Ink jet ink composition and recording method

Abstract

To provide an inkjet ink composition that is excellent in suppression of curling of recording media, discharge stability, and suppression of ink transfer to recording media.SOLUTION: An aqueous inkjet ink composition is provided, which contains a color material, an acetylene glycol-based surfactant, glycerin, and a 6- to 8-membered lactam, wherein the content of the glycerin is 9 mass% or less relative to the total mass of the ink composition, and the mass ratio of the content of the 6- to 8-membered lactam to the content of the acetylene glycol-based surfactant is 0.5 or more and less than 5.SELECTED DRAWING: None

Description

[Technical field]

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

[0002] Inkjet recording methods are capable of recording high-definition images with a relatively simple device, and have made rapid developments in various fields. On the other hand, there are problems with recording media curling when recording with water-based inks, and ink drying and thickening at the nozzles can easily cause deflection and non-ejection. For this reason, various studies have been conducted to improve the performance of inks, including these points. For example, Patent Document 1 discloses an inkjet recording ink that contains a pigment, colloidal silica, an acetylene glycol surfactant, and trimethylglycine, which is a betaine. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-7444 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, the above method was not sufficient in terms of suppressing curling of the recording medium, ejection stability, and suppression of ink transfer onto the recording medium. [Means for solving the problem]

[0005] The inkjet ink composition of the present invention is an aqueous inkjet ink composition comprising a colorant, an acetylene glycol surfactant, glycerin, and 6- to 8-membered ring lactams, wherein the content of the glycerin is 9 mass% or less based on the total mass of the ink composition, and the mass ratio of the content of the 6- to 8-membered ring lactams to the content of the acetylene glycol surfactant is 0.5 or more and less than 5.

[0006] The inkjet recording method of the present invention is a recording method including an ink depositing step of ejecting the inkjet ink composition from an inkjet head and depositing it on a recording medium. [Brief description of the drawings]

[0007] [Figure 1] FIG. 2 is a diagram illustrating an example of a recording apparatus used in the present embodiment. [Diagram 2] 1 shows ink compositions and evaluation results of examples of this embodiment. [Diagram 3] 4 shows ink compositions and evaluation results of comparative examples of this embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Below, an embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described in detail, but the present invention is not limited to this embodiment, and various modifications are possible without departing from the gist of the present invention.

[0009] 1. Inkjet ink composition The aqueous inkjet ink composition according to this embodiment (hereinafter simply referred to as the "ink composition") is an aqueous inkjet ink composition that contains a colorant, an acetylene glycol surfactant, glycerin, and 6- to 8-membered ring lactams, wherein the content of the glycerin is 9 mass% or less with respect to the total mass of the ink composition, and the mass ratio of the content of the 6- to 8-membered ring lactams to the content of the acetylene glycol surfactant is 0.5 or more and less than 5.

[0010] Organic solvents with high moisturizing properties, such as glycerin, are excellent moisturizers and can prevent ink from drying in the nozzles and thickening, causing flight deviations and non-ejection (deterioration of intermittency). On the other hand, these organic solvents tend to cause curling on the recording medium on which they are used. This is presumably because the organic solvents with high moisturizing properties promote the absorption of ink into the recording medium, and the absorbed ink is retained on the recording medium, which delays the drying of water from the recording medium, making curling more likely to occur and more likely to remain. Among organic solvents with high moisturizing properties, glycerin is a particularly excellent moisturizer and can prevent ink from drying. On the other hand, it also makes the recording medium more likely to curl. There are two types of curl: curl that occurs immediately when ink is applied to the recording medium, and curl that remains on the recording medium after time has passed since recording and the ink has dried. The above curl can include both types of curl. Therefore, by setting the content of glycerin in the ink to a predetermined level or less, it is possible to prevent curling of the recording medium. In this study, when the glycerin content in the ink was reduced to a specified level, the compatibility of the acetylene glycol surfactant contained in the ink with water decreased. As a result, separation of the acetylene glycol surfactant in the ink was observed. This leads to a decrease in the storage stability of the ink, and a decrease in the ejection stability when the ink is ejected from an inkjet head due to the separated components. In particular, in a recording device, when the ink dries in the nozzle, phase separation is likely to occur between the acetylene glycol surfactant and water, which leads to a decrease in ejection stability, such as non-ejection when the ink is ejected from the nozzle or, even if the ink is ejected, flight deviation occurs. In addition, when the inkjet head is left uncapped for a long period of time, phase separation of the acetylene glycol surfactant is also likely to occur.

[0011] In addition, the acetylene glycol surfactant has the function of making it easier for the ink to penetrate and be absorbed into the recording medium, but if the acetylene glycol surfactant is not sufficiently dissolved in water, this function cannot be fully expressed. As a result, the ink remains on the surface of the recording medium, and this adheres to the components of the path that transports the recording medium in the recording device, and then adheres to another recording medium. Or it adheres directly to another recording medium. In this way, the other recording medium is soiled. This is also called ink transfer. This type of ink transfer is likely to occur.

[0012] When the glycerin content in the ink is below a certain level, the solubility of the acetylene glycol surfactant in water, which is the main solvent component of the ink, is poor and it is prone to separation. This is presumably because the ink has low moisture retention, water evaporates easily from the ink, reducing the amount of water in the ink, or because the presence of glycerin increases the solubility of the acetylene glycol surfactant in water, resulting in low solubility when the glycerin content is low.

[0013] Therefore, when 6- to 8-membered ring lactams were added to the ink at a predetermined mass ratio to the acetylene glycol surfactant, the acetylene glycol surfactant was less likely to phase separate from water, and the ejection stability and transfer suppression were excellent. The 6- to 8-membered ring lactams improved the solubility of the acetylene glycol surfactant in water, and the transfer suppression was excellent. In addition, the 6- to 8-membered ring lactams also had moisturizing properties, but curling of the recording medium was less likely to occur, and the curl suppression was also excellent.

[0014] Each component of the ink composition of this embodiment will be described in detail below.

[0015] 1.1.Colorants The coloring material is not particularly limited, but examples thereof include dyes and pigments. Among these, it is preferable to use pigments because they can be used with a wide range of recording media and are resistant to fading due to light, gas, etc.

[0016] The pigment is not particularly limited, but examples thereof include azo pigments (including, for example, azo lakes, insoluble azo pigments, condensed azo pigments, chelate azo pigments, etc.), polycyclic pigments (for example, phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, etc.), nitro pigments, nitroso pigments, organic pigments such as aniline black, carbon black (for example, furnace black, thermal lamp black, acetylene black, channel black, etc.), metal oxides, etc. Examples of pigments include inorganic pigments such as metal sulfides and metal chlorides; and extender pigments such as silica, calcium carbonate and talc. The pigments may be used alone or in combination of two or more.

[0017] The pigment is not particularly limited, but examples thereof include self-dispersing pigments in which a hydrophilic group is introduced onto the surface of the pigment particles by utilizing a chemical reaction, and resin-dispersed pigments. Resin-dispersed pigments are pigments dispersed in resin. The resin used to disperse the pigment is also called dispersant resin. Dispersant resin means a resin that is applied to the surface of a pigment to improve the pigment's water dispersibility. Resin-dispersed pigments are pigments in which dispersant resin is adsorbed, attached, or coated on the pigment.

[0018] The dispersant resin can be a water-soluble resin, a water-insoluble resin, etc. The resin-dispersed pigment can be prepared, for example, by a method in which the dispersant resin and the pigment are stirred in water to disperse the pigment, or a method in which the dispersant resin and the pigment are stirred in an organic solvent or the like, and then transferred to an aqueous layer for emulsification.

[0019] Self-dispersing pigments are pigments in which functional groups for improving the water dispersibility of the pigment are introduced directly or indirectly onto the surface of the pigment by chemical bonding. The functional groups are hydrophilic groups, such as carboxyl groups, sulfo groups, and phosphorus-containing groups such as phosphate groups and phosphonic groups.

[0020] The pigment preferably contains at least one of a self-dispersing pigment and a pigment dispersed by a dispersant resin, and more preferably contains a self-dispersing pigment. When a dispersant resin or other dispersant is used, each of them may be used alone or in combination of two or more. As the dye, known dyes can be used.

[0021] The content of the colorant relative to the total amount of the ink composition is preferably 0.5% by mass or more, more preferably 1.0 to 14% by mass, even more preferably 2.0 to 12% by mass, even more preferably 4.0 to 10% by mass, and still more preferably 6.0 to 8.0% by mass.

[0022] 1.2. Lactams with 6-8 membered rings The ink composition of the present embodiment contains a lactam having a 6- to 8-membered ring, preferably a lactam having a 6- or 7-membered ring, and more preferably a lactam having a 7-membered ring.

[0023] The lactams refer to compounds having a structure in which a carboxyl group and an amino group in the molecule are subjected to dehydration condensation to form a ring.

[0024] As described above, when the ink composition contains a low content of an organic solvent with high moisture retention, in particular glycerin, the ink exhibits excellent curl suppression, but the solubility of the acetylene glycol surfactant in water decreases, resulting in poor ejection stability and poor transfer suppression. The ink composition of this embodiment contains a 6- or 7-membered ring lactam, and thus the acetylene glycol surfactant has excellent solubility in water, excellent ejection stability, excellent transfer inhibition, and excellent curl inhibition.

[0025] The lactams may or may not have a substituent on the lactam ring, and may be, for example, derivatives having a substituent on the lactam ring.

[0026] The compound of a seven-membered ring lactam (having six carbon atoms constituting the lactam ring) is not particularly limited, but examples thereof include ε-caprolactam and its derivatives, etc. Among these, it is preferable to contain ε-caprolactam from the viewpoint of improving the ejection stability, etc. Examples of the six-membered lactams include δ-lactams and their derivatives.

[0027] The mass ratio of the content of the 6- to 8-membered ring lactams to the content of the acetylene glycol surfactant is 0.5 to 5. The mass ratio is preferably 1.0 to 4.0, more preferably 2.0 to 3.5, and even more preferably 2.5 to 3.0. When the mass ratio is equal to or higher than the above range, the water solubility and transferability of the acetylene glycol surfactant are superior, and when the mass ratio is equal to or lower than the above range, the ejection stability is superior.

[0028] The 6- to 8-membered ring lactam may be a compound that is solid as a simple substance at room temperature. If the content of the 6- to 8-membered ring lactam is excessive, the discharge stability may decrease due to the lactam itself, and therefore it is preferable to contain the lactam in an amount not exceeding a predetermined amount.

[0029] The content of the 6- to 8-membered ring lactams relative to the total mass of the ink composition is preferably 0.1% by mass or more, or preferably 4.0% by mass or less, more preferably 0.5 to 3.5% by mass, more preferably 1.0 to 3.0% by mass, and even more preferably 2.0 to 2.5% by mass. When the content of the 6- to 8-membered ring lactams relative to the total mass of the ink composition is within the above range, the water solubility, transferability, and ejection stability of the acetylene glycol surfactant are more excellent.

[0030] 1.3. Acetylene glycol surfactants By including an acetylene glycol surfactant in the ink composition, the ink composition ejected from the nozzle is easily turned into droplets, and can be ejected well, continuously, and stably. In other words, ejection is stabilized. This makes it possible to prevent the ink from being ejected from the nozzle or to prevent the ink from flying in a curved path. Furthermore, among surfactants, acetylene glycol surfactants cause less foaming of the ink, and are therefore preferable in terms of excellent ejection stability.

[0031] In addition, when the ink composition does not contain an acetylene glycol surfactant and thus the ejection is unstable, the ejection tends to be unstable from the beginning regardless of whether the ink in the nozzles is dried or not.

[0032] In addition, the ink composition contains an acetylene glycol surfactant, which improves the wetting and spreading properties and permeability of the ink composition, particularly when recording on an absorbent recording medium such as plain paper, and tends to provide excellent image quality and color development. In addition, the ink easily permeates the recording medium, which makes it difficult for the ink to remain on the recording medium, and therefore provides excellent transferability of the ink.

[0033] The acetylene glycol surfactant is not particularly limited, but examples thereof include acetylene glycol and its alkylene oxide adducts, specifically represented by the following formula (1).

[0034] [ka] In the above formula (1), R 1 , R 1' , R 2 , and R 2' each independently represents a linear or branched alkyl group having 1 to 5 carbon atoms; -OR 3 -OR 3' are each independently -OH or -O(C m H 2m O) n H. Here, m is an integer of 1 to 5. Also, n is 25 or less, and the added alkylene oxide (C m H2m O) is the average degree of polymerization.

[0035] The number of carbon atoms in the main chain of the compound represented by formula (1) is preferably 6 to 15. More preferably, it is any one of 8, 10, 12, and 14, more preferably 10 or 12, and even more preferably 10.

[0036] In this specification, the term "main chain" refers to the main chain of acetylene glycol as determined based on the IUPAC nomenclature. The acetylene glycol surfactant may be used alone or in combination of two or more.

[0037] R 1 , and R 1' are each preferably a straight-chain alkyl group having 1 to 5 carbon atoms, more preferably a straight-chain alkyl group having 2 to 4 carbon atoms, and further preferably a straight-chain propyl group.

[0038] R 2 , and R 2' are each preferably a linear alkyl group having 1 to 5 carbon atoms, more preferably a linear alkyl group having 1 to 3 carbon atoms, and further preferably a methyl group.

[0039] m is preferably 1 to 4, more preferably 2 to 3, and even more preferably 2. n is preferably 20 or less, more preferably 16 or less, and even more preferably 12 or less. On the other hand, n is preferably 4 to 25, more preferably 6 to 25, and even more preferably 8 to 25.

[0040] Also, -OR 3 -OR 3' are each preferably represented by -OH, and -OR 3 -OR 3' It is also preferred that both are represented by --OH.

[0041] Further specific structures of the acetylene glycol surfactants include, but are not limited to, for example, 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.

[0042] Among the acetylene glycol surfactants, the -OR 3 -OR 3' The compound in which is -OH is particularly preferred because the ink composition has excellent wettability and permeability to a recording medium and has particularly excellent image quality, but on the other hand, it tends to have particularly poor solubility in water. For this reason, the ink composition of the present embodiment is particularly useful.

[0043] The content of the acetylene glycol surfactant is preferably 5.0% by mass or less relative to the total amount of the ink composition, more preferably 0.1 to 4.0% by mass, more preferably 0.2 to 3% by mass, even more preferably 0.3 to 2% by mass, and even more preferably 0.4 to 1.0% by mass, still more preferably 0.5 to 0.9% by mass, and more preferably 0.6 to 0.8% by mass. When the content of the acetylene glycol-based surfactant is in the above range or more, the ejection stability tends to be improved, and when the content of the acetylene glycol-based surfactant is in the above range or less, phase separation of the acetylene glycol-based surfactant in the ink composition is easily prevented, and the ejection stability tends to be improved. In addition, the mass ratio of the content of the 6- to 8-membered ring lactam to the content of the acetylene glycol surfactant is preferably easily set within the above-mentioned range.

[0044] Among acetylene glycol surfactants, those with an HLB value of 5 or less are preferred. In this case, the permeability of the ink composition tends to be further improved. The HLB value is preferably 0 or more, more preferably 1 to 4, even more preferably 2 to 4, and particularly preferably 3 to 4. When the HLB value is in the above range or more, phase separation is less likely to occur, and ejection stability tends to be improved, which is preferable.When the HLB value is in the above range or less, transfer is less likely to occur, which is preferable. Here, the HLB value is a value that represents the balance between the hydrophobicity and hydrophilicity of a surfactant, and the smaller the HLB value, the more hydrophobic the surfactant is, and the larger the HLB value, the more hydrophilic the surfactant is. In the present invention, the HLB value is calculated by the Griffin method.

[0045] The acetylene glycol surfactant having an HLB value of 5 or less is not particularly limited. For example, among the acetylene glycols represented by the above formula (1), -OR 3 -OR 3' are each independently -OH or -O(C m H 2m O) n H, and n is preferably independently 15 or less, more preferably 10 or less, and even more preferably 5 or less. In the formula (1), -OR 3 -OR 3' is particularly preferred.

[0046] The specific structure of the acetylene glycol surfactant having an HLB value of 5 or less is not particularly limited, but examples thereof include 2,4,7,9-tetramethyl-5-decyne-4,7-diol or its alkylene oxide adducts, each of which independently has an added mole number n of 15 or less.

[0047] The content of the acetylene glycol surfactant having an HLB value of 5 or less relative to the total mass of the ink composition may be in the same range as the content of the acetylene glycol surfactant described above relative to the total mass of the ink composition, and is preferably 0.05 to 0.5% by mass, more preferably 0.1 to 0.4% by mass, and even more preferably 0.2 to 0.3% by mass. The mass ratio of the content of 6- to 8-membered ring lactams to the content of the acetylene glycol surfactant having an HLB value of 5 or less may be in the same range as the above-mentioned range of the mass ratio of the content of 6- to 8-membered ring lactams to the content of the acetylene glycol surfactant. Further, the mass ratio is preferably from 1.5 to 15, more preferably from 2 to 13, and further preferably from 5 to 10. When the content and mass ratio are within the above ranges, the acetylene glycol surfactant is more excellent in water solubility, ejection stability, transfer suppression, and the like, which is preferable.

[0048] The ink composition of the present embodiment may contain an acetylene glycol surfactant having an HLB value of greater than 5. When an acetylene glycol surfactant having an HLB value of greater than 5 is contained, the acetylene glycol surfactant has better water solubility, ejection stability, and the like, which is preferable. The ink may contain both an acetylene glycol surfactant having an HLB value of more than 5 and an acetylene glycol surfactant having an HLB value of not more than 5. In this case, the acetylene glycol surfactant is preferred because it has particularly excellent water solubility, ejection stability, transfer inhibition, and the like. The HLB value of the acetylene glycol surfactant is more preferably at least 6, even more preferably at least 7, and particularly preferably at least 8. The upper limit of the HLB value is preferably 14 or less, 13 or less, or 12 or less.

[0049] Specific examples of the structure of the acetylene glycol surfactant having an HLB value of more than 5 include, for example, the acetylene glycol represented by the above formula (1), which has the structure: -OR 3 -OR 3' However, independently of each other, -O(C m H 2mO) n H, and n is preferably independently 6 or greater. n is more preferably 11 or greater, and further preferably 16 or greater. Although not particularly limited, examples thereof include 5,8-dimethyl-6-dodecyne-5,8-diol or an alkylene oxide adduct thereof, 4,7-dimethyl-5-decyne-4,7-diol or an alkylene oxide adduct thereof, and an alkylene oxide adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, in which any one or each of the mole numbers of addition of the adducts is within the above-mentioned range or more.

[0050] The content of the acetylene glycol surfactant having an HLB value of more than 5 relative to the total mass of the ink composition may be in the same range as the content of the above-mentioned acetylene glycol surfactant relative to the total mass of the ink composition. The mass ratio of the content of 6- to 8-membered ring lactams to the content of the acetylene glycol surfactant having an HLB value of greater than 5 may be in the same range as the range of the mass ratio of the content of the above-mentioned 6- to 8-membered ring lactams to the content of the acetylene glycol surfactant.

[0051] The mass ratio of the acetylene glycol surfactant having an HLB value of 5 or less to the content (total content) of acetylene glycol surfactants is preferably 0.6 or less, more preferably 0.1 to 0.5, and even more preferably 0.2 to 0.4.

[0052] Glycerin The inkjet ink composition of this embodiment contains glycerin, and the content of glycerin is 9 mass % or less relative to the total mass of the ink composition. Glycerin has excellent moisturizing properties, and the ink containing glycerin suppresses drying of the water in the ink and provides excellent ejection stability. In addition, the acetylene glycol surfactant has excellent water solubility and excellent transfer suppression. On the other hand, curling is likely to occur, so by setting the glycerin content in the ink to 9% by mass or less, curling can be effectively suppressed. The content is preferably 0.5 to 7% by mass, more preferably 1 to 5% by mass, and further preferably 2 to 4% by mass. When the content is within the above range, the ejection stability, transfer suppression, curl suppression, etc. are more excellent.

[0053] 1.5.Resin The inkjet ink composition of this embodiment may contain a resin. Among the resins, the dispersant resin for dispersing the pigment has been described above, so the other resins will be described below. In the case where the ink contains a resin, the ink has excellent transfer suppression and is therefore preferred. In addition, as described below, in the case where the ink contains a resin, the water solubility of the acetylene glycol surfactant can be improved, and the ink has excellent transfer suppression and ejection stability. The resin may be a water-soluble resin, resin particles, etc. The water-soluble resin is preferred. The content of the resin in the ink is preferably 0.1 to 5% by mass, more preferably 0.2 to 3% by mass, and even more preferably 0.2 to 2% by mass.

[0054] 1.5.1. Water-soluble resin The resin may be a water-soluble resin, which is preferable. Examples of the water-soluble resin include, but are not limited to, urethane resin, acrylic resin, polyalkylene oxide resin, polyvinyl alcohol resin, and carboxymethyl cellulose resin. Among these, urethane resin and acrylic resin are preferable, and urethane resin is more preferable.

[0055] In the present invention, the "water-soluble resin" refers to a resin that dissolves in water or an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent. In particular, it is a resin that dissolves in water. Specifically, it refers to a resin that does not remain undissolved or the entire mixed liquid does not appear cloudy when mixed with water at 1% by mass at room temperature and stirred. Preferably, it is a resin that can exist in water or an aqueous medium, particularly in water, in a state without a particle size when measured by dynamic light scattering. Moreover, the ink is contained in the ink in a dissolved state in the solvent component of the ink.

[0056] The water-soluble urethane resin means a water-soluble urethane resin having a polar group in the molecular structure. The polar group may be in the form of a salt. The polar group is preferably an acid group. Examples of the acid group include phosphorus-containing groups such as a carboxyl group, a sulfonic acid group, and a phosphoric acid group.

[0057] As described above, when the ink composition contains an acetylene glycol-based surfactant, the acetylene glycol-based surfactant has low solubility in water, etc., and therefore tends to undergo phase separation from the water as the ink composition dries, resulting in a decrease in intermittency and clogging recovery properties; however, when the ink contains a water-soluble resin, the above-mentioned phase separation is more effectively prevented.

[0058] The water-soluble urethane resin has repeating units derived from polyisocyanate and polyol, among which those having repeating units derived from polyol having an acid group are preferred, and resins having repeating units derived from polyisocyanate, polyol having no acid group, and polyol having an acid group are preferred. The water-soluble urethane resin may further have repeating units derived from polyamine.

[0059] The polyisocyanate refers to a compound having two or more isocyanate groups in its molecular structure, and is not particularly limited, but examples thereof include aliphatic polyisocyanates and aromatic polyisocyanates.

[0060] The aliphatic polyisocyanate is not particularly limited, but examples thereof include polyisocyanates having a chain structure such as tetramethylene diisocyanate, dodecamethylene diisocyanate, hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, 2-methylpentane-1,5-diisocyanate, and 3-methylpentane-1,5-diisocyanate; and polyisocyanates having a cyclic structure such as isophorone diisocyanate, hydrogenated xylylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 1,4-cyclohexane diisocyanate, methylcyclohexylene diisocyanate, and 1,3-bis(isocyanatemethyl)cyclohexane.

[0061] The aromatic polyisocyanate is not particularly limited, but examples thereof include tolylene diisocyanate, 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-dibenzyl diisocyanate, 1,5-naphthylene diisocyanate, xylylene diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, α,α,α',α'-tetramethylxylylene diisocyanate, and the like.

[0062] A polyol is a compound having two or more hydroxyl groups in its molecular structure. The polyol in the present embodiment is not particularly limited, but may be a polyol having no acid group or a polyol having an acid group.

[0063] The polyol having no acid group is not particularly limited, but examples thereof include polyether polyol, polyester polyol, and polycarbonate polyol.

[0064] The polyether polyol is not particularly limited, but examples thereof include addition polymers of alkylene oxides and polyols, and glycols.

[0065] The alkylene oxide is not particularly limited, and examples thereof include ethylene oxide, propylene oxide, butylene oxide, α-olefin oxide, etc. Examples of polyols to be addition polymerized with the alkylene oxide include diols such as 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 4,4-dihydroxyphenylpropane, 4,4-dihydroxyphenylmethane, hydrogenated bisphenol A, dimethylolurea and derivatives thereof, etc.; triols such as glycerin, trimethylolpropane, 1,2,5-hexanetriol, 1,2,6-hexanetriol, pentaerythritol, trimethylolmelamine and derivatives thereof, and polyoxypropylenetriol, etc.

[0066] Examples of glycols include (poly)alkylene glycols such as tetramethylene glycol, hexamethylene glycol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol, and (poly)tetramethylene glycol; ethylene glycol-propylene glycol copolymers; and the like.

[0067] The polyester polyol is not particularly limited, but examples thereof include acid esters. The acid components constituting the acid ester are not particularly limited, but examples thereof include aromatic dicarboxylic acids such as phthalic acid, naphthalenedicarboxylic acid, biphenyldicarboxylic acid, and tetrahydrophthalic acid; alicyclic dicarboxylic acids such as hydrogenated products of these aromatic dicarboxylic acids; aliphatic dicarboxylic acids such as malonic acid, succinic acid, tartaric acid, oxalic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, alkyl succinic acid, linoleic acid, maleic acid, fumaric acid, mesaconic acid, citraconic acid, and itaconic acid; and the like. Anhydrides, salts, derivatives (alkyl esters, acid halides) of these can also be used as the acid component. In addition, components forming an ester with the acid component are not particularly limited, but examples thereof include polyols such as diols and triols; glycols such as (poly)alkylene glycols; and the like. Examples of polyols and glycols include those exemplified as components constituting the above-mentioned polyether polyols.

[0068] The polycarbonate polyol is not particularly limited, and may be, for example, a polycarbonate polyol produced by a known method, specifically, an alkanediol-based polycarbonate diol such as polyhexamethylene carbonate diol, etc. Also, a polycarbonate diol obtained by reacting a carbonate component such as alkylene carbonate, diaryl carbonate, dialkyl carbonate, etc., or phosgene with an aliphatic diol component, etc. may be used.

[0069] The polyol having an acid group is not particularly limited, and examples thereof include polyols having an acid group such as a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, a phosphonic acid group, etc. Among these, it is preferable that the polyol is at least one of phosphorus-containing groups such as a carboxyl group, a sulfonic acid group, and a phosphoric acid group, and it is more preferable that the polyol is a carboxyl group.

[0070] The polyol having a carboxylic acid group is not particularly limited, but examples thereof include dimethylol acetic acid, dimethylol propionic acid, dimethylol butanoic acid, and dimethylol butyric acid.

[0071] The acid group of the polyol having an acid group may be in a salt state. The cation forming such a salt is not particularly limited, but may be, for example, an alkali metal ion or an organic amine cation. The alkali metal ion is not particularly limited, but may be, for example, lithium, sodium, potassium, etc. The organic amine cation is not particularly limited, but may be, for example, ammonium ion, dimethylamine, etc.

[0072] The polyamine is not particularly limited, but examples thereof include monoamines having a plurality of hydroxy groups, such as dimethylolethylamine, diethanolmethylamine, dipropanolethylamine, and dibutanolmethylamine; bifunctional polyamines, such as ethylenediamine, propylenediamine, hexylenediamine, isophoronediamine, xylylenediamine, diphenylmethanediamine, hydrogenated diphenylmethanediamine, and hydrazine; and trifunctional or higher polyamines, such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, polyamidepolyamine, and polyethylenepolyimine.

[0073] The acid value of the water-soluble urethane resin is preferably 40 to 100 mgKOH / g, more preferably 40 to 90 mgKOH / g, even more preferably 45 to 80 mgKOH / g, and even more preferably 50 to 70 mgKOH / g. The acid value of the water-soluble urethane resin is not particularly limited, but can be adjusted, for example, by the amount of polyol having an acid group. In addition, the method of measuring the acid value can be the method described in the examples below.

[0074] The weight average molecular weight of the water-soluble urethane resin is preferably 5000 to 150000, more preferably 10000 to 100000, even more preferably 15000 to 50000, even more preferably 20000 to 30000, and even more preferably 20000 to 23000. The weight average molecular weight within the above range tends to improve the ejection reliability. The weight average molecular weight of the water-soluble urethane resin is not particularly limited, but can be adjusted, for example, by the reaction temperature and reaction time of the polyisocyanate and the polyol. In addition, the method of measuring the weight average molecular weight can be the method described in the examples below.

[0075] The number average molecular weight of the water-soluble urethane resin is preferably 2000 to 7000, more preferably 3500 to 5000. The number average molecular weight within the above range tends to improve the ejection reliability. The weight average molecular weight of the water-soluble urethane resin is not particularly limited, but can be adjusted, for example, by the reaction temperature and reaction time of the polyisocyanate and the polyol. In addition, the method of measuring the weight average molecular weight can be the method described in the examples below.

[0076] The water-soluble acrylic resin may have the same composition as the acrylic resin of the resin particles described later. However, in order to make the resin water-soluble, it is preferable to increase the content of hydrophilic groups in the molecule. Examples of hydrophilic groups include acid groups, polyoxyalkylene groups, and hydroxyl groups.

[0077] The content of the water-soluble resin is in the same range as the content of the resin described above, but is preferably 0.05% by mass or more, and more preferably 0.1 to 5.0% by mass, based on the total amount of the ink composition. It is further preferably 0.1 to 4.0% by mass, more preferably 0.2 to 3.0% by mass, even more preferably 0.3 to 2.0% by mass, even more preferably 0.3 to 1.0% by mass, and even more preferably 0.4 to 0.8% by mass. When the content of the water-soluble resin is in the above range, the water solubility, ejection stability, transfer suppression, etc. of the acetylene glycol surfactant are more excellent.

[0078] 1.5.2.Resin particles The resin may be resin particles. The resin particles are not water-soluble resins, but resin particles dispersed in a solvent in the ink. Examples of such resins include resin emulsions. When the resin is in the form of resin particles, like the water-soluble resin described above, the acetylene glycol surfactant is more effectively prevented from undergoing phase separation from water.

[0079] The resin particles are not particularly limited, but examples thereof include urethane resins, acrylic resins, fluorene resins, polyolefin resins, rosin-modified resins, terpene resins, polyester resins, polyamide resins, epoxy resins, vinyl chloride resins, or ethylene vinyl acetate resins. From the viewpoint of intermittency and clogging recovery, it is preferable to use these resin particles in the form of emulsion. The resin dispersion particles may be used alone or in combination of two or more kinds. Urethane-based resins, acrylic-based resins and polyester-based resins are preferred, and urethane-based resins and acrylic-based resins are more preferred.

[0080] The urethane resin is a general term for resins having a urethane bond, and is not particularly limited, but examples thereof include polyether-type urethane resins having an ether bond in the main chain, polyester-type urethane resins having an ester bond in the main chain, and polycarbonate-type urethane resins having a carbonate bond in the main chain. The urethane resin may be a preparation prepared by a known method, or a commercially available product.

[0081] The acrylic resin is a general term for a polymer obtained by polymerizing at least an acrylic monomer such as (meth)acrylic acid or a (meth)acrylic acid ester as one component. The acrylic resin is not particularly limited, but examples thereof include a polymerized (meth)acrylic monomer such as (meth)acrylic acid or a (meth)acrylic acid ester, and a copolymerized (meth)acrylic monomer with another monomer, such as a styrene-acrylic resin. The acrylic resin may be a preparation prepared by a known method, or a commercially available product may be used.

[0082] When the resin is in the form of resin particles, they are preferably the same as the water-soluble resin. The content of the resin particles in the ink can be in the same range as the content of the above-mentioned resin or water-soluble resin. The glass transition point of the resin of the resin particles is preferably −50 to 70° C., more preferably −10 to 50° C., and further preferably 0 to 40° C. When the glass transition point is above the above range, ejection stability is superior, and when it is below the above range, transfer inhibition is superior, which is preferable.

[0083] 1.6. Betaine Betaine means a compound having a positive charge and a negative charge at non-adjacent positions in the same molecule, with no dissociable hydrogen bonded to the positively charged atom, forming an intramolecular salt, and having no charge as a whole molecule. In the present embodiment, the betaine is preferably one in which the positively charged site is a quaternary ammonium cation.

[0084] By including betaine in the ink composition, it is possible to prevent the ink composition from drying in the nozzles of the inkjet head, causing deflection of the ink composition and non-ejection, and the ink composition tends to have excellent intermittency. The intermittency is the degree to which non-ejection and deflection of the ink occur due to the ink drying in the nozzles from which the ink was not ejected during recording, etc., and the ink thickens.

[0085] 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 them, it is preferable to contain at least one of trimethylglycine, γ-butyrobetaine, and carnitine, and it is more preferable to contain at least one of trimethylglycine and γ-butyrobetaine. This tends to further improve clogging recovery. Note that betaine may be used alone or in combination of two or more.

[0086] The number of carbon atoms constituting the betaine is preferably 4 to 12, more preferably 4 to 7, and further preferably 4 to 6. When the number of carbon atoms of the betaine is within the above range, stability against contamination by electrostatic foreign matter tends to be further improved.

[0087] The content of betaine is preferably 1.0% by mass or more relative to the total amount of the ink composition. It is further preferably 3.0 to 13% by mass, more preferably 5.0 to 10% by mass, even more preferably 6.0 to 9.0% by mass, and even more preferably 6.0 to 8.0% by mass. When the content of betaine is 3.0% by mass or more, the ejection stability and curl resistance tend to be excellent, and when the content of betaine is 13% by mass or less, phase separation of the acetylene glycol surfactant in the ink composition can be suppressed, and clogging recovery tends to be excellent.

[0088] 1.7. Inorganic oxide particles The ink composition of this embodiment may or may not contain inorganic oxide particles. The inorganic oxide particles refer to fine particles of an inorganic oxide that are dispersed in a dispersion medium.

[0089] The ink composition containing inorganic oxide particles tends to have better curl resistance. In addition, when the ink composition contains both betaine and inorganic oxide particles, the curl resistance tends to be particularly good. On the other hand, in terms of better ejection stability, it is preferable that the content of inorganic oxide particles is small, and it is more preferable that the ink composition does not contain inorganic oxide particles.

[0090] The inorganic oxide particles are not particularly limited, but examples thereof include 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. The inorganic oxide particles may form a salt. In addition, the inorganic oxide particles may be used alone or in combination of two or more.

[0091] Among these, from the viewpoint of improving curl resistance, it is preferable to contain at least one of silica, alumina, titania, and zirconia, and it is more preferable to contain silica.

[0092] The inorganic oxide particles have an average particle size of preferably 100 nm or less, more preferably 20 to 100 nm, further preferably 30 to 80 nm, and even more preferably 40 to 60 nm. When the inorganic oxide particles have an average particle size in the above range, they tend to have excellent intermittency.

[0093] The average particle size of inorganic oxide particles can be measured by a particle size distribution measuring device that uses dynamic light scattering as the measurement principle. Such particle size distribution measuring devices are not particularly limited, but an example thereof is the "Zeta Potential, Particle Size, and Molecular Weight Measuring System ELSZ2000ZS" (product name) manufactured by Otsuka Electronics Co., Ltd., which uses a homodyne optical system as a frequency analysis method. The above-mentioned average particle size means the average particle size based on the number of particles.

[0094] The content of inorganic oxide particles is preferably 8.0% by mass or less (does not exceed 8.0% by mass) based on the total amount of the ink composition as solid content mass. More preferably, it is 5.0% by mass or less, even more preferably, it is 4.0% by mass or less, and particularly preferably, it is 2.0% by mass or less. Furthermore, it is preferably 1% by mass or less, more preferably, it is 0.5% by mass or less, and even more preferably, it is 0.1% by mass or less. The lower limit is 0% by mass or more, and it does not have to be included.

[0095] On the other hand, it is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, even more preferably 1.0% by mass or more, and particularly preferably 2.0% by mass or more. By having the content of inorganic oxide particles in the above range or more, curl resistance tends to improve. On the other hand, when it is less than the above range, ejection stability is more excellent, which is preferable.

[0096] 1.8. Organic Solvents The ink composition of the present embodiment may contain an organic solvent. The organic solvent is not particularly limited, and examples thereof include monohydric alcohols, polyols, and glycol ethers. Among them, it is more preferable to contain polyols, and it is even more preferable to contain polyols having a normal boiling point of more than 280°C. The organic solvent may be used alone or in combination of two or more kinds. The above-mentioned glycerin is also one of the organic solvents of polyols.

[0097] The monohydric alcohols are not particularly limited, but examples thereof include methanol, ethanol, 1-propanol, isopropanol, 1-butanol, 2-butanol, isobutanol, and 2-methyl-2-propanol.

[0098] The glycol ethers are not particularly limited, but examples thereof include triethylene glycol monomethyl ether, triethylene glycol dimethyl ether, triethylene glycol monobutyl ether, diethylene glycol monobutyl ether, and dipropylene glycol monopropyl ether.

[0099] Polyols are compounds having a structure in which a hydrocarbon, which may have an alkylene oxide structure in the molecule, is substituted with two or more hydroxyl groups. Examples include alkane polyols having alkane diols or more, condensation of the hydroxyl groups between two alkane polyols, and (poly)alkylene oxide structures of alkanes.

[0100] Among the polyols, examples of polyols having a standard boiling point of more than 280° C. include, but are not limited to, triethylene glycol, tetraethylene glycol, glycerin, etc. Examples of polyols having a standard boiling point of 280° C. or less include, but are not limited to, ethylene glycol, diethylene glycol, pentaethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, 1,3-propanediol, 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, etc.

[0101] Among organic solvents, polyols with a normal boiling point of over 280°C have high moisture retention and excellent ink ejection stability. They are also preferable because they increase the water solubility of acetylene glycol surfactants and suppress phase separation of the acetylene glycol surfactants. However, they tend to curl easily.

[0102] The content of polyols having a normal boiling point of more than 280° C. in the ink is preferably 25% by mass or less, more preferably 0.5 to 23% by mass, even more preferably 1.0 to 20% by mass, and particularly preferably 5.0 to 15.0% by mass. Further, 10.0 to 15.0% by mass is more preferable. On the other hand, 10.0% by mass or less is also preferable.

[0103] When the content of the polyol having a normal boiling point of more than 280° C. in the ink is within the above range, curling is more effectively suppressed, which is preferable.When the content is more than the above range, ejection stability and water solubility of the acetylene glycol surfactant are more effectively improved, which is preferable.

[0104] The content of the polyol having a normal boiling point of 280° C. or less in the ink is preferably 0.5 to 20% by mass, and when the content is within the above range, ejection stability is more excellent, which is preferable. The content of the organic solvent is preferably from 1.0 to 30% by mass, more preferably from 5.0 to 25% by mass, and even more preferably from 10 to 20% by mass, relative to the total amount of the ink-jet ink composition.

[0105] 1.9. Alkaline The ink composition of the present embodiment may contain an alkali. The alkali is not particularly limited, but examples thereof include organic bases and inorganic bases. The organic base is not particularly limited, but examples thereof include triethanolamine, diethanolamine, monoethanolamine, tripropanolamine, etc. The inorganic base is not particularly limited, but examples thereof include lithium hydroxide, sodium hydroxide, potassium hydroxide, etc.

[0106] The content of the alkali is preferably 0.01 to 1.0 mass %, more preferably 0.01 to 0.5 mass %, even more preferably 0.05 to 0.5 mass %, and still more preferably 0.1 to 0.5 mass %, relative to the total amount of the ink-jet ink composition.

[0107] 1.10.Water The water contained in the ink composition of this embodiment is not particularly limited, but examples thereof include ion-exchanged water, ultrafiltered water, reverse osmosis water, and distilled water.

[0108] The ink of the present embodiment is a water-based ink composition, and a water-based ink composition is an ink composition in which the solvent component contained in the ink is at least mainly water.

[0109] The water content relative to the total amount of the ink composition is preferably 50.0% by mass or more, more preferably 50.0 to 98.0% by mass, even more preferably 52.5 to 72.5% by mass, more preferably 55 to 70% by mass, even more preferably 57.5 to 67.5% by mass, and still more preferably 60 to 65% by mass.

[0110] 1.11.Other Ingredients In addition to the above-mentioned components, the ink composition of the present embodiment may contain other known components that can be used in conventional ink compositions. The other components are not particularly limited, but may include, for example, a dissolution aid, a viscosity adjuster, a pH adjuster, an antioxidant, a preservative, a corrosion inhibitor, a chelating agent for capturing a specific metal ion that affects dispersion, other additives, and organic solvents other than those mentioned above. The other components may be used alone or in combination of two or more.

[0111] 2. Recording medium The recording medium used for recording with the ink composition of this embodiment is not particularly limited, but examples thereof include absorbent recording media, low absorbent recording media, and non-absorbent recording media, and among these, absorbent recording media are preferred.

[0112] Examples of the absorbent recording medium include, but are not limited to, plain paper such as electrophotographic paper having high ink permeability, inkjet paper (paper exclusively for inkjet printers having an ink absorbing layer made of silica particles or alumina particles, or an ink absorbing layer made of a hydrophilic polymer such as polyvinyl alcohol (PVA) or polyvinylpyrrolidone (PVP)), and fabrics.

[0113] The low-absorbency recording medium is not particularly limited, but examples thereof include art paper, coated paper, cast paper, and the like, which are used in general offset printing and have relatively low ink permeability.

[0114] Non-absorbent recording media are not particularly limited, but examples 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.; or metal plates and plastic films produced 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. The present embodiment is preferable because it can be used for recording on the above-mentioned recording medium. In particular, when the ink is used for recording on an absorbent recording medium, curling is likely to occur, but in the case of the present embodiment, curling is effectively suppressed, which is particularly useful.

[0115] 3. Recording method The recording method of the present embodiment includes an ink deposition step of ejecting the ink composition of the present embodiment from an inkjet head and depositing it on a recording medium, and may also include other steps, such as a transport step of transporting the recording medium, as necessary.

[0116] 3.1.Ink application process In the ink deposition step, the ink composition of the present embodiment 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 a nozzle.

[0117] Inkjet heads used in the ink application step include a line head that performs recording by a line recording method and a serial head that performs recording by a serial recording method.

[0118] In the line recording method using a line head, for example, an inkjet head (line head) having a width equal to or greater than the recording width of the recording medium is fixed to the recording device. Then, the recording medium is moved along the sub-scanning direction (the recording medium transport direction), 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 in one scan. Scanning is an operation in which the inkjet head ejects ink onto the recording medium while changing the relative positions of the recording medium and the inkjet head. In the case of the line recording method, it is useful because it allows continuous high-speed recording on a large number of recording media. On the other hand, it takes a relatively short time from when the ink adheres to the recording medium until the ink on the recording medium comes into contact with the members of the recording medium transport path of the recording device, and it also takes a relatively short time until the recorded recording medium is stacked on the paper discharge tray. For this reason, transfer is particularly likely to occur, but the ink of this embodiment can suppress transfer and is particularly useful.

[0119] In a serial recording method using a serial head, for example, an inkjet head is mounted on a carriage that can move in the width direction of the recording medium. The carriage is then moved in the main scanning direction (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.

[0120] 3.2.Transportation process The inkjet recording method of the present embodiment may include a transport step. In the transport step, the recording medium is transported in a predetermined direction in the recording device. More specifically, the recording medium is transported from a paper feed section to a paper discharge section of the recording device using a transport roller or a transport belt provided in the recording device. During the transport process, the ink composition discharged from the inkjet head adheres to the recording medium, forming a recorded matter. The ink adhesion step and the transport step may be performed simultaneously or alternately.

[0121] 4. Recording device The recording apparatus of the present embodiment includes an inkjet head having nozzles for ejecting inkjet ink onto a recording medium, and a transport means for transporting the recording medium. The inkjet head includes pressure chambers to which ink is supplied and nozzles for ejecting the ink. The transport means includes a transport roller and a transport belt provided within the recording apparatus.

[0122] An example of a recording device according to this embodiment will be described below with reference to Fig. 1. In the XYZ coordinate system shown in Fig. 1, 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 in the recording device, and the Z direction indicates the height direction of the device.

[0123] As an example, the recording device 10 is a line recording type inkjet printer capable of high speed and high density printing. The recording device 10 includes a feed section 12 that stores a recording medium P such as paper, a conveying section 14, a belt conveying section 16, a recording section 18, an Fd (face down) discharge section 20 as an "discharge section", an Fd (face down) placement section 22 as a "placement section", an inversion path section 24 as an "inversion conveying mechanism", an Fu (face up) discharge section 26, and a Fu (face up) placement section 28.

[0124] 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 out the recording media P stored in the feeding tray 30 to the transport path 11.

[0125] The recording medium P stored in the feed tray 30 is fed by the feed roller 32 along the transport path 11 to the transport section 14. The transport section 14 includes a transport drive roller 34 and a transport driven roller 36. The transport drive roller 34 is driven to rotate by a drive source (not shown). In the transport section 14, the recording medium P is nipped between the transport drive roller 34 and the transport driven roller 36 and transported to the belt transport section 16 located downstream of the transport path 11.

[0126] The belt conveying section 16 comprises 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 supporting an upper section 42a of the endless belt 42 between the first roller 38 and the second roller 40.

[0127] The endless belt 42 is driven to move from the +X direction to the -X direction in the upper section 42a by the first roller 38 or the second roller 40 driven by a drive source (not shown). Therefore, the recording medium P conveyed from the conveying unit 14 is further conveyed in the belt conveying unit 16 to the downstream side of the conveying path 11.

[0128] 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 be a serial type in which the inkjet head is provided on a carriage that reciprocates 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 44. When the recording medium P is transported in the upper section 42a of the endless belt 42, the inkjet head 48 ejects ink toward the recording medium P to perform recording. The recording medium P is transported to the downstream side of the transport path 11 by the belt transport unit 16 while recording is being performed.

[0129] A line-type inkjet head (line head) is a head that is used in a recording device in which the nozzle area formed in a direction intersecting the transport direction of the recording medium P is provided so as to cover the entire recording area in the 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. 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 recording device supports.

[0130] Further, a first branching section 50 is provided downstream of the conveying path 11 of the belt conveying section 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 section 20 or the Fu discharge section 26 and a reversing path 52 of the reversing path section 24 that reverses the recorded surface of the recording medium P and conveys the recording medium P again to the recording section 18. The recording medium P that is switched to the reversing path 52 by the first branching section 50 and conveyed has its recorded surface reversed during the conveying process in the reversing path 52, and is conveyed again to the recording section 18 so that the surface opposite to the initial recorded surface faces the inkjet head 48.

[0131] 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 as to convey the recording medium P toward the Fd discharge section 20 or to convey the recording medium P toward the Fu discharge section 26.

[0132] The recording medium P transported toward the Fd discharge section 20 at the second branch section 54 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. Moreover, the recording medium P transported toward the Fu discharge section 26 at the second branch section 54 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 the side opposite to the Fu placement section 28.

[0133] When the recording device is a serial printer, the inkjet head has a length smaller than the width of the recording medium, and the inkjet head moves to perform recording in multiple passes (multi-pass). In a serial printer, the head is mounted on a carriage that moves in a predetermined direction, and the inkjet head moves with the movement of the carriage to eject the ink composition onto the recording medium. In this way, recording is performed in two or more passes (multi-pass). A pass is also called a scan or a main scan. A sub-scan is performed between passes to transport the recording medium. In other words, main scans and sub-scans are performed alternately. EXAMPLES

[0134] 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.

[0135] 1. Preparation of Inkjet Ink Composition Each component was placed in a mixing tank so as to obtain the composition shown in the table, mixed and stirred, and then filtered through a membrane filter to obtain inkjet ink compositions of Examples and Comparative Examples. The numerical values ​​of each component shown in each example in the table represent mass % unless otherwise specified. The contents (mass %) of pigments, resins, and inorganic oxide particles in the table represent solids concentrations.

[0136] The ratio of specific lactam to active agent in the table is the mass ratio of 6- to 8-membered ring lactams to acetylene glycol surfactant.

[0137] The materials shown in the table are as follows: <Coloring agent> CAB-O-JET300 (Cabot Corporation, 15% solids. Self-dispersing pigment.) <Resin dispersed particles> Resin dispersion particles 1: Seiko PMC, X-436, Tg: 33°C, acid value 33mgKOH / g, styrene acrylic resin emulsion) Resin dispersion particles 2: A styrene-acrylic resin emulsion was prepared using styrene and acrylic monomer. Tg: 10°C, acid value: 33mgKOH / g. <Water-soluble urethane resin> Water-soluble urethane resin 1: Water-soluble urethane resin 1 was prepared by the following method. First, a four-neck flask equipped with a stirrer, a thermometer, a nitrogen gas inlet tube, and a reflux tube 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 rate of isocyanate groups was confirmed by FT-IR, and the reaction was continued at 80°C until the desired residual rate was reached (secondary reaction) to obtain a reaction liquid. The resulting reaction liquid was cooled to 40°C, and then ion-exchanged water was added, and an aqueous potassium hydroxide solution was added while stirring at high speed with a homomixer. Methyl ethyl ketone was distilled off from the resulting liquid by heating and reducing the pressure, and a liquid containing water-soluble urethane resin 1 was obtained. 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 the water-soluble urethane resin 1 was measured by potentiometric titration using a potassium hydroxide-methanol titrant solution, and the acid value was 65 mgKOH / g. The water-soluble urethane resin 1 thus obtained had a weight average molecular weight of about 21,000 in terms of polystyrene as measured by gel permeation chromatography (GPC). Water-soluble urethane resin 2: 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. In addition, when the acid value and weight average molecular weight were measured by the same measuring method 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 about 21,000. <Inorganic oxide particles> "Cataloid SI-45P" (manufactured by JGC Catalysts and Chemicals, silica particle dispersion sol, average particle size 45 nm) <Lactams> ·2-Pyrrolidone (5-membered ring lactams), ·HEP: 1-(2-hydroxyethyl)-2-pyrrolidone (5-membered ring lactams) ε-caprolactam (CPL) (7-membered ring lactams) <Betaine> Trimethylglycine <Organic solvent> ·Glycerin ·Triethylene glycol ·1,2-Hexanediol <Acetylene glycol surfactant> "Olfine E1010": an acetylene glycol surfactant manufactured by Nissin Chemical Industry Co., Ltd. In the above formula (1), -OR 3 -OR 3' A compound in which the alkylene oxide group is present. HLB value: 11. "Surfynol 104PG50": an acetylene glycol surfactant manufactured by Air Products Japan, Inc. In the above formula (1), -OR 3 -OR 3' Compound where is -OH. HLB value: 4. Surfynol 420: Acetylene glycol surfactant manufactured by Air Products Japan, Inc. HLB value: 4. <Other surfactants> - "BYK348": A silicone-based surfactant manufactured by BYK Japan. <Alkaline> Triethanolamine <Water> Ion-exchanged water

[0138] 2. Evaluation 2.1. Discharge reliability (intermittency) We prepared a modified Seiko Epson LX-10050MF inkjet recording device. As shown in Figure 1, the line recording method was used. Each ink composition of the Examples and Comparative Examples was filled in the ink cartridge, and a recording medium (A4 size Xerox P paper, copy paper manufactured by Fuji Xerox Co., Ltd., basis weight 64 g / m) was then placed in the ink cartridge. 2 Printing was performed on a 100% tungsten carbide (1000 x 1000 mm, paper thickness 88 μm) in an environment with a temperature of 25°C and a humidity of 50%. A test pattern was printed at a duty of 100%. 30 sheets were printed in succession, and a one-minute idle time was provided between each sheet during which no ink was ejected from the inkjet head. After printing was completed, a nozzle check was performed. The evaluation results are shown in the table. [Evaluation Criteria] A: No non-ejecting nozzles. B: The number of non-ejecting nozzles is within 1%. C: The number of non-ejecting nozzles exceeds 1%.

[0139] 2.2. Transferability A 20mm x 20mm solid pattern was recorded on a recording medium using the same device, recording medium, and recording environment as above. This was done in an environment with a temperature of 25°C and a humidity of 50% RH. Recording was continued until the thickness of the recorded recording paper stacked on the paper output tray reached 1cm. The condition of ink transfer from the feed roller to the rear end surface of the stacked recording paper was visually observed. The evaluation results are shown in the table. [Evaluation Criteria] A: When observed from a distance of 30 cm, no transfer is visible. B: When observed from a distance of 30 cm, the transfer is visible, but when observed from a distance of 80 cm, the transfer is not visible. C: Observed from a distance of 80 cm, the transfer is visible.

[0140] 2.3. Curl resistance A solid pattern was printed with a print duty of 100% using the same device, print medium, and printing environment as described above. This was the same test pattern as for transferability. After recording, the recording medium was left face up (recorded surface facing up) for one week. The degree to which the edge of the paper rose above the floor was measured. The evaluation results are shown in the table below. [Evaluation Criteria] A: The amount of lift is less than 10mm. B: The amount of floating is 10mm or more but less than 20mm. C: The amount of lift is 20 mm or more.

[0141] 2.4. Solubility Each ink was placed in a 100 ml bottle, sealed, and left in a 60°C thermostatic chamber for 24 hours. After leaving it, the appearance was visually observed. This is an evaluation of the water solubility of the acetylene glycol surfactant. The evaluation results are shown in the table. A: No oily separation. B: There is a slight cloudiness. C: Oily separation is visible.

[0142] 3. Evaluation results As can be seen from the evaluation results in the table, all of the examples contained a colorant, an acetylene glycol-based surfactant, glycerin, and 6- to 8-membered ring lactams, the glycerin content was 9 mass% or less relative to the total mass of the ink composition, and the mass ratio of the 6- to 8-membered ring lactams to the acetylene glycol-based surfactant content was 0.5 or more and less than 5, and all of the examples were excellent in curl resistance, solubility, transfer inhibition, and ejection stability.

[0143] In contrast, in Comparative Example 1, the mass ratio of the content of the 6- to 8-membered ring lactam to the content of the acetylene glycol surfactant was less than 0.5, and the solubility was poor. In Comparative Example 2, the mass ratio of the content of the 6- to 8-membered ring lactam to the content of the acetylene glycol surfactant was 5 or more, and the ejection stability was poor. Comparative Example 9 did not contain glycerin and was inferior in transfer inhibition and ejection stability. [Explanation of symbols]

[0144] 10 recording device, 11 transport path, 12 feeding section, 14 transport section, 16 belt transport section, 18 recording section, 20 Fd discharge section, 22 Fd placement section, 24 inversion path section, 26 Fu discharge section, 28 Fu placement section, 30 feed tray, 32 feed roller, 34 transport drive roller, 36 transport 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 inversion path, 54 second branch section, 56 discharge roller pair, 64 discharge drive roller, 68 drive shaft, 76 placement surface, 78 convex portion, 80 first urging member, 82 second urging member, 84, 86 support shaft, P recording medium.

Claims

1. The composition contains a coloring material, an acetylene glycol surfactant, glycerin, and a lactam having a 6- to 8-membered ring, the content of glycerin is 9% by mass or less based on the total mass of the ink composition, the mass ratio of the content of the 6- to 8-membered ring lactams to the content of the acetylene glycol surfactant is 0.5 or more and less than 5; Aqueous-based ink-jet ink composition.

2. The ink-jet ink composition of claim 1 , further comprising a resin.

3. The ink-jet ink composition of claim 1 comprising a betaine.

4. The ink-jet ink composition of claim 2 , wherein the resin is a water-soluble resin.

5. the ratio of the content of the 6- to 8-membered ring lactams to the content of the acetylene glycol surfactant is 2 to 4; The ink-jet ink composition of claim 1.

6. The ink-jet ink composition according to claim 2 , wherein the resin is a water-soluble urethane-based resin.

7. The colorant contains at least one of a self-dispersed pigment and a pigment dispersed by a dispersant resin. The ink-jet ink composition of claim 1.

8. The content of inorganic fine particles is not more than 0.05% by mass based on the total mass of the ink composition. The ink-jet ink composition of claim 1.

9. 2. The ink-jet ink composition according to claim 1, wherein the content of the glycerin is 0.5 to 9% by mass based on the total mass of the ink composition.

10. The 6- to 8-membered lactams include ε-caprolactam. The ink-jet ink composition of claim 1.

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

12. The acetylene glycol surfactant includes an acetylene glycol surfactant having an HLB value of 5 or less. The ink-jet ink composition of claim 1.

13. An ink depositing step of ejecting the ink-jet ink composition according to any one of claims 1 to 12 from an ink-jet head and depositing the ink-jet ink composition on a recording medium, Recording method.

14. Recording is performed using the line recording method. The recording method according to claim 13.

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