Ink jet recording method and recording apparatus

Abstract

To provide an ink jet recording method capable of suppressing transfer of a recorded product to be obtained, and excellent in clogging recoverability and storage stability.SOLUTION: An ink jet recording method includes a first adhesion step of ejecting an ink composition from an ink jet head to cause the ink composition to adhere to one face of a recording medium, a feeding step of transporting the recording medium by a transport roller to feed the other face, which is a face opposite to the one face subjected to the first adhesion step, to a position facing the ink jet head, and a second adhesion step of ejecting the ink composition from the ink jet head to cause the ink composition to adhere to the other face fed, wherein the ink composition contains a pigment, an acetylene glycol-based surfactant, a lactam compound having a lactam ring as a six- to eight-membered ring, a solvent component, and a water-soluble urethane resin dissolved in the solvent component, the solvent component contains water, and the ink composition is an aqueous ink.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an inkjet 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, various studies have been conducted on the ejection stability when performing double-sided printing using an ink composition. For example, Patent Document 1 discloses an inkjet recording apparatus in which the ink contains colloidal silica to improve paper stacking properties by reducing wetting friction, and the control means controls the drying means or conveying means so that the ink starts drying within 0.4 seconds after the ink is deposited on the recording medium. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-006556 Summary of the Invention [Problem to be solved by the invention]

[0004] In the case of a water-based ink composition, the recording medium is transported, discharged, and stacked inside the recording device before the ink is sufficiently dried. When performing double-sided printing, after printing on the first recording side, the recording medium is immediately brought into contact with a transport roller to turn over, and the ink adheres to the contact surface of the transport roller, which easily stains the recording medium to be transported next. There are problems with such ink staining, and when attempting to prevent ink staining, the ink ejection stability and clogging recovery performance deteriorate. [Means for solving the problem]

[0005] The inkjet recording method of the present invention includes a first adhesion step of ejecting an ink composition from an inkjet head to adhere it to one side of a recording medium, a feeding step of transporting the recording medium by a transport roller and feeding the other side of the recording medium, which is the side opposite to the one side subjected to the first adhesion step, to a position facing the inkjet head, and a second adhesion step of ejecting the ink composition from the inkjet head to adhere it to the other side that has been fed, wherein the ink composition includes a pigment, an acetylene glycol-based surfactant, a lactam compound having a 6- to 8-membered lactam ring, a solvent component, and a water-soluble urethane resin dissolved in the solvent component, and the solvent component includes water, so that the ink composition is an aqueous ink.

[0006] The recording apparatus of the present invention is an inkjet recording apparatus for obtaining a recorded matter by the inkjet recording method described above, and includes the ink composition, the inkjet head, and the transport roller. [Brief explanation of the drawings]

[0007] [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] FIG. 1 is a diagram illustrating an example of an inkjet recording apparatus used in an inkjet recording method. [Figure 4] FIG. 1 is a diagram illustrating an example of an inkjet recording apparatus used in an inkjet recording method. DETAILED DESCRIPTION OF THE INVENTION

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

[0009] 1. Inkjet recording method The inkjet recording method according to this embodiment (hereinafter also simply referred to as "the recording method") comprises: a first deposition step of ejecting an ink composition from an inkjet head to deposit it on one side of a recording medium; a feeding step of transporting the recording medium by a transport roller and feeding the other side of the recording medium, which is the side opposite to the one side subjected to the first deposition step, to a position facing the inkjet head; and a second deposition step of ejecting the ink composition from the inkjet head to deposit it on the other side that has been fed, wherein the ink composition comprises a pigment, an acetylene glycol-based surfactant, a lactam compound having a 6- to 8-membered lactam ring, a solvent component, and a water-soluble urethane resin dissolved in the solvent component, and the solvent component contains water, making the ink composition an aqueous ink.

[0010] When recording on both sides of a recording medium using an aqueous ink composition, if the recording medium is immediately transported and discharged by a transport roller after the ink composition has adhered to the recording medium, the undried ink composition may adhere to the transport roller, or the ink composition adhered to the transport roller may adhere to the contact surface of the discharged recording material, 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 permeability is desirable as a means of suppressing transfer. Rapid penetration of the ink into the recording medium allows the ink to penetrate into the recording medium before the recording medium comes into contact with the transport roller or another recording medium, thereby suppressing transfer.

[0011] 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.

[0012] In contrast, in this embodiment, an acetylene glycol surfactant is used as a component to improve ink penetration, and a water-soluble urethane resin that is less likely to form foreign matter is used, making it possible to suppress transfer by forming a film on the surface of the recording medium early without reducing clogging recovery. However, the use of acetylene glycol surfactants tends to cause phase separation in the ink composition, resulting in reduced storage stability. Therefore, a lactam compound having a 6- to 8-membered lactam ring was used in combination. This suppressed phase separation in the ink composition and improved storage stability. In this way, it was possible to provide an ink composition that is excellent in clogging recovery properties, transfer resistance, and storage stability.

[0013] It is believed that the ink composition of the present invention has excellent clogging recovery properties, transfer resistance, and storage stability 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.

[0014] Each step included in this recording method and the ink composition used in this recording method will be described in detail below.

[0015] This recording method comprises a first adhesion step of ejecting an ink composition from an inkjet head to adhere it to one side of a recording medium, a feeding step of transporting the recording medium by a transport roller and feeding the other side, which is the side opposite to the one side subjected to the first adhesion step, to a position facing the inkjet head, and a second adhesion step of ejecting the ink composition from the inkjet head to adhere it to the other fed side. The fact that this recording method includes the first adhesion step and the second adhesion step means that recording is performed on both sides of the recording medium, and the present invention is particularly effective in such situations.

[0016] In the first and second deposition steps, the ink composition is ejected from the inkjet head and deposited on the 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.

[0017] The inkjet heads used in the first and second attachment steps include a line head that performs recording by a line method and a serial head that performs recording by a serial method.

[0018] The inkjet head used in this recording method is preferably a line head having a length equal to or greater than the length of the recording area of ​​the recording medium in a direction perpendicular to the transport direction, and the first and second deposition steps are preferably performed by scanning once each while moving the relative position of the inkjet head, which is a line head, and the recording medium. Such a recording method enables high-speed printing, while increasing the opportunity for the ink composition to come into contact with the transport roller before penetrating or drying, making the effects of the present invention even more effective.

[0019] 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.

[0020] In the feeding process, the recording medium that has completed the first attachment process is transported by a transport roller and fed to a position facing the inkjet head so that the side opposite to the side that underwent the first attachment process becomes the side that will undergo the second attachment process. This is the operation of turning the recording medium over. In this case, the diameter of the transport roller is preferably 2 cm or more, more preferably 3 cm or more, and even more preferably 4 cm or more. The use of such a transport roller increases the radius R of curvature when the recording medium is curved by the transport roller, reducing idle rotation of the recording medium and facilitating inversion, which is preferable. This allows the rotation speed of the roller to be increased, allowing the recording medium to be inverted quickly, which is preferable because it increases the recording speed. Meanwhile, in such cases, the ink adheres, and the ink composition that has not yet dried is more likely to be transferred to the transport roller, etc., making the effects of the present invention even more effective. The upper limit of the diameter of the transport roller is not limited, but may be 15 cm or less, or may be 10 cm or less.

[0021] If the outer peripheral surface of the transport roller is made of rubber, it is easy to invert and feed the recording medium that has completed the first adhesion step, and it is also easy to transfer the ink composition that has not yet dried to the transport roller, so the effects of the present invention are even more effective in such situations.

[0022] The rubber is preferably a synthetic rubber, such as styrene butadiene rubber, butadiene rubber, chloroprene rubber, butyl rubber, nitrile rubber, ethylene propylene rubber, ethylene propylene diene rubber, acrylic rubber, urethane rubber, or silicone rubber. In particular, rubbers having an ethylene propylene structure or a diene structure, such as styrene butadiene rubber, butadiene rubber, ethylene propylene rubber, and ethylene propylene diene rubber, are preferred, with rubbers having an ethylene propylene structure being particularly preferred.

[0023] In the feeding step, if the recording medium moves while contacting the outer peripheral surface of the transport roller over at least half of the circumference, the transport direction of the recording medium can be changed significantly starting from the transport roller, which is preferable because it shortens the time required to turn the recording medium over and the length of the transport path of the recording medium. On the other hand, since the recording speed is increased, the ink composition that has not yet dried can be easily transferred to the transport roller, making the effects of the present invention even more effective.

[0024] The recording speed of this recording method is preferably 4.5 m / min or more and 15.0 m / min or less, calculated as the conveying speed of the recording medium, which corresponds to the speed at which 15 to 50 A4 sheets (approximately 30 cm long) are printed in one minute. The printing speed is preferably 10 sheets / minute or more, more preferably 15 sheets / minute or more, and even more preferably 20 sheets / minute or more. In this embodiment, double-sided printing is used, so one double-sided printed sheet is counted as one sheet. Therefore, the number of pages is twice the number of sheets / minute. A4 size recording media are preferred. However, since the recording medium is turned over once per recording, which may result in ink transfer, the size of the recording medium is not limited. It is preferable to use sheets / minute as an indicator. When the speed is in the above range or higher, the time from when the ink is applied until the recording medium is transported by the transport roller is short, and when recording media recorded at such a speed are discharged and stacked in the disposal section of the recording device, there are more opportunities for the surfaces of the recording media to come into contact with each other before the ink composition penetrates or dries, making the effects of the present invention even more effective. There is no upper limit to the printing speed, but it is preferably 50 sheets / minute or less, and more preferably 40 sheets / minute or less.

[0025] 2. Ink composition In this recording method, the ink composition contains a pigment, an acetylene glycol surfactant, a lactam compound having a 6- to 8-membered lactam ring, a solvent component, and a water-soluble urethane resin dissolved in the solvent component, and the solvent component contains water, making it an aqueous ink. Use of such an ink composition makes it possible to achieve a recording method that is excellent in clogging recovery, transfer resistance, and storage stability.

[0026] 2.1.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 sulfur-containing groups such as 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.

[0027] 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.

[0028] 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.

[0029] 2.2. Acetylene glycol surfactants The ink composition contains an acetylene glycol-based surfactant. The inclusion of an acetylene glycol-based surfactant improves the ink's penetration and provides excellent transfer resistance. It also improves the ink's ejection characteristics and ejection stability. However, acetylene glycol-based surfactants have low water solubility, which can easily cause phase separation in the ink composition and reduce clogging recovery. The acetylene glycol surfactant may be used alone or in combination of two or more.

[0030] To further enhance the effects of the present invention, the acetylene glycol surfactant contained in the ink composition preferably has an HLB value of not more than 5. The lower limit of the HLB value is 0 or more, and preferably 1 or more. Furthermore, it is preferable to include those having an HLB of 5 or less and those having an HLB of more than 5, more preferable to include those having an HLB of 5 or less and those having an HLB of 7 or more, and even more preferable to include those having an HLB of 5 or less and those having an HLB of 10 or more. In this case, the HLB is 20 or less, and preferably 15 or less.

[0031] 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 104PG50 (HLB value=4), Surfynol 104, Surfynol 420, Surfynol 82, Surfynol DF110D, Surfynol 104S, Surfynol 420, Surfynol 82, and Surfynol MD-20 (all trade names, manufactured by Nissin Chemical Industry Co., Ltd.), and Olfine E1010 (trade name, HLB value: 13 to 14, manufactured by Air Products 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 at least one of Surfynol 104PG50 and Olfine E1010, and it is more preferable for the ink composition to contain Surfynol 104PG50 and Olfine E1010.

[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 A of the acetylene glycol surfactant is preferably 0.05% by mass or more and 5.0% by mass or less, 0.1% by mass or more and 3.0% by mass or less, or 0.2% by mass or more and 2.0% by mass or less, relative to the total amount of the ink composition. By setting the content A of the acetylene glycol surfactant within the above range, transfer resistance, clogging recovery, 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 1.0% by mass or less, more preferably 0.1% by mass or more and 0.5% by mass or less, even 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 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 1% by mass, from 0% to 0.5% by mass, or from 0% to 0.1% by mass, relative to the total amount of the ink composition.

[0038] 2.3. 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 a molecule form a ring through a dehydration condensation reaction. When the ink composition contains a lactam compound having a 6- to 8-membered ring, the ink composition improves transfer resistance, clogging recovery, and ejection stability. 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 ink composition tends to have further improved transfer resistance, clogging recovery, and ejection stability.

[0040] In the ink composition, the mass ratio A / B of the acetylene glycol surfactant content A to the lactam compound content B is preferably from 0.05 to 3.0, from 0.1 to 1.5, or from 0.2 to 1.0, more preferably from 0.25 to 0.6, and even more preferably from 0.3 to 0.5. When the mass ratio A / B is within the above range, the transfer resistance, clogging recovery, and ejection stability tend to be further improved. The mass ratio of the content of the acetylene glycol surfactant having an HLB value of 5 or less to the content B of the lactam compound may be within the above range, more preferably 0.05 to 0.3, and even more preferably 0.05 to 0.2.

[0041] The content B of the 6- to 8-membered ring lactam compound is preferably 0.1% by mass to 10% by mass, 0.5% by mass to 5.0% by mass, or 1.0% by mass to 3.0% by mass, relative to the total amount of the ink composition. By setting the content B of the 6- to 8-membered ring lactam compound within the above range, transfer resistance, clogging recovery, and ejection stability tend to be further improved.

[0042] 2.4.Water-soluble urethane resin The ink composition contains a water-soluble urethane resin dissolved in a solvent component. The inclusion of the water-soluble urethane resin improves transfer resistance, clogging recovery, and ejection stability. The water-soluble resin may be used alone or in combination of two or more.

[0043] The water-soluble urethane resin used in this embodiment is a water-soluble resin that dissolves 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-based 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 those that do not have an acid group, such as aliphatic polyether diols such as polyethylene glycol and polypropylene glycol; polyester polyols; polycarbonate polyols; diols having a carboxyl group such as 2,2-dimethylolpropionic acid, 2,2-dimethylolbutanoic acid, 2,2-dimethylolheptanoic acid, 2,2-dimethyloloctanoic acid, and tartaric acid; and diols having a sulfonic acid group such as 3-(2,3-dihydroxypropoxy)-1-propanesulfonic acid. Further, examples of polyols having an acid group such as a phosphoric acid group or a phosphonic acid group include polyols.

[0047] The acid value of the water-soluble urethane 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 water-soluble urethane resin within the above range, transfer resistance, clogging recovery, and ejection stability tend to be further improved. The acid value may be determined by potentiometric titration.

[0048] 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, clogging recovery, and ejection stability tend to be further improved. The weight-average molecular weight may be determined by GPC.

[0049] The content of the water-soluble resin is preferably 0.3% by mass to 3.0% by mass, 0.3% by mass to 2.0% by mass, or 0.4% 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, clogging recovery, and ejection stability tend to be further improved.

[0050] The ink may contain other water-soluble resins, such as acrylic resins, polyalkylene oxide resins, polyvinyl alcohol resins, and carboxymethyl cellulose resins.

[0051] 2.5.Resin particles From the viewpoint of clogging recovery, it is preferable that the ink composition does not contain resin particles. The resin particles are a resin emulsion or the like. The resin particles are a non-water-soluble resin dispersed in the ink. The resin particles are not particularly limited as long as they are water-soluble, and examples thereof include resin particles made of urethane-based resin, acrylic-based resin, fluorene-based resin, polyolefin-based resin, rosin-modified resin, terpene-based resin, polyester-based resin, polyamide-based resin, epoxy-based resin, vinyl chloride-based resin, or ethylene vinyl acetate-based resin.

[0052] 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 no more than 0.00% by mass. By setting the content of resin particles within the above range, the effects of the present invention can be more effectively and reliably achieved.

[0053] 2.6. Solvent Components The ink composition is a water-based ink and contains water as a solvent component, and may further contain an organic solvent.

[0054] 2.6.1.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.

[0055] 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.

[0056] 2.6.2. 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.

[0057] Polyhydric alcohols have two or more hydroxyl groups in the molecule, and examples thereof include polyols and alkanediols.

[0058] 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, triethylene glycol monobutyl ether, dipropylene glycol, trimethylolpropane, and glycerin. Examples include those having three or more hydroxyl groups in the molecule, those having an ether group in the skeleton (an intermolecular condensation product of alkanediol), and alkanediols having four or less carbon atoms. Among these, it is preferable to use glycerin, triethylene glycol, or triethylene glycol monobutyl ether in order to more effectively and reliably achieve the effects of the present invention.

[0059] 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, clogging recovery, and ejection stability. Alkanediols having 5 or more carbon atoms are preferred. By including 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-alkanediols are preferred.

[0060] The solvent component of the ink composition preferably contains, as a water-soluble organic solvent, a polyol such as glycerin having a normal boiling point of 280° C. or higher. By containing a polyol having a normal boiling point of 280° C. or higher, transfer resistance, clogging recovery, 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.

[0061] 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, or 15% by mass to 25% 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.

[0062] The content of the polyols is preferably from 5.0% to 30% by mass, and more preferably from 10% to 20% 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.

[0063] The content of the alkanediols is preferably from 2.0% to 10% by mass, or from 3.0% 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.

[0064] 2.7. 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 2.8.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 chelating agent, and a rust inhibitor.

[0070] 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.

[0071] The content of the pH adjuster is preferably 0.01 to 3.0 mass%, 0.1 to 2.0 mass%, or 0.5 to 1.5 mass%, relative to the total amount of the ink composition. 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.

[0072] 3. Inkjet recording device The inkjet recording apparatus of this embodiment is an inkjet recording apparatus for obtaining a recorded matter by the inkjet recording method described above, and includes the ink composition, the inkjet head, and the transport roller. In this embodiment, the transport roller transports the recording medium, which has undergone the first adhesion step, and feeds the other side of the recording medium, which is the side opposite to one side of the recording medium, to a position facing the inkjet head, where the second adhesion step is performed. Such a roller is the transport roller, and is a roller that transports the recording medium between the first adhesion step and the second adhesion step. In particular, it is a roller involved in the operation of turning over the recording medium. For example, a roller in a transport path along which the recording medium is transported when double-sided printing is performed, but not when single-sided printing is performed, is a transport roller of this embodiment. In addition, rollers that are used to transport the recording medium when double-sided printing is performed, but are not used to transport the recording medium when single-sided printing is performed, are transport rollers in this embodiment. However, these are merely examples, and the transport rollers are not limited to these. The transport path is the path along which the recording medium is transported.

[0073] One embodiment of an inkjet recording apparatus is shown in Figure 3. The inkjet recording apparatus may have an intermediate transport roller 117 as shown in Figure 3. The transport roller 117 is a roller that transports the recording medium between the first and second adhesion steps and is also called an intermediate roller. Adjacent to the transport roller 117 are rollers 118 and 119, which rotate in accordance with the transport roller 117 and assist the transport roller 117. The outer circumferential surface of the transport roller 117 is preferably made of rubber, which applies appropriate rotational resistance to the recording medium P passing by, allowing the recording medium P to be transported stably, and further enhancing the effectiveness of the effects of the present invention. When performing double-sided printing, the recording medium moves in contact with the outer circumferential surface of the transport roller 117, and the recording medium P is fed back to a position facing the inkjet head H in an inverted state. Furthermore, it is preferable for the diameter of such transport roller 117 to be 2 cm or more, as this makes it easier to turn over the recording medium P and further enhances the effects of the present invention. The inkjet head H is a line head. The inkjet recording apparatus has a motor (not shown) that drives rollers such as the transport roller 117.

[0074] An example of a recording method in the inkjet recording device shown in Fig. 3 is shown. First, in the inkjet recording device shown in Fig. 3, the motor is rotated in the forward direction to rotate the pickup roller 115, thereby feeding the paper P from the stack in the paper tray 113. The fed paper P is then fed by the intermediate roller 117 and the paper feed roller 120 through the transport path C1 until its leading edge reaches the printing start position. Then, when the leading edge of the paper P reaches the printing start position, printing on the front side begins.

[0075] After printing on the front side of the paper P is complete, the recording device reverses the printing surface of the paper P. This reversal is achieved by reversing the motor. When the motor is reversed, the paper feed roller 120, which is rotating in reverse, sends the paper P, whose front side has been printed, to the rear of the printing device. The sent-out paper P first enters below the intermediate roller 117, rotates around it as the intermediate roller 117 rotates forward, and then returns to the paper feed roller 120 from the upper part of the intermediate roller 117. This reverses the printing surface of the paper P from the front side to the back side. Then, after the entire paper P has passed the paper feed roller 120, the direction of rotation of the motor is reversed, and the paper P is fed until its leading edge reaches the printing start position, and printing on the back side begins. When printing on the back side is complete, the controller ejects the printed paper P to the paper output tray 125, ending the printing operation. The area below the intermediate roller 117 is a transport path along which the recording medium is transported when double-sided printing is performed, and is a transport path along which the recording medium is not transported when single-sided printing is performed, and the intermediate roller 117 here is the transport roller of this embodiment.

[0076] The intermediate roller 117 is a roller that moves while the recording medium is in contact with the outer circumferential surface of the transport roller over more than half the circumference during the feeding process, and may be a transport roller with a diameter of 2 cm or more.

[0077] Compared to the recording device example shown in Figure 4 (described later), the recording medium moves at a larger angle when it comes into contact with the outer circumferential surface of the transport roller, and the angle at which the recording medium's transport direction changes from the transport roller is larger in the recording device example shown in Figure 3. This allows the length of the recording medium transport path when reversing the recording medium to be relatively short, which is preferable because it allows the recording device to be made more compact. Furthermore, this is also preferable because the recording medium can be accurately transported even when the diameter of the transport roller is relatively large and the reversing operation is fast.

[0078] It is preferable that the transport roller is located on the side of the inkjet head that is opposite to the horizontal plane that includes the recording surface of the recording medium when the ink adhesion process is performed, since this makes it possible to make the length of the transport path of the recording medium relatively short when the recording medium is turned over. The transport roller preferably has a larger diameter than the roller located closest in the transport direction of the recording medium to the portion of the recording medium where the ink deposition step is performed. The transport roller is preferably a drive roller.

[0079] Next, another aspect of the inkjet recording apparatus is shown in Figure 4. The inkjet recording apparatus according to this embodiment will be described in further detail with reference to Figure 4. In the XYZ coordinate system shown in Figure 4, the X direction indicates the length direction of the recording medium, the Y direction indicates the width direction of the recording medium in the transport path within the recording apparatus, and the Z direction indicates the height direction of the apparatus.

[0080] 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 8, an Fd (face-down) discharge unit 20 as an "discharge unit," an Fd (face-down) placement unit 22 as a "placement unit," a reversing path unit 24 as a "reversing conveyance mechanism," an Fu (face-up) discharge unit 26, and an Fu (face-up) placement unit 28.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] The recording unit 8 includes a line-type inkjet head 48 and a head holder 46 that holds the inkjet head 48. The recording unit 8 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 so as to face the upper section 42a of the endless belt 42 that is supported by a support 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.

[0086] A first branching section 50 is provided downstream of the conveying path 11 of the belt conveying unit 16. The first branching 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 unit 24 that reverses the recorded side of the recording medium P and conveys the recording medium P again to the recording unit 8. The recording medium P that is switched to the reversing path 52 by the first branching 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 8 so that the side opposite to the initially recorded side faces the inkjet head 48.

[0087] 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.

[0088] 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. Of the above rollers, for example, the rollers in the reversing path section 24 are transport rollers of this embodiment.

[0089] 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.

[0090] 4. 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.

[0091] 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).

[0092] 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. [Example]

[0093] 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.

[0094] 1 and 2, Tables 1 and 2 show the compositions of the ink compositions of Examples and Comparative Examples and the evaluation results thereof.

[0095] 1. Preparation of Ink Composition Each component was placed in a mixing tank, mixed and stirred, and filtered through a membrane filter to obtain the inkjet ink composition shown in Tables 1 and 2. The numerical values ​​for each component shown in the tables represent % by mass unless otherwise specified. The numerical values ​​for colorants in the tables represent % by mass of the colorant solids content.

[0096] The details of the abbreviations and product ingredients used in Tables 1 and 2 are as follows, and the numbers to the right of the solvent abbreviations indicate the SP values ​​of the solvents. [Colorant] Carbon black (product name "CAB-O-JET300", self-dispersing pigment, manufactured by Cabot Corporation)

[0097] [Water-soluble resin] 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.

[0098] 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.

[0099] 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.

[0100] 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%.

[0101] [Resin particles] Urethane resin particles (product name "WBR-2122C", manufactured by Taisei Fine Chemical Co., Ltd.) [Lactam compounds] ε-caprolactam 2-Pyrrolidone 1-(2-hydroxyethyl)-2-pyrrolidone [Acetylene glycol surfactants] Surfynol 104PG50 (product name, manufactured by Nissin Chemical Industry Co., Ltd.) Olfine E1010 (product name, manufactured by Air Products) [Other surfactants] BYK348 (product name, silicone surfactant, manufactured by BYK Japan) [Water-soluble organic solvent] Glycerin Triethylene glycol Triethylene glycol monobutyl ether 1,2-Hexanediol [Betaine] Trimethylglycine (betaine anhydrous, manufactured by Tokyo Chemical Industry Co., Ltd.) [pH adjuster] Triethanolamine

[0102] 2. Evaluation Method The recording device was a PX-S270T (product name, manufactured by Seiko Epson Corporation), an inkjet printer with a double-sided printing mechanism, modified to become a line inkjet printer equipped with a line head. The recording device was configured as shown in Figure 3. The recording device is equipped with a double-sided printing rubber roller (diameter 4 cm, ethylene propylene diene rubber) at the position of roller 117 in Fig. 3, and has a mechanism for ejecting the paper with the printed surface of the first attachment step facing downwards after double-sided printing. The recording medium is inverted as it is conveyed while in contact with the outer circumferential surface of the double-sided printing roller. A4-size copy paper "Xerox P Paper" (manufactured by Fuji Xerox Co., Ltd., basis weight: 64 g / m) was used as the recording medium. 2 The recording was carried out using a recording medium (paper thickness: 88 μm) and the recording device.

[0103] 2.1. Transfer resistance (double-sided printing) The ink composition obtained above was filled into the recording device described above, and a black solid pattern was printed on both sides at a resolution of 600 dpi x 600 dpi under an environment of 10°C temperature and 80% relative humidity. This was continued until the thickness of the stacked paper reached 1 cm. The stacking speed was 15 sheets / min. The 1 cm thick stack of recorded materials obtained was evaluated based on the transfer marks on the side of the stacked paper using the following method. (Evaluation criteria) A: When observed from a distance of 30 cm from the laminated paper, no transfer marks were visible. 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.

[0104] 2.2.Discharge stability After confirming that the nozzle discharge state was normal in the above device, the ink composition obtained above was filled and a test pattern was printed on a recording medium. The inkjet head was then filled with ink and allowed to idle for 5 minutes, after which the test pattern was printed again and the number of nozzles in which the ink impact position was misaligned was counted. A landing position misalignment of 50% or more relative to the distance between adjacent nozzles was defined as having occurred, and evaluation was performed according to the following criteria. (Evaluation criteria) A: There were no nozzles where the landing position was shifted. B: The number of nozzles where the landing position shifted was less than 1% of the total number of nozzles C: The number of nozzles where the landing position shifted was more than 1% but less than 3% of the total number of nozzles D: The number of nozzles where the landing position was misaligned was more than 3% of the total number of nozzles.

[0105] 2.3.Clogging recovery After confirming that there were no non-ejecting nozzles in the above device, the inkjet head was left uncapped at 40°C for one week. After leaving it, 0.5cc 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: (Evaluation criteria) A: Cleaning was performed three times or less, and the non-ejecting nozzle disappeared. B: Cleaning was performed four or five times and the non-ejecting nozzle was eliminated. C: Cleaning was performed six times and no non-ejecting nozzles were found. D: Even after cleaning six times, there were still non-ejecting nozzles.

[0106] 2.4.Storage stability The ink composition obtained above was placed in a 100 mL glass bottle, sealed, and then the glass bottle was placed in a thermostatic chamber at 60°C and left for one week. After leaving the bottle, it was removed and allowed to cool sufficiently to room temperature, and then viscosity was measured in accordance with JIS Z8809 using a vibration viscometer. The rate of increase in viscosity after leaving the bottle relative to the initial viscosity before leaving it was calculated, and storage stability was evaluated according to the following criteria. (Evaluation criteria) A: The viscosity change rate was less than ±1%, and no aggregates were observed. B: The viscosity change rate was ±1% or more, but no aggregates were observed. C: Viscosity change rate is ±1% or more, and aggregates are observed

[0107] 3. Evaluation Results The compositions and evaluation results of the inks used in each example are shown in Tables 1 and 2. Tables 1 and 2 show that excellent transfer resistance can be achieved when recording is performed using an inkjet recording method comprising: a first deposition step of ejecting an ink composition from an inkjet head and depositing it on one side of a recording medium; a feeding step of transporting the recording medium by a transport roller and feeding the other side, opposite to the one side subjected to the first deposition step, to a position facing the inkjet head; and a second deposition step of ejecting the ink composition from the inkjet head and depositing it on the other side, wherein the ink composition comprises a pigment, an acetylene glycol surfactant, a lactam compound having a 6- to 8-membered lactam ring, a solvent component, and a water-soluble urethane resin dissolved in the solvent component, the solvent component including water, and the ink composition is an aqueous ink.

[0108] 4. Reference evaluation: Transfer resistance (single-sided printing) As a reference evaluation, transfer resistance was evaluated in the same manner as the above-described transfer resistance evaluation method, except that printing was performed on only one side. The results are shown in Tables 1 and 2. The results of the reference evaluation show that the effects of the present invention are even more effective when double-sided printing is performed. [Explanation of symbols]

[0109] 8...recording section, 10...recording device, 11...conveying path, 12...feeding section, 14...conveying section, 16...belt conveying section, 20...Fd discharge section, 22...Fd placement section, 24...reversing path section, 26...Fu discharge section, 28...Fu placement section, 30...feed tray, 32...feeding roller, 34...conveying drive roller, 36...conveying 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 portion, 52...reverse path, 54...second branch portion, 56...discharge roller pair, 64...discharge drive roller, 68...drive shaft, 76...loading surface, 78...convex portion, 80...first urging member, 82...second urging member, 84, 86...support shaft, 113...paper tray, 115...pickup roller, 117...convex roller, 118, 119, 120...roller, 125...paper discharge tray, H...inkjet head, P...recording medium.

Claims

1. a first deposition step of ejecting an ink composition from an inkjet head and depositing it on one side of a recording medium; a feeding step of feeding the recording medium by a feeding roller, and feeding the other surface of the recording medium, which is the surface opposite to the one surface on which the first adhering step has been performed, to a position facing the inkjet head; a second deposition step of ejecting the ink composition from the inkjet head and depositing it on the other surface to which the ink composition has been fed; the ink composition includes a pigment, an acetylene glycol surfactant, a lactam compound having a 6- to 8-membered lactam ring, a solvent component, and a water-soluble urethane resin dissolved in the solvent component; the solvent component contains water, and the ink composition is a water-based ink; Inkjet recording method.

2. the content of the water-soluble urethane resin is 0.3% by mass or more and 3.0% by mass or less with respect to the total amount of the ink composition; The inkjet recording method according to claim 1 .

3. the content of the lactam compound is 0.5% by mass or more and 5.0% by mass or less with respect to the total amount of the ink composition; The inkjet recording method according to claim 1 .

4. the content of the acetylene glycol surfactant is 0.2% by mass or more and 2.0% by mass or less with respect to the total amount of the ink composition; The inkjet recording method according to claim 1 .

5. The acid value of the water-soluble urethane resin is 40 to 100 mgKOH / g. The inkjet recording method according to claim 1 .

6. In the 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 0.1 or more and 1.5 or less. The inkjet recording method according to claim 1 .

7. The pigment is a self-dispersing pigment. The inkjet recording method according to claim 1 .

8. The lactam compound includes ε-caprolactam. The inkjet recording method according to claim 1 .

9. The solvent component contains a polyol organic solvent having a normal boiling point of 280°C or higher. The inkjet recording method according to claim 1 .

10. The diameter of the transport roller is 2 cm or more. The inkjet recording method according to claim 1 .

11. In the feeding step, the recording medium moves while contacting the outer peripheral surface of the transport roller over at least half a circumference. The inkjet recording method according to claim 1 .

12. The outer circumferential surface of the conveying roller is made of rubber. The inkjet recording method according to claim 1 .

13. the inkjet head is a line head having a length equal to or greater than the length of a recording area of ​​the recording medium in a direction intersecting the transport direction, the first and second deposition steps are each performed by scanning once while moving the relative positions of the inkjet head and the recording medium; The inkjet recording method according to claim 1 .

14. The printing speed is 15 sheets / minute or more. The inkjet recording method according to claim 1 .

15. An inkjet recording apparatus for obtaining a recorded matter by the recording method according to any one of claims 1 to 14, comprising: an ink jet head including the ink composition, the ink jet head, and the transport roller; Inkjet recording device.

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