JP2009256422A - Photocurable ink composition, inkjet recording method, recorded matter, ink set for inkjet recording, ink cartridge, and recording device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photocurable ink composition highly satisfying both of storage stability and photocuring properties in image printing. <P>SOLUTION: The photocurable ink composition contains 5 mass% or more of a dendritic polymer as a polymerizable compound and a hindered phenol compound as a polymerization inhibitor. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an ink composition that is cured by light such as ultraviolet rays, and particularly relates to a photocurable ink composition that can satisfy both storage stability and photocurability during image printing. The present invention also relates to an ink jet recording method using the photocurable ink composition and a recorded matter thereof. Furthermore, the present invention relates to an ink set for ink jet recording, an ink cartridge, and a recording apparatus provided with the photocurable ink composition.

The ink jet recording method is a printing method in which printing is performed by causing a droplet of an ink composition to fly and adhere to a recording medium such as paper. This ink jet recording method is characterized in that a high-resolution and high-quality image can be printed at high speed. The ink composition used in the ink jet recording method generally contains an aqueous solvent as a main component and contains a coloring component and a wetting agent such as glycerin for the purpose of preventing clogging.
On the other hand, paper or fabrics that are difficult to penetrate water-based ink compositions, or materials such as metals, plastics, and the like that do not penetrate, such as phenol, melamine, vinyl chloride, acrylic, polycarbonate, PET, PP, and PE When printing on a recording medium such as a film, the ink composition is required to contain a component capable of stably fixing the coloring material to the recording medium.

In response to such a requirement, a photocurable inkjet ink containing a colorant, a photocuring agent (radical polymerizable compound), a (photoradical) polymerization initiator, and the like is disclosed (for example, Patent Document 1). reference.). According to this ink, it is said that the ink can be prevented from bleeding into the recording medium and the image quality can be improved.
In addition, the polymerizable compound used in this case is preferably a highly polymerizable compound. However, many photocurable inks using a polymerizable compound having high polymerizability are polymerized by radicals generated by heat and thicken or cure over time, and lack storage stability. If the photocurable ink is thickened or hardened during storage, ink ejection properties and image quality at the time of printing by inkjet recording or the like will be affected.

  Therefore, in order to solve such a problem lacking in storage stability, a technique for suppressing unnecessary polymerization during storage of a polymerizable compound having high polymerizability by adding a polymerization inhibitor to the ink composition. It has been reported.

  As a polymerization inhibitor used in the photocurable ink, a hindered amine light stabilizer (HALS) is known (for example, see Patent Documents 2 to 4). Patent Document 2 describes that weather resistance is obtained by including a hindered amine light stabilizer (HALS) in the ink composition, and Patent Document 3 has excellent character quality, no color mixing, and high definition. It describes that an image can be recorded.

  However, since the polymerization inhibitor inherently suppresses polymerization, there is a concern that the polymerization and curing of the ink during image printing may be deteriorated. On the other hand, Patent Document 4 discloses a photocurable ink composition that can satisfy both storage stability and photocurability during image printing while containing a hindered amine light stabilizer (HALS).

  By the way, patent document 5 is related with the photocurable sheet used as an adhesive agent which adhere | attaches photocurable resin board | substrates in the case of preparation of an optical information recording medium. According to Patent Document 5, the hindered phenol compound, which is a polymerization inhibitor, is encapsulated in a microcapsule so that the effect of addition can be generated only after curing, thereby curing without deteriorating curability. Prevents subsequent film discoloration. However, in Patent Document 5, since microencapsulation is necessary, there is a limit to its versatility, and there is no mention of improving the storage stability of the photocurable composition itself.

Various techniques have been devised as in Patent Documents 1 to 5 described herein, and a photocurable ink composition that can further satisfy both storage stability and photocurability at the time of image printing. The current situation is that something is desired.
US Pat. No. 5,562,001 JP 2003-268026 A JP 2004-238456 A JP 2007-138084 A JP 2005-154552 A

  The present invention is intended to improve the above-described conventional technique, and to provide a photocurable ink composition that can satisfy both storage stability and photocurability at the time of image printing to a higher degree.

As a result of intensive studies, the present inventor has achieved the above object by adopting the following configuration, and has achieved the present invention.
That is, the present invention is as follows.
(1) A photocurable ink composition containing 5% by mass or more of a dendritic polymer as a polymerizable compound and a hindered phenol compound as a polymerization inhibitor.
(2) The photocurable ink composition according to (1), wherein the content of the dendritic polymer is 5 to 30% by mass.
(3) The photocurable ink composition according to (1) or (2), wherein an addition ratio of the dendritic polymer and the hindered phenol compound is 10: 1 to 150: 1 on a mass basis.
(4) The photocurable ink composition according to any one of (1) to (3), further containing allyl glycol and / or an N-vinyl compound as the polymerizable compound.
(5) An inkjet recording method in which an image is formed using the photocurable ink composition according to any one of (1) to (4) above.
(6) A recorded matter in which an image is formed on a recording medium by the inkjet recording method described in (5) above.
(7) An ink set for ink jet recording comprising a plurality of photocurable ink compositions, wherein at least one photocurable ink composition according to any one of (1) to (4) above is used. Ink set for inkjet recording.
(8) An ink cartridge comprising the ink set for ink jet recording described in (7) above.
(9) A recording apparatus including the ink cartridge according to (8).

According to the photocurable ink composition of the present invention, by containing 5% by mass or more of a dendritic polymer as a polymerizable compound and using a hindered phenol compound as a polymerization inhibitor, It is possible to inactivate the generated radicals and further suppress the increase in viscosity over time compared to the conventional product. On the other hand, such a hindered phenol compound does not inhibit radical polymerization due to ultraviolet irradiation at the time of printing of a polymerizable compound such as a dendritic polymer, and maintains the same photocurability as when no polymerization inhibitor is added. Can do.
Therefore, an ink jet recording method capable of stably discharging ink even after long-term storage and giving an image quality excellent in curability, its recorded matter, and ink for ink jet recording satisfying both storage stability and photocurability at the time of image printing A set, an ink cartridge, and a recording apparatus can be provided.

  Hereinafter, the photocurable ink composition of the present invention will be described in detail.

The photocurable ink composition of the present invention contains a dendritic polymer as a polymerizable compound. Dendritic polymers can be broadly classified into six structures as shown below ("dendritic polymers-a world of high functionality with multi-branched structures-" supervised by Keigo Aoi / Masaaki Enomoto, NT Co., Ltd.・ See S).
I Dendrimer
II Linear dendritic polymer
III Dendrigraft polymer
IV Hyperbranched polymer
V star hyperbranched polymer
VI Hypergraft polymer

  Among these, I to III have a degree of branching (DB) of 1 and have a defect-free structure, whereas IV to VI have a random branch structure that may contain defects. is doing. In particular, dendrimers can be arranged with high density and concentration of reactive functional groups on the outermost surface compared to generally used linear polymers. Expectation is high. In addition, even if the hyperbranched polymer, dendrigraft polymer or hypergraft polymer is not as large as the dendrimer, it is possible to introduce many reactive functional groups on the outermost surface, and it is excellent in curability.

  Unlike conventional linear polymers and branched polymers, these dendritic polymers repeat highly branched structures in three dimensions and are highly branched. Therefore, it is possible to keep the viscosity low compared to a linear polymer having the same molecular weight.

  Examples of the method for synthesizing the dendrimer used in the present invention include a Divergent method for synthesizing from the center to the outside and a Convergent method for synthesizing from the outside to the center.

  The dendrimer, hyperbranched polymer, dendrigraft polymer and hypergraft polymer used in the present invention are preferably solid at room temperature and have a number average molecular weight in the range of 1,000 to 100,000, particularly in the range of 2000 to 50,000. Are preferably used. When it is not solid at room temperature, the maintainability of the formed image is deteriorated. In addition, when the molecular weight is lower than the above range, the fixed image becomes fragile, and when the molecular weight is higher than the above range, the viscosity of the ink becomes too high even if the addition amount is lowered, in terms of flight characteristics. It is no longer practical.

  The dendrimers, hyperbranched polymers, dendrigraft polymers and hypergraft polymers used in the present invention are dendrimers, hyperbranched polymers, dendrigraft polymers and hypergraft polymers having a radically polymerizable functional group on the outermost surface. Preferably there is. By adopting a structure capable of radical polymerization on the outermost surface, the polymerization reaction proceeds rapidly.

  Examples of the polymer having a dendrimer structure include amidoamine dendrimers (US Pat. Nos. 4,507,466, 4,558,120, 4,568,737, 4,587,329, and 4). 631,337, 4,694,064), phenyl ether dendrimers (US Pat. No. 5,041,516, Journal of American Chemistry 112 (1990, pages 7638-7647)) Etc. As for the amidoamine dendrimer, a dendrimer having a terminal amino group and a carboxylic acid methyl ester group is commercially available as “Starburst ™ (PAMAM)” from Aldrich. In addition, the terminal amino group of the amidoamine-based dendrimer can be reacted with various acrylic acid derivatives and methacrylic acid derivatives to synthesize amidoamine-based dendrimers having corresponding terminals, and then used.

  Examples of acrylic acid derivatives and methacrylic acid derivatives that can be used include acrylic acid such as methyl, ethyl, n-butyl, t-butyl, cyclohexyl, palmityl, and stearyl, or alkyl esters of methacrylic acid, acrylic acid such as acrylic acid amide, and isopropylamide. Alternatively, methacrylic acid alkylamides may be mentioned, but not limited thereto.

Various examples of the phenyl ether dendrimer are described in, for example, the above Journal of American Chemistry Vol. 112 (1990, pages 7638-7647). For example, 3,5-dihydroxybenzyl alcohol is used, A second-generation benzyl alcohol was synthesized by reacting with 5-diphenoxybenzyl bromide, the OH group was converted to Br using CBr ₄ and triphenylphosphine, and then reacted with 3,5-dihydroxybenzyl alcohol in the same manner. The next generation benzyl alcohol is synthesized, and the following reaction is repeated to synthesize the desired dendrimer. As for the phenyl ether dendrimer, the terminal can be substituted with one having various chemical structures instead of the terminal benzyl ether bond. For example, when synthesizing the dendrimer described in Journal of American Chemistry Vol. 112, various alkyl halides are used instead of the benzyl bromide, a phenyl ether dendrimer having a terminal structure having a corresponding alkyl group can be obtained. In addition, polyamine dendrimers (Macromol. Symp. 77, 21 (1994)) and derivatives obtained by modifying terminal groups thereof can be used.

  As the hyperbranched polymer, for example, hyperbranched polyethylene glycol can be used. A hyperbranched polymer uses a monomer that has two or more kinds of reaction points corresponding to a branched portion and one kind of another reaction point corresponding to a connecting portion in one molecule, and the target polymer in one step. It is obtained by synthesis (Macromolecules, 29 (1996), 3831-3838). For example, a 3,5-dihydroxybenzoic acid derivative is an example of a monomer for a hyperbranched polymer. An example of the production of hyperbranched polymer is 3,5-bis obtained from 1-bromo-8- (t-butyldiphenylsiloxy) -3,6-dioxaoctane and methyl 3,5-dihydroxybenzoate. 3,5-bis ((8'-hydroxy-3 ', 6) which is a hydrolyzate of methyl ((8'-(t-butyldiphenylsiloxy) -3 ', 6'-dioxaoctyl) oxy) benzoate The hyperbranched polymer poly [bis (triethyleneglycol) benzoate] can be synthesized by heating methyl '' -dioxaoctyl) oxy) benzoate with dibutyltin diacetate in a nitrogen atmosphere.

  When 3,5-dihydroxybenzoic acid is used, the hyperbranched polymer terminal group becomes a hydroxyl group, and therefore, hyperbranched polymers having various terminal groups are synthesized by using an appropriate alkyl halide for the hydroxyl group. be able to.

  The properties of monodisperse polymers or hyperbranched polymers with a dendrimer structure are governed by the chemical structure of the main chain and the chemical structure of the terminal group, but the characteristics are particularly dependent on the difference of the substituents in the terminal group and chemical structure. Are very different. Those having a polymerizable group at the terminal are particularly useful because of their reactivity, the gelation effect after photoreaction is great. A dendrimer having a polymerizable group can be obtained by chemically modifying a compound having a polymerizable group at the end of one having a basic atomic group such as an amino group, a substituted amino group, or a hydroxyl group at the end.

  For example, it is synthesized by adding, for example, an isocyanate group-containing vinyl compound to a polyfunctional compound obtained by Michael addition of an active hydrogen-containing (meth) acrylate compound to an amino dendrimer. Moreover, the dendrimer which has a polymerizable group at the terminal is obtained by making (meth) acrylic acid chloride etc. react with an amino dendrimer, for example. Examples of the vinyl compound providing such a polymerizable group include compounds having an ethylenically unsaturated bond capable of radical polymerization. Examples thereof include acrylic acid, methacrylic acid, itaconic acid, crotonic acid, and isocrotonic acid. And compounds having ethylenically unsaturated bonds capable of various radical polymerization described later, such as unsaturated carboxylic acids such as maleic acid and salts thereof.

  In the present invention, the above dendrimer, hyperbranched polymer, dendrigraft polymer and hypergraft polymer may be used alone or in combination with other types of dendrimers and hyperbranched polymers.

In the photocurable ink composition of the present invention, the amount of the dendritic polymer added is 5% by mass or more, more preferably 10 to 30% by mass, and still more preferably 10 to 20% by mass. If it is the said range, the suitability as a photocurable ink can be preferably maintained.
When the addition amount of the dendrimer is less than 5% by mass, the curability as the photocurable ink composition becomes insufficient. If the addition amount of the dendrimer is 30% by mass or less, problems such as the viscosity, dispersion stability, and storage stability of the ink composition do not occur.

The photocurable ink composition of the present invention contains the dendritic polymer as a polymerizable compound and preferably allyl glycol and / or an N-vinyl compound as a dilution monomer.
The amount of allyl glycol and / or N-vinyl compound added is preferably in the range of 20% by mass to 80% by mass. If it is less than 20% by mass, problems such as viscosity, dispersion stability and storage stability of the ink composition occur, and if it exceeds 80% by mass, the curability as a photocurable ink composition may be insufficient. . More preferably, it is the range of about 20-70 mass%.

Examples of the N-vinyl compound include N-vinylformamide, N-vinylcarbazole, N-vinylacetamide, N-vinylpyrrolidone, N-vinylcaprolactam, acryloylmorpholine, and derivatives thereof, and have excellent curability. In particular, N-vinylformamide is preferable.
In particular, allyl glycol and N-vinylformamide are monofunctional radically polymerizable monomers, and are preferable because they are unlikely to cause unwanted polymerization by reacting with a photopolymerization initiator during storage.

In addition, the photocurable ink composition of the present invention may contain a polymerizable compound other than the dendritic polymer and allyl glycol and / or N-vinyl compound.
Such a polymerizable compound is not particularly limited, and examples thereof include monomers.
A monomer refers to a molecule that can be a structural unit of the basic structure of a polymer. Moreover, as a monomer used in this invention, there are a monofunctional monomer, a bifunctional monomer, and a polyfunctional monomer, and any of them can be used. Any of the monomers preferably has a PII value (Primary Irritation Index, primary skin irritation) of 2 or less.

  Monofunctional monomers, bifunctional monomers and polyfunctional monomers having a PII value of 2 or less that can be used in the present invention are exemplified in Table 1 below.

  In addition, the viscosity in the said table | surface is a measured value in 25 degreeC.

  The polymerizable compound of the present invention may contain an oligomer in addition to the aforementioned monomer.

  The photocurable ink composition of the present invention contains a hindered phenol compound as a polymerization inhibitor. By adding a hindered phenol compound as a polymerization inhibitor to a photocurable ink composition containing a specific amount of a dendritic polymer, storage stability and photocurability in image printing can be achieved to a higher degree.

  Although it does not specifically limit as a hindered phenol compound, For example, Irgastab UV-22 and Irganox series (made by Ciba Specialty Chemicals) are mentioned. These compounds may be used alone or as a mixture of two or more.

  The content of the hindered phenol compound in the photocurable ink composition of the present invention is preferably such that the addition ratio (mass basis) of the dendritic polymer: hindered phenol compound is in the range of 10: 1 to 150: 1. The range of 20: 1 to 100: 1 is more preferable, and the range of 40: 1 to 80: 1 is particularly preferable. If the addition amount of the hindered phenol compound is less than 150: 1 in terms of the addition ratio of the dendritic polymer: hindered phenol compound, the desired storage stability improving effect cannot be obtained, while 10: 1 When it exceeds, the deterioration of curability will appear remarkably.

In addition, the photocurable ink composition of the present invention contains a photoradical polymerization initiator as a polymerization initiator.
The radical photopolymerization initiator is not particularly limited, and examples thereof include benzyl dimethyl ketal, α-hydroxyalkylphenone, α-aminoalkylphenone, acylphosphine oxide, oxime ester, thioxanthone, α-dicarbonyl, anthraquinone and the like. It is done.

  Also, Vicure 10, 30 (manufactured by Stauffer Chemical), Irgacure 127, 184, 500, 651, 2959, 907, 369, 379, 754, 1700, 1800, 1850, 1870, 819, OXE01, Darocur 1173, TPO, ITX Photopolymerization initiators available under the trade names of Ciba Specialty Chemicals, Quanture CTX (Aceto Chemical), Kayacure DETX-S (Nippon Kayaku), and ESACURE KIP150 (Lamberti) are also used. can do.

The photocurable ink composition of the present invention may contain a polymerization accelerator.
Although it does not specifically limit as a polymerization accelerator, Darocur EHA, EDB (made by Ciba Specialty Chemicals) etc. are mentioned.

Moreover, the photocurable ink composition of the present invention may contain a color material.
The coloring material used in this case may be either a dye or a pigment, but the pigment is more advantageous from the viewpoint of the durability of the printed matter.
As dyes used in the present invention, direct dyes, acid dyes, food dyes, basic dyes, reactive dyes, disperse dyes, vat dyes, soluble vat dyes, reactive disperse dyes, etc. are usually used for inkjet recording. Various dyes can be used.

As the pigment used in the present invention, inorganic pigments and organic pigments can be used without any particular limitation.
As the inorganic pigment, in addition to titanium oxide and iron oxide, carbon black produced by a known method such as a contact method, a furnace method, or a thermal method can be used. Organic pigments include azo pigments (including azo lakes _, insoluble azo pigments, condensed azo pigments, chelate azo pigments), polycyclic pigments (for example, phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazines). Pigments, thioindigo pigments, isoindolinone pigments, quinofullerone pigments, etc.), dye chelates (for example, basic dye chelates, acidic dye chelates, etc.), nitro pigments, nitroso pigments, aniline black, and the like.

  Specific examples of the pigment include carbon black, No. manufactured by Mitsubishi Chemical Corporation. 2300, no. 900, MCF88, No. 33, no. 40, no. 45, no. 52, MA7, MA8, MA100, no. 2200B, etc. are Raven 5750, 5250, 5000, 3500, 1255, 700, etc. made by Columbia, and Regal 400R, 330R, 660R, Mogu L, 700, Monarch 800, 880, made by Cabot, 900, 1000, 1100, 1300, 1400, etc. are Color Black FW1, FW2, FW2V, FW18, FW200, ColorBlack S150, S160, S170, Printex 35, U, the same V, the same 140 U, the Special Black 6, the same 5, the same 4 A, the same 4, and the like.

Examples of pigments used in yellow ink include C.I. I. Pigment Yellow 1, 2, 3, 12, 13, 14, 16, 17, 73, 74, 75, 83, 93, 95, 97, 98, 109, 110, 114, 120, 128, 129, 138, 150, 151, 154, 155, 180, 185, 213 and the like.
Examples of pigments used for magenta ink include C.I. I. Pigment Red 5, 7, 12, 48 (Ca), 48 (Mn), 57 (Ca), 57: 1, 112, 122, 123, 168, 184, 202, 209, C.I. I. Pigment violet 19 and the like.

Further, examples of pigments used for cyan ink include C.I. I. And CI Pigment Blue 1, 2, 3, 15: 3, 15: 4, 60, 16, and 22.
According to a preferred embodiment of the present invention, the pigment preferably has an average particle size in the range of 10 to 200 nm, more preferably about 50 to 150 nm.
The addition amount of the color material in the photocurable ink composition is preferably in the range of about 0.1 to 25% by mass, and more preferably in the range of about 0.5 to 15% by mass.
The photocurable ink composition of the present invention can also be applied to clear inks that do not contain a color material.

  According to a preferred embodiment of the present invention, these pigments can be made into a photocurable ink composition as a pigment dispersion obtained by dispersing them in an aqueous medium with a dispersant or a surfactant. As a preferable dispersant, a dispersant commonly used for preparing a pigment dispersion, for example, a polymer dispersant can be used.

  When the photocurable ink composition contains a color material, a plurality of ink compositions containing the color material may be provided for each color. For example, in addition to the basic four colors of yellow, magenta, cyan, and black, when adding the same series of dark and light colors for each color, in addition to light magenta, dark red, and cyan, in addition to magenta In addition to light light cyan, dark blue, and black, light gray, light black, and dark matte black can be used.

In addition, the photocurable ink composition of the present invention includes a wetting agent, a penetrating solvent, a pH adjuster, a preservative, a fungicide, and the like as other publicly known components that can be used in an ultraviolet curable ink. You may do it.
In addition to this, surfactants, leveling additives, matting agents, polyester resins, polyurethane resins, vinyl resins, acrylic resins, rubber resins, and waxes are added to adjust film properties as necessary. I can do it.

  Further, the photocurable ink composition of the present invention may be a one-component type or a two-component type.

The photocurable ink composition of the present invention undergoes a curing reaction by light irradiation.
The irradiation light source is not particularly limited, but the irradiation light source is preferably light having a wavelength of 350 nm or more and 450 nm or less.
The dose of ultraviolet rays, 10 mJ / cm ² or more and 10,000 / cm ² or less, and preferably 50 mJ / cm ² or more, conducted at 6,000 mJ / cm ² or less. If it is the amount of ultraviolet irradiation within such a range, a sufficient curing reaction can be performed.

Examples of the ultraviolet irradiation include lamps such as metal halide lamps, xenon lamps, carbon arc lamps, chemical lamps, low pressure mercury lamps, and high pressure mercury lamps. For example, a commercially available product such as an H lamp, D lamp, or V lamp manufactured by Fusion System can be used.
Further, ultraviolet irradiation can be performed by an ultraviolet light emitting semiconductor element such as an ultraviolet light emitting diode (ultraviolet LED) or an ultraviolet light emitting semiconductor laser.

The present invention can also provide an ink jet recording method in which an image is formed on a recording medium using the above-described photocurable ink composition.
As the ink jet recording method, any of the conventionally known methods can be used, and in particular, a method of ejecting droplets using vibration of a piezoelectric element (using an ink jet head that forms ink droplets by mechanical deformation of an electrostrictive element). Recording method) and a method using thermal energy, it is possible to perform excellent image recording.
According to the ink jet recording method of the present invention, since image formation is performed using a photocurable ink composition having excellent storage stability and photocurability at the time of image printing, ink can be stably ejected even after long-term storage. Image quality with excellent curability can be obtained.

  In addition, according to the present invention, a recorded matter recorded by the ink jet recording method can be provided, whereby a recorded matter with excellent image quality can be obtained.

  The present invention is also an ink set for inkjet recording comprising a plurality of photocurable ink compositions, wherein the ink set comprises at least one photocurable ink composition of the present invention described above. Can be provided. The ink set of the present invention is excellent in storage stability and photocurability during image printing.

The present invention can also provide an ink cartridge comprising the above-described ink set for ink-jet recording of the present invention.
According to the ink cartridge of the present invention, it is possible to easily carry a photocurable ink composition having excellent storage stability and photocurability during image printing.

The present invention can also provide a recording apparatus comprising the above-described ink cartridge of the present invention.
The recording apparatus of the present invention is excellent in storage stability and photocurability during image printing.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these.

[Examples 1 to 14, Reference Example 1, Comparative Examples 1 to 3]
(Preparation of pigment dispersion)
In Examples, Reference Examples and Comparative Examples, pigment dispersions were prepared by the method shown below.
As a coloring material, C.I. I. Pigment Black 7 (carbon black) 15% by mass, Discol N-509 (manufactured by Dainichi Seika Kogyo Co., Ltd.) 3.5% by mass as a dispersant, allyl glycol (manufactured by Nippon Emulsifier Co., Ltd.) 100% by mass, mixed and stirred to obtain a mixture. This mixture was subjected to a dispersion treatment for 6 hours together with zirconia beads (diameter 1.5 mm) using a sand mill (manufactured by Yaskawa Seisakusho).
Thereafter, zirconia beads were separated by a separator to obtain a black pigment dispersion.

  In the same manner, pigment dispersions corresponding to the respective colors, that is, cyan pigment dispersion (CI Pigment Blue 15: 3), magenta pigment dispersion (CI Pigment Violet-19), yellow pigment dispersion (CI Pigment Yellow 155) was prepared.

(Preparation of ink composition)
In Examples, Reference Examples and Comparative Examples, a polymerizable compound, a polymerization inhibitor, a radical photopolymerization initiator, and a dispersant are mixed and completely dissolved to prepare an ink composition. The ink composition is stirred while stirring the pigment dispersion. The product was gradually dropped into the ink solvent. After completion of the dropping, the mixture was stirred at room temperature for 1 hour to obtain an ink composition. Then, each ink composition was filtered with a 5-micrometer membrane filter, and it was set as the photocurable ink composition (Examples 1-14, Reference Example 1, Comparative Examples 1-3) shown in Tables 2-4.
In addition, the numerical value in a table | surface shows "mass%."

[Storage stability test]
The photocurable ink compositions of the above Examples, Reference Examples and Comparative Examples are left in an environment of 60 ° C. × 5 days, and the initial viscosity (mPa · s) and the viscosity after standing (mPa · s) are measured by a rheometer. (Measured by Physica, MCR-300) at a measurement temperature of 20 ° C. The viscosity of the photocurable ink composition changes when the polymerizable compound generates radicals by the action of light, heat or the like under storage. The rate of change in viscosity was evaluated by the following index, and the results are shown in Tables 2 to 4.

Storage stability evaluation index AA: Initial viscosity and rate of change in viscosity after standing are less than ± 5%.
A: The initial viscosity and the rate of change in viscosity after standing are ± 5% or more and ± 10% or less.
B: The initial viscosity and the rate of change in viscosity after standing are numerical values greater than ± 10%.

[Print test (curability test)]
Using an ink jet printer PX-G920 (manufactured by Seiko Epson Corporation), the ink described in Examples and Reference Examples and the ink described in Comparative Examples were filled in the RED nozzle array. A RED solid pattern was printed on an OHP film at room temperature or in a 40 ° C. environment and normal pressure. (The actual print color is the ink color filled in the RED nozzle row). Then, after performing printing and a curing process under a curing condition such that an integrated light amount at 365 nm is 400 mJ / cm ² by an ultraviolet irradiation device, the curability was evaluated by the following index. The results are shown in Tables 2-4.

Printing evaluation AA: Printing is possible under normal temperature environment A: Printing is not possible under normal temperature environment, but printing is possible under 40 ° C environment B: Printing is not possible under 40 ° C environment

Curability evaluation index AA: Curability is not a problem, and there is no problem with surface nail rub A: Although scratches are caused by surface nail rub (although the curability is inferior), there is no problem in practical use B: Hardening failure Occurs and the liquid part remains

  As is apparent from Tables 2 to 4, the examples according to the present invention obtained highly satisfactory results with respect to storage stability and curability when printed by an ink jet printer.

Claims (9)

  A photocurable ink composition containing 5% by mass or more of a dendritic polymer as a polymerizable compound and a hindered phenol compound as a polymerization inhibitor.   The photocurable ink composition according to claim 1, wherein the content of the dendritic polymer is 5 to 30% by mass.   The photocurable ink composition according to claim 1 or 2, wherein the addition ratio of the dendritic polymer and the hindered phenol compound is 10: 1 to 150: 1 on a mass basis.   The photocurable ink composition according to any one of claims 1 to 3, further comprising allyl glycol and / or an N-vinyl compound as the polymerizable compound.   An ink jet recording method for forming an image using the photocurable ink composition according to claim 1.   A recorded matter in which an image is formed on a recording medium by the ink jet recording method according to claim 5.   An inkjet recording ink set comprising a plurality of photocurable ink compositions, the inkjet recording ink comprising at least one photocurable ink composition according to any one of claims 1 to 4. set.   An ink cartridge comprising the ink set for inkjet recording according to claim 7.   A recording apparatus comprising the ink cartridge according to claim 8.