Inkjet Ink and Image Recording Method

Abstract

To provide an inkjet ink and an image recording method capable of recording a white image excellent in image quality and abrasion resistance and excellent in yellowing resistance.SOLUTION: There is provided an inkjet ink which contains a pigment (A), an organic solvent (B), a polymerizable compound (C), and a polymerization initiator (D). The pigment (A) contains a white pigment. The proportion of the white pigment in the pigment (A) is 95 mass% or more. The polymerizable compound (C) contains a polymerizable oligomer which is a polymerizable compound having a molecular weight of 800 or more. The proportion of the polymerizable oligomer in the polymerizable compound (C) is 30 mass% or more. The proportion of the organic solvent (B) in the inkjet ink is 50 mass% or more. The image recording method is also provided.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to an inkjet ink and an image recording method.

Background Art

[0002] As one type of image recording method, there is known an image recording method in which ink is applied onto a substrate, and the applied ink is irradiated with active energy rays such as ultraviolet rays to cure the ink and obtain an image.

[0003] On the other hand, inks using white pigments such as titanium dioxide as pigments in the ink have also been studied. For example, Patent Document Ⅰ discloses an ink containing titanium dioxide that cures upon irradiation with active energy rays.

Prior Art Documents

Patent Documents

[0004]

Patent Document Ⅰ

Summary of the Invention

Problems to be Solved by the Invention

[0005] Inks that cure upon irradiation with active energy rays are advantageous in that they can record images with excellent image quality and abrasion resistance. Inks that cure upon irradiation with active energy rays contain a polymerizable compound. As a result of the study by the present inventor, it has been found that when an ink containing a white pigment and a polymerizable compound is cured by irradiation with active energy rays to record a white image, the recorded white image may yellow when exposed to heat or light. This yellowing is considered to be a problem specific to white images. Therefore, it is considered that there may be cases where yellowing resistance (i.e., resistance to yellowing) is required for the above white images.

[0006] The problem that one embodiment of this invention aims to solve is to provide an inkjet ink and an image recording method that can record a white image that is excellent in image quality and scratch resistance, and also excellent in yellowing resistance. [Means for solving the problem]

[0007] This disclosure includes the following aspects: <1> It contains a pigment (A), an organic solvent (B), a polymerizable compound (C), and a polymerization initiator (D), Pigment (A) contains a white pigment, and the proportion of the white pigment in pigment (A) is 95% by mass or more. The polymerizable compound (C) contains a polymerizable oligomer that is a polymerizable compound with a molecular weight of 800 or more, and the proportion of the polymerizable oligomer in the polymerizable compound (C) is 30% by mass or more. The proportion of organic solvent (B) in the inkjet ink is 50% by mass or more. Inkjet ink. <2> The white pigment contains titanium dioxide. <1> The inkjet inks listed above. <3> The volume-average particle size of the white pigment is 250 nm or larger. <1> or <2> The inkjet inks listed above. <4> The polymerizable oligomer contains urethane acrylate, and the proportion of urethane acrylate in the polymerizable oligomer is 80% by mass or more. <1> ~ <3> Inkjet ink as described in one of the following. <5> The mass ratio of polymerizable oligomers to white pigments is 0.5 to 2.0. <1> ~ <4> Inkjet ink as described in one of the following. <6> Organic solvent (B) includes organic solvents with a boiling point of 200°C or lower. <1> ~ <5> Inkjet ink as described in one of the following. <7> On the substrate, <1> ~ <6> An ink application step in which an inkjet ink described in any one of the above is applied by the inkjet method, A heating step in which the inkjet ink applied to the substrate is heated to a temperature of 50°C or higher, An irradiation process in which an activated energy ray is irradiated onto a heated inkjet ink, Image recording method, including [Effects of the Invention]

[0008] According to one embodiment of the present invention, an inkjet ink and an image recording method are provided that can record a white image with excellent image quality and scratch resistance, as well as excellent yellowing resistance. [Modes for carrying out the invention]

[0009] In this disclosure, a numerical range represented by "~" means a range that includes the numbers written before and after "~" as the lower and upper limits, respectively. In this disclosure, the amount of each component in the composition means the total amount of any multiple substances present in the composition, unless otherwise specified, if there are multiple substances corresponding to each component in the composition. In the numerical ranges described in stages within this disclosure, the upper or lower limit stated in one numerical range may be replaced with the upper or lower limit of another numerical range described in stages, or with the values ​​shown in the examples. In this disclosure, the term "process" includes not only independent processes but also any process that cannot be clearly distinguished from other processes, as long as its intended purpose is achieved. In this disclosure, a preferred combination of embodiments is a more preferred embodiment. In this disclosure, "(meth)acrylate" is a concept that encompasses both acrylate and methacrylate, "(meth)acryloyl group" is a concept that encompasses both acryloyl group and methacryloyl group, and "(meth)acrylic acid" is a concept that encompasses both acrylic acid and methacrylic acid.

[0010] In this disclosure, "image" means any film formed using ink, and "image recording" means the formation of an image (i.e., a film). In addition, the concept of "image" in the present disclosure also includes solid images.

[0011] 〔Inkjet Ink〕 The inkjet ink of the present disclosure (hereinafter also simply referred to as "ink") contains a pigment (A), an organic solvent (B), a polymerizable compound (C), and a polymerization initiator (D), the pigment (A) contains a white pigment, and the proportion of the white pigment in the pigment (A) is 95% by mass or more, the polymerizable compound (C) contains a polymerizable oligomer which is a polymerizable compound having a molecular weight of 800 or more, and the proportion of the polymerizable oligomer in the polymerizable compound (C) is 30% by mass or more, the proportion of the organic solvent (B) in the ink is 50% by mass or more.

[0012] According to the ink of the present disclosure, a white image excellent in image quality, rubbing resistance, and yellowing resistance can be recorded. Specifically, the ink of the present disclosure contains the polymerizable compound (C) and the polymerization initiator (D), thereby exhibiting a function of curing by irradiation with active energy rays. By such a function, the performance of recording an image excellent in image quality and rubbing resistance is ensured. In the ink of the present disclosure, since the proportion of the white pigment in the pigment (A) is 95% by mass or more, recording of a white image becomes possible.

[0013] Furthermore, the ink of the present disclosure can record a white image excellent in yellowing resistance. That is, yellowing of the recorded white image can be suppressed. Yellowing is a problem peculiar to white images. The reason why yellowing can be suppressed is not clear, but it is presumed as follows. Yellowing of the white image is considered to occur due to the polymerizable compound in the ink. In particular, the influence of the polymerizable monomer which is a polymerizable compound having a molecular weight of less than 800 in the ink is considered to be large (see Ink A11 and A12 (both comparative examples) in the [Examples] section described later). Therefore, the present inventor (1)Reducing the content of the polymerizable monomer in the ink and relatively increasing the content of the polymerizable oligomer. Specifically, the proportion of the polymerizable oligomer (i.e., the polymerizable compound having a molecular weight of 800 or more) in the polymerizable compound (C) is 30% by mass or more, and (2)Reducing the content of the polymerizable compound in the ink. Specifically, the proportion of the organic solvent (B) in the ink is 50% by mass or more. It has been found that yellowing of the white image can be effectively suppressed while maintaining the performance of recording an image excellent in image quality and abrasion resistance (i.e., the performance as an ink on the active energy ray curable side). The ink of the present disclosure is based on the above findings.

[0014] Hereinafter, each component that can be contained in the ink of the present disclosure will be described.

[0015] <Pigment (A)> The ink of the present disclosure contains a pigment (A). Here, the pigment (A) means all pigments that can be contained in the ink. In the ink of the present disclosure, the pigment (A) contains a white pigment, and the proportion of the white pigment in the pigment (A) is 95% by mass or more. That is, the ink of the present disclosure substantially functions as a white ink for recording a white image.

[0016] Examples of the white pigment include titanium dioxide (TiO2), barium sulfate, calcium carbonate, silica, zinc oxide, zinc sulfide, mica, talc, pearl, and the like. Among the white pigments, titanium dioxide, barium sulfate, calcium carbonate, or zinc oxide is preferable, and titanium dioxide is more preferable.

[0017] The white pigment that can be contained in the pigment (A) may be only one kind or two or more kinds. The white pigment that can be contained in the pigment (A) preferably contains titanium dioxide. In this case, the proportion of titanium dioxide in the total amount of white pigment is preferably 50% to 100% by mass, more preferably 60% to 100% by mass, and even more preferably 80% to 100% by mass.

[0018] The volume-average particle size of the white pigment is preferably 150 nm or larger, more preferably 200 nm or larger, and even more preferably 250 nm or larger. When the volume-average particle diameter is 150 nm or larger, it is possible to record white images with superior abrasion resistance and opacity. Here, opacity refers to one of the properties of a white image, meaning the property of covering up the background on which the white image is recorded (for example, a substrate, a colored image recorded on the substrate, etc.) with the white image. From the viewpoint of further improving ink ejection performance, the upper limit of the volume-average particle diameter of the white pigment is preferably 400 nm or less, more preferably 350 nm or less, and even more preferably 300 nm or less.

[0019] In this disclosure, the volume-average particle size of the white pigment refers to the value obtained by measurement using the dynamic scattering method. The measurement of the volume-average particle size of the white pigment by the dynamic scattering method is performed using a sample obtained by diluting a sample containing the white pigment (e.g., a white pigment dispersion used as a raw material for ink, ink, etc.) with tripropylene glycol monomethyl ether to a concentration of 0.02% by mass of the white pigment. An example of a measuring device is the Zetasizer Nano ZS (manufactured by Malvern Panalytical).

[0020] Pigment (A) may contain pigments other than white pigment, as long as the proportion of white pigment in pigment (A) is 95% by mass or more. Pigments other than white pigments can be appropriately selected from known pigments.

[0021] The pigment (A) content in the ink is preferably 1% to 20% by mass, more preferably 3% to 17% by mass, and even more preferably 5% to 15% by mass, relative to the total amount of ink. The preferred range for the content of white pigment in the ink is the same as the preferred range for the content of pigment (A) in the ink. However, as mentioned above, pigment (A) may contain pigments other than white pigment, so the content of white pigment in the ink and the content of pigment (A) in the ink do not need to be the same value.

[0022] The inks of this disclosure may contain a dispersant for dispersing the pigment (A). Preferably, polymeric dispersants are used as dispersants. Examples of polymer dispersants include polyamidoamines and their salts, polycarboxylic acids and their salts, high molecular weight unsaturated acid esters, modified polyurethanes, and polyether esters.

[0023] Commercially available polymer dispersants may be used. Examples of commercially available polymer dispersants include: DISPERBYK-101, DISPERBYK-102, DISPERBYK-103, DISPERBYK-106, DISPERBYK-110, DISPERBYK-111, DISPERBYK-161, DISPERBYK-162, DISPERBYK-16 3, DISPERBYK-164, DISPERBYK-166, DISPERBYK-167, DISPERBYK-168, DISPERBYK-170, DISPERBYK-171, DISPERBYK-174, DISPERBYK-182 (manufactured by BYK Chemie); SOLSPERSE3000, SOLSPERSE5000, SOLSPERSE9000, SOLSPERSE12000, SOLSPERSE13240, SOLSPERSE13940, SOLSPERSE17000, SOLSPERSE22000, SOLSPERSE24000, SOLSPERSE26000, SOLSPERSE28000, SOLSPERSE32000, SOLSPERSE36000, SOLSPERSE39000, SOLSPERSE41000, SOLSPERSE71000 (manufactured by Lubrizol); These are some examples.

[0024] Known dispersion devices can be used to disperse the pigment (A), including, for example, ball mills, sand mills, bead mills, roll mills, jet mills, paint shakers, attritors, ultrasonic dispersers, and dispersers.

[0025] In the ink, the ratio of the dispersant content to the pigment (A) content (i.e., dispersant content / pigment (A) content) is preferably 0.01 to 1.0 by mass, more preferably 0.03 to 0.8, even more preferably 0.03 to 0.5, and still more preferably 0.03 to 0.3, from the viewpoint of dispersion stability. The preferred range for the ratio of the dispersant content to the white pigment content in the ink (i.e., dispersant content / white pigment content) is the same as the preferred range for the dispersant content / pigment (A) content. However, as mentioned above, pigment (A) may contain pigments other than white pigment, so the dispersant content / white pigment content and the dispersant content / pigment (A) content do not need to be the same value.

[0026] <Organic solvent (B)> The inks of this disclosure contain an organic solvent (B). Here, organic solvent (B) refers to all organic solvents that may be contained in the ink. The proportion of organic solvent (B) in the ink of this disclosure (i.e., the content of organic solvent (B) relative to the total amount of ink) is 50% by mass or more. As mentioned above, having an organic solvent (B) proportion of 50% by mass or more in the ink contributes to improving the resistance to yellowing of white images (i.e., suppressing yellowing). The proportion of organic solvent (B) in the ink is preferably 55% by mass or more, and more preferably 60% by mass or more. The upper limit of the proportion of organic solvent (B) in the ink depends on the amounts of other components, but examples include 90% by mass, 80% by mass, etc.

[0027] The organic solvent included in organic solvent (B) is not particularly limited and can be selected from any organic solvent commonly used in the printing industry. The organic solvent (B) may consist of only one type of organic solvent, or it may consist of two or more types. Examples of organic solvents (B) include glycol ethers, alcohols, ketones, esters, pyrrolidones, organic carbonates, and the like.

[0028] Examples of glycol ethers include ethylene glycol monomethyl ether, diethylene glycol diethyl ether, diethylene glycol butyl methyl ether, triethylene glycol monobutyl ether, and the like. Examples of ketones include methyl ethyl ketone. Examples of esters include linear esters and cyclic esters (lactones). Examples of chain-like esters include 3-methoxybutyl acetate and ethylene glycol monomethyl ether acetate. An example of a cyclic ester (lactone) is γ-butyrolactone. Examples of pyrrolidones include N-methyl-2-pyrrolidone. Examples of organic carbonates include propylene carbonate.

[0029] The organic solvent (B) is preferably a glycol ether, an organic carbonate, or an ester, with diethylene glycol diethyl ether, ethylene glycol monomethyl ether, 3-methoxybutyl acetate, or γ-butyrolactone being preferred, and diethylene glycol diethyl ether, ethylene glycol monomethyl ether, or 3-methoxybutyl acetate being particularly preferred.

[0030] From the viewpoint of optimizing the viscosity of the ink (and improving the ejection stability in the case of inkjet colored inks), it is preferable that the proportion of at least one compound selected from the group consisting of glycol ethers, organic carbonates, and esters in the organic solvent (B) is 80% to 100% by mass (more preferably 90% to 100% by mass, and even more preferably 95% to 100% by mass).

[0031] From the viewpoint of further improving image quality, the organic solvent (B) preferably contains an organic solvent with a boiling point of 200°C or lower. In this case, the proportion of the organic solvent with a boiling point of 200°C or less in the organic solvent (B) is preferably 50% to 100% by mass, more preferably 60% to 100% by mass, and even more preferably 80% to 100% by mass.

[0032] In this disclosure, the boiling point refers to the boiling point at 1 atmosphere (101325 Pa).

[0033] Preferred organic solvents with a boiling point of 200°C or lower include 3-methoxybutyl acetate, diethylene glycol diethyl ether, ethylene glycol monomethyl ether, and ethylene glycol mono-n-butyl ether. For organic solvents with a boiling point of 200°C or less, a boiling point of 75°C or higher is preferable, and 100°C or higher is more preferable, from the viewpoint of discharge stability.

[0034] <Polymerizable compound (C)> The inks of this disclosure contain polymerizable compound (C). Here, polymerizable compound (C) refers to all polymerizable compounds that may be contained in the ink. Polymerizable compound (C) may consist of only one type of polymerizable compound or two or more types. The polymerizable compound (C) can be any polymerizable compound (for example, the polymerizable oligomer and polymerizable monomer described later), as long as it contains a polymerizable group. As the polymerizable group, an ethylenically unsaturated group is preferred. The ethylenically unsaturated group is preferably a (meth)acryloyl group, a vinyl group, an allyl group, or a styryl group, with the (meth)acryloyl group or a vinyl group being more preferred.

[0035] (Polymerizable oligomer) The polymerizable compound (C) in the ink of this disclosure comprises at least one polymerizable oligomer which is a polymerizable compound with a molecular weight of 800 or more. The proportion of polymerizable oligomers in polymerizable compound (C) (i.e., the content of polymerizable oligomers relative to polymerizable compound (C)) is 30% by mass or more. As mentioned above, having a proportion of polymerizable oligomers in polymerizable compound (C) of 30% by mass or more contributes to improved resistance to yellowing of white images (i.e., suppression of yellowing). The proportion of polymerizable oligomers in polymerizable compound (C) is preferably 40% by mass or more, and more preferably 50% by mass or more. The upper limit of the proportion of polymerizable oligomers in polymerizable compound (C) is preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 75% by mass or less.

[0036] Furthermore, the proportion of polymerizable oligomers in the total solid content of the ink of this disclosure is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more. The proportion of polymerizable oligomers in the total solids of the ink of this disclosure is preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 75% by mass or less.

[0037] Here, total solids in ink refers to all components of the ink excluding the solvent (e.g., organic solvent (B)).

[0038] Furthermore, the proportion of polymerizable oligomers in the total amount of the ink of this disclosure is preferably 3.0% by mass or more, more preferably 5.0% by mass or more, and even more preferably 7.0% by mass or more. The proportion of polymerizable oligomers in the total amount of the ink of this disclosure is preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less.

[0039] In the ink of this disclosure, the mass ratio of polymerizable oligomer to white pigment (hereinafter also referred to as the mass ratio [polymerizable oligomer / white pigment]) is preferably 0.3 to 2.5, and more preferably 0.5 to 2.0. When the mass ratio of polymerizable oligomer / white pigment is 0.3 or higher, the scratch resistance of white images is further improved. When the mass ratio of polymerizable oligomer / white pigment is 2.5 or less, the resistance to yellowing of white images is further improved (i.e., yellowing is further suppressed).

[0040] Polymerizable oligomers are polymerizable compounds with a molecular weight of 800 or more. The molecular weight of the polymerizable compound as a polymerizable oligomer is preferably 1000 or more, more preferably 1500 or more, and even more preferably 2000 or more. The upper limit of the molecular weight of the polymerizable compound as a polymerizable oligomer is preferably 15,000, more preferably 10,000, and even more preferably 7,000.

[0041] In this disclosure, the molecular weight of polymerizable compounds with a molecular weight of 800 or more as polymerizable oligomers is calculated based on the structure of the polymerizable compound. However, if the polymerizable compound has a molecular weight distribution, the weight-average molecular weight (Mw) measured by gel permeation chromatography (GPC) is used as the molecular weight. The above GPC was performed using HLC-8020GPC (manufactured by Tosoh Corporation), with three TSKgel® Super Multipore HZ-H columns (manufactured by Tosoh Corporation, 4.6 mm ID × 15 cm) and THF (tetrahydrofuran) as the eluent. Furthermore, GPC is performed using a differential refractive index (RI) detector with a sample concentration of 0.45 mass%, a flow rate of 0.35 ml / min, a sample injection volume of 10 μl, and a measurement temperature of 40°C. The calibration curve will be prepared using eight samples from Tosoh Corporation's "Standard Samples TSK standard, polystyrene": "F-40", "F-20", "F-4", "F-1", "A-5000", "A-2500", "A-1000", and "n-propylbenzene".

[0042] As polymerizable oligomers, (meth)acrylate compounds are preferred, difunctional to hexafunctional (meth)acrylate compounds are preferred, difunctional to tetrafunctional (meth)acrylate compounds are more preferred, difunctional to trifunctional (meth)acrylate compounds are even more preferred, and difunctional (meth)acrylate compounds are particularly preferred.

[0043] Furthermore, preferred (meth)acrylate compounds include urethane (meth)acrylate, bisphenol A epoxy (meth)acrylate, and modified epoxy (meth)acrylate, with urethane (meth)acrylate being particularly preferred. Furthermore, acrylate compounds are preferred as the (meth)acrylate compound.

[0044] From the viewpoint of further improving the resistance of white images to yellowing, the polymerizable oligomer preferably contains urethane acrylate. In this case, the proportion of urethane acrylate in the polymerizable oligomer is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more.

[0045] Commercially available polymerizable oligomers may be used. Examples of commercially available polymerizable oligomers include those used in the examples described later. In addition to those used in the examples described later, for example; Sartomer's CN996 (bifunctional oligomer, urethane acrylate, weight-average molecular weight (Mw) = 2850); UA-122P (bifunctional oligomer, urethane acrylate, Mw=1100) manufactured by Shin-Nakamura Chemical Industry Co., Ltd. Manufactured by Nippon Synthetic Chemical Co., Ltd.: Shiko UV-6630B (bifunctional oligomer, urethane acrylate, Mw=3000), Shiko UV-3310B (bifunctional oligomer, urethane acrylate, Mw=5000); Other examples include:

[0046] (polymerizable monomer) The polymerizable compound (C) in the ink of this disclosure may contain at least one polymerizable monomer which is a polymerizable compound with a molecular weight of less than 800. From the standpoint of further improving the resistance to yellowing of white images and the ejection stability, The proportion of polymerizable monomers in polymerizable compound (C) is preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 40% by mass or less. The proportion of polymerizable monomers in polymerizable compound (C) may be 0% by mass, 5% or more by mass, 10% or more by mass, or 20% or more by mass.

[0047] The polymerizable monomer may be a monofunctional polymerizable monomer, a difunctional polymerizable monomer, a trifunctional or more polymerizable monomer, or two or more of these polymerizable monomers.

[0048] Examples of monofunctional polymerizable monomers include: Monofunctional (meth)acrylates such as phenoxyethyl acrylate (PEA), cyclic TMP formal acrylate (CTFA), isobornyl acrylate (IBOA), tetrahydrofurfuryl acrylate (THFA), 2-(2-ethoxyethoxy)ethyl acrylate, octadecyl acrylate (ODA), tridecyl acrylate (TDA), isodecyl acrylate (IDA), and lauryl acrylate; Vinyl ethers such as triethylene glycol divinyl ether, diethylene glycol divinyl ether, 1,4-cyclohexanedimethanol divinyl ether, and ethylene glycol monovinyl ether; N-vinylamides such as N-vinylcaprolactam (NVC) and N-vinylpyrrolidone (NVP); N-(meth)acryloylamines such as N-acryloylmorpholine (ACMO); These are some examples.

[0049] Examples of bifunctional polymerizable monomers include hexanediol diacrylate, polyethylene glycol diacrylate (e.g., tetraethylene glycol diacrylate), dipropylene glycol diacrylate, neopentyl glycol diacrylate, and ethoxylated or propoxylated glycol diacrylate (e.g., propoxylated neopentyl glycol diacrylate).

[0050] Examples of polymerizable monomers with three or more functionalities include trimethylolpropane triacrylate, pentaerythritol triacrylate, tri(propylene glycol) triacrylate, bis(pentaerythritol) hexaacrylate, and ethoxylated or propoxylated polyol polyacrylates (e.g., ethoxylated trimethylolpropane triacrylate).

[0051] <Photopolymerization initiator> The inks of this disclosure preferably contain at least one photopolymerization initiator. Examples of photopolymerization initiators include radical photopolymerization initiators such as benzophenone, 1-hydroxycyclohexylphenyl ketone, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one, 2-benzyl-2-dimethylamino-(4-morpholinophenyl)butan-1-one, isopropylthioxanthone, benzyldimethyl ketal, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, and bis(2,6-dimethylbenzoyl)-2,4,4-trimethylpentylphosphine oxide. These radical photopolymerization initiators are well known. Commercially available radical photopolymerization initiators include IRGACURE®, Darocur®, LUCIRIN® (all manufactured by BASF), and Omnirad (manufactured by IGM Resins BV).

[0052] The photopolymerization initiator content in the ink of this disclosure is preferably 1% to 20% by mass, and more preferably 1% to 10% by mass, based on the total amount of ink.

[0053] (Surfactants) The inks of this disclosure may contain at least one surfactant. Examples of surfactants include those described in Japanese Patent Publication No. 62-173463 and Japanese Patent Publication No. 62-183457. Examples of surfactants include anionic surfactants such as dialkyl sulfosuccinates, alkylnaphthalene sulfonates, and fatty acid salts; nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, acetylene glycols, polyoxyethylene-polyoxypropylene block copolymers, and siloxanes; and cationic surfactants such as alkylamine salts and quaternary ammonium salts. The amount of surfactant that may be contained in the ink of this disclosure can be appropriately selected, but is preferably 0.0001% to 1% by mass, and more preferably 0.01% to 1% by mass, relative to the total amount of ink.

[0054] (Polymerization inhibitor) The inks of this disclosure may contain at least one polymerization inhibitor. Polymerization inhibitors include p-methoxyphenol, quinones (e.g., hydroquinone, benzoquinone, methoxybenzoquinone, etc.), phenothiazines, catechols, alkylphenols (e.g., dibutylhydroxytoluene (BHT), etc.), alkylbisphenols, zinc dimethyldithiocarbamate, copper dimethyldithiocarbamate, copper dibutyldithiocarbamate, copper salicylate, thiodipropionates, mercaptobenzimidazole, phosphites, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl (TEMPOL), and tris(N-nitroso-N-phenylhydroxylamine)aluminum salt (also known as cuperone Al). Among these, at least one selected from p-methoxyphenol, catechols, quinones, alkylphenols, TEMPO, TEMPOL, and tris(N-nitroso-N-phenylhydroxylamine)aluminum salt is preferred, and at least one selected from p-methoxyphenol, hydroquinone, benzoquinone, BHT, TEMPO, TEMPOL, and tris(N-nitroso-N-phenylhydroxylamine)aluminum salt is more preferred. The content of the polymerization inhibitor in the ink of this disclosure can be appropriately selected, but is preferably 0.0001% to 1% by mass, and more preferably 0.01% to 1% by mass, relative to the total amount of the colored ink.

[0055] (Other ingredients) The inks of this disclosure may contain other components not mentioned above, as necessary. Other components include, for example, resins, sensitizers, UV absorbers, antioxidants, colorfastness inhibitors, conductive salts, and basic compounds. For other components, refer to publicly available documents such as International Publication No. 2017 / 169371, International Publication No. 2017 / 104318, and International Publication No. 2019 / 087808 as appropriate.

[0056] <Physical properties> The viscosity of the inks of this disclosure is preferably 0.5 mPa·s to 30 mPa·s, more preferably 2 mPa·s to 20 mPa·s, preferably 2 mPa·s to 15 mPa·s, and even more preferably 3 mPa·s to 10 mPa·s. The viscosity is measured at 25°C using a viscometer, for example, using a TV-22 viscometer manufactured by Toki Sangyo Co., Ltd.

[0057] The surface tension of the inks disclosed herein is preferably 60 mN / m or less, more preferably 20 mN / m to 50 mN / m, and even more preferably 25 mN / m to 45 mN / m. The surface tension is measured at 25°C using a surface tensimeter, for example, by the plate method using an automatic surface tensimeter (product name "CBVP-Z") manufactured by Kyowa Interface Science Co., Ltd.

[0058] [Image recording method] The image recording method disclosed herein is: An ink application step is performed on a substrate by an inkjet method, A heating step in which the ink applied to the substrate is heated to a temperature of 50°C or higher, The process involves irradiating the heated ink with active energy rays, Includes. The image recording method disclosed herein uses the ink disclosed herein, and therefore achieves the same effects as those achieved by the ink disclosed herein (i.e., the effect of being able to record a white image with excellent image quality and scratch resistance, as well as excellent resistance to yellowing).

[0059] <Ink application process> In the ink application process, the above-mentioned ink is applied to the substrate by an inkjet method. The type of base material is not particularly limited and includes, for example, paper, paper laminated with plastic (e.g., polyethylene, polypropylene, polystyrene, etc.), metal plates (e.g., plates of metals such as aluminum, zinc, and copper), plastic films (e.g., films made of polyvinyl chloride (PVC), cellulose diacetate, cellulose triacetate, cellulose propionate, cellulose butyrate, cellulose acetate butyrate, cellulose nitrate, polyethylene terephthalate (PET), polyethylene (PE), polystyrene (PS), polypropylene (PP), polycarbonate (PC), polyvinyl acetal, acrylic resin, etc.), paper laminated or vapor-deposited with the aforementioned metals, and plastic films laminated or vapor-deposited with the aforementioned metals.

[0060] The ink application method by the inkjet method (hereinafter also referred to as the inkjet recording method) is not particularly limited as long as it is a method capable of recording an image, and known methods can be used. Examples of inkjet recording methods include a charge control method that ejects ink using electrostatic attraction, a drop-on-demand method (pressure pulse method) that utilizes the vibration pressure of a piezoelectric element, an acoustic inkjet method that converts an electrical signal into an acoustic beam, irradiates the ink with it, and ejects the ink using the radiation pressure, and a thermal inkjet (bubble jet®) method that heats the ink to form bubbles and utilizes the resulting pressure. Since the ink of this disclosure contains an organic solvent, a drop-on-demand method is preferred as the ink application method.

[0061] Inkjet heads used in inkjet recording methods include a shuttle method, which uses a short serial head and records while scanning the head in the width direction of the substrate, and a line method, which uses a line head in which recording elements are arranged to cover the entire area of ​​one side of the substrate.

[0062] In the line method, the substrate can be scanned in a direction intersecting the arrangement direction of the recording elements, allowing for pattern formation across the entire substrate surface. This eliminates the need for a transport system such as a carriage that scans the short head. Furthermore, the line method eliminates the need for complex scanning control of the carriage and the substrate; only the substrate moves, resulting in faster recording speeds compared to the shuttle method.

[0063] The amount of ink droplets ejected from the inkjet head is preferably 1 pL (picoliters) to 100 pL, more preferably 3 pL to 80 pL, and even more preferably 3 pL to 50 pL.

[0064] <Heating process> In the heating process, the ink applied to the substrate is heated. This allows the ink on the substrate to be heated and dried. Here, drying the ink means removing at least some of the solvent (e.g., organic solvent (B)) from the ink. In this process, the ink applied to the substrate is preferably heated to a temperature of 50°C or higher. The heating temperature is preferably 50°C to 100°C, and more preferably 50°C to 90°C. Furthermore, the heating time is preferably 1 second or more, more preferably 5 seconds or more, and particularly preferably 8 seconds or more. There is no particular upper limit on the heating time, but a preferred upper limit is 60 seconds, more preferably 30 seconds, and most preferably 20 seconds.

[0065] <Irradiation process> In the irradiation process, the ink, which has been heated in the heating process, is irradiated with active energy rays. This hardens the ink, allowing for the production of a white image with excellent scratch resistance.

[0066] As the active energy rays, alpha rays, gamma rays, electron beams, X-rays, ultraviolet rays, visible light, or infrared light may be used. The peak wavelength of the active energy rays depends on the absorption characteristics of the sensitizer when one is used, but is preferably 200 nm to 600 nm, more preferably 300 nm to 450 nm, and even more preferably 350 nm to 420 nm.

[0067] The irradiation energy of the active energy ray is preferably 10 mJ / cm². 2 ~10000 mJ / cm 2 More preferably 100 mJ / cm² 2 ~5000 mJ / cm 2 That is the case.

[0068] As the active energy source, any common active energy source such as mercury lamps, metal halide lamps, gas lasers, solid-state lasers, and GaN-based semiconductor ultraviolet light-emitting devices (light-emitting diodes (LEDs), laser diodes (LDs), etc.) can be used without any particular limitations. As an example of an LED, Nichia Corporation has launched a violet LED with a main emission spectrum having wavelengths between 365 nm and 420 nm. For even shorter wavelengths, an example of an LED is the one disclosed in U.S. Patent No. 6,084,250, which emits active energy rays with a wavelength center between 300 nm and 370 nm. Other ultraviolet LEDs are also available and can emit radiation in different ultraviolet bands.

[0069] The irradiation time for the active energy ray is preferably 0.01 seconds to 120 seconds, more preferably 0.1 seconds to 90 seconds. Specific methods for irradiating with active energy rays include a shuttle method in which an active energy ray irradiation device is mounted on a single-length serial head and irradiation is performed while scanning the head in the width direction of the recording medium, and a single-pass method in which active energy ray irradiation devices are arranged to cover the entire area of ​​one side of the recording medium. The irradiation conditions of the active energy rays and the basic irradiation method may be referred to, for example, in known documents such as Japanese Patent Laid-Open No. 60-132767.

[0070] When performing heat drying, the irradiation of the active energy rays is preferably performed after a certain period of time (preferably 0.01 second to 0.5 second, more preferably 0.01 second to 0.3 second, still more preferably 0.01 second to 0. (15 seconds). Furthermore, the curing of the colored ink may be completed by a separate light source without driving. In International Publication No. 99 / 54415, as an irradiation method, a method using an optical fiber or a method of irradiating ultraviolet light to the recording unit by applying a collimated light source to a mirror provided on the side surface of the head unit is disclosed, and such a curing method can also be applied to the image forming method of the present embodiment.

Examples

[0071] Hereinafter, examples of the present disclosure will be shown, but the present disclosure is not limited to the following examples. "Part" means part by mass.

[0072] 〔Preparation of Inkjet Ink〕 ​​​​​​​​​​​​​​​​​​​​​​• NPGPODA (propoxylated neopentyl glycol diacrylate, polymerizable monomer, manufactured by Sartomer) … 45.47 copies • FIRSTCURE ST-1 (nitroso polymerization inhibitor, Tris(N-nitroso-N-phenylhydroxylamine)aluminum salt, manufactured by Albemarle) …0.3 parts

[0075] <Preparation of dispersion W2> Dispersion W2 was calcined in the same manner as the preparation of dispersion W1, except that the dispersion time using a bead mill was set to 5 hours. The volume-average particle size of titanium dioxide in dispersion W2 (simply referred to as "particle size" in Table 1) was 200 nm.

[0076] <Preparation of inks A1-A16> Each component in the composition shown in Table 1 was mixed to prepare inks A1 to A16. In Table 1, the numbers in the column for each component represent the mass percentage of the total ink volume, and a blank space indicates that the corresponding component is not present. The volume-average particle size of titanium dioxide in each ink was 300 nm. The details of each component shown in Table 1 are as follows:

[0077] -Polymerizable oligomers (polymerizable compounds with a molecular weight of 800 or higher)- Genomer4215… Manufactured by Rahn AG. Urethane acrylate (specifically, bifunctional urethane acrylate (molecular weight 5000)). • UV7630B… Nippon Synthetic Chemical Co., Ltd. "Shiko (registered trademark) UV-7630B". Urethane acrylate (specifically, hexafunctional urethane acrylate (molecular weight 2200)). • Genomer 4136… Manufactured by Rahn AG. Urethane acrylate (specifically, trifunctional urethane acrylate (molecular weight 4000)). • Genomer4622… Manufactured by Rahn AG. Urethane acrylate (specifically, hexafunctional urethane acrylate (molecular weight 915)). • Genomer2255… Manufactured by Rahn AG. A bifunctional modified epoxy acrylate (molecular weight 850). • POLYESTER ACRYLATE 03-849 … Manufactured by Rahn AG. Trifunctional polyester acrylate (molecular weight 4100)

[0078] -Polymerizable monomers (polymerizable compounds with a molecular weight of less than 800)- • IBOA… Isobornyl acrylate (molecular weight 208) • PEA… Phenoxyethyl acrylate (molecular weight 192) • NVC … N-vinylcaprolactam (molecular weight 139) • SR341… Manufactured by Sartomer. 3-methyl-1,5-pentanediol diacrylate (molecular weight 226). • SR344… Manufactured by Sartomer. Polyethylene glycol (400) diacrylate (molecular weight 508) • NPGPODA… Manufactured by Sartomer. Propoxylated neopentyl glycol diacrylate (molecular weight 328).

[0079] -Polymerization initiator- • Omnirad 819… "Omnirad 819" (bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide) manufactured by IGM Resins BV. • Omnirad 2959… "Omnirad 2959" (1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one) manufactured by IGM Resins BV. -Polymerization inhibitor- • UV22 … BASF's "IRGASTAB® UV22" (Poly[oxy(methyl-1,2-ethanediyl)]-α,α',α”-1,2,3-propanetriyltris[-[(1-oxo-2-propen-1-yl)oxy]-2,6-bis(1,1-dimethylethyl)-4-(phenylenemethylene)cyclohexa-2,5-dien-1-one]; hindered phenol polymerization inhibitor) - Surfactants - • BYK-331… "BYK® 331" (silicone-based surfactant (polyether-modified polysiloxane compound)) manufactured by BYK Chemie. -Organic Solvents- Butoxyl… 3-methoxybutyl acetate (boiling point 172°C).

[0080] [Image Recording] An inkjet printer (product name "DMP-2831 printer", manufactured by FUJIFILM Dimatix) was used as the image recording device. One of the inks A1 to A12 was applied to a 188μm Viewfull PET substrate (manufactured by KIMITO, polyethylene terephthalate sheet (thickness 188μm)), the applied ink was heated and dried at 70°C for 60 seconds, and then the heated and dried ink was cured by irradiating it with UV (ultraviolet) light using a UV (ultraviolet) irradiation device (product name "CSOT-40", one 4kW metal halide lamp, manufactured by GS Japan Storage Battery Co., Ltd.) to obtain an image. The UV irradiation energy was 900 mJ / cm². 2 That's what I decided. This image recording was performed under the conditions of an image resolution of 1500 dpi × 1500 dpi and an ink droplet size of 10 pL. The images recorded included a 10cm x 10cm solid image and a 1pt line image.

[0081] 〔evaluation〕 The following evaluations were performed on the obtained images (i.e., solid images and line images). The results are shown in Table 1.

[0082] <Image Quality> Using a dot analyzer DA6000 (manufactured by Oji Keisoku Co., Ltd.), the radius of a 1pt line image was measured, and the image quality (line quality) was evaluated according to the evaluation criteria below. In the following evaluation criteria, the highest rank for image quality is A.

[0083] -Image Quality Evaluation Criteria- A: The quality score was less than 4.0. B: The radiance score was between 4.0 and 6.0. C: The quality score was 6.0 or higher.

[0084] <Heat yellowing resistance> The substrate on which the solid image was recorded was stored at 100°C for 1000 hours. The yellow density of the solid image before and after saving was measured using an FD-7 (manufactured by Konica Minolta), and the increase in yellow density ΔY (= yellow density of the solid image after saving - yellow density of the solid image before saving) was calculated. Based on the obtained ΔY, the thermal yellowing resistance of the image (i.e., resistance to yellowing when exposed to heat) was evaluated according to the following evaluation criteria. In the following evaluation criteria, rank A represents the best performance in terms of heat yellowing resistance (i.e., resistance to yellowing when exposed to heat).

[0085] - Evaluation Criteria for Resistance to Heat Yellowing - A: ΔY is 0. B: ΔY is greater than or equal to 0 and less than 0.1. C:ΔY is 0.1 or greater.

[0086] <Resistance to light yellowing> The solid image was subjected to UV irradiation at 100,000 Lux for 1,000 hours using a low-temperature cycle xenon weathermeter XL75 (manufactured by Suga Test Instruments Co., Ltd.). The yellow density of solid images before and after UV irradiation was measured using an FD-7 (manufactured by Konica Minolta), and the increase in yellow density ΔY (= yellow density of solid image after UV irradiation - yellow density of solid image before UV irradiation) was calculated. Based on the obtained ΔY, the thermal yellowing resistance of the image (i.e., resistance to yellowing when exposed to light) was evaluated according to the following evaluation criteria. In the following evaluation criteria, rank A represents the best performance in terms of resistance to light yellowing (i.e., resistance to yellowing when exposed to light).

[0087] -Evaluation Criteria for Resistance to Light-induced Yellowing- A: ΔY is 0. B: ΔY is greater than or equal to 0 and less than 0.1. C:ΔY is 0.1 or greater.

[0088] <Abrasion resistance> A JSPS-type friction test (hereinafter also referred to as the abrasion resistance test) was performed on the solid image with a load of 500g for 100 back-and-forth cycles. The opacity of solid images before and after the scratch resistance test was measured using a Rhopoint Instruments NOVO SHADE DUO+ handheld reflectometer. Based on each concealment rate, the concealment rate difference ΔC (concealment rate after scratch resistance test - concealment rate before scratch resistance test) was calculated. In the following evaluation criteria, rank A represents the best abrasion resistance.

[0089] - Criteria for evaluating abrasion resistance - A: ΔC is 0. B: ΔC is between 0 and 5 (inclusive). C:ΔC is 10 or greater.

[0090] [Table 1]

[0091] As shown in Table 1, the ink of the example contains a pigment (A), an organic solvent (B), a polymerizable compound (C), and a polymerization initiator (D), wherein the pigment (A) contains a white pigment, with the proportion of the white pigment in the pigment (A) being 95% by mass or more, the polymerizable compound (C) contains a polymerizable oligomer which is a polymerizable compound with a molecular weight of 800 or more, with the proportion of the polymerizable oligomer in the polymerizable compound (C) being 30% by mass or more, and the proportion of the organic solvent (B) in the ink being 50% by mass or more. With this ink, it was possible to record white images with excellent image quality and scratch resistance, as well as excellent resistance to heat yellowing and light yellowing. In contrast, ink A13 (comparative example), in which the proportion of organic solvent (B) in the ink was less than 50% by mass, showed reduced resistance to heat yellowing and light yellowing. In inks A14 to A16 (all comparative examples), in which the proportion of polymerizable oligomers in polymerizable compound (C) was less than 30% by mass, heat yellowing resistance and light yellowing resistance were also reduced.

[0092] In a comparison between inks A1 and A11, ink A1, which contains 80% or more urethane acrylate in its polymerizable oligomer, exhibited superior resistance to thermal and light-induced yellowing of white images.

[0093] In a comparison of inks A1, A7, and A9, inks A1 and A9, which have a mass ratio of polymerizable oligomer / white pigment of 0.5 or higher, exhibited superior scratch resistance for white images. In a comparison of inks A1, A6, and A8, inks A1 and A8, which have a mass ratio of polymerizable oligomer / white pigment of 2.0 or less, showed superior resistance to thermal and light-induced yellowing of white images.

[0094] In a comparison of inks A1 and A12, ink A1, in which the volume-average particle size of the white pigment is 250 nm or larger, exhibited superior scratch resistance and opacity of white images.

Claims

1. The ink contains a pigment (A), an organic solvent (B), a polymerizable compound (C), and a polymerization initiator (D), the pigment (A) contains a white pigment, and the proportion of the white pigment in the pigment (A) is 95 mass% or more; the polymerizable compound (C) contains a polymerizable oligomer that is a polymerizable compound having a molecular weight of 800 or more, and the proportion of the polymerizable oligomer in the polymerizable compound (C) is 30 mass% or more; the proportion of the organic solvent (B) in the inkjet ink is 50% by mass or more; Inkjet ink.

2. The ink-jet ink of claim 1 , wherein the white pigment comprises titanium dioxide.

3. 3. The ink-jet ink according to claim 1, wherein the white pigment has a volume average particle size of 250 nm or more.

4. 4. The ink-jet ink according to claim 1, wherein the polymerizable oligomer contains a urethane acrylate, and the proportion of the urethane acrylate in the polymerizable oligomer is 80% by mass or more.

5. 5. The ink-jet ink according to claim 1, wherein the mass ratio of the polymerizable oligomer to the white pigment is 0.5 to 2.

0.

6. The ink-jet ink according to any one of claims 1 to 5, wherein the organic solvent (B) comprises an organic solvent having a boiling point of 200°C or less.

7. an ink applying step of applying the inkjet ink according to any one of claims 1 to 6 onto a substrate by an inkjet method; a heating step of heating the inkjet ink applied to the substrate to a temperature of 50°C or higher; an irradiation step of irradiating the heated inkjet ink with active energy rays; An image recording method comprising: