Ink set and recording method

Abstract

To obtain an image excellent in visibility and optical density using a white ink and a color ink.SOLUTION: There is provided an ink set comprising a non-white ink composition and a white ink composition, wherein the non-white ink composition and the white ink composition are an aqueous inkjet ink, the non-white ink composition comprises a silicone-based surfactant A having a maximum peak in the molecular weight region of 300 or more in the molecular weight region of 3000 to 20000 in the molecular weight distribution by gel permeation chromatography and comprises a silicone-based surfactant B having no maximum peak in the molecular weight region of 300 or more in the molecular weight region of 3000 or more in the molecular weight distribution by gel permeation chromatography and having an HLB value of 10.5 or less according to the Griffin method.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an ink set and a recording method. [Background technology]

[0002] The inkjet recording method is capable of recording high-resolution images using a relatively simple device, and has been rapidly developing in various fields. Among these methods, when recording on a transparent recording medium, a method has been studied in which a background image is formed using white ink to serve as a background for a color ink image, and the color image and the background image are superimposed to improve the visibility of the color image.

[0003] Among these, Patent Document 1 discloses an ink set for the purpose of providing an ink set that can suppress misregistration of images when recording on a heated recording medium using an ink with a high solids content and an ink with a low solids content, the ink set comprising a first ink composition and a second ink composition, the first ink composition and the second ink composition being aqueous inkjet ink compositions containing solids including a colorant and an organic solvent, the first ink composition having a solids content that is 5% by mass or more higher than the second ink composition, and the second ink composition having an organic solvent content that is 7% by mass or more higher than the first ink composition, and the ink set is used in an inkjet recording method in which the inks are applied to a heated recording medium. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-167518 Summary of the Invention [Problem to be solved by the invention]

[0005] However, images recorded using white ink for the background image and color ink for the color image are still insufficient in terms of visibility and density. [Means for solving the problem]

[0006] The ink set of the present invention is an ink set comprising a non-white ink composition containing a non-white coloring material, and a white ink composition containing a white coloring material, wherein the non-white ink composition and the white ink composition are water-based inkjet inks, and the non-white ink composition contains a silicone-based surfactant A that, in a molecular weight distribution measured by gel permeation chromatography, has a maximum peak in a molecular weight range of 3,000 to 20,000 within a molecular weight range of 300 or more, and the white ink composition contains a silicone-based surfactant B that, in a molecular weight distribution measured by gel permeation chromatography, does not have a maximum peak at a molecular weight of 3,000 or more within a molecular weight range of 300 or more, and has an HLB value of 10.5 or less as measured by the Griffin method.

[0007] Furthermore, the recording method of the present invention is a recording method for recording on a recording medium using the above-mentioned ink set, and includes a white ink applying step of ejecting a white ink composition from an inkjet head and applying it to the recording medium, and a non-white ink applying step of ejecting a non-white ink composition from the inkjet head and applying it to the recording medium. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram of an inkjet recording apparatus that can be used in this embodiment. [Figure 2] FIG. 1 is a schematic side view of an inkjet recording apparatus that can be used in the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described in detail with reference to the drawings as necessary, but the present invention is not limited to this, and various modifications are possible without departing from the spirit of the present invention. In the drawings, the same elements are given the same reference numerals, and redundant explanations will be omitted. Furthermore, positional relationships such as up, down, left, and right will be based on the positional relationships shown in the drawings unless otherwise specified. Furthermore, the dimensional ratios of the drawings are not limited to those shown in the drawings.

[0010] 1. Ink set The ink set according to this embodiment is an ink set comprising a non-white ink composition containing a non-white coloring material, and a white ink composition containing a white coloring material, wherein the non-white ink composition and the white ink composition are water-based inkjet inks, and the non-white ink composition contains a silicone-based surfactant A that, in a molecular weight distribution measured by gel permeation chromatography, has a maximum peak at a molecular weight of 300 or more in a range of 3,000 to 20,000, and the white ink composition contains a silicone-based surfactant B that, in a molecular weight distribution measured by gel permeation chromatography, does not have a maximum peak at a molecular weight of 3,000 or more in a range of 300 or more, and has an HLB value of 10.5 or less as measured by the Griffin method.

[0011] When recording on a transparent recording medium or a non-white recording medium, a method is known in which a white ink composition is first applied to form a background image, and then a non-white ink composition is applied on top of the background image to form a color image, thereby improving the visibility of the color image.

[0012] In this case, the white ink used for the background image is preferably one that wets and spreads easily on the recording medium, fills the surface of the recording medium well, and has excellent hiding power. In particular, when recording on a low-absorbency recording medium or a non-absorbent recording medium, a white ink composition with higher hiding power and excellent visibility is preferred. However, such a white ink with excellent hiding power has the problem of easily mixing with a non-white ink composition applied on top of it. It has been found that such mixing causes the background image and the color image to mix, resulting in a whitish image and poor optical density.

[0013] In contrast to this, in the present embodiment, by using silicone surfactants with different properties in the non-white ink composition and the white ink composition, it is possible to suppress mixing of the non-white ink composition and the white ink composition without impairing the hiding power of the white ink composition, and to obtain an image with excellent image visibility and optical density.

[0014] Furthermore, instead of the conventional method of depositing a non-white ink composition on top of a white ink composition, studies have recently been conducted on the simultaneous deposition of a non-white ink composition and a white ink composition to obtain an image with excellent hiding power and visibility. The ink set of this embodiment can obtain an image with excellent image visibility and optical density even in such a simultaneous recording method. The configuration of the ink set of this embodiment will be described in detail below.

[0015] An ink set is intended for recording by simultaneously using each of the ink compositions included in the ink set. Each of the ink compositions included in the ink set may be contained in a separate ink container, or may be contained in a separate chamber of an integrated ink container.

[0016] 1.1. Non-white ink composition The non-white ink composition is a water-based inkjet ink composition that contains a non-white colorant, a predetermined silicone-based surfactant A, and water, and may also contain organic solvents, resin particles, wax, other surfactants, and the like, as necessary.

[0017] In this embodiment, "water-based ink" refers to ink that contains at least water as a main solvent component, and "inkjet ink" refers to ink that is ejected from an inkjet head using an inkjet method and used for recording.

[0018] 1.1.1. Non-white coloring material The non-white coloring material means a coloring material other than a white coloring material, and may be a pigment or a dye.

[0019] The pigment is not particularly limited, but examples thereof include inorganic pigments such as carbon blacks (CI Pigment Black 7) such as furnace black, lamp black, acetylene black, and channel black, iron oxide, and titanium oxide; and organic pigments such as quinacridone pigments, quinacridonequinone pigments, dioxazine pigments, phthalocyanine pigments, anthrapyrimidine pigments, anthanthrone pigments, indanthrone pigments, flavanthrone pigments, perylene pigments, diketopyrrolopyrrole pigments, perinone pigments, quinophthalone pigments, anthraquinone pigments, thioindigo pigments, benzimidazolone pigments, isoindolinone pigments, azomethine pigments, and azo pigments. The pigments may be used alone or in combination of two or more.

[0020] The dye is not particularly limited, but examples thereof include acid dyes, basic dyes, direct dyes, reactive dyes, and disperse dyes. The above dyes may be used alone or in combination of two or more.

[0021] The content of the non-white colorant relative to the total amount of the non-white ink composition is preferably 0.5 to 10% by mass, more preferably 1.0 to 8.0% by mass, and even more preferably 2.0 to 6.0% by mass. 2.5 to 5.0% by mass is even more preferable. By keeping the content of the non-white colorant within the above range, ejection stability in the inkjet method tends to be further improved.

[0022] 1.1.2.Surfactants The non-white ink composition of this embodiment contains a predetermined silicone surfactant A, and may contain the silicone surfactant B described below or other surfactants as needed.

[0023] 1.1.2.1. Silicone surfactant A Silicone surfactant A has, in the molecular weight distribution measured by gel permeation chromatography (GPC), a maximum peak in the molecular weight range of 300 or more in the molecular weight range of 3,000 to 20,000. By including such a silicone surfactant A, mixing of the non-white ink composition and the white ink composition is suppressed, further improving the visibility and optical density of the image.

[0024] The silicone surfactant A has a maximum peak in the molecular weight range of 300 or more of 3,000 to 20,000, preferably 4,000 to 15,000, and more preferably 5,000 to 10,000. When the maximum peak in the molecular weight range of 300 or more is 3,000 or more, mixing of the non-white ink composition and the white ink composition is suppressed, and the visibility and optical density of the image tend to be further improved. When the maximum peak in the molecular weight range of 300 or more is 20,000 or less, the ejection stability tends to be further improved.

[0025] The maximum peak of silicone surfactant A in the molecular weight range of 300 or more can be identified from a GPC molecular weight distribution chart obtained by plotting the logarithm of molecular weight M (LogM) on the horizontal axis and the derivative of concentration fraction (dw / d(LogM)) on the vertical axis. Here, "maximum peak" refers to the largest peak (mountain) in the molecular weight range of 300 or more. Furthermore, "maximum peak in the molecular weight range of 300 or more" means that peaks below 300 are ignored. In other words, although there may be a maximum peak below 300, it refers to the maximum peak when limited to the molecular weight range of 300 or more.

[0026] Although not particularly limited, for example, the measurement conditions for GPC measurement in this embodiment can be the conditions described in the Examples, and the molecular weight can be determined using standard polystyrene.

[0027] The silicone surfactant A is not particularly limited, but examples thereof include polysiloxane compounds such as dimethylsiloxane, methylphenylsiloxane, and diphenylsiloxane. These polysiloxane compounds may also be modified organosiloxanes in which terminal or side chain groups have been modified with polyether groups, etc. These silicone surfactants A may be used alone or in combination of two or more.

[0028] Among these, modified organosiloxanes are preferred as the silicone surfactant A, and polyether-modified organosiloxanes are more preferred. Examples of such polyether-modified organosiloxanes include modified organosiloxanes in which the terminals are modified with polyether groups, as shown in general formula (1), and modified organosiloxanes in which the side chains are modified with polyether groups, as shown in general formula (3). The use of such silicone surfactant A further suppresses mixing of the non-white ink composition with the white ink composition. This prevents the image of the non-white ink composition from becoming whitish due to mixing with the white ink composition, increases the density of the image of the non-white ink composition, and tends to further improve the optical density. In particular, by including silicone surfactant B (described below) in the white ink composition, mixing of the non-white ink composition with the white ink composition can be suppressed even when the non-white ink composition and the white ink composition are more likely to mix. It is presumed that the silicone surfactant A has a relatively high molecular weight, which suppresses mixing of the non-white ink composition with the white ink composition, but this is not the only reason. This is also preferable in terms of suppressing aggregation unevenness in the image. [ka] (In the formula, R 1 each independently represents an alkylene group having 1 to 6 carbon atoms or a single bond, and X 1each independently represents a polyether group represented by general formula (2), and a represents an integer of 10 to 80. [ka] (In the formula, R 2 represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a (meth)acrylic group; EO represents an ethylene oxide group; PO represents a propylene oxide group; the order of EO and PO is not particular; b is an integer of 1 or greater; c is an integer of 0 or greater; and b+c is an integer of 1 or greater. [ka] (In the formula, R 3 each independently represents an alkyl group having 1 to 6 carbon atoms; X 2 each independently represents a polyether group represented by general formula (4), d and e are integers of 1 or more, and d+e represents an integer of 2 to 50. [ka] (In the formula, R 4 represents an alkylene group having 1 to 6 carbon atoms or a single bond, and R 5 represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, EO represents an ethylene oxide group, PO represents a propylene oxide group, the order of EO and PO is not particular, f is an integer of 1 or more, g is an integer of 0 or more, and f+g is an integer of 1 or more.

[0029] R 1 , R 3 , and R 4 The alkylene group having 1 to 6 carbon atoms represented by the formula (R) is not particularly limited, but examples thereof include a methylene group, an ethylene group, a propylene group, a butylene group, a pentylene group, and a hexylene group. 1 , R 4 is preferably an alkylene group having 1 to 6 carbon atoms.

[0030] R 2 and R 5The alkyl group having 1 to 6 carbon atoms represented by the formula (I) is not particularly limited, but examples thereof include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a t-butyl group, an n-pentyl group, a neopentyl group, and an n-hexyl group.

[0031] R 1 , R 4 may be a single bond. A single bond is R 1 , R 4 indicates that the atom on the right and the atom on the left are directly connected by a single bond.

[0032] In general formulas (1) and (2), a is an integer of 10 to 80, preferably an integer of 20 to 70, and more preferably an integer of 30 to 60. Furthermore, b is an integer of 1 or more, preferably an integer of 2 to 30, and more preferably an integer of 5 to 20. Furthermore, c is an integer of 0 or more, preferably an integer of 0 to 30, and more preferably an integer of 0 to 20. Furthermore, b+c is an integer of 1 or more, preferably an integer of 1 to 60, more preferably an integer of 2 to 40, and even more preferably an integer of 5 to 20.

[0033] In general formulas (3) and (4), d and e each represent an integer of 1 or greater, preferably 5 to 40, and more preferably 10 to 20. d+e represents an integer of 2 to 50, preferably 5 to 40, and more preferably 10 to 30. f represents an integer of 1 or greater, preferably 2 to 30, and more preferably 5 to 20. g represents an integer of 0 or greater, preferably 0 to 30, and more preferably 0 to 20. f+g represents an integer of 1 or greater, preferably 1 to 60, more preferably 2 to 40, and even more preferably 5 to 20.

[0034] The content of the silicone surfactant A is preferably 0.1 to 5.0 mass %, more preferably 0.3 to 3.0 mass %, and even more preferably 0.6 to 1.5 mass %, relative to the total amount of the non-white ink composition. When the content of the silicone surfactant A is within this range, mixing of the non-white ink composition and the white ink composition is further suppressed, which tends to further improve the visibility and optical density of the image.

[0035] Among the silicone surfactants A, modified organosiloxanes represented by general formula (1), the terminals of which are modified with polyether groups, are preferred because they provide superior image visibility and suppression of aggregation unevenness.

[0036] 1.1.2.2. Silicone surfactant B The non-white ink composition may further contain, and preferably contains, a silicone surfactant B, which will be described later. This tends to further improve the visibility of the image. The silicone surfactant B contained in the non-white ink composition may be the same as or different from the silicone surfactant B contained in the white ink composition.

[0037] The content of silicone surfactant B relative to the total amount of the non-white ink composition is preferably 0.1 to 5.0 mass%, more preferably 0.3 to 3.0 mass%, and even more preferably 0.6 to 1.5 mass%. When the content of silicone surfactant B is within this range, the visibility of the image tends to be further improved.

[0038] 1.1.2.3. Other surfactants The other surfactant is not particularly limited, but examples thereof include acetylene glycol surfactants, fluorine-based surfactants, and silicone surfactants other than the above-mentioned silicone surfactants A and B. The other surfactants may be used alone or in combination of two or more.

[0039] The acetylene glycol surfactant is not particularly limited, but examples thereof include alkylene oxide adducts of 2,4,7,9-tetramethyl-5-decyne-4,7-diol and 2,4,7,9-tetramethyl-5-decyne-4,7-diol, and alkylene oxide adducts of 2,4-dimethyl-5-decyne-4-ol and 2,4-dimethyl-5-decyne-4-ol.

[0040] The fluorine-based surfactant is not particularly limited, but examples thereof include perfluoroalkyl sulfonates, perfluoroalkyl carboxylates, perfluoroalkyl phosphates, perfluoroalkyl ethylene oxide adducts, perfluoroalkyl betaines, and perfluoroalkyl amine oxide compounds.

[0041] The other silicone surfactants are not particularly limited as long as they do not satisfy the requirements of silicone surfactants A and B, and examples thereof include polysiloxane compounds and polyether-modified organosiloxanes.

[0042] The content of the other surfactants is preferably 0.1 to 5.0 mass %, more preferably 0.3 to 3.0 mass %, and even more preferably 0.6 to 1.5 mass %, relative to the total amount of the non-white ink composition.

[0043] 1.1.3.Water The water content of the non-white ink composition is preferably 40 to 98% by mass, more preferably 50 to 90% by mass, even more preferably 55 to 85% by mass, more preferably 60 to 80% by mass, and even more preferably 65 to 75% by mass.

[0044] 1.1.4. Organic Solvents The organic solvent is not particularly limited as long as it is a water-soluble organic solvent, and examples thereof include polyols. Polyols are alkane polyols or condensates formed by intermolecular condensation of hydroxyl groups of alkane polyols, and have two or more hydroxyl groups in the molecule. Examples of polyols include triol or higher polyols such as glycerin. Examples of polyols include glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,2-pentanediol, 1,2-hexanediol, 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol. Glycols have two hydroxyl groups in the molecule. Glycols preferably have 2 to 10 carbon atoms, more preferably 3 to 6, and even more preferably 3 to 4.

[0045] Examples of organic solvents include glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, triethylene glycol monomethyl ether, and triethylene glycol monobutyl ether; nitrogen-containing solvents such as 2-pyrrolidone, N-methyl-2-pyrrolidone, and N-ethyl-2-pyrrolidone; and alcohols such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butanol, 2-butanol, tert-butanol, isobutanol, n-pentanol, 2-pentanol, 3-pentanol, and tert-pentanol. Examples of nitrogen-containing solvents include amides. Examples of amides include cyclic amides and non-cyclic amides. Examples of cyclic amides include lactams. Examples of the non-cyclic amides include N,N-dialkylamides, such as N,N-dialkylalkoxyamides. The organic solvents may be used alone or in combination of two or more.

[0046] Among these, polyols are preferred, and glycols are more preferred. By using such an organic solvent, mixing of the non-white ink composition and the white ink composition is further suppressed, and the visibility and optical density of the image tend to be further improved.

[0047] The content of the organic solvent is preferably 5 to 30% by mass, more preferably 10 to 30% by mass, and even more preferably 15 to 25% by mass, relative to the total amount of the non-white ink composition. When the content of the organic solvent is within this range, mixing of the non-white ink composition and the white ink composition is further suppressed, and the visibility, optical density, and ejection stability of the image tend to be further improved.

[0048] The non-white ink composition preferably contains an organic solvent having a normal boiling point of 280° C. or less, and more preferably contains an organic solvent having a normal boiling point of 170 to 250° C. By including an organic solvent having a normal boiling point of 170 to 250° C., drying properties are improved, optical density is improved, and aggregation unevenness tends to be reduced.

[0049] Furthermore, the non-white ink composition preferably contains an organic solvent whose normal boiling point is less than 200° C. By containing an organic solvent whose normal boiling point is less than 200° C., the drying properties are improved, the optical density is improved, and aggregation unevenness tends to be reduced.

[0050] The content of the organic solvent having a normal boiling point of less than 200°C is preferably 30 to 80% by mass, more preferably 40 to 75% by mass, and even more preferably 50 to 70% by mass, relative to 100% by mass of the organic solvent contained in the non-white ink composition. When the content of the organic solvent having a normal boiling point of less than 200°C is within the above range, drying properties are improved, optical density is improved, and aggregation unevenness tends to be further reduced. Discharge stability is also excellent.

[0051] Furthermore, the content of the water-soluble organic solvent, which is a polyol having a normal boiling point of more than 280°C, is preferably 1% by mass or less, more preferably 0.5% by mass or less, and may even be 0% by mass, relative to the total mass of the ink composition. When the content of the water-soluble organic solvent having a normal boiling point of more than 280°C is within the above range, the optical density tends to be improved, aggregation unevenness is further reduced, and abrasion resistance tends to be improved. Furthermore, it is even more preferable that the content of the water-soluble organic solvent having a normal boiling point of more than 280°C be within the above range.

[0052] 1.1.5.Resin particles The non-white ink composition may further contain resin particles. The use of resin particles tends to further improve abrasion resistance. The resin particles are not particularly limited, but examples include resin particles made of urethane-based resins, acrylic-based resins (including styrene-acrylic-based resins), fluorene-based resins, polyolefin-based resins, rosin-modified resins, terpene-based resins, polyester-based resins, polyamide-based resins, epoxy-based resins, vinyl chloride-based resins, vinyl chloride-vinyl acetate copolymers, ethylene-vinyl acetate-based resins, and the like. The resin particles may be in the form of an emulsion.

[0053] Among these, acrylic resin particles, urethane resin particles, or polyester resin particles can be mentioned. The use of such resin particles tends to further improve abrasion resistance. These resin particles are often handled in an emulsion form, but may also be in the form of a powder. Furthermore, the resin particles can be used alone or in combination of two or more types.

[0054] Urethane resin is a general term for resins having urethane bonds. In addition to urethane bonds, the urethane resin may be a polyether urethane resin containing ether bonds in the main chain, a polyester urethane resin containing ester bonds in the main chain, or a polycarbonate urethane resin containing carbonate bonds in the main chain.

[0055] Acrylic resin is a general term for polymers obtained by polymerizing at least an acrylic monomer such as (meth)acrylic acid or a (meth)acrylic acid ester as one component. Examples include resins obtained from acrylic monomers and copolymers of acrylic monomers with other monomers. Examples include acrylic-vinyl resins, which are copolymers of acrylic monomers and vinyl monomers. Another example of a vinyl monomer is styrene. Other usable acrylic monomers include acrylamide and acrylonitrile.

[0056] Among these, acrylic resins are preferred, and styrene-acrylic resins are more preferred. The styrene-acrylic resins are not particularly limited, but examples thereof include styrene-acrylic acid copolymers, styrene-methacrylic acid copolymers, styrene-methacrylic acid-acrylic acid ester copolymers, styrene-α-methylstyrene-acrylic acid copolymers, and styrene-α-methylstyrene-acrylic acid-acrylic acid ester copolymers. By using such resins, the abrasion resistance of the resulting recorded matter tends to be further improved.

[0057] The polyolefin resin has an olefin such as ethylene, propylene, or butylene in its structural skeleton, and any known polyolefin resin can be appropriately selected and used.

[0058] The content of the resin particles is preferably 0.5 to 6.0% by mass, more preferably 1.0 to 5.0% by mass, and even more preferably 2.0 to 4.0% by mass, relative to the total mass of the non-white ink composition. When the content of the resin particles is within this range, abrasion resistance tends to be further improved.

[0059] Wax The wax is not particularly limited, but examples thereof include hydrocarbon waxes and ester waxes, which are condensates of fatty acids with monohydric alcohols or polyhydric alcohols. The hydrocarbon wax is not particularly limited, but examples thereof include paraffin waxes and polyolefin waxes such as polyethylene waxes and polypropylene waxes. These waxes may be used alone or in combination of two or more. Among these waxes, from the viewpoint of improving abrasion resistance, hydrocarbon waxes are preferred, polyolefin waxes are more preferred, and polyethylene waxes are even more preferred.

[0060] The wax may be in the form of an emulsion, for example, in which wax particles are dispersed in water.

[0061] The wax content is preferably 0.1 to 5.0% by mass, more preferably 0.3 to 3.0% by mass, and even more preferably 0.6 to 1.5% by mass, relative to the total amount of the non-white ink composition, which tends to further improve the abrasion resistance of the resulting recorded matter.

[0062] 1.1.7.Other Ingredients The non-white ink composition according to this embodiment may also contain various additives, such as a solubilizing agent, a viscosity adjusting agent, a pH adjusting agent, an antioxidant, a preservative, an antifungal agent, a corrosion inhibitor, and a chelating agent, as appropriate.

[0063] 1.2. White ink composition The white ink composition is a water-based inkjet ink composition that contains a white colorant, a predetermined silicone-based surfactant B, and water, and may contain an organic solvent, resin particles, wax, and other components as necessary. Each component is described below. Note that, in addition to the components described below, the white ink composition may also be, and preferably is, similar to the types and amounts of components that may be contained in the white ink composition described above for the non-white ink composition.

[0064] 1.2.1.White color material The white coloring material is not particularly limited, but examples thereof include white inorganic coloring materials such as CI Pigment White 6, 18, and 21, titanium oxide, zinc oxide, zinc sulfide, antimony oxide, magnesium oxide, and zirconium oxide. In addition to these white inorganic coloring materials, white organic coloring materials such as white hollow resin particles and polymer particles can also be used.

[0065] The content of the white colorant is preferably 2 to 20% by mass, more preferably 3 to 17% by mass, more preferably 5 to 15% by mass, and even more preferably 7.5 to 12.5% ​​by mass, relative to the total amount of the white ink composition. When the content of the white colorant is within the above range, an image with high hiding power can be obtained, and ejection stability in the inkjet method tends to be further improved.

[0066] Surfactants The white ink composition of this embodiment contains a predetermined silicone surfactant B, and may contain the silicone surfactant A described above or other surfactants as necessary.

[0067] 1.2.2.1. Silicone surfactant B Silicone surfactant B has a molecular weight distribution measured by gel permeation chromatography that does not have a maximum peak at a molecular weight of 300 or more at a molecular weight of 3,000 or more, and has an HLB (Hydrophile-Lipophile Balance) value (HLB) of 10.5 or less according to the Griffin method. The inclusion of such silicone surfactant A further improves the wettability of the white ink composition to a recording medium, thereby improving its hiding power. Therefore, images obtained using the white ink composition as a background image have further improved image visibility and optical density.

[0068] Silicone surfactant B does not have a maximum peak in the molecular weight range of 300 or more at a molecular weight of 3,000 or more; specifically, it does not have a peak in the molecular weight range of 300 or more, or even if it has a peak in the molecular weight range of 300 or more, the maximum peak is less than 3,000. By using a silicone surfactant B that satisfies the above molecular weight conditions, the wettability of the white ink composition to the recording medium is further improved, allowing the recording medium surface to be sufficiently covered with the white ink composition, and further improving the visibility of the image. In particular, when the recording medium is a low-absorbency recording medium or a non-absorbency recording medium, wettability tends to be further improved. On the other hand, there is a tendency for the white ink composition and non-white ink composition to mix more easily. Silicone surfactant B is also preferable because of its excellent abrasion resistance.

[0069] The maximum peak of silicone surfactant B in the molecular weight range of 300 or more can be measured by the same method as for silicone surfactant A.

[0070] The silicone surfactant B has an HLB value of 10.5 or less, preferably 2.0 to 10.3, more preferably 3.0 to 10.1, and even more preferably 4.0 to 10.0. An HLB value of 10.5 or less improves the wettability of the white ink composition to a recording medium, thereby improving the visibility of the image. An HLB value of 2.0 or more tends to improve the optical density of the resulting image and reduce aggregation unevenness.

[0071] Here, the HLB value is a value that represents the degree of affinity of a surfactant for water and oil. By setting the HLB value within the above range, it is possible to improve the wettability of ink droplets when they land on a highly hydrophobic, poorly absorbent substrate. By improving the wettability, white spots and color bleeding on the substrate are suppressed, which tends to further improve the visibility of the image. The HLB value in this embodiment is defined and calculated using the Griffin method.

[0072] The silicone surfactant B is not particularly limited, but examples thereof include polysiloxane compounds such as dimethylsiloxane, methylphenylsiloxane, and diphenylsiloxane. In particular, examples of polysiloxane compounds include modified organosiloxanes in which terminal or side chain groups are modified with polyether groups or the like. These silicone surfactants B may be used alone or in combination of two or more.

[0073] Examples of silicone surfactant B include those in which, in the above general formula (1), a is smaller than that of the silicone surfactant A contained in the non-white ink composition. Alternatively, examples include those in the above general formula (3) in which d+e is smaller than that of the silicone surfactant A contained in the non-white ink composition. Silicone surfactant B has a molecular weight that is relatively smaller than that of the silicone surfactant A contained in the non-white ink composition.

[0074] The content of silicone surfactant B is preferably 0.1 to 5.0 mass% relative to the total amount of the white ink composition, more preferably 0.3 to 3.0 mass%, and even more preferably 0.6 to 1.5 mass%. When the content of silicone surfactant B is 0.1 mass% or more, the wettability of the white ink composition to the recording medium is further improved, and the visibility of the image tends to be further improved. Furthermore, when the content of silicone surfactant B is 5.0 mass% or less, mixing of the non-white ink composition and the white ink composition is further suppressed, and the visibility and optical density of the image tend to be further improved.

[0075] 1.2.2.2. Silicone surfactant A The white ink composition may or may not further contain the above-mentioned silicone surfactant A. If it contains a silicone surfactant A, the silicone surfactant A contained in the white ink composition may be the same as or different from the silicone surfactant A contained in the non-white ink composition.

[0076] The content of silicone surfactant A is preferably 5.0% by mass or less, more preferably 3.0% by mass or less, and even more preferably 1.5% by mass or less, relative to the total amount of the white ink composition. It is further preferably 1% by mass or less, more preferably 0.5% by mass or less, even more preferably 0.2% by mass or less, even more preferably 0.1% by mass or less, and even more preferably 0.05% by mass or less. The lower limit is 0% by mass or more, and 0% by mass is preferred. When the content of silicone surfactant A is within the above range, the optical density of the image is superior, which is preferred.

[0077] In another embodiment, when silicone surfactant A is contained, the content is preferably 0.1 to 5.0 mass %, more preferably 0.3 to 3.0 mass %, and even more preferably 0.6 to 1.5 mass %.

[0078] Furthermore, whether or not silicone surfactant A is included, the content of silicone surfactant A in the white ink composition is preferably less than the content of silicone surfactant B, more preferably by 0.5% by mass or more, even more preferably by 1.0% by mass or more, and even more preferably by 1.0 to 5.0% by mass or less. This tends to further improve the visibility and optical density of the image.

[0079] 1.2.2.3. Other surfactants The white ink composition may further contain the other surfactants described above. The content of the other surfactants relative to the total amount of the white ink composition is preferably 0.1 to 5.0% by mass, more preferably 0.3 to 3.0% by mass, and even more preferably 0.6 to 1.5% by mass.

[0080] 1.2.3.Water The water content is preferably 55 to 85% by mass, more preferably 60 to 80% by mass, and even more preferably 65 to 75% by mass, relative to the total amount of the white ink composition.

[0081] 1.2.4. Organic Solvents Examples of the organic solvent include the same organic solvents as those exemplified for the non-white ink composition. The organic solvent used in the white ink composition may be the same as or different from the organic solvent used in the non-white ink composition.

[0082] Among these, glycols and polyols are preferred, and glycols are more preferred. By using such organic solvents, mixing of the non-white ink composition and the white ink composition is further suppressed, which tends to further improve the visibility and optical density of the image.

[0083] The content of the organic solvent is preferably 5 to 35 mass %, more preferably 10 to 30 mass %, and even more preferably 15 to 25 mass %, relative to the total amount of the white ink composition. By keeping the content of the organic solvent within this range, mixing of the non-white ink composition and the white ink composition is further suppressed, which tends to further improve the visibility and optical density of the image.

[0084] The white ink composition preferably contains an organic solvent with a normal boiling point of 170 to 250° C. By including an organic solvent with a normal boiling point of 170 to 250° C., the drying properties are improved, the optical density is improved, and aggregation unevenness tends to be reduced.

[0085] Furthermore, the white ink composition preferably contains an organic solvent whose normal boiling point is less than 200° C. By containing an organic solvent whose normal boiling point is less than 200° C., the drying properties are improved, the optical density is improved, and aggregation unevenness tends to be reduced.

[0086] The content of the organic solvent having a normal boiling point of less than 200°C is preferably 30 to 80% by mass, more preferably 40 to 75% by mass, and even more preferably 50 to 70% by mass, relative to 100% by mass of the organic solvent contained in the white ink composition. When the content of the organic solvent having a normal boiling point of less than 200°C is within the above range, drying properties are improved, optical density is improved, and aggregation unevenness tends to be reduced.

[0087] Furthermore, the content of the water-soluble organic solvent having a normal boiling point of more than 280° C. is preferably 1% by mass or less, more preferably 0.5% by mass or less, and may be 0% by mass, relative to the total mass of the ink composition. When the content of the water-soluble organic solvent having a normal boiling point of more than 280° C. is within the above range, the optical density tends to be improved, aggregation unevenness is further reduced, and abrasion resistance tends to be improved.

[0088] 1.2.5.Resin particles The white ink composition may further contain resin particles. The use of resin particles tends to further improve abrasion resistance. Examples of the resin particles include the same as those exemplified for the non-white ink composition. The resin particles used in the white ink composition may be the same as or different from the resin particles used in the non-white ink composition.

[0089] The content of the resin particles is preferably 0.5 to 6.0% by mass, more preferably 1.0 to 5.0% by mass, and even more preferably 2.0 to 4.0% by mass, relative to the total mass of the white ink composition. When the content of the resin particles is within this range, abrasion resistance tends to be further improved.

[0090] Wax The white ink composition may further contain a wax. The use of a wax tends to further improve rub resistance. Examples of the wax include the same waxes as those exemplified for the non-white composition. The wax used in the white ink composition may be the same as or different from the wax used in the non-white ink composition.

[0091] The wax content is preferably 0.1 to 5.0% by mass, more preferably 0.3 to 3.0% by mass, and even more preferably 0.6 to 1.5% by mass, relative to the total amount of the white ink composition, which tends to further improve the abrasion resistance of the resulting recorded matter.

[0092] 1.2.7.Other Ingredients The white ink composition according to this embodiment may also contain various additives, such as a dissolution aid, a viscosity adjuster, a pH adjuster, an antioxidant, a preservative, an antifungal agent, a corrosion inhibitor, and a chelating agent, as appropriate.

[0093] 1.3. Method for preparing ink composition The method for preparing the non-white ink composition and the white ink composition is not particularly limited, but examples include a method in which the above-mentioned components are mixed and stirred sufficiently so that the components are uniformly mixed.

[0094] 2. Recording method The recording method of this embodiment is a recording method for recording on a recording medium using the ink set described above, and includes a white ink adhering step of ejecting a white ink composition from an inkjet head and adhering it to the recording medium, and a non-white ink adhering step of ejecting a non-white ink composition from an inkjet head and adhering it to the recording medium, and may also include a drying step and other steps as necessary.

[0095] The recording method of this embodiment has two modes for applying the white ink composition and the non-white ink composition, which will be described later.

[0096] In this embodiment, when there is no particular distinction between a white inkjet head and a non-white inkjet head, they are simply referred to as "inkjet heads." Similarly, when there is no particular distinction between a white ink composition and a non-white ink composition, they are simply referred to as "ink compositions."

[0097] Furthermore, "main scanning" refers to the operation of ejecting an ink composition from the inkjet head and depositing it on a recording medium while moving the position of the inkjet head relative to the recording medium. The inkjet head can be mounted on a carriage, for example. The inkjet head may also be moved by moving the carriage, and in this case, the operation is also referred to as movement of the inkjet head.

[0098] Furthermore, the "main scanning direction" refers to the direction in which the inkjet head moves relative to the recording medium, and is the width direction of the recording medium. Note that "main scanning" refers to the movement of the inkjet head relative to the recording medium, and the inkjet head may move relative to the recording medium, or the recording medium may move relative to the inkjet head. The direction of such relative positional movement is the main scanning direction. The movement of the inkjet head relative to the recording medium can also be referred to as the movement of the recording medium relative to the inkjet head. In other words, it is the movement of the relative positions of the inkjet head and the recording medium.

[0099] On the other hand, "sub-scanning" refers to the operation of moving the relative positions of the inkjet head and the recording medium in the sub-scanning direction, which is a direction that intersects with the main scanning direction. For example, recording can be performed by repeating the process of depositing an ink composition to a certain area of ​​a recording medium in a main scan, moving the recording medium a small distance in a sub-scan, and then performing a next main scan to deposit an ink composition adjacent to or partially overlapping the previously deposited ink composition. Note that "sub-scanning" also refers to movement of the inkjet head relative to the recording medium, and the inkjet head may move relative to the recording medium, or the recording medium may move relative to the inkjet head. The direction of such relative movement is the sub-scanning direction.

[0100] Printing can be performed by performing main scanning and sub-scanning multiple times, for example, by alternately repeating main scanning and sub-scanning.

[0101] 2.1. First attachment mode In the first application mode, a white ink composition and a non-white ink composition are applied in sequence to a recording medium, thereby laminating a non-white ink layer and a white ink layer. This is also called laminate printing or laminate printing. In this mode, in the white ink application step and the non-white ink application step, a white ink image formed by the white ink composition and a non-white ink image formed by the non-white ink composition are formed by being superimposed on the recording medium.

[0102] In the first deposition mode, the order of deposition is not limited as long as the white ink composition and the non-white ink composition are deposited by different main scans, and the white ink composition may be deposited first onto the recording medium, and then the non-white ink composition may be deposited on top of the layer of the white ink composition, or the non-white ink composition may be deposited first, and then the white ink composition may be deposited on top of the layer of the non-white ink composition. The image obtained by the former is an image that can be seen from the side of the recording medium to which the ink composition has been deposited, and the image obtained by the latter is an image that can be seen from the side of the recording medium to which the ink composition has not been deposited.

[0103] When the first deposition mode is implemented, for example, a white ink composition and a non-white ink composition are deposited in the same scanning region of a recording medium by different main scanning operations, thereby forming a layer containing a white ink composition and a layer containing a non-white ink composition in a laminated state. This ensures hiding power by the layer containing the white ink composition, thereby further improving the color development and visibility of the non-white ink composition formed thereon, and achieving high-quality image quality.

[0104] Furthermore, when a white ink composition is applied first and then a non-white ink composition is applied thereon, an image can be formed that can be viewed from the ink-applied side. Conversely, when the recording medium is transparent and a non-white ink composition is applied first and then a white ink composition is applied thereon, an image can be formed that can be viewed from the ink-free side.

[0105] In the first deposition mode, different main scans for depositing the white ink composition and the non-white ink composition to the same scanning area may be performed multiple times, respectively. For example, it is possible to record the white ink composition in four passes, and then record the non-white ink composition in four passes.

[0106] 2.2. Second attachment mode In the second application mode, the white ink composition and the non-white ink composition are simultaneously applied to the recording medium. This is also referred to as simultaneous printing or simultaneous ejection. In this mode, the white ink application step and the non-white ink application step involve multiple main scans in which the ink compositions are ejected and applied to the recording medium while moving the position of the inkjet head relative to the recording medium, and the white ink composition and the non-white ink composition are applied to the same scanned area of ​​the recording medium during the same main scan.

[0107] In this embodiment, since there is no need to laminate ink composition layers, such as a layer of a white ink composition and a layer of a non-white ink composition, the recording speed can be improved. In addition, when the recording medium is transparent, the image obtained looks the same when viewed from the front and the back. Therefore, for example, in the case of a recorded product that is to be attached to a window or glass, an image that can be viewed from both the front and back can be obtained.

[0108] When the second deposition mode is implemented, for example, a layer containing a white ink composition and a non-white ink composition is formed by depositing the white ink composition and the non-white ink composition in the same scanning region of the recording medium by the same main scanning. That is, the white ink deposition step and the non-white ink deposition step are performed by the same main scanning.

[0109] In the second deposition mode, main scanning to deposit the white ink composition and non-white ink composition onto the scanned region may be performed multiple times on the same region. That is, it is preferable that a layer containing the white ink composition and non-white ink composition is deposited onto a region on the recording medium by one main scanning, and then a layer containing the white ink composition and non-white ink composition is deposited on top of that by another main scanning. In this case, the main scanning to deposit the white ink composition and non-white ink composition will pass over the same region multiple times. The more scanning is performed, the more ink can be deposited onto the desired region in multiple separate passes (multiple passes), which tends to further improve the image quality of the resulting record.

[0110] When recording an arbitrary area, the number of times the inkjet head passes over that area is referred to as the "number of passes." For example, if four main scans are performed over the same area to deposit the white ink composition and the non-white ink composition, the number of passes is referred to as "four passes." For example, in the example of FIG. 1, if the length of one sub-scan in the sub-scanning direction is one-fourth the length of the nozzle row of the inkjet head aligned in the sub-scanning direction, four main scans are performed over the same portion (same scanning area) of a rectangular scanning area that is the length of one sub-scan in the sub-scanning direction and extends in the main scanning direction. The number of scans viewed in this manner is referred to as the number of scans or the number of passes. The number of scans is one or more, preferably two or more, more preferably three or more, even more preferably four or more, and particularly preferably eight or more. From the perspective of excellent image quality, a number above the above range is preferred. There is no upper limit, but a number below 24 is preferred, a number below 12 is more preferred, a number below 8 is even more preferred, and a number below 4 is even more preferred. From the perspective of fast recording speed, a number below the above range is preferred. The number of scans is set for each ink type.

[0111] In the second deposition mode, a layer containing the white ink composition may be formed by a main scanning direction different from the main scanning direction used to form the layer containing the white ink composition and the non-white ink composition, and the layer containing the white ink composition and the non-white ink composition may be laminated together with another layer containing the white ink composition separately from the layer containing the white ink composition. By forming a layer containing the white ink composition in this manner, an image with even higher color development can be obtained. The formation of the layer containing the white ink composition may be performed before or after the formation of the layer containing the white ink composition and the non-white ink composition. If the formation of the layer containing the white ink composition is performed before the formation of the layer containing the white ink composition, the image will be viewed from the recording surface side of the recording medium. If the formation of the layer is performed after the formation of the layer, the image will be viewed from the opposite side of the recording surface side of the recording medium.

[0112] 2.3. White ink application process The white ink deposition step is a step of ejecting a white ink composition from an inkjet head and depositing it onto a recording medium. Discharge of the ink composition by the inkjet method can be performed using a known inkjet recording device. The ejection method is not particularly limited, and examples that can be used include a piezo method and a method of ejecting ink by heating the ink to generate bubbles.

[0113] The amount of the white ink composition deposited is preferably 2.0 to 20 mg / inch per unit area of ​​the region on the recording medium where the white ink composition is deposited (hereinafter also referred to as the "white ink composition deposited region"). 2 and more preferably 3.0 to 10 mg / inch 2 The area for checking the amount of adhesion is, for example, about 2 x 2 mm.

[0114] 2.4. Non-white ink application process The non-white ink deposition step is a step of ejecting a non-white ink composition from an inkjet head and depositing it onto a recording medium.

[0115] The amount of the non-white ink composition deposited is preferably 2.0 to 20 mg / inch per unit area of ​​the region on the recording medium where the non-white ink composition is deposited (hereinafter also referred to as the "region where the non-white ink composition is deposited"). 2 and more preferably 3.0 to 10 mg / inch 2 When the amount of the non-white ink composition deposited is within the above range, the image quality and abrasion resistance of the resulting recorded matter tend to be superior.

[0116] With regard to the amount of the non-white ink composition adhered, in the adhesion region where the white ink composition and the non-white ink composition are adhered, the ratio of the amount of the white ink composition adhered to the amount of the non-white ink composition adhered (amount of white ink composition / amount of non-white ink composition adhered) is preferably 2 or less, and more preferably 0.1 to 2. In the first adhesion mode, the ratio of the adhesion amounts is more preferably 0.5 to 1.5, and even more preferably 0.8 to 1.3. In the second adhesion mode, the ratio of the adhesion amounts is more preferably 0.2 to 1, and even more preferably 0.3 to 0.7.

[0117] The deposition amounts and deposition ratios of the above ink compositions may be measured per unit area of ​​the deposition region on the recording medium where the white ink composition and the non-white ink composition are deposited, and in this case, may be measured in the region where the deposition amount of the non-white ink composition is the greatest.

[0118] 2.5. Number of passes The white ink application step and the non-white ink application step include a step of performing a main scan multiple times on the same scanning area on the recording medium, in which the ink composition is ejected and applied to the recording medium while moving the position of the inkjet head relative to the recording medium, and the number of main scans on the same scanning area, i.e., the number of passes, is preferably 8 or less, and more preferably 1 to 8. Keeping the number of passes within the above range tends to further improve productivity.

[0119] 2.6.Primary drying process The recording method of this embodiment may include a primary drying step in which the white ink composition and non-white ink composition applied to the recording medium are dried using a drying mechanism. The primary drying step involves heating the recording medium before the ejection step, or heating or blowing air onto the recording medium during the ejection step or shortly after the ink has been applied to the recording medium, thereby quickly drying the ink. The primary drying step is a step for drying at least a portion of the ink's solvent component to an extent that at least the ink flow is reduced. The primary drying step may be performed by applying the ink to a heated recording medium, or may be performed shortly after application to promote drying. In the primary drying step, it is preferable that the ink droplets that have landed on the recording medium begin to dry within 0.5 seconds at the latest after the ink droplets land on the recording medium. The drying unit (drying mechanism) for drying the ink on the recording medium is not particularly limited, and examples include a platen heater, a hot air heater, an IR heater, or the like, which have a heating function, and a blower, or the like, which do not have a heating function.

[0120] Drying mechanisms include a conduction type, in which heat is conducted from a member in contact with the recording medium to the recording medium to heat it; a radiation type, in which IR or other radiation is radiated to the recording medium to heat it; and an air blowing type, in which air is blown toward the recording medium. Air blowing types include a method in which hot air is blown onto the recording medium while also heating it, and a method in which room-temperature air is used to promote drying of the ink without heating. Methods that do not involve heating are preferred because they can prevent the ink in the nozzles of the inkjet head from drying out and reducing ejection stability. It is also preferred to use either the conduction type or the radiation type in combination with the air blowing type. When using both types, the air blowing type may be a method that does not involve heating, but is also preferred.

[0121] In the primary drying step, the surface temperature of the recording medium is preferably 50° C. or less, and more preferably 45° C. or less, and even more preferably 30 to 42° C., and even more preferably 32 to 40° C. When the surface temperature of the recording medium is within the above range, the drying properties are further improved, mixing of the non-white ink composition and the white ink composition is further suppressed, and the visibility and optical density of the image are further improved, and the abrasion resistance of the resulting recorded matter tends to be further improved.

[0122] When a blower is used, the wind speed near the recording medium is preferably 0.5 to 10 m / s, more preferably 1 to 5 m / s, and even more preferably 2 to 3 m / s. The wind temperature is preferably 45°C or less, more preferably 40°C or less, even more preferably 32°C or less, and particularly preferably 20 to 27°C.

[0123] 2.7.Secondary drying process The secondary drying step is a step of heating the recording medium after the ink application step. The secondary drying step is a step of heating the recording medium sufficiently to complete the recording and make the recorded material usable. The secondary drying step is a step of sufficiently drying the ink solvent component and heating the resin contained in the ink to flatten the ink coating. The secondary drying step is preferably initiated more than 0.5 seconds after the ink is applied to the recording medium. For example, it is preferable to start heating a certain recording area of ​​the recording medium more than 0.5 seconds after the ink has been completely applied to that area. The surface temperature of the low-absorbency or non-absorbency recording medium at this time is preferably 50 to 100°C, more preferably 60 to 90°C, and even more preferably 70 to 80°C. Keeping the surface temperature of the recording medium within the above range tends to further improve the abrasion resistance of the resulting recorded material. The secondary drying mechanism can be a conduction type, a radiation type, a blower type, or the like.

[0124] 2.8. Recording Media In the recording method of this embodiment, a low-absorbency recording medium or a non-absorbency recording medium is preferred as the recording medium. While low-absorbency recording media and non-absorbency recording media have excellent water resistance and abrasion resistance, they tend to easily repel treatment liquids and aqueous ink compositions and have low adhesion to the ink compositions, making the present invention particularly useful. Other examples of recording media include absorbency recording media. Absorbency recording media include recording media made of an ink-absorbent substrate and those provided with an ink-absorbent ink-receiving layer. Examples of absorbency recording media include inkjet paper, plain paper, and fabric.

[0125] The low-absorbency recording medium is not particularly limited, but examples thereof include coated paper having a coating layer on the surface for receiving oil-based ink, and examples of coated paper include, but are not particularly limited to, printing paper such as art paper, coated paper, and matte paper.

[0126] Non-absorbent recording media are not particularly limited, but examples include films and plates of plastics such as polyvinyl chloride, polyethylene, polypropylene, polyethylene terephthalate (PET), polycarbonate, polystyrene, polyurethane, etc.; plates of metals such as iron, silver, copper, aluminum, etc.; metal plates and plastic films manufactured by vapor deposition of these various metals, and alloy plates such as stainless steel and brass; and recording media in which a plastic film such as polyvinyl chloride, polyethylene, polypropylene, polyethylene terephthalate (PET), polycarbonate, polystyrene, polyurethane, etc. is adhered (coated) to a paper substrate.

[0127] "Low-absorbency recording medium" or "non-absorbency recording medium" is defined as a medium that absorbs water in an amount of 10 mL / m2 or less within 30 msec from the start of contact in the Bristow method. 2This refers to a recording medium that is as follows: The Bristow method is the most widely used method for measuring liquid absorption in a short period of time, and is also adopted by the Japan Pulp and Paper Technical Association (JAPANTAPPI). Details of the test method are described in Standard No. 51 "Paper and paperboard - Liquid absorbency test method - Bristow method" of the "JAPANTAPPI Paper and Pulp Testing Methods 2000 Edition."

[0128] 3. Recording device As an example of an inkjet device, a perspective view of a serial printer is shown in Fig. 1. As shown in Fig. 1, the serial printer 20 includes a conveying unit 220 and a recording unit 230. The conveying unit 220 conveys the recording medium F fed to the serial printer to the recording unit 230, and ejects the recording medium after recording outside the serial printer. Specifically, the conveying unit 220 has feed rollers and conveys the fed recording medium F in the sub-scanning direction T1.

[0129] The recording unit 230 also includes a carriage 234 that carries an inkjet head 231 having a nozzle array that ejects an ink composition onto the recording medium F sent from the transport unit 220, and a carriage movement mechanism 235 that moves the carriage 234 in the main scanning directions S1 and S2 of the recording medium F. Although hidden in the figure, the nozzle array is provided on the underside of the inkjet head 231, with multiple nozzles lined up along the sub-scanning direction.

[0130] In the case of a serial printer, an inkjet head 231 having a length smaller than the width of the recording medium is provided, and the inkjet head moves to perform recording in multiple passes (multi-pass). In addition, in a serial printer, the inkjet head 231 is mounted on a carriage 234 that moves in a predetermined direction, and the inkjet head moves in conjunction with the movement of the carriage, thereby ejecting the ink composition onto the recording medium. In this way, recording is performed in two or more passes (multi-pass). A pass is also called a main scan. A sub-scan is performed to transport the recording medium between passes. In other words, main scans and sub-scans are performed alternately. In other words, main scans and sub-scans are each performed multiple times.

[0131] Furthermore, the inkjet device of this embodiment is not limited to the serial printer, but may be the line printer described above. A line printer is a printer that performs printing on a printing medium in a single scan using a line head, which is an inkjet head having a length equal to or greater than the printing width of the printing medium.

[0132] Figure 2 is a side view of the inkjet head and its surroundings of the inkjet device of Figure 1. The inkjet device 100 includes a carriage 2, an inkjet head 3, a platen 4, a platen heater 4a, a preheater 7, an IR heater 8, a blower fan 8a, an afterheater 5, and a cooling fan 5a. Recording is performed on a recording medium 1.

[0133] The drying mechanism used in the primary drying step can be a conduction type using a platen heater 4a or a preheater 7, a radiation type using an IR heater 8, or a blower type using a blower fan 8a. At least one of these can be used to perform the primary drying step. When blowing air using the blower fan 8a, air can be blown to the ink adhering to the recording medium near the position facing the inkjet head 4 in the recording medium transport direction, thereby promoting evaporation. The afterheater 5 is a drying mechanism used in the secondary drying step. [Example]

[0134] The present invention will be described in more detail below using examples and comparative examples, but the present invention is not limited to the following examples.

[0135] 1. Preparation of Ink Composition Ink compositions were obtained by mixing the components to obtain the compositions shown in Tables 1 and 2 below. Tables 1 and 2 show the compositions in mass %. The pigment and resin particles in the tables indicate the solid content. The pigment was previously mixed with a water-soluble styrene acrylic resin dispersant in water at a mass ratio of pigment:dispersant = 2:1, followed by stirring to prepare a pigment dispersion, which was then used in the preparation of the ink compositions.

[0136] [Table 1]

[0137] [Table 2]

[0138] The materials shown in Tables 1 and 2 are as follows. <Pigments> White colorant: titanium dioxide Non-white pigment: Pigment Blue 15:3 <Resin particles> Joncryl 537J (acrylic resin particles, manufactured by BASF) <Organic solvents (by boiling point)> Propylene glycol (normal boiling point 188°C) 1,3-butanediol (normal boiling point 207°C) 1,5-pentanediol (normal boiling point 239°C) Glycerin (normal boiling point 290°C) 1,2-Hexanediol (standard boiling point 223°C) <Silicone surfactant A> BYK333 (Maximum peak: 6760) BYK Japan Preparation Example 1 (Maximum peak: 6500) BYK3480 (Maximum peak: 4330) manufactured by BYK Japan <Silicone surfactant B (by HLB)> KF-6204 (maximum peak: less than 3000, HLB: 10) manufactured by Shin-Etsu Silicone Co., Ltd. Tegowet 280 (Maximum peak: less than 3000, HLB: 3.5) manufactured by EVONIK Tegowet 270 (Maximum peak: less than 3000, HLB: 2.5) manufactured by EVONIK <Other surfactants> SAG503A (HLB: 11, maximum peak: less than 3000, manufactured by Nissin Chemical Industry Co., Ltd., silicone surfactant, Silface SAG503A) PD002W (Nisshin Chemical Industry Co., Ltd., acetylene glycol surfactant, Olfine PD002W) <Water> Ion-exchanged water

[0139] 1.1. Preparation Example 1 (Silicone-based surfactant B) A specific organohydrogenpolysiloxane was reacted with a polyether having a corresponding carbon-carbon double bond at the molecular end using platinum catalyst. Structural analysis of the resulting product using a liquid chromatography mass spectrometer (LC-MS) revealed that in the above general formula (3), d = 4 to 6, e = 13 to 15, f = 4 to 12, g = 0, R 3 =CH3, R 4 =-CH2-, R 5 Silicone surfactant B of Preparation Example 1 satisfying =H was obtained.

[0140] 1.2.Molecular weight distribution measurement The molecular weight distributions of silicone surfactant A and silicone surfactant B in Tables 1 and 2 were measured by gel permeation chromatography, and the maximum peak was obtained in the range of molecular weights of 300 or more. The measurement conditions were as follows. <Measurement conditions> Solvent: Tetrahydrofuran Column: TSKgel Super HZM-N x 2 · +TSKgel guardcolumn SuperHZ-L Column temperature: 40℃ ·Injection volume: 25μL Detector: Differential Refractive Index (RI) ·Flow rate: 0.35mL / min Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corporation) A calibration curve using 13 samples with Mw = 1,000,000 to 500 was used.

[0141] 2. Evaluation Method A printer (modified Seiko Epson SC-S80650) was prepared, and each ink composition was loaded into one nozzle row of the inkjet head. The inkjet head used for the printer had a nozzle row with a nozzle density of 360 dpi and 360 nozzles. The printer also had a platen heater opposite the inkjet head for primary drying, and controlled the surface temperature of the recording medium to the values ​​listed in Tables 3 to 5. Furthermore, a secondary heater was provided downstream of the printer, and during secondary drying, the surface temperature of the recording medium was adjusted to 70°C. Here, the primary drying mechanism in this example was equipped with a platen heater and a blower fan, and the fan's air speed was the value listed in the table. The air speed was measured near the surface of the recording medium directly below the inkjet head. The air temperature was measured in advance to avoid being affected by the platen heater, and was measured near the surface of the recording medium.

[0142] Using the printer configured in this manner, a solid pattern was recorded on PET50A (a transparent PET film manufactured by Lintec) at a recording resolution of 720 x 720 dpi under the conditions shown in Tables 3 to 5. The white ink composition and non-white ink composition were ejected from the inkjet head using the following two methods. In both methods, the number of ink droplets per pass was adjusted to achieve the ink deposition amount shown in the table.

[0143] <Layered construction> The nozzle for the white ink composition was positioned upstream of the nozzle for the non-white ink compositions in the media transport direction, and the white ink composition was printed first using the number of passes shown in the table, and then the non-white ink compositions were printed over the same area using the number of passes shown in the table. Tables 3 and 4 show examples and comparative examples related to layered printing.

[0144] <Simultaneous typing> In an inkjet head, of the multiple nozzle rows aligned in the main scanning direction, nozzle row 1 was filled with a white ink composition and nozzle row 2 was filled with a non-white ink composition, and the white ink composition and non-white ink composition were simultaneously recorded in the same area. Table 5 shows examples and comparative examples related to simultaneous printing.

[0145] 2.1.Image quality (visibility) The recorded matter obtained as described above was placed on black paper, and the ease of visibility of the image was visually observed from the side to which the non-white ink composition was attached, and the visibility was evaluated according to the following evaluation criteria. Note that if the amount of attached white ink composition is small or if the white ink composition does not wet and spread easily, the hiding power of the image is insufficient, allowing the black of the black paper underneath to show through and making it difficult to see. If the solid content of the attached white ink composition is high, the image tends to be more visible. (Evaluation criteria) A: Images are easy to see and recognize B: Looks slightly dark but is easy to see C: Looks black but is visible D: Appears black and is difficult to see

[0146] 2.2.Image Quality (OD Value) The solid image of the recorded matter obtained as described above was measured for OD value under the following measurement conditions using a colorimeter (i1Pro2, manufactured by X-rite), and the color development was evaluated according to the following evaluation criteria. Note that when the white ink and the color ink are mixed, the OD value decreases. (Measurement conditions) Measurement device: i1Pro2 (manufactured by X-rite) Measurement conditions: D50 light source, status T, standard observer 2° Background: Blank paper (Evaluation criteria) A:OD value is 1 or more B: 0.8 or more and less than 1 C: 0.6 or more and less than 0.8 D: 0.4 or more and less than 0.6

[0147] 2.3.Image Quality (Agglomeration Unevenness) The pattern image of the recorded matter obtained as described above was visually observed to observe whether or not there was bleeding unevenness (aggregation unevenness caused by adjacent ink droplets gathering together). Aggregation unevenness was evaluated according to the following evaluation criteria. (Evaluation criteria) A: There does not appear to be any unevenness in the color shading within the pattern. B: Minor variations in shading are slightly visible C: Fine variations in shading are clearly visible D: Significant unevenness in shade is visible

[0148] 2.4.Abrasion resistance The recorded matter obtained as described above was subjected to a rub fastness test (JIS P 8136) using a Gakushin-type rub fastness tester AB-301 (manufactured by Tester Sangyo Co., Ltd.) in which a gold-width No. 3 cloth was rubbed back and forth 50 times under a load of 500 g. The rub resistance was evaluated according to the following evaluation criteria. (Evaluation criteria) A: No peeling of the image is observed B: Peeling of over 0% but less than 10% C: Peeling of 10% to less than 40% D: More than 40% peeling

[0149] Productivity In the case of layered printing, the total number of passes for the white ink and non-white ink was used, and in the case of simultaneous printing, the number of passes for simultaneous printing was used, and the number of passes required for printing was used as an index of productivity. The productivity evaluation criteria are as follows: (Evaluation criteria) A: 8 passes or less B: 9-12 passes C: 13-16 passes D: 17 passes or more

[0150] 3. Evaluation Results [Table 3]

[0151] [Table 4]

[0152] [Table 5]

[0153] The evaluation results showed that both the image quality (visibility) and the image quality (OD value) were excellent in all Examples using a non-white ink composition containing silicone surfactant A and a white ink composition containing silicone surfactant B. On the other hand, all Comparative Examples using a non-white ink composition containing silicone surfactant B were inferior in either image quality (visibility) or image quality (OD value). Furthermore, a comparison of the evaluation results between Examples 1 to 9 and Comparative Example 1 shows that visibility was poor when the white ink composition did not contain silicone surfactant B.

[0154] Comparing Examples 1 to 9 and Comparative Example 2, it is clear that when a silicone surfactant is used as the surfactant, visibility is excellent.

[0155] Comparing Examples 1 to 9 and Comparative Example 3, it is clear that when a silicone surfactant with an HLB value of 10.5 or less is used, visibility is excellent.

[0156] A comparison between Example 1 and Example 3 suggests that visibility is superior when the content of silicone surfactant A in the white ink composition is lower than the content of silicone surfactant B.

[0157] Comparing Example 1 and Example 4, it can be seen that visibility is superior when the amount of white ink contained in the white ink composition is 14% by mass compared to when the amount is 10% by mass.

[0158] Comparing Example 1 and Example 5, it can be seen that when the content of silicone surfactant B in the white ink composition is 0.5% by mass, visibility is superior to when the content is 1.0% by mass.

[0159] A comparison of Examples 1, 7, and 30 reveals that the OD value and aggregation unevenness are better when the white ink composition contains a larger amount of organic solvent with a normal boiling point of less than 200°C relative to the total amount of organic solvent. Furthermore, Example 30 tended to have slightly more ink ejection problems from the head. The ejection stability was better when the organic solvent with a normal boiling point of less than 200°C was not too high. The above results suggest that the same is true for non-white ink compositions.

[0160] A comparison of Example 1 and Example 9 reveals that when the solvent content of the white ink composition contains glycerin, the OD value and aggregation unevenness are inferior in systems that do not contain glycerin. This suggests that when a white ink composition contains a solvent with a high boiling point, the OD value and aggregation unevenness are inferior. It also suggests that the same results apply to non-white ink compositions.

[0161] A comparison of Example 10 and Comparative Example 4 reveals that when the non-white ink composition does not contain a surfactant, the OD value is poor.

[0162] A comparison of Example 10 and Comparative Example 5 reveals that when the non-white ink composition does not contain silicone surfactant A, the OD value is inferior.

[0163] A comparison of Example 10 and Comparative Example 6 shows that when the non-white ink composition does not contain silicone surfactant B, the OD value is not inferior even when the non-white ink composition does not contain silicone surfactant A. This suggests that by including silicone surfactant B and silicone surfactant A in the non-white ink composition, it is possible to obtain an ink set that is excellent in at least visibility and OD value.

[0164] A comparison between Example 10 and Example 13 reveals that when the non-white ink composition does not contain silicone surfactant B, visibility is poor.

[0165] Comparing Example 10 with Examples 17 and 18, it can be seen that the higher the primary heating temperature in the drying step is within a predetermined range, the better the OD value and the aggregation unevenness are.

[0166] Comparing Example 10 with Examples 19 and 20, it can be seen that the higher the wind speed in the drying step within a predetermined range, the better the OD value and the aggregation unevenness.

[0167] Comparing Example 10 with Examples 21 and 22, it can be seen that the higher the air temperature in the drying step is within a predetermined range, the better the OD value and the unevenness of aggregation are.

[0168] Comparing Example 23 and Example 24, it can be seen that when simultaneous printing is performed, visibility is slightly inferior to when layered printing is performed, but the number of passes can be reduced and productivity can be significantly improved. [Explanation of symbols]

[0169] 20...serial printer, 220...transport unit, 230...recording unit, 231...inkjet head, 234...carriage, 235...carriage movement mechanism, F...recording medium, S1, S2...main scanning direction, T2...sub-scanning direction, 1...recording medium, 2...carriage, 3...inkjet head, 4...platen, 4a...platen heater, 5...after heater, 5a...cooling fan, 7...pre-heater, 8...IR heater, 8a...blower fan, 100...inkjet device.

Claims

1. An ink set comprising a non-white ink composition containing a non-white colorant and a white ink composition containing a white colorant, the non-white ink composition and the white ink composition are water-based inkjet inks, the non-white ink composition contains a silicone surfactant A that, in a molecular weight distribution measured by gel permeation chromatography, has a maximum peak in a molecular weight range of 300 or more in a molecular weight range of 3,000 to 20,000; the white ink composition contains a silicone surfactant B that, in a molecular weight distribution measured by gel permeation chromatography, does not have a maximum peak at a molecular weight of 3,000 or more in a range of molecular weights of 300 or more, and has an HLB value measured by the Griffin method of 10.5 or less; the content of the silicone surfactant A in the non-white ink composition is 0.1 to 1.0% by mass with respect to the total amount of the non-white ink composition; the content of the silicone surfactant A in the white ink composition is 0.05% by mass or less with respect to the total amount of the white ink composition; Ink set.

2. the content of the silicone surfactant A in the white ink composition is less than the content of the silicone surfactant B, the content of the silicone surfactant B in the white ink composition is 0.1 to 5 mass % with respect to the total amount of the white ink composition; The ink set according to claim 1 .

3. the non-white ink composition contains the silicone surfactant B, The ink set according to claim 1 or 2.

4. The silicone surfactant A includes a compound having a structure represented by general formula (1) or general formula (3). The ink set according to any one of claims 1 to 3. 【Chemical 1】 (In the formula, R 1 each independently represents an alkylene group having 1 to 6 carbon atoms or a single bond; X 1 teeth, Each independently represents a polyether group represented by general formula (2), and a represents an integer of 10 to 80. 【Chemistry 2】 (In the formula, R 2 represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a (meth)acrylic group; EO represents an ethylene oxide group; PO represents a propylene oxide group; the order of EO and PO is not particular; b is an integer of 1 or more; c is an integer of 0 or more; and b+c is an integer of 1 or more. 【Chemistry 3】 (In the formula, R 3 each independently represents an alkyl group having 1 to 6 carbon atoms; X 2 each independently represents a polyether group represented by general formula (4), d and e are integers of 1 or more, and d+e represents an integer of 2 to 50. 【Chemistry 4】 (In the formula, R 4 represents an alkylene group having 1 to 6 carbon atoms or a single bond, and R 5 is a hydrogen atom or carbon atom represents an alkyl group having a prime number of 1 to 6, EO represents an ethylene oxide group, PO represents a propylene oxide group, the order of EO and PO is not particular, f is an integer of 1 or more, g is an integer of 0 or more, and further f+g is an integer of 1 or more.

5. the white ink composition contains an organic solvent in an amount of 5% by mass to 30% by mass relative to the total amount of the white ink composition; the non-white ink composition contains an organic solvent in an amount of 5% by mass or more and 30% by mass or less relative to the total amount of the non-white ink composition; The ink set according to any one of claims 1 to 4.

6. the white ink composition contains an organic solvent having a normal boiling point of 170 to 250°C, the non-white ink composition contains an organic solvent having a normal boiling point of 170 to 250°C; The ink set according to any one of claims 1 to 5.

7. the white ink composition contains 30 to 80 mass% of an organic solvent having a normal boiling point of less than 200°C out of 100 mass% of organic solvents, the non-white ink composition contains 30 to 80 mass% of an organic solvent having a normal boiling point of less than 200°C out of 100 mass% of organic solvents; The ink set according to claim 5 or 6.

8. the white ink composition further contains resin particles, the non-white ink composition further contains resin particles; The ink set according to any one of claims 1 to 7.

9. A recording method for recording on a recording medium using the ink set according to any one of claims 1 to 8, comprising: a white ink deposition step of ejecting the white ink composition from an inkjet head and depositing it onto the recording medium; a non-white ink deposition step of ejecting the non-white ink composition from an inkjet head and depositing it on the recording medium, Recording method.

10. In the white ink applying step and the non-white ink applying step, a white ink image formed by the white ink composition and a non-white ink image formed by the non-white ink composition are formed by being superimposed on the recording medium. The recording method according to claim 9.

11. The white ink applying step and the non-white ink applying step include: a main scanning operation is performed a plurality of times to eject an ink composition onto the recording medium while moving the position of the inkjet head relative to the recording medium; the main scanning is performed by depositing the white ink composition and the non-white ink composition onto the same scanning area of ​​the recording medium in the same main scanning; The recording method according to claim 9 or 10.

12. The white ink applying step and the non-white ink applying step include: a step of performing a main scan in which the ink composition is ejected and deposited on the recording medium while moving the position of the inkjet head relative to the recording medium a plurality of times in the same scanning area on the recording medium, the number of times of the main scanning for the same scanning area is 8 or less; The recording method according to any one of claims 9 to 11.

13. a primary drying step of drying the white ink composition and the non-white ink composition applied to the recording medium by a drying mechanism; The recording method according to any one of claims 9 to 12.

14. the surface temperature of the recording medium in the primary drying step is 45° C. or less; The recording method according to claim 13.

Images