inkjet ink

Abstract

To provide an inkjet ink that can be adjusted to an appropriate viscosity range and has excellent properties such as continuous and intermittent printing capabilities. [Solution] An inkjet ink is provided comprising a solvent containing a first solvent which is a glycol ether and a second solvent which is an alcohol having C1 to C3 carbon atoms, and a polyvinyl acetal resin, wherein the ratio of the second solvent to the total amount of the solvent is 5% by mass or more and 50% by mass or less. The first solvent may be propylene glycol monomethyl ether.

Description

Technical Field

[0001] The present invention relates to inkjet ink.

Background Art

[0002] For example, when printing characters or the like on the surface of a non-absorbent printing object such as plastic by an inkjet printing method, generally, the printed characters or the like are heated and dried. In recent years, a solvent-based inkjet ink that uses only an organic solvent as a solvent has been gradually put into practical use.

[0003] Patent Document 1 discloses an oil-based ink containing 10.0 parts by weight of an oil-soluble dye (metal complex dye), 60.0 parts by weight of ethyl alcohol, 17.0 parts by weight of normal propyl alcohol, 8.0 parts by weight of a terpene phenol copolymer resin, 2.0 parts by weight of a polyvinyl butyral resin (PVB), and 3.0 parts by weight of oleoylsarcosine (solubilizer).

[0004] Patent Document 2 discloses an inkjet ink containing 20 parts by mass of a black pigment dispersion, 63.9 parts by mass of propylene glycol monomethyl ether (PGME), 8 parts by mass of a polyvinyl butyral resin (PVB), 8 parts by mass of a sebacic acid ester, 0.1 parts by mass of an organosilicon surfactant, and 0.1 parts by mass of a fluorocarbon surfactant.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] For example, inkjet ink is held at the tip of the print nozzle by negative pressure within the printer's mechanism when printing is stopped. However, if the ink has low viscosity, there is a concern that the ink may leak out, such as by dripping. The appropriate viscosity for inkjet ink is preferably around 4 to 15 mPa·s (60 rpm).

[0007] In water-based inks, viscosity increases in proportion to the amount of resin (fixing component) dissolved, making it easy to adjust to an appropriate viscosity range. Other viscosity adjustment methods include incorporating small amounts of thickeners or gelling agents. On the other hand, solvent-based inks, as exemplified in prior art literature, exhibit less viscosity increase due to the dissolution of resins, and selecting suitable thickeners for the solvent is difficult. Furthermore, dissolving excessive amounts of resin or other materials in the solvent can lead to problems such as poor dispensing and precipitation during low-temperature storage.

[0008] Therefore, the object of the present invention is to provide an inkjet ink that can be adjusted to an appropriate viscosity range and has excellent properties such as continuous printing and intermittent printing. [Means for solving the problem]

[0009] An inkjet ink according to one embodiment of the present invention comprises a solvent containing a first solvent which is a glycol ether and a second solvent which is an alcohol having C1 to C3 carbon atoms, and a polyvinyl acetal resin, wherein the ratio of the second solvent to the total amount of the solvent is 5% by mass or more and 50% by mass or less.

[0010] In the inkjet ink according to one embodiment of the present invention, the first solvent may be propylene glycol monomethyl ether.

[0011] An inkjet ink according to one embodiment of the present invention may further contain a tackifier.

[0012] In the inkjet ink according to one embodiment of the present invention, the ratio of the second solvent to the total amount of the solvent is 25% by mass or more and 48% by mass or less, and the ratio of the polyvinyl acetal resin to the total amount of the inkjet ink may be 0.1% by mass or more and 3.0% by mass or less.

[0013] In the inkjet ink according to one embodiment of the present invention, the ratio of the polyvinyl acetal resin to the total amount of the inkjet ink is 0.1% by mass or more and 3.0% by mass or less, and the viscosity of the entire inkjet ink as measured by a rotational viscometer (60 rpm) may be 4 mPa·s or more and 15 mPa·s or less. [Effects of the Invention]

[0014] According to one embodiment of the present invention, an inkjet ink can be provided that can be adjusted to an appropriate viscosity range and has excellent properties such as continuous printability and intermittent printability. [Brief explanation of the drawing]

[0015] [Figure 1] Figure 1 shows the relationship between the addition ratio of polyvinyl butyral resin (PVB) and ink viscosity. [Modes for carrying out the invention]

[0016] In the following embodiments, "dissolution" is defined as the state in which a substance is added to a liquid, mixed, and left for 24 hours without precipitation, turbidity, or other issues, and the solution remains transparent. "Mismatch" is defined as the state in which dissolution is achieved between two or more substances.

[0017] The inkjet ink of the present invention comprises a colorant, a resin, and an organic solvent.

[0018] [Coloring agent] As the coloring agent, for example, various dyes that dissolve in an organic solvent can be used. More specifically, as the dye, various oil-soluble dyes that dissolve well in both the first solvent and the second solvent described later are used. As the dye, those that dissolve in both alcohol and ketone as a single substance are preferable.

[0019] Among the oil-soluble dyes, preferably, metal complex dyes are used, and more preferably, metal complex dyes mainly composed of chromium are used. Specific examples of the oil-soluble dye include, but are not limited to, for example, one or more of the following various dyes.

[0020] (Yellow) As the yellow metal complex dye, for example, C.I. Solvent Yellow 19, 21, 25, 32, 41, 61, 62, 65, 79, 81, 82, 83, 83:1, 88, 89, 90, 151; VALIFAST (registered trademark) YELLOW 3108, 3120, 3150, 3170, 3180, 4120, 4121 manufactured by Orient Chemical Industries, Ltd.; Ne SuperColor Yellow C-131 manufactured by Central Synthetic Chemical Co., Ltd.; Oleosol (registered trademark) Fast Yellow 2G, GCN manufactured by Tago Chemical Co., Ltd.; Orasol (registered trademark) Yellow 141, 152, 157, 190 manufactured by BASF Japan Ltd.; Intraplast Yellow 2GLN, 3R manufactured by Sensient; Savinyl Yellow 2GLS01, RLS, RLSN, 2RLS manufactured by CLARIANT Co., Ltd. are mentioned.

[0021] As other oil-soluble yellow dyes, for example, C.I. Solvent Yellow 2, 14, 15, 16, 56, 76, 80, 91; AIZEN (registered trademark) S.B.N. Yellow 543, SPILON (registered trademark) Yellow C-GNH, C-2GH manufactured by Hodogaya Chemical Co., Ltd.; Oplas (registered trademark) Yellow 140, VALIFAST (registered trademark) YELLOW 1101, 1109, 1151, 1171 manufactured by Orient Chemical Industries Co., Ltd.; Alcohol Yellow Y-10, Oil Yellow CH manufactured by Chuo Gosei Kagaku Co., Ltd.; DIARESIN (registered trademark) Yellow L3G manufactured by Mitsubishi Chemical Corporation can be mentioned.

[0022] (Orange) As metal complex dyes of orange, for example, C.I. Solvent Orange 5, 6, 11, 20, 41, 54, 56, 58, 59, 62, 99; VALIFAST (registered trademark) ORANGE 2210, 3208, 3209, 3210 manufactured by Orient Chemical Industries Co., Ltd.; Neo Super Color Orange C-232 manufactured by Chuo Gosei Kagaku Co., Ltd.; Orasol Orange 245, 247, 251, 272 manufactured by BASF Japan Ltd.; Intraplast Orange G, RLN manufactured by Sensient; Savinyl Orange RLS, RLSE manufactured by CLARIANT can be mentioned.

[0023] As other oil-soluble dyes of orange, for example, C.I. Solvent Orange 1, 2, 14, 36, 44, 45, 57; VALIFAST (registered trademark) ORANGE 1201 manufactured by Orient Chemical Industries Co., Ltd. can be mentioned.

[0024] (Red) Examples of red metal complex salt dyes include CI Solvent Red 8, 91, 99, 100, 102, 109, 118, 119, 122, 124, 125, 127, 130, 132, 142, 160, 218, 233; VALIFAST® Red 2303, 2320, 3304, 3306, 3311, 3312, 3320, PINK 2310N from Orient Chemical Industry Co., Ltd.; Neo Super Color RED C-431, PINK C-331 from Chuo Synthetic Chemical Co., Ltd.; Oleosol Fast RED BL, PINK FB from Taoka Chemical Co., Ltd.; Orasol Red 330, 335, 355, 363, 365, 385, 395, 471, Pink from BASF Japan Ltd. Examples include Sensient's Intraplast Red GC and Scarlet 3GL; and CLARIANT's Savinyl Red 3BLS, 3GLS, and Pink 6BLS.

[0025] Other oil-soluble red dyes include, for example, CI Solvent Red 1, 3, 23, 24, 25, 27, 35, 49, 78, 81, 82, 83, 84, 96, 121, 123, 128, 129, 131, 133, 134, and CI Disperse Red 9; Orient Oil Pink OP, SPIRIT Red 102, and VALIFAST® Red 1308, 1320, 1355, 1364, and 1388 from Orient Chemical Industries, Ltd.; AIZEN SPILON Fiery Red BH, Red C-GH, C-BH, and Pink BH from Hodogaya Chemical Co., Ltd.; and AL Red 2308 and Alcohol Pink P-30 from Chuo Synthetic Chemical Co., Ltd.

[0026] (Brown) Examples of brown metal complex salt dyes include CI Solvent Brown 37, 42, 43, 44; Orasol Brown 324, 326 from BASF Japan Ltd.; and Intraplast Brown GC from Sensient.

[0027] Other oil-soluble dyes for brown include, for example, CI Solvent Brown 3, 23, 24, 25, and 58.

[0028] (green) Examples of green oil-soluble dyes include CI Solvent Green 3, 16, 21, and 22; and VALIFAST® GREEN 1501 manufactured by Orient Chemical Industry Co., Ltd.

[0029] (blue) Examples of blue metal complex salt dyes include CI Solvent Blue 24, 25, 38, 44, 45, 55, 64, 67, and 70; VALIFAST® Blue 2606, 2620, and 2670 from Orient Chemical Industries, Ltd.; Neo Super Color Blue C-555 from Chuo Synthetic Chemicals, Inc.; Orasol Blue 825 and 855 from BASF Japan Ltd.; Intraplast Blue GN from Sensient Inc.; and Savinyl Blue RS and GLS from CLARIANT Inc.

[0030] Other oil-soluble blue dyes include, for example, CI Solvent Blue 5, 11, 12, 46, 73, and 75; Orient Oil Blue 603, VALIFAST® Blue 1621, 1631, and 2604 from Orient Chemical Industries, Ltd.; AIZEN SPILON Blue C-RH, GNH, and SPT Blue 121 from Hodogaya Chemical Co., Ltd.; and Alcohol Blue B-10 from Chuo Synthetic Chemical Co., Ltd.

[0031] (violet) Examples of oil-soluble violet dyes include CI Solvent Violet 1, 2, 19, 21; VALIFAST® VIOLET 1701, 1704 manufactured by Orient Chemical Industry Co., Ltd.; and AIZEN SPILON Violet C-RH, ECH manufactured by Hodogaya Chemical Co., Ltd.

[0032] (black) Examples of black metal complex salt dyes include CI Solvent Black 22, 27, 28, 29, 34, 35, 43; VALIFAST® BLACK 3804, 3807, 3808, 3810, 3820, 3830, 3840, 3866, 3870, 3877, 3878 from Orient Chemical Industries, Ltd.; Orasol® Black X45, X51, X55 from BASF Japan Ltd.; Intraplast Black CN, RLS from Sensient; and Savinyl Black RLSN01 from CLARIANT Inc.

[0033] Other oil-soluble black dyes include, for example, CI Solvent Black 3, 5, 7, 23, 25, 30, 47, and 123; VALIFAST® BLACK 1807 and 1815 from Orient Chemical Industries, Ltd.; and RLS (Solvent Black 29) and CN (Solvent Black 28) from Instraplast.

[0034] Oil-soluble dyes can be blended in appropriate amounts, one or more types, depending on the color and color density of the inkjet ink. When using metal complex dyes as oil-soluble dyes, the amount blended is preferably 5.0% by mass or more, and more preferably 7.0% by mass or more, of the total amount of inkjet ink. The amount blended for metal complex dyes is preferably 15.0% by mass or less, and more preferably 12.0% by mass or less, of the total amount of inkjet ink. The amount blended for metal complex dyes is preferably 5.0% by mass or more and 15.0% by mass or less, and more preferably 7.0% by mass or more and 12.0% by mass or less, of the total amount of inkjet ink.

[0035] The above-mentioned dye formulation amounts refer to the amount of only one type of metal complex dye used, or the total amount of the two or more metal complex dyes used in combination.

[0036] [resin] The resins used can be divided into, for example, polyvinyl acetal resin and other resins. Polyvinyl acetal resin is mainly used as a thickening resin for inkjet inks, while other resins are mainly used as fixing resins for inkjet inks.

[0037] Examples of polyvinyl acetal resins include resins produced by acetalizing polyvinyl alcohol resin with aldehydes having 1 to 4 carbon atoms, such as formaldehyde, acetaldehyde, propionaldehyde, and butyraldehyde, or aromatic aldehydes, such as benzaldehyde and methylbenzaldehyde. Of these, polyvinyl butyral resin (PVB) is preferred, more preferably polyvinyl butyral resin with a number average molecular weight Mn of 50,000 or less, and particularly preferably polyvinyl butyral resin with a number average molecular weight Mn of 40,000 or less. The number average molecular weight Mn of the polyvinyl butyral resin is preferably 10,000 or more, and more preferably 13,000 or more.

[0038] If the number-average molecular weight (Mn) of polyvinyl butyral resin is less than 10,000, the overall thickening effect of the ink by dissolving the resin in an organic solvent cannot be sufficiently obtained, making it difficult to adjust the ink to the desired viscosity range. On the other hand, if the number-average molecular weight (Mn) of polyvinyl butyral resin exceeds 50,000, the solubility of the resin in organic solvents decreases, raising concerns about resin precipitation.

[0039] The amount of polyvinyl acetal resin added is, for example, 0.05% by mass or more and 12.0% by mass or less relative to the total amount of inkjet ink. For example, if the flash point of the first solvent, described later, is higher than that of the second solvent, the amount of polyvinyl acetal resin added may be 0.05% by mass or more and 4.0% by mass or less relative to the total amount of inkjet ink, preferably 0.1% by mass or more and 3.0% by mass or less. In this case, if the amount of polyvinyl acetal resin added is less than 0.05% by mass, the overall viscosity-enhancing effect of the ink due to dissolving the resin in the organic solvent cannot be sufficiently obtained, and so-called ink dripping, where ink drips from the printer's print head, is likely to occur. If the amount of polyvinyl acetal resin added exceeds 4.0% by mass, the viscosity of the inkjet ink may increase, making ejection unstable and potentially reducing continuous printing performance. Also, if the amount of polyvinyl acetal resin added exceeds 4.0% by mass, low-temperature storage performance may also decrease.

[0040] For example, if the flash point of the first solvent, described later, is lower than that of the second solvent, the amount of polyvinyl acetal resin may be 0.5% by mass or more and 12.0% by mass or less relative to the total amount of inkjet ink, preferably 1.0% by mass or more and 10.0% by mass or less. In this case, if the amount of polyvinyl acetal resin is less than 0.5% by mass, the ejection of the inkjet ink may become unstable, which may reduce continuous printing performance. If the amount of polyvinyl acetal resin exceeds 12.0% by mass, the absolute amount of other resins that are fixing components (phenol resin, ketone resin, etc.) may be small, and the fixing performance to the substrate may be insufficient.

[0041] Other resins used as fixing resins include, for example, phenolic resins, vinyl chloride resins, ketone resins, and polyester resins. Of these, phenolic resins and ketone resins are preferably used. More preferably, phenolic resins are used when the flash point of the first solvent is higher than that of the second solvent, and ketone resins are used when the flash point of the first solvent is lower than that of the second solvent.

[0042] Examples of phenolic resins include various phenolic resins having a softening point VT(°C) of 65°C to 130°C. The softening point VT(°C) of the phenolic resin is preferably 65°C to 125°C, and more preferably 80°C to 120°C.

[0043] If a phenolic resin is included, it will adhere well to non-porous substrates (non-polar substrates). Examples of non-porous substrates (non-polar substrates) include OPP (Oriented PolyPropylene: biaxially oriented polypropylene), CPP (Cast PolyPropylene: unoriented polypropylene), aluminum, and PE.

[0044] As the phenolic resin, a thermoplastic resin such as novolac resin is particularly preferred. As the phenolic resin, two types of phenolic resins with different softening points VT(°C), each having a softening point VT(°C) within the above range, may be used in combination.

[0045] As a vinyl chloride resin, for example, a vinyl chloride-vinyl acetate copolymer is preferred. The vinyl chloride-vinyl acetate copolymer preferably has a number average molecular weight Mn of 15,000 or more and 35,000 or less, more preferably 20,000 or more and 30,000 or less, and particularly preferably 22,000 or more and 27,000 or less. If the number average molecular weight Mn is below the above range, the ink's adhesion to the substrate may decrease, resulting in reduced abrasion resistance of the print. If the number average molecular weight Mn exceeds the above range, the viscosity of the inkjet ink may become too high, making it difficult to eject it properly as droplets from the nozzles of the inkjet head.

[0046] Examples of ketone resins include formaldehyde resin, cyclohexanone-formaldehyde resin, and ketone-aldehyde condensation resin. Specific examples of ketone resins include TEGO® Variplus SK, TEGO® Variplus AP, and TEGO® Variplus CA, all manufactured by Evonik.

[0047] Specific examples of polyester resins include Unitika Ltd.'s Elitel® series KT-0507, KT-8701, KT-8803, KT-9204, KT-9511, KA-1449S, KA-5071S, and Toyobo MC Corporation's Byronal® series MD-1100, MD-1200, MD-1245, MD-1335, MD-1480, MD-1500, MD-1930, MD-1985, MD-2000, etc.

[0048] The amount of other resins is the remainder obtained by subtracting the amount of polyvinyl acetal resin from the total amount of resin components in the inkjet ink. Preferably, the amount of other resins is greater than the amount of polyvinyl acetal resin. For example, the amount of other resins is 3.0% by mass or more and 30.0% by mass or less relative to the total amount of inkjet ink.

[0049] When phenolic resin is used as another resin, its blending amount is, for example, 3.0% by mass or more and 10.0% by mass or less, preferably 4.0% by mass or more and 7.0% by mass or less.

[0050] On the other hand, when ketone resin is used as another resin, the preferred amount is defined by the total amount with polyvinyl acetal resin. The total amount of polyvinyl acetal resin and ketone resin is, for example, 8.0% by mass or more and 35.0% by mass or less, and preferably 10.0% by mass or more and 30.0% by mass or less. If the total amount of polyvinyl acetal resin and ketone resin is less than 10.0% by mass, the liquid dripping may be insufficient, and if it exceeds 30.0% by mass, continuous printing performance may decrease due to nozzle clogging, and low-temperature storage performance may also decrease.

[0051] The amount of other resins used is the amount of that single resin if only one type is used, and the total amount of the two resins used if two or more types of resins are used in combination.

[0052] [Organic solvents] The organic solvent preferably includes, for example, a first solvent and a second solvent having different solubility parameters (SP values). The "SP value" can be defined, for example, by either the Hildebrand solubility parameter or the Hansen solubility parameter. In this specification, the Hildebrand solubility parameter is defined as the "SP value," and the Hansen solubility parameter is defined as the "HSP value." In this specification, when simply referred to as the "SP value," the SP value refers to the Hildebrand solubility parameter.

[0053] <First Solvent> As the first solvent, various solvents with an SP value of less than 11 are used. For example, as the first solvent, at least one solvent selected from the group consisting of ketones and ethers, with an SP value of less than 11, is used.

[0054] Specific examples of ketones, though not limited to these, include one or more of the following types of ketones.

[0055] 2-Butanone [Methyl ethyl ketone (MEK), number of carbon atoms: 4, SP value: 9.3, flash point: -5.6℃], Acetone [Dimethyl ketone, number of carbon atoms: 3, SP value: 10, flash point: -10℃], 2-Pentanone [Methyl propyl ketone (MPK), number of carbon atoms: 5, SP value: 8.7, flash point: 7.2℃], 3-Pentanone [Diethyl ketone (DEK), number of carbon atoms: 5, SP value: 8.8, flash point: 13℃], 3-Methyl-2-butanone [Methyl isopropyl ketone (MIPK), number of carbon atoms: 5, SP value :8.5, flash point:-1.0℃], 2-methyl-4-pentanone [methyl isobutyl ketone (MIBK), carbon number:6, SP value:8.4, flash point:3℃], 2,6-dimethyl-4-heptanone [diisobutyl ketone (DIBK), carbon number:9, SP value:7.8, flash point:60℃], cyclohexanone [carbon number:6, SP value:9.3, flash point:44℃], 4-hydroxy-4-methylpentan-2-one [diacetone alcohol, carbon number:6, SP value:9.2, flash point:58℃].

[0056] Specific examples of ether include, but are not limited to, one or more of the following types of ether.

[0057] 1,4-Dioxane [Dioxane, SP value: 10, flash point: 15.6℃], Diethyl ether [SP value: 7.4, flash point: -45℃], 1,1-Dimethyldiethyl ether [Diisopropyl ether, SP value: 6.9, flash point: -28℃], 2-Ethoxyethanol [Ethyl cellosolve (EGMEE), SP value: 10.5, flash point: 45℃], 2-Butoxyethanol [Butyl cellosolve (EGMBE), SP value: 9.5, flash point: 63℃], tert-Butyl methyl ether [MTBE, flash point: -28℃].

[0058] Glycol ether can also be used as the ether.

[0059] Specific examples of glycol ethers, though not limited to those listed below, include one or more of the following types of glycol ethers.

[0060] 1-Methoxy-2-propanol [propylene glycol monomethyl ether (PM), SP value: 10.2, flash point: 32°C], 2-(2-methoxyethoxy)ethanol [methyl carbitol], 2-(2-ethoxyethoxy)ethanol [ethyl carbitol, SP value: 10.2, flash point: 96°C], 2-(2-butoxyethoxy)ethanol [butyl carbitol, SP value: 10.2], 2-[2-(2-methoxyethoxy)ethoxy]ethanol [methyl triglyceride] [L], 1-butoxy-2-propanol [propylene glycol-1-monobutyl ether (PNB)], 3-methoxy-3-methyl-1-butanol [methyl methoxybutanol (MMB)], 2-[2-(hexyloxy)ethoxy]ethanol [hexyl diglycol], 1-(methoxymethyl)ethyl propionate [methotate], 1 or 2-(methoxymethylethoxy)propanol [dipropylene glycol monomethyl ether (DPM), isomer mixture].

[0061] <Second solvent> As the second solvent used in combination with the first solvent, various solvents having an SP value of 11 or higher are used. As the second solvent, for example, an alcohol with an SP value of 11 or higher is used. The number of carbon atoms in the alcohol is, for example, 1 to 4, preferably 1 to 3.

[0062] Examples of alcoholic beverages, though not limited to those listed below, include one or more of the following types of alcohol.

[0063] Methanol [methyl alcohol, number of carbon atoms: 1, SP value: 14.5~14.8], ethanol [ethyl alcohol, number of carbon atoms: 2, SP value: 12.7], ethanolamine [amino alcohol, number of carbon atoms: 2, flash point: 85℃], 1-propanol [propyl alcohol, number of carbon atoms: 3, SP value: 11.97], 2-propanol [isopropyl alcohol (IPA), number of carbon atoms: 3, SP value: 11.5], propanolamine [number of carbon atoms: 3, flash point: 77℃], 1-butanol [butyl alcohol, number of carbon atoms: 4, SP value: 11.4], 2-butanol [sec-butyl alcohol, number of carbon atoms: 4, SP value: 11], dimethylaminoethanol [number of carbon atoms: 4, flash point: 41℃].

[0064] Among these alcohols, those with 1 to 3 carbon atoms, in particular, have lower boiling points and higher volatility compared to other alcohols with an SP value of 11 or higher, which can improve the drying speed of inkjet ink after printing.

[0065] As the second solvent, it is preferable to use an alcohol having 1 to 3 carbon atoms alone (including cases where two or more alcohols having 1 to 3 carbon atoms are used in combination; the same applies hereinafter), but it is also possible to use such alcohols having 1 to 3 carbon atoms in combination with other alcohols. However, when used in combination, it is preferable that the amount of alcohol having 1 to 3 carbon atoms be 70% by mass or more of the total amount of the second solvent in order not to impair the quick-drying properties of the inkjet ink. From the viewpoint of quick-drying properties, the upper limit of the amount of alcohol having 1 to 3 carbon atoms is 100% by mass of the total amount of the second solvent. In other words, it is preferable that the entire amount of the second solvent be alcohol having 1 to 3 carbon atoms.

[0066] <Other solvents (third solvents)> The organic solvent may include other solvents different from the first and second solvents. For example, at least one solvent selected from the group consisting of glycols, esters, and acetals can be used as the other solvent.

[0067] Specific examples of glycols, though not limited to these, include one or more of the following esters.

[0068] 1,2-Propanediol [propylene glycol, flash point: 99°C], 1,3-Propanediol [POD], 1,4-Butanediol [butylene glycol, flash point: 134°C], 1,2-Pentanediol [1,2-amyl glycol], 1,4-Pentanediol, 1,5-Pentanediol [pentamethylene glycol], 1,2-Hexanediol [1,2-hexylene glycol], 1,6-Hexanediol [1,6-hexylene glycol].

[0069] Specific examples of esters, though not limited to these, include one or more of the following types of esters.

[0070] Ethyl acetate (SP value: 9.1, flash point: 7.2°C), methyl acetate (SP value: 9.6), n-butyl acetate (SP value: 8.5, flash point: 22°C), sec-butyl acetate (SP value: 8.3), 3-methoxybutyl acetate (3-methoxybutyl acetate), pentyl ethaneate (SP value: 8.5), propyl acetate (n-propyl acetate, SP value: 8.8), isopropyl ethaneate (SP value: 8.4), ethyl(R)-2-hydroxypropanoate (ethyl lactate), methyl-2-hydroxypropanoate (methyl lactate), butyl-2-hydroxypropanoate (butyl lactate).

[0071] Glycol esters can also be used as esters.

[0072] Specific examples of glycol esters, though not limited to those listed below, include one or more of the following types of glycol esters.

[0073] 1-Acetoxy-2-ethoxyethane [ethylene glycol monoethyl ether acetate], 1-methoxy-2-propanyl acetate [propylene glycol monomethyl ether acetate (PGMEA)], 2-(2-butoxyethoxy)ethyl acetate [butyl carbitol acetate, SP value: 8.5], 2-(2-ethoxyethoxy)ethyl acetate [ethyl carbitol acetate].

[0074] Carbonate esters can also be used as esters.

[0075] Specific examples of carbonate esters include, but are not limited to, one or more of the following types of carbonate esters.

[0076] Dimethyl carbonate [flash point: 17°C], diethyl carbonate [SP value: 8.8, flash point: 25°C], ethyl methyl carbonate [SP value: 9.4, flash point: 23°C].

[0077] Specific examples of acetals, though not limited to these, include one or more types of acetals such as dimethoxymethane [methylal, flash point: -17.8°C].

[0078] <Regarding the amount of solvent> The mixing ratio of the second solvent to the total amount of the first solvent, the second solvent, and other organic solvents (total amount of organic solvents) may be appropriately set considering the changes in ink properties due to changes in the mixing balance of the first and second solvents. For example, we will explain how continuous printability, intermittent printability, quick drying, and low-temperature storage properties typically change depending on the solvent mixing ratio.

[0079] Regarding continuous printability, if the amount of the first solvent is small and the amount of the second solvent is large, the amount of insoluble components increases, which can easily lead to nozzle clogging and a decrease in printability. However, this can be resolved by increasing the amount of the first solvent and decreasing the amount of the second solvent. In other words, when comparing the first and second solvents, the first solvent is a good solvent, and the second solvent is a poor solvent.

[0080] Regarding intermittent printability, if there is a large amount of the primary solvent (good solvent) and a small amount of the secondary solvent (poor solvent), the resin and other materials dissolve easily, making film formation difficult and resulting in poor intermittent printability. On the other hand, if there is a small amount of the primary solvent and a large amount of the secondary solvent, film formation becomes easier, resulting in excellent intermittent printability.

[0081] Regarding quick-drying properties, the more solvents with lower flash points there are, the faster the drying time. Regarding low-temperature storage, similar to continuous printing properties, a lower concentration of the primary solvent and a higher concentration of the secondary solvent results in more insoluble components, which can easily lead to precipitate formation in low-temperature environments. However, this can be resolved by increasing the concentration of the primary solvent and decreasing the concentration of the secondary solvent.

[0082] Based on the above, the preferred range of the mixing ratio of the second solvent will be explained separately for (1) the case where the flash point of the first solvent is higher than that of the second solvent, and (2) the case where the flash point of the first solvent is lower than that of the second solvent.

[0083] (1) When the flash point of the first solvent is higher than that of the second solvent In this case, the blending ratio of the second solvent (second solvent / first solvent + second solvent + other solvents) is preferably 5% by mass or more and 48% by mass or less, more preferably 10% by mass or more and 48% by mass or less, and particularly preferably 25% by mass or more and 48% by mass or less.

[0084] If the amount of the secondary solvent (poor solvent) is less than 10% by mass and the amount of the primary solvent (good solvent) is too high, continuous printing performance is excellent, but because resins and other materials dissolve easily, film formation becomes difficult, resulting in poor intermittent printing performance. Conversely, if the amount of the secondary solvent (poor solvent) is more than 48% by mass and the amount of the primary solvent (good solvent) is low, the amount of insoluble components increases, which may reduce solubility. As a result, aggregates during continuous printing may clog the nozzle, reducing continuous printing performance. On the other hand, by increasing the amount of the secondary solvent (poor solvent) to more than 48% by mass, film formation becomes easier, and intermittent printing performance is excellent.

[0085] (2) When the flash point of the first solvent is lower than that of the second solvent In this case, the mixing ratio of the second solvent (second solvent / first solvent + second solvent + other solvents) is preferably 5% by mass or more and 35% by mass or less, more preferably 5% by mass or more and 30% by mass or less, and particularly preferably 5% by mass or more and 30% by mass or less. If the second solvent (poor solvent) is less than 5% by mass and the first solvent (good solvent) is too much, continuous printing performance is excellent, but because resins and the like dissolve easily, film formation becomes difficult and intermittent printing performance is poor. Also, if the second solvent (poor solvent) is more than 35% by mass and the first solvent (good solvent) is little, the amount of insoluble components increases, and the solubility may decrease. As a result, aggregates during continuous printing may clog the nozzle, and continuous printing performance may decrease. On the other hand, by increasing the amount of the second solvent (poor solvent) to more than 35% by mass, film formation becomes easier and intermittent printing performance is excellent.

[0086] Furthermore, when comparing cases where the organic solvent includes other solvents such as esters and glycols with cases where it does not, it is preferable to use only the first and second solvents in combination, and not to use any other solvents.

[0087] [Tackifier] The inkjet ink of the present invention may further contain a tackifier.

[0088] As a tackifier, at least one compound selected from the group consisting of terpene phenol resins and rosin esters is used.

[0089] The terpene phenol resin preferably has a hydroxyl value of 30 mg KOH / g or more and 70 mg KOH / g or less, and the rosin ester preferably has an acid value of 0.1 or more and 20 or less.

[0090] If the hydroxyl value of the terpene phenol resin is less than 30 mgKOH / g, or the acid value of the rosin ester is less than 0.1, film formation is easy, but the film tends to be thick. As a result, the film does not easily break during dispensing after decapping, which may lead to a decrease in the evaluation of intermittent printability.

[0091] On the other hand, tackifiers with a hydroxyl value exceeding 70 mgKOH / g of terpene phenol resin, or a rosin ester acid value exceeding 20, are highly polar and therefore have high solubility (affinity) for water. As a result, even if the inkjet ink is exposed to the outside air within the nozzle and comes into contact with moisture in the air, it may not quickly precipitate on the liquid surface and form a good film that can suppress the evaporation of the solvent.

[0092] Therefore, the viscosity of the inkjet ink increases during the decapping time, which can easily cause nozzle clogging and reduce intermittent printability. In addition, the adhesion of characters and other elements tends to decrease, especially when the surface of the substrate is made of non-porous and low-polarity plastics. Moreover, as mentioned above, tackifiers with high hydroxyl value or acid value are specialized, and there is a challenge in that there are few types and limited options for properties.

[0093] In contrast, tackifiers with hydroxyl value or acid value within the above range offer a wide variety of properties and a rich selection of options. Furthermore, they possess moderate solubility in two solvents, a first solvent and a second solvent, with different SP values, which is neither too low nor too high, allowing them to dissolve well in inkjet inks.

[0094] Therefore, it is possible to improve the continuous printing performance of inkjet inks, as well as the intermittent printing performance, making it less likely for nozzles to clog during decapping time. Furthermore, it is possible to ensure sufficient adhesion of characters and other elements even on the surface of substrates made of low-polarity plastics.

[0095] Here, we will explain the relationship between the tackifier and the first solvent (SP value < 11). The tackifier (terpene phenol resin) that dissolves only in the second solvent (alcohol) has a high hydroxyl value of 70 mgKOH / g or more and is easily miscible with water. Therefore, unless the amount of tackifier added is increased, the effect of adding the tackifier will not be easily observed. On the other hand, if the amount of tackifier added is excessive, continuous printability may decrease, similar to when the amount of resin is excessive.

[0096] Therefore, by using a first solvent that is compatible with a second solvent and in which a tackifier with a low hydroxyl value is soluble, it becomes possible to use tackifiers with a hydroxyl value in the range of 30 mg KOH / g to 70 mg KOH / g. As a result, the amount of tackifier can be reduced and continuous printability can be improved. Similarly, when the tackifier is a rosin ester, tackifiers with an acid value of 100 or more dissolve in the second solvent (alcohol) alone.

[0097] Examples of terpene phenol resins include a basic skeleton (C5H8) in which isoprene is sequentially bonded at the head and tail. p A copolymer of terpenes and phenols having (where p is an integer), and various terpene-phenol resins having the above-mentioned hydroxyl value can be used.

[0098] Specific examples of terpene phenol resins, though not limited to those listed below, include the following various compounds.

[0099] The following are products from the YS Polystar series manufactured by Yasuhara Chemical Co., Ltd.: U115 [Hydroxyl value: 30 mg KOH / g], T80 [Hydroxyl value: 60 mg KOH / g], T100 [Hydroxyl value: 60 mg KOH / g], T115 [Hydroxyl value: 60 mg KOH / g], T130 [Hydroxyl value: 60 mg KOH / g], and T145 [Hydroxyl value: 60 mg KOH / g].

[0100] The following are examples of the SylVares (registered trademark) series manufactured by Kraton: TP95 (hydroxyl value: 40 mg KOH / g), TP105 (hydroxyl value: 40 mg KOH / g), TP115 (hydroxyl value: 50 mg KOH / g), TP2040, TP2019, TP2040HM, 1095, 1105, and 1115.

[0101] Furthermore, as rosin esters, various rosin esters can be used, which are esters of rosin mainly composed of abietin-type or pimaline-type resin acid having an alkylated hydrophenanthrene nucleus with a monobasic carboxylic acid, and alcohols, with acid values ​​within the above range.

[0102] Examples of rosins include those made from resin acids containing unsaturated bonds, such as abietic acid and dextropimaric acid, and hydrogenated rosins mainly composed of hydrogenated dihydroabietic acid and tetrahydroabietic acid. Examples of alcohols include glycerin, pentaerythritol, and triethylene glycol.

[0103] Specific examples of rosin esters, though not limited to these, include the following various compounds.

[0104] Harima Chemicals Co., Ltd.'s Haritack® series includes SE-10 [rosin ester (hydrogenated), acid value: 2-10], FK100 [disproportionated rosin ester, acid value: 5 or less], FK125 [disproportionated rosin ester, acid value: 14-20], F85 [rosin ester (hydrogenated), acid value: 4-12], PH [rosin ester (hydrogenated), acid value: 7-16], AQ-90A [special rosin resin, acid value: 100-110], and the Hariester® series includes MSR-4 [acid value: 120-150]. DS-70L (acid value: 8 or less), Harimac series R-80 (acid value: 20 or less); Arakawa Chemical Industries, Ltd.'s Ester Gum (registered trademark) AA-G (rosin ester, acid value: 0.1-7.0), Ester Gum (registered trademark) 105 (rosin ester, acid value: 20 or less), Pencel (registered trademark) AZ (rosin ester, acid value: 35-50); Kraton's SylValite (registered trademark) series RE80HP, RE85GB, RE100L.

[0105] One or more of these tackifiers can be used.

[0106] The amount of tackifier is, for example, 0.5% by mass or more relative to the total amount of inkjet ink, preferably 1.5% by mass or more. The amount of tackifier is, for example, 10% by mass or less, preferably 4.5% by mass or less. The amount of tackifier is, for example, preferably 0.5% by mass or more and 10% by mass or less relative to the total amount of inkjet ink, and more preferably 1.5% by mass or more and 4.5% by mass or less.

[0107] If the amount of tackifier is below this range, a good film that can sufficiently suppress solvent evaporation may not form when the inkjet ink is exposed to the outside air in the nozzle during decapping time, which can increase the viscosity of the inkjet ink and reduce intermittent printability. On the other hand, if the amount of tackifier exceeds the above range, solubility may be insufficient, which can reduce continuous printability. In addition, the tackifier may precipitate more easily, which can reduce low-temperature storage.

[0108] In contrast, by setting the amount of tackifier within the above range, it is possible to further improve the intermittent printing performance of inkjet ink while suppressing a decrease in continuous printing performance.

[0109] When using two or more tackifiers in combination, the total amount should be within the range specified above. For example, it is possible to use terpene phenol resin and rosin ester in combination. In that case, the mixing ratio of terpene phenol resin and rosin ester can be appropriately changed according to the specifications.

[0110] <Other ingredients> In addition to the above components, the inkjet ink may also contain a surfactant. Examples of surfactants that can be used include silicone acrylate surfactants, silicone surfactants, and silicone oils.

[0111] Silicone acrylate surfactants suppress the wetting and spreading of organic solvents on the surface of the substrate, thereby improving print clarity and image quality. The proportion of surfactants such as silicone acrylate surfactants is preferably 0.1% by mass or more, and preferably 5% by mass or less, of the total amount of inkjet ink, based on the amount of active ingredients in the surfactant.

[0112] <Viscosity of inkjet inks> The inkjet ink of the present invention, containing the above components, preferably has a viscosity of 4 mPa·s to 15 mPa·s as measured by a rotational viscometer (60 rpm). Of the above components, the viscosity of the inkjet ink is mainly adjusted by the polyvinyl acetal resin. If the ink viscosity is less than 4 mPa·s, dripping is likely to occur from the print head when the printer is not printing. On the other hand, if the ink viscosity exceeds 15 mPa·s, as described above, a mixed solvent of the first and second solvents is used, and this exceeds the solubility limit of the resin such as polyvinyl acetal resin and the dye. In that case, there is a high possibility of precipitate formation in harsh environments such as low-temperature storage, so the upper limit of the ink viscosity is preferably around 15 mPa·s.

[0113] Figure 1 shows the relationship between the addition ratio of polyvinyl butyral resin (PVB) and ink viscosity. Figure 1 illustrates how ink viscosity changes as the addition ratio of polyvinyl butyral resin (PVB) to inkjet ink increases. Figure 1 shows the cases where the organic solvent is propylene glycol monomethyl ether (PM), n-propyl alcohol (NPA), ethanol, and diethyl ketone (DEK).

[0114] Referring to Figure 1, regardless of the type of organic solvent, the viscosity of the inkjet ink increases with increasing polyvinyl butyral resin (PVB) addition ratio, but the degree of viscosity increase differs. Therefore, in this invention, while considering that various properties such as continuous and intermittent printing properties do not deteriorate, the desired ink viscosity was achieved by adjusting the type of organic solvent used, the blending ratio of polyvinyl acetal resin and organic solvent, and the blending ratio of the first and second solvents in the organic solvent in a balanced manner.

[0115] The ink viscosity was measured at a high rotational speed of 60 rpm, taking into consideration the thixotropic properties of the ink. Thixotropic fluids are materials that exhibit high viscosity at low rotational speeds but low viscosity under constant stress at high rotational speeds. Viscosity measurements were taken at high rotational speeds to define the viscosity of Newtonian fluids, which have a constant viscosity under any stress.

[0116] The inkjet ink of the present invention can be used in on-demand inkjet printers. In particular, it can be suitably used in on-demand piezo-type inkjet printers. [Examples]

[0117] <Example 1> After mixing the following components, the mixture was filtered using a 5 μm membrane filter to prepare the inkjet ink.

[0118] [Table 1]

[0119] The components listed in the table are as follows:

[0120] Coloring agent: Metal complex salt dye [VALIFAST® BLACK 3810 manufactured by Orient Chemical Industry Co., Ltd.] First solvent: 1-Methoxy-2-propanol [Propylene glycol monomethyl ether (PM), SP value: 10.2, flash point: 32°C] Second solvent: Ethanol [ethyl alcohol, carbon number: 2, SP value: 12.7, flash point: 16℃] Polyvinyl acetal resin (PVB): S-REC® BL-1H manufactured by Sekisui Chemical Co., Ltd. [Number average molecular weight Mn = 20,000] Phenolic resin: Phenolite (registered trademark) TD-2131 manufactured by DIC Corporation [softening point VT = 88℃~95℃] Tackifier: Rosin ester [Harima Chemicals Ltd.'s Haritack (registered trademark) SE-10, acid value: 2-10] Surfactant: Silicone-based surfactant [TEGO(registered trademark) Glide A116 manufactured by Evonik] The mixing ratio of the second solvent to the total amount of organic solvent (second solvent / first solvent + second solvent) was 36.4% by mass.

[0121] <Example 2> An inkjet ink was prepared in the same manner as in Example 1, except that the same amount of ethyl carbitol [diethylene glycol monoethyl ether, SP value: 10.2, flash point: 96°C] was added as the first solvent instead of propylene glycol monomethyl ether (PM). The mixing ratio of the second solvent to the total amount of organic solvent (second solvent / first solvent + second solvent) was 36.4% by mass.

[0122] <Example 3> An inkjet ink was prepared in the same manner as in Example 1, except that the same amount of 1-propanol [n-propyl alcohol (NPA), SP value: 11.97, flash point: 27°C] was added as the second solvent instead of ethanol. The mixing ratio of the second solvent to the total amount of organic solvent (second solvent / first solvent + second solvent) was 36.4% by mass.

[0123] <Example 4> An inkjet ink was prepared in the same manner as in Example 1, except that the amount of the first solvent was 73.0% by mass and the amount of the second solvent was 5.6% by mass. The mixing ratio of the second solvent to the total amount of organic solvent (second solvent / first solvent + second solvent) was 7.1% by mass.

[0124] <Example 5> An inkjet ink was prepared in the same manner as in Example 1, except that the amount of the first solvent was 60.0% by mass, the amount of the second solvent was 9.3% by mass, and an additional 9.3% by mass of propylene glycol [flash point: 134°C] was added as another solvent. The ratio of the second solvent to the total amount of organic solvents (second solvent / first solvent + second solvent + other solvents) was 11.8% by mass.

[0125] <Example 6> An inkjet ink was prepared in the same manner as in Example 1, except that the amount of the first solvent was 60.0% by mass and the amount of the second solvent was 18.6% by mass. The mixing ratio of the second solvent to the total amount of organic solvent (second solvent / first solvent + second solvent) was 23.7% by mass.

[0126] <Example 7> An inkjet ink was prepared in the same manner as in Example 1, except that the amount of the first solvent was 57.0% by mass and the amount of the second solvent was 21.6% by mass. The mixing ratio of the second solvent to the total amount of organic solvent (second solvent / first solvent + second solvent) was 27.5% by mass.

[0127] <Example 8> An inkjet ink was prepared in the same manner as in Example 1, except that the amount of the first solvent was 41.0% by mass and the amount of the second solvent was 37.6% by mass. The mixing ratio of the second solvent to the total amount of organic solvent (second solvent / first solvent + second solvent) was 47.8% by mass.

[0128] <Example 9> An inkjet ink was prepared in the same manner as in Example 1, except that the amount of the first solvent was 20.5% by mass, the amount of the second solvent was 37.6% by mass, and 20.5% by mass of propylene glycol [flash point: 134°C] was added as an additional solvent. The mixing ratio of the second solvent to the total amount of organic solvents (second solvent / first solvent + second solvent + other solvents) was 47.8% by mass.

[0129] <Comparative Example 1> An inkjet ink was prepared in the same manner as in Example 1, except that the amount of the first solvent was 35.0% by mass and the amount of the second solvent was 43.6% by mass. The ratio of the second solvent to the total amount of organic solvent (second solvent / first solvent + second solvent) was 55.5% by mass.

[0130] <Comparative Example 2> The inkjet ink materials were stirred in the same manner as in Example 1, except that 50.0% by mass of propylene glycol [flash point: 134°C] was added as the other solvent instead of the first solvent, and 28.6% by mass of 1-propanol [n-propyl alcohol (NPA), SP value: 11.97, flash point: 27°C] was added as the second solvent instead of ethanol. However, the ink could not be prepared because the solubility of the dye, resin, and tackifier in the solvent was extremely insufficient (poor dissolution). The mixing ratio of the second solvent to the total amount of organic solvent (second solvent / second solvent + other solvent) was 36.4% by mass.

[0131] <Comparative Example 3> An inkjet ink was prepared in the same manner as in Example 1, except that the second solvent was not added, and 28.6% by mass of ethyl carbitol [diethylene glycol monoethyl ether, SP value: 10.2, flash point: 96°C] was added as the first solvent. The mixing ratio of the second solvent to the total amount of organic solvent (second solvent / first solvent + second solvent) was 0.0% by mass.

[0132] <Example 10> An inkjet ink was prepared in the same manner as in Example 1, except that the same amount of S-REC® BL-10 [number average molecular weight Mn=15,000] manufactured by Sekisui Chemical Co., Ltd. was used as the polyvinyl acetal resin (PVB), instead of S-REC® BL-1H.

[0133] <Example 11> An inkjet ink was prepared in the same manner as in Example 1, except that the same amount of S-REC® BL-5Z [number average molecular weight Mn=32,000] manufactured by Sekisui Chemical Co., Ltd. was used as the polyvinyl acetal resin (PVB), instead of S-REC® BL-1H.

[0134] <Comparative Example 4> An inkjet ink was prepared in the same manner as in Example 1, except that the amount of the first solvent was 51.0% by mass, the amount of the second solvent was 29.0% by mass, and polyvinyl acetal resin (PVB) was not included. The mixing ratio of the second solvent to the total amount of organic solvent (second solvent / first solvent + second solvent) was 36.3% by mass.

[0135] <Example 12> An inkjet ink was prepared in the same manner as in Example 1, except that the amount of the first solvent was 50.8% by mass, the amount of the second solvent was 29.15% by mass, and the amount of polyvinyl acetal resin (PVB) was 0.05% by mass. The mixing ratio of the second solvent to the total amount of organic solvent (second solvent / first solvent + second solvent) was 36.5% by mass.

[0136] <Example 13> An inkjet ink was prepared in the same manner as in Example 1, except that the amount of the first solvent was 50.8% by mass, the amount of the second solvent was 29.1% by mass, and the amount of polyvinyl acetal resin (PVB) was 0.1% by mass. The mixing ratio of the second solvent to the total amount of organic solvents (second solvent / first solvent + second solvent) was 36.4% by mass.

[0137] <Example 14> An inkjet ink was prepared in the same manner as in Example 1, except that the amount of the first solvent was 49.0% by mass, the amount of the second solvent was 28.0% by mass, and the amount of polyvinyl acetal resin (PVB) was 3.0% by mass. The mixing ratio of the second solvent to the total amount of organic solvents (second solvent / first solvent + second solvent) was 36.4% by mass.

[0138] <Example 15> An inkjet ink was prepared in the same manner as in Example 1, except that the amount of the first solvent was 48.4% by mass, the amount of the second solvent was 27.6% by mass, and the amount of polyvinyl acetal resin (PVB) was 4.0% by mass. The mixing ratio of the second solvent to the total amount of organic solvents (second solvent / first solvent + second solvent) was 36.3% by mass.

[0139] <Comparative Example 5> An inkjet ink was prepared in the same manner as in Example 1, except that the amount of the first solvent was 47.7% by mass, the amount of the second solvent was 27.3% by mass, polyvinyl acetal resin (PVB) was not included as a fixing component, and the amount of phenol resin was 10.0% by mass. The mixing ratio of the second solvent to the total amount of organic solvent (second solvent / first solvent + second solvent) was 36.4% by mass.

[0140] <Example 16> An inkjet ink was prepared in the same manner as in Example 1, except that the same amount of rosin ester [Arakawa Chemical Industries, Ltd.'s Ester Gum (registered trademark) AA-G, acid value: 0.1-7.0] was added instead of Haritack (registered trademark) SE-10 as a tackifier. The mixing ratio of the second solvent to the total amount of organic solvent (second solvent / first solvent + second solvent) was 36.4% by mass.

[0141] <Example 17> An inkjet ink was prepared in the same manner as in Example 1, except that the same amount of rosin ester [Ester Gum 105, manufactured by Arakawa Chemical Industries, Ltd., acid value: 20 or less] was added instead of Haritack (registered trademark) SE-10 as a tackifier. The mixing ratio of the second solvent to the total amount of organic solvent (second solvent / first solvent + second solvent) was 36.4% by mass.

[0142] <Example 18> An inkjet ink was prepared in the same manner as in Example 1, except that the same amount of rosin ester [Pencel® AZ, manufactured by Arakawa Chemical Industries, Ltd., acid value: 35-50] was added instead of Haritack® SE-10 as a tackifier. The mixing ratio of the second solvent to the total amount of organic solvent (second solvent / first solvent + second solvent) was 36.4% by mass.

[0143] <Example 19> An inkjet ink was prepared in the same manner as in Example 1, except that the same amount of terpene phenol resin [YS Polystar U115 manufactured by Yasuhara Chemical Co., Ltd., hydroxyl value: 30 mg KOH / g] was added instead of Haritack (registered trademark) SE-10 as a tackifier. The mixing ratio of the second solvent to the total amount of organic solvent (second solvent / first solvent + second solvent) was 36.4% by mass.

[0144] <Example 20> An inkjet ink was prepared in the same manner as in Example 1, except that the same amount of terpene phenol resin [TP115 from the SylVares (registered trademark) series manufactured by Kraton, hydroxyl value: 50 mg KOH / g] was added instead of Haritack (registered trademark) SE-10 as a tackifier. The mixing ratio of the second solvent to the total amount of organic solvent (second solvent / first solvent + second solvent) was 36.4% by mass.

[0145] <Example 21> An inkjet ink was prepared in the same manner as in Example 1, except that the same amount of terpene phenol resin [YS Polystar T80 manufactured by Yasuhara Chemical Co., Ltd., hydroxyl value: 60 mg KOH / g] was added instead of Haritack (registered trademark) SE-10 as a tackifier. The mixing ratio of the second solvent to the total amount of organic solvent (second solvent / first solvent + second solvent) was 36.4% by mass.

[0146] <Example 22> An inkjet ink was prepared in the same manner as in Example 1, except that the same amount of terpene phenol resin [YS Polystar S145 manufactured by Yasuhara Chemical Co., Ltd., hydroxyl value: 100 mg KOH / g] was added instead of Haritack (registered trademark) SE-10 as a tackifier. The mixing ratio of the second solvent to the total amount of organic solvent (second solvent / first solvent + second solvent) was 36.4% by mass.

[0147] <Example 23> An inkjet ink was prepared in the same manner as in Example 1, except that the amount of the first solvent was 52.6% by mass, the amount of the second solvent was 30.0% by mass, and the amount of rosin ester (tackifier) ​​was 0.5% by mass. The ratio of the second solvent to the total amount of organic solvents (second solvent / first solvent + second solvent) was 36.3% by mass.

[0148] <Example 24> An inkjet ink was prepared in the same manner as in Example 1, except that the amount of the first solvent was 52.1% by mass, the amount of the second solvent was 30.0% by mass, and the amount of rosin ester (tackifier) ​​was 1.0% by mass. The mixing ratio of the second solvent to the total amount of organic solvent (second solvent / first solvent + second solvent) was 36.5% by mass.

[0149] <Example 25> An inkjet ink was prepared in the same manner as in Example 1, except that the amount of the first solvent was 46.7% by mass, the amount of the second solvent was 26.9% by mass, and the amount of rosin ester (tackifier) ​​was 9.5% by mass. The ratio of the second solvent to the total amount of organic solvents (second solvent / first solvent + second solvent) was 36.5% by mass.

[0150] <Example 26> An inkjet ink was prepared in the same manner as in Example 1, except that the amount of the first solvent was 46.5% by mass, the amount of the second solvent was 26.6% by mass, and the amount of rosin ester (tackifier) ​​was 10.0% by mass. The mixing ratio of the second solvent to the total amount of organic solvents (second solvent / first solvent + second solvent) was 36.4% by mass.

[0151] [Evaluation Method] <Continuous Printability Test> Using an on-demand piezo-type inkjet printer, the letters A through F were continuously printed on the surface of corona-treated OPP at a resolution of 300 x 300 dpi using the inkjet inks prepared in the examples and comparative examples, with a font size of 8.5pt.

[0152] Next, the printed alphabet images were observed, and the number of prints without defects or missing prints due to poor ink ejection, mainly caused by nozzle clogging, was recorded. Continuous printability was then evaluated according to the following criteria.

[0153] ○: Over 40,000 times. △: More than 20,000 times, but less than 40,000 times. ×: Less than 20,000 times.

[0154] <Intermittent Printability Test> Using the same inkjet printer as in the continuous printability test, approximately 8.5pt characters were printed on the surface of corona-treated OPP at a resolution of 300 x 300 dpi using the inkjet inks prepared in the examples and comparative examples.

[0155] Next, the inkjet printer was left to stand for a certain period of time in a room temperature, low humidity (25°C, 30%) environment in a decaffeined state, and then printed again. The standing time at which clear, smudge-free characters could be printed was recorded. Intermittent printability was evaluated based on these records according to the following criteria.

[0156] ○: Clear printing was possible even with a decapping time of 10 minutes or more. △: Clear printing was possible even with a decapping time of 5 minutes or more. ×: Clear printing was not possible unless the decapping time was less than 5 minutes.

[0157] <Quick-drying test> Using the same inkjet printer as in the continuous printability test, approximately 8.5pt characters were printed on the surface of corona-treated OPP at a resolution of 300 x 300 dpi using the inkjet inks prepared in the examples and comparative examples.

[0158] Next, the drying time required for the printed text to become completely removable when rubbed with a cotton swab after being allowed to dry for a certain period of time was recorded, and the quick-drying properties were evaluated according to the following criteria.

[0159] ○: Less than 10 seconds. ○△: 10 seconds or more, less than 13 seconds. △: 13 seconds or more, less than 15 seconds. ×: 15 seconds or more.

[0160] <Low-temperature storage test> The inkjet inks prepared in the examples and comparative examples were placed in transparent containers with lids and stored in a low-temperature incubator (approximately 5°C) for 24 hours. After storage, the containers were removed and visually inspected for the presence or absence of precipitates.

[0161] ○: No precipitates were observed. △: Mild precipitation such as cloudiness or turbidity was observed. ×: Clear precipitates were present.

[0162] <Drip Test> Using the same inkjet printer as in the continuous printability test, 1,000 solid prints of a 1-inch square area were printed on the surface of corona-treated OPP at a resolution of 600 x 300 dpi under 40°C conditions, using the inkjet inks prepared in the examples and comparative examples. After printing stopped, the inkjet printer was left in a non-printing state for 30 minutes. After this period, the inkjet printer head was visually inspected to check for ink leakage.

[0163] ○: No ink leakage (dripping) was observed. △: Drips were observed after printing. ×: Liquid dripping was observed during printing.

[0164] <Viscosity measurement> The viscosity of the inkjet inks prepared in the examples and comparative examples was measured using a rotational viscometer (TVE-35L (model number) manufactured by Toki Sangyo Co., Ltd.) at a rotational speed of 60 rpm and a measurement temperature of 20°C.

[0165] The results are shown in Tables 2 to 7.

[0166] [Table 2]

[0167] [Table 3]

[0168] [Table 4]

[0169] [Table 5]

[0170] [Table 6]

[0171] [Table 7]

[0172] <Evaluation Results> From a comparison of Examples 1-26 and Comparative Examples 1-5 in Tables 2-7, it was found that the inkjet ink contains a solvent comprising a first solvent which is glycol ether and a second solvent which is an alcohol with C1-C3 atoms, along with a polyvinyl acetal resin, and that the ratio of the second solvent to the total amount of the solvent is 5% by mass or more and 50% by mass or less, thereby allowing adjustment to an appropriate viscosity range and providing excellent properties such as continuous and intermittent printing capabilities.

[0173] More specifically, in Examples 1 to 26, there were no "X" ratings in any of the evaluations for continuous printability, intermittent printability, quick drying, low-temperature storage, and drip resistance. Furthermore, the ink viscosity measured with a rotational viscometer (60 rpm) was generally within the appropriate range for inkjet inks, approximately 4 to 15 mPa·s (60 rpm).

[0174] In contrast, in Comparative Example 1 in Table 3, the proportion of the second solvent to the total amount of organic solvent exceeded 50% by mass, resulting in poor continuous printability and low-temperature storage performance. It is thought that a high amount of the second solvent leads to insufficient solubility of the dye, resin, and tackifier in the solvent, causing precipitates to form during low-temperature storage. Furthermore, it is thought that the stability of the ink decreased, and aggregates during continuous printing clogged the nozzles, resulting in reduced continuous printability.

[0175] In Comparative Example 2 of Table 3, the first solvent, which has excellent dissolving power for resins and other materials, was not used, and the solubility of the dye, resin, and tackifier in the solvent was extremely insufficient (poor dissolution). As a result, it was not possible to prepare an ink for evaluation. Consequently, it was not possible to test each evaluation item, and all evaluation items were marked with a "×".

[0176] In Comparative Example 3 of Table 3, since only the first solvent, which is a good solvent, was used and the second solvent was not used, even if nozzle clogging occurred, the clog was dissolved and resolved by the subsequently supplied ink, thus maintaining good continuous printing performance. On the other hand, because the resin etc. dissolves easily, it is thought that the formation of a film at the nozzle tip was difficult and the decapping performance worsened, resulting in a decrease in intermittent printing performance. In addition, because only the first solvent, which has a relatively high flash point, was used, the quick-drying performance was reduced.

[0177] In Comparative Example 4 of Table 4, polyvinyl butyral resin was not used as a thickening resin, and the amount of phenolic resin added was small at 5.0% by mass. As a result, the overall thickening effect of the ink could not be sufficiently obtained, and the ink could not be adjusted to the desired viscosity range. Consequently, dripping occurred during printing, and satellites (ink splatters) occurred in addition to the printed pattern.

[0178] In Comparative Example 5 of Table 5, polyvinyl butyral resin was not used as a thickening resin, but because the amount of phenolic resin was high at 10.0% by mass, it was possible to adjust the ink to the desired viscosity range. However, due to the high amount of phenolic resin, aggregates formed during continuous printing, clogging the nozzles and reducing continuous printability. Furthermore, the solubility of the phenolic resin in the solvent was insufficient, and slight precipitation such as cloudiness and turbidity was observed during low-temperature storage.

[0179] Next, we will compare Examples 1 to 26 and explain the more preferred examples. From the comparison between Example 1 and Example 2 in Table 2, it was found that, among the propylene glycol monomethyl ether (PM) and ethyl carbitol that can be used as the first solvent, propylene glycol monomethyl ether (PM) was preferred in the quick-drying evaluation. Furthermore, it was found that among the first solvents, the ink viscosity was higher when using a glycol ether with 6 carbon atoms than when using a glycol ether with 4 carbon atoms.

[0180] From a comparison of Example 1 and Example 3 in Table 2, it was found that, among the two usable second solvents, ethanol and n-propyl alcohol (NPA), ethanol was preferred in the evaluation of quick-drying properties. Furthermore, it was found that among the second solvents, using an alcohol with 3 carbon atoms resulted in higher ink viscosity than using an alcohol with 2 carbon atoms.

[0181] From the results of Examples 1 to 3, it was found that, from the viewpoint of improving quick-drying properties, a C4 glycol ether is preferred as the first solvent, and a C2 alcohol is preferred as the second solvent.

[0182] A comparison of Examples 4-6 in Table 2 and Examples 7-9 in Table 3 shows that when the ratio of the second solvent to the total amount of solvent is 25% by mass or more and 48% by mass or less, excellent results were obtained in continuous printing, intermittent printing, quick drying, low-temperature storage, and dripping evaluation. However, a comparison of Example 8 and Example 9 showed that even when the blending ratio of the second solvent was 47.8% by mass, the use of propylene glycol as another solvent resulted in slightly inferior quick drying and low-temperature storage. In other words, it is preferable to use only the first and second solvents in combination, and not to use any other solvents.

[0183] On the other hand, in Example 4, because there was a large amount of the first solvent, which is a good solvent, even if nozzle clogging occurred, the subsequent supply of ink dissolved and resolved the clog, so it is thought that continuous printing performance was maintained in a good state. On the other hand, because it was difficult to form a film at the nozzle tip, the decapping performance was poor and intermittent printing performance was reduced. Furthermore, because there was a large amount of the first solvent, which has a relatively high flash point (low volatility), the quick-drying performance was also slightly inferior. In addition, in Example 9, because there was a small amount of the first solvent, which is a good solvent, and it was poorly soluble, it is thought that nozzle clogging due to precipitates was reduced, resulting in reduced continuous printing performance and low-temperature storage performance.

[0184] A comparison of Example 1 in Table 2 and Examples 10 and 11 in Table 4 revealed that if the number-average molecular weight Mn of the compounded polyvinyl acetal resin (PVB) is between 13,000 and 40,000, there is no significant difference between them, and they exhibit excellent continuous printability, intermittent printability, quick drying, low-temperature storage, and drip resistance.

[0185] From a comparison of Example 1 in Table 2, Example 12 in Table 4, and Examples 13-15 in Table 5, it was found that the amount of polyvinyl acetal resin (PVB) blended is preferably 0.1% by mass or more and 3.0% by mass or less.

[0186] From a comparison of Example 1 in Table 2 and Examples 16-18 in Table 6, it was found that when rosin ester is used as a tackifier, the acid value of the rosin ester should be between 0.1 and 20. Furthermore, from a comparison of Examples 19-20 in Table 6 and Examples 21-22 in Table 7, it was found that when terpene phenol resin is used as a tackifier, the hydroxyl value of the terpene phenol resin should be between 30 mg KOH / g and 70 mg KOH / g.

[0187] From a comparison of Example 1 in Table 2 and Examples 23-26 in Table 7, it was found that the amount of tackifier added is preferably greater than 0.5% by mass and less than 10.0% by mass.

Claims

1. A solvent comprising a first solvent which is a glycol ether, and a second solvent which is an alcohol having C1 to C3 carbon atoms, Contains polyvinyl acetal resin, An inkjet ink in which the ratio of the second solvent to the total amount of the aforementioned solvent is 5% by mass or more and 50% by mass or less.

2. The inkjet ink according to claim 1, wherein the first solvent is propylene glycol monomethyl ether.

3. The inkjet ink according to claim 1, further comprising a tackifier.

4. The ratio of the second solvent to the total amount of the aforementioned solvent is 25% by mass or more and 48% by mass or less. The inkjet ink according to any one of claims 1 to 3, wherein the ratio of the polyvinyl acetal resin to the total amount of the inkjet ink is 0.1% by mass or more and 3.0% by mass or less.

5. The ratio of the polyvinyl acetal resin to the total amount of the inkjet ink is 0.1% by mass or more and 3.0% by mass or less. The inkjet ink according to any one of claims 1 to 3, wherein the viscosity of the entire inkjet ink, as measured by a rotational viscometer (60 rpm), is 4 mPa·s or more and 15 mPa·s or less.

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