is described as mass. The ink mainly composed of the colored microcapsule dispersion produced by the method for producing the colored microcapsule dispersion of the present invention is not limited to the ink produced in the present invention, for example, a film that does not dissolve the pigment in the dispersion medium Colored microcapsules coated with a conductive resin, free pigment particles that do not dissolve in a dispersion medium that is not coated with a film-forming resin, free film-forming resin dispersion particles that do not dissolve in a dispersion medium that is not coated with a pigment, or a dispersion medium It can be composed of a film-forming resin dissolved in the resin, a dispersion medium, and a drying inhibitor, a penetrating agent, and the like used as necessary.

  The present invention is characterized in that the ink composition described above can produce an ink in which a dissolved film-forming resin is present in an optimum range in an aqueous medium as a dispersion medium.

  However, if the resin component dissolved in the ink is less than 0.01% by mass of the film-forming resin, when the ink is printed on the recording paper, the microcapsule particles in the resulting ink layer can adhere to the recording paper and As a result, the bonding force between the capsule particles is insufficient, and as a result, there is a disadvantage that the durability of the printed matter such as friction is inferior.

  Conversely, if the resin component dissolved in the ink exceeds 2% by mass of the film-forming resin, when the ink is printed on the recording paper, the microcapsule particles in the resulting ink layer can adhere to the recording paper and Although the binding force between capsule particles increases, in addition to the disadvantage that the time until the dissolved film-forming resin is insolubilized on the recording paper, that is, the time until the water resistance immediately after printing is developed, is increased. As compared with water-soluble resins such as polymer dispersants, the resin is more likely to be clogged due to moisture evaporation at the nozzle end face, and the ink jet stability is likely to be worse.

  It is obtained when the ink is printed on the recording paper by making the resin component dissolved in the ink out of the film-forming resin, for example, 0.01-2% by mass, more preferably 0.1-1% by mass. The ability of the microcapsule particles in the ink layer to adhere to the recording paper and the bonding force between the microcapsule particles is increased, the durability of the printed matter is improved, and clogging due to water evaporation at the nozzle end surface is eliminated. Injection stability is greatly improved.

  In the present invention, the aqueous medium means only water or a medium containing water as a main component and an organic solvent as necessary. In the present invention, it is preferable to select a chemical composition, a mass ratio of constituent components, and the like as an aqueous medium serving as an ink dispersion medium so as not to dissolve the film-forming resin as much as possible.

  In the present invention, the film-forming resin used to coat the pigment may be any resin that forms a film, and is not limited to natural resins or synthetic resins, and various film-forming resins can be used. Resin, acrylic resin, polyester resin, and polyurethane resin.

  However, in order to stably disperse the colored microcapsules in an aqueous medium, the film-forming resin needs to have a highly hydrophilic property, and thus a large amount of the film-forming resin is often dissolved in the ink. Will do. In this case, the dissolved resin may promote the aggregation of the microcapsules by long-term storage due to cross-linking between particles accompanying the entanglement of the resin layer covering the microcapsules. In addition, when ink jet recording is performed, ejection abnormalities are liable to occur due to an increase in the viscosity of ink accompanying the evaporation of moisture at the nozzle end face and adhesion of ink concentrate around the nozzle.

  On the other hand, when the hydrophilicity of the film-forming resin is low, the dispersion stability of the colored microcapsules in which the pigment is coated with the film-forming resin in the aqueous medium becomes lower.

  Therefore, it is often necessary to minimize the dissolution of the film-forming resin in the aqueous medium and to enable stable dispersion in the aqueous medium.

  In order to stably disperse the colored microcapsules in the aqueous medium, for example, there may be a method of using a film-forming resin which is originally hydrophilic or poor in hydrophilicity using a surfactant or a dispersant. From the viewpoint that the image exhibits better water resistance and good ejection stability, it is preferable to prepare the image so as not to contain a surfactant or a dispersant.

  As a method for preparing this surfactant or dispersant so as not to contain it, for example, a film-forming resin obtained by neutralizing a resin that can be dispersed in an aqueous medium by neutralization with a neutralizer is used. Good to do. As a film-forming resin obtained by neutralizing a resin that can be dispersed in an aqueous medium by neutralization with a neutralizing agent, the resin that can be dispersed in an aqueous medium by neutralization with a base is typically neutralized with a base. And a film-forming resin. In the present invention, this resin that can be stably dispersed in an aqueous medium by itself without the aid of a surfactant, a dispersant or the like may be referred to as a self-water dispersible resin.

  In the production method of the present invention, for example, a self-water dispersible resin obtained by using a resin having an acid value and neutralizing it with a base is preferably used as the film-forming resin. As the resin having an acid value, for example, those having an acid value of 50 to 180 are used. The acid value means the number of milligrams (mg) of potassium hydroxide (KOH) necessary to neutralize 1 g of the resin, and is expressed in mg · KOH / g (hereinafter, the unit is abbreviated). Such a resin can be obtained, for example, by neutralizing all or part of the acid value of the resin having the specific acid value. In this case, the pH of the ink is 7.5 to 9.0. It is preferable to do so.

  When the acid value is less than 50, the surface hydrophilicity of the microcapsule particles is poor, and the dispersion stability tends to be insufficient. When the acid value exceeds 180, the hydrophilicity of the resin is remarkably increased, and the coating of the pigment with the resin is difficult. This is unsuitable because it tends to be insufficient due to swelling or the like, and tends to cause aggregation of microcapsule particles or clogging of nozzles.

  On the other hand, when the pH of the final ink is lower than 7.5, the dispersion stability of the colored microcapsule particles tends to decrease, and when the pH is 9.0 or more, the pigment coating of the colored microcapsule particles swells. This is inappropriate because it tends to be insufficient due to, for example, aggregation of the microcapsule particles and nozzle clogging.

  Optimally, a film-forming resin obtained by neutralizing a film-forming resin component with a base using a resin having an acid value of 50 to 180 is used to make an ink in which 0.01 to 2% by mass of the film-forming resin component is dissolved. When used, the ink having a pH of 7.5 to 9.0 has a remarkable effect in a jet ink mainly composed of a colored microcapsule aqueous dispersion produced by the production method of the present invention.

  The molecular weight range of the film-forming resin is not particularly limited, but is preferably a molecular weight range of 1000 or more and 100,000 or less in terms of weight average molecular weight. If the molecular weight of the film-forming resin is less than 10,000, sufficient film formation is often not achieved, and this is inappropriate because it tends to cause nozzle clogging due to aggregation of microcapsule particles. In particular, in order to sufficiently coat the pigment with a film-forming resin, the molecular weight of the resin is preferably 10,000 or more and 100,000 or less.

  A preferred film-forming resin used in the production method of the present invention is a styrene resin or a (meth) acrylic resin, for example, at least one monomer selected from the group consisting of styrene, substituted styrene, and (meth) acrylic acid ester. And a self-water dispersible resin obtained by at least partially neutralizing a copolymer of (meth) acrylic acid with a base.

  (Meth) acrylic acid is a generic term for acrylic acid and methacrylic acid, and in the present invention, either one is essential, but more suitable film-forming resins are both acrylic acid and methacrylic acid. It has a structure derived from.

  In the jet ink formed from the colored microcapsule aqueous dispersion produced in the present invention, for example, to reduce dissolution of the self-water dispersible resin as a film-forming resin in an aqueous medium, all carboxyl groups Of the monomer components having, the ratio of acrylic acid should be smaller and the ratio of methacrylic acid should be increased.

  That is, the self-water dispersible resin as the optimum film-forming resin is mainly composed of at least one monomer selected from the group consisting of styrene, substituted styrene, and (meth) acrylic acid ester, and includes acrylic acid and methacrylic acid. A self-water dispersible resin in which methacryl is copolymerized more than acrylic acid and is at least partially neutralized with a base.

  In order to make the final ink pH basic, neutralization, that is, a base, may be added to a resin that can be dispersed in an aqueous medium by neutralization. Examples of the base include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide and lithium hydroxide, basic substances such as ammonia, triethylamine and morpholine, triethanolamine, diethanolamine and N-methyldiethanolamine. Alcohol amines can be used. As the base, it is preferable to employ a volatile base that is easily volatile at a high temperature at which the film-forming resin does not decompose.

  However, neutralizing a higher acid number resin with a stronger base increases the solubility of the film-forming resin in the ink, so the strength of the base and the amount used (neutralization rate) are adjusted. It is preferable to do. In inkjet recording, alcohol bases, particularly triethanolamine, are the most suitable bases because they have very little adverse effects on nozzle clogging, dispersion stability during storage, and water resistance of printed matter.

  In the production method of the present invention, the neutralization rate of the film-forming resin with respect to the acid groups is 100 mol% or less, preferably 60 mol% or less. It is particularly preferable to use alcoholamine as a base so that the neutralization rate with respect to the acid group of the film-forming resin is 60 mol% or less.

  The pigment used in the colored microcapsule dispersion type aqueous dispersion of the present invention and the jet ink prepared from the dispersion is not particularly limited, and any known and conventional pigments can be used. For example, carbon black, Inorganic pigments such as titanium black, titanium white, zinc sulfide and bengara, azo pigments such as phthalocyanine pigments, monoazo and disazo, organic pigments such as phthalocyanine pigments and quinacridone pigments are used. When obtaining a color image, it is preferable to use a chromatic pigment as the ink.

  The amount of the pigment used is not particularly defined as long as the effect of the present invention is achieved, but it is preferably prepared so that the amount is usually 0.5 to 20% by mass in the finally obtained ink. .

  Finally, the ink can contain an organic solvent that does not dissolve or hardly dissolves the film-forming resin, if necessary. The organic solvent used for the ink is used as an anti-drying agent or a penetrating agent as an example.

  The anti-drying agent has an effect of preventing the ink from drying at the jet nozzle opening of the ink jet, and usually has a boiling point equal to or higher than the boiling point of water. As such an anti-drying agent, any conventionally known ones can be used. For example, polyhydric alcohols such as ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, and glycerin. There is kind.

  In particular, glycerin is bonded to the film-forming resin on the surface of the microcapsule particles by strong hydrogen bonds to further enhance the dispersion stability of the microcapsule particles, and at the same time, even if a small amount of the film-forming resin is dissolved in the ink, Further, it is more preferable in that it is connected with a strong hydrogen bond to prevent drying at the nozzle end face.

  The penetrant is for penetrating ink into the recording medium and adjusting the dot diameter on the recording medium. Examples of penetrants include lower alcohols such as ethanol and isopropyl alcohol, ethylene glycol hexyl ether, diethylene glycol butyl ether, and the like. And alkyl alcohol propylene oxide adducts such as propylene glycol propyl ether.

  Depending on the type and concentration of the film-forming resin, or the combination of the organic solvent concentration in the aqueous medium, the organic solvent dissolves 2% by mass or more of the resin coated on the pigment and deteriorates the jetting characteristics. Therefore, depending on the type of organic solvent, the addition amount is suppressed in consideration of the pH range of the ink so that the content in the ink is 2 mass% or less, more preferably 1 mass% or less. There is a need to.

  The addition amount of these organic solvents is preferably 1 to 80% by mass in the case of an anti-drying agent and 0.1 to 10% by mass in the case of a penetrant.

  In the jet ink produced from the colored microcapsule aqueous dispersion produced by the production method of the present invention, the method for measuring the components dissolved in the ink of the film-forming resin is a solid component other than the resin. When the amount is small, for example, the microcapsule particles can be sedimented by an ultracentrifuge, and the supernatant can be sufficiently dried and directly measured as a non-volatile content. If the solid content or high-boiling organic solvent other than the resin is present in a large amount in the ink, the centrifugal sediment is sufficiently dried, and then the resin is analyzed by a thermal analyzer based on the difference in thermal decomposition temperature. The amount of the resin component dissolved in the ink can be determined by measuring the ratio of the pigment and the pigment and converting the ratio from the ratio of the resin and the pigment charged in the ink. In the latter method, the dispersion in the aqueous medium is composed only of colored microcapsules and does not include free pigment particles that are not coated with the film-forming resin or particles that are not formed of the film-forming resin. In particular, it can be measured with high accuracy. If the ink contains additives such as anti-drying agents and penetrants, perform measurement after drying and removing the former additives at a temperature at which the pigment and film-forming resin do not decompose. Thus, the measurement accuracy can be further increased.

  A specific method of obtaining an aqueous dispersion by the method for producing a colored microcapsule-dispersed aqueous dispersion of the present invention and further obtaining a jet ink from the aqueous dispersion includes a pigment using a film-forming resin having an acid value. In the case of coating, the following method is preferable. According to this method, the resin and pigment-derived components dispersed in the aqueous medium consist only of colored microcapsules, and free pigment particles that are not covered with the film-forming resin, or film-formability that does not contain the pigment. It is possible to easily obtain an ink which contains no resin particles or dissolved film-forming resin at all or contains a very small amount of ink.

In the method of the present invention, for example, the following (1) to (5) can be performed in this order.
(1) A pigment is dispersed in a film-forming resin having an acid value to obtain a solid coloring compound. (Kneading process)

  In this process, for example, a pigment is uniformly dissolved or dispersed in the resin in a solution or heated and melted using a conventionally known kneading apparatus such as a roll, a kneader, or a bead mill. It can carry out by taking out as a thing (solid coloring compound).

  In particular, when fine dispersion of the pigment in the resin is necessary, as a means for dispersing the pigment, a dispersion means that forms a state in which a relatively high shear force is applied can be used. Specifically, it is preferable to perform dispersion under a high shear force using two rolls.

  (2) At least water, an organic solvent that dissolves the resin, a base, and the solid coloring compound are mixed together to obtain a pigment suspension in which at least a part of the resin is dissolved by dispersion. (Suspension process)

  The organic solvent that dissolves the resin functions as a good solvent for the resin, and the organic solvent can be appropriately selected for the resin. For example, ketone-based solvents such as acetone, dimethyl ketone, and methyl ethyl ketone. Solvents, alcohol solvents such as methanol, ethanol and isopropyl alcohol, chlorine solvents such as chloroform and methylene chloride, aromatic solvents such as benzene and toluene, ester solvents such as ethyl acetate, ethylene glycol monomethyl ether, ethylene glycol Any solvent can be used as long as it can dissolve a glycol ether solvent such as dimethyl ether or a resin such as amides.

  The dispersion medium used in this step is mainly water that functions as a poor solvent for the film-forming resin and is preferably used as water-based ink for ink jet recording, and therefore has a purity higher than that of ion-exchanged water.

  In this step, it is preferable that the mixed liquid of water and organic solvent is uniform. If not uniform, if necessary, a surfactant may be used, or it may be mechanically emulsified into an O / W type, or may be assisted. It is preferable to use a solvent in a uniform manner. For the reasons described above, surfactants, if used, are kept to a minimum.

  An organic solvent that dissolves the resin used as necessary to form the dispersion medium may be used alone, but only with water and a base, a pigment suspension excellent in dispersion stability is formed. If it is difficult to obtain, a hydrophilic organic solvent may be partially used as a co-solvent for the resin to give better emulsion stability. In addition, the organic solvent and cosolvent which melt | dissolve the said resin may use together 1 type, or 2 or more types.

  In the case where the resin is a copolymer of (meth) acrylic acid and at least one monomer selected from the group consisting of styrene, substituted styrene, and (meth) acrylic acid ester, for example, a ketone solvent such as methyl ethyl ketone is used. Mainly, at least one combination selected from alcohol solvents such as isopropyl alcohol is preferably used as a cosolvent.

  The ratio of water and organic solvent is not particularly defined as long as the effect in the jet ink formed from the colored microcapsule aqueous dispersion produced by the production method of the present invention is achieved, but the weight ratio of water / organic solvent is 10 An amount that is between 1/1 and 1/1 is preferred.

  By this process, the film-forming resin having an acid value present on the surface of the solid coloring compound is gradually neutralized by a base at least partly or entirely of the acid value. From the solid form of the compound, The mixture becomes suspended.

  As a stirring method for obtaining a suspension, any known and commonly used method can be employed. For example, in addition to a conventional uniaxial propeller-type stirring blade, a stirring blade or a stirring vessel having a shape suitable for the purpose is used. Usually, it can be easily suspended.

  When a suspension is obtained, if it does not become fine particles by mere mixing and stirring, where a large shear force does not work, or if the pigment is relatively easy to aggregate, in addition to that, a higher shear force is applied to stabilize the fine particles. May be. As the disperser in this case, for example, a high-pressure homogenizer, a beadless disperser known by a trade name of microfluidizer or nanomizer, or the like is preferably used because of less pigment re-aggregation.

  (3) The film-forming resin component dissolved in the pigment suspension is deposited on the pigment surface to obtain microcapsules. (Reprecipitation process)

  This step is a step of depositing the dissolved resin component and the dispersed resin component present in the suspension on the pigment surface in the pigment suspension obtained in the suspension step. The term “reprecipitation” in this step does not mean that the pigment or the particles in a semi-capsule state in which the dissolved resin or dispersion resin is adsorbed on the pigment surface is separated and settled from the liquid medium of the suspension. Therefore, what is obtained in this step is not a simple mixture in which the solid component and the liquid component are clearly separated, but the microcapsules coated with the dissolved resin or the dispersed resin on the pigment surface are stably present in the liquid medium of the suspension. It is a dispersed colored resin particle (colored microcapsule) aqueous dispersion.

  The resin is deposited on the surface of the microcapsule in the pigment suspension in the suspension step, for example, at least partially in the pigment suspension in which the film-forming resin is dissolved and / or dispersed. It can be easily carried out by adding water or an aqueous medium functioning as a poor solvent and / or removing the organic solvent from the pigment suspension.

  However, a method in which water or an aqueous medium that functions as a poor solvent for the resin is further added to the pigment suspension is preferable because there are few aggregates. In reprecipitation, by dropping water or an aqueous medium while gently stirring the suspension, it becomes possible to reliably deposit (reprecipitate) the resin on the pigment surface while preventing the formation of aggregates.

  In order to prevent the obtained dispersion from drying, it is preferable that an anti-drying agent is present in the aqueous medium in advance or is added after reprecipitation.

  In this way, colored resin particles having a desired particle size can be obtained by the above (1) kneading step (2) suspension step (3) reprecipitation step. Usually, the average particle size range is 0.01 to 1 μm.

  (4) Removal and / or concentration of low boiling point organic solvent from the microcapsule dispersion obtained in the reprecipitation step (solvent removal step)

  The aqueous dispersion of colored resin particles obtained in the reprecipitation process can be used as it is, but the colored resin particles are often in a swollen state due to the coexisting organic solvent. In order to improve safety against fire or pollution, it is preferable to further remove the solvent.

  The organic solvent thus removed can be recycled and reused in a closed system without being incinerated for the purpose of continuous production, for example.

  The colored resin particle (colored microcapsule) aqueous dispersion obtained through the steps (1) to (4) has all components derived from the resin and pigment used for the preparation thereof exclusively from the colored microcapsules. The resulting aqueous dispersion is substantially free of three components: free pigment particles, particles of film-forming resin only, and dissolved film-forming resin. However, since it is extremely difficult to make the dissolved film-forming resin component zero, the content is generally 0.01% by mass or more in the total components constituting the dispersion.

  The dispersion thus obtained usually consists essentially of colored microcapsules in which a pigment is coated with a film-forming resin and a dispersion medium alone. The content of the colored microcapsules in the dispersion is usually 10 to 40% by mass with respect to the total of the dispersion and the dispersion medium. Of course, when various additives are included in the steps so far, they are also included in the dispersion.

(5) Ink process The submicron-order colored resin particle aqueous dispersion obtained by the above process, which contains no or almost no liquid medium other than water, is basically used as an aqueous ink for ink jet recording. Although it can be used, it is preferable to further adjust the ink in consideration of dispersion stability and ejection characteristics.

  Ink adjustment includes, for example, addition of the above-mentioned anti-drying agent and penetrating organic solvent, concentration adjustment / viscosity adjustment, pH adjusting agent, surfactant for dispersion / defoaming / penetration into paper, preservative, Chelating agents, plasticizers, antioxidants, ultraviolet absorbers and the like can be added as necessary. However, various additives may be selected from those which do not dissolve the film-forming resin present on the surface of the colored microcapsules and use only those having such properties, or those that can dissolve the resin. It is necessary to devise measures such as minimizing the amount used so that it does not substantially dissolve. Surfactants should not be used at all in all of the steps that can be employed in the ink preparation of the present invention, not only from the final adjustment, but also from the viewpoint of the water resistance of the image obtained from the ink. preferable.

  Also, if the recording medium is something other than impervious like glass, metal or film (permeable recording medium), it is different from the film-forming resin to the extent that it does not affect the jetting stability. Other water-soluble resins can also be added.

  In order to avoid clogging of nozzles due to coarse particles, usually, coarse particles are removed by centrifugation or filtration after the solvent removal step (4), or desired after ink adjustment in the ink step (5). Filter with a filter of particle size.

  The jet ink produced from the colored microcapsule dispersion type aqueous dispersion produced by the production method of the present invention can be employed in a known and conventional inkjet recording system printer such as a piezo system or an on-demand system. The ink can be used for forming an image on a known and commonly used recording material such as paper, resin-coated paper, ink jet recording paper, glass, metal, film, ceramics, and the like.

  The colored microcapsule-dispersed water jet ink of the present invention is excellent in transparency, color developability, and dispersion stability, and can be applied to other general inks, paints, and color filters in addition to inkjet recording.

The jet ink produced from the colored macrocapsule aqueous dispersion produced by the production method of the present invention also includes the following embodiments.
1. Colored microcapsule dispersion type in which an ink containing pigmented microcapsules coated with a film-forming resin in an aqueous medium contains 0.01 to 2% by mass of the resin component dissolved in the ink among the film-forming resins. Aqueous jet ink.

2. The colored microcapsule-dispersed aqueous jet ink according to 1 above, wherein the acid value of the film-forming resin is 50 to 180 and the pH of the ink is 7.5 to 9.0.

3. 3. The colored microcapsule-dispersed water jet ink according to 1 or 2 above, wherein the film-forming resin has a molecular weight of 10,000 or more.

4). The colored microcapsule-dispersed aqueous jet inks according to 1 to 3, which contain glycerin in an aqueous medium.

5. The colored microcapsule-dispersed aqueous jet ink according to 1 to 4, which is a self-water dispersible resin obtained by neutralizing at least part of a film-forming resin having an acid value of 50 to 180 with a base.

6). 5. The colored microcapsule-dispersed aqueous jet ink as described in 5 above, wherein the base is alcohol amine.

7). 6. The colored microcapsule-dispersed water jet ink as described in 6 above, wherein the alcohol amine is triethanolamine.

8). The colored microcapsule-dispersed aqueous jet ink according to claim 5, which is neutralized at a neutralization rate equal to or less than 60 mol% of the acid groups of the film-forming resin.

A preferred embodiment of the production method of the present invention will be described as follows, taking as an example the case where it is applied to an ink for inkjet recording.
(1) A pigment is dispersed in a film-forming styrene- (meth) acrylic acid copolymer resin having an acid value of 50 to 180 based on a carboxyl group and having a weight average molecular weight of 1 to 100,000 using two rolls. , Get a solid coloring compound.

(2) Water, methyl ethyl ketone is mainly used as a low-boiling organic solvent for dissolving the resin, and isopropyl alcohol is used in combination as a low-boiling water-soluble organic solvent that functions as a co-solvent for the water and methyl ethyl ketone. Water containing an alcoholamine in an amount sufficient to make the film-forming resin self-dispersible, and a glycerin as an anti-drying agent, with a neutralization rate equal to or less than 60 mol% of the acid groups of the film-forming resin. Is prepared as a main liquid medium, and the solid colored compound chips of (1) above are mixed therein, and a pigment suspension is obtained by stirring. More preferably, the suspension can be further finely divided so that there is no re-aggregation using Nanomizer (trademark), which is a disperser capable of giving a high shearing force and obtaining a sufficient suspension state. Do.

(3) While stirring the pigment suspension, an aqueous solution containing glycerin is dropped, and the components derived from the pigment and the film-forming resin are substantially colored resin particles having an average particle diameter of 0.01 to less than 1 μm (coloring An aqueous dispersion consisting only of microcapsules) is obtained.
(4) Methyl ethyl ketone and isopropyl alcohol are distilled off from the resulting colored resin particle aqueous dispersion to form an ink base.
(5) An ink adjusting agent is added to the ink base to adjust the concentration and physical properties, followed by filtration, and the colored microcapsules are 0.5 to 20% by mass in terms of pigment and pH 7.5 to 11 is used for ink jet recording. Use water-based ink.

  Next, the present invention will be described more specifically with reference to examples and comparative examples. In the following examples, “part” represents “part by mass”.

Example 1
16 parts of a two-roll kneaded product of 8 parts of quinacridone pigment and 8 parts of styrene-acrylic acid-methacrylic acid resin (styrene / acrylic acid / methacrylic acid = 77/10/13; molecular weight 50,000 / acid value 160) It is put into a mixed solution of 46 parts of water, 4 parts of glycerin, 1.7 parts of triethanolamine, 18 parts of methyl ethyl ketone, and 8 parts of isopropyl alcohol, stirred at room temperature for 3 hours, and further pressure using a disperser Nanomizer (manufactured by Nanomizer). Dispersion treatment was performed at 98 MPa to obtain a pigment suspension.

  While stirring, a mixed liquid of 6 parts of glycerin and 69 parts of water was dropped into 93.7 parts of the obtained suspension at a rate of 5 ml per minute to obtain a magenta colored resin particle aqueous dispersion. Methyl ethyl ketone, isopropyl alcohol and a part of water were distilled off from the obtained capsule liquid using a rotary evaporator to obtain a final aqueous magenta colored resin particle dispersion.

  To 92 parts of this aqueous dispersion, 3 parts of glycerin as an anti-drying agent and 5 parts of propylene glycol propyl ether as a penetrant are added, so that the concentration is 2.7% by mass in terms of pigment of the colored microcapsules in the ink. After adjustment and stirring, the mixture was filtered using a 1 μm filter to obtain a water-based ink for inkjet recording.

  The microcapsules in the obtained water-based ink had an average particle diameter of 0.15 μm and the pH was 8.4. Form microcapsule particles with aqueous ink using an ultracentrifuge at an acceleration rate of 9.8 km / s 2 · 3 hours, and dry the resulting precipitate in an oven at 105 ° C for 140 hours to form a film. After only the resin and the pigment were obtained, the ratio of the resin and the pigment was obtained using a thermal analyzer, and only the film-forming resin component dissolved in the ink was obtained.

This ink exhibits stable dispersion without agglomerates after storage for 1 year at room temperature, printing using a piezo-type ink jet printer is stable, and the resulting printed matter is vivid magenta (printing) The printing density was 1.3 after the recording paper immediately after printing was immersed in purified water for 24 hours, and there was no change from before printing.

Claims (7)

(1) a kneading step in which a pigment is dispersed in a film-forming resin having an acid value to obtain a solid coloring compound;
(2) At least water, an organic solvent that dissolves the film-forming resin, a base, and the solid coloring compound are mixed, and dispersion is performed to obtain a pigment suspension in which at least a part of the film-forming resin is dissolved by dispersion. Turbidity process,
(3) A method for producing an aqueous dispersion of colored microcapsules, comprising a reprecipitation step of depositing a film-forming resin component dissolved in the pigment suspension on the pigment surface. The colored microcapsule aqueous dispersion according to claim 1, wherein the reprecipitation step is performed by adding water or an aqueous medium that functions as a poor solvent to the film-forming resin to the pigment suspension. Method. The method for producing an aqueous dispersion of colored microcapsules according to claim 1, wherein the reprecipitation step is performed by removing the organic solvent from the pigment suspension. The method for producing a colored microcapsule aqueous dispersion according to any one of claims 1 to 3, wherein the film-forming resin is a self-water dispersible resin obtained by neutralizing a resin having an acid value of 50 to 180 with a base. The method for producing an aqueous dispersion of colored microcapsules according to claim 4, wherein the neutralization rate of the film-forming resin with respect to the acid value is 60% or less. The method for producing an aqueous dispersion of colored microcapsules according to any one of claims 1 to 3, wherein the film-forming resin is a styrenic resin and contains both acrylic acid and methacrylic acid as monomer components of the copolymer . Colored microcapsule aqueous dispersions prepared by the process according to any one of claims 1 to 6.