Inkjet recording method and inkjet recording device

Abstract

This inkjet recording method comprises the following steps [a] and [b], wherein: in step [a], a medium to be recorded on is not heated, and in step [b], the medium to be recorded on is heated by a heating means, the medium to be recorded on being an absorbent medium to be recorded on. Step [a]: An ink application step in which an inkjet ink containing at least a polymerizable compound, a polymerization initiator, and water is applied to the medium to be recorded on. Step [b]: An irradiation step in which the inkjet ink that has been applied to the medium to be recorded on through at least step [a] is irradiated with active energy rays controlled by a means other than the heating means.

Description

Inkjet recording method and inkjet recording apparatus

[0001] The present invention relates to an inkjet recording method and an inkjet recording apparatus.

[0002] The inkjet recording method has the advantages of being easy to achieve full color, being quiet, being able to obtain high-resolution images at low cost, being capable of high-speed printing, being able to print on curved surfaces as well as flat surfaces, being able to print on large areas easily, etc. Therefore, the inkjet recording method is not limited to personal use, and in recent years has been rapidly spreading as an inkjet printer for commercial use for signage, window films, posters, car wrapping, wallpaper, etc.

[0003] As an inkjet recording method, a method using solvent-free UV ink is known. However, although this method has excellent coating film strength and substrate versatility, it is environmentally unfriendly and unsafe, and the ink is highly viscous, resulting in a thick ink layer and poor surface smoothness of the printed film. In recent years, recording methods using UV-curable water-based ink have also been developed (e.g., Patent Documents 1 and 2).

[0004] UV-curable water-based inks are environmentally friendly and safe because they are water-based. However, when UV-curable water-based inks are applied to a recording medium, the curable components spread as the ink penetrates the recording medium. Even if the ink is irradiated with active energy rays in this state, the curable components solidify in a separate state without contacting each other. This results in poor coating strength, particularly washing fastness, of the resulting printed matter.

[0005] This problem is particularly noticeable in the case of absorbent recording media.

[0006] If the ink is heated when it is applied to prevent penetration, the inkjet head will heat up and the aqueous medium in the ink will evaporate, increasing the ink concentration. This will increase the ink viscosity, causing nozzle clogging and solidifying the ink at the nozzle ejection section, making stable inkjet ejection impossible.

[0007] JP 2022-067314 A JP 2011-218571 A

[0008] An object of the present invention is to provide an inkjet recording method and an inkjet recording apparatus that can obtain a printed coating film with high wash fastness by suppressing penetration of the ultraviolet-curable water-based ink into a recording medium while maintaining stable inkjet ejection in inkjet recording using the ultraviolet-curable water-based ink.

[0009] The present inventors have found that the above-mentioned problems can be solved by not heating the recording medium during the ink application step in which an ultraviolet-curable water-based ink is applied to the recording medium, but by heating the recording medium during the subsequent actinic energy ray irradiation step.

[0010] [1] An inkjet recording method comprising the following steps [a] and [b], in which the recording medium is not heated in the step [a], and the recording medium is heated by a heating means in the step [b], wherein the recording medium is an absorbent recording medium: step [a]: an ink application step of applying an inkjet ink containing at least a polymerizable compound, a polymerization initiator, and water to the recording medium; and step [b]: an irradiation step of irradiating the inkjet ink applied to the recording medium that has been subjected to at least the step [a] with active energy rays controlled by a means other than the heating means.

[0011] [2] An inkjet recording method comprising the following steps [a] and [b], in which the recording medium is not heated in the step [a], and the recording medium is heated by a heating means in the step [b], wherein the polymerizable compound in the step [a] exists as particles in the inkjet ink: step [a]: an ink application step of applying an inkjet ink containing at least a polymerizable compound, a polymerization initiator, and water to the recording medium; and step [b]: an irradiation step of irradiating the inkjet ink applied to the recording medium that has been subjected to at least the step [a] with active energy rays controlled by a means other than the heating means.

[0012] [3] The inkjet recording method according to [1] or [2], wherein the light source of the actinic energy rays is a light-emitting diode having an emission peak wavelength in the range of 350 to 420 nm.

[0013] [4] The inkjet recording method according to [1] or [3], wherein the absorbent recording medium is a fabric.

[0014] [5] The inkjet recording method according to [2] or [3], wherein the particles have an average particle size of 10 nm or more and 200 nm or less.

[0015] [6] The inkjet recording method according to any one of [1] to [5], wherein the polymerizable compound contains a (meth)acrylate compound.

[0016] [7] The inkjet recording method according to any one of [1] to [6], wherein the heating temperature of the recording medium in the step [b] is 30° C. or higher and 70° C. or lower.

[0017] [8] The inkjet recording method according to any one of [1] to [7], wherein a heating element is used as the heating means.

[0018] [9] The inkjet recording method according to any one of [1] to [8], wherein the heating of the recording medium in the irradiation step [b] is performed from the side opposite to the ink-applied side.

[0019]

[10] An inkjet recording apparatus used to record an image on an absorbent recording medium, comprising: an ink applying means [c] that applies an inkjet ink containing a polymerizable compound, a polymerization initiator, and water to the absorbent recording medium without heating the absorbent recording medium; an irradiation means [d] that irradiates the inkjet ink applied to the absorbent recording medium with active energy rays; and a heating means [e] that heats the absorbent recording medium during the irradiation of the active energy rays, wherein the irradiation means [d] and the heating means [e] are each independently controllable.

[0020]

[11] An inkjet recording apparatus used to record an image on a recording medium, comprising: an ink applying unit [c] that applies an inkjet ink containing a polymerizable compound, a polymerization initiator, and water to the recording medium without heating the recording medium; an irradiation unit [d] that irradiates the inkjet ink applied to the recording medium with active energy rays; and a heating unit [e] that heats the recording medium during the irradiation of the active energy rays, wherein the irradiation unit [d] and the heating unit [e] are each independently controllable; and the polymerizable compound exists as particles in the inkjet ink.

[0021]

[12] The inkjet recording apparatus according to

[10] or

[11] , wherein the light source of the actinic energy rays is a light-emitting diode having an emission peak wavelength in the range of 350 to 420 nm.

[0022]

[13] The inkjet recording apparatus according to

[10] , wherein the absorbent recording medium is a fabric.

[0023]

[14] The inkjet recording apparatus according to

[11] , wherein the particles have an average particle size of 10 nm or more and 200 nm or less.

[0024]

[15] The inkjet recording apparatus according to any one of

[10] to

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

[0025]

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

[10] to

[15] , wherein a heating element is used as the heating means [e].

[0026]

[17] The inkjet recording apparatus according to any one of

[10] to

[15] , wherein the heating means [e] is located on the absorbent recording medium or on the surface of the recording medium opposite to the ink application surface.

[0027] According to the inkjet recording method and inkjet recording apparatus of the present invention, in inkjet recording using an ultraviolet-curable water-based ink that is excellent in environmental friendliness and safety, it is possible to suppress the penetration of the ultraviolet-curable water-based ink into a recording medium while maintaining stable inkjet ejection, thereby obtaining a printed coating film with high washing fastness. Therefore, according to the present invention, high-quality printed images can be efficiently obtained by improving the ink ejection stability and coating film strength such as washing fastness in inkjet recording.

[0028] An embodiment of the present invention will be described below, but the present invention is not limited to this embodiment.

[0029] In the present invention, when expressed as "X to Y" (X and Y are arbitrary numbers), unless otherwise specified, it includes the intention of "X or more and Y or less", as well as the intention of "preferably larger than X" and "preferably smaller than Y".

[0030] In the present invention, when it is expressed as "X or more" (X is any number) or "Y or less" (Y is any number), it also includes the intention that "it is preferably larger than X" or "it is preferably less than Y".

[0031] Inkjet Recording Method An inkjet recording method according to one embodiment of the present invention (hereinafter sometimes referred to as "inkjet recording method 1") comprises the following steps [a] and [b], in which the recording medium is not heated in step [a], and the recording medium is heated by a heating means in step [b], and is characterized in that the recording medium is an absorbent recording medium. Step [a]: an ink application step (hereinafter sometimes referred to as "ink application step [a]") of applying 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 a recording medium. Step [b]: an irradiation step (hereinafter sometimes referred to as "irradiation step [b]") of irradiating the inkjet ink applied to the recording medium that has been subjected to at least step [a] with active energy rays controlled by a means separate from the heating means.

[0032] An inkjet recording method according to another embodiment of the present invention (hereinafter, sometimes referred to as "inkjet recording method 2") comprises the following steps [a] and [b], in which the recording medium is not heated in the step [a], and the recording medium is heated by a heating means in the step [b], and is characterized in that the polymerizable compound in the step [a] is present as particles in the inkjet ink. Step [a]: an ink application step of applying an inkjet ink containing at least a polymerizable compound, a polymerization initiator, and water, i.e., the inkjet ink of the present invention, to a recording medium, i.e., ink application step [a]. Step [b]: an irradiation step of irradiating the inkjet ink applied to the recording medium that has been subjected to at least step [a] with active energy rays controlled by a means separate from the heating means, i.e., irradiation step [b].

[0033] Inkjet recording method 1 and inkjet recording method 2 of the present invention (hereinafter, these may be collectively referred to as "inkjet recording methods of the present invention") may further include other steps as necessary. For example, they may include a step of heating the recording medium after the irradiation step [b] (hereinafter, this may be referred to as an "after-heating step"). Furthermore, they may also include a pretreatment agent application step of applying a pretreatment agent to the recording medium before the ink application step [a].

[0034] [Mechanism] In the inkjet recording method of the present invention, the recording medium is not heated in the ink application step [a], but is heated by a heating means in the irradiation step [b]. Heating the recording medium evaporates the aqueous medium in the ink applied to the recording medium. By heating in the irradiation step [b], the aqueous medium does not completely evaporate to the point where only solids remain, but some of the aqueous medium evaporates, increasing the ink concentration. As a result, the viscosity of the ink increases. By increasing the viscosity of the ink on the recording medium, even if the recording medium is an absorbent recording medium, penetration of the ink into the recording medium is suppressed, and when irradiated with actinic energy rays, ink penetration can be limited to near the surface of the recording medium. This allows the curing components in the ink to cure in a cohesive state, improving the washfastness of the printed coating film.

[0035] In particular, when the recording medium is an absorbent recording medium, the ink hardens while wrapping around the fibers of the absorbent recording medium. This further improves washing fastness (Inkjet Recording Method 1). Furthermore, if the polymerizable compound exists as particles in the inkjet ink, even if the recording medium is an absorbent recording medium, the ink does not penetrate too far into the recording medium and tends to remain near the surface. As a result, it is possible to suppress a decrease in image density and form a coating film with excellent washing fastness (Inkjet Recording Method 2).

[0036] If heating is performed between the ink application step [a] and the actinic energy ray irradiation step [b] in order to evaporate the aqueous medium in the ink, but not during the irradiation step [b], space for each of the three steps is required on the apparatus, which is undesirable as it increases the size of the apparatus. Furthermore, if heating is performed continuously from the ink application step [a] to the actinic energy ray irradiation step [b], the ejection head is heated, as described above, and inkjet ejection stability is impaired.

[0037] In contrast, in the present invention, heating is not performed in the ink application step [a], but is performed in the irradiation step [b], thereby solving the above-mentioned problems. In the present invention, it is sufficient that heating is performed in the irradiation step [b], but not in the ink application step [a], and heating periods may exist before or after the irradiation step [b].

[0038] [Ink Application Step [a]] In the ink application step [a] of the inkjet recording method of the present invention, the inkjet ink of the present invention contained in the ink set is applied onto a recording medium from, for example, an inkjet head of an inkjet printer. 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. The inkjet method employed in the present invention is a preferred method from the viewpoints of compactness of the recording apparatus and high-speed recording. In other words, an inkjet printer is preferred as the ink application means [c] in the inkjet recording apparatus of the present invention described below. The preferred embodiments of the inkjet method below correspond to preferred embodiments of the ink application means [c] in the inkjet recording apparatus of the present invention.

[0039] In image formation by the inkjet method, inkjet ink is ejected onto a recording medium by applying energy, thereby forming a colored image.

[0040] The inkjet method is not particularly limited, and may be any of 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, or an acoustic inkjet method that converts an electrical signal into an acoustic beam and irradiates it onto the ink, thereby ejecting the ink using radiation pressure.

[0041] The inkjet head used in the inkjet system may be of an on-demand system or a continuous system. Furthermore, there are no particular limitations on the ink nozzles used when recording by the inkjet system, and they can be appropriately selected depending on the purpose.

[0042] The inkjet method according to the present invention includes a method of ejecting a large number of low-density inks called photo inks in a small volume, a method of improving image quality by using multiple inks of substantially the same hue but different densities, and a method of using colorless, transparent ink.

[0043] Inkjet printing methods include a shuttle method, which uses a short serial head and performs printing by scanning the head in the width direction of the recording medium, and a line method, which uses a line head in which printing elements are arranged to cover the entire area of ​​one side of the recording medium. The line method allows image printing over the entire surface of the recording medium by scanning the recording medium in a direction perpendicular to the direction of the printing element arrangement, eliminating the need for a carriage or other transport system for scanning the short head. Furthermore, the line method eliminates the need for complex scanning control of the carriage movement and the recording medium, and only the recording medium moves, allowing for faster printing speeds than the shuttle method.

[0044] [Irradiation Step [b]] The irradiation step [b] in the inkjet recording method of the present invention is a step carried out after the ink application step [a] described above. The irradiation step [b] is a step of irradiating the recording medium to which the inkjet ink has been applied with active energy rays. In the present invention, the recording medium is heated in this irradiation step [b]. Suitable active energy ray sources and the like for this irradiation step [b] correspond to suitable embodiments of the irradiation means [d] of the inkjet recording apparatus of the present invention described below.

[0045] In the irradiation step [b], the polymerizable compound contained in the inkjet ink of the present invention is polymerized by the action of the polymerization initiator by irradiating with active energy rays, thereby forming a cured film of the inkjet ink. Furthermore, by carrying out heating in this irradiation step [b], as described above, penetration of the ink into the recording medium is suppressed, and the washing fastness of the formed printed image is effectively improved.

[0046] As described above, the inkjet ink of the present invention undergoes a curing reaction when irradiated with actinic energy rays. This reaction is a reaction in which the polymerization initiator contained in the inkjet ink of the present invention decomposes upon irradiation with actinic energy rays to generate radicals, which then initiate and accelerate the polymerization reaction of the polymerizable compound, thereby curing the inkjet ink.

[0047] When the recording medium is treated in advance with a pretreatment agent containing an acidic compound, the inkjet ink is further aggregated (fixed) by the acid supplied from the acidic compound during irradiation with active energy rays, and the image quality (abrasion resistance, blocking resistance, etc.) is improved.

[0048] Examples of usable actinic energy rays include α-rays, γ-rays, electron beams, X-rays, ultraviolet rays, visible light, and infrared light. As described below, the polymerization initiator preferably used in the inkjet ink of the present invention has high absorption, particularly for light in the ultraviolet region. From this perspective, the emission peak wavelength of the actinic energy ray source to be irradiated 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. There may be one or more emission peak wavelengths within the above wavelength range.

[0049] The irradiation energy of the active energy rays is 0.1 J / cm ２ or more, for example, 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 proceed smoothly, and a more excellent effect of improving the coating strength can be obtained.

[0050] Mercury lamps and gas / solid-state lasers are mainly used as sources of actinic radiation. Mercury lamps, halogen lamps, and metal halide lamps are widely known as light sources used to cure UV-curable water-based inks. However, there is currently a strong demand for mercury-free lamps from the perspective of environmental protection. For this reason, replacement with GaN-based semiconductor UV-light-emitting devices would be extremely useful from both an industrial and environmental perspective.

[0051] In this situation, LEDs and laser diodes (LDs) are small, have a long life, are highly efficient, and are low cost, and are expected to serve as sources of actinic energy rays, particularly as light sources for photocurable inkjet printers. Furthermore, LEDs and laser diodes (LDs) are preferred in that they have a longer lamp life and their illuminance changes relatively slowly over time compared to heat-generating lamps such as mercury lamps, halogen lamps, and metal halide lamps, making them more likely to provide stable printing quality.

[0052] For these reasons, in the present invention, it is preferable to use LEDs and LDs as the active energy ray source. In particular, UV-LEDs and UV-LDs can be used as the ultraviolet light source. For example, Nichia Corporation has marketed a purple LED whose main emission spectrum has wavelengths between 365 nm and 420 nm.

[0053] In the present invention, a particularly preferred active energy ray source is a UV-LED, and a particularly preferred UV-LED is one having an emission peak wavelength in the range of 350 to 420 nm. That is, in the present invention, from the viewpoints of cost and curability, it is preferred to use a light-emitting diode having an emission peak wavelength in the range of 350 to 420 nm.

[0054] In the present invention, the active energy ray source is controlled by a control means separate from the heating means, for reasons that will be described later.

[0055] As described above, in the irradiation step [b], the recording medium is heated by a heating means. This heating means corresponds to the heating means (e) in the inkjet recording apparatus of the present invention, which will be described later. Here, "heating" means applying heat to the recording medium by the heating means. More specifically, for example, when a heating element such as a hot plate is used as the heating means, the heating means is a heating element having a power density of 0.05 W / cm. ２ This means applying heat to the recording medium using the above-mentioned heating element. The heating means does not include the aforementioned active energy ray sources. That is, although active energy ray sources include those that generate heat, such as mercury lamps, they do not fall under the category of the heating means. The reason for this is as follows.

[0056] When an active energy ray source that generates heat is used as the heating means, such a heating means typically does not have a mechanism for adjusting the heating conditions of the active energy ray source, making it difficult to precisely control the amount of heat applied to the recording medium, which may result in a decrease in the quality stability of the resulting ink coating. Furthermore, when an active energy ray source that generates heat is used as the heating means, the amount of heat generated depends on the irradiation conditions of the active energy ray, so the amount of heat applied to the recording medium under specified irradiation conditions of the active energy ray may be either too much or too little. For example, insufficient heating results in insufficient evaporation of the aqueous medium in the ink. Conversely, excessive heating not only results in significant energy loss and poor productivity, but also may cause thermal degradation of the recording medium, such as deformation and discoloration. Furthermore, curing and drying of the outermost surface of the ink coating may prevent evaporation of the aqueous medium deeper in the coating, which may result in insufficient drying or curing. In particular, when the recording medium is an absorbent recording medium, insufficient drying or curing may easily cause bleeding, so temperature control, along with irradiance control, is particularly important in the irradiation step [b]. Therefore, it is necessary to control the active energy ray irradiation conditions and the heating conditions separately.

[0057] In the irradiation step [b], the heating temperature of the recording medium by the heating means, which is performed in conjunction with the irradiation of the active energy rays, may be a temperature at which the aqueous medium contained in the inkjet ink of the present invention can smoothly evaporate. While not particularly limited, the temperature is preferably 30°C or higher, more preferably 35°C or higher, even more preferably 40°C or higher, and particularly preferably 60°C or higher. On the other hand, the heating temperature is preferably 120°C or lower, more preferably 100°C or lower, even more preferably 80°C or lower, and particularly preferably 70°C or lower. A heating temperature above the lower limit can efficiently evaporate and remove volatile components such as water in the ink, which tends to further enhance curability. A heating temperature below the upper limit can prevent thermal deterioration of the recording medium and prevent a shortened lifespan due to a rise in temperature of the active energy source. Furthermore, if the heating temperature is too high, the temperature will rise not only in the recording medium but also in the vicinity of the ejection head, potentially resulting in impaired ejection stability. A heating temperature below the upper limit can suppress ejection defects due to a rise in temperature of the ejection head. In response to the recent trend toward smaller and lighter equipment, more compact recording devices are also desired. In this case, the distance between the ink applying means and the active energy ray irradiating means becomes shorter. As a result, the ink applying means becomes more susceptible to the temperature caused by heating. Therefore, as described above, the effect of suppressing ejection defects by controlling the heating temperature becomes more pronounced. Here, the heating temperature refers to the surface temperature of the recording surface of the recording medium. When a heating element such as a hot plate is used as the heating means, the temperature of the heating element can be considered to be the surface temperature.

[0058] From the viewpoint of obtaining a high-resolution printed image, the recording medium is preferably heated from the edge direction of the recording medium irradiated with active energy rays or from the side opposite to the ink-applied surface, and more preferably from the side opposite to the ink-applied surface. The recording medium may be heated from a combination of heating means from multiple directions.

[0059] The heating means, i.e., the heating means [e] described below, is not particularly limited and may be either hot air heating or radiant heating. It is preferable to use a hot air heating means such as a hot air heater because of its excellent drying efficiency. On the other hand, radiant heating is preferable because there is no risk of drying the ink nozzle discharge portion with hot air, and because the printed image before fixing is not directly exposed to hot air, making it easier to obtain a high-resolution printed image. Examples of radiant heating means that can be used include heating elements such as hot plates and infrared heaters. More specific examples include ceramic heaters, halogen heaters, and quartz tube heaters. Of these, it is preferable to use a heating element such as a hot plate for heating because it allows for precise temperature setting and has little temperature unevenness.

[0060] When heating using a heating element such as a hot plate, heating may be performed by directly contacting the heating element with the recording medium, or by placing a heat conductor such as a metal plate between the heating element and the recording medium.

[0061] The heating may be performed simultaneously with the irradiation of active energy rays, or heating may be performed for 20 seconds or less before or after the irradiation of active energy rays. Furthermore, as described above, an after-heating step may be further performed. When the after-heating step is performed, the heating temperature, heating means, and heating method may be the same as those used in the irradiation step [b].

[0062] [Recording Medium] Recording media include absorbent recording media and non-absorbent recording media. As mentioned above, the problem of decreased washing fastness due to ink penetration is prominent in absorbent recording media, so the inkjet recording method of the present invention is particularly effective when an absorbent recording medium is used as the recording medium.

[0063] The term "absorbent recording medium" refers to a recording medium having a surface that is highly absorbent of ink. More quantitatively, the absorbent surface is a recording medium having a high ink absorption rate within 30 msec from the start of contact in the Bristow method. １／２ Water absorption up to 0.3g / m ２ On the other hand, a recording medium having a water absorption capacity of 0.3 g / m or more is called an absorbent recording medium. ２The smaller recording medium is a non-absorbent recording medium.

[0064] Examples of the absorbent recording medium include paper, fabric, nonwoven fabric, leather, wood, and composite materials thereof. Among the absorbent recording media, fabric is preferably used because it can provide a significant effect of heating during irradiation with active energy rays according to the present invention.

[0065] The material constituting the fabric is 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, and blends of these fibers are also possible. Of these, cotton and polyester are preferred, and cotton is more preferred.

[0066] On the other hand, examples of non-absorbent recording media include plastic materials such as polyesters such as polyethylene terephthalate (PET), polyolefins such as polyvinyl chloride (PVC), polyethylene (PE), and polypropylene (PP), glass, ceramics, metals, and composites of these.

[0067] [Inkjet Ink] The inkjet ink of the present invention contains at least a polymerizable compound, a polymerization initiator, and water. That is, in the inkjet recording method of the present invention, an ultraviolet-curable water-based ink can be used.

[0068] [Polymerizable Compound] The polymerizable compound contained in the inkjet ink of the present invention is not particularly limited as long as it is a compound having polymerizability, and known polymerizable monomers, polymerizable resins, polymerizable oligomers, etc. Among these, polymerizable oligomers are preferred, and ultraviolet-curable oligomers are more preferred.

[0069] Specific examples of the polymerizable compound include (meth)acrylamide compounds, (meth)acrylate compounds, vinyl compounds, maleimide compounds, vinyl sulfone compounds, N-vinylamide compounds, and derivatives thereof. These polymerizable compounds are more preferably bifunctional or higher. The polymerizable compound is further preferably a (meth)acrylamide compound, a (meth)acrylate compound, or a vinyl compound, and particularly preferably a bifunctional or higher functional (meth)acrylamide compound or a (meth)acrylate compound.

[0070] In the present invention, "(meth)acrylate" means acrylate or methacrylate. The same applies to "(meth)acryloyl" and "(meth)acrylic".

[0071] These polymerizable compounds may be used alone or in combination of two or more. When two or more types are used in combination, it is preferable to use a mixture of two or more types selected from (meth)acrylamide compounds, (meth)acrylate compounds, vinyl compounds, maleimide compounds, vinyl sulfone compounds, and N-vinylamide compounds, and it is more preferable that at least one of them is a (meth)acrylamide compound or a (meth)acrylate compound.

[0072] From the viewpoint of improving water solubility, the polymerizable compound may have a hydrophilic functional group such as a (poly)ethyleneoxy chain, a (poly)propyleneoxy chain, an ionic group (e.g., a carboxyl group, a sulfo group), or a hydroxyl group in the molecule. When the polymerizable compound contains a hydrophilic functional group, dispersibility in an aqueous medium can be improved. Here, "(poly)ethyleneoxy chain" means an ethyleneoxy chain or a polyethyleneoxy chain. The same applies to "(poly)propyleneoxy chain".

[0073] 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, with polyfunctional (meth)acrylate compounds being preferred.

[0074] The ultraviolet-curable oligomer is not particularly limited as to whether it is ionic or not, and may be nonionic or ionic (anionic, cationic, or amphoteric). Here, "nonionic" means, for example, that the hydrophilic group of the ultraviolet-curable oligomer is composed of an ether bond or a hydroxyl group that does not ionically dissociate in water. "Ionic" (anionic, cationic, or amphoteric) means, for example, that the ultraviolet-curable oligomer has a carboxyl group or an amino group that can ionically dissociate in water.

[0075] As the ultraviolet-curable oligomer, for example, any one of the following <1> to <3> is preferable.

[0076] <1> Having a structural unit derived from a compound represented by the following formula (1):

[0077]

[0078] (In formula (1), X is an alkylene group; Y is a (meth)acryloyl group, an allyl group, an acyl group, or a hydrogen atom; and n is an integer of 2 or greater.)

[0079] <2> A compound having a structural unit derived from a polyisocyanate compound (A), wherein the compound (A) has three or more isocyanate groups in one molecule.

[0080] <3> A compound having a structural unit derived from the polyisocyanate compound (A), a structural unit derived from the compound (B') shown below, and a structural unit derived from the compound (C') shown below.

[0081] The ultraviolet-curable oligomer as in the above item <3> is usually produced by reacting a polyisocyanate compound (A), a compound (B') and a compound (C').

[0082] Compound (B'): A compound containing two or more polymerizable unsaturated bonds and capable of bonding with the polyisocyanate compound (A). Compound (C'): A water-soluble compound capable of bonding with the polyisocyanate compound (A).

[0083] The ultraviolet-curable oligomer preferably contains a structural unit derived from a (meth)acrylate, particularly a structural unit derived from a polyfunctional (meth)acrylate. Furthermore, the ultraviolet-curable oligomer preferably contains a structural unit derived from a polyfunctional (meth)acrylate and a structural unit derived from a polyalkylene glycol. That is, from the viewpoint of reactivity, the ultraviolet-curable oligomer is preferably such that the compound (B') is a hydroxyl group-containing polyfunctional (meth)acrylate (B). Furthermore, from the viewpoint of water dispersibility, the compound (C') is preferably a polyalkylene glycol (C). Such an ultraviolet-curable oligomer is usually produced by reacting a polyisocyanate compound (A), a hydroxyl group-containing polyfunctional (meth)acrylate (B), and a polyalkylene glycol (C).

[0084] In the present invention, the term "structural unit derived from X" refers to a structural unit that is incorporated into the molecular structure of an ultraviolet-curable oligomer by using compound X as a raw material and reacting compound X with another compound. The "structural unit derived from X" is not necessarily limited to using compound X as a raw material. In other words, even if the structural unit is formed from a raw material other than X, it is considered to be an "structural unit derived from X" as long as the chemical structure is the same.

[0085] As described above, a preferred embodiment of the compound (B') is a hydroxyl group-containing polyfunctional (meth)acrylate (B), but a preferred embodiment of the compound (B') may also be "a compound (B") containing a hydroxyl group and two or more polymerizable unsaturated bonds." 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 carboxy group, an amino group, or the like. Examples of the polymerizable unsaturated bond include a carbon-carbon double bond and a carbon-carbon triple bond, and among these, a carbon-carbon double bond is preferred. More specific examples of the polymerizable unsaturated bond include carbon-carbon double bonds derived from a vinyl group, a (meth)acryloyl group, or the like.

[0086] The water-soluble compound in compound (C') includes a water-soluble polymer. Specific examples of the water-soluble compound in compound (C') include polyglycerin, polyhydroxy(meth)acrylate, polyamine, quaternary aminated polystyrene, sulfonated polystyrene, polyether, polyalkylene glycol, etc. Among these, nonionic water-soluble compounds such as polyglycerin, polyhydroxy(meth)acrylate, and polyalkylene glycol are preferred, with polyalkylene glycol being particularly preferred. Each of these water-soluble compounds may be a copolymer. Compound (C') has the structure of such a water-soluble compound and the structure of a "compound capable of bonding to polyisocyanate compound (A)." Here, the structure of the "compound capable of bonding to polyisocyanate compound (A)" can be selected from structures similar to those exemplified for compound (B') above.

[0087] The structural unit derived from the polyisocyanate compound (A) forms a urethane bond by bonding with the structural unit derived from the hydroxyl group-containing polyfunctional (meth)acrylate (B) and the structural unit derived from the polyalkylene glycol (C). This urethane bond may be substituted with a urea bond or an amide bond.

[0088] In the present invention, when the hydroxyl group-containing polyfunctional (meth)acrylate (B) is converted into the above-mentioned compound (B') or compound (B"), or when the polyalkylene glycol (C) is converted into the above-mentioned compound (C'), the preferred embodiments or specific embodiments in such cases can be similarly applied to the embodiments or specific embodiments that are preferred in the case of using the hydroxyl group-containing polyfunctional (meth)acrylate (B) or polyalkylene glycol (C) described below.

[0089] Each compound constituting the ultraviolet-curable oligomer represented by <1>, <2>, and <3> above will be described below. In the present invention, the term "oligomer" is not limited to a specific molecular weight range, etc., and it is sufficient if it has the structure shown below. The inkjet ink of the present invention may contain only one type of ultraviolet-curable oligomer, or may contain two or more types.

[0090] <Polyisocyanate Compound (A)> The polyisocyanate compound (A) is a compound having a total of two or more isocyanate groups in one molecule.

[0091] The type of polyisocyanate compound (A) is not particularly limited, and examples thereof include chain aliphatic polyisocyanates, aromatic polyisocyanates, alicyclic polyisocyanates, etc. Among these, it is preferable that the polyisocyanate compound (A) contains a polyisocyanate trimer compound from the viewpoints of weather resistance and hardness.

[0092] The ultraviolet-curable oligomer may contain only one of these polyisocyanate compounds (A) or two or more of them in combination. In addition, as the polyisocyanate compound (A), a polyisocyanate having two or more structures selected from a chain aliphatic structure, an aromatic structure, and an alicyclic structure may also be used.

[0093] From the viewpoint of adhesion to a substrate in particular, the polyisocyanate compound (A) preferably has 3 or more isocyanate groups, and more preferably has 6 or less isocyanate groups. As the polyisocyanate compound (A), a trimer obtained by trimerization of hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, phenylene diisocyanate, or the like is preferred, and a trimer of hexamethylene diisocyanate is particularly preferred.

[0094] <Compound containing a polymerizable unsaturated bond> In the compound containing a polymerizable unsaturated bond, the number of polymerizable unsaturated bonds is preferably 1 or more, more preferably 2 or more, and even more preferably 4 or more, and is preferably 8 or less, more preferably 6 or less. The compound containing a polymerizable unsaturated bond is preferably a compound that can bond to the polyisocyanate compound (A).

[0095] (Compound (B')) The compound (B') is a compound containing two or more polymerizable unsaturated bonds and capable of bonding to the polyisocyanate compound (A). Examples of the compound (B') include compounds having a hydroxyl group, an amino group, or a carboxy group. Examples of the compound (B') include polyfunctional vinyl monomers, polyfunctional allyl monomers, and polyfunctional (meth)acrylates. Among these, the hydroxyl group-containing polyfunctional (meth)acrylate (B) is preferred as the compound (B').

[0096] <Hydroxyl Group-Containing Polyfunctional (Meth)acrylate (B)> The hydroxyl group-containing polyfunctional (meth)acrylate (B) has one or more hydroxyl groups and two or more (meth)acryloyl groups. Specific examples of the hydroxyl group-containing polyfunctional (meth)acrylate (B) include (meth)acrylic acid partial esters of polyhydric alcohols. The hydroxyl group-containing polyfunctional (meth)acrylate forms a good crosslinked structure due to the involvement of multiple (meth)acryloyl groups in the curing reaction, and can improve physical properties such as contamination resistance and abrasion resistance.

[0097] The number of hydroxyl groups in the hydroxyl group-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 group-containing polyfunctional (meth)acrylate (B) is preferably 8 or less, and more preferably 6 or less.

[0098] In producing the ultraviolet-curable oligomer, these hydroxyl group-containing polyfunctional (meth)acrylates (B) may be used alone or in combination of two or more.

[0099] As the hydroxyl group-containing polyfunctional (meth)acrylate (B), particularly from the viewpoint of the coating film strength of the obtained cured film, those having one hydroxyl group and 3 to 5 (meth)acryloyl groups, such as dipentaerythritol penta(meth)acrylate and pentaerythritol tri(meth)acrylate, are preferred. Dipentaerythritol penta(meth)acrylate is particularly preferred as the hydroxyl group-containing polyfunctional (meth)acrylate (B) because it forms a good crosslinked structure and increases the mechanical strength of the cured film.

[0100] <Water-soluble compound> (Compound (C')) The compound (C') is a water-soluble compound that can bond with the polyisocyanate compound (A). The compound (C') is preferably a compound containing one terminal hydroxyl group, as this provides good water dispersibility.

[0101] As mentioned above, the compound (C') may be a water-soluble polymer, and among these, polyalkylene glycol (C) is particularly preferred.

[0102] The polyalkylene glycol (C) is not limited, but preferably has a mono-substituted structure. That is, it is preferable that one of the hydroxyl groups of the glycol is substituted. The substituted structure is preferably a structure that does not bond with isocyanate. The polyalkylene glycol (C) may be a mixture of a compound having a mono-substituted structure and a compound having a non-mono-substituted structure.

[0103] The mono-substituted structure is not limited, but from the viewpoint of making the ultraviolet-curable oligomer nonionic, polyalkylene glycol mono-substituted ether is preferred, polyethylene glycol mono-substituted ether, polytrimethylene glycol mono-substituted ether or polypropylene glycol mono-substituted ether is more preferred, and polyethylene glycol mono-substituted ether is even more preferred.

[0104] Among the polyalkylene glycol mono-substituted ethers, polyalkylene glycol mono-substituted ethers that do not contain an ionic substituent in the ether moiety are more preferred. As the polyalkylene glycol mono-substituted ether, for example, one represented by the following formula (1) is more preferred.

[0105]

[0106] (In formula (1), X is an alkylene group; Y is an alkyl group, a (meth)acryloyl group, an allyl group, an acyl group, or a hydrogen atom; and n is an integer of 2 or more.)

[0107] In formula (1), X 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 high-temperature storage stability, X in formula (1) is even more preferably an ethylene group. From the viewpoint of coating film strength, Y is preferably a (meth)acryloyl group, an allyl group, or an acyl group, more preferably an allyl group.

[0108] In formula (1), n ​​is usually 2 or more, preferably 5 or more, more preferably 6 or more, from the viewpoint of the coating film strength of the obtained cured film, and is usually 500 or less, preferably 100 or less, more preferably 50 or less.

[0109] In producing the ultraviolet-curable oligomer, only one of these polyalkylene glycols (C) may be used, or two or more of them 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)).

[0110] <Average particle size> In the inkjet ink of the present invention, the polymerizable compound is preferably present as particles. If the polymerizable compound is present as particles in the inkjet ink, the ink does not penetrate too much into the recording medium and tends to remain near the surface, even if the recording medium is an absorbent recording medium. As a result, a decrease in image density can be suppressed and a coating film with excellent washing fastness can be formed.

[0111] In particular, the polymerizable compound is preferably present in the inkjet ink as particles having an average particle size of 10 nm or more and 200 nm or less, and more preferably present as particles having an average particle size of 20 nm or more and 150 nm or less.

[0112] When the average particle size of the polymerizable compound is within the above range, the dispersion stability is good. The average particle size of the polymerizable compound is, for example, the volume average particle size (D ５０ )

[0113] In the examples described later, the average particle size of the polymerizable compound particles in the aqueous dispersion of the polymerizable compound is measured, and the average particle size of the polymerizable compound particles in this aqueous dispersion is almost the same as the average particle size of the polymerizable compound particles in the ink.

[0114] In the present invention, as long as the polymerizable compound exists as particles, it is included in the above-mentioned state of "existing as particles" even if there is aggregation or other substances are contained within the particles.

[0115] The average particle size of the polymerizable compound means the particle size (primary particle size) of the polymerizable compound particles.

[0116] From the viewpoint of enhancing the water resistance of the cured product, the inkjet ink of the present invention preferably contains a water-insoluble polymerizable compound. Here, "water-insoluble" means that the solubility of the polymerizable compound in water at 25°C is less than 0.01 g / mL. The solubility in water can be adjusted by the type and content of hydrophilic functional groups possessed by the polymerizable compound.

[0117] A water-insoluble polymerizable compound can exist as particles in an aqueous medium. However, aqueous inks containing polymerizable compound particles are prone to nozzle clogging and may degrade the ink ejection stability. This is because the polymerizable compound is merely dispersed in the aqueous medium, not dissolved, and therefore is prone to precipitation at the nozzle of the inkjet head. Furthermore, once solidified at the nozzle ejection section, it is difficult to wash away with water. For this reason, when the polymerizable compound exists as particles in an inkjet ink, it is particularly important to suppress evaporation of the aqueous medium in the ink application step [a], thereby enabling the effects of the present invention to be more effectively achieved.

[0118] Components other than the polymerizable compound contained in the inkjet ink of the present invention will be described below.

[0119] [Colorant] The inkjet ink used in the inkjet recording method of the present invention may contain a colorant.

[0120]

[0043] As the colorant used in the inkjet ink, various dyes or pigments known as colorants used in inks can be used. From the viewpoints of irradiation with actinic energy rays and long-term storage durability of printed images, the inkjet ink of the present invention preferably contains a pigment as the colorant.

[0121] <Dye> Dyes that can be used in the present invention are not particularly limited, and examples thereof include water-soluble dyes such as acid dyes, direct dyes, and reactive dyes, disperse dyes, etc. Among these, anionic dyes are preferred.

[0122] (Water-Soluble Dyes) Examples of water-soluble dyes include azo dyes, methine dyes, azomethine dyes, xanthene dyes, quinone dyes, phthalocyanine dyes, triphenylmethane dyes, and diphenylmethane dyes.

[0123] <Pigment> Conventional organic and inorganic pigments can be used as the pigment. Examples include azo pigments such as azo lakes, insoluble azo pigments, condensed azo pigments, and chelate azo pigments; polycyclic pigments such as phthalocyanine pigments, perylene and perylene pigments, anthraquinone pigments, quinacridone pigments, dioxane pigments, thioindigo pigments, isoindolinone pigments, and quinophthaloni 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. Anionic pigments are preferred as the pigment.

[0124] These dyes and pigments may be used alone or in combination of two or more.

[0125] [Aqueous Medium] The inkjet ink of the present invention is an aqueous ink. "Aqueous ink" means an ink containing an aqueous medium. The aqueous medium is water and / or a water-soluble organic solvent. The aqueous medium used in the present invention is preferably water or a mixture of water and a water-soluble organic solvent.

[0126] Water-soluble organic solvents include those that function as moisturizing solvents to increase the moisture retention and wettability of the ink, and those that are used as aqueous media to adjust the viscosity of the ink and improve its handling and ejection properties. The two are not clearly distinguished, and water-soluble organic solvents used as moisturizing solvents also function as aqueous media.

[0127] In the present invention, the term "water-soluble organic solvent" refers to a compound that is soluble in water. The solubility of the water-soluble organic solvent in water is not limited, but a compound that can dissolve in water at any ratio is preferred. Furthermore, even if a compound is difficult to exhibit the properties of a solvent by itself (for example, a compound that is solid or has high viscosity at room temperature), the compound is included in the water-soluble organic solvent as long as it can be used as a solvent by being uniformly mixed with water.

[0128] Examples of the water-soluble organic solvent include polyhydric alcohols; ethers such as polyhydric alcohol alkyl ethers and polyhydric alcohol aryl ethers; nitrogen-containing heterocyclic compounds; amides; amines; and sulfur-containing compounds.

[0129] Specific examples of the water-soluble organic solvent include ethylene glycol, diethylene glycol, 1,2-propanediol (propylene glycol), 1,3-propanediol, 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, and 1,6-pentanediol. Polyhydric alcohols such as hexanediol, 1,2-hexanediol, 1,6-hexanediol, 1,3-hexanediol, 2,5-hexanediol, 1,5-hexanediol, glycerin, 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 petriol; ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether polyhydric alcohol alkyl ethers such as ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, and the like; polyhydric alcohol aryl ethers such as ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, and the like; 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; amides such as formamide, N-methylformamide, N,N-dimethylformamide, 3-methoxy-N,N-dimethylpropionamide, and 3-butoxy-N,N-dimethylpropionamide; amines such as monoethanolamine, diethanolamine, and triethylamine; sulfur-containing compounds such as dimethyl sulfoxide, sulfolane, and thiodiethanol; propylene carbonate, ethylene carbonate, and the like.

[0130] Among these, propylene glycol and diethylene glycol ethyl methyl ether are preferred.

[0131] As the water-soluble organic solvent, it is preferable to use an organic solvent having a boiling point of 250° C. or less, since this not only functions as a moisturizing solvent but also provides good drying properties.

[0132] As the water-soluble organic solvent, polyol compounds having 8 or more carbon atoms and glycol ether compounds are also preferably used.

[0133] Specific examples of polyol compounds having 8 or more carbon atoms include 2-ethyl-1,3-hexanediol and 2,2,4-trimethyl-1,3-pentanediol.

[0134] Specific examples of glycol ether compounds include polyhydric alcohol 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 polyhydric alcohol aryl ethers such as ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether.

[0135] These water-soluble organic solvents may be used alone or in combination of two or more.

[0136] [Polymerization initiator] The inkjet ink of the present invention contains a polymerization initiator. The polymerization initiator is a photoradical polymerization initiator that generates radicals, which are active species, by the energy of light (ultraviolet rays) received when irradiated with active energy rays, and initiates photopolymerization of the polymerizable compound. This causes the ink present on the surface of the recording medium to cure, thereby forming an image.

[0137] The polymerization initiator may be contained in the ink in a state where it is not encapsulated in the polymerizable compound, or in a state where it is encapsulated in particles of the polymerizable compound, or may be contained in both of these states.

[0138] The polymerization initiator may be a fat-soluble polymerization initiator (hereinafter may be referred to as a "fat-soluble initiator") or a water-soluble polymerization initiator (hereinafter may be referred to as a "water-soluble initiator"). Here, the term "fat-soluble initiator" refers to a polymerization initiator that is compatible with a polymerizable compound such as an ultraviolet-curable oligomer or that is soluble in an organic solvent. The term "water-soluble initiator" refers to an initiator that is soluble in water at a concentration of 1% by mass or more. The same applies to the "fat-soluble sensitizer" and "water-soluble sensitizer" described below.

[0139] The polymerization initiator used in the present invention is not limited to the following, but examples thereof include aromatic ketones, acylphosphine oxide compounds, aromatic onium salt compounds, organic peroxides, thio compounds (thioxanthone compounds, thiophenyl group-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.

[0140] Among these, the polymerization initiator preferably contains at least one of an acylphosphine oxide compound and a thioxanthone compound. Use of such a polymerization initiator tends to improve the curability of the ink.

[0141] 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'-bisdiethylaminobenzophenone, Michler's ketone, benzil, 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-diphenylethan-1-one, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-1-{4-[4-(2-hydroxy-2-methylpropionyl)benzyl]phenyl}2-methylpropan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone-1,2-dione, Methylamino-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-morpholinopropan-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-methylpropan-1-one, methylbenzofilformate, azobisisobutyronitrile, benzoyl peroxide, and di-tert-butyl peroxide.

[0142] Examples of the water-soluble polymerization initiator include, but are not limited to, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one, sodium phenyl(2,4,6-trimethylbenzoyl)phosphinate, and 2-(3-dimethylamino-2-hydroxypropoxy)-3,4-dimethyl-9H-thioxanthone-9-one methochloride.

[0143] 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 Ltd.

[0144] 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, the fat-soluble initiator may be encapsulated in particles of a polymerizable compound such as an ultraviolet-curable oligomer, and the water-soluble initiator may be dissolved in an aqueous medium.

[0145] As the polymerization initiator, in addition to the above-mentioned photoradical polymerization initiator, a thermal radical polymerization initiator may be used in combination.

[0146] [Surfactant] The inkjet ink of the present invention preferably contains a surfactant in order to improve the flatness of the coating film formed and the wettability with the substrate.

[0147] As the surfactant, any of silicone surfactants, fluorine surfactants, amphoteric surfactants, nonionic surfactants and anionic surfactants can be used.

[0148] The silicone surfactant is not particularly limited and can be appropriately selected depending on the purpose. Among them, those that do not decompose even at high pH are preferred, and examples thereof include side-chain modified polydimethylsiloxane, both-end modified polydimethylsiloxane, one-end modified polydimethylsiloxane, and both-end modified polydimethylsiloxane of the side chain. Those having a polyoxyethylene group or a polyoxyethylene polyoxypropylene group as the modifying group are particularly preferred because they exhibit good properties as aqueous surfactants. Polyether-modified silicone surfactants can also be used as the silicone surfactant. Examples of polyether-modified silicone surfactants include compounds in which a polyalkylene oxide structure is introduced into the Si part side chain of dimethylsiloxane.

[0149] As the fluorine-based surfactant, a compound having 2 to 16 fluorine-substituted carbon atoms is preferred, and a compound having 4 to 16 fluorine-substituted carbon atoms is more preferred. As the fluorine-based surfactant, for example, perfluoroalkyl sulfonic acid compounds, perfluoroalkyl carboxylic acid compounds, perfluoroalkyl phosphate ester compounds, perfluoroalkyl alkylene oxide adducts, and polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups on the side chain are preferred because of their low foaming properties. Examples of perfluoroalkyl sulfonic acid compounds include perfluoroalkyl sulfonic acid and perfluoroalkyl sulfonate salts. Examples of perfluoroalkyl carboxylic acid compounds include perfluoroalkyl carboxylic acids and perfluoroalkyl carboxylate salts. Examples of perfluoroalkyl phosphate ester compounds include perfluoroalkyl phosphate esters and perfluoroalkyl phosphate ester salts. Examples of perfluoroalkyl alkylene oxide adducts include perfluoroalkyl ethylene oxide adducts. Examples of polyoxyalkylene ether polymer compounds having a perfluoroalkyl ether group on the side chain include sulfate salts of polyoxyalkylene ether polymers having a perfluoroalkyl ether group on the side chain, and salts of polyoxyalkylene ether polymers having a perfluoroalkyl ether group on the side chain. Counter ions of the salts in these fluorine-based surfactants include Li, Na, K, NH ４ , N.H. ３ CH ２ CH ２ OH, NH ２ (CH ２ CH ２ OH) ２ , NH(CH ２ CH ２ OH) ３ etc.

[0150] Among these, polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups in the side chains are more preferred because they have particularly low foaming properties, and fluorine-based surfactants represented by the following formulas (3A) and (3B) are particularly preferred.

[0151] CF ３ CF ２ (CF ２ CF ２ ) ｓ -CH ２ CH ２ O (CH ２ CH ２ O) ｔ H (3A) In the compound represented by formula (3A), 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, in order to impart water solubility.

[0152] C ｒ F ２ｒ＋１ -CH ２ CH(OH)CH ２ -O-(CH ２ CH ２ O) ｃ -Z (3B) In the compound represented by formula (3B), Z is H, C ｄ F ２ｄ＋１ , C.H. ２ CH(OH)CH ２ -C ｅ F ２ｅ＋１ , or C ｆ H ２ｆ＋１ It is. C ｄ F ２ｄ＋１ In the formula, d is an integer of 1 to 6. ２ CH(OH)CH ２ -C ｅ F ２ｅ＋１ In the formula, e is an integer of 4 or more and 6 or less. ｆ H ２ｆ＋１ In the formula, f is an integer of 1 or more and 19 or less, r is an integer of 1 or more and 6 or less, and c is an integer of 4 or more and 14 or less.

[0153] Commercially available fluorine-based surfactants can be used, such as 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.); Fullard FC-93, FC-95, FC-98, FC-129, FC-135, FC-170C, FC-430, and FC-431 (all manufactured by Sumitomo 3M Limited); Megafac F-470, F-1405, and F-474 (all manufactured by DIC Corporation); and Zonyl TBS, FSP, FSA, FSN-100, FSN, and FSO-1. 00, 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 Dai-ichi 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.), and the like.

[0154] Examples of amphoteric surfactants include lauryl aminopropionate, lauryl dimethyl betaine, stearyl dimethyl betaine, and lauryl dihydroxyethyl betaine.

[0155] Examples of nonionic surfactants 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.

[0156] Examples of anionic surfactants include polyoxyethylene alkyl ether acetates, dodecylbenzenesulfonates, laurates, and salts of polyoxyethylene alkyl ether sulfates.

[0157] These may be used alone or in combination of two or more.

[0158] As mentioned above, the silicone surfactant is not particularly limited and can be appropriately selected depending on the purpose, but polyether-modified silicone surfactants having a polyoxyethylene group or a polyoxyethylene polyoxypropylene group as the modifying group are particularly preferred because they exhibit good properties as aqueous surfactants.

[0159] Such surfactants may be synthesized appropriately or commercially available products, such as those available from BYK Japan K.K., Shin-Etsu Chemical Co., Ltd., Dow Corning Toray Silicone Co., Ltd., Nippon Emulsion Co., Ltd., and Kyoeisha Chemical Co., Ltd.

[0160] The polyether-modified silicone surfactant is not particularly limited and can be appropriately selected depending on the purpose. For example, it may be a surfactant represented by the following formula (2) in which a polyalkylene oxide structure is introduced into the Si moiety side chain of dimethylpolysiloxane.

[0161]

[0162] (In formula (2), p, q, a, and b represent integers. R and R′ represent hydrocarbon groups.)

[0163] As the polyether-modified silicone surfactant, commercially available products can be used. Commercially available products include, for example, KF-618, KF-642, KF-643 (Shin-Etsu Chemical Co., Ltd.), SAG001, SAG002, SAG003, SAG005, SAG503, SAG008 (Nissin Chemical Industry Co., Ltd.), EMALEX-SS-5602, SS-1906EX (Nippon Emulsion Co., Ltd.), FZ-2105, FZ-2118, FZ-2154, FZ-2161, FZ-2162, FZ-2163, FZ-2164 (Dow Corning Toray Silicone Co., Ltd.), BYK-347, BYK-348, BYK-349 (BYK Japan KK), TSF4440, TSF4452, TSF4453 (Toshiba Silicon Co., Ltd.), and the like.

[0164] [Sensitizer] The inkjet ink of the present invention may contain a sensitizer. When a sensitizer is present in the ink together with a polymerization initiator, the sensitizer in the system absorbs actinic energy rays to become excited, and upon contact with the polymerization initiator, promotes decomposition of the polymerization initiator, thereby enabling a curing reaction with higher sensitivity.

[0165] The sensitizer may be either fat-soluble or water-soluble, similar to the polymerization initiator. If the sensitizer is fat-soluble, it can be encapsulated in particles of a polymerizable compound such as an ultraviolet-curable oligomer.

[0166] Examples of sensitizers that can be used include aliphatic amines, amines having an aromatic group, and cyclic amine compounds such as piperidine; thioxanthone compounds, alkoxyanthracene compounds, urea compounds such as o-tolylthiourea; sulfur compounds such as sodium diethylthiophosphate and soluble salts of aromatic sulfinic acids; nitrile compounds such as N,N'-disubstituted-p-aminobenzonitrile; phosphorus compounds such as tri-n-butylphosphine and sodium diethyldithiophosphate; Michler's ketone, N-nitrosohydroxylamine derivatives, oxazolidine compounds, tetrahydro-1,3-oxazine compounds; and nitrogen compounds such as condensates of formaldehyde or acetaldehyde with diamines.

[0167] These sensitizers may be used alone or in combination of two or more.

[0168] [Other Resin Components] In addition to the components described above, the inkjet ink of the present invention may contain, as necessary, any oligomer component other than the polymerizable compound, any resin component, or any monomer component (collectively referred to as "other resin components"). The other resin components may be encapsulated in particles of the polymerizable compound, may be dissolved in the aqueous medium, or may be dispersed alone in the ink or may be in a composite state with other components.

[0169] [Other Additives] In addition to the above components, the inkjet ink of the present invention may contain other additives, if necessary.

[0170] Examples of other additives include known additives such as anti-fading agents, emulsion stabilizers, penetration enhancers, ultraviolet absorbers, preservatives, antifungal agents, rust inhibitors, pH adjusters, viscosity adjusters, dispersants, dispersion stabilizers, antifoaming agents, solid wetting agents, chelating agents, etc. These various additives may be added directly after preparing the ink, or may be added during the preparation of the ink.

[0171] For other additives, reference can be made to the descriptions in paragraphs 0088 to 0096 of JP-A No. 2010-65205 and paragraphs 0083 to 0090 of JP-A No. 2010-70669, as appropriate.

[0172] [Content of Each Component] The content of water in the inkjet ink of the present invention is not particularly limited and can be appropriately selected depending on the purpose. From the viewpoint of the drying property and ejection reliability of the ink, the content of water in the inkjet ink of the present invention is usually 10% by mass or more, preferably 20% by mass or more, and more preferably 40% by mass or more, and is usually 90% by mass or less, preferably 80% by mass or less.

[0173]

[0042] 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 is used 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 purpose. The content of the water-soluble organic solvent in the inkjet ink of the present invention is usually 10% by mass or more and usually 50% by mass or less, preferably 40% by mass or less, from the viewpoints of drying property, ejection reliability, wettability with the substrate, etc.

[0174] The content of volatile components relative to the total amount of the inkjet ink of the present invention is preferably 70% by mass or more, more preferably 75% by mass or more, and preferably 95% by mass or less, and more preferably 90% by mass or less. When the content of volatile components is equal to or greater than the above lower limit, ejection reliability is high. When the content of volatile components is equal to or less than the above upper limit, coating strength can be increased. The volatile components in the inkjet ink of the present invention refer to components that, after 1 g of the inkjet ink is placed on an aluminum dish with a diameter of 10 cm and dried at 80°C for 4 hours, are reduced by 90% or more compared to before drying.

[0175] From the viewpoint of drying property and ejection reliability, the inkjet ink of the present invention is prepared so that the total solids concentration, which is the concentration of components other than the aqueous medium, i.e., water and / or a water-soluble organic solvent, 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.

[0176] When a mixture of water and a water-soluble organic solvent is used as the aqueous medium of the ink-jet ink of the present invention, the ratio of water to the water-soluble organic solvent (the total of the water-soluble organic solvent that also serves as a moisturizing solvent and the water-soluble organic solvent used as the aqueous medium) is preferably such that the ratio of water to water-soluble organic solvent is 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), from the viewpoint of improving drying properties and jetting properties.

[0177]

[0044] The content of the polymerizable compound in the inkjet ink of the present invention is usually 3% by mass or more, preferably 5% by mass or more, and more preferably 7% by mass or more, from the viewpoint of the performance of the resulting printed coating film and actinic energy ray curability. On the other hand, the content of the polymerizable compound in the inkjet ink of the present invention is usually 20% by mass or less, preferably 15% by mass or less, and more preferably 12% by mass or less, from the viewpoint of ejection stability. 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, and usually 90% by mass or less, preferably 85% by mass or less, and more preferably 80% by mass or less.

[0178]

[0044] From the viewpoints of improving image density, 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. From the same viewpoints, the content of the colorant in the total solid 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.

[0179] The content of the polymerization initiator in 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, even more preferably 0.4% by mass or more, and usually 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. Having the content of the polymerization initiator within this range sufficiently improves the curing rate and prevents residual polymerization initiator and coloration caused by the polymerization initiator. From the same perspective, the content of the polymerization initiator in the total solids 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, even more preferably 3% by mass or more, and 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.

[0180]

[0042] When the inkjet ink of the present invention contains a surfactant, its content is not particularly limited and can be appropriately selected depending on the purpose, but from the viewpoint of achieving excellent wettability and ejection stability and improved image quality, the content of the surfactant in the ink is usually 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.03% by mass or more, and usually 5% by mass or less, preferably 3% by mass or less, more preferably 1% by mass or less. From the same viewpoint, the content of the surfactant in the total solid content of the inkjet ink of the present invention is usually 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and usually 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less.

[0181]

[0043] When the inkjet ink of the present invention contains a sensitizer, the content thereof is usually 0.01% by mass or more, preferably 0.03% by mass or more, more preferably 0.05% by mass or more, and usually 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 content of the sensitizer is within the above range, the effect of the sensitizer can be sufficiently obtained. 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 usually 8% by mass or less, preferably 6% by mass or less, and more preferably 5% by mass or less.

[0182] [Viscosity of Inkjet Ink] 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. The viscosity of the inkjet ink can be measured using a digital viscometer DV-I+ manufactured by BROOKFIELD.

[0183] <Inkjet Recording Apparatus> The inkjet recording apparatus of the present invention can be suitably used in various recording apparatuses using an inkjet recording method, such as printers, facsimile machines, copying machines, printer / fax / copier combination machines, and three-dimensional modeling apparatuses. In the present invention, the recording apparatus is an apparatus capable of ejecting ink, various treatment liquids, etc. onto a recording medium. This recording apparatus includes not only a head portion that ejects ink, but also means related to feeding, transporting, and discharging the recording medium, as well as other devices known as pre-processing devices and post-processing devices.

[0184] An inkjet recording apparatus in one embodiment of the present invention (hereinafter may be referred to as "inkjet recording apparatus 1") is an inkjet recording apparatus used to record an image on an absorbent recording medium, and comprises an ink applying means [c] that applies an inkjet ink containing a polymerizable compound, a polymerization initiator, and water to the absorbent recording medium without heating the absorbent recording medium, an irradiation means [d] that irradiates the inkjet ink applied to the absorbent recording medium with active energy rays, and a heating means [e] that heats the absorbent recording medium during the irradiation of the active energy rays, and is characterized in that the irradiation means [d] and the heating means [e] can be individually controlled.

[0185] An inkjet recording apparatus according to another embodiment of the present invention (hereinafter, may be referred to as "inkjet recording apparatus 2") is an inkjet recording apparatus used for recording an image on a recording medium, and comprises an ink applying unit [c] that applies an inkjet ink containing a polymerizable compound, a polymerization initiator, and water to the recording medium without heating the recording medium, an irradiation unit [d] that irradiates the inkjet ink applied to the recording medium with active energy rays, and a heating unit [e] that heats the recording medium during the irradiation of the active energy rays, wherein the irradiation unit [d] and the heating unit [e] are each independently controllable, and the polymerizable compound exists as particles in the inkjet ink.

[0186] The inkjet recording apparatus 1 and inkjet recording apparatus 2 of the present invention (hereinafter, these may be collectively referred to as "inkjet recording apparatuses of the present invention") may further include a drying means that does not involve heating in order to promote evaporation of the aqueous medium contained in the ink. The drying means includes, for example, a means for drying the printed surface and the back surface of the recording medium.

[0187] As described above, the irradiation means [d] for irradiating with active energy rays in the inkjet recording apparatus of the present invention may be a means using a light source such as a halogen lamp, a metal halide lamp, an LED, or an LD. Among these, it is preferable to use a light-emitting diode having an emission peak wavelength in the range of 350 to 420 nm. Preferred aspects of the recording medium, ink-applying means [c], heating means [e], and inkjet ink are the same as those described above in relation to the inkjet recording method.

[0188] The inkjet recording apparatus of the present invention is not limited to those that visualize meaningful images such as letters and figures using ink. For example, it also includes those that form patterns such as geometric shapes and those that create three-dimensional images. Furthermore, the recording apparatus includes not only desktop types but also wide-width recording apparatuses that can print on A0-sized recording media, and continuous feed printers that can use, for example, continuous paper wound into a roll as the recording medium. Furthermore, unless otherwise specified, the recording method or active energy ray irradiation method of the recording apparatus includes both a shuttle method in which recording is performed while moving a serial head, and a line method in which recording is performed using a line head. For shuttle-type recording apparatuses, see, for example, JP 2022-181182 A and JP 2010-280828 A.

[0189] <<Applications>> The inkjet ink of the present invention used in the inkjet recording method and inkjet recording apparatus of the present invention is water-based and therefore has excellent environmental and safety properties. According to the inkjet recording method and inkjet recording apparatus of the present invention, a printed coating film with excellent coating properties, particularly high washing fastness, can be formed using such an environmentally and safety-friendly water-based ink. Therefore, the inkjet recording method and inkjet recording apparatus of the present invention can be suitably used for various applications, such as for fabrics for clothing such as T-shirts, other textiles that may become wet with water, wallpaper for interior decoration, and home furnishings.

[0190] An embodiment of the present invention will be described below, but the present invention is not limited to this embodiment.

[0191] [Ink Preparation] <Preparation of Polymerizable Compound Aqueous Dispersion> A water-insoluble polymerizable compound (ultraviolet-curable oligomer) was produced by reacting 0.4 mol of a hexamethylene diisocyanate trimer, 0.8 mol of dipentaerythritol pentaacrylate, and 0.4 mol of polyethylene glycol monoallyl ether (n = 30 to 40 in the above formula (1)). The polymerizable compound and an oil-soluble initiator (GENOPOL TX-2, manufactured by RAHN) were mixed at 60°C in the ratio shown in Table 1, and while stirring, ion-exchanged water that had been preheated to 60°C was added dropwise until the solids concentration reached 20% by mass, to obtain an aqueous dispersion. The average particle size (D ５０ ) was measured using a particle size distribution analyzer, MICROTRAC WAVE II-EX150 (manufactured by Microtrac Bell Co., Ltd.) and found to be 29 nm.

[0192] <Preparation of Ink 1> Ion-exchanged water, the aqueous dispersion of the polymerizable compound, 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 and BYK-349 (both manufactured by BYK Japan) as surfactants, and a dispersion of C.I. Pigment Blue 15:3 (shown as "Cy" in Table 1) as a pigment dispersion were added and mixed to obtain the composition ratio shown in Table 1, to obtain Ink 1. The viscosity of Ink 1 at 25°C was 8 mPa s.

[0193] <Preparation of Inks 2 to 4> Inks 2 to 4 were obtained in the same manner as Ink 1, except that the type and blending ratio of the pigment dispersion, the blending ratio of the water-soluble sensitizer, and the type and blending ratio of the surfactant were changed as shown in Table 1 below. [Pigment dispersions] C.I. Pigment Red 122 Dispersion (Ma in Table 1) C.I. Pigment Yellow 155 Dispersion (Ye in Table 1) C.I. Pigment Black 7 Dispersion (Bk in Table 1)

[0194] The viscosities of Inks 2 to 4 at 25°C were as follows: Ink 2: Viscosity = 10 mPa·s Ink 3: Viscosity = 7 mPa·s Ink 4: Viscosity = 7 mPa·s

[0195] The content ratio of each component in Table 1 indicates the content of the component in the aqueous dispersion or solution when the component is in the form of an aqueous dispersion or solution.

[0196]

[0197] [Examples 1 to 6, Comparative Examples 1 to 3] In a UV inkjet printer, inks 1 to 4 were set as inkjet inks, and cotton fabric was set as a recording medium. Step [a]: The ink application step was carried out under the following settings. (Settings for the ink application step (ink application means [c])) Resolution: 600 x 600 dpi Number of passes: 8 passes Image: 5 x 8 cm solid image

[0198] Thereafter, in step [b], an irradiation step was carried out at a temperature shown in Table 2 and a current density of 2 W / cm ２ The fabric for which the ink application process had been completed was placed on a hot plate (heating means [e]) of 10 seconds after which an LED (irradiation means [d]) with an emission peak wavelength of 385 nm was used as an active energy ray source, and the illuminance was adjusted to the illuminance shown in Table 2, and the fabric was irradiated with 7 J / cm ２ However, in Comparative Examples 1 to 3, heating with a hot plate was not performed. When no heating was performed, the temperature of the fabric during irradiation with active energy rays was room temperature (23° C.).

[0199] [Evaluation of washing fastness] The printed coating films obtained by the above procedure were evaluated for washing fastness by the following method. The fabrics with printed coating films obtained in Examples 1 to 6 and Comparative Examples 1 to 3 were washed in a washing machine for 50 minutes, and the change in image density (ΔE) before and after washing was determined using a spectrodensitometer / colorimeter (X-rite eXact Advance, manufactured by X-Rite Corporation) and evaluated as follows. ΔE was calculated using the following formula:

[0200]

[0201] ⊚: ΔE is 2.0 or less for each color, and is excellent in practical use. ○: ΔE is 3.0 or less for each color, and is no problem in practical use. ×: ΔE is greater than 3.0 for some colors, and is problematic in practical use.

[0202] The evaluation results are shown in Table 2. The printed coating film portions of Examples 1 to 6 and Comparative Examples 1 to 3 were not hard or stiff, and had the same feel as unprinted fabric.

[0203]

[0204]

[0046] From Table 2, it can be seen that the inkjet recording method and inkjet recording apparatus of the present invention can form printed images with high washing fastness and excellent coating strength while maintaining stable inkjet ejection. In the above examples, inks 1 to 4, which contain the same polymerizable compound and polymerization initiator, were used. However, considering the mechanism by which stable inkjet ejection is maintained by step [a] and the mechanism by which penetration of the inkjet ink into the recording medium is suppressed by step [b], thereby improving washing fastness, similar effects can be expected with other inkjet inks.

[0205] Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the present invention. This application is based on Japanese Patent Application No. 2023-193822, filed on November 14, 2023, and is incorporated by reference in its entirety.

Claims

1. An inkjet recording method comprising the following steps [a] and [b], in which the recording medium is not heated in the step [a], and is heated by a heating means in the step [b], and the recording medium is an absorbent recording medium: Step [a]: an ink application step of applying an inkjet ink containing at least a polymerizable compound, a polymerization initiator and water to the recording medium; Step [b]: an irradiation step of irradiating the inkjet ink applied to the recording medium that has been subjected to at least the step [a] with active energy rays controlled by a means other than the heating means.

2. An inkjet recording method comprising the following steps [a] and [b], in which the recording medium is not heated in the step [a], and the recording medium is heated by a heating means in the step [b], and the polymerizable compound in the step [a] exists as particles in the inkjet ink. Step [a]: an ink application step of applying an inkjet ink containing at least a polymerizable compound, a polymerization initiator and water to a recording medium. Step [b]: an irradiation step of irradiating the inkjet ink applied to the recording medium that has been subjected to at least the step [a] with active energy rays controlled by a means other than the heating means.

3. The ink-jet recording method according to claim 1 or 2, wherein the light source of the active energy rays is a light-emitting diode having an emission peak wavelength in the range of 350 to 420 nm.

4. The ink-jet recording method according to claim 1, wherein the absorbent recording medium is a fabric.

5. The ink jet recording method according to claim 2, wherein the average particle size of the particles is from 10 nm to 200 nm.

6. The ink jet recording method according to claim 1 or 2, wherein the polymerizable compound includes a (meth)acrylate compound.

7. The inkjet recording method according to claim 1 or 2, wherein the heating temperature of the recording medium in the step [b] is 30° C. or higher and 70° C. or lower.

8. The ink-jet recording method according to claim 1 or 2, wherein the heating means is a heating element.

9. The inkjet recording method according to claim 1 or 2, wherein the heating of the recording medium in the irradiation step [b] is carried out from the side opposite to the side to which the ink is applied.

10. An inkjet recording apparatus used for recording an image on an absorbent recording medium, comprising: an ink application means [c] for applying an inkjet ink containing a polymerizable compound, a polymerization initiator and water to the absorbent recording medium without heating the absorbent recording medium; an irradiation means [d] for irradiating the inkjet ink applied to the absorbent recording medium with active energy rays; and a heating means [e] for heating the absorbent recording medium when irradiating the active energy rays, wherein the irradiation means [d] and the heating means [e] are each individually controllable.

11. An inkjet recording apparatus used for recording an image on a recording medium, comprising: an ink application means [c] for applying an inkjet ink containing a polymerizable compound, a polymerization initiator and water to the recording medium without heating the recording medium; an irradiation means [d] for irradiating the inkjet ink applied to the recording medium with active energy rays; and a heating means [e] for heating the recording medium when irradiating the active energy rays, wherein the irradiation means [d] and the heating means [e] are each individually controllable, and the polymerizable compound exists as particles in the inkjet ink.

12. The ink jet recording apparatus according to claim 10 or 11, wherein the light source of the active energy rays is a light emitting diode having an emission peak wavelength in the range of 350 to 420 nm.

13. The ink jet recording apparatus according to claim 10, wherein the absorbent recording medium is a fabric.

14. The ink jet recording apparatus according to claim 11, wherein the average particle size of the particles is 10 nm or more and 200 nm or less.

15. The ink jet recording apparatus according to claim 10 or 11, wherein the polymerizable compound includes a (meth)acrylate compound.

16. The ink-jet recording method according to claim 10 or 11, wherein a heating element is used as the heating means [e].

17. An ink jet recording apparatus according to claim 10 or 11, wherein the heating means [e] is located on the absorbent recording medium or on the surface of the recording medium opposite to the surface on which ink is applied.