JP2022146841A - Ink set, image forming method, and image forming apparatus - Google Patents

Abstract

To solve a problem that color bleeding occurs when, after providing a recording medium with white ink, color ink is provided to the region where the recording medium was provided with the white ink.SOLUTION: Provided is an ink set comprising white ink and color ink. In the white ink and the color ink, a difference in static surface tension at 25°C is 1.0 mN/m or less and, in the white ink and the color ink, differences in dynamic surface tension at 25°C at a bubble lifetime of 15 msec, 150 msec, and 1500 msec according to the maximum bubble pressure method are each independently 1.0 mN/m or less.SELECTED DRAWING: None

Description

The present invention relates to an ink set, an image forming method, and an image forming apparatus.

In recent years, the ink jet recording method has rapidly become popular because it enables easy recording of a color image and the running cost is low. However, this method has the problem that depending on the combination of ink and recording medium, image defects typified by bleeding of characters are likely to occur, and the image quality is greatly reduced. There is known a technique of performing pretreatment on a recording medium in advance by using a recording medium.
Also, when printing on a dark-colored recording medium, a white base is formed by applying white ink to the recording medium to which the pretreatment liquid has been applied, and color ink is applied to the white base. A technique is known for improving the color developability of an image by imparting it.

For example, Patent Document 1 describes a process of applying a treatment liquid to at least an inkjet ink printed area of a fabric, a process of heating the fabric to which the treatment liquid has been applied, and applying a white ink for inkjet textile printing to the inkjet ink printed area to which the treatment liquid has been applied. An inkjet printing method is disclosed that includes the steps of printing a composition and printing a colored ink composition for inkjet printing other than white.

However, 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, there is a problem that color bleeding occurs.

The present invention is an ink set comprising a white ink and a color ink, wherein a difference in static surface tension at 25° C. between the white ink and the color ink is 1.0 mN/m or less; In the color ink, the difference in dynamic surface tension at 25° C. at bubble lifetimes of 15 msec, 150 msec, and 1500 msec measured by the maximum bubble pressure method is independently 1.0 mN/m or less. Regarding the ink set to be used.

According to the present invention, an ink set that suppresses the occurrence of color bleeding when applying color ink to a region of a recording medium to which white ink has been applied after applying white ink to the recording medium is provided. can provide.

FIG. 1 is a schematic diagram showing an example of an image forming apparatus. FIG. 2 is a schematic diagram showing an example of a housing means. FIG. 3 is a schematic diagram showing a chart printed using an inkjet printing device.

An embodiment of the present invention will be described below.

<<Ink Set>>
The ink set of the present disclosure preferably has a white ink and a color ink and, if necessary, a pretreatment liquid and the like. Also, the number of white inks and color inks may be one or more.
The “ink set” in the present disclosure may be a white ink and a color ink that exist independently of each other. It is not limited to the case where the storage means is manufactured and sold in an integrated state. For example, even if the white ink storage means and the color ink storage means are manufactured and sold independently, if it is assumed that the white ink and the color ink are used together, or if the white ink and the color ink are used together. It is included in the ink set if it substantially induces
A “white ink” in the present disclosure is a liquid composition that forms a white image when applied to a recording medium. When the pretreatment liquid is used, the white ink is a liquid composition that forms a white image by being applied to the area of the recording medium to which the pretreatment liquid has been applied. By forming a white image on the recording medium, the white ink functions, for example, as a base for a color image formed by the color ink applied to the area to which the white ink is applied, and the color development of the color image. improve. In addition, "white" is a color commonly referred to as white, white, etc., and includes a slightly colored one.
“Color ink” in the present disclosure is a liquid composition that forms a color image by being applied to a region of a recording medium to which white ink has been applied. In addition, "color" represents a color that is not included in the above "white", and includes, for example, black, cyan, magenta, and yellow.
The “pretreatment liquid” in the present disclosure is applied to the recording medium, and by contacting the white ink or color ink applied later to the area to which the pretreatment liquid is applied, the white ink or color ink is a liquid composition that causes aggregation or thickening in

In the white ink and color ink contained in the ink set, the difference in static surface tension at 25° C. is 1.0 mN/m or less, preferably 0.8 mN/m or less, and 0.6 mN/m or less. is more preferably 0.5 mN/m or less. The above difference in static surface tension represents an absolute value and is 0 mN/m or more. Further, when a plurality of white inks or color inks are used, it is sufficient that the above static surface tension difference is satisfied in a predetermined combination of white inks and color inks. It is preferable to satisfy the static surface tension difference.
In addition, in the white ink and the color ink, the difference in dynamic surface tension at 25° C. at bubble life times of 15 msec, 150 msec, and 1500 msec measured by the maximum bubble pressure method is independently 1.0 mN/m or less. , 0.9 mN/m or less. The above difference in dynamic surface tension represents an absolute value and is 0 mN/m or more. In addition, when a plurality of white inks or color inks are used, it is sufficient that the above difference in dynamic surface tension is satisfied in a predetermined combination of white inks and color inks. It is preferable to satisfy the dynamic surface tension difference. Moreover, the above-mentioned "independently" means that they may be the same or different as long as the difference in dynamic surface tension at each bubble lifetime is 1.0 mN/m or less.
Since the ink set satisfies the difference in static surface tension and the difference in dynamic surface tension, after the white ink is applied to the recording medium, color is applied to the area of the recording medium to which the white ink is applied. When applying ink, the occurrence of color bleeding can be suppressed.

First, the reason why the occurrence of color bleeding is suppressed in the ink set will be described.
In general, when printing on a dark-colored recording medium, white ink is applied to the recording medium to form a base that is a white image. Applying the ink improves the color developability of the color image. However, when the color ink is applied within a short time (for example, within 20 seconds) after applying the white ink, the recording medium has low permeability (including non-permeability) when the amount of white ink applied is large. or when applying color ink without heating the recording medium to which the white ink has been applied until the color ink is applied after applying the white ink, the white ink is not dried properly. Due to the sufficiency, color bleed can occur where white and colored inks mix. In addition, due to insufficient drying of the white ink in the same manner as described above, the drying property of the color ink that is subsequently applied to the area to which the white ink has been applied decreases, resulting in density unevenness in the color image. Some beading can also occur.
On the other hand, by using an ink set containing a white ink and a color ink having the relationship between the static surface tension and the dynamic surface tension as described above, even if the drying of the white ink may be insufficient, the color The occurrence of bleeding is suppressed.

In addition, in the case where the white ink is insufficiently dried as described above, when using a plurality of color inks, in addition to color bleeding where the white ink and each color ink are mixed, on the area to which the white ink is applied Color bleeding, in which color inks come into contact with each other and mix, can also occur.
In such a case, the difference in dynamic surface tension between the color inks at 25° C. when the bubble life time is 15 msec according to the maximum bubble pressure method is preferably 1.0 mN/m or less, and 0.0 mN/m or less. It is more preferably 9 mN/m or less. By satisfying the above difference in dynamic surface tension, color bleeding occurring between color inks can be suppressed. The above difference in dynamic surface tension represents an absolute value and is 0 mN/m or more. In addition, it is preferable that all combinations of color inks satisfy the above difference in dynamic surface tension. For example, when using black ink, cyan ink, magenta ink, and yellow ink as a plurality of color inks, 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. Moreover, the above-mentioned "independently" means that the color inks may be the same or different as long as the difference in dynamic surface tension between the color inks is 1.0 mN/m or less.

In the case of using a plurality of color inks as described above, when using black ink, cyan ink, magenta ink, and yellow ink as the plurality of color inks, when the bubble lifetime is 15 msec by the maximum bubble pressure method for each ink The dynamic surface tension at 25° C. preferably satisfies the following relational expression (1). Ink located on the left side of the following relational expression (1) has a greater visual impact on areas of inks of other colors when color bleeding occurs. It is possible to suppress the occurrence of color bleeding such that the ink located on the left side in Equation (1) penetrates the ink located on the right side.

The static surface tension at 25° C. of the white ink and color ink contained in the ink set is preferably 40.0 mN/m or less, more preferably 36.0 mN/m or less. , 30.0 mN/m or less. By satisfying the above static surface tension in the white ink and the color ink, it is possible to suppress not only beading between the white ink and the color ink, but also beading between different color inks. When a plurality of white inks or color inks are used, it is sufficient that the above static surface tension is satisfied in a predetermined combination of white ink and color ink. It preferably satisfies the surface tension. Moreover, the above-mentioned "independently" means that the white ink and the color ink may be the same or different as long as the static surface tension is 40.0 mN/m or less.

<White ink and color ink>
The white ink and color ink each contain an organic solvent, water, coloring material, resin, surfactant, and other components depending on the purpose. Moreover, when using the pretreatment liquid, at least one selected from the colorant and the resin is preferably anionic (these may be collectively referred to as an "anionic compound"). Since at least one selected from the colorant and the resin is anionic, the white ink or the color ink aggregates when the white ink or the color ink comes into contact with the component (aggregating agent, etc.) contained in the pretreatment liquid. Alternatively, it causes an increase in viscosity, whereby white ink or color ink can be retained on the surface of the recording medium.

-Organic solvent-
Although the organic solvent is not particularly limited, for example, it is preferable to use one having an equilibrium water content of 30% by mass or more in an environment at a temperature of 23° C. and a relative humidity of 80% (also referred to as a wetting agent). Higher amounts and higher boiling points are more preferred. 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 also contributes to the improvement of ink ejection stability and maintenance mechanism of the image forming apparatus. It is also related to prevention of sticking of waste ink in printing.
The equilibrium moisture content (%) was determined by keeping the temperature and humidity in the desiccator at 23°C ± 1°C and the relative humidity at 80% ± 3% using a potassium chloride/sodium chloride saturated aqueous solution. A petri dish weighed by 1 g each is stored, and the water content in equilibrium is measured and calculated by the following formula.
Equilibrium water content (% by mass) = [water content absorbed by organic solvent/(organic solvent content + water content absorbed by organic solvent)] x 100

Examples of the wetting agent include polyhydric alcohols having an equilibrium water content of 30% by mass or more in an environment with a temperature of 23° C. and a relative humidity of 80%. Specific examples of such polyhydric alcohols include diethylene glycol (bp 245° C., equilibrium water content 43% by mass), triethylene glycol (bp 285° C., equilibrium water content 39% by mass), tetraethylene glycol (bp 324° C. to 330° C. ° C., equilibrium water content 37% by mass), 1,3-butanediol (bp 203° C. to 204° C., equilibrium water content 35% by mass), glycerin (bp 290° C., equilibrium water content 49% by mass), diglycerin (bp 270° C./ 20 hPa, equilibrium water content 38% by mass), 1,2,3-butanetriol (bp 175° C./33 hPa, equilibrium water content 38% by mass), and 1,2,4-butanetriol (bp 190° C. to 191° C./24 hPa, equilibrium water content of 41% by mass) and the like. These may be used individually by 1 type, and may use 2 or more types together. Among these, glycerin and 1,3-butanediol are preferred.

Specific examples of wetting agents other than polyhydric alcohols include 2-methyl-1,3-butanediol (bp 214° C.), 3-methyl-1,3-butanediol (bp 203° C.), dipropylene glycol (bp 232 ℃), 1,5-pentanediol (bp 242 ℃), propylene glycol (bp 187 ℃), 2-methyl-2,4-pentanediol (bp 197 ℃), ethylene glycol (bp 196 ℃ ~ 198 ℃), 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 to 260°C), 1,2,6-hexane triol (bp 178°C), trimethylolethane (solid, mp 199°C to 201°C), trimethylolpropane (solid, mp 61°C), and the like.

The content of the organic solvent is preferably 10.0% by mass or more and 75.0% by mass or less, more preferably 15.0% by mass or more and 50.0% by mass or less, relative to the mass of each ink. When it is 10.0% by mass or more, the moisturizing effect of each ink is improved, and when it is 75.0% by mass or less, the drying property of each ink on the recording medium is improved.

When using a low-permeability (including non-permeability) recording medium, the organic solvent should have a solubility parameter of 9.0 (J/cm ³ ) ^1/2 or more and 11.8 (J/cm ³ ) ¹ . ^/2 is preferably used. Specific examples of the organic solvent having a solubility parameter of 9.0 (J/cm ³ ) ^1/2 or more and less than 11.8 (J/cm ³ ) ^1/2 include 3-ethyl-3-oxetanemethanol (SP value: 11.31 (J/cm ³ ) ^1/2 ), 3-methyl-3-oxetanemethanol (SP value: 11.79 (J/cm ³ ) ^1/2 ), β-methoxy-N, N- dimethylpropionamide (SP value: 9.19 (J/cm ³ ) ^1/2 ), β-butoxy-N,N-dimethylpropionamide (SP value: 9.03 (J/cm ³ ) ^1/2 ), 1,2-hexanediol (SP value: 11.8 (J/cm ³ ) ^1/2 ), 2-ethyl-1,3-hexanediol (SP value: 11.07 (J/cm ³ ) ^1/2 ), 2,2,4-trimethyl-1,3-pentanediol (SP value: 11.19 (J/cm ³ ) ^1/2 ), diethylene glycol monoethyl ether (SP value: 10.14 (J/cm ³ ) ^1/2 ), 3-methoxy-1-butanol (SP value: 9.64 (J/cm ³ ) ^1/2 ), 3-methoxy-3-methyl-1-butanol (SP value: 9.64 ( J/cm ³ ) ^1/2 ), 3-methyl-1,5-pentanediol (SP value: 11.8 (J/cm ³ ) ^1/2 ), methylpropylene triglycol (SP value: 9.43 ( J/cm ³ ) ^1/2 ), diethylene glycol mono-n-butyl ether (SP value: 9.86 (J/cm ³ ) ^1/2 ), diethylene glycol monomethyl ether (SP value: 10.34 (J/cm ³ ) ^1/2 ), triethylene glycol monomethyl ether (SP value: 10.12 (J/cm ³ ) ^1/2 ), propylene glycol monopropyl ether (SP value: 9.82 (J/cm ³ ) ^1/2 ) , propylene glycol monomethyl ether (SP value: 10.19 (J/cm ³ ) ^1/2 ), propylene glycol monobutyl ether (SP value: 9.69 (J/cm ³ ) ^1/2 ), 3-methoxy-1 -butanol (SP value: 10.65 (J/cm ³ ) ^1/2 ), 3-methoxy-1-propanol (SP value: 10.41 (J/cm ³ ) ^1/2 ), dipropylene glycol monomethyl ether (SP value: 9.84 (J/cm ³ ) ^1/2 ), 3-methyl-1,5-pen tandiol (SP value: 11.80 (J/cm ³ ) ^1/2 ) and the like. These may be used individually by 1 type, and may use 2 or more types together.

The content of the organic solvent with a solubility parameter of 9.0 (J/cm ³ ) ^1/2 or more and less than 11.8 (J/cm ³ ) ^1/2 is 5.0% by mass with respect to the mass of each ink. 60.0 mass % or less is preferable, and 10.0 mass % or more and 30.0 mass % or less is more preferable. When it is 5.0% by mass or more and 60.0% by mass or less, it is preferable from the viewpoint of suppressing color bleeding and beading (in other words, controlling static surface tension and dynamic surface tension), and improving the color development properties of each ink. It is also preferable from the point of view.

It should be noted that the mass ratio of the coloring material and the organic solvent is related to the improvement of the ejection stability of the ink and the suppression of adhesion of the waste ink in the maintenance mechanism of the image forming apparatus, so it is preferable to adjust the mass ratio appropriately. For example, when ink containing a large amount of coloring material and a small amount of organic solvent is ejected from an inkjet head, evaporation of water near the ink meniscus of the nozzle may progress, resulting in ejection failure.

-water-
As water, for example, ion-exchanged water, ultrafiltrated water, reverse osmosis water, pure water such as distilled water, and ultrapure water can be used.
The content of water in each ink is not particularly limited and can be appropriately selected according to the purpose. % or more and 90.0 mass % or less is preferable, and 20.0 mass % or more and 60.0 mass % or less is more preferable.

-coloring material-
White ink contains white colorant, and color ink contains color colorant. In addition, in the present disclosure, when a white coloring material and a colored coloring material are not distinguished, they are simply referred to as a coloring material.

A pigment or the like can be used as the coloring material. An inorganic pigment or an organic pigment can be used as the pigment. These may be used individually by 1 type, and may use 2 or more types together. Examples of pigments that can be used include black pigments, yellow pigments, magenta pigments, cyan pigments, white pigments, green pigments, orange pigments, glossy color pigments such as gold and silver, and metallic pigments.

Examples of inorganic pigments include titanium oxide, iron oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, chrome yellow, and carbon black. Among these, carbon black is preferred. Examples of carbon black include channel black, furnace black, gas black and lamp black produced by known methods such as contact method, furnace method and thermal method.

Organic pigments include, for example, azo pigments, polycyclic pigments, dye chelates, nitro pigments, nitroso pigments, and aniline black. Among these, azo pigments and polycyclic pigments are preferred. Examples of azo pigments include azo lakes, insoluble azo pigments, condensed azo pigments, and chelate azo pigments. Examples of polycyclic pigments include phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, indigo pigments, thioindigo pigments, isoindolinone pigments, and quinoflurone pigments. Dye chelates include, for example, basic dye chelates and acid dye chelates.

Specific examples of organic pigments include C.I. I. 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, 183, 185, 213, C.I. I. Pigment Orange 5, 13, 16, 17, 36, 43, 51, C.I. I. 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 red), 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, 219, C.I. I. Pigment Violet 1 (rhodamine lake), 3, 5:1, 16, 19, 23, 38, C.I. I. Pigment Blue 1, 2, 15 (phthalocyanine blue), 15:1, 15:2, 15:3 (phthalocyanine blue), 16, 17:1, 56, 60, 63; C.I. I. Pigment Green 1, 4, 7, 8, 10, 17, 18, 36 and the like.

The BET specific surface area of the pigment is preferably 10 m ² /g or more and 1500 m ² /g or less, more preferably 20 m ² /g or more and 600 m ² /g or less, and even more preferably 50 m ² /g or more and 300 m ² /g or less. In order to use pigments with the desired BET specific surface area, general size reduction or grinding treatments (eg, ball milling, jet milling, sonication) may be performed.
The cumulative 50% volume particle diameter D50 of the pigment is preferably ₅₀ nm or more and 350 nm or less in each ink.
The content of the pigment is preferably 1.0% by mass or more and 15.0% by mass or less, more preferably 1.5% by mass or more and 10.0% by mass or less, based on the mass of the ink in terms of solid content. When it is 1.0% by mass or more, the color developability and image density of each ink are improved, and when it is 15.0% by mass or less, the ejection property of each ink is stabilized.

The coloring material may also be a composite pigment in which particles of an organic pigment or inorganic pigment are coated with an organic pigment or carbon black. The composite pigment can be produced by a method of precipitating an organic pigment in the presence of inorganic pigment particles, a mechanochemical method of mechanically mixing and grinding an inorganic pigment and an organic pigment, or the like. Furthermore, if necessary, a layer of an organosilane compound formed from polysiloxane and alkylsilane may be provided between the inorganic pigment and the organic pigment to improve the adhesion between the two.
The mass ratio of the organic pigment or inorganic pigment particles and the organic pigment or carbon black covering the particles is 3:1 to 1:3 from the viewpoint of improving color developability, coloring strength, color tone, and transparency. Preferred is 3:2 to 1:2.
Composite pigments include silica/carbon black composite material, silica/phthalocyanine PB15:3 composite material, silica/disazo yellow composite material, silica/quinacridone PR122 composite material, etc. manufactured by Toda Kogyo Co., Ltd., from the viewpoint of having a small primary average particle size. is preferred.
For example, when inorganic pigment particles having a primary particle diameter of 20 nm are coated with an equal amount of organic pigment, the primary particle diameter of the composite pigment is about 25 nm. If the primary particles can be dispersed using an appropriate dispersant, a composite pigment-dispersed ink with a very fine dispersed particle diameter of 25 nm can be produced. In composite pigments, the organic pigment on the surface of the coating contributes to dispersion, but the properties of the inorganic pigment in the center also appear through a thin layer of organic pigment with a thickness of about 2.5 nm, so both are dispersed and stabilized at the same time. It is also required to select a pigment dispersant that can

In the ink set, when the pretreatment liquid is used in addition to the white ink and the color ink, as described above, the coloring material is preferably anionic, and more preferably an anionic pigment. Examples of anionic pigments include surfactant-dispersed pigments in which a pigment is dispersed with a surfactant, resin-dispersed pigments in which a pigment is dispersed in a resin, resin-coated dispersed pigments in which the surface of a pigment is coated with a resin, and Although there are self-dispersing pigments having hydrophilic groups, it is preferable that they are water-dispersible in any form of dispersion.

When the anionic pigment is a resin-coated dispersed pigment or self-dispersed pigment, it preferably has at least one hydrophilic group on its surface. Hydrophilic groups include -COOM, -SO ₃ M, -PO ₃ HM, -PO ₃ M ₂ , -CONM ₂ , -SO ₃ NM ₂ , -NH-C ₆ H ₄ -COOM, -NH-C ₆ H _{4 - SO3M} , -NH- _{C6H4 - PO3HM} , -NH _{- C6H4 - PO3M2} , -NH _{- C6H4 - CONM2} , -NH-C6H4- SO ₃ NM ₂ and the like. These hydrophilic groups can be introduced by known methods. Moreover, the counter ion represented by M in the hydrophilic group is preferably a quaternary ammonium ion. Specific examples of quaternary ammonium ions include tetramethylammonium ion, tetraethylammonium ion, tetrapropylammonium ion, tetrabutylammonium ion, tetrapentylammonium ion, benzyltrimethylammonium ion, benzyltriethylammonium ion, and tetrahexylammonium ion. mentioned. Among these, tetraethylammonium ion, tetrabutylammonium ion, benzyltrimethylammonium ion and the like can be mentioned, and tetrabutylammonium ion is preferred. Each ink using such a pigment is excellent in storage stability over time, and viscosity increase upon evaporation of water is suppressed. It is presumed that this is because the hydrophilic group having the quaternary ammonium ion can stably maintain the dispersion of the pigment even when the water-rich ink evaporates and becomes organic solvent-rich.

As the coloring material other than those having a hydrophilic group on the surface, a polymer emulsion in which a pigment is contained in fine polymer particles is preferable. The pigment may be enclosed in the polymer microparticles or adsorbed on the surface of the polymer microparticles. In this case, not all pigments need to be encapsulated or adsorbed, and some may be dispersed in the emulsion. Examples of polymers for fine polymer particles include vinyl-based polymers, polyester-based polymers, and polyurethane-based polymers, with vinyl-based polymers and polyester-based polymers being preferred.

-resin-
The resin is not particularly limited, but a resin having excellent film-forming properties and having solvent resistance, water resistance, and weather resistance is useful in image formation. Synthetic resins, natural polymer compounds and the like can be mentioned. Moreover, the resin is preferably a water-dispersible resin (in the form of resin particles).
In the ink set, when the pretreatment liquid is used in addition to the white ink and the color ink, the resin is preferably anionic as described above.

Examples of condensed synthetic resins include polyester resins, polyurethane resins, polyepoxy resins, polyamide resins, polyether resins, poly(meth)acrylic resins, acryl-silicone resins, fluorine-based resins, and the like.
Examples of addition synthetic resins include polyolefin resins, polystyrene resins, polyvinyl alcohol resins, polyvinyl ester resins, polyacrylic acid resins, and unsaturated carboxylic acid resins.
Examples of natural polymer compounds include celluloses, rosins, and natural rubber.
When applying ink to a low-permeability (including non-permeability) recording medium such as commercial printing paper or film, it is preferable to use a polyurethane resin from the viewpoint of improving the fixability of the ink.

From the viewpoint of further improving the fixability of the ink, the polyurethane resin preferably has a structure derived from a polyol having a structure represented by the following structural formula (A).

Polyol raw materials having a structure represented by structural formula (A) include terephthalic acid and isophthalic acid.
The proportion of the polyol raw material having the structure represented by structural formula (A) is preferably 10 to 30% by mass, preferably about 50% by mass, relative to the total polyol raw material. When the ratio of the polyol raw material having the structure represented by the structural formula (A) is within the above range, the alcohol resistance is improved.

As the water-dispersible resin, the resin itself has a hydrophilic group and has self-dispersibility, and the resin itself does not have dispersibility but is imparted with dispersibility by a surfactant or a resin having a hydrophilic group. etc. can be used. Among these, ionomers of polyester resins or polyurethane resins, and emulsions of resin particles obtained by emulsification and suspension polymerization of unsaturated monomers are preferable.
In the case of emulsion polymerization of unsaturated monomers, the unsaturated monomers, polymerization initiator, surfactant, chain transfer agent, chelating agent, pH adjuster, etc. are added and reacted in water to form a resin emulsion. Therefore, the water-dispersible resin can be easily obtained, the resin structure can be easily changed, and the desired properties can be easily obtained.

The water-dispersible resin preferably has an ink pH of 4 to 12 from the viewpoint of suppressing the breakage of molecular chains such as dispersion destruction and hydrolysis under strong alkaline or strong acid conditions. From the viewpoint of miscibility with water-dispersible colorants, the pH is more preferably 7 to 11, and even more preferably 8 to 10.5.

The water-dispersible resin has the function of fixing the water-dispersible colorant to the recording medium, and has the function of improving the fixability of the colorant by forming a film at room temperature or higher. Therefore, the minimum film-forming temperature (MFT) of the water-dispersible resin is preferably 100° C. or less.
If the glass transition temperature of the water-dispersible resin is −40° C. or lower, the viscosity of the resin film becomes strong and tackiness occurs in printed matter. The content of the water-dispersible resin in the ink is preferably 0.5% by mass or more and 20.0% by mass or less, and preferably 1.0% by mass or more and 15.0% by mass or less, based on the mass of the ink as a solid content. more preferred.
On the other hand, when ink is applied to low-permeability (including non-permeability) recording media such as commercial printing paper and film, and when polyurethane resin is used as the resin, the content of polyurethane resin is the mass of the ink. is 3.0% by mass or more, and the solid content mass ratio between the coloring material and the polyurethane resin is preferably 1.0: (2.0 to 12.0), and 1.0: (2.0 to 11.0) is more preferred.

-Surfactant-
The white ink and color ink preferably contain a surfactant as a means of suppressing color bleeding and beading (in other words, controlling static and dynamic surface tension). Examples of surfactants that can be used include polyether-modified siloxane compounds, acetylene glycol surfactants, and acetylene alcohol surfactants. Further, in addition to the surfactants described above, fluorine-based surfactants, silicone-based surfactants, and the like may be used in combination. By using a surfactant, it becomes difficult for each ink to wet the ink-repellent film on the nozzle plate of the inkjet head, and ejection failure due to ink adhering to the nozzle can be suppressed, and ejection stability is improved. .

As the polyether-modified siloxane compound, those represented by the following general formulas (1) to (5) are preferred.

In general formula (1), R represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, m is an integer of 0 to 23, n is an integer of 1 to 10, a is an integer of 1 to 23, b is 0 Represents an integer from ~23.

In general formula (2), R ₂ and R ₃ each independently represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, m is an integer of 1 to 8, c and d are each independently 1 to 10 represents an integer of

In general formula (3), R ₄ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and e represents an integer of 1 to 8.

In general formula (4), R ₅ represents a polyether group of general formula (5) below, and f represents an integer of 1-8.

In general formula (5), R ₆ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, g represents an integer of 0-23, and h represents an integer of 0-23. However, there is no case where g and h are 0 at the same time.

Specific examples of the compound represented by the general formula (1) include compounds represented by the following structural formulas (1) to (8).

Specific examples of the compound represented by the general formula (2) include compounds represented by the following structural formula (9).

Specific examples of the compound represented by the general formula (3) include compounds represented by the following structural formula (10).

Specific examples of the compound represented by the general formula (4) include compounds represented by the following structural formulas (11) to (13).

Furthermore, commercially available polyether-modified siloxane compounds include, for example, 71ADDITIVE, 74ADDITIVE, 57ADDITIVE, 8029ADDITIVE, 8054ADDITIVE, 8211ADDITIVE, 8019ADDITIVE, 8526ADDITIVE, FZ-2123, FZ-2191 manufactured by TORAY Dow Corning; Materials Co. TSF4440, TSF4441, TSF4445, TSF4446, TSF4450, TSF4452, TSF4460; Nisshin Chemical Co., Ltd. Silface SAG002, Silface SAG003, Silface SAG005, Silface SAG503A, Silface SAG008, Silface SJM003 TEGO WetKL245, TEGO Wet250, TEGO Wet260, TEGO Wet265, TEGO Wet270, TEGO Wet280 manufactured by Evonik; BYK-345, BYK-347, BYK-348, BYK-375, BYK-377 manufactured by BYK-Chemie Japan; mentioned.

As the acetylene glycol surfactant and the acetylene alcohol surfactant, commercially available products can be used. Examples of commercially available products include Surfynol 104, Surfynol 104E, Surfynol 420, Surfynol 440 and Surfynol 465. , Surfynol SE, Surfynol SEF, Surfynol PSA-336, Surfynol DF110D, Surfynol DF58, Olfine E1004, Olfine E1010, Olfine E1020, Olfine PD-001, Olfine PD-002W, Olfine PD-004, Olfine PD- 005, Olphine EXP. 4001, Olfine EXP. 4200, Olfine EXP. 4123, Olfine EXP. 4300 (both manufactured by Nissin Chemical Industry Co., Ltd.) and the like.

The content of the surfactant is preferably 0.001% by mass or more and 5.0% by mass or less, more preferably 0.5% by mass or more and 3.0% by mass or less, relative to the mass of the ink. When the amount is 0.001% by mass or more, the effect of adding the surfactant can be obtained. Moreover, when it exceeds 5.0 mass, the addition effect is saturated.

-Other ingredients-
As other components, various known additives can be used as necessary. Examples include inhibitors, ultraviolet absorbers, oxygen absorbers, light stabilizers, and the like.

--Foam inhibitor--
A foam suppressing agent is used to suppress foaming of the ink by adding a small amount to the ink. Here, foaming means that a liquid becomes a thin film and envelops air. Characteristics such as surface tension and viscosity of the ink are involved in the generation of bubbles. That is, a liquid with high surface tension, such as water, is less likely to foam because a force acts to reduce the surface area of the liquid as much as possible. On the other hand, high-viscosity, high-permeability ink tends to foam due to its low surface tension, and the foam generated due to the viscosity of the solution tends to be maintained and is difficult to disappear.
Generally, the foam suppressor destroys the foam by locally lowering the surface tension of the foam film, or by scattering the foam suppressor insoluble in the foaming liquid on the surface of the foaming liquid. When a polyether-modified siloxane compound that has an extremely strong function of lowering surface tension is used as a surfactant in the ink, the surface tension of the foam film can be locally reduced even if a foam inhibitor based on the former mechanism is used. can't Therefore, it is preferable to use a foam inhibitor that is insoluble in the latter bubbling liquid, but in this case, the stability of the ink may decrease due to the foam inhibitor that is insoluble in the solution.
On the other hand, the antifoaming agent represented by the following general formula (6) has a high compatibility with the polyether-modified siloxane compound, although the effect of lowering the surface tension is not as strong as that of the polyether-modified siloxane compound. As a result, the foam inhibitor is efficiently incorporated into the foam film, and the surface tension of the polyether-modified siloxane compound and the foam inhibitor is locally unbalanced, causing the foam to break. It is thought that

In general formula (6), R ₇ and R ₈ each independently represent an alkyl group having 3 to 6 carbon atoms, and R ₉ and R ₁₀ each independently represent an alkyl group having 1 to 2 carbon atoms. , n represents an integer of 1 to 6.

Examples of compounds represented by general formula (6) include 2,4,7,9-tetramethyldecane-4,7-diol and 2,5,8,11-tetramethyldodecane-5,8-diol. is mentioned. Among these, 2,5,8,11-tetramethyldodecane-5,8-diol is preferable because of its high antifoaming effect and high compatibility with ink.
The content of the foam inhibitor is preferably 0.01% by mass or more and 10.0% by mass or less, more preferably 0.1% by mass or more and 5.0% by mass or less, relative to the mass of the ink. When the amount is 0.01% by mass or more, a foam-suppressing effect can be obtained, and when the amount is 10% by mass or less, it is possible to suppress the influence on physical properties of the ink such as viscosity and particle size.

--pH adjuster--
The pH adjuster is not particularly limited as long as it can adjust the pH of the ink, and can be appropriately selected according to the purpose. substances, phosphonium hydroxides, and alkali metal carbonates. The pH of the ink is preferably 7 to 11 from the viewpoint of improving the ejection stability of the ink.

Examples of alcoholamines include diethanolamine, triethanolamine, 2-amino-2-ethyl-1,3-propanediol, and the like.
Examples of hydroxides of alkali metal elements include lithium hydroxide, sodium hydroxide, and potassium hydroxide.
Examples of ammonium hydroxide include ammonium hydroxide and quaternary ammonium hydroxide.
Phosphonium hydroxides include, for example, quaternary phosphonium hydroxides.
Alkali metal carbonates include, for example, lithium carbonate, sodium carbonate, and potassium carbonate.

-- Antiseptic and antifungal agents --
Examples of antiseptic and antifungal agents include sodium dehydroacetate, sodium sorbate, sodium 2-pyridinethiol-1-oxide, sodium benzoate, and sodium pentachlorophenol.

--Chelating reagent--
Chelating reagents include, for example, sodium ethylenediaminetetraacetate, sodium nitrilotriacetate, sodium hydroxyethylethylenediaminetriacetate, sodium diethylenetriaminepentaacetate, and sodium uramyl diacetate.

--anti-rust--
Rust inhibitors include, for example, acidic sulfites, sodium thiosulfate, ammonium thiodiglycolate, diisopropylammonium nitrite, pentaerythritol tetranitrate, and dicyclohexylammonium nitrite.

--Antioxidant--
Examples of antioxidants include phenol antioxidants (including hindered phenol antioxidants), amine antioxidants, sulfur antioxidants, phosphorus antioxidants, and the like.

--Ultraviolet absorber--
Examples of UV absorbers include benzophenone UV absorbers, benzotriazole UV absorbers, salicylate UV absorbers, cyanoacrylate UV absorbers, and nickel complex UV absorbers.

- Physical properties of each ink -
The physical properties of each ink are not particularly limited and can be appropriately selected according to the purpose.
For example, the viscosity of each ink at 25° C. is preferably 5 mPa·s or more and 25 mPa·s or less, more preferably 6 mPa·s or more and 20 mPa·s or less. When the viscosity is 5 mPa·s or more, the effect of improving image density and character quality can be obtained. When the viscosity is 25 mPa·s or less, the ink ejection property can be improved.
The viscosity can be measured at 25° C. using, for example, a viscometer (RE-85L, manufactured by Toki Sangyo Co., Ltd.).

-Manufacturing method of each ink-
Each ink can be produced through a stirring and mixing step of stirring and mixing various materials and a step of heating the obtained mixture at 40° C. or higher and lower than 70° C. for 6 hours or longer. This stirring and mixing can be performed by, for example, a sand mill, homogenizer, ball mill, paint shaker, ultrasonic disperser, or the like.

<Pretreatment liquid>
The pretreatment liquid contains a flocculant and, if necessary, resin particles, wax particles, an organic solvent, water, a surfactant, other components, and the like.

- Flocculant -
In the present disclosure, the term “aggregating agent” refers to a component that causes aggregation or thickening in white ink or color ink when the pretreatment liquid comes into contact with white ink or color ink. Specifically, for example, a component that agglomerates water-dispersible particles such as a coloring material or resin contained in white ink or color ink (for example, the anionic compound described above). By using a pretreatment liquid containing such an aggregating agent, the white ink or color ink in contact with the pretreatment liquid is caused to coagulate or thicken, thereby retaining the white ink or color ink on the surface of the recording medium. can.
Examples of the flocculant include cationic compounds such as inorganic metal salts, organic acid metal salts, organic acid ammonium salts, and cationic polymers.

Examples of 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 hydrogen sulfate, potassium hydrogen sulfate, sodium nitrate, potassium nitrate, sodium carbonate, potassium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, sodium chloride, and potassium chloride.

Examples of organic acid metal salts include sodium L-aspartate, magnesium L-aspartate, calcium ascorbate, sodium L-ascorbate, sodium succinate, disodium succinate, aluminum citrate, potassium citrate, citric acid Calcium, 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, and and potassium sodium tartrate.

The above inorganic metal salt and organic acid metal salt are each preferably at least one selected from calcium salts, magnesium salts, nickel salts, and aluminum salts. When these salts are used, the aggregation function of the water-dispersible particles contained in the white ink or color ink is improved, and the occurrence of color bleeding and beading is further suppressed. It is also preferable from the viewpoint of storage stability of the pretreatment liquid.

Organic acid ammonium salts include ammonium acetate, ammonium propionate, ammonium lactate, ammonium oxalate, ammonium tartrate, ammonium succinate (diammonium succinate), diammonium malonate, diammonium hydrogen citrate, triammonium citrate, and Examples include ammonium L-glutamate.

As the cationic polymer, for example, a quaternary ammonium salt type cationic polymer compound is preferable. Polyvinyl alcohol dialkylammonium salt polymer, dialkyldiallylammonium salt polymer, and the like.
Further, other cationic polymers include cationic special modified polyamine compounds, cationic polyamide polyamine compounds, cationic urea-formalin resin compounds, cationic polyacrylamide compounds, cationic alkylketene dimers, cationic dicyandiamide compounds, cationic Dicyandiamide-formalin condensate compounds, cationic dicyandiamide-polyamine condensate compounds, cationic polyvinylformamide compounds, cationic polyvinylpyridine compounds, cationic polyalkylenepolyamine compounds, and cationic epoxypolyamide compounds.
Particularly preferred cationic polymers include compounds represented by the following general formulas (7) to (9).

In general formula (7), R ₁₀ represents a methyl group or an ethyl group, Y ^- represents a halogen ion, and n represents an integer.

In general formula (8), Y ^— represents a halogen ion, nitrate ion, nitrite ion, or acetate ion, R ₁₁ represents H or CH ₃ , R ₁₂ , R ₁₃ and R ₁₄ each independently represents H or an alkyl group, and n represents an integer.

In general formula (9), R represents a methyl group or an ethyl group, ^Y- represents a halogen ion, nitrate ion, nitrite ion, or acetate ion, and n represents an integer.

The content of the flocculant is 0.1% by mass or more and 30.0% by mass or less with respect to the mass of the pretreatment liquid from the viewpoint of the solubility of the flocculant and the viewpoint of suppressing the occurrence of color bleeding and beading. It is preferably 1.0% by mass or more and 20.0% by mass or less.

-Resin particles-
The pretreatment liquid preferably contains resin particles. By containing resin particles in the pretreatment liquid, it is possible to improve the adhesiveness between the white ink and the color ink and the recording medium.

Since the resin particles coexist with a cationic compound flocculant in the pretreatment liquid, from the viewpoint of long-term storage stability, the resin particles are dispersed by steric hindrance rather than the generally used charge repulsion type emulsion. Nonionic resin particles are preferred. When anionic resin particles, which are charge-repulsive emulsions, are used, aggregation occurs when they coexist with an inorganic metal salt, which is an example of a flocculant. Agglomeration occurs instantaneously. Further, when cationic resin particles are used, they are sufficiently stable when left at room temperature, but increase in viscosity occurs when they are left under heating as an accelerated test in anticipation of long-term stability. Therefore, as described above, the resin particles are preferably nonionic resin particles.
The method for determining that the resin particles are nonionic resin particles is not particularly limited. -17A) does not detect materials containing acidic functional groups such as carboxyl and sulfo groups, or basic functional groups such as amino groups.

Examples of nonionic resin particles include polyolefin resins, chlorinated polyolefin resins, polyvinyl acetate resins, polyvinyl chloride resins, polyester resins, polyurethane resins, acrylic resins, styrene-butadiene resins, and polymerization resins used for polymerization of these resins. A copolymer of a polar compound or the like can be used. Ethylene-vinyl acetate copolymer resin, ethylene-vinyl acetate-vinyl chloride copolymer resin, and chlorinated olefin resin are more preferable. These resins can further improve the adhesion between the white ink and color ink and the recording medium.

The glass transition temperature (Tg) of the nonionic resin particles is preferably -30°C or higher and 30°C or lower, more preferably -25°C or higher and 25°C or lower. When the temperature is -30°C or higher, the resin film becomes tough, and the layer formed by the pretreatment liquid becomes more robust. Further, when the temperature is 30° C. or less, the film-forming property of the resin is improved and the flexibility is ensured, so that the adhesiveness between the white ink and the color ink and the recording medium can be further improved.

The content (solid content) of the resin particles is preferably 0.5% by mass or more and 20.0% by mass or less with respect to the mass of the pretreatment liquid. When the amount is 0.5% by mass or more and 20.0% by mass or less, the adhesiveness between the white ink and the color ink and the recording medium can be further improved.

-wax particles-
The wax particles are not particularly limited, and water-dispersible wax or the like can be used. Specifically, plant waxes such as carnauba wax, candelilla wax, beeswax, rice wax, lanolin, animal waxes, paraffin waxes, microcrystalline waxes, polyethylene waxes, polypropylene waxes, oxidized polyethylene waxes, petroleum waxes such as petrolatum, Mineral waxes such as montan wax and ozokerite, carbon wax, Hoechst wax, polyethylene wax, synthetic waxes such as stearic acid amide, and the like. Among these, paraffin wax and polyethylene wax are preferable from the viewpoint of being able to further improve the adhesion between white ink and color ink and the recording medium and from the viewpoint of dispersibility in the pretreatment liquid.

The melting point of the wax particles is preferably 50° C. or higher and 130° C. or lower, more preferably 60° C. or higher and 120° C. or lower. When the melting point is within the above range, the adhesiveness between the white ink and the color ink and the recording medium can be further improved.

The wax content (solid content) is preferably 0.05% by mass or more and 5.0% by mass or less, and is 0.1% by mass or more and 3.0% by mass or less with respect to the mass of the pretreatment liquid. is more preferable. When the amount is 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, when a white ink layer is formed after applying a pretreatment liquid containing wax, and an image is formed with color inks on the white ink layer, color bleeding is more likely to occur than with a pretreatment liquid that does not contain wax. may become.

-Organic solvent-
The organic solvent is not particularly limited, and a water-soluble organic solvent or the like can be used. Examples of water-soluble organic solvents include polyhydric alcohols, ethers such as polyhydric alcohol alkyl ethers and polyhydric alcohol aryl ethers, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds. be done.

Specific examples of water-soluble organic solvents include ethylene glycol, diethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, and 1,4-butane. Diol, 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, 1,5-pentanediol, 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- Polyhydric alcohols such as 1,3-pentanediol and petriol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, propylene glycol monoethyl Polyhydric alcohol alkyl ethers such as ethers, polyhydric alcohol aryl ethers such as ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether, 2-pyrrolidone, N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone , 1,3-dimethyl-2-imidazolidinone, ε-caprolactam, nitrogen-containing heterocyclic compounds such as γ-butyrolactone, formamide, N-methylformamide, N,N-dimethylformamide, 3-methoxy-N,N- Amides such as dimethylpropionamide and 3-butoxy-N,N-dimethylpropionamide, amines such as monoethanolamine, diethanolamine and triethylamine, sulfur-containing compounds such as dimethylsulfoxide, sulfolane and thiodiethanol, propylene carbonate, ethylene carbonate etc.
It is preferable to use an organic solvent having a boiling point of 250° C. or less because it not only functions as a wetting agent but also provides good drying properties.
Further, when at least one selected from 1,2-propanediol, 1,3-butanediol, and 1,2-butanediol is contained as an organic solvent, the surface of the recording medium is easily wetted, which is preferable.

The content of the organic solvent is not particularly limited and can be appropriately selected according to the purpose. % or more and 60.0 mass % or less is preferable, and 10.0 mass % or more and 30.0 mass % or less is more preferable.

-water-
As water, for example, ion-exchanged water, ultrafiltrated water, reverse osmosis water, pure water such as distilled water, and ultrapure water can be used.
The content of water in the pretreatment liquid is not particularly limited and can be appropriately selected according to the purpose. 90.0% by mass or less is preferable, and 20.0% by mass or more and 60.0% by mass or less is more preferable.

-Surfactant-
Any of silicone surfactants, fluorine surfactants, amphoteric surfactants, nonionic surfactants, and anionic surfactants can be used as surfactants.

The silicone-based surfactant is not particularly limited and can be appropriately selected according to the purpose. Among them, those that do not decompose even at high pH are preferable. Those having an oxyethylene group or a polyoxyethylene polyoxypropylene group are particularly preferred because they exhibit good properties as water-based surfactants. As the silicone-based surfactant, a polyether-modified silicone-based surfactant can also be used, and examples thereof include compounds in which a polyalkylene oxide structure is introduced into the side chain of the Si portion of dimethylsiloxane.

Examples of fluorine-based surfactants include perfluoroalkylsulfonic acid compounds, perfluoroalkylcarboxylic acid compounds, perfluoroalkylphosphoric acid ester compounds, perfluoroalkylethylene oxide adducts, and perfluoroalkyl ether groups in side chains. A polyoxyalkylene ether polymer compound having a low foaming property is preferable. Examples of perfluoroalkylsulfonic acid compounds include perfluoroalkylsulfonic acids, perfluoroalkylsulfonates, and the like. Examples of perfluoroalkylcarboxylic acid compounds include perfluoroalkylcarboxylic acids and perfluoroalkylcarboxylic acid salts. Examples of polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups in side chains include sulfuric acid ester salts of polyoxyalkylene ether polymers having perfluoroalkyl ether groups in side chains, and polyoxyalkylene ether polymers having perfluoroalkyl ether groups in side chains. Examples thereof include salts of oxyalkylene ether polymers. Counter ions of salts in these _{fluorosurfactants} include Li, Na, K, _NH4 , _NH3CH2CH2OH , _{NH2 ( CH2CH2OH} ) ₂ , and _{NH ( CH2CH2OH} ). ₃ and the like.

Examples of amphoteric surfactants include laurylaminopropionate, lauryldimethylbetaine, stearyldimethylbetaine, lauryldihydroxyethylbetaine and the like.

Nonionic surfactants include, for example, polyoxyethylene alkylphenyl ethers, polyoxyethylene alkyl esters, polyoxyethylene alkylamines, polyoxyethylene alkylamides, polyoxyethylene propylene block polymers, sorbitan fatty acid esters, polyoxyethylene sorbitan Examples include fatty acid esters and ethylene oxide adducts of acetylene alcohol.

Examples of anionic surfactants include polyoxyethylene alkyl ether acetate, dodecylbenzene sulfonate, laurate, polyoxyethylene alkyl ether sulfate and the like.

-Other ingredients-
As other components, antifoaming agents, antiseptic antifungal agents, antirust agents and the like may be contained as necessary.

-- Defoamer --
The antifoaming agent is not particularly limited, and examples thereof include silicone antifoaming agents, polyether antifoaming agents, and fatty acid ester antifoaming agents. These may be used individually by 1 type, or may use 2 or more types together. Among these, silicone-based antifoaming agents are preferred because of their excellent foam breaking effect.

-- Antiseptic and antifungal agents --
The antiseptic and antifungal agent is not particularly limited, and examples thereof include 1,2-benzisothiazolin-3-one.

--anti-rust--
The rust inhibitor is not particularly limited, and examples thereof include 1,2,3-benzotriazole, acid sulfites, sodium thiosulfate and the like.

<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. , OHP sheets, and general-purpose printing paper. Among these, color bleeding and beading are likely to occur, and from the viewpoint that the effect obtained by applying the ink set of the present disclosure is remarkable, low-permeability recording media such as commercial printing paper, signage, etc. Impermeable recording media, fabrics, and the like are preferred. In addition, unlike films and papers, cloth has a surface structure rich in unevenness, so the amount of white ink and color ink applied tends to be large, which causes color bleeding and beading. It is a recording medium that makes it easier.

A cloth will be described as an example of the recording medium. In the present disclosure, the term “fabric” refers to fiber in the form of woven fabric, knitted fabric, non-woven fabric, or the like. The fibers are preferably organic fibers such as synthetic fibers, semi-synthetic fibers, regenerated fibers, and natural fibers. Synthetic fibers include, for example, polyester, polyamide, acrylic, polyolefin, polyvinyl alcohol, polyvinyl chloride, polyurethane, and polyimide fibers. Semi-synthetic fibers include, for example, fibers of acetate, diacetate, triacetate, and the like. Regenerated fibers include, for example, fibers such as polynosic, rayon, lyocell, and cupro. Natural fibers include, for example, fibers such as cotton, linen, silk, and wool. Among the fibers that form the fabric, synthetic fibers such as polyester are more likely to cause color bleeding and beading than natural fibers such as cotton, and it is also difficult to retain white ink on the surface. However, the ink set of the present disclosure works well on such fabrics, suppresses color bleeding and beading, and also allows white ink to stay on the surface.

The fabric is preferably dark in color because the fibers used in the fabric are colored by chemically or physically retaining a coloring agent such as a pigment or dye in or on the fabric. When the fabric has a dark color, a white undercoat may be formed between the fabric and the color image for the purpose of improving the color developability of the color image formed on the fabric. This is because it is preferable to use the ink set having the white ink and the color ink of the present disclosure. In the present disclosure, the term “dark-colored fabric” means that the lightness (L ^* ) of the fabric is 60> when measured using a spectrophotometer (for example, X-rite exact (manufactured by X-Rite)). It represents a fabric that satisfies the range of L ^* , preferably a fabric that satisfies the range of 50>L ^* , more preferably a fabric that satisfies the range of 40>L ^* , and a fabric that satisfies the range of 30>L ^* . More preferably, it is particularly preferable that the fabric satisfies the range of 20>L ^* .

<<Image forming apparatus and image forming method>>
The image forming apparatus includes a white ink storage unit that stores white ink, a color ink storage unit that stores color ink, a white ink application unit that applies white ink to a recording medium, and a white ink application unit that applies white ink to a recording medium. and a color ink application means for applying color ink to the area marked with the color ink, and may have other configurations as necessary. Other configurations include, for example, pretreatment liquid containing means for containing the pretreatment liquid, pretreatment liquid applying means for applying the pretreatment liquid to the recording medium, and white ink, color ink, or ink applied to the recording medium. Examples include heating means for heating various liquids such as pretreatment liquid. When the image forming apparatus has pretreatment liquid storage means and pretreatment liquid application means, the white ink application means can be rephrased as means for applying white ink to the area of the recording medium to which the pretreatment liquid has been applied. can be done.
The image forming method includes a white ink application step of applying white ink to a recording medium, and a color ink application step of applying color ink to a region of the recording medium to which the white ink has been applied, and You may have other processes according to. Other processes include, for example, a pretreatment liquid application step of applying a pretreatment liquid to a region of the recording medium to which the white ink is applied before the white ink application step, and a white ink applied to the recording medium, a color A heating step of heating various liquids such as ink or pretreatment liquid can be used. When the image forming method includes the pretreatment liquid application step, the white ink application step can be rephrased as a step of applying white ink to the area of the recording medium to which the pretreatment liquid has been applied.

<Image forming apparatus>
An image forming apparatus will be described with reference to FIGS. FIG. 1 is a schematic diagram showing an example of an image forming apparatus. FIG. 2 is a schematic diagram showing an example of storage means (white ink storage means, color ink storage means, or pretreatment liquid storage means).

An image forming apparatus 400 shown in FIG. 1 is an image forming apparatus having a serial type inkjet head. A mechanical unit 420 is provided inside the exterior 401 of the image forming apparatus 400 . The storage portion 411 in the pretreatment liquid storage means 410p for the pretreatment 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 is, for example, an aluminum laminate. It is formed by a packaging member such as a film. The accommodating portion 411 is accommodated in, for example, a plastic container case 414 . Thereby, each containing means 410 is used as a cartridge.

On the other hand, a cartridge holder 404 is provided on the far side of the opening when the cover 401c of the apparatus main body is opened. Each accommodating means 410 is detachably attached to the cartridge holder 404 . As a result, the discharge port 413 of each container 410 and the inkjet ejection head 434 communicate with each other through each supply tube 436, and the pretreatment liquid and each ink can be ejected from the inkjet ejection head 434 onto the recording medium.
In the image forming apparatus 400 shown in FIG. 1, the pretreatment liquid is applied to the recording medium by an ink jet ejection method, but the application method of the pretreatment liquid is not limited to this. For example, it may be applied by a blade coating method, a roll coating method, a spray coating method, or the like.

The image forming apparatus 400 may have heating means for heating various liquids such as white ink, color ink, or pretreatment liquid applied to the recording medium. It is preferable not to have heating means for heating the recording medium to which the white ink has been applied. Such a heating means is provided for the purpose of suppressing color bleeding and beading caused by insufficient drying of the white ink by heating and drying the white ink. This is because the ink set can suppress color bleeding and beading without a heating means. Examples of the heating means include known heating means such as a roll heater, a drum heater, a hot air generator, and a heat press.

<Image forming method>
Application methods in the white ink application step, the color ink application step, and the pretreatment liquid application step of the image forming method include, for example, an ejection method and a coating method. The white ink applying process and the color ink applying process are preferably an ejection method, and more preferably an inkjet ejection method.

The ejection method is not particularly limited and can be appropriately selected depending on the intended purpose. and a method using a charge control type head.

Examples of coating methods include blade coating, gravure coating, gravure offset coating, wire bar coating, bar coating, roll coating, knife coating, air knife coating, comma coating, U comma coating, AKKU coating method, smoothing coating method, micro gravure coating method, reverse roll coating method, four or five roll coating method, dip coating method, curtain coating method, slide coating method, die coating method and the like.

The image forming method may have a heating step of heating various liquids such as white ink, color ink, or pretreatment liquid applied to the recording medium. Moreover, it is preferable not to have a heating step of heating the recording medium to which the white ink has been applied. Such a heating step is provided for the purpose of suppressing color bleeding and beading caused by insufficient drying of the white ink by heating and drying the white ink. This is because the ink set can suppress color bleeding and beading without a heating step.
In the image forming method, the time from applying the white ink to the recording medium to applying the color ink to the area of the recording medium to which the white ink has been applied is 20 seconds or less. is preferred. The above time is the time for drying the white ink, and in view of the purpose of suppressing color bleeding and beading caused by insufficient drying of the white ink, it is generally longer than 20 seconds. This is preferable because the ink set of the present disclosure can suppress color bleeding and beading even within 20 seconds.

^The amount of white ink applied to the recording medium in the white ink application step varies greatly depending ^on the type of recording medium. and more preferably 5 g/m ² or more and 400 g/m ² or less. When fabric is used as the recording medium, it 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 150 g/m ² or more and 300 g. /m ² or less.

^The amount of color ink to be applied to the recording medium in the color ink application step varies greatly depending ^on the type of recording medium. is preferred, and 5 g/m ² or more and 30 g/m ² or less is more preferred. When fabric is used as the recording medium, the density is preferably 5 g/m ² or more and 50 g/m ² or less, more preferably 10 g/m ² or more and 30 g/m ² or less.

^The amount of the pretreatment liquid to be applied to the recording medium in the pretreatment liquid application step varies greatly depending on the type of recording medium. It is preferably m ² or less, more preferably 1 g/m ² or more and 400 g/m ² or less. When fabric is used as the recording medium, it is preferably 100 g/m ² or more and 500 g/m ² or less, more preferably 200 g/m ² or more and 500 g/m ² or less, and 300 g/m ² or more and 400 g. /m ² or less.

Examples of the present invention will be described below, but the present invention is not limited to these examples.

<Example of preparation of pigment dispersion>
-Preparation Example 1: Preparation of surface-modified black pigment dispersion-
100 g of Black Pearls (registered trademark) 1000 manufactured by Cabot Corporation (BET specific surface area of 343 m ² /g, dibutyl phthalate absorption (DBPA) of 105 mL/100 g of carbon black), 100 mmol of sulfanilic acid, and 1 L of ion-exchanged high-purity water at room temperature. Mixed with a Silverson mixer (6,000 rpm).
Next, 100 millimoles of nitric acid was added to the resulting slurry, and after 30 minutes, sodium nitrite (100 millimoles) dissolved in 10 mL of ion-exchanged high-purity water was slowly added. Further, the mixture was heated to 60° C. with stirring and allowed to react 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 mass % tetrabutylammonium hydroxide solution (methanol solution), and after 30 minutes, a modified pigment dispersion was obtained. Then, this dispersion and ion-exchanged high-purity water were subjected to ultrafiltration with a dialysis membrane, followed by ultrasonic dispersion to obtain a surface-modified black pigment dispersion containing 20% by mass of pigment solids.
The resulting surface-modified black pigment dispersion had a pigment surface treatment level of 0.75 mmol/g. The particle size _D50 was 120 nm.

-Preparation Example 2: Preparation of surface-modified magenta pigment dispersion-
1 kg of a pigment dispersion SMART Magenta 3122BA (Pigment Red 122 surface-treated dispersion, pigment solid content 14.5% by mass) manufactured by SENSIENT was precipitated with a 0.1 N HCl aqueous solution.
Next, the pH was adjusted to 9 with a 10 mass % tetraethylammonium hydroxide aqueous solution, and after 30 minutes, a modified pigment dispersion was obtained. A modified pigment dispersion containing a pigment bound with at least one aminobenzoic acid group or tetraethylammonium aminobenzoate salt and ion-exchanged high-purity water are subjected to ultrafiltration with a dialysis membrane, followed by ultrasonic dispersion to obtain a solid pigment. A surface-modified magenta pigment dispersion containing 20 wt.
The resulting surface-modified magenta pigment dispersion was measured with a particle size distribution analyzer (Nanotrac UPA-EX150, manufactured by Nikkiso Co., Ltd.), and the cumulative ₅₀ % volume particle diameter D50 was 104 nm.

-Preparation Example 3: Preparation of surface-modified cyan pigment dispersion-
1 kg of a pigment dispersion SMART Cyan 3154BA (Pigment Blue 15:4 surface-treated dispersion, pigment solid content 14.5% by mass) manufactured by SENSIENT was precipitated with a 0.1 N HCl aqueous solution.
Next, the pH was adjusted to 9 with a 40 mass % benzyltrimethylammonium hydroxide solution (methanol solution), and after 30 minutes, a modified pigment dispersion was obtained. Using a modified pigment dispersion containing a pigment bound to at least one aminobenzoic acid group or benzyltrimethylammonium aminobenzoate and ion-exchanged high-purity water, ultrafiltration is performed with a dialysis membrane, followed by ultrasonic dispersion to obtain a pigment. A surface-modified cyan pigment dispersion containing 20% by weight of solids was obtained.
The resulting surface-modified cyan pigment dispersion was measured with a particle size distribution analyzer (Nanotrac UPA-EX150, manufactured by Nikkiso Co., Ltd.), and the cumulative 50% volume particle diameter _D50 was 116 nm.

-Preparation Example 4: Preparation of surface-modified yellow pigment dispersion-
1 kg of a pigment dispersion SMART Yellow 3074BA (Pigment Yellow 74 surface treatment dispersion, pigment solid content 14.5% by mass) manufactured by SENSIENT is adjusted to pH 9 with a 10% by mass tetrabutylammonium hydroxide solution (methanol solution), After 30 minutes a modified pigment dispersion was obtained. Using a modified pigment dispersion containing a pigment bound to at least one aminobenzoic acid group or tetrabutylammonium aminobenzoate salt and ion-exchanged high-purity water, ultrafiltration is performed with a dialysis membrane, followed by ultrasonic dispersion to obtain a pigment. A surface modified yellow pigment dispersion containing 20% solids was obtained.
The resulting surface-modified yellow pigment dispersion was measured with a particle size distribution analyzer (Nanotrac UPA-EX150, manufactured by Nikkiso Co., Ltd.), and the cumulative ₅₀ % volume particle diameter D50 was 145 nm.

-Preparation Example 5: Preparation of Magenta Pigment-Containing Polymer Fine Particle Dispersion-
After the interior of a 1 L flask equipped with a mechanical stirrer, thermometer, nitrogen gas inlet tube, reflux tube, and dropping funnel was sufficiently replaced with nitrogen gas, 11.2 g of styrene, 2.8 g of acrylic acid, and 12 g of lauryl methacrylate were added. 0 g, 4.0 g of polyethylene glycol methacrylate, 4.0 g of styrene macromer, and 0.4 g of mercaptoethanol were mixed in a flask and heated to 65°C. Next, styrene 100.8 g, acrylic acid 25.2 g, lauryl methacrylate 108.0 g, polyethylene glycol methacrylate 36.0 g, hydroxylethyl methacrylate 60.0 g, styrene macromer 36.0 g, mercaptoethanol 3.6 g, azobismethyl valero. A mixed solution of 2.4 g of nitrile and 18 g of methyl ethyl ketone was dropped into the flask over 2.5 hours. After dropping, a mixed solution of 0.8 g of azobismethylvaleronitrile and 18 g of methyl ethyl ketone was dropped into the flask over 0.5 hours. After stirring for 1 hour at 65° C., 0.8 g of azobismethylvaleronitrile was added and further stirred for 1 hour. After completion of the reaction, 364 g of methyl ethyl ketone was added into the flask to obtain 800 g of polymer solution A having a concentration of 50% by mass.
Next, 28 g of polymer solution A, 42 g of C.I. 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 ion-exchanged water were sufficiently stirred, and then rolled on a roll mill. was kneaded using The obtained paste was poured into 200 g of pure water and stirred sufficiently, and methyl ethyl ketone and water were distilled off using an evaporator. Pressure filtration was performed with a membrane filter to obtain a magenta pigment-containing polymer fine particle dispersion containing 15% by mass of pigment and having a solid content of 20% by mass.
The resulting magenta pigment-containing polymer fine particle dispersion was measured with a particle size distribution analyzer (Nanotrac UPA-EX150, manufactured by Nikkiso Co., Ltd.), and the cumulative ₅₀ % volume particle diameter D50 was 127 nm.

-Preparation Example 6: Preparation of Cyan Pigment-Containing Polymer Fine Particle Dispersion-
In Preparation Example 5, C.I. I. A cyan pigment-containing polymer fine particle dispersion was prepared in the same manner as in Preparation Example 5, except that a phthalocyanine pigment (CI Pigment Blue 15:3) was used instead of Pigment Red 122.
The polymer fine particles in the resulting cyan pigment-containing polymer fine particle dispersion were measured with a particle size distribution analyzer (Nanotrac UPA-EX150, manufactured by Nikkiso Co., Ltd.), and the cumulative 50% volume particle diameter _D50 was 93 nm.

-Preparation Example 7: Preparation of Yellow Pigment-Containing Polymer Fine Particle Dispersion-
Pigment Red 122 as the pigment in Preparation Example 5 was changed to a bisazo yellow pigment (CI Pigment Yellow 155) in the same manner as in Preparation Example 5 to obtain a yellow pigment-containing polymer fine particle dispersion was prepared.
The polymer fine particles in the resulting yellow pigment-containing polymer fine particle dispersion were measured with a particle size distribution analyzer (Nanotrac UPA-EX150, manufactured by Nikkiso Co., Ltd.), and the cumulative ₅₀ % volume particle diameter D50 was 76 nm.

-Preparation Example 8: Preparation of Black Pigment-Containing Polymer Fine Particle Dispersion-
Pigment Red 122 as the pigment was changed to carbon black (FW100, manufactured by Degussa) in the same manner as in Preparation Example 5 to prepare a black pigment-containing polymer fine particle dispersion.
The polymer fine particles in the black pigment-containing polymer fine particle dispersion thus obtained were measured with a particle size distribution analyzer (Nanotrac UPA-EX150 manufactured by Nikkiso Co., Ltd.), and the cumulative ₅₀ % volume particle diameter D50 was 104 nm.

-Preparation Example 9: Preparation of polymer-dispersed white pigment dispersion-
DISPERBYK-2081 (manufactured by BYK Japan Co., Ltd.) copolymer solution 55.6 g, titanium oxide (TITONE R-25, manufactured by Sakai Chemical Industry Co., Ltd.) 517 g, β-methoxy-N,N-dimethyl-propionamide 50 g, and ion-exchanged water After sufficiently stirring 377.4 g, it was put into a bead mill (Dyno Mill) and dispersed until the cumulative 50% volume particle diameter _D50 became 300 nm or less. Furthermore, in order to remove coarse particles, this dispersion was pressure-filtered through a polyvinylidene fluoride membrane filter having an average pore size of 5.0 μm to obtain a polymer-dispersed white pigment dispersion containing 50% by mass of white pigment.
The pigment particles in the resulting polymer-dispersed white pigment dispersion were measured with a particle size distribution analyzer (Nanotrac UPA-EX150, manufactured by Nikkiso Co., Ltd.), and the cumulative 50% volume particle diameter _D50 was 283 nm.

<Synthesis example of resin particles>
-Synthesis Example 1: Synthesis of water-dispersible polyurethane resin A-
830 parts by mass of terephthalic acid, 830 parts by mass of isophthalic acid, 374 parts by mass of ethylene glycol, 598 parts by mass of neopentyl glycol, while introducing nitrogen gas into a reaction vessel equipped with a thermometer, a nitrogen gas introduction tube, and a stirrer. And 0.5 parts by mass of dibutyl tin oxide was charged, and polycondensation reaction was performed at 180 ° C. to 230 ° C. for 15 hours until the acid value became 1 mgKOH / g or less, hydroxyl value 74.5 mgKOH / g, acid value 0 A polyester polyol P-1 having an average molecular weight of 1,500 and 2 mg KOH/g was obtained.
Next, 1,660 parts by mass of orthophthalic acid, 1,637 parts by mass of diethylene glycol, and 0.5 parts by mass of dibutyltin oxide were charged while introducing nitrogen gas into a reaction vessel equipped with a thermometer, a nitrogen gas introduction tube, and a stirrer. Polycondensation reaction is performed at 180° C. to 230° C. for 15 hours at 230° C. until the acid value becomes 1 mgKOH/g or less, resulting in a polyester polyol having an aromatic cyclic structure with a hydroxyl value of 190 mg KOH/g and an acid value of 0.3 mg KOH/g. Got Q-1.
Next, 1000 parts by mass of the obtained polyester polyol P-1 was dehydrated at 100° C. under reduced pressure, then cooled to 80° C., 907 parts by mass of methyl ethyl ketone was added, and thoroughly stirred to dissolve. - 80 parts by weight of dimethylolpropionic acid were added. After that, 281 parts by mass of isophorone diisocyanate was added and reacted at 75° C. for 8 hours to carry out a urethanization step. After confirming that the isocyanate value was 0.1% by mass or less, the mixture was cooled to 50° C., 340 parts by mass of the obtained polyester polyol Q-1 was added to make a uniform solution, and then 60 parts by mass of triethylamine was added. After neutralization, 7,000 parts by mass of water was added to solubilize. After removing methyl ethyl ketone from the obtained transparent reaction product at 40° C. to 60° C. under reduced pressure, water is added to adjust the concentration to obtain a stable translucent colloidal water-dispersible polyurethane having a non-volatile content of 30% by mass. An aqueous dispersion containing resin A was obtained. The water-dispersible polyurethane resin A has a structure represented by the above structural formula (A).

-Synthesis Example 2: Synthesis of water-dispersible polyurethane resin B-
1000 parts by mass of polyester polyol P-1 obtained in the same manner as in Synthesis Example 1 was dehydrated at 100° C. under reduced pressure, cooled to 80° C., added with 907 parts by mass of methyl ethyl ketone, and thoroughly stirred to dissolve. , and 80 parts by mass of 2,2′-dimethylolpropionic acid were added.
Next, 281 parts by mass of isophorone diisocyanate was added and reacted at 75° C. for 8 hours to effect urethanization. After confirming that the isocyanate value was 0.1% by mass or less, the mixture was cooled to 50° C., neutralized by adding 60 parts by mass of triethylamine, and then water-solubilized by adding 7000 parts by mass of water. Methyl ethyl ketone is removed from the obtained transparent reaction product at 40° C. to 60° C. under reduced pressure, and water is added to adjust the concentration to obtain a stable translucent colloidal water-dispersible polyurethane resin having a non-volatile content of 30%. An aqueous dispersion containing B was obtained. The water-dispersible polyurethane resin B has a structure represented by the above structural formula (A).

-Synthesis Example 3: Synthesis of water-dispersible polyurethane resin C-
664 parts by mass of terephthalic acid, 631 parts by mass of isophthalic acid, 472 parts by mass of 1,4-butanediol, and neopentyl glycol while introducing nitrogen gas into a reaction vessel equipped with a thermometer, a nitrogen gas introduction tube, and a stirrer. 447 parts by mass and 0.5 parts by mass of dibutyltin oxide were charged, esterified at 180° C. to 230° C. for 5 hours, and then polycondensed at 230° C. for 6 hours until the acid value became 1 mgKOH/g or less. . Next, the mixture was cooled to 120°C, 321 parts by mass of adipic acid and 268 parts by mass of 2,2'-dimethylolpropionic acid were added, the temperature was raised to 170°C again, and the mixture was reacted at this temperature for 20 hours to obtain an acid value of 46.0°C. A polyester polyol P-2 having a carboxyl group content of 5 mgKOH/g and a hydroxyl value of 59.8 mgKOH/g was obtained.
1,000 parts by mass of the obtained polyester polyol P-2 was dehydrated at 100° C. under reduced pressure, then cooled to 80° C., 812 parts by mass of methyl ethyl ketone was added, thoroughly stirred and dissolved, and 1,4-butanediol was added. 20 parts by weight were added. Next, 198 parts by mass of dicyclohexylmethane-4,4′-diisocyanate (hydrogenated MDI) was added and reacted at 75° C. for 8 hours. After confirming that the isocyanate value was 0.1% by mass or less, the mixture was cooled to 50° C., neutralized by adding 84 parts by mass of triethylamine, and then water-solubilized by adding 7000 parts by mass of water. Methyl ethyl ketone is removed from the obtained transparent reaction product at 40° C. to 60° C. under reduced pressure, and water is added to adjust the concentration to obtain a stable translucent colloidal water-dispersible polyurethane resin having a non-volatile content of 30%. An aqueous dispersion containing C was obtained. The water-dispersible polyurethane resin C has a structure represented by the above structural formula (A).

-Synthesis Example 4: Synthesis of water-dispersible polyurethane resin D-
1,000 parts by mass of polyester polyol P-1 obtained in the same manner as in Synthesis Example 1 was dehydrated at 100° C. under reduced pressure, cooled to 80° C., added with 907 parts by mass of methyl ethyl ketone, and thoroughly stirred to dissolve. and 80 parts by mass of 2,2'-dimethylolpropionic acid was added.
Next, 281 parts by mass of isophorone diisocyanate was added and reacted at 75° C. for 8 hours to effect urethanization. After confirming that the isocyanate value was 0.1% by mass or less, the mixture was cooled to 50° C., neutralized by adding 60 parts by mass of triethylamine, and then water-solubilized by adding 7,000 parts by mass of water. After removing methyl ethyl ketone from the obtained transparent reaction product at 40° C. to 60° C. under reduced pressure, water is added to adjust the concentration to obtain a stable translucent colloidal water-dispersible polyurethane having a non-volatile content of 30% by mass. An aqueous dispersion containing Resin D was obtained. The water-dispersible polyurethane resin D has a structure represented by the above structural formula (A).

-Synthesis Example 5: Synthesis of acrylic-silicone resin-
After sufficiently replacing the inside of a 1 L flask equipped with a mechanical stirrer, thermometer, nitrogen gas introduction tube, reflux tube, and dropping funnel with nitrogen gas, 8.0 g of Latemul S-180 ( Reactive anionic surfactant manufactured by Kao Corporation) was added and mixed, and the temperature was raised to 65°C. Next, 3.0 g of t-butyl peroxobenzoate and 1.0 g of sodium isoascorbate as reaction initiators were added, and after 5 minutes, 45 g of methyl methacrylate, 160 g of 2-ethylhexyl methacrylate, 5 g of acrylic acid, and butyl methacrylate were added. A mixture of 45 g, 30 g of cyclohexyl methacrylate, 15 g of vinyltriethoxysilane, 8.0 g of Latemul S-180, and 340 g of deionized water was added dropwise over 3 hours. Then, after heating and maturing at 80° C. for 2 hours, the mixture was cooled to room temperature and adjusted to pH 7-8 with sodium hydroxide. Then, the ethanol was distilled off by an evaporator, and the water content was adjusted to obtain 730 g of an aqueous dispersion containing acrylic-silicone resin particles with a solid content of 40% by mass. The cumulative 50% volume particle diameter _D50 of the resin particles in the aqueous dispersion was measured with a particle size distribution measuring device (manufactured by Nikkiso Co., Ltd., Nanotrac UPA-EX150) and found to be 125 nm.

<Production example of white ink and color ink>
-Production Example 1: Production of Ink 1-
In a container equipped with a stirrer, 1.00 parts by mass of 2-ethyl-1,3-hexanediol, 22.00 parts by mass of glycerin, 11.00 parts by mass of 1,3-butanediol, 2,5, 0.320 parts by mass of 8,11-tetramethyldecane-5,8-diol and 0.08 parts by mass of Unidyne DSN403N were added and mixed with stirring for 30 minutes. Next, 0.05 parts by mass of an antiseptic and antifungal agent (Proxel GXL, manufactured by Avecia), 0.30 parts by mass of 2-amino-2-ethyl-1,3-propanediol, and the magenta pigment-containing polymer fine particle dispersion of Preparation Example 5. 40.00 parts by mass of the liquid, 20.00 parts by mass of the aqueous dispersion of the water-dispersible polyurethane resin A of Synthesis Example 1, and 100 parts by mass of high-purity water were added, and mixed and stirred for 60 minutes. Next, the resulting mixture was pressure-filtered through a polyvinylidene fluoride membrane filter having an average pore size of 1.2 μm to remove coarse particles and dust to obtain Ink 1 .

-Production Examples 2 to 45: Production of Inks 2 to 45-
Inks 2 to 45 were obtained in the same manner as in Production Example 1 except that the formulation of the ink was changed to the materials shown in Tables 1 to 9 below. In Tables 1 to 9 below, the unit of content of various materials is "% by mass", and the display of content is not the amount of solid content (or the amount of active ingredient) but the total amount.

Details of various materials shown in Tables 1 to 9 below are as follows.
--coloring material--
・ AC-RW7: White pigment dispersion, manufactured by Dainichiseika Kogyo Co., Ltd., pigment solid content 45.3% by mass
--resin--
・ Super Flex 300: Polyurethane dispersion, solid content 33.0% by mass, glass transition temperature (Tg) = -42 ° C., manufactured by Daiichi Kogyo Seiyaku Co., Ltd. ・ Takelac W-6110: Polyurethane dispersion, solid content 33.4 % by mass, glass transition temperature (Tg) = -20°C, manufactured by Mitsui Chemicals --Surfactant--
・ TEGO Wet270: polyether-modified siloxane compound, manufactured by Evonik, active ingredient 100%
・ Silface SAG503A: polyether-modified siloxane compound, manufactured by Nissin Chemical Industry Co., Ltd., active ingredient 100%
・ Surfynol 104E: manufactured by Nissin Chemical Industry Co., Ltd., active ingredient 50%
・ Unidyne DSN403N: polyoxyethylene perfluoroalkyl ether, manufactured by Daikin Industries, Ltd., active ingredient 100%
--antifungal agent--
・Proxel GXL: An antifungal agent mainly composed of 1,2-benzisothiazolin-3-one (manufactured by Avecia, component 20%, containing dipropylene glycol)

<Physical properties of white ink and color ink>
Next, various physical properties of the obtained inks 1 to 45 were measured as follows. Table 10 shows the results.

-viscosity-
The viscosity of the ink was measured at 25° C. using a viscometer (RE-85L, manufactured by Toki Sangyo Co., Ltd.).

-pH-
The pH of the ink was measured at 25° C. using a pH meter (HM-30R type, manufactured by TOA-DKK).

－Static surface tension－
The static surface tension of the ink was measured at 25° C. using an automatic surface tensiometer (DY-300, manufactured by Kyowa Interface Science Co., Ltd.).

－Dynamic surface tension－
The dynamic surface tension of the ink at bubble life times of 15 msec, 150 msec, and 1500 msec by the maximum bubble pressure method was measured at 25° C. using SITA_DynoTester (manufactured by SITA).

<Production example of pretreatment liquid>
-Production Example 1: Production of pretreatment liquid 1-
7.5 parts by mass of ammonium lactate is weighed into a glass beaker, and 50.00 parts by mass of high-purity water is added, followed by stirring for 5 minutes. Next, 10.00 parts by mass of propylene glycol and Olfine EXP. After adding 0.1 part by mass of 4300, 0.05 part by mass of Proxel GXL and 0.1 part by mass of 1,2,3-benzotriazole, the mixture was mixed and stirred for 15 minutes. Furthermore, high-purity water was added to make a total of 100 parts by mass, and the mixture was mixed and stirred for 10 minutes. This mixture was subjected to pressure filtration through a polyvinylidene fluoride membrane filter having an average pore size of 5.0 μm to remove dust such as insoluble matter, and a pretreatment liquid 1 was prepared.

-Production Examples 2 to 16: Production of pretreatment solutions 2 to 16-
Pretreatment liquids 2 to 16 were obtained in the same manner as in Production Example 1, except that the formulation of the pretreatment liquid was changed to the materials shown in Tables 11 to 13 below. In Tables 11 to 13 below, the unit of content of various materials is "% by mass", and the display of content is not the amount of solid content (or the amount of active ingredient) but the total amount.

Details of various materials shown in Tables 11 to 13 below are as follows.
-- Cationic polymer --
・Charol DC-902P: polydimethyldiallylammonium chloride, solid content 51.0% by mass, manufactured by Daiichi Kogyo Seiyaku Co., Ltd. ・DK8610: polyamine resin, solid content 55.0% by mass, manufactured by Seiko PMC Co., Ltd.--Nonionic resin particles--
・Takelac W-635: polyurethane emulsion, solid content 35% by mass, manufactured by Mitsui Chemicals, Inc. ・SUMIKAFLEX850HQ: ethylene-vinyl chloride-vinyl acetate copolymer, solid content 50% by mass, manufactured by Sumitomo Chemical Co., Ltd. ・SUMIKAFLEX951HQ: ethylene -Vinyl acetate-vinyl versatate copolymer, solid content 55% by mass, manufactured by Sumitomo Chemical Co., Ltd.--Cationic resin particles--
・ Arrow Base CB-1200: Solid content 23% by mass, manufactured by Unitika Ltd. --Surfactant--
・Olfine EXP. 4300, manufactured by Nissin Chemical Industry Co., Ltd., active ingredient 60% by mass
--wax--
・AQUACER497: Paraffin wax, active ingredient 50% by mass, BYK Japan Co., Ltd. ・AQUACER539: Modified paraffin wax, active ingredient 35%, BYK Japan Co., Ltd. ・AQUACER531: Modified polyethylene wax, active ingredient 45% by mass, BYK Japan Made by Co., Ltd.--Antifungal agent--
・Proxel GXL: An antifungal agent mainly composed of 1,2-benzisothiazolin-3-one (manufactured by Avecia, component 20%, containing dipropylene glycol)

<Storage stability of pretreatment liquid>
Next, the obtained pretreatment solutions 1 to 16 were stored in a heated environment of 60° C. for 10 days, and changes in the pretreatment solutions during storage were evaluated according to the following evaluation criteria. The results are shown in Tables 11-13.
(Evaluation criteria)
A: No noticeable change B: Aggregation or thickening occurs, making it difficult to use as a pretreatment liquid

<Image formation using ink set>
(Examples 1 to 18, Comparative Examples 1 to 7)
Using an inkjet printer (Direct to Garment Printer RICOH Ri 6000, manufactured by Ricoh Co., Ltd.) under environmental conditions adjusted to 23°C ± 0.5°C and 50% ± 5% RH, the amount of ink ejected becomes uniform. By varying the driving voltage of the piezoelectric element, the setting was made so that the same amount of ink adhered to the recording medium.
First, as shown in Table 14, a predetermined amount of pretreatment liquid was applied to a predetermined recording medium by a predetermined application method. After that, if the recording medium is coated paper, vinyl chloride film, or PET film, it is dried in an oven at 70°C for 120 seconds. was dried in a 165° C. oven for 90 seconds.
Next, the white ink and color ink contained in the predetermined ink set shown in Table 14 are filled in the inkjet printing apparatus, and the predetermined application shown in Table 14 is applied to the area of the recording medium to which the pretreatment liquid has been applied. 17 seconds after the application of the white ink, color ink was applied in a predetermined application amount shown in Table 14 to the area of the recording medium to which the white ink had been applied. to form the chart shown in FIG. Note that the recording medium was not heated between the application of the white ink and the application of the color ink.
Next, if the recording medium on which the chart shown in FIG. 3 is formed is coated paper, PVC film, or PET film, it is dried in an oven at 70° C. for 5 minutes. Sample images were obtained by drying in a 130° C. oven for 3 minutes and, in the case of dark cotton T-shirts, drying in a 165° C. oven for 2 minutes.
In FIG. 3, W represents a white solid image portion as a background, Y represents a yellow solid image portion formed on the ground W, and M represents a magenta solid image formed on the ground W. An image portion is represented, C represents a cyan solid image portion formed on the ground W, R represents a red solid image portion formed on the ground W, and B represents a blue color formed on the ground W. , G represents a green solid image formed on the background W, K represents a black solid image formed on the background W, and k1 to k6 formed on the background W. and y represents a yellow letter "R" formed on the background W. The chart shown in FIG. 3 was created based on an image converted into data without color correction using software Photoshop (manufactured by Adobe) and printed at 600 dpi×600 dpi.

Details of various recording media shown in Table 14 below are as follows.
・OK Top Coat +: Coated paper, 157 g/m ² , manufactured by Oji Paper Co., Ltd. ・NIJ-PVCM: PVC film, base thickness 120 μm / adhesive 25 μm, manufactured by Nitie Co., Ltd. ・Lumirror #50-T11: Transparent PET film, easy adhesion treatment, manufactured by Toray Industries, Inc. 00300-ACT: Dark colored polyester T-shirt, Glimmer 00300-ACT Black, manufactured by TMS Co., Ltd. 00085-CVT: Dark colored cotton T-shirt, Printstar 00085-CVT Black , TMS Co., Ltd.

Hunter whiteness, color bleeding, and beading were evaluated as follows for each sample image obtained. The results are shown in Table 15.

[Hunter Whiteness]
The image density in the white solid image portion of the obtained sample image was measured using a spectrophotometer (X-rite exact, manufactured by X-rite), and the Hunter whiteness was calculated by the following formula (1). and evaluated based on the following evaluation criteria. The image density was measured by placing a sample image on five sheets of medium-thick colored high-quality paper (manufactured by Hokuetsu Corporation) stacked one on top of the other. However, in Examples 1 to 3, the recording media used were originally white, and there was no significance in measuring the Hunter whiteness, so they were not evaluated.
(Evaluation criteria)
A+: Hunter whiteness is 85 or more A: Hunter whiteness is 80 or more and less than 85 B: Hunter whiteness is 75 or more and less than 80 C: Hunter whiteness is 70 or more and less than 75 D: Hunter white degree is less than 70

[Color Bleed]
In the solid image portion of each color of the obtained sample image, color bleeding (for example, color boundary bleeding between white and yellow) between adjacent solid image portions of white and adjacent solid image portions of other colors. The degree of color bleeding (for example, color boundary bleeding between black and yellow) was visually observed and evaluated based on the following evaluation criteria.
(Evaluation criteria)
A+: No color boundary bleeding A: Very slight color boundary bleeding B: Slight color boundary bleeding C: Color boundary bleeding D: Significant color boundary Bleeding occurs

[Beading]
The degree of beading (density unevenness) in the solid image portion of each color of the obtained sample image was visually observed and evaluated based on the following evaluation criteria.
(Evaluation criteria)
A: No density unevenness B: Slight density unevenness C: Density unevenness D: Significant density unevenness

400 image forming apparatus 401 exterior of image forming apparatus 401c cover of apparatus main body 404 cartridge holder 410p pretreatment liquid storage means 410w white ink storage means 410k black ink storage means 410c cyan ink storage means 411 storage section 413 outlet 414 storage container case 420 Mechanism 434 Ink jet ejection head 436 Supply tube

JP 2008-266853 A

Claims (14)

An ink set having white ink and color ink,
The difference in static surface tension at 25° C. between the white ink and the color ink is 1.0 mN/m or less,
In the white ink and the color ink, the difference in dynamic surface tension at 25° C. at bubble life times of 15 msec, 150 msec, and 1500 msec measured by the maximum bubble pressure method is independently 1.0 mN/m or less. An ink set characterized by: The ink set according to claim 1, wherein the white ink and the color ink each independently have a static surface tension of 40.0 mN/m or less at 25°C. the ink set has a plurality of color inks including black ink, cyan ink, magenta ink, and yellow ink;
Between the color inks, the difference in dynamic surface tension at 25° C. when the bubble life time is 15 msec by the maximum bubble pressure method is independently 1.0 mN/m or less,
2. Dynamic surface tension at 25° C. with a bubble lifetime of 15 msec according to the maximum bubble pressure method in the black ink, the cyan ink, the magenta ink, and the yellow ink satisfies the following relational expression (1): The ink set described in .

The ink set further includes a pretreatment liquid,
The pretreatment liquid contains water and a flocculant,
The ink set according to any one of claims 1 to 3, wherein the aggregating agent is at least one selected from the group consisting of inorganic metal salts, organic acid metal salts, organic acid ammonium salts, and cationic polymers. . 5. The ink set according to claim 4, wherein the pretreatment liquid further contains nonionic resin particles. 6. The ink set according to claim 4, wherein the pretreatment liquid further contains wax particles. 7. The ink set according to claim 6, wherein the wax particles are paraffin wax. An image forming method comprising: a white ink application step of applying white ink to a recording medium; and a color ink application step of applying color ink to a region of the recording medium to which the white ink has been applied, ,
The difference in static surface tension at 25° C. between the white ink and the color ink is 1.0 mN/m or less,
In the white ink and the color ink, the difference in dynamic surface tension at 25° C. at bubble life times of 15 msec, 150 msec, and 1500 msec measured by the maximum bubble pressure method is independently 1.0 mN/m or less. An image forming method characterized by: 9. The image forming method according to claim 8, further comprising a pretreatment liquid applying step of applying a pretreatment liquid to a region of the recording medium to which the white ink is to be applied before the white ink applying step. 10. The image forming method according to claim 8, wherein a heating step of heating the recording medium to which the white ink has been applied is not provided between the white ink applying step and the color ink applying step. 3. A time period between application of the white ink to the recording medium and application of the color ink to the area of the recording medium to which the white ink has been applied is within 20 seconds. 11. The image forming method according to any one of 8 to 10. The image forming method according to any one of Claims 8 to 11, wherein the recording medium is dark-colored fabric. a white ink containing means containing white ink; a color ink containing means containing color ink; a white ink applying means for applying the white ink to a recording medium; An image forming apparatus comprising: a color ink applying unit for applying the color ink to an area,
The difference in static surface tension at 25° C. between the white ink and the color ink is 1.0 mN/m or less,
In the white ink and the color ink, the difference in dynamic surface tension at 25° C. at bubble life times of 15 msec, 150 msec, and 1500 msec measured by the maximum bubble pressure method is independently 1.0 mN/m or less. An image forming apparatus characterized by: 14. The recording medium according to claim 13, further comprising pretreatment liquid containing means for containing a pretreatment liquid, and pretreatment liquid applying means for applying the pretreatment liquid in advance to a region of the recording medium to which the white ink is to be applied. The described image forming apparatus.

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