JP4411824B2 - Aqueous pigment dispersion and method for producing ink composition using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an aqueous pigment dispersion and a method for producing an ink composition using the same, and is particularly suitable for inkjet recording.
[0002]
[Prior art]
The aqueous pigment dispersion is obtained by dispersing a pigment in a liquid medium containing water as a main component, and can be obtained by various production methods. For example, all the components of the dispersion composition are mixed together and dispersed with a disperser, the amount of liquid components in the components is reduced, the solid concentration is increased, and the remaining liquid components are added after dispersing with a disperser A method of adding a slight amount of a liquid component to a solid component such as pigment or resin in a constituent component to obtain a solid or semi-solid kneaded material, and then dissolving the kneaded material in a liquid medium to obtain a pigment dispersion, etc. Is mentioned.
[0003]
Among them, the method of preparing a solid or semi-solid kneaded material and dissolving the solid in a liquid medium to obtain a pigment dispersion can cause a higher share to act on the pigment particles than the method of dispersing the liquid dispersion. Therefore, the pigment can be made fine and coarse particles can be reduced, which is an effective production method.
[0004]
Japanese Patent Application Laid-Open No. 6-157954 discloses an adjustment method in which a pigment and a polymer dispersant are obtained by a 2-roll milling apparatus and then dispersed in an aqueous carrier medium to obtain a pigment dispersion. According to the embodiment, the pigment dispersion is obtained by mixing a dispersion of a pigment, a polymer dispersant, potassium hydroxide as a neutralizer, and water.
[0005]
However, in the above production method, pre-kneading with a 2-roll milling device allows the pigment to be finer than the non-kneaded one and the dispersibility in the aqueous carrier medium can be improved. There has been a problem that pigment aggregates generated when the body is dispersed in an aqueous carrier medium cannot be completely prevented.
[0006]
In JP-A-10-88042, a film-forming resin having an acid value and a colorant are dispersed to obtain a solid coloring compound, and then water, an organic solvent for dissolving the film-forming resin, a base and a solid coloring compound are mixed. A manufacturing method for obtaining a pigment dispersion comprising a reprecipitation step of obtaining a colorant suspension and depositing a dissolved resin component on the colorant surface in the colorant suspension is disclosed. It is also disclosed that it is preferable to use a beadless dispersion apparatus in the step of obtaining a colored suspension.
[0007]
However, in the production method, an organic solvent that dissolves the film-forming resin is an essential component, and in order to maintain the dispersion stability of the colored resin particle aqueous dispersion, a step of removing the organic solvent is required. A method of distillation under reduced pressure is generally used to remove the organic solvent, but there is a problem that the energy cost required for distillation is high. Further, in the reprecipitation step, it is necessary to add a certain amount or more of water, and there has been a problem that when obtaining a high-concentration colored resin particle aqueous dispersion, water must be removed and concentrated by some method.
[0008]
A 2-roll mill (two rolls) of a kneading apparatus which is commonly preferred in JP-A-6-155794 and JP-A-10-88042 is an open-type kneading apparatus, and a kneaded product during kneading Therefore, evaporation of volatile components is inevitable. In addition, since the kneading by the 2-roll mill (two rolls) is a method in which the kneaded product is passed between the two rolls, the kneaded product must be in a form suitable for kneading in advance. For example, it is not suitable for kneading a slurry-like kneaded material having a low viscosity.
[0009]
For this reason, although the optimum range varies depending on the type of pigment and resin used, there are cases where certain restrictions are imposed on the composition of the kneaded product, such as the pigment / resin ratio, the molecular weight of the resin, and the amount of solvent or plasticizer used as an additive. Is almost. Above all, receiving restrictions on the pigment / resin ratio and resin molecular weight, which will determine the basic characteristics of the aqueous pigment dispersion, impedes the degree of freedom in designing the resulting aqueous pigment dispersion. It is not preferable.
[0010]
In JP-A-6-155794, a dispersion of a pigment and a polymer dispersant is mixed in an aqueous solution of potassium hydroxide as a neutralizing agent. In JP-A-10-88042, water, a film-forming resin is used. A solid coloring compound is mixed in a mixed solvent of an organic solvent and a base to be dissolved. In any of the production methods, the resin in the kneaded product is neutralized with a base and dispersed in a solvent, and the base in the solvent is consumed as the kneaded product is dissolved and dispersed. Further, since only the surface portion of the kneaded product comes into contact with the base, the opportunity for contact with the base is reduced in the central portion of the kneaded product, compared to the surface portion of the kneaded product at the start of mixing. For this reason, the surface state of each dispersed particle tends to be non-uniform.
[0011]
[Problems to be solved by the invention]
The present invention has been made to solve the above problems, and provides an aqueous pigment dispersion excellent in pigment dispersion stability and long-term storage stability, and a production method capable of obtaining an ink composition using the same. The task is to do.
[0012]
[Means for Solving the Problems]
In order to obtain an aqueous pigment dispersion excellent in pigment dispersion stability and long-term storage stability and an ink composition using the same, the inventors further blend a basic compound with a mixture containing a resin and a pigment. After producing a kneaded product by kneading with high viscosity, it was found that the problem can be solved by a production method using a collision type disperser when the kneaded product is dispersed in an aqueous solvent.
[0013]
That is, in order to solve the above problems, the inventors kneaded a mixture containing a resin having an anionic group, a pigment, and a basic compound to obtain a kneaded product for a solid or semi-solid aqueous pigment dispersion. Then, the manufacturing method of the aqueous pigment dispersion characterized by disperse | distributing the said kneaded material for aqueous pigment dispersions in an aqueous solvent using a collision-type disperser is provided.
[0014]
The inventors also provide a method for producing an ink composition comprising a step of diluting an aqueous pigment dispersion obtained by the method for producing an aqueous pigment dispersion with an aqueous solvent to obtain an ink composition.
In the present specification, the raw material mixture before kneading in the production process of the aqueous pigment dispersion kneaded product is referred to as a mixture, and the raw material mixture during or after kneading is referred to as a kneaded product.
[0015]
In the prior art, a kneaded product is made from a resin and a pigment, and then the kneaded product is dissolved and dispersed in an aqueous solvent containing a basic compound. As the process proceeds, the basic compound in the solvent is consumed, so that the pigment particles dissolved and dispersed from the surface of the kneaded product in the initial stage of dispersion, and the pigment particles located in the central part of the kneaded product and dissolved and dispersed in the final stage of dispersion. Then, the contact opportunity with the base in an aqueous solvent differs. For this reason, in the method of neutralizing the resin when the kneaded material is dissolved and dispersed in an aqueous solvent, the surface state of the individual dispersed particles tends to be non-uniform. The uneven surface of the dispersed particles becomes a factor that inhibits the dispersion stability of the aqueous pigment dispersion.
[0016]
In the production method of the present invention, since the resin and pigment having an anionic group are kneaded in the presence of a basic compound, a kneaded product with the pigment is produced while neutralizing the anionic group of the resin with the basic compound. For this reason, the neutralized state of the resin is made uniform during kneading. Compared to the case where no basic compound is present, the dispersibility and solubility of the resin are improved, and the resin is partially dissolved or swollen and kneaded with the pigment. This promotes resin adsorption on the pigment surface.
[0017]
Further, the kneaded product in which the resin is neutralized during the kneading process can be dissolved and dispersed in an aqueous solvent without the presence of a basic compound. For this reason, the surface state of the dispersed particles is made uniform, and an aqueous pigment dispersion and ink composition excellent in dispersion stability can be obtained.
[0018]
A kneaded product containing a resin having an anionic group, a pigment, and a basic compound is dissolved and dispersed by mixing and stirring with an aqueous solvent. The pigment particle size in the aqueous pigment dispersion just mixed and stirred is sufficiently fine, but some coarse particles that are insufficiently micronized are also included. It is insufficient. In order to ensure sufficient dispersion stability, an aqueous pigment dispersion having good dispersion stability can be obtained by dissolving and dispersing the kneaded material in an aqueous solvent and then using a collision type disperser.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
[0020]
(Resin having an anionic group)
The resin having an anionic group is obtained by polymerizing a monomer containing a monomer having at least one kind of anionic group, and the monomer containing an anionic group functions as a hydrophilic group. In addition, it is preferable that the other monomer used for superposition | polymerization contains the hydrophobic monomer which has a hydrophobic group. As the resin having an anionic group, it is preferable to use a resin in which a monomer component having a hydrophilic group composed of an anionic group and a monomer component having a hydrophobic group coexist.
[0021]
Such resins include styrene resins, acrylic resins, maleic resins, polyvinyl acetate resins, polyvinyl sulfonate resins, polyester resins, polyurethane resins, polyamide resins, polyvinyl alcohol resins. Examples thereof include resins, polypyrrolidone resins, and cellulose resins.
[0022]
(Monomer having an anionic group)
Examples of the monomer having an anionic group include monomers having a carboxylic acid, a sulfonic acid, and a phosphoric acid group. In particular, from the viewpoint of dispersion stability and long-term storage stability, a monomer having a carboxyl group is preferred, and examples thereof include (meth) acrylic acid and maleic anhydride.
[0023]
In the present invention, in view of dispersion stability and long-term storage stability, it is particularly preferable to use a (meth) acrylic acid-based monomer having a structure derived from (meth) acrylic acid.
[0024]
(Hydrophobic monomer having a hydrophobic group)
As a hydrophobic monomer having a hydrophobic group used in the resin,
(Meth) acrylic acid alkyl esters such as methyl (meth) acrylate and ethyl (meth) acrylate;
(Meth) acrylic acid allyl esters such as phenyl (meth) acrylate, benzyl (meth) acrylate, phenylethyl (meth) acrylate;
Sulfonic acid group-containing (meth) acrylic acid esters such as sulfoethyl (meth) acrylate and sulfopropyl (meth) acrylate;
Hydroxyl-containing (meth) acrylic acid esters such as hydroxyethyl (meth) acrylate and hydroxypropyl (meth) acrylate;
Styrene monomers such as styrene, α-methylstyrene, vinyltoluene;
Examples include acrylonitrile, acrylamide, vinyl acetate, vinyl chloride, vinyl pyrrolidone, vinyl alcohol, ethylene, and the like.
[0025]
Of these, styrene monomers, and more preferably styrene monomers are preferred.
These can be used alone or in combination of two or more.
In addition, (meth) acrylate shows an acrylate and / or methacrylate, (meth) acrylic acid shows acrylic acid and / or methacrylic acid.
[0026]
(Copolymer resin)
Further, from the viewpoints of dispersion stability and long-term storage stability, the resin having an anionic group is preferably a copolymer resin comprising a styrene monomer component which is a hydrophobic monomer component and a monomer component having an anionic group.
At this time, the monomer having an anionic group is preferably a hydrophilic monomer.
[0027]
In the copolymer resin comprising a styrene monomer component and a monomer component having an anionic group, the styrene monomer component is 50% by mass or more, preferably 70% by mass or more, preferably from the viewpoint of dispersion stability and long-term storage stability. It is preferably contained in an amount of 95% by mass or less.
[0028]
By setting the content of the styrene monomer component in the copolymer resin to 50% by mass or more, the hydrophobicity of the copolymer resin is increased, and the resin is more firmly coated with the pigment in the aqueous system. As a result, when the ink composition prepared through the aqueous pigment dispersion is used for inkjet, even if the resin-coated particles are heated, the particle size is stable, and the particle size stability is improved. In addition, the ejection stability is improved and a high print density is obtained. Further, it is effective for improving the durability of the coating film on the recording medium. If it exceeds 95% by mass, the content of the monomer component having an anionic group that contributes to dispersion is lowered, and there is a possibility that dispersion stability in water and long-term storage stability are lowered.
[0029]
In the present invention, the term “monomer” refers to a monomer before polymerization, and the term “monomer component” refers to a structure derived from a monomer contained in a resin.
[0030]
(Resin acid value)
From the viewpoint of long-term storage stability, the acid value of the resin is in the range of 60 to 300 mgKOH / g, preferably 100 to 180 mgKOH / g, more preferably 120 to 170 mgKOH / g. The acid value is the number of milligrams (mg) of potassium hydroxide (KOH) necessary to neutralize 1 g of resin, and is an amount expressed in mgKOH / g.
[0031]
If the acid value is less than 60, the hydrophilicity becomes small and the dispersion stability of the pigment may be lowered. On the other hand, if the acid value is greater than 300, pigment aggregation tends to occur, and the water resistance of a printed product using the ink composition may decrease.
[0032]
(Weight average molecular weight of resin having an anionic group)
The weight average molecular weight of the resin having an anionic group is 3000 to 50000, more preferably 4000 to 40000, and still more preferably 5000 to 30000. The reason why it is 3000 or more is that the lower the molecular weight, the better the initial dispersibility, but the long-term storage stability tends to decrease. If it exceeds 50,000, not only will the viscosity of the aqueous pigment dispersion increase, but also the dispersibility and solubility of the resin will tend to decrease.
[0033]
(Glass transition point of resin)
The glass transition point of the resin is 90 ° C. or higher, preferably 100 ° C. or higher, substantially 150 ° C. or lower.
[0034]
When the glass transition point is 90 ° C. or higher, the durability of the image formed by the ink composition is improved, and the thermal stability of the ink composition is improved. For this reason, even if the water-based ink composition for ink-jet recording prepared from the water-based pigment dispersion is used for thermal jet type ink-jet recording, it does not cause a characteristic change that causes ejection failure by heating, which is preferable. The glass transition point of the resin can be adjusted by changing the molecular weight.
[0035]
(Pigment)
Known pigments can be used without particular limitation. For example, inorganic pigments such as carbon black, titanium black, titanium white, zinc sulfide, and bengara; azo pigments such as monoazo and disazo, organic pigments such as phthalocyanine pigment, quinacridone pigment, and lake pigment;
[0036]
The pigment is blended in the mixture by 35% by mass or more, preferably 40% by mass or more. In general, in order to obtain an ink composition having a constant pigment concentration by diluting the aqueous pigment dispersion, it is necessary to increase the concentration in the aqueous pigment dispersion as much as possible because it is possible to produce more ink compositions. It will be advantageous. However, increasing the pigment concentration deteriorates the storage stability of the aqueous pigment dispersion, so that the dispersion stability of the pigment and the stability of the kneaded product for the aqueous pigment dispersion are practically 60 masses. % Or less is preferable, and more preferably 50% by mass or less.
[0037]
(Mass ratio of resin / pigment)
For kneading, a resin having a resin / pigment mass ratio of a certain amount or more is indispensable. The optimum amount of resin is an amount that can uniformly coat the surface of the pigment. If an excessive amount of resin exceeding this optimum amount is contained, the particles do not adhere to the surface of the pigment and are dispersed in the aqueous solvent. The resin present in the state or dissolved state increases, which is not preferable because the viscosity of the aqueous pigment dispersion increases or the dispersion stability is impaired. The amount capable of uniformly covering the pigment surface varies depending on the structure and surface activity of the pigment, and can be appropriately selected according to the individual pigment.
The resin / pigment mass ratio in the kneaded product for an aqueous pigment dispersion of the present invention is preferably 1/10 to 2/1, and more preferably 1/10 to 1/1.
[0038]
(Solid content ratio)
In general, when a pigment and a resin are kneaded, kneading is performed in the presence of an organic solvent or water that dissolves or swells the resin. The solid content ratio in the kneaded product is appropriately selected and determined according to the purpose of use of the kneaded product and the kneading apparatus to be used.
[0039]
Also in the present invention, kneading a mixture containing various organic solvents and water is preferable in order to obtain a kneaded product for an aqueous pigment dispersion having good pigment dispersion. The solid content ratio of the resin and the pigment in the mixture of the present invention is preferably in the range of 50 to 80% by mass as the solid content ratio. When the solid content ratio is less than 50% by mass, the viscosity of the kneaded product is reduced and the share for pulverizing the raw material is not sufficiently generated, and when the aqueous pigment dispersion or the ink composition is produced, the pigment is large. Aggregated particles may be mixed. And by increasing the solid content ratio, the viscosity of the kneaded product during kneading is kept moderately high, the share of the kneaded product from the kneading machine during kneading is increased, and the pulverization of the pigment in the kneaded product and the pigment resin The coating can proceed simultaneously. If the solid content ratio exceeds 80% by mass, kneading becomes difficult even if the resin is sufficiently softened by heating.
[0040]
(Basic compound)
By mixing a resin having an anionic group and a basic compound, a kneaded product for an aqueous pigment dispersion in which the anionic group is neutralized is obtained. As a result, the affinity between the aqueous pigment dispersion kneaded product and water is improved, and when the aqueous pigment dispersion is produced, the aqueous pigment dispersion kneaded material is quickly dissolved and dispersed in water, thereby improving the production efficiency. Further, the dispersion state of the resin-coated pigment particles in the aqueous pigment dispersion becomes more stable, and the dispersion stability and long-term storage stability are also improved.
[0041]
In addition, when a basic compound is blended, the pigment can be kneaded in a state in which the resin is sufficiently covered by the interaction between the basic compound and the resin having an anionic group. Therefore, the pigment is finely pulverized during the kneading, and the coarse particles are likely to be reduced. The step of removing the coarse particles in the subsequent step can be omitted, and the yield can be improved.
[0042]
As the basic compound, any of an inorganic basic compound and an organic basic compound can be used. In terms of easy adjustment of alkali strength, inorganic basic compounds are more preferable.
[0043]
Examples of the organic basic compound include amines. For example, common amines such as methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine and triethylamine can be exemplified. In the case of amine, since it is generally liquid, it can be used as it is.
[0044]
Examples of inorganic basic compounds include hydroxides of alkali metals such as potassium and sodium, ammonium hydroxide; carbonates of alkali metals such as potassium and sodium; carbonates of alkaline earth metals such as calcium and barium; It can be illustrated.
[0045]
Among them, a strong alkali is preferable because it is effective for enhancing the dispersibility of the resin by neutralizing the resin containing an anionic group. Specifically, an alkali metal such as potassium hydroxide or sodium hydroxide is preferable. Hydroxides are preferred.
The inorganic basic compound is preferably used in the form of an aqueous solution having a concentration of about 20 to 50% by mass from the viewpoint of improving the mixing property.
[0046]
(Amount of basic compound added)
The addition amount of the basic compound to the resin having an anionic group of the present invention needs to be 20% or more as the neutralization rate. If the addition amount of the basic compound is less than 20%, neutralization of the anionic group of the resin becomes insufficient, resulting in insufficient dispersibility and solubility of the resin, resulting in poor kneadability. A neutralization rate of 40% or more is preferred, and the upper limit is not particularly limited, but is preferably 200% or less. The most preferable neutralization rate range is 50% to 120%.
[0047]
In addition, the neutralization rate of this invention is a value calculated by the following formula.
Neutralization rate (%) = ((mass of basic compound (g) × 56 × 1000) / (resin acid value × basic compound equivalent × resin amount (g))) × 100
[0048]
(Kneading method)
In the present invention, instead of directly dispersing the pigment in the aqueous solvent, the pigment is first kneaded with a resin and then dispersed in the aqueous solvent. Therefore, since the pigment is finely pulverized during the kneading, coarse particles can be reduced.
[0049]
At this time, since the basic compound is added as described above, the coarse particles are remarkably reduced by the interaction between the basic compound and the resin having an anionic group. Therefore, the step of removing the coarse particles can be omitted, and the production efficiency can be improved and the yield can be improved.
[0050]
In the present invention, it is preferable to knead so that the mass of the mixture (kneaded material) does not substantially change so that water, water-soluble organic solvent, and the like do not evaporate during kneading. Therefore, there is always a certain amount of solvent in the mixture from the start to the end of kneading, and the solvent that wets the pigment surface at the beginning of kneading is replaced with a resin that is preferably dissolved, swollen or partially dissolved by the solvent. Thus, the coating of the pigment with the resin proceeds smoothly and the pigment is sufficiently coated. As a result, the dispersion stability and long-term storage stability of the aqueous pigment dispersion and the ink composition are remarkably improved.
[0051]
Further, after the kneading is completed, almost the same amount of the solvent remains as when the kneading is started, and the dissolution and dispersion of the kneaded product can be advanced in a very short time.
For this purpose, a kneader for kneading in a closed system is preferable, and a kneader equipped with a stirring tank and a uniaxial or multiaxial stirring blade is preferably used. The number of stirring blades is not particularly limited, but two or more stirring blades are preferable in order to obtain a high kneading action.
[0052]
When a kneader having such a configuration is used, a water-based pigment dispersion can be produced by producing a kneaded product for an aqueous pigment dispersion and then diluting and dispersing it directly with an aqueous solvent in the same stirring tank. .
The fact that the mass does not substantially change means that the weight of the kneaded product during or after kneading is maintained in the range of 90% by mass or more with respect to the charged amount of the mixture before kneading.
[0053]
Examples of such an apparatus include a Henschel mixer, a pressure kneader, a Banbury mixer, a planetary mixer, and the like, and a planetary mixer is particularly suitable. In the present invention, since the kneading is performed in a state where the pigment concentration and the solid content concentration of the pigment and the resin are high, the viscosity of the kneaded material varies in a wide range depending on the kneaded state of the kneaded material. This is because it can deal with a wide range from low viscosity to high viscosity.
[0054]
The planetary mixer has a structure to stir and knead the kneaded material in the stirring tank using biaxial stirring blades that rotate and revolve with each other, and the dead space where the stirring blades do not reach in the stirring tank Less is. Moreover, although the shape of a blade | wing is thick and can apply high load, on the other hand, it can also be used like the normal stirrer which rotates a stirring blade in a stirring tank. For this reason, there is a wide range of materials to be kneaded from the high load region to the low load region, and all operations of adding an aqueous solvent to the kneaded material after completion of the kneading, diluting, stirring, and dispersing are performed in a planetary manner. It can be carried out in the same mixer without removing the kneaded material from the mixer.
[0055]
(Planetary mixer in Figs. 1 to 3)
1 to 3 show an example of the configuration of a planetary mixer. In the figure, reference numeral 1 denotes a stirring tank, and this hollow cylindrical stirring tank 1 is roughly divided into two vertically. During stirring, the upper member 2 and the lower member 3 are integrated to form a closed system. Inside the upper member 2 of the agitation tank 1, as shown in an enlarged view in FIG. 2, agitation blades 4 and 5 made of frame-type blades are held by a single rotor 6. When the rotor 6 rotates (revolves), the stirring blades 4 and 5 rotate (rotate) in the same direction. Then, as shown in FIG. 3, the two stirring blades 4 and 5 each perform a so-called planetary motion (planetary motion) along with the revolution motion of the rotor 6. FIG. 3 shows the locus of the tips of the two stirring blades 4 and 5 in one revolution.
[0056]
In the planetary mixer, a powerful shearing force acts between the stirring blades 4 and 5 and between the stirring blades 4 and 5 and the inner surface of the stirring tank 1 by such planetary motion of the stirring blades 4 and 5. High stirring, kneading and dispersing action can be obtained.
When kneading using a closed kneader such as a planetary mixer, the current consumption gradually increases with time, reaches a maximum value within 30 minutes, and then gradually decreases.
[0057]
That is, when the mixture is heated while being heated to a predetermined temperature (for example, 40 to 70 ° C., depending on the type of resin), the resin becomes viscous and mixed with the pigment. A large load is applied to the rotation of the blades 4 and 5. At this time, a large shearing force is applied to the material between the stirring blades 4 and 5 and between the stirring blades 4 and 5 and the stirring tank 1, and the pigment is efficiently pulverized. It is sufficiently dispersed, mixed and coated with resin. Especially when a closed kneader such as a planetary mixer is used, since effective kneading is performed, the resin, pigment and water-soluble organic solvent are almost completely mixed within 30 minutes, and the stirring blades 4 and 5 The load on is reduced. As a result, current consumption gradually decreases.
[0058]
Thus, in the present invention, when mixing is performed using a closed system kneader such as a planetary mixer, one or more consumptions in the graph of the relationship between the kneading time and the power consumption of the kneading machine (planetary mixer). The characteristic that the maximum value of electric power is obtained is seen.
[0059]
When kneaded in such a closed system, the mass of the kneaded material does not substantially change during kneading with respect to the mass of the charged mixture, and a kneaded product for an aqueous pigment dispersion having the same composition as the charged is obtained. Manufacturing stability is improved.
[0060]
Further, since the kneading is performed at a high pigment concentration and solid content concentration from the beginning of kneading, the pigment is crushed by the shearing force applied by kneading, and undispersed coarse particles are reduced. As a result, it is not necessary to remove coarse particles in a later step, and the yield is improved.
In addition, when removing a water-soluble organic solvent, it can also be removed by heating and drying after kneading.
[0061]
If the kneading step is performed using an open kneader such as a two-roll or three-roll, for example, the organic solvent and water in the kneaded product will evaporate due to the temperature rise during kneading. The ratio has risen significantly. For this reason, the effect of adding a basic compound to the mixture to neutralize the anionic group of the resin and improving its dispersibility or solubility is diminished.
[0062]
Furthermore, when kneading is performed using an open system such as a roll kneader, the pigment receives a share between the rolls and is finely pulverized, but the solid content ratio significantly increases at the end of kneading as described above. Therefore, the kneaded product surface is in a dry state. Therefore, when an aqueous pigment dispersion is prepared in the subsequent dispersion step, it is necessary to add water or an aqueous solvent to the kneaded product to pulverize and dissolve the solid chip and disperse the pigment. Therefore, a burden is imposed on the dispersion process following roll meat grinding, and the dispersion time is prolonged, and even if dispersion is performed for a long time, coarse particles are easily formed.
[0063]
(Aqueous solvent)
The aqueous solvent is water or a mixed solvent of water and a water-soluble organic solvent.
As the water-soluble organic solvent, known ones can be used without particular limitation.
[0064]
For example, glycols such as ethylene glycol, diethylene glycol, triethylene glycol tetraethylene glycol, propylene glycol, polyethylene glycol, polypropylene glycol;
Diols such as butanediol, pentanediol, hexanediol, and diols of the same family;
Glycol esters such as propylene glycol laurate;
Diethylene glycol ethers such as ethylene glycol monobutyl ether and carbitol;
Monoglycol ethers such as cellosolve including diethylene glycol monoethyl, diethylene glycol monobutyl, diethylene glycol monohexyl, propylene glycol ether, dipropylene glycol ether, and triethylene glycol ether;
Alcohols such as methanol, ethanol, isopropyl alcohol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, butyl alcohol, pentyl alcohol, and alcohols of the same family;
Alternatively, other various solvents known as water-soluble organic solvents such as sulfolane, esters, ketones, lactones such as γ-butyrolactone, lactams such as N- (2-hydroxyethyl) pyrrolidone, glycerin and its derivatives, etc. Can be mentioned.
[0065]
These water-soluble organic solvents can be used alone or in combination.
The selection of the water-soluble organic solvent is determined depending on the resin to be used, but a solvent having a certain degree of solubility is preferable, and the addition amount is adjusted depending on the solubility of the resin.
[0066]
Among them, polyhydric alcohols having a high boiling point, low volatility, and high surface tension are preferable because they also serve as drying inhibitors in aqueous pigment dispersions and ink compositions, and particularly glycols such as diethylene glycol and triethylene glycol. Are preferred. Glycols are generally often contained in ink compositions and are preferred because they remain in the final product without any problem.
[0067]
In addition, although an aqueous solvent changes also with resin to be used, it is 10-50 mass% normally in the mixture of preparation, Preferably 20-40 mass% is mix | blended. The amount added is about 1/2 to 5 times the amount of resin, and preferably about 1 to 4 times the amount of resin. If the amount of the aqueous solvent is less than ½ of the resin amount, the resin cannot be dissolved, partially dissolved, or swollen, and the dispersion stability of the pigment may be lowered. On the other hand, if it exceeds 5 times, the viscosity of the mixture for kneading is lowered and sufficient kneading cannot be performed, so that the dispersibility of the pigment is lowered and the ink composition may cause deterioration in image quality such as ejection failure. In addition, as described above, in the case where another component derived from a basic compound or the like and serving as a solvent is blended, it is preferable to determine the composition and blending amount of the aqueous solvent in consideration of this. .
[0068]
Further, the aqueous solvent is preferably blended in a mass ratio of 1/55 times or more, preferably 1/3 to 1 time, with respect to the pigment. As a result, the kneading step proceeds while the resin is always in a semi-dissolved or swollen state, and the resin coating is favorably performed on the pigment surface. If it is less than 1/5 times, the surface of the pigment cannot be sufficiently wet at the initial stage of kneading, or the resin cannot be dissolved, partially dissolved, or swollen, and the effect cannot be sufficiently obtained.
[0069]
The mixing ratio of the aqueous solvent water and the water-soluble organic solvent may be appropriately selected in consideration of the characteristics of the resin or pigment used.
[0070]
(Production method of aqueous pigment dispersion; collision type disperser)
The kneaded product for an aqueous pigment dispersion is usually a semisolid or solid kneaded product. This aqueous pigment dispersion kneaded material is dispersed to produce an aqueous pigment dispersion. The pigment in the aqueous pigment dispersion kneaded product has already been crushed when the aqueous pigment dispersion kneaded product is produced, so that the dispersion time for obtaining the aqueous pigment dispersion is short and the production efficiency is improved.
[0071]
[0072]
The aqueous pigment dispersion kneaded product of the present invention dissolves and disperses quickly because of its good solubility and dispersibility in water due to the interaction between the resin having an anionic group and the basic compound. Thus, it is a major characteristic of the kneaded product for an aqueous pigment dispersion according to the present invention that it dissolves and disperses quickly in water and is stably maintained.
[0073]
Dispersion by a collision-type disperser during dissolution and dispersion of the kneaded material in an aqueous solvent improves dispersion stability, particularly dispersion stability during heating. The kneaded product for the aqueous pigment dispersion is solid or semi-solid and cannot be directly dispersed using a collision-type disperser. Therefore, it is once dissolved and dispersed in an aqueous solvent and then dispersed by a collision-type dispersion device.
[0074]
(Collision type disperser)
The collision-type disperser is a disperser that collides a liquid medium that has been once pressurized by a high-pressure pump and disperses it by an impact force or the like at this time. Collision-type dispersers can be roughly divided into two types according to the object to be collided. There are a method in which liquid media collide with each other and a method in which a liquid medium collides with an object to be collided. Examples of methods for causing liquid media to collide with each other include nanomizer, genus PY, optimizer, Aqua, and microfluidizer. A homogenizer etc. are mentioned as an example of the system which makes a liquid medium collide with a collision target object.
[0075]
Dispersion by a bead mill using a general medium as a wet disperser causes insufficient resin adsorption to the newly formed pigment surface due to the progress of the crushing of the pigment, or peels off the resin once adsorbed to the pigment surface. The action works and inhibits dispersion stability. On the other hand, dispersion by a collision type disperser is preferable in order to ensure dispersion stability because the progress of pigment crushing and the peeling action of the adsorbing resin hardly occur. This is particularly effective for ensuring the storage stability of the dispersion.
[0076]
(Solid content concentration of aqueous pigment dispersion)
The solid content concentration of the aqueous pigment dispersion at this time is preferably as high as possible from the viewpoint of reducing the processing amount and increasing the production efficiency. However, if the solid content concentration is too high, the viscosity increases and exceeds the upper limit of dispersion by the collision type dispersion device. Therefore, the upper limit of the solid content concentration of the aqueous pigment dispersion is determined by the dispersion upper limit viscosity of the device. Also, the viscosity of the dispersion at the same solid content concentration varies depending on the type, blending amount, etc. of the resin, pigment, and aqueous solvent. A preferable range is from 10% by mass to 50% by mass.
[0077]
(Method of dissolving and dispersing a kneaded product for an aqueous pigment dispersion in an aqueous solvent)
As a method for dissolving and dispersing the kneaded product for the aqueous pigment dispersion in the aqueous solvent, a method of mixing and stirring with the aqueous solvent in a kneader having a stirring tank and a stirring blade following kneading, a solid or semi-solid kneaded product may be used. Examples thereof include a method of mixing and stirring with an aqueous solvent using a take-out stirrer.
[0078]
(Method for producing ink composition)
The ink composition can be produced by further diluting the aqueous pigment dispersion obtained as described above with an aqueous solvent. The concentration of the pigment contained in the ink composition is preferably 2 to 10% by mass.
[0079]
The composition of the aqueous solvent for diluting the aqueous pigment dispersion is designed for the purpose of preventing drying at the nozzle, adjusting the viscosity, adjusting the pigment concentration, and the like. Examples of the water-soluble organic solvent used for the aqueous solvent include the compounds exemplified in the item of the aqueous solvent described above. The type and amount of the water-soluble organic solvent to be used can be appropriately selected and determined according to the target ink composition.
[0080]
(Manufacture of ink composition)
The dispersed particles in the aqueous pigment dispersion of the present invention already have sufficient dispersion stability, and there is no need for a dispersion process by a dispersing device or the like when preparing an ink composition. Just do it. At that time, instead of directly mixing the aqueous pigment dispersion and the aqueous organic solvent, additive, etc., the aqueous organic solvent, additive, etc. can be mixed with water and then mixed with the aqueous pigment dispersion with stirring. preferable.
[0081]
(Additive of ink composition)
In addition to the aqueous solvent and the aqueous pigment dispersion, known additives and the like can be blended in the ink composition.
Examples of compounds that can be blended include alkali agents, pH adjusters, surfactants, preservatives, chelating agents, plasticizers, antioxidants, ultraviolet absorbers, and ultraviolet curable resins.
[0082]
In the present invention, for example, an ink composition can be produced by adding an aqueous pigment dispersion, a water-soluble solvent, and various additives as necessary, and stirring uniformly.
[0083]
This ink composition can be suitably used as an ink for inkjet recording. The inkjet method to be applied is not particularly limited, but examples of known ones such as a continuous jet type (charge control type, spray type, etc.), on-demand type (piezo type, thermal type, electrostatic suction type, etc.) can do.
And when this ink composition is applied to these various ink jet systems, it becomes possible to discharge ink very stably.
[0084]
【Example】
Hereinafter, the present invention will be described in detail with reference to examples.
Unless otherwise specified, “part” means “part by mass” and “%” means “mass%”.
[0085]
The resin used in this example is as follows.
Resin A: Resin having a monomer composition ratio of styrene / methacrylic acid / acrylic acid = 77/13/10 (mass ratio), a mass average molecular weight of 12000, an acid value of 151 mgKOH / g, and a glass transition point of 107 ° C.
[0086]
[Example 1]
(Kneading)
A mixture of the following composition is charged into a 50 L planetary mixer PLM-V-50V (manufactured by Inoue Mfg. Co., Ltd.), the jacket is heated, and the speed is low until the content temperature reaches 60 ° C. (rotation speed: 21 rpm) Kneading was performed at a revolution speed of 14 rpm), and after the temperature of the contents reached 60 ° C., the speed was changed to a high speed (spinning speed: 35 rpm, revolution speed: 24 rpm) and kneading was continued.
[0087]
Resin A 1000g
Fastgen Super Magenta RTS 4750g
(Dainippon Ink Chemical Co., Ltd.)
Phthalimidomethylated 3,10-dichloroquinacridone 250g
(Average number of phthalimidomethyl groups per molecule 1.4)
Diethylene glycol 3500g
34 mass% aqueous potassium hydroxide solution 447 g
Ion exchange water 1000g
[0088]
The planetary mixer current when switching to high speed was 5A. Thereafter, the kneading was continued, and the maximum current value of the planetary mixer was 15A. After continuing the kneading for 1 hour after showing the maximum current value, the current value of the planetary mixer was 10A. After showing the maximum current value, kneading was performed for 3 hours. The kneaded product was solid.
[0089]
8000 g of ion-exchanged water was added at the following addition amount to dissolve the kneaded product and taken out from the planetary mixer. The kneaded product taken out was liquid (hereinafter referred to as a kneaded product aqueous solution). The solid content concentration in the aqueous kneaded product was 32%.
[0090]
0g-1600g 200g every 10 minutes
1600g-3600g 500g every 5 minutes
3600g-6600g 1000g every 5 minutes
6600g-8000g Stir for 10 minutes after batch addition
[0091]
(dispersion)
The obtained aqueous kneaded product solution was filtered through a stainless steel 300 mesh and subjected to dispersion treatment with a collision type disperser: Nanomizer LA-33 (manufactured by Nanomizer Co., Ltd.). LA-33 has a pressure fluctuation due to the single piston pressure pump specification, and the operating pressure was set at the maximum pressure when pressurized.
[0092]
Distribution condition: Number of passes 1 pass
Operating pressure 98MPa (maximum pressure value)
To 100 parts of the kneaded product aqueous solution after the nanomizer treatment, 78 parts of ion-exchanged water was added and stirred to obtain an aqueous pigment dispersion having a solid content concentration of 18%.
[0093]
(Adjustment of ink composition)
After mixing with the following composition using an aqueous pigment dispersion, the mixture was filtered through a membrane filter having a pore size of 5 μm to obtain an ink composition. In the blending order, the aqueous pigment dispersion was added to the aqueous solvent in which the composition other than the aqueous pigment dispersion was metered and mixed, and mixed uniformly. The ink composition had a viscosity of 2.9 mPa · s, a surface tension of 42 mN / m, and a pH of 10.0.
[0094]
Aqueous pigment dispersion 25.0 parts
Diethylene glycol 11.0 parts
Sannix GP-600 5.0 parts
(Manufactured by Sanyo Chemical Industries)
Ion exchange water 59.0 parts
[0095]
(Printing evaluation of ink composition)
The obtained ink composition was filled into a commercially available inkjet printer EM-900C (manufactured by Seiko Epson Corporation), and printing evaluation was performed. The continuous discharge stability was good, and a clear printed matter was obtained.
[0096]
[Comparative Example 1]
・ Production of aqueous resin solution
A methyl ethyl ketone solution of Resin A was prepared with the following composition.
Methyl ethyl ketone (hereinafter abbreviated as MEK) 50 g
Resin A 50g
To this, 267 g of ion-exchanged water and 17 g of 34 mass% potassium hydroxide (KOH) aqueous solution were added and stirred well to obtain a resin A solution.
[0097]
For this resin A solution, MEK was removed under reduced pressure conditions of a water bath temperature of 45 ° C. and 40 hPa to obtain a resin-dissolved alkaline aqueous solution.
The solid content concentration of the obtained resin-dissolved alkaline aqueous solution was measured, and ion-exchanged water was added and stirred so that the solid content concentration was 20% by mass to obtain a resin-dissolved alkaline aqueous solution H1.
[0098]
・ Pigment dispersion
In a 250 ml polyethylene bottle, 400 g of φ1.2 mm zirconia beads were added, and 48 g of the following composition was further added, followed by treatment with a paint conditioner (manufactured by Toyo Seiki) for 4 hours.
[0099]
Resin-dissolved alkaline aqueous solution H1 10.0 g
Fastgen Super Magenta RTS 9.5g
(Dainippon Ink Chemical Co., Ltd.)
Phthalimidomethylated 3,10-dichloroquinacridone 0.5g
Ion exchange water 8.0g
Diethylene glycol 20.0g
8.7 g of ion-exchanged water was additionally mixed into the treated dispersion, and then taken out to obtain an aqueous pigment dispersion having a solid content concentration of 18%.
[0100]
[Reference Example 1]
(Kneading)
The aqueous kneaded product obtained in Example 1 was used.
(dispersion)
Dispersion was performed for 2 hours in a paint shaker using a 250 ml container.
Kneaded aqueous solution 100g
Ion exchange water 30g
φ1.25mm zirconia beads 370g
To 100 parts of the kneaded aqueous solution after the paint shaker treatment, 67 parts of ion-exchanged water was added and stirred to obtain an aqueous pigment dispersion having a solid concentration of 18%.
[0101]
[Reference Example 2]
(Kneading)
The aqueous kneaded product obtained in Example 1 was used.
(dispersion)
To 100 parts of the kneaded product aqueous solution, 27 parts of ion exchange water was added and mixed uniformly using a dispersion stirrer to adjust the solid content concentration to 25%. This aqueous kneaded product was dispersed with a bead mill.
[0102]
Dispersion condition: Number of passes 4 passes (4 passes through the disperser)
Disperser Nanomill NM-G2L (Asada Tekko Co., Ltd.)
Beads φ0.3mm zirconia beads
Cooling water temperature 10 ℃
Rotation speed 2660rpm (disk peripheral speed 12.5m / sec)
Feed rate 200g / min
39 parts of ion-exchanged water was added to 100 parts of the kneaded product aqueous solution after the bead mill treatment and stirred to obtain an aqueous pigment dispersion having a solid concentration of 18%.
[0103]
[Reference Example 3]
(Kneading)
The aqueous kneaded product obtained in Example 1 was used.
(dispersion)
Dispersion using a disperser was not performed, and 78 parts of ion-exchanged water was added to 100 parts of the kneaded aqueous solution and stirred to obtain an aqueous pigment dispersion having a solid content concentration of 18%.
[0104]
(Evaluation of storage stability)
The storage stability of the ink composition using the aqueous pigment dispersion was evaluated by the following method. In this evaluation method, triethylene glycol mono-n-butyl ether (hereinafter referred to as TEGmBE) is selected from water-soluble organic solvents generally used in ink compositions for inkjet recording, and a large excess of TEGmBE is added. This is a test method used as a storage stability acceleration test.
The initial viscosity of the obtained composition was measured with an E-type viscometer. After standing at room temperature for 24 hours, the viscosity was measured, and then heated at 60 ° C. for 20 hours to measure the viscosity.
[0105]
(Adjustment of composition for storage stability evaluation)
To an aqueous solvent in which 40 parts of TEGmBE and 10 parts of ion-exchanged water were mixed, 50 parts of an aqueous pigment dispersion having a solid content concentration of 18% obtained in Example 1 and Comparative Example 1 and Reference Examples 1 to 3 were added and mixed by stirring. A composition for storage stability evaluation was obtained.
[0106]
(Storage stability evaluation results)
The storage stability test results of each sample were as follows.
[0107]
Sample Initial value Room temperature 60 ℃
Example 1 10.03 11.13 19.97
Comparative Example 1 Gelation − −
Reference Example 1 12.65 25.81 Gelation
Reference Example 2 11.04 18.27 Gelation
Reference Example 3 13.16 20.10 Gelation
[0108]
It can be seen that Example 1 does not gel in the above evaluation, which is an accelerated test for evaluating long-term storage stability, and is excellent in long-term storage stability. Comparative Example 1 gelled in the initial stage (for this reason, subsequent measurements; measurements after standing at room temperature for 24 hours and measurements after heating at 60 ° C. for 20 hours were not performed).
[0109]
【The invention's effect】
By the production method of the present invention, it is possible to obtain an aqueous pigment dispersion and an ink composition excellent in pigment dispersion stability and long-term storage stability.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an example of the configuration of a planetary mixer.
FIG. 2 is a partially enlarged view of a planetary mixer.
FIG. 3 is an explanatory diagram showing the trajectory of a stirring blade in a planetary mixer.
[Explanation of symbols]
1 ... Stirring tank
2 ... Upper part of stirring tank
3 ... Lower part of stirring tank
4 and 5 ... Stirring blade
6 ... Rotor

Claims (8)

After kneading a mixture having a solid content ratio of 50 to 80% by mass containing a resin having an anionic group, a pigment, and a basic compound to obtain a solid or semi-solid aqueous pigment dispersion kneaded product, the aqueous A method for producing an aqueous pigment dispersion, wherein the kneaded product for a pigment dispersion is dispersed in an aqueous solvent using a collision type disperser. 2. The method for producing an aqueous pigment dispersion according to claim 1, wherein the basic compound is used in such an amount that the neutralization rate of the resin having an anionic group is 20% or more. The method for producing an aqueous pigment dispersion according to claim 1 or 2, wherein a mass ratio of the resin / pigment in the kneaded product for an aqueous pigment dispersion is 1/10 to 2/1. The method for producing an aqueous pigment dispersion according to any one of claims 1 to 3, wherein 10 to 50% by mass of an aqueous solvent is blended in the mixture. The method for producing an aqueous pigment dispersion according to any one of claims 1 to 4, wherein the kneading is performed so that the mass of the mixture does not substantially change during the kneading. The method for producing an aqueous pigment dispersion according to any one of claims 1 to 5, wherein the aqueous pigment dispersion is kneaded using a closed kneader having a stirring tank and stirring blades. The method for producing an aqueous pigment dispersion according to claim 6, wherein the kneader is a planetary mixer. The manufacturing method of the ink composition which dilutes the aqueous pigment dispersion obtained by the manufacturing method of the aqueous pigment dispersion as described in any one of Claims 1-7 with an aqueous solvent, and manufactures an ink composition.

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