Ink set, image forming method, and image forming apparatus

Abstract

To provide an ink set which is excellent in friction fastness and can suppress color bleeding and beading.SOLUTION: An ink set has white ink and color ink, wherein the white ink and the color ink each independently contain water dispersible resin particles having a crosslinkable functional group, and a blocked isocyanate compound having a functional group that can be crosslinked with the water dispersible resin particles having the crosslinkable functional group, an absolute value of a difference in static surface tension at 25°C between the white ink and the color ink is 1.0 mN / m or less, and absolute values of differences in dynamic surface tension at 25°C in bubble life time of 15 msec, 150 msec and 1,500 msec by a maximum bubble pressure method between the white ink and the color ink are each independently 1.0 mN / m or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an ink set, an image forming method, and an image forming apparatus. [Background technology]

[0002] Inkjet printing has become rapidly popular in recent years due to its ease of recording color images and low running costs. Inkjet printing is also used to dye (print) fabrics (woven, knitted, or nonwoven fabrics, etc.). While screen printing and roller printing have traditionally been used for printing fabrics, inkjet printing is being investigated for its advantages in terms of high-mix, low-volume production and immediate printability. Pigment printing, which involves blending pigments and fixing resins into an ink composition to print on fabrics, is also being considered. In pigment printing, physically fixing the pigment to the fabric fibers is crucial.

[0003] For example, when printing on dark-colored recording media, a technique is known in which a white base is formed by applying white ink to a recording media that has been treated with a pretreatment solution, and then color ink is applied to the white base to improve the color reproduction of the image (see Patent Document 1). [Overview of the project] [Problems that the invention aims to solve]

[0004] The present invention aims to provide an ink set that exhibits excellent friction resistance and can suppress the occurrence of color bleeding and beading. [Means for solving the problem]

[0005] The present invention, as a means for solving the aforementioned problems, is an ink set having white ink and color ink, wherein the white ink and the color ink each independently contain water-dispersible resin particles having a crosslinkable functional group and a blocked isocyanate compound having a functional group that can crosslink with the water-dispersible resin particles having a crosslinkable functional group, wherein the absolute value of the difference in static surface tension between the white ink and the color ink at 25°C is 1.0 mN / m or less, and the absolute value of the difference in dynamic surface tension between the white ink and the color ink at 25°C at bubble lifetimes of 15 msec, 150 msec, and 1,500 msec by the maximum bubble pressure method is each independently 1.0 mN / m or less. [Effects of the Invention]

[0006] According to the present invention, it is possible to provide an ink set that has excellent friction resistance and can suppress the occurrence of color bleeding and beading. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a schematic perspective view showing an example of the image forming apparatus of the present invention. [Figure 2] Figure 2 is a schematic perspective view showing an example of a housing means for the image forming apparatus of the present invention. [Figure 3] Figure 3 is a schematic diagram showing an example of a chart printed using the image forming apparatus of the present invention. [Modes for carrying out the invention]

[0008] (Ink set) The ink set of the present invention preferably comprises white ink and colored ink, and further comprises a pretreatment solution, and may further comprise other components as needed.

[0009] In the aforementioned ink set, the white ink and the color ink each independently contain water-dispersible resin particles having a crosslinkable functional group and a blocked isocyanate compound having a functional group that can be crosslinked with the water-dispersible resin particles having the crosslinkable functional group. The absolute value of the difference in static surface tension between the white ink and the color ink at 25°C is 1.0 mN / m or less. The absolute values ​​of the difference in dynamic surface tension between the white ink and the color ink at 25°C at bubble lifetimes of 15 msec, 150 msec, and 1,500 msec, measured by the maximum bubble pressure method, are each independently 1.0 mN / m or less.

[0010] In this specification, "ink set" means that the white ink and the color ink exist independently of each other. For example, the ink set is not limited to cases where the white ink containing the white ink and the color ink containing the color ink are manufactured and sold as an integrated unit. For example, even if the white ink containing the white ink containing the color ink containing the color ink is manufactured and sold independently, the ink set is included in the present invention if it is assumed that the white ink and the color ink will be used together, or if the use of the white ink and the color ink together is substantially encouraged.

[0011] In this specification, "white ink" refers to a liquid composition that forms a white image when applied to a recording medium. Furthermore, if the ink set includes the pretreatment liquid, the "white ink" refers to a liquid composition that forms a white image when applied to a region of the recording medium to which the pretreatment liquid has been applied. The white ink forms a white image on the recording medium, and for example, functions as a base for a color image formed by the color ink applied to the area to which the white ink is applied, thereby improving the color reproduction of the color image. In this specification, "white" refers to the color commonly known as white or white, and includes those that are slightly colored.

[0012] There are no particular restrictions on the Hunter whiteness of the white image formed on the recording medium with the white ink, and it can be appropriately selected depending on the purpose, but it is preferably 75 or higher, more preferably 80 or higher, and particularly preferably 85 or higher. When the Hunter whiteness is 75 or higher, the color reproduction of the color image can be improved. The Hunter whiteness can be calculated by measuring the color values ​​L, a, and b of a white image formed on a recording medium using a spectrophotometer (e.g., X-Rite eXact, manufactured by X-Rite), and using the following formula (1). Note that L, a, and b are color representation methods defined by the International Commission on Illumination (CIE), and L * a * , and b * It is also written as follows. Hunter whiteness = 100 - sqr[(100 - L)] 2 +(a 2 +b 2 )] ... Calculation formula (1)

[0013] The ink set may have one type of white ink, or it may have two or more types.

[0014] In this specification, "color ink" refers to a liquid composition that forms a color image when applied to an area of ​​a recording medium to which the white ink has been applied. In this specification, "color" refers to a color not included in "white," and includes, for example, black, cyan, magenta, or yellow.

[0015] The ink set may have one type of color ink or two or more types.

[0016] In this specification, "pretreatment solution" is a liquid composition that is applied to a recording medium and, upon contact with the white ink or color ink subsequently applied to the area to which the pretreatment solution has been applied, causes aggregation or thickening of the white ink or color ink.

[0017] [Static surface tension] The absolute value of the difference in static surface tension at 25°C between the white ink and the color ink in the ink set is 1.0 mN / m or less, preferably 0.8 mN / m or less, more preferably 0.6 mN / m or less, and even more preferably 0.5 mN / m or less. As the absolute value of the difference in static surface tension at 25°C between the white ink and the color ink in the ink set approaches 0 mN / m, color bleeding and beading can be further suppressed. Since the difference in static surface tension is expressed as an absolute value, it is 0 mN / m or more. If the absolute value of the difference in static surface tension at 25°C between the white ink and the color ink in the ink set exceeds 1.0 mN / m, color bleeding will occur when the color ink is applied to the area of ​​the recording medium to which the white ink has been applied after the white ink has been applied to the recording medium.

[0018] Furthermore, if the ink set has multiple white inks or color inks, it is sufficient that the absolute value of the difference in static surface tension for a given combination of white ink and color ink is 1.0 mN / m or less, but it is preferable that the absolute value of the maximum difference in static surface tension for a given combination of white ink and color ink is 1.0 mN / m or less, and it is more preferable that the absolute value of the difference in static surface tension for all combinations of white ink and color ink is 1.0 mN / m or less.

[0019] The static surface tension of the white ink and the color ink in the ink set at 25°C is preferably 40.0 mN / m or less, more preferably 36.0 mN / m or less, and even more preferably 30.0 mN / m or less, independently of each other. By having the static surface tension of the white ink and the color ink at 25°C be 40.0 mN / m or less independently of each other, it is possible to suppress not only color bleeding between the white ink and the color ink, but also the occurrence of color bleeding between one color ink and another color ink.

[0020] Furthermore, if the ink set has multiple white inks or color inks, it is preferable that the static surface tension of each predetermined white ink and color ink is 40.0 mN / m or less, and it is more preferable that the static surface tension of all white inks and color inks is 40.0 mN / m or less, independently.

[0021] Here, "each independently" means that the static surface tensions of the white ink and the color ink at 25°C are both 40.0 mN / m or less, and may be the same or different.

[0022] The static surface tension of the white ink or the color ink at 25°C can be measured using an automatic surface tension meter (e.g., DY-300, manufactured by Kyowa Interface Science Co., Ltd.) by the plate method (Wilhelmy method). Furthermore, the temperature of 25°C in this measurement is the temperature of the white ink or the color ink itself, not the temperature of the recording medium.

[0023] [Dynamic surface tension] Preferably, the absolute values ​​of the difference in dynamic surface tension between the white ink and the color ink at 25°C at bubble lifetimes of 15 msec, 150 msec, and 1,500 msec, as measured by the maximum bubble pressure method, are independently 1.0 mN / m or less and 0.9 mN / m or less. Color bleeding and beading can be further suppressed as the absolute values ​​of the difference in dynamic surface tension between the white ink and the color ink at 25°C at bubble lifetimes of 15 msec, 150 msec, and 1,500 msec, as measured by the maximum bubble pressure method, independently approach 0 mN / m. Since the difference in dynamic surface tension is expressed as an absolute value, it is 0 mN / m or greater. If the absolute values ​​of the difference in dynamic surface tension between the white ink and the color ink in the ink set at 25°C at bubble lifetimes of 15 msec, 150 msec, and 1,500 msec according to the maximum bubble pressure method independently exceed 1.0 mN / m, then color bleeding will occur when the color ink is applied to the area of ​​the recording medium to which the white ink has been applied after the white ink has been applied to the recording medium.

[0024] Furthermore, if the ink set has multiple white inks or color inks, it is sufficient that the absolute values ​​of the difference in dynamic surface tension at 25°C at bubble lifetimes of 15 msec, 150 msec, and 1,500 msec according to the maximum bubble pressure method for a given combination of white inks and color inks are each independently 1.0 mN / m or less. However, it is preferable that the absolute values ​​of the maximum difference in dynamic surface tension at 25°C at bubble lifetimes of 15 msec, 150 msec, and 1,500 msec according to the maximum bubble pressure method for a given combination of white inks and color inks are each independently 1.0 mN / m or less. It is even more preferable that for all combinations of white inks and color inks, the absolute values ​​of the difference in dynamic surface tension at 25°C at bubble lifetimes of 15 msec, 150 msec, and 1,500 msec according to the maximum bubble pressure method are each independently 1.0 mN / m or less.

[0025] Here, "each independently" means that the absolute values ​​of the difference in dynamic surface tension at 25°C when the bubble lifetime is 15 msec, the absolute values ​​of the difference in dynamic surface tension at 25°C when the bubble lifetime is 150 msec, and the absolute values ​​of the difference in dynamic surface tension at 25°C when the bubble lifetime is 1,500 msec may be the same or different, as long as they are all 1.0 mN / m or less.

[0026] Furthermore, the dynamic surface tension of the white ink or the colored ink at 25°C at bubble lifetimes of 15 msec, 150 msec, and 1,500 msec using the maximum bubble pressure method can be measured using a portable dynamic surface tensimeter (e.g., SITA Pro line t15, manufactured by Eiko Seiki Co., Ltd.).

[0027] The reason why color bleeding is suppressed in the aforementioned ink set is explained below.

[0028] It is known that adding a crosslinkable resin having a polycarbonate-based skeleton and a blocked isocyanate compound to an ink composition improves the friction fastness of images, and that incorporating an alkaline (basic) compound into the ink composition enhances the redispersibility of the crosslinkable resin (see Japanese Patent Publication No. 6794746). However, this ink composition has the problem of being prone to image defects such as blurring of text, resulting in a significant decrease in image quality.

[0029] Furthermore, when printing on dark-colored recording media, a white image base is formed by applying white ink to the recording media, and the color reproduction of the color image is improved by subsequently applying color ink to the areas where white ink has been applied. However, when applying color ink a short time after applying white ink (for example, within 20 seconds), when a large amount of white ink is applied, when the recording media has low permeability (including non-permeable), or when applying color ink without heating the recording media with white ink applied between the time the white ink was applied and the color ink was applied, there was a problem that color bleeding, where the white ink and color ink mix, could occur due to insufficient drying of the white ink. Similarly, due to insufficient drying of the white ink, the drying properties of the color ink applied later to the areas where white ink was applied were reduced, and beading, which is uneven density in color images, could also occur.

[0030] In contrast, in the ink set of the present invention, the absolute value of the difference in static surface tension between the white ink and the color ink at 25°C is 1.0 mN / m or less, and the absolute value of the difference in dynamic surface tension between the white ink and the color ink at 25°C at bubble lifetimes of 15 msec, 150 msec, and 1,500 msec using the maximum bubble pressure method is independently 1.0 mN / m or less. Therefore, even if the drying of the white ink is insufficient, the occurrence of color bleeding can be suppressed.

[0031] Furthermore, when multiple color inks are used in cases where the white ink is not sufficiently dried as described above, in addition to color bleeding where the white ink and each color ink mix, color bleeding may also occur where the color inks come into contact with each other and mix on the area where the white ink is applied.

[0032] In contrast, the ink set preferably has an absolute value of 1.0 mN / m or less for each of the multiple color inks at 25°C with a bubble lifetime of 15 msec using the maximum bubble pressure method, and more preferably 0.9 mN / m or less. By having an absolute value of 1.0 mN / m or less for each of the multiple color inks at 25°C with a bubble lifetime of 15 msec using the maximum bubble pressure method, color bleeding between the multiple color inks can be suppressed. Since the difference in dynamic surface tension between the multiple color inks at 25°C with a bubble lifetime of 15 msec using the maximum bubble pressure method is expressed as an absolute value, it is 0 mN / m or more.

[0033] Furthermore, for a predetermined combination of color inks among the plurality of color inks, it is sufficient if the absolute value of the difference in dynamic surface tension at 25°C with a bubble lifetime of 15 msec using the maximum bubble pressure method is 1.0 mN / m or less. However, it is preferable that for a predetermined combination of color inks among the plurality of color inks, the absolute value of the maximum difference in dynamic surface tension at 25°C with a bubble lifetime of 15 msec using the maximum bubble pressure method is 1.0 mN / m or less. And it is preferable that for all combinations of color inks, the absolute value of the difference in dynamic surface tension at 25°C with a bubble lifetime of 15 msec using the maximum bubble pressure method is independently 1.0 mN / m or less.

[0034] For example, if the ink set has black ink, cyan ink, magenta ink, and yellow ink as the plurality of color inks, it is preferable that the absolute value of the difference in dynamic surface tension at 25°C with a bubble lifetime of 15 msec using the maximum bubble pressure method is 1.0 mN / m or less for all of the following: between black ink and cyan ink, between black ink and magenta ink, between black ink and yellow ink, between cyan ink and magenta ink, between cyan ink and yellow ink, and between magenta ink and yellow ink.

[0035] Here, "each independently" means that the absolute values ​​of the differences in dynamic surface tension between the multiple color inks at 25°C at 15 msec are all 1.0 mN / m or less, and may be the same or different.

[0036] Furthermore, as described above, when the ink set has the plurality of color inks, and the plurality of color inks include black ink, cyan ink, magenta ink, and yellow ink, it is preferable that the dynamic surface tension of each color ink at 25°C at a bubble lifetime of 15 msec using the maximum bubble pressure method satisfies the following relation (1). In relation (1) below, the color ink located on the left (i.e., the color ink with a larger value of dynamic surface tension at 25°C at 15 msec among the plurality of color inks) has a greater visual impact on the area of ​​other color inks when color bleeding occurs. However, by satisfying relation (1) below, it is possible to suppress the occurrence of color bleeding in which the color ink located on the left in relation (1) below penetrates the color ink located on the right (i.e., the color ink with a smaller value of dynamic surface tension at 25°C at 15 msec among the plurality of color inks). Black ink > Cyan ink ≥ Magenta ink ≥ Yellow ink ... Relationship (1)

[0037] <White ink and colored ink> The white ink and the color ink (hereinafter, the white ink and the color ink may be collectively abbreviated as "ink") each independently contains water-dispersible resin particles having a crosslinkable functional group and a blocked isocyanate compound having a functional group that can crosslink with the water-dispersible resin particles having a crosslinkable functional group, and further preferably contains an organic solvent, water, a colorant, and a surfactant, and further optionally contains other components.

[0038] Here, "each independently" means that the compositions of the white ink and the color ink may be the same or different, as long as they both contain water-dispersible resin particles having a crosslinkable functional group and a blocked isocyanate compound having a functional group that can be crosslinked with the water-dispersible resin particles having a crosslinkable functional group.

[0039] Furthermore, if the ink set includes the white ink and the color ink, as well as the pretreatment liquid, it is preferable that at least one selected from the colorant and the resin is anionic (these may be collectively referred to as "anionic compounds"). By having at least one selected from the colorant and the resin be anionic, when the white ink or the color ink comes into contact with a component (such as a flocculant) contained in the pretreatment liquid, the white ink or the color ink will coagulate or thicken, thereby allowing the white ink or the color ink to remain on the surface of the recording medium.

[0040] -Water-dispersible resin particles having crosslinkable functional groups- The water-dispersible resin particles having the crosslinkable functional group (hereinafter sometimes abbreviated as "water-dispersible resin particles") are not particularly limited and can be appropriately selected according to the purpose. They may be self-emulsifying types with hydrophilic components necessary for stable dispersion in water, or they may become water-dispersible by the use of an external emulsifier.

[0041] There are no particular restrictions on the type of water-dispersible resin particles, and they can be appropriately selected according to the purpose. However, it is preferable that they have film elongation and tensile strength, and urethane resin is more preferable because it offers greater design flexibility and therefore makes it easier to obtain the desired film properties.

[0042] The aforementioned urethane resin is not particularly limited as long as it has a urethane skeleton and is water-dispersible, and can be appropriately selected according to the purpose. However, from the viewpoint of material compatibility with the inkjet ejection head, it is preferable to use an anionic urethane resin (anionic resin having a urethane skeleton) having anionic functional groups such as carboxyl groups, sulfo groups, and hydroxyl groups.

[0043] Specific examples of the aforementioned anionic urethane resin include Superflex 460, Superflex 460S, Superflex 470, Superflex 840 (all manufactured by Daiichi Kogyo Seiyaku Co., Ltd.); Takelac® WS-4022, Takelac® WS-5100, Takelac® WS-5984, or Takelac® WS-6021 (all manufactured by Mitsui Chemicals Polyurethane Co., Ltd.).

[0044] As the urethane resin, in addition to urethane bonds, polyether-type urethane resins containing ether bonds in the main chain, polyester-type urethane resins containing ester bonds in the main chain, and polycarbonate-type urethane resins containing carbonate bonds in the main chain can be used. Among these, polycarbonate-type urethane resins and polyester-type urethane resins are preferred.

[0045] These urethane resins may be used individually or in combination of two or more. Furthermore, within a range that does not impede the effects of the present invention, in addition to the water-dispersible resin particles having the above-mentioned physical properties, other water-dispersible resins, such as acrylic resin, acrylic-styrene resin, vinyl acetate resin, or acrylic-vinyl acetate resin, may be used individually or in combination of two or more.

[0046] There are no particular restrictions on the volume-average particle size of the water-dispersible resin particles, and they can be appropriately selected depending on the purpose, but a size of 0.01 μm or more and 0.15 μm or less is preferred, and a size of 0.02 μm or more and 0.1 μm or less is more preferred. The volume-average particle size of the aforementioned water-dispersible resin particles can be measured, for example, using a particle size distribution analyzer (Nanotrac WaveII-UT151, manufactured by Microtrac MRB Co., Ltd.).

[0047] There are no particular restrictions on the content (solid content) of the water-dispersible resin particles in the white ink or the color ink, and it can be appropriately selected depending on the purpose. However, it is preferably 3% by mass or more and 15% by mass or less, and more preferably 5% by mass or more and 13% by mass or less, based on the total mass of the white ink or the color ink. If the content (solid content) of the water-dispersible resin particles is 15% by mass or more, the ink discharge stability may decrease, and if it is 3% by mass or less, the friction fastness may decrease significantly.

[0048] -Water-dispersible resin particles having crosslinkable functional groups and blocked isocyanate compounds having crosslinkable functional groups- A blocked isocyanate compound having a functional group that can be crosslinked with the water-dispersible resin particles having the crosslinkable functional group (hereinafter sometimes abbreviated as "blocked isocyanate compound") is blended as a crosslinking agent for the water-dispersible resin particles having the crosslinkable functional group.

[0049] The aforementioned blocked isocyanate compound refers to a compound in which the isocyanate group is protected by a blocking agent, and the blocking agent dissociates upon heating, regenerating the active isocyanate group. It is conceivable that the isocyanate group generated by this heating reacts with the water-dispersible resin particles, such as the urethane resin, with each other, or with the crosslinkable functional groups of the water-dispersible resin particles and with the functional groups or active hydrogen sites of recording media such as fabrics, to form crosslinked structures such as urethane bonds or urea bonds.

[0050] The blocking agent is not particularly limited and can be appropriately selected depending on the purpose. Examples include phenolic compounds, aromatic secondary amine compounds, cyclic amine compounds, lactam compounds, oxime compounds, or sodium sulfite. These may be used individually or in combination of two or more.

[0051] More specifically, the blocked isocyanate compound is preferably one having a urethane skeleton.

[0052] Specific examples of the blocked isocyanate compounds having the urethane skeleton include products such as the Elastron® series, Elastron® BN series (all manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), Takenate® series (manufactured by Mitsui Chemicals, Inc.), or Adekabon Titer HUX series (manufactured by ADEKA Corporation). More preferably, commercially available products such as Elastron® E-37, Elastron® H-3-DF, Elastron® H-15, Elastron® NEW BAP-15, Elastron® F-29, Elastron® W-11P (all manufactured by Daiichi Kogyo Seiyaku Co., Ltd.); Takenate® XWB-ST001, Takenate® XWB-ST047 (both manufactured by Mitsui Chemicals, Inc.); Adekabon Titer HUX-3861, Adekabon Titer HUX-3560 (both manufactured by ADEKA Corporation) can be used.

[0053] From a durability standpoint, ink films generally require a thickness of around 10 μm to 300 μm. However, such thick films have the problem of impairing the original texture of recording media such as cloth. The ink set of the present invention is advantageous in that, by using the blocked isocyanate compound, sufficient durability can be ensured without forming a thick ink film as in the conventional method, and thus the original texture of the recording medium is not impaired. In particular, the ink set is advantageous in that by combining the water-dispersible resin particles such as urethane resin with the blocked isocyanate compound, an ink film with strong adhesion and durability can be formed.

[0054] There are no particular restrictions on the content of the blocked isocyanate compound in the white ink and the color ink, and they can be appropriately selected depending on the purpose. However, independently, the content is preferably 0.05 parts by mass or more per 1 part by mass (solid content) of the water-dispersible resin particles having the crosslinkable functional group, more preferably 0.05 to 0.6 parts by mass, more preferably 1.0 part by mass or less, more preferably 0.05 to 0.6 parts by mass, and even more preferably 0.1 to 0.55 parts by mass, from the viewpoint of the film properties of the resulting ink film.

[0055] Furthermore, friction fastness can be confirmed by measuring the friction fastness using a Type I friction tester (clock meter) method in accordance with the method specified in JIS L 0849. In both dry and wet tests, a grade of 3-4 or higher is preferable, and a grade of 4-5 or higher is more preferable.

[0056] Here, "each independently" means that the content of the blocked isocyanate compound in the white ink and the color ink may be the same or different.

[0057] -Organic Solvents- There are no particular restrictions on the organic solvent, and it can be appropriately selected depending on the purpose. However, it is preferable to use one that has an equilibrium water content of 30% by mass or more in an environment of 23°C and 80% relative humidity (RH) (hereinafter sometimes referred to as "wetting agent"). Among these, organic solvents with high equilibrium water content and boiling point (bp) are more preferable. The selection of such an organic solvent is related to the suppression of color bleeding and beading (in other words, the control of static and dynamic surface tension), but it is also related to improving ink ejection stability and suppressing the adhesion of waste ink in the maintenance mechanism of the image forming apparatus.

[0058] The aforementioned equilibrium moisture content (%) was calculated by using a saturated aqueous solution of potassium chloride and sodium chloride mixed in a ratio of 6:4 (potassium chloride:sodium chloride, parts by mass), maintaining the temperature and humidity inside a desiccator at 23°C ± 1°C and RH 80% ± 3%, storing petri dishes containing 1 g each of the organic solvents in this desiccator, measuring the moisture content at equilibrium, and calculating it using the following formula (2). Equilibrium moisture content (mass%) = [Amount of moisture absorbed by organic solvent / (Amount of organic solvent + Amount of moisture absorbed by organic solvent)] × 100 ... Calculation formula (2)

[0059] Examples of the aforementioned wetting agents include polyhydric alcohols having an equilibrium water content of 30% by mass or more in an environment with a temperature of 23°C and 80% RH. Specifically, such polyhydric alcohols include diethylene glycol (bp245°C, equilibrium water content 43% by mass), triethylene glycol (bp285°C, equilibrium water content 39% by mass), tetraethylene glycol (bp324°C~330°C, equilibrium water content 37% by mass), 1,3-butanediol (bp203°C~204°C, equilibrium water content 35% by mass), glycerin (bp290°C, equilibrium water content 49% by mass), diglycerin (bp270°C / 20hPa, equilibrium water content 38% by mass), 1,2,3-butanetriol (bp175°C / 33hPa, equilibrium water content 38% by mass), or 1,2,4-butanetriol (bp190°C~191°C / 24hPa, equilibrium water content 41% by mass). These may be used individually or in combination of two or more. Among these, glycerin and 1,3-butanediol are preferred as the wetting agents.

[0060] Examples of the wetting agent other than the polyhydric alcohol include 2-methyl-1,3-butanediol (bp 214°C), 3-methyl-1,3-butanediol (bp 203°C), dipropylene glycol (bp 232°C), 1,5-pentanediol (bp 242°C), propylene glycol (bp 187°C), 2-methyl-2,4-pentanediol (bp 197°C), ethylene glycol (bp 196°C - 198°C), tripropylene glycol (bp 267°C), hexylene glycol (bp 197°C), polyethylene glycol (viscous liquid to solid), polypropylene glycol (bp 187°C), 1,6-hexanediol (bp 253°C - 260°C), 1,2,6-hexanetriol (bp 178°C), trimethylolethane (solid, melting point (mp) 199°C - 201°C), or trimethylolpropane (solid, mp 61°C), etc. These may be used alone or in combination of two or more.

[0061] The content of the organic solvent (wetting agent) in the white ink or the color ink is not particularly limited and can be appropriately selected according to the purpose. However, it is preferably 10.0% by mass or more and 75.0% by mass or less, and more preferably 15.0% by mass or more and 50.0% by mass or less with respect to the total mass of the white ink or the color ink. When the content of the organic solvent (wetting agent) is 10.0% by mass or more, the moisturizing effect in the white ink or the color ink is improved, and when it is 75.0% by mass or less, the drying property of the white ink or the color ink on the recording medium is improved.

[0062] Also, when using a recording medium with low permeability (including non-permeability), as the organic solvent, those with a solubility parameter (SP value) of 9.0 (cal / cm 3 ) 1 / 2 or more and 11.8 (cal / cm 3 ) 1 / 2 or less are preferably used. The solubility parameter is 9.0 (cal / cm 3 ) 1 / 2 or more and 11.8 (cal / cm 3 ) 1 / 2Specifically, the following organic solvents include 3-ethyl-3-oxetanemethanol (SP value: 11.31 (cal / cm³)). 3 ) 1 / 2 ), 3-methyl-3-oxetanemethanol (SP value: 11.79 (cal / cm³) 3 ) 1 / 2 ), β-methoxy-N,N-dimethylpropionamide (3-methoxy-N,N-dimethylpropionamide) (SP value: 9.19 (cal / cm³) 3 ) 1 / 2 ), β-butoxy-N,N-dimethylpropionamide (3-butoxy-N,N-dimethylpropionamide) (SP value: 9.03 (cal / cm³) 3 ) 1 / 2 ), 1,2-Hexanediol (SP value: 11.8 (cal / cm³) 3 ) 1 / 2 ), 2-ethyl-1,3-hexanediol (SP value: 10.6 (cal / cm³) 3 ) 1 / 2 ), 2,2,4-trimethyl-1,3-pentanediol (SP value: 10.8 (cal / cm³) 3 ) 1 / 2 ), diethylene glycol monoethyl ether (SP value: 10.14 (cal / cm³) 3 ) 1 / 2 ), 3-methoxy-1-butanol (SP value: 9.64 (cal / cm³) 3 ) 1 / 2 ), 3-methoxy-3-methyl-1-butanol (SP value: 9.64 (cal / cm³) 3 ) 1 / 2 ), 3-methyl-1,5-pentanediol (SP value: 11.8 (cal / cm³) 3 ) 1 / 2 ), methylpropylene glycol (SP value: 9.43 (cal / cm³) 3 ) 1 / 2 ), diethylene glycol mono-n-butyl ether (SP value: 9.86 (cal / cm³) 3 ) 1 / 2 ), diethylene glycol monomethyl ether (SP value: 10.34 (cal / cm³) 3 ) 1 / 2), triethylene glycol monomethyl ether (SP value: 10.12 (cal / cm³) 3 ) 1 / 2 ), propylene glycol monopropyl ether (SP value: 9.82 (cal / cm³) 3 ) 1 / 2 ), propylene glycol monomethyl ether (SP value: 10.19 (cal / cm³) 3 ) 1 / 2 ), propylene glycol monobutyl ether (SP value: 9.69 (cal / cm³) 3 ) 1 / 2 ), 3-methoxy-1-butanol (SP value: 10.65 (cal / cm³) 3 ) 1 / 2 ), 3-methoxy-1-propanol (SP value: 10.41 (cal / cm³) 3 ) 1 / 2 ), dipropylene glycol monomethyl ether (SP value: 9.84 (cal / cm³) 3 ) 1 / 2 ), or 3-methyl-1,5-pentanediol (SP value: 11.8 (cal / cm³) 3 ) 1 / 2 Examples include the following. These may be used individually or in combination of two or more.

[0063] The solubility parameter in the white ink or the color ink is 9.0 (cal / cm³). 3 ) 1 / 2 More than 11.8(cal / cm 3 ) 1 / 2 The content of the following organic solvents is not particularly limited and can be appropriately selected depending on the purpose, but it is preferably 0.5% to 5.0% by mass, and more preferably 1.0% to 4.0% by mass, relative to the total mass of the white ink or the color ink. The solubility parameter is 9.0 (cal / cm³). 3 ) 1 / 2 More than 11.8(cal / cm 3 ) 1 / 2The content of the following organic solvents is preferably 0.5% by mass or more and 5.0% by mass or less, from the viewpoint of suppressing color bleeding and beading (in other words, controlling static surface tension and dynamic surface tension), and also from the viewpoint of the color development of the white ink or the color ink.

[0064] -water- The aforementioned water is not particularly limited and can be appropriately selected depending on the purpose. Examples include pure water such as ion-exchanged water, ultrafiltered water, reverse osmosis water, or distilled water, or ultrapure water (high-purity water). These may be used individually or in combination of two or more types.

[0065] There are no particular restrictions on the water content in the white ink or the color ink, and it can be appropriately selected depending on the purpose. However, from the viewpoint of drying properties and discharge reliability of the white ink or the color ink, it is preferable that the water content be 10.0% by mass or more and 90.0% by mass or less, and more preferably 20.0% by mass or more and 60.0% by mass or less, relative to the total mass of the white ink or the color ink.

[0066] -Colorants- The white ink contains a white colorant, and the color ink contains a colorant. In this specification, when the white colorant and the colorant are not distinguished, they are simply referred to as "colorant."

[0067] As the coloring material, pigments can be used. There are no particular restrictions on the pigment; inorganic pigments or organic pigments can be used. These may be used individually or in combination of two or more.

[0068] Examples of the aforementioned pigments include black pigment, yellow pigment, magenta pigment, cyan pigment, white pigment, green pigment, orange pigment, or glossy pigment or metallic pigment (such as gold or silver).

[0069] There are no particular limitations on the inorganic pigments, and they can be appropriately selected depending on the purpose. Examples include titanium dioxide, iron oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, chromium yellow, or carbon black. Among these, titanium dioxide is preferred as the white pigment, and carbon black is preferred as the black pigment.

[0070] There are no particular restrictions on the carbon black mentioned above, and it can be appropriately selected depending on the purpose. Examples include channel black, furnace black, gas black, or lamp black manufactured by known methods such as the contact method, furnace method, or thermal method.

[0071] There are no particular limitations on the organic pigment, and it can be appropriately selected depending on the purpose. Examples include azo pigments, polycyclic pigments, dye chelates, nitro pigments, nitroso pigments, or aniline black. Among these, azo pigments or polycyclic pigments are preferred.

[0072] Examples of the azo pigments include azo lakes, insoluble azo pigments, condensed azo pigments, and chelated azo pigments.

[0073] Examples of the aforementioned polycyclic pigments include phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, indigo pigments, thioindigo pigments, isoindolinone pigments, or quinophthalone pigments.

[0074] Examples of the aforementioned dye chelates include basic dye type chelates and acid dye type chelates.

[0075] Specifically, the organic pigments mentioned above include CI Pigment Yellow 1, 3, 12, 13, 14, 17, 24, 34, 35, 37, 42 (yellow iron oxide), 53, 55, 74, 81, 83, 95, 97, 98, 100, 101, 104, 408, 109, 110, 117, 120, 128, 139, 150, 151, 155, 153, 180, and 183. , 185, or 213; CI Pigment Orange 5, 13, 16, 17, 36, 43, or 51; CI Pigment Red 1, 2, 3, 5, 17, 22, 23, 31, 38, 48:2 (Permanent Red 2B(Ca)), 48:3, 48:4, 49:1, 52:2, 53:1, 57:1 (Brilliant Carmine 6B), 60:1, 63:1, 63:2, 64:1, 81, 83, 88, 101 (red iron oxide), 104, 105, 106, 108 (cadmium red), 112, 114, 122 (quinacridone magenta), 123, 146, 149, 166, 168, 170, 172, 177, 178, 179, 185, 190, 193, 209, or 219; CI Pigment Violet Examples include 1 (Rhodamine Lake), 3, 5:1, 16, 19, 23, or 38; CI Pigment Blue 1, 2, 15 (Phthalocyanine Blue), 15:1, 15:2, 15:3 (Phthalocyanine Blue), 15:4, 16, 17:1, 56, 60, or 63; CI Pigment Green 1, 4, 7, 8, 10, 17, 18, or 36.

[0076] There are no particular restrictions on the BET specific surface area of ​​the aforementioned pigment, and it can be appropriately selected depending on the purpose, but 10m 2 / g or more 1,500m 2 Preferably less than / g, 20m 2 / g or more 600m 2 More preferably less than / g, 50m 2 / g or more 300m 2 A value of less than / g is even more preferable.

[0077] Pigments with the desired BET specific surface area can be obtained by general size reduction or grinding processes. The size reduction or grinding treatment is not particularly limited and can be appropriately selected from known methods, such as ball mill grinding, jet mill grinding, or ultrasonic treatment. The pigment may be treated individually or in combination of two or more types.

[0078] There are no particular restrictions on the cumulative 50% volume particle size D50 of the pigment, and it can be appropriately selected depending on the purpose, but it is preferable that it is between 50 nm and 350 nm in the white ink or the color ink. The cumulative 50% volume particle size D50 of the aforementioned pigment can be measured, for example, by a particle size distribution analyzer (Nanotrac WaveII-UT151, manufactured by Microtrac MRB Co., Ltd.).

[0079] There are no particular restrictions on the pigment content (solid content) in the white ink or the color ink, and it can be appropriately selected depending on the purpose. However, it is preferably 1.0% by mass or more and 15.0% by mass or less, and more preferably 1.5% by mass or more and 10.0% by mass or less, relative to the total mass of the white ink or the color ink. When the pigment content (solid content) is 1.0% by mass or more, the color development and image density of the white ink or the color ink are improved, and when it is 15.0% by mass or less, the discharge performance of the white ink or the color ink is stabilized.

[0080] Specific examples of the aforementioned composite pigments that are suitable from the viewpoint of having a small primary mean particle size include silica / carbon black composite material, silica / phthalocyanine PB15:3 composite material, silica / disazo yellow composite material, or silica / quinacridone PR122 composite material (all manufactured by Toda Kogyo Co., Ltd.).

[0081] For example, if inorganic pigment particles with a primary particle size of 20 nm are coated with an equal amount of organic pigment, the primary particle size of this composite pigment will be approximately 25 nm. If this can be dispersed down to the primary particle size using a suitable dispersant, a very fine composite pigment dispersion ink with a dispersed particle size of 25 nm can be produced. In this composite pigment, the organic pigment on the coating surface contributes to the dispersion, but the properties of the inorganic pigment at the center also become apparent through the thin layer of organic pigment, which is about 2.5 nm thick. Therefore, it is necessary to select a pigment dispersant that can simultaneously disperse and stabilize both.

[0082] Furthermore, if the ink set includes the pretreatment liquid in addition to the white ink and the color ink, then, as described above, the colorant is preferably anionic, and more preferably an anionic pigment.

[0083] Examples of the aforementioned anionic pigments include surfactant-dispersed pigments in which the pigment is dispersed in a surfactant, resin-dispersed pigments in which the pigment is dispersed in a resin, resin-coated dispersed pigments in which the surface of the pigment is coated with a resin, and self-dispersed pigments in which hydrophilic groups are provided on the surface of the pigment. In any of these dispersion forms, it is preferable that they be water-dispersible.

[0084] When the anionic pigment is the resin-coated dispersion pigment or the self-dispersing pigment, it is preferable that it has at least one hydrophilic group on its surface.

[0085] Examples of the hydrophilic groups include -COOM, -SO3M, -PO3HM, -PO3M2, -CONM2, -SO3NM2, -NH-C6H4-COOM, -NH-C6H4-SO3M, -NH-C6H4-PO3HM, -NH-C6H4-PO3M2, -NH-C6H4-CONM2, or -NH-C6H4-SO3NM2. These hydrophilic groups can be introduced by known methods. In the hydrophilic groups, "M" indicates a counterion.

[0086] Furthermore, the counterion represented by M in the hydrophilic group is preferably a quaternary ammonium ion. Specific examples of the quaternary ammonium ion include tetramethylammonium ion, tetraethylammonium ion, tetrapropylammonium ion, tetrabutylammonium ion, tetrapentylammonium ion, benzyltrimethylammonium ion, benzyltriethylammonium ion, or tetrahexylammonium ion. Among these, tetraethylammonium ion, tetrabutylammonium ion, or benzyltrimethylammonium ion are preferred, and tetrabutylammonium ion is more preferred. The white ink or color ink using such a pigment exhibits excellent storage stability over time, and the increase in viscosity during water evaporation is suppressed. This is presumed to be because, even when water evaporates from a water-rich ink and it becomes rich in organic solvents, the hydrophilic group having a quaternary ammonium ion maintains stable dispersion of the pigment.

[0087] As a colorant other than a colorant having hydrophilic groups on its surface, a polymer emulsion containing pigment in polymer microparticles is preferred. The pigment may be encapsulated within the polymer microparticles or adsorbed on the surface of the polymer microparticles. In this case, it is not necessary for all of the pigment to be encapsulated within the polymer microparticles or adsorbed on the surface of the polymer microparticles; some may be dispersed in the emulsion. Examples of polymers for the polymer microparticles include vinyl polymers, polyester polymers, or polyurethane polymers. These may be used individually or in combination of two or more. Among these, vinyl polymers or polyester polymers are preferred for the polymer microparticles.

[0088] Furthermore, the mass ratio of the colorant to the organic solvent is related to improving the ink ejection stability and suppressing the adhesion of waste ink in the maintenance mechanism of the image forming apparatus, so it is preferable to adjust it as appropriate. For example, when an inkjet ejection head ejects ink with a high colorant content and a low organic solvent content, the evaporation of moisture near the ink meniscus of the nozzle may progress, leading to ejection failure.

[0089] - Surfactants - Preferably, the white ink and the colored ink each contain a surfactant as a means of suppressing color bleeding and beading (in other words, controlling static and dynamic surface tension).

[0090] Examples of the surfactants that can be used include polyether-modified siloxane compounds, acetylene glycol surfactants, acetylene alcohol surfactants, or fluorine-based surfactants. These may be used individually or in combination of two or more. In addition, silicone-based surfactants may be used in combination with these surfactants. By using the surfactants, the white ink and the color ink become less likely to wet the ink-repellent film on the nozzle plate of the inkjet ejection head, thereby suppressing ejection failures caused by the white ink and the color ink adhering to the nozzles and improving ejection stability.

[0091] The polyether-modified siloxane compound is preferably one represented by any of the following general formulas (1) to (5).

[0092] [ka]

[0093] In the general formula (1) above, R1 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, m represents an integer from 0 to 23, n represents an integer from 1 to 10, a represents an integer from 1 to 23, and b represents an integer from 0 to 23.

[0094] [ka]

[0095] In the general formula (2) above, R2 and R3 each independently represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, m represents an integer from 1 to 8, and c and d each independently represent an integer from 1 to 10.

[0096] [ka]

[0097] In the general formula (3) above, R4 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and e represents an integer from 1 to 8.

[0098] [ka]

[0099] In the above general formula (4), R5 represents the polyether group of the following general formula (5), and f represents an integer from 1 to 8.

[0100] [ka]

[0101] In the general formula (5) above, R6 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, g represents an integer from 0 to 23, and h represents an integer from 0 to 23. However, g and h cannot be 0 at the same time.

[0102] Examples of compounds represented by the general formula (1) include those represented by any of the following structural formulas (1) to (8).

[0103] [ka]

[0104] [ka]

[0105] [ka]

[0106] [ka]

[0107] [ka]

[0108] [ka]

[0109] [ka]

[0110] [ka]

[0111] Examples of compounds represented by the general formula (2) include the compound represented by the following structural formula (9).

[0112] [ka]

[0113] Examples of compounds represented by the general formula (3) include the compound represented by the following structural formula (10).

[0114] [ka]

[0115] Examples of compounds represented by the general formula (4) include those represented by any of the following structural formulas (11) to (13).

[0116] [ka]

[0117] [ka]

[0118] [ka]

[0119] Furthermore, commercially available polyether-modified siloxane compounds include, for example, DOWSIL 71 Additive, DOWSIL 74 Additive, DOWSIL 57 Additive, DOWSIL 8029 Additive, DOWSIL 8054 Additive, DOWSIL 8019 Additive, DOWSIL 8526 Additive, DOWSIL FZ-2123, DOWSIL FZ-2191 (all manufactured by DuPont-Toray Specialty Materials Co., Ltd.); TSF4440, TSF4445, TSF4446, TSF4450, TSF4452, TSF4460 (all manufactured by Momentive Performance Materials, Inc.); Silface® SAG002, Silface® SAG003, Silface® SAG005, Silface® SAG503A, Silface® SAG008, Silface® Examples include SJM003 (manufactured by Nisshin Chemical Industry Co., Ltd.); TEGO® WetKL245, TEGO® Wet250, TEGO® Wet260, TEGO® Wet265, TEGO® Wet270, TEGO® Wet280 (manufactured by Evonik); BYK-345, BYK-347, BYK-348, BYK-375, or BYK-377 (manufactured by Bic Chemie Japan Co., Ltd.).

[0120] Furthermore, commercially available products can be used as the acetylene glycol surfactant and the acetylene alcohol surfactant. Examples of commercially available products include Surfinol 104E, Surfinol 420, Surfinol 440, Surfinol 465, Surfinol SE, Surfinol SE-F, Surfinol PSA-336, Surfinol DF110D, Surfinol DF58, Orfin E1004, Orfin E1010, Orfin E1020, Orfin PD-001, Orfin PD-002W, Orfin PD-004, Orfin PD-005, Orfin EXP.4001, Orfin EXP.4200, Orfin EXP.4123, or Orfin EXP.4300 (all manufactured by Nisshin Chemical Industry Co., Ltd.).

[0121] The fluorine-based surfactant is not particularly limited and can be appropriately selected depending on the purpose, but perfluoroalkyl sulfonic acid compounds, perfluoroalkyl carboxylic acid compounds, perfluoroalkyl phosphate ester compounds, perfluoroalkyl ethylene oxide adducts, or polyoxyalkylene ether polymer compounds having a perfluoroalkyl ether group in the side chain are preferred because they have low foaming properties.

[0122] Examples of the perfluoroalkyl sulfonic acid compound include perfluoroalkyl sulfonic acid or perfluoroalkyl sulfonate salt. Examples of the perfluoroalkylcarboxylic acid compound include perfluoroalkylcarboxylic acids or perfluoroalkylcarboxylic acid salts. Examples of polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups in their side chains include sulfate ester salts of polyoxyalkylene ether polymers having perfluoroalkyl ether groups in their side chains, or salts of polyoxyalkylene ether polymers having perfluoroalkyl ether groups in their side chains.

[0123] There are no particular restrictions on the counterion of the salt in the aforementioned fluorine-based surfactant, and it can be appropriately selected depending on the purpose. Examples include Li, Na, K, NH4, NH3CH2CH2OH, NH2(CH2CH2OH)2, or NH(CH2CH2OH)3.

[0124] There are no particular restrictions on the content of the surfactant in the white ink or the color ink, and it can be appropriately selected depending on the purpose. However, it is preferably 0.001% by mass or more and 5.0% by mass or less, and more preferably 0.01% by mass or more and 3.0% by mass or less, relative to the total mass of the white ink or the color ink. When the surfactant content is 0.001% by mass or more, the effect of adding the surfactant is easily obtained, and when it exceeds 5.0% by mass, the effect of adding the surfactant may saturate.

[0125] -Other ingredients- As necessary, various known additives can be used as the other components in the white ink or the color ink. Examples of the aforementioned additives include antifoaming agents, pH adjusters, preservatives and antifungal agents, chelating agents, rust inhibitors, antioxidants, ultraviolet absorbers, oxygen absorbers, light stabilizers, or other resins other than the aforementioned water-dispersible resin particles. These may be used individually or in combination of two or more.

[0126] --Foam inhibitor (antifoaming agent)-- The foam-suppressing agent is used to suppress foaming of the white ink or the color ink by adding a small amount to the white ink or the color ink. Here, "foaming" refers to the process where a liquid forms a thin film that encloses air. The surface tension and viscosity of the white or colored ink are involved in the formation of these bubbles. Specifically, liquids with high surface tension, such as water, are less likely to foam because a force acts to minimize the surface area of ​​the liquid. In contrast, highly viscous and highly permeable inks have low surface tension, making them more prone to foaming, and the viscosity of the solution helps maintain the generated bubbles, making them less likely to dissipate.

[0127] Typically, the aforementioned foam inhibitors either destroy bubbles by locally reducing the surface tension of the foam film, or by scattering foam inhibitors insoluble in the foaming liquid on the surface of the foaming liquid. When a polyether-modified siloxane compound, which has an extremely strong surface tension-reducing effect, is used as a surfactant in the ink, the surface tension of the foam film cannot be locally reduced even when using foam inhibitors by the former mechanism. Therefore, it is preferable to use foam inhibitors insoluble in the foaming liquid, but in this case, the stability of the ink may decrease due to the foam inhibitor being insoluble in the solution.

[0128] In contrast, foam inhibitors containing compounds represented by the following general formula (6) do not reduce surface tension as strongly as polyether-modified siloxane compounds, but they have high compatibility with polyether-modified siloxane compounds. Therefore, it is thought that the foam inhibitor is efficiently incorporated into the foam film, and the difference in surface tension between the polyether-modified siloxane compound and this foam inhibitor causes a locally unbalanced state on the surface of the foam film, leading to foam collapse.

[0129] [ka]

[0130] In the general formula (6) above, R7 and R8 each independently represent an alkyl group having 3 to 6 carbon atoms, and R9 and R 10 Each of these independently represents an alkyl group with 1 to 2 carbon atoms, and n represents an integer from 1 to 6.

[0131] Examples of compounds represented by the general formula (6) include 2,4,7,9-tetramethyldecane-4,7-diol or 2,5,8,11-tetramethyldodecane-5,8-diol. Among these, 2,5,8,11-tetramethyldodecane-5,8-diol is preferred because of its anti-foaming effect and high compatibility with ink.

[0132] There are no particular restrictions on the content of the anti-foaming agent in the white ink or the color ink, and it can be appropriately selected depending on the purpose. However, it is preferably 0.01% by mass or more and 10.0% by mass or less, and more preferably 0.1% by mass or more and 5.0% by mass or less, relative to the total mass of the white ink or the color ink. A foam suppression effect can be obtained when the content of the anti-foaming agent is 0.01% by mass or more, and it is possible to suppress the effect on ink properties such as viscosity and particle size when it is 10% by mass or less.

[0133] --pH adjuster-- The pH adjusting agent is not particularly limited as long as it can adjust the pH of the white ink or the color ink, and can be appropriately selected depending on the purpose. Examples include alcoholamines, alkali metal element hydroxides, ammonium hydroxides, phosphonium hydroxides, or alkali metal carbonates. These may be used individually or in combination of two or more. Among these, alcoholamines are preferred as the pH adjusting agent.

[0134] Examples of the aforementioned alcoholamines include diethanolamine, triethanolamine, or 2-amino-2-ethyl-1,3-propanediol.

[0135] Examples of alkali metal element hydroxides include lithium hydroxide, sodium hydroxide, or potassium hydroxide.

[0136] Examples of the ammonium hydroxide include ammonium hydroxide or quaternary ammonium hydroxide.

[0137] Examples of the phosphonium hydroxide include quaternary phosphonium hydroxides.

[0138] Examples of alkali metal carbonates include lithium carbonate, sodium carbonate, or potassium carbonate.

[0139] The content of the pH adjusting agent in the white ink or the color ink is not particularly limited, as long as it can adjust the white ink or the color ink to the desired pH, and can be appropriately selected depending on the purpose. The pH of the white ink or the colored ink is preferably 7 to 11 from the viewpoint of improving ink discharge stability.

[0140] --Preservative and fungicidal agent-- There are no particular restrictions on the aforementioned preservative and antifungal agent, and it can be appropriately selected depending on the purpose. Examples include 1,2-benzothiazolin-3-one, sodium dehydroacetate, sodium sorbate, sodium 2-pyridinethiol-1-oxide, sodium benzoate, or sodium pentachlorophenol. These may be used individually or in combination of two or more.

[0141] The content of the preservative and antifungal agent in the white ink or the color ink is not particularly limited, as long as it does not impair the effects of the present invention, and can be appropriately selected depending on the purpose.

[0142] --Chelating reagent-- The chelating reagent is not particularly limited and can be appropriately selected depending on the purpose. Examples include sodium ethylenediaminetetraacetate, sodium nitrilotriacetate, sodium hydroxyethylethylenediaminetriacetate, sodium diethylenetriaminepentaacetate, and sodium uramildiacetate. These may be used individually or in combination of two or more.

[0143] The content of the preservative and antifungal agent in the white ink or the color ink is not particularly limited, as long as it does not impair the effects of the present invention, and can be appropriately selected depending on the purpose.

[0144] --Rust Inhibitor-- The rust inhibitor is not particularly limited and can be appropriately selected depending on the purpose. Examples include acidic sulfites, sodium thiosulfate, ammonium thiodiglycolate, diisopropylammonium nitrite, pentaerythritol tetranitrate, or dicyclohexylammonium nitrite. These may be used individually or in combination of two or more.

[0145] The content of the rust inhibitor in the white ink or the color ink is not particularly limited, as long as it does not impair the effects of the present invention, and can be appropriately selected depending on the purpose.

[0146] --Antioxidant-- The antioxidant is not particularly limited and can be appropriately selected depending on the purpose. Examples include phenolic antioxidants (including hindered phenolic antioxidants), amine antioxidants, sulfur-based antioxidants, or phosphorus-based antioxidants. These may be used individually or in combination of two or more.

[0147] The content of the antioxidant in the white ink or the color ink is not particularly limited, as long as it does not impair the effects of the present invention, and can be appropriately selected depending on the purpose.

[0148] --UV absorber-- There are no particular restrictions on the UV absorber, and it can be appropriately selected depending on the purpose. Examples include benzophenone-based UV absorbers, benzotriazole-based UV absorbers, salicylate-based UV absorbers, cyanoacrylate-based UV absorbers, or nickel complex salt-based UV absorbers. These may be used individually or in combination of two or more.

[0149] The amount of ultraviolet absorber in the white ink or the color ink is not particularly limited, as long as it does not impair the effects of the present invention, and can be appropriately selected depending on the purpose.

[0150] --Other resins-- The aforementioned other resins are not particularly limited as long as they do not impair the effects of the present invention, and can be appropriately selected depending on the purpose. However, resins that have excellent film-forming properties and possess solvent resistance, water resistance, and weather resistance are useful in image formation. Examples include condensation-type synthetic resins, addition-type synthetic resins, or natural polymer compounds. These may be used individually or in combination of two or more.

[0151] Examples of the aforementioned condensation-type synthetic resins include polyester resins, polyepoxy resins, polyamide resins, polyether resins, poly(meth)acrylic resins, acrylic-silicone resins, or fluororesins. In this specification, "(meth)acrylic" means acrylic or methacrylic.

[0152] Examples of the addition-type synthetic resins include polyolefin resins, polystyrene resins, polyvinyl alcohol resins, polyvinyl ester resins, polyacrylic acid resins, or unsaturated carboxylic acid resins.

[0153] Examples of the aforementioned natural polymer compounds include celluloses, rosins, and natural rubber.

[0154] The content of the other resins in the white ink or the color ink is not particularly limited, as long as it does not impair the effects of the present invention, and can be appropriately selected depending on the purpose.

[0155] <<Physical properties of white or colored inks>> The physical properties of the white ink or the color ink are not particularly limited, and can be appropriately selected according to the purpose, as long as the absolute value of the difference in static surface tension between the white ink and the color ink at 25°C is 1.0 mN / m or less, and the absolute value of the difference in dynamic surface tension between the white ink and the color ink at 25°C at bubble lifetimes of 15 msec, 150 msec, and 1,500 msec using the maximum bubble pressure method is independently 1.0 mN / m or less.

[0156] For example, the viscosity of the white ink or the color ink at 25°C is preferably 5 mPa·s or more and 25 mPa·s or less, and more preferably 6 mPa·s or more and 20 mPa·s or less. A viscosity of 5 mPa·s or more at 25°C for the white ink or the color ink improves image density and character quality. Furthermore, a viscosity of 25 mPa·s or less at 25°C for the white ink or the color ink improves ink ejection performance. The viscosity of the white ink or the colored ink can be measured at 25°C using, for example, a viscometer (RE-85L, manufactured by Toki Sangyo Co., Ltd.).

[0157] <<Manufacturing method for white ink or colored ink>> The white ink or the colored ink can be produced as a mixture by a stirring and mixing process in which various materials are stirred and mixed. The stirring and mixing in the stirring and mixing step can be carried out using, for example, a sand mill, homogenizer, ball mill, paint shaker, ultrasonic disperser, or other similar device.

[0158] <Pretreatment solution> The aforementioned pretreatment liquid contains water and a coagulant, and preferably further contains resin particles, wax particles, an organic solvent, and a surfactant, and may further contain other components as needed.

[0159] -water- As the water mentioned above, for example, pure water such as ion-exchanged water, ultrafiltered water, reverse osmosis water, or distilled water, or ultrapure water (high-purity water) can be used.

[0160] There are no particular restrictions on the water content in the pretreatment solution, and it can be appropriately selected depending on the purpose. However, from the viewpoint of the drying properties of the pretreatment solution, it is preferable that the water content be 10.0% by mass or more and 90.0% by mass or less, and more preferably 20.0% by mass or more and 60.0% by mass or less, relative to the total mass of the pretreatment solution.

[0161] -Agglutinant- In this specification, "coagulant" refers to a component that causes aggregation or thickening in the white ink or color ink when the pretreatment solution comes into contact with the white ink or color ink. Specifically, examples include a component that aggregates the colorant or water-dispersible resin particles (e.g., the anionic compound) contained in the white ink or color ink. By using a pretreatment solution containing such a coagulant, aggregation or thickening occurs in the white ink or color ink upon contact with the pretreatment solution, thereby allowing the white ink or color ink to be retained on the surface of the recording medium.

[0162] There are no particular restrictions on the flocculant, and it can be appropriately selected depending on the purpose. Examples include cationic compounds. These may be used individually or in combination of two or more. Among these, the flocculant is preferably at least one selected from the group consisting of inorganic metal salts, organic acid metal salts, organic acid ammonium salts, and cationic polymers, and more preferably at least one selected from the group consisting of inorganic metal salts and cationic polymers.

[0163] Examples of the inorganic metal salts include magnesium sulfate, aluminum sulfate, manganese sulfate, nickel sulfate, iron(II) sulfate, copper(II) sulfate, zinc sulfate, iron(II) nitrate, iron(III) nitrate, cobalt nitrate, strontium nitrate, copper(II) nitrate, nickel(II) nitrate, lead(II) nitrate, manganese(II) nitrate, nickel(II) chloride, calcium chloride, tin(II) chloride, strontium chloride, barium chloride, magnesium chloride, sodium sulfate, potassium sulfate, lithium sulfate, sodium bisulfate, potassium bisulfate, sodium nitrate, potassium nitrate, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, sodium chloride, or potassium chloride. Among these, magnesium sulfate or potassium chloride are preferred as the inorganic metal salt.

[0164] Examples of the aforementioned organic acid metal salts include sodium L-aspartate, magnesium L-aspartate, calcium ascorbate, sodium L-ascorbate, sodium succinate, disodium succinate, aluminum citrate, potassium citrate, calcium citrate, tripotassium citrate, trisodium citrate, disodium citrate, zinc lactate, aluminum lactate, potassium lactate, calcium lactate, sodium lactate, magnesium lactate, calcium acetate, potassium tartrate, calcium tartrate, DL-sodium tartrate, or potassium sodium tartrate.

[0165] Preferably, the inorganic metal salt and the organic acid metal salt are at least one selected from calcium salts, magnesium salts, nickel salts, and aluminum salts. When these salts are used, the aggregation function for the water-dispersible particles contained in the white ink or the color ink is improved, and the occurrence of color bleeding and beading can be further suppressed. These salts are also preferable from the viewpoint of the storage stability of the pretreatment solution.

[0166] Examples of the aforementioned ammonium organic acid salts include ammonium acetate, ammonium propionate, ammonium lactate, ammonium oxalate, ammonium tartrate, ammonium succinate (diammonium succinate), diammonium malonate, diammonium hydrogen citrate, triammonium citrate, or ammonium L-glutamate.

[0167] The cationic polymer is preferably a quaternary ammonium salt type cationic polymer compound, specifically, dialkylallylammonium chloride polymer, dialkylaminoethyl (meth)acrylate quaternary ammonium salt polymer, modified polyvinyl alcohol dialkylammonium salt polymer, or dialkyldiallylammonium salt polymer. In this specification, "(meth)acrylate" means acrylate or methacrylate.

[0168] Other cationic polymers include cationic special modified polyamine compounds, cationic polyamide polyamine compounds, cationic urea-formaldehyde resin compounds, cationic polyacrylamide compounds, cationic alkyl ketene dimers, cationic dicyandiamide compounds, cationic dicyandiamide-formaldehyde condensation compounds, cationic dicyandiamide-polyamine condensation compounds, cationic polyvinylformamide compounds, cationic polyvinylpyridine compounds, cationic polyalkylene polyamine compounds, or cationic epoxy polyamide compounds.

[0169] Particularly preferred cationic polymers include compounds represented by any of the following general formulas (7) to (10).

[0170] [ka]

[0171] In the above general formula (7), R 11 Each of these independently represents either a methyl group or an ethyl group, Y- represents a halogen ion, and n represents an integer.

[0172] [ka]

[0173] In the above general formula (8), Y - R represents a halogen ion, nitrate ion, nitrite ion, or acetate ion. 12 represents H or CH3, and R 13 , R 14 , and R 15 Each of these independently represents either H or an alkyl group, and n represents an integer.

[0174] [ka]

[0175] In the above general formula (9), R 16 Each of these independently represents either a methyl group or an ethyl group, Y - represents a halogen ion, nitrate ion, nitrite ion, or acetate ion, and n represents an integer.

[0176] [ka]

[0177] In the above general formula (10), Y - represents a halogen ion, nitrate ion, nitrite ion, or acetate ion, X represents a halogen atom, n represents an integer from 1 to 3, and m represents an integer from 1 to 3.

[0178] There are no particular restrictions on the content of the coagulant in the pretreatment solution, and it can be appropriately selected depending on the purpose. However, from the viewpoint of the solubility of the coagulant and the viewpoint of suppressing the occurrence of color bleeding and beading, it is preferable that the content is 0.1% by mass or more and 30.0% by mass or less, and more preferably 1.0% by mass or more and 20.0% by mass or less, relative to the total mass of the pretreatment solution.

[0179] -Resin particles- The pretreatment solution preferably contains resin particles. The presence of resin particles in the pretreatment solution improves the adhesion between the white ink and the color ink and the recording medium.

[0180] Since the resin particles coexist with a cationic compound flocculant in the pretreatment solution, it is preferable from the viewpoint of long-term storage stability that they be nonionic resin particles dispersed by steric hindrance, rather than the commonly used charge-repulsion emulsion. If anionic resin particles, which are a charge-repulsion emulsion, are used, flocculation will occur when they coexist with an inorganic metal salt, which is an example of the flocculant, and in particular, flocculation will occur instantaneously when they coexist with a polyvalent metal salt that produces a trivalent cation upon dissociation. Furthermore, if cationic resin particles are used, they are sufficiently stable when left at room temperature, but when left to stand under heating as an accelerated test anticipating long-term stability, viscosity will increase. Therefore, as stated above, it is preferable that the resin particles are nonionic resin particles.

[0181] The method for determining that the resin particles are nonionic resin particles is not particularly limited, but examples include a method in which solid components are isolated from the pretreatment liquid by centrifugation, and then a thermal decomposition GC-MS (e.g., GC-17A, manufactured by Shimadzu Corporation, etc.) is used to show that no material containing acidic functional groups such as carboxyl groups and sulfo groups, or basic functional groups such as amino groups, is detected.

[0182] There are no particular limitations on the nonionic resin particles, and they can be appropriately selected depending on the purpose. For example, polyolefin resins, chlorinated polyolefin resins, polyvinyl acetate resins, polyvinyl chloride resins, polyester resins, polyurethane resins, acrylic resins, styrene-butadiene resins, or copolymers of polymerizable compounds used in the polymerization of these resins can be used. These may be used individually or in combination of two or more. Among these, ethylene-vinyl acetate copolymer resins, ethylene-vinyl acetate-vinyl chloride copolymer resins, ethylene-vinyl acetate-versatile vinyl copolymers, or chlorinated olefin resins are preferred for the nonionic resin particles. These resins can further improve the adhesion between the white ink and the color ink and the recording medium.

[0183] There are no particular restrictions on the glass transition temperature (Tg) of the nonionic resin particles, and it can be appropriately selected depending on the purpose, but it is preferably -30°C or higher and 30°C or lower, and more preferably -25°C or higher and 25°C or lower. When the glass transition temperature (Tg) of the nonionic resin particles is -30°C or higher, the resin film becomes tougher, and the layer formed by the pretreatment liquid becomes more robust. Furthermore, when the glass transition temperature (Tg) of the nonionic resin particles is 30°C or lower, the film-forming properties of the resin are improved and flexibility is ensured, so the adhesion between the white ink and the color ink and the recording medium can be further improved.

[0184] There are no particular restrictions on the volume-average particle diameter of the nonionic resin particles, and they can be appropriately selected depending on the purpose, but a diameter of 0.05 μm or more and 2.0 μm or less is preferred, and a diameter of 0.1 μm or more and 1.0 μm or less is more preferred. The volume-average particle size of the nonionic resin particles can be measured, for example, using a particle size distribution analyzer (Nanotrac WaveII-UT151, manufactured by Microtrac MRB Co., Ltd.).

[0185] There are no particular restrictions on the content (solid content) of the resin particles in the pretreatment solution, and it can be appropriately selected according to the purpose, but it is preferable that it is 0.5% by mass or more and 20.0% by mass or less of the total mass of the pretreatment solution. By having a resin particle content (solid content) of 0.5% by mass or more and 20.0% by mass or less, the adhesion between the white ink and the color ink and the recording medium can be further improved.

[0186] -Wax particles- There are no particular restrictions on the wax particles, and they can be appropriately selected depending on the purpose. For example, water-dispersible wax particles can be used. Specifically, examples of wax particles include plant or animal waxes such as carnauba wax, candelilla wax, beeswax, rice wax, or lanolin; petroleum waxes such as paraffin wax, microcrystalline wax, polyethylene wax, polypropylene wax, oxidized polyethylene wax, or petrolatum; mineral waxes such as montane wax or ozokerite; and synthetic waxes such as carbon wax, Hoechst wax, polyethylene wax, or stearic acid amide. These may be used individually or in combination of two or more. Among these, paraffin wax or polyethylene wax particles are preferred, with paraffin wax particles being more preferred, from the viewpoint of further improving the adhesion between the white ink and the color ink and the recording medium, and from the viewpoint of dispersibility in the pretreatment liquid.

[0187] There are no particular restrictions on the melting point of the wax particles, and they can be appropriately selected depending on the purpose, but a melting point of 50°C to 130°C is preferred, and a melting point of 60°C to 120°C is more preferred. A melting point of 50°C to 130°C for the wax particles can further improve the adhesion between the white ink and the color ink and the recording medium.

[0188] There are no particular restrictions on the volume-average particle size of the wax particles, and they can be appropriately selected depending on the purpose, but a size of 1 μm to 20 μm is preferred, and a size of 1 μm to 5 μm is more preferred. The volume-average particle size of the wax particles can be measured, for example, using a particle size distribution analyzer (Nanotrac WaveII-UT151, manufactured by Microtrac MRB Co., Ltd.).

[0189] There are no particular restrictions on the content (solid content) of the wax particles in the pretreatment solution, and it can be appropriately selected according to the purpose. However, it is preferably 0.05% by mass or more and 5.0% by mass or less, and more preferably 0.1% by mass or more and 3.0% by mass or less, relative to the total mass of the pretreatment solution. By having a wax particle content (solid content) of 0.05% by mass or more and 5.0% by mass or less, the white ink can be retained near the surface of the recording medium, and the Hunter whiteness can be improved. However, if a white ink layer is formed after applying the pretreatment solution containing the wax particles, and an image is formed on the white ink layer with color ink, color bleeding may be more likely to occur compared to a pretreatment solution that does not contain wax particles.

[0190] -Organic Solvents- The organic solvent is not particularly limited and can be appropriately selected depending on the purpose. For example, a water-soluble organic solvent can be used. Examples of the water-soluble organic solvent include polyhydric alcohols, ethers (e.g., polyhydric alcohol alkyl ethers or polyhydric alcohol aryl ethers), nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds. These may be used individually or in combination of two or more.

[0191] Specific examples of the aforementioned water-soluble organic solvents include ethylene glycol, propylene glycol, diethylene glycol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 3-methyl-1,3-butanediol, triethylene glycol, polyethylene glycol, polypropylene glycol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 2,4-pentanediol, and 1,5-pentanediol. Polyhydric alcohols such as 1,2-hexanediol, 1,6-hexanediol, 1,3-hexanediol, 2,5-hexanediol, 1,5-hexanediol, glycerin, 1,2,6-hexanetriol, 2-ethyl-1,3-hexanediol, ethyl-1,2,4-butanetriol, 1,2,3-butanetriol, 2,2,4-trimethyl-1,3-pentanediol, or petriol; ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol Examples include polyhydric alcohol alkyl ethers such as glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, or propylene glycol monoethyl ether; polyhydric alcohol aryl ethers such as ethylene glycol monophenyl ether or ethylene glycol monobenzyl ether; nitrogen-containing heterocyclic compounds such as 2-pyrrolidone, N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, ε-caprolactam, or γ-butyrolactone; amides such as formamide, N-methylformamide, N,N-dimethylformamide, 3-methoxy-N,N-dimethylpropionamide, or 3-butoxy-N,N-dimethylpropionamide; amines such as monoethanolamine, diethanolamine, or triethylamine; sulfur-containing compounds such as dimethyl sulfoxide, sulfolane, or thiodiethanol; propylene carbonate; and ethylene carbonate.

[0192] Since the aforementioned organic solvent not only functions as a wetting agent but also provides good drying properties, it is preferable to use an organic solvent with a boiling point of 250°C or lower. Furthermore, it is preferable that the organic solvent contains at least one selected from propylene glycol, 1,3-butanediol, and 1,2-butanediol, as this makes the recording medium surface more easily wettable.

[0193] There are no particular restrictions on the content of the organic solvent in the pretreatment liquid, and it can be appropriately selected depending on the purpose. However, from the viewpoint of the drying properties and discharge reliability of the pretreatment liquid, it is preferable that the content is 5.0% by mass or more and 60.0% by mass or less, and more preferably 10.0% by mass or more and 30.0% by mass or less, relative to the total mass of the pretreatment liquid.

[0194] - Surfactants - There are no particular restrictions on the surfactant, and it can be appropriately selected depending on the purpose. Any of the following can be used: silicone-based surfactants, fluorine-based surfactants, amphoteric surfactants, nonionic surfactants, or anionic surfactants. These may be used individually or in combination of two or more.

[0195] There are no particular limitations on the silicone-based surfactant, and it can be appropriately selected depending on the purpose. However, those that do not decompose even at high pH are preferred. Examples include side-chain modified polydimethylsiloxane, both-end modified polydimethylsiloxane, one-end modified polydimethylsiloxane, or both-end modified polydimethylsiloxane. Among these, silicone-based surfactants having a polyoxyethylene group or a polyoxyethylene polyoxypropylene group as a modifying group are particularly preferred because they exhibit good properties as aqueous surfactants. Furthermore, polyether-modified silicone-based surfactants can also be used as the silicone-based surfactant. Examples include compounds in which a polyalkylene oxide structure is introduced into the Si side chain of dimethylsiloxane.

[0196] There are no particular restrictions on the fluorine-based surfactant, and it can be appropriately selected depending on the purpose. However, the same fluorine-based surfactants as those contained in the white ink and the color ink can be used, and the preferred embodiment is the same.

[0197] The amphoteric surfactant is not particularly limited and can be appropriately selected depending on the purpose. Examples include laurylaminopropionate, lauryldimethylbetaine, stearyldimethylbetaine, or lauryldihydroxyethylbetaine.

[0198] The nonionic surfactant is not particularly limited and can be appropriately selected depending on the purpose. Examples include polyoxyethylene alkylphenyl ether, polyoxyethylene alkyl ester, polyoxyethylene alkylamine, polyoxyethylene alkylamide, polyoxyethylene propylene block polymer, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, or ethylene oxide adduct of acetylene alcohol.

[0199] The anionic surfactant is not particularly limited and can be appropriately selected depending on the purpose. Examples include polyoxyethylene alkyl ether acetate, dodecylbenzenesulfonate, lauryl salt, or salt of polyoxyethylene alkyl ether sulfate.

[0200] -Other ingredients- The other components in the pretreatment solution are not particularly limited as long as they do not impair the effects of the present invention, and can be appropriately selected according to the purpose. Examples include defoaming agents, anti-corrosion and anti-fungal agents, or rust inhibitors.

[0201] --Antifoaming agent-- The antifoaming agent is not particularly limited and can be appropriately selected according to the purpose. For example, silicone-based antifoaming agents, polyether-based antifoaming agents, fatty acid ester-based antifoaming agents, etc. can be mentioned. Also, the same ones as the antifoaming agent (foam suppressant) in the white ink or the color ink can be used. These can be used alone or in combination of two or more. Among these, the silicone-based antifoaming agent is preferable as the antifoaming agent in terms of excellent defoaming effect.

[0202] --Antiseptic and mildew-proof agent, rust preventive agent-- The antiseptic and mildew-proof agent is not particularly limited and can be appropriately selected according to the purpose. For example, the same ones as the antiseptic and mildew-proof agent in the white ink or the color ink can be used. Also, the rust preventive agent is not particularly limited and can be appropriately selected according to the purpose. For example, the same ones as the rust preventive agent in the white ink or the color ink can be used.

[0203] <Recording medium> The recording medium to which the white ink, the color ink, the pretreatment liquid, etc. are applied is not particularly limited and can be appropriately selected according to the purpose. For example, plain paper, glossy paper, special paper, fabric, film, OHP sheet, or general-purpose printing paper, etc. can be mentioned. Among these, from the viewpoint that the recording medium is likely to cause color bleeding and beading, and the effects obtained by applying the ink set are remarkable, low-permeability recording media such as commercial printing paper, non-permeable recording media such as for signage, or fabric, etc. are preferable. Note that, unlike film, paper, etc., the fabric has a surface structure rich in irregularities, so the amount of white ink, color ink, etc. applied is likely to increase, and accordingly, it is a recording medium in which color bleeding and beading are likely to occur.

[0204] As an example of the recording medium, fabric will be described. In this specification, "fabric" refers to a form in which fibers are made into woven fabric, knitted fabric, non-woven fabric, etc.

[0205] The aforementioned fibers are preferably synthetic fibers, semi-synthetic fibers, regenerated fibers, or organic fibers such as natural fibers.

[0206] Examples of the synthetic fibers include polyester, polyamide, acrylic, polyolefin, polyvinyl alcohol, polyvinyl chloride, polyurethane, or polyimide.

[0207] Examples of the aforementioned semi-synthetic fibers include acetate, diacetate, or triacetate.

[0208] Examples of the regenerated fibers include polynosic, rayon, lyocell, or cupro. Examples of the aforementioned natural fibers include cotton, linen, silk, or wool.

[0209] Among the fibers forming the aforementioned fabric, synthetic fibers such as polyester are more prone to color bleeding and beading than natural fibers such as cotton, and it is also more difficult to retain white ink on the surface. However, the aforementioned ink set is advantageous because it works suitably even on such fabrics, suppressing color bleeding and beading, and also making it possible to retain white ink on the surface.

[0210] Preferably, the fabric is dark in color, as the fibers used in the fabric are colored by chemically or physically retaining colorants such as pigments or dyes internally or on the surface. When the fabric is dark in color, a white base can be formed between the fabric and the color image to improve the color development of the color image formed on the fabric. This makes it preferable to use the ink set having the white ink and the color ink.

[0211] In this specification, "dark-colored fabric" refers to the lightness (L) of the fabric. * When measured using a spectrophotometer (e.g., X-Rite eXact, manufactured by X-Rite), 60 > L *This represents fabrics that meet the range of 50 > L * It is preferable that the fabric meets the range of 40 > L * It is more preferable that the fabric meets the range of 30 > L * It is even more preferable that the fabric satisfies the range of 20 > L * It is particularly preferable that the fabric meets the specified range.

[0212] (Ink cartridge) The ink cartridge of the present invention comprises the ink set of the present invention, the ink set, a container, and, if necessary, other components. The aforementioned ink cartridge has advantages in that it eliminates the need to directly touch the ink during tasks such as ink replacement, thus eliminating concerns about staining hands or clothing, and also prevents foreign matter such as dust from contaminating the ink.

[0213] The ink cartridge may house the ink set integrally, or it may house the white ink and the color ink separately. Furthermore, if the ink set has multiple white inks and color inks, the ink cartridge may house each white ink and each color ink integrally, or they may house them separately.

[0214] There are no particular restrictions on the container, and its shape, structure, size, material, etc. can be appropriately selected according to the purpose. For example, containers having an ink bag made of aluminum laminate film, resin film, etc. are preferred.

[0215] There are no particular restrictions on the method for manufacturing the ink cartridge, and it can be manufactured using any known method as appropriate.

[0216] Preferably, the ink cartridge is designed so that an ink set, for example, contained in a container such as an ink bag, is further housed in a cartridge case (for example, a plastic case) and detachably attached to an image forming apparatus. This simplifies ink replenishment and replacement, improving work efficiency.

[0217] (Image forming apparatus and image forming method) The image forming apparatus of the present invention comprises a white ink storage means, a color ink storage means, a white ink dispensing means, and a color ink dispensing means, and may further include other means as needed.

[0218] The image forming method of the present invention comprises a step of applying white ink and a step of applying color ink, and may include other steps as needed.

[0219] The image forming method of the present invention is preferably carried out using the image forming apparatus of the present invention. The image forming method of the present invention will be described below, along with a description of the image forming apparatus of the present invention.

[0220] <Means for containing white ink> The aforementioned white ink containing means is a means for containing white ink. The white ink containing means may be the ink cartridge of the present invention. The white ink contained in the white ink containing means is the white ink included in the ink set of the present invention.

[0221] <Means for storing colored ink> The aforementioned color ink storage means is a means for storing color ink. The aforementioned color ink storage means may be the ink cartridge of the present invention. The color ink contained in the color ink storage means is the color ink included in the ink set of the present invention.

[0222] <Means for applying white ink and process for applying white ink> The white ink application means is a means for applying white ink to a recording medium. The white ink application step is a step of applying white ink to a recording medium. The white ink application step is preferably performed by the white ink application means. The recording medium is not particularly limited and can be appropriately selected according to the purpose. However, those described in the <recording medium> of the (ink set) can be used, and the preferred embodiments are the same.

[0223] The method of applying the white ink is not particularly limited and can be appropriately selected according to the purpose. Examples include a discharge method or a coating method. Among these, the method of applying the white ink is preferably a discharge method, and more preferably an inkjet discharge method.

[0224] The discharge method is not particularly limited and can be appropriately selected according to the purpose. Examples include a method using a piezoelectric element actuator, a method of applying thermal energy, a method using an actuator utilizing electrostatic force, or a method using a continuous injection type charge control type head.

[0225] The amount of the white ink applied (adhered) to the recording medium varies greatly depending on the type of the recording medium. From the viewpoints of improving image quality and drying property, it is preferably 1 g / m 2 or more and 500 g / m 2 or less, and more preferably 5 g / m 2 or more and 400 g / m 2 or less. When the cloth is used as the recording medium, the amount of the white ink applied (adhered) to the recording medium is preferably 50 g / m 2 or more and 500 g / m 2 or less, more preferably 100 g / m 2 or more and 400 g / m 2 or less, and even more preferably 150 g / m 2 or more and 300 g / m 2The following is even more preferable:

[0226] <Means for applying colored ink and process for applying colored ink> The color ink application means is a means for applying color ink to the area of ​​the recording medium to which the white ink has been applied. The color ink application step is a step of applying color ink to the area of ​​the recording medium to which the white ink has been applied. The color ink application step is preferably carried out by the color ink application means.

[0227] There are no particular restrictions on the method of applying the color ink, and it can be appropriately selected depending on the purpose. For example, the same method as the method of applying the white ink can be used, and the same is true for preferred embodiments.

[0228] The amount of color ink applied (adhered) to the recording medium varies greatly depending on the type of recording medium, but from the viewpoint of improving image quality and drying properties, 1 g / m² is used. 2 More than 50g / m 2 Preferably, it is 5 g / m 2 More than 30g / m 2 The following is more preferable: Furthermore, when the aforementioned fabric is used as the recording medium, the amount of color ink applied (adhered) to the recording medium shall be 5 g / m². 2 More than 50g / m 2 Preferably, it is 10 g / m 2 More than 30g / m 2 The following is more preferable:

[0229] In the image forming method described above, the time between the application of the white ink to the recording medium and the application of the color ink to the area of ​​the recording medium to which the white ink has been applied (i.e., the time between the white ink application step and the color ink application step) should be as short as possible from the viewpoint of productivity. The time between the application of the white ink to the recording medium and the application of the color ink to the area of ​​the recording medium to which the white ink has been applied is the time required for the white ink to dry (aggregate and / or thicken), and is intended to suppress color bleeding and beading caused by insufficient drying (aggregation and / or thickening) of the white ink. The image forming method of the present invention uses the white ink and the color ink having the relationship between static surface tension and dynamic surface tension described in the (ink set) section above, and after the white ink has been applied to the recording medium, the color ink has been applied to the area of ​​the recording medium to which the white ink has been applied, thereby suppressing color bleeding and beading.

[0230] <Other means and other processes> Other means include, for example, means for containing the pretreatment liquid, means for applying the pretreatment liquid, and means for heating or drying. Other processes include, for example, a pretreatment solution application step and a heating or drying step.

[0231] <<Pre-treatment liquid storage means>> The aforementioned pretreatment liquid containment means is a means for containing the pretreatment liquid. The pretreatment liquid contained in the pretreatment liquid containment means is the pretreatment liquid included in the ink set of the present invention.

[0232] <<Means for applying pretreatment solution and process for applying pretreatment solution>> The pretreatment liquid application means is a means for applying the pretreatment liquid to the area of ​​the recording medium to which the white ink is applied in advance. The pretreatment liquid application step is a step of applying the pretreatment liquid to the area of ​​the recording medium to which the white ink will be applied, prior to the white ink application step. The pretreatment liquid application step is preferably carried out by the pretreatment liquid application means.

[0233] If the image forming apparatus has the pretreatment liquid storage means and the pretreatment liquid application means, the white ink application means can be rephrased as a means for applying the white ink to the area of ​​the recording medium to which the pretreatment liquid has been applied. Furthermore, if the image forming method includes the pretreatment liquid application step, the white ink application step can be rephrased as the step of applying the white ink to the area of ​​the recording medium to which the pretreatment liquid has been applied.

[0234] There are no particular restrictions on the method of applying the pretreatment solution, and it can be appropriately selected depending on the purpose. For example, the same method as the method of applying the white ink can be used, and the preferred embodiment is also the same.

[0235] The amount of pretreatment solution applied (adhered) to the recording medium varies greatly depending on the type of recording medium, but from the viewpoint of improving image quality and drying properties, 0.1 g / m² is recommended. 2 More than 500g / m 2 Preferably, it is 1 g / m 2 More than 400g / m 2 The following is more preferable: Furthermore, when the aforementioned fabric is used as the recording medium, the amount of the pretreatment solution applied to the recording medium (amount of adhesion) shall be 100 g / m². 2 More than 500g / m 2 Preferably, it is 200 g / m². 2 More than 500g / m 2 It is more preferable that the following conditions apply: 300 g / m² 2 More than 400g / m 2 The following is even more preferable:

[0236] <<Means of heating or drying and heating or drying process>> The heating or drying means is a means for heating or drying the white ink, the color ink, or the pretreatment solution, or other liquids applied to the recording medium. The heating or drying step is a step of heating or drying the white ink, the color ink, or the pretreatment solution, or other liquids applied to the recording medium. The heating or drying step is preferably carried out by the heating or drying means.

[0237] The heating or drying means is not particularly limited and can be appropriately selected from known heating means, such as a roll heater, drum heater, hot air generator, or heat press.

[0238] Furthermore, the drying step is not particularly limited as long as it can dry the various liquids such as the white ink, color ink, or pretreatment solution applied to the recording medium, and examples include a method of air drying after applying the various liquids. In this specification, "drying step" means applying one liquid and then applying another liquid more than 20 seconds later. For example, if the time between the application of the white ink to the recording medium and the application of the color ink to the area of ​​the recording medium to which the white ink has been applied is more than 20 seconds, the image forming method will include a drying step. Therefore, if another liquid is applied within 20 seconds of the application of one liquid, it will not be included in the drying step.

[0239] Furthermore, as described above, even if the image forming method does not include a heating or drying step between the white ink application step and the color ink application step in which the recording medium to which the white ink has been applied is heated or dried, the occurrence of color bleeding and beading can be suppressed. Therefore, from the viewpoint of image forming efficiency, it is preferable that the image forming method does not include a heating or drying step between the white ink application step and the color ink application step in which the recording medium to which the white ink has been applied is heated or dried. Similarly, it is preferable that the image forming apparatus does not have a heating or drying means for heating or drying the recording medium to which the white ink has been applied between the application of the white ink by the white ink application means and the application of the color ink by the color ink application means.

[0240] The image forming apparatus of the present invention will be described in detail below with reference to Figures 1 and 2, but the present invention is not limited thereto.

[0241] Figure 1 is a schematic perspective view showing an example of an image forming apparatus of the present invention. Figure 2 is a schematic perspective view showing an example of a housing means (white ink housing means, color ink housing means, or pre-treatment liquid housing means) of an image forming apparatus of the present invention.

[0242] The image forming apparatus 400 shown in Figure 1 is an image forming apparatus having a serial-type inkjet ejection head. A mechanism unit 420 is provided inside the outer casing 401 of the image forming apparatus 400. The storage sections 411 of the pre-treatment liquid storage means 410p for the pre-treatment liquid, the white ink storage means 410w for the white ink, the black ink storage means 410k for the black ink, and the cyan ink storage means 410c for the cyan ink are formed from a packaging material such as aluminum laminate film. The storage sections 411 are housed in a storage container case 414 made of plastic, for example. Thus, each storage means 410 is used as an ink cartridge.

[0243] Meanwhile, a cartridge holder 404 is provided at the back of the opening when the cover 401c of the main body of the image forming apparatus 400 is opened. Each of the storage means 410 (p, w, k, and c) is detachably mounted on the cartridge holder 404. As a result, the discharge ports 413 of each storage means 410 (p, w, k, and c) and the inkjet ejection head 434 are connected via each supply tube 436, enabling the inkjet ejection head 434 to eject the pretreatment liquid and each ink to the recording medium. In the image forming apparatus 400 shown in Figure 1, the pretreatment solution is applied to the recording medium by an inkjet ejection method. However, the method of applying the pretreatment solution is not limited to this, and the aforementioned application methods can be used.

[0244] The image forming apparatus 400 may have heating or drying means for heating or drying various liquids such as white ink, color ink, or pretreatment solution applied to the recording medium, but it is preferable that it does not have heating or drying means for heating or drying the recording medium to which the white ink has been applied between the time the white ink is applied and the time the color ink is applied. Such heating or drying means are provided for the purpose of suppressing color bleeding and beading caused by insufficient drying of the white ink by heating or drying the white ink, but the ink set of the present invention can suppress color bleeding and beading even without heating or drying means. [Examples]

[0245] The present invention will be specifically described below with reference to preparation examples, manufacturing examples, examples, and comparative examples, but the present invention is not limited in any way to these preparation examples, manufacturing examples, and examples.

[0246] Pigment dispersions or pigment-containing polymer fine particle dispersions were prepared by the methods described in Preparation Examples 1 to 9 below.

[0247] (Preparation Example 1: Preparation of Surface-Modified Black Pigment Dispersion) BLACK PEARLS (registered trademark) 1000 (BET specific surface area 343 m²) manufactured by Cabot Corporation. 2 100 g of carbon black (containing dibutyl phthalate absorption (DBPA) 105 mL / 100 g), 100 mmol of sulfanilic acid, and 1 L of high-purity water were mixed at room temperature (23°C ± 0.5°C) using a Silverson® mixer at 6,000 rpm to obtain a slurry. Next, 100 mmol of nitric acid was added to the resulting slurry, and after 30 minutes, 100 mmol of sodium nitrite dissolved in 10 mL of high-purity water was slowly added. The mixture was then heated to 60°C while stirring and reacted for 1 hour to obtain a modified pigment in which sulfanilic acid was added to carbon black. Next, the pH was adjusted to 9 with a 10% by mass tetrabutylammonium hydroxide methanol solution, and a modified pigment dispersion was obtained after 30 minutes. Then, this modified pigment dispersion and high-purity water were subjected to ultrafiltration using a dialysis membrane, and further ultrasonic dispersion was performed to obtain a surface-modified black pigment dispersion containing 20% ​​by mass of pigment solids. The surface treatment level of the pigment in the obtained surface-modified black pigment dispersion was 0.75 mmol / g, and when measured with a particle size distribution analyzer (Nanotrac WaveII-UT151, Microtrac MRB Co., Ltd.), the cumulative 50% volume particle size D50 was 120 nm.

[0248] (Preparation Example 2: Preparation of Surface-Modified Magenta Pigment Dispersion) 1 kg of SMART Magenta 3122BA (CI Pigment Red 122 surface-treated dispersion, pigment solids content 14.5% by mass), a pigment dispersion manufactured by SENSIENT, was acid-precipitation with a 0.1 N hydrochloric acid aqueous solution. Next, the pH was adjusted to 9 with a 10% by mass aqueous solution of tetraethylammonium hydroxide, and a modified pigment dispersion was obtained after 30 minutes. The modified pigment dispersion, which contained a pigment bonded to at least one aminobenzoic acid group or tetraethylammonium aminobenzoate salt, was ultrafiltered using a dialysis membrane with high-purity water, and further ultrasonic dispersion was performed to obtain a surface-modified magenta pigment dispersion containing 20% ​​by mass of pigment solids. When the obtained surface-modified magenta pigment dispersion was measured using a particle size distribution analyzer (Nanotrac WaveII-UT151, manufactured by Microtrac MRB Co., Ltd.), the cumulative 50% volume particle size D50 was found to be 104 nm.

[0249] (Preparation Example 3: Preparation of Surface-Modified Cyanide Pigment Dispersion) 1 kg of SENSIENT's pigment dispersion SMART Cyan 3154BA (CI pigment blue 15:4 surface-treated dispersion, pigment solids content 14.5% by mass) was acid-dilated with a 0.1 N hydrochloric acid aqueous solution. Next, the pH was adjusted to 9 with a 40% by mass benzyltrimethylammonium hydroxide methanol solution, and a modified pigment dispersion was obtained after 30 minutes. The modified pigment dispersion, which contained a pigment bonded to at least one aminobenzoic acid group or benzyltrimethylammonium aminobenzoate salt, was ultrafiltered using a dialysis membrane with high-purity water, and further ultrasonic dispersion was performed to obtain a surface-modified cyanide pigment dispersion containing 20% ​​by mass of pigment solids. When the obtained surface-modified cyanide pigment dispersion was measured using a particle size distribution analyzer (Nanotrac WaveII-UT151, manufactured by Microtrac MRB Co., Ltd.), the cumulative 50% volume particle size D50 was found to be 116 nm.

[0250] (Preparation Example 4: Preparation of Surface-Modified Yellow Pigment Dispersion) 1 kg of SENSIENT's SMART Yellow 3074BA pigment dispersion (CI Pigment Yellow 74 surface-treated dispersion, pigment solids content 14.5% by mass) was adjusted to pH 9 with a 10% by mass tetrabutylammonium hydroxide methanol solution, and a modified pigment dispersion was obtained after 30 minutes. The modified pigment dispersion, containing a pigment bonded to at least one aminobenzoic acid group or tetrabutylammonium aminobenzoate salt, was ultrafiltered using a dialysis membrane with high-purity water, and further ultrasonic dispersion was performed to obtain a surface-modified yellow pigment dispersion containing 20% ​​pigment solids. When the obtained surface-modified yellow pigment dispersion was measured using a particle size distribution analyzer (Nanotrac WaveII-UT151, manufactured by Microtrac MRB Co., Ltd.), the cumulative 50% volume particle size D50 was found to be 145 nm.

[0251] (Preparation Example 5: Preparation of Magenta Pigment-Containing Polymer Microparticle Dispersion) After thoroughly purging a 1 L flask equipped with a mechanical stirrer, thermometer, nitrogen gas inlet tube, reflux tube, and dropping funnel with nitrogen gas, 11.2 g of styrene, 2.8 g of acrylic acid, 12.0 g of lauryl methacrylate, 4.0 g of polyethylene glycol methacrylate, 4.0 g of styrene macromer, and 0.4 g of mercaptoethanol were mixed in the flask and the temperature was raised to 65°C. Next, a mixed solution of 100.8 g of styrene, 25.2 g of acrylic acid, 108.0 g of lauryl methacrylate, 36.0 g of polyethylene glycol methacrylate, 60.0 g of hydroxylethyl methacrylate, 36.0 g of styrene macromer, 3.6 g of mercaptoethanol, 2.4 g of azobismethylvaleronitrile, and 18 g of methyl ethyl ketone was added dropwise to the flask over 2.5 hours. After dropwise addition, a mixed solution of 0.8 g of azobismethylvaleronitrile and 18 g of methyl ethyl ketone was added dropwise to the flask over 0.5 hours. After stirring at 65°C for 1 hour, 0.8 g of azobismethylvaleronitrile was added and the mixture was stirred for another hour. After the reaction was complete, 364 g of methyl ethyl ketone was added to the flask to obtain 800 g of polymer solution A with a concentration of 50% by mass.

[0252] Next, 28 g of polymer solution A, 42 g of CI pigment red 122, 13.6 g of 1 mol / L potassium hydroxide aqueous solution, 20 g of methyl ethyl ketone, and 13.6 g of high-purity water were thoroughly stirred and then kneaded using a roll mill. The resulting paste was added to 200 g of high-purity water and thoroughly stirred. Methyl ethyl ketone and water were then removed using an evaporator. To further remove coarse particles, the dispersion was pressure filtered through a polyvinylidene fluoride membrane filter with an average pore size of 5.0 μm to obtain a magenta pigment-containing polymer fine particle dispersion containing 15% by mass of pigment solids and 20% by mass of total solids. When the obtained magenta pigment-containing polymer fine particle dispersion was measured using a particle size distribution analyzer (Nanotrac WaveII-UT151, manufactured by Microtrac MRB Co., Ltd.), the cumulative 50% volume particle size D50 was found to be 127 nm.

[0253] (Preparation Example 6: Preparation of a dispersion of cyanide pigment-containing polymer microparticles) A cyan pigment-containing polymer fine particle dispersion containing 15% by mass of pigment solids and 20% by mass of total solids was prepared in the same manner as in Preparation Example 5, except that CI Pigment Red 122 as the pigment was replaced with a phthalocyanine pigment (CI Pigment Blue 15:3). When the polymer microparticles in the obtained cyanide pigment-containing polymer microparticle dispersion were measured using a particle size distribution analyzer (Nanotrac WaveII-UT151, manufactured by Microtrac MRB Co., Ltd.), the cumulative 50% volume particle size D50 was found to be 93 nm.

[0254] (Preparation Example 7: Preparation of a dispersion of yellow pigment-containing polymer microparticles) A yellow pigment-containing polymer fine particle dispersion containing 15% by mass of pigment solids and 20% by mass of total solids was prepared in the same manner as in Preparation Example 5, except that CI Pigment Red 122 as the pigment was replaced with bisazo yellow pigment (CI Pigment Yellow 155). When the polymer microparticles in the obtained yellow pigment-containing polymer microparticle dispersion were measured using a particle size distribution analyzer (Nanotrac WaveII-UT151, manufactured by Microtrac MRB Co., Ltd.), the cumulative 50% volume particle size D50 was found to be 76 nm.

[0255] (Preparation Example 8: Preparation of a dispersion of polymer microparticles containing black pigment) A black pigment-containing polymer fine particle dispersion containing 15% by mass of pigment solids and 20% by mass of total solids was prepared in the same manner as in Preparation Example 5, except that CI Pigment Red 122 as the pigment was replaced with carbon black (FW100, manufactured by Degussa). When the polymer microparticles in the obtained black pigment-containing polymer microparticle dispersion were measured using a particle size distribution analyzer (Nanotrac WaveII-UT151, manufactured by Microtrac MRB Co., Ltd.), the cumulative 50% volume particle size D50 was found to be 104 nm.

[0256] (Preparation Example 9: Preparation of Polymer-Dispersed White Pigment Dispersion) 55.6 g of DISPERBYK-2081 copolymer solution (manufactured by BYK Japan), 517 g of titanium dioxide (TITONE R-25, manufactured by Sakai Chemical Industry Co., Ltd.), 50 g of β-methoxy-N,N-dimethylpropionamide, and 377.4 g of high-purity water were thoroughly stirred, then added to a bead mill (Dinomill) and dispersed until the cumulative 50% volume particle size D50 was 300 nm or less. To further remove coarse particles, this dispersion was pressure filtered through a polyvinylidene fluoride membrane filter with an average pore size of 5.0 μm to obtain a polymer-dispersed white pigment dispersion containing 50% by mass of white pigment solids. When the pigment particles in the obtained polymer-dispersed white pigment dispersion were measured using a particle size distribution analyzer (Nanotrac WaveII-UT151, manufactured by Microtrac MRB Co., Ltd.), the cumulative 50% volume particle size D50 was found to be 283 nm.

[0257] White ink and colored ink were manufactured using the methods described in the following manufacturing examples 1-1 to 1-50.

[0258] (Manufacturing Example 1-1: Manufacturing of Ink 1) In a container equipped with a stirrer, 2.00 parts by mass of 2,2,4-trimethyl-1,3-pentanediol, 25.00 parts by mass of glycerin, 5.00 parts by mass of propylene glycol, and 0.12 parts by mass of 2,4,7,9-tetramethyldecane-4,7-diol were added and mixed and stirred for 30 minutes. Next, 0.05 parts by mass of a preservative and antifungal agent (PROXEL® GXL) and 26.67 parts by mass of the magenta pigment-containing polymer fine particle dispersion of Preparation Example 5 were added and mixed and stirred for 20 minutes. 33.33 parts by mass of Takelac® WS-6021 as water-dispersible resin particles, 1.25 parts by mass of Takenate® XWB-ST001 as a crosslinking agent, and high-purity water in an amount totaling 100 parts by mass were added and mixed and stirred for 60 minutes. Next, the resulting mixture was pressure-filtered through a polyvinylidene fluoride membrane filter with an average pore size of 1.2 μm to remove coarse particles and debris, thereby obtaining ink 1.

[0259] (Manufacturing examples 1-2 to 1-50: Manufacturing of inks 2 to 50) In manufacturing example 1-1, inks 2 to 50 were obtained in the same manner as in manufacturing example 1-1, except that the ink formulation was changed to the materials and content shown in Tables 1-1 to 1-10 below. In Tables 1-1 to 1-10 below, the unit for the content of each material is "mass%", and the content is indicated as the total amount, not the solid content or active ingredient amount.

[0260] The details of the various materials shown in Tables 1-1 to 1-10 below are as follows.

[0261] --Colorants-- • Polymer-dispersed white pigment dispersion: AC-AW62 (manufactured by Dainichi Seika Kogyo Co., Ltd., pigment solids content 50% by mass)

[0262] --Water-dispersible resin particles-- • Superflex 460: Polyurethane dispersion, 38% solids by mass, manufactured by Daiichi Kogyo Seiyaku Co., Ltd. • Superflex 460S: Polyurethane dispersion, 38% solids by mass, manufactured by Daiichi Kogyo Seiyaku Co., Ltd. • Superflex 470: Polyurethane dispersion, 38% solids by mass, manufactured by Daiichi Kogyo Seiyaku Co., Ltd. • Takelac (registered trademark) WS-5984: Polyurethane dispersion, solid content 40% by mass, manufactured by Mitsui Chemicals, Inc. • Takelac (registered trademark) WS-6021: Polyurethane dispersion, solid content 30% by mass, manufactured by Mitsui Chemicals, Inc.

[0263] --Blocky-isocyanate compounds-- • Elastron (registered trademark) E-37: Active ingredient 28% by mass, manufactured by Daiichi Kogyo Seiyaku Co., Ltd. • Elastron (registered trademark) H-3-DF: Active ingredient 27.5% by mass, manufactured by Daiichi Kogyo Seiyaku Co., Ltd. • Takenate (registered trademark) XWB-ST001: Active ingredient 40% by mass, manufactured by Mitsui Chemicals, Inc. • Adekabon Titer HUX-3861: Active ingredient 35% by mass, manufactured by ADEKA Corporation

[0264] --Surfactants-- • Compound represented by structural formula (8): Polyether-modified siloxane compound, 100% active ingredient • TEGO (registered trademark) Wet 270: Polyether-modified siloxane compound, manufactured by Evonik, 100% active ingredient. • Silface SAG503A: Polyether-modified siloxane compound, manufactured by Nisshin Chemical Industry Co., Ltd., 100% active ingredient. Surfinol 104E: 2,4,7,9-tetramethyl-5-decine-4,7-diol, manufactured by Nisshin Chemical Industry Co., Ltd., active ingredient 50% • Unidyne DSN403N: Polyoxyethylene perfluoroalkyl ether, manufactured by Daikin Industries, Ltd., 100% active ingredient.

[0265] --Preservative and fungicidal agent-- • PROXEL (registered trademark) GXL: A preservative and antifungal agent primarily composed of 1,2-benzothiazolin-3-one (manufactured by Abyssia, 20% active ingredient, contains dipropylene glycol)

[0266] [Table 1-1]

[0267] [Table 1-2]

[0268] [Table 1-3]

[0269] [Table 1-4]

[0270] [Table 1-5]

[0271] [Table 1-6]

[0272] [Table 1-7]

[0273] [Table 1-8]

[0274] [Table 1-9]

[0275] [Table 1-10]

[0276] <Physical properties of white and colored inks> For inks 1-50 obtained in manufacturing examples 1-1 to 1-50, various physical properties such as viscosity, pH, static surface tension, and dynamic surface tension were measured as follows. The results are shown in Tables 2-1 and 2-2 below.

[0277] -viscosity- The viscosity of inks 1-50 obtained in manufacturing examples 1-1 to 1-50 was measured at 25°C using a viscometer (RE85L, manufactured by Toki Sangyo Co., Ltd.).

[0278] -pH- The pH of inks 1-50 obtained in manufacturing examples 1-1 to 1-50 was measured at 25°C using a pH meter (HM-30R model, manufactured by Toa DKK Co., Ltd.).

[0279] -Static surface tension- The static surface tension of inks 1-50 obtained in manufacturing examples 1-1 to 1-50 was measured at 25°C using the plate method (Wilhelmy method) with an automatic surface tensimeter (DY-300, manufactured by Kyowa Interface Science Co., Ltd.).

[0280] -Dynamic surface tension- The dynamic surface tension of inks 1-50 obtained in manufacturing examples 1-1 to 1-50 at bubble lifetimes of 15 msec, 150 msec, and 1,500 msec using the maximum bubble pressure method was measured at 25°C using a portable dynamic surface tensimeter (SITA Pro line t15, manufactured by Eiko Seiki Co., Ltd.). In Tables 2-1 and 2-2 below, under "Relationship between dynamic surface tensions of colored inks (15 msec)," "B" represents black ink, "C" represents cyan ink, "M" represents magenta ink, and "Y" represents yellow ink.

[0281] [Table 2-1]

[0282] [Table 2-2]

[0283] The pretreatment solution was prepared according to the methods described in the following manufacturing examples 2-1 to 2-12.

[0284] (Manufacturing Example 2-1: Manufacturing of Pretreatment Solution 1) 12.50 parts by mass of magnesium sulfate was weighed into a glass beaker, and 50.00 parts by mass of high-purity water was added, followed by stirring for 5 minutes. Next, 3.00 parts by mass of propylene glycol, 17.14 parts by mass of nonionic resin emulsion (Takelac® W-635), 0.05 parts by mass of preservative and antifungal agent (PROXEL® GXL), and 0.10 parts by mass of 1,2,3-benzotriazole were added, and the mixture was mixed and stirred for 15 minutes. Further, high-purity water was added to bring the total to 100 parts by mass, and the mixture was mixed and stirred for 10 minutes. This mixture was pressure filtered through a polyvinylidene fluoride membrane filter with an average pore size of 5.0 μm to remove insoluble matter and other debris, and pretreatment solution 1 was prepared.

[0285] (Manufacturing Examples 2-2 to 2-12: Manufacturing of Pretreatment Solutions 2-12) In Production Example 2-1, pretreatment solutions 2 to 12 were prepared in the same manner as in Production Example 2-1, except that the formulation of the pretreatment solution was changed to the materials and contents shown in Tables 3-1 and 3-2 below. In Tables 3-1 and 3-2 below, the unit for the content of each material is "mass%", and the content is indicated as the total amount, not the solid content or active ingredient amount.

[0286] The details of the various materials shown in Tables 3-1 and 3-2 below are as follows.

[0287] --Cationic polymer-- • Sharol (registered trademark) DC-902P: Polydimethyldiallylammonium chloride, solids content 51.0% by mass, manufactured by Daiichi Kogyo Seiyaku Co., Ltd. • DK6810: Polyamine resin, solids content 55.0% by mass, manufactured by Seikoh PMC Co., Ltd.

[0288] --Nonionic resin particles-- • Takelac (registered trademark) W-635: Polyurethane emulsion, solids content 35% by mass, manufactured by Mitsui Chemicals, Inc. • SUMIKAFLEX-850HQ: Ethylene-vinyl acetate-vinyl chloride copolymer, solids content 50% by mass, manufactured by Sumitomo Chemical Co., Ltd. • SUMIKAFLEX-951HQ: Ethylene-vinyl acetate-vinyl versatate copolymer, solids content 55% by mass, manufactured by Sumitomo Chemical Co., Ltd.

[0289] --wax-- AQUACER 497: Paraffin wax, 50% by mass of active ingredient, manufactured by BYK Japan Co., Ltd. AQUACER 539: Modified paraffin wax, 35% by mass of active ingredient, manufactured by BYK Japan Co., Ltd. AQUACER 531: Modified polyethylene wax, 45% by mass of active ingredient, manufactured by BYK Japan Co., Ltd.

[0290] --Preservative and fungicidal agent-- • PROXEL (registered trademark) GXL: A preservative and antifungal agent primarily composed of 1,2-benzothiazolin-3-one (manufactured by Abyssia, 20% active ingredient, contains dipropylene glycol)

[0291] [Table 3-1]

[0292] [Table 3-2]

[0293] Image formation using an ink set was performed according to the methods described in Examples 1 to 16 and Comparative Examples 1 to 7 below.

[0294] (Examples 1-14 and Comparative Examples 1-7) Under environmental conditions adjusted to 23℃±0.5℃ and 50%±5%RH, an inkjet printing device (Direct to Garment Printer RICOH Ri 6000, manufactured by Ricoh Co., Ltd.) was used, and the drive voltage of the piezoelectric element was varied to ensure that the amount of ink ejected was uniform, so that the same amount of ink was deposited on the recording medium.

[0295] First, as shown in Tables 4-1 and 4-2 below, a predetermined pretreatment solution was applied to a predetermined recording medium using a predetermined application method (coating method) to achieve a predetermined adhesion amount. Then, if the recording medium was a dark-colored polyester T-shirt (00300-ACT), it was dried in an oven at 130°C for 90 seconds, and if it was a dark-colored cotton T-shirt (00085-CVT), it was dried in an oven at 165°C for 90 seconds.

[0296] Next, the white ink and color ink contained in the predetermined ink sets shown in Tables 4-1 and 4-2 below were filled into the inkjet printing apparatus, respectively. White ink was applied to the area of ​​the recording medium to which the pretreatment liquid had been applied in the predetermined amounts shown in Tables 4-1 and 4-2 below to form a solid image. Seventeen seconds after the application of the white ink, color ink was applied to the area of ​​the recording medium to which the white ink had been applied in the predetermined amounts shown in Tables 4-1 and 4-2 below to form the chart shown in Figure 3. Furthermore, the recording medium was not heated between the application of white ink and the application of color ink.

[0297] Next, if the recording medium on which the chart shown in Figure 3 was formed was a dark-colored polyester T-shirt (00300-ACT), it was dried in an oven at 130°C for 3 minutes, and if it was a dark-colored cotton T-shirt (00085-CVT), it was dried in an oven at 165°C for 2 minutes to obtain a sample image. In Figure 3, "W" represents the solid white background image, "Y" represents the solid yellow background image formed on the background W, "M" represents the solid red background image formed on the background W, "C" represents the solid cyan background image formed on the background W, "P" represents the solid magenta background image formed on the background W, "V" represents the solid blue background image formed on the background W, "G" represents the solid green background image formed on the background W, "K" represents the solid black background image formed on the background W, "k1" to "k6" represent the black letter "R" formed on the background W, and "y" represents the yellow letter "R" formed on the background W. The chart shown in Figure 3 was created based on an image digitized without color correction using the software Photoshop® (manufactured by Adobe®), and printed at 600dpi x 600dpi.

[0298] (Example 15) In printing the sample image of Example 1, the sample image was obtained using the same method as in Example 1, except that the time from the application of white ink to the application of color ink was changed from 17 seconds to 60 seconds.

[0299] (Example 16) In printing the sample image of Example 1, the sample image was obtained using the same method as in Example 1, except that there was no 17-second interval between the application of white ink and the application of color ink, and the white ink was dried in a 165°C oven for 90 seconds immediately after application before the color ink was applied.

[0300] The details of the various recording media shown in Tables 4-1 and 4-2 below are as follows. • 00300-ACT: Dark-colored polyester T-shirt, glimmer(registered trademark) 00300-ACT Black, manufactured by Toms Co., Ltd. • 00085-CVT: Dark-colored cotton T-shirt, Printstar® 00085-CVT Black, manufactured by Toms Co., Ltd.

[0301] In Tables 4-1 and 4-2 below, "White Ink-Color Ink Application Time" indicates the time from the application of white ink to the application of color ink in the printing of sample images for Examples 1-16 and Comparative Examples 1-7. Furthermore, in Tables 4-1 and 4-2 below, "heating step after white ink application" indicates whether or not a heating step was performed after the application of white ink and before the application of color ink in the printing of sample images for Examples 1 to 16 and Comparative Examples 1 to 7, and if a heating step was performed, the heating conditions (temperature and time) were specified.

[0302] [Table 4-1]

[0303] [Table 4-2]

[0304] <Evaluation of sample images> For each sample image obtained in Examples 1-16 and Comparative Examples 1-7, Hunter whiteness, color bleed, beading, and abrasion fastness were evaluated as follows. The results are shown in Tables 5-1 to 5-4 below.

[0305] -Hunter Whiteness- The color values ​​L, a, and b of the image density in the solid white areas of each sample image obtained in Examples 1 to 16 and Comparative Examples 1 to 7 were measured using a spectrophotometer (X-Rite eXact, manufactured by X-Rite). Hunter whiteness was calculated using the following formula (1) and evaluated based on the following evaluation criteria. Image density was measured by placing the sample image on top of five sheets of medium-weight black colored paper (manufactured by Hokuetsu Corporation). Hunter whiteness = 100 - sqr[(100 - L)] 2 +(a 2 +b 2 )] ... Calculation formula (1) [Evaluation Criteria] A+: Hunter whiteness is 85 or higher. A: Hunter whiteness is between 80 and 85. B: Hunter whiteness is 75 or higher but less than 80. C: Hunter whiteness is between 70 and 75. D: Hunter whiteness is less than 70.

[0306] -Color Breed- In each sample image obtained in Examples 1-16 and Comparative Examples 1-7, the degree of color bleeding between solid color image areas and adjacent solid white image areas (e.g., color boundary blurring between "W" and "Y" in Figure 3), and the degree of color bleeding between one solid color image area and another adjacent solid color image area (e.g., color boundary blurring between "K" and "y" or "k1" and "Y" in Figure 3) were visually observed by expert evaluators and evaluated based on the following evaluation criteria. [Evaluation Criteria] A+: No color boundary bleeding occurs. A: There is a very slight blurring of the color boundaries. B: There is slight bleeding at the color boundaries. C: Color boundary blurring is occurring. D: Significant color bleeding occurs at the color boundaries.

[0307] -Beading- In the solid color image portions of each sample image obtained in Examples 1-16 and Comparative Examples 1-7, the degree of beading (density unevenness) was observed visually by a professional evaluator and evaluated based on the following evaluation criteria. [Evaluation Criteria] A: No unevenness in concentration has occurred. B: There is slight unevenness in concentration. C: Unevenness in concentration is occurring. D: Significant unevenness in concentration is occurring.

[0308] -Friction fastness- The friction test was conducted using a Type I friction tester (clock meter) method in accordance with the method specified in JIS L 0849. Dry friction was tested according to the dry test specified in JIS L0849, and wet friction was tested according to the wet test specified in JIS L0849. The results were evaluated based on the following evaluation criteria. [Evaluation Criteria] A: Color chart is grade 4-5 ~ grade 5 B: Color chart is grade 3-4 ~ grade 4 C: Color chart is grade 2-3 ~ grade 3 D: Color chart is Grade 2 or lower

[0309] [Table 5-1]

[0310] [Table 5-2]

[0311] [Table 5-3]

[0312] [Table 5-4]

[0313] Examples of embodiments of the present invention include the following: <1> An ink set having white ink and colored ink, The white ink and the color ink each independently contain water-dispersible resin particles having a crosslinkable functional group and a blocked isocyanate compound having a functional group that can crosslink with the water-dispersible resin particles having a crosslinkable functional group. The absolute value of the difference in static surface tension between the white ink and the color ink at 25°C is 1.0 mN / m or less. This ink set is characterized in that the absolute values ​​of the difference in dynamic surface tension between the white ink and the color ink at 25°C at bubble lifetimes of 15 msec, 150 msec, and 1,500 msec, measured by the maximum bubble pressure method, are independently 1.0 mN / m or less. <2> The white ink and the color ink each independently contain 0.1 to 0.55 parts by mass of the blocked isocyanate compound per 1 part by mass of the water-dispersible resin particles having the crosslinkable functional group, <1> This is the ink set described in [the document]. <3> The static surface tension of the white ink and the color ink at 25°C is independently 40.0 mN / m or less. <1> from <2> It is an ink set as described in one of the following. <4> The aforementioned color inks are a plurality of color inks including black ink, cyan ink, magenta ink, and yellow ink. The absolute values ​​of the difference in dynamic surface tension between the aforementioned multiple color inks at 25°C with a bubble lifetime of 15 msec using the maximum bubble pressure method are, independently, 1.0 mN / m or less. The dynamic surface tension of the black ink, cyan ink, magenta ink, and yellow ink at 25°C with a bubble lifetime of 15 msec using the maximum bubble pressure method satisfies the following relation (1): <1> from <3> It is an ink set as described in one of the following. Black ink > Cyan ink ≥ Magenta ink ≥ Yellow ink ... Relationship (1) <5> The aforementioned ink set further comprises a pretreatment solution, The aforementioned pretreatment liquid contains water and a coagulant. The flocculant is at least one selected from the group consisting of inorganic metal salts, organic acid metal salts, organic acid ammonium salts, and cationic polymers. <1> from <4> It is an ink set as described in one of the following. <6> The pretreatment solution further contains nonionic resin particles, <5> This is the ink set described in [the document]. <7> The pretreatment solution further contains wax particles, <5> from <6> It is an ink set as described in one of the following. <8> The wax particles are paraffin wax particles, <7> This is the ink set described in [the document]. <9> A white ink application process for applying white ink to a recording medium, A color ink application step of applying color ink to the area of ​​the recording medium to which the white ink has been applied, Includes, The white ink and the color ink each independently contain water-dispersible resin particles having a crosslinkable functional group and a blocked isocyanate compound having a functional group that can crosslink with the water-dispersible resin particles having a crosslinkable functional group. The absolute value of the difference in static surface tension between the white ink and the color ink at 25°C is 1.0 mN / m or less. The image forming method is characterized in that the absolute values ​​of the difference in dynamic surface tension between the white ink and the color ink at 25°C at bubble lifetimes of 15 msec, 150 msec, and 1,500 msec, measured by the maximum bubble pressure method, are independently 1.0 mN / m or less. <10> The process further includes a pretreatment liquid application step in which a pretreatment liquid is applied to the area of ​​the recording medium to which the white ink is to be applied, prior to the white ink application step. <9> This is the image formation method described above. <11> The process of applying the white ink and the process of applying the color ink does not include a heating or drying step of heating or drying the recording medium to which the white ink has been applied. <9> from <10> This is an image formation method described in any of the following. <12> The time between the application of the white ink to the recording medium and the application of the color ink to the area of ​​the recording medium to which the white ink has been applied is 20 seconds or less. <9> from <11> This is an image formation method described in any of the following. <13> The recording medium is a dark-colored cloth, <9> from <12> This is an image formation method described in any of the following. <14> The white ink and the color ink each independently contain 0.1 to 0.55 parts by mass of the blocked isocyanate compound per 1 part by mass of the water-dispersible resin particles having the crosslinkable functional group, <9> from <13> This is an image formation method described in any of the following. <15> The static surface tension of the white ink and the color ink at 25°C is independently 40.0 mN / m or less. <9> from <14> This is an image formation method described in any of the following. <16> The aforementioned color inks are a plurality of color inks including black ink, cyan ink, magenta ink, and yellow ink. The absolute values ​​of the difference in dynamic surface tension between the aforementioned multiple color inks at 25°C with a bubble lifetime of 15 msec using the maximum bubble pressure method are, independently, 1.0 mN / m or less. The dynamic surface tension of the black ink, cyan ink, magenta ink, and yellow ink at 25°C with a bubble lifetime of 15 msec using the maximum bubble pressure method satisfies the following relation (1): <9> from <15> This is an image formation method described in any of the following. Black ink > Cyan ink ≥ Magenta ink ≥ Yellow ink ... Relationship (1) <17> The aforementioned pretreatment liquid contains water and a coagulant. The flocculant is at least one selected from the group consisting of inorganic metal salts, organic acid metal salts, organic acid ammonium salts, and cationic polymers. <10> from <16> This is an image formation method described in any of the following. <18> The pretreatment solution further contains nonionic resin particles, <17> This is the image formation method described above. <19> The pretreatment solution further contains wax particles, <17> from <18> This is an image formation method described in any of the following. <20> The wax particles are paraffin wax particles, <19> This is the image formation method described above. <21> A white ink storage means containing white ink, A color ink storage means containing color inks, A means for applying the white ink to the recording medium, A color ink application means for applying the color ink to the area of ​​the recording medium to which the white ink has been applied, It has, The white ink and the color ink each independently contain water-dispersible resin particles having a crosslinkable functional group and a blocked isocyanate compound having a functional group that can crosslink with the water-dispersible resin particles having a crosslinkable functional group. The absolute value of the difference in static surface tension between the white ink and the color ink at 25°C is 1.0 mN / m or less. The image forming apparatus is characterized in that the absolute values ​​of the difference in dynamic surface tension between the white ink and the color ink at 25°C at bubble lifetimes of 15 msec, 150 msec, and 1,500 msec, measured by the maximum bubble pressure method, are independently 1.0 mN / m or less. <22> A pretreatment liquid container means containing a pretreatment liquid, A pretreatment solution application means for applying the pretreatment solution to the area of ​​the recording medium to which the white ink is applied in advance, The aforementioned further having <21> This is the image forming apparatus described in [reference]. <23> The heating or drying means for heating or drying the recording medium to which the white ink has been applied is not included. <21> from <22> This is an image forming apparatus as described in any of the above. <24> The recording medium is a dark-colored cloth, <21> from <23> This is an image forming apparatus as described in any of the above. <25> The white ink and the color ink each independently contain 0.1 to 0.55 parts by mass of the blocked isocyanate compound per 1 part by mass of the water-dispersible resin particles having the crosslinkable functional group, <21> from <24> This is an image forming apparatus as described in any of the above. <26> The static surface tension of the white ink and the color ink at 25°C is independently 40.0 mN / m or less. <21> from <25> This is an image forming apparatus as described in any of the above. <27> The aforementioned color inks are a plurality of color inks including black ink, cyan ink, magenta ink, and yellow ink. The absolute values ​​of the difference in dynamic surface tension between the aforementioned multiple color inks at 25°C with a bubble lifetime of 15 msec using the maximum bubble pressure method are, independently, 1.0 mN / m or less. The dynamic surface tension of the black ink, cyan ink, magenta ink, and yellow ink at 25°C with a bubble lifetime of 15 msec using the maximum bubble pressure method satisfies the following relation (1): <21> from <26> This is an image forming apparatus as described in any of the above. Black ink > Cyan ink ≥ Magenta ink ≥ Yellow ink ... Relationship (1) <28> The aforementioned pretreatment liquid contains water and a coagulant. The flocculant is at least one selected from the group consisting of inorganic metal salts, organic acid metal salts, organic acid ammonium salts, and cationic polymers. <22> from <27> This is an image forming apparatus as described in any of the above. <29> The pretreatment solution further contains nonionic resin particles, <28> This is the image forming apparatus described in [reference]. <30> The pretreatment solution further contains wax particles, <28> from <29> This is an image forming apparatus as described in any of the above. <31> The wax particles are paraffin wax particles, <30> This is the image forming apparatus described in [reference].

[0314] The aforementioned <1> from <8> The ink set described in any of the above <9> from <20> The image forming method described above, and the <21> from <31> An image forming apparatus described in any of the above can solve the aforementioned problems of the conventional method and achieve the objectives of the present invention. [Explanation of symbols]

[0315] 400 Image forming apparatus 401 Exterior of the image forming apparatus 401c Cover of the main body of the image forming apparatus 404 Cartridge Holder 410p Pretreatment liquid containment means 410W White Ink Storage Method 410k Black Ink Storage 410c Cyan Ink Storage Means 411 Detention Unit 413 Outlet 414 Storage container case 420 Mechanism Department 434 Inkjet ejection head 436 Supply Tube [Prior art documents] [Patent Documents]

[0316] [Patent Document 1] Japanese Patent Publication No. 2008-266853

Claims

1. An ink set comprising white ink, colored ink, and pretreatment solution, The white ink and the color ink each independently contain water-dispersible resin particles having a crosslinkable functional group and a blocked isocyanate compound having a functional group that can crosslink with the water-dispersible resin particles having a crosslinkable functional group. The absolute value of the difference in static surface tension between the white ink and the color ink at 25°C is 1.0 mN / m or less. The absolute values ​​of the difference in dynamic surface tension between the white ink and the color ink at 25°C at bubble lifetimes of 15 msec, 150 msec, and 1,500 msec, as measured by the maximum bubble pressure method, are each independently 1.0 mN / m or less. The aforementioned pretreatment liquid contains water and a coagulant. An ink set characterized in that the flocculant is at least one selected from the group consisting of inorganic metal salts, organic acid metal salts, organic acid ammonium salts, and cationic polymers.

2. The ink set according to claim 1, wherein the white ink and the color ink each independently contain 0.1 to 0.55 parts by mass of the blocked isocyanate compound per 1 part by mass of the water-dispersible resin particles having the crosslinkable functional group.

3. The ink set according to claim 1, wherein the static surface tension of the white ink and the color ink at 25°C is independently 40.0 mN / m or less.

4. The aforementioned color inks are a plurality of color inks including black ink, cyan ink, magenta ink, and yellow ink. The absolute values ​​of the differences in dynamic surface tension between the aforementioned multiple color inks at 25°C with a bubble lifetime of 15 msec using the maximum bubble pressure method are, independently, 1.0 mN / m or less. The ink set according to claim 1, wherein the dynamic surface tension of the black ink, the cyan ink, the magenta ink, and the yellow ink at 25°C during a bubble lifetime of 15 msec by the maximum bubble pressure method satisfies the following relational expression (1). Black ink > Cyan ink ≥ Magenta ink ≥ Yellow ink ... Relationship (1)

5. The ink set according to claim 1, wherein the pretreatment liquid further contains nonionic resin particles.

6. The ink set according to claim 1, wherein the pretreatment liquid further contains wax particles.

7. The ink set according to claim 6, wherein the wax particles are paraffin wax particles.

8. A step of applying white ink to a recording medium, A color ink application step of applying color ink to the area of ​​the recording medium to which the white ink has been applied, Prior to the white ink application step, a pretreatment liquid application step is performed in which a pretreatment liquid is applied to the area of ​​the recording medium to which the white ink is to be applied. Includes, The white ink and the color ink each independently contain water-dispersible resin particles having a crosslinkable functional group and a blocked isocyanate compound having a functional group that can crosslink with the water-dispersible resin particles having a crosslinkable functional group. The absolute value of the difference in static surface tension between the white ink and the color ink at 25°C is 1.0 mN / m or less. The absolute values ​​of the difference in dynamic surface tension between the white ink and the color ink at 25°C at bubble lifetimes of 15 msec, 150 msec, and 1,500 msec, as measured by the maximum bubble pressure method, are each independently 1.0 mN / m or less. The aforementioned pretreatment liquid contains water and a coagulant. Image forming method characterized in that the flocculant is at least one selected from the group consisting of inorganic metal salts, organic acid metal salts, organic acid ammonium salts, and cationic polymers.

9. The image forming method according to claim 8, wherein between the white ink application step and the color ink application step, there is no heating or drying step of heating or drying the recording medium to which the white ink has been applied.

10. The image forming method according to claim 8, wherein the time between the application of the white ink to the recording medium and the application of the color ink to the area of ​​the recording medium to which the white ink has been applied is 20 seconds or less.

11. The image forming method according to claim 8, wherein the recording medium is a dark-colored cloth.

12. A white ink containing means containing white ink, A color ink storage means containing color inks, A means for applying the white ink to the recording medium, A color ink application means for applying the color ink to the area of ​​the recording medium to which the white ink has been applied, A pretreatment liquid container means containing a pretreatment liquid, A pretreatment solution application means for applying the pretreatment solution to the area of ​​the recording medium to which the white ink is applied in advance, It has, The white ink and the color ink each independently contain water-dispersible resin particles having a crosslinkable functional group and a blocked isocyanate compound having a functional group that can crosslink with the water-dispersible resin particles having a crosslinkable functional group. The absolute value of the difference in static surface tension between the white ink and the color ink at 25°C is 1.0 mN / m or less. The absolute values ​​of the difference in dynamic surface tension between the white ink and the color ink at 25°C at bubble lifetimes of 15 msec, 150 msec, and 1,500 msec, as measured by the maximum bubble pressure method, are each independently 1.0 mN / m or less. The aforementioned pretreatment liquid contains water and a coagulant. An image forming apparatus characterized in that the flocculant is at least one selected from the group consisting of inorganic metal salts, organic acid metal salts, organic acid ammonium salts, and cationic polymers.

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