Inkjet ink set and inkjet recording apparatus

Abstract

The invention provides an inkjet ink set and an inkjet recording apparatus. The inkjet ink set includes a base coat liquid and one or more inkjet inks. The primer liquid contains first binder resin particles, a first aqueous medium, and a first surfactant. Each of the inkjet inks contains a second pigment, second binder resin particles, a second aqueous medium, and a second surfactant. At a temperature of 20 DEG C, the density [rho] 1 of the primer liquid and the density [rho] 2 of the inkjet ink having the highest density among the one or more inkjet inks satisfy the relationship represented by mathematical formula (1). (1) Rho1-Rho2 > 0.05 g / cm < 3 >.

Description

Technical Field

[0001] The present invention relates to an ink set for inkjet and an inkjet recording apparatus. Background Art

[0002] In inkjet printing on non-permeable recording media, inkjet ink droplets of each color ejected onto the recording medium may mix and cause color mixing and bleeding. Therefore, inkjet ink used for inkjet printing on non-permeable recording media is required to have pinning performance (performance that enables ejected ink droplets to remain at the ejection position).

[0003] In response to such a demand, for example, an inkjet ink containing a pigment, polyester resin fine particles having a particle size of 30 to 300 nm, and a water-soluble epoxy compound has been proposed. Summary of the invention

[0004] However, even the above-mentioned inkjet inks do not have sufficient pinning performance.

[0005] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an inkjet ink set having excellent pinning performance and an inkjet recording apparatus using the inkjet ink set.

[0006] The inkjet ink set of the present invention comprises a primer and one or more inkjet inks. The primer contains first binder resin particles, a first aqueous medium and a first surfactant. The inkjet inks each contain a second pigment, a second binder resin particle, a second aqueous medium and a second surfactant. At a temperature of 20° C., the density ρ1 of the primer and the density ρ2 of the inkjet ink with the highest density among the one or more inkjet inks satisfy the relationship of the following mathematical formula (1).

[0007] ρ1-ρ2>0.05g / cm 3 ··· (1)

[0008] The inkjet recording device of the present invention comprises: a primer liquid; one or more inkjet inks; a conveying section for conveying a recording medium; a primer liquid ejecting head for ejecting the primer liquid onto the recording medium; and one or more recording heads, which are arranged downstream of the primer liquid ejecting head in the conveying direction of the recording medium and eject the inkjet ink onto at least a portion of the area on the recording medium where the primer liquid has been ejected. The inkjet inks each contain a second pigment, a second binding resin particle, a second aqueous medium, and a second surfactant. At a temperature of 20°C, the density ρ1 of the primer liquid and the density ρ2 of the inkjet ink having the highest density among the one or more inkjet inks satisfy the relationship of the following mathematical formula (1).

[0009] ρ1-ρ2>0.05g / cm 3··· (1)

[0010] [Effects of the Invention]

[0011] The ink jet ink set and the ink jet recording apparatus of the present invention have excellent pinning performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a cross-sectional view of an example of an inkjet recording apparatus according to the second embodiment.

[0013] Figure 2 This is an evaluation image formed for evaluating the pinning performance in Examples. DETAILED DESCRIPTION

[0014] Hereinafter, embodiments of the present invention will be described. In addition, in this specification, unless otherwise specified, the volume median diameter (D 50 ) is a value measured using a dynamic light scattering particle size distribution measuring apparatus (“Zetasizer (registered trademark in Japan) Nano ZS” manufactured by Malvern).

[0015] The elongation at break is a value measured by a tensile test at 25° C. using a tensile testing machine in accordance with “JIS (Japanese Industrial Standard) K7127-1999”.

[0016] Unless otherwise specified, the measured value of the glass transition temperature (Tg) is a value measured using a differential scanning calorimeter (for example, "DSC-60" manufactured by Shimadzu Corporation) in accordance with "JIS (Japanese Industrial Standard) K7121-2012". In the endothermic curve (vertical axis: heat flow (DSC signal); horizontal axis: temperature; heating rate 5°C / min) measured using a differential scanning calorimeter, the inflection point temperature caused by the glass transition (specifically, the temperature of the intersection of the extrapolated line of the baseline and the extrapolated line of the descending line) corresponds to Tg (glass transition temperature).

[0017] In this specification, an acryl group and a methacryl group may be collectively referred to as a “(meth)acryl group.” Each component described in this specification may be used alone or in combination of two or more.

[0018] <First embodiment: inkjet ink set>

[0019] The first embodiment of the present invention relates to an ink set for inkjet (hereinafter, sometimes referred to as an ink set). The ink set comprises a primer and one or more inkjet inks (hereinafter, sometimes referred to as inks). The primer contains first binding resin particles, a first aqueous medium and a first surfactant. Each ink contains a second pigment, a second binding resin particle, a second aqueous medium and a second surfactant. At a temperature of 20°C, the density ρ1 of the primer and the density ρ2 of the highest density ink among the one or more inks satisfy the relationship of the following mathematical formula (1).

[0020] ρ1-ρ2>0.05g / cm 3 ··· (1)

[0021] In the ink set of the present embodiment, the ink is, for example, a single ink (e.g., black ink). Also, in the ink set of the present embodiment, the ink is, for example, a combination of multiple inks (e.g., a four-color ink combination consisting of a cyan ink containing a cyan pigment, a yellow ink containing a yellow pigment, a magenta ink containing a magenta pigment, and a black ink containing a black pigment). The primer is, for example, an ink further containing a first pigment (e.g., a white ink containing a white pigment) or a primer that does not contain a pigment (a primer that is not an ink). The primer is, for example, used by being ejected from the ejection head of an inkjet recording device and applied to a recording medium, or by being applied to a recording medium using a brush, a sprayer, a rod coater, or the like.

[0022] When forming an image using the ink set of this embodiment, first, a primer is applied to the image forming area of ​​the recording medium to perform a primer treatment on the recording medium. Next, the image is formed by ejecting ink onto the recording medium that has been primed. When the ink set of this embodiment includes a plurality of inks, when forming an image, a multi-color image (e.g., a color image) is formed by ejecting the plurality of inks in a predetermined order.

[0023] The ink set of this embodiment is suitable for forming an image on a non-absorbent recording medium (particularly a flexible package). Compared with an absorbent recording medium (e.g., ordinary paper), the ink absorption of the non-absorbent recording medium is poor. In the non-absorbent recording medium, the absorption amount of the aqueous medium is, for example, 1.0 g / m 2As follows. Examples of non-absorbent recording media include: recording media made of resin, recording media made of metal, and recording media made of glass. Examples of recording media made of resin include: resin sheets and resin films. The resin contained in the recording medium made of resin is preferably a thermoplastic resin. Specific resins include: polyethylene, polypropylene, polyvinyl chloride, and polyethylene terephthalate (PET). Examples of recording media made of resin include: OPP film (biaxially oriented polypropylene film) and PET film. When the ink set of this embodiment is used to form an image on a recording medium made of resin, the front side (printing side) of the recording medium may also be subjected to corona discharge treatment.

[0024] The ink set of this embodiment is preferably used for front printing. Here, front printing refers to printing on the front side (the side visible to the observer) of a transparent recording medium. When an observer observes the recording medium printed on the front side, the positional relationship is "observer, image, recording medium", and the observer directly observes the image.

[0025] In addition, when printing on a transparent recording medium, printing on the back side of the recording medium (the side opposite to the side visible to the observer) is called back side printing. When an observer observes the recording medium printed on the back side, the positional relationship is "observer, recording medium, image", and the observer observes the image through the recording medium.

[0026] The ink set of the present embodiment has the above-mentioned structure, and therefore has excellent pinning performance. The reason why the ink set of the present embodiment produces the above-mentioned effect is presumed as follows. The ink set of the present embodiment satisfies mathematical formula (1). That is, the primer liquid has a sufficiently high density compared to the ink. After the ink is sprayed onto a recording medium that has been primed with such a high-density primer liquid, the ink droplets are not easy to diffuse from the ink-applied position. In addition, the ink set of the present embodiment can more effectively suppress the phenomenon of the above-mentioned ink droplets diffusing from the ink-applied position by making both the ink and the primer liquid contain binding resin particles. As a result, the ink set of the present embodiment has excellent pinning performance. The following is a more detailed description of the ink set of the present embodiment.

[0027] At a temperature of 20°C, the density ρ1 of the primer solution and the density ρ2 of the highest density ink among the one or more inks satisfy the relationship of mathematical formula (1). The density ρ1 and the density ρ2 preferably satisfy mathematical formula (1a). By making the density ρ1 and the density ρ2 satisfy mathematical formula (1) (particularly satisfying mathematical formula (1a)), the ink set of this embodiment can exhibit excellent pinning performance.

[0028] ρ1-ρ2>0.05g / cm 3 ··· (1)

[0029] 0.07g / cm 3 <ρ1-ρ2<0.13g / cm 3 ···(1a)

[0030] [Primer]

[0031] The primer solution contains first binding resin particles, a first aqueous medium and a first surfactant. The primer solution preferably further contains a first pigment. By making the primer solution further contain the first pigment, the ink set of this embodiment can provide good hiding power for the formed image when forming an image on a transparent recording medium. In this case, the primer solution can also further contain a pigment-coated resin.

[0032] At 20°C, the density of the primer solution is preferably 1.10 g / cm 3 Above 1.20g / cm 3 Below, more preferably 1.12 g / cm 3 Above 1.16g / cm 3 By setting the density ρ1 of the primer liquid to 1.10 g / cm 3 As described above, the ink set of this embodiment can exhibit a more excellent pinning performance. 3 The following can provide good ejection stability for the primer liquid.

[0033] (First Binding Resin Particles)

[0034] The first binding resin particles are dispersed in the first aqueous medium and function as a binder in an image formed by the primer solution to optimize the fixability of the pigments (eg, the first pigment and the second pigment) to the recording medium.

[0035] The elongation at break of the first binder resin particles at 25° C. is preferably 60% or less, more preferably 1% or more and 20% or less, and further preferably 2% or more and 5% or less. By setting the elongation at break of the first binder resin particles at 25° C. to 60% or less, the adhesion and scratch resistance of the image formed by the ink set of this embodiment to the recording medium can be optimized.

[0036] The volume median diameter of the first binding resin particles is preferably 5 nm to 300 nm, more preferably 100 nm to 250 nm, and further preferably 160 nm to 240 nm. By making the volume median diameter of the first binding resin particles 5 nm to 300 nm, the dispersion stability of the first binding resin particles relative to the first aqueous medium can be optimized.

[0037] The glass transition temperature of the resin contained in the first binder resin particles (hereinafter sometimes referred to as the first binder resin) is preferably 20° C. to 90° C., and more preferably 30° C. to 45° C. By setting the glass transition temperature of the first binder resin to 20° C. or more, the spraying stability of the primer liquid can be further optimized. By setting the glass transition temperature of the first binder resin to 90° C. or less, the adhesion of the image formed by the ink set of this embodiment can be further optimized.

[0038] The first binding resin particles in the primer are preferably contained in a ratio of 3.0% to 20.0% by mass, more preferably 3.0% to 8.0% by mass, and further preferably 12.0% to 17.0% by mass. By making the first binding resin particles contain more than 3.0% by mass, the ink set of this embodiment can exert a more excellent pinning performance, and can optimize the adhesion and scratch resistance of the formed image to the recording medium. By making the first binding resin particles contain less than 20.0% by mass, the jetting stability of the primer can be optimized.

[0039] When the primer solution also contains the first pigment, the first pigment and the first binding resin particles are preferably contained in a total ratio of 12.0% by mass to 20.0% by mass, more preferably 15.0% by mass to 18.0% by mass. On the other hand, when the primer solution does not contain the first pigment, the first binding resin particles are preferably contained in a ratio of 10.0% by mass to 18.0% by mass, more preferably 12.0% by mass to 17.0% by mass.

[0040] The first binding resin particles include, for example, polyurethane resin particles, acrylic resin particles, polyolefin resin particles, and polyester resin particles, preferably polyurethane resin particles. The polyurethane resin particles contain polyurethane resin. The content of the polyurethane resin in the polyurethane resin particles is preferably 80% by mass or more, more preferably 90% by mass or more, and further preferably 100% by mass.

[0041] The polyurethane resin refers to a monomer copolymer containing polyisocyanate and a diol compound or a bisphenol compound. Examples of polyisocyanate include diisocyanate. Examples of diisocyanate include aliphatic diisocyanate, alicyclic diisocyanate, and aromatic diisocyanate.

[0042] (First aqueous medium)

[0043] The first aqueous medium refers to a medium containing water. The first aqueous medium can be used as a solvent or a dispersion medium. Specific examples of the first aqueous medium include: an aqueous medium containing water and a water-soluble organic solvent.

[0044] The content of water in the primer liquid is preferably 50.0 mass % to 85.0 mass %, and more preferably 70.0 mass % to 78.0 mass %.

[0045] Examples of the water-soluble organic solvent in the primer solution include glycol compounds, glycol ether compounds, lactam compounds, nitrogen-containing compounds, acetate compounds, thiodiglycol, glycerol, and dimethyl sulfoxide.

[0046] Examples of the diol compound include ethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol, 1,2-pentanediol, 1,5-pentanediol, 1,2-octanediol, 1,8-octanediol, 3-methyl-1,3-butanediol, 3-methyl-1,5-pentanediol, diethylene glycol, triethylene glycol, and tetraethylene glycol.

[0047] Examples of the glycol ether compound include diethylene glycol diethyl ether (diethoxydiglycol), diethylene glycol monobutyl ether, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol diethyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, and propylene glycol monomethyl ether. The glycol ether compound is preferably diethylene glycol monobutyl ether or triethylene glycol monobutyl ether.

[0048] Examples of the lactam compound include 2-pyrrolidone and N-methyl-2-pyrrolidone.

[0049] Examples of the nitrogen-containing compound include 1,3-dimethylimidazolidinone, formamide, and dimethylformamide.

[0050] As an example of the acetate compound, diethylene glycol monoethyl ether acetate can be mentioned.

[0051] The water-soluble organic solvent in the primer solution is preferably a glycol ether compound, more preferably diethylene glycol monobutyl ether or triethylene glycol monobutyl ether.

[0052] The content ratio of the water-soluble organic solvent in the primer liquid is preferably from 1.0 mass % to 25.0 mass %, and more preferably from 5.0 mass % to 10.0 mass %.

[0053] The total content of water and the glycol ether compound in the first aqueous medium is preferably 90% by mass or more, more preferably 99% by mass or more, and even more preferably 100% by mass.

[0054] The first aqueous medium preferably contains only water and diethylene glycol monobutyl ether, or only water and triethylene glycol monobutyl ether.

[0055] (First Surfactant)

[0056] The first surfactant optimizes the compatibility and dispersion stability of the components contained in the primer solution. In addition, the first surfactant provides wettability of the primer solution to the recording medium. The first surfactant in the primer solution is preferably a nonionic surfactant.

[0057] Examples of nonionic surfactants in the primer include acetylene glycol surfactants (surfactants containing acetylene glycol compounds), silicone surfactants (surfactants containing silicone compounds), and fluorine surfactants (surfactants containing fluorine resins or fluorine-containing compounds). Examples of acetylene glycol surfactants include ethylene oxide adducts of acetylene glycol and propylene oxide adducts of acetylene glycol. The primer preferably contains a silicone surfactant.

[0058] The content ratio of the first surfactant in the primer liquid is preferably 0.05 mass % to 2.0 mass %, and more preferably 0.1 mass % to 0.5 mass %.

[0059] (First Pigment)

[0060] The first pigment forms first pigment particles together with the pigment coating resin, for example. The first pigment particles are composed of, for example, a core containing the first pigment and a pigment coating resin coating the core. The first pigment particles are dispersed in the first aqueous medium, for example.

[0061] As described above, the primer is preferably a white ink. In this case, the first pigment is a white pigment. On the other hand, the primer may be a color ink. In this case, the first pigment is a color pigment.

[0062] Examples of white pigments include zinc white, titanium dioxide, antimony white, zinc sulfide, barite powder, barium carbonate, clay, silicon dioxide, white carbon, talc, calcium carbonate, mica, kaolin, and alumina white. Preferably, the white pigment is titanium dioxide.

[0063] Examples of color pigments include yellow pigments, orange pigments, red pigments, blue pigments, violet pigments, and black pigments. Examples of yellow pigments include CI Pigment Yellow (74, 93, 95, 109, 110, 120, 128, 138, 139, 151, 154, 155, 173, 180, 185, and 193). Examples of orange pigments include CI Pigment Orange (34, 36, 43, 61, 63, and 71). Examples of red pigments include CI Pigment Red (122 and 202). Examples of blue pigments include CI Pigment Blue (15, more specifically 15:3). Examples of violet pigments include CI Pigment Violet (19, 23, and 33). Examples of black pigments include CI Pigment Black (7).

[0064] The volume median diameter of the first pigment particles is preferably 10 nm to 300 nm, and more preferably 40 nm to 120 nm. By setting the volume median diameter of the first pigment particles to be 10 nm or more, the ink set of this embodiment can easily provide the desired image density for the formed image. By setting the volume median diameter of the first pigment particles to be 300 nm or less, excellent storage stability can be provided to the primer solution.

[0065] The first pigment in the primer is preferably contained in a ratio of 8.0% by mass or more and 25.0% by mass or less, more preferably 10.0% by mass or more and 15.0% by mass or less. By making the first pigment in the primer more than 8.0% by mass, it is possible to provide a good hiding power for the image formed by the primer. By making the first pigment in the primer less than 25.0% by mass, it is possible to provide excellent storage stability for the primer.

[0066] (Pigment coated resin)

[0067] The pigment coating resin is attached to the surface of the first pigment to optimize the dispersion stability of the first pigment relative to the first aqueous medium. In addition, a part of the pigment coating resin may not be attached to the surface of the first pigment, but may be free in the first aqueous medium. Examples of the pigment coating resin include polyether resins, (meth) acrylic resins, styrene-(meth) acrylic resins, and styrene-maleic acid resins.

[0068] In the primer, the content of the pigment coating resin is preferably 0.1% by mass or more and 5.0% by mass or less, and more preferably 0.5% by mass or more and 2.0% by mass or less. By making the content of the pigment coating resin 0.1% by mass or more, the dispersion stability of the first pigment relative to the first aqueous medium can be further optimized. By making the content of the pigment coating resin 5.0% by mass or less, the spraying stability of the primer can be further optimized.

[0069] In the primer, the ratio of the mass of the pigment coating resin to the mass of the first pigment is preferably 0.10 to 0.50, and more preferably 0.20 to 0.30. By making the ratio of the mass of the pigment coating resin to the mass of the first pigment 0.10 to 0.50, the dispersion stability of the first pigment relative to the first aqueous medium can be further optimized.

[0070] (Other ingredients)

[0071] The primer solution may further contain well-known additives (more specifically, for example, a dissolution stabilizer, an anti-drying agent, an antioxidant, a viscosity adjuster, a pH adjuster, and a mildew preventer) as necessary.

[0072] (Method for producing primer solution)

[0073] For example, a primer can be produced by mixing a first binder resin particle dispersion containing first binder resin particles, a first aqueous medium, and other components added as needed (e.g., a first pigment dispersion containing a first pigment). In the production of the primer, after the components are uniformly mixed, foreign matter and coarse particles can also be removed by a filter (e.g., a filter with a pore size of 5 μm or less).

[0074] (Preferred components)

[0075] The primer solution preferably has any one of components 1 to 9 in Table 1 below. In addition, in Table 1, the elongation at break of "polyurethane resin particles a" is 1% to 5%. The volume median diameter of "polyurethane resin particles a" is 180nm to 220nm. "Polyurethane resin particles a" contain a polyurethane resin having a glass transition temperature of 35°C to 42°C. The elongation at break of "polyurethane resin particles b" is 45% to 55%. The volume median diameter of "polyurethane resin particles b" is 8nm to 12nm. "Polyurethane resin particles b" contain a polyurethane resin having a glass transition temperature of 72°C to 78°C. The numerical range shown in Table 1 represents the numerical range of the preferred content ratio [mass %] of each component. For example, "10.0-13.0" of the white pigment of component 1 means that the white pigment is contained in a ratio of 10.0% to 13.0% by mass. The abbreviations used in Table 1 are as follows.

[0076] GEGMBE: Diethylene glycol monobutyl ether

[0077] TEGMBE: triethylene glycol monobutyl ether

[0078]

Table 1

[0079]

[0080] [Ink]

[0081] The ink contains a second pigment, second binder resin particles, a second aqueous medium, and a second surfactant. The ink preferably further contains a pigment-coating resin. As described above, the ink set of this embodiment includes one or more inks.

[0082] The density ρ2 of the ink with the highest density among the one or more inks at a temperature of 20°C is preferably 1.00 g / cm 3 Above 1.09g / cm 3 Below, more preferably 1.02 g / cm 3 Above 1.06g / cm 3 By making the density ρ2 of the ink 1.00 g / cm 3 Above 1.09g / cm 3 Next, the ink set of the present embodiment can exhibit more excellent pinning performance.

[0083] (Second Pigment)

[0084] In the ink, the second pigment forms second pigment particles together with the pigment coating resin. The second pigment particles are composed of, for example, a core containing the second pigment and a pigment coating resin coating the core. The second pigment particles are dispersed in the second aqueous medium.

[0085] As described above, the ink is preferably a color ink. In this case, the second pigment is a color pigment. On the other hand, the ink may also be a white ink. In this case, the second pigment is a white pigment. Examples of white pigments and color pigments used in the ink may include the same substances as those exemplified as white pigments and color pigments used in the primer.

[0086] The volume median diameter of the second pigment particles is preferably 10 nm or more and 300 nm or less, and more preferably 70 nm or more and 130 nm or less. By setting the volume median diameter of the second pigment particles to be 10 nm or more, the ink set of this embodiment can easily provide the desired image density for the formed image. By setting the volume median diameter of the second pigment particles to be 300 nm or less, the ink can be provided with excellent storage stability.

[0087] The content ratio of the second pigment in the ink is preferably 1.0 mass % or more and 8.0 mass % or less, and more preferably 1.5 mass % or more and 3.0 mass % or less. By setting the content ratio of the second pigment in the ink to 1.0 mass % or more, it is possible to provide a desired image density for an image formed by the ink set of this embodiment. By setting the content ratio of the second pigment in the ink to 8.0 mass % or less, it is possible to provide the ink with excellent storage stability.

[0088] (Pigment coated resin)

[0089] The pigment coating resin is attached to the surface of the second pigment to optimize the dispersion stability of the second pigment relative to the second aqueous medium. In addition, a part of the pigment coating resin may not be attached to the surface of the second pigment, but may be free in the second aqueous medium. Examples of the pigment coating resin include polyether resins, (meth) acrylic resins, styrene-(meth) acrylic resins, and styrene-maleic acid resins.

[0090] In the ink, the content of the pigment coating resin is preferably 0.1% by mass or more and 4.0% by mass or less, and more preferably 0.5% by mass or more and 1.5% by mass or less. By making the content of the pigment coating resin 0.1% by mass or more, the dispersion stability of the second pigment relative to the second aqueous medium can be further optimized. By making the content of the pigment coating resin 4.0% by mass or less, the jetting stability of the ink can be further optimized.

[0091] [Second Binding Resin Particles]

[0092] The second binding resin particles are present in the second aqueous medium in a dispersed state. The second binding resin particles play a role of a binder in the image formed by the ink set of this embodiment, optimizing the fixability of the second pigment relative to the recording medium. In addition, the second binding resin particles provide scratch resistance to the image formed by the ink set of this embodiment.

[0093] The elongation at break of the second binder resin particles at 25° C. is preferably 1% to 100%, more preferably 40% to 60%. By setting the elongation at break of the second binder resin particles to 100% or less at 25° C., the adhesion and scratch resistance of the image formed by the ink set of this embodiment to the recording medium can be optimized.

[0094] The volume median diameter of the second binding resin particles is preferably 5 nm to 150 nm, more preferably 5 nm to 40 nm, and further preferably 5 nm to 20 nm. By making the volume median diameter of the second binding resin particles 5 nm to 150 nm, the dispersion stability of the second binding resin particles relative to the second aqueous medium can be optimized.

[0095] The glass transition temperature of the resin contained in the second binder resin particles (hereinafter sometimes referred to as the second binder resin) is preferably 45° C. to 90° C., and more preferably 70° C. to 80° C. By setting the glass transition temperature of the second binder resin to 45° C. or higher, the ejection stability of the ink can be further optimized. By setting the glass transition temperature of the second binder resin to 90° C. or lower, the adhesion of the image formed by the ink set of this embodiment can be further optimized.

[0096] The second binding resin particles include, for example, polyurethane resin particles, polyolefin resin particles, and polyester resin particles, preferably polyurethane resin particles or polyester resin particles. In the case where the second binding resin particles contain at least one of polyurethane resin particles and polyester resin particles, the elongation at break of the second binding resin particles is preferably 60% or less. The specific information about the polyurethane resin particles in the ink may be the same as the specific information about the polyurethane resin particles in the primer, so repeated records are omitted. The polyester resin particles contain polyester resin. The content ratio of the polyester resin in the polyester resin particles is preferably 80% by mass or more, more preferably 90% by mass or more, and further preferably 100% by mass.

[0097] Polyester resin can be obtained by polycondensation of one or more polyols with one or more polycarboxylic acids. Examples of polyols used to synthesize polyester resins include diols (e.g., diol compounds and bisphenol compounds) and trivalent or higher alcohols. Examples of polycarboxylic acids used to synthesize polyester resins include dicarboxylic acids and trivalent or higher carboxylic acids. In addition, polycarboxylic acid derivatives (e.g., polycarboxylic acid anhydrides and polycarboxylic acid halides) that can form ester bonds by polycondensation can also be used instead of polycarboxylic acids.

[0098] In the ink, the content ratio of the second binding resin particles is preferably 2.0 mass % or more and 12.0 mass % or less, and more preferably 4.0 mass % or more and 6.0 mass % or less. By making the content ratio of the second binding resin particles 2.0 mass % or more, the scratch resistance and adhesion to the recording medium of the image formed by the ink set of this embodiment can be further optimized. By making the content ratio of the second binding resin particles 12.0 mass % or less, the jetting stability of the ink can be further optimized.

[0099] [Second aqueous medium]

[0100] The second aqueous medium refers to a medium containing water. The second aqueous medium can be used as a solvent or a dispersion medium. Specific examples of the second aqueous medium include: an aqueous medium containing water and a water-soluble organic solvent.

[0101] The content of water in the ink is preferably 40.0% by mass or more and 80.0% by mass or less, and more preferably 60.0% by mass or more and 70.0% by mass or less.

[0102] Examples of the water-soluble organic solvent in the ink are the same as those of the water-soluble organic solvent in the primer solution. The water-soluble organic solvent in the ink is preferably a glycol compound or a glycol ether compound, more preferably 1,2-propylene glycol, 1,3-propylene glycol, 3-methyl-1,3-butanediol or triethylene glycol monobutyl ether.

[0103] The content ratio of the water-soluble organic solvent in the ink is preferably 10.0 mass % to 40.0 mass %, and more preferably 24.0 mass % to 32.0 mass %.

[0104] The total content of water, the glycol compound, and the glycol ether compound in the second aqueous medium is preferably 90% by mass or more, more preferably 99% by mass or more, and even more preferably 100% by mass.

[0105] The second aqueous medium preferably contains only water, 1,2-propylene glycol and triethylene glycol monobutyl ether, or only water, 1,3-propylene glycol and triethylene glycol monobutyl ether, or only water, 1,2-propylene glycol and 3-methyl-1,3-butanediol, or only water and triethylene glycol monobutyl ether.

[0106] (Second Surfactant)

[0107] The second surfactant optimizes the compatibility and dispersion stability of the components contained in the ink. Examples of the second surfactant in the ink can be the same as the type and content ratio of the first surfactant contained in the above-mentioned primer. The second surfactant is preferably a silicone surfactant. That is, the first surfactant and the second surfactant are each preferably a silicone surfactant.

[0108] The content ratio of the second surfactant in the ink is preferably 0.05 mass % to 2.0 mass %, and more preferably 0.1 mass % to 0.5 mass %.

[0109] [Other ingredients]

[0110] The ink may further contain well-known additives (more specifically, for example, a dissolution stabilizer, an anti-drying agent, an antioxidant, a viscosity adjuster, a pH adjuster, and an antifungal agent) as necessary.

[0111] [Ink Manufacturing Method]

[0112] For example, the ink can be manufactured by mixing the second pigment dispersion containing the second pigment, the second binder resin particle dispersion containing the second binder resin particles, the second aqueous medium, the second surfactant, and other components (e.g., additives) added as needed. In the manufacture of the ink, after the components are uniformly mixed, foreign matter and coarse particles can also be removed by a filter (e.g., a filter with a pore size of 5 μm or less).

[0113] (Preferred components)

[0114] The ink preferably has any one of the components 10 to 15 in Table 2 below. In addition, in Table 2, "polyurethane resin particles b" are the same as those in Table 1 above. The elongation at break of "polyurethane resin particles c" is 2% to 6%. The volume median diameter of "polyurethane resin particles c" is 25nm to 35nm. "Polyurethane resin particles c" contain a polyurethane resin having a glass transition temperature of 75°C to 81°C. "PEs particles a" are polyester resin particles having an elongation at break of 8% to 12%. The volume median diameter of "PEs particles a" is 75nm to 95nm. "PEs particles a" contain a polyester resin having a glass transition temperature of 62°C to 68°C. The numerical range shown in Table 2 represents the numerical range of the preferred content ratio [mass %] of each component. For example, "1.8-2.4" of the color pigment of component 10 means that the color pigment is contained in a ratio of 1.8% to 2.4% by mass. The abbreviations used in Table 2 are as follows.

[0115] TEGMBE: triethylene glycol monobutyl ether

[0116] MBD: 3-Methyl-1,3-butanediol

[0117]

Table 2

[0118]

[0119] <Second Embodiment: Inkjet Recording Device>

[0120] The second embodiment of the present invention relates to an inkjet recording device. The inkjet recording device of this embodiment comprises: a primer; one or more inkjet inks; a conveying section for conveying a recording medium; a primer injection head for injecting the primer onto the recording medium; and one or more recording heads, which are arranged downstream of the primer injection head in the conveying direction of the recording medium (hereinafter sometimes described as the sheet conveying direction), and inject ink onto at least a portion of the area on the recording medium where the primer has been injected. The primer contains first binding resin particles, a first aqueous medium, and a first surfactant. Each ink contains a second pigment, a second binding resin particle, a second aqueous medium, and a second surfactant. At a temperature of 20°C, the density ρ1 of the primer and the density ρ2 of the highest density ink among the one or more inks satisfy the relationship of the following mathematical formula (1).

[0121] ρ1-ρ2>0.05g / cm 3 ··· (1)

[0122] The recording medium is preferably a non-absorbent recording medium. The primer liquid and ink provided by the inkjet recording device of the present embodiment are respectively the same as the primer liquid and ink provided by the ink set of the first embodiment. Therefore, it can be said that the inkjet recording device of the present embodiment is an inkjet recording device provided with the ink set of the first embodiment. In addition, the detailed information about the ink set has been described in the first embodiment, so the description thereof is omitted. The inkjet recording device of the present embodiment uses the ink set of the first embodiment, so the pinning performance is excellent.

[0123] In the following, the inkjet recording device of the present embodiment is described with reference to the accompanying drawings. In addition, for ease of understanding, the referenced drawings mainly schematically represent the various structural elements, and for the convenience of drawing, the size and number of the various structural elements shown in the drawings may be different from the actual ones.

[0124] Figure 1 FIG. 2 is a diagram showing a main part of an inkjet recording device 100 as an example of an inkjet recording device according to the present embodiment. Figure 1 As shown, the inkjet recording device 100 mainly includes a conveying unit 1, a line print head, and a drying device 13. The line print head has a primer liquid ejection head 11 and a recording head 12. The inkjet recording device 100 also includes a paper supply tray 2, a paper supply roller 3, a paper supply driven roller 4, a conveyor belt 5, a conveyor belt driving roller 6, a conveyor belt driven roller 7, a discharge roller 8, a discharge driven roller 9, and a paper discharge tray 10. The conveyor belt 5, the conveyor belt driving roller 6, and the conveyor belt driven roller 7 constitute a part of the conveying unit 1. In the inkjet recording device 100, Figure 1At the middle left end, a paper feed tray 2 is provided. The paper feed tray 2 stores recording media M. At one end of the paper feed tray 2, a paper feed roller 3 and a paper feed driven roller 4 are provided. The recording media M stored in the paper feed roller 3 are taken out one by one from the recording medium M at the top position, and are conveyed to the conveyor belt 5, thereby feeding the paper. The paper feed driven roller 4 is pressed against the paper feed roller 3 and rotates drivenly.

[0125] On the downstream side of the sheet conveying direction between the paper feed roller 3 and the paper feed driven roller 4 ( Figure 1 The conveyor belt 5 is set to rotate freely. The conveyor belt 5 is mounted on the conveyor belt driving roller 6 and the conveyor belt driven roller 7. The conveyor belt driving roller 6 is arranged on the downstream side of the conveyor belt driven roller 7 in the sheet conveying direction. The conveyor belt driving roller 6 drives the conveyor belt 5. The conveyor belt driven roller 7 is arranged on the upstream side of the conveyor belt driving roller 6 in the sheet conveying direction. The conveyor belt driven roller 7 is driven by the conveyor belt driving roller 6 through the conveyor belt 5 to rotate. The conveyor belt driving roller 6 is driven to rotate in the clockwise direction, and the recording medium M is moved along the conveyor belt. Figure 1 The sheet is conveyed in the conveying direction indicated by the arrow X.

[0126] Further, a discharge roller 8 and a discharge driven roller 9 are provided on the downstream side of the conveyor belt 5 in the sheet conveying direction. The discharge roller 8 is driven to move along the sheet conveying direction. Figure 1 The ejection driven roller 9 is pressed against the upper part of the ejection roller 8 and rotates in a driven manner. A paper ejection tray 10 is provided on the downstream side of the ejection roller 8 and the ejection driven roller 9 in the sheet conveying direction. The recording medium M ejected outside the device housing is loaded on the ejection tray 10.

[0127] The primer liquid ejection head 11 is disposed above the conveyor belt 5. The primer liquid ejection head 11 ejects the primer liquid toward the image forming region (e.g., the entire surface of the recording medium M) of the recording medium M conveyed on the conveyor belt 5. Thus, the primer liquid ejection head 11 performs primer treatment on the image forming region of the recording medium M.

[0128] The primer liquid jet head 11 is preferably a circulation head. As described in the first embodiment, the primer liquid needs to have a relatively high density, so it often contains a relatively large amount of solid components (for example, the first bonding resin particles and the first pigment). Therefore, when using a common head (non-circulation head) to spray the primer liquid, the solid components of the primer liquid sometimes agglomerate. In contrast, by making the primer liquid jet head 11 a circulation head, the solid components of the primer liquid can be effectively suppressed from agglomerating.

[0129] The recording head 12 is arranged downstream of the primer liquid jet head 11 in the sheet conveying direction. The recording head 12 includes a cyan ink recording head 12C, a magenta ink recording head 12M, a yellow ink recording head 12Y, and a black ink recording head 12K. Above the conveyor belt 5, the cyan ink recording head 12C, the magenta ink recording head 12M, the yellow ink recording head 12Y, and the black ink recording head 12K are arranged in order from the upstream side to the downstream side in the sheet conveying direction. Each of the cyan ink recording head 12C to the black ink recording head 12K is supported at a certain height and has a predetermined interval relative to the top surface of the conveyor belt 5. The cyan ink recording head 12C to the black ink recording head 12K form an image on the primer-treated recording medium M conveyed on the conveyor belt 5. The cyan ink recording head 12C to the black ink recording head 12K respectively store color inks of four different colors (cyan, magenta, yellow, and black). A color image is formed on the recording medium M by ejecting color ink from each of the cyan ink recording head 12C to the black ink recording head 12K.

[0130] The drying device 13 is arranged downstream of the recording head 12 in the sheet conveying direction. The drying device 13 dries the recording medium M during conveyance, for example, by heating the recording medium M during conveyance or blowing air on the recording medium M during conveyance. In addition, the conveying unit 1 preferably also preheats the recording medium M while conveying the recording medium M. By combining the drying of the recording medium M by the drying device 13 with the preheating of the recording medium M by the conveying unit 1, the primer liquid and ink sprayed on the recording medium M can be quickly dried. As a result, the inkjet recording device 100 can exert a better pinning performance. The preheating temperature is, for example, not less than 40°C and not more than 60°C. In the case where the drying device 13 dries the recording medium M by heating, the drying temperature is, for example, not less than 80°C and not more than 120°C.

[0131] As described above, an example of the inkjet recording device of the present embodiment has been described, but the inkjet recording device of the present embodiment is not limited to Figure 1 For example, Figure 1 In the embodiment, an inkjet recording device 100 having four recording heads 12 corresponding to four colors of ink is used as an example for description. However, the number of recording heads provided in the inkjet recording device of this embodiment is not particularly limited as long as it is 2 or more, and can be, for example, 2 or more and 10 or less, and preferably 3 or more and 5 or less.

[0132] In addition, the inkjet recording apparatus 100 sequentially ejects four color inks of cyan, magenta, yellow, and black, but the types, combinations, and ejection order of the inks are not limited thereto.

[0133] Furthermore, the inkjet recording device of this embodiment may not have a heating unit. Furthermore, the conveying unit may not be preheated. Furthermore, the inkjet recording device of this embodiment may also have a serial-type primer spray head and a recording head. Furthermore, the inkjet recording device of this embodiment may also be a multifunctional all-in-one machine having the functions of a scanner, a copier, a printer, or a fax machine.

[0134] [Example]

[0135] Hereinafter, examples of the present invention will be described, but the present invention is not limited to the following examples.

[0136] [Preparation of Pigment Dispersion]

[0137] By the following method, a pigment dispersion having the composition shown in Table 3 was prepared. In Table 3, the pigments of each color are as follows.

[0138] White pigment: Tayca Corporation "JR-804", titanium dioxide particles

[0139] Yellow pigment: BASF Corporation "Palcohol Yellow D1115J"

[0140] Cyan pigment: "Heliogen (Japanese registered trademark) Blue D7088" manufactured by BASF Corporation

[0141] (Preparation of Resin A)

[0142] Resin A for obtaining the "pigment coating resin (resin A-Na)" in Table 3 was prepared by the following method. Specifically, a stirrer, a nitrogen inlet tube, a condenser, and a dropping funnel were set in a four-necked flask. Next, 100 parts by mass of isopropanol and 300 parts by mass of methyl ethyl ketone were placed in the flask. Nitrogen was bubbled in the flask contents while heating and reflux at 70°C.

[0143] Next, solution L1 was prepared. Specifically, 40.0 parts by mass of styrene, 10.0 parts by mass of methacrylic acid, 40.0 parts by mass of methyl methacrylate, 10.0 parts by mass of butyl acrylate, and 0.4 parts by mass of azobisisobutyronitrile (AIBN, polymerization initiator) were mixed to obtain a monomer solution, i.e., solution L1. After the contents of the flask were heated under reflux at 70°C, solution L1 was added dropwise to the flask over 2 hours. After the addition, the contents of the flask were heated under reflux at 70°C for another 6 hours.

[0144] Next, solution L2 was prepared. Specifically, 0.2 parts by mass of AIBN and 150.0 parts by mass of methyl ethyl ketone were mixed to obtain solution L2. Solution L2 was added dropwise to the flask over 15 minutes. After the addition, the contents of the flask were heated and refluxed at 70°C for another 5 hours. Thus, resin A (styrene-(meth) acrylic resin) was obtained. The weight average molecular weight (Mw) of the obtained resin A was 20,000 and the acid value was 100 mgKOH / g.

[0145] The weight average molecular weight Mw of the resin A is measured using a gel filtration chromatograph ("HLC-8020GPC" manufactured by Tosoh Corporation) under the following conditions.

[0146] Chromatographic column: "TSKgel Super MultiporeHZ-H" manufactured by Tosoh Corporation (semi-micro column of 4.6 mm I.D. × 15 cm)

[0147] Number of columns: 3

[0148] Eluent: Tetrahydrofuran

[0149] Flow rate: 0.35mL / min

[0150] Sample injection volume: 10 μL

[0151] Measurement temperature: 40℃

[0152] Detector: IR detector

[0153] The calibration curve was created using TSKgel standard polystyrenes F-40, F-20, F-4, F-1, A-5000, A-2500, and A-1000 manufactured by Tosoh Corporation and n-propylbenzene.

[0154] Also, the acid value of the resin A is measured according to the method described in "JIS (Japanese Industrial Standard) K0070-1992 (Testing methods for acid value, saponification value, ester value, iodine value, hydroxyl value and unsaponifiable matter of chemical products)".

[0155] (Preparation of white pigment dispersion)

[0156] Resin A was heated in a warm bath at 70°C, and an aqueous sodium hydroxide solution in an amount required for neutralization of Resin A was added to Resin A. More specifically, an aqueous sodium hydroxide solution of 1.1 times the mass of the neutralization equivalent was added to Resin A. Thus, an aqueous solution of Resin A (Resin A-Na) neutralized with sodium hydroxide was obtained. The pH value of the aqueous solution of Resin A-Na was 8.

[0157] As shown in Table 3, in a vessel of a media type wet disperser ("DYNO (Japanese registered trademark) MILL" manufactured by Willy A. Bachofen (WAB)), 6.0 parts by mass of the above aqueous solution containing resin A-Na, 50.0 parts by mass of white pigment, 0.5 parts by mass of surfactant ("OLFINE (Japanese registered trademark) E1010" manufactured by Nissin Chemical Industry Co., Ltd., ethylene oxide adduct of acetylene glycol) and water were placed to prepare a mixed solution. The amount of water added was such that the total amount of the mixed solution was 100.0 parts by mass.

[0158] Next, a medium (zirconia beads with a diameter of 1.0 mm) was filled into the container so that the filling rate was 70% by volume of the container capacity, and the mixed liquid (contents of the container) was dispersed using a medium-type disperser to obtain a white pigment dispersion.

[0159] (Preparation of Yellow Pigment Dispersion and Cyan Pigment Dispersion)

[0160] Except for changing the type and amount of pigment to the components shown in Table 3, a yellow pigment dispersion and a cyan pigment dispersion were prepared according to the preparation method of the white pigment dispersion.

[0161] The white pigment dispersion, yellow pigment dispersion, and cyan pigment dispersion were diluted 300 times with water to obtain dilute solutions. The dilute solutions were measured using a dynamic light scattering particle size distribution measuring device ("Zetasizer (Japanese registered trademark) Nano ZS" manufactured by Malvern) to obtain the volume median diameter (D 50 ). Thus, it was confirmed that pigment particles having a volume median diameter in the range of 70 nm to 130 nm were dispersed in each pigment dispersion.

[0162]

Table 3

[0163] White pigment dispersion Yellow pigment dispersion Cyan pigment dispersion White pigment 50.0 - - Yellow pigment - 15.0 - Cyan Pigment - - 15.0 Pigment coating resin (resin A-Na) 6.0 6.0 6.0 Surfactants 0.5 0.5 0.5 water The remainder The remainder The remainder total 100.0 100.0 100.0

[0164] [Binder resin particle dispersion]

[0165] Prepare the binder resin particle dispersions (A) to (E) shown in Table 4 as the binder resin particle dispersions used in the examples. Table 4 also shows the solid content concentration of each binder resin particle (recorded as "concentration" in Table 4), the specific information of the binder resin particles contained in each binder resin particle dispersion, the elongation at break, the volume median diameter (recorded as "diameter" in Table 4), and the glass transition temperature (Tg). In addition, in Table 4, "(R)" indicates a registered trademark in Japan. The "Super Flex (registered trademark in Japan)" series is a product of Dai-ichi Kogyo Seiyaku Co., Ltd. The "Elitel (registered trademark in Japan)" series is a product of Unitika Co., Ltd.

[0166]

Table 4

[0167]

[0168] <Preparation of ink set>

[0169] Ink sets of Examples 1 to 9 and Comparative Examples 1 to 5 were prepared by the following method.

[0170] [Example 1]

[0171] As an ink set of Example 1, a primer liquid, a yellow ink (first ink), and a cyan ink (second ink) prepared by the following method were combined.

[0172] (Preparation of Primer Liquid)

[0173] 23.2 parts by mass of white pigment dispersion (11.6 parts by mass of white pigment, 1.4 parts by mass of pigment coating resin), 12.5 parts by mass of binder resin particle dispersion (A) (5.0 parts by mass of polyurethane resin particles A), 8.0 parts by mass of triethylene glycol monobutyl ether, 0.3 parts by mass of silicone surfactant ("SILFACE (Japanese registered trademark) SAG 503A" manufactured by Nissin Chemical Industry Co., Ltd.) and ion exchange water were mixed to obtain a mixed solution (I). The amount of ion exchange water added was such that the total amount of the mixed solution (I) was 100.0 parts by mass.

[0174] The mixture (I) was stirred at 400 rpm using a stirrer ("THREE-ONE MOTOR BL-600" manufactured by Shinto Scientific Co., Ltd.). Next, the stirred mixed solution (I) was filtered using a filter with a pore size of 5 μm to remove foreign matter and coarse particles. As a result, a primer solution (white ink) used in the ink set of Example 1 having the composition shown in Table 5 was obtained.

[0175] (Preparation of yellow ink)

[0176] 14.3 parts by mass of yellow pigment dispersion (2.1 parts by mass of yellow pigment, 0.9 parts by mass of pigment coating resin), 15.0 parts by mass of binder resin particle dispersion (B) (5.0 parts by mass of polyurethane resin particles B), 20.0 parts by mass of 1,2-propylene glycol, 8.0 parts by mass of triethylene glycol monobutyl ether, 0.3 parts by mass of silicone surfactant ("SILFACE (Japanese registered trademark) SAG 503A" manufactured by Nissin Chemical Industry Co., Ltd.) and ion exchange water were mixed to obtain a mixed solution (II). The amount of ion exchange water added was such that the total amount of the mixed solution (II) was 100.0 parts by mass.

[0177] The mixture (II) was stirred at 400 rpm using a stirrer ("THREE-ONE MOTOR BL-600" manufactured by Shinto Scientific Co., Ltd.). Next, the stirred mixed solution (II) was filtered using a filter with a pore size of 5 μm to remove foreign matter and coarse particles. As a result, a yellow ink (first ink) used in the ink set of Example 1 having the composition shown in Table 6 was obtained.

[0178] (Preparation of cyan ink)

[0179] 14.3 parts by mass of cyan pigment dispersion (2.1 parts by mass of cyan pigment, 0.9 parts by mass of pigment coating resin), 15.0 parts by mass of binder resin particle dispersion (B) (5.0 parts by mass of polyurethane resin particles B), 20.0 parts by mass of 1,2-propylene glycol, 8.0 parts by mass of triethylene glycol monobutyl ether, 0.3 parts by mass of silicone surfactant ("SILFACE (Japanese registered trademark) SAG 503A" manufactured by Nissin Chemical Industry Co., Ltd.) and ion exchange water were mixed to obtain a mixed solution (III). The amount of ion exchange water added was such that the total amount of the mixed solution (III) was 100.0 parts by mass.

[0180] The mixture (III) was stirred at 400 rpm using a stirrer ("THREE-ONE MOTOR BL-600" manufactured by Shinto Scientific Co., Ltd.). Next, the stirred mixed solution (III) was filtered using a filter with a pore size of 5 μm to remove foreign matter and coarse particles. As a result, a cyan ink (second ink) used in the ink set of Example 1 having the composition shown in Table 7 was obtained.

[0181] [Examples 2 to 8 and Comparative Examples 1 to 5]

[0182] Ink sets of Examples 2 to 8 and Comparative Examples 1 to 5 were prepared according to the method for preparing the ink set of Example 1 except for the following changes. In the preparation of the ink sets of Examples 2 to 8 and Comparative Examples 1 to 5, the types and amounts of the components used in the preparation of the primer, yellow ink, and cyan ink were changed to achieve the compositions of the inks shown in Tables 5 to 7. In addition, in Examples 3 to 6 and Comparative Examples 1 to 2 and 5, a primer containing no white pigment (a primer that is not an ink) was used.

[0183]

Table 5

[0184]

[0185]

Table 6

[0186]

[0187]

Table 7

[0188]

[0189] <Evaluation>

[0190] The ink sets of Examples 1 to 9 and Comparative Examples 1 to 5 were evaluated for pinning performance, scratch resistance of the formed images, and adhesion to recording media according to the following methods.

[0191] [Evaluation Machine]

[0192] A textile printer ("MMP8130" manufactured by Mastermind Co., Ltd.) was used as an evaluation machine. The evaluation machine is an inkjet recording device that uses color ink and white ink to form an image. The evaluation machine mainly includes a white ink head (equivalent to a primer injection head) that injects white ink onto a recording medium, a plurality of color ink injection heads (equivalent to a recording head) that inject color ink onto a recording medium, and a conveying unit that conveys the recording medium. The white ink head is a circulation head. The conveying unit includes a mechanism for conveying and preheating the recording medium.

[0193] Each ink set to be evaluated was filled into the evaluation machine. Specifically, the primer liquid ejection head of the evaluation machine was filled with the primer liquid shown in Tables 5 to 7. In addition, the recording head of the evaluation machine was filled with the color ink (yellow ink and cyan ink) shown in Tables 5 to 7.

[0194] As a non-absorbent recording medium, a PET film ("FE2000" manufactured by FUTAMURA CHEMICAL CO., LTD., without surface treatment) was used.

[0195] [Pinning performance]

[0196] In the evaluation of the pinning performance, the preheating temperature of the conveying section is set to 50°C. First, the primer liquid is sprayed out using an evaluation machine to perform primer treatment on the entire surface of the above-mentioned PET film. Next, the yellow ink (first ink) is sprayed out using the evaluation machine to form a yellow stripe image consisting of a plurality of vertical lines with a line width of 5 pixels on the above-mentioned PET film. Next, the cyan ink (second ink) is sprayed out using the evaluation machine to form a cyan stripe image consisting of a plurality of horizontal lines with a line width of 5 pixels on the above-mentioned PET film. Thus, a grid-like image (vertical lines: yellow ink; horizontal lines: cyan ink) is formed on the above-mentioned PET film. Then, after the pre-drying time T (2 seconds or 180 seconds) shown in Table 8, it is dried at 110°C for 5 minutes. This grid-like image is used as an evaluation image.

[0197] In the evaluation of the pinning performance, the bleeding of the intersection of the evaluation images was observed by an optical microscope. Figure 2 As shown, in the evaluation image, there are vertical lines A of yellow ink, horizontal lines B of cyan ink, and the intersection of vertical lines A and horizontal lines B. In the intersection, the yellow ink and the cyan ink are mixed with each other to produce a mixed color part C formed by the mixed color ink. The mixed color part C not only stays at the intersection, but also seeps into the vertical line A and the horizontal line B. The distance that the mixed color part C seeps into the vertical line A (the width of the mixed color part C invading the vertical line A) is taken as the bleeding width X. The ink group with excellent pinning performance has a smaller value of the bleeding width X because the mixed color ink is not easy to bleed. On the contrary, the ink group with poor pinning performance has a larger value of the bleeding width X because the mixed color ink is easy to bleed. The pinning performance of the ink group is judged according to the following criteria.

[0198] (Evaluation criteria for pinning performance)

[0199] A (particularly good): The bleeding width X is 50 μm or less

[0200] B (good): The bleeding width X is more than 50 μm and less than 150 μm

[0201] C (poor): the bleeding width X is 150 μm or more

[0202] [Adhesion]

[0203] First, use the primer liquid injection head of the evaluation machine to spray the primer liquid on the entire surface of the recording medium (PET film) for primer treatment. Then, use the recording head of the evaluation machine to spray yellow ink (first ink) on the recording medium to form a yellow solid image (printing coverage 100%) on the recording medium. Then, after the pre-drying time T (2 seconds or 180 seconds) shown in Table 8, the recording medium is dried at 110°C for 20 minutes. Then, the recording medium is left to stand for 24 hours. The recording medium after standing is used as an evaluation sheet (PET film).

[0204] For the evaluation sheet, a grid test (Cross-cut method) was performed according to JIS (Japanese Industrial Standard) K5600-5-6:1999. Specifically, for the solid image on the evaluation sheet, 6 grid-shaped cuts (like a Go board) with 2 mm intervals were cut and pressed horizontally and vertically to form 25 square grids with a side of 2 mm. A tape ("Cellotape (Japanese registered trademark) CT-18S" manufactured by Michelbon Co., Ltd.) was adhered to the yellow solid image of the evaluation sheet, and the tape was peeled off at an angle of about 60 degrees. The tape was peeled off at a speed of 1 second from the start of peeling to the end of peeling. After the tape was peeled off, the yellow solid image on the evaluation sheet was visually observed to confirm whether the yellow solid image was peeled off. The area where the tape was pasted in the yellow solid image was taken as 100% by area, and the area ratio of the yellow solid image peeled off together with the tape (peeling rate [area %]) was calculated. The adhesion to the recording medium was evaluated according to the following criteria.

[0205] (Evaluation criteria for adhesion)

[0206] A (excellent): There is no image peeling at all (peeling rate 0 area %).

[0207] B (good): The peeling rate exceeds 0 area % and is less than 80 area %.

[0208] C (poor): The peeling rate is 80 area % or more.

[0209] [Scratch resistance]

[0210] According to the evaluation method of adhesion, an evaluation sheet (PET film) was prepared. Copy paper ("CC90" manufactured by Mondi) (hereinafter sometimes referred to as evaluation paper) was placed on the evaluation sheet. Next, a rectangular weight (mass 1 kg) with a bottom size of 5 cm × 4 cm was placed on the evaluation paper. The weight was placed at a position corresponding to the position directly above the yellow solid image. Next, the two ends of the evaluation paper were held and the evaluation paper was moved horizontally. During the horizontal movement, the weight moved back and forth 5 times on the upper side of the yellow solid image. Thus, the yellow solid image was rubbed on the evaluation paper with a load of 1 kg. Then, a reflection densitometer ("FD-9" manufactured by Konica Minolta, Ltd.) was used to measure the image density of the area on the evaluation paper that was in contact with the yellow solid image. The measurement conditions were observation light source "D50", lighting condition "M2", field of view "2°", and concentration state "I". In addition, during the measurement, the image density of the area on the evaluation paper that was not in contact with the yellow solid image was used as the background value. The value obtained by subtracting the background value from the measured image density (FD value) was used as the evaluation value of the scratch resistance. The scratch resistance was evaluated according to the following criteria.

[0211] (Evaluation criteria for scratch resistance)

[0212] A (good): FD value is less than 0.02.

[0213] B (bad): FD value is 0.02 or more.

[0214]

Table 8

[0215]

[0216] As shown in Tables 3 to 8, the ink sets of Examples 1 to 9 include a primer and one or more inks. The primer contains a first binder resin particle, a first aqueous medium, and a first surfactant. Each ink contains a second pigment, a second binder resin particle, a second aqueous medium, and a second surfactant. At a temperature of 20°C, the density ρ1 of the primer and the density ρ2 of the highest density ink among the one or more inks satisfy the relationship of the following mathematical formula (1).

[0217] ρ1-ρ2>0.05g / cm 3 ··· (1)

[0218] The ink sets of Examples 1 to 8 had excellent pinning properties. In addition, the ink sets of Examples 1 to 8 also formed images that were excellent in scratch resistance and adhesion to recording media.

[0219] On the other hand, the ink sets of Comparative Examples 1 to 5 did not satisfy the above formula (1). As a result, the ink sets of Comparative Examples 1 to 5 had poor pinning performance. In addition, the image formed by the ink set of Comparative Example 4 also had poor scratch resistance.

Claims

1. An ink set for inkjet, A primer and one or more inkjet inks are provided. The primer solution contains first binding resin particles, a first aqueous medium and a first surfactant. The inkjet inks each contain a second pigment, second binder resin particles, a second aqueous medium, and a second surfactant, At a temperature of 20° C., the density ρ1 of the primer solution and the density ρ2 of the inkjet ink with the highest density among the one or more inkjet inks satisfy the relationship of the following mathematical formula (1): p1-p2>0.05g / cm 3 ... (1).

2. The inkjet ink set according to claim 1, wherein: The first binder resin particles have a volume median diameter of 100 nm or more and 250 nm or less.

3. The inkjet ink set according to claim 1 or 2, characterized in that: The primer further contains a first pigment, and the total content of the first pigment and the first binder resin particles in the primer is 12.0 mass % or more and 20.0 mass % or less. Alternatively, the primer solution does not contain the first pigment, and the content ratio of the first binder resin particles in the primer solution is 10.0 mass % or more and 18.0 mass % or less.

4. The inkjet ink set according to claim 1 or 2, characterized in that: The density ρ1 is 1.10 g / cm 3 Above 1.20g / cm 3 the following.

5. The inkjet ink set according to claim 1 or 2, characterized in that: The density ρ2 is 1.00 g / cm 3 Above 1.09g / cm 3 the following.

6. The inkjet ink set according to claim 1 or 2, characterized in that: The first binder resin particles include polyurethane resin particles.

7. The inkjet ink set according to claim 1 or 2, characterized in that: The second binder resin particles contain at least one of polyurethane resin particles and polyester resin particles. The second binding resin particles have an elongation at break of 60% or less.

8. The inkjet ink set according to claim 1 or 2, wherein: For printing on non-absorbent recording media.

9. The inkjet ink set according to claim 1 or 2, wherein: For front printing.

10. An inkjet recording device comprising: Primer; one or more inkjet inks; A conveying unit for conveying the recording medium; A primer liquid spray head sprays the primer liquid onto the recording medium; as well as One or more recording heads are arranged downstream of the primer liquid ejecting head in the conveying direction of the recording medium, and eject the inkjet ink to at least a part of the area on the recording medium where the primer liquid has been ejected, The primer solution contains first binding resin particles, a first aqueous medium and a first surfactant. The inkjet inks each contain a second pigment, second binder resin particles, a second aqueous medium, and a second surfactant, At a temperature of 20° C., the density ρ1 of the primer solution and the density ρ2 of the inkjet ink with the highest density among the one or more inkjet inks satisfy the relationship of the following mathematical formula (1): p1-p2>0.05g / cm 3 ... (1).

Images