Radiation-curable inkjet ink composition and inkjet recording method

Abstract

To provide a radioactive ray-curable inkjet composition excellent in adhesion of an ink coated film, scratch resistance, and anti-blocking property.SOLUTION: A radioactive ray-curable inkjet ink composition contains a polymerizable monomer A including a monofunctional monomer B, and a polyfunctional monomer C, where the polymerizable monomer A contains 20 mass% or more of a polymerizable monomer A1, where a glass transition point of a homopolymer thereof is 50°C or higher to a total amount of the polymerizable monomer, the weighted average of glass transition points of homopolymers of the polymerizable monomers with containing mass ratios of respective polymerizable monomers A as weights is 25°C or higher and 40°C or lower, the content of the monofunctional monomer B is 50 mass% or more and 80 mass% or less to a total amount of the polymerizable monomer A, and the polyfunctional monomer C includes a predetermined vinyl group-containing (meth)acrylate C1.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a radiation-curable inkjet ink composition and an inkjet recording method. [Background technology]

[0002] The inkjet recording method is capable of recording high-resolution images using a relatively simple device and has been rapidly developing in various fields. Among these methods, various radiation-curable inkjet ink compositions and inkjet recording methods using the same have been proposed. For example, Patent Document 1 describes a specific actinic energy ray-curable ink containing a polymerizable compound, a pigment, and a fluorine-based surfactant in specific proportions, with the aim of providing an actinic energy ray-curable ink that can produce a laminated cured product with high stretchability and high color density even when forming an image by inkjet. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-115105 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the invention described in Patent Document 1 contains 85% by mass or more of monofunctional monomers relative to the total amount of the polymerizable compounds, and inks containing such a large amount of monofunctional monomers have excellent adhesion of the ink coating film, but form soft cured ink coating films, which are prone to blocking of the ink coating film. On the other hand, simply reducing the content of monofunctional monomers results in the ink containing a large amount of polyfunctional monomers, which have a relatively high viscosity, and not only is this likely to increase the viscosity of the ink, but the adhesion of the ink coating film is also likely to decrease and the abrasion resistance is also likely to decrease. [Means for solving the problem]

[0005] The inkjet ink composition of the present invention is a radiation-curable inkjet ink composition containing polymerizable monomer A including monofunctional monomer B and polyfunctional monomer C, wherein polymerizable monomer A contains 20 mass % or more of polymerizable monomer A1, the polymerizable monomer A1 having a homopolymer glass transition temperature of 50°C or higher, relative to the total amount of polymerizable monomers, and the weighted average of the glass transition temperatures of the homopolymers of polymerizable monomer A, where the mass ratio of each polymerizable monomer A contained is used as the weight, is 25°C or higher and 40°C or lower, the content of monofunctional monomer B is 50 mass % or higher and 80 mass % or lower, relative to the total amount of polymerizable monomer A, and polyfunctional monomer C contains vinyl group-containing (meth)acrylate C1 represented by the following general formula (I): H2C=CR 1 -CO-OR 2 -O-CH=CH-R 3 (I) (In the formula, R 1 is a hydrogen atom or a methyl group, and R 2 is a divalent organic residue having 2 to 20 carbon atoms, and R 3 is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms.

[0006] The inkjet recording method of the present invention also comprises an ink deposition step of ejecting the radiation-curable inkjet ink composition from an inkjet head and depositing it onto a recording medium, and an irradiation step of irradiating the radiation-curable inkjet ink composition deposited on the recording medium with radiation. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram of a recording apparatus that can be used in this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, an embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described in detail with reference to the drawings as necessary, but the present invention is not limited to this, and various modifications are possible without departing from the spirit of the present invention. In the drawings, the same elements are given the same reference numerals, and redundant explanations will be omitted. Furthermore, positional relationships such as up, down, left, and right will be based on the positional relationships shown in the drawings unless otherwise specified. Furthermore, the dimensional ratios of the drawings are not limited to those shown in the drawings.

[0009] In this specification, "(meth)acryloyl" means at least one of acryloyl and its corresponding methacryloyl, "(meth)acrylate" means at least one of acrylate and its corresponding methacrylate, and "(meth)acrylic" means at least one of acrylic and its corresponding methacrylic.

[0010] 1. Radiation-curable inkjet ink composition The radiation-curable inkjet ink composition (hereinafter simply referred to as the “ink composition”) of this embodiment contains a polymerizable monomer A containing a monofunctional monomer B and a polyfunctional monomer C, wherein the polymerizable monomer A contains 20 mass% or more of polymerizable monomer A1, the polymerizable monomer A1 having a homopolymer glass transition temperature of 50°C or higher, relative to the total amount of polymerizable monomers; the weighted average of the glass transition temperatures of the homopolymers of the polymerizable monomer A, where the mass ratio of each polymerizable monomer A contained is used as the weight, is 25°C or higher and 40°C or lower; the content of the monofunctional monomer B is 50 mass% or higher and 80 mass% or lower, relative to the total amount of the polymerizable monomer A; and the polyfunctional monomer C contains a vinyl group-containing (meth)acrylate C1 represented by the following general formula (I): H2C=CR 1 -CO-OR 2 -O-CH=CH-R 3 (I) (In the formula, R 1 is a hydrogen atom or a methyl group, and R 2 is a divalent organic residue having 2 to 20 carbon atoms, and R 3is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms.

[0011] In this embodiment, the term "radiation-curable inkjet ink composition" refers to an inkjet ink composition that is cured by irradiation with radiation. Examples of radiation include ultraviolet light, electron beams, infrared light, visible light, and X-rays. Among these, ultraviolet light is preferred as the radiation source, since radiation sources are readily available and widely used, and materials suitable for curing by ultraviolet radiation are readily available and widely used.

[0012] The ink-jet ink composition refers to an ink composition that is ejected from an ink-jet head by an ink-jet method and adhered to a recording medium.

[0013] In the past, studies have been conducted to increase the proportion of monofunctional monomers contained in polymerizable monomers in order to improve the adhesion of ink coating films to recording media. However, when recorded matter was produced using such ink compositions, it was found that the high proportion of monofunctional monomers made it easier for soft ink coating films to be formed, resulting in problems such as ink coating film blocking.

[0014] In contrast to this, in the present embodiment, the content of monofunctional monomer B is relatively reduced compared to conventional methods, and the content of polyfunctional monomer C is used in a relatively large amount, thereby improving the blocking resistance of the ink coating film, and by using a polymerizable monomer A1 having a predetermined homopolymer glass transition temperature and adjusting the weighted average of the homopolymer glass transition temperatures of polymerizable monomer A, adhesion and abrasion resistance are ensured.

[0015] Furthermore, by using the predetermined polyfunctional monomer C1, an increase in viscosity of the ink composition that would otherwise occur if the polyfunctional monomer C were used in a relatively large amount is suppressed.

[0016] The components, properties, and production method of the ink composition according to this embodiment will be described below.

[0017] 1.1. Polymerizable Monomer A In this embodiment, those having a polymerizable unsaturated bond are collectively referred to as polymerizable monomer A. When the polymerizable monomer A in this embodiment is defined from the viewpoint of the number of polymerizable functional groups of the polymerizable monomer, it includes a monofunctional monomer B having one polymerizable functional group and a polyfunctional monomer C having multiple polymerizable functional groups.

[0018] Furthermore, when the polymerizable monomer A of this embodiment is defined from the viewpoint of the glass transition temperature of the homopolymer, it includes a polymerizable monomer A1 having a glass transition temperature of 50° C. or higher, a polymerizable monomer A2 having a glass transition temperature of the homopolymer lower than −20° C., and a polymerizable monomer A3 having a glass transition temperature of −20° C. or higher but lower than 30° C. Therefore, all polymerizable monomers A correspond to one or more of the monofunctional monomer B, the polyfunctional monomer C, and the polymerizable monomer A1, the polymerizable monomer A2, and the polymerizable monomer A3.

[0019] Hereinafter, the monofunctional monomer B and the polyfunctional monomer C will be described in detail from the viewpoint of the number of polymerizable functional groups of the polymerizable monomer, and then the polymerizable monomer A will be described in detail from the viewpoint of the glass transition temperature of the homopolymer, such as the polymerizable monomer A1, the polymerizable monomer A2, and the polymerizable monomer A3.

[0020] 1.1.1. Definition by number of polymerizable functional groups The polymerizable monomer A of the present embodiment includes a monofunctional monomer B and a polyfunctional monomer C. The monofunctional monomer B and the polyfunctional monomer C will be described in detail below.

[0021] 1.1.1.1. Monofunctional Monomer B The lower limit of the content of the monofunctional monomer B is 50% by mass, preferably 52.5% by mass, more preferably 55% by mass, and even more preferably 57.5% by mass, relative to the total amount of the polymerizable monomer A. When the content of the monofunctional monomer B is 50% by mass or more, adhesion is improved. Furthermore, the upper limit of the content of the monofunctional monomer B is 80% by mass, preferably 75% by mass, more preferably 72.5% by mass, and even more preferably 70% by mass, relative to the total amount of the polymerizable monomer A. When the content of the monofunctional monomer B is 80% by mass or less, blocking resistance is improved.

[0022] The monofunctional monomer B is not particularly limited, but examples thereof include nitrogen-containing monofunctional monomers, aromatic group-containing monofunctional monomers, saturated aliphatic group-containing monofunctional monomers, and monofunctional (meth)acrylates having a crosslinked condensed ring structure. Alternatively, or in addition to these, other monofunctional monomers may be included as needed. The monofunctional monomer is not particularly limited, but for example, a conventionally known monofunctional monomer having a polymerizable functional group, particularly a polymerizable functional group having a carbon-carbon unsaturated double bond, can be used. Examples of monofunctional monomers are given below, but the monofunctional monomers in this embodiment are not limited to the following.

[0023] The nitrogen-containing monofunctional monomer is not particularly limited, and examples thereof include nitrogen-containing monofunctional vinyl monomers such as N-vinylcaprolactam, N-vinylformamide, N-vinylcarbazole, N-vinylacetamide, and N-vinylpyrrolidone; nitrogen-containing monofunctional acrylate monomers such as acryloylmorpholine; and nitrogen-containing monofunctional acrylamide monomers such as (meth)acrylamide, N-hydroxymethyl(meth)acrylamide, diacetone acrylamide, N,N-dimethyl(meth)acrylamide, and dimethylaminoethyl acrylate benzyl chloride quaternary salt.

[0024] The content of the nitrogen-containing monofunctional monomer is preferably 1.0% by mass or more and 10.0% by mass or less, more preferably 3.0% by mass or more and 9.0% by mass or less, and even more preferably 5.0% by mass or more and 8.0% by mass or less, based on the total amount of polymerizable monomer A. When the content of the nitrogen-containing monofunctional monomer is within the above range, adhesion and blocking resistance tend to be further improved.

[0025] The aromatic group-containing monofunctional monomer is not particularly limited, but examples thereof include phenoxyethyl (meth)acrylate, benzyl (meth)acrylate, alkoxylated 2-phenoxyethyl (meth)acrylate, ethoxylated nonylphenyl (meth)acrylate, alkoxylated nonylphenyl (meth)acrylate, p-cumylphenol EO-modified (meth)acrylate, and 2-hydroxy-3-phenoxypropyl (meth)acrylate.

[0026] The content of the aromatic group-containing monofunctional monomer is preferably 20% by mass or more and 50% by mass or less, more preferably 22% by mass or more and 45% by mass or less, and even more preferably 25% by mass or more and 40% by mass or less, based on the total amount of polymerizable monomer A. When the content of the aromatic group-containing monofunctional monomer is within the above range, adhesion and blocking resistance tend to be further improved.

[0027] The saturated aliphatic group-containing monofunctional monomer is not particularly limited, and examples thereof include alicyclic group-containing (meth)acrylates such as isobornyl (meth)acrylate (IBXA), tert-butylcyclohexanol acrylate (TBCHA), and 2-(meth)acrylic acid-1,4-dioxaspiro[4,5]dec-2-ylmethyl; isoamyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, octyl (meth)acrylate, and decyl (meth)acrylate. Examples of the saturated aliphatic group-containing (meth)acrylate include linear or branched aliphatic group-containing (meth)acrylates such as acrylate, isodecyl (meth)acrylate, isomyristyl (meth)acrylate, isostearyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, butoxyethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, and 2-hydroxypropyl (meth)acrylate; and lactone-modified flexible (meth)acrylates. Note that the saturated aliphatic group-containing monofunctional monomer is not a compound having a crosslinked condensed ring structure.

[0028] The content of the saturated aliphatic group-containing monofunctional monomer is preferably 5.0% by mass or more and 40% by mass or less, more preferably 10% by mass or more and 30% by mass or less, and even more preferably 15% by mass or more and 25% by mass or less, relative to the total amount of polymerizable monomer A. When the content of the saturated aliphatic group-containing monofunctional monomer is within the above range, adhesion and blocking resistance tend to be further improved.

[0029] Examples of monofunctional (meth)acrylates having a bridged condensed ring structure include dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, and dicyclopentanyl (meth)acrylate. Here, the bridged condensed ring structure refers to a structure in which two or more ring structures share a side in a one-to-one relationship and two or more atoms of the same ring structure or different ring structures that are not adjacent to each other are linked.

[0030] 1.1.1.2. Polyfunctional Monomer C The content of polyfunctional monomer C is 20% by mass or more and 50% by mass or less, preferably 25% by mass or more and 47.5% by mass or less, more preferably 30% by mass or more and 45% by mass or less, and even more preferably 35% by mass or more and 42.5% by mass or less, relative to the total amount of polymerizable monomer A. When the content of polyfunctional monomer C is 50% by mass or less, relative to the total amount of polymerizable monomer A, adhesion tends to be improved. Furthermore, when the content of polyfunctional monomer C is 20% by mass or more, relative to the total amount of polymerizable monomer A, blocking resistance tends to be improved.

[0031] The polyfunctional monomer C contains a vinyl group-containing (meth)acrylate C1 represented by the following general formula (I), and may also contain other polyfunctional monomers C2 as needed. H2C=CR 1 -CO-OR 2 -O-CH=CH-R 3 (I) (In the formula, R 1 is a hydrogen atom or a methyl group, and R 2 is a divalent organic residue having 2 to 20 carbon atoms, and R 3 is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms.

[0032] In the above formula (I), R 2 Examples of the divalent organic residue having 2 to 20 carbon atoms represented by the formula (I) include a linear, branched, or cyclic alkylene group having 2 to 20 carbon atoms, which may be substituted; an alkylene group having 2 to 20 carbon atoms and having an oxygen atom via an ether bond and / or an ester bond in its structure, which may be substituted; and a divalent aromatic group having 6 to 11 carbon atoms, which may be substituted. Among these, alkylene groups having 2 to 6 carbon atoms, such as an ethylene group, an n-propylene group, an isopropylene group, and a butylene group, and alkylene groups having 2 to 9 carbon atoms and having an oxygen atom via an ether bond in its structure, such as an oxyethylene group, an oxy-n-propylene group, an oxyisopropylene group, and an oxybutylene group, are preferred. Furthermore, from the viewpoint of further reducing the viscosity of the ink composition and further improving the curability of the ink composition, R 2is an alkylene group having 2 to 9 carbon atoms and an oxygen atom by an ether bond in the structure, such as an oxyethylene group, an oxy-n-propylene group, an oxyisopropylene group, or an oxybutylene group, and more preferably has a glycol ether chain.

[0033] In the above formula (I), R 3 Suitable monovalent organic residues having 1 to 11 carbon atoms and represented by the formula (I) are linear, branched, or cyclic alkyl groups having 1 to 10 carbon atoms, which may be substituted, and aromatic groups having 6 to 11 carbon atoms, which may be substituted. Among these, alkyl groups having 1 to 2 carbon atoms, such as methyl or ethyl groups, and aromatic groups having 6 to 8 carbon atoms, such as phenyl and benzyl groups, are preferably used.

[0034] When each of the above organic residues is a group that may be substituted, the substituent is divided into a group containing carbon atoms and a group not containing carbon atoms. First, when the above substituent is a group containing carbon atoms, the carbon atom is counted in the number of carbon atoms of the organic residue. Examples of the group containing carbon atoms include, but are not limited to, a carboxyl group and an alkoxy group. Next, examples of the group not containing carbon atoms include, but are not limited to, a hydroxyl group and a halo group.

[0035] Specific examples of the compound of formula (I) include, but are not limited to, 2-vinyloxyethyl (meth)acrylate, 3-vinyloxypropyl (meth)acrylate, 1-methyl-2-vinyloxyethyl (meth)acrylate, 2-vinyloxypropyl (meth)acrylate, 4-vinyloxybutyl (meth)acrylate, 1-methyl-3-vinyloxypropyl (meth)acrylate, 1-vinyloxymethylpropyl (meth)acrylate, 2-methyl-3-vinyloxypropyl (meth)acrylate, 1,1-dimethyl-2-vinyloxypropyl (meth)acrylate, dimethyl (meth)acrylate, 3-vinyloxybutyl (meth)acrylate, 1-methyl-2-vinyloxypropyl (meth)acrylate, 2-vinyloxybutyl (meth)acrylate, 4-vinyloxycyclohexyl (meth)acrylate, 6-vinyloxyhexyl (meth)acrylate, 4-vinyloxymethylcyclohexylmethyl (meth)acrylate, 3-vinyloxymethylcyclohexylmethyl (meth)acrylate, 2-vinyloxymethylcyclohexylmethyl (meth)acrylate, p-vinyloxymethylphenylmethyl (meth)acrylate, (meth)acrylate m-vinyloxymethylphenylmethyl (meth)acrylate, o-vinyloxymethylphenylmethyl (meth)acrylate, 2-(2-vinyloxyethoxy)ethyl (meth)acrylate (VEEA), 2-(2-vinyloxyethoxy)ethyl acrylate, 2-(vinyloxyisopropoxy)ethyl (meth)acrylate, 2-(vinyloxyethoxy)propyl (meth)acrylate, 2-(vinyloxyethoxy)isopropyl (meth)acrylate, 2-(vinyloxyisopropoxy)propyl (meth)acrylate, 2-(vinyloxyisopropoxy)propyl (meth)acrylate, 2-(vinyloxyisopropyl)(meth)acrylate (meth)acrylate 2-(vinyloxyethoxyethoxy)ethyl, (meth)acrylate 2-(vinyloxyethoxyisopropoxy)ethyl, (meth)acrylate 2-(vinyloxyisopropoxyethoxy)ethyl, (meth)acrylate 2-(vinyloxyisopropoxyisopropoxy)ethyl, (meth)acrylate 2-(vinyloxyethoxyethoxy)propyl, (meth)acrylate 2-(vinyloxyethoxyisopropoxy)propyl, (meth)acrylate 2-(vinyloxyisopropoxyethoxy)propyl, (meth)acrylate 2-(vinyloxyisopropoxyethoxy)propyl,2-(vinyloxyisopropoxyisopropoxy)propyl (meth)acrylate, 2-(vinyloxyethoxyethoxy)isopropyl (meth)acrylate, 2-(vinyloxyethoxyisopropoxy)isopropyl (meth)acrylate, 2-(vinyloxyisopropoxyethoxy)isopropyl (meth)acrylate, 2-(vinyloxyisopropoxyisopropoxy)isopropyl (meth)acrylate, 2-(vinyloxyethoxyethoxyethoxy)ethyl (meth)acrylate, 2-(vinyloxy) Examples of suitable polyfunctional monomers include 2-(2-vinyloxyethoxy)ethyl (meth)acrylate, 2-(isopropenoxyethoxy)ethyl (meth)acrylate, 2-(isopropenoxyethoxyethoxy)ethyl (meth)acrylate, 2-(isopropenoxyethoxyethoxy)ethyl (meth)acrylate, 2-(isopropenoxyethoxyethoxyethoxy)ethyl (meth)acrylate, polyethylene glycol monovinyl ether (meth)acrylate, and polypropylene glycol monovinyl ether (meth)acrylate. Among these specific examples, 2-(2-vinyloxyethoxy)ethyl acrylate (VEEA) is particularly preferred because it allows for easy balancing of the curability and viscosity of the ink composition. By including such a polyfunctional monomer C1, it is possible to reduce the viscosity of the ink composition even when the proportion of the polyfunctional monomer in the ink composition is increased.

[0036] The content of the vinyl group-containing (meth)acrylate C1 is preferably from 1.0% to 50% by mass, more preferably from 15% to 45% by mass, and even more preferably from 30% to 40% by mass, relative to the total amount of polymerizable monomer A. When the content of the vinyl group-containing (meth)acrylate C1 is within the above range, adhesion and blocking resistance tend to be further improved, and the viscosity of the ink composition tends to be further reduced.

[0037] Furthermore, the polyfunctional monomer C may contain another polyfunctional monomer C2 other than the vinyl group-containing (meth)acrylate C1. When the other polyfunctional monomer C2 is contained, the content of the other polyfunctional monomer C2 is preferably 10% by mass or less, more preferably 5.0% by mass or less, and even more preferably 3.0% by mass or less, relative to the total amount of the ink composition. The lower limit of the content of the other polyfunctional monomer C2 may be 0% by mass. When the content of the other polyfunctional monomer C2 is within the above range, it tends to be possible to suppress an increase in the viscosity of the ink composition, even when the proportion of the polyfunctional monomer in the ink composition is increased.

[0038] The polyfunctional monomer C2 is not particularly limited, and examples thereof include polyfunctional (meth)acrylates excluding vinyl ether group-containing (meth)acrylates. Specific examples thereof include dipropylene glycol diacrylate (DPGDA), diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, dipropylene glycol dimethacrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate (HDDA), 1,9-nonanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, dimethylol-tricyclodecane di(meth)acrylate, and EO (ethylene oxide) adduct di(meth) of bisphenol A. Examples of the acrylate include bifunctional (meth)acrylates such as acrylate, PO (propylene oxide) adduct di(meth)acrylate of bisphenol A, hydroxypivalic acid neopentyl glycol di(meth)acrylate, and polytetramethylene glycol di(meth)acrylate; and trifunctional or higher polyfunctional (meth)acrylates such as trimethylolpropane tri(meth)acrylate, EO-modified trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, glycerin propoxy tri(meth)acrylate, caprolactone-modified trimethylolpropane tri(meth)acrylate, pentaerythritol ethoxy tetra(meth)acrylate, and caprolactam-modified dipentaerythritol hexa(meth)acrylate.

[0039] 1.1.2. Definition of homopolymer by glass transition temperature Next, polymerizable monomer A, polymerizable monomer A1, polymerizable monomer A2, and polymerizable monomer A3 will be described in detail from the viewpoint of the glass transition temperature of the homopolymer of polymerizable monomer A. The glass transition temperature of the homopolymer of each polymerizable monomer can be obtained from the safety data sheet (SDS) or catalog information of the polymerizable monomer.

[0040] In the present embodiment, the weighted average of the glass transition temperatures of homopolymers of polymerizable monomer A, where the weights are the mass ratios of the polymerizable monomers A contained in the polymerizable monomer A, is from 25° C. to 40° C., preferably from 27.5° C. to 37.5° C., and more preferably from 30° C. to 35° C. When the weighted average of the glass transition temperatures of the homopolymers is within the above range, the abrasion resistance of the ink coating tends to be improved.

[0041] The weighted average of the glass transition temperatures of the homopolymers can be adjusted by the glass transition temperatures of the homopolymers of the polymerizable monomers used and the mass ratio of the polymerizable monomers A used.

[0042] Here, a method for calculating the weighted average of the glass transition temperatures of the homopolymers of the polymerizable monomers will be described. The weighted average of the glass transition temperatures of the homopolymers is called Tg All , the glass transition temperature of the homopolymer of each polymerizable monomer is Tg N , the content mass ratio of the polymerizable monomer is X N (% by mass). N is a number starting from 1 depending on the type of polymerizable monomer contained in the ink composition. For example, if three types of polymerizable monomers are used, Tg1, Tg2, and Tg3 will result. The weighted average Tg of the glass transition temperatures of homopolymers All is the glass transition temperature Tg of the homopolymer calculated for each polymerizable monomer. N and the mass ratio X N Therefore, the following equation (2) holds true. Tg All =ΣTg N ×X N ···(2)

[0043] The glass transition temperature of a homopolymer of a polymerizable monomer can be measured by differential scanning calorimetry (DSC) in accordance with JIS K 7121. The measuring device used may be, for example, a DSC6220 model manufactured by Seiko Electronics Co., Ltd., and the sample used may be one in which the polymerizable monomer has been polymerized to such an extent that the glass transition temperature of the homopolymer becomes constant.

[0044] 1.1.2.1. Polymerizable Monomer A1 The polymerizable monomer A1 is a polymerizable monomer having a glass transition temperature of 50°C or higher when formed into a homopolymer. The content of the polymerizable monomer A1 is 20% by mass or higher and 50% by mass or lower, preferably 22.5% by mass or higher and 40% by mass or lower, and more preferably 25% by mass or higher and 30% by mass or lower, relative to the total amount of the polymerizable monomer A. When the content of the polymerizable monomer A1 is within the above range, the scratch resistance of the ink coating tends to be improved. Furthermore, even when the polymerizable monomer A contains, for example, a certain amount of the polymerizable monomer A2, the homopolymer of which has a glass transition temperature of -20°C or lower, as described below, it becomes easy to adjust the weighted average glass transition temperature of the homopolymer of the polymerizable monomer A to 25°C or higher and 40°C or lower.

[0045] The polymerizable monomer A1 preferably includes a polymerizable monomer A11 having a homopolymer glass transition temperature of 90°C or higher, and more preferably includes isobornyl acrylate (IBXA, having a homopolymer glass transition temperature of 94°C), which also corresponds to the monofunctional monomer B. The content of the polymerizable monomer A11 is preferably 10% by mass or more and 50% by mass or less, more preferably 15% by mass or more and 40% by mass or less, and even more preferably 20% by mass or more and 30% by mass or less, based on the total amount of the polymerizable monomer A. The content of the isobornyl acrylate is preferably 5.0% by mass or more and 40% by mass or less, more preferably 10% by mass or more and 30% by mass or less, and even more preferably 15% by mass or more and 25% by mass or less, based on the total amount of the polymerizable monomer A. When the polymerizable monomer A1 includes a polymerizable monomer A11 having a homopolymer glass transition temperature of 90°C or higher, the abrasion resistance of the ink coating film tends to be improved. Furthermore, by including isobornyl acrylate, the scratch resistance of the ink coating film is further improved, and in addition, the viscosity of the ink composition tends to decrease due to the moderate bulkiness of its molecular structure.

[0046] 1.1.2.2. Polymerizable Monomer A2 Polymerizable monomer A2 is a polymerizable monomer having a homopolymer glass transition temperature of less than -20°C. Polymerizable monomer A2 preferably contains a polymerizable monomer having a homopolymer glass transition temperature of -30°C or higher but less than -20°C, and more preferably contains phenoxyethyl acrylate (PEA, homopolymer glass transition temperature -22°C), which also corresponds to the monofunctional monomer B described above. When polymerizable monomer A2 contains such a polymerizable monomer, it tends to be easier to adjust the glass transition temperature of the homopolymer of polymerizable monomer A within a predetermined range. Furthermore, in particular, when it contains phenoxyacrylate, in addition to the above, it tends to be easier to improve the solubility of the polymerization initiator, and it tends to be easier to adjust the curability of the ink composition.

[0047] The content of polymerizable monomer A2 relative to the total amount of polymerizable monomer A is preferably 25% by mass or more and 50% by mass or less, more preferably 30% by mass or more and 45% by mass or less, and even more preferably 35% by mass or more and 40% by mass or less, relative to the total amount of polymerizable monomer A. When the content of polymerizable monomer A2 is within this range, the glass transition temperature of the homopolymer of polymerizable monomer A can be adjusted to a predetermined range, and the adhesion and blocking resistance of the ink coating tend to be improved in a balanced manner.

[0048] 1.1.2.3. Polymerizable Monomer A3 The polymerizable monomer A3 is a polymerizable monomer having a glass transition temperature of a homopolymer of -20°C or higher and lower than 30°C. When the polymerizable monomer A contains the polymerizable monomer A3, the content of the polymerizable monomer A3 is preferably less than 40% by mass, more preferably less than 20% by mass, even more preferably less than 10% by mass, and still more preferably less than 5.0% by mass, relative to the total amount of the polymerizable monomer A. The lower limit of the content of the polymerizable monomer A3 may be 0% by mass. When the content of the polymerizable monomer A3 is less than 40% by mass, the adhesion and blocking resistance of the polymerizable monomer A tend to be improved in a balanced manner.

[0049] 1.2.Colorants The ink composition according to this embodiment may further contain a coloring material. By containing a coloring material, the ink composition according to this embodiment can be used as a colored ink composition. The coloring material can be at least one of a pigment and a dye.

[0050] The total content of coloring materials is preferably 1.0 to 20% by mass, more preferably 2.0 to 15% by mass, and even more preferably 2.0 to 10% by mass, relative to the total amount of the ink composition. The ink composition according to this embodiment may contain no coloring materials, or may contain coloring materials to such an extent that coloring is not intended (for example, 0.1% by mass or less).

[0051] Furthermore, by using a pigment as a coloring material, the light resistance of the ink composition tends to be improved. Either inorganic or organic pigments can be used as the pigment. One type of pigment may be used alone, or two or more types may be used in combination.

[0052] As inorganic pigments, carbon blacks (CI (Colour Index Generic Name) Pigment Black 7) such as furnace black, lamp black, acetylene black, and channel black, iron oxide, and titanium oxide can be used.

[0053] Examples of organic pigments include azo pigments such as insoluble azo pigments, condensed azo pigments, azo lakes, and chelate azo pigments; polycyclic pigments such as phthalocyanine pigments, perylene and perinone pigments, anthraquinone pigments, quinacridone pigments, dioxane pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone pigments; dye chelates (for example, basic dye chelates, acid dye chelates, etc.); dye lakes (basic dye lakes, acid dye lakes), nitro pigments, nitroso pigments, aniline black, and daylight fluorescent pigments.

[0054] 1.3.Polymerization initiator The polymerization initiator is not particularly limited, but examples thereof include known polymerization initiators such as acylphosphine oxide-based polymerization initiators, alkylphenone-based polymerization initiators, titanocene-based polymerization initiators, and thioxanthone-based polymerization initiators. Among these, acylphosphine oxide-based polymerization initiators are preferred. Use of such a polymerization initiator further improves the curability of the ink composition, and in particular tends to further improve the curability in a curing process using UV-LED light.

[0055] The acylphosphine oxide polymerization initiator is not particularly limited, but examples thereof include 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, and bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide.

[0056] The content of the polymerization initiator relative to the total amount of the ink composition is preferably 1.0% by mass to 20% by mass, more preferably 3.0% by mass to 15% by mass, even more preferably 5.0% by mass to 10% by mass, and particularly preferably 7.0% by mass to 9.0% by mass. When the content of the polymerization initiator is within the above range, the curability of the ink coating film and the solubility of the polymerization initiator tend to be further improved.

[0057] 1.4.Polymerization inhibitors The ink composition according to this embodiment may further contain a polymerization inhibitor. The polymerization inhibitor may be used alone or in combination of two or more.

[0058] The polymerization inhibitor is not particularly limited, but examples thereof include p-methoxyphenol, hydroquinone monomethyl ether (MEHQ), 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl, hydroquinone, cresol, t-butylcatechol, 3,5-di-t-butyl-4-hydroxytoluene, 2,2'-methylenebis(4-methyl-6-t-butylphenol), 2,2'-methylenebis(4-ethyl-6-butylphenol), 4,4'-thiobis(3-methyl-6-t-butylphenol), and hindered amine compounds.

[0059] The content of the polymerization inhibitor is preferably 0.05 to 1.0 mass %, and more preferably 0.05 to 0.5 mass %, relative to the total amount of the ink composition.

[0060] 1.5.Slip Agents The ink composition according to this embodiment may further contain a slip agent. The slip agent may be used alone or in combination of two or more.

[0061] The slip agent is preferably a silicone surfactant, more preferably a polyester-modified silicone or a polyether-modified silicone. Examples of polyether-modified silicones include BYK-378, 3455, BYK-UV3500, 3510, and 3530 (all manufactured by BYK Additives & Instruments). Examples of polyester-modified silicones include BYK-3570 (manufactured by BYK Additives & Instruments).

[0062] The content of the slip agent is preferably 0.01% by mass or more and 2.0% by mass or less, and more preferably 0.05% by mass or more and 1.0% by mass or less, relative to the total amount of the ink composition.

[0063] Dispersants The dispersant is not particularly limited, but examples thereof include dispersants commonly used in preparing pigment dispersions, such as polymer dispersants. Specific examples thereof include those containing one or more of polyoxyalkylene polyalkylene polyamines, vinyl polymers and copolymers, acrylic polymers and copolymers, polyesters, polyamides, polyimides, polyurethanes, amino polymers, silicon-containing polymers, sulfur-containing polymers, fluorine-containing polymers, and epoxy resins as the main component. The dispersants may be used alone or in combination of two or more.

[0064] Commercially available polymer dispersants include the Ajisper series manufactured by Ajinomoto Fine-Techno Co., Ltd., the Solsperse series (Solsperse 36000, etc.) available from Avecia and Noveon, the Disperbic series manufactured by BYK Additives & Instruments, and the Disparlon series manufactured by Kusumoto Chemicals Co., Ltd.

[0065] The content of the dispersant is preferably 0.1% by mass or more and 5.0% by mass or less, more preferably 0.3% by mass or more and 3.0% by mass or less, and even more preferably 0.5% by mass or more and 1.5% by mass or less, relative to the total amount of the ink composition.

[0066] 1.7.Other Ingredients In addition to the components described above, the composition of this embodiment may contain one or more optional components that can be used in conventional inkjet ink compositions. Specific examples of such optional components include colorants such as dyes, surfactants, penetrants, humectants, solubilizers, viscosity adjusters, pH adjusters, antioxidants, preservatives, antifungal agents, corrosion inhibitors, chelating agents for capturing metal ions that affect dispersion, and other additives and solvents. Each of these may be used alone or in combination of two or more.

[0067] 2. Inkjet recording method The inkjet recording method of this embodiment includes an ink deposition step of ejecting the radiation-curable inkjet ink composition described above from an inkjet head and depositing it onto a recording medium to perform recording, and an irradiation step of irradiating radiation onto the recording surface of the ink composition deposited on the recording medium. The above-described ejection method is also referred to as an inkjet method.

[0068] 2.1.Ink application process In the ink deposition step, the heated ink composition is ejected from the inkjet head and deposited on the recording medium. More specifically, the pressure generating means is driven to eject the ink composition filled in the pressure generating chamber of the inkjet head from the nozzle.

[0069] Inkjet heads used in the ink deposition step include line heads that perform recording by a line method and serial heads that perform recording by a serial method.

[0070] In the line method using a line head, for example, an inkjet head having a width equal to or greater than the recording width of the recording medium is fixed to the inkjet device. The recording medium is then moved in the sub-scanning direction (the longitudinal direction of the recording medium, the transport direction), and ink droplets are ejected from the nozzles of the inkjet head in conjunction with this movement to record an image on the recording medium.

[0071] In the serial method using a serial head, for example, an inkjet head is mounted on a carriage that can move in the width direction of the recording medium. The carriage is then moved in the main scanning direction (the horizontal or width direction of the recording medium), and ink droplets are ejected from the nozzle openings of the head in conjunction with this movement, thereby recording an image on the recording medium.

[0072] 2.2.Irradiation process In the irradiation step, radiation is irradiated onto the ink composition attached to the recording medium. When irradiated with radiation, a polymerization reaction of the polymerizable monomer is initiated, curing the ink composition and forming an ink coating. If a photopolymerization initiator is present, it generates active species (initiation species) such as radicals, acids, and bases, and the polymerization reaction of the polymerizable monomer is promoted by the function of the initiation species. Furthermore, if a photosensitizer is present, it absorbs radiation and becomes excited, and upon contact with the photopolymerization initiator, it promotes the decomposition of the photopolymerization initiator, thereby achieving a more rapid curing reaction.

[0073] Here, examples of the radiation include ultraviolet light, infrared light, visible light, and X-rays, as described above. The radiation source is provided downstream of the inkjet head and irradiates the ink composition with the radiation. The radiation source is not particularly limited, but examples thereof include ultraviolet light-emitting diodes. Use of such a radiation source can reduce the size and cost of the device. Because ultraviolet light-emitting diodes as an ultraviolet light source are small, they can be installed inside the inkjet device.

[0074] For example, ultraviolet light-emitting diodes can be attached to a carriage (at both ends along the medium width direction and / or on the medium transport direction side) on which an inkjet head that ejects the ink composition is mounted. Furthermore, due to the composition of the ink composition described above, low-energy, high-speed curing can be achieved.

[0075] 3. Inkjet device The inkjet device of this embodiment includes an inkjet head having a nozzle for ejecting an ink composition and a pressure chamber to which the composition is supplied, and a radiation source for irradiating the composition with radiation, and uses the ink composition described above as the ink composition.

[0076] As an example of an inkjet device, a perspective view of a serial printer is shown in Fig. 1. As shown in Fig. 1, the serial printer 20 includes a conveying unit 220 and a recording unit 230. The conveying unit 220 conveys the recording medium F fed to the serial printer to the recording unit 230, and ejects the recording medium after recording outside the serial printer. Specifically, the conveying unit 220 has feed rollers and conveys the fed recording medium F in the sub-scanning direction T1.

[0077] The recording unit 230 also includes an inkjet head 231 that ejects a radiation-curable inkjet ink composition onto the recording medium F sent from the conveying unit 220, a radiation source 232 that irradiates the adhered radiation-curable inkjet ink composition with radiation, a carriage 234 that carries these elements, and a carriage movement mechanism 235 that moves the carriage 234 in the main scanning directions S1 and S2 of the recording medium F.

[0078] Although FIG. 1 shows an embodiment in which the radiation source is mounted on a carriage, the present invention is not limited to this, and the radiation source may be one that is not mounted on a carriage.

[0079] The inkjet device described above may be a serial printer or a line printer.

[0080] 4. Recording Media The material of the recording medium is not particularly limited, but examples include plastics such as polyvinyl chloride, polyethylene terephthalate, polypropylene, polyethylene, polycarbonate, cellulose diacetate, cellulose triacetate, cellulose propionate, cellulose butyrate, cellulose acetate butyrate, cellulose nitrate, polyethylene terephthalate, polyethylene, polystyrene, polypropylene, polycarbonate, and polyvinyl acetal, as well as plastics whose surfaces have been treated, glass, paper, metal, and wood. [Example]

[0081] The present invention will be described in more detail below using examples and comparative examples, but the present invention is not limited to the following examples.

[0082] 1. Preparation of Ink Composition The ink compositions of each example were obtained by placing the components in a mixing tank, mixing and stirring, and filtering through a 5 μm membrane filter so as to obtain the composition shown in Table 1. The numerical values ​​of each component shown in each example in the table represent % by mass unless otherwise specified.

[0083] [Table 1]

[0084] The abbreviations and product ingredients used in Table 1 are as follows: [Monofunctional Monomer] IBXA (Osaka Organic Chemical Industry, Ltd., isobornyl acrylate) PEA (product name "Viscoat #192", manufactured by Osaka Organic Chemical Industry Ltd., phenoxyethyl acrylate) ACMO (KJ Chemicals Co., Ltd., acryloylmorpholine) [Polyfunctional Monomer] VEEA (Nippon Shokubai Co., Ltd., 2-(2-vinyloxyethoxy)ethyl acrylate) DPGDA (product name "SR508", manufactured by Sartomer Corporation, dipropylene glycol diacrylate) [Polymerization initiator] Irg.819 (trade name "IRGACURE 819", manufactured by BASF, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide) TPO (trade name "IRGACURE TPO", manufactured by BASF, 2,4,6-trimethylbenzoyldiphenylphosphine oxide) [Polymerization inhibitor] MEHQ (product name "p-methoxyphenol", manufactured by Kanto Chemical Co., Ltd., hydroquinone monomethyl ether) [Slip agent] BYK-UV3500 (BYK Additives & Instruments, polyether-modified polydimethylsiloxane with acryloyl groups) [Colorant] Carbon black (product name "MA-100", manufactured by Mitsubishi Chemical Corporation) [Dispersant] Solsperse 36000 (Lubrizol, polymer dispersant)

[0085] 2. Evaluation Method 2.1. Evaluation of blocking resistance Each radiation-curable inkjet composition was applied to a polyvinyl chloride film, which was a recording medium, using a bar coater to a coating thickness of 10 μm, and the cumulative energy was set at an irradiation intensity of 200 mJ / cm 2 The ink was applied to the printed surface of the recording material by irradiating the recording material with ultraviolet light at a wavelength of 500 g / cm. 2 The recorded images were left for 24 hours in an environment of 20-25°C / 40-60% RH while a load of 1000kJ / 1000kcal was applied. After leaving the recorded images, the recorded images were visually inspected for peeling and transfer to the reverse side, and the blocking resistance was evaluated according to the following evaluation criteria. [Evaluation criteria] A: No peeling of the recorded pattern image is observed, and no image transfer is observed even when the recorded materials are stacked. B: No peeling of the recorded pattern image is observed, but slight image transfer is observed when the recorded materials are stacked. C: Peeling is observed in the recorded pattern image.

[0086] 2.2.Evaluation of adhesion The ink coating film obtained by the method described in the above-mentioned blocking resistance test was evaluated by a cross-cut test in accordance with JIS K5600-5-6. More specifically, the blade of a cutter was placed perpendicular to the ink coating film, and squares with 1 mm spacing between the cuts were created to create a 10 x 10 grid. A transparent adhesive tape (25 mm wide) approximately 75 mm long was attached to the grid, and the tape was rubbed thoroughly with a finger so that the cured film was visible. Next, within 5 minutes of application, the tape was firmly peeled from the cured film at an angle of approximately 60° in 0.5 to 1.0 seconds, and the state of the grid was visually observed (cut peel).

[0087] Similarly, without forming an incision with a cutter, transparent adhesive tape was applied to the ink coating film, and within 5 minutes, the tape was firmly peeled off from the cured film at an angle of approximately 60° in 0.5 to 1.0 seconds, and the ink coating film was visually observed (tape peel). Based on the results of the cut peel and tape peel, adhesion was evaluated according to the following evaluation criteria. [Evaluation criteria] A: No peeling was observed in both cut peel and tape peel. B: Peeling was observed with cut peel, but not with tape peel. C: Peeling was observed in both cut peel and tape peel.

[0088] 2.3. Evaluation of abrasion resistance The ink coating film obtained by the method described in the above-mentioned blocking resistance test was rubbed with a friction element consisting of a Gakushin-type rub fastness tester AB-301 (trade name, manufactured by Tester Sangyo Co., Ltd.) equipped with a white cotton cloth (compliant with JIS L 0803) under a load of 200 g, or rubbed back and forth 20 times until the recorded matter peeled off. The recording medium was then visually inspected for peeling of the recorded matter, and the rub resistance was evaluated according to the following evaluation criteria. [Evaluation criteria] A: No scratches are observed on the image, and no ink composition is observed adhering to the white cotton cloth. B: Scratches on the image or adhesion of the ink composition to the white cotton cloth are observed. C: Scratches were observed on the image and the ink composition was adhered to the white cotton cloth.

[0089] 3. Evaluation Results A comparison of Examples 1 to 5 and Comparative Examples 1 to 6 revealed that the ink composition according to this embodiment exhibited superior blocking resistance, adhesion, and abrasion resistance of the ink coating film compared to the ink compositions according to Comparative Examples 1 to 6, which did not satisfy the constituent requirements of the ink composition. [Explanation of symbols]

[0090] 20... serial printer, 220... transport unit, 230... recording unit, 231... inkjet head, 232... radiation source, 234... carriage, 235... carriage moving mechanism, F... recording medium, S1, S2... main scanning direction, T1... sub-scanning direction

Claims

1. The composition contains a polymerizable monomer A including a monofunctional monomer B and a polyfunctional monomer C, the polymerizable monomer A contains 20 mass% or more of a polymerizable monomer A1 having a glass transition temperature of a homopolymer of 50°C or higher, based on the total amount of the polymerizable monomer A; a weighted average of glass transition temperatures of homopolymers of the polymerizable monomer A, the weight being determined by the content mass ratio of each polymerizable monomer A, of 25° C. or higher and 40° C. or lower; the content of the monofunctional monomer B is 50% by mass or more and 80% by mass or less with respect to the total amount of the polymerizable monomer A, The polyfunctional monomer C includes a vinyl group-containing (meth)acrylate C1 represented by the following general formula (I): the content of the polymerizable monomer A3, which may be contained in the polymerizable monomer A and has a glass transition temperature of a homopolymer of −20° C. or more and less than 30° C., is less than 40 mass % with respect to the total amount of the polymerizable monomer A; Radiation-curable inkjet ink compositions. H 2 C=CR 1 -CO-OR 2 -O-CH=CH-R 3 ・・・ (I) (In the formula, R 1 is a hydrogen atom or a methyl group, and R 2 is a divalent organic residue having 2 to 20 carbon atoms, and R 3 is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms.

2. the polymerizable monomer A includes a polymerizable monomer A2 having a glass transition temperature of a homopolymer of lower than −20° C.; The radiation-curable ink-jet ink composition of claim 1 .

3. the polymerizable monomer A1 includes a polymerizable monomer A11 having a glass transition temperature of a homopolymer of 90° C. or higher, the content of the polymerizable monomer A11 is 20 mass% or more based on the total amount of the polymerizable monomer A; The radiation-curable inkjet ink composition according to claim 1 or 2.

4. The polymerizable monomer A1 includes isobornyl acrylate. The radiation-curable inkjet ink composition according to any one of claims 1 to 3.

5. the content of the polyfunctional monomer C2 other than the vinyl group-containing (meth)acrylate C1, which may be contained in the polyfunctional monomer C, is 10 mass % or less with respect to the total amount of the ink composition; The radiation-curable inkjet ink composition according to any one of claims 1 to 4.

6. an ink deposition step of ejecting the radiation-curable inkjet ink composition according to any one of claims 1 to 5 from an inkjet head and depositing it on a recording medium; an irradiation step of irradiating the radiation-curable inkjet ink composition adhered to the recording medium with radiation, Inkjet recording method.

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