JP2018053161A - Photocurable ink, ink storage body and image formation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photocurable ink capable of forming a white image high in storage stability compared with the conventional one and high in the degree of whiteness.SOLUTION: Provided is a photocurable ink comprising: a first liquid including polymerizable compound and a photoinitiator; and a second liquid including water, in which droplets formed by the second liquid are dispersed into the first liquid, and including a surfactant in which HLB value by a Griffin method is 0.1 to 2.5.SELECTED DRAWING: Figure 2

Description

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

  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 is a photocurable ink containing a first liquid containing a polymerizable compound and a photopolymerization initiator, and a second liquid containing water. The liquid droplets formed by the second liquid are dispersed in the first liquid, and contain a surfactant having an HLB value of 0.1 to 2.5 by the Griffin method. And

  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 an example of the ink container which accommodated the photocurable ink which concerns on this embodiment. It is a figure which shows typically the image forming method using 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 the Example or the comparative example ((a) is Comparative Example 1, (b) is Example 1, (c) is 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), water A second liquid (W) containing (C). 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). Further, the ink 10 contains a surfactant (D) having an HLB value of 0.1 or more and 2.5 or less by the Griffin method.

  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 having many voids in the film 106 can be formed. An image can be obtained. This is because the water (C) contained in the ink 10 evaporates during the curing of the ink 10 and / or after the curing, so that the portion where the water (C) was present becomes a void. It is estimated to be.

  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) contains a polymerizable compound and a photopolymerization initiator. The polymerizable compound 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 contained in the first liquid (O) in the ink 10 reacts with a polymerization factor (radical or the like) generated from a photopolymerization initiator described later, and is a polymer compound by a chain reaction (polymerization reaction). It is a compound which becomes a film formed from (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.

  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]
The first liquid (O) is further hydrophobic in addition to the polymerizable compound (A) and the photopolymerization initiator (B) described above, as long as the effects of the present invention are not impaired in accordance with 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) is an aqueous solution containing water (C). In other words, the second liquid (W) is an aqueous liquid. The second liquid (W) is a liquid that is incompatible with the first liquid (O).

  The second liquid (W) is dispersed by forming droplets 101 in the first liquid (O). After the ink 10 is cured, the water (C) in the cured film 106 is evaporated, so that the gap 105 is formed in the space where the droplet 101 formed by the second liquid (W) was present. Is formed. The air gap 105 scatters incident light, so that the film 106 formed by the ink 10 looks white.

  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 so-called first liquid (O) and second liquid (O) in the ink 10 form a 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 second liquid is dispersed by forming droplets in the first liquid” means that the second liquid forms a closed interface with the first liquid. In addition, it means that a plurality of particles are present in the first 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 second liquid and the first liquid cannot be recognized. In this case, the second liquid and the first liquid are compatible with each other. A solution is formed.

  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, and the second liquid (W ) Is preferably dispersed in the first liquid liquid (O). When a liquid containing the first liquid (O) and the second liquid (W) is stored in a predetermined container for a long time, the layer made of the first liquid (O) and the second liquid are stored in the container. Two layers of liquid (W) are formed and separated 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, the ink 10 is porous because the water (C) of the ink 10 is evaporated during the curing of the ink 10 and / or after the ink 10 is cured, so that the portion where the water (C) was present becomes a void. The film 106 can be formed. Thereby, a void having a size substantially the same as that of the droplet 101 formed by the second liquid (W) containing water (C) can be formed in the film 106. 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 0.15 μm or more and 5 μm or less, and further preferably 0.2 μm or more and 2.5 μm or less. Note that when the diameter in the film 106 is larger than 20 μm, the mechanical strength of the film 106 may decrease.

  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 Accordingly, the volume-based median diameter d50 of the droplet 101 formed by the second liquid (W) in the first liquid (O) is preferably 0.1 μm or more and 20 μm or less. Further, the volume-based median diameter d50 of the droplet 101 formed by the second liquid (W) in the first liquid (O) is more preferably 0.1 μm or more and 10 μm or less, and 0.15 μm. More preferably, it is in the range of 5 μm or less. Moreover, it is especially preferable that they are 0.2 micrometer or more and 2.5 micrometers 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.

[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 strength of the film 106 may be reduced or the degree of whiteness may be reduced.

[Other additive components]
In addition to the above-mentioned water (C), the second liquid (W) may contain additional additive components in a range not impairing the effects of the present invention, depending on various purposes. 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.

  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 adjusting agents include, but are not limited to, water-soluble salts such as sodium chloride and potassium chloride, and surfactants. 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.

<Surfactant (D)>
The surfactant (D) contained in the ink 10 is a surfactant having an HLB value of 0.1 to 2.5 by the Griffin method. When the ink 10 contains the surfactant (D), the stability of the droplet 101 formed by the second liquid (W) is improved, and as a result, the storage stability of the ink 10 is improved.

As used herein, “surfactant” refers to a molecule having at least one hydrophilic part and one hydrophobic part in its molecular structure. In the present specification, the “HLB value” is an index representing the degree of affinity of the surfactant (D) to water and oil. In this specification, the HLB value is an HLB value calculated by the Griffin method, and is calculated by the following equation (1).
HLB value = 20 × (formula weight of hydrophilic part) / (molecular weight of surfactant) (1)

  Here, the “hydrophilic part” refers to a hydrophilic group contained in the molecular structure of the surfactant (D), and is preferably a polyoxyalkylene group or a polyhydric alcohol group. Examples of the polyoxyalkylene group include a polyoxyethylene group (polyethylene oxide; EO) and a polyoxypropylene group (polypropylene oxide; PO). Examples of the polyhydric alcohol group include glycerin, trimethylolpropane, pentaerythritol, sorbitol, sorbitan, and sucrose (sucrose).

  The “hydrophobic part” refers to a hydrophobic group contained in the molecular structure of the surfactant (D), preferably an aliphatic hydrocarbon group derived from an aliphatic alcohol, alkylphenol, fatty acid, or the like, or Is an aromatic hydrocarbon group.

  The hydrophilic part and hydrophobic part of the surfactant (D) in the molecular structure may be bonded directly, or may be bonded via an ester bond, glycoside bond, amide bond, or the like. Good.

  In general, when preparing a W / O emulsion in which many droplets formed by an aqueous phase are stably dispersed in an oil phase, a surfactant having an HLB value of about 3 to 6 should be used. It has been known. However, as a result of intensive studies by the present inventors, when preparing a W / O emulsion using the first liquid (O) and the second liquid (W), the HLB value is 0.1 or more. It was found that a highly stable W / O emulsion can be obtained by using a surfactant of 2.5 or less.

  The reason for this is not clear, but the present inventors consider as follows. As represented by the formula (1), the HLB value of the surfactant is proportional to the ratio of the formula amount of the hydrophilic portion in one molecule of the surfactant. That is, the smaller the formula amount of the hydrophilic portion, the smaller the HLB value, and the larger the formula amount of the hydrophobic portion, the smaller the HLB value. Therefore, as the size of the hydrophobic portion relative to the size of the hydrophilic portion increases, the HLB value also increases. Therefore, the surfactant having a small HLB value has a molecular structure in which the hydrophobic part is bulky relative to the hydrophilic part.

  When a surfactant is placed in a liquid containing an aqueous phase and an oil phase, the surfactant is placed at the interface between the aqueous phase and the oil phase so that the hydrophilic portion faces the aqueous phase and the hydrophobic portion faces the oil phase. line up. Therefore, in the W / O emulsion, the surfactant is adsorbed on the surface of the droplet so as to surround the droplet formed by the aqueous phase. At this time, the hydrophilic part of the surfactant faces inward and the hydrophobic part faces outward. Thus, when a surfactant is included in the W / O emulsion, the droplets formed by the aqueous phase are surrounded by the hydrophobic portion of the surfactant.

  Therefore, by using a surfactant (D) having a small HLB value as a surfactant as in this embodiment, droplets formed by an aqueous phase (second liquid (W)) by a bulky hydrophobic portion. Can be surrounded. Thereby, the repulsive force of the droplets formed by the aqueous phase (second liquid (W)) can be increased, and as a result, the droplets can be prevented from coalescing. For this reason, the storage stability of the ink 10 can be improved.

  The HLB value of the surfactant (D) is 0.1 or more and 2.5 or less. When the HLB value is less than 0.1, the hydrophilic group of the surfactant is remarkably small with respect to the hydrophobic part, so that the surfactant is between the first liquid (O) and the second liquid (W). It becomes difficult to adsorb to the interface. For this reason, the droplet formed by the second liquid (W) cannot be sufficiently surrounded by the surfactant. As a result, the storage stability of the W / O emulsion is lowered, and the storage stability of the ink is lowered. In addition, when the HLB value is larger than 2.5, the three-dimensional bulkiness of the hydrophobic portion of the surfactant is reduced, and it is sufficient that the droplets formed by the second liquid (W) are united. It cannot be suppressed. The HLB value of the surfactant (D) is more preferably 0.5 or more and 2.3 or less. By keeping the HLB value of the surfactant (D) within the above range, the storage stability of the ink 10 can be further improved.

  The surfactant (D) preferably has a weight average molecular weight of 900 or more and 6000 or less, more preferably 1500 or more and 6000 or less, and particularly preferably 2000 or more and 5000 or less. When the weight average molecular weight is less than 900, the three-dimensional bulkiness of the hydrophobic portion becomes small, and the droplets formed by the second liquid (W) cannot be sufficiently prevented from coalescing. Further, when the weight average molecular weight is 6000 or less, the viscosity of the ink 10 can be lowered, and as a result, the ejection stability of the ink 10 by the ink jet method can be improved.

  The surfactant (D) is preferably a nonionic surfactant. When an ionic surfactant is used as the surfactant (D), it may be difficult to dissolve in the first liquid (O). On the other hand, nonionic surfactants tend to be more soluble in the first liquid (O) than ionic surfactants. Therefore, when the surfactant (D) is a nonionic surfactant, the ink 10 is a W in which droplets formed by the second liquid (W) are dispersed in the first liquid (O). It becomes easy to make / O emulsion.

  As the surfactant (D), one type of surfactant may be used alone, or a plurality of types of surfactants may be used in combination.

  Surfactant (D) is an aromatic hydrocarbon having an aliphatic hydrocarbon group, an aromatic hydrocarbon group, and an aliphatic hydrocarbon group as a substituent having 8 to 400 carbon atoms in the molecular structure. It preferably has at least one selected from the group consisting of groups. When the surfactant (D) has the above-described hydrocarbon group, the three-dimensional bulkiness of the hydrophobic portion of the surfactant (D) increases, and as a result, the storage stability of the ink 10 can be improved. it can.

  The surfactant (D) more preferably has a structure in which fatty acid is condensed in its molecular structure. That is, the surfactant (D) preferably has a structure represented by the following formula (1) in its molecular structure.

[In Formula (1), R ¹ represents a hydrocarbon group, and x represents an integer of 2 or more and 15 or less. ]

  At this time, the carbon number of the structure in which the above-mentioned fatty acids are condensed is preferably 8 or more and 400 or less. Since the surfactant (D) has a structure in which fatty acids are condensed, the three-dimensional bulkiness of the hydrophobic portion of the surfactant (D) can be improved more efficiently.

  The surfactant (D) particularly preferably has a polyricinoleic acid structure, which is a structure in which ricinoleic acid is condensed in its molecular structure. That is, the surfactant (D) preferably has a structure represented by the following formula (2) in its molecular structure.

  Thereby, the storage stability of the ink 10 can be remarkably improved. In this case, the degree of condensation of ricinoleic acid is not particularly limited, but is preferably 2 or more and 15 or less.

[In Formula (2), n represents an integer of 2 or more and 15 or less. ]

  The molecular weight of the hydrophobic part of the surfactant (D) is not particularly limited, but is preferably 200 or more and 5000 or less, more preferably 1000 or more and 4600 or less, and 2000 or more and 4600 or less. It is particularly preferred. By setting the molecular weight of the hydrophobic part of the surfactant (D) within the above range, the three-dimensional bulkiness of the hydrophobic part can be increased without greatly increasing the viscosity of the ink 10. As a result, storage stability can be improved without reducing the ejection stability of the ink 10.

  The surfactant (D) preferably has a polyglycerin structure, which is a structure in which glycerin is condensed in the molecular structure. That is, the surfactant (D) preferably has a structure represented by the following formula (3) in its molecular structure. Since the polyglycerin structure has many oxyethylene groups and hydroxyl groups in its molecular structure, it has high hydrophilicity even at a small degree of polymerization, that is, a small molecular weight. Therefore, the function as a surfactant can be expressed without increasing the bulkiness of the hydrophilic portion of the surfactant (D). As described above, the surfactant (D) surrounds the periphery of the droplet 101 in the ink 10 such that the hydrophilic portion faces inward and the hydrophobic portion faces outward. At this time, by reducing the bulk height of the hydrophilic portion, the number of the surfactant (D) surrounding the periphery of one droplet 101 can be increased, and the dispersion stability of the droplet 101 is improved. It is considered possible.

[In Formula (3), R ² represents a hydrogen atom or a monovalent substituent, and y represents an integer of 6 to 16. ]

  Specific examples of the surfactant (D) include sucrose fatty acid esters such as sucrose stearate ester, sucrose palmitate ester, sucrose oleate ester, sucrose laurate ester, and sorbitan trioleate. And sorbitan fatty acid esters represented by sorbitan tristearate and polyglycerin fatty acid esters represented by polyglycerin condensed ricinoleic acid ester. These materials may use commercially available products. Among these, as the surfactant (D), polyglycerol condensed ricinoleic acid ester is particularly preferable. Polyglycerin condensed ricinoleic acid ester is a compound having a structure represented by the above formula (2) and a structure represented by the above formula (3) in its molecular structure.

  The content of the surfactant (D) is preferably 0.1% by mass or more and 20% by mass or less when the total amount of the ink 10 is 100% by mass. By setting the content of the surfactant (D) to 0.1% by mass or more, the second liquid (W) can be sufficiently dispersed as droplets in the first liquid (O). Moreover, it can suppress that the viscosity of the ink 10 raises by content of surfactant (D) being 20 mass% or less.

<Inorganic particles (E)>
The ink 10 may contain inorganic particles (E) in addition to the above components. The inorganic particles (E) 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 the inorganic particles (E), coalescence of the droplets 101 can be suppressed, and the droplets 101 can be maintained in a desired size for a long period.

  The present inventors presume the mechanism by which the above-described effects are obtained when the ink 10 contains inorganic particles (E) as follows. That is, the ink 10 includes a plurality of inorganic particles (E), and at least some of the inorganic particles (E) are adsorbed on the interface between the first liquid (O) and the second liquid (W). Existing. That is, the inorganic particles (E) are arranged at the interface between the first liquid (O) and the droplet 101. At this time, paying attention to one inorganic particle (E), at least a part of the inorganic particle (E) protrudes from the interface between the first liquid (O) and the droplet 101 to the first liquid (O) side. Will be. Therefore, even if two or more droplets 101 having the inorganic particles (E) adsorbed on the interface in this manner approach each other, the inorganic particles (E) adsorbed on the interface rebound sterically. The coalescence of the droplets 101 is suppressed. As a result, it is considered that a state in which the first liquid (W) is stably dispersed in the second liquid (O) is formed.

Such an inorganic particle (E) is not particularly limited as long as it is a particle containing 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 (E) may be one type or a plurality of types. Moreover, you may use multiple types of inorganic particle as an inorganic particle (E).

  Although the kind of inorganic material contained in the inorganic particles (E) is not particularly limited, silicon dioxide, mica, aluminum oxide, boehmite, iron oxide, titanium oxide, barium titanate, zirconium oxide, zinc oxide, and It is preferable to use at least one metal oxide selected from the group consisting of niobium oxide. 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 (E).

  Furthermore, it is preferable to use inorganic particles having a high refractive index as the inorganic particles (E). At this time, the refractive index of the inorganic particles (E) 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 (E) 0.05 or more larger than the refractive index of the cured product obtained by curing the polymerizable compound (A), the inorganic particles (E) 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 (E) 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 (E) 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 (E). By using titanium oxide particles as the inorganic particles (E), 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 (E) contained in the ink 10 is preferably 5 nm or more and 100 nm or less. By reducing the size of the inorganic particles (E), the inorganic particles (E) 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 ink 10 contains inorganic particles (Db), the ink 10 contains a plurality of inorganic particles (Db), all of which are the interfaces between the droplets 101 and the oily liquid (O). It does not have to be adsorbed. That is, some of the plurality of inorganic particles (Db) contained in the ink 10 may be dispersed in the oily liquid (O).

  When the ink 10 includes inorganic particles (E), the content of the inorganic particles (E) 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 (E) within the above range, the dispersion stability of the droplets 101 can be improved. Further, since the ink 10 contains the surfactant (D), the inorganic particles (E) may be aggregated by the surfactant (D) and the dispersion stability of the inorganic particles (E) may be reduced. . However, by setting the content of the inorganic particles (E) within the above range, aggregation of the inorganic particles (E) can be suppressed and dispersion stability of the inorganic particles (E) can be expected.

<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>
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, a polymerizable compound and a photopolymerization initiator 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) as needed, and the 2nd liquid (W) is adjusted.

  Next, the surfactant (D) is added to and mixed with the prepared first liquid (O). Thereafter, the second liquid (W) is added while stirring the first liquid (O) to which the surfactant (D) has been added, 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 adding the inorganic particles (E) to the ink 10, after preparing the first liquid (O) containing the polymerizable compound (A) and the photopolymerization initiator (B), the inorganic particles (E) are prepared. Is added to the first liquid (O). Then, it is preferable to form the droplet 101 by 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. 1 is a diagram illustrating an example of an ink container according to the present embodiment. FIG. 1A illustrates an ink container as an ink bag, and FIG. 1B illustrates an ink cartridge as an ink container. Examples of cases are shown respectively.

  As shown in FIG. 1A, 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. 1B, 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).

[1] Step of placing the ink 10 on the base material 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. 2 (a)), as shown in FIG. 2 (b), 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, in the ink 10 according to this embodiment, the second liquid (W) containing water (C) forms droplets, and the droplets are dispersed in the first liquid (O). It has a form. 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 water (C) contained in the second liquid (W) evaporates during and / or after the first liquid (O) is cured. . 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.

  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 water (C) 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 3 and Comparative Examples 1 to 4, respectively. First, the first liquid (O) in which the respective components are mixed at the ratio shown in Table 1 is placed in a bottle (20 mL), and a homogenizer (AHG-160D, manufactured by ASONE) to which a shaft generator (HT1008, manufactured by ASONE) is attached. Stir. And water (C) which is the 2nd liquid (W) was added there slowly, Then, it stirred and mixed for 3 minutes. The rotational speed of the homogenizer at this time was 15000 rpm. The ratio shown in Table 1 is mass%.

[Constituent materials]
≪First liquid (O) ≫
(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)

≪Second liquid (W) ≫
(C-1) Ion exchange water

≪Surfactant (D) ≫
(D-1) Tylabazole H818 (polyglycerin condensed ricinoleic acid ester, Taiyo Kagaku HLB value: 1.1-2)
(D-2) Ryoto sugar ester S-170 (sucrose stearate ester, HLB value: 1 manufactured by Mitsubishi Chemical Foods, Inc.)
(D-3) OP-80R (Sorbitan monooleate, NOF HLB value: 4.3) (for comparative example)

[Preparation]
Example 1
A first liquid (O) was prepared by dissolving 3.0 parts by mass of a photopolymerization initiator (B-1) in 72.0 parts by mass of a polymerizable compound (A-1). Thereafter, 5.0 parts by mass of the surfactant (D-1) was added to the prepared first liquid (O) to dissolve the surfactant (D-1). While stirring under the above-described stirring conditions, 20.0 parts by mass of water (C-1) as the second liquid (W) was added to this solution. 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)
In Example 1, the ratio of the polymerizable compound (A-1) was changed to 74.0 parts by mass, and the ratio of the surfactant (D-1) was changed to 3.0 parts by mass. 2 was prepared.

(Example 3)
A first liquid (O) was prepared by dissolving 3.0 parts by mass of the photopolymerization initiator (B-1) in 77.5 parts by mass of the polymerizable compound (A-1). Then, 0.5 mass part of surfactant (D-2) was added to the prepared 1st liquid (O), and surfactant (D-2) was dissolved. While stirring under the above-described stirring conditions, 20.0 parts by mass of water (C-1) as the second liquid (W) was added to this solution. 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) to prepare ink 3 of Example 3.

(Comparative Example 1)
A first liquid (O) was prepared by dissolving 3.0 parts by mass of the photopolymerization initiator (B-1) in 94.0 parts by mass of the polymerizable compound (A-1). Thereafter, 3.0 parts by mass of surfactant (D-1) was added to the prepared first liquid (O) to dissolve the surfactant (D-1), and ink 4 of Comparative Example 1 was prepared.

(Comparative Example 2)
A first liquid (O) was prepared by dissolving 3.0 parts by mass of the photopolymerization initiator (B-1) in 77.0 parts by mass of the polymerizable compound (A-1). While stirring under the above-described stirring conditions, 20.0 parts by mass of water (C-1) as the second liquid (W) was added to the prepared first liquid (O), and ink 5 of Comparative Example 2 was added. Was prepared.

(Comparative Example 3)
By dissolving 3.0 parts by mass of the photopolymerization initiator (B-1) in 97.0 parts by mass of the polymerizable compound (A-1) to prepare the first liquid (O), Ink 6 was prepared.

(Comparative Example 4)
A first liquid (O) was prepared by dissolving 3.0 parts by mass of the photopolymerization initiator (B-1) in 74.0 parts by mass of the polymerizable compound (A-1). Thereafter, 3.0 parts by mass of the surfactant (D-3) was added to the prepared first liquid (O) to dissolve the surfactant (D-3). While stirring under the above-described stirring conditions, 20.0 parts by mass of water (C-1) as the second liquid (W) was added to this solution. 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), and ink 7 of Comparative Example 4 was prepared.

<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) was placed 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 the inks of Examples 2 to 3, Comparative Example 1 and Comparative Example 3, films were formed in the same procedure.

  Ink 5 of Comparative Example 2 and Ink 7 of Comparative Example 4 were droplets (estimated as water droplets) that merged with the upper part of the liquid in the container when about 1 minute passed after preparation. At the time when 10 minutes passed, the two layers were completely separated. Therefore, the ink 5 of Comparative Example 2 and the ink 7 of Comparative Example 4 were judged to have low storage stability, and no film was formed or evaluated. These layers after separation into two layers are respectively an oil layer composed of a first liquid (O) containing a polymerizable compound (A-1) and a photopolymerization initiator (B-1), and water (C-1 ).

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

  Ink 4 of Comparative Example 1 and Ink 6 of Comparative Example 3 were transparent as a result of viewing the obtained white image. Therefore, it was determined that a white image with a high degree of whiteness could not be formed for the ink 4 of Comparative Example 1 and the ink 6 of Comparative Example 3, and measurement of lightness (L * value) was omitted.

  The results are summarized in Table 2.

[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 after storage was visually evaluated.

  The results are summarized in Table 2. In addition, when the ink in the sample tube after storage is observed to be separated into two or more layers (layer separation) by visual observation, the storage stability is x, and when it is not recognized, the storage stability is stored. 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 blade of a razor (FAS-10, manufactured by Feather Safety Razor) was applied to the upper surface of the film (ink layer) forming a white image, 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 observation was performed at a magnification of 8000 to 12000 times and an acceleration voltage of 5.0 kV. In the observation, Pt—Pd was vapor-deposited on the cross section.

<Summary of results>
The film formed by the ink 4 of Comparative Example 1 and the ink 6 of Comparative Example 3 which is an ink not containing water (C-1) as the second liquid (W) was transparent as a result of visual observation. . When cross sections of the respective films were observed, there were almost no voids in the films formed by the ink 4 of Comparative Example 1 and the ink 6 of Comparative Example 3. As an example, the observation result of the film cross section of the ink 4 of Comparative Example 1 is shown in FIG.

  Ink 5 of Comparative Example 2 and Ink 7 of Comparative Example 4 were separated into two layers immediately after preparation. This is because the surfactant (C) that adsorbs to the interface between the first liquid (O) and the second liquid (W) and stabilizes the droplets formed by the second liquid (W) is added. It is thought that this is because it has not. When the film is formed in a layer-separated state, it is considered that the film is formed in a state of being divided into two layers even on the base material. Therefore, it is considered that a transparent film can be obtained as in Comparative Examples 1 and 3. .

  On the other hand, the films formed by the inks 1 to 3 of Examples 1 to 3 which are ink containing water (C-1) as the second liquid all had a high degree of whiteness. When cross-sectional observation of each film was performed, many voids having a diameter of 0.1 μm or more and 20 μm or less existed in any film. As an example, a cross-sectional SEM image of a film formed with the ink 1 of Example 1 is shown in FIG. Since the films formed of the inks 1 to 3 of Examples 1 to 3 all have such voids, it is presumed that incident light was irregularly reflected by the voids and the degree of whiteness was increased.

  Note that each ink in each example is a milky-white ink, and is considered to form an emulsion. Considering the result of cross-sectional observation of the formed film, the second liquid (W) is the first liquid. It is presumed that a W / O type emulsion dispersed in the liquid (O) is 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 20 μm or less.

  Inks 1 to 3 of Examples 1 to 3 are all inks containing water (C-1), which is the first liquid (W). No layer separation occurred even after storage for 1 week. 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.

O first liquid 101 droplet (second liquid)

Claims (18)

A photocurable ink containing a first liquid containing a polymerizable compound and a photopolymerization initiator, and a second liquid containing water,
Droplets formed by the second liquid are dispersed in the first liquid;
A photocurable ink comprising a surfactant having an HLB value of 0.1 to 2.5 by the Griffin method.   The photocurable ink according to claim 1, wherein the surfactant has a weight average molecular weight of 900 or more and 6000 or less.   The photocurable property according to claim 1 or 2, wherein the water content is 5% by mass or more and 50% by mass or less when the total amount of the photocurable ink is 100% by mass. ink.   The photocurable ink according to any one of claims 1 to 3, wherein a volume-based median diameter of the droplet is 0.1 µm or more and 10 µm or less.   The photocurable ink according to any one of claims 1 to 4, wherein the viscosity at 25 ° C is 1 mPa · s or more and 75 mPa · s or less.   The photocurable ink according to any one of claims 1 to 5, wherein the surfactant is a nonionic surfactant.   In the molecular structure of the surfactant, an aliphatic hydrocarbon group having 8 to 400 carbon atoms, an aromatic hydrocarbon group, and an aromatic hydrocarbon group having an aliphatic hydrocarbon group as a substituent, The photocurable ink according to any one of claims 1 to 6, comprising at least one selected from the group consisting of: The photocurable ink according to any one of claims 1 to 7, wherein the surfactant has a structure represented by the following formula (1) in its molecular structure.

[In Formula (1), R ¹ represents a hydrocarbon group, and x represents an integer of 2 or more and 15 or less. ] The photocurable ink according to claim 1, wherein the surfactant has a structure represented by the following formula (2) in its molecular structure.

[In Formula (2), n represents an integer of 2 or more and 15 or less. ]   The photocurable ink according to any one of claims 1 to 9, wherein the hydrophobic part of the surfactant has a molecular weight of 200 or more and 5000 or less.   The photocurable ink according to any one of Claims 1 to 10, wherein the surfactant has a polyglycerin structure in its molecular structure.   The content of the surfactant is 0.1% by mass or more and 20% by mass or less when the total amount of the photocurable ink is 100% by mass. The photocurable ink composition according to claim 1.   A light containing a first liquid containing a polymerizable compound and a photopolymerization initiator, a second liquid containing water, and a polyglycerin fatty acid ester having an HLB value of 0.1 to 2.5. Curable ink.   The photocurable ink according to claim 13, wherein the polyglycerol fatty acid ester is a polyglycerol condensed ricinoleic acid ester.   The content of the polyglycerin fatty acid ester is 0.1% by mass or more and 20% by mass or less when the total amount of the photocurable ink is 100% by mass. The photocurable ink as described.   An ink container in which the photocurable ink according to any one of claims 1 to 15 is contained.   The arrangement | positioning process which arrange | positions the photocurable ink as described in any one of Claims 1 thru | or 15 on a base material, and the light irradiation which irradiates light to the said photocurable ink arrange | positioned on the said base material And an image forming method.   The image forming method according to claim 17, wherein the arranging step is a step of ejecting the photocurable ink from an ink jet recording head and arranging the ink on the substrate.