Ink set and recording method

Abstract

To provide an ink set that ensures good coverage of the white ink on the recording medium, thereby reducing the occurrence of unevenness in color images (non-white images). [Solution] An ink set according to one embodiment of the present invention comprises a white ink composition containing a white colorant and a non-white ink composition containing a non-white colorant, and is used for recording on a low-absorption recording medium or a non-absorption recording medium, wherein the white ink composition and the non-white ink composition are water-based inkjet inks, and the white ink composition contains a polyether-modified silicone surfactant with a weight-average molecular weight Mw of 2000 or less.

Description

[Technical Field]

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

[0002] Inkjet recording methods, which enable the recording of high-resolution images with relatively simple equipment, are undergoing rapid development in various fields. In this context, in order to obtain good visibility of color images (non-white images) even when recording on recording media such as transparent film, a method of layering and coating white ink compositions (hereinafter also referred to as "white ink") and non-white ink compositions (hereinafter also referred to as "color ink") is being employed.

[0003] For example, Patent Document 1 describes an inkjet recording method in which a white ink composition and a non-white ink composition are layered and attached to a low-absorption recording medium or a non-absorption recording medium. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-025233 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, when color ink is layered on top of white ink for recording, insufficient coverage of the white ink on the recording medium can result in unevenness in the color image (non-white image). [Means for solving the problem]

[0006] One embodiment of the ink set according to the present invention is: The present invention comprises a white ink composition containing a white colorant and a non-white ink composition containing a non-white colorant, It is used for recording on a low-absorbing recording medium or a non-absorbing recording medium. The white ink composition and the non-white ink composition are aqueous inkjet inks. The white ink composition contains a polyether-modified silicone surfactant having a weight average molecular weight Mw of 2000 or less.

[0007] One aspect of the recording method according to the present invention is a recording method performed using the ink set of the above aspect, a white ink adhesion step of adhering the white ink composition to a recording medium by an inkjet method, and a non-white ink adhesion step of adhering the non-white ink composition to the recording medium by an inkjet method. The recording medium is a low-absorbing recording medium or a non-absorbing recording medium.

Brief Description of the Drawings

[0008] [Figure 1] A schematic cross-sectional view schematically showing an inkjet recording apparatus. [Figure 2] A perspective view showing an example of the configuration around the carriage of an inkjet recording apparatus. [Figure 3] A diagram (Table 1) showing an example of the composition of a white ink composition. [Figure 4] A diagram (Table 2) showing an example of the composition of a non-white ink composition. [Figure 5] A diagram (Table 3) showing each example, each comparative example, each reference example, and evaluation results.

Modes for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present invention will be described. The embodiments described below illustrate examples of the present invention. The present invention is not limited to the following embodiments, and also includes various modified forms implemented within the scope of not changing the gist of the present invention. Note that not all of the configurations described below are essential configurations of the present invention.

[0010] In this specification, a numerical range represented by "~" means a range that includes the numbers written before and after "~" as the lower and upper limits, respectively. In this specification, "(meth)acrylic" means acrylic or methacrylic, and "(meth)acrylate" means acrylate or methacrylate.

[0011] 1. Ink set An ink set according to one embodiment of the present invention comprises a white ink composition containing a white colorant and a non-white ink composition containing a non-white colorant, and is used for recording on a low-absorption recording medium or a non-absorption recording medium, wherein the white ink composition and the non-white ink composition are water-based inkjet inks, and the white ink composition contains a polyether-modified silicone surfactant with a weight-average molecular weight Mw of 2000 or less.

[0012] Recently, when color ink was overlaid on white ink for recording, unevenness occurred in the color image (non-white image). This unevenness occurred when the white ink was stored for a long period of time, but not when the white ink was not stored for a long period of time.

[0013] Upon investigation, it was found that the white ink's wetting properties on the recording medium decreased after long-term storage, resulting in insufficient coverage of the recording medium. This insufficient coverage caused the white ink to adhere unevenly to the recording medium, which in turn resulted in uneven wetting properties of the color ink applied on top of it, ultimately causing unevenness in the color image.

[0014] Further investigation revealed that the amount of silicone-based surfactant in the white ink decreased after long-term storage compared to the time of manufacture. This is presumed to be because the silicone-based surfactant was hydrolyzed by water during long-term storage.

[0015] Therefore, by using a polyether-modified silicone surfactant with a weight-average molecular weight Mw below a predetermined level, which is less susceptible to hydrolysis, the white ink can be properly filled onto the recording medium, and as a result, the occurrence of unevenness in color images can be reduced.

[0016] In this invention, "ink set" refers to a set of inks comprising at least a white ink composition and a non-white ink composition. An ink set is a set of inks used for recording. The non-white ink composition in an ink set may consist of only one or two or more. The same applies to the white ink composition in an ink set.

[0017] 1.1 White ink composition The ink set according to this embodiment has a white ink composition containing a white colorant, the white ink composition is a water-based inkjet ink and contains a polyether-modified silicone surfactant with a weight-average molecular weight Mw of 2000 or less.

[0018] The following describes each component contained in the white ink composition.

[0019] 1.1.1 White coloring material The white ink composition contains a white colorant.

[0020] Examples of white pigments include CI Pigment White 1, which is basic lead carbonate; CI Pigment White 4, which is made of zinc oxide; CI Pigment White 5, which is made of a mixture of zinc sulfide and barium sulfate; CI Pigment White 6, which is made of titanium dioxide; CI Pigment White 6:1, which is made of titanium dioxide containing other metal oxides; CI Pigment White 7, which is made of zinc sulfide; CI Pigment White 18, which is made of calcium carbonate; CI Pigment White 19, which is made of clay; CI Pigment White 20, which is made of titanium mica; CI Pigment White 21, which is made of barium sulfate; CI Pigment White 22, which is made of gypsum; CI Pigment White 26, which is made of magnesium oxide and silicon dioxide; CI Pigment White 27, which is made of silicon dioxide; and CI Pigment White 28, which is made of anhydrous calcium silicate. Among these, it is preferable to use CI Pigment White 6, which has excellent color development and opacity. Furthermore, the white colorant may be made from particles having a hollow structure, and known particles with a hollow structure can be used.

[0021] The volume-average particle size of the white colorant is preferably 30 nm to 500 nm, more preferably 50 nm to 450 nm, and even more preferably 200 nm to 400 nm. Setting the volume-average particle size of the white colorant within this range tends to ensure ejection stability from the inkjet head and also tends to improve opacity. In this specification, unless otherwise specified, "volume-average particle diameter" refers to the volume-based particle size distribution, which is the particle diameter at a cumulative distribution of 50 vol%. The volume-average particle diameter is measured using the dynamic light scattering method or the laser diffraction method described in JIS Z8825. Specifically, a particle size analyzer that uses the dynamic light scattering method as its measurement principle (for example, "Microtrac UPA" manufactured by Nikkiso Co., Ltd.) can be used.

[0022] In this specification, the term "white" when referring to a white ink composition, white pigment, etc. does not refer only to pure white, but includes colors with hues or luster colored with chromatic or achromatic colors within a range where they can be visually recognized as white. It also includes those named and sold as those that suggest being white inks or white pigments.

[0023] More quantitatively, "white" means that the recorded matter, for example in CIELAB, not only includes colors with L * equal to 100, but also includes colors with L * equal to 60 or more and 100 or less, and a * and b * each equal to ±10 or less. More specifically, for example, when a white ink composition is recorded in an amount sufficient to fully cover the surface of a recording medium made of a transparent film, the lightness (L * ) and chromaticity (a * , b * ) of the recorded part of the recorded matter, when measured using a spectrophotometer conforming to CIELAB, are preferably within the above range. The recorded matter recorded in an amount sufficient to be fully covered is, for example, an adhesion amount of 15 mg / inch 2 . More preferably, 80 ≦ L * ≦ 100, -4.5 ≦ a * ≦ 2, -10 ≦ b * ≦ 2.5. Examples of the recording medium made of a transparent film include LAG Jet E-1000ZC (manufactured by Lintec Corporation). Examples of the spectrophotometer conforming to CIELAB include Spectrolino (trade name, manufactured by GretagMacbeth), and the measurement conditions are set as D50 light source, 2° observation field, DIN NB density, Abs white standard, No filter, Reflectance measurement mode, and measurement is performed. Note that those other than "white" are regarded as "non-white".

[0024] The content of the white colorant is preferably 1 to 30% by mass, more preferably 2 to 25% by mass, even more preferably 4 to 20% by mass, particularly preferably 6 to 15% by mass, and most particularly preferably 8 to 12% by mass, relative to the total amount of the white ink composition. When the content of the white colorant is within the above range, it tends to be possible to obtain better friction fastness and better color development (whiteness).

[0025] To improve the dispersibility of the white colorant in the ink composition, it is preferable to either surface-treat the colorant or incorporate a dispersant.

[0026] The surface treatment of the white colorant is preferably a physical or chemical treatment that directly or indirectly bonds functional groups such as carbonyl groups, carboxyl groups, aldehyde groups, hydroxyl groups, sulfone groups, ammonium groups, and salts thereof to the surface of the colorant. In particular, the surface treatment is more preferably a treatment that modifies the surface of the colorant by oxidizing or sulfonating the surface of the colorant with, for example, ozone, hypochlorous acid, or fuming sulfuric acid.

[0027] When a dispersant is added to a white ink composition, it is preferable to use a dispersant that has both a hydrophobic portion (hydrophobic group) and a hydrophilic portion (hydrophilic group) in its molecular structure. Such a dispersant has the effect of the hydrophobic portion adsorbing to the surface of the colorant particles and the hydrophilic portion orienting towards the aqueous medium side of the ink composition. This action tends to make it possible to include the colorant in the ink composition as a dispersion more stably. Such dispersants are not particularly limited, but examples include acrylic resins, styrene-(meth)acrylic acid copolymers, styrene-(meth)acrylic acid-(meth)acrylate copolymers and other styrene-acrylic resins, styrene-maleic acid resins, and their salts, formalin condensates of aromatic sulfonates, and one or more selected from this group can be used. Commercially available dispersants may also be used.

[0028] When dispersing a white colorant with a dispersant, the ratio of the white colorant to the dispersant is preferably 10:1 to 1:10, and more preferably 4:1 to 1:3.

[0029] Alternatively, a method may be used in which the particles of the white colorant are coated with a resin or other material to impart dispersibility. Possible methods for coating the white colorant include acid precipitation, phase inversion emulsification, and miniemulsion polymerization.

[0030] 1.1.2 Specific polyether-modified silicone surfactants The white ink composition contains a polyether-modified silicone surfactant with a weight-average molecular weight Mw of 2000 or less (hereinafter also referred to as "specific polyether-modified silicone surfactant").

[0031] We hypothesize that with such specific polyether-modified silicone surfactants, the steric hindrance of the bulky polyether-modified group prevents water molecules from approaching the polydimethylsiloxane skeleton, which is easily cleaved by hydrolysis. In other words, we hypothesize that if the length of the polydimethylsiloxane skeleton is shorter and the molecular weight is lower, the steric hindrance of the polyether-modified group can more effectively suppress the approach of water molecules. Therefore, we hypothesize that with specific polyether-modified silicone surfactants with a lower molecular weight, hydrolysis can be reduced, and the white ink can be properly filled onto the recording medium even after long-term storage.

[0032] The weight-average molecular weight Mw of a specific polyether-modified silicone surfactant is 2000 or less, preferably 1800 or less, more preferably 1600 or less, and preferably 1500 or less. Even more preferable. The lower limit of the weight-average molecular weight Mw is not particularly limited, but is preferably 500 or more, more preferably 1000 or more, and even more preferably 1200 or more.

[0033] The weight-average molecular weight Mw is preferably measured by gel permeation chromatography (GPC). For example, the weight-average molecular weight Mw is represented in the molecular weight distribution in GPC as the maximum peak in the range of molecular weights above 300. The maximum peak in the molecular weight range of 300 or more can be identified from a molecular weight distribution chart obtained in GPC, where the horizontal axis is the logarithm of molecular weight M (LogM) and the vertical axis is the differential value of the concentration fraction (dw / d(LogM)). 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 with molecular weights below 300 are ignored. In other words, there may be a maximum peak below 300 molecular weight, but this is the maximum peak when considering only the molecular weight range of 300 or more.

[0034] While not particularly limited, for example, the measurement conditions in the GPC measurement in this embodiment can be those described in the examples below, and the molecular weight can be determined using standard polystyrene.

[0035] Certain polyether-modified silicone surfactants may also preferably be polyether-modified silicone surfactants with modified polyether groups at both ends. A polyether-modified silicone surfactant has polyether-modified groups at both ends of a polydimethylsiloxane skeleton. It is particularly preferable that the surfactant is a polyether-modified silicone surfactant represented by the following formula (1). In the case of such a polyether-modified silicone surfactant, since it has a structure modified at both ends, it is presumed that the bulky polyether-modified group can cover the short polydimethylsiloxane skeleton from both sides, making it more difficult for water molecules to approach. As a result, hydrolysis of the polydimethylsiloxane skeleton can be further reduced, and the white ink tends to fill the recording medium better even after long-term storage. [ka] (In the formula, a is an integer from 1 to 30, x and y are each independent integers from 1 to 4, m and n are each independent integers from 1 to 20, o and p are each independent integers from 0 to 20, m+n is from 2 to 40, o+p is from 0 to 40, R 1 and R 2 Each of these is independently selected from the group consisting of a hydrogen atom, a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, and a (meth)acrylic group. E is an ethylene group, and P is a propylene group. The order between the OE (EO) and OP (PO) units is not significant.

[0036] In equation (1); a is an integer from 1 to 30, but is preferably 25 or less, more preferably 20 or less, even more preferably 2 to 17, even more preferably 5 to 15, and especially preferably 7 to 13. x and y are each independent integers between 1 and 4, preferably between 1 and 3, and more preferably between 2 and 3. m and n are each independent integers between 1 and 20, preferably between 2 and 15, more preferably between 4 and 10, and even more preferably between 5 and 8. o and p are each independent integers between 0 and 20, but are preferably between 0 and 10, more preferably between 0 and 5, even more preferably between 0 and 3, particularly preferably between 0 and 1, and most particularly preferably 0. m+n is between 2 and 40, preferably between 4 and 30, more preferably between 8 and 20, and even more preferably between 10 and 15. o+p is between 0 and 40, preferably between 0 and 20, more preferably between 0 and 10, even more preferably between 0 and 3, particularly preferably between 0 and 1, and most particularly preferably 0. R 1 and R 2 Each of these is independently selected from the group consisting of a hydrogen atom, a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, and a (meth)acrylic group, but a hydroxyl group is preferred. The order between OE (EO) units and OP (PO) units is not restricted; in other words, if there is one or more OE (EO) units and one OP (PO) unit, the order of the units does not matter. P is a propylene group, and examples include a 1,2-propylene group and a 1,3-propylene group, with the 1,2-propylene group being preferred.

[0037] Certain polyether-modified silicone surfactants may also be side-chain-modified polyether-modified silicone surfactants. Side-chain-modified polyether-modified silicone surfactants are polyether-modified silicone surfactants having polyether-modified groups in the side chains of the polydimethylsiloxane skeleton. In particular, a silicone-based surfactant represented by the following formula (2) may also be used. Even with such a side-chain modified structure, it is hypothesized that the bulky polyether-modified group can cover the short polydimethylsiloxane skeleton, making it more difficult for water molecules to approach. As a result, hydrolysis of the polydimethylsiloxane skeleton can be further reduced, and the white ink tends to fill the recording medium better even after long-term storage. [ka] (In the formula, R 3 Each independently represents an alkyl group having 1 to 6 carbon atoms, and R 4 This represents an alkylene group with 1 to 4 carbon atoms, R 5 ∫ represents a group selected from the group consisting of a hydrogen atom, a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, and a (meth)acrylic group. EO represents an ethylene oxide group, PO represents a propylene oxide group, the order between the EO and PO units is not significant, d and e are integers greater than or equal to 1, d+e represents an integer between 2 and 50, f is an integer between 1 and 20, and g is an integer between 0 and 20.

[0038] In equation (2); d+e is an integer between 1 and 50, but is preferably between 1 and 25, more preferably between 1 and 20, even more preferably between 1 and 17, even more preferably between 1 and 15, particularly preferably between 1 and 13, and most particularly preferably between 1 and 7. It is preferable that d and e are each half of d+e. R 4 The group is an alkylene group having 1 to 4 carbon atoms, preferably 1 to 3, and more preferably 2 to 3. f is an integer from 1 to 20, preferably from 2 to 15, and more preferably from 4 to 10. Yes, and more preferably 5 to 8. g is an integer between 0 and 20, but is preferably between 0 and 10, more preferably between 0 and 5, even more preferably between 0 and 3, particularly preferably between 0 and 1, and most particularly preferably 0. R 5 The group is selected from the group consisting of a hydrogen atom, a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, and a (meth)acrylic group, but a hydroxyl group is preferred.

[0039] Certain polyether-modified silicone surfactants may be obtained by synthesis. For example, they can be synthesized by the addition reaction of a silicone oil having a Si-H structure with a polyether having a carbon-carbon double bond at its terminus.

[0040] In the case of the polyether-modified silicone surfactant of formula (1), more specifically, it is preferable to synthesize it by an addition reaction between a silicone oil represented by the following formula (A) and a polyether represented by the following formula (B) using a Pt-based catalyst or the like. This allows for the preferred synthesis of the polyether-modified silicone surfactant represented by the above formula (1). [ka] (In the formula, b is an integer between 1 and 30.) b is a numerical value corresponding to a in formula (1) of the resulting polyether-modified silicone surfactant, and may be within a preferred range for a in formula (1).

[0041] In formula (A), b is an integer between 1 and 30, but is preferably 25 or less, more preferably 20 or less, even more preferably 2 to 17, even more preferably 5 to 15, and particularly preferably 7 to 13. In the case of the polyether-modified silicone surfactant of formula (2), more specifically, R of formula (2) 4 It is preferable to synthesize the silicone oil by an addition reaction using a Pt-based catalyst or the like, in which the polyether-modified group portion, including the one mentioned above, is substituted with a hydrogen atom, and a polyether represented by the following formula (B). In this case as well, the silicone oil has a Si-H structure. [ka] (In the formula, c is an integer from 1 to 40, R 6 R represents an ethylene group or a propylene group. 7 (The group is selected from the group consisting of hydrogen atoms, hydroxyl groups, alkyl groups having 1 to 6 carbon atoms, and (meth)acrylic groups.)

[0042] In equation (B); The allyl group portion of formula (B) reacts with the -H of the Si-H in the silicone oil to form the polyether-modified group portion of formula (1) or formula (2). To obtain the silicone-based surfactant of formula (1), one can use the polyether of formula (B) that corresponds to the polyether-modified group of formula (1). When obtaining a silicone-based surfactant of formula (2), the polyether-modified group of formula (2) corresponds to You can use a polyether of formula (B) that does the following. Furthermore, c is preferably an integer between 1 and 20. 6 When is an ethylene group, c is preferably 2 to 15, more preferably 4 to 10, and even more preferably 5 to 8. c is an integer from 1 to 20, but R 6 When is a propylene group, it is preferably 1 to 10, more preferably 1 to 5, and even more preferably 1 to 3. R 6The group is either an ethylene group or a propylene group, but an ethylene group is preferred. R 7 The group is selected from the group consisting of a hydrogen atom, a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, and a (meth)acrylic group, but a hydroxyl group is preferred.

[0043] The surface tension of a 0.1% by mass aqueous solution of a polyether-modified silicone surfactant having a weight-average molecular weight Mw of 2000 or less is preferably 28 mN / m or less, more preferably 26 mN / m or less, even more preferably 24 mN / m or less, and particularly preferably 23.5 mN / m or less. The lower limit of the surface tension is not particularly limited, but is preferably 15 mN / m or more, more preferably 17 mN / m or more, and even more preferably 20 mN / m or more. When ink is stored for a long period, silicone-based surfactants tend to decrease due to hydrolysis, which can worsen ink filling. However, if the ink has the surface tension range mentioned above, it tends to have excellent wetting and spreading properties, and better ink filling, especially after long-term storage.

[0044] The content of a specific polyether-modified silicone surfactant is preferably 0.05 to 2.0% by mass relative to the total amount of the white ink composition. In this case, the white ink can be filled more effectively on the recording medium, and as a result, the occurrence of unevenness in color images tends to be reduced. The lower limit of the content is preferably 0.05% by mass or more relative to the total amount of the white ink composition, more preferably 0.10% by mass or more, even more preferably 0.15% by mass or more, particularly preferably 0.20% by mass or more, even more preferably 0.25% by mass or more, and especially preferably 0.30% by mass or more. The upper limit of the content is preferably 2.0% by mass or less relative to the total amount of the white ink composition, more preferably 1.5% by mass or less, even more preferably 1.0% by mass or less, particularly preferably 0.70% by mass or less, even more preferably 0.50% by mass or less, and especially preferably 0.40% by mass or less.

[0045] 1.1.3 Water The white ink composition is a water-based inkjet ink. "Water-based" means that it contains at least water as a solvent component, and may contain water as the main solvent component. "Inkjet ink" refers to an ink composition used for recording by ejecting it from an inkjet head using an inkjet method.

[0046] Examples of suitable water include pure water such as ion-exchanged water, ultrafiltered water, reverse osmosis water, and distilled water, as well as ultrapure water, which has reduced ionic impurities. Furthermore, using water sterilized by ultraviolet irradiation or the addition of hydrogen peroxide can suppress the growth of bacteria and fungi when storing the white ink composition for a long period of time.

[0047] The water content is preferably 50% by mass or more, more preferably 50 to 100% by mass, in the liquid medium component. Furthermore, it is preferably 60 to 90% by mass, and more preferably 70 to 80% by mass. The liquid medium refers to a solvent component such as water or an organic solvent. Furthermore, the water content is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more, relative to the total mass of the white ink composition. There is no particular upper limit to the water content, but for example, it is preferably 99% by mass or less, more preferably 90% by mass or less, 80% by mass or less, and 70% by mass or less, relative to the total mass of the white ink composition. It is less than 60% by mass.

[0048] 1.1.4 Alkaline The white ink composition may contain an alkali. Examples of alkalis include inorganic alkalis and organic alkalis.

[0049] Examples of inorganic alkalis include lithium hydroxide, sodium hydroxide, potassium hydroxide, potassium dihydrogen phosphate, disodium hydrogen phosphate, potassium carbonate, sodium carbonate, sodium bicarbonate, and ammonia.

[0050] Examples of organic alkalis include triethanolamine, diethanolamine, monoethanolamine, trippropanolamine, triisopropanolamine, diisopropanolamine, and trishydroxymethylaminomethane (THAM).

[0051] The alkali content is preferably 0.1% by mass or less, more preferably 0.07% by mass or less, even more preferably 0.05% by mass or less, particularly preferably 0.03% by mass or less, and most particularly preferably 0% by mass (no alkali). If alkali is present, the lower limit of the content may be 0.01% by mass or more, 0.02% by mass or more, or 0.03% by mass or more, based on the total amount of the white ink composition. Since alkali tends to promote the hydrolysis of polyether-modified silicone surfactants, when the alkali content is within the above range, the hydrolysis of polyether-modified silicone surfactants can be more suppressed, and the ink tends to fill better after long-term storage. Conversely, in the case of the ink set according to this embodiment, since a specific polyether-modified silicone surfactant is used, even if the alkali content is within the above range, it tends to improve ink settling after long-term storage.

[0052] The inorganic alkali content is preferably less than 0.03% by mass of the total amount of the white ink composition, more preferably less than 0.02% by mass, even more preferably less than 0.01% by mass, and most preferably 0% by mass (not present). If inorganic alkali is present, the lower limit of the content may be 0.001% by mass or more, 0.005% by mass or more, or 0.01% by mass or more, based on the total amount of the white ink composition. Inorganic alkalis tend to particularly accelerate the hydrolysis of polyether-modified silicone surfactants. Therefore, when the inorganic alkali content is within the above range, the hydrolysis of polyether-modified silicone surfactants can be further suppressed, and the ink tends to fill better after long-term storage. Conversely, with the ink set according to this embodiment, since a specific polyether-modified silicone surfactant is used, even if the inorganic alkali content is within the above range, the ink tends to settle better after long-term storage.

[0053] 1.1.5 Organic Solvents The white ink composition may contain an organic solvent. The inclusion of an organic solvent tends to improve the wetting and spreading of the ink, resulting in better coverage of the white ink on the recording medium, and consequently, a reduction in the occurrence of unevenness in color images.

[0054] Examples of organic solvents include esters, alkylene glycol ethers, cyclic esters, amides, alcohols, and polyhydric alcohols.

[0055] Examples of esters include ethylene glycol monomethyl ether acetate, ethylene glycol Recall monoethyl ether acetate, ethylene glycol monobutyl ether acetate, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, Examples include glycol monoacetates such as propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl ether acetate, and methoxybutyl acetate, and glycol diesters such as ethylene glycol diacetate, diethylene glycol diacetate, propylene glycol diacetate, dipropylene glycol diacetate, ethylene glycol acetate propionate, ethylene glycol acetate butyrate, diethylene glycol acetate butyrate, diethylene glycol acetate propionate, diethylene glycol acetate butyrate, propylene glycol acetate propionate, propylene glycol acetate butyrate, dipropylene glycol acetate butyrate, and dipropylene glycol acetate propionate.

[0056] The alkylene glycol ethers can be any monoether or diether of alkylene glycol, with alkyl ethers being preferred. Specific examples include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, tetraethylene glycol monoethyl ether, tetraethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, and tripropylene glycol monobutyl ether. Examples include alkylene glycol monoalkyl ethers such as ethyl ether; and alkylene glycol dialkyl ethers such as ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, diethylene glycol methyl ethyl ether, diethylene glycol methyl butyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol dibutyl ether, triethylene glycol methyl butyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol dibutyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, dipropylene glycol dimethyl ether, dipropylene glycol diethyl ether, and tripropylene glycol dimethyl ether.

[0057] Examples of cyclic esters include cyclic esters (lactones) such as β-propiolactone, γ-butyrolactone, δ-valerolactone, ε-caprolactone, β-butyrolactone, β-valerolactone, γ-valerolactone, β-hexanolactone, γ-hexanolactone, δ-hexanolactone, β-heptanolactone, γ-heptanolactone, δ-heptanolactone, ε-heptanolactone, γ-octanolactone, δ-octanolactone, ε-octanolactone, δ-nonalactone, ε-nonalactone, and ε-decanolactone, as well as compounds in which the hydrogen atoms of the methylene group adjacent to the carbonyl group are substituted with alkyl groups having 1 to 4 carbon atoms.

[0058] Examples of amides include cyclic amides and acyclic amides. Examples of amides include alkoxyalkylamides.

[0059] Examples of cyclic amides include lactams. Examples of lactams include pyrrolidones such as 2-pyrrolidone, 1-methyl-2-pyrrolidone, 1-ethyl-2-pyrrolidone, 1-propyl-2-pyrrolidone, 1-butyl-2-pyrrolidone, and 1-(2-hydroxyethyl)pyrrolidine-2-one.

[0060] Examples of alkoxyalkylamides include 3-methoxy-N,N-dimethylpropionamide, 3-methoxy-N,N-diethylpropionamide, 3-methoxy-N,N-methylethylpropionamide, 3-ethoxy-N,N-dimethylpropionamide, 3-ethoxy-N,N-diethylpropionamide, 3-ethoxy-N,N-methylethylpropionamide, 3-n-butoxy-N,N-dimethylpropionamide, 3-n-butoxy-N,N-diethylpropionamide, 3-n-butoxy-N,N-methylethylpropionamide, and 3-n-propoxy-N,N-dimethylpropionamide. Examples include propionamide, 3-n-propoxy-N,N-diethylpropionamide, 3-n-propoxy-N,N-methylethylpropionamide, 3-iso-propoxy-N,N-dimethylpropionamide, 3-iso-propoxy-N,N-diethylpropionamide, 3-iso-propoxy-N,N-methylethylpropionamide, 3-tert-butoxy-N,N-dimethylpropionamide, 3-tert-butoxy-N,N-diethylpropionamide, 3-tert-butoxy-N,N-methylethylpropionamide, N,N-dimethylisobutyrateamide, etc.

[0061] Examples of alcohols include compounds in which one hydrogen atom of an alkane is replaced by a hydroxyl group. The alkane preferably has 10 or fewer carbon atoms, more preferably 6 or fewer, and even more preferably 3 or fewer. The alkane has 1 or more carbon atoms, preferably 2 or more. The alkane may be linear or branched. Examples of alcohols include methanol, ethanol, n-propyl alcohol, iso-propyl alcohol, n-butanol, 2-butanol, tert-butanol, iso-butanol, n-pentanol, 2-pentanol, 3-pentanol, and tert-pentanol, 2-phenoxyethanol, benzyl alcohol, and phenoxypropanol.

[0062] Polyhydric alcohols are molecules that contain two or more hydroxyl groups. Examples of polyhydric alcohols include alkanediols and polyols.

[0063] Alkanediols include, for example, compounds in which an alkane is substituted with two hydroxyl groups. Examples of alkanediols include 1,2-alkanediols, which are a general term for compounds in which hydroxyl groups are substituted at the 1st and 2nd positions of an alkane, and other alkanediols other than 1,2-alkanediols.

[0064] Examples of 1,2-alkanediols include ethylene glycol, 1,2-propanediol (propylene glycol), 1,2-butanediol (1,2BD), 1,2-pentanediol (1,2PD), 1,2-hexanediol (1,2HD), 1,2-heptanediol, 1,2-octanediol, 1,2-nonanediol, 1,2-decanediol, 3-methyl-1,2-butanediol, and 3-methyl-1,2-pentanediol. 4-methyl-1,2-pentanediol, 3,4-dimethyl-1,2-pentanediol, 3-ethyl-1,2-pentanediol, 4-ethyl-1,2-pentanediol, 3-methyl-1,2-hexanediol, 4-methyl-1,2-hexanediol, 5-methyl-1,2-hexanediol, 3,4-dimethyl-1,2-hexanediol, 3,5-dimethyl-1,2-hexanediol, 4,5-dimethyl-1,2-hexane Examples include diols, 3-ethyl-1,2-hexanediol, 4-ethyl-1,2-hexanediol, and 3-ethyl-4-methyl-1,2-hexanediol.

[0065] Other examples of alkanediols include 1,3-propanediol, 1,3-butylene glycol (also known as 1,3-butanediol), 1,4-butanediol, 2,3-butanediol, 1,5-pentanediol, 2,4-pentanediol, 2-methyl-1,3-propanediol, 3-methyl-1,3-butanediol, 3-methyl-1,5-pentanediol, 2-ethyl-1,3-hexanediol, 2-methyl-1,3-pentanediol, 3-methyl-1,5-pentanediol, 2-methylpentane-2,4-diol, 1,6-hexanediol, 2-ethyl-2-methyl-1,3-propanediol, and 2-methyl-2-propyl-1,3-propanediol.

[0066] Among alkane diols, diols of alkanes with 5 or more carbon atoms are preferred, and diols of alkanes with 5 to 10 carbon atoms are more preferred. Alternatively, diols of alkanes with 4 or fewer carbon atoms are also preferred, and diols of alkanes with 2 to 3 carbon atoms are more preferred.

[0067] Examples of polyols include condensates formed by the intermolecular condensation of two or more alkanediol molecules via hydroxyl groups, and compounds having three or more hydroxyl groups.

[0068] Examples of condensates formed by the intermolecular condensation of two or more alkanediol molecules at their hydroxyl groups include dialkylene glycols such as diethylene glycol and dipropylene glycol, and trialkylene glycols such as triethylene glycol and tripropylene glycol. A condensate formed by the intermolecular condensation of two or more diols of alkanes having 4 or fewer carbon atoms via hydroxyl groups is preferred, and a condensate formed by the intermolecular condensation of two or more diols of alkanes having 2 to 3 carbon atoms via hydroxyl groups is more preferred.

[0069] Compounds having three or more hydroxyl groups are compounds with an alkane or polyether structure as their backbone and containing three or more hydroxyl groups. Examples of compounds having three or more hydroxyl groups include glycerin, trimethylolethane, trimethylolpropane, 1,2,5-hexanetriol, 1,2,6-hexanetriol, pentaerythritol, and polyoxypropylenetriol.

[0070] Organic solvents may be used individually or in combination of two or more types.

[0071] The content of the organic solvent is preferably 5 to 50% by mass, more preferably 5 to 40% by mass, and even more preferably 10 to 30% by mass, based on the total amount of the white ink composition. It is also preferable to have the content of alkanediols within the above range.

[0072] The white ink composition preferably contains 5% by mass or less, more preferably 3% by mass or less, even more preferably 1% by mass or less, particularly preferably 0.5% by mass or less, and most preferably 0% by mass (not contained), of an organic solvent with a standard boiling point exceeding 280°C, relative to the total amount of the white ink composition. Examples of organic solvents with a standard boiling point exceeding 280°C include triethylene glycol and glycerin.

[0073] 1.1.6 Resin particles The white ink composition may contain resin particles. The resin particles function as a so-called fixing resin, improving the adhesion and abrasion resistance of the ink components attached to the recording medium. The resin particles may be in powder form, but an emulsion form is preferred.

[0074] Examples of resins used for resin particles include urethane resins, acrylic resins, fluorene resins, polyolefin resins, rosin-modified resins, terpene resins, polyester resins, polyamide resins, epoxy resins, vinyl chloride resins, ethylene vinyl acetate resins, vinyl acetate resins, butadiene resins, styrene resins, crosslinked acrylic resins, crosslinked styrene resins, benzoguanamine resins, phenolic resins, silicone resins, epoxy resins, paraffinic resins, and fluororesins.

[0075] Urethane resins are a general term for resins that contain urethane bonds. In addition to urethane bonds, urethane resins may also use polyether-type urethane resins containing ether bonds in the main chain, polyester-type urethane resins containing ester bonds in the main chain, polycarbonate-type urethane resins containing carbonate bonds in the main chain, etc. As the urethane resin, commercially available products may be used. For example, you may select and use from commercially available products such as Superflex 210, 460, 460s, 840, E-4000 (product name, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), Rezamin D-1060, D-2020, D-4080, D-4200, D-6300, D-6455 (product name, manufactured by Dainichi Seika Kogyo Co., Ltd.), Takelac WS-6020, WS-6021, W-512-A-6 (product name, manufactured by Mitsui Chemicals Polyurethane Co., Ltd.), SanCure 2710 (product name, manufactured by LUBRIZOL), Permarin UA-150 (product name, manufactured by Sanyo Chemical Industries, Ltd.).

[0076] Acrylic resins are a general term for polymers obtained by polymerizing at least one acrylic monomer, such as (meth)acrylic acid or (meth)acrylic acid ester. Examples include resins obtained from acrylic monomers and copolymers of acrylic monomers with other monomers. For example, acrylic-vinyl resins, which are copolymers of acrylic monomers and vinyl monomers, are examples. Furthermore, copolymers with vinyl monomers such as styrene are examples. For example, styrene-acrylic resins are examples. Acrylic monomers such as acrylamide and acrylonitrile can also be used.

[0077] As the acrylic resin, commercially available products may be used, for example, selected from FK-854 (product name, manufactured by Chuo Rika Kogyo Co., Ltd.), Movinyl 6969D, 952B, 718A (product name, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), Nipol LX852, LX874 (product name, manufactured by Nippon Zeon Co., Ltd.), Polysol AT860 (manufactured by Showa Denko K.K.), Boncoat AN-1190S, YG-651, AC-501, AN-1170, 4001 (product name, manufactured by DIC Corporation, acrylic resin emulsion), etc.

[0078] In this specification, the acrylic resin may be a styrene-acrylic resin as described above.

[0079] Styrene-acrylic resins are copolymers obtained from styrene monomers and acrylic monomers, and examples 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. As for styrene-acrylic resins, commercially available products may be used, such as Joncryl 62J, 7100, 390, 711, 511, 7001, 631, 632, 741, 450, 840, 74J, HRC-1645J, 734, 852, 7600, 775, 537J, 1535, PDX-7630A, 352J, 352D, PDX-7145, 538J, 7640, 7641, 631, 790, 780, 7610 (product names, manufactured by BASF), Movinyl 966A, 975N (product names, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.).

[0080] The vinyl chloride resin may also be a vinyl chloride-vinyl acetate copolymer.

[0081] Polyolefin resins have olefins such as ethylene, propylene, and butylene as their structural framework, and known types can be appropriately selected and used. Commercially available polyolefin resins can be used, for example, Arrowbase CB-1200, CD-1200 (trade names, manufactured by Unitika Ltd.), Hi-Tec E-6500 (trade name, manufactured by Toho Chemical Co., Ltd., polyethylene wax emulsion), SN-2002 (trade name, manufactured by Toho Chemical Co., Ltd., polyester resin emulsion), etc.

[0082] Examples of commercially available resin emulsions include Microgel E-1002, E-5002 (product names from Nippon Paint Co., Ltd., styrene-acrylic resin emulsion), Boncoat AN-1190S, YG-651, AC-501, AN-1170, 4001, 5454 (product names from DIC Corporation, styrene-acrylic resin emulsion), Polysol AM-710, AM-920, AM-2300, AP-4735, AT-860, PSASE-4210E (acrylic resin emulsion), and Polysol AP-7020 (styrene-acrylic resin emulsion). Polysol SH-502 (vinyl acetate resin emulsion), Polysol AD-13, AD-2, AD-10, AD-96, AD-17, AD-70 (ethylene vinyl acetate resin emulsion), Polysol PSASE-6010 (ethylene vinyl acetate resin emulsion) (product name of Showa Denko Co., Ltd.), Polysol SAE1014 (product name, styrene-acrylic resin emulsion, manufactured by Nippon Zeon Co., Ltd.), Saibinol SK-200 (product name, acrylic resin emulsion, manufactured by Saiden Chemical Co., Ltd.), AE-120A (product name of JSR Corporation, acrylic resin emulsion) Lujon), AE373D (product name manufactured by E-Tech, carboxy-modified styrene-acrylic resin emulsion), Seikadine 1900W (product name manufactured by Dainichi Seika Kogyo, ethylene-vinyl acetate resin emulsion), Vinibran 2682 (acrylic resin emulsion), Vinibran 2886 (vinyl acetate-acrylic resin emulsion), Vinibran 5202 (acrylic acetate resin emulsion) (product name manufactured by Nisshin Chemical Industry Co., Ltd.), Vinibran 700, 2586 (manufactured by Nisshin Chemical Industry Co., Ltd.), Elitel KA-5071S, KT-8803, KT-9204, KT-8701 , KT-8904, KT-0507 (Unitika Corporation product name, polyester resin emulsion), Hi-Tec E-6500 (Toho Chemical Co., Ltd. product name, polyethylene wax emulsion), SN-2002 (Toho Chemical Co., Ltd. product name, polyester resin emulsion), Takelac W-6020, W-635, W-6061, W-605, W-635, W-6021 (Mitsui Chemicals Polyurethane Co., Ltd. product name, urethane resin emulsion), Superflex 870, 800, 150, 420, 460, 470, 610, 620, 700 (Daiichi Kogyo Seiyaku Co., Ltd. product name,Urethane resin emulsion), Permarin UA-150 (manufactured by Sanyo Chemical Industries, Ltd., urethane resin emulsion), SunCure 2710 (manufactured by Lubrizol Japan, urethane resin emulsion), NeoRez R-9660, R-9637, R-940 (manufactured by Kusumoto Chemicals Co., Ltd., urethane resin emulsion), Adekabon Titer You may also select and use from among HUX-380, 290K (made by ADEKA Corporation, urethane resin emulsion), Movinyl 966A, Movinyl 7320 (made by Nippon Synthetic Chemical Co., Ltd.), Joncryl 7100, 390, 711, 511, 7001, 631, 632, 741, 450, 840, 74J, HRC-1645J, 734, 852, 7600, 775, 537J, 1535, PDX-7630A, 352J, 352D, PDX-7145, 538J, 7640, 7641, 631, 790, 780, 7610 (all made by BASF), NK Binder R-5HN (made by Shin Nakamura Chemical Industry Co., Ltd.), Hydran WLS-210 (non-crosslinked polyurethane: made by DIC Corporation), etc. ,

[0083] Furthermore, the glass transition temperature (Tg) of the resin particles is preferably 50°C or higher, more preferably 60°C or higher, and even more preferably 70°C or higher. On the other hand, it is preferably 120°C or lower, more preferably 100°C or lower, and 90°C or lower. It is even more preferable that the temperature be below this range, and particularly preferable that it be 80°C or lower. If the glass transition temperature (Tg) of the resin particles is within the above range, it may be possible to obtain a product with superior clogging recovery properties. The glass transition temperature (Tg) of the resin particles can be confirmed by a standard method using differential scanning calorimetry (DSC), etc.

[0084] The content of resin particles (solids) is preferably 3% by mass or more, more preferably 5% by mass or more, even more preferably 8% by mass or more, and particularly preferably 10% by mass or more, based on the total amount of the white ink composition. Furthermore, the content of resin particles (solids) is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less, based on the total amount of the white ink composition.

[0085] 1.1.7 Wax The white ink composition may contain wax. The wax is not particularly limited, but examples include hydrocarbon waxes and ester waxes, which are condensates of fatty acids with monohydric or polyhydric alcohols. The hydrocarbon wax is not particularly limited, but examples include paraffin wax and polyolefin waxes such as polyethylene wax and polypropylene wax. These waxes may be used individually or in combination of two or more.

[0086] Examples of commercially available paraffin waxes include AQUACER497 and AQUACER539 (product names, manufactured by BYK).

[0087] Examples of commercially available polyolefin waxes include Chemipearl S120, S650, S75N (product names, manufactured by Mitsui Chemicals, Inc.), AQUACER501, AQUACER506, AQUACER513, AQUACER515, AQUACER526, AQUACER593, and AQUACER582 (product names, manufactured by BYK).

[0088] The wax (solids) content is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, even more preferably 1.0% by mass or more, and particularly preferably 1.5% by mass or more, based on the total amount of the white ink composition. Furthermore, the wax (solids) content is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less, based on the total amount of the white ink composition.

[0089] 1.1.8 Metal encapsulants The white ink composition may contain a metal saturating agent (chelating agent). The metal saturating agent can remove specific ions from the reaction solution.

[0090] Examples of metal encapsulants include ethylenediaminetetraacetic acid and its salts, such as EDTA (ethylenediaminetetraacetic acid), EDTA-2Na (ethylenediaminetetraacetic acid disodium dihydrogen salt), EDTA-3Na (ethylenediaminetetraacetic acid trisodium monohydrogen salt), EDTA-4Na (ethylenediaminetetraacetic acid tetrasodium salt), and EDTA-3K (ethylenediaminetetraacetic acid tripotassium monohydrogen salt); DTPA, DTPA-2Na (diethylenetriaminepentaacetic acid disodium salt), and DTPA-5Na (diethylene Examples include diethylenetriaminepentaacetic acid and its salts, such as nitrilotriacetic acid pentasodium salt (nitrilopentaacetic acid pentasodium salt); nitrilotriacetic acid and its salts, such as NTA, NTA-2Na (nitrilotriacetic acid disodium salt), and NTA-3Na (nitrilotriacetic acid trisodium salt); ethylenediamine-N,N'-disuccinic acid and its salts; 3-hydroxy-2,2'-iminodisuccinic acid and its salts; L-aspartic acid-N,N'-diacetic acid and its salts; and N-(2-hydroxyethyl)iminodiacetic acid and its salts. Also, ethylenediaminetetramethylene Examples include phosphonic acids and their salts; ethylenediamine tetrametaphosphate and its salts; ethylenediamine pyrophosphate and its salts; and ethylenediamine metaphosphate and its salts.

[0091] Metal sealants may be used individually or in combination of two or more types.

[0092] If a metal sealant is included, its content can be, for example, 0.005% by mass or more and 0.1% by mass or less, preferably 0.01% by mass or more and 0.05% by mass or less, relative to the total amount of the white ink composition.

[0093] 1.1.9 Other ingredients The white ink composition may optionally contain additives other than alkalis, such as pH adjusters, preservatives / fungicides, rust inhibitors, viscosity modifiers, solubilizers, and antioxidants. When such additives are included, the content is preferably 0.1 to 5% by mass, more preferably 0.1 to 3% by mass, and even more preferably 0.1 to 1% by mass, relative to the total amount of the white ink composition.

[0094] 1.1.10 Physical Properties 1.1.10.1 Contact angle It is preferable that the contact angle change rate of the white ink composition with respect to polyethylene terephthalate, as determined by the following formula (3), is less than 10%. Contact angle change rate (%) = |Contact angle of the ink composition at 5000 ms after 12 months at 25°C - Contact angle of the ink composition at 5000 ms before storage| / Contact angle of the ink composition at 5000 ms before storage × 100 ... Equation (3)

[0095] The surface tension of the white ink tended to remain relatively unchanged before and after long-term storage. This is because, even if the silicone-based surfactant undergoes hydrolysis, reducing its content and generating hydrolyzed products, the decrease in the ink's surface tension is also influenced by other components such as organic solvents. As a result, the surface tension remains relatively unchanged before and after long-term storage. On the other hand, detailed investigation revealed that the contact angle with a given substrate changes before and after long-term storage. It was found that the above-mentioned specific polyether-modified silicone surfactant can reduce the change in the contact angle with the given substrate before and after long-term storage, improve the filling of the white ink on the recording medium, and as a result reduce the occurrence of unevenness in color images. Acetylene glycol-based surfactants are less susceptible to hydrolysis and their contact angle does not change before and after long-term storage, but they have poor ink wetting properties on low-absorption or non-absorption recording media.

[0096] The contact angle change rate of the white ink composition with respect to polyethylene terephthalate, as determined by formula (3) above, is more preferably less than 8%, even more preferably less than 5%, and particularly preferably less than 3%.

[0097] Furthermore, it is also preferable that the percentage change in contact angle (%) when "leaving at 25°C for 12 months" is changed to "40°C for 2 months" in the conditions of formula (3) above is within the above range.

[0098] 1.1.10.2 Viscosity The viscosity of the white ink composition is preferably 1.0 to 10 mPa·s at 20°C, more preferably 2.0 to 10 mPa·s, even more preferably 3.0 to 8.0 mPa·s, and particularly preferably 4.0 to 6.0 mPa·s. In particular, a viscosity of 4.0 mPa·s or higher tends to yield better color development. A viscosity of 6.0 mPa·s or lower tends to yield better discharge stability.

[0099] 1.1.10.3 Surface tension The surface tension of the white ink composition is preferably 10 to 40 mN / m at 20°C, more preferably 15 to 35 mN / m, even more preferably 20 to 30 mN / m, and particularly preferably 20 to 27 mN / m.

[0100] 1.2 Non-white ink compositions The ink set according to this embodiment has a non-white ink composition containing a non-white colorant, and the non-white ink composition is a water-based inkjet ink. The non-white ink composition may have the same composition as the white ink composition, except that it contains a non-white material instead of a white colorant and does not necessarily contain the aforementioned specific polyether-modified silicone surfactant. The non-white ink composition is an ink having a color other than white, and the color is not limited to black ink, yellow ink, magenta ink, cyan ink, or orange ink, green ink, etc.

[0101] The components contained in the non-white ink composition are described below. Unless otherwise specified, components common to the white ink composition described above may have the same composition as those in the white ink composition.

[0102] 1.2.1 Non-white colorants The non-white ink composition contains a non-white colorant. The non-white colorant is a colorant other than the white colorant mentioned above, and examples include non-white pigments and dyes. As pigments, for example, inorganic pigments and organic pigments can be used.

[0103] While there are no particular limitations on the inorganic pigments, examples include carbon blacks such as CI Pigment Black 6 (Lamp Black, Vegetable Black), CI Pigment Black 7 (Furnace Black, Channel Black, Thermal Black, Acetylene Black), CI Pigment Black 8 (Charcoal Black), and CI Pigment Black 10 (Graphite).

[0104] Commercially available carbon black products include Mitsubishi Chemical Corporation's No. 2300, 900, MCF88, No. 20B, No. 33, No. 40, No. 45, No. 52, MA7, MA8, MA100, No. 2200B, etc.; and Degussa's Color Black FW1, FW2, FW2V, FW18, FW200, S150, S160, S170, Pritex 35, U, V, 140U, etc. Examples include Shallblack 6, 5, 4A, 4, 250, etc.; Columbia Carbon's Conductex SC, Raven 1255, 5750, 5250, 5000, 3500, 1255, 700, etc.; and Cabot's Regal 400R, 330R, 660R, Mogul L, Monarch 700, 800, 880, 900, 1000, 1100, 1300, 1400, Elftex 12, etc.

[0105] Examples of organic pigments include quinacridone pigments, quinacridone quinone pigments, dioxazine pigments, phthalocyanine pigments, anthrapyrimidine pigments, ancenthrone pigments, indanthrone pigments, flavanthrone pigments, perylene pigments, diketopyrrolopyrrole pigments, perinone pigments, quinophthalone pigments, anthraquinone pigments, thioindigo pigments, benzimimidazolone pigments, isoindolinone pigments, azomethine pigments, or azo pigments.

[0106] Specific examples of organic pigments include the following:

[0107] Examples of cyan pigments include CI Pigment Blue 1, 2, 3, 15:3, 15:4, 15:34, 16, 22, 60, etc.; CI Bat Blue 4, 60, etc. Preferably, one or more mixtures selected from the group consisting of CI Pigment Blue 15:3, 15:4, and 60 can be exemplified.

[0108] Examples of magenta pigments include CI Pigment Red 5, 7, 12, 48(Ca), 48(Mn), 57(Ca), 57:1, 112, 122, 123, 168, 184, 202, and CI Pigment Violet 19. Preferably, one or more mixtures selected from the group consisting of CI Pigment Red 122, 202, and 209, and CI Pigment Violet 19 can be exemplified.

[0109] Examples of yellow pigments include CI Pigment Yellow 1, 2, 3, 12, 13, 14C, 16, 17, 73, 74, 75, 83, 93, 95, 97, 98, 119, 110, 114, 128, 129, 138, 150, 151, 154, 155, 180, 185, etc. Preferably, one or more mixtures selected from the group consisting of CI Pigment Yellow 74, 109, 110, 128, 138, 150, and 180 can be exemplified.

[0110] Other colored pigments can also be used. For example, orange pigment and green pigment can be used.

[0111] Pigments may be used individually or in combination of two or more types.

[0112] As with white pigments, it is preferable to either surface treat the pigment or incorporate a dispersant to improve its dispersibility in the ink composition, as described above.

[0113] The dyes used are not particularly limited and include acid dyes, direct dyes, reactive dyes, and basic dyes. Dyes may be used individually or in combination of two or more.

[0114] There are no particular restrictions on the dyes used, but for example, CI Acid Yellow 17, 23, 42, 44, 79, 142; CI Acid Red 52, 80, 82, 249, 254, 289; CI Acid Blue 9, 45, 249; CI Acid Black 1, 2, 24, 94; CI Food Black 1, 2; CI Direct Yellow 1, 12, 24, 33, 50, 55, 58, 86, 132, 14 Examples include 2, 144, 173, CI Direct Red 1, 4, 9, 80, 81, 225, 227, CI Direct Blue 1, 2, 15, 71, 86, 87, 98, 165, 199, 202, CI Direct Black 19, 38, 51, 71, 154, 168, 171, 195, CI Reactive Red 14, 32, 55, 79, 249, and CI Reactive Black 3, 4, 35.

[0115] The content of the non-white colorant is preferably 0.1% by mass or more and 10% by mass or less, more preferably 1% by mass or more and 8% by mass or less, and even more preferably 2% by mass or more and 6% by mass or less, based on the total amount of the non-white ink composition.

[0116] 1.2.2 Water The non-white ink composition is a water-based inkjet ink. The "water-based" composition can be the same as that of the white ink composition described above.

[0117] The water content is preferably 50% by mass or more in the liquid medium component, and more preferably 5% by mass. The concentration is 0 to 100% by mass. More preferably, it is 60 to 90% by mass, and more preferably 75 to 85% by mass. The liquid medium refers to a solvent component such as water or an organic solvent. Furthermore, the water content is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more, relative to the total mass of the non-white ink composition. There is no particular upper limit to the water content, but for example, it is preferably 99% by mass or less, more preferably 90% by mass or less, and 80% by mass or less, relative to the total mass of the non-white ink composition.

[0118] 1.2.3 Polyether-modified silicone surfactants The non-white ink composition may contain a polyether-modified silicone surfactant. In this case, it is preferable because the surface tension of the non-white ink composition can be easily adjusted to a range suitable for inkjet inks.

[0119] The polyether-modified silicone surfactant is not limited to the polyether-modified silicone surfactant with a weight-average molecular weight Mw of 2000 or less (specific polyether-modified silicone surfactant). In other words, the non-white ink composition may contain a specific polyether-modified silicone surfactant, or it may contain a polyether-modified silicone surfactant other than the specific polyether-modified silicone surfactant (hereinafter also referred to as "other polyether-modified silicone surfactant").

[0120] As for specific polyether-modified silicone surfactants, the explanation is omitted as it is as described above.

[0121] The weight-average molecular weight Mw of other polyether-modified silicone surfactants is not particularly limited, but is preferably 8000 or less, more preferably 7000 or less, and even more preferably 5000 or less. The lower limit of the weight-average molecular weight Mw is also not particularly limited, but is preferably greater than 2000, more preferably greater than 3000, and even more preferably greater than 4000. Furthermore, the weight-average molecular weight Mw of other polyether-modified silicone surfactants is preferably measured by gel permeation chromatography (GPC), as described above.

[0122] The surface tension of a 0.1% by mass aqueous solution of other polyether-modified silicone surfactants is preferably 35 mN / m or less, more preferably 33 mN / m or less, even more preferably 30 mN / m or less, and particularly preferably 28 mN / m or less. The lower limit of the surface tension is not particularly limited, but is preferably 15 mN / m or more, more preferably 17 mN / m or more, and even more preferably 20 mN / m or more.

[0123] Other polyether-modified silicone surfactants include, for example, BYK-333 (product name of BIC Chemie Japan, weight-average molecular weight Mw of 4000-7000), BYK-3480 (product name of BIC Chemie Japan, weight-average molecular weight Mw of 4000-4500), and PD508 (product name of Nisshin Chemical Industry Co., Ltd., weight-average molecular weight Mw of 6230).

[0124] The content of polyether-modified silicone surfactants in non-white ink compositions can be similar to the content of specific polyether-modified silicone surfactants in white ink compositions.

[0125] 1.2.4 Organic Solvents Non-white ink compositions may contain organic solvents. The inclusion of organic solvents tends to improve ink wetting and spreading, and to further reduce the occurrence of unevenness in color images.

[0126] The composition of the organic solvent in the non-white ink composition can be the same as that of the white ink composition described above.

[0127] 1.2.5 Alkaline The non-white ink composition may contain alkali. The alkali composition in the non-white ink composition can be the same as that of the white ink composition described above.

[0128] The alkali content is preferably 0.01 to 3% by mass, more preferably 0.05 to 1% by mass, and even more preferably 0.1 to 0.5% by mass, relative to the total amount of the non-white ink composition.

[0129] 1.2.6 Resin particles The non-white ink composition may contain resin particles. The composition of resin particles in the non-white ink composition can be the same as that of the white ink composition described above.

[0130] The content of resin particles (solids) is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, even more preferably 1% by mass or more, and particularly preferably 2% by mass or more, based on the total amount of the non-white ink composition. Furthermore, the content of resin particles (solids) is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 8% by mass or less, based on the total amount of the non-white ink composition.

[0131] 1.2.7 Wax The non-white ink composition may contain wax. The composition of wax in the non-white ink composition can be the same as that of the white ink composition described above.

[0132] 1.2.8 Metal sealants The non-white ink composition may contain a metal sealant. The composition of the metal sealant in the non-white ink composition can be the same as that of the white ink composition described above.

[0133] 1.2.9 Other Ingredients The non-white ink composition may optionally contain additives other than alkalis, such as pH adjusters, preservatives / fungicides, rust inhibitors, viscosity modifiers, solubilizers, and antioxidants. When such additives are included, the content is preferably 0.1 to 5% by mass, more preferably 0.1 to 3% by mass, and even more preferably 0.1 to 1% by mass, relative to the total amount of the non-white ink composition.

[0134] 1.2.10 Physical Properties The viscosity and surface tension of the non-white ink composition can be the same as those of the white ink composition described above.

[0135] 1.3 Application The ink set according to this embodiment is used for recording on a low-absorption recording medium or a non-absorption recording medium.

[0136] A low-absorption or non-absorption recording medium refers to a recording medium that does not absorb liquid at all or absorbs very little liquid. Quantitatively, a low-absorption or non-absorption recording medium is defined as "a recording medium that absorbs liquid at all or very little liquid from the start of contact in the Bristow method." 1 / 2 Up to 10 mL / m² of water absorption capacity 2 This refers to the recording medium described below. The Bristow method is the most widely used method for measuring liquid absorption in a short time and is also used by the Japan Pulp and Paper Technology Association (JAPAN TAPPI). Details of the test method can be found in "JAPAN T This is described in standard No. 51, "Paper and cardboard - Liquid absorbency test method - Bristow method," of the APPI Paper and Pulp Test Methods 2000 edition. In contrast, absorbent recording media refer to recording media that do not fall under the categories of low-absorbent recording media or non-absorbent recording media.

[0137] Examples of low-absorption recording media include recording media with a low-absorption coating layer on their surface, known as coated paper. Examples of paper-based recording media include art paper, coated paper, matte paper, and other printing papers. Examples of plastic-based recording media include those coated with polymers on the surface of polyvinyl chloride, polyethylene terephthalate, polycarbonate, polystyrene, polyurethane, polyethylene, polypropylene, etc., or those coated with silica, titanium, or other particles together with a binder.

[0138] Examples of non-absorbent recording media include those in which a plastic coating is applied to a substrate such as paper, those in which a plastic film is adhered to a substrate such as paper, and plastic films that do not have an absorbent layer (receiving layer). Examples of such plastics include polyvinyl chloride, polyethylene terephthalate, polycarbonate, polystyrene, polyurethane, polyethylene, and polypropylene.

[0139] 2. Recording Method A recording method according to one embodiment of the present invention is a recording method performed using the above-described ink set, comprising a white ink attachment step of attaching the above-described white ink composition to a recording medium by an inkjet method, and a non-white ink attachment step of attaching the above-described non-white ink composition to a recording medium by an inkjet method, wherein the recording medium is a low-absorption recording medium or a non-absorption recording medium.

[0140] According to the recording method of this embodiment, by using the above-described ink set, the white ink can be well filled onto the recording medium, and as a result, the occurrence of unevenness in the color image can be reduced.

[0141] The following describes each step of the recording method according to this embodiment.

[0142] Regarding low-absorption or non-absorption recording media, the explanation is omitted as it is as described above.

[0143] 2.1 White ink application process The recording method according to this embodiment includes a white ink application step in which the above-described white ink composition is applied to a recording medium by an inkjet method.

[0144] The "inkjet method" is a method of ejecting droplets of inkjet ink from the nozzles of an inkjet head and adhering them to a recording medium.

[0145] The amount of white ink composition deposited is preferably 4 to 30 mg / inch per unit area of ​​the region on the recording medium where the white ink composition is deposited. 2 More preferably, 6-25 mg / inch 2 And more preferably 8-20 mg / inch 2 And, particularly preferably, 10-15 mg / inch 2 Furthermore, it is preferable that the maximum amount of the white ink composition that adheres is within the above range.

[0146] The order of the white ink application step and the non-white ink application step described later is not particularly limited, but it is preferable that the non-white ink application step is performed after the white ink application step, so that the white ink composition and the non-white ink composition are layered and applied to the recording medium. That is, a white image formed by the white ink composition is first formed on the recording medium, and then the non-white ink composition is applied A preferred method involves superimposing the resulting color image onto a white image on a recording medium. In this case, color image inconsistencies are likely to occur, making the recording method according to this embodiment more effective.

[0147] The method of application for the white ink application process and the non-white ink application process described later is preferably carried out by scanning (hereinafter also referred to as "scanning"), in which the inkjet head ejects ink and adheres it to the recording medium while the relative positions of the inkjet head and the recording medium move. In this scanning process, the inkjet head may move relative to the recording medium, or the recording medium may move relative to the inkjet head. In other words, the movement of the inkjet head relative to the recording medium can also be described as the movement of the recording medium relative to the inkjet head. That is, it is the movement of the relative positions of the inkjet head and the recording medium. The inkjet head can be mounted on a carriage, for example. The inkjet head may be moved as the carriage moves; in this case as well, it is the movement of the inkjet head.

[0148] The number of scans performed on the same scanning area in the recording medium is not particularly limited and may be one or more scans, independently of the white ink application step and the non-white ink application step.

[0149] When the same scanning area on a recording medium is scanned multiple times, the inkjet head that ejects ink passes over the same area on the recording medium multiple times. The more times the scanning is performed, the more ink can be applied to the desired area in multiple passes, which tends to improve the image quality of the resulting recording. From the viewpoint of achieving better image quality, the number of scans is preferably 2 or more, more preferably 3 or more, even more preferably 4 or more, and particularly preferably 6 or more. There is no upper limit, but from the viewpoint of achieving better productivity, it is preferably 24 or less, more preferably 12 or less, and even more preferably 8 or less. The number of scans is set for each type of ink.

[0150] In cases where multiple passes are used, it is preferable to record by performing the scan (main scan) and sub-scan multiple times each. For example, the main scan and sub-scan can be performed alternately and repeatedly. For example, when recording in 4 passes, if the length of one sub-scan in the sub-scanning direction is one-quarter the length of the nozzle row aligned in the sub-scanning direction of the inkjet head, then four main scans will be performed on the same portion (same scanning area) of a rectangular scanning region that is the length of one sub-scan in the sub-scanning direction and extends in the main scanning direction. The number of scans in this view is called the number of scans or the number of passes. "Sub-scanning" refers to the operation of moving the relative position of the inkjet head and the recording medium in the sub-scanning direction. The "sub-scanning direction" is the direction that intersects with the main scanning direction (i.e., the direction in which the inkjet head moves relative to the recording medium). For example, by applying ink to a certain area of ​​the recording medium during a main scan, moving the recording medium slightly during a sub-scan, and then performing the next main scan, the process of applying ink adjacent to or partially overlapping the previously applied ink can be repeated to record data. Note that "sub-scan" also refers to the movement of the inkjet head relative to the recording medium; 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 called the sub-scan direction.

[0151] On the other hand, it is preferable that the number of scans performed on the same scanning area in the recording medium be one in the white ink application step and one in the non-white ink application step. In this case, white Insufficient coverage of the ink on the recording medium is common, and unevenness in the color image is likely to occur. However, according to the recording method of this embodiment, even in such a configuration, good coverage of the white ink on the recording medium can be achieved, and the occurrence of unevenness in the color image can be reduced.

[0152] If the number of scans performed on the same scanning area in the recording medium is set to one in the white ink application process and one in the non-white ink application process, the scans may be performed using the same scan or different scans.

[0153] 2.2 Non-white ink application process The recording method according to this embodiment includes a non-white ink attachment step in which the above-mentioned non-white ink composition is attached to a recording medium by an inkjet method.

[0154] The amount of 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. 2 More preferably, 3.0 to 10 mg / inch 2 And more preferably 6.0 to 8.0 mg / inch 2 Furthermore, it is preferable that the maximum amount of non-white ink composition that adheres is within the above range.

[0155] 2.3 Primary drying process The recording method according to this embodiment may include a primary drying step in the white ink application step. In this case, drying performance is further improved, and the abrasion resistance of the resulting recording can be further improved, but the white ink tends to not fill the recording medium sufficiently, and unevenness in the color image is more likely to occur. However, according to the recording method according to this embodiment, even in this configuration, the white ink can be filled well on the recording medium, and the occurrence of unevenness in the color image tends to be reduced.

[0156] The primary drying process involves heating the recording medium before the white ink application process, or applying heat or airflow to the recording medium during the white ink application process or shortly after the ink has adhered to the recording medium, in order to quickly dry the ink. The primary drying step is a process for drying at least a portion of the solvent component of the ink that has adhered to the recording medium, to the extent that it reduces the flow of the ink. The primary drying step may be performed by allowing the ink to adhere to a heated recording medium, or it may be performed early after adhesion to accelerate drying. In the primary drying process, it is preferable that the drying of ink droplets that have landed on the recording medium begins no later than 0.5 seconds after the droplets land. The drying unit (drying mechanism) for drying the ink on the recording medium is not particularly limited, but examples include platen heaters, hot air heaters, IR heaters, etc., which have a heating function, and blowers, etc., which do not have a heating function.

[0157] Types of drying mechanisms include conduction type, which heats the recording medium by transferring heat from a component in contact with the recording medium to the recording medium; radiation type, which heats the recording medium by radiating radiation such as IR to the recording medium; and airflow type, which blows air towards the recording medium.

[0158] The fan-type method includes methods that heat the recording medium while applying hot air, and methods that promote ink drying with room temperature air without heating. The method without heating is preferable because it suppresses the drying of ink in the inkjet head nozzles and the resulting decrease in ejection stability. It is also preferable to use the fan-type method in combination with either the conduction type or the radiation type. When used in combination, the fan-type method does not require heating, which is also preferable.

[0159] In the primary drying process, the surface temperature of the recording medium is preferably 60°C or lower, and more preferably The temperature is preferably 55°C or lower. More preferably 30-50°C, and even more preferably 40-45°C. On the other hand, it is more preferably 40°C or lower, even more preferably 35°C or lower, particularly preferably 30°C or lower, and even more preferably 25-28°C. When the surface temperature of the recording medium is within the above range, drying properties are improved, and the abrasion resistance of the resulting recorded material tends to be improved. Furthermore, clogging recovery, ejection stability, and color development are also better, which is preferable. Furthermore, the primary drying process may be omitted, or the primary drying process may not involve heating. In this case, the surface temperature of the recording medium on the platen should remain below the above range.

[0160] When using a fan-type system, 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 lower, more preferably 40°C or lower, even more preferably 32°C or lower, and particularly preferably 20 to 27°C.

[0161] 2.4 Secondary drying process The recording method according to this embodiment may include a step of heating and drying the recording medium to which the ink has been applied (secondary drying step). The secondary drying step is a step of drying the recording material sufficiently so that it can be used after recording is complete. The secondary drying step is a step of sufficiently drying the solvent components of the ink and heating the resins contained in the ink to flatten the ink coating film.

[0162] The secondary drying process is preferably initiated more than 0.5 seconds after the non-white ink composition has adhered to the recording medium. For example, it is preferable to start heating and drying a recording area of ​​the recording medium more than 0.5 seconds after the adhesion of the non-white ink composition to that area is completely finished.

[0163] The surface temperature of the recording medium in the secondary drying process is preferably 50°C or higher, more preferably 60°C or higher, and even more preferably 70°C or higher. In the secondary drying process, heating the surface temperature of the recording medium to 60°C or higher tends to result in excellent drying properties and better moisture resistance and friction resistance. Furthermore, the secondary drying mechanism can be a conduction type, a radiation type, a forced-air type, or the like.

[0164] 2.5 Recording device An example of a recording device suitable for the recording method according to this embodiment will be described with reference to the drawings.

[0165] Figure 1 is a schematic cross-sectional view illustrating the inkjet recording device 1. Figure 2 is a perspective view showing an example of the configuration around the carriage of the inkjet recording device 1 shown in Figure 1. As shown in Figures 1 and 2, the inkjet recording device 1 comprises an inkjet head 2, an IR heater 3, a platen heater 4, a heating heater 5, a cooling fan 6, a preheater 7, a ventilation fan 8, a carriage 9, a platen 11, a carriage movement mechanism 13, a transport means 14, and a control unit CONT. The operation of the entire inkjet recording device 1 is controlled by the control unit CONT shown in Figure 2.

[0166] The inkjet head 2 has an inkjet head that ejects a white ink composition and an inkjet head that ejects a non-white ink composition, and can record onto the recording medium M by ejecting the white ink composition and the non-white ink composition from the nozzles of the respective inkjet heads and adhering them to the recording medium M.

[0167] In this embodiment, the inkjet head 2 is a serial inkjet head that scans the recording medium M one or more times in the main scanning direction relative to the recording medium M to deposit a white ink composition and a non-white ink composition onto the recording medium M. The inkjet head 2 is mounted on a carriage 9 shown in Figure 2. The inkjet head 2 is scanned one or more times in the main scanning direction relative to the recording medium M by the operation of a carriage movement mechanism 13 that moves the carriage 9 in the media width direction of the recording medium M. The media width direction is the main scanning direction of the inkjet head 2. Scanning in the main scanning direction is also called main scanning.

[0168] Here, the main scanning direction is the direction in which the carriage 9, on which the inkjet head 2 is mounted, moves. In Figure 1, this is the direction that intersects the sub-scanning direction, which is the transport direction of the recording medium M indicated by arrow SS. In Figure 2, the width direction of the recording medium M, i.e., the direction represented by S1-S2, is the main scanning direction MS, and the direction represented by T1→T2 is the sub-scanning direction SS. Note that in one scan, scanning is performed in the main scanning direction, i.e., in either the direction of arrow S1 or arrow S2.

[0169] The cartridge 12 that supplies ink to the inkjet head 2 includes a plurality of independent cartridges. The cartridge 12 is detachably mounted on the carriage 9 on which the inkjet head 2 is mounted. Each of the plurality of cartridges may be filled with a different type of ink, and ink is supplied from the cartridge 12 to each nozzle. In this embodiment, the example shown is that the cartridge 12 is mounted on the carriage 9, but it is not limited to this, and may be provided in a location other than the carriage 9, with ink supplied to each nozzle by a supply pipe (not shown).

[0170] Conventional known methods can be used for ejection from the inkjet head 2. In this embodiment, a method is used that ejects droplets using the vibration of a piezoelectric element, that is, an ejection method that forms ink droplets by the mechanical deformation of an electrostrictive element.

[0171] The inkjet recording device 1 is equipped with a ventilation fan 8, an IR heater 3, and a platen heater 4 for drying the ink ejected from the inkjet head 2 and adhering to the recording medium M. The primary drying process can be performed by using these ventilation fan 8, IR heater 3, and platen heater 4 in appropriate combinations. In the primary drying process, it is not always necessary to heat the recording medium M; the ventilation fan 8 may be used alone to provide airflow at room temperature.

[0172] Furthermore, by using the IR heater 3, the recording medium M can be heated radiantly by infrared radiation from the inkjet head 2 side. This makes it easier for the inkjet head 2 to be heated at the same time, but the temperature can be raised without being affected by the thickness of the recording medium M, compared to when the recording medium M is heated from the back side by a platen heater 4 or the like. In addition, various fans (e.g., ventilation fan 8) may be provided to dry the ink on the recording medium M by blowing warm air or air at the same temperature as the environment onto the recording medium M.

[0173] The platen heater 4 can heat the recording medium M via the platen 11 at a position opposite the inkjet head 2 so that the ink ejected by the inkjet head 2 can dry quickly from the moment it adheres to the recording medium M. The platen heater 4 can heat the recording medium M by conduction, thereby allowing ink to adhere to the heated recording medium M.

[0174] Furthermore, it is preferable that the surface temperature of the recording medium M, due to heating by the IR heater 3 and the platen heater 4, be within the range described in the primary drying step above.

[0175] The heating element 5 is a heater for drying and solidifying the ink attached to the recording medium M, in other words, a heater for secondary drying. The heating element 5 can be used in the secondary drying process. When the heating element 5 heats the recording medium M on which the image is recorded, moisture and other substances contained in the ink evaporate more quickly and are scattered, and an ink film is formed by the resin particles that may be contained in the ink. In this way, the ink film is firmly fixed or adhered to the recording medium M, resulting in excellent film-forming properties, and a high-quality image can be obtained in a short time.

[0176] The surface temperature of the recording medium M due to heating by the heating element 5 is preferably within the range described in the secondary drying step above. When the temperature is within the aforementioned range, high-quality images tend to be obtained in a short time.

[0177] The inkjet recording device 1 may have a cooling fan 6. After the ink recorded on the recording medium M dries, the ink on the recording medium M is cooled by the cooling fan 6, thereby forming an ink coating film with good adhesion on the recording medium M.

[0178] Furthermore, the inkjet recording device 1 may be equipped with a preheater 7 that preheats the recording medium M before ink is applied to it. In addition, the inkjet recording device 1 may be equipped with a ventilation fan 8 to allow the ink applied to the recording medium M to dry more efficiently.

[0179] Below the carriage 9 are a platen 11 that supports the recording medium M, a carriage movement mechanism 13 that moves the carriage 9 relative to the recording medium M, and a transport means 14 which is a roller that transports the recording medium M in the sub-scanning direction. The operation of the carriage movement mechanism 13 and the transport means 14 is controlled by the control unit CONT.

[0180] In other embodiments of this invention, the inkjet recording apparatus may be a line-type inkjet recording apparatus in which the inkjet head 2 is a line head. For example, in Figure 1, the inkjet head 2 is a line head having a length greater than or equal to the recording width in the width direction of the recording medium, and its position is fixed. Ink is ejected from the inkjet head 2 onto the conveyed recording medium M and adheres to the recording medium. In this case, recording is performed by one main scan. When the inkjet head 2 is a line head, the other configurations can be the same as in the serial type described above.

[0181] 3. Examples The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, "%" below refers to mass.

[0182] 3.1 Preparation of white ink composition and non-white ink composition To obtain the inks, the white ink composition was prepared using the composition shown in Table 1 (Figure 3), and the non-white ink composition using the composition shown in Table 2 (Figure 4). Each component was placed in a container, and pure water was added so that the total volume of each composition reached 100% by mass. The mixture was then mixed and stirred with a magnetic stirrer for 2 hours. After further mixing by dispersion in a bead mill filled with 0.3 mm diameter zirconia beads, the mixture was stirred for 1 hour and then filtered using a 5 μm PTFE membrane filter. The units of the values ​​in Tables 1 and 2 are in mass percent.

[0183] The white pigment (CI Pigment White 6, which is titanium dioxide) used in the preparation of the white ink composition is prepared by mixing 3 parts by mass of white pigment with 1 part by mass of dispersant and 10 parts by mass of ion-exchanged water, using a styrene-acrylic resin that can be synthesized using 55% by mass of styrene, 20% by mass of acrylic acid, and 30% by mass of methyl methacrylate as a dispersant. After premixing, the mixture is dispersed using a bead mill disperser (Kotobuki Kogyo Co., Ltd., UAM-015) with 0.03 mm diameter zirconia beads at a peripheral speed of 10 m / s and a liquid temperature of 30°C for 15 minutes. The coarse particles are then separated by centrifugation using a centrifuge (Kuboyama Shoji Co., Ltd., Model-3600) to obtain a pigment dispersion, which is then used.

[0184] The black pigment used in the preparation of the non-white ink composition is the self-dispersing pigment "CAB-O-JET300" (manufactured by Cabot, 15% solids content).

[0185] In Tables 1 and 2, the "Colorant" column indicates the mass percentage of the pigment, calculated from the solid content concentration. The "Resin Particles" column shows the net amount of solid content added to the emulsion.

[0186] The surfactants described in "Example 1" and "Example 2" in Table 1 are obtained by synthesis as follows.

[0187] Using the compounds of formula (A) and formula (B) mentioned above, the surfactant of formula (1) is synthesized. Specifically, hexaethylene glycol monoallyl ether (in formula (B), c is 6, R 6 is an ethylene group, R 7 To a 20 mL solution of tetrahydrofuran containing 7.0 g of a compound (where b is a hydroxyl group), 5.8 g of the compound with b=7 in formula (A) and 0.1 mL of chloroplatinic acid are added, and the mixture is reacted by stirring at 65°C for 24 hours. After the reaction is complete, the solvent is removed by rotary evaporation to obtain a polyether-modified silicone surfactant (Example 1). Similarly, by changing b in formula (A), a polyether-modified silicone surfactant (Example 2) is obtained.

[0188] The structure of the polyether-modified silicone surfactant (Example 1) is given by formula (1): a=7, x, y = 3, n, m = 7, o, p=0, R 1 , R2 = hydroxyl group, That is the case.

[0189] The structure of the polyether-modified silicone surfactant (Example 2) is given by formula (1): a=17, x, y = 3, n, m = 7, o, p=0, R 1 , R 2 = hydroxyl group, That is the case.

[0190] The following is a supplementary explanation regarding the information in Tables 1 and 2. <Resin particles> • Movinyl 6969D: (Product name manufactured by Nippon Synthetic Chemical Industry Co., Ltd., acrylic resin emulsion, glass transition temperature 71°C) <wax> • AQUACER539: (Product name manufactured by BYK, paraffin wax) <Surfactants> • BYK3420: (Product name manufactured by BIC Chemie Japan, a polyether-modified silicone surfactant with a weight-average molecular weight (Mw) of 2000 or less) • PD002W: "Orphine PD002W" (product name manufactured by Nisshin Chemical Industry Co., Ltd., acetylene glycol-based surfactant) • BYK333: (Product name manufactured by BIC Chemie Japan, a polyether-terminated silicone-based surfactant) Example 1: (Polyether-terminated silicone surfactants with a weight-average molecular weight (Mw) of 2000 or less) Example 2: (Polyether-terminated silicone surfactants with a weight-average molecular weight (Mw) of 2000 or less) • BYK349: (Product name manufactured by BIC Chemie Japan, a polyether side-chain modified silicone surfactant) The surface tension of a 0.1% by mass aqueous solution of a surfactant (0.1% aq. surface tension) is measured using an automatic surface tensimeter CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.) by checking the surface tension when a platinum plate is wetted with a 0.1% by mass aqueous solution of the surfactant at a temperature of 20°C. <Chelating agent> • EDTA: (Ethylenediaminetetraacetic acid)

[0191] The measurement conditions for the weight-average molecular weight (Mw) of surfactants using GPC are as follows: [Measurement conditions] • Solvent: Tetrahydrofuran • Column: TSKgelSuperHZM-N x 2 · +TSKgel guardcolumn SuperHZ-L Column temperature: 40°C ·Injection volume: 25μL • Detector: Differential refraction (RI) ·Flow rate: 0.35mL / min • Calibration curve: A calibration curve was used based on 13 samples of standard polystyrene (STKstandard polystyrene, manufactured by Tosoh Corporation) with Mw values ​​ranging from 1,000,000 to 500.

[0192] 3.2 Printing Conditions A modified "SC-R5050" printer (manufactured by Seiko Epson Corporation) was prepared, and each ink composition was filled into one nozzle row of the inkjet head. The white ink composition and non-white ink composition were filled after being left at room temperature for 12 months. The printer head used has a nozzle density of 360 dpi and contains 360 nozzles. The printer also includes a platen heater and a feed fan as a primary drying mechanism. Specifically, the printer has a platen heater for primary drying located opposite the inkjet head, and controls the surface temperature of the recording medium to 45°C. The air velocity is set to 2 m / s, which is the air velocity near the surface of the recording medium directly below the inkjet head. The air temperature is measured in advance near the surface of the recording medium to avoid the influence of the platen heater and is set to 25°C. Furthermore, a secondary heater is installed downstream of the printer, and during secondary drying, the surface temperature of the recording medium is adjusted to 75°C. Using a printer configured in this way, a gradation pattern was recorded on PET50A (Lintec, transparent PET film) with the ink combinations listed in Table 3 (Figure 5), at a recording resolution of 720 x 720 dpi, and with a white ink composition adhesion amount of 13 mg / inch. 2 , Non-white ink composition deposition amount 7 mg / inch 2 The number of passes in the application process for both the white ink composition and the non-white ink composition is recorded as 6 passes.

[0193] 3.3 Evaluation Test 3.3.1 Contact angle change rate For both the initial ink and the ink after 12 months at room temperature (25°C) for each white ink composition, the 5000ms contact angle with PET50A (Lintec, transparent PET film) was measured using a "Fully Automatic Contact Angle Meter DMo-902" (Kyowa Interface Science Co., Ltd.). The evaluation was then based on the rate of change calculated using the following formula, according to the following evaluation criteria. Note that the surface tension of both the white and non-white ink compositions remained unchanged after 12 months at 25°C. However, the contact angle of some inks changed as shown in the table. Rate of change (%) = [{(Contact angle of ink left at 25°C for 12 months at 5000ms) - (Contact angle of initial ink at 5000ms)} / (Contact angle of initial ink at 5000ms)] × 100 (Evaluation Criteria) A: Rate of change is less than 5% B: Rate of change is 5% or more but less than 10% C: Rate of change is between 10% and less than 15% D: Change rate of 15% or more

[0194] 3.3.2 Filled Using only the white ink composition, a test pattern was recorded under the above printing conditions, and it was confirmed whether the background of the recording medium was visible in the printed material. The coverage was then evaluated according to the following evaluation criteria. Each ink used was left at room temperature (25°C) for 12 months. (Evaluation Criteria) A: The ink has spread sufficiently, and the background of the recording medium cannot be seen even with the naked eye or a magnifying glass. B: The ink spreads evenly, and the background of the recording medium cannot be seen with the naked eye. C: The ink has not spread sufficiently, and the background of the recording medium is slightly visible to the naked eye. D: The ink spread is insufficient, and the background of the recording medium is visible and noticeable.

[0195] 3.3.3 Unevenness Under the above printing conditions, a black ink pattern is recorded over a white ink pattern, and the black ink pattern surface of the printed material is observed to determine if unevenness has occurred in the image according to the following evaluation criteria. Each ink used will be left at room temperature (25°C) for 12 months. Furthermore, if the white ink does not fill the area well, unevenness will occur on the black ink surface that is recorded on top of it. This is because the way the black ink wets and spreads differs in areas where the white ink does not fill well. And while unevenness in white ink is less noticeable, unevenness in black (non-white) ink is more noticeable. (Evaluation Criteria) A: There are no inconsistencies in the formed image. B: The unevenness is not visible to the naked eye, but it can be seen with a magnifying glass. C: Unevenness can be confirmed by visual inspection.

[0196] 3.4 Evaluation Results The evaluation results are shown in Tables 1 and 3.

[0197] The results shown in Table 3 indicate that the example comprises a white ink composition containing a white colorant and a non-white ink composition containing a non-white colorant, and is used for recording on a low-absorption recording medium or a non-absorption recording medium. Both the white ink composition and the non-white ink composition are water-based inkjet inks, and the white ink composition contains a polyether-modified silicone surfactant with a weight-average molecular weight Mw of 2000 or less. In all examples, the white ink fills the recording medium well, and it can be seen that the occurrence of unevenness in color images (non-white images) can be reduced.

[0198] In contrast, each of the comparative examples that did not meet the above requirements showed inferior filling and unevenness.

[0199] Although not shown in the table, if the same printing conditions as above are used, except for using ink that has been left at room temperature for 12 months, and the filling and unevenness are evaluated using each of the white inks W01 to W08 and the black ink K01 in the same manner as above, the example using W05 will have a filling of D and unevenness of C, the example using W06 will have a filling of B and unevenness of B, and all other examples will have a filling of A and unevenness of A.

[0200] Furthermore, although not shown in the table, if the same printing conditions as above are used, except that the number of passes in the application process for the white ink composition and the non-white ink composition is set to one, and the filling and unevenness are evaluated in the same way as described above, the evaluation of filling and unevenness will be the same as when the number of passes is set to six.

[0201] The following conclusions can be drawn from the embodiments described above.

[0202] One form of an ink set is, The present invention comprises a white ink composition containing a white colorant and a non-white ink composition containing a non-white colorant, It is used for recording on low-absorption or non-absorption recording media. The white ink composition and the non-white ink composition are water-based inkjet inks. The white ink composition contains a polyether-modified silicone surfactant having a weight average molecular weight Mw of 2000 or less.

[0203] In one embodiment of the above ink set, The change rate of the contact angle of the white ink composition with respect to polyethylene terephthalate, obtained by the following formula, may be less than 10%. Contact angle change rate (%) = |Contact angle at 5000 ms of the ink composition after standing for 12 months at 25°C - Contact angle at 5000 ms of the ink composition before standing| / Contact angle at 5000 ms of the ink composition before standing × 100

[0204] In any of the above embodiments of the ink set, The surface tension of a 0.1 mass% aqueous solution of the polyether-modified silicone surfactant may be 28 mN / m or less.

[0205] In any of the above embodiments of the ink set, The white ink composition may have an alkali content of 0.1 mass% or less based on the total amount of the white ink composition.

[0206] In any of the above embodiments of the ink set, The white ink composition may have an inorganic alkali content of less than 0.03 mass% based on the total amount of the white ink composition.

[0207] In any of the above embodiments of the ink set, The content of the polyether-modified silicone surfactant in the white ink composition may be 0.05 to 2.0 mass% based on the total amount of the white ink composition.

[0208] In any of the above embodiments of the ink set, The non-white ink composition may contain a polyether-modified silicone surfactant.

[0209] In any of the above embodiments of the ink set, The white ink composition and the non-white ink composition may contain an organic solvent.

[0210] One method of recording is: A recording method using an ink set according to any of the above embodiments, A white ink application step in which the white ink composition is applied to a recording medium by an inkjet method, The process includes a non-white ink application step in which the non-white ink composition is applied to the recording medium by an inkjet method, The recording medium is either a low-absorption recording medium or a non-absorption recording medium.

[0211] In one embodiment of the above recording method, The white ink application process may include a primary drying step.

[0212] In any embodiment of the above recording method, The non-white ink application step is performed after the white ink application step. The white ink composition and the non-white ink composition may be layered and attached to the recording medium.

[0213] In any embodiment of the above recording method, The white ink application step and the non-white ink application step are performed by scanning, in which the inkjet head and the recording medium move relative to each other while ink is ejected from the inkjet head and applied to the recording medium. The number of scans performed on the same scanning area in the recording medium may be one for the white ink application step and one for the non-white ink application step.

[0214] The present invention is not limited to the embodiments described above, and various modifications are possible. For example, the present invention includes configurations that are substantially identical to the configurations described in the embodiments, for example, configurations that have the same function, method and result, or configurations that have the same purpose and effect. The present invention also includes configurations in which non-essential parts of the configurations described in the embodiments are replaced. Furthermore, the present invention includes configurations that produce the same effects or achieve the same purpose as the configurations described in the embodiments. Furthermore, the present invention includes configurations that add known technology to the configurations described in the embodiments. [Explanation of Symbols]

[0215] 1... Inkjet recording device, 2... Inkjet head, 3... IR heater, 4... Platen heater, 5... Heating heater, 6... Cooling fan, 7... Preheater, 8... Ventilation fan, 9... Carriage, 11... Platen, 12... Cartridge, 13... Carriage movement mechanism, 14... Transport means, CONT... Control unit, MS... Main scanning direction, SS... Sub-scanning direction, M... Recording medium.

Claims

1. The present invention comprises a white ink composition containing a white colorant and a non-white ink composition containing a non-white colorant, It is used for recording on low-absorption or non-absorption recording media. The white ink composition and the non-white ink composition are water-based inkjet inks. The aforementioned white ink composition contains a polyether-modified silicone surfactant with a weight-average molecular weight Mw of 2000 or less, in the form of an ink set.

2. The ink set according to claim 1, wherein the contact angle change rate of the white ink composition with respect to polyethylene terephthalate, as determined by the following formula, is less than 10%. Contact angle change rate (%) = |5000ms contact angle of ink composition after 12 months at 25°C - 5000ms contact angle of ink composition before storage| / 5000ms contact angle of ink composition before storage × 100

3. The ink set according to claim 1 or claim 2, wherein the surface tension of a 0.1% by mass aqueous solution of the polyether-modified silicone surfactant is 28 mN / m or less.

4. The ink set according to claim 1 or claim 2, wherein the white ink composition contains an alkali content of 0.1% by mass or less relative to the total amount of the white ink composition.

5. The ink set according to claim 1 or claim 2, wherein the white ink composition contains less than 0.03% by mass of inorganic alkali relative to the total amount of the white ink composition.

6. The ink set according to claim 1 or claim 2, wherein the content of the polyether-modified silicone surfactant in the white ink composition is 0.05 to 2.0% by mass relative to the total amount of the white ink composition.

7. The ink set according to claim 1 or claim 2, wherein the non-white ink composition contains a polyether-modified silicone surfactant.

8. The ink set according to claim 1 or claim 2, wherein the white ink composition and the non-white ink composition contain an organic solvent.

9. A recording method using the ink set described in claim 1, A white ink application step in which the white ink composition is applied to a recording medium by an inkjet method, The process includes a non-white ink application step in which the non-white ink composition is applied to the recording medium by an inkjet method, A recording method wherein the recording medium is a low-absorption recording medium or a non-absorption recording medium.

10. The recording method according to claim 9, wherein the white ink application step includes a primary drying step.

11. The non-white ink application step is performed after the white ink application step. The recording method according to claim 9, wherein the white ink composition and the non-white ink composition are layered and attached to the recording medium.

12. The white ink application step and the non-white ink application step involve the inkjet head and the recording medium moving relative to each other while the inkjet head ejects ink. This is performed by scanning, which involves extracting and adhering the material to the recording medium. The recording method according to claim 9, wherein the number of scans performed on the same scanning area in the recording medium is one for the white ink application step and one for the non-white ink application step.

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