JP2007161941A - Method for producing water-based pigment dispersion for ink-jet recording, water-based pigment dispersion for ink-jet recording and water-based ink for ink-jet recording - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a water-based ink that secures dispersion stability of pigment in a water-based ink, has excellent chroma and transparency in an obtained color image and is suitable for ink-jet suitability. <P>SOLUTION: In the method for producing a water-based pigment dispersion for ink-jet recording comprises mixing at least pigment, a dispersion resin and an aqueous medium containing a water-soluble organic solvent with stirring and removing the water-soluble organic solvent to give a water-based pigment dispersion containing a microcapsule pigment obtained by coating the surface of the pigment with the dispersion resin, pigment and an aqueous medium in which relation between the solubility parameter (A) of the pigment and the solubility parameter (B) of the aqueous medium is in the range of 0.95≤B/A≤1.17 and the solubility parameter (A) of the pigment is in the range of 13.5≤A≤19.5 are used as the pigment and aqueous medium. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing an aqueous pigment dispersion, an aqueous pigment dispersion obtained by the method, and an aqueous ink using the aqueous pigment dispersion, and more specifically, an aqueous pigment dispersion excellent in inkjet suitability and the use thereof. The present invention relates to a water-based ink.

  Until now, dyes have been used in ink jet recording liquids (inks) that require high definition. An image formed with a recording liquid using a dye has characteristics such as high transparency, high definition, and excellent color rendering, but often has problems in light resistance and water resistance. In recent years, in order to solve the problems of light fastness and water fastness of images, pigment inks in which an ink coloring material is replaced with a dye and an organic pigment or carbon black have been manufactured (Patent Documents 1 to 5). However, when an organic pigment or carbon black is used as a coloring material, the recorded image has high definition and high color rendering unless the pigment is very finely dispersed and stabilized in the ink. There is a problem of not becoming.

  Further, regarding the adaptability to a printer, particularly when used as an ink for an ink jet printer, unlike an ink using a water-soluble dye, the pigment does not dissolve in an aqueous medium, so there is a specific problem. That is, if the pigment in the ink is not very finely dispersed and stabilized, there is a problem that nozzle clogging occurs in the head of the printer.

  In addition, when using ink containing pigments in applications such as OHP sheets that recognize images by projecting with a backlight, colorful OHP projections are required unless the pigments are finely dispersed to ensure high transparency. There is a problem that images cannot be obtained. This means that the pigment contained in the ink needs to be more finely dispersed (Patent Document 6).

Japanese Patent Laid-Open No. 57-10660 Japanese Patent Laid-Open No. 57-10661 Japanese Patent Laid-Open No. 1-15542 JP-A-2-255875 Japanese Patent Laid-Open No. 2-27676 JP 2001-164157 A

  However, the ultrafine particles have a property that their surfaces are chemically very active and therefore easily aggregate. Once aggregated, the particles do not sufficiently separate even if stirred with a stirrer or the like. For this reason, in the prior art, even if a pigment having a small primary particle diameter is used, the pigment particles are aggregated in the dispersion step, and as a result, an ultrafine pigment dispersion cannot be obtained. For this reason, the saturation, transparency, and ink ejection stability, which are indispensable for improving the color image quality, often do not reach the level obtained with dye inks.

  Therefore, the object of the present invention is to ensure the dispersion stability of pigment particles in aqueous ink using ultrafine pigment particles, and is excellent in saturation and transparency in a color image obtained thereby, and at the same time, excellent in ink jet aptitude. It is to provide a water-based ink. Another object of the present invention is to provide a method for producing an aqueous pigment dispersion from which the above excellent aqueous ink can be easily obtained, and an aqueous pigment dispersion produced by the production method.

  As a result of intensive studies to solve the above-described problems of the prior art, the present inventors have found that the above object can be achieved by the present invention described below. That is, in the present invention, at least after mixing and stirring an aqueous medium containing a pigment, a dispersion resin, and a water-soluble organic solvent, the surface of the pigment is coated with the dispersion resin by removing the water-soluble organic solvent. In the method for producing an aqueous pigment dispersion for inkjet recording (hereinafter referred to as an aqueous pigment dispersion) to obtain an aqueous pigment dispersion containing the microcapsule pigment, the solubility parameter (A) of the pigment as the pigment and the aqueous medium. And the solubility parameter (B) of the aqueous medium are in the range of 0.95 ≦ B / A ≦ 1.17, and the solubility parameter (A) of the pigment is 13.5 ≦ A ≦ 19. A method for producing an aqueous pigment dispersion characterized by using one within the range of .5.

  As a preferable form of the manufacturing method of the aqueous pigment dispersion concerning this invention, the following form is mentioned. The manufacturing method of the aqueous pigment dispersion whose content of the said dispersion resin in an aqueous pigment dispersion is 20% or more with respect to content of the said pigment on a mass reference | standard. A method for producing an aqueous pigment dispersion, wherein the dispersion resin is an amphiphilic block copolymer.

  Another embodiment of the present invention is an aqueous pigment dispersion produced by any one of the production methods described above. Furthermore, another embodiment of the present invention is a water-based ink for ink-jet recording (hereinafter referred to as a water-based ink) characterized by comprising at least the water-based pigment dispersion.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the aqueous pigment dispersion by which the conditions which coat | cover a microparticle pigment with a small primary particle size with a macromolecular organic compound and make it microcapsule is provided. The aqueous pigment dispersion obtained by this method is one in which aggregation is suppressed, and by using this, an aqueous ink in which the dispersion stability of the contained pigment particles is ensured is provided. Such water-based ink can form a color image with further improved saturation and transparency, and is excellent in ink jet aptitude.

  Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. The present inventors diligently studied a method for producing a microcapsule pigment dispersion by phase inversion emulsification as means for solving the above-described problems of the prior art. As a result, the ratio between the solubility parameter of the pigment (hereinafter sometimes abbreviated as SP value) and the SP value of the aqueous medium in which the pigment is dispersed affects the characteristics of the aqueous pigment dispersion and aqueous ink to be produced. I found out that In particular, it has been found that there is a suitable range between the above two SP values when producing a pigment dispersion because it affects the characteristics of an image recorded using an aqueous ink containing the aqueous pigment dispersion. To the present invention. Hereinafter, the forming material used in the manufacturing method of the present invention will be described, and then the SP value characterizing the manufacturing method according to the present invention will be described.

First, pigments that can be used in the present invention will be described. As the pigment, carbon black or an organic pigment can be used, and specific examples include the following. The following carbon black is preferably used as the pigment used in the black ink. For example, carbon black pigments such as furnace black, lamp black, acetylene black, channel black, etc., for example, the following commercially available products or newly prepared ones can be used.
Raven 7000, Ray Van 5750, Ray Van 5250, Ray Van 5000 ULTRA, Ray Van 3500, Ray Van 2000, Ray Van 1500, Ray Van 1250, Ray Van 1200, Ray Van 1190 ULTRA II, Ray Van 1170, Ray Van 1255 (above, Columbia)
Black Pearls L, Regal 400R, Legal 330R, Legal 660R, Mogul L, Monarch 700, Monak 800, Monak 880, Monak 900, Monak 1000, Monak 1100, Monak 1300, Monak 1400, Valcan XC-72R (above, manufactured by Cabot Corporation),
Color Black FW1, Color Black FW2, Color Black FW2V, Color Black FW18, Color Black FW200, Color Black S150, Color Black S160, Color Black S170, Printex 35, Printex U, Printex V , Printex 140U, Printex 140V, Special Black 6, Special Black 5, Special Black 4A, Special Black 4 (above, manufactured by Degussa)
No. 25, no. 33, no. 40, no. 47, no. 52, no. 900, no. 2300, MCF-88, MA600, MA7, MA8, MA100 (above, manufactured by Mitsubishi Chemical Corporation), etc.

Specific examples of the organic pigment include the following.
Insoluble azo pigments such as toluidine red, toluidine maroon, Hansa yellow, benzidine yellow, pyrazolone red, soluble azo pigments such as ritole red, helio bordeaux, pigment scarlet, permanent red 2B, vat dyes such as alizarin, indantron, thioindigo maroon Derivatives from dyes, phthalocyanine pigments such as phthalocyanine blue and phthalocyanine green, quinacridone pigments such as quinacridone red and quinacridone magenta, perylene pigments such as perylene red and perylene scarlet, isoindolinone yellow and isoindolinone orange Indolinone pigments, benzimidazolone yellow, benzimidazolone orange, benzimidazolone red and other imidazolone pigments, pyranthrone red, Pylanthrone pigments such as Throne Orange, thioindigo pigments, condensed azo pigments, thioindigo pigments, diketopyrrolopyrrole pigments, flavanthron yellow, acylamide yellow, quinophthalone yellow, nickel azo yellow, copper azomethine yellow, perinone Orange, anthrone orange, dianthraquinonyl red, dioxazine violet, etc.

The organic pigment is represented by the color index (CI) number as follows.
C. I. Pigment Yellow 12, 13, 14, 17, 20, 24, 74, 83, 86, 93, 97, 109, 110, 117, 120, 125, 128, 137, 138, 147, 148, 150, 151, 153, 154, 155, 166, 168, 180, 185; C.I. I. Pigment Orange 16, 36, 43, 51, 55, 59, 61, 71; C.I. I. Pigment Red 9, 48, 49, 52, 53, 57, 97, 122, 123, 149, 168, 175, 176, 177, 180, 192, 215, 216, 217, 222, 223, 224, 226, 227, 228, 238, 240, 254, 255, 272; I. Pigment Violet 19, 23, 29, 30, 37, 40, 50; C.I. I. C.I. Pigment Blue 15, 15: 1, 15: 3, 15: 4, 15: 6, 22, 22, 60; I. Pigment Green 7 and 36; C.I. I. Pigment Brown 23, 25, 26, etc. In particular, among these pigments, the following are preferable.
C. I. Pigment Yellow 74, 93, 97, 110, 120, 128, 138, 147, 148, 150, 151, 154, 155, 180, 185, C.I. I. Pigment red 122, C.I. I. Pigment violet 19, C.I. I. Pigment Blue 15, 15: 1, 15: 3, 15: 4, etc.

  Furthermore, in the present invention, since it is intended for use in water-based inks, it is preferable that the primary particles be finely divided. Examples of the method for making the pigment fine particles include the methods listed below. For example, there are a method of applying strong grinding with a bead mill or the like, and a mechanical method using a jet mill or the like. In addition, there are a method of synthesizing a pigment having a primary particle size as small as possible and a low surface activity at the time of pigment synthesis, and a method of atomization by an evaporation method in an inert gas, that is, a gas phase method.

  In the method for producing a pigment dispersion according to the present invention, it is preferable to use a fine pigment having a primary particle size of 50 nm or less. When the primary particle size is larger than 50 nm, when using an aqueous ink in which the pigment is dispersed, pigment particles having a particle size of 300 nm or more as a preferable particle size distribution of the fine particle pigment increase. In such a case, when the pigment dispersion produced in the present invention is used as an ink coloring material, it is difficult to obtain an image excellent in coloring power and transparency. The pigment used in the present invention is preferably a fine particle pigment having an average particle size of 20 nm to 50 nm and a particle size distribution of 10 nm to 200 nm.

  According to the study by the present inventors, even when the primary particle diameter of the pigment is controlled to be in the range of 50 nm or less, the pigment aggregates before entering the dispersion step of dispersing the pigment in the aqueous medium using the dispersion resin, There are cases where secondary particles, and further dry aggregation, become aggregated particles. When the pigment particles that have been in such a state are to be dispersed to the state of primary particles in the dispersion step, if the pigment particles have a primary particle size of around 100 nm as in the prior art, Yes. However, when the primary particle size suitable for the present invention is 50 nm or less, the active energy on the pigment surface increases, and a strong cohesive force is generated between the pigment particles. Therefore, when fine particles having a primary particle size of 50 nm or less are used, fine particles having a particle size equivalent to the primary particle size are formed from the aggregate formed by secondary particle formation, and the stable dispersion state is set. It will be very difficult to get.

  When pigment particles are used as a coloring material for aqueous ink, it is particularly required that the pigment is stably dispersed in an aqueous medium. In general, since pigments have poor dispersibility, a method of adding a dispersant and dispersing the pigment in an aqueous medium is employed in order to obtain a uniform dispersion system. However, there are many cases where sufficient dispersibility cannot be obtained even by a method using this dispersant. For this reason, inks in which pigments are dispersed often have problems such as increased viscosity and increased particle size, resulting in poor stability, especially when stored for a long period of time.

  In the method for producing a pigment dispersion according to the present invention, the above-described problems are solved by a configuration that makes it possible to easily obtain a microcapsule pigment having a configuration in which pigment particles are coated with an organic polymer compound. That is, by using a microcapsule pigment, the surface activity of the pigment particles is lowered, and as a result, the pigment can be stably dispersed in an aqueous medium without using a dispersant. Here, microencapsulation appears to be similar to mixed dispersion of pigment particles and organic polymer compound, but is completely different. That is, the microcapsule pigment is obtained by coating the surface of the pigment particles with the organic polymer compound firmly and uniformly, and the resin on the surface is hardly peeled off and exhibits high stability. The microcapsule pigment obtained by the production method according to the present invention exhibits high storage stability and ejection stability in a finely dispersed state even in an aqueous medium. As a result, the degree of freedom in ink design is great. Become.

  In addition, the followings can be mentioned as major characteristics when a microcapsule pigment is obtained in the present invention and used in an aqueous ink. Since the microcapsule pigment has the pigment particles coated with an organic polymer compound, glossiness and transparency can be imparted to the obtained recorded matter without newly adding a resin component to the ink. In addition, since the microcapsule pigment having a structure coated with an organic polymer compound is excellent in paper penetrability, it is possible to impart excellent scratching properties to an image obtained by the penetrability. Next, the microencapsulation of the pigment in the method for producing a pigment dispersion according to the present invention will be described.

As a method for microencapsulating pigment particles, conventionally known methods include a chemical production method, a physical production method, a physicochemical production method, and a mechanical production method. The main methods include the following.
Interfacial polymerization method: A method in which two kinds of monomers or two kinds of reactants are separately dissolved in a dispersed phase and a continuous phase, and both substances are reacted at the interface between them to form a wall film.
In-situ polymerization method: a method in which a liquid or gaseous monomer and catalyst, or two reactive substances are supplied from either one of the continuous phase core particles to cause a reaction to form a wall film.
In-liquid cured coating method: A method in which a wall film is formed by insolubilizing droplets of a polymer solution containing core material particles in a liquid with a curing agent or the like.
Coacervation (phase separation) method: A method in which a polymer solution in which core material particles are dispersed is separated into a coacervate (concentrated phase) and a dilute phase having a high polymer concentration to form a wall film.
In-liquid drying method: Prepare a liquid in which the core material is dispersed in the wall membrane material solution, put the dispersion in a liquid in which the continuous phase of this dispersion is not miscible, and make a composite emulsion to dissolve the wall membrane material. A method of forming a wall film by gradually removing the medium.
Melt dispersion cooling method: Uses a wall film material that melts into a liquid state when heated and solidifies at room temperature. This material is heated and liquefied, core material particles are dispersed in it, cooled to fine particles, and cooled to a wall film. Forming method.
Air suspension coating method: A method of forming a wall membrane by suspending powder core material particles in the air with a fluidized bed and spraying and mixing the coating solution of the wall membrane material while floating in an air stream.
Spray drying method: A method in which an encapsulated stock solution is sprayed and brought into contact with hot air to evaporate and dry volatile components to form a wall film.
However, particularly when used for inkjet applications, it is preferable to use a phase inversion method suitable for the purpose of obtaining a finer and more uniform microcapsule pigment.

  Here, the phase inversion method is the following method. That is, a dispersion resin having self-dispersibility or solubility in water and a composite or composite of an organic pigment or carbon black, or a mixture having at least an organic pigment or carbon black and an organic polymer compound is aqueous. In this method, the organic solvent phase is used, and water is added to the organic solvent phase, or the organic solvent phase is added to water to perform self-dispersion (phase inversion emulsification). In the above phase inversion method, there is no problem even if the organic solvent phase is mixed with a recording liquid vehicle or additives. In particular, it is more preferable to mix a vehicle for recording liquid because a dispersion liquid for recording liquid can be directly produced.

  As a result of intensive studies on the method for producing a microcapsule pigment dispersion by phase inversion emulsification, the present inventors have reached the present invention. That is, when the relationship between the solubility parameter (A) of the pigment and the solubility parameter (B) of the aqueous medium is 0.95 ≦ B / A ≦ 1.17, the pigment is effective as a water-based ink forming material. It was found that a dispersion can be obtained. In addition, the aqueous medium in the above is a dispersion medium of a pigment containing a water-soluble organic solvent, and a mixed medium of a water-soluble organic solvent and water is preferably used. Hereinafter, it is simply referred to as an aqueous medium. More specifically, the ratio represented by B / A was recorded using the characteristics of the pigment dispersion produced, the characteristics of the water-based ink containing the dispersion, and the water-based ink. We found that it affects the characteristics of the image.

  That is, if the ratio of the solubility parameter (B) of the aqueous medium to the solubility parameter (A) of the pigment is greater than 1.17, the wettability of the pigment with respect to the aqueous medium becomes insufficient. Sex worsens. As a result, the properties of the pigment dispersion produced and the aqueous ink containing the dispersion, as well as the properties of images recorded using the aqueous ink, tend to deteriorate.

  On the other hand, when the ratio of the solubility parameter (B) of the aqueous medium to the solubility parameter (A) of the pigment is less than 0.95, the wettability of the pigment with respect to the aqueous medium is improved, but the following disadvantages occur. In this case, since the wettability of the dispersion resin to the aqueous medium is improved, the dispersion resin does not encapsulate the pigment well during phase inversion emulsification, and the dispersibility of the pigment is deteriorated. As a result, it was found that the characteristics of the aqueous pigment dispersion to be produced and the characteristics of the aqueous ink containing the pigment dispersion, as well as the characteristics of images recorded using the aqueous ink, tend to deteriorate. .

Furthermore, in order to achieve the object of the present invention, it was found that the solubility parameter (A) of the pigment is required to be 13.5 or more and 19.5 or less.
It should be noted that the solubility parameter in the present invention is also referred to as an SP value and is specific to a substance, such as 23.43 for water, 9.75 for acetone, and 9.1 for tetrahydrofuran. Is the value of If the aqueous medium is a mixture, it can be calculated according to the volume ratio. For example, in the case of a 1: 1 (volume ratio) mixture of water and tetrahydrofuran, the solubility parameter of this aqueous medium is (23.43 × 1 + 9.1 × 1) / (1 + 1) = 16.265. .
However, the solubility parameter (A) of the pigment is a value obtained as follows. First, water is put into a beaker, and the pigment is floated on the water surface. Acetone was added little by little, and the solubility parameter (A) of the pigment was calculated from the volume ratio of water and acetone when the pigment began to sink into the solution.

  In the present invention, a microcapsule pigment is formed. In this case, the dispersion resin to be a capsule material is preferably an amphiphilic block copolymer. Here, amphipathic means having at least one of the following properties. In other words, it has the property of being soluble in two types of solvents that are not soluble in each other, the property of having both a portion that is soluble in a certain solvent and a portion that is not soluble, or a portion that is incompatible with a certain solvent. Is the nature. The dispersion resin used in the present invention is particularly preferably a copolymer composed of a hydrophilic polymerization chain portion and a hydrophobic polymerization chain site. The block copolymer is a copolymer in which polymer segments having different repeating unit structures are bonded by a covalent bond, and is also called a block copolymer or a block polymer.

Specific materials for forming microcapsule capsules include the following.
Polyamide, polyurethane, polyester, polyurea, epoxy resin, polycarbonate, urea resin, melamine resin, phenol resin, silicone resin, polysaccharide, gelatin, gum arabic, dextran, casein, protein, natural rubber, carboxypolymethylene, polyvinyl alcohol, polyvinyl Pyrrolidone, polyvinyl acetate, polyvinyl chloride, polyvinylidene chloride, cellulose, ethyl cellulose, methyl cellulose, nitrocellulose, hydroxyethyl cellulose, cellulose acetate, polyethylene, polystyrene, nylon, (meth) acrylic acid polymer or copolymer, (meta ) Acrylic acid ester polymer or copolymer, (meth) acrylic acid- (meth) acrylic acid ester copolymer, styrene- (meth) acrylic acid copolymer Styrene - maleic acid copolymer, alginic acid soda, fatty acids, paraffin, beeswax, water wax, hardened beef tallow, carnauba wax, albumin and the like.
Among these, it is particularly preferable to use an anionic organic polymer compound having an anionic group such as a carboxylic acid group or a sulfonic acid group.

  The anionic organic polymer compound suitable in the above will be described in more detail. Specifically, by neutralizing an anionic group in organic polymer compounds having an anionic group such as a carboxyl group, a sulfonic acid group, and a phosphonic acid group using an alkali metal hydroxide as described below. What is obtained is mentioned. As the alkali metal hydroxide, organic amines such as ammonia and triethylamine, sodium hydroxide, potassium hydroxide, lithium hydroxide, and the like can be used. The anionic organic polymer compound obtained by neutralizing an anionic group with an alkali metal hydroxide as described above is provided with self-dispersibility or solubility in water by neutralization. A particularly desirable self-dispersing ability or dissolving ability is such that the carboxyl group in the organic polymer compound having a carboxyl group is neutralized with a base. The anionic group-containing organic polymer compounds used in the present invention may have two or more types of anionic groups as mentioned above in the compound.

Any organic polymer compound having an anionic group as described above may be used as long as it can impart water self-dispersibility and solubility by neutralizing the anionic group. Good. For example, the following are mentioned.
Polyvinyl resin, polyester resin, amino resin, acrylic resin, epoxy resin, polyurethane resin, polyether resin, polyamide resin, unsaturated polyester resin, phenol resin, silicone resin, and fluorine resin Molecular compounds or mixtures thereof, such as resins having an anionic group

  Further, the content of the dispersion resin as described above in the aqueous pigment dispersion should be 20% (mass basis) or more with respect to the organic pigment or carbon black pigment to be coated with the resin. preferable. That is, if it is less than 20%, sufficient dispersibility of the pigment cannot be obtained when it is used as an ink, scratch resistance of an image formed with the ink cannot be obtained sufficiently, and the pigment is not easily dispersed finely. This is because it may cause another problem such as.

  The aqueous medium used in the method for producing an aqueous pigment dispersion according to the present invention contains at least a water-soluble organic solvent, and is preferably a mixed solvent of water and a water-soluble organic solvent. In this case, the water-soluble organic solvent is selected from the balance with the solubility parameter of the pigment so that the solubility parameter of the aqueous medium falls within the range defined in the present invention. In addition, it is preferable to use an evaporator or the like that can easily remove the water-soluble organic solvent.

  The aqueous ink according to the present invention contains an aqueous pigment dispersion obtained by the production method according to the present invention, and further contains an aqueous medium. The aqueous medium used in this case is also preferably composed of a mixed solvent of water and a water-soluble organic solvent. As the water-soluble organic solvent used in this case, those having an effect of preventing ink drying are particularly preferable. The water used in the present invention is preferably deionized water rather than general water containing various ions.

Specific examples of the water-soluble organic solvent used in the present invention include the following.
Alkyl alcohols having 1 to 5 carbon atoms such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, isobutyl alcohol, n-pentanol;
Amides such as dimethylformamide and dimethylacetamide;
Ketones or ketoalcohols such as acetone and diacetone alcohol;
Ethers such as tetrahydrofuran and dioxane;
Oxyethylene or oxypropylene copolymers such as diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, polyethylene glycol, polypropylene glycol;
Alkylene glycols in which the alkylene group contains 2 to 6 carbon atoms, such as ethylene glycol, propylene glycol, trimethylene glycol, triethylene glycol, 1,2,6-hexanetriol;
Glycerin;
Lower alkyl ethers such as ethylene glycol monomethyl (or ethyl) ether, diethylene glycol monomethyl (or ethyl) ether, triethylene glycol monomethyl (or ethyl) ether;
Lower dialkyl ethers of polyhydric alcohols such as triethylene glycol dimethyl (or ethyl) ether, tetraethylene glycol dimethyl (or ethyl) ether;
Alkanolamines such as monoethanolamine, diethanolamine, triethanolamine;
Sulfolane, N-methyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, etc. Water-soluble organic solvents such as those described above can be used alone or as a mixture.

  The content of the water-soluble organic solvent as described above contained in the aqueous ink according to the present invention is not particularly limited, but is preferably in the range of 3% by mass to 50% by mass with respect to the total mass of the ink. . The content of water contained in the ink is preferably in the range of 50% by mass to 95% by mass with respect to the total mass of the ink.

  In addition to the above-described components, various additives may be added to the water-based ink according to the present invention as necessary in order to obtain an ink having a desired physical property value. As additives, for example, viscosity modifiers, antifoaming agents, antiseptics, fungicides, surfactants, antioxidants, and the like can be added. The selection of the surfactant is preferably determined so that the surface tension of the ink is 30 mN / m or more.

  As described above, the aqueous ink according to the present invention is particularly effective when used in ink jet recording. As an ink jet recording method, there are a recording method in which mechanical energy is applied to ink to eject the ink, and an ink jet recording method in which thermal energy is applied to the ink to eject the ink by foaming of the ink. The water-based ink of the present invention is particularly suitable for these ink jet recording methods.

  Next, an example of an ink jet recording apparatus suitable for recording using the aqueous ink according to the present invention will be described below. First, FIG. 1 and FIG. 2 show an example of a head configuration which is a main part of an ink jet recording apparatus using thermal energy.

FIG. 1 is a cross-sectional view of the head 13 along the ink flow path, and FIG. 2 is a cross-sectional view taken along line AB in FIG. The head 13 is obtained by adhering a heating element substrate 15 and a glass, ceramic, silicon or plastic plate having a flow path (nozzle) 14 through which ink passes. The heating element substrate 15 includes a protective layer 16, electrodes 17-1 and 17-2, a heating resistor layer 18, a heat storage layer 19, and a substrate 20. The protective layer 16 is made of silicon oxide, silicon nitride, silicon carbide, or the like. The electrodes 17-1 and 17-2 are made of aluminum, gold, aluminum-copper alloy, or the like. The heating resistor layer 18 is made of a high melting point material such as HfB ₂ , TaN, TaAl or the like. The heat storage layer 19 is formed of thermal silicon oxide, aluminum oxide or the like. The substrate 20 is formed of a material with good heat dissipation such as silicon, aluminum, aluminum nitride.

  When a pulsed electric signal is applied to the electrodes 17-1 and 17-2 of the head 13, the region indicated by n of the heating element substrate 15 rapidly generates heat, and bubbles are generated in the ink 21 in contact with the surface. Will occur. Then, the meniscus 23 is projected by the pressure, and the ink 21 is ejected through the nozzle 14 of the head, becomes an ink droplet 24 from the ejection orifice 22, and flies toward the recording material 25. FIG. 3 shows an external view of an example of a multi-head in which a large number of heads shown in FIG. 1 are arranged. This multi-head is made by adhering a glass plate 27 having multi-nozzles 26 and a heating head 28 similar to that described in FIG.

  FIG. 4 shows an example of an ink jet recording apparatus incorporating this head. In FIG. 4, reference numeral 61 denotes a blade as a wiping member, one end of which is held and fixed by a blade holding member, and forms a cantilever. The blade 61 is disposed at a position adjacent to the recording area by the recording head 65, and in this example, is held in a form protruding in the moving path of the recording head 65.

  Reference numeral 62 denotes a cap on the projection port surface of the recording head 65, which is disposed at a home position adjacent to the blade 61, moves in a direction perpendicular to the moving direction of the recording head 65, contacts the ink ejection port surface, and performs capping. The structure to perform is provided. Further, reference numeral 63 denotes an ink absorber provided adjacent to the blade 61 and, like the blade 61, is held in a form protruding in the moving path of the recording head 65. The blade 61, the cap 62, and the ink absorber 63 constitute an ejection recovery unit 64, and the blade 61 and the ink absorber 63 remove moisture, dust, and the like from the ejection port surface.

  Reference numeral 65 denotes a recording head which has discharge energy generating means and performs recording by discharging ink onto a recording material facing the discharge port surface on which the discharge port is arranged. Reference numeral 66 denotes a recording head mounted with the recording head 65. It is a carriage for moving. The carriage 66 is slidably engaged with the guide shaft 67, and a part of the carriage 66 is connected to a belt 69 (not shown) driven by a motor 68. As a result, the carriage 66 can move along the guide shaft 67, and the recording area and its adjacent area can be moved by the recording head 65.

  Reference numeral 51 denotes a paper feed unit for inserting a recording material, and 52 denotes a paper feed roller driven by a motor (not shown). With these configurations, the recording material is fed to a position facing the ejection port surface of the recording head 65, and is discharged to a paper discharge portion provided with a paper discharge roller 53 as recording progresses. In the above configuration, when the recording head 65 finishes recording and returns to the home position, the cap 62 of the ejection recovery unit 64 is retracted from the moving path of the recording head 65, but the blade 61 protrudes into the moving path. As a result, the ejection port of the recording head 65 is wiped.

  When the cap 62 is in contact with the ejection surface of the recording head 65 to perform capping, the cap 62 moves so as to protrude into the moving path of the recording head. When the recording head 65 moves from the home position to the recording start position, the cap 62 and the blade 61 are at the same position as that at the time of wiping described above. As a result, the ejection port surface of the recording head 65 is wiped even during this movement. The above-mentioned movement of the recording head to the home position is not only at the end of recording or at the time of ejection recovery, but also to the home position adjacent to the recording area at a predetermined interval while the recording head moves the recording area for recording. Then, the wiping is performed with this movement.

  FIG. 5 is a diagram illustrating an example of an ink cartridge that contains ink supplied to the recording head via an ink supply member, for example, a tube. Here, reference numeral 40 denotes an ink container, for example, an ink bag, in which supply ink is stored, and a rubber plug 42 is provided at the tip thereof. By inserting a needle (not shown) into the stopper 42, the ink in the ink bag 40 can be supplied to the head. An ink absorber 44 receives waste ink. The ink container preferably has a liquid contact surface made of polyolefin, particularly polyethylene.

  The ink jet recording apparatus used in the present invention is not limited to the one in which the head and the ink cartridge are separated as described above, but is preferably used in an apparatus in which they are integrated as shown in FIG. It is done. In FIG. 6, reference numeral 70 denotes a recording unit, in which an ink storage portion that stores ink, for example, an ink absorber is stored. The ink in the ink absorber is ejected as ink droplets from a head portion 71 having a plurality of orifices. It is preferable for the present invention to use polyurethane as the material of the ink absorber. Alternatively, a structure may be used in which the ink container is an ink bag with a spring or the like inside without using an ink absorber. Reference numeral 72 denotes an atmosphere communication port for communicating the inside of the cartridge with the atmosphere. The recording unit 70 is used in place of the recording head 65 shown in FIG. 4 and is detachable from the carriage 66.

  Next, a preferred example of an ink jet recording apparatus using mechanical energy will be described. As such a thing, an on-demand inkjet recording head can be mentioned. The head includes a nozzle forming substrate having a plurality of nozzles, a pressure generating element made of a piezoelectric material and a conductive material disposed opposite to the nozzles, and ink filling the periphery of the pressure generating element. Then, the pressure generating element is displaced by the applied voltage, and a small droplet of ink is ejected from the nozzle. An example of the configuration of a recording head, which is a main part of the on-demand ink jet recording apparatus, is shown in FIG.

  The head includes an ink flow path 80 communicating with an ink chamber (not shown), an orifice plate 81 for ejecting ink droplets of a desired volume, a vibration plate 82 that directly applies pressure to ink, and the vibration plate. A piezoelectric element 83 that is joined to 82 and is displaced by an electrical signal, and a substrate 84 for indicating and fixing the orifice plate 81, the diaphragm 82, and the like.

  In FIG. 7, the ink flow path 80 is made of a photosensitive resin or the like, and the orifice plate 81 has a discharge port 85 formed by drilling a metal such as stainless steel or nickel by electroforming or pressing. The diaphragm 82 is formed of a metal film such as stainless steel, nickel, or titanium, and a highly elastic resin film. The piezoelectric element 83 is formed of a dielectric material such as barium titanate or PZT. The recording head configured as described above operates as follows. A pulsed voltage is applied to the piezoelectric element 83 to generate strain stress. The energy deforms the vibration plate bonded to the piezoelectric element 83, pressurizes the ink in the ink flow path 80 vertically, and discharges ink droplets (not shown) from the discharge port 85 of the orifice plate 81 to perform recording. Done. Such a recording head is used by being incorporated in an ink jet recording apparatus similar to that shown in FIG. The detailed operation of the ink jet recording apparatus can be performed in the same manner as described above.

  EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples. However, the present invention is not limited to the following examples unless it exceeds the gist. In the following description, “parts” and “%” are based on mass unless otherwise specified.

<Comparative Example 1>
As the dispersion resin, a triblock copolymer having the following constitution (polymerization ratio: A: B: C = 110: 42: 16) (Mn = 19,700, Mw / Mn = 1.24) was used. The triblock copolymer comprises isobutyl vinyl ether (A block), 2- (2-methoxyethyl) ethyl vinyl ether (B block) and ethyl 4- (2-vinyloxy) ethoxybenzoate (C block). As the pigment, cyan copper phthalocyanine pigment (P-1) (manufactured by Toyo Ink) (SP value = 13.2) was used.

  Then, 2 parts of the triblock copolymer and 2 parts of the cyan copper phthalocyanine pigment were co-dissolved in 46.2 parts of tetrahydrofuran (SP value = 9.1, specific gravity = 0.89). Next, 18 parts of a potassium hydroxide aqueous solution having a concentration of 0.1 mol / l was added thereto and stirred while applying ultrasonic waves. At this time, the amount of potassium hydroxide was finely adjusted so that the pH was about 9.0. The solubility parameter of this aqueous medium is (9.1 × 46.2 / 0.89 + 23.43 × 18) / (46.2 / 0.89 + 18) = 12.8. Then, the aqueous pigment dispersion was obtained by evaporating tetrahydrofuran using a rotary evaporator.

  In the production example of the aqueous pigment dispersion described above, the ratio between the solubility parameter (A) of the pigment and the solubility parameter (B) of the aqueous medium containing tetrahydrofuran is B / A≈12.8 / 13.2. ≈ 0.97.

  The obtained aqueous pigment dispersion was mixed with each solvent so that the content in the ink was 16% glycerin and 4.0% isopropyl alcohol to prepare an ink. At that time, the dispersion resin (triblock copolymer) and the pigment were finally adjusted with water so that the total solid concentration in the ink was 5%.

<Comparative Examples 2-7>
In Comparative Example 1, the aqueous pigment dispersions of Comparative Examples 2 to 7 and the same conditions as in Comparative Example 1 except that the amount of tetrahydrofuran used when co-dissolving the dispersion resin (triblock copolymer) and the pigment was changed. An ink was prepared. In preparing the pigment dispersion, the amount of tetrahydrofuran was changed to 37.1 parts, 31.0 parts, 14.4 parts, 10.7 parts, 7.4 parts and 3.8 parts, respectively. And it was set as the aqueous pigment dispersion and ink of Comparative Examples 2-7 in order of this manufacturing condition. Table 1 shows the ratio B / A between the solubility parameter (A) of the pigment and the solubility parameter (B) of the aqueous medium containing tetrahydrofuran in these production examples.

<Example 1>
An aqueous pigment dispersion and ink were prepared under the same conditions as in Comparative Example 1 except that 2 parts of cyan copper phthalocyanine pigment (P-2) (manufactured by Toyo Ink) (SP value = 13.5) was used as the pigment. This was taken as Example 1.

  In the production example of the pigment dispersion described above, the ratio between the solubility parameter (A) of the pigment and the solubility parameter (B) of the aqueous medium containing tetrahydrofuran is B / A≈0.95.

<Examples 2-3 and Comparative Examples 8-11>
In Example 1, an aqueous pigment dispersion and an ink were prepared under the same conditions as in Comparative Example 1 except that the amount of tetrahydrofuran used when the dispersion resin (triblock copolymer) and the pigment were co-dissolved was changed. Specifically, in preparing the pigment dispersion, the amount of tetrahydrofuran was 37.1 parts, 31.0 parts, 14.4 parts, 10.7 parts, 7.4 parts and 3.8 parts, respectively. changed. And it was set as the aqueous pigment dispersion and ink of Examples 2-3 and Comparative Examples 8-11 in order of this manufacturing condition. The ratio B / A between the solubility parameter (A) of the pigment and the solubility parameter (B) of the aqueous medium containing tetrahydrofuran in the production examples of these pigment dispersions is shown in Table 1, respectively.

<Comparative Example 12>
An aqueous pigment dispersion and ink were prepared under the same production conditions as in Comparative Example 1 except that 2 parts of cyan copper phthalocyanine pigment (manufactured by Toyo Ink) (P-3) (SP value = 14.2) was used as the pigment. This was designated as Comparative Example 12.

  In the production example of the pigment dispersion described above, the ratio between the solubility parameter (A) of the pigment and the solubility parameter (B) of the aqueous medium containing tetrahydrofuran is B / A≈0.90.

<Examples 4-6, Comparative Examples 13-15>
An aqueous pigment dispersion and an ink were prepared under the same conditions as in Comparative Example 12 except that the amount of tetrahydrofuran used when the dispersion resin (triblock copolymer) and the pigment were co-dissolved was changed. Specifically, the amount of tetrahydrofuran during the production of the pigment dispersion was changed to 37.1 parts, 31.0 parts, 14.4 parts, 10.7 parts, 7.4 parts and 3.8 parts. And it was set as Examples 4-6 and Comparative Examples 13-15 in order of this manufacturing condition. Table 1 shows the ratio B / A between the solubility parameter (A) of the pigment and the solubility parameter (B) of the aqueous medium containing tetrahydrofuran in these production examples.

<Comparative Example 16>
An aqueous pigment dispersion and ink were produced under the same production conditions as in Comparative Example 1 except that 2 parts of cyan copper phthalocyanine pigment (P-4) (manufactured by Ciba Specialty Chemicals) (SP value = 17.4) was used as the pigment. Was prepared. And what was obtained was set as Comparative Example 16.

  In the production example of the pigment dispersion described above, the ratio between the solubility parameter (A) of the pigment and the solubility parameter (B) of the aqueous medium containing tetrahydrofuran is B / A≈0.74.

<Comparative Examples 17-18, Examples 7-9, Comparative Example 19>
In Comparative Example 16, an aqueous pigment dispersion and an ink were prepared under the same conditions as in Comparative Example 16 except that the amount of tetrahydrofuran used when the dispersion resin (triblock copolymer) and the pigment were co-dissolved was changed. Specifically, the amount of tetrahydrofuran during the production of the pigment dispersion was changed to 37.1 parts, 31.0 parts, 14.4 parts, 10.7 parts, 7.4 parts and 3.8 parts, respectively. . And it was set as the aqueous pigment dispersion and ink of Comparative Examples 17-18, Examples 7-9, and Comparative Example 19 in order of this manufacturing condition. The ratio B / A between the solubility parameter (A) of the pigment and the solubility parameter (B) of the aqueous medium containing tetrahydrofuran in these production examples is shown in Table 1, respectively.

<Comparative Example 20>
An aqueous pigment dispersion and an ink were prepared under the same production conditions as in Comparative Example 1 except that 2 parts of cyan copper phthalocyanine pigment (P-5) (manufactured by Toyo Ink) (SP value = 19.5) was used as the pigment. . This was designated as Comparative Example 20.

  In the production example of the pigment dispersion described above, the ratio of the solubility parameter (A) of the pigment and the solubility parameter (B) of the aqueous medium containing tetrahydrofuran is B / A≈0.66.

<Comparative Examples 21-24, Examples 10-11>
In Comparative Example 20, an aqueous pigment dispersion and an ink were prepared under the same production conditions as in Comparative Example 20, except that the amount of tetrahydrofuran used when co-dissolving the dispersion resin (triblock copolymer) and the pigment was changed. The amount of tetrahydrofuran in the production of the pigment dispersion was changed to 37.1 parts, 31.0 parts, 14.4 parts, 10.7 parts, 7.4 parts and 3.8 parts, respectively. And it was set as the aqueous pigment dispersion and ink of Comparative Examples 21-24 and Examples 10-11 in order of this manufacturing condition. The ratio B / A between the solubility parameter (A) of the pigment and the solubility parameter (B) of the aqueous medium containing tetrahydrofuran in these production examples is shown in Table 1, respectively.

<Comparative Example 25>
An aqueous pigment dispersion and an ink were prepared under the same production conditions as in Comparative Example 1 except that 2 parts of cyan copper phthalocyanine pigment (manufactured by Toyo Ink) (P-6) (SP value = 19.8) was used as the pigment. This was designated as Comparative Example 25.

  In the production example of the pigment dispersion described above, the ratio between the solubility parameter (A) of the pigment and the solubility parameter (B) of the aqueous medium containing tetrahydrofuran is B / A≈0.65.

<Comparative Examples 26-31>
In Comparative Example 25, an aqueous pigment dispersion and an ink were prepared under the same conditions as in Comparative Example 25 except that the amount of tetrahydrofuran used when the dispersion resin (triblock copolymer) and the pigment were co-dissolved was changed. The amount of tetrahydrofuran in the production of the pigment dispersion was changed to 37.1 parts, 31.0 parts, 14.4 parts, 10.7 parts, 7.4 parts and 3.8 parts, respectively. And it was set as the aqueous pigment dispersion and ink of Comparative Examples 26-31 in order of this manufacturing condition. The ratio B / A between the solubility parameter (A) of the pigment and the solubility parameter (B) of the aqueous medium containing tetrahydrofuran in these production examples is shown in Table 1, respectively.

  Table 1 shows the production conditions of the pigment dispersions of Comparative Examples 1 to 31 and Examples 1 to 11 described above, the type of pigment used, the amount of tetrahydrofuran, and the SP value of the aqueous solvent used for the production of the pigment dispersion / The SP value (B / A) of the pigment is shown. The lower part of Table 1 is the B / A value in each production example.

<Evaluation>
Using the inks obtained above, the following items were evaluated by the following methods and criteria. The evaluation results are shown in Table 2 and Table 3, respectively.

(1) Discharge stability Using a Canon inkjet recording head evaluation apparatus CANVAS and a Canon printer BJF900 print head, the ejection speed variation of each ink was determined under the same conditions as the head drive conditions for printing with a printer. The evaluation results are shown in Table 2.
A: Less than 1 m / s.
○: 1 m / s or more and less than 3 m / s.
X: 3 m / s or more.

(2) Transparency A solid part was printed on a Canon OHP film (CF-102) using the above-described apparatus and each ink, and the transparency of each image was evaluated. The evaluation was performed according to the following criteria by a sensory test by five people. The evaluation results are shown in Table 3.
A: Very high.
○: High.
X: Inferior.

It is a longitudinal cross-sectional view which shows an example of the head of an inkjet recording device. It is a cross-sectional view showing an example of the head of the ink jet recording apparatus. FIG. 2 is an external perspective view of a head in which the head shown in FIG. It is a schematic perspective view which shows an example of an inkjet recording device. It is a longitudinal cross-sectional view which shows an example of an ink cartridge. It is a perspective view which shows an example of a recording unit. It is a schematic sectional drawing which shows another structural example of an inkjet recording head.

Explanation of symbols

13: head 14: ink nozzle 15: heating element substrate 16: protective layer 17-1, 17-2: electrode 18: heating resistor layer 19: heat storage layer 20: substrate 21: ink 22: discharge orifice (micropore)
23: Meniscus 24: Ink droplet 25: Recording material 26: Multi-nozzle 27: Glass plate 28: Heat generating head 40: Ink bag 42: Plug 44: Ink absorber 45: Ink cartridge 51: Paper feed unit 52: Paper feed Roller 53: Paper discharge roller 61: Blade 62: Cap 63: Ink absorber 64: Discharge recovery unit 65: Recording head 66: Carriage 67: Guide shaft 68: Motor 69: Belt 70: Recording unit 71: Head unit 72: Air Communication port 80: Ink channel 81: Orifice plate 82: Vibration plate 83: Piezoelectric element 84: Substrate 85: Ejection port

Claims (5)

  Contains a microcapsule pigment formed by coating the surface of the pigment with the dispersion resin by mixing and stirring at least an aqueous medium containing the pigment, the dispersion resin, and the water-soluble organic solvent, and then removing the water-soluble organic solvent. In the method for producing an aqueous pigment dispersion for inkjet recording to obtain an aqueous pigment dispersion, the relationship between the solubility parameter (A) of the pigment and the solubility parameter (B) of the aqueous medium as the pigment and the aqueous medium is as follows. Use is made of a pigment having a solubility parameter (A) in the range of 0.95 ≦ B / A ≦ 1.17 and in the range of 13.5 ≦ A ≦ 19.5. A method for producing an aqueous pigment dispersion for inkjet recording.   The method for producing an aqueous pigment dispersion for ink-jet recording according to claim 1, wherein the content of the dispersion resin in the aqueous pigment dispersion for ink-jet recording is 20% or more with respect to the content of the pigment on a mass basis. .   The method for producing an aqueous pigment dispersion for ink jet recording according to claim 1 or 2, wherein the dispersion resin is an amphiphilic block copolymer.   An aqueous pigment dispersion for inkjet recording, which is produced by the production method according to any one of claims 1 to 3. An aqueous inkjet recording ink comprising at least the aqueous pigment dispersion for inkjet recording according to claim 4.

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