Ink jet ink composition, recording method, and recording apparatus

Abstract

To provide an ink jet ink composition capable of suppressing transfer of a recorded product to be obtained, and excellent in ejection stability and compatibility.SOLUTION: An ink jet ink composition includes: a pigment; an acetylene glycol-based surfactant having an HLB value of 5 or less; a lactam compound having a six- to eight-membered lactam ring; a solvent component; and a water-soluble resin dissolved in the solvent component, in which the content of the water-soluble resin is 0.3 mass% or more based on the total mass of the ink jet ink composition, the solvent component includes water, and the ink jet ink composition is an aqueous ink.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Inkjet recording methods are capable of recording high-resolution images using relatively simple equipment and have been rapidly developing in various fields. Among these methods, various studies have been conducted on the ejection reliability of ink compositions used in recording. For example, Patent Document 1 discloses an ink composition containing a self-dispersing pigment, a resin, and an organic solvent, and intended for use in an ink container having a specified ink chamber and a specified ink inlet, with the aim of providing an ink composition that can suppress the formation of aggregates in the ink container. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-061896 Summary of the Invention [Problem to be solved by the invention]

[0004] However, if a recording medium is transported, discharged, or stacked inside a recording apparatus before the aqueous ink composition has sufficiently dried, ink transfer is likely to occur. On the other hand, when attempting to prevent such ink transfer, there are concerns that the ink ejection reliability may decrease or the compatibility with other components in the ink may become poor. [Means for solving the problem]

[0005] The inkjet ink composition of the present invention comprises a pigment, an acetylene glycol surfactant having an HLB value of 5 or less, a lactam compound having a 6- to 8-membered lactam ring, a solvent component, and a water-soluble resin dissolved in the solvent component, wherein the content of the water-soluble resin is 0.3 mass % or more relative to the total mass of the inkjet ink composition, and the solvent component contains water, making the inkjet ink composition an aqueous ink.

[0006] The recording method of the present invention includes a discharge step of discharging the ink-jet ink composition from an ink-jet head and depositing it on a recording medium.

[0007] The recording apparatus of the present invention comprises the ink-jet ink composition described above and an ink-jet head that ejects the ink-jet ink composition. [Brief explanation of the drawings]

[0008] [Figure 1] Table 1 shows the compositions of ink compositions used in the examples and the evaluation results thereof. [Figure 2] Table 2 shows the compositions of ink compositions used in the examples and the evaluation results thereof. [Figure 3] Table 3 shows the compositions of ink compositions used in the examples and the evaluation results thereof. [Figure 4] Table 4 shows the compositions of ink compositions used in the examples and the evaluation results thereof. [Figure 5] FIG. 1 is a diagram illustrating an example of an inkjet recording apparatus used in an inkjet recording method according to an embodiment of the present invention. [Figure 6] FIG. 2 is a diagram showing an example of a continuous supply ink container that is an ink container. [Figure 7] FIG. 2 is a diagram showing an example of an ink cartridge as an ink container. [Figure 8] FIG. 2 is a diagram showing an example of an ink bottle as an ink container. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described in detail with reference to the drawings as necessary, but the present invention is not limited to this, and various modifications are possible without departing from the spirit of the present invention. In the drawings, the same elements are given the same reference numerals, and redundant explanations will be omitted. Furthermore, positional relationships such as up, down, left, and right will be based on the positional relationships shown in the drawings unless otherwise specified. Furthermore, the dimensional ratios of the drawings are not limited to those shown in the drawings.

[0010] 1. Inkjet ink composition The inkjet ink composition according to this embodiment (hereinafter simply referred to as the "ink composition") comprises a pigment, an acetylene glycol surfactant having an HLB value of 5 or less, a lactam compound having a 6- to 8-membered lactam ring, a solvent component, and a water-soluble resin dissolved in the solvent component, wherein the content of the water-soluble resin is 0.3 mass % or more relative to the total mass of the inkjet ink composition, and the solvent component contains water, making it an aqueous ink.

[0011] When recording using an aqueous ink composition, if the ink composition is applied to a recording medium and then immediately transported and discharged by a transport roller, the undried ink composition may adhere to the transport roller or to the contact surface of a recording material discharged immediately before or after, resulting in transfer. One cause of this transfer is thought to be insufficient penetration of the ink composition into the recording medium. Therefore, improving the ink permeability is desirable as a means of suppressing transfer. Rapid penetration of the ink into the recording medium allows the ink to penetrate the recording medium before the recording medium comes into contact with the transport roller or another recording medium, thereby suppressing transfer.

[0012] Furthermore, even if the ink composition is sufficiently permeated and absorbed into the recording medium, it is conceivable that the ink may still transfer to rollers in a recording device or to another recording medium before drying. In this regard, it is conceivable that adding resin particles as a fixing resin to the ink composition would improve ink fixability and suppress ink transfer. However, such resins tend to aggregate at the gas-liquid interface and become foreign matter when stored in an ink container, which creates new issues with jetting reliability. Therefore, the use of components that replace such resins is desirable as a means of suppressing transfer without reducing jetting reliability. Furthermore, transfer occurs early after the ink is applied to the recording medium, before the ink has dried sufficiently. Therefore, it is believed to be effective to form a film on the surface of the recording medium to which the ink has adhered, before the ink has dried sufficiently, before the ink has dried sufficiently.

[0013] In this embodiment, in order to improve the ink penetration, an acetylene glycol surfactant with an HLB value of 5 or less is used as a component for improving the penetration. In addition, by using a water-soluble resin that is less likely to form foreign matter at the gas-liquid interface, it is possible to suppress transfer by forming a film on the surface of the recording medium early without reducing the ejection reliability. Furthermore, acetylene glycol surfactants with an HLB value of 5 or less, which improve ink penetration, tend to undergo phase separation in the ink composition, resulting in decreased ejection stability. Therefore, a lactam compound having a 6- to 8-membered lactam ring was used in combination. This suppresses phase separation, resulting in excellent ejection reliability. This makes it possible to provide an ink composition with excellent ejection reliability, transfer resistance, and compatibility.

[0014] It is believed that the ink composition of the present invention has excellent ejection reliability, transfer resistance, and compatibility due to the synergistic effect of using the above-mentioned components in combination, although the reasons for this are not limited to those mentioned above.

[0015] The inkjet ink composition of this embodiment is used by being ejected by an inkjet recording apparatus, and in the inkjet recording apparatus, the ink tank that supplies the ink composition or the ink container that supplies the ink composition to the inkjet recording apparatus preferably has a structure that generates an ink liquid surface that is a gas-liquid interface between the ink composition and a gas. As described above, when a gas-liquid interface is present, problems are particularly likely to occur regarding ejection reliability, and therefore the effects of the present invention are even more effective when such an ink tank or ink container is used.

[0016] The ink tank is not particularly limited, but examples thereof include a tank provided in a recording device, such as a continuous supply ink container or a sub-tank, into which an inkjet ink composition is supplied.

[0017] An example of the configuration of a continuous supply ink container and a sub-tank is shown in Figure 6. Note that while Figure 6 shows the configuration of a continuous supply ink container and a sub-tank together, a recording device may have at least one of a sub-tank and a continuous supply ink container. A continuous supply ink container is a type of ink tank, that is, a continuous supply ink tank. 6, a continuous supply ink container 601 includes an ink storage chamber 604 having an ink supply port 602 and an air supply port 603. Air supplied from the air supply port 603 is supplied as air G from the bottom of the ink storage chamber 604, moves upward within the ink storage chamber 604, and is supplied to an air layer K above a layer of ink I within the ink storage chamber 604, where it becomes part of the air layer.

[0018] The continuous supply ink container 601 has a configuration that enables continuous printing by injecting (replenishing) the ink composition, and when the continuous supply ink container is filled with ink, an ink liquid level E (gas-liquid interface) is generated within the container. The ink liquid surface is the interface between the ink layer and the air layer above the ink layer in an ink tank or ink container, and is a horizontal surface. The ink liquid surface has a predetermined area. If the recording device has a continuous supply ink container, supplying ink to the continuous supply ink container from ink supply port 602 prevents the ink in the continuous supply ink container from decreasing below a predetermined level, enabling continuous printing. Ink can be supplied from ink supply port 602 from, for example, an ink bottle, which will be described later. If the recording device has a continuous supply ink container, the recording device does not need to have a sub-tank, and ink can be supplied directly to the inkjet head from ink flow path 605.

[0019] 6, a sub-tank 606 is a relay tank for the ink composition provided in the recording apparatus. The sub-tank 606 may be connected to a continuous supply ink container 601 via an ink flow path 605. If a recording device has a subtank, even if the ink supply to the subtank is interrupted for a while, it can continue printing for a while using the ink in the subtank. Ink can be supplied to the subtank from a continuous supply ink container as shown in Figure 6, or from an ink cartridge, which will be described later. When ink is supplied from an ink cartridge, the recording device has an ink supply mechanism (ink cartridge mounting mechanism) not shown, and an ink cartridge is mounted in the ink supply mechanism, and ink is supplied from the ink cartridge to the subtank via the ink supply mechanism and the ink flow path. In this case, the recording device does not have a continuous supply ink container.

[0020] In addition, the height of the sub-tank 606 can also generate ink pressure to supply the ink composition to the inkjet head 607. The direction in which the ink is supplied to the inkjet head is IK. Compared to continuous supply ink containers, sub-tanks have a higher degree of freedom in terms of placement location, and are therefore preferable because they can be easily placed in a location that makes it easy to supply the ink composition to the inkjet head 607 . In this sub-tank 606, as shown in FIG. 6, an ink liquid surface (air-liquid interface) is also generated at the boundary between the layer of ink I in the sub-tank and the air layer above it.

[0021] The supply of ink from the ink tank to the inkjet head may be performed by generating ink pressure based on the relationship between the ink level in the ink tank and the inkjet head, or by generating ink pressure using an ink pump (not shown). In the case where the recording device has a sub-tank and a continuous supply ink container, the ink is similarly supplied from the continuous supply ink container to the sub-tank.

[0022] The ink container is not particularly limited, but examples thereof include those that supply ink-jet ink compositions to a structure provided in a recording apparatus, such as an ink cartridge or an ink bottle.

[0023] An example of the configuration of an ink cartridge is shown in Figure 7. As shown in Figure 7, ink cartridge 701 is used by being attached to an ink supply mechanism (not shown) of a recording device, and includes a storage chamber 704 having an ink supply port 702 and an atmosphere communication port 703. When the ink composition is used and the ink I in storage chamber 704 decreases, air is supplied from atmosphere communication port 703, creating an air layer and an ink liquid surface (gas-liquid interface) in storage chamber 704. Note that a foam-free type is preferable as the ink cartridge, and a non-pack type is also preferable.

[0024] An example of the configuration of an ink bottle is shown in Figure 8. As shown in Figure 8, ink bottle 801 includes a container body 802 capable of containing an ink composition, and an ink refill port 803 attached to the tip side of container body 802. Although not particularly limited, for example, ink refill port 803 of ink bottle 801 can be inserted into ink inlet 602 of a continuous supply ink container, and the ink composition contained in ink bottle 801 can be supplied to the continuous supply ink container. In the ink bottle, an ink liquid level is formed at the boundary between a layer of ink (not shown) and an air layer above it.

[0025] When the ink tank or ink container has an ink surface as described above, the maximum area of ​​the ink surface is preferably 400 mm 2 More preferably, it is 500 mm or more.2 More preferably, it is 600 mm or more. 2 More preferably, it is 700 mm or more. 2 The upper limit of the maximum area of ​​the ink surface is not particularly limited and depends on the size of the recording device, etc., but is, for example, 1000 mm 2 The effect of the present invention is further enhanced when the maximum area of ​​the ink liquid surface is within the above range. The maximum area of ​​the ink liquid surface refers to the largest cross-sectional area of ​​the horizontal cross section of the portion of the ink tank, ink accommodating body, or the like that contains the ink.

[0026] Components constituting the ink composition of this embodiment will be described in detail below.

[0027] 1.1.Pigments The ink composition contains a pigment. Examples of the pigment include self-dispersing pigments, which utilize a chemical reaction on the pigment particle surface to introduce hydrophilic functional groups onto the pigment surface, thereby imparting dispersion stability to the pigment and dispersing it. Examples of the hydrophilic functional groups include phosphorus-containing groups such as carboxyl groups and phosphonic acid groups, and sulfo groups. Further, a resin-dispersed pigment is used, which is a resin dispersant that adheres to and adsorbs onto the pigment surface, thereby imparting dispersion stability to the pigment. From the viewpoint of improving ejection reliability, transfer resistance, and compatibility, it is preferable to include a self-dispersed pigment. Self-dispersing pigments are preferred because they do not require a dispersant such as a dispersant resin to disperse the pigment, and even when the pigment content of the ink is increased, the ink viscosity can be relatively low, and they have excellent ejection stability and color development. The pigments may be used alone or in combination of two or more.

[0028] Examples of self-dispersing pigments include organic pigments such as azo pigments (including, for example, azo lakes, insoluble azo pigments, condensed azo pigments, and chelate azo pigments), polycyclic pigments (such as phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone pigments), nitro pigments, nitroso pigments, and aniline black; inorganic pigments such as carbon black (such as furnace black, thermal lamp black, acetylene black, and channel black), metal oxides, metal sulfides, and metal chlorides; and extender pigments such as silica, calcium carbonate, and talc. Among these, carbon black is preferred as the pigment from the viewpoint of more effectively and reliably achieving the effects of the present invention.

[0029] The pigment content is preferably 1.0% by mass to 15% by mass, 3.0% by mass to 10% by mass, or 5.0% by mass to 8.0% by mass, relative to the total amount of the ink composition. By keeping the pigment content within the above ranges, the effects of the present invention tend to be more effectively and reliably achieved.

[0030] 1.2. Acetylene glycol surfactants The ink composition contains an acetylene glycol surfactant with an HLB value of 5 or less. By containing an acetylene glycol surfactant with an HLB value of 5 or less (hereinafter simply referred to as "acetylene glycol surfactant," and unless otherwise specified, this refers to an HLB value of 5 or less), the ink has improved permeability and excellent transfer resistance. Furthermore, the ink ejection characteristics are improved, as are the ejection reliability and ejection stability. On the other hand, acetylene glycol surfactants have low water solubility, which makes them prone to phase separation in the ink composition and tends to reduce compatibility. From the same viewpoint, the HLB value of the acetylene glycol surfactant contained in the ink composition is preferably 4 or less. The lower limit is 0 or more, and although not limited thereto, 1 or more is preferred, and 2 or more is more preferred. The acetylene glycol surfactant may be used alone or in combination of two or more.

[0031] Furthermore, the acetylene glycol surfactants contained in the ink composition preferably include those with an HLB value of 5 or less and those with an HLB value of more than 5, more preferably those with an HLB value of 5 or less and those with an HLB value of 7 or more, and even more preferably those with an HLB value of 5 or less and those with an HLB value of 10 or more. The upper limit of the HLB value is 20 or less, and preferably 15 or less. Among acetylene glycol-based surfactants, those with an HLB value of 5 or less tend to improve ink penetration, but are more likely to cause phase separation in the ink composition, compared to those with an HLB value of more than 5. For this reason, when the acetylene glycol-based surfactants include those with an HLB value of 5 or less and those with an HLB value of more than 5, the content of the acetylene glycol-based surfactant in the ink can be increased, which is preferable because it allows for further improvement in the ink ejection characteristics, penetration, and suppression of phase separation.

[0032] In this specification, the term "HLB value (hydrophilic lipophilic balance)" refers to a value calculated by the Griffin method. Specifically, the HLB value of a surfactant can be calculated according to the following formula (H): HLB value = 20 × (mass % of hydrophilic groups) (H)

[0033] Commercially available acetylene glycol surfactants include, for example, Surfynol 104 (HLB value=4), Surfynol 420 (HLB value=4), Surfynol 82 (HLB value=4), Surfynol DF110D (HLB value=3), Surfynol 104S (HLB value=4), Surfynol 104PG50 (HLB value=4), Surfynol 420 (HLB value=4), Surfynol 82 (HLB value=4), and Surfynol MD-20 (HLB value=4) (all trade names, manufactured by Nissin Chemical Industry Co., Ltd.). From the viewpoint of more effectively and reliably achieving the effects of the present invention, it is preferable for the ink composition to contain Surfynol 104PG50 or Surfynol 420.

[0034] Specific examples of the acetylene glycol surfactant compound include 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol or an alkylene oxide adduct thereof, 5,8-dimethyl-6-dodecyne-5,8-diol or an alkylene oxide adduct thereof, 2,4,7,9-tetramethyl-5-decyne-4,7-diol or an alkylene oxide adduct thereof, and 4,7-dimethyl-5-decyne-4,7-diol or an alkylene oxide adduct thereof.

[0035] The content of the acetylene glycol surfactant is preferably from 0.01% to 3.0% by mass, from 0.05% to 1.0% by mass, or from 0.1% to 0.8% by mass, relative to the total amount of the ink composition. By keeping the content of the acetylene glycol surfactant within the above ranges, transfer resistance, ejection reliability, and ejection stability tend to be further improved. The content of the acetylene glycol surfactant having an HLB value of 5 or less may be within the above range, which is preferable from the above viewpoint, and is more preferably 0.1% by mass or more and 0.5% by mass or less, more preferably 0.1% by mass or more and 0.4% by mass or less, and even more preferably 0.1% by mass or more and 0.3% by mass or less.

[0036] The ink composition of this embodiment may contain other surfactants in addition to the acetylene glycol surfactant. Examples include fluorine-based surfactants and silicone-based surfactants. Examples of fluorine-based surfactants include perfluoroalkyl sulfonates, perfluoroalkyl carboxylates, perfluoroalkyl phosphates, and perfluoroalkyl ethylene oxide adducts. Examples of silicone-based surfactants include polysiloxane compounds and polyether-modified organosiloxanes.

[0037] The content of the other surfactants is not particularly limited as long as it does not impair the effects of the present invention, but is, for example, from 0% to 3% by mass, from 0% to 1% by mass, or from 0% to 0.1% by mass, relative to the total amount of the ink composition.

[0038] 1.3. Lactam compounds The ink composition contains a lactam compound having a 6- to 8-membered ring. A lactam compound has a structure in which a carboxy group and an amino group in the molecule form a ring through a dehydration condensation reaction. When the ink composition contains a lactam compound having a 6- to 8-membered ring, transfer resistance, ejection reliability, and ejection stability are improved. From the same viewpoint, the ink composition preferably contains a lactam compound having a 6- or 7-membered ring, and more preferably contains a lactam compound having a 7-membered ring. In addition, when a lactam compound is an n-membered ring, it means that the number of atoms constituting the ring is n. As the lactam compound, one type may be used alone, or two or more types may be used in combination.

[0039] Specific examples of the lactam compound having a 6- to 8-membered ring include ε-caprolactam, δ-valerolactam, ω-heptalactam, and 5-(methylamino)pentanoic acid lactam, and the ink composition preferably contains ε-caprolactam. When the ink composition contains ε-caprolactam, the transfer resistance, ejection reliability, and ejection stability tend to be further improved.

[0040] In the ink composition, the mass ratio (A / B) of the content A of the acetylene glycol surfactant having an HLB value of 5 or less to the content B of the lactam compound is preferably from 0.01 to 0.7, from 0.02 to 0.6, or from 0.03 to 0.5, more preferably from 0.05 to 0.4, and even more preferably from 0.1 to 0.3. When the mass ratio (A / B) is within the above range, the transfer resistance, ejection reliability, and ejection stability tend to be further improved.

[0041] The content of the 6- to 8-membered ring lactam compound relative to the total amount of the ink composition is preferably 0.1% by mass to 15% by mass, 0.5% by mass to 10% by mass, or 1.0% by mass to 8.0% by mass, more preferably 2.0 to 5.0% by mass, and more preferably 2.0 to 3.0% by mass. By setting the content of the 6- to 8-membered ring lactam compound within the above range, there is a tendency for the transfer resistance, ejection reliability, and ejection stability to be further improved.

[0042] 1.4.Water-soluble resin The ink composition contains a water-soluble resin dissolved in a solvent component. The inclusion of the water-soluble resin improves transfer resistance, ejection reliability, and ejection stability. Examples of water-soluble resins include urethane-based resins, acrylic-based resins, polyalkylene oxide-based resins, polyvinyl alcohol-based resins, and carboxymethyl cellulose-based resins. Among these, from the viewpoint of further improving transfer resistance, ejection reliability, and ejection stability, it is preferable to include a urethane-based resin or an acrylic resin as the water-soluble resin, and it is more preferable to include a urethane resin. Note that one type of water-soluble resin may be used alone, or two or more types may be used in combination.

[0043] The water-soluble resin used in this embodiment is a water-soluble resin that is dissolved in the ink's solvent component, which contains water, but is not a resin that adheres to or adsorbs onto the pigment, and is not a dispersant resin that disperses ink components such as the pigment. A water-soluble resin is one in which, for example, when 1% by mass of the resin is mixed with water at room temperature (25°C) and stirred, there is no visible residue left behind or the entire mixture becoming cloudy.

[0044] The urethane resin is not limited as long as it is a water-soluble resin having a urethane bond in the molecule, and examples thereof include those having repeating units derived from polyisocyanate and polyol.

[0045] Examples of polyisocyanates include aliphatic polyisocyanates such as tetramethylene diisocyanate, dodecamethylene diisocyanate, hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, and 2,4,4-trimethylhexamethylene diisocyanate; isophorone diisocyanate, dicyclohexylmethane-4,4-diisocyanate (hydrogenated MDI), cyclohexylene diisocyanate, methylcyclohexylene diisocyanate (hydrogenated TDI), bis(2-isocyanate), alicyclic polyisocyanates such as 2,5- or 2,6-norbornane diisocyanate, and the like; and aromatic polyisocyanates such as tolylene diisocyanate, 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-dibenzyl diisocyanate, 1,5-naphthylene diisocyanate, xylylene diisocyanate, and 1,3-phenylene diisocyanate.

[0046] Examples of polyols include polyether polyols such as polyethylene glycol and polypropylene glycol, polyester polyols, and polycarbonate polyols, which do not have an acid group, and polyols having an acid group such as a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, or a phosphonic acid group.

[0047] The acrylic resin is not limited as long as it is a water-soluble resin obtained by polymerizing an acrylic monomer such as (meth)acrylic acid or a (meth)acrylic acid ester as one component. (Meth)acrylic refers to a concept that includes both "methacrylic" and "acrylic." The (meth)acrylic resin is not particularly limited, but examples include polymers of (meth)acrylic monomers such as (meth)acrylic acid or a (meth)acrylic acid ester, and copolymers of (meth)acrylic monomers with other monomers. From the viewpoint of making the effects of the present invention more effective and reliable, it is preferable to use a styrene-acrylic resin as the water-soluble resin.

[0048] The urethane-based resin and acrylic-based resin used in this embodiment are preferably those obtained by the methods described in the examples below. By using such methods, the effects of the present invention can be achieved more effectively and reliably.

[0049] The acid value of the water-soluble resin is preferably 40 to 100 mgKOH / g, 40 to 90 mgKOH / g, 45 to 80 mgKOH / g, or 50 to 70 mgKOH / g. By setting the acid value of the urethane resin within the above range, transfer resistance, ejection reliability, and ejection stability tend to be further improved. The acid value may be determined by potentiometric titration.

[0050] The weight-average molecular weight of the water-soluble resin is preferably 5,000 to 150,000, 10,000 to 100,000, 15,000 to 50,000, or 20,000 to 30,000. By setting the weight-average molecular weight of the water-soluble resin within the above range, transfer resistance, ejection reliability, and ejection stability tend to be further improved. The weight-average molecular weight may be determined by GPC.

[0051] The content of the water-soluble resin is 0.3% by mass or more, preferably 0.3% by mass to 3.0% by mass, 0.3% by mass to 2.0% by mass, or 0.3% by mass to 0.8% by mass, relative to the total amount of the ink composition. By keeping the content of the water-soluble resin within the above range, transfer resistance, ejection reliability, and ejection stability tend to be further improved.

[0052] 1.5.Resin particles The ink composition preferably does not contain resin particles. Resin particles are, for example, resin emulsions. Resin particles are non-water-soluble resins dispersed in ink. The resin particles are not particularly limited as long as they are not water-soluble resins, and examples thereof include resin particles made of urethane-based resins, acrylic-based resins, fluorene-based resins, polyolefin-based resins, rosin-modified resins, terpene-based resins, polyester-based resins, polyamide-based resins, epoxy-based resins, vinyl chloride-based resins, or ethylene vinyl acetate-based resins.

[0053] The ink composition preferably contains no more than 0.1% by mass of resin particles relative to the total amount of the ink composition, more preferably no more than 0.05% by mass, and even more preferably 0.00% by mass. By keeping the content of resin particles within the above range, the effects of the present invention can be more effectively and reliably achieved.

[0054] 1.6. Solvent Components The ink composition is a water-based ink and contains water as a solvent component, and may further contain an organic solvent.

[0055] 1.6.1.Water It is preferable that the water be one from which ionic impurities have been removed as much as possible. Examples of such water include, but are not limited to, pure water such as ion-exchanged water, ultrafiltered water, reverse osmosis water, and distilled water, as well as ultrapure water.

[0056] The water content is preferably 55 to 99% by mass, more preferably 60 to 90% by mass, and even more preferably 65 to 80% by mass, relative to the total amount of the ink composition.

[0057] 1.6.2. Water-soluble organic solvents The ink composition preferably contains a water-soluble organic solvent as a solvent component. By containing a water-soluble organic solvent, the ink composition has excellent transfer resistance and ejection stability, and tends to suppress evaporation of water during storage. Examples of water-soluble organic solvents include polyhydric alcohols, glycol ethers, nitrogen-containing solvents, esters, and cyclic esters. Among these, it is preferable to contain polyhydric alcohols as the water-soluble organic solvent.

[0058] Polyhydric alcohols have two or more hydroxyl groups in the molecule, and examples thereof include polyols and alkanediols.

[0059] Specific examples of polyol compounds include ethylene glycol, propylene glycol, 1,2-propanediol, 1,2-butanediol, 1,3-propanediol, 1,4-butanediol, diethylene glycol, triethylene glycol, dipropylene glycol, trimethylolpropane, and glycerin. Examples include those with three or more hydroxyl groups in the molecule, those with an ether group in the skeleton (an intermolecular condensation product of alkanediol), and alkanediols with four or less carbon atoms. Among these, it is preferable to use glycerin or triethylene glycol in order to more effectively and reliably achieve the effects of the present invention.

[0060] The ink composition preferably contains an alkanediol compound having 5 or more carbon atoms as a water-soluble organic solvent. By containing an alkanediol compound having 5 or more carbon atoms, transfer resistance, ejection reliability, and ejection stability tend to be further improved. The upper limit of the carbon number is not particularly limited, but is, for example, 15 or less, 12 or less, or 10 or less. 1,2-alkanediol is preferred.

[0061] Specific examples of alkanediol compounds include 1,2-hexanediol, 1,2-pentanediol, 1,2-octanediol, 1,6-hexanediol, 2-methyl-2,4-pentanediol, 2-ethyl-2-methyl-1,3-propanediol, 2-methyl-2-propyl-1,3-propanediol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 3-methyl-1,3-butanediol, 2-ethyl-1,3-hexanediol, 3-methyl-1,5-pentanediol, and 2-methylpentane-2,4-diol. Among these, 1,2-hexanediol is preferred from the viewpoint of further improving transfer resistance, ejection reliability, and ejection stability.

[0062] Among these, it is preferable that the ink composition contains, as the water-soluble organic solvent, a polyol having a normal boiling point of 280° C. or higher, such as glycerin. By containing a polyol having a normal boiling point of 280° C. or higher, the transfer resistance, ejection reliability, and ejection stability tend to be further improved. The content of the polyol having a normal boiling point of 280° C. or higher in the ink is preferably 0.5 to 10% by mass, more preferably 1.0 to 7.0% by mass, even more preferably 2.0 to 6.0% by mass, and particularly preferably 3.0 to 6.0% by mass. The content of polyhydric alcohols including polyols having a normal boiling point of 280° C. or higher in the ink may be within the above range.

[0063] The content of the water-soluble organic solvent is preferably 5.0% by mass to 40% by mass, 10% by mass to 30% by mass, 11% by mass to 25% by mass, or 12% by mass to 20% by mass, relative to the total amount of the ink composition. By keeping the content of the water-soluble organic solvent within the above range, the effects of the present invention tend to be more effectively and reliably achieved.

[0064] The content of the polyols is preferably 5.0% by mass to 30% by mass, 10% by mass to 20% by mass, or 12% by mass to 15% by mass, relative to the total amount of the ink composition. By being within such a range, the effects of the present invention tend to be more effectively and reliably achieved.

[0065] The content of the alkanediols is preferably 1.0% by mass to 15% by mass, 2.0% by mass to 10% by mass, or 3.0% by mass to 7.0% by mass, relative to the total amount of the ink composition. By being within such a range, the effects of the present invention tend to be more effectively and reliably achieved.

[0066] 1.7. Inorganic oxide particles The ink composition may contain inorganic oxide particles. Inorganic oxide particles refer to fine particles of an inorganic oxide dispersed in a dispersion medium. When inorganic oxide particles are contained, curling of the recording medium generally tends to be suppressed. Note that one type of inorganic oxide particle may be used alone, or two or more types may be used in combination.

[0067] The inorganic oxide particles are not particularly limited, but include, for example, metal oxides such as silica, alumina, titania, zirconia, antimony oxide, tin oxide, tantalum oxide, zinc oxide, cerium oxide, lead oxide, and indium oxide; metal nitrides such as silicon nitride, titanium nitride, and aluminum nitride; metal carbides such as silicon carbide and titanium carbide; metal sulfides such as zinc sulfide; metal carbonates such as calcium carbonate and magnesium carbonate; metal sulfates such as calcium sulfate and magnesium sulfate; metal silicates such as calcium silicate and magnesium silicate; metal phosphates such as calcium phosphate; metal borates such as aluminum borate and magnesium borate, and composites thereof. From the viewpoint of more effectively and reliably achieving the effects of the present invention, silica is preferred. The inorganic oxide particles may also form salts.

[0068] The content of inorganic oxide particles is preferably not more than 0.1% by mass, more preferably not more than 0.05% by mass, and even more preferably not more than 0.00% by mass, relative to the total amount of the ink composition. By keeping the content of inorganic oxide particles within the above range, the effects of the present invention tend to be more effectively and reliably achieved. Inorganic oxide particles do not have to be included.

[0069] 1.8. Betaine Betaine refers to a compound that has a positive charge and a negative charge at non-adjacent positions in the same molecule, and the positively charged atom is not bound to a dissociable hydrogen atom, forming an intramolecular salt, and the molecule as a whole has no charge. In this embodiment, the betaine is preferably one in which the positively charged site is a quaternary ammonium cation.

[0070] By including betaine in the ink composition, deflection of the ink composition or ejection failure caused by the ink composition drying in the nozzle of the inkjet head can be prevented, and ejection stability tends to be excellent.

[0071] The number of carbon atoms in the betaine compound is preferably 4 to 12, more preferably 4 to 7, and even more preferably 4 to 6. When the number of carbon atoms in the betaine is within the above range, ejection stability tends to be further improved.

[0072] The betaine is not particularly limited, but examples thereof include trimethylglycine, γ-butyrobetaine, homarine, trigonelline, carnitine, homoserine betaine, valine betaine, lysine betaine, ornithine betaine, alanine betaine, stachydrine, and glutamic acid betaine. Among these, trimethylglycine is preferred. This tends to further improve ejection stability. Note that the betaine may be used alone or in combination of two or more.

[0073] The betaine content is preferably from 0.0% to 15% by mass, from 1.0% to 10% by mass, or from 3.0% to 8.0% by mass, relative to the total amount of the ink composition. By keeping the betaine content within the above ranges, the effects of the present invention tend to be more effectively and reliably achieved.

[0074] 1.9.Other Ingredients The ink composition of this embodiment may contain components other than those described above, as necessary. Examples of such components include a pH adjuster, a wetting agent, and a chelating agent.

[0075] Examples of pH adjusters include inorganic acids (e.g., sulfuric acid, hydrochloric acid, nitric acid, etc.), inorganic bases (e.g., lithium hydroxide, sodium hydroxide, potassium hydroxide, ammonia, etc.), organic bases (triethanolamine, diethanolamine, monoethanolamine, tripropanolamine), organic acids (e.g., adipic acid, citric acid, succinic acid, etc.), etc. From the viewpoint of more effectively and reliably achieving the effects of the present invention, triethanolamine is preferred.

[0076] The content of the pH adjuster relative to the total amount of the ink composition is preferably 0.01 to 1.5 mass%, 0.05 to 1.0 mass%, 0.1 to 0.8 mass%, or 0.3 to 0.7 mass%. By keeping the content of the pH adjuster within the above range, the effects of the present invention tend to be more effectively and reliably achieved.

[0077] 2. Recording media The recording medium used for recording with the ink composition of this embodiment is not particularly limited, but examples include absorbent recording media, low absorbent recording media, and non-absorbent recording media, and among these, absorbent recording media are preferred.

[0078] Absorbent recording media include, but are not limited to, plain paper such as electrophotographic paper with high ink permeability, inkjet paper, and fabric. Examples of inkjet paper include inkjet paper with an ink absorbing layer made of silica particles or alumina particles, or a hydrophilic polymer such as polyvinyl alcohol (PVA) or polyvinylpyrrolidone (PVP).

[0079] Low-absorbency recording media are not particularly limited, but examples thereof include art paper, coated paper, cast paper, etc., which are used in general offset printing and have relatively low ink permeability. Non-absorbency recording media are not particularly limited, but examples thereof include plastic films and plates such as polyvinyl chloride, polyethylene, polypropylene, polyethylene terephthalate (PET), polycarbonate, polystyrene, polyurethane, etc.; metal plates such as iron, silver, copper, aluminum, etc.; metal plates and plastic films manufactured by vapor deposition of these various metals, alloy plates such as stainless steel and brass, and recording media in which a plastic film such as polyvinyl chloride, polyethylene, polypropylene, polyethylene terephthalate (PET), polycarbonate, polystyrene, polyurethane, etc. is adhered (coated) to a paper substrate.

[0080] 3. Inkjet recording method The inkjet recording method of this embodiment includes a discharge step of discharging the ink composition from an inkjet head and depositing it onto a recording medium, and may include other steps as necessary. Examples of other steps include a transport step of transporting the recording medium.

[0081] In the ejection step, the ink composition is ejected from an inkjet head and deposited on a recording medium. More specifically, a pressure generating means provided in the inkjet head is driven to eject the ink composition filled in the pressure generating chamber of the inkjet head from the nozzle. This ejection method is also called an inkjet method.

[0082] The inkjet head used in the ejection step includes a line head that performs recording by a line method and a serial head that performs recording by a serial method, and it is preferable to use a line head. When a line head is used, the recording speed is high, so that after the ink is attached to the recording medium, the time until the ink comes into contact with the transport roller or another recording medium is short, and the effect of the present invention is more effective.

[0083] In the line method using a line head, for example, an inkjet head having a width equal to or greater than the recording width of the recording medium is fixed to the recording device. The recording medium is then moved along a 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. An image is recorded on one surface of a single recording medium by performing a single scan in which ink droplets are ejected from the nozzles while the recording medium is moved along the scanning direction.

[0084] In the serial method using a serial head, for example, the inkjet head is mounted on a carriage that can move in the width direction of the recording medium. The carriage is then moved in the main scanning direction (the width direction of the recording medium), and ink droplets are ejected from the nozzles of the inkjet head in conjunction with this movement to record an image on the recording medium.

[0085] In the conveying process, the recording medium is conveyed in a predetermined direction within the recording device. More specifically, the recording medium is conveyed from the paper feed section to the paper discharge section of the recording device using a conveying roller or conveying belt provided within the recording device. During this conveying process, ink ejected from the inkjet head adheres to the recording medium, forming a recorded product. Conveyance may be performed continuously or intermittently.

[0086] 4. Inkjet recording device The inkjet recording apparatus of this embodiment has the ink composition described above and an inkjet head that ejects the ink composition. The inkjet head has a pressure chamber to which ink is supplied and a nozzle that ejects the ink. The inkjet recording apparatus may further have a transport means that transports the recording medium. The transport means is composed of a transport roller or a transport belt provided within the recording apparatus.

[0087] The inkjet recording device may have either a continuous supply ink container or a sub-tank as shown in Fig. 6, may be configured to allow attachment of an ink cartridge as shown in Fig. 7, or may be configured to allow supply of the ink composition from an ink bottle as shown in Fig. 8. In this case, the generation of foreign matter on the ink liquid surface can be suppressed, and the effects of the present invention are even more effective.

[0088] The inkjet recording apparatus according to this embodiment will be described below with reference to Fig. 5. In the XYZ coordinate system shown in Fig. 5, the X direction indicates the length direction of the recording medium, the Y direction indicates the width direction of the recording medium on the transport path within the recording apparatus, and the Z direction indicates the height direction of the apparatus.

[0089] As an example, the recording device 10 is a line-type inkjet printer capable of high-speed, high-density printing. The recording device 10 includes a feed unit 12 that stores recording media P such as paper, a conveyance unit 14, a belt conveyance unit 16, a recording unit 18, an Fd (face-down) discharge unit 20 as an "discharge unit," an Fd (face-down) loading unit 22 as a "loading unit," a reversing path unit 24 as a "reversing conveyance mechanism," an Fu (face-up) discharge unit 26, and an Fu (face-up) loading unit 28.

[0090] The feeding unit 12 is disposed at the bottom of the recording device 10. The feeding unit 12 includes a feeding tray 30 that stores recording media P, and a feeding roller 32 that sends the recording media P stored in the feeding tray 30 to the transport path 11.

[0091] The recording medium P stored in the feed tray 30 is fed by a feed roller 32 along the conveying path 11 to the conveying unit 14. The conveying unit 14 includes a conveying drive roller 34 and a conveying driven roller 36. The conveying drive roller 34 is driven to rotate by a drive source (not shown). In the conveying unit 14, the recording medium P is nipped between the conveying drive roller 34 and the conveying driven roller 36 and conveyed to the belt conveying unit 16 located downstream of the conveying path 11.

[0092] The belt conveying section 16 includes a first roller 38 located upstream on the conveying path 11, a second roller 40 located downstream, an endless belt 42 rotatably attached to the first roller 38 and the second roller 40, and a support 44 that supports the upper section 42a of the endless belt 42 between the first roller 38 and the second roller 40.

[0093] The endless belt 42 is driven by the first roller 38 or the second roller 40, which is driven by a drive source (not shown), so as to move from the +X direction to the −X direction in the upper section 42a. Therefore, the recording medium P conveyed from the conveying unit 14 is further conveyed downstream of the conveying path 11 in the belt conveying unit 16.

[0094] The recording unit 18 includes a line-type inkjet head 48 and a head holder 46 that holds the inkjet head 48. The recording unit 18 may also be a serial type in which the inkjet head is mounted on a carriage that moves back and forth in the Y-axis direction. The inkjet head 48 is disposed to face the upper section 42a of the endless belt 42 supported by the support body 44. The inkjet head 48 ejects ink toward the recording medium P as the recording medium P is transported in the upper section 42a of the endless belt 42, thereby performing recording. The recording medium P is transported downstream of the transport path 11 by the belt transport unit 16 while recording is being performed.

[0095] It should be noted that a "line-type inkjet head" is a head used in an inkjet recording device in which the nozzle area formed in a direction intersecting the transport direction of the recording medium P is arranged so as to be able to cover the entire intersecting direction of the recording medium P, and an image is formed by fixing one of the head or the recording medium P and moving the other. It should be noted that the nozzle area in the intersecting direction of the line head does not have to be able to cover the entire intersecting direction of all recording media P that the inkjet recording device is compatible with.

[0096] Furthermore, a first branch section 50 is provided downstream of the conveying path 11 of the belt conveying unit 16. The first branch section 50 is configured to be switchable between the conveying path 11 that conveys the recording medium P to the Fd discharge unit 20 or the Fu discharge unit 26 and a reversing path 52 of the reversing path section 24 that reverses the recorded side of the recording medium P and conveys the recording medium P again to the recording unit 18. Note that the recording medium P that is switched to the reversing path 52 by the first branch section 50 and conveyed has its recorded side reversed during the conveying process on the reversing path 52, and is conveyed again to the recording unit 18 so that the side opposite to the initially recorded side faces the inkjet head 48.

[0097] A second branch section 54 is further provided downstream of the first branch section 50 along the conveying path 11. The second branch section 54 is configured to be able to switch the conveying direction of the recording medium P so that the recording medium P is conveyed toward the Fd discharge section 20 or the recording medium P is conveyed toward the Fu discharge section 26.

[0098] The recording medium P transported from the second branching section 54 toward the Fd discharge section 20 is discharged from the Fd discharge section 20 and placed on the Fd placement section 22. At this time, the recording medium P is placed so that the recorded surface faces the Fd placement section 22. Also, the recording medium P transported from the second branching section 54 toward the Fu discharge section 26 is discharged from the Fu discharge section 26 and placed on the Fu placement section 28. At this time, the recording medium P is placed so that the recorded surface faces away from the Fu placement section 28.

[0099] Although the above description is of an example in which a line-type inkjet head is used, the inkjet recording apparatus according to this embodiment may also be a printer that uses a serial-type inkjet head (serial printer). In a serial printer, printing is performed by transporting the recording medium in a transport direction while moving the inkjet head in a direction intersecting the transport direction. [Example]

[0100] The present invention will be described in more detail below using examples and comparative examples, but the present invention is not limited to the following examples.

[0101] 1. Preparation of Ink Composition 1 to 4 are shown in Tables 1 to 4, which show the compositions of the ink compositions. The inkjet ink compositions of each example were obtained by placing the components in a mixing tank, mixing and stirring, and filtering through a membrane filter to obtain the compositions shown in Tables 1 to 4. The numerical values ​​for each component shown in each example in the tables represent mass % unless otherwise specified. The numerical values ​​for the pigment, inorganic oxide particles, and resin in the tables represent the mass % of the solid content of the pigment, inorganic oxide particles, and resin, respectively.

[0102] Details of the abbreviations and product ingredients used in Tables 1 to 4 are as follows, and the numbers to the right of the solvent abbreviations indicate the SP values ​​of the solvents.

[0103] [Pigment particles: self-dispersing pigment] CAB-O-JET300 (product name, solids content 15%, manufactured by Cabot Corporation)

[0104] [resin] Water-soluble urethane resin 1: Prepared by the following method. First, a four-neck flask equipped with a stirrer, thermometer, nitrogen gas inlet tube, and reflux condenser was prepared. 41.7 parts by weight of isophorone diisocyanate, 40.1 parts by weight of polypropylene glycol (number average molecular weight 2,000), 13.2 parts by weight of dimethylolpropionic acid, and 200.0 parts by weight of methyl ethyl ketone were placed in this four-neck flask and reacted at 80°C for 6 hours under a nitrogen gas atmosphere (primary reaction). Next, 0.6 parts by weight of ethylenediamine, 2.0 parts by weight of methanol, 2.4 parts by weight of dimethylolpropionic acid, and 100.0 parts by weight of methyl ethyl ketone were added. The residual isocyanate group percentage was confirmed by FT-IR, and the reaction was continued at 80°C until the desired residual percentage was reached (secondary reaction), yielding a reaction solution. The resulting reaction solution was cooled to 40°C, and then ion-exchanged water was added. A potassium hydroxide aqueous solution was then added while stirring at high speed with a homomixer. Methyl ethyl ketone was distilled off from the resulting liquid by heating under reduced pressure, and a liquid containing water-soluble urethane resin 1 was obtained.

[0105] For the obtained water-soluble urethane resin 1, hydrochloric acid was added to a liquid containing the water-soluble urethane resin 1 to precipitate the water-soluble urethane resin, and the resin was then vacuum-dried overnight at 40°C and dissolved in tetrahydrofuran to prepare a sample.The acid value of water-soluble urethane resin 1 was measured by potentiometric titration using a potassium hydroxide-methanol titrant, and was found to be 65 mgKOH / g.Furthermore, the weight-average molecular weight of the urethane resin, calculated as polystyrene, for the obtained water-soluble urethane resin 1, measured by gel permeation chromatography (GPC), was found to be approximately 21,000.

[0106] Water-soluble urethane resin 2: Prepared by the following method. Water-soluble urethane resin 2 was prepared in the same manner as water-soluble urethane resin 1, except that the amount of polypropylene glycol added was reduced and the amount of dimethylolpropionic acid added in the primary and secondary reactions was increased in the preparation of water-soluble urethane resin 1. Furthermore, when the acid value and weight-average molecular weight were measured using the same methods as for water-soluble urethane resin 1, the acid value of water-soluble urethane resin 2 was 75 mgKOH / g and the weight-average molecular weight was approximately 21,000.

[0107] · Water-soluble acrylic resin: Prepared by the following method. 20.0 parts of a styrene-acrylic acid copolymer with an acid value of 65 mg KOH / g and a weight-average molecular weight of 8,000 were dissolved in ion-exchanged water using sodium hydroxide equivalent to the acid value to obtain an aqueous solution. The resulting aqueous solution was pressure-filtered using a microfilter (manufactured by Fujifilm) with a pore size of 3.0 μm, and an appropriate amount of water was added to prepare an aqueous solution of the resin. The resin content in the aqueous solution was 20.0%.

[0108] Emulsion resin 1: X436 (product name, styrene acrylic resin emulsion, Tg 33°C, acid value 33 mgKOH / g, manufactured by Seiko PMC Corporation) Emulsion resin 2: A styrene-acrylic resin emulsion was prepared using styrene and acrylic monomers. The Tg was 10°C and the acid value was 33mgKOH / g.

[0109] [Lactam compounds] HEP (N-hydroxyethylpyrrolidone) 2-Pyrrolidone ε-caprolactam [Inorganic oxide particles] Silica SI-30 (product name, manufactured by JGC Catalysts and Chemicals Co., Ltd.) [Betaines] Trimethylglycine (betaine anhydrous, manufactured by Tokyo Chemical Industry Co., Ltd.) [Acetylene glycol surfactant] Olfine E1010 (product name, HLB value: 13-14, manufactured by Air Products) Surfynol 104PG50 (product name, HLB value: 4, manufactured by Nissin Chemical Industry Co., Ltd.) Surfynol 420 (product name, HLB value: 4, manufactured by Nissin Chemical Industry Co., Ltd.) [Other surfactants] BYK348 (product name, silicone surfactant, manufactured by BYK Japan) [pH adjuster] Triethanolamine [Solvent components] Glycerin Triethylene glycol 1,2-Hexanediol

[0110] 2. Evaluation Method A modified LX-10050 (product name, manufactured by Seiko Epson Corporation), a line inkjet printer equipped with a line head, was used as the recording device. In the modified printer, a stainless steel sub-tank was installed between the ink cartridge and the head. In Figure 6, the continuous supply ink container was eliminated, and ink was supplied from the ink cartridge to the head via the ink supply mechanism and ink flow path. The area of ​​the ink liquid surface (gas-liquid interface) where the ink composition filled in the subtank comes into contact with the internal air is 800 mm 2 When printing, the recording medium was A4 size copy paper "Xerox P Paper" (manufactured by Fuji Xerox Co., Ltd., basis weight: 64 g / m 2 , paper thickness: 88 μm) was used.

[0111] 2.1. Discharge reliability due to foreign matter at the gas-liquid interface After confirming that there were no non-ejecting nozzles in the above device, 40 cc of ink composition was filled into the sub-tank and left at 40°C for one week. Subsequently, continuous printing was performed using one of the line heads (600 nozzles) until 40 cc of ink composition was used. During this process, fresh ink that had not been left standing was supplied to the sub-tank to prevent the ink from running out. After printing, 0.5 cc of ink was sucked from the nozzles, and the nozzle surface was wiped with a rubber wiper (cleaning). The number of cleanings required until no non-ejecting nozzles were found was evaluated as follows. After the evaluation, recording devices in which non-ejecting nozzles were found were examined, and foreign matter was observed in the inkjet head and also in the sub-tank. (Evaluation criteria) A: Cleaning was performed three times or less and the non-ejecting nozzle was eliminated. B: Cleaning was performed 4 to 10 times, and the non-ejecting nozzle was eliminated. C: There were still non-ejecting nozzles even after cleaning 10 times

[0112] 2.2. Transfer resistance Under conditions of 25°C temperature and 50% relative humidity, printing duty: 100%, ink deposition amount: 4.5 mg / inch 2 At a printing speed of 30 sheets per minute, 1 x 1 cm solid patterns were printed in the printable printing area, spaced 1 cm apart, and the sheets were ejected face down, continuing until the stacked thickness reached 1 cm. The ink used was the initial ink that had not been left standing. Evaluation was performed using the following method based on the ink transfer marks (ink stains) on the side of the stacked paper. (Evaluation criteria) A: When observed from a distance of 30 cm from the laminated paper, the transfer marks were barely visible or not visible at all. B: When observed from a distance of 30 cm from the laminated paper, the transfer marks were visible, but when observed from a distance of 80 cm from the laminated paper, they were not visible. C: When observed from a distance of 80 cm from the laminated paper, transfer marks were visible.

[0113] 2.3.Compatibility The ink composition obtained above was placed in a 100 mL bottle, sealed, and left to stand in a thermostatic chamber at 60° C. for 24 hours, after which it was evaluated according to the following criteria based on the occurrence of phase separation and cloudiness. (Evaluation criteria) A: No separation or cloudiness between the oil and water layers was observed. B: No visible separation of the oil and water layers was observed, but slight cloudiness was observed. C: Separation of the oil and water layers was visible.

[0114] 2.4.Discharge stability After confirming that the nozzle discharge state of the recording device was normal, the ink composition obtained above was filled and printing was carried out. The ink was an initial ink that had not been left to stand. The same test pattern as for the transfer resistance test was printed, and 30 sheets were printed in a row. After printing, a nozzle check pattern was recorded to check for any non-ejecting nozzle patterns. If no non-ejecting nozzle patterns were found, and the nozzle check pattern showed a landing position deviation of 0.5 times or more the distance between adjacent nozzles, it was determined that there was a landing position deviation, and ejection stability was evaluated according to the following criteria. The evaluation was performed on one head consisting of 600 nozzles. (Evaluation criteria) A: There were no non-ejecting nozzles or misaligned landing positions. B: Non-ejecting nozzles and misaligned droplet landing positions were confirmed in five or fewer nozzles. C: Non-ejecting nozzles and misaligned droplet landing positions were confirmed in six or more nozzles.

[0115] 3. Evaluation Results The compositions and evaluation results of the inks used in each example are shown in Tables 1 to 4. These results show that an inkjet ink composition containing a pigment, an acetylene glycol surfactant having an HLB value of 5 or less, a lactam compound having a 6- to 8-membered lactam ring, a solvent component, and a water-soluble resin dissolved in the solvent component, wherein the content of the water-soluble resin is 0.3% by mass or more relative to the total mass of the inkjet ink composition, and the solvent component is an aqueous ink containing water, has excellent ejection reliability, transfer resistance, compatibility, and / or ejection stability.

[0116] Although not shown in the table, the above recording device was modified to not have a sub-tank and instead supply ink to the inkjet head from an ink pack, and evaluated in the same manner as in Comparative Example 4. The ejection reliability due to the gas-liquid interface was rated A. The ink pack did not produce an ink liquid surface (gas-liquid interface), and no foreign matter was generated. However, it was necessary to immediately stop printing when the ink in the ink pack ran out. Furthermore, when the same procedure was carried out as in Example 1 except that the sub-tank was changed to one with an ink liquid area of ​​1000 mm, the evaluation of foreign matter at the air-liquid interface was rated B. However, the maximum capacity of the sub-tank was increased, and the number of pages that could be recorded with the ink in the sub-tank increased. [Explanation of symbols]

[0117] 10...recording device, 11...conveyance path, 12...feed section, 14...conveyance section, 16...belt conveyance section, 18...recording section, 20...Fd discharge section, 22...Fd placement section, 24...reversal path section, 26...Fu discharge section, 28...Fu placement section, 30...feed tray, 32...feed roller, 34...conveyance drive roller, 36...conveyance 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 branch section, 52...reversal path, 54...second branch section, 56...discharge route roller pair, 64...discharge drive roller, 68...drive shaft, 76...placing surface, 78...convex portion, 80...first urging member, 82...second urging member, 84, 86...support shaft, P...recording medium, E...air-liquid interface, I...ink, 601...continuous supply ink container, 602...ink supply port, 603...atmosphere supply port, 604...ink storage chamber, 605...ink flow path, 606...subtank, 607...inkjet head, 701...ink cartridge, 702...ink supply port, 703...atmosphere communication port, 704...storage chamber, 801...ink bottle, 802...container body, 803...ink refill port.

Claims

1. An inkjet ink composition comprising a pigment, an acetylene glycol surfactant having an HLB value of 5 or less, a lactam compound having a 6- to 8-membered lactam ring, a solvent component, and a water-soluble resin dissolved in the solvent component, the content of the water-soluble resin is 0.3% by mass or more relative to the total mass of the inkjet ink composition, the solvent component contains water, making it a water-based ink; Inkjet ink composition.

2. It is used by being ejected by an inkjet recording device, an ink tank to which the inkjet ink composition is supplied in the inkjet recording apparatus, or an ink container to which the inkjet ink composition is supplied to the inkjet recording apparatus, has a structure in which an ink liquid surface, which is a gas-liquid interface between the inkjet ink composition and a gas, is formed; The ink-jet ink composition of claim 1 .

3. The maximum area of ​​the ink surface is 500 mm 2 That's all. The ink-jet ink composition of claim 2.

4. In the inkjet ink composition, a mass ratio (A / B) of a content A of the acetylene glycol surfactant to a content B of the lactam compound is 0.01 or more and 0.7 or less. The ink-jet ink composition of claim 1 .

5. The water-soluble resin includes a urethane resin. The ink-jet ink composition of claim 1 .

6. The inkjet ink composition contains no more than 0.1% by mass of resin particles relative to the total amount of the inkjet ink composition. The ink-jet ink composition of claim 1 .

7. The inkjet ink composition contains no more than 0.1% by mass of inorganic oxide particles relative to the total amount of the inkjet ink composition. The ink-jet ink composition of claim 1 .

8. The pigment comprises a self-dispersed pigment. The ink-jet ink composition of claim 1 .

9. The lactam compound includes ε-caprolactam. The ink-jet ink composition of claim 1 .

10. the solvent component contains an alkanediol compound having 5 or more carbon atoms as a water-soluble organic solvent; The ink-jet ink composition of claim 1 .

11. The solvent component contains a polyol having a normal boiling point of 280°C or higher as a water-soluble organic solvent. The ink-jet ink composition of claim 1 .

12. Used for recording on absorbent recording media, The ink-jet ink composition of claim 1 .

13. a discharge step of discharging the inkjet ink composition according to any one of claims 1 to 12 from an inkjet head to cause the ink composition to adhere to a recording medium; Inkjet recording method.

14. the inkjet head is a line head; The inkjet recording method according to claim 13.

15. An ink-jet recording medium comprising the ink-jet ink composition according to any one of claims 1 to 12 and an ink-jet head that ejects the ink-jet ink composition. Inkjet recording device.

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