Ink set and inkjet recording method

Abstract

The present application provides an ink set and an inkjet recording method. The ink set includes an ink for inkjet and a pretreatment liquid. The ink for inkjet contains a pigment, anionic polyurethane resin particles, and an aqueous medium. The pretreatment liquid contains nonionic polyurethane resin particles, (meth)acrylic resin particles, and polyester resin particles.

Description

TECHNICAL FIELD

[0001] The present application relates to an ink set and an inkjet recording method. BACKGROUND

[0002] There is an inkjet recording apparatus which uses an aqueous ink for inkjet containing a pigment and an aqueous medium. The inkjet recording apparatus sometimes forms an image on a non-penetrable recording medium such as an OPP (biaxially stretched polypropylene) film.

[0003] After an image is formed on a non-penetrable recording medium using an inkjet recording apparatus, the ink for inkjet can be repelled by the recording medium, resulting in a white space or the like in the image. Also, the adhesion of an image formed on a non-penetrable recording medium using an inkjet recording apparatus to the recording medium is often low, and the image can be peeled off from the recording medium when rubbed against other members. Therefore, with respect to the ink for inkjet used for these uses, it is required to ensure proper wet spreading even when an image is formed on a non-penetrable recording medium, and also to be able to form an image having excellent adhesion to the recording medium.

[0004] In response to such a requirement, for example, an ink set provided with an ink for inkjet and a pretreatment liquid has been proposed, the ink for inkjet containing a pigment, an organic solvent, water, and a silicone surfactant, and the pretreatment liquid containing water-insoluble resin fine particles and a pigment flocculating agent. The above-described ink set is able to form an image having excellent adhesion to a recording medium. SUMMARY

[0005] However, even the above-described ink set is difficult to form an image having excellent adhesion to a recording medium while ensuring proper wet spreading of the ink for inkjet.

[0006] The present application has been made in view of the above-described problems, and it is an object to provide an ink set and an inkjet recording method which are able to form an image having excellent adhesion to a recording medium while ensuring proper wet spreading of an ink for inkjet.

[0007] The ink set according to the present application is provided with an ink for inkjet and a pretreatment liquid. The ink for inkjet contains a pigment, anionic polyurethane resin particles, and an aqueous medium. The pretreatment liquid contains nonionic polyurethane resin particles, (meth)acrylic resin particles, and polyester resin particles.

[0008] The inkjet recording method according to the present application forms an image on a recording medium using the above-described ink set, and is provided with a coating step of coating the pretreatment liquid on the recording medium, and an image forming step of forming an image on the recording medium by ejecting the ink for inkjet from a recording head after the coating of the pretreatment liquid.

[0009] EFFECTS OF THE INVENTION

[0010] The ink set and inkjet recording method according to the present application can form an image having excellent adhesion to a recording medium while ensuring that the ink for inkjet has appropriate wet spreading properties. DETAILED DESCRIPTION

[0011] Hereinafter, the present application embodiments will be described. In addition, in the following, unless otherwise specified, the measurement value of the volume median diameter (D 50 ) is a value measured using a dynamic light scattering type particle size distribution measuring device (for example, "Zetasizer (Japanese registered trademark) Nano ZS" manufactured by Malvern Corporation).

[0012] In the present specification, a propenyl group and a methacryl group are sometimes collectively referred to as "(meth)acryl group". Each component described in the present specification can be used singly or in combination of two or more.

[0013] <First Embodiment: Ink Set>

[0014] Hereinafter, the ink set according to the first embodiment of the present application will be described. The ink set of the present application is provided with an ink for inkjet (hereinafter, sometimes simply referred to as ink) and a pretreatment liquid. The ink contains a pigment, anionic polyurethane resin particles, and an aqueous medium. The pretreatment liquid contains nonionic polyurethane resin particles, (meth)acrylic resin particles, and polyester resin particles.

[0015] The ink set of the present application is suitable for forming an image on a non-penetrable recording medium. The non-penetrable recording medium has a poor ink permeability compared to a penetrable recording medium. In the non-penetrable recording medium, the absorption amount of the aqueous medium is, for example, 1.0 g / m 2 Hereinafter. The non-penetrable recording medium can be exemplified by, for example, a resin-made recording medium, a metal-made recording medium, and a glass-made recording medium. The resin-made recording medium can be exemplified by, for example, a resin sheet and a resin film. The resin contained in the resin-made recording medium is preferably a thermoplastic resin. Specific resins can be exemplified by, for example, polyethylene, polypropylene, polyvinyl chloride, and polyethylene terephthalate (PET). The resin-made recording medium can be exemplified by, for example, an OPP film. In the case where the ink set of the present application is used to form an image on a resin-made recording medium, a corona discharge treatment can also be performed on the surface (print surface) of the recording medium.

[0016] The ink set of the present application is capable of forming an image having excellent adhesion to a recording medium while ensuring that the ink has proper wet-spreading properties, by having the above-described structure. The reason is presumed as follows. In the ink set of the present application, the pre-treatment liquid contains nonionic polyurethane resin particles, (meth)acrylic resin particles, and polyester resin particles. The pre-treatment liquid applied to the recording medium forms a film (pre-treatment coating film) containing the three kinds of resin particles as main components. Among them, non-porous recording media are mostly made of non-polar materials as main components, like OPP films. In contrast, the pre-treatment coating film contains nonionic polyurethane resin particles as non-polar resin particles, and thus has excellent affinity with non-polar materials. Also, the (meth)acrylic resin particles can optimize the affinity of the pre-treatment coating film with non-polar materials. Therefore, the pre-treatment coating film has excellent adhesion to the recording medium (substrate adhesion).

[0017] Also, the pigment component (e.g., pigments and pigment-coating resins described later) contained in the ink has hydrophilicity. In contrast, the pre-treatment coating film contains (meth)acrylic resin particles and polyester resin particles as hydrophilic resin particles, and thus has moderate hydrophilicity on its surface. Therefore, the pre-treatment coating film has excellent affinity with the pigment component. In particular, the (meth)acrylic resin particles contained in the pre-treatment coating film can optimize the affinity of the pigment component with the pre-treatment coating film. Also, the ink contains anionic polyurethane resin particles. The anionic polyurethane resin particles function as a binding resin particle that protects the pigment component after the ink forms an image. Also, the anionic polyurethane resin particles have polarity, and thus have excellent affinity with the pre-treatment coating film. As a result, the ink set of the present application can provide excellent adhesion between the image formed by the ink and the pre-treatment coating film (coating film adhesion). Therefore, the image formed by the ink set of the present application has excellent adhesion to the recording medium, because it can provide excellent substrate adhesion and coating film adhesion.

[0018] Also, the ink easily and properly wet-spreads on the surface of the pre-treatment coating film containing polyester resin particles. Therefore, the ink set of the present application can ensure that the ink has proper wet-spreading properties. Also, in a well-known ink, the components contained in the ink sometimes easily aggregate after a binding resin particle is added. In contrast, in the ink set of the present application, anionic polyurethane resin particles are used as the binding resin particle. Among them, the pigment component contained in the ink often has anionicity. Therefore, in the ink, electrostatic repulsion occurs between the anionic polyurethane resin particles and the pigment component, and thus the above-described aggregation is inhibited. Thus, the ink set of the present application can make the ink have proper wet-spreading properties and make the image have excellent adhesion to the recording medium, while inhibiting the aggregation of the ink.

[0019] [Ink]

[0020] The ink in the ink set of the present application contains a pigment, anionic polyurethane resin particles, and an aqueous medium. The ink preferably further contains a pigment-coating resin.

[0021] (Pigment)

[0022] In the ink, the pigment forms a pigment particle, for example, together with the pigment-coating resin. The pigment particle is formed, for example, of a core containing the pigment and a pigment-coating resin coating the core. The pigment-coating resin is present, for example, dispersed in the solvent. The volume median diameter of the pigment particle is preferably 30 nm or more and 200 nm or less, more preferably 70 nm or more and 130 nm or less, from the viewpoint of optimizing the color density, the color hue, or the stability of the ink.

[0023] The pigment may, for example, be a yellow pigment, an orange pigment, a red pigment, a blue pigment, a violet pigment, and a black pigment. The yellow pigment may, for example, be C.I. Pigment Yellow (74, 93, 95, 109, 110, 120, 128, 138, 139, 151, 154, 155, 173, 180, 185, and 193). The orange pigment may, for example, be C.I. Pigment Orange (34, 36, 43, 61, 63, and 71). The red pigment may, for example, be C.I. Pigment Red (122 and 202). The blue pigment may, for example, be C.I. Pigment Blue (15, more specifically 15:3). The violet pigment may, for example, be C.I. Pigment Violet (19, 23, and 33). The black pigment may, for example, be C.I. Pigment Black (7).

[0024] In the ink, the proportion of the pigment is preferably 0.5% by mass or more and 10.0% by mass or less, more preferably 1.5% by mass or more and 5.0% by mass or less. By making the proportion of the pigment 0.5% by mass or more, the ink is able to form an image having a desired image density. Also, by making the proportion of the pigment 10.0% by mass or less, the flowability of the ink can be ensured.

[0025] (Pigment-coating resin)

[0026] The pigment-coating resin is a resin that is soluble in the aqueous medium of the ink. For example, a part of the pigment-coating resin is present on the surface of the pigment particle, optimizing the dispersibility of the pigment particle. For example, a part of the pigment-coating resin is present in a state of being dissolved in the aqueous medium of the ink.

[0027] The pigment-coated resin is preferably a styrene-(meth)acrylic resin. The styrene-(meth)acrylic resin has styrene units and repeating units from at least one of (meth)acrylic acid alkyl ester and (meth)acrylic acid. Examples of the (meth)acrylic acid alkyl ester include (meth)acrylic acid methyl ester, (meth)acrylic acid ethyl ester, (meth)acrylic acid propyl ester, and (meth)acrylic acid butyl ester. The styrene-(meth)acrylic resin is preferably a copolymer of styrene, methyl methacrylate, methacrylic acid, and butyl acrylate.

[0028] The content ratio of the pigment-coated resin in the ink is preferably 0.1 mass% or more and 4.0 mass% or less, and more preferably 0.5 mass% or more and 1.5 mass% or less. By setting the content ratio of the pigment-coated resin to 0.1 mass% or more and 4.0 mass% or less, the ejection stability of the ink can be ensured.

[0029] The content of the pigment-coated resin in the ink is preferably 10 parts by mass or more and 60 parts by mass or less, and more preferably 20 parts by mass or more and 30 parts by mass or less, with respect to 100 parts by mass of the pigment. By setting the content of the pigment-coated resin to 10 parts by mass or more and 60 parts by mass or less, the ejection stability of the ink can be optimized.

[0030] (Anionic polyurethane resin particles)

[0031] The anionic polyurethane resin particles contain an anionic polyurethane resin. The content ratio of the anionic polyurethane resin in the anionic polyurethane resin particles is preferably 80 mass% or more, more preferably 90 mass% or more, and further preferably 100 mass%. The anionic polyurethane resin refers to a resin having anionicity among polyurethane resins. The anionic polyurethane resin particles are likely to coexist with a pigment component having anionicity in the ink because they have anionicity.

[0032] The volume median diameter of the anionic polyurethane resin particles is preferably 5 nm or more and 150 nm or less, and more preferably 30 nm or more and 70 nm or less. By setting the volume median diameter of the anionic polyurethane resin particles to 5 nm or more, the storage stability of the ink can be optimized. By setting the volume median diameter of the anionic polyurethane resin particles to 150 nm or less, the ejection stability of the ink can be optimized.

[0033] The content ratio of the anionic polyurethane resin particles in the ink is preferably 1.0 mass% or more and 12.0 mass% or less, and more preferably 2.0 mass% or more and 6.0 mass% or less. By setting the content ratio of the anionic polyurethane resin particles to 1.0 mass% or more, the adhesion of an image formed by the ink set of the present application to a recording medium can be further optimized. By setting the content ratio of the anionic polyurethane resin particles to 12.0 mass% or less, the ejection stability of the ink can be optimized.

[0034] (polyurethane resin)

[0035] The polyurethane resin refers to a monomer copolymer containing a polyisocyanate and a diol compound or a bisphenol compound.

[0036] The polyisocyanate can be exemplified by, for example, diisocyanates. The diisocyanates can be exemplified by, for example, aliphatic diisocyanates, alicyclic diisocyanates and aromatic diisocyanates.

[0037] The aliphatic diisocyanates can be exemplified by, for example, ethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate and 1,6-hexamethylene diisocyanate.

[0038] The alicyclic diisocyanates can be exemplified by, for example, hydrogenated 4,4'-diphenylmethane diisocyanate, 1,4-cyclohexane diisocyanate, methylcyclohexylene diisocyanate, isophorone diisocyanate and norbornane diisocyanate.

[0039] The aromatic diisocyanates can be exemplified by, for example, 4,4'-diphenylmethane diisocyanate, m-xylylene diisocyanate, toluene diisocyanate and naphthalene diisocyanate.

[0040] The diol compound can be exemplified by, for example, ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 2-buten-1,4-diol, 1,5-pentanediol, 2-penten-1,5-diol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, dipropylene glycol, 1,4-benzenediol, polyethylene glycol, polypropylene glycol and polytetramethylene glycol.

[0041] The bisphenol compound can be exemplified by, for example, bisphenol A, hydrogenated bisphenol A, bisphenol A ethylene oxide adduct (e.g., polyoxyethylene (2,2)-2,2-bis(4-hydroxyphenyl)propane) and bisphenol A propylene oxide adduct.

[0042] (aqueous medium)

[0043] The aqueous medium contained in the ink refers to a medium containing water. The aqueous medium can be used as a solvent, and can also be used as a dispersion medium. Specific examples of the aqueous medium can be exemplified by water and an aqueous medium containing a water-soluble organic solvent.

[0044] (water)

[0045] The proportion of water contained in the ink is preferably 25.0% by mass or more and 80.0% by mass or less, and more preferably 40.0% by mass or more and 70.0% by mass or less.

[0046] (water-soluble organic solvent)

[0047] The water-soluble organic solvent in the ink can be exemplified by, for example, glycol compounds, glycol ether compounds, lactam compounds, nitrogen-containing compounds, acetate compounds, thiodiglycol, glycerol, and dimethyl sulfoxide.

[0048] The glycol compounds can be exemplified by, for example, ethylene glycol, 1,3-propanediol, 1,2-propanediol, 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.

[0049] The glycol ether compounds can be exemplified by, for example, diethylene glycol diethyl ether, diethylene glycol monobutyl ether, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol diethyl ether, dipropylene glycol methyl ether, triethylene glycol monomethyl ether (methyl triethylene glycol), triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, and propylene glycol monomethyl ether.

[0050] The lactam compounds can be exemplified by, for example, 2-pyrrolidone and N-methyl-2-pyrrolidone.

[0051] The nitrogen-containing compounds can be exemplified by, for example, 1,3-dimethylimidazolidinone, formamide, and dimethylformamide.

[0052] The acetate compounds can be exemplified by, for example, diethylene glycol monoethyl ether acetate.

[0053] The water-soluble organic solvent is preferably a glycol compound or a glycol ether compound, and more preferably 1,2-propanediol, triethylene glycol monobutyl ether, dipropylene glycol methyl ether, or triethylene glycol monomethyl ether.

[0054] The content ratio of the water-soluble organic solvent in the ink is preferably 10.0% by mass or more and 50.0% by mass or less, and more preferably 25.0% by mass or more and 40.0% by mass or less.

[0055] (Surfactant)

[0056] The ink preferably further contains a surfactant. The surfactant optimizes the compatibility and dispersion stability of the respective components contained in the ink. Also, the surfactant optimizes the wettability of the ink with respect to the recording medium. The surfactant in the ink is preferably a nonionic surfactant.

[0057] The nonionic surfactant in the ink is, for example, an acetylene glycol surfactant (a surfactant containing an acetylene glycol compound), a silicone surfactant (a surfactant containing a silicone compound), and a fluorine surfactant (a surfactant containing a fluororesin or a fluorine-containing compound). The acetylene glycol surfactant can be exemplified by, for example, an oxirane adduct of acetylene glycol and a propylene oxide adduct of acetylene glycol.

[0058] The ink preferably contains a silicone surfactant.

[0059] The content ratio of the surfactant in the ink is preferably 0.01 mass% or more and 1.00 mass% or less, more preferably 0.02 mass% or more and 0.10 mass% or less.

[0060] (Other components)

[0061] The ink can further contain, as necessary, well-known additives (more specifically, a dissolution stabilizer, a drying inhibitor, an antioxidant, a viscosity modifier, a pH modifier, and a mildew preventive).

[0062] (Method for producing the ink)

[0063] For example, the ink can be produced by uniformly mixing, with a stirrer, a pigment dispersion liquid containing a pigment, a dispersion liquid containing anionic polyurethane resin particles, and other components (for example, water and a surfactant) added as necessary. In the production of the ink, after the components are uniformly mixed, foreign matter and coarse particles can be removed by a filter (for example, a filter having a pore diameter of 5 μm or less).

[0064] (Pigment dispersion liquid)

[0065] The pigment dispersion liquid refers to a dispersion liquid containing a pigment. The pigment dispersion liquid preferably further contains a pigment-coating resin. The dispersion medium of the pigment dispersion liquid is preferably water.

[0066] The content ratio of the pigment in the pigment dispersion liquid is preferably 5.0 mass% or more and 25.0 mass% or less, more preferably 10.0 mass% or more and 20.0 mass% or less. The content ratio of the pigment-coating resin in the pigment dispersion liquid is preferably 1.0 mass% or more and 10.0 mass% or less, more preferably 2.0 mass% or more and 6.0 mass% or less.

[0067] The pigment dispersion liquid can be produced by wet dispersion of a pigment, a pigment-coating resin, a dispersion medium (for example, water), and components (for example, a surfactant) added as necessary, using a medium-type wet disperser. In the wet dispersion of the medium-type wet disperser, for example, a small-diameter bead (for example, a bead having a diameter of 0.5 mm or more and 1.0 mm or less) can be used as a medium. The material of the bead is not particularly limited, and a hard material (for example, glass and zirconia) is preferred. 50 The material of the bead is not particularly limited, and a hard material (for example, glass and zirconia) is preferred.

[0068] (PREFERRED COMPONENTS)

[0069] The ink is preferably composed of each of components 1 to 4 in Table 1 and components 5 to 8 in Table 2 below. Furthermore, in Tables 1 and 2 below, "ratio" indicates a preferred range of proportions [mass %]. For example, "3.5-4.1" for the proportion of cyan pigment in component 1 means that it contains 3.5% to 4.1% by mass of cyan pigment. "e-1" refers to D... 50 These are anionic polyurethane resin particles with a diameter between 55.0 nm and 68.0 nm. "e-2" refers to D... 50 These are anionic polyurethane resin particles with a size between 9.0 nm and 11.0 nm. "e-3" refers to D... 50 These are anionic polyurethane resin particles with a size between 36.0 nm and 44.0 nm. "DPGME" stands for dipropylene glycol methyl ether.

[0070] Table 1

[0071]

[0072] Table 2

[0073]

[0074] [Pretreatment solution]

[0075] The pretreatment solution contains nonionic polyurethane resin particles, (meth)acrylic resin particles, and polyester resin particles. Preferably, the pretreatment solution further contains an aqueous medium.

[0076] (Nonionic polyurethane resin particles)

[0077] The nonionic polyurethane resin particles contain nonionic polyurethane resin. The proportion of nonionic polyurethane resin in the nonionic polyurethane resin particles is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 100% by mass. Nonionic polyurethane resin refers to a polyurethane resin that is neither anionic nor cationic.

[0078] The median volume diameter of the nonionic polyurethane resin particles is preferably 50 nm to 1000 nm, more preferably 70 nm to 180 nm. By ensuring the median volume diameter of the nonionic polyurethane resin particles is 50 nm or more, the storage stability of the pretreatment solution can be optimized. By ensuring the median volume diameter of the nonionic polyurethane resin particles is 1000 nm or less, the coatability of the pretreatment solution can be optimized. Furthermore, when the pretreatment solution is coated onto the recording medium using an inkjet printing method, the ejection stability of the pretreatment solution can be optimized.

[0079] The content ratio of the nonionic polyurethane resin particles in the pre-treatment liquid is preferably 2.0 mass% or more and 15.0 mass% or less, more preferably 3.0 mass% or more and 5.0 mass% or less. By making the content ratio of the nonionic polyurethane resin particles 2.0 mass% or more, the adhesion of the image formed by the ink set of the present application to the recording medium can be further optimized. By making the content ratio of the nonionic polyurethane resin particles 12.0 mass% or less, the coatability of the pre-treatment liquid can be optimized. Also, in the case where the pre-treatment liquid is applied to the recording medium by the inkjet method, the ejection stability of the pre-treatment liquid can be optimized.

[0080] ((METH)ACRYLATE RESIN PARTICLES)

[0081] The (meth)acrylate resin particles contain a (meth)acrylate resin. The content ratio of the (meth)acrylate resin in the (meth)acrylate resin particles is preferably 80 mass% or more, more preferably 90 mass% or more, further preferably 100 mass%. The (meth)acrylate resin preferably has a hydroxyl group. The (meth)acrylate resin has a repeating unit from at least one of an alkyl (meth)acrylate and a (meth)acrylic acid. The (meth)acrylate resin preferably further has a repeating unit from a hydroxyalkyl (meth)acrylate (e.g., 2-hydroxyethyl (meth)acrylate).

[0082] The volume median diameter of the (meth)acrylate resin particles is preferably 30 nm or more and 200 nm or less, more preferably 70 nm or more and 120 nm or less. By making the volume median diameter of the (meth)acrylate resin particles 50 nm or more, the storage stability of the pre-treatment liquid can be optimized. By making the volume median diameter of the (meth)acrylate resin particles 200 nm or less, the coatability of the pre-treatment liquid can be optimized. Also, in the case where the pre-treatment liquid is applied to the recording medium by the inkjet method, the ejection stability of the pre-treatment liquid can be optimized.

[0083] The content ratio of the (meth)acrylate resin particles in the pre-treatment liquid is preferably 1.0 mass% or more and 10.0 mass% or less, more preferably 2.0 mass% or more and 5.0 mass% or less. By making the content ratio of the (meth)acrylate resin particles 1.0 mass% or more, the adhesion of the image formed by the ink set of the present application to the recording medium can be further optimized. By making the content ratio of the (meth)acrylate resin particles 10.0 mass% or less, the coatability of the pre-treatment liquid can be optimized. Also, in the case where the pre-treatment liquid is applied to the recording medium by the inkjet method, the ejection stability of the pre-treatment liquid can be optimized.

[0084] (POLYESTER RESIN PARTICLES)

[0085] The polyester resin particles contain a 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.

[0086] The polyester resin can be obtained by polycondensation of one or more polyhydric alcohols and one or more polybasic carboxylic acids. The polyhydric alcohols used for the synthesis of the polyester resin are, for example, dihydric alcohols (e.g., diol compounds and bisphenol compounds) and trihydric or higher alcohols. The polybasic carboxylic acids used for the synthesis of the polyester resin are, for example, dibasic carboxylic acids and tribasic or higher carboxylic acids. In addition, polybasic carboxylic acid derivatives (e.g., polycarboxylic anhydrides and polycarboxylic acid halides) capable of forming ester bonds by polycondensation can be used instead of the polybasic carboxylic acids. The diol compounds and bisphenol compounds used for the synthesis of the polyester resin can be the same compounds as the examples of the diol compounds and bisphenol compounds used for the synthesis of the polyurethane resin.

[0087] The trihydric or higher alcohols can be, for example, sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, dipropylene glycerol, 2-methylglycerol, 2-methyl-1,2,4-butanetriol, trimethylol ethane, trimethylol propane, and 1,3,5-trihydroxytoluene.

[0088] The dibasic carboxylic acids can be, for example, maleic acid, fumaric acid, citraconic acid, mesaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, adipic acid, sebacic acid, azelaic acid, malonic acid, succinic acid, alkyl succinic acids (more specifically, n-butyl succinic acid, isobutyl succinic acid, n-octyl succinic acid, n-dodecyl succinic acid, isododecyl succinic acid), and alkenyl succinic acids (more specifically, n-butenyl succinic acid, isobutenyl succinic acid, n-octenyl succinic acid, n-dodecenyl succinic acid, isododecenyl succinic acid).

[0089] The tribasic or higher carboxylic acids can be, for example, 1,2,4-benzene tricarboxylic acid (trimellitic acid), 2,5,7-naphthalene tricarboxylic acid, 1,2,4-naphthalene tricarboxylic acid, 1,2,4-butanetrimellitic acid, 1,2,5-hexanetrimellitic acid, 1,3-dicarboxy-2-methyl-2-methylene carboxy propane, 1,2,4-cyclohexanetrimellitic acid, tetra(methylene carboxy)methane, 1,2,7,8-octanetetra carboxylic acid, pyromellitic acid, and Empol trimer acid.

[0090] The volume median diameter of the polyester resin particles is preferably 50 nm or more and 200 nm or less, and more preferably 70 nm or more and 150 nm or less. By making the volume median diameter of the polyester resin particles 50 nm or more, the storage stability of the pretreatment liquid can be optimized. By making the volume median diameter of the polyester resin particles 200 nm or less, the coatability of the pretreatment liquid can be optimized. Also, in the case where the pretreatment liquid is applied to the recording medium by the inkjet method, the ejection stability of the pretreatment liquid can be optimized.

[0091] The content ratio of the polyester resin particles in the pretreatment liquid is preferably 1.0% by mass or more and 10.0% by mass or less, and more preferably 2.0% by mass or more and 5.0% by mass or less. By making the content ratio of the polyester resin particles 1.0% by mass or more, the wet spreading property of the ink can be further optimized. By making the content ratio of the polyester resin particles 10.0% by mass or less, the coatability of the pretreatment liquid can be optimized. Also, in the case where the pretreatment liquid is applied to the recording medium by the inkjet method, the ejection stability of the pretreatment liquid can be optimized.

[0092] The total content ratio of the (meth)acrylic resin particles and the polyester resin particles in the pretreatment liquid is preferably 2.0% by mass or more and 15.0% by mass or less, and more preferably 3.0% by mass or more and 6.0% by mass or less. By making the total content ratio described above 2.0% by mass or more, the wet spreading property of the ink can be further optimized while further optimizing the adhesion of the image formed by the ink set of the present application to the recording medium. By making the total content ratio described above 15.0% by mass or less, the coatability of the pretreatment liquid can be optimized. Also, in the case where the pretreatment liquid is applied to the recording medium by the inkjet method, the ejection stability of the pretreatment liquid can be optimized.

[0093] (Aqueous medium)

[0094] The aqueous medium contained in the pretreatment liquid is a medium containing water. The aqueous medium can be used as a solvent, and can also be used as a dispersion medium. Specific examples of the aqueous medium can include water and an aqueous medium containing a water-soluble organic solvent.

[0095] (Water)

[0096] The content ratio of water in the pretreatment liquid is preferably 25.0% by mass or more and 80.0% by mass or less, and more preferably 40.0% by mass or more and 70.0% by mass or less.

[0097] (Water-soluble organic solvent)

[0098] The water-soluble organic solvent in the pretreatment liquid is not particularly limited as long as it has compatibility with the other components. By including a water-soluble organic solvent in the pretreatment liquid, the drying property of the pretreatment liquid can be optimized. Specific examples of the water-soluble organic solvent in the pretreatment liquid include methanol, ethanol, 1-propanol, 2-propanol, 1,2-propanediol, acetone, tetrahydrofuran, and acetonitrile. The water-soluble organic solvent in the pretreatment liquid is preferably 2-propanol, 1,2-propanediol, or methanol.

[0099] The proportion of the water-soluble organic solvent in the pretreatment liquid is preferably 10.0% by mass or more and 50.0% by mass or less, and more preferably 20.0% by mass or more and 30.0% by mass or less.

[0100] (Surfactant)

[0101] The pretreatment liquid preferably further includes a surfactant. The surfactant can optimize the compatibility and dispersion stability of the components included in the pretreatment liquid. Also, the surfactant optimizes the wettability of the recording medium with the pretreatment liquid. The surfactant in the pretreatment liquid is preferably a nonionic surfactant.

[0102] The nonionic surfactant in the pretreatment liquid can be the same compound as the examples of the nonionic surfactant in the ink. The pretreatment liquid preferably includes an acetylenic diol surfactant.

[0103] The proportion of the surfactant in the pretreatment liquid is preferably 0.01% by mass or more and 1.00% by mass or less, and more preferably 0.02% by mass or more and 0.10% by mass or less.

[0104] (PREFERRED COMPONENTS)

[0105] The pretreatment liquid preferably has each of the components 1 to 4 in Table 3 below, the components 5 to 8 in Table 4 below, and the components 9 to 11 in Table 5 below. In addition, in Tables 3 to 5 below, "a-1" indicates that the (meth)acrylic resin particles and the polyester resin particles have a D50 of 78.0 nm or more and 96.0 nm or less. 50 "a-2" indicates that the (meth)acrylic resin particles and the polyester resin particles have a D50 of 81.0 nm or more and 99.0 nm or less. 50 "a-3" indicates that the (meth)acrylic resin particles and the polyester resin particles have a D50 of 81.0 nm or more and 99.0 nm or less. 50 "(b-1) indicates that the nonionic polyurethane resin particles have a D50 of 101.0 nm or more and 123.0 nm or less. 50 "(b-2) indicates that the nonionic polyurethane resin particles have a D50 of 101.0 nm or more and 123.0 nm or less. 50 "(b-3) indicates that the nonionic polyurethane resin particles have a D50 of 126.0 nm or more and 154.0 nm or less. 50Nonionic polyurethane resin particles with a wavelength of 630.0 nm to 770.0 nm are used. "Ratio" indicates a preferred range of proportions [mass %]. Therefore, for example, the proportion "4.6-5.6" of resin particles "a-1" in component 1 means: a mixture of (meth)acrylic resin particles and polyester resin particles in a proportion of 4.6% to 5.6% by mass, and D... 50 It is a mixture of particles with a wavelength between 78.0 nm and 96.0 nm.

[0106] Table 3

[0107]

[0108] Table 4

[0109]

[0110] Table 5

[0111]

[0112] (Pretreatment solution preparation method)

[0113] For example, a pretreatment solution can be prepared by uniformly mixing a dispersion containing nonionic polyurethane resin particles, a dispersion containing (meth)acrylic resin particles and polyester resin particles, and other components (e.g., water, water-soluble organic solvents, and surfactants) as needed, using a mixer. In the preparation of the pretreatment solution, after the components are uniformly mixed, foreign matter and coarse particles can also be removed by passing the mixture through a filter (e.g., a filter with a pore size of 5 μm or less).

[0114] <Second Implementation Method: Inkjet Recording Method>

[0115] Next, the inkjet recording method according to the second embodiment of the present invention will be described. The inkjet recording method of the present invention forms an image on a recording medium using the ink group according to the first embodiment, and includes a pretreatment step and an image forming step. The pretreatment step refers to coating a pretreatment liquid onto the recording medium, and the image forming step refers to forming an image on the recording medium by ejecting ink from a recording head after the pretreatment step. Because the inkjet recording method of the present invention uses the ink group according to the first embodiment, it is able to form an image with excellent adhesion to the recording medium while ensuring that the ink has appropriate wetting and spreading properties. The recording medium is preferably a non-permeable recording medium.

[0116] [Pretreatment process]

[0117] In this process, the pre-treatment liquid is applied to the recording medium. The method of applying the pre-treatment liquid to the recording medium is not particularly limited, and for example, bar coating, spray coating, inkjet spraying, and dipping can be given. The method of applying the pre-treatment liquid is preferably inkjet spraying.

[0118] In this process, on the surface of the recording medium, the application of the pre-treatment liquid can be performed only to the region to which ink is jetted, or the application of the pre-treatment liquid can be performed to the entire surface of the recording medium.

[0119] In this process, the amount of the pre-treatment liquid applied is, for example, an amount such that the liquid film thickness of the pre-treatment liquid formed on the recording medium is 2 μm or more and 10 μm or less.

[0120] During the progress of this process or after this process, the recording medium can also be heated to promote drying of the liquid film of the pre-treatment liquid. By drying the liquid film of the pre-treatment liquid, a pre-treatment coating film mainly composed of nonionic polyurethane resin particles, (meth)acrylic resin particles, and polyester resin particles is formed on the recording medium.

[0121] [Ink jetting process]

[0122] In this process, ink is jetted from a recording head to the recording medium after the pre-treatment process, whereby a desired image is formed. The recording head is not particularly limited, and for example, a piezoelectric recording head and a thermal jet recording head can be given. During the progress of this process or after this process, the recording medium can also be heated to promote drying of the ink.

[0123]

Example

[0124] Hereinafter, examples of the present application will be described. However, the present application is not limited to the following examples.

[0125] In this example, the volume median diameter (D 50 ) is a value measured using a dynamic light scattering type particle size distribution measuring device ("Zetasizer (Japanese registered trademark) Nano ZS" manufactured by Malvern). In addition, in the measurement, the measurement object was diluted with ion exchange water as necessary, and then the measurement was performed.

[0126] [Preparation of pre-treatment liquid]

[0127] The pre-treatment liquids (P-1) to (P-14) were prepared by the following method. First, the commercially available pre-treatment liquid used in the preparation of the pre-treatment liquid will be described below.

[0128] (Pre-treatment liquid dispersion)

[0129] A-1: "A-647GEX" manufactured by Takemoto Oil & Fat Co., Ltd.

[0130] A-2: "A-645GH" manufactured by Takemoto Oil & Fat Co., Ltd.

[0131] A-3: "A-615GE" manufactured by Takemoto Oil & Fat Co., Ltd.

[0132] A-4: "A-640" manufactured by Takemoto Oil & Fat Co., Ltd.

[0133] A-5: "Joncryl (Japan Registered Trademark) PDX-6102B" manufactured by BASF Co.

[0134] B-1: "NS-310X-A" manufactured by Takemoto Oil & Fat Co., Ltd.

[0135] B-2: "Super Flex (Japan Registered Trademark) 500M" manufactured by the First Industrial Co., Ltd.

[0136] B-3: "Super Flex (Japan Registered Trademark) E-2000" manufactured by the First Industrial Co., Ltd.

[0137] B-4: "ETERNACOLL (Japan Registered Trademark) UW-1527DF" manufactured by UBE Industries, Ltd.

[0138] Specific information of each of the pretreatment liquid dispersions is shown in detail in Table 6 below.

[0139] [Table 6]

[0140]

[0141] The pretreatment liquids (P-1) to (P-14) were prepared by mixing each of the components described in Tables 7 and 8 below. The "surfactant" is an acetylene glycol surfactant (SURFYNOL (Japan Registered Trademark) 440 manufactured by Shin-Etsu Chemical Co., Ltd., an ethylene oxide adduct of acetylene glycol).

[0142] [Table 7]

[0143]

[0144] [Table 8]

[0145]

[0146] [Preparation of pigment dispersions]

[0147] The pigment dispersions (C) and (Y) for ink preparation were prepared. The components contained in each of the pigment dispersions and the amounts thereof are shown in Table 9 below.

[0148] [Table 9]

[0149]

[0150] In Table 9, "Resin A-Na" indicates Resin A (pigment-coating resin) which has been neutralized by sodium hydroxide (NaOH). The "blue pigment" and the "yellow pigment" are as follows, respectively.

[0151] Blue pigment: "Heliogen (Japan registered trademark) Blue D7088" manufactured by BASF Corporation

[0152] Yellow pigment: "Palcohol Yellow D1115J" manufactured by BASF Corporation

[0153] [Preparation of Resin A]

[0154] Resin A used for obtaining "Resin A-Na" of Table 9 was prepared by the following method. Specifically, a stirrer, a nitrogen introduction tube, a condenser, and a dropping funnel were provided in a four-necked flask. Next, 100 parts by mass of isopropyl alcohol and 300 parts by mass of methyl ethyl ketone were put in the flask. Nitrogen bubbling was performed in the contents of the flask while heating under reflux at 70°C.

[0155] 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. Solution L1 was added dropwise to the flask over 2 hours while heating under reflux at 70°C. After the addition, the contents of the flask were further heated under reflux at 70°C for 6 hours.

[0156] 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 further heated under reflux at 70°C for 5 hours. Thus, Resin A (styrene-(meth)acrylic acid 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.

[0157] Here, the weight average molecular weight Mw of Resin A was measured using a gel filtration chromatograph ("HLC-8020 GPC" manufactured by TOSOH CORPORATION) under the following conditions.

[0158] Column: "TSKgel SuperMultipore HZ-H" (4.6 mm I.D. x 15 cm semi-micro column) manufactured by TOSOH CORPORATION

[0159] Number of columns: 3

[0160] Eluent: Tetrahydrofuran

[0161] Flow rate: 0.35 mL / min

[0162] Sample injection amount: 10 μL

[0163] Measurement temperature: 40°C

[0164] Detector: IR detector

[0165] A calibration curve was created using TSKgel standard polystyrene F-40, F-20, F-4, F-1, A-5000, A-2500, and A-1000 manufactured by Tosoh Corporation, and n-propylbenzene.

[0166] Further, the acid value of the resin A was measured according to the method described in "JIS (Japanese Industrial Standards) K0070-1992 (Test methods for acid value, saponification value, ester value, iodine value, hydroxyl value, and unsaponifiable matter of chemical products)".

[0167] (Pigment dispersion liquid (C))

[0168] The resin A was heated with a water bath at 70°C, and an aqueous solution of sodium hydroxide in an amount required for neutralization of the resin A was added to the resin A. More specifically, an aqueous solution of sodium hydroxide in an amount of 1.1 times the mass of the neutralization equivalent was added to the resin A. Thus, an aqueous solution of the resin A after neutralization with sodium hydroxide (resin A-Na) was obtained. The pH of the aqueous solution of the resin A-Na was 8.

[0169] An aqueous solution containing 5 parts by mass of the resin A-Na, 15 parts by mass of the cyan pigment, and water, the total amount being 100 parts by mass, were put in a vessel of a media-type wet disperser (Willy A. Bachofen Co., Ltd. (WAB Co., Ltd.) manufactured "DYNO (Japanese Registered Trademark) MILL") in the proportions shown in Table 9. In addition, water was added so that the mass of the water, including the mass of the water contained in the aqueous solution of sodium hydroxide used for neutralization of the resin A and the mass of the water produced by the neutralization reaction, reached 80 parts by mass.

[0170] Next, media (zirconia beads with a diameter of 1.0 mm) were filled in the vessel so that the filling rate reached 70% by volume of the capacity of the vessel. The contents of the vessel were subjected to dispersion treatment using the media-type wet disperser. Thus, a pigment dispersion liquid for cyan ink, i.e., pigment dispersion liquid (C), was obtained.

[0171] The pigment dispersion liquid (C) was diluted 300 times with water to obtain a diluted liquid. The diluted liquid was measured using a dynamic light scattering particle size distribution measuring device ("Zetasizer (Japanese registered trademark) Nano ZS" manufactured by Malvern), and the volume median diameter (D50) of the pigment particles contained in the pigment dispersion liquid (C) was calculated. 50 As a result, it was confirmed that the pigment particles having a volume median diameter in the range of 70 nm or more and 130 nm or less were dispersed in the pigment dispersion liquid (C).

[0172] (Pigment dispersion liquid (Y))

[0173] The pigment dispersion liquid (Y) was prepared according to the method for preparing the pigment dispersion liquid (C), except that the kinds and amounts of the ingredients described in Table 9 were used. The pigment dispersion liquid (Y) is a pigment dispersion liquid for yellow ink.

[0174] [Preparation of inks]

[0175] The inks (I-9) were prepared by the following method. The commercially available ink dispersions used in the preparation of each ink are described below.

[0176] (Ink dispersions)

[0177] E-1: "ETERNACOLL (Japanese registered trademark) UW-1527DF" manufactured by UBE Industries, Ltd.

[0178] E-2: "Super Flex (Japanese registered trademark) 170" manufactured by DKS

[0179] E-3: "Super Flex (Japanese registered trademark) 210" manufactured by DKS

[0180] E-4: "NS-310X" manufactured by Takemoto Oil & Fat Co., Ltd.

[0181] The specific information of each ink dispersion is described in detail in Table 10 below.

[0182] [Table 10]

[0183] Resin particles Solid content concentration [mass%] D 50 [nm]]]> E-1 Anionic polyurethane resin particles 29.8 61.5 E-2 Anionic polyurethane resin particles 33.0 10.0 E-3 Anionic polyurethane resin particles 35.0 40.0 E-4 Nonionic polyurethane resin particles 14.0 112.0

[0184] (Ink (I-1))

[0185] A pigment dispersion liquid (C) 25.0 parts by mass (containing cyan pigment 3.75 parts by mass, resin A-Nal.25 parts by mass), an ink-dispersion liquid (E-1) 10.1 parts by mass (containing resin particles 3.0 parts by mass), 1,2-propanediol 25.0 parts by mass, triethylene glycol monobutyl ether (butyl triethylene glycol) 8.0 parts by mass, a silicone surfactant ("SILFACE (registered trademark) SAG503A" manufactured by Nippon Shokubai Co., Ltd., polyether-modified siloxane compound) 0.04 parts by mass, and water were put in a beaker. The amount of water added was an amount to make the total amount of the mixture in the beaker 100 parts by mass. Using a blender ("Three-one motor BL-600" manufactured by Shinto Scientific Co., Ltd.), the contents of the beaker were mixed at a rotation speed of 400 rpm to obtain a mixed liquid. The mixed liquid was filtered using a filter (pore size 5 μm) to remove foreign matter and coarse particles contained in the mixed liquid. Thus, an ink (I-1) of a cyan ink was obtained.

[0186] (Inks (I-2) to (I-9))

[0187] Inks (I-2) to (I-8) of a cyan ink and an ink (I-9) of a yellow ink were produced in accordance with the production method of the ink (I-1), except that the materials used were changed as shown in Table 11 below.

[0188] The abbreviations used in Table 11 below are explained below.

[0189] %: mass %

[0190] Surfactant: silicone surfactant ("SILFACE (registered trademark) SAG503A" manufactured by Nippon Shokubai Co., Ltd., polyether-modified siloxane compound)

[0191] DPGME: dipropylene glycol methyl ether

[0192] [Table 11]

[0193]

[0194] <Preparation of ink sets>

[0195] The ink sets of Examples 1 to 22 and Comparative Examples 1 to 9 were prepared by combining the inks and the pretreatment liquids as shown in Table 12 below.

[0196] <Evaluation>

[0197] The wettability and spreadability of the inks and the adhesion of the images formed were evaluated for each of the ink sets by the following methods. The results of the evaluation are shown in Table 12 below.

[0198] [evaluation machine]

[0199] An inkjet recording apparatus (test machine manufactured by Ricoh Office Imaging Systems, Inc.) using a line-type head system was used as the evaluation machine. The evaluation machine was equipped with four recording heads (manufactured by Ricoh Corporation, "KJ4B-HD06MHG-STDV") and a conveyance table, which were arranged in parallel along the printing direction. From the upstream to the downstream in the printing direction, the recording heads were a black ink recording head, a cyan ink recording head, a magenta ink recording head, and a yellow ink recording head, respectively. Each recording head had 2656 nozzles. The distance between the recording heads was set to 55 cm. The recording heads were set to apply a voltage of 21 V, a driving frequency of 20 kHz, a droplet discharge amount of 3 pL, a head temperature of 32°C, a resolution of 600 dpi, and a pre-discharge flushing number of 1000 times. When the evaluation machine was used to form an image, the conveyance table was preheated to 40°C. Also, when the evaluation machine was used to form an image, the conveyance speed of the image was set to 30 m / min. An OPP film (manufactured by Toray Industries, Inc., "TORAY FAN (registered trademark)") was used as the recording medium.

[0200] [Pre-treatment]

[0201] Each of the pre-treatment liquids possessed by the ink sets was applied to the recording medium using a bar coater #01 (sold by AS ONE Corporation). The application amount of the pre-treatment liquid was an amount that made the thickness of the liquid film 6 μm. Then, the recording medium was dried at 80°C for 2 minutes. Thus, a pre-treatment coating film was formed on the recording medium. Thus, the recording medium after the pre-treatment process was obtained.

[0202] [Wetting spreadability]

[0203] A striped image (hereinafter, referred to as an evaluation image) composed of 14 parallel fine lines (1-pixel lines) was formed on the recording medium after the pre-treatment process using the evaluation machine. Next, for each of the films on which the evaluation image was formed, drying was performed at 80°C for 120 seconds using a drying machine (ON-300SB, sold by AS ONE Corporation). The line width of each fine line was measured for the dried evaluation image. The average value of the measured line widths (average line width) was used as the evaluation value of the wetting spreadability of the ink. The greater the evaluation value, the more excellent the wetting spreadability of the ink was judged to be. The wetting spreadability of the ink was determined according to the following criteria.

[0204] (Criteria for wetting spreadability)

[0205] A (good): evaluation value was 70 μm or more

[0206] B (poor): evaluation value was 50 μm or more and less than 70 μm

[0207] C (particularly poor): evaluation value was less than 50 μm

[0208] [Substrate adhesion]

[0209] On the pre-treatment coating film on the recording medium after the pre-treatment process, 6 grid-shaped (checkered pattern) cuts at 1 mm intervals were cut in the longitudinal direction to form 25 square grids of 1 mm on a side. On the pre-treatment coating film on which the cuts were made, a tape (manufactured by Cellotape Co., Ltd., "Cellotape (Japanese Registered Trademark) CT-24") was attached, and the tape was peeled off (peeling treatment) at an angle of about 60 degrees. The tape peeling was performed at a speed of 1 second from the start of peeling to the end of peeling. After the peeling treatment, the recording medium was observed, and the number of grids peeled off was counted from the 25 grids formed on the pre-treatment coating film. The substrate adhesion was determined according to the following criteria.

[0210] (Criteria for determination of substrate adhesion)

[0211] A (particularly good): No grid peeled off

[0212] B (good): The number of grids peeled off was 1 or more but less than 3

[0213] C (poor): The number of grids peeled off was 4 or more but less than 6

[0214] D (particularly poor): The number of grids peeled off was 7 or more

[0215] [Coating film adhesion]

[0216] On the recording medium after the pre-treatment process, a solid image (40 mm x 40 mm, print coverage 100%) was formed. For the film after the image forming process, drying was performed using the above dryer at 80°C for 120 seconds. On the solid image on the recording medium after drying, 6 grid-shaped (checkered pattern) cuts at 1 mm intervals were cut in the longitudinal direction to form 25 square grids of 1 mm on a side. On the solid image on which the cuts were made, a tape (manufactured by Cellotape Co., Ltd., "Cellotape (Japanese Registered Trademark) CT-24") was attached, and the tape was peeled off (peeling treatment) at an angle of about 60 degrees. The tape peeling was performed at a speed of 1 second from the start of peeling to the end of peeling. After the peeling treatment, the recording medium was observed, and the number of grids peeled off was counted from the 25 grids formed on the solid image. The coating film adhesion was determined according to the following criteria.

[0217] (Criteria for determination of coating film adhesion)

[0218] A (particularly good): No grid peeled off

[0219] B (good): The number of grids peeled off was 1 or more but less than 3

[0220] C (poor): The number of cells peeled off is 4 or more and less than 6

[0221] D (particularly poor): The number of cells peeled off is 7 or more

[0222] [Table 12]

[0223]

[0224] As shown in Tables 6 to 12, the ink sets of Examples 1 to 22 have an ink and a pretreatment liquid. The ink contains a pigment, anionic polyurethane resin particles, and an aqueous medium. The pretreatment liquid contains nonionic polyurethane resin particles, (meth)acrylic resin particles, and polyester resin particles. The ink sets of Examples 1 to 22 ensure that the ink has appropriate wet-spreading properties while also forming an image having excellent adhesion to a recording medium.

[0225] On the other hand, the ink sets of Comparative Examples 1 to 9 are not satisfactory in terms of the above-described structure, and at least one of the wet-spreading properties, the substrate adhesion, and the coating film adhesion of the ink is poor.

[0226] Specifically, the ink of the ink sets of Comparative Examples 1 to 3 does not contain anionic polyurethane resin particles, but instead contains nonionic polyurethane resin particles in place thereof. It is judged that the image formed by the ink containing nonionic polyurethane resin particles is insufficient in terms of adhesion to a hydrophilic pretreatment coating film. Therefore, the coating film adhesion of the ink sets of Comparative Examples 1 to 3 is poor.

[0227] The pretreatment liquid of the ink sets of Comparative Examples 4 to 6 does not contain nonionic polyurethane resin particles, but instead contains anionic polyurethane resin particles in place thereof. It is judged that the pretreatment coating film not containing nonionic polyurethane resin particles is insufficient in terms of adhesion to a nonpolar recording medium such as an OPP film. Therefore, the substrate adhesion of the ink sets of Comparative Examples 4 to 6 is poor.

[0228] In the ink set of Comparative Example 7, the ink does not contain anionic polyurethane resin particles, and the pretreatment liquid does not contain nonionic polyurethane resin particles. Therefore, the substrate adhesion and the coating film adhesion of the ink set of Comparative Example 7 are both poor.

[0229] The pretreatment liquid of the ink set of Comparative Example 8 does not contain (meth)acrylic resin particles. It is judged that the pretreatment coating film not containing (meth)acrylic resin particles is insufficient in terms of adhesion to a nonpolar recording medium such as an OPP film. Therefore, the substrate adhesion of the ink set of Comparative Example 8 is poor.

[0230] The ink set of Comparative Example 9 has a pretreatment liquid not containing polyester resin particles. It is judged that the pretreatment coating film not containing polyester resin particles has low hydrophilicity, and the ink is difficult to wet and spread. Therefore, the wet and spreadability of the ink in the ink set of Comparative Example 9 is poor. Also, the coating film adhesion of the ink set of Comparative Example 9 is also poor.

Claims

1. An ink set comprising an ink for inkjet and a pretreatment liquid, characterized in that, the ink for inkjet contains a pigment, anionic polyurethane resin particles, and an aqueous medium, the pretreatment liquid contains nonionic polyurethane resin particles, (meth)acrylic resin particles, and polyester resin particles, the proportion of the anionic polyurethane resin particles in the ink for inkjet is 1.0 mass% or more and 12.0 mass% or less, the proportion of the nonionic polyurethane resin particles in the pretreatment liquid is 2.0 mass% or more and 15.0 mass% or less, the proportion of the (meth)acrylic resin particles is 2.0 mass% or more and 10.0 mass% or less, the proportion of the polyester resin particles is 2.0 mass% or more and 10.0 mass% or less.

2. An inkjet recording method, forming an image on a recording medium using the ink set according to claim 1, the inkjet recording method comprises a coating step and an image forming step, the coating step is a step of coating the pretreatment liquid on the recording medium, the image forming step is a step of forming an image on the recording medium by ejecting the ink for inkjet from a recording head after the coating of the pretreatment liquid.

3. The inkjet recording method according to claim 2, characterized in that, The recording medium is an aqueous medium having an absorption of 1.0 g / m 2 The following non-penetrable recording medium.

Images