JP2007270085A - Particle dispersion and ink composition using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a particle dispersion excellent in dispersion stability in which various particles can be stably dispersed with time, and to provide an ink composition excellent in pigment dispersion stability obtained by applying the same, particularly an ink composition for inkjet excellent in discharge properties in which occurrence of nozzle clogging caused by pigment settling is suppressed even if it is applied to an inkjet recording system. <P>SOLUTION: The particle dispersion contains particles dispersed with a dispersant composed of a condensation product obtained by using a metal alkoxide and/or a partial hydrolyzate thereof. The dispersant preferably has an acidic group or a basic group according to the charge of the particles. It is possible to form an ink composition excellent in pigment dispersion stability by using a pigment such as a white pigment as a dispersed particle. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a particle dispersion and an ink composition using the same, and more specifically, a particle dispersion using a specific dispersant and excellent in particle dispersion stability, and a pigment as the particle. The present invention relates to an ink composition containing the used pigment dispersion.

Various polymer dispersants used to stably disperse particles in a dispersion medium have been developed. These dispersants are firmly adsorbed on particles that are dispersions, and are dispersed by modifying their surfaces. It has a function of preventing sedimentation and aggregation of particles in the medium.
However, the adsorption of the dispersant to the particles is mainly ionic adsorption, and there is a problem that the dispersibility is deteriorated due to a decrease in the adsorbing ability of the dispersant due to an environmental change during storage of the dispersion and time. In particular, in the case of metal pigments and inorganic pigments, the specific gravity is large, and sufficient interaction cannot be obtained in a state where the organic dispersant is adsorbed on the inorganic particles. Therefore, there are problems such as difficulty in redispersion, and it has been difficult to achieve dispersion stability over time and maintenance of redispersibility.

An application example of such a particle dispersion is an ink composition. In the ink composition, various pigments are widely used as a coloring material in that the hue of the formed image does not change. The uniform dispersibility of the pigment greatly affects the performance of the ink composition.
High concealability and coloring power are essential for ink compositions, especially white ink compositions. This is because, when printing on a colored medium, if the concealability is low, the color of the print medium is transparent, resulting in poor color reproducibility. When printing on a colored medium, white ink is first applied, and ink of other colors is applied thereon. Therefore, the amount of white ink used is large compared to other colors, and the demand is surely increasing. As a method for applying the white ink, screen printing is often used, but there are problems such as being limited to plane printing and difficult to draw finely.

On the other hand, ink-jet ink is simpler and more compact than conventional printing methods, and is non-contact printing, so printing on a three-dimensional medium is possible, and its use is further expanded.
By applying the white ink by the ink jet method, the problems caused by the conventional screen printing have been solved, and printing on a three-dimensional medium and fine drawing have become possible.
However, in ink jet printing, it is necessary for the ink viscosity to be low in order to ensure ink dischargeability. If the dispersion stability of the white pigment with excellent concealment is not sufficient, pigment settling will occur, and the ink jet nozzle will When clogging occurs and a printed image is defective or is remarkable, ink cannot be ejected and printing is not possible.

For this reason, a novel dispersant has been proposed for the purpose of improving the dispersion stability of a titanium oxide white pigment that is useful as a white pigment but has a large specific gravity and thus easily settles (see, for example, Patent Document 1). However, the dispersibility was not sufficient for application to a low-viscosity ink composition.
For this reason, a technique has also been proposed in which a titanium oxide pigment is surface-treated using silica and alumina in a specific ratio and is combined with a polymer dispersant having an acidic group to achieve dispersion stabilization (see, for example, Patent Document 2). .) However, this method is effective only for titanium oxide pigments having a specific surface property, and is not a dispersion technique applied to a wide range of pigments. In addition, a technique has been proposed in which a pigment is directly covalently bonded with a coupling agent to increase pigment dispersibility. However, it is not sufficient from the viewpoint of versatility because it requires the effort of surface treatment and the combined use of a dispersant. For this reason, it is a low-viscosity composition and can achieve dispersion stability of various pigments. At present, an ink composition excellent in the dispersion stability of a pigment using the same is awaited.
JP 2002-347336 A JP 2004-59857 A

  An object of the present invention made in consideration of the above problems is to provide a particle dispersion excellent in dispersion stability capable of stably dispersing various particles over time. Another object of the present invention is due to the precipitation of the pigment applied to such an ink composition having excellent dispersion stability of the pigment, particularly the ink jet recording method. An object of the present invention is to provide an ink-jet ink composition excellent in dischargeability in which occurrence of nozzle clogging is suppressed.

  As a result of intensive investigations, the present inventors have found that a dispersant using a metal alkoxide has excellent adsorption stability to pigments, and can improve the dispersion stability of various particles, especially inorganic pigment particles, and suppress sedimentation. Furthermore, the present inventors have found that further improvement in dispersion stability can be achieved by introducing an acidic group at the end of the dispersant to increase the adsorption efficiency of the dispersant to the particles.

That is, the present invention is as follows.
<1> A particle dispersion containing particles dispersed with a dispersant comprising a condensate obtained by using a metal alkoxide and / or a partial hydrolyzate thereof.
<2> The particle dispersion according to <1>, further comprising one or more compounds selected from the group consisting of acidic compounds and basic compounds.
<3> An ink composition comprising a pigment dispersed with a dispersant comprising a condensate obtained by using a metal alkoxide and / or a partial hydrolyzate thereof.

  ADVANTAGE OF THE INVENTION According to this invention, the particle dispersion excellent in the dispersion stability which can be stably disperse | distributed with time can be provided by adsorb | sucking to various particles and giving a high interaction. In addition, by applying the particle dispersion of the present invention, nozzle clogging due to pigment sedimentation occurs even in an ink composition excellent in pigment dispersion stability, especially in an ink jet recording system. It is possible to provide an ink-jet ink composition excellent in suppressed ejection properties.

Details of the present invention will be described below.
The particle dispersion of the present invention comprises particles dispersed with a dispersant comprising a condensate obtained by using a metal alkoxide compound and / or a partial hydrolyzate thereof.
First, the dispersant which is a characteristic component of the present invention will be described.
[Dispersant comprising a condensate obtained by using a metal alkoxide and / or a partial hydrolyzate thereof]
In order to maintain long-term dispersion stability of the particles, a dispersant that adsorbs the particles efficiently and has a strong adsorption force and stably gives a high interaction is preferable. Dispersing agents that are inferior in adsorptivity to particles have poor adsorption efficiency and weak adsorption power, and the dispersibility decreases with time, or the amount of dispersant necessary to ensure stable adsorption increases. This is undesirable because it causes problems such as increasing the viscosity of the system.

In the present invention, a condensate obtained by using a compound selected from metal alkoxide compounds and partial hydrolysates of metal alkoxide compounds is used as a dispersant. Hereinafter, such a dispersant is appropriately referred to as a specific dispersant.
Specifically, the specific dispersant of the present invention is obtained by introducing a metal alkoxide group in the molecule of the polymer dispersant having a polymer structure described in detail below, preferably at one end of the polymer structure. be able to.

In the specific dispersant of the present invention, the structural unit constituting the polymer is a copolymer containing a structural unit selected from a structural unit having a urethane bond, a structural unit having a vinyl bond, a structural unit having an ester bond, and the like. Is mentioned.
Examples of the metal alkoxide compound used for introducing an adsorbing group with particles into such a copolymer (polymer compound) include the following compounds. In the following structural formula, R represents an alkyl group having 17 or more carbon atoms.

  Examples of the condensate obtained by using the metal alkoxide compound used to introduce the adsorbing group or the partial hydrolyzate of the metal alkoxide compound include the following compounds. In the following structural formula, R represents an alkyl group having 17 or more carbon atoms, and n is in the range of 1 to 10.

  Examples of the polymer compound into which such an adsorption site is introduced include the following polymers and oligomers. In the following formula, Y represents a binding position to which the aforementioned adsorption site is bonded.

In the above formula, the compounds represented by (1) and (2) are oligomers. The compounds represented by (3) and (4) are polymer compounds having a weight average molecular weight of about 500 to 50,000, n represents the number of polymerization of the described structural units, and these depend on the molecular weight. Selected.
The compound represented by (5) to (9) is a copolymer containing the described structural units at the written weight ratio, and the weight average molecular weight is about 1000 to 50,000. Thus, the adsorption site may be present not only at the terminal but also in the side chain.
In the compound represented by (10), m represents the polymerization number of the described structural unit, and is in the range of 13-15.
As described above, the polymer dispersant of the present invention has a structure in which the adsorptive group described above is introduced at the position Y in (1) to (10).

  From the viewpoint that the polymer structure constituting the dispersant contains an alkylene oxide structure such as an ethylene oxide structural unit or a propylene oxide structural unit, thereby adjusting the affinity with the dispersion medium and improving the dispersion stability. More preferred. A preferable introduction amount of the alkylene oxide group is preferably about 5 to 2000, more preferably 10 to 1500 in one molecule of the specific dispersant.

  The specific dispersant according to the present invention is composed of a metal alkoxide compound and / or a condensate obtained by using a partial hydrolyzate of the metal alkoxide compound. Here, as the metal alkoxide compound used as a raw material, An alkoxide compound of an element selected from Si, Ti, Al, Zr and the like can be mentioned. In order to introduce this into the molecule of the polymer dispersant, for example, an element selected from silicon, titanate, aluminum, zirconium, etc. A commercially available coupling agent can be appropriately selected and used.

Examples of the metal alkoxide compound include tetra-i-propoxy titanium, tetra-n-butoxy titanium, tetra-octoxy titanium, tetrakis (2-ethylhexoxy) titanium, tetrasteoxy titanium, di-i-propoxy bis (acetylacetonato) titanium. , Di-n-butoxy bis (triethanolaminato) titanium, dihydroxy bis (lactato) titanium, titanium-i-propoxyoctylene glycolate, titanium stearate, tri-n-butoxytitanium monostearate, titanium lactate , Γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, γ-chloropropyltriethoxysilane, N-β (amino Silane compounds such as ethyl) γ-aminopropylmethyldimethoxysilane, N-β (aminoethyl) γ-aminopropyltrimethoxysilane, zirconium butyrate, zirconium acetylacetonate, acetylacetone zirconium butyrate, zirconium lactate, zirconium butyrate stearate Zirconium-based compounds such as rate can be used.
By using these, a dispersant having a metal alkoxide group in the molecule can be obtained. This dispersant is excellent in adsorptivity to particles, and there is no particular limitation on the type of particles that can be dispersed as described later, but among them, it is characterized by high adsorptivity to metal particles.

The metal alkoxide compound is self-condensable, and pigment adsorption groups (specifically metal alkoxy groups) can be concentrated on the pigment surface in the dispersant molecule by self-condensation.
In general, several metal alkoxy groups exist at the end of the main chain of the polymer compound or within the polymer main chain. However, in the polymer dispersant of the present invention, the pigment adsorbing group as in the compounds exemplified above is used. It is also possible to create a dispersant having a block structure of a structural unit having a side chain and a copolymer component (other structural unit) not having the same, and the resulting dispersant has many particles in the molecule. Therefore, strong and stable adsorption is possible. The adsorbing groups introduced here may be the same, for example, a plurality of different adsorbing groups, and any kind and number of adsorbing groups may be introduced into the polymer dispersant depending on the purpose. Can do.
The type of the metal alkoxide compound used for forming the specific dispersant is preferably selected in relation to the metal-based particles from the viewpoint of the effect. From such a viewpoint, for example, the metal alkoxide compound is used for dispersing the particles containing titanium oxide. As the dispersant, a dispersant having a titanium alkoxide group in the molecule obtained using a titanium coupling agent is suitable.

(Method for producing dispersant)
Such a dispersant is prepared by, for example, reacting a compound having a hydroxyl group such as ethylene glycol with a titanium coupling agent, and reacting the obtained intermediate or condensate with an isocyanate compound and polycaprolactam diol. The obtained terminal NCO urethane can be obtained by reacting under pressure to carry out urethanization.

  The dispersant according to the present invention preferably has an acid group or a basic group in the vicinity thereof in addition to the metal alkoxide group. This acidic group or basic group enables further highly efficient adsorption to the particles. That is, when the particle surface has a positive charge, by introducing an acidic group, it is possible to achieve further adsorption stability by forming an ionic interaction in addition to the interaction caused by the metal alkoxide group. If the particle surface has a negative charge, the adsorption stability can be improved by introducing a basic group.

Examples of acidic groups that can be introduced into the dispersant include acidic groups derived from phosphoric acid, sulfonic acid, phosphonic acid, carboxylic acid, and the like. Among them, acid groups such as phosphoric acid groups and sulfonic acid groups that are highly acidic. Has an excellent effect. Only one kind of these acid groups may be introduced, or two or more kinds, for example, sulfonic acid and phosphonic acid may be introduced.
As the introduction amount of the acidic group, for example, when the phosphate group is taken as an example, the amount of the phosphate group relative to the metal alkoxide group can take any value in the range of 20: 0 to 1:20 (number). The number of phosphoric acid groups is preferably 5 or less with respect to the metal alkoxide group 1, and the ratio of both is preferably in the range of 1: 1 to 1: 2. In the case of other acid groups such as a sulfonic acid group, the introduction amount is preferably in the same range.

  Thus, when a metal alkoxide group and an acidic group exist in a dispersing agent, since multipoint adsorption | suction to particle | grains can be carried out, it is preferable that both exist, and it is more preferable that both exist in the vicinity. There is no problem even if there are a large number of acidic groups relative to the metal alkoxide group, but if the number of acidic groups is too large, the interaction force to the dispersion medium will be reduced and the function as a dispersant will be reduced. It is considered preferable to limit the amount to 20 times the alkoxide group.

  As the basic group, general basic groups such as primary to quaternary amines, pyridine and the like can be used. The amount of the basic group relative to the metal alkoxide group is the same as that of the phosphoric acid group, and can take any value in the range of 20: 0 to 1:20 (number). 1 to 2 is most preferable, and it is preferable that the metal alkoxide and the basic group are present in the vicinity.

Examples of the method for introducing an acidic group or basic group into the dispersant include a method of using a material having an acidic group or basic group from the beginning in the metal alkoxide material that is the raw material of the dispersant. For example, Plenact KR238S (trade name: manufactured by Ajinomoto Fine Techno Co., Ltd.), which is a titanium coupling agent having a phosphate group in its structure, and Plenact KR44 (trade name: brand name: manufactured by Ajinomoto Fine Techno Co., Ltd.). Ajinomoto Finetechno Co., Ltd.) and the like, and addition and coexistence of acidic compounds and basic compounds in a particle dispersion containing a dispersant having a metal alkoxide group. It does not matter if it is applied.
When a condensate of a metal alkoxide compound and polyphosphoric acid is contained in the dispersant, a better effect is exhibited.

As the acidic compound and the basic compound used in the latter method, it is preferable to select those that are dissolved or uniformly dispersed in the dispersion medium of the dispersion. If the compound to be used is poor in solubility or dispersibility in the dispersion medium, the adsorption to the pigment may be insufficient and the desired dispersion stability may not be obtained. Even when such a compound is not completely dissolved, when measured by the 90-degree scattering photometry method, the transmitted light T% when these compounds are dissolved and dispersed in a dispersion medium should be 20% or more. Can be judged as good.
Examples of acidic compounds that can be used in the present invention include sulfonic acid, phosphoric acid, phosphonic acid, sulfamic acid, carboxylic acid, boric acid or alkali metal salts and ammonium salts of these acids. An acid is preferred, and examples of the basic compound include compounds having a primary, secondary, or tertiary amino group, a nitrogen-containing heterocycle such as pyridine, pyrimidine, and pyrazine.
In addition, a synergist dispersant in which the above acid group or basic group is incorporated into a pigment derivative type compound can be used in combination.
The addition amount of the acidic compound and / or the basic compound is preferably in the range of 0.1 to 50% by mass and preferably in the range of 0.5 to 25% by mass in the total solid content of the dispersion.

Specific examples of the dispersant having a metal alkoxide group thus obtained include the exemplified alkoxide compound or the alkoxide at the Y site of the compounds represented by (1) to (10) exemplified above. A compound obtained by introducing a condensate obtained by using a compound is preferred.
Two or more polymer dispersants may be used in combination depending on the purpose.
The weight average molecular weight (Mw) of the polymer dispersant is preferably in the range of 300 to 2,000,000, more preferably in the range of 1,000 to 100,000.

The dispersant used for the preparation of the dispersion of the present invention is preferably selected from those that dissolve or uniformly disperse in the dispersion medium. If the polymer dispersant to be used is poor in solubility or dispersibility in the dispersion medium, adsorption to the pigment may be insufficient, and the desired dispersion stability may not be obtained. Even when such a compound is not completely dissolved, when measured by the 90-degree scattering photometry method, the transmitted light T% when these compounds are dissolved and dispersed in a dispersion medium should be 20% or more. Can be judged as good.
In the present invention, the amount of the specific dispersant used in the particle dispersion is preferably in the range of 1 to 10% by mass, particularly preferably in the range of 1 to 4% by mass, based on the total amount of particles. In the range of the addition amount, sufficient adsorptivity to the particles and stability thereof are achieved, and a dispersion in which stable dispersibility of the particles is achieved can be obtained.

(particle)
The particles in the dispersion of the present invention are not particularly limited and are used for any of metal particles, metal oxide particles, ceramic particles, inorganic particles such as inorganic pigments, organic resin particles such as polymer resin particles, and organic pigments. However, from the viewpoint of interaction formation with a metal alkoxide group, metal particles are suitable, and in particular, metal-based particles containing the same type of metal as the metal in the metal alkoxide used for adjusting the dispersant. Preferred examples include a combination of a dispersant having titanium alkoxide groups and titanium oxide particles, a dispersant having aluminum alkoxide groups and aluminum oxide particles, a dispersant having silane alkoxide groups and silica particles, and the like. .

(Dispersion medium)
The dispersion medium used in the particle dispersion of the present invention is not particularly limited and is appropriately selected depending on the purpose of use of the dispersion. From the viewpoint of the environment, a polymerizable compound can be used without adding a special solvent. It is preferable to use itself as a dispersion medium.
The addition amount of the dispersion medium is preferably in the range of 50 to 99% by mass, and preferably in the range of 60 to 97% by mass in the total solid content of the dispersion.

(Other compounds)
The particle dispersion of the present invention can contain known additives for the purpose of improving dispersion stability and other purposes. Examples of such additives include surface tension modifiers, viscosity modifiers, and the like, and these compounds can be contained in a range of 0.005 to 5 mass% in the total solid content of the dispersion.
(Preparation of particle dispersion)
The particle dispersion of the present invention can be prepared as follows.
For example, first, particles such as pigments and the polymer dispersant of the present invention are kneaded using a small amount of a dispersion medium and pulverized into stable primary particles. Thereafter, a dispersion medium is added little by little, and dilution is performed in consideration of suitability for use of the dispersion such as coating or discharge suitability while suppressing aggregation. Alternatively, the polymer dispersant may be dissolved and dispersed in the dispersion medium before adding the particles.

[Ink composition]
The particle dispersion of the present invention is excellent in dispersion stability of particles, and can be applied to various fields. In particular, an ink composition that requires stable dispersion of metal-based particles such as titanium oxide particles. Especially, it can be said that the effect is remarkable by applying to a white ink composition.
The ink composition of the present invention comprises a pigment dispersed with a dispersant comprising a condensate obtained by using a metal alkoxide and / or a partial hydrolyzate thereof. The dispersant used here may be the same as the dispersant made of the condensate obtained by using the metal alkoxide and / or the partial hydrolyzate thereof explained in the particle dispersion.

  The ink composition of the present invention comprises a pigment which is a colorant dispersed by the specific dispersant, and can be suitably used for ultraviolet curable ink jet recording. The ink composition of the present invention further contains a curable compound and a polymerization initiator in order to develop ultraviolet curability.

  Here, it is preferable to select a dispersant that dissolves in the curable compound that is a dispersion medium. When the solubility of the polymer dispersant used in the curable compound is low or insoluble, adsorption to the pigment may be insufficient, and the desired dispersion stability may not be obtained.

  The amount of the specific dispersant used in the ink composition of the present invention is preferably in the range of 1 to 10% by mass, particularly preferably in the range of 1 to 4% by mass, based on the total amount of the pigment. In the range of this addition amount, sufficient adsorptivity to the pigment is achieved, and the surface tension of the ink composition decreases due to the surfactant action resulting from the increase in viscosity of the ink composition and the polymer dispersant, There is no concern of lowering the ejectability by inkjet.

Hereinafter, each component other than the specific dispersant used in the ink composition of the present invention will be described.
[Pigment]
The pigment preferably used in the present invention will be described.
The pigment is not particularly limited, and all commercially available inorganic pigments, organic pigments, hollow particles, and the like can be used. Further, a pigment dispersed in an insoluble resin or the like as a dispersion medium, or a pigment covalently bonded to the pigment surface can be used.

Although it does not necessarily limit as a pigment which can be used for this invention, For example, the organic or inorganic pigment of the following number described in a color index can be used.
Examples of red or magenta pigments include Pigment Red 3, 5, 19, 22, 31, 38, 43, 48: 1, 48: 2, 48: 3, 48: 4, 48: 5, 49: 1, and 53: 1. 57: 1, 57: 2, 58: 4, 63: 1, 81, 81: 1, 81: 2, 81: 3, 81: 4, 88, 104, 108, 112, 122, 123, 144, 146 149, 166, 168, 169, 170, 177, 178, 179, 184, 185, 208, 216, 226, 257, Pigment Violet 3, 19, 23, 29, 30, 37, 50, 88, Pigment Orange 13 16, 20, 36,
As the blue or cyan pigment, Pigment Blue 1, 15, 15: 1, 15: 2, 15: 3, 15: 4, 15: 6, 16, 17-1, 22, 27, 28, 29, 36, 60 Pigment Green 7, 26, 36, 50,
As the yellow pigment, Pigment Yellow 1, 3, 12, 13, 14, 17, 34, 35, 37, 55, 74, 81, 83, 93, 94, 95, 97, 108, 109, 110, 137, 138 139, 153, 154, 155, 157, 166, 167, 168, 180, 185, 193,
As the black pigment, Pigment Black 7, 28, 26,
As a white pigment, Pigment White 6, 18, 21
Etc. can be used according to the purpose.

Among the above, since the white pigment capable of forming an image with excellent concealability is difficult to obtain dispersion stability, the ink composition of the present invention is particularly excellent when such a white pigment is used. Effect is obtained. Hereinafter, the white pigment most preferably used in the present invention will be described.
Specific examples of the inorganic white pigment include basic lead carbonate (2PbCO ₃ Pb (OH) ₂ , so-called silver white), zinc oxide (ZnO, so-called zinc white), titanium oxide (TiO ₂ , so-called titanium white). Strontium titanate (SrTiO ₃ , so-called titanium strontium white), etc. can be used.
Of these, titanium oxide has a lower specific gravity than other inorganic white pigments, a large refractive index, and is chemically and physically stable. Excellent durability against alkalis and other environments. Therefore, titanium oxide is preferred as the white pigment.

Titanium oxide is generally rarely used untreated and is treated with silica, alumina, zinc, zirconia, and organic matter, and the weather resistance and lipophilicity differ depending on the treatment method. Just choose.
When used in an ink composition as in the present invention, titanium oxide treated with alumina, silica, zinc, zirconia, or a basic organic material is preferred. With respect to titanium oxide treated with these materials, the amount treated with alumina, zinc, zirconia, basic organic matter, that is, the amount of these compounds attached to the titanium oxide surface is 50% of the total weight of the surface deposit. It is preferable that it is mass% or more.
The inorganic white pigment is not limited to titanium oxide, and other white pigments, that is, the white pigments listed above or other known inorganic white pigments may be appropriately used depending on the purpose.
In addition, in the said dispersing agent, since the dispersing agent which has a titanium alkoxide group is excellent in affinity with this titanium oxide particle, the outstanding dispersion stability is achieved in this combination.

Since the organic white pigment has a specific gravity smaller than that of the inorganic white pigment, it can stably exist in a dispersion having a low viscosity. Examples of the organic white pigment include resin particles made of highly cross-linked resin materials such as melamine and acrylic, and low molecular resin particles having a molecular weight of about 500 described in US Pat. No. 5,514,213. It is done.
The organic white pigment is also available as a commercial product. For example, the Shigenox series manufactured by Hakko Chemical Co., Ltd. can be used.

The hollow particles exhibit high concealability due to light scattering in the voids in the particles and have a specific gravity smaller than that of the inorganic white pigment and can exist stably in a dispersion having a low viscosity. Inorganic, organic and inorganic / organic mixed hollow particles can be used.
As specific examples of the hollow particles, an opt bead series manufactured by Nissan Chemical Industries, an SX series manufactured by JSR, a microsphere MFL series manufactured by Matsumoto Yushi Seiyaku, etc. can be used.

  For example, ball mill, sand mill, attritor, roll mill, jet mill, homogenizer, paint shaker, kneader, agitator, Henschel mixer, colloid mill, ultra-fine pigment dispersion when adjusting the ink composition using these white pigments. Any known dispersing device such as a sonic homogenizer, a pearl mill, or a wet jet mill can be used.

As a dispersion medium containing various components such as pigments in the ink composition, a curable compound such as a cationically polymerizable compound, which is a low molecular weight component described in detail below, is prepared as a dispersion medium without adding a special solvent. However, depending on the purpose, a more appropriate solvent may be added.
The ink composition of the present invention is a radiation curable ink, and after applying the ink onto a recording medium, the ink composition is cured by irradiating with ultraviolet rays to form an image. Therefore, a solvent is used from the viewpoint of curability. It is preferable not to add. Specifically, in the case of using a solvent for ink preparation, there is a concern that if the solvent remains in the cured ink image, the solvent resistance of the formed image may be deteriorated. This is because the problem of (Volatile Organic Compound) occurs.
As the dispersion medium in the ink composition of the present invention, it is preferable to use only a curable compound, and in particular, to select a curable compound having a low viscosity from the viewpoints of dispersion suitability and improved handling of the ink composition.

The average particle diameter of the pigment particles is preferably 0.05 to 1.0 μm, and the selection of the pigment, the dispersant, the dispersion medium, the dispersion conditions, and the filtration so that the maximum particle diameter is 5 μm or less, preferably 1 μm or less. Set conditions. By controlling the particle size, clogging of the head nozzle can be suppressed, and ink storage stability, ink transparency, and curing sensitivity can be maintained.
In addition, the value measured by the light-scattering method is employ | adopted here for the average particle diameter and maximum particle diameter of a pigment.
The preferable content of the pigment in the ink composition of the present invention is in the range of 0.1 to 50% by mass, and more preferably in the range of 0.5 to 40% by mass. With this content, it is possible to form an image with excellent hiding power.

[Curable compound]
The ink composition of the present invention contains a curable compound. The curable compound is cured by an initiating species generated from a coexisting radical polymerization initiator or cationic polymerization initiator to form an ink image.
The curable compound used in the present invention is not particularly limited, and any compound having a generally known curable group can be used regardless of the type of monomer, oligomer, or polymer. Thus, in consideration of the relation with the polymer dispersant used in combination and the viscosity of the ink composition, a monomer or a relatively low molecular weight oligomer is preferable.
One or more curable compounds may be used in combination for the purpose of adjusting the reaction rate, ink physical properties, cured film physical properties, and the like.
As the curable compound, a radical polymerizable compound or a cationic polymerizable compound can be used. Hereinafter, each compound will be described.

(Radically polymerizable compound)
The radical polymerizable compound is a compound having an ethylenically unsaturated bond capable of radical polymerization, and may be any compound as long as it has at least one ethylenically unsaturated bond capable of radical polymerization in the molecule. , Oligomers, polymers and the like having a chemical form. Only one kind of such radically polymerizable compounds may be used, or two or more kinds thereof may be used in combination at an arbitrary ratio in order to improve desired properties. A polyfunctional compound having two or more functional groups is more preferable than a monofunctional compound. More preferably, two or more polyfunctional compounds are used in combination for controlling performance such as reactivity and physical properties.

In the ink composition of the present invention, (meth) acrylate can be suitably used as the radical polymerizable compound. Examples of the (meth) acrylate include the following compounds.
In addition, (meth) acrylate represents that it can take the structure of both an acrylate and a methacrylate. The same applies hereinafter.

Specific examples of monofunctional (meth) acrylates include hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, tert-octyl (meth) acrylate, isoamyl (meth) acrylate, decyl (meth) acrylate, and isodecyl (meth). Acrylate, stearyl (meth) acrylate, isostearyl (meth) acrylate, cyclohexyl (meth) acrylate, 4-n-butylcyclohexyl (meth) acrylate, bornyl (meth) acrylate, isobornyl (meth) acrylate, benzyl (meth) acrylate, 2-ethylhexyl diglycol (meth) acrylate, butoxyethyl (meth) acrylate, 2-chloroethyl (meth) acrylate, 4-bromobutyl (meth) acrylate, cyanoeth (Meth) acrylate, benzyl (meth) acrylate, butoxymethyl (meth) acrylate, 3-methoxybutyl (meth) acrylate, alkoxymethyl (meth) acrylate, alkoxyethyl (meth) acrylate, 2- (2-methoxyethoxy) ethyl ( (Meth) acrylate, 2- (2-butoxyethoxy) ethyl (meth) acrylate, 2,2,2-tetrafluoroethyl (meth) acrylate, 1H, 1H, 2H, 2H perfluorodecyl (meth) acrylate, 4-butyl Phenyl (meth) acrylate, phenyl (meth) acrylate, 2,4,5-tetramethylphenyl (meth) acrylate, 4-chlorophenyl (meth) acrylate, phenoxymethyl (meth) acrylate, phenoxyethyl (meth) acrylate Over DOO, glycidyl (meth) acrylate, glycidyl Giro carboxybutyl (meth) acrylate, glycidyl Giro carboxyethyl (meth) acrylate, glycidyl Giro hydroxypropyl (meth) acrylate,

  Tetrahydrofurfuryl (meth) acrylate, hydroxyalkyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate 4-hydroxybutyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylate, diethylaminopropyl (meth) acrylate, tri Methoxysilylpropyl (meth) acrylate, trimethylsilylpropyl (meth) acrylate, polyethylene oxide monomethyl ether (meth) acrylate Oligoethylene oxide monomethyl ether (meth) acrylate, polyethylene oxide (meth) acrylate, oligoethylene oxide (meth) acrylate, oligoethylene oxide monoalkyl ether (meth) acrylate polyethylene oxide monoalkyl ether (meth) acrylate, dipropylene glycol (meth) acrylate, Polypropylene oxide monoalkyl ether (meth) acrylate, oligopropylene oxide monoalkyl ether (meth) acrylate, 2-methacryloyloxytyl succinic acid, 2-methacryloyloxyhexahydrophthalic acid, 2-methacryloyloxyethyl-2-hydroxy Propyl phthalate, butoxydiethylene glycol (meth) acrylate, trifluoroethyl (meth) Chlorate, perfluorooctylethyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, ethylene oxide modified phenol (meth) acrylate, ethylene oxide modified cresol (meth) acrylate, ethylene oxide modified nonylphenol (meth) acrylate , Polyethylene oxide modified nonylphenol (meth) acrylate, ethylene oxide modified-2-ethylhexyl (meth) acrylate, carbitol (meth) acrylate, oligoester (meth) acrylate, epoxy (meth) acrylate, urethane (meth) acrylate, methyl ( (Meth) acrylate, n-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acryl Rate, allyl (meth) acrylate, glycidyl (meth) acrylate, benzyl (meth) acrylate, dimethylaminomethyl (meth) acrylate, and the like.

  Specific examples of the bifunctional (meth) acrylate include 1,6-hexanediol di (meth) acrylate, 1,10-decanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, and 2,4-dimethyl. -1,5-pentanediol di (meth) acrylate, butylethylpropanediol (meth) acrylate, ethoxylated cyclohexanemethanol di (meth) acrylate, polyethylene glycol di (meth) acrylate, oligoethylene glycol di (meth) acrylate, Ethylene glycol di (meth) acrylate, 2-ethyl-2-butyl-butanediol di (meth) acrylate, hydroxypivalic acid neopentyl glycol di (meth) acrylate, ethylene oxide modified bisphenol A di ( ) Acrylate, bisphenol F polyethoxydi (meth) acrylate, polypropylene glycol di (meth) acrylate, oligopropylene glycol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, 2-ethyl-2-butylpropanediol Di (meth) acrylate, 1,9-nonanedi (meth) acrylate, propoxylated ethoxylated bisphenol A di (meth) acrylate, tricyclodecane di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) ) Acrylate, tetraethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, ethylene glycol Di (meth) acrylate, triethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate.

  Specific examples of trifunctional (meth) acrylates include trimethylolpropane tri (meth) acrylate, trimethylolethane tri (meth) acrylate, trimethylolpropane alkylene oxide-modified tri (meth) acrylate, pentaerythritol tri (meth) acrylate , Dipentaerythritol tri (meth) acrylate, trimethylolpropane tri ((meth) acryloyloxypropyl) ether, isocyanuric acid alkylene oxide modified tri (meth) acrylate, propionate dipentaerythritol tri (meth) acrylate, tri ((meta ) Acryloyloxyethyl) isocyanurate, hydroxypivalaldehyde modified dimethylolpropane tri (meth) acrylate, sorbitol tri (meth) acrylate Rate, propoxylated trimethylolpropane tri (meth) acrylate, ethoxylated glycerin triacrylate, trimethylolethane tri (meth) acrylate, trimethylolpropane tri (meth) acrylate.

  Specific examples of tetrafunctional (meth) acrylates include pentaerythritol tetra (meth) acrylate, sorbitol tetra (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, dipentaerythritol tetra (meth) acrylate propionate, ethoxylated penta Examples include erythritol tetra (meth) acrylate, dipentaerythritol tetra (meth) acrylate, and tetramethylolmethane tetra (meth) acrylate.

  Specific examples of pentafunctional (meth) acrylates include sorbitol penta (meth) acrylate, dipentaerythritol penta (meth) acrylate, and the like.

  Specific examples of hexafunctional (meth) acrylate include dipentaerythritol hexa (meth) acrylate, sorbitol hexa (meth) acrylate, phosphazene alkylene oxide modified hexa (meth) acrylate, captolactone modified dipentaerythritol hexa (meth) acrylate , Etc.

  In the present invention, the polymerizable compound is at least selected from (a) at least one trifunctional or higher (meth) acrylate, and (b) a monofunctional (meth) acrylate and a bifunctional (meth) acrylate. It is preferable to include one type from the viewpoints of viscosity adjustment, crosslinking density adjustment, and physical property control after curing (strength, adhesiveness, etc.). In this case, the mixing ratio (molar ratio) of (a) :( b) is preferably 15:85 to 40:60, and more preferably 20:80 to 50:50.

Examples of radically polymerizable compounds other than the listed compounds include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, crotonic acid, isocrotonic acid, maleic acid and their salts, esters, urethanes, amides, and the like. Examples thereof include anhydrides, acrylonitrile, styrene, various unsaturated polyesters, unsaturated polyethers, unsaturated polyamides, and unsaturated urethanes. Specific examples include acrylic acid derivatives such as bis (4-acryloxypolyethoxyphenyl) propane and diacetone acrylamide, methacrylic derivatives such as 2,2-bis (4-methacryloxypolyethoxyphenyl) propane, and allyl glycidyl. Derivatives of allyl compounds such as ether, diallyl phthalate, triallyl trimellitate, etc. are mentioned, and more specifically, “Crosslinking agent handbook” (Yamashita Shinzo, 1981 Taiseisha), “UV / EB curing handbook (raw material) Ed.) "(Kyoto Kato ed., Kobunshi Publishing Co., Ltd. (1985))," Application and Market of UV / EB Curing Technology "(Radtech Research Group, 79 pages (1989), CMC)," Polyester Resin Commercial products or industries described in "Handbook" (by Eiichiro Takiyama, Nikkan Kogyo Shimbun (1988)) Known radical polymerizable or crosslinkable monomers may be used oligomers and polymers.
When the radically polymerizable compound is used as the curable compound, the content in the ink composition is preferably 5 to 95% by mass, more preferably 10 to 90% by mass, and more preferably 50 to 90% by mass with respect to the total amount of the ink composition. % Is particularly preferred.

(Cationically polymerizable compound)
The cationically polymerizable compound can be arbitrarily selected for the purpose of adjusting the degree of polymerization and the physical properties of the ink composition. Among these, oxirane compounds, oxetane compounds, vinyl ethers, styrenes, and the like are preferable from the viewpoint of polymerization rate and versatility. These may be used alone or in combination of two or more. Examples are shown below.

[Oxirane compounds]
Examples of the oxirane compound include aromatic epoxides and alicyclic epoxides. Aromatic epoxides include di- or polyglycidyl ethers produced by the reaction of polyphenols having at least one aromatic nucleus or their alkylene oxide adducts and epichlorohydrin, such as bisphenol A or its alkylene oxides. Examples thereof include di- or polyglycidyl ethers of adducts, di- or polyglycidyl ethers of hydrogenated bisphenol A or alkylene oxide adducts thereof, and novolak type epoxy resins. Here, examples of the alkylene oxide include ethylene oxide and propylene oxide.

Examples of the alicyclic epoxide include cyclohexene oxide obtained by epoxidizing a compound having at least one cycloalkane ring such as cyclohexene or cyclopentene ring with an appropriate oxidizing agent such as hydrogen peroxide or peracid. Preferred examples include cyclopentene oxide-containing compounds. Examples of the aliphatic epoxide include dihydric polyhydridyl ethers of aliphatic polyhydric alcohols or alkylene oxide adducts thereof, and typical examples thereof include diglycidyl ether of ethylene glycol, diglycidyl ether of propylene glycol or 1,6. -Diglycidyl ether of alkylene glycol such as diglycidyl ether of hexanediol, polyglycidyl ether of polyhydric alcohol such as di- or triglycidyl ether of glycerin or its alkylene oxide adduct, diglycidyl of polyethylene glycol or its adduct of alkylene oxide Polyalkylene glycol diglycol represented by diglycidyl ether of ether, polypropylene glycol or its alkylene oxide adduct Jill ether, and the like. Here, examples of the alkylene oxide include ethylene oxide and propylene oxide.
Among these oxirane compounds, aromatic epoxides and alicyclic epoxides are preferable from the viewpoint of excellent curing speed, and alicyclic epoxides are particularly preferable.
Further, among the oxirane compounds, those having a small number of functional groups are preferable because they can simultaneously have solubility and viscosity adjusting effects as described above.

  Examples of monofunctional epoxides used in the present invention include, for example, phenyl glycidyl ether, p-tert-butylphenyl glycidyl ether, butyl glycidyl ether, 2-ethylhexyl glycidyl ether, allyl glycidyl ether, 1,2-butylene oxide, 1 , 3-butadiene monooxide, 1,2-epoxydodecane, epichlorohydrin, 1,2-epoxydecane, styrene oxide, cyclohexene oxide, 3-methacryloyloxymethylcyclohexene oxide, 3-acryloyloxymethylcyclohexene oxide, 3- Examples include vinylcyclohexene oxide.

  Examples of polyfunctional epoxides include, for example, bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, bisphenol S diglycidyl ether, brominated bisphenol A diglycidyl ether, brominated bisphenol F diglycidyl ether, brominated bisphenol S diglycidyl. Ether, epoxy novolac resin, hydrogenated bisphenol A diglycidyl ether, hydrogenated bisphenol F diglycidyl ether, hydrogenated bisphenol S diglycidyl ether, 3,4-epoxycyclohexylmethyl-3 ′, 4′-epoxycyclohexanecarboxylate, 2 -(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy) cyclohexane-meta-dioxane, bis (3,4-epoxycyclohexyl) Til) adipate, vinylcyclohexene oxide, 4-vinylepoxycyclohexane, bis (3,4-epoxy-6-methylcyclohexylmethyl) adipate, 3,4-epoxy-6-methylcyclohexyl-3 ′, 4′-epoxy-6 '-Methylcyclohexanecarboxylate, methylenebis (3,4-epoxycyclohexane), dicyclopentadiene diepoxide, ethylene glycol di (3,4-epoxycyclohexylmethyl) ether, ethylenebis (3,4-epoxycyclohexanecarboxylate) , Epoxyhexahydrophthalate dioctyl, epoxyhexahydrophthalate di-2-ethylhexyl, 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, Resin triglycidyl ether, trimethylolpropane triglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ethers, 1,1,3-tetradecadiene dioxide, limonene dioxide, 1,2,7,8-di Examples thereof include epoxy octane, 1,2,5,6-diepoxycyclooctane and the like.

[Oxetane compounds]
The oxetane compound in the present invention refers to a compound having an oxetane ring, and arbitrarily selected from known oxetane compounds as described in JP-A Nos. 2001-220526, 2001-310937, and 2003-341217. Can be used.
As the compound having an oxetane ring that can be used in the ink composition of the present invention, a compound having 1 to 4 oxetane rings in its structure is preferable, and as described above, the viscosity and tackiness of the ink composition are particularly preferable. From the viewpoint, it is preferable to use a compound having one oxetane ring. By using such a compound, it becomes easy to maintain the viscosity of the ink composition in a good handling property range, and it is possible to obtain high adhesion of the cured ink to the recording medium. .

  Examples of monofunctional oxetanes include oxetane compounds used in the present invention, such as 3-ethyl-3-hydroxymethyloxetane, 3- (meth) allyloxymethyl-3-ethyloxetane, and (3-ethyl-3 -Oxetanylmethoxy) methylbenzene, 4-fluoro- [1- (3-ethyl-3-oxetanylmethoxy) methyl] benzene, 4-methoxy- [1- (3-ethyl-3-oxetanylmethoxy) methyl] benzene, [ 1- (3-ethyl-3-oxetanylmethoxy) ethyl] phenyl ether, isobutoxymethyl (3-ethyl-3-oxetanylmethyl) ether, isobornyloxyethyl (3-ethyl-3-oxetanylmethyl) ether, isobornyl (3-Ethyl-3-oxetanylmethyl) ether, 2-ethyl Hexyl (3-ethyl-3-oxetanylmethyl) ether, ethyldiethylene glycol (3-ethyl-3-oxetanylmethyl) ether, dicyclopentadiene (3-ethyl-3-oxetanylmethyl) ether, dicyclopentenyloxyethyl (3- Ethyl-3-oxetanylmethyl) ether, dicyclopentenyl (3-ethyl-3-oxetanylmethyl) ether, tetrahydrofurfuryl (3-ethyl-3-oxetanylmethyl) ether, tetrabromophenyl (3-ethyl-3-oxetanyl) Methyl) ether, 2-tetrabromophenoxyethyl (3-ethyl-3-oxetanylmethyl) ether, tribromophenyl (3-ethyl-3-oxetanylmethyl) ether, 2-tribromophenoxyethyl (3-ethyl) Ru-3-oxetanylmethyl) ether, 2-hydroxyethyl (3-ethyl-3-oxetanylmethyl) ether, 2-hydroxypropyl (3-ethyl-3-oxetanylmethyl) ether, butoxyethyl (3-ethyl-3- Oxetanylmethyl) ether, pentachlorophenyl (3-ethyl-3-oxetanylmethyl) ether, pentabromophenyl (3-ethyl-3-oxetanylmethyl) ether, bornyl (3-ethyl-3-oxetanylmethyl) ether, and the like. .

  Examples of the polyfunctional oxetane include 3,7-bis (3-oxetanyl) -5-oxa-nonane, 3,3 ′-(1,3- (2-methylenyl) propanediylbis (oxymethylene)) bis. -(3-ethyloxetane), 1,4-bis [(3-ethyl-3-oxetanylmethoxy) methyl] benzene, 1,2-bis [(3-ethyl-3-oxetanylmethoxy) methyl] ethane, 1, 3-bis [(3-ethyl-3-oxetanylmethoxy) methyl] propane, ethylene glycol bis (3-ethyl-3-oxetanylmethyl) ether, dicyclopentenylbis (3-ethyl-3-oxetanylmethyl) ether, tri Ethylene glycol bis (3-ethyl-3-oxetanylmethyl) ether, tetraethylene glycol bis (3-ethyl) -3-oxetanylmethyl) ether, tricyclodecanediyldimethylene (3-ethyl-3-oxetanylmethyl) ether, trimethylolpropane tris (3-ethyl-3-oxetanylmethyl) ether, 1,4-bis (3- Ethyl-3-oxetanylmethoxy) butane, 1,6-bis (3-ethyl-3-oxetanylmethoxy) hexane, pentaerythritol tris (3-ethyl-3-oxetanylmethyl) ether, pentaerythritol tetrakis (3-ethyl-3 -Oxetanylmethyl) ether, polyethylene glycol bis (3-ethyl-3-oxetanylmethyl) ether, dipentaerythritol hexakis (3-ethyl-3-oxetanylmethyl) ether, dipentaerythritol pentakis (3-ethyl) 3-oxetanylmethyl) ether, dipentaerythritol tetrakis (3-ethyl-3-oxetanylmethyl) ether, caprolactone-modified dipentaerythritol hexakis (3-ethyl-3-oxetanylmethyl) ether, caprolactone-modified dipentaerythritol pentakis ( 3-ethyl-3-oxetanylmethyl) ether, ditrimethylolpropanetetrakis (3-ethyl-3-oxetanylmethyl) ether, EO-modified bisphenol A bis (3-ethyl-3-oxetanylmethyl) ether, PO-modified bisphenol A bis ( 3-ethyl-3-oxetanylmethyl) ether, EO-modified hydrogenated bisphenol A bis (3-ethyl-3-oxetanylmethyl) ether, PO-modified hydrogenated bisphenol A bis (3-ethyl) And polyfunctional oxetanes such as ru-3-oxetanylmethyl) ether and EO-modified bisphenol F (3-ethyl-3-oxetanylmethyl) ether.

[Vinyl ethers]
Examples of monofunctional vinyl ethers include, for example, methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, n-butyl vinyl ether, t-butyl vinyl ether, 2-ethylhexyl vinyl ether, n-nonyl vinyl ether, lauryl vinyl ether, cyclohexyl vinyl ether, cyclohexyl methyl vinyl ether, 4 -Methylcyclohexyl methyl vinyl ether, benzyl vinyl ether, dicyclopentenyl vinyl ether, 2-dicyclopentenoxyethyl vinyl ether, methoxyethyl vinyl ether, ethoxyethyl vinyl ether, butoxyethyl vinyl ether, methoxyethoxyethyl vinyl ether, ethoxyethoxyethyl vinyl ether, methoxypolyethylene glycol vinyl D Ter, tetrahydrofurfuryl vinyl ether, 2-hydroxyethyl vinyl ether, 2-hydroxypropyl vinyl ether, 4-hydroxybutyl vinyl ether, 4-hydroxymethylcyclohexyl methyl vinyl ether, diethylene glycol monovinyl ether, polyethylene glycol vinyl ether, chloroethyl vinyl ether, chlorobutyl vinyl ether, chloro Examples thereof include ethoxyethyl vinyl ether, phenylethyl vinyl ether, phenoxy polyethylene glycol vinyl ether and the like.

  Examples of polyfunctional vinyl ethers include, for example, ethylene glycol divinyl ether, diethylene glycol divinyl ether, polyethylene glycol divinyl ether, propylene glycol divinyl ether, butylene glycol divinyl ether, hexanediol divinyl ether, bisphenol A alkylene oxide divinyl ether, bisphenol F alkylene oxide. Divinyl ethers such as divinyl ether; trimethylolethane trivinyl ether, trimethylolpropane trivinyl ether, ditrimethylolpropane tetravinyl ether, glycerin trivinyl ether, pentaerythritol tetravinyl ether, dipentaerythritol pentavinyl ether, dipentaerythritol hex Vinyl ether, ethylene oxide-added trimethylolpropane trivinyl ether, propylene oxide-added trimethylolpropane trivinyl ether, ethylene oxide-added ditrimethylolpropane tetravinyl ether, propylene oxide-added ditrimethylolpropane tetravinyl ether, ethylene oxide-added pentaerythritol tetravinyl ether, propylene oxide-added penta And polyfunctional vinyl ethers such as erythritol tetravinyl ether, ethylene oxide-added dipentaerythritol hexavinyl ether, and propylene oxide-added dipentaerythritol hexavinyl ether.

[Styrenes]
Specific examples include styrene, methyl styrene, dimethyl styrene, trimethyl styrene, ethyl styrene, isopropyl styrene, chloromethyl styrene, methoxy styrene, acetoxy styrene, chloro styrene, dichloro styrene, bromo styrene, vinyl benzoic acid methyl ester, 3 -Methylstyrene, 4-methylstyrene, 3-ethylstyrene, 4-ethylstyrene, 3-propylstyrene, 4-propylstyrene, 3-butylstyrene, 4-butylstyrene, 3-hexylstyrene, 4-hexylstyrene, 3 -Octylstyrene, 4-octylstyrene, 3- (2-ethylhexyl) styrene, 4- (2-ethylhexyl) styrene, allylstyrene, isopropenylstyrene, butenylstyrene, octenylstyrene, 4- - butoxycarbonyl styrene, 4-methoxystyrene, and a 4-t-butoxystyrene.

In the present invention, it is preferable from the viewpoint of curing speed that the curable compound includes at least one selected from an oxirane compound and an oxetane compound which are cationic polymerizable compounds. In this case, the mixing ratio (molar ratio) of oxirane compound: oxetane compound is preferably 90:10 to 10:90, and more preferably 70:30 to 30:70. Also. It is also preferable to use an oxetane compound and styrene at a mixing ratio of 90:10 to 50:50.
When the cationic polymerizable compound is used as the curable compound, the content in the ink composition is preferably 5 to 95% by mass, more preferably 10 to 90% by mass, and more preferably 50 to 90% by mass with respect to the total amount of the ink composition. Is particularly preferred.

[Initiator]
The ink composition of the present invention contains a known initiator capable of generating a starting species by ultraviolet exposure and curing the curable compound. As the initiator, a radical polymerization initiator or a cationic polymerization initiator can be used, and a curable compound to be used, that is, a compound that is compatible with the radical polymerizable compound or the cationic polymerizable compound is selected and used in combination.

(Radical polymerization initiator)
Preferred radical polymerization initiators that can be used in the present invention include (a) aromatic ketones, (b) acylphosphine compounds, (c) aromatic onium salt compounds, (d) organic peroxides, and (e) thio compounds. (F) hexaarylbiimidazole compound, (g) ketoxime ester compound, (h) borate compound, (i) azinium compound, (j) metallocene compound, (k) active ester compound, (l) carbon halogen bond And (m) an alkylamine compound.
The radical polymerization initiator in the present invention may be used alone or in combination.
The radical polymerization initiator in the present invention is preferably 0.01 to 35% by mass, more preferably 0.1 to 30% by mass, and still more preferably 0.5 to 30% by mass, based on the total amount of the radical polymerizable compound. It is suitable to contain in the range of%.

(Cationic polymerization initiator)
When a cationically polymerizable compound is used as the curable compound, the ink composition of the present invention preferably contains an acid generator. This acid generator (hereinafter also referred to as “cationic polymerization initiator”) refers to a compound that generates an acid upon irradiation with actinic rays or actinic radiation to initiate cationic polymerization, and appropriately uses known compounds and mixtures thereof. You can choose to use.

  Examples of the cationic polymerization initiator in the present invention include diazonium salts, phosphonium salts, sulfonium salts, iodonium salts, imide sulfonates, oxime sulfonates, diazodisulfones, disulfones, and o-nitrobenzyl sulfonates.

Further, these cationic polymerization initiators, or compounds obtained by introducing a group or compound having an equivalent function into the main chain or side chain of the polymer, such as US Pat. No. 3,849,137 and German Patent No. 3914407. JP, 63-26653, JP, 55-164824, JP, 62-69263, JP, 63-146038, JP, 63-163452, JP, 62-153853, The compounds described in JP-A 63-146029 can be used.
Further, compounds capable of generating an acid by light described in US Pat. No. 3,779,778, European Patent 126,712 and the like can also be used.

  A cationic polymerization initiator can use the said compound individually by 1 type or in combination of 2 or more types. The content of the cationic polymerization initiator in the ink composition is preferably 0.1 to 20% by mass, and more preferably 0.5 to 10% by mass. When the content of the cationic polymerization initiator is within the above range, excellent curability is obtained, and problems such as embrittlement of the obtained cured ink image and generation of acid due to the remaining initiator do not occur.

[Other ingredients]
In the ink composition of the present invention, various additives can be used in combination with the above-described essential components as necessary, as long as the effects of the present invention are not impaired. These additives will be described.

[Sensitizing dye]
A sensitizing dye can be added to the ink composition of the present invention in order to accelerate the decomposition of the polymerization initiator by irradiation with actinic rays. A sensitizing dye absorbs specific actinic radiation and enters an electronically excited state. The sensitizing dye in an electronically excited state is brought into contact with the polymerization initiator to cause actions such as electron transfer, energy transfer, and heat generation, thereby causing a chemical change of the polymerization initiator, that is, decomposition, radical, acid or base. It promotes the generation of.

As the sensitizing dye, a compound corresponding to the wavelength of actinic radiation that generates an initiating species in the polymerization initiator used in the ink composition may be used, but it should be used for a curing reaction of a general ink composition. In view of the above, examples of preferred sensitizing dyes include those belonging to the following compounds and having an absorption wavelength in the 350 nm to 450 nm region.
Polynuclear aromatics (for example, anthracene, pyrene, perylene, triphenylene), thioxanthones (for example, isopropylthioxanthone), xanthenes (for example, fluorescein, eosin, erythrosine, rhodamine B, rose bengal), cyanines (for example, thiaxene) Carbocyanine, oxacarbocyanine), merocyanines (eg, merocyanine, carbomerocyanine), thiazines (eg, thionine, methylene blue, toluidine blue), acridines (eg, acridine orange, chloroflavin, acriflavine), anthraquinones ( For example, anthraquinone), squalium (for example, squalium), coumarins (for example, 7-diethylamino-4-methylcoumarin), and the like can be mentioned. Xanthones may be mentioned as preferred class.

  More preferable examples of the sensitizing dye include compounds represented by the following general formulas (V) to (IX).

In the general formula (V), A ¹ represents a sulfur atom or NR ⁵⁰ , R ⁵⁰ represents an alkyl group or an aryl group, and L ² represents a basic nucleus of the dye in combination with the adjacent A ¹ and the adjacent carbon atom. Represents a nonmetallic atomic group to be formed, R ⁵¹ and R ⁵² each independently represent a hydrogen atom or a monovalent nonmetallic atomic group, and R ⁵¹ and R ⁵² are bonded to each other to form an acidic nucleus of the dye. Also good. W represents an oxygen atom or a sulfur atom. )

In general formula (VI), Ar ¹ and Ar ² each independently represent an aryl group, and are linked via a bond with —L ³ —. Here, L ³ represents —O— or —S—. W is synonymous with that shown in Formula (V).

In the general formula (VII), A ² represents a sulfur atom or NR ⁵⁹ , L ⁴ represents a nonmetallic atomic group that forms a basic nucleus of the dye together with adjacent A ² and a carbon atom, R ⁵³ , R ⁵⁴ , R ⁵⁵ , R ⁵⁶ , R ⁵⁷ and R ⁵⁸ each independently represent a monovalent nonmetallic atomic group, and R ⁵⁹ represents an alkyl group or an aryl group.

In general formula (VIII), A ³ and A ⁴ each independently represent —S— or —NR ⁶² — or —NR ⁶³ —, wherein R ⁶² and R ⁶³ each independently represent a substituted or unsubstituted alkyl group, substituted Or an unsubstituted aryl group, L ⁵ and L ⁶ each independently represent a nonmetallic atomic group that forms a basic nucleus of a dye in cooperation with adjacent A ³ , A ^4, and adjacent carbon atoms; ⁶⁰ and R ⁶¹ are each independently a hydrogen atom or a monovalent nonmetallic atomic group, or can be bonded to each other to form an aliphatic or aromatic ring.

In the general formula (IX), R ⁶⁶ represents an aromatic ring or a hetero ring which may have a substituent, and A ⁵ represents an oxygen atom, a sulfur atom or ═NR ⁶⁷ . R ⁶⁴ , R ⁶⁵ and R ⁶⁷ each independently represent a hydrogen atom or a monovalent nonmetallic atomic group, and R ⁶⁷ and R ⁶⁴ , and R ⁶⁵ and R ⁶⁷ each represent an aliphatic or aromatic ring. Can be combined to form.
Preferable specific examples of the compounds represented by formulas (V) to (IX) include the following.

[Co-sensitizer]
The ink composition of the present invention can also contain a co-sensitizer. In the present invention, the co-sensitizer has functions such as further improving the sensitivity of the sensitizing dye to actinic radiation or suppressing polymerization inhibition of the polymerizable compound by oxygen.
Examples of such co-sensitizers include amines such as M.I. R. Sander et al., “Journal of Polymer Society”, Vol. 10, 3173 (1972), Japanese Patent Publication No. 44-20189, Japanese Patent Publication No. 51-82102, Japanese Patent Publication No. 52-134692, Japanese Patent Publication No. 59-138205. No. 60-84305, JP-A 62-18537, JP-A 64-33104, Research Disclosure 33825, and the like. Specific examples include triethanolamine. P-dimethylaminobenzoic acid ethyl ester, p-formyldimethylaniline, p-methylthiodimethylaniline and the like.

  Other examples of co-sensitizers include thiols and sulfides, for example, thiol compounds described in JP-A-53-702, JP-B-55-500806, JP-A-5-142773, and JP-A-56. And the like. Specific examples include 2-mercaptobenzothiazole, 2-mercaptobenzoxazole, 2-mercaptobenzoimidazole, 2-mercapto-4 (3H) -quinazoline, β-mercaptonaphthalene. Etc.

  Other examples include amino acid compounds (eg, N-phenylglycine), organometallic compounds described in Japanese Patent Publication No. 48-42965 (eg, tributyltin acetate), and hydrogen described in Japanese Patent Publication No. 55-34414. Donors, sulfur compounds described in JP-A-6-308727 (eg, trithiane), phosphorus compounds described in JP-A-6-250387 (diethyl phosphite, etc.), Si-H described in JP-A-8-65779 , Ge—H compounds and the like.

[Polymerization inhibitor]
In the present invention, it is preferable to use a polymerization inhibitor that inhibits the progress of polymerization other than the cationic polymerization in order to effectively proceed the polymerization by the cationic polymerization initiator.
Suitable polymerization inhibitors include phenolic hydroxyl group-containing compounds and quinones, N-oxide compounds, piperidine 1-oxyl free radical compounds, pyrrolidine 1-oxyl free radical compounds, N-nitrosophenylhydroxylamines, and cations. It is a compound selected from the group consisting of dyes. Preferred polymerization inhibitors include haloid quinone, p-methoxyphenol, di-t-butyl-p-cresol, pyrogallol, resorcinol, catechol, t-butylcatechol, hydroquinone, benzoquinone, 4,4-thiobis (3-methyl-6- t-butylphenol), 2,2'-methylenebis (4-methyl-6-t-butylphenol), 2,2,6,6-tetramethylpiperidine and its derivatives, di-t-butylnitroxide, 2,2,6 , 6-tetramethylpiperidine-N-oxide and its derivatives, such as piperidine 1-oxyl free radical, 2,2,6,6-tetramethylpiperidine 1-oxyl free radical, 4-oxo-2,2,6,6 -Tetramethylpiperidine 1-oxyl free radical, 4-hydroxy Ci-2,2,6,6-tetramethylpiperidine 1-oxyl free radical, 4-acetamido-2,2,6,6-tetramethylpiperidine 1-oxyl free radical, 4-maleimide-2,2,6 6-tetramethylpiperidine 1-oxyl free radical, 4-phosphonoxy-2,2,6,6-tetramethylpiperidine 1-oxyl free radical, 3-carboxy-2,2,5,5-tetramethylpyrrolidine 1-oxyl Examples include free radicals, N-nitrosophenylhydroxylamine cerium salt, N-nitrosophenylhydroxylamine aluminum salt, crystal violet, methyl violet, ethyl violet, and Victoria Pure Blue BOH. The addition amount of the polymerization inhibitor is preferably about 0.01% by mass to about 5% by mass with respect to the mass of the ink composition.

[Ultraviolet absorber]
From the viewpoint of improving the weather resistance of the resulting image and preventing discoloration, an ultraviolet absorber can be used.
Examples of the ultraviolet absorber are described in JP-A-58-185679, JP-A-61-190537, JP-A-2-782, JP-A-5-97075, JP-A-9-34057, and the like. Benzotriazole compounds, benzophenone compounds described in JP-A No. 46-2784, JP-A No. 5-194843, US Pat. No. 3,214,463, etc., JP-B Nos. 48-30492 and 56-21141 Cinnamic acid compounds described in JP-A-10-88106, JP-A-4-298503, JP-A-8-53427, JP-A-8-239368, JP-A-10-182621, JP The triazine compounds described in JP-A-8-501291, Research Disclosure No. Examples thereof include compounds described in No. 24239, compounds that emit ultraviolet light by absorbing ultraviolet rays typified by stilbene and benzoxazole compounds, so-called fluorescent brighteners, and the like.
The amount added is appropriately selected according to the purpose, but is generally about 0.01 to 10% by mass of the ink composition.

〔Antioxidant〕
An antioxidant can be added to improve the stability of the ink composition. Examples of the antioxidant include European published patents, 223739, 309401, 309402, 310551, 310552, 359416, and 3435443. JP, 54-85535, 62-262417, 63-113536, 63-163351, JP-A-2-262654, JP-A-2-71262, Examples thereof include those described in Kaihei 3-121449, JP-A-5-61166, JP-A-5-119449, US Pat. No. 4,814,262, US Pat. No. 4,980,275, and the like.
The addition amount is appropriately selected according to the purpose, but is generally about 0.001 to 1% by mass of the ink composition.

〔solvent〕
In order to improve the adhesion to the recording medium, it is also effective to add a very small amount of an organic solvent to the ink composition of the present invention.
Examples of the solvent include ketone solvents such as acetone, methyl ethyl ketone, diethyl ketone, and cyclohexanone, alcohol solvents such as methanol, ethanol, 2-propanol, 1-propanol, 1-butanol, and tert-butanol, chloroform, and methylene chloride. Chlorine solvents, aromatic solvents such as benzene and toluene, ester solvents such as ethyl acetate, butyl acetate and isopropyl acetate, ether solvents such as diethyl ether, tetrahydrofuran and dioxane, ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, etc. And glycol ether solvents.
In this case, it is effective to add the solvent within a range that does not cause the problem of solvent resistance and VOC, and the amount is preferably 0.1 to 5% by mass, more preferably 0.1 to 3% by mass with respect to the whole ink composition. % Range.

[Polymer compound]
Various polymer compounds can be added to the ink composition in order to adjust film properties. Examples of the polymer compound include styrene polymers, acrylic polymers, cyclic ether polymers, polyvinyl butyral resins, polyurethane resins, polyamide resins, polyester resins, epoxy resins, phenol resins, polycarbonate resins, polyvinyl butyral resins, and polyvinyl formal resins. Shellac, vinyl resin, acrylic resin, rubber resin, wax, and other natural resins can be used. Two or more of these may be used in combination. Of these, copolymerization of styrene monomers, acrylic monomers, and cyclic ethers is preferred. Furthermore, as a copolymer composition of the polymer binder, a copolymer containing “cyclic ether group-containing monomer” and “vinyl ether group-containing monomer” as a structural unit is also preferably used.
The addition amount is appropriately selected according to the purpose, but is generally about 0.01 to 10.0% by mass of the ink composition.

[Surfactant]
Examples of the surfactant include those described in JP-A Nos. 62-173463 and 62-183457. For example, anionic surfactants such as dialkylsulfosuccinates, alkylnaphthalenesulfonates, fatty acid salts, polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, acetylene glycols, polyoxyethylene / polyoxypropylene blocks Nonionic surfactants such as copolymers, and cationic surfactants such as alkylamine salts and quaternary ammonium salts. An organic fluoro compound may be used in place of the surfactant. The organic fluoro compound is preferably hydrophobic. Examples of the organic fluoro compounds include fluorine surfactants, oily fluorine compounds (eg, fluorine oil) and solid fluorine compound resins (eg, tetrafluoroethylene resin). No. (columns 8 to 17) and those described in JP-A Nos. 62-135826.
The addition amount is appropriately selected according to the purpose, but is generally about 0.001 to 5.0% by mass of the ink composition.

In addition to this, if necessary, for example, leveling additives, matting agents, waxes for adjusting film physical properties, polymerization to inhibit the adhesion to recording media such as polyolefin and PET, and the like, The tackifier which does not do can be contained.
As the tackifier, specifically, a high molecular weight adhesive polymer described in JP-A-2001-49200, 5-6p (for example, (meth) acrylic acid and an alkyl group having 1 to 20 carbon atoms). An ester with an alcohol having, an ester of (meth) acrylic acid with an alicyclic alcohol having 3 to 14 carbon atoms, a copolymer comprising an ester of (meth) acrylic acid with an aromatic alcohol having 6 to 14 carbon atoms) And a low molecular weight tackifying resin having a polymerizable unsaturated bond.

[Preferred physical properties of ink composition]
The ink composition of the present invention preferably has an ink viscosity of 50 mPa · s or less, more preferably 30 mPa · s or less at the temperature at the time of ejection in consideration of ejection properties. It is preferable to adjust and determine the composition ratio. The ink viscosity at 25 ° C. is 10 to 300 mPa · s, preferably 10 to 100 mPa · s. By setting the viscosity at room temperature high, even when a porous recording medium is used, ink penetration into the recording medium can be prevented, uncured monomer can be reduced, and odor can be reduced. Dot bleeding at the time of landing can be suppressed, and as a result, the image quality is improved. If the ink viscosity at 25 ° C. is less than 10 mPa · s, the effect of preventing bleeding is small. Conversely, if the ink viscosity is more than 500 mPa · s, problems may occur in the delivery of the ink liquid.

  The surface tension of the ink composition of the present invention is preferably 20 to 30 mN / m, more preferably 23 to 28 mN / m. When recording on various recording media such as polyolefin, PET, coated paper, and non-coated paper, 20 mN / m or more is preferable from the viewpoint of bleeding and penetration, and 30 mN / m or less is preferable in terms of wettability.

[Inkjet recording method]
The ink composition of the present invention can be suitably used as an ink for inkjet recording. There are no particular restrictions on the ink jet recording method, for example, a charge control method that ejects ink using electrostatic attraction, a drop-on-demand method (pressure pulse method) that uses the vibration pressure of a piezo element, and an electrical signal that is acoustic Either an acoustic ink jet system that irradiates ink by irradiating it with ink instead of using a beam, or a thermal ink jet system that uses ink to form bubbles by heating the ink and use the generated pressure. Also good. The inkjet recording method includes a method of ejecting a large number of low-density inks called photo inks in a small volume, a method of improving image quality using a plurality of inks having substantially the same hue and different concentrations, and colorless and transparent. A method using ink.
Among these, the ink is suitable as a drop-on-demand type (pressure pulse type) ink jet recording ink using a piezo element.

The ejected ink composition of the present invention is irradiated with actinic radiation to cure the ink composition and form an image. This process will be described.
The ink composition ejected on the recording medium is cured by irradiation with actinic radiation. This is because the polymerization initiator contained in the ink composition of the present invention is decomposed by irradiation with actinic radiation to generate radicals, acids, bases and other initiation species, and the polymerization reaction of the polymerizable compound by the function of the initiation species This is because it is created and promoted. At this time, if a sensitizing dye is present together with the polymerization initiator in the ink composition, the sensitizing dye in the system absorbs actinic radiation to be in an excited state, and promotes decomposition of the polymerization initiator by contacting with the polymerization initiator. And a more sensitive curing reaction can be achieved.

  Here, α rays, γ rays, electron beams, X rays, ultraviolet rays, visible light, infrared rays, or the like can be used as the active radiation used. Although the peak wavelength of actinic radiation is based also on the absorption characteristic of a sensitizing dye, it is preferable that it is 200-600 nm, for example, it is more preferable that it is 300-450 nm, and it is still more preferable that it is 350-420 nm.

In addition, the polymerization initiation system of the ink composition of the present invention has sufficient sensitivity even with a low output actinic radiation. Thus, the output of the active radiation is preferably 2,000 mJ / cm ² or less, more preferably from 10 to 2,000 mJ / cm ^2, more preferably be 20 to 1,000 mJ / cm ² Particularly preferably, it is 50 to 800 mJ / cm ² .
Furthermore, the actinic radiation is, the exposure surface illuminance of, for example, 10 to 2,000 mW / cm ^2, preferably, suitably be irradiated at 20 to 1,000 mW / cm ^2.

Mercury lamps and gas / solid lasers are mainly used as actinic radiation sources, and mercury lamps and metal halide lamps are widely known as light sources used for curing UV photocurable ink jet recording inks. Yes. However, from the viewpoint of environmental protection, mercury-free is strongly desired, and replacement with a GaN-based semiconductor ultraviolet light-emitting device is very useful industrially and environmentally. Furthermore, LED (UV-LED) and LD (UV-LD) are small, have a long life, have high efficiency, and are low in cost, and are expected as light sources for photo-curable ink jets.
Further, a light emitting diode (LED) and a laser diode (LD) can be used as the active radiation source. In particular, when an ultraviolet light source is required, an ultraviolet LED and an ultraviolet LD can be used. For example, Nichia Corporation has introduced a purple LED whose main emission spectrum has a wavelength between 365 nm and 420 nm. When even shorter wavelengths are required, US Pat. No. 6,084,250 discloses an LED that can emit actinic radiation centered between 300 nm and 370 nm. Other ultraviolet LEDs are also available and can emit radiation in different ultraviolet bands. The actinic radiation source particularly preferred in the present invention is a UV-LED, particularly preferably a UV-LED having a peak wavelength at 350 to 420 nm.
Incidentally, it is preferable that maximum illumination intensity of the LED on a recording medium is 10 to 2,000 mW / cm ^2, more preferably 20 to 1,000 mW / cm ^2, particularly preferably 50 to 800 mW / cm ² .

The ink composition of the present invention is suitably irradiated with such actinic radiation for, for example, 0.01 to 120 seconds, preferably 0.1 to 90 seconds.
Actinic radiation irradiation conditions and a basic irradiation method are disclosed in JP-A-60-132767. Specifically, the light source is provided on both sides of the head unit including the ink ejection device, and the head unit and the light source are scanned by a so-called shuttle method. Irradiation with actinic radiation takes a certain time (for example, 0.01 to 0.5 seconds, preferably 0.01 to 0.3 seconds, more preferably 0.01 to 0.15 seconds) after ink landing. Will be done. In this way, by controlling the time from ink landing to irradiation to an extremely short time, it is possible to prevent the ink that has landed on the recording medium from spreading before curing. Further, since the ink can be exposed to a porous recording medium before the ink penetrates to a deep part where the light source does not reach, residual unreacted monomer can be suppressed, and as a result, odor can be reduced. .
Further, the curing may be completed by another light source that is not driven. WO99 / 54415 pamphlet discloses a method using an optical fiber or a method of irradiating a recording unit with UV light by applying a collimated light source to a mirror surface provided on the side surface of the head unit as an irradiation method. The curing method can also be applied to the ink jet recording method of the present invention.
In this manner, the ink composition of the present invention can form an image on the surface of a recording medium by being cured with high sensitivity by irradiation with actinic radiation.

(Recording medium)
The recording medium on which the ink composition of the present invention or the ink for ink jet recording is discharged is not particularly limited, and any medium can be used according to the purpose as long as it is a dimensionally stable support. Moreover, it is not necessarily a flat thing, It can record also on the medium which has a situation.
Examples of the material used for the recording medium include paper, paper laminated with plastic (eg, polyethylene, polypropylene, polystyrene, etc.), metal plate (eg, aluminum, zinc, copper, etc.), and plastic film (eg, diacetic acid). Cellulose, cellulose triacetate, cellulose propionate, cellulose butyrate, cellulose acetate butyrate, cellulose nitrate, polyethylene terephthalate, polyethylene, polystyrene, polypropylene, polycarbonate, polyvinyl acetal, etc.), paper or plastic film on which the above metals are laminated or deposited Etc.

EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples.
Example 1
[Synthesis Example 1: Synthesis of Dispersant 1]
After 0.8 g of purified ethylene glycol is dissolved in 50 ml of dehydrated xylene under a nitrogen atmosphere, a titanium coupling agent having a basic group in the molecule (Plenact KR44: trade name, manufactured by Ajinomoto Fine Techno Co., Ltd.) 4.0 g (solid content) was added, the mixture was reacted for 2 hours at a temperature of 110 ° C., and the solvent was distilled off under reduced pressure to obtain 4.8 g of liquid substance A.
Next, 2.5 g of liquid substance A obtained above with purified acetone 50 g, hexamethylene diisocyanate and polycaprolactone diol (Placcel L205AL: trade name, manufactured by Daicel Chemical Industries) were reacted with a terminal NCO urethane (Mw = 4500) 17.9 g was dissolved and reacted in a pressure reactor at 90 ° C. for 2 hours for urethanization, and the solvent was distilled off under reduced pressure to disperse Dispersant 1 having a titanium alkoxide group in the molecule. Obtained.

[Synthesis Example 2: Synthesis of Dispersant 2]
25 g of polycaprolactone diol (Placcel L205AL) subjected to dehydration under reduced pressure was dissolved in 100 ml of purified xylene under a nitrogen atmosphere, and then a titanium coupling agent having a phosphate group in the molecule (Plenact KR38S: trade name, Ajinomoto Fine) (Techno Co., Ltd.) 20 g (solid content) (Ajinomoto Fine Techno Co., Ltd.) was added and reacted at 110 ° C. for 2 hours, and the solvent was distilled off under reduced pressure to obtain 43 g of liquid substance B.
Next, 25 g of the liquid substance B obtained above and 54 g of terminal NCO urethane (Mw = 4500) obtained by reacting hexamethylene diisocyanate and polycaprolactone diol (Placcel L205AL) were dissolved in 100 g of purified acetone, followed by pressure reaction. The reaction was carried out in an apparatus at 90 ° C. for 2 hours for urethanization, and the solvent was distilled off under reduced pressure to obtain Dispersant 2 having a phosphoric acid group and a titanium alkoxide group in the molecule.

[Synthesis Example 3: Synthesis of Dispersant 3]
25 g of polycaprolactone diol (Placcel L205AL) dehydrated under reduced pressure was dissolved in 100 ml of purified xylene under a nitrogen atmosphere, and then 20 g (solid content) of a titanium coupling agent having a phosphate group in the molecule (preneact KR38S). The mixture was reacted for 2 hours at a temperature of 110 ° C., and the solvent was distilled off under reduced pressure to obtain 43 g of liquid substance C.
Next, 25 g of the liquid substance C obtained above and 66 g of terminal NCO urethane (Mw = 5500) obtained by reacting hexamethylene diisocyanate and polypropylene glycol (Mw = 200) were dissolved in 100 g of purified acetone. The resulting mixture was reacted at 90 ° C. for 2 hours for urethanization, and the solvent was distilled off under reduced pressure to obtain Dispersant 3 having a phosphate group, a titanium alkoxide group, an ethylene oxide structural unit, and a propylene oxide structural unit in the molecule. .

[Synthesis Example 4: Synthesis of Dispersant 4]
In a pressure reactor, 8 g of dehydrated ethylene glycol was dissolved in 50 ml of purified xylene under a nitrogen atmosphere, and then 40 g of titanium coupling agent (preneact KR44) having a basic group in the molecule (solid content) And heated for 2 hours so as to maintain a temperature of 110 ° C., reacted, and the solvent was distilled off under reduced pressure to obtain 48 g of liquid substance D.
Next, 25 g of the liquid substance D obtained above and 198 g of terminal COOH polyester (Mw = 5000) obtained by reacting adipic acid and polycaprolactone diol (Placcel L205AL) are subjected to a condensation reaction under reduced pressure, and a base is formed in the molecule. Dispersant 4 having a functional group and a titanium alkoxide group was obtained.

[Synthesis Example 5: Synthesis of Dispersant 5]
In a pressure reactor, 8 g of dehydrated ethylene glycol was dissolved in 50 ml of purified xylene under a nitrogen atmosphere, and then 2.0 g of titanium coupling agent (preneact KR44) having a basic group in the molecule (solid) The mixture was heated for 2 hours so as to maintain a temperature of 110 ° C., reacted, and the solvent was distilled off under reduced pressure to obtain 4.3 g of liquid substance E.
Next, 25 g of the liquid substance E obtained above and 178 g of terminal COOH polyester (Mw = 4500) obtained by reacting adipic acid and polyethylene glycol (Mw = 200) are subjected to a condensation reaction under reduced pressure, and a base is formed in the molecule. Dispersant 5 having a functional group, a titanium alkoxide group, an ethylene oxide structural unit, and a propylene oxide structural unit was obtained.

[Synthesis Example 6: Synthesis of Comparative Dispersant 1]
The terminal NCO urethane (Mw = 4500) obtained by reacting hexamethylene diisocyanate and polycaprolactone diol (Placcel L205AL) was reacted with methanol at 80 ° C. for 3 hours to obtain comparative dispersant 1.
[Synthesis Example 7: Synthesis of Comparative Dispersant 2]
Comparative NCO urethane (Mw = 4500) obtained by reacting hexamethylene diisocyanate and polycaprolactone diol (Placcel L205AL) and 3-hydroxybutanoic acid are reacted at 80 ° C. for 3 hours, and a comparative dispersant having an acid group in the molecule 2 was obtained.
[Synthesis Example 8: Synthesis of Comparative Dispersant 3] A terminal-containing NCO urethane (Mw = 4500) obtained by reacting a base-containing hexamethylene diisocyanate and polycaprolactone diol (Placcel L205AL) with ethylenediamine,
The reaction was carried out at 50 ° C. for 1 hour to obtain Comparative Dispersant 3 having a basic group in the molecule.
[Synthesis Example 9: Synthesis of surface-treated pigment A]
Preneact KR9SA 0.3 g was added to 100 ml of dehydrated and purified THF, and 10 g of pigment (alumina-treated titanium oxide, average particle size: 0.20 μm transmission electron microscope, particle surface alumina treatment rate 60%) was added and stirred for 30 minutes. Went. Thereafter, the solvent was distilled off, followed by drying under reduced pressure at 100 ° C. for 2 hours to obtain surface-treated pigment A.

(Examples 1-3, Comparative Examples 1-3)
[Ink adjustment 1]
In the following compounding ratio, pigment, initiator, sensitizing dye, three kinds of curable compounds, dispersants 1 to 5 obtained in Synthesis Examples 1 to 6, and comparative dispersants 1 to 3 are dispersed with a disperser, and ink composition I made a thing.
(Ink formula 1)
Pigment: Alumina-treated titanium oxide (average particle diameter measured by transmission electron microscope image: 0.20 μm,
Particle surface alumina treatment rate 60%) 15% by mass
Initiator: Triphenylsulfonium salt (UVI-6992, manufactured by Dow Chemical Company)
15% by mass
Sensitizing dye: 9,10-dibutoxyanthracene 1% by mass
Polymerizable compound: 3,4-epoxycyclohexylmethyl-3 ′, 4′-epoxycyclohexanecarboxylate (Celoxide 2021A: manufactured by Daicel UC Corporation)
45% by mass
Polymerizable compound: 3,7-bis (3-oxetanyl) -5-oxanonane (OXT-22)
1: Toagosei Co., Ltd.) 20% by mass
Dispersant: Dispersant obtained in Synthesis Examples 1-6, compound shown in Table 1 2% by mass

(Comparative Example 3)
An ink of Comparative Example 3 was prepared according to Ink Formula 1 except that the pigment of Ink Formula 1 was changed to Surface Treatment Pigment A.

(Examples 4-6, Comparative Examples 4-6)
[Ink adjustment 2]
In the following compounding ratio, pigment, initiator, sensitizing dye, three kinds of curable compounds, dispersants 1 to 5 obtained in Synthesis Examples 1 to 6, and comparative dispersants 1 to 3 are dispersed with a disperser, and ink composition I made a thing.
(Ink formula 2)
Pigment: silica-treated titanium oxide (average particle diameter measured by transmission electron microscope image: 0.21 μm,
Particle surface silica treatment rate 60%) 15% by mass
Initiator: Triphenylsulfonium salt (UVI-6992, manufactured by Dow Chemical Company)
15% by mass
Sensitizing dye: 9,10-dibutoxyanthracene 1% by mass
Polymerizable compound: 3,4-epoxycyclohexylmethyl-3 ′, 4′-epoxycyclohexanecarboxylate (Celoxide 2021A: manufactured by Daicel UCB)
22% by mass
Polymerizable compound: 3,7-bis (3-oxetanyl) -5-oxetane (OXT-221: manufactured by Toagosei Co., Ltd.) 45% by mass
Dispersant: Dispersant obtained in Synthesis Examples 1 to 6, compounds shown in Table 2 2% by mass

  Evaluation of the viscosity, dispersibility, sedimentation, redispersibility, concealability, ejection stability, curability, adhesion, and weather resistance of the ink compositions of Examples 1 to 6 and Comparative Examples 1 to 4 by the following methods. did. The results are shown in Tables 1 and 2 above.

[Evaluation of ink composition]
1. Dispersibility The dispersibility of the ink composition was observed using an optical microscope and evaluated according to the following criteria.
1-1. Presence / absence of aggregated particles The particle diameter of the particles was measured using an optical microscope. When particles of 1 μm or more were observed, it was determined that the pigment particles were aggregated.
○: No particle of 1 μm or more (no aggregation of pigment is observed).
X: There are particles of 1 μm or more (aggregation is observed).
1-2. Particle size distribution Particle size and distribution were measured by laser light scattering and evaluated according to the following criteria. The smaller the average particle size, the more the aggregation is suppressed, indicating a state close to monodispersion, and the larger the volume frequency of such particles, the more uniformly dispersed it is determined. , Evaluation: If A to C, it is determined that the ink composition has a practically no problem level.
A: The average particle diameter is 0.5 μm or less, and 90% or more of the total volume frequency exists within ± 25% of the average particle diameter.
B: Although the average particle size is 0.5 μm or less, the particles existing within ± 25% of the average particle size are less than 10% of the total volume frequency.
C: The average particle diameter is 1.0 μm or less, and 90% or more of the total volume frequency exists within ± 25% of the average particle diameter.
D: The average particle size is 1.0 μm or less, and particles existing within ± 25% of the average particle size are less than 10% of the total volume frequency.
E: The average particle diameter is 1.0 μm or more.

2. Discharge stability The ink composition was continuously printed for 60 minutes by an inkjet printer (printing density 300 dpi, droplet ejection frequency 4 kHz, nozzle number 64). The ejection state and the formed image were observed and evaluated according to the following criteria.
A: The liquid could be discharged for 60 minutes without any problem.
B: Some satellites were generated.
C: Nozzle missing in the image.
D: Printing failed due to nozzle clogging before 60 minutes passed.

3. Storage stability After the prepared ink was stored at 75% RH and 60 ° C. for 3 days, the ink viscosity at the injection temperature was measured, and the increase in the ink viscosity was expressed as a viscosity ratio after storage / before storage. When the viscosity does not change and is close to 1.0, the storage stability is good, and when it exceeds 1.5 or 0.9 or less, clogging may occur at the time of injection, and it is evaluated as not preferable.

As shown in Tables 1 and 2, the ink composition of the present invention using the specific dispersant is excellent in dispersibility, ejection stability, and temporal stability of dispersion in both ink preparation examples 1 and 2. You can see that Furthermore, the image formed with the ink composition of the present invention had good coating curability, adhesion to the substrate, and concealment.
With such an ink composition, there is little clogging and ink supply to the apparatus is stable. On the other hand, the ink composition of the comparative example not containing the dispersant according to the present invention was inferior in ink dispersibility and temporal stability, and could not satisfy the ejection stability.

(Examples 7-9, Comparative Examples 7-9)
[Ink adjustment 3]
Disperse pigments, radical initiators, two curable compounds, dispersants 1-5 obtained in Synthesis Examples 1-6, and comparative dispersants 1-3 with a disperser at the following blending ratio to create an ink composition. did.
(Ink formula 3)
Pigment: Alumina-treated titanium oxide (average particle diameter measured by transmission electron microscope image: 0.20 μm,
Particle surface alumina treatment rate 60%) 15% by mass
Polymerizable compound 1: 1,6-hexanediol diacrylate 50% by mass
Polymerizable compound 2: triethylene glycol divinyl ether 28% by mass
Polymerization initiator: IRGACURE 184 (manufactured by CSC) 5% by mass
Dispersant: Dispersant obtained in Synthesis Examples 1-6, compound shown in Table 1 2% by mass

(Comparative Example 3)
An ink was prepared according to ink formulation 3 except that the pigment of ink formulation 3 was changed to surface-treated pigment A.

(Example 10-12, Comparative Example 10-12)
[Ink adjustment 4]
Disperse pigments, photoinitiators, sensitizing dyes, two types of photocurable compounds and dispersants 1 to 5 obtained in Synthesis Examples 1 to 6 and comparative dispersants 1 to 3 with a disperser at the following blending ratio. An ink composition was prepared.
(Ink formula 1)
Pigment: silica-treated titanium oxide (average particle diameter measured by transmission electron microscope image: 0.21 μm,
Particle surface asilica treatment rate 60%) 15% by mass
Polymerizable compound 1: 1,6-hexanediol diacrylate 50% by mass
Polymerizable compound 2: 38.8% by mass of triethylene glycol divinyl ether
Polymerization initiator: IRGACURE 184 (manufactured by CSC) 5% by mass
Dispersant: Dispersant obtained in Synthesis Examples 1 to 6, compounds shown in Table 4 2% by mass
(Comparative Example 12)
An ink was prepared according to ink formulation 4 except that the pigment of ink formulation 4 was changed to surface-treated pigment A.

Viscosity, dispersibility, sedimentation, redispersibility, concealability, ejection stability, curability, adhesion, and weather resistance evaluation of the ink compositions of Examples 7 to 12 and Comparative Examples 7 to 12 were evaluated by the following methods. did. The results are shown in Tables 3 to 4 above.
As shown in Tables 3 to 4, in any of the ink preparation examples 3 and 4, the ink composition of the present invention using the specific dispersant is excellent in dispersibility, ejection stability, and dispersion stability over time. You can see that Furthermore, the image formed with the ink composition of the present invention had good coating curability, adhesion to the substrate, and concealment.
From the above results, the ink composition to which the particle dispersion of the present invention is applied has little clogging in both the cationic curable composition and the radical curable composition, and the ink supply to the apparatus is stable. I understand that. On the other hand, the comparative ink composition containing no dispersant according to the present invention is inferior in ink dispersibility and temporal stability even when a radically polymerizable composition is used, and satisfies the ejection stability. I couldn't let you.

Claims (3)

  A particle dispersion comprising particles dispersed with a dispersant comprising a condensate obtained by using a metal alkoxide compound and / or a partial hydrolyzate of a metal alkoxide compound.   The particle dispersion according to claim 1, further comprising one or more compounds selected from the group consisting of acidic compounds and basic compounds.   An ink composition comprising a pigment dispersed with a dispersant comprising a condensate obtained by using a metal alkoxide and / or a partial hydrolyzate thereof.