Image formation method

Abstract

To provide an image formation method which can form a high-quality image with good workability, in image formation by an inkjet method.SOLUTION: An image formation method includes a landing step of discharging droplets of inkjet ink from an inkjet head, and landing the droplets onto a base material, wherein the inkjet ink contains an aqueous solvent, a pigment, a fixing resin, and a temperature-responsive polymer, the temperature-responsive polymer has a lower limit critical consolute temperature to water, with respect to the total amount of the inkjet ink, a content of the pigment is within the range of 2 to 10 mass%, a content of the fixing resin is within the range of 1 to 10 mass%, a content of the temperature-responsive polymer is within the range of 0.01 to 1 mass%, and the landing step heats the droplets at the lower limit critical consolute temperature of ±10°C.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an image forming method, and more particularly to an image forming method using an inkjet method that is capable of forming high-quality images with good workability. [Background technology]

[0002] In forming an image by the inkjet method, droplets of inkjet ink (hereinafter also simply referred to as "ink") are ejected from an inkjet head (hereinafter also simply referred to as "head") toward a substrate, and after the droplets land on the substrate, the solvent is dried to form a coating (image). When an image is formed on a non-absorbent substrate made of PET (polyethylene terephthalate) or the like by such an inkjet method, there are problems such as adjacent ink droplets being pulled together after the ink lands on the substrate and before drying, resulting in streaking defects, or in the case of adjacent different ink droplets, colors mixing and bleeding.

[0003] To solve this problem, it is conceivable to introduce a heated platen into the image forming apparatus, so that the solvent is instantly dried and thickened after the ink hits the substrate. However, to prevent the bleeding, it is necessary to heat the platen to a high temperature, which causes the meniscus surface of the head to dry out and the ink to stick to the area around the head, resulting in ejection failure.

[0004] It is also disclosed that additives are added to the ink to give it thixotropy, and that as the ink circulates within the head, shear is applied and the viscosity is low; however, when the ink is ejected and lands on a substrate, the viscosity increases in a state of low shear, making it difficult for the ink to be absorbed by the absorbent substrate, resulting in the formation of a high-density image without the need for platen heating.

[0005] For example, Patent Document 1 describes an aqueous inkjet ink in which the ink viscosity at low shear is 1.5 times or more that at high shear by adding a water-soluble polymer compound to impart thixotropy to the ink. Patent Document 1 describes that when the ink is circulated and ejected by the head, it has a low viscosity at high shear, but when it lands, it becomes high viscosity due to low shear, and prevents the concentration from decreasing due to the absorbing base material. However, Patent Document 1 does not describe an attempt to control the viscosity increase of the ink by combining the thixotropy of the ink itself with the drying conditions. It is assumed that a method of controlling the thixotropy of the ink itself as in Patent Document 1 alone cannot achieve both good ejection properties and high-quality image formation.

[0006] Patent Document 2 also describes a water-based inkjet ink to which a water-soluble temperature-responsive polymer has been added. Patent Document 2 describes the effect of suppressing the penetration of the ink into the paper substrate and increasing the concentration. Patent Document 2 describes that the temperature-responsive polymer is added in an amount of about 5 mass % to the entire ink, which is more than twice the amount of the coloring material. It also describes that when heat is applied, the resin shrinks and covers the coloring material, thereby fixing the coloring material. However, Patent Document 2 does not control the thixotropy so as to change the viscosity of the ink inside the head and when it lands. Therefore, it is assumed that the ink described in Patent Document 2 cannot achieve both good ejection properties and high-quality image formation. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2011-225859 A [Patent Document 2] Japanese Patent Application Publication No. 11-236523 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been made in consideration of the above problems and circumstances, and an object of the present invention is to provide an image forming method by an inkjet method that is capable of forming high-quality images with good workability. [Means for solving the problem]

[0009] In order to solve the above problems, the present inventors, in the process of studying the causes of the above problems, studied the composition of an inkjet ink using a temperature-responsive polymer, using the viscosity of the inkjet ink at high shear when circulating in the head and the viscosity at low shear when landing as indicators. As a result, they found that by using a combination of a temperature-responsive polymer and a fixing resin in an inkjet ink containing a water-based solvent and a pigment, and including each in a predetermined content range, it is possible to obtain an ink that has a low viscosity when circulating in the head and a sufficiently high viscosity when landing with slight temperature adjustment, and arrived at the present invention. By having the above characteristics, the ink is an inkjet ink that can maintain good ejection properties and form high-quality images at the same time. That is, the above problems according to the present invention are solved by the following means.

[0010] 1. An image forming method having a landing step of ejecting droplets of ink-jet ink from an ink-jet head and landing them on a substrate, The ink-jet ink contains a water-based solvent, a pigment, a fixing resin, and a temperature-responsive polymer; the temperature-responsive polymer has a lower critical solution temperature with respect to water; the content of the pigment is within a range of 2 to 10% by mass, the content of the fixing resin is within a range of 1 to 10% by mass, and the content of the temperature responsive polymer is within a range of 0.01 to 1% by mass, relative to a total amount of the ink-jet ink; The image forming method according to the present invention, characterized in that, in the impacting step, heating is performed within a range of the lower critical solution temperature ±10°C.

[0011] 2. The image forming method according to 1 above, wherein the ink-jet ink has a viscosity of 15 mPa·s or less at a shear rate of 1000 (1 / s) at 25°C and a viscosity of 45 mPa·s or more at a shear rate of 1 (1 / s) at any temperature within a range of the lower critical solution temperature ±10°C.

[0012] 3. The image forming method according to 1 or 2, wherein the ink-jet ink has a viscosity of 100 mPa s or more at a shear rate of 1 (1 / s) at any temperature within a range of the lower critical solution temperature ±10°C when the aqueous solvent is removed from the ink-jet ink so that the mass of the ink-jet ink is 80% of the initial mass.

[0013] 4. The image forming method according to any one of 1 to 3 above, wherein the lower critical solution temperature of the temperature-responsive polymer in water is within a range of 30 to 60°C.

[0014] 5. The image forming method according to any one of items 1 to 4, wherein the temperature-responsive polymer comprises a water-soluble cellulose resin.

[0015] 6. The image forming method according to any one of 1 to 5 above, wherein the content of the aqueous solvent is within a range of 50 to 90% by mass relative to the total amount of the inkjet ink.

[0016] 7. The image forming method according to any one of items 1 to 6, wherein the fixing resin contains at least one resin selected from the group consisting of polyacrylic resins, polyurethane resins, and polyester resins.

[0017] 8. The image forming method according to any one of items 1 to 7, wherein the ink-jet ink further contains a thixotropic agent.

[0018] 9. The image forming method according to 8 above, wherein the thixotropy-imparting agent contains cellulose nanofiber or smectite clay mineral.

[0019] 10. The image forming method according to 8 or 9 above, wherein the content of the thixotropy-imparting agent is within the range of 0.01 to 1% by mass based on the total amount of the inkjet ink.

[0020] 11. The image forming method according to any one of 1 to 10, wherein the viscosity of the droplets when they land on the substrate or immediately after they land is 150 mPa·s or more.

[0021] 12. The image forming method according to any one of items 1 to 11, wherein the landing step includes heating the droplets on the substrate within a range of 30 to 60°C.

[0022] 13. The image forming method according to 11 or 12 above, wherein the period immediately after the droplets land on the substrate is within 100 msec after the droplets land on the substrate.

[0023] 14. The inkjet head is provided with an ink circulation mechanism, the ink-jet ink is circulated in the ink-jet head so that the ink-jet ink has a viscosity of 15 mPa s or less; and 14. The image forming method described in any one of items 1 to 13, wherein the landing step is performed so that the droplets, when they land on the substrate or immediately after they land, have a mass loss rate of 20% or less from the inkjet ink and a viscosity of 100 mPa s or more.

[0024] 15. The inkjet head, a pressure chamber into which the ink-jet ink is injected via an injection path; a pressure generating means for generating a pressure fluctuation in the pressure chamber; a nozzle communicating with the pressure chamber and serving as a flow path for the ink-jet ink to be ejected from the pressure chamber to the outside in response to a pressure fluctuation in the pressure chamber; two or more circulation paths that communicate with the pressure chamber and discharge the ink-jet ink inside the nozzle and return the ink to the injection path; 15. The image forming method according to claim 14, further comprising: Effect of the Invention

[0025] The above-mentioned means of the present invention can provide an inkjet ink that can maintain good ejection properties while forming a high-quality image. In addition, an image forming method can be provided that can form a high-quality image with good workability in image formation by the inkjet method. The mechanism of expression or action of the effects of the present invention is not clear, but is speculated as follows.

[0026] The inkjet ink of the present disclosure contains an aqueous solvent, a pigment, a fixing resin, and a temperature-responsive polymer, the temperature-responsive polymer having a lower critical solution temperature with respect to water, and the content of the pigment is within a range of 2 to 10 mass %, the content of the fixing resin is within a range of 1 to 10 mass %, and the content of the temperature-responsive polymer is within a range of 0.01 to 1 mass % with respect to the total amount of the inkjet ink. In this specification, unless otherwise specified, the lower critical solution temperature of the temperature-responsive polymer refers to the lower critical solution temperature with respect to water.

[0027] By setting the ink composition within the above range, the viscosity at high shear can be kept low, for example, the ink viscosity (25°C) at a shear rate of 1000 (1 / s) can be set to 15 mPa s or less, which allows the ink to circulate smoothly in the head and be ejected smoothly from the head.

[0028] By setting the composition of the ink within the above range, the viscosity at the time of landing can be made high, for example, the viscosity at a shear rate of 1 (1 / s) at any temperature within the range of the lower critical solution temperature of the temperature-responsive polymer ±10°C can be made 45 mPa·s or more. In other words, the maximum viscosity at a shear rate of 1 (1 / s) within the range of the lower critical solution temperature of the temperature-responsive polymer ±10°C can be made 45 mPa·s or more. If the viscosity at the temperature satisfies the above regulation, good pinning can be achieved at the time of landing without removing the aqueous solvent from the ink with only slight temperature adjustment, and the image obtained can be of high quality. That is, the ink of the present invention has a high viscosity required for good pinning within the range of the lower critical solution temperature of the temperature-responsive polymer with water ±10°C. This allows a large amount of aqueous solvent to remain in the ink from the time of ejection to the time of landing, so that adhesion of the ink solids to the periphery of the head is suppressed, ejection failure is less likely to occur, and maintenance is easy.

[0029] In addition, by using a thermoresponsive polymer in combination with a fixing resin, it is possible to impart water resistance to the coating film of the ink obtained by image formation. This effect is believed to be obtained by entangling the thermoresponsive polymer with the fixing resin during the image formation process. Furthermore, this entanglement improves the fixation of the coating film of the ink obtained by image formation to the substrate.

[0030] The image forming method of the present invention includes a landing step of ejecting droplets of an ink-jet ink from an ink-jet head equipped with an ink circulation mechanism and landing the droplets on a substrate, and the ink-jet ink is circulated in the ink-jet head so that the viscosity of the ink-jet ink is 15 mPa s or less, which is a viscosity that allows the ink to be smoothly circulated in the head and ejected from the head.

[0031] In the image forming method of the present invention, the landing step is performed so that the ink droplets when they land on the substrate or immediately after they land have a mass loss rate of 20% or less from the ink circulating in the head and a viscosity of 100 mPa s or more. If the mass loss rate and viscosity of the ink droplets when they land on the substrate or immediately after they land are within the above ranges, good pinning is possible and the resulting image can be of high quality. Furthermore, adhesion of ink solids to the periphery of the head is suppressed, ejection defects are less likely to occur, and maintenance is easy. [Brief description of the drawings]

[0032] [Figure 1] FIG. 1 is a schematic diagram showing the main components of an inkjet image forming apparatus including an example of an inkjet head that can be used in the image forming method of the present invention. [Diagram 2] FIG. 2 is an enlarged cross-sectional view of a head chip of the inkjet head shown in FIG. [Diagram 3] FIG. 2 is a plan view of a nozzle plate of the inkjet head shown in FIG. 1; [Figure 4] Graph used to determine crossover distortion (%) of the ink in Example 1 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] The inkjet ink of the present disclosure is an inkjet ink containing a water-based solvent, a pigment, a fixing resin, and a temperature-responsive polymer, the temperature-responsive polymer having a lower critical solution temperature with respect to water, and the content of the pigment in the total amount of the inkjet ink is within a range of 2 to 10% by mass, the content of the fixing resin is within a range of 1 to 10% by mass, and the content of the temperature-responsive polymer is within a range of 0.01 to 1% by mass. This feature is a technical feature common to the following embodiments of the inkjet ink of the present disclosure.

[0034] In an embodiment of the ink of the present disclosure, from the viewpoint of achieving both good jetting properties and high-quality image formation, it is preferred that the viscosity at a shear rate of 1000 (1 / s) at 25°C is 15 mPa s or less, and the viscosity at a shear rate of 1 (1 / s) at any temperature within a range of ±10°C of the lower critical solution temperature is 45 mPa s or more.

[0035] As an embodiment of the ink of the present disclosure, from the viewpoint of maintaining both good jetting properties and forming high-quality images, it is preferable that the ink-jet ink has a viscosity of 100 mPa s or more at a shear rate of 1 (1 / s) at any temperature within a range of the lower critical solution temperature ±10°C when the aqueous solvent is removed from the ink-jet ink so that the ink has a mass of 80% of the initial mass (hereinafter, this state is also referred to as "ink drying rate 20%).

[0036] This allows the ink to maintain the viscosity required for bleeding resistance even at an ink drying rate of 20%, allowing a large amount of water-based solvent to remain in the ink from the time it is ejected until it lands on the surface. This prevents ink solids from adhering to the area around the head, reduces ejection problems, and makes maintenance easier.

[0037] In an embodiment of the ink of the present disclosure, from the viewpoint of maintaining good jetting properties while forming a high-quality image, the lower critical solution temperature of the temperature-responsive polymer in water is preferably within a range of 30 to 60° C. In addition, the temperature-responsive polymer preferably contains a water-soluble cellulose resin.

[0038] In an embodiment of the ink of the present disclosure, from the viewpoint of achieving both good ejection properties and high-quality image formation, the content of the aqueous solvent relative to the total amount of the inkjet ink is preferably within the range of 50 to 90 mass %.

[0039] In an embodiment of the ink of the present disclosure, from the viewpoint of exerting the effects of the present invention, it is preferable that the fixing resin contains at least one resin selected from the group consisting of a polyacrylic resin, a polyurethane resin, and a polyester resin.

[0040] In an embodiment of the ink of the present disclosure, from the viewpoint of maintaining good ejection properties while forming a high-quality image, it is preferable that the ink-jet ink further contains a thixotropy-imparting agent. From the same viewpoint, it is preferable that the thixotropy-imparting agent contains cellulose nanofiber or smectite clay mineral. From the same viewpoint, it is preferable that the content of the thixotropy-imparting agent is within the range of 0.01 to 1% by mass with respect to the total amount of the ink-jet ink.

[0041] The image forming method of the present disclosure includes a landing step of ejecting droplets of inkjet ink from an inkjet head equipped with an ink circulation mechanism and landing them on a substrate, the landing step being characterized in that the inkjet ink is circulated within the inkjet head so that the viscosity of the inkjet ink is 15 mPa s or less, and the landing step is performed so that the droplets, when they land on the substrate or immediately after landing, have a mass loss rate of 20% or less from the inkjet ink and a viscosity of 100 mPa s or more. This feature is a technical feature common to the following embodiments of the image forming method of the present invention.

[0042] In an embodiment of the image forming method of the present disclosure, from the viewpoint of further exerting the effects of the present invention, it is preferable that the viscosity of the droplets when they land on the substrate or immediately after they land is 150 mPa·s or more.

[0043] In an embodiment of the image forming method of the present disclosure, from the viewpoint of further exerting the effects of the present invention, it is preferable that the landing step includes heating the droplets on the substrate within a range of 30 to 60° C. In addition, it is preferable that the immediately after landing is within 100 msec after the droplets land on the substrate.

[0044] In an embodiment of the image forming method of the present disclosure, when the substrate is a non-absorbent substrate, the effect of the present invention is more remarkable, which is preferable.

[0045] As an embodiment of the image forming method of the present disclosure, from the viewpoint of further exerting the effects of the present invention, it is preferable that the inkjet head comprises a pressure chamber into which the inkjet ink is injected via an injection path, a pressure generating means for generating pressure fluctuations in the pressure chamber, a nozzle communicating with the pressure chamber and serving as a flow path for the inkjet ink to be ejected from the pressure chamber to the outside due to the pressure fluctuations in the pressure chamber, and two or more circulation paths communicating with the pressure chamber and discharging the inkjet ink inward from the nozzle and returning it to the injection path.

[0046] In an embodiment of the image forming method of the present disclosure, from the viewpoint of further exerting the effects of the present invention, it is preferable to use the ink-jet ink of the present invention as the ink-jet ink.

[0047] The present invention, its components, and embodiments for carrying out the present invention will be described in detail below. In this application, the symbol "to" is used to mean that the numerical values ​​before and after the symbol "to" are included as the lower and upper limits.

[0048] [Inkjet ink overview] <Inkjet ink composition> The ink of the present disclosure is an inkjet ink containing a water-based solvent, a pigment, a fixing resin, and a temperature-responsive polymer, the temperature-responsive polymer having a lower critical solution temperature with respect to water, and characterized in that the content of the pigment is within a range of 2 to 10 mass %, the content of the fixing resin is within a range of 1 to 10 mass %, and the content of the temperature-responsive polymer is within a range of 0.01 to 1 mass %, relative to the total amount of the inkjet ink.

[0049] In this specification, the aqueous solvent refers to water or a solvent containing water and an aqueous solvent. An aqueous solvent is a solvent that is compatible with water at room temperature.

[0050] The ink of the present disclosure may contain, in addition to the aqueous solvent, pigment, fixing resin, and temperature-responsive polymer, any optional components that do not impair the effects of the present invention. Examples of the optional components include a thixotropic agent, a pigment dispersant, a surfactant, etc. Each component of the ink of the present invention will be described below.

[0051] (Temperature-responsive polymer) The temperature-responsive polymer contained in the ink of the present disclosure is a polymer having a lower critical solution temperature (hereinafter also referred to as "LCST") with respect to water. The temperature-responsive polymer has a property of dissolving in water below the LCST and not dissolving in water, for example gelling, above the LCST. In other words, an aqueous solution of the temperature-responsive polymer has a property of undergoing a phase change with the LCST as the critical point. This property is reversible. With the temperature-responsive polymer having this property, the ink of the present invention can adjust the viscosity of the ink in the head and when it lands on the substrate to appropriate ranges, respectively, and can maintain good ejection properties while forming high-quality images.

[0052] The LCST of the temperature-responsive polymer in water can be measured, for example, by measuring the phase transition temperature of an aqueous solution of the temperature-responsive polymer using a differential scanning calorimeter (DSC), or by measuring the change in light transmittance of the aqueous solution while slowly increasing (decreasing) the temperature of the aqueous solution of the temperature-responsive polymer.

[0053] The LCST of the temperature-responsive polymer is preferably in the range of 30 to 60° C., more preferably in the range of 40 to 50° C. If the LCST of the temperature-responsive polymer is 30° C. or higher, the viscosity of the ink does not increase excessively in the temperature range in which the ink usually circulates inside the head. If the LCST of the temperature-responsive polymer is 60° C. or lower, the viscosity of the ink droplets can be increased to a desired level without increasing the temperature to a high temperature at the time of landing and without removing the aqueous solvent.

[0054] As described below, the aqueous solvent contained in the ink may consist of water, but may also contain an optional aqueous solvent other than water. When the aqueous solvent contains water and an aqueous solvent, the LCST of the temperature-responsive polymer with respect to the aqueous solvent may differ from the LCST of the temperature-responsive polymer with respect to water. The difference between the two is preferably within about 10°C. In other words, the LCST of the temperature-responsive polymer with respect to the aqueous solvent is preferably within the range of the LCST of the temperature-responsive polymer with respect to water ±10°C.

[0055] Specific examples of temperature-responsive polymers include water-soluble cellulose resins, poly(N-substituted (meth)acrylamides), poly(N-vinyl acylamides), poly((meth)acrylic acid alkyl esters), and other temperature-responsive polymers. Of these, water-soluble cellulose resins are preferred as the temperature-responsive polymer used in the ink of the present invention. In this specification, (meth)acrylamide is a general term for acrylamide and methacrylamide. Similarly, (meth)acrylic acid is a general term for acrylic acid and methacrylic acid.

[0056] The water-soluble cellulose resin is a resin that is imparted with water solubility by replacing some of the hydrogen atoms of the OH groups that cellulose has, thereby eliminating hydrogen bonds. Examples of the substituent that replaces the hydrogen atoms of the OH groups include an alkyl group, a hydroxyalkyl group, and a carboxy group. The preferred substituents are a methyl group, a hydroxypropyl group, and a hydroxyethyl group. The substituents may be used alone or in combination of two or more.

[0057] Specific examples of the water-soluble cellulose resin include methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose, and carboxymethyl cellulose.

[0058] The substituent in the poly(N-substituted (meth)acrylamide) is preferably an alkyl group which may have an ether bond (-O-) between carbon atoms. The alkyl group may be cyclic, linear or branched, or may be a combination of these. The nitrogen atom has one or two substituents, and when there are two substituents, they may be bonded to form a ring. The number of carbon atoms in the alkyl group is preferably 1 to 10.

[0059] Specific examples of poly(N-substituted (meth)acrylamide) include poly(N-ethylacrylamide), poly(Nn-propyl(meth)acrylamide), poly(N-isopropyl(meth)acrylamide), poly(N-cyclopropyl(meth)acrylamide), and poly(N,N-diethyl(meth)acrylamide).

[0060] The poly(N-substituted (meth)acrylamide) does not have to be composed of a single monomer. In other words, the poly(N-substituted (meth)acrylamide) may be a copolymer of N-substituted (meth)acrylamides having different substituents. Furthermore, the poly(N-substituted (meth)acrylamide) may be a copolymer of at least one monomer selected from the monomers constituting the following polymers, for example, poly(N-vinyl acylamides) and poly((meth)acrylic acid alkyl esters).

[0061] Examples of poly(N-vinyl acyl amide) include poly(N-vinyl acetamide), poly(N-vinyl propionic acid amide), poly(N-vinyl butyric acid amide), and poly(N-vinyl isobutyric acid amide).

[0062] Examples of poly((meth)acrylic acid alkyl esters) include poly(n-butyl methacrylate), poly(dodecyl methacrylate), poly(n-hexyl methacrylate), poly(methyl methacrylate), and poly(n-octyl methacrylate).

[0063] Other temperature-responsive polymers include poly(N,N-acrylpyrrolidone), poly(N-acrylpiperidine), and their copolymers, alternating copolymers of polyisobutyl vinyl ether and maleic anhydride, poly(2-methyl-5-vinylpyridine), poly(vinyl alcohol), poly(N-vinylpyrrolidone), poly(N-vinylsuccinic acid), poly(vinylsulfonic acid), poly(oxyethylene), poly(tetrahydrofuran), amylopectin, amylose, poly(vinyl acetate), poly(propylene glycol), polyvinyl methyl ether (PVME), and polyvinyl methyl oxazolidinone.

[0064] In the present invention, as the temperature-responsive polymer, one of these may be used alone, or two or more of them may be used in combination.

[0065] The weight average molecular weight of the temperature-responsive polymer is not particularly limited, but is preferably from 10,000 to 100,000, and more preferably from 20,000 to 80,000. If the weight average molecular weight of the temperature-responsive polymer is 10,000 or more, the polymer and the fixing resin are mutually entangled, and it becomes easier to impart water resistance to the ink coating (image). Also, if the weight average molecular weight is 100,000 or less, there is little risk of the ink viscosity becoming too high and the ejection property becoming poor.

[0066] The weight average molecular weight of the temperature-responsive polymer is a polystyrene-equivalent weight average molecular weight measured by gel permeation chromatography (GPC).

[0067] The temperature-responsive polymer may be a commercially available product, such as water-soluble cellulose resin, which is a product name of Shin-Etsu Chemical Co., Ltd., such as Metolose SM-04 (methylcellulose resin, LCST: 55°C) or Metolose 60SH-03 (hydroxypropylmethylcellulose resin, LCST: 75°C).

[0068] Commercially available poly(N-substituted (meth)acrylamides) include poly(N-isopropylacrylamide) (LCST: 35° C., weight average molecular weight: 30,000) manufactured by Sigma-Aldrich Corporation.

[0069] The content of the temperature responsive polymer in the ink of the present invention is within the range of 0.01 to 1% by mass based on the total amount of the ink. If the content of the temperature responsive polymer is within the above range, the above-mentioned effects of the present invention can be obtained by blending the temperature responsive polymer. The content of the temperature responsive polymer is preferably within the range of 0.05 to 0.8% by mass.

[0070] (fixing resin) The ink of the present invention contains a fixing resin. By containing a fixing resin in addition to a temperature-responsive polymer, the ink of the present invention can appropriately adjust the viscosity of the ink inside the head and when it lands on the substrate, and can impart water resistance to the coating film of the ink obtained by image formation. The fixing resin further functions as a binder for the pigment, which is a colorant, and has the function of improving the adhesion of the coating film to the substrate, particularly a non-absorbent substrate, and improving the abrasion resistance of the coating film obtained by using the ink. The fixing resin is preferably a water-insoluble resin. The water-insoluble resin as the fixing resin is preferably used in the form of fine particles dispersed in an aqueous solvent.

[0071] The water-insoluble resin microparticles have a form in which the inherently water-insoluble resin is dispersed in an aqueous solvent as microparticles. The microparticles may be, for example, a form in which the water-insoluble resin is forcibly emulsified using an emulsifier or the like and dispersed in an aqueous solvent as microparticles. Alternatively, the water-insoluble resin may be self-emulsified by introducing a hydrophilic functional group into the molecule thereof to form stable microparticles in the aqueous solvent without using an emulsifier or dispersion stabilizer. The aqueous solvent in which the water-insoluble resin microparticles are dispersed may be the same aqueous solvent as described above, and usually water or a water / alcohol mixed solvent is used. Hereinafter, the water-insoluble resin microparticles dispersed in an aqueous solvent are also referred to as an aqueous dispersion.

[0072] In the present invention, the term "water-insoluble resin" refers to a resin which, when dried at 105° C. for 2 hours and then dissolved in 100 g of water at 25° C., dissolves in an amount of 10 g or less, preferably 5 g or less, and more preferably 1 g or less. However, when the resin has a salt-forming group, the dissolution amount is the amount dissolved when the salt-forming group of the resin is 100% neutralized with acetic acid or sodium hydroxide depending on the type of the resin.

[0073] The fixing resin according to the present invention is preferably a water-insoluble resin such as a polyester resin, a polyurethane resin, or a polyacrylic resin. As the fixing resin according to the present invention, one of these may be used alone or two or more of them may be used in combination.

[0074] The fixing resin is contained in the range of 1 to 10% by mass relative to the total mass of the ink (100% by mass). If the content of the fixing resin is within the above range, the above-mentioned effects of the present invention can be obtained by blending the fixing resin. The content of the fixing resin is preferably within the range of 2 to 8% by mass, and more preferably within the range of 3 to 6% by mass.

[0075] With regard to the contents of the temperature-responsive polymer and the fixing resin in the ink, the ratio (percentage) of the content of the temperature-responsive polymer to the total content of the temperature-responsive polymer and the fixing resin is preferably within a range of 0.1 to 20% by mass. This ratio is more preferably 0.5 to 10% by mass. By having the ratio of the content of the temperature-responsive polymer to the total content of the temperature-responsive polymer and the fixing resin within the above range, it is easy to achieve both water resistance and good pinning characteristics of the coating film (image) obtained from the ink.

[0076] [Polyester Resin] The polyester resin used as the fixing resin can be obtained by using a polyhydric alcohol component and a polycarboxylic acid component such as a polycarboxylic acid, a polycarboxylic acid anhydride, or a polycarboxylic acid ester.

[0077] The polyhydric alcohol component may be a dihydric alcohol (diol), specifically, an alkylene glycol having 2 to 36 carbon atoms (ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butylene glycol, 1,6-hexanediol, etc.), an alkylene ether glycol having 4 to 36 carbon atoms (diethylene glycol, triethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, polybutylene glycol, etc.), an alicyclic diol having 6 to 36 carbon atoms, Examples of such alicyclic diols include 1,4-cyclohexanedimethanol, hydrogenated bisphenol A, and the like, adducts of the above-mentioned alicyclic diols with alkylene oxides having a carbon number of 2 to 4 (ethylene oxide (hereinafter abbreviated as EO), propylene oxide (hereinafter abbreviated as PO), butylene oxide (hereinafter abbreviated as BO)) (number of moles added is in the range of 1 to 30), and adducts of bisphenols (bisphenol A, bisphenol F, bisphenol S, and the like) with alkylene oxides having a carbon number of 2 to 4 (EO, PO, BO, and the like) (number of moles added is in the range of 2 to 30). These may be used alone or in combination of two or more.

[0078] Examples of the polyvalent carboxylic acid component include divalent carboxylic acids (dicarboxylic acids), specifically alkane dicarboxylic acids having 4 to 36 carbon atoms (succinic acid, apidic acid, sebacic acid, etc.), alkenyl succinic acids (dodecenyl succinic acid, etc.), alicyclic dicarboxylic acids having 4 to 36 carbon atoms (dimer acids (dimerized linoleic acid), etc.), alkene dicarboxylic acids having 4 to 36 carbon atoms (maleic acid, fumaric acid, citraconic acid, mesaconic acid, etc.), and aromatic dicarboxylic acids having 8 to 36 carbon atoms (phthalic acid, isophthalic acid, terephthalic acid or derivatives thereof, naphthalenedicarboxylic acid, etc.). These may be used alone or in combination of two or more.

[0079] The number average molecular weight of the polyester resin is preferably within a range of 1,000 to 50,000, and more preferably within a range of 2,000 to 20,000.

[0080] As the polyester resin, a commercially available product may be used. As a commercially available product, for example, a dispersion liquid in which the polyester resin is dispersed in an aqueous solvent as an aqueous dispersion may be used. Examples of commercially available dispersion liquids include the following. In the examples, the number average molecular weight of the polyester resin contained in the product (dispersion liquid) is shown in parentheses. These may be used alone or in combination of two or more types.

[0081] The following are all trade names: Elitel KA-5034 (manufactured by Unitika Ltd., number average molecular weight: 8500), Elitel KA-5071S (manufactured by Unitika Ltd., number average molecular weight: 8500), Elitel KA-1449 (manufactured by Unitika Ltd., number average molecular weight: 7000), Elitel KA-0134 (manufactured by Unitika Ltd., number average molecular weight: 8500), Elitel KA-3556 (manufactured by Unitika Ltd., number average molecular weight: 8000), Elitel KA-6137 (manufactured by Unitika Ltd., number average molecular weight: 5000), Elitel KZA-6034 (manufactured by Unitika Ltd., number average molecular weight: 6500), Examples of such products include Elitel KT-8803 (manufactured by Unitika Ltd., number average molecular weight: 15,000), Elitel KT-8701 (manufactured by Unitika Ltd., number average molecular weight: 13,000), Elitel KT-9204 (manufactured by Unitika Ltd., number average molecular weight: 17,000), Elitel KT-8904 (manufactured by Unitika Ltd., number average molecular weight: 17,000), Elitel KT-0507 (manufactured by Unitika Ltd., number average molecular weight: 17,000), Elitel KT-9511 (manufactured by Unitika Ltd., number average molecular weight: 17,000), and Vylonal MD-2000 (manufactured by Toyobo Co., Ltd., number average molecular weight: 18,000).

[0082] [Polyurethane resin] The polyurethane resin used as the fixing resin may have a hydrophilic group. Examples of the hydrophilic group include a carboxy group (-COOH) and its salts, and a sulfonic acid group (-SO 3 H) and salts thereof. The above salts include alkali metal salts such as sodium salts and potassium salts, and amine salts. Of the above hydrophilic groups, a carboxy group or a salt thereof is preferred.

[0083] The polyurethane resin is preferably an aqueous dispersion in which a self-emulsifying polyurethane having a water-soluble functional group in its molecule is dispersed in an aqueous solvent, or an aqueous dispersion in which a forced-emulsifying polyurethane emulsified under strong mechanical shearing force in combination with a surfactant is dispersed in an aqueous solvent. The polyurethane resin in the aqueous dispersion can be obtained by reacting a polyol with an organic polyisocyanate and a hydrophilic group-containing compound.

[0084] Examples of polyols that can be used in preparing the aqueous dispersion of the polyurethane resin include polyester polyols, polyether polyols, polycarbonate polyols, and polyolefin polyols.

[0085] Examples of polyester polyols include low molecular weight polyols such as ethylene glycol, diethylene glycol, triethylene glycol, 1,2- and 1,3-propylene glycol, neopentyl glycol, 1,3- and 1,4-butanediol, 3-methylpentanediol, hexamethylene glycol, 1,8-octanediol, 2-methyl-1,3-propanediol, bisphenol A, hydrogenated bisphenol A, trimethylolpropane, and cyclohexanedimethanol; and condensates with polyvalent carboxylic acids such as succinic acid, glutaric acid, adipic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, tetrahydrofuran acid, endomethinetetrahydrofuran acid, and hexahydrophthalic acid.

[0086] Examples of polyether polyols include polyethylene glycol, polypropylene glycol, polyethylene polytetramethylene glycol, polypropylene polytetramethylene glycol, and polytetramethylene glycol.

[0087] Examples of polycarbonate polyols include compounds obtained by reacting carbonic acid derivatives such as diphenyl carbonate, dimethyl carbonate, or phosgene with diols. Examples of the diols include ethylene glycol, diethylene glycol, triethylene glycol, 1,2- and 1,3-propylene glycol, neopentyl glycol, 1,3- and 1,4-butanediol, 3-methylpentanediol, hexamethylene glycol, 1,8-octanediol, 2-methyl-1,3-propanediol, bisphenol A, hydrogenated bisphenol A, trimethylolpropane, and cyclohexanedimethanol.

[0088] Examples of organic polyisocyanates that can be used to prepare the aqueous dispersion of polyurethane resin include aromatic isocyanates such as tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), polymeric MDI, xylylene diisocyanate (XDI), and tetramethylxylylene diisocyanate (TMXDI); aliphatic isocyanates such as hexamethylene diisocyanate (HMDI); and alicyclic isocyanates such as isophorone diisocyanate (IPDI) and 4,4'-dicyclohexylmethane diisocyanate (hydrogenated MDI, H12MDI). These may be used alone or in combination of two or more.

[0089] Examples of hydrophilic group-containing compounds that can be used in preparing the aqueous dispersion of the polyurethane resin include carboxylic acid-containing compounds such as 2,2-dimethylolpropionic acid, 2,2-dimethylolbutanoic acid, 2,2-dimethylolbutyric acid, 2,2-dimethylolvaleric acid, and glycine, and derivatives thereof such as sodium salts, potassium salts, and amine salts; and sulfonic acid-containing compounds such as taurine (i.e., aminoethylsulfonic acid) and ethoxypolyethylene glycol sulfonic acid, and derivatives thereof such as sodium salts, potassium salts, and amine salts.

[0090] The polyurethane resin can be obtained by a known method, for example, by mixing the above-mentioned polyol, organic polyisocyanate, and hydrophilic group-containing compound and reacting them at 30 to 130° C. for 30 minutes to 50 hours.

[0091] The polyurethane resin is polymerized by extending the chain with a chain extender to become a polyurethane resin having a hydrophilic group. The chain extender is preferably water and / or an amine compound. By using water or an amine compound as the chain extender, the chain extender reacts with free isocyanate in a short time, and the isocyanate-terminated prepolymer can be efficiently extended.

[0092] Examples of the amine compound as a chain extender include aliphatic polyamines such as ethylenediamine and triethylenediamine, aromatic polyamines such as metaxylenediamine and toluylenediamine, polyhydrazino compounds such as hydrazine and adipic acid dihydrazide, etc. The amine compound may contain, together with the polyamine, a monovalent amine such as dibutylamine, methyl ethyl ketoxime, etc. as a reaction terminator to the extent that the polymerization is not significantly inhibited.

[0093] In addition, in the synthesis of polyurethane resin, a solvent that is inactive with isocyanate and can dissolve urethane prepolymer may be used. Examples of such solvents include dioxane, methyl ethyl ketone, dimethylformamide, tetrahydrofuran, N-methyl-2-pyrrolidone, toluene, and propylene glycol monomethyl ether acetate. These hydrophilic organic solvents used in the reaction step are preferably finally removed.

[0094] In addition, in the synthesis of polyurethane resins, catalysts such as amine catalysts (e.g., triethylamine, N-ethylmorpholine, triethyldiamine, etc.), tin-based catalysts (e.g., dibutyltin dilaurate, dioctyltin dilaurate, tin octoate, etc.), and titanium-based catalysts (e.g., tetrabutyl titanate, etc.) may be added to promote the reaction.

[0095] The number average molecular weight of the polyurethane resin is preferably as large as possible by introducing a branched structure or an internal crosslinked structure, and the number average molecular weight is preferably 50,000 to 10,000,000. By setting the molecular weight within the above range, the polyurethane resin becomes less soluble in a solvent, so that a coating film with excellent weather resistance and water resistance can be obtained. In this specification, the number average molecular weight (Mn) is a value measured by gel permeation chromatography (GPC). The number average molecular weight (Mn) can be determined, for example, from a calibration curve prepared with a polystyrene standard sample using Shimadzu Corporation's "RID-6A" (column: Tosoh Corporation's "TSK-GEL", solvent: tetrahydrofuran (THF), column temperature: 40°C).

[0096] The polyurethane resin may be a commercially available product, for example, a dispersion in which the polyurethane resin is dispersed in an aqueous solvent as an aqueous dispersion.

[0097] Commercially available examples of the dispersion liquid of the polyurethane resin include WBR-016U (manufactured by Taisei Fine Chemical Co., Ltd.), Superflex 620, Superflex 650, Superflex 500M, Superflex E-2000 (all manufactured by Daiichi Kogyo Seiyaku Co., Ltd., "Superflex" is a registered trademark of the company), Permarin UC-20 (manufactured by Sanyo Chemical Industries, Ltd., "Permarin" is a registered trademark of the company), Parasurf UP-22 (manufactured by Ohara Palladium Chemical Co., Ltd.), and Evaphanol HA-560 (manufactured by Nicca Chemical Co., Ltd.).

[0098] [Polyacrylic resin] Examples of the polyacrylic resin used as the fixing resin include a (co)polymer of a (meth)acrylic acid ester component, and a copolymer of a (meth)acrylic acid ester component and a polymerizable component other than a (meth)acrylic acid ester component, such as a styrene component.

[0099] Examples of the (meth)acrylic acid ester component include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, cyclohexyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, isobornyl (meth)acrylate, benzyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, Examples of suitable acrylate crosslinkers include acrylate crosslinkers, ...

[0100] Examples of the styrene component include styrene, 4-methylstyrene, 4-hydroxystyrene, 4-acetoxystyrene, 4-acetylstyrene, and styrenesulfonic acid, etc. These components may be used alone or in combination of two or more kinds.

[0101] The number average molecular weight (Mn) of the polyacrylic resin is preferably 1000 to 50000, and more preferably 2000 to 20000. When the number average molecular weight (Mn) of the polyacrylic resin is 1000 or more, the cohesive force of the coating film is strong and the adhesion is improved, whereas when it is 50000 or less, the solubility in organic solvents is good, and miniaturization of the particle size of the emulsion dispersion is promoted.

[0102] The polyacrylic resin may be a commercially available product, for example, a dispersion in which the polyacrylic resin is dispersed in an aqueous solvent as an aqueous dispersion.

[0103] Examples of commercially available dispersions of the polyacrylic resin include Delpet 60N and 80N (manufactured by Asahi Kasei Corporation, "Delpet" is a registered trademark of the company), Dianale BR52, BR80, BR83, BR85, and BR88 (manufactured by Mitsubishi Chemical Corporation, "Dianale" is a registered trademark of the company), KT75 (manufactured by Denka Company, Ltd.), Vinyblan 2680, 2682, 2684, and 2685 (manufactured by Nissin Chemical Industry Co., Ltd., "Vinyblan" is a registered trademark of the company), and Mowinyl 6800D (manufactured by Japan Coating Resins).

[0104] Among these, it is preferable that the fixing resin contains an acid structure. If the fixing resin contains an acid structure, it becomes possible to disperse in an aqueous solvent without the addition of a surfactant, that is, self-emulsification becomes possible, and the water resistance of the coating film is improved. Such self-emulsifying resins can be dispersed and stabilized in an aqueous solvent only by the ionicity of the molecules. Examples of acid structures include a carboxyl group (-COOH), a sulfonic acid group (-SO 3 The acid structure may be present in a side chain or at the end of the resin.

[0105] It is preferable that the acid structure is partially or entirely neutralized. By neutralizing the acid structure, the water dispersibility of the resin can be improved. As an example of a neutralizing agent for neutralizing the acid structure, organic amines are preferable, and it is preferable to use organic amines such as trimethylamine, triethylamine, tripropylamine, tributylamine, N-methyldiethanolamine, and triethanolamine.

[0106] (Pigments) The pigment contained in the ink according to the present invention may be any of conventionally known organic and inorganic pigments, including 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, dioxandine 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.

[0107] Specific examples of organic pigments that can be preferably used include the following pigments.

[0108] Examples of pigments for magenta or red include CI Pigment Red 2, CI Pigment Red 3, CI Pigment Red 5, CI Pigment Red 6, CI Pigment Red 7, CI Pigment Red 15, CI Pigment Red 16, CI Pigment Red 48:1, CI Pigment Red 53:1, CI Pigment Red 57:1, CI Pigment Red 122, CI Pigment Red 123, CI Pigment Red 139, CI Pigment Red 144, CI Pigment Red 149, CI Pigment Red 166, CI Pigment Red 177, CI Pigment Red 178, CI Pigment Red 202, CI Pigment Red 222, and CI Pigment Violet 19.

[0109] Examples of pigments for orange or yellow include CI Pigment Orange 31, CI Pigment Orange 43, CI Pigment Yellow 12, CI Pigment Yellow 13, CI Pigment Yellow 14, CI Pigment Yellow 15, CI Pigment Yellow 15:3, CI Pigment Yellow 17, CI Pigment Yellow 74, CI Pigment Yellow 93, CI Pigment Yellow 128, CI Pigment Yellow 94, CI Pigment Yellow 138, and CI Pigment Yellow 155. In particular, CI Pigment Yellow 155 is preferred in terms of the balance between color tone and lightfastness.

[0110] Examples of pigments for green or cyan include CI Pigment Blue 15, CI Pigment Blue 15:2, CI Pigment Blue 15:3, CI Pigment Blue 16, CI Pigment Blue 60, CI Pigment Green 7, and the like.

[0111] Examples of black pigments include CI Pigment Black 1, CI Pigment Black 6, and CI Pigment Black 7.

[0112] The pigment content in the ink of the present invention is within the range of 2 to 10% by mass. If the pigment content is within the above range, the ink functions as an inkjet ink, and high-quality image formation is possible while maintaining good ejection properties. The pigment content is preferably within the range of 3 to 7% by mass.

[0113] (Pigment dispersant) The ink of the present invention optionally contains a pigment dispersant to disperse the pigment. The pigment dispersant is not particularly limited, but is preferably a polymer dispersant having an anionic group, and is preferably one having a number average molecular weight in the range of 5,000 to 200,000.

[0114] Examples of pigment dispersants include block copolymers and random copolymers having a structure derived from two or more monomers selected from styrene, styrene derivatives, vinylnaphthalene derivatives, acrylic acid, acrylic acid derivatives, maleic acid, maleic acid derivatives, itaconic acid, itaconic acid derivatives, fumaric acid, and fumaric acid derivatives, as well as salts thereof, polyoxyalkylenes, and polyoxyalkylene alkyl ethers.

[0115] The pigment dispersant preferably has an acryloyl group and an acidic group. The acidic group is preferably neutralized with a neutralizing base before addition. The neutralizing base is not particularly limited, but is preferably an organic base such as ammonia, monoethanolamine, diethanolamine, triethanolamine, or morpholine.

[0116] The amount of the pigment dispersant added is preferably within a range of 10 to 100% by mass, and more preferably within a range of 10 to 40% by mass, based on the pigment.

[0117] It is particularly preferred that the pigment has a form of a so-called capsule pigment in which the pigment is coated with the pigment dispersant. As a method for coating the pigment with the pigment dispersant, various known methods can be used, and preferred examples thereof include a phase inversion emulsification method, an acid precipitation method, and a method in which the pigment is dispersed in a polymerizable surfactant, a monomer is supplied thereto, and the monomer is coated while being polymerized.

[0118] A particularly preferred method is to dissolve the pigment dispersant in an organic solvent such as methyl ethyl ketone, partially or completely neutralize the acidic groups in the resin with a base, add the pigment and ion-exchanged water, disperse the pigment, remove the organic solvent, and add water as necessary to prepare the dispersion.

[0119] The average particle size of the pigment in the dispersed state in the ink is preferably 50 nm or more and less than 200 nm. This can improve the dispersion stability of the pigment and the storage stability of the ink. The particle size of the pigment can be measured by a commercially available particle size measuring device using a dynamic light scattering method, an electrophoresis method, or the like, but the measurement by the dynamic light scattering method is simple and can measure the particle size range with high accuracy.

[0120] The pigment can be used by dispersing it with a pigment dispersant and other additives required for various desired purposes using a dispersing machine.

[0121] As the dispersing machine, a conventionally known ball mill, sand mill, line mill, high-pressure homogenizer, etc. can be used. Among them, dispersing the pigment with a sand mill is preferable because it results in a sharp particle size distribution. The material of the beads used for the sand mill dispersion is not particularly limited, but is preferably zirconia or zircon from the viewpoint of preventing the generation of bead fragments and contamination of ion components. Furthermore, the diameter of the beads is preferably within the range of 0.3 to 3 mm.

[0122] (Water-based solvent) The ink of the present invention contains an aqueous solvent. The aqueous solvent contains water as an essential solvent, and preferably contains a known aqueous solvent for viscosity adjustment and the like. When the aqueous solvent contains an aqueous solvent, it is preferable to adjust the type and amount of the aqueous solvent to be combined with water so that the temperature-responsive polymer has a lower critical solution temperature with respect to the aqueous solvent.

[0123] The water contained in the ink according to the present invention is not particularly limited, and may be ion-exchanged water, distilled water, or pure water.

[0124] The aqueous solvent contained in the ink is preferably an aqueous solvent that, when used in combination with water, does not significantly change the LCST of the temperature-responsive polymer in an aqueous solvent from the LCST of the temperature-responsive polymer in water. As described above, the difference between the LCST of the temperature-responsive polymer in an aqueous solvent and the LCST of the temperature-responsive polymer in water is preferably within approximately 10°C.

[0125] Examples of the aqueous solvent include alcohols, polyhydric alcohols, amines, amides, glycol ethers, and 1,2-alkanediols having 4 or more carbon atoms.

[0126] Examples of alcohols include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol, t-butanol, 3-methoxy-1-butanol, 3-methoxy-3-methylbutanol, 1-octanol, 2-octanol, n-nonyl alcohol, tridecyl alcohol, n-undecyl alcohol, stearyl alcohol, oleyl alcohol, and benzyl alcohol.

[0127] Examples of polyhydric alcohols include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycols having 5 or more ethylene oxide groups, propylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycols having 4 or more propylene oxide groups, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, and thiodiglycol.

[0128] Examples of amines include ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, diethylenediamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, and tetramethylpropylenediamine.

[0129] Examples of amides include formamide, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0130] Examples of glycol ethers include ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, and tripropylene glycol monomethyl ether.

[0131] Examples of 1,2-alkanediols having 4 or more carbon atoms include 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol, and 1,2-heptanediol.

[0132] Particularly preferred aqueous solvents are polyhydric alcohols, which can effectively suppress bleeding during high-speed printing. Specifically, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, and tripropylene glycol are preferred.

[0133] The ink may contain one or a combination of two or more selected from these aqueous solvents.

[0134] The water content in the ink of the present disclosure is preferably within a range of 20 to 80% by mass, more preferably within a range of 40 to 70% by mass, based on the total mass of the ink. The aqueous solvent content in the ink is preferably within a range of 10 to 60% by mass, based on the total mass of the ink. The content ratio of water and aqueous solvent in the ink is preferably adjusted so that the LCST of the temperature-responsive polymer with respect to the aqueous solvent is within a range of the LCST of the temperature-responsive polymer with respect to water ±10°C.

[0135] In the ink of the present disclosure, it is preferable that the ink contains substantially only an aqueous solvent as a solvent, i.e., does not contain a non-aqueous solvent. The content of the aqueous solvent in the ink is preferably within a range of 50 to 95% by mass, more preferably within a range of 50 to 90% by mass, as the total content of water and the aqueous solvent.

[0136] (Thixotropic agent) The ink of the present disclosure may optionally contain a thixotropy-imparting agent. The thixotropy-imparting agent is used for the purpose of further enhancing the effect of maintaining good ejection properties of the ink of the present disclosure while forming a high-quality image by imparting thixotropy to the ink, that is, low viscosity at high shear and high viscosity at low shear.

[0137] The thixotropy-imparting agent can be any material that can impart thixotropy to the ink without any particular limitation. The thixotropy-imparting agent is preferably in a particulate form (however, the particulate form includes a fibrous form), and more preferably has an aspect ratio of 20 or more.

[0138] When the thixotropy-imparting agent is in the form of particles, the shape is preferably elliptical, scaly, plate-like, needle-like, fibrous, etc. The aspect ratio of the thixotropy-imparting agent, which indicates the ratio of the major axis to the minor axis, is preferably 20 or more. When the aspect ratio is 20 or more, thixotropy is easily imparted by the ink. The major axis of the thixotropy-imparting agent is preferably 2 μm or less. When the major axis of the thixotropy-imparting agent exceeds 2 μm, the inkjet ejection property may be affected.

[0139] In this specification, the cross section for measuring the aspect ratio of the thixotropic agent is a cross section parallel to the length direction of the particle and cut in the thickness direction. The aspect ratio is a value calculated from the average particle long diameter and average particle short diameter of 50 particles obtained from the cross section. Here, when the particle shape is scaly or plate-like, the short diameter is the thickness of the particle, and the long diameter is the length of the long side of the cross section for measuring the aspect ratio of the particle, or the long side length or maximum diameter when the particle is viewed in plan. When the particle shape is needle-like or fibrous, the long diameter is the length of the particle, and the short diameter is the long diameter of the cross section perpendicular to the length direction of the particle, or the maximum width when the particle is viewed in plan.

[0140] Examples of the material of the thixotropic agent include polysaccharides, inorganic particles, etc. Specific examples of the polysaccharides include cellulose, chitin, chitosan, xanthan gum, welan gum, succinoglycan, guar gum, locust bean gum and derivatives thereof, glycomannan, agar, carrageenan, etc.

[0141] The polysaccharide is preferably a natural polysaccharide having a weight-average molecular weight of about several million, specifically, xanthan gum, guar gum, carrageenan, etc.

[0142] In addition, in the ink of the present disclosure, as a thixotropy-imparting agent, polysaccharide nanofibers are preferably used, which are obtained by extremely finely breaking down aggregates of polysaccharides, such as those from trees and the shells of crustaceans, such as crabs and shrimp, into fibers by a conventionally known method, such as an oxidation treatment using a catalyst, or a mechanical treatment using a grinder, etc. The polysaccharide in the polysaccharide nanofiber is preferably at least one of cellulose, chitin, and chitosan, and cellulose is more preferable.

[0143] In this specification, the term "nanofiber" refers to a fiber having a width of about 1 to 100 nm and an aspect ratio of 100 or more. The length and width of the nanofiber can be measured, for example, using an electron microscope. The width of the nanofiber may be measured, for example, by measuring the width in a plan view, or by measuring the diameter of a cross section perpendicular to the length direction of the nanofiber. In either case, the "width" of the nanofiber is the average of the maximum widths of 50 nanofibers. The "length" of the nanofiber is the average length of 50 nanofibers. The aspect ratio of the nanofiber is calculated by dividing the length by the width.

[0144] In the ink according to the present disclosure, when polysaccharide nanofibers are used as the thixotropic agent, nanofibers of smaller size are preferred. The width of the nanofiber is preferably 1 to 50 nm, more preferably 1 to 5 nm. The length of the nanofiber is preferably 0.5 to 2 μm, more preferably 1 to 5 μm, but is not limited thereto. The aspect ratio of the nanofiber is more preferably within the range of 100 to 400, and even more preferably within the range of 100 to 300.

[0145] In polysaccharide aggregates, polysaccharides such as cellulose, chitin, and chitosan exist in a state where structural units called microfibrils are bound together. These microfibrils are 3 to 4 nm wide and several μm long (e.g., 2 to 5 μm), but it is difficult to unravel them one by one. When polysaccharide aggregates are mechanically crushed by most conventional methods, nanofibers with a width of about 20 to 50 nm are obtained. In the present invention, such nanofibers may be used as polysaccharide nanofibers, but it is more preferable to use TEMPO oxidized nanofibers that have been unraveled by TEMPO oxidation into finer units, for example, microfibril units.

[0146] TEMPO oxidation is an oxidation reaction catalyzed by 2,2,6,6-tetramethyl-1-piperidine-oxy radical (TEMPO). By oxidizing polysaccharide aggregates in the presence of TEMPO, extremely fine nanofibers with a width of, for example, 3 to 4 nm and a length of several μm (for example, 2 to 5 μm) equivalent to microfibrils can be obtained.

[0147] The cellulose nanofiber used as the thixotropic agent is obtained by converting cellulose into nanofibers. Examples of the form of nanofibered cellulose include powdered cellulose and microcrystalline cellulose.

[0148] Suitable examples of cellulose nanofibers that can be used include LeoCrysta (registered trademark) manufactured by Daiichi Kogyo Seiyaku Co., Ltd., TEMPO oxidized cellulose nanofiber, Cellenpia TC-01A, Cellenpia TC-02X ("Cellenpia" is a registered trademark) manufactured by Nippon Paper Industries Co., Ltd., IMa-10002, BMa-10002, WMa-10002, AMa-10002, FMa-10002 manufactured by Sugino Machine Ltd., ELEX-☆ and ELEX-S manufactured by Daio Paper Co., Ltd., and AuroVisco manufactured by Oji Paper Co., Ltd.

[0149] As the inorganic particles, particles of various natural or synthetic clay minerals are preferred. As the clay mineral, smectite clay minerals are preferred. Smectite clay minerals are classified as layered silicate minerals or phyllosilicates of bentonite group minerals. Smectite clay minerals are classified into montmorillonite subgroup and saponite subgroup according to the layered structure. The montmorillonite subgroup includes montmorillonite, nontronite, and beidellite. The saponite subgroup includes hectorite, saponite, and sauconite.

[0150] The smectite clay mineral may be a natural or synthetic product. The smectite clay mineral is a layered material in which platelets are stacked, and when used as a thixotropic agent, it is usually used as delaminated plate-like particles. When the smectite clay mineral is synthetic, it has a smaller aspect ratio and a smaller impurity content than natural products.

[0151] The plate-like particles of the smectite clay mineral preferably have a thickness in the range of 0.2 to 3.0 nm and a length in the range of 10 to 150 nm. More preferably, the plate-like particles have a thickness in the range of 0.2 to 2.0 nm and a length in the range of 10 to 125 nm. The aspect ratio is the length of the plate-like particle divided by the thickness, and is preferably 20 or more. More preferably, the aspect ratio is in the range of 20 to 200.

[0152] The length and thickness of the plate-like particle can be measured, for example, using an electron microscope. The thickness of the plate-like particle is, for example, the average value of the thicknesses of 50 plate-like particles measured at a specific cross section. The "length" of the plate-like particle is the average value of the length of 50 plate-like particles measured as the maximum diameter when viewed in plan. The aspect ratio of the plate-like particle is calculated by dividing the length by the thickness.

[0153] As the smectite clay mineral, for example, Laponite (manufactured by Big Chemie), a synthetic layered silicate, can be used. Laponite is a synthetic low-charge clay whose structure and chemical composition are close to that of the natural smectite clay mineral hectorite. The main particles of Laponite are disc-shaped with a maximum diameter of 30 nm and a thickness of 1 nm.

[0154] As the smectite clay mineral, commercially available products may be used, such as Laponite RD (manufactured by BYK-Chemie Co., Ltd.), Kunipia F and Kunipia G, which are refined bentonites manufactured by Kunimie Kogyo Co., Ltd., and the like.

[0155] Furthermore, as the inorganic particles, nanofibers, such as alumina nanofibers (minor diameter 4 nm, major diameter 1400 nm) manufactured by Kawaken Fine Chemicals, may be used.

[0156] The content of the thixotropy-imparting agent in the ink of the present disclosure is preferably within a range of 0.01 to 1 mass % relative to the total amount of the ink, and more preferably within a range of 0.08 to 0.5 mass %, from the viewpoint of imparting thixotropy to the ink and further enhancing the effects of the present invention.

[0157] In the ink of the present disclosure, the thixotropic agent may be used alone or in combination of two or more. In the ink of the present invention, the thixotropic agent is preferably made of two or more materials. Furthermore, one of the two or more materials is preferably a smectite clay mineral. Preferable combinations of thixotropic agents include a combination of cellulose nanofibers and smectite clay minerals, and a combination of xanthan gum and smectite clay minerals. In particular, a combination of cellulose nanofibers and smectite clay minerals is preferable.

[0158] It is believed that even when cellulose nanofibers and smectite clay minerals are used alone, they can impart elastic properties to the ink by forming a specific gel structure, for example, at an ink drying rate of 20%. As a result, inks containing cellulose nanofibers or smectite clay minerals can easily achieve the properties (1-4) and (1-5) described below. Furthermore, the use of cellulose nanofibers and smectite clay minerals in combination further enhances the above-mentioned elastic properties, which is preferable.

[0159] The ratio of smectite clay minerals to other thixotropic agents can be selected according to the ink viscosity and thixotropy, but the mass ratio of smectite clay minerals to other thixotropic agents can be adjusted within the range of 10:1 to 1:10. By combining them, the thixotropy of the ink is greatly improved and image quality is improved compared to adding each agent alone. The reason for the improved thixotropy is speculation, but it is thought that the smectite clay minerals carry an electric charge, and the smectite clay minerals and other thixotropic agents electrically associate to form a structure.

[0160] (Surfactant) The ink can optionally contain a surfactant, which can improve the ejection stability of the ink and control the spread (dot diameter) of the ink droplets that land on the substrate.

[0161] The surfactant may be used without particular limitation as long as it does not impair the effects of the present invention. However, when an anionic compound is contained in other components of the ink, the ionicity of the surfactant is preferably anionic, nonionic, or betaine type.

[0162] In the present invention, fluorine-based or silicone-based surfactants having high static surface tension reducing ability, anionic surfactants such as dioctyl sulfosuccinate having high dynamic surface tension reducing ability, and nonionic surfactants such as relatively low molecular weight polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, acetylene glycols, Pluronic (registered trademark) type surfactants, and sorbitan derivatives are preferably used. It is also preferable to use a fluorine-based or silicone-based surfactant in combination with a surfactant having high dynamic surface tension reducing ability.

[0163] By adding a silicone-based or fluorine-based surfactant as the surfactant, it is possible to further suppress ink mixing on substrates made of various hydrophobic resins such as PVC sheets, and substrates with slow absorption such as printing paper, thereby obtaining high-quality printed images.

[0164] The silicone surfactant is preferably a polyether-modified polysiloxane compound, such as KF-351A and KF-642 manufactured by Shin-Etsu Chemical Co., Ltd., and BYK345, BYK347, and BYK348 manufactured by BYK-Chemie.

[0165] The fluorine-based surfactant means a surfactant in which part or all of the hydrogen atoms bonded to the carbon of the hydrophobic group of a normal surfactant are replaced with fluorine. Among these, those having a perfluoroalkyl group in the molecule are preferred.

[0166] Some of the above fluorinated surfactants are commercially available from Dainippon Ink and Chemicals under the trade name Megafac F, from Asahi Glass Co., Ltd. under the trade name Surflon, from Minnesota Mining and Manufacturing Company under the trade name Fluorad FC, from Imperial Chemical Industries, Inc. under the trade name Monflor, from E.I. duPont Nemelas & Co. under the trade name Zonyls, and from Farbewerke-Hoechst under the trade name Licowet VPF.

[0167] The content of the surfactant in the ink is not particularly limited, but is preferably within the range of 0.1 to 5.0% by mass.

[0168] (Other additives) In addition to the above-described additives, various well-known additives such as viscosity adjusters, resistivity adjusters, film-forming agents, ultraviolet absorbers, antioxidants, anti-fading agents, anti-mold agents, and anti-rust agents may be appropriately selected and used in the ink of the present disclosure, as necessary, within a range that does not impair the effects of the present invention, in accordance with the purpose of improving ejection stability, compatibility with print heads and ink cartridges, storage stability, image storage stability, and other performances.

[0169] Specific examples thereof include oil droplet fine particles such as liquid paraffin, dioctyl phthalate, tricresyl phosphate, and silicone oil; ultraviolet absorbents described in JP-A-57-74193, JP-A-57-87988, JP-A-62-261476, and the like; discoloration inhibitors described in JP-A-57-74192, JP-A-57-87989, JP-A-60-72785, JP-A-61-146591, JP-A-1-95091, JP-A-3-13376, and the like; and fluorescent brightening agents described in JP-A-59-42993, JP-A-59-52689, JP-A-62-280069, JP-A-61-242871, JP-A-4-219266, and the like.

[0170] The ink is prepared by mixing the above-mentioned components so as to obtain the above-mentioned content. Preferably, the pigment is dispersed in a part of the aqueous solvent with a pigment dispersant, and then mixed with the other components. When a fixing resin is contained, the fixing resin is dispersed in a part of the aqueous solvent with a surfactant added as necessary, and then mixed with the other components.

[0171] <Physical properties of inkjet ink> The ink-jet ink of the present disclosure preferably satisfies the following conditions (1-1) and (1-2) regarding viscosity characteristics, and more preferably satisfies condition (1-3) in addition to these.

[0172] (1-1) The viscosity at a shear rate of 1000 (1 / s) at 25°C is 15 mPa s or less. (1-2) The viscosity of the temperature-responsive polymer at a shear rate of 1 (1 / s) at any temperature within the range of the lower critical solution temperature of the temperature-responsive polymer in water ±10°C is 45 mPa s or more. In other words, the maximum viscosity of the temperature-responsive polymer at a shear rate of 1 (1 / s) within the range of the lower critical solution temperature of the temperature-responsive polymer in water ±10°C is 45 mPa s or more. (1-3) When the ink drying rate is 20%, the viscosity at a shear rate of 1 (1 / s) at any temperature within the range of the lower critical solution temperature of the temperature-responsive polymer in water ±10°C is 100 mPa s or more. In other words, when the ink drying rate is 20%, the maximum viscosity at a shear rate of 1 (1 / s) within the range of the lower critical solution temperature of the temperature-responsive polymer in water ±10°C is 100 mPa s or more.

[0173] In the above (1-1) to (1-3), the viscosity can be measured by a rotational viscometer. An example of the rotational viscometer is MCR-102 manufactured by Anton Paar. In this specification, the viscosity is measured at 25°C unless otherwise specified.

[0174] An ink drying rate of 20% refers to the state in which the aqueous solvent has been removed from the inkjet ink so that the mass is 80% of the initial mass. The ink drying rate can be calculated from the mass before and after drying at a temperature condition of 60°C using the following formula (A).

[0175] Formula (A) Ink drying rate [%] = (W BEFORE -W AFTER ) / W BEFORE ×100 However, in formula (A), W BEFORE W represents the mass of the ink before drying (initial mass). AFTER indicates the mass of the ink after drying. Specifically, the ink is dried by dropping about 100 mL of ink onto a glass substrate, weighing it to determine the mass of the ink before drying, and then heating it to 60°C on a hot plate that allows for mass measurement.

[0176] To obtain the viscosity when the ink drying rate is 20%, the drying is stopped when the mass of the ink becomes 80% of the initial mass (mass before drying), and the viscosity is measured using the dried ink obtained.

[0177] With regard to the above (1-1), it is more preferable that the ink of the present invention has a viscosity of 10 mPa s or less at a shear rate of 1000 (1 / s). There is no particular lower limit to the viscosity at a shear rate of 1000 (1 / s), but from the viewpoint of inkjet ejection properties, it is preferably about 5 mPa s.

[0178] With regard to (1-2) above, the ink of the present invention preferably has a viscosity of 70 mPa s or more, and more preferably 100 mPa s or more, at a shear rate of 1 (1 / s) at any temperature within a range of ±10° C. between the lower critical solution temperature of the temperature-responsive polymer in water. There is no particular upper limit to the viscosity in this case, but from the viewpoint of ease of head maintenance, it is preferably about 1000 mPa s.

[0179] With regard to (1-3) above, the ink of the present invention preferably has a viscosity of 100 mPa s or more, and more preferably 150 mPa s or more, at a shear rate of 1 (1 / s) at any temperature within a range of ±10°C of the lower critical solution temperature of the temperature-responsive polymer in water at an ink drying rate of 20%. There is no particular upper limit to the viscosity in this case, but from the viewpoint of ease of head maintenance, it is preferably about 1000 mPa s.

[0180] Here, in the ink of the present disclosure, if the viscosity at a shear rate of 1 (1 / s) at any temperature within a range of ±10°C of the lower critical solution temperature of the temperature-responsive polymer in water is at least 45 mPa s, then when the ink impacts on a substrate, the occurrence of color mixing and the like can be easily suppressed with only slight temperature adjustment and without removing the aqueous solvent from the ink.

[0181] The viscosity of the ink increases as the ink drying rate increases. In an ink that satisfies the above (1-3), by setting the ink drying rate to a maximum of 20%, a viscosity of 100 mPa s can be achieved at a shear rate of 1 (1 / s) at any temperature within a range of ±10°C of the lower critical solution temperature of the temperature-responsive polymer in water. This makes it possible to suppress the occurrence of color mixing and other problems when the ink lands on the substrate, without removing excessive amounts of the water-based solvent from the ink, by simply making slight temperature adjustments.

[0182] The inkjet ink of the present disclosure preferably further satisfies at least one of the following conditions (1-4) and (1-5), and more preferably satisfies both of them.

[0183] (1-4) When the ink drying rate is 20%, and the strain is changed at an angular frequency of ω10 rad / s and an oscillation angle of γ1 to 1000% at any temperature within a range of ±10°C of the lower critical solution temperature of the temperature-responsive polymer in water, the loss tangent (tan δ) at a strain of 1% is less than 1. (1-5) When the ink drying rate is 20%, and the strain is changed at an angular frequency of ω10 rad / s and an oscillation angle of γ1 to 1000% at any temperature within a range of ±10°C of the lower critical solution temperature of the temperature-responsive polymer in water, the crossover strain between the storage modulus and the loss modulus is 20% or more.

[0184] The loss tangent (tan δ) in (1-4) and the storage modulus and loss modulus in (1-5) can be measured by a rheometer (viscoelasticity measuring device). An example of the rheometer is MCR-102 manufactured by Anton Paar. In this specification, the loss tangent may be simply referred to as "tan δ".

[0185] In this specification, tan δ, storage modulus, and loss modulus can be measured using a rheometer, specifically, MCR-102 manufactured by Anton Paar, in oscillation mode, at any temperature within the range of the lower critical solution temperature of the temperature-responsive polymer in water ±10°C, under measurement conditions of an angular frequency ω of 10 rad / s and an oscillation angle γ of 1 to 1000%. During measurement, the oscillation angle γ of the cone plate of the rheometer is changed to distort the measurement sample. Here, since the measurement sample is distorted following the oscillation angle γ, the oscillation angle γ of the cone plate and the distortion of the measurement sample have the same value.

[0186] In (1-4), the tan δ at 1% strain is used as an index in the above measurement. If tan δ is less than 1 at 1% strain under the measurement conditions, the ink has more elastic properties, and compared with inks with similar viscosities, the pinning properties are better and image quality is improved. In (1-4), tan δ at 1% strain is more preferably 0.8 or less, and even more preferably 0.6 or less.

[0187] In (1-5), the crossover strain between the storage modulus and the loss modulus when the strain is changed in the above measurement is used as an index. Specifically, the crossover strain indicates the strain value (%) at the intersection of a graph in which the vertical axis is the storage modulus (Pa) and the horizontal axis is the strain (%), both of which are logarithmic, and a graph in which the vertical axis is the loss modulus (Pa) and the horizontal axis is the strain (%), both of which are logarithmic. If the crossover strain (%) is 20% or more under the measurement conditions, the ink will have more elastic properties, and image quality will be improved as described above. It is more preferable that the crossover strain is 30% or more, and even more preferable that it is 40% or more.

[0188] In (1-4), when a similar measurement is performed not with an ink drying rate of 20% but with an ink drying rate of 0%, i.e., with the ink of the present invention, the loss tangent (tan δ) at a strain of 1% is preferably less than 1, more preferably 0.8 or less, and even more preferably 0.6 or less.

[0189] Furthermore, in (1-5), when a similar measurement is performed not with an ink drying rate of 20% but with an ink drying rate of 0%, i.e., for the ink of the present invention, the crossover distortion is preferably 20% or more, more preferably 30% or more, and even more preferably 40% or more.

[0190] The ink of the present disclosure has almost no difference in tan δ and crossover strain when the ink drying rate is 0% and when the ink drying rate is 20%. In other words, even when the ink drying rate is 0%, the ink behaves elastically within a range of ±10°C of the lower critical solution temperature of the temperature-responsive polymer in water, making it easy to pin and forming a high-quality image.

[0191] [Image formation method overview] The image forming method of the present disclosure is an image forming method having a landing step in which droplets of inkjet ink are ejected from an inkjet head having an ink circulation mechanism and landed on a substrate, and has the following features. (2-1) The inkjet ink contains an aqueous solvent, a pigment, and a thixotropic agent, and is circulated within the inkjet head so that the viscosity of the ink is 15 mPa·s or less. (2-2) The landing process is carried out so that the mass loss rate of the droplets when they land on the substrate or immediately after landing is within 20% from that of the inkjet ink and the viscosity is 100 mPa s or more.

[0192] The image forming method of the present disclosure usually further includes a drying step of removing the aqueous solvent from the ink droplets on the substrate after the landing step. The drying step allows the desired image to be formed on the substrate. The image forming method of the present disclosure may also include a step of forming a primer layer on the surface of the substrate before forming a coating film with the ink (hereinafter, also referred to as a "primer layer forming step"). In this case, the ink droplets are landed on the primer layer in the landing step.

[0193] (Primer layer formation process) The primer layer can be formed by applying a primer ink containing a resin and a solvent onto a substrate and drying it. Alternatively, the primer layer may be formed by applying a primer ink containing an active energy polymerizable compound and a polymerization initiator and irradiating the coating with active energy.

[0194] The method of applying the primer ink is not particularly limited, and may be any method such as roll coating, spin coating, spray coating, dipping, screen printing, inkjet, gravure printing, offset printing, etc. Among these, when the surface roughness of the substrate is to be finely controlled, the screen printing method or inkjet method is preferred, and the inkjet method is particularly preferred.

[0195] Furthermore, after the primer ink is applied, the method for curing or drying the coating film is appropriately selected depending on the type of primer ink, and may be, for example, a method of heating or irradiating with active energy.

[0196] (Impact process) In the landing step, if the viscosity of the ink inside the head is 15 mPa s or less in accordance with the above (2-1), the ink can be circulated in the head and ejected from the head smoothly. It is preferable that the ink is circulated in the head so that the viscosity of the ink is 10 mPa s or less.

[0197] With regard to the above (2-2), the mass reduction rate from the inkjet ink (hereinafter also simply referred to as "mass reduction rate") can be defined in the same way as the ink drying rate described above. If the mass reduction rate and viscosity of the ink droplets when they land on the substrate or immediately after they land are within the above ranges, good pinning is possible and the resulting image can be of high quality. Furthermore, adhesion of ink solids to the area around the head is suppressed, ejection defects are less likely to occur, and maintenance is easy.

[0198] Here, the above-mentioned "immediately after landing" refers to, for example, within 100 msec after the ink droplet lands on the substrate. If the mass reduction rate of the ink droplet within 100 msec after landing on the substrate is within 20% and the viscosity is 100 mPa·s or more, the above-mentioned effect is sufficiently exhibited. Hereinafter, the time when the ink droplet lands on the substrate or immediately after landing is also referred to as "at the time of landing on the substrate." The viscosity of the ink droplet when it lands on the substrate is preferably 150 mPa·s or more, more preferably 200 mPa·s or more, and even more preferably 300 mPa·s or more. The time immediately after landing is approximately 30 msec when the substrate is transported at a high speed (100 m / min), and approximately 100 msec when the substrate is transported at a high speed (50 m / min).

[0199] In the image forming method of the present disclosure, the ink or device is appropriately selected to satisfy the above conditions (2-1) and (2-2). In the image forming method of the present invention, the ink is the ink of the present invention described above, so that the conditions (2-1) and (2-2) can be achieved without any particular change to the device. That is, in the image forming method of the present invention, it is preferable to use the ink of the present invention. When the ink of the present invention is used, the condition (2-2) can be achieved, for example, within the range of the LCST of the temperature-responsive polymer ±10°C. That is, when the ink of the present invention is used, in order to satisfy the condition (2-2), it is preferable to heat the ink droplets on the substrate within the range of the LCST of the temperature-responsive polymer ±10°C in the landing step.

[0200] In the image forming method of the present disclosure, in order to satisfy the condition (2-2), it is preferable to heat the ink droplets on the substrate at a temperature in the range of 30 to 60° C. in the landing step. That is, the image forming method of the present invention may have a step of heating the ink droplets at 30 to 60° C. as necessary so that the state of the ink droplets when they land on the substrate has a mass reduction rate of 20% or less and a viscosity of 100 mPa s or more. This temperature is sufficiently low, and there is almost no concern that the ink will solidify around the head and cause ejection defects.

[0201] Heating may be performed using a non-contact heating device such as a thermostatic oven or a hot air blower, or a contact heating device such as a hot plate or a heated roller.

[0202] The heating temperature can be obtained by measuring any one of (a) the ambient temperature, such as the furnace temperature or hot air temperature, when a non-contact heating device such as a thermostatic oven or a hot air blower is used; (b) the temperature of the contact heating part, when a contact heating device such as a hot plate or a hot roller is used; or (c) the surface temperature of the ink droplets. It is more preferable to measure (c) the surface temperature of the ink droplets as the measurement location.

[0203] (drying process) The drying process is a process of removing components other than solid components such as the aqueous solvent (hereinafter also referred to as "volatile components") from the ink droplets after the landing process, and forming a coating film constituting a target image on the substrate, or on the primer layer if a primer layer is present. As described above, the ink droplets after the landing process are in a state where the mass reduction rate is within 20%. Since the inkjet ink contains, for example, about 50 to 95% by mass of the aqueous solvent, the remaining volatile components including the aqueous solvent are removed by the drying process.

[0204] In the drying step, while removing volatile components, if the ink contains a fixing resin, the drying is preferably performed under conditions such that the fixing resin does not completely fuse. The drying temperature is preferably within a range of, for example, 60 to 110°C. The drying time is preferably within a range of, for example, 5 to 60 seconds. The drying in the drying step can be performed, for example, by the same method as the heating in the landing step.

[0205] (base material) The substrate that can be used in the present invention is not particularly limited, but is preferably a non-absorbent substrate. By using a non-absorbent substrate, the effect of the image forming method of the present invention is more remarkable. In the present invention, non-absorbency means non-absorbency to water.

[0206] Examples of non-water-absorbent substrates include known plastic films. Specific examples include polyester films such as polyethylene terephthalate, polyethylene films, polypropylene films, polyamide films such as nylon, polystyrene films, polyvinyl chloride films, polycarbonate films, polyacrylonitrile films, polylactic acid films, and other biodegradable films. In addition, in order to impart gas barrier properties, moisture resistance, and aroma retention, films coated with polyvinylidene chloride on one or both sides, and films vapor-deposited with metal oxides can also be preferably used. As the non-water-absorbent film, both unstretched and stretched films can be preferably used.

[0207] In addition to these, examples of non-water-absorbent substrates include substrates made of inorganic compounds such as metals and glass.

[0208] It can also be suitably used as a packaging material for retort foods, in which a thermosetting resin is provided as a coating layer on a metal substrate. The packaging material for retort foods is made of a film in which a thermoplastic resin layer or an aluminum foil layer, such as polypropylene on the food side and polyester on the outside, is laminated to block air, moisture, and light and seal the food inside.

[0209] In the present invention, the thickness of the substrate is preferably within the range of 10 to 120 μm, more preferably 12 to 60 μm.

[0210] (Inkjet head) The image forming method of the present disclosure is applied to image formation using an inkjet head equipped with an ink circulation mechanism.

[0211] The inkjet head is not particularly limited as long as it has an ink circulation mechanism, and may be either an on-demand type or a continuous type inkjet head. Examples of on-demand type inkjet heads include electro-mechanical conversion types including single cavity type, double cavity type, bender type, piston type, share mode type and shared wall type, and electro-thermal conversion types including thermal inkjet type and bubble jet type ("Bubble Jet" is a registered trademark of Canon Inc.).

[0212] Of the above inkjet heads, inkjet heads using a piezoelectric element as the electro-mechanical conversion element used in the electro-mechanical conversion method (also called a "piezo type inkjet head") are preferable.

[0213] The inkjet head may be either a scanning type or a line type inkjet head, but the line type is preferable.

[0214] A line-type inkjet head is an inkjet head that has a length equal to or greater than the width of the printing range. As a line-type inkjet head, a single head that is equal to or greater than the width of the printing range may be used, or multiple heads may be combined to form a head that is equal to or greater than the width of the printing range.

[0215] Furthermore, a plurality of heads may be arranged in parallel so that the nozzles are arranged in a staggered arrangement, thereby increasing the resolution of the heads as a whole.

[0216] The inkjet head used in the image forming method of the present disclosure preferably includes a pressure chamber into which inkjet ink is injected via an injection path, a pressure generating means for generating pressure fluctuations in the pressure chamber, a nozzle communicating with the pressure chamber and serving as a flow path for the inkjet ink to be ejected from the pressure chamber to the outside due to the pressure fluctuations in the pressure chamber, and two or more circulation paths communicating with the pressure chamber and discharging the inkjet ink inside the nozzle and returning it to the injection path. Such an inkjet head will be described below with reference to the drawings.

[0217] Fig. 1 is a schematic diagram of the main part of an inkjet image forming apparatus 100 equipped with an example of an inkjet head that can be used in the image forming method of the present invention, and shows a partial cross section of an inkjet head 1. Note that the inkjet head etc. shown in Fig. 1 are merely examples, and the inkjet head etc. to which the image forming method of the present invention can be applied are not limited to this.

[0218] In the inkjet image forming apparatus 100, ink droplets are discharged from the inkjet head 1 onto a substrate 109 being transported in a fixed direction (sub-scanning direction) by a transport means 108, the droplets land on the substrate, and an image is formed by drying the droplets. In a one-pass type inkjet image forming apparatus, the inkjet head 1 is fixedly disposed, and while the substrate 109 is being transported, ink droplets are discharged from the nozzle 22 toward the substrate 109, the droplets land on the substrate, and an image is formed. In a scan type inkjet image forming apparatus, the inkjet head 1 is mounted on a carriage mechanism 107, and while the carriage mechanism 107 reciprocates in the main scanning direction, the ink droplets are discharged from the nozzle 22 toward the substrate 109, the droplets land on the substrate, and an image is formed. The transport means 108 and the carriage mechanism 107 are driven and controlled by the control unit 104.

[0219] Although not shown in Fig. 1, the inkjet image forming apparatus 100 has a non-contact or contact heater that adjusts the temperature of the ink droplets when they land. The heater can also be used in the drying process.

[0220] 1 shows only one inkjet head 1, but generally, multiple inkjet heads 1 for ink of each color, such as yellow (Y), magenta (M), cyan (C), black (K), etc., are mounted on the inkjet image forming apparatus 100. In the inkjet image forming apparatus 100, an ink tank 101 that stores ink and a common ink chamber 41 of the inkjet head 1 are connected by an ink transfer pipe 102 that serves as a transfer path and an ink return pipe 103 that serves as a recovery path.

[0221] A transfer pump 105a whose driving is controlled by a control unit 104 of the inkjet image forming apparatus 100 is provided in the ink transfer tube 102. When the transfer pump 105a is driven, the ink in the ink tank 101 is transferred to the inkjet head 1 through the ink transfer tube 102.

[0222] Furthermore, a transfer side sub-tank 111a is provided in the ink transfer tube 102. The transfer side sub-tank 111a is configured as a buffer space in which ink to be transferred to the inkjet head 1 is temporarily stored. The pressure of the ink in the ink transfer tube 102 can be controlled by a transfer pressure control pump 110a constituting a pressure control means via the transfer side sub-tank 111a. The transfer pressure control pump 110a is controlled by a control unit 104a in the inkjet head 1.

[0223] A return pump 105b whose driving is controlled by the control unit 104 is provided in the middle of the ink return pipe 103. When the return pump 105b is driven, the ink in the inkjet head 1 is returned to the ink tank 101 via the ink return pipe 103.

[0224] Furthermore, a return side sub-tank 111b is provided in the ink return tube 103. The return side sub-tank 111b is configured as a buffer space in which ink returned from the inkjet head 1 is temporarily stored. The pressure of ink in the ink return tube 103 can be controlled by a return pressure control pump 110b constituting a pressure control means via the return side sub-tank 111b. The return pressure control pump 110b is controlled by a control unit 104a in the inkjet head 1.

[0225] The pressure control means is not limited to being composed of the transfer pressure control pump 110a and the return pressure control pump 110b, and may be composed of any one of them. In this case, the return pressure control pump 110b serves as the first pressure control means, and the transfer pressure control pump 110a serves as the second pressure control means.

[0226] Although not particularly limited, the ink tank 101 is preferably divided into an ink transport chamber 101b and an ink return chamber 101c by a partition plate 101a that does not reach the bottom surface of the tank. In this case, one end of the ink transport tube 102 is disposed in the ink transport chamber 101b, and one end of the ink return tube 103 is disposed in the ink return chamber 101c. The partition plate 101a is provided to sufficiently degas the ink so that air bubbles contained in the ink returned to the ink return chamber 101c do not flow back into the ink transport tube 102. Since the air bubbles themselves have high buoyancy, the air bubbles are prevented from passing under the partition plate 101a and flowing into the ink transport chamber 101b. Such an embodiment is preferable when circulating ink.

[0227] Inkjet head 1 is composed of an ink manifold 4 that forms a common ink chamber 41, a wiring board 3 adhered to this ink manifold 4, a head chip 2 adhered to the underside of wiring board 3, and a nozzle plate 21 adhered to the underside of head chip 2.

[0228] The ink manifold 4 is made of a synthetic resin material or the like and is shaped like a horizontally long box having an opening 4a on its bottom surface. The opening 4a of this ink manifold 4 is closed by a wiring board 3 bonded to its bottom surface. The internal space of the ink manifold 4 becomes a common ink chamber 41 in which ink transferred from the ink tank 101 is stored. The wiring board 3 is, for example, a glass board. On this wiring board 3, a wiring pattern (not shown) is formed which is connected to a power supply circuit (not shown) via an FPC board.

[0229] An ink supply tube 5a, which serves as a flow path for supplying ink into the common ink chamber 41, is connected to the common ink chamber 41. The ink supply tube 5a is connected to the common ink chamber 41 on the side (upper side) farther from the wiring board 3. A connection part 7a is provided at the upper end side of the ink supply tube 5a. The connection part 7a is detachably connected to a connection part 106a on the inkjet image forming apparatus 100 side. The connection part 106a on the inkjet image forming apparatus 100 side is connected to the ink transport tube 102. This enables the inkjet head 1 to transport ink from the ink tank 101 and supply ink to the common ink chamber 41.

[0230] In addition, an ink recovery tube 5b, which serves as a flow path for recovering ink from the common ink chamber 41, is connected to the common ink chamber 41. The ink recovery tube 5b is connected to the common ink chamber 41 on the side (upper side) farther from the wiring board 3. A connection part 7b is provided at the upper end side of the ink recovery tube 5b. The connection part 7b is detachably connected to a connection part 106b on the inkjet image forming apparatus 100 side. The connection part 106b on the inkjet image forming apparatus 100 side is connected to an ink return tube 103. This enables the inkjet head 1 to recover ink from the common ink chamber 41 and return ink to the ink tank 101.

[0231] In the inkjet head 1, a flow path from the ink supply pipe 5a to the buffer space portion 6 midway through the ink recovery pipe 5b serves as a main flow path F1.

[0232] Fig. 2 is an enlarged cross-sectional view of the head chip 2 of the inkjet head 1. Fig. 3 is a plan view of the nozzle plate 21 of the inkjet head 1.

[0233] A plurality of ink channels (pressure chambers) 23 and a plurality of dummy channels (pseudo pressure chambers) 25 are formed in the head chip 2. Each ink channel 23 and each dummy channel 25 is a through hole drilled from the upper surface to the lower surface of the head chip 2. The upper end of each ink channel 23 communicates with a common ink chamber 41 via an injection hole 31a opened in the wiring substrate 3. Each ink channel 23 is filled with ink flowing in from the injection hole 31a due to the potential energy of the ink in the ink tank 101 and the pressure controlled by the transfer pressure control pump 110a caused by the transfer pump 105a.

[0234] The lower end of each ink channel 23 communicates with the outside (downward) via the nozzle 22. In this inkjet head 1, the area inward from the nozzle 22 is inside the ink channel 23. If a communication path exists between the ink channel 23 and the nozzle 22, the area inward from the nozzle 22 is inside the communication path. The upper end of each dummy channel 25 is closed by the wiring board 3, and the lower end is closed by the nozzle plate 21, forming a sealed air chamber. The ink channels 23 and the dummy channels 25 are arranged in one direction (the direction of the arrow X in FIG. 2) to form a channel row.

[0235] Both walls of each ink channel 23 (partitions between the ink channel 23 and the dummy channel 25) are formed by a pair of piezoelectric elements (drive walls) 24, 24 that serve as pressure generating means. The piezoelectric elements 24, 24 are shear deformed by application of a voltage from a power supply circuit (not shown) via the wiring pattern of the FPC board and the wiring board 3. The shear deformation of the piezoelectric elements 24, 24 that form both walls of the ink channel 23 causes pressure fluctuations in the ink channel 23 (reduced pressure due to expansion or increased pressure due to contraction). The pressure fluctuations (reduced pressure or increased pressure) in the ink channel 23 apply pressure to the ink inward of the nozzle 22, i.e., inside the ink channel 23, and the ink is ejected through the nozzle 22.

[0236] Two piezoelectric elements 24, 24 (a pair) are provided per ink channel 23, forming both walls of each ink channel 23. There is a gap between the piezoelectric element 24 that forms the wall of one ink channel 23 and the piezoelectric element 24 that forms the wall of an adjacent ink channel 23, and this gap is a dummy channel 25. Therefore, each ink channel 23 can be driven (reduced or increased pressure) independently.

[0237] An introduction path 425 is formed in the head chip 2. The introduction path 425 is provided at one end of a channel row formed by each ink channel 23 and each dummy channel 25, and is located outside the channel row. The introduction path 425 is a through hole drilled from the upper surface to the lower surface of the head chip 2, and the cross-sectional opening area is larger than the cross-sectional opening area of ​​one ink channel 23. The introduction path 425 has an upper end that communicates with the common ink chamber 41 via an introduction hole 31c opened in the wiring board 3, and ink flows in from the introduction hole 31c due to the potential energy of the ink in the ink tank 101 and the pressure controlled by the transfer pressure control pump 110a caused by the transfer pump 105a.

[0238] A flat nozzle plate 21 adhered to the underside of the head chip 2 has a plurality of nozzles 22 formed therein corresponding to the ink channels 23. The nozzles 22 are through holes that connect the ink channels 23 to the outside. The ink in each ink channel 23 is given an ejection pressure by the action of the piezoelectric element 24, and is ejected through the nozzles 22 toward the outside (downward) substrate. In other words, the nozzles 22 serve as flow paths for ink that is ejected from inside each ink channel 23 to the outside (downward). The underside of the nozzle plate 21 serves as the ink ejection surface 1S.

[0239] The inkjet head 1 is equipped with a nozzle circulation mechanism that discharges ink injected into the ink channel 23 from the vicinity of the nozzle 22 and returns the ink to the injection path to the ink channel 23. Each ink channel 23 is connected to two individual ink circulation paths 26a, 26a.

[0240] The individual ink circulation paths 26a and 26a communicate with the ink channel 23 at both ends in the longitudinal direction of the cross section of the ink channel 23. Since air bubbles often remain near both ends of the ink channel 23, it is preferable to provide the individual ink circulation paths 26a and 26a at both ends in the longitudinal direction of the cross section of the ink channel 23. The individual ink circulation paths 26a and 26a may communicate with the ink channel 23 at any point of the ink channel 23. The number of individual ink circulation paths 26a for one ink channel 23 may be increased or decreased, but is preferably two or more. Ink containing a temperature-responsive polymer or fixing resin is thixotropic, but if there are two or more circulation paths as described above, ink stagnation is unlikely to occur even when such ink is used, and bubbles near the nozzles are easily removed.

[0241] The individual ink circulation paths 26a and 26a are configured by a flow path forming groove 28 formed on the upper surface of the nozzle plate 21 with a starting end near the nozzle 22 and closed by the lower surface of the head chip 2.

[0242] Two introduction grooves 425a and 425a communicate with the introduction path 425. The introduction grooves 425a and 425a communicate with the introduction path 425 at both sides of the introduction path 425. The introduction grooves 425a and 425a may communicate with the introduction path 425 at any point of the introduction path 425. Furthermore, the number of introduction grooves 425a and 425a for one introduction path 425 may be increased or decreased.

[0243] Lead-in grooves 425a and 425a are formed on the upper surface of nozzle plate 21 with starting ends in the vicinity of lead-in path 425, and are closed by the lower surface of head chip 2 to form a flow path.

[0244] A common ink circulation path 421 is formed on the lower surface of head chip 2. Common ink circulation path 421 is configured by butting a groove formed on the lower surface of head chip 2 and a groove 422 formed on the upper surface of nozzle plate 21 together.

[0245] The common ink circulation path 421 is composed of a plurality of flow paths formed in the direction of the channel row (X direction). The individual ink circulation paths 26a, 26a communicating with each ink channel 23 are joined by communicating with the common ink circulation path 421. Due to the pressure difference between the inside of each ink channel 23 and the inside of the common ink circulation path 421, ink flows from each ink channel 23 to the common ink circulation path 421. In addition, the introduction grooves 425a, 425a are connected to the common ink circulation path 421. Due to the pressure difference between the inside of the introduction path 425 and the inside of the common ink circulation path 421, ink flows from the introduction path 425 to the common ink circulation path 421. Then, these flows join together to generate ink flow in the common ink circulation path 421.

[0246] The other end side of the common ink circulation path 421 is connected to the lower end of a discharge channel 424 formed in the head chip 2. The discharge channel 424 is provided at a position outside the other end side of the channel row formed by each ink channel 23 and each dummy channel 25. Since the ink flow rate in the discharge channel 424 is greater than the ink flow rate in the introduction path 425 by the amount of ink that has passed through each ink channel 23 and merges therein, the cross-sectional opening area of ​​the discharge channel 424 is made large in order not to increase the flow path resistance.

[0247] The ink discharged from the individual ink circulation path 26a communicating with the ink channel 23, which is a pressure chamber, to the common ink circulation path 421 passes through the discharge channel 424, the ink discharge chamber 412, and the ink discharge pipe 5c, reaches the buffer space portion 6, and is returned to the ink tank 101 by the above-mentioned path. Then, the ink is introduced again into the injection path to the ink channel 23.

[0248] 1, an ink discharge chamber 412 is provided in the ink manifold 4, located above the discharge channel 424. The ink discharge chamber 412 is provided adjacent to the common ink chamber 41 in the ink manifold 4. The ink discharge chamber 412 is separated from the common ink chamber 41 by a partition wall 45. The partition wall 45 can be formed integrally with the ink manifold 4.

[0249] In this way, a portion of the ink that has flowed into the ink channel 23 from the injection hole 31a (ink that is not ejected from the nozzle 22) passes through the individual ink circulation paths 26a, 26a, the common ink circulation path 421, reaches the discharge channel 424, and passes through the discharge hole 31b formed in the wiring substrate 3 to reach the ink discharge chamber 412. In addition, the ink that has flowed into the introduction path 425 from the introduction hole 31c passes through the introduction grooves 425a, 425a and the common ink circulation path 421 to reach the discharge channel 424, and passes through the discharge hole 31b to reach the ink discharge chamber 412.

[0250] An ink discharge tube 5c forming a flow path for discharging ink from the ink discharge chamber 412 is connected to the ink discharge chamber 412 via a circulation path connecting portion 5d. The circulation path connecting portion 5d is located above the discharge channel 424 and is provided at a position outside the other end side of the channel row formed by the ink channels 23 and the dummy channels 25. The upper end side of the ink discharge tube 5c merges with the ink recovery tube 5b. The ink recovery tube 5b and the ink discharge tube 5c are merged by being connected to the buffer space portion 6.

[0251] In the inkjet head 1, a flow path from the introduction path 425 and the individual ink circulation paths 26a, 26a through the common ink circulation path 421, the discharge channel 424, the discharge hole 31b, the ink discharge chamber 412, and the ink discharge pipe 5c to the buffer space portion 6 is the circulation path 423. The circulation path 423 is a flow path that communicates with the introduction path 425 and the ink channel 23, discharges the ink in the introduction path 425 and the ink channel 23, and merges with the ink recovery pipe 5b in the buffer space portion 6. However, the circulation path 423 does not need to be limited in any way as long as it discharges ink from the individual ink circulation paths 26a, 26a near the nozzle 22 and returns the ink to the injection path to the ink channel 23. Then, the part to the circulation path 423 through the introduction hole 31c and each injection hole 31a is the sub-flow path F2. EXAMPLES

[0252] The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. In the examples, the terms "parts" and "%" are used, but they represent "parts by mass" or "% by mass" unless otherwise specified.

[0253] [Examples 1 to 13, Comparative Examples 1 to 5] Using the following materials, inkjet inks of the examples and comparative examples having the compositions shown in Table I or Table II were prepared.

[0254] (Temperature-responsive polymer) -Metolose SM-04 (trade name, manufactured by Shin-Etsu Chemical Co., Ltd., methylcellulose resin, LCST for water: 55°C) -Metolose 60SH-03 (product name, manufactured by Shin-Etsu Chemical Co., Ltd., hydroxypropyl methylcellulose resin, LCST in water: 75°C) Poly(N-isopropylacrylamide) (Sigma-Aldrich, LCST in water: 35°C, weight average molecular weight: 30,000)

[0255] Magenta pigment: JM2120 (trade name, manufactured by DIC Corporation, compound name: PR202 / PV19) Pigment dispersant: Joncryl 819 (trade name: manufactured by BASF, an acrylic dispersant having a carboxyl group neutralized with sodium hydroxide, acid value 75 mg KOH / g, solid content 20% by mass) Water; Ion-exchanged water

[0256] (Aqueous Solvent) Ethylene glycol Propylene glycol Glycerin

[0257] (fixing resin) Vylonal MD-2000 (product name; manufactured by Toyobo Co., Ltd.; aqueous dispersion of polyester resin with a number average molecular weight of 18,000; solid content 40% by mass) Movinyl 6800D (product name; manufactured by Japan Coating Resins Co., Ltd.; aqueous dispersion of polyacrylic resin; solid content 45% by mass) Evaphanol HA-560 (product name; manufactured by Nicca Chemical Co., Ltd.; aqueous dispersion of polyurethane resin; solid content 35% by mass)

[0258] (Surfactant) · KF-351A (product name, manufactured by Shin-Etsu Chemical Co., Ltd., polyether-modified polysiloxane compound) · Olfine E1010 (product name, manufactured by Nissin Chemical Industry Co., Ltd., acetylene glycol) (Thixotropic agent) Cellenpia TC-01A (product name, Nippon Paper Industries, cellulose nanofiber, average width 3-4 nm, average length 0.8 μm, aspect ratio 200)

[0259] (Preparation of Pigment Dispersion) A mixture of 4 parts by mass of magenta pigment (JM2120), 1.6 parts by mass of pigment dispersant (Joncryl 819) as solid content, and 30.5 parts by mass of an aqueous solvent consisting of ethylene glycol and ion-exchanged water in a mass ratio of 100:68 was premixed, and then dispersed using a sand grinder filled with 0.5 mm zirconia beads at a volume ratio of 50%, to prepare a pigment dispersion with a pigment content of 18% by mass. The average particle size of the pigment particles contained in this pigment dispersion was 110 nm. The average particle size was measured using a Zetasizer 1000HS manufactured by Marballoon Co., Ltd.

[0260] (Preparation of Inkjet Inks) The pigment dispersion liquid obtained above and each of the above components were mixed to obtain the composition shown in Table I or Table II, and the resulting mixture was filtered through a 1 μm filter to obtain an inkjet ink. In addition, the content (mass %) of each component in Table I or Table II indicates the content of solids contained in the component when a dispersion or solution is used as the component. For example, for Vylonal MD-2000 in Example 1, the content of the polyester resin itself excluding the amount of water as a dispersion medium is 5.0 mass %. Also, a blank in the composition column of Table I or Table II indicates that the component is not contained.

[0261] (Evaluation of ink properties) The ink obtained above was evaluated for the following physical properties (A1) to (A8). The results are shown in Table I or Table II. (A1), (A2), (A5), and (A6) were evaluated using the ink obtained above as is, that is, when the ink drying rate was 0%.

[0262] (A1) Viscosity at a shear rate of 1000 (1 / s) (25°C) (A2) Viscosity at shear rate 1 (1 / s) (LCST+5℃) (A3) Viscosity at shear rate of 1 (1 / s) with ink drying rate of 20% (LCST+5℃) (A4) Viscosity at shear rate of 1 (1 / s) with ink drying rate of 50% (LCST+5℃) (A5) Loss tangent (tanδ) at 1% strain (LCST+5℃) (A6) Crossover strain between storage modulus and loss modulus (LCST+5℃) (A7) Loss tangent (tan δ) at 1% strain with ink drying rate of 20% (LCST+5℃) (A8) Crossover strain between storage modulus and loss modulus at an ink drying rate of 20% (LCST+5°C)

[0263] In the above, LCST+5°C means the LCST+5°C of the temperature-responsive polymer contained in each ink relative to water. However, for Comparative Example 6, since it does not contain a temperature-responsive polymer, the measurement temperature was 60°C instead of LCST+5°C. In (A2), if the viscosity at LCST+5°C at a shear rate of 1 (1 / s) is 45 mPa s or more, the above condition (1-2) is satisfied. In (A3), if the viscosity at a shear rate of 1 (1 / s) with an ink drying rate of 20% is 100 mPa s or more, the above condition (1-3) is satisfied.

[0264] The above (A1) to (A8) were measured using MCR-102 manufactured by Anton Paar. (A4) was measured only in Comparative Example 5. (A5) to (A8) were measured in the oscillation mode of MCR102, changing the strain under measurement conditions of an angular frequency ω of 10 rad / s and an oscillation angle γ in the range of 1 to 1000%. The time settings were 300 measurement points, a measurement interval of 2S, a shear rate of 1 (1 / s), and a linear change in temperature from 10°C to LCST+5°C.

[0265] FIG. 4 shows a graph illustrating the relationship between the loss tangent (tan δ), storage modulus G' (logarithm), and loss modulus G" (logarithm) and strain (logarithm) for the ink of Example 1, measured under the above conditions with an ink drying rate of 20%. From this graph, the loss tangent (tan δ) at a strain of 1% (A5) and the crossover strain (A6) can be found.

[0266] (Evaluation of ink printing characteristics) For the inks obtained above, an inkjet image forming apparatus (an inkjet printer manufactured by Tritec Corp.) was used, and a head was a Konica Minolta KM1024iMHE (having a mechanism for circulating ink within the head through two or more circulation paths) at a resolution of 720 x 720 dpi to evaluate the following print characteristics (B1), (B2) and (B4). Note that for (B3), an ink coating film was formed by the following method and evaluated. The results are shown in Table I or Table II.

[0267] (B1) Injection properties Solid and linear images were printed on a PET substrate, and the state of streaks in the solid areas and the state of formation of linear areas were evaluated according to the following evaluation criteria.

[0268] (Evaluation Criteria) ◎: There are no streaks in solid areas, and straight lines are printed neatly. ○: No streaks in solid areas, some unevenness in straight lines. ×: There are white streaks in the solid areas and gaps in the straight lines.

[0269] (B2) Image quality (pinning) An image having white characters of 4 pt, 6 pt, and 8 pt in the solid area was printed on a PET substrate, and the quality of the characters was evaluated according to the following evaluation criteria.

[0270] (Evaluation Criteria) ◎: All blank characters are printed clearly. 〇: Characters of 6pt or larger are printed clearly. ×: There is bleeding in characters of 6pt or larger.

[0271] (B3) Adhesion to substrate A PET substrate was used as the substrate, and the substrate fixability of the ink coating film was evaluated by the following method. The ink coating film was obtained by applying the ink to the substrate with a wire bar #7 and drying at 100° C. for 3 minutes. The obtained ink coating film (100 mm×100 mm, 10 μm thick) was cut with a cutter to create 25 squares of 5 vertical×5 horizontal, and Nichiban Cellotape (registered trademark) was applied and peeled off to evaluate the adhesion state according to the following evaluation criteria.

[0272] (Evaluation Criteria) ◎: No peeling. ○: Peeling is within 5 squares. ×: Peeling is 6 squares or more.

[0273] (B4) Paint film water resistance A solid image was printed on a PET substrate. Water was dropped onto the resulting printed image (ink coating) with a dropper, and the surface of the printed image was rubbed with a cotton swab 10 times to evaluate the condition of the printed image according to the following evaluation criteria:

[0274] (Evaluation Criteria) ◎: No change in printed image. ◯: The printed image is almost unchanged. The density is slightly lighter. ×: The printed image has changed and is distorted.

[0275] [Table 1]

[0276] [Table 2]

[0277] As can be seen from Tables I and II, in ink-jet printing using the inks of the examples, the ink was ejected well from the head, and high-quality printed images were obtained. [Industrial Applicability]

[0278] According to the inkjet ink of the present disclosure, it is possible to maintain good ejection properties while forming a high-quality image in image formation by the inkjet method. Also, according to the image formation of the present disclosure, it is possible to form a high-quality image with good workability in image formation by the inkjet method. [Explanation of symbols]

[0279] 1: Inkjet head (end shooter type) 11: Inkjet head (MEMS type) 2: Head chip 21: Nozzle plate 22: Nozzle 23: Ink channel 24: Piezoelectric element 25: Dummy channel 26a: Individual ink circulation path 28: Flow path forming groove 3: Wiring board 31a: Injection hole 31b: Discharge hole 31c:Introduction hole 4: Ink manifold 41: Common ink chamber 412: Ink discharge chamber 421: Common ink circulation path 422: Groove 423: Circulation route 424: Discharge channel 425:Introduction path 425a: Introduction groove 45: Bulkhead 5a: Ink supply pipe 5b: Ink recovery pipe 5c: Ink discharge pipe 5d: Circulation route connection part 6: Buffer space 7a: Connection 7b: Connection F1: Main flow path F2: Sub-channel 100: Inkjet recording device 101: Ink tank 102: Ink transport pipe 103: Ink return pipe 104: Control unit 104a: Control unit 105a: Transfer pump 105b: Return pump 107: Carriage mechanism 108: Means of transportation 109: Base material 110a: Transfer pressure control pump 110b: Return pressure control pump 111a: Transfer side sub-tank 111b: Return side subtank

Claims

1. 1. An image forming method having a landing step of ejecting droplets of ink-jet ink from an ink-jet head and landing the droplets on a substrate, The ink-jet ink contains a water-based solvent, a pigment, a fixing resin, and a temperature-responsive polymer; the temperature-responsive polymer has a lower critical solution temperature with respect to water; a content of the pigment is within a range of 2 to 10% by mass, a content of the fixing resin is within a range of 1 to 10% by mass, and a content of the temperature responsive polymer is within a range of 0.01 to 1% by mass, relative to a total amount of the ink-jet ink; The image forming method according to the present invention, characterized in that, in the impacting step, heating is performed within a range of the lower critical solution temperature ±10° C.

2. 2. The image forming method according to claim 1, wherein the ink-jet ink has a viscosity of 15 mPa·s or less at a shear rate of 1000 (1 / s) at 25° C. and a viscosity of 45 mPa·s or more at a shear rate of 1 (1 / s) at any temperature within a range of the lower critical solution temperature ±10° C.

3. 3. The image forming method according to claim 1, wherein the ink-jet ink has a viscosity of 100 mPa s or more at a shear rate of 1 (1 / s) at any temperature within a range of the lower critical solution temperature ±10° C. in a state in which the aqueous solvent has been removed from the ink-jet ink so that the ink-jet ink has a mass of 80% of its initial mass.

4. 4. The image forming method according to claim 1, wherein the lower critical solution temperature of the temperature-responsive polymer in water is within a range of 30 to 60°C.

5. The image forming method according to claim 1 , wherein the temperature responsive polymer comprises a water-soluble cellulose resin.

6. 6. The image forming method according to claim 1, wherein a content of the aqueous solvent in the total amount of the ink-jet ink is within a range of 50 to 90% by mass.

7. 7. The image forming method according to claim 1, wherein the fixing resin comprises at least one resin selected from the group consisting of a polyacrylic resin, a polyurethane resin, and a polyester resin.

8. The image forming method according to claim 1 , wherein the ink-jet ink further comprises a thixotropic agent.

9. The image forming method according to claim 8 , wherein the thixotropy-imparting agent comprises cellulose nanofiber or a smectite clay mineral.

10. 10. The image forming method according to claim 8, wherein the content of the thixotropy imparting agent is within a range of 0.01 to 1% by mass based on the total amount of the ink-jet ink.

11. 11. The image forming method according to claim 1, wherein the viscosity of the droplets when they land on the substrate or immediately after they land on the substrate is 150 mPa·s or more.

12. 12. The image forming method according to claim 1, wherein the step of applying the droplets to the substrate comprises heating the droplets on the substrate at a temperature in the range of 30 to 60° C.

13. 13. The image forming method according to claim 11, wherein the period immediately after the droplets land is within 100 msec after the droplets land on the substrate.

14. The inkjet head is provided with an ink circulation mechanism, The ink-jet ink is circulated in the ink-jet head so that the ink-jet ink has a viscosity of 15 mPa·s or less; and 14. The image forming method according to claim 1, wherein the landing step is performed such that the droplets, when they land on the base material or immediately after they land, have a mass loss rate of 20% or less from the inkjet ink and a viscosity of 100 mPa·s or more.

15. The inkjet head is a pressure chamber into which the ink-jet ink is injected via an injection path; a pressure generating means for generating a pressure fluctuation in the pressure chamber; a nozzle communicating with the pressure chamber and serving as a flow path for the ink-jet ink to be ejected from the pressure chamber to the outside in response to a pressure fluctuation in the pressure chamber; two or more circulation paths that communicate with the pressure chamber and discharge the ink-jet ink inside the nozzle and return the ink to the injection path; The image forming method according to claim 14 , comprising:

Images