JP4081693B2 - Water-based ink for ink jet recording and method for producing the same - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a water-based ink for ink-jet recording, and particularly relates to a water-based ink for ink-jet recording in which a self-water dispersible resin containing a colorant is dispersed in an aqueous medium.
[0002]
[Prior art]
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.
[0003]
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. .
[0004]
Various so-called water-based pigment inks have been proposed in the past in order to improve the above-mentioned drawbacks. For example, a resin-dissolved ink in which carbon black or an organic pigment is 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.
[0005]
The resin-dissolved water-based ink is likely to cause abnormal ejection due to an increase in ink viscosity in the vicinity of the nozzle and the worst nozzle clogging as the ink moisture evaporates. Moreover, since water-soluble resin is used, it cannot be said that water resistance is sufficient.
[0006]
Resin-dispersed water-based inks have the advantage that the increase in viscosity due to water evaporation of the ink is relatively small, and the water resistance is excellent. Specifically, in JP-A-58-45272, an ink composition containing a urethane polymer latex containing a dye, in JP-A-62-95366, a polymer and an oily dye are dissolved in a water-insoluble organic solvent. Further, an ink containing a dye encapsulated in polymer particles by evaporating the solvent after mixing with an aqueous solution containing a surfactant and emulsifying is proposed. Japanese Patent Application Laid-Open No. Sho 62-254833 discloses an organic solvent at the time of encapsulation. A method for producing a colorant aqueous suspension by reducing the interfacial tension between water and water to 10 dynes or less has been proposed. JP-A-1-170672 also discloses a recording liquid containing a macroencapsulated dye. However, the dispersion stability of the colored resin dispersions obtained from them is not always sufficient, and foaming is caused by the influence of the surfactant used during encapsulation. Hear, jetting characteristics of the ink jet it is not necessarily sufficient. Japanese Patent Application Laid-Open No. 3-221137 discloses a method of forming a microcapsule using a self-dispersing resin that self-disperses to a level of 0.1 μm or less as a general microcapsule, a manufacturing method thereof, and a use thereof. Although proposed, it is limited to a resin that self-disperses to a level of 0.1 μm or less, so that there are few resins that can be used, and the inkjet characteristics of the resulting microcapsules are not always sufficient.
[0007]
[Problems to be solved by the invention]
The problem to be solved by the present invention is to achieve stable ink jet ejection without sacrificing the features of a resin-dispersed water-based ink excellent in print quality, water resistance and light resistance, excellent dispersion stability, and nozzle clogging. An object of the present invention is to provide a water-based ink for ink-jet recording in which colored resin particles having a colorant encapsulated by a self-water dispersible resin are dispersed in an aqueous medium.
[0008]
[Means for Solving the Problems]
As a result of intensive studies in order to solve the above problems, the present inventors have come to solve the present invention.
[0009]
That is, the present invention relates to a self-water dispersible resin (A) obtained by neutralizing at least a part of acid groups of a synthetic resin (a) having an acid value of 50 or more and 280 or less with a base (b), preferably an alcohol amine. The colored resin particles in which the colorant (B) is encapsulated are dispersed in an aqueous medium (C) containing water as an essential component, preferably an aqueous medium containing a water-soluble organic solvent as a drying inhibitor. A water-based ink for ink-jet recording is provided.
[0010]
In the present invention, the organic solvent solution of the self-water dispersible resin (A) in which at least a part of the acid groups of the synthetic resin (a) having an acid value of 50 to 280 is neutralized with the base (b) is colored. The colored resin solution in which the colorant (B) is dispersed or dissolved and the aqueous medium (C) containing water as an essential component are mixed to perform phase inversion emulsification, and the colorant (B) is encapsulated in the resin (A). A method for producing a water-based ink for ink-jet recording, comprising dispersing the colored resin particles in an aqueous medium (C) and then removing the organic solvent from the obtained aqueous dispersion.
[0011]
The water-based ink for inkjet recording of the present invention is obtained by dispersing colored microcapsules composed of colored resin particles in which a colorant (B) is encapsulated with a water-dispersible resin (A) in an aqueous medium containing water as an essential component. is there.
[0012]
The water-dispersible resin (A) is a synthetic resin (a) having an acid value of 50 or more and 280 or less, and at least some of the acid groups are neutralized by a base (b), that is, an alkaline neutralizing agent. Is.
[0013]
When the acid value of the synthetic resin (a) is less than 50, the water dispersion stability of the obtained colorant particles is not sufficient, and when the acid value exceeds 280, the water dispersible resin dissolved in the organic solvent. The water-dispersible resin acid for ink-jet recording is prone to agglomeration during neutralization with a base of the resin and clogging of nozzles due to dissolution of some resin when added to water. The value is in the range of 50 to 280, preferably in the range of 70 to 250.
[0014]
The acid group of the synthetic resin (a) is, for example, a carboxylic acid group, a sulfonic acid group, a sulfinic acid group, and the like, and is not particularly limited. Of these, a carboxyl group is common and good self-water Give dispersible resin.
[0015]
Further, even if the glass transition temperature of this synthetic resin (a) is less than 50 ° C., the fixability of characters after printing on the recording paper is good, but the nozzle clogging and storage stability are further improved. In consideration, a glass transition temperature of preferably 50 ° C. or higher, more preferably 60 ° C. or higher is suitable for inkjet recording.
[0016]
As such a synthetic resin (a), any resin may be used as long as it satisfies the above-mentioned characteristics. Substituted styrene such as styrene or α-methylstyrene, methyl acrylate, ethyl acrylate, butyl acrylate At least one monomer unit selected from acrylic acid esters such as 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, and 2-ethylhexyl methacrylate; A copolymer containing at least one monomer unit selected from acrylic acid and methacrylic acid is preferable, and a styrene monomer, an acrylic acid monomer, and a methacrylic acid mono monomer are more preferable as essential monomer components of the self-water dispersible resin (A). In particular, when the constituent ratio of these essential monomer components is 60 to 90 mol% of styrene monomer, 5 to 15 mol% of acrylic acid monomer, and 5 to 25 mol% of methacrylic acid monomer. Enables excellent colored resin particles without nozzle clogging for inkjet recording.
[0017]
The molecular weight range of the resin (a) is not particularly limited, but a molecular weight of 1000 or more and 100,000 or less is more preferable. Of course, the self-water dispersible resin obtained from such a resin is not particularly limited as long as it forms stable colored resin particles in combination with an aqueous medium. May be used.
[0018]
The acid group of the synthetic resin (a) described above is neutralized with the base (b), that is, neutralization with an alkaline neutralizing agent needs to be neutralized to the extent that the water-dispersible resin does not dissolve in water, and does not dissolve. An alkaline neutralizing agent may be added in excess, but it is preferable to neutralize 60 mol% or more of the acid groups of the synthetic resin (a). When the neutralization rate is 60 mol% or more, the resulting colored resin particles are fine and excellent in dispersion stability.
[0019]
The amount of the self-water dispersible resin (A) used is not particularly defined as long as the effect of the present invention is achieved, but is preferably such an amount as 0.5 to 20% by weight in the finally obtained water-based ink.
[0020]
Examples of the base (b) (alkaline neutralizing agent) include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide and lithium hydroxide, basic substances such as ammonia, triethylamine and morpholine, and triethanolamine. Alcoholamines such as diethanolamine and N-methyldiethanolamine can be used, and alcoholamine is particularly preferable. When the alcohol amine is used, an ink for ink jet recording having excellent dispersion stability of the colored resin particles (B) and improved nozzle clogging due to particle aggregation due to evaporation of moisture and organic solvent can be obtained.
[0021]
As a method for adding and neutralizing the base (b) according to the synthetic resin (a) having an acid group used in the present invention, it is added in advance to an organic solvent solution of the resin or an organic solvent solution of the resin There is a method of adding to the aqueous medium when mixing the aqueous medium and the aqueous medium, but the best conditions may be selected for its use.
[0022]
The colorant in the present invention includes inorganic pigments such as carbon black, 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. In addition, oil-based dyes such as monoazo, disazo, metal complex, anthraquinone, triallylmethane, and the like, and dyes such as disperse dyes are used, but are not limited thereto. When these colorants are added, they may be used as they are or in the form of solutions or dispersions. These colorants are present in the form of being dispersed or dissolved in the resin forming the microcapsules. The amount of the colorant to be used is not particularly defined as long as the effect of the present invention is achieved, but is preferably such an amount that it is 0.5 to 20% by weight in the finally obtained water-based ink.
[0023]
As the self-water dispersible resin of the present invention, it is not necessary to use self-water dispersible resins having a dispersibility capable of self-dispersing to a level of 0.1 μm or less as disclosed in JP-A-3-221137. . Further, in order to form a microcapsule, the water-based ink of the present invention does not necessarily require the use of a surfactant.
[0024]
In the present invention, the colorant is preferably dispersed or dissolved in advance in an organic solvent solution containing a self-water dispersible resin before being dispersed in an aqueous medium. That is, in the presence of an organic solvent, the synthetic resin (a), the base (b), and the colorant (B) are mixed well using a stirrer or a dispersing device, and the colorant is dissolved or dispersed and the synthetic resin is dispersed in water by itself. Then, the droplets of the self-water dispersible resin solution containing the colorant are dispersed in the aqueous medium by mixing the colored resin solution and the aqueous medium.
[0025]
As a preferable production method in the present invention, a coloring agent is dispersed or dissolved in an organic solvent solution containing a synthetic resin (a) generally called a mill base, and a base is further mixed and dissolved in the colored mill base. It is preferable to add to a self-dispersing resin (first stage) and then to mix and emulsify with an aqueous medium containing water as an essential component by dropping or the like, that is, to perform phase inversion emulsification (second stage). In this case, a colored solution containing a self-water dispersible resin may be added to an aqueous medium containing water as an essential component, but conversely, it is more uniform to add an aqueous medium to a colored solution containing the resin. It is preferable at the point from which the aqueous dispersion of this is obtained. If necessary, it can also be obtained by forcibly emulsifying with a surfactant. However, it is preferred not to use surfactants and protective colloids because they tend to reduce the physical properties of the final particles. According to the phase inversion emulsification method, the colorant (B) is encapsulated in the resin (A), and the integrated particles are preferably dispersed in the aqueous medium.
[0026]
Examples of the organic solvent used for dissolving the resin include ketone solvents such as acetone, dimethyl ketone, and methyl ethyl ketone, alcohol solvents such as methanol, ethanol, and isopropyl alcohol, chlorine solvents such as chloroform and methylene chloride, benzene, Aromatic solvents such as toluene, ester solvents such as ethyl acetate, glycol ether solvents such as ethylene glycol monomethyl ether and ethylene glycol dimethyl ether, amides and other resins can be used. When the component is an acrylic resin, at least one combination selected from a ketone solvent and an alcohol solvent is preferable. The amount of the organic solvent used is not particularly defined as long as the effect of the present invention is achieved, but is preferably such that the weight ratio of the synthetic resin / the organic solvent is 1/1 to 1/20.
[0027]
In the synthetic resin solution, as necessary, a dispersant, a plasticizer, an antioxidant, an ultraviolet absorber and the like may be used together with a solvent, a resin, and a colorant as additives.
Since water used in the aqueous medium mixed with the colored resin solution is mainly used as jet ink, water of a grade higher than ion exchange water is preferable in order to avoid nozzle clogging. In order to prevent the ink for inkjet recording from drying, it is preferable that a water-soluble organic solvent is present in the ink as an anti-drying agent. The anti-drying agent may be added to the aqueous medium at the time of phase inversion emulsification or after emulsification. As such an anti-drying agent, it 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, conventionally known polyhydric alcohols such as ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, glycerin or their alkyl ethers, N-methyl- There are pyrrolidones such as 2-pyrrolidone and 2-pyrrolidone, amides, dimethyl sulfoxide, imidazolidinone, and the like, but are not limited to these. In particular, in the present invention, glycerin is the main drying inhibitor. Shows the most excellent anti-drying effect. The amount of the anti-drying agent varies depending on the type, but usually it is appropriately selected from the range of 1 to 150 parts by weight with respect to 100 parts by weight of water, but a combination of glycerin and other anti-drying agents is used. In this case, 10 to 50 parts by weight is preferable.
[0028]
In addition, a water-soluble organic solvent having a permeability imparting effect is added as a permeability imparting agent to the above-mentioned aqueous medium in which water is essential in order to allow the ink attached by jetting to the paper to permeate the paper better. May be. As such a permeability imparting agent, lower alcohols such as ethanol and isopropyl alcohol, glycol ethers such as diethylene glycol-N-butyl ether, and the like can be used, but are not limited thereto. The amount of the penetrability imparting agent is not particularly defined as long as the effect of the present invention is achieved, but is preferably such an amount that it becomes 0.1 to 10% by weight in the finally obtained water-based ink.
[0029]
If necessary, the water-based ink of the present invention may contain additives such as a water-soluble resin, a pH adjuster, a surfactant for dispersing / defoaming / penetrating paper, a preservative, and a chelating agent. . These additives may be added to the aqueous medium in advance, or may be added when the self-water dispersible resin solution containing the colorant is mixed with the aqueous medium, or may be added after mixing them. However, it is preferable to avoid adding additives after the final filtration.
[0030]
As described above, the water-based ink for inkjet recording in the present invention is preferably obtained by a phase inversion emulsification method. That is, as a first step, a colored mill base is prepared in which a colorant is dispersed or dissolved in a solution containing a synthetic resin (a) neutralized with a base (b). As the second stage, an encapsulation process is carried out to obtain water-dispersible resin particles encapsulating the colorant by mixing the colored mill base obtained in the first stage with an excess amount of an aqueous medium. In the production of the water-based ink, as a third step, a desolvation step for removing the organic solvent used in the first step of the mill base step is added in order to enhance the dispersion stability of the capsule particles in the water-based ink for inkjet recording. Is preferred. If necessary in this desolvation step, water may be removed. Of course, this third step may be omitted in some cases. In addition, it is preferable to perform the process of removing a large particle size by filter filtration, centrifugation, etc. after the process of a 2nd or 3rd step is complete | finished.
[0031]
【Example】
Next, the present invention will be described more specifically with reference to examples and comparative examples. In the following examples, “part” represents “part by weight”.
(Millbase example 1)
Carbon black 20 parts Styrene acrylic acid resin 20 parts (styrene / methyl methacrylate / butyl acrylate / acrylic acid / 2-ethylhexyl acrylate = 60/20/10/7/3; molecular weight 20,000 / acid value 55 / (Glass transition temperature 68 ° C)
Methyl ethyl ketone 60 parts Glass beads 150 parts of the mixture was kneaded in a paint shaker for 4 hours,
Methyl ethyl ketone 30 parts Isopropyl alcohol 40 parts were added and the contents were taken out to obtain 170 parts of a mill base solution.
(Millbase example 2)
Carbon black 20 parts Styrene acrylic acid resin 20 parts (styrene / methyl methacrylate / methacrylic acid / 2-ethylhexyl acrylate = 59/15/15/11; molecular weight 40,000, acid value 100, glass transition temperature 60 ℃)
Methyl ethyl ketone 60 parts Glass beads 150 parts of the mixture was kneaded in a paint shaker for 4 hours,
Methyl ethyl ketone 30 parts Isopropyl alcohol 40 parts were added and the contents were taken out to obtain 170 parts of a mill base solution.
(Millbase example 3)
Carbon black 20 parts Styrene acrylic acid resin 20 parts (styrene / acrylic acid / methacrylic acid = 65/10/25; molecular weight 45,000 / acid value 241 / glass transition temperature 116 ° C.)
Methyl ethyl ketone 50 parts Glass beads 150 parts of the mixture were kneaded in a paint shaker for 4 hours,
40 parts of methyl ethyl ketone and 40 parts of isopropyl alcohol were added and the contents were taken out to obtain 170 parts of a mill base solution.
Example 1
While stirring and adding 2.1 parts of N-methyl-diethanolamine (equivalent to 90% resin neutralization) to 170 parts of the mill base of Example 1, 5 ml of a mixed solution of 200 parts of glycerin and 600 parts of ion-exchanged water is used per minute. Was added dropwise at a rate of 1 to obtain colored microcapsules. Methyl ethyl ketone and isopropyl alcohol were distilled off from the obtained capsule liquid using a rotary evaporator to obtain a final colored microcapsule aqueous dispersion. This aqueous dispersion was filtered using a 3 μm filter to obtain an aqueous ink for inkjet recording.
[0032]
The microcapsules in the obtained water-based ink had an average particle size of 0.23 μm, showed stable dispersion over a long period without aggregates, and printing using an inkjet printer was stable and obtained. The printed matter was free from bleeding and excellent in water and light resistance.
[0033]
As a result of adding N-methyldiethanolamine to the resin solution excluding carbon black from Millbase Example 1 corresponding to a neutralization rate of 100% and dropping water in the same manner to obtain a resin self-dispersed emulsion, the average particle size of the dispersion The diameter was 0.51 μm.
(Example 2)
While adding 2.9 parts of N-methyl-diethanolamine (equivalent to a resin neutralization rate of 68%) to 170 parts of the mill base of Example 2 and stirring, 5 ml of a mixed solution of 200 parts of glycerin and 600 parts of ion-exchanged water per minute is used. Was added dropwise at a rate of 1 to obtain colored microcapsules. Methyl ethyl ketone and isopropyl alcohol were distilled off from the obtained capsule liquid using a rotary evaporator to obtain a final colored microcapsule aqueous dispersion. 200 parts of glycerin was added to the obtained microcapsule aqueous dispersion, and after stirring, the mixture was filtered using a 3 μm filter to obtain an aqueous ink for inkjet recording.
[0034]
The microcapsules in the obtained water-based ink had an average particle diameter of 0.21 μm, showed stable dispersion over a long period without aggregates, and printing using an inkjet printer was stable and obtained. The printed matter was free from bleeding and excellent in water and light resistance.
[0035]
As a result of adding N-methyldiethanolamine to the resin solution excluding carbon black from Millbase Example 2 corresponding to a neutralization rate of 100% and adding water in the same manner to obtain a resin self-dispersed emulsion, the average particle size of the dispersion The diameter was 0.52 μm.
(Example 3)
Add 11.7 parts of triethanolamine (equivalent to 100% resin neutralization) to 170 parts of the mill base of Example 3 and stir a mixture of 80 parts of glycerin and 300 parts of ion-exchanged water at a rate of 5 ml per minute. The solution was added dropwise to obtain a colored microcapsule precursor solution (aggregated dispersion). The obtained capsule precursor solution is dispersed for 1 hour using a paint shaker using glass beads as a dispersion medium, and then a liquid mixture of 80 parts of glycerin and 300 parts of ion-exchanged water is dropped at a rate of 5 ml / min to obtain a capsule liquid. It was. Methyl ethyl ketone and isopropyl alcohol were distilled off from the obtained capsule liquid using a rotary evaporator to obtain a final colored microcapsule aqueous dispersion, followed by filtration using a 1.2 μm filter, and a water-based ink for inkjet recording. did.
[0036]
The microcapsules in the obtained aqueous ink had an average particle diameter of 0.10 μm, showed stable dispersion over a long period without agglomerates, and printing using an inkjet printer was stable and obtained. The printed matter was free from bleeding and excellent in water and light resistance.
[0037]
(Comparative Example 1)
60 parts of glycerin was added to the microcapsule aqueous dispersion of Example 6 (triethylamine neutralization rate 48.5%) using resin A-3 (acid value: equivalent to solid content 40) of JP-A-3-221137, After stirring, the mixture was filtered using a 3 μm filter to obtain an inkjet recording ink. The microcapsules in the obtained water-based ink have an average particle size of 0.7 μm, and there are visible aggregates on the bottom of the container during long-term storage, and printing using an inkjet printer is not possible. It was stable.
[0038]
(Comparative Example 2)
Mill base 170 parts of this mill base using a styrene acrylic resin having an acid value of 310 and a glass transition temperature of 119 ° C. instead of the resin of mill base example 3 using styrene monomer / acrylic acid monomer / methacrylic acid monomer = 55/15/30; In the same manner as in Example 3 in which 16.5 parts of triethanolamine (corresponding to a neutralization ratio of the resin of 100%) was added to the mixture, aggregation occurred in the middle of the process, and the particle size was stabilized. Microcapsules were not obtained.
[0039]
【The invention's effect】
The water-based ink for ink-jet recording of the present invention is a stable ink-jet ejection that does not kill the features of the resin-dispersed water-based ink excellent in print quality, water resistance, and light resistance, has excellent dispersion stability, and does not clog nozzles. Enable the characteristics.

Claims (7)

Coloring in which the colorant (B) is encapsulated by the self-water dispersible resin (A) obtained by neutralizing at least some of the acid groups of the synthetic resin (a) having an acid value of 50 or more and 280 or less with the base (b) Resin particles are dispersed in an aqueous medium containing water as an essential component, the essential monomer component of the synthetic resin (a) is a styrene monomer, an acrylic acid monomer, a methacrylic acid monomer, and the synthetic resin ( A water-based ink for ink jet recording , wherein the glass transition temperature of a) is 50 ° C. or higher . The self-water-dispersible resin (A) is a self-water-dispersible resin (A) in which 60 mol% or more of the acid groups of the synthetic resin (a) are neutralized with a base (b). Water-based ink for inkjet recording. 3. The inkjet according to claim 1, wherein the synthetic resin (a) has an essential monomer component composition ratio of 60 to 90 mol% of a styrene monomer, 5 to 15 mol% of an acrylic acid monomer, and 5 to 25 mol% of a methacrylic acid monomer. Water-based ink for recording. The water-based ink for ink jet recording according to claim 1, wherein the base (b) is an alcohol amine. The water-based ink for inkjet recording according to claim 1, further comprising a water-soluble organic solvent as a drying inhibitor. The water-based ink for inkjet recording according to claim 5, wherein the water-soluble organic solvent as the drying inhibitor is glycerin. A colorant (B) is dispersed in an organic solvent solution of a self-water dispersible resin (A) in which at least a part of acid groups of a synthetic resin (a) having an acid value of 50 or more and 280 or less is neutralized with a base (b). Alternatively, the dissolved colored resin solution and the aqueous medium (C) containing water as an essential component are mixed to perform phase inversion emulsification, and the colored resin particles containing the colorant (B) in the resin (A) are aqueous. A step of dispersing in the medium (C) and then removing the organic solvent from the obtained aqueous dispersion, and the essential monomer components of the synthetic resin (a) are styrene monomer, acrylic acid monomer, A method for producing a water-based ink for inkjet recording, which is an acrylic acid monomer, and the synthetic resin (a) has a glass transition temperature of 50 ° C or higher.