Ink, ink jet recording method and ink jet recording system

Abstract

An object of the present invention is to provide an ink or the like that reduces folding cracks and cutting and peeling during processing of a recorded matter to be formed.SOLUTION: The ink of the present invention is an ink containing a polymerizable compound that is polymerized by actinic radiation, wherein a content of a multifunctional (meth)acrylate having a glycerol skeleton with respect to 100 parts by mass of the polymerizable compound is equal to or greater than 20 parts by mass, and the ink contains a gelling agent.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an ink, an inkjet recording method, and an inkjet recording system. [Background technology]

[0002] Actinic ray-curable inks are known as inks used in various printing fields. Actinic ray-curable inks contain, as a liquid component, a compound that polymerizes when exposed to actinic rays (polymerizable compound). Actinic ray-curable inks can be cured by exposure to actinic rays, and can firmly adhere a colorant to a recording medium (Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-195468 [Patent Document 2] Japanese Patent Application Publication No. 2017-088863 [Patent Document 3] International Publication No. 2016 / 096603 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, the uses of recorded matter formed using actinic radiation-curable inks have expanded, and after the recorded matter is formed, it may be further processed, such as by bending or cutting. However, it has been found that the inks described in Patent Documents 1 to 3 are not adequately compatible with these processes, and are prone to cracking when bent and peeling when cut.

[0005] The problem to be solved by the present invention is to provide an ink or the like that reduces fold cracks and peeling due to cutting during processing of the resulting recorded matter. [Means for solving the problem]

[0006] The present inventors have investigated the causes of the above problems in order to solve the above problems. As a result, they have found the following and arrived at the present invention. The ink contains a polyfunctional (meth)acrylate having a specific amount of glycerol skeleton, and a gelling agent. This makes it possible to reduce fold cracks and peeling during cutting when processing recorded matter formed using the ink. That is, the above-mentioned problems of the present invention are solved by the following means.

[0007] 1. An ink containing a polymerizable compound that polymerizes when exposed to actinic radiation, the content of the polyfunctional (meth)acrylate having a glycerol skeleton is 20 parts by mass or more relative to 100 parts by mass of the polymerizable compound; Contains gelling agents An ink characterized by:

[0008] 2. The content of the trifunctional (meth)acrylate having a glycerol skeleton relative to 100 parts by mass of the polymerizable compound is 20 parts by mass or more. 2. The ink according to claim 1,

[0009] 3. The content of the polyfunctional (meth)acrylate having a glycerol skeleton relative to 100 parts by mass of the polymerizable compound is within the range of 30 parts by mass or more and 60 parts by mass or less. 3. The ink according to claim 1 or 2.

[0010] 4. The polyfunctional (meth)acrylate having a glycerol skeleton is a propylene oxide modified product. 3. The ink according to claim 1 or 2.

[0011] 5. The number of propylene oxide modifications in the polyfunctional (meth)acrylate having a glycerol skeleton is in the range of 3 to 9. 5. The ink according to claim 4,

[0012] 6. The number of propylene oxide modifications in the polyfunctional (meth)acrylate having a glycerol skeleton is in the range of 3 to 4. 6. The ink according to claim 5,

[0013] 7. The ratio Am / Wm of the mass Am of the polyfunctional (meth)acrylate having a glycerol skeleton to the mass Wm of the gelling agent is in the range of 3.5 or more and 16 or less. 3. The ink according to claim 1 or 2.

[0014] 8. The gelling agent contains at least one of a ketone wax, an ester wax, a glycerol wax, and a pentaerythritol wax. 3. The ink according to claim 1 or 2.

[0015] 9. The gelling agent has an alkyl group, The alkyl group has 22 or less carbon atoms. 3. The ink according to claim 1 or 2.

[0016] 10. The gelling agent contains the ester wax. 9. The ink according to claim 8,

[0017] 11. The water content is within the range of 0.5 to 1.0% by mass relative to the total mass of the ink. 3. The ink according to claim 1 or 2.

[0018] 12. Used in inkjet recording 3. The ink according to claim 1 or 2.

[0019] 13. An inkjet recording method using the ink according to item 1 or 2, a step of heating the ink to 50° C. or higher, discharging the ink from an inkjet head, and causing the ink to land on a recording medium; An inkjet recording method comprising:

[0020] 14. An inkjet recording system using the ink according to item 1 or 2, an inkjet head that ejects the ink; and an irradiation unit that irradiates the ink that has landed on the recording medium with actinic rays; An inkjet recording system comprising: [Effects of the Invention]

[0021] The above-described means of the present invention can reduce fold cracks and peeling during cutting when a recorded matter formed using the ink is processed.

[0022] The mechanism by which the effects of the present invention are manifested or the mechanism of action is not clear, but is speculated as follows.

[0023] Generally, the greater the number of polymerizable functional groups per molecule of a polymerizable compound, the greater the hardness of the resulting polymer. Furthermore, the greater the branched structure of a polymerizable compound, the greater the hardness of the resulting polymer. Therefore, the hardness of the resulting polymer can be adjusted by adjusting the number of polymerizable functional groups, the branched structure, etc. of the polymerizable compound.

[0024] The ink of the present invention contains a polyfunctional (meth)acrylate having a glycerol skeleton as a polymerizable compound. In other words, the compound has a branched structure within the molecule, and the number of (meth)acryloyl groups is three or more. This allows the polymer obtained by polymerizing the compound to have appropriate hardness while also having flexibility. Therefore, it is believed that the resulting recorded material will be less likely to crack even when bent.

[0025] The ink of the present invention contains a gelling agent. Inks containing a gelling agent have low viscosity at high temperatures and high viscosity at low temperatures. Therefore, the ink easily wets the recording medium upon impact, which has the effect of suppressing cracking of the ink layer in the resulting recorded matter. Furthermore, as described above, the polymer obtained by polymerizing this compound has an appropriate hardness. As a result, even when the recorded matter is cut, the ink layer and the recording medium are sufficiently adhered, and because the ink layer is hard, it is thought that the ink layer is unlikely to peel off even when the cut area is rubbed. [Brief explanation of the drawings]

[0026] [Figure 1] FIG. 1 is a schematic diagram illustrating a configuration of an inkjet recording apparatus. DETAILED DESCRIPTION OF THE INVENTION

[0027] The ink of the present invention is an ink containing a polymerizable compound that polymerizes when exposed to actinic radiation, and the ink contains a polyfunctional (meth)acrylate having a glycerol skeleton in an amount of 20 parts by mass or more per 100 parts by mass of the polymerizable compound, and also contains a gelling agent. The above features are technical features common to or corresponding to the following embodiments.

[0028] In an embodiment of the present invention, from the viewpoint of reducing fold cracks and peeling during cutting of the recorded material, it is preferable that the content of the trifunctional (meth)acrylate having a glycerol skeleton is 20 parts by mass or more per 100 parts by mass of the polymerizable compound.

[0029] In an embodiment of the present invention, from the viewpoint of reducing fold cracks and peeling during cutting of the recorded material, it is preferable that the content of the polyfunctional (meth)acrylate having a glycerol skeleton is in the range of 30 parts by mass or more and 60 parts by mass or less per 100 parts by mass of the polymerizable compound.

[0030] In an embodiment of the present invention, from the viewpoint of reducing fold cracks and peeling during cutting of the recorded material, the polyfunctional (meth)acrylate having a glycerol skeleton is preferably a propylene oxide modified product.

[0031] In an embodiment of the present invention, from the viewpoint of reducing fold cracks and peeling during cutting of a recorded material, the number of modifications of propylene oxide in the polyfunctional (meth)acrylate having a glycerol skeleton is preferably in the range of 3 to 9. Furthermore, the number of modifications of propylene oxide in the polyfunctional (meth)acrylate having a glycerol skeleton is more preferably in the range of 3 to 4.

[0032] In an embodiment of the present invention, from the viewpoint of image quality, it is preferable that the ratio Am / Wm of the mass Am of the polyfunctional (meth)acrylate having a glycerol skeleton to the mass Wm of the gelling agent is in the range of 3.5 or more and 16 or less.

[0033] In an embodiment of the present invention, from the viewpoint of ink viscosity, it is preferable that the gelling agent contains at least one of a ketone wax, an ester wax, a glycerol wax, and a pentaerythritol wax.

[0034] In an embodiment of the present invention, from the viewpoint of the viscosity of the ink, it is preferable that the gelling agent has an alkyl group, and the number of carbon atoms in the alkyl group is 22 or less.

[0035] In an embodiment of the present invention, from the viewpoint of the viscosity of the ink, it is preferable that the gelling agent contains the ester wax.

[0036] In an embodiment of the present invention, from the viewpoint of the viscosity of the ink, the water content is preferably within a range of 0.5 to 1.0% by mass relative to the total mass of the ink.

[0037] In an embodiment of the present invention, the ink is preferably used for inkjet recording from the viewpoint of ink viscosity.

[0038] An inkjet recording method according to an embodiment of the present invention is an inkjet recording method using the ink described above, and includes the steps of heating the inkjet ink to 50° C. or higher, ejecting the inkjet ink from an inkjet head, and allowing the ink to land on a recording medium.

[0039] An inkjet recording system according to an embodiment of the present invention is an inkjet recording system that uses the ink described above, and includes an inkjet head that ejects the ink, and an irradiation unit that irradiates the ink that has landed on a recording medium with actinic rays.

[0040] Hereinafter, one or more embodiments of the present invention will be described with reference to the drawings. However, the scope of the present invention is not limited to the disclosed embodiments. In this application, the symbol "to" is used to mean that the numerical values ​​before and after it are included as the lower limit and upper limit.

[0041] 1. Ink composition The ink of this embodiment is an ink containing a polymerizable compound that polymerizes when exposed to actinic radiation. The content of a polyfunctional (meth)acrylate having a glycerol skeleton is 20 parts by mass or more per 100 parts by mass of the polymerizable compound. The ink also contains a gelling agent.

[0042] 1-1. Polymerizable compounds In this specification, the "polymerizable compound that polymerizes when exposed to actinic rays" is also simply referred to as a "polymerizable compound." The ink of this embodiment contains a polymerizable compound. As a result, the ink of this embodiment can be cured by exposure to actinic rays, and the colorant can be firmly attached to the recording medium.

[0043] The ink of this embodiment contains a polyfunctional (meth)acrylate having a glycerol skeleton as a polymerizable compound. The ink of this embodiment may further contain a polymerizable compound other than the polyfunctional (meth)acrylate having a glycerol skeleton. The polymerizable compound may be contained alone or in combination of two or more types.

[0044] Specifically, the term "polymerizable compound" refers to a compound that polymerizes or crosslinks when irradiated with actinic rays. Examples of actinic rays include electron beams, ultraviolet rays, alpha rays, gamma rays, and X-rays. Of these, the actinic rays are preferably ultraviolet rays or electron beams, and more preferably ultraviolet rays.

[0045] 1-1-1. Polyfunctional (meth)acrylate with a glycerol skeleton The structural formula of glycerol is shown below.

[0046] [ka]

[0047] In this embodiment, the "glycerol skeleton" refers to the portion of glycerol shown in the above structural formula (1) in which the hydrogen atoms of the three hydroxy groups have been removed. In other words, the "polyfunctional (meth)acrylate having a glycerol skeleton" refers to a compound in which the hydrogen atoms of the hydroxy groups have been replaced with other groups and which has two or more (meth)acryloyl groups at its terminals.

[0048] In this specification, "(meth)acrylate" is a general term for "acrylate" and "methacrylate" and means either or both of them. "(meth)acryloyl group" is a general term for "acryloyl group" and "methacryloyl group" and means either or both of them.

[0049] The polyfunctional acrylate having a glycerol skeleton may be modified by introducing a polyoxyalkylene group between the glycerol skeleton and the (meth)acryloyl group. Among these, the polyfunctional acrylate having a glycerol skeleton is preferably a propylene oxide modified product. The number of propylene oxide modifications is preferably within the range of 3 to 9, more preferably within the range of 3 to 4.

[0050] By controlling the structure of the polyoxyalkylene group, it is possible to control the three-dimensional structure and molecular weight of the polyfunctional acrylate having a glycerol skeleton, and thereby control the hardness of the polymer, the viscosity of the ink, etc. As a result, it is possible to further reduce fold cracking and cutting peeling during processing of the resulting recorded matter. Furthermore, when used as an inkjet ink, the viscosity can be adjusted to exhibit good ejection properties.

[0051] The polyfunctional (meth)acrylate having a glycerol skeleton is not particularly limited as long as it satisfies the above definition. Examples of the polyfunctional (meth)acrylate having a glycerol skeleton include glycerin diacrylate, glycerin dimethacrylate, ethylene oxide-modified glycerin diacrylate, ethylene oxide-modified glycerin dimethacrylate, propylene oxide-modified glycerin diacrylate, propylene oxide-modified glycerin dimethacrylate, glycerin triacrylate, glycerin trimethacrylate, ethylene oxide-modified glycerin triacrylate, ethylene oxide-modified glycerin trimethacrylate, propylene oxide-modified glycerin triacrylate, and propylene oxide-modified glycerin trimethacrylate.

[0052] The polyfunctional (meth)acrylate having a glycerol skeleton may be a compound in which three or more (meth)acryloyl groups are added to a polyglycerol skeleton. Examples of such compounds include ethylene oxide-modified diglycerol tetraacrylate, ethylene oxide-modified diglycerol tetramethacrylate, propylene oxide-modified diglycerol tetraacrylate, propylene oxide-modified diglycerol tetramethacrylate, ethylene oxide-modified tetraglycerol hexaacrylate, ethylene oxide-modified tetraglycerol hexamethacrylate, propylene oxide-modified tetraglycerol hexaacrylate, and propylene oxide-modified tetraglycerol hexamethacrylate.

[0053] Examples of polyfunctional acrylates having a glycerol skeleton are represented by the following structural formulas (2) to (5). Note that structural formulas (2) and (3) represent the structure of a difunctional acrylate, structural formula (4) represents the structure of a trifunctional acrylate, and structural formula (5) represents the structure of a tetrafunctional acrylate. Furthermore, structural formula (5) is a compound in which four acryloyl groups are added to a diglycerol skeleton. Note that in this embodiment, the acryloyl groups in the following structural formulas (2) to (5) may be methacryloyl groups.

[0054] [ka]

[0055] In structural formulas (2) to (5), R1, R2, R3, and R4 each independently represent an alkylene group, a polyoxyalkylene group, or a hydrogen atom.

[0056] The alkylene group is not particularly limited, and examples thereof include a methylene group, an ethylene group, an n-propylene group, an isopropylene group, an n-butylene group, and an isobutylene group.

[0057] The polyoxyalkylene group is not particularly limited, and examples thereof include -(CH2CH2O) n -, the structure represented by -(CH2CH2CH2O)n -, where n is an integer of 1 or more.

[0058] Commercially available polyfunctional (meth)acrylates having a glycerol skeleton are preferably certified by the Japan Organics Resources Association as having a biomass content of 35% or more. "Biomass content" refers to the content (dry weight ratio) of biomass raw materials contained in a product. Certified commercial products include, for example, glycerin diacrylate "Aronix (registered trademark) M-920" (45% plant-based raw material, manufactured by Toagosei Co., Ltd.) and glycerin triacrylate "Aronix (registered trademark) M-930" (37% plant-based raw material, manufactured by Toagosei Co., Ltd.).

[0059] The ratio of plant raw materials is expressed by the following formula (1), based on the description in the Toa Gosei Group Research Annual Report 26TREND2020 No. 23. Formula (1) Ratio of plant raw materials [%] = (molecular weight of plant-derived raw material skeleton ÷ total molecular weight) × 100

[0060] Other commercially available products include, for example, propoxylated (3) glyceryl triacrylate "SR9020NS" (manufactured by Sartomer Co., Ltd.), diglycerin EO-modified acrylate "Aronix (registered trademark) M-460" (30% plant-based raw material, manufactured by Toa Gosei Co., Ltd.), propoxylated (3.5) glyceryl triacrylate "EM2387" (manufactured by Choko Materials Industry Co., Ltd.), and ethoxylated (3) glyceryl triacrylate "EM2388" (manufactured by Choko Materials Industry Co., Ltd.).

[0061] The (meth)acrylate having a glycerol skeleton is preferably trifunctional rather than difunctional. This can further reduce fold cracking and cutting peeling during processing of the resulting recorded matter. In addition, (meth)acrylates having a glycerol skeleton with different numbers of functional groups may be used in combination.

[0062] In the ink of this embodiment, the content of the polyfunctional (meth)acrylate having a glycerol skeleton is 20 parts by mass or more relative to 100 parts by mass of the polymerizable compound. In addition, the content of the trifunctional (meth)acrylate having a glycerol skeleton is preferably 20 parts by mass or more relative to 100 parts by mass of the polymerizable compound. This further reduces fold cracks and cutting peeling during processing of the resulting recorded matter.

[0063] The content of the polyfunctional (meth)acrylate having a glycerol skeleton relative to 100 parts by mass of the polymerizable compound is preferably in the range of 30 parts by mass or more and 60 parts by mass or less. This further reduces fold cracking and cutting peeling during processing of the resulting recorded matter. Furthermore, when used as an inkjet ink, the viscosity can be adjusted to exhibit good ejection properties.

[0064] In the ink of this embodiment, the ratio (Am / Wm) of the mass Am of the polyfunctional (meth)acrylate having a glycerol skeleton to the mass Wm of the gelling agent is preferably in the range of 3.5 or more and 16 or less. This further reduces fold cracking and cutting peeling during processing of the resulting recorded matter. Furthermore, when used as an inkjet ink, the viscosity can be adjusted to exhibit good ejection properties.

[0065] Furthermore, by including a polyfunctional (meth)acrylate having a glycerol skeleton, the solubility parameter (HSP value) of the entire polymerizable compound is likely to decrease. This tends to increase the compatibility between the polymerizable compound and the gelling agent, i.e., the solubility of the gelling agent is likely to increase, making it easier to include a large amount of gelling agent in the ink. As a result, the pinning ability of the ink can be improved. From the viewpoint of the pinning ability of the ink, it is preferable that the mass ratio of the polyfunctional (meth)acrylate having a glycerol skeleton to the gelling agent be within the above range.

[0066] 1-1-2. Other polymerizable compounds The other polymerizable compounds include mainly radically polymerizable compounds and cationic polymerizable compounds, and among these, the polymerizable compound is preferably a radically polymerizable compound.

[0067] Examples of the radical polymerizable compound include unsaturated carboxylic acid esters and (meth)acrylates. Of these, the polymerizable compound is preferably a (meth)acrylate. The (meth)acrylate may be monofunctional or polyfunctional.

[0068] Examples of monofunctional (meth)acrylates include isoamyl acrylate, stearyl acrylate, lauryl acrylate, octyl acrylate, decyl acrylate, isomyristyl acrylate, isostearyl acrylate, 2-ethylhexyl-diglycol acrylate, butoxyethyl acrylate, phenoxyethyl acrylate, cumylphenoxylethyl acrylate, tetrahydrofurfuryl acrylate, isobornyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxybutyl acrylate, and t-butylcyclohexyl acrylate.

[0069] Examples of bifunctional (meth)acrylates include 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, hydroxypivalic acid neopentyl glycol di(meth)acrylate, and polytetramethylene glycol di(meth)acrylate.

[0070] Examples of tri- or higher functional (meth)acrylates include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, and dipentaerythritol hexa(meth)acrylate.

[0071] Examples of the cationically polymerizable compound include epoxy compounds and vinyl ether compounds.

[0072] Examples of epoxy compounds include 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate, bis(3,4-epoxycyclohexylmethyl)adipate, ε-caprolactone-modified 3,4-epoxycyclohexylmethyl 3',4'-epoxycyclohexanecarboxylate, 1-methyl-4-(2-methyloxiranyl)-7-oxabicyclo[4,1,0]heptane, 2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)cyclohexanone-meta-dioxane, bis(2,3-epoxycyclopentyl)ether, 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, and glycerin triglycidyl ether.

[0073] Examples of vinyl ether compounds include monovinyl ether compounds such as ethyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, octadecyl vinyl ether, cyclohexyl vinyl ether, hydroxybutyl vinyl ether, 2-ethylhexyl vinyl ether, cyclohexanedimethanol monovinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, isopropenyl ether-o-propylene carbonate, dodecyl vinyl ether, diethylene glycol monovinyl ether, octadecyl vinyl ether, etc. Examples of vinyl ether compounds include di- or trivinyl ether compounds such as ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, propylene glycol divinyl ether, dipropylene glycol divinyl ether, butanediol divinyl ether, hexanediol divinyl ether, cyclohexanedimethanol divinyl ether, trimethylolpropane trivinyl ether, etc.

[0074] The other polymerizable compounds preferably include a monofunctional polymerizable compound. The content of the monofunctional polymerizable compound is preferably 50 parts by mass or less relative to 100 parts by mass of the polymerizable compound. Furthermore, the content of the monofunctional polymerizable compound is preferably 40 parts by mass or less relative to the total mass of the ink. When the content of the monofunctional polymerizable compound is 5 parts by mass or more, the degree of crosslinking of the polymer is appropriately reduced, and the flexibility of the cured film can be further increased. As a result, fold cracks in the recorded material can be further reduced. When the content of the monofunctional polymerizable compound is 50 parts by mass or less, the degree of crosslinking of the polymer is not too low. As a result, the degree of curing of the cured film can be further increased, and peeling during cutting can be further reduced.

[0075] The other polymerizable compounds may include a polyfunctional polymerizable compound in addition to a monofunctional polymerizable compound. By including a polyfunctional polymerizable compound, peeling during cutting can be further reduced. The content mass ratio of the monofunctional polymerizable compound to the polyfunctional polymerizable compound is preferably within the range of 0 to 0.6, more preferably within the range of 0.1 to 0.4. Here, the "content mass ratio of the monofunctional polymerizable compound to the polyfunctional polymerizable compound" is expressed as (mass of the monofunctional polymerizable compound) / (mass of the polyfunctional polymerizable compound). Note that the "mass of the polyfunctional polymerizable compound" includes the mass of the polyfunctional acrylate having a glycerol skeleton.

[0076] The monofunctional polymerizable compound preferably contains a compound having a benzene ring in the molecule. By having a benzene ring in the molecule, a stack structure of benzene rings is formed due to the interaction between the benzene rings (π-π interaction), and the hardness of the cured film is further increased. It is preferable that the molecule has one or two benzene rings. Therefore, by having a benzene ring in the molecule of the monofunctional polymerizable compound, it is possible to further reduce fold cracks in the recorded material and further reduce peeling during cutting.

[0077] A compound having a benzene ring in the molecule may be modified by introducing a polyoxyalkylene group such as an ethylene oxide group or a propylene oxide group. Among these, a compound having a benzene ring in the molecule is preferably an ethylene oxide modified compound. This appropriately reduces the degree of crosslinking of the polymer, further increasing the flexibility of the cured film. The weighted average (by mass) of the repeat number in the ethylene oxide group is preferably 2 or more, more preferably 4 or more. Furthermore, from the viewpoint of easily forming a stack structure of benzene rings, the weighted average (by mass) of the repeat number in the ethylene oxide group is preferably 8 or less.

[0078] When the cured film is stretched by bending the recorded material, the stack of benzene rings temporarily separates. This makes the cured film easier to stretch and makes the bent cured film less likely to break, thereby further reducing fold cracks in the recorded material. Furthermore, the temporarily separated benzene rings re-form a stack structure when the stretching is released, so the strength of the cured film is maintained. In other words, it is believed that by using an ethylene oxide-modified compound having a benzene ring in the molecule, fold cracks in the recorded material can be reduced without reducing the strength of the cured film.

[0079] The compound having a benzene ring in the molecule may be either a radically polymerizable compound or a cationically polymerizable compound, but is preferably a radically polymerizable compound, and more preferably a (meth)acrylate.

[0080] Examples of monofunctional (meth)acrylates having a benzene ring in the molecule include phenoxyethyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, cumylphenoxylethyl acrylate, phenol acrylate, nonylphenol (meth)acrylate, cresol (meth)acrylate, etc. Furthermore, examples of monofunctional (meth)acrylates having a benzene ring in the molecule include ethylene oxide modified products and propylene oxide modified products of these.

[0081] The content of the compound having a benzene ring in the molecule relative to 100 parts by mass of the polymerizable compound is preferably 40 parts by mass or less, and more preferably in the range of 5 to 25 parts by mass. By including a compound having a benzene ring in the molecule, the hardness of the cured film can be further increased, and peeling of the recorded material upon cutting can be reduced. By having the content of the compound having a benzene ring in the molecule be 40 parts by mass or less, the flexibility of the cured film is not excessively reduced, and fold cracking of the recorded material can be further reduced.

[0082] The content of the polymerizable compound having a melting point of 25°C or higher is preferably 3 parts by mass or less relative to 100 parts by mass of the polymerizable compound. When forming an inkjet ink, from the viewpoint of further improving ejection stability, the content of the polymerizable compound having a melting point of 25°C or higher is more preferably 1 part by mass or less, even more preferably 0.1 parts by mass or less, and particularly preferably 0% by mass. In other words, the polymerizable compound preferably has a melting point of less than 25°C.

[0083] Examples of polymerizable compounds having a melting point of 25° C. or higher include octadecyl acrylate, tris(2-acryloyloxyethyl) isocyanurate, and behenyl acrylate.

[0084] Whether the melting point of a polymerizable compound is 25° C. or higher can be determined by whether the polymerizable compound is liquid or solid at 25° C. That is, it can be determined by whether the polymerizable compound has fluidity at 25° C. The melting point of a polymerizable compound may be measured by a thermal analysis method such as differential scanning calorimetry (DSC) or differential thermal analysis (DTA).

[0085] The weight average molecular weight (Mw) of the polymerizable compound is preferably within a range of 160 to 300, and more preferably within a range of 200 to 300. The weight average molecular weight can be measured using gel permeation chromatography (GPC).

[0086] In this embodiment, the "equivalent weight of the polymerizable group" refers to the acrylic equivalent weight when the polymerizable compound is, for example, an acrylate. The "weighted average equivalent weight of the polymerizable group" refers to the sum of values ​​obtained by multiplying the equivalent weight of the polymerizable group of each polymerizable compound by the mass ratio of each polymerizable compound in the total amount of all polymerizable compounds.

[0087] The weighted average equivalent weight (by mass) of the polymerizable group in the entire polymerizable compound is preferably in the range of 160 to 300 g / eq, more preferably in the range of 180 to 300 g / eq, and even more preferably in the range of 200 to 300 g / eq. By being 160 g / eq or more, the degree of crosslinking of the polymer is appropriately reduced, and the flexibility of the cured film can be further increased. As a result, fold cracking of the recorded material can be further reduced. By being 300 g / eq or less, the degree of crosslinking of the polymer is not reduced too much. As a result, the hardness of the cured film can be further increased, and peeling upon cutting can be further reduced.

[0088] The weighted average value (mass basis) of the polymerizable group equivalent weight is preferably within the range of 160 to 200 g / eq when the ink contains a yellow pigment as a colorant. The weighted average value (mass basis) of the polymerizable group equivalent weight is preferably within the range of 160 to 210 g / eq when the ink contains a black pigment as a colorant. The weighted average value (mass basis) of the polymerizable group equivalent weight is preferably 200 to 250 g / eq or less when the ink contains a red pigment as a colorant. The weighted average value (mass basis) of the polymerizable group equivalent weight is preferably within the range of 200 to 260 g / eq when the ink contains a blue pigment as a colorant.

[0089] Yellow pigments and black pigments are likely to absorb actinic radiation. Therefore, when a yellow pigment or a black pigment is used, it is preferable to set the weighted average value lower than when other pigments such as red pigments and blue pigments are used, in order to facilitate sufficient curing of the ink.

[0090] The content of the polymerizable compound is not particularly limited, but is preferably in the range of 1 to 97% by mass relative to the total mass of the ink, more preferably in the range of 30 to 95% by mass, even more preferably in the range of 50 to 95% by mass, and particularly preferably in the range of 70 to 95% by mass.

[0091] 1-2. Gelling agent The ink of this embodiment contains a gelling agent, which causes a sol-gel phase transition before irradiation with actinic rays. Specifically, when the ink is heated to, for example, 80°C, the gelling agent dissolves in the polymerizable compound contained in the ink, causing the ink to become a sol. When the ink is heated to around room temperature, for example, 35°C, the gelling agent crystallizes in the ink, causing the ink to become a gel. In this specification, a compound that can cause the ink to undergo a sol-gel phase transition in this way is referred to as a "gelling agent."

[0092] At around room temperature, the gelling agent crystallizes into plates in the ink. At this time, the gelling agent crystallized into plates preferably forms a three-dimensional space, and the polymerizable compound is encapsulated in this three-dimensional space. Hereinafter, this structure will be referred to as a "house of card structure." When a house of card structure is formed, the liquid polymerizable compound is retained within the space, further enhancing the gelling properties of the ink. This makes it more difficult for the dots formed by the ink landing on the recording medium to wet and spread, enhancing the pinning properties of the ink.

[0093] The ink of this embodiment has a low viscosity at high temperatures and a high viscosity at low temperatures due to the sol-gel phase transition. Therefore, the ink easily wets the recording medium when it lands, which can prevent the ink layer from cracking in the resulting recording material. As a result, it is believed that peeling during cutting of the recording material can be reduced.

[0094] Examples of gelling agents that readily form a house-of-cards structure include ketone-based waxes, ester-based waxes, glycerol-based waxes, pentaerythritol-based waxes, petroleum-based waxes, vegetable-based waxes, animal-based waxes, mineral-based waxes, hydrogenated castor oil, modified waxes, higher fatty acids, higher alcohols, hydroxystearic acid, fatty acid amides (N-substituted fatty acid amides and special fatty acid amides), higher amines, synthetic waxes, dibenzylidene sorbitol, dimer acid, and dimer diol.

[0095] Among these, from the viewpoint of further increasing the solubility in the polymerizable compound, the gelling agent is preferably a ketone wax, an ester wax, a glycerol wax, or a pentaerythritol wax. The gelling agent may be contained alone or in combination of two or more kinds.

[0096] Examples of ketone waxes include fatty acid ketones such as dibehenyl ketone, distearyl ketone, dieicosyl ketone, dipalmityl ketone, dilauryl ketone, dimyristyl ketone, myristyl palmityl ketone, and palmityl stearyl ketone.

[0097] Examples of ester waxes include fatty acid esters and sucrose fatty acid esters. Examples of fatty acid esters include fatty acid esters of monoalcohols such as behenyl behenate, icosyl icosanoate, stearyl stearate, palmityl stearate, myristyl myristate, cetyl myristate, and oleyl palmitate. Examples of fatty acid esters include fatty acid esters of polyhydric alcohols such as glycerin fatty acid esters, sorbitan fatty acid esters, propylene glycol fatty acid esters, ethylene glycol fatty acid esters, and polyoxyethylene fatty acid esters.

[0098] Examples of glycerol-based waxes include liquid fatty acid triglycerides having 6 to 30 carbon atoms. Examples of liquid fatty acid triglycerides having 6 to 30 carbon atoms include heptanoic acid or octanoic acid triglycerides. Examples of heptanoic acid or octanoic acid triglycerides include sunflower oil, corn oil, soybean oil, marrow oil, grapeseed oil, sesame seed oil, hazelnut oil, apricot oil, macadamia oil, arara oil, castor oil, avocado oil, caprylic / capric acid triglyceride, jojoba oil, and shea butter oil.

[0099] Examples of pentaerythritol waxes include pentaerythritol fatty acid esters, such as pentaerythritol tetrastearate.

[0100] Examples of higher fatty acids include behenic acid, arachidic acid, stearic acid, palmitic acid, myristic acid, lauric acid, oleic acid, and erucic acid.

[0101] Examples of higher alcohols include stearyl alcohol and behenyl alcohol.

[0102] The gelling agent preferably has an alkyl group from the viewpoint of further enhancing gelling properties, and more preferably is a ketone wax represented by the following general formula (G1) or an ester wax represented by the following general formula (G2).

[0103] General formula (G1): Ra-CO-Rb General formula (G2): Rc-COO-Rd

[0104] In general formula (G1), Ra and Rb each independently represent a linear alkyl group having 12 to 22 carbon atoms. In general formula (G2), Rc and Rd each independently represent a linear alkyl group having 12 to 22 carbon atoms.

[0105] In general formulas (G1) and (G2), when the carbon numbers of Ra to Rd are 12 or more, the crystallinity of the gelling agents represented by general formulas (G1) and (G2) is further increased, and more sufficient spaces are generated in the house-of-card structure that is formed. As a result, the polymerizable compound is more easily encapsulated in the spaces, and the gelling and pinning properties of the ink are further improved.

[0106] Furthermore, when the carbon numbers of Ra to Rd are 22 or less, the melting points of the gelling agents represented by general formula (G1) and general formula (G2) do not become too high, and the solubility of the gelling agents increases.

[0107] Examples of ketone waxes represented by general formula (G1) include dibehenyl ketone (carbon number: 21-22), distearyl ketone (carbon number: 17-18), dieicosyl ketone (carbon number: 19-20), dipalmityl ketone (carbon number: 15-16), dimyristyl ketone (carbon number: 13-14), dilauryl ketone (carbon number: 11-12), and lauryl myristyl ketone. (number of carbon atoms: 11-14), lauryl palmityl ketone (11-16), myristyl palmityl ketone (13-16), myristyl stearyl ketone (13-18), myristyl behenyl ketone (13-22), palmityl stearyl ketone (15-18), palmityl behenyl ketone (15-22), stearyl behenyl ketone (17-22), etc. The number of carbon atoms in the parentheses above indicates the number of carbon atoms in each of the two alkyl groups separated by the carbonyl group.

[0108] Examples of ester waxes represented by general formula (G2) include behenyl behenate (carbon number: 21-22), icosanoic acid icosyl (carbon number: 19-20), stearyl stearate (carbon number: 17-18), palmityl stearate (carbon number: 17-16), lauryl stearate (carbon number: 17-12), cetyl palmitate (carbon number: 15-16), stearyl palmitate (carbon number: 15-18), and milli Examples include myristyl myristate (carbon number: 13-14), cetyl myristate (carbon number: 13-16), octyldodecyl myristate (carbon number: 13-20), stearyl oleate (carbon number: 17-18), stearyl erucate (carbon number: 21-18), stearyl linoleate (carbon number: 17-18), behenyl oleate (carbon number: 18-22), and arachidyl linoleate (carbon number: 17-20). The number of carbon atoms in the parentheses above indicates the number of carbon atoms in each of the two alkyl groups separated by the ester group.

[0109] The content of the gelling agent is preferably in the range of 0.5 to 10% by mass, and more preferably in the range of 1.5 to 8% by mass, relative to the total mass of the ink. A content of 0.5% by mass or more can further enhance the gelling properties and pinning properties of the ink. Furthermore, a content of 10% by mass or less can further enhance the solubility of the gelling agent in the polymerizable compound.

[0110] 1-3.Other The ink of this embodiment may further contain other components such as a colorant, a polymerization initiator, a polymerization inhibitor, and a surfactant, as long as the effects of the present invention are achieved.

[0111] 1-3-1. Coloring agents The colorant is not particularly limited and may be a dye or a pigment, but is preferably a pigment because it has good dispersibility in the components of the ink and excellent weather resistance. The pigment can be selected from, for example, yellow pigments, red pigments, blue pigments, black pigments, and white pigments depending on the color of the image to be formed.

[0112] Examples of yellow pigments include Pigment Yellow (PY) 1, 3, 12, 13, 14, 17, 34, 35, 37, 55, 74, 81, 83, 93, 94, 95, and 97. Examples of yellow pigments include Pigment Yellow (PY) 108, 109, 110, 137, 138, 139, 153, 154, 155, 157, 166, 167, 168, 180, 185, and 193.

[0113] Examples of red pigments include Pigment Red (PR) 3, 5, 19, 22, 31, 38, 43, 48:1, 48:2, 48:3, 48:4, 48:5, 49:1, 53:1, 57:1, 57:2, 58:4, 63:1, 81, 81:1, 81:2, 81:3, 81:4, 88, 104, 108, 112, 122, 123, 144, 146, 149, 166, 168, 169, 170, 177, 178, 179, 184, 185, 202, 208, 216, 226, and 257; Pigment Violet (PV) 3, 19, 23, 29, 30, 37, 50, and 88; and Pigment Orange (PO). Examples include 13, 16, 20, 36, etc.

[0114] Examples of blue pigments include Pigment Blue (PB) 1, 15, 15:1, 15:2, 15:3, 15:4, 15:6, 16, 17:1, 22, 27, 28, 29, 36, and 60.

[0115] Examples of black pigments include CI Pigment Black 7, 26, 28, and the like.

[0116] The white pigment may be any pigment that imparts a white color to the cured film formed by curing the white ink. Examples of the white pigment include inorganic pigments such as titanium oxide, zinc oxide, calcium carbonate, barium sulfate, and aluminum hydroxide. Among these, titanium oxide is preferred as the white pigment.

[0117] The crystalline form of titanium oxide may be any of rutile, anatase, or brookite. However, from the viewpoint of facilitating particle size reduction, the crystalline form is preferably anatase, which has a low specific gravity. From the viewpoint of further enhancing the concealing properties of the formed image, the crystalline form is preferably rutile, which has a high refractive index in the visible light region.

[0118] The content of the colorant is preferably within a range of 0.1 to 10% by mass, and more preferably within a range of 1 to 5% by mass, relative to the total mass of the ink. In particular, the content of the white pigment is preferably within a range of 3 to 8% by mass.

[0119] 1-3-2. Pigment dispersants When the colorant is a pigment, the ink may contain a pigment dispersant for dispersing the pigment. Examples of the pigment dispersant include hydroxy group-containing carboxylic acid esters, salts of long-chain polyaminoamides and high-molecular-weight acid esters, salts of high-molecular-weight polycarboxylic acids, salts of long-chain polyaminoamides and polar acid esters, high-molecular-weight unsaturated acid esters, polymer copolymers, modified polyurethanes, modified polyacrylates, polyether ester-type anionic surfactants, naphthalene sulfonic acid formalin condensate salts, aromatic sulfonic acid formalin condensate salts, polyoxyethylene alkyl phosphate esters, polyoxyethylene nonylphenyl ether, and stearylamine acetate.

[0120] The content of the pigment dispersant is preferably in the range of 10 to 200 parts by mass, and more preferably in the range of 20 to 100 parts by mass, per 100 parts by mass of the pigment. When the content of the pigment dispersant is 10 parts by mass or more per 100 parts by mass of the pigment, the dispersion stability of the pigment is improved. When the content of the pigment dispersant is 200 parts by mass or less per 100 parts by mass of the pigment, the ejection stability is improved when the ink is made into an inkjet ink.

[0121] 1-3-3. Polymerization initiator The ink may contain a polymerization initiator. The polymerization initiator may be any one that can initiate polymerization of the polymerizable compound by irradiation with actinic rays. For example, when the ink contains a radically polymerizable compound, a radical polymerization initiator is used as the polymerization initiator. When the ink contains a cationic polymerizable compound, a cationic polymerization initiator (photoacid generator) is used as the polymerization initiator. Note that when the ink can be sufficiently cured without a polymerization initiator, such as by irradiation with an electron beam, a polymerization initiator is not necessary.

[0122] Examples of the radical polymerization initiator include an intramolecular bond cleavage type radical polymerization initiator and an intramolecular hydrogen abstraction type radical polymerization initiator.

[0123] Examples of intramolecular bond cleavage type radical polymerization initiators include acetophenone-based initiators such as diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyl dimethyl ketal, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, 4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl)ketone, 1-hydroxycyclohexyl-phenyl ketone, 2-methyl-2-morpholino(4-methylthiophenyl)propan-1-one, and 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone. Examples of intramolecular bond cleavage type radical polymerization initiators include benzoins such as benzoin, benzoin methyl ether, and benzoin isopropyl ether. Examples of the intramolecular bond cleavage type radical polymerization initiator include acylphosphine oxide initiators such as 2,4,6-trimethylbenzoindiphenylphosphine oxide and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide. Examples of the intramolecular bond cleavage type radical polymerization initiator include benzyl glyoxy ester and methylphenyl glyoxy ester.

[0124] Examples of intramolecular hydrogen abstraction radical polymerization initiators include benzophenone-based initiators such as benzophenone, o-benzoylmethylbenzoate, 4-phenylbenzophenone, 4,4'-dichlorobenzophenone, hydroxybenzophenone, 4-benzoyl-4'-methyl-diphenyl sulfide, acrylated benzophenone, 3,3',4,4'-tetra(t-butylperoxycarbonyl)benzophenone, and 3,3'-dimethyl-4-methoxybenzophenone. Examples of intramolecular hydrogen abstraction radical polymerization initiators include thioxanthone-based initiators such as 2-isopropylthioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, and 2,4-dichlorothioxanthone. Examples of intramolecular hydrogen abstraction radical polymerization initiators include aminobenzophenone-based initiators such as Michler's ketone and 4,4'-diethylaminobenzophenone. Examples of the intramolecular hydrogen abstraction type radical polymerization initiator include 10-butyl-2-chloroacridone, 2-ethylanthraquinone, 9,10-phenanthrenequinone, and camphorquinone.

[0125] An example of a cationic polymerization initiator is a photoacid generator. An example of a photoacid generator is an aromatic onium compound, B(C6F5)4 - , PF6 - , AsF6 - , SbF6 - , CF3SO3 - Examples of the aromatic onium compound include diazonium, ammonium, iodonium, sulfonium, and phosphonium salts. Examples of the photoacid generator include sulfonates that generate sulfonic acid, halides that photogenerate hydrogen halide, and iron-allene complexes.

[0126] The content of the polymerization initiator is not particularly limited as long as the ink is sufficiently cured by irradiation with actinic rays while the ink's coatability onto the surface of a recording medium is not impaired. The content of the polymerization initiator is preferably within a range of 0.1 to 20% by mass, and more preferably within a range of 1 to 10% by mass, relative to the total mass of the ink.

[0127] 1-3-4. Polymerization inhibitors The ink may contain a polymerization inhibitor, which can prevent the monomers in the ink from polymerizing due to the influence of light, heat, air, etc. during storage.

[0128] Examples of polymerization inhibitors include (alkyl)phenols, hydroquinone, catechol, resorcinol, p-methoxyphenol, t-butylcatechol, t-butylhydroquinone, pyrogallol, 1,1-picrylhydrazyl, phenothiazine, p-benzoquinone, nitrosobenzene, 2,5-di-t-butyl-p-benzoquinone, dithiobenzoyl disulfide, picric acid, cupferron, aluminum N-nitrosophenylhydroxylamine, tri-p-nitrophenylmethyl, N-(3-oxyanilino-1,3-dimethylbutylidene)aniline oxide, dibutyl cresol, cyclohexanone oxime cresol, guaiacol, o-isopropylphenol, butylaldoxime, methyl ethyl ketoxime, and cyclohexanone oxime.

[0129] The content of the polymerization inhibitor is not particularly limited, but is preferably in the range of 0.05 to 10% by mass relative to the total mass of the ink.

[0130] 1-3-5.Surfactants The ink may contain a surfactant in order to adjust the surface tension.

[0131] Examples of surfactants include anionic surfactants such as dialkyl sulfosuccinates, alkyl naphthalene sulfonates, and fatty acid salts. Examples of surfactants include nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, acetylene glycols, and polyoxyethylene or polyoxypropylene block copolymers. Examples of surfactants include cationic surfactants such as alkylamine salts and quaternary ammonium salts. Examples of surfactants include silicone-based surfactants and fluorine-based surfactants.

[0132] The content of the surfactant is not particularly limited, but is preferably in the range of 0.001 to 10% by mass, and more preferably in the range of 0.001 to 1% by mass, relative to the total mass of the ink.

[0133] In this embodiment, in addition to the above components, the ink may contain, as necessary, a fixing resin, a viscosity adjuster, a resistivity adjuster, a film-forming agent, an ultraviolet absorber, an antioxidant, a color-fading inhibitor, an anti-mold agent, an anti-rust agent, and the like.

[0134] 1-3-6.Water The ink may contain water in order to adjust the viscosity, surface tension, etc. The water is not particularly limited, and examples thereof include pure water such as ion-exchanged water, ultrafiltered water, reverse osmosis water, and distilled water. The water may also be ultrapure water.

[0135] The water content (moisture content) is not particularly limited, but is preferably within the range of 0.5 to 1.0% by mass relative to the total mass of the ink.

[0136] 2. Ink properties The viscosity of the ink at 60°C is preferably in the range of 10 to 25 mPa·s, and more preferably in the range of 10 to 15 mPa·s. This improves the stability of the ink when it is heated and ejected from the head when used as an inkjet ink. The viscosity of the ink at 60°C can be adjusted by the type and content of the polymerizable compound. The viscosity of the ink at 60°C can also be adjusted by the type and content of the gelling agent.

[0137] The viscosity of the ink at 80°C is preferably in the range of 6 to 25 mPa·s, and more preferably in the range of 7 to 15 mPa·s. This improves the stability of the ink when it is heated and ejected from the head when used as an inkjet ink. The viscosity of the ink at 80°C can be adjusted by the type and content of the polymerizable compound. The viscosity of the ink at 80°C can also be adjusted by the type and content of the gelling agent.

[0138] The viscosity of the ink can be measured using a rheometer. For example, the ink is heated to 100°C, and while measuring the viscosity using a stress-controlled rheometer, the ink is cooled to 20°C under conditions of a shear rate of 11.7 (1 / s) and a temperature decrease rate of 0.1°C / s to obtain a temperature curve of viscosity. From the obtained temperature curve, the viscosity at 60°C or 80°C is read. Note that, as the stress-controlled rheometer, for example, a "Physica MCR301" (cone plate diameter: 75 mm, cone angle: 1.0°, manufactured by Anton Paar Co., Ltd.) can be used.

[0139] 3. Ink preparation method The ink of this embodiment can be prepared by mixing the above-described polymerizable compound, gelling agent, and any other components under heating. The resulting mixture is preferably filtered through a predetermined filter. When preparing an ink containing a pigment, it is preferable to first prepare a pigment dispersion containing the pigment and the polymerizable compound, and then mix the pigment dispersion with other components. The pigment dispersion may further contain a dispersant.

[0140] The pigment dispersion can be prepared by dispersing a pigment in a polymerizable compound. The pigment can be dispersed using, for example, a ball mill, a sand mill, an attritor, a roll mill, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, a wet jet mill, a paint shaker, or the like. A dispersant may be added to disperse the pigment.

[0141] When multiple types of polymerizable compounds are used, the polymerizable compounds may first be mixed to prepare a polymerizable composition, and then the polymerizable composition, the gelling agent, and any other components may be mixed under heating.

[0142] 4. Inkjet recording method In the recording method using the ink of this embodiment, after the ink is applied to a recording medium, the ink is cured by irradiating it with actinic radiation, thereby allowing the colorant to adhere firmly to the recording medium.

[0143] The method for applying the ink to the recording medium is not particularly limited, and examples of the method for applying the ink include spray coating, dipping, screen printing, gravure printing, offset printing, and inkjet printing.

[0144] In particular, the ink of this embodiment is preferably applied using an inkjet method. The inkjet method allows for the production of recorded matter easily and inexpensively. Each step in the inkjet recording method will now be described.

[0145] 4-1. Step of applying ink to recording medium In this step, the ink is ejected from an inkjet head and applied to the surface of the recording medium at positions corresponding to the image to be formed.

[0146] The ejection method from the inkjet head may be either an on-demand method or a continuous method. Examples of on-demand inkjet heads include single-cavity, double-cavity, bender, and piston types. Examples of on-demand inkjet heads include electro-mechanical conversion types such as shear mode and shared wall types. Examples of on-demand inkjet heads include electro-thermal conversion types such as thermal inkjet and bubble jet (registered trademark) types. In addition, the inkjet head may be either a scan type or a line type.

[0147] The ink is heated and solubilized before being ejected from the inkjet head. Therefore, it is preferable to set the temperature of the ink filled in the inkjet head to the gelling temperature of the ink + 10°C or higher and the gelling temperature + 30°C or lower. By setting the temperature of the ink in the inkjet head to the gelling temperature + 10°C or higher, gelation of the ink inside the inkjet head or on the nozzle surface can be reduced, and deterioration of ejection properties can be reduced. By setting the temperature of the ink in the inkjet head to the gelling temperature + 30°C or lower, deterioration of the ink at high temperatures can be reduced.

[0148] Specifically, it is preferable to heat the ink to 50° C. or higher, then eject it from the inkjet head and allow it to land on a recording medium. By heating the ink of this embodiment to 50° C. or higher, it is possible to set the temperature of the ink to a gelation temperature +10° C. or higher.

[0149] There are no particular limitations on the method for heating the ink. For example, at least one of the ink tanks that make up the head carriage, the ink supply system (supply pipes, an anterior ink tank immediately before the head, etc.), piping with filters, and the piezo head can be heated. For heating, a panel heater, ribbon heater, or heated water can be used.

[0150] The amount of ink droplets ejected is preferably within the range of 2 to 20 pL from the viewpoint of further increasing the recording speed and image quality.

[0151] The recording medium is not particularly limited. Examples of recording media include ordinary uncoated paper, coated paper, synthetic paper such as YUPO (registered trademark), and various plastics used in flexible packaging. The various plastics may be films, and examples of the various plastic films include polypropylene (PP) film, polyethylene terephthalate (PET) film, and biaxially oriented polystyrene sheet "OPS" (registered trademark). Examples of the various plastic films include biaxially oriented polypropylene (OPP) film, biaxially oriented nylon (ONy) film, polyvinyl chloride (PVC) film, polyethylene (PE) film, and triacetyl cellulose (TAC) film. Other plastics include polycarbonate, (meth)acrylic resin, acrylonitrile-butadiene-styrene copolymer (ABS resin), polyacetal, polyvinyl alcohol (PVA), and rubbers.

[0152] The ink may be applied to the recording medium by directly impacting the ejected ink onto the recording medium, or by impacting the ejected ink onto an intermediate transfer body to form an intermediate image, which is then transferred from the intermediate transfer body to the recording medium.

[0153] 4-2. Ink curing process In this process, the ink droplets applied to the recording medium are irradiated with actinic radiation to harden the ink droplets, thereby forming an image (recorded product) made of a cured ink film.

[0154] The actinic radiation can be selected from, for example, electron beams, ultraviolet rays, alpha rays, gamma rays, X-rays, etc., but ultraviolet rays or electron beams are preferred. The ultraviolet rays are preferably light having a peak wavelength in the range of 360 to 410 nm. The ultraviolet rays are preferably emitted from a light-emitting diode (LED) light source. LEDs emit less radiant heat than conventional light sources (e.g., metal halide lamps). Therefore, when exposed to actinic radiation, LEDs make it difficult for the ink to melt and are less likely to cause uneven gloss.

[0155] 5. Inkjet Recording System The inkjet recording system of this embodiment uses the ink of this embodiment. The inkjet recording system of this embodiment has an inkjet head that ejects ink and an irradiation unit that irradiates the ink that has landed on a recording medium with active rays. That is, the inkjet recording system of this embodiment includes the ink of this embodiment and an inkjet recording apparatus, and the inkjet recording apparatus has the inkjet head and the irradiation unit.

[0156] Fig. 1 is a schematic diagram showing the configuration of an inkjet recording apparatus 100. As shown in Fig. 1, the inkjet recording apparatus 100 has an inkjet head 110, a transport unit 120, and an irradiation unit 130. In Fig. 1, the arrow indicates the transport direction of the recording medium.

[0157] The inkjet head 110 has nozzles 111. The number of nozzles 111 may be equal to or greater than the number of inks used in image formation (for example, four). The nozzles 111 have ejection openings in a nozzle surface 113. The nozzle surface 113 faces the transport unit 120 when recording (forming an image) on the recording medium 200. The nozzles 111 eject ink from the ejection openings onto the recording medium 200 transported by the transport unit 120.

[0158] The inkjet head 110 may be provided with a device for adjusting the temperature of the ink. By adjusting the temperature of the ink, the viscosity of the ink can be reduced, and the ejection properties of the ink can be improved.

[0159] The inkjet head 110 may be a scan-type inkjet head whose width in a direction perpendicular to the transport direction of the recording medium 200 is smaller than that of the recording medium 200. Alternatively, the inkjet head 110 may be a line-type inkjet head whose width in a direction perpendicular to the transport direction of the recording medium 200 is larger than that of the recording medium 200.

[0160] During recording, the conveying unit 120 conveys the recording medium 200 so that the recording medium 200 faces the inkjet head 110 and moves directly below the inkjet head 110 in the vertical direction. For example, the conveying unit 120 includes a drive roller 121, a driven roller 122, and a conveying belt 123.

[0161] The irradiation unit 130 irradiates the upper surface of the transport unit 120 with active rays. This allows the active rays to be irradiated onto the ink droplets that have landed on the transported recording medium 200, thereby hardening the droplets. The irradiation unit 130 is preferably located downstream of the inkjet head 110 and directly above the transport unit 120.

[0162] In addition to the above configuration, the inkjet recording apparatus 100 may also have an ink tank (not shown) for storing ink before ejection, an ink flow path (not shown) that allows ink to flow between the ink tank and the inkjet head 110, etc. The inkjet recording apparatus 100 may also have a control unit (not shown) that controls the operations of the inkjet head 110, the transport unit 120, and the irradiation unit 130.

[0163] The inkjet recording apparatus 100 may include an intermediate transfer body and a transfer unit (neither of which are shown). The inkjet head 110 ejects ink onto the surface of the intermediate transfer body, causing the ink droplets to aggregate and form an intermediate image on the surface of the intermediate transfer body. The transfer unit then transfers the intermediate image from the surface of the intermediate transfer body to the surface of a recording medium. The irradiation unit 130 irradiates the intermediate image transferred to the surface of the recording medium with active rays, thereby curing the ink droplets. [Example]

[0164] The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto. In the examples, the terms "parts" and "%" are used, but they represent "parts by mass" or "% by mass" unless otherwise specified. In the following examples, all procedures were carried out at room temperature (25°C) unless otherwise specified.

[0165] 1. Preparation and synthesis of materials The materials used to prepare the ink are listed below.

[0166] 1-1. Polymerizable compounds [(Meth)acrylate having a glycerol skeleton: Monomer 1] The number of functional groups herein means the number of (meth)acryloyl groups. M-930: Glycerin triacrylate "M-930" (manufactured by Toagosei Co., Ltd., number of functional groups: 3) M-460: Diglycerin EO-modified acrylate "M-460" (manufactured by Toagosei Co., Ltd., number of functional groups: 4) SR9020: Propoxylated (3) glyceryl triacrylate "SR9020NS" (manufactured by Arkema Co., Ltd., number of functional groups: 3) EM2387: Propoxylated (3.5) glyceryl triacrylate "EM2387" (manufactured by Choko Materials Industry Co., Ltd., number of functional groups: 3) EM2388: Ethoxylated (3) glyceryl triacrylate "EM2388" (manufactured by Choko Materials Industry Co., Ltd., number of functional groups: 3) MX-1: Ethoxylated (6) glyceryl triacrylate (number of functional groups: 3) MX-2: Propoxylated (12) glyceryl triacrylate (number of functional groups: 3) MX-3: Propoxylated (6) glyceryl triacrylate (number of functional groups: 3) MX-4: Propoxylated (9) glyceryl triacrylate (number of functional groups: 3) MX-1 to MX-4 were synthesized by known methods.

[0167] [Other Monomers: Monomer 2] M144: Phenol 4EO modified acrylate "MIRAMER M144" (manufactured by MIWON Co., Ltd.) M164: Nonylphenol 4EO modified acrylate "MIRAMER M164" (manufactured by MIWON Co., Ltd.) APG-200: Tripropylene glycol diacrylate "APG-200" (Shin-Nakamura Chemical Co., Ltd.) CN2270: Polyester acrylate oligomer "CN2270NS" (manufactured by Arkema Inc.) A600: 14EO modified diacrylate "A-600" (manufactured by Shin-Nakamura Chemical Co., Ltd.) EM2382: 3EO modified trimethylolpropane triacrylate "EM2382" (manufactured by Choko Materials Industry Co., Ltd.) M360: 3PO-modified trimethylolpropane triacrylate "MIRAMER M360" (manufactured by MIWON Co., Ltd.) EC: Polyester acrylate "ETERCURE 6361-100" (manufactured by Choko Materials Industry Co., Ltd.)

[0168] 1-2. Pigment dispersion The following components were placed in a stainless steel beaker and heated to 65°C on a hot plate while stirring for 1 hour. Pigment dispersant "EFKA-7701" (manufactured by BASF Ltd.) 9.0 parts by mass Tripropylene glycol diacrylate 71.0 parts by mass

[0169] The stirred mixture was cooled to room temperature, and the mixture was placed in a stainless steel beaker together with the following ingredients and 200 g of zirconia beads (0.3 mm diameter, manufactured by Nikkato Corporation) in a glass bottle, which was then sealed. Details of the pigment will be described later. Pigment 20.0 parts by mass

[0170] The resulting pigment-containing liquid was dispersed using a paint shaker, and the zirconia beads were removed to obtain a pigment dispersion. The dispersion time was 4 hours when using cyan and black pigments, and 6 hours when using magenta and yellow pigments.

[0171] Details of the pigment are shown. Cyan pigment (C): Pigment Blue 15:4 "Chromofine Blue 6332JC" (Dainichiseika Color & Chemicals Mfg. Co., Ltd.) Magenta pigment (M): Mixed crystal of Pigment Violet 19 and Red 202 "CINQUASIA MAGENTA RT-355D" (manufactured by BASF Ltd.) Yellow pigment (Y): Pigment Yellow 185 "D1155" (BASF Ltd.) Black pigment (K): Pigment Black 7 "#52" (Mitsubishi Chemical Corporation)

[0172] 1-3. Gelling agents WEP3: Behenyl behenate "WEP-3" (carbon number 21-22, manufactured by NOF Corporation) SS: Stearyl stearate "Excepal SS" (carbon number 17-18, manufactured by Kao Corporation) PTS: Pentaerythritol tetrastearate (Tokyo Chemical Industry Co., Ltd.) The number of carbon atoms represents the number of carbon atoms in each of the two alkyl groups separated by the ester group.

[0173] 1-4. Polymerization initiator Polymerization initiator 1: bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide "Omnirad 819" (manufactured by IGM Resins BV) Polymerization initiator 2: 2-isopropylthioxanthone "Speedcure 2-ITX" (Arkema Co., Ltd.)

[0174] 1-5. Polymerization inhibitors Polymerization inhibitor: 4,4'-[(1,10-dioxo-1,10-decanediyl)bis(oxy)]bis[2,2,6,6-tetramethyl]-1-piperidinyloxy "Irgasutab UV-10" (manufactured by BASF Ltd.)

[0175] 1-6.Surfactants Surfactant: Polyether-modified silicone "KF-352A" (Shin-Etsu Chemical Co., Ltd.)

[0176] 2. Ink Preparation The pigment dispersion, polymerizable compound, gelling agent, polymerization initiator, polymerization inhibitor, and surfactant were placed in a stainless steel beaker in the following proportions. The mixture was stirred at 105°C for 45 minutes. The stirred mixture was then filtered through a Teflon (registered trademark) 3 μm membrane filter (manufactured by ADVANTEC Corporation) to obtain Ink 1. The amounts added were calculated as solids.

[0177] (Monomer 1) Propoxylated (3) glyceryl triacrylate "SR9020" 23.6% by mass (Monomer 2) Phenol 4EO modified acrylate "M144" 12.2% by mass Tripropylene glycol diacrylate "APG-200" 20.2% by mass 3EO modified trimethylolpropane triacrylate "EM2382" 8.6% by mass 3PO-modified trimethylolpropane triacrylate "M360" 14.2% by mass Polyester acrylate "EC" 10.9% by mass (pigment dispersion) Black pigment 2.0% by mass Pigment dispersant 0.9% by mass (gelling agent) Behenyl behenate "WEP-3" 1.5% by mass Stearyl stearate "Exepar SS" 2.2% by mass Polymerization initiator 1 3.0% by mass Polymerization initiator 2 0.5% by mass Polymerization inhibitor 0.1% by mass Surfactant 0.1% by mass

[0178] Each ink was prepared in the same manner as ink 1, except that the type and amount of polymerizable compound and the type and amount of gelling agent were changed as shown in Tables I to IV.

[0179] 3. Image Formation For each ink, a monochromatic image was formed using a line-type inkjet recording device. The temperature of the inkjet head of the inkjet recording device was set to 80°C. A 5cm x 5cm solid image was printed on a recording medium "OK Topcoat + 127g" (manufactured by Oji Paper Co., Ltd.). The temperature of the recording medium (paper substrate) was set to 40°C. After the image was formed, an LED lamp (395nm, water-cooled LED, manufactured by Phoseon Technology Co., Ltd.) placed downstream of the recording device illuminated the image with 300mJ / cm. 2 The ink was cured by irradiating it with ultraviolet light.

[0180] A piezo head was used as the ejection recording head for image formation. Ink was ejected from the ejection recording head at a droplet volume of 9.0 pL and a droplet velocity of approximately 6 m / s, and recording was performed at a resolution of 1200 dpi x 1200 dpi. The recording speed was 500 mm / s. Image formation was performed in an environment of 23°C and 55% RH. Note that "dpi" refers to the number of dots per inch (2.54 cm).

[0181] 4. Evaluation 4-1.Bending cracks Using a paper folding machine "AFV-564FKT" (manufactured by Horizon Co., Ltd.), the image formed on the recording medium was folded in half. The state of the image was then observed, and the percentage of the area of ​​the portion of the recording medium that was not exposed due to cracks (non-exposed portion) was determined by image analysis. The fold crack resistance was evaluated according to the following criteria. A score of 3 or higher (3-5) was considered to be acceptable for practical use. 5: No cracks were observed in the image. 4: Cracks were observed in the image, but only a small amount of white background was exposed. 3: Cracks were observed in the image, but less than half of the white background was exposed. 2: Cracks were observed in the image, and white background was exposed over more than half of the area. 1: Cracks were observed in the image, and white was exposed in the entire area.

[0182] 4-2. Cutting and peeling (image abrasion resistance) The image-formed portion of the recording medium was cut using a desktop paper cutter "PC-P430" (manufactured by Horizon Co., Ltd.). The cut portion was rubbed with a finger, and the degree of peeling of the coating film (image) was evaluated according to the following criteria. A score of 3 or higher (3 to 5) was considered to be acceptable for practical use. 5: No peeling of the coating occurred. 4: Peeling was observed, but not visible to the naked eye. 3: Peeling was present, but was difficult to see with the naked eye. 2: Peeling was observed and was visible to the naked eye. 1: Large peeling was observed and was clearly visible.

[0183] For evaluation 4, no peeling was visible to the naked eye, but when the coating film (image) was observed at 100x magnification using an optical microscope, the peeled length of the ink layer was 30 μm or less. For evaluation 3, similar microscopic observation revealed that the peeled length of the ink layer was within the range of 31 to 100 μm. For ink layers where the peeled length was more than 100 μm, it was visible to the naked eye.

[0184] 4-3. Pinning (granularity) The image was observed under a microscope (200x magnification). The average droplet diameter of 10 randomly selected locations was calculated, and the absolute value of the difference from the ideal droplet diameter (60 μm) was calculated. A value of 3 or more (3-4) was considered acceptable for practical use. 4: The absolute value of the difference from the preferred droplet size was less than 3 μm. 3: The absolute value of the difference from the suitable droplet diameter was 3 μm or more and less than 5 μm. 2: The absolute value of the difference from the suitable droplet diameter was 5 μm or more and 7 μm or less. 1: The absolute value of the difference from the preferred droplet size was greater than 7 μm.

[0185] The composition of each ink and the evaluation results are shown in Tables I to IV. Note that the composition of the ink only shows the type and amount of polymerizable compound that was changed, the type and amount of gelling agent that was added, and the type of pigment. The other components were the same as those in ink 1 above. The types of pigments are K: black pigment, C: cyan pigment, M: magenta pigment, and Y: yellow pigment, respectively. The amount of pigment added in each ink was the same as that in ink 1 above.

[0186] [Table 1]

[0187] [Table 2]

[0188] [Table 3]

[0189] [Table 4]

[0190] Tables V to VIII show the parts by mass of each monomer in the polymerizable compound of each ink when the total monomer amount is 100 parts by mass. "Monomer 1 total" represents the total parts by mass of Monomer 1 (a (meth)acrylate having a glycerol skeleton). "Monomer 1 + 2 total" represents the total parts by mass of Monomer 1 (a (meth)acrylate having a glycerol skeleton) and Monomer 2 (other monomers), i.e., the total parts by mass of all monomers, which is 100.0 parts by mass. Monomer 1 / gelling agent (Am / Wm) represents the ratio of the mass Am of the polyfunctional (meth)acrylate having a glycerol skeleton to the mass Wm of the gelling agent.

[0191] [Table 5]

[0192] [Table 6]

[0193] [Table 7]

[0194] [Table 8]

[0195] From the examples and comparative examples, it is clear that the ink of the present invention can reduce fold cracks and peeling during cutting in the recorded matter that is formed.

[0196] Examples 1 to 7 and 9 to 25 reveal the following. The content of the trifunctional (meth)acrylate having a glycerol skeleton relative to 100 parts by mass of the polymerizable compound is 20 parts by mass or more, which can further reduce fold cracks and peeling during cutting in the resulting recorded matter.

[0197] Examples 1 to 6 reveal the following. The content of the polyfunctional (meth)acrylate having a glycerol skeleton relative to 100 parts by mass of the polymerizable compound is in the range of 30 parts by mass to 60 parts by mass, which can further reduce fold cracks and peeling during cutting in the resulting recorded matter.

[0198] Examples 1, 7, 9, 11 to 14 and 22 reveal the following. The polyfunctional (meth)acrylate having a glycerol skeleton is a propylene oxide modified product. This can further reduce fold cracks and peeling during cutting in the resulting recorded matter. Furthermore, by setting the modification number within the range of 3 to 9, particularly 3 to 4, fold cracks and peeling during cutting can be further reduced.

[0199] The following can be seen from the examples. The ratio Am / Wm of the mass Am of the polyfunctional (meth)acrylate having a glycerol skeleton to the mass Wm of the gelling agent is in the range of 3.5 or more and 16 or less. This makes it possible to further reduce fold cracks and peeling during cutting in the resulting recorded matter. [Explanation of symbols]

[0200] 100 Inkjet recording device 110 Inkjet head 111 Nozzle 113 Nozzle surface 120 Conveyor 121 Drive roller 122 driven roller 123 Conveyor Belt 130 Irradiation unit 200 Recording Media

Claims

1. An ink containing a polymerizable compound that is polymerized by actinic radiation, the content of the polyfunctional (meth)acrylate having a glycerol skeleton is 20 parts by mass or more relative to 100 parts by mass of the polymerizable compound; Contains gelling agents An ink characterized by:

2. The content of the trifunctional (meth)acrylate having a glycerol skeleton relative to 100 parts by mass of the polymerizable compound is 20 parts by mass or more. The ink of claim 1 .

3. The content of the polyfunctional (meth)acrylate having a glycerol skeleton relative to 100 parts by mass of the polymerizable compound is in the range of 30 parts by mass or more and 60 parts by mass or less.

3. The ink according to claim 1 or claim 2.

4. The polyfunctional (meth)acrylate having a glycerol skeleton is a propylene oxide modified product.

3. The ink according to claim 1 or claim 2.

5. The number of propylene oxide modifications in the polyfunctional (meth)acrylate having a glycerol skeleton is within the range of 3 to 9.

5. The ink of claim 4.

6. The number of propylene oxide modifications in the polyfunctional (meth)acrylate having a glycerol skeleton is within the range of 3 or more and 4 or less.

6. The ink of claim 5.

7. The ratio Am / Wm of the mass Am of the polyfunctional (meth)acrylate having a glycerol skeleton to the mass Wm of the gelling agent is in the range of 3.5 or more and 16 or less.

3. The ink according to claim 1 or claim 2.

8. The gelling agent includes at least one of a ketone-based wax, an ester-based wax, a glycerol-based wax, and a pentaerythritol-based wax.

3. The ink according to claim 1 or claim 2.

9. the gelling agent has an alkyl group, The alkyl group has 22 or less carbon atoms.

3. The ink according to claim 1 or claim 2.

10. The gelling agent contains the ester wax.

9. The ink of claim 8.

11. The water content is in the range of 0.5 to 1.0% by mass relative to the total mass of the ink.

3. The ink according to claim 1 or claim 2.

12. Used in inkjet recording 3. The ink according to claim 1 or claim 2.

13. An inkjet recording method using the ink according to claim 1 or 2, a step of heating the ink to 50° C. or higher, discharging the ink from an inkjet head, and causing the ink to land on a recording medium; An inkjet recording method comprising:

14. An inkjet recording system using the ink according to claim 1 or 2, an inkjet head that ejects the ink; and an irradiation unit that irradiates the ink that has landed on the recording medium with actinic rays; An inkjet recording system comprising:

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