Inkjet recording method and inkjet recording apparatus

Abstract

To provide an inkjet recording method capable of recording an image having excellent abrasion resistance and color development in a dark area.SOLUTION: There is provided an inkjet recording method which comprises: a first recording step of applying an aqueous first ink to a recording medium; and a second recording step of applying an aqueous second ink to the recording medium so as to overlap at least a portion of the area to which the first ink is applied of the recording medium. The first ink is a chromatic color ink containing a first pigment, first wax particles, a silicone-based surfactant and an urethane resin, the second ink is a neutral color ink containing carbon black, second wax particles and an acetylene glycol-based surfactant, the maximum absorbance of the second ink in the wavelength range of 400 nm to 780 nm is 210 or more and the cumulative 50% particle diameter on a volume basis of the first wax particles is smaller than the cumulative 50% particle diameter on a volume basis of the first pigment.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] In recent years, inkjet recording methods have been used not only for printing documents at home and in offices but also for commercial printing and industrial printing. In particular, the opportunity to print posters and advertisements using large-format inkjet printers has been increasing. For such printers, since it is required to be able to record an image with good fastness such as gas resistance and light resistance, ink containing a pigment as a coloring material (pigment ink) is widely used.

[0003] An image recorded using a large-format inkjet printer needs to withstand scraping and peeling due to external forces in the printing process and posting environment, and is required to have scratch resistance. Further, when recording an image by using a achromatic ink containing a black coloring material and a chromatic ink containing a colored coloring material in combination, it is required to be able to record an image excellent in color developability, particularly color reproducibility in dark areas.

[0004] To meet these requirements, various inks have been developed. For example, an ink containing wax particles formed of a chain hydrocarbon such as polyolefin, which can improve the scratch resistance of an image, has been proposed (Patent Documents 1 and 2). Further, an inkjet recording method capable of recording an image with improved color reproducibility by printing a chromatic ink and an achromatic ink so as to overlap each other has been proposed (Patent Document 3).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] The inventors of the present invention examined the characteristics of an image recorded by the inkjet recording method proposed in Patent Document 3 using the achromatic ink and the chromatic ink proposed in Patent Document 1. As a result, it was found that while the rubbing resistance of the image was good, the color reproducibility (color development property) in the dark part was insufficient. Further, the characteristics of an image recorded by the inkjet recording method proposed in Patent Document 3 were also examined using an achromatic ink and a chromatic ink prepared by changing the colorants of the ink proposed in Patent Document 2 to black pigments and color pigments. As a result, it was found that while the rubbing resistance of the image was good, the color reproducibility (color development property) in the dark part was insufficient.

[0007] When the recorded image was analyzed, it was found that voids were generated in the layer formed by the chromatic ink with the addition of wax particles, and the surface smoothness of the image decreased. Also, it was found that aggregates of wax particles were mixed in the layer formed by the achromatic ink, and the wax particles and the pigments were present in a non-uniform state. That is, it was speculated that the color reproducibility in the dark part became insufficient due to the decrease in the surface smoothness of the image and the non-uniform state of the wax particles and the pigments.

[0008] Therefore, an object of the present invention is to provide an inkjet recording method capable of recording an image excellent in rubbing resistance and color development property in the dark part. Another object of the present invention is to provide an inkjet recording apparatus used for this inkjet recording method.

Means for Solving the Problems

[0009] That is, according to the present invention, there is provided an inkjet recording method including a first recording step of applying an aqueous first ink to a recording medium, and a second recording step of applying an aqueous second ink to the recording medium so as to overlap at least a part of the region of the recording medium to which the first ink is applied, wherein the first ink is a colored ink containing a first pigment, first wax particles, a silicone-based surfactant, and a urethane resin, the second ink is an achromatic ink containing carbon black, second wax particles, and an acetylene glycol-based surfactant, the maximum absorbance of the second ink in the wavelength range of 400 nm to 780 nm is 210 or more, and the volume-based cumulative 50% particle diameter of the first wax particles is smaller than the volume-based cumulative 50% particle diameter of the first pigment.

Advantages of the Invention

[0010] According to the present invention, it is possible to provide an inkjet recording method capable of recording an image excellent in rubbing resistance and color developability in a dark part. Further, according to the present invention, it is possible to provide an inkjet recording apparatus used in this inkjet recording method.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0012] The present invention will be described in more detail below with reference to preferred embodiments. In the description of this specification, "CI" means the abbreviation for "color index". Furthermore, "unit" means a unit structure corresponding to a monomer of 1, unless otherwise specified. When the compound is a salt, the salt is present in the aqueous ink in the form of dissociation into ions, but for convenience, it is expressed as "containing a salt". Aqueous inkjet inks are sometimes simply referred to as "ink". Physical property values ​​are values ​​at room temperature (25°C), normal pressure (1 atm = 101,325 Pa), and normal humidity (relative humidity 50%), unless otherwise specified.

[0013] "Hue angle" refers to the hue angle of the ink. The hue angle is measured using the CIE L * C * This is the hue angle (h) in the h color system. "Chromatic colors" are colors that have the three properties of "lightness," "hue," and "saturation." "Achromatic colors" are colors that only have "lightness," such as white, black, and intermediate grays. Note that the achromatic inks actually used do not have a hue at all, since the coloring material itself has a slight hue. However, achromatic inks are not completely devoid of hue, as they are called "colors" in the L * C * In h color space, L * Since the color is near the axis, it is treated as having no hue. * |≦20. The physical properties of ink, such as "hue angle," "lightness," "hue," and "chroma," can be measured using a spectrophotometer or similar. These physical properties can be measured using a sample prepared by appropriately diluting the ink with water (ion-exchanged water, deionized water, etc.).

[0014] In order to record an image that has both abrasion resistance and color development in dark areas, the present inventors have investigated recording an image using an ink containing various wax particles, which are components for improving the abrasion resistance of the image, and various surfactants and additives. As a result, they have found that by satisfying the following requirements (i) to (v), an image that is excellent in abrasion resistance and color development in dark areas can be recorded, and have arrived at the present invention. (i) A first recording step of applying a first aqueous ink to a recording medium, and a second recording step of applying a second aqueous ink to the recording medium so as to overlap at least a part of the region of the recording medium to which the first ink is applied. This is an inkjet recording method. (ii) The first ink is a colored ink containing a first pigment, first wax particles, a silicone-based surfactant, and a urethane resin. (iii) The second ink is an achromatic ink containing carbon black, second wax particles, and an acetylene glycol-based surfactant. (iv) The maximum absorbance of the second ink in the wavelength range of 400 nm to 780 nm is 210 or more. (v) The volume-based cumulative 50% particle diameter of the first wax particles is smaller than the volume-based cumulative 50% particle diameter of the first pigment.

[0015] Regarding the reason why the rubbing resistance of the recorded image is improved, the present inventors have speculated as follows. The surface of the image recorded with the ink containing wax particles is imparted with slipperiness, and the rubbing resistance generated when an external force is applied is reduced, thereby improving the rubbing resistance. By using the first ink and the second ink each containing wax particles, it is considered that the rubbing resistance of the image can be effectively improved.

[0016] Also, in order to infer the reason why the color development property in the dark part of the recorded image is improved, the present inventors analyzed the recorded image. As a result, the following phenomenon was confirmed. The volume-based cumulative 50% particle diameter (D 50 ) of the first wax particles is the volume-based cumulative 50% particle diameter (D 50) If it is smaller than , wax particles with a smaller particle size can effectively penetrate into the voids formed by the aggregation of the first pigment and fill the voids. Further, when the first ink containing a silicone-based surfactant is used, the first ink spreads and the height of the ink dot decreases, improving the smoothness of the layer formed by the first ink. Furthermore, when the first ink containing a silicone-based surfactant and the first wax particles is used, the second ink is less likely to bounce on the layer formed by the first ink and can spread sufficiently.

[0017] Generally, when an ink containing a silicone-based surfactant with a low surface energy is used, the silicone-based surfactant tends to localize on the surface of the layer formed by the ink, so that the ink landing later is more likely to bounce. However, since most of the surface of the wax particles is occupied by highly hydrophobic hydrocarbons, the penetration and evaporation of the landed first ink proceed. Therefore, most of the silicone-based surfactant is adsorbed onto the first wax particles. As a result, the localization of the silicone-based surfactant on the surface of the layer formed by the first ink is suppressed, and it is considered that the second ink can spread sufficiently without being bounced. Furthermore, when the first ink contains a urethane resin, the surface energy of the layer formed by the first ink increases, and the second ink is more likely to spread. As described above, the generation of voids in the layer formed by the first ink is suppressed and the smoothness is improved, and the second ink is more likely to spread, so it is considered that the color development property in the dark part of the image is improved.

[0018] In order to speculate on other reasons for the improvement in color development in the dark areas of the recorded image, the inventors further analyzed the recorded image. As a result, the following phenomena were confirmed. By using a second ink containing carbon black and having a maximum absorbance of 210 or more in the wavelength range of 400 nm to 780 nm, the color tone of the image becomes darker, and the color development in the dark area can be effectively expressed. The bronze phenomenon refers to a phenomenon in which the reflected light appears to be a color different from the original color due to the wavelength dependence of the refractive index on the surface of the pigment particles present on the recording medium. It is known that when the bronze phenomenon occurs significantly, the color development of the image deteriorates. By applying the second ink so as to overlap at least a part of the area where the first ink is applied, the bronze phenomenon of the layer formed by the first ink can be effectively suppressed. Furthermore, when using a second ink containing an acetylene glycol-based surfactant, the second ink spreads and the height of the ink dots becomes lower, and the smoothness of the layer formed by the second ink is improved. Also, when using a second ink containing an acetylene glycol-based surfactant and second wax particles, the aggregation of the wax particles is suppressed, and the wax particles and carbon black exist in a uniformly dispersed state.

[0019] Normally, most of the surface of the wax particles is occupied by highly hydrophobic hydrocarbons. For this reason, the wax particles tend to aggregate, and the wax particles and the pigment tend to exist in a non-uniform state. When a silicone-based surfactant is contained in the second ink, the silicone-based surfactant is likely to adsorb to carbon black, which is more hydrophobic than the wax particles, so it is difficult to suppress the aggregation of the wax particles. On the other hand, when an acetylene glycol-based surfactant, which has lower hydrophobicity than the silicone-based surfactant and has a chemical structure similar to the wax forming the wax particles, is added to the second ink, the acetylene glycol-based surfactant selectively adsorbs to the wax particles. Thereby, it is considered that the aggregation of the wax particles is suppressed.

[0020] <Ink Cartridge> The ink cartridge includes ink and an ink storage unit for storing this ink. And the ink stored in this ink storage unit is the first ink and the second ink described above. FIG. 1 is a cross-sectional view schematically showing an example of the ink cartridge. As shown in FIG. 1, an ink supply port 12 for supplying ink to the recording head is provided on the bottom surface of the ink cartridge. The inside of the ink cartridge is an ink storage unit for storing ink. The ink storage unit is composed of an ink storage chamber 14 and an absorber storage chamber 16, and these communicate with each other through a communication port 18. Further, the absorber storage chamber 16 communicates with the ink supply port 12. The ink storage chamber 14 stores liquid ink 20, and the absorber storage chamber 16 stores absorbers 22 and 24 that hold the ink in an impregnated state. The ink storage unit may not have an ink storage chamber for storing liquid ink, and may be in a form in which the entire amount of the stored ink is held by the absorber. Also, the ink storage unit may not have an absorber and may be in a form in which the entire amount of the ink is stored in a liquid state. Furthermore, an ink cartridge configured to have an ink storage unit and a recording head may also be used.

[0021] <Inkjet Recording Method and Inkjet Recording Apparatus> The inkjet recording method of the present invention includes a first recording step of applying an aqueous first ink to a recording medium, and a second recording step of applying an aqueous second ink to the recording medium so as to overlap at least a part of the region of the recording medium to which the first ink has been applied. The first ink is a colored ink containing a first pigment, first wax particles, a silicone-based surfactant, and a urethane resin. The second ink is an achromatic ink containing carbon black, second wax particles, and an acetylene glycol-based surfactant. The maximum absorbance of the second ink in the wavelength range of 400 nm to 780 nm is 210 or more. And the volume-based cumulative 50% particle diameter of the first wax particles is smaller than the volume-based cumulative 50% particle diameter of the first pigment.

[0022] Furthermore, the inkjet recording apparatus of the present invention is an apparatus suitably used for the above-described inkjet recording method. That is, the inkjet recording apparatus of the present invention is an apparatus used for an inkjet recording method having a first recording step and a second recording step. The first recording step is a step of applying an aqueous first ink to a recording medium. The second recording step is a step of applying an aqueous second ink to the recording medium so as to overlap at least a part of the region of the recording medium to which the first ink has been applied. The first ink is a colored ink containing a first pigment, first wax particles, a silicone-based surfactant, and a urethane resin. The second ink is an achromatic ink containing carbon black, second wax particles, and an acetylene glycol-based surfactant. The maximum absorbance of the second ink in the wavelength range of 400 nm to 780 nm is 210 or more. And the volume-based cumulative 50% particle diameter of the first wax particles is smaller than the volume-based cumulative 50% particle diameter of the first pigment.

[0023] Figure 2 is a diagram schematically showing an example of an inkjet recording apparatus used for the inkjet recording method of the present invention. (a) is a perspective view of the main part of the inkjet recording apparatus, and (b) is a perspective view of the head cartridge. The inkjet recording apparatus is provided with a conveying means (not shown) for conveying the recording medium 32 and a carriage shaft 34. A head cartridge 36 can be mounted on the carriage shaft 34. The head cartridge 36 includes recording heads 38 and 40 and is configured such that an ink cartridge 42 can be set. While the head cartridge 36 is conveyed in the main scanning direction along the carriage shaft 34, ink (not shown) is ejected from the recording heads 38 and 40 toward the recording medium 32. Then, an image is recorded on the recording medium 32 by the recording medium 32 being conveyed in the sub-scanning direction by the conveying means (not shown).

[0024] Examples of ink ejection methods include methods of imparting mechanical energy to the ink and methods of imparting thermal energy to the ink. Further, as a recording medium for recording an image, it is preferable to use a recording medium having ink absorbency. Examples of the recording medium having ink absorbency include recording media based on paper such as glossy paper, art paper, and plain paper.

[0025] The inkjet recording method of the present invention is preferably a method of recording an image in a unit area of a recording medium by scanning a recording head a plurality of times with respect to the unit area of the recording medium from the start of application of the first ink to the start of application of the second ink. Then, it is preferable to scan the recording head 4 or more times with respect to the unit area of the recording medium from the start of application of the first ink to the start of application of the second ink to record an image in the unit area, and it is more preferable to scan 8 or more times and 24 or less times to record an image in the unit area. If the number of scans of the recording head from the start of application of the first ink to the start of application of the second ink is less than 4 (3 or less), the second ink may be applied before the wax particles sufficiently fill the voids formed by the aggregation of the first pigment. The second ink is likely to be applied while the wax particles do not sufficiently fill the voids of the first pigment. For this reason, the smoothness of the layer formed by the first ink may be reduced, and the effect of improving the color development in the dark part may be reduced.

[0026] Further, the time from the start of application of the first ink to the start of application of the second ink (application start time difference) is preferably 3 seconds or more, and more preferably 5 seconds or more and 36 seconds or less. If the application start time difference is less than 3 seconds, the second ink is likely to be applied while the adsorption of the silicone-based surfactant to the first wax particles is somewhat insufficient. For this reason, the second ink may be repelled, and the smoothness of the layer formed by the second ink may be reduced, and the effect of improving the color development in the dark part may be reduced.

[0027] After the application of the first ink is completed, it is preferable to start the application of the second ink. If the application of the second ink is started before the application of the first ink is completed, the second ink is likely to be applied while the penetration and wet spreading of the first ink on the recording medium are somewhat insufficient. For this reason, the first ink and the second ink may be excessively mixed, and the effect of improving color development in the dark part may be reduced.

[0028] (Water-based ink) In the inkjet recording method of the present invention, a first ink which is a colored water-based ink and a second ink which is an achromatic water-based ink are used. The first ink contains a first pigment, first wax particles, a silicone-based surfactant, and a urethane resin. The second ink contains carbon black, second wax particles, and an acetylene glycol-based surfactant. Hereinafter, when simply referred to as "ink", it means either the "first ink" or the "second ink". Also, when simply referred to as "pigment", it means either the "first pigment" or "carbon black". Further, when simply referred to as "wax particles", it means either the "first wax particles" or the "second wax particles".

[0029] [Pigment] Examples of the first pigment include organic pigments such as azo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, imidazolone pigments, diketopyrrolopyrrole pigments, and dioxazine pigments. The content (% by mass) of the first pigment in the first ink is preferably 0.50% by mass or more and 15.00% by mass or less, more preferably 0.50% by mass or more and 10.00% by mass or less, based on the total mass of the first ink.

[0030] The second ink contains carbon black as a pigment. The content of carbon black in the second ink is preferably an amount such that the color tone of the recorded image becomes darker and the color development in the dark area can be effectively expressed. Specifically, the content of carbon black in the second ink is an amount such that the maximum absorbance of the second ink in the wavelength range of 400 nm to 780 nm is 210 or more, preferably 400 or more. That is, the maximum absorbance of the second ink in the wavelength range of 400 nm to 780 nm is preferably 400 or more, and more preferably 700 or more and 2100 or less. If the maximum absorbance of the second ink in the wavelength range of 400 nm to 780 nm is less than 400, the lightness of the second ink may be slightly higher. For this reason, the darkness of the recorded image may be slightly insufficient, and the effect of improving the color developability in the dark area may be reduced.

[0031] The content (% by mass) of carbon black in the second ink is preferably 0.60% by mass or more based on the total mass of the second ink, and more preferably 2.00% by mass or more and 6.00% by mass or less. If the content of carbon black is less than 0.60% by mass, the maximum absorbance of the second ink in the wavelength range of 400 nm to 780 nm may decrease. For this reason, the darkness of the recorded image may be slightly insufficient, and the effect of improving the color developability in the dark area may be reduced.

[0032] The content (% by mass) of carbon black in the second ink is preferably a mass ratio of 0.08 times or more and 2.00 times or less, and more preferably 0.30 times or more and 1.50 times or less, with respect to the content (% by mass) of the first pigment in the first ink. If the above mass ratio is less than 0.08 times, the lightness of the second ink may be slightly higher than the chroma of the first ink. For this reason, the darkness of the recorded image may be slightly insufficient, and the effect of improving the color developability in the dark area may be reduced. On the other hand, if the above mass ratio exceeds 2.00 times, the lightness of the second ink may be slightly lower than the chroma of the first ink. For this reason, the chroma of the recorded image may be slightly insufficient, and the effect of improving the color developability in the dark area may be reduced.

[0033] The maximum absorbance of the second ink in the wavelength range of 400 nm to 780 nm can be measured and calculated according to the following procedure. Dilute the second ink with water so that the maximum absorbance in the wavelength range of 400 nm to 780 nm becomes 1 to obtain a diluted solution. Put the obtained diluted solution into a quartz glass cell with an optical path length of 10 mm, use a spectrophotometer to measure the absorption spectrum (absorbance) in the wavelength range of 400 nm to 780 nm, and select the maximum absorbance in the measured absorption spectrum. As the spectrophotometer, for example, the product named "Spectophotometer U-3900H" (manufactured by HITACHI) can be used. Then, the maximum absorbance in the wavelength range of 400 nm to 780 nm can be calculated by multiplying the selected maximum absorbance by the dilution ratio when diluting the second ink. The peak detection conditions when measuring the absorption spectrum can be, for example, sampling interval: 0.5 nm, threshold value: 0.01, sensitivity: 1. Also, pure water is used as the reference.

[0034] Examples of the pigment dispersion method include resin-dispersed pigments using a resin as a dispersant, self-dispersing pigments in which a hydrophilic group is bonded to the particle surface of the pigment, etc. Also, resin-bonded pigments in which an organic group containing a resin is chemically bonded to the particle surface of the pigment, microcapsule pigments in which the surface of the pigment particles is coated or encapsulated with a resin, etc. can be used. It is also possible to use a combination of pigments with different dispersion methods.

[0035] As the resin (resin dispersant) for dispersing the pigment in an aqueous medium, a resin having a hydrophilic unit and a hydrophobic unit as constituent units is preferable. The resin dispersant is preferably an acrylic resin having an acrylic component such as a unit derived from (meth)acrylic acid or a unit derived from (meth)acrylate ester, and more preferably a water-soluble acrylic resin. Among them, a water-soluble acrylic resin in the form of a random copolymer is particularly preferable. Hereinafter, "(meth)acrylic" means "acrylic" and "methacrylic", and "(meth)acrylate" means "acrylate" and "methacrylate".

[0036] The hydrophilic unit is a unit having a hydrophilic group such as an acid group or a hydroxy group. The hydrophilic unit can be formed, for example, by polymerizing a monomer having a hydrophilic group. Specific examples of the monomer having a hydrophilic group include acidic monomers having a carboxylic acid group such as (meth)acrylic acid, itaconic acid, maleic acid, and fumaric acid; acidic monomers having a sulfonic acid group such as styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, and 3-sulfopropyl (meth)acrylate; anionic monomers such as anhydrides and salts of these acidic monomers; monomers having a hydroxy group such as 2-hydroxyethyl (meth)acrylate and 3-hydroxypropyl (meth)acrylate; monomers having an ethylene oxide group such as methoxy (mono, di, tri, poly)ethylene glycol (meth)acrylate; and the like. Examples of the cation constituting the salt of the anionic monomer include ions such as lithium, sodium, potassium, ammonium, and organic ammonium. The acid value of the resin used as the resin dispersant is preferably 50 mgKOH / g or more and 200 mgKOH / g or less.

[0037] As the self-dispersing pigment, those in which anionic groups such as a carboxylic acid group, a sulfonic acid group, and a phosphonic acid group are bonded directly or via another atomic group (-R-) to the particle surface of the pigment can be used. The anionic group may be either in the acid form or the salt form, and in the case of the salt form, it may be in a state where a part thereof is dissociated or a state where all of it is dissociated. When the anionic group is in the salt form, examples of the cation serving as the counter ion include an alkali metal cation, ammonium, and organic ammonium. Specific examples of the other atomic group (-R-) include a linear or branched alkylene group having 1 to 12 carbon atoms; an arylene group such as a phenylene group and a naphthylene group; a carbonyl group; an imino group; an amide group; a sulfonyl group; an ester group; an ether group; and the like. Also, a group formed by combining these groups may be used.

[0038] [Wax Particles] The first ink contains first wax particles. The second ink contains second wax particles. The first wax particles and the second wax particles may be of the same type or different types.

[0039] Wax particles are particles formed of wax. The wax may be a composition containing components other than wax or wax itself. The wax particles may be dispersed by a dispersant such as a surfactant or a resin.

[0040] Wax (in the narrow sense) is an ester of a higher monohydric or dihydric alcohol insoluble in water and a fatty acid, including animal waxes and plant waxes, but not including fats and oils. In the broad sense, it includes high-melting fats, mineral waxes, petroleum waxes, and blends and modified products of various waxes. Any wax in the broad sense can be used in the ink without particular limitation. Waxes in the broad sense can be classified into natural waxes, synthetic waxes, blends (compounded waxes) of these, and modified products (modified waxes) of these.

[0041] Examples of natural waxes include animal waxes such as beeswax, spermaceti wax, and lanolin; plant waxes such as carnauba wax, candelilla wax, rice wax, and palm wax; mineral waxes such as montan wax; and petroleum waxes such as paraffin wax, microcrystalline wax, and petrolatum. Examples of synthetic waxes include hydrocarbon waxes such as Fischer-Tropsch wax and polyolefin waxes (e.g., polyethylene wax, polypropylene wax). Compounded waxes are mixtures of the above various waxes. Modified waxes are those obtained by subjecting the above various waxes to modification treatments such as oxidation, hydrogenation, alcohol modification, acrylic modification, and urethane modification.

[0042] The wax particles are preferably particles formed of at least one wax selected from the group consisting of polyethylene, Fischer-Tropsch wax, microcrystalline wax, paraffin wax, ozokerite, and ceresin. Since these waxes do not contain ester sites or carboxy sites in their skeletons, they easily form highly crystalline wax particles. By using highly crystalline wax particles, when an external force is applied, the crystal interfaces slide and spread, and the wax particles deform, making it easier to release the force and enabling the recording of an image with excellent abrasion resistance.

[0043] The content (mass %) of the first wax particles in the first ink is preferably 0.01 mass % or more and 1.00 mass % or less based on the total mass of the first ink. Also, the content (mass %) of the second wax particles in the second ink is preferably 0.01 mass % or more and 1.00 mass % or less based on the total mass of the second ink.

[0044] The content (mass %) of the second wax particles in the second ink is preferably 0.10 times or more and 5.00 times or less, more preferably 0.15 times or more and 3.00 times or less, in terms of the mass ratio to the content (mass %) of the first wax particles in the first ink. If the above mass ratio is less than 0.10 times, the abrasion resistance of the layer formed with the second ink may be slightly lower than that of the layer formed with the first ink. Since the layer formed with the second ink is arranged so as to overlap with the layer formed with the first ink, the contribution of the layer formed with the second ink to the abrasion resistance of the image is large. For this reason, it may be difficult for the wax particles to protect the layer formed with the second ink, and the effect of improving the abrasion resistance of the image may decrease. On the other hand, if the above mass ratio exceeds 5.00 times, the scattering intensity by the second wax of the layer formed with the second ink may be slightly larger than the scattering intensity by the first wax of the layer formed with the first ink. Since the layer formed with the second ink is arranged so as to overlap with the layer formed with the first ink, the contribution of the layer formed with the second ink to the color development property of the image is large. For this reason, incident light may be scattered by the layer formed with the second ink, and it may be difficult for the incident light to reach the layer formed with the first ink, and the effect of improving the color development property of the image may decrease.

[0045] The cumulative 50% particle diameter based on the volume of the first wax particles is smaller than the cumulative 50% particle diameter based on the volume of the first pigment in the first ink. In this specification, when simply referred to as "average particle diameter", it means "cumulative 50% particle diameter (D 50 )" based on volume. The "cumulative 50% particle diameter based on volume" of the wax particles is the diameter of the particles that reach 50% when integrated from the small particle diameter side with reference to the total volume of the measured particles in the particle diameter integration curve. This "cumulative 50% particle diameter based on volume (D 50) can be measured using a particle size distribution measuring apparatus by dynamic light scattering method. As the particle size distribution measuring apparatus by dynamic light scattering method, a particle size analyzer (for example, trade name "UPA-EX150", manufactured by Nikkiso Co., Ltd.) etc. can be used. The measurement conditions at this time can be, for example, SetZero: 30 seconds, number of measurements: 3 times, measurement time: 180 seconds, shape: true sphere, refractive index: 1.59. Of course, the particle size distribution measuring apparatus and measurement conditions to be used etc. are not limited to the above.

[0046] The volume-based cumulative 50% particle diameter of the wax particles is preferably 10 nm or more and 200 nm or less, and more preferably 20 nm or more and 150 nm or less. Further, the volume-based cumulative 50% particle diameter of the first wax particles is preferably 0.10 times or more and 0.60 times or less, and more preferably 0.25 times or more and 0.50 times or less, as a ratio to the volume-based cumulative 50% particle diameter of the first pigment. When the above ratio is less than 0.10 times, the amount of deformation of the wax particles may become insufficient, it may become difficult to release external force, and the effect of improving the rubbing resistance of the image may decrease. On the other hand, when the above ratio exceeds 0.60 times, the wax particles may become difficult to enter the voids formed by the aggregation of the first pigment, and the effect of improving the color developability in the dark part may decrease.

[0047] [Silicone-based surfactant] The first ink contains a silicone-based surfactant. The silicone-based surfactant is preferably a compound represented by any of the following general formulas (1), (3), and (4). In the following general formulas (1), (3), and (4), "C2H4O" represents an ethylene oxide unit, and "C3H6O" represents a propylene oxide unit. The ethylene oxide unit and the propylene oxide unit may be arranged in either a random state or a block state. "Each unit is arranged in a random state" means that each unit is arranged irregularly. On the other hand, "each unit is arranged in a block state" means that the blocks formed by each unit gathering together are arranged regularly.

[0048] TIFF2025102729000001.tif25170(In the general formula (1), R1 represents an alkylene group, R2 represents a hydrogen atom or an alkyl group, m and n each independently represent an integer of 1 or more, and a and b each independently represent an integer of 0 or more)

[0049] TIFF2025102729000002.tif26170(In the general formula (3), R3 represents a hydrogen atom or an alkyl group, R4 represents an alkylene group, p represents an integer of 1 or more, and c and d each independently represent an integer of 0 or more)

[0050] TIFF2025102729000003.tif26170(In the general formula (4), R5 represents a hydrogen atom or an alkyl group, R6 represents an alkylene group, q and r each independently represent an integer of 1 or more, and e and f each independently represent an integer of 0 or more)

[0051] The silicone surfactant is more preferably a compound represented by the general formula (1). The silicone surfactant represented by the general formula (1) has a stronger adsorption force to the wax particles than the silicone surfactants represented by the general formula (3) and the general formula (4). Therefore, by using the silicone surfactant represented by the general formula (1), the aggregation of the wax particles can be effectively suppressed, and the color developability in the dark part can be further enhanced.

[0052] The content (mass %) of the silicone surfactant in the first ink is preferably 0.10 mass % or more and 0.50 mass % or less based on the total mass of the first ink.

[0053] [Acetylene glycol-based surfactant] The second ink contains an acetylene glycol-based surfactant. The acetylene glycol-based surfactant is preferably a compound represented by the following general formula (2). In the following general formula (2), "C2H4O" represents an ethylene oxide unit. The acetylene glycol-based surfactant represented by the general formula (2) has a strong adsorption force to wax particles. Therefore, by using the acetylene glycol-based surfactant represented by the general formula (2), aggregation of wax particles can be suppressed, and the wax particles and the carbon black pigment can be effectively present in a uniform state, and the color development property in the dark part can be further enhanced.

[0054] TIFF2025102729000004.tif27170(In the general formula (2), s and t each independently represent an integer of 0 or more and 15 or less)

[0055] The content (mass%) of the acetylene glycol-based surfactant in the second ink is preferably 0.05 mass% or more and 1.00 mass% or less based on the total mass of the second ink. Further, the content (mass%) of the acetylene glycol-based surfactant in the second ink is preferably 0.20 times or more and 8.00 times or less in terms of the mass ratio to the content (mass%) of the silicone-based surfactant in the first ink. More preferably, it is 0.30 times or more and 6.00 times or less. If the above mass ratio is less than 0.20 times, the wet spreading of the second ink may be slightly insufficient compared to the wet spreading of the first ink. For this reason, the smoothness of the layer formed by the second ink is likely to decrease, and the effect of improving the color development property in the dark part may decrease. On the other hand, if the above mass ratio exceeds 8.00 times, the wet spreading of the first ink may be slightly insufficient compared to the wet spreading of the second ink. For this reason, the smoothness of the layer formed by the first ink is likely to decrease, and the effect of improving the color development property in the dark part may decrease.

[0056] [Urethane resin] The first ink contains a urethane resin. The content (mass%) of the urethane resin in the first ink is preferably 0.30 mass% or more and 2.00 mass% or less based on the total mass of the first ink. The urethane resin can be obtained, for example, by reacting a polyisocyanate and a polyol. Further, it may be a product obtained by further reacting a polyamine, a crosslinking agent, a chain extender, etc.

[0057] 〔Polyisocyanate〕 A polyisocyanate is a compound having two or more isocyanate groups in its molecule. Examples of the polyisocyanate include aliphatic polyisocyanates and aromatic polyisocyanates. Examples of the aliphatic polyisocyanate include polyisocyanates having a chain structure such as tetramethylene diisocyanate, hexamethylene diisocyanate, dodecamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, 2-methylpentane-1,5-diisocyanate, and 3-methylpentane-1,5-diisocyanate; polyisocyanates having a cyclic structure such as isophorone diisocyanate, hydrogenated xylylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 1,4-cyclohexane diisocyanate, methylcyclohexylene diisocyanate, and 1,3-bis(isocyanatomethyl)cyclohexane; etc.

[0058] Examples of the aromatic polyisocyanate include tolylene diisocyanate, 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-dibenzyl diisocyanate, 1,5-naphthylene diisocyanate, xylylene diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, and α,α,α',α'-tetramethylxylylene diisocyanate; etc.

[0059] Polyol The polyol is a compound having two or more hydroxyl groups in its molecule. Examples of the polyol include polyols having no acid groups such as polyether polyols, polyester polyols, and polycarbonate polyols; polyols having acid groups; and the like.

[0060] Examples of the polyether polyol include addition polymers of alkylene oxides and polyols; glycols such as (poly)alkylene glycols; and the like. Examples of the polyester polyol include acid esters and the like. Examples of the polycarbonate polyol include alkane diol-based polycarbonate diols and the like. The number average molecular weight of the polyol having no acid group is preferably 450 or more and 4,000 or less.

[0061] Examples of the polyol having an acid group include polyols containing acid groups such as carboxylic acid groups, sulfonic acid groups, and phosphonic acid groups in their molecules. In particular, it is preferable to use a urethane resin synthesized by further using a polyol having an acid group such as dimethylolpropionic acid or dimethylolbutanoic acid in addition to the polyol having no acid group, and it is more preferable to use a water-soluble urethane resin. The acid group may be in the form of a salt. Examples of the cation constituting the salt include ions such as lithium, sodium, potassium, ammonium, and organic ammonium. When the water-soluble urethane resin has an acid group, it usually becomes water-soluble by being neutralized with a neutralizing agent such as a hydroxide of an alkali metal (such as lithium, sodium, potassium) or aqueous ammonia.

[0062] Polyamine Examples of polyamines include monoamines having a plurality of hydroxyl groups such as dimethylol ethylamine, diethanol methylamine, dipropanol ethylamine, and dibutanol methylamine; bifunctional polyamines such as ethylenediamine, propylenediamine, hexylenediamine, isophoronediamine, xylylenediamine, diphenylmethanediamine, hydrogenated diphenylmethanediamine, and hydrazine; trifunctional or higher polyamines such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, polyamide polyamine, and polyethylene polyimine; etc. For convenience, compounds having a plurality of hydroxyl groups and one "amino group or imino group" are also listed as "polyamines".

[0063] [Crosslinking agent, chain extender] The urethane resin may have units derived from a crosslinking agent or a chain extender. The crosslinking agent is usually used when synthesizing a prepolymer. The chain extender is usually used when extending the chain of a prepolymer synthesized in advance. As the crosslinking agent and the chain extender, water, the aforementioned polyisocyanate, polyol, polyamine, etc. can be appropriately selected and used according to applications such as crosslinking and chain extension. As the chain extender, those capable of crosslinking the urethane resin can also be used.

[0064] The urethane resin may be either a water-soluble urethane resin or a water-insoluble urethane resin. Among them, it is preferable to use a water-soluble urethane resin. Since the water-soluble urethane resin is likely to exist in an adsorbed state on the surface layer of the pigment and wax particles, the characteristics of the water-soluble urethane resin are strongly manifested on the surface of the layer formed by the first ink. As a result, the surface energy of the image is likely to increase, the second ink is less likely to be repelled, and the color developability in the dark part can be further enhanced.

[0065] Whether a certain resin is a water-soluble resin or resin particles (water-insoluble resin) can be determined according to the method shown below. First, prepare a liquid (resin content: about 10% by mass) containing a resin neutralized with a base (such as sodium hydroxide or potassium hydroxide) in an amount equal to or greater than the acid value. Next, dilute the prepared liquid with pure water to prepare a sample with a resin content of about 1% by mass. Then, measure the particle size of the resin in the sample by the dynamic light scattering method. If particles having a particle size are not measured, it is determined that the resin is a water-soluble resin, and if particles having a particle size are measured, it is determined that the resin is resin particles. The measurement conditions at this time can be set, for example, as SetZero: 30 seconds, number of measurements: 3 times, measurement time: 180 seconds. As the particle size distribution measuring device, a particle size analyzer by the dynamic light scattering method (for example, UPA-EX150, manufactured by Nikkiso Co., Ltd.) can be used. Of course, the particle size distribution measuring device and measurement conditions used are not limited to the above.

[0066] [Aqueous medium] The ink is an aqueous ink containing an aqueous medium that is water or a mixed solvent of water and a water-soluble organic solvent. Deionized water (ion-exchanged water) is preferably used as the water. The content (% by mass) of water in the ink is preferably 50.00% by mass or more and 95.00% by mass or less based on the total mass of the ink. As the water-soluble organic solvent, any of those that can be used in inks for inkjet, such as alcohols, glycols, (poly)alkylene glycols, nitrogen-containing compounds, and sulfur-containing compounds, can be used. The content (% by mass) of the water-soluble organic solvent in the ink is preferably 3.00% by mass or more and 50.00% by mass or less based on the total mass of the ink.

[0067] [Other components] In addition to the above-described components, the ink may contain water-soluble organic compounds that are solid at 25°C, such as polyhydric alcohols like trimethylolpropane and trimethylolethane, and urea derivatives like urea and ethylene urea. Further, the ink may contain various additives such as surfactants other than the aforementioned silicone-based surfactants and acetylene glycol-based surfactants, pH adjusters, defoamers, rust preventives, antiseptics, fungicides, antioxidants, anti-reducing agents, and chelating agents, as necessary.

[0068] [Physical properties of the ink] The ink is an aqueous ink applicable to the inkjet method. Therefore, from the viewpoint of reliability, it is preferable to appropriately control its physical property values. The viscosity of the ink at 25°C is preferably 1.0 mPa·s or more and 10.0 mPa·s or less, and more preferably 1.0 mPa·s or more and 5.0 mPa·s or less. The surface tension of the ink at 25°C is preferably 20 mN / m or more and 60 mN / m or less, and more preferably 25 mN / m or more and 45 mN / m or less. The pH of the ink at 25°C is preferably 7.0 or more and 10.0 or less. [Examples]

[0069] Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples. However, the present invention is not limited to the following examples as long as the gist thereof is not exceeded. Unless otherwise specified, "parts" and "%" regarding component amounts are based on mass.

[0070] [Measurement method of physical properties] (Average particle diameter (D 50 )) The pigment dispersion and the aqueous dispersion of wax particles were each diluted with pure water to prepare samples. For the prepared samples, a particle size analyzer by dynamic light scattering method (trade name "NanoTrack UPA-EX150", manufactured by Microtrac·BEL) was used to measure the average particle diameter (volume-based cumulative 50% particle diameter (D 50(nm)) were each measured. The measurement conditions were SetZero: 30 seconds, number of measurements: 3 times, measurement time: 120 seconds, shape: true sphere, refractive index: 1.59.

[0071] (Acid value of resin) The resin was dispersed or dissolved in water to prepare a sample. For the prepared sample, using a potentiometric automatic titrator, potentiometric titration was performed with a methyl glycol chitosan 200 / N titrant to measure the number of anionic functional groups per 1 g of resin. The measured number of anionic functional groups was converted to the mass of KOH to obtain the acid value of the resin (mgKOH / g). As the potentiometric automatic titrator, the product named "AT510" (manufactured by Kyoto Electronics Industry) was used.

[0072] <Preparation of pigment dispersion> (Pigment dispersions 1 to 6) Each component shown in Table 1 (unit: part) and 85 parts of 0.3 mm zirconia beads were put into a batch vertical sand mill (manufactured by Imex) and dispersed for 3 hours while cooling with water, and then centrifuged to remove non-dispersed matter containing coarse particles. Next, pressure filtration was performed using a cellulose acetate filter with a pore size of 3.0 μm (manufactured by Advantec) to obtain pigment dispersions 1 to 6. The average particle diameter of the pigment in the obtained pigment dispersion is shown in Table 1. As the aqueous acrylic resin solution, a 20.0% aqueous acrylic resin solution obtained by neutralizing a styrene-acrylic acid copolymer with an acid value of 170 mgKOH / g and a weight average molecular weight of 8,000 to 1 equivalent of acid value with a 10.0% aqueous potassium hydroxide solution and then diluting with water was used. Details of each component in Table 1 are shown below. · C.I. Pigment Blue 15:3: Product name "Hostaperm Blue B2G" (manufactured by Hoechst) · Magenta solid solution pigment: Solid solution of C.I. Pigment Red 202 and C.I. Pigment Violet 19, product name "Sin-Kashi-a Magenta D4500J" (manufactured by Sankyo Chemical) · C.I. Pigment Yellow 74: Product name "Fast Yellow 011" (manufactured by Dainichi Seika Kogyo) · Carbon black: Product name "Black Pearls 880" (manufactured by Cabot)

[0073] TIFF2025102729000005.tif68170

[0074] (Pigment dispersion 7) A solution obtained by dissolving 5.0 g of concentrated hydrochloric acid in 5.5 g of water was cooled to 5°C, and 1.6 g of 4-aminophthalic acid (treatment agent) was added in this state. The container containing this solution was placed in an ice bath, and while stirring to keep the temperature of the solution below 10°C, a solution obtained by dissolving 1.8 g of sodium nitrite in 9.0 g of ion-exchanged water at 5°C was added. After stirring for 15 minutes, 6.0 g of carbon black (specific surface area: 260 m 2 / g) was added with stirring, and the mixture was further stirred for 15 minutes to obtain a slurry. The obtained slurry was filtered through filter paper (trade name "Standard Filter Paper No. 2", manufactured by Advantec), and the particles were washed thoroughly with water and dried in an oven at 110°C. After replacing the counter ion from sodium ion to potassium ion by the ion exchange method, an appropriate amount of ion-exchanged water was added to adjust the pigment content. In this way, a pigment dispersion 7 containing a self-dispersing pigment in which the phthalic acid group with a pigment content of 15.00% and a counter ion of potassium ion was bonded to the particle surface of carbon black was obtained. The average particle diameter of the pigment in the pigment dispersion 7 was 65 nm.

[0075] <Preparation of Aqueous Dispersion of Wax Particles> (Aqueous Dispersions of Wax Particles 1 to 7) A four-necked flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube was prepared. 225 g of ion-exchanged water and 50 g of polyethylene wax were placed in this four-necked flask, melted while maintaining the temperature at 90 to 95°C, and stirred. 25 g of a liquid containing an ethylene-acrylic resin was added, and after subjecting it to a dispersion treatment for 15 minutes using an ultrasonic homogenizer while maintaining the temperature at 90 to 95°C, it was cooled to room temperature to obtain a dispersion. Ion-exchanged water was added to the obtained dispersion to adjust the solid content to 10.00%, and an aqueous dispersion of wax particles 1 was obtained. The average particle diameter of the wax particles 1 in the obtained aqueous dispersion was 40 nm. Also, except for appropriately changing the time of the dispersion treatment by the ultrasonic homogenizer so as to obtain the average particle diameter described in Table 2, in the same manner as in the case of the aqueous dispersion of wax particles 1, aqueous dispersions of wax particles 2 to 7 were obtained.

[0076] (Aqueous dispersion of wax particles 8 to 16) Except for using the waxes of the types shown in Table 2 instead of polyethylene wax, in the same manner as in the case of the aqueous dispersion of wax particles 1 described above, aqueous dispersions of wax particles 8 to 16 were obtained. The average particle diameters of the wax particles in the obtained aqueous dispersions are shown in Table 2. The average particle diameters of the wax particles were adjusted by changing the time of the dispersion treatment by the ultrasonic homogenizer.

[0077] TIFF2025102729000006.tif131170

[0078] <Preparation of silicone-based surfactant> (Silicone-based surfactant 1) The product name "KF6017" (Shin-Etsu Chemical) was used as "silicone-based surfactant 1". This "silicone-based surfactant 1" corresponds to the compound represented by the general formula (1).

[0079] (Silicone-based surfactant 2) The product name "BYK-348" (manufactured by BYK) was used as "silicone-based surfactant 2". This "silicone-based surfactant 2" corresponds to the compound represented by the general formula (1).

[0080] (Silicone surfactant 3) The product name "X-22-4952" (manufactured by Shin-Etsu Chemical Co., Ltd.) was used as "Silicone surfactant 3". This "Silicone surfactant 3" corresponds to the compound represented by the general formula (3).

[0081] (Silicone surfactant 4) The product name "FZ-2231" (manufactured by Dow Corning Toray Co., Ltd.) was used as "Silicone surfactant 4". This "Silicone surfactant 4" corresponds to the compound represented by the general formula (4).

[0082] <Preparation of acetylene glycol-based surfactant> (Acetylene glycol-based surfactant 1) The product name "Surfynol 440" (manufactured by Nissin Chemical Industry Co., Ltd.) was used as "Acetylene glycol-based surfactant 1". This "Acetylene glycol-based surfactant 1" corresponds to the compound represented by the general formula (2).

[0083] (Acetylene glycol-based surfactant 2) The product name "Surfynol 465" (manufactured by Nissin Chemical Industry Co., Ltd.) was used as "Acetylene glycol-based surfactant 2". This "Acetylene glycol-based surfactant 2" corresponds to the compound represented by the general formula (2).

[0084] (Acetylene glycol-based surfactant 3) The product name "Surfynol 104PG50" (manufactured by Nissin Chemical Industry Co., Ltd.) was used as "Acetylene glycol-based surfactant 3". This "Acetylene glycol-based surfactant 3" corresponds to the compound represented by the general formula (2).

[0085] (Acetylene glycol-based surfactant 4) The product name "Acetylenol E100" (manufactured by Nissin Chemical Industry Co., Ltd.) was used as "Acetylene glycol-based surfactant 4". This "Acetylene glycol-based surfactant 4" corresponds to the compound represented by the general formula (2).

[0086] (Acetylene glycol surfactant 5) The product name "Surfinol 2502" (manufactured by Nissin Chemical Industry Co., Ltd.) was used as "Acetylene glycol surfactant 5". This "Acetylene glycol surfactant 5" does not correspond to the compound represented by the general formula (2).

[0087] <Preparation of urethane resin> (Liquid containing urethane resin 1) A four-necked flask equipped with a stirrer, a thermometer, a nitrogen gas inlet tube, and a reflux tube was prepared. Into this four-necked flask, 41.70 parts of isophorone diisocyanate, 40.10 parts of polypropylene glycol (number average molecular weight 2,000), 13.20 parts of dimethylolpropionic acid, and 200.00 parts of methyl ethyl ketone were added. After reacting at 80°C for 6 hours under a nitrogen gas atmosphere, 0.60 part of ethylenediamine, 2.00 parts of methanol, 2.40 parts of dimethylolpropionic acid, and 100.00 parts of methyl ethyl ketone were added. The residual rate of the isocyanate group was confirmed by FT-IR, and the reaction was carried out at 80°C until the desired residual rate was obtained to obtain a reaction solution. After cooling the obtained reaction solution to 40°C, ion-exchanged water was added, and an aqueous potassium hydroxide solution was added while stirring at high speed with a homomixer to obtain a liquid. Methyl ethyl ketone was distilled off from the obtained liquid by heating under reduced pressure, and a liquid containing water-soluble urethane resin 1 with a urethane resin (solid content) content of 20.00% was obtained.

[0088] (Liquid containing urethane resin 2) Commercially available polyether urethane resin particles (product name "Takelac W5661", manufactured by Mitsui Chemicals, solid content 35%) were used as "Liquid containing urethane resin 2".

[0089] <Preparation of aqueous solution of acrylic resin> A four-necked flask equipped with a stirrer, a reflux cooling device, and a nitrogen gas inlet tube was prepared. 200.00 parts of ethylene glycol monobutyl ether was placed in this four-necked flask, stirred under a nitrogen gas atmosphere, and heated to 130 °C. 65.00 parts of styrene, 20.00 parts of butyl acrylate, 15.00 parts of acrylic acid, and 4.00 parts of t-butyl peroxide were added dropwise over 3 hours. After aging for 2 hours, ethylene glycol monobutyl ether was distilled off under reduced pressure to obtain a resin. To the obtained resin, an equimolar amount of potassium hydroxide and an appropriate amount of ion-exchanged water were added based on its acid value, and the mixture was heated to 80 °C and dissolved. Thereby, an aqueous solution of an acrylic resin with an acrylic resin (solid content) content of 20.00% was obtained.

[0090] <Preparation of Dispersion of Acrylic Resin Particles> 18.00 parts of butyl methacrylate, 0.35 part of methacrylic acid, 2.00 parts of a polymerization initiator, and 2.00 parts of n-hexadecane were placed in a flask equipped with a stirring device, a nitrogen inlet tube, a reflux cooling device, and a thermometer, and stirred for 30 minutes while introducing nitrogen gas. 2,2’-Azobis(2-methylbutyronitrile) was used as the polymerization initiator. Next, 78.00 parts of a 6.00% aqueous solution of polyoxyethylene cetyl ether (trade name “NIKKOL BC-20”, manufactured by Nikko Chemicals Co., Ltd.) was added dropwise, and the mixture was stirred for 30 minutes to obtain a mixture. The mixture was emulsified by irradiating ultrasonic waves for 3 hours using an ultrasonic irradiator, and then a polymerization reaction was carried out at 80 °C for 4 hours under a nitrogen atmosphere. After cooling to 25 °C and filtering, an appropriate amount of pure water was added to obtain a dispersion of acrylic resin particles with a resin (solid content) content of 20.00%.

[0091] <Preparation of Ink> (First Ink 1 - 37, Second Ink 1 - 40) Mix the components shown in the upper rows of Tables 3-1 to 3-4 and 4-1 to 4-4 (unit: %) and stir well. After that, perform pressure filtration using a polypropylene filter with a pore size of 1.0 μm (manufactured by Advantec) to prepare Ink 1 to 37 of the first type and Ink 1 to 40 of the second type. The characteristics of the inks are shown in the lower rows of Tables 3-1 to 3-4 and 4-1 to 4-4. The pH of the prepared inks was adjusted using a 0.25 mol / L sulfuric acid aqueous solution so that all of them were within the range of 8.5 to 9.0. The details of the product names in Tables 3-1 to 3-4 and 4-1 to 4-4 are shown below. · FS-300: Fluorine-based surfactant (manufactured by Zonyl) · NIKKOL BC-20: Polyoxyethylene alkyl ether-based surfactant (manufactured by Nikko Chemicals)

[0092] TIFF2025102729000007.tif175170

[0093] TIFF2025102729000008.tif175170

[0094] TIFF2025102729000009.tif176170

[0095] TIFF2025102729000010.tif209170

[0096] TIFF2025102729000011.tif134170

[0097] TIFF2025102729000012.tif134170

[0098] TIFF2025102729000013.tif134170

[0099] TIFF2025102729000014.tif133170

[0100] (Ink 38 of the first type, Ink 41 of the second type) The colored ink composition C01 prepared in the same manner as in Example 7 described in JP-A-2023-79394 was used as the first ink 38, and the black ink composition B07 was used as the second ink 41. The average particle diameter of the wax particles used in the preparation of the first ink 38 was equivalent to the average particle diameter of the wax particles in the first ink 1. The average particle diameter of the pigment used in the preparation of the first ink 38 was controlled to be equivalent to the average particle diameter of the pigment in the first ink 1. The maximum absorbance of the second ink 41 in the wavelength range of 400 nm to 780 nm was 1,400. The first ink 38 is an ink that does not contain a urethane resin.

[0101] (First Ink 39, Second Ink 42) The composition B-1 prepared in the same manner as in Example 3 described in JP-A-2021-31821 was used as the first ink 39, and the composition A-3 was used as the second ink 42. The average particle diameter of the wax particles used in the preparation of the first ink 39 was equivalent to the average particle diameter of the wax particles in the first ink 1. The average particle diameter of the pigment used in the preparation of the first ink 39 was controlled to be equivalent to the average particle diameter of the pigment in the first ink 1. The maximum absorbance of the second ink 42 in the wavelength range of 400 nm to 780 nm was 1,225. The second ink 42 is an ink that does not contain an acetylene glycol-based surfactant.

[0102] <Evaluation> Each ink (first ink and second ink) of the combinations shown in the evaluation conditions of Tables 5-1 and 5-2 was filled into an ink cartridge, and the inkjet recording apparatus equipped with a recording head that discharges ink by thermal energy was set. As the inkjet recording apparatus, a modified machine with the trade name "PIXUS PRO-10S" (manufactured by Canon) was used. In this example, the recording duty of a solid image recorded under the condition of applying 8 ink droplets of 3.5 ng per droplet to a unit area of 1 / 600 inch × 1 / 600 inch was defined as 100%. The ratios of the application amounts (recording duty (%)) of the first ink and the second ink were set to First ink:Second ink = 20:80, 40:60, 50:50, 60:40, and 80:20, respectively. Also, as the recording medium, a product with the trade name "Canon Photo Paper, Glossy Pro [Platinum Grade] PT-201" (manufactured by Canon) was used. In the present invention, according to the evaluation criteria of each item shown below, "AA", "A", and "B" were set as acceptable levels, and "C" was set as an unacceptable level. The evaluation results are shown in Tables 5-1 and 5-2.

[0103] (Method of Applying Ink) In Example 1, the ejection port row of the recording head was divided into 24 parts, and the number of main scans (number of recording passes) when applying the first ink and the second ink to the unit area was set to 24 times. The first ink was set to be ejected from the ejection ports corresponding to 12 / 24 of the upstream ejection port row in the sub-scanning direction in the 1st to 12th passes. The second ink was set to be ejected from the ejection ports corresponding to 12 / 24 of the downstream ejection port row in the sub-scanning direction in the 13th to 24th passes. In this case, the difference in the number of main scans (application start pass difference) between the pass starting the application of the first ink and the pass starting the application of the second ink is 12 times. In Examples and Comparative Examples (other examples) other than Example 1, the number of divisions of the ejection port row of the recording head and the number of main scans were adjusted to control the number of recording passes. Also, the ejection port rows for ejecting the first ink and the second ink, and the application start pass were adjusted to control the application order and pass difference of the ink.

[0104] In order to keep the application time difference between the first ink and the second ink constant, for convenience, each ink was ejected only in one direction of the main scan of the recording head to record an image. Specifically, first, the first ink was ejected from the upstream ejection port row and applied to the recording medium. Next, while returning the carriage on which the recording head was mounted to the home position, the recording medium was conveyed in the sub-scanning direction with a width corresponding to the area where the previous ink was applied. Thereafter, the second ink was also applied to the recording medium in the same procedure as in the case of the first ink. In Example 1, the application time difference (application start time difference) between the first ink and the second ink was set to 18 seconds. In other examples, the scanning speed of the recording head and the width of the recording medium in the main scanning direction were adjusted to control the application start time difference. When the paths for starting the application of the first ink and the second ink were the same, the application start time difference was small, so it was indicated as "-" in the column of "Application start time difference (seconds)" in Table 5. Even in this case, the second ink was applied so as to overlap at least a part of the area where the first ink was applied.

[0105] When the application of the second ink was started after the application of the first ink was completed, it was indicated as "○" in the column of "Second ink application after the first ink ends" in Table 5. When ejecting in this way, the path for applying the first ink and the path for applying the second ink were set so as not to overlap. When the path for applying the first ink and the path for applying the second ink overlapped, and when the application of the second ink was started and then the application of the first ink was started, it was indicated as "×" in the column of "Second ink application after the first ink ends" in Table 5.

[0106] (Scratch resistance) Using the above inkjet recording apparatus, a total of 25 solid images (200 mm × 200 mm) were recorded under the condition of applying each ink in an overlapping manner to a recording medium at the ratio of the application amounts of the above-described 5 patterns. The total application amounts (recording duty) of the first ink and the second ink were set to 20%, 40%, 60%, 80%, and 100%. After drying the recorded images at 25°C for 24 hours, a friction test was carried out under the conditions of 500 g load and 50 reciprocations and 100 reciprocations using a Gakushin type testing machine (abrasion resistance testing machine, manufactured by Imoto Seisakusho) conforming to JIS L 0849:2013. The images after the friction test were visually observed, and the rub resistance of the images was evaluated according to the evaluation criteria shown below. AA: There were no rubbing marks on the image even after 100 reciprocations. A: There were no rubbing marks on the image even after 50 reciprocations, but there were rubbing marks after 100 reciprocations. B: There were rubbing marks on the image after 50 reciprocations, but the white background of the recording medium under the image was not visible. C: There were rubbing marks on the image after 50 reciprocations, and the white background of the recording medium under the image was also visible.

[0107] (Dark part color development property) Using the above inkjet recording apparatus, a total of 25 solid images (200 mm × 200 mm) were recorded under the condition of applying each ink in an overlapping manner to a recording medium at the ratio of the application amounts of the above-described 5 patterns. The total application amounts (recording duty) of the first ink and the second ink were set to 20%, 40%, 60%, 80%, and 100%. After drying the recorded images at 25°C for 24 hours, using the M1 light source of a spectrocolorimeter (trade name "eXact", manufactured by X-Rite), the hue angle (h), chroma (C * C * ), and lightness (L * ) in the CIE L * *a*b color system were measured. Then, the dark part color development property of the image was evaluated according to the evaluation criteria shown below according to the hue angle (h). Different evaluation criteria according to the hue angle (h) were adopted because the preferred color tones felt visually differed depending on the type of color.

[0108] When the hue angle (h) is 0° or more and less than 60° and 300° or more and less than 360° AA: Among 25 images, there was an image with a maximum chroma of 45 or more at lightness (L * ) of 20. A: Among 25 images, there was an image with a maximum chroma of 42 or more and less than 45 at lightness (L * ) of 20. B: Among 25 images, there was an image with a maximum chroma of 40 or more and less than 42 at lightness (L * ) of 20. C: All 25 images had a maximum chroma of less than 40 at lightness (L * ) of 20.

[0109] When the hue angle (h) is 60° or more and less than 180° AA: Among 25 images, there was an image with a maximum chroma of 35 or more at lightness (L * ) of 30. A: Among 25 images, there was an image with a maximum chroma of 32 or more and less than 35 at lightness (L * ) of 30. B: Among 25 images, there was an image with a maximum chroma of 30 or more and less than 32 at lightness (L * ) of 30. C: All 25 images had a maximum chroma of less than 30 at lightness (L * ) of 30.

[0110] When the hue angle (h) is 180° or more and less than 300° AA: Among 25 images, there was an image with a maximum chroma of 50 or more at lightness (L * ) of 20. A: Among 25 images, there was an image with a maximum chroma of 47 or more and less than 50 at lightness (L * ) of 20. B: Among 25 images, there was an image with a maximum chroma of 45 or more and less than 47 at lightness (L * ) of 20. C: All 25 images had a maximum chroma of less than 45 at lightness (L * ) of 20.

[0111] TIFF2025102729000015.tif245170

[0112] TIFF2025102729000016.tif245170

Claims

1. A first recording step of applying an aqueous first ink to a recording medium, and a second recording step of applying an aqueous second ink to the recording medium so as to overlap at least a part of the region of the recording medium to which the first ink has been applied, the inkjet recording method comprising: wherein the first ink is a colored ink containing a first pigment, first wax particles, a silicone-based surfactant, and a urethane resin; the second ink is an achromatic ink containing carbon black, second wax particles, and an acetylene glycol-based surfactant; the maximum absorbance of the second ink in the wavelength range of 400 nm to 780 nm is 210 or more; and the cumulative 50% particle diameter based on volume of the first wax particles is smaller than the cumulative 50% particle diameter based on volume of the first pigment, the inkjet recording method being characterized by this.

2. The inkjet recording method according to claim 1, wherein, between the start of application of the first ink and the start of application of the second ink, the recording head is scanned four or more times with respect to a unit area of the recording medium to record an image in the unit area.

3. The inkjet recording method according to claim 1, wherein the silicone-based surfactant is represented by the following general formula (1). (In the general formula (1), R １ represents an alkylene group, R ２ represents a hydrogen atom or an alkyl group, m and n each independently represent an integer of 1 or more, and a and b each independently represent an integer of 0 or more).

4. The inkjet recording method according to claim 1, wherein the acetylene glycol-based surfactant is represented by the following general formula (2). (In the general formula (2), s and t each independently represent an integer of 0 or more and 15 or less)

5. The inkjet recording method according to claim 1, wherein the first wax particles and the second wax particles are each formed of at least one wax selected from the group consisting of polyethylene, Fischer-Tropsch wax, microcrystalline, paraffin, ozokerite, and ceresin.

6. The inkjet recording method according to any one of claims 1 to 5, wherein the maximum absorbance of the second ink in the wavelength range of 400 nm to 780 nm is 400 or more.

7. The inkjet recording method according to any one of claims 1 to 5, wherein the content (% by mass) of the carbon black in the second ink is 0.60% by mass or more based on the total mass of the second ink.

8. The inkjet recording method according to any one of claims 1 to 5, wherein the content (mass%) of the carbon black in the second ink is 0.08 times or more and 2.00 times or less in terms of the mass ratio to the content (mass%) of the first pigment in the first ink.

9. The inkjet recording method according to any one of claims 1 to 5, wherein the content (mass%) of the second wax particles in the second ink is 0.10 times or more and 5.00 times or less in terms of the mass ratio to the content (mass%) of the first wax particles in the first ink.

10. The content (mass%) of the acetylene glycol-based surfactant in the second ink is in terms of the mass ratio to the content (mass%) of the silicone-based surfactant in the first ink. The inkjet recording method according to any one of claims 1 to 5, wherein it is 0.20 times or more and 8.00 times or less.

11. The inkjet recording method according to any one of claims 1 to 5, wherein the cumulative 50% particle diameter of the first wax particles based on volume is 0.10 times or more and 0.60 times or less in terms of the ratio to the cumulative 50% particle diameter of the first pigment based on volume.

12. A method of recording an image on a unit area of the recording medium by scanning a recording head a plurality of times with respect to the unit area of the recording medium between the start of application of the first ink and the start of application of the second ink, The inkjet recording method according to any one of claims 1 to 5, wherein the time from the start of application of the first ink to the start of application of the second ink is 3 seconds or more.

13. A method of recording an image on a unit area of the recording medium by scanning a recording head a plurality of times with respect to the unit area of the recording medium between the start of application of the first ink and the start of application of the second ink, The inkjet recording method according to any one of claims 1 to 5, wherein the application of the second ink is started after the application of the first ink is completed.

14. An inkjet recording apparatus used for an inkjet recording method having a first recording step of applying an aqueous first ink to a recording medium and a second recording step of applying an aqueous second ink to the recording medium so as to overlap at least a part of the area of the recording medium to which the first ink is applied, The first ink is a colored ink containing a first pigment, first wax particles, a silicone-based surfactant, and a urethane resin. The second ink is an achromatic ink containing carbon black, second wax particles, and an acetylene glycol-based surfactant, the maximum absorbance of the second ink in the wavelength range of 400 nm to 780 nm is 210 or more, An inkjet recording apparatus characterized in that a volume-based cumulative 50% particle diameter of the first wax particles is smaller than a volume-based cumulative 50% particle diameter of the first pigment.

Images