Inkjet ink composition and inkjet recording method

Abstract

To provide an inkjet ink composition excellent in gloss, discharge stability, and storage stability.SOLUTION: An inkjet ink composition includes a metallic pigment and a liquid medium. The liquid medium includes one or more selected from the group consisting of an organic solvent and water. The metallic pigment is surface-modified with a predetermined surface treatment agent. The metallic pigment is a scaly particle. A volume average particle diameter D50 (μm) of the metallic pigment is 1.0 μm or smaller. A ratio (D50 / Z) of the volume average particle diameter D50 (μm) to an average thickness Z (μm) of the metallic pigment is 17 or larger. The inkjet ink composition is used for recording by being discharged from an inkjet head. A ratio (D50 / L) of the volume average particle diameter D50 (μm) to a nozzle diameter L (μm) of the inkjet head is 0.050 or smaller.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Metallic pigment compositions using metallic pigments are being developed in various fields, such as inkjet printing and coatings, to provide recordings and substrates with excellent metallic luster, making them suitable for specific applications.

[0003] For example, Patent Document 1 discloses a non-aqueous inkjet composition containing surface-treated metal powder and having a predetermined dissolved oxygen reduction rate, with the aim of providing an ink composition that is excellent in ejection stability and storage stability even when an ink composition containing metal powder is used. Patent Document 1 discloses that ejection stability and storage stability are improved by surface treatment so that the surface of the metal powder has the activity necessary to react with oxygen contained in the composition and the activity to the extent that it does not react with water, etc. contained in the composition. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2017-43722 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, it was still insufficient in terms of gloss and dispensing stability. [Means for solving the problem]

[0006] The inkjet ink composition of the present invention contains a metal pigment and a liquid medium, the liquid medium contains one or more selected from the group consisting of an organic solvent and water, the metal pigment is surface-modified with a surface treatment agent, and the surface treatment agent contains one or more selected from the group consisting of a compound represented by the following formula (1) and a compound represented by the following formula (2). The metal pigment is a scaly particle. The volume average particle diameter D ,

[0007] , 50 , , , , 50 , 2 , , (μm) is 1.0 μm or less, The ratio (D 50 (μm)) of the volume average particle diameter D 50 to the average thickness Z (μm) of the metal pigment is 17 or more, and it is used for recording by discharging from an inkjet head. The ratio (D 50 (μm)) of the volume average particle diameter D 50 to the nozzle diameter L (μm) of the inkjet head is 0.050 or less. It is an inkjet ink composition. (R 1 -)P(O)(OH)2(1)<关于公式编号的内容,保留原文编号 (In the above formula (1), R 1 is a hydrocarbon group having 14 or more carbon atoms which may be substituted with a substituent.)<关于公式编号的内容,保留原文编号 (R 2 -O-) a P(O)(OH) 3-a (2)<关于公式编号的内容,保留原文编号 (In the above formula (2), R 2 are each independently a hydrocarbon group having a carbon skeleton of 14 or more carbon atoms which may be substituted with a substituent, and a is 1 or 2.)<关于公式编号的内容,保留原文编号 <关于公式编号的内容,保留原文编号

[0007] <关于公式编号的内容,保留原文编号 The inkjet recording method of the present invention includes an attaching step of discharging the above inkjet ink composition from an inkjet head having a nozzle diameter L (μm) and attaching it to a recording medium.<关于公式编号的内容,保留原文编号 The ratio (D 50 (μm)) of the volume average particle diameter D 50 to the nozzle diameter L (μm) is 0.050 or less.<关于公式编号的内容,保留原文编号

Brief Description of the Drawings

[0008] [Figure 1] This figure shows an example of a recording device used in the adhesion method of this embodiment. [Figure 2] This figure shows a cross-sectional view of a key part of an example of an inkjet head used in this embodiment. [Modes for carrying out the invention]

[0009] The embodiments of the present invention (hereinafter referred to as "these embodiments") will be described in detail below, with reference to the drawings as necessary. However, the present invention is not limited thereto, and various modifications are possible without departing from its essence. In the drawings, the same elements will be denoted by the same reference numerals, and redundant explanations will be omitted. Furthermore, unless otherwise specified, positional relationships such as up, down, left, and right will be based on the positional relationships shown in the drawings. Moreover, the dimensional ratios in the drawings are not limited to those shown.

[0010] 1. Inkjet ink composition The inkjet ink composition of this embodiment comprises a metal pigment and a liquid medium, wherein the liquid medium comprises one or more selected from the group consisting of organic solvents and water, the metal pigment is surface-modified with a surface treatment agent, the surface treatment agent comprises one or more selected from the group consisting of compounds represented by the following formula (1) and compounds represented by the following formula (2), the metal pigment is in the form of flake particles, and the volume average particle diameter D of the metal pigment 50 The (μm) is 1.0 μm or less, and the volume-average particle size D is the average thickness Z (μm) of the metal pigment. 50 (μm) ratio (D 50 The volume-average particle diameter D is 17 or greater, ejected from the inkjet head for recording, and the volume-average particle diameter D is 17 or greater relative to the nozzle diameter L (μm) of the inkjet head. 50 (μm) ratio (D 50 The value of / L is 0.05 or less. (R 1 -)P(O)(OH)2(1) (In the above formula (1), R 1(This refers to a hydrocarbon group having 14 or more carbon atoms, which may be substituted with substituents.) (R 2 -O-) a P(O)(OH) 3-a (2) (In the above equation (2), R 2 Each of these is an independent hydrocarbon group having a carbon skeleton with 14 or more carbon atoms, which may be substituted with substituents, and a is 1 or 2.

[0011] Conventionally, inkjet ink compositions containing metal pigments surface-treated with fluorine-based surface treatment agents have been studied with the aim of improving ejection stability and storage stability. However, there was still room for further investigation into improving ejection stability when ejected at high temperatures and storage stability when stored for long periods at high temperatures. Furthermore, even better gloss is desired. In addition, there is a need for the development of ink components that are environmentally friendly while pursuing excellent metallic gloss.

[0012] Furthermore, thin, flaky (flat) metallic pigments have been developed with the aim of further improving gloss. In this way, the larger the surface area of ​​each metallic pigment particle and the thinner it is, the larger the surface area of ​​the metallic pigment per unit mass. This makes it easier for the flaky metallic particles to orient themselves so that their plane is more parallel to the plane of the recording medium, and the resulting recording material has superior gloss as the flaky metallic particles form a glossy layer. This orientation is also called "leafing."

[0013] However, while such flaky metallic pigments improve the gloss of the resulting recordings, they tend to aggregate easily and have reduced ejection stability. Furthermore, aggregation can sometimes prevent the desired gloss from being achieved.

[0014] Furthermore, when ink passes through a narrow channel, the surface direction of the flake-like particles is aligned with the direction of ink flow. This allows the flake-like particles to move within the ink channel without resisting the flow of ink. On the other hand, if flake-like particles stack on their main surface to form coarse particles, the surface direction of the flake-like particles will not be aligned with the direction of ink flow, making it difficult for them to move within the ink channel and potentially reducing the ejection stability.

[0015] In contrast, the inkjet ink composition of this embodiment can improve gloss, ejection stability, and storage stability by including a metal pigment having a predetermined shape and surface-treated with a predetermined surface treatment agent, and a liquid medium, etc.

[0016] The inkjet ink composition and the inkjet recording method thereof according to this embodiment will be described in detail below.

[0017] 1.1. Metallic Pigments The metal pigment of this embodiment is surface-treated with a predetermined surface treatment agent described later, and is in the form of flake-like particles, with a volume-average particle diameter D of the above metal pigment. 50 The (μm) is 1.0 μm or less, and the volume-average particle size D is the average thickness Z (μm) of the metal pigment. 50 (μm) ratio (D 50 The volume-average particle diameter D is 17 or greater, ejected from the inkjet head for recording, and the volume-average particle diameter D is 17 or greater relative to the nozzle diameter L (μm) of the inkjet head. 50 (μm) ratio (D 50 The value of / L is 0.05 or less.

[0018] The relationship between the metal pigment and the surface treatment agent in this embodiment is not particularly limited, but for example, the metal particles and the surface treatment agent may be chemically bonded by surface modification with a specific surface treatment agent described later, through which the -OH groups on the surface of the metal pigment react with the phosphate groups or phosphonic acid groups of the surface treatment agent.

[0019] The metallic pigment is not particularly limited, but for example, the entire metallic pigment may be made of a metallic material, or it may have a base made of a non-metallic material and a coating made of a metallic material covering the surface of the base. The base made of a non-metallic material may be, for example, a flaky resin, and its entire surface may be coated with a metallic material.

[0020] The content of the metal pigment may preferably be 0.1% by mass or more, 0.3% by mass or more, 0.5% by mass or more, 1.0% by mass or more, or 1.5% by mass or more, relative to the total amount of the inkjet ink composition. Furthermore, the content of the metal pigment may preferably be 20% by mass or less, 15% by mass or less, 10% by mass or less, 5.0% by mass or less, 3.0% by mass or less, or 2.0% by mass or less, relative to the total amount of the inkjet ink composition.

[0021] 1.1.1. Constituent Materials The metal species constituting the metallic pigment is not particularly limited, but for example, elemental metals and various alloys can be used. Examples of such metallic species include aluminum, silver, gold, platinum, nickel, chromium, tin, zinc, indium, titanium, iron, and copper. Among these, it is preferable that the metallic pigment includes one or more selected from the group consisting of aluminum and aluminum alloys. This tends to result in particularly excellent gloss among various metallic materials, and also exhibits excellent ejection stability and storage stability due to its relatively low specific gravity compared to other metallic materials. Furthermore, it is also excellent in suppressing the increase in production costs of colored products manufactured using the inkjet ink composition. Note that the metallic pigment may be used alone or in combination of two or more types.

[0022] 1.1.2.Shape As for the shape of metal pigments, the ratio (D 50 / Z) and ratio (D 50While the range of / L is not particularly limited, the metal pigment may be of any shape, such as flake (flat), spherical, spindle-shaped, or needle-shaped. Among these, the metal pigment is preferably flake-shaped, and more preferably, the metal pigment is flake-shaped and thin. When the metal pigment is flake-shaped, the gloss of the resulting colored material tends to be further improved because the broad surface area of ​​the particles is arranged along the surface of the recording medium.

[0023] In particular, when the metallic pigment is in the form of flakes and is thin, the number of metallic pigment particles increases compared to other embodiments containing the same mass of metallic pigment, and the total surface area of ​​the metallic pigment increases. Therefore, when the metallic pigment is in the form of flakes and is thin, it tends to leaf out easily when colored and has a superior gloss.

[0024] In this embodiment, "scaly" refers to a shape such as a flat plate or a curved plate, where, when observed from a predetermined angle, for example, the area when viewed from a plan view is larger than the area when observed from an angle perpendicular to the observation direction. As an indicator of such a scaly shape, the area S1 [μm²] when observed from the direction in which the projected area is maximized, i.e., the area when viewed from a plan view. 2 ] and the area S0 [μm²] observed from the direction perpendicular to the observation direction that yields the largest observed area. 2 A ratio S1 / S0 can be used for ]. The ratio S1 / S0 is preferably 2 or more. More preferably 2 to 1000, more preferably 5 to 500, even more preferably 8 to 100, and even more preferably 10 to 80.

[0025] In calculating S1 / S0, there are no particular limitations, but for example, observations can be made on any 50 particles of the metal pigment, and the average value of the calculated values ​​for these particles can be adopted. Such observations are not particularly limited, but can be performed using, for example, electron microscopy or atomic force microscopy (hereinafter also referred to as AFM). Alternatively, the volume-average particle diameter D relative to the average thickness Z (μm) of the metal pigment, as described later, can be used.50 (μm) ratio (D 50 The value of / Z) can be calculated and used as an indicator of scaly growth within the above range.

[0026] When metal pigments are flaky, it tends to be difficult to improve their discharge stability even after surface treatment. However, according to this embodiment, even when metal pigments are flaky, it is possible to improve discharge stability while ensuring excellent gloss due to the flaky shape.

[0027] Unless otherwise specified, the physical properties of pigment particles observed below are based on the AFM method. While not specifically limited to this method, an atomic force microscope such as the NanoNavi E-Sweep (manufactured by SII Nanotechnology Co., Ltd.) can be used.

[0028] 1.1.3. Thickness The average thickness Z of the metal pigment is preferably 100 nm or less, more preferably 50 nm or less, even more preferably 30 nm or less, even more preferably 25 nm or less, and even more preferably 20 nm or less. Furthermore, the average thickness Z of the metal pigment is preferably 1 nm or more, more preferably 3 nm or more, and even more preferably 5 nm or more. An average thickness of 100 nm or less of the metal pigment tends to result in superior gloss.

[0029] 1.1.4. Volume-average particle diameter Volume average particle size D of metallic pigments 50 The volume average particle size D of the metal pigment is preferably 1.5 μm or less, more preferably 1.0 μm or less, even more preferably 0.8 μm or less, and even more preferably 0.6 μm or less. Furthermore, 0.5 μm or less is preferred, and 0.4 μm or less is more preferred. 50 The volume average particle diameter D is preferably 0.1 μm or larger, more preferably 0.2 μm or larger, and even more preferably 0.3 μm or larger. 50 When the volume average particle size is 1.5 μm or less, the dispensing stability tends to improve further. 50When the thickness is 0.1 μm or greater, gloss tends to improve further.

[0030] Note that the volume-average particle diameter D 50 This refers to the median diameter of the volume distribution of a particle dispersion measured using laser diffraction and scattering. When multiple measurement results are expressed as the cumulative abundance ratio for each size, it is the particle size that represents exactly 50% of the median value in the cumulative distribution. If the metal particles are flaky, the volume-average particle diameter is determined based on the shape and size of the metal particles when converted to a spherical form.

[0031] Volume-average particle size D relative to the average thickness Z (μm) of the metallic pigment 50 (μm) ratio (D 50 / Z) is 17 or more, preferably 17 to 60, more preferably 20 to 48, and even more preferably 25 to 40. 50 A / Z value of 17 or higher tends to result in superior gloss.

[0032] Furthermore, the volume-average particle size D of the metal pigment relative to the nozzle diameter L (μm) of the inkjet head of a recording device used for recording by ejecting from the inkjet head. 50 (μm) ratio (D 50 / L) is 0.050 or less, preferably 0.010 to 0.050, more preferably 0.015 to 0.040, and even more preferably 0.020 to 0.030. D 50 A value of 0.050 or less per liter tends to indicate superior discharge stability.

[0033] Here, the nozzle diameter L (μm) of the inkjet head used simultaneously with the inkjet ink composition of this embodiment is preferably 40 μm or less, more preferably 5 μm to 30 μm, even more preferably 10 μm to 30 μm, and even more preferably 15 μm to 30 μm.

[0034] 1.2. Surface treatment agents The surface treatment agent of this embodiment is used for surface treatment of the metal pigment of this embodiment and contains one or more compounds selected from the group consisting of compounds represented by formula (1) and compounds represented by formula (2). Among these, the compound represented by formula (1) is preferred from the viewpoint of excellent gloss, discharge stability, and storage stability. The surface treatment agent may be used alone or in combination of two or more types. (R 1 -)P(O)(OH)2(1) (In the above formula (1), R 1 (This refers to a hydrocarbon group having 14 or more carbon atoms, which may be substituted with substituents.) (R 2 -O-) a P(O)(OH) 3-a (2) (In the above equation (2), R 2 Each of these is an independent hydrocarbon group having 14 or more carbon atoms, which may be substituted with substituents, and a is 1 or 2.

[0035] As described above, the surface treatment agent has a hydrophilic phosphate group or phosphonic acid group and a hydrophobic hydrocarbon group. The reason why treating metal pigments with the surface treatment agent of this embodiment results in excellent gloss, discharge stability, and storage stability is thought to be, for example, that the phosphate group or phosphonic acid group chemically bonds with the OH groups on the surface of the metal pigment through reaction. Furthermore, it is thought that the hydrophobic groups that do not participate in bonding with the metal pigment surface moderately cover the surface of the metal pigment, thereby improving gloss, discharge stability, and storage stability.

[0036] In the above equations (1) and (2), R 1 and R 2 Each of these is a hydrocarbon group having 14 or more carbon atoms, which may be substituted with substituents. A hydrocarbon group having 14 or more carbon atoms is a hydrocarbon group having a skeleton in which 14 or more carbon atoms are bonded in succession. Here, R 1 and R 2 The carbon number does not include the carbon number of substituents.

[0037] The types of substituents are not particularly limited, but examples include carboxyl groups, hydroxyl groups, amino groups, oxyalkylene groups, etc. 1 and R 2 In each case, some of the hydrogen atoms of the hydrocarbon group may be substituted by such substituents, but R 1 and R 2 The number of substituents on each group is preferably 1 or less (including unsubstituted hydrocarbon groups), and more preferably unsubstituted.

[0038] Also, R 1 and R 2 The hydrocarbon group may be a saturated hydrocarbon group that does not have double or triple bonds between carbon atoms, or an unsaturated hydrocarbon group that has double or triple bonds between carbon atoms. Furthermore, the hydrocarbon group may be an aromatic hydrocarbon group whose carbon skeleton has an aromatic ring structure, or a chain-like or cyclic aliphatic hydrocarbon group, etc.

[0039] Among them, R 1 and R 2 The aliphatic hydrocarbon group is preferably a chain-like aliphatic hydrocarbon group. The chain-like aliphatic hydrocarbon group includes branched-chain and linear types, but is preferably linear.

[0040] Such R 1 and R 2 Specific examples include, but are not limited to, n-tetradecyl group, n-pentadecyl group, n-hexadecyl group (n-cetyl group), n-heptadecyl group, n-octadecyl group, n-nonadecyl group, n-icosyl group, n-tetracosyl group, and so on.

[0041] Furthermore, in formula (1), the hydrocarbon group R 1 In R, one of the carbon atoms is directly bonded to the phosphorus atom in formula (1), but 1 In this, the carbon atom directly bonded to the phosphorus atom is preferably R 1 It is the carbon atom at the end of the molecular chain.

[0042] Similarly, in formula (2), the hydrocarbon group R 2 If any of the carbon atoms in is (R) of formula (2) 2 It is directly bonded to the oxygen atom in -O-), and that oxygen atom is directly bonded to the phosphorus atom of P, but R 2 The atom directly bonded to the oxygen atom in is preferably R 2 It is the carbon atom at the end of the molecular chain.

[0043] R 1 and R 2 The carbon number is 14 or more, preferably 15 to 30, more preferably 16 to 27, even more preferably 17 to 25, and even more preferably 18 to 24, from the viewpoint of excellent gloss, discharge stability, and storage stability.

[0044] The content of the surface treatment agent is preferably 1.0% to 50% by mass, more preferably 3.0% to 40% by mass, even more preferably 5.0% to 30% by mass, and even more preferably 10% to 20% by mass, relative to the total amount of metal pigment in this embodiment. A surface treatment agent content within the above range tends to result in excellent discharge stability and storage stability.

[0045] 1.3.Liquid medium The inkjet ink composition of this embodiment includes a liquid medium. The liquid medium refers to a liquid component that can disperse solutes such as metal particles. It is also called a solvent component. The components of the liquid medium are not particularly limited, but examples include water and various organic solvents.

[0046] The inkjet ink composition of this embodiment may be an aqueous composition containing water as the main liquid medium component, or a solvent-based composition containing an organic solvent as the main liquid medium component. An aqueous composition is defined as a composition containing water as the main liquid medium component. The water content is preferably 40% by mass or more of the total amount of the composition.

[0047] Furthermore, a solvent-based composition is a composition that contains an organic solvent as the main liquid medium component. The content of the organic solvent is preferably 60% by mass or more of the total amount of the composition. The water content of the solvent-based composition is preferably 2% by mass or less, more preferably 1% by mass or less, even more preferably 0.5% by mass or less, and the lower limit is 0% by mass.

[0048] When the inkjet ink composition is an aqueous or solvent-based composition, it is preferable because the viscosity of the ink can be relatively low, resulting in excellent ejection stability and a glossy finish that allows the ink to leaf easily.

[0049] The inkjet ink composition of this embodiment is preferably not an ultraviolet-curing composition.

[0050] The liquid medium content may preferably be 60% by mass or more, 70% by mass or more, or 80% by mass or more, relative to the total amount of the inkjet ink composition. Alternatively, the liquid medium content may preferably be 98% by mass or less, 90% by mass or less, or 80% by mass or less, relative to the total amount of the inkjet ink composition.

[0051] If the inkjet ink composition is an aqueous composition, the water content may be 30% by mass or more, preferably 40% by mass or more, 50% by mass or more, 60% by mass or more, 70% by mass or more, or 80% by mass or more, relative to the total amount of the liquid medium. Alternatively, the water content may be preferably 98% by mass or less, preferably 90% by mass or less, 80% by mass or less, 70% by mass or less, 60% by mass or less, 50% by mass or less, or 40% by mass or less, relative to the total amount of the liquid medium.

[0052] If the inkjet ink composition is an aqueous composition, the water content is preferably more than 40% by mass of the total amount of the inkjet ink composition, and may be 50% by mass or more, 60% by mass or more, 70% by mass or more, or 80% by mass or more. Furthermore, the water content may be preferably 98% by mass or less, 90% by mass or less, 80% by mass or less, 70% by mass or less, 60% by mass or less, or 50% by mass or less of the total amount of the liquid medium.

[0053] The aqueous composition may further contain an organic solvent as a liquid medium component. The content of the organic solvent may be 40% by mass or less, preferably 30% by mass or less, 20% by mass or less, or 15% by mass or less, based on the total amount of the aqueous composition. Furthermore, the content of the organic solvent may be 0% by mass or more, preferably 0.5% by mass or more, 1% by mass or more, or 5% by mass or more, based on the total amount of the aqueous composition.

[0054] When the inkjet ink composition of this embodiment is a solvent-based composition, the content of the organic solvent may be 70% by mass or more, preferably 80% by mass or more, 90% by mass or more, or 98% by mass or more, based on the total amount of the liquid medium. Alternatively, the content of the organic solvent may be preferably 98% by mass or less, preferably 90% by mass or less, or 80% by mass or less, based on the total amount of the liquid medium.

[0055] Furthermore, if the inkjet ink composition is a solvent-based composition, the content of the organic solvent is preferably 60% by mass or more, but may be 70% by mass or more, 80% by mass or more, or 90% by mass or more, based on the total amount of the inkjet ink composition. Also, the content of the organic solvent is preferably 98% by mass or less, 90% by mass or less, or 80% by mass or less, based on the total amount of the inkjet ink composition.

[0056] 1.3.1. Organic Solvents The inkjet ink composition of this embodiment may contain a water-soluble organic solvent. Such organic solvents are not particularly limited and may include, for example, alcohols, hydrocarbon compounds, ether compounds, glycol ethers, ketones, esters, propylene carbonate, N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, cyclohexanone, acetonitrile, and the like.

[0057] Among these, when the inkjet ink composition of this embodiment is an aqueous composition, it is preferable to use a glycol-based compound as the organic solvent. By using a glycol-based compound, the gloss, ejection stability, and storage stability of the resulting recorded material tend to be further improved as a synergistic effect with the surface treatment agent described above. Note that one type of organic solvent may be used alone, or two or more types may be used in combination.

[0058] The organic solvent is not particularly limited, but examples include monoalcohol compounds such as methanol, ethanol, n-propyl alcohol, iso-propyl alcohol, n-butanol, 2-butanol, tert-butanol, iso-butanol, n-pentanol, 2-pentanol, 3-pentanol, and tert-pentanol; 1,2-hexanediol, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,3-propanediol, and 1,2-butanediol. Examples include glycol compounds such as 1,2-pentanediol, 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol; aromatic alcohol compounds such as 2-phenoxyethanol, phenoxydiglycol, (methoxyphenoxy)ethanol, methylphenoxyethanol, bis(β-hydroxyethyl)hydroquinone ether, nonylphenol, phenol, cresol, resorcinol, catechol, hydroquinone, naphthol, and furfuryl alcohol; and polyhydric alcohol compounds such as glycerin.

[0059] Among these, it is preferable that the inkjet ink composition contains at least one glycol-based compound as an organic solvent, and it is preferable to use two or more in combination. By using such alcohol compounds as organic solvents, the gloss, ejection stability, and storage stability of the resulting recorded material tend to be further improved as a synergistic effect with the surface treatment agent mentioned above. Furthermore, from a similar viewpoint, it is preferable to use at least one of 1,2-hexanediol and propylene glycol, and it is more preferable to use both 1,2-hexanediol and propylene glycol.

[0060] On the other hand, if the inkjet ink composition of this embodiment is a solvent-based composition, it is preferable to use one or more organic solvents selected from the group consisting of glycol ethers and esters as the organic solvent. By using glycol ethers and / or esters, the gloss, ejection stability, and storage stability of the resulting recorded material tend to be further improved as a synergistic effect with the surface treatment agent described above. Note that one type of organic solvent may be used alone, or two or more types may be used in combination.

[0061] Glycol ethers are not particularly limited, but examples include triethylene glycol monomethyl ether, triethylene glycol dimethyl ether, triethylene glycol monobutyl ether, diethylene glycol monobutyl ether, diethylene glycol diethyl ether, dipropylene glycol monopropyl ether, tetraethylene glycol monobutyl ether, and the like.

[0062] Examples of esters include ethyl acetate, propyl acetate, and butyl acetate, although these are not particularly limited. Examples of esters include cyclic esters. Examples of cyclic esters include lactones such as γ-butyrolactone, although these are not particularly limited.

[0063] By using such glycol ethers and / or esters as organic solvents, the gloss, ejection stability, and storage stability of the resulting recordings tend to be further improved as a synergistic effect with the surface treatment agents mentioned above.

[0064] Furthermore, from a similar viewpoint, it is preferable to use one or more selected from the group consisting of diethylene glycol diethyl ether, tetraethylene glycol monobutyl ether, and γ-butyrolactone, more preferably two or more, and even more preferably three or more.

[0065] 1.4. Resin The inkjet ink composition of this embodiment may further contain a resin. While not particularly limited, examples of such resins include urethane resins, acrylic resins (including styrene-acrylic resins), fluorene resins, polyolefin resins, rosin-modified resins, terpene resins, polyester resins, polyamide resins, epoxy resins, vinyl chloride resins, vinyl chloride-vinyl acetate copolymers, ethylene vinyl acetate resins, and resin particles. Among these, urethane resins, acrylic resins, polyolefin resins, and polyester resins are preferred. These resin particles are often handled in emulsion form, but may also be supplied in powder form. Furthermore, the resin particles can be used individually or in combination of two or more types.

[0066] Urethane resins are a general term for resins that have urethane bonds. There are no particular limitations on urethane resins, but for example, polyether-type urethane resins containing ether bonds in the main chain in addition to urethane bonds, polyester-type urethane resins containing ester bonds in the main chain, and polycarbonate-type urethane resins containing carbonate bonds in the main chain may also be used.

[0067] Acrylic resins are a general term for polymers obtained by polymerizing at least one acrylic monomer, such as (meth)acrylic acid or (meth)acrylic acid ester, and are not particularly limited. Examples include resins obtained from acrylic monomers and copolymers of acrylic monomers with other monomers. For example, acrylic-vinyl resins, which are copolymers of acrylic monomers and vinyl monomers, are examples. Examples of vinyl monomers include styrene.

[0068] The resin content is preferably 0.02% by mass or more and 0.20% by mass or less, more preferably 0.08% by mass or more and 0.12% by mass or less, and even more preferably 0.06% by mass or more and 0.16% by mass or less, relative to the total amount of the inkjet ink composition.

[0069] 1.5. Method for Manufacturing Metallic Pigments The method for preparing the metal pigment is not particularly limited, and known methods can be used. Such methods are not particularly limited, but for example, a metal film can be formed on one side of a sheet-like substrate using a vapor deposition method, and then the metal film can be peeled off and pulverized from the sheet-like substrate to obtain a flaky metal pigment. This vapor deposition method allows for the production of a flaky metal pigment with less variation in film thickness and high surface flatness, thereby more effectively exhibiting the metallic luster and other properties inherent to the metal pigment. The thickness of the thin film corresponds to the thickness of the flaky metal pigment. Furthermore, the metal pigment obtained in this way may be classified as needed to adjust its particle size distribution as desired. In addition, ion plating or sputtering may be used instead of the vapor deposition method described above.

[0070] Furthermore, when preparing metallic pigments made of aluminum or aluminum alloys, it is preferable to prepare them by crushing a film formed by vapor deposition, from the viewpoint of more effectively expressing their luster and other properties. This method can also be used when preparing relatively thin metallic pigments.

[0071] The sheet-like substrate used in the above vapor deposition method is not particularly limited, but for example, a plastic film such as polyethylene terephthalate (PET) can be used. In addition, a release agent such as silicone oil may be applied to the film-forming surface of the sheet-like substrate in advance to improve release properties, or a release resin layer may be formed. The resin used for the release resin layer is not particularly limited, but examples include polyvinyl alcohol, polyvinyl butyral, polyethylene glycol, polyacrylic acid, polymethacrylic acid, polyacrylic acid ester, polymethacrylic acid ester, polyacrylamide, cellulose derivatives such as cellulose acetate butyrate, and modified nylon resin.

[0072] The peeling and pulverization of metal films are not particularly limited, but are carried out by applying external force, for example, by irradiating the film with ultrasound in an organic solvent or by stirring it with a homogenizer. The organic solvent used is not particularly limited, but examples include alcohols such as methanol, ethanol, propanol, and butanol; hydrocarbon compounds such as n-heptane, n-octane, decane, dodecane, tetradecane, toluene, xylene, cymene, durene, indene, dipentene, tetrahydronaphthalene, decahydronaphthalene, and cyclohexylbenzene; and ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol methyl ethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, and diethylene glycol methyl ethyl ether. Ether compounds such as ether, diethylene glycol monobutyl ether acetate, diethylene glycol n-butyl ether, tripropylene glycol dimethyl ether, triethylene glycol diethyl ether, propylene glycol monomethyl ether acetate, 1,2-dimethoxyethane, bis(2-methoxyethyl) ether, and p-dioxane; polar organic solvents such as propylene carbonate, γ-butyrolactone, N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, cyclohexanone, and acetonitrile can be suitably used. By using such organic solvents, it is possible to prevent unintended oxidation of metal pigments while reducing variations in size, shape, and properties between individual particles.

[0073] 1.6. Surface treatment method When metal pigments are used after surface treatment, known surface treatment methods can be used. While not particularly limited, such methods can be used, for example, by adding a surface treatment agent to a dispersion in which the metal pigment is dispersed in an organic solvent and irradiating it with ultrasound, the surface treatment agent can be bonded to the surface of the metal pigment. The amount of surface treatment agent used can be appropriately added in the amounts described above. Furthermore, heating may be performed when surface treatment is carried out using ultrasound. The heating temperature is preferably 40°C or higher, and more preferably 50°C or higher. It is believed that heating at such temperatures causes the surface of the metal pigment and the surface treatment agent to form covalent bonds, thereby increasing the bonding strength.

[0074] Furthermore, while the above-mentioned surface treatment agent may be applied directly to the surface of the metal pigment, it may also be applied to a metal pigment that has been pre-treated with an acid or base. This allows for more reliable chemical modification of the metal pigment surface by the surface treatment agent, and enables the effects of the present invention described above to be expressed more effectively. In addition, treatment with an acid or base can remove the oxide film of the metal pigment, thereby improving its glossiness.

[0075] The acid used for pretreatment is not particularly limited, but examples include hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, boric acid, acetic acid, carbonic acid, formic acid, benzoic acid, chlorous acid, hypochlorous acid, sulfurous acid, hyposulfurous acid, nitrite, hyponitrite, phosphorous acid, and hypophosphorous acid. On the other hand, the base used for pretreatment is not particularly limited, but examples include sodium hydroxide, potassium hydroxide, and calcium hydroxide.

[0076] 1.7. Other Ingredients The inkjet ink composition may contain components other than those described above. Such components are not particularly limited, but examples include leveling agents, binders, surfactants, penetration enhancers, humectants, chelating agents, etc., which can be added as appropriate and as needed.

[0077] 2. Inkjet recording method The inkjet recording method of this embodiment includes an adhesion step of ejecting the inkjet ink composition from an inkjet head having a nozzle diameter L (μm) and adhering it to a recording medium, wherein the volume average particle diameter D of the inkjet composition is relative to the nozzle diameter L (μm). 50 (μm) ratio (D 50 An inkjet recording method having a value of 0.05 or less (L) comprises the following adhesion steps. It may also include other steps as needed.

[0078] 2.1. Adhesion Process In the adhesion process, an inkjet ink composition (hereinafter also simply referred to as "ink") is ejected from the inkjet head and adhered to the recording medium. More specifically, a pressure generating means provided within the inkjet head is driven to eject the ink filled in the pressure generating chamber of the inkjet head from the nozzle. This ejection method is also called the inkjet method.

[0079] Inkjet heads used in the deposition process include line heads that record using a line method and serial heads that record using a serial method.

[0080] In a line-type system using a line head, for example, an inkjet head with a width greater than the recording width of the recording medium is fixed to the recording device. The recording medium is then moved along the sub-scanning direction (the direction in which the recording medium is transported), and ink droplets are ejected from the nozzles of the inkjet head in conjunction with this movement, thereby recording an image on the recording medium.

[0081] In a 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 along the main scanning direction (the width direction of the recording medium), and ink droplets are ejected from the nozzles of the inkjet head in conjunction with this movement, thereby recording an image on the recording medium.

[0082] 2.2.Primary heating process The inkjet recording method according to this embodiment preferably includes a heating step, which is a step of rapidly heating the ink adhering to the recording medium. In the heating step, at least a portion of the liquid medium of the inkjet ink composition adhering to the recording medium is dried to the extent that the flow of the ink is reduced. The heating step may be performed so that the ink adheres to the heated recording medium, or it may be performed so that the ink adheres to the recording medium immediately after adhesion. Furthermore, it is preferable to perform the heating step for each inkjet ink composition to be adhered. It is preferable to start heating the ink droplet within 0.5 seconds after the ink droplet adheres to the recording medium. Such a heating step is a heating step in the ink adhesion step and is also called a primary heating step.

[0083] Having a primary heating step is preferable because it allows the ink composition to dry quickly on the recording medium, thereby suppressing ink bleeding. For example, without a primary heating step, ink droplets adhering to the recording medium remain wet for some time, causing them to clump together and resulting in bleeding and degradation of image quality. This tendency is particularly pronounced when the ink is an aqueous or solvent-based composition. Furthermore, in inkjet recording methods, recording may be performed using inks such as black ink, cyan ink, yellow ink, and magenta ink in addition to the inkjet ink composition of this embodiment. These inks are particularly prone to image quality degradation when a primary heating step is not present. For this reason, it is preferable that the recording method includes a primary heating step.

[0084] In the heating process, it is preferable to use an IR heater, microwave radiation, a platen heater, or a fan to blow warm air onto the recording medium.

[0085] The heating step can be performed before the ink application step, simultaneously with the application, or shortly after the application, and it is preferable that it be performed simultaneously. The ink application step can be carried out with this heating sequence.

[0086] The heating temperature of the recording medium and the recorded material in the heating process is preferably 30°C to 50°C, and more preferably 40°C to 50°C. The above heating temperature is the surface temperature of the recording medium at the time of ink application if heating is performed before adhesion, or the surface temperature of the recording medium at the time of heating if heating is performed after adhesion.

[0087] From the viewpoint of ease of handling of recorded materials and the aforementioned image quality, it is conceivable to prematurely dry the ink composition adhering to the recording medium by heating. However, if drying is accelerated, the inkjet ink composition of this embodiment may dry before sufficient leafing has occurred, resulting in a decrease in gloss, or the aggregation of metal pigments in the nozzle may be promoted by such platen heating, potentially reducing ejection stability. However, by using the ink composition of this embodiment, it is preferable to obtain a recorded material with excellent gloss without impairing ejection stability, even when such heating is performed.

[0088] 2.3. Post-heating process The recording method of this embodiment may include a post-heating step (secondary heating step) for heating the recording medium after the ink adhesion step. The post-heating step is a heating step that heats the recording medium sufficiently to complete the recording and allow the recorded material to be used. The post-heating step is a heating step for thoroughly drying the liquid medium of the ink. Preferably, the post-heating step is started more than 0.5 seconds after the ink has adhered to the recording medium. For example, it is preferable to start heating a recording area of ​​the recording medium more than 0.5 seconds after the adhesion of ink to that area is completely finished.

[0089] The heating of the recording medium in the post-heating step can be carried out, for example, using an appropriate heating means. In this case, the surface temperature of the recording medium is preferably 45°C or higher, and preferably 50°C or higher. There is no upper limit, but 120°C or lower is preferred. Furthermore, 75°C or lower, 70°C or lower, or 60°C or lower are even more preferred. In addition, the heating temperature is preferably below the softening point of the recording medium's substrate.

[0090] 2.4 Recording media The recording medium used in this embodiment is not particularly limited, but examples include absorbent recording media, low-absorbent recording media, or non-absorbent recording media.

[0091] Absorbent recording media are not particularly limited, but examples include plain paper such as electrophotographic paper with high ink permeability, inkjet paper (inkjet-specific paper equipped with an ink-absorbing layer composed of silica particles or alumina particles, or an ink-absorbing layer composed of hydrophilic polymers such as polyvinyl alcohol (PVA) or polyvinylpyrrolidone (PVP)), and art paper, coated paper, and cast paper used in general offset printing, which have relatively low ink permeability.

[0092] Examples of non-absorbent recording media include, but are not limited to, films and plates of plastics such as polyvinyl chloride, polyethylene, polypropylene, polyethylene terephthalate (PET), polycarbonate, polystyrene, and polyurethane; plates of metals such as iron, silver, copper, and aluminum; metal plates or plastic films made by vapor deposition of these metals; plates of alloys such as stainless steel and brass; and recording media in which films of plastics such as polyvinyl chloride, polyethylene, polypropylene, polyethylene terephthalate (PET), polycarbonate, polystyrene, and polyurethane are bonded (coated) to a paper substrate.

[0093] Low-absorption recording media are recording media whose recording surface has the second lowest absorption rate after non-absorbent recording media. Examples of low-absorption recording media include those with a coating layer (receiving layer) on the surface for receiving liquids. For example, printing paper is an example of a recording media whose base material is paper. The coating layer is one that does not easily absorb ink, and examples include those coated with particles such as inorganic compounds together with a binder.

[0094] Low-absorbent or non-absorbent recording media are recording media that do not absorb liquid at all or absorb very little liquid. For example, a non-absorbent or low-absorbent recording media is defined as "a recording medium that does not absorb liquid at all or very little liquid in the Bristow method from the start of contact for 30 msec." 1 / 2 Up to 10 mL / m² of water absorption capacity 2 A recording medium that is one of the following is preferred.

[0095] The Bristow method is the most widely used method for measuring liquid absorption in a short time and is also adopted by the Japan Paper & Pulp Technology Association (JAPAN TAPPI). Details of the test method are described in standard No. 51 "Paper and cardboard - Liquid absorbency test method - Bristow method" of the "JAPAN TAPPI Paper & Pulp Test Methods 2000 Edition".

[0096] In contrast, absorbent recording media refer to recording media that do not fall under the categories of non-absorbent or low-absorbent.

[0097] Furthermore, the shape of the recording medium is not particularly limited and may be any form, such as a sheet, plate, or object.

[0098] 3. Inkjet recording device As an example of a recording device that performs the recording method of this embodiment, one can be exemplified by a device equipped with an inkjet head that ejects an ink composition and performs recording by the recording method described above.

[0099] 3.1. Outline of the device configuration Figure 1 is a schematic cross-sectional view illustrating a recording device. As shown in Figure 1, the recording device 1 comprises an inkjet head 2, an IR heater 3, a platen 4, a heating element 5, a cooling fan 6, a preheater 7, and a ventilation fan 8. The inkjet head is mounted on a carriage (not shown) and performs a main scan in the back-to-front direction to deposit ink onto the recording medium M. The platen 4 is also provided with a platen heater (not shown). The recording device 1 includes a control unit (not shown) that controls each part to perform recording. The inkjet head 2 receives ink from an ink reservoir (not shown).

[0100] 3.2. Configuration related to the inkjet head The inkjet head 2, which is an inkjet head, is configured to record onto the recording medium M by ejecting and depositing an ink composition from the nozzles of the inkjet head 2. The inkjet head 2 shown in Figure 1 is a serial inkjet head that deposits ink onto the recording medium M by scanning it multiple times in the main scanning direction relative to the recording medium M. The inkjet head 2 is mounted on a carriage (not shown). The inkjet head 2 is scanned multiple times in the main scanning direction relative to the recording medium M by the operation of a carriage movement mechanism that moves the carriage in the media width direction of the recording medium M (back-to-front direction in the figure). The media width direction is the main scanning direction of the inkjet head 2. Scanning in the main scanning direction is also called the main scan.

[0101] Here, the main scanning direction is the direction in which the carriage equipped with the inkjet head 2 moves. In Figure 1, this direction intersects with the sub-scanning direction, which is the transport direction of the recording medium M indicated by arrow SS. Recording is then performed on the recording medium M by repeatedly performing the main scanning of the inkjet head 2 and the sub-scanning, which is the transport of the recording medium M.

[0102] Conventional methods can be used for ejecting ink droplets from the inkjet head 2. For example, a method that uses the vibration of a piezoelectric element to eject droplets, that is, an ejection method that forms ink droplets by the mechanical deformation of an electrostrictive element, can be used.

[0103] 3.3.Primary heating mechanism The recording device 1 may be equipped with a primary heating mechanism that performs a primary heating process to heat the recording medium M when ejecting ink from the inkjet head 2 and adhering it to the recording medium. The primary heating mechanism can be of the conduction type, blower type, radiant type, etc. The conduction type conducts heat to the recording medium from a component in contact with the recording medium. For example, a platen heater can be used. Although not shown, the platen heater is provided integrally with the platen 4. The blower type sends ambient temperature air or warm air to the recording medium to dry the ink. For example, a blower fan can be used. The radiant type heats the recording medium by radiating heat-generating radiation to it. For example, IR radiation can be used. Although not shown, a heater similar to the platen heater may be provided immediately downstream of the platen 4 in the SS direction. These primary heating mechanisms may be used individually or in combination.

[0104] For example, the primary heating mechanism includes an IR heater 3 and a platen heater.

[0105] Furthermore, by using the IR heater 3, the recording medium M can be heated radiantly by infrared radiation from the inkjet head 2 side. This makes it easier for the inkjet head 2 to be heated at the same time, but the temperature can be raised without being affected by the thickness of the recording medium M, compared to when the recording medium M is heated from the back side by a platen heater or the like.The primary heating mechanism may also include various fans (e.g., ventilation fan 8) that blow hot air or air at the same temperature as the environment onto the recording medium M to dry the ink on the recording medium M.

[0106] The platen heater can heat the recording medium M via the platen 4 at a position opposite the inkjet head 2. The platen heater is capable of heating the recording medium M by conduction and is used as needed in the inkjet recording method.

[0107] Furthermore, the recording device 1 may be equipped with a preheater 7 that preheats the recording medium M before ink is applied to it.

[0108] 3.4. Post-heating mechanism The system may also include a post-heating mechanism that performs a post-heating step after the adhesion process to heat the recording medium, dry the ink, and fix it in place.

[0109] The heating element 5 used in the post-heating mechanism dries and solidifies the ink adhering to the recording medium M. When the heating element 5 heats the recording medium M on which the image is recorded, moisture and other substances contained in the ink evaporate more quickly, and an ink film is formed by the resin contained in the ink. In this way, the ink film firmly fixes or adheres to the recording medium M, resulting in excellent film-forming properties, and a high-quality image can be obtained in a short time. The recording device 1 may have a cooling fan 6. After the ink recorded on the recording medium M dries, the ink on the recording medium M is cooled by the cooling fan 6, thereby forming an ink coating film with good adhesion on the recording medium M.

[0110] 3.5. Others The recording device shown in Figure 1 is a serial printer that performs recording using a so-called serial method. The recording device may also be a line printer equipped with a line head that performs recording using a line method.

[0111] The line head has a nozzle row in which multiple nozzles are arranged in the width direction of the recording medium, and has a length greater than or equal to the width of the recording medium M being transported, allowing an image to be recorded on the transported recording medium M in the width direction of the recording medium all at once. Recording can be performed in a single scan. Alternatively, after performing one scan by transporting the recording medium, it is possible to perform recording with two or more scans by returning the recording medium in the reverse direction of transport and transporting it again for another scan.

[0112] The scanning may be performed by a head whose position is fixed relative to the transported recording medium, or by a head that moves while scanning is performed relative to the recording medium fixed in the platen area.

[0113] Furthermore, a recording device capable of line-type recording can be configured similarly to the one shown in Figure 1, except that the inkjet head 2 is replaced with a line head. Specifically, the heating mechanisms such as the ventilation fan 8, IR heater 3, platen heater, and preheater 7, which are located above the inkjet head 2 in Figure 1, can be similarly placed above or below the line head. Alternatively, a post-heating mechanism such as the heating heater 5 and cooling fan 6 shown in Figure 1 may also be included.

[0114] 3.6. Details of the inkjet head Figure 2 is a schematic cross-sectional view of the main part of an inkjet head 100, which is an example of an inkjet head in a recording device. In Figure 2, the flow of ink from the ink supply chamber 40 to the nozzle hole 12 during the ink ejection operation is schematically shown by dashed arrows.

[0115] Note that in Figure 2, the piezoelectric element 32 is shown in a simplified form. Also, the inkjet head 100 is configured to include a communication plate 110 and a cover 150.

[0116] As shown in Figure 2, the inkjet head 100 comprises a nozzle plate 10 having a plurality of nozzle holes 12, a plurality of pressure chambers 20 communicating with each of the plurality of nozzle holes 12 formed in the nozzle plate 10, a diaphragm 30 that changes the volume of each of the plurality of pressure chambers 20, and an ink supply chamber 40 that supplies ink to the plurality of pressure chambers 20. Note that the plurality of components are arranged in the depth direction of the drawing, and Figure 2 shows a cross-section of one set of these components.

[0117] The nozzle plate 10 has a plurality of nozzle holes 12 for ejecting ink, and these nozzle holes 12 are arranged in a row, and a nozzle surface 13 is formed on the surface of the nozzle plate 10. The number of nozzle holes 12 provided on the nozzle plate 10 is not particularly limited. The diameter of the nozzle holes 12 is the nozzle diameter L.

[0118] The inkjet head 100 includes a pressure chamber substrate 120 for forming a pressure chamber 20. As shown in Figure 2, the pressure chamber substrate 120 includes a communication plate 110 between it and the nozzle plate 10 as a flow path forming substrate. The communication plate 110 partitions the space between the nozzle plate 10 and the pressure chamber substrate 120, thereby forming an ink supply chamber 40 (liquid storage section), a supply port 126 communicating with the ink supply chamber 40, and a pressure chamber 20 communicating with the supply port 126. That is, the ink supply chamber 40, the supply port 126, and the pressure chamber 20 are partitioned by the nozzle plate 10, the communication plate 110, the pressure chamber substrate 120, and the diaphragm 30.

[0119] The communication plate 110 has a communication hole 127 that communicates from the pressure chamber 20 to the nozzle hole 12. An ink discharge port 128 is formed at the end of the communication hole 127, which is formed on the surface of the communication plate 110 that contacts the nozzle plate 10. The discharge port 128 communicates with the nozzle hole 12 formed in the nozzle plate 10.

[0120] The diaphragm 30 is provided in contact with the pressure chamber substrate 120, and a piezoelectric element 32 is formed in contact with the diaphragm 30. The piezoelectric element 32 is electrically connected to a piezoelectric element drive circuit (not shown) and can operate (vibrate, deform) based on signals from the piezoelectric element drive circuit. The diaphragm 30 deforms due to the operation of the piezoelectric element 32, and by changing the volume of the pressure chamber 20, the internal pressure of the pressure chamber 20 can be changed. The piezoelectric element 32 is not particularly limited, but for example, an element that deforms when a voltage is applied (an electromechanical conversion element) can be mentioned.

[0121] Furthermore, the inkjet head 100 includes a compliance sheet 140 and a cover 150 that houses a piezoelectric element 32 as components that form part of the ink flow path. The compliance sheet 140 forms a supply port 126 that communicates with the ink supply chamber 40 between itself and the communication plate 110. The compliance sheet 140 is also a flexible elastic film and has the function of acting as a damper for ink ejection and flow, and of deforming when the volume of ink expands, thereby suppressing damage to the inkjet head 100.

[0122] In this embodiment, the ink supply chamber 40, the supply port 126, the pressure chamber 20, and the communication hole 127 are described separately, but all of these are liquid flow paths, and as long as the pressure chamber 20 is formed, the flow path can be designed in any way.

[0123] The pressure chamber 20 formed by the above configuration is a space partitioned by the communication plate 110, the pressure chamber substrate 120, and the diaphragm 30, and does not include the supply port 126, the communication hole 127, the discharge port 128, and the nozzle hole 12. In other words, the pressure chamber 20 is the space opposite to the parts that apply pressure to the ink, such as the diaphragm 30, the pressure chamber substrate 120, and the communication plate 110, and the space adjacent to this space whose cross-sectional area in the direction of ink movement is equal to that of this space, and the volume of the pressure chamber 20 is this volume. Thus, the pressure chamber 20 is defined as a space whose volume changes with the displacement of the diaphragm 30, and does not include a constricted flow path or the like that communicates with this space. The volume of the pressure chamber is preferably 1000 to 4000 pl, more preferably 1500 to 3700 pl, and even more preferably 2000 to 3300 pl. The volume of the pressure chamber is the volume per pressure chamber.

[0124] The distance from the pressure chamber to the nozzle of the inkjet head is the distance from the end of the pressure chamber where the ink flows towards the nozzle hole to the tip of the nozzle hole. In the example in Figure 2, the distance from the pressure chamber to the nozzle of the inkjet head refers to the distance from the pressure chamber 20 to the nozzle hole 12, and in the example in Figure 2, it is equal to the sum of the thickness direction length d1 of the communication plate 110 and the thickness direction length of the nozzle plate 10.

[0125] The distance from the pressure chamber of the inkjet head to the nozzle is not limited, but preferably 5 mm or less. More preferably 0.2 to 4 mm, more preferably 0.5 to 3 mm, even more preferably 0.7 to 2 mm, and still more preferably 0.8 to 1.5 mm. When the distance from the pressure chamber of the inkjet head to the nozzle is greater than the above range, it is preferable because it allows for greater design flexibility in the positioning of the pressure chamber and nozzles within the inkjet head.

[0126] When there is a narrow ink channel between the pressure chamber and the nozzle of an inkjet head, as shown in Figure 2, the following problems are likely to occur.

[0127] When flaky metal pigments flow through narrow channels, such as tubular passages, the orientation of the flaky surfaces is parallel to the direction of ink movement, allowing the metallic pigment to move more easily. This facilitates ink flow and positively impacts ink ejection stability. However, when the metallic pigment becomes unstable, the surfaces of the flaky metallic pigment tend to overlap and aggregate, forming coarse particles. When flaky metallic pigments are layered and form coarse particles, the orientation of the surfaces becomes less likely to be parallel to the direction of ink movement, making movement difficult, and the flaky shape disappears. In such cases, the ink composition becomes difficult to circulate within the print head. The narrow, tubular flow path from the pressure chamber to the nozzle of an inkjet print head is presumably a factor contributing to this difficulty in ink composition flow.

[0128] However, since the ink composition used in the recording method of this embodiment contains a metal pigment treated with a specific phosphorus-based treatment agent, such a decrease in fluidity is less likely to occur, and stable ejection can be achieved even at high ejection frequencies. [Examples]

[0129] 1. Preparation of inkjet ink composition Each example of an inkjet ink composition was obtained by placing the components into a mixing tank to achieve the composition shown in Tables 1-3, mixing and stirring, and then filtering. Unless otherwise specified, the numerical values ​​for each component in Tables 1-3 represent mass percent. Furthermore, the numerical values ​​for metal pigments in the tables represent mass percent of the solid content.

[0130] [Table 1]

[0131] [Table 2]

[0132] [Table 3]

[0133] The abbreviations and product ingredient details used in Tables 1-3 are as follows. <Metallic Pigments> • Metallic pigments: These are pigments prepared as follows. A release layer was formed on a polyethylene terephthalate (PET) substrate by coating it with an acetone solution of release resin using a roll coater. Next, an aluminum layer was formed on the release layer in a vacuum deposition apparatus to achieve the desired film thickness for each example. The film thickness was adjusted by controlling the amount of deposition.

[0134] A PET substrate with an aluminum layer formed on it was immersed in a tetrahydrofuran (THF) tank and irradiated with ultrasound to peel the aluminum layer from the PET substrate and pulverize it, obtaining a dispersion in which aluminum particles were dispersed in THF. Next, an appropriate amount of diethylene glycol diethyl ether was added to the aluminum particles after removing the THF using a centrifuge to obtain an aluminum pigment suspension with an aluminum concentration of 5%.

[0135] The resulting aluminum pigment suspension (5%, diethylene glycol diethyl ether) is further pulverized using a circulating high-power ultrasonic grinder (20 kHz) until the desired average particle size is achieved, resulting in the sizes (D) listed in Tables 1-3. 50 An aluminum pigment having the following properties was obtained.

[0136] Then, Jeffamine M2070, a poly(oxyethylene / oxypropylene)amine dispersant, was added to the aluminum pigment suspension to a concentration ratio of 5%. The suspension was then subjected to sonication and heat treatment at 55°C for 1 hour to break down agglomeration and disperse the aluminum pigment down to the primary particles.

[0137] For each example, a surface treatment agent was added to an aluminum pigment suspension dispersed down to primary particles, such that the mass ratio of the aluminum pigment concentration matched the mass ratio shown in the table. The surface treatment agent was then reacted with the pigment surface by heat treatment at 55°C for 3 hours under ultrasonic irradiation, and further heat treatment was performed under different conditions to prepare an aluminum dispersion. In this way, an aluminum dispersion with an organic solvent as the liquid medium was obtained. In each example, a separate sample of this dispersion was taken for confirmation, and diethylene glycol diethyl ether was removed by centrifugation. Upon confirmation of diethylene glycol diethyl ether, the presence of the surface treatment agent in each example was not detected. From this, it is presumed that the surface treatment agent is attached to the metal pigment. For the water-based composition example, the aluminum dispersion was centrifuged to remove the organic solvent and replaced with water to obtain an aluminum dispersion with water as the liquid medium. The aluminum dispersion was mixed with the other components listed in the table to obtain the ink compositions shown in the table.

[0138] <Resin> • Paraloid B60: Acrylic resin, manufactured by Dow Chemical Company. • Rezamin D1030: Water-based urethane resin, manufactured by Dainichi Seika Kogyo Co., Ltd. <Organic solvents> • BTGH: Tetraethylene glycol monobutyl ether ·γBL:γ-butyrolactone DEDG: Diethylene glycol diethyl ether • PG: Propylene glycol · 1,2-Hexanediol <Surface treatment agent> • Cetyl phosphate: A surface treatment agent represented by the above formula (2), wherein R in formula (2) 2 ga n - A mixture of a compound with a hexadecyl group (n-cetyl group) where a is 1 and a compound with a hexadecyl group (n-cetyl group) where a is 2. • Octadecyl phosphate: A surface treatment agent represented by formula (2) above, wherein R in formula (2) 2 It is a mixture of a compound where a is 1 and a compound where a is 2, where a is an n-octadecyl group. • Octadecylphosphonic acid: A surface treatment agent represented by the above formula (1), wherein R in formula (1) 1 It is a compound in which the group is an n-octadecyl group. • Tetracosyl phosphate: A surface treatment agent represented by the above formula (2), wherein R in formula (2) 2 It is a mixture of a compound in which a is 1 and a compound in which a is 2, where a is an n-tetracosyl group. • Tridecyl phosphate: A surface treatment agent represented by the above formula (2), wherein R in formula (2) 2 A mixture of a compound in which a is an n-tridecyl group and a compound in which a is 2. • Dodecyl phosphate: A surface treatment agent represented by the above formula (2), wherein R in formula (2) 2 A mixture of a compound in which a is an n-dodecyl group and a compound in which a is 2. • FHP: (CHEMINOX FHP-2-OH (trade name), 2-(perfluorohexyl)ethylphosphonic acid, manufactured by Unimatec Co., Ltd.) Octadecyltrimethoxysilane

[0139] 2. Measurement Method and Evaluation Method 2.1. Shape etc. Volume average particle size (D) of metallic pigments 50The particle size distribution was measured using a Microtrac MT-3300 (Microtrac-Bell, a laser diffraction / scattering particle size distribution analyzer). The average thickness Z of the metal pigment was measured using atomic force microscopy with NanoNavi E-Sweep (SII Nanotechnology). All metal pigments were found to be flaky.

[0140] 2.2. Gloss Evaluation A modified Seiko Epson SC-S80650 was used as the recording device. The nozzle density of the inkjet head nozzle row was set to 360 npi and 360 nozzles. Ink was filled into the inkjet head, and the drive waveform of the inkjet head was optimized to ensure optimal ejection of the filled ink. The inkjet head was configured as shown in Figure 2, with a distance of 1 mm from the pressure chamber to the nozzle and a pressure chamber volume of 2900 pl. During recording, the platen heater was controlled, and as a heating process, the surface temperature of the recording medium on the platen during recording was set to the heating temperature (°C) shown in Tables 1-3. Simultaneously, secondary heating was activated to perform a post-heating process, and the surface temperature of the substrate during the post-heating process was set to 50°C. For recording, a polyvinyl chloride film (Mactac5829R, manufactured by Mactac) was used as the substrate.

[0141] The amount of ink adhering to the recording pattern during recording is 3 mg / inch. 2 The recording resolution was set to 1440 x 1440 dpi. A recording test was then conducted. The resulting recordings were left in a constant temperature chamber (temperature 40°C, humidity 100%) for 5 days. After that, the recordings were removed from the constant temperature chamber, and the gloss of the recorded portion was measured at a tilt angle of 60° using a MINOLTA MULTI GLOSS 268 gloss meter. The gloss of the solvent-based composition and the water-based composition were evaluated based on the following evaluation criteria. A higher value tends to indicate a better metallic luster. The evaluation results are shown in 1-3.

[0142] [Evaluation criteria for solvent-based compositions] A: The gloss level is 350 or higher. B: The gloss level is between 300 and 350. C: Glossiness is between 270 and 300. D: Glossiness is less than 270.

[0143] [Evaluation criteria for aqueous compositions] A: The gloss level is 250 or higher. B: The gloss level is between 200 and 250. C: Glossiness is between 150 and 200. D: Glossiness is less than 150.

[0144] 2.3. Evaluation of Discharge Stability After installing the recording device in a temperature-controlled room, the above recording test was performed continuously for 5 hours under conditions of 40°C and 80% humidity. After recording, a nozzle inspection was performed to check for nozzle dispensing defects, i.e., non-dispensing or misalignment of the target point. Misalignment of the target point was considered defective if it deviated by 30% or more from the normal position in terms of the distance between nozzles. Then, the solvent-based composition and the aqueous-based composition were evaluated based on the following evaluation criteria. This test was conducted to confirm the dispensing stability during recording. The evaluation results are shown in 1 to 3.

[0145] [Evaluation Criteria for Solvent-Based Compositions] A: The number of nozzles with dispensing problems is less than 1% of the total number of nozzles. B: The number of nozzles with dispensing problems is between 1% and 3% of the total number of nozzles. C: The number of nozzles with dispensing problems is 3% or more of the total number of nozzles.

[0146] [Evaluation Criteria for Water-Based Compositions] A: The number of nozzles with poor dispensing performance is less than 2% of the total number of nozzles. B: The number of nozzles with poor dispensing performance is between 2% and 5% of the total number of nozzles. C: The number of nozzles with dispensing problems is 5% or more of the total number of nozzles.

[0147] 2.4. Storage Stability Evaluation The inkjet ink composition prepared above was put into a screw tube, and with the lid on, it was left standing in a thermostat at 45°C for 10 days. The volume average particle diameter D at 20°C before standing 50 and the volume average particle diameter D at 20°C after standing for 5 days 50 were measured with a particle size distribution meter, and the viscosity change rate was calculated, and the storage stability was evaluated according to the following evaluation criteria. The evaluation results are shown as 1 to 3.

[0148] 〔Evaluation Criteria〕 A: The increase rate of the volume average particle diameter D 50 is 1% or less. B: The increase rate of the volume average particle diameter D 50 is more than 1% and 3% or less. D: The increase rate of the volume average particle diameter D 50 is more than 3%.

[0149] 3. Evaluation Results According to the comparison between Examples 1 to 20 and Comparative Examples 1 to 18, the inkjet ink composition according to the present embodiment is excellent in gloss, ejection stability, and storage stability as compared with the inkjet ink compositions according to Comparative Examples 1 to 18 that do not satisfy the constituent requirements of the inkjet ink composition.

[0150] The ink contains a metal pigment treated with a compound represented by formula (1) or formula (2), the volume average particle diameter D of the metal pigment 50 (μm) is 1.0 μm or less, and the ratio of the volume average particle diameter D 50 (μm) to the average thickness Z (μm) of the metal pigment (D 50 / Z) is 17 or more, and the ratio of the metal pigment volume average particle diameter D 50 (μm) to the nozzle diameter L (μm) (D 50 / L) is 0.050 or less. All of the examples were excellent in gloss and ejection stability.

[0151] In Comparative Examples 1, 2, and 12, the volume average particle diameter D of the metal pigment 50 (μm) is not 1.0 μm or less, and the ratio of the metal pigment volume average particle diameter D 50 (μm) to the nozzle diameter L (μm) (D50 The discharge stability was poor, as the value ( / L) was not below 0.050.

[0152] Comparative Examples 3, 4, 5, and 13 show the volume-average particle size D relative to the average thickness Z (μm) of the metal pigment. 50 (μm) ratio (D 50 The / Z value was not 17 or higher, resulting in inferior gloss.

[0153] Comparative Examples 6-10 and 14-17 did not contain metal pigments treated with the compound represented by formula (1) or formula (2) in their inks, and exhibited inferior gloss and ejection stability.

[0154] Comparative Examples 11 and 18 show the volume-average particle size D of the metal pigment relative to the nozzle diameter L (μm). 50 (μm) ratio (D 50 The discharge stability was poor, as the value ( / L) was not below 0.050. [Explanation of Symbols]

[0155] 10...Recording device, 11...Transport path, 12...Feeding section, 14...Transporting section, 16...Belt transport section, 18...Recording section, 20...Fd discharge section, 22...Fd mounting section, 24...Reversal path section, 26...Fu discharge section, 28...Fu mounting section, 30...Feeding tray, 32...Feeding roller, 34...Transporting drive roller, 36...Transporting driven roller, 38...First roller, 40...Second roller, 42...Endless belt, 42a...Upper section of endless belt, 44...Support, 46...Head holder, 48...Inkjet head, 50...First branching section, 52...Reversal path, 54...Second branching section, 56...Discharge roller pair, 64...Discharge drive roller, 68...Drive shaft, 76...Mounting surface, 78...Convex section, 80...First biasing member, 82...Second biasing member, 84, 86...Support shaft, P...Recording medium.

Claims

1. An adhesion step in which an inkjet ink composition is ejected from the nozzle of an inkjet head and attached to a recording medium, The adhesion step includes a primary heating step of heating the inkjet ink composition that has adhered to the recording medium, The aforementioned adhesion process is performed on the recording medium supported by the platen, The aforementioned primary heating step is performed on the recording medium supported by the platen, The surface temperature of the recording medium in the primary heating step is 30 to 50°C. The inkjet ink composition Metallic pigments, A liquid medium, The liquid medium comprises one or more selected from the group consisting of organic solvents and water. The aforementioned metal pigment is surface-modified with a surface treatment agent. The surface treatment agent comprises one or more compounds selected from the group consisting of compounds represented by the following formula (1) and compounds represented by the following formula (2). The aforementioned metal pigment is in the form of flake-like particles. Volume average particle size D of the metal pigment 50 (μm) is 1.0 μm or less, The volume-average particle diameter D relative to the average thickness Z (μm) of the metal pigment 50 Ratio of (μm) (D 50 / Z) is 17 or more, The volume-average particle diameter D of the nozzle has a nozzle diameter L (μm). 50 Ratio of (μm) (D 50 / L) is 0.050 or less. Inkjet recording method. (R 1 -)P(O)(OH) 2 (1) (In the above formula (1), R 1 (This refers to a hydrocarbon group having 14 or more carbon atoms, which may be substituted with substituents.) (R 2 -O-) a P(O)(OH) 3-a (2) (In the above formula (2), R 2 Each of these is an independent hydrocarbon group having a carbon skeleton with 14 or more carbon atoms, which may be substituted with substituents, and a is 1 or 2.

2. The inkjet ink composition is either an aqueous composition or a solvent-based composition. The inkjet recording method according to claim 1.

3. The inkjet ink composition is an aqueous composition in which the water content is 40% by mass or more of the total amount of the inkjet ink composition, or a solvent-based composition in which the organic solvent content is 60% by mass or more of the total amount of the inkjet ink composition. The inkjet recording method according to claim 1 or 2.

4. Volume average particle size D of the metal pigment 50 (μm) is 0.5 μm or less. The inkjet recording method according to any one of claims 1 to 3.

5. The average thickness Z (nm) is 30 nm or less. The inkjet recording method according to any one of claims 1 to 4.

6. The nozzle diameter L (μm) is 30 μm or less. The inkjet recording method according to any one of claims 1 to 5.

7. The content of the surface treatment agent is 1.0 to 50% by mass relative to the total amount of the metal pigment. The inkjet recording method according to any one of claims 1 to 6.

8. The aforementioned R 1 and R 2 At least one of them contains an unsubstituted hydrocarbon group, The inkjet recording method according to any one of claims 1 to 7.

9. The aforementioned R 1 and R 2 At least one of them contains a hydrocarbon group having 15 to 30 carbon atoms. The inkjet recording method according to any one of claims 1 to 8.

10. The aforementioned metal pigment includes one or more selected from the group consisting of aluminum and aluminum alloys. The inkjet recording method according to any one of claims 1 to 9.

11. The content of the liquid medium is 60% by mass or more relative to the total amount of the inkjet ink composition. The inkjet recording method according to any one of claims 1 to 10.

12. After the adhesion step and the primary heating step, a heating step is further performed. The inkjet recording method according to any one of claims 1 to 11.

13. The aforementioned primary heating step is performed by heating with a platen heater. The inkjet recording method according to any one of claims 1 to 12.

14. The surface temperature of the recording medium in the primary heating step is 30 to 45°C. The inkjet recording method according to any one of claims 1 to 13.

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