JP2018080322A - Photocurable ink, ink container, and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photocurable ink which has higher storage stability and is capable of forming a white image with a higher degree of whiteness as compared with conventional ones.SOLUTION: The photocurable ink contains: a first liquid containing a polymerizable compound and a photopolymerization initiator; and a second liquid incompatible with the first liquid. Droplets formed by the second liquid are dispersed in the first liquid. The photocurable ink contains first particles and second particles having higher hydrophilicity than the first particles. The first particles are adsorbed on an interface between the first liquid and the second liquid, and the second particles are present in the second liquid.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a photocurable ink, an ink container, and an image forming method.

  In recent years, in the commercial printing market, there is a strong demand for a method for forming an image on a recording medium (base material) other than white, such as a transparent or translucent film or colored paper. When an image is formed on a recording medium other than white, a white image may be formed.

  As an ink for forming a white image, a photocurable ink containing a polymerizable compound and a low boiling point solvent has been proposed (Patent Document 1). In Patent Document 1, since the low boiling point solvent volatilizes when the photocurable ink is cured, the cured film obtained by curing the photocurable ink is a porous film having a large number of voids in the film. Become. The light is scattered by the large number of voids, so that the cured film has a white color.

JP 2005-298757 A

  However, in Patent Document 1, the low boiling point solvent is present in the ink so as to be compatible with the polymerizable compound. For this reason, the voids in the formed cured film tend to be very minute. As a result, the degree of whiteness of the cured film formed using the ink described in Patent Document 1 was insufficient.

  Patent Document 1 also describes an ink using water as a low boiling point solvent. However, since the ink containing water described in Patent Document 1 is mixed into two layers of a water layer and an oil layer when time passes after mixing, the storage stability is low.

  In view of the above-described problems, an object of the present invention is to provide a photocurable ink capable of forming a white image having higher storage stability and higher whiteness than conventional ones.

  The photocurable ink as one aspect of the present invention contains a first liquid containing a polymerizable compound and a photopolymerization initiator, and a second liquid that is incompatible with the first liquid. , A photocurable ink in which droplets formed by the second liquid are dispersed in the first liquid, the first particles and the first particles having higher hydrophilicity than the first particles. The first particles are adsorbed on the interface between the first liquid and the second liquid, and the second particles are the second liquid. It is characterized by being inside.

  According to the present invention, it is possible to provide a photocurable ink which can form a white image having higher storage stability and higher whiteness than before.

It is a figure which shows typically the image forming method using the photocurable ink which concerns on this embodiment. It is a figure which shows an example of the ink container which accommodated the photocurable ink which concerns on this embodiment. It is a cross-sectional SEM image of the film | membrane formed with the photocurable ink of Examples 1-2 and the comparative example 1. FIG. It is a cross-sectional SEM image of the film | membrane formed with the photocurable ink of Examples 3-4 and Comparative Example 2.

  Hereinafter, embodiments of the present invention will be described in detail. It should be noted that the present invention is not limited to the following embodiments, and is appropriately modified with respect to the following embodiments based on ordinary knowledge of those skilled in the art without departing from the spirit of the present invention. Those with improvements and the like are also included in the scope of the present invention.

  The photocurable ink 10 (hereinafter referred to as “ink 10”) according to the present embodiment includes a first liquid (O) containing a polymerizable compound (A) and a photopolymerization initiator (B), 1 liquid (O) and an incompatible second liquid (W). In the ink 10, the second liquid (W) forms droplets, and the droplets formed by the second liquid (W) are dispersed in the first liquid (O). Furthermore, the ink 10 contains inorganic particles (Eb) that are first particles and particles (D) that are second particles. The first particles (Eb) are adsorbed on the interface between the first liquid (O) and the second liquid (W), and the particles (D) are in the second liquid (W). Existing. That is, the second liquid (W) contains particles (D).

  The “ink” in the present invention is a composition having fluidity such as liquid or gel, and is disposed on the substrate to form a film or to color the surface or the inside of the substrate. Refers to the composition. That is, the “ink” in the present invention includes those that do not contain a dye or pigment, and also includes those that are colorless in the state of the ink before being applied to the substrate.

  The ink 10 is particularly preferably used when a white image is formed by applying an ink jet onto a substrate and curing it by light irradiation. That is, the ink 10 is suitable as a photocurable ink for inkjet. When the ink 10 is cured to form an ink film 106 (hereinafter, also simply referred to as “film 106”), a film in which many voids exist in the film 106 can be formed. Furthermore, aggregates of particles (D) are formed in the voids. Many voids are formed in the film 106 because the volatile component such as water (C) contained in the ink 10 evaporates during and / or after the ink 10 is cured. It is presumed that the existing part becomes a gap. Moreover, it is presumed that the aggregates of the particles (D) are formed in the voids because the volatile components are evaporated and the particles (D) are aggregated as described above. In the film 106, in addition to light being scattered by the voids, light is also scattered by aggregates of particles (D) present in the voids. Therefore, the ink 10 can form a film with a higher degree of whiteness than a film having only voids, and a white image with a higher degree of whiteness than before can be obtained.

  Hereinafter, each component of the ink 10 will be described in detail.

<First liquid (O)>
The first liquid (O) contained in the ink 10 is a liquid having hydrophobicity. The first liquid (O) is preferably an oily liquid. Moreover, it is preferable that a 1st liquid (O) is a photocurable liquid hardened | cured by irradiating active energy rays, such as an ultraviolet light.

  The first liquid (O) includes a polymerizable compound (A) and a photopolymerization initiator (B). The polymerizable compound (A) is not particularly limited as long as it is a compound having a polymerizable functional group, and monomers, oligomers, polymers, mixtures thereof and the like can be used. When using a solid polymerizable compound, it is preferable to mix with a liquid polymerizable compound and dissolve the solid polymerizable compound in the liquid polymerizable compound.

  The first liquid (O) is a liquid that is incompatible with the second liquid (W) described later. Since the first liquid (O) and the second liquid (W) are incompatible with each other, an interface is generated between the first liquid (O) and the second liquid (W). Thereby, the second liquid (W) can form the droplet 101. By controlling the size and dispersion state of the droplets 101, the size of the void 105 existing in the film 106 after the ink 10 according to the present embodiment is cured can be controlled. The degree of whiteness can be increased.

[Polymerizable compound (A)]
The polymerizable compound (A) contained in the first liquid (O) in the ink 10 reacts with a polymerization factor (radical or the like) generated from the photopolymerization initiator (B) described later, and a chain reaction (polymerization reaction). ) To form a film formed from a polymer compound (polymer).

  The polymerizable compound (A) may be composed of one type of polymerizable compound or may be composed of a plurality of types of polymerizable compounds.

  Examples of such a polymerizable compound (A) include a radical polymerizable compound. The radical polymerizable compound is preferably a compound having at least one acryloyl group or methacryloyl group, that is, a (meth) acrylic compound.

  Examples of monofunctional (meth) acrylic compounds having one acryloyl group or methacryloyl group include phenoxyethyl (meth) acrylate, phenoxy-2-methylethyl (meth) acrylate, phenoxyethoxyethyl (meth) acrylate, and 3-phenoxy. 2-hydroxypropyl (meth) acrylate, 2-phenylphenoxyethyl (meth) acrylate, 4-phenylphenoxyethyl (meth) acrylate, 3- (2-phenylphenyl) -2-hydroxypropyl (meth) acrylate, EO-modified p-cumylphenol (meth) acrylate, 2-bromophenoxyethyl (meth) acrylate, 2,4-dibromophenoxyethyl (meth) acrylate, 2,4,6-tribromophenoxyethyl (meth) acrylate EO-modified phenoxy (meth) acrylate, PO-modified phenoxy (meth) acrylate, polyoxyethylene nonylphenyl ether (meth) acrylate, isobornyl (meth) acrylate, 1-adamantyl (meth) acrylate, 2-methyl-2- Adamantyl (meth) acrylate, 2-ethyl-2-adamantyl (meth) acrylate, bornyl (meth) acrylate, tricyclodecanyl (meth) acrylate, dicyclopentanyl (meth) acrylate, dicyclopentenyl (meth) acrylate, Cyclohexyl (meth) acrylate, 4-butylcyclohexyl (meth) acrylate, acryloylmorpholine, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2 Hydroxybutyl (meth) acrylate, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, butyl (meth) acrylate, amyl (meth) acrylate, isobutyl (meth) acrylate, t -Butyl (meth) acrylate, pentyl (meth) acrylate, isoamyl (meth) acrylate, hexyl (meth) acrylate, heptyl (meth) acrylate, octyl (meth) acrylate, isooctyl (meth) acrylate, 2-ethylhexyl (meth) Acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, isodecyl (meth) acrylate, undecyl (meth) acrylate, dodecyl (meth) acrylate, lauryl (medium) Acrylate), stearyl (meth) acrylate, isostearyl (meth) acrylate, benzyl (meth) acrylate, 1-naphthylmethyl (meth) acrylate, 2-naphthylmethyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, butoxy Ethyl (meth) acrylate, ethoxydiethylene glycol (meth) acrylate, polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, methoxyethylene glycol (meth) acrylate, ethoxyethyl (meth) acrylate, methoxypolyethylene glycol (meth) Acrylate, methoxypolypropylene glycol (meth) acrylate, diacetone (meth) acrylamide, isobutoxymethyl (Meth) acrylamide, N, N-dimethyl (meth) acrylamide, t-octyl (meth) acrylamide, dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, 7-amino-3,7-dimethyloctyl (meth) Examples thereof include, but are not limited to, acrylate, N, N-diethyl (meth) acrylamide, N, N-dimethylaminopropyl (meth) acrylamide and the like.

  As a commercial item of the above monofunctional (meth) acrylic compound, Aronix M101, M102, M110, M111, M113, M117, M5700, TO-1317, M120, M150, M156 (above, manufactured by Toagosei Co., Ltd., “Aronix” is registered. Trademark), MEDOL10, MIBDOL10, CHDOL10, MMDOL30, MEDOL30, MIBDOL30, CHDOL30, LA, IBXA, 2-MTA, HPA, Viscoat # 150, # 155, # 158, # 190, # 192, # 193, # 220, # 2000, # 2100, # 2150 (above, manufactured by Osaka Organic Chemical Industry), light acrylate BO-A, EC-A, DMP-A, THF-A, HOP-A, HOA-MPE, HOA-MPL, PO-A , P-200A, NP-4EA NP-8EA, epoxy ester M-600A (above, manufactured by Kyoeisha Chemical Co., Ltd.), KAYARAD TC110S, R-564, R-128H (above, manufactured by Nippon Kayaku), NK ester AMP-10G, AMP-20G (above, Shin-Nakamura) Chemical Industries), FA-511A, 512A, 513A (Hitachi Chemical Co., Ltd.), PHE, CEA, PHE-2, PHE-4, BR-31, BR-31M, BR-32 (Daiichi Kogyo Seiyaku) Manufactured), VP (manufactured by BASF), ACMO, DMAA, DMAPAA (manufactured by Kojin) and the like, but are not limited thereto.

  Examples of the polyfunctional (meth) acrylic compound having two or more acryloyl groups or methacryloyl groups include trimethylolpropane di (meth) acrylate, trimethylolpropane tri (meth) acrylate, and EO-modified trimethylolpropane tri (meth) acrylate. , PO-modified trimethylolpropane tri (meth) acrylate, EO, PO-modified trimethylolpropane tri (meth) acrylate, dimethyloltricyclodecane diacrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, ethylene Glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, polypropylene glycol di ( ) Acrylate, 1,4-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, 1,3-adamantane dimethanol diacrylate, o- Xylylene di (meth) acrylate, m-xylylene di (meth) acrylate, p-xylylene di (meth) acrylate, 1,9-nonanediol diacrylate, 1,10-decanediol diacrylate, tris (2-hydroxyethyl) isocyanurate tri (Meth) acrylate, tris (acryloyloxy) isocyanurate, bis (hydroxymethyl) tricyclodecane di (meth) acrylate, dipentaerythritol penta (meth) acrylate, dipentaerythritol hexa (meta Acrylate, EO-modified 2,2-bis (4-((meth) acryloxy) phenyl) propane, PO-modified 2,2-bis (4-((meth) acryloxy) phenyl) propane, EO, PO-modified 2,2- Examples include bis (4-((meth) acryloxy) phenyl) propane, but are not limited thereto.

  Commercially available products of the above polyfunctional (meth) acrylic compounds include Iupimer UV SA1002, SA2007 (above, manufactured by Mitsubishi Chemical, “Iupimer” is a registered trademark), Biscote # 195, # 230, # 215, # 260, # 335HP, # 295, # 300, # 360, # 700, GPT, 3PA (above, manufactured by Osaka Organic Chemical Industry), Light Acrylate 4EG-A, 9EG-A, NP-A, DCP-A, BP-4EA, BP-4PA , TMP-A, PE-3A, PE-4A, DPE-6A (above, manufactured by Kyoeisha Chemical), A-DCP, A-HD-N, A-NOD-N, A-DOD-N (above, Shin-Nakamura) Chemical Industry), KAYARAD PET-30, TMPTA, R-604, DPHA, DPCA-20, -30, -60, -120, HX-620, D-310, D- 330 (above, manufactured by Nippon Kayaku), Aronix M208, M210, M215, M220, M240, M305, M309, M310, M315, M325, M400 (above, manufactured by Toagosei), Lipoxy VR-77, VR-60, VR -90 (manufactured by Showa Denko, “Lipoxy” is a registered trademark) and the like, but is not limited thereto.

  In the above-described compound group, (meth) acrylate means acrylate or methacrylate having an alcohol residue equivalent thereto. The (meth) acryloyl group means an acryloyl group or a methacryloyl group having an alcohol residue equivalent thereto. EO represents ethylene oxide, and EO-modified compound A refers to a compound in which the (meth) acrylic acid residue and alcohol residue of compound A are bonded via a block structure of an ethylene oxide group. PO represents propylene oxide, and PO-modified compound B refers to a compound in which the (meth) acrylic acid residue and alcohol residue of compound B are bonded via a block structure of a propylene oxide group.

  Moreover, it is preferable that the (meth) acryl compound which is a polymeric compound (A) is a compound with the low solubility of water with respect to a (meth) acryl compound. In particular, when the total mass of the (meth) acrylic compound is 100% by mass, the solubility of water at 25 ° C. is preferably 0.01% by mass or more and 2.0% by mass or less. Similarly, when the polymerizable compound (A) is composed of a plurality of types of (meth) acrylic compounds, the mixture of the (meth) acrylic compounds that are the polymerizable compounds (A) has low water solubility. A mixture is preferred. In particular, when the total mass of the mixture of (meth) acrylic compounds is 100% by mass, the solubility of water at 25 ° C. is preferably 0.01% by mass or more and 2.0% by mass or less.

  By using a (meth) acryl compound having low water solubility as the polymerizable compound (A), water (C) contained in the droplet 101 formed by the second liquid (W) is converted into the first liquid. The amount dissolved in the polymerizable compound (A) contained in (O) can be reduced. Thereby, the movement of the water (C) contained in the second liquid (W) in the ink 10 through the (meth) acrylic compound that is the polymerizable compound (A) can be suppressed. As a result, the droplet 101 can be maintained in a desired size. That is, the stability of the droplet 101 formed by the second liquid (W) in the ink 10 can be improved. By improving the stability of the droplets 101 in the ink 10, a white image with a high degree of whiteness can be formed even when the ink 10 stored for a long time is used. In particular, when the solubility of water is 2.0% by mass or less, the droplet 101 can be maintained in a desired size for a long time. Further, when the size of the droplet 101 is increased, various physical property values are changed, for example, the viscosity of the ink 10 is decreased. However, by improving the stability of the droplet 101 as described above, changes in physical properties such as the viscosity of the ink can be suppressed for a long period of time. Even when the second liquid (W) contains an additive component other than water (C) as described later, water at 25 ° C. with respect to the (meth) acrylic compound that is the polymerizable compound (A). The solubility of is almost unchanged. Therefore, even in such a case, the stability of the size of the droplet 101 can be improved by setting the solubility of water as described above.

  In addition, the solubility of the water in 25 degreeC with respect to the (meth) acrylic compound which is polymeric compound (A) can be measured using a Karl Fischer moisture measuring device with the following procedure. First, after (meth) acrylic compound (a mixture of plural kinds of (meth) acrylic compounds if included) and water in a sample tube at a ratio of 8: 2 (mass ratio) and shaking, (meth) The sample tube is allowed to stand until the acrylic compound and water are separated. Thereafter, the separated (meth) acrylic compound is separated, and the amount of water contained in the (meth) acrylic compound is measured using a Karl Fischer moisture meter (MKC-510, manufactured by Kyoto Electronics Industry Co., Ltd.). All of the above experiments are performed in a 25 ° C. environment.

  The mixing ratio of the polymerizable compound (A) in the first liquid (O) is 70% by mass or more and 99.99% by mass or less when the total mass of the first liquid (O) is 100% by mass. It is preferable. Moreover, it is more preferable that it is 80 to 99.9 mass%, and it is preferable that it is 90 to 99 mass%.

  By setting the blending ratio of the polymerizable compound (A) in the first liquid (O) to 70% by mass or more with respect to the total mass of the first liquid (O), the mechanical strength of the formed film 106 is increased. Can be increased. Further, by setting the blending ratio to 99.99% by mass or less with respect to the total mass of the first liquid (O), the curing speed of the ink 10 can be increased and the reaction efficiency can be increased.

[Photoinitiator (B)]
The photopolymerization initiator (B) contained in the first liquid (O) in the ink 10 is a compound that senses light of a predetermined wavelength and generates a polymerization factor (radical or the like). Specifically, the photopolymerization initiator (B) is a polymerization initiator that generates a polymerization factor by light (infrared rays, visible rays, ultraviolet rays, far ultraviolet rays, charged particle beams such as X-rays, electron beams, radiation, etc.). is there. More specifically, for example, a polymerization initiator that generates a polymerization factor by light having a wavelength of 150 nm to 400 nm is preferable.

  The photopolymerization initiator (B) may be composed of one type of photopolymerization initiator, or may be composed of a plurality of types of photopolymerization initiators.

  Examples of such a photopolymerization initiator (B) include a radical generator.

  Examples of the radical generator include 2- (o-chlorophenyl) -4,5-diphenylimidazole dimer, 2- (o-chlorophenyl) -4,5-di (methoxyphenyl) imidazole dimer, 2- It may have a substituent such as (o-fluorophenyl) -4,5-diphenylimidazole dimer, 2- (o- or p-methoxyphenyl) -4,5-diphenylimidazole dimer 2, 4,5-triarylimidazole dimer; benzophenone, N, N′-tetramethyl-4,4′-diaminobenzophenone (Michler ketone), N, N′-tetraethyl-4,4′-diaminobenzophenone, 4-methoxy -4'-dimethylaminobenzophenone, 4-chlorobenzophenone, 4,4'-dimethoxybenzophenone, 4,4'-diamino Benzophenone derivatives such as nzophenone; 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1,2-methyl-1- [4- (methylthio) phenyl] -2-morpholino-propane- Α-amino aromatic ketone derivatives such as 1-one; 2-ethylanthraquinone, phenanthrenequinone, 2-t-butylanthraquinone, octamethylanthraquinone, 1,2-benzanthraquinone, 2,3-benzanthraquinone, 2-phenylanthraquinone 2,3-diphenylanthraquinone, 1-chloroanthraquinone, 2-methylanthraquinone, 1,4-naphthoquinone, 9,10-phenantharaquinone, 2-methyl-1,4-naphthoquinone, 2,3-dimethylanthraquinone, etc. Quinones; benzoin methyl ester Benzoin ether derivatives such as ether, benzoin ethyl ether and benzoin phenyl ether; benzoin derivatives such as benzoin, methyl benzoin, ethyl benzoin and propyl benzoin; benzyl derivatives such as benzyl dimethyl ketal; 9-phenylacridine, 1,7-bis (9 , 9'-acridinyl) heptane derivatives; N-phenylglycine derivatives such as N-phenylglycine; acetophenone, 3-methylacetophenone, acetophenone benzyl ketal, 1-hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy-2- Acetophenone derivatives such as phenylacetophenone; thioxanthones such as thioxanthone, diethylthioxanthone, 2-isopropylthioxanthone, 2-chlorothioxanthone 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis (2,4,6-trimethylbenzoyl) phenylphosphine oxide, bis- (2,6-dimethoxybenzoyl) -2,4,4-trimethyl Acylphosphine oxide derivatives such as pentylphosphine oxide; 1,2-octanedione, 1- [4- (phenylthio)-, 2- (O-benzoyloxime)], ethanone, 1- [9-ethyl-6- Oxime ester derivatives such as (2-methylbenzoyl) -9H-carbazol-3-yl]-, 1- (O-acetyloxime); xanthone, fluorenone, benzaldehyde, fluorene, anthraquinone, triphenylamine, carbazole, 1- ( 4-Isopropylphenyl) -2-hydride Carboxymethyl-2-methylpropan-1-one, 2-hydroxy-2-methyl-1 but one, and the like, but are not limited to.

  Commercially available products of the above radical generator include Irgacure 184, 369, 651, 500, 819, 907, 784, 2959, CGI-1700, -1750, CG24-61, Darocur 1173, Lucirin TPO, LR8893, LR8970 (above, BASF) “Darocur” and “Lucirin” are registered trademarks), Ubekrill P36 (manufactured by UCB), and the like, but are not limited thereto.

  The blending ratio of the photopolymerization initiator (B) in the first liquid (O) is 0.01% by mass or more and 15% by mass or less when the total mass of the first liquid (O) is 100% by mass. It is preferable that it is 0.1 mass% or more and 10 mass% or less.

  By setting the blending ratio of the photopolymerization initiator (B) in the first liquid (O) to 0.01% by mass or more with respect to the total mass of the first liquid (O), the curing speed of the ink 10 is increased. Thus, the reaction efficiency can be increased. Moreover, the mechanical strength of the film | membrane 106 formed can be raised by making this compounding ratio into 15 mass% or less with respect to the total mass of a 1st liquid (O).

[Other additive components]
In addition to the polymerizable compound (A) and the photopolymerization initiator (B) described above, the first liquid (O) can be further hydrophobicized within a range that does not impair the effects of the present invention according to various purposes. May contain an additive component. Examples of such an additive component include, but are not limited to, an antioxidant, a polymer component, and a polymerization inhibitor.

<Second liquid (W)>
The second liquid (W) contained in the ink 10 is a hydrophilic liquid. The second liquid (W) preferably contains water (C). In other words, the second liquid (W) is preferably an aqueous liquid. The second liquid (W) is a liquid that is incompatible with the first liquid (O). Furthermore, the second liquid (W) contains particles (D) that are second particles.

  The second liquid (W) is dispersed by forming droplets 101 in the first liquid (O). When such an ink 10 is cured, a volatile component such as water (C) in the second liquid (W) evaporates during and / or after the ink 10 is cured, whereby the second liquid ( A gap 105 is formed in the space where the droplet 101 of W) was present. In the present embodiment, since the second liquid (W) has the particles (D), the particles (D) aggregate in the above evaporation process, and the particles ( The aggregate 107 of D) is formed. The gaps 105 and the aggregates 107 of the particles (D) scatter incident light, so that the film 106 formed with the ink 10 looks whiter than a film having only voids.

  The ink 10 is preferably an emulsion in which the droplets 101 formed by the second liquid (W) are stably dispersed in the first liquid (O). That is, it is preferable that the first liquid (O) and the second liquid (W) in the ink 10 form a so-called W / O type (water-in-oil type) emulsion. It is preferable to use the ink 10 as such an emulsion because the particle size (size) and dispersibility of the droplet 101 formed by the second liquid (W) can be stably maintained. That is, it is preferable because the storage characteristics of the ink 10 are improved.

  In this specification, “the first liquid is dispersed in a form of droplets in the second liquid” means that the first liquid forms a closed interface with the second liquid. In addition, it means that a plurality of particles exist in the second liquid in a particle state. In this definition, the size (diameter) of the particle is 1 nm or more, and this particle is referred to as “droplet”. If the size of the particles is less than 1 nm, the interface between the first liquid and the second liquid cannot be recognized. In this case, the first liquid and the second liquid are compatible with each other. A solution is formed.

  The ink 10 is formed by the second liquid (W) without separating the first liquid (O) and the second liquid (W) even if the ink 10 is left in a 25 ° C. atmosphere for a predetermined time or longer. It is preferable that the droplet 101 to be dispersed is dispersed in the first liquid (O). When a liquid containing the first liquid and the second liquid is stored in a predetermined container for a long time, two layers of a layer made of the first liquid and a layer made of the second liquid are generated in the container. , So that the other layer is present on one layer. In this specification, such separation into two layers is referred to as “layer separation”.

  Even if the ink 10 is stirred and mixed for 3 minutes at a rotational speed of 15000 rpm or more and then left in an atmosphere at 25 ° C. for 1 hour, the first liquid (O) and the second liquid (W) are separated. It is preferred not to separate the layers. Further, it is more preferable that the layers do not separate even if left for 24 hours under the above-mentioned conditions, and it is particularly preferable that the layers do not separate even if left for one week.

  When confirming that the layers are not separated after stirring and mixing, it is preferable to confirm by the following procedure. First, the target ink is put into a bottle (20 mL) and stirred and mixed for 3 minutes at a rotation speed of 15000 rpm or more using a homogenizer (AHG-160D, manufactured by ASONE). At this time, HT1008 manufactured by ASONE may be used as the shaft generator. Thereafter, the mixed ink is transferred to a light-shielded sample tube, and left in an atmosphere at 25 ° C., and observed at regular intervals.

  As described above, in the ink 10, the portion where the volatile component was present is a void due to evaporation of volatile components such as water (C) contained in the ink 10 during and / or after the ink 10 is cured. Thus, the porous film 106 can be formed. At this time, when there are many voids having a diameter of 0.1 μm or more and 20 μm or less, incident light incident on the film 106 can be efficiently scattered, and the film 106 with a high degree of whiteness can be realized. The voids in the film 106 are more preferably 0.1 μm or more and 1 μm or less, and further preferably 0.2 μm or more and 0.5 μm or less. Note that when the diameter of the void in the film 106 is larger than 20 μm, the concealing property of the film 106 may be lowered.

  Here, the size of the void formed after the ink 10 is cured depends on the size of the droplet 101 in the ink 10, and according to the study by the present inventors, these two sizes are almost the same. I found out that Therefore, the volume-based median diameter d50 of the droplet 101 of the second liquid (W) in the first liquid (O) is preferably 0.1 μm or more and 20 μm or less. The volume-based median diameter d50 of the droplet 101 of the second liquid (W) in the first liquid (O) is more preferably 0.1 μm or more and 1 μm or less, and is 0.2 μm or more and 0.00. More preferably, it is 5 μm or less. The volume-based median diameter d50 can be calculated from, for example, a volume-based particle size distribution obtained by measurement by a light scattering particle size distribution measurement method.

  In addition, as described above, the ink 10 aggregates the particles (D) in the voids 105 formed in the film 106 by aggregation of the particles (D) when volatile components such as water (C) evaporate. Aggregates can be formed. At this time, the size of the aggregate of the formed particles (D) is preferably 0.001 μm or more and 1 μm or less, and more preferably 0.01 μm or more and 0.5 μm or less. By setting the size of the aggregate of the particles (D) to be 0.001 μm or more and 1 μm or less, incident light can be efficiently scattered, and the degree of whiteness of the film 106 can be improved. In addition, the size of the aggregate of the formed particles (D) depends on the content of the particles (D) in the second liquid (W). Details will be described later.

[Water (C)]
The mixing ratio of water (C) in the ink 10 is preferably 5% by mass or more and 50% by mass or less, preferably 10% by mass or more and 30% by mass or less, when the total mass of the ink 10 is 100% by mass. It is more preferable.

  By setting the blending ratio of water (C) in the ink 10 to 5 mass% or more, the volume of voids formed in the film 106 can be increased, and the degree of whiteness of the film 106 can be increased. When the blending ratio of water (C) in the ink 10 is larger than 50% by mass, the concealing property of the film 106 may be lowered or the degree of whiteness may be lowered.

[Particle (D)]
The particles (D) as the second particles contained in the second liquid (W) in the ink 10 according to the present embodiment are high refractive index particles having a refractive index of 1.4 or more and 2.8 or less. Preferably there is. As described above, when the ink 106 is cured to form the film 106, volatile components in the second liquid (W) are evaporated, and a large number of voids are formed in the film 106. At this time, in this embodiment, the second liquid (W) contains the particles (D), so that aggregates of the particles (D) are formed inside the voids in the film 106. By forming an aggregate of particles (D) inside the voids in the film 106, a film having a higher degree of whiteness than a film having only voids can be formed. A white image with a high degree can be obtained.

  The refractive index of the particles (D) is preferably 1.6 or more and 2.8 or less, more preferably 1.7 or more and 2.8 or less, and further preferably 1.9 or more and 2.8 or less. It is particularly preferably 2.0 or more and 2.8 or less. By using particles having a high refractive index as the particles (D), the difference in refractive index between the aggregate of particles (D) formed in the voids in the film 106 and the voids (air; refractive index 1). Can be increased. Thereby, light can be efficiently scattered by the aggregate of particles (D), and the degree of whiteness of the film 106 can be improved.

  The material of the particles (D) is not particularly limited, and the particles (D) may be inorganic particles or resin particles. Inorganic particles tend to have a higher refractive index than resin particles. Therefore, from the viewpoint of increasing the efficiency of light scattering by the aggregate of particles (D) formed in the voids in the film 106 obtained by curing the ink 10, the particles (D) may be inorganic particles. preferable.

  Particle (D) is a particle containing at least one selected from the group consisting of silicon dioxide, mica, aluminum oxide, boehmite, titanium oxide, barium titanate, zirconium oxide, zinc oxide, barium sulfate, and niobium oxide. It is more preferable that These materials have a high refractive index, and the degree of whiteness of the formed film 106 can be further improved by using the particles (D) as particles containing these materials. Among these, the particles (D) are particularly preferably titanium oxide particles from the viewpoint of high refractive index and material cost.

  The particles (D) are preferably dispersed in the second liquid (W). By dispersing the particles (D) in the second liquid (W), the particles (D) are prevented from aggregating and settling in the ink state (the state before the film 106 is formed). Can do. When the particles (D) aggregate and settle, the droplet 101 formed by the second liquid (W) may settle or the droplets 101 may be united. Therefore, the storage stability of the ink 10 can be improved by dispersing the particles (D) in the second liquid (W).

  The particles (D) are preferably dispersed in the second liquid (W) by a resin or a surfactant as a dispersant. Alternatively, it is preferable that a hydrophilic group is introduced into the surface of the particle (D) by a surface treatment and is dispersed in the second liquid (W) by the hydrophilic group. Alternatively, at least a part of the surface of the particle (D) is coated with a compound containing at least one element selected from the group consisting of silicon, zirconium, and aluminum, whereby the second liquid (W) It is preferable to be dispersed in By taking any one of these forms, the particles (D) can be stably dispersed in the second liquid (W) over a long period of time, and the storage stability of the ink 10 can be improved.

  As the dispersant for dispersing the particles (D) in the second liquid (W), conventionally known resins and surfactants that can be used in the pigment ink composition can be used without particular limitation. In this embodiment, since the second liquid (W) is an aqueous liquid containing water (C), the dispersant is preferably a water-soluble resin. The dispersant is preferably an anionic dispersant or a nonionic dispersant. Suitable dispersants for this embodiment include anionic dispersants such as polyacrylic acid and styrene-acrylic acid copolymers. Moreover, polyvinyl pyrrolidone, polypropylene glycol, etc. which are nonionic dispersing agents are mentioned.

  In the present embodiment, it is preferable that the second liquid (W) contains the dispersant as described above. Moreover, it is preferable that the dispersing agent as described above is adsorbed or bound to at least a part of the surface of the particle (D). Furthermore, it is preferable that at least a part of the surface of the particle (D) is coated with the dispersant as described above.

  Examples of the surface treatment for dispersing the particles (D) in the second liquid (W) include a surface modification treatment with a silane coupling agent such as an alkoxysilane having a hydrophilic group such as an epoxy group or an amino group. . As a result of the surface modification treatment with the silane coupling agent, a hydrophilic group such as an epoxy group or an amino group can be introduced on the surface of the particle (D).

  Further, as the surface treatment for dispersing the particles (D) in the second liquid (W), the particles (D) are combined with a compound containing at least one element selected from the group consisting of silicon, zirconium, and aluminum. The surface treatment to heat is also mentioned.

  The volume-based median diameter d50 of the particles (D) is preferably 5 nm to 500 nm, more preferably 5 nm to 300 nm, and particularly preferably 50 nm to 300 nm. By setting the volume-based median diameter d50 of the particles (D) to 500 nm or less, the size of the droplet formed by the second liquid (W) in the ink 10 can be sufficiently reduced. The degree of whiteness can be improved. Further, by setting the volume-based median diameter d50 of the particles (D) to 5 nm or more, the size of the aggregates of the particles (D) formed in the voids formed in the film 106 is made sufficient. The degree of whiteness of the film 106 can be increased.

  The particles (D) are preferably achromatic. Since the particles (D) are achromatic, light in a specific wavelength region in the visible light region is not selectively absorbed or reflected, so that the degree of whiteness of the film 106 can be increased.

  The blending ratio of the particles (D) is preferably 1% by mass or more and 20% by mass or less, preferably 5% by mass or more and 15% by mass or less, when the total mass of the second liquid (W) is 100% by mass. It is more preferable that

  By setting the mixing ratio of the particles (D) in the second liquid (W) to 1% by mass or more, the size of the aggregates of the particles (D) formed in the voids formed in the film 106 is sufficient. The degree of whiteness of the film 106 can be increased. When the mixing ratio of the particles (D) in the second liquid (W) is larger than 20% by mass, the dispersion of the particles (D) may be unstable, and the storage stability of the ink 10 is lowered. There is a case.

  In the present embodiment, high refractive index particles having a refractive index of 1.4 or more and 2.8 or less are used as the particles (D), but the present invention is not limited to this. The particles (D) according to another embodiment of the present invention are white pigment particles. The particles (D) according to another embodiment of the present invention are a group consisting of silicon dioxide, mica, aluminum oxide, boehmite, titanium oxide, barium titanate, zirconium oxide, zinc oxide, barium sulfate, and niobium oxide. Particles containing at least one selected from According to any of these embodiments, it is possible to realize a photocurable ink that can form a white image having higher storage stability and higher whiteness than conventional ones.

[Other additive components]
In addition to the volatile component such as water (C) and the particles (D) described above, the second liquid (W) may contain additional components as long as the effects of the present invention are not impaired depending on various purposes. May be contained. In addition, as an additional component used here, a component incompatible with the above-mentioned 1st liquid (O) is used. Examples of such an additive component include, but are not limited to, a hydrophilic antioxidant, a hydrophilic organic solvent, and a hydrophilic specific gravity adjuster. In addition, when a plurality of types of volatile components including water (C) are added to the second liquid (W), when the film 106 is formed by the ink 10, both of these volatile components evaporate. Conceivable. Accordingly, in this case, the gap 105 in the film 106 obtained by curing the ink 10 is formed by evaporation of volatile components including water (C) contained in the second liquid (W). .

  The specific gravity adjusting agent can suppress the floating (creaming) of the droplet of the second liquid (W) caused by the specific gravity difference between the first liquid (O) and the second liquid (W). Examples of such water-soluble specific gravity adjusters include, but are not limited to, water-soluble salts such as sodium chloride and potassium chloride. The blending ratio of the salt as the specific gravity adjusting agent varies depending on the specific gravity of the first liquid (O), but when the total mass of the second liquid (W) is 100% by mass, 1% by mass to 5% by mass. % Or less is preferable.

<Other additive components>
In addition to the first liquid (O) and the second liquid (W) described above, the ink 10 contains additional additives according to various purposes within a range not impairing the effects of the present invention. It may be. An emulsifier (E) etc. are mentioned as such an additional component. As described above, the ink 10 has a form in which the droplets 101 formed by the second liquid (W) are dispersed in the first liquid (O), but the emulsifier (E) Has the function of stabilizing dispersion. Examples of such an emulsifier (E) include a surfactant (Ea) and inorganic particles (Eb). As the emulsifier (E), either the surfactant (Ea) or the inorganic particles (Eb) may be used alone, or these may be used in combination or in combination with other emulsifiers (E). Also good.

[Surfactant (Ea)]
The ink 10 preferably contains a surfactant (Ea). As a result, the dispersion stability of the droplets 101 dispersed in the ink 10 can be improved, and the size of the droplets 101 can be controlled. That is, since the ink 10 contains the surfactant (Ea), coalescence of the droplets 101 can be suppressed and the droplets 101 can be maintained in a desired size for a long period. By including the surfactant (Ea), the first liquid (O) and the second liquid (W) are not separated into layers even when the ink 10 is left in an atmosphere at 25 ° C. for a predetermined time or longer. In addition, the droplet 101 formed by the second liquid (W) can be dispersed in the first liquid (O).

  The surfactant (Ea) may be composed of one type of surfactant or may be composed of a plurality of types of surfactants.

  The surfactant (Ea) is preferably a nonionic surfactant. Since the surfactant (Ea) is a nonionic surfactant, it is easy to form a W / O emulsion in which droplets of the second liquid (W) are dispersed in the first liquid (O). Examples of the nonionic surfactant include hydrocarbon surfactants.

  Examples of the hydrocarbon-based surfactant include polyoxyalkylene alkyl ethers obtained by adding an alkylene oxide having 2 to 4 carbon atoms to an alkyl alcohol having 1 to 50 carbon atoms.

  Polyoxyalkylene alkyl ether includes methyl alcohol ethylene oxide adduct, decyl alcohol ethylene oxide adduct, lauryl alcohol ethylene oxide adduct, cetyl alcohol ethylene oxide adduct, oleyl alcohol ethylene oxide adduct, stearyl alcohol ethylene oxide adduct And stearyl alcohol ethylene oxide / propylene oxide adduct. In addition, the terminal group of the alkyl alcohol polyalkylene oxide adduct is not limited to a hydroxyl group that can be produced by simply adding a polyalkylene oxide to an alkyl alcohol. This hydroxyl group may be converted to other substituents, for example, a polar functional group such as a carboxyl group, an amino group, a pyridyl group, a thiol group, or a silanol group, or a hydrophobic functional group such as an alkyl group or an alkoxy group.

  As the polyoxyalkylene alkyl ether, a commercially available product may be used. Commercially available products include, for example, NOF made by NOF (“NONION” is a registered trademark), BLAUNON series, FINESURF series, BASF made Pluriol series (“Pluriol” is a registered trademark), Kao The EMULGEN series (“EMULGEN” is a registered trademark) and the like are exemplified, but not limited thereto.

  When the ink 10 contains a surfactant (Ea), the content of the surfactant (Ea) is preferably 0.001% by mass or more and 20% by mass or less with respect to the total amount of the ink 10, for example. . More preferably, it is 0.01 mass% or more and 10 mass% or less, More preferably, it is 0.1 mass% or more and 10 mass% or less. By setting the content of the surfactant (Ea) within the above range, the dispersion stability of the droplet 101 can be improved.

[Inorganic particles (Eb)]
The ink 10 contains inorganic particles (Eb) that are first particles. The inorganic particles (Eb) can improve the dispersion stability of the droplets 101 dispersed in the ink 10 and can control the size of the droplets 101. That is, since the ink 10 contains inorganic particles (Eb), coalescence of the droplets 101 can be suppressed, and the droplets 101 can be maintained in a desired size for a long period of time. That is, even if the ink 10 is left in an atmosphere of 25 ° C. for a certain period of time or longer, the first liquid (O) and the second liquid (W) are not separated into layers by the second liquid (W). The formed droplet 101 can be dispersed in the first liquid (O).

  The inventors presume the mechanism by which the above-described effect is obtained when the ink 10 contains inorganic particles (Eb) as follows. That is, the ink 10 includes a plurality of inorganic particles (Eb), and at least some of the inorganic particles (Eb) are adsorbed on the interface between the first liquid (O) and the second liquid (W). Existing. That is, inorganic particles (Eb) are arranged at the interface between the first liquid (O) and the droplet 101. At this time, paying attention to one inorganic particle (Eb), at least a part of the inorganic particle (Eb) protrudes from the interface between the first liquid (O) and the droplet 101 to the first liquid (O) side. doing. That is, the inorganic particles (Eb) are disposed at the interface between the first liquid (O) and the second liquid (W), but the inorganic particles (Eb) are substantially the first liquid ( It can be said that it is contained in O). This is because the interface is formed between the first liquid (O) and the second liquid (W), so that the inorganic particles (Eb) originally dispersed in the first liquid (O) It is thought that this is because the above-mentioned state is obtained by adsorbing to the interface. Therefore, even when two or more droplets 101 having the inorganic particles (Eb) adsorbed on the interface approach each other, the inorganic particles (Eb) adsorbed on the interface repel in a three-dimensional manner. The unity between 101 is suppressed. As a result, it is considered that a state in which the second liquid (W) is stably dispersed in the first liquid (O) is formed.

  Such an inorganic particle (Eb) is not particularly limited as long as it contains an inorganic material, and may appropriately have a surface modification layer or an adsorption layer made of an organic material or an inorganic material on the particle surface. . The inorganic material contained in the inorganic particles (Eb) may be one kind or plural kinds. Moreover, you may use multiple types of inorganic particle as an inorganic particle (Eb).

  The kind of the inorganic material contained in the inorganic particles (Eb) is not particularly limited, but from silicon dioxide, mica, aluminum oxide, boehmite, titanium oxide, barium titanate, zirconium oxide, zinc oxide, and niobium oxide. It is preferable to use at least one metal oxide selected from the group consisting of: Among these, it is preferable to use at least one selected from the group consisting of silicon dioxide, aluminum oxide, and titanium oxide from the viewpoint of dispersion stability of the droplet 101 and material cost of the inorganic particles (Eb).

  Furthermore, it is preferable to use inorganic particles having a high refractive index as the inorganic particles (Eb). At this time, the refractive index of the inorganic particles (Eb) is preferably 0.05 or more larger than the refractive index of the cured product obtained by curing the polymerizable compound (A).

  By making the refractive index of the inorganic particles (Eb) 0.05 or more larger than the refractive index of the cured product obtained by curing the polymerizable compound (A), the inorganic particles (Eb) and the polymerizable compound (A) The light reflectance at the interface with the cured product (polymer) obtained by curing can be increased. As a result, the light incident on the film 106 is irregularly reflected or diffused even at the interface between the inorganic particles (Eb) and the cured product obtained by curing the polymerizable compound (A), and the degree of whiteness of the film 106 is increased. Further improvement can be achieved. As a result, the degree of whiteness of the white image formed using the ink 10 can be further improved.

  The refractive index of the cured product obtained by curing the polymerizable compound (A) is about 1.5. Therefore, the refractive index of the inorganic particles (Eb) is not particularly limited, but is preferably 1.7 or more and 2.8 or less.

  From the above, it is particularly preferable to use titanium oxide particles as the inorganic particles (Eb). By using titanium oxide particles as the inorganic particles (Eb), the degree of whiteness of the film 106 can be improved while improving the dispersion stability of the droplets 101. Titanium oxide particles are also advantageous from the viewpoint of cost. The refractive index of titanium oxide is 2.52 to 2.71 although it varies depending on the crystal form.

  The volume-based median diameter d50 of the inorganic particles (Eb) contained in the ink 10 is preferably 5 nm or more and 100 nm or less. By reducing the size of the inorganic particles (Eb), the inorganic particles (Eb) can be easily adsorbed to the interface between the droplets 101 dispersed in the ink 10 and the first liquid (O). The dispersion stability of the droplet 101 is improved.

  When the median diameter of the droplet 101 is R and the median diameter of the inorganic particles (Eb) is r, the ratio (R / r) is preferably 5 or more and 400 or less. When the ratio (R / r) is smaller than 5, the inorganic particles (Eb) are too large for the droplet 101, and the inorganic particles (Eb) are present at the interface between the droplet 101 and the first liquid (O). It tends to be difficult to adsorb. When the ratio (R / r) is larger than 400, the inorganic particles (Eb) are too small with respect to the droplet 101, and the droplet 101 and the first liquid (O) are stabilized in order to stabilize the dispersion of the droplet 101. ) Tends to increase the amount of inorganic particles (Eb) adsorbed on the interface. In any case, if the ratio (R / r) is outside the above range, the dispersion stabilizing effect by the inorganic particles (Eb) is reduced, which is not preferable.

  The coverage of the droplet 101 when the inorganic particles (Eb) are adsorbed on the interface between the droplet 101 and the first liquid (O) is preferably 50% or more and 100% or less. More preferably, it is 70% or more and 100% or less, more preferably 80% or more and 100% or less, and particularly preferably 90% or more and 100% or less. By setting the coverage of the inorganic particles (Eb) to the droplets 101 to 50% or more, even if the droplets 101 coated with the inorganic particles (Eb) come into contact with each other, the inorganic particles (Eb) are three-dimensional. The coalescence of the droplets 101 can be suppressed by the repulsion. As a result, the dispersion stability of the droplet 101 can be further improved.

  The ink 10 contains a plurality of inorganic particles (Eb), but not all of them may be adsorbed on the interface between the droplet 101 and the first liquid (O). That is, some of the plurality of inorganic particles (Eb) contained in the ink 10 may be dispersed in the first liquid (O). Thus, the inorganic particles (Eb) that are the first particles are dispersed in the first liquid (O) when they are not adsorbed on the interface, and on the other hand, are the second particles. The particles (D) are present in the second liquid (W). That is, it can be said that the particles (D) as the second particles are particles having higher hydrophilicity than the inorganic particles (Eb) as the first particles.

  As described above, the inorganic particles (Eb) include an inorganic material having a large specific gravity such as a metal oxide, and tend to have a higher specific gravity than the first liquid (O) and the second liquid (W). According to the Stokes equation, which is an equation representing the sedimentation velocity (termination velocity) when small particles settle in the fluid, it is dispersed in the fluid (liquid component in the ink 10) by reducing the particle diameter of the particles. It is known that the sedimentation rate of the particles can be reduced. Although depending on the viscosity of the liquid component in the ink 10, the sedimentation rate can be extremely reduced by using particles having a particle size of 100 nm or less as the inorganic particles (Eb). As a result, it becomes easy to keep the state in which the inorganic particles (Eb) are dispersed in the ink 10 for a long time, and sedimentation can be suppressed.

  The content of the inorganic particles (Eb) in the ink 10 is preferably 0.1% by mass or more and 20% by mass or less with respect to the total amount of the ink 10, for example. More preferably, it is 1.0 mass% or more and 15 mass% or less, More preferably, it is 5.0 mass% or more and 10 mass% or less. By setting the content of the inorganic particles (Eb) within the above range, the dispersion stability of the droplets 101 can be improved.

<Physical properties of photocurable ink>
The viscosity of the ink 10 at 25 ° C. is preferably 1 mPa · s or more and 75 mPa · s or less. The viscosity of the ink 10 is more preferably 1 mPa · s or more and 30 mPa · s or less. By setting the viscosity of the ink 10 to 1 mPa · s or more and 75 mPa · s or less, it is possible to improve the ejection stability when the ink 10 is ejected by the inkjet method.

<Method for Preparing Photocurable Ink Composition>
The ink 10 has a form in which the second liquid (W) forms the droplets 101 and is dispersed in the first liquid (O). Therefore, it is preferable to prepare the ink 10 by the following preparation method.

  First, the polymerizable compound (A) and the photopolymerization initiator (B) are mixed. To this, an additional component is added and mixed as needed, and a 1st liquid (O) is prepared. Moreover, an additional component is added and mixed with water (C) and particle | grains (D) as needed, and the 2nd liquid (W) is prepared.

  Next, while stirring the prepared first liquid (O), the second liquid (W) is put into the first liquid (O) and further stirred. By doing so, the droplet 101 of the second liquid (W) can be formed in the first liquid (O).

  Examples of the stirring means include a homogenizer, an ultrasonic disperser, and a stirrer. Among these, it is preferable to use a homogenizer or an ultrasonic disperser from the viewpoint of reducing the particle size of the droplet 101 formed by the second liquid (W). Although depending on the composition of the ink 10, the particle size of the droplets 101 dispersed in the ink 10 can be controlled by the stirring conditions.

  In addition, when a surfactant (Ea) or inorganic particles (Eb) is added as an emulsifier (E) to the ink 10, a first liquid (O) containing a polymerizable compound (A) and a photopolymerization initiator (B) is added. ), The surfactant (Ea) and the inorganic particles (Eb) are added to the first liquid (O). Thereafter, it is preferable to form the droplet 101 of the second liquid (W) by adding the second liquid (W) and further stirring the liquid while stirring the liquid.

<Ink container>
The ink 10 is stored in an ink container. In other words, the ink container according to this embodiment contains the ink 10. Hereinafter, the ink container according to the present embodiment will be described in more detail.

  The ink container according to the present embodiment is an ink container that contains a photocurable ink. In this specification, the “container” is a concept including a container and a package, and refers to one that contains a photocurable ink directly or indirectly. That is, the container is one in which a container is filled with photocurable ink, or at least a container filled with photocurable ink is sealed with a package. That is, it can be said that the ink container according to the present embodiment has a container, and the ink 10 is stored in the container.

  The ink container is used for storing and transporting the photocurable ink before using the photocurable ink in the image forming apparatus. When using the ink container, the photocurable ink contained in the ink container is used. This is supplied to the image forming apparatus.

  Examples of the ink container include, but are not limited to, an ink cartridge, a bag (pack), a bottle, a tank, a bottle, and a can. Among these, an ink cartridge, a bag, a bottle, and a tank are preferable, and a bag is more preferable from the viewpoint of being widely used and easily controlling moisture permeability and oxygen permeability to desired values.

  The usage mode of the ink container is not particularly limited. For example, the ink container, which is a separate body from the image forming apparatus, is attached to the image forming apparatus, and the ink container is photocured from the ink container. There is a mode (1) like a cartridge for supplying ink to the image forming apparatus. Further, there is an aspect (2) like a bottle that supplies an ink composition to an ink tank or the like of the image forming apparatus from an ink container that is a separate body from the image forming apparatus. Furthermore, there is an aspect (3) in which the ink container is provided in advance as a part of the image forming apparatus. In the case of the mode (1) and the mode (3), the photocurable resin is applied to the head of the image forming apparatus from the mounted ink container or the provided ink container through a connecting portion such as an ink tube. Ink can be supplied to form an image. In the aspect (2), after the photocurable ink is transferred from the ink container to the ink tank or the like of the image forming apparatus, it is photocured from the ink tank to the head of the image forming apparatus through a connection portion such as an ink tube. An image can be formed by supplying an ink.

  FIG. 2 is a diagram illustrating an example of an ink container according to the present embodiment. FIG. 2A illustrates an ink container as an ink bag, and FIG. 2B illustrates an ink cartridge as an ink container. Examples of cases are shown respectively.

  As shown in FIG. 2A, the ink bag 20 according to the present embodiment includes a bag 21 that stores the ink 10 and an ink supply port 22 that communicates with the inside of the bag 21. The ink 10 stored in the ink bag 20 is supplied to the image forming apparatus via the ink supply port 22. In the state where the ink bag 20 is not attached to the image forming apparatus, the opening of the ink supply port 22 is preferably closed by a valve provided inside.

  The shape, size, structure, material, and the like of the bag 21 are not particularly limited, but a bag formed of a film having low air permeability is preferable. Examples of the film include an aluminum laminate film, a polyamide film, a polyethylene terephthalate (PET) film, a polyethylene film, a polypropylene film, a polystyrene film, an ethylene vinyl acetate polymer film, an ethylene vinyl alcohol copolymer film, and a polybutadiene film. The resin film can be preferably used.

  As shown in FIG. 2B, the ink cartridge 30 according to this embodiment includes the above-described ink bag 20 and a case 31 that houses the ink bag 20 and protects the ink bag 20. Here, the ink supply port 22 of the ink bag 20 is exposed to the outside of the case 31 from a notch provided in the side surface of the case 31. The ink 10 is supplied to the image forming apparatus via the ink supply port 22 in a state where the ink cartridge 30 is mounted in the cartridge holder of the image forming apparatus. As described above, by adopting a configuration in which the ink supply body is detachably mounted on the image forming apparatus as an ink cartridge, it is possible to further improve work efficiency such as replenishment or replacement of the photocurable ink. The ink cartridge 30 may further include a recording head having an ejection port that communicates with the ink supply port 22.

<Image forming method>
The image forming method according to the present embodiment is a method for forming an image by disposing the ink 10 according to the present embodiment described above on a substrate. More specifically, in the image forming method according to the present embodiment, the step of placing the ink 10 on the base material 102 that is a recording medium (placement step), and the ink 10 placed on the base material 102 is irradiated with light. Irradiating step (light irradiation step). The “image” in this specification includes a solid pattern filled with a single color within a certain range.

[1] Step of placing the ink 10 on the recording medium 102 (placement step)
In this step, the ink 10 is disposed on the base material 102. Preferably, the ink 10 is ejected from an ink jet recording head and disposed on the substrate 102. By disposing the ink jet recording head and disposing it, the resolution of the image to be formed can be increased. The method of ejecting ink by the ink jet method is not particularly limited, but since the ink 10 contains the polymerizable compound (A), a method of ejecting droplets by applying mechanical energy to the ink (piezo jet method) is preferable. .

  Note that the type of the base material 102 that is a recording medium is not particularly limited, and paper, a polymer material such as vinyl chloride or PET, metal, wood, cloth, glass, ceramics, or the like can be used. In addition, the shape of a base material is not specifically limited, A film, a board may be sufficient, and another solid thing may be sufficient.

[2] A step of irradiating the ink 10 disposed on the substrate 102 with light (light irradiation step)
After the ink 10 is placed on the base material 102 (FIG. 1A), as shown in FIG. 1B, light 103 such as ultraviolet light is irradiated. As a result, the ink 10 is cured.

  The type of light 103 irradiated in this step is not particularly limited, and can be selected according to the sensitivity wavelength of the ink 10. Specifically, it is preferable to appropriately select and use ultraviolet light having a wavelength of 150 nm to 400 nm, X-rays, electron beams, and the like.

Among these, the light irradiated onto the ink 10 is particularly preferably ultraviolet light. This is because many commercially available photopolymerization initiators are sensitive to ultraviolet light. Examples of light sources that emit ultraviolet light include high pressure mercury lamps, ultrahigh pressure mercury lamps, low pressure mercury lamps, deep-UV lamps, carbon arc lamps, chemical lamps, metal halide lamps, xenon lamps, light emitting diode (LED) lamps, and KrF excimer lasers. , ArF excimer laser, F ₂ excimer laser, and the like, and an ultra-high pressure mercury lamp or LED lamp is particularly preferable. Further, the number of light sources used may be one or plural.

  As described above, the ink 10 according to the present embodiment has a form in which the second liquid (W) forms droplets and the droplets are dispersed in the first liquid (O). When the ink 10 is irradiated with light, the first liquid (O) is cured to form a cured product 104.

  At this time, the second liquid (W) is not cured, and the volatile component containing water (C) in the second liquid (W) is not cured during and / or after the first liquid (O) is cured. Evaporate. As a result, a gap 105 having a size corresponding to the particle size of the droplet 101 is formed in a portion where the droplet 101 formed by the second liquid (W) was present. Further, when the volatile component containing water (C) evaporates, the particles (D) contained in the second liquid (W) aggregate. As a result, aggregates 107 of particles (D) are formed in the voids 105.

  In addition, you may provide the heating process by a heater etc. in the middle of the said light irradiation process, and / or after a process, and the drying process by ventilation. Thereby, evaporation of the second liquid (W) is promoted, and the film 106 can be dried quickly.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail using an Example, the technical scope of this invention is not limited to a following example. Note that “parts” and “%” used below are all based on mass unless otherwise specified.

<Preparation of photocurable ink>
The constituent materials shown below were blended in the ratios shown in Table 1 and stirred to prepare photocurable inks of Examples 1 to 4 and Comparative Examples 1 to 3, respectively. Homogenizer (AHG-160D, manufactured by ASONE) equipped with a shaft generator (HT1008, manufactured by ASONE) in which the first liquid (O) in which the respective components are mixed in the ratios shown in Table 1 and Table 2 is placed in a bottle (20 mL). Stir with. And after adding the 2nd liquid (W) slowly there, it stirred and mixed for 3 minutes. The rotational speed of the homogenizer at this time was 15000 rpm. In addition, the ratio shown in Table 1 and Table 2 is the mass%.

[Constituent materials]
(Polymerizable compound (A))
(A-1) Biscoat # 230 (1,6-hexanediol diacrylate, manufactured by Osaka Organic Chemicals)

(Photopolymerization initiator (B))
(B-1) Lucirin TPO (2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, manufactured by BASF)

(Water (C))
(C-1) Ion exchange water

(Particle (D))
(D-1) 5 mass% TTO-W-5
TTO-W-5 (an aqueous dispersion containing 31% by mass of titanium oxide particles, manufactured by Ishihara Sangyo) was diluted with ion-exchanged water so that the concentration of titanium oxide particles was 5% by mass, and 5% by mass TTO- W-5 was prepared. TTO-W-5 is titanium oxide particles whose surface is treated with silicon dioxide. The volume-based median diameter d50 of the titanium oxide particles contained in TTO-W-5 is 50 nm.

(D-2) 5 mass% STS-21
STS-21 (an aqueous dispersion having a titanium oxide particle content of 40% by mass, manufactured by Ishihara Sangyo Co., Ltd.) is diluted with ion-exchanged water so that the concentration of titanium oxide particles becomes 5% by mass, and 5% by mass STS-21 is obtained. Prepared. STS-21 is titanium oxide particles dispersed with ammonium polyacrylate. The volume-based median diameter d50 of the titanium oxide particles contained in STS-21 is 20 nm.

(Emulsifier (E))
(Inorganic particles (Eb))
(Eb-1) Titanium oxide particles (MT-100HD) acrylic monomer dispersion Titanium oxide particles MT-100HD (manufactured by Teika) are dispersed in biscoat # 230 (1,6-hexanediol diacrylate, manufactured by Osaka Organic Chemical Co., Ltd.) A dispersion was obtained.
The volume-based median diameter d50 of the titanium oxide particles MT-100HD contained in this dispersion was measured using a dynamic light scattering particle size distribution measuring device (Nanotrack UPA-EX150, manufactured by Nikkiso), and found to be 53 nm. It was. Further, the content of titanium oxide particles MT-100HD contained in this dispersion was 28% by mass.

(Eb-2) NANOBYK-3605 (1,6-hexanediol diacrylate dispersion of silicon dioxide particles, manufactured by BYK)
The volume-based median diameter d50 of the silicon dioxide particles contained in NANOBYK-3605 is 25 nm. Moreover, content of the silicon dioxide particle contained in NANOBYK-3605 is 50 mass%.

[Preparation]
Example 1
10.0 parts by mass of the photopolymerization initiator (B-1) was dissolved in 51.9 parts by mass of the polymerizable compound (A-1). To this, 18.1 parts by mass of dispersion (Eb-1) of inorganic particles (Eb) was further added to prepare a first liquid (O). While stirring the prepared first liquid (O) under the above-described stirring conditions, 20.0 parts by mass of particles (D-1) were added as the second liquid (W). Thereafter, the mixture was further stirred to form a W / O emulsion in which droplets formed by the second liquid (W) were dispersed in the first liquid (O), whereby the ink 1 of Example 1 was prepared.

(Example 2)
Ink 2 of Example 2 was prepared by using particles (D-2) instead of particles (D-1) as the second liquid (W) in Example 1.

(Example 3)
In Example 1, Ink 3 of Example 3 was used by using 10.0 parts by mass of inorganic particle (Eb) dispersion (Eb-2) instead of inorganic particle (Eb) dispersion (Eb-1). Prepared.

Example 4
In Example 3, the ink (4) of Example 4 was prepared using the particles (D-2) instead of the particles (D-1) as the second liquid (W).

(Comparative Example 1)
In Example 1, ink 5 of Comparative Example 1 was prepared using ion-exchanged water (C-1) instead of particles (D-1) as the second liquid (W).

(Comparative Example 2)
In Example 3, Ink 6 of Comparative Example 2 was prepared using ion-exchanged water (C-1) instead of particles (D-1) as the second liquid (W).

(Comparative Example 3)
A first liquid (O) was prepared by dissolving 3.0 parts by mass of the photopolymerization initiator (B-1) in 56.0 parts by mass of the polymerizable compound (A-1). While the prepared first liquid (O) was stirred under the above-described stirring conditions, 41.0 parts by mass of water (C-1) was added. Thereafter, the ink 7 of Comparative Example 3 was prepared by further stirring.

<Evaluation of photocurable ink>
[Film formation]
14 μL of the prepared ink 1 of Example 1 was dropped on a slide glass (S1111 manufactured by Matsunami Glass Industrial Co., Ltd.) using a micropipette. Further, a 100 μm-thick PET film (manufactured by Teijin DuPont Films, Tetron HL92W, “Tetron” is a registered trademark) was applied thereon, and an area of 26 mm × 26 mm was filled with ink 1.

Next, light emitted from a UV light source equipped with an ultrahigh pressure mercury lamp was irradiated for 20 seconds through a PET film after passing through a diffusion plate. Thereby, the ink 1 was hardened. The irradiation light used was UV light having a wavelength of 365 nm and an illuminance of 15 mW / cm ² .

  After light irradiation, the PET film was peeled off from the slide glass. Thereafter, the film was allowed to stand at room temperature to evaporate water contained in the cured film, thereby forming a film having a thickness of about 20 μm on the PET film.

  For each of the inks of Examples 2 to 4, Comparative Example 1 and Comparative Example 2, films were formed in the same procedure.

  Ink 7 of Comparative Example 3 started to appear as droplets (estimated as water droplets) that merged with the upper part of the liquid in the container when about 1 minute passed after preparation, and 10 minutes passed. At that time, it was completely separated into two layers. Therefore, since the ink 7 of Comparative Example 3 had low storage stability, film formation and evaluation were not performed. Each of these layers after being separated into two layers is composed of an oil layer composed of a first liquid (O) containing a polymerizable compound (A-1) and a photopolymerization initiator (B-1), and water (C). It is thought that it is a water layer. Even if the film is formed in such a state where the layers are separated, it is considered that a substantially transparent film can be obtained.

[Evaluation of degree of whiteness of white image]
Evaluation of the degree of whiteness of the white image obtained by the above method was performed by measuring the lightness (L * value) and the concealment rate (opacity). The brightness and the concealment rate were measured by a SCI method including specularly reflected light using a spectrocolorimeter (manufactured by Konica Minolta, CM-2600d).

  The results are summarized in Table 3 or Table 4.

[Evaluation of storage stability]
Each prepared ink was put into a light-shielded sample tube and stored at 25 ° C. for 1 week. The storage stability of each ink was visually evaluated from the viewpoints of sedimentation and dispersion stability.

  The results are summarized in Table 3 or Table 4. In addition, when the presence of a precipitate was observed when the sample tube after storage was tilted, the sedimentation property was evaluated as x. In addition, when it is recognized that the ink in the sample tube after storage is separated into two or more layers (layer separation) by visual observation, the dispersion stability is indicated as x. When the ink is not recognized, the dispersion stability is indicated. Was marked as ○.

[Membrane cross-sectional observation]
The cross section of the white image obtained by the Example and the comparative example was observed with the following method.

  A film (ink layer) forming a white image was immersed in liquid nitrogen for 10 minutes and frozen. Next, the blade of a razor (FAS-10, manufactured by Feather Safety Razor) was applied to the upper surface of the frozen ink layer, and the ink layer was cut by hitting with a hammer from above. Then, it fixed to the sample stand for scanning electron microscope (SEM) observations with the cut surface facing up.

  The cross section was observed using SEM (S-4800 (manufactured by Hitachi)). The magnification was 3000 to 70000 times and the acceleration voltage was 5.0 kV. In the observation, Pt—Pd was vapor-deposited on the cross section.

  First, each of the inks of Examples 1 and 2 and Comparative Example 1 which are inks using the titanium oxide particles (Eb-1) which are inorganic particles (Eb) as the emulsifier (E) will be examined. In each of the inks of Examples 1 and 2 and Comparative Example 1, the titanium oxide particles (Eb-1) are present in the first liquid (O). It is thought that it is adsorbed at the interface between O) and the second liquid (W).

  All the films formed by the inks of Examples 1 and 2 which are the ink containing the particles (D) in the second liquid (W) were formed by the ink 5 of Comparative Example 1 not containing the particles (D). Both brightness and concealment rate were higher than the film. Therefore, a white image with a high degree of whiteness could be formed by containing the particles (D) in the second liquid (W).

  In FIG. 3, the cross-sectional SEM image of the film | membrane formed with each ink of Examples 1-2 and the comparative example 1 is shown. 3A and 3B are cross-sectional SEM images of the film formed with the ink 1 of Example 1. FIG. 3C and 3D are cross-sectional SEM images of the film formed with the ink 2 of Example 2. FIG. 3E and 3F are cross-sectional SEM images of the film formed with the ink 5 of Comparative Example 1. FIG. As shown in FIG. 3, when the cross-sectional observation of each film was performed, many voids having a diameter of 0.1 μm or more and 5 μm or less existed in any film. These films are considered to exhibit whiteness due to the irregular reflection of incident light by the large number of voids.

  In addition, aggregates of particles (D) were formed in the voids of the films formed by the inks of Examples 1 and 2 which are inks containing particles (D) in the second liquid (W). (FIGS. 3A to 3D). Therefore, by containing the particles (D) in the second liquid (W), aggregates of the particles (D) could be formed inside the voids in the formed film. In Examples 1 and 2, in addition to the irregular reflection of incident light due to the air gap, it is presumed that the degree of whiteness is further increased by the irregular reflection of the incident light by the aggregates of the particles (D).

  Next, each ink of Examples 3 to 4 and Comparative Example 2 which are inks using silicon dioxide particles (Eb-2) which are inorganic particles (Eb) as an emulsifier (E) will be examined. In each of the inks of Examples 1 and 2 and Comparative Example 1, the titanium oxide particles (Eb-1) are present in the first liquid (O). It is thought that it is adsorbed at the interface between O) and the second liquid (W).

  All the films formed by the inks of Examples 3 to 4, which are inks containing particles (D) in the second liquid (W), were formed by the ink 6 of Comparative Example 2 that does not contain particles (D). Both brightness and concealment rate were higher than the film. Therefore, a white image with a high degree of whiteness could be formed by containing the particles (D) in the second liquid (W).

  In FIG. 4, the cross-sectional SEM image of the film | membrane formed with each ink of Examples 3-4 and the comparative example 2 is shown. 4A and 4B are cross-sectional SEM images of the film formed with the ink 3 of Example 3. FIG. 4C and 4D are cross-sectional SEM images of the film formed with the ink 4 of Example 4. FIG. 4E and 4F are cross-sectional SEM images of a film formed with the ink 6 of Comparative Example 2. FIG. As shown in FIG. 4, when cross-sectional observation of each film was performed, many voids having a diameter of 0.1 μm or more and 10 μm or less existed in any film. These films are considered to exhibit whiteness due to the irregular reflection of incident light by the large number of voids.

  In addition, aggregates of particles (D) were formed in the voids of the films formed by the inks of Examples 3 to 4 which are inks containing particles (D) in the second liquid (W). (FIGS. 4A to 4D). Therefore, by containing the particles (D) in the second liquid (W), aggregates of the particles (D) could be formed inside the voids in the formed film. In Examples 3 to 4, in addition to the irregular reflection of the incident light due to the air gap, it is presumed that the degree of whiteness is further increased by the irregular reflection of the incident light by the aggregate of the particles (D).

  Each ink in each example is a milky white ink and is considered to form an emulsion. In view of the result of cross-sectional observation of the formed film, the second liquid (W) is the first liquid (W). It is presumed that a W / O emulsion dispersed in the liquid (O) was formed. In addition, since it was found that the size of the voids in the film and the size of the droplet of the second liquid (W) in the ink are substantially the same, the size of the droplet is 0. It is considered to be 1 μm or more and 10 μm or less.

  Ink 7 of Comparative Example 3 is an ink containing the second liquid (W), but as described above, after completion of preparation by stirring and mixing, layer separation has begun when about 1 minute has passed, At 10 minutes, the layers were completely separated. In addition, since it is thought that a film | membrane is formed in the state divided into two layers also on the base material when forming a film | membrane in the state which separated the layer, it is thought that a substantially transparent film | membrane is obtained.

  On the other hand, each of the inks of Examples 1 to 4 is an ink containing the second liquid (W). However, after the preparation was completed by stirring and mixing, the layers were separated even after storage for 1 week. It did not occur. Therefore, it can be said that each ink in each example is a photocurable ink that can form a white image having high storage stability and high whiteness.

  Moreover, it has confirmed that many particle | grains existed in the surface of the space | gap of the film | membrane formed with each ink of Examples 1-4. This is thought to indicate that the inorganic particles (Eb) are adsorbed on the interface of the liquid droplets (water droplets) in each ink to stabilize the emulsion. In addition, since the plurality of inorganic particles (Eb) are arranged without gaps at the gap interface, it is considered that the coverage of the droplets by the inorganic particles (Eb) is almost 100%.

O 1st liquid D particle | grain 101 droplet (2nd liquid)

Claims (20)

A liquid droplet containing a first liquid containing a polymerizable compound and a photopolymerization initiator and a second liquid incompatible with the first liquid, and formed by the second liquid, A photocurable ink dispersed in the first liquid, comprising:
Containing first particles and second particles having higher hydrophilicity than the first particles,
The first particles are adsorbed at an interface between the first liquid and the second liquid;
The photocurable ink, wherein the second particles are present in the second liquid.   The photocurable ink according to claim 1, wherein the second liquid contains water.   3. The photocurable ink according to claim 1, wherein a refractive index of the second particles is 1.4 or more and 2.8 or less.   The photocurable ink according to any one of claims 1 to 3, wherein the volume-based median diameter of the second particles is 5 nm or more and 500 nm or less.   The concentration of the second particles in the second liquid is 1% by mass or more and 20% by mass or less when the total mass of the second liquid is 100% by mass. The photocurable ink according to any one of claims 1 to 4.   The content of the second liquid is 5% by mass or more and 50% by mass or less when the total mass of the photocurable ink is 100% by mass. The photocurable ink as described in any one of Claims.   The photocurable ink according to any one of claims 1 to 6, wherein a volume-based median diameter of the droplets is 0.1 µm or more and 20 µm or less.   The photocurable ink according to any one of claims 1 to 7, wherein the second particles are inorganic particles.   The photocurable ink according to claim 1, wherein the second particles are titanium oxide particles.   The photocurable ink according to any one of claims 1 to 9, wherein the polymerizable compound is a radical polymerizable compound.   The photocurable ink according to any one of claims 1 to 10, wherein the first liquid further contains a surfactant.   The photocurable ink according to any one of claims 1 to 11, wherein the volume-based median diameter of the first inorganic particles is 5 nm or more and 100 nm or less.   The photocurable ink according to any one of claims 1 to 12, wherein the second particles are dispersed in the second liquid by a dispersing agent.   The photocurable ink according to any one of claims 1 to 13, wherein the second particle has a hydrophilic group on a surface thereof.   2. The second particle according to claim 1, wherein at least a part of the surface of the second particle is coated with a compound containing at least one element selected from the group consisting of silicon, zirconium, and aluminum. The photocurable ink according to any one of 14. Containing a plurality of the first particles,
Some of the plurality of first particles are adsorbed on an interface between the first liquid and the second liquid,
The photocurable property according to any one of claims 1 to 15, wherein another part of the plurality of first particles is present in the first liquid. ink. A liquid droplet containing a first liquid containing a polymerizable compound and a photopolymerization initiator and a second liquid incompatible with the first liquid, and formed by the second liquid, A photocurable ink dispersed in the first liquid, comprising:
The photocurable ink, wherein the first liquid contains first particles, and the second liquid contains second particles.   An ink container in which the photocurable ink according to any one of claims 1 to 17 is contained. An arrangement step of arranging the photocurable ink according to any one of claims 1 to 17 on a substrate;
A light irradiation step of irradiating the photocurable ink disposed on the substrate with light.   The image forming method according to claim 19, wherein the arranging step is a step of discharging the photocurable ink from an ink jet recording head and arranging the ink on the substrate.