Inkjet recording method

Abstract

An inkjet recording method includes: an ink applying step of applying an inkjet ink containing at least a polymerizable compound, a polymerization initiator, and water to an absorbent recording medium; and an irradiation step of irradiating the absorptive recording medium with an active energy ray while applying the inkjet ink, the surface temperature of the recording surface of the absorptive recording medium being 35 DEG C or more at the start of the ink applying step.

Description

Technical Field

[0001] The present invention relates to an inkjet recording method. Background Art

[0002] Inkjet recording boasts the following advantages: ease of full-color printing, low noise levels, the ability to produce high-resolution images at low cost, high-speed printing, the ability to print not only on flat but also curved surfaces, and the ease of printing on large areas. Consequently, inkjet recording is no longer limited to personal use; in recent years, it has rapidly gained popularity as a commercial inkjet printer for applications such as signatures, window films, posters, car wraps, and wallpaper.

[0003] As an inkjet recording method, the method using solvent-free UV ink is known. However, although this method is excellent in coating strength and substrate versatility, it is environmentally and safety-related, the ink thickness becomes thick due to high viscosity, and the surface smoothness of the printed film is also poor.

[0004] In recent years, recording methods using UV-curable water-based inks have also been developed. However, while UV-curable water-based inks are environmentally friendly and safe, they have weak coating strength unless they are cured after drying. Furthermore, a pretreatment solution must be applied before applying the ink (e.g., Patent Documents 1 and 2).

[0005] The problem of weak coating film strength is particularly prominent when an absorbent recording medium such as cloth is used as the recording medium.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 2022-067314

[0009] Patent Document 2: Japanese Patent Application Laid-Open No. 2011-218571 Summary of the Invention

[0010] Problems to be solved by the invention

[0011] An object of the present invention is to provide an inkjet recording method capable of improving the strength of a printed coating film without requiring pretreatment in inkjet recording using an ultraviolet curable aqueous ink.

[0012] Solutions for solving problems

[0013] The present inventors have conducted repeated in-depth research and found that the above-mentioned technical problem can be solved by the following method: the inkjet application process of applying ultraviolet curable water-based ink to the absorptive recording medium and the irradiation process of active energy rays are carried out simultaneously, and the surface temperature of the recording surface of the absorptive recording medium at this time is set to a specific range.

[0014] The present invention has been completed based on such knowledge, and the gist of the present invention is as follows.

[0015] [1] An inkjet recording method comprising: an ink imparting step of imparting an inkjet ink containing at least a polymerizable compound, a polymerization initiator, and water to an absorptive recording medium; and an irradiation step of irradiating the absorptive recording medium with active energy rays while imparting the inkjet ink, wherein the surface temperature of the recording surface of the absorptive recording medium is 35° C. or higher at the start of the ink imparting step.

[0016] [2] The inkjet recording method according to [1], wherein the surface temperature of the recording surface of the absorptive recording medium is 120° C. or lower.

[0017] [3] The inkjet recording method according to [2], wherein the surface temperature of the recording surface of the absorptive recording medium is 100° C. or lower.

[0018] [4] The inkjet recording method according to any one of [1] to [3], wherein the absorptive recording medium is heated by a heating unit at the start of the ink applying step.

[0019] [5] The inkjet recording method according to [4], wherein heating is performed from the side opposite to the recording surface of the absorptive recording medium.

[0020] [6] The inkjet recording method according to [4] or [5], wherein the heating unit is a heating plate.

[0021] [7] The inkjet recording method according to any one of [1] to [6], wherein the absorptive recording medium is a cloth.

[0022] [8] The inkjet recording method according to any one of [1] to [7], wherein the inkjet ink contains 70% by mass or more of a volatile component relative to the total amount of the inkjet ink.

[0023] [9] The inkjet recording method according to any one of [1] to [8], wherein the content of the water relative to the total amount of the inkjet ink is 40% by mass or more.

[0024]

[10] The inkjet recording method according to any one of [1] to [9], wherein the light source of the active energy ray is a light-emitting diode having a peak emission wavelength in the range of 350 to 420 nm.

[0025]

[11] The inkjet recording method according to any one of [1] to

[10] , wherein the inkjet ink contains a sensitizer and / or a surfactant.

[0026]

[12] The inkjet recording method according to any one of [1] to

[11] , wherein a pretreatment agent is not applied to the absorptive recording medium before the ink applying step.

[0027]

[13] The inkjet recording method according to any one of [1] to

[12] , wherein the polymerizable compound is present in the form of particles in the inkjet ink.

[0028]

[14] The inkjet recording method according to

[13] , wherein the average particle size of the particles is 10 nm or more and 200 nm or less.

[0029]

[15] The inkjet recording method according to any one of [1] to

[14] , wherein the polymerizable compound contains a (meth)acrylate compound.

[0030]

[16] The inkjet recording method according to any one of [1] to

[15] , wherein the inkjet ink contains a pigment.

[0031]

[17] The inkjet recording method according to any one of [1] to

[16] , wherein the irradiation energy of the active energy ray is 0.1 J / cm 2 above.

[0032]

[18] The inkjet recording method according to any one of [1] to

[17] , wherein the method of applying the inkjet ink to the absorptive recording medium is a reciprocating method.

[0033]

[19] The inkjet recording method according to any one of [1] to

[18] , wherein the irradiation method of the active energy ray is a reciprocating method.

[0034]

[20] The inkjet recording method according to any one of [1] to

[19] , wherein the inkjet ink contains a water-soluble organic solvent.

[0035]

[21] The inkjet recording method according to any one of [1] to

[20] , wherein the viscosity of the inkjet ink at 25°C is 1 mPa·sec or more and 25 mPa·sec or less.

[0036] Effects of the Invention

[0037] According to the inkjet recording method of the present invention, a printed coating film having sufficient strength can be formed without pretreatment in inkjet recording using an ultraviolet curable aqueous ink that is excellent in environmental and safety.

[0038] Therefore, a high-quality printed image can be obtained efficiently by reducing the number of steps in inkjet recording and improving the coating film strength. DETAILED DESCRIPTION

[0039] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

[0040] In the present invention, when expressed as "X to Y" (X and Y are arbitrary numbers), unless otherwise specified, it means "X or more and Y or less", and also means "preferably greater than X" and "preferably less than Y".

[0041] The inkjet recording method of the present invention is the following inkjet recording method, which includes: an ink imparting step, imparting an inkjet ink containing at least a polymerizable compound, a polymerization initiator and water (hereinafter sometimes referred to as "the inkjet ink of the present invention") to an absorptive recording medium; and an irradiation step, irradiating the absorptive recording medium with active energy rays while imparting the inkjet ink, and at the start of the ink imparting step, the surface temperature of the recording surface of the absorptive recording medium is above 35°C.

[0042] Hereinafter, the simultaneous application of the active energy ray while applying the ink may be referred to as "simultaneous irradiation".

[0043] The inkjet recording method of the present invention may further include other steps as needed. For example, it may further include a drying step of drying and removing the solvent in the inkjet ink imparted to the absorptive recording medium such as fabric.

[0044] Alternatively, a pretreatment agent application step may be performed before the ink application step to apply a pretreatment agent to the recording medium. However, the inkjet recording method of the present invention preferably does not include such a pretreatment agent application step. Specifically, in the present invention, by performing simultaneous irradiation, a printed coating film having sufficient strength can be formed even without performing the pretreatment agent application step before the ink application step. Therefore, the ability to omit the pretreatment agent application step is also a feature of the present invention.

[0045] 〔mechanism〕

[0046] The mechanism by which the inkjet recording method of the present invention, which involves simultaneous irradiation, can improve the strength of the printed coating film is considered to be as follows.

[0047] When applying inkjet ink to an absorptive recording medium such as fabric and then irradiating it with active energy rays, as in conventional methods, the ink penetrates the absorptive recording medium before irradiation with the active energy rays, causing the curing components (polymerizable compound and polymerization initiator) in the ink to separate. Consequently, the curing reaction does not proceed fully even after irradiation with the active energy rays. Consequently, the resulting printed coating film does not achieve sufficient strength.

[0048] In the inkjet recording method of the present invention, the curing reaction of the ink proceeds immediately by irradiating the ink with active energy rays. The ink solvent is easily volatilized by the heat of the curing reaction, so the ink becomes thicker and less likely to penetrate into the absorbent recording medium.

[0049] In addition, during this simultaneous irradiation, by setting the surface temperature of the recording surface of the absorptive recording medium to above 35°C at the beginning of the ink imparting process, the curing reaction of the above-mentioned ink and the volatilization of the ink solvent can be promoted, and the penetration of the ink into the absorptive recording medium can be further effectively suppressed.

[0050] In view of the above, it is believed that according to the present invention, the separation of the solidified components in the ink can be suppressed, and the strength of the printed coating film can be improved. Therefore, it is believed that in the present invention, the polymerizable compound is particularly effective when it exists in the form of particles in the ink.

[0051] Furthermore, it is considered that the above-mentioned technical problem caused by the penetration of the ink into the absorptive recording medium becomes a technical problem particularly in a system where the ink contains a solvent (aqueous ink or solvent ink).

[0052] [Ink application process]

[0053] In the ink applying step of the inkjet recording method of the present invention, the inkjet ink of the present invention contained in the ink set is applied from, for example, an inkjet head of an inkjet printer onto an absorptive recording medium such as cloth.

[0054] The method for applying the inkjet ink of the present invention is not particularly limited as long as it is a method that can apply the inkjet ink in a desired image pattern.

[0055] From the viewpoint of compactness of the recording apparatus and high-speed recording performance, the inkjet method employed in the present invention is a preferred method.

[0056] In image formation using the inkjet method, energy is supplied to eject inkjet ink onto a recording medium, thereby forming a colored image.

[0057] It depends on the image to be formed, but the amount of ink used in image formation is usually 30 g / m 2 For example, when printing is performed with 8 passes, the amount of ink ejected per pass is one eighth of the amount of ink, that is, 3.75 g / m 2 Below left and right.

[0058] There is no particular limitation on the inkjet method, and it can be any of the known methods, such as a charge control method that uses electrostatic attraction to eject ink, a drop-on-demand method (pressure pulse method) that uses the vibration pressure of a piezoelectric element, an acoustic inkjet method that converts an electrical signal into a sound beam and irradiates the ink to eject the ink using radiation pressure, etc.

[0059] The inkjet head used in the inkjet method may be either an on-demand method or a continuous method. Furthermore, the ink nozzles used for recording by the inkjet method are not particularly limited and may be appropriately selected depending on the intended purpose.

[0060] It should be noted that the inkjet method includes: a method of ejecting a large amount of low-concentration ink called photo ink in a small volume, a method of using multiple inks of substantially the same hue but different concentrations to improve image quality, and a method of using colorless and transparent ink.

[0061] Inkjet methods include a reciprocating method that uses a short serial head to record while scanning the head along the width direction of the recording medium, and a line method that uses a line head with recording elements arranged corresponding to the entire area of ​​one side of the recording medium.

[0062] The line method records images across the entire surface of the recording medium by scanning the recording medium in a direction perpendicular to the arrangement of the recording elements. This eliminates the need for a carriage or other transport system for scanning with a short head. Furthermore, since only the recording medium is moved, eliminating the need for carriage movement and complex scanning control, recording speeds can be significantly increased compared to reciprocating methods.

[0063] However, through multiple passes, even the lower layer of the ink layer printed on the recording medium is irradiated with a certain amount of active energy rays, thereby making it easy to obtain the significant effect achieved by simultaneous irradiation in the present invention. Therefore, the reciprocating method is preferably used in the present invention.

[0064] In the present invention, at least at the start of the ink application step, the surface temperature of the recording surface of the absorptive recording medium is set to 35° C. or higher. This temperature condition will be described later.

[0065] [Irradiation process]

[0066] The irradiation step in the inkjet recording method of the present invention is a step performed simultaneously with the ink applying step, and is a step of irradiating the absorptive recording medium to which the inkjet ink has been applied with active energy rays.

[0067] The simultaneous irradiation in the present invention means starting the irradiation of the active energy ray at the same time as the start of the inkjet ink application step, or starting the irradiation of the active energy ray within 10 seconds after the start of the inkjet ink application step.

[0068] More specifically, "simultaneously with the start of the inkjet ink application process" refers to the simultaneous discharge of the inkjet ink and the irradiation of the active energy ray. For example, a reciprocating inkjet recording apparatus, described below, having an inkjet head and an active energy ray irradiation unit on a carriage, and simultaneously discharging the inkjet ink and irradiating the active energy ray while scanning the carriage, constitutes simultaneous irradiation in the present invention.

[0069] Irradiation with active energy rays causes the polymerizable compound contained in the inkjet ink of the present invention to polymerize under the action of the polymerization initiator, thereby forming a cured film of the inkjet ink, thereby more effectively improving the abrasion resistance and blocking resistance of the image.

[0070] The inkjet ink of the present invention undergoes a curing reaction upon exposure to active energy rays. This reaction involves the decomposition of the polymerization initiator contained in the inkjet ink of the present invention upon exposure to active energy rays, generating free radicals that initiate and accelerate the polymerization reaction of the polymerizable compound, thereby curing the inkjet ink.

[0071] When treated with a pretreatment agent containing an acidic compound, upon irradiation with the active energy rays, the inkjet ink is further aggregated (fixed) by the acid supplied by the acidic compound, resulting in improved image quality (such as abrasion resistance and blocking resistance). However, as described above, treatment with a pretreatment agent can be omitted in the present invention.

[0072] As active energy rays, α rays, γ rays, electron beams, X-rays, ultraviolet rays, visible light, infrared light, and the like can be used. As described later, the polymerization initiator preferably used in the inkjet ink of the present invention has a high absorption of light in the ultraviolet region. From this perspective, the emission peak wavelength of the active energy ray source used for irradiation is preferably in the range of 200 to 600 nm, more preferably in the range of 300 to 450 nm, and even more preferably in the range of 350 to 420 nm.

[0073] The emission peak wavelength may be one or more within the above wavelength range.

[0074] The irradiation energy of the active energy ray is particularly preferably 0.1 J / cm 2 More than, for example, particularly preferably 0.5 to 10 J / cm 2 When the irradiation energy is equal to or greater than the above lower limit, the polymerization reaction of the polymerizable compound can be smoothly advanced, thereby achieving a more excellent effect of improving the coating film strength.

[0075] As active energy ray sources, mercury lamps, gas / solid lasers, etc. are mainly used. As light sources used for curing ultraviolet curable aqueous inks, mercury lamps, halogen lamps, and metal halide lamps are widely known.

[0076] However, there is a strong demand for mercury-free light sources from an environmental perspective. Replacing these light sources with GaN-based semiconductor UV light-emitting devices is highly beneficial both industrially and environmentally. Furthermore, LEDs and laser diodes (LDs) are expected to be used as light sources for photocurable inkjet printers due to their compact size, long lifespan, high efficiency, and low cost.

[0077] In the present invention, LEDs and LDs can be used as active energy ray sources. In particular, UV-LEDs and UV-LDs can be used as ultraviolet light sources. For example, Nichia Chemical Co., Ltd. has marketed a violet LED with a main emission spectrum between 365 nm and 420 nm.

[0078] In the present invention, a particularly preferred active energy ray source is a UV-LED, and a UV-LED having a peak emission wavelength in the range of 350 to 420 nm is particularly preferred.

[0079] In the present invention, from the viewpoint of cost and curability, it is preferred to use a light-emitting diode having a peak emission wavelength in the range of 350 to 420 nm.

[0080] For the same reason as in the ink applying step, the irradiation method in the irradiation step performed simultaneously with the ink applying step is also preferably performed in a reciprocating manner.

[0081] In the present invention, at least at the start of the ink applying step performed simultaneously with the irradiation step, the surface temperature of the recording surface of the absorptive recording medium is set to 35° C. or higher. This temperature condition is described below.

[0082] [Surface temperature of the recording surface at the start of simultaneous irradiation]

[0083] In the inkjet recording method of the present invention, the surface temperature of the recording surface of the absorptive recording medium (hereinafter sometimes simply referred to as "surface temperature") is set to 35° C. or higher at the start of the ink applying step.

[0084] When the surface temperature of the absorptive recording medium is 35° C. or higher, the solvent (eg, water, aqueous medium, etc.) in the ink applied to the absorptive recording medium such as cloth is efficiently volatilized and removed, thereby improving curability.

[0085] From this viewpoint, the surface temperature of the absorptive recording medium at the start of simultaneous irradiation is preferably 40° C. or higher, more preferably 45° C. or higher. On the other hand, the surface temperature is preferably 120° C. or lower, more preferably 100° C. or lower.

[0086] Meanwhile, the surface temperature of the absorptive recording medium at the start of simultaneous irradiation is preferably below the boiling point of the solvent with the highest content among the solvents contained in the ink. Specifically, it is preferably below 120°C, and more preferably below 100°C. A surface temperature below 120°C prevents drying of the ink on the surface of the ink ejection nozzle due to the influence of the surface temperature of the absorptive recording medium, which could lead to poor ink ejection.

[0087] In order to adjust the surface temperature of the absorptive recording medium to the above-mentioned range at the start of simultaneous irradiation, it is preferable to heat the absorptive recording medium by a heating unit at the start of simultaneous irradiation.

[0088] The heating means is not particularly limited, and for example, a hot air heater or an infrared heater can be used. More specifically, a ceramic heater, a halogen heater, a quartz tube heater, and the like can be used.

[0089] Furthermore, a heating plate may be used as the heating means, which is preferable because it can keep the recording medium at a uniform temperature.

[0090] In order to minimize the influence on the recording surface of the absorptive recording medium, the heating of the absorptive recording medium by the heating means is preferably performed from the side opposite to the recording surface of the absorptive recording medium.

[0091] In the inkjet recording method of the present invention, the surface temperature of the absorptive recording medium can be above 35°C as long as the simultaneous irradiation ink imparting process starts, that is, when the inkjet ink is imparted to the absorptive recording medium. Moreover, the above-mentioned surface temperature can also be set before imparting the inkjet ink to the absorptive recording medium and after imparting the inkjet ink to the absorptive recording medium, that is, before and after the simultaneous irradiation. It is preferred to maintain the above-mentioned surface temperature in all processes before, during and after imparting.

[0092] [Recorded medium]

[0093] In the inkjet recording method of the present invention, an absorptive recording medium is used as the recording medium.

[0094] In the present invention, the absorptive recording medium refers to a recording medium having a surface that is highly absorptive to ink. More quantitatively, the time from the start of contact to 30 msec in the Bristow method is 1 / 2 The water absorption is 0.3g / m2 The above recording medium is an absorbent recording medium. On the other hand, the water absorption is less than 0.3 g / m 2 The recording medium is set as a non-absorbing recording medium.

[0095] Examples of the absorptive recording medium include paper, cloth, nonwoven fabric, leather, wood, and composite materials thereof. Among the absorptive recording media, cloth is preferably used because it can achieve the significant effect of the simultaneous irradiation of the present invention.

[0096] The raw materials constituting the fabric are not particularly limited, and examples thereof include natural fibers such as cotton, linen, wool, and silk; synthetic fibers such as polypropylene, polyester, acetate, triacetate, polyamide, and polyurethane; and biodegradable fibers such as polylactic acid. The raw materials constituting the fabric may also be blends of these fibers.

[0097] Among these, cotton and polyester are preferred, and cotton is more preferred.

[0098] On the other hand, non-absorptive recording media include polyesters such as polyethylene terephthalate (PET), polyolefins such as polyvinyl chloride (PVC), polyethylene (PE), and polypropylene (PP), plastic materials such as glass, ceramics, metals, or composite materials thereof. As shown in the comparative and reference examples described below, the effects of the present invention achieved through simultaneous irradiation cannot be achieved with non-absorptive recording media.

[0099] [Inkjet recording device]

[0100] The inkjet recording apparatus used to implement the inkjet recording method of the present invention may be any of various recording apparatuses employing the inkjet recording method. For example, the inkjet recording method of the present invention can be preferably used in printers, facsimile machines, copiers, printer / fax / copier all-in-ones, and 3D modeling devices.

[0101] In the present invention, the recording device refers to a device that can eject ink, various processing liquids, etc. onto a recording medium.

[0102] The recording apparatus includes not only a head portion that ejects ink but also units related to the supply, transport, and discharge of the recording medium, as well as devices called a pre-processing device and a post-processing device.

[0103] The recording device may include a heating unit for heating the absorptive recording medium, a drying unit for heating the absorptive recording medium, and an irradiation unit for irradiating the absorptive recording medium with active energy rays. The heating unit and the drying unit may heat and dry the printing surface and the back surface of the recording medium, for example.

[0104] As mentioned above, the irradiation means for irradiating the active energy ray includes a halogen lamp, a metal halide lamp, an LED lamp, etc. The light source for curing the ink irradiates the active energy ray from the side to cure the ink, thereby forming a printed image.

[0105] The recording device is not limited to a recording device that visualizes meaningful images such as text and graphics using ink, but also includes a device that forms patterns such as geometric patterns, and a device that shapes three-dimensional images.

[0106] The recording apparatus includes not only desktop types but also wide-format recording apparatuses capable of printing on A0-size recording media, for example, continuous printers capable of using rolled continuous paper as recording media.

[0107] The recording method or active energy ray irradiation method of the recording device includes, unless otherwise specified, a reciprocating method in which a serial head is moved while recording or irradiating, and a line method in which a line head is used for recording. Examples of reciprocating recording devices include Japanese Patent Application Laid-Open No. 2022-181182 and Japanese Patent Application Laid-Open No. 2010-280828.

[0108] As described above, the recording method or the active energy ray irradiation method of the recording device is preferably a reciprocating method in order to obtain the significant effect of the present invention by simultaneous irradiation. More specifically, a configuration in which the carriage includes an inkjet head and an active energy ray irradiation unit is preferred.

[0109] [Inkjet ink]

[0110] The inkjet ink of the present invention contains at least a polymerizable compound, a polymerization initiator, and water. That is, an ultraviolet curable aqueous ink can be used in the inkjet recording method of the present invention.

[0111] [Polymerizable compound]

[0112] The polymerizable compound contained in the inkjet ink of the present invention is not particularly limited as long as it is a polymerizable compound, and known polymerizable monomers, polymerizable resins, polymerizable oligomers, etc. can be used. Among the above, polymerizable oligomers are preferred, and ultraviolet curable oligomers are more preferred.

[0113] Specific examples of polymerizable compounds include (meth)acrylamide compounds, (meth)acrylate compounds, vinyl compounds, maleimide compounds, vinyl sulfone compounds, N-vinylamide compounds, and derivatives thereof. These compounds are more preferably difunctional or higher. The polymerizable compound is further preferably a (meth)acrylamide compound, a (meth)acrylate compound, or a vinyl compound, and is particularly preferably a difunctional or higher (meth)acrylamide compound.

[0114] In the present invention, "(meth)acrylate" means acrylate or methacrylate. The same applies to "(meth)acryloyl" and "(meth)acrylic acid".

[0115] These polymerizable compounds may be used alone or in combination of two or more. When two or more are used in combination, it is preferred to use a mixture of two or more selected from (meth)acrylamide compounds, (meth)acrylate compounds, vinyl compounds, maleimide compounds, vinyl sulfone compounds, and N-vinylamide compounds, and it is more preferred that at least one of them is a (meth)acrylamide compound.

[0116] From the viewpoint of improving water solubility, the polymerizable compound may have a poly(ethyleneoxy) chain, a poly(propyleneoxy) chain, an ionic group (eg, a carboxyl group, a sulfonic group, etc.), a hydroxyl group, etc. in the molecule.

[0117] As the (meth)acrylate compound, either a monofunctional (meth)acrylate compound (a compound having one (meth)acryloyl group) or a polyfunctional (meth)acrylate compound can be used, and a polyfunctional (meth)acrylate compound is preferred.

[0118] There are no particular restrictions on the ionicity of the UV-curable oligomer, and the UV-curable oligomer may be nonionic or ionic (anionic, cationic, or amphoteric). Nonionic refers to, for example, that the hydrophilic groups of the UV-curable oligomer are composed of ether bonds or hydroxyl groups that do not undergo ion dissociation in water. Ionic (anionic, cationic, or amphoteric) refers to, for example, that the UV-curable oligomer has carboxyl groups or amino groups that can undergo ion dissociation in water.

[0119] As the ultraviolet curable oligomer, for example, the following are preferred <1> ~ <3> Any of .

[0120] <1> An ultraviolet curable oligomer having a structural unit derived from a compound represented by the following formula (1).

[0121] [Chemical Formula 1]

[0122]

[0123] (In formula (1), X is an alkylene group, and Y is any of a (meth)acryloyl group, an allyl group, an acyl group, and a hydrogen atom. n is an integer of 2 or greater.)

[0124] <2> An ultraviolet curable oligomer having a structural unit derived from a polyisocyanate compound (A), wherein the compound (A) is a compound having three or more isocyanate groups in one molecule.

[0125] <3> An ultraviolet curable oligomer having a structural unit derived from a polyisocyanate compound (A), a structural unit derived from a compound (B') shown below, and a structural unit derived from a compound (C') shown below.

[0126] described <3> The ultraviolet curable oligomer is usually produced by reacting a polyisocyanate compound (A), a compound (B'), and a compound (C').

[0127] Compound (B'): A compound containing two or more polymerizable unsaturated bonds and capable of bonding to the polyisocyanate compound (A).

[0128] Compound (C'): A water-soluble compound capable of bonding to the polyisocyanate compound (A).

[0129] As ultraviolet curable oligomer, it is preferably the ultraviolet curable oligomer comprising the structural unit derived from (meth) acrylate, particularly preferably the ultraviolet curable oligomer comprising the structural unit derived from multifunctional (meth) acrylate.More preferably, it is the ultraviolet curable oligomer comprising the structural unit derived from multifunctional (meth) acrylate and the structural unit derived from polyalkylene glycol.That is, from the viewpoint of reactivity, compound (B ') is preferably hydroxy-containing multifunctional (meth) acrylate (B).From the viewpoint of water dispersibility, compound (C ') is preferably polyalkylene glycol (C).Such ultraviolet curable oligomer is usually manufactured by reacting polyisocyanate compound (A), hydroxy-containing multifunctional (meth) acrylate (B) and polyalkylene glycol (C).

[0130] In the present invention, a "structural unit derived from X" refers to a structural unit that is incorporated into the molecular structure of a UV-curable oligomer by reacting compound X with other compounds using compound X as a raw material. A "structural unit derived from X" is not necessarily limited to one made from compound X. In other words, even when formed from a raw material other than X, as long as the chemical structure is the same, it constitutes a "structural unit derived from X."

[0131] As described above, a preferred embodiment of compound (B') includes a hydroxyl-containing polyfunctional (meth)acrylate (B). A preferred embodiment of compound (B') is "a compound (B) containing a hydroxyl group and two or more polymerizable unsaturated bonds."

[0132] The "compound capable of bonding to the polyisocyanate compound (A)" in the compound (B') may be a compound in which the hydroxyl group of the compound (B") is substituted with a carboxyl group, an amino group, or the like. Examples of polymerizable unsaturated bonds include carbon-carbon double bonds and carbon-carbon triple bonds, with carbon-carbon double bonds being preferred. More specifically, examples of polymerizable unsaturated bonds include carbon-carbon double bonds derived from vinyl groups, (meth)acryloyl groups, and the like.

[0133] The water-soluble compound in compound (C') includes water-soluble polymers, and specific examples thereof include polyglycerol, polyhydroxy (meth)acrylate, polyamine, quaternized polystyrene, sulfonated polystyrene, polyether, and polyalkylene glycol. Among them, polyglycerol, polyhydroxy (meth)acrylate, and polyalkylene glycol, which are nonionic water-soluble compounds, are preferred, and polyalkylene glycol is particularly preferred. Each of these water-soluble compounds may be a copolymer.

[0134] Compound (C') has the structure of such a water-soluble compound and the structure of a "compound capable of bonding to the polyisocyanate compound (A)." The structure of the "compound capable of bonding to the polyisocyanate compound (A)" can be selected from the same structures as those exemplified above as compound (B').

[0135] The structural unit derived from the polyisocyanate compound (A) bonds with the structural unit derived from the hydroxyl-containing polyfunctional (meth)acrylate (B) and the structural unit derived from the polyalkylene glycol (C) to form a urethane bond. Each of these urethane bonds may be substituted with a urea bond or an amide bond.

[0136] In the present invention, when the hydroxyl-containing polyfunctional (meth)acrylate (B) is the above-mentioned compound (B') or compound (B"), or when the polyalkylene glycol (C) is the above-mentioned compound (C'), the preferred embodiments or specific embodiments in this case can be similarly applied to the preferred embodiments or specific embodiments in the case of using the hydroxyl-containing polyfunctional (meth)acrylate (B) or polyalkylene glycol (C) described later.

[0137] Hereinafter, each compound constituting the ultraviolet curable oligomer will be described. In the present invention, the term "oligomer" is not limited to a specific molecular weight range, and any oligomer may have the structure shown below.

[0138] The inkjet ink may contain only one type of ultraviolet curable oligomer, or may contain two or more types.

[0139] <Polyisocyanate compound (A)>

[0140] The polyisocyanate compound (A) is a compound having a total of two or more isocyanate groups in one molecule.

[0141] The type of polyisocyanate compound (A) is not particularly limited, and examples thereof include linear aliphatic polyisocyanates, aromatic polyisocyanates, alicyclic polyisocyanates, etc. Among them, the polyisocyanate compound (A) preferably comprises a trimer compound of polyisocyanate from the viewpoint of weather resistance and hardness.

[0142] Chain aliphatic polyisocyanates are compounds having a chain aliphatic structure and two or more isocyanate groups. From the viewpoints of weather resistance and stretchability, chain aliphatic polyisocyanates are preferred. The chain aliphatic structure in the chain aliphatic polyisocyanate is not particularly limited, but is preferably a linear or branched alkylene group having 1 to 12 carbon atoms, preferably 1 to 6 carbon atoms. Examples of chain aliphatic polyisocyanates include aliphatic diisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, and dimer acid diisocyanate, or trimer compounds of these polyisocyanates.

[0143] Aromatic polyisocyanates are compounds having an aromatic structure and two or more isocyanate groups. From the perspective of coating film strength, aromatic polyisocyanates are preferred. The aromatic structure in the aromatic polyisocyanate is not particularly limited, but is preferably an aromatic structure having 6 to 13 carbon atoms. Examples of aromatic polyisocyanates include aromatic diisocyanates such as toluene diisocyanate, xylylenediisocyanate, diphenylmethane diisocyanate, m-phenylenediisocyanate, and naphthalene diisocyanate, or trimer compounds of these polyisocyanates.

[0144] Alicyclic polyisocyanates are compounds having an alicyclic structure and two or more isocyanate groups. The alicyclic structure in the alicyclic polyisocyanate is not particularly limited, and the number of carbon atoms is generally 5 or more, preferably 6 or more, generally 15 or less, preferably 14 or less, and more preferably 13 or less. The alicyclic structure is particularly preferably a cycloalkylene group. Examples of alicyclic polyisocyanates include diisocyanates having an alicyclic structure such as bis(isocyanate methyl)cyclohexane, cyclohexane diisocyanate, bis(isocyanate cyclohexyl)methane, and isophorone diisocyanate, or trimer compounds of these polyisocyanates.

[0145] The ultraviolet curable oligomer may use only one of these polyisocyanate compounds (A) or two or more thereof. As the polyisocyanate compound (A), a polyisocyanate having two or more of a chain aliphatic structure, an aromatic structure, and an alicyclic structure may be used.

[0146] In particular, from the viewpoint of adhesion to a substrate, the polyisocyanate compound (A) is preferably a polyisocyanate compound having 3 or more and 6 or less isocyanate groups.

[0147] The polyisocyanate compound (A) is preferably a trimer obtained by trimerization of hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, phenylene diisocyanate, or the like, and particularly preferably a trimer of hexamethylene diisocyanate.

[0148] <Compounds containing polymerizable unsaturated bonds>

[0149] In the compound containing a polymerizable unsaturated bond, the number of polymerizable unsaturated bonds is preferably 1 or more, more preferably 2 or more, further preferably 4 or more, and is preferably 8 or less, more preferably 6 or less.

[0150] The compound containing a polymerizable unsaturated bond is preferably a compound capable of bonding to the polyisocyanate compound (A).

[0151] (Compound (B'))

[0152] The compound (B') contains two or more polymerizable unsaturated bonds and is a compound capable of bonding to the polyisocyanate compound (A).

[0153] Examples of the compound (B') include compounds having any of a hydroxyl group, an amino group, and a carboxyl group. Examples of the compound (B') include polyfunctional vinyl monomers, polyfunctional allyl monomers, and polyfunctional (meth)acrylates. Among them, the compound (B') is preferably a hydroxyl-containing polyfunctional (meth)acrylate (B).

[0154] <Hydryl-containing multifunctional (meth)acrylate (B)>

[0155] The hydroxyl-containing polyfunctional (meth)acrylate (B) has one or more hydroxyl groups and two or more (meth)acryloyl groups. Specifically, a (meth)acrylic acid partial ester of a polyol is exemplified. The hydroxyl-containing polyfunctional (meth)acrylate forms a favorable crosslinked structure through the participation of multiple (meth)acryloyl groups in the curing reaction, thereby improving physical properties such as stain resistance and abrasion resistance.

[0156] The number of hydroxyl groups in the hydroxyl-containing polyfunctional (meth)acrylate (B) is preferably 3 or less, more preferably 2 or less, and even more preferably 1. The number of (meth)acryloyl groups in the hydroxyl-containing polyfunctional (meth)acrylate (B) is preferably 8 or less, more preferably 6 or less.

[0157] Examples of the hydroxyl group-containing polyfunctional (meth)acrylate (B) include pentaerythritol tri(meth)acrylate, dipentaerythritol penta(meth)acrylate, caprolactone-modified dipentaerythritol penta(meth)acrylate, caprolactone-modified pentaerythritol tri(meth)acrylate, ethylene oxide-modified dipentaerythritol penta(meth)acrylate, ethylene oxide-modified pentaerythritol tri(meth)acrylate, 2-hydroxy-1,3-dimethacryloxypropane, and 2-hydroxy-3-acryloxypropyl methacrylate.

[0158] In the production of the ultraviolet curable oligomer, only one of these hydroxyl group-containing polyfunctional (meth)acrylates (B) may be used, or two or more thereof may be used in combination.

[0159] In particular, from the perspective of coating film strength of the resulting cured film, the hydroxyl-containing polyfunctional (meth)acrylate (B) preferably has one hydroxyl group and three or more and five or less (meth)acryloyl groups. For example, dipentaerythritol penta(meth)acrylate and pentaerythritol tri(meth)acrylate are preferred. In particular, from the perspective of forming a good cross-linked structure and improving the mechanical strength of the cured film, dipentaerythritol penta(meth)acrylate is preferred.

[0160] <Water-soluble compounds>

[0161] (Compound (C'))

[0162] The compound (C') is a water-soluble compound capable of bonding to the polyisocyanate compound (A).

[0163] In order to improve water dispersibility, the compound (C') is preferably a compound having one hydroxyl group terminal.

[0164] As mentioned above, examples of the compound (C') include water-soluble polymers, and among these, polyalkylene glycol (C) is particularly preferred.

[0165] The polyalkylene glycol (C) is not limited, but preferably has a monosubstituted structure. That is, one hydroxyl group in the diol is preferably substituted. The substituted structure is preferably one that is not bonded to an isocyanate.

[0166] The polyalkylene glycol (C) may be a mixture of a compound having a monosubstituted structure and a compound having a non-monosubstituted structure.

[0167] The monosubstituted structure is not limited, but from the viewpoint of making the ultraviolet curable oligomer nonionic, it is preferably a polyalkylene glycol monosubstituted ether, more preferably a polyethylene glycol monosubstituted ether, a polytrimethylene glycol monosubstituted ether or a polypropylene glycol monosubstituted ether, and still more preferably a polyethylene glycol monosubstituted ether.

[0168] The molecular weight (number average molecular weight when not a single molecular weight) of the polyalkylene glycol (C) is not limited, but is usually 100 or more, preferably 200 or more, and usually 5000 or less, preferably 2000 or less.

[0169] Among the polyalkylene glycol monosubstituted ethers, those having no ionic substituent in the ether moiety are more preferred. For example, a compound represented by the following formula (1) is more preferred.

[0170] [Chemical Formula 2]

[0171]

[0172] (In formula (1), X is an alkylene group, and Y is any of an alkyl group, a (meth)acryloyl group, an allyl group, an acyl group, and a hydrogen atom. n is an integer of 2 or greater.)

[0173] Specific examples of the polyalkylene glycol monosubstituted ether represented by the above formula (1) include the following.

[0174] Compounds in which Y=alkyl: polyethylene glycol monomethyl ether, polyethylene glycol lauryl ether, polyethylene glycol cetyl ether, polyethylene glycol stearyl ether, polyethylene glycol tridecyl ether, polyethylene glycol oleyl ether, polyethylene glycol octylphenyl ether, polyoxyethylene oleyl cetyl ether, polypropylene glycol monomethyl ether, and the like.

[0175] Compounds in which Y=(meth)acryloyl group: polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, poly(ethylene glycol-propylene glycol) mono(meth)acrylate, poly(ethylene glycol-tetramethylene glycol) mono(meth)acrylate, poly(propylene glycol-tetramethylene glycol) mono(meth)acrylate, etc.

[0176] Compounds wherein Y=allyl: polyethylene glycol monoallyl ether, polypropylene glycol monoallyl ether, poly(ethylene glycol-propylene glycol) monoallyl ether, and the like.

[0177] Compounds where Y=acyl: polyethylene glycol monolaurate, polypropylene glycol monolaurate, poly(ethylene glycol-propylene glycol) monolaurate, polyethylene glycol monostearate, polyethylene glycol monooleate, and the like.

[0178] Among these, X in formula (1) is preferably an alkylene group having 1 to 3 carbon atoms, more preferably an ethylene group, a trimethylene group, or a propylene group. From the viewpoint of pigment dispersion stability or storage stability at high temperatures, X is more preferably an ethylene group.

[0179] From the viewpoint of coating film strength, Y is preferably a (meth)acryloyl group, an allyl group, or an acyl group, and more preferably an allyl group.

[0180] From the viewpoint of the coating film strength of the obtained cured film, n in formula (1) is usually 2 or more, preferably 5 or more, more preferably 6 or more, and usually 500 or less, preferably 100 or less, more preferably 50 or less.

[0181] In the production of the ultraviolet curable oligomer, only one of these polyalkylene glycols (C) may be used, or two or more thereof may be used in combination. The polyalkylene glycol (C) may be a mixture of compounds having different molecular weights (compounds having different n in formula (1)).

[0182] <Average Particle Size>

[0183] In the inkjet ink, the polymerizable compound is preferably present in the form of particles, more preferably in the form of particles having an average particle size of 10 nm to 200 nm, and even more preferably in the form of particles having an average particle size of 20 nm to 150 nm. When the average particle size of the polymerizable compound is within the above range, dispersion stability is excellent.

[0184] Here, the average particle size of the polymerizable compound is, for example, a volume average particle size (D 50 ).

[0185] In the Examples described below, the average particle size of the polymerizable compound particles in the polymerizable compound aqueous dispersion is measured. The average particle size of the polymerizable compound particles in the aqueous dispersion is substantially equal to the average particle size of the polymerizable compound particles in the ink.

[0186] In the present invention, as long as the polymerizable compound exists in the form of particles, even if there is aggregation or even if other substances are contained in the particles, it is included in the state of "existing in the form of particles" described above.

[0187] The above-mentioned average particle size of the polymerizable compound refers to the particle size (primary particle size) of the polymerizable compound particles.

[0188] Hereinafter, components other than the polymerizable compound contained in the inkjet ink of the present invention will be described.

[0189] [Colorant]

[0190] The inkjet ink used in the inkjet recording method of the present invention may contain a colorant.

[0191] As the colorant used in the inkjet ink, various dyes or pigments known as colorants for ink can be used. From the viewpoint of irradiation with active energy rays and long-term storage durability of printed images, it is preferable to use a pigment.

[0192] <Dye>

[0193] The dye that can be used in the present invention is not particularly limited, and examples thereof include water-soluble dyes such as acid dyes, direct dyes, and reactive dyes, and disperse dyes. Among them, anionic dyes are preferred.

[0194] (Water-soluble dyes)

[0195] Examples of the water-soluble dye include azo dyes, methine dyes, azomethine dyes, xanthene dyes, quinone dyes, phthalocyanine dyes, triphenylmethane dyes, and diphenylmethane dyes.

[0196] <Pigment>

[0197] As pigments, conventionally known organic pigments and inorganic pigments can be used. For example, azo pigments such as azo lakes, insoluble azo pigments, condensed azo pigments, and chelated azo pigments; polycyclic pigments such as phthalocyanine pigments, perylene and perylene pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone pigments; dye lakes such as basic dye lakes and acid dye lakes; organic pigments such as nitro pigments, nitroso pigments, aniline black, and daylight fluorescent pigments; and inorganic pigments such as carbon black, titanium oxide, and iron oxide pigments. Among these, anionic pigments are preferred.

[0198] These dyes and pigments may be used alone or in combination of two or more.

[0199] [Water-based media]

[0200] The inkjet ink of the present invention is an aqueous ink. "Aqueous ink" refers to an ink containing an aqueous medium. The aqueous medium refers to water and / or a water-soluble organic solvent.

[0201] The aqueous medium used in the present invention is preferably water or a mixture of water and a water-soluble organic solvent.

[0202] Water-soluble organic solvents include those that function as moisturizing solvents to improve the ink's moisture retention and wettability, and those that function as aqueous media to adjust ink viscosity and improve operability and ejectability. There's no clear distinction between the two; a water-soluble organic solvent used as a moisturizing solvent also functions as an aqueous media.

[0203] In the present invention, a water-soluble organic solvent refers to a compound that is soluble in water. The solubility of a water-soluble organic solvent in water is not limited, but preferably a compound that can dissolve in water in any proportion. In addition, even a compound that is difficult to have the characteristics of a solvent alone (for example, a compound that is solid or has high viscosity at room temperature) is also included in the water-soluble organic solvent as long as it can be used as a solvent by uniformly mixing with water.

[0204] Examples of the water-soluble organic solvent include ethers such as polyols, polyol alkyl ethers, and polyol aryl ethers, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds.

[0205] Specific examples of the water-soluble organic solvent include the following.

[0206] Polyols such as ethylene glycol, diethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 3-methyl-1,3-butanediol, triethylene glycol, polyethylene glycol, polypropylene glycol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 2,4-pentanediol, 1,5-pentanediol, 1,2-hexanediol, 1,6-hexanediol, 1,3-hexanediol, 2,5-hexanediol, 1,5-hexanediol, glycerol, 1,2,6-hexanetriol, 2-ethyl-1,3-hexanediol, ethyl-1,2,4-butanetriol, 1,2,3-butanetriol, 2,2,4-trimethyl-1,3-pentanediol, and 3-methyl-1,3,5-pentanetriol.

[0207] Polyol alkyl ethers such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, propylene glycol monomethyl ether, and propylene glycol monoethyl ether.

[0208] Polyol aryl ethers such as ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether.

[0209] Nitrogen-containing heterocyclic compounds such as 2-pyrrolidone, N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, ε-caprolactam, and γ-butyrolactone.

[0210] Amides such as formamide, N-methylformamide, N,N-dimethylformamide, 3-methoxy-N,N-dimethylpropionamide, and 3-butoxy-N,N-dimethylpropionamide.

[0211] Amines such as monoethanolamine, diethanolamine, and triethylamine.

[0212] Sulfur-containing compounds such as dimethyl sulfoxide, sulfolane, and thiodiethanol.

[0213] Propylene carbonate, ethylene carbonate.

[0214] From the viewpoint of not only functioning as a moisturizing solvent but also obtaining good drying properties, it is preferable to use an organic solvent having a boiling point of 250° C. or lower as the water-soluble organic solvent.

[0215] As the water-soluble organic solvent, polyol compounds and glycol ether compounds having 8 or more carbon atoms can also be preferably used.

[0216] Specific examples of the polyol compound having 8 or more carbon atoms include 2-ethyl-1,3-hexanediol and 2,2,4-trimethyl-1,3-pentanediol.

[0217] Specific examples of glycol ether compounds include polyol alkyl ethers such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, tetraethylene glycol monomethyl ether, and propylene glycol monoethyl ether; and polyol aryl ethers such as ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether.

[0218] These water-soluble organic solvents may be used alone or in combination of two or more.

[0219] [Polymerization initiator]

[0220] The inkjet ink of the present invention contains a polymerization initiator.

[0221] The polymerization initiator is a photoradical polymerization initiator that generates free radicals as active species by using the energy of light (ultraviolet rays) received by irradiation with active energy rays, thereby initiating photopolymerization of the polymerizable compound. This allows the ink on the surface of the recording medium to cure and form an image.

[0222] The polymerization initiator may be contained in the ink in a state not encapsulated in the polymerizable compound, or in a state encapsulated in particles of the polymerizable compound, or in both states.

[0223] The polymerization initiator may be a fat-soluble polymerization initiator (hereinafter sometimes referred to as a "fat-soluble initiator") or a water-soluble polymerization initiator (hereinafter sometimes referred to as a "water-soluble initiator").

[0224] Here, a "fat-soluble initiator" refers to a polymerization initiator that is compatible with a polymerizable compound such as a UV-curable oligomer, or that is soluble in an organic solvent. A "water-soluble initiator" refers to an initiator that dissolves in water at a concentration of 1% by mass or more. This also applies to the "fat-soluble sensitizer" and "water-soluble sensitizer" described below.

[0225] The polymerization initiator used in the present invention is not limited to the following, and examples thereof include aromatic ketones, acylphosphine oxide compounds, aromatic onium salt compounds, organic peroxides, thio compounds (thioxanthone compounds, sulfur-phenyl-containing compounds), α-aminoalkylphenone compounds, hexaarylbiimidazole compounds, ketoxime ester compounds, borate compounds, azinium compounds, metallocene compounds, active ester compounds, compounds having a carbon-halogen bond, and alkylamine compounds.

[0226] Among these, the polymerization initiator preferably contains at least one of an acylphosphine oxide compound and a thioxanthone compound. The use of such a polymerization initiator tends to improve the curability of the ink.

[0227] Examples of the fat-soluble polymerization initiator include, but are not limited to, acetophenone, 2,2-diethoxyacetophenone, p-dimethylaminoacetophenone, benzophenone, 2-chlorobenzophenone, p,p'-dichlorobenzophenone, p,p'-bis(diethylamino)benzophenone, Michler's ketone, benzyl, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin n-propyl ether, benzoin isobutyl ether, benzoin n-butyl ether, benzyl methyl ketal, 2,2-dimethoxy-1,2-diphenylethane-1-one, 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-1-{4-[4-(2-hydroxy-2-methylpropionyl)benzyl]phenyl}-2-methylpropane-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone-1, 2-Dimethylamino-2-(4-methylbenzyl)-1-(4-morpholin-4-yl-phenyl)butan-1-one, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropane-1-one, thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2-isopropylthioxanthone, 4-isopropylthioxanthone, 2-hydroxy-2-methyl-1-phenyl-1-one, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropane-1-one, methyl benzoylformate, azobisisobutyronitrile, benzoyl peroxide, and di-tert-butyl peroxide, etc.

[0228] Examples of water-soluble polymerization initiators include, but are not limited to, 1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propane-1-one, sodium phenyl(2,4,6-trimethylbenzoyl)phosphonate, and 2-(3-dimethylamino-2-hydroxypropoxy)-3,4-dimethyl-9H-thioxanthone-9-one methyl chloride.

[0229] Examples of commercially available polymerization initiators include GENOPOL TX-2 manufactured by RAHN, and Irgacure (registered trademark) 369, Irgacure (registered trademark) 500, and Irgacure (registered trademark) 2959 manufactured by BASF Japan.

[0230] The polymerization initiator may be used alone or in combination of two or more. For example, a fat-soluble initiator and a water-soluble initiator may be used in combination, with the fat-soluble initiator being encapsulated in particles of a polymerizable compound such as an ultraviolet-curable oligomer, and the water-soluble initiator being dissolved in an aqueous medium.

[0231] As the polymerization initiator, a thermal radical polymerization initiator may be used in combination with the above-mentioned photoradical polymerization initiator.

[0232] [Surfactant]

[0233] The inkjet ink of the present invention preferably contains a surfactant for the purpose of improving the flatness of the formed coating film and wettability with the substrate.

[0234] As the surfactant, any of silicone-based surfactants, fluorine-based surfactants, amphoteric surfactants, nonionic surfactants, and anionic surfactants can be used.

[0235] There are no particular restrictions on the silicone surfactants, and they can be appropriately selected according to the purpose. Among them, silicone surfactants that do not decompose even at high pH are preferred, and examples thereof include: side chain modified polydimethylsiloxane, two-end modified polydimethylsiloxane, single-end modified polydimethylsiloxane, side chain two-end modified polydimethylsiloxane, etc. Silicone surfactants having polyoxyethylene, polyoxyethylene polyoxypropylene as modifying groups show good properties as water-based surfactants and are therefore particularly preferred. As silicone surfactants, polyether-modified silicone surfactants can also be used. As polyether-modified silicone surfactants, for example, compounds obtained by introducing a polyalkylene oxide structure into the Si side chain of dimethylsiloxane can be listed.

[0236] The fluorine-based surfactant is preferably a fluorine-substituted compound having 2 to 16 carbon atoms, and more preferably a fluorine-substituted compound having 4 to 16 carbon atoms.

[0237] As the fluorine-based surfactant, for example, perfluoroalkylsulfonic acid compounds, perfluoroalkylcarboxylic acid compounds, perfluoroalkylphosphate compounds, perfluoroalkylalkylene oxide adducts, and polyoxyalkylene ether polymer compounds having a perfluoroalkyl ether group in a side chain are preferred because of their low foaming properties.

[0238] Examples of the perfluoroalkylsulfonic acid compound include perfluoroalkylsulfonic acid and perfluoroalkylsulfonic acid salts.

[0239] Examples of the perfluoroalkyl carboxylic acid compound include perfluoroalkyl carboxylic acids and perfluoroalkyl carboxylate salts.

[0240] Examples of the perfluoroalkyl phosphate compound include perfluoroalkyl phosphate esters and perfluoroalkyl phosphate salts.

[0241] Examples of the perfluoroalkyl alkylene oxide adduct include perfluoroalkyl ethylene oxide adducts.

[0242] Examples of the polyoxyalkylene ether polymer compound having a perfluoroalkyl ether group in a side chain include sulfate ester salts of polyoxyalkylene ether polymers having a perfluoroalkyl ether group in a side chain and salts of polyoxyalkylene ether polymers having a perfluoroalkyl ether group in a side chain.

[0243] Examples of the counter ions of the salts in these fluorine-based surfactants include Li, Na, K, NH 4 , NH 3 CH 2 CH 2 OH, NH 2 (CH 2 CH 2 OH) 2 , and NH (CH 2 CH 2 OH) 3 .

[0244] Among these, polyoxyalkylene ether polymer compounds having a perfluoroalkyl ether group in a side chain have particularly low foaming properties and are therefore more preferred. Fluorine-based surfactants represented by the following formulas (3A) and (3B) are particularly preferred.

[0245] CF3CF2(CF2CF2) s -CH2CH2O(CH2CH2O) t H(3A)

[0246] In the compound represented by formula (3A), in order to impart water solubility, s is preferably an integer of 0 or more and 10 or less, and t is preferably an integer of 0 or more and 40 or less.

[0247] C r F 2r+1 -CH2CH(OH)CH2-O-(CH2CH2O) c -Z(3B)

[0248] In the compound represented by formula (3B), Z is H, C d F 2d+1 (d is an integer of 1 to 6), CH2CH(OH)CH2-C e F 2e+1 (e is an integer of 4 to 6) or C f H 2f+1 (f is an integer greater than or equal to 1 and less than or equal to 19).

[0249] r is an integer of 1 to 6. c is an integer of 4 to 14.

[0250] As the fluorine-based surfactant, commercially available products can be used. Examples of commercially available products include: Surflon (registered trademark) S-111, S-112, S-113, S-121, S-131, S-132, S-141, and S-145 (all manufactured by Asahi Glass Co., Ltd.); Fluorad FC-93, FC-95, FC-98, FC-129, FC-135, FC-170C, FC-430, and FC-431 (all manufactured by Sumitomo 3M Co., Ltd.); and MEGAFACE. F-470, F-1405, F-474 (all manufactured by DIC Corporation); Zonyl TBS, FSP, FSA, FSN-100, FSN, FSO-100, FSO, FS-300, UR (all manufactured by DuPont); FT-110, FT-250, FT-251, FT-400S, FT-150, FT-400SW (all manufactured by NEOS Co., Ltd.); Polyfox PF-136A, PF-156A, PF-151N, PF-154, PF-159 (manufactured by OMNOVA), NOIGEN FN-1287 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), UNIDYNE DSN-403N (manufactured by Daikin Industries, Ltd.), LE-604, LE-605, LE-606, LE-607 (manufactured by Kyoeisha Chemical Co., Ltd.), etc.

[0251] Examples of the amphoteric surfactant include lauryl aminopropionate, lauryl dimethyl betaine, stearyl dimethyl betaine, and lauryl dihydroxyethyl betaine.

[0252] Examples of the nonionic surfactant include polyoxyethylene alkylphenyl ethers, polyoxyethylene alkyl esters, polyoxyethylene alkylamines, polyoxyethylene alkylamides, polyoxyethylene propylene block polymers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, acetylene alcohol derivatives, and acetylene glycol derivatives.

[0253] Examples of the anionic surfactant include polyoxyethylene alkyl ether acetates, dodecylbenzenesulfonates, laurates, and salts of polyoxyethylene alkyl ether sulfates.

[0254] These may be used alone or in combination of two or more.

[0255] As described above, there are no particular limitations on the silicone surfactant, and any suitable surfactant may be selected depending on the intended purpose. Polyether-modified silicone surfactants having polyoxyethylene or polyoxyethylene-polyoxypropylene groups as modifying groups exhibit excellent properties as water-based surfactants and are therefore particularly preferred.

[0256] As such a surfactant, a suitably synthesized one may be used, or a commercially available product may be used. Commercially available products are available, for example, from BYK Co., Ltd., Shin-Etsu Chemical Co., Ltd., Toray Dow Corning Silicone Co., Ltd., Nihon Emulsion Co., Ltd., Kyoeisha Chemical Co., Ltd., and the like.

[0257] The polyether-modified silicone surfactant is not particularly limited and can be appropriately selected depending on the intended purpose. Examples thereof include compounds represented by the following formula (2) in which a polyalkylene oxide structure is introduced into the Si side chain of dimethylpolysiloxane.

[0258] [Chemical Formula 3]

[0259]

[0260] (In formula (2), p, q, a, and b represent integers. R and R' represent hydrocarbon groups.)

[0261] As the polyether-modified silicone-based surfactant, a commercially available product can be used. Examples of commercially available products include KF-618, KF-642, and KF-643 (Shin-Etsu Chemical Co., Ltd.), SAG001, SAG002, SAG003, SAG005, SAG503, and SAG008 (Nissin Chemical Co., Ltd.), Emalex-SS-5602 and SS-1906EX (Nihon Emulsion Co., Ltd.), FZ-2105, FZ-2118, FZ-2154, FZ-2161, FZ-2162, FZ-2163, and FZ-2164 (Toray DowCorning Silicone Co., Ltd.), BYK-33 and BYK-387 (BYK Corporation), and TSF4440, TSF4452, and TSF4453 (Toshiba Silicone Co., Ltd.).

[0262] [Sensitizer]

[0263] The inkjet ink of the present invention may contain a sensitizer. If the sensitizer is present in the ink together with the polymerization initiator, the sensitizer in the system absorbs active energy rays and becomes excited. Contact with the polymerization initiator promotes the decomposition of the polymerization initiator, enabling a more sensitive curing reaction.

[0264] Like the polymerization initiator, the sensitizer may be fat-soluble or water-soluble. If the sensitizer is fat-soluble, it can be encapsulated in particles of a polymerizable compound such as an ultraviolet curable oligomer.

[0265] As sensitizers, the following can be used: aliphatic amines, cyclic amine compounds such as amines or piperidines having aromatic groups, thioxanthone compounds, alkoxyanthracene compounds, urea compounds such as o-tolylthiourea; sulfur compounds such as sodium diethylthiophosphate or soluble salts of aromatic sulfinic acids, nitrile compounds such as N,N'-disubstituted p-aminobenzonitrile, phosphorus compounds such as tri-n-butylphosphine or sodium diethyldithiophosphate; Michler's ketone, N-nitrosohydroxylamine derivatives; nitrogen compounds such as oxazolidine compounds, tetrahydro-1,3-oxazine compounds, condensates of formaldehyde or acetaldehyde and diamines, etc.

[0266] These sensitizers may be used alone or in combination of two or more.

[0267] [Other resin components]

[0268] In addition to the above-mentioned components, the inkjet ink of the present invention may also contain any oligomer component, any resin component, or any monomer component other than the polymerizable compound (collectively referred to as "other resin components") as needed. The other resin components may be encapsulated in particles of the polymerizable compound or dissolved in an aqueous medium. The other resin components may be dispersed in the ink alone or in a complexed state with other components.

[0269] [Other additives]

[0270] The inkjet ink of the present invention may contain other additives as needed in addition to the above-mentioned components.

[0271] Examples of other additives include known additives such as anti-fading agents, emulsion stabilizers, penetration enhancers, ultraviolet absorbers, preservatives, mildew inhibitors, rust inhibitors, pH adjusters, viscosity adjusters, dispersants, dispersion stabilizers, defoamers, solid wetting agents, and chelating agents. These additives may be added directly after or during ink preparation.

[0272] For other additives, the description in paragraphs 0088 to 0096 of JP-A-2010-65205 and the description in paragraphs 0083 to 0090 of JP-A-2010-70669 can be appropriately referred to.

[0273] [Content of each ingredient]

[0274] The water content in the inkjet ink of the present invention is not particularly limited and may be appropriately selected depending on the intended purpose. From the perspectives of ink drying properties and ejection reliability, the water content in the inkjet ink of the present invention is typically 10% by mass or greater, preferably 20% by mass or greater, more preferably 40% by mass or greater, and typically 90% by mass or less, preferably 80% by mass or less.

[0275] When the inkjet ink of the present invention contains a water-soluble organic solvent, its content (the total content of the water-soluble organic solvent that also serves as a moisturizing solvent and the water-soluble organic solvent that serves as an aqueous medium) is not particularly limited and can be appropriately selected depending on the type of water-soluble organic solvent used and the intended purpose. From the perspectives of drying properties, ejection reliability, and wettability with the substrate, the content of the water-soluble organic solvent is generally 10% by mass or more, typically 50% by mass or less, and preferably 40% by mass or less.

[0276] The content of the volatile component is preferably 70% by mass or more, more preferably 75% by mass or more, and preferably 95% by mass or less, more preferably 90% by mass or less, based on the total amount of the inkjet ink of the present invention.

[0277] When the content of the volatile component is not less than the above lower limit, discharge reliability is high, and when the content of the volatile component is not more than the above upper limit, coating film strength can be enhanced.

[0278] The volatile components in the inkjet ink of the present invention are components that are reduced by 90% or more after 1 g of the inkjet ink is placed on an aluminum plate with a diameter of 10 cm and dried at 80° C. for 4 hours compared to before drying.

[0279] From the viewpoint of drying properties and ejection reliability, the inkjet ink of the present invention is prepared so that the total solid content concentration of components other than water and / or water-soluble organic solvent, i.e., aqueous medium, is usually 5% by mass or more, preferably 7% by mass or more, more preferably 9% by mass or more, and usually 30% by mass or less, preferably 25% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less.

[0280] From the viewpoint of improving drying properties and spraying properties, when a mixture of water and a water-soluble organic solvent is used as the aqueous medium, the ratio of water to the water-soluble organic solvent (the total of the water-soluble organic solvent serving as a moisturizing solvent and the water-soluble organic solvent serving as the aqueous medium) is preferably water: water-soluble organic solvent, usually 1:0.05 to 1:1.5 (mass ratio), preferably 1:0.1 to 1:1.2 (mass ratio), and more preferably 1:0.15 to 1:1.1 (mass ratio).

[0281] From the perspective of the resulting printed coating performance and active energy ray curability, the content of the polymerizable compound in the inkjet ink of the present invention is generally 3% by mass or greater, preferably 5% by mass or greater, and more preferably 7% by mass or greater. On the other hand, from the perspective of ejection stability, the content of the polymerizable compound in the inkjet ink of the present invention is generally 20% by mass or less, preferably 15% by mass or less, and more preferably 12% by mass or less.

[0282] From the same viewpoint, the content of the polymerizable compound in the total solid content of the inkjet ink of the present invention is usually 30% by mass or more, preferably 50% by mass or more, more preferably 60% by mass or more, and usually 90% by mass or less, preferably 85% by mass or less, more preferably 80% by mass or less.

[0283] From the perspectives of improving image density, achieving good fixability, and ejection stability, the content of the colorant in the inkjet ink of the present invention is usually 0.1% by mass or more, preferably 1% by mass or more, and usually 8% by mass or less, preferably 6% by mass or less.

[0284] From the same viewpoint, the content of the colorant in the total solids content of the inkjet ink of the present invention is usually 1% by mass or more, preferably 5% by mass or more, and usually 40% by mass or less, preferably 30% by mass or less.

[0285] The content of the polymerization initiator in the inkjet ink of the present invention is generally 0.05% by mass or more, preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.4% by mass or more, and generally 8% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, even more preferably 2% by mass or less, and particularly preferably 1% by mass or less. When the content of the polymerization initiator is within this range, the curing speed can be sufficiently increased while avoiding undissolved residues of the polymerization initiator and coloration caused by the polymerization initiator.

[0286] From the same viewpoint, the content of the polymerization initiator in the total solid content of the inkjet ink of the present invention is usually 0.5% by mass or more, preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more, and is usually 20% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less, and particularly preferably 8% by mass or less.

[0287] When the inkjet ink of the present invention contains a surfactant, the content thereof is not particularly limited and may be appropriately selected depending on the intended purpose. To achieve excellent wettability and ejection stability, and to enhance image quality, the surfactant content in the ink is typically 0.001% by mass or greater, preferably 0.01% by mass or greater, and more preferably 0.03% by mass or greater, and typically 5% by mass or less, preferably 3% by mass or less, and more preferably 1% by mass or less.

[0288] From the same viewpoint, the content of surfactant in the total solid content of the inkjet ink of the present invention is usually 0.01 mass% or more, preferably 0.1 mass% or more, more preferably 0.2 mass% or more, and usually 10 mass% or less, preferably 5 mass% or less, more preferably 3 mass% or less.

[0289] When the inkjet ink of the present invention contains a sensitizer, its content is generally 0.01% by mass or more, preferably 0.03% by mass or more, more preferably 0.05% by mass or more, and generally 4% by mass or less, preferably 3% by mass or less, more preferably 1% by mass or less, and even more preferably 0.7% by mass or less. When the sensitizer content is within this range, the effects of the sensitizer can be fully achieved.

[0290] From the same viewpoint, the content of the sensitizer in the total solid content of the inkjet ink of the present invention is usually 0.05% by mass or more, preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more, and is usually 8% by mass or less, preferably 6% by mass or less, and more preferably 5% by mass or less.

[0291] [Viscosity of inkjet ink]

[0292] The viscosity of the inkjet ink of the present invention at 25°C is preferably 25 mPa·sec or less, more preferably 20 mPa·sec or less, and even more preferably 10 mPa·sec or less. The lower limit of the viscosity of the inkjet ink of the present invention at 25°C is not particularly limited, but is preferably 1 mPa·sec or more, more preferably 2 mPa·sec or more, and even more preferably 5 mPa·sec or more.

[0293] The viscosity of the inkjet ink can be measured using a digital viscometer DV-I+ manufactured by Brookfield.

[0294] 〔use〕

[0295] The inkjet ink used in the inkjet recording method of the present invention is aqueous, and therefore has excellent environmental and safety characteristics. The inkjet recording method of the present invention enables the formation of printed coatings with excellent coating properties using such aqueous inks. Therefore, the inkjet recording method of the present invention is preferably used in various applications, including fabrics for clothing such as T-shirts, textiles, interior wallpaper, and home furnishings.

[0296] Example

[0297] Hereinafter, examples of the present invention will be described, but the present invention is not limited to these examples.

[0298] [Ink Preparation]

[0299] <Preparation of Aqueous Dispersion of Polymerizable Compound>

[0300] 0.4 mol of a trimer of hexamethylene diisocyanate, 0.8 mol of dipentaerythritol pentaacrylate, and 0.4 mol of polyethylene glycol monoallyl ether (n=30-40 in the above formula (1)) were reacted to produce a polymerizable compound (nonionic ultraviolet curable oligomer).

[0301] To 20 parts by mass of the polymerizable compound, 2 parts by mass of a fat-soluble initiator (GENOPOL TX-2 manufactured by RAHN) was added, and the mixture was maintained at 60°C. While stirring, ion-exchanged water preheated to 60°C was added dropwise until the solid content concentration reached 20% by mass, thereby obtaining an aqueous dispersion having a solid content concentration of 20% by mass.

[0302] The average particle size (D 50 ) was measured using a particle size distribution meter MICROTRAC WAVEII-EX150 (manufactured by Microtrac BEL Co., Ltd.) and the result was 29 nm.

[0303] <Preparation of Ink 1>

[0304] Ion-exchanged water, the polymerizable compound aqueous dispersion (solids concentration 20% by mass), propylene glycol (PG) and diethylene glycol ethyl methyl ether (EM) as water-soluble organic solvents, water-soluble initiator 1, water-soluble sensitizer 1, BYK-347 manufactured by BYK Japan Co., Ltd. as a surfactant, and EMACOL SF CYANAE2034F manufactured by Sanyo Pigments (represented as "Cy" in Table 1) as a pigment dispersion were added and mixed to achieve the composition ratio shown in Table 1 to obtain Ink 1.

[0305] The viscosity of the ink 1 at 25° C. was 6.5 mPa·s. The water content and the volatile component content in the ink 1 were 65% by mass and 85% by mass, respectively.

[0306] <Preparation of Inks 2 to 4>

[0307] Inks 2 to 4 were obtained in the same manner as Ink 1 except that the following pigment dispersions were used and the type and blending ratio of the pigment dispersions and the blending ratio of the water-soluble sensitizer were changed as shown in Table 1 below.

[0308] Pigment dispersion: EMACOL SF MAGENTA AG2172F manufactured by Sanyo Pigment Co., Ltd. (represented as "Ma" in Table 1).

[0309] Pigment dispersion: EMACOL SF YELLOWAG2242F manufactured by Sanyo Pigment Co., Ltd. (described as "Ye" in Table 1).

[0310] Pigment dispersion: EMACOL SF BLACKAE2078F manufactured by Sanyo Pigment Co., Ltd. (described as "Bk" in Table 1).

[0311] The viscosities, water contents, and volatile component contents of Inks 2 to 4 at 25° C. are as follows, respectively.

[0312] Ink 2: Viscosity = 7.2 mPa·s

[0313] Water content = 64 mass%

[0314] Volatile component content = 84% by mass

[0315] Ink 3: Viscosity = 6.4 mPa·s

[0316] Water content = 66 mass%

[0317] Volatile component content = 86% by mass

[0318] Ink 4: Viscosity = 6.2 mPa·s

[0319] Water content = 65 mass%

[0320] Volatile component content = 85% by mass

[0321] The content ratio of each component in Table 1 indicates the content ratio of the component contained in the aqueous dispersion or solution when the component is prepared as an aqueous dispersion or solution.

[0322] [Table 1]

[0323]

[0324] [Example 5]

[0325] A commercially available reciprocating UV inkjet printer was loaded with the ink 1 as the inkjet ink and a cotton fabric as the recording medium. A heating plate was placed on the platform, and the recording medium was placed on the heating plate. The printing settings were set as follows. While applying the ink 1 to the recording medium, the medium was irradiated with active energy rays to form a printed coating film.

[0326] (Print Settings)

[0327] Resolution: 600×720dpi.

[0328] Number of passes: 16 passes.

[0329] Image: 5 x 16.5 cm solid color image.

[0330] An LED with a peak emission wavelength of 385 nm was used as the active energy ray source. The illuminance, cumulative light intensity, and heater temperature were set to the conditions shown in Table 2. The illuminance and cumulative light intensity were measured using an ultraviolet cumulative light meter ("H12684" manufactured by Hamamatsu Photonics).

[0331] [Examples 6 to 8, Comparative Examples 1 to 20, Reference Examples 1 to 7]

[0332] A printed coating film was obtained in the same manner as in Example 5 except that the ink type, recording medium type, illuminance and cumulative light amount of the active energy ray, irradiation timing of the active energy ray, and heater temperature were changed as shown in Table 2.

[0333] It should be noted that (electrodecorated) PET used as a recording medium refers to a non-absorbing electrodecorated transparent film formed of polyethylene terephthalate subjected to surface treatment.

[0334] The heater temperature corresponds to the surface temperature of the recording medium. Room temperature refers to a temperature of 20 to 30°C.

[0335] In Table 2, "while printing" means that irradiation was performed simultaneously according to the present invention. "After printing" means that irradiation with active energy rays was performed after the ink application step was completed.

[0336] [Evaluation of coating film strength]

[0337] The printed coating films obtained in Examples, Comparative Examples, and Reference Examples were evaluated for coating film strength by the following method.

[0338] <Evaluation of coating strength (cotton)>

[0339] The printed coatings on the cotton obtained in Examples 5 to 8 and Comparative Examples 1 to 8 and 17 to 20 were visually observed while the printed coatings were wetted with running water and the substrate was rubbed. The concentration changes before and after rinsing were evaluated as follows. The evaluation results are shown in Table 2.

[0340] ○: Little change in image density, no practical problem.

[0341] Δ: The image density changes greatly, but white spots are few.

[0342] ×: The image density varies greatly and there are many white spots, which is problematic in practical use.

[0343] <Evaluation of coating strength (electro-decorated PET)>

[0344] The printed coating films of the electro-decorated PET obtained in Comparative Examples 9 to 16 and Reference Examples 1 to 7 were rubbed with a cotton swab dipped in water and the color shift to the cotton swab was visually observed and evaluated as follows. The evaluation results are shown in Table 2.

[0345] ○: There is no color transfer even when wiping with water.

[0346] ×: Color shifts when wiped with water, or the printed coating peels off.

[0347] [Table 2]

[0348]

[0349]

[0350] As apparent from Table 2, the inkjet recording method of the present invention can form a printed image having excellent coating film strength.

[0351] In contrast, in Comparative Examples 1 to 8 in which active energy rays were irradiated after application of ink, and Comparative Examples 17 to 20 in which the surface temperature of the recording surface of the absorptive recording medium was lower than 35° C., the coating film strength was poor.

[0352] In Comparative Examples 9 to 16 in which the active energy rays were irradiated while applying ink to a non-absorbing recording medium such as (electro-decorated) PET, separation of the cured component due to penetration did not occur, and thus the effect of the simultaneous irradiation of the present invention could not be achieved.

[0353] As shown in Reference Examples 1 to 7, even with non-absorptive recording media such as (electrodecorated) PET, the problem of reduced coating film strength does not occur even when irradiated with active energy rays after printing. In other words, the technical problem of the present invention is considered to be unique to printing on absorptive recording media such as fabric.

[0354] While the present invention has been described in detail using specific embodiments, it will be apparent to one skilled in the art that various modifications can be made without departing from the spirit and scope of the invention.

[0355] This application is based on Japanese Patent Application No. 2023-055780 filed on March 30, 2023, the entire contents of which are incorporated herein by reference.

Claims

1. An inkjet recording method comprising: an ink applying step of applying an inkjet ink containing at least a polymerizable compound, a polymerization initiator, and water to an absorptive recording medium; as well as an irradiation step of irradiating the absorptive recording medium with active energy rays while applying the inkjet ink, When the ink applying step is started, the surface temperature of the recording surface of the absorptive recording medium is 35° C. or higher.

2. The inkjet recording method according to claim 1, wherein The surface temperature of the recording surface of the absorptive recording medium is 120° C. or lower.

3. The inkjet recording method according to claim 2, wherein The surface temperature of the recording surface of the absorptive recording medium is 100° C. or lower.

4. The inkjet recording method according to claim 1 or 2, wherein When the ink applying step is started, the absorptive recording medium is heated by a heating unit.

5. The inkjet recording method according to claim 4, wherein The absorptive recording medium is heated from the side opposite to the recording surface.

6. The inkjet recording method according to claim 4, wherein The heating unit is a heating plate.

7. The inkjet recording method according to claim 1 or 2, wherein The absorbent recording medium is a cloth.

8. The inkjet recording method according to claim 1 or 2, wherein The inkjet ink contains 70% by mass or more of a volatile component relative to the total amount of the inkjet ink.

9. The inkjet recording method according to claim 1 or 2, wherein The content of the water relative to the total amount of the inkjet ink is 40% by mass or more.

10. The inkjet recording method according to claim 1 or 2, wherein The light source of the active energy ray is a light emitting diode having a peak emission wavelength in the range of 350 to 420 nm.

11. The inkjet recording method according to claim 1 or 2, wherein The inkjet ink contains a sensitizer and / or a surfactant.

12. The inkjet recording method according to claim 1 or 2, wherein Before the ink applying step, no pretreatment agent is applied to the absorptive recording medium.

13. The inkjet recording method according to claim 1 or 2, wherein In the inkjet ink, the polymerizable compound exists in the form of particles.

14. The inkjet recording method according to claim 13, wherein The average particle size of the particles is 10 nm or more and 200 nm or less.

15. The inkjet recording method according to claim 1 or 2, wherein The polymerizable compound includes a (meth)acrylate compound.

16. The inkjet recording method according to claim 1 or 2, wherein The inkjet ink contains a pigment.

17. The inkjet recording method according to claim 1 or 2, wherein The irradiation energy of the active energy ray is 0.1 J / cm 2 above.

18. The inkjet recording method according to claim 1 or 2, wherein The inkjet ink is applied to the absorptive recording medium in a reciprocating manner.

19. The inkjet recording method according to claim 1 or 2, wherein The active energy ray irradiation method is a reciprocating method.

20. The inkjet recording method according to claim 1 or 2, wherein The inkjet ink contains a water-soluble organic solvent.

21. The inkjet recording method according to claim 1 or 2, wherein The inkjet ink has a viscosity at 25° C. of 1 mPa·sec or more and 25 mPa·sec or less.

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